JPH06270546A - Thermal recording material - Google Patents

Abstract

PURPOSE:To provide a thermal recording material reduced in the lowering of recording sensitivity even when the thermal recording material is exposed to high temp. and also reduced in the lowering of the whiteness of a blank part. CONSTITUTION:In a thermal recording material wherein a recording layer containing a colorless or light-colored basic dye is provided on a support, a dispersion (average particle size; 0.3-2mum) obtained by emulsifying and dispersing a soln. of 4,4'-isopropylidene diphenol and dibenzyl oxalate in a hydrophobic org. solvent along with an aqueous medium in a fine particulate state and subsequently removing the hydrophobic solvent is added to the recording layer.

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 which is excellent in recording sensitivity and recording image quality and has little decrease in whiteness on a white paper portion.

2. Description of the Related Art Conventionally, a heat-sensitive recording material utilizing a color reaction between a colorless or light-colored basic dye and a color-developing agent to bring a color-developed image by bringing both color-forming substances into contact with each other by heat is well known. . Since such a thermosensitive recording medium is relatively inexpensive and the recording device is compact and its maintenance is relatively easy, it is used not only as a recording medium for facsimiles and various computer machines but also in a wide range of fields. . However, as the field of use expands, the recording apparatus is constantly required to have higher sensitivity for thermal recording paper in order to make it more compact and to use less energy for recording.
As a method for obtaining a high-sensitivity heat-sensitive recording paper, an intermediate layer containing a pigment as a main component is provided between the support and the heat-sensitive recording layer, the particle diameter of the color-forming material in the recording layer is made smaller, or the recording is performed. Although a method of adding a sensitizer having an appropriate melting point in the layer has been proposed and practiced, a thermal recording paper having higher sensitivity and high image quality is demanded.

Further, the heat-sensitive recording material contains a heat-fusible substance added to the heat-sensitive color forming layer in order to enhance the recording sensitivity when the heat-sensitive recording material is left in an environment of about 50 ° C. for a long time during transportation or storage. However, there is also a problem that the whiteness of the white paper portion is reduced due to the dispersion of the white spots. Then, there is a problem that this phenomenon is apt to be prominently exhibited particularly in a high-sensitivity thermosensitive recording material. Therefore, there is a strong demand for a thermosensitive recording medium which has excellent recording sensitivity even after being exposed to a high temperature condition for a long time and which has a small decrease in whiteness in a white paper portion.

[0004]

In view of the above situation, an object of the present invention is to provide a heat-sensitive recording material in which the recording sensitivity is not significantly reduced even when exposed to a high temperature condition and the whiteness of the blank portion is not significantly reduced. To do.

[0005]

DISCLOSURE OF THE INVENTION The present inventors have proposed a thermosensitive recording medium comprising a support and a recording layer containing a colorless or light-colored basic dye and a coloring agent. ，
The hydrophobic organic solution in which 4'-isopropylidenediphenol and oxalic acid dibenzyl ester are dissolved is finely dispersed by emulsification with an aqueous medium, and then the hydrophobic organic solvent is removed to obtain a dispersion. The inventors have found that the object is achieved and have completed the present invention.

[0006]

According to the present invention, a hydrophobic organic solution in which 4,4'-isopropylidene diphenol and oxalic acid dibenzyl ester are dissolved as described above is finely emulsified and dispersed with an aqueous medium, and then the hydrophobic organic solvent is removed. The resulting dispersion has significant characteristics when used. 4,
4'-isopropylidenediphenol is widely known as a color developing agent, but has a low recording sensitivity when used alone. Then, as a result of attempting to use various sensitizers in combination with 4,4'-isopropylidenediphenol in order to enhance recording sensitivity, dibenzyl oxalate as a sensitizer was particularly excellent in recording sensitivity and recording image quality. Although effective, the whiteness was low and there was room for improvement. Therefore, after further various studies,
By using an emulsified mixture of 4,4'-isopropylidene diphenol and oxalic acid dibenzyl ester, it was possible to prevent a decrease in whiteness. The average particle size of the dispersion obtained by removing the hydrophobic organic solvent was 0.3.
If it is less than μm, background fog occurs, and if it exceeds 2 μm, desired recording sensitivity cannot be obtained.

