JPH04189877A - Water-based recording ink - Google Patents

Abstract

PURPOSE:To provide the subject ink for ink-jet printer, having excellent light- resistance, water-resistance, chemical resistance and storage stability and containing a pigment and more than a specific amount of a high-molecular weight water-soluble polymer. CONSTITUTION:The objective ink at least contains preferably 3-10wt.% of a pigment (e.g. carbon black) and >=20wt.%, preferably >=100wt.% (based on the pigment) of a water-soluble polymer having a molecular weight of >=10,000 (e.g. gelatin, polypeptide, methylcellulose, CMC and PVA).

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application 1] The present invention relates to an aqueous recording ink used in an inkjet printer that performs recording using liquid ink.

[Prior Art 1 Conventionally, examples of using pigments as colorants in recording liquid inks include JP-A No. 61-283875, JP-A No. 64-6074,
It is described in JP-A-1-31881 and the like. Further, examples containing water-soluble polymers are described in JP-A-55-80477, JP-A-58-13675, JP-A-62-124167, JP-A-62-225577, and the like.

[Problem to be Solved by the Invention 1] Conventionally, aqueous recording inks that use pigments as colorants have the following problems compared to uniformly dissolved inks that use dyes as colorants:
Although it has characteristics such as excellent light resistance and chemical resistance of recorded materials, and the ability to increase the density, it is easy to cause pigment aggregation and sedimentation.
It was difficult to ensure reliability during recording due to clogging, decreased density, etc. Furthermore, when aqueous recording ink is stored at low temperatures below 0°C, the ink freezes, and even after thawing by heating or other means, pigment particles often aggregate, resulting in long-term storage stability depending on the environment in which the ink is stored. Securing the necessary resources was a major issue.

SUMMARY OF THE INVENTION The present invention is intended to solve these problems, and one of its objects is to provide a new aqueous recording ink.

Another object of the present invention is that even if the ink dries and solidifies near the ink ejection nozzle, the ink can quickly return to its original state by adding and supplying new ink, etc., and changes in the particle size of the pigment can be prevented. To provide an aqueous recording ink that prevents ink discharge failure, clogging, and density drop during recording, ensures discharge reliability, and provides high print quality and storage stability of recorded materials. It is in.

Another object of the present invention is to prevent the pigments in the ink from agglomerating during cryopreservation at low temperatures, and to restore the particle size to its pre-freezing state by thawing by means such as heating, so that it can be stored for long periods of time in the environment. An object of the present invention is to provide an aqueous recording ink with excellent stability.

Means for Solving 1 Problem] The aqueous recording ink of the present invention is characterized by containing at least a pigment and a water-soluble polymer having a molecular weight of 10,000 or more in an amount of 20% by weight or more based on the pigment.

[Example 1 Examples of the present invention will be described in detail below. Conventionally, water has been mainly used as a solvent for ink because of its low viscosity, excellent safety, ease of handling, low cost, and lack of odor. In addition, in order to improve the properties of this main solvent, alcohols such as ethanol, propatool, isopropanol, etc., polyethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, polyethylene glycol, glycerin, etc. A water-soluble organic solvent such as a nitrogen-containing organic solvent such as alcohols, monoetherified products, dietherized products, or esterified products thereof, N-methyl 2-pyrrolidone, and 1,3-dimethylimidazolidinone can be added.

Pigments that are colorants are not particularly limited, and include carbon blacks such as fast black, lamp black, acetylene black, and channel black, metals such as copper, iron, and titanium oxide, toluidine red, permanent carmine FB, Organic pigments such as Fast Yellow AAA, Disazo Orange PMP, Lake Red C, Brilliant Carmine 6B, Phthalocyanine Blue, Quinacridone Red, Dioxane Violet, Victoria Pure Blue, Alkali Blue Toner, and Aldonitroaniline Black can be used. In order to improve the wettability of these pigments, surface treatments such as oxidation may be applied. The amount of pigment added is preferably 1 to 30% by weight, more preferably 3 to 10% by weight.

The water-soluble polymers used in the present invention include gelatin,
One and/or two or more water-soluble polymers with an average molecular weight of 10,000 or more are generally called polymer dispersants such as botinopeptide, methylcellulose-sulfoxymethylcellulose, hydroxymethylcellulose, polyvinyl alcohol, and polyvinylpyrrolidone. They can be used in combination. The amount added is 2 times the amount of pigment added.
It is preferably 0% by weight or more, more preferably 100% by weight or more. However, as the amount added increases, the viscosity of the ink also increases, so it is preferable to limit the amount added to about 20% by weight based on the total ink.

