JP2008184504A - Ink-jet ink - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink-jet ink excellent in ink curability by light irradiation, fixability onto printing media and ink storability, containing an active energy ray-reactive polymeric compound. <P>SOLUTION: The ink-jet ink essentially comprises water, such a polymeric compound as to have multiple side chains on its hydrophilic main chain and be crosslinkable among the side chains on being irradiated with active energy rays, and a coloring material; wherein the coloring material consists of black titanium oxide. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an inkjet ink containing an active energy ray-reactive polymer compound.

  The ink jet recording method is capable of recording high-definition images with a relatively simple apparatus, and has been rapidly developed in various fields. In addition, there are various uses, and a recording medium or ink suitable for each purpose is used.

  In particular, in recent years, the recording speed has been greatly improved, and an ink jet printer having performance capable of withstanding light printing applications has also been developed. However, in order to bring out the performance of the ink jet printer, an ink jet special paper to which ink jet ink absorbability is required is necessary.

  In an inkjet system that requires inkjet special paper, the applicable recording media are limited, and the cost of the recording medium is increasing. Attempts have been made to record images on inkjet recording media that are not inkjet special paper. Yes.

  In response to the above problems, a hot-melt ink composition made of a solid wax or the like at room temperature is used, and is liquefied by heating or the like, sprayed by applying some energy, adhered onto the recording medium, and cooled and solidified. A hot melt ink jet recording method for forming recording dots has been proposed (see Patent Documents 1 and 2). Since this hot-melt ink is solid at room temperature, it does not get dirty during handling, and since there is substantially no ink evaporation during melting, nozzle clogging does not occur. Furthermore, it is said to be an ink composition that solidifies immediately after adhering, has little color bleeding, and provides good print quality regardless of the paper quality to be printed. However, an image recorded by such a method has problems such as deterioration in quality due to the rising of the dots and insufficient scratch resistance because the ink dots are in the form of soft wax.

On the other hand, an inkjet recording ink that is cured by irradiation with active energy rays has been disclosed (see Patent Document 3). In addition, a so-called non-aqueous ink containing a pigment as a coloring material, a triacrylate or higher polyacrylate as a polymerizable material, and having a ketone or alcohol as a main solvent has been proposed (see Patent Document 4). . Also, a water-based active energy ray-curable ink jet recording ink composition containing an active energy ray-curable group having an unsaturated double bond, a polyurethane compound, a basic compound, a colorant, a water-soluble organic solvent, and water Has been proposed (see Patent Document 5). Furthermore, a water-based inkjet ink comprising a self-dispersing pigment having one or more hydrophilic groups bonded to the surface of pigment particles, an ultraviolet curable monomer made of a vinyl compound, a photopolymerization initiator, and water. It has been proposed (see Patent Document 6).
U.S. Pat. No. 4,390,369 U.S. Pat. No. 4,484,948 U.S. Pat. No. 4,228,438 Japanese Patent Publication No. 5-64667 JP 2002-80767 A JP 2002-275404 A

  However, in the methods described in the above Patent Documents 3 to 6, it is known that the curability by light irradiation differs depending on the color of the ink, and in particular, the black image is inferior in curability. Carbon black is generally used for the formation of black images. However, since carbon black has strong absorption in the ultraviolet region, it is difficult to cause a crosslinking reaction triggered by light irradiation, resulting in poor adhesion of the ink to the recording medium. There arises a problem of deterioration in fixing property.

  On the other hand, in order to increase the amount of radicals generated by light irradiation, a method of increasing the addition amount of the polymerization initiator and a method of increasing the polymerizable resin that is crosslinked by light irradiation can be considered. This is not preferable because the storage stability of the ink itself and the increase of the ink viscosity are accompanied.

  Accordingly, the present invention has been made in view of the above problems, and its purpose is to contain an active energy ray-reactive polymer compound that is excellent in ink curability by light irradiation, fixability to a recording medium, and ink storage stability. It is to provide an inkjet ink.

  The above object of the present invention is achieved by the following configurations.

  1. It contains at least water, a polymer compound having a plurality of side chains in the hydrophilic main chain, and a crosslinkable cross-link between the side chains by irradiation with active energy rays, and the color material is titanium black. An inkjet ink characterized by the above.

  2. 2. The inkjet according to 1 above, wherein a modification rate of the side chain with respect to the hydrophilic main chain of the polymer compound capable of cross-linking between the side chains is 0.8 mol% or more and 4.0 mol% or less. ink.

  3. 3. The ink-jet ink as described in 1 or 2 above, wherein the degree of polymerization of the hydrophilic main chain of the polymer compound capable of cross-linking between the side chains is 200 or more and 500 or less.

  4). The content ratio of the polymer compound that can be cross-linked between the side chains with respect to the total mass of the ink is 0.8% by mass or more and less than 5% by mass. Inkjet ink.

  According to the present invention, an ink-jet ink containing an active energy ray-reactive polymer compound that is excellent in ink curability by light irradiation, fixability to a recording medium, and ink storability can be provided.

  Hereinafter, the best mode for carrying out the present invention will be described in detail.

  As a result of intensive studies in view of the above problems, the present inventor has at least water, a polymer having a plurality of side chains in a hydrophilic main chain, and capable of cross-linking between side chains by irradiation with active energy rays. Ink jet ink containing a compound and a colorant, and using titanium black as a black colorant, has excellent ink curability by light irradiation, fixing to a recording medium, and ink storage stability, active energy ray reactivity As soon as an ink-jet ink containing a polymer compound can be realized, the present invention has been achieved.

  Details of the ink-jet ink of the present invention will be described below.

  In the inkjet ink of the present invention (hereinafter, also simply referred to as ink), a polymer compound having a plurality of side chains in a hydrophilic main chain and capable of crosslinking between side chains by irradiation with active energy rays (hereinafter, referred to as “ink”). It is also characterized by containing a crosslinkable polymer compound).

<Crosslinkable polymer compound>
By applying the crosslinkable polymer compound according to the present invention to ink, it exhibits sufficient curability by irradiation with low energy active energy rays, the resolution of the formed image is high, the gloss is good, and the color An ink jet ink with little bleeding between them can be obtained.

  Next, the crosslinkable polymer compound according to the present invention will be described.

  The hydrophilic main chain of the crosslinkable polymer compound according to the present invention includes saponified polyvinyl acetate, polyvinyl acetal, polyethylene oxide, polyalkylene oxide, polyvinyl pyrrolidone, polyacrylamide, polyacrylic acid, hydroxyethyl cellulose, methyl cellulose, hydroxy And propyl cellulose.

