RU2339668C2 - Water ink, ink-jet recording method, ink cartridge, recording unit, ink-jet recording unit and method of image generation - Google Patents

Abstract

FIELD: printing industry.

SUBSTANCE: invention is referred to water ink, which may be used in methods and units of ink-jet printing. Water ink contains at least water, a quantity of water soluble organic solvents and dyestuff. Dyestuff is a pigment containing pigment particle with at least one ionisable group linked directly with pigment particle surface or through other atomic group. The quantity of water soluble organic solvents includes favourable medium or unfavourable media for pigment. Completely or practically completely, unfavourable medium does not solvate pigment. Completely or practically completely, the said ionisable group is not exposed to ion dissociation in unfavourable medium. Water soluble organic solvent is specific by maximum value of permeability index (Ka) among corresponding Ka values for the said amount of water soluble organic solvents defined by Bristow method and is the unfavourable medium. Content of the said quantity of water soluble organic solvents is from 3 wt % to 50 wt % from total ink weight. When total content (wt %) of favourable medium in water ink is identified by X and total content (wt %) of unfavourable medium in water ink is identified by Y, X:Y ratio is from 10:5 or more to 10:30 or less. Content (wt %) of pigment is from 0.1 wt % to 15 wt % from total ink weight. Ink-jet method of recording, ink cartridge, recording unit, ink-jet recording unit and method of image generation using the said water ink are also described. Water ink covers sufficient part of surface if used in small amounts, ensures excellent stability when stored. Generated image has high printing density.

EFFECT: ensuring high printing density.

25 cl, 18 dwg, 11 tbl, 9 ex

Description

FIELD OF THE INVENTION

The invention relates to aqueous inks that contain water, a water-soluble organic solvent, and a pigment. In particular, the invention relates to aqueous inks that can be used in recording methods and in a recording apparatus using an inkjet method, that is, inkjet recording methods (image forming methods or recording methods), and to inkjet recording methods, an ink cartridge, a recording unit , an inkjet recording device, and an image forming method that uses aqueous ink.

BACKGROUND OF THE INVENTION

It is well known that inks that contain pigments as coloring agents (pigment inks) form images having good durability, such as water resistance or light fastness. In recent years, various methods have been proposed to increase the print density of the image formed with the use of such inks, and when recording color images in which areas of different colors are directly in contact, the prevention of color mixing (blurring) at the boundary areas of the corresponding color images is more effectively achieved.

To achieve a significant increase in image density, it is proposed, for example, to use inks containing self-dispersible carbon black and a special salt (see, for example, Japanese Patent Application Laid-open No. 2000-198955). A method is also provided in which an inkjet ink comprising a composition of a pigment, fine polymer particles, a water-soluble organic solvent and water, and an aqueous solution containing a polyvalent metal salt is applied to a recording medium, and the ink composition is reacted with an aqueous solution of a polyvalent metal salt with the formation of high-quality images (see, for example, Japanese Patent Application Laid-open No. 2000-63719). In both of these methods, the pigment present in the ink is in a dispersed state, and its flocculation is forced on the surface of the recording medium, which prevents the penetration of the pigment into the recording medium and makes it possible to obtain images having a significantly higher density and without diffusion.

In addition, since pigment flocculation is caused in the pigment ink on the recording medium, it remains on the surface of the recording medium. In particular, when pigment inks are used to print images on plain paper, a blurriness can occur when the surface of the print is scratched intensively even after a sufficient time has elapsed after printing, or a blurriness can occur when something is written with a water-based ink marker on already printed image. That is, the disadvantage of pigment inks is their low resistance to scratching and to the marker. A number of efforts have been undertaken previously to improve scratch resistance. For example, it has been proposed to increase scratch resistance by adding a water-soluble emulsion to self-dispersible pigment inks (see, for example, Japanese Patent Applications Laid-open Nos. H03-56573, 2001-329199 and 2001-329200).

SUMMARY OF THE INVENTION

However, according to studies conducted by the inventors of the present invention, it was found that in the above methods, due to flocculation of pigment particles on the recording medium, the surface area of the coloring material (which is called the "surface coverage") may not be sufficient when compared with the amount of ink droplet . This means that in the above methods, more ink is required to achieve the same image density that is achieved with pigment inks in which the conventional pigment is dispersed using a polymer dispersing agent or other similar means. In this regard, there is a need to improve these methods. There is also known a method by which ink is produced that penetrate significantly into the recording medium while providing a greater degree of surface coverage, even with small amounts of ink droplets. However, when the resulting ink has high permeability, they can penetrate not only the surface of the recording medium, but also inside the recording medium, thereby making it impossible to achieve a sufficient image density.

The authors of the present invention studied the advantages and disadvantages of individual traditional inks and analyzed the characteristic features of the images themselves. As a result, it was found that at a higher concentration of the dye in the ink, it is in excess on the surface of the recording medium, and the formed points become visually more heterogeneous, or the dye penetrates into the recording medium, as a result of which it is useless to use without participation in the formation colors.

The authors of the present invention have found that at least one of the above technological problems can be solved, and this will allow to obtain an image superior in quality to those that are formed in traditional cases. The problems identified by the authors of the present invention are listed below. An object of the present invention is to solve at least one of the following problems.

(1) The problem is that when a pigment flocculation is present on the surface of the recording medium that is present in the dispersed ink, the surface area of the coating medium of the recording medium (referred to as “surface coverage”) is insufficient in comparison with the amount of ink droplet , and therefore, in order to achieve the same image density, it is necessary to apply more ink.

(2) The problem is that when receiving ink with high permeability, ink can penetrate not only the surface of the recording medium, but also deep into the recording medium, which prevents the coloring matter from being distributed on the surface of the recording medium and its surroundings at a high concentration and does not allow to achieve high image density.

Therefore, the aim of the present invention is to provide, as a pigment ink, aqueous inks that have a sufficiently large degree of surface coverage, even when a small amount of ink droplets are used, and can form images having a high print density, and, in addition, have a higher resistance during storage.

Another objective of the present invention is the development of aqueous ink, which allows to achieve higher resistance to scratching, by adding a water-soluble polymer to the aqueous ink of the above composition.

Another objective of the present invention is the development of aqueous inks that have a sufficiently large degree of surface coverage even when using a small amount of ink droplets, and can also form images with a high print density in an image forming method including the step of applying aqueous pigment containing ink to a recording medium and the step of applying to the recording medium a reaction liquid capable of causing the destruction of the pigment dispersion in aqueous ink upon contact with aqueous ink ami (hereinafter, this method is also often referred to as a "two-fluid system").

An additional objective of the present invention is the development of a set of aqueous ink / reaction liquid, an inkjet recording method, an ink cartridge, a recording unit and an inkjet recording device that use aqueous ink having the above composition.

An additional objective of the present invention is the development of an image forming method that can effectively prevent color mixing (blurring) on adjacent regions of images of the corresponding color when recording on plain paper, when regions of color images with different colors are directly adjacent to each other.

The above objectives achieved by the present invention are described below. Namely, the aqueous ink of an embodiment of the present invention is aqueous ink, which includes at least water, several water-soluble organic solvents, and a coloring matter, wherein the coloring matter is a pigment containing a pigment particle having at least one an ionic group bonded to the surface of the pigment particle directly or through another atomic group, and where several water-soluble organic solvents include a favorable environment or favorable pigment environments and an unfavorable environment for pigment, and where the adverse environment completely or practically does not solvate the pigment, and where the ionic group does not undergo ionic dissociation at all or almost in an unfavorable environment, and where is a water-soluble organic solvent that exhibits maximum value for Ka among the corresponding Ka values for water-soluble organic solvents determined by the Bristow method is an unfavorable environment th.

Aqueous inks according to another embodiment of the present invention are also aqueous inks, which include at least water, several water-soluble organic solvents, and a coloring matter, wherein the coloring matter is a pigment containing a pigment particle having at least one ionogenic a group bonded to the surface of the pigment particle directly or through another atomic group, and where the plurality of water-soluble organic solvents includes a favorable environment either the favorable environment for the pigment and the unfavorable environment or the unfavorable environment for the pigment, and where the adverse environment completely or practically does not solvate the pigment, and where the ionic group completely or practically does not undergo ionic dissociation in the adverse environment, and where the water-soluble organic solvent that exhibits the maximum the Ka value among the corresponding Ka values for the water-soluble organic solvents determined by the Bristow method is unfavorable redoy, and wherein the ink further comprises a water-soluble polymer which is totally or substantially not adsorbed on the pigment.

Aqueous inks according to another embodiment of the present invention are aqueous inks that are used in an image forming method including the step of applying to the recording medium an aqueous ink containing a pigment, and the stage of applying to the recording medium a reaction liquid capable of causing an unstable state of pigment dispersion in aqueous ink in contact with aqueous ink, in which aqueous ink having the aforementioned composition is used as aqueous ink.

An image forming method according to another embodiment of the present invention is an image forming method in which an ink jet recording method is recorded on a recording medium by using black ink and at least one color ink, in which aqueous ink having the aforementioned composition is used as black ink, and in which when forming an image consisting of an image formed using black ink and an image formed using color In the case of ink that directly adjacent to each other, a run for applying black ink to form an image is performed, and then a run is applied for applying color ink to an area where an image has already been generated using the previous run.

The present invention can provide aqueous inks that, as pigment inks, have a sufficiently high degree of surface coverage even when using a small amount of ink droplets and can form images with a high print density and additionally have better storage stability. In another embodiment of the present invention, aqueous inks can be provided which, in addition to the above effects, have higher scratch resistance. In yet another embodiment of the present invention, aqueous inks are provided that have a sufficiently high degree of surface coverage even with a small amount of ink droplets and can form images with a high print density also in the case of a system in which a reaction liquid capable of destroying a pigment dispersion state in aqueous ink, fixed on the recording medium, and then to form the image, aqueous ink is applied to the part on which the reaction liquid was already applied. According to the present invention, by virtue of the use of such aqueous inks, an inkjet recording method can also be proposed by which high-quality images with a high print density can be formed using a small amount of ink. An ink cartridge, a recording unit, and an inkjet recording device in which such aqueous ink is used may also be provided according to the present invention. The present invention may further provide an image forming method that is capable of effectively preventing color mixing (blurring) at the boundary regions of the images of the respective colors when recording directly adjacent to each other regions of color images having colors different from each other on plain paper.

BRIEF DESCRIPTION OF THE DRAWINGS

In FIG. 1 shows a vertical section through a recording head.

In FIG. 2 shows a vertical section through a recording head.

In FIG. 3 shows a perspective view of the recording head, where the recording head shown in FIG. 1 is set to a multi-mode state.

In FIG. 4 is a perspective view illustrating an example of an inkjet recording device.

In FIG. 5 shows a vertical section of an ink cartridge.

In FIG. 6 is a perspective view illustrating an example of a recording unit.

In FIG. 7 is a view illustrating an example of a construction of a recording head.

In FIG. 8 is a view illustrating an example construction of a recording head.

In FIG. 9 is a view illustrating an example construction of a recording head.

In FIG. 10 is a view illustrating an example construction of a recording head.

In FIG. 11 is a view illustrating an example of a construction of a recording head.

In FIG. 12 is a view illustrating an example construction of a recording head.

In FIG. 13 is a view illustrating an example construction of a recording head.

In FIG. 14A, 14B, 14C and 14D are views for schematically illustrating what happens to an ink drop when it acts on the surface of a recording medium.

In FIG. 15 is a schematic sectional side view illustrating an example of an inkjet recording device.

BEST MODE FOR CARRYING OUT THE INVENTION

Further, the present invention is described in more detail by presenting preferred embodiments of the present invention.

First, the concepts of an unfavorable environment and a favorable environment are described in the present invention. Their detailed definitions are given below. When a pigment used as a coloring matter comprises a pigment particle having at least one ionogenic group bonded to the surface of the pigment particle directly or through another atomic group, a water-soluble organic solvent in which the dispersion stability of the pigment contained therein is high and water-soluble an organic solvent in which the dispersion stability of the pigment contained therein is low, is determined as a favorable environment and unfavorable environment, respectively. Also, the pigment and the adverse environment are mutually characterized by the fact that the adverse environment completely or practically does not solvate the pigment, and the ionogenic group of the pigment completely or practically does not undergo ionic dissociation in the adverse environment.

A distinctive feature of the present invention is that the water-soluble organic solvents that are contained in the aqueous ink together with the pigment and are designed to disperse the pigment are divided into solvents that manifest themselves as the above-described adverse environment, and solvents that manifest themselves as a favorable environment. Then, as a result of using such a composition, images can be effectively obtained without the spreading phenomenon even on plain paper, on which various problems would arise during image formation using conventional aqueous inks, and, in addition, aqueous inks that have a sufficiently large size can be obtained. the degree of surface coverage even when applying ink in a small amount, which allows you to form an image with a high print density. Also, when using such aqueous inks, an increase in printing speed, a reduction in the size of the recording device and a reduction in operating costs, including the cost of consumables, can be achieved, and in addition, the generated images can have better strength, a significantly higher image density can be achieved. , and high quality images can be formed. The inventors of the present invention have found that the indicated beneficial effects can be achieved, and have created the present invention.

The aqueous inks of the present invention are inks that include at least water, several water-soluble organic solvents, and a coloring material, in which the coloring material is a pigment containing a pigment particle having at least one ionogenic group associated with the surface of the pigment particle directly or through another atomic group, and water-soluble organic solvents include a favorable environment or favorable environment for the pigment, and an adverse medium or adverse environments for the pigment, where the adverse environment completely or practically does not solvate the pigment, and the ionogenic group is completely or practically not subjected to ionic dissociation in the adverse environment. When such aqueous inks are used as inks, water, water-soluble organic solvents having a favorable environment and an unfavorable environment for a pigment, and a pigment and a pigment dispersion are mixed in a predetermined proportion.

Imaging mechanism

The following describes the image forming mechanism in the present invention by providing an example. When the aqueous ink of the present invention is applied to a recording medium, in particular plain paper, and images are printed on it, it is believed that a very good image density and print quality can be obtained for the reasons stated above.

Namely, as shown in FIG. 14A, when a drop of ink 1301 of the present invention is applied to a recording medium 1300, which is exemplified by plain paper, and an image is printed on it, the ratio i) of the water in the ink begins to change immediately after the ink contacts the recording medium, ii) a favorable environment, and adverse environment for pigment; and iii) pigment. More specifically, as shown in FIG. 14A and 14B, after a drop of ink 1301 is in contact with the surface of the recording medium 1300, the ink is fixed on the recording medium. As soon as they are fixed, first, upon evaporation of water, the unfavorable medium 1307, which has a high Ka value among water-soluble organic solvents in ink, diffuses in a form close to the right circle in the vicinity of the surface of the recording medium, and an ink dot begins to form.

In FIG. 14B, 14C and 14D show a schematic illustration of what happens to the ink before it is fixed as a result of their contact with the surface of the recording medium 1300. Considering how the ink dot expands in this case, it is believed that the concentration of the adverse medium becomes higher on the outer border 1302 points in contact with a part of the ink and paper, compared with the concentration in the Central part 1303 points. As a result, the ink dot diffuses into the nearby surface of the recording medium in a shape close to the correct circle, and, during this diffusion, the concentration of the adverse medium 1307 increases sharply with respect to the pigment. As a result, at the outer boundary 1302 of the penetrating liquid, the proportion of the adverse environment for the pigment increases sharply, and the adverse environment practically does not solvate the pigment, and the ionic group of the pigment practically does not undergo ionic dissociation in water-soluble organic solvents. Therefore, the dispersion of the pigment becomes unstable, which causes flocculation or destruction of the dispersion. Consequently, the ink dot diffuses with an almost regular round border on the surface of the recording medium (see Fig. 14B), and this leads to the pigment 1304 remaining on the surface of the recording medium 1300, so that it appears as if the edge of the pigment is formed on parts of the outer border of a point. Thus, a pigment point of a regular round shape is formed and in this form becomes fixed on the surface of the recording medium (see Fig. 14C). At this point in time, the formation of the pigment point is completed, but the water-soluble organic solvents and water 1306 in the ink expand radially with further diffusion. Namely, after the formation of the pigment point ends, the water-soluble organic solvents and the water 1306 in the ink also diffuse into the nearby surface of the recording medium. In the future, due to evaporation and penetration of water-soluble organic solvents into the central part 1303 with a high content of a favorable environment, pigment also precipitates on this part, due to which point 1305 is formed. An image formed using the method described above can have enough a high degree of surface coverage even when using a small amount of ink droplet, high image density and high quality while preventing blurring.

How to distinguish between a favorable environment and an unfavorable environment

According to the foregoing proposed mechanism, a favorable environment and an unfavorable environment used in the present invention is considered to be an environment that may or may not, accordingly, maintain the state of pigment dispersion. Accordingly, when a favorable environment and an unfavorable environment are selected in the preparation of the aqueous ink of the present invention, it is preferable to know in advance to what extent the dispersion state of the pigment used is stabilized, and to choose an environment based on the result. Further, regarding the effect of the present invention, the authors of the present invention conducted various studies on the criteria for evaluating a favorable environment and an unfavorable environment, which determine the effect of the present invention. As a result, they found that the evaluation method described below is effective.

