JPH0767856B2 - Thermal recording - Google Patents

Description

The present invention relates to a heat-sensitive recording material, and more particularly to a heat-sensitive recording material having excellent print pixel reproducibility and excellent cutting suitability and bending suitability.

"Prior Art" Conventionally, a thermosensitive recording that utilizes a color reaction between a color-forming agent and a color-forming agent that develops color by contacting the color-forming agent, by contacting both color-forming substances with heat to obtain a color-developed image. The body is well known. Since such a thermal 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 computers but also in a wide range of fields.

Then, with the diversification of applications, to a thermal recording medium that has excellent reproducibility of printing pixels in any area from low density to high density and can obtain a high quality recorded image comparable to silver halide photography. Are increasing in demand. Further, with the increase in speed of recording equipment, there is an increasing demand for a thermal recording material having excellent dynamic recording sensitivity.

In order to obtain such a high quality and highly sensitive thermal recording material,
For example, the glass transition temperature is 60 ° C between the support and the recording layer.
An intermediate layer made of the following film-forming polymeric substance may be provided (JP-A-54-92263), or an intermediate layer made of an oil-absorbing pigment may be provided (JP-A-59-155097, 61-44683). ), And a method for improving smoothness and heat insulation by combining these layers in a multilayer manner (Japanese Patent Laid-Open Nos. 61-11286 and 61-193880).
No.) etc. have been proposed.

However, satisfactory results have not always been obtained because new defects are accompanied with the improvement. That is, for example, in the method of providing the intermediate layer made of the film-forming polymer substance, the dot re-limitability is improved as the smoothness is improved, but the gas adhesion to the thermal head is increased, and the void of the intermediate layer is increased. Probably because of a small amount, the heat insulating property is insufficient and a satisfactory recording sensitivity cannot be obtained. Further, in the method of providing the intermediate layer mainly composed of the oil-absorbing pigment, the dust adherence to the thermal head hardly occurs and the recording sensitivity is good, but the recording medium is cut probably because the adhesive force of the intermediate layer is weak. At the same time, paper dust is likely to be generated and the recording layer is peeled off when the recording medium is bent.

[Problems to be Solved by the Invention] An object of the present invention is to achieve excellent reproducibility of print pixels in any area from low density to high density and to record with high image quality without the above-mentioned drawbacks. The object is to provide a thermosensitive recording medium from which an image can be obtained.

"Means for Solving Problems" The above-mentioned object of the present invention is achieved by providing an intermediate layer having a specific composition between the support and the recording layer.
Thus, the present invention provides a thermosensitive recording medium having a thermosensitive recording layer provided on a support, a pigment having an apparent specific gravity of 0.7 g / cm ³ or less, and a glass transition temperature between the support and the recording layer. Is -20 ° C
The thermosensitive recording medium is characterized by comprising an intermediate layer having a solid content ratio of 100: 8 to 100: 30 with respect to the polymer emulsion binder.

"Function" As described above, the thermosensitive recording medium of the present invention comprises a pigment having an apparent specific gravity of 0.7 g / cm ³ or less and a polymer emulsion binder having a glass transition temperature of -20 ° C between the support and the recording layer. It is to provide an intermediate layer having a solid content ratio of 100: 8 to 100: 30, and as the pigment, various inorganic pigments and organic pigments are known, for example, calcined kaolin, talc, light calcium carbonate. Amorphous silica, polystyrene fine powder, urea formalin resin fine powder, and the like are preferred specific examples. Among these various pigments, calcined kaolin and amorphous silica are particularly excellent in the heat insulating property and, therefore, more excellent in the effect of improving the recording sensitivity.

Examples of the polymer emulsion binder having a glass transition temperature of -20 ° C or lower include various polydienes such as natural rubber, polyisoprene and polybutadiene, and various polyalkenes such as polyethylene, polybutene, polypropylene and polyisobutylene. It is preferably used. Among them, natural rubber and polyisoprene have suitable elasticity and adhesiveness, and are therefore preferable in that the desired effects of the present invention can be achieved in a very balanced manner.