In the present invention, the amount of 4,4'-isopropylidene diphenol and dibenzyl dioxalate used is not particularly limited, but generally 4,4 'with respect to 100 parts by weight of the basic dye. -Isopropylidene diphenol or dibenzyl oxalate is 1
The amount is adjusted in the range of 0 to 1000 parts by weight, preferably 50 to 500 parts by weight, and the amount of 4,4'-isopropylidene diphenol is 5 to 1000 parts by weight, preferably 100 parts by weight of dibenzyl oxalate. Is 10
It is desirable to adjust in the range of about 300 parts by weight.

In the present invention, when a hydrophobic organic solution in which 4,4'-isopropylidene diphenol and oxalic acid dibenzyl ester are dissolved is finely emulsified and dispersed with an aqueous medium, an acetoacetyl group-modified polyvinyl is used as an emulsifier. Alcohol, acetoacetyl group-modified saponified polyvinyl alcohol, carboxy-modified polyvinyl alcohol,
A modified polyvinyl alcohol such as silicon modified polyvinyl accol is preferable, and an acetoacetyl group-modified polyvinyl alcohol (including an acetoacetyl group-modified partially saponified polyvinyl silcol) is particularly preferable because an excellent water resistance effect can be obtained by the reaction with an aldehyde compound. Used. Further, non-modified polyvinyl alcohol, nonionic surfactant, ionic surfactant and the like can be used in combination within a range that does not impair the effects of the present invention. The amount of the modified polyvinyl alcohol used as an emulsifier is not particularly limited, but is 0.5 to 200 parts by weight with respect to 100 parts by weight of dibenzyl oxalate.
It is preferable to use 1 to 100 parts by weight.

The hydrophobic organic solvent is not particularly limited, and toluene, xylene, benzene,
Methyl isobutyl ketone, ethyl acetate, butyl acetate, methylene chloride and the like can be mentioned. Further, it is possible to use the hydrophobic organic solvent in combination with a water-soluble organic solvent such as methanol, ethanol, propanol or methyl ethyl ketone. The amount of the organic solvent used should be appropriately adjusted according to the amounts of 4,4'-isopropylidenediphenol and dibenzyl oxalate added, and the type of the organic solvent, and is not particularly limited. However, the ratio of the organic solvent to the total amount of the organic solvent, 4,4'-isopropylidene diphenol, and oxalic acid dibenzyl ester is generally 10 to 60% by weight, preferably 20.
It is desirable to adjust the content to be in the range of about 60% by weight.

In the heat-sensitive recording material of the present invention, various known compounds can be used as the colorless or light-colored basic dye contained in the recording layer. 3,3
-Bis (p-dimethylaminophenyl) -6-dimethylaminophthalide, 3- (4-diethylamino-2-methylphenyl) -3- (4-dimethylaminophenyl)-
6-dimethylaminophthalide, 3-diethylamino-7
-Dibenzylamino-benzo [a] fluorane, 3-
(N-Ethyl-Np-tolyl) amino-7-N-methylanilinofluorane, 3-diethylamino-7-anilinofluorane, 3-diethylamino-7-dibenzylaminofluorane, 3,6- Bis (diethylamino) fluorane-γ-anilinolactam, 3-cyclohexylamino-6-chlorofluorane, 3-diethylamino-
6-methyl-7-chlorofluorane, 3-diethylamino-7-chlorofluorane, 3- (N-ethyl-N-isoamyl) amino-6-methyl-7-anilinofluorane, 3- (N-methyl) -N-cyclohexyl) amino-
6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-di (n-butyl) amino-6-methyl-7-anilinofluorane, 3-di (N-pentyl) amino-6-methyl-
7-anilinofluorane, 3-diethylamino-7-
(O-chlorophenylamino) fluorane, 3-di (n
-Butyl) amino-7- (o-chlorophenylamino)
Fluorane, 3-diethylamino-7- (o-fluorophenylamino) fluorane, 3-di (n-butyl) amino-7- (o-fluorophenylamino) fluorane, 3- (N-ethyl-p-toluidino)- 6-methyl-7-anilinofluorane, 3- (N-ethyl-p-toluidino) -6-methyl-7- (p-toluidino) fluorane, 3- (N-ethyl-N-furfurylamino)-
6-methyl-7-anilinofluorane, 3-diethylamino-6-chloro-7-anilinofluorane, 3- (N
-Methyl-N-n-propylamino) -6-methyl-7
-Anilinofluorane, 3,3-bis [1- (4-methoxyphenyl) -1- (4-dimethylaminophenyl)
Ethylene-2-yl] -4,5,6,7-tetrachlorophthalide, 3,3-bis [1- (4-methoxyphenyl) -1- (4-pyrrolidinophenyl) ethylene-2-
Il] -4,5,6,7-tetrachlorophthalide, 3,
3-bis [1,1-bis (4-pyrrolidinophenyl) ethylene-2-yl] -4,5,6,7-tetrabromophthalide, 3-p- (p-anilinoanilino) anilino-
6-methyl-7-chlorofluorane, 2,2-bis {4
-[6 '-(N-cyclohexyl-N-methylamino)
-3'-methylspiro [phthalide-3,9'-xanthen-2'-ylamino] phenyl} propane, 3,6
-Bis (dimethylamino) fluorene-9-spiro-
3 '-(6'-dimethylamino) phthalide and the like can be mentioned. Of course, it is not limited to these, and two or more kinds may be used in combination as required. Among these dyes, 3-diethylamino-7- (o-chlorophenylamino) fluorane and 3-di (nbutylamino) -7- (o-chlorophenylamino) fluorane exhibit the desired effects without fail. This is one of the preferred embodiments because a heat-sensitive recording material having a white paper portion with high whiteness can be obtained.

