JPH04216992A - Binder for coated sheet - Google Patents

Abstract

PURPOSE:To improve the adhesion and water resistance by using an aqueous solution of (meth)acrylamide copolymer or a grafted copolymer of thereof and polyvinyl alcohol, and a water-soluble zirconium compound as a curing agent. CONSTITUTION:An aqueous solution of copolymer of copolymer of 50 to 95wt.% of acrylamide or methacrylamide, 5 to 25wt.% of vinyl monomer having a carboxyl group and 0 to 45wt.% of copolymerizable alpha, beta-ethylene monomer, and a water-soluble zirconium compound are used as a curing agent. For example, an aqueous solution of 15 parts of polyvinylalcohol dissolved in 170 parts of water is stirred under heating by a stirrer in a reactor with a reflux cooler. Further 0.27 part of hydrogen peroxide is added to the aqueous solution and this mixture is allowed to flow back. In addition, 65 parts of acrylamide, 15 parts of acrylonitrile, 5 parts of acrylic acid and 115 parts of water are dripped into the aqueous mixture solution and are matured to complete a chemical reaction. Finally, an aqueous solution of zirconium carbonate is added to the obtained aqueous copolymer solution as a curing agent to produce a thermally sensitive coating liquid.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a binder for coated paper, and more specifically, the present invention relates to a binder for coated paper, and more specifically, it is a binder for coated paper that has strong adhesive strength, light resistance, good dispersibility and workability, and has excellent water resistance. This relates to paper binders.

0002

[Background Art] In recent years, the development and practical application of thermal recording methods, pressure-sensitive recording methods, and magnetic recording methods have been actively progressing. Among them, thermal recording methods have a feel similar to that of plain paper and are relatively inexpensive. For this reason, it has been put to practical use in the fields of computer output, calculator printers, medical measuring equipment recorders, facsimiles, automatic ticket vending machines, thermal copying, etc. The thermal recording paper used in this thermal recording method is usually manufactured in the same manner as so-called general coated paper such as art paper and coated paper. That is, in the production of art paper, coated paper, etc., inorganic pigments such as titanium oxide, calcium carbonate, clay, aluminum hydroxide, clay, and kaolin are added to casein, starch, or synthetic base paper in the form of rolls or sheets. It is coated using a coating liquid dispersed in water together with various binders such as latex, and then dried. Furthermore, mechanical treatment such as supercalendering is performed. Generally, these binders also have the function of uniformly dispersing the pigment in the coating liquid, but a dispersant may be used separately. Similarly, in thermal recording paper, leuco dye-based coloring components such as fluoran compounds and phthalide compounds, color developers such as phenolic compounds, sensitizers, fillers, etc. are used in magnetic recording paper, and in magnetic recording paper, γ-oxidation For pressure-sensitive recording paper, a coating liquid in which fine particles of clay such as kaolin or phenolic resin are uniformly dispersed together with a binder is applied to base paper (wood pulp paper, synthetic pulp paper, and synthetic paper are also used). ) and dried.

Binders for general coated paper such as art paper and coated paper, and various coated papers such as heat-sensitive recording paper, pressure-sensitive recording paper, and magnetic recording paper, include pigments, dyes, magnetic powders, and various other materials. Good dispersibility of additives, good adhesion, uniform and strong coating film, good water resistance, good viscosity stability, excellent workability, and economically inexpensive. In addition, as a binder for thermal paper, it must have good thermal response and not cause fogging, thermal head fusion, thermal head deterioration, etc. In addition, binders for pressure-sensitive paper are required to have high whiteness, excellent yellowing resistance after aging, and excellent printing properties.

Conventionally known binders for coated paper include, for example, polyvinyl alcohol, starch and modified products thereof, casein, gelatin, soybean protein, carboxymethylcellulose, gum arabic, methylcellulose, hydroxyethylcellulose, sodium alginate, polyacrylamide, Water-soluble substances such as sodium polyacrylate, alkaline modified styrene-maleic anhydride copolymer, styrene-butadiene copolymer, styrene-butadiene-acrylonitrile copolymer, ethylene-vinyl acetate copolymer, vinylidene chloride/acrylic Aqueous emulsions such as acid ester copolymers, vinylidene chloride/acrylonitrile copolymers, acrylonitrile/acrylic acid ester copolymers, polyurethane resins, chlorinated polypropylene resins, butadiene/acrylonitrile copolymers, vinyl acetate resins, etc. are known. There is.

