JPH0725163A - Production of 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, a specific aromatic compd. and an org. carboxylic acid salt of alkaline earth metal on a sheet like substrate. CONSTITUTION:A colorless or light-colored dye precursor, a coupler being an aromatic compd. having two or more functional groups represented by general formula (wherein X is an oxygen atom or a sulfur atom) and an org. carboxylic acid salt of alkaline earth metal are separately dispersed in an aq. soln. of a water-soluble polymer such as polyvinyl alcohol under stirring and the respective dispersions are mixed to prepare a coating soln. for a thermal color forming layer. This coating soln. is applied to a sheet like substrate such as paper, synthetic paper or a plastic film and dried to form the thermal color forming layer to obtain a thermal recording material. As a concrete example of the aromatic compd. represented by the general formula, there 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 decoloring under high humidity, and it has excellent oil resistance, plasticizer resistance, etc., that is, chemical resistance. ) 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,
It is widely used in printers for chemical 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.
-164579 and JP-A-62-169681). However, the obtained thermal recording material has its whiteness,
There are very few things that are well balanced in terms of recording sensitivity, print storability, and price. Therefore, development of new technology for preventing decolorization phenomenon 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. Technology (Japanese Patent Laid-Open No. 5-14
7357) was proposed. The heat-sensitive recording material thus obtained satisfied all the above conditions. However, since this developer compound is a completely new one that has never existed in the past, a new technical problem that has not been experienced with the conventionally used phenolic developer has been raised.

This is because when the coating liquid for forming a thermosensitive color developing layer containing the above-mentioned new color developer compound is stored for a long period of time, the whiteness of the coating liquid is gradually lowered, and therefore, the thermal sensitivity produced by using this coating liquid is decreased. This is a phenomenon in which the whiteness of the recording material becomes unsatisfactory. The above-mentioned problems do not occur if such a thermosensitive color forming layer-forming coating liquid is applied immediately after its preparation. However, in the case of industrially producing a heat-sensitive recording material, the coating solution may be stored for 1 day or more, for example, several days depending on the process, and therefore, the problem of the decrease in the whiteness of the coating solution over time may occur. , The solution was desired.

[0008]

DISCLOSURE OF THE INVENTION The present invention has no problem that the whiteness of a thermal recording material is lowered even when it is manufactured using a coating solution which has been stored for a long period of time. It is intended to provide a method for producing a heat-sensitive recording material having high properties, high whiteness, and excellent long-term storage properties such as oil resistance of a color image and plasticizer resistance.

[0009]

In order to obtain a heat-sensitive recording material having high whiteness and excellent storability of a color image, the present inventors have developed a dye precursor in which one molecule When an aromatic compound having two or more sulfonylamino (thio) carbonylamino groups is used for the above purpose, the above problems can be solved by adding an organic carboxylic acid salt of an alkaline earth metal to the coating liquid for forming a thermosensitive color developing layer. They found that they could be solved, and completed the present invention.

That is, the present invention provides a colorless or light-colored dye precursor on at least one surface of a sheet-like substrate and the following chemical formula (I) in one molecule:

[Chemical 3] (However, in the formula (I), X represents an oxygen or sulfur atom)
When a coating solution containing a developer containing an aromatic compound having two or more functional groups represented by the above is applied to form a thermosensitive color developing layer, the coating solution further contains the aromatic compound of the developer. It is characterized by containing 0.1% or more by dry weight of an organic carboxylate of an alkaline earth metal.

In the method for producing a thermosensitive recording medium of the present invention, the developer aromatic compound of the formula (I) is represented by the following general formula (I
I):

[Chemical 4] (In the formula (II), R represents an unsubstituted or substituted benzene ring, and Z represents a divalent alkylene group, oxygen atom, sulfur atom, sulfonyl group, or carbonyl group) It is preferable that the alkaline earth metal organic carboxylate selected from the aromatic compounds represented by is calcium oxalate. When the developer compound of the formula (II) is used, the storability of the color image is particularly good, and when calcium oxalate is used in the coating liquid, the effect balance becomes good, and the price and availability are high. It is also desirable in terms of ease of use.

