JPH089269B2 - Thermal recording material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a thermal recording paper, and more particularly to a high-sensitivity thermal recording paper having good thermal response and a small amount of sticking to the thermal head. Is.

[Prior Art] A thermal recording paper generally comprises a single-layer or multi-layer thermosensitive coloring layer containing a binder or a thermochromic substance as a main component on a support such as paper, plastic film or synthetic paper. is there.

A color image can be obtained by simply heating the thermosensitive recording paper,
Further, it is preferred that the recording apparatus can be made relatively simple and compact, and is widely used as various information recording sheets.

In particular, in recent years, thermal facsimiles and thermal printers using such a thermal recording material have been improved in the apparatus, and high-speed recording, which has been difficult in the past, has become possible. Such equipment,
With the increase in speed in the field of hardware, the thermal recording paper used is also required to have improved recording sensitivity, and many proposals have been made regarding this.

Up to now, it has been considered effective to improve the recording sensitivity of the thermal recording paper by smoothing the support and providing heat insulation with an undercoat layer.

As a method for this, hydrophobic polymer particles having a lower thermal conductivity than that of the inorganic pigment are contained in the undercoat layer (JP-A-59-20).
4595 and JP-A-60-3697), or in order to further add heat insulating properties to air, hollow fine particles are contained in the undercoat layer (JP-A-59-171685 and JP-A-59-225987). Gazette) is proposed. But these methods
Although effective in improving the recording sensitivity, it was an insufficient technique in terms of adhesion of lees to the thermal head, which is as important as the recording sensitivity in practical use.

Therefore, it has been proposed to provide a layer in which highly oil-absorbing silicon oxide is combined with hydrophobic polymer particles as an undercoat layer to prevent the adhesion of lees to the thermal head (JP-A-61-89).
No. 883). However, when such highly oil-absorbing silicon oxide is added, the amount of the color-melting component of the heat-sensitive color-developing layer absorbed in the undercoat layer is increased, and the image becomes dull.

[Problems to be Solved by the Invention] Accordingly, the present invention has a high recording sensitivity, can effectively prevent adhesion of lees, and can prevent bleeding of an image when colored with high energy. Intended to provide paper.

[Means for Solving the Problems] The present invention provides a thermosensitive recording sheet having a thermosensitive recording layer containing an electron-donating colorless dye and an electron-accepting compound provided on a support, and between the support and the thermosensitive coloring layer. Average particle size of 5 μm
The following polystyrene and oil absorption of 50ml / 100g or more 100ml / 1
The present invention relates to a heat-sensitive recording material characterized by comprising an undercoat layer containing a pigment in the range of less than 00 g in a weight ratio of 1/4 to 4/1.

The inventors of the present invention have found that by providing an undercoat layer under a thermosensitive coloring layer and using polystyrene as a filler for the undercoat layer, higher recording sensitivity can be obtained than when an inorganic pigment is used as a filler. I knew However,
When polystyrene is used alone, it cannot be said to be a desirable heat-sensitive recording material because of its insufficient absorbency of lees. Therefore, by mixing an inorganic pigment in order to improve the absorptivity, it was possible to obtain a desirable heat-sensitive recording material having a high recording sensitivity and a high absorptivity.

Polystyrene has high thermal conductivity and can obtain high recording sensitivity. Polystyrene has an average particle size of 5 μm or less,
It is preferable to use fine particles having a particle size of 0.5 to 2 μm. If the particle size is larger than 5 μm, an undercoat layer having high smoothness cannot be formed. It should be taken into consideration that particles having a particle size smaller than 0.5 μm tend to further reduce the absorbency of lees.

The pigment to be mixed with polystyrene in the undercoat layer has an oil absorption of 50 ml / 100 g or more and less than 100 ml / 100 g (JIS k5101)
belongs to. Examples of such pigments include calcined clay, calcium carbonate, magnesium carbonate and the like. In this case, if the oil absorption amount is 100 ml / 100 g or more, the residue absorbency is improved, but when printing with high energy, the print density is reduced, which is not appropriate.

The polystyrene and the pigment are generally 1: 4 to 4: 1.
Used by mixing in the range of (weight ratio). When the amount of the pigment in the oil absorption range is more than 1: 4, the high recording sensitivity cannot be maintained, and when the amount of the polystyrene is more than 4: 1, the high lees absorbency cannot be maintained.

An adhesive is used when forming an undercoat layer comprising the polystyrene and the pigment. The amount of the adhesive used is 1 to 20 parts (weight ratio) based on 100 parts of the total amount of polystyrene and pigment. As the adhesive to be used, generally known water-soluble polymer aqueous emulsion is used, and specific examples thereof include those shown below.

Polyvinyl alcohol, methyl cellulose, hydroxyethyl cellulose, starch, starch derivative, styrene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, polyamide, SBR latex, polystyrene-acrylic acid ester emulsion, polyvinyl acetate emulsion and the like.

