JP5359102B2 - Ink set and ink jet recording method using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink set which can control bronzing in pigment ink to acquire a printing image excellent in scratch-resistance, printing consistency, and glossiness, and to provide a method for inkjet-recording using this ink set. <P>SOLUTION: The ink set comprises: a pigment ink including following (a), (b), and (c) components; and a colorless ink including an aqueous polymer having a Tg of 25&deg;C or more. The method for inkjet-recording comprises: discharging a pigment ink from an inkjet head; adhering ink drops to a recording medium to form an image; and thereafter discharging a colorless ink onto this image from the inkjet head. (a) A polymer of a monomer containing an oxyalkylene chain and/or a copolymer of a monomer containing an oxyalkylene chain and other monomers in which the content of a constitutional unit originating in the monomer containing an oxyalkylene chain is 15% by weight or more based on the whole copolymer weight, (b) a pigment, and (c) an aqueous medium. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to an ink set comprising a pigment ink containing a pigment as a colorant and a colorless ink containing a water-soluble polymer, and an ink jet recording method using the ink set.

Inkjet printers are rapidly becoming popular for both personal use and business use due to the ease of full color, low noise, high-resolution images at low cost, and high-speed printing. I am doing.
At present, aqueous recording liquids are mainly used as recording liquids for ink jet printers, and printed materials with high resolution are being obtained.

  Conventionally, the aqueous recording liquid mainly contains a water-soluble dye and a liquid medium. However, the printed matter obtained with this aqueous recording liquid has insufficient water resistance, light resistance, ozone resistance and the like because the aqueous recording liquid contains a water-soluble dye.

  Therefore, in recent years, a pigment dispersion type aqueous recording liquid (hereinafter sometimes simply referred to as “ink”) in which a pigment is dispersed in an aqueous medium has been developed instead of such a dye.

  However, generally, a recorded matter recorded by an inkjet method using a pigment-dispersed ink tends to have high light resistance, but since the pigment particles after printing are present above the ink receiving layer of the recording medium, Insufficient fixability and scratch resistance, unevenness in glossiness and texture may occur between areas with a large amount of pigment ink attached and areas with a small amount of pigment ink, resulting in high-definition images such as silver salt photographs. It has been a problem that it is difficult to use and has a lower glossiness than that using a dye as a coloring material.

  Therefore, after forming an image by the ink jet recording method, a clear ink containing an aqueous polymer such as polymer fine particles and not containing a colorant component is ejected to form a coat layer, thereby improving the fixability and glossiness of the printed image. Attempts to improve (see, for example, Patent Documents 1 to 4) and attempts to suppress uneven glossiness of printed images by adjusting the discharge amount of clear ink or the like between a portion with a large amount and a small amount of pigment ink attached. (See, for example, Patent Documents 5 to 7).

  However, even if the fixability and glossiness are improved by forming a coat layer with a conventional clear ink on the recorded image recorded by the inkjet method using the conventional pigment ink, the gloss of the recorded image itself by the pigment ink is improved. Due to its low nature, glossiness was still insufficient as compared with silver salt photographs.

In addition, with a pigment ink, a bronze phenomenon appears in a printed image, and a color that is complementary to the color of the pigment itself is observed. In particular, in phthalocyanine blue, the light absorption maximum wavelength of the pigment is 620 nm, but visible light having a wavelength of 660 nm in the vicinity thereof is strongly refracted and scattered, and a red bronze phenomenon, which is a complementary color, appears. Light scattering increases in proportion to an increase in the absorption coefficient. Therefore, the bronze phenomenon becomes more pronounced with pigments with higher coloring power and with higher pigment concentration, and the hue of the printed image differs depending on the viewing angle. It becomes visible.
For this reason, suppression of the bronze phenomenon has been a problem for pigment inks.
WO2000 / 06390 Publication JP 2001-39006 A Japanese Patent Laid-Open No. 2002-201428 JP 2005-81754 A JP 2003-286428 A JP 2005-52984 A JP 2006-27194 A

  An object of the present invention is to provide an ink set capable of suppressing a bronze phenomenon in pigment ink and obtaining a printed image having excellent scratch resistance, print density and gloss, and an ink jet recording method using the ink set. It is in.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have used a polymer containing 15% by weight or more of a structural unit derived from a monomer containing an oxyalkylene chain as a pigment dispersant. In addition, the discharge property of the pigment ink is improved, the gloss of the obtained recorded matter is excellent, and further, the recording is performed by overcoating with a colorless ink containing a water-soluble polymer having a Tg of 25 ° C. or more. It has been found that the print density, scratch resistance, and bronze phenomenon can be improved while maintaining the gloss of the product at a high level.

  The present invention has been achieved on the basis of such findings, and the gist thereof is as follows.

[1] An ink set comprising a pigment ink containing the following components (a), (b) and (c), and a colorless ink containing an aqueous polymer having a Tg of 25 ° C. or more , wherein the pigment ink further comprises An ink set comprising a polyvinyl alcohol resin, wherein the polyvinyl alcohol resin contains an ionic dissociation group selected from the group consisting of an acidic group, a basic group, and salts thereof .
(A) Polymer of monomer containing oxyalkylene chain and / or copolymer of monomer containing oxyalkylene chain and other monomer, derived from monomer containing oxyalkylene chain (B) Pigment (c) Aqueous medium Copolymer having a content of 15% by weight or more based on the whole copolymer

[2] The ink set according to [1], wherein the aqueous polymer is a water-soluble polymer.

[3] The ink set according to [1] or [2], wherein the monomer containing the oxyalkylene chain is represented by the following general formula (1).

(In the formula (1), R ¹ is vinyl group, acryloyloxy group, acryloylamino group, methacryloyloxy group, methacryloylamino group, acrylamino group, styryl group, vinyl ether group, vinylsilyl group, cyanovinyl group, or 2-cyanoacryloyl. R ² represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or an optionally substituted phenyl group, h and j are each independently an integer of 1 to 5, i is (It is an integer from 1 to 100, k is an integer from 0 to 50, and i + k ≧ 2.)

[4] The ink set according to any one of [1] to [3], wherein the other monomer is a hydrophobic monomer and / or an anionic monomer.

[5] The ink set according to any one of [1] to [4], wherein the content of the structural unit derived from the anionic monomer is 10% by weight or less based on the entire copolymer.

[6] The ink set according to any one of [1] to [5], wherein the water-soluble polymer is a copolymer of a hydrophobic monomer and a hydrophilic monomer.

[ 7 ] The polyvinyl alcohol resin according to any one of [ 1 ] to [6], wherein the polymer includes a structural unit derived from vinyl alcohol represented by the following general formula (3) and a hydrophobic group. Ink set.

(In formula (3), R ³ represents a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms)

[ 8 ] The ink set according to any one of [ 1 ] to [ 7 ], wherein the polyvinyl alcohol-based resin is a block copolymer.

[ 9 ] A pigment ink containing the following components (a), (b), and (c) is ejected from an ink jet head, and the pigment ink droplets are attached to a recording medium to form an image. An inkjet recording method of discharging a colorless ink containing the above aqueous polymer onto an image from an inkjet head, wherein the pigment ink further contains a polyvinyl alcohol resin, and the polyvinyl alcohol resin has an acidic group and An ink jet recording method comprising an ionic dissociation group selected from the group consisting of a basic group and a salt thereof .
(A) Polymer of monomer containing oxyalkylene chain and / or copolymer of monomer containing oxyalkylene chain and other monomer, derived from monomer containing oxyalkylene chain (B) Pigment (c) Aqueous medium Copolymer having a content of 15% by weight or more based on the whole copolymer

  According to the ink set of the present invention and the ink jet recording method using the ink set, it is possible to suppress the bronzing phenomenon of the pigment ink and obtain a printed image having excellent scratch resistance, print density, and glossiness.

  Hereinafter, embodiments of the present invention will be described in detail. However, the description of the constituent elements described below is an example (representative example) of the embodiments of the present invention, and the present invention does not exceed the gist thereof. These contents are not specified.

In the following, “(meth) acrylate” means “acrylate and / or methacrylate”, and “(meth) acryl” means “acryl and / or methacryl”.
Further, “(co) polymer” and “polymer” mean “polymer and / or copolymer”.

The ink set of the present invention includes a pigment ink containing the following components (a), (b) and (c) (hereinafter sometimes referred to as “the pigment ink of the present invention”) and an aqueous solution having a Tg of 25 ° C. or higher. A colorless ink containing a polymer (hereinafter sometimes referred to as “colorless ink of the present invention”), and the ink jet recording method of the present invention uses such an ink set. The pigment ink of the present invention is ejected from the inkjet head, and the pigment ink droplets are attached to a recording medium to form an image, and then the colorless ink of the present invention is ejected from the inkjet head onto the image. Features.
(A) Polymer of monomer containing oxyalkylene chain and / or copolymer of monomer containing oxyalkylene chain and other monomer, derived from monomer containing oxyalkylene chain (B) Pigment (c) Aqueous medium Copolymer having a content of 15% by weight or more based on the whole copolymer

[Pigment ink]
The pigment ink of the present invention is (a) a polymer of a monomer containing an oxyalkylene chain, and / or a copolymer of a monomer containing an oxyalkylene chain and another monomer, which contains an oxyalkylene chain. A copolymer containing 15% by weight or more of a constituent unit derived from the monomer, (b) a pigment, and (c) an aqueous medium, (a) The component (co) polymer is used as a polymer dispersant for dispersing a pigment.
Hereinafter, a polymer of a monomer containing an oxyalkylene chain is referred to as “polymer (a)”, and a copolymer of a monomer containing an oxyalkylene chain and another monomer is referred to as “copolymer (a)”. These may be collectively referred to as “(co) polymer (a)”.

{(Co) polymer (a)}
<Operational effect of (co) polymer (a)>
(Co) polymer (a), that is, a copolymer (a) of a monomer containing an oxyalkylene chain and / or a copolymer (a) containing 15% by weight or more of a structural unit derived from a monomer containing an oxyalkylene chain The reason why the gloss of the printed matter is increased by using the pigment ink of the present invention using the pigment dispersant as a pigment dispersant is not clear, but is considered as follows.
That is, on the paper, hydrophilic alkylene oxide chains interact with each other in a state of retaining water, forming a loose and large network, and forming a highly smooth film on the surface of the printed material. It is thought to improve the performance.

In the present invention, as the (co) polymer (a) as the polymer dispersant, only a homopolymer of a monomer containing an oxyalkylene chain (that is, the polymer (a)) may be used. A copolymer of a monomer containing a chain and another monomer, the copolymer containing 15% by weight or more of a structural unit derived from a monomer containing an oxyalkylene chain (that is, copolymer (a)) May be used alone, or the polymer (a) and the copolymer (a) may be mixed and used. As described later, the monomer containing an oxyalkylene chain in the copolymer (a). Since the effect of improving the pigment dispersibility, fixability, and the like can be further improved by the effects of the structural unit derived from the above and the structural unit derived from the other monomer, the (co) polymer (a ) As a copolymer ( ) Is preferably used.
As for the polymer (a) and the copolymer (a), one type may be used alone, or two or more types having different monomer types and monomer compositions may be used in combination.

<Monomer containing oxyalkylene chain>
The (co) polymer (a) as the polymer dispersant in the pigment ink of the present invention is not particularly limited as long as it is a (co) polymer containing 15% by weight or more of a structural unit derived from an oxyalkylene chain. Preferably, the monomer containing an oxyalkylene chain is represented by the following general formula (1).

(In the formula (1), R ¹ is vinyl group, acryloyloxy group, acryloylamino group, methacryloyloxy group, methacryloylamino group, acrylamino group, styryl group, vinyl ether group, vinylsilyl group, cyanovinyl group, or 2-cyanoacryloyl. R ² represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or an optionally substituted phenyl group, h and j are each independently an integer of 1 to 5, i is (It is an integer from 1 to 100, k is an integer from 0 to 50, and i + k ≧ 2.)

In general formula (1), the total of i and k is more preferably 2 to 100. This is because if the sum of i and k is 1 or less, the gloss of printed matter on photographic paper decreases, and if it exceeds 100, the fixability to paper decreases.
The alkyl groups of the phenyl group R ^2, include alkyl groups having 1 to 20 carbon atoms.

  Specific examples of the monomer containing the oxyalkylene chain represented by the general formula (1) include polyethylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, ethoxypolyethylene glycol (meth) acrylate, and ethoxydiethylene glycol (meth). Acrylate, Lauroxy polyethylene glycol (meth) acrylate, stearoxy polyethylene glycol (meth) acrylate, nonylphenoxy polyethylene glycol (meth) acrylate, phenoxy polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate, poly (ethylene glycol-propylene) Glycol) (meth) acrylate, polyethylene glycol-polypropylene glycol (medium) ) Acrylate, poly (ethylene glycol-tetramethylene glycol) (meth) acrylate, poly (propylene glycol-tetramethylene glycol) (meth) acrylate, propylene glycol polybutylene glycol (meth) acrylate, octoxy polyethylene glycol polypropylene glycol (meth) Examples include acrylate, stearoxy polyethylene glycol-polypropylene glycol (meth) acrylate, allyloxy polyethylene glycol-polypropylene glycol (meth) acrylate, and nonylphenoxy poly (ethylene glycol-propylene glycol) (meth) acrylate.

  As the monomer containing an oxyalkylene chain used in the present invention, those represented by the following general formula (2) are particularly preferred from the viewpoint of the effect of improving dispersion stability due to their high hydrophilicity. Specific examples of the monomer containing a chain include, for example, polyethylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, ethoxypolyethylene glycol (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, and lauroxy polyethylene glycol (meth) acrylate. , Stearoxy polyethylene glycol (meth) acrylate, nonylphenoxy polyethylene glycol (meth) acrylate, phenoxy polyethylene glycol (meth) acrylate, and the like.

(In formula (2), R ¹ and R ² have the same meaning as in formula (1), and m is an integer of 1 to 50.)

In particular, among the monomers represented by the general formula (2), those in which R ¹ is a (meth) acryloyloxy group and R ² is an alkyl group having 1 to 20 carbon atoms are more preferable. Examples include polyethylene glycol (meth) acrylate, ethoxy polyethylene glycol (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, lauroxy polyethylene glycol (meth) acrylate, stearoxy polyethylene glycol (meth) acrylate, and the like.

  These monomers containing an oxyalkylene chain may be used alone or in a combination of two or more.

<Other monomers>
In the copolymer (a), the other monomer that is copolymerized with the monomer containing an oxyalkylene chain is not particularly limited, and a conventionally known polymerizable monomer can be used, but a hydrophobic monomer and / or Anionic monomers are preferably used.

(Hydrophobic monomer)
The hydrophobic monomer is not particularly limited, and conventionally known hydrophobic monomers can be used, and aromatic ring-containing monomers and / or aliphatic hydrocarbon group-containing monomers as described below are preferably used.

  The aromatic ring-containing monomer is an aromatic heterocyclic ring-containing monomer or an aromatic hydrocarbon ring-containing monomer. For example, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, phenoxyethylene glycol (meth) acrylate, phenoxydiethylene glycol (meta ) Acrylate, 2-naphthyl (meth) acrylate, 9-anthracenyl (meth) acrylate, 1-pyrenylmethyl (meth) acrylate, styrene, vinylnaphthalene, α-methylstyrene, t-butylstyrene, p-methylstyrene, o-methoxy Styrene, m-methoxystyrene, p-methoxystyrene, ot-butoxystyrene, mt-butoxystyrene, pt-butoxystyrene, o-chloromethylstyrene, m-chloromethylstyrene, p- Lolo methyl styrene, vinyl toluene, ethyl vinyl benzene, 4-vinyl biphenyl, 1,1-diphenyl ethylene, vinyl phenol, vinyl benzoate, vinyl naphthalene, benzyl vinyl ether.

