JPH08118815A - Thermal recording material - Google Patents

Abstract

PURPOSE: To obtain a thermal recording material having a high sensitivity, a superior image shelf stability, and a superior heat resistance of white paper by incorporating at least one of specific compounds as a color developer and 1,4-dibenzyloxybenzene and the like as a sensitizer in a thermally color-forming layer. CONSTITUTION: In a thermal recording material provided with a thermal recording layer containing a leuco dye and a color developer on one surface of a substrate mainly used for a label for food and a protective layer thereon, at least one of compounds represented by a separate general formula is incorporated as a color developer and at least one selected out of 1,4- dibenzyloxybenzene, methyl ρ-benzoyloxybenzonate, and 4,4'-diallyloxydiphenyl sulfone is incorporated as a sensitizer in the thermally color-forming layer. In the formula, R represents hydrogen atom, alkyl group, aryl group, alkenyl group, or aralkyl group. On the other surface of the paper substrate, release paper is attached through a pressure-sensitive adhesive 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 having high sensitivity, excellent image storability and heat resistance of a blank sheet.

[0002]

2. Description of the Related Art Many thermal recording methods have been known for a long time. For example, a heat-sensitive recording material using an electron-donating colorless dye and an electron-accepting compound is disclosed in JP-B-43-4.
No. 160, No. 45-14039, etc., and these thermal recording systems have been applied to various fields such as facsimiles, printers, and labels in recent years, and their needs are expanding. Especially for applications such as labels, with the miniaturization and speeding up of the device, color development at low energy, that is, high sensitivity and image storability, and heat resistance in a microwave oven, that is, heat resistance of blank paper are required. ing.

In order to increase the sensitivity, a compound having a low melting point with good compatibility between a leuco dye and a color developer, a so-called sensitizer (Japanese Patent Laid-Open No. 82382/1985 and Japanese Patent Publication No. 42590/1988).
No.), an intermediate layer of a pigment having a high oil absorption property is provided (Japanese Patent Publication No. 57-52915, etc.), or a leuco dye or a developer is atomized (Japanese Patent Laid-Open No. 58-76293).
Various means such as are made. On the other hand, various methods have been proposed to improve the heat resistance of the heat-sensitive recording material. For example, in Japanese Patent Laid-Open No. 59-207283,
Use of a leuco dye having a substituted amino group at at least the 3rd and 7th positions and parahydroxybenzoic acid ester, and using at least one dispersant of hydroxyethyl cellulose and carboxyl group-modified polyvinyl alcohol as a dispersant for the dye. It is said that the oil resistance and heat resistance are improved. Further, in Japanese Patent Application Laid-Open No. 2-577, by using metabis (3,4-dihydroxycumyl) benzene as a developer in a leuco-type thermosensitive color developing material, heat responsiveness, image storability (heat resistance) To form an excellent thermal recording material.
Further, in recent years, the heat resistance of a blank sheet has been demanded along with the demand for a label that can be used in a microwave oven and the like. The heat resistance of white paper is greatly affected by the sensitizer.In the conventional system, when a sensitizer is used, the heat resistance of the white paper is not good, and there is a case that the sensitivity is sufficiently satisfied only with no sensitizer and atomization. I couldn't get it.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to obtain a heat-sensitive recording material having high sensitivity, excellent image storability and heat resistance of blank paper.

[0005]

DISCLOSURE OF THE INVENTION As a result of intensive studies by the present inventors to improve these drawbacks, the heat-sensitive recording material of the present invention contains a leuco dye and a developer on one surface of a support. A heat-sensitive recording material having a heat-sensitive recording layer containing a protective layer formed thereon, wherein at least one compound represented by the following chemical formula 2 (general formula 1) is used as the developer in the heat-sensitive recording layer.
And 1,4-dibenzyloxybenzene as a sensitizer, p-benzoyloxybenzoic acid methyl ester,
It is characterized by containing at least one selected from 4,4'-diallyloxydiphenyl sulfone.

The heat-sensitive recording material of the present invention is also characterized in that release paper is attached to the other surface of the paper support through a pressure-sensitive adhesive layer.

[0007]

Embedded image (In the formula, R represents a hydrogen atom, an alkyl group, an aryl group, an alkenyl group or an aralkyl group.)

