JP2018039932A - Aqueous ink, ink cartridge, and inkjet recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide aqueous ink which can suppress lowering of dischargeability by scorch caused by zirconia, in ink discharged in a thermal method.SOLUTION: Aqueous ink is used for an inkjet recording method which discharges ink from a recording head by action of thermal energy to record images on a recording medium. The aqueous ink contains a zirconium oxide, a pigment, a resin dispersant and resin particles, where a content of the zirconium oxide (in terms of Zr; ppm) is 0.5 ppm or more and 20.0 ppm or less, the pigment is a phthalocyanine pigment and the like, and the resin particles are formed of an acrylic resin, has 50% diameter (D50) based on volume distribution of 10 nm or more and 50 nm or less and has a glass transition temperature of 20°C or less.SELECTED DRAWING: None

Description

  The present invention relates to an aqueous ink, an ink cartridge, and an ink jet recording method.

  In recent years, it has become possible to record high-definition and color-developing images as realized by silver salt photography and offset printing by the inkjet recording method. As coloring materials used in ink, there are dyes and pigments, and pigments are widely used from the viewpoint of image fastness such as gas resistance, light resistance and water resistance.

  In addition, with the diversification of applications such as photographic printing and graphic art printing, a wider color reproduction range is required. Therefore, in addition to the basic three primary colors of cyan, magenta, and yellow, so-called special color inks other than the basic three primary colors such as red, green, blue, orange, and violet are added to increase the color reproduction range. Various studies have been conducted. Accordingly, the types of pigments used in the ink jet recording method are also diversified. Examples include phthalocyanine pigments that have been widely used as cyan pigments; quinacridone pigments that have been widely used as magenta pigments; azo pigments that have been widely used as yellow pigments. In addition to these pigments, various types of pigments such as diketopyrrolopyrrole pigments, dioxazine pigments, perinone pigments, perylene pigments, and anthraquinone pigments have been used.

  In photo printing and graphic art printing, images with higher definition and gloss are required. Many inks used for such applications contain so-called resin-dispersed pigments in which pigments are dispersed by a resin dispersant. The resin-dispersed pigment is physically adsorbed on the particle surface of the pigment by the hydrophobic unit, and disperses the essentially hydrophobic pigment in the aqueous medium by the hydration power of the hydrophilic unit. The hydrophobic pigment is stably dispersed in the ink by the action of the resin dispersant. However, when the dispersion state of the pigment becomes unstable and affects the ink discharge performance from the recording head, image unevenness or the like is likely to occur. Therefore, the demand for ink ejection properties is higher than ever. In particular, when the ink ejection properties change with an increase in the cumulative number of ejections from the recording head, image unevenness due to the difference in ejection properties according to the cumulative number of ejections of each nozzle occurs. Accordingly, it has been demanded that the ink ejection performance does not change even if the cumulative number of ejections is different for each nozzle.

  The dispersion method of the resin-dispersed pigment used in the ink for inkjet is roughly divided into two methods, a media dispersion method and a medialess dispersion method. The media dispersion method is a method of applying a physical force to the pigment using a medium such as beads, and uses a ball mill or a bead mill. The medialess dispersion method is a method in which a force such as shear stress or cavitation is generated using a liquid, and the force is applied to a pigment to disperse, and a high-speed homogenizer or a high-pressure disperser is used.

  In the medialess dispersion method using a high-speed homogenizer, there is a limit to the shear stress that can be applied to the particles, and thus stirring for a long time may be required, and the types of pigments that can be dispersed may be limited. Further, in the medialess dispersion method using a high-pressure disperser, clogging occurs in the chamber or the number of passes required for dispersion increases, so that dispersion often takes time. For this reason, mainly from the viewpoint of productivity and versatility, the media distribution method is widely adopted instead of the medialess distribution method.

  Examples of beads used in the media dispersion method include glass beads, alumina beads, and zirconia beads. Among these, zirconia beads, which are high-density beads, are widely used because they can give a stronger force to the pigment. However, it is known that zirconia is mixed into an ink prepared using a pigment dispersed using zirconia beads due to wear of the beads. However, even if zirconia is mixed, the content of zirconia in the water-based ink is controlled to a considerably low level such as several tens of ppm at the highest in terms of zirconium (Zr). However, even with such a content, in the case of the thermal method in which ink is ejected from the recording head by the action of thermal energy, kog containing zirconia or the like may be deposited on the heater for applying thermal energy. is there.

  When kogation accumulates on the heater, the thermal energy imparted to the ink is reduced, and the discharge performance is reduced. This causes a change in ejection performance according to the cumulative ejection number of the nozzles. That is, a nozzle with a small cumulative number of ejections has good ejection properties, but a nozzle with a large cumulative number of ejections has poor ejection properties, and this difference leads to image unevenness. In the case of a so-called piezo method in which ink is ejected by deformation of a piezo element, kogation does not occur, and thus problems such as change in ejection property and image unevenness due to kogage do not occur.

  In order to suppress kogation on the heater, for example, an ink has been proposed in which the total content of a specific metal such as zirconium, a metal ion, and a metal oxide is 30 ppm or less in terms of metal (Patent Document 1). In order to improve the ejection properties, for example, a black, cyan, magenta, and yellow ink set using a urethane resin emulsion having a small average particle diameter has been proposed (Patent Document 2).

