JPH0725160A - Thermal recording material - Google Patents

Abstract

PURPOSE:To obtain a thermal recording material forming a developed color image good in long-term preservability by providing a thermal color forming layer containing a dye precursor and a specific coupler allowing the dye precutsor to form a color on a sheet like substrate containing a specific inorg. acid salt. CONSTITUTION:A specific amt. of a hardly water-soluble or water-insoluble alkaline earth metal acid salt such as light calcium carbonate or magnesium carbonate is compounded with a sheet like substrate such as paper or a plastic film. A specific amt. of a colorless or light-colored dye precursor and a specific amt. of an aromatic compd. having at least two functional groups represented by general formula (wherein X is an oxygen atom or a sulfur atom) are added to and mixed with a polyvinyl alcohol aq. soln. to prepare a coating soln. for a thermal color forming layer. This coating soln is applied to the aforementioned sheet like substrate and dried to laminate the thermal color forming layer to obtain a thermal recording material. As a concrete example of the compd. represented by the general formula, this is bis(p- toluenesulfonylaminocarbonylamino)ketone.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal recording material. More specifically, the present invention provides a method in which an image formed by heat is erased with time, and under relatively high temperature,
In addition, there is very little discoloration under high humidity, and it is excellent in oil resistance, plasticizer resistance, etc., that is, chemical resistance, and in addition, white paper part (non-printed part) under high temperature, high humidity, or contact with plasticizer. ) The present invention relates to a heat-sensitive recording material with extremely small background stain. That is, the heat-sensitive recording material of the present invention can be used not only as a heat-sensitive recording type ticket for an automatic ticket vending machine, but also as a ticket, a commuter ticket, or the like that requires preservability, water, a plasticizer, an oil or fat. It is suitable as a label for POS bar code system that is attached to the packaging surface of food wrapped in polyvinyl chloride film that cannot avoid contact with it, and also as facsimile paper or word processor paper for long-term storage, or CRT. It is also useful as an image printer paper.

[0002]

2. Description of the Related Art A thermal recording material is generally composed of a support such as paper, synthetic paper or plastic film on which a color-forming substance such as an electron-donating leuco dye and an organic acid substance such as an electron-accepting phenolic compound. It is formed by providing a thermosensitive coloring layer containing as a main component a color-developing substance as described above, and a recorded image can be recorded by reacting these coloring components with thermal energy. Such a thermal recording material is disclosed in Japanese Examined Patent Publication No.
No. 4160, Japanese Patent Publication No. 45-14039, and Japanese Patent Laid-Open No.
It is disclosed in No. 8-27736 and is widely put into practical use.

The thermal recording medium having the above-mentioned structure (this is called a dye type thermal recording medium) has a compact recording apparatus, is inexpensive, and is easy to maintain. , Fax, vending machine,
Widely used in printers for scientific measuring instruments, CRTs, and printers for medical measurement.

However, in the conventional dye-type thermosensitive recording medium, it is known that the color-developed image disappears over time because the color-developing reaction is reversible. This decolorization is exposed to light, high humidity,
The image is accelerated in a high-temperature atmosphere, and further progresses rapidly due to contact with a plasticizer and oil, and the image is erased to an unreadable level.

Many techniques have been disclosed to suppress this decoloring phenomenon (for example, Japanese Patent Laid-Open No. 60-78782).
JP-A-59-167292, JP-A-59-114
096, JP-A-59-93387, JP-A-56-1
4796, JP-A-58-199189, JP-A-62.
No. 164579 and JP-A No. 62-169681), the resulting thermosensitive recording medium has extremely few balance of whiteness, recording sensitivity, print storability, and price. Phenomenon prevention technology has been demanded.

In order to solve these problems, the present inventors have newly used a completely new sulfonyl (thio) urea compound, which is different from the conventional phenolic compound, as a developer for developing the above-mentioned dye precursor. A technique has been proposed (Japanese Patent Laid-Open No. 5-147357). The heat-sensitive recording material thus obtained satisfied all the above conditions. However, since this developer compound is a completely new compound that has never existed in the past, a new technical problem that has not been experienced with the conventional phenolic color developers has also been raised.

