JPH02121881A - Thermal recording paper - Google Patents

Abstract

PURPOSE:To reduce the amount of the refuse adhered to a thermal head by using talc and heavy calcium carbonate as the pigment in a bottom coat layer in combination. CONSTITUTION:A bottom coat layer and a thermal color forming layer are laminated to a support in this order and, as the pigment contained in the bottom coat layer, talc and heavy calcium carbonate are used in combination. Since a bulky layer can be smoothly formed by this method, thermal recording paper having high sensitivity and reduced in the amount of the refuse adhered to a thermal head can be provided. The bottom coat layer is easily obtained by coating a support composed of proper material quality such as paper, a plastic film, synthetic film or a metal foil with a coating solution and the coating amount in this case is generally 1-15g/cm<2> (dry wt.) and it is most pref. that the pigment is contained in an amount of 50-95% by wt. of the total coating amount and the mixing ratio of talc and heavy calcium carbonate is pref. set to 8/2-4/6 on a wt. basis.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a thermal recording paper, and more particularly, to a thermal recording paper that has good thermal responsiveness and has almost no amount of lees adhering to a thermal head. .

[Prior Art] Thermosensitive recording paper is popular because it can produce colored images simply by heating it, and the recording device can be made relatively simple and compact, so it is widely used as a variety of information recording paper. It is used for.

Particularly in recent years, improvements have been made in the equipment of thermal facsimile machines and thermal printers that use such thermal recording bodies, and high-speed recording, which was difficult in the past, has become possible.

As the speed of such equipment and hardware increases, the thermal recording paper used is required to have improved recording sensitivity, and many proposals have been made in this regard. This thermosensitive recording paper is generally made up of a support such as paper, plastic film, synthetic paper, etc., and a single or multilayer thermosensitive coloring layer containing a binder or a thermochromic substance as a main component.

In order to improve the recording sensitivity of heat-sensitive recording paper, a method has been proposed in which an undercoat layer is cast coated to improve smoothness and improve adhesion of the heat-sensitive coloring layer of the heat-sensitive head. (Unexamined Japanese Patent Publication No. 54-
(No. 83841, Japanese Unexamined Patent Publication No. 56-21889) However, coating by cast coating is not suitable for manufacturing low-cost, high-consumption paper such as heat-sensitive recording paper due to its operability.

There are also examples in which smoothness is improved by applying a supercoat after applying the undercoat layer (Japanese Patent Application Laid-open No. 86792/1983).

However, superimposition impairs the heat insulation properties required of the undercoat layer, and as a result, sufficient sensitivity improvement effects are lost.

In addition, clay having a plate-like shape is used as a pigment for undercoating,
Talc is used to improve the smoothness of the undercoat layer, and at the same time, the low oil absorption of clay and talc is used to prevent the molten components of the heat-sensitive coloring layer from being absorbed into the undercoat layer, thereby preventing a drop in color density and improving sensitivity. However, in this method, the molten components are not absorbed into the undercoat layer, so it is difficult to prevent scum from adhering to the thermal head. Can not do it.

[Problems to be Solved by the Invention] The present invention improves the drawbacks of the conventional techniques described above, improves the smoothness and bulk of the undercoat layer, increases sensitivity, and reduces the amount of scum that adheres to the thermal head. The purpose is to provide thermal recording paper.

[Means for Solving the Problems] The present invention provides a heat-sensitive recording paper in which a heat-sensitive recording layer containing an electron-donating colorless dye and an electron-accepting compound is provided between the support and the heat-sensitive recording layer. The desired effect is achieved by selecting a combination of talc and ground calcium carbonate as pigments in the undercoat layer.

Since talc has good affinity with organic substances, it is considered to have good compatibility with the heat-melting components in the heat-sensitive coloring layer, and is therefore effective in preventing the adhesion of head residue. However, because its particle shape is scale-like, it is difficult to form a bulky layer even when used as a pigment for an undercoat layer, and therefore sufficient sensitivity cannot be obtained, making it a preferred material. I couldn't say yes. On the other hand, heavy calcium carbonate is made by mechanically crushing limestone, so it has a wider particle size distribution than synthetic calcium carbonate, and if it is used alone as an undercoat pigment, the smoothness of the undercoat layer will decrease. However, sufficient sensitivity cannot be obtained.

However, as a result of intensive research by the present inventors, we were able to form a bulky layer smoothly by using a combination of talc and heavy calcium carbonate. It has been found that it is possible to provide thermal recording paper with a low amount of lees adhering to it.

Although the present inventor does not insist on the reason why a bulky layer can be obtained by combining talc and heavy calcium carbonate, it can be considered as follows.

Talc has a scale-like particle shape, while ground calcium carbonate has a spherical particle shape compared to talc. Moreover, since both talc and heavy carbonate calcilyl\ have the same specific gravity of 2.7, it is thought that they are uniformly dispersed in the coating color.