  Among these, from the viewpoint of pigment affinity, none such as benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, phenoxyethylene glycol (meth) acrylate, phenoxydiethylene glycol (meth) acrylate, styrene, and α-methylstyrene. Monomers having a substituted phenyl group are preferred, and styrene and benzyl methacrylate are more preferred.

  The aliphatic hydrocarbon group contained in the aliphatic hydrocarbon group-containing monomer may be linear, cyclic, or branched.

Examples of the monomer having a linear or branched aliphatic hydrocarbon group include the following.
Olefins such as ethylene, propylene, 1-butene and isobutene;
Methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, i-propyl (meth) acrylate, butyl (meth) acrylate, i-butyl (meth) acrylate, t-butyl (meth) acrylate, amyl ( (Meth) acrylate, i-amyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, i-octyl (meth) acrylate, decyl (meth) acrylate, i-decyl (meth) acrylate, dodecyl ( (Meth) acrylate, i-dodecyl (meth) acrylate, stearyl (meth) acrylate, i-stearyl (meth) acrylate, (meth) acrylate esters of behenyl (meth) acrylate;
Vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether;
Nitriles such as acrylonitrile and methacrylonitrile;
Vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride;
Allyl compounds such as allyl acetate and allyl chloride;
Dicarboxylic acid ester derivatives such as maleic acid ester and itaconic acid ester;
Vinylsilyl compounds such as vinyltrimethoxysilane;
Vinyl esters such as vinyl acetate and isopropenyl acetate.

  Examples of the monomer having a cyclic aliphatic hydrocarbon group include cyclopropyl (meth) acrylate, cyclobutyl (meth) acrylate, cyclopentyl (meth) acrylate, cyclohexyl (meth) acrylate, cycloheptyl (meth) acrylate, cyclooctyl (meth) ) Acrylate, cyclononyl (meth) acrylate, cyclodecyl (meth) acrylate, isobornyl (meth) acrylate, norbornyl (meth) acrylate, adamantyl (meth) acrylate and other (meth) acrylate esters; cyclopentene, cycloheptene, cyclooctene, cyclododecene, 1,5-cyclooctadiene, cyclopentadiene, 1,5,9-cyclododecatriene, 1-chloro-1,5-cyclooctadiene, dicyclo Ntajien, ethylidene norbornene, 5-norbornene-2-carboxylate, and 5-norbornene-2,3-dicarboxylic acid dimethyl and cyclic olefins and the like.

  Among these, a monomer having a linear alkyl structure and a monomer containing an aliphatic hydrocarbon group having a cyclic structure are preferable from the viewpoint of affinity with the pigment.

  These hydrophobic monomers may be used alone or in combination of two or more.

(Anionic monomer)
As an anionic monomer, what is illustrated below can be used, However It is not limited to these, A conventionally well-known thing can be used.

Carboxylic acid monomers such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, or salts thereof;
Vinyl sulfonic acid, allyl sulfonic acid, methacryl sulfonic acid, styrene sulfonic acid, 2-acrylamide ethane sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 2-methacrylamide ethane sulfonic acid, 2-methacrylamide-2-methyl Propanesulfonic acid, 2-acryloyloxyethanesulfonic acid, 3-acryloyloxypropanesulfonic acid, 4-acryloyloxybutanesulfonic acid, 2-methacryloyloxyethanesulfonic acid, 3-methacryloyloxypropanesulfonic acid, 4-methacryloyloxybutanesulfone Sulfonic acid monomers such as acids or salts thereof;
Vinylphosphonic acid, methacryloxyethyl phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, dibutyl-2-acryloyloxyethyl phosphate, dibutyl-2-methacryloyloxyethyl phosphate, Phosphoric monomers such as dioctyl-2- (meth) acryloyloxyethyl phosphate or salts thereof.

  The anionic monomer is preferably a monomer having a carboxyl group or a salt thereof, and more preferably acrylic acid or a salt thereof, from the viewpoint of print quality such as low print density or bleeding. The anionic monomer is preferably a salt. Of these, alkali metal salts and alkaline earth metal salts are particularly preferable.

  These anionic monomers may be used individually by 1 type, and may use 2 or more types together.

(Other monomers)
The copolymer (a) includes a structural unit derived from a monomer containing an oxyalkylene chain, a structural unit derived from a hydrophobic monomer and / or a structural unit derived from an anionic monomer, and other polymerizable monomers (hereinafter, “ It may be referred to as “other monomer X].” May contain a structural unit derived from other monomers X. The other monomer X is not particularly limited, and a conventionally known monomer can be used.

Specifically, examples of the other monomer X include hydrophilic nonionic monomers as exemplified below.
(Meth) acrylamide, N-alkyl (meth) acrylamide having 1 to 6 carbon atoms in the alkyl group, N, N-dialkyl (meth) acrylamide, C 1-3 in carbon number in the alkyl group, diacetone (meth) acrylamide, N -Methylol (meth) acrylamide, N-2-hydroxyethyl (meth) acrylamide, N, N-diethanol (meth) acrylamide, N-vinylacetamide, N-methyl-N-vinylacetamide, N-vinylformamide, N-methyl Amide group-containing monomers such as -N-vinylformamide, N- (2- (polyethylene glycol) ethyl) (meth) acrylamide, N, N- (2,2 '-(polyethylene glycol) diethyl) (meth) acrylamide;
Monomers having primary amino groups such as aminoethyl (meth) acrylate and aminopropyl (meth) acrylate;
Secondary such as methylaminoethyl (meth) acrylate, methylaminopropyl (meth) acrylate, ethylaminoethyl (meth) acrylate, ethylaminopropyl (meth) acrylate, 2-vinylpyridine, 4-vinylpyridine A monomer having an amino group;
Monomers having a tertiary amino group such as dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylate, diethylaminopropyl (meth) acrylate;
2-vinylpyridine, 4-vinylpyridine, 1-vinylimidazole, N-vinylpyrrolidone, 2-vinyl-2-oxazoline, 5-methyl-2-vinyl-2-oxazoline, N-vinyloxazolidone, 2-N-pyrrolidoneethyl Monomers having a heterocyclic ring such as (meth) acrylate, N-vinylcaprolactam, 9-vinylcarbazole, N-vinylphthalimide;
Monomers containing a hydroxyl group such as 2-hydroxyethyl (meth) acrylic acid ester, 2-hydroxypropyl (meth) acrylic acid ester, 2,3-dihydroxypropyl (meth) acrylate, 2-hydroxyethyl vinyl ether;
Hexasaccharides such as glucose, mannose, galactose, glucosamine, mannosamine, galactosamine, pentasaccharides such as arabinose, xylose, ribose, maltose, lactose, trehalose, cellobiose, isomaltose, gentiobiose, melibiose, laminaribiose, chitobiose, xylobiose Disaccharides such as mannobiose and sophorose, other oligosaccharides such as maltotriose, isomaltotriose, maltotetraose, maltopentaose, mannotriose and manninotriose, polysaccharides such as cellulose and modified cellulose A monomer having a structure as derived and having a glycosyl group, such as a monomer such as glucosylethyl methacrylate;
Monomers having a polyvinyl alcohol structure:

  Among these, an amide group-containing monomer, a monomer having a heterocyclic ring, a monomer containing a hydroxyl group, and a monomer having a polyvinyl alcohol structure are particularly preferable because of high dispersion stability when used as a dispersant, and particularly an alkyl group. N-alkyl (meth) acrylamide having 1 to 6 carbon atoms, N-2-hydroxyethyl (meth) acrylamide, N-vinylpyrrolidone, 2-hydroxyethyl (meth) acrylate, and a monomer having a polyvinyl alcohol structure Particularly preferred.

  These other monomers X may be used individually by 1 type, and may use 2 or more types together.

  In addition, the copolymer (a) according to the present invention is produced by, for example, performing radical polymerization described later using each monomer in a predetermined ratio, and has a polyvinyl alcohol structure among the monomers described above. Regarding the monomer, it is possible to carry out copolymerization with a monomer containing an oxyalkylene chain in the state of vinyl acetate and, if necessary, other monomers, and then saponify to introduce the polyvinyl acetate part as polyvinyl alcohol. it can.

<Composition of copolymer (a)>
In the copolymer (a) according to the present invention, the content of the structural unit derived from the monomer containing the oxyalkylene chain may be 15% by weight or more with respect to the entire copolymer, and the composition thereof is particularly limited. Although it is not a thing, it is preferable that content of the structural unit derived from an anionic monomer is 10 weight% or less with respect to the whole copolymer. Among them, the structural unit derived from the anionic monomer is preferably 0.001% by weight or more and 10% by weight or less, and particularly preferably 0.01% by weight or more and 10% by weight or less of the entire copolymer. . When the content of the structural unit derived from the anionic monomer exceeds 10% by weight of the entire copolymer, the gloss of the printed matter on the photographic paper decreases, and when the content of the structural unit derived from the anionic monomer is too small, the dispersion stability And fixability to paper will be reduced.

  In addition, a structural unit derived from a hydrophobic monomer and a structural unit derived from a monomer containing an oxyalkylene chain, and a structural unit derived from other monomer X used as necessary, in the copolymer (a) according to the present invention. The content of is not particularly limited as long as the content of the structural unit derived from the monomer containing the oxyalkylene chain is 15% by weight or more based on the entire copolymer, but the amount is as follows. Is preferred.

  That is, the structural unit derived from the hydrophobic monomer is preferably 5% by weight or more and 70% by weight or less of the entire copolymer. If the content of the structural unit derived from the hydrophobic monomer is less than this lower limit, the copolymer (a) is difficult to adsorb to the pigment, the free copolymer (a) increases and the viscosity of the pigment ink increases. If the amount is larger than the upper limit, the water solubility of the copolymer (a) is lowered and the pigment dispersibility is deteriorated. The more preferable content of the structural unit derived from the hydrophobic monomer is 10% by weight or more and 60% by weight or less of the entire copolymer.

  The copolymer (a) according to the present invention is characterized in that the content of the structural unit derived from a monomer containing an oxyalkylene chain is 15% by weight or more based on the entire copolymer. The content of the structural unit derived from a monomer containing an alkylene chain is particularly preferably 20% by weight or more and 90% by weight or less of the entire copolymer. If the content of the structural unit derived from the monomer containing the oxyalkylene chain is less than this lower limit, the gloss of the printed matter on the photographic paper is lowered, and if it exceeds this upper limit, the fixability to the paper is lowered. . A more preferable content of the structural unit derived from the monomer containing the oxyalkylene chain of the copolymer (a) is 30% by weight or more and 80% by weight or less of the entire copolymer.

  Moreover, it is preferable that the structural unit derived from the other monomer X introduce | transduced as needed is 30 weight% or less of the whole copolymer. By introducing other structural units derived from the monomer X, effects such as improved dispersion stability and ejection properties may be obtained. However, if the amount introduced is larger than this upper limit, the effect of the present invention is reduced. Resulting in. When copolymer (a) contains the structural unit derived from the other monomer X, the more preferable content is 0.1 to 20 weight% of the whole copolymer.

<Structure of copolymer (a)>
The structure of the copolymer (a) according to the present invention may be any of a random copolymer, a diblock copolymer, a triblock or more multiblock copolymer, a gradient copolymer, a graft copolymer, a star copolymer, etc. preferable.

<Molecular weight>
The number average molecular weight (Mn) of the (co) polymer (a) used in the present invention is preferably 150,000 or less, more preferably 100,000 or less, and particularly preferably 1,000 or more and 50,000 or less. If the molecular weight is larger than this range, the viscosity of the pigment ink is increased and the discharge property is lowered. If the molecular weight is smaller, the (co) polymer (a) is peeled off from the pigment and the dispersibility is lowered. There is a case.

<Water-soluble and water-dispersible>
The (co) polymer (a) according to the present invention is preferably a water-soluble or water-dispersible polymer, and more preferably a water-soluble polymer from the viewpoint of pigment dispersibility.

  As used herein, the term “water-soluble polymer” refers to a 2% by weight aqueous solution of the polymer at 25 ° C. in a state where 100 mol% of ionic groups present in the polymer are neutralized. Immediately after the preparation of the aqueous solution, the aqueous solution has a transparent appearance and no precipitation is observed. The term “water-dispersible polymer” as used herein refers to a 2% by weight aqueous dispersion of the polymer at 25 ° C. in a state in which 100 mol% of ionic groups present in the polymer is neutralized. , Which does not cause precipitation immediately after preparation of the dispersion.

The above-mentioned “ionic group” refers to a group that can dissociate into ions in water, and examples thereof include an amino group, a carboxyl group, a sulfonic acid group, and salts thereof. The above-mentioned "in a state where 100 mol% of the ionic groups present in the polymer is neutralized" means a state where 100 mol% of the ionic groups contained in the polymer is converted into a salt by the neutralizing agent. Point to. As a procedure for confirming that the polymer is contained in the above definition range, for example, the ratio of the ionic groups in the polymer that are neutralized to form a salt (degree of neutralization of the ionic groups) is measured. The degree of neutralization of the ionic group is adjusted to 100 mol%, and this is dissolved or dispersed in water at 25 ° C. and 2 wt% concentration, and the appearance is visually observed. The degree of neutralization of the ionic group is determined by measuring the composition ratio of the ionic group with respect to the whole polymer by, for example, ¹ H-NMR, and the counter ion of the polymer forming the salt, for example, the carboxyl group forms a salt with Na. , Measure Na ⁺ charge, and divide the amount that is actually Na ⁺ salt by the amount of charge that is calculated from the composition ratio assuming that it is all Na ⁺ salt. Can be sought. As a result of the measurement, when the neutralization degree is less than 100%, the neutralization degree is adjusted by adding an alkali. As another method, from the synthesis of the polymer to the preparation of the ink, it is assumed that the addition of alkali neutralizes the ionic groups of the remaining monomers without polymerizing with the ionic groups in the polymer at the same rate. The degree of neutralization of the ionic groups in the polymer can also be estimated by dividing the number of moles of alkali added in the series of steps by the number of moles of the entire ionic groups of the charged monomer at the time of polymer synthesis.

  In the present invention, such “water-soluble polymer” and “water-dispersible polymer” are collectively referred to as “aqueous polymer”.

  As the (co) polymer (a), the solubility of the polymer in water at 25 ° C. is 2 even in a state where 50 mol% of the ionic groups present in the polymer are neutralized. What is more than weight% is more preferable. In addition, even when 50 mol% of ionic groups present in the polymer are neutralized, in a 2 wt% aqueous dispersion of the polymer at 25 ° C., no precipitation occurs immediately after preparation of the dispersion. Is more preferable.

  As the (co) polymer (a), a polymer whose solubility in water at 25 ° C. is 2% by weight or an aqueous dispersion of the polymer having a concentration of 2% by weight at 25 ° C. Those that do not cause precipitation immediately after are particularly preferred.

  When such a water-soluble or water-dispersible, preferably water-soluble (co) polymer (a) is used as a polymer dispersant for a pigment ink which is an aqueous pigment dispersion, excellent pigment dispersibility can be obtained. In addition, the effect of obtaining a print image excellent in the dischargeability of ink from the discharge nozzle, scratch resistance, print density, and glossiness is also exhibited.

