JP2005001378A - Surface coating agent for ink-jet recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface coating agent for an ink-jet recording medium that is excellent in dispersion-stability and avails the recording medium with which a recorded image of high gloss and high resolution almost equal to a color photograph can be obtained in the case of coating the surface of the recording medium at the ink-jet recording method. <P>SOLUTION: The surface coating agent for the ink-jet recording medium includes (A) an anion colloidal silica treated with a coupling agent and (B) a polymer emulsion or a water-soluble polymer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a surface coating agent for an ink jet recording medium. More specifically, the present invention is excellent in dispersion stability, and is applied to the surface of a recording medium such as paper, pigment coated paper, resin film, etc. The present invention also relates to a surface coating agent for an ink jet recording medium that can obtain a high-gloss and high-resolution recording image comparable to a color photograph.

The ink jet recording method is rapidly spreading because it has low noise and can perform high-speed recording, multiple colors, and compact equipment.
With the recent increase in the speed of inkjet recording devices, higher definition of recorded images, and full color, the required quality of recording media has become increasingly severe, with high gloss that is comparable to color photography. A recording medium capable of obtaining a resolution-recorded image is desired.

  In particular, recently, high-speed printing and multi-color printing that are not comparable to the previous ones are performed, so with conventional recording media, glossiness, ink absorption, when multiple colors of ink adhere to the same location Insufficient color developability, color sharpness, fineness, and the like, resulting in a problem that a high-resolution recorded image that satisfies the currently required quality cannot be obtained.

As a method for solving the above problems, the present inventors have already applied a method (Patent Document 1: Japanese Patent Laid-Open No. 2000-238418) for coating a recording medium with a polymer emulsion having a specific particle diameter and anionic colloidal silica. is suggesting.
However, this method has a problem that the quality of glossy paper tends to deteriorate with time in the manufacturing process, although a high-resolution recorded image can be obtained with a certain degree of gloss.

  That is, when this coating agent is applied to the surface of a recording medium such as recording paper, a cationic substance contained in the ink fixing layer previously applied to the surface of the recording medium is mixed in the coating agent. Therefore, when the excess coating agent is scraped off for recycling, the dispersion stability of the anionic colloidal silica or polymer emulsion in the coating agent decreases due to the contamination from this ink fixing layer, The glossiness may be adversely affected, and the anionic colloidal silica and the polymer emulsion may be thickened and gelled, which may make stable production difficult.

In general, as a means for improving the dispersion stability of a coating agent, there is a method of adding a dispersing agent such as a water-soluble polymer, but in this method, a coating agent satisfying the recent requirements as described above can be obtained. Absent. Also, dispersion stability is improved by a method of reducing the concentration of the coating agent, but in this case, the drying load in the production process increases and the quality of the glossy paper tends to be lowered.
Thus, simultaneously improving the dispersion stability of the coating agent, increasing the gloss of the recorded image obtained by printing with the full color ink after coating the coating agent, and increasing the resolution comparable to a color photograph. Satisfaction was extremely difficult. On the other hand, dye-based inks have been mainly used as inks for printing with full-color inks, but pigment-based inks have recently been used. Therefore, a recording medium capable of giving a high-resolution recording image to both of these inks is desired.

JP 2000-238418 A

  The present invention has been made in view of such circumstances, and is excellent in dispersion stability and has a high glossiness equivalent to that of a color photograph when coated on the surface of a recording medium in an ink jet recording system. An object of the present invention is to provide a surface coating agent for an ink jet recording medium that provides a recording medium from which a recorded image can be obtained. Furthermore, it aims at providing the surface coating agent for inkjet recording media excellent in the printability of both dye-type ink and pigment-type ink.

  As a result of intensive studies to achieve the above object, the present inventors have found that a surface coating agent comprising an anionic colloidal silica treated with a coupling agent, preferably a silane coupling agent, and a polymer emulsion. However, it has excellent dispersion stability, and by using a recording medium coated with this, high-gloss recording that is comparable to a color photograph with high gloss when printed with either dye-based ink or pigment-based ink. The inventors found that an image can be obtained and completed the present invention.

