JPH05309949A - Thermal recording material - Google Patents

Abstract

PURPOSE:To obtain a thermal recording material generating no background fog at the time of high temp. by preventing the formation of a hydrate in the wet dispersion of 4-hydroxy-4'-isopropoxydiphenylsulfone used as a developer. CONSTITUTION:4-hydroxy-4'-isopropoxydiphenylsUlfone finely pulverized at 50 deg.C or higher by wet dispersion and containing no hydrate is used as a developer and a thermal color forming layer containing said developer and a dye precursor is formed on a sheet like support.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermosensitive recording medium, and more particularly to a thermosensitive recording medium excellent in whiteness and storability of recorded images.

[0002]

2. Description of the Related Art A heat-sensitive recording material for recording a color image by utilizing a heat-coloring reaction between a colorless or light-colored leuco dye and a phenol or an organic acid is disclosed in JP-B-43-4160.
No. 45-14039 and 48-2
It is disclosed in Japanese Patent No. 7736 and is widely put into practical use. In recent years, such a thermosensitive recording medium forms a colored image by simply heating, a recording apparatus can be made relatively compact, and maintenance is easy, and no noise is generated. Due to such advantages as fax, computer output machine, label,
Widely used as various information recording materials such as automatic ticket vending machines, CD / ATM, order output machines for family restaurants, data output machines for scientific research equipment, and printers.

With the expansion of the range of application of such a thermal recording material, the thermal recording material may come into contact with cosmetic cream or oil or a polymer sheet containing a plasticizer, or may be exposed to severe conditions such as high temperature and high humidity. Opportunities to get down are increasing. For example, 2,2- which has been conventionally used as a developer
In a heat-sensitive recording material using bis (4-hydroxyphenyl) propane (bisphenol A) or benzyl p-hydroxybenzoate (JP-A-52-140483), when a color image is placed under high temperature and high humidity. In addition, the color density of the image portion is lowered, and when it is brought into contact with a plasticizer or oil, the image is erased to an unreadable level. On the other hand, under these conditions, a phenomenon in which the white paper portion is colored to cause so-called background fog is also recognized.

As a developer capable of solving the above problems,
Many uses of hydroxydiphenyl sulfone derivatives have been proposed. Among them, 4-hydroxy-4'-isopropoxydiphenyl sulfone is known as a color developer having advantages such as high whiteness and sensitivity of the obtained thermosensitive coloring layer and excellent preservability of the obtained colored image. Has been.

Generally, dyes, color developers, sensitizers and the like used in a thermal recording material are used by making them into fine particles by wet dispersion, but recently, due to a demand for high sensitivity of the thermal recording material, particles are recently used. There is a tendency for the miniaturization to proceed further. However, when the miniaturization of 4-hydroxy-4'-isopropoxydiphenyl sulfone particles is advanced, the melting point thereof is extremely lowered, and it has been recognized that a severe background fog is generated on the white paper part of the thermosensitive recording medium at high temperature. There is.

The thermal recording medium may be exposed to a relatively high temperature during storage, in a state of being set in a device, or after printing, but it is necessary to avoid the occurrence of background fogging at such time. I won't. As a measure of this background fog, the coloring density of the white background portion when it was brought into contact with an iron plate at 70 ° C. for 5 seconds was used, and this was defined as static sensitivity. It is desirable that this value be as low as possible and practically 0.2
The following is desirable.

The present inventors have found that the above melting point lowers 4
As a result of earnest research on the cause of the abnormally high static sensitivity of the thermosensitive color developing layer containing -hydroxy-4'-isopropoxydiphenyl sulfone, it was found that 4-
Hydroxy-4'-isopropoxydiphenyl sulfone particle surface is contacted with water molecules to give 4-hydroxy-4'-
It was found that a hydrate of isopropoxydiphenyl sulfone was produced, and this hydrate was the cause of the above melting point drop. Compared to the original melting point of 4-hydroxy-4′-isopropoxydiphenyl sulfone (about 127 ° C.),
4-Hydroxy-4'-isopropoxydiphenyl sulfone hydrate exhibits an extremely low melting point of 40 to 60 ° C, which makes the thermal sensitivity of the thermosensitive recording medium extremely high.