When a heat-sensitive recording material using the above-mentioned new developer compound is kept at high temperature under extremely high humidity,
This is a phenomenon in which the white paper part may develop color. At the same time, if the thermosensitive recording medium is brought into contact with a film containing a large amount of a plasticizer at high temperature for a long time, the white paper portion may be slightly colored as described above. Although this color development does not impair the practicality as an ordinary thermosensitive recording medium, when it is used as a commercial product, it may give an unfavorable impression depending on the application. Was desired.

Further, as a technique having some similarities in structure to the present invention, as disclosed in JP-A-55-41277, a specific fluoran compound and a color thereof are developed under heating. When a bisphenol compound is used, neutral paper or alkaline paper is used as the support, and as disclosed in JP-A-55-156087, a phenol compound is used as a color developer for heat-sensitive recording paper, Also, a paper using neutral paper as a support, a paper using a bisphenol compound as a color developer as disclosed in JP-A-55-14281, and a paper showing a pH of 6 to 9 during hot water extraction as a support. Used, JP-A-56-
As disclosed in Japanese Patent No. 115292, it is known to use paper having a pH of 6.5 to 9.0 by cold water extraction and having a nitrocresol adsorptivity of a certain value or less.

However, the above-mentioned JP-A-55-41277,
In the heat-sensitive recording materials of Nos. 55-156087 and 55-14281, only the case where the color developer is a phenolic compound is targeted, and therefore, there is a technical problem in using the specific color developer compound of the present invention. There was no recognition and therefore could not teach the subject of the invention and its solution at all. Further, the invention described in the above-mentioned JP-A-56-115292 captures only the basicity of the base paper, and in recognition of the invention, the organic developer is a phenolic developer,
Or, it is limited only to the case of using a carboxylic acid type developer, and thus cannot teach the object of the present invention and the solution thereof.

[0010]

DISCLOSURE OF THE INVENTION The present invention has excellent long-term storability of a color image such as oil resistance, plasticizer resistance, moisture resistance, and heat resistance of a printed portion, and is excellent in high temperature under extremely high humidity. It is an object of the present invention to provide a thermosensitive recording medium in which the white paper portion exhibits little coloration even when held, and the white paper portion exhibits extremely little coloration even when it is brought into contact with a film containing a considerable amount of a plasticizer for a long time.

[0011]

The present inventors have found that when a specific sulfonyl (thio) urea compound which gives a print excellent in long-term storage property is used as a developer, a specific alkaline earth is contained in a sheet substrate. The present invention has been completed by finding that the above problems can be solved by containing a metal salt.

The thermosensitive recording medium according to the present invention is formed on a sheet-like substrate and at least one surface of the sheet-like substrate,
And a colorless or light-colored dye precursor, and a thermosensitive coloring layer containing the dye precursor and a color developer that reacts under heat to develop a color, and the color developer has the following in one molecule: Chemical formula (I):

[Chemical 3] (However, in the formula (I), X represents an oxygen or sulfur atom)
And an aromatic compound having at least two functional groups represented by: and the sheet-like substrate contains 1% or more by dry weight of the poorly water-soluble or water-insoluble inorganic acid salt of an alkaline earth metal. It is characterized by being present.

In the heat-sensitive recording material of the present invention, the developer compound of the formula (I) has the following general formula (II):

[Chemical 4] (In the formula (II), R represents an unsubstituted or substituted benzene ring group, and Z represents a divalent alkylene group, oxygen atom, sulfur atom, sulfonyl group, or carbonyl group. It is preferable that the sheet-shaped substrate is paper and the alkaline earth metal inorganic acid salt is calcium carbonate. When the developer compound of the formula (II) is used, the storability of the color image is particularly good, and the effect balance is good when calcium carbonate is contained in the sheet-shaped substrate made of paper, and It is also desirable in terms of price and availability.

[0014]

The poorly water-soluble or insoluble alkaline earth metal inorganic acid salt used in the present invention is not particularly limited as long as it is white. In the technique of heat-sensitive recording material, oil absorption, crystal structure, etc. of the inorganic pigment to be used may be a problem, but the present invention does not have such limitation. Specific examples of the inorganic acid salt include light calcium carbonate,
Examples thereof include ground calcium carbonate, ultrafine calcium carbonate, magnesium carbonate, barium carbonate, calcium silicate, a complex salt of calcium carbonate and calcium hydroxide, and surface-treated calcium carbonate and calcium silicate. These inorganic acid salts may be used alone or in combination of two or more.