However, such binders have drawbacks in water resistance, workability, foamability, whiteness, etc., and do not necessarily give satisfactory results from a practical standpoint. In addition, although water-based emulsions have water resistance, they have drawbacks such as fogging of the background and fusion of thermal heads, and are not sufficient. In order to improve these drawbacks, in JP-A-59-1796, the properties of polyvinyl alcohol and acrylic polymers were matched by graft copolymerization of acrylic monomers such as acrylamide and methacrylamide to polyvinyl alcohol. Furthermore, it is said to improve its performance as a binder by providing good workability and whiteness of the background. Furthermore, in JP-A-59-78887 and JP-A-59-232,893, (meth)acrylamide and (meth)acrylonitrile are graft copolymerized to polyvinyl alcohol, and this polymer is mixed with polyvinyl alcohol or carboxy-modified polyvinyl alcohol. A uniform coating layer is obtained by
It is said that it can prevent deterioration of recorded images, but
Water resistance was still not sufficient.

Furthermore, Japanese Patent Laid-Open No. 1-192898 proposes adding water and oil resistance to paper using a reinforcing agent made of a mixture of a polyvinyl alcohol-based synthetic resin and a soluble zirconium compound. There is no description of it as a paper binder, and its performance is not clear. Furthermore, Shinkin Kogyo (February 1974 issue, p. 7)
) proposes the use of a mixture of modified starch and a water-soluble zirconium compound as a paper strength enhancer, but there is no specific description of it as a binder for thermal paper, and its performance is not clear. Further, if starch is used as a binder for thermal paper, it is not practical because it causes problems such as residue adhering to the thermal head.

[0007]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention has been developed as a binder for coated paper, which has good viscosity stability and
It has excellent workability, satisfies the above requirements such as being able to obtain a uniform and strong coating film, has the required adhesive strength and water resistance, and in the case of heat-sensitive recording paper, has the stability of the colored image of leuco dye. The purpose of the present invention is to provide a binder that has improved dispersion performance, does not cause shock when mixing the dye dispersion liquid and the binder, and has dispersion performance in itself.

[0008]

[Means for Solving the Problems] The present invention has been made to achieve the above objects, and the gist thereof is as follows: 1) A) Acrineamide or methacrylamide 50-9
5% by weight B) 5 to 25% by weight of at least one type of vinyl monomer having a carboxyl group C) 0 to 45% by weight of a copolymerizable α,β-ethylenic monomer A binder for coated paper that uses a zirconium compound as a hardening agent. 2) A) 5-80% by weight of polyvinyl alcohol, B) 15-85% by weight of acrylamide or methacrylamide, C) 5-20% by weight of at least one type of vinyl monomer having a carboxyl group, D) Copolymerizable α, β - A binder for coated paper using an aqueous solution of a graft copolymer comprising 0 to 75% by weight of an ethylenic monomer and a water-soluble zirconium compound as a curing agent.

Here, the vinyl monomer having a carboxyl group is not particularly limited as long as it is water-soluble and has a vinyl group, such as a monocarboxylic acid or dicarboxylic acid or a salt thereof, but for example, (meth)acrylic acid , (meth)acrylic acid metal salt, (meth)acrylic acid ammonium salt,
Examples include maleic acid, metal salts of maleate, fumaric acid, metal salts of fumarate, itaconic acid, and metal salts of itaconic acid.

The copolymerizable α,β-ethylenic monomer is not particularly limited as long as it is an acrylic monomer that has some degree of solubility in water, but for example,
Methyl (meth)acrylate, ethyl (meth)acrylate, hydroxylethyl (meth)acrylate, hydroxypropyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate-methyl chloride quaternary salt, N-dimethylaminopropyl (meth)acrylamide, N-dimethylaminopropyl (meth)acrylamide-methyl chloride quaternary salt, acrylonitrile, 2-acrylamido-2-methylpropanesulfonic acid metal salt, diacetone acrylamide, vinyl acetate, vinyl ethers , vinyl compounds such as vinyl ketones, vinyl sulfonate metal salts,
Examples include N-vinyl-2-pyrrolidone, N-methylolacrylamide, allyl acetoacetate, and the like.