（式中、Ｒ¹は水素原子またはメチル基を示し、Ｒ²は炭素数１〜２２の飽和もしくは不飽和の直鎖状または分岐状の脂肪族炭化水素基を示す。）
（ｃ）α，β−不飽和カルボン酸およびその塩類から選ばれる少なくとも１種のモノマー：０．５〜３０質量％
（ｄ）（ａ）〜（ｃ）のモノマーと共重合可能なモノマー：０〜２０質量％
を提供する。 That is, the present invention
1. (A) an anionic colloidal silica treated with a coupling agent, and (B) a polymer emulsion or a water-soluble polymer, a surface coating agent for an ink jet recording medium,
2. (B) The surface coating agent for an inkjet recording medium according to 1 above, wherein the average particle size of the polymer emulsion is 0.02 to 0.15 μm,
3. 1 or 2 surface coating agent for inkjet recording media, wherein the coupling agent is a silane coupling agent;
4). (C) the surface coating agent for an inkjet recording medium according to any one of 1 to 3, further comprising (C) anionic colloidal silica;
5. The (B) polymer emulsion is a copolymer obtained by copolymerizing the following monomers (a) to (d) at the ratio shown below, and the copolymer has a glass transition temperature of 0 to 200 ° C. The surface coating agent for an inkjet recording medium according to any one of 1 to 4,
(A) At least one monomer selected from styrene and α-methylstyrene: 5 to 95% by mass
(B) At least one monomer selected from acrylic acid ester and methacrylic acid ester represented by the following general formula (1): 0.5 to 94.5% by mass

(In the formula, R ¹ represents a hydrogen atom or a methyl group, and R ² represents a saturated or unsaturated linear or branched aliphatic hydrocarbon group having 1 to 22 carbon atoms.)
(C) At least one monomer selected from α, β-unsaturated carboxylic acid and salts thereof: 0.5 to 30% by mass
(D) Monomer copolymerizable with monomers (a) to (c): 0 to 20% by mass
I will provide a.

The surface coating agent for an ink jet recording medium of the present invention contains an anionic colloidal silica treated with a coupling agent and a polymer emulsion or a water-soluble polymer. It is not easily affected by foreign matter mixed in, contributes to stable production of recording media, and can be expected to be stable in operation. In addition, by applying the surface coating agent of the present invention to a recording medium, the color clarity, resolution, and gloss of an image printed on the recording medium by a recording apparatus can be increased, which is comparable to a color photograph. A high-resolution recorded image can be obtained.
In addition, it is possible to provide a surface coating agent for inkjet recording media that is excellent in printability of both dye-based inks and pigment-based inks. As a result, the inkjet is excellent in versatility regardless of the type of inkjet printer. This can contribute to the production of recording media.

Hereinafter, the present invention will be described in more detail.
The surface coating agent for inkjet recording media according to the present invention comprises (A) an anionic colloidal silica treated with a coupling agent, and (B) a polymer emulsion or a water-soluble polymer. is there.
In the present invention, the anionic colloidal silica treated with the coupling agent is a colloidal solution in which spherical silica is dispersed in water, and the silanol groups on the particle surface are negatively charged, sodium hydroxide, sodium silicate, It exhibits anionicity by neutralization with a base such as an organic amine.

As such anionic colloidal silica, commercially available products can be used. For example, silica dol (manufactured by Nippon Chemical Industry Co., Ltd.), Adelite AT (manufactured by Asahi Denka Kogyo Co., Ltd.), cataloid ( Catalytic Chemical Industry Co., Ltd.), Snowtex (Nissan Chemical Industry Co., Ltd.), etc., but a sol-like aqueous dispersion having a pH of 8-12 and a weight concentration of 20-50% It is preferable from the viewpoint of compatibility stability with the combined emulsion.
The average particle diameter of the anionic colloidal silica is not particularly limited, but is preferably 0.01 to 0.15 μm, more preferably 0.02 to 0.12 μm. If the average particle size is less than 0.01 μm, the ink absorbability may be lowered, and if it exceeds 0.15 μm, the sharpness of the recorded image may be lowered.

The coupling agent used for the treatment of anionic colloidal silica is not particularly limited, and various known coupling agents can be used, but from the viewpoint of excellent reactivity with colloidal silica, It is preferable to use a silane coupling agent.
Examples of the silane coupling agent include vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, γ-chloropropyltrimethoxysilane, γ-chloropropylmethyldichlorosilane, γ-chloropropylmethyldimethoxysilane, γ- Chloropropylmethyldiethoxysilane, γ-aminopropyltriethoxysilane, N- (β-aminoethyl) -γ-aminopropyltrimethoxysilane, N- (β-aminoethyl) -γ-aminopropylmethyldimethoxysilane, γ -Mercaptopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldimethoxysila Can be used. These may be used alone or in combination of two or more.

