JP2000345085A - Aqueous ink composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an aqueous ink composition in which the agglomeration of a pigment is prevented and which does not exhibit the decrease in density of printed letters by dispersing, in an aqueous medium, a surface-modified pigment dispersible and/or dissolvable in water in the absence of a dispersant and by adjusting the concentration of a free polyvalent cation in the ink to a specified value or lower. SOLUTION: The concentration of the free polyvalent cation in the ink is adjusted to 100 ppm or lower. Calcium, magnesium, and iron ions, etc., are listed as the polyvalent cation. Preferable pigments to be surface-modified are carbon black and organic pigments. Especially preferably, the surface-modified pigment is prepared by oxidizing carbon black or an organic pigment with a halogenic acid compound (e.g. sodium or calcium hypochlorite). The cocentration of the free polyvalent cation in the ink can be decreased preferably by purifying a dispersion containing the surface-modified pigment oxidized and dispersed therein by reverse osmosis, ultrafiltration, electrodialysis, or the like and then preparing the ink.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dispersion type aqueous ink using carbon black or an organic pigment as a colorant. More specifically, the present invention relates to an improvement in an aqueous ink composition containing a surface-modified pigment that can be dispersed and / or dissolved in water.

[0002]

2. Description of the Related Art Conventionally, water-soluble dyes have been used as recording liquids for aqueous writing instruments and ink jet printers. In recent years, pigments such as carbon black have been used as colorants in order to improve the image quality and durability of recorded matters.

For example, JP-A-64-6074 and JP-A-64-31881 describe aqueous pigment inks in which carbon black is dispersed with a surfactant or a polymer dispersant.

However, with these inks, when the ink content of the colorant is increased in order to increase the print density of the recorded matter, there arises a problem that the viscosity of the ink sharply increases at the same time. Also, in order to stably disperse, an excess of a surfactant or a polymer dispersant is necessary, but these cause the generation of bubbles and a decrease in defoaming property. There is a problem that leads to deterioration of stability.

In order to solve these problems, Japanese Patent Laid-Open Publication No.
JP-A-3498 and JP-A-10-120958 disclose that a certain amount or more of surface active hydrogen or a salt thereof is introduced into carbon black, and the carbon black treated alone without a surfactant or a polymer dispersant is spontaneously used. A dispersion using a surface-modified carbon black that can be dispersed in a liquid is described. Further, JP-A-10-95941 proposes an inkjet ink containing the above-mentioned surface-modified carbon black and glycol ethers.

[0006]

The ink using the surface-modified carbon black which can be spontaneously dispersed as described above is extremely effective in reducing the viscosity of the ink and the printing stability. However, in the case of an aqueous pigment ink in which carbon black is dispersed with a surfactant or a polymer dispersant described in JP-A-64-6074 and JP-A-64-31881, the carbon black used as a raw material is dispersed in the dispersion step. The ionic substance originally contained hardly desorbs, whereas the spontaneously dispersed surface-modified carbon black system desorbs the ionic substance from the pigment in the surface modification step using an oxidizing agent etc.・ Is dissociated and ionized,
There is ion generation due to decomposition of the oxidizing agent and the like used for surface oxidation, and when these ions particularly contain polyvalent cations, the pigments in the ink gradually aggregate and precipitate, thereby lowering the printing density. Problems were found to occur.

Accordingly, the present invention provides a water-based ink composition containing a surface-modified pigment that can be dispersed and / or dissolved in water without a dispersant, thereby preventing aggregation of the pigments in the ink and lowering the print density. The purpose of the present invention is to provide an aqueous ink composition which does not have a water content.

[0008]

The aqueous ink composition of the present invention is an aqueous ink composition containing at least an aqueous medium and a surface-modified pigment that can be dispersed and / or dissolved in water without a dispersant, The polyvalent cation released in the ink may have a concentration of 100 ppm or less.

[0009]

DETAILED DESCRIPTION OF THE INVENTION The aqueous ink composition of the present invention is obtained by dispersing a surface-modified pigment which can be dispersed and / or dissolved in water without a dispersant such as a surfactant or a water-soluble resin in an aqueous medium. It is. Further, the concentration of the polyvalent cation released into the ink was adjusted to 100 ppm or less.