In the present invention, 4,4'-isopropylidenediphenol is used as a color-developing agent, but various known compounds can be used in combination as long as the desired effects of the present invention are not impaired. To be done. 4-cumylphenol, hydroquinone monobenzyl ether, 1,1-bis (4-hydroxyphenyl) cyclohexane, 4,4 '
-Dihydroxydiphenyl-2,2-butane, 4,4 '
-Dihydroxydiphenylmethane, 2,2-bis (4-
Hydroxyphenyl) -4-methylpentane, 2,2-
Bis (4-hydroxyphenyl) heptane, bis (4-
Hydroxyphenylthioethoxy) methane, 1,5-di (4-hydroxyphenylthio) -3-oxapentane, 1,1-bis (4-hydroxyphenyl) -1-phenylethane, 1,4-bis [α- Methyl-α- (4 '
-Hydroxyphenyl) ethyl] benzene, 1,3-bis [α-methyl-α- (4'-hydroxyphenyl) ethyl] benzene, 4,4'-dihydroxydiphenyl sulfide, bis (4-hydroxy-3-methylphenyl) ) Sulfine, 2,4'-dihydroxydiphenyl sulfone, 4,4'-dihydroxydiphenyl sulfone,
4-hydroxy-4'-methyldiphenyl sulfone, 4
-Hydroxy-4'-isopropoxydiphenyl sulfone, 4-hydroxyphenyl-4'-benzyloxyphenyl sulfone, 4-hydroxy-3 ', 4'-tetramethylene biphenyl sulfone, 3,4-dihydroxyphenyl-p-tolyl sulfone , Benzyl 4-hydroxybenzoate, butyl bis (p-hydroxyphenyl) acetate, methyl bis (p-hydroxyphenyl) acetate, (4
-Hydroxyphenylthio) acetic acid-2- (4-hydroxyphenylthio) ethyl ester, di (p-hydroxyphenylthioethyl) ether, N, N'-di-m-chlorophenylthiourea, N- (phenoxyethyl)- Four
-Phenolic compounds such as hydroxyphenylsulfonamide, 4- [3- (p-tolylsulfonyl) propyloxy] salicylic acid, 4- [2- (p-methoxyphenoxy) ethyloxy] salicylic acid, 5- [p- (2- p
-Methoxyphenoxyethoxy) cumyl] salicylic acid,
Aromatic carboxylic acids such as p-chlorobenzoic acid, salts of these aromatic carboxylic acids with polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin, nickel, and antipyrine of zinc thiocyanate. Organic acidic substances such as complexes.

In the present invention, oxalic acid dibenzyl ester is used as the heat-fusible substance, but it is possible to use the following other compounds in combination as long as the desired effects of the present invention are not impaired. . For example stearic acid amide,
Methoxycarbonyl-N-stearic acid benzamide,
N-benzoylstearic acid amide, N-eicosanoic acid amide, ethylenebistearic acid amide, behenic acid amide, methylenebisstearic acid amide, N-methylolstearic acid amide, dibenzyl terephthalate, dimethyl terephthalate, dioctyl terephthalate, p- Benzyl benzyloxybenzoate, phenyl 1-hydroxy-2-naphthoate, 2-naphthylbenzyl ether, m-
Terphenyl, p-benzylbiphenyl, tolylbiphenyl ether, di (p-methoxyphenoxyethyl) ether, 1,2-di (3-methylphenoxy) ethane,
1,2-di (4-methylphenoxy) ethane, 1,2-
Di (4-methoxyphenoxy) ethane, 1,2-di (4
-Chlorophenoxy) ethane, 1,2-diphenoxyethane, 1- (4-methoxyphenoxy) -2- (2-methylphenoxy) ethane, p-methylthiophenylbenzyl ether, 1,4-di (phenylthio) butane, p
-Acetotoluidide, p-acetophenetidide, N-acetoacetyl-p-toluidine, di (β-biphenylethoxy) benzene, p-di (vinyloxyethoxy) benzene, 1-isopropylphenyl-2-phenylethane and the like are exemplified. To be done.

