JP2001054982A - Thermal recording material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal recording material excellent in thermal response and whiteness. SOLUTION: In a thermal recording material containing an electron donative dye precursor which is usually colorless or pale colored and an electron acceptive compound which reacts with the precursor by heating and colors it, 4-hydroxy-4'-isopropoxydiphenyl sulfone as the electron acceptive compound is wet-crushed with sulfone-modified polyvinyl alcohol and partially saponified polyvinyl alcohol, and the mixture is added into a thermal recording layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording material. More specifically, the present invention relates to a heat-sensitive recording material having high thermal responsiveness and excellent whiteness.

[0002]

2. Description of the Related Art In general, a heat-sensitive recording material utilizes a color reaction between a colorless or pale-colored basic leuco dye and an organic or inorganic developer, and is heated by a heat head, a hot pen, a laser beam, or the like. This is to obtain a recorded image by contacting a coloring substance. Such a heat-sensitive recording material has advantages such as a simple recording apparatus, easy maintenance, and no generation of noise, and is widely used for various printer papers, facsimile papers, labels, and the like.

In particular, in recent years, heat-sensitive recording materials have been used for financial-related recording paper, such as receipts for gas, water, and electricity bills, financial institution ATM usage statements, and various receipts.

[0004] As the use and demand of the heat-sensitive recording material are expanding in various ways, the heat-sensitive recording material has a high thermal response, an image preservability,
A heat-sensitive recording material having excellent whiteness has been required.

[0005] Many proposals have been made to meet such demands. Particularly, as an electron-accepting compound,
4-hydroxy- described in JP-A-60-13852
4'-Isopropoxydiphenyl sulfone is known as an effective material.

However, this 4-hydroxy-4 '
-When isopropoxydiphenyl sulfone is pulverized to a submicron particle size, during wet pulverization for preparing a dispersion or during storage of the dispersion, the finely pulverized crystals take in water molecules and hydrate. And crystals grow. This crystal growth significantly reduces the thermal responsiveness.

As a wet pulverization method for suppressing the crystal growth of 4-hydroxy-4'-isopropoxydiphenyl sulfone, JP-A-1-237191 and JP-A-5-16.
No. 2,456, JP-A-6-143825, etc., but it is hard to say that all of them have obtained sufficient effects.

[0008]

The heat-sensitive recording material of the present invention suppresses the hydration of 4-hydroxy-4'-isopropoxydiphenyl sulfone, and provides a heat-sensitive recording material having excellent heat responsiveness and whiteness. The purpose was to.

[0009]

Means for Solving the Problems As a result of intensive studies, the present inventors have invented a heat-sensitive recording material of the present invention which can solve the problems. That is, the present invention relates to a heat-sensitive recording material containing an electron-donating, usually colorless to light-colored dye precursor, and an electron-accepting compound which reacts upon heating to form the dye precursor. A thermosensitive recording material characterized in that 4-hydroxy-4'-isopropoxydiphenyl sulfone is wet-ground with a sulfonated polyvinyl alcohol and a partially saponified polyvinyl alcohol as a compound in a thermosensitive recording layer.

In addition, the 4-hydroxy-4'-isopropoxydiphenyl sulfone obtained by wet grinding with a sulfonated polyvinyl alcohol and a partially saponified polyvinyl alcohol has an average particle size of 1.5 μm or less. It is a recording material.

The heat-sensitive recording material is characterized in that the content ratio by weight of the sulfonated polyvinyl alcohol to the partially saponified polyvinyl alcohol is in the range of 1: 9 to 9: 1.

[0012] Further, the present invention is characterized in that the sulfone group-modified polyvinyl alcohol and the partially saponified polyvinyl alcohol are contained in an amount of 3 to 15% by weight based on 4-hydroxy-4'-isopropoxydiphenyl sulfone. It is a recording material.

The sulfonated polyvinyl alcohol has a saponification degree of 80 to 90% and a polymerization degree of 20.
A heat-sensitive recording material having a range of 0 to 500.

The partially saponified polyvinyl alcohol has a saponification degree of 70-90% and a polymerization degree of 300-8.
00 is a heat-sensitive recording material.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the heat-sensitive recording material of the present invention will be described in detail. The heat-sensitive recording material of the present invention is provided with a heat-sensitive recording layer which develops color by heat on a support.

As the support used in the present invention, paper is mainly used. In addition to paper, various woven fabrics, nonwoven fabrics, synthetic resin films, synthetic resin laminated paper, synthetic paper, metal sheets, vapor-deposited sheets, Can be arbitrarily used according to the purpose.

