JP2002120462A - Heat-sensitive recording material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-sensitive recording material such as a heat-sensitive recording paper sheet which is excellent in thermal responding property, preservation stability of an image, and in particular, in plasticizer resistance. SOLUTION: For this heat-sensitive recording material, a heat-sensitive coloring layer containing a leuco dye which is colorless or slightly tinted at a normal temperature, and an organic acidic substance which reacts with the leuco dye by heating and develops a color, is provided on a supporting body. In such a heat-sensitive recording material, a mixture of 4,4'-dihydroxy diphenylsulfone containing 50 to 95 wt.% of 4,4'-dihydroxy diphenylsulfone, and 2,4'-dihydroxy diphenylsulfone is used as the organic acidic substance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive recording material, and more particularly, to a heat-sensitive recording material having excellent heat responsiveness, storage stability of an image, and particularly excellent plasticizer resistance.

[0002]

2. Description of the Related Art A thermosensitive recording material comprising a support and a thermosensitive coloring layer containing a colorless or pale-colored leuco dye at room temperature and an organic acid substance which reacts with the leuco dye by heating to form a color is provided by a computer. It is used in many fields such as printers such as outputs and calculators, recorders for various measuring instruments, facsimile machines, automatic ticketing machines, thermocopiers, and labels.

[0003] As the application of the heat-sensitive recording material expands, there is a demand for higher performance and higher price. There have been many proposals for new leuco dyes, organic acidic substances or sensitizers in order to improve the performance, but it is difficult to sufficiently satisfy various requirements.

[0004] Among organic acidic substances, 4,4'-dihydroxydiphenylsulfone is known to have relatively excellent plasticizer resistance.
JP, JP-A-58-119893, JP-A-61-11893
JP-A-160292 proposes that the use of 4,4′-dihydroxydiphenylsulfone as an organic acidic substance improves the stability of a color image to a plasticizer or the stability of a background portion. However, 4,4'-dihydroxydiphenyl sulfone has a high melting point and is inferior in compatibility with general-purpose dyes and general-purpose sensitizers.

In order to compensate for such a drawback, Japanese Patent Laid-Open No.
No. 2406 proposes using 4,4′-dihydroxydiphenyl sulfone as an organic acidic substance and acylacetic acid anilides as a sensitizer. 4,4 '
-When dihydroxydiphenylsulfone and acylacetic acid anilide are used in combination, a heat-sensitive recording material having excellent coloring sensitivity and plasticizer resistance can be provided, but on the other hand, the heat resistance of the background tends to decrease.

On the other hand, it is known that 2,4'-dihydroxydiphenylsulfone has a higher color density than 4,4'-dihydroxydiphenylsulfone.
For example, JP-A-63-3991, JP-B-7-12
No. 749 proposes that the coloring density is improved by using 2,4′-dihydroxydiphenyl sulfone as an organic acidic substance. However, when 2,4'-dihydroxydiphenylsulfone was used, there was a drawback that the plasticizer resistance was significantly reduced as compared with the case where 4,4'-dihydroxydiphenylsulfone was used.

Also, Japanese Patent No. 2745172 discloses that
2,4'-dihydroxydiphenyl sulfone and 4,4 '
A mixture of dihydroxydiphenylsulfones in which 2,4′-dihydroxydiphenylsulfone contains 7
It has been proposed to use those present as 0-95% by weight as organic acidic substances. When the mixture at this mixing ratio is used as the organic acidic substance, the color density is further improved and the 2,4'- Dihydroxydiphenyl sulfone, 4,
4'-dihydroxydiphenyl sulfone had the advantage of not impairing the high weather resistance, particularly the light resistance. However, according to the study of the present inventors, it was not sufficiently satisfactory from the viewpoint of plasticizer resistance.

[Problems to be solved by the invention]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a heat-sensitive recording material having excellent heat responsiveness, storage stability of an image, and especially excellent plasticizer resistance. It is in.