  Among these, when the hydrophilic main chain is a saponified product of polyvinyl acetate, the introduction of the side chain is simplified and the handleability is improved. The degree of polymerization of the hydrophilic main chain of the polymer compound that can be cross-linked between the side chains is preferably 200 or more and 500 or less. If the degree of polymerization of the hydrophilic main chain is 200 or more, a moderate increase in viscosity during the crosslinking reaction can be imparted, and color bleeding and beading described later can be sufficiently prevented. Further, when the degree of polymerization of the hydrophilic main chain is 500 or less, an increase in viscosity when added to the ink can be suppressed, and good emission stability can be obtained.

  For the side chain, a modifying group such as a photodimerization type, a photodecomposition type, a photopolymerization type, a photomodification type, and a photodepolymerization type can be introduced. From the viewpoint of reactivity with the color material to be combined, the side chain is preferably nonionic, anionic, or amphoteric (betaine compound). Particularly, when the color material is combined with an anionic dye or an anionic pigment, the side chain is It is preferably nonionic or anionic, and particularly preferably nonionic.

  The modification rate of the side chain with respect to the hydrophilic main chain is preferably 0.8 mol% or more and 4.0 mol% or less, and more preferably 1.5 mol% or more and 3.0 mol% or less. More preferable from the viewpoint of reactivity. If the modification rate of the side chain with respect to the hydrophilic main chain is 0.8 mol% or more, it has sufficient crosslinkability, and the object effect of the present invention can be obtained. On the other hand, if it is 4.0 mol% or less, the crosslinking density is appropriate, so that a flexible image film can be easily obtained and the film strength is particularly good.

  As the photodimerization-type modifying group, those in which a diazo group, a cinnamoyl group, a stilbazonium group, a stilquinolium group or the like is introduced are preferable. For example, a photosensitive resin described in JP-A-60-129742 (Composition).

  The photosensitive resin described in JP-A-60-129742 is a compound represented by the following general formula (1) in which a stilbazonium group is introduced into a polyvinyl alcohol structure.

In the formula, R ₁ represents an alkyl group having 1 to 4 carbon atoms, and A ⁻ represents a counter anion.

  The photosensitive resin described in JP-A-56-67309 includes a 2-azido-5-nitrophenylcarbonyloxyethylene structure represented by the following general formula (2) in the polyvinyl alcohol structure, or the following general formula. This is a resin composition represented by (3) and having a 4-azido-3-nitrophenylcarbonyloxyethylene structure.

  Further, a modifying group represented by the following general formula (4) is also preferably used.

  In the formula, R represents an alkylene group or an aromatic ring. A benzene ring is preferred.

  As the photopolymerization type modifying group, for example, a resin represented by the following general formula (5) shown in JP-A Nos. 2000-181062 and 2004-189841 is preferable from the viewpoint of reactivity.

In the formula, R ₂ represents a methyl group or a hydrogen atom, n represents 1 or 2, X represents — (CH ₂ ) _m —COO— or —O—, and Y represents an aromatic ring or a single bond. And m represents an integer from 0 to 6.

  Moreover, it is also preferable to use the photopolymerization type | mold modified group represented by following General formula (6) described in Unexamined-Japanese-Patent No. 2004-161942 for a conventionally well-known water-soluble resin.

In the formula, R ₃ represents a methyl group or a hydrogen atom, and R ₄ represents a linear or branched alkylene group having 2 to 10 carbon atoms.

  In such an active energy ray-crosslinked polymer compound, the main chain originally having a certain molecular weight is cross-linked between the side chains through a cross-linking bond. The effect of increasing the molecular weight per photon is remarkably large compared to a conventionally known active energy ray-curable resin produced by polymerization.

  Furthermore, since ink using a conventionally known active energy ray-curable resin is a component that is involved in curing almost all of the materials other than the color material, the dots after curing rise and the image quality represented by gloss is significantly deteriorated. On the other hand, the ink-jet ink according to the present invention requires a small amount of the crosslinkable polymer compound and has a large amount of dry components, so that the image quality after drying is improved and the fixability is also good.

  The addition amount in the ink of the polymer compound having a plurality of side chains in the hydrophilic main chain according to the present invention and capable of crosslinking between the side chains by irradiating with active energy rays is 0.8% by mass or more. 5.0 mass% or less is preferable. If the addition amount is within this range, the crosslinking efficiency is improved, and the ink is ejected from the head and adhered to the base material, and then crosslinked, so that the viscosity of the ink after crosslinking is rapidly increased and the beading resistance and color bleed resistance are increased. Will improve. When the addition amount is less than 0.8% by mass, the objective effect of the present invention obtained due to insufficient crosslinkability is reduced. When the addition amount exceeds 5.0% by mass, the ink viscosity increases and affects intermittent emission stability. May affect.

  In the ink-jet ink of the present invention, when a polymer compound having a photopolymerizable modifying group is used, it is preferable to use a known photopolymerization initiator, and it is particularly preferable to use a water-soluble photopolymerization initiator.

  As the water-soluble photopolymerization initiator applicable in the inkjet ink of the present invention, a compound represented by the following general formula (7) is preferable from the viewpoint of compatibility with a polymer compound and sensitivity.

  In the formula, n represents an integer of 1 to 5.

  The photopolymerization initiator is preferably grafted to the side chain with respect to the hydrophilic main chain of the polymer compound according to the present invention.

  A sensitizer may be used in combination with the inkjet ink of the present invention in order to enhance its function. Any sensitizer may be used, but aliphatic amines, amines containing aromatic substituents, amines such as piperidine, urea compounds such as urea, alkylurea, urea containing aromatic substituents, sodium diethyl Sulfur compounds such as dithiophosphates, soluble salts of aromatic sulfinic acids, phosphorus compounds such as tri-n-butylphosphine and netium diethyldithiophosphide, Michler's ketone, N-nitrisohydroxylamine derivatives, oxazolidine compounds, tetrahydro-1,3- Examples thereof include oxazine compounds, condensates of formaldehyde or acetaldehyde and diamines, polymerized amines of reaction products of epoxy resins and amines, nitrogen compounds such as triethanolamine triacrylate, and nitrile compounds.

  Among these, amine compounds are preferable from the viewpoint of ink storage stability and emission stability, and alkanolamines such as monoethanolamine, dimethylethanolamine, diethanolamine, methyldiethanolamine, and triethanolamine are more soluble in ink. Is particularly preferred.

  The amount of the sensitizer to be added is 0.1 to 10% by mass with respect to the total amount of the ink. Furthermore, it is preferable that it is 0.5 to 5%. If the amount is less than 0.1% by mass, the effects of the present invention cannot be sufficiently obtained. If the amount exceeds 10% by mass, the film physical properties of the image deteriorate, and the image weather resistance such as abrasion resistance and water resistance becomes insufficient. .

  Next, other components of the inkjet ink of the present invention will be described.