The 4-hydroxy-4'-isopropoxydiphenyl sulfone used in the heat-sensitive recording material of the present invention is described in JP-A-60-13852.

The wet milling method of 4-hydroxy-4'-isopropoxydiphenyl sulfone used in the heat-sensitive recording material of the present invention may be a conventionally known method, for example, a ball mill, a sand mill, a glass bead mill or the like. Wet mills can be used.

The sulfonated polyvinyl alcohol used in the heat-sensitive recording material of the present invention has a saponification degree of 80 to 90.
%, And a polymerization degree in the range of 200 to 500 is preferably used.

The partially saponified polyvinyl alcohol used in the heat-sensitive recording material of the present invention preferably has a saponification degree in the range of 70 to 90% and a polymerization degree in the range of 300 to 800.

A sulfone group-modified polyvinyl alcohol,
The content ratio by weight of the partially saponified polyvinyl alcohol is 1:
It is preferably used in the range of 9 to 9: 1. If the weight ratio of the sulfone group-modified polyvinyl alcohol is too large beyond this range, that is, if the content weight ratio of the partially saponified polyvinyl alcohol is too small, the hydration of 4-hydroxy-4′-isopropoxydiphenyl sulfone The crystal growth is remarkable, and the liquid stability is significantly reduced. In the opposite case, the grinding efficiency of 4-hydroxy-4'-isopropoxydiphenyl sulfone will decrease.

It is also preferred that 4-hydroxy-4'-isopropoxydiphenylsulfone is wet-ground with a sulfone group-modified polyvinyl alcohol and a partially saponified polyvinyl alcohol and has an average particle size of 1.5 μm or less. More specifically, it is 1.0 μm or less. When the average particle size is larger than 1.5 μm,
Thermal responsiveness decreases.

The electron-donating, usually colorless or light-color, electron-donating dye precursor used in the heat-sensitive recording material of the present invention is typified by those generally used in pressure-sensitive recording paper and heat-sensitive recording paper. However, there is no particular limitation.

As a specific example, 3,3-bis (p-
Dimethylaminophenyl) -6-dimethylaminophthalide (crystal violet lactone), 3,3-bis (p-dimethylaminophenyl) phthalide, 3- (N,
N-diethyl) amino-7-dibenzylaminofluoran, 3- (N, N-diethyl) amino-7-phenylfluoran, 3- (N, N-diethyl) amino-6-methyl-7-anilino Fluoran, 3- (N, N-dibutyl) amino-6-methyl-7-anilinofluoran, 3
-(N, N-dipentyl) amino-6-methyl-7-anilinofluoran, 3- (N-ethyl, N-tolyl) amino-6-methyl-7-anilinofluoran, 3- (N
-Methyl, N-propyl) amino-6-methyl-7-anilinofluoran, 3- (N-ethyl, N-isoamyl) amino-6-methyl-7-anilinofluoran, benzoylleucomethylene blue, p- Known substances such as nitrobenzoyl leucomethylene blue, 3-methylspirodinaphthopyran, 3-ethylspirodinaphthopyran, and 3-benzylspirodinaphthopyran can be used, but the electron donor used in the heat-sensitive recording material of the present invention can be used. The colorless or light-colored electron-donating dye precursor having no color is not limited thereto, and may be used alone or as a mixture of two or more as necessary.

In the heat-sensitive recording material of the present invention, a heat-fusible substance can be contained in the heat-sensitive recording layer in order to improve the thermal response. In this case, those having a melting point of 60 # C to 180 # C are preferable, and those having a melting point of 80 # C to 140 # C are more preferable.

Specifically, stearic acid amide, N-hydroxymethylstearic acid amide, N-stearylstearic acid amide, ethylenebisstearic acid amide,
N-stearyl urea, benzyl-2-naphthyl ether, m-terphenyl, 4-benzylbiphenyl, 2,
2′-bis (4-methoxyphenoxy) diethyl ether, α, α′-diphenoxyxylene, bis (4-methoxyphenyl) ether, diphenyl adipate, dibenzyl oxalate, di (4-chlorobenzyl) oxalate,
Known heat-fusible substances such as dimethyl terephthalate, dibenzyl terephthalate, phenyl benzenesulfonate, bis (4-allyloxyphenyl) sulfone, 4-acetylacetophenone, acetoacetic anilides, and fatty acid anilides are exemplified. These compounds can be used alone or in combination of two or more. Also,
In order to obtain sufficient thermal responsiveness, it is preferable that the heat-fusible substance accounts for 5 to 50% by weight of the total solid content of the heat-sensitive recording layer.

