JPH11269419A - Jet printing ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a jet printing ink using a water-based pigment which has tinting favorably comparable to an ink using a dye and is excellent in weatherability inherent in pigment and dispersion stability of an ink, especially an ink of a plurality of pigments mixed. SOLUTION: In a jet printing ink in which at least a pigment is dispersed as the colorant in an aqueous medium, on the surface of the pigment is provided a thin film of a fine particle having a high refractive index. Preferably, the fine particle having a high refractive index is an inorganic pigment having a refractive index of not smaller than 1.9 and has a particle diameter of not greater than 0.1 micron.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink-jet ink, and more particularly to an ink-jet ink excellent in coloring property, dispersion stability and weather resistance.

[0002]

2. Description of the Related Art Conventionally, as an ink-jet ink, there has been known an ink in which various water-soluble dyes are dissolved in an aqueous liquid as described in Japanese Patent Application Laid-Open No. 55-65269. .

However, the ink using the water-soluble dye as described above has a problem in weather resistance of a recorded image because the dye has poor weather resistance. That is, when the image is exposed to sunlight, fluorescent light, light from a projector, or the like, the image has a defect that the image becomes unreadable, disappears, or fades.

As a form for solving the problem of poor weather resistance, for example, Japanese Patent Publication No. 56-18623 and Japanese Patent Laid-Open No.
As described in No. 8463, there is known one using a water-dispersible pigment.

[0005] However, inks using pigments have the disadvantage that, although the weather resistance is improved, the coloring properties are generally poor and clear color images cannot be obtained.

[0006] Further, an ink using a pigment is generally produced by performing a dispersing process using a dispersing machine using a dispersant, a resin or the like suitable for each pigment. Here, when two or more types of pigments are mixed and used to increase the color purity, a method of mixing each pigment ink is used. In particular, when the dispersant used in each pigment ink is different, color separation and the like are performed. Yields
There was a problem that a uniform and stable dispersion state could not be obtained.

[0007]

DISCLOSURE OF THE INVENTION The present invention has a coloring property comparable to that of an ink using a dye, and is excellent in the original weather resistance of a pigment. An object of the present invention is to provide an ink-jet ink using an aqueous pigment having excellent properties.

[0008]

Means for Solving the Problems The present invention has been made to achieve the above object, and the invention according to claim 1 is to disperse at least a pigment as a colorant in an aqueous liquid. An ink-jet ink characterized in that a thin film made of fine particles having a high refractive index is provided on the surface of a pigment.

According to a second aspect of the present invention, there is provided an ink-jet ink according to the first aspect, wherein the fine particles having a high refractive index are inorganic pigments having a refractive index of 1.9 or more.

According to a third aspect of the present invention, there is provided the ink-jet ink according to the first aspect, wherein the fine particles having a high refractive index have a diameter of 0.1 μm or less.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

The pigment used in the present invention may be any pigment that can be dispersed in water or an aqueous solvent.
Alternatively, inorganic pigments can be used. For example, azo lakes, insoluble azo pigments, condensed azo pigments, azo pigments such as chelate azo pigments, phthalocyanine pigments, quinacridone pigments, anthraquinone pigments, perylene pigments,
Thioindigo pigments, isoindolinone pigments, quinophthalone pigments, dioxazine pigments, metal complex pigments,
Organic pigments such as fluorescent pigments, and inorganic pigments such as barium sulfate, barium carbonate, alumina white, titanium oxide, iron oxide pigments, and carbon black can be used, but are not limited thereto.

The particle size of these pigments is determined in consideration of the prevention of nozzle clogging, the coloring property, the transparency, and the dispersion stability of the ink over time, since the produced ink is used in an ink jet system. In this case, it is preferable that the particle size is small, and that the maximum particle size is 0.5 μm or less is used.

By covering the surface of the pigment with a thin film having a high refractive index, it is possible to further enhance the color of the pigment.

As the material having a high refractive index, an inorganic pigment having a refractive index of 1.9 or more is preferable.
Examples thereof include zinc sulfide, lead titanate, and zirconium oxide, with titanium dioxide being preferred.