In order to satisfy the above-mentioned requirements as a binder for coated paper, the base polymer must have an affinity with paper and a high binding force, and be water-soluble but insoluble. Copolymers of monomers such as acrylamide, acrylonitrile, and methacrylic acid esters are based on the idea that they need to be not easily soluble but difficult to dissolve in water after being applied to paper and drying. Although they have good workability and whiteness of the background, they are somewhat lacking in water resistance, so we copolymerized vinyl monomers with carboxyl groups as crosslinking sites and used a curing agent to improve water resistance. ing. On the other hand, polyvinyl alcohol has strong adhesion to paper, high light resistance, oil absorption, and excellent printing properties, and is suitable for thermal paper, except for its disadvantages such as poor workability and poor background whiteness. Since it satisfies the above conditions as a binder, we designed the molecule based on the idea that a polymer that has both of the above components has its own characteristics, and since a mixture of both components will cause phase separation, polyvinyl alcohol is used as a backbone polymer, and by graft copolymerizing an acrylic monomer such as (meth)acrylamide and a vinyl monomer having a carboxyl group to this to introduce an acrylic copolymer chain into the polyvinyl alcohol side chain. By using a water-soluble zirconium compound as a curing agent, it is possible to obtain a binder that maintains high water resistance, has even better workability, and has excellent light resistance and color development against leuco dyes. especially,
By introducing a vinyl monomer having a carboxyl group into the side chain of the copolymer, it has good compatibility with polyvinyl alcohol and carboxy-modified polyvinyl alcohol, and can be easily mixed with dispersions of leuco dyes and color developers. can. Furthermore, the zirconium compound used as a curing agent is
It also undergoes a crosslinking reaction with the hydroxyl group of polyvinyl alcohol,
Since reaction with carboxyl groups creates stronger bonds, the water resistance of the copolymer becomes more effective by introducing a monomer having carboxyl groups into the side chain of the copolymer. It is also safer than other curing agents and does not cause coloring after application and drying.

In the copolymer composition of the present invention, (meth)
If the composition ratio of acrylamide is less than 50% by weight, the heat resistance (less sticking) will be poor, and if it is more than 95% by weight, the water resistance will be poor. In addition, if the vinyl monomer having a carboxyl group is less than 5% by weight, the number of crosslinking points with the zirconium compound will decrease, resulting in poor water resistance;
If the amount is more than 5% by weight, the pot life will be shortened and it will be difficult to use it as a binder. Furthermore, if the copolymerizable α,β-ethylenic monomer is more than 45% by weight, workability, fluidity, heat resistance, etc. will be poor.

Furthermore, in the composition of the graft copolymer, if the polyvinyl alcohol content is less than 5% by weight, the adhesion to the base paper will be weak, and if it is more than 80% by weight, the workability will be poor. If the amount of (meth)acrylamide is less than 15% by weight, the heat resistance (less sticking) will be poor;
If it is more than 5% by weight, water resistance will be poor. In addition, if the vinyl monomer having a carboxyl group is less than 5% by weight, there will be fewer crosslinking points with the zirconium compound, resulting in poor water resistance, and if it is more than 25% by weight, the pot life will be shortened.
It becomes difficult to use it as a binder. moreover,
If the copolymerizable α,β-ethylenic monomer is more than 45% by weight, workability, fluidity, heat resistance, etc. will be poor.

[0014] Although there are no particular restrictions on the production of the copolymer or graft copolymer aqueous solution of the present invention, it can be produced, for example, by the following method. However, of course, it may be manufactured by other methods. That is,
Add 1 to 3 ml of an aqueous solution of a mixture of (meth)acrylamide and a copolymer composition monomer to a boiling or constant temperature aqueous solution to which a peroxide is added in advance as a polymerization initiator.
The mixture is quantitatively added dropwise to react over a period of time, and the reaction is further aged for about 2 to 4 hours to complete the reaction. In addition, peroxide and a reducing agent are added as a polymerization initiator to an aqueous solution of a mixture of (meth)acrylamide and a copolymer composition monomer, which is controlled at a constant temperature, to react, and the reaction is further aged for about 2 to 4 hours. bring it to an end. Furthermore, as a method for producing a graft copolymer, (meth)acrylamide and copolymer composition monomers are added in an aqueous solution of polyvinyl alcohol that is boiled or controlled at a constant temperature to which a peroxide is added as a polymerization initiator in advance. An aqueous solution of the mixture is quantitatively added dropwise for about 1 to 3 hours to react, and the reaction is further aged for about 2 to 4 hours to complete the reaction.