When such a coating color is applied onto a base paper, the scale-like talc is oriented parallel to the base paper, and the heavy calcium carbonate is evenly distributed between them, increasing the voids in the layer and at the same time increasing the layer thickness. The effect of increasing the voids in the coating film, which also increases the voids on the surface and causes an increase in sensitivity and a decrease in the amount of lees adhering to the thermal head, is remarkable. Compare the cross-sectional photos of layers coated on base paper with the same amount of coating. The increase in thickness is significant, and it can be seen that the number of voids in the coating film is increasing. For example, Figure 1 shows the cross section of Example 1 in which an undercoat layer containing both talc and ground calcium carbonate as pigments was coated and dried on a support (high-quality paper).
It was observed at a magnification of 00x, and Figure 2 shows Comparative Example 3.
The cross section was similarly observed at 2000x magnification for the undercoat layer using the same amount of pigment consisting only of talc on the same support, but compared to the case of talc alone in Figure 2, the In the case of Figure 1, the thickness increases by 25-30%, and the increase in voids in the coating film can be said to be dramatic.Moreover, even on the surface of the undercoat layer, compared to the case of talc alone as shown in Figure 2, the number of voids in the coating film increases dramatically. In the case of the present invention shown in FIG. 1, many voids are observed.

The undercoat layer can be easily obtained by applying it to a support made of a suitable material such as paper, plastic film, synthetic paper, metal foil, etc. using a conventional coating machine.

In this case, the coating amount for forming the undercoat layer is 1
~15g/1m' (dry weight) is a numerical value, and it is most preferable that the pigment is included in the amount by 50 to 95% by weight based on the total coating amount, and the blending ratio of talc and heavy calcium carbonate is The weight ratio is preferably in the range of 8/2 to 4/6.

The heat-sensitive coloring layer formed on the undercoat layer is formed by a conventional method. For example, the following can be used as colorless or light-colored color-forming lactone compounds.

Crystal violet lactone 3-(N-ethyl-N
-isopentylamino)-6-methyl-7anilinofluorane.

3-diethylamino-6-methyl-7-anilinofluorane.

3-diethylamino-6-methyl-7-(o,p-dimethylanilino)fluoran.

3-(N-ethyl-p-)luidino)-6-methyl7-
Anilinofluorane.

3-pyrrolidino-6-methyl-7-anilinofluorane.

3-Dibutylamino-6-methyl-7-anilinofluorane 3-(N-cyclohexine-N-methylamino)6-methyl-7-anilinofluorane.

3-diethylamino-7-<o-chloroanilino)fluoran.

3-diethylamino-7-(m luanilino) fluoran.

trifluoromethi 3-diethylamino Luolan.

6-methyl-7 Krolov 3-diethylamino-6-methylfluorane.

Typical examples of the encapsulating agent made of 3-cyclohexylaminone, 6-chlorofluoraphenol, or an organic acid include the following.

Bisphenol A Benzyl P-hydroxybenzoate.

n-Butyl di(4-hydroxyphenyl)acetate.

Bisphenol S 4-hydroxy4 Nilsulfone.

Isoprobyloxydife 1.1-di(4-hydroxyphenyl)cyclohexane.

1.7-di(hydroxyphenylthio)-35-dioxahep, tan As the so-called sensitizer, known thermofusible organic compounds with a melting point of 50150°C are generally used, and the following representative examples can be listed. .

p-hydroxynaphthoic acid phenyl ester 5p-benzylbiphenylbenzyl naphthyl ether pendyl terephthalate p-benzyloxybenzoic acid benzyl carbonate diphenyl.

Ditrilyl carbonate.

The organic or inorganic pigments used in the heat-sensitive coloring layer are not limited by oil absorption, etc., and include, for example, calcium carbonate, silica, rti zinc, zinc titanium,
In addition to inorganic fine powders such as aluminum hydroxide, zinc hydroxide, barium sulfate, clay, talc, and surface-treated calcium carbonate and silica, organic materials such as urea-formalin resin, styrene/methacrylic acid donor polymer, and polystyrene resin A fine powder of the above-mentioned type may be used within a range that satisfies the requirements of the present invention.

Furthermore, the heat-sensitive coloring layer of the present invention can contain various waxes as required. Known waxes such as paraffinamide wax, bisimide wax, and metal salts of higher fatty acids may be used.

In addition, adhesives include polyvinyl alcohol of various molecular weights, starch and its derivatives, methoxycellulose,
Cellulose derivatives such as carboxymethylcellulose, methylcellulose, and ethylcellulose, sodium polyacrylate, polyvinylpyrrolidone, acrylic amide/acrylic ester copolymer, acryl amide/acrylic ester/methacrylic acid ternary copolymer, styrene/maleic anhydride Acid copolymer alkali salt, polyacrylamide.