[Means for Solving the Problems]

That is, the present invention provides a heat-sensitive recording material comprising a support and a thermosensitive coloring layer containing a colorless or pale-colored leuco dye at room temperature and an organic acidic substance which reacts with the leuco dye to form a color when heated. Wherein 4,4'-dihydroxydiphenylsulfone and 2,4'-dihydroxydiphenylsulfone are used as organic acidic substances in 50 to 9
A thermosensitive recording material characterized by being mixed and used in a weight ratio of 5: 5 to 50.

Hereinafter, the present invention will be described in detail. In the present invention, the leuco dye used as a color former is a substance which is colorless or pale at room temperature and which reacts with an organic acidic substance by heating to develop a color. Such leuco dyes include, for example, 7'-anilino-3 '-(dibutylamino)-
6'-methylfluoran, 7'-anilino-3 '-(dipentylamino) -6'-methylfluoran, 3,3-
Bis (p-dimethylaminophenyl) -6-dimethylaminophthalide, 3- (p-dimethylaminophenyl)-
3- (2-phenyl-3-indolyl) phthalide, 3-
(P-dimethylaminophenyl) -3- (1,2-dimethyl-3-indolyl) phthalide, 3,3-bis (9-
Ethyl-3-carbazolyl) -5-dimethylaminophthalide, 3,3-bis (2-phenyl-3-indolyl)
Triallylmethane dyes such as -5-dimethylaminophthalide, and diphenylmethane dyes such as 4,4'-bisdimethylaminobenzhydridobenzyl ether, and thiazine dyes such as benzoylleucomethylene blue, for example, And spiro dyes such as 3-methylspirodinaphthopyran, fluoran dyes and other dyes such as leuco auramine dyes, indoline dyes and indigo dyes. These leuco dyes may be used alone or in combination.
More than one species can be used.

In the present invention, as the organic acidic substance,
4,4'-dihydroxydiphenyl sulfone and 2,4 '
A mixture of dihydroxydiphenylsulfone.
4,4'-dihydroxydiphenyl sulfone and 2,
The use ratio of 4′-dihydroxydiphenyl sulfone is as follows:
The former is 50 to 95% by weight, and the latter is 5 to 50% by weight.
It is. If emphasis is placed on the balance between color development sensitivity and storage stability, 4,4'-dihydroxydiphenyl sulfone / 2,2
When the weight ratio of 4'-dihydroxydiphenyl sulfone is 70,
The range of / 30 to 50/50 is preferred. This 4,4'-
Dihydroxydiphenyl sulfone and 2,4′-dihydroxydiphenyl sulfone may be mixed in advance,
They may be mixed during the production of the heat-sensitive recording material. When dihydroxydiphenylsulfone is produced as a mixture of isomers, it is also advantageous to use a mixture containing 4,4′-dihydroxydiphenylsulfone and 2,4′-dihydroxydiphenylsulfone in a predetermined ratio. The total amount of diphenyl sulfone used varies depending on the type of leuco dye to be used, but usually 1 to 6 parts by weight, preferably 1.5 to 5 parts by weight, per 1 part by weight of the leuco dye.
2.5 parts by weight.

Further, 4,4'-dihydroxydiphenylsulfone and 2,4'-dihydroxydiphenylsulfone used as organic acidic substances in the present invention may be used as a mixture with a small amount of other organic acidic substances. Specific examples of such other organic acidic substances include, for example, p-octylphenol, p-tert-butylphenol, p-phenylphenol, p-hydroxyacetophenone, α-naphthol, p-tert-octylcatechol, 2,2′- Dihydroxybiphenyl, 1,1-bis (p-hydroxyphenyl) butane, 2,2-bis (4-hydroxyphenyl) propane, 2,2-bis- (3-methyl-4-hydroxyphenyl) propane, 2,2 -Bis (3,5-
Dimethyl-4-hydroxyphenyl) propane, 2,2
-Bis (3,5-dichloro-4-hydroxyphenyl)
Propane, bis (3-allyl-4-hydroxyphenyl) sulfone, bis (3,4-dihydroxyphenyl)
Sulfone, 1,1-bis (4-hydroxyphenyl) cyclohexane, bis (4-hydroxyphenyl ether) bis {2- (4-hydroxyphenylthio) ethoxy} methane, 4- (4-isopropoxybenzenesulfonyl) phenol, Dimethyl 4-nidroxyphthalate,
Phenols such as butyl bis (4-hydroxyphenyl) acetate, benzyl p-hydroxybenzoate, and 3,5-ditert-butylsalicylic acid; organic carboxylic acids such as benzoic acid, phthalic acid and salicylic acid; and other dihydroxydiphenylsulfone isomers And metal salts such as zinc salicylate. The amount of such other organic acidic substance used may be less than 50%, preferably less than 10% of the organic acidic substance.

