JP2005111867A - Thermal recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal recording medium which shows high sensitivity; outstanding texture heat resistance/recording part water resistance; and is free from a phenomenon in which the texture and the printing part generate a bloom. <P>SOLUTION: In this thermal recording medium, a developer and an ethylene glycol ditolyl ether as a sensitizer are used and ground in a constant mixing series in the presence of a styrene maleic anhydride copolymer ammonium salt with a degree of esterification of not less than 50% and an average molecular weight of 10,000 to 60,000 as a dispersant. Preferably, the developer is at least one kind selected from among a 4-hydroxy-4'-isopropyloxydiphenyl sulfone, a 2,4'-dihydroxydiphenyl sulfone, a 4,4'-dihydroxydiphenyl sulfone and a bis-(3-allyl-4-hydroxyphenyl) sulfone. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a heat-sensitive recording material having high sensitivity and excellent record storage stability.

  The heat-sensitive recording medium is generally a support in which a heat-sensitive recording layer mainly comprising an electron-donating colorless or light-colored basic dye and an electron-accepting developer is provided on a support. By heating with a laser beam or the like, the colorless dye precursor and the developer react instantaneously to obtain a recorded image, and these heat-sensitive recording materials have been put into practical use (for example, Patent Documents 1 and 2). reference.).

  Such a thermal recording medium has advantages such as that recording can be obtained with a relatively simple device, maintenance is easy, noise is not generated, and a recording recorder, a facsimile, a printer, and a computer terminal. It is used in a wide range of fields such as machines, labels, and ticket vending machines.

  The color developing layer of the thermal recording material that develops color by heating and records an image contains a combination of a basic dye and a developer that develops color by reacting with the basic dye upon heating (hereinafter referred to as a developer). Yes. In this case, as the basic dye, for example, a colorless or light leuco dye having a lactone, lactam or spiropyran ring is used, and as a developer, 4,4′-isopropylidenediphenol (generic name bisphenol A) or the like is used. Various acidic substances are used.

  Such a combination of a basic dye and a developer has been applied to many heat-sensitive recording materials because of its clear color tone, and has a good appearance, good touch, high color density, Although it has excellent characteristics such as the ability to obtain a color hue of the color, there is a problem in the storage stability of the record, such as the thermal recording part disappears easily upon contact with chemicals contained in water, foods, and cosmetics. Because of this drawback, the current situation is that there are certain restrictions on its use, and there is a strong demand for improvement.

  Furthermore, in recent years, from the trend of miniaturization along with labor saving of equipment, higher sensitivity has been demanded in order to ensure the clearness of the recording section. As a method for increasing the sensitivity, a thermofusible substance having a melting point lower than that of a basic dye or developer has been used as a sensitizer (hereinafter referred to as a sensitizer). A method of lowering the color development start temperature by melting a dye and a developer is well known (see, for example, Patent Documents 3, 4, and 5).

  Such a heat-fusible substance is singulated or dispersed in water together with a basic dye or a developer as necessary, and is atomized by a wet pulverization method using a grinder such as a sand grinder, ball mill, or attritor. To achieve high sensitivity. In addition, by combining these sensitizers and fatty acid amides to promote acid generation more efficiently, it can be expected to improve not only sensitivity but also storage stability. Sensitizers and fatty acid amides (methylol stearic acid amide) , Methylol behenic acid amide, stearic acid amide) is known to be desirable.

However, while these sensitizers and fatty acid amides can be expected to have very effective effects, they cannot be easily atomized by ordinary wet pulverization, and dispersion after pulverization and the liquid after pulverization are unstable. Thus, the expected sensitivity improvement effect cannot be obtained. To solve this problem, liquid stability after pulverization is achieved by combining a specific developer, sensitizer, and fatty acid amide and finely pulverizing with a specific ammonium styrene maleic anhydride copolymer salt as a dispersant. And a proposal for improving the color developability of a thermosensitive recording material using the same (see, for example, Patent Document 6). However, it has been found that the obtained heat-sensitive recording material has a problem that powdering of the background with a sensitizer or powdering on a printed matter occurs.
Japanese Patent Publication No.43-4160 Japanese Examined Patent Publication No. 45-14039 JP 49-34842 A JP-A-53-39139 JP-A 61-16888 JP-A-6-64320

  An object of the present invention is to provide a heat-sensitive recording material that is highly sensitive and excellent in record storability, and that provides a heat-sensitive recording material that is free from the occurrence of powdering of the background and printed matter.