In the heat-sensitive recording material of the present invention, the sheet-like substrate contains a sparingly water-soluble or water-soluble inorganic acid salt of an alkaline earth metal. Such a sheet-like substrate is effective for suppressing the color development of the white part even under high temperature and high humidity conditions.

By incorporating the alkaline earth metal salt into the sheet-shaped support, the heat-sensitive recording material obtained as described above is exposed to extremely high humidity at high temperature, or when it is exposed to a plasticizer and high temperature. The mechanism that suppresses the color development tendency of the white paper part when contacted for a long time under is not necessarily clear, but it is not as simple as due to the basicity of the alkaline earth metal salt, It is believed that this is due to the unique interaction with the specific novel color-developing sulfonyl (thio) urea compound used in the present invention.

The amount of the alkaline earth metal salt added to the sheet-like substrate is 1% by weight or more, preferably 1 to 30% by weight, more preferably 1% by weight or more based on the total dry weight of the sheet-like substrate to which it is added. Is 2 to 20% by weight. If the amount added is less than 1% by weight, the effect of suppressing the tendency of the white part to develop color under high temperature and high humidity or in contact with a plasticizer for a long time is not sufficient, and it is 30% or more. If added, the mechanical strength of the resulting sheet-shaped substrate will be insufficient, and the function of the thermosensitive coloring layer as a support cannot be sufficiently achieved.

The sheet-like substrate used in the thermosensitive recording medium of the present invention can be selected from paper (lignocellulosic material), synthetic paper made of polyolefin resin, plastic film and the like. From an economic standpoint, it is most preferred to use paper as the sheet substrate.

The effect of the present invention is not limited to the heat-sensitive recording material having a constitution in which the heat-sensitive color forming layer is directly applied to the sheet-like substrate containing the above-mentioned alkaline earth metal. That is, the effect of the present invention is sufficiently exhibited even if a single coating layer or a plurality of coating layers are present between the thermosensitive coloring layer and the sheet-shaped substrate containing the alkaline earth metal. . That is, in the thermosensitive recording material of the present invention, the thermosensitive coloring layer may be directly coated on the sheet-like substrate, and a single coating layer or a plurality of coating layers are present between the support and the thermosensitive coloring layer. You may have. In addition, the weight of the sheet substrate,
There is no particular limitation on the thickness and the like, and as long as it can maintain a practically sufficient function as a sheet-like substrate, it can be lightweight. If the sheet substrate is made of paper, the lower limit of the basis weight of the paper substrate is approximately 30 g / m ² approximately, is preferably 40 to 100 g / m ^2. The single-layer or multiple-layer coating layer existing between the sheet-shaped substrate and the thermosensitive coloring layer is, for example, an undercoat layer, and the coating amount thereof is preferably 1 to 10 g / m ² . This coating layer is generally arranged for the purpose of improving the smoothness, heat insulation, and printing runnability of the thermosensitive recording medium, and is mainly composed of inorganic pigments represented by calcined clay, hollow fine particles and And / or plastic fine particles, and a binder for binding them to a sheet-like substrate.

The sheet-like substrate may contain other inorganic pigments, organic-inorganic dyes, if necessary, in addition to the alkaline earth metal salt.
A fluorescent dye or the like may be contained within a range that does not impair the effects of the present invention. Especially when the sheet substrate is made of paper,
An internal sizing agent such as an alkyl ketene dimer or alkenyl succinic anhydride may be used in order to efficiently retain and contain an alkaline earth metal in the paper. Further, the sheet substrate may be subjected to surface treatment such as size press. Further, if necessary, an inorganic pigment for preventing blocking or improving slipperiness, for example, on the surface opposite to the surface coated with the thermosensitive coloring layer of the sheet-like substrate, and preventing generation of static electricity. A back coat layer containing a conductive agent or the like may be provided.

