JPH0679864B2 - Thermal recording sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application In the present invention, an undercoat is used as a support, and a heat-sensitive layer is applied on top of it to obtain good print quality, and to prevent contamination of the thermal head. It relates to a small number of heat-sensitive recording sheets.

(B) Conventional Technology and Problems Conventionally, a great number of processes have been studied for a heat-sensitive recording sheet for obtaining an image by utilizing physical and chemical changes of a substance due to thermal energy. Particularly, a so-called two-component color-developing heat-sensitive recording sheet is typical.

In the two-component color-developing heat-sensitive recording sheet, two kinds of heat-reactive compounds are dispersed in the form of fine particles, and a binder and the like are mixed and coated on a support. One or both of them is melted and brought into contact by heating. Records are obtained by utilizing the color reaction that occurs.

These two-component color thermosensitive recording sheets are inexpensive, do not require development, and are easy to handle, and have recently become the mainstream as image receiving recording paper for facsimile communication.

However, when a thermal recording sheet is used for a facsimile, the recording speed is slow because it is thermal recording. It is considered that this is mainly due to the poor thermal response between the thermal recording head and the sheet. Good thermal recording heads have been developed, but thermal recording sheets are still insufficient. As an example of such measures, an undercoat layer made of a pigment having a high oil absorption property is provided on a support, and a heat-sensitive layer is provided on the undercoat layer, whereby a pigment having a large heat capacity is separated from the heat-sensitive layer, so that sufficient color development can be achieved with a small heat energy. The concentration is obtained. However, pigments having a high oil absorbing property are poorly dispersed in an aqueous system and the concentration of the coating solution is low, resulting in a very disadvantageous runnability. Further, the use of a highly oil-absorbing pigment in the undercoat layer causes almost no staining of the thermal head due to the heat-fusible components in the thermal layer and adhesion to the thermal head. The reason for this is that the pigment directly below the thermal recording layer is used. It is considered that the color developing agent and the color developer melted by the heat of the head are promptly absorbed by the pigment coating layer because the layer has high oil absorption. However, on the contrary, in the case of recording with high energy, the color-developing agent having increased fluidity is absorbed by the pigment and is concealed, so that the effect of increasing the print density may be reduced.

(C) Object of the Invention In view of the present situation, the present inventors have found that the thermal recording sheet has a good thermal response and is capable of high-speed recording, and the thermal head is less contaminated and is effective even when a high thermal pulse is used. By conducting various researches on materials, and by including a pigment with an oil absorption of 50 ml / 100 g or more and titanium dioxide in the undercoat layer, a thermal recording sheet with good thermal response and good thermal head contamination can be obtained. The inventors have found that they can be obtained and have reached the present invention.

(D) Means for Solving the Problems That is, according to the present invention, the undercoat layer of the thermal recording sheet has
Pigment with an oil absorption of 50 ml / 100 g or more specified in SK5101 and 50 ml / 10
The present invention relates to a heat-sensitive recording sheet containing 0 g or less of titanium dioxide.

The titanium dioxide used in the present invention has an oil absorption of 50.
Any anatase type titanium dioxide, rutile type titanium dioxide, chlorinated titanium dioxide, surface treated titanium dioxide, various kinds of synthetic titanium dioxide, etc. may be used as long as they are ml / 100 g or less.

The ratio of titanium dioxide to the total pigment contained in the undercoat layer is preferably 5 to 80%.

Paper is generally used as the support of the present invention, but a plastic film or the like can be used if necessary.

Examples of pigments other than titanium dioxide used in the undercoat include calcined kaolin, talc, calcium carbonate, diatomaceous earth, aluminum hydroxide, magnesium hydroxide, silica, urea-formalin filler, and cellulose filler.

The undercoat layer is applied at ² to 15 g / m ² .

The thermosensitive coloring layer provided on the undercoat layer contains a color former and a developer as main components, but if necessary, waxes,
Metal soap, ultraviolet absorber, etc. are added.

Further, it does not matter if the above pigment is mixed.