The heat-sensitive recording layer constituting the heat-sensitive recording material of the present invention is obtained by mixing each aqueous dispersion obtained by finely pulverizing each color-forming component, a binder, etc., applying the mixture on a support, and drying. can get. The layer configuration of the heat-sensitive recording layer may be a single layer or a multilayer.

As the binder used in the heat-sensitive recording layer, various binders used in ordinary coating can be used.

Specifically, starches, hydroxymethylcellulose, methylcellulose, ethylcellulose,
Carboxymethylcellulose, gelatin, casein, polyvinyl alcohol, modified polyvinyl alcohol, sodium alginate, polyvinylpyrrolidone, polyacrylamide, acrylamide / acrylate copolymer,
Acrylamide / acrylic acid ester / methacrylic acid terpolymer, alkaline salt of polyacrylic acid, alkaline salt of polymaleic acid, alkaline salt of styrene / maleic anhydride copolymer, alkaline salt of ethylene / maleic anhydride copolymer Water-soluble binder such as alkali salt of isobutylene / maleic anhydride copolymer, and styrene / butadiene copolymer, acrylonitrile / butadiene copolymer, methyl acrylate / butadiene copolymer, acrylonitrile / butadiene / styrene terpolymer Water-dispersible binders such as polymers, polyvinyl acetate, vinyl acetate / acrylate copolymers, ethylene / vinyl acetate copolymers, polyacrylates, styrene / acrylate copolymers, and polyurethanes. But limited to this Not to.

In the heat-sensitive recording layer, as pigments, diatomaceous earth, talc, kaolin, calcined kaolin, heavy calcium carbonate, precipitated calcium carbonate, magnesium carbonate, zinc oxide, aluminum oxide, aluminum hydroxide, magnesium hydroxide, titanium dioxide , Barium sulfate, zinc sulfate,
Inorganic pigments such as amorphous silica, amorphous calcium silicate and colloidal silica, and organic pigments such as melamine resin filler, urea-formalin resin filler, polyethylene powder and nylon powder can be used.

The heat-sensitive recording layer has a head wear prevention,
For the purpose of preventing sticking, etc., zinc stearate,
Higher fatty acid metal salts such as calcium stearate, higher fatty acid amides such as stearic acid amide, lubricants such as paraffin, polyethylene wax, polyethylene oxide and caster wax, and ultraviolet absorption such as benzophenone and benzotriazole for the purpose of improving light resistance Agent, dispersion
As a wetting agent, a surfactant containing an anionic or nonionic high molecular weight, a fluorescent dye, an antifoaming agent or the like is added as necessary.

The method for forming the heat-sensitive recording layer is not particularly limited, and the heat-sensitive recording layer can be formed according to a conventionally known technique. Specific examples include various printing methods,
Apply a coating solution to the support by a method such as air knife coating, rod blade coating, bar coating, blade coating, gravure coating, curtain coating, or E-bar coating, and form a heat-sensitive recording layer by drying. Can be done.

The coating amount of the heat-sensitive recording layer is usually from 0.1 to 2.0 g / m ^{2 as} the coating amount of the dye precursor. 0.1g / m ²
If it is smaller than this, sufficient recording density cannot be obtained,
Also, if the amount exceeds 2.0 g / m ² , no improvement in color sensitivity is observed, and this is disadvantageous in cost.

In the heat-sensitive recording material of the present invention, if necessary, one or more undercoat layers composed of a single layer or a plurality of layers of pigments or resins can be provided between the support and the heat-sensitive recording layer. When the heat-sensitive recording material of the present invention is provided with a undercoat layer, the coating amount of the undercoat layer is preferably ^{1~30g / m 2, 3~20g / m} 2 is more preferable.

As the pigment for the undercoat layer, calcined kaolin is generally used. In addition, diatomaceous earth, talc, kaolin, heavy calcium carbonate, precipitated calcium carbonate, magnesium carbonate, zinc oxide, aluminum oxide , Aluminum hydroxide, magnesium hydroxide,
Use of inorganic pigments such as titanium dioxide, barium sulfate, zinc sulfate, amorphous silica, amorphous calcium silicate, and colloidal silica, and organic pigments such as melamine resin filler, urea-formalin resin filler, polyethylene powder, and nylon powder. Can be.