In the present invention, the anionic colloidal silica treated with the coupling agent can be usually obtained by adding a coupling agent to the anionic colloidal silica.
Specific treatment methods include, for example, a method in which anionic colloidal silica is preferably heated to 40 to 95 ° C., particularly about 70 ° C., and a coupling agent is continuously added dropwise thereto, and an anionic colloidal silica and a coupling agent are added. After charging and mixing at room temperature, reacting by heating to the above temperature, dropping the coupling agent to the anionic colloidal silica under reduced pressure, dropping the coupling agent and the alkali catalyst simultaneously onto the anionic colloidal silica Method, a method in which a coupling agent and an acid catalyst are simultaneously dropped onto an anionic colloidal silica, a method in which a coupling agent is dissolved in a solvent, and a reaction system containing an anionic colloidal silica, a coupling agent by an emulsifier A method of supplying to a reaction system containing anionic colloidal silica in an emulsified state, etc. Among them, it is possible to use a method in which anionic colloidal silica is heated to drop a coupling agent, or a method in which anionic colloidal silica and a coupling agent are charged at room temperature, mixed and then heated to react. preferable.

When the anionic colloidal silica is treated with the silane coupling agent, the amount of the silane coupling agent used is, for example, the addition amount of the silane coupling agent is usually 0 with respect to the effective amount of SiO _{2 in} the colloidal silica. 0.01 to 20% by mass, preferably 0.02 to 10% by mass, more preferably 0.05 to 5.0% by mass. If the amount added is less than 0.01% by mass, a sufficient effect of improving the dispersion stability cannot be obtained, and at the same time, the suitability of the pigment ink may be insufficient, and if it exceeds 20% by mass, the dispersion stability may be lowered. is there.

The (B) polymer emulsion or water-soluble polymer used in the surface coating agent of the present invention is not particularly limited and can be appropriately selected and used, but it is preferable to use a polymer emulsion. is there.
Examples of the water-soluble polymer include cellulose polymers such as methylcellulose, methylhydroxyethylcellulose, methylhydroxypropylcellulose, hydroxyethylcellulose, starch and modified products thereof, gelatin and modified products thereof, casein, pullulan, gum arabic, karaya gum, albumin and the like. Natural polymer resins or derivatives thereof, polyvinyl alcohol and modified products thereof. These may be used alone or in combination of two or more.

On the other hand, examples of the polymer emulsion include, for example, an ethylene-vinyl acetate copolymer emulsion resin, an aqueous urethane resin, an acrylic emulsion resin such as a (meth) acrylate polymer or copolymer, and an SBR latex. , NBR latex, and the like. These may be used alone or in combination of two or more.
In the present invention, it is particularly preferable to use a copolymer containing a copolymer obtained by copolymerizing the monomers (a) to (d) at the above ratio.
In this case, the specific types and copolymerization ratios of the monomers (a) to (d) are determined in consideration of the performance of the obtained surface coating agent for an ink jet recording medium.
The monomer (a) is at least one monomer selected from styrene and α-methylstyrene, and the copolymerization ratio thereof is preferably 5 to 95% by mass, more preferably 30 to 90% by mass. If it is less than 5% by mass, the print gloss may be insufficient, and if it exceeds 95% by mass, the light resistance may be insufficient.

The monomer (b) is at least one monomer selected from the acrylic ester and methacrylic ester represented by the above formula (1), and the copolymerization ratio is preferably 0.5 to 94.5 mass. %, More preferably 1 to 85% by mass. If the amount is less than 0.5% by mass, the sharpness of the color of the recorded image may be lowered. If the amount exceeds 94.5% by mass, the resolution of the recorded image may be lowered.
In the formula (1), examples of the saturated or unsaturated linear or branched aliphatic hydrocarbon group having 1 to 22 carbon atoms include methyl, ethyl, n-butyl, s-butyl, t-butyl, A pentyl, 2-ethylhexyl, lauryl, a stearyl group etc. are mentioned.

  Specific examples of the monomer (b) include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, and lauryl acrylate. Lauryl methacrylate, stearyl acrylate, stearyl methacrylate and the like. These may be used alone or in combination of two or more. Among these, it is particularly preferable to use an acrylate ester for improving the transportability in the recording apparatus and the resolution of the recorded image in a well-balanced manner.