  (1) The present invention provides a thermosensitive recording medium comprising a thermosensitive recording layer containing a colorless or light-colored basic dye, a color developer capable of reacting with the dye, and a sensitizer on the support. The sensitizer is ethylene glycol ditolyl ether, and the developer and the sensitizer in the presence of a styrene maleic anhydride copolymer ammonium salt having an esterification degree of 50% or more and an average molecular weight of 10,000 to 60,000 as a dispersant. The heat-sensitive recording material is characterized by being used after being finely pulverized in the same mixed system of the agent.

  (2) As the developer, 4-hydroxy-4'-isopropyloxydiphenylsulfone, 2,4'-dihydroxydiphenylsulfone, 4,4'-dihydroxydiphenylsulfone, bis (3-allyl-4-hydroxyphenyl) sulfone The heat-sensitive recording material according to (1), wherein at least one selected from the group consisting of:

  (3) The heat-sensitive recording material according to (1) or (2), wherein at least one methylol stearate amide, methylol behenic acid amide or stearic acid amide is added to the heat-sensitive recording layer.

  (4) At least one 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 1,1-di (3-tertiarybutyl-4-) is added to the thermosensitive recording layer. Adding 5 to 50% by mass of hydroxy-6-methylphenyl) butane or 1,1,3-tris (2-methyl-4-hydroxy-5-tertiarybutylphenyl) butane to the developer; The heat-sensitive recording material according to (1), (2) or (3), which is characterized.

  In the presence of an ammonium salt of a styrene maleic anhydride copolymer having an esterification degree of 50% or more and an average molecular weight of 10,000 to 60,000 as a sensitizer for the thermal recording material, By using fine pulverization in the same mixed system of sensitizers, the thermal recording medium with good sensitivity and greatly improved recording storage stability, and no problem of powder blowing on the printing surface, is stable. Is obtained. Particularly selected from 4-hydroxy-4'-isopropyloxydiphenylsulfone, 2,4'-dihydroxydiphenylsulfone, 4,4'-dihydroxydiphenylsulfone, and bis (3-allyl-4-hydroxyphenyl) sulfone as the developer. It is preferable to use at least one kind selected from the viewpoint of thermal characteristics and heat resistance.

  Preferably, at least one methylol stearate amide, methylol behenic acid amide or stearic acid amide is added to the heat sensitive recording layer, and more preferably at least one 1,1,3-tris is added to the heat sensitive recording layer. (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 1,1-di (3-tertiarybutyl-4-hydroxy-6-methylphenyl) butane or 1,1,3-tris (2-methyl By adding 5 to 50% by weight of 4-hydroxy-5-tertiarybutylphenyl) butane with respect to the developer, a heat-sensitive recording material having good sensitivity and excellent image storage stability can be obtained.

  The styrene maleic anhydride copolymer in the present invention is an ammonium salt having an esterification degree of 50% or more. In general, it is often a sodium salt including other dispersants such as styrene maleic anhydride, but in the case of heat-sensitive recording paper, a sodium salt cannot be used due to problems such as corrosion of the heating element head. Further, in the case of an ammonium salt, there is a problem that aggregation occurs during pulverization, and pulverization is possible by using an ester having a degree of esterification of 50% or more.

  In the present invention, the average molecular weight of the styrene maleic anhydride copolymer ammonium salt is 10,000 to 60,000, and if it is less than 10,000, gelation occurs during pulverization and pulverization is impossible. On the other hand, if it is larger than 60000, the dispersibility is very poor because of the increase in viscosity, and similarly, pulverization is impossible.

  In the present invention, the addition amount of ammonium styrene maleic anhydride copolymer is preferably in the range of 3 to 10% by mass with respect to the total amount of the sensitizer, developer and methylol amide. Particularly stable in this range, gelation does not occur at the time of pulverization, and there is no problem of lowering the pulverization concentration, and stable characteristics can be obtained.

  In the present invention, the liquid temperature at the time of the mixed system pulverization of the developer and the sensitizer is preferably set to 40 ° C. or less, and more preferably in the range of 15 to 35 ° C. By this range, the particle size is particularly good, the particle size is fine, the particle size stability after pulverization is good, and gelation does not occur.

  The addition amount of the fatty acid amide added in the present invention is 5 to 100% by mass, preferably 10 to 50% by mass with respect to the developer. This range is particularly good, and gelation does not occur during pulverization.