[0012]

In the method of the present invention, the alkaline earth metal carboxylic acid salt added to the coating solution for forming the thermosensitive color developing layer is not particularly limited as long as it is white, but a compound that is difficult to dissolve in water is preferable. It produces a stable effect. Specific examples thereof include calcium stearate, magnesium stearate, barium stearate, monocarboxylic acid salts such as calcium oleate, calcium oxalate, magnesium oxalate, barium oxalate, calcium malonate, dicarboxylic acids such as calcium succinate. I can give you some salt. These carboxylic acid salts may be used alone or in a mixture of two or more thereof.

The organic carboxylic acid salt of an alkaline earth metal is added to the coating solution for forming the thermosensitive color developing layer, for example, when the dispersion of the specific aromatic compound of the present invention used as a developer is prepared. It may be added during the dispersion step, or after the dispersion of the developer compound, the alkaline earth metal salt may be added as a powder, solution or dispersion to the dispersion and used. Or, when the dye precursor dispersion or the like is mixed with the color developer dispersion to prepare a thermosensitive color developing layer coating solution, the alkaline earth metal salt is mixed as a powder, solution or dispersion. May be.

In the method of the present invention, the mechanism by which the addition of an organic carboxylic acid salt of an alkaline earth metal suppresses the deterioration of the whiteness of the coating solution over time is not clear. It is presumed that it is not a simple one, such as keeping the temperature at a constant level, but rather a gradual but specific interaction between the color developer and the alkaline earth metal carboxylate.

The amount of the alkaline earth metal carboxylate added is 0.1% or more, preferably 0.1 to 30% by weight, based on the weight of the aromatic compound of the developer in the coating liquid for the thermosensitive color developing layer. It is more preferably 1 to 10% by weight. If the amount added is less than 0.1% by weight, the effect of maintaining and improving whiteness may not be sufficient. Further, even if it is added in an amount of 30% by weight or more, the whiteness improving effect is saturated, and the sensitivity of the resulting heat-sensitive recording material may be rather deteriorated.

The thermosensitive coloring layer of the thermosensitive recording medium produced by the production method of the present invention comprises a dye precursor,
That is, it contains a leuco dye, an aromatic compound having two or more functional groups represented by the chemical formula (I) in one molecule, and an alkaline earth metal carboxylate. Further, the thermosensitive coloring layer has, if necessary, various inorganic or organic pigments and a melting point of 50 to 150 known as a sensitizer.
It may contain a heat-fusible aromatic compound at 0 ° C., a conventionally known phenol-based or organic acid-based developer, antioxidant, ultraviolet absorber, or wax. Further, the thermosensitive coloring layer contains a binder for fixing the above components to the support.

The aromatic compound having two or more functional groups represented by the above chemical formula (I) in one molecule which can be used in the present invention is described in, for example, JP-A-5-1473.
No. 57, and specific examples thereof are as follows. 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) diphenyl sulfone and the like. These compounds may be used alone or as a mixture of two or more thereof.

The leuco dye used as the dye precursor in the present invention can be selected from conventionally known ones such as triphenylmethane type compounds, fluorane type compounds, and diphenylmethane type compounds. For example, 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-6-methyl-7
(O-chloroanilino) fluorane, 3-diethylamino-7- (m-trifluoromethylanilino) fluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-6-methylfluorane,
One or more selected from 3-cyclohexylamino-6-chlorofluorane, 3- (N-ethyl-N-hexylamino) -6-methyl-7- (p-chloroanilino) fluorane and the like can be used. .