First, a pigment dispersion solution is prepared which contains 50 wt.% Of each water soluble organic solvent to be evaluated and 45 wt.% Water, and also contains 5 wt.% Of the pigment used in the ink. Then, the dispersion solution thus prepared was stored at 60 ° C. for 48 hours, and the solution in which the average pigment particle size in the dispersion solution was larger than the average pigment particle size in the aqueous dispersion solution containing 5 wt.% Pigment and 95 wt. .% water was defined as an unfavorable environment, and a solution in which the average particle size of the pigment in the dispersion solution did not change or became smaller as a favorable environment.

In particular, an assessment of whether the water-soluble organic solvent used is a favorable medium or an unfavorable medium for a particular pigment is carried out as follows. First, two types of dispersion solutions are prepared: a dispersion solution of a specific pigment and an aqueous solution of dispersion B of a specific pigment, each of which contains an estimated water-soluble organic solvent.

Dispersion Solution A: A pigment dispersion solution having a composition in which the concentration of the estimated water-soluble organic solvent is 50 wt.%, The pigment concentration is 5 wt.% And the water concentration is 45 wt.%.

An aqueous dispersion solution B: An aqueous dispersion solution having a composition in which the pigment concentration is 5 wt.% And the water concentration is 95 wt.%.

Further, the above dispersion A solution was stored at 60 ° C for 48 hours, and then cooled to ordinary temperature, and the average pigment particle size in the resulting dispersion A solution was measured using a fiber optic particle size analyzer (trademark: FPAR-1000; manufactured by Otsuka Electronics Co., Ltd.). Also, the above aqueous solution of dispersion B is not stored when heated, and in this state, the average pigment particle size is measured using a fiber optic particle size analyzer in the same way as in the above definition. Then, the mean particle size values of the respective pigments in the above dispersion solution A and the aqueous dispersion solution B are denoted as particle size (A) and particle size (B), and based on these values, a distinction is made between a favorable environment and an unfavorable environment according to the following definitions.

- Adverse environment: when the particle size (A) is larger than the particle size (B), the estimated water-soluble organic solvent is defined as an adverse environment.

- Favorable environment: when the particle size (A) is equal to or smaller than the particle size (B), the estimated water-soluble organic solvent is defined as a favorable environment.

Using a favorable environment and an unfavorable environment evaluated in this way, ink was prepared with the composition of the present invention. As a result, it was possible to confirm the achievement of the good results announced earlier.

Determination of solvation and ionic dissociation

Further, for the case of pigment and adverse environment, an explanation is given as to why the adverse environment completely or practically does not solvate the pigment and at least one ionogenic group attached to the surfaces of the pigment particles directly or through another atomic group is completely or practically not exposed. ionic dissociation in an unfavorable environment.

One factor in the dispersion of pigment particles is Coulomb repulsion due to ionic dissociation. In a pigment, the surface of pigment particles on which at least one ionic group is attached directly or through another atomic group, the ionogenic group undergoes ion dissociation in the medium, and because of this, the pigment particles are electrostatically charged, and the Coulomb repulsion force resulting from this , becomes one factor in the dispersion of pigment particles in the medium. One of the indicators of such ionic dissociation is the attractive force acting between the ions in the medium. When two electric charges q ₁ and q ₂ having different polarities are located at points separated by a distance r in a medium having a relative dielectric constant γ _r with respect to the dielectric constant in vacuum γ ₀ , it is known that the attractive force F acting on two electric charges will be expressed by the following equation (1).

Equation (1)

Here, it is believed that the above equation (1) is also applicable to the ionogenic group attached to the surfaces of the pigment particles. With an increase in this attractive force F, the distance between the ion and its counterion becomes shorter, or the ions mutually completely transform into an ionic bond, so that the Coulomb repulsion force weakens due to a decrease in the charge of pigment particles or compression of the double electric layer, and the dispersion of pigment particles becomes unstable . Then, when using a water-soluble organic solvent having a small relative dielectric constant γ _r with respect to the dielectric constant in vacuum γ ₀ , it is obvious that the interionic attractive force between the ions of the ionic group attached to the surfaces of the pigment particles increases, the ionic group of the pigment practically does not undergo ionic dissociation in water-soluble organic solvents, and the dispersibility of pigment particles is reduced due to the Coulomb repulsion force.

However, it was difficult to explain the dispersibility of the pigments only on the basis of the degree of dissociation of the ionic groups depending on the solvent.

Accordingly, as another factor that affects the dispersion of pigment particles, the authors of the present invention drew attention to the solvation of the pigment medium. The solvation referred to in the present invention is the affinity of the solvent for the pigment and depends on how many places on the pigment have affinity for the medium. Examples of sites having an affinity for the medium may include places on the surface of the pigment particle to which the ionic group is not attached. For example, where groups comprising ionogenic groups are attached to surfaces of pigment particles with a high density, locations on the surface of pigment particles with affinity for the medium are exposed (uncovered) in a small area, and, as expected, the medium can solvate the pigment with labor due to the combined influence due to spatial difficulty, due to the ionogenic groups that cover the surface of the pigment particles at high density, which leads to a decrease in the dispersibility of Igmenta.

When a combination of water-soluble organic solvents with such a pigment is used in aqueous ink, in which dispersion due to Coulomb repulsion occurs as a result of ionic dissociation of the ionic group of the pigment, and dispersion due to solvation of the pigment by the medium completely or practically does not occur, images are formed based on the method described previously. Therefore, images with high print density and no blurring can be obtained.

The following is an example of a method for evaluating that a water-soluble organic solvent does not completely or practically solvate a pigment, and the ionogenic group of a pigment does not completely or practically undergo ionic dissociation in water-soluble organic solvents, i.e., the pigment is not dispersed in a water-soluble organic solvent.

First, the pigment is prepared for use in the case where a pigment comprising a pigment particle having at least one ionogenic group bonded to the surface of the pigment particle directly or through another atomic group does not undergo ionic dissociation of the pigment. If such a pigment is available and meets the above conditions, then it can be used in the preparation of the pigment. If it is in the form of a pigment or ink dispersion solution in which the pigment is dispersed in a state where ionic dissociation has already occurred, other components, such as medium, are removed by washing with a non-ionic dissociation group that remains solid, by washing, by evaporation or other similar methods. In particular, ultrafiltration or centrifugation and drying, or other similar methods under reduced pressure and at elevated temperature, are effective. Preferably, the obtained pigment can be continuously turned into powder using a mortar or other similar device.

Then, the ground pigmented product obtained as described above is added to various types of water-soluble organic solvents at a concentration of 0.05 wt.%, Followed by stirring for 1 hour. In this case, there may also be combinations of water-soluble organic solvents with pigment, in which a clear separation of the solid-liquid phases can be visually established. Such a combination, in which case solid-liquid phase separation occurs, can be evaluated as a combination in which a water-soluble organic solvent completely or practically does not solvate the pigment, and the ionogenic group of the pigment does not completely or practically undergo ionic dissociation in a water-soluble organic solvent, i.e., a combination in which the pigment is not dispersed in a water-soluble organic solvent.

In order to conduct the assessment with greater reliability, the following can be done. In order for a pigment that is practically not dispersible in a water-soluble organic solvent to sufficiently precipitate, mixtures of the pigment and a water-soluble organic solvent make it possible to settle. The conditions under which sedimentation is carried out depend on the viscosity and other similar properties of the solvent, and a standard temperature and a time period of 100 hours can be used. After that, 50 wt.% Of the upper part of the liquid phase is carefully selected, and the collected liquid phase is filtered to remove large particles floating in it. The pore size of the microfilter used for filtration can be determined depending on the particle size of the pigment. As a standard, it can be 10 times the average particle size of the pigment in the aqueous dispersion. After that, the concentration of the pigment contained in the obtained filtrate (a solution of a dispersion of a coloring substance in a solvent) is measured.

As an example of methods for measuring pigment concentration, measurement based on absorption can be used. In particular, the measurement is carried out as follows. To an aqueous colorant dispersion solution in which the colorant is dispersed in water at a known concentration (Ck wt%), pure water is added in a predetermined amount to dilute the latter with a given degree of dilution and absorbance is measured at 550 nm. The measured value of this absorption is denoted as (ABS1). Further, the dye dispersion solution in the solvent in which the concentration is to be determined is diluted with pure water at the same dilution degree as above, where absorbance at 550 nm is also measured. The measured value of this absorption is denoted as (ABS2). As a result, the concentration of the colorant in the colorant dispersion solution in the solvent is calculated according to the following expression (2).

Expression (2)

The concentration of the coloring matter in the solution of the dispersion of the coloring matter in the solvent (wt.%) =

[Ck x (ABS2)] / (ABS2).

Using the ratio of the concentration of the coloring matter in the solution of the dispersion of the coloring matter in the solvent, determined, as shown above, to the initial concentration of the coloring matter (0.05 wt.% In the above example) in a mixture of the coloring matter and a water-soluble organic solvent, the content (%) of the coloring dispersion substances in the solvent is determined by the following expression (3).

Expression (3)

The content of the dispersion of the coloring matter in the solvent (%) = [(concentration of the coloring matter in the solution of the dispersion of the coloring matter in the solvent) / (initial concentration of the coloring matter)] × 100.

Regarding the content in which the dispersion content of the coloring matter in the solvent, determined as shown above, is equal to or less than 16, preferably 10 or less, and more preferably 5 or less, it can be concluded that the coloring matter is practically not dispersed in water-soluble organic solvent. It is believed that the water-soluble organic solvent completely or practically did not solvate the coloring matter, and the ionogenic group of the pigment was completely or practically not subjected to ionic dissociation in the water-soluble organic solvent.

Below will be described an example of a method for assessing that a pigment is a pigment that is completely or practically not solvated by a water-soluble organic solvent, and an example of a method for evaluating that an ionic group of a pigment is completely or practically not subjected to ionic dissociation in water-soluble organic solvents that are acceptable, in addition , for the valuation method described above.

First, as an example of a method for assessing that a pigment that is completely or practically not solvated by a water-soluble organic solvent, a measurement of the degree of adsorption of the surfactant on the pigment can be given. As previously described, the degree of solvation depends on how many pigments have affinity for the medium, such as a water-soluble organic solvent. It can be said that the number and size of such sites correlates with the level of adsorption of the surfactant. That is, in a pigment completely or practically solvated by a water-soluble organic solvent, sites having the above affinity are in a large amount or are large, and therefore, the adsorption of a surfactant is also high. Conversely, in a pigment completely or practically unsolvated by a water-soluble organic solvent, sites having the above affinity are small or small in size, and therefore, the adsorption of the surfactant is also low.

A surfactant has such properties that, depending on its concentration, the surface tension of the liquid changes significantly. Therefore, it is believed that measuring surface tension is an effective way of assessing the degree of adsorption of a surfactant on a pigment. For example, when comparing the surface tension of an aqueous solution containing a surfactant in a certain concentration with the surface tension of a liquid consisting of a surfactant at the same concentration, pigment at a certain concentration and water, the effective concentration of a surfactant that promotes lowering the surface tension in the first fluid is essentially the effective concentration of the surfactant of the second fluid when The surfactant is almost not adsorbed on the pigment. Therefore, the surface tension of the first fluid is also equal to the surface tension of the second fluid. Conversely, when a surfactant is adsorbed on the pigment in large quantities, the effective concentration of the surfactant decreases in the liquid containing the pigment, and therefore, the degree of decrease in surface tension is less than the degree of decrease in surface tension in an aqueous solution of surface pigment-free active substance. That is, since the pigment does not have the effect of significantly lowering the surface tension of the liquid, the amount of surfactant adsorbed on the pigment can be estimated from the difference in surface tension of an aqueous solution containing a surfactant in a certain concentration and a liquid consisting of a surfactant active substance in the same concentration, pigment in a specific concentration and water.

In particular, a liquid is first prepared consisting of a surfactant and water and containing a surfactant at a concentration of 2 mmol / kg (liquid 1) and a liquid consisting of a surfactant, pigment and water and having a surfactant a substance at a concentration of 2 mmol / kg, and a pigment at a concentration of 5 wt.% (liquid 2). No special restrictions are imposed on the surfactant, as long as it is able to noticeably change the surface tension of liquids depending on its concentration. A surfactant that provides a surface tension of 50 mN / m or less in liquid 1 may be preferred. In particular, a surfactant having a structure represented by the following structural formula (1) or structural formula (2) is preferred:

Structural Formula (1)

(In structural formula (1), R represents an alkyl group and n represents an integer).

Structural Formula (2)

(In structural formula (2), m and n each represent an integer).

In the preparation of the above liquid (2), where the pigment is removed from the ink, it is preferable that previously other components other than the pigment are removed by ultrafiltration or centrifugation and drying, or other similar methods under reduced pressure and elevated temperature. The reason for this is that if other components other than pigment, such as a solvent, a surfactant, additives and so on, which are contained in the ink, remain in large quantities, it is likely that such components will change the surface tension of the liquid or change the degree of adsorption of the surfactant on the pigment, and therefore it is likely that accurate evaluation results will not be obtained. Preferably, a liquid consisting of a pigment recovered from ink and water and containing a pigment at a concentration of 5 wt.% Has a surface tension of 65 mN / m or more.

Liquid 1 and liquid 2, prepared according to the above procedure, are mixed sufficiently, and then the surface tension of each liquid is measured. If the surface tension of liquid 1 is denoted by A (mN / m) and the surface tension of liquid 2 is denoted by B (mN / m), and the condition BA ≤ 10, and preferably BA ≤ 5, is satisfied, then we conclude that the surfactant is completely or practically not adsorbed on the pigment. Then they conclude that such a pigment is completely or practically not solvated by a medium, such as a water-soluble organic solvent.

An example of a method for evaluating that the ionic group of a pigment is completely or practically not subjected to ionic dissociation in water-soluble organic solvents will be described. For example, such an assessment can be made by measuring the electrophoresis of particles or by measuring the zeta potential.

When the ionic groups of the pigment undergo dissociation in a water-soluble organic solvent, electric charges appear on the pigment, and therefore their movement in a specific direction according to their polarity, i.e., the so-called electrophoresis in the presence of an electric field occurs. Also, a pigment bearing electrical charges causing electrophoresis has a specific or greater value of the absolute value of the zeta potential in a water-soluble organic solvent. On the contrary, if a pigment, which, although it has ionogenic groups, is not involved completely or essentially in movement in a specific direction in the presence of an electric field, that is, electrophoresis is completely or practically not occurring, then it is considered that it has a (very) small absolute value values of the zeta potential and completely or practically does not carry electric charges, that is, the ionogenic pigment groups completely or practically do not undergo ionic dissociation.

In particular, the pigment or ink containing the pigment is diluted with various types of water-soluble organic solvents. When pigment-containing inks are used, components other than pigment, such as water and medium, are also inevitably contained in the diluted solution. However, they have practically no effect, since the ink is diluted to a very low concentration, and it can be considered that the combined effect between the water-soluble organic solvent present in large excess and the pigment is dominant.

This diluted solution is measured using a zeta potential measurement system with an electron microscope (trademark: ZEECOM; manufactured by Microtec Nition). In the case when the particles completely or practically do not move in a particular direction when voltage is applied to them and do not undergo electrophoresis at all or almost, or in the case when the measured absolute value of the zeta potential is (very) small, we conclude that the ionogenic group of the pigment is completely or practically does not undergo ionic dissociation.

The aqueous inks of the present invention can have the same composition as any conventional aqueous pigment-based inks, except that, in particular, water-soluble organic solvents are included, as described above. More specifically, the aqueous ink of the present invention, which includes at least water, several water-soluble organic solvents and a coloring matter, is primarily characterized in that the coloring matter is a pigment containing a pigment particle having at least , one ionic group bound to the surface of the pigment particle directly or through another atomic group, and water-soluble organic solvents include at least one favorable medium, and, at least one adverse environment that is distinguished using the evaluation method described above, where the adverse environment completely or practically does not solvate the pigment, and the ionogenic group completely or practically does not undergo ionic dissociation in the adverse environment, and a water-soluble organic solvent that exhibits the maximum value Ka among the corresponding Ka values of water-soluble organic solvents determined by the Bristow method is an adverse environment. As a result, the pigment in the ink can have a very high dispersion stability, and at the same time, the ink can have a sufficiently high degree of surface coverage even when using a small amount of ink droplets applied to the recording medium, in particular plain paper, and can also be formed image with very good print quality and high print density.

The value of Ka water-soluble organic solvent

In the present invention, it is important that the water-soluble organic solvent exhibiting a maximum Ka value among the corresponding Ka values of the water-soluble organic solvents contained in the aqueous ink is an adverse environment.

The Ka value determined by the Bristow method is described below. This value is used as a measure that shows the permeability of the liquid in the recording medium. This is described below with an ink case. If the ink permeability is denoted by the amount of ink V per 1 m ² , then the number of penetrated ink V (ml / m ² = μm) in the recording medium after a certain time t, after the ink droplets have been ejected, is described by the following expression of the Bristow's equation ) (four).

Expression (4)

Almost all ink instantly after being applied to the recording medium is absorbed in the recording medium on the rough parts of its surface (rough parts of the surface of the recording medium) and slightly penetrates inward (in the deep direction) of the recording medium. The time during which this occurs is the contact time ( t _W ), and the amount of ink absorbed during the contact time in the recording medium on its rough parts is V _r . When the time exceeds the contact time, after the ink is applied to the recording medium, the ink penetrates inside (in the depth direction) of the recording medium in an amount proportional to the exponent 1/2 of the time exceeding the contact time, i.e. ( t - t _W ) ^{1 / 2} , whereby the amount of penetrated ink V increases. Ka is the proportionality coefficient of part of this increase and takes on a value corresponding to the penetration rate. In addition, the Ka value can be measured using a Bristow method for dynamic fluid permeability testing (e.g., the trademark Dynamic Permeability Tester S manufactured by Toyo Seiki Seisaku-sho, Ltd.).

