JPH03193488A - Thermal recording material - Google Patents

Abstract

PURPOSE:To obtain thermal paper improved in pencil writing properties, wherein an erasor may be used and similar to general office paper in touch by adding a specific compound to a thermal color forming layer and using a compound imparting specific tear strength as the water-soluble polymer in a protective layer. CONSTITUTION:A coating solution for thermal recording containing a compound represented by formula [wherein X is -O- or -COO-, R1 - R6 are respectively a hydrogen atom, a 1 - 8 alkyl group, an aryl group or an aralkyl group and may be mutually bonded to form an aromatic ring and n is an integer of 1 - 10] is prepared to be applied to a support and the coated support is dried to obtain thermal recording paper. A protective layer consisting of a water-soluble polymer and pigment is provided to the thermal recording layer. At this time, the water-soluble polymer is used so that the tear strength of the formed film is 1kg/mm or more at 20 deg.C under a relative humidity condition of 60%. Further, starch particles are contained in the protective layer in an amount of 5.0 - 50.0% by wt. of the protective layer.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a heat-sensitive recording material, and more specifically, it has high thermal responsiveness and is writable with a lead cap or mechanical pencil (hereinafter simply referred to as a lead cap). Excellent recordability)
The present invention relates to thermal recording paper which has characteristics comparable to general office paper in that it can be erased with an eraser, and which has a texture similar to that of ordinary paper.

(Prior Art) Recording materials using an electron-donating colorless dye precursor and an electron-accepting compound are already well known as pressure-sensitive paper, thermal paper, light-sensitive pressure-sensitive paper, current-carrying thermal recording paper, thermal transfer paper, and the like. For example, UK Patent No. 2140449, US Patent No. 448
No. 0052, No. 4436920, Special Publication No. 1986-23
No. 992, JP-A-57-179836, JP-A No. 60-12
For details, see No. 3556 and No. 60-123557. In particular, thermal paper is Special Publication No. 43-4160, Special Publication No. 45-1
For details, see Publication No. 4039, etc. These thermal papers are relatively inexpensive, and recording devices based on the thermal recording method are compact, easy to maintain, and inexpensive, so they are used in a wide range of fields such as facsimile machines, printers, plotters, and word processors. In recent years, with the increase in the amount of information, especially in the field of facsimile, and the spread of information network services using dedicated optical fiber communication networks, there has been a demand for faster information transmission. Materials with excellent responsiveness are being provided one after another. This type of thermal paper is a material that has an extremely smooth recording layer surface for the purpose of efficiently transferring heat from the head to the recording paper, as a means of efficiently utilizing the thermal energy provided by the thermal head. There are many
Compared to general office paper, the material has a high gloss and is smooth to the touch. Thermal paper has a unique texture, such as being sticky or sticking to your hands, which is unpleasant to the touch, and a high gloss that makes it feel shiny or unnatural, which makes thermal paper widely popular. Over time, this issue has been brought into closer focus as a problem. In addition to its texture, regular thermal paper also had the disadvantage that it did not write well with a pencil, and the tip of a writing instrument would slip, making it difficult to write.In addition, it was completely impossible to erase the writing with a pencil with an eraser. , it quickly becomes colored and smeared, so further quality improvements are desired as office recording media.

One of the ways to solve these problems is laser facsimile, which uses a toner heat fixing method that uses plain paper as a recording medium, but because of this recording method, the equipment is large, expensive, and requires a high-output power supply. It also has the major disadvantage of requiring regular maintenance and inspection.

For this reason, it is a recording medium that uses the conventional thermal recording method, and has the characteristics of high thermal responsiveness, performance as general office paper, that is, good pencil writing properties, and the ability to use an eraser, as well as a surface gloss. There is a strong demand for thermal paper that is low in weight and has a texture similar to that of ordinary paper.

In response to such demands, for example, special calender treatments such as those disclosed in JP-A-1-196388 and JP-A-188388, as well as JP-A 1-255588 and JP-A 1-2212, are available.
Various improvements from the overcoat layer have been reported, such as No. 79 and JP-A No. 1-221277, but none of them are sufficient in terms of the texture of plain paper, the feel of writing with a pencil, whether an eraser can be used, etc. .

(Objective of the Invention) Therefore, an object of the present invention is to provide general office paper with high thermal responsiveness, good pencil writing properties, and the ability to use an eraser, as well as a so-called texture such as texture and surface gloss. Our goal is to provide close thermal paper.