《Coloring material》
The ink-jet ink of the present invention is characterized by the use of titanium black as a color material constituting the black ink. However, the black ink requires carbon black and the color materials shown below together with titanium black. It can be mixed according to.

The titanium black according to the present _invention, TiO (titanium oxide nitride) prepared by reducing TiO 2, TiO ₂ and the like.

  Examples of the pigment that can be used in combination with the titanium black according to the present invention include conventionally known organic or inorganic pigments. For example, azo pigments such as azo lake pigments, insoluble azo pigments, condensed azo pigments, chelate azo pigments, phthalocyanine pigments, perylene and perylene pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc. And polycyclic pigments, dye lakes such as basic dye type lakes and acid dye type lakes, organic pigments such as nitro pigments, nitroso pigments and daylight fluorescent pigments, and inorganic pigments. Specific examples of applicable pigments are listed below, but the present invention is not limited to these exemplified pigments.

  Examples of magenta or red pigments include C.I. I. Pigment red 2, C.I. I. Pigment red 3, C.I. I. Pigment red 5, C.I. I. Pigment red 6, C.I. I. Pigment red 7, C.I. I. Pigment red 15, C.I. I. Pigment red 16, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 53: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 139, C.I. I. Pigment red 144, C.I. I. Pigment red 149, C.I. I. Pigment red 166, C.I. I. Pigment red 177, C.I. I. Pigment red 178, C.I. I. And CI Pigment Red 222.

  Examples of orange or yellow pigments include C.I. I. Pigment orange 31, C.I. I. Pigment orange 43, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 13, C.I. I. Pigment yellow 14, C.I. I. Pigment yellow 15, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 94, C.I. I. Pigment yellow 128, C.I. I. Pigment yellow 138, C.I. I. Pigment yellow 150, pigment yellow 180, and the like.

  Examples of green or cyan pigments include C.I. I. Pigment blue 15, C.I. I. Pigment blue 15: 2, C.I. I. Pigment blue 15: 3, C.I. I. Pigment blue 15: 4, C.I. I. Pigment blue 16, C.I. I. Pigment blue 60, C.I. I. And CI Pigment Green 7.

  On the other hand, as described above, the curability due to light irradiation varies depending on the color of the ink, and it is known that the curability of black ink is particularly poor. Generally, carbon black is used as a coloring material for black ink, but since it has strong absorption in the ultraviolet region, a crosslinking reaction that is triggered by light irradiation with active energy rays hardly occurs. Problems such as poor ink adhesion and poor fixability occur.

On the other hand, the titanium black according to the present invention is also called black titanium oxide, and is a novel black fine powder mainly composed of low-order titanium oxide. Features include blackness, electrical conductivity, high refractive index, non-toxicity, etc., and applications in the cosmetics and electronic materials fields are being promoted. As a manufacturing method, the raw material TiO ₂ powder is thermally active and easily releases a part of oxygen to take on the properties of ash to blue gray, such as NH ₃ gas, H ₂ gas, Ti powder, etc. Is used as a reducing agent. Titanium black absorbs less UV light than carbon black, and is easily cured by UV light.

(Method for producing pigment dispersion)
As a method for dispersing the pigment, for example, various dispersing machines such as a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, and a paint shaker can be used. It is also preferable to use a centrifugal separator or a filter for the purpose of removing the coarse particles of the pigment dispersion.

(Surfactant applicable to pigment dispersion)
In preparing the pigment dispersion, if necessary, a surfactant or a polymer dispersant may be contained as a pigment dispersant. The type of surfactant and polymer dispersant is not particularly limited. Examples of the surfactant include higher fatty acid salts, alkyl sulfates, alkyl ester sulfates, alkyl sulfonates, sulfosuccinates, and naphthalene sulfonates. , Alkyl phosphate, polyoxyalkylene alkyl ether phosphate, polyoxyalkylene alkyl phenyl ether, polyoxyethylene polyoxypropylene glycol, glycerin ester, sorbitan ester, polyoxyethylene fatty acid amide, amine oxide and the like As the polymer dispersant, a water-soluble resin is preferably used from the viewpoint of ejection stability. For example, styrene, a styrene derivative, a vinyl naphthalene derivative, acrylic acid, an acrylic acid derivative, maleic acid, maleic acid. acid Examples thereof include block copolymers composed of two or more monomers selected from conductors, itaconic acid, itaconic acid derivatives, fumaric acid, fumaric acid derivatives, random copolymers, and salts thereof. Styrene-acrylic acid-alkyl acrylate ester copolymer, styrene-acrylic acid copolymer, styrene-maleic acid-alkyl acrylate copolymer, styrene-maleic acid copolymer, styrene-methacrylic acid-acrylic acid Examples thereof include an alkyl ester copolymer, a styrene-methacrylic acid copolymer, a styrene-maleic acid half ester copolymer, a vinyl naphthalene-acrylic acid copolymer, and a vinyl naphthalene-maleic acid copolymer.

  The amount of each polymer dispersant added to the total mass of the ink is preferably 0.1 to 10% by mass, and more preferably 0.3 to 5% by mass. Two or more of these polymer dispersants can be used in combination.

(Particle size of pigment particles)
The particle size of the pigment particles includes the particle size (primary particle size) obtained by directly observing the particles with an electron microscope, and the dispersed particle size (secondary particle size) using a particle size measuring device utilizing light scattering. There is a viscosity-converted particle size obtained from the intrinsic viscosity.

  The primary particle diameter of the pigment in the ink of the present invention is preferably 10 nm or more and 1000 nm or less, more preferably 10 nm or more and 70 nm, from the viewpoint of light resistance and dispersion stability. If it is smaller than 10 nm, the light resistance will not deteriorate, and if it exceeds 100 nm, it will cause clogging of the head due to aggregation. Here, in order to obtain primary particles, the major axis of 1000 pigment particles is measured with a transmission electron microscope, and the average value (number average) can be obtained.

"solvent"
In the inkjet ink of the present invention, it is preferable to use a water-soluble organic solvent. Examples of the water-soluble organic solvent that can be used in the present invention include alcohols (for example, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol, pentanol, hexanol, cyclohexanol, benzyl). Alcohol), polyhydric alcohols (for example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol Etc.), polyhydric alcohol ethers (for example, ethylene glycol monomethyl ether, ethylene glycol) Ether monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether , Triethylene glycol monobutyl ether, ethylene glycol monophenyl ether, propylene glycol monophenyl ether, etc.), amines (for example, ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, mole) Phosphorus, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine, etc.), amides (eg, formamide, N, N-dimethylformamide, N , N-dimethylacetamide, etc.), heterocyclic rings (for example, 2-pyrrolidone, N-methyl-2-pyrrolidone, cyclohexylpyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, etc.), sulfoxides ( For example, dimethyl sulfoxide etc.), sulfones (for example, sulfolane etc.), urea, acetonitrile, acetone etc. are mentioned. Preferable water-soluble organic solvents include polyhydric alcohols. Furthermore, it is particularly preferable to use a polyhydric alcohol and a polyhydric alcohol ether in combination.

