JP3033093B2 - Image recording ink and image recording method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an image recording method used in an ink jet or ink mist recording method in which fine droplet ink or atomized ink is ejected from a recording head to perform recording on plain paper. Regarding ink, especially in plain paper used in business or personal fields, stable monochrome and color recording is possible, high-speed and high-quality printing is possible, and there is no worry about clogging, and image recording with excellent storage stability For inks.

[Prior art] Conventionally, ink jet recording methods can be roughly classified into two types, a continuous type and an on-demand type. The former is a charge control type (Hertz type), and the latter is an electromechanical conversion type (Kyser type). System), electric heat exchange system (valve jet, thermal inkjet), and electrostatic suction system (slit jet, electric field control system).

Further, as an ink mist recording method, there is a method in which recording ink is atomized by ultrasonic energy, a charge is applied to the generated mist ink, and the charged ink mist is electrostatically recorded on paper.

Ink used in such a jet recording method includes:
There are mainly water-based inks and non-aqueous inks, but water-based inks dominate in terms of odor, safety, and bleeding.

Water-based inks are currently used in which various water-soluble dyes or pigments are dissolved or dispersed in water or a liquid medium composed of water and a water-soluble organic solvent, and various additives are added as necessary.

The advantage of these jet recordings is that direct recording makes the process simple and noiseless. Coloring is easy. High-speed recording is possible. Low running cost is possible because plain paper can be used. High-resolution recording is possible because minute ink is used. And its potential has been attracting attention for some time.

In recent years, the era of full-scale commercialization of jet printers having the above characteristics as printers for OA equipment such as personal computers is considered to have arrived.

However, as a product, it is still at the beginning of the growth period, and there are many technical issues that need to be solved.

In the above recording method, although required items are slightly different depending on the method, the following items are required in common: 1) a high-quality recorded image without bleeding 2) a high drying / fixing speed of the ink; No tailing 3) Stable ejection without clogging in the nozzle and ink circulation path 4) Good dispersion stability, storage stability and safety of ink 5) High recording density 6) Printed matter It is particularly important that the light resistance, weather resistance, and water resistance of the film are good.

At present, intensive studies are being made on both the recording ink and the apparatus in order to satisfy all of the above requirements, and considerable improvements have been recognized depending on the required performance.

However, the most common factor that hinders the spread is plain paper commonly used in offices and homes (copy paper in Japan and copy paper and bond paper in other countries are called plain paper). Printing / image quality is poor. (Therefore, designated paper is prepared as a measure against the punishment.) That is, when the image forming ink adheres to the recording paper, the drying property is poor, and as shown in FIG.
Since the ink flows along the cellulose fibers of the recording paper, the quality of printing / image is significantly reduced. Therefore, an image forming ink in which these disadvantages are improved is strongly desired.

From such a viewpoint, various plain paper recording inks have been conventionally proposed.

For example, Japanese Patent Application Laid-Open Publication No. 55-29546 proposes a method in which a specific surfactant is added to lower the surface tension to increase the absorbability of ink on paper. Japanese Patent No. 57862 discloses a method for controlling the spread and absorption of dots by adding a strong base substance to increase the pH and chemically dissolving a sizing agent or pulp material which is a water-resistant treatment agent for plain paper. Japanese Patent Application Laid-Open No. 58-13675 proposes a method in which polyvinylpyrrolidone having a molecular weight of 40,000 or more is contained in an ink to control the spread of dots and the absorbability to paper.

[Problems to be Solved by the Invention] However, such conventional proposals have the following problems.

When high-speed printing is performed on plain paper, although a certain effect is recognized, the fixing speed of ink containing a surfactant is increased due to ink penetration, but the surface tension is low. Is not improved, and bleeding occurs, thereby deteriorating print quality. Further, there is a problem that bubbles are easily generated in the nozzle due to foaming due to the surfactant, and stable ejection cannot be obtained.

In addition, the ink containing a strong base substance has high absorbency and fixability of the ink, but does not have sufficient drying properties, and tailing and diffusion of the ink along the fibers of the paper are not improved, and bleeding occurs. There is a problem that printing quality cannot be obtained.