(Structure of the Invention) The object of the present invention is to (1) provide a heat-sensitive recording layer on a paper support using a coloring reaction between an electron-donating colorless dye precursor and an electron-accepting compound; In a heat-sensitive recording material provided with a protective layer consisting of a water-soluble polymer and a pigment, the heat-sensitive coloring layer contains a compound represented by the following general formula (1), and as the water-soluble polymer in the protective layer, The tear strength of the produced film at 20°C and relative humidity of 60% is 1k.
1. A heat-sensitive recording material characterized in that it uses a compound having a temperature of g/s- or more.

(In the above formula, × represents -〇- or -COO-, R5-R
6 is a hydrogen atom, an alkyl group having 1 to 8 carbon atoms,
Indicates an aryl group or an aralkyl group. Note that substituent R7~
R6 may be bonded to each other to form an aromatic ring. n is 1
represents an integer from to 10. (2) The heat-sensitive recording material according to claim (1), wherein the protective layer contains starch particles in an amount of 5.0% to 50.0% by weight based on the total weight of the protective layer. achieved. The thermal paper obtained by the present invention has high thermal responsiveness, has excellent writing quality especially on lead lids, has the ability to be erased freely with an eraser, and has a pleasant texture.
It has a glossy surface and a good texture, making it a new material that breaks the conventional concept of thermal paper.

Specific examples of the compound (1) used in the present invention include the following compounds.

1-phenoxy-2-naphthoxy(1) ethane, 1-phenoxy-4-naphthoxy(2) butane, 1-(2-isopropylphenoxy)-2-naphthoxy(2) ethane, 1-(4-methylphenoxy)- 3-naphthoxy (2
) Propane, 1-(2-methylphenoxy)-2-naphthoxy(2)-ethane% 1-(3-methylphenoxy)-2-naphthoxy(2)ethane, 1-phenoxy-2
-Naphthoxy(2)-ethane, 1-phenoxy-6-naphthoxy(2)-hexane, 1-(2-phenylphenoxy)-2-phenoxyethane, 1-(4-phenylphenoxy'I -2-(2- Methylphenoxy)ethane, 1,4-diphenoxybutane, 1,4-di(4-methylphenoxy)butane, 1,2-di(3,4-dimethylphenoxy)ethane, 1-(4-phenylphenoxy)
-3-phenoxypropane, 1-phenoxy-2-(4
-butylphenoxy)ethane, 2-naphthoxyacetic acid phenol ester, 2-naphthoxyacetic acid 2,5-dimethylphenol ester, phenoxyacetic acid ρ-phenylphenol ester, phenoxyacetic acid β-naphthol ester, 2-naphthoxyacetic acid p-cresol ester ,
2-naphthoxyacetic acid m-cresol ester, 1,2-
Diphenoxyethane, 1-(2-methylphenoxy)-
2-phenoxyethane, 1-(3-methylphenoxy)
-2-phenoxyethane, 1-(4-methylphenoxy)-2-phenoxyethane, 1-(2,3-dimethylphenoxy)-2-phenoxyethane, 1-(2,4-dimethylphenoxy)-2-phenoxy Ethane, +-(3
, 4-dimethylphenoxy)-2-phenoxyethane,
1-(3,5-dimethylphenoxy)-2-phenoxyethane, 1-(4-ethylphenoxy)-2-phenoxyethane, 1-(4-isopropylphenoxy)-2-
Phenoxyethane, 1-(4-t-butylphenoxy)-2-phenoxyethane, 1,2-di(2-methylphenoxy)-ethane, 1-(4-methylphenoxy)-
2-(2-methylphenoxy)ethane, 1-(3,4-
dimethylphenoxy) -2-(2-methylphenoxy)ethane, 1-(4-ethylphenoxy)-2-(2-
Methylphenoxy)ethane, 1-(4-isopropylphenoxy)-2-(2-methylphenoxy)ethane, 1
-(4-tert-butylphenoxy)-2-(2-methylphenoxy)ethane, 1,2-di(3-methylphenoxy)-ethane, 1-(4-methylphenoxy)-2-(3
-methylphenoxy)ethane, 1-(2,3-dimethylphenoxy)-2-(3-methylphenoxy)ethane,
1-(2,4-dimethylphenoxy')-2-(3-methylphenoxy)ethane, +-(3,4-dimethylphenoxy')-2-(3-methylphenoxy)ethane,
1-(4-ethylphenoxy)-2-(3-methylphenoxy)ethane, 1-(4-inpropylphenoxy')
)-2-(3-methylphenoxy)ethane, 1-(4-
t-butylphenoxy) -2-(3-methylphenoxy)ethane, 1,2-di(4-methylphenoxy)-ethane, 1-(2,3-dimethylphenoxy) -2-(
4-Methylphenoxy)ethane, 1-(2,4-dimethylphenoxy)-2-(4-methylphenoxy)ethane, 1-(2,5-dimethylphenoxy')-2-(4
-methylphenoxy)ethane, 1-(3,4-dimethylphenoxy'J -2-(4-methylphenoxy)ethane, 1-(4-ethylphenoxy)-2-(4-methylphenoxy)ethane, 1-( 4-isopropylphenoxy)-2-(4-methylphenoxy)ethane, 1-(4
-t-butylphenoxy) -2-(4-methylphenoxy)ethane, 1,2-di(2,3-dimethylphenoxy)-ethane, 1-(2,5-dimethylphenoxy)
-2-(2,3-dimethylphenoxy)ethane, 1.2
-di(2,4-dimethylphenoxy)-ethane, 1-(
4-ethylphenoxy)-2-(2,4-dimethylphenoxy)ethane, 1-(4-t-butylphenoxy)-
2-(2,4-dimethylphenoxy)ethane, 1,2-
Di(2゜5-dimethylphenoxy)-ethane, 1-(
3゜4-dimethylphenoxy')-2-(2,5-dimethylphenoxy)ethane, 1-(4-ethylphenoxy)-2-(2,5-dimethylphenoxy)ethane, 1-
(4-t-butylphenoxy)-2-(2,5-dimethylphenoxy)ethane, 1゜2-di(3,4-dimethylphenoxy)-ethane, 1,2-di(3,5-dimethylphenoxy) -ethane, 1,2-di(4-ethylphenoxy)-ethane, 1,3-di(4-methylphenoxy)
-Propane, 1-(4-methylphenoxy)-2-naphthoxy(1)-ethane, 1-(2,5-dimethylphenoxy)-2-naphthoxy(1)-ethane, 1,2-dinaphthoxy(1)-ethane , etc. For purification of the heat-sensitive coloring layer of the present invention, various known ones can be used as in the conventional ones. For example, as for electron-donating colorless dye precursors, triphenylmethane phthalide compounds and fluoran compounds are used.

