JP2009051049A - Thermal recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal recording medium having sufficient coloring sensitivity, a waterproof property, head tailing resistance, a coloring prevention property in storage, and good surface strength, in particular, a thermal recording medium needing no installation of a protective layer on a thermal recording layer. <P>SOLUTION: In the thermal recording medium, a thermal recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting developer is formed on a support, and the thermal recording layer contains an acrylic resin and a polyacrylamide resin. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a heat-sensitive recording material having sufficient color development sensitivity and excellent in water resistance, head residue resistance, color development prevention during storage, and surface strength.

  In general, a recorded image is obtained by utilizing a color development reaction caused by heat between a colorless or light-colored electron-donating leuco dye (hereinafter referred to as a dye) and an electron-accepting developer (hereinafter referred to as a developer). Thermal recording media are widely used in the fields of facsimiles, computers, and various measuring instruments because of their very vivid color development and the advantages of no noise during recording, relatively inexpensive equipment, compactness, and easy maintenance. Has been. Recently, in addition to labels and tickets, applications such as outdoor measurement handy terminals and delivery slips that are used as output media for various printers and plotters have been rapidly expanding. For this reason, higher color sensitivity, printing runnability, and printing surface strength are required for the quality of the thermal recording material. In addition, since labels, tickets, handy terminal paper, delivery slips, etc. are used outdoors, they can withstand use in harsh environments such as moisture, moisture, sunlight, and high temperatures, and are highly water-resistant. Is required to prevent color development.

  Therefore, in order to improve the water resistance of the heat-sensitive recording medium, an acrylic resin is contained in the heat-sensitive recording layer, and in order to improve the water resistance and head-casing resistance of the heat-sensitive recording medium, an acrylic polymer or acrylic emulsion is added to the heat-sensitive recording layer. Techniques (Patent Documents 1 and 2) using a resin and colloidal silica in combination are performed.

JP-A-9-207435 JP 7-266711 A

  The conventional methods described above do not have sufficient performance such as high water resistance and head scum resistance required for recent thermal recording media. When an acrylic resin is contained in the heat-sensitive recording layer and its protective layer, the water resistance is improved, but the problem is that the acrylic resin is softened by the heat from the thermal head of the heat-sensitive recording printer and head debris is generated. For this reason, thermal recording materials that have improved water resistance and head-casing resistance by containing an acrylic resin and colloidal silica in the thermal recording layer are disclosed in Patent Documents 1 and 2, but the colloidal silica itself has. Due to the influence of the activity, it reacts with the dye and developer contained in the heat-sensitive recording layer during storage, which causes a problem that the white portion is colored.

  Therefore, the present invention has a sufficient color development sensitivity and is excellent in water resistance, head residue resistance, color development prevention during storage, and printability (surface strength), particularly a protective layer on the thermal recording layer. It is an object of the present invention to provide a heat-sensitive recording material that does not need to be provided.

  As a result of intensive studies, the present inventors have provided a heat-sensitive recording layer provided with a colorless or light-colored electron-donating leuco dye and an electron-accepting developer on the support. It has been found that the above-mentioned problems can be solved by using a heat-sensitive recording material containing an acrylic resin and a polyacrylamide resin, and the present invention has been completed.

  According to the present invention, it is possible to obtain a heat-sensitive recording material having sufficient color development sensitivity, excellent in water resistance, head residue resistance, color development prevention during storage, and surface strength. In particular, an excellent effect is exhibited in a heat-sensitive recording material having no protective layer.

  The acrylic resin used in the present invention is a polymer obtained by copolymerizing acrylic acid, methacrylic acid, acrylic acid and methacrylic acid derivatives (acrylamide, acrylonitrile, etc.) maleic acid and derivatives thereof, styrene and derivatives thereof, and the like as main components. The composition ratio, synthesis method, etc. are not particularly limited, but it is preferable to contain a core-shell type acrylic resin in the heat-sensitive recording layer from the viewpoint of water resistance and head residue resistance. . In the present invention, the glass transition temperature (Tg) and the minimum film-forming temperature (MFT) of the acrylic resin are not particularly limited, but from the viewpoint of water resistance, the glass transition temperature (Tg) is 50 ° C. or less. The minimum film-forming temperature is preferably 25 ° C. or lower, and more preferably, the glass transition temperature (Tg) is 0 to 50 ° C., and the minimum film-forming temperature (MFT) is preferably 0 to 25 ° C. More preferably, the glass transition temperature (Tg) is 15 to 40 ° C., and the minimum film forming temperature (MFT) is preferably 5 to 15 ° C.