Further, in the present invention, a sensitizer can be used in the heat-sensitive coloring layer as long as the desired effect is not impaired. As the sensitizer, a heat-soluble organic compound having a melting point of 50 to 150 ° C. is used. Specific examples of such a sensitizer include stearic acid amide, palmitic acid amide, linoleic acid amide, and stearic acid anilide. Nitrogen compound, 4-hydroxybenzoic acid benzyl ester,
4-benzyloxybenzoic acid benzyl ester, 2-naphthoic acid phenyl ester, 2-naphthoic acid benzyl ester, 1-hydroxy-2-naphthoic acid phenyl ester, oxalic acid dibenzyl ester, oxalic acid di (4-
Ester compounds such as methylbenzyl ester), terephthalic acid dibenzyl ester, isophthalic acid-n-butyl ester, and p-toluenesulfonic acid phenyl ester;
4-benzylbiphenyl, m-terphenyl, 4-acetylbiphenyl, fluorene, fluoranthene, 2,6
-Diisopropylnaphthalene, 3-benzylacenaphthene, 1,2-bis- (3,4-dimethylphenyl) ethane, 1,2-bis (2,4-dimethylphenyl) ethane, 1,2-bis (2,4 , 5-trimethylphenyl)
Aromatic compounds such as ethane, 2-benzyloxynaphthalene, 1,4-diethoxynaphthalene, 1,2-diphenoxyethane, 1,2-di (m-tolyloxy) ethane,
1,2-diphenoxybenzene, 1,4-diphenoxybenzene, 4- (4′-methylphenoxy) biphenyl, diphenylsulfone, 4-methyldiphenylsulfone, 4,4′-diisopropoxydiphenylsulfone,
Examples thereof include ether compounds such as 4,4'-diphenoxydiphenylthioether, benzyl-4-methylthiophenylether, and 1,2-bis (phenoxymethyl) benzene, and sulfur-containing compounds. Preferred sensitizers include benzyl 4-benzyloxybenzoate,
Ester compounds such as 2-naphthoic acid benzyl ester, oxalic acid dibenzyl ester, terephthalic acid dibenzyl ester, 4-acetylbiphenyl, 1,2-bis-
Aromatic compounds such as (3,4-dimethylphenyl) ethane and 1,2-bis (2,4-dimethylphenyl) ethane; ether compounds such as 1,2-diphenoxyethane;
Sulfone compounds such as diphenylsulfone and 4-methyldiphenylsulfone are exemplified. More preferably, 4
-Acetyl biphenyl, oxalic acid dibenzyl esters or diphenyl sulfone.

The amount of the sensitizer to be used varies depending on the type of the leuco dye and the organic acidic substance used, but is usually 1 to 6 parts by weight, preferably 1.5 to 2 parts by weight, per 1 part by weight of the leuco dye. 0.5 parts by weight.

When high image storability is required, it is desirable to provide an overcoat layer in addition to the heat-sensitive recording material of the present invention.