JP 2001-187851 A JP 2012-188609 A

  As a result of the study by the present inventors, the technique proposed in Patent Document 1 can provide an effect when carbon black is used as a pigment, but cannot be obtained when a specific organic pigment is used. I understood it. In addition, it has been found that the ink set proposed in Patent Document 2 causes a change in ejection performance according to the cumulative number of ejections, although no dot omission or flying curve occurs.

  Accordingly, an object of the present invention is to provide an ink that can suppress a decrease in dischargeability due to kogation caused by zirconia in ink discharged by a thermal method. Another object of the present invention is to provide an ink cartridge and an ink jet recording method using the ink.

  The above object is achieved by the present invention described below. That is, according to the present invention, a water-based ink used in an ink jet recording method for recording an image on a recording medium by ejecting ink from a recording head by the action of thermal energy, in which zirconium oxide, a pigment, and the pigment are dispersed. The zirconium-based content (ppm) of the zirconium oxide is 0.5 ppm or more and 20.0 ppm or less based on the total mass of the ink, and the pigment is a phthalocyanine pigment. Quinacridone pigment, diketopyrrolopyrrole pigment, dioxazine pigment, perinone pigment, perylene pigment, and anthraquinone pigment are at least one selected from the group consisting of an acrylic resin and a volume distribution. Standard 50% particle size (D50) is 10 nm or more and 50 n Less and, and an aqueous ink, wherein the glass transition temperature of 20 ° C. or less is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the ink which can suppress the fall of the discharge property by the kog caused by a zirconia can be provided in the ink discharged by a thermal system. In addition, according to the present invention, it is possible to provide an ink cartridge and an ink jet recording method using the ink.

It is sectional drawing which shows typically one Embodiment of the ink cartridge of this invention. FIG. 2 is a diagram schematically illustrating an example of an ink jet recording apparatus used in the ink jet recording method of the present invention, in which (a) is a perspective view of a main part of the ink jet recording apparatus, and (b) is a perspective view of a head cartridge.

  Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is dissociated into ions in the ink, but is expressed as “contains a salt” for convenience. In addition, water-based ink for inkjet may be simply referred to as “ink”. Further, the physical property values are values at normal temperature (25 ° C.) unless otherwise specified. The particle size of the resin particles is a volume-based value measured by a dynamic light scattering method.

  The present inventors examined an ink containing a specific pigment (phthalocyanine pigment, quinacridone pigment, diketopyrrolopyrrole pigment, dioxazine pigment, perinone pigment, perylene pigment, and anthraquinone pigment) as a coloring material. As a result, when the content of zirconium oxide mixed in the ink is 0.5 ppm or more in terms of zirconium concentration, the specific pigment is affected by the action of zirconium oxide when thermal energy for ejection is applied. It was found that the dispersion state became unstable. Since the pigment particles in which the dispersion state is unstable are easily deposited as kogation on the heater, the jettability is reduced by kogation. The reason why the discharge performance is lowered by kogation when the ink containing the specific pigment and the predetermined amount of zirconium oxide is discharged from the thermal recording head is considered as follows.

  Since the specific pigment has a polar group such as an N—H bond or a C═O bond in its molecular structure, a highly hydrophilic portion exists on the pigment particle surface. Since the highly hydrophilic portion hardly interacts with the hydrophobic portion of the resin dispersant, not only the adsorption force to the resin dispersant is weak, but also hydrophilic zirconium oxide is easily attracted. When energy for ejection is applied to the ink, the resin dispersant is easily detached from the highly hydrophilic portion of the specific pigment, and the adsorption of the resin dispersant is caused by the presence of hydrophilic zirconium oxide. It becomes easy to be disturbed. If the resin dispersant cannot be adsorbed on the surface of the pigment particles that should be stabilized by the adsorption of the resin dispersant, the surface energy becomes unstable. Here, since the specific pigment has a structure in which a plurality of aromatic rings are connected in the structure, there are many π electrons on the particle surface of the pigment. The π electrons cause a strong interaction between the pigment particles, and the dispersion state of the pigment becomes unstable. Thus, it is considered that the ink dischargeability is reduced by depositing the pigment that has become unstable in terms of surface energy as a kogation on the heater. In addition, as the cumulative number of ejections from the nozzles increases, the amount of accumulated kogation increases, and the ejection performance is more likely to deteriorate. In this way, when the cumulative number of ejections is different among a plurality of nozzles, the level of degradation of ejection properties is also different, and this difference is considered to be recognized as image unevenness.

  The inventors of the present invention have made various studies on techniques for ensuring the ink discharge performance using the specific pigment. As a result, it has been found that by containing specific resin particles in the ink, the accumulation of kogation on the heater can be suppressed, and a decrease in ejection performance can be avoided. The present inventors presume the reason why the specific resin particles are effective as follows. The specific resin particles to which the thermal energy at the time of discharge is applied in the vicinity of the heater are slightly destabilized and adhere to the heater. Furthermore, the resin particles in which the dispersion state is slightly destabilized are easily detached from the heater surface and are in an equilibrium state of adhesion and desorption. Then, even if pigment kogation is deposited on the resin particles, the kogation is detached from the heater surface together with the resin particles. Thereby, accumulation of kogation on the heater can be suppressed. That is, the specific resin particles have a role of forming a protective layer on the heater surface and protecting the heater from kogation deposition. Therefore, it is considered that stable discharge performance can be obtained regardless of the cumulative number of discharges for each nozzle.