  In order to prevent color development during production, the thermal recording material is usually produced by controlling the drying so that the maximum temperature of the thermal recording material does not exceed 60 ° C. For this reason, it is preferable to use a resin having a low minimum film forming temperature (MFT) that sufficiently forms a film at about 60 ° C. in order to improve water resistance. Generally, the minimum film forming temperature and the glass transition temperature (Tg) are used. Therefore, if the thermal recording layer contains a resin having a low minimum film forming temperature, that is, a resin having a low glass transition temperature, the resin softens due to the heat from the thermal head of the thermal recording printer. Will occur. For this reason, the apparent glass transition of acrylic resin by mixing colloidal silica around acrylic resin by mixing acrylic resin and colloidal silica with low minimum film-forming temperature (MFT) in the prior art. A technique has been used to control the temperature (Tg) and the minimum film-forming temperature (MFT) to obtain excellent water resistance and head-cass resistance. However, due to the activity of colloidal silica itself, A new problem arises that the white part is colored by reacting with the contained dye or developer. As described above, in the conventional technique, an acrylic resin having a glass transition temperature (Tg) of 50 ° C. or lower and a minimum film-forming temperature of 25 ° C. or lower is used, which is excellent in water resistance, head residue resistance, and coloring prevention property during storage. It was difficult to obtain a thermal recording material.

  However, the present inventors have used an acrylic resin having a low Tg and a low MFT, which has conventionally had a problem in head-casing resistance, although water resistance is good by using an acrylic resin and polyacrylamide in combination. It has been found that it can be contained in the present invention, and the present invention has been completed. Further, the present invention has a color-preventing property during storage because the heat-sensitive recording layer does not contain colloidal silica.

  In the present invention, the glass transition temperature (Tg) is determined based on the scanning differential calorimeter (20 mg of 10 mg sample in a nitrogen atmosphere) for each component (monomer) constituting the resin in accordance with JIS K-7122. The glass transition temperature of the resin (Tg) = Tg1 × α1 + Tg2 × α2 +... + Tgn × αn (Tg1, Tg2,... Tgn: The glass transition temperature of each measured simple substance, α1, α2,... Αn: the weight fraction (%) of each single composition relative to the total weight of the resin. The minimum film-thickening temperature (MFT) is based on JIS K-6828. A resin adjusted to 20% by weight is spread over the entire surface of the slide glass, dried at a predetermined temperature, and the dried resin is uniform. The minimum temperature was a continuous film and the film was not clouded.

  In the present invention, examples of the core-shell type acrylic resin include a core-shell type emulsion in which an acrylic resin, a styrene acrylic resin or a styrene methacrylic resin is used for the core portion, and a styrene acrylic resin or a styrene methacrylic resin is used for the shell portion. Specific examples include Jonkrill 74J, Jonkrill 537, PDX7677 (above, manufactured by BASF), and the like. Among them, examples of the core-shell type acrylic resin having a glass transition temperature (Tg) of 50 ° C. or lower and a minimum film-forming temperature (MFT) of 25 ° C. or lower include Jonkrill 74J and PDX7677, but are not limited thereto. Absent.

  On the other hand, examples of the acrylic resin that is not a core-shell type include mobile 718, mobile 8020, mobile 8030, mobile 9000 (manufactured by Clariant Polymer Co., Ltd.), SA-532 (manufactured by Nippon Shokubai Co., Ltd.), and the like. Is not to be done.

  The present invention utilizes a reaction between a polyacrylamide resin and a carboxyl group (including a carbonyl group) of an acrylic resin, and includes an acrylic resin having a carboxyl group contained in a heat-sensitive recording layer and an amide of the polyacrylamide resin. The group reacts to make the hydrophilic group part of both the acrylic resin and the acrylamide resin hydrophobic, so that high water resistance is imparted. In addition, since polyacrylamide resin reacts with a binder having a carboxyl group or a hydroxyl group other than the acrylic resin in the heat-sensitive recording layer, the binder in the heat-sensitive recording layer behaves like an enormous polymer. The heat resistance and surface strength of the entire layer are improved. For this reason, it is considered that by including polyacrylamide in the heat-sensitive recording layer, in addition to the water resistance, the head residue resistance and the surface strength (printability) are improved.

  Furthermore, since the polyacrylamide resin is bonded to the binder in the heat-sensitive recording layer, the instantaneous heat from the thermal head affects the bonded portion of the polyacrylamide resin and the binder. It is considered that the acrylamide resin does not elute, in other words, it does not cause a problem in printing runnability (head residue resistance).