[0008]

The object of the present invention is to include 4-hydroxy-4'-isopropoxydiphenyl sulfone as a developer, but the static sensitivity of the thermosensitive coloring layer does not become abnormally high. An object of the present invention is to provide a thermosensitive recording medium having a high whiteness, a high sensitivity, and a colored image which is excellent in storage stability.

[0009]

DISCLOSURE OF THE INVENTION The inventors of the present invention have focused their attention on the thermal behavior of 4-hydroxy-4'-isopropoxydiphenyl sulfone hydrate. , It melted at 40 to 60 ° C. and, at the same time, released water and returned to the original 4-hydroxy-4′-isopropoxydiphenyl sulfone. Furthermore, based on such knowledge, a process for making fine particles of 4-hydroxy-4′-isopropoxydiphenylsulfone into fine particles under various heating conditions was examined, and the temperature of the dispersion liquid was set to 50 ° C. or higher to carry out dispersion. The inventors have found that the formation of hydrates can be prevented, and have completed the present invention.

The heat-sensitive recording material of the present invention comprises a sheet-shaped substrate,
A sheet-like substrate having a substantially colorless dye precursor and a heat-sensitive color-developing layer containing a color developer which reacts with the dye precursor under heating to develop a color thereof; It is characterized in that the developer contains 4-hydroxy-4'-isopropoxydiphenyl sulfone which has been dispersed into fine particles at a temperature of 50 ° C or higher.

[0011]

In the heat-sensitive recording material of the present invention, the color-developing agent contained in the heat-sensitive color-developing layer contains 4-hydroxy-4'-isopropoxydiphenyl sulfone, and the color-developing compound is 50 ° C.
The particles are dispersed into fine particles at the above temperature. The temperature of the dispersion liquid in this dispersion microparticulation process is 50 to 90.
C. is preferable, and 50 to 70.degree. C. is more preferable. When the temperature of the dispersion liquid is 90 ° C. or higher, water easily evaporates, and the particle size is less likely to be reduced, which causes problems. If it is less than 50 ° C., a hydrate of the above color-developing compound remains.

At the time of dispersing 4-hydroxy-4'-isopropoxydiphenyl sulfone, various protective colloids and surfactants can be used as a dispersant. Specifically, as a dispersant, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, starch, modified starch, gelatin, acacia, casein, styrene-maleic anhydride copolymer salt, ethylene-
Maleic anhydride copolymer salt, isobutylene-maleic anhydride copolymer salt, polyvinyl alcohol, carboxy modified polyvinyl alcohol, sulfone modified polyvinyl alcohol, polyethylene glycol derivative, acetylene glycol derivative, polyoxyethylene derivative, sulfonate, fatty acid ester , And an alkylamine salt can be used. These may be used alone or in combination of two or more. The dispersant is preferably used in a concentration of 0.5 to 50% by weight, based on the weight of 4-hydroxy-4'-isopropoxydiphenyl sulfone.

The leuco dye used as the dye precursor in the present invention can be selected from conventionally known ones such as triphenylmethane compounds, fluorane compounds and diphenylmethane compounds. That is, as the dye precursor,
For example, 3- (4-diethylamino-2-ethoxyphenyl) -3- (1-ethyl-2-methylindole-3
-Yl) -4-azaphthalide, crystal violet lactone, 3- (N-ethyl-N-isopentylamino) -6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinoflu Oran, 3
-Diethylamino-6 methyl-7- (o, p-dimethylanilino) fluorane, 3- (N-ethyl-Np-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-
Diethylamino-7- (m-trifluoromethylanilino) fluorane, 3-diethylamino-6-methyl-7
-Chlorofluorane, 3-diethylamino-6-methylfluorane, 3-cyclohexylamino-6-chlorofluorane, and 3- (N-ethyl-N-hexylamino) -6-methyl-7- (p-chloroanilino ) One or more selected from fluoran and the like can be used.