  The water-soluble organic solvent may be used alone or in combination. The total amount of the water-soluble organic solvent added to the ink is 5 to 60% by mass, preferably 10 to 35% by mass.

(Inkjet ink set)
In the present invention, an inkjet ink set may be configured together with the black ink containing titanium black of the present invention and other color inks such as yellow ink, magenta ink, and cyan ink.

(Colorless ink)
In the ink-jet ink set according to the present invention, a colorless ink (also referred to as a transparent ink) that does not substantially contain a coloring material can be used in combination.

  In the present invention, the colorless ink containing substantially no color material means a state in which the content of the color material is 0.1% or less with respect to the total ink mass, and preferably contains no color material. is there.

  The component contained in the colorless ink according to the present invention may be either uniformly dissolved or present in a non-uniform dispersion system. Examples of the resin that can be added include a water-based dissolved resin, a water-based dispersed resin, an organic solvent-based dissolved resin, an organic solvent-based dispersed resin, and the like. A resin dispersed in an aqueous system is preferred. Although colorless inks obtained by removing only the color material from the ink-jet ink used can be used, it is preferable to add the following additives in order to add various functions.

  Examples of resins that are dissolved in water include polyvinyl alcohol, gelatin, polyethylene oxide, polyvinyl pyrrolidone, polyacrylic acid, polyacrylamide, polyurethane, dextran, dextrin, color ginnan (κ, ι, λ, etc.), agar, pullulan, water-soluble Polyvinyl butyral, hydroxyethyl cellulose, carboxymethyl cellulose and the like can be added.

  As the resin dispersed in an aqueous system, it is particularly preferable to add fine particles of a thermoplastic resin because the glossiness of the image is improved. As the thermoplastic resin fine particles, the thermoplastic resin that can be added to the surface layer of the recording medium or the kind described in the description of the fine particles can be used. In particular, it is preferable to apply those which do not cause thickening or precipitation even when added to the ink. The average particle size of the thermoplastic resin particles is preferably 0.5 μm or less. The fine particles of the thermoplastic resin to be added are preferably those that melt and soften in the range of 0 to 150 ° C.

<< Other additives for inkjet ink >>
In the ink of the present invention, if necessary, various known additives such as ejection stability, print head and ink cartridge compatibility, storage stability, image storage stability, and other performance improvement purposes, for example, , Viscosity modifier, Surface tension modifier, Specific resistance modifier, Film forming agent, Dispersant, Surfactant, Ultraviolet absorber, Antioxidant, Anti-fading agent, Antifungal agent, Rust inhibitor, etc. For example, polystyrene, polyacrylates, polymethacrylates, polyacrylamides, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, or a copolymer thereof, urea resin, or melamine Organic latex such as resin, liquid paraffin, dioctyl phthalate, tricresyl phosphate, silicone oil and other oil droplets, ON or nonionic surfactants, UV absorbers described in JP-A-57-74193, JP-A-57-87988, and JP-A-62-261476, JP-A-57-74192, JP-A-57-87989, 60-72785, 61-146591, anti-fading agents described in JP-A-1-95091 and 3-13376, JP-A-59-42993, 59-52689, 62- 280069, 61-242871, and JP-A-4-219266, etc., optical brighteners, pH adjusters such as sulfuric acid, phosphoric acid, citric acid, sodium hydroxide, potassium hydroxide, potassium carbonate, etc. Can be mentioned.

(latex)
In the inkjet ink of the present invention, latex may be added to the ink. Examples thereof include latex such as styrene-butadiene copolymer, polystyrene, acrylonitrile-butadiene copolymer, acrylic ester copolymer, polyurethane, silicon-acrylic copolymer, and acrylic-modified fluorine-fatting. The latex may be obtained by dispersing polymer particles using an emulsifier, or may be dispersed without using an emulsifier. A surfactant is often used as an emulsifier, but a polymer having a water-soluble group such as a sulfonic acid group or a carboxylic acid group (for example, a polymer in which a solubilizing group is graft-bonded, a single group having a solubilizing group). It is also preferable to use a polymer obtained from a monomer and a monomer having an insoluble part.

  In the ink-jet ink of the present invention, it is particularly preferable to use soap-free latex. Soap-free latex is a latex that does not use an emulsifier and a polymer having a water-soluble group such as a sulfonic acid group or a carboxylic acid group (for example, a polymer in which a solubilizing group is graft-bonded, a solubilizing group) A polymer obtained from a monomer having an insoluble part and a monomer having an insoluble part).

  In recent years, as latex polymer particles, there are also latexes in which core-shell type polymer particles having different compositions at the center and outer edge of the particles are dispersed in addition to the latex in which the polymer particles are uniform throughout. However, this type of latex can also be preferably used.

  In the inkjet ink of the present invention, the average particle size of the polymer particles in the latex is preferably 10 nm or more and 300 nm or less, and more preferably 10 nm or more and 100 nm or less. When the average particle size of the latex exceeds 300 nm, the glossiness of the image is deteriorated, and when it is less than 10 nm, the water resistance and scratch resistance become insufficient. The average particle size of the polymer particles in the latex can be determined by a commercially available particle size measuring instrument using a light scattering method, an electrophoresis method, or a laser Doppler method.

  In the inkjet ink of the present invention, the latex is preferably added so that the solid content is 0.1% by mass or more and 20% by mass or less based on the total mass of the ink. It is particularly preferable that the content be 5% by mass or more and 10% by mass or less. If the amount of latex solids added is less than 0.1% by mass, it is difficult to exert a sufficient effect on the weather resistance, and if it exceeds 20% by mass, the ink viscosity increases over time and the ink storage stability is increased. There are many problems that arise.

(Outgoing stabilizer for thermal)
The ink-jet ink of the present invention may be used in a thermal ink-jet printer. At this time, in order to solve the clogging of the head called kogation, (M ₁ ) ₂ SO ₄ , CH ₃ COO (M ₁ ), Ph-COO (M ₁ ) disclosed in Japanese Patent Laid-Open No. 2001-81379 ), (M ₁ ) NO ₃ , (M ₁ ) Cl, (M ₁ ) Br, (M ₁ ) I, (M ₁ ) ₂ SO ₃ and (M ₁ ) ₂ CO ₃ good. Here, M ₁ represents an alkali metal, ammonium or organic ammonium, and Ph represents a phenyl group. Examples of the alkali metal include Li, Na, K, Rb, and Cs. Examples of organic ammonium include methylammonium, dimethylammonium, trimethylammonium, ethylammonium, diethylammonium, triethylammonium, trihydroxymethylamine, dihydroxymethylamine, monohydroxymethylamine, monoethanolammonium, diethanolammonium, and triethanol. Ammonium, N-methylmonoethanolammonium, N-methyldiethanolammonium, monopropanolammonium, dipropanolammonium, tripropanolammonium, etc. are mentioned.

