JPH06206376A - Thermal recording sheet - Google Patents

Abstract

(57) [Summary] [Object] To provide a heat-sensitive recording sheet having good color development and sticking resistance, excellent image storability such as plasticizer resistance and water resistance, and excellent printability. [Structure] A heat-sensitive recording sheet in which a heat-sensitive recording layer and a protective layer are sequentially laminated on a support. The heat-sensitive recording layer comprises a polyhydroxy compound as a binder component, a polymer latex having a glass transition temperature of 50 ° C. or less, and a specific hydrophobic layer. A water-dispersible polymer that is polymerized mainly with a vinyl monomer and has a softening point of 150-
A water-dispersible polymer of 260 ° C., a water-dispersible polymer obtained by polymerizing mainly a polymer latex having a glass transition temperature of 50 ° C. or less and a specific hydrophobic vinyl monomer as a protective layer, and having a softening point of the protective layer. In the case of one layer, 200 to 350 ° C. is used, and in the case of two or more layers, a lower layer having a temperature range of 150 to 260 ° C. is used as a main component, and preferably the uppermost layer has a softening point of 200.
A specific water-dispersible polymer is used in the case of one protective layer at ˜350 ° C.

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 sheet, and more particularly to a heat-sensitive recording sheet having good color development and sticking resistance, excellent image storability such as plasticizer resistance and water resistance, and excellent printability. It is about the seat.

[0002]

2. Description of the Related Art In recent years, heat-sensitive recording sheets that develop color by heat have been widely used for facsimiles, word processors, plotters, labels and the like. The reason is that the printing method obtains a colored image by an instantaneous chemical reaction due to heat,
This is because the device is small, the recording speed is fast, there is little noise and environmental pollution, and the cost is low. However, in a heat-sensitive recording method using a dye precursor or an acidic substance that is usually used as a color-forming component, in addition to coloring the white paper portion with an organic solvent such as toluene or methyl ethyl ketone, an eraser,
In some cases, the colored parts may disappear due to dibutyl phthalate, dioctyl phthalate, etc., which are used as plasticizers for synthetic resins such as vinyl chloride, or hair styling agents. There is. In addition, when a problem such as discoloration of the coloring part or coloring of the white paper part occurs when using a magic ink, a highlighter pen, or when a color is developed, the sticking phenomenon between the thermal head and the thermal recording layer, or the sticking to the thermal head Coloring defects may occur due to accumulation of dust.
Furthermore, for labels, ATM / CD, etc., printing is often performed on the surface layer, and printability such as surface strength is required.

Among these drawbacks, in order to improve the storage stability against organic solvents, chemicals, etc., aromatic dyes are used instead of the recording method using a dye precursor and an acidic substance which are usually used in a thermosensitive recording layer as a coloring component. A heat-sensitive recording method using a color-forming component of an isocyanate and an imino compound has also come to be used. (JP-A-58-38733 and JP-A-58-1)
There are various proposals for improving the above-mentioned drawbacks by providing a protective layer containing a water-soluble polymer substance, a water-dispersible polymer substance or the like as a main component on the heat-sensitive recording layer. (JP-A-55-955
No. 93, No. 57-188392, No. 58-12289.
No. 2, No. 59-1797, No. 59-45191, No. 60-115484, No. 62-42884). However, even when these water-soluble polymer substances and the like are provided in the protective layer, a small amount cannot provide sufficient chemical resistance, and therefore it is necessary to increase the amount of the protective layer. , When the color image becomes unclear, or when chemical resistance is obtained but water resistance is poor, printability is poor,
A satisfactory thermal recording sheet could not be obtained due to the drawbacks such as the occurrence of problems during thermal color development. Further, when offset printing is performed on the surface of the heat-sensitive recording sheet, if the surface strength is weak, picking occurs, the printing finish is poor, and debris is deposited on the blanket portion and the like, resulting in poor workability.

