JPH023827B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field] The present invention relates to an aqueous ink composition used for inkjet recording. [Prior Art] The properties required of the above ink are that the dye content is sufficiently high and the density of the printed image is high, that the image has sufficiently high water resistance and light resistance, viscosity, and surface tension. The physical property values such as For example, it is possible to print characters with high quality. Many of these characteristics are contradictory. For example, if the content of dye in the ink is increased in order to increase the image density, clogging becomes more likely to occur or precipitation occurs more easily during storage. In order to solve these problems, a number of measures have been taken, such as selecting dyes with high solubility, selecting organic solvents that dissolve dyes well, and adding surfactants. Although inks that can withstand practical use have been developed by taking these measures, it cannot be said that image density and clogging resistance are sufficiently high, and improvements in these properties are desired. [Objective] The present invention provides an inkjet recording method that does not cause clogging even after being left unused for a long period of time.
The purpose of this invention is to provide an aqueous ink that allows normal recording. [Structure] The present invention was made to achieve the above object, and contains a dye having a sulfonic acid, carboxylic acid, or phenol group as a molecular structure, and an ammonium ion having the following general formula as its counter ion. This is an aqueous ink composition for inkjet recording, characterized by: [In the formula, R ₁ , R ₂ , R ₃ , and R ₄ are an alkyl group having 1 to 4 carbon atoms, a hydroxyl group, or an alkyl group having 1 to 4 carbon atoms partially substituted with a halogen, and R ₁ , R ₂ ,
At least one of R ₃ and R ₄ is the above substituted alkyl group. ] The above alkyl group depends on the type and amount of organic solvent used in the ink and the type of dye, but in particular, the alkyl group has 1 carbon number.
-4 is preferred. As the substituent, a hydroxyl group or a halogen is preferable. The effect remains the same even if there are not only one type of these substituents but also multiple types in the molecule.
When the number of carbon atoms is 5 or more, the solubility of the dye in water becomes poor. Moreover, amine salts in which any one of R ₁ to _{R 4} is hydrogen also have poor solubility, and when amines are used in ink, they tend to cause a bad odor. Specific examples of the above dyes include acid dyes, direct dyes, and reactive dyes according to the Color Index classification. More specific examples include CI acid yellow 17 and CI acid dyes.
Acid Yellow 23, CI Acid Yellow 42,
CI Assisted Yellow 44, CI Assisted Yellow 79,
CI Assisted Yellow 142, CI Assisted Red 35,
CI Assured Dred 42, CI Assured Dred 52, CI
82, 87, 92, 134, 249, 254, 289, 289, 289, 1 CI 1, 9 9, 15 CI 59, 93 CI assisted blue, 93 CI assisted blue 24. 9 , CI Assisted Black 2, etc. CI Direct Yellow 33 is a direct dye.
CI Direct Yellow 44, CI Direct Yellow 50, CI Direct Yellow 86, CI Direct Yellow 144, CI Direct Orange 26, CI Direct Red 9, CI Direct Red 17, CI Direct Red 28, CI Direct Red 81, CI
Direct Red 83, CI Direct Red 89,
CI Direct Red 225, CI Direct Red
227, CI Direct Blue 15, CI Direct Blue 76, CI Direct Blue 86, CI Direct Blue 200, CI Direct Blue 201, CI Direct Blue 202, CI Direct Black 19, CI Direct Black 22, CI Direct Black 32,
CI Direct Black 38, CI Direct Black 51, CI Direct Black 154 are listed, and reactive dyes include CI Reactive Yellow 17,
CI Reactive Red 6 and CI Reactive Blue 2 are preferred examples used in the present invention. The dyes mentioned above are generally commercially available, and they are commercially available in the form of sodium salts, potassium salts, amine salts, and free acid forms. The dye used in the present invention includes sulfonic acid, carboxylic acid,
If the phenol group is in the form of a free acid, it can be used as is, but when it is in the form of other sodium salts or amine salts, it must be used in the free acid form or directly converted into the quaternary ammonium salt of the present invention. It is necessary to convert it into . Examples of methods for converting salts such as sodium into free acids include adding an acid such as hydrochloric acid or acetic acid to an aqueous solution of the dye and separating the resulting dye precipitate by filtration, or extracting with a solvent if no precipitate is formed. . Alternatively, it can be converted into a free acid using an ion exchange resin. Examples of methods for directly converting it into a quaternary ammonium salt include a method using an ion exchange resin and a method in which quaternary ammonium ions are added to a dye solution and then solvent extraction is performed. The ammonium ion as a counter ion is a quaternary ammonium ion, and _R1 to _R4 are substituted alkyl groups having at least one carbon. As a specific example, etc. In order to use these quaternary ammonium ions as counter ions for the dye, when the dye is obtained as a free acid, it is added to the ink as a hydroxide ion. That is, a dye salt is formed by adding a compound having the following general formula to an ink. In the present invention, it is not essential that all of the acidic groups such as sulfonic acid, carboxylic acid, and phenol groups in the dye be quaternary ammonium salts, and quaternary ammonium ions in an amount equivalent to or more than the dye are present in the ink. It can also be included. Even if the dye is precipitated from solution with a strong acid such as hydrochloric acid to obtain the free acid, all of the acidic groups may not be in the form of the free acid, depending on the structure of the dye. Also desired PH