The thermosensitive coloring layer of the thermosensitive recording material of the present invention comprises a colorless or light-colored dye precursor involved in the thermosensitive coloring reaction, and the above-mentioned chemical formula (I) in one molecule as a color developer for developing the color.
An aromatic compound having at least two functional groups represented by, and a binder for fixing these components to a support. Further, in the thermosensitive coloring layer, if necessary, various inorganic or organic pigments, a heat-fusible aromatic compound having a melting point of 50 to 150 ° C. known as a sensitizer, a conventionally known phenol-based or organic acid-based color developer Agent,
Antioxidants, UV absorbers, and / or waxes may be included.

Aromatic compounds having at least two functional groups represented by the above-mentioned compound (I) in one molecule which can be used in the present invention are disclosed in JP-A-5-14735.
This is disclosed in Japanese Patent Publication No. 7, but the following is a specific example. Bis (p-toluenesulfonylaminocarbonylamino) ketone, 1,2-bis (p-toluenesulfonylaminocarbonylamino) ethane, 1,
1,6,6-Tetra (p-toluenesulfonylaminocarbonylamino) hexane, 1,5-bis (p-toluenesulfonylaminocarbonylamino) -3-oxapentane, 1,5-bis (p-toluenesulfonylaminocarbonyl) Amino) -3-thiopentane, 1,3-bis (p-toluenesulfonylaminocarbonylamino)-
2-Propanone, 1,5-bis (p-toluenesulfonylaminocarbonylamino) -3- [2 '-(p-toluenesulfonylaminocarbonylamino) ethyl] -3
-Azapentane, 1,3-bis (p-toluenesulfonylaminocarbonylaminomethyl) -benzene, 1,4
-Bis (p-toluenesulfonylaminocarbonylaminomethyl) -benzene, 4,4'-bis (p-toluenesulfonylaminocarbonylamino) -diphenylmethane, 4,4'-bis (o-toluenesulfonylaminocarbonylamino) -diphenylmethane 4,4'-bis (benzenesulfonylaminocarbonylamino) -diphenylmethane, 4,4'-bis (p-toluenesulfonylaminothiocarbonylamino) -diphenylmethane,
4,4'-bis (1-naphthalenesulfonylaminocarbonylamino) -diphenylmethane, 2,2-bis [4 ', 4 "-(p-toluenesulfonylaminocarbonylamino) phenyl] propane, 1,2-bis [4 ′
-(P-toluenesulfonylaminocarbonylamino)
Phenyloxy] ethane, 2,5-bis (p-toluenesulfonylaminocarbonylaminomethyl) furan,
1,3-bis (p-toluenesulfonylaminocarbonylamino) benzene, 1,4-bis (p-toluenesulfonylaminocarbonylamino) benzene, 1,5-bis (p-toluenesulfonylaminocarbonylamino)
Naphthalene, 1,8-bis (p-toluenesulfonylaminocarbonylamino) naphthalene, 4,4'-bis (p-toluenesulfonylaminocarbonylamino) diphenyl ether, 3,3'-bis (p-toluenesulfonylaminocarbonylamino) Diphenyl sulfone,
And 4,4'-bis (p-toluenesulfonylaminocarbonylamino) diphenylsulfone These compounds may be used alone or in combination of two or more thereof.

The leuco dye used as a dye precursor in the present invention can be selected from conventionally known ones such as triphenylmethane type, fluorane type and diphenylmethane type compounds. Examples of such dye precursors include 3-
(4-Diethylamino-2-ethoxyphenyl) -3-
(1-Ethyl-2-methylindol-3-yl) -4
-Azaphthalide, crystal violet lactone, 3
-(N-ethyl-N-isopentylamino) -6-methyl-7-anilinofluorane, 3-diethylamino-6
-Methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7- (o, p-dimethylanilino) fluorane, 3- (N-ethyl-N-p-toluidino)-
6-methyl-7-anilinofluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, 3-
(N-cyclohexyl-N-methylamino) -6-methyl-7-anilinofluorane, 3-diethylamino-7
-(O-chloroanilino) fluorane, 3-dibutylamino-7- (o-chloroanilino) fluorane, 3-diethylamino-7- (m-trifluoromethylanilino) fluorane, 3-diethylamino-6-methyl-7
-Chlorofluorane, 3-diethylamino-6-methylfluorane, and 3-cyclohexylamino-6-chlorofluorane, 3- (N-ethyl-N-hexylamino) -6-methyl-7- (p-chloroanilino ) One or more selected from fluoran and the like can be used.