In the thermosensitive recording medium produced by the production method of the present invention, a color developer having two or more functional groups represented by the above chemical formula (I) in one molecule, within the range that does not impair the desired effect. A phenol compound or an organic acid compound conventionally used as a developer can be used together with the aromatic compound. These conventional color developers include, for example, 2,2-bis (4-hydroxyphenyl) propane (bisphenol A), 1,1-bis (4-hydroxyphenyl) -1-phenylethane,
1,4-bis [(1-methyl-1- (4'-hydroxyphenyl) ethyl] benzene, 1,3-bis [(1-methyl-1- (4'-hydroxyphenyl) ethyl] benzene, dihydroxydiphenyl ether (JP-A 1-1
80382), benzyl p-hydroxybenzoate (JP-A-52-140483), bisphenol S, 4-
Hydroxy-4'-isopropyloxydiphenyl sulfone (JP-A-60-13852), 1,1-di (4-
Hydroxyphenyl) cyclohexane, 1-di (4-hydroxyphenylthio) -3,5-dioxaheptane (JP-A-59-52694), and 3,3'-diallyl-4,4'-dihydroxydiphenylsulfone ( JP-A-60-208286) and the like.

Further, in the thermosensitive recording medium produced by the production method of the present invention, a non-phenolic color developing agent is represented by the above 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-58-2).
No. 22887, JP-A-59-133096), a sulfonylurea-based 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) Urea, N- (p
-Toluenesulfonyl) -N'-benzylurea and the like.

Further, in the heat-sensitive recording material produced by the production method of the present invention, it is preferable to use a heat-fusible substance (so-called sensitizer) together 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), dibenzyl terephthalate (special JP-A-58-98285), benzyl p-benzyloxybenzoate (JP-A-57-201691),
Diphenyl carbonate, ditolyl carbonate (JP-A-58-1364)
89), m-terphenyl (JP-A-57-89994).
No.), 1,2-bis (m-tolyloxy) ethane (JP-A-60-56588), 1,5-bis (p-methoxyphenoxy) -3-oxapentane (JP-A-62-18).
1183), oxalic acid diesters (JP-A-64-1)
583), 1,4-bis (p-tolyloxy) benzene (JP-A-2-153787), diphenyl sulfone (JP-B-59-25673), p-toluenesulfonic acid phenyl ester (JP-A-59-73990). ), Mesitylenesulfonic acid p-tolyl ester (JP-A-2-8)
No. 0285), 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 (JP-A-60-4707)
No. 0) and the like are included.

The thermosensitive coloring layer formed by the production method of the present invention may contain a pigment, and examples of such a pigment include silica, clay, calcined clay, barium sulfate,
Light calcium carbonate, heavy calcium carbonate, ultrafine calcium carbonate, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, magnesium carbonate, aluminum silicate, talc, alkali-modified clay, surface-treated calcium carbonate, silica, etc. Inorganic pigments and organic fine powders such as urea-formalin resin, styrene / methacrylic acid copolymer, and polystyrene resin can be used.

The thermosensitive coloring layer produced by the production method of the present invention may further contain a hindered phenol compound or an ultraviolet absorber. They are, for example, JP-A-57-151394 and JP-A-58-160191.
JP-A-58-69096, JP-A-59-2884
JP-A-59-95190 and JP-A-60-2228.
No. 8, JP-A-60-255485, JP-A-61-44.
686, JP-A-62-169683, JP-A-63-
17081 and compounds disclosed in JP-A-1-249385 and the like.

The content of the above-mentioned dye precursor in the thermosensitive coloring layer is generally preferably 5 to 20% by weight based on the dry weight of the thermosensitive coloring layer, and two dyes represented by the above chemical formula (I) are contained in one molecule. Generally, the content of the aromatic compound having the above functional group is preferably 5 to 50% by weight. The amount of the alkaline earth metal carboxylate added is as described above.

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, its content is preferably 5 to 40% by weight based on the dry weight of the thermosensitive color developing layer, and when a sensitizer is used in combination, The content is preferably 10 to 40% by weight. 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 metal salt of higher fatty acid can be used.

Regarding the binder, polyvinyl alcohol 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 Polymers, acrylic acid amides / acrylic acid esters / methacrylic acid terpolymers, styrene / maleic anhydride copolymers alkaline salts, polyacrylamides, sodium alginates, gelatin, and water-soluble polymeric materials such as casein, 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.