  Examples of the polyacrylamide resin of the present invention include those commercially available from Dick Hercules, Arakawa Chemical Industries, Harima Kasei, BASF, Kao, etc. as polyacrylamide paper strength enhancers (for internal and external additives). However, it is not limited to these. Of the polyacrylamide-based paper strength agents, nonionic modified polyacrylamide resins are preferable because they are excellent in color development sensitivity and printability (surface strength).

  Since the heat-sensitive recording material of the present invention is excellent in water resistance as described above, a protective layer on the heat-sensitive recording layer can be omitted.

  The blending amount of the acrylic resin used in the present invention is preferably 1 to 30% by weight (hereinafter, parts by weight are converted to solids) with respect to the total solid content of the heat-sensitive recording layer, and more preferably 2 to 10% by weight. preferable. When the blending amount of the acrylic resin is 1% by weight or less, water resistance cannot be obtained, and when it is 30% by weight or more, high color development sensitivity is hardly obtained.

  As a compounding quantity of the polyacrylamide resin used by this invention, Preferably it is 0.1-5 weight part (henceforth, a weight part is converted into solid content) with respect to 100 weight part of heat-sensitive layer total solid content, More preferably Is 0.5 to 2 parts by weight. When the compounding amount of the polyacrylamide type paper strength agent is 0.1 parts by weight or less, good printability (surface strength) cannot be obtained, and when it is 5 parts by weight or more, high color development sensitivity is difficult to obtain, and the coating is increased. The viscosity becomes significant.

  Examples of various materials used in the heat-sensitive color developing layer of the present invention include a binder and a cross-linking agent that can be used in combination as long as the desired effects on the above-mentioned problems are not impaired. Not only can it be used for each coating layer provided as needed, including the under layer.

  As the developer used in the present invention, any known ones in the field of conventional pressure-sensitive or heat-sensitive recording paper can be used and are not particularly limited. For example, 4,4′-isopropyl Dendiphenol, 1,1-bis (4-hydroxyphenyl) cyclohexane, 2,2-bis (4-hydroxyphenyl) -4-methylpentane, 4,4′-dihydroxydiphenyl sulfide, hydroquinone monobenzyl ether, 4-hydroxy Benzyl benzoate, 4,4′-dihydroxydiphenylsulfone, 2,4′-dihydroxydiphenylsulfone, 4-hydroxy-4′-isopropoxydiphenylsulfone, 4-hydroxy-4′-n-propoxydiphenylsulfone, bis (3 -Allyl-4-hydroxyphenyl) sulfone, 4-hydroxy-4'- Allyloxydiphenylsulfone, 4-hydroxy-4'-methyldiphenylsulfone, 4-hydroxyphenyl-4'-benzyloxyphenylsulfone, 3,4-dihydroxyphenyl-4'-methylphenylsulfone, JP-A-8-59603 Aminobenzenesulfonamide derivatives, bis (4-hydroxyphenylthioethoxy) methane, 1,5-di (4-hydroxyphenylthio) -3-oxapentane, butyl bis (p-hydroxyphenyl) acetate, bis (p -Hydroxyphenyl) acetic acid methyl, 1,1-bis (4-hydroxyphenyl) -1-phenylethane, 1,4-bis [α-methyl-α- (4′-hydroxyphenyl) ethyl] benzene, 1,3 -Bis [α-methyl-α- (4′-hydroxyphenyl) ethyl] benzene , Di (4-hydroxy-3-methylphenyl) sulfide, 2,2′-thiobis (3-tert-octylphenol), 2,2′-thiobis (4-tert-octylphenol), described in International Publication No. WO 97/16420 Phenolic compounds such as diphenylsulfone cross-linking compounds, developer compositions described in International Publication WO 02/098674, compounds described in International Publication WO 02/081229 or JP-A No. 2002-301873, 4,4′- Bis-3- (phenoxycarbonylamino) methylphenylureido) diphenylsulfone (trade name: UU manufactured by Asahi Kasei Corporation), thiourea compounds such as N, N′-di-m-chlorophenylthiourea, p-chlorobenzoic acid, stearyl gallate Bis [4- (n-octyloxycarbonylamino) salicylate zinc] 2 Japanese, 4- [2- (p-methoxyphenoxy) ethyloxy] salicylic acid, 4- [3- (p-tolylsulfonyl) propyloxy] salicylic acid, 5- [p- (2-p-methoxyphenoxyethoxy) cumyl] Aromatic carboxylic acids of salicylic acid, and salts of these aromatic carboxylic acids with polyvalent metal salts such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, nickel, as well as antipyrine complexes of zinc thiocyanate, terephthalate Examples include complex zinc salts of aldehyde acid and other aromatic carboxylic acid. A phenolic compound such as the diphenylsulfone cross-linking compound described in International Publication No. WO 97/16420 is available as a trade name D-90 manufactured by Nippon Soda Co., Ltd. The compounds described in International Publication No. WO02 / 081229 or JP-A-2002-301873 are available as trade names D-102 and D-100 manufactured by Nippon Soda Co., Ltd. These developers can be used alone or in combination of two or more. Among these, 4-hydroxy-4′-isopropoxydiphenyl sulfone is particularly preferable because of excellent color development sensitivity. In addition, a metal chelate color-developing component such as a higher fatty acid metal double salt and a polyvalent hydroxyaromatic compound described in JP-A-10-258577 can also be contained.