  In the present invention, by using ethylene glycol ditolyl ether as a sensitizer, a heat-sensitive recording material having high sensitivity and less likely to cause powdering of the background is obtained. As long as the effects of the present invention are not impaired, about 30% by mass of the sensitizer and other sensitizers can be used. For example, naphthol derivatives such as 2-benzyloxynaphthalene, biphenyl derivatives such as p-benzylbiphenyl and 4-allyloxybiphenyl, 1,2-bis (3-methylphenoxy) ethane, 2,2′-bis (4-methoxy) Polyether compounds such as phenoxy) diethyl ether and bis (4-methoxyphenoxy) ether, ester derivatives such as diphenyl carbonate, dibenzyl oxalate and oxalic acid (p-methylbenzyl) ester, diphenyl such as 4,4′-diallyloxydiphenylsulfone Examples thereof include sulfone derivatives. The amount of the sensitizer in the heat-sensitive recording layer is 30 to 300% by mass, preferably 50 to 200% by mass with respect to the developer. In this range, the sensitization effect is good, the hot melt adheres to the heating element head (debris adherence), and printing troubles do not occur.

  In the heat-sensitive recording material of the present invention, the basic dye is typically represented by a pressure-sensitive recording material or mono used in a heat-sensitive recording material. For example, 3-dibutylamino-6-methyl-7-anilinofur Oran, 3- (N-ethyl-N-isoamylamino) -6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3- (N-ethyl-N- Ethoxypropylamino) -6-methyl-7-anilinofluorane, 3- (N-methyl-N-propylamino) -6-methyl-7-anilinofluorane, 3- (N-methyl-cyclohexylamino) ) -6-Methyl-7-anilinofluorane, 3- (N-ethyl-4'-toluidino) -6-methyl-7-anilinofluorane, 3-diethylamino-7- (m-trifluoro) Chill) - leuco dyes of anilinofluoran like fluoran and the like.

  Specific examples of the developer in the present invention include acidic clay, activated clay, zeolite, bentonite, kaolin and other clay materials, p-phenylphenol, p-hydroxyacetophenone, 4-hydroxy-4'-methyldiphenylsulfone. 4-hydroxy-4'-isopropoxydiphenyl sulfone, 4-hydroxy-4'-benzenesulfonyloxydiphenyl sulfone, 1,1-bis (4-hydroxyphenyl) propane, 1,1-bis (4-hydroxyphenyl) Pentane, 1,1-bis (4-hydroxyphenyl) hexane, 1,1-bis (4-hydroxyphenyl) cyclohexane, 1,1-bis (4-hydroxyphenyl) cyclododecane, 2,2-bis (4- Hydroxyphenyl) propane, 2,2-bis (4-hydroxyphene) L) Hexane, 2,2-bis (4-hydroxyphenyl) octane, 1,1-bis (4-hydroxyphenyl) -2-ethylhexane, 2,2-bis (3-chloro-4-hydroxyphenyl) propane 1,1-bis (4-hydroxyphenyl) -1-phenylethane, 1,3-di- [2- (4-hydroxyphenyl) -2-propyl] benzene, 1,3-di- [2- ( 3,4-dihydroxyphenyl) -2-propyl] benzene, 1,4-di- [2- (4-hydroxyphenyl) -2-propyl] benzene, 4,4'-dihydroxydiphenyl ether, 4,4'-dihydroxy Diphenyl sulfone, 2,4'-dihydroxydiphenyl sulfone, 3,3'-dichloro-4,4'-dihydroxydiphenyl sulfone, 3,3'-diallyl 4,4'-dihydroxydiphenylsulfone, 3,3'-dichloro-4,4'-dihydroxydiphenyl sulfide, methyl 2,2-bis (4-hydroxyphenyl) acetate, 2,2-bis (4-hydroxyphenyl) Butyl acetate, 4,4'-thiobis (2-t-butyl-5-methylphenol), benzyl p-hydroxybenzoate, chlorobenzyl p-hydroxybenzoate, dimethyl 4-hydroxyphthalate, benzyl gallate, gallic acid Stearyl, salicylanilide, 5-chlorosalicylanilide, novolak phenol resin, modified terpene phenol resin, 3,5-di-t-butylsalicylic acid, 3,5-di-t-nonylsalicylic acid, 3,5-didodecylsalicylic acid, 3-methyl-5-t-dodecylsalicylic acid, 5-cyclohexylsali Examples thereof include tylic acid, 3,5-bis (α, α-dimethylbenzyl) salicylic acid, 3-methyl-5- (α-methylbenzyl) salicylic acid and the like, and metal salts such as zinc, nickel, aluminum and calcium. It is done. In particular, at least one selected from 4-hydroxy-4′-isopropyloxydiphenylsulfone, 2,4′-dihydroxydiphenylsulfone, 4,4′-dihydroxydiphenylsulfone, and bis (3-allyl-4-hydroxyphenyl) sulfone. The kind is preferably used, and the amount of the basic dye in the heat-sensitive recording layer is 10 to 300% by mass, preferably 40 to 200% by mass, based on the developer. Within this range, color development and image storage stability are particularly good, and no further effect is observed even in a range beyond this range.