As the resin of the undercoat layer, various water-soluble resins or water-dispersible resins used in ordinary coating can be used. For example, starches, hydroxymethylcellulose, methylcellulose, ethylcellulose, carboxymethylcellulose, gelatin, casein, polyvinyl alcohol, modified polyvinyl alcohol, sodium alginate, polyvinylpyrrolidone, polyacrylamide, acrylamide / acrylate copolymer, acrylamide / acrylate / Methacrylic acid terpolymer, alkaline salt of polyacrylic acid, alkaline salt of polymaleic acid, alkaline salt of styrene / maleic anhydride copolymer, alkaline salt of ethylene / maleic anhydride copolymer, isobutylene / maleic anhydride Water-soluble resin such as an alkali salt of a copolymer, and styrene /
Butadiene copolymer, acrylonitrile / butadiene copolymer, methyl acrylate / butadiene copolymer, acrylonitrile / butadiene / styrene terpolymer, polyvinyl acetate, vinyl acetate / acrylate copolymer, ethylene / vinyl acetate Examples include copolymers, polyacrylates, styrene / acrylate copolymers, and water-dispersible resins such as polyurethane.

In the heat-sensitive recording material of the present invention, after a heat-sensitive recording layer is provided, one or more protective layers containing a water-soluble resin or a water-dispersible resin as a main component are further provided thereon to improve image storability. Can be done. Further, a resin that forms a film with an electron beam or ultraviolet light may be used. Dry coating amount of the protective layer is preferably ^{0.2~10g / m 2, 0.5~5g / m} 2 is more preferable.

The water-soluble resin or water-dispersible resin of the protective layer is appropriately selected from conventionally known water-soluble polymers or water-dispersible resins. That is, examples of the water-soluble resin include polyvinyl alcohol, modified polyvinyl alcohol, starch and derivatives thereof, cellulose derivatives such as hydroxyethylcellulose, methylcellulose, ethylcellulose and carboxymethylcellulose, polyvinylpyrrolidone, polyacrylamide, acrylamide / acrylic acid ester copolymer , Acrylamide / acrylic ester / methacrylic acid terpolymer, alkali salt of polyacrylic acid, alkali salt of polymaleic acid, alkali salt of styrene / maleic anhydride copolymer, alkali salt of ethylene / maleic anhydride copolymer And alkali salts of isobutylene / maleic anhydride copolymer, sodium alginate, gelatin, casein, acid neutralized products of chitosan, and the like.

Examples of the water-dispersible resin include styrene / butadiene copolymer, acrylonitrile / butadiene copolymer, methyl acrylate / butadiene copolymer, acrylonitrile / butadiene / styrene terpolymer,
Polyvinyl acetate, vinyl acetate / acrylate copolymer, ethylene / vinyl acetate copolymer, polyacrylate, styrene / acrylate copolymer, polyurethane, and the like can be used.

The protective layer may contain a pigment for the purpose of improving the recording running property, the writing property and the like. Specific examples of pigments include diatomaceous earth, talc, kaolin,
Calcined kaolin, heavy calcium carbonate, precipitated calcium carbonate, magnesium carbonate, zinc oxide, aluminum oxide,
Inorganic pigments such as aluminum hydroxide, magnesium hydroxide, titanium dioxide, barium sulfate, zinc sulfate, amorphous silica, amorphous calcium silicate, colloidal silica, melamine resin filler, urea-formalin resin filler, polyethylene powder, nylon Organic pigments such as powder can be used.

In the protective layer, higher fatty acid metal salts such as zinc stearate and calcium stearate, higher fatty acid amides such as stearic acid amide, paraffin and polyethylene are used for the purpose of improving recording running properties such as head abrasion prevention and sticking prevention. Lubricants such as wax, oxidized polyethylene and caster wax are added as needed.

The method for forming the undercoat layer and the protective layer is as follows.
There is no particular limitation, and it can be formed according to a conventionally known technique. Specific examples include various printing methods, air knife coating, rod blade coating,
It can be formed by applying a coating liquid by a method such as bar coating, blade coating, gravure coating, curtain coating, E-bar coating, and drying.

If necessary, the image quality can be improved by applying a super calender treatment after the application of the undercoat layer, the application of the heat-sensitive recording layer, or the application of the protective layer.

[0044]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. still,
All copies shown in the examples are on a weight basis.

(1) Preparation of heat-sensitive coating liquid <Preparation of dispersion liquid> Dispersions A to T were prepared by the following method.