Fetch 7 gin-based compounds, indolyl phthalide-based compounds, Oicoolamine-based compounds, rhodamine lactam-based compounds, triphenylmethane-based compounds.

There are various compounds such as triazene compounds, spiropyran compounds, and fluorene compounds. Specific examples of phthalides are U.S. Reissue Patent Specification Letter No. 23゜024, U.S. Patent Specification Letter No. 3.491,111, and U.S. Patent Specification Letter No. 3.491,11.
No. 2, No. 3,491゜116 and No. 3.509
．． No. 174, and specific examples of fluorans are U.S. Patent Specifications No. 3,624.107, U.S. Pat.

No. 3,681,390, No. 3,920,510, No. 3,959.571, specific examples of spiropyrans are U.S. Patent Specification Letter No. 3,971°808, pyridine and pyrazine compounds Type is U.S. Patent Specification Letter 3.77
No. 5,424, No. 3.853.869, No. 4,2
No. 46.318, and specific examples of fluorene compounds are described in Japanese Patent Application No. 61-240989. Among these, 2-7 arylamino-3-H, halogeno, furkyl, or alkoxy-6-substituted 7-minofluorane, which develops a black color, is particularly effective.

Specific examples include 2-7 nilino 3-methyl-6-diethyl 7minofluorane and 2-7 nilino 3-methyl-6-N-cyclohexyl-N-methyl 7minofluorane.

2-p-riooanilino-3-methyl-6-dibutylaminofluorane, 2-7nilino-3-methyl-6-sioctylaminofluorane, 2-7nilino-3-rio-6-diethyl-7minofluorane, 2-7 Nilino 3-methyl-6-dibutylaminofluorane, 2-7 Nilino 3-methyl-6-N-ethyl-N-isoamyl 7minofluorane, 2-7 Nilino 3-methyl-6-N-ethyl -N-dodecyl 7minofluorane, 2-anilino-
3-methoxy-6-cyptyl 7minofluorane +2-o
-ri07nilino-6-dibutylaminofluorane, 2
-p-chloro7nilino3-ethyl-6-N-ethyl-
N-isoamylaminofluorane, 2-0-rioo7nilino-6-p-butylanilinofluorane, 2-7nilino-3-pentadecyl-6-diethyl-7minofluorane, 2-7nilino-3-ethyl-6-dibutylamino Fluoran, 2-7nilino-3-methyl-6-dibutylaminofluoran, 2-0-toluidino-3-methyl-6-
Diitubrobyl aminofluorane.