In addition, the Ka value in the present invention, measured by the Bristow method, is a value measured using plain paper as a recording medium (e.g., PB paper, supplied by CANON INC., Used in copying machines or page-printing devices ( laser printers) using an electrophotographic system, and in printers using an inkjet recording system, and PPC paper, which is paper used in copiers that use electronic photographic system). Also, with regard to the measurement conditions, it is assumed that they are common for offices and other similar institutions, for example, temperatures from 20 ° C to 25 ° C and humidity from 40% to 60%.

In addition, according to studies carried out by the authors of the present invention, from the point of view of improving the quality of the image being formed, it is preferable that the Ka value for ink be selected less than 1.5 ml / m ² / ms ^1/2 , more preferably, the Ka value is selected from 0.2 ml / m ² / ms ^1/2 or to less than 1.5 ml / m ² / ms ^1/2 . That is, if the ink can have such a composition that the Ka value is less than 1.5 ml / m ² / ms ^1/2 , then the solid-liquid phases are separated at an early stage during the penetration of ink into the recording medium and can be formed high quality images.

Water soluble polymer

As stated above, when the pigment is present in large quantities on the surface of the recording medium, vigorous scratching of the print surface may cause blurriness even after a sufficient time has elapsed after printing, or blurriness of the print may occur if something is written using a water-based marker ink on images after printing. That is, pigment inks have the disadvantage of being characterized by low scratch and marker resistance.

In the aqueous ink of the present invention having the composition described above, a water-soluble polymer that is completely or practically not adsorbed on the pigment can be added. This improves scratch resistance. The reason why this increased scratch resistance is achieved is discussed below. The water-soluble polymer contained in the ink practically does not interact with the pigment in the solution. However, when ink is applied to the recording medium, water evaporates, as a result of which the water-soluble polymer penetrates between the pigment particles during pigment flocculation, and the mutual bond strength between the pigment particles increases. As a result, the pigment can be more firmly attached to the recording medium with an increase in scratch resistance.

Adsorption of a water-soluble polymer on a pigment

The pigment used in the present invention is characterized in that the adverse environment completely or practically does not solvate the pigment. The pigment is additionally characterized in that it also does not interact with the water-soluble polymer, namely, the water-soluble polymer is practically not adsorbed on the surface of the pigment particles. If a water-soluble polymer is adsorbed on the surface of the pigment particles, the ionogenic groups present on the surface of the pigment particles are coated with a water-soluble polymer. This makes it difficult to achieve a positive effect of the present invention, in which an unfavorable environment contributes to the flocculation of the pigment, and it is believed that this greatly affects the image performance. Accordingly, the water-soluble polymer in the present invention may preferably be a water-soluble polymer that does not adsorb on the pigment in the ink and remains in a free state.

The previously described method for measuring the degree of adsorption of a surfactant on the surface of pigment particles is an affordable method for assessing that an adverse medium does not solvate the pigment. In both this method and the method for evaluating that a water-soluble polymer is not adsorbed on the pigment, a method can be used in which the surface tension of an aqueous solution containing a water-soluble polymer is compared with the surface tension of an aqueous solution containing a water-soluble polymer, a pigment and water, estimating how much water-soluble polymer is adsorbed on the pigment.

In particular, a liquid was first prepared comprising a water-soluble polymer and water, and containing a water-soluble polymer at a concentration of 0.1 wt.% (Liquid 3), a liquid including a water-soluble polymer, a pigment and water, and containing a water-soluble polymer at a concentration of 0.1 wt. % and pigment at a concentration of 5 wt.% (liquid 4), and a liquid including pigment and water, and containing pigment at a concentration of 5.0 wt.% (liquid 5).

Liquid 3, liquid 4 and liquid 5, prepared according to the above procedure, were mixed enough, and then the surface tension of each liquid was measured at ordinary temperature (25 ° C). If the surface tension of the liquid 3 is denoted by C (dyne / cm), the surface tension of the liquid 4 by D (dyne / cm) and the surface tension of the liquid 5 by E (dyne / cm), and if the ratio DC ≤ 10 is satisfied, and preferably - DC ≤ 5, and the ratio in the following expression (5), it is concluded that the water-soluble polymer is completely or practically not adsorbed on the pigment.

Expression (5)

The surface tension measured in the state where the water-soluble polymer is practically not adsorbed on the pigment, namely, the surface tension measured in the state when the water-soluble polymer does not lead to any changes in the surface tension of the liquid, is the surface tension E of the liquid 5. Also, the surface tension, measured when the water-soluble polymer is in a free state in an aqueous solution, namely surface tension, measured under the assumption that the state in which ohm, the adsorption of the water-soluble polymer on the pigment has reached saturation, and the free polymers present in the aqueous solution are the surface tension C of liquid 5. Therefore, the E-C value represents the level of change in surface tension from the beginning to the end of the adsorption.

In contrast, the surface tension measured in the state where the pigment and the water-soluble polymer are mixed is the surface tension D of the liquid 4. It is believed that the water-soluble polymer in the liquid 4 is in two states: (1) the state in which it is adsorbed on the pigment , and (2) the state in which it is present as free polymers in an aqueous solution. Despite the fact that it is difficult to accurately determine the details of states (1) and (2) relative to the total mass of the water-soluble polymer added to liquid 4, they can be estimated to a certain extent based on the above expression (5). Thus, the D-C value represents the level of change in surface tension from the beginning to the end of adsorption, that is, the change made by the water-soluble polymer.

For example, when the difference between the surface tension D and the surface tension C is small, namely, the value (DC) / (EC) is 0.3 or less, it is considered that the state of the surface tension D and the state of the surface tension C are very close to friend, and the state of surface tension D is close to the concentration of free polymers necessary for the manifestation of surface tension C. Conversely, when the difference between surface tension D and surface tension C is large, and (DC) / (EC) becomes more than 0.3, it is believed that the surface tension state D and the surface tension state C are different from each other, and it is believed that the surface tension state D does not characterize the concentration of free polymers required for the manifestation of surface tension C, and a water-soluble polymer is adsorbed on the pigment.

Two-fluid system

When the aqueous ink of the present invention is used as the aqueous ink used in an image forming method (in a two-fluid system), comprising the step of applying aqueous ink containing a pigment to a recording medium, and the step of applying a reaction liquid capable of creating a state of dispersion of the pigment in aqueous ink when contact with aqueous ink on the recording medium, compared with cases in which images are formed using a traditional two-fluid system, the ink may have a sufficiently large shuyu degree of surface coatings, even when using a small amount of ink droplets can be obtained an image with high print density. The reason why the above effect is achieved is discussed below.

The traditional two-fluid system is used to obtain images with a high print density by leaving a large amount of coloring matter in part of the layer surface of the recording medium. Therefore, the aqueous ink and the reaction liquid are brought into contact with each other immediately before, or at the same time, when the aqueous ink and the reaction liquid are applied to the recording medium to complete the reaction. Accordingly, in some cases, a small degree of surface coverage can be achieved for a large number of drops of ink.

However, with regard to the present invention, it provides a time difference between the application of the reaction liquid to the recording medium and the application of aqueous ink, as a result of which the reactive components of the reaction liquid are present in a smaller amount in the place where the ink penetrated in the depth direction a little further from the part surface of the recording medium than on a part of the surface of the recording medium. The aqueous ink of the present invention is applied to a recording medium in accordance with this method, whereby the phenomenon shown in FIG. 14A, 14B and 14C, occurs before the pigment reacts with the reactive component. Further, the remainder of the coloring matter, penetrating in the depth direction a little further from a part of the surface of the recording medium, reacts quickly with reactive components present in large quantities at the place where the ink penetrated in the direction deep into a little further from the surface of the recording medium. Therefore, the ink has a sufficiently large degree of surface coverage on a part of the surface of the recording medium, and the colorant is prevented from penetrating deep into the recording medium, whereby images with a high print density can be obtained.

On the other hand, if aqueous ink that is not covered by the present invention is applied to the recording medium, it is very difficult to cause flocculation of the coloring matter in the desired places without carefully balancing the rate of penetration of the liquid medium with the rate of flocculation of the coloring matter. Therefore, if such aqueous inks are applied that are not within the scope of the present invention, the anti-spatter behavior may be lower, the ink may have a small degree of surface coverage with a large number of ink droplets, and images with a high print density cannot be obtained.

Water ink

In the aqueous ink of the present invention, with regard to the pigment used, it is important that the composition includes water-soluble organic solvents, as described above. Apart from the case when ink can be a traditional ink. An aqueous medium, a coloring matter, a water-soluble polymer, and other components that make up the aqueous ink of the present invention are described below.

Water environment

The following describes the aqueous medium forming the aqueous ink of the present invention. The aqueous medium is a mixed solvent of water and water-soluble organic solvents. In the present invention, as stated above, water-soluble organic solvents are grouped into solvents, which are a favorable environment and an unfavorable environment for pigment. Then, based on the results of such an assessment, it is required that, in the preparation of the ink, water-soluble organic solvents are selected and suitably mixed so that at least a favorable environment and an unfavorable environment are mixed, and the content of each water-soluble organic solvent is in the range indicated in the present invention.

Water-soluble organic solvents may in particular include, for example, alkyl alcohols having from 1 to 4 carbon atoms, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol and tert-butyl alcohol; amides such as dimethylformamide and diethylacetamide; ketones or keto alcohols such as acetone and diacetone alcohol; ethers such as tetrahydrofuran and dioxane; polyalkylene glycols such as polyethylene glycol and polypropylene glycol; alkylene glycols in which alkylene groups have from 2 to 6 carbon atoms, such as ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol and diethylene glycol; lower alkyl ether acetates such as polyethylene glycol monomethyl ether acetate; glycerol; lower alkyl esters of polyhydric alcohols, such as ethylene glycol monomethyl (or ethyl) ether, diethylene glycol methyl (or ethyl) ether and triethylene glycol monomethyl (or ethyl) ether; and N-methyl-2-pyrrolidone, 2-pyrrolidone, and 1,3-dimethyl-2-imidazolidinone. It is also preferred that deionized water is used as water.

There are no particular restrictions on the content of water-soluble organic solvents in the aqueous ink of the present invention. It may be preferable that their content is in the range from 3 wt.% To 50 wt.% Of the total ink mass. It may also be preferable that the water in aqueous ink has a content of from 50 wt.% To 95 wt.% Of the total weight of the ink.

In a preferred embodiment of the present invention, when the total content (wt.%) Of the favorable environment in the ink is denoted by X, and the total content (wt.%) Of the adverse environment in the ink is denoted by Y, the types and contents of the water-soluble organic solvents included aqueous ink, adjusted so that the ratio of X: Y [total content (wt.%) unfavorable environment: total content (wt.%) unfavorable environment] was within the range from X: Y = 10: 5 or more to 10:30 or less preferably from X: Y = 10: 5 or more to 10:10 or less, and more preferably from X: Y = 10: 6 or more to 10:10 or less. In addition, “ratio of X: Y = 10: 5 or more to 10:30 or less” means that Y may be from 5 or more to 30 or less when X is 10.

According to studies by the inventors of the present invention, when the favorable environment contained in the aqueous ink reaches a high concentration, the aqueous ink may have a higher storage stability, but it is difficult to achieve a high print density. Also, when, on the other hand, the favorable environment contained in the aqueous ink reaches a low concentration, a high print density can be achieved, but the aqueous ink may have insufficient storage stability. To solve such a problem, the ratio of the favorable environment to the adverse environment in water-soluble organic solvents in the ink can be adjusted as described above, as a result of which both storage stability and high print density can be achieved for the ink. Furthermore, as described above, in the present invention, the Kristow value determined by the Bristow method, which is a measure showing the permeability in the recording medium, is controlled by selecting each water-soluble organic solvent introduced into the ink. This makes it possible to achieve an effect that was previously unattainable, that is, an effect in which ink has a sufficiently high degree of surface coverage even with a small amount of ink droplets and can print with high density.

Coloring matter

The colorant contained in the aqueous ink of the present invention is described below. As a colorant included in the aqueous ink of the present invention, a pigment containing a pigment particle having at least one ionogenic group bonded to the surface of the pigment particle directly or through another atomic group is used. As long as this condition is met, no specific restrictions are imposed on it. You can apply the following pigments: a pigment containing a pigment particle, which is a compound with an ionic group attached using the diazocomposition method to the surface of the pigment particle; a pigment containing a pigment particle with an ionic group introduced by surface oxidation treatment, such as surface treatment of the pigment particle with sodium hypochlorite or treatment with ozone in water; and a pigment on which a dispersant having an ionic group, a surfactant, a polymer dispersant, or other similar substances is adsorbed. Any of these pigments may be used individually or as a mixture of two or more types.

In particular, it is preferable to use a pigment containing a pigment particle having at least one group selected from the group consisting of -COOM1, -SO ₃ M1 and -PO ₃ H (M1) ₂ (where M1 represents a hydrogen atom, alkaline metal, ammonium or organic ammonium) chemically bonded directly or through another atomic group to the surface of the pigment particle. In addition, it is preferable to use those in which such another atomic group is an alkylene group having from 1 to 12 carbon atoms, a substituted or unsubstituted phenylene group, or a substituted or unsubstituted naphthylene group. In the case of a pigment containing a pigment particle having a —COOM1 group from the above ionic groups chemically bonded directly or via another atomic group to the surface of the pigment particle, it can be relatively water resistant and therefore may be more preferred for use.

In particular, it is also preferable to use a pigment containing a pigment particle having a —C ₆ H ₄ —COOM1 group or —C ₆ H ₃ - (COOM1) ₂ group (where M1 represents a hydrogen atom, an alkali metal, ammonium or organic ammonium) introduced on the surface of the pigment. In particular, a pigment particle into which a —C ₆ H ₃ - (COOM1) ₂ group has been introduced leads to preferred results in the composition of the present invention.

As for the amount in which the above -C ₆ H ₄ -COOM1 group or -C ₆ H ₃ - (COOM1) ₂ group is introduced on the surface of the pigment particles, the preferred results in the present invention are achieved when the amount introduced per unit surface area The pigment particle is large. This is attributed to the fact that, as previously described, the degree of solvation of the pigment by water-soluble organic solvents decreases with an increase in ionogenic groups due to spatial difficulty or another similar phenomenon.

There are no particular restrictions on the pigment used in the aqueous ink of the present invention, and any of them listed below can be used.

As the pigment used in black ink, carbon black is preferred. Any carbon black can be used, for example furnace black, lamp black, acetylene black or duct gas black. In particular, commercially available products may be used, for example RAVEN 7000, RAVEN 5750, RAVEN 5250, RAVEN 5000 ULTRA, RAVEN 3500, RAVEN 2000, RAVEN 1500, RAVEN 1250, RAVEN 1200, RAVEN 1190 ULTRA-II, RAVEN 1170 and RAVEN 1255 (the above products are manufactured by Columbian Carbon Japan Limited); BLACK PEARLS L, REGAL 400R, REGAL 330R, REGAL 660R, MOGUL L, MONARCH 700, MONARCH 800, MONARCH 880, MONARCH 900, MONARCH 1000, MONARCH 1100, MONARCH 1300, MONARCH 1400, MONARCH 2000 and VALCAN XC-72 (the above products manufactured by Cabot Corp.); COLOR BLACK FW1, COLOR BLACK FW2, COLOR BLACK FW2V, COLOR BLACK FW18, COLOR BLACK FW200, COLOR BLACK S150, COLOR BLACK S160, COLOR BLACK S170, PRINTEX 35, PRINTEX U, PRINTEX 140U, PRINTEX BLACK 6 SPECIAL 5, SPECIAL BLACK 4A and SPECIAL BLACK 4 (the above products are manufactured by Degussa Corp.); and No.25, No.33, No.40, No.47, No.52, No.900, No.2300, MCF-88, MA600, MA7, MA8 and MA100 (the above products are manufactured by Mitsubishi Chemicals, Inc. ) Carbon black specially prepared for the present invention may also be used. However, in the present invention, the examples are in no way limited to carbon blacks, and any conventionally known carbon black can be used. In addition to carbon black, magnetic fine particles of magnetite, ferrite or other similar particles and black titanium can also be used as black pigment. Pigment particles used in other inks than black ink may include various types of organic pigment particles. Such organic pigments may include, for example, insoluble azo pigments such as toluidine red, toluidine chestnut, hansa yellow, benzidine yellow and pyrazolone red; soluble azo pigments such as lithol red, sunny burgundy, scarlet pigment and persistent red 2B; vat dye derivatives such as alizarin, indatron and thioindigooid chestnut; pigments such as phthalocyanine, such as phthalocyanine blue and phthalocyanine green; quinacridone-type pigments such as quinacridone red and quinacridone purple; pigments such as perylene, such as perylene red and perylene red; isoindolinone type pigments such as isoindoline yellow and isoindoline orange; imidazolone type pigments such as benzimidazolone yellow, benzimidazolone orange and benzimidazolone red; pigment-type pigments such as piratron red and pyratron orange; and indigo pigments, azo condensation products pigments, thioindigo pigments, diketopyrrolopyrroles pigments, vat yellow, acylamide yellow, quinophthalone yellow, azo nickel chelate yellow, copper chelate with azomethine yellow, perinone orange, anthrone orange, dianthraquinazinyl red, diantraquinazinyl red. Of course, without limitation for these pigments, other organic pigments can also be used.