The color forming agent used in the present invention is not particularly limited as long as it is used for general thermal recording paper, thermal recording paper and the like. Specific examples are (1) 3,3-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (crystal violet lactone) 3,3 as a triarylmethane compound.
-Bis (p-dimethylaminophenyl) phthalide, 3-
(P-Dimethylaminophenyl) -3- (1,2-dimethylindol-3-yl) phthalide, 3- (p-dimethylaminophenyl) -3- (2-methylindole-3)
-Yl) phthalide, 3- (p-dimethylaminophenyl) -3- (2-phenylindol-3-yl) phthalide, 3,3-bis- (1,2dimethylindol-3-yl) -5-dimethyl Aminophthalide, 3,3-bis- (1,2
-Dimethylindol-3-yl) -6-dimethylaminophthalide, 3,3-bis- (9-ethylcarbazole-
3-yl) -5-dimethylaminophthalide, 3,3-bis- (2-phenylindol-3-yl) -5-dimethylaminophthalide, 3-p-dimethylaminophenyl-
3- (1-methylpyrrol-2-yl) -6-dimethyl-
Aminophthalide, etc .: (2) 4,4′-bis-dimethylaminobenzhydrin benzyl ether as a diphenylmethane compound,
N-halophenyl leuco auramine, N-2,4,5-trichlorophenyl leuco auramine, etc .: (3) Rhodamine B-anilinolactam, rhodamine B-p-nitroanilinolactam, rhodamine B as a xanthene compound -P-chloroanilinolactam,
3-diethylamino-7-dipentylaminofluorane, 3-diethylamino-7-octylaminofluorane, 3-diethylamino-7-phenylfluorane, 3
-Diethylamino-7-3,4-dichloroanilinofluorane, 3-diethylamino-7- (2-chloroanilino) fluorane, 3-diethylamino-6-methyl-7
-Anilinofluora, 3-piperidino-6-methyl-7
-Anilinofluorane, 3-ethyl-tolylamino-6
-Methyl-7-anilinofluorane, 3-ethyl-tolylamino-6-methyl-7-phenyltylfluorane,
3-Diethylamino-7- (4-nitroalinino) fluorane, etc .: (4) Thiazine-based compounds such as benzoylleuco methylene blue, p-nitrobenzoylleucomethylene blue, etc .: (5) Spiro-based compounds such as 3-methyl-
Spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3,3'-dichloro-spiro-dinaphthopyran, 3-benzylspiro-dinaphthopyran, 3-methylnaphtho- (3-methoxy-benzo) -spiropyran, 3
There may be mentioned -propyl-spiro-dibenzopyran and the like, or a mixture thereof. These are determined by the application and the desired properties.

As the developer used in the present invention, a phenol derivative and an aromatic carboxylic acid derivative are preferable, and bisphenols are particularly preferable. 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,
Examples of 3,5-α-methylbenzyl salicylic acid and carboxylic acid include polyvalent metal salts thereof.

Examples of waxes include paraffin wax, kauna pallow wax, polyethylene wax, stearic acid amide, and higher fatty acid ester.

Examples of the metal soap include zinc stearate, aluminum stearate, calcium stearate and the like.

Water-soluble binders are generally used, and polyvinyl alcohol, hydroxyethyl cellulose, ethylene maleic anhydride copolymer, styrene-maleic anhydride copolymer, isobutylene-anhydrous-maleic acid copolymer, starch derivative, casein. , Gelatin and the like.

Sensitivity enhancers have a sharp melting point of 80 to 140 ° C and have good thermal response, and specifically include benzoic acid and terephthalic acid esters, naphthalene sulfonic acid esters, and naphthyl ether derivatives. Sensitizers such as anthryl ether derivatives, aliphatic ether-based compounds, phenanthrene, and fluorene can be used. Also, the above waxes can be used as a sensitizer.

As the binder for the undercoat layer, styrene-butadiene rubber latex, acrylic resin emulsion or the like may be used in addition to the above.