[0015] Here, there are no particular restrictions on polyvinyl alcohol, but for example, polyvinyl alcohol with a degree of polymerization of 500 to 2,500
Complete saponification, intermediate saponification, partial saponification, acid-modified poval, etc. are used. The peroxide used as a polymerization initiator is not necessarily limited, but examples include hydrogen peroxide, tert-butyl hydroperoxide, ammonium persulfate, potassium peroxide, azobisisobutyronitrile, 2,2'-azobis( Water-soluble compounds such as 2-aminopropane dihydrochloride are preferred. There is no particular restriction on the amount of polymerization initiator used, but it is usually 0% relative to the monomer.
．． It is desirable to use about 1 to 5.0% by weight. The reducing agent is not necessarily limited, but for example, triethanolamine, diethanolamine, sodium sulfite, sodium thiosulfate, etc. are used. There is no particular restriction on the amount of reducing agent used, but it is usually 0.1% of the monomer.
It is used in an amount of about 10.0% by weight.

There is no particular restriction on the polymerization temperature, but in the case of graft polymerization, it is desirable to be high in order to increase the reaction rate and to make the monomer composition distribution of the copolymer uniform. is preferred because it is the most effective and does not require cooling after dissolving the polyvinyl alcohol. In order for the polymer film formed on paper applied as a copolymer for a coating solution to have sufficient strength, it is better for the copolymer to have a high molecular weight. The molecular weight results in high viscosity and poor workability. As a copolymer liquid with relatively high film strength and good workability,
For example, the viscosity of a 10% aqueous solution at room temperature is 10 to 50 cps.
In order to prepare an aqueous copolymer or graft copolymer solution with a viscosity within this range, the degree of polymerization of polyvinyl alcohol as a backbone polymer and the amount of polymerization initiator used must be within the above range. be. It is preferable that the degree of saponification of polyvinyl alcohol be close to complete saponification so that it has strong adhesion, but intermediate saponification is used in order to have good water resistance and to prevent gelation when the temperature drops. It is more preferable.

The zirconium compound as a curing agent is water-soluble and stable for a long time in an aqueous solution when mixed with the aqueous solution of the above copolymer or graft copolymer.
Sodium zirconium phosphate, carbonate, and Examples include water-soluble zirconium compounds such as zirconium/ammonium, zirconium hydroxide, basic zirconium carbonate, zirconium acetate, and zirconium/potassium carbonate. However, these specific examples are not intended to limit the invention.

[0018] When the above copolymer or graft copolymer and curing agent are mixed, both react and the viscosity increases, so the coating liquid prepared by mixing has poor workability during coating. Since the time during which the viscosity remains within a suitable range is limited, it is preferable to apply it to the paper to be used within the pot life. The mixing ratio of the copolymer or graft copolymer and the water-soluble zirconium compound is 10/1 to 10/1 based on the balance between the pot life of the mixed coating solution and the performance when applied to paper to form a coating layer.
10/5 is suitable, and from the same viewpoint, the pH of the mixed coating liquid and the concentrations of the above-mentioned copolymer and water-soluble zirconium compound are preferably 5 to 9 and 3 to 10% by weight, respectively.

When the binder for thermal paper of the present invention is used for leuco dye-based thermal recording paper, it strengthens the binding of the color former component, color developer component, filler, etc. to the base paper, and prevents yellowing of the recording paper. In addition to eliminating this problem, it also improves water resistance and light resistance after coloring with a color former. The color-forming compounds that serve as the color-forming agent components are leucolactone compounds and spiropyran compounds, and typical examples thereof are 3,3-bis(p-dimethylaminophenyl)-phthaloid, 3,3-bis(p-dimethylamino phenyl)-6-dimethylamino-phthalide (crystal violet lactone), 3-N-ethyl-N-isoamylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinoflurane Oran,
3-N-methyl-N-cyclohexyl-6-methyl-7
- Examples include anilinofluorane. In addition, as the color developer component that reacts with the above dye to develop color, a phenolic compound or an organic acid is effective, and it is solid at room temperature, and
Those having the property of liquefying or vaporizing at 0°C or higher are desirable, such as 4,4-isopropylidenediphenol (bisphenol A), 4-tert-butylphenol,
Methyl p-hydroxybenzoate, bisphenol S, 3
, 4-dihydroxyphenyl-p-tolylsulfone, and the like. Examples of the organic acid include homopolymerization oligomers of organic acid monomers such as stearic acid, benzoic acid, acrylic acid, and itaconic acid, and copolymerization oligomers thereof with styrene, acrylamide, and the like.