(Crosslinking agent)
The inkjet ink of the present invention may contain a crosslinking agent. Specific examples of the crosslinking agent include, for example, epoxy-based curing agents (for example, diglycidyl ethyl ether, ethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,6-diglycidyl cyclohexane, N, N— Diglycidyl-4-glycidyloxyaniline, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, etc.), aldehyde-based curing agents (for example, formaldehyde, glioxal, etc.), active halogen-based curing agents (for example, 2,4-dichloro-4-hydroxy) -1,3,5, -s-triazine, etc.), active vinyl compounds (for example, 1,3,5-trisacryloyl-hexahydro-s-triazine, bisvinylsulfonylmethyl ether, etc.), aluminum alum, boric acid or Its salt And the like.

(Anti-fading agent)
In the ink-jet ink of the present invention, a known anti-fading agent can be used in conventional ink-jet inks. This anti-fading agent suppresses fading caused by light irradiation and fading caused by various oxidizing gases such as ozone, active oxygen, NOx, and SOx. Examples of such anti-fading agents include antioxidants described in JP-A-57-74192, JP-A-57-87989, and JP-A-60-72785, and ultraviolet absorbers described in JP-A-57-74193. Hydrazides described in JP-A-61-154989, hindered amine-based antioxidants described in JP-A-61-146591, nitrogen-containing heterocyclic mercapto-based compounds described in JP-A-61-177279, The thioether antioxidants described in 1-111577 and 1-36479, hindered phenol antioxidants having a specific structure described in JP-A-1-36480, JP-A-7-195824 and 8-150773. Ascorbic acids described in No. 7, zinc sulfate described in JP-A-7-149037, thiocyanic acid described in JP-A-7-314882 Thiourea derivatives described in JP-A-7-314883, sugars described in JP-A-7-276790 and 8-108617, and phosphate-based antioxidants described in JP-A-8-118791. Examples thereof include nitrites, sulfites, and thiosulfates described in JP-A-8-300807, and hydroxylamine derivatives described in JP-A-9-267544 as anti-fading agents. Furthermore, polycondensates of dicyandiamide and polyalkylene polyamine described in JP-A No. 2000-266928 and the like are also effective anti-fading agents in inkjet.

(PH buffer)
In the inkjet ink of the present invention, a pH buffer agent may be added to the ink. For example, organic acids and inorganic acids. Examples of the organic acid include non-volatile phthalic acid, terephthalic acid, salicylic acid, benzoic acid, sebacic acid, lauric acid, palmitic acid, ascorbic acid, citric acid, malic acid, lactic acid, succinic acid, succinic acid, and polyacrylic acid. And various organic acids such as benzylic acid.

(Defoamer)
In the inkjet ink of the present invention, an antifoaming agent can be added, and a commercially available product can be used without any particular limitation as the antifoaming agent. Examples of such commercially available products include KF96, 66, 69, KS68, 604, 607A, 602, 603, KM73, 73A, 73E, 72, 72A, 72C, 72F, 82F, 70, 71 manufactured by Shin-Etsu Silicone. 75, 80, 83A, 85, 89, 90, 68-1F, 68-2F (trade name), and the like. Although there is no restriction | limiting in particular in the compounding quantity of these compounds, It is preferable to mix | blend 0.001-2 mass% in the ink of this invention. If the compounding amount of the compound is less than 0.001% by mass, bubbles are likely to be generated at the time of preparing the ink, and it is difficult to remove small bubbles in the ink. During printing, repellency may occur in the ink and the print quality may be deteriorated.

(Surfactant)
Surfactants preferably used in the inkjet ink of the present invention include alkyl sulfates, alkyl ester sulfates, dialkyl sulfosuccinates, alkyl naphthalene sulfonates, alkyl phosphates, polyoxyalkylene alkyl ether phosphates, Anionic surfactants such as fatty acid salts, nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyalkylene alkyl phenyl ethers, acetylene glycols, polyoxyethylene-polyoxypropylene block copolymers, glycerin esters, Activators such as sorbitan esters, polyoxyethylene fatty acid amides, amine oxides, and cationic surfactants such as alkylamine salts and quaternary ammonium salts.

<Preparation of ink>
There is no particular limitation on the preparation of the inkjet ink of the present invention. However, when an ink containing a dispersion such as a pigment, a disperse dye, inorganic fine particles, or resin fine particles is prepared, aggregation and settling do not occur in the preparation process. It is preferable to prepare an ink. If necessary, a preparation method such as adjusting the order of addition of the dispersion, solvent, water, photosensitive resin and other additives, and the addition rate can be taken. In addition, for the purpose of stabilizing the dispersion and redispersing the agglomeration generated during the blending of the ink during or after the blending, a dispersion process using a bead mill or ultrasonic waves, a heating process, or the like may be performed.

《Ink physical properties》
(viscosity)
Although there is no restriction | limiting in particular in the viscosity of the inkjet ink of this invention, It is preferable that the viscosity in 25 degreeC is 2 mPa * s or more and 10 mPa * s or less. Moreover, it is preferable that the viscosity of the inkjet ink of the present invention has no shear rate dependency.

  The ink viscosity (mPa · s) in the present invention is not particularly limited as long as it is tested with a standard solution for calibration of a viscometer specified in JIS Z 8809, and is measured at 25 ° C. according to a known method. As the viscosity measuring device, a rotary, vibration or capillary type viscometer can be used, for example, a Saybolt viscometer, a Redwood viscometer, etc., for example, a cone plate type manufactured by Tokimec E type viscometer, Toki Sangyo E Type Viscometer (rotary viscometer), Tokyo Keiki B type viscometer BL, Yamaichi Denki FVM-80A, Nametor Kogyo Viscoliner VISCO MATE MODEL VM-1A, DD-1 manufactured by Denki Co., Ltd. can be exemplified.

(surface tension)
Moreover, in the inkjet ink of this invention, it is preferable that surface tension is 40 mN / m or less, More preferably, it is 25-35 mN / m.