It may be necessary to add less than or more than an equivalent amount of quaternary ammonium hydroxide to adjust the ink to the desired value. Furthermore, the amount of quaternary ammonium ions to be added must be determined by taking into consideration the amount of anions contained as impurities in the ink, such as sulfate ions, chloride ions, carbonate ions, bicarbonate ions, acetate ions, and the like. In the present invention, these anions as impurities are contained at 0.1wt% in the ink.
The quaternary ammonium ion as a counter ion is preferably contained in the ink in an equivalent amount of 30 or more calculated from all the acidic groups in the dye to make the present invention most effective. Can be done. The ink of the present invention uses water as a solvent component, but in order to adjust the physical properties of the ink to desired values, to prevent the ink from drying, to improve the solubility of the dye, etc. water and a water-soluble organic solvent. That is, polyhydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, and glycerin, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, and triethylene glycol monoethyl ether. Alkyl ethers of polyhydric alcohols such as ethylene glycol monomethyl ether and triethylene glycol monoethyl ether, others, N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethylimidazolidinone, dimethylformamide, triethanolamine etc. These may be used alone or in combination of two or more. Particularly preferred among these are diethylene glycol, polyethylene glycol 20-600, triethylene glycol, ethylene glycol, glycerin, and N-methyl-2-pyrrolidone, which can improve dye solubility and prevent moisture evaporation. The effect of preventing clogging can be obtained. The content of the above-mentioned water-soluble organic solvent in the ink can range from 5 to 80% based on the total weight of the ink, but it is preferably used within the range of 10 to 60% in view of viscosity, drying properties, etc. In addition to the dye and solvent described above, the following additives can be added to the ink of the present invention. For example, as preservatives and fungicides, sodium dehydroacetate, sodium sorbate, 2-pyridinethiol-
Sodium 1-oxide, sodium benzoate, sodium pentachlorophenol, etc. can be used in the present invention. As the PH adjuster, any substance can be used as long as it can control the PH of the ink within the range of 8.0 to 12.0 without adversely affecting the ink to be prepared. Examples include amines such as diethanolamine and triethanolamine, hydroxides of alkali metal elements such as lithium hydroxide, sodium hydroxide, and potassium hydroxide, and alkali metal hydroxides such as ammonium hydroxide, lithium carbonate, sodium carbonate, and potassium carbonate. carbonates, etc. Specific electrical conductivity regulators include, for example, inorganic salts such as potassium chloride, ammonium chloride, sodium sulfate, and sodium carbonate, and water-soluble amines such as triethanolamine. Examples of the chelating reagent include sodium ethylenediaminetetraacetate, sodium nitrilotriacetate, sodium hydroxyoxyethylethylenediaminetriacetate, sodium diethylenetriaminepentaacetate, and sodium uramildiacetate. Examples of rust preventives include acidic sulfites, sodium thiosulfate, ammonium thioglycolate, diisopropylammonium nitrite, pentaerythritol tetranitrate, and dicyclohexylammonium nitrite. In addition, depending on the purpose, water-soluble ultraviolet absorbers, water-soluble infrared absorbers, water-soluble polymer compounds, dye solubilizers, surfactants, etc. can be added. When adding salts containing cations other than hydrogen ions among the above additives, reduce the amount added or change the cations to hydrogen ions or quaternary ammonium ions and add them to the ink. It is preferable that 30 or more of the total number of moles of cations therein be quaternary ammonium ions. In the present invention, by using the above-mentioned quaternary ammonium as a counter ion of the dye, clogging after discontinuation of use for a long period of time is significantly reduced. Therefore, since the content of dye in the ink can be increased, the image density can be increased. Furthermore, dyes with good water resistance generally have a large molecular weight and are prone to clogging, but the present invention makes it possible to use these dyes in inks and improve water resistance. Although the reason why the clogging properties are significantly improved by the present invention is not clear, by using quaternary ammonium as a counter ion for dyes, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol,
It is thought that the solubility in polyhydric alcohols such as polyethylene glycol and their ethers, and N-methyl-2-pyrrolidone is improved, or that the evaporation of water in the ink is suppressed. Next, examples and comparative examples will be described. Example 1 Dye Direct Braz 154 (acid type) 4wt% Diethylene glycol 15wt% N-methyl-2-pyrrolidone 10wt% Polyethylene glycol 200 5wt% Methyltriethanolammonium hydroxide (40% aqueous solution) 4.1wt% Purified water Remaining amount An ink was prepared by mixing the two. Then, a nickel nozzle (diameter 30 μm) having an appearance as shown in FIG. 1 and a cross section as shown in FIG. 2 was prepared.