In the thermosensitive color-developing layer of the thermosensitive recording material of the present invention, a fragrance having two or more functional groups represented by the following chemical formula (I) in one molecule is provided within a range that does not impair the desired effect. With the group compound, a conventionally used color developer consisting of phenols or organic acids can be used in combination. These conventional color developers include, for example, 2,2-bis (4-hydroxyphenyl) propane (bisphenol A), 1,1-bis (4-hydroxyphenyl) -1-phenylethane and 1,4-bis [ (1
-Methyl-1- (4'-hydroxyphenyl) ethyl]
Benzene, 1,3-bis [(1-methyl-1- (4'-
Hydroxyphenyl) ethyl] benzene, dihydroxydiphenyl ether (JP-A-1-180382), p
-Benzyl hydroxybenzoate (JP-A-52-1404
83), bisphenol S, 4-hydroxy-4'-
Isopropyloxydiphenyl sulfone (JP-A-60-
13852), 1,1-di (4-hydroxyphenyl) cyclohexane, 1,7-di (4-hydroxyphenylthio) -3,5-dioxaheptane (JP-A-59-59).
52694) and 3,3'-diallyl-4,4'-
Dihydroxydiphenyl sulfone (JP-A-60-208)
No. 286) and the like.

In the thermosensitive coloring layer of the thermosensitive recording medium of the present invention, a non-phenolic developer is represented by the above-mentioned chemical formula (I) in one molecule within a range that does not inhibit the desired effect. It can also be used together with an aromatic compound having two or more functional groups. Examples of these non-phenolic color developing agents include thiourea type color developing agents (JP-A-58-93190 and JP-A-58-2228).
87, JP-A-59-133096), a sulfonylurea type developer (JP-A-5-32061), and specific compounds include N, N'-bis (3-chlorophenyl) thiourea. , N, N'-bis (3-trifluoromethylphenyl) thiourea, N- (P-toluenesulfonyl) -N'-phenylurea, N- (P-toluenesulfonyl) -N '-(m-tolyl) Examples thereof include urea and N- (P-toluenesulfonyl) -N'-benzylurea.

Further, in the heat-sensitive recording material of the present invention, it is preferable to use a heat-fusible substance (so-called sensitizer) in the heat-sensitive color forming layer. As such a sensitizer, a heat-fusible organic compound having a melting point of 50 to 150 ° C. is generally used.
They are, for example, 1-hydroxy-2-naphthoic acid phenyl ester (JP-A-57-191089), p-
Benzylbiphenyl (JP-A-60-82382), benzylnaphthyl ether (JP-A-58-87094)
No.), dibenzyl terephthalate (JP-A-58-982).
85), benzyl p-benzyloxybenzoate (JP-A-57-201691), diphenyl carbonate, ditolyl carbonate (JP-A-58-136489), m-terphenyl (JP-A-57-89994), 1,2-bis (m-
Tolyloxy) ethane (JP-A-60-56588),
1,5-bis (p-methoxyphenoxy) -3-oxapentane (JP-A-62-181183), oxalic acid diesters (JP-A-64-1583), 1,4-bis (p-tolyloxy) Benzene (JP-A-2-15378
No. 3), diphenyl sulfone (Japanese Patent Publication No. 59-25673)
No.), p-toluenesulfonic acid phenyl ester (JP-A-59-73990), mesitylenesulfonic acid p-tolyl ester (JP-A-2-80285), 4,4'-.
Diallyloxydiphenyl sulfone, 4,4'-diisopentyloxydiphenyl sulfone, 4,4'-dimethoxydiphenyl sulfone (Japanese Patent Publication No. 2-9951), and 4,4'-di-n-pentyloxydiphenyl sulfone (special (Kaisho 60-47070) and the like.

The thermosensitive coloring layer of the thermosensitive recording medium of the present invention preferably contains an inorganic or organic pigment. Examples of these pigments include silica, clay, calcined clay, light calcium carbonate, heavy calcium carbonate, ultrafine calcium carbonate, magnesium carbonate, barium carbonate, calcium silicate, a complex salt of calcium carbonate and calcium hydroxide, and a surface-treated carbonate. Examples thereof include calcium and calcium silicate, and organic fine powders such as urea-formalin resin, styrene / methacrylic acid copolymer, and polystyrene resin.