  By adding at least one of methylol stearic acid amide, methylol behenic acid amide, or stearic acid amide to the heat-sensitive recording material of the present invention, the color developability is further improved. When the addition amount is in the range of 10 to 50% by mass with respect to the developer, better color developability can be obtained.

  In the heat-sensitive recording material of the present invention, 1,1,3-tris (2-methyl-4hydroxy-5-cyclohexylphenyl) butane, 1,1-di (3-tertiarybutyl-4-hydroxy-6) is used for the heat-sensitive recording layer. Addition of at least one of -methylphenyl) butane or 1,1,3-tris (2-methyl-4-hydroxy-5-tertiarybutylphenyl) butane improves the image storage stability. The addition amount is 5 to 50% by mass, preferably 10 to 25% by mass, based on the developer. Within this range, the water-resistant record storage stability is particularly good while having heat resistance.

  In the heat-sensitive recording material of the present invention, the binder for bonding and supporting the heat-sensitive recording layer on the support includes polyvinyl alcohol, starch and derivatives thereof, cellulose derivatives such as methyl cellulose, hydroxymethyl cellulose, carboxymethyl cellulose, and ethyl cellulose, polyvinyl pyrrolidone, and polyacrylamide. , Polyacrylic acid soda, acrylamide / acrylic acid ester copolymer, acrylamide / acrylic acid ester / methacrylic acid terpolymer, styrene / maleic anhydride copolymer alkali salt, isobutylene / maleic anhydride copolymer alkali salt In addition to water-soluble polymers such as sodium alginate, gelatin, casein, and gum arabic, polyvinyl acetate, polyurethane, polyacrylic acid, polyacrylic acid ester, polymethacrylic acid ester, Vinyl / vinyl acetate copolymer, ethylene / vinyl acetate copolymer, an aqueous emulsion, etc., such as polybutyl methacrylate.

  In the heat-sensitive recording material of the present invention, if necessary, auxiliary additives such as fillers, surfactants, lubricants and the like commonly used in this type of heat-sensitive recording material are added to the heat-sensitive recording layer in the heat-sensitive recording layer as necessary. Can be used together. In this case, as fillers, for example, calcium carbonate, silica, alumina, magnesium carbonate, talc, barium sulfate, zinc oxide, titanium oxide, surface-treated calcium carbonate or silica and other inorganic fine powders, urea / formalin Examples thereof include organic fine powders such as resins, styrene / methacrylic acid copolymers, and polystyrene. Examples of the lubricant include higher fatty acids or esters thereof, amides or metal salts, various waxes, condensates of aromatic carboxylic acids and amines, benzoic acid phenyl esters, higher linear glycols and other heat-fusible organics. Compounds. Add fine powders such as aluminum stearate to improve the clarity of color images, and add lubricants such as linseed oil, tung oil, wax, paraffin, polyethylene wax, chlorinated paraffin, higher fatty acid metal salts The running performance of the head can be further improved.

  In the heat-sensitive recording material of the present invention, one or more overcoat layers can be provided for the purpose of protecting the recording layer. To form an overcoat layer, for example, polyvinyl alcohol, acetoacetylated polyvinyl alcohol, carboxy-modified polyvinyl alcohol, sulfonic acid-modified polyvinyl alcohol, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, casein, gum arabic, oxidized starch, etherified starch And water-soluble resins such as esterified starch, styrene-butadiene copolymer emulsion, vinyl acetate-ethylene copolymer emulsion, methacrylate-butadiene copolymer, and styrene-acrylic copolymer emulsion.

  Furthermore, in the overcoat layer, surfactants such as sodium dioctylsulfa succinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate / sodium salt, alginates, fatty acid metal salts, etc., as necessary ), Water resistant agents such as glyoxal, methylol melamine, potassium persulfate, sodium persulfate, ammonium persulfate, ultraviolet absorbers such as benzophanone and triazole, various auxiliary agents such as antifoaming agents, fluorescent dyes, coloring dyes, etc. Can also be added.

  In addition, pigments can be added to such an overcoat layer in order to impart writing instrument suitability and imprint fixability. Examples of such pigments include light calcium carbonate, heavy calcium carbonate, talc, kaolin, and silicic acid. Inorganic pigments such as magnesium carbonate, clay, zinc oxide, aluminum oxide, and aluminum hydroxide, and organic pigments such as styrene microballs, nylon powder, polyethylene powder, urea / formaldehyde resin filler, and raw starch.

  In the heat-sensitive recording material of the present invention, paper is generally used as the support, but a resin film, synthetic paper, non-woven fabric, etc. can also be used. Various known techniques in the heat-sensitive recording body manufacturing field, such as providing a protective layer on the back surface of the support, and further applying an adhesive process or a magnetic recording layer to the back surface of the support, can be added.

  It is also possible to provide an undercoat layer on the support and between the heat-sensitive recording layer. As an apparatus used for coating the undercoat layer and the heat-sensitive recording layer, a coater head such as a blade coater, an air knife coater, a roll coater, a rod coater, or a curtain coater can be used.

Furthermore, in order to improve the surface smoothness of the coated material, a machine calendar, a super calendar, a gloss calendar, a brushing, or the like can be used. Moreover, the coating amount in the case of providing an undercoat layer is not specifically limited, but 3-20 g / m < ² >, preferably 5-10 g / m < ² > is appropriate. The coating amount of the thermosensitive recording layer on the support is not limited, but is usually in the range of ^{3 to} 15 g / m ^2, preferably 4 to 10 g / m ² .

  The present invention will be described in more detail below by way of examples, but the present invention is not particularly limited thereby. In the following description, all parts and% are based on mass.

[Adjustment of undercoat layer]
Water 107 parts by mass 10% sodium hexametaphosphate 8 parts by mass calcined kaolin (trade name: Ansilex manufactured by Engelhard) 100 parts by mass 25% starch oxide solution 24 parts by mass 48% SBR latex 25 parts by mass An undercoat layer coating solution having a ratio of 45% was prepared.

[Formation of undercoat layer]
The obtained undercoat layer coating solution was applied and dried on a 50 g / m ² base paper with a blade coater so that the dry coating amount was 6 g / m ² to form an undercoat layer.

[Adjustment of thermal recording layer]
By dispersing for 10 hours under the following conditions, liquid A and liquid B having the following component compositions were obtained.
[Adjustment of liquid A]
10% modified polyvinyl alcohol solution (Nippon Gosei Co., Ltd., Goceran L3266)
600 parts by mass 3-dibutylamino-6-methyl-7-anilinofluorane 600 parts by mass Water 1000 parts by mass The liquid A was pulverized to 1.5 μm in volume average using Dynomill (manufactured by Shinmaru Enterprises).
[Adjustment of liquid B]
15% styrene maleic anhydride copolymer ammonium salt (average molecular weight 50,000 to 60,000)
200 parts by mass 4-hydroxy-4'-isopropyloxydiphenylsulfone 300 parts by mass ethylene glycol ditolyl ether 300 parts by mass water 1300 parts by mass Using Dinomil (manufactured by Shinmaru Enterprises) while maintaining the B liquid at 20 to 25 ° C The average was pulverized to 1.5 μm.

[Formation of thermal recording layer]
Next, using the prepared liquid A and liquid B, a thermosensitive recording layer coating liquid comprising the following components was prepared, and 300 m / min with an air knife coater so that the dry mass was 5 g / m ² on the undercoat layer. And dried. Thereafter, the coated paper was calendered and finished so that the Beck smoothness was 400 to 600 seconds to obtain a heat-sensitive recording material of Example 1.
[Thermosensitive recording layer coating solution]
Polyvinyl alcohol solution (10% aqueous solution) 500 parts by mass Calcium carbonate 50 parts by mass A liquid 110 parts by mass B liquid 350 parts by mass 50% zinc stearate dispersion 20 parts by mass

On the heat-sensitive recording layer prepared in Example 1, the following overcoat layer coating solution was dried and applied at 300 m / min with a rod coater so as to have a dry coating amount of 2 g / m ^2, and calendared. A thermal recording material of Finishing Example 2 was obtained so that the Beck smoothness was 800 to 1500 seconds.
[Overcoat layer coating solution]
Water 115 parts by mass Polyvinyl alcohol solution (5% aqueous solution) 100 parts by mass 20% acrylic emulsion resin (OM1050 manufactured by Mitsui Chemicals, Inc.) 50 parts by mass amorphous synthetic silica (Mizukasil P527 manufactured by Mizusawa Chemical Co., Ltd.) 10 5 parts by weight of 50% by weight zinc stearate dispersion

