A. Technical Field
The present invention relates to an ink jet recording material and a coating agent therefor, more particularly, relates to: an ink jet recording material which displays sufficient water resistance and further, excellent definition of initial images; and a coating agent therefor to give such an ink jet recording material.
Ink jet recording apparatuses are machines such as printers, facsimile machines, and copiers. For the ink jet recording apparatus, U.S. Pat. No. 5,486,854 issued Jan. 23, 1996 is hereby incorporated by reference. The ink jet recording apparatus is to make a recording by jetting ink from a recording means (i.e. a recording head which is a part of the ink jet recording apparatus) onto a recording material, wherein the recording material is, for example, a paper sheet, or a plastic sheet such as transparent PET sheet.
The ink jet recording material, generally, suffers from a lack of water resistance. That is, an exposure to water usually will dissolve and destroy the image (the imaged ink). To prevent this, the image must be rendered water-resistant, and further, if the ink is, for example, an organic dye, then the image must also be fixed. Examples of known methods of giving the image the water resistance to thereby fix the image include arts to fix dyes with mordants and arts involving the use of adsorptive pigments. However, operations thereof are complicated, or the optimal method is different according to the composition of the ink, so the above known methods are not commonly usable means.
In comparison, JP-A-035090/1998 discloses a water-resistant composition for ink jet recording sheets, comprising a polymer containing an amino group (and/or quaternary ammonium salt) and a carboxyl group (and/or acid anhydride) and a crosslinking agent containing at least two oxazoline groups, as a method of not giving the image the water resistance, but carrying out a water-resisting pretreatment for the recording material. However, as to this technique, not only is the resultant water-resistification insufficient, but also there are problems on the definition of initial images.
An object of the present invention is to provide: an ink jet recording material which displays sufficient water resistance and further, excellent definition of initial images; and a coating agent therefor to give such an ink jet recording material.
To solve the above problems, the present invention provides the following:
A first coating agent for ink jet recording materials, according to the present invention, comprises: an aqueous polymer having a carboxyl group; and a water-soluble polymer having an oxazoline group as a crosslinking agent.
A second coating agent for ink jet recording materials, according to the present invention, comprises a polymer and a crosslinking agent, wherein the polymer has both a structural unit, as formed by ring-opening polymerization of an oxazoline compound, and a carboxyl group.
An ink jet recording material, according to the present invention, has on at least one face thereof a coated and cured layer of the above present invention first coating agent and/or a coated and cured layer of the above present invention second coating agent.
These and other objects and the advantages of the present invention will be more fully apparent from the following detailed disclosure.
The first coating agent, according to the present invention, comprises: an aqueous polymer having a carboxyl group; and a water-soluble polymer having an oxazoline group as a crosslinking agent.
The aqueous polymer having a carboxyl group is not especially limited if it is a polymer that has a carboxyl group and further is aqueous (that is, water-soluble or water-dispersible). To obtain the polymer having a carboxyl group, a monomer having a carboxyl group is, for example, polymerized as a raw material, or a carboxyl group is introduced into a polymer (as prepared beforehand) by denaturation. To obtain the aqueous polymer, a hydrophilic monomer (available whether it has a carboxyl group or not) is, for example, used in the ratio of preferably 10 mol % or higher, more preferably 50 mol % or higher, to the entire monomer component.
Examples of the monomer having a carboxyl group include: unsaturated monocarboxylic acids, such as acrylic acid, methacrylic acid, and crotonic acid; unsaturated dicarboxylic acids, such as maleic acid, itaconic acid, citraconic acid, and fumaric acid; and unsaturated dicarboxylic anhydrides, such as maleic anhydride, itaconic anhydride, and citraconic anhydride.
Examples of the method, in which a carboxyl group is introduced into a polymer (as prepared beforehand) by denaturation, include a method including the step of jumping up a polymer, having an OH group in opposite terminal portions, with pyromellitic dianhydride.
Examples of the hydrophilic monomer include: monomers having a carboxyl group; and other monomers, such as hydroxyethyl acrylate, hydroxyethyl methacrylate, vinylpyrrolidone, dimethylaminoethyl acrylate, and chloridized-triaminoethyl methacrylate.