The heat-sensitive recording material of the present invention is mainly used for food labels. Conventionally, its image storability is important, and its resistance to plasticizers such as vinyl chloride film for packaging and food oils. Image storability such as oil resistance, vinegar resistance, alcohol resistance, or light resistance is required, and the color developer (bisphenol A, p-benzylphenyl) that has been generally used in the past for Faximili is used. Benzoic acid) is not sufficient, and a protective layer mainly composed of a water-soluble polymer substance is provided on the thermosensitive coloring layer (J.
No. 9909), the above-mentioned sensitizer is appropriately used for higher sensitivity, and the above-mentioned intermediate layer is further provided, if necessary, to achieve both high sensitivity and image storability.

For the label of the present invention, a release paper is usually provided on the other surface of the support through a pressure-sensitive adhesive layer, and the support and the pressure-sensitive adhesive layer are further used. It is also possible to provide a permeation-preventing layer or the like between and, but is not limited thereto.

The leuco dye, the color developer and the sensitizer for the heat-sensitive layer are generally used by being crushed together with the water-soluble polymer compound. Then used.

The pigment for the above-mentioned intermediate layer is porous and highly heat-insulating in accordance with JIS in terms of sensitivity and improvement of adhesion of dust.
Inorganic powder having an oil absorption of 50 ml / 100 g or more according to the K5101 method is used, for example, calcined kaolin, activated clay, silica, calcium carbonate, diatomaceous earth, etc. are mainly used, and further kaolin, talc, etc. can be used in combination. Examples of the water-based adhesive include styrene-butadiene latex, acrylic resin emulsion, styrene-maleic anhydride copolymer, polyvinyl alcohol, hydroxyethyl cellulose, starch, starch derivative, casein, gelatin, etc., and other dispersants and defoaming agents. Agents and lubricants can also be added, and those used for general coated paper can be used.

The thermosensitive coloring layer provided on one side of the support is
Electron-donating colorless dyes and electron-accepting color developers and sensitizers (sensitizers) are the main components, but if necessary waxes, metal soaps, UV absorbers, etc. are added, and pigments are added. Etc. may be mixed.

The leuco dye used in the present invention includes
It is not particularly limited as long as it is used for general pressure sensitive recording paper, heat sensitive recording paper and the like. Specific examples are: (1) As the triarylmethane compound, 3,3-
Bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (crystal violet lactone)
3,3-bis (p-dimethylaminophenyl) phthalide, 3- (p-dimethylaminophenyl) -3- (1,
2-dimethylindol-3-yl) phthalide, 3-
(P-Dimethylaminophenyl) -3- (2-methylindol-3-yl) phthalide, 3- (p-dimethylaminophenyl) -3- (2-phenylindole-3-
Yl) phthalide, 3,3-bis- (1,2-dimethylindol-3-yl) -5-dimethylaminophthalide,
3,3-bis- (1,2-dimethylindol-3-yl) -6-dimethylaminophthalide, 3,3-bis-
(9-Ethylcarbazol-3-yl) -5-dimethylaminophthalide, 3,3-bis- (2-phenylindol-3-yl) -5-dimethylaminotalide, 3-p
-Dimethylaminophenyl-3- (1-methylpyrrol-2-yl) -6-dimethyl-aminophthalide and the like.

(2) As the diphenylmethane compound, 4,4'-bis-dimethylaminobenzhydrin benzyl ether, N-halophenyl leuco auramine,
N-2,4,5-trichlorophenyl leuco auramine and the like.

(3) Rhodamine B-anilinolactam, rhodamine B-p-nitroanilinolactam, rhodamine B-p-chloroanilinolactam, 3-diethylamino-7-dibenzylaminofluorane, as xanthene compounds. 3-diethylamino-7-octylaminofluorane, 3-diethylamino-7-phenylfluorane, 3-diethylamino-7- (3,4-dichloro) anilinofluorane, 3-diethylamino-7-
(2-chloroanilino) fluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-piperidino-6-methyl-7-anilinofluorane, 3-ethyl-tolylamino-6-methyl-7-ani Rinofluorane, 3-ethyl-tolylamino-6-methyl-7-phenethylfluorane, 3-diethylamino-7- (4-nitroanilino) fluorane, 3-dibutylamino-6-
Methyl-7-anilinofluorane and the like.