As a method for preparing a thin film composed of an inorganic pigment, in the case of a metal oxide, the pigment is immersed in an organic metal compound solution, dried, and then calcined to decompose the organic metal compound, whereby the metal oxide is decomposed. A method of forming a thin film, or suspending a pigment in a dilute acidic solution of a metal salt, hydrolyzing the metal salt to precipitate a hydrated metal oxide,
A method of forming a thin film made of a metal oxide by baking, a method of utilizing hydrolysis of a metal alkoxide, and the like are generally used.

As a specific preparation method, when a thin film of titanium dioxide fine particles is formed as an inorganic pigment, the color pigment is suspended at room temperature in a dilute acid solution of titanium dinitrate sulfate, and then heated and boiled rapidly to add water. A method for completing the decomposition, or after suspending the color pigment in a dilute acidic solution of titanium dioxide at room temperature, adding an appropriate amount of urea,
A method in which hydrolysis is performed at a temperature of up to 90 ° C. is exemplified.

When the above method is used, a thin film made of a metal oxide having a fine particle size, specifically, a uniform particle size of 0.1 μm or less is formed. The size of 0.1 micron is transparent and improves the reflectivity due to the high refractive index, and the effect of concealing the color of the coloring pigment is small. It is suitable for a pigment, and even if it is a pigment, it is possible to obtain coloring properties comparable to those of a dye.

Further, even though the pigments thus obtained are different in type and color, the surface characteristics can be made the same by the high refractive index layer. It is not necessary to change the type and dispersing method of the dispersing agent for each pigment when dispersing into an ink. Therefore, even when two or more kinds of pigments are mixed to increase the color purity, there is no problem such as color separation, and an ink having good dispersion stability over time can be obtained.

By dispersing the pigment thus obtained together with an aqueous resin or a dispersant in an aqueous solvent, an ink-jet ink is obtained.

The aqueous resin is used for fixing a coloring agent to a recording medium and improving the water resistance of the recorded matter, and a water-soluble resin or a water-dispersible resin can be used. As the water-soluble resin, generally known polyvinyl alcohol, polyvinylpyrrolidone, sodium polyacrylate, polyacrylamide, polyethyleneimine, gelatin, gum arabic, cellulose derivative, sodium alginate, melamine, urea resin and the like can be used. is there. Also,
Examples of the water-dispersible resin include styrene-maleic acid copolymer, latex such as methyl methacrylate-to-butadiene copolymer, latex of acrylic polymer, latex of vinyl polymer, and the like. Are used alone or as a mixture.

As the dispersing agent, an anionic, nonionic, cationic or zwitterionic activator is used. Examples of anionic surfactants include alkyl sulfate salts, fatty acid salts, alkyl aryl sulfonates, alkyl naphthalene sulfonates, dialkyl sulfonates, dialkyl sulfosuccinates, polyoxyethylene alkyl ether salts, and formalin naphthalene sulfonic acid. And condensates. Examples of the nonionic activator include polyoxyethylene alkyl ether, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene fatty acid ester, glycerin fatty acid ester, silicone type, fluorine type and the like. Examples of the cationic activator include a quaternary ammonium salt and an alkylamine salt. Examples of amphoteric surfactants include dimethylalkyl lauryl betaine, alkyl glycine, imidazolinium betaine and the like. In practice, these dispersants are used alone or as a mixture.

As the aqueous solvent, those which can be mixed with water can be used as appropriate. For example, alkyl alcohols such as methyl alcohol, ethyl alcohol, and isopropyl alcohol, alkylene glycols such as ethylene glycol, propylene glycol, butylene glycol, 1,2,6-hexanetriol and diethylene glycol, and poly such as polyethylene glycol and polypropylene glycol. Use is made of alkylene glycols, ethers such as tetrahydrofuran and dioxane, amides such as dimethylformamide and dimethylacetamide, and lower alkyl ethers of polyhydric alcohols such as glycerin, ethylene glycol monomethyl ether, diethylene glycol methyl ether and triethylene glycol methyl ether. It is possible.

In addition, it is possible to add a pH adjuster, an antioxidant, a fungicide, an antifoaming agent and the like, if necessary.

The preparation of the ink can be obtained by dispersing a colorant in an aqueous solvent together with an aqueous resin, a dispersant and various additives. The dispersing method is performed using a dispersing machine such as a homogenizer, a paint shaker, a ball mill, and a sand mill.