  Further, as a result of the study by the present inventors, the technical problem of “decrease in ink discharge performance due to koge caused by zirconia” does not occur for inks containing color materials such as carbon black and azo pigments. It has been found. Since carbon black is a pigment having very high hydrophobicity, the resin dispersant is not easily detached, and adsorption of the resin dispersant to the pigment is not hindered by hydrophilic zirconium oxide. For this reason, in the case of an ink containing carbon black as a color material, the dispersion state of the pigment leading to kogation hardly occurs. Further, although a highly hydrophilic site exists on the surface of the azo pigment particles, the interaction between the pigment particles hardly occurs due to other structures. Further, since zirconium oxide is also difficult to adhere, the dispersion state of the pigment leading to kogation is unlikely to occur. For the above reasons, “decrease in ink discharge due to kog caused by zirconia” is considered to be a technical problem peculiar to ink containing a specific pigment as a colorant.

<Ink>
The water-based ink of the present invention is a water-based ink used in an ink jet recording method for recording an image on a recording medium by ejecting ink from a recording head by the action of thermal energy, and is a resin dispersion for dispersing zirconium oxide, pigment, and pigment. Containing an agent and resin particles. Hereinafter, the components constituting the ink of the present invention and the physical properties of the ink will be described in detail. In addition, this invention is not limited by the following description, unless the summary is exceeded.

(Zirconium oxide)
The ink of the present invention contains zirconium oxide. Zirconium oxide is unintentionally mixed due to contamination in the ink production process, such as a pigment dispersion process. Zirconium oxide usually exists as fine solid crystals in the ink. The element may contain other elements such as yttrium. Whether the ink contains zirconium oxide can be confirmed, for example, as follows. First, ink is ejected from the recording head using thermal energy to deposit kogation on the heater portion of the recording head. Next, the constituent components of the deposited koge are analyzed by a technique such as X-ray electron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS), or electron energy loss spectroscopy (EELS). It can be said that zirconium compounds such as zirconium oxide are hardly mixed into the ink due to the constituent material of the aqueous ink other than the pigment dispersed by the resin dispersant. For example, even if a very small amount of a zirconium compound is mixed due to a constituent material such as water or a water-soluble organic solvent, the content is below a level that can be analyzed. For this reason, if it can be confirmed that zirconium is present in the ink by inductively coupled plasma optical emission spectrometry (ICP-OES), it can be estimated that zirconium oxide is present in the ink. For the same reason, it can be estimated that the zirconium content (ppm) in the ink measured by ICP-OES is derived from zirconium oxide.

  The zirconium equivalent content of zirconium oxide can be determined from the measurement of the zirconium concentration by inductively coupled plasma optical emission spectrometry (ICP-OES). The zirconium conversion content (ppm) of zirconium oxide in the ink is 0.5 ppm or more and 20.0 ppm or less based on the total mass of the ink. When the zirconium content is less than 0.5 ppm, the discharge performance does not deteriorate due to kogation, so that the discharge performance does not change according to the cumulative number of discharges for each nozzle. On the other hand, if the zirconium content is more than 20.0 ppm, the zirconium content is too high, so that no matter how the resin particles are selected and contained, the dischargeability cannot be suppressed.

(Pigment)
The pigment contained in the ink of the present invention is at least one selected from the group consisting of phthalocyanine pigments, quinacridone pigments, diketopyrrolopyrrole pigments, dioxazine pigments, perinone pigments, perylene pigments, and anthraquinone pigments. Examples of the phthalocyanine pigment include C.I. I. Pigment blue 15: 3, C.I. I. Pigment blue 15: 6, C.I. I. Pigment green 7, C.I. I. Pigment green 36, C.I. I. And CI Pigment Green 58. Examples of quinacridone pigments include C.I. I. Pigment red 122, C.I. I. Pigment red 202, C.I. I. Pigment violet 19, C.I. I. Pigment red 202 and C.I. I. A solid solution such as a combination with Pigment Violet 19 can be used. Examples of the diketopyrrolopyrrole pigment include C.I. I. Pigment red 254, C.I. I. Pigment red 255, C.I. I. Pigment red 264, C.I. I. Pigment red 272, C.I. I. And CI Pigment Orange 71. Examples of the dioxazine pigment include C.I. I. And CI Pigment Violet 23. Examples of perinone pigments include C.I. I. And CI Pigment Orange 43. Examples of perylene pigments include C.I. I. And CI Pigment Red 149. Examples of anthraquinone pigments include C.I. I. And CI Pigment Red 177. These pigments may be used alone or in combination of two or more. Furthermore, you may use combining said pigment and pigments other than said pigment.

  The content (% by mass) of the pigment in the ink is preferably 0.20% by mass or more and 10.00% by mass or less based on the total mass of the ink. If the pigment content is less than 0.20% by mass, the color developability of the image may be lowered. On the other hand, if the pigment content is more than 10.00% by mass, the viscosity of the ink may increase excessively, resulting in ejection failure.