Organic pigments used in the present invention, when indicated by the Color Index (C.I.) Number, may include, for example, the following:

C.I. yellow pigment 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 97, 109, 110, 117, 120, 125, 128, 137, 138, 147, 148, 150, 151, 153, 154, 166, 168, 180, 185;

C.I. pigment orange 16, 36, 43, 51, 55, 59, 61, 71 etc .;

C.I. pigment red 9, 48, 49, 52, 53, 57, 97, 122, 123, 149, 168, 175, 176, 177, 180, 192, 215, 216, 217, 220, 223, 224, 226, 228, 238, 240, 251, 255, 272;

C.I. purple pigment 19, 23, 29, 30, 37, 40, 50;

C.I. blue pigment 15, 15: 1, 15: 3, 15: 4, 15: 6, 22, 60, 64;

C.I. pigment green 36;

C.I. brown pigment 23, 25, 26.

In the present invention, the pigment may preferably be in a content of from 0.1 wt.% To 15 wt.%, And particularly preferably from 1 wt.% To 10 wt.% Of the total weight of the ink.

Water soluble polymer

A water soluble polymer that can be added to the aqueous ink of the present invention is described below. In the present invention, the water-soluble polymer is evaluated as described previously with respect to its pigment adsorbability. Then, based on the results of such an assessment, a water-soluble polymer, which is completely or practically not adsorbed on the pigment, should be selected and mixed accordingly to obtain ink.

The water soluble polymer used in the present invention may preferably be an ionic polymer or a nonionic polymer having a hydrophilic group. The ionic polymer may preferably be a homopolymer consisting of an ionic monomer, or a copolymer of a hydrophobic monomer and an ionic monomer. The nonionic polymer is preferably a homopolymer consisting of a nonionic monomer, or a copolymer of a hydrophobic monomer and a nonionic monomer. Also, in the present invention, these polymers can be used in combination. They are described below by listing specific groups of monomers.

Ionogenic Monomer

The ionic monomer may preferably be an anionic monomer. In particular, it may include acrylic acid, methacrylic acid, maleic acid, and styrene sulfonic acid. Any of them can be used individually or in an appropriate combination of two or more types. Of course, in the present invention, the examples are by no means limited to them.

Nonionic monomer

The nonionic monomer may particularly include, for example, polyvinyl ether derivatives such as polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylamide, polyvinyl methyl ether, polyvinyl ethyl ether and polyvinyl butyl ether; polysaccharides such as cellulose, methyl cellulose and ethyloxyethyl cellulose; alginic acid esters with polyhydric alcohol; water soluble urea resin; dextrin derivatives; casein; polyvinyl ether compounds; and polyalkylene oxides such as polyethylene oxide and polypropylene oxide, including a copolymer of both. Any of these may be used individually or in an appropriate combination of two or more types. Of course, in the present invention, the examples are by no means limited to them.

Hydrophobic monomer

The hydrophobic monomer may particularly include, for example, styrene, vinylnaphthalene, alkyl methacrylates such as methyl methacrylate; phenylmethyl methacrylate, benzyl methacrylate, 2-ethoxyethyl methacrylate, methacrylonitrile, 2-trimethylsiloxyethyl methacrylate, glycidyl methacrylate, p-tolyl methacrylate, sorbyl methacrylate, alkyl acrylates such as methyl acrylate; phenyl acrylate, benzyl acrylate, acrylonitrile, 2-trimethylsiloloxyethyl acrylate, glycidyl acrylate, p-tolyl acrylate, and sorbyl acrylate. Any of these may be used individually or in an appropriate combination of two or more types. Of course, in the present invention, the examples are by no means limited to them.

Polymer

The water-soluble polymer of the present invention may preferably be a homopolymer consisting of an ionic monomer, a homopolymer consisting of a nonionic monomer, a copolymer consisting of an ionic monomer and a hydrophobic monomer, or a copolymer consisting of a nonionic monomer and a hydrophobic monomer, any of which can be used in combinations, or branched polymers, representative of which are block copolymers, random copolymers and grafted copolymers, or s used salts thereof. In addition, as specific examples of salts, they may include alkali metal salts such as sodium, lithium and potassium, and ammonium salts, alkylamine salts and alkanolamine salts. Any of these may be used individually or in an appropriate combination of two or more types.

When the above copolymers are anionic, they can have acid numbers in the range of 100 to 500, and the dispersion of the acid number can preferably be in the range of 20% of the average acid number. By adjusting the acid number within the above region, the pigment can be stably dispersed in the ink.

The water-soluble polymer may have a weight average molecular weight in the range of 1,000 to 30,000, and more preferably in the range of 3,000 to 15,000, and may also preferably have a molecular weight distribution of Mw / Mn (Mw: weight average molecular weight, Mn: number average molecular weight) equal to 3 or less. Also, the segment of the ionic polymer chain may preferably have a weight average molecular weight (Mw) in the range of 1000 to 20,000, and more preferably in the range of 3,000 to 20,000. Since the content of the segment of the ionic polymer chain in the water-soluble polymer is controlled in the above region, high viscosity can be prevented. ink, and the pigment may have dispersion stability; moreover, both characteristics are achieved together at a high level. Also, if the water-soluble polymer has a wide molecular weight distribution, properties based on the molecular weight of the water-soluble polymer described above can be difficult to obtain. Therefore, the water-soluble polymer may preferably have a uniform molecular weight distribution. Such a water-soluble polymer may preferably be introduced in the range from 0.1 wt.% To 5.0 wt.% Of the total ink mass. In addition, the concentration ratio (wt.%) Of the pigment and the water-soluble polymer contained in the ink (P / B ratio) may preferably be from 0.02 to 150.

In an embodiment in which a water-soluble polymer is added to aqueous ink, the aim is to produce aqueous ink that can simultaneously satisfy three characteristics, that is, high print density, anti-spatter and high scratch resistance. In particular, it is known in the art that in order to increase scratch resistance, it is effective to add a large amount of water-soluble polymer. However, if the amount of added anionic polymers increases, the dispersion of the pigment in the ink becomes unstable due to the salting out effect and the pigment may tend to flocculate.

The idea of the present invention can be explained on the basis of the salting out effect. Salting out is a phenomenon in which the solubility of a dissolved substance hydrated in a solution for stable dissolution decreases, and this dissolved substance begins to precipitate, since ions are generated in large quantities as a result of adding additional electrolyte to imbalance the hydration balance and, therefore, hydrated water is removed from this solute that hydrates with great difficulty.

The pigment dispersed by ionogenic groups is hydrated with a large number of water molecules in solution and is in a stable dispersed state. The salt of the anionic polymer is added to this solution, as a result of which the hydration of the ions generated when the polymer is dissolved also occurs, and therefore water molecules are in short supply. In this case, water molecules that hydrate the pigment are selected, as a result of which the stability of the pigment dispersion is greatly reduced. In addition, the addition of anionic polymer in large quantities has a negative effect on the thickening and storage stability of the ink. In addition, it is known that the presence of anionic polymer in the ink in large quantities makes the ink very permeable to the recording medium, which leads to poor print quality.

As a result of studies conducted by the inventors of the present invention, they found that a nonionic polymer that does not have an ionic group and is considered to contribute little to the stability of the pigment dispersion can be added to the ink, resulting in ink that provides printing with enhanced scratch resistance and high stability of the pigment dispersion. It has been found that when only non-ionic polymer is added to the ink, a larger amount of polymer can be added than when only an anionic polymer is added, and furthermore, scratch resistance is greatly improved. However, with respect to spreading, it has been found that when only a nonionic polymer is used, the performance is worse than when only an anionic polymer is used. The reason is that the ion concentration in the ink does not increase, even if a nonionic polymer that does not have an ionic group is added to the ink, and pigment flocculation does not occur due to a salting out effect.

Accordingly, in the present invention, it has been found that the above three technical problems can be solved by using an anionic polymer and a nonionic polymer in combination; moreover, the first is effective in promoting pigment flocculation, improving print density and preventing spreading, and the second is effective in increasing scratch resistance. Thus, the added water-soluble polymers are separated from a functional point of view. It was also found in the evaluation of a real image that high print density, spreading control and high scratch resistance can be simultaneously achieved when an anionic polymer and a nonionic polymer are used in combination.

Further, the authors of the present invention put forward an assumption about the reason for high scratch resistance. In the process of applying pigment ink to the recording medium and then evaporating the water in the ink, water-soluble polymers are deposited or adsorbed on the surface of the recording medium, as a result of which a flocculation force acts to enhance pigment flocculation. Accordingly, even when the pigment comes in contact with the external environment, for example, the print surface is scratched severely or something is written with a marker with water ink on the image, the pigment peeling from the surface of the recording medium decreases, therefore, the scratch resistance increases. In order to enhance the flocculation force between the pigment particles to improve scratch resistance, it is more preferable to use a copolymer of an ionic monomer and a hydrophobic monomer, a copolymer of a nonionic monomer and a hydrophobic monomer, or other similar copolymers that are considered capable of increasing the binding force between the pigment particles and enhance the adsorption force water-soluble polymers on the surfaces of pigment particles.

Other components

In addition to the components described above, the aqueous ink of the present invention can use a moisture retention compound as an ink component, such as urea, a urea derivative, trimethylolpropane or trimethylolethane, in order to provide moisture retention. In ink, a moisture retention compound such as urea, a urea derivative, or trimethylolpropane can usually be contained at a concentration of from 0.1 wt.% To 20.0 wt.%, And more preferably from 3.0 wt.% To 10 , 0 wt.% Of the total mass of ink.

In addition to the components described above, various additives, such as a surfactant, a pH adjuster, a corrosion inhibitor, an antiseptic agent, an anti-mold agent, an antioxidant, an anti-reduction agent, an evaporation accelerator, and a chelating agent, can be added to the aqueous ink of the present invention.

The surfactant used in the present invention may preferably be a compound having a structure represented by the following structural formula (1) or structural formula (2).

Structural Formula (1)

(In structural formula (1), R represents an alkyl group and n represents an integer).

Structural Formula (2)

(In structural formula (2), m and n each represent an integer).

Color ink

The imaging method of the present invention is implemented, which is an inkjet recording method in which recording is performed on plain paper using black ink and at least one color ink, and characterized in that the aqueous ink having the above composition is used as black ink, and when forming an image consisting of an image formed by black ink and an image formed by color inks that are directly adjacent to each other It is carried run for applying the black ink to form an image, and then carried run for applying the color ink to the area where the image has already been formed as a result of previous run.

Here, color ink is described in the case where the ink of the present invention is used in black ink only. In the image forming method of the present invention, any of the conventionally known water based inkjet ink can be used.

Color ink colorant may include water soluble colorants. In particular, it is preferable to use a water-soluble dye having an anionic group as a solubility enhancing group. The color of the color inks used in the present invention can be suitably selected from cyan, magenta, yellow, red, green, blue, and orange.

The water-soluble dye having the anionic group used in the present invention can be any of the water-soluble acid dyes, direct dyes, and active dyes listed in COLOR INDEX, without any specific restrictions. Dyes not included in the COLOR INDEX list can also be used. In particular, it is preferable to use the following dyes having anionic groups, for example, a sulfonic group. Any of these dyes can be used in ink in the range of concentrations from 1 wt.% To 10 wt.%, And preferably from 1 wt.% To 5 wt.%.

Specific dyes may include the following:

C.I. Direct yellow 8, 11, 12, 27, 28, 33, 39, 44, 50, 58, 85, 86, 87, 88, 98, 100, 110;

C.I. Direct red 2, 4, 9, 11, 20, 23, 24, 31, 39, 46, 62, 75, 79, 80, 83, 89, 95, 197, 201, 218, 220, 224, 225, 226, 227, 228, 230;

C.I. Direct blue 1, 15, 22, 25, 41, 76, 77, 80, 86, 90, 98, 106, 108, 120, 158, 163, 168, 199, 226;

C.I. Direct yellow 1, 3, 7, 11, 17, 23, 25, 29, 36, 38, 40, 42, 44, 76, 98, 99;

C.I. Acid Red 6, 8, 9, 13, 14, 18, 26, 27, 32, 35, 42, 51, 52, 80, 83, 87, 89, 92, 94, 106, 114, 115, 133, 134, 145, 158, 198, 249, 265, 289;

C.I. Acid blue 1, 7, 9, 15, 22, 23, 25, 29, 40, 43, 59, 62, 74, 78, 80, 90, 100, 102, 104, 117, 127, 138, 158, 161.

The color ink colorant may include, in addition to the above water-soluble dyes, the following 1-3. These colorants are preferred since they exhibit good water resistance when applied to a recording medium.

1. Dyes having a carboxyl group as a solubility enhancing group.

2. Fat-soluble dyes.

3. Pigments.

There are no special restrictions on fat-soluble dyes, as long as they are dyes listed in the COLOR INDEX color index. There are also no special restrictions even when they are new dyes not listed in the COLOR INDEX color index. In particular, they may include the following. Any of these dyes can be used in ink in the range of concentrations from 1 wt.% To 10 wt.% And preferably from 1 wt.% To 5 wt.%.

C.I. Fat-soluble yellow dye 1, 49, 62, 74, 79, 82, 83, 89, 90, 120, 121, 151, 153, 154;

C.I. Fat-soluble red dye 25, 31, 86, 92, 97, 118, 132, 160, 186, 187, 219;

C.I. Fat-soluble blue dye 33, 38, 42, 45, 53, 65, 67, 70, 104, 114, 115, 135.

When the pigment is used as a coloring substance of color ink, the pigment may preferably have a concentration of from 1 wt.% To 20 wt.% And more preferably from 2 wt.% To 12 wt.% Of the total ink weight. The pigment used for color inks in the present invention may include the following. Of course, in the present invention, the examples in no way limit them. The pigments obtained for the first time for the present invention can also be used for granted.

C.I. Pigment yellow 1, 2, 3, 13, 16, 74, 83, 128;

C.I. Pigment red 5, 7, 12, 48 (Ca), 48 (Mn), 57 (Ca), 112, 122;

C.I. Pigment blue 1, 2, 3, 15: 3, 16, 22;

C.I. Cube blue 4, 6.

In the case where a pigment is used as a coloring ink of a color ink, there is no particular limitation on the dispersant used to disperse the pigment in the ink as long as it is a water-soluble resin. Preferably, the resin has a weight average molecular weight in the range of 1000 to 30000, and more preferably in the range of 3000 to 15000.

Such a dispersant may include block copolymers, random copolymers and grafted copolymers or their salts, consisting of two monomers (at least one of which is a hydrophilic monomer) selected from styrene, styrene derivatives, vinylnaphthalene derivatives, vinylnaphthalene derivatives, ethers aliphatic alcohol and α, β-unsaturated carboxylic acids, acrylic acid, derivatives of acrylic acid, maleic acid, derivatives of maleic acid, itaconic acid, derivatives of itaconic acid, fum aroic acid, derivatives of fumaric acid, vinyl acetate, vinylpyrrolidone, acrylamide and its derivatives, and so on. Natural resins, such as rosin, shellac and starch, can also preferably be used. These resins are soluble in an aqueous solution in which the base has already been dissolved and are alkali soluble resins. In addition, any of these water-soluble resins may be present at a concentration of from 0.1 wt.% To 5.0 wt.% Of the total ink mass.

The aqueous medium used in color inks is water or a mixed solvent of water and a water-soluble organic solvent. As for water, it is preferable to use water purified by ion exchange (deionized water), rather than ordinary water containing various ions.

Specific examples of the water-soluble organic solvent may in particular include, for example, alkyl alcohols having from 1 to 4 carbon atoms, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol and tert-butyl alcohol alcohol; amides such as dimethylformamide and diethylacetamide; ketones or keto alcohols such as acetone and diacetone alcohol; ethers such as tetrahydrofuran and dioxane; polyalkylene glycols such as polyethylene glycol and polypropylene glycol; alkylene glycols in which alkylene groups have from 2 to 6 carbon atoms, such as ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol and diethylene glycol; lower alkyl ether acetates such as polyethylene glycol monomethyl ether acetate; glycerol; lower alkyl esters of polyhydric alcohols, such as ethylene glycol monomethyl (or ethyl) ether, diethylene glycol methyl (or ethyl) ether and triethylene glycol monomethyl (or ethyl) ether; and N-methyl-2-pyrrolidone, 2-pyrrolidone, and 1,3-dimethyl-2-imidazolidinone. Of these water-soluble organic solvents, the following are particularly preferred: polyhydric alcohols, such as diethylene glycol, and lower alkyl esters of polyhydric alcohols, such as ethylene glycol monomethyl (or ethyl) ether.

The water-soluble organic solvent in color inks may preferably be present in a content of from 3 wt.% To 50 wt.% And more preferably from 3 wt.% To 40 wt.% Of the total ink. Also, water may preferably be present in a content of from 10 wt.% To 90 wt.% And more preferably from 30 wt.% To 80 wt.% Of the total ink weight.

In addition to the above components, the color ink used in the present invention may optionally be supplemented with a surfactant, antifoam, antiseptic and so on, in order to obtain inks having the required physical characteristics.