<Synthesis Method of (Co) polymer (a)>
The method for synthesizing the (co) polymer (a) is not particularly limited. For example, a known polymerization method such as radical polymerization, ionic polymerization, polyaddition, polycondensation can be selected, and the (co) polymer (a) Derivatives or modified products of the (co) polymer (a) synthesized by these known methods may be used. Of these, the (co) polymer (a) synthesized using a radical polymerization method is preferred because the synthesis method is simple.

  The radical polymerization reaction can be performed without a solvent or in the presence of a solvent, but the polymerization reaction is preferably performed in the presence of a solvent.

  As a polymerization reaction solvent, ethers such as diethyl ether, tetrahydrofuran, diphenyl ether, anisole and dimethoxybenzene; amides such as N, N-dimethylformamide and N, N-dimethylacetamide; acetonitrile, propionitrile, benzonitrile and the like Nitriles; Carbonyl compounds such as acetone, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, butyl acetate, ethylene carbonate, and propylene carbonate; alcohols such as methanol, ethanol, propanol, isopropanol, n-butyl alcohol, t-butyl alcohol, and isoamyl alcohol Aromatic hydrocarbons such as benzene, toluene, xylene; chlorobenzene, methylene chloride, chloroform, chlorobenzene, carbon tetrachloride And halogenated hydrocarbons. Among these, preferred aqueous solvents as a polymerization reaction solvent.

  The aqueous solvent refers to a solvent obtained by mixing 100% water or water and a polar organic solvent at an arbitrary ratio. The polar organic solvent used here is not particularly limited as long as it can be mixed with water at an arbitrary ratio, and specific examples thereof include methanol, ethanol, isopropanol, acetonitrile, acetone, dimethylformamide, dimethyl sulfoxide, and tetrahydrofuran. Of these, methyl alcohol, ethyl alcohol, and isopropyl alcohol are particularly preferable.

  These solvents may be a single solvent composed of only one kind or a mixed solvent composed of two or more kinds.

A known radical polymerization initiator can be used for the radical polymerization reaction in the synthesis of the (co) polymer (a).
As the polymerization initiator, either a water-soluble polymerization initiator or an oil-soluble polymerization initiator can be used.

  Examples of the water-soluble polymerization initiator include 2,2′-azobis (2-amidinopropane) dihydrochloride, 4,4′-azobis (4-cyanovaleric acid), 2,2′-azobis [2- (2-Imidazolin-2-yl) propane] dihydrochloride, 2,2′-azobis [2- (2-imidazolin-2-yl) propane] disulfate dihydrate, 2,2′-azobis [ N- (2-carboxyethyl) -2-methylpropionamide], 2,2′-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl) propane} dihydrochloride, 2, 2′-azobis (1-imino-1-pyrrolidino-2-methylpropane) dihydrochloride, 2,2′-azobis {2-methyl-N- [2- (1-hydroxybutyl)] propionamide}, 2 , 2'-azobis [2 (5-methyl-imidazolin-2-yl) propane] dihydrochloride, 2,2′-azobis [2- (3,4,5,6, -tetrahydropyrimidin-2-yl) propane] dihydrochloride, etc. Azo compound-based initiators; oxidizing agents such as potassium persulfate, sodium persulfate, ammonium persulfate, hydrogen peroxide alone; or these oxidizing agents and sodium sulfite, sodium hyposulfite, ferrous sulfate, ferrous nitrate, Redox initiators combined with water-soluble reducing agents such as sodium formaldehyde sulfoxylate and thiourea can be mentioned.

  These may be used alone or in combination of two or more.

  Examples of oil-soluble polymerization initiators include 2,2′-azobisisobutyronitrile, 2,2′-azobis (2-methylbutyronitrile), 1,1′-azobiscyclohexane 1-carbonitrile, , 2′-azobis-4-methoxy-2,4-dimethylvaleronitrile, 2,2′-azobis-2,4-dimethylvaleronitrile, dimethyl-2,2′-azobis (2-methylpropionate), Azo compound-based initiators such as 1,1′-azobis (1-acetoxy-1-phenylethane), 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile); acetylcyclohexylsulfonyl peroxide; Isobutyryl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, 2,4-dicarbonate Lobenzoyl peroxide, t-butylperoxypivalate, 3,5,5-trimethylhexanonyl peroxide, octanoyl peroxide, decanoyl peroxide, lauroyl peroxide, stearoyl peroxide, propionitrile peroxide, saxi Nick acid peroxide, acetyl peroxide, t-butylperoxy-2-ethylhexanoate, benzoyl peroxide, parachlorobenzoyl peroxide, t-butylperoxyisobutyrate, t-butylperoxymaleic acid, t-butyl peroxylaurate, cyclohexanone peroxide, t-butyl peroxyisopropyl carbonate, 2,5-dimethyl-2,5-dibenzoylperoxyhexane, -Butyl peroxyacetate, t-butyl peroxybenzoate, diisobutyl diperoxyphthalate, methyl ethyl ketone peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, t-butyl cumi Ruperoxide, t-butyl hydroperoxide, di-t-butyl peroxide, diisopropylbenzene hydroperoxide, paramentane hydroperoxide, pinane hydroperoxide, 2,5-dimethylhexane-2,5-dihydroperoxide and cumene Peroxide polymerization initiators such as peroxides; hydroperoxides (tret-butylhydroxyperoxide, cumenehydroxyperoxides, etc.), dialkyl peroxides (lauroyl peroxide, etc.) ) And oil-soluble peroxides such as diacyl peroxide (benzoyl peroxide, etc.), tertiary amines (triethylamine, tributylamine, etc.), naphthenates, mercaptans (mercaptoethanol, lauryl mercaptan, etc.), organometallic compounds (triethyl) And oil-soluble redox polymerization initiators used in combination with oil-soluble reducing agents such as aluminum, triethylboron, and diethylzinc.

  These may be used alone or in combination of two or more.

  In the radical polymerization reaction, in addition to the above polymerization initiator, a known one such as a chain transfer agent, a chain terminator, or a polymerization accelerator is added and used in order to adjust the obtained (co) polymer to a preferred molecular weight. be able to.

When carrying out the polymerization reaction, the raw material monomer (this monomer is a monomer containing an oxyalkylene chain or a mixture of a monomer containing an oxyalkylene chain and the above-mentioned other monomers), a polymerization reaction solvent, radical initiation The order of addition of the agents and the like is arbitrary, and examples include a method in which a monomer, a polymerization reaction solvent, and a radical polymerization initiator are charged all at once in a reaction vessel and then the temperature is increased to perform a polymerization reaction. In this case, the monomer or radical polymerization initiator may be added as it is or in a solution. As another method, after a polymerizable monomer and a polymerization reaction solvent are charged into a reaction vessel and the temperature is raised, a monomer solution containing a radical polymerization initiator, a polymerization reaction solvent, or a mixture thereof is continuously added. Or a method in which a polymerization reaction is carried out by adding in portions.
Among these, from the viewpoint of simplicity of operation, a method in which the polymerization reaction is performed by raising the temperature after charging the raw materials all at once is preferable.

  The amount of the polymerization reaction solvent is not particularly limited, but is usually 1 part by weight or more, usually 2000 parts by weight or less, preferably 1000 parts by weight or less with respect to 100 parts by weight of the monomer.

  The amount of the polymerization initiator used varies depending on the type of the polymerization initiator used and is not particularly limited, but is usually 0.1 parts by weight or more and 15 parts by weight or less with respect to 100 parts by weight of the monomer.

  The polymerization temperature is not particularly limited, but is usually 0 ° C or higher, preferably 20 ° C or higher, and the upper limit is usually 200 ° C or lower, preferably 150 ° C or lower.

  The (co) polymer obtained by the polymerization is not particularly problematic if it is used as it is, but it is preferable to purify it according to a conventional method and use it for the next pigment dispersion step. As a purification method, the (co) polymer is insoluble, the (co) polymer solution is dropped into a solvent in which the monomer and the polymerization initiator are soluble, the (co) polymer is precipitated, and reprecipitation purification is repeated. The (co) polymer solution is insoluble in the (co) polymer and the monomer and polymerization initiator are soluble, and the fractionated precipitate is purified by repeated precipitation, filtration, and distillation under reduced pressure. After removing unreacted monomer and reaction solvent by distillation, etc., low-molecular impurities and low-molecular weight oligomer components are removed using a method of replacing the solvent with water and / or an aqueous solvent, and using an ultrafiltration membrane or a dialysis membrane. The method of doing is mentioned.

{Pigment}
The pigment used in the present invention may be appropriately selected from those commonly used in each application, and is not particularly limited. Examples of typical pigments include calcium carbonate, kaolin clay, talc, bentonite, and mica. Extender pigments; metal oxide pigments such as titanium oxide, zinc oxide, goethite, magnetite, chromium oxide; titanium yellow, titanium buff, antimony yellow, vanadium tin yellow, cobalt green, cobalt chrome green, manganese green Composite oxide pigments such as cobalt blue, cerulean blue, manganese blue, tungsten blue, Egyptian blue and cobalt black; sulfide pigments such as lithobon, cadmium red yellow and cadmium red; Phosphate pigments such as violet, cobalt violet, lithium cobalt phosphate, sodium cobalt phosphate, potassium potassium phosphate, cobalt ammonium phosphate, nickel phosphate, copper phosphate; yellow lead, molybdate orange Chromate pigments; metal complex pigments such as ultramarine and Prussian blue; metal powder pigments such as aluminum paste, bronze powder, zinc powder, stainless steel flakes, nickel flakes; carbon black, bismuth oxychloride Inorganic pigments such as pearlescent pigments and nacreous conductive pigments such as basic carbonates, titanium dioxide, coated mica, ITO (indium tin oxide), ATO (antimony tin oxide), quinacridone pigments, Quinacridone quinone pigments, dioxazine pigments, phthalos Nine pigments, anthrapyrimidine pigments, ansanthrone pigments, indanthrone pigments, flavanthrone pigments, perylene pigments, diketopyrrolopyrrole pigments, perinone pigments, quinophthalone pigments, anthraquinone pigments, thioindigo pigments Examples thereof include organic pigments such as pigments, metal complex pigments, azomethine pigments, and azo pigments.

  Specific examples of the pigment include pigments having the following pigment numbers and known carbon blacks generally used in the color material field. Note that terms such as “CI Pigment Red 2” mentioned below mean a color index (CI).

  Red colorant: C.I. I. Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 12, 14, 15, 16, 17, 21, 22, 23, 31, 32, 37, 38, 41, 47, 48, 48: 1, 48: 2, 48: 3, 48: 4, 49, 49: 1, 49: 2, 50: 1, 52: 1, 52: 2, 53, 53: 1, 53: 2, 53: 3, 54, 57, 57: 1, 57: 2, 58, 58: 4, 60, 63, 63: 1, 63: 2, 64, 64: 1, 68, 69, 81, 81: 1, 81: 2, 81: 3, 81: 4, 83, 88, 90: 1, 101, 101: 1, 104, 108, 108: 1, 109, 112, 113, 114, 122, 123, 144, 146, 147, 149, 151, 166, 168, 169, 170, 172, 173, 174, 175, 176, 177, 78, 179, 181, 184, 185, 187, 188, 190, 193, 194, 200, 202, 206, 207, 208, 209, 210, 214, 216, 220, 221, 224, 230, 231, 232, 233, 235, 236, 237, 238, 239, 242, 243, 245, 247, 249, 250, 251, 253, 254, 255, 256, 257, 258, 259, 260, 262, 263, 264, 265, 266, 267, 268, 269, 270, 271, 272, 273, 274, 275, 276;

  Blue colorant: C.I. I. Pigment Blue 1, 1: 2, 9, 14, 15, 15: 1, 15: 2, 15: 3, 15: 4, 15: 6, 16, 17, 19, 25, 27, 28, 29, 33, 35, 36, 56, 56: 1, 60, 61, 61: 1, 62, 63, 66, 67, 68, 71, 72, 73, 74, 75, 76, 78, 79;

  Green colorant: C.I. I. Pigment Green 1, 2, 4, 7, 8, 10, 13, 14, 15, 17, 18, 19, 26, 36, 45, 48, 50, 51, 54, 55;

  Yellow colorant: C.I. I. Pigment Yellow 1, 1: 1, 2, 3, 4, 5, 6, 9, 10, 12, 13, 14, 16, 17, 23, 24, 31, 32, 34, 35, 35: 1, 36, 36: 1, 37, 37: 1, 40, 41, 42, 43, 48, 53, 55, 61, 62, 62: 1, 63, 65, 73, 74, 75, 81, 83, 87, 93, 94, 95, 97, 100, 101, 104, 105, 108, 109, 110, 111, 116, 119, 120, 126, 127, 127: 1, 128, 129, 133, 134, 136, 138, 139, 142, 147, 148, 150, 151, 153, 154, 155, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 172, 173 174, 175, 176, 180, 181, 182, 183, 184, 185, 188, 189, 190, 191, 191: 1, 192, 193, 194, 195, 196, 197, 198, 199, 200, 202, 203, 204, 205, 206, 207, 208;

  Orange colorant: C.I. I. Pigment Orange 1, 2, 5, 13, 16, 17, 19, 20, 21, 22, 23, 24, 34, 36, 38, 39, 43, 46, 48, 49, 61, 62, 64, 65, 67, 68, 69, 70, 71, 72, 73, 74, 75, 77, 78, 79;

  Violet colorant: C.I. I. Pigment Violet 1, 1: 1, 2, 2: 2, 3, 3: 1, 3: 3, 5, 5: 1, 14, 15, 16, 19, 23, 25, 27, 29, 31, 32, 37, 39, 42, 44, 47, 49, 50

  Brown colorant: C.I. I. Pigment Brown 1, 6, 11, 22, 23, 24, 25, 27, 29, 30, 31, 33, 34, 35, 37, 39, 40, 41, 42, 43, 44, 45

  Black colorant: C.I. I. Pigment Black 1, 31, 32

  Among the above pigments, the red pigment is preferably a quinacridone pigment, a xanthene pigment, a perylene pigment, an anthanthrone pigment, or a monoazo pigment. I. Pigment Red-5, -7, -12, -112, -81, -122, -123, 146, -147, -168, -173, -202, -206, -207, -209, etc. Examples include solid solution pigments composed of two or more types of pigments. Of these, quinacridone pigments are more preferable from the standpoint of pigment stability and hue.

  Of the above-mentioned pigments, as the yellow pigment, monoazo pigments and disazo pigments are preferable because the color development as printed matter is better than other pigments. Among them, C.I. I. Pigment-1, -3, -16, -17, -74, -120, -128, -151, -155, and -175 are particularly preferred from the viewpoint of the color. I. CI Pigment Yellow-74 and -155 are non-halogen compounds, and are particularly preferable from the viewpoint of having a small influence on the environment and hue.

  Among the above-mentioned pigments, a copper phthalocyanine pigment is preferable as a blue pigment, since color development as a printed material is better than other pigments. Among them, C.I. I. Pigment Blue-15: 3 is preferable from the viewpoints of stability and hue. Further, as described above, the phthalocyanine pigment is advantageous in that the bronze phenomenon prevention effect according to the present invention becomes remarkable because the bronze phenomenon easily appears.

  Further, as the carbon black used in the present invention, various carbon blacks such as acetylene black, channel black and furnace black can be used. Among these, channel black or furnace black is preferable, and furnace black is particularly preferable.

The DBP oil absorption amount of the carbon black is preferably 40 ml / 100 g or more, more preferably 50 ml / 100 g or more, and particularly preferably 60 ml / 100 g or more from the viewpoint of printing density. The upper limit is preferably 250 ml / 100 g or less, particularly preferably 200 ml / 100 g or less.
However, from the viewpoint of glossiness with photographic paper, a range of 30 to 100 ml / 100 g is preferable, and a range of 30 to 70 ml / 100 g is particularly preferable.