The monomer (c) is at least one monomer selected from α, β-unsaturated carboxylic acids and salts thereof, and the copolymerization ratio is preferably 0.5 to 30% by mass, more preferably, 1 to 20% by mass. If it is less than 0.5% by mass, the resolution of the recorded image may be lowered, and if it exceeds 30% by mass, the water resistance may be lowered.
Specific examples of the monomer (c) include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, and their sodium, potassium and ammonium salts. These may be used alone or in combination of two or more. In particular, sodium salt or ammonium salt of acrylic acid or methacrylic acid is preferable from the viewpoint of cost and adhesion strength to the substrate.

The monomer (d) is an arbitrary monomer that can be copolymerized with the monomers (a) to (c), as long as the effect of the coating agent of the present invention is not impaired. , 20% by mass or less, preferably 0.1 to 15% by mass. If it exceeds 20% by mass, the print gloss may be lowered.
Specific examples of the monomer (d) include, for example, acrylamide, methacrylamide, N-hydroxymethyl acrylamide, 2-hydroxyethyl acrylate, methoxypolyethylene glycol methacrylate, vinyl acetate, acrylonitrile, methylene bisacrylamide, polyethylene glycol diacrylate, Examples thereof include divinylbenzene, trimethylolpropane triacrylate, styrenesulfonic acid and its salts, 2-acrylamido-2-methylpropanesulfonic acid and its salts.

  The glass transition temperature Tg of the polymer in the polymer emulsion in the present invention is not particularly limited, but is preferably 0 to 200 ° C, more preferably 20 to 180 ° C. When the glass transition temperature is less than 0 ° C, the thermal stability of the coating layer (coating film) is insufficient, and there is a risk of causing problems such as fusion when the coated surfaces are overlaid. There is a possibility that a coating layer (coating film) cannot be formed.

In the present invention, the glass transition temperature Tg of the polymer is a value calculated from the following Fox (FOX) equation.
In the following formula 1, Tg _{a to} Tg _d represent the glass transition temperature (K) of the homopolymer of each monomer of the above (a) to (d), and a to d represent the above (a) to (d). The copolymerization mass ratio of each monomer is shown, and a + b + c + d = 1.

The polymerization method and polymerization conditions for obtaining the polymer emulsion (B) are not particularly limited. For example, a usual emulsion polymerization method or the like can be used. In particular, the solid content of the polymer emulsion is 20 to 50. It is preferable to select production conditions such that the mass% and the average particle size are 0.02 to 0.15 μm, particularly 0.03 to 0.10 μm.
Here, if the average particle size is less than 0.02 μm, the print gloss may be lowered, whereas if it exceeds 0.15 μm, the sharpness of the recorded image may be lowered.

  Specifically, an emulsifier or the like is dissolved in water and, for example, the copolymer components (a), (b), (c), and (d) are added to emulsify, and a radical polymerization initiator is added to simultaneously react. In addition to the method of carrying out emulsion polymerization, there are methods of supplying the above-mentioned copolymerization component or radical polymerization initiator to the reaction system by methods such as continuous dropping and split charging, among these, the aggregate The continuous dripping method is preferred from the viewpoint that it is difficult to generate byproducts. In each of the above methods, a method of supplying the monomer composition to the reaction system in an emulsified state with an emulsifier can also be used. The polymerization temperature is preferably 40 to 95 ° C. In addition, in the emulsion polymerization method by continuous dripping, the method described in Japanese Patent Application No. 2002-146402 can be employed in which the copolymerization component is divided and polymerized in two stages.

In the case of employing emulsion polymerization, various conventionally known emulsifiers can be used as the emulsifier, but an anionic emulsifier is preferably used from the viewpoint of efficiently controlling the average particle size of the copolymer emulsion. preferable. Examples of such anionic emulsifiers include higher alcohol sulfates, alkylbenzene sulfonates, aliphatic sulfonates, dialkyl sulfosuccinates, alkyl naphthalene sulfonates, alkyl diphenyl ether disulfonates, and polyoxyethylene alkyl ethers. Emulsifiers such as sulfate ester salt, polyoxyethylene alkylphenyl ether sulfate ester, allyl alkylphenyl polyethylene oxide sulfate ester salt, and allyl alkyl sulfosuccinic acid diester salt can be used.
In addition, nonionic emulsifiers such as polyoxyethylene alkylphenyl ether, polyoxyethylene alkyl ether, polyoxyethylene alkyl ester, and polymer emulsifiers such as sodium polystyrene sulfonate and sulfonated polyvinyl alcohol are used in combination with anionic emulsifiers. There is no problem.