The above-mentioned color forming agent component and color developing agent component can be used alone or in a mixture of two or more as necessary. Examples of fillers include inorganic substances such as calcium carbonate, talc, titanium oxide, clay, and kaolin, and synthetic resins such as polystyrene. These can be used alone or in combination
Can be used by mixing more than one species. The appropriate mixing ratio of the color former, developer, filler, and binder is 1:0.1 to 1:0.3; if the amount of binder is less than this ratio, the binding force will be weak and the performance as a binder will be lost. However, as the amount of binder increases, the color development sensitivity decreases.

When producing a heat-sensitive coating composition, in addition to the above-mentioned color forming agent, developer, filler, and binder, in order to stabilize color development, if necessary, an anti-fading agent, an anti-coloring agent, and a sensitizer are added. Auxiliary agents may be added, and wax or the like may also be added to prevent thermal head fusion.

[0022]

EXAMPLES Next, the present invention will be explained in more detail with reference to Synthesis Examples, Examples, and Comparative Examples. In the examples, "parts" represent "parts by weight" unless otherwise specified.

Synthesis Example 1 In a reactor equipped with a stirrer and a reflux condenser, 15 parts of polyvinyl alcohol with a degree of saponification of 88% and a degree of polymerization of 1500 were mixed with 170 parts of water.
The aqueous solution was heated with stirring to raise the temperature to the boiling point, and 0.27 parts of hydrogen peroxide was added and refluxed. To this, a monomer aqueous solution containing 65 parts of acrylamide, 15 parts of acrylonitrile, 5 parts of acrylic acid, and 115 parts of water was added dropwise over 3 hours, and the mixture was aged for 2 hours to complete the reaction. The concentration of the graft copolymer at this time was 35% by weight, but this was diluted with water to adjust the concentration of the graft copolymer to 10% by weight. An aqueous graft copolymer solution having a viscosity of 20 cps was obtained.

Synthesis Example 2 180 parts of water was placed in a reactor equipped with a stirrer and a reflux condenser, heated while stirring to raise the temperature to 80°C, and 1.0 part of ammonium persulfate and 1.3 parts of triethanolamine were added.
Added a section. To this, 77.5 parts of acrylamide, 7.5 parts of methyl methacrylate, 15 parts of acrylic acid and 10 parts of water were added.
A monomer aqueous solution containing 5 parts of the monomer aqueous solution was added dropwise over 3 hours while maintaining the temperature of the reaction solution at 80° C., and then aged for 2 hours to complete the reaction. The concentration of the copolymer at this time is
The copolymer concentration was 35% by weight, but this was diluted with water to adjust the concentration of the copolymer to 10% by weight, and as shown in Table 1, 20%
An aqueous copolymer solution having a viscosity of 18 cps at °C was obtained.

Synthesis Example 3 Acrylamide 7 was placed in a reactor equipped with a stirrer and a reflux condenser.
2.5 parts, 7.5 parts of methyl methacrylate, 10.0 parts of 2-hydroxypropyl methacrylate, 1 part of acrylic acid
Add a monomer aqueous solution containing 0 parts of diethanolamine, 6.0 parts of diethanolamine, and 400 parts of water, and add 3 parts of nitrogen while keeping the temperature at 20°C.
It blew for 0 minutes. Add 4 potassium persulfate to this monomer aqueous solution.
．． 0 parts was added, reacted, and aged for 2 hours to complete the reaction. The concentration of the copolymer at this time is 20% by weight, but by diluting this with water, the concentration of the copolymer becomes 10% by weight.
The viscosity at 20°C is 40 as shown in Table 1.
An aqueous copolymer solution of cps was obtained.

Synthesis Example 4 A graft copolymer was obtained in the same manner as Synthesis Example 1 except that the monomer composition was changed as shown in Table 1.

[0027]

[Table 1] Example 1 a) Preparation of heat-sensitive coating liquid and its stability (liquid I) 3-N-ethyl-N-isoamylamino-6-
16 parts of methyl-7-anilinofluorane, 10 parts by weight of partially oxidized polyvinyl alcohol (degree of polymerization 500, degree of saponification 88%) aqueous solution, 4 parts water and (liquid II) 16 parts bisphenol A, 8 parts p-benzylbiphenyl parts, 10 parts by weight of partially saponified polyvinyl alcohol (degree of polymerization 500, degree of saponification 88%) aqueous solution,
Each liquid consisting of 4 parts of water was mixed separately in a ball mill for 3 hours to prepare a dispersion. Furthermore, 10 parts of liquid I, 3 parts of liquid II
0 parts, 60 parts of a 40% dispersion of calcium carbonate, 10 parts of a 30% dispersion of zinc stearate, 17 parts of the 35% aqueous copolymer solution obtained in Production Example 1, 1 part of a 45% aqueous solution of zirconium ammonium carbonate as a hardening agent. .5 parts were mixed and further 47 parts of water was added to obtain a heat-sensitive coating liquid. Further, the coating solution was left at room temperature for 24 hours, and the stability of the coating solution was examined. The results are shown in Table 2. ○: The coating liquid remained uniform. Δ: Slight layer separation was observed or the viscosity was slightly increased. ×: Either layer separation occurred or the viscosity increased considerably.