(4) Examples of thiazine compounds include benzoyl leuco methylene blue and p-nitrobenzoyl leuco methylene blue.

(5) As the spiro compounds, 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3,3'-dichloro-spiro-dinaphthopyran, 3-benzylspiro-dinaphthopyran, 3-methylnaphtho- ( 3-methoxy-benzo) -spiropyran,
Mention may be made of 3-propyl-spiro-dibenzopyran and the like, or mixtures thereof. These are determined by the application and the desired properties.

Specific examples of the developer represented by the general formula 1 according to the present invention include 2,4'-dihydroxydiphenyl sulfone, 4,4'-dihydroxydiphenyl sulfone and 4-hydroxy-4'-methyldiphenyl sulfone. , 4-hydroxy-4'-isopropyloxydiphenyl sulfone, 4-chloro-4'-hydroxydiphenyl sulfone, 4-benzyloxy-4'-hydroxydiphenyl sulfone, 4-hydroxy-4'-butoxydiphenyl sulfone and the like. .

As the color developer used in the present invention, in addition to the compound represented by the formula (1), a color developer such as a phenol derivative or an aromatic carboxylic acid derivative is used in combination within a range that does not cause any trouble. Is also possible. Specifically, as phenols, p-octylphenol, p-tert-butylphenol, p-phenylphenol, 1,1-bis (p-
Hydroxyphenyl) propane, 2,2-bis (p-hydroxyphenyl) propane, 1,1-bis (p-hydroxyphenyl) pentane, 1,1-bis (p-hydroxyphenyl) hexane, 2,2-bis ( p-hydroxyphenyl) hexane, 1,1-bis (p-hydroxyphenyl) -2-ethyl-hexane, 2,2-bis (4
-Hydroxy-3,5-dichlorophenyl) propane and the like. As the aromatic carboxylic acid derivative, p
-Hydroxybenzoic acid, ethyl p-hydroxybenzoate, butyl p-hydroxybenzoate, 3,5-di-tert
-Butylsalicylic acid, 3,5-di-α-methylbenzylsalicylic acid and carboxylic acid include polyvalent metal salts thereof.

Examples of waxes include paraffin wax, carnauba wax, microcrystalline wax, polyethylene wax, higher fatty acid amide,
For example, ethylene bis stearamide, higher fatty acid ester and the like can be mentioned.

Examples of the metal soap include higher fatty acid polyvalent metal salts, that is, zinc stearate, aluminum stearate, calcium stearate, zinc oleate and the like.

As the sensitizer for improving the sensitivity used in the present invention, 1,4-dibenzyloxybenzene, P-benzoyloxybenzoic acid methyl ester, or 4,4'-
Although it is diallyloxydiphenyl sulfone, it is also possible to use other sensitizers together as long as it does not cause any trouble. Specifically, benzoic acid and terephthalic acid esters, naphthalene sulfonic acid esters, naphthyl ether derivatives,
A sensitizer such as an anthryl ether derivative, an aliphatic ether type, or phenanthrene or fluorene can be used in combination. Also, the above waxes can be used together as a sensitizer. The amount of these sensitizers used is
20-300% by weight is added to the dye, especially 50-
200% by weight is a preferable addition amount.

These are dispersed and applied in a binder (adhesive). The binder is generally water-soluble, polyvinyl alcohol, hydroxyethyl cellulose, hydroxypropyl cellulose, ethylene-maleic anhydride copolymer, styrene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, Examples thereof include polyacrylic acid, starch derivatives, casein, gelatin and the like. In addition, a water-proofing agent (gelling agent, cross-linking agent) may be added to these binders for the purpose of imparting water resistance, or a hydrophobic polymer emulsion, specifically, styrene-butadiene rubber latex, acrylic resin emulsion, etc. It can also be added.

Paper is generally used as the support, but a resin film, synthetic paper, non-woven fabric or the like may be used. As an apparatus used for coating the intermediate layer and the heat-sensitive recording layer, a coater head such as a blade coater, an air knife coater, a roll coater, a rod coater or a curtain coater can be used.

Further, in order to improve the surface smoothness of the coated product, a machine calendar, a super calendar,
Devices such as gloss calendar and brushing can be used.