1 indicates a nozzle hole, and 2 indicates a test ink. Using this, a buffered aqueous solution of sodium carbonate and sodium hydrogen carbonate adjusted to a pH value of 10.0 was discharged from a nozzle attached to the head at a pressure of 400 atmospheres, and the discharge amount per hour and discharge position (at a position 50 mm away from the nozzle) was measured. Then, the ink with the above composition was applied to the nozzle using a 1 μ microsyringe, and the nozzle was heated at 50°C.
After placing it in a constant temperature and humidity chamber adjusted to 25% RH for 5 days, it was taken out and attached to the original head, and the buffer solution was jetted out in the same manner as before drying, and the amount and position of the jet was measured. The results are shown in Table 1. Those in which the discharge amount decreased by 2% or more than before drying were rated as X, those in which the discharge was not discharged rapidly were rated as XX, and those in which the discharge amount changed by less than 2% were rated as ○. Further, among the discharged products, those with a change in discharge position of less than 1 mm were evaluated as ○, those with a change of 1 to 3 mm were evaluated as X, and those with a change of 3 mm or more were evaluated as XX. Comparative Examples 1 to 6 Instead of methyltriethanolammonium hydroxide in Example 1, sodium hydroxide, ammonium hydroxide, triethylamine, tripropylamine, potassium hydroxide, and tetrapentylammonium hydroxide were added to the same molar concentration. The same test as in Example 1 was conducted using the added material. The results are shown in Table 1. In Comparative Example 5, the dye did not dissolve, the ink could not be filtered, and printing could not be performed. Example 2 Dye Acid Dred 254 (acid type) 3wt% Ethylene glycol 10wt% Diethylene glycol 20wt% Glycerin 5wt% Ethyltriethanolammonium hydroxide 1.8wt% An ink having the above composition was prepared. Quaternary ammonium ions accounted for 93% of all cations in the ink. A test similar to Example 1 was conducted using this ink. The results are shown in Table 1. Comparative Example 7 A similar test was conducted using sodium hydroxide instead of ethyltriethanolammonium hydroxide in Example 2. The results are shown in Table 1. Comparative Example 8 A similar test was conducted using potassium hydroxide instead of ethyltriethanolammonium hydroxide in Example 2. The results are shown in Table 1.

【table】

[Table] [Effects] The ink composition of the present invention significantly reduces clogging after discontinuing use for a long period of time. Therefore,
Since the dye content in the ink can be increased, the image density can be increased. Furthermore, dyes with good water resistance generally have a large molecular weight and are prone to clogging, but the present invention makes it possible to use these dyes in ink, thereby improving water resistance.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a nozzle used in the tests of Examples and Comparative Examples, and FIG. 2 is a sectional view thereof. 1... Nozzle hole, 2... Test ink.

[Claims]

1 Acrylic copolymer () obtained by copolymerizing an acrylic monomer having an epoxy group and a monomer copolymerizable therewith in the presence of a chlorinated polyolefin and a basic nitrogen-containing acrylic monomer and an acrylic copolymer () obtained by copolymerizing the same with a monomer copolymerizable with it, in a weight ratio of ()/() = 1/20 to 20/1. Coating composition.