JP2502637B2 - Aqueous ink composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to an inkjet recording ink, for example, a water-based ink composition used in an inkjet recording method of any type such as a charge control type and an on-demand type, and a fountain pen or the like. Writing instruments, recorders, plotters, etc.
It is also used as a general recording ink.

[Prior Art] In order to perform good recording for a long time in ink jet recording, it is necessary that the ink used satisfies the following conditions.

1) The ink has appropriate values in characteristic values such as viscosity, surface tension, specific electric conductivity, and density according to the droplet generation method and the droplet flight direction control method. 2) Chemistry even after long-term storage. In order to satisfy the above conditions, there should be no precipitation or change in physical properties due to changes, 3) high density of recorded image, excellent water resistance and light resistance. Many proposals have been made so far and some results have been obtained.

However, in recent years, there is an increasing demand for inks that can be printed on not only inkjet paper but also general paper, but with many conventional inks, it takes time to dry when printed on size-processed paper such as general high-quality paper. Therefore, there is a problem that the image is rubbed by the paper discharge system of the printer to stain the background.

A method of adding a surfactant or the like to the ink to improve the permeability of the ink to the paper in order to improve the drying property of the image
55-65262, etc. However, with this method, the surface tension of the ink is lowered, so that the drying property is certainly improved, but there is a drawback that bleeding called feathering easily occurs around the image.

[Object] The present invention solves the above problems of the prior art, and provides a highly reliable ink that is excellent in water resistance and image sharpness and does not cause nozzle clogging or precipitation during storage. It is an object.

[Structure] The structure of the present invention for achieving the above-mentioned object is such that the ratio of the number of carboxylic acid groups to the number of sulfonic acid groups in one molecule is 0.3 or more, and the counter cation of these acid groups is the fourth group.
An aqueous ink composition comprising a dye which is a primary ammonium ion or a lithium ion.

 The above dyes used in the present invention will be described below.

The dye used in the present invention has at least one carboxylate group and sulfonate group in the molecule. Generally, the water-soluble dye contains a sulfonate. Dyes having a sulfonate group generally have good solubility in water and are preferable in terms of clogging resistance and storage stability, but generally do not give sufficient water resistance to printed images. In order to improve water resistance with a dye containing a sulfonate group, it is generally effective to make the dye molecule larger, but as the molecule is made larger, the solubility decreases, and the sharpness of the absorption spectrum disappears and the color changes. It tends to become cloudy. One of the reasons that the water resistance of a printed image of a dye having only a sulfonate group is not sufficiently high is that the acid dissociation constant of the sulfonate is large, so that the dye is dissociated even after the dye is attached to the recording medium, Alternatively, it is due to the fact that it can be dissociated immediately when immersed in water.

On the other hand, since the carboxylic acid group of the dye used in the present invention has a small dissociation constant, when the pH of the ink adheres to the recording medium and the pH of the ink is lowered, the dye is apt to precipitate and deposit. Particularly, fine paper used for general recording. Is a rosin-sized acidic paper, and since its surface has a considerable amount of acidic substances, its pH drops to 5 or less when the ink is deposited on the recording paper. Most of the sulfonic acid does not affect the solubility of the dye because it is dissociated even at this pH value, but most of the carboxylic acid becomes a free carboxylic acid at this pH.

The present invention is based on such a principle. In the ink of the present invention, since the dye in the ink attached to the recording paper immediately precipitates, the obtained image has excellent water resistance, and the surface tension of the ink is low, so that the ink is quickly Image bleeding is unlikely to occur even when penetrating into a recording medium.

Dyes containing a carboxylate group are excellent in terms of resolution of a water resistant image as described above, but when a cation is used as a sodium ion or ammonium ion which has been conventionally used, its solubility is It is not enough, and clogging easily occurs when the printing of the printer is stopped for a long time. It is a quaternary ammonium ion or lithium ion that imparts sufficient solubility, and a quaternary ammonium having a C _{1 to} C ₄ alkyl group or a C _{1 to} C ₄ alkyl group substituted with a hydroxyl group is particularly preferable. It is a thing. If a quaternary ammonium ion having an alkyl group of C ₅ or more is used, the solubility of the dye will be reduced.