Furthermore, in order to improve the wettability of the pigment during production, a conventional water-soluble ionic or nonionic surfactant can be added. For example, anionic surfactants include higher fatty acid salts, higher alkyl dicarboxylate salts,
Cationic surfactants include higher alcohol sulfate salts, higher alkyl sulfonate salts, condensates of higher fatty acids and amino acids, sulfosuccinate salts, naphthenates, etc., and examples of cationic surfactants include aliphatic amine salts, quaternary ammonium salts, and sulfonium salts. , phosphonium salts, etc., amphoteric surfactants such as betaine type, nonionic surfactants such as fatty acid ester type of botanoxyethylene compound, polyethylene oxide condensation type, etc. can be used. However, the addition of a hydrocarbon surfactant also improves the wettability between the ink and the paper surface and promotes the penetration of the ink into the paper, so the addition of a fluorine surfactant, which has less of this effect, is also useful. .

In addition, pH control agents such as potassium dihydrogen phosphate and disodium hydrogen phosphate, anti-mold agents, hexachlorophene, sorbic acid, p-hydroxybenzoic acid ester, ethylenediaminetetraacetic acid (EDTA), etc. may be included as necessary. can. Further, for the purpose of preventing nozzle drying, urea, thiourea, ethylene urea, etc. can be added.

Table 1 shows the ink compositions of Examples 1 to 9 of the present invention and Comparative Examples 1 to 3. All numerical values in Table 1 are weight %.

MAloo used here is carbon black manufactured by Mitsubishi Chemical Industries, KETRed309, KETYellow40.
3. KETBlueEx-1 is an organic pigment for color toner manufactured by Dainippon Ink and Chemicals. In addition, PVPK-30 used as a water-soluble resin is polyvinylpyrrolidone with an average molecular weight of 40.000 manufactured by Tokyo Kasei Co., Ltd., and Celogen 5
A is carboxymethylcellulose sodium with an average molecular weight of 30.000 manufactured by Dai-Kogyo Seiyaku Co., Ltd., and Denkapoval B-03 is manufactured by Denki Kagaku Kogyo Co., Ltd. with an average molecular weight of 60.00.
0 partially saponified borivinyl alcohol. As for other ingredients, GE210D is a water-soluble pigment dispersant manufactured by Kyoeisha Yushi Kagaku Kogyo Co., Ltd., and TrilonBS is B
This is EDTA manufactured by AS F, and is added in small amounts as a preservative for water-soluble inks.

Each ink sample is prepared by first dissolving twice the predetermined amount of a water-soluble resin or pigment dispersant in pure water, and after complete dissolution, carbon black is added in an amount twice the predetermined amount. This mixture of dispersant and carbon black is stirred and mixed using a mixer for 2 hours, and then dispersed using a sand mill for 8 hours. After that, Toyo Roshi N○2 was used to remove large particles.
The mixture is filtered under pressure at a pressure of 2 kg/cm 2 to obtain a dispersion.

Next, dilute this dispersion with pure water and add an organic solvent or
Preservatives and the like were added with stirring to prepare a predetermined composition.

The ink samples of Examples 1 to 9 and Comparative Examples 1 to 3 thus obtained were measured for viscosity at 20°C using a B-type viscometer No. 1 rotor (manufactured by Tokyo Keiki Co., Ltd.) and an IVL-8T type surface tension meter. (manufactured by Kyowa Interface Science Co., Ltd.) to measure the surface tension at 25°C, and furthermore, the discharge nozzle diameter was 50 μm, the piezoelectric element driving voltage was 50 mm, the driving frequency was 2 kHz, and the resolution was 3.
Each water-based ink was printed using a prototype 9-nozzle evaluation machine with 00 dots/inch, and the printed sample was observed under a microscope at 200 times magnification (print quality evaluation by this method. After solid printing, align the recording paper with the printed surface to check for ink transfer. We conducted a drying time evaluation to investigate the time it takes for the dot to disappear, a fixation evaluation by rubbing strongly with your finger after leaving it for 2 hours after solid printing, and an ejection stability evaluation to investigate the appearance of dots in the print after being left at 40°C for 2 days. .

Also, the environmental temperature when the glass sample bottle is sealed is -20
Storage stability was evaluated by observing and examining the degree of aggregation of pigment particles in the ink after freezing it at °C for 2 days and thawing it at room temperature using a microscope. The results are shown in Table 2.