As an apparatus used for coating, an undercoat, a heat sensitive layer,
Both can use an air knife, a blade, a roll, etc. with a coater head.

Further, in order to improve the surface smoothness of the coated material, machine calendar, super calendar, gloss calendar, brushing, etc. can be used.

(E) Action When titanium dioxide is contained in the undercoat layer as in the present invention, due to its high specific gravity, many pigments are present below the undercoat layer and have oil absorption above, such as calcined kaolin and silica. Due to the large amount of the metal, the thermal melt adhering to the thermal head can be quickly absorbed by the undercoat layer.

In addition, since it contains titanium dioxide, it is considered that the pigments in the undercoat layer become denser, and the pigment becomes a heat insulating layer to improve the color developing sensitivity.

Also, oil-absorbing pigments such as calcined kaolin and silica are poorly dispersed in an aqueous system, but the presence of titanium dioxide improves the liquidity of the undercoat-like coating liquid, and the concentration can be increased, resulting in good operability. Since a smooth undercoat layer is obtained, the color developing sensitivity of the heat-sensitive layer coating solution is also improved.

As described above, it is possible to obtain a heat-sensitive recording sheet which has good color-developing sensitivity and has little thermal head contamination.

(F) Examples Examples of the present invention will be shown below, but the present invention is not limited thereto.

In addition, "part" and "%" in an Example show "weight part" and "weight%", respectively.

Example 1 50 parts of calcined kaolin (oil absorption of 70 ml / 100 g) and 50 parts of rutile titanium dioxide (oil absorption of 33 ml / 100 g) are dispersed in a 1% hexametaphosphoric acid aqueous solution to obtain a 60% slurry. To this, 5 parts of phosphorylated starch (MS4600) and 15 parts of latex (JSR0692) are added and mixed thoroughly. An undercoat paper was obtained by coating and drying the base paper so that the coating amount was 5 g / m ² . 20 g of crystal violet lactone dispersed in polyvinyl alcohol aqueous solution with a ball mill
A heat-sensitive coating liquid was prepared by mixing 100 g of -bis (p-hydroxyphenyl) propane and adding it to 30 g of a 21% stearic acid amide dispersion liquid. This heat-sensitive coating liquid was applied onto the undercoat paper so that the coating amount was 5 g / m ² . Further, calendering was performed at a pressure of 10 kg / cm to obtain a recording sheet.

Examples 2 and 3 Recording sheets were obtained in the same manner as in Example 1 except that the pigment composition of the undercoat layer was changed as shown in Table 1.

The anatase type titanium dioxide of Example 3 had an oil absorption of 18
The one used was ml / 100g.

Comparative Examples 1 to 4 Recording sheets were obtained in the same manner as in Example 1 except that the pigment composition of the undercoat layer was changed as shown in Table 1.

The recording sheets obtained in the above Examples and Comparative Examples are 500 g / m 2.
Recording was performed using a thin film head made by Matsushita Electronics Co., Ltd. (head voltage: 16 V, conduction width: 1 msec and 3 msec) with ^two thermal head pressures. The recorded densities were measured with a Macbeth densitometer. The results are shown in Table 1 including the amount of dust attached to the thermal head.

(G) Effects of the Invention In the present invention, an undercoat layer containing a pigment having an oil absorption of 50 ml / 100 g or more and titanium dioxide is provided between the heat-sensitive layer and the support, so that excellent color developability and less fouling of the thermal head It is intended to provide a thermosensitive recording sheet.

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Claims (2)

[Claims] 1. The amount of oil absorption defined by JIS K5101 on the support is 50 ml.
/ 100 g or more pigment and 50 ml / 100 g or less provided with an undercoat layer containing titanium dioxide, further provided on the undercoat layer a thermosensitive coloring layer containing an electron-donating colorless dye and an electron-accepting compound as main components A heat-sensitive recording sheet characterized in that 2. The heat-sensitive recording sheet according to claim 1, wherein the titanium dioxide contained in the undercoat layer is 5 to 80% by weight based on all pigments.