Even if these quaternary ammonium and lithium ions are used as cations, sufficient solubility may not be given when the dye has only carboxylate in the molecule and does not contain sulfonate. In particular, when the dye molecule is large and the molecular weight is large, it becomes difficult to dissolve the dye. In such a case, the solubility can be improved by using a dye having a structure having both carboxylate and sulfonate as hydrophilic groups in the molecule. However, even in such a case, the number of carboxylate groups / carboxylate ratio is 0.3.
When the amount is less than the above, the effect of dye precipitation described above becomes small, so that the effects of water resistance and image bleeding prevention are almost lost. A preferred ratio is 0.5 or more.

Specific examples of the dye that can be used in the present invention will be given below.

These dyes can be used alone, or several kinds can be selected from these compounds and mixed and used. Further, for the purpose of adjusting color tone, improving solubility, and the like, a dye which has been conventionally used as an inkjet ink, a writing ink, a dye or the like can be mixed and used. The conventionally used dyes can be selected from known documents such as color index. Examples of these dyes include direct conversion dyes described in the color index as preferable ones, and examples of the dyes include CI direct yellow 33, CI direct yellow 44, CI direct yellow 50, and CI direct Yellow 86, CI Direct Yellow 144,
CI Direct Orange 26, CI Direct Orange 102, CI Direct Red 4, CI Direct
Red 95, CI Direct Red 242, 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, C.
I. Direct Blue 15, CI Direct Blue 76,
CI Direct Blue 86, CI Direct Blue 20
Examples include 0, CI direct blue 201, CI direct blue 202, CI direct black 19, CI direct black 22, CI direct black 32, CI direct black 51, and CI direct black 154.

When these dyes are added to the ink of the present invention, they should be added within a range that does not impair the effects of the present invention. Specifically, the weight ratio to the dye of the present invention is 30
%.

The amount of the dye used in the present invention added to the ink is 0.5 to 20 wt%, preferably 1.0 to 5 wt% based on the total weight of the ink.
%.

Further, all of the cations of the dye used in the present invention are fourth
It need not be a primary ammonium ion or a lithium ion. In fact, it is difficult to make all the cations of these dyes into predetermined cations.

For example, when a dye after production is precipitated with an acid to obtain an acid-type dye, if other cations are contained in the liquid at the time of acid precipitation, the dye may be precipitated while containing the ion. Because there are many. Furthermore, even if a dye containing no cations other than hydrogen ions is obtained by acid precipitation, the dye is dissolved to form an ink. This is because sodium, potassium, etc. are often contained. Furthermore, many additives such as preservatives are generally marketed as sodium acid, and it is disadvantageous to use these compounds by exchanging them with quaternary ammonium or lithium ions because the manufacturing cost becomes high. Among the total cations contained in the ink of the present invention, the higher the ratio of quaternary ammonium and lithium is, the more preferable it is, but the effect is recognized by containing 20% or more, and preferably by containing 50% or more, It is possible to prevent clogging when printing is stopped.

The ink of the present invention uses water as a main solvent component, but in order to adjust the physical properties of the ink to desired values, in order to prevent the ink from drying and to prevent the nozzle clogging during the print pause period. Alternatively, a water-soluble organic solvent may be mixed with water for the purpose of improving the solubility of the dye. As this organic solvent, it is necessary to have physical properties that dissolve the dye well, but as preferable examples of this solvent, glycerin, ethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol having a molecular weight of 200 to 1500, propylene glycol, Polyhydric alcohols such as dipropylene glycol can be mentioned. In the ink of the present invention, in addition to these polyhydric alcohols, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether,
Ethers of polyhydric alcohols such as diethylene glycol monobutyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, and triethylene glycol monoethyl ether, other N-methyl-2-pyrrolidone, 1,3-dimethylimidazolidinone, 2-pyrrolidone An organic solvent such as can be added.

The content of these organic solvents in the ink can be used in the range of 5 to 80% with respect to the total weight of the ink, but the physical properties of the ink,
It is particularly preferable to use within the range of 10 to 60% from the viewpoint of drying property.

In the present invention, conventionally known compounds can be added in addition to the above dyes and solvents.

For example, as antiseptic / antifungal agents, dehydroacetate, sorbate, 2-pyridinethiol-1-oxide sodium, benzoate, pentachlorophenol sodium,
2,4-dimethyl-6-acetoxy-m-dioxane, 1,2
Examples thereof include compounds such as -benzthiazolin-3-one.