<Dispersion A> 200 g of 3- (N, N-dibutyl) amino-6-methyl-7-anilinofluorane was added to 10% sulfonated polyvinyl alcohol (L-3266 manufactured by Nippon Synthetic Chemical Industry Co., Ltd.). The dispersion was dispersed in a mixture of 200 g of an aqueous solution and 600 g of water, and pulverized by a bead mill until the average particle diameter became 1 μm.

<Dispersion B> 200 g of 4-hydroxy-4'-isopropoxydiphenyl sulfone was modified with 10% sulfone group-modified polyvinyl alcohol (L-3266 manufactured by Nippon Synthetic Chemical Industry Co., Ltd., degree of saponification 85%, degree of polymerization 300).
10 g of an aqueous solution and 10% partially saponified polyvinyl alcohol (KL-05 manufactured by Nippon Synthetic Chemical Industry Co., Ltd., saponification degree 80
%, Degree of polymerization 500) An aqueous solution was dispersed in a mixture of 190 g of water and 600 g of water, and pulverized by a bead mill until the average particle diameter became 0.7 μm.

<Dispersion C> 200 g of 4-hydroxy-4'-isopropoxydiphenyl sulfone was modified with 10% sulfonate-modified polyvinyl alcohol (L-3266 manufactured by Nippon Synthetic Chemical Industry Co., Ltd., degree of saponification 85%, degree of polymerization 300).
20 g of an aqueous solution and 10% partially saponified polyvinyl alcohol (KL-05 manufactured by Nippon Synthetic Chemical Industry Co., Ltd., saponification degree 80
%, Degree of polymerization 500), dispersed in a mixture of 180 g of an aqueous solution and 600 g of water, and pulverized by a bead mill until the average particle diameter becomes 0.7 μm.

<Dispersion D> 200 g of 4-hydroxy-4'-isopropoxydiphenyl sulfone was modified with 10% sulfonate-modified polyvinyl alcohol (L-3266 manufactured by Nippon Synthetic Chemical Industry Co., Ltd., degree of saponification 85%, degree of polymerization 300).
100 g of an aqueous solution and 10% partially saponified polyvinyl alcohol (KL-05 manufactured by Nippon Synthetic Chemical Industry Co., Ltd., saponification degree 80
%, Polymerization degree 500) in a mixture of 100 g of an aqueous solution and 600 g of water, and pulverized by a bead mill until the average particle diameter becomes 0.7 μm.

<Dispersion E> 200 g of 4-hydroxy-4'-isopropoxydiphenylsulfone was modified with 10% sulfone group-modified polyvinyl alcohol (L-3266, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., degree of saponification 85%, degree of polymerization 300).
100 g of an aqueous solution and 10% partially saponified polyvinyl alcohol (KL-05 manufactured by Nippon Synthetic Chemical Industry Co., Ltd., saponification degree 80
%, Degree of polymerization 500) The mixture was dispersed in a mixture of 100 g of an aqueous solution and 600 g of water, and pulverized by a bead mill until the average particle diameter became 1.4 μm.

<Dispersion F> 200 g of 4-hydroxy-4'-isopropoxydiphenyl sulfone was modified with 10% sulfone group-modified polyvinyl alcohol (L-3266 manufactured by Nippon Synthetic Chemical Industry Co., Ltd., degree of saponification 85%, degree of polymerization 300).
100 g of an aqueous solution and 10% partially saponified polyvinyl alcohol (KL-05 manufactured by Nippon Synthetic Chemical Industry Co., Ltd., saponification degree 80
%, Degree of polymerization 500) The mixture was dispersed in a mixture of 100 g of an aqueous solution and 600 g of water, and pulverized by a bead mill until the average particle diameter became 1.6 μm.

<Dispersion G> 200 g of 4-hydroxy-4'-isopropoxydiphenylsulfone was modified with 10% sulfone group-modified polyvinyl alcohol (L-3266 manufactured by Nippon Synthetic Chemical Industry Co., Ltd., degree of saponification 85%, degree of polymerization 300).
10 g of an aqueous solution and 10% partially saponified polyvinyl alcohol (KL-05 manufactured by Nippon Synthetic Chemical Industry Co., Ltd., saponification degree 80
%, Degree of polymerization 500) An aqueous solution was dispersed in a mixture of 10 g of water and 780 g of water, and pulverized by a bead mill until the average particle diameter became 0.7 μm.

<Dispersion H> 200 g of 4-hydroxy-4'-isopropoxydiphenyl sulfone was modified with 10% sulfonated polyvinyl alcohol (L-3266, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., saponification degree 85%, polymerization degree 300).
30 g of an aqueous solution and 10% partially saponified polyvinyl alcohol (KL-05 manufactured by Nippon Synthetic Chemical Industry Co., Ltd., saponification degree 80
%, Degree of polymerization: 500) An aqueous solution was dispersed in a mixture of 30 g of water and 740 g of water, and pulverized by a bead mill until the average particle diameter became 0.7 μm.