[0004]

DISCLOSURE OF THE INVENTION The present invention provides a heat-sensitive recording sheet having good color developability, excellent image storability such as plasticizer resistance and water resistance, and having no problems at the time of printing and thermal color development. With the goal.

[0005]

Means for Solving the Problems As a result of intensive studies to solve these problems, the present inventors have found that the heat-sensitive recording layer of a heat-sensitive recording sheet contains a water-dispersible polymer in an amount of 20% by weight or more based on all binders. Preferably, the polyhydroxy compound is used in an amount of 20 to 80% by weight of the total binder, and the protective layer is
A water-dispersible polymer obtained by mainly polymerizing at least one kind of hydrophobic vinyl-based monomer having a glass transition temperature of 55 ° C. or more in the presence of a polymer latex having a glass transition temperature of 50 ° C. or less. Y having a softening point of 200 to 350 ° C. is used as the main component of the protective layer, or a water-dispersible polymer X similarly obtained having a softening point of 150 to 260 ° C. is used as the lower layer and the uppermost layer is used. By using a water-soluble polymer or polymer latex having a softening point of 200 to 350 ° C.,
Preferably, by using the water-dispersible polymer Y having a softening point of 200 to 350 ° C., which is obtained in the same manner as the lower layer, as the uppermost layer, color development and printability are good, and image storage such as water resistance and chemical resistance is preserved. A heat-sensitive recording sheet having improved properties was obtained.

The reason for this is unknown, but the polymer latex is polymerized with a hydrophobic vinyl monomer, and the resulting composition structurally has a core-shell structure.
The core part uses a relatively soft latex, the shell part is a relatively hard polymer, and by setting the softening point of the composition to a specific range, chemical resistance, plasticizer resistance, and adhesion are achieved in the core part. It is expected that it has the effect of improving the strength and water resistance, and the effect of improving the chemical resistance and the plasticizer resistance as well as the sticking resistance of the shell part. By using the water-dispersible polymer having the core-shell structure of the present invention as the binder of the heat-sensitive recording layer, the printability is improved by the core part, the color development is good by the shell part, and the adhesive strength is strong. Therefore, it is possible to reduce the amount of the binder, and further, the color development is favorable. Further, it is considered that the uppermost layer and the lower layer of the protective layer are properly used in combination with a polymer having a softening point within a specific range so that the characteristics can be harmonized. In particular, if the softening point of the polymer used for the uppermost protective layer is low, sticking will occur during color development, and if it is too high, the adhesive strength will be poor and printability will be a problem. When the protective layer is one layer, the specific water-dispersible polymer of the present invention having a softening point of 200 to 350 ° C. can be used as the main component, and when the protective layer is two or more layers, the specific water of the present invention is used as the lower layer. By using a dispersible polymer having a softening point of 150 to 260 ° C. as a main component, a conventionally known water-dispersible polymer or water-soluble polymer having a softening point range of 200 to 350 ° C. as a main component of the uppermost layer. Although a polymer can be used, preferably, the plasticizer resistance, chemical resistance, etc. are improved by using the specific water-dispersible polymer of the present invention used in the case of one layer also in the uppermost layer. . Since the polymer used in the lower layer has little influence on the sticking property, a polymer having a softening point lower than that of the uppermost layer can be used, and the adhesive strength becomes strong, but if it is lower than 150 ° C., the sticking property becomes poor. If the softening point is higher than 260 ° C., printability may begin to be adversely affected, possibly due to the problem of affinity with the heat-sensitive recording layer and the upper protective layer.

The glass transition temperature of the present invention is a temperature at which a glassy solid state changes to a rubber state and is measured by a temperature change of specific heat or a temperature change of specific volume. The specific heat and the specific volume rapidly change at the transition temperature. Change. As a measuring method, a differential thermal analysis method (DTA method) or a differential scanning calorimetry method (DSC method) is used. The softening point is the temperature at which a material begins to deform and soften due to heating, and like the glass transition temperature, DT.
The A method and the DSC method are used. When there are a plurality of peaks of the softening point measured by the DTA method and the DSC method, the highest temperature, which is the softening point of the shell portion of the polymer having a great influence on the sticking property, is adopted. Examples of the glass transition temperature of polymers are shown in "Handbook of Polymer Materials" (edited by The Polymer Society of Japan) as the glass transition point of polymer materials, and in "Chemical Dictionary" (edited by the Editorial Committee for Chemistry). It is listed as temperature.