When a higher image storability is required, it is desirable to use a known storage stabilizer together with the heat-sensitive recording material of the present invention, if necessary. Examples of the storage stabilizer include tris (2,6-dimethyl-4-tert-butyl-3-hydroxybenzyl) isocyanurate,
Tris (3,5-ditert-butyl-4-hydroxybenzyl) isocyanurate, tris (2- (3- (3,5-
Di-tert-butyl-4-hydroxyphenyl) propionyloxy) ethyl) isocyanurate, 1,3,5-tris (3,5-dimethyl-4-hydroxybenzyl) -2,
4,6-trimethylbenzene, 1,1,3-tris (2
-Methyl-4-hydroxy-5-tert-butylphenyl)
Butane, 1,1,3-tris (2-methyl-4-hydroxy-5-cyclohexylphenyl) butane, 4,4 ′
-Butylidenebis (2-tert-butyl-5-methylphenol), 4,4'-thiobis (2-tert-butyl-5-methylphenol), 2,2'-methylenebis (6-tert-butyl-4-methylphenol) Hindered phenol compounds such as phenol), 4-benzyloxy-4 ′-(2-methylglycidyloxy) diphenylsulfone, 4,4′-
Epoxy compounds such as diglycidyloxydiphenylsulfone, and sodium-2,2'-methylenebis (4,6-di-tert-butylphenyl) phosphate are also included. These storage stabilizers are usually used in an amount of 0.1 to 10 parts by weight based on 1 part by weight of the dye.

When long-term light fastness is required, the heat-sensitive recording material of the present invention may be used in the heat-sensitive coloring layer and / or in the heat-sensitive coloring layer.
Alternatively, it is preferable to add an ultraviolet absorber to the overcoat layer. As the ultraviolet absorber, for example,
2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-
Octoxybenzophenone, 2,2'-dihydroxy-
2-hydroxybenzophenones such as 4-methoxybenzophenone, 2- (2-hydroxy-5-methylphenyl) benzotriazole, 2- (2-hydroxy-5
-Tert-octylphenyl) benzotriazole, 2-
(2-hydroxy-3,5-ditert-butylphenyl)-
5-chlorobenzotriazole, 2- (2-hydroxy3,5-dicumylphenyl) benzotriazole, 2,
2'-methylenebis (4-tert-octyl-6-benzotriazolyl) phenol, 2- (2-hydroxy-3-
2- (2) such as polyethylene glycol ester of tert-butyl-5-carboxyphenyl) benzotriazole
-Hydroxyphenyl) benzotriazoles, phenyl salicylate, resorcinol monobenzoate,
2,4-di-tert-butylphenyl-3,5-di-tert-butyl-4-hydroxybenzoate, hexadecyl-3,5
Benzoates such as di-tert-butyl-4-hydroxybenzoate, substituted oxanilides such as 2-ethyl-2′-ethoxyoxanilide, 2-ethoxy-4′-dodecyloxanilide, ethyl-α-cyano- cyanoacrylates such as β, β-diphenylacrylate, methyl-2-cyano-3-methyl-3- (p-methoxyphenyl) acrylate, 2- (2-hydroxy-4-octoxyphenyl) -s-triazine, 2- (2-hydroxy-4-methoxyphenyl) -4,6-diphenyl-s-triazine, 2- (2-hydroxy-4-propoxy-5-methylphenyl) -4,6-bis (2,4-
And triazole triazines such as (di-tert-butylphenyl) -s-triazine.

Further, various additives can be added to the heat-sensitive recording material of the present invention depending on the use and the like. Examples of such additives include binders for fixing the leuco dye dispersed on the fine particles and the organic acidic substance in a state of being separated from each other, for example, polyvinyl alcohol (PVA), latex, methylcellulose, carboxymethylcellulose, polyacrylic acid Casein, gelatin, starch or derivatives thereof, and white pigments added for the purpose of whiteness of the thermosensitive coloring layer, slipperiness of a writing instrument, sticking, for example, calcium carbonate, kaolin, clay, talc, titanium oxide, etc. Can be These additives may be mixed or separately applied to a support such as paper or film to form a thermosensitive coloring layer.