<Dispersion I> 200 g of 4-hydroxy-4'-isopropoxydiphenyl sulfone was modified with 10% sulfonate-modified polyvinyl alcohol (L-3266, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., saponification degree 85%, polymerization degree 300).
200 g of an aqueous solution and 10% partially saponified polyvinyl alcohol (KL-05, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., saponification degree 80
%, Degree of polymerization 500) An aqueous solution was dispersed in a mixture of 200 g of water and 400 g of water, and pulverized by a bead mill until the average particle diameter became 0.7 μm.

<Dispersion J> 200 g of 4-hydroxy-4'-isopropoxydiphenylsulfone was modified with 10% sulfonate-modified polyvinyl alcohol (L-3266, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., degree of saponification 85%, degree of polymerization 300).
180 g of an aqueous solution and 10% partially saponified polyvinyl alcohol (KL-05, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., saponification degree 80
%, Degree of polymerization 500) An aqueous solution was dispersed in a mixture of 20 g of water and 600 g of water, and pulverized by a bead mill until the average particle diameter became 0.7 μm.

<Dispersion K> 200 g of 4-hydroxy-4'-isopropoxydiphenyl sulfone was modified with 10% sulfone group-modified polyvinyl alcohol (L-3266, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., saponification degree 85%, polymerization degree 300).
190 g of an aqueous solution and 10% partially saponified polyvinyl alcohol (KL-05 manufactured by Nippon Synthetic Chemical Industry Co., Ltd., saponification degree 80
%, Degree of polymerization 500) An aqueous solution was dispersed in a mixture of 10 g of water and 600 g of water, and pulverized by a bead mill until the average particle diameter became 0.7 μm.

<Dispersion L> 200 g of 4-hydroxy-4'-isopropoxydiphenyl sulfone was modified with 10% sulfonated polyvinyl alcohol (L-3266, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., degree of saponification 85%, degree of polymerization 300).
100 g of an aqueous solution and 10% partially saponified polyvinyl alcohol (KL-03 manufactured by Nippon Synthetic Chemical Industry Co., Ltd., saponification degree 80
%, Degree of polymerization: 300) The mixture was dispersed in a mixture of 100 g of an aqueous solution and 600 g of water, and pulverized by a bead mill until the average particle diameter became 0.7 μm.

<Dispersion M> 200 g of 4-hydroxy-4'-isopropoxydiphenyl sulfone was modified with 10% sulfonate-modified polyvinyl alcohol (L-3266 manufactured by Nippon Synthetic Chemical Industry Co., Ltd., degree of saponification 85%, degree of polymerization 300).
100 g of an aqueous solution and 10% partially saponified polyvinyl alcohol (GL-05 manufactured by Nippon Synthetic Chemical Industry Co., Ltd., saponification degree 88
%, Polymerization degree 500) in a mixture of 100 g of an aqueous solution and 600 g of water, and pulverized by a bead mill until the average particle diameter becomes 0.7 μm.

<Dispersion N> 200 g of 4-hydroxy-4'-isopropoxydiphenyl sulfone was modified with 10% sulfone group-modified polyvinyl alcohol (L-3266 manufactured by Nippon Synthetic Chemical Industry Co., Ltd., degree of saponification 85%, degree of polymerization 300).
100 g of an aqueous solution and 10% partially saponified polyvinyl alcohol (KP-08 manufactured by Nippon Synthetic Chemical Industry Co., Ltd., saponification degree 72
%, Degree of polymerization 800) was dispersed in a mixture of 100 g of an aqueous solution and 600 g of water, and pulverized by a bead mill until the average particle diameter became 0.7 μm.

<Dispersion O> 200 g of 4-hydroxy-4'-isopropoxydiphenyl sulfone was modified with 10% sulfone group-modified polyvinyl alcohol (L-3266 manufactured by Nippon Synthetic Chemical Industry Co., Ltd., degree of saponification 85%, degree of polymerization 300).
It was dispersed in a mixture of 200 g of an aqueous solution and 600 g of water, and pulverized by a bead mill until the average particle diameter became 0.7 μm.