In the present invention, a state in which a pigment is stably present in water with a minimum particle size that can be dispersed in water without using a dispersant is referred to as "dispersion and / or dissolution".
The minimum dispersible particle size is a minimum particle size that does not become smaller even when the dispersion time is increased. By introducing a large amount of hydrophilic functional groups on the surface of carbon black or organic pigments and modifying the surface, the water-soluble dye spontaneously disperses as small as a single molecule in water, with the smallest particle size at which the pigment can be dispersed It is thought that it will be dispersed.

The surface modification for "dispersing and / or dissolving" is carried out by applying a hydrophilic functional group such as a carboxyl group, a carbonyl group or a hydroxyl group, or a salt thereof directly to the surface of the pigment or by applying an alkyl, alkyl ether or aryl group to the surface of the pigment. It is performed by joining through such as. Specifically, a method of introducing a carboxyl group, a carbonyl group, a hydroxyl group, or the like by oxidizing the pigment surface with an oxidizing agent in water by a chemical treatment, and applying these functional groups or active species containing the functional groups to the pigment surface And the like.

The aqueous ink of the present invention preferably contains the surface-modified pigment in a range of 1 to 15% based on the total amount of the ink. Within this range, an aqueous ink having a sufficient print density can be obtained.

If the concentration of the polyvalent cation released into the aqueous ink of the present invention and the amount of the surface-modified pigment added are 100 ppm or less, it is possible to prevent aggregation of the pigments in the ink. . Polyvalent cations that are originally contained in dispersion materials such as calcium, magnesium, and iron, and that are desorbed and ionized from pigments during the oxidation / dispersion process, or decomposition by-products of calcium hypochlorite, an oxidizing agent Of calcium and the like.

The concentration of free polyvalent cations in the ink can be reduced by purifying a dispersion of the oxidized and dispersed surface-treated pigment by a reverse osmosis membrane, ultrafiltration, electrodialysis or the like, and then preparing the ink. This is preferable so as not to deteriorate the dispersibility of the dispersion.

Quantification of released polyvalent cations is possible, for example, by the following analytical method. The ink can be obtained by separating a liquid component with an ultrafiltration filter, diluting the liquid component to an appropriate concentration with ultrapure water, and measuring the diluted solution by ion chromatography.

Incidentally, carbon black and organic pigments include:
As described above, there are those originally containing calcium or the like as impurities and those containing copper ions as chelates in the molecular structure. If these are present inside the pigment or disperse by being strongly adsorbed on the pigment surface, etc., and are not desorbed even after being left, even if the total amount of the above substances contained in the ink exceeds 100 ppm, the No aggregation occurs.

In the present invention, it is preferable to use carbon black and an organic pigment as a pigment for surface modification.

Specific examples of preferred carbon blacks in the present invention include # 20B, # 40, MA100, etc. as carbon blacks manufactured by Mitsubishi Chemical Corporation. Examples of carbon black manufactured by Degussa include color black FW18, color black S170, and special black 250. As carbon black made by Columbia Carbon, Conductex SC,
Raven 1255 and the like. Monarch 700, Monarch 8 as carbon black manufactured by Cabot
80, Elftex 12 and the like. These are only examples of carbon black suitable for the present invention, and the present invention is not limited by these.

Preferred organic pigments in the present invention include azo pigments, phthalocyanine pigments, anthraquinone pigments, quinacridone pigments, thioindigo pigments, triphenylmethane lake pigments, and oxazine lake pigments. Further, if insoluble in an aqueous medium, vat dyes, oil-soluble dyes, disperse dyes, and the like can be used. Specifically, the yellow type includes C.I. I. Pigment Yellow 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 1
3, 14, 15, 16, 17, 65, and 83. Further, as the red system, C.I. I. Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 1
2, 13, 14, 15, 16, 17, 18, 19, 2,
1, 22, 23, 30, 31, 32, 37, 38, 3
9, 40, 49, 50, 51, 52, 53, 55, 6
0, 64, 83, 87, 88, 89, 90, 112, 1
14, 123, 163 and the like. As the blue type, C.I. I. Pigment Blue 2, 3, 15, 16, 2
2, 25, etc., as a black type, C.I. I. Pigment Black 1.