2-7 Nilino 3-methyl-6-N-isobutyl-N-
Ethyl 7minofluorane, 2-7nilino 3-methyl-
Examples include 6-N-ethyl-N-tetrahydrofurfuryl-7minofluorane, 2-7nilino-3-chloro-6-N-ethyl-N-isoamylaminofluorane, and the like. Two or more of these can also be used in combination. Note that this electron-donating colorless dye precursor is coated on the final thermal paper so that it has a durability of 0.3 to 1097.

Furthermore, regarding electron-accepting compounds that are constituent components of the heat-sensitive coloring layer, phenol derivatives, metal salts of aromatic carboxylic acids, acid clay, and bentonite are used.

Novolac resins, metal-treated novolac resins, metal complexes, etc. are used. Examples of these are JP-B No. 4゜-9309, JP-A No. 45-14039, and JP-A-52-14048.
No. 3, JP-A-48-51510, JP-A-57-210
No. 886, JP-A-58-87089, JP-A-59-1
No. 1286, JP-A-60-176795, JP-A-61
-95988 etc.

To give some examples of these, phenol derivatives include 2,2''-bis(4-hydroxyphenyl)propane, 4-phenylphenol, 1,1-bis(3-chloro-4-hydroxyphenyl)cyclohexane, 1.1
-bis(4-hydroxyphenyl)cyclohexane, 1
．． 1-bis(3-chloro-4-hydroxyphenyl)
-2-ethylbutane, 4+ 4'-5ec-isooctylidene diphenol, 4+4'-5ec-butylidene diphenol, 4-p-methylphenylphenol, 4
．． 4'-methylcyclohexylidenephenol, 4.
4'-isopentylidenephenol, bis(3-7ly-4-hydroxyphenyl)sulfone, 4-hydroxyphenyl-3'4° dimethylphenylsulfone, 4
-(4-isobutoxyphenylsulfonyl)phenol, bis(2-(4-hydroxyphenylthio)ethoxy)methane, benzyl p-hydroxybenzoate, and the like. Salicylic acid derivatives include 4-pentadecylsalicylic acid, 3,5-di(α-methylbenzyl)salicylic acid, 3
, 5-di(ter-octyl)salicylic acid, 5-α-(
p-α-methylbenzylphenyl)ethylsalicylic acid,
3-α-methylbenzyl-5-tert-octylsalicylic acid, 5-tetradecylsalicylic acid, 4-hexyloxysalicylic acid, 4-cyclohexyloxysalicylic acid, 4-decyloxysalicylic acid, 4-dodecyloxysalicylic acid, 4-penta Examples include decyloxysalicylic acid, 4-octadecyloxysalicylic acid, etc., and their zinc, aluminum, calcium, and copper salts. Among these, bisphenols are preferred.

The ether compound of the present invention can be used with other sensitizers such as those described in JP-A-58-57989. Compounds disclosed in JP-A-58-87094 and the like can also be used in combination. Representative examples thereof include aromatic ethers, esters, and/or aliphatic 7-amides or ureides.

Two or more of these thermofusible substances, ie, sensitizers, may be used in combination, and in order to obtain sufficient thermal responsiveness, it is preferable to use them in an amount of 10 to 200% by weight based on the electron-accepting compound. , more preferably 20 to 150
Weight%.

Dispersion of these materials, color forming agent, color developer, and thermofusible substance is performed in a water-soluble binder. Each material is dispersed to a size of several microns or less using a ball mill, sand mill, etc. together with a water-soluble binder solution. The sensitizer may be added to either the color former, the color developer, or both and dispersed simultaneously, or in some cases, a eutectic may be prepared in advance and dispersed.

The binder used in the heat-sensitive coloring layer in the present invention is preferably a compound that dissolves at least 5% by weight in water at 25°C, and specifically includes polyvinyl alcohol, methylcellulose, carboxymethylcellulose, starches (modified starch, ), gelatin, 7-rabbi 7-gum,
Saponification of casein, styrene-maleic anhydride copolymer hydrolyzate, carboxy-modified polyvinyl alcohol, alkyl-modified polyvinyl alcohol, itaconic acid-modified polyvinyl alcohol, maleic acid-modified polyvinyl alcohol, polyacrylamide, vinyl acetate-polyacrylic acid copolymer Things can be given. These binders are used not only for dispersion but also for the purpose of improving coating film strength, and for this purpose, styrene-butadiene copolymers,
Synthetic polymer latex binders such as vinyl acetate copolymer, 7-crylonitrile-butadiene copolymer, methyl acrylate-butadiene copolymer, and polyvinylidene chloride can also be used in combination.