The heat-sensitive color forming layer of the heat-sensitive recording material of the present invention may further contain a hindered phenol compound or an ultraviolet absorber. They are disclosed, for example, in JP-A-57-15139.
4, JP-A-58-160191, JP-A-58-69.
096, JP-A-59-2884, JP-A-59-95
190, JP-A-60-22288, JP-A-60-2
55485, JP-A-61-44686, JP-A-62.
It can be selected from the compounds described in JP-A-169683, JP-A-63-17081, JP-A-1-249385 and the like.

In the present invention, the content of the dye precursor in the thermosensitive color developing layer is generally 5 to 2 based on the dry weight of the thermosensitive color developing layer.
It is preferably 0% by weight, and the content of the aromatic compound having two or more functional groups represented by the above chemical formula (I) in one molecule contained in the color developer is generally 5%.
It is preferably ˜50% by weight.

When an organic or inorganic pigment is contained in the thermosensitive coloring layer of the thermosensitive recording medium of the present invention, its content is
It is preferably from 5 to 50% by weight based on the dry weight of the thermosensitive coloring layer. When the thermosensitive coloring layer contains an antioxidant or an ultraviolet absorber, its content is 1 of the dry weight of the thermosensitive coloring layer.
It is preferably from 10 to 10% by weight. When a conventionally known phenol-based or organic acid-based color developer is used in combination, the content is preferably 5 to 40% by weight based on the dry weight of the thermosensitive color developing layer, and the content of the sensitizer is 10 to 10. 40% by weight is preferred. When waxes are contained in the thermosensitive color developing layer, the content thereof is preferably 2 to 20% by weight, and the content of the binder is generally 5 to 20% by weight.

As the waxes, known waxes such as paraffin, amide wax, bisimide wax, and higher fatty acid metal salt can be used.

Regarding the binder, polyvinyl alcohols having various molecular weights, starch and its derivatives, cellulose derivatives such as methoxycellulose, carboxymethylcellulose, methylcellulose and ethylcellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylic acid amide / acrylic acid ester Polymer, acrylic acid amide / acrylic acid ester / methacrylic acid terpolymer, styrene / maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, gelatin, and water-soluble polymer material such as kaizen, and
Polyvinyl acetate, polyurethane, styrene / butadiene copolymer, polyacrylic acid, polyacrylic ester,
At least one of vinyl chloride / vinyl acetate copolymer, polybutyl methacrylate, ethylene / vinyl acetate copolymer, and styrene / butadiene / acrylic copolymer
A latex containing seeds can be used.

To produce the thermosensitive recording medium of the present invention, a thermosensitive coloring layer may be formed directly on at least one surface of the sheet-shaped substrate, or one layer may be provided between the sheet-shaped substrate and the thermosensitive coloring layer. The above undercoat layer may be formed, an overcoat layer may be formed on the thermosensitive coloring layer, or the above-mentioned undercoat layer may be formed on a sheet-shaped substrate, and the thermosensitive coloring layer may be formed thereon. May be formed, and an overcoat layer may be further formed thereon. If necessary, a coating layer such as a printing layer may be further provided on the overcoat layer, and a backcoat layer may be provided on the surface of the sheet-shaped substrate opposite to the surface coated with the thermosensitive color developing layer. The coating amount of the heat-sensitive coloring layer is preferably from 1 to 15 g / m ² in a state where the coating liquid layer is dried, particularly preferably 2 to 10 g / m ^2.

[0034]

EXAMPLES The present invention will be specifically described with reference to the following examples. Unless otherwise specified, "parts" and "%" in the examples mean "parts by weight" and "% by weight", respectively.

Example 1 A thermosensitive recording paper was prepared by the following operation. (1) Preparation Ingredients Amount of Dispersion A (parts) 3-dibutylamino-6-methyl-7 - using a sand grinder anilinofluoran 20 polyvinyl alcohol 10% solution 10 Water 70 The composition, average particle size Was 1 μm or less.