[0026]

The present invention will be described in detail below with reference to specific examples of the present invention. <Example 1> 100 parts by weight of a phthalocyanine-based blue pigment was added to 1000 parts by weight of a sulfuric acid solution of dititanium sulfate, and the mixture was stirred at a rotation speed of 5,000 rpm and heated to boiling at 130 ° C for 2 hours. After cooling, the mixture was neutralized with sodium hydroxide and washed with water until no sulfate ion was detected, to obtain a blue colorant slurry (A) having a solid content of 50%.

10 parts by weight of a blue colorant slurry (A), an aqueous solution of an acrylic resin (manufactured by Johnson Corporation: Joncryl 61)
J: 31.0% of solid content) 5 parts by weight, 20 parts by weight of ethylene glycol, 5 parts by weight of glycerin, 1 part by weight of a nonionic activator (manufactured by Kao: Emulgen 109P), and 59 parts by weight of water are mixed and mixed in a sand mill. After the dispersion for 3 hours, the mixture was filtered through a membrane filter of 1 micron and subsequently 0.4 micron to obtain an inkjet ink.

When this ink was recorded on plain paper using an ink jet printer (HG5130, manufactured by Seiko Epson Corporation), an image having excellent colorability comparable to that of an ink using a dye was obtained. No change was observed in the density of the image even after exposing the
An image having excellent weather resistance was obtained.

Example 2 Anthraquinone red pigment 1
00 parts by weight was added to 1000 parts by weight of a sulfuric acid acid solution of titanium titanate, and the mixture was stirred at a rotation speed of 5000 rpm. Then, 25 parts by weight of urea was added and further stirred for 1 hour. Thereafter, the mixture is heated to 85 ° C. and reacted for 3 hours. After cooling, the mixture was neutralized with sodium hydroxide and washed with water until no sulfate ion was detected, to obtain a red colorant slurry (B) having a solid content of 50%.

The quinophthalone-based yellow pigment was treated in the same manner as the above-mentioned red pigment to obtain a yellow colorant slurry (C) having a solid content of 50%.

5 parts by weight of a red colorant slurry (B), 5 parts by weight of a yellow colorant slurry (C), an aqueous solution of an acrylic resin (John Krill 61J, manufactured by Johnson Co .; solid content 31.
0%) 5 parts by weight of ethylene glycol, 20 parts by weight of ethylene glycol, 5 parts by weight of glycerin, 1 part by weight of a nonionic activator (manufactured by Kao: Emulgen 109P), and 59 parts by weight of water were mixed, and dispersed by a sand mill for 3 hours. Filtration through a 1 micron and subsequently a 0.4 micron membrane filter gave an inkjet ink.

When this ink was recorded on plain paper using an ink jet printer (HG5130, manufactured by Seiko Epson Corporation), good recording could be performed.

Further, this ink did not show any sediment even after storage at 60 ° C. for 3 months, and there was no change in the recording / printing characteristics.

[0034]

According to the ink-jet ink of the present invention, a thin film composed of fine particles having a high refractive index is provided on the surface of a pigment used as a coloring agent. The inorganic pigment has a diameter of 0.1 micron or less. For example, a thin film made of a metal oxide having a uniform particle size of 0.1 μm or less is formed.

The size of 0.1 μm is transparent, and reflects the color of the color pigment because of the improvement in reflectivity due to the high refractive index and the small effect of hiding the color of the color pigment. It is suitable for increasing the lightness, and even if the colorant is a pigment, it is possible to obtain colorability comparable to that of a dye. Moreover, since it is a pigment, it also has weather resistance.

Further, even though the pigments thus obtained are different in type and color, the surface characteristics can be made the same by the high refractive index layer. It is not necessary to change the type and dispersing method of the dispersing agent for each pigment when dispersing into an ink. Therefore, even when two or more kinds of pigments are mixed to increase the color purity, there is no problem such as color separation, and an ink having good dispersion stability over time can be obtained.

Claims (3)

[Claims] An ink-jet ink comprising at least a pigment dispersed as a colorant in an aqueous liquid.
An ink-jet ink comprising a pigment and a thin film made of fine particles having a high refractive index provided on the surface of the pigment. 2. The ink jet ink according to claim 1, wherein the fine particles having a high refractive index are inorganic pigments having a refractive index of 1.9 or more. 3. The ink jet ink according to claim 1, wherein the fine particles having a high refractive index have a diameter of 0.1 μm or less.