Physical properties of ink

The black ink and color ink used in the present invention, consisting of the components described above, can preferably have properties that allow them to be ejected accordingly from the inkjet recording head (print head). From the point of view of ejecting from the inkjet printhead, each ink may preferably have a surface tension of 1 to 15 mPa / s and 25 mN / m or more, and more preferably a surface tension of 1 to 5 mPa / s and 25 mN / m to 50 mN / m or more. Also, when black ink and color ink are used in combination, it is further preferred that the surface tension of the color ink is lower than the surface tension of the black ink. In particular, it is preferred that black ink has a surface tension of 35 to 50 mN / m, and color ink has a surface tension of 25 to 35 mN / m.

Reaction liquid

The reaction liquid used in the present invention contains a reactive component having the function of bringing the dispersion of the dye in the ink to an unstable state. The reactive component decreases the stability of the dispersion of the colorant and causes the colorant to flocculate when the ink in which the colorant is dispersed or dissolved in the aqueous medium as a result of the action of ionic groups is contacted with the above reactive component on the recording medium. In addition, bringing the dispersion of the coloring matter in the ink to an unstable state means that a flocculation or gelation state is thereby caused when the ink and the reaction liquid are mixed on the recording medium.

Specific examples of the reactive component may include metal salts (in particular polyvalent metal ions and their salts), low molecular weight cationic compounds and cationic high molecular weight polymers. The reactive component is described below.

Polyvalent metal ion and its salt

Polyvalent metal ions may, in particular, include, for example, divalent metal ions such as Ca ²⁺ , Cu ²⁺ , Ni ²⁺ , Mg ²⁺ , Zn ²⁺ , Sr ²⁺ and Ba ²⁺ , and ions trivalent metal such as Al ³⁺ , Fe ³⁺ , Cr ³⁺ and Y ³⁺ . To introduce polyvalent metal ions into the reaction liquid, a method is known in which a polyvalent metal salt is added to the reaction liquid. By salt is meant metal salts consisting of the aforementioned polyvalent metal ions and related anions, and they must be soluble in water. Preferred anions for salt formation may include, for example, Cl ^- , NO ₃ ^- , I ^- , Br ^- , ClO ₃ ^- , SO ₄ ^2- , CO ₃ ^2- , CH ₃ COO ^- and HCOO ^- . Of course, in the present invention, the examples in no way limit them. In the present invention, from the point of view of the ability of the reaction liquid to react with aqueous ink, staining and, moreover, ease of handling of the reaction liquid, polyvalent metal ions may preferably include Ca ²⁺ , Mg ²⁺ , Sr ²⁺ , Al ³⁺ and Y ³⁺ . In addition, Ca ²⁺ is particularly preferred. Also, with regard to anions, NO ^3- is particularly preferred in terms of solubility and so on.

In the reaction liquid, polyvalent metal ions may preferably be present in a content of from 0.01% or more to 10% or less, and more preferably from 1.0% or more to 5% or less, based on the total mass of the reaction liquid, taking into account the effect due to the present invention. In particular, in order to sufficiently manifest the function of bringing the dispersion of the coloring matter to an unstable state contained in aqueous ink, and to achieve a high level image density, polyvalent metal ions can preferably be present in a content of from 2.0 wt.% Or more to 4, 0 wt.% Or less of the total mass of the reaction liquid. In addition, the content of polyvalent metal ions in the reaction liquid may be more than 10 wt.%. However, their excessive introduction is usually not necessary, since, for example, even if their content is more than 20 wt.%, One should not expect that the function of bringing the dispersion of the coloring matter to an unstable state will be enhanced.

The reaction liquid may preferably be colorless and transparent. However, it is not always necessary that the reaction liquid has no absorption in the visible region. More specifically, if it exhibits absorption in the visible region, it can be used as long as such absorption does not substantially affect the image.

Means for applying the reaction liquid

As methods for applying the reaction liquid to the recording medium, coating methods such as roller coating, coating with excess removal using a bar and spray coating are applicable. A method is also applicable in which, using the inkjet recording method in the case of ink, the reaction liquid selectively binds only to the image forming regions with which the ink is to be bound, and near the image forming regions. As a result of studies by the present inventors regarding how to apply the reaction liquid to the recording medium, they came to the conclusion that the best way is to coat the roller. The reason is that even when the reaction liquid is applied in a small amount, the distribution state of the reactive component near a part of the surface layer of the recording medium is more uniform than using other methods, and, in addition, the image quality can be higher due to the fact that it does not contain heterogeneity in areas of a continuous image, and also due to the diffusion of ink through the coating, after the ink has been applied.

When images are formed using a two-fluid system, various methods are applicable as a means by which the reaction liquid and aqueous ink are brought into contact with each other on a recording medium. However, the authors of the present invention came to the conclusion that, in order to obtain the effect of the present invention more significant, the best is the method in which aqueous ink is applied to the recording medium after the fixation of the reaction liquid to the recording medium is completed, that is, after as droplets of the reaction liquid soaked into the recording medium.

In addition, the point in time at which the fixation ends is related to the point in time at which the Ka (t-tw) ^1/2 value represented by the Bristow equation is larger than the amount of reaction liquid actually applied to the recording medium. This refers to the point in time at which droplets of the reaction liquid are absorbed into the recording medium and means “t-seconds after” calculated from the Ka value according to the Bristow method and the amount of reaction liquid.

Physical properties and applied amount of reaction liquid

Preferably, the permeability of the reaction liquid to the recording medium is from 1.3 ml / m ^-2 / ms ^-1/2 or more to 6.0 ml / m ^-2 / ms ^-1/2 or less, and more preferably from 3.0 ml / m ^-2 / ms ^-1/2 or more up to 6.0 ml / m ^-2 / ms ^-1/2 or less, in units of Ka, found by the Bristow method. Also, the reaction liquid may preferably be applied in an amount of from 0.5 g / m ² or more to 5 g / m ² or less, and more preferably from more than 2.0 g / m ² to 3.0 g / m ² or less.

In addition, the applied amount of the reaction liquid can accordingly be adjusted by adjusting the physical properties of the reaction liquid, the rotation speed of the roller used in the coating apparatus, the contact pressure of the roller on the recording medium, and so on.

Image forming method

The image forming method of the present invention is described below by providing specific examples. The image forming method of the present invention is an image forming method in which recording using an inkjet recording system on a recording medium such as plain paper using black ink and at least one color ink is carried out, and characterized in that the water ink having the composition described above is used as black ink, and to form an image consisting of an image formed by black ink and an image formed by the above color inks that are directly adjacent to each other, run (scan) to apply black ink to form an image, and then run to apply color ink to the area where the image was already formed by the previous run. Therefore, specific methods are described below.

In FIG. 8 is an example of a recording head used in implementing the image forming method of the present invention. The recording head has, as shown in FIG. 8, a line of ejection holes Bk for ejecting black ink therefrom and a line of ejection holes C, M, and Y for ejecting three color inks therefrom: cyan (C), magenta (M), and yellow (Y), respectively.

In the image forming method of the present invention, when full color images are formed, a recording head may be used in which ink is applied by using a recording head in which a line of ejection openings for ejecting black ink therefrom and a line of ejection openings for ejecting color ink therefrom offset relative to each other in the direction of the secondary run. In particular, for example, when implementing the image forming method using the recording head shown in FIG. 8, when only black images are formed, use the entire area of the line of ejection holes for black ink. When full color images are formed by mixing the black image and the color image, the images can preferably be formed so that black ink uses part a of the ejection aperture line for black ink, and C, M and Y color ink uses part b of the ejection aperture line for color ink. The case in which images are formed by mixing black images and color images is described below in more detail.

In FIG. 8 is an example of a recording head used in the present invention. The recording head has a line of ejection holes Bk for ejecting black ink from it, and a line of ejection holes C, M, and Y for ejecting three color inks from it: cyan (C), magenta (M), and yellow (Y), respectively. First, using part a of the line of the ejection holes for black ink, the print head is driven (scanned) in the horizontal direction of the pattern (the direction of the primary run) with the formation of a black image in one pass on the recording medium. Next, the recording medium is moved a distance a in the vertical direction of the pattern (the direction of the secondary run (scan)), where, during the next primary scan, in the forward direction for the print head, use part b of the ejection hole lines for color ink to form a color image in one a print pass on a recording medium on its image area formed on the first part a of the line of ejection holes for black ink. Here, part a of the line of ejection holes for black ink forms an image in the next area. This is repeated to form images by mixing black images and color images.

In FIG. 9 shows another example of a recording head used in the present invention. In that shown in FIG. 9, as in the case of FIG. 8, black ink uses part a of the line of ejection openings for black ink, and C, M and Y color ink uses part b corresponding to the entire region of the lines of ejection openings for black ink, forming images by mixing black images in the same manner as described above color images.

In FIG. 10 is another example of a recording head used in the present invention. In that shown in FIG. 10, and also in FIG. 8, black ink uses part a of the line of ejection openings for black ink, and C, M and Y color ink uses part b corresponding to the entire region of the lines of ejection openings for color ink, forming images by mixing black images and color images. Here, in the recording head of FIG. 10, a distance for drawing paper a ′ at a time is set between part a of the line of ejection openings for black ink and part b of lines of ejection openings for color ink. Hence, for a recording head constructed in this way, it follows that an excess in time difference is created corresponding to a single run during reciprocating motion, until a black image is formed and then a color image is formed. Therefore, the design of the recording head shown in FIG. 10 is more preferable than the design of the recording head shown in FIG. 9, to prevent blurring between the black image and the color image.

In FIG. 11 shows another example of a recording head used in the present invention. Where in the recording head shown in FIG. 11, a recording head is used in which the line of ejection openings for black ink and the lines of ejection openings for color ink are arranged on one straight line, in the direction of the secondary run, a black image is first formed and then a color image is formed in accordance with the paper draw.

In FIG. 12 is yet another example of a recording head used in the present invention. In the recording head of FIG. 12, the ejection hole lines for color inks are provided symmetrically in the initial run direction in two rows for each cyan ink (C1, C2), magenta ink (M1, M2) and yellow ink (Y1, Y2), so that the ejection order of color ink is the same in both forward and reverse directions during the initial run. As a result, images by mixing black images and color images can be formed by a bi-directional printing method. In this case, first, part a of the line of ejection holes for black ink is used to form a black image, and then the recording medium is moved a distance a in the direction of the secondary run, where, during the movement in the reverse direction of the next primary run in the print head, use part b ejection orifice lines for color ink for color image forming with one-pass printing on the recording medium for recording image region previously formed by using a part of line of ejection openings for black ink, when a portion of line of ejection openings of the black ink forms an image on the next region. This is repeated to form an image by mixing black images and color images.

Also in the recording head, as adapted for the bi-directional printing shown in FIG. 12 and in the recording head described with reference to FIG. 10, the lines of ejection openings can be arranged such that a distance for drawing paper a ′ at a time is set between part a of the line of ejection openings for black ink and part b of lines of ejection openings for color ink (see FIG. 13), so that in order to provide a time difference corresponding to a one-time run in a reciprocating motion when forming a black image and then forming a color image, whereby the recording head is designed more preferably to prevent fuss The signs of blurring between a black image and a color image.

Above, an image forming method has been described. It is taken for granted that the shapes of the recording head used in the image forming method of the present invention are in no way limited to those shapes shown in FIG. 8-13. Also, depending on the recording recorder used, the number of passes differs, and therefore printing is in no way limited to single-pass printing.

When images are formed by mixing black images and color images on plain paper, the aqueous ink of the present invention can be used for black ink. For such a design, it is believed that, as indicated above, flocculation or destruction of the dispersion of the pigment included in the black ink on the surface of the paper occurs relatively quickly compared to other inks. In the image forming method of the present invention, the aqueous ink of the present invention is used for black ink, and also image formation using color ink is performed after image formation using black ink. More preferably, the color ink is applied by run (scanning) with a delay of at least one run after applying black ink by run. With this design, no blurring due to color mixing between black ink and color ink does not occur on the surface of the paper even when in contact with color ink, as a result of which images can be formed with effective anti-blur effect. More specifically, the above-mentioned positive effects are obtained only by providing a time difference between the formation of images using black ink and the formation of images using color ink, without the need for a multi-pass printing method, which takes printing time to complete printing by running several times, or a method that leads to the use of large equipment separately providing a recovery system for every black ernil and color ink.

The use of the aqueous ink of the present invention also allows the pigment in the ink to effectively remain on the recording medium for the previously mentioned reasons, and therefore makes it possible to print at a higher density with less ink than the ejection amount (drop volume) for conventional ink. In addition, since printing can be done with a small amount of ink, the cost of image formation can be reduced, and ink can be fixed in a shorter time than traditional ink. Such effects should also be expected.

Inkjet recording method, recording unit, cartridge and recording device

An example of an inkjet recording device preferred for the present invention is described below. First, an example of the construction of the recording head is shown in FIG. 1 and 2, which is the main structural component of an inkjet recording device that uses thermal energy. In FIG. 1 shows a cross section of the recording head 13 along its ink channel, and FIG. 2 shows a cross section along line A-B in FIG. 1. The recording head 13 is made by gluing glass, ceramic or plastic plates, or other similar plates having channels (nozzles) 14 through which ink passes to the substrate element of the heating element 15.

The substrate element of the heating element 15 consists of a protective layer 16 formed by silicon oxide, silicon nitride, silicon carbide or other similar compounds, electrodes 17-1 and 17-2 made of aluminum, gold, an alloy of aluminum with copper or other similar materials, a layer a heating resistor 18 made of a high melting material such as HfB ₂ , TaN or TaAl, a heat storage layer 19 made of thermally oxidized silicon, aluminum oxide or other similar substances, and a substrate 20 made from a material having good heat dissipation properties, such as silicon, aluminum or aluminum nitride.

When pulsed electrical signals are supplied to the electrodes 17-1 and 17-2 of the recording head 13, heat is sharply released in the region indicated by n in the substrate element of the heating resistor 15, so that bubbles form in the ink 21, which come in contact with the surface of this region. The resulting pressure extrudes the meniscus 23, and the ink 21 is ejected through the nozzle 14 from the ejection opening 22 in the form of a tiny drop of ink 24 for delivery to the recording medium 25.

In FIG. 3 shows the appearance of an example multi-head including the recording head shown in FIG. 1 is an enlarged view. This multi-head is made by gluing a glass plate 27 having a multi-nozzle 26 to a heating head 28 similar to that shown in FIG. one.

In FIG. 4 shows an example of an inkjet recording device in which such a recording head is installed. In FIG. 4, 61 indicates a plate serving as a wiping member, which is a console, one end of which is the fixed end held by the plate holding member. The plate 61 is set to a position near the area in which the recording head 65 is recording. Also in the example shown in the drawing, the plate 61 is held so that it protrudes along the direction of the recording head 65.

The number 62 denotes a cover for the front surface of the ejection openings for ink of the recording head 65, which is located in the initial position next to the plate 61, and is designed so that it moves in the direction perpendicular to the direction in which the recording head moves and comes into contact with the surface ejection openings for ink for closing. Also, the number 63 indicates the ink collector located next to the plate 61, and, like in the plate 61, it is held so that it protrudes in the direction of the recording head 65. The above plate 61, cap 62 and collector 63 constitute an ejection recovery unit 64, in which the plate 61 and the collector 63 remove water, dust and so on from the outer surface of the ejection ink hole.

The number 65 denotes a recording head having means for generating ejection energy, and it ejects ink onto a recording medium mounted opposite the outer surface of the ejection opening provided with ejection holes for recording. The number 66 indicates the holder in which the recording head 65 is attached so that the recording head 65 can move. The cartridge 66 is movably connected to the circular guide 67. A portion of the holder 66 is connected (not shown) to a belt 69 driven by the motor 68. Thus, the cartridge 66 can move along the circular guide 67, and therefore, the recording head 65 can move from the area records to the area adjacent to it.

The number 51 indicates the feed unit through which the recording media is inserted, and the number 52 indicates a paper feed roller driven by a motor (not shown). With this design, the recording medium is fed to a position opposite the outer surface of the ejection opening of the recording head 65 and, as the recording proceeds, output to a paper output device provided with a paper output roller 53.

In the above construction, the cover 62 of the exhaust recovery unit 64 is removed from the direction of movement of the recording head 65 when the recording head 65 is returned to its original position after recording is completed, and the plate 61 protrudes in the direction of movement. As a result, the outer surface of the ejection opening of the recording head 65 is rubbed.

In addition, when the lid 62 comes into contact with the outer surface of the ejection opening of the recording head 65 to close, the lid 62 moves in such a way that it protrudes in the direction of movement of the recording head. When the recording head 65 moves from its initial position to the position at which recording begins, the cover 62 and the plate 61 are in the same position as the above position when wiping the outer surface of the ejection opening. As a result, the outer surface of the ejection opening of the recording head 65 is also wiped during this movement.

The aforementioned movement of the recording head to its initial position is performed at the end of recording or ejection recovery, and, in addition, the recording head moves to its original position, immediately adjacent to each recording area at predetermined intervals as the recording area moves to record when the outer surface the ejection hole is rubbed in accordance with this movement.