  On the other hand, the radical polymerization initiator used in the emulsion polymerization is not particularly limited, and examples thereof include peroxides such as hydrogen peroxide, ammonium persulfate, sodium persulfate, and potassium persulfate, and those peroxides. Various redox initiators usually used in combination, and azo initiators such as 2,2-azobis (aminodipropane) hydrochloride can be used. Further, if necessary, a molecular weight modifier such as dodecyl mercaptan, dialkylamine, or allyl alcohol may be used.

  In the surface coating agent for an ink jet recording medium of the present invention, the composition ratio of (A) the anionic colloidal silica treated with the coupling agent and (B) the polymer emulsion or the water-soluble polymer is preferably 9 in solid content ratio. 0.7 / 0.3 to 4/6, more preferably 9.5 / 0.5 to 5/5, and still more preferably 9.3 / 0.7 to 6/4. If the ratio of the polymer emulsion exceeds 60% by mass, the sharpness of the recorded image may be deteriorated, and if it is less than 3% by mass, the glossiness may decrease.

The ratio (X) / (Y) of the average particle size (X) of the anionic colloidal silica and the average particle size (Y) of the polymer emulsion is preferably 0.2 to 2.0, more preferably It is in the range of 0.3 to 1.5. If (X) / (Y) is outside the range of 0.2 to 2.0, the sharpness and glossiness of the recorded image may be reduced.
In the present invention, each average particle diameter refers to a value measured by an electrophoretic light scattering photometer (ELS-800, manufactured by Otsuka Electronics Co., Ltd.).

  The surface coating agent of the present invention may further contain (C) anionic colloidal silica that is not subjected to a coupling treatment. In this case, the amount added is treated with a coupling agent. It is good to set it as 500 mass parts or less with respect to 100 mass parts of anionic colloidal silica. Beyond this, there is a high possibility that the dispersion stability is particularly impaired.

As described above, the surface coating agent for an inkjet recording medium of the present invention contains (A) an anionic colloidal silica treated with a coupling agent, and (B) a polymer emulsion or a water-soluble polymer. The proportion of these components in the entire surface coating agent is usually 10 to 100% by mass, preferably 30 to 100% by mass.
In addition to the components (A) and (B) described above, the surface coating agent for an inkjet recording medium of the present invention includes a binder, a paper strength enhancer, a surface sizing agent, a charging agent generally used in paper processing and the like. Inhibitors, viscosity modifiers, dyes, UV absorbers, antioxidants, antifoaming agents, antifungal agents, anti-slip agents, film-forming aids, etc. may be used in combination. In this case, the blending ratio of these additives is not particularly limited as long as it does not inhibit the functions of the anionic colloidal silica treated with the coupling agent (A) and (B) the polymer emulsion. It is 0.1-50 mass% with respect to the whole surface coating agent, Preferably it is 1-30 mass%.

The substrate (inkjet recording medium) to be coated with the surface coating agent of the present invention is not particularly limited as long as it is suitable for inkjet recording. For example, natural pulp paper, pigment coated paper, and synthetic paper can be used. In addition, cloth and plastic film sheets such as polyethylene terephthalate can also be used.
When the surface coating agent is applied to the substrate, the coating amount is not particularly limited, but if it is less than 0.1 g / m ² , the thickness of the coating film is insufficient and the gloss of the recording medium is insufficient, resulting in 40 g / beyond m ^2, it becomes costly, 0.1~40g / m ^2, it is particularly preferably 1 to 30 g / m ^2. Also, the coating method is not particularly limited, and a conventionally used method such as an air doctor coater, an air knife coater, a blade coater, a roll coater, a curtain coater, a gravure coater, or a spray is adopted. can do.
When paper is used as the substrate, prior to coating, silica or alumina, or a mixture of these and a polymer latex binder is applied to the base paper as an ink fixing agent, and then the surface coating of the present invention is applied thereto. An agent may be applied.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated more concretely, this invention is not limited to the following Example. In the following description, “mass%” and “part by mass” are abbreviated as “%” and “part”, respectively, unless otherwise specified.