  The 50% particle diameter (D50) based on the volume distribution of the pigment in the ink is preferably 10 nm or more and 300 nm or less, and more preferably 20 nm or more and 200 nm or less. The D50 of the pigment can be measured, for example, using a dynamic light scattering type particle size measuring apparatus.

(Resin dispersant)
The ink of the present invention contains a resin dispersant for dispersing a pigment in the ink. That is, the pigment used as the color material in the ink of the present invention is a dispersion-type resin dispersed pigment that is dispersed in the ink by a resin dispersant. By including the resin dispersed pigment as a color material, an image with high glossiness can be recorded. The resin dispersant usually has a unit having an anionic group (hydrophilic unit) and a unit having no anionic group (hydrophobic unit). The hydrophilic unit is a unit for ensuring affinity for an aqueous medium. The hydrophobic unit is a unit for adsorbing on the pigment particle surface by hydrophobic interaction. Examples of the pigment that is dispersed in the ink by the resin dispersant include those obtained by physically adsorbing and dispersing the resin dispersant on the particle surface of the pigment, and microcapsule pigments. The microcapsule pigment is one in which the particle surface of the pigment is coated with a resin dispersant and dispersed in ink.

  It is preferable to use a water-soluble resin as the resin dispersant. The “water-soluble resin” in the present invention means a resin that can be dissolved in an aqueous medium and exist in the aqueous medium without forming particles having a particle size. If the resin dispersant is water-dispersible (water-insoluble), the storage stability of the ink may be slightly reduced.

Whether or not the resin used as the resin dispersant is water-soluble can be determined according to the following method. First, a liquid (resin solid content: 10% by mass) containing a resin neutralized with an alkali corresponding to an acid value (sodium hydroxide, potassium hydroxide, etc.) is prepared. Next, the prepared liquid is diluted 10 times (volume basis) with pure water to prepare a sample solution. And when the particle diameter of resin in a sample solution is measured by a dynamic light scattering method, when the particle | grains which have a particle diameter are not measured, it can be judged that the resin is water-soluble. The measurement conditions at this time can be as follows, for example.
[Measurement condition]
SetZero: 30 seconds Number of measurements: 3 times Measurement time: 180 seconds

  As the particle size distribution measuring apparatus, a particle size analyzer (for example, trade name “UPA-EX150”, manufactured by Nikkiso) using a dynamic light scattering method can be used. Of course, the particle size distribution measuring apparatus and measurement conditions to be used are not limited to the above.

  Among these, as the resin dispersant, it is preferable to use a (meth) acrylic resin having a unit having an anionic group (hydrophilic unit) and a unit having no anionic group (hydrophobic unit). In the following description, “(meth) acryl” means “acryl” and “methacryl”, and “(meth) acrylate” means “acrylate” and “methacrylate”.

  The unit having an anionic group (hydrophilic unit) can be formed, for example, by polymerizing a monomer having an anionic group. Specific examples of the monomer having an anionic group include monomers having a carboxy group such as (meth) acrylic acid, itaconic acid, maleic acid and fumaric acid, and anhydrides and salts of these monomers. Examples of the cation constituting the monomer salt having an anionic group include ions such as lithium, sodium, potassium, ammonium, and organic ammonium.

  The unit having no anionic group (hydrophobic unit) can be formed, for example, by polymerizing a monomer having no anionic group. Specific examples of the monomer having no anionic group include monomers having an aromatic ring such as styrene, α-methylstyrene, benzyl (meth) acrylate, 2-vinylpyridine, 4-vinylpyridine, 1-vinylimidazole; Monomers having an aliphatic group such as (meth) acrylate, methyl (meth) acrylate, (iso) propyl (meth) acrylate, (n-, iso-, t-) butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate And so on.

  The ink of the present invention contains two types of resins, a resin dispersant and resin particles. Which resin contained in the ink is a resin in which a pigment is dispersed can be determined by the following method. A liquid prepared by concentrating or diluting the ink to have a total solid content of about 10% by mass is centrifuged at 12,000 rpm for 1 hour. Thereby, the liquid layer containing a water-soluble organic solvent or a resin that does not contribute to dispersion is separated from the precipitated component containing the pigment, and the precipitated component is recovered. And it can be judged that resin contained in the collect | recovered sedimentation component is resin which has disperse | distributed a pigment. That is, the resin contained as a main component in the sedimentation component is a resin (resin dispersant) that contributes to the dispersion of the pigment. On the other hand, the resin contained as a main component in the liquid layer is a resin that does not contribute to the dispersion of the pigment.

(Resin particles)
The ink of the present invention contains specific resin particles. The volume distribution standard 50% particle diameter (D50) of the resin particles is 10 nm or more and 50 nm or less. If the D50 of the resin particles is less than 10 nm, the resin particles are likely to aggregate with each other, and it becomes difficult to form a protective layer on the heater, so that the effect of improving the ink ejection property cannot be obtained. On the other hand, if the D50 of the resin particles is more than 50 nm, the resin particles are less likely to adhere to the heater, and the effect of improving the ink ejection properties cannot be obtained.