Examples of the aqueous polymer having a carboxyl group, as preferably usable in the present invention, include: polyvinyl alcohols having a carboxyl group (for example, anionic KEPS series made by Dai-ichi Kogyo Seiyaku Co., Ltd., and K Polymer made by Kuraray Co., Ltd.); (meth)acrylic ester copolymers (for example, Arolon made by Nippon Shokubai Co., Ltd.); vinyl ether-maleic anhydride copolymers (Gantrez AN series made by ISP); and aqueous polymers having both a structural unit, as formed by ring-opening polymerization of an oxazoline compound, and a carboxyl group. Particularly preferable ones are the aqueous polymers having both a structural unit, as formed by ring-opening polymerization of an oxazoline compound, and a carboxyl group.
Examples of the above aqueous polymer having both a structural unit, as formed by ring-opening polymerization of an oxazoline compound, and a carboxyl group include a polymer having a structural unit of general formula (1) below: 
wherein: each of R1 and R2, independently of each other, denotes a
hydrogen atom or a methyl group;
R3 denotes a divalent organic residue;
R4 denotes a monovalent organic residue;
Z denotes a halogen atom;
a denotes an integer of 1xcx9c1,000;
b denotes an integer of 3xcx9c110,000; and
n denotes an integer of 3xcx9c5,000.
This polymer can be synthesized by carrying out cationic polymerization of an oxazoline compound in the presence of an unsaturated halide to synthesize a polyoxazoline macromonomer having a radical-polymerizable double bond at a polymerization-initiating terminal, and then copolymerizing this polyoxazoline macromonomer and a monomer having a carboxyl group, as is illustrated by the following chemical reaction formula: 
wherein R1, R2, R3, R4, Z, a, b, and n are the same as those in general formula (1).
Examples of the oxazoline compound, as usable in the above cationic polymerization, include 2-methyl-2-oxazoline, 2-ethyl-2-oxazoline, 2-(n-propyl)-2-oxazoline, 2-(i-propyl)-2-oxazoline, 2-(n-butyl)-2-oxazoline, 2-(i-butyl)-2-oxazoline, and 2-(t-butyl)-2-oxazoline. Preferable ones among them are compounds with not more than 3 carbon atoms in R4, of which specific examples include 2-ethyl-2-oxazoline.
Examples of the above unsaturated halide include chloromethylstyrene, allyl chloride, epichlorohydrin, and chloroethyl vinyl ether. A preferable one among them is chloromethylstyrene.
As to the monomer having a carboxyl group, compounds in which R2 is a hydrogen atom or a methyl group are preferable among the above-exemplified monomers having a carboxyl group. Specific examples of such compounds include acrylic acid and methacrylic acid.
Therefore, preferable examples of the aqueous polymer having both a structural unit, as formed by ring-opening polymerization of an oxazoline compound, and a carboxyl group include poly(2-methyl-2-oxazoline)/(meth)acrylic acid copolymers, poly(2-ethyl-2-oxazoline)/(meth)acrylic acid copolymers, poly(2-(n-propyl)-2-oxazoline)/(meth)acrylic acid copolymers, poly(2-(i-propyl)-2-oxazoline)/(meth)acrylic acid copolymers, poly(2-(n-butyl)-2-oxazoline)/(meth)acrylic acid copolymers, poly(2-(i-butyl)-2-oxazoline)/(meth)acrylic acid copolymers, and poly(2-(t-butyl)-2-oxazoline)/(meth)acrylic acid copolymers.
The above aqueous polymer having both a structural unit, as formed by ring-opening polymerization of an oxazoline compound, and a carboxyl group is available whether it contains a structural unit other than the structural unit of general formula (1) above or not.
In addition, in the above general formula (1), a is an integer of 1xcx9c1,000, preferably 1xcx9c500, and b is an integer of 3xcx9c10,000, preferably 3xcx9c5,000, and n is an integer of 3xcx9c5,000, preferably 10xcx9c5,000, more preferably 2xcx9c100, still more preferably 5xcx9c500.
The weight-average molecular weight of the above aqueous polymer having both a structural unit, as formed by ring-opening polymerization of an oxazoline compound, and a carboxyl group is preferably in the range of 50,000xcx9c1,000,000, more preferably 100,000xcx9c500,000.
Examples of the water-soluble polymer having an oxazoline group as a crosslinking agent, as contained in the first coating agent according to the present invention, include a polymer containing an oxazoline group as obtained by polymerizing a monomer component which comprises an addition-polymerizable oxazoline and, if necessary, further comprises a monomer copolymerizable therewith. Examples of the addition-polymerizable oxazoline include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-4-ethyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, 2-isopropenyl-5-ethyl-2-oxazoline, and 2-isopropenyl-4,5-dimethyl-2-oxazoline. These may be used either alone respectively or in combinations with each other. A preferable one among them is 2-isopropenyl-2-oxazoline, because it is industrially easily available.