Note that Xerox PPC paper was used as the recording paper. In addition, the unit of viscosity in Table 2 is mPa5, and the unit of surface tension is d.
yn/cm. The symbols in Table 2 are based on each evaluation result: O: Excellent, no problem, no change, △: Slight U, slight change, ×: Poor, clearly problematic, clearly changed. The results of a three-level subjective evaluation of ``Yes'' and ``Yes'' are shown.

The aqueous recording ink of the present invention showed high printing quality with no smearing in all evaluations conducted this time, sufficient drying and fixing properties, and good ejection stability and dispersion stability when thawing after freezing. The results were obtained.

This is thought to be because the water-soluble polymer component adsorbs onto the pigment surface, forms a protective colloid layer, and functions as a cushioning agent when the pigment aggregates. Furthermore, since the addition of a water-soluble polymer can provide higher pigment dispersibility without lowering the surface tension of the ink than a hydrocarbon dispersant, it is also effective in improving printing quality. Furthermore, as in Example 6, when a volatile solvent such as ethanol is used to improve drying performance, with ordinary dispersion ink, the solvent evaporates near the nozzle, causing precipitated and fixed pigments. It was difficult to use because the ink was easily clogged, but if a water-soluble polymer is used to impart pigment redispersibility as in the present invention, precipitated and fixed pigments can be quickly redispersed. Because I will return,
It achieves both high print quality and quick drying without clogging.

However, as in Comparative Example 1, the average molecular weight shown in the present invention was 10.
If a liquid moisturizing component such as glycerin is used instead of a water-soluble polymer component of 1,000 or more, redispersibility of the pigment after solidification is not imparted, and the ejection stability and freeze stability are insufficient. In addition, pigment fixation properties on paper are poor, and when recorded materials are rubbed, they can become smudged and density decreases. In addition, a dispersant is required to disperse the pigment, and this surface active action unnecessarily promotes ink penetration into the paper, resulting in deterioration of print quality.

As in Comparative Example 2, the water-soluble polymer is 20% by weight based on the pigment.
In the case of the following addition amounts, fixing properties are imparted, but pigment redispersibility is insufficient and ejection stability and freeze stability are not imparted. It can be seen that this problem is not improved even when a liquid moisturizing component is used in combination as in Comparative Example 3. The reason for this is that liquid moisturizing ingredients have a small average molecular weight and the interaction between each molecule is small, so the protective colloid layer around the pigment flows out due to solvent evaporation, freezing, etc., and easily separates from the pigment, resulting in stable fixation. This is thought to be because it is difficult to form a layer (fixed layer).

Regarding water resistance after printing, the ink penetrates into the paper to a certain extent, and due to its anchoring effect, it is less prone to staining than dye-based inks, even if redispersibility is imparted, such as with the water-based recording ink of the present invention. A sufficient level was obtained without any decrease in density or bleeding.

Furthermore, when the above-mentioned print quality evaluation was performed using the aqueous recording ink of the present invention on recycled papers such as Xerox's new CK paper, R paper, and Honshu Paper Co., Ltd.'s Yamayur) paper, it was found that the above three types of recycled paper However, good print quality with little bleeding etc. could be obtained.

Although the embodiments of the present invention have been described in detail above, the aqueous recording ink of the present invention is not limited to these configurations, materials, and manufacturing methods.

[Effects of the Invention] According to the present invention, in an aqueous recording ink to be used for inkjet printers, the principle characteristics of conventionally using pigments as colorants, that is, the uniform dissolution system using dyes as colorants, can be improved. Compared to conventional ink, it has excellent light resistance, water resistance, and chemical resistance for recorded materials, and can be made to be highly concentrated. By adding and supplying a liquid component such as ink, the ink is quickly redispersed, returning to its original state such as pigment particle size, and preventing ink ejection failure, clogging, etc. during recording.
This has the effect of providing an aqueous recording ink that can prevent a decrease in density and ensure reliability.

Furthermore, according to the aqueous recording ink of the present invention, the pigments in the ink do not aggregate during frozen storage at low temperatures below o'c, and return to the state before freezing by thawing by means such as heating. Another object of the present invention is to provide an aqueous recording ink that has excellent long-term storage stability depending on the environment.

Claims (1)

[Claims] An aqueous recording ink comprising at least a pigment and a water-soluble polymer having a molecular weight of 10,000 or more in an amount of 20% by weight or more based on the pigment.