[1] (A) Production of anionic colloidal silica treated with a coupling agent [Production Example 1]
An apparatus equipped with a stirrer, a thermometer, a reflux condenser, and a dropping funnel was charged with 985 parts of anionic colloidal silica having an average particle size of 50 nm and a solid content of 40% (catalyst chemical industry Co., Ltd .: Cataloid SI-45P) And heated to 75 ° C. Next, 15 parts of γ-glycidoxypropylmethyldimethoxysilane was added dropwise over 15 minutes while maintaining at 75 ° C. with stirring, and the reaction was completed by incubating at the same temperature for 30 minutes. This was cooled to obtain an anionic colloidal silica (S-1) treated with a coupling agent.

[Production Example 2]
The same procedure as in Production Example 1 was performed except that the anionic colloidal silica was changed to one having an average particle size of 20 nm and a solid content of 30% (manufactured by Nippon Chemical Industry Co., Ltd., Silica Doll-30), and a coupling agent An anionic colloidal silica (S-2) treated with the above was obtained.

[2] (B-1) Production of polymer emulsion [Production Example 3]
In an apparatus equipped with a stirrer, thermometer, reflux condenser, dropping funnel and nitrogen introduction tube, 641 parts of deionized water, 9 parts of sodium salt (emulsifier) of polyoxyethylene (n = 5) lauryl ether sulfate and the following table 10 parts of the monomer composition shown in 1 was charged and heated to 75 ° C. under a nitrogen stream. Next, while maintaining at 75 ° C. with stirring, 10 parts of a deionized aqueous solution in which 1.5 parts of ammonium persulfate was dissolved was added to initiate the polymerization reaction. Next, 290 parts of the remaining monomer composition was added dropwise over 2 hours while maintaining the temperature at 75 ° C. Further, the polymerization reaction was completed by incubating at the same temperature for 1 hour. After cooling, the pH was adjusted to 8.0 with 10% ammonia water and diluted with deionized water to obtain a copolymer emulsion 1 having a solid content of 30%, a glass transition temperature of 70 ° C., and an average particle size of 0.053 μm. .

[Production Example 4]
A copolymer emulsion 2 having a solid content of 30%, a glass transition temperature of 63 ° C., and an average particle size of 0.061 μm was obtained except that the monomer composition was changed to the composition shown in Table 2 below. Got.

[Production Example 5]
In a reactor similar to Production Example 3, 490 parts of deionized water and 13 parts of the emulsion of the monomer composition shown in Table 3 below were charged and heated to 70 ° C. under a nitrogen stream. Subsequently, while maintaining the temperature at 70 ° C. with stirring, 10 parts of a deionized aqueous solution in which 2.3 parts of sodium persulfate was dissolved was added to initiate the polymerization reaction. Subsequently, 640 parts of the emulsion of the remaining monomer composition was added dropwise over 3 hours while maintaining the temperature at 100 ° C. Further, the polymerization reaction was completed by incubating at the same temperature for 1 hour. After cooling, the pH is adjusted to 7.7 with 10% sodium hydroxide and diluted with deionized water to obtain a copolymer emulsion 3 having a solid content of 40%, a glass transition temperature of 91 ° C., and an average particle size of 0.085 μm. Obtained.

Table 4 summarizes the monomer composition, glass transition temperature, and average particle size of the copolymer emulsions 1 to 3 obtained in Production Examples 3 to 5. The average particle diameter is a value measured by an electrophoretic light scattering photometer (ELS-800, Otsuka Electronics Co., Ltd.).
In Table 4, St is styrene, MMA is methyl methacrylate, BA is n-butyl acrylate, EA is ethyl acrylate, EMA is ethyl methacrylate, MAA is methacrylic acid, and AA is acrylic. Acid, MAm represents methacrylamide.

[3] (B-2) Production of water-soluble polymer [Production Example 6]
10 parts of commercially available polyvinyl alcohol (PVA217, manufactured by Kuraray Co., Ltd.) was added to 90 parts of ion-exchanged water, heated to 50 ° C., stirred for 2 hours with a stirrer, and 10% aqueous polyvinyl alcohol solution (water-soluble polymer 1). )

[Example 1]
The coupling agent-treated anionic colloidal silica (S-1) synthesized in Production Example 1 and the polymer emulsion 1 produced in Production Example 3 were combined with the coupling agent-treated anionic colloidal silica (S-1) and polymer. The mixture was mixed so that the solid content ratio with emulsion 1 was 9/1 and diluted with purified water to prepare a surface coating agent having a solid content of 30%.