  As the electron-donating leuco dye used in the present invention, those known in the conventional pressure-sensitive or heat-sensitive recording paper field can be used, and are not particularly limited, but include triphenylmethane compounds, fluorane compounds. Compounds, fluorene compounds, divinyl compounds and the like are preferable. Specific examples of typical colorless or light-colored dyes (dye precursors) are shown below. These dye precursors may be used alone or in combination of two or more.

<Triphenylmethane leuco dye>
3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (also known as crystal violet lactone); 3,3-bis (p-dimethylaminophenyl) phthalide (also known as malachite green lactone)

<Fluoran leuco dye>
3-diethylamino-6-methylfluorane; 3-diethylamino-6-methyl-7-anilinofluorane; 3-diethylamino-6-methyl-7- (o, p-dimethylanilino) fluorane; 3-diethylamino- 6-methyl-7-chlorofluorane; 3-diethylamino-6-methyl-7- (m-trifluoromethylanilino) fluorane; 3-diethylamino-6-methyl-7- (o-chloroanilino) fluorane; Diethylamino-6-methyl-7- (p-chloroanilino) fluorane; 3-diethylamino-6-methyl-7- (o-fluoroanilino) fluorane; 3-diethylamino-6-methyl-7- (m-methylanilino) fluorane 3-diethylamino-6-methyl-7-n-octylanilinofluorane; 3-diethylamino-6-methyl-7-n-octylaminofluorane; 3-diethylamino-6-methyl-7-benzylaminofluorane; 3-diethylamino-6-methyl-7-dibenzylaminofluorane;
3-diethylamino-6-chloro-7-methylfluorane; 3-diethylamino-6-chloro-7-anilinofluorane; 3-diethylamino-6-chloro-7-p-methylanilinofluorane; 3-diethylamino -6-ethoxyethyl-7-anilinofluorane; 3-diethylamino-7-methylfluorane; 3-diethylamino-7-chlorofluorane; 3-diethylamino-7- (m-trifluoromethylanilino) fluorane; 3-diethylamino-7- (o-chloroanilino) fluorane; 3-diethylamino-7- (p-chloroanilino) fluorane; 3-diethylamino-7- (o-fluoroanilino) fluorane; 3-diethylamino-benzo [a] fluorane ;
3-dibutylamino-6-methyl-7- (o); 3-dibutylamino-6-methyl-7- (o; 3-dibutylamino-6-methyl-7- (o , P-dimethylanilino) fluorane; 3-dibutylamino-6-methyl-7- (o-chloroanilino) fluorane; 3-dibutylamino-6-methyl-7- (p-chloroanilino) fluorane; 3-dibutylamino- 6-methyl-7- (o-fluoroanilino) fluorane; 3-dibutylamino-6-methyl-7- (m-trifluoromethylanilino) fluorane; 3-dibutylamino-6-methyl-chlorofluorane; 3-dibutylamino-6-ethoxyethyl-7-anilinofluorane; 3-dibutylamino-6-chloro- 7-anilinofluorane; 3-dibutylamino-6-methyl-7-p-methylanilinofluorane; 3-dibutylamino-7- (o-chloroanilino) fluorane; 3-dibutylamino-7- (o- 3-di-n-pentylamino-6-methyl-7-anilinofluorane; 3-di-n-pentylamino-6-methyl-7- (p-chloroanilino) fluorane; Di-n-pentylamino-7- (m-trifluoromethylanilino) fluorane; 3-di-n-pentylamino-6-chloro-7-anilinofluorane; 3-di-n-pentylamino-7 -(P-chloroanilino) fluorane; 3-pyrrolidino-6-methyl-7-anilinofluorane; 3-piperidino-6-methyl-7-anilinofluorane 3- (N-methyl-N-propylamino) -6-methyl-7-anilinofluorane; 3- (N-methyl-N-cyclohexylamino) -6-methyl-7-anilinofluorane; -(N-ethyl-N-cyclohexylamino) -6-methyl-7-anilinofluorane; 3- (N-ethyl-N-xylamino) -6-methyl-7- (p-chloroanilino) fluorane; (N-ethyl-p-toludino) -6-methyl-7-anilinofluorane; 3- (N-ethyl-N-isoamylamino) -6-methyl-7-anilinofluorane; 3- (N- Ethyl (N-isoamylamino) -6-chloro-7-anilinofluorane; 3- (N-ethyl-N-tetrahydrofurfurylamino) -6-methyl-7-anilinofluorane; Til-N-isobutylamino) -6-methyl-7-anilinofluorane; 3- (N-ethyl-N-ethoxypropylamino) -6-methyl-7-anilinofluorane; 3-cyclohexylamino-6 -Chlorofluorane; 2- (4-oxahexyl) -3-dimethylamino-6-methyl-7-anilinofluorane; 2- (4-oxahexyl) -3-diethylamino-6-methyl-7-ani Linofluorane; 2- (4-oxahexyl) -3-dipropylamino-6-methyl-7-anilinofluorane; 2-methyl-6-p- (p-dimethylaminophenyl) aminoanilinofluorane 2-methoxy-6-p- (p-dimethylaminophenyl) aminoanilinofluorane; 2-chloro-3-methyl-6-p- (p-phenylaminophenyl); 2-chloro-6-p- (p-dimethylaminophenyl) aminoanilinofluorane; 2-nitro-6-p- (p-diethylaminophenyl) aminoanilinofluorane; -Amino-6-p- (p-diethylaminophenyl) aminoanilinofluorane; 2-diethylamino-6-p- (p-diethylaminophenyl) aminoanilinofluorane; 2-phenyl-6-methyl-6-p -(P-phenylaminophenyl) aminoanilinofluorane; 2-benzyl-6-p- (p-phenylaminophenyl) aminoanilinofluorane; 2-hydroxy-6-p- (p-phenylaminophenyl) Aminoanilinofluorane; 3-methyl-6-p- (p-dimethylaminophenyl) aminoanilinov Oran; 3-diethylamino-6-p- (p-diethylaminophenyl) aminoanilinofluorane; 3-diethylamino-6-p- (p-dibutylaminophenyl) aminoanilinofluorane; 2,4-dimethyl-6 -[(4-Dimethylamino) anilino] -fluorane