  The surface tension (mN / m) of the ink referred to in the present invention is a value obtained by measuring the surface tension measured at 25 ° C., and the measurement method is described in general interface chemistry, colloid chemistry reference books, etc. For example, New Experimental Chemistry Course Volume 18 (Interface and Colloid), The Chemical Society of Japan, published by Maruzen Co., Ltd. 68-117 can be referred to. Specifically, it can be determined using a ring method (Dunoi method) or a platinum plate method (Wilhelmy method), but in the present invention, it is represented by a surface tension value (mPa · s) measured by the platinum plate method. For example, it can be measured using a surface tension meter CBVP-Z manufactured by Kyowa Interface Science.

(Electrical conductivity)
In the inkjet ink of the present invention, from the viewpoint of ink storage stability, the electrical conductivity is preferably 1 mS / m or more and 500 mS / m or less, more preferably 1 mS / m or more and 200 mS / m or less, More preferably, they are 10 mS / m or more and 100 mS / m or less. When the electric conductivity of the ink exceeds 500 mS / m, an emission defect due to deposition of a coloring material occurs. Moreover, if it is 1 ms / m or less, sufficient electrostatic repulsion for allowing the dispersion to exist stably cannot be obtained, and it will also aggregate. Therefore, the dispersion can be stably present by setting the electric conductivity to 1 mS / m or more and 500 mS / m.

  In the ink of the present invention, there is no particular limitation as a means for achieving a desired electrical conductivity, but in the present invention, a pigment is used as a coloring material, and a polymer compound (polymer dispersing agent) is used as a pigment dispersant. By appropriately selecting or combining a method or a method using an electrical conductivity modifier, for example, an inorganic salt such as potassium chloride, ammonium chloride, sodium sulfate, sodium nitrate, or sodium chloride, or an aqueous amine such as triethanolamine Can be achieved.

  The measurement of the electrical conductivity of the ink in the present invention should be easily performed according to the method described in JIS K 0400-13-10 (1999) or the method disclosed in JP-A-61-61164. Can do.

(Ion concentration adjustment)
In preparing the inkjet ink of the present invention, it is preferable to adjust the ion concentration as appropriate.

  An aqueous dye solution having a predetermined concentration is measured by ICP-AES, and the ion concentration of the ink state is calculated in terms of the dye concentration used in the ink. By using distilled water or ion-exchanged water, the ion concentration at the time of ink formation can be estimated.

  Next, other additives are added to prepare an ink, and the ion concentration in the ink is measured by ICPAES. When the target ion concentration is exceeded, the ion concentration can be lowered by passing the aqueous dye solution through an ion exchange resin. Ion exchange can be performed a plurality of times to further reduce the ion concentration. If the desired ion concentration is not reached, the additives other than the dye are also subjected to treatment such as ion exchange. Moreover, you may add processes, such as filtration by an activated carbon process or an ultrafiltration membrane, as needed.

"recoding media"
As a recording medium applicable in the recording method using the inkjet ink of the present invention, various papers, various films, various cloths, various woods, various inkjet recording media, and the like can be used. When using a paper medium such as a printing coated paper as the recording medium, as described above, the active energy ray to be irradiated is a low-illuminance high-pressure mercury lamp, low-pressure mercury lamp, LED or the like that generates a small amount of heat, It is preferable from the viewpoint of cockling.

[Coated paper for printing]
Coated paper for printing is coated paper often used in printing. Generally, high-quality paper or medium-quality paper is used as the base paper, and after applying a pigment such as clay on the surface of the paper, smoothness is improved. Therefore, it is produced by applying a calendar process. Such processing improves whiteness, smoothness, print ink acceptability, halftone dot reproducibility, print gloss, print opacity, and the like. The paper is classified into art paper, coated paper, lightweight coated paper, etc., depending on the coating amount, and is classified into glossy, dull, matte, etc., depending on the gloss of the paper.

Art paper is coated paper having a coating amount of about 20 g / m ^{2 on} one side, and is generally prepared by applying a pigment to the paper surface and then applying a calendar treatment. There are special art, average art, matte (matte) art, single art (single side coating), double art (double side coating), and more specifically, OK Kanto N, Satin Kanto N, SA Kanou, Ultra Satin Kinto N, OK Ultra Aqua Satin, OK Kanto Single Side, N Art Post, NK Special Side Art, Thunderbird Super Art N, Thunderbird Super Art MN, Thunderbird Art N, Thunderbird Dull Art N, Hi McKinley Art, Hi McKinley Mat, High McKinley Pure Dull Art, Hi McKinley Super Dal, Hi McKinley Mat Elegance, Hi McKinley Deep Mat, etc.

The coated paper is a coated paper having a coating amount of about 10 g / m ^{2 on} one side, and is generally produced by processing with a coating apparatus provided in the middle of the paper machine. The coating amount is less than that of art paper, and the smoothness is slightly reduced, but the advantages are low cost and light weight. There is also a type of coated paper with a smaller coating amount, such as a light-weight coat and a finely coated paper. Specific examples of these coated papers include POD gloss coat, OK top coat +, OK top coat S, aurora coat, mu coat, mu white, thunderbird coat N, utrilo coat, pearl coat, white pearl coat, POD mat coat, New Age, New Age W, OK top coat mat N, OK royal coat, OK top coat dull, Z coat, Silver diamond, Ulite, Neptune, Mu mat, White mu mat, Thunderbird mat coat N, Utrilogros mat, New V mat, white new V mat, etc. are mentioned.

[Non-absorbent recording medium]
As the non-absorbable recording medium, all commonly used various films can be used. For example, there are a polyester film, a polyolefin film, a polyvinyl chloride film, a polyvinylidene chloride film, and the like. Resin-coated paper that is photographic printing paper or YUPO paper that is synthetic paper can also be used.

<Inkjet recording method>
The recording method using the ink-jet ink of the present invention is characterized in that the ink-jet ink of the present invention is ejected onto a recording medium by an ink-jet head and the ink is cured by irradiation with active energy rays. Furthermore, it is preferable to introduce a drying step after the ink is cured.

  Hereinafter, a method for irradiating the inkjet ink with active energy rays will be described.

[Active energy ray irradiation]
(Active energy rays)
Examples of the active energy rays in the present invention include electron beams, ultraviolet rays, α rays, β rays, γ rays, X-rays, etc., but they are dangerous to the human body and easy to handle. Electron beams and ultraviolet rays that are widely used are preferred. In the present invention, ultraviolet rays are particularly preferable.

  When using an electron beam, the amount of the electron beam to be irradiated is preferably in the range of 0.1 to 30 Mrad. If it is less than 0.1 Mrad, a sufficient irradiation effect cannot be obtained, and if it exceeds 30 Mrad, the support or the like may be deteriorated.

  When ultraviolet rays are used, the light source is, for example, a low pressure, medium pressure, high pressure mercury lamp, metal halide lamp, xenon lamp having a light emission wavelength in the ultraviolet region, cold cathode tube, hot cathode tube having an operating pressure of several hundred Pa to 1 MPa. A conventionally well-known thing, such as LED, is used.