The amount of the addition-polymerizable oxazoline, as used, is not especially limited, but is preferably 5 weight % or larger, more preferably in the range of 30xcx9c60 weight %, of the entire monomer component. In the case where the amount is smaller than 5 weight %, the extent of the curing is insufficient. In the case where the amount exceeds 60 weight %, it will have a bad effect on the water resistance.
Examples of the monomer copolymerizable with the addition-polymerizable oxazoline include: (meth)acrylic esters, such as methyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, polyethylene glycol mono(meth)acrylate, 2-hydroxyethyl (meth)acrylate, and 2-aminoethyl (meth)acrylate and its salts; unsaturated nitriles, such as (meth)acrylonitrile; unsaturated amides, such as (meth)acrylamide, N-ethylol(meth)acrylamide, and N-(2-hydroxyethyl)(meth)acrylamide; vinyl esters, such as vinyl acetate and vinyl propionate; vinyl ethers, such as methyl vinyl ether and ethyl vinyl ether; xcex1-olefins, such as ethylene and propylene; halogen-containing xcex1,xcex2-unsaturated monomers, such as vinyl chloride, vinylidene chloride, and vinyl fluoride; and xcex1,xcex2-unsaturated aromatic monomers, such as styrene, xcex1-methylstyrene, and sodium styrenesulfonate. These may be used either alone respectively or in combinations with each other.
To obtain the water-soluble polymer, the ratio of the hydrophilic monomer to the entire monomer component to be polymerized is preferably 50 weight % or higher, particularly preferably in the range of 60xcx9c90 weight %. Examples of the hydrophilic monomer include addition-polymerizable oxazolines, 2-hydroxyethyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, polyethylene glycol mono(meth)acrylate, and 2-aminoethyl (meth)acrylate and its salts, and further, sodium (meth)acrylate, ammonium (meth)acrylate, (meth)acrylonitrile, (meth)acrylamide, N-methylol(meth)acrylamide, N-(2-hydroxyethyl)(meth)acrylamide, and sodium styrenesulfonate, as are selected from among the aforementioned monomer components.
The aqueous polymer having a carboxyl group is contained in the first coating agent in the ratio of preferably 5xcx9c95 weight %, more preferably 10xcx9c90 weight %, still more preferably 50xcx9c90 weight %, in terms of solid content, to the entire weight of the first coating agent. The water-soluble polymer having an oxazoline group, as used as the crosslinking agent, is contained in the first coating agent in the ratio of preferably 5xcx9c95 weight %, more preferably 10xcx9c90 weight %, still more preferably 10xcx9c50 weight %, in terms of solid content, to the entire weight of the first coating agent.
The first coating agent may further comprise components other than the aqueous polymer having a carboxyl group and the water-soluble polymer having an oxazoline group as the crosslinking agent, if necessary. Examples of such other components include: curing catalysts, such as paratoluenesulfonic acid (PTSA); organic or inorganic fine particles; dye mordants; pigments; dispersants; and ultraviolet absorbing agents.
The second coating agent, according to the present invention, comprises a polymer and a crosslinking agent, wherein the polymer has both a structural unit, as formed by ring-opening polymerization of an oxazoline compound, and a carboxyl group. Incidentally, this xe2x80x9cpolymer having both a structural unit, as formed by ring-opening polymerization of an oxazoline compound, and a carboxyl groupxe2x80x9d is mentioned in detail above.
Examples of the crosslinking agent, as used for the second coating agent, include the water-soluble polymer having an oxazoline group as mentioned in detail above, and further, melamine, aziridine, isocyanate, and epoxy.
The polymer having both a structural unit, as formed by ring-opening polymerization of an oxazoline compound, and a carboxyl group is contained in the second coating agent in the ratio of preferably 5xcx9c95 weight %, more preferably 10xcx9c90 weight %, still more preferably 50xcx9c90 weight %, in terms of solid content, to the entire weight of the second coating agent. The crosslinking agent is contained in the second coating agent in the ratio of preferably 5xcx9c95 weight %, more preferably 10xcx9c90 weight %, still more preferably 10xcx9c50 weight %, in terms of solid content, to the entire weight of the second coating agent.
The second coating agent may further comprise components other than the polymer having both a structural unit, as formed by ring-opening polymerization of an oxazoline compound, and a carboxyl group and the crosslinking agent, if necessary. Examples of such other components include: curing catalysts, such as paratoluenesulfonic acid (PTSA); organic or inorganic fine particles; dye mordants; pigments; dispersants; and ultraviolet absorbing agents.