<Fluorene leuco dye>
3,6,6′-tris (dimethylamino) spiro [fluorene-9,3′-phthalide]; 3,6,6′-tris (diethylamino) spiro [fluorene-9,3′-phthalide]
<Divinyl leuco dye>
3,3-bis- [2- (p-dimethylaminophenyl) -2- (p-methoxyphenyl) ethenyl] -4,5,6,7-tetrabromophthalide; 3,3-bis- [2- (P-dimethylaminophenyl) -2- (p-methoxyphenyl) ethenyl] -4,5,6,7-tetrachlorophthalide; 3,3-bis- [1,1-bis (4-pyrrolidinophenyl) ) Ethylene-2-yl] -4,5,6,7-tetrabromophthalide; 3,3-bis- [1- (4-methoxyphenyl) -1- (4-pyrrolidinophenyl) ethylene-2- Yl] -4,5,6,7-tetrachlorophthalide

<Others>
3- (4-diethylamino-2-ethoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl) -4-azaphthalide; 3- (4-diethylamino-2-ethoxyphenyl) -3- ( 1-octyl-2-methylindol-3-yl) -4-azaphthalide; 3- (4-cyclohexylethylamino-2-methoxyphenyl) -3- (1-ethyl-2-methylindol-3-yl)- 3,3-bis (1-ethyl-2-methylindol-3-yl) phthalide; 3,6-bis (diethylamino) fluorane-γ- (3′-nitro) anilinolactam; -Bis (diethylamino) fluorane-γ- (4'-nitro) anilinolactam; 1,1-bis- [2 ', 2', 2 ", 2" -tetrakis- (p-dimethyla Nophenyl) -ethenyl] -2,2-dinitrileethane; 1,1-bis- [2 ′, 2 ′, 2 ″, 2 ″ -tetrakis- (p-dimethylaminophenyl) -ethenyl] -2- β-naphthoylethane; 1,1-bis- [2 ′, 2 ′, 2 ″, 2 ″ -tetrakis- (p-dimethylaminophenyl) -ethenyl] -2,2-diacetylethane; bis- [2, 2,2 ′, 2′-Tetrakis- (p-dimethylaminophenyl) -ethenyl] -methylmalonic acid dimethyl ester