In the present invention, the specific pigment and the binder, which form the main components of the intermediate layer, are preferably blended so that the solid content ratio is in the range of 100: 8 to 100: 30 in terms of adhesiveness and recording sensitivity. . For example, if the content of the binder is larger than this range, the heat insulating property is lowered and the desired recording sensitivity cannot be obtained, possibly because the void ratio of the intermediate layer is decreased, and the adhesion of dust to the thermal head is also increased. If the amount of the binder is less than the above range, the adhesive force of the pigment particles will be reduced, and paper dust will be generated when the recording material is cut, and the recording layer will be peeled off when the recording material is bent. .

In order to form the specific intermediate layer as described above on the support, a pigment and a polymer emulsion-based binder are generally mixed to prepare an aqueous coating solution, which is applied to the support.
The method of drying is adopted. The coating solution may contain a usual water-soluble polymer, a polymer emulsion having a high glass transition temperature, or the like within a range that does not impair the desired effects of the present invention, but the amount used is It is desirable to keep 20 parts by weight or less for 100 parts by weight of the pigment. Also,
Various auxiliaries, which will be described later, which are added when the coating liquid for forming the heat-sensitive recording layer is prepared can be added, but the amount of the auxiliary should be carefully monitored.

The coating method of the coating liquid is not particularly limited, and coating and drying are performed by a coating device equipped with an appropriate coater head such as an air knife coater, a gravure coater, a roll coater and a bar coater.

In the present invention, the coating amount of the intermediate layer having the above-mentioned specific composition on the support is preferably such that the thickness is in the range of about 8 to 20 μm. If it is less than 8 μm, a sufficient improvement effect cannot be obtained, and even if it is applied over 20 μm, no further improvement effect can be expected, which is uneconomical, and it takes a lot of time for the drying process. The effect is derived.

The heat-sensitive recording layer is applied onto the intermediate layer thus formed and dried to produce the heat-sensitive recording material of the present invention. Regarding the combination of the color former and the color former contained in the recording layer Are not particularly limited, and any combination can be used as long as they are brought into contact with each other by heat to cause a color reaction, for example, a colorless or pale basic dye and an inorganic or organic acidic substance. And a combination of a higher fatty acid metal salt such as ferric stearate and a phenol such as gallic acid. Further, it can be applied to various heat-sensitive recording materials such as a heat-sensitive recording material in which a diazonium compound, a coupler and a basic substance are combined, so that a recorded image can be obtained by heat.

However, the particular intermediate layer of the present invention provided on the support exhibits excellent effects particularly in the combination of the basic dye and the acidic substance, and thus is particularly preferably applied to such a combination.