Quaternary ammonium hydroxide or lithium hydroxide is preferable as the pH adjuster, but lithium carbonate, quaternary ammonium hydroxide or lithium hydroxide may be used for fine adjustment of the pH or to impart a buffer property to the ink.
Basic compounds such as secondary ammonium carbonate, lithium hydrogen carbonate, sodium carbonate, sodium hydroxide and triethanolamine can be added. The ink of the present invention can have excellent water resistance and a clear image by setting its pH value as low as possible within the range where the dye does not precipitate. By setting the ink pH value in that way,
This is because the dye containing the carboxylic acid group can be precipitated more quickly after the ink is attached to the medium. Therefore, the preferred pH value of the ink of the present invention is in the range of 0.5 to 6 higher than the pH value at which the dye causes precipitation, and more specifically 4.5.
It is -10.0, More preferably, it is 5.0-9.0.

A surfactant or a surface tension lowering agent can be added to the ink of the present invention for the purpose of lowering the surface tension of the ink to improve the drying property of the ink, or improving the solubility of the dye. Specific examples of these compounds include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl esters, polyoxyethylene alkyl sorbitan esters, polyoxyethylene alkyl amines, glycerin fatty acid ester, sorbitan fatty acid. Nonionic surfactants such as esters, propylene glycol fatty acid esters and polyoxyethylene glycol fatty acid esters; alkyl sulfates, polyoxyethylene alkyl ether sulfates, polyoxyethylene alkyl ether acetic acid solutions, alkylbenzene sulfonates, N
-Acyl amino acid salts, alkyl sulfosuccinates,
Anionic surfactants such as alkyl phosphates; Cationic surfactants such as quaternary amines such as benzalkonium salts; perfluoroalkyl phosphates, perfluoroalkyl carboxylates, perfluoroalkyl Examples thereof include fluorine-based surfactants such as betaines.

By adding these compounds to make the surface tension of the ink 50 dyne / cm or less, the absorptivity of the ink to the recording medium is enhanced, and the drying is quickly performed. Therefore, the effect of the present invention can be further enhanced thereby.

Examples of the rust preventive agent include acidic sulfite, sodium thiosulfate, ammonium thioglycolate, diisopropylammonium nitrite, pentaerythritol tetranitrate, and dicyclohexylammonium nitrite.

In addition, a water-soluble ultraviolet absorber, a water-soluble infrared absorber, a water-soluble polymer compound, a dye dissolving agent and the like can be added depending on the purpose.

Hereinafter, the present invention will be specifically described with reference to examples. In addition, the amount (%) of each component described in the examples is based on weight.

Example 1 Ink composition Compound No. 1 dye 2.5% Glycerin 5% Diethylene glycol 8% Polyethylene glycol 300 5% Diethylene glycol monobutyl ether 5% Sodium dehydroacetate 0.3% Purified water Remaining amount The ink of the above formulation was prepared, stirred and filtered. To obtain a test ink. The pH value of the ink was adjusted to 7.5. The surface tension was 35.8 dyne / cm.

This ink was filled in a charge control type inkjet printer (Ricoh: inkjet processor for word processor report 5600J) for printing.
The following items were evaluated for the ink.

Water resistance of image The image formed by printing was immersed in water for 1 minute, the image density before and after the immersion was measured, and the fading rate (%) was determined by the following formula.

Dryability Measure the time until the ink in the solid image area does not transfer to the filter paper.

Image clarity Significant feathering is observed x, Feathering with only small feathers △, Feathering rarely occurs ○, Preservability −20 ° C, room temperature, storage at 50 ° C for 3 months And physical properties before and after storage (viscosity, surface tension, electrical conductivity)
When the difference was less than 10% and no precipitate was observed, the result was marked with ◯, and the others were marked with x.

Nozzle clogging test After removing the printer cover from the printer that has stopped printing, leave it for 2 weeks at 40 ° C and 20%, and then print again. Was designated as x.

 The results of each of the above tests are shown in Table 1.

Comparative Examples 1 and 2 An ink using a dye in which the cation was changed from tetramethylammonium ion to sodium ion and ammonium ion (NH ₄ ) in Example 1 was prepared and the same test was conducted.

Comparative Example 3 An ink was prepared by replacing the dye of Example 1 with the dye of the following structure having a structural formula similar to the dye used in Example 1, and the same test was conducted.