After dispersion, these dispersions are mixed, and if necessary, pigments, metal soaps, waxes, surfactants, antistatic agents,
Ultraviolet absorbers, antifoaming agents, conductive agents, fluorescent dyes, etc. may be added.

As the pigment, calcium carbonate, barium sulfate, lithopone, waxite, kaolin, silica, amorphous silica, etc. are used.

As the metal soap, higher fatty acid metal salts are used, such as zinc stearate, calcium stearate, aluminum stearate, and the like.

The wax according to the present invention has a melting point of 40 to 120°C, and includes paraffin wax, polyethylene wax, carnauba wax, microcrystalline wax, camphoria wax, montan wax, fatty acid amide wax, and the like. Among these, paraffin wax, microcrystalline wax, montan wax, and fatty acid 7-amide waxes are preferred, and paraffin wax, montan wax, and methylolstear 0-7-mid wax having a melting point of 50 to 100'C are particularly preferred.

Furthermore, surfactants, antistatic agents, ultraviolet absorbers, antioxidants, antifoaming agents, conductive agents, fluorescent dyes, coloring dyes, and the like may be added as necessary.

As the surfactant, a sulfosuccinic acid-based alkali metal salt and a fluorine-containing surfactant are used.

Further, it is preferable to add a decoloring inhibitor to the heat-sensitive color forming layer in order to prevent decoloring of the image-printed area and to make the generated image more robust. Phenol compounds, especially hindered phenol compounds, are effective as anti-fading agents, such as I
, L3-1 lis(2-methyl-4-hydroxy-ter
t-butylphenyl)butane, 1.1.3-tris(2
-ethyl-4-hydroxy-5-tert-butylphenyl] butane, Il, 3-tris (3,5-di-te
rt-butyl-4-hydroxyphenyl)butane, 1.
1.3-tris(2-methyl-4-hydroxy-5-t
ertbutylphenyl)propane, 2.2'-methylene-bis(6-tert-butyl-4-methylphenol), 2°2'-methylene-bis-(6-tert-butyl-4-ethylphenol), 4 .4'-butylidene-
Bis(6-tert-butyl-3-methylphenol)
, 4,4'-thio-bis-(3-methyl-5-tert
-butylphenol), etc. The amount of such phenolic compound used is 1 to 20% of the color developer.
It is preferable to use 0% by weight, more preferably 5% by weight.
~50% by weight.

After each of these materials is mixed, it is applied to a support. The support may include paper, synthetic paper, various synthetic resin bases, etc., and is not particularly limited, but for the purpose of the present invention, it is most preferable to use a paper support. Further, there are no particular limitations on conventional knowledge such as applying an undercoat to the support in advance or calendering.

The method of forming the recording layer in the present invention is not particularly limited, and the recording layer may be coated using an existing coating method such as an air knife coater, blade coater bar coater, gravure coater, or air curtain coater. It may be layered simultaneously with the protective layer described later or may be applied sequentially. Further, there is no particular limitation on the coating amount of the heat-sensitive recording layer, and the dry coating amount is usually 1 to +2 9/
I+(, particularly preferably 3 to +09/n().

Furthermore, the thermal paper of the present invention is characterized in that a protective layer is formed on the thermal recording layer thus formed, which has the texture of paper, provides pencil writing properties, and allows use of an eraser. . That is, a protective layer consisting of a water-soluble polymer and a pigment is provided on the heat-sensitive recording layer, and the water-soluble polymer is such that the tear strength of the formed film at 20° C. and relative humidity of 60% is 1 kg/mm or more. By using a chemical compound, more preferably containing starch particles in an amount of 5.0% to 50.0% by weight based on the total weight of the protective layer, the texture of paper and lead writing properties are imparted, and the eraser is It became possible to use it.

The water-soluble polymer forming the protective layer is preferably a binder that is highly resistant to solvents, oils, etc., has good film-forming properties, and has a strong coating film strength, especially from the viewpoint of pencil writing properties and suitability for use with an eraser. From this point of view, we have extensively studied binders from various mechanical factors, and as a result, we have arrived at the present invention. Tear strength is measured by the following method. First, the water-soluble polymer is formed into a film by a drum casting method.

