JPH04189878A - Water-based recording ink - Google Patents

Abstract

PURPOSE:To provide the subject dispersion-type ink for ink-jet printer, having excellent light-resistance, chemical resistance, water-resistance and storage stability and composed of carbon black having a pH lower than a specific level and a specific organic amine. CONSTITUTION:The objective ink having a surface tension of preferably >=45dyn/cm at 25 deg.C is produced by using (A) a carbon black having a pH of <=6 and (B) an organic amine of formula (R<1> is H, 1-6C alkyl or 1-6C hydroxyalkyl; R<2> is H or 1-6C alkyl) (e.g. N,N-dimethylethanolamine, N-methylethanolamine or N-methyldiethanolamine).

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a dispersion type aqueous recording ink for use in an inkjet printer that performs recording using liquid ink.

[Prior art 1 Conventionally, examples of using carbon black as a coloring agent in recording liquid ink are disclosed in Japanese Patent Application Laid-open No. 6.1-283875 and Japanese Patent Application Laid-open No. 6.1-283875.
4-6074, JP-A-1-31881, etc. Further, an example in which an aqueous pigment ink contains an amine derivative having a hydroxyalkyl (alkanol) group is described in JP-A-60-76576.

1 Problem to be Solved by the Invention 1 Conventionally, by using carbon black as a colorant, high light resistance, chemical resistance, and water resistance can be imparted to recorded materials, but on the other hand, carbon black is added for the purpose of improving the dispersibility of carbon black. Since the hydrocarbon surfactant lowers the surface tension of the ink and improves its wettability with the recording paper more than necessary, deterioration of printing quality such as bleeding may occur depending on the recording paper.

For this reason, the addition of amine derivatives having a hydroxyalkyl group has been proposed, but those in which the nitrogen atom of the amine is not substituted with a lower alkyl group have poor wettability with carbon black and are not compatible with hydrocarbon surfactants. Concomitant use was necessary. Similarly, during ink storage, ensuring long-term storage stability has been 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 carbon black has
An object of the present invention is to provide an aqueous recording ink that takes advantage of high light resistance, chemical resistance, and water resistance and has excellent storage stability of recorded materials.

Another object of the present invention is to maintain a high surface tension of ink, ensure ink ejection reliability, achieve high resolution recording, and obtain high quality print quality with reduced bleeding. Our objective is to provide recording ink.

Another object of the present invention is to provide a highly stable aqueous recording ink that does not cause agglomeration of carbon black in the ink during storage.

Means for Solving the Problem 1 The aqueous recording ink of the present invention is characterized by comprising at least carbon black having a pH of 6 or less and a specific organic amine represented by the following general formula.

\ N-C2H4-OH / In the formula, R1 is at least one selected from the group consisting of hydrogen, a lower alkyl group, or a lower hydroxyalkyl group.
It is a substituent of a species. R2 is at least one substituent selected from the group consisting of hydrogen and lower alkyl groups.

Moreover, in this specification, a lower alkyl group refers to a straight chain or branched alkyl group having 1 to 6 carbon atoms. Furthermore, the surface tension of the ink is 45 dyn/cm at 25°C.
It is characterized by the above.

[Examples] 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, for the purpose of improving the properties of water-soluble organic solvents, such as alcohols such as ethanol and propatool, polyhydric alcohols such as ethylene glycol, diethylene glycol, and glycerin, or their ethers and esters. I can do it.

Carbon black, which is a coloring agent, is desired to have good affinity with water, which is the main solvent. It has many coating layers of substances and has a pH of 6 or less. The pH of this carbon black refers to a value obtained by the following measuring method. That is, 3 g of carbon black to be measured and 100 g of distilled water
g into a beaker, measure the total weight, and boil this for 1 hour. After cooling to room temperature, the weight of the gold was measured, distilled water was added in an amount equal to the weight loss due to boiling, the mixture was stirred and allowed to stand for 10 minutes, and the pH of the supernatant liquid was measured using a glass electrode pH meter.

Commercially available carbon black whose pH is 6 or less by the above measurement method is, for example, Mitsubishi Chemical Industries, Ltd. registered trademark 92400.
B, #2350, #2200B, #1000, MAl
oo, MA7, MA8, MAll, Degussa registered trademark Special Black 5502 Special Black 35
0, Special Black 250, Special Black 1
00, Printex 150T, Printex U, Printex V, Printex 140U, Printex 140v, registered trademark of Columbia Carbon Co., Ltd. -
Raben 1255, Raben 1200, Raben 117
0, Raben 1060, Raben 1040, Rapen 1
030, Cabot Registered Trademark Monarch 1300, Mogul L5 Regal 400, Palcan Also, those treated with a surface modification method such as plasma treatment and whose pH has become 6 or less can also be used. The amount added is preferably 1 to 30% by weight, more preferably 3 to 12% by weight based on the total weight of the ink.