In FIG. 5 is a view showing an example of an ink cartridge that holds ink introduced into the recording head through an ink supply member, such as a tube. Here, the numeral 40 denotes an ink tank, for example, an ink cartridge that contains the input ink. Its top is equipped with a stopper 42 made of rubber. A needle (not shown) can be inserted into this stopper 42 so that ink from the ink can 40 can be supplied to the head. The number 44 denotes the collection, which accepts the used ink. Preferably, the ink tank is made of a polyolefin, in particular polyethylene, where its surface is in contact with the ink liquid.

The inkjet recording apparatus used in the present invention is not limited to the apparatus described above, in which the head and ink cartridge are installed separately, and is preferably also used in the apparatus in which they are integral, as shown in FIG. 6. In FIG. 6, the number 70 denotes a recording unit in which an ink tank with ink contained therein is placed, for example, an ink collector. The recording unit is designed so that ink in such an ink collector is ejected in the form of droplets of ink from a head 71 having a plurality of openings. As the material for the ink collector, it is preferable to use polyurethane. Instead of the ink collector, the recording unit can be so designed that the ink tank is an ink cartridge provided internally with a spring or the like. The number 72 indicates the opening of the air channel through which the interior of the cartridge communicates with the atmosphere. This recording unit 70 is a recording unit used in place of the recording head 65 shown in FIG. 4, and it is removably mounted in the holder 66.

A preferred example of an inkjet recording apparatus using mechanical energy is described below. A mechanical energy-using inkjet recording device may include a discrete jet ejection recording head, which is provided with a nozzle base having a plurality of nozzles, a pressure generating device consisting of a piezoelectric material and a conductive material located opposite the nozzles, and ink that with the help of a nearby pressure generating device, it is filled, and in which the pressure generating device is made in order to subject it to movement due to supply voltage for ejecting the smallest drops of ink from the nozzles. An example of the construction of the recording head, which is the main component of the device, is shown in FIG. 7.

The recording head consists of an ink channel 80 communicating with an ink chamber (not shown), a plate with openings 81 for ejecting droplets of ink of a desired volume, a vibration plate 82 that generates pressure for directly acting on the ink, a piezoelectric device 83, which is connected to this vibration plate 82 and is designed to subject it to movement in accordance with electrical signals, and the base 84 for supporting and fixing the plate with holes 81, the vibration plate 82 and so on.

In FIG. 7, the channel 80 is made of a photosensitive resin or other similar material, and the plate with holes 81 is made of metal, such as stainless steel or nickel, and an ejection hole 85 is obtained, resulting from the hole being formed by electroforming or pressing. The vibration plate 82 is made of a metal film of stainless steel, nickel, titanium or other similar metals, and a highly elastic resin. The piezoelectric device 83 is made of a dielectric material such as barium titanate or PZT (Pb-Zr-Ti).

The recording head, consisting of the elements described above, operates as follows. The pulse voltage is supplied to the piezoelectric device 83 to create a stress-strain state, the energy thus obtained changes the shape of the vibration plate attached to the piezoelectric device 83, and the ink inside the ink channel 80 is compressed vertically so that ink droplets (not shown) are ejected ejection holes 85 of the plate with holes 81 for recording. Such a recording head is used in a position when it is inserted into the similar inkjet recording device shown in FIG. 4. The individual nodes of the inkjet recorder may operate in the same manner as described above.

EXAMPLES

Further, the present invention will be described in more detail using examples, comparative examples and control examples. However, the present invention is not limited to the following examples. In the following description, unless otherwise indicated, “part (s)” and “%” mean “part (s) by weight” and “wt.%”.

Preparation of pigment dispersion solutions

Preparation of Pigment A Dispersion Solution

1.55 g of p-aminobenzoic acid was added at 5 ° C to a solution of 5 g of concentrated hydrochloric acid dissolved in 5.5 g of water. This solution was stirred in an ice bath, the temperature of which was almost always maintained at 10 ° C or less, and a solution of 1.8 g of sodium nitrite dissolved in 9 g of water with a temperature of 5 ° C was added to this solution. Then, the resulting solution was further stirred for 15 minutes, 6 g of carbon black having a specific surface area of 220 m ² / g and a dibutyl phthalate adsorption value of 105 ml / 100 g were added and mixed with it. After that, the solution was stirred for another 15 minutes. The resulting suspension was filtered through a paper filter (trademark: Standard Filter Paper No. 2, supplied by ADVANTEC) and the pigment particles were thoroughly washed with water and dried in an oven heated to 110 ° C to obtain self-dispersing carbon black A.

Water was added to the resulting self-dispersing carbon black A so as to obtain a dispersion solution with a pigment concentration of 10 wt.%. Using the above method, a pigment A dispersion solution was obtained in which a self-dispersing carbon black A (Pigment A) having a —C ₆ H ₄ —COONa group introduced onto the surface of the carbon black was dispersed in water.

The density of the ionogenic group of the prepared self-dispersing carbon black A was measured, and it was 2.6 μmol / m ² . When measuring the density of the ionogenic group, an ionomer (manufactured by Toa DKK) was used to measure the concentration of sodium ion in the above pigment A dispersion solution, and the result was converted to the density of the ionogenic group of self-dispersing carbon black A.

Preparation of Pigment B Dispersion Solution

1.5 g of 4-aminophthalic acid was added to a solution of 5 g of concentrated hydrochloric acid dissolved in 5.5 g of water. This solution was stirred in an ice bath, the temperature of which was almost always maintained at 10 ° C or less, and a solution of 1.8 g of sodium nitrite dissolved in 9 g of water with a temperature of 5 ° C was added to this solution. Then, the resulting solution was further stirred for 15 minutes, 6 g of carbon black having a specific surface area of 220 m ² / g and dibutyl phthalate adsorption value of 105 ml / 100 g were added and mixed. After that, the solution was stirred for another 15 minutes. The resulting suspension was filtered through a paper filter (trademark: Standard Filter Paper No. 2, supplied by ADVANTEC) and the pigment particles were thoroughly washed with water and dried in an oven heated to 110 ° C to obtain self-dispersing carbon black B.

Water was added to the resulting self-dispersing carbon black B so as to obtain a dispersion solution with a pigment concentration of 10 wt.%. Using the above method, a pigment B dispersion solution was obtained in which a self-dispersing carbon black B (Pigment B) having a —C ₆ H ₃ - (COONa) ₂ group introduced onto the surface of the carbon black was dispersed in water.

The density of the ionogenic group of the prepared self-dispersing carbon black B was measured in the same manner as for the self-dispersing carbon black A, and it was 3.1 μmol / m ² .

Preparation of pigment dispersion solution C

1.55 g of p-aminobenzoic acid was added 2.5 g of concentrated hydrochloric acid dissolved in 5.5 g of water. This solution was stirred in an ice bath, the temperature of which was almost always maintained at 10 ° C or less, and a solution of 0.9 g of sodium nitrite dissolved in 9 g of water with a temperature of 5 ° C was added to this solution. Then, the resulting solution was further stirred for 15 minutes, 9 g of carbon black having a specific surface area of 220 m ² / g and dibutyl phthalate adsorption value of 105 ml / 100 g were added and mixed. After that, the solution was stirred for another 15 minutes. The resulting suspension was filtered through a paper filter (trademark: Standard Filter Paper No. 2, supplied by ADVANTEC), and the pigment particles were thoroughly washed with water and dried in an oven heated to 110 ° C. to give self-dispersing carbon black C.

Water was added to the resulting self-dispersing carbon black C to obtain a dispersion solution with a pigment concentration of 10 wt.%. Using the above method, a pigment C dispersion solution was obtained in which a self-dispersing carbon black (Pigment C) having a —C ₆ H ₄ —COONa group introduced onto the surface of the carbon black was dispersed in water.

The density of the ionogenic group of the prepared self-dispersing carbon black C was measured in the same manner as for the self-dispersing carbon black A, and it was 1.0 μmol / m ² .

Preparation of Pigment D Dispersion Solution

0.7 g of 4-aminophthalic acid was added to a solution of 2.5 g of concentrated hydrochloric acid dissolved in 5.5 g of water. This solution was stirred in an ice bath, the temperature of which was almost always maintained at 10 ° C or less, and a solution of 0.9 g of sodium nitrite dissolved in 9 g of water with a temperature of 5 ° C was added to this solution. Then, the resulting solution was further stirred for 15 minutes, 10 g of carbon black having a specific surface area of 220 m ² / g and dibutyl phthalate adsorption value of 105 ml / 100 g were added and mixed. After that, the solution was stirred for another 15 minutes. The resulting suspension was filtered through a paper filter (trademark: Standard Filter Paper No. 2, supplied by ADVANTEC), and the pigment particles were thoroughly washed with water and dried in an oven heated to 110 ° C. to give self-dispersible carbon black D.

Water was added to the resulting self-dispersing carbon black D so as to obtain a dispersion solution with a pigment concentration of 10 wt.%. Using the above method, a pigment dispersion solution D was prepared in which a self-dispersing carbon black D (Pigment D) having a —C ₆ H ₃ - (COONa) ₂ group introduced onto the surface of the carbon black was dispersed in water.

The density of the ionogenic group of the prepared self-dispersing carbon black D was measured in the same manner as for the self-dispersing carbon black A, and it was 1.4 μmol / m ² .

Assessment of a water-soluble organic solvent as a favorable / unfavorable environment

The following experiment was carried out in order to select a water-soluble organic solvent acting as a favorable environment or an unfavorable medium for the pigment contained in the above pigment dispersion solution. First, A-D pigment dispersion solutions having a solids content of 10% by weight were used to prepare aqueous solutions. These aqueous solutions and corresponding water-soluble organic solvents were used to prepare the dispersion A evaluation solution and the dispersion B evaluation aqueous solution to evaluate a favorable / unfavorable environment according to the following ratio of components in the mixture.

The ratio of components in dispersion solutions to assess a favorable environment / adverse environment

Dispersion A Assessment Solution

• each pigment dispersion solution with a solids content of 10 wt.% 50 pieces • each water soluble organic solvent shown in table 1 50 pieces

 Estimated aqueous dispersion solution B

• each pigment dispersion solution with a solids content of 10 wt.% 50 pieces • clean water 50 pieces

Next, 10 g of a dispersion A solution for evaluating a favorable / unfavorable environment, which was prepared as described above, was placed in a clear glass bottle with a cap and the bottle was closed with a cap. After that, its content was thoroughly mixed and left to stand for 48 hours in a thermostat at 60 ° C. After that, the dispersion solution, taken out from a 60 ° C thermostat, was used as a measurement sample and the average pigment particle size in the pigment dispersion solution was measured using a fiber optic particle size analyzer (trademark: FPAR-1000; manufactured by Otsuka Electronics Co. , Ltd.). The obtained value was used to assess the average pigment particle size in dispersion solution A (average pigment particle size, measured without dilution). Meanwhile, the aqueous solution of dispersion B was not stored for evaluation when heated, and the average pigment particle size in this dispersion was measured using a fiber optic particle size analyzer. Then, with regard to the average particle sizes in the dispersion A evaluation solution and in the dispersion B aqueous solution, when the average particle size in the dispersion A solution was larger than the average particle size in the dispersion B aqueous solution, the water-soluble organic solvent was evaluated as an unfavorable environment, and when the average particle size in the dispersion A solution was equal to or smaller than the average particle size in the aqueous dispersion B solution, the water-soluble organic solvent was evaluated as a favorable environment.

Measurement of the Ka value of a water-soluble organic solvent

First, to measure the Ka value of each water-soluble organic solvent, an aqueous dye solution was prepared with a dye concentration of 0.5 wt.%, Having the composition shown below. Such an aqueous dye solution was used to color a colorless transparent sample to make it visible so that the value of Ka could be easily measured.

• water soluble dye C.I. Pigment Blue 199 0.5 parts • pure water 99.5 pieces

Further, using this aqueous 0.5 wt.% Dye solution and each water-soluble organic solvent to be measured, each of the aqueous 20% solutions of colored water-soluble organic solvents having the composition shown below was prepared.

• the above aqueous 0.5 wt.% Dye solution 0.80 pieces • water-soluble organic solvent shown in table 1 20 pieces

Using an aqueous 20 wt.% Solution of each colored water-soluble organic solvent prepared as described above as a measurement sample, the Ka value of an aqueous 20 wt.% Solution of each water-soluble organic solvent was measured using the Bristow method using a dynamic permeability meter (trademark: Dynamic Permeability Tester S; manufactured by Toyo Seiki Seisaku-sho, Ltd.).

Evaluation and Measurement Results

As for the water-soluble organic solvents used in the ink, measured as described above, the results of the assessment as to whether they were favorable environments or unfavorable environments for solutions of pigment dispersions A - D, and the results of measuring the value of Ka in an aqueous 20% solution of each a water-soluble organic solvent is shown in table 1. In addition, the characters “0” and “X” in the table indicate a favorable environment and an unfavorable environment, respectively.

Table 1 Water soluble organic solvent Pigment Dispersion Solution The value of Ka 20% solution A B C D ml / m ² / ms ^1/2 Polyethylene glycol 600 X X X X 0.17 Glycerol 0 0 0 0 0.13 Trimethylolpropane 0 0 0 0 0.19

Assessment of pigment dispersibility in a water-soluble organic solvent

The following experiment was conducted to evaluate the combination of pigment and water-soluble organic solvents that are components of the aqueous ink of the present invention, that is, a combination in which the water-soluble organic solvent completely or practically does not solvate the pigment, and also the ionogenic groups on the surface of the pigment particles are completely or practically not exposed ionic dissociation in a water-soluble organic solvent, i.e. a combination in which the pigment is practically dispersible I am in a water soluble organic solvent.

Using the method described above, studies have been conducted of combinations of self-dispersible carbon black A-D and various water-soluble organic solvents. A-D self-dispersing carbon blacks were each dried in an oven at 110 ° C. After that, the obtained self-dispersing carbon black A-D was each crushed in a mortar or other similar method to obtain crushed products. Then, these pigments were each added to each water-soluble organic solvent to be measured so that the pigment concentration was 0.05 wt.%, Followed by stirring for 1 hour. The resulting mixtures were examined to find that at this point in time there was a combination of pigment and a water-soluble organic solvent, in which a clear separation of the solid-liquid phases could be visually determined. For such a combination, it was possible to conclude that the water-soluble organic solvent completely or practically does not solvate the pigment, and also the ionogenic groups on the surfaces of the pigment particles do not completely or practically undergo ionic dissociation in a water-soluble organic solvent, i.e., the pigment practically did not disperse in a water-soluble organic solvent.

The following measurement was additionally made to evaluate the combination in which the pigment was practically not dispersible in a water-soluble organic solvent. First, the mixtures of each pigment and each water-soluble organic solvent, which were obtained above, were allowed to stand at ordinary temperature for 100 hours. After that, 50 wt.% Of the upper part of the liquid phase was taken and filtered through a filter with a pore size of 1.2 μm. Then, with regard to the obtained filtrate (a solution of a dispersion of a coloring matter in a solvent), the concentration of the coloring matter contained in the filtrate was measured by the method described below. In addition, the method described below is an example of methods for measuring. In the present invention, the examples are by no means limited.

The concentration of the coloring matter in the filtrate was measured using the method described below. First, to a dye dispersion solution in which the dye was dispersed in water at a known concentration (Ck wt%), pure water was added in a predetermined amount to dilute it to a predetermined dilution degree to obtain a mixture, and the absorbance of the mixture was measured at 550 nm. The measured value of this absorption was designated as (ABS1). Then, the solution of the dye dispersion in the solvent (filtrate), in which the dye concentration was to be determined, was diluted with pure water to the same degree of dilution as above, and the absorbance was also measured at 550 nm. The measured value of this absorption was designated as (ABS2). As a result, the dye concentration in the dye dispersion solution in the solvent was calculated according to the following expression (2).

Expression (2)

The concentration of the coloring matter in the solution of the dispersion of the coloring matter in the solvent (wt.%) =

[Ck x (ABS2)] / (ABS2).

Using the ratio of the concentration of the coloring matter in the solution of the dispersion of the coloring matter in the solvent (filtrate), as defined above, to the initial concentration of the coloring matter (initial concentration: 0.05 wt.% In the above example) in a mixture of a coloring matter and a water-soluble organic solvent, was determined the percentage dispersion (%) of a particular coloring matter in a particular water-soluble organic solvent (hereinafter “the percentage of dispersion of a coloring matter in a solvent”), as represented by the following expression (3).

Expression (3)

The percentage dispersion (%) of the coloring matter in a water-soluble organic solvent = [(concentration of the coloring matter in the solution of the dispersion of the coloring matter in the solvent) / (initial concentration of the coloring matter)] × 100.

The percent dispersion of the coloring matter in the solvent obtained by the above measurement and the results of visual observation of the solid-liquid phase separation evidence described above are shown in Table 2 below. In addition, the AD pigments in the table are referred to as AD self-dispersing carbon blacks (hereinafter "AD pigments").

table 2 Pigment Water soluble organic solvent Solid-liquid separation The percentage of dispersion of the coloring matter in the solvent A Polyethylene glycol 600 Yes 2,8 Glycerol No 88.3 B Polyethylene glycol 600 Yes 2.2 Glycerol No 85,4 C Polyethylene glycol 600 No 18.2 Glycerol No 99,4 D Polyethylene glycol 600 No 17.1 Glycerol No 99.7

From the results shown in Table 2 above, it can be concluded that, since solid-liquid phase separation occurred with a combination of pigment A and polyethylene glycol 600 and a combination of pigment B and polyethylene glycol 600, these water-soluble organic solvents completely or practically do not solvate the pigment, and also, the ionic groups of the pigment completely or practically do not undergo ionic dissociation in a water-soluble organic solvent, i.e., the pigment is practically not dispersed in a water-soluble organic solvent. solvent is.