The water-soluble polymer solution was cast onto a drum with a diameter of 738 mrrI set at a surface temperature of 70° C., and taken out after drying. The thickness of the formed film is 50μ±10μ, and this is adjusted by the paste concentration, the number of coatings, and the drum rotation speed. This formed film was sampled in the horizontal direction to a width of 63.5 mm x length of 1.40 mm, the thickness was measured, and the thickness was measured in a specified environment (20 mm).
℃, 60%) and measured using an Elmendorf tear strength meter.

Specific examples of such binders include those with a relatively high degree of polymerization among unmodified polyvinyl alcohols, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, styrene-maleic anhydride copolymer hydrolyzate, carboxy-modified polyvinyl alcohol,
Examples include saponified products of furkyl-modified polyvinyl alcohol, silica-modified polyvinyl alcohol, polyacrylic 7mide, starch, vinyl acetate-polyacrylic acid copolymer, etc., but depending on the degree of polymerization, saponification degree, additives, etc. Tear strength at 60%RH is 1 kg/mm
Any binder that has a high quality can be used.

Various known pigments can be used as pigments, but
Among these, a combination of silica and light calcium carbonate is particularly preferred because it provides good writing properties and causes less bleeding of water-based ink. The amount added is also not particularly limited, but if it exceeds 50% of the total weight of the protective layer, the color density tends to decrease due to its hiding power.

These materials are thoroughly mixed with a binder using a dispersing machine such as a homogenizer mixer or a mixer to prepare a coating liquid for the protective layer. In addition, various additives such as those used in the heat-sensitive recording layer, such as metal soap, wax, etc., may be added to the coating liquid as necessary.
Surfactants, antistatic agents, ultraviolet absorbers, antifoaming agents, conductive agents, fluorescent dyes, coloring dyes, and the like may be added. This protective layer coating solution is coated on the already prepared heat-sensitive recording layer to obtain the heat-sensitive paper of the present invention. Further, the protective layer may be applied simultaneously with the coloring layer or sequentially. There is no particular limitation on the amount of coating, but generally the dry coating amount is 0°5 to 8.09/.
It is desirable to set it to rd.

The heat-sensitive recording paper thus obtained has a texture similar to that of general office paper in terms of feel, surface gloss, etc., has excellent pencil writing properties, and can be used with an eraser. Furthermore, in order to improve the feel and writability, the protective layer should contain 5.0 to 50.0% of the total weight of the protective layer.
Preferably, the starch particles contain % by weight of starch particles,
Furthermore, addition of 10.0% to 30.0% by weight is most preferable. The addition of starch particles further improves the feel and pencil writing properties. If the amount added exceeds 50.0% of the total weight of the protective layer, the roughness will increase rapidly, and if it is less than 5.0%, no effect will be seen.

Also, regarding the type of starch, it is potato starch.

In addition to starches such as wheat starch, corn starch, tapioca starch, sago starch, and rice starch, these starches are processed into oxidized starch, esterified starch, etherified starch, pregelatinized starch, roasted dextrin, enzyme-modified dextrin, and enzyme-degraded dextrin. There are modified starches such as , crosslinked starch, grafted starch, etc., and the present invention is not particularly limited to these types of starch, but wheat starch is most preferably used.

After coating and drying, post-processing is also possible using known techniques, such as calendar processing to improve sensitivity and image quality, and a thin layer of resin on the opposite side of the recording layer formation surface to prevent static electricity. Providing layers, etc. may be implemented as necessary.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited only to the following Examples.

(Example-1) ■Formation of thermosensitive recording layer As an electron-donating colorless dye precursor 2-7 Nilino 3-
Methyl-6-N ethyl-N iso7mil7minofluorane 109, bisphenol A20 as electron-accepting compound
9. As an ether compound, 1,2-di(3-methylphenoxy)-ethane 209 was dispersed in a ball mill overnight with a 5% polyvinyl alcohol (Cura 1PVA-105) aqueous solution of 1009, and the average particle size was adjusted to 1.
Each dispersion liquid was obtained by reducing the particle size to 5 μm or less. Further, calcium carbonate 809 was dispersed with a 0.5% sodium hexametaphosphate solution 1609 using a homogenizer. These dispersions were mixed in a ratio of 59 parts of the electron-donating colorless dye precursor dispersion liquid, 109 parts of the electron-accepting compound dispersion liquid, 109 parts of the 2-di(3-methylphenoxy)-ethane dispersion liquid, and 159 parts of the calcium carbonate dispersion liquid. Mix and further add 21% zinc stearate emulsion 39 and paraffin wax dispersion with a melting point of 68°C (Htdrin D-337 manufactured by Middle East Yushi Co., Ltd.) 2
9 was added to obtain a coating liquid for heat-sensitive recording. This heat-sensitive recording coating liquid was coated on a high-quality paper with a basis weight of 649 using a coating bar so that the dry weight of the heat-sensitive coloring layer was 597 rrr, and was dried at 50° C. for 3 minutes to obtain a heat-sensitive recording paper.