The polyhydroxy compound used in the heat-sensitive recording layer of the present invention is a water-soluble polymer having a hydroxyl group, and specific examples thereof include polyvinyl alcohol, methylcellulose hydroxyethylcellulose and hydroxypropylcellulose. -, Carboxymethyl cellulose, starch, starch derivatives and the like. Polyvinyl alcohol is preferred as the polyhydroxy compound used in the present invention. In particular, polyvinyl alcohol having a saponification degree of 90 mol% or more and a polymerization degree of 1000 or more is preferable.

The polymer latex used at the time of polymerization of the water-dispersible polymer X or Y of the present invention means a styrene-butadiene copolymer, a methyl methacrylate-butadiene copolymer, a methyl methacrylate-styrene-butadiene diene copolymer. Polymer, acrylonitrile-butadiene copolymer, styrene polymer, isoprene polymer, butadiene polymer, vinyl acetate-acrylic acid ester copolymer, acrylic acid ester polymer, vinyl acetate-ethylene copolymer, vinyl chloride polymer Among the polymers, vinylidene chloride polymers and the like or their derivatives, those having a glass transition temperature of 50 ° C. or lower. Fifty
If the temperature exceeds ℃, the heat colorability is poor and the printability is deteriorated.
The lower limit of the glass transition temperature that can be used is limited by the lower limit of the present invention of the softening point of the obtained water-dispersible polymer X or Y, but is about -30 ° C. Water-dispersible polymer X of the present invention
Alternatively, the hydrophobic vinyl-based monomer used during the polymerization of Y is one that produces a hydrophobic polymer by polymerization,
Specifically, styrene, an aromatic vinyl compound such as methylstyrene, methyl methacrylate, ethyl methacrylate,
Methacrylic acid ester such as isopropyl methacrylate,
Polymers such as nitrile compounds such as acrylonitrile and methacrylonitrile, p-carbomethoxyphenyl acrylate, 2,4-dichlorophenyl acrylate, glycidyl methylolmethacrylate acrylate, and vinyl chloride have a glass transition temperature of 55. Those above ℃ are used. The upper limit of the glass transition temperature is limited by the upper limit of the present invention of the softening point of the obtained water-dispersible polymer X or Y. Incidentally, the water-soluble vinyl-based monomer is preliminarily copolymerized with the water-dispersible polymer X or Y of the present invention with the polymer latex used at the time of polymerization, or in the presence of the polymer latex, the hydrophobic vinyl-based monomer is used. It is possible to improve the water dispersibility, the plasticizer resistance and the like of the polymer obtained by using it together when the monomer is polymerized. Examples of the water-soluble vinyl monomer include acrylamide, methacrylamide, acrylic acid, methacrylic acid, dimethylaminoethyl methacrylate, dimethylaminopropyl methacrylamide, and the like. The water-dispersible polymer X or Y of the present invention can be obtained by a conventionally known polymerization method. Examples thereof include radical polymerization using a peroxide such as ammonium persulfate and potassium persulfate, and a redox method performed by using a peroxide and a reducing agent such as sodium thiosulfate together.

When the protective layer of the heat-sensitive recording sheet of the present invention has two or more layers, a water-soluble polymer or polymer latex having a softening point of 200 to 350 ° C. is also used as the uppermost layer, and In addition to the specific water-dispersible polymer X or Y of the present invention, a conventionally used water-soluble polymer or polymer latex is used in each protective layer of the heat-sensitive recording sheet to the extent that the effect of the present invention is not impaired. Although they may be used in combination, about 30% by weight or less of the total protective layer is preferable. Specific examples of the polymer latex include:
The polymer latex used at the time of polymerization of the water-dispersible polymer X or Y of the present invention described above is used. Examples of the water-soluble polymer include polyvinyl alcohol, carboxymethyl cellulose, methyl cellulose, ethyl cellulose, hydroxymethyl cellulose, polyacrylamide, starch, dextrin, gelatin, casein, sodium alginate, polyvinylpyrrolidone, sodium polyacrylate, polyethylene oxide and the like or derivatives thereof. Can be used. Other materials for the protective layer include kaolin, calcined kaolin, aluminum silicate, aluminum hydroxide, calcium carbonate, silicon oxide, talc, magnesium carbonate, titanium oxide, and other inorganic pigments, polystyrene, urea-formalin, and polyacrylics. Organic pigments, such as
Crosslinking agents such as dialdehyde type, epoxy type, polyamine type, diglycidyl type, dimethylol urea, ferric chloride, zirconium carbonate, ammonium chloride, higher fatty acid metal salts such as zinc stearate for sticking improvement, paraffin, polyethylene, etc. The waxes, defoaming agents, surfactants, etc. are appropriately added and used in combination. The coating amount of the protective layer is adjusted so as to have almost no effect on the color developability, but is generally about 1 to 10 g / m ² , and preferably 1 to 6 g / m ^2.
The coating is applied in one layer or several layers.

As the colorless or light-colored dye precursor, the acidic substance, and the binder used in the heat-sensitive recording layer of the present invention, conventionally known ones are used.

Dye precursors include crystal violet lactone, 3-indolino-3-p-dimethylaminophenyl-6-dimethylaminophthalide, 3-diethylamino-7-chlorofluorane, 3-diethylamino-7-cyclohexylamino. Fluorane, 3-diethylamino-5-methyl-7-t-butylfluorane, 3-
Diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-p-butylanilinofluorane, 2- (N-phenyl-N-ethyl) aminofluorane, 3-diethylamino- 7-dibenzylaminofluorane, 3-cyclohexylamino-
6-chlorofluorane, 3-diethylamino-6-methyl-7-xylidinofluorane, 2-anilino-3-methyl-6- (N-ethyl-p-toluidino) fluorane, 3-pyrrolidino-6-methyl- 7-anilinofluorane, 3-pyrrolidino-7-cyclohexylaminofluorane, 3-piperidino-6-methyl-7-toluidinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3 -(N-methylcyclohexylamino) -6-methyl-7-anilino) fluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3
-Dibutylamino-6-methyl-7-anilinofluorane is used.

As acidic substances, 4,4'-isopropylidenediphenol, 4,4'-isopropylidenebis (2-chlorophenol), 4,4'-isopropylidenebis (2-tert-butylphenol), 4 ，
4'-Secondary butylidene diphenol, 4,4 '
-(1-Methyl-normalhexylidene) diphenol, 4-phenylphenol, 4-hydroxydiphenol, methyl-4-hydroxybenzoate, phenyl-4-hydroxybenzoate, 4-hydroxyacetophenone, salicylic acid anilide, 4,4 '-Cyclohexylidenediphenol, 4,4'-cyclohexylidenebis (2-methylphenol), 4,4'-benzylidenediphenol, 4,4'-thiobis (6-tercarybutyl-3-methylphenol) ,, 4,4'-isopropylidene bis (2-methylphenol), 4,4 '
-Ethylenebis (2-methylphenol), 4,4'-
Cyclohexylidene bis (2-isopropylphenol), 2,2'-dihydroxydiphenyl, 2,2'-
Methylenebis (4-chlorophenol), 2,2'-methylenebis (4-methyl-6-t-butylphenol), 1,1'-bis (4-hydroxyphenol)-
Cyclohexane, 2,2'-bis (4'-hydroxyphenyl) propane, novolac type phenol resin, halogenated novolac type phenol resin, α-naphthol,
β-naphthol, 3,5-di-t-butylsalicylic acid,
3,5-di-α-methylbenzylsalicylic acid, 3-methyl-5-t-butylsalicylic acid, monoanilide paraethoxybenzoic acid phthalate, bis (4-hydroxyphenyl) sulfone, 4-hydroxy-4′-isopropyloxy Diphenyl sulfone, di- (3-allyl-4-
Hydroxyphenyl) sulfone, 2,4′-dihydroxydiphenyl sulfone, parabenzyloxybenzoic acid, parahydroxybenzoic acid benzyl ester are used.

A core-shell water-dispersible polymer of the present invention,
In addition to polyhydroxy compounds, binders used in the heat-sensitive recording layer include styrene-acrylic, polyacrylamide, gum arabic, water-soluble binders such as casein and their derivatives, styrene-butadiene latex,
Latex such as acrylic latex is used.

A sensitizer can be used in the heat-sensitive recording layer in order to improve sensitivity. For example, aromatic ethers such as 2-benzyloxynaphthalene, oxalates such as oxalic acid di-p-methylbenzyl ester, esters such as naphthalenesulfonic acid ester and benzoate, aromatics such as p-benzylbiphenyl. Examples include family-based and phenanthrene. Examples of pigments used in the heat-sensitive recording layer include diatomaceous earth, talc, kaolin, calcined kaolin, calcium carbonate, magnesium carbonate, titanium oxide, zinc oxide, silicon oxide, aluminum hydroxide, and urea-formalin resin. Other additives include higher fatty acid metal salts such as zinc stearate and calcium stearate,
Waxes such as paraffin, oxidized paraffin, polyethylene and polyethylene oxide, wetting agents such as dioctyl sulfosuccinate, UV absorbers such as benzophenone and benzotriazole, surfactants, fluorescent dyes and the like are used.

When an intermediate layer is provided between the support of the present invention and the thermosensitive recording layer for the purpose of improving color development, an inorganic or organic pigment used in the thermosensitive recording layer, a hollow organic pigment, or a binder is used. To be In addition, a dispersant for pigments, a viscosity modifier, an antifoaming agent and the like are also added as appropriate.

As the support used in the present invention, paper is used, but synthetic paper, metal foil, laminated paper of polyethylene or the like, film of polyethylene terephthalate or the like may be used alone or in combination. . The apparatus used for coating the intermediate layer, the heat-sensitive recording layer, and the protective layer are an air knife coater, a gravure coater,
Roll coater, rod coater, curtain coater,
A die coater, a lip coater, a blade coater, etc. are used. In particular, when an intermediate layer is provided below the heat-sensitive recording layer, a size press device, a gate roll device, etc. used in the paper making process of paper are also used. Also, printing methods such as offset and silk screen are used. Furthermore, in order to improve the surface smoothness of the coated product, a machine calendar,
Super calendar, gloss calendar, brushing, etc. are used.

[0018]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.
The parts and% in the examples mean parts by weight and% by weight.

Example 1 Preparation of coating liquid for heat-sensitive recording layer (A) liquid 3-dibutylamino-6-methyl-7-anilinofluorane (solid) 12 parts 10% polyacrylicamide (Showa Denko KK, Paulol S -680) (Solid 1.8 parts) 18 parts Water 30 parts (B) Liquid 4,4'-isopropylidenediphenol (solid) 40 parts p-Benzylbiphenyl (solid) 40 parts Zinc stearate (solid) 20 parts 10% Polyacrylamide (Parole S-680) (Solid 5 parts) 50 parts Water 100 parts Liquid (A) and liquid (B) are separately separated by a sand grinder with a volume average particle diameter of about 1.5 μm by a laser diffraction method. Dispersed up to. Subsequently, a water-dispersible polymer (synthetic product L) used as a binder component was prepared as follows. Methyl methacrylate, acrylonitrile and acrylamide were polymerized in the presence of a polymer latex of acrylonitrile-acrylic acid-styrene-butadiene (glass transition temperature, 5 ° C). (Softening point: 235 ° C.) The thermosensitive recording layer coating liquid was prepared by the following formulation. Calcium carbonate (manufactured by Shiraishi Kogyo, Brt15) (solid) 8 parts (B) liquid 30 parts 20% water-dispersible polymer (synthetic compound L) water dispersion 14 parts 10% polyvinyl alcohol (Nippon Gosei Kagaku Co., Ltd., NM-11) 26 parts (A) liquid 12 parts water 100 parts

Preparation of Protective Layer Coating Liquid (C) Using the water-dispersible polymer (synthetic product L) used in the heat-sensitive recording layer, a protective layer coating liquid (C) was prepared with the following formulation. 20% water-dispersible polymer (synthetic product L) aqueous dispersion 100 parts calcium carbonate (Brt15) (solid) 2 parts 20% zinc stearate dispersion 2 parts epoxy crosslinking agent (solid content 20%) 2 parts water 50 Department

On one side of a paper having a basis weight of 60 g / m ² , a thermosensitive recording layer coating liquid was applied in a solid amount of 6 g / m ² and dried, and then a protective layer coating liquid (C) was applied in a solid amount of 3 g / m ² ; After drying, it was subjected to a super calendar treatment to obtain a heat-sensitive recording sheet of the present invention.

Example 2 Preparation of coating liquid (D) for protective layer Methyl methacrylate-acrylonitrile-butadiene-
Polymeric latex of acrylamide (glass transition temperature,
(16 ° C.), methyl methacrylate and methyl acrylate were polymerized to obtain a water-dispersible polymer (synthetic product M).
(Softening point; 170 ° C.) The protective layer coating liquid (D) was prepared by the following formulation. 20% water-dispersible polymer (synthetic M) water dispersion 100 parts Epoxy cross-linking agent (solid content 20%) 2 parts Calcium carbonate (Brt15) (solid) 2 parts water 50 parts In the same manner as in Example 1, 6 g of coating liquid for thermosensitive recording layer
m ² coating and after drying, protective layer coating liquid (D) is 2 g / m ^{2 in} solid
After coating and drying, the coating solution (C) for the protective layer was applied in a solid amount of 1 g / m ² and dried, and then subjected to super calendering to obtain a heat-sensitive recording sheet of the present invention.

Example 3 A thermosensitive recording sheet of the present invention was obtained in the same manner as in Example 1 except that the following protective layer coating liquid (E) was used instead of the protective layer coating liquid (C). Preparation of protective layer coating liquid (E) Acrylonitrile is polymerized in the presence of a polymer latex of acrylonitrile-acrylic acid-styrene-butadiene (glass transition temperature, 38 ° C) to prepare a water-dispersible polymer (synthetic compound N). Got (Softening point: 315 ° C.) The protective layer coating liquid (E) was prepared by the following formulation. 20% water-dispersible polymer (synthetic N) aqueous dispersion 100 parts calcium carbonate (Brt15) (solid) 2 parts 20% zinc stearate dispersion 2 parts water 50 parts

Example 4 Instead of the water-dispersible polymer (synthetic compound M) used in the protective layer coating liquid (D) of Example 2, a water-dispersible polymer (synthetic compound L) was used.
A thermosensitive recording sheet was obtained in the same manner as in Example 2 except that was used.

Example 5 In the preparation of the uppermost protective layer coating liquid (C) in Example 2,
A thermosensitive recording sheet was obtained in the same manner as in Example 2 except that polyvinyl alcohol (softening point: 230 ° C.) was used instead of the water-dispersible polymer (synthetic product L).

Example 6 In the preparation of the uppermost protective layer coating liquid (C) in Example 2,
A thermosensitive recording sheet was obtained in the same manner as in Example 2 except that the water-dispersible polymer (synthetic product N) was used instead of the water-dispersible polymer (synthetic product L).

Example 7 Polyvinyl alcohol (NM-11) was used as a binder component in the preparation of the coating liquid for the thermosensitive recording layer used in Example 2.
A heat-sensitive recording sheet was obtained in the same manner as in Example 2 except that the water-dispersible polymer (synthetic material L) was used instead of the above, and only the synthetic material L was used.

Example 8 In the preparation of the coating liquid for the thermosensitive recording layer used in Example 2, the content of the binder component was 4 parts of the water-dispersible polymer X (synthetic product L) and 36 parts of NM-11. A heat-sensitive recording sheet was obtained in the same manner as in Example 2 except for the above.

Example 9 In the preparation of the coating liquid for the thermosensitive recording layer used in Example 2, the content of the binder component was 27 parts of the water-dispersible polymer X (synthetic product L) and 13 parts of NM-11. A heat-sensitive recording sheet was obtained in the same manner as in Example 2 except for the above.

Comparative Example 1 Instead of the water-dispersible polymer (synthetic compound L) used in the protective layer coating liquid (C) of Example 1, a water-dispersible polymer (synthetic compound M) was used.
A thermosensitive recording sheet was obtained in the same manner except that was used.

Comparative Example 2 In the preparation of the protective layer (C) of Example 1, methacrylic acid was used instead of the polymer latex (glass transition temperature, 10 ° C.) used during the polymerization of the water-dispersible polymer (Compound L). A water-dispersible polymer (synthetic product O) (softening point: 245 ° C.) obtained by using a polymer latex of methyl-styrene-acrylic acid (glass transition temperature, 70 ° C.) was used as a water-dispersible polymer (synthetic product L). A thermosensitive recording sheet was obtained in the same manner as in Example 1 except that it was used instead of Here, the water-dispersible polymer (synthetic product O) corresponds to outside the scope of the present invention.

Comparative Example 3 An example except that a water-dispersible polymer (Compound O) was used in place of the water-dispersible polymer (Compound L) in the preparation of the protective layer (D) of Example 2. A thermal recording sheet was obtained in the same manner as in 2.

Comparative Example 4 In the preparation of the protective layer coating liquid (D) of Example 2, instead of the vinyl-based monomers methyl acrylate and methyl methacrylate used in the polymerization of the water-dispersible polymer (synthetic product L). A water-dispersible polymer (synthetic product P) obtained by using methyl acrylate, methyl methacrylate, and butadiene in the above (softening point: 125
C) was obtained. Here, except that the water-dispersible polymer (synthetic compound P) was used in place of the water-dispersible polymer X (synthetic compound L),
A thermosensitive recording sheet was obtained in the same manner as in Example 2.

Comparative Example 5 In the preparation of the protective layer coating liquid (D) of Example 2, instead of the water-dispersible polymer (Compound M), a polymer latex of acrylonitrile-acrylic acid-styrene-butadiene was used (glass). Same as Example 2 except that a water-dispersible polymer (synthetic product Q) (softening point: 290 ° C.) obtained by polymerizing acrylonitrile and methyl methacrylate in the presence of a transition temperature of 38 ° C.) was used. A thermosensitive recording sheet was obtained.

Comparative Example 6 The procedure of Example 1 was repeated except that polyvinyl alcohol (softening point: 230 ° C.) was used instead of the water-dispersible polymer (synthetic product L) used in the protective layer coating liquid (C). A thermosensitive recording sheet was obtained.

Comparative Example 7 Example 5 Instead of the water-dispersible polymer (synthetic product L) used in the coating liquid (D) for protective layer, polyvinyl alcohol (softening point;
A thermosensitive recording sheet was obtained in the same manner except that (210 ° C.) was used.

Comparative Example 8 In the preparation of the coating liquid for the thermosensitive recording layer used in Example 2, 10% polyvinyl alcohol (NM-11) was used as the binder component instead of the 20% water-dispersible polymer (Compound L). )
To 40 parts, and polyvinyl alcohol (NM-1
1) A thermosensitive recording sheet was obtained in the same manner as in Example 2 except that it was used alone.