It is preferable that the 90% particle size (D90) based on the volume distribution of the resin particles and the 50% particle size (D50) based on the volume distribution of the pigment satisfy the relationship of the following formula (1). That is, it is preferable that D90 (nm) of the resin particles is not more than D50 (nm) of the pigment. When the relationship of the following formula (1) is satisfied, it becomes difficult for the pigment to enter the gap generated on the heater due to the separation of the resin particles, so that the ink discharge performance can be further improved.
Resin particle D90 ≦ pigment D50 (1)

  The resin particles contained in the ink of the present invention are formed of an acrylic resin. Resin particles formed of, for example, a urethane resin other than an acrylic resin have high agglomeration properties. Therefore, if they adhere to the heater, they are unlikely to be detached, and the effect of improving ejection properties cannot be obtained.

  The glass transition temperature of the resin particles is 20 ° C. or less. The temperature in the nozzle in a general use environment is considered to be around 20 ° C. For this reason, if the glass transition temperature of the resin particles is more than 20 ° C., the ratio of the resin particles in a glass state is increased, and the resin particles are less likely to adhere to the heater, thereby improving the discharge property. Can't get. The glass transition temperature Tg (° C.) of the resin particles can be measured according to JIS K 6240: 2011 using a differential scanning calorimeter. At this time, for example, using the dried resin particles as a measurement sample, the glass transition temperature can be measured by increasing the temperature from room temperature (25 ° C.) to 200 ° C. at a rate of 10 ° C./min.

  The acid value of the resin particles is preferably 120 mgKOH / g or more and 180 mgKOH / g or less. When the acid value of the resin particles is less than 120 mgKOH / g, the water solubility is lowered and the dispersion state is likely to be unstable, and once adhering to the heater, it is difficult to detach, so the effect of improving the discharge property is reduced. Sometimes. On the other hand, when the acid value of the resin particles is more than 180 mgKOH / g, the water solubility becomes high and the dispersion state may be excessively stabilized. For this reason, it becomes difficult for the resin particles to adhere to the heater, and the effect of improving the dischargeability may be reduced.

  The content (% by mass) of the resin particles in the ink is preferably 0.2% by mass or more and 2.0% by mass or less based on the total mass of the ink. If the content of the resin particles is less than 0.2%, the amount of the resin particles is small, and the portion where the resin particles do not adhere on the heater tends to increase, and the effect of improving the discharge property may be reduced. . On the other hand, when the content of the resin particles is more than 2.0% by mass, the amount of the resin particles may be too much, and the resin particles are thickly deposited on the heater and are not easily detached. For this reason, the effect which improves discharge property may fall.

(Aqueous medium)
The ink of the present invention is an aqueous ink containing at least water as an aqueous medium. The aqueous medium can further contain a water-soluble organic solvent. As water, it is preferable to use deionized water (ion exchange water). The content (% by mass) of water in the ink is preferably 10.00% by mass or more and 90.00% by mass or less based on the total mass of the ink.

  The water-soluble organic solvent is not particularly limited as long as it is water-soluble. As the water-soluble organic solvent, for example, alcohol, polyhydric alcohol, polyglycol, glycol ether, nitrogen-containing polar solvent, sulfur-containing polar solvent and the like can be used. Among these, it is preferable to use at least a water-soluble organic solvent such as polyethylene glycol having a number average molecular weight of about 200 to 2,000 and 1,2-alkanediol. The content (% by mass) of the water-soluble organic solvent in the ink is preferably from 3.00% by mass to 50.00% by mass based on the total mass of the ink, and from 15.00% by mass to 40.00%. More preferably, it is at most mass%. If the content of the water-soluble organic solvent in the ink is outside the above range, ejection failure may occur.

(Other resins)
The ink of the present invention may further contain a resin (other resin) other than the above resin particles. Other resin types and forms may be used as long as they can stably exist in the water-based ink. Examples of other resins include (meth) acrylic resins, polyamide resins, polyester resins, polyvinyl alcohol resins, polyolefin resins, polyurethane resins, and the like. A base may be added to improve the solubility of these resins. Examples of the base include organic amines such as monoethanolamine, diethanolamine, triethanolamine, aminemethylpropanol, and N, N-dimethylethanolamine; inorganic bases such as potassium hydroxide and sodium hydroxide.

(Other additives)
In addition to the above-described components, the ink of the present invention contains water-soluble organic compounds that are solid at room temperature, such as polyhydric alcohols such as trimethylolpropane and trimethylolethane, and urea and derivatives thereof, as necessary. May be. Furthermore, the ink of the present invention contains a surfactant, a pH adjuster, a rust inhibitor, an antiseptic, an antifungal agent, an antioxidant, an anti-reduction agent, an evaporation accelerator, a chelating agent, and a water-soluble agent as necessary. Various additives such as a functional resin may be contained.

  Among the above additives, it is preferable to contain a fluorosurfactant. Since resin particles having a small particle size are likely to adhere to the heater surface and the resin particles are likely to be fused together, it is considered that there are some resin particles that are not easily detached from the heater surface. When a fluorosurfactant is added to ink containing resin particles with such a small particle size, the fluorosurfactant is adsorbed on the surface of the resin particles to suppress the fusion of the resin particles, and ink ejection The property can be further improved. Furthermore, since the fluorosurfactant has higher orientation to the interface and higher adsorbability to the resin particles than other surfactants, it is considered that the ink ejection properties can be further improved. .