The color developer used in the present invention includes 4-
A color-developing compound other than hydroxy-4'-isopropoxydiphenyl sulfone can be used in combination to improve the color developing performance of the heat-sensitive color developing layer. Examples of such other color-developing compounds include 2,2-bis (4-
Hydroxyphenyl) propane (bisphenol A),
1,1-bis (4-hydroxyphenyl) -1-phenylethane, α, α′-bis (4-hydroxyphenyl)
-1,4-diisopropylbenzene, α, α'-bis (4-hydroxyphenyl) -1,3-diisopropylbenzene, dihydroxydiphenyl ether (JP-A-1)
-180382), benzyl p-hydroxybenzoate (JP-A-52-140483), bisphenol S,
1,1-di (4-hydroxyphenyl) cyclohexane, 1,7-di (4-hydroxyphenylthio) -3,
5-dioxaheptane (JP-A-59-52694),
3,3'-diallyl-4,4'-dihydroxydiphenyl sulfone (JP-A-60-208286), and N
-Arylsulfonylureas and the like can be used. Examples of the N-arylsulfonylureas include N- (p-toluenesulfonyl) -N'-phenylurea and N- (p-toluenesulfonyl) -N '-(p-
Trilyl) -urea, and 4,4'-bis (p-toluenesulfonylaminocarbonylamino) -diphenylmethane.

Further, in the present invention, a heat-fusible substance (so-called sensitizer) may be used in combination in the heat-sensitive color forming layer within a range that does not impair the desired effect. As such a sensitizer, a heat-fusible organic compound having a melting point of 50 to 150 ° C. is used, and examples thereof include 1-hydroxy-2-naphthoic acid phenyl ester (Japanese Patent Application Laid-Open No. 57-191089).
No.), p-benzylbiphenyl (JP-A-60-8238).
No. 2), benzylnaphthyl ether (JP-A-58-87)
094), dibenzyl terephthalate (JP-A-58-58).
98285), 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)
No.), 1,5-bis (p-methoxyphenoxy) -3-
Oxapentane (JP-A-62-181183), oxalic acid diester (JP-A-64-1583), and 1,4-bis (p-tolyloxy) benzene (JP-A-2).
-153783) and the like.

The thermosensitive coloring layer of the present invention may contain a hindered phenol compound or an ultraviolet absorber for the purpose of improving the storage stability of a colored image. Examples of these compounds include JP-A-57-151394, JP-A-58-160191, JP-A-58-69096, JP-A-59-2884, JP-A-59-95190, and JP-A-59-95190. 60-22288, JP-A-60-255485.
JP-A-61-44686 and JP-A-62-1696.
83, JP-A-63-17081, and JP-A-1-
249385 and the like, and specific examples thereof include 1,1,3-tris (3′-cyclohexyl-4′-hydroxyphenyl) butane, 1,
1,3-tris (2-methyl-4-hydroxy-5-t
ert-butylphenyl) butane, 4,4′-thiobis (3-methyl-6-tert-butylphenol),
1,3,5-trimethyl-2,4,6-tris (3,5
-Di-tert-butyl-4-hydroxybenzyl) benzene, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, p-octylphenyl salicylate, 2- (2'-hydroxy-5'-methylphenyl)
Benzotriazole, ethyl-2-cyano-3,3'-
Diphenyl acrylate, and tetra (2, 2, 6,
6, -Tetramethyl-4-piperidyl) 1,2,3,4
-Butane tetracarboate etc.

The heat-sensitive color forming layer of the present invention may contain a color image stabilizing agent composed of at least one compound having an aziridinyl group or an epoxy group. The compound having an aziridinyl group used in the present invention,
For example, the following compounds can be mentioned. Two
4-bis (1-aziridinylcarbonylamino) toluene, bis [4- (1-aziridinylcarbonylamino)
Phenyl] methane, bis [3-chloro-4- (1-aziridinylcarbonylamino) phenyl] methane, 2,2
-Bis [4- (1-aziridinylcarbonyloxy) phenyl] propane, 1,4-bis (1-aziridinylcarbonyloxy) benzene, and 1,4-bis (1-
Aziridinylcarbonyl) benzene.