As the binder used in the present invention, generally known binders are used, and specifically, fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, carboxy-modified polyvinyl alcohol, amide-modified polyvinyl alcohol having a polymerization degree of 200 to 1900. , Sulfonic acid modified polyvinyl alcohol, butyral modified polyvinyl alcohol, other modified polyvinyl alcohol, cellulose derivatives such as hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, ethyl cellulose, acetyl cellulose, styrene-maleic anhydride copolymer, styrene-butadiene Copolymer, polyvinyl chloride, polyvinyl acetate, polyacrylamide, polyacrylic ester, polyvinyl butyllar, polystyrene and the like Copolymers, polyamide resins, silicone resins, petroleum resins, terpene resins, ketone resins, and the Khumalo resin. Among these, use of a saponification degree of 90% or less and / or unmodified polyvinyl alcohol is preferable from the viewpoints of color development sensitivity, water resistance, and surface strength.
These polymer substances are used by dissolving them in water, alcohol, ketones, esters, hydrocarbons and other solvents, and are used in the form of emulsification or paste dispersion in water or other media to achieve the required quality. It is also possible to use it together.
As a compounding quantity of a binder, 1 to 30 weight% is preferable with respect to the heat-sensitive layer total solid. When the blending amount of the binder is 1% by weight or less, the water resistance and surface strength are low, and when it is 30% by weight or more, high color development sensitivity is difficult to obtain.

  Examples of the crosslinking agent used in the present invention include glyoxal, methylol melamine, melamine formaldehyde resin, melamine urea resin, polyamine epichlorohydrin resin, polyamide epichlorohydrin resin, potassium persulfate, ammonium persulfate, sodium persulfate, chloride chloride Examples include ferric iron, magnesium chloride, borax, boric acid, alum, ammonium chloride and the like.

  Examples of the lubricant used in the present invention include fatty acid metal salts such as zinc stearate and calcium stearate, waxes, and silicone resins.

  In addition, benzophenone and triazole ultraviolet absorbers, dispersants, antifoaming agents, antioxidants, fluorescent dyes, and the like can be used.

  Moreover, in this invention, a conventionally well-known sensitizer can be used in the range which does not inhibit the desired effect with respect to the said subject. Such sensitizers include ethylene bisamide, montanic acid wax, polyethylene wax, 1,2-di- (3-methylphenoxy) ethane, p-benzylbiphenyl, β-benzyloxynaphthalene, 4-biphenyl-p-tolyl ether. , M-terphenyl, 1,2-diphenoxyethane, 4,4′-ethylenedioxy-bis-benzoic acid dibenzyl ester, dibenzoyloxymethane, 1,2-di (3-methylphenoxy) ethylene, 1 , 2-diphenoxyethylene, bis [2- (4-methoxy-phenoxy) ethyl] ether, methyl p-nitrobenzoate, dibenzyl oxalate, di (p-chlorobenzyl) oxalate, di (p-methyl oxalate) Benzyl), dibenzyl terephthalate, benzyl p-benzyloxybenzoate, di-p-to Carbonate, phenyl-α-naphthyl carbonate, 1,4-diethoxynaphthalene, 1-hydroxy-2-naphthoic acid phenyl ester, 4- (m-methylphenoxymethyl) biphenyl, orthotoluenesulfonamide, paratoluenesulfonamide. Although it can illustrate, it is not restrict | limited in particular to these. These sensitizers may be used alone or in combination of two or more.

  Examples of the filler used in the present invention include inorganic or organic fillers such as silica, calcium carbonate, kaolin, calcined kaolin, diatomaceous earth, talc, titanium oxide and aluminum hydroxide, and these are used alone or in combination of two or more. From the viewpoint of coating layer strength and printing runnability, it is desirable to use calcium carbonate and silica in combination, and further, calcium carbonate having an average particle diameter of 3 μm or more and an average particle diameter of 5 to 10 μm. It is preferable to use silica having an oil absorption of 150 ml / 100 g or more and a specific surface area of 150 m 2 / g or less in combination. When calcium carbonate and silica are used, the weight ratio of calcium carbonate / silica is preferably 20/80 to 80/20, more preferably 40/60 to 60/40. Basic leuco dye 1 About 0.5-10 weight part is preferable with respect to a weight part.

In the present invention, 4,4′-butylidene (6-tert-butyl-3-methylphenol) is used as a stabilizer for imparting oil resistance and the like of recorded images within a range that does not impair the desired effect on the above-described problems. 2,2′-di-t-butyl-5,5′-dimethyl-4,4′-sulfonyldiphenol, 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenylbutane, 4-benzyloxy-4 '-(2,3-epoxy-2-methylpropoxy) diphenylsulfone, epoxy resin Etc. can also be added.

  The types and amounts of the basic leuco dye, developer, and other various components used in the heat-sensitive recording material of the present invention are determined according to required performance and recording suitability, and are not particularly limited. A developer of 0.5 to 10 parts, a sensitizer of 0.5 to 10 parts, and a filler of about 0.5 to 10 parts are used with respect to 1 part of the functional leuco dye.