  The content (% by mass) of the fluorosurfactant in the ink is preferably 0.01% by mass or more and 0.30% by mass or less based on the total mass of the ink. If the content of the fluorosurfactant is less than 0.01% by mass, the effect of further improving the dischargeability may be reduced. On the other hand, when the content of the fluorosurfactant is more than 0.30% by mass, the adhesion of the resin particles to the heater surface tends to be hindered, and the effect of improving the ink ejection property may be reduced.

<Ink cartridge>
The ink cartridge of the present invention includes ink and an ink storage unit that stores the ink. And the ink accommodated in this ink accommodating part is the ink of this invention demonstrated above. FIG. 1 is a cross-sectional view schematically showing an embodiment of the ink cartridge of the present invention. As shown in FIG. 1, an ink supply port 12 for supplying ink to the recording head is provided on the bottom surface of the ink cartridge. The inside of the ink cartridge is an ink storage portion for storing ink. The ink storage portion is composed of an ink storage chamber 14 and an absorber storage chamber 16, which communicate with each other via a communication port 18. The absorber housing chamber 16 communicates with the ink supply port 12. The ink storage chamber 14 stores liquid ink 20, and the absorber storage chamber 16 stores absorbers 22 and 24 that hold the ink in an impregnated state. The ink storage unit may have a form in which the entire amount of ink stored is held by an absorber without having an ink storage chamber for storing liquid ink. Further, the ink storage portion may have a form that does not have an absorber and stores the entire amount of ink in a liquid state. Further, the ink cartridge may be configured to have an ink storage portion and a recording head.

<Inkjet recording method>
The ink jet recording method of the present invention is a method of recording an image on a recording medium by discharging the ink of the present invention described above from an ink jet recording head. As a method of ejecting ink, a method of applying thermal energy to the ink is employed. Other than using the ink of the present invention, the steps of the ink jet recording method may be known.

  2A and 2B are diagrams schematically showing an example of an ink jet recording apparatus used in the ink jet recording method of the present invention. FIG. 2A is a perspective view of a main part of the ink jet recording apparatus, and FIG. 2B is a perspective view of a head cartridge. It is. The ink jet recording apparatus is provided with a conveying means (not shown) for conveying the recording medium 32 and a carriage shaft 34. A head cartridge 36 can be mounted on the carriage shaft 34. The head cartridge 36 includes recording heads 38 and 40, and is configured such that an ink cartridge 42 is set. While the head cartridge 36 is conveyed along the carriage shaft 34 in the main scanning direction, ink (not shown) is ejected from the recording heads 38 and 40 toward the recording medium 32. Then, the recording medium 32 is conveyed in the sub-scanning direction by a conveying unit (not shown), whereby an image is recorded on the recording medium 32.

  Any recording medium may be used as a recording medium on which an image is recorded using the ink of the present invention. Among them, it is preferable to use paper having permeability such as plain paper and a recording medium having a coat layer (glossy paper or art paper). In particular, it is preferable to use a recording medium having a coating layer that can cause at least a part of the pigment particles in the ink to be present on or near the surface of the recording medium. Such a recording medium can be selected according to the purpose of use of the recorded matter on which the image is recorded. For example, in order to express glossy paper suitable for obtaining a photo-quality glossy image, paintings, photographs, graphic images, etc. to your liking, the texture of the substrate (drawing paper tone, canvas tone, Art paper that makes use of Japanese paper tones) can be used. Among these, it is particularly preferable to use so-called glossy paper whose surface of the coating layer has gloss.

  In the ink jet recording method of the present invention, it is preferable to discharge water-based ink heated to 40 ° C. or more from the recording head. When the temperature of the ink is less than 40 ° C., a part of the resin particles is in a glass state and is difficult to adhere on the heater, so that the effect of improving the dischargeability may be reduced. In order to heat the ink to a predetermined temperature or higher, a means for controlling the ink temperature may be used. Examples of the means for controlling the temperature of the ink include a heater for adjusting the ink temperature disposed so as to contact the recording head and a heater for discharging the ink. In order to heat the ink by the ink discharge heater, for example, a current that does not discharge ink may be repeatedly supplied. The temperature of the ink can be read by a temperature sensor provided in the recording head.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further in detail, this invention is not limited at all by the following Example, unless the summary is exceeded. In addition, what is described as “parts” and “%” with respect to the component amounts is based on mass unless otherwise specified.

<Synthesis of resin particles>
(Resin particles E1 to E13)
While putting 100.0 parts of ethylene glycol monobutyl ether into a four-necked flask equipped with a stirrer, a reflux cooling device, and a nitrogen gas introduction tube, nitrogen gas was introduced and the temperature was raised to 110 ° C. with stirring. A mixture of monomers having the types and compositions (units: parts) shown in Table 1-1 and 1.3 parts of an ethylene glycol monobutyl ether solution of t-butyl peroxide (polymerization initiator) were added dropwise over 3 hours. After aging for 2 hours, the pressure was reduced to remove ethylene glycol monobutyl ether to obtain a solid resin (shell polymer). A shell polymer having a solid content (shell polymer) content of 30.0% by adding potassium hydroxide equivalent to the acid value and an appropriate amount of ion-exchanged water to the obtained shell polymer and neutralizing and dissolving at 80 ° C. An aqueous solution of was obtained.