The thermal recording material of Example 3 was obtained in the same manner as in Example 1 except that the B liquid of Example 1 was changed to the following C liquid and the thermal recording layer coating liquid was adjusted with the following contents.
[Adjustment of liquid C]
15% styrene maleic anhydride copolymer ammonium salt (average molecular weight 50,000 to 60,000)
210 parts by mass 4-hydroxy-4'-isopropyloxydiphenylsulfone 300 parts by mass ethylene glycol ditolyl ether 300 parts by mass methylol stearate amide 30 parts by mass water 1365 parts by mass Dinomil (Shinmaru Enterprise) Volume average, 1.5 μm.
[Thermosensitive recording layer coating solution]
Polyvinyl alcohol solution (10% aqueous solution) 500 parts by mass Calcium carbonate 50 parts by mass A liquid 110 parts by mass C liquid 367 parts by mass 50% zinc stearate dispersion 20 parts by mass

  A heat-sensitive recording material of Example 4 was obtained in the same manner as in Example 1 except that 4-hydroxy-4'-isopropyloxydiphenyl sulfone in Liquid B of Example 1 was changed to 2,4'-dihydroxydiphenyl sulfone. .

  A heat-sensitive recording material of Example 5 was obtained in the same manner as in Example 1 except that 4-hydroxy-4'-isopropyloxydiphenyl sulfone in Liquid B of Example 1 was changed to 4,4'-dihydroxydiphenyl sulfone. .

  The heat sensitivity of Example 6 was the same as Example 1 except that 4-hydroxy-4'-isopropyloxydiphenylsulfone in the B liquid of Example 1 was changed to bis- (3-allyl-4-hydroxyphenyl) sulfone. A record was obtained.

  The heat sensitivity of Example 7 was the same as Example 1 except that 50 parts by mass of 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane was added to the B liquid of Example 1. A record was obtained.

  The heat sensitivity of Example 8 was the same as Example 1 except that 50 parts by mass of 1,1-di (3-tertiarybutyl-4-hydroxy-6-methylphenyl) butane was added to the B liquid of Example 1. A record was obtained.

  Example 9 was carried out in the same manner as in Example 1 except that 50 parts by mass of 1,1,3-tris (2-methyl-4-hydroxy-5-tertiarybutylphenyl) butane was added to the B liquid of Example 1. A heat-sensitive recording material was obtained.

  The heat sensitivity of Example 10 was the same as Example 6 except that 30 parts by mass of 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane was added to the B liquid of Example 6. A record was obtained.

  The heat sensitivity of Example 11 was the same as Example 6 except that 75 parts by mass of 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane was added to the B liquid of Example 6. A record was obtained.

  A thermosensitive recording material of Example 12 was obtained in the same manner as in Example 3 except that the methylol stearate amide in liquid C of Example 3 was changed to methylol behenate amide.

  A thermosensitive recording material of Example 13 was obtained in the same manner as in Example 3 except that the methylol stearate amide in liquid C of Example 3 was changed to stearic acid amide.

  The heat sensitivity of Example 14 was the same as Example 6 except that 50 parts by mass of 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane was added to the B liquid of Example 6. A record was obtained.

  The heat sensitivity of Example 15 was the same as Example 6 except that 15 parts by mass of 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane was added to the B liquid of Example 6. A record was obtained.

  The heat-sensitive recording material of Example 16 was prepared in the same manner as in Example 1 except that 4-hydroxy-4'-isopropyloxydiphenyl sulfone in Liquid B of Example 1 was changed to 4,4'-isopropylidenediphenol. Obtained.

(Comparative Example 1)
A heat-sensitive recording material of Comparative Example 1 was obtained in the same manner as in Example 1 except that the average molecular weight of the 15% styrene maleic anhydride copolymer ammonium salt of Liquid B of Example 1 was changed to 5000 to 8000.

(Comparative Example 2)
Although the molecular weight of 15% styrene maleic anhydride copolymer ammonium salt of the liquid B of Example 1 was changed to 80,000 to 100,000, an attempt was made to grind in the same manner as in Example 1, but the liquid gelled and the thermal recording of Comparative Example 2 was performed. I couldn't get a body.

(Comparative Example 3)
Example 1 except that the 15% styrene maleic anhydride copolymer ammonium salt having a molecular weight of 50,000 to 60000 in the liquid B of Example 1 was changed to a 10% modified polyvinyl alcohol solution (manufactured by Nihon Gosei Co., Ltd., Gocelan L3266). In the same manner, a heat-sensitive recording material of Comparative Example 3 was obtained.