The volatile content of carbon black is preferably 8% by weight or less, and particularly preferably 4% by weight or less.
From the viewpoint of the storage stability of the recording liquid, the pH is preferably 3 or more, more preferably 6 or more, and the upper limit is preferably 11 or less, particularly preferably 9 or less.
The BET specific surface area is usually 100 m ² / g or more, preferably 150 m ² / g or more, and the upper limit is preferably 700 m ² / g or less, particularly preferably 600 m ² / g or less.

  Here, the DBP oil absorption is a value measured by the method of JISK6221A, the volatile content is a value measured by the method of JISK6221, pH is a value measured by a glass electrode meter with a mixture of carbon black and distilled water, and the BET specific surface area is that of JISK6217. It is the value measured by the method.

  From the viewpoint of safety, it is preferable to use carbon black in which the polycyclic aromatic component is reduced by baking at 600 to 1500 ° C. or washing with water, warm water, a solvent, or the like. In particular, baking at a high temperature is more preferable because the functional group on the surface of the carbon black is removed, whereby the dispersant is more efficiently adsorbed more firmly on the surface of the carbon black.

  Specific examples of the carbon black include products shown in the following (1) to (4).

(1) # 2700B, # 2650, # 2650B, # 2600, # 2600B, 2450B, 2400B, # 2350, # 2300, # 2300B, # 2200B, # 1000, # 1000B, # 990, # 990B, # 980, # 980B, # 970, # 960, # 960B, # 950, # 950B, # 900, # 900B, # 850, # 850B, MCF88, MCF88B, MA600, MA600B, # 750B, # 650B, # 52, # 52B, # 50, # 47, # 47B, # 45, # 45B, # 45L, # 44, # 44B, # 40, # 40B, # 33, # 33B, # 32, # 32B, # 30, # 30B, # 25, # 25B, # 20, # 20B, # 10, # 10B, # 5, # 5B, CF9, CF9B, # 95, # 260, MA77 MA77B, MA7, MA7B, MA8, MA8B, MA11, MA11B, MA100, MA100B, MA100R, MA100RB, MA100S, MA230, MA220, MA200RB, MA14, # 3030B, # 3040B, # 3050B, # 3230B, # 3350B (and above, Mitsubishi Chemical company product).

(2) Monarch 1400, Black Pearls 1400, Monarch 1300, Black Pearls 1300, Monarch 1100, Black Pearls 1100, Monarch 1000, Black Pearls 1000, Monarch 900, Black Pearl 900 800, Monarch 700, Black Pearls 700, Black Pearls 2000, Vulcan XC72R, Vulcan XC72, Vulcan PA90, Vulcan 9A32, Mogul L, Black Pearls L, Regal 660R, Regal 660R ck Pearls 570, Black Pearls 520, Regal 400R, Regal 400, Regal 330R, Regal 330, Regal 300R, Black Pearls 490, Black Pearls 480, Black Pearls 470, Black Pearls 470, Black Pearls 470, Black Pearls 470
450, Black Pearls 430, Black Pearls 420, Black Pearls 410, Regal 350R, Regal 350R, Regal 250R, Regal 250, Regal 99R, Regal 99I, Elftex Pellets 115, Elftex 8t 80, Elftex 8t , Black Pearls 170, Black Pearls 160, Black Pearls
130, Monarch 120, Black Pearls 120 (above, Cabot product).

(3) Color Black FW1, Color Black FW2, Color
Black FW2V, Color Black FW18, Color Black
FW200, Special Black 4, Special Black 4A, Special Black 5, Special black 6, Color black S160, Color Black S170, Printex U, Printex 150, Printex V, PrintP. 80, Printex 75, Printex 55, Printex 45, Printex 40, Printex P, Printex 60, Printex
XE, Printex L6, Printex L, Printex 300, Printex 30, Printex 3, Printex 35, Printex 25, Printex 200, Printex A, Printex G, Special Black 550S Degussa product).

(4) Raven 7000, Raven 5750, Raven 5250, Raven 5000 ULTRA, Raven 3500, Raven 2000, Raven
1500, Raven 1250, Raven 1250, Raven 1200, Raven 1170, Raven 1060 ULTRA, Raven 1040, Raven 1035, Raven 1020, Raven 1000, Raven 890H, Raven 890H, Raven 890, Raven 890H, Raven 890H, Raven 890H, Raven 890H 500, Raven 450, Raven 430, Raven 420, Raven 410, CONDUCTEX 975 ULTRA, CONDUCTEX SC ULTRA, Raven H2O, Raven C ULTRA (above, a product of Columbia).

  As the pigment according to the present invention, one of the above pigments may be used alone, or two or more of them may be used in combination. It can also be used in combination with other colorants such as dyes.

The size of the primary particles of these pigments may be arbitrarily set according to the purpose, but is usually 10 nm or more and 800 nm or less, preferably 500 nm or less, more preferably 300 nm or less, and further preferably 200 nm. Hereinafter, it is particularly preferably 100 nm or less.
Here, the primary particle diameter of the pigment is an arithmetic average diameter (number average) measured by an electron microscope.

  In addition, as the above-mentioned pigment, those that are not chemically modified and that do not contain impurities other than the pigment, such as a crystallization inhibitor for promoting the reduction in the particle size of the pigment, It is preferable because it does not inhibit the adsorption of the polymer (a) to the pigment. However, in order to give the pigment self-dispersibility, a pigment having self-dispersibility which has been subjected to known chemical modification in advance can also be used. That is, the pigment used in the pigment ink of the present invention may be an untreated pigment or a pigment whose surface is chemically modified as described above, and any pigment can be used.

{Aqueous medium}
Examples of the aqueous medium used in the pigment ink of the present invention include water and / or a water-soluble organic solvent.
Although it will not specifically limit if it is generally used for this use as a water-soluble organic solvent, Specifically, it is a thing with a vapor pressure smaller than water, and the following are mentioned.

Ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, 1,3-propylene glycol, isopropylene glycol, polypropylene glycol, pentamethylene glycol, trimethylene glycol, butylene Glycol, isobutylene glycol, thiodiglycol, 1,2-hexanediol, 1,6-hexanediol, 2-ethyl-1,3-hexanediol, 1,2-pentanediol, 1,5-pentanediol, 2- Methyl-2,4-pentanediol, 1,3-propanediol, 1,4-butanediol, 1,7-heptanediol, 1,8-octanediol, 2 Butene-1,4-diol, polyhydric alcohols such as glycerin;
Ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol mono-t-butyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monophenyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl Ether, diethylene glycol monoethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, diethylene glycol mono-t-butyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, Propylene glycol monoethyl ether, propylene glycol monobutyl ether, propylene glycol mono-t-butyl ether, propylene glycol monopropyl ether, propylene glycol monoisopropyl ether, propylene glycol monophenyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, Polyhydric alcohol ethers such as dipropylene glycol monobutyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monoisopropyl ether;
Ketones such as acetonylacetone;
Esters such as γ-butyrolactone, diacetin, triethyl phosphate;
Lower alkoxy alcohols such as 2-methoxyethanol and 2-ethoxyethanol;
Amines such as ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, triethylenetetramine, tetraethylenepentamine, pentamethyldiethylenetriamine;
Amides such as formamide, N, N-dimethylformamide, N-methylformamide, N, N-dimethylacetamide;
2-pyrrolidone, N-ethylpyrrolidone, N-methyl-2-pyrrolidone, cyclohexylpyrrolidone, morpholine, N-ethylmorpholine, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, imidazole, methylimidazole, hydroxyimidazole , Heterocycles such as dimethylaminopyridine, 1,3-propane sultone, hydroxyethylpiperazine, piperazine;
Sulfoxides such as dimethyl sulfoxide;
Sulfones such as sulfolane.

  These may be used alone or in combination of two or more.

  The aqueous medium used in the present invention is preferably water or a mixture of water and the above-mentioned water-soluble organic solvent.

{Production method of pigment ink}
The method for producing the pigment ink of the present invention is not particularly limited, but an aqueous pigment dispersion is prepared by mixing and dispersing in advance a pigment, an aqueous medium and a (co) polymer (a) as a dispersant, A method of preparing a pigment ink by further adding an aqueous medium or various additives added as necessary to the aqueous pigment dispersion is preferable.

<Method for preparing aqueous pigment dispersion>
In preparing the aqueous pigment dispersion, the mixing method and the order of addition of the pigment, the aqueous medium, the (co) polymer (a) and the like are arbitrary. For example, an untreated pigment, a pigment whose surface is chemically modified as described above, a pigment treated with a known dispersant such as a surfactant, or a treated pigment such as a pigment adsorbed with a dye; Examples thereof include a method in which the polymer (a) is contacted with an aqueous medium, followed by mixing and dispersion treatment. Alternatively, the treated pigment as described above may be dispersed in an aqueous medium and then contacted with the (co) polymer (a) to form an aqueous pigment dispersion.

  Among them, a method in which an untreated pigment is brought into contact with the (co) polymer (a) and an aqueous medium, and mixed and dispersed is preferable because the effect of the present invention becomes remarkable.

As the disperser used for the dispersion treatment, various dispersers that are generally used for pigment dispersion can be used.
The disperser is not particularly limited, and a paint shaker, ball mill, sand mill, attritor, pearl mill, coball mill, homomixer, homogenizer, wet jet mill, ultrasonic homogenizer, and the like can be used. Glass beads, zirconia beads, alumina beads, magnetic beads, and styrene beads can be used for those using media as a disperser. Among these, a particularly preferable dispersion treatment method is a method of carrying out dispersion treatment with a mill using beads as a medium and then dispersing with an ultrasonic homogenizer.

  A method for obtaining an aqueous pigment dispersion having a preferable pigment dispersion particle diameter is not particularly limited, but the dispersion medium size of the disperser is reduced, the filling rate of the dispersion medium is increased, For example, a method for increasing the pigment concentration, a method for increasing the treatment time, or a method for appropriately combining these methods.

  In addition, when an undesirable phenomenon such as thickening or foaming of the dispersion occurs due to heat generation during the dispersion treatment, it is desirable to perform the dispersion treatment while cooling.

  A part of the (co) polymer (a) dispersed and added to the pigment exists as a free polymer not adsorbed on the pigment. Aqueous pigment dispersions can be used as they are in the preparation of pigment inks, but only in cases where excess free polymer may cause the dispersion to thicken or the pigment ink ejection properties and glossiness to deteriorate. This free polymer may be removed to some extent by methods such as external filtration and microfiltration.

The upper limit of the average dispersed particle size of the pigment in the aqueous pigment dispersion according to the present invention is usually 500 nm or less, preferably 200 nm or less. Further, the lower limit of the average dispersed particle size of the pigment is usually 10 nm or more.
Examples of the method for measuring the average dispersed particle size of the pigment include a method of measuring using an electron microscope such as SEM or TEM, or a method of measuring using a commercially available dynamic light scattering measuring device.

<Aqueous pigment dispersion composition>
The pigment concentration in the aqueous pigment dispersion according to the present invention is usually 30% by weight or less, preferably 20% by weight or less. Here, if the pigment concentration is too high, the pigment becomes poorly dispersed, the viscosity of the dispersion increases, the dispersion becomes gelled, and the dispersion cannot be used due to dispersion failure. If the pigment concentration is too low, there is a problem that it takes a lot of time and effort to concentrate at the time of ink production.

  In addition, the content of the (co) polymer (a) in the aqueous pigment dispersion for dispersing the pigment is preferably in the range of about 1 to 500 parts by weight with respect to 100 parts by weight of the pigment. More preferably, it is 10-200 weight part. If the amount of the (co) polymer (a) is too small, the pigment becomes unstable in dispersion in an aqueous medium and causes aggregation. On the other hand, the adsorption amount of the (co) polymer (a) with respect to the pigment is limited by the hydrophilic-hydrophobic balance of the polymer, the total surface area of the pigment particles, the affinity between the hydrophobic group and the pigment particle surface, and the like ( If the amount of the (co) polymer (a) is too large, it is not preferable because it causes thickening of the dispersion and dispersion instability.

  The aqueous pigment dispersion may contain components other than the above-mentioned aqueous medium, pigment, and (co) polymer (a) according to the present invention. Polymers exemplified as other additives that may be contained in the pigment ink, and other components may be contained.

<Preparation and composition of pigment ink>
The pigment ink of the present invention is prepared by adjusting the colorant concentration of the above-mentioned aqueous pigment dispersion as necessary, further adding various additives according to the use, and dispersing treatment as necessary.

  As the colorant, in addition to the pigment in the aqueous pigment dispersion described above, a self-dispersible pigment surface-treated for purposes such as toning, a pigment dispersed with a dye, a surfactant, a polymer dispersant, etc. Alternatively, a dye or the like may be additionally included.

The concentration of the total colorant in the pigment ink of the present invention is preferably 0.1% by weight or more, more preferably 0.5% by weight or more, and the upper limit is 20% by weight, based on the total amount of the pigment ink. Hereinafter, it is preferably 15% by weight or less, particularly preferably 10% by weight or less. If the colorant concentration is too high, the viscosity is increased and the discharge property is deteriorated. If the colorant concentration is too low, the print density is too low. On the other hand, the amount of the colorant added to the aqueous pigment dispersion is usually 100 parts by weight or less, preferably 75 parts by weight or less, more preferably 50 parts by weight or less with respect to 100 parts by weight of the pigment in the aqueous pigment dispersion. The amount is particularly preferably 25 parts by weight or less. If the additional amount of the colorant is too large, the effect of the present invention is reduced.
Therefore, the content of the pigment in the pigment ink of the present invention is 0.1% by weight or more, particularly 0.5% by weight or more, in order to sufficiently increase the discharge property and the print density while suppressing the thickening. It is preferably 20% by weight or less, more preferably 10% by weight or less.

  Further, the content of the (co) polymer (a) in the pigment ink of the present invention is the same as the content of the (co) polymer (a) in the aqueous pigment dispersion described above with respect to 100 parts by weight of the pigment. The amount is preferably in the range of about 1 to 500 parts by weight, more preferably 10 to 200 parts by weight.

The solvent used in the pigment ink of the present invention preferably contains water and a water-soluble organic solvent, and can further contain other components as desired.
The concentration of the water-soluble organic solvent in the pigment ink of the present invention may be appropriately selected and determined. Usually, it is preferably 1% by weight or more and 45% by weight or less, more preferably 40% by weight or less based on the pigment ink. Further, the water content in the pigment ink may be an amount that can appropriately set the concentration of the above-described colorant, water-soluble organic solvent, and optional additive components described below.
Here, examples of the water-soluble organic solvent include those exemplified as the aqueous medium used in the pigment ink of the present invention.

<Additives>
The pigment ink of the present invention may contain various additives other than the (co) polymer (a), the pigment, and the aqueous medium as required, as long as the effects of the present invention are not impaired.
Examples of such additives include pigment inks such as penetration enhancers, surface tension modifiers, hydrotropic agents, pH adjusters, chelating agents, preservatives, viscosity modifiers, moisturizers, antifungal agents, and rust inhibitors. Known additives can be used.

  The content of these additives in the pigment ink of the present invention is generally 30% by weight or less, particularly preferably 15% by weight or less, based on the total amount of the pigment ink.

  Examples of penetration enhancers include lower alcohols such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol and pentanol, carbitols such as ethylene glycol monobutyl ether and triethylene glycol monobutyl ether glycol ether, and surfactants 1 A seed | species or 2 or more types is mentioned.