  In a four-necked flask equipped with a stirrer, a reflux cooling device, and a nitrogen gas inlet tube, a 30.0% aqueous solution of each shell polymer in an amount (unit: part) shown in Table 1-2 was added, and nitrogen gas was added. The mixture was introduced and heated to 80 ° C. with stirring. A mixture of each monomer having the type and composition ratio (unit: part) shown in Table 1-3 was prepared. And after adding the mixture and water of the quantity (unit: part) shown in Table 1-2 in the said 4 necked flask, 1.0 part of potassium persulfate (polymerization initiator) is melt | dissolved in 16.7 parts of water. The liquid thus obtained was added dropwise over 3 hours. After aging for 2 hours, an appropriate amount of ion-exchanged water was added to adjust the solid content. As a result, an aqueous dispersion of resin particles having a core-shell structure with a resin (solid content) content of 10.0% was obtained. Table 2 shows the particle size (D50 and D90) based on the volume distribution of the resin particles in the obtained aqueous dispersion, the glass transition temperature, and the acid value.

  The particle size (D50 and D90) based on the volume distribution of the resin particles is determined by using a dynamic light scattering type particle size measuring device, SetZero: 30 s, number of measurements: 3 times, measurement time: 180 seconds, refractive index: 1 .5 measurement conditions. The product name “Nanotrack UPA-EX150” (manufactured by Nikkiso) was used as the particle size measuring apparatus of the dynamic light scattering method. The glass transition temperature Tg (° C.) of the resin particles was measured according to JIS K 6240: 2011 using a differential scanning calorimeter (trade name “Q200”, manufactured by TA Instruments). At this time, the dried resin particles were used as measurement samples, and the glass transition temperature was measured by increasing the temperature from room temperature (25 ° C.) to 200 ° C. at a rate of 10 ° C./min.

(Resin particles U1)
With reference to the description of “Synthesis Example 15” (Preparation of Urethane Resin Emulsion B) in JP 2012-188609 A, resin particles made of a urethane resin having a resin (solid content) content of 10.0% An aqueous dispersion was obtained.

<Preparation of pigment dispersion>
(Pigment dispersions D1 to D25)
The components (unit: part) shown in Tables 3-1 and 3-2 were mixed to obtain a mixture. The “resin aqueous solution” in Table 3-2 is an aqueous solution of a resin (resin dispersant) for dispersing the pigment. As the aqueous resin solution, an aqueous solution (content (solid content): 20.0%) of an acrylic resin (trade name “Johncrill 683”, manufactured by BASF) was used. The mixture obtained under the conditions shown in Table 3-2 was dispersed, and then centrifuged at 5,000 rpm for 30 minutes to remove aggregating components. Next, an appropriate amount of ion-exchanged water was added to prepare pigment dispersions D1 to D25.

Dispersion of the pigment using a media type disperser (indicated as “BM”) is performed by putting the mixture in a media type disperser (trade name “Bead Mill LMZ2”, manufactured by Ashizawa Finetech Co., Ltd.) with a filling ratio of zirconia beads of 80%. The process was carried out under conditions of a peripheral speed of 12 m / s. Dispersion of the pigment using a medialess disperser (indicated as “NM”) uses a high-pressure collision type disperser (trade name “Nanomizer”, manufactured by Yoshida Kikai Kogyo Co., Ltd.), and the mixture is subjected to a pressure of 150 MPa and 50 passes. Implemented by processing. Dispersion using a high-pressure collision type disperser took about twice as long as the dispersion time required to obtain a similar pigment dispersion using a media type disperser. Content (%) of pigment and resin in the prepared pigment dispersion, zirconium-based content of zirconium oxide (denoted as “Zr” (unit: ppm)), and 50% particle size based on the volume distribution of pigment ( D50 (nm)) is shown in Table 3-2. The zirconium equivalent content of zirconium oxide was obtained by diluting the prepared pigment dispersion with ion-exchanged water as a measurement sample, and using inductively coupled plasma emission spectroscopy (trade name “ICP-OES720”, manufactured by Agilent Technologies). ). The measurement was performed by a calibration curve method using a zirconium standard stock solution (trade name “ZrO (NO ₃ ) ₂ .HNO ₃ (0.1 mol / L) solution”, manufactured by Kanto Chemical Co., Inc.). Further, the 50% particle size (D50) of the pigment in the pigment dispersion based on the volume distribution is determined using a dynamic light scattering type particle size measuring device, SetZero: 30 s, number of measurements: 3 times, measurement time: 180 Measured under measurement conditions of seconds and refractive index: 1.5. The product name “Nanotrack UPA-EX150” (manufactured by Nikkiso) was used as the particle size measuring apparatus of the dynamic light scattering method.

