JPH0485375A - Ink composition for ink jet printing - Google Patents

Abstract

PURPOSE:To provide the title composition free from clogging of a nozzle and excellent in delivery stability, etc., by mixing a pigment, a polymer dispersant, an aqueous medium containing a nonvolatile organic solvent, and a drying and agglomeration inhibitor comprising a urea/sugar alcohol mixture. CONSTITUTION:The title composition is produced by mixing a pigment (e.g., carbon black), a polymer dispersant (e.g., a dispersant comprising an addition polymer), an aqueous medium consisting of water and a nonvolatile organic solvent (e.g., diethylene glycol), and a drying and agglomeration inhibitor com prising a mixture of urea and a sugar alcohol (e.g., sorbitol). The suitable amounts of the urea and the sugar alcohol respectively are 5-30 pts.wt. and 5-20 pts.wt. based on 100 pts.wt. ink composition.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an ink composition for inkjet, and more specifically, to an aqueous pigment ink for inkjet that uses a pigment as a colorant, and which has excellent drying prevention properties. The present invention also relates to an inkjet ink composition that has excellent resolubility even when dried.

[Prior art and its problems] Conventionally, inkjet recording methods have been excellent in quietness, recording speed, printing quality, running cost, etc., and have been widely used.

On the other hand, this method has the problem of nozzle clogging, and it has not been put into practical use by taking steps to prevent drying, such as using a high-boiling point solvent for the ink medium, or by installing a cleaning mechanism or nozzle cap inside the printer. There is.

In order to solve the above problem, dyes are usually used as coloring agents. This is because even if the ink solidifies in the nozzle portion due to drying, the dye can be easily redissolved by washing or the like. However, recorded materials using dyes have the drawback of insufficient light fastness and water fastness.

Although the use of pigments as colorants in inks solves these fastness problems, there is a fundamental problem in that the pigment particles clog the fine nozzle holes of the printer. Furthermore, there is a problem that the ink becomes solid upon drying, making it difficult to put pigment ink into practical use.

Particularly in the case of pigment inks, when they solidify upon drying, the pigment particles aggregate and clog the nozzle holes, or, like dye inks, cannot be dissolved even if you try to re-dissolve them using an ink medium or a specific cleaning solution, and the nozzle particles become clogged. There was a major practical problem in that the blockage could not be resolved.

The present inventor previously solved the former problem by using a specific polymer dispersant as a pigment dispersant and by incorporating a nonvolatile organic solvent such as ethylene glycol into the ink composition.

However, there are problems with drying of the pigment ink and subsequent pigment aggregation, and a pigment ink with sufficient performance has not yet been provided.

Therefore, an object of the present invention is to provide an aqueous pigment ink that is most suitable for inkjet printing and the like.

[Means for Solving the Problems] According to the present invention, the pigment, a polymer dispersant, an aqueous medium, and a drying/aggregation prevention agent are comprised, and the aqueous medium is comprised of water and a nonvolatile organic solvent, and the drying/aggregation prevention agent is The above object has been achieved by an inkjet ink composition characterized in that the inhibitor is a mixture of urea and a sugar alcohol.

[Function] By adding a specific drying/agglomeration inhibitor to pigmented ink containing a polymer dispersant and a non-volatile organic solvent, the drying of the ink is delayed and the ink nozzle is not clogged (the ink is stably ejected, Furthermore, even if the ink dries and solidifies,
By washing the nozzle with water, the dried ink is easily dissolved, and it is possible to provide an aqueous pigment ink in which the ink can be re-discharged without agglomeration of the pigment.

[Preferred Embodiments] Next, the present invention will be described in more detail by citing preferred embodiments.

The pigments used in the present invention are organic pigments and inorganic pigments that have been conventionally used in various coloring fields, and any conventionally known pigments can be used, such as azo-based, phthalocyanine-based, quinacridone-based, Anthraquinone series, dioxazine series, indigo/thioindigo series, perinone/
Perylene series, isoindorenone series, azomethine azo series,
Examples include carbon black, and fluorescent plastic pigments such as resin particles colored with fluorescent dyes and the like can also be preferably used.

The proportion of the pigment used in the ink composition of the present invention may be any concentration as long as it provides sufficient coloring density to the recorded object; % is preferred.

Furthermore, the polymer dispersant used in the present invention has the functions of both a dispersant and a binder, and improves the dispersion stability of pigment particles dispersed in the ink, and also improves the dispersion stability of pigment particles dispersed in the ink, and improves the dispersion stability of the pigment particles adhered to the recording object. It has the effect of adhering particles.