■ Formation of protective layer 7.4% polyvinyl alcohol (Kuraray PVA-ll7
; Tear strength 4, Q kg/mm at2Q℃60
XRH) Aqueous solution 409.69. Add water 1009 to 30% zinc stearate emulsion 13.39 and mix well to obtain a protective layer stock solution. Further, amorphous silica (Nipseal E-150J, manufactured by Nippon Silica) 279 and sodium hexametaphosphate 0.279 were dispersed together with water 739 using a homogenizer to obtain a silica dispersion. Similarly, light calcium carbonate (light calcium carbonate PC manufactured by Shiraishi Kogyo Co., Ltd.)
) 279, sodium hexametaphosphate 0.279 and water 63
9 was dispersed using a homogenizer to obtain a light calcium carbonate dispersion. These dispersions were combined into protective layer stock solution 4009, light calcium carbonate dispersion 6,459, and amorphous silica dispersion 1.
They were mixed at a ratio of 0.09 to obtain a coating liquid for a protective layer. Coat this as a protective layer on the coloring layer of the heat-sensitive recording paper prepared previously and apply the dry weight of 2. The desired thermal paper was obtained by applying the coating so as to obtain Os/rrf.

(Example-2) In Example-1, 7.4% polyvinyl alcohol (Kuraray pv^-117; tear strength 4-Okg/mm a
Thermal paper was prepared in the same manner as in Example-1, except that a 7.4% polyvinyl alcohol (Cura 1 PVA-+24; tear strength 1.6 kg/mmat 20°C 60 $RH) aqueous solution was used instead of the t2Q''C6OXR1 () aqueous solution. I got it.

(Example-3) In Example-1, 7.4% polyvinyl alcohol (Cura 1 PVA-117i tear strength 4.0 kg/mm
at20'C6OXRH) 7,4% instead of aqueous solution
A thermal paper was obtained in the same manner as in Example 1 except that an aqueous solution of polyvinyl alcohol (Cura 1 PVA-217; tear strength 5, Q kg/mmat 20° C. 60XR) I was used.

(Example-4) In Example-1, 7.4% polyvinyl alcohol (Cura 1PVA-1+7; tear strength 4, Q kg/mn+
at2Q”C6OXRH) 7.4% instead of aqueous solution
A thermal paper was obtained in the same manner as in Example 1, except that an aqueous solution of polyvinyl alcohol (Kura1 PVA-224; tear strength 5.0 kg/Il1mat2Q°C 60tR) was used.

(Example-5) In Example-1, 7.4% polyvinyl fluorol (Cura 1PVA-117i tear strength 4.0 kg/mm
at20"C60t RH]7.4 instead of aqueous solution
%Fulkyl modified polyvinyl alcohol (Cura 1 MP-
+02; Tear strength 2, 1 kg/mm at20
A thermal paper was obtained in the same manner as in Example-1 except that an aqueous solution (°C 60XRH) was used.

(Example-6) In Example-1, wheat starch 7 was added to the protective layer coating liquid.
．． A thermal paper was obtained in the same manner as in Example-1 except that 729 was added.

(Example-7) In Example-1, 1 part of wheat starch was added to the protective layer coating liquid.
A thermal paper was obtained in the same manner as in Example-1 except that 6.629 was added.

(Example-8) In Example-1, wheat starch 2 was added to the protective layer coating liquid.
．． A thermal paper was obtained in the same manner as in Example-1 except that 329 was added.

(Example-9) In Example-1, 0 wheat starch was added to the protective layer coating liquid.
．． 95! A thermal paper was obtained using the same birch as in Example 1 except that J was added.

(Example-10) In Example-1, wheat starch 4 was added to the protective layer coating liquid.
A thermal paper was obtained in the same manner as in Example-1 except that 6.319 was added.

(Example-11) Heat-sensitive layer was prepared in the same manner as in Example-1 except that 4-(4-isopropoxyphenylsulfonyl)phenol was used instead of bisphenol in preparing the heat-sensitive layer nutrient solution. Got paper.