<Preparation of ink>
Each component (unit:%) shown in the middle row of Tables 4-1 to 4-7 was mixed, stirred sufficiently, and then pressurized with a cellulose acetate filter having a pore size of 1.2 μm (trade name “Minisart”, manufactured by Sartorius). Each ink was prepared by filtration. The polyethylene glycol used had a number average molecular weight of 1,000. Some inks were prepared using two types of pigment dispersions in combination to adjust the zirconium content. The lower part of Tables 4-1 to 4-7 shows the pigment type, the zirconium equivalent content of zirconium oxide in the ink (indicated as “Zr”, ppm, measurement conditions are the same as above), and D50 (nm) of the pigment. And D50 and D90 (nm) of the resin particles. Further, in the lower part of Tables 4-1 to 4-7, the glass transition temperature (° C.) of the resin particles, the acid value (mgKOH / g) of the resin particles, the content (%) of the resin particles, and the fluorine-based surface activity The content (%) of the agent was shown. Details of the components used are shown below.
・ Megafac 444: Trade name of fluorosurfactant (manufactured by DIC)
・ Zonyl FSO-100: trade name of fluorosurfactant (manufactured by DuPont)
・ Acetylenol E100: trade name of nonionic acetylene glycol surfactant (manufactured by Kawaken Fine Chemicals)
・ Proxel GXL (S): Trade name of antiseptic (manufactured by Arch Chemicals)

The meanings of the abbreviations for the pigment types in Tables 4-1 to 4-7 are shown below.
QA: quinacridone pigment PC: phthalocyanine pigment DPP: diketopyrrolopyrrole pigment DO: dioxazine pigment PN: perinone pigment PL: perylene pigment AQ: anthraquinone pigment CB: carbon black AZ: azo pigment

<Evaluation>
The following evaluation was performed using an ink jet recording apparatus (trade name “PIXUS PRO-10”, manufactured by Canon Inc.) equipped with a recording head for discharging ink by thermal energy. In the above-described ink jet recording apparatus, an image recorded under a condition that the resolution is 600 dpi × 600 dpi and 8 drops of 3.8 ng of ink are applied to a unit area of 1/600 inch × 1/600 inch has a recording duty of 100%. Define that there is. In the present invention, “AA”, “A” and “B” are acceptable levels and “C” is unacceptable levels in the evaluation criteria for the following items. The evaluation results are shown in Table 5.

(Dischargeability)
Ink was filled in the ink cartridge and set in the above-described ink jet recording apparatus. Under the condition that only a part of the nozzles of the recording head was used, 150 sheets of a solid image of 20 cm × 30 cm having a recording duty of 100% were recorded. During recording, the recording head and ink were heated to the “ink temperature” shown in Tables 5-1 and 5-2 by the sub-heater of the recording head. After recording 100 sheets and 150 sheets, a nozzle check pattern was recorded on a recording medium (trade name “Canon Photo Paper / Glossy Gold, manufactured by Canon.) The recorded nozzle check pattern was visually confirmed and in accordance with the evaluation criteria shown below. Ink ejection properties were evaluated.
AA: There was no unevenness in both nozzle check patterns after 100 sheets were recorded and after 150 sheets were recorded.
A: The nozzle check pattern after recording 100 sheets was not uneven, but the nozzle check pattern after recording 150 sheets was uneven.
B: There was unevenness in part of the nozzle check pattern after recording 100 sheets.
C: There was unevenness throughout the nozzle check pattern after 100 sheets were recorded.

Claims (9)

A water-based ink used in an ink jet recording method for recording an image on a recording medium by discharging ink from a recording head by the action of thermal energy,
Containing zirconium oxide, a pigment, a resin dispersant for dispersing the pigment, and resin particles,
The zirconium equivalent content (ppm) of the zirconium oxide is 0.5 ppm or more and 20.0 ppm or less based on the total mass of the ink,
The pigment is at least one selected from the group consisting of a phthalocyanine pigment, a quinacridone pigment, a diketopyrrolopyrrole pigment, a dioxazine pigment, a perinone pigment, a perylene pigment, and an anthraquinone pigment,
The resin particles are formed of an acrylic resin, have a volume distribution standard 50% particle size (D50) of 10 nm or more and 50 nm or less, and a glass transition temperature of 20 ° C. or less. ink. 2. The aqueous solution according to claim 1, wherein a 90% particle size (D90) based on the volume distribution of the resin particles and a 50% particle size (D50) based on the volume distribution of the pigment satisfy the relationship of the following formula (1): ink.
Resin particle D90 ≦ pigment D50 (1)   The water-based ink according to claim 1 or 2, wherein the acid value of the resin particles is 120 mgKOH / g or more and 180 mgKOH / g or less.   The water-based ink according to any one of claims 1 to 3, wherein a content (% by mass) of the resin particles is 0.2% by mass or more and 2.0% by mass or less based on the total mass of the ink.   The water-based ink according to claim 1, further comprising a fluorine-based surfactant.   The aqueous ink according to claim 5, wherein the content (% by mass) of the fluorosurfactant is 0.01% by mass or more and 0.30% by mass or less based on the total mass of the ink. An ink cartridge comprising ink and an ink containing portion for containing the ink,
An ink cartridge, wherein the ink is the water-based ink according to any one of claims 1 to 6. An inkjet recording method for recording an image on a recording medium by discharging ink from a recording head by the action of thermal energy,
An ink jet recording method, wherein the ink is the water-based ink according to any one of claims 1 to 6.   The ink jet recording method according to claim 8, wherein the water-based ink heated to 40 ° C. or more is discharged from the recording head.

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