The ink jet recording material, according to the present invention, has on at least one face thereof a coated and cured layer of the present invention first coating agent and/or a coated and cured layer of the present invention second coating agent.
The ink jet recording material is a sheet-shaped material as used to record images thereon with ink jet recording apparatuses. Examples of such ink jet recording materials include: paper, synthetic paper such as Tyvek (made by E.I. Du Pont DE NEMOURS and Co., Ltd.); cloths, such as canvas, clothing fabrics and non-woven composites; films or sheets of plastics such as polyvinyl chloride, polypropylene, and polyethylene terephthalate (PET).
The amount of the present invention first or second coating agent, as coated, is preferably in the range of 3xcx9c50 g, more preferably 5xcx9c40 g, per square meter. In the case where the amount is smaller than 3 g, water cannot sufficiently be absorbed from ink. In the case where the amount exceeds 50 g, much time and energy are necessary for drying the sheet. In addition, the coating thickness is preferably in the range of 1xcx9c50 xcexcm, more preferably 5xcx9c40 xcexcm. In the case where the coating thickness is less than 1 xcexcm, water cannot sufficiently be absorbed from ink. In the case where the coating thickness exceeds 50 xcexcm, the improvement of the ink absorbency cannot be expected very much, so there are economical disadvantages.
The curing temperature is preferably in the range of 50xcx9c200xc2x0 C., more preferably 80xcx9c150xc2x0 C. The curing time depends on the curing temperature, but is preferably in the range of 1xcx9c60 minutes, more preferably 1xcx9c30 minutes.
(Effects and Advantages of the Invention):
Coating an ink jet recording material with the present invention coating agent for ink jet recording materials can give an ink jet recording material which displays sufficient water resistance and further, excellent definition of initial images.
Hereinafter, the present invention is more specifically illustrated by the following examples of some preferred embodiments in comparison with comparative examples not according to the invention. However, the invention is not limited to the below-mentioned examples. In addition, in the examples, unless otherwise noted, the units xe2x80x9c%xe2x80x9d and xe2x80x9cpart(s)xe2x80x9d denote those by weight.
 less than Synthesis of FX-AA as an Aqueous Polymer having a Carboxyl Group and further a Structural Unit of General Formula (1) greater than 
A mixture of 297 g of 2-ethyl-2-oxazoline, 9.2 g of chloromethylstyrene (mixture of m- and p-isomers) and 252.4 g of ethanol was charged into a 1-liter autoclave, and then heated at 130xc2x0 C. for 4 hours, thus obtaining an ethanol solution of poly(2-ethyl-2-oxazoline) macromonomer with a styrene functional group at a polymerization-initiating terminal. Then, 43.2 g of acrylic acid, 3.5 g of 2,2xe2x80x2-azobis(isobutyronitrile) and 50 g of ethanol were added to this ethanol solution, and the resultant mixture was heated within the range of 105 to 135xc2x0 C. for 6 hours. The reaction mixture was cooled, thus obtaining an ethanol solution of a poly(2-ethyl-2-oxazoline) macromonomer/acrylic acid copolymer (655.3 g of FX-AA; solid content=59.6 weight %).
 less than Synthesis of Water-soluble Polymer (A) having an Oxazoline Group as a Crosslinking Agent greater than 
A mixture of 29 parts of deionized water and 1 part of V-50 (polymerization initiator made by Wako Pure Chemical Industries, Ltd.: 2,2xe2x80x2-azobis(2-amidinopropane) dihydrochloride) were charged into a flask having a stirrer, a reflux condenser, a nitrogen-introducing tube, a dropping funnel, and a thermometer, and then heated to 60xc2x0 C. under a slow nitrogen gas current. Thereto, a monomer mixture was added from the dropping funnel over a period of 1 hour, with this monomer mixture having been prepared beforehand and comprising 0.4 parts of ethyl acrylate, 5.6 parts of methyl methacrylate, 4 parts of methoxypolyethylene glycol methacrylate (NK Ester AM-90G made by Shin-Nakamura Chemical Industrial Co., Ltd.), and 10 parts of 2-isopropenyl-2-oxazoline. During the reaction, nitrogen gas was continuously run, and the temperature in the flask was kept at 60xc2x11xc2x0 C. After the end of the addition, the same temperature was maintained for 9 hours, and then the mixture was cooled, thus obtaining an aqueous solution of a polymer (water-soluble polymer (A)) containing a 2-oxazoline group, of which the nonvolatile content was 40%, and the pH was 8.3.