Example 2 Ink Composition Compound of Compound Example 5 2.5% Glycerin 5% Ethylene glycol 10% Polyethylene glycol 200 5% N-Methyl-2-pyrrolidone 3% Diethylene glycol monobutyl ether 3% 2-Pyridinethiol-1-oxide sodium 0.1
% Water Remaining Ink having the above formulation was prepared in the same manner as in Example 1 and the same test was conducted. The surface tension of the ink was 41.5 dyne / cm.

Comparative Example 4 As a dye similar to Compound 5, the dye having the following structure was used instead of the dye used in Example 2, and the same test was performed.

Example 3 Ink Composition Dye of Compound Example 11 3% Diethylene glycol 20% 1,3-Dimethylimidazolidinone 5% 2,4-Dimethyl-6-acetoxy-m-dioxane 0.2% Fluorosurfactant 1% Water Remaining amount The ink of the above formulation was prepared in the same manner as in Example 1 and the same test was conducted. The surface tension of the ink was 28.3 dyne / cm.

Comparative Example 5 As a dye similar to Compound 11, an ink was prepared by using the following dye instead of the dye used in Example 3 and the same test was conducted.

Example 4 Ink Composition Dye of Compound Example 4 2% Ethylene glycol 10% Diethylene glycol 10% Dipropylene glycol 7% Ethylene glycol monophenyl ether 2% 2-Pyridinethiol-1-oxide sodium 0.2
% Water Remaining Ink having the above formulation was prepared in the same manner as in Example 1 and the same test was conducted. The surface tension of the ink was 38.5 dyne / cm.

Comparative Example 6 and Comparative Example 7 An ink having the same formulation as in Example 4 was prepared using the dyes of Compound Example 4 in which the cations were replaced with trimethylamine and potassium ion, respectively, and the same test was conducted.

Example 5 Dye of Compound Example 13 3% Glycerin 5% Diethylene Glycol 20% Diethylene Glycol Monobutyl Ether 5% 1,2-Benzthiazolin-3-one 0.2% Water Remainder Ink Surface Tension 38.3 dyne / cm Comparative Example 8 Compound 13 As a similar dye, an ink was prepared by using the following dye instead of the dye used in Example 5, and the same test was conducted.

Example 6 An ink was prepared by using Compound 8 instead of Compound 13 of Example 5, and a similar test was conducted.

The results are shown in Table 1. Printing was performed on commercially available bond paper, electrophotographic paper (PPC paper), computer paper, and there was a similar tendency on all papers.
Regarding the water resistance, the drying time and the sharpness of the image of No. 1, the results on PPC paper are shown.

Example 7 Ink Composition Dye of Compound Example No. 16 2.5 wt% Glycerin 5 wt% Diethylene glycol 8 wt% Diethylene glycol monobutyl ether 5 wt% Sodium dehydroacetate 0.3 wt% Purified water remaining amount The ink of the above formulation was prepared, stirred and filtered for testing. I got the ink. The pH of the ink was adjusted to 7.5 with lithium hydroxide. The surface tension was 36 mN / m.

Example 8 An ink was prepared in the same manner as in Example 7 except that the dye (17) was used instead of the compound (16) of Example 7. Ink
The pH was adjusted to 7.5 with tetramethylammonium hydroxide. The surface tension was 36 mN / m.

Comparative Example 9 An ink was prepared in the same manner as in Example 7 except that the exemplified compound Y-3 was used instead of the dye of Example 7. Ink
The pH was adjusted to 7.5 with sodium hydroxide. The surface tension was 36 mN / m.

These inks were filled in a charge control type inkjet printer (Ricoh: inkjet processor for word processor report 5600) for printing. Ink evaluation was performed in the same manner as in Example 1.

 The results are shown in Table 2 below.

[Effect] As described above, the ink of the present invention is capable of imparting high image water resistance and sharpness while preventing clogging, and at the same time imparting high drying property. In the ink of the present invention, the dye further causes precipitation on the surface of the paper, so that generally, a higher image density can be obtained as compared with the conventional ink.

Front page continuation (72) Inventor Nobufumi Nagai 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (56) References JP 61-43673 (JP, A) JP 61- 43674 (JP, A) JP 58-2364 (JP, A) JP 63-30573 (JP, A) JP 63-19288 (JP, A)

Claims (1)

(57) [Claims] 1. A dye in which the ratio of the number of carboxylic acid groups to the number of sulfonic acid groups in one molecule is 0.3 or more, and the counter cations of these acid groups are quaternary ammonium ions or lithium ions. A water-based ink composition comprising: