JP2004237747A - Thermal recording material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal recording material which comprises a support substrate having no texture color and can yield a sharp image even in high-speed printing. <P>SOLUTION: This thermal recording material comprises a modified polyvinyl alcohol containing 1 to 20 mol% α-olefin units having 4 or less carbon atoms contained in a heat-sensitive color forming layer. A dispersant for a heat-sensitive dye or a developer which develops color from the heat-sensitive dye upon heating is also provided which consists of the modified polyvinyl alcohol. Further, a binder for a thermal recording material is also provided which consists of the modified polyvinyl alcohol. The thermal recording material may comprise a protective layer consisting of the modified polyvinyl alcohol provided on a heat-sensitive color forming layer provided on a support. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a thermosensitive recording material. Further, the present invention relates to a heat-sensitive dye and a dispersant excellent in dispersibility of a color developer, which are suitable for producing a heat-sensitive recording material. Further, the present invention relates to a binder which exhibits an excellent color-forming state and can form a heat-sensitive color-forming layer having good water resistance. Further, the present invention relates to a heat-sensitive recording material having a specific protective layer which has excellent color-forming sensitivity and can improve the storage stability such as water resistance, oil resistance, and plasticizer resistance of a coating film and a color-developed portion.

  In recent years, heat-sensitive recording materials provided with a heat-sensitive coloring layer on paper, plastic film, or metallized paper, on which a recorded image is obtained by causing a chemical or physical change by heat energy to form a color, are simply heated. It has the advantages of producing a recorded image, eliminating the need for complicated processing such as development and fixing, eliminating the noise during recording, and making the recording system relatively inexpensive.It has the advantages of a computer, word processor, telex, facsimile, etc. It is also widely used as a recording material for various computers. The thermosensitive recording material is usually a colorless or slightly light-colored leuco dye, and a binder to a two-component heat-sensitive component such as a developer such as an organic acid or a phenolic compound which reacts with the leuco dye when heated to form a leuco dye. To give a binding property, and apply the obtained heat-sensitive composition to a sheet substrate to form a heat-sensitive layer.

  Recently, especially when used for facsimile, etc., the printing speed is increasing year by year, and therefore, a heat-sensitive recording material capable of coping with a sharper and higher printing speed is demanded. Further, as for the recorded image, a thermosensitive recording material is required which can obtain a precise and clean image not only for characters but also for drawings and photographs. Therefore, the heat-sensitive dye and the developer are stably dispersed at a particle size of 1 μm or less, and are present in the heat-sensitive coloring layer at a high density and thinly, and the background color of the support material is not recognized. There is a need for a heat-sensitive recording material having excellent storage stability such as oil resistance and plasticizer resistance.

  Conventionally, as a dispersant for a heat-sensitive dye and a developer, low molecular weight partially saponified polyvinyl alcohol, low molecular weight sulfonic acid group-containing modified polyvinyl alcohol, styrene or an alkali of a copolymer of α-olefin and maleic anhydride are used. Although metal salts or ester compounds have been used, none of them has achieved sufficient performance. Polyvinyl alcohol having a low molecular weight and being partially saponified has insufficient dispersibility of a heat-sensitive dye and a color developer, and cannot disperse the heat-sensitive dye and the color developer stably at a particle size of 1 μm or less. Although low molecular weight sulfonic acid group-containing modified polyvinyl alcohol has a certain level of dispersing performance, it has a problem that the background color of the support material is considerably recognized. When the maleic anhydride copolymer is blended with a binder or the like when used as a coating liquid, aggregation of the dispersed particles and thickening often occur due to poor compatibility with the binder, and furthermore, as a support material. There is a problem that background color is considerably recognized.

  Further, as a binder for a heat-sensitive recording material, for example, water-soluble polymers such as polyvinyl alcohol, methyl cellulose, hydroxy cellulose, polyvinyl pyrrolidone, and oxidized starch are known. However, although the heat-sensitive layer formed using such a binder is excellent in the coating property on the sheet substrate, the color-developed state is not sufficient, the water resistance is not sufficient, and the image storability is poor. There's a problem. Further, as a surface protective layer for a heat-sensitive recording material, for example, polyvinyl alcohol, acrylamide-modified polyvinyl alcohol, acetoacetate-ester-modified polyvinyl alcohol, aldehyde-modified polyacrylamide / styrene copolymer, and the like are known. A heat-sensitive recording material formed using a layer has a problem that storage stability such as water resistance, oil resistance, and plasticizer resistance is poor.

JP-A-06-048030 JP-A-64-061287 JP 05-208554 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide a heat-sensitive recording material that does not have a background color of a support base material and that can obtain a clear image even during high-speed printing. It is a further object of the present invention to provide a dispersant having excellent dispersibility of a heat-sensitive dye and a developer which is suitable for producing a heat-sensitive recording material. It is a further object of the present invention to provide a binder for a heat-sensitive recording material which exhibits an excellent color-forming state and can form a heat-sensitive layer having good water resistance. It is a further object of the present invention to provide a surface protective layer for a heat-sensitive recording material, which has excellent color-forming sensitivity and can improve the storage stability such as water resistance, oil resistance, and plasticizer resistance of a coating film and a colored portion.

  The present inventors have conducted intensive studies in order to solve the above-mentioned problems, and as a result, a heat-sensitive recording material having, in a heat-sensitive coloring layer, modified polyvinyl alcohol containing 1 to 20 mol% of α-olefin units having 4 or less carbon atoms; A dispersant for a heat-sensitive dye composed of modified polyvinyl alcohol or a color developer that causes the heat-sensitive dye to develop a color when heated; a binder for a heat-sensitive recording material composed of the modified polyvinyl alcohol; and a thermosensitive coloring layer provided on a support Then, a heat-sensitive recording material having a protective layer made of the modified polyvinyl alcohol was found, and the present invention was completed.

  The heat-sensitive recording material of the present invention has good color developability in a printed portion and almost no fog (coloration of a background portion) in a non-printed portion. Further, the heat-sensitive recording material of the present invention is excellent in high-speed printability and image resolution, and therefore is suitably used in fields requiring high-speed print such as facsimile. Since the dispersant of the present invention is excellent in dispersibility of the heat-sensitive dye and the color developer, a high-concentration and low-viscosity aqueous dispersion containing the heat-sensitive dye or the color developer having a fine particle diameter as a dispersoid can be obtained. . The resulting aqueous dispersion has excellent coatability on the surface of the base paper during the production of the thermal recording paper, and the dispersoids of the thermal dye and the developer are dispersed in fine particles. Of thermosensitive recording paper having a very high temperature. Further, the modified PVA used for the dispersant in the present invention is also applicable to a binder for a heat-sensitive recording material, a protective layer, and is excellent in color development performance, water resistance, oil resistance, plasticizer resistance, PVC film resistance, etc. A heat-sensitive recording material having improved storage stability can be obtained.

  The modified polyvinyl alcohol used in the present invention (hereinafter, polyvinyl alcohol may be abbreviated as PVA) needs to have an α-olefin unit having 4 or less carbon atoms in a content of 1 to 20 mol%, It is preferably from 1 to 18 mol%, more preferably from 2 to 15 mol%. When the content of the α-olefin unit is less than 1 mol%, the dispersing performance of the heat-sensitive dye and the color developer decreases, and after the aqueous dispersion is prepared, the dispersoids aggregate or the water resistance is insufficient. For this reason, a satisfactory thermosensitive recording material cannot be obtained. When the content of the α-olefin unit is more than 20 mol%, the density of the printed portion of the heat-sensitive recording material becomes low, and it becomes difficult to prepare an aqueous dispersion.

It is necessary that the modified PVA used in the present invention has a viscosity-average polymerization degree (hereinafter abbreviated as polymerization degree) of 50 to 8000, preferably 100 to 6000, more preferably 100 to 5,000. The degree of polymerization of PVA is represented by a viscosity-average degree of polymerization (P) obtained from the intrinsic viscosity [η] measured at 30 ° C. in water for a polymer purified after re-saponification according to JIS-K6726. It is.
P = ([η] × 10 ³ /8.29) ^{(1 / 0.62)}
Among the above-mentioned modified PVAs, a modified PVA having a relatively low degree of polymerization is usually used when used as a dispersant for a heat-sensitive dye or a developer, and usually 3,000 when used as a binder for a heat-sensitive recording material. A modified PVA having the following degree of polymerization is used. When used as a surface protective layer of a heat-sensitive recording material, a modified PVA having a degree of polymerization of 3000 or less is preferably used. When the degree of polymerization is less than 50, it is difficult to form fine particles of the heat-sensitive dye and the developer when used as a dispersant or a binder, and the dispersoids are aggregated after preparing the aqueous dispersion. When used as a binder or a surface protective layer, the intended performance is not exhibited. When the degree of polymerization is greater than 8000, the concentration of the printed portion of the heat-sensitive recording material decreases when used as a dispersant or binder, and the viscosity of the aqueous dispersion becomes too high, making it difficult to handle or disperse. The solids concentration of the liquid cannot be increased. When used as a surface protective layer, the viscosity of the polymer solution becomes too high and handling becomes difficult, so that a uniform surface protective layer cannot be obtained.

  The degree of saponification of the modified PVA used in the present invention needs to be 40 to 99.99 mol%, preferably 50 to 99.9 mol%, more preferably 60 to 99.5 mol%. The degree of saponification is also appropriately selected according to the use of the heat-sensitive recording material, as in the case of the degree of polymerization. In general, when the degree of saponification is less than 40 mol%, the water solubility decreases, the dispersing performance of the heat-sensitive dye and the developer decreases, and the dispersoid aggregates after adjusting the aqueous dispersion. The desired thermal recording material cannot be obtained. If the degree of saponification is greater than 99.99 mol%, the density of the printed portion of the heat-sensitive recording material decreases, and the viscosity of the aqueous dispersion becomes too high to make handling difficult. The concentration cannot be increased.

  The modified PVA containing 1 to 20 mol% of α-olefin units having 4 or less carbon atoms used in the present invention can be obtained by saponifying a copolymer of a vinyl ester and an α-olefin. Examples of the vinyl ester include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl versatate. Vinyl acetate is preferred from the viewpoint of obtaining the modified PVA in the present invention. The α-olefin has 4 or less carbon atoms and includes, for example, ethylene, propylene, n-butene, isobutene and the like.Ethylene is preferred from the viewpoint of obtaining the heat-sensitive recording material of the present invention. . The modified PVA used in the present invention is modified with an anionic group or a cationic group as required. The type of the monomer unit having an anion group or a cationic group is not particularly limited, and the unit having a carboxyl group may be fumaric acid, maleic acid, itaconic acid, maleic anhydride, phthalic anhydride, trimellitic anhydride or anhydride. A monomer unit derived from itaconic acid or the like; a monomer unit derived from ethylene sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid or the like as a unit having a sulfonic acid group; Vinyloxyethyltrimethylammonium chloride, vinyloxybutyltrimethylammonium chloride, vinyloxyethyldimethylamine, vinyloxymethyldiethylamine, N-acrylamidomethyltrimethylammonium chloride, N-acryl as units having a cationic group Bromide trimethylammonium chloride, N- acrylamide dimethylamine, allyl trimethyl ammonium chloride, methallyl trimethylammonium chloride, dimethyl allyl amine, include monomeric units derived from allyl ethyl amine. Among these monomer units, maleic anhydride, half ester derived from maleic anhydride, itaconic acid, allylsulfonic acid, 2-acrylamide-2-, in view of availability and copolymerizability. More preferred are monomer units derived from methylpropanesulfonic acid, N-acrylamidomethyltrimethylammonium chloride, and N-acrylamidoethyltrimethylammonium chloride. The content of the monomer unit having these characteristic groups is usually 10 mol% or less, and preferably 0.1 to 8 mol%.

  The modified PVA used in the present invention may contain a unit other than the vinyl alcohol unit and the vinyl ester unit as long as the effect of the present invention is not impaired. Examples of such a unit include acrylic acid and salts thereof; acrylic esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate and i-propyl acrylate; methacrylic acid and salts thereof; methyl methacrylate, methacrylic acid Methacrylic esters such as ethyl acrylate, n-propyl methacrylate and i-propyl methacrylate; acrylamide; acrylamide derivatives such as N-methylacrylamide and N-ethylacrylamide; methacrylamide; N-methylmethacrylamide; N-ethylmethacryl Methacrylamide derivatives such as amides; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether and i-propyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; salts Vinyl halides such as vinyl, vinylidene chloride, vinyl fluoride, and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid, its salts or esters; itaconic acid, its salts or esters; vinyl trimethoxy Vinylsilyl compounds such as silane; and isopropenyl acetate. The content of these units is preferably at most 10 mol%, more preferably at most 5 mol%, even more preferably at most 3 mol%.

  The content of the modified PVA in the heat-sensitive coloring layer of the heat-sensitive recording material is not particularly limited, but is preferably 3 to 30 parts by weight, and more preferably 5 to 20 parts by weight based on 100 parts by weight of the total amount of the heat-sensitive dye and the developer. Part by weight is more preferred, and 7-16 parts by weight is even more preferred.

  When preparing an aqueous dispersion of a thermal dye or a developer in the present invention, the above-mentioned modified PVA is used as a dispersant to disperse the thermal dye or the developer. The amount of the dispersant is not particularly limited, but is preferably 3 to 30 parts by weight, more preferably 5 to 20 parts by weight, and more preferably 5 to 20 parts by weight, per 100 parts by weight of the thermal dye or 100 parts by weight of the developer. Parts by weight are even more preferred. Usually, it is preferable to separately prepare the aqueous dispersions of the heat-sensitive dye and the color developer, and then mix and use the two. The concentration of the dispersoid in the aqueous dispersion is preferably from 20 to 70% by weight, more preferably from 40 to 60% by weight.

  The dispersion of the heat-sensitive dye or the developer is carried out using a sand grinder containing a large number of glass beads having an average diameter of 0.2 to 3 mm (preferably 0.3 to 0.8 mm). The dispersing time is in the range of 1 hour to 1 week (preferably 3 hours to 4 days, especially 1 to 4 days when obtaining fine particles having an average diameter of 0.45 μm or less). By using the dispersant of the present invention, the particle size is 0.1 to 1 μm (preferably 0.3 to 0.8 μm, more preferably 0.2 to 0.6 μm, and still more preferably 0.2 to 0. 45 μm) is obtained as an aqueous dispersion containing a heat-sensitive dye or a developer as a dispersoid.

  The thermal dye used in the present invention is not particularly limited as long as it is used for general pressure-sensitive recording paper or thermal recording paper. Specific examples include 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (crystal violet lactone) and 3- (p-dimethylaminophenyl) -3- (1, 2-dimethylindol-3-yl) phthalide, 3- (p-dimethylaminophenyl) -3- (2-phenylindol-3-yl) phthalide, 3,3-bis- (9-ethylcarbazol-3-yl) A) triarylmethane compounds such as -5-dimethylaminophthalide; diphenylmethane compounds such as 4,4'-bisdimethylaminobenzhydrin benzyl ether and N-halophenylleuco auramine; rhodamine B-anilinolactam; 3-diethylamino-7-benzylaminofluoran, 3-diethylamino-7-butylaminofluora , 3-diethylamino-7- (chloroanilino) fluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-piperidino-6-methyl-7-anilinofluoran, 3-ethyl-tolylamino-6 Methyl-7-anilinofluoran, 3-cyclohexyl-methylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-chloro-7- (β-ethoxyethyl) aminofluoran, 3-diethylamino -6-chloro-7-([gamma] -chloropropyl) aminofluoran, 3- (N-ethyl-N-isoamyl) -6-methyl-7-phenylaminofluoran, 3-dibutylamino-6-methyl-7 Xanthene compounds such as anilinofluorane; benzoyl leucomethylene blue, p-nitrobenzoyl leucometi Thiazine-based compounds such as benzoyl; spiro-based compounds such as 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3-benzylspiro-dinaphthopyran, 3-methylnaphtho- (3-methoxy-benzo) -spiropyran; And these are used alone or as a mixture of two or more. These thermal dyes are appropriately selected and used depending on the use of the thermal recording material.

  As the developer used in the present invention, phenol derivatives and aromatic carboxylic acid derivatives are preferable, and bisphenols are particularly preferable. Specifically, as phenols, p-octylphenol, p-tert-butylphenol, p-phenylphenol, 1,1-bis (p-hydroxyphenyl) propane, 2,2-bis (p-hydroxyphenyl) propane, 1,1-bis (p-hydroxyphenyl) pentane, 1,1-bis (p-hydroxyphenyl) hexane, 2,2-bis (p-hydroxyphenyl) hexane, 1,1-bis (p-hydroxyphenyl) Examples of -2-ethyl-hexane, 2,2-bis (4-hydroxy-3,5-dichlorophenyl) propane, dihydroxydiphenyl ether, and aromatic carboxylic acid derivatives include p-hydroxybenzoic acid, ethyl p-hydroxybenzoate, and p-hydroxybenzoic acid. -Butyl hydroxybenzoate, 3,5-di-tert-butylsalicylic acid 3,5-di -α- methylbenzyl salicylic acid, polyvalent metal salts of the carboxylic acid and the like.

  In the present invention, it is preferable to use an aqueous binder for the thermosensitive coloring layer. The water-based binder is not particularly limited, and any known water-based binder can be used. When such a water-based binder is mixed with each dispersion of the heat-sensitive dye and the developer, the solution develops color or agglomerates. It is preferable that the viscosity is not reduced or the viscosity is not increased. Specific examples thereof include starch and derivatives thereof, hydroxymethylcellulose, hydroxyethylcellulose, carboxymethylcellulose, methylcellulose, cellulose derivatives such as ethylcellulose, the α-olefin-modified PVA used in the present invention, polyvinyl alcohol, sodium polyacrylate, polyvinyl Pyrrolidone, acrylamide / acrylic acid ester copolymer, acrylamide / acrylic acid ester / methacrylic acid terpolymer, styrene / maleic anhydride copolymer alkaline salt, isobutylene / maleic anhydride copolymer alkaline salt, polyacrylamide, Water-soluble polymers such as sodium alginate, gelatin, casein; polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylate, vinyl chloride / vinyl acetate Polymers, polybutyl methacrylate, an emulsion such as ethylene / vinyl acetate copolymers, styrene / butadiene copolymer, latexes such as styrene / butadiene / acrylic copolymer. Among these, the above-mentioned α-olefin-modified PVA used in the present invention is preferable because the strength of the formed film is large. The preferred addition amount of the aqueous binder is 1 to 20 parts by weight based on 100 parts by weight of the total amount of the thermal dye and the developer.

  In the heat-sensitive coloring layer of the heat-sensitive recording material of the invention, in addition to the heat-sensitive dye and the developer, various substances described below can be added, if necessary. In order to further improve the coating suitability, the whiteness, the color sensitivity, the dispersibility, and the like, auxiliary additives added to the heat-sensitive recording material include, for example, fillers, surfactants, and heat-soluble substances (or lubricants). , An antifoaming agent, a dispersing agent, a wetting agent, a pressure coloring inhibitor and the like can be used in combination. In the present invention, as a method for forming the thermosensitive coloring layer, known coating methods such as an air knife method, a plate method, a gravure method, a roll coater method, a spray method, a dip method, a bar method, and an extrusion method can be used. .

  The material for the protective layer formed on the heat-sensitive coloring layer in the heat-sensitive recording material of the present invention is not particularly limited, and any known materials can be used. Specific examples thereof include starch and its derivatives, hydroxymethylcellulose, hydroxyethylcellulose, carboxymethylcellulose, methylcellulose, cellulose derivatives such as ethylcellulose, arabic gum, the above-mentioned α-olefin-modified PVA, polyvinyl alcohol, acrylic acid (or (Methacrylic acid) ester copolymer alkali salt, polyvinylpyrrolidone, acrylamide (or methacrylamide) / acrylic acid (or methacrylic acid) ester copolymer, styrene / maleic anhydride copolymer alkali salt, isobutylene / maleic anhydride Alkali salts of copolymers, alkali salts of diisobutylene / maleic anhydride copolymers, water-soluble polymers such as polyacrylamide, sodium alginate, gelatin, casein An emulsion of polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylate, vinyl chloride / vinyl acetate copolymer, polybutyl methacrylate, ethylene / vinyl acetate copolymer, styrene / butadiene copolymer, styrene / butadiene / Latexes such as acrylic copolymers. The requirements as a protective layer forming agent have excellent film forming performance, and the obtained film needs to have water resistance, plasticizer resistance, oil resistance, organic solvent resistance, etc., It is a water-soluble polymer that has sufficient film-forming performance even under relatively low-temperature drying conditions of 100 ° C. or less in order to prevent the heat-sensitive coloring layer from coloring during coating. From this viewpoint, the above-mentioned α-olefin-modified PVA used in the present invention is preferable as the protective layer forming agent.

As the filler, kaolin, clay, talc, calcium carbonate, calcined clay, titanium oxide, diatomaceous earth, silica, aluminum oxide, synthetic aluminum silicate, synthetic magnesium silicate, polystyrene fine particles, polyvinyl acetate fine particles, urea-formalin Fine resin particles and the like. As the lubricant, higher fatty acids, higher fatty acid amides, higher fatty acid metal salts, paraffin wax, microcrystalline wax and the like can be used. It is necessary that the preferable amount of the protective layer forming agent is 20% by weight or more of all components of the protective layer. If the addition amount is less than 20% by weight, water resistance, oil resistance, plasticizer resistance and the like are undesirably reduced. The coating amount of the solid content of the protective layer is appropriately selected so long as heat conduction from the thermal head to the coloring layer is not hindered, but is usually 1 to 10 g / m ² , preferably ² to 7 g / m ² . .

  In the present invention, the support material of the heat-sensitive recording material is not particularly limited. For example, paper, synthetic fiber paper, synthetic resin film, and the like can be appropriately used. Among them, it is generally preferable to use paper.

  The present invention will be described in more detail by way of examples. In the following, “parts” and “%” mean “parts by weight” and “% by weight”, respectively, unless otherwise specified. In the following description, the viscosity is a value measured at 30 ° C. and a rotor rotation speed of 12 rpm using a B-type viscometer manufactured by Tokyo Keiki.

Example 1
(1) Preparation of coating solution (dispersion of thermal dye and developer)
A. Preparation of aqueous dispersion of heat-sensitive dye Leuco dye (manufactured by Yamada Chemical Co., Ltd., trade name: S-205) 20%
Concentration 10% ethylene-modified PVA aqueous solution 20%
(Ethylene 4 mol% copolymerization modification, polymerization degree 500, saponification degree 87 mol%)
59.9% of water
Antifoaming agent (trade name: Surfynol 440, manufactured by Nissin Chemical Industry Co., Ltd.)
0.1%
B. Preparation of aqueous dispersion of developer Bisphenol A 20%
Concentration 10% ethylene-modified PVA aqueous solution 20%
(The same as that used to prepare the aqueous dispersion of the thermal dye)
59.9% of water
Antifoaming agent (trade name: Surfynol 440, manufactured by Nissin Chemical Industry Co., Ltd.)
0.1%
C. Preparation of aqueous dispersion of pigment 10% stearamide 20% calcium carbonate
5% ethylene-modified PVA aqueous solution 30%
(The same as that used to prepare the aqueous dispersion of the thermal dye)
40% water

The aqueous dispersions A, B, and C were separately prepared, and were preliminarily stirred in a beaker for 15 minutes.
Next, each of the aqueous dispersions A and B was transferred to a sand grinder (a batch type desktop sand grinder manufactured by Kansai Paint Co., Ltd.), and 300 cc of glass beads (soda quartz glass having a diameter of 0.5 mm) were added thereto. ), And dispersed over 6 hours under cooling.
Next, the aqueous dispersion C was dispersed for 2 minutes using a homogenizer (10000 rpm). The physical properties of the obtained aqueous dispersion A of the heat-sensitive dye were evaluated by the following methods.
-Particle size of dispersoid:
Six hours after the start of the dispersion, the particle diameter was measured by a laser diffraction particle size analyzer (manufactured by Shimadzu Corporation, model: SALD-1000).
・ Viscosity of aqueous dispersion:
After dispersing for 6 hours, the viscosity of the aqueous dispersion after about 1 hour had elapsed was measured at 30 ° C.
・ Whiteness of aqueous dispersion:
After the completion of the dispersion for 6 hours, the whiteness of the aqueous dispersion obtained after about 1 hour was measured with a model (Z-1001DP, manufactured by Nippon Denshoku Industries Co., Ltd.). The degree of whiteness indicates that 0 is completely white, and the larger the negative value, the more colored.

(2) Production of heat-sensitive recording paper 1 part of the aqueous dispersion A, 4 parts of the aqueous dispersion B, 2 parts of the aqueous dispersion C, and 10% polyvinyl alcohol (polymerization degree 1750, saponification degree 98.5) (Mol%) aqueous solution was mixed and stirred to prepare a coating solution for a thermosensitive coloring layer. The surface of the base paper (basis weight: high quality paper of 52 g / m ² ) was coated with a coating liquid of 6 g / m ² (in terms of solid content) using a wire bar coater, and then dried at 50 ° C. for 10 minutes. Then, the surface was treated with a super calender (linear pressure: 30 kg / cm) to produce a heat-sensitive recording paper.
The performance of the obtained thermosensitive recording paper was evaluated by the following method.
・ Coloring density of printing part of thermal recording paper:
After printing on the thermal recording paper using a thermal facsimile printer (Ricoh 300, manufactured by Ricoh Co., Ltd.), measure the color density of the printed area with a Macbeth densitometer (Macbeth, Model: RD-514). did.
・ Coloring density of non-printed area of thermal recording paper:
Using the same Macbeth densitometer as above, the coloring density of the non-printed portion of the thermal recording paper was measured.
・ Macbeth concentration:
Perfect white (0.00), Perfect black (1.82)
Table 1 shows the evaluation results for the aqueous dispersion A of the thermal dye and the thermal recording paper.

Examples 2 to 6
A coating solution was prepared in the same manner as in Example 1 except that the ethylene-modified PVA shown in Table 1 was used instead of the ethylene-modified PVA used in Example 1 (dispersion of a thermosensitive dye and a developer). ) To produce a thermal recording paper. Table 1 shows the results.

Comparative Examples 1 to 5
A coating solution was prepared in the same manner as in Example 1 except that various polyvinyl alcohols shown in Table 1 were used instead of the ethylene-modified PVA used in Example 1 (a heat-sensitive dye and a developer). Dispersing) to produce a thermosensitive recording paper. Table 1 shows the results.

Example 7
In Example 1, instead of PVA (polymerization degree 1750, saponification degree 98.5 mol%) used as a binder in the production of the thermosensitive recording paper, ethylene-modified PVA (ethylene 4 mol% copolymerization modification, polymerization degree 1700, saponification degree) (98 mol%), a coating solution was prepared (dispersion of a thermosensitive dye and a developer) in the same manner as in Example 1 to produce a thermosensitive recording paper. Table 1 shows the results. From these results, it is understood that the above-mentioned ethylene-modified PVA used in the present invention is excellent as a binder for a heat-sensitive recording material.

Example 8
(3) Production of protective layer One part of the aqueous dispersion A used in Example 1, 6 parts of the aqueous dispersion B, and a 10% aqueous solution of polyvinyl alcohol (polymerization degree 1750, saponification degree 98.5 mol%) were used. Two parts were mixed and stirred to prepare a coating solution for the thermosensitive coloring layer. The surface of the base paper (basis weight: high quality paper of 52 g / m ² ) was coated with a coating liquid of 6 g / m ² (in terms of solid content) using a wire bar coater, and then dried at 50 ° C. for 10 minutes. Then, the surface was treated with a super calender (linear pressure: 30 kg / cm). Further, the following aqueous dispersion D was coated on the color-forming layer so that the dry weight became 3 g / m ² , a protective layer was provided, and a two-layer thermosensitive recording paper was manufactured.
With respect to the obtained heat-sensitive recording paper, the water resistance, oil resistance and PVC film property of the colored portion were evaluated by the following methods.
D. Preparation of aqueous dispersion for protective layer 60% kaolin dispersion 6%
30% zinc stearate 4%
90% aqueous solution of 10% ethylene-modified PVA
(Ethylene 4 mol% copolymerization modification, polymerization degree 1300, saponification degree 99.0 mol%)
・ Water resistance test:
The test piece is immersed in water at room temperature for 24 hours, taken out, and evaluated based on the elution state of the protective layer and the residual concentration after drying.
・ Oil resistance test:
According to a conventional method, cottonseed oil is applied to a test piece, and evaluation is made based on each residual concentration after standing at 20 ° C. and 40 ° C. for 24 hours.
・ PVC film resistance test:
A soft polyvinyl chloride film is superimposed on the test piece, and the concentration is measured when both are contacted at 20 ° C. under a load of 300 g / m ² for 24 hours.
Table 2 shows the evaluation results of the protective layer on the thermal recording paper.

Examples 9 to 12, Comparative Examples 6 to 8
In the same manner as in Example 8, except that the aqueous dispersion D for the protective layer prepared using various PVAs shown in Table 2 was used instead of the aqueous dispersion D for the protective layer used in Example 8, To produce thermal recording paper. Table 2 shows the results.

  As is clear from Table 2, it can be seen that Examples 8 to 12 have improved water resistance, oil resistance and PVC film performance as compared with Comparative Examples 6 to 8.

Claims (3)

A heat-sensitive recording material having, in a heat-sensitive coloring layer, a modified polyvinyl alcohol containing 1 to 20 mol% of an α-olefin unit having 4 or less carbon atoms. A binder for a heat-sensitive recording material comprising a modified polyvinyl alcohol containing 1 to 20 mol% of an α-olefin unit having 4 or less carbon atoms. A heat-sensitive recording material having a protective layer made of a modified polyvinyl alcohol containing 1 to 20 mol% of an α-olefin unit having 4 or less carbon atoms on a thermosensitive coloring layer provided on a support.