  As the surfactant, any one or more of nonionic surfactants, anionic surfactants, cationic surfactants, amphoteric surfactants, polymer surfactants and the like can be used. Can be used. Of these, nonionic surfactants, anionic surfactants and polymer surfactants are preferred.

  Nonionic surfactants include, for example, polyoxyethylene alkyl ethers, polyoxyethylene alkyl aryl ethers, polyoxyethylene derivatives, oxyethylene / oxypropylene block copolymers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid Examples thereof include esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, polyoxyethylene fatty acid esters, polyoxyethylene alkylamines, acetylene glycols, and acetylene alcohols.

  Examples of the anionic surfactant include fatty acid salts, alkyl sulfate esters, alkyl benzene sulfonates, alkyl naphthalene sulfonates, alkyl sulfosuccinates, alkyl diphenyl ether sulfonates, alkyl phosphates, polyoxyethylene alkyl sulfates. Examples include ester salts, polyoxyethylene alkylaryl sulfate esters, alkane sulfonates, naphthalene sulfonate formalin condensates, polyoxyethylene alkyl phosphates, α-olefin sulfonates, and the like.

  Polymeric surfactants include polyacrylic acid, styrene / acrylic acid copolymer, styrene / acrylic acid / acrylic acid ester copolymer, styrene / maleic acid copolymer, styrene / maleic acid / acrylic acid ester copolymer, styrene / methacrylic acid. Examples include copolymers, styrene / methacrylic acid / acrylic acid ester copolymers, styrene / maleic acid half ester copolymers, styrene / styrene sulfonic acid copolymers, vinyl naphthalene / maleic acid copolymers, vinyl naphthalene / acrylic acid copolymers, and salts thereof.

  Examples of the cationic surfactant include, but are not limited to, tetraalkylammonium salts, alkylamine salts, benzalkonium salts, alkylpyridium salts, imidazolium salts, and the like.

  In addition, silicone surfactants such as polysiloxane oxyethylene adducts, fluorine surfactants such as perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, oxyethylene perfluoroalkyl ethers, rhamnolipids, lysolecithins, etc. Surfactants such as biosurfactants can also be used.

  The content of these surfactants may be appropriately selected and determined. Usually, by adding in the range of 0.001 wt% or more and 5 wt% or less with respect to the pigment ink, the quick drying property and the print quality of the printed matter can be further improved.

  Examples of the surface tension adjusting agent include one or more alcohols such as diethanolamine, triethanolamine, glycerin, and diethylene glycol, nonions, cations, anions, and amphoteric surfactants.

  As the hydrotropic agent, one or more of urea, alkylurea, ethyleneurea, propyleneurea, thiourea, guanidate, halogenated tetraalkylammonium and the like are preferable.

  As a humectant, 1 type (s) or 2 or more types, such as glycerol and diethylene glycol, can also be added as what also serves as a water-soluble organic solvent.

  Furthermore, a solid moisturizing agent (a water-soluble substance having a water retaining function and solid at 25 ° C.) can also be added. Preferred solid humectants include saccharides, sugar alcohols, hyaluronate, trimethylolpropane, 1,2,6-triol and the like. Examples of the saccharide include monosaccharides, disaccharides, oligosaccharides (including trisaccharides and tetrasaccharides), and polysaccharides. Specifically, glucose, fructose, ribose, xylose, arabinose, galactose, sorbit, maltose, and lactose. , Sucrose, trehalose and the like. Examples of sugar alcohols include maltitol, sorbitol, xylitol and the like, and these solid moisturizers may be used alone or in combination of two or more.

  Although it does not specifically limit as a chelating agent, 1 type (s) or 2 or more types, such as a sodium salt of ethylenediaminetetraacetic acid, a diammonium salt of ethylenediaminetetraacetic acid, are used. These are preferably used in the range of 0.005 wt% or more and 0.5 wt% or less with respect to the pigment ink.

  The antifungal agent is not particularly limited, but sodium dehydroacetate, dichlorophen, sorbic acid, sodium benzoate, p-hydroxybenzoate, 1,2-benzisothiazolin-3-one (product name: Proxel GXL (manufactured by Arch Chemicals) or the like is used. These are preferably contained in the range of 0.05% by weight or more and 1% by weight or less with respect to the pigment ink.

Further, in order to adjust the pH of the pigment ink and obtain the stability of the pigment ink, it is not particularly limited, but sodium hydroxide, potassium hydroxide, lithium hydroxide, nitric acid, ammonia, diethanolamine, triethanolamine, etc. PH adjusters and buffer solutions such as phosphoric acid can be used.
The pH of the pigment ink is usually in the neutral to alkaline range, and is preferably adjusted to about pH 6-11.

  Further, the pigment ink of the present invention may contain a resin other than the above-mentioned (co) polymer (a) as long as the effects of the present invention are not impaired. Specific examples of such resins include vinyl resins such as acrylic resins, styrene-acrylic resins, polyvinyl alcohol resins, vinyl acetate resins, polyester resins, polyamide resins, polyurethane resins, epoxy resins, and butadiene. Well-known resins such as resin, petroleum resin and fluorine resin can be used. Among these, water-soluble or water-dispersible resins are preferable. Of these, polyvinyl alcohol resins and acrylic resins are more preferable, and polyvinyl alcohol resins are particularly preferable. Among the polyvinyl alcohol resins, the following resins are more preferable.

  Preferred polyvinyl alcohol-based resins include those containing a constituent unit derived from vinyl alcohol represented by the following general formula (3) in the polymer (hereinafter sometimes referred to as “vinyl alcohol constituent unit”) and a hydrophobic group. (Hereinafter sometimes referred to as “polymer (I)”). In the polymer (I), only one type of vinyl alcohol structural unit represented by the following general formula (3) may be contained, or two or more types may be contained. Moreover, only 1 type of hydrophobic groups may be contained and 2 or more types may be contained.

(In formula (3), R ³ represents a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms)

Specific examples of R ³ in the general formula (3) include methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, t-butyl group, sec-butyl group, pentyl group, isopentyl group, neopentyl group. And alkyl groups such as a group, t-pentyl group, and hexyl group. Among these, a hydrogen atom or an alkyl group having a small number of carbon atoms is preferable, specifically, an alkyl group having 1 to 3 carbon atoms is preferable, and a hydrogen atom or a methyl group is particularly preferable.

  Examples of the vinyl alcohol structural unit represented by the general formula (3) include vinyl alcohol, α-methyl vinyl alcohol, α-ethyl vinyl alcohol, α-propyl vinyl alcohol, α-butyl vinyl alcohol, and α-hexyl vinyl alcohol. The structural unit derived from etc. is mentioned.

  On the other hand, examples of the hydrophobic group include aliphatic hydrophobic groups such as alkyl groups, alkenyl groups, and alkynyl groups, alicyclic hydrophobic groups such as cyclohexyl groups and isobornyl groups, and aromatic groups such as phenyl groups and naphthyl groups. System hydrophobic groups. These groups may be unsubstituted or may further have a substituent.

  In order to introduce the vinyl alcohol structural unit represented by the general formula (3) and the hydrophobic group into the polymer structure, a polymerizable monomer that induces a vinyl alcohol structural unit such as a vinyl ether monomer or a vinyl ester monomer and a hydrophobic group are introduced. After polymerizing with a polymerizable monomer having a functional group and introducing them into the polymer structure, the side chain portion of the vinyl ether monomer or vinyl ester monomer is modified by the above general formula (3 It may be converted into a vinyl alcohol structural unit represented by

  Examples of vinyl ether monomers that derive the vinyl alcohol structural unit represented by the general formula (3) include methyl vinyl ether, ethyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, t-butyl vinyl ether, isobutyl vinyl ether, cyclohexyl vinyl ether, Examples thereof include n-hexadecyl vinyl ether, 2-chloroethyl vinyl ether, phenyl vinyl ether, benzyl vinyl ether, and trimethylsilyl vinyl ether.

  Examples of the vinyl ester monomer for deriving the vinyl alcohol structural unit include, for example, vinyl acetate, vinyl propionate, vinyl laurate, vinyl stearate, vinyl pivalate, vinyl formate, vinyl caproate, vinyl caprate, myristine. Vinyl acetate, vinyl palmitate, vinyl 2-ethylhexanoate, vinyl cyclohexanecarboxylate, vinyl monochloroacetate, vinyl adipate, vinyl methacrylate, vinyl crotonate, vinyl sorbate, vinyl benzoate, vinyl cinnamate, these α -Substituent etc. are mentioned.

  Further, the vinyl alcohol structural unit and the hydrophobic group represented by the general formula (3) contained in the polymer (I) are a main chain and / or a side chain portion in the polymer structure by a modification reaction or a modification reaction. May be introduced.

  The polymer (I) only needs to contain a vinyl alcohol structural unit represented by the general formula (3) and a hydrophobic group, and is represented by an oxyalkylene group, a hydroxyl group, an amide group, a pyrrolidone group, an oxazoline group, and the like. Hydrophilic groups, carboxylic acid groups, sulfonic acid groups, acidic groups typified by phosphoric acid groups, amino groups, pyridinium groups, basic groups typified by imidazolium groups, and acidic groups and basic groups and their It may contain an ionic dissociation group which is a salt. Among them, the polymer (I) preferably contains an ionic dissociation group that is an acidic group, a basic group, or a salt thereof.

  Further, the hydrophobic group and the ionic dissociation group contained in the polymer (I) are preferably contained in the polymer structure as a monomer-derived constitutional unit. That is, the polymer (I) is a polymer containing the vinyl alcohol structural unit represented by the general formula (3), a structural unit derived from a monomer having a hydrophobic group, and a structural unit derived from a monomer having an ionic dissociation group. It is particularly preferred.

  The form of the polymer (I) is not particularly limited, such as a random copolymer, a diblock copolymer, a triblock or more multiblock copolymer, a gradient copolymer, a graft copolymer, a star copolymer, etc. Among them, a block copolymer is preferable.

  The number average molecular weight (Mn) of the polymer (I) is preferably 150,000 or less, more preferably 100,000 or less, particularly preferably 3000 or more and 60,000 or less. If the molecular weight is larger than this range, the viscosity of the pigment ink is increased, and the discharge property is lowered.

In the pigment ink of the present invention, the content of all the resins including the (co) polymer (a) and the polymer (I) is usually 0.05% by weight or more, preferably 0.25% by weight or more, more preferably The upper limit is usually 40% by weight or less, preferably 30% by weight or less, and more preferably 15% by weight or less. Moreover, as a use ratio of the (co) polymer (a) and other resins, the weight ratio of the (co) polymer (a) to the other resin is suitably in the range of 99: 1 to 1:99. The content of the (co) polymer (a) is specifically determined in the pigment ink in order to effectively exhibit the above-described improvement effect by the (co) polymer (a). It is preferably 5% by weight or more, more preferably 10% by weight or more, and particularly preferably 20% by weight or more of the total amount of all resins.
In particular, when the (co) polymer (a) and the polymer (I) are used in combination, the (co) polymer (a): the polymer (I) = 50 to 1: 1 to 5 (weight ratio). It is preferable to use together in the range.

Further, polymer fine particles may be added to the pigment ink of the present invention in order to further improve the fixability of the image on the recording medium and the abrasion resistance. The polymer fine particles are not particularly limited, but those having an ionic group on the surface and a particle diameter of 10 to 150 nm are preferable.
The amount of the polymer fine particles used may be appropriately selected and determined within a range that does not impair the effects of the present invention. % By weight, more preferably 10 to 50% by weight.

[Colorless ink]
The colorless ink of the present invention contains an aqueous polymer having a Tg (glass transition temperature) of 25 ° C. or higher (hereinafter simply referred to as “aqueous polymer”), preferably a water-soluble polymer. The colorless ink is ejected onto an image formed by an inkjet recording method using the above pigment ink, and the image is overcoated with an aqueous polymer, thereby improving the scratch resistance and image quality.

As used herein, “aqueous polymer” is a generic term for “water-soluble polymer” and “water-dispersible polymer”, and among these, “water-soluble polymer” is present in the polymer. In a state in which 100 mol% of the ionic group is neutralized, the appearance of the aqueous solution is transparent and no precipitation is observed immediately after preparation of the aqueous solution of the polymer at 25 ° C. with a concentration of 2% by weight. Point.
In addition, the “water-dispersible polymer” as used in the present specification refers to a water dispersion at a concentration of 2% by weight at 25 ° C. in a state where 100 mol% of ionic groups present in the polymer is neutralized. In the case of a liquid, the liquid does not cause precipitation immediately after preparation of the dispersion.

{Aqueous polymer}
The aqueous polymer contained in the colorless ink of the present invention is not particularly limited as long as it has a Tg of 25 ° C. or higher and can prepare a transparent or stable aqueous ink, and is composed of structural units derived from hydrophilic monomers described later. Even a homopolymer that is composed of a plurality of structural units derived from hydrophilic monomers included in the same classification, for example, a structural unit derived from a cationic monomer and a structural unit derived from a nonionic hydrophilic monomer Consists of copolymers, constituent units derived from anionic monomers, and copolymers composed of a plurality of hydrophilic monomers with different classifications such as copolymers composed of constituent units derived from nonionic hydrophilic monomers The copolymer may be a copolymer composed of one or more hydrophobic monomer-derived structural units and one or more hydrophilic monomer-derived structural units. It is preferably a polymer.

  When the aqueous polymer is a copolymer, the structure may be any of random copolymer, diblock copolymer, triblock or more multiblock copolymer, gradient copolymer, graft copolymer, star copolymer, etc. preferable.

The Tg of this aqueous polymer is 25 ° C. or higher, preferably 30 ° C. or higher, more preferably 40 ° C. or higher. When Tg is lower than 25 ° C., the scratch resistance of the printed material overcoated with the colorless ink may be lowered near room temperature, and the (co) polymer (a) which is a dispersant in the pigment ink. )), The low Tg polymer in the colorless ink does not uniformly overcoat the surface of the printed matter, and the polymer tends to be unevenly distributed. On the other hand, in the case of an aqueous polymer having a Tg of 25 ° C. or higher, even if the ink is used at a temperature lower than 25 ° C., it is dissolved or dispersed in water, so that the surface of the printed matter can be uniformly coated like a film. There is a high tendency, and furthermore, there is a high tendency that the scratch resistance of the printed matter by the coat layer is improved. In particular, when the aqueous polymer is a water-soluble polymer, the surface of the printed material can be uniformly coated like a film, and further, the scratch resistance of the printed material can be improved by the coating layer.
Although there is no restriction | limiting in particular in the upper limit of Tg of an aqueous polymer, Usually, it is about 150 degreeC.
The Tg of the aqueous polymer can be determined by differential scanning calorimetry (DSC).

  When the Tg of the (co) polymer (a) in the pigment ink of the present invention and the other polymer component contained in the pigment ink is 25 ° C. or higher and these are water-soluble or water-dispersible, The aqueous polymer in the colorless ink of the invention and the polymer in the pigment ink may be the same.

<Structural unit derived from hydrophilic monomer>
The structural unit derived from the hydrophilic monomer constituting the aqueous polymer includes a structural unit derived from a cationic monomer, a structural unit derived from an anionic monomer, and a structural unit derived from a nonionic hydrophilic monomer, which are classified according to the following. The

1) Structural unit derived from a cationic monomer A structural unit derived from a cationic monomer is one in which a cationic group is contained in the structural unit, and the cationic group can have a cationic charge in an aqueous medium. Examples thereof include aliphatic amines, aromatic amines, cyclic amines, and groups derived from imides. These may be any of primary amine, secondary amine, tertiary amine, and quaternary ammonium salt structures, or these may be known quaternary alkyl halides, benzyl halides, alkyl or aryl sulfonic acids, or dialkyl sulfates. Those quaternized with an agent are also included. Among these, a quaternary ammonium salt structure that is most likely to be dissociated in an aqueous solution is more preferable.