Such polymer dispersants can be roughly divided into condensation polymers and addition polymers based on their structure. Any existing ones can be used, and condensation polymers are preferable, such as special polymers. There is a polyester dispersant described in JP-A No. 60-26070, and examples of addition polymerization dispersants include addition polymers of monomers having α,β-ethylenically unsaturated groups.

Particularly preferred are addition polymer based dispersants, which are obtained by copolymerization of a heptamer forming the lipophilic part and a monomer forming the hydrophilic part.

The above addition-polymerizable polymer dispersant can be prepared by mixing hydrophilic and lipophilic monomers in appropriate proportions and using any conventional mixed polymerization method, such as solution polymerization method, suspension polymerization method, emulsion polymerization method, etc. It can also be obtained by the polymerization method of Known additives such as polymerization regulators can also be used if necessary. As long as the polymerization medium used at that time is water or a hydrophilic solvent that can be used as an aqueous medium for ink, the polymerization liquid obtained as is can be used as an ink medium, or the polymer can be used as a solution for ink. After separating from
It can also be used after being redissolved in an appropriate medium.

The polymer dispersant obtained in this way is not particularly defined by its molecular weight, but those having a molecular weight in the range of 1,000 to 100,000 are It is preferable from the viewpoint of properties such as viscosity of an ink composition using it and quality such as fastness of recorded matter.

In the present invention, the above-mentioned polymer dispersant can be used as it is as a binder for the pigment in the ink, but if the amount of the polymer dispersant alone is insufficient as a binder and the abrasion resistance of writing is not sufficient, In addition to or in place of the above-mentioned dispersant, other water-soluble resins may also be added.

Examples of such water-soluble resins include alkali metal resins such as acrylic resins, styrene-maleic anhydride resins, maleated oils, maleated polybutadiene, maleated alkyd resins, maleated petroleum resins, maleated rosin esters, and polyvinylpyrrolidone. , ammonia, amine salts, etc. are preferred, and are used in amounts that do not excessively increase the viscosity of the ink.

The amount of the above-mentioned dispersant or water-soluble resin used in the ink composition varies depending on the type and brand of the pigment and cannot be further specified, but it is approximately 3 to 100 parts by weight per 100 parts by weight of the pigment. This is the percentage of

Further, the aqueous medium constituting the ink composition of the present invention is composed of water and a non-volatile organic solvent, and the non-volatile organic solvent has the effect of preventing the ink from drying in the nozzle, such as ethylene glycol, Examples include diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, methyl cellosolve acetate, methyl carpitol, ethyl carpitol, butyl carpitol, glycerin, etc. These nonvolatile organic solvents are used in an amount of 30 parts by weight per 100 parts by weight of water. It is preferable to use it in a proportion of 80 to 80 parts by weight.

One component of the drying/agglomeration inhibitor used in the present invention is urea. Urea is 5 to 30 parts by weight per 100 parts by weight of ink.
Preferably, they are used in parts by weight.

Yet another component is sugar alcohols obtained by reducing sugars, specifically sorbitol obtained from monosaccharides, maltitol obtained from disaccharides, maltotriitol obtained from trisaccharides, and Examples include so-called oligosaccharide alcohols obtained from sugars or higher sugars. These sugar alcohols are contained in an amount of 5 to 2 parts per 100 parts by weight of the ink.
Preferably, a proportion of 0 parts by weight is used.

The above sugar alcohols are industrially easily available as a solution of a mixture of the various sugar alcohols mentioned above, but oligosaccharide alcohols alone are very viscous and when added to ink, the ink viscosity increases, making it difficult to create practical inks. cannot be provided. For this reason, in the present invention, a sugar alcohol mixture containing not much oligosaccharide alcohol, a sugar alcohol obtained from monosaccharide, disaccharide, or trisaccharide containing no oligosaccharide alcohol, or a mixture thereof is used. is preferable.

Furthermore, in the present invention, other conventionally known additives may be added as necessary.

The ink jet ink composition of the present invention comprises the above-mentioned components and formulations, and various methods can be employed for its production. For example, the various ingredients listed above are mixed, mixed with pigment using a conventionally known dispersing machine such as a ball mill, homo mixer sand grinder, speed line mill, roll mill, etc., and then the concentration, viscosity, and other physical property values are adjusted. Then, coarse particles can be removed by filtration, centrifugation, etc. to obtain ink.