In the present invention, a polymer dispersant is used instead of a typical hydrocarbon surfactant because it lowers the surface tension of the ink. Examples of polymeric dispersants include proteins such as gelatin and casein, natural gums such as gum arabic, glucoxides such as saponin, cellulose derivatives such as methylcellulose, carboxymethylcellulose, and hydroxymethylcellulose, natural polymers such as lignin sulfonate, and shellac. Polyacrylate, styrene-acrylic acid copolymer salt, vinylnaphthalene-acrylic acid copolymer salt, styrene-maleic acid copolymer salt, vinylnaphthalene-maleic acid copolymer salt, β-naphthalenesulfonic acid formalin condensation Anionic polymers such as sodium salts of polyphosphoric acid, polyphosphoric acid, nonionic polymers such as polyvinyl alcohol, polyvinylpyrrolidone, and polyethylene glycol, and one type or a mixture of two or more of these can be used. can. The amount added is 0.0 based on the total weight of the ink.
It is preferably 5 to 30% by weight, more preferably 0°1
~15% by weight.

Furthermore, it is preferable to add the above-mentioned polymer dispersant or an aqueous acrylic styrene emulsion as a component for fixing carbon black on paper.

When using a resin component for fixing carbon black,
It is preferable to add a resin content of 5% by weight or more, preferably 20% by weight or more, based on the amount of pigment added.

Further, specific organic amines used in the present invention are mono- and jetanolamines represented by the general formula %, such as N,N-dimethylethanolamine, N-dimethylethanolamine, and N-dimethylethanolamine.

These include N-diethylethanolamine, N,N-dipropylethanolamine, N,N-dibutylethanolamine, N-methylethanolamine, and N-methyljetanolamine.

The following may be considered as the effects of organic amines.

In other words, if the pH of the ink is 6 or less, it is expected that the electrical repulsion of the carbon black in the dispersed state will decrease, making the dispersion state unstable and causing particle aggregation, especially due to changes in the environmental temperature. It becomes easier. Also, pH1
If it is 0 or more, the protective colloid action of the polymeric dispersant may be hindered, resulting in precipitation, dispersion stability may be inhibited, and ink performance may deteriorate. Furthermore, since the ink of the present invention has a high possibility of coming into contact with the human body, it is preferable to adjust the pH to around neutrality from the viewpoint of safety. not adjusted to the value. Therefore, the amount added is preferably 0.01 to 10% by weight based on the total weight of the ink.

In addition to the above, benzoic acid, dichlorophene, hexachlorophene, sorbic acid, p-hydroxybenzoic acid ester,
Ethylenediaminetetraacetic acid (EDTA) and the like can be contained as a fungicide, preservative, and rust preventive. Furthermore, urea, thiourea, ethylene urea, etc. can be contained for the purpose of preventing nozzle drying.

Table 1 shows the ink compositions of Examples 1 to 6 of the present invention and Comparative Examples 1 to 4. All numerical values in Table 1 are weight %.

In addition, the carbon blacks with a pH of 6 or less used were Raven 1225, Raven 1250 (registered trademark of Colombian Carbon Co., Ltd.), MAloo (registered trademark of Mitsubishi Chemical Industries, Ltd.), and carbon black #950 with a pH of 8°0 used as a comparative example. (Mitsubishi Chemical Industries, Ltd. registered trademark).

Furthermore, Denkapoval B-03 is used as a dispersant.
(registered trademark of Denki Kagaku Kogyo Co., Ltd.) is partially saponified polyvinyl alcohol, Labelin FHL (registered trademark of Dai-Kogyo Seiyaku Co., Ltd.) is sodium salt of β-naphthalene sulfonic acid formalin condensate, Joncryl-615 (registered trademark of Johnson Co., Ltd.) is a salt of styrene-acrylic acid copolymer 30.
A 5% aqueous solution, Shellac GBN (registered trademark of Gifu Shellac Seisakusho), is a shellac resin.

Comparative Example 4: Sansepara 100 (registered trademark of Sanyo Chemical Co., Ltd.), which is sodium dioctyl sulfosuccinate, was used as a dispersant.
It was used for.