In addition, the ink containing polyvinylpyrrolidone having a molecular weight of 40,000 or more has a problem that the margin for clogging of the nozzle is very low, the bleeding cannot be sufficiently improved, and tailing occurs due to poor drying property. .

As described above, it has been found that the above 1) to 6) cannot be satisfied with ink having a high penetration dependency on plain paper.

Therefore, the present invention solves such a problem, and an object of the present invention is to eject ink droplets or mist-like ink from a recording head and attach the ink onto plain paper to perform printing. Alternatively, in the ink mist recording method, an ink for image formation which does not cause printing or image bleeding on plain paper, has good drying / fixing properties, has no tailing, and has excellent ejection stability without clogging. To provide.

[Means for Solving the Problems] The image recording ink of the present invention contains at least water, a colorant, and organic three-dimensionally crosslinked organic ultrafine particles having an average particle diameter of 0.5 μm or less. Is characterized in that a surface functional group is introduced into it. Further, the image recording ink of the present invention is characterized in that the surface functional group has an adsorbing power to the colorant. Further, the image recording ink of the present invention is characterized in that the surface functional group has an adsorbing power to a medium such as paper. Further, the image recording ink of the present invention is characterized in that it contains the organic ultrafine particles in an amount of 5 to 40% by weight. Further, the image recording ink of the present invention is characterized in that the colorant is contained in an amount of 0.5 to 10% by weight. Further, the image recording ink of the present invention is characterized in that the colorant is a pigment having a particle size of 0.1 μm or less. Further, the image recording ink of the present invention is characterized in that the colorant is a dye. The viscosity of the ink at 20 ° C. is 1.2 to 10 centipoise. The image forming method of the present invention uses an image recording ink in which the colorants are yellow, cyan, and magenta, respectively, and ejects the ink from a recording head as fine droplet ink or mist-like ink on plain paper. It is characterized by recording.

[Example] The inventor of the present invention described the bleeding and drying properties of jet ink and plain paper (front and back of copy paper, bond paper).
As a result of minute observations from all angles, the dye or pigment, which is a colorant, is adsorbed on the surface of the organic three-dimensionally crosslinked organic ultrafine particles that are uniformly dispersed, and as shown in FIG. A film is formed while maintaining
I found it to take root.

That is, the bleeding, drying and fixing properties were solved by the intermolecular force between the organic ultrafine particles and the colorant and the adhesion of the resin particles to the paper.

It is possible to adjust the hardness / softness of the particles by three-dimensionally crosslinking the organic ultrafine particles according to the degree of crosslinking, and to impart hydrophilicity / hydrophobicity by freely introducing surface functional groups. And surface charge and the like can be freely controlled.

Also, since the internal three-dimensionally cross-linked, it is difficult for the resin particles to fuse due to the interfacial tension during solvent evaporation, the primary film forming power is weak, so that no clogging or aggregation occurs, and When the resin is easily redispersed in a solvent and dried sufficiently on paper, a strong film is formed due to the adhesion of the resin to the paper.

If the fixability is insufficient, it is also possible to fix by heat curing.

The organic ultrafine particles used in the present invention are very suitable for synthesis by emulsion polymerization, and the crosslinking of the polymer particles is achieved by copolymerizing a polyfunctional monomer having a plurality of double bonds.

Specifically, a microgel of Nippon Paint Co., Ltd. can be mentioned. The main component of the resin is styrene / acrylate (styrene, methyl methacrylate, n-butyl acrylate) resin, and its particle size, shape, degree of cross-linking, surface functional groups, multilayer structure, etc. can be freely adjusted. Since the surfactant to be used is also of a high molecular type, it is preferable that the generation of bubbles is less likely to occur.

If the amount of addition is less than 5% by weight in terms of solid content, bleeding, drying property and fixing property cannot be solved,
If the content is more than 40% by weight, problems occur in the ejection stability and dispersion stability, so the content is preferably from 5% by weight to 40% by weight.

As the colorant used in the present invention, a water-soluble dye used in conventional inks and by adding other ink components,
Any dye can be used as long as it does not cause color change or precipitate formation.