Diphenylmethane 10 diphenylsulfone 10 polyvinyl alcohol 10% solution 10 Water 70 The composition - [0036] (2) Preparation Ingredients Amount of Dispersion B (parts) of 4,4'-bis (p- toluenesulfonyl aminocarbonylamino) Using a sand grinder, it was pulverized until the average particle diameter became 1 μm or less.

(3) Coating of thermosensitive coloring layer To 60 parts of the above liquid A and 240 parts of the above liquid B, 29 parts of papermaking clay, 12 parts of 25% zinc stearate dispersion, and 10 parts of 10% aqueous polyvinyl alcohol solution. Were mixed and stirred to prepare a coating liquid. This coating solution was applied to one side of a high-quality paper having a basis weight of 50 g / m ² in which 4% by weight of calcium carbonate (trademark: LW600, manufactured by Yabashi Industry Co., Ltd.) was internally added, and a coating amount after drying was 6.5 g / m ² . And dried to form a thermosensitive coloring layer.

(4) Super calender treatment The thermal recording material obtained as described above was treated with a super calender, and the Beck smoothness of the surface was 800 to 800.
It was set to 1000 seconds.

(5) White paper part color density measurement, color development test, humidity resistance test and plasticizer test (a) White paper part color density measurement The color density of the unprinted white paper part of the above sample was measured with a Macbeth reflection densitometer RD-914. did. This is referred to as blank paper color density.

(I) Color development test For the above samples, a thermosensitive color development tester THP manufactured by Okura Electric Co., Ltd.
Using MD, printing voltage 21.7V, printing pulse 1.0ms
Printed under the conditions. The color density of the printed portion was measured in the same manner as above. This color density value is referred to as a color development sensitivity value.

(U) A portion of the printed sample was put at 40 ° C. and 90 ° C.
After being kept for 24 hours in the environmental tester set to%, the color density of the printed portion and the color density of the blank portion were measured in the same manner as above. These values will be referred to as the print density and the wet color development color density after the humidity resistance test.

(E) A part of the printed sample is a vinyl chloride film containing a plasticizer (in this test, manufactured by Mitsui Toatsu Chemicals,
(Trademark: MAT-W used) sandwiched between the two, further sandwiched between the glass plate and kept in an environment of 40 ℃ for 24 hours,
After that, the color density of the printed area and the color density of the blank area were measured in the same manner as above. These values are referred to as the print density after the plasticizer test and the plasticizer background color density. The test results are shown in Table 1.

Example 2 (1) Preparation of Pigment Undercoat Paper 1 part of a dispersant (Poise 520, manufactured by Kao Corporation) and 1.5 parts of carboxymethyl cellulose in terms of solid content were dissolved in 120 parts of water, and this solution was dissolved in the solution. 53 parts of a calcined clay pigment (trade name: Ansilex, manufactured by Engelhard) was added and sufficiently dispersed using a homogenizer. The dispersion thus obtained was mixed with 10 parts of a styrene-butadiene copolymer emulsion (solid content 50%), and the resulting coating liquid was added with 4% by weight of calcium carbonate to obtain a basis weight of 50 g / m ² . A pigment-undercoated paper was prepared by coating one surface of a high-quality paper so that the coating amount after drying was 8.0 g / m ² .

(2) Preparation and Test of Thermosensitive Coloring Layer The above pigment undercoat paper was coated with the same coating solution for thermosensitive coloring layer as in Example 1 so that the coating amount after drying was 5.0 g / m ^2. Was coated and dried to form a thermosensitive coloring layer. The obtained thermosensitive recording medium was subjected to the same super calendering treatment as in Example 1 and subjected to the same tests as in Example 1. The test results are shown in Table 1.

Example 3 A thermal recording paper was manufactured and tested in the same manner as in Example 1. However, in the coating of the thermosensitive coloring layer, magnesium carbonate (trademark: star magnesium carbonate, instead of high-quality paper having a basis weight of 50 g / m ² containing 4% by weight of calcium carbonate)
Kamishima Chemical Co., Ltd.) 4% by weight internally added basis weight 50 g / m ²
High quality paper was used. The test results are shown in Table 1.

Example 4 A thermal recording paper was manufactured and tested in the same manner as in Example 2. However, in the preparation and test of the thermosensitive color developing agent, 3-dibutylamino-6-methyl-7-
Instead of 20 parts of anilinofluorane, 20 parts of 3- (N-isopentyl-N-ethylamino) -6-methyl-7-anilinofluorane were used. The test results are shown in Table 1.