<Dispersion P> 200 g of 4-hydroxy-4'-isopropoxydiphenyl sulfone was partially saponified with 10% polyvinyl alcohol (K available from Nippon Synthetic Chemical Industry Co., Ltd.).
L-05, saponification degree 80%, polymerization degree 500) aqueous solution 200
g of water and 600 g of water, and pulverized by a bead mill until the average particle diameter becomes 0.7 μm.

<Dispersion Q> 200 g of 4-hydroxy-4'-isopropoxydiphenyl sulfone was dispersed in a mixture of 200 g of an aqueous solution of 10% hydroxymethylcellulose (Metroze SM-15 manufactured by Shin-Etsu Chemical Co., Ltd.) and 600 g of water. It was pulverized with a bead mill until the average particle diameter became 0.7 μm.

<Dispersion R> 200 g of 4-hydroxy-4'-isopropoxydiphenylsulfone was added to an anionic surfactant (Disperse Aid W2 manufactured by San Nopco Co., Ltd.).
2) Dispersed in a mixture of 20 g and 780 g of water, and pulverized with a bead mill until the average particle diameter became 0.7 μm.

<Dispersion S> 200 g of benzyl-2-naphthyl ether (200 g) aqueous solution of 10% sulfone group-modified polyvinyl alcohol (L-3266 manufactured by Nippon Synthetic Chemical Industry Co., Ltd., degree of saponification 85%, degree of polymerization 300), water 600 g And then pulverized with a bead mill until the average particle diameter becomes 1 μm.

<Dispersion T> 200 g of aluminum hydroxide
800 g of a 0.5% aqueous solution of sodium polyacrylate
And stirred for 10 minutes with a homomixer.

Example 1 Using these dispersions, the respective materials were mixed in the following proportions, and water was added so that the concentration of the heat-sensitive coating solution became a 15% aqueous solution. A liquid was prepared. Dispersion A 30 parts Dispersion B 70 parts Dispersion S 100 parts Dispersion T 50 parts 40% zinc stearate dispersion 10 parts 10% completely saponified PVA aqueous solution (NM-11 manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) 40 parts

(2) Preparation of heat-sensitive coated paper A coating liquid having the following composition was coated on a high-quality paper having a basis weight of 40 g / m ^{2 so} as to have a solid content of 10 g / m ² and dried. ,
A heat-sensitive coated paper was prepared. Calcined kaolin 100 parts 50% styrene butadiene latex 24 parts Water 200 parts

(3) Preparation of heat-sensitive recording material The heat-sensitive coating liquid prepared in (1) was applied onto the heat-sensitive coating paper prepared in (2) at a coating amount of the dye precursor of 0.3 g / m ² . The resultant was coated and dried to prepare a heat-sensitive recording material.

Example 2 A thermosensitive recording material was obtained in the same manner as in Example 1 except that Dispersion B was changed to Dispersion C.

Example 3 A heat-sensitive recording material was obtained in the same manner as in Example 1 except that Dispersion B was changed to Dispersion D.

Example 4 A thermosensitive recording material was obtained in the same manner as in Example 1 except that Dispersion B was changed to Dispersion E.

Example 5 A thermosensitive recording material was obtained in the same manner as in Example 1 except that Dispersion B was changed to Dispersion F.

Example 6 A heat-sensitive recording material was obtained in the same manner as in Example 1 except that Dispersion B in Example 1 was changed to Dispersion G.

Example 7 A heat-sensitive recording material was obtained in the same manner as in Example 1, except that Dispersion B was changed to Dispersion H.

Example 8 A heat-sensitive recording material was obtained in the same manner as in Example 1, except that Dispersion B was changed to Dispersion I.

Example 9 A thermosensitive recording material was obtained in the same manner as in Example 1 except that Dispersion B in Example 1 was changed to Dispersion J.

Example 10 A thermosensitive recording material was obtained in the same manner as in Example 1, except that Dispersion B in Example 1 was changed to Dispersion K.

Example 11 A thermosensitive recording material was obtained in the same manner as in Example 1 except that Dispersion B was changed to Dispersion L.

Example 12 A thermosensitive recording material was obtained in the same manner as in Example 1, except that Dispersion B was changed to Dispersion M.

Example 13 A thermosensitive recording material was obtained in the same manner as in Example 1 except that Dispersion B in Example 1 was changed to Dispersion N.

Comparative Example 1 A heat-sensitive recording material was obtained in the same manner as in Example 1, except that Dispersion B was changed to Dispersion O.

Comparative Example 2 A thermosensitive recording material was obtained in the same manner as in Example 1, except that Dispersion B was changed to Dispersion P.