  Examples of the cationic monomer that introduces this structural unit into the aqueous polymer include the following acrylate and methacrylate monomers, vinylpyridine monomers, aminostyrene monomers, and the like. It may be a sex monomer.

  Acrylate and methacrylate monomers include amino (methyl, ethyl, propyl or butyl) acrylate or methacrylate, methylamino (methyl, ethyl, propyl or butyl) acrylate or methacrylate, ethylamino (methyl, ethyl, propyl or butyl) acrylate Or methacrylate, n-propylamino (methyl, ethyl, propyl or butyl) acrylate or methacrylate, butylamino (methyl, ethyl, propyl or butyl) acrylate or methacrylate, dimethylamino (methyl, ethyl, propyl or butyl) acrylate or methacrylate, Diethylamino (methyl, ethyl, propyl or butyl) acrylate or methacrylate, di-n-propylamino (methyl, ethyl , Propyl or butyl) acrylate or methacrylate, diisopropylamino (methyl, ethyl, propyl or butyl) acrylate or methacrylate, di-n-butylamino (methyl, ethyl, propyl or butyl) acrylate or methacrylate, di-sec-butylamino ( Methyl, ethyl, propyl or butyl) acrylate or methacrylate, diisobutylamino (methyl, ethyl, propyl or butyl) acrylate or methacrylate, or a neutralized salt thereof such as hydrogen halide, sulfuric acid, nitric acid, organic acid, alkyl halide, Quaternized compounds such as benzyl halide, dimethyl sulfate, and diethyl sulfate are listed.

  Examples of vinyl pyridine monomers include vinyl pyridine, 2-methyl-5-vinyl pyridine, 2-ethyl-5-vinyl pyridine, or neutralized salts of these with hydrogen halide, sulfuric acid, nitric acid, organic acids, and alkyl halides. Quaternized compounds such as benzyl halide, dimethyl sulfate, diethyl sulfate and the like.

  Examples of aminostyrene monomers include N, N-dimethylaminostyrene, N, N-dimethylaminomethylstyrene, or neutralized salts thereof such as hydrogen halide, sulfuric acid, nitric acid, organic acids, alkyl halides, benzyl halides, Quaternized compounds such as dimethyl sulfate and diethyl sulfate are listed.

  One kind of these structural units derived from the cationic monomer may be contained in the aqueous polymer, or two or more kinds thereof may be contained.

  Among these, a quaternary ammonium salt, a structural unit derived from a cationic monomer having a structure in which a tertiary amine is quaternized with an alkyl halide, benzyl halide, dimethyl sulfate, diethyl sulfate or the like is preferable, and methacryl or acryloyloxyethyltrimethyl is preferable. A structural unit derived from a monomer of an ammonium salt, meta or acryloyloxyethyldimethylbenzyl chloride salt is more preferable.

2) A structural unit derived from an anionic monomer An anionic monomer-derived structural unit includes an anionic group in the structural unit, and the anionic group can have an anionic charge in an aqueous medium, pKa is a functional group of 8 or less, and examples thereof include acidic groups derived from acids such as carboxylic acid, sulfonic acid, phosphoric acid, and alkali metal salt and alkaline earth metal salt structures thereof. Among these, a structural unit derived from a carboxylic acid, an alkali metal salt of a carboxylic acid, or an alkaline earth metal salt structure of a carboxylic acid is more preferable (hereinafter, an alkali metal salt and / or an alkaline earth metal salt is referred to as “alkaline (earth ) Metal salt ").

  Examples of the anionic monomer that introduces this structural unit into the aqueous polymer include the following monomers, but are not limited to these and may be conventionally known anionic monomers.

Carboxylic acid monomers such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid;
Vinyl sulfonic acid, allyl sulfonic acid, methacryl sulfonic acid, styrene sulfonic acid, 2-acrylamide ethane sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 2-methacrylamide ethane sulfonic acid, 2-methacrylamide-2-methyl Propanesulfonic acid, 2-acryloyloxyethanesulfonic acid, 3-acryloyloxypropanesulfonic acid, 4-acryloyloxybutanesulfonic acid, 2-methacryloyloxyethanesulfonic acid, 3-methacryloyloxypropanesulfonic acid, 4-methacryloyloxybutanesulfone Sulfonic acid monomers such as acids;
Vinylphosphonic acid, methacryloxyethyl phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, dibutyl-2-acryloyloxyethyl phosphate, dibutyl-2-methacryloyloxyethyl phosphate, Phosphoric monomers such as dioctyl-2- (meth) acryloyloxyethyl phosphate;
Metal salts or ammonium salts of the above carboxylic acid monomers, sulfonic acid monomers, phosphoric acid monomers such as alkali metals and alkaline earth metals.

  One type of these anionic monomer-derived structural units may be contained in the aqueous polymer, or two or more types may be contained.

  Among them, a structural unit derived from a carboxylic acid monomer is preferable, and a structural unit derived from acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid and / or an alkali metal (earth) salt thereof is more preferable.

3) A structural unit derived from a nonionic hydrophilic monomer A structural unit derived from a nonionic hydrophilic monomer includes a nonionic hydrophilic group and does not include an anionic group and a cationic group in the structural unit. Yes, the hydrophobic group may or may not be included.

  More specifically, the nonionic hydrophilic group is a hydrophilic chemistry such as an amide bond, a polyalkyl ether bond having 2 to 5 carbon atoms (repeat number 2 or more), a hydroxyl group, a thiol group, an amide group, or a sulfonamide group. Refers to a bond or functional group.

  Examples of the nonionic hydrophilic monomer that introduces this structural unit into the aqueous polymer include the following monomers, but are not limited to these and may be conventionally known nonionic hydrophilic monomers.

N-vinyl-2-pyrrolidone, N-vinyl oxazolidone, N-vinyl-5-methyloxazolidone, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2,3-dihydroxypropyl (meth) acrylate , 2-N-pyrrolidoneethyl (meth) acrylate, N- (meth) acryloylpiperidine, N- (meth) acryloylpyrrolidine, N-vinyl lactam containing 4 to 9 carbon atoms, vinyl alcohol, caprolactone-modified hydroxyethyl (Meth) acrylate, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, allyl alcohol, methallyl alcohol, glycerin monoallyl ether, (meth) acrylamide, alkyl group having 1 to 6 carbon atoms -Alkyl (meth) acrylamide, N, N-dialkyl (meth) acrylamide having 1 to 3 carbon atoms in the alkyl group, diacetone (meth) acrylamide, N-methyl (meth) acrylamide, N-methylol (meth) acrylamide, N 2-hydroxyethylacrylamide, N, N-diethanolacrylamide, N-vinylacetamide, N-methyl-N-vinylacetamide, N-vinylformamide, N-methyl-N-vinylformamide, p-hydroxymethylstyrene, p- Ring opening structure of (2-hydroxyethyl) styrene, p- (2-hydroxyethyloxycarbonyl) styrene, alkylene oxide having 2 to 5 carbon atoms, and the like.
Moreover, all the monomers illustrated as a monomer containing the above-mentioned oxyalkylene chain are contained in a nonionic hydrophilic monomer.

  One type of structural unit derived from these nonionic hydrophilic monomers may be contained in the aqueous polymer, or two or more types of structural units may be contained.

<Constitutional unit derived from hydrophobic monomer>
A structural unit derived from a hydrophobic monomer is distinguished from a structural unit derived from a hydrophilic monomer as follows.
That is, the structural unit derived from a hydrophobic monomer is a structural unit that does not contain an anionic group and a cationic group nonionic hydrophilic group but contains a hydrophobic group.

Examples of the hydrophobic group include a group derived from an aliphatic hydrocarbon having 1 or more carbon atoms and a group derived from an aromatic hydrocarbon.
Here, the aliphatic hydrocarbon is saturated or unsaturated, and may be linear, branched or cyclic. In these aliphatic hydrocarbons and aromatic hydrocarbons, one or more hydrogen atoms may be substituted with halogen atoms such as fluorine, bromine, iodine and chlorine. Further, in the aromatic hydrocarbon, one or more hydrogen atoms may be substituted with an aliphatic hydrocarbon group (one or more carbon atoms).

  As the hydrophobic group contained in the aqueous polymer according to the present invention, among them, a group derived from an aliphatic hydrocarbon having 4 to 12 carbon atoms and a group derived from an aromatic hydrocarbon are more preferable. A group derived from hydrogen (particularly an aliphatic hydrocarbon having 4 to 18 carbon atoms), an aliphatic cyclic hydrocarbon, or an aromatic hydrocarbon is more preferable.

  Examples of the hydrophobic monomer that introduces this structural unit into the aqueous polymer include the following acrylate monomers, methacrylate monomers, styrene monomers, vinyl ether monomers, acrylonitrile monomers, allyl ester monomers, and the like. It may be a conventionally known hydrophobic monomer.

  Examples of acrylate monomers include methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, dodecyl acrylate, octadecyl acrylate, Chloromethyl acrylate, dichloromethyl acrylate, trichloromethyl acrylate, trifluoromethyl acrylate, bromoethyl acrylate, vinyl acrylate, allyl acrylate, propargyl acrylate, i-propyl acrylate, i-butyl acrylate, acrylic Sec-butyl acid, t-butyl acrylate, isodecyl acrylate, 2-ethylhexyl acrylate, isopentyl acrylate, isopropenyl acrylate, 3-butenyl acrylate, cycloacrylate Xylyl, cyclopentyl acrylate, isobornyl acrylate, dicyclopentenyl acrylate, phenyl acrylate, naphthyl acrylate, anthracenyl acrylate, diphenylethyl acrylate, benzyl acrylate, phenethyl acrylate, phenylbutyl acrylate, diphenylethyl acrylate , Diphenylmethyl acrylate, triphenylmethyl acrylate, naphthylmethyl acrylate, naphthylethyl acrylate, and the like.

  Examples of methacrylate monomers include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, Chloromethyl methacrylate, dichloromethyl methacrylate, trichloromethyl methacrylate, trifluoromethyl methacrylate, bromoethyl methacrylate, vinyl methacrylate, allyl methacrylate, propargyl methacrylate, i-propyl methacrylate, i-butyl methacrylate, methacryl Sec-butyl acid, t-butyl methacrylate, isodecyl methacrylate, 2-ethylhexyl methacrylate, isopentyl methacrylate, ethyl methacrylate Propenyl, 3-butenyl methacrylate, cyclohexyl methacrylate, cyclopentyl methacrylate, isobornyl methacrylate, dicyclopentenyl methacrylate, phenyl methacrylate, naphthyl methacrylate, anthracenyl methacrylate, diphenylethyl methacrylate, benzyl methacrylate, phenethyl methacrylate , Phenylbutyl methacrylate, diphenylethyl methacrylate, diphenylmethyl methacrylate, triphenylmethyl methacrylate, naphthylmethyl methacrylate, naphthylethyl methacrylate, and the like.

  Examples of the styrene monomer include styrene, o-methoxystyrene, m-methoxystyrene, p-methoxystyrene, ot-butoxystyrene, mt-butoxystyrene, pt-butoxystyrene, o-chloromethylstyrene, m-chloromethylstyrene, p-chloromethylstyrene, etc. are mentioned.

  Examples of the vinyl ether monomer include methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, benzyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether and the like.

  Examples of acrylonitrile monomers include acrylonitrile and methacrylonitrile, and specific examples of allyl ester monomers include allyl acetate.

  Of these, styrenes and (meth) acrylates (acrylic acid, aliphatic hydrocarbons having 4 to 12 carbon atoms or esters of aromatic compounds) are preferred, and styrene, n-butyl (meth) acrylate, ( T-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, and benzyl (meth) acrylate are preferred.

  One type of structural unit derived from these hydrophobic monomers may be contained in the aqueous polymer, or two or more types may be contained.

  In order to introduce the structural units derived from these hydrophobic monomers into the aqueous polymer, the above-mentioned hydrophobic monomers may be directly polymerized to introduce them, or polymers obtained by polymerizing natural polymers or monomers. May be introduced by performing a modification or modification reaction to convert it into a different structural unit.

<Composition of aqueous polymer>
As described above, the aqueous polymer in the colorless ink of the present invention may be a polymer of a hydrophilic monomer or a copolymer of a hydrophobic monomer and a hydrophilic monomer. It is a copolymer of a monomer and a hydrophilic monomer.

  The content of the structural unit derived from the hydrophobic monomer in the aqueous polymer according to the present invention can be arbitrarily determined as long as the polymer maintains water solubility, but is preferably in the range of 0 to 98 mol%. Preferably it is 10-90 mol%.

<Molecular weight>
The number average molecular weight (Mn) of the aqueous polymer in the colorless ink of the present invention is not particularly limited, but is usually 200,000 or less, preferably 100,000 or less, more preferably 50,000 or less, and the colorlessness obtained when the molecular weight is larger than this range. As the viscosity of the ink increases, the discharge performance decreases. In addition, about the minimum of the number average molecular weight (Mn) of aqueous polymer, in order to acquire the quantitative improvement and the image quality improvement effect by an aqueous polymer reliably, it is preferable that it is usually 1000 or more especially 3000 or more.

<Water-soluble and water-dispersible>
As the aqueous polymer contained in the colorless ink of the present invention, the solubility of the polymer in water at 25 ° C. is 2% by weight or more even in a state where 50 mol% of ionic groups present in the polymer are neutralized. Is more preferable. In addition, even when 50 mol% of ionic groups present in the polymer are neutralized, in a 2 wt% aqueous dispersion of the polymer at 25 ° C., no precipitation occurs immediately after preparation of the dispersion. Is more preferable.

  As an aqueous polymer contained in the colorless ink, an aqueous dispersion is prepared in the case where the solubility of the polymer in water at 25 ° C. is 2% by weight or more and an aqueous dispersion of the polymer in 2% by weight at 25 ° C. Those that do not cause precipitation immediately after are particularly preferred.

<Method for synthesizing aqueous polymer>
As the method for synthesizing the aqueous polymer in the colorless ink of the present invention, various known methods, for example, known polymerization methods such as radical polymerization, ionic polymerization, polyaddition and polycondensation can be selected. It may be a derivative or modified product of the polymer synthesized in (1). Among these, an aqueous polymer synthesized by a radical polymerization method is more preferable because the synthesis method is simple.
The radical polymerization reaction can be carried out by the method described in the section <Method for synthesizing (co) polymer (a)> in [Pigment ink] described above.

<Ink composition>
The colorless ink of the present invention used as an overcoat liquid is usually prepared by adjusting the above-mentioned aqueous polymer concentration as necessary, and further adding and mixing various additives depending on the application.

The concentration of the aqueous polymer in the colorless ink of the present invention is preferably 0.01% by weight or more, more preferably 0.1% by weight or more with respect to the total amount of the colorless ink, and the upper limit is 50% by weight or less, preferably 30% by weight. % Or less, and particularly preferably 20% by weight or less. If the concentration of the aqueous polymer is too high, the viscosity increases and the discharge properties deteriorate, and if it is too low, the effect of the overcoat decreases.
In addition, in the colorless ink of this invention, only 1 type of the above-mentioned aqueous polymer may be contained, and 2 or more types may be contained.