By applying the coating liquid having the above composition to any support such as paper, recycled paper, synthetic paper, film, plastic film, foamed plastic film, non-woven fabric, etc., the desired thermal recording material can be obtained. Moreover, you may use the composite sheet which combined these as a support body. Basic leuco dye, color developer, and materials to be added as necessary are finely pulverized to a particle size of several microns or less by a pulverizer such as a ball mill, attritor or sand glider, or an appropriate emulsifying device. Depending on the conditions, various additive materials are added to obtain a coating solution. The means for applying is not particularly limited, and can be applied in accordance with well-known conventional techniques. For example, an off-knife equipped with various coaters such as an air knife coater, a rod blade coater, a bill blade coater, a roll coater, a curtain coater, and a spray coater. A machine coater or an on-machine coater is appropriately selected and used. The coating amount of the heat-sensitive recording layer is not particularly limited and is usually in the range of ² to 12 g / m ^{2 by} dry weight.

  In the heat-sensitive recording material of the present invention, an undercoat layer such as a polymer material containing a filler can be provided under the heat-sensitive recording layer for the purpose of increasing the color development sensitivity. It is also possible to correct the curl by providing a backcoat layer on the opposite side of the support from the thermosensitive recording layer. Also, various known techniques in the heat-sensitive recording material field can be added as appropriate, such as applying a smoothing process such as supercalendering after coating each layer.

EXAMPLES The present invention will be specifically described below with reference to examples, but the scope of the present invention is not limited to these examples. In each example, “parts” means “parts by weight” unless otherwise specified.

[Example 1]
A composition comprising the following composition was stirred and dispersed to prepare an undercoat layer coating solution.
<Undercoat layer coating solution>
Baked kaolin (manufactured by BASF, trade name: Ansilex 93) 100 parts Styrene-butadiene latex (solid content 48%) 40 parts Polyvinyl alcohol aqueous solution (10% solution) 30 parts Water 160 parts Next, undercoat layer coating liquid is supported After coating so that the coating amount was 8.0 g / m ^{2 on} one side (basis weight 50 g / m ² fine paper), drying was performed to obtain an undercoat layer coated paper.

Each of the dye, developer, and sensitizer materials was prepared in advance as a dispersion having the following composition, and wet grinding was performed with a sand grinder until the average particle size became 0.5 μm.
<Liquid A: Developer dispersion>
4-hydroxy-4'-isopropoxydiphenylsulfone
(Product name: NY-DS, manufactured by API Corporation) 6.0 parts Polyvinyl alcohol aqueous solution (10% solution) 18.8 parts Water 11.2 parts <Liquid B: Dye dispersion>
3-di-n-butylamino-6-methyl-7-anilinofluorane (manufactured by Yamamoto Kasei Co., Ltd., trade name: ODB-2) 3.0 parts Polyvinyl alcohol aqueous solution (10% solution) 6.9 parts water 3 .9 parts <C solution: sensitizer dispersion>
1,2-di- (3-methylphenoxy) ethane (trade name: KS232, manufactured by Sanko Co., Ltd.) 6.0 parts Polyvinyl alcohol aqueous solution (10% solution) 18.8 parts Water 11.2 parts

The above dispersions were mixed at the ratio shown below to obtain a thermal recording layer coating solution. The coating solution is applied and dried on the undercoat layer coated paper so that the coating amount after drying is 6.0 g / m ^2, and processed with a super calender so that the Beck smoothness is 200 to 600 seconds. A record was obtained.
Liquid A 36.0 parts Liquid B 13.8 parts Liquid C 36.0 parts Silica (manufactured by Mizusawa Chemical Co., Ltd., trade name: P537) 25% dispersion 26.0 parts Calcium carbonate (manufactured by Shiraishi Calcium Co., Ltd., trade name: Tunex) E, average particle size: 4.4 μm) 50% dispersion 13.0 parts Zinc stearate (manufactured by Chukyo Yushi Co., Ltd., trade name: Hydrin Z-7-30) 30% dispersion 6.7 parts Polyvinyl alcohol aqueous solution (10 %solution)
(Kuraray Co., Ltd., trade name: PVA217, polymerization degree: 1750, saponification degree: 88 mol%)
20.0 parts acrylic resin (manufactured by BASF, trade name: Jonkrill 74J (styrene acrylic type, core-shell type), solid content concentration 45%, glass transition point 22 ° C., minimum film forming temperature 5 ° C.) 10.0 parts poly Acrylamide resin (manufactured by Seiko PMC, trade name: ST5050, nonionic, solid content 25%) 1.8 parts