  In particular, when a paper-based medium such as a coated paper for printing is used as the recording medium, as described above, the amount of heat generated by the low-intensity high-pressure mercury lamp, low-pressure mercury lamp, LED, etc. is used as the active energy ray to be irradiated. A small one is preferable from the viewpoint of cockling.

(Light irradiation conditions after ink landing)
As the irradiation condition of the active energy ray, it is preferable that the active energy ray is irradiated for 0.001 to 1.0 seconds after the ink has landed on the recording medium, and more preferably 0.001 to 0.00. 5 seconds. In order to form a high-definition image, it is particularly important that the irradiation timing is as early as possible.

(Irradiation method of active energy rays)
As a method for irradiating active energy rays, a basic method is disclosed in Japanese Patent Application Laid-Open No. 60-132767. According to this, the light source is provided on both sides of the head unit, and the head and the light source are scanned by the shuttle method. Irradiation is performed after a certain period of time after ink landing. Further, the curing is completed by another light source that is not driven. In US Pat. No. 6,145,979, as an irradiation method, a method using an optical fiber or a method of irradiating a recording unit with ultraviolet rays by applying a collimated light source to a mirror surface provided on the side surface of the head unit is disclosed. . Any of these irradiation methods can be used in the inkjet recording method of the present invention.

  Also preferred is a method in which the irradiation of active energy rays is divided into two stages, and the active energy rays are first irradiated by the above-described method within 0.001 to 2.0 seconds after ink landing, and further the active energy rays are irradiated. It is one of. By dividing the irradiation of the active energy ray into two stages, it is possible to further suppress the shrinkage of the recording material that occurs during ink curing.

(Drying after curing)
In the ink jet recording method according to the present invention, it is preferable to dry the ink jet ink discharged onto the recording medium for the purpose of removing unnecessary water-soluble organic solvent and the like after irradiating and curing the active energy ray.

  The ink drying means is not particularly limited. For example, a method of drying the recording medium by bringing the back surface of the recording medium into contact with a heating roller or a flat heater, a means of blowing hot air on the printing surface with a dryer, or a decompression process. A method for removing volatile components and the like can be appropriately selected or combined.

(Printer parts)
As a member used in the ink jet printer used in the ink jet recording method according to the present invention, an object having a low transmittance or reflectance with respect to active energy rays is used in order to prevent irradiation of the head surface due to irregular reflection of actinic rays, for example, ultraviolet rays. preferable.

  The irradiation unit preferably has a shutter mounted. For example, when ultraviolet rays are used, the ratio of illuminance when opening and closing the shutter is preferably shutter open / shutter close = 10 or more, more preferably 100 or more. Preferably it is 10,000 or more.

  Next, an inkjet printer that can be applied in the inkjet recording method according to the present invention will be described.

〔inkjet printer〕
As an ink jet printer that can be used in the present invention, for example, image formation is arranged horizontally, and the back surface of the recording medium in a predetermined range on the upper surface (the surface opposite to the image forming surface side) is driven by the suction device. Equipped with a platen that is sucked and supported by a recording head, a recording head that discharges ink from a nozzle outlet toward a recording medium, and an irradiation unit that includes these recording head and actinic rays, and moves in the scanning direction during image formation A carriage, a drive circuit board mounted on the carriage and for driving the carriage, a guide member extending along the scanning direction to guide the movement of the carriage, and extending along the scanning direction; In the longitudinal direction, the linear scale on which the optical pattern is arranged and the optical pattern that is mounted on the carriage and arranged on the linear scale are read. Device configured by a linear encoder sensor that outputs a clock signal and the like.

(Inkjet recording head)
The ink jet recording head (ink jet print head) to be used may be an on-demand system or a continuous system. In addition, as a discharge method, an electro-mechanical conversion method (for example, a single cavity type, a double cavity type, a bender type, a piston type, a shear mode type, a shared wall type, etc.), an electro-thermal conversion method (for example, a thermal type) Examples thereof include an ink jet type, a bubble jet (registered trademark) type, an electrostatic suction type (for example, an electric field control type, a slit jet type, etc.), and a discharge type (for example, a spark jet type). The electro-mechanical conversion method is preferable, but any discharge method may be used.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, although the display of "part" or "%" is used in an Example, unless otherwise indicated, "part by mass" or "mass%" is represented.

<< Preparation of crosslinkable polymer compound >>
56 g of glycidyl methacrylate, 48 g of p-hydroxybenzaldehyde, 2 g of pyridine and 1 g of N-nitroso-phenylhydroxyamine ammonium salt were put in a reaction vessel, respectively, and stirred in a hot water bath at 80 ° C. for 8 hours.

  Next, 45 g of polyvinyl acetate saponified product having a degree of polymerization of 300 and a saponification rate of 98% was dispersed in 225 g of ion-exchanged water, and then 4.5 g of phosphoric acid was added to this solution to obtain p- (3 -Methacryloxy-2-hydroxypropyloxy) benzaldehyde was added to polyvinyl alcohol so that the modification rate was 3 mol%, and the mixture was stirred at 90 ° C. for 6 hours. After cooling the obtained solution to room temperature, 30 g of basic ion exchange resin was added and stirred for 1 hour. The ion exchange resin was filtered and then diluted with pure water to obtain a 15% by mass aqueous solution of the crosslinkable polymer compound. A crosslinkable polymer compound is a polymer compound that has a plurality of side chains in a saponified polyvinyl acetate that is a hydrophilic main chain, and can be crosslinked between side chains by irradiating active energy rays. is there.

<Preparation of ink>
[Preparation of Ink 101]
Ink 101 was prepared according to the following method.

  The following compositions were sequentially mixed and dispersed using a bead mill, and then filtered through a # 3000 metal mesh filter to prepare ink 101.

Crosslinkable polymer compound 1 3 parts as solid content Diethylene glycol 8 parts 2-pyrrolidinone 10 parts 1,2-hexanediol 6 parts Sensitizer: Triethanolamine 1 part Activator: Olphine E1010 (manufactured by Nissin Chemical Industry Co., Ltd.) 1 Polymerization initiator: Irgacure 2959 (Ciba Specialty Chemicals)
1 part Pigment: Cab-O-Jet300 (Carbot black carbon black self-dispersing pigment)
3 parts as solid content Antifungal agent: Proxel GXL (manufactured by Avicia) 0.2 parts Ion exchange water was added to each of the above compositions to finish 100 parts.

[Preparation of Ink 102]
The following compositions were sequentially mixed, dispersed using a bead mill, and then filtered through a # 3000 metal mesh filter to prepare ink 102.