 Specifically, Direct Black # 19 (CI35255) Direct Black # 154 Food Black # 2 (CI27755) Acid Yellow # 23 (CI19140) Acid Red # 87 (CI45380) Acid Red # 106 (CI45100) Acid Blue # 9 (CI42090) Direct Blue # 86 (CI74180).

As the pigment, a substance in which ordinary organic / inorganic pigments are dispersed in fine particles is used, and a substance in which the pigment particle diameter is reduced to 0.1 μm or less is preferable.

If the amount of the dye / pigment is less than 0.5% by weight, the color tone / concentration cannot be obtained, and if it exceeds 10% by weight, clogging is likely to occur.

As the solvent used in the present invention, water or a mixed solvent of water and a water-soluble organic solvent is used.

 As the water, it is preferable to use distilled pure water.

Examples of the water-soluble organic solvent used by mixing with water include C 1-4 alkyl alcohols, ketones, ethers, polyalkylene glycols, alkylene glycols, glycerin, and lower alkyl ethers of polyhydric alcohols. Used.

These water-soluble organic solvents can be used alone, but two or more kinds of solvents can be mixed and used in order to impart proper ink physical properties.

As the physical properties of the ink of the present invention, the viscosity at 20 ° C. is 1.2 cp.
If it is lower than that, in high-speed printing, drying problems will occur,
If it is larger than 10 cp, it is clogged, and a problem occurs in ejection stability.

Although the basic constitution of the present invention is as described above, in addition to the above, conventionally known dispersants, surfactants, viscosity adjusters, surface tension adjusters, specific resistance adjusters, pH adjusters, antifungal agents are required. It can be added accordingly.

In addition, when used in an ink-jet method of ejecting ink by the action of thermal energy, thermal properties (for example, specific heat, thermal expansion coefficient, thermal conductivity, etc.) are adjusted.

Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not intended to limit the present invention.

Example 1 All the ink composition amounts (%) shown in the following examples are% by weight.

Direct Black # 19 3% Microgel solution with 20% solid content 75% Diethylene glycol 10% Distilled pure water 12% The above components are mixed and stirred well in a container, filtered through a membrane filter with a pore size of 0.5 μm, and recorded. An ink for use was prepared.

Example 2 Garbon black (pigment) 5% Microgel solution having a solid content of 20% 80% Diethylene glycol 10% Distilled pure water 5% After mixing and stirring the above components, the pigment particle size was 0.1% with a ball mill.
The dispersion was performed until the particle diameter became equal to or less than μm, thereby preparing a recording ink.

Example 3 An ink having the following composition was prepared by the method described in Example 1.

Direct Black # 19 3% Microgel solution with 20% solid content 80% Diethylene glycol 10% Distilled pure water 7% Acid Yellow # 23 3% Microgel solution with 20% solid content 80% Diethylene glycol 10% Distilled pure water 7% Acid Red # 87 3% Microgel solution with 20% solid content 80% Diethylene glycol 10% Distilled pure water 7% Acid Blue # 9 3% Microgel solution with 20% solid content 80% Diethylene glycol 10% Distilled pure water 7% Compare Example 1 An ink having the following composition was prepared by the method described in Example 1.

Direct Black # 19 1% Glycerin 20% Dodecylbenzenesulfonic acid 2% Sodium dehydroacetate 0.1% Distilled pure water 76.9% Comparative Example 2 An ink having the following composition was prepared by the method described in Example 1.

Direct Black # 19 2% Glycerin 5% Triethylene glycolic acid 10% 10N potassium hydroxide aqueous solution 2% Sodium dehydroacetate 0.1% Distilled pure water 80.9% Comparative Example 3 An ink having the following composition by the method described in Example 1 Was prepared.

Direct Black # 19 2.5% Polyvinylpyrrolidone 0.5% Ethylene glycol 17% Anhydrous potassium carbonate 0.2% Sodium acetate trihydrate 0.05% Best side 0.1% Ethylenediaminetetraacetic acid 0.2% Sodium Distilled pure water 79.45% Ink recording method Commercially-available on-demand type inkjet printer Discharge orifice diameter 50μm, piezo oscillator drive voltage 50
V, frequency 5KHz prototype multi-head Bubble jet printer using heating elements (orifice diameter 50μm, heater size 30 × 150μm, number of nozzles 2
4 lines, drive voltage 30V, frequency 3KHz) Charged ink mist recording method using ultrasonic atomization (ultrasonic vibrator driving frequency 1.5MHz, driving voltage 50V) Evaluation when high-speed recording is performed by the above 4 methods Table 1 shows the results and the ink physical property measurement results.