  The colorless ink of the present invention basically does not contain a colorant, but may contain a small amount of dye or the like as long as it does not significantly change the hue of the printed matter.

  Further, the colorless ink of the present invention may contain various additives as necessary within a range not impairing the effects of the present invention. As such an additive, <addition of the above-mentioned [pigment ink] Additives other than the resin and polymer fine particles exemplified in <Agent> can be used in the same manner as in the case of pigment ink.

The colorless ink of the present invention preferably contains water and a water-soluble organic solvent, and the concentration of the water-soluble organic solvent may be appropriately selected and determined, but is usually 1% by weight or more and 45% by weight with respect to the whole colorless ink. In the following, it is preferably 40% by weight or less. In addition, the content of water in the recording liquid may be an amount that can appropriately set the concentration of the above-described aqueous polymer, water-soluble organic solvent, and any additive added as necessary.
As the water-soluble organic solvent, one or two or more of those exemplified in the section of {Aqueous medium} of the above [Pigment ink] can be used.

[Ink set]
The ink set of the present invention includes one or more pigment inks containing the above-described pigment as a colorant, the (co) polymer (a) as a dispersant for the pigment, and an aqueous medium, and Tg And one or more colorless inks containing an aqueous polymer at 25 ° C. or higher.

[Inkjet recording system]
The ink-jet recording method of the present invention comprises the above-described colorless ink of the present invention after the pigment ink of the present invention is ejected from an ink-jet head and ink droplets of the pigment ink are adhered to a recording medium to form an image. Is ejected from the inkjet head onto the image.

  In the ink jet recording system of the present invention, an ink cartridge that individually contains pigment ink and colorless ink is mounted on an ink jet printer, and ink is ejected from an ink jet head so that the ink adheres to a recording medium for recording. Therefore, it can be suitably implemented. There is no particular limitation on the ink jet printer used here, and each pigment ink is first ejected onto the recording medium in an arbitrary order, and an ink droplet of the pigment ink is adhered to the recording medium to form an image, and then the colorless ink is used. As long as it can be discharged onto the image. In this case, a part of the pigment ink can be discharged first, then the colorless ink can be discharged, and finally the remaining pigment ink can be discharged.

  The method of discharging the colorless ink of the present invention from the inkjet head and applying the overcoat includes a method of forming a coat layer with the colorless ink at the same time as forming an image with the pigment ink, Although there is a method of forming a coat layer with ink, any method may be selected. Examples of a method for simultaneously ejecting pigment ink and colorless ink include a method of simultaneously forming an image and a coat layer using a carriage in which a pigment ink recording head and a colorless ink recording head are arranged in series. . As a method for forming a coat layer with colorless ink after image formation with pigment ink, for example, another carriage equipped with a head for colorless ink is installed in a downstream portion for conveying a recording medium, and immediately after image formation with pigment ink. For example, a method of discharging colorless ink, a method of setting the recording medium after image formation again in the printer, and discharging only colorless ink can be considered.

  The amount of the colorless ink used is not particularly limited, but the weight ratio of the pigment in the pigment ink attached on the recording medium to the aqueous polymer in the colorless ink attached on the recording medium is usually 10: 0.01 to 10: 100, The concentration of the aqueous polymer in the colorless ink and the discharge amount of the colorless ink are preferably adjusted so that the ratio is preferably 10: 0.1 to 10:50, more preferably 10: 1 to 10:20. . If the ratio of the aqueous polymer to the pigment is too small, the improvement effect of the present invention is reduced, and if it is too large, the glossiness may be lowered.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

[Example 1]
(1) Synthesis of Random Copolymer 1 (Poly (styrene-co-methoxypolyethyleneglycolacrylate-co-sodium acrylate)) To a flask equipped with a condenser, a nitrogen inlet tube, a stirrer, and a thermometer, the inside of which was purged with nitrogen. 2,2′-Asobis (2,4-dimethylvaleronitrile) 2.57 g was charged as a catalyst, methanol 278 g as a solvent, styrene 41.28 g as a monomer, methoxypolyethylene glycol acrylate (“Kyoeisha Chemical Co., Ltd.” “light acrylate 130A”) ”, M = 9) in the general formula (2), 153.01 g, and 5.71 g of acrylic acid were charged into the flask. The bath temperature was raised from room temperature to 70 ° C. over 30 minutes, and a polymerization reaction was carried out at 70 ° C. for 5 hours. A solution prepared by dissolving 1.07 g of catalyst 2,2′-azobis (2,4-dimethylvaleronitrile) in 10 g of methanol was added to the reaction system, and polymerization reaction was further performed for 3 hours.

  After completion of the reaction, the reaction solution was cooled to room temperature, 13.18 g of 5N sodium hydroxide aqueous solution was added with stirring, and then distilled water was added while removing methanol with an evaporator to obtain a crude polymer aqueous solution. After removing impurities from the crude polymer aqueous solution by ultrafiltration, the polymer aqueous solution was concentrated and dried to obtain random copolymer 1. The number average molecular weight (Mn) of the random copolymer 1 determined by gel permeation chromatography (GPC) was 12800, and the molecular weight distribution was 1.7.

The number average molecular weight (Mn) of the random copolymer 1 was measured under the following conditions using GPC.
Column packing: Styrene-divinylbenzene copolymer Solvent: Tetrahydrofuran Flow rate: 0.7ml / min
Temperature: 40 ° C
Calibration was performed using polystyrene.
In addition, this time, it measured using the following apparatuses, detectors, and columns.
Apparatus: Waters 2690 manufactured by Nippon Waters Co., Ltd.
Detector: Waters 2410 manufactured by Nippon Waters Co., Ltd.
Column: Shodex KF-604 / KF-603 / KF-602.5 manufactured by Showa Denko KK

The structure of this random copolymer 1 was confirmed by ¹ H-NMR using d-DMSO (dimethyl sulfoxide) as a solvent. The composition ratio of styrene units, methoxypolyethylene glycol acrylate units, and sodium acrylate units in random copolymer 1 determined by ¹ H-NMR was 54/29/17 (molar ratio), 26/66/8 (weight). Ratio).

When differential scanning calorimetry (DSC) of random copolymer 1 was performed, Tg was not observed within the measurement range of −20 ° C. to 140 ° C., and since it was a soft polymer at room temperature, Tg of random copolymer 1 was Presumed to be -20 ° C or lower.
Distilled water was added to random copolymer 1 to obtain an aqueous solution having a polymer concentration of 13.3% by weight. The appearance of this aqueous solution was colorless and transparent at 25 ° C.

(2) Synthesis of block copolymer 1 (polyvinyl alcohol-b-poly (sodium acrylate-co-methyl acrylate-co-sodium methacrylate-co-benzyl methacrylate-co-styrene)) A flask equipped with a condenser, a nitrogen introducing tube, a stirrer, and a thermometer was charged with 3587 g of vinyl acetate, 1907 g of chloroform as a chain transfer agent and a solvent, and the temperature was raised to 70 ° C. over 1 hour. Next, a catalyst solution in which 0.3 g of azobis (2-methylbutyronitrile) was dissolved as a catalyst in 534 g of chloroform was dropped over 6 hours. Thereafter, a catalyst solution in which 0.5 g of azobis (2-methylbutyronitrile) as a catalyst was dissolved in 444.5 g of chloroform was dropped over 5 hours. After dropwise addition of the catalyst solution, the mixture was heated and polymerized for 10 hours under reflux conditions. After completion of the reaction, while continuously dropping 0.01N sodium hydroxide / methanol solution into the reaction solution, unreacted vinyl acetate and chloroform were distilled off under reduced pressure at an internal temperature of 40 ° C. to obtain a polyvinyl acetate methanol solution (polymer A concentration of 74% by weight) was obtained. The number average molecular weight (Mn) of this polyvinyl acetate determined by GPC was 3500, and the molecular weight distribution was 2.4.

The terminal structure of the polyvinyl acetate was —CCl ₃ . This is because, in ¹ H-NMR (solvent CDCl ₃ ), a peak of a methylene group (peak of chemical shift δ = 2.8 to 3.2) was observed adjacent to the end of the polyvinyl acetate, Since the number average molecular weight (Mn) (3500) calculated by using -CCl ₃ as the terminal structure and the number average molecular weight (Mn) obtained from GPC coincide with each other, a group (—CCl It was confirmed that polyvinyl acetate having ₃ ) was synthesized.

  Next, a condenser, a nitrogen inlet tube, a stirrer, and a thermometer-equipped flask with the inside replaced with nitrogen were used. 5 g of the polyvinyl acetate methanol solution 1353 g as a macroinitiator was charged, and the temperature was raised from room temperature to 60 ° C. over 1 hour. When the internal temperature reached 60 ° C., a catalyst solution in which 0.6 g of cuprous bromide as a catalyst and 12.0 g of tris (2-dimethylamino) ethylamine as a ligand were dissolved in 30 g of methanol was added. After addition of the catalyst solution, the mixture was heated and polymerized for 30 hours under reflux conditions.

  The number average molecular weight (Mn) of the reaction product increased with the lapse of the polymerization reaction time. Table 1 shows the molar ratio of each monomer of methyl acrylate (MA), benzyl methacrylate (BzMA), and styrene (St) in the polymer calculated from the amount of monomer consumption in the polymerization solution, obtained from gas chromatography. . As is clear from Table 1, the composition of the block copolymer linked with polyvinyl acetate changes with an increase in its number average molecular weight (Mn), and the monomer composition in this block copolymer changes toward the end ( Gradient was confirmed to be polyvinyl acetate-b-poly (methyl acrylate-co-benzyl methacrylate-co-styrene).

  Moreover, the number average molecular weight (Mn) of this polymer calculated | required from GPC was 16300, and molecular weight distribution was 1.63. In this polyvinyl acetate block copolymer, the linking group connecting the polyvinyl acetate block and the other block is a dichloromethylene group.

  Next, in a reaction kettle equipped with a condenser, a stirrer and a thermometer, the above polymerization solution 502 g was dissolved in a mixed solvent of 276 g of methanol, 552 g of tetrahydrofuran and 138 g of water. 728 g was added and reacted at 65 ° C. for 7 hours. After completion of the reaction, 550 g of tetrahydrofuran (THF) and 140 g of water were added to the polymer mass obtained by removing the supernatant and suspended, and then 280 g of methanol was added to precipitate the polymer. The supernatant was removed again, 300 g of water was added, neutralized with acetic acid, the solution was heated to 90 ° C., and residual THF and methanol were distilled off to obtain an aqueous polymer solution. Thereafter, impurities were removed from the polymer aqueous solution using an ultrafiltration membrane (“ACP-1050” manufactured by Asahi Kasei Corporation). Polyvinyl alcohol-b-poly (sodium acrylate-co-methyl acrylate-co-methacrylic acid) in which the copolymer linked to the polyvinyl alcohol block is a gradient copolymer by concentrating and drying the polymer aqueous solution after ultrafiltration Sodium-co-benzyl methacrylate-co-styrene). In this block copolymer 1, the linking group that links the polyvinyl alcohol block and the other block is one in which part or all of the chlorine atoms in the linking group (dichloromethylene group) described above are replaced with hydrogen atoms.

  The structure of the block copolymer 1 was confirmed by H-NMR using heavy water as a solvent. The composition ratio of vinyl alcohol units, sodium acrylate units, methyl acrylate units, sodium methacrylate units, benzyl methacrylate units, and styrene units in the block polymer determined by H-NMR was 25: 26: 21: 2. : 21: 5 (molar ratio), 11: 25: 19: 2: 38: 5 (weight ratio). Moreover, the number average molecular weight (Mn) of the polymer calculated | required from GPC was 14000, and molecular weight distribution was 1.59.

The number average molecular weight (Mn) of the block copolymer 1 was measured under the following conditions using GPC.
Column packing material: Polyhydroxymethacrylate Solvent: Water / acetonitrile
(70/30 (v / v), 0.2M Tris-HCl buffer, 0.1M KCl included)
Flow rate: 0.7mL / min
Temperature: 40 ° C
Calibration was performed using polyethylene glycol.
In addition, this time, it measured using the following apparatuses, detectors, and columns.
Apparatus: Waters 2695 made by Nippon Waters Co., Ltd.
Detector: Waters 2410 manufactured by Nippon Waters Co., Ltd.
Column used: Shodex OHpak SB-G, SB-804HQ, SB-803HQ, manufactured by Showa Denko KK
SB-802.5HQ

When differential scanning calorimetry (DSC) of the block copolymer 1 was performed, the Tg of the block copolymer 1 was 62 ° C.
Distilled water was added to the block copolymer 1 to obtain an aqueous solution having a polymer concentration of 10.0% by weight. The appearance of this aqueous solution was yellowish brown transparent at 25 ° C.

(3) Preparation of Cyan Pigment Dispersion (A) Pigment Blue-15: 3 (manufactured by Dainichi Seika Kogyo Co., Ltd .; powder; solid content 100% by weight) 28.0 g, aqueous solution of random copolymer 1 (concentration 13.3%) %) 84.2 g, block copolymer 1 aqueous solution (concentration 10.0 wt%) 14.0 g and deionized water 153.8 g were mixed, pre-dispersed with a homomixer for 60 minutes, and then 0.3 mmφ zirconia beads were used as media. Was dispersed at 25 ° C. for 7 hours and further at 40 ° C. for 1 hour to remove the beads, and the pigment concentration was adjusted to 8% by weight to obtain a dispersion (α).
Place the dispersion (α) in a 500 ml tall beaker, immerse the beaker in ice water, disperse for 120 minutes with an ultrasonic homogenizer (Nippon Seiki Seisakusho; US-600T; used chip 36 mmφ), and pigment dispersion (A) Got.

(4) Preparation of pigment ink I <pigment ink formulation>
Pigment dispersion (A): 5.63 g
Distilled water: 6.60 g
Glycerin: 1.13 g
2-pyrrolidone: 0.77 g
1,6-hexanediol: 0.74 g
Olfine E1010 (Surfactant manufactured by Air Products): 0.15 g

  Each component was mixed by the above pigment ink formulation, stirred for 15 minutes, and subjected to ultrasonic dispersion treatment for 30 minutes to obtain pigment ink I having a pH of 8.1.

(5) Synthesis of Random Copolymer 2 (Poly (Sodium Acrylate-co-n-Butyl Acrylate-co-Styrene)) To a flask equipped with a condenser, a nitrogen inlet tube, a stirrer and a thermometer, the inside of which was substituted with nitrogen. 30 g of 2,2′-azobis (2,4-dimethylvaleronitrile) was charged as a catalyst, 3500.0 g of tetrahydrofuran as a solvent, 600.0 g of acrylic acid as a monomer, 600.0 g of n-butyl acrylate, and 400.0 g of styrene as described above. Was placed in the flask. The bath temperature was raised from room temperature to 70 ° C. over 1 hour, and the polymerization reaction was carried out at 70 ° C. for 8 hours.

  After completion of the reaction, the reaction solution was cooled to room temperature, neutralized with a sodium hydroxide / methanol solution, and precipitated in isopropyl alcohol. The precipitate was filtered and vacuum dried to obtain a mixture of poly (sodium acrylate-co-n-butyl acrylate-co-styrene) and sodium acrylate. The random copolymer 2 determined by GPC had a number average molecular weight (Mn) of 11000 and a molecular weight distribution of 1.6.

  The measurement of the number average molecular weight (Mn) of the random copolymer 2 was performed using GPC under the same conditions as the measurement of the number average molecular weight (Mn) of the random copolymer 1.