The coating amount when the intermediate layer is provided is not particularly limited, but if it is too small, the effect is small,
If it is too large, the strength of the paper will be weak and it is not economical, so 3-20 g / m ² , preferably 5-10 g / m ² is suitable. Although the coating amount of the support of the thermosensitive recording layer is not limited, usually, 3 to 15 g / m ² by dry weight, preferably in the range of 4~10g / m ^2. The color developer represented by the general formula (1) is used in an amount of 5 to 300 parts by weight, preferably 20 to 150% by weight, based on the dye.

In the present invention, a protective layer is further provided on the heat-sensitive recording layer for solvent resistance and the like, but an adhesive such as polyvinyl alcohol used for the heat-sensitive color forming layer is smeared, and if necessary, Further, it is possible to add pigments, waxes, waterproofing agents and the like.

[0028]

The heat-sensitive recording material obtained by the method of the present invention has a heat-sensitive color-forming layer containing a leuco dye and a color developer on one side of a support as described above, and a protective layer provided on the heat-sensitive color-forming layer. It is a heat-sensitive recording material in which a release paper is provided on the opposite surface of the body via a pressure-sensitive adhesive layer. In the thermosensitive coloring layer, the compound represented by the formula (1) and 1,4-dibenzyloxybenzene,
p-Benzoyloxybenzoic acid methyl ester, 4,
By containing at least one selected from 4'-diallyloxydiphenyl sulfone, it was possible to obtain a heat-sensitive recording material having heat resistance of white paper, high sensitivity and excellent image storability. It is considered that this is because the compatibility with the color developer and the sensitizer has made it possible to achieve both heat resistance and high sensitivity.

[0029]

Next, the present invention will be described in more detail with reference to examples. All parts and% shown below are based on weight. Unless otherwise noted, the value indicating the smear amount indicates the smear amount after drying.

Example 1 1. Preparation of the mid layer 1 Ansilex (calcined kaolin manufactured by Engelhardt, oil absorption by JIS-K5101 method 80 ml / 100g) 100 parts 10% sodium hexametaphosphate 4 parts 20% MS4600 (manufactured by Nippon Shokuhin) 30 parts 48% styrene-butadiene copolymer latex 40 parts Water 90 parts with stirring to disperse the intermediate layer 1 coating liquid, and smear it with 50 g / m ² base paper with a blade coater at an amount of 8.5 g / m ² to form the intermediate layer 1. did.

2. Preparation of thermosensitive coloring layer [Preparation of solution A] 3-dibutylamino-6-methyl-7-anilinofluorane 35 parts 5% polyvinyl alcohol 105 parts Solution A was volume averaged using Dynomill (manufactured by Shinmaru Enterprises). It was crushed to a diameter of 0.5 μm.

[Preparation of solution B] 2,4′-dihydroxyphenyl sulfone 50 parts 1,4-dibenzyloxybenzene 100 parts 5% polyvinyl alcohol 100 parts 40% zinc stearate emulsion (Hydrin SZ40 manufactured by Chukyo Yushi Co., Ltd.) 20 Part B liquid was pulverized with Dynomill (manufactured by Shinmaru Enterprises) to a volume average diameter of 1.1 μm.

[Preparation of Solution C] Light calcium carbonate 35 parts 10% Sodium hexametaphosphate 3.5 parts Water 63 parts A, B and C solutions are mixed, and further 10% PVA solution is made solid to 20% of total solids. Was added so as to obtain a thermosensitive coloring layer coating solution. This thermosensitive color developing layer coating solution was applied on the above-mentioned intermediate layer so that the hand coating bar application amount was 5 g / m ² to obtain a thermosensitive coloring layer.

Subsequently, the following protective layer liquid was smeared on the thermosensitive coloring layer of Example 1 with a hand-painted bar so that the coating amount was 3 g / m ² .
The heat-sensitive recording material was obtained by performing a Beck smoothing treatment on a calendar for 600 to 800 seconds.

[Composition of protective layer liquid] 10% polyvinyl alcohol 100 parts 40% zinc stearate emulsion liquid (Hydrin SZ40 made by Chukyo Yushi Co., Ltd.) 5 parts 20% silicic acid (Mizukasil P527 made by Mizusawa Chemical Co., Ltd.) 50 parts

Example 2 A heat-sensitive recording material was obtained in the same manner as in Example 1 except that 1,4-dibenzyloxybenzene was replaced by methyl P-benzoyloxybenzoate.