As described here, polystyrene, the pigment in the oil absorption range, and the adhesive are dispersed in an aqueous medium in any order,
A coating liquid is prepared by mixing, and the coating liquid is coated on a support so that the coating weight is 1 to 15 g / m ² as a dry weight, to form an undercoat layer. The coating can be performed using a usual coating machine.

The support is paper, plastic film, synthetic paper,
It can be selected from those made of an appropriate material such as metal foil.

A thermosensitive coloring layer is formed on the undercoat layer thus provided.

The heat-sensitive coloring layer may be formed by an ordinary method. The following can be used as the colorless or light-colored electron donating dye.

Crystal violet lactone 3- (N-ethyl-)
N-isopentylamino) -6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7- (o, p-dimethylani Rino) Fluoran, 3- (N-ethyl-p-toluidino) -6-methyl-
7-anilinofluoran, 3-pyrrolidino-6-methyl-7-anilinofluoran, 3-dibutylamino-6-methyl-7-anilinofluoran, 3- (N-cyclohexyne-N-methylamino ) -6
-Methyl-7-anilinofluorane, 3-diethylamino-7- (o-chloroanilino) fluorane, 3-diethylamino-7- (m-trifluoromethylanilino) fluorane, 3-diethylamino-6-methyl-7- The following compounds are mentioned as typical examples of chlorofluorane, 3-diethylamino-6-methylfluorane, 3-cyclohexylamino-6-chlorofluorane, and electron-accepting compounds (developers).

Bisphenol A, benzyl p-hydroxybenzoate, n-butyl di (4-hydroxyphenyl) acetate, bisphenol S, 4-hydroxy-4′-isopropyloxydiphenyl sulfone, 1,1-di (4-hydroxyphenyl) cyclohexane, 1,7-di (hydroxyphenylthio) -3,5-dioxaheptane, in addition to this, substances which can be usually contained in the heat-sensitive color developing layer may be optionally contained. For example, as the so-called sensitizer, a heat-fusible organic compound having a known melting point of 50 to 150 ° C. is generally used, and the following representative examples can be enumerated.

p-Hydroxynaphthoic acid phenyl ester, p-benzyl biphenyl, benzyl naphthyl ether, benzyl terephthalate, benzyl p-benzyloxybenzoate, diphenyl carbonate, ditolyl carbonate, and as organic or inorganic pigments, there are no restrictions such as oiling properties. In addition, for example, calcium carbonate, silica, zinc oxide, titanium oxide, aluminum hydroxide, zinc hydroxide, barium sulfate, clay, talc, inorganic fine powders such as surface-treated calcium carbonate and silica, and urea-formalin. Resins, styrene / methacrylic acid copolymers, organic fine powders such as polystyrene resins, and the like can be used as necessary.

In addition to this, various waxes may be contained as required. Known materials such as paraffin, amide wax, bisimide wax, and metal salt of higher fatty acid may be used.

Further, as the adhesive, polyvinyl alcohol of various molecular weights, starch and its derivatives, methoxycellulose, carboxymethylcellulose, methylcellulose,
Cellulose derivatives such as ethyl cellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylic acid amide /
Acrylic acid ester copolymer, acrylic acid amide / acrylic acid ester / methacrylic acid terpolymer, styrene / maleic anhydride copolymer alkali salt, polyacrylamide, sodium alginate, gelatin, casein, etc. Others, polyvinyl acetate, polyurethane, styrene / butadiene copolymer, polyacrylic acid, polyacrylic acid ester, vinyl chloride / vinyl acetate copolymer, polybutyl methacrylate, ethylene / vinyl acetate copolymer, styrene / butadiene / acryl A latex such as a system copolymer can be used.

[Examples] Next, the present invention will be specifically described by way of examples. Unless otherwise specified, parts and% in the examples are parts by weight and% by weight, respectively.
Indicates.

Example-1 Water 100 parts Calcined clay (Ansilex, manufactured by Engelhart, oil absorption 80 ml / 100 g) 20 parts Polystyrene particle dispersion (L8801 manufactured by Asahi Kasei (particle size 0.5 μ
m) Solid content 48%) 40 parts were dispersed by a homogenizer for 5 minutes and then mixed with 50 parts of 10% polyvinyl alcohol (G17 manufactured by Nippon Gosei Co., Ltd.) to prepare an undercoat liquid. The coating amount of this undercoat layer coating solution on 50 g / m ² high-quality paper
It was applied and dried so that the amount became 7 g / m ² .

On the other hand, as a coating liquid for the thermosensitive coloring layer, dispersion A 3- (N-isopentyl-N-ethylamino) -6-methyl-7-anilinofluorane 20 parts Polyvinyl alcohol 10% liquid 10 parts water 70 parts Was pulverized with a sand grinder to an average particle size of 2 μm.

Dispersion Benzyl p-hydroxybenzoate 20 parts Polyvinyl alcohol 10% liquid 10 parts Water 70 parts This composition was ground to an average particle size of 2 μm with a sand grinder.