In addition to the above conclusion, the conclusion that the above pigment is a pigment that is completely or practically not solvated by a water-soluble organic solvent, which was made on the basis of measurements, and the conclusion that ionogenic groups on the surfaces of pigment particles are completely or practically not subjected to ionic dissociation in water-soluble organic solvents , which was made on the basis of measurements, were respectively made using the methods described below.

In particular, a liquid was first prepared containing a surfactant having a structure represented by the following structural formula (1) or structural formula (2), and water, and containing a surfactant at a concentration of 2 mmol / kg (liquid 1), and a liquid consisting of a surfactant, a pigment (any one of the AD pigments) and water, and containing a surfactant at a concentration of 2 mmol / kg, and a pigment at a concentration of 5 wt.% (liquid 2). To prepare liquid 1 and liquid 2, the corresponding components were mixed, followed by stirring at ordinary temperature for 30 minutes.

Structural Formula (1)

(In structural formula (1), R represents an alkyl group and n represents an integer.)

Structural Formula (2)

(In structural formula (2), m and n each represent an integer.)

In addition, for the preparation of liquids, the above pigments A-D were each added to water, so that the concentration of pigment in the water was 5 wt.%, And the surface tension of each of the liquids was measured at normal temperature (25 ° C). As a result, it was found that, in the cases for all A-D pigments, surface tension was equal to the surface tension (72 mN / m) of water at normal temperature and A-D pigments themselves did not have the effect of lowering the surface tension of the liquid.

The results of measuring surface tension A and surface tension B at normal temperature, related to the above liquid 1 and liquid 2, respectively, and the difference "B-A" in surface tension between liquid 2 and liquid 1, are shown in table 3.

Table 3 Pigment Surface-active substance Fluid 1 Fluid 2 Formula R n m + n Surface tension BUT
(mn / m) AT
(mn / m) Ba
(mn / m) A (one) C ₁₆ H ₃₃ twenty - 40,0 41.3 1.3 (one) C ₁₆ H ₃₃ 40 - 47.9 48.7 0.8 (2) - - four 34.2 38.8 4.6 (2) - - 10 37.0 40.1 3,1 (2) - - thirty 42.7 45.9 3.2 B (one) C ₁₆ H ₃₃ twenty - 40,0 40,4 0.4 (one) C ₁₆ H ₃₃ 40 - 47.9 48.1 0.2 (2) - - four 34.2 38,0 3.8 (2) - - 10 37.0 39.3 2,3 (2) - - thirty 42.7 45.0 2,3 C (one) C ₁₆ H ₃₃ twenty - 40,0 70.5 30.5 (one) C ₁₆ H ₃₃ 40 - 47.9 65.1 17,2 (2) - - four 34.2 66.5 32,3 (2) - - 10 37.0 67.7 30.7 (2) - - thirty 42.7 58.2 15,5 D (one) C ₁₆ H ₃₃ twenty - 40,0 69.6 29.6 (one) C ₁₆ H ₃₃ 40 - 47.9 60,4 12.5 (2) - - four 34.2 60,2 26.0 (2) - - 10 37.0 61,4 24.4 (2) - - thirty 42.7 55.0 12.3

As is evident from the results shown in table 3, in the case of pigment A and pigment B, the difference "BA" between the surface tension A of the liquid 1 and the surface tension B of the liquid 2 shows lower values than in the case of pigment C and pigment D. This means that in the case of pigment A and pigment B, the effective concentrations of surfactants that contribute to lowering the surface tension of liquids are substantially equal, regardless of the presence or absence of pigments. That is, we can assume that surfactants are completely or practically not adsorbed on pigment A and pigment B. Thus, we can conclude that, for the above reasons, pigment A and pigment B are completely or practically not solvated by a medium, such as water-soluble organic solvent.

Then, with regard to pigments that are completely or practically not solvated by media, such as the above water-soluble organic solvents, the conclusion that ionogenic groups of pigments are completely or practically not subjected to ionic dissociation in water-soluble organic solvents was made as follows, which is described when Pigment B was taken as an example.

In particular, at first, pigment B was so diluted with each of several water-soluble organic solvents to obtain evaluation liquids that it was present at a very low concentration. As a dilution standard, a level is set that allows the pigment particles to be sufficiently visible when using a zeta potential measurement using a microscope type instrument mentioned below. Regarding the evaluation of liquids prepared as described above, it is observed whether particles move or not move in a particular direction when voltage is applied using a zeta potential measuring system such as a microscope (trademark: ZEECOM; manufactured by Microtec Nition), with which you can really observe the movement of particles. When they are convinced that the pigment particles are moving, then their zeta potential is measured. In addition, when measuring the zeta potential, the viscosity values at the measurement temperature and the dielectric constant of the water-soluble organic solvents used are necessary, and therefore it is preferable that they be checked or measured in advance.

The results obtained from the above observation and measurement are shown in table 4.

Table 4 Water soluble organic solvent Electrophoresis Zeta potential
(mV) Polyethylene glycol 600 Not happening - Glycerol Going on -29

As can be seen from Table 4, clear electrophoresis appears when evaluating a liquid using glycerin as a water-soluble organic solvent, while when evaluating a liquid using a water-soluble organic solvent, such as polyethylene glycol 600 or another similar solvent, no movement of particles in a particular direction was manifested in the evaluated fluid, and we can conclude that the particles practically do not undergo electrophoresis. That is, it can be concluded that in such a water-soluble organic solvent in which the particles practically do not undergo electrophoresis, the ionogenic groups on the surfaces of the pigment particles B completely or practically do not undergo ionic dissociation in the water-soluble organic solvent for the reasons mentioned earlier.

Evaluation of adsorption of a water-soluble polymer on a pigment

The following experiment was conducted to evaluate the combination of a pigment and a water-soluble polymer in the case where the water-soluble polymer is added to the aqueous ink of the present invention, i.e., a combination for which it can be concluded that the water-soluble polymer is completely or practically not adsorbed on the surfaces of the pigment particles. In addition, water-soluble polymers used to evaluate the degree of adsorption of water-soluble polymers on a pigment are examples. In the present invention, the examples are in no way limited to the following water-soluble polymers.

The conclusion about whether adsorption occurred or did not occur was made by choosing three types of water-soluble polymers: styrene-acrylic acid copolymer, polyvinylpyrrolidone and ethyl acrylate-acrylic acid copolymer. Anionic polymers, styrene-acrylic acid copolymer and ethyl acrylate-acrylic acid copolymer had an average acid number of about 150 and had a weight average molecular weight of 10,000 for both water-soluble polymers.

In particular, first a liquid was prepared consisting of each of the above water-soluble polymers and water, and containing a water-soluble polymer at a concentration of 0.1 wt.% (Liquid 3), a liquid consisting of each of the above water-soluble polymers, a pigment (any one of the pigments B and C) and water and containing a water-soluble polymer at a concentration of 0.1 wt.%, And a pigment at a concentration of 5 wt.% (Liquid 4), and a liquid consisting of any one of the pigments and water and containing a pigment at a concentration of 5, 0 wt.% (Liquid 5). To prepare liquid 3, liquid 4 and liquid 5, the corresponding components were mixed, followed by stirring at ordinary temperature for 30 minutes. In addition, the surface tension of the above liquid 5 was measured at normal temperature (25 ° C). As a result, it was found that all surface tensions were equal to the surface tension (72 mN / m) of water at normal temperature, and pigments B and C themselves did not have the effect of lowering the surface tension of the liquid.

The results of measuring surface tension C and surface tension D at normal temperature, respectively, in the above liquid 3 and liquid 4, the difference "D-C" surface tension between liquid 4 and liquid 3 and the value (D-C) / (E-C) are shown in table 5.

Table 5 Pigment Water soluble polymer Liquid
3 Fluid 4 Surface tension C
(mn / m) D
(mn / m) DC
(mn / m) (DC) /
(E-C) B Styrene Acrylic Acid Copolymer 63.5 65.5 2.0 0.24 Polyvinylpyrrolidone 68.9 69.2 0.3 0.10 Copolymer
ethyl acrylate-acrylic acid 44,4 46.1 1.7 0.06 C Styrene Acrylic Acid Copolymer 63.5 71.0 7.5 0.90 Polyvinylpyrrolidone 68.9 70.0 1,1 0.38 Copolymer
ethyl acrylate -
acrylic acid 44,4 55.6 11,2 0.41

As is evident from the results shown in Table 5, the values of (D-C) / (E-C) for pigment B are 0.3 or less. This means that the effective concentration of water-soluble organic solvents, which contribute to lowering the surface tension of liquids, are essentially equal, regardless of the presence or absence of pigments. That is, we can conclude that water-soluble organic solvents are completely or practically not adsorbed on pigment B. In addition, what is not shown in table 5, it was found that the styrene-acrylic acid-hydroxyacrylate copolymer having both anionic and nonionic components in one molecule (weight average molecular weight: 15000; acid number: 160) also satisfy the above conditions and are completely or practically not adsorbed on pigment B.

Ink preparation

Examples 1-9

To prepare the ink of Examples 1-9, the components shown in Table 6 below were mixed and thoroughly mixed, followed by pressure filtration through a 3.0 μm microfilter (supplied by Fuji Photo Film Co., Ltd.)

Here, the ink was prepared so that water-soluble organic solvents included a favorable environment for the pigment in each ink and an unfavorable environment for this pigment, a pigment and an adverse environment had such a relationship that the adverse environment completely or practically did not solvate the pigment, and ionogenic groups on the surfaces of the pigment particles completely or practically did not undergo ionic dissociation in an unfavorable environment, and also a water-soluble organic solvent exhibiting maxim Flax Ka value among the respective Ka values of water-soluble organic solvent, determined by the Bristow method was unfavorable environment.

Table 6 Examples one 2 3 four 5 6 7 8 9 Pigment A Dispersion 50,0 - 50,0 Pigment Dispersion B - 50,0 - 50,0 50,0 50,0 50,0 50,0 50,0 Pigment Dispersion C - - - - - - - - - Pigment Dispersion D - - - - - - - - - Glycerol 5,0 5,0 7.0 7.0 5,0 5,0 5,0 5,0 10.0 PEG 600 15.0 15.0 3,5 3,5 15.0 15.0 15.0 15.0 10.0 Trimethylolpropane - - - - - - - - - ACETYLENOL E-100 (*) 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Styrene copolymer - acrylic acid - - - - 1,5 - - - - Polyvinylpyrrolidone - - - - - 1,5 1,5 - 1,5 Copolymer
ethyl acrylate -
acrylic acid - - - - - - 0.5 - 0.5 Copolymer Acrylate - Hydroxyacrylate - - - - - - - 1,5 - Pure water 29.9 29.9 39,4 39,4 28,4 28,4 27.9 28,4 27.9 (*): Acetylene glycol adduct with ethylene oxide (surfactant supplied by Kawaken Fine Chemicals Co., Ltd.)

Comparative Examples 1-5 and Control Example 1

To prepare the ink of comparative examples 1-5 and control example 1, the components shown in table 7 below were mixed and thoroughly mixed, followed by pressure filtration through a microfilter with a pore size of 3.0 μm (supplied by Fuji Photo Film Co., Ltd.) .

Table 7 Comparative examples Test case one 2 3 four 5 one Pigment A Dispersion - - 50,0 - - - Pigment Dispersion B - - - 50,0 - 50,0 Pigment Dispersion C 50,0 - - - 50,0 - Pigment Dispersion D - 50,0 - - - - Glycerol 5,0 5,0 5,0 5,0 - 10.0 PEG 600 15.0 15.0 10.0 10.0 15.0 10.0 Trimethylolpropane - - 7.0 7.0 - - ACETYLENOL E-100 (*) 0.1 0.1 0.1 0.1 0.1 0.1 Styrene copolymer - acrylic acid - - - - - - Polyvinylpyrrolidone - - - - - - Copolymer
ethyl acrylate -
acrylic acid - - - - - - Copolymer Acrylate - Hydroxyacrylate - - - - - - Pure water 29.9 29.9 27.9 27.9 34.9 29.9 (*): Acetylene glycol adduct with ethylene oxide (surfactant supplied by Kawaken Fine Chemicals Co., Ltd.)

Examination of ink, whose composition is unknown

Recognizing whether or not ink whose composition is unknown (ink in which the solvent is subjected to examination) is ink that is intended for the present invention can be carried out using the assessment methods described above. Methods for the examination of ink whose compositions are unknown are described below.

In particular, the type and content of the water-soluble organic solvent contained in the ink in which the solvent is examined is identified first. For example, inks where a solvent is diluted with methanol to a predetermined concentration is analyzed, analyzed using a gas chromatography mass spectrometry device (trade name: TRACE DSQ; manufactured by ThermoQuest) to identify the type of water-soluble organic solvent contained in the ink in which is subject to examination by solvent.

It is further evaluated whether the water-soluble organic solvent thus identified is a favorable environment or an unfavorable environment. In the evaluation method favorable environment / adverse environment described previously, a dispersion is prepared in which the pigment is dispersed in a water-soluble organic solvent and water. In order to prepare such a dispersion from ink, the pigment and dispersant must be extracted from the ink. However, in this case, the pigment and dispersant can change their properties during the extraction process. This possibility cannot be denied.

To overcome this problem, the authors of the present invention conducted various studies of methods for evaluating a favorable environment / adverse environment, which use ink on their own, whose composition is unknown, and in which the results obtained are consistent with the result obtained using the favorable environment / adverse environment assessment method. described earlier. As a result, they found that the following method is preferred as a method for examination.

First, a diluted ink solution was prepared in which 100 parts of the water-soluble organic solvent to be examined were added to 100 parts of ink whose composition was unknown. More specifically, a dilute ink solution was obtained in which the content of the water-soluble organic solvent to be examined reached 50% by weight (hereinafter, the “ink in which the solvent was subjected to examination”). Further, the ink in which the solvent is subjected to examination was stored under heating at a temperature of 60 ° C for 48 hours, and then the average particle size of the pigment contained therein was measured using a fiber optic particle size analyzer (trademark: FPAR-1000 ; manufactured by Otsuka Electronics Co., Ltd.). Meanwhile, as a control, a diluted ink solution was prepared to evaluate a favorable environment / unfavorable environment in which 100 parts of water was added to 100 parts of ink whose composition was unknown (hereinafter “the diluted ink solution to be examined”), and the average particle size was measured the pigment contained in it, in a situation where it was not stored when heated. A favorable / unfavorable environment was then evaluated in accordance with such a standard that the solvent is assessed as an unfavorable environment when the measured value of the average pigment particle size in the ink in which the solvent is subjected to examination is larger than the measured value of the average pigment particle size in the subject examination diluted ink solution, and as a favorable environment when the average pigment particle size is equal to or smaller.

As for the ink prepared in the above examples, assuming that they were ink, whose composition was unknown, they were subjected to examination by the above method, in which the ink was intended for the present invention. Here, a description will be made by taking the ink case of Example 1 as an example.

In particular, a sample prepared by dispersing the ink in Example 1 and diluting it with methanol was used and analyzed using a gas chromatography mass spectrometry apparatus (trademark: TRACE DSQ; manufactured by ThermoQuest). As a result, the presence of glycerol and polyethylene glycol 600 was established. Next, to 100 parts of the ink in Example 1, an equal amount of 100 parts of each of the above two types of water-soluble organic solvents subject to examination was added to prepare two types of ink in which the solvent was subjected to examination, where A favorable / unfavorable environment assessment is made using the ink in which the solvent is subject to examination. More specifically, two types of examined diluted ink solutions having a composition as shown in Table 8 (indicated as solvent inks 1 and 2 in Table 8) are prepared so that the water-soluble organic solvents to be examined, each was present at a content of about 50 wt.%. Further, they were kept under heating at a temperature of 60 ° C for 48 hours, and then the average particle size of their pigments was measured using a fiber optic particle size analyzer (trademark: FPAR-1000; manufactured by Otsuka Electronics Co., Ltd.) . Meanwhile, as a control, a diluted ink solution was prepared to evaluate a favorable / unfavorable environment in which 100 parts of water was added to 100 parts of the ink in Example 1 (hereinafter, “diluted ink solution to be examined”) and the average particle size of the pigment contained was measured in it, in a situation where it was not stored when heated. A favorable / unfavorable environment was then evaluated in accordance with such a standard that the solvent is assessed as an unfavorable environment when the measured value of the average pigment particle size in the ink in which the solvent is subjected to examination is larger than the measured value of the average pigment particle size in the subject examination diluted ink solution, and as a favorable environment when the average pigment particle size is equal to or smaller.

Table 8 Composition (parts) Solvent Ink 1 Solvent Ink 2 Ink Example 1 one hundred one hundred Glycerol one hundred - Polyethylene glycol 600 - one hundred

The average pigment particle size in each diluted ink solution to be tested was measured as described previously, and the average pigment particle size in each of the inks in which the solvent was examined was 1 and 2 (stored by heating at 60 ° C. for 48 hours ) Then, the solvent was evaluated as an unfavorable environment when the measured value of the average pigment particle size in each of the inks where the solvent was examined, 1 and 2, was larger than the average pigment particle size in the diluted ink solution being tested, and as a favorable environment when the average pigment particle size was equal to or smaller. The evaluation results are shown in table 9. In addition, the symbols “0” and “X” in the table indicate a favorable environment and an unfavorable environment, respectively.