Examples of the compound having an epoxy group used in the present invention include the following compounds.

[0019]

[Chemical 1]

[0020]

[Chemical 2]

The thermosensitive coloring layer of the present invention contains a binder for binding the above-mentioned component particles and adhering the thermosensitive coloring layer to the sheet-like support. Examples of such binders include polyvinyl alcohols of various molecular weights, starch and its derivatives, cellulose derivatives such as methoxycellulose, carboxymethylcellulose, methylcellulose, and ethylcellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylic acid amide / Acrylic ester copolymer, acrylic acid amide / acrylic acid ester / methacrylic acid terpolymer, styrene / maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, gelatin, and water-soluble polymer such as casein Materials, and polyvinyl acetate, polyurethane, styrene / butadiene copolymer, polyacrylic acid, polyacrylic acid ester, vinyl chloride / vinyl acetate copolymer,
Examples thereof include latexes of polybutyl methacrylate, ethylene / vinyl acetate copolymer, styrene / butadiene / acrylic copolymer and the like.

The heat-sensitive color forming layer of the heat-sensitive recording material of the present invention may optionally contain waxes, organic or inorganic white pigments and the like.

Known waxes such as paraffins, amide waxes, bisimide waxes, and metal salts of superabsorbent fatty acids can be used as the above waxes.

Examples of organic or inorganic pigments include calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay, calcined clay, talc, and surface-treated calcium carbonate and silica. Inorganic fine powder, and organic fine powder such as urea-formalin resin, styrene / methacrylic acid copolymer, and polystyrene resin can be used.

The content of the dye precursor in the thermosensitive color developing layer is generally 5 to 20% by weight, and the content of the developer is generally 5 to 40% by weight. When the sensitizer is contained, its content is preferably 10 to 40% by weight. When the hindered phenol compound or the ultraviolet absorber is contained, its content is preferably 1 to 10% by weight. When the aziridine compound or the epoxy compound is contained, its content is preferably 1 to 30% by weight. The waxes and the white pigment are preferably contained in 5 to 20% by weight and 10 to 50% by weight, respectively, and the content of the binder is generally 5 to 20% by weight.

The support used in the thermosensitive recording medium of the present invention is paper, coated paper having a surface coated with a pigment, latex, etc., synthetic paper having a multi-layer structure made of a polyolefin resin, a plastic film or the like. You can choose from composite sheets.

At least one of such sheet-like supports
A coating solution containing a mixture of the above-mentioned required components is applied on the surface and dried to form a thermosensitive color developing 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 still more preferably from 2 to 10 g / m ^2.

In the heat-sensitive recording material of the present invention, a protective layer may be formed on the heat-sensitive layer for the purpose of improving the oil resistance and plasticizer resistance of the color image.

[0029]

The present invention will be further described with reference to the following examples. In the examples, "parts" and "%" are unless otherwise specified.
Represents "parts by weight" and "% by weight", respectively.

Example 1 A thermosensitive recording paper was prepared by the following procedure . 1) Preparation Ingredient Weight portion of the dye precursor dispersion A 3- (N-ethyl--N--isopentylamino) - 20 6-methyl-7-anilinofluoran polyvinyl alcohol 10% solution 10 Water 70 The above composition The product was crushed at room temperature using an IMEX sand grinder until the average particle size was 1 μm or less.

[0031] 2) using a sand grinder to Developer Dispersion Preparation Ingredient Weight unit 4-hydroxy-4'-isopropoxydiphenylsulfone 20 polyvinyl alcohol 10% solution 10 Water 70 The composition of B, the dispersion The average particle size is 1 μm while maintaining the temperature at 50 ° C to 60 ° C.
Grind until the following:

[0032] 2) using a sensitizer dispersion C a sand grinder to prepare Ingredient Weight unit oxalate di para methylbenzyl ester 20 polyvinyl alcohol 10% solution 10 Water 70 The composition of an average particle size of the 1μm or less Grind until room temperature.