The surface-treated pigment used in the aqueous ink of the present invention is prepared by introducing a carboxyl group, a carbonyl group, a hydroxyl group or the like by oxidizing the pigment surface with an oxidizing agent in water by the chemical treatment as described above. And a method in which these functional groups or active species containing the functional groups are grafted onto the pigment surface. However, it is particularly preferable to oxidize carbon black or an organic pigment with a halogen acid compound. Examples of the halogen acid compound include an aqueous solution of sodium hypochlorite, calcium hypochlorite, an aqueous solution of sodium hypobromite, an aqueous solution of sodium hypoiodite, calcium hypochlorite, and the like. Since hypofluorite is extremely unstable, it cannot be used substantially for preparing a surface-treated pigment.

The aqueous medium of the aqueous ink composition of the present invention is a medium for retaining the surface-modified pigment and imparting properties as an ink, and contains at least water, a humectant, and a penetration enhancer. And, if necessary, further a fixing agent, a pH adjusting agent, an antioxidant, an ultraviolet absorber, a preservative,
A fungicide and the like can be added.

Preferred water for the present invention is pure water such as ion-exchanged water, ultrafiltration water, reverse osmosis water, distilled water, or ultrapure water. Further, it is preferable to use water sterilized by ultraviolet irradiation, hydrogen peroxide addition, or the like, since mold and bacteria can be prevented from occurring when the ink composition is stored for a long period of time.

The humectant that can be used in the present invention is selected from water-soluble and highly hygroscopic materials, and is selected from glycerin, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, and dipropylene. Glycol, polypropylene glycol, 1,3-
Propanediol, 1,4-butanediol, 1,5-
Pentanediol 1,6-hexanediol, 1,2,2
Polyols such as 6-hexanetriol and pentaerythritol, lacrams such as 2-pyrrolidone, N-methyl-2-pyrrolidone and ε-caprolactam, urea, thiourea, ethylene urea, 1,3-dimethylimidazolidinone and the like And saccharides such as urea, maltitol, sorbitol, gluconolactone, and maltose.

These humectants can be added together with other ink additives in such an amount that the viscosity of the ink at 25 ° C. becomes 25 cPs or less.

The permeation enhancer which can be used in the present invention is one which has improved permeation by improving the wettability to a recording medium, and has a low surface tension of an aqueous solution. Selected from agents.

Examples of the water-soluble organic solvent include lower alcohols such as ethanol and propanol, cellosolves such as ethylene glycol monomethyl ether and ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, ethylene glycol mono-n-butyl ether, and the like. Examples thereof include carbitols such as diethylene glycol-n-butyl ether and triethylene glycol-n-butyl ether, and 1,2-alkyl diols such as 1,2-hexanediol and 1,2-octane diol.

Examples of the surfactant include anionic surfactants such as fatty acid salts and alkyl sulfate salts, nonionic surfactants such as polyoxyethylene alkyl ether and polyoxyethylene phenyl ether, Surfynol 61 and 82, 104, 440, 465, 485
Acetylene glycol-based nonionic surfactants, cationic surfactants, amphoteric surfactants, and the like can be used (all of which are trade names, manufactured by Air Products and Chemicals). Since the surface-modified pigment of the present invention is a colorant that can be dispersed and / or dissolved in water without using a dispersant composed of a surfactant, these surfactants used in the ink of the present invention are: , Can be used only for promoting penetration. That is, in order to usually impart dispersibility to the pigment, it is necessary to select a combination in which the pigment and each material adsorb, but in the present invention,
The selection can be made only by the penetration promoting property without considering the combination.

As the fixing agent, water-soluble resins can be used, and water-soluble rosins, alginic acids, polyvinyl alcohol, hydroxypropyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose,
Methylcellulose, styrene-acrylic acid resin, styrene-acrylic acid-acrylate resin, styrene-
Maleic acid resin, styrene-maleic acid half ester resin, acrylic acid-acrylic acid ester resin, isobutylene-maleic acid resin, rosin-modified maleic acid resin, polyvinylpyrrolidone, gum arabic starch, polyallylamine, polyvinylamine, polyethyleneimine, etc. Can be Since the surface-modified carbon black of the present invention is a colorant that can be dispersed and / or dissolved in water without using a dispersant composed of a water-soluble resin, the water-soluble resin used in the ink of the present invention is: It can be used only for fixing. That is, usually, in order to impart dispersibility to the pigment, it is necessary to select a combination in which the pigment and each material adsorb, but in the present invention, it is possible to select only the fixing property without considering the combination.