B) Production of heat-sensitive recording paper The heat-sensitive coating liquid obtained in step a) was applied to the surface of 60 g/m2 high-quality paper with No. The recording paper was coated using a No. 16 wire bar and dried to obtain a recording paper with a coating amount of 5 g (solid content)/m 2 .

C) Evaluation method of thermal recording paper Using the thermal recording paper obtained as in b) as a sample, the quality was evaluated by the following method. The measurement results are shown in Table 2. Image density measurement: Pulse width 1.
Color was developed at a voltage of 18 V for 2 ms, and the color density was measured using a Macbeth densitometer. The higher the number, the darker the color is. Oil resistance: Cottonseed oil was applied to the printed thermal paper, left for 24 hours, and the density of the colored area was measured. Stickiness;
The deposits on the head during image printing were observed. ○: Almost no deposits were observed. △: Slight adhesion is observed. x: Adhesive matter is observed on the head. Water resistance: 0.2 g of water at 20° C. was poured onto the colored printed heat-sensitive layer, and after being exposed for 1 minute, the colored printed portion was observed by rubbing with a fingertip. ○: The printed portion was hardly peeled off. Δ: The printed portion was slightly peeled off. ×: The printed portion peeled off.

Examples 2 to 5 The monomer composition in Example 1 a) is shown in Table 1 Synthesis Examples 2 to 4.
Tests similar to those in Example 1 a) to c) were conducted using the copolymers and zirconium compound curing agents changed as follows. Table 2 shows the properties of the obtained thermal recording paper.

Comparative Example 1 The same tests as in Example 1 (a) to (c) were conducted using polyacrylamide instead of the copolymer used in Example 1 (a). Table 2 shows the properties of the obtained thermal recording paper.

Comparative Example 2 Partially saponified polyvinyl alcohol (polymerization degree 1500, saponification degree 88) was used instead of the copolymer used in Example 1a).
%), tests similar to those in Example 1 a) to c) were conducted. Table 2 shows the properties of the obtained thermal recording paper.

Comparative Example 3 A heat-sensitive coating solution was prepared in Example 1 (a) without using the curing agent, and the same tests as in Examples 1 (a) to (c) were conducted. Table 2 shows the properties of the obtained thermal recording paper.

As shown in Test Results Table 2, by using a mixture of the copolymer or graft copolymer of the present invention and a water-soluble zirconium compound as a binder, a uniform coating solution can be obtained. The heat-sensitive recording paper used had good color development, improved water resistance and solvent resistance, and little sticking.

[0035]

Effects of the Invention According to the present invention, a binder for coated paper using an aqueous solution of a (meth)acrylamide copolymer or its graft copolymer to polyvinyl alcohol and a water-soluble zirconium compound as a hardening agent has a high viscosity stability. It satisfies various conditions such as being easy to work with and producing a uniform and strong coating film. It also has the adhesive strength and water resistance required for thermal recording paper, and has the stability of colored images produced by leuco dyes. It is useful as a binder for coated paper because it improves the properties of the dye and does not cause shock when mixing the dye dispersion and the binder.

Claims (2)

[Claims] [Claim 1] A) Acrylamide or methacrylamide 50-9
5% by weight B) 5 to 25% by weight of at least one type of vinyl monomer having a carboxyl group C) 0 to 45% by weight of a copolymerizable α,β-ethylenic monomer A binder for coated paper that uses a zirconium compound as a hardening agent. 2. A) 5 to 80% by weight of polyvinyl alcohol, B) 15 to 85% by weight of acrylamide or methacrylamide, C) 5 to 20% by weight of at least one type of vinyl monomer having a carboxyl group, and D) Copolymerizable. A binder for coated paper using an aqueous solution of a graft copolymer comprising 0 to 75% by weight of an α,β-ethylenic monomer and a water-soluble zirconium compound as a curing agent.