The sheet-like substrate used in the production method of the present invention uses a rosin sizing agent, so-called acidic paper made with a sulfated earth, and an inorganic salt of an alkaline earth metal such as calcium carbonate as an internal pigment. The paper can be selected from papers made by papermaking, coated papers whose surface is coated with a pigment and / or latex, laminated papers, synthetic papers made of polyolefin resins, plastic films, and the like.

On at least one surface of such a sheet-like substrate, a coating solution containing a mixture of the above-mentioned required components is applied and dried to form a thermosensitive coloring layer, thereby producing a thermosensitive recording material. The coating amount of the thermosensitive coloring layer is 1 to 1 when the coating liquid layer is dried.
It is preferably 5 g / m ² and particularly preferably ² to 10 g / m ² .

In the thermosensitive recording medium produced by the production method of the present invention, a single or a plurality of coating layers can be formed as an undercoat layer between the thermosensitive coloring layer and the sheet-like substrate. Further, a coating layer such as a protective layer or a printing layer may be further formed on the thermosensitive coloring layer, or a backcoat layer may be formed on the side opposite to the surface coated with the thermosensitive coloring layer.

[0031]

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 procedure . (1) Preparation Component Amount of Dispersion A (dye precursor) (parts) 3-dibutylamino-6-methyl-7-anilinofluorane 20 polyvinyl alcohol 10% liquid 10 water 70 The above composition was used with a sand grinder. The powder was pulverized until the average particle diameter became 1 μm or less.

(2) Preparation Component Amount of Dispersion B (Developer) (Part) 4,4′-bis (p-toluenesulfonyl aminocarbonylamino) -diphenyl 10 diphenylsulfone 10 polyvinyl alcohol 10% liquid 10 water 70 The above composition was pulverized using a sand grinder until the average particle size became 1 μm or less.

(3) Preparation Component Amount of Dispersion C (Alkaline Earth Metal Carboxylate) (Part) Calcium Oxalate 13 Polyvinyl Alcohol 10% Liquid 13 Water 74 The above composition was used with a sand grinder to give an average particle size of It was pulverized until it became 5 μm or less.

(4) Formation of thermosensitive coloring layer In 60 parts of solution A, 240 parts of solution B, and 23 parts of solution C,
Clay pigment for papermaking 26 parts, 25% zinc stearate dispersion 12 parts, and 10% polyvinyl alcohol aqueous solution 8
0 part was mixed and stirred to prepare a thermosensitive color developing layer coating solution. At this time, using the coating solution for the thermosensitive color developing layer immediately after preparation and the coating solution left at room temperature for 3 days after preparation, one side of the base paper having a basis weight of 50 g / m ² has a coating amount after drying of 6.5 g / m ² respectively. The coating was dried so as to be m ^2, and a thermosensitive coloring layer was formed.

(5) Supercalender treatment The thermal recording material obtained as described above was treated with a supercalender and the surface smoothness was 800 to 100.
It was set to 0 seconds.

(6) Whiteness, color development test and oil resistance test (a) Whiteness The whiteness of the above thermal recording paper sample was measured using a Hunter whiteness meter (manufactured by Toyo Seiki Seisakusho).

(I) Color development test Further, among the above-mentioned samples, the thermal recording material produced by using the coating liquid for the thermosensitive color developing layer immediately after preparation was printed with a thermosensitive color development tester THPMD manufactured by Okura Electric Co., Ltd. at a printing voltage of 21. Printing was performed under the conditions of 7 V and a printing pulse of 1.0 ms. The color density of the printed portion was measured with a Macbeth reflection densitometer RD-914. This color density value is referred to as a color development sensitivity value.

(U) Printing Oil Resistance Test Next, this sample was immersed in a commercially available salad oil prepared at 20 ° C. for 24 hours, the surface was wiped, and the residual color density was measured in the same manner as above. This is referred to as the concentration value after the oil resistance test. The results of the above tests are shown in Table 1.

Example 2 (1) Preparation of Pigmented Undercoat Paper 85 parts of calcined clay (trademark: Ansilex) was added to 320 parts of water.
To 40 parts of a styrene-butadiene copolymer emulsion (solid content 50%), and
10% oxidized starch aqueous solution 50 parts were mixed, on one side of the resulting coating liquid having a basis weight of 48 g / m ² base paper, the coating amount after drying was coated so as to 8.0 g / m ² A pigment-undercoated paper was obtained.