In order to prepare a coating liquid for a recording layer containing these substances, water is generally used as a dispersion medium, and a basic dye, a coloring agent, and further a basic dye, a coloring agent, and the like are necessary by a stirring / grinding machine such as a ball mill, an attritor or a sand mill. A sensitizer or the like added according to the above is dispersed together or separately to prepare a coating liquid.
In the coating liquid, starch, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, arabic gum as an adhesive,
Polyvinyl alcohol, diisobutylene / maleic anhydride copolymer salt, styrene / maleic anhydride copolymer salt,
The ethylene / acrylic acid copolymer salt, the styrene / acrylic acid copolymer salt, the styrene / butadiene copolymer emulsion, etc. are 10 to 40% by weight of the total solid content, preferably 15
It is used at about 30% by weight.

It is also possible to use various pigments in combination in the coating liquid, for example, kaolin, clay, calcium carbonate, calcined clay, calcined kaolin, titanium oxide, diatomaceous earth,
Inorganic pigments such as fine particulate anhydrous silica and activated clay, styrene microballs, nylon powder, polyethylene powder, urea / formalin resin filler, and organic pigments such as raw starch particles can be used.

Furthermore, various auxiliaries can be added to the coating liquid, for example, sodium dioctylsulfosuccinate, sodium dodecylbenzenesulfonate, sodium lauryl alcohol sulfate / sodium salt, alginate, fatty acid metal salt and the like. Dispersant, benzophenone type,
Examples thereof include UV absorbers such as triazole-based, antifoaming agents, fluorescent dyes, coloring dyes, and antioxidants.

In the present invention, the method for forming the recording layer and the like are not particularly limited, and the recording layer can be formed according to a conventionally known and commonly used technique, for example, air knife coating, varibar blade coating, pure blade coating, It can be formed by a method of coating and drying a coating liquid on a support by short dwell coating, curtain coating or the like. The coating amount of the coating liquid is also not particularly limited, and is usually ² to 12 g / m ² , preferably 3 to 10 g / m ² in dry weight.
It is in the range of m ² . As the support, paper, synthetic paper, plastic film or the like is appropriately selected and used.

In the present invention, it is possible to further improve the storability of a recorded image by providing a resin layer on the thermal recording material and / or on the back surface side thereof, if necessary.
Further, in the field of heat-sensitive recording material manufacturing, such as providing an undercoat layer on the support to improve image quality and sensitivity, processing the back surface of the recording material into an adhesive label by processing with an adhesive, and providing a magnetic layer on the back surface of the recording material. Various known techniques can be added. Further, the image quality and the image density can be improved by performing a super calendering process after forming the recording layer.

[0018]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. In addition, "part" and "%" in an example show "weight part" and "weight%", respectively, unless there is particular notice.

Example 1 Preparation of Solution A 10 parts of 3-di (n-butyl) amino-6-methyl-7-anilinofluorane, 5% aqueous solution of methylcellulose 5
Parts and 10 parts of water were pulverized with a horizontal sand mill until the average particle size became 0.5 μm. Preparation of solution B A solution obtained by dissolving 20 parts of 4,4′-isopropylidene diphenol and 25 parts of oxalic acid dibenzyl ester in a mixed solvent of 100 ml of toluene and 50 ml of ethyl acetate was used to prepare 8% of acetoacetyl group-modified polyvinyl alcohol. Emulsified and dispersed in 120 parts of the aqueous solution using a TK homomixer, and the solvent was removed by an evaporator to obtain a liquid B having an average particle diameter of 0.8 μm. Formation of recording layer Liquid A 25 parts, liquid B 90 parts, fine particle silicon oxide (oil absorption 18
0 ml / 100 g) 7 parts, light calcium carbonate (oil absorption 90 ml / 100 g) 8 parts, 10% aqueous solution of silicon-modified polyvinyl alcohol 100 parts, zinc stearate 30
% 15% aqueous dispersion and 140 parts of water are mixed and stirred, and the recording layer coating solution is applied and dried on one side of a high-quality paper of 50 g / m ² so that the coating amount after drying is 4 g / m ^2. To form a recording layer.