Examples of the pH adjusting agent include lithium hydroxide, sodium hydroxide, potassium hydroxide, aqueous ammonia, hydroxides of alkali metals such as triethanolamine and diethanolamine or amines.

As antioxidants and ultraviolet absorbers, allohanates such as allohanate and methyl allohanate;
L-ascorbic acid and salts thereof such as biurets such as biuret, dimethyl biuret, and tetramethyl biuret;
8, 900, 1130, 384, 292, 123, 14
4, 622, 770, 292, Irgacor 252,
153, Irganox 1010, 1076, 103
5, MD1024 or the like, or a lanthanide oxide or the like is used.

Examples of preservatives and fungicides include sodium benzoate, sodium pentachlorophenol,
-Pyridinethiol-1-oxide sodium, sodium sorbate, sodium dehydroacetate, 1,2-
It can be selected from dibenzisothiazolin-3-one (Proxel CRL, Proxel BDN, Proxel GXL, Proxel XL-2, Proxel TN, manufactured by ICI) and the like.

[0032]

EXAMPLES (Example 1) # 40 as carbon black
100 g (trade name, manufactured by Mitsubishi Chemical Corporation) was mixed with 1 kg of water and pulverized by a ball mill using zirconia beads. An aqueous solution of sodium hypochlorite 40
After adding 0 g, the mixture was boiled for 10 hours to perform wet oxidation. The resulting undiluted dispersion was filtered through a glass fiber filter paper GA-100 (trade name, manufactured by Advantech Toyo Co., Ltd.), and further washed with water. The wet cake was re-dispersed in 5 kg of water, and the conductivity was reduced by using an ultrafiltration system minitan (trade name, manufactured by Millipore) using a ultrafiltration membrane having a molecular weight cut off of 100,000 to a pigment concentration of 15 wt% while conducting the conductivity. 3mS / c
and a pigment dispersion was prepared by desalting and refining to about m.

30 g of the obtained pigment dispersion, 10 g of glycerin and 5 g of 2-pyrrolidone as moisturizing components, 4 g of tert-pentanol as a permeation promoting component and Nissan Nonion NS-220 as a nonionic surfactant (trade name, Nippon Oil & Fat) 1 g), ultrapure water was added to make the total amount 100 g, and triethanolamine was further added until the ink pH reached 7.5. The mixture was stirred for 2 hours and filtered with a stainless steel filter having a pore size of about 5 μm to prepare an aqueous ink.

The aqueous ink is separated into liquid components using a centrifugal ultrafiltration unit Ultrafree 15 / fraction molecular weight 10,000 (trade name, manufactured by Nippon Millipore), and the liquid components are separated into ion chromatograph DX-500 ( Nippon Dionex Corporation
As a result, the released polyvalent cation was calcium and the concentration was 45 ppm.

Example 2 A water-based ink was prepared in the same manner as in Example 1 except that the degree of desalination and purification was 5 mS / cm. The released polyvalent cation was only calcium and had a concentration of 100 ppm.

Example 3 As an organic pigment, C.I. I. 40 g of Vat Blue 35 was mixed with 1 kg of water and pulverized by a ball mill using zirconia beads. 150 g of an aqueous solution of sodium hypochlorite was added to this ground stock solution,
The wet oxidation was carried out with stirring for an hour. The resulting undiluted dispersion was filtered through a glass fiber filter paper GA-100 (trade name, manufactured by Advantech Toyo Co., Ltd.), and further washed with water.
The wet cake was re-dispersed in 5 kg of water, and the pigment concentration was 15 wt.% Using an ultrafiltration membrane having a molecular weight cut off of 100,000 using an ultrafiltration system Minitan (trade name, manufactured by Millipore).
%, While desalting and refining to an electric conductivity of 2 mS / cm while concentrating to 2%, thereby preparing a pigment dispersion.