Crosslinkable polymer compound 1 3 parts as solid content Diethylene glycol 8 parts 2-pyrrolidinone 10 parts 1,2-hexanediol 6 parts Sensitizer: Triethanolamine 1 part Activator: Olphine E1010 (manufactured by Nissin Chemical Industry Co., Ltd.) 1 Polymerization initiator: Irgacure 2959 (Ciba Specialty Chemicals)
1 part Pigment: Titanium black (Tilac D Ako Kasei Co., Ltd.) 3 parts as solid content Dispersant: Jonkrill 70 (Jonkrill Co., Ltd.) 4 parts Antifungal agent: Proxel GXL (Avicia) 0.2 part or more Ion exchanged water was added to each of the compositions to finish 100 parts.

[Preparation of inks 103 to 109]
In the preparation of the ink 102, instead of the crosslinkable polymer compound 1, crosslinkable polymer compounds 2 to 7 having the modification rate and the polymerization degree shown in Table 1 were used, and the addition amount was as shown in Table 1. Inks 103 to 109 were prepared in the same manner except that the inks were changed to.

[Preparation of Ink 110]
The following compositions were sequentially mixed and dispersed using a bead mill, and then filtered through a # 3000 metal mesh filter to prepare ink 110.

Active energy ray reactive compound: A-TMPT-3EO (manufactured by Shin-Nakamura Chemical Co., Ltd.)
3 parts as solid content Diethylene glycol 8 parts 2-pyrrolidinone 10 parts 1,2-hexanediol 6 parts Activator: Olphine E1010 (manufactured by Nissin Chemical Industry Co., Ltd.) 1 part Polymerization initiator: Irgacure 2959 (manufactured by Ciba Specialty Chemicals) )
1 part Pigment: Cab-O-Jet300 (Carbot black carbon black self-dispersing pigment)
3 parts as solid content Antifungal agent: Proxel GXL (manufactured by Avicia) 0.2 parts Ion exchange water was added to each of the above compositions to finish 100 parts.

[Preparation of ink 111]
Ink 111 was prepared in the same manner as in the preparation of the ink 110 except that titanium black (Tilac D Ako Kasei Co., Ltd.) was used instead of carbon black.

<< Image formation and evaluation >>
(Image printing)
A piezo head having a nozzle diameter of 23 μm, a driving frequency of 18 kHz, a nozzle number of 256, a minimum liquid amount of 4 pl, and a nozzle density of 180 dpi (where dpi represents the number of dots per 2.54 cm) is mounted on both ends of the piezo head. An on-demand type ink jet printer having a maximum recording density of 1440 × 1440 dpi was prepared by arranging a 120 W / cm metal halide lamp (MAL 400NL, power supply power 3 kW · hr, manufactured by Nippon Battery Co., Ltd.).

  While irradiating a metal halide lamp, inks 101 to 111 were ejected to record an image on a polyethylene terephthalate film. As an image, a solid black image of 5 cm × 5 cm was printed, and after image recording, the image was formed by drying with warm air for 30 seconds using a dryer.

(Evaluation of ink curability)
The surface of the solid black image created above was touched with a finger, and the presence or absence of image adhesion to the finger was visually observed, and ink curability was evaluated according to the following criteria.

◎: Ink does not adhere to fingers at all after palpation after printing ○: Ink slightly adheres to fingers during palpation after printing, but there is no problem with image performance △: Ink adheres to fingers during palpation after printing Deterioration of image performance is observed. ×: Ink adheres to fingers during palpation after printing, and significant image deterioration is recognized (Evaluation of image fixability)
The image produced by the above printing method was dried in an environment of 23 ° C. and 50% RH for 24 hours, and then the surface of each solid black image was rubbed with a rolled tissue paper, and the formed image peeling was visually observed. The image fixability was evaluated according to the following criteria.

◎: Image peeling is not observed at all ○: Image peeling is slightly observed, but there is no problem in image performance Δ: Image peeling is partially generated ×: Most of image is peeled off (Ink Evaluation of preservability)
About the inks 101 to 111 prepared above, each was filled in a glass bottle and sealed, and then stored in a constant temperature bath at 40 ° C. for 7 days. The ink viscosity change rate was measured according to the following equation, and based on the ink change rate, The ink storage stability was evaluated according to the following criteria.

Ink viscosity change rate (%) = {| ink viscosity before storage−ink viscosity after storage | / ink viscosity before storage} × 100
A: Ink viscosity change rate is less than 5% B: Ink viscosity change rate is 5% or more and less than 10% Δ: Ink viscosity change rate is 10% or more and less than 20% ×: Ink viscosity change rate is 20 Table 1 shows the results obtained as described above.

  As is clear from the results shown in Table 1, the ink 101 as a comparative example uses carbon black as a pigment and a crosslinkable polymer as a binder. Satisfactory performance in terms of sex has not been obtained. On the other hand, the ink 102 which is different only by changing the pigment to titanium black has greatly improved the curability of the ink by ultraviolet irradiation, and the curability and the fixability to a polyethylene terephthalate film as a recording medium are greatly improved. . This is because the amount of light absorbed by the color material in the ultraviolet wavelength region is reduced by using titanium black as a pigment, and light irradiation to the photoinitiator in the ink is efficiently performed. Conceivable. This tendency is effective even in the inks 103 to 109 in which the modification rate of the crosslinkable polymer compound (the ratio of the crosslinking group added to the hydrophilic main chain), the polymerization degree, and the addition amount are changed. It turns out that it expresses.

  On the other hand, it can be seen that inks 110 and 111 using an active energy ray-reactive compound as a binder are inferior in curability after printing and light irradiation regardless of the type of pigment used. This is considered to be due to the fact that the amount of added resin required for curing is small. However, the increase in the amount of resin is accompanied by an increase in ink viscosity, and it becomes difficult to achieve both emission properties and curability. In addition, a decrease in curability results in a decrease in fixability (ink 110). On the other hand, the fixability of the ink 111 tends to be slightly improved, but this is considered to be affected by the difference in the light absorption amount in the UV wavelength region due to the change of the pigment type as described above.

Claims (4)

It contains at least water, a polymer compound having a plurality of side chains in the hydrophilic main chain, and a crosslinkable cross-link between the side chains by irradiation with active energy rays, and the color material is titanium black. An inkjet ink characterized by the above. The modification rate of the side chain with respect to the hydrophilic main chain of the polymer compound that can be cross-linked between the side chains is 0.8 mol% or more and 4.0 mol% or less. Inkjet ink. The inkjet ink according to claim 1 or 2, wherein the polymer compound capable of crosslinking between the side chains has a degree of polymerization of a hydrophilic main chain of 200 or more and 500 or less. The content ratio of the polymer compound that can be cross-linked between the side chains with respect to the total mass of the ink is 0.8% by mass or more and less than 5% by mass. The inkjet ink as described.