Various types of basic dyes that are colorless or light-colored are known, and the following are exemplified. 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide, 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, 3,3-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) -6-dimethylaminophthalide, 3,3-bis (2-phenylindol-3-yl) -6-dimethyl Triallylmethane dyes such as aminophthalide and 3-p-dimethylaminophenyl-3- (1-methylpyrrol-3-yl) -6-dimethylaminophthalide, 4,4'-bis-dimethylaminobenzhi Diphenylmethane dyes such as drill benzyl ether, N-halophenyl-leuco auramine and N-2,4,5-trichlorophenyl leuco auramine, thiazine dyes such as benzoyl leuco methylene blue and p-nitrobenzoyl leuco methylene blue, 3-methyl -Spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3-phenyl-spiro-dinaphthopyra 3-benzyl - spiro - dinaphthopyran, 3-methyl - naphtho - (6'-methoxybenzo) spiropyran, 3-propyl - spiro -
Spiro dyes such as dibenzopyran, lactam dyes such as rhodamine-B anilinolactam, rhodamine (p-nitroanilino) lactam, rhodamine (o-chloroanilino) lactam, 3-dimethylamino-7-methoxyfluorane, 3-diethylamino -6-Methoxyfluorane, 3-diethylamino-7-methoxyfluorane, 3
-Diethylamino-7-chlorofluorane, 3-diethylamino-6-methyl-7-chlorofluorane, 3-diethylamino-6,7-dimethylfluorane, 3- (N-
Ethyl-p-toluidino) -7-methylfluorane, 3
-Diethylamino-7-N-acetyl-N-methylaminofluorane, 3-diethylamino-7-N-methylaminofluorane, 3-diethylamino-7-dibenzylaminofluorane, 3-diethylamino-7-N-methyl -N-benzylaminofluorane, 3-dimethylamino-7-N-chloroethyl-N-methylaminofluorane, 3-diethylamino-7-N-diethylaminofluorane, 3- (N-ethyl-p-triidino)- 6-Methyl-7-phenylaminofluorane, 3- (N-cyclopentyl-N-ethylamino) -6-methyl-7-anilinofluorane, 3- (N-ethyl-p-triidino) -6-methyl -7- (p-toluidino) fluorane, 3-diethylamino-6-methyl-7-phenylaminofluorane, 3- Ethylamino-7- (2-carbomethoxy - phenylamino) fluoran, 3- (N-
Ethyl-N-isoamylamino) -6-methyl-7-phenylaminofluorane, 3- (N-cyclohexyl-)
N-methylamino) -6-methyl-7-phenylaminofluorane, 3-pyrrolidino-6-methyl-7-phenylaminofluorane, 3-piperidino-6-methyl-7
-Phenylaminofluorane, 3-diethylamino-6
-Methyl-7-xylidinofluorane, 3-diethylamino-7- (o-chlorophenylamino) fluorane,
3-dibutylamino-7- (o-chlorophenylamino) fluorane, 3-pyrrolidino-6-methyl-7-p
-Butylphenylaminofluorane, 3-N-methyl-
N-tetrahydrofurfurylamino-6-methyl-7-
Fluoran dyes such as anilinofluorane and 3-N-ethyl-N-tetrahydrofurfurylamino-6-methyl-7-anilinofluorane.

Various types of inorganic or organic acidic substances that develop color when contacted with a basic dye are known, and the following are exemplified.

Inorganic acidic substances such as activated clay, acid clay, attapulgite, bentonite, colloidal silica, aluminum silicate, 4-tert-butylphenol, 4-hydroxydiphenoxide, α-naphthol, β-naphthol, 4
-Hydroxyacetophenol, 4-tert-octylcatechol, 2,2'-dihydroxydiphenol, 2,2'-
Methylene bis (4-methyl-6-tert-butylphenol) 4,4'-isopropylidene bis (2-tert-butylphenol), 4,4'-sec-butylidene diphenol,
4-phenylphenol, 4,4'-isopropylidene diphenol (bisphenol A), 2,2'-methylenebis (4-chlorophenol), hydroquinone, 4,4 '
-Cyclohexylidene diphenol, benzyl 4-hydroxybenzoate, dimethyl 4-hydroxyphthalate, hydroquinone monobenzyl ether, novolac type phenol resin, phenolic compounds such as phenolic polymers, benzoic acid, p-tert-butylbenzoic acid, Trichlorobenzoic acid, terephthalic acid, 3-sec-butyl-4-hydroxybenzoic acid, 3-cyclohexyl-4-hydroxybenzoic acid, 3,5-dimethyl-4-hydroxybenzoic acid,
Salicylic acid, 3-isopropylsalicylic acid, 3-tert-
Butyl salicylic acid, 3-benzyl salicylic acid, 3- (α
-Methylbenzyl) salicylic acid, 3-chloro-5- (α
-Methylbenzyl) salicylic acid, 3,5-di-tert-butylsalicylic acid, 3-phenyl-5- (α, α-dimethylbenzyl) salicylic acid, 3,5-di-α-methylbenzylsalicylic acid and other aromatic carboxylic acids And organic acid substances such as salts of these phenolic compounds and aromatic carboxylic acids with polyvalent metals such as zinc, magnesium, aluminum, calcium, titanium, manganese, tin and nickel.