Comparative Example 1 A thermal recording paper was manufactured and tested in the same manner as in Example 1. However, in the coating of the thermosensitive coloring layer, 4% by weight of papermaking clay was internally added instead of high-quality paper having a basis weight of 50 g / m ² in which 4% by weight of calcium carbonate was internally added, and rosin sizing agent and sulphate were added. It was the internal sizing agent basis weight 50 g / m ²
High quality paper was used. The test results are shown in Table 1.

Comparative Example 2 A thermal recording paper was manufactured and tested in the same manner as in Example 2. However, in the preparation and test of the thermosensitive color developing material, 4% by weight of clay for papermaking was internally added instead of high-quality paper having a basis weight of 50 g / m ² in which 4% by weight of calcium carbonate was internally added, and rosin sizing agent and sulfate 50 basis weight with soil as internal sizing agent
A fine paper of g / m ² was used. The test results are shown in Table 1.

Comparative Example 3 A thermal recording paper was manufactured and tested in the same manner as in Example 4. However, in the preparation and test of the thermosensitive coloring layer, 4% by weight of clay for papermaking was internally added instead of high-quality paper having a basis weight of 50 g / m ² in which 4% by weight of calcium carbonate was internally added, and rosin sizing agent and sulfate 50 basis weight with soil as internal sizing agent
A fine paper of g / m ² was used. The test results are shown in Table 1.

Comparative Example 4 A thermal recording paper was manufactured and tested in the same manner as in Example 1. However, in coating the thermosensitive coloring layer, aluminum hydroxide (trademark: Heidilite, manufactured by Showa Denko) is used within 4% by weight instead of high-quality paper having a basis weight of 50 g / m ² with 4% by weight of calcium carbonate added. The added high-quality paper having a basis weight of 50 g / m ² was used. The test results are shown in Table 1.

[0051]

[Table 1]

As is clear from Table 1, in all of the examples of the present invention in which the sheet-like substrate of the thermosensitive recording medium contains an inorganic salt of an alkaline earth metal, the background color density after the humidity resistance test was low. In addition, good results were obtained that the background color density after the plasticizer test was low. However, in the comparative example in which the sheet-like substrate of the thermosensitive recording medium did not contain the inorganic salt of alkaline earth metal, the background color density after the humidity resistance test and the background color density after the plasticizer test showed high values. The effect of suppressing the background color density after the humidity resistance test and the background color density after the plasticizer test is peculiar to the specific alkaline earth metal salt used in the present invention, as in Comparative Example 4, It is clear from the fact that the addition of aluminum hydroxide having high alkalinity does not suppress the background color density after the moisture resistance test and the background color density after the plasticizer test.

[0053]

EFFECT OF THE INVENTION In the thermosensitive recording medium of the present invention, an image formed by heating is decolored with time, or at a relatively high temperature,
Very little color disappears in high humidity, and excellent chemical resistance such as oil resistance and plasticizer resistance. In addition, high temperature of white paper part (non-printed part), high humidity, or contact with plasticizer It has an excellent property that the background stain is extremely small, and is of extremely high practical value.

Claims (2)

[Claims] 1. A sheet-like substrate, a colorless or light-colored dye precursor which is formed on at least one surface of the sheet-like substrate, and a color which develops a color by reacting with the dye precursor under heating. And a thermosensitive coloring layer containing an agent, wherein the developer has the following chemical formula (I) in one molecule: (However, in the formula (I), X represents an oxygen or sulfur atom)
And an aromatic compound having at least two functional groups represented by, and the sheet-like substrate contains 1% or more by dry weight of the poorly water-soluble or water-insoluble inorganic acid salt of an alkaline earth metal. A heat-sensitive recording material characterized by the following. 2. The developer aromatic compound of formula (I)
The following general formula (II): (In the formula (II), R represents an unsubstituted or substituted benzene ring group, and Z represents a divalent alkylene group, oxygen atom, sulfur atom, sulfonyl group, or carbonyl group. 2. The sheet-like substrate is paper, and the alkaline earth metal inorganic acid salt is calcium carbonate.
The heat-sensitive recording material described in.