Example 3 A thermosensitive recording material was obtained in the same manner as in Example 1 except that 1,4-dibenzyloxybenzene was replaced by 4,4'-diallyloxydiphenyl sulfone.

Example 4 In the same manner as in Example 1, 2,4'-dihydroxydiphenylsulfone was replaced with 4,4'-dihydroxydiphenylsulfone, and a heat-sensitive recording material was obtained in the same manner.

Example 5 A thermosensitive recording material was obtained in the same manner as in Example 1, except that 4-hydroxy-4'-methyldiphenylsulfone was used instead of 2,4'-dihydroxydiphenylsulfone.

Comparative Example 1 A thermosensitive recording material was obtained in the same manner as in Example 1 except that 1,4-dibenzyloxybenzene in the thermosensitive coloring layer was omitted.

Comparative Example 2 In Example 1, 1,4-dibenzyloxybenzene in the thermosensitive coloring layer was replaced with dibenzyl oxalate (manufactured by Dainippon Ink and Co., Ltd., HS-2).
A thermosensitive recording material was obtained in the same manner except that it was replaced with 046).

Comparative Example 3 A thermosensitive recording material was obtained in the same manner as in Example 1, except that 1,4-dibenzyloxybenzene in the thermosensitive coloring layer was replaced with stearic acid amide.

Comparative Example 4 The compound of the formula (1) in the thermosensitive color developing layer of Example 1 was 4,4'-
A heat-sensitive recording material was obtained in the same manner except that isopropylidene diphenol (bisphenol A) was used instead.

Next, the thermal recording materials of Examples 1 to 3 and Comparative Examples 1 to 4 were evaluated as follows, and the results are shown in Table 1 below.
It was shown to. The evaluation methods are as follows.

[Sensitivity] The sensitivity is a labeler (ISHIDA
IF21EX, 0.65 ms, 23 V) is a value measured by a Macbeth densitometer RD-918. The larger the number, the higher the sensitivity, and at least 1.0 or more is practically desirable.

[Heat resistance of blank paper] The heat resistance of blank paper was measured by leaving the above-mentioned thermal recording material in an environment of 90 ° C. or 100 ° C. for 1 hour, and measuring the density of the background (unprinted) portion with Macbeth densitometer RD-918. It was measured at.

[Image storage stability] The image storage stability is the storage stability with a plasticizer, and three diamond laps G (manufactured by Mitsubishi Plastics) are superposed on the image area at 40 ° C. for 24 hours. The residual rate of the image when processed is shown. The larger the number, the better the storage stability, and in practice, 80% or more is desirable.

[0048]

[Table 1]

As shown in Table 1 above, the heat-sensitive recording materials of Examples 1 to 3 are particularly excellent in sensitivity, heat resistance of the blank area at 90 ° C. and 100 ° C., and stability of the image area. Example 4
In Nos. 5 and 5, the heat resistance and image stability of the blank area at 90 ° C. and 100 ° C. are excellent, and the sensitivity is at a sufficient level.

Since the heat-sensitive recording material of Comparative Example 1 contains no sensitizer, the heat resistance of the blank area is at a sufficient level, but the sensitivity and image stability are poor. Since the heat-sensitive recording materials of Comparative Examples 2 and 3 use the sensitizers other than the present invention, the heat resistance of the blank area is inferior. Since the thermosensitive recording material of Comparative Example 4 uses the color developing agent other than the present invention, the sensitivity, the heat resistance of the blank portion, and the image stability are not at a sufficient level.

[0051]

As is clear from the examples, the present invention has high sensitivity, heat resistance of blank paper, and excellent image storability.

Claims (2)

[Claims] 1. A thermosensitive recording material having a leuco dye and a color developer containing a leuco dye and a color developer on one surface of the support, and a protective layer formed thereon. At least one compound represented by the following chemical formula 1 (general formula 1), and 1,4-dibenzyloxybenzene as a sensitizer, p-benzoyloxybenzoic acid methyl ester,
A heat-sensitive recording material comprising at least one selected from 4,4'-diallyloxydiphenyl sulfone. Embedded image (In the formula, R represents a hydrogen atom, an alkyl group, an aryl group, an alkenyl group or an aralkyl group.) 2. The heat-sensitive recording material according to claim 1, wherein release paper is attached to the other surface of the support through a pressure-sensitive adhesive layer.