The thermal recording sheets obtained in Examples 1 to 9 and Comparative Examples 1 to 8 were evaluated by the following methods, and the evaluation results are shown in Table 1. The glass transition temperature and softening point were measured by a differential thermal analyzer and a differential scanning calorimeter. The unit in the table is ° C. "Thermochromativity" Labeler on the market (ISHIDA, IF21
The color was developed by EX) and the density was measured by a Macbeth type reflection densitometer. The higher the number, the higher the concentration. “Sticking resistance” The sound was evaluated by a color tester manufactured by Okura Electric Co., Ltd., and the evaluation was made based on the sound, white spots in the colored part, and shrinkage of the colored part. ◯: No sticking, Δ: Some sticking but can be used, X: Sticking is large and cannot be used. “Plasticizer resistance” Three sheets of lap film are placed on a heat-colored sheet, and a load is applied at 50 ° C. Leave it overnight under the condition of 90% RH. The colored portion after the treatment was visually evaluated. ○: No difference before and after treatment, △: Some difference before and after treatment,
X: Large difference between before and after the treatment "Water resistance" The sheet that was thermally colored was immersed in pure water at room temperature for 24 hours, and the decrease in the coloring density was visually evaluated. ◯: Almost no decrease in density, Δ: Can be used although there is some decrease in density, ×: Large decrease in density “Printability” Printing with an offset ink on a RI printing machine (manufactured by Akira Mfg. Co., Ltd.) and peeling of the coating layer The degree of (picking) was evaluated. ○: No picking occurred, △: Some picking tendency, ×: Picking occurred

[0039]

[Table 1]

[0040]

The heat-sensitive recording sheet of the present invention is excellent in color developability and sticking property, and is excellent in image storability such as plasticizer resistance and water resistance and printability.

Claims (4)

[Claims] 1. A thermosensitive recording sheet in which a thermosensitive recording layer and a protective layer are sequentially laminated on a support, in the presence of a polymer latex having a glass transition temperature of 50 ° C. or less as a binder component of the thermosensitive recording layer. Water-dispersible polymer X having a softening point of 150 to 260 ° C. obtained by polymerizing mainly at least one kind of hydrophobic vinyl-based monomer having a temperature of 55 ° C. or higher.
Containing 20% by weight or more of the total binder in the heat-sensitive recording layer, the protective layer is one layer, and mainly contains at least one kind of the hydrophobic vinyl-based monomer in the presence of the polymer latex. A heat-sensitive recording sheet comprising a water-dispersible polymer Y having a softening point of 200 to 350 ° C. obtained by polymerization as a main component. 2. A thermosensitive recording sheet in which a thermosensitive recording layer and a protective layer are sequentially laminated on a support, and in the presence of a polymer latex having a glass transition temperature of 50 ° C. or less as a binder component in the thermosensitive recording layer. A water-dispersible polymer X having a softening point of 150 to 260 ° C., which is obtained by polymerizing mainly at least one hydrophobic vinyl-based monomer having a transition temperature of 55 ° C. or higher, is used as a binder for all binders in the thermosensitive recording layer. 20 wt% or more, the protective layer is two or more layers, the lower protective layer is mainly composed of the water-dispersible polymer X, the uppermost protective layer,
A heat-sensitive recording sheet comprising a water-soluble polymer or polymer latex having a softening point of 200 to 350 ° C. as a main component. 3. A polyhydroxy compound as a binder component of the heat-sensitive recording layer is used as a binder component of the whole heat-sensitive recording layer.
The heat-sensitive recording sheet according to claim 1 or 2, wherein the heat-sensitive recording sheet contains 0 to 80% by weight. 4. The uppermost protective layer has a glass transition temperature of 50.
Glass transition temperature 5 in the presence of polymer latex below ℃
3. A water-dispersible polymer Y having a softening point of 200 to 350 [deg.] C., which is obtained by polymerizing mainly at least one kind of hydrophobic vinyl-based monomer having a temperature of 5 [deg.] C. or more, as a main component. Alternatively, the heat-sensitive recording sheet described in 3.