Example 2 In preparation of solution A, 3-di (n-butyl) -amino-6 was used.
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that 10 parts of 3-di (n-butyl) amino-7 (o-chlorophenylamino) fluorane was used instead of 10 parts of -7-anilinofluorane. It was

Example 3 Preparation of liquid D A composition comprising 100 parts of calcined clay [trade name: Ansilex, manufactured by EMC, oil absorption: 110 ml / 100 g], 100 parts of a 10% aqueous solution of polyvinyl alcohol, and 200 parts of water was prepared. By mixing and stirring, a coating liquid for the undercoat layer was obtained. On one side of the fine preparation 45 g / m ² of the heat-sensitive recording material, after coating and drying as the coating amount after drying D solution is 8 g / m ^2, the coating recording layer was prepared in the same manner as in Example 1 Application amount after drying is 4g / m
After coating and drying so as to be ² , a super calender treatment was performed to obtain a heat-sensitive recording material.

Comparative Example 1 In the preparation of solution B, a composition comprising 20 parts of 4,4'-isopropylidene diphenol, 25 parts of oxalic acid dibenzyl ester, 10 parts of a 5% aqueous solution of methylcellulose and 35 parts of water was averaged by a horizontal sand mill. A thermosensitive recording medium was obtained in the same manner as in Example 1 except that the particles were pulverized to a particle size of 0.8 μm.

Comparative Example 2 In the preparation of solution A, di (β-biphenylethoxy) benzene (mp = 81. C) was used instead of dibenzyl oxalate ^.
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that

Comparative Example 3 In the preparation of solution A, 1,2-diphenoxyethane (mp = 97. C) was used instead of dibenzyl oxalate ^.
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that was used.

Comparative Example 4 In the preparation of solution B, the average particle size after removing the organic solvent was 4 μm.
A thermosensitive recording medium was obtained in the same manner as in Example 1 except that emulsification and dispersion was carried out so that m was obtained.

The following seven evaluation tests were carried out on the thus obtained seven kinds of thermal recording materials, and the results are shown in [Table 1]. [Recording Sensitivity] A thermosensitive recording medium left for 24 hours in an atmosphere of 50 ° C. and 75% RH was measured by a thermosensitive recording medium evaluation machine [trade name: TH
-PMD, made by Okura Electric Co., Ltd., applied voltage 16 V, pulse cycle 0.51 ms, pulse width 1 ms and 2 m
Recording was performed under the condition of s, and the obtained recording density was measured with a Macbeth densitometer [RD-914 type, manufactured by Macbeth Co.] in a visual mode.

[Recording Image Quality] As for the recording image quality, the recorded image was visually evaluated, and the evaluation criteria were as follows. ○: excellent △: inferior ×: extremely inferior

[Whiteness] A thermosensitive recording material was measured at 50 ° C. and 75% R
The sample was left in an H atmosphere for 24 hours, and its whiteness was measured with a blue filter with a dental hunter reflectometer (manufactured by Toyo Seiki Seisakusho).

[0029]

[Table 1]

[0030]

As is clear from the results of [Table 1], all of the thermosensitive recording materials of the present invention were excellent in recording sensitivity and recording image quality and had little deterioration in recording sensitivity and whiteness. .

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ken Fukuda 4-3-1 Jōkoji, Amagasaki City, Hyogo Prefecture Kanzaki Paper Co., Ltd. Kanzaki Mill

Claims (2)

[Claims] 1. A thermosensitive recording medium comprising a support and a recording layer containing a colorless or light-colored basic dye and a coloring agent, wherein 4,4'-isopropylidenediphenol and shushu are contained in the recording layer. A thermosensitive recording medium comprising a dispersion obtained by finely emulsifying a hydrophobic organic solution in which an acid dibenzyl ester is dissolved with an aqueous medium and then removing the hydrophobic organic solvent. 2. The heat-sensitive recording material according to claim 1, wherein the average particle diameter of the dispersion obtained by removing the hydrophobic organic solvent is 0.3 μm to 2 μm.