[Example] Next, the present invention will be described in more detail with reference to Examples and Comparative Examples. In the text, parts or percentages are based on weight unless otherwise specified.

Example Carbon Black [Product Name Carbon Black #100
0, manufactured by Mitsubishi Kasei] 100 part dispersant [
Product name J-62, made by Johnson Polymer, resin content 34
%] 100 parts water
Mix 350 parts of the above ingredients,
The dispersion was treated with Paint Conditioner R (manufactured by Red Devil Co., Ltd.) for 2 hours, and then subjected to an ultracentrifuge to remove poorly dispersed coarse particles to obtain a black aqueous dispersion [A].

Add 260 parts of ethylene glycol to this dispersion A, 115 parts of diethylene glycol, and 115 parts of water.
Add 400 parts and mix and stir to obtain a pigment concentration of 7.5% and a viscosity of 3.7 cp [25°C]
and black ink II with a surface tension of 44 dyne/cm.
] was obtained.

Cyanine Blue [Product Name: Cyanine Blue 4930, manufactured by Dainichiseika Chemical Co., Ltd. 100 parts Dispersant [Product Name: J-62, manufactured by Johnson Polymer Co., Ltd., resin content 34% Co., 120 parts water]
350 parts ethylene glycol
260 parts of ethylene glycol were mixed, subjected to pigment dispersion treatment in the same manner, and further 26 parts of ethylene glycol was added.
0 parts diethylene glycol 115 parts water
Add 400 parts and mix and stir until the pigment concentration is 7% and the viscosity is 4. Ocp[2
5° C.] and a surface tension of 46 dyne/crn [nl] was obtained.

Examples and comparative examples of inks to which a drying/agglomeration inhibitor was added for the above Inks I and H are shown in Table 2 below.

The sugar alcohol has a composition shown in Table 1 below.

(Margin below) Table 1 (Margin below) Each ink of these Examples and Comparative Examples was filled into an ink cartridge [manufactured by DICONIX, nozzle diameter 60 μm], and after confirming that the ink was ejected, it was stored indoors or under heating. The ink was left in this state for a predetermined period of time, and it was examined whether the ink was ejected normally (item A in Table 3). Furthermore, when the nozzle was solidified by drying the ink, the nozzle part was immersed in distilled water for 15 minutes, the water from the nozzle was wiped off, and the ability to eject was checked again (item B in Table 3). These results are shown in Table 3 below.

(Margins below) ○: Ink is discharged normally ×: Ink hardens in the nozzle and does not discharge m: Not tested Also, 2 g of each ink of Example 1.3, Comparative Examples 1.2.3 and 5 was applied to a diameter of 45 mm, Place in a Petri dish with a depth of 8 mm and place 45
After drying at ℃ for 3 hours, 4 g of water was added and left for 1 hour.

The particle size distribution of this pigment dispersion was measured to find out the average particle size. The results are shown in Table 4 below.

[Measuring device: Coulter Submicron Particle Analyzer] (The following is a blank space) Table A: Average particle size before heating B: Average particle size after heating: Examples 1.2 and 3 that cannot be measured because the pigment is not redispersed The ink was an ink that could be stably ejected without clogging the nozzles. Furthermore, even when the ink solidified under heating at 45° C. as a drying condition, the pigment was dissolved by water without agglomerating, making it possible to easily solve nozzle clogging.

[Effect] According to the present invention as described above, by adding a specific drying/agglomeration inhibitor to pigment ink containing a polymer dispersant and a nonvolatile organic solvent, drying of the ink is delayed and ink nozzles are prevented from clogging. (Even if the ink is stably discharged and the ink dries and solidifies, washing the nozzle with water will easily dissolve the dried ink and prevent the pigment from agglomerating.) Pigment ink can be provided.

Claims (1)

[Scope of Claims] 1. Comprised of a pigment, a polymer dispersant, an aqueous medium, and a drying/aggregation prevention agent, the aqueous medium comprising water and a nonvolatile organic solvent, and the drying/aggregation prevention agent comprising urea and a sugar alcohol. An inkjet ink composition characterized by being a mixture of. 2. The inkjet ink composition according to claim 1, wherein the sugar alcohol is a sugar alcohol obtained by reducing monosaccharide to trisaccharide, or a mixture thereof. 3. Urea is 5 to 30% by weight based on 100 parts by weight of ink
The ink composition for inkjet according to claim 1, which is within the range of . 4. Sugar alcohol: 5 to 2 parts per 100 parts by weight of ink
The inkjet ink composition according to claim 1, wherein the content is in the range of 0% by weight.