(2) Formation of thermosensitive coloring layer and various tests Using the coating solution for the thermosensitive coloring layer immediately after preparation described in Example 1 and the coating solution left for 3 days at room temperature after preparation, the above pigment-undercoated paper was coated with The thermosensitive coloring layer was formed by coating and drying so that the coating amount after drying was 5.0 g / m ² . The heat-sensitive recording paper obtained was subjected to the calendar treatment described in Example 1 and subjected to each test. The test results are shown in Table 1.

Example 3 (1) Preparation of Pigmented Undercoat Paper 76 parts of calcined clay (trademark: Ansilex, manufactured by Engelhard) and 9 parts of light calcium carbonate (trademark: Brilliant, manufactured by Shiraishi Kogyo) were added to 320 parts of water. The dispersion was dispersed, and 40 parts of a styrene-butadiene copolymer emulsion (solid content 50%) and 50 parts of a 10% oxidized starch aqueous solution were mixed to prepare a coating liquid. This coating solution on one side of base paper having a basis weight 48 g / m ^2, the coating amount after drying was coated so as to 8.0 g / m ^2, to obtain a pigment undercoat paper.

(2) Formation of thermosensitive coloring layer and various tests In 60 parts of solution A, 240 parts of solution B, and 7 parts of solution C described in Example 1, 28 parts of a clay pigment for papermaking, 25% zinc stearate dispersion liquid 12 parts and 80 parts of 10% polyvinyl alcohol aqueous solution were mixed and stirred to obtain a thermosensitive color developing layer coating solution. At this time, the thermosensitive color developing layer coating solution immediately after the production and after the preparation 3
Using the coating liquid left at room temperature for a day, the coating amount after drying on the surface of the above-mentioned pigment-undercoated paper was 5.0 g / m ^{2 respectively.}
Was coated and dried to form a thermosensitive coloring layer. The heat-sensitive recording material thus obtained was subjected to the same calendering treatment as in Example 1 and subjected to each test. The test results are shown in Table 1.

Example 4 (1) Preparation Component Amount of Dispersion D (parts) Calcium stearate 13 Polyvinyl alcohol 10% liquid 13 Water 74 The above composition was pulverized using a sand grinder until the average particle size became 5 μm or less. .

(2) Formation of Thermosensitive Coloring Layer In 60 parts of solution A and 240 parts of solution B described in Example 1,
8 parts of the above dispersion D, 28 parts of the clay pigment for papermaking, 12 parts of 25% zinc stearate dispersion, and 80 parts of 10% polyvinyl alcohol aqueous solution were mixed and stirred to obtain a coating liquid. In the same manner as in Example 1, the coating liquid immediately after preparation and the coating liquid left at room temperature for 3 days after preparation were used, and the basis weight was 50 g.
/ M ² on one side of the base paper, the coating amount after drying is 6.5 g /
A thermosensitive color forming layer was formed by coating and drying so as to give m ² .
This was subjected to the same calendar treatment as in Example 1 and subjected to each test. The test results are shown in Table 1.

[0046] Example 5 (1) using a sand grinder to Dispersion Preparation component of E (parts) magnesium oxalate 13 polyvinyl alcohol 10% solution 13 Water 74 The composition, milled to an average particle diameter becomes 5μm or less did.

(2) Formation of Thermosensitive Coloring Layer In 60 parts of solution A and 240 parts of solution B described in Example 1,
8 parts of the above dispersion E, 28 parts of clay pigment for papermaking, 12 parts of 25% zinc stearate dispersion, and 80 parts of 10% polyvinyl alcohol aqueous solution were mixed and stirred to obtain a coating liquid. In the same manner as in Example 1, the coating liquid immediately after preparation and the coating liquid left at room temperature for 3 days after preparation were used, and the basis weight was 50 g.
/ M ² on one side of the base paper, the coating amount after drying is 6.5 g /
A thermosensitive color forming layer was formed by coating and drying so as to give m ² .