After dissolving 30.0 g of the random copolymer and sodium acrylate mixture in 970.0 g of water, sodium acrylate was removed by ultrafiltration. After removing the sodium acrylate, the polymer aqueous solution was concentrated and dried to obtain the random copolymer 2.
The structure of this random copolymer 2 was confirmed by H-NMR using heavy water as a solvent. The composition ratio of the sodium acrylate unit, n-butyl acrylate unit, and styrene unit in the random copolymer 2 determined by H-NMR is 47:21:32 (molar ratio), 42:26:32 (weight ratio). Met.
When differential scanning calorimetry (DSC) of random copolymer 2 was performed, Tg of random copolymer 2 was 65 ° C.
Distilled water was added to the random copolymer 2 to obtain an aqueous solution having a polymer concentration of 13.3% by weight. The appearance of this aqueous solution was colorless and transparent at 25 ° C.

(6) Preparation of colorless ink I <colorless ink formulation>
Random copolymer 2 aqueous solution: 1.35 g
Distilled water: 10.86 g
Glycerin: 1.13 g
2-pyrrolidone: 0.77 g
1,6-hexanediol: 0.74 g
Olfine E1010 (Surfactant manufactured by Air Products): 0.15 g

  Each component was mixed in the colorless ink composition, stirred for 15 minutes, and subjected to ultrasonic dispersion treatment for 30 minutes to obtain colorless ink I containing 1.2% by weight of random copolymer 2.

(7) Preparation of recorded matter A cartridge filled with pigment ink I and colorless ink I was mounted on an ink jet recording printer (Canon BJ-S700 printer), and commercially available glossy paper (Canon Inc.) was used as printing paper. The solid image 1 of Example 1 was obtained by using the glossy paper SP-101) and performing two recording head scans of the scan for ejecting the recording liquid and the scan for ejecting colorless ink in the glossy paper mode.

[Example 2]
(1) Preparation of colorless ink II <colorless ink formulation>
Aqueous solution of block copolymer 1 (Example 1 (2)): 1.35 g
Distilled water: 10.86 g
Glycerin: 1.13 g
2-pyrrolidone: 0.77 g
1,6-hexanediol: 0.74 g
Olfine E1010 (Surfactant manufactured by Air Products): 0.15 g

  Each component was mixed in the colorless ink composition, stirred for 15 minutes, and subjected to ultrasonic dispersion treatment for 30 minutes to obtain colorless ink II containing 0.9% by weight of block copolymer 1.

(2) Production of recorded matter The cartridge filled with the pigment ink I prepared in Example 1 and the colorless ink II described above was mounted on an ink jet recording printer (Canon BJ-S700 printer) as a printing paper. Using commercially available glossy paper (Glossy Paper SP-101 manufactured by Canon Inc.), the recording head scan of Example 2 was performed by two recording head scans, a scan for ejecting the recording liquid in the glossy paper mode and a scan for ejecting colorless ink. A solid image 2 was obtained.

Example 3
(1) Synthesis of Random Copolymer 3 (Poly (isobornyl methacrylate-co-methoxypolyethyleneglycol acrylate-co-sodium acrylate)) Flask with condenser, nitrogen introduction tube, stirrer, and thermometer with the inside replaced with nitrogen 1875 g of tetrahydrofuran as a solvent, 301.72 g of isobornyl methacrylate, 654.90 g of methoxypolyethylene glycol acrylate (“Light Acrylate 130A” manufactured by Kyoeisha Chemical Co., Ltd.), and 293.38 g of acrylic acid as a monomer were placed in the flask. It is. After raising the bath temperature to 60 ° C., 5.57 g of 2,2′-azobis (isobutyronitrile) was added as a catalyst, and a polymerization reaction was carried out for 5 hours. The bath temperature was raised to 70 ° C., and the polymerization reaction was further performed for 2 hours.

  After completion of the reaction, the reaction mixture was cooled to room temperature and neutralized with a 5N aqueous sodium hydroxide solution, distilled water was added, and THF was removed by heating to obtain a crude aqueous polymer solution. After removing impurities from the crude polymer aqueous solution by ultrafiltration, the polymer aqueous solution was concentrated and dried to obtain random copolymer 3. The random copolymer 3 determined by GPC had a number average molecular weight (Mn) of 12000 and a molecular weight distribution of 1.9.

  The measurement of the number average molecular weight (Mn) of the random copolymer 3 was performed using GPC under the same conditions as the measurement of the number average molecular weight (Mn) of the block copolymer 1.

The structure of the obtained random copolymer 3 was confirmed by ¹ H-NMR. The composition ratio of the isobornyl methacrylate unit, the methoxypolyethylene glycol acrylate unit, and the sodium acrylate unit in the polymer determined by ¹ H-NMR was 26/20/54 (molar ratio), 28/47/25 (weight ratio). )Met.
The Tg of Random Copolymer 3 was estimated to be 25 ° C. or higher because the appearance was a solid with no softness near room temperature.
Distilled water was added to the random copolymer 3 to obtain an aqueous solution having a polymer concentration of 13.0% by weight. The appearance of this aqueous solution was colorless and transparent at 25 ° C.

(2) Preparation of colorless ink III <colorless ink formulation>
Aqueous solution of random copolymer 3: 1.38 g
Distilled water: 10.83 g
Glycerin: 1.13 g
2-pyrrolidone: 0.77 g
1,6-hexanediol: 0.74 g
Olfine E1010 (Surfactant manufactured by Air Products): 0.15 g

  Each component was mixed in the colorless ink composition, stirred for 15 minutes, and subjected to ultrasonic dispersion treatment for 30 minutes, to obtain colorless ink III containing 1.2% by weight of random copolymer 3.

(3) Preparation of recorded matter A cartridge filled with pigment ink I and colorless ink III was mounted on an inkjet recording printer (Canon BJ-S700 printer), and commercially available glossy paper (Canon Inc.) was used as printing paper. The solid image 3 of Example 3 was obtained by using the glossy paper SP-101) and performing two recording head scans of the scan for ejecting the recording liquid and the scan for ejecting colorless ink in the glossy paper mode.

[Comparative Example 1]
(1) Preparation of recorded matter A cartridge filled with pigment ink I is mounted on an ink jet recording printer (Canon BJ-S700 printer), and commercially available glossy paper (Glossy paper manufactured by Canon Inc.) is used as printing paper. A solid image 4 of Comparative Example 1 using no colorless ink was obtained by one recording head scan of only the scan for discharging the recording liquid in the glossy paper mode using SP-101).

[Comparative Example 2]
(1) Preparation of colorless ink IV <colorless ink formulation>
Aqueous solution of random copolymer 1 (Example 1 (1)): 1.35 g
Distilled water: 10.86 g
Glycerin: 1.13 g
2-pyrrolidone: 0.77 g
1,6-hexanediol: 0.74 g
Olfine E1010 (Surfactant manufactured by Air Products): 0.15 g

  Each component was mixed in the colorless ink composition, stirred for 15 minutes, and subjected to ultrasonic dispersion treatment for 30 minutes to obtain a colorless ink containing 1.2% by weight of random copolymer 1.

(2) Production of recorded matter A cartridge filled with pigment ink I and colorless ink IV is mounted on an ink jet recording printer (Canon BJ-S700 printer), and commercially available glossy paper (Canon Inc.) is used as printing paper. ) Glossy paper SP-101) was used, and a solid image 5 of Comparative Example 2 was obtained by two recording head scans of a scan for discharging the recording liquid and a scan for discharging colorless ink in the glossy paper mode.

[Comparative Example 3]
(1) Preparation of Cyan Pigment Dispersion (B) Pigment Blue-15: 3 (manufactured by Dainichi Seika Kogyo Co., Ltd .; powder; solid content 100% by weight) 28.0 g, aqueous solution of random copolymer 2 (concentration 13.3 wt. %) (Example 1 (5)) 210.5 g, block copolymer 1 aqueous solution (block copolymer concentration 10.0 wt%) (Example 1 (2)) 1.4 g, and deionized water 40.1 g were mixed. After pre-dispersing for 60 minutes with a homomixer, using a bead mill with 0.3 mmφ zirconia beads as media, dispersing at 25 ° C. for 7 hours and further at 40 ° C. for 1 hour, removing the beads, and a pigment concentration of 8% by weight To obtain a dispersion (β).

  Disperse (β) in a 500 ml tall beaker, immerse the beaker in ice water, disperse for 120 minutes with an ultrasonic homogenizer (Nippon Seiki Seisakusho; US-600T; used chip 36 mmφ), and pigment dispersion (B) Got.

(2) Preparation of pigment ink II <pigment ink formulation>
Pigment dispersion (B): 5.63 g
Distilled water: 6.60 g
Glycerin: 1.13 g
2-pyrrolidone: 0.77 g
1,6-hexanediol: 0.74 g
Olfine E1010 (Surfactant manufactured by Air Products): 0.15 g

  Each component was mixed with the above pigment ink formulation, stirred for 15 minutes, and subjected to ultrasonic dispersion treatment for 30 minutes to obtain pigment ink II having a pH of 8.4.

(3) Preparation of recorded matter A cartridge filled with pigment ink II and colorless ink I was mounted on an inkjet recording printer (Canon BJ-S700 printer), and commercially available glossy paper (Canon Inc.) was used as printing paper. The solid image 6 of Comparative Example 3 was obtained by two recording head scans, a scan for ejecting the recording liquid in the glossy paper mode and a scan for ejecting the colorless ink.

[Evaluation of recorded material]
For the solid images 1 to 6 obtained in Examples 1 to 3 and Comparative Examples 1 to 3, the following characteristics (A), (B), (C), and (D) were evaluated, respectively. Are shown in Table 2.

(A) Bronzing resistance of recorded matter The solid images of Examples 1 to 3 and Comparative Examples 1 to 3 which were dried at room temperature for 1 day or more were visually observed, and bronzing resistance was evaluated according to the following criteria.
○: Bronze phenomenon is not observed.
Δ: A slight bronze phenomenon is observed.
X: Bronze phenomenon is observed.

(B) Angle dependency of hue of recorded matter The angle dependency of hues of solid images of Examples 1 to 3 and Comparative Examples 1 to 3 dried at room temperature for one day or more were respectively multi-angle spectroscopy manufactured by Color Techno System Co., Ltd. The measurement was made with a colorimeter (X-Rite MA68II). The values of L *, a *, and b * in the CIELAB color system of each solid image are measured at five angles of 15 °, 25 °, 45 °, 75 °, and 110 ° when viewed from the regular reflection light. The difference (Δa *) between the value of a * at 45 ° and the value of a * at 15 ° was used as an index of hue angle dependency.
When Δa * is large, red that is a complementary color appears by visual observation, and when Δa * is small, the appearance of complementary color by visual observation is also small, and Δa * is also correlated with the magnitude of bronze phenomenon. Although it is not, it can be regarded as a general index of bronzing resistance.

(C) Glossiness of recorded matter The glossiness (Gloss) of the solid images of Examples 1 to 3 and Comparative Examples 1 to 3 which were dried at room temperature for 1 day or more was measured. The measurement was performed using a Haze-Gloss meter (Cat. No. 4601 manufactured by BYK Gardner), and the Gloss value was measured at 20 °.

(D) Optical density (OD) of recorded matter
The optical density (OD) of the solid images of Examples 1 to 3 and Comparative Examples 1 to 3 which were dried at room temperature for 1 day or more was measured by “GretagMacbeth ^™ SpectroEye ^™ ” manufactured by Macbeth.

The following can be understood from the above results.
In Examples 1 to 3 in which the Tg of the water-soluble polymer that is a component of the colorless ink was adjusted within the range of the present invention, the bronzing phenomenon of the recorded matter was clearly suppressed by the overcoat as compared with Comparative Example 1, and the hue angle dependency And the optical density was improved.
In Comparative Example 2 in which overcoating was performed with a water-soluble polymer having a Tg lower than the range of the present invention, no visual bronzing suppression was observed, and the gloss was slightly lowered compared to Comparative Example 1 without a coating, No improvement in image quality was observed.
Comparative Example 3 is a water-soluble pigment ink using a styrene-acrylic copolymer as a dispersant instead of the (co) polymer (a) containing an oxyalkylene chain, and adjusting the Tg within the range of the present invention. This is a polymer overcoat. Although the bronzing phenomenon is suppressed by the overcoat and both the glossiness and the OD are improved, the glossiness of the image is clearly lower than that of the example of the present invention. In Comparative Example 3, because the (co) polymer (a) containing an oxyalkylene chain was not used in the pigment ink, the gloss before the overcoat was as low as 37. Although not as high as the embodiments of the present invention are achieved.
In general, printed matter with extremely high gloss tends to decrease the print density against the gloss, but the use of the pigment ink and colorless ink of the present invention greatly reduces the high gloss. Therefore, it is possible to achieve both high printing density, high scratch resistance, and good images with suppressed bronzing.

Claims (9)

An ink set comprising a pigment ink containing the following components (a), (b) and (c), and a colorless ink containing an aqueous polymer having a Tg of 25 ° C. or higher , wherein the pigment ink is further a polyvinyl alcohol type An ink set comprising a resin, wherein the polyvinyl alcohol-based resin contains an ionic dissociation group selected from the group consisting of acidic groups, basic groups, and salts thereof .
(A) Polymer of monomer containing oxyalkylene chain and / or copolymer of monomer containing oxyalkylene chain and other monomer, derived from monomer containing oxyalkylene chain (B) Pigment (c) Aqueous medium Copolymer having a content of 15% by weight or more based on the whole copolymer   The ink set according to claim 1, wherein the aqueous polymer is a water-soluble polymer. The ink set according to claim 1, wherein the monomer containing the oxyalkylene chain is represented by the following general formula (1).

(In the formula (1), R ¹ is vinyl group, acryloyloxy group, acryloylamino group, methacryloyloxy group, methacryloylamino group, acrylamino group, styryl group, vinyl ether group, vinylsilyl group, cyanovinyl group, or 2-cyanoacryloyl. R ² represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or an optionally substituted phenyl group, h and j are each independently an integer of 1 to 5, i is (It is an integer from 1 to 100, k is an integer from 0 to 50, and i + k ≧ 2.)   The ink set according to any one of claims 1 to 3, wherein the other monomer is a hydrophobic monomer and / or an anionic monomer.   The ink set according to any one of claims 1 to 4, wherein the content of the structural unit derived from the anionic monomer is 10% by weight or less based on the entire copolymer.   The ink set according to any one of claims 1 to 5, wherein the water-soluble polymer is a copolymer of a hydrophobic monomer and a hydrophilic monomer. The ink set according to any one of claims 1 to 6, wherein the polyvinyl alcohol-based resin contains a structural unit derived from vinyl alcohol represented by the following general formula (3) and a hydrophobic group in the polymer.

(In formula (3), R ³ represents a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms) The ink set according to any one of claims 1 to 7 , wherein the polyvinyl alcohol-based resin is a block copolymer. A pigment ink containing the following components (a), (b) and (c) is ejected from an inkjet head, and the pigment ink droplets are attached to a recording medium to form an image. An ink jet recording method in which a colorless ink containing a polymer is ejected onto an image from an ink jet head, wherein the pigment ink further contains a polyvinyl alcohol resin, and the polyvinyl alcohol resin comprises an acidic group and a basic group. And an ionic dissociation group selected from the group consisting of these salts .
(A) Polymer of monomer containing oxyalkylene chain and / or copolymer of monomer containing oxyalkylene chain and other monomer, derived from monomer containing oxyalkylene chain (B) Pigment (c) Aqueous medium Copolymer having a content of 15% by weight or more based on the whole copolymer