30 g of the resulting pigment dispersion, 10 g of glycerin and 5 g of diethylene glycol as a humectant, 5 g of diethylene glycol-mono-n-butyl ether as a penetration enhancer and 1 g of Surfynol 465 as an acetylene glycol-based surfactant were mixed. Then, ultrapure water was added to make the total amount 100 g, and ammonia water was further added until the ink pH reached 8.5. The mixture was stirred for 2 hours and filtered with a stainless steel filter having a pore size of about 5 μm to prepare an aqueous ink.

As a result of measuring the released polyvalent cations in the same manner as in Example 1, the ionic species was cobalt and the concentration was 25 p.
pm. Cobalt is C.I. I. Bat blue 35
It is presumed that a part of was decomposed and ionized by the oxidation of hypochlorous acid.

Example 4 A water-based ink was prepared in the same manner as in Example 3, except that the degree of desalting and purification was 5 mS / cm. The released polyvalent cation was cobalt at a concentration of 100 ppm.

Comparative Example 1 A water-based ink was prepared in the same manner as in Example 1, except that the degree of desalination and purification was 6 mS / cm. The released polyvalent cation was only calcium and had a concentration of 125 ppm.

Comparative Example 2 A water-based ink was prepared in the same manner as in Example 1, except that the degree of desalting and purification was 10 mS / cm. The liberated polyvalent cation was calcium at a concentration of 200 ppm.

Comparative Example 3 A water-based ink was prepared in the same manner as in Example 3, except that the degree of desalination and purification was 8 mS / cm. The released polyvalent cation was cobalt at a concentration of 110 ppm.

Comparative Example 4 A water-based ink was prepared in the same manner as in Example 3, except that the degree of desalting and purification was 15 mS / cm. The released polyvalent cation was cobalt at a concentration of 150 ppm.

<Evaluation Method> (Aggregation resistance)
The mixture was centrifuged at a centrifugal acceleration of G for 2 hours, and the absorbance per weight% of the pigment on the upper part of the centrifuge tube was measured to obtain the initial absorbance. The inks of Examples and Comparative Examples were heated at 80 ° C. × 5 days, and then left at room temperature for 1 day. Then, the absorbance was measured in the same manner as in the measurement of the initial absorbance. The ratio of absorbance / initial absorbance after standing is 98% or more for A, 9
The degree of coagulation resistance was determined by setting 5 to 98% B and less than 95% C. The results are summarized in Table 1.

[0045]

[Table 1]

As shown in Table 1, in Examples 1 to 4 in which the concentration of the released polyvalent cation in the ink of the present invention is 100 ppm or less, the aggregation resistance is A or B, and the aggregation / sedimentation is Even after accelerated storage at 80 ° C, the initial 95
%, The pigment concentration in the ink was maintained, the aggregation of the pigments in the ink was prevented, and the aqueous ink composition in which the print density did not decrease could be provided. On the other hand, when the polyvalent cation concentration is 10
In Comparative Examples 1 to 4 in which the content exceeded 0 ppm, the agglomeration resistance was C, and the pigment concentration decreased more as the cation concentration increased.

Continued on front page F term (reference) 2C056 FC01 2H086 BA53 BA55 4J037 AA02 AA30 CA05 CA14 CC01 CC02 CC13 CC15 CC16 CC17 DD20 DD27 EE19 EE28 EE33 EE43 FF05 FF15 FF22 FF23 4J039 BA04 BC17 BC39 BC60 EA15 EA15 EA15 EA15 EA15 EA15 EA15 EA15

Claims (3)

[Claims] 1. An aqueous ink composition comprising a surface-modified pigment which can be dispersed and / or dissolved in water at least without an aqueous medium and a dispersant, wherein the concentration of a polyvalent cation released in the ink is 100 ppm or less. A water-based ink composition, characterized in that: 2. The method according to claim 1, wherein the surface-modified pigment is a surface-modified pigment which can be dispersed and / or dissolved in water without a dispersant obtained by oxidizing carbon black with a halogen acid compound. The aqueous ink composition according to claim 1. 3. The surface-modified pigment is a surface-modified pigment which can be dispersed and / or dissolved in water without a dispersant obtained by oxidizing an organic pigment with a halogen acid compound. The aqueous ink composition according to claim 1.