* 1. Average particle size measurement Electrophoretic light scattering photometer ELS-800 (manufactured by Otsuka Electronics) * 2. Viscosity measurement B-type viscometer (rotation speed: 60 rpm, 20 ° C) (manufactured by Tokyo Keiki) * 3. Surface tension measurement surface Tensiometer HVL-ST type (manufactured by Kyowa Interface Science) * 4. Bleeding evaluation Observation at 100x and 400x with a microscope and visual observation ◎: Dots are retained on the fiber without bleeding along the fiber ：: Slight bleeding along the fiber but not visible. わ: Slight bleeding visually. ×: Slightly bleeding and jagged edges. * 5. Evaluation of drying / fixing property 3 seconds after printing and 6 seconds after printing. , Rub with paper edge after 12 seconds ◎: no tail after 3 seconds ○: no tail after 6 seconds △: tail after 6 seconds ×: tail after 12 seconds * 6. Evaluation Leave the cap at room temperature for 1 month ○: Printing possible ×: Printing not possible * 7. Is stored at 40 ° C for 3 months and there is no foreign matter, off-flavor, aggregation or precipitation ○: No ×: Yes * 8. Recording density Measurement of reflection O / D value by Macbeth densitometer * 9. ○: no ×: present ×: present As can be seen from Table 1, the recording inks of Examples 1 to 3 obtained good results in common for each recording method. Was done.

Further, the recording inks of Example 3, black, yellow,
A clear full-color image could be reproduced by superimposing cyan and magenta in each color.

On the other hand, in the case of the recording ink as in Comparative Examples 1 to 3, it can be seen that sufficiently satisfactory recording cannot be performed.

Further, as can be seen from Examples 1 to 3, it can be seen that high-density recording is achieved because the drying property and fixing property do not depend on absorption into paper.

[Effects of the Invention] As described above, according to the image recording ink of the present invention, bleeding on plain paper, which has conventionally been a problem, excellent drying and fixing properties, and clogging, ink preservability, It has the effect of enabling high-speed recording with excellent water resistance of printed matter and clear recording at high density.

It also has the effect of enabling easy redispersion in the solvent.

In addition, by using three process color inks (and using black if necessary), a high-resolution full-color image can be recorded.

[Brief description of the drawings]

 FIG. 1 is a schematic view showing bleeding of ink on paper fibers. FIG. 2 is a schematic view showing an ink dot of the present invention. 1 ... paper fiber 2 ... ink

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C09D 11/00-11/20

Claims (9)

(57) [Claims] (1) at least water, a colorant, and an average particle size of 0.5
An image recording ink comprising: organic ultrafine particles having an internal three-dimensional cross-linkage of not more than μm; and a surface functional group introduced into the organic ultrafine particles. 2. The image recording ink according to claim 1, wherein said surface functional group has an adsorbing power to said colorant. 3. The image recording ink according to claim 1, wherein the surface functional group has an adsorbing power to a medium such as paper. 4. The ink for image recording according to claim 1, wherein said organic ultrafine particles are contained in an amount of 5 to 40% by weight. 5. The image recording ink according to claim 1, wherein said colorant is contained in an amount of 0.5 to 10% by weight. 6. The image recording ink according to claim 1, wherein the colorant is a pigment having a particle size of 0.1 μm or less. 7. The image recording ink according to claim 1, wherein said colorant is a dye. 8. The image recording ink according to claim 1, wherein the viscosity of the ink at 20 ° C. is 1.2 to 10 centipoise. 9. An image recording ink according to claim 1, wherein said colorants are yellow, cyan, and magenta, respectively, and said ink is ejected from a recording head as fine droplet ink or mist-like ink onto plain paper. An image forming method characterized by recording.