For each ink sample, first, twice the predetermined amount of organic amines or dispersant is dissolved in pure water, and after complete dissolution, twice the amount of carbon black is added. This dispersant and carbon black mixture was stirred for 2 hours with a mixer.
Mix and then disperse using a sand mill for 8 hours.

After that, to remove large particles, 2kg/2kg was added using Toyo Roshi No. 2.
A dispersion liquid is obtained by pressure filtration at a pressure of Cm2. Next, this dispersion liquid was diluted with pure water to prepare an ink sample so as to have a predetermined composition.

Regarding the ink samples of Examples 1 to 6 and Comparative Examples 1 to 4 thus obtained, the surface tension of the ink at 25°C was measured using an HVL-3T type surface tension meter (manufactured by Kyowa Kaimenwa Gakusha), The pH at 25°C was also measured using a glass electrode pH meter manufactured by Horiba, and the discharge nozzle diameter was 50 μm, piezoelectric element driving voltage was 150 V, and driving frequency was 2 k.
Using a prototype 9-nozzle evaluation machine with a resolution of 300 dots/inch at Hz, we evaluated the print quality by observing the print sample under a microscope at 200x magnification, and evaluated the continuous ejection stability by checking whether there were any missing dots during 24-hour continuous printing. went. The weight of the ejected ink was 0.18 μg/dot.

The ink ejection speed was 5 m/s. In addition, storage stability was evaluated by examining the degree of aggregation of carbon black particles by microscopic observation in a thermostatic chamber at an ambient temperature of 70° C. and humidity of 85% for 30 days in a sealed glass sample bottle. The results are shown in Table 2.

Table 2 Note that Xerox PPC paper was used as the recording paper. Also, the symbols in Table 2 are based on each evaluation result: O: No problem, △
Shows the results of a three-level subjective evaluation: : There is a Wakachi problem, ×: There is a clear problem.

The unit of surface tension is dyn/cm.

All of the ink samples of Examples 1 to 6 had high printing quality without bleeding in all evaluations conducted this time, and sufficient results were obtained in terms of dispersion stability during ejection and long-term storage. However, ink samples using carbon black with a pH higher than 6 as in Comparative Example 1 had little effect on the dispersion stability of organic amines, and nozzle clogging during ejection and aggregation of carbon black during storage were observed. . In addition, as in Comparative Example 2, ink containing an excessive amount of secondary or higher grade ethanolamines among organic amines tends to increase ink viscosity, so in such cases, monoethanolamines should be added. It is. Furthermore, in an ink sample that does not contain organic amines like Comparative Example 3, the pH of the ink is higher than 8, and even if short-term dispersion stability is good, long-term dispersion stability cannot be ensured. Agglomeration of carbon black was also observed in the storage stability evaluation.

This is thought to be because the pH of the ink gradually decreases due to the influence of carbon dioxide gas in the air during storage of the ink. Comparative Example 4, in which a hydrocarbon-based anionic surfactant was added to improve the wettability and dispersibility of carbon black, had excellent storage stability, but the ink surface tension was 45 d y n
/ cm, causing defects during ink ejection, and bleeding and spreading on paper, deteriorating print quality.

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.

[Effect of the Invention 1] According to the present invention, an aqueous recording ink for use in an inkjet printer is provided, which has a high recording preservation property by taking advantage of the light resistance, chemical resistance, and water resistance of carbon black. It has the effect of being able to.

Furthermore, it is possible to provide an aqueous recording ink that prevents nozzle clogging on plain paper, ensures ejection reliability, achieves high resolution recording, and provides high quality print quality.

Furthermore, even during long-term storage, carbon black in the ink does not aggregate, making it possible to provide an aqueous recording ink with excellent stability.

Claims (2)

[Claims] (1) An aqueous recording ink characterized by comprising carbon black having a pH of at least 6 or less and a specific organic amine represented by the following general formula. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ In the formula, R^1 is at least one substituent selected from the group consisting of hydrogen, a lower alkyl group, or a lower hydroxyalkyl group. R^2 is at least one substituent selected from the group consisting of hydrogen and lower alkyl groups. In addition, in this specification, a lower alkyl group has 1 to 1 carbon atoms.
6 straight chain or branched alkyl group. (2) The surface tension of the ink is 45 dyn/cm at 25°C
The aqueous recording ink according to claim 1, characterized in that it has the above properties.