(Comparative Example 4)
The average molecular weight of 15% styrene maleic anhydride copolymer ammonium salt of liquid C of Example 3 was changed to 5,000 to 8000, and an attempt was made to grind in the same manner as in Example 3. A record could not be obtained.

(Comparative Example 5)
The average molecular weight of 15% styrene maleic anhydride copolymer ammonium salt in the B liquid of Example 3 was changed to 80,000 to 100,000, and pulverization was attempted in the same manner as in Example 3. A record could not be obtained.

(Comparative Example 6)
15% styrene maleic anhydride copolymer ammonium salt having a molecular weight of 50,000 to 60,000 in the liquid C of Example 3 was changed to a 10% modified polyvinyl alcohol solution (manufactured by Nippon Gosei Co., Ltd., Gocelan L3267). However, the liquid gelled and the heat-sensitive recording material of Comparative Example 6 could not be obtained.

(Comparative Example 7)
A heat-sensitive recording material of Comparative Example 7 was obtained in the same manner as in Example 1 except that the ethylene glycol ditolyl ether in the B liquid of Example 1 was changed to 2-benzyloxynaphthalene.

(Comparative Example 8)
[Adjustment of thermal recording layer]
[Adjustment of liquid D]
15% styrene maleic anhydride copolymer ammonium salt (average molecular weight 50,000 to 60,000)
100 parts by mass 4-hydroxy-4'-isopropyloxydiphenylsulfone 300 parts by mass water 650 parts by mass While maintaining the D liquid at 20 to 25 ° C., the volume average is pulverized to 1.5 μm using Dinomill (manufactured by Shinmaru Enterprises). did.
[Adjustment of liquid E]
15% styrene maleic anhydride copolymer ammonium salt (average molecular weight 50,000 to 60,000)
100 parts by mass Ethylene glycol ditolyl ether 300 parts by mass Water 650 parts by mass While maintaining the liquid E at 20 to 25 ° C., the volume average was pulverized to 1.5 μm using a Dinomill (manufactured by Shinmaru Enterprises).
The thermosensitive recording material of Comparative Example 8 was obtained in the same manner as in Example 1 except that 350 parts by mass of B liquid were changed to 175 parts by mass of D liquid and 175 parts by mass of E liquid by adjusting the thermosensitive recording layer in Example 1. It was.

The following items were evaluated for the heat-sensitive recording materials obtained in Examples 1 to 16 and Comparative Examples 1 to 8.
[Crushing status]
The situation at the time of grinding was judged. Practically more than Δ is necessary.
○: No problem in grinding and grinding liquid.
Δ: No problem during pulverization, but liquid viscosity after pulverization slightly increases.
X: Causes gelation and cannot be pulverized.

[Whiteness]
The whiteness was measured according to JIS-P8123, and the reflectance was measured with an amber filter using a hunter reflectometer. Practically 85% or more is necessary.
[Sensitivity and saturation concentration evaluation]
Using a Kyocera head having a head resistance of 1335Ω with a test machine manufactured by Okura Electric Co., Ltd., the sensitivity was printed with an energy of 0.37 mj / dot, and the print density of the image area was measured. Saturation density was printed using a Kyocera head having a head resistance of 1335Ω with a test machine manufactured by Okura Electric Co., Ltd., with an energy of 0.54 mj / dot, and the printing density of the image area at that time was measured. Practically 1.20D or more is necessary. In addition, after printing under these conditions, heat resistance and water resistance were evaluated for storage stability.

[Skin dust blowing evaluation]
Wrapping the color-developing surface of the thermal paper in a blank paper state so as to contact the paper tube, put it in a cellophane pack, seal it, and leave it in a dryer at 60 ° C. for 8 hours. After 8 hours, the thermal paper wound around the paper tube is taken out and left at room temperature for 24 hours. After 24 hours, the paper tube is taken out and the presence or absence of powder blowing on the color developing surface side is visually determined. Judgment was made with two samples, and bad results were adopted.
○ ... No powder spraying on the background.
Δ: Part of powdering of the background is recognized.
X ... Powder spraying of the background portion is recognized entirely.

[Powder evaluation of printed part]
Printing was performed with an energy of 0.80 mj / dot using a Kyocera head having a head resistance of 1335Ω with a test machine manufactured by Okura Electric Co., Ltd. Wrap the print surface in contact with the paper tube, put it in a cellophane pack, seal it, and leave it at room temperature for 24 hours. The paper tube is taken after 24 hours, and the presence or absence of powder blowing on the printing surface side is visually determined. Judgment was made with two samples, and bad results were adopted.
○ ... No powder blown on the printed part.
Δ: Part of powder spraying on the printed part is observed.
X: Powder spraying of the printed part is recognized entirely.