In the present invention, the use ratio of the color former and the color former in the recording layer is appropriately selected according to the type of the color former and the color former used and is not particularly limited, but for example, basic colorless When a dye and an acidic substance are used, it is generally 1 to 50 parts by weight, preferably 1 to 1 part by weight of a basic colorless dye.
~ 10 parts by weight of acidic material are used.

To prepare a coating liquid containing these substances, generally, water is used as a dispersion medium, and a coloring agent and a color developing agent are dispersed together or separately by a ball mill, an attritor, a sand mill or the like, and a pulverizer to prepare a coating liquid. Is prepared as.

In such a coating liquid, starch is usually used as a binder,
Hydroxyethyl cellulose, methyl cellulose, carboxoxyethyl cellulose, gelatin, casein, gum arabic, polyvinyl alcohol, diisobutylene / maleic anhydride copolymer salt, styrene / maleic anhydride copolymer salt, ethylene / acrylic acid copolymer salt, Styrene / acrylic acid copolymer salt, natural rubber emulsion, styrene / butadiene copolymer emulsion / acrylonitrile / butadiene copolymer emulsion, methyl methacrylate / butadiene copolymer emulsion, polychloroprene emulsion, vinyl acetate emulsion, ethylene / acetic acid Vinyl emulsion, etc.
70 wt%, preferably about 15 to 50 wt% is added.

Furthermore, various auxiliary agents can be added to the coating liquid,
For example, sodium dioctyl sulfosuccinate, sodium dodecylbenzene sulfonate, sodium lauryl alcohol sulfate / sodium salt, alginate, dispersant such as fatty acid metal salt, benzophenone-based, triazole-based UV absorber, other antifoaming agent, fluorescent Examples thereof include dyes and coloring dyes.

In addition, lubricants such as zinc stearate, calcium stearate, polyethylene wax, carnauba wax, paraffin wax, and ester wax, calcium carbonate, zinc oxide, aluminum oxide, titanium dioxide, silicon dioxide, aluminum hydroxide, barium sulfate, if necessary.
Inorganic pigments such as zinc sulfate, talc, kaolin, clay, calcined clay, colloidal silica, styrene microballs, nylon powder, polyethylene powder, urea
Formalin resin filler, organic pigment such as raw starch, stearic acid amide, stearic acid methylenebisamide, oleic acid amide, palmitic acid amide, fatty acid amides such as coconut fatty acid amide, dibenzyl terephthalate, 1,
2-di (3-methylphenoxy) ethane, 1,2-diphenoxyethane, 4,4'-ethylenedioxy-bis-benzoic acid diphenylmethyl ester, 1,1,3-tris (2-methyl-4-) Hydroxy-5-tert-butylphenyl) butane, 2,2'-methylenebis (4-methyl-6-tert-
Butylphenol), 4,4'-butylindene bis (6
It is also possible to add hindered phenols such as -tert-butyl-3-methylphenol) and various known heat-fusible substances.

When an inorganic or organic pigment is contained in the recording layer, it is preferable to use a pigment having a particle diameter as small as possible, and it is particularly preferable to use a pigment having an average particle diameter of 2 μm or less.

In the present invention, the method for forming the recording layer is not particularly limited, and is formed by a method in which the coating liquid is applied onto the intermediate layer by a coating apparatus equipped with a suitable coater head such as an air knife coater or a blade coater, and dried. To be done. Also, the coating amount of the coating liquid is not particularly limited,
Usually, the dry weight is in the range of ² to 12 g / m ² , preferably 3 to 10 g / m ² .

Also, the support is not particularly limited, and high-quality paper, base paper produced by Yankee machine, single-sided glossy base paper, double-sided glossy base paper, cast coated paper, art paper, coated paper, medium coated paper, etc., Synthetic fiber paper, synthetic resin film and the like are used appropriately.

The intermediate layer and the recording layer may be coated and dried, and if necessary, subjected to smoothing treatment such as super calendering. Further, an overcoat layer can be provided on the recording layer for the purpose of protecting the recording layer, and various known techniques in the field of thermal recording media such as providing a backing layer on a support can be added. .