Comparative Example 3 A thermosensitive recording material was obtained in the same manner as in Example 1, except that Dispersion B in Example 1 was changed to Dispersion Q.

Comparative Example 4 A heat-sensitive recording material was obtained in the same manner as in Example 1 except that Dispersion B was changed to Dispersion R.

The heat-sensitive recording materials prepared in Examples 1 to 13 and Comparative Examples 1 to 4 each had a Beck smoothness of 30 on the heat-sensitive coated surface.
After calendering to 0 to 800 seconds, it was subjected to the following evaluation. The evaluation results are shown in Tables 1 and 2.

[Thermal Responsiveness Test] A print test was performed using a facsimile tester TH-PMD manufactured by Okura Electric. Using a thermal head with a dot density of 8 dots / mm and a head resistance of 1685 Ω, a head voltage of 21 V and a pulse width of 0.
Printing was performed by applying current at 8, and 1.0 msec, and the color density was measured with a Macbeth RD-918 reflection densitometer (visual filter). The larger the value, the better the thermal response.

[Whiteness test] Untreated immediately after the production of the heat-sensitive recording material using a digital hunter reflectometer (Amber filter) manufactured by Toyo Seiki Seisaku-sho, Ltd.
After standing for 4 hours, the whiteness was measured. The higher the value, the better the whiteness.

[Dispersion Stability Test] Prepared Dispersions BP
The average particle size after 3 days of standing was measured. Those having no change in the average particle size are ○, and the average particle size is slightly larger,
Those with a size of less than μm were rated Δ, and those with a size exceeding 1.5 μm were rated X.

[0089]

[Table 1]

[0090]

[Table 2]

As shown in Tables 1 and 2, Examples 1 to 13
Are superior in thermal responsiveness as compared with Comparative Examples 1 to 4. This is because the stability of the wet grinding liquid of the electron-accepting compound used in Examples 1 to 13 is excellent. Comparative Example 1
In the wet grinding liquids of the electron accepting compounds of Nos. 1 to 3, the thermal responsiveness is remarkably reduced due to the increase in the average particle diameter due to crystal growth.

Examples 1 to 13 are superior to Comparative Example 4 in whiteness. In Examples 1 to 13, a protective colloid was formed by wet-milling an electron-accepting compound together with a polymer, which led to an improvement in whiteness.

[0093]

As is clear from the examples, the heat-sensitive dye containing an electron-donating, usually colorless or pale-colored dye precursor and an electron-accepting compound which reacts upon heating to form the dye precursor. In the recording material, 4-hydroxy-4′-isopropoxydiphenyl sulfone as the electron-accepting compound wet-ground with a sulfone group-modified polyvinyl alcohol and a partially saponified polyvinyl alcohol is used in the heat-sensitive recording layer to provide a thermal response. A heat-sensitive recording material having excellent properties and whiteness was obtained.

Claims (6)

[Claims] 1. A thermosensitive recording material comprising an electron-donating, usually colorless or pale-colored dye precursor, and an electron-accepting compound which reacts upon heating to form the dye precursor. As 4-hydroxy-4'-
A heat-sensitive recording material, characterized in that isopropoxydiphenyl sulfone is wet-ground with a sulfone group-modified polyvinyl alcohol and a partially saponified polyvinyl alcohol in a heat-sensitive recording layer. 2. An average particle diameter of 4-hydroxy-4′-isopropoxydiphenyl sulfone which is wet-ground with a sulfonated polyvinyl alcohol and a partially saponified polyvinyl alcohol is 1.5 μm or less. Item 6. The heat-sensitive recording material according to Item 1. 3. The heat-sensitive material according to claim 1, wherein the weight ratio of the sulfonated polyvinyl alcohol to the partially saponified polyvinyl alcohol is in the range of 1: 9 to 9: 1. Recording material. 4. A method according to claim 1, wherein said sulfonated polyvinyl alcohol and said partially saponified polyvinyl alcohol are reacted with 4-hydroxy-4′-isopropoxydiphenyl sulfone.
The heat-sensitive recording material according to any one of claims 1 to 3, wherein the heat-sensitive recording material is contained in an amount of 3 to 15% by weight. 5. The sulfonated polyvinyl alcohol has a saponification degree of 80 to 90% and a polymerization degree of 200 to 90%.
The heat-sensitive recording material according to any one of claims 1 to 4, wherein the range is 500. 6. The partially saponified polyvinyl alcohol has a saponification degree of 70 to 90% and a polymerization degree of 300 to 800.
The heat-sensitive recording material according to any one of claims 1 to 5, wherein