Formation of thermosensitive coloring layer 75 parts of solution A, 125 parts of solution B, 30 parts of calcium carbonate, 200 parts of 10% polyvinyl alcohol aqueous solution, 17 parts of 30% paraffin dispersion liquid, 17 parts of 30% zinc stearate dispersion liquid are mixed and stirred to apply. It was a liquid. The resulting coating liquid was applied and dried on the undercoat layer formed as described above so that the coating amount after drying was 4.5 g / m ² to obtain a thermosensitive recording paper.

Example-2 Water 100 parts Light calcium carbonate (Callite SA oil absorption of Shiraishi Chuken 60
ml / 100g) 20 parts Polystyrene particle dispersion (L8801, Asahi Kasei, solid content 48)
%) 40 parts was dispersed with a homogenizer for 5 minutes, and then mixed with 50 parts of 10% polyvinyl alcohol (G17 manufactured by Nippon Gosei Co., Ltd.) to prepare an undercoat layer coating solution. This undercoat layer coating solution was applied and dried on a high-quality paper of 50 g / m ^{2 so} that the coating amount was 7 g / m ² .

A thermosensitive coloring layer was provided on the undercoat layer in the same manner as in Example 1 to produce a thermosensitive recording paper.

Comparative Example-1 100 parts water Synthetic silica (Solex CM oil absorption 150 ml / 10 manufactured by Tokuyama Soda)
0g) 20 parts Polystyrene particle dispersion (L8801, Asahi Kasei, solid content 48)
%) 40 parts was dispersed with a homogenizer for 5 minutes, and then an undercoat coating liquid was prepared in the same manner as in Example-1 and similarly coated on the same support to form an undercoat layer. A thermosensitive coloring layer similar to that in Example 1 was provided on this undercoat layer.

Comparative Example-2 100 parts of water Ansilex 40 parts was dispersed with a homogenizer for 5 minutes, an undercoat coating solution was prepared in the same manner as in Example-1, and the same support was similarly coated to form an undercoat layer. A thermosensitive coloring layer similar to that in Example 1 was provided on the undercoat layer to obtain a thermosensitive recording paper.

Comparative Example-3 Water 100 parts Polystyrene particle dispersion (L8801 manufactured by Asahi Kasei, solid content 48
%) 82 parts was dispersed with a homogenizer for 5 minutes, and then an undercoat coating liquid was prepared in the same manner as in Example-1 and similarly coated on the same support to form an undercoat layer. A thermosensitive coloring layer similar to that in Example 1 was provided on this undercoat layer.

Table 1 shows the results of measurement of the sensitivity and the degree of adhesion of lees on the thermal recording papers obtained in Examples-1 and 2 and Comparative Examples-1 to 3.

The data in Table 1 shows that the heat-sensitive recording material of the present invention has 0.44 mJ, especially 0.44 mJ even at high applied energy of 0.54 mJ.
It shows that the color density is excellent as in the case of No. 1 and that it also gives a good result in terms of the degree of cake-like adhesion. It can be said that maintaining a constant color density in a wide applied energy range (0.1 mJ or more) is an extremely desirable property for the opportunity design of printers and the like and for good image quality of thermal recording paper.

On the other hand, Comparative Example-1 is an example using a highly oil-absorptive pigment, but shows that the image density is lowered when a high applied energy of 0.54 mJ. Comparative example-2 is a case where polystyrene is not used and the color density is low. Comparative Example-3 is an example using only polystyrene. Although a favorable color density was shown in a wide applied energy range, the degree of adhesion of lees could not be practically used.

 These measurements were performed as follows.

(1) Sensitivity It was measured using an actual machine thermal facsimile modified for testing. The pulse width is modulated under the conditions of 1 line recording time 10 msec / line and scanning line density 8 × 8 dots / mm, and the applied energy per dot is adjusted to 0.44 mJ and 0.54 mJ,
64 lines were printed.

The color density at that time was measured with a Masbeth densitometer RD-514, and the value representative of the recording sensitivity was used.

(2) Deposition degree of lees The state of lees deposition on the thermal head was visually inspected. ○
Indicates that there is almost no adhesion of lees and is practically good, Δ indicates that there is adhesion of lees, but there is almost no problem in practice, and x indicates that there is a large amount of lees adhesion and it is impractical.

[Advantages of the Invention] According to the present invention, it is possible to provide a high-sensitivity heat-sensitive recording paper which has high thermal sensitivity, has no image blemishes when colored with high energy, and has almost no amount of residue adhered to the heat-sensitive head. Became.

Claims (1)

[Claims] 1. A thermosensitive recording paper comprising a support and a thermosensitive coloring layer containing a colorless or light-colored electron-donating dye and an electron-accepting compound, wherein polystyrene having an average particle diameter of 5 μm or less and oil absorption of 50 ml / 100 g or more. A heat-sensitive recording material comprising an undercoat layer containing a pigment of less than 100 ml / 100 g in a weight ratio of 1/4 to 4/1 and provided between the support and the heat-sensitive color forming layer.