4) Preparation of Pigmented Undercoat Paper Fired clay (trademark: Ansilex, Engelhard)
A styrene / butadiene copolymer emulsion (with a solid content of 50 parts) was obtained by dispersing 85 parts in 320 parts of water.
%) And 50 parts of 10% oxidized starch aqueous solution were mixed to prepare a coating solution. This coating liquid has a basis weight of 48 g.
/ M ² of base paper with a coating amount after drying of 7.0 g / m ²
To prepare a pigment-undercoated paper.

5) Formation of Thermosensitive Coloring Layer Onto 60 parts of the above liquid A, 120 parts of liquid B and 120 parts of liquid C, 24 parts of calcined clay, 12 parts of 25% zinc stearate dispersion, and 10 parts of 30% paraffin dispersion. , And 10%
100 parts of an aqueous polyvinyl alcohol solution are mixed and stirred,
A coating liquid was prepared. This coating solution on one surface of the base paper basis weight of 50 g / m ^2, the coating amount after drying by coating and drying so that 5.0 g / m ² to form a thermosensitive coloring layer was prepared thermosensitive recording paper ..

The thermosensitive recording paper obtained as described above was treated with a super calender and the surface smoothness was adjusted to 6
It was set to 00 to 1000 seconds.

The sample thus obtained was heated for 5 seconds under the conditions of a temperature of 70 ° C. and a pressure of 0.2 kg / cm ² using a tilt tester manufactured by Toyo Seiki Co., Ltd. The color density at this time was measured using a Macbeth densitometer RD-914, and the measured value was used to express the static sensitivity. The measurement results are shown in Table 1.

Example 2 A thermosensitive recording paper was prepared in the same manner as in Example 1. However, modified starch was used in place of polyvinyl alcohol in the preparation of the solution B used for forming the thermosensitive coloring layer. 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, in preparing the liquid B used for forming the thermosensitive color developing layer, dispersion was performed while maintaining the temperature of the dispersion liquid at 30 to 40 ° C. The test results are shown in Table 1.

Comparative Example 2 A thermal recording paper was prepared in the same manner as in Example 1. However, in preparing the liquid B used for forming the thermosensitive color developing layer, dispersion was performed while maintaining the temperature of the dispersion liquid at 5 to 15 ° C. The test results are shown in Table 1.

Comparative Example 3 A thermosensitive recording paper was prepared in the same manner as in Example 2. However, in preparing the liquid B used for forming the thermosensitive color developing layer, dispersion was performed while maintaining the temperature of the dispersion liquid at 5 to 15 ° C. The test results are shown in Table 1.

[0041]

[Table 1]

As is clear from Table 1, in the heat-sensitive recording material of the present invention, 4 contained in the heat-sensitive color forming layer as a developer.
The fine particles of -hydroxy-4'-isopropoxydiphenyl sulfone prevent the formation of hydrates in the wet dispersion, and therefore the obtained thermosensitive coloring layer has low static sensitivity and does not show abnormal coloring. It is a thing. On the other hand, the thermosensitive recording media of Comparative Examples 1 to 3 have abnormally high static sensitivity, which indicates that a hydrate is formed in the color-developing compound.

[0043]

EFFECT OF THE INVENTION When 4-hydroxy-4'-isopropoxydiphenyl sulfone particles as a color developer are formed by wet dispersion, the temperature of the dispersion liquid is set to 50 ° C. or higher to prevent the formation of hydrate. The thermosensitive recording medium of the invention containing such a color developer has low static sensitivity, a clear color image and high whiteness in the non-color portion, and is excellent in practicality.

Claims (1)

[Claims] 1. A sheet-like substrate, a dye precursor which is formed on at least one surface of the sheet-like substrate and is substantially colorless, and a developer which reacts with the dye precursor under heating to develop a color thereof. A thermosensitive coloring layer containing an agent, wherein the developer is dispersed into fine particles at a temperature of 50 ° C. or higher.
A heat-sensitive recording material containing hydroxy-4'-isopropoxydiphenyl sulfone.