Table 9 Measured sample Evaluation results Solvent Ink 1 0 Solvent Ink 2 X Examined diluted ink solution -

As shown in table 9, the results obtained also by the assessment of the favorable environment / adverse environment using ink in which the solvent is subjected to examination, dilution of real ink, glycerin (used in the ink 1, in which the solvent is examined) was evaluated as a favorable environment, and polyethylene glycol 600 (used in ink 2, in which the solvent is subjected to examination) - as an unfavorable environment, as in the evaluation results shown in table 1, where it was determined but that the results relating to these two, are in line with each other. Thus, from the above-described real inks, it was proved that a method for evaluating whether a water-soluble organic solvent used in the ink is a favorable medium or an unfavorable medium for pigment in the ink is useful. Accordingly, it is believed that an evaluation method using samples obtained by diluting the ink as described above is also effectively used as an evaluation method for a favorable / unfavorable environment.

Quality control

Using the ink of each of Examples 5-9 and Control Example 1, a quality assessment was conducted based on the following criteria 1-5. The evaluation results are shown in table 10.

1. Print Density (Typical Ink)

Using the ink of each of Examples 1–9, Comparative Examples 1–5, and Test Example 1, printouts that printed characters having sections of a solid image of 2 cm x 2 cm were obtained by setting the ejection amount per drop of ink in the range of 30 ng ± 10%. The printouts were stored during the day and then the print density of the areas of the solid image was measured. To measure the print density used densitometer for measurements in reflected light (trademark: MACBETH RD-918; manufactured by Macbeth). The criteria for evaluating print density (typical ink) are listed below.

In addition, when printing, a modification of the BJS700 inkjet recording device (manufactured by CANON INC.), Which has a multi-head recording with a discrete type of jet ejection, in which thermal energy is supplied to the ink in accordance with the recording signals for ejecting ink, was used. As for the printer driver, the default mode was selected. The default condition settings are shown below.

Paper Type: Plain paper.

Print Quality: Standard.

Color Control: Automatic.

The following print sheets (1) - (5) were used as recording media.

(1) PPC paper PB Paper (supplied by CANON INC.).

(2) PPC paper SC250 (supplied by CANON INC).

(3) PPC paper 4024 (supplied by Xerox Corp.).

(4) PPC paper PROWBER BOND (supplied by Fox River

Paper Co.).

(5) PPC paper for CANON (supplied by Noizidler Ltd.).

Criteria for evaluation:

A: The print density on five types of paper averages 1.4 or more, or the print density on paper having the lowest print density is 1.25 or more.

B: The print density on five types of paper averages 1.4 or more, and the print density on paper having the lowest print density is less than 1.25.

C: The print density on five types of paper is on average less than 1.4.

2. Print Density (Low Ink)

Printouts were obtained in the same manner as above, except that the amount of ejection per drop of ink was set in the range of 24 ng ± 10%. Print density was measured, giving an estimate based on the same criteria as above.

3. Storage resistance

The ink of each of examples 1-9, comparative examples 1-5 and control example 1 was placed in a short bottle, which was then hermetically sealed and stored for 2 weeks in an oven at 60 ° C. Then examined the condition of the ink. Criteria for assessing shelf life are given below.

Criteria for evaluation:

A: The pigment is uniformly and stably dispersed in the ink.

C: The pigment turned gel, or the top of the ink became transparent, or the ink was clearly thickened.

4. Spreading

To perform a spread assessment, color inks were prepared (cyan ink, magenta ink, and yellow ink). To prepare the color ink, the following components were mixed and thoroughly mixed, followed by pressure filtration through a 3.0 μm microfilter (supplied by Fuji Photo Film Co., Ltd.).

Blue ink C.I. Straight Blue 199 3.5 parts Glycerol 7.5 parts Diethylene glycol 7.5 parts ACETYLENOL E-100 1.0 part Pure water 80.5 parts Magenta ink C.I. Acid Red 289 2.5 parts Glycerol 7.5 parts Diethylene glycol 7.5 parts ACETYLENOL E-100 1.0 part Pure water 81.5 parts Yellow ink C.I. Direct yellow 86 2.5 parts Glycerol 7.5 parts Diethylene glycol 7.5 parts ACETYLENOL E-100 1.0 part Pure water 81.5 parts

Using the black ink of each of examples 1-9, comparative examples 1-5 and control example 1, and the color inks obtained as described above, printouts were obtained on which images were printed so that areas of the solid image were black and corresponding colors (yellow, magenta and cyan) and areas of the continuous image of the secondary colors (red, green and blue) of the corresponding colors were in direct contact with each other. The level of blurring occurring at the boundaries between the black regions and the regions of the corresponding colors was examined visually. The criteria for evaluating the spread are given below. In addition, the BJS700 inkjet recorder (manufactured by CANON INC.) And PB Paper (supplied by CANON INC.) Were used to print.

Criteria for evaluation:

AA: No blurry at all.

A: There is almost no blurring.

B: There is a blur, but which does not essentially create a problem.

C: Blurring occurs to such an extent that the borders between the colors are fuzzy.

5. Scratch resistant

Using the inks of each of Examples 1-9, Comparative Examples 1-5, and Control Example 1, prints were obtained in which sections of solid black images of 1 inch × 0.5 inch each and characters were printed. Silbon paper and cargo (surface pressure 40 g / cm ² ) were placed on it onto areas of continuous images of the printouts obtained, and plain paper and Silbon paper were rubbed together. After that, Silbon paper and cargo were removed in order to visually determine the extent to which the solid images were smeared or to some extent transferred to areas of the white base. The criteria for evaluating scratch resistance are given below. In addition, the BJS700 inkjet recorder (manufactured by CANON INC.) And ultra-white paper (trademark: SW-101; supplied by CANON INC.) Were used to print.

Criteria for evaluation:

AA: There is no smearing in the areas of the white base, or scratches in the areas of solid black images.

A: Slight blurring in areas of the white base and scratches in areas of solid black images.

B: Smears in areas of the white base and scratches in areas of solid black images are noticeable to some extent.

C: Visible smudges in areas of the white base and scratches in areas of solid black images.

Table 10 Print density Blurry Durability
during storage Scratch resistant Ink quantity Primary colors Secondary colors Usual Small Example one BUT BUT AA AA BUT - 2 BUT BUT AA AA BUT - 3 BUT BUT AA AA BUT - four BUT BUT AA AA BUT - 5 BUT BUT AA AA BUT BUT 6 BUT BUT AA AA BUT AA 7 BUT BUT AA AA BUT AA 8 BUT BUT AA AA BUT AA 9 BUT BUT AA AA BUT AA Comparative example one BUT BUT AA BUT BUT - 2 BUT BUT AA BUT BUT - 3 FROM FROM AT AT BUT - four FROM FROM AT AT BUT - 5 BUT AT AA BUT BUT - Test case one BUT BUT AA AA BUT AT

Evaluation of image quality obtained in a two-fluid system

Using black ink of examples 1 and 2 and comparative examples 1-4, obtained as described above, a quality assessment was carried out based on the following criteria 1 and 2. The evaluation results are shown in table 11.

Preparation of the reaction liquid

To prepare the reaction liquids, the components listed below were mixed and thoroughly mixed, followed by pressure filtration through a 3.0 μm microfilter (supplied by Fuji Photo Film Co., Ltd.).

Magnesium Nitrate (Hexahydrate) 15.0 wt.% Trimethylolpropane 25.0 wt.% ACETYLENOL E-100 1.0 wt.% (adduct of acetylene glycol and ethylene oxide; available from Kawaken Fine Chemicals Co., Ltd.) Pure water 59.0 wt.%

Quality control

1. Print Density

Using the ink from Examples 1 and 2 and Comparative Examples 1-4 and the reaction liquid obtained as described above, printouts on which characters having portions of a solid image of 2 cm × 2 cm were printed were obtained. The printouts were stored during the day and then the print density of the areas of the solid image was measured. To measure the print density used densitometer for measurements in reflected light (trademark: MACBETH RD-918; manufactured by Macbeth). The criteria for evaluating print density (typical ink) are listed below.

In addition, when receiving prints, we used a modification of the BJS700 inkjet recording device (manufactured by CANON INC.), Which has a multi-head recording with a discrete type of jet ejection, in which thermal energy is supplied to the ink in accordance with the recording signals for ink ejection, which was modified so which had a mechanism for applying the reaction liquid to the recording medium using a coating roller, as shown in FIG. 15. To apply the reaction liquid and each ink, the ink was applied so that the amount of ejection per drop of ink was in the range of 30 ng ± 10%, immediately after the reaction liquid was fixed on the recording medium (on the material onto which the image was transferred). Also, for applying the reaction liquid, the speed of the roller and the pressure of the roller in the area of contact with the recording medium were adjusted so that its applied amount was 2.4 g / m ² .

As for the printer driver, the default mode was selected. The default condition settings are shown below.

Paper Type: Plain paper.

Print Quality: Standard.

Color Control: Automatic.

The following sheets were used as recording media for printing (1) - (7).

(1) PB Paper (supplied by CANON INC.).

(2) SC250 (supplied by CANON INC.).

(3) PPC paper 4200 (supplied by Xerox Corp.).

(4) PPC paper 4024 (supplied by Xerox Corp.).

(5) Super-white Paper SW-101 (available from CANON INC.).

(6) Fox River PPC paper PROWBER BOND (supplied by Fox River Paper Co.).

(7) PPC paper Hammer Mill Jet (supplied by International Paper Co.).

Criteria for evaluation:

AA: The print density on five types of paper averages 1.45 or more, or the print density on paper having the lowest print density is 1.3 or more.

A: The print density on five types of paper averages from 1.4 or more to less than 1.45, and the print density on paper having the lowest print density is 1.25 or more, but less than 1.3.

B: The print density on the five types of paper is on average 1.4 or more, but less than 1.45, and the print density on the paper having the lowest print density is less than 1.25.

C: The print density on five types of paper averages less than 1.4.

2. Blurry

Printouts were obtained using the black ink of Examples 1 and 2, comparative examples 1-4, the same color inks (cyan ink, magenta ink, and yellow ink) as the ink obtained as described above and the reaction liquid obtained as described above . On recording media coated with a reaction liquid with a deposition quantity of 2.4 g / m ² , the images were printed so that sections of a continuous image of black and the corresponding colors (yellow, purple and blue) and areas of a continuous image of secondary colors (red, green and blue) the corresponding colors were directly in contact with each other. The level of blurring occurring at the boundaries between the black regions and the regions of the corresponding colors was examined visually. The criteria for evaluating the spread are given below.

In addition, prints were obtained using a BJS700 inkjet recorder (manufactured by CANON INC.), Which was modified to have a mechanism for applying the reaction liquid to the recording medium using a coating roller, as shown in FIG. 15, and PB Paper (available from CANON INC.).

Criteria for evaluation:

AA: No blurry at all.

A: There is almost no blurring.

B: There is a blur, but which does not essentially create a problem.

C: Blurring occurs to such an extent that the borders between the colors are fuzzy.

Table 11 Print density Blurry Primary colors Secondary colors Example one AA AA AA 2 AA AA AA Comparative example one AA AA BUT 2 AA AA BUT 3 BUT AA BUT four BUT AA BUT

This application claims the priority of Japanese Patent Application No. 2004-189906, filed June 28, 2004, 2004-189910, filed June 28, 2004 and 2004-190554, filed June 28, 2004, the contents of which are hereby incorporated by reference to them.

Claims (25)

1. Aqueous inks, including at least water, a variety of water-soluble organic solvents and a coloring matter, in which the coloring matter is a pigment containing a pigment particle having at least one ionogenic group bonded to the surface of the pigment particle directly or through another atomic group, and wherein said plurality of water-soluble organic solvents includes a favorable environment or favorable environment for a pigment and an unfavorable environment or adverse environment for a pigment, and in which the adverse environment completely or practically does not solvate the pigment, and in which said ionic group is completely or practically not subjected to ionic dissociation in an unfavorable environment, and in which a water-soluble organic solvent that has a maximum permeability index (Ka) among the corresponding Ka values of said plurality of water-soluble organic solvents, as determined by the Bristow method, is an adverse environment, and moreover, the content of the aforementioned set of water-soluble organic solvents is from 3 to 50 wt.% of the total mass of ink, and moreover, when designating the total content (wt.%) of favorable environment in aqueous ink by X and the total content (wt.%) of adverse environment in aqueous ink by Y, the ratio X: Y is from 10: 5 or more to 10:30 or less , moreover, the content (wt.%) of the pigment is from 0.1 to 15 wt.% of the total mass of ink. 2. Aqueous ink according to claim 1, for which, when designating the surface tension of a liquid containing a surfactant and water and having a surfactant concentration of 2 mmol / kg, by A (mN / m), and when designating the surface tension a liquid containing a surfactant, a pigment and water and having a surfactant concentration of 2 mmol / kg and a pigment concentration of 5 wt.%, by means of B, satisfies the reciprocal ratio B-A 10 10. 3. The aqueous ink according to claim 1, in which the pigment completely or practically does not cause electrophoresis in an unfavorable environment. 4. The aqueous ink according to claim 1, wherein said ionic group is selected from the group consisting of —COOM1, —SO ₃ M1, and —PO ₃ H (M1) ₂ , where M1 represents a hydrogen atom, an alkali metal, ammonium, or organic ammonium . 5. The aqueous ink of claim 1, wherein said other atomic group is selected from the group consisting of an alkylene group having from 1 to 12 carbon atoms, a substituted or unsubstituted phenylene group, and a substituted or unsubstituted naphthylene group. 6. The aqueous ink according to claim 1, in which the Ka value determined by the Bristow method is less than 1.5 ml / m ² / ms ^1/2 . 7. The aqueous ink according to claim 1, in which the Ka value determined by the Bristow method is 0.2 ml / m ² / ms ^1/2 or greater. 8. Aqueous ink according to claim 1, in which the content (wt.%) Of the pigment is from 1 to 10 wt.% Of the total mass of ink. 9. The aqueous ink according to claim 1, which additionally contains a water-soluble polymer that is completely or practically not adsorbed on the pigment. 10. Aqueous ink according to claim 9, in which the water-soluble polymer has an ionic hydrophilic group. 11. The aqueous ink according to claim 9, in which the water-soluble polymer has a nonionic hydrophilic group. 12. Aqueous ink according to claim 9, which contain many water-soluble polymers. 13. The aqueous ink according to claim 9, in which the water-soluble polymer is a water-soluble polymer formed by the copolymerization of a monomer having an ionic hydrophilic group in a molecule and a monomer having a nonionic hydrophilic group in the molecule. 14. Aqueous inks that are used in an image forming method including a step of applying an aqueous ink containing a pigment to a recording medium, and a step of applying a reaction liquid to the recording medium that is capable of causing an unstable state of pigment dispersion in aqueous ink when in contact with aqueous ink where the water inks are water inks according to claim 1. 15. A set of aqueous ink and a reaction liquid, which is used in an image forming method including a step of applying aqueous ink containing a pigment to a recording medium, and a stage of applying a reaction liquid to the recording medium that is capable of causing an unstable state of pigment dispersion in aqueous ink when contact with aqueous ink, where the aqueous ink is aqueous ink according to claim 1. 16. A method of forming an image, which includes stages (i) applying aqueous pigment-containing ink to a recording medium, and (ii) applying a reaction liquid to a recording medium capable of causing an unstable state of a pigment dispersion in aqueous ink upon contact with aqueous ink, where water inks are water inks according to claim 1, and where stage (i) is carried out after the reaction liquid is completely fixed on the recording medium in stage (ii). 17. Aqueous ink according to claim 1, which is used for inkjet recording. 18. The inkjet recording method, which includes the step of ejecting ink by the inkjet method and the step of recording onto a recording medium, in which the ink is aqueous ink according to claim 1. 19. The inkjet recording method according to claim 18, wherein the recording medium satisfies a condition determining that a water-soluble organic solvent that has a maximum Ka value among the corresponding Ka values of said plurality of water-soluble organic solvents, as determined by the Bristow method, is an adverse environment. 20. An ink cartridge including an ink tank that contains ink, where the ink is ink according to claim 1. 21. The recording unit, which includes an ink tank containing ink, and a recording head for ejecting ink from it, where the ink is aqueous ink according to claim 1. 22. An inkjet recording device including an ink tank containing ink, and a recording head for ejecting ink therefrom, where the ink is aqueous ink according to claim 1. 23. An image forming method that records in an inkjet manner on a recording medium by using black ink and at least one color ink, in which water ink according to claim 17 is used as black ink, and the pigment used in black ink contains carbon black, and in which when forming an image consisting of an image formed by black ink and an image formed by color inks that are directly adjacent to each other, a run for applying black ink to form an image is performed, and then a run for applying color ink to the region where an image has already been generated by the aforementioned previous run. 24. The image forming method of claim 23, wherein the color ink is applied in a run with a delay of at least one run after applying black ink by run. 25. The image forming method of claim 23, wherein the ink is applied as a result of using a recording head, in which a line of ejection openings for ejecting black ink therefrom and a line of ejection openings for ejecting color ink from them are placed offset from each other in the direction of the secondary run .

Images