The heat-sensitive recording material of the present invention thus obtained has an intermediate layer of a specific composition between the support and the heat-sensitive recording layer, and therefore has excellent pixel reproducibility in any area from low density to high density. It is a heat-sensitive recording material which is excellent in cutting suitability and bending suitability.

The reason why such an excellent effect is obtained is not necessarily clear, but a pigment having a small apparent specific gravity and a polymer emulsion-based binder having a low glass transition temperature are used to form a smooth and highly heat-insulating and elastic surface on the support. It is presumed that this is because the intermediate layer is formed. In particular, a polymer emulsion-based binder having a low glass transition temperature rapidly forms a film during application and drying to provide rubber-like elasticity and strength, and the synergistic action with a pigment having a small apparent specific gravity causes the above-mentioned intermediate layer to have It is presumed that such characteristics can be exerted.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. Unless otherwise specified, "parts" and "%" in the examples mean "parts by weight" and "% by weight" respectively.

Example 1 [Formation of intermediate layer] Calcined clay (trade name: Ansilex, apparent specific gravity: 0.2)
2g / cm ³ , Engel Hard Co., Ltd. 100 parts Natural rubber (glass transition temperature: -60 ° C, solid content: 60%, Guthrie Co., Ltd.) 20 parts Polyvinyl alcohol 10% aqueous solution 15 parts Water 100 parts The above composition Was mixed to prepare a coating solution for the intermediate layer. The obtained coating liquid was applied to a high-quality paper with a basis weight of 50 g / m ² and the coating amount after drying was 10 g / m ²
An intermediate layer was formed by coating and drying so as to have a thickness (12 μm).

[Formation of Recording Layer] Preparation of Liquid A 3- (N-cyclohexyl-N-methylamino) -6-
Methyl-7-phenylaminofluorane 10 parts Dibenzyl terephthalate 20 parts Methylcellulose 5% aqueous solution 15 parts Water 80 parts This composition was ground with a sand mill until the average particle size became 3 μm.

Preparation of Solution B 4,4′-isopropylidenediphenol 30 parts Methylcellulose 5% aqueous solution 30 parts Water 70 parts This composition was ground with a sand mill until the average particle size became 3 μm.

Solution A 125 parts, solution B 130 parts, silicon oxide pigment (oil absorption 180 ml / 10
0g) Stir 30 parts, 20% oxidized starch aqueous solution 150 parts, water 55 parts
A recording layer coating liquid was obtained by mixing.

The obtained coating liquid on the intermediate layer, the coating amount after drying 5g / m
^A thermosensitive recording paper was obtained by applying and drying so that it became ² .

Example 2 An intermediate layer having a two-layer structure was formed by coating the intermediate layer of Example 1 with a coating solution for the intermediate layer so that the coating amount after drying was 5 g / m ² (thickness: 7 μm). Layers were formed.

The coating liquid for recording layer was applied and dried on this intermediate layer in the same manner as in Example 1 to obtain a thermosensitive recording paper.

Example 3 [Formation of Intermediate Layer] Amorphous silica (trade name: Mizuka Seal P-527, apparent specific gravity: 0.18 g / cm ³ , manufactured by Mizusawa Chemical Co., Ltd.) 100 parts polyisoprene (trade name: LIR-30, glass transition temperature) : −5
(0 ° C., solid content: 45%, manufactured by Kuraray Co., Ltd.) 25 parts Polyvinyl alcohol 10% aqueous solution 15 parts Water 100 parts The above composition was mixed to prepare an intermediate layer coating liquid. The obtained coating liquid was applied to a high-quality paper with a basis weight of 50 g / m ² and the coating amount after drying was 10 g / m ²
An intermediate layer was formed by coating and drying so as to have a thickness (12 μm).

The coating liquid for recording layer was applied and dried on this intermediate layer in the same manner as in Example 1 to obtain a thermosensitive recording paper.