[High-definition printability]
Bar code printing was performed with IP-21EX manufactured by Ishida Labeler Co., Ltd., and the printed part was determined visually and by a bar code reader (Symbol II, LASERCHECK II) according to the following criteria. Judgment was made on 10 sheets, and the worst result was adopted.
○ ・ ・ ・ The barcode is clearly printed and read by the barcode reader.
There is no problem.
△ ・ ・ ・ Some barcodes are missing, but reading with a barcode reader is a problem.
None.
× ・ ・ ・ An error occurred when reading the barcode reader.
[Heat resistance evaluation]
After printing the sample, the sample was allowed to stand under DRY conditions at 60 ° C. for 24 hours, and then the color density of the background portion was measured and the readability of the printed portion was visually observed. The color density of the background portion is preferably 0.2 OD or less.
[Water resistance evaluation]
After printing the sample, immerse the sample in water at 20 ° C and let it stand for 24 hours before measuring the color density. At least 0.5 OD or more is required.
The above results are shown in Table 1. The print density was measured using Macbeth RD918. In Table 1, the blank items indicate that the heat-sensitive recording material was not obtained because the pulverized liquid was gelled.

  As described in Table 1, a styrene-maleic anhydride copolymer ammonium salt having an esterification degree of 50% or more and an average molecular weight of 10,000 to 60,000 is used as a developer and a sensitizer, as a sensitizer. In the presence of, a heat-sensitive recording material having a high sensitivity and excellent storage stability and free from dust generation on the background or printing portion can be obtained. In particular, 4-hydroxy-4'-isopropyloxydiphenylsulfone, 2,4'-dihydroxydiphenylsulfone, 4,4'-dihydroxydiphenylsulfone, and bis- (3-allyl-4-hydroxyphenyl) sulfone as developers. By using at least one kind, a heat-sensitive recording material having high sensitivity, excellent heat resistance of the background portion and water resistance of the recording portion, and no powder blowing on the background or printing portion was obtained.

Further, the addition of methylol stearic acid amide, methylol behenic acid amide or stearic acid amide improved the sensitivity further.
Further, 1,1,3-tris (2-methyl-4hydroxy-5-cyclohexylphenyl) butane, 1,1-di (3-tertiarybutyl-4-hydroxy-6-methylphenyl) butane or 1,1 , 3-Tris (2-methyl-4-hydroxy-5-tertiarybutylphenyl) butane is added in an amount of 5 to 50% by mass with respect to the developer, thereby further improving the water-resistant record storage stability. I was able to plan.
In Comparative Example 7, powdering of the background portion and the printed portion occurred, and the evaluation was x. In Examples 1 to 16 and Comparative Examples 1, 3, and 8, the evaluation was good and good.

Claims (4)

  In a heat-sensitive recording medium provided with a heat-sensitive recording layer containing a colorless or light-colored basic dye, a color developer capable of reacting with the dye, and a sensitizer on a support, the sensitizer is ethylene. In the presence of an ammonium salt of styrene maleic anhydride copolymer having a degree of esterification of 50% or more and an average molecular weight of 10,000 to 60,000 as a dispersant, it is slightly mixed in the same mixed system of the developer and sensitizer. A heat-sensitive recording material characterized by being used after being pulverized.   In the heat-sensitive recording layer, the developer is 4-hydroxy-4'-isopropyloxydiphenylsulfone, 2,4'-dihydroxydiphenylsulfone, 4,4'-dihydroxydiphenylsulfone, bis (3-allyl-4- The heat-sensitive recording material according to claim 1, wherein the recording material is at least one developer selected from hydroxyphenyl) sulfone.   3. The heat-sensitive recording material according to claim 1, wherein at least one of methylol stearate amide, methylol behenic acid amide, or stearic acid amide is added to the heat-sensitive recording layer.   In the thermosensitive recording layer, 1,1,3-tris (2-methyl-4hydroxy-5-cyclohexylphenyl) butane, 1,1-di (3-tertiarybutyl-4-hydroxy-6-methylphenyl) butane Alternatively, at least one of 1,1,3-tris (2-methyl-4-hydroxy-5-tertiarybutylphenyl) butane is added in an amount of 5 to 50% by mass based on the developer. Item 4. The thermal recording material according to item 1, 2 or 3.