[Examples 2 to 5]
All the examples except that the solid content ratio of the coupling agent-treated anionic colloidal silica (S-1) and the polymer emulsion 1 was changed to 7/3, 5/5, 3/7, and 1/9, respectively. In the same manner as in No. 1, a surface coating agent having a solid content of 30% was prepared.

[Example 6]
Surface coating with a solid content of 30% was performed in the same manner as in Example 1 except that the coupling agent-treated anionic colloidal silica was changed to the coupling agent-treated anionic colloidal silica (S-2) synthesized in Production Example 2. A working agent was prepared.

[Examples 7 to 10]
Examples All except that the solid content ratio of the coupling agent-treated anionic colloidal silica (S-2) and the polymer emulsion 1 was changed to 7/3, 5/5, 3/7, and 1/9, respectively. In the same manner as in No. 1, a surface coating agent having a solid content of 30% was prepared.

[Example 11]
The coupling agent-treated anionic colloidal silica (S-1) synthesized in Production Example 1 and the polymer emulsion 2 produced in Production Example 4 were combined with the coupling agent-treated anionic colloidal silica (S-1) and polymer. The mixture was mixed so that the solid content ratio with the emulsion 2 was 7/3 and diluted with purified water to prepare a surface coating agent having a solid content of 30%.

[Example 12]
A surface coating agent having a solid content of 30% was prepared in the same manner as in Example 11 except that the polymer emulsion was changed to the polymer emulsion 3 produced in Production Example 5.

[Example 13]
Surface coating with a solid content of 30% was performed in the same manner as in Example 11 except that the coupling agent-treated anionic colloidal silica was changed to the coupling agent-treated anionic colloidal silica (S-2) synthesized in Production Example 2. A working agent was prepared.

[Example 14]
Surface coating with a solid content of 30% was performed in the same manner as in Example 12 except that the coupling agent-treated anionic colloidal silica was changed to the coupling agent-treated anionic colloidal silica (S-2) synthesized in Production Example 2. A working agent was prepared.

[Example 15]
A surface coating agent having a solid content of 20% was prepared in the same manner as in Example 1 except that the component (B) was changed to the water-soluble polymer 1 obtained in Production Example 6.

[Comparative Example 1]
The coupling agent-treated anionic colloidal silica (S-1) synthesized in Production Example 1 was diluted with purified water to prepare a surface coating agent having a solid content of 30%.

[Comparative Example 2]
The coupling agent-treated anionic colloidal silica (S-2) synthesized in Production Example 2 was directly used as the surface coating agent.

[Comparative Example 3]
An anionic colloidal silica (H-1) having an average particle size of 50 nm and a solid content of 40% and the polymer emulsion 1 have a solid content ratio of 5/5 to the anionic colloidal silica (H-1) and the polymer emulsion 1. Were mixed and diluted with purified water to prepare a surface coating agent having a solid content of 30%.

[Comparative Example 4]
An anionic colloidal silica (H-2) having an average particle size of 30 nm and a solid content of 30% and the polymer emulsion 1 have a solid content ratio of 5/5 to the anionic colloidal silica (H-2) and the polymer emulsion 1. And a surface coating agent having a solid content of 30% was prepared.

  About the surface coating agent obtained in each of the above Examples and Comparative Examples, 3% of ammonium chloride, which is a typical foreign matter mixed in the surface coating agent from the ink fixing layer, is added to the solid content of the surface coating agent. And dispersion stability was evaluated. The results are shown in Table 5.

In Table 5, the dispersion stability was evaluated according to the following criteria.
A: No increase in viscosity is observed even after 1 day has elapsed since the addition of salt. O: No increase in viscosity is observed after 3 hours have elapsed since the addition of salt. Thickening is observed after 3 hours, but fluidity is maintained. X: Loss of fluidity within 3 hours after addition of salt

  As shown in Table 5, the surface coating agents of Examples 1 to 15 containing the anionic colloidal silica treated with the coupling agent and the polymer emulsion or the water-soluble polymer were compared with the coating agent of the comparative example. It can be seen that the dispersion stability is excellent.