(Comparative Example-1) In Example-1, 7.4% polyvinyl alcohol (Clari PVA-1+7; tear strength 4, (l kH/
am at20'C6OXR)7 instead of Il aqueous solution
．． 4% polyvinyl alcohol (Kura-L, PVA-10
5i tear strength 0.8kg/mmat) 9℃60χRH)
A thermal paper was obtained in the same manner as in Example-1 except that an aqueous solution was used.

(Comparative Example-2) In Example-1, 7.4% polyvinyl alcohol (Clari PVA-117i tear strength 4.0 kg/mm
at2Q"C60χRH) 7.4% instead of aqueous solution
A thermal paper was obtained in the same manner as in Example-1 except that an aqueous solution of polyvinyl alcohol (Clari PVA-205i tear strength 0.7 kg/mmat 20°C 60XR) was used.

(Comparative Example-3) The procedure was the same as in Example-1 except that parabenzylbiphenyl was used instead of 1°2-di(3-methylphenoxy)ethane in preparing the heat-sensitive layer coating solution. A thermal paper was obtained.

The thermal paper obtained as described above was treated with a calendar and evaluated by the following method. The results are shown in Table 1.

(Color density) Kyocera @ thermal head (LT-216-8MPD
I) and a thermal printing experimental device having a pressure port of 100kc+/crtr just before the head, the head voltage was 2.
Printing was performed at a pulse intensity of 1.0 using a pressure roll under the conditions of 4 V and a pulse cycle of 10 m5, and the print density was measured using a Macbeth Co., Ltd. RD-918 type J meter.

(Fog Density) The density of the red printed portion (fog) was also measured in the same manner as the color density.

(Pencil writing properties) Writing was performed on the obtained thermal paper using a pencil and a mechanical pencil, and the writing quality, pencil stickiness, etc. were evaluated for the density of He%B%H, and the results were evaluated on the following four levels.

◎; Can write very smoothly. Even at H density, the pencil sticks well and writes well.

O: Can write smoothly without applying pressure.

In addition, the density of the writing area where the pencil sticks well is also high.

Δ: Difficult to write without applying some pressure. Regarding the darkness of H, it is very difficult to write, and the tip of the writing instrument feels slippery, making it uncomfortable.

Also, the density of the writing part is low enough that there is no problem in practical use.

×: The writing instrument slips even when I apply a lot of pressure, and the pencil doesn't stick well, and even at the density of B, the density is weak, making it very difficult to write.

Exceeds the practical tolerance for general office use.

(Eraser usage test) The pencil writing part was covered with a plastic eraser (Keeρ manufactured by Hosha).
) and evaluated the degree of erasure and the presence or absence of fog in the following three grades.

0: Disappears to the same level as ordinary office paper, leaving almost no trace. It doesn't turn over at all.

Δ: Some writing marks remain, but there is no fog and there is no problem in practical use.

X: Most of the writing marks remain and cannot be erased. Or, the area rubbed with the eraser will become covered, making it impractical.

(Texture) Ten people who are employed in general office work (those who have handled facsimile paper) were asked to touch the sample, and compared it with Xerox Paper P-A4, the texture was ranked into the following four levels. evaluated.

◎: 9 Å or more out of 10 people evaluated the feel as the same.

O; 7 to 8 people rated it as having the same feel.

674 to 6 people rated it as having the same feel.

X: The same texture was evaluated as 3 Å or less. As shown in Table 1, the present invention provides a material that has high thermal response, excellent writing performance with a lead cap, can be used with an eraser, and has a good texture such as texture. It is clear that a thermal paper surprisingly similar to ordinary paper was obtained.

Table - Table

Claims (2)

[Claims] (1) A heat-sensitive recording layer that utilizes a color reaction between an electron-donating colorless dye precursor and an electron-accepting compound is provided on a paper support, and a protective layer made of a water-soluble polymer and a pigment is further provided on the heat-sensitive recording layer. In the prepared heat-sensitive recording material, the heat-sensitive coloring layer contains a compound represented by the following general formula (I), and the water-soluble polymer in the protective layer is used as the water-soluble polymer at 20°C.
A heat-sensitive recording material characterized by using a compound having a tear strength of 1 kg/mm or more at a relative humidity of 60%. ▲There are mathematical formulas, chemical formulas, tables, etc.▼(I) [In the above formula, X represents -O- or -COO-, and R_1~
R_6 each represents a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, an aryl group, or an aralkyl group. Note that the substituent R
_1 to R_6 may be bonded to each other to form an aromatic ring. n represents an integer from 1 to 10. ] (2) 5.0% by weight based on the total weight of the protective layer in the protective layer
The heat-sensitive recording material according to claim 1, characterized in that it contains ~50.0% by weight of starch particles.