[0019]

The present invention will be specifically described below based on examples and comparative examples. Example 1 (1) Preparation of Solution A 20 g of 7'-anilino-3 '-(dibutylamino) -6'-methylfluorane as a leuco dye and 100 g of a 10% aqueous solution of polyvinyl alcohol were sufficiently ground by a ball mill, and the average Solution A in which powder having a particle size of 0.8 μm was suspended was prepared. (2) Preparation of Solution B 20 g of 4,4'-dihydroxydiphenylsulfone and 100 g of a 10% aqueous solution of polyvinyl alcohol as organic acidic substances were sufficiently ground with a ball mill to obtain an average particle size of 0.1 g.
Liquid B in which 8 μm powder was suspended was prepared. (3) Preparation of Solution C 20 g of 2,4′-dihydroxydiphenylsulfone and 100 g of a 10% aqueous solution of polyvinyl alcohol as an organic acidic substance were sufficiently ground with a ball mill to obtain an average particle size of 0.1 g.
Liquid C in which 8 μm powder was suspended was prepared. (4) Preparation of solution D As a sensitizer, 20 g of parabenzylbiphenyl and 10 g of
100 g of a polyvinyl alcohol aqueous solution was sufficiently ground by a ball mill, and a powder having an average particle diameter of 0.8 μm was suspended therein.
The liquid was adjusted. (5) Preparation of thermosensitive recording paper The above dispersions A, B and C were mixed at a weight ratio of 1: 1.4: 0.6, and 200 g of the mixture was mixed with 50 g of calcium carbonate.
g was sufficiently dispersed to form a coating solution. The coating solution was applied on a base paper and dried to prepare a thermosensitive recording paper having an applied amount of 6 g / m ² after drying.

(6) Color Test A dynamic color test (24 V, 1.0 m) was performed on the heat-sensitive recording paper thus prepared, and the color density of the printed portion and the background were measured. The dynamic color development test uses a printing tester (manufactured by Okura Electric Co., Ltd.) and measures the color density using a Macbeth reflection densitometer R
The measurement was performed using D-914. (7) Humidity resistance test The thermosensitive recording paper subjected to the dynamic color development test was placed in a thermo-hygrostat (50).
At 90 ° C. and a relative humidity of 90%) for 24 hours, and then measure the color density of the printed portion and the background using a Macbeth reflection densitometer RD-914.
The measurement was performed by using (8) Plasticizer resistance test A vinyl chloride wrap is brought into close contact with the entire printing surface of the thermosensitive recording paper on which the dynamic coloring test was performed. The test thermosensitive recording paper was stored in a dryer (40 ° C.) for 24 hours, and then the color density of the printed portion and the background was measured using a Macbeth reflection densitometer RD-914. (9) Heat resistance test The thermosensitive recording paper subjected to the dynamic color development test was dried in a constant temperature drier (80
C.) for 24 hours, and then measuring the color density of the printed portion and the background using a Macbeth reflection densitometer RD-914. Table 1 shows the results of the dynamic color test, the humidity resistance test, the plasticizer resistance test, and the heat resistance test.

Example 2 In preparing the thermal recording paper of Example 1, the dispersions A, B and C were mixed in a weight ratio of 1: 1.4: 0.6 instead of 1: 1.4: 0.6.
A heat-sensitive recording paper was prepared in exactly the same manner as in Example 1 except for mixing at 1.2: 0.8, and the test was performed in the same manner as in Example 1. Table 1 shows the results.

Example 3 In preparing the thermosensitive recording paper of Example 1, the dispersions A, B and C were mixed at a weight ratio of 1: 1.4: 0.6 instead of 1: 1.4: 0.6.
A thermosensitive recording paper was prepared in exactly the same manner as in Example 1 except that the mixture was mixed at 1: 1, and the test was performed in the same manner as in Example 1. Table 1 shows the results.

Example 4 In preparing the thermosensitive recording paper of Example 2, instead of mixing the dispersions A, B and C in a weight ratio of 1: 1.2: 0.8, the dispersions A, B, C and A thermosensitive recording paper was prepared in exactly the same manner as in Example 2 except that D was mixed at a weight ratio of 1: 1.2: 0.8: 2, and a test was performed in the same manner as in Example 2. Table 1 shows the results.

Example 5 A heat-sensitive recording paper was prepared in exactly the same manner as in Example 4 except that m-terphenyl was used in place of parabenzylbiphenyl when preparing the solution D in Example 4. The test was performed as in the case. Table 1 shows the results.