[Comparative Example 1]
Except for replacing the acrylic resin of Example 1 with completely saponified polyvinyl alcohol (Kuraray Co., Ltd., trade name: PVA117, degree of polymerization: 1750, degree of saponification: 98 mol%) and no polyacrylamide resin. A heat-sensitive recording material was obtained in the same manner as in Example 1.
[Comparative Example 2]
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the acrylic resin of Example 1 was replaced with completely saponified polyvinyl alcohol (trade name: PVA117).
[Comparative Example 3]
A heat-sensitive recording material was obtained in the same manner as in Example 1 except that the polyacrylamide resin of Example 1 was not used.
[Comparative Example 4]
The acrylic resin of Example 1 was mixed with 5 parts of other acrylic resin (manufactured by Clariant Polymer Co., Ltd., trade name: Mobile 9000, solid content concentration 40%) and spherical colloidal silica (manufactured by Clariant Japan Co., Ltd., trade name: clebosol 40R12, solid content). A thermosensitive recording material was obtained in the same manner as in Example 1 except that 5 parts (concentration: 40%) was substituted and no polyacrylamide resin was added.

  The thermosensitive recording materials obtained in the above-described examples and comparative examples were evaluated as follows. The results are shown in Table 1.

[Color development sensitivity]
Using TH-PMD manufactured by Okura Electric Co., Ltd., printing was performed on the created thermal recording medium at an applied energy of 0.34 mJ / dot and 0.25 mJ / dot. The image density after printing and after the quality test was measured with a Macbeth densitometer (RD-914, using an amber filter).

[water resistant]
-Image remaining rate Using a TH-PMD manufactured by Okura Electric Co., Ltd., a thermal recording medium printed with an applied energy of 0.34 mJ / dot was immersed in water and allowed to stand at 23 ° C. for 24 hours. Measurement was performed with a Macbeth densitometer, and the image residual ratio was calculated by the following formula.
Image residual ratio (%) = density after test / density before test × 100

- Soak the water pressure-sensitive thermosensitive recording material in water for 3 minutes, after the recording surface under a load of 300 g / cm ² in the two-folded such that the inner, stripped While recording surface is wet, at 105 ° C. The color was developed for 2 minutes, and the degree of peeling of the recording surface was visually judged and evaluated according to the following criteria.
◎: No peeling of recording surface ○: Little peeling of recording surface △: Some peeling of recording surface is observed ×: Many peeling of recording surface

-Water blocking resistance 50 μl of water drops are hung on the surface of the heat-sensitive recording medium, folded in half so that the recording surface is inside, a load of 10 g / cm ² is applied on the recording medium on which the water drops have been dropped, and 23 ° C. and 50% Rh. The recording surface was peeled off for 24 hours, and then the recording surface was peeled off, and the color was developed at 105 ° C. for 2 minutes. The degree of peeling of the recording surface was visually determined and evaluated according to the following criteria.
◎: No peeling of recording surface ○: Little peeling of recording surface △: Some peeling of recording surface is observed ×: Many peeling of recording surface

[Preservation of white paper during storage]
The heat-sensitive recording material was allowed to stand for 72 hours in a blower dryer maintained at 60 ° C., and the difference in whiteness before and after the test was measured using a Hunter whiteness meter (filter: Am).
○: Decrease in whiteness is less than 2 points Δ: Whiteness is reduced by 2 points or more and less than 10% ×: Whiteness is reduced by 10 points or more [surface strength]

Using a Prüfbau printer, 0.25 ml (printing unit pressure: 50 kgf) of sheet-fed ink (manufactured by Toyo Ink Mfg. Co., Ltd., trade name: TK High Unity MZ Ind.) And 0.015 ml of dampening water (dampening water unit) Pressure: 20 kgf) Using the surface of the thermosensitive recording layer (printing speed: 100 m / min) is checked to check the surface condition, visually determining whether the coating layer is peeled off, and evaluating according to the following criteria: did.
○: Almost no peeling of coating layer Δ: Some peeling of coating layer ×: Many peeling of coating layer

[Printability (head residue)]
30 cm long grid printing was performed with a label printer (printer name: Respre R-8) manufactured by SATO, and the head residue and print samples adhering to the thermal head after printing were visually observed.
○: Head debris hardly adheres to the thermal head ×: Head debris adheres to the thermal head and the printed part is faded

Claims (1)

In a heat-sensitive recording material provided with a heat-sensitive recording layer containing a colorless or light-colored electron-donating leuco dye and an electron-accepting developer on a support, the heat-sensitive recording layer contains an acrylic resin and a polyacrylamide resin. A heat-sensitive recording material characterized by