(3) Formation of overcoat layer 5 parts of kaolinite clay dispersion (solid content concentration 60%),
35% 10% modified polyvinyl alcohol aqueous solution, 10%
22 parts of an aqueous casein solution, 1 part of 25% zinc stearate dispersion, 2 parts of dimethylol urea crosslinking agent and 35 parts of water were mixed and stirred to obtain a coating liquid. This coating solution was applied and dried on the thermosensitive color developing layer so that the coating amount after drying was 1.5 g / m ² to form an overcoat layer to obtain a thermosensitive recording material. Using the above thermosensitive recording medium, after the same super calender treatment as in Example 1, the same test as in Example 1 was performed. The test results are shown in Table 1.

Comparative Example 1 A thermosensitive recording paper was prepared in the same manner as in Example 1. However,
Calcium oxalate dispersion C was not added when preparing the coating solution for the thermosensitive color developing layer. The test results are shown in Table 1.

Comparative Example 2 In the same manner as in Example 2, a thermal recording paper was prepared. However,
The coating liquid prepared in Comparative Example 1 was used as the coating liquid for the thermosensitive color developing layer. The test results are shown in Table 1.

Comparative Example 3 A thermal recording paper was prepared in the same manner as in Example 1. However, the calcium oxalate dispersion C was not added at the time of preparing the coating solution for the thermosensitive color developing layer, and instead the sodium stearate powder 3 was used.
Parts were added, and the mixture was thoroughly stirred and used. The test results are shown in Table 1.

[0052]

[Table 1]

As is clear from Table 1 above, in all of the examples of the method of the present invention in which the thermosensitive color developing layer contains a carboxylate of an alkaline earth metal, the thermosensitive coloring layer formed by using the coating solution stored for a long period of time was used. The decrease in whiteness of the recording material with time was small. On the other hand, in the comparative example in which the thermosensitive color developing layer did not contain a carboxylate of an alkaline earth metal, the whiteness of the thermosensitive recording medium formed using the coating liquid stored for a long period of time decreased with time. The fact that this effect is unique to the alkaline earth metal carboxylate alone means that in Comparative Example 3, even if basic sodium stearate is added to the thermosensitive coloring layer, the effect of suppressing the decrease in whiteness is It is clear from the fact that it did not develop, and rather the whiteness decreased due to it.

[0054]

The thermal recording material produced by the production method of the present invention is
In the thermosensitive coloring layer, an aromatic compound having two or more functional groups represented by the above-mentioned chemical formula (I) in one molecule is contained as a developer, and the thermosensitive coloring layer is formed. Since the coating liquid further contains an alkaline earth metal carboxylate, the whiteness is high even in the thermosensitive color forming layer formed by using the coating liquid stored for a long period of time, and the obtained recorded image is stored. It is highly stable and has extremely high practical value.

Front Page Continuation (72) Inventor Yukio Ochiai 1850 Todaka, Nichinan City, Miyazaki Prefecture Oji Paper Co., Ltd. Nichinan Mill

Claims (2)

[Claims] 1. A colorless or light-colored dye precursor is provided on at least one surface of a sheet-like substrate and the following chemical formula (I): (However, in the formula (I), X represents an oxygen or sulfur atom)
When a coating liquid containing a developer containing an aromatic compound having two or more functional groups represented by the above is applied to form a heat-sensitive color-developing layer, the coating liquid is further mixed with the developer aromatic compound. A method for producing a heat-sensitive recording material, characterized by containing 0.1% or more by dry weight of the organic carboxylic acid salt of an alkaline earth metal. 2. The developer aromatic compound of formula (I)
The following general (II) (In the formula (II), R represents an unsubstituted or substituted benzene ring group, Z is a divalent alkyl group,
The heat-sensitive material according to claim 1, which is selected from an aromatic compound represented by an oxygen atom, a sulfur atom, a sulfonyl group, or a carbonyl group, and wherein the alkaline earth metal organic carboxylate is calcium oxalate. Recording body manufacturing method.