Example 6 Example 4 was prepared in the same manner as in Example 4, except that 4-acetylbiphenyl was used instead of parabenzylbiphenyl.
A thermosensitive recording paper was prepared in exactly the same manner as described above, and a test was performed in the same manner as in Example 4. Table 1 shows the results.

Example 7 A thermosensitive recording paper was prepared in exactly the same manner as in Example 4 except that benzyloxynaphthalene was used in place of parabenzylbiphenyl when preparing the solution D in Example 4. The test was performed in the same manner as in the above. Table 1 shows the results.

Example 8 A thermosensitive recording paper was prepared in exactly the same manner as in Example 4 except that in preparing the solution D in Example 4, di (4-methylbenzyl ester) oxalate was used instead of parabenzylbiphenyl. The test was performed in the same manner as in Example 4. Table 1 shows the results
Shown in

Example 9 A heat-sensitive recording paper was prepared in exactly the same manner as in Example 4 except that diphenyl sulfone was used in place of parabenzylbiphenyl in the preparation of the solution D in Example 4. The test was performed similarly. Table 1 shows the results.

Example 10 A thermosensitive recording paper was prepared in exactly the same manner as in Example 4 except that stearic amide was used in place of parabenzylbiphenyl in the preparation of solution D in Example 4. The test was performed in the same manner as in the above. Table 1 shows the results.

Comparative Example 1 In preparing the thermosensitive recording paper of Example 1, instead of mixing the dispersions A, B and C in a weight ratio of 1: 1.4: 0.6, the dispersions A and B were mixed in a ratio of 1: 1.4. A thermosensitive recording paper was prepared in exactly the same manner as in Example 1 except that the mixture was mixed at a weight ratio of 2, and the test was performed in the same manner as in Example 1. Table 1 shows the results.

Comparative Example 2 In preparing the thermosensitive recording paper of Example 1, instead of mixing the dispersions A, B and C at a weight ratio of 1: 1.4: 0.6, the dispersions A and C were mixed at a ratio of 1: 1.4. A thermosensitive recording paper was prepared in exactly the same manner as in Example 1 except that the mixture was mixed at a weight ratio of 2, and the test was performed in the same manner as in Example 1. Table 1 shows the results.

Comparative Example 3 In preparing the thermosensitive recording paper of Example 1, instead of mixing the dispersions A, B and C in a weight ratio of 1: 1.4: 0.6, the dispersions A, B and C were mixed. A heat-sensitive recording paper was prepared in exactly the same manner as in Example 1 except that the mixture was mixed at a weight ratio of 1: 0.6: 1.4, and a test was performed in the same manner as in Example 1. Table 1 shows the results
Shown in

Comparative Example 4 In preparing the thermosensitive recording paper of Example 1, instead of mixing the dispersions A, B and C in a weight ratio of 1: 1.4: 0.6, the dispersions A, B and C were mixed. A thermosensitive recording paper was prepared in exactly the same manner as in Example 1 except that the mixture was mixed at a weight ratio of 1: 0.4: 1.6, and a test was conducted in the same manner as in Example 1. Table 1 shows the results
Shown in

[0034]

[Table 1]

[0035]

According to the present invention, the mixture of 4,4'-dihydroxydiphenylsulfone and 2,4'-dihydroxydiphenylsulfone mixed at a predetermined ratio, which is used as the organic acidic substance, is formed by the interaction between the two. A heat-sensitive recording material having excellent heat responsiveness, storage stability of an image, and especially excellent plasticizer resistance as compared with the case where used alone is provided.

Claims (2)

[Claims] 1. A thermosensitive recording material comprising a support having thereon a thermosensitive coloring layer containing a colorless or pale-colored leuco dye at room temperature and an organic acid substance capable of reacting with the leuco dye to form a color when heated. As a substance, 4,4'-
A heat-sensitive recording material comprising a mixture of dihydroxydiphenylsulfone and 2,4'-dihydroxydiphenylsulfone in a weight ratio of 50 to 95: 5 to 50. 2. The heat-sensitive recording material according to claim 1, wherein the weight ratio of 4,4′-dihydroxydiphenylsulfone / 2,4′-dihydroxydiphenylsulfone is 70/30 to 50/50.