[Examples 16 to 30, Comparative Examples 5 to 8]
Each surface coating agent prepared in Examples 1 to 15 and Comparative Examples 1 to 4 was dried on a paper having a basis weight of 85 g / m ² and a Steecht size of 6 seconds using an applicator bar # 4. After coating at 5 g / m ² , drying was performed at 100 ° C. for 40 seconds to obtain a test paper.
These test papers were dye-based inks (ICC21, ICM21, ICY21, ICLC21, ICLM21, ICDY21, ICBK21, all Seiko Epson (PMC950, manufactured by Seiko Epson Corporation) that are compatible with dye inks. The color was clearly printed, the resolution of the recorded image, and the glossiness were evaluated. The results are shown in Table 6.

  In addition, pigment inks (ICBK22, ICC22, ICY22, all manufactured by Seiko Epson Corporation) are used for the above test papers with an ink jet printer (PX-V700, manufactured by Seiko Epson Corporation) that supports pigment inks. They were used for full color printing, and the color clarity, the resolution of the recorded image, and the scratch resistance were evaluated. The results are shown in Table 7.

In Tables 6 and 7, each item was evaluated according to the following criteria.
(1) Vividness of color development The color of the recorded image and the vividness of the color development were visually determined according to the following criteria.
◎: Excellent color and color vividness, no color fading ○: Slight color fading but no problem in practical use △: Slightly inferior color or color development ×: Color fading , The vividness of color and color development is inferior

(2) Resolution of recorded image The degree of bleeding of the recorded image was visually determined according to the following criteria.
◎: No blurring ○: Slightly blurring, but no problem in practical use △: Slight blurring is observed ×: Bleeding is large

(3) Glossiness The glossiness of the printed test paper was visually determined according to the following criteria.
◎: Glossiness is very high and excellent ○: Glossiness is high to some extent △: Glossiness is not so much and slightly inferior ×: There is no glossiness and inferior

(4) Scratch resistance After 10 minutes from printing, the printed surface was lightly rubbed 3 times with a tissue paper, and how much the recorded image was retained was judged visually according to the following criteria.
◎: The recorded image is almost completely retained. ○: The recorded image is slightly retained and the original image can be read sufficiently. △: The recorded image has lost its clarity and what is the original image. X: Most of the pigment-based ink on the surface has disappeared

As shown in Table 6, tests of Examples 16 to 30 in which a coating agent containing an anionic colloidal silica treated with the coupling agent of Examples 1 to 15 and a copolymer emulsion or a water-soluble polymer was applied. It can be seen that when the paper is printed with a dye-based ink, the color sharpness, the resolution of the recorded image, and the glossiness are superior to the comparative example.
Moreover, as shown in Table 7, when the test papers of Examples 16 to 30 were printed with pigment-based inks, not only the color sharpness and the resolution of the recorded image were superior to those of the comparative examples. It can be seen that it is excellent in scratch resistance. In addition, the glossiness of the test papers of Examples 16 to 30 printed using the pigment-based ink was evaluated as ◯ or ◎.

Claims (5)

  A surface coating agent for an ink jet recording medium, comprising (A) an anionic colloidal silica treated with a coupling agent, and (B) a polymer emulsion or a water-soluble polymer.   2. The surface coating agent for an ink jet recording medium according to claim 1, wherein the average particle size of the (B) polymer emulsion is 0.02 to 0.15 [mu] m.   The surface coating agent for an ink jet recording medium according to claim 1, wherein the coupling agent is a silane coupling agent.   The surface coating agent for an inkjet recording medium according to any one of claims 1 to 3, further comprising (C) anionic colloidal silica. The (B) polymer emulsion contains a copolymer obtained by copolymerizing the following monomers (a) to (d) at the ratio shown below, and the glass transition temperature of this copolymer is 0 to 200 ° C. The surface coating agent for an inkjet recording medium according to any one of claims 1 to 4, wherein the surface coating agent is provided.
(A) At least one monomer selected from styrene and α-methylstyrene: 5 to 95% by mass
(B) At least one monomer selected from acrylic acid ester and methacrylic acid ester represented by the following general formula (1): 0.5 to 94.5% by mass

(In the formula, R ¹ represents a hydrogen atom or a methyl group, and R ² represents a saturated or unsaturated linear or branched aliphatic hydrocarbon group having 1 to 22 carbon atoms.)
(C) At least one monomer selected from α, β-unsaturated carboxylic acid and salts thereof: 0.5 to 30% by mass
(D) Monomer copolymerizable with monomers (a) to (c): 0 to 20% by mass