Comparative Example 1 In Example 1, the coating amount after drying the intermediate layer coating solution was 3 g / m 2.
Thermal recording paper was obtained in the same manner as in Example 1 except that coating and drying were performed so that the thickness became ² (thickness: 5 μm).

Comparative Example 2 [Formation of Intermediate Layer] Calcined clay (trade name: Ansilex, apparent specific gravity: 0.2)
2g / cm ³ , Engel Hard Co., Ltd. 100 parts Styrene-butadiene copolymer latex (glass transition temperature: -4 ° C, solid content: 48%) 25 parts Polyvinyl alcohol 10% aqueous solution 15 parts Water 100 parts The above composition The materials were mixed to prepare a coating solution for the intermediate layer. The obtained coating liquid basis weight is 50 g / m ² and the coating amount after drying is 10 g / m 2.
² (thickness: 12 μm) was applied and dried to form an intermediate layer.

The coating liquid for recording layer was applied and dried on this intermediate layer in the same manner as in Example 1 to obtain a thermosensitive recording paper.

Comparative Example 3 [Formation of Intermediate Layer] Calcined clay (trade name: Ansilex, apparent specific gravity: 0.2)
2g / cm ³ , manufactured by Engel Hard Co., Ltd. 100 parts Natural rubber (glass transition temperature: −60 ° C., solid content: 60%, Guthrie Co., Ltd.) 100 parts Polyvinyl alcohol 10% aqueous solution 15 parts Water 100 parts Was mixed to prepare a coating solution for the intermediate layer. The obtained coating liquid was applied to a high-quality paper with a basis weight of 50 g / m ² and the coating amount after drying was 10 g / m ²
An intermediate layer was formed by coating and drying so as to have a thickness (12 μm).

The coating liquid for recording layer was applied and dried on this intermediate layer in the same manner as in Example 1 to obtain a thermosensitive recording paper.

Using the thermal printer (SONY UP-701 type, TV printer), the 6 types of thermal recording papers thus obtained were recorded with printing pulse times of 3 ms and 8 ms, and the color density was recorded by the Macbeth densitometer (RD-100R type). , Using an amber filter), and the results are shown in Table 1. Further, the reproducibility of the printed pixels, the cutting suitability, and the bending suitability were evaluated, and the results are also shown in Table 1.

The reproducibility of the printed pixels was evaluated by the ratio of the area of the printed dots to the area of one dot of the thermal head (dot reproduction rate), and the evaluation criteria were as follows.

◎ …… 86% or more ○ …… 70 to 85% × …… 69% or less In addition, cutting suitability is evaluated based on the occurrence of paper dust when the recording part and the blank part of the recording paper are cut with a cutter. The evaluation criteria are as follows.

∘: No paper dust was generated and the recording layer was not peeled off.

A: No paper dust was generated, but the recording layer was slightly peeled off.

X: Paper dust is remarkably generated and the recording layer is often peeled off.

Further, the foldability was evaluated by the condition of the recording layer surface when the recording layer side of the recording paper was folded inside and returned, and the evaluation criteria were as follows.

A: No peeling of the recording layer.

○: The recording layer was slightly peeled off.

X: Peeling of the recording layer is remarkable.

"Effect" As is clear from the results shown in Table 1, the thermal recording materials obtained in the examples of the present invention have excellent reproducibility of print pixels in any range from low density to high density, and The recording material was excellent in cutting suitability and bending suitability.

Claims (3)

[Claims] 1. A thermosensitive recording medium comprising a thermosensitive recording layer provided on a support, wherein an apparent specific gravity is between the support and the recording layer.
The solid content ratio of the pigment which is 7 g / cm ² or less and the polymer emulsion binder whose glass transition temperature is -20 ° C or less is
A thermosensitive recording medium characterized by having an intermediate layer of 100: 8 to 100: 30. 2. The heat-sensitive recording material according to claim 1, wherein the polymer emulsion binder is at least one selected from polydienes and polyalkenes. 3. The heat-sensitive recording material according to claim 1 or 2, wherein the intermediate layer has a thickness of 8 to 20 μm.