In addition to water-soluble polymers such as sodium alginate, gelatin, and casein, polyvinyl acetate, polyurethane, styrene/butadiene copolymer, polyacrylic acid, polyacrylic acid ester, vinyl chloride/vinyl acetate copolymer, polybutyl methacrylate, Latex such as ethylene/vinyl acetate copolymer, styrene/butadiene/acrylic copolymer, etc. can be used.

[Example] Next, the present invention will be explained using a specific example. Also, unless otherwise specified, parts and percentages in steel indicate parts by weight and percentages by weight, respectively.

Example 1 Water
100 parts talc (MPIO-52, manufactured by Pfizer MSP).

Particle size 0.9μm, oil absorption 52 wheels 1/100y)
50 parts heavy calcium carbonate (NS2300.

Made by Nitto Funka, 1 particle diameter is 1.0 μ, oil absorption is 34.5 soj! /10h)
50 parts 10 g Polyvinyl alcohol aqueous solution (Nippon Gosei LO5) 10 parts were dispersed with a homogenizer for 5 minutes, and then mixed with 50 parts of 10% polyvinyl alcohol (Nippon Gosei GH17),
This was used as an undercoat layer coating solution. This undercoat layer coating liquid was applied at 50g/m"
It was coated and dried on high-quality paper so that the coating amount was 727 m''.

FIG. 1 is an mv and mirror photograph of the cross section of the undercoat layer formed on the support in this manner, observed at a magnification of 2000 times. According to FIG. 1, it is possible to clearly understand the state in which flaky talc is uniformly mixed with spherical heavy calcium carbonate to form a bulky layer. Furthermore, according to FIG. 1, it is observed that the upper part of the cross section of the base paper (surface of the undercoat layer) maintains smoothness due to talc, and voids are formed due to heavy calcium carbonate.

On the other hand, as a coating liquid for the heat-sensitive coloring layer, ■ Preparation of dispersion A 20 parts fluoran 10% polyvinyl alcohol 10 parts water
70 parts of this composition was ground in a sand grinder to an average particle size of 2 microns.

■ Preparation of dispersion B Benzyl p-hydroxybenzoate 20 parts Polyvinyl alcohol 10% M 10 parts Water
70 parts of this composition was ground in a sand grinder to an average particle size of 2 microns.

■ Composition of thermosensitive coloring layer: 75 parts of liquid A, 125 parts of liquid B, 30 parts of calcium carbonate, 1
200 parts of 0% polyvinyl alcohol aqueous solution.

17 parts of a 30% paraffin dispersion and 17 parts of a 30% zinc stearate dispersion were mixed and stirred to prepare a coating liquid.

The obtained coating liquid was applied to undercoated paper so that the coating amount after drying was 4.5y/+*'' and dried to obtain thermal recording paper.The performance of the obtained thermal recording paper was as follows. They are summarized in Table 1.

Example 2 Water
100 parts Taruri (Micro Ace, P-4, made by Nippon Taruri, 1 particle size 1.5μ, oil absorption 40m1/100y)
50 copies/100. ) 50 parts 10% polyvinyl alcohol (Nippon Gosei GLO5) 1
After dispersing 0 part with a homogenizer for 5 minutes, the mixture was mixed with 50 parts of 10% polyvinyl alcohol (Nippon Synthetic [GH17]) to prepare an undercoat layer coating liquid. Add this undercoat layer to '3017m
Coat and dry on high-quality paper No. 2 so that the coating amount is 7 g/J. Further, the same treatment as in Example 1 was performed to form a heat-sensitive coloring layer.

Comparative example 1 water
100 parts Talc (MPIO-52, Pfizer H5P
Particle diameter 0.9μm) 100
After dispersing 10 parts of 10% polyvinyl alcohol with a homogenizer for 5 minutes, prepare an undercoat layer coating solution in the same manner as in the Ml, and apply the coating amount to 50 g/I12 high-quality paper to 7 g/m.
” was coated and dried to form an undercoat layer. On top of that, the same treatment as in Example 1 was performed to form a heat-sensitive coloring layer.
A thermosensitive recording paper was obtained.

Comparative example 2 water
100 parts heavy calcium carbonate (NS2300.Nitto Powdering Particle Size 1.0μ Plow) 10
After dispersing 10 parts of 10% polyvinyl alcohol for 5 minutes using a homogenizer, an undercoat layer coating solution was prepared in the same manner as in Example 1. A thermosensitive recording paper was obtained by using the same support and thermosensitive coloring layer dispersion as in Example 1 and carrying out the same treatment as in Example 1.

Comparative example 3 water
100 parts talc (Micro Ace P-42 manufactured by Nippon Talc, particle size 1.5 μM> 10
After dispersing 10 parts of 10% polyvinyl alcohol for 5 minutes with a homogenizer, an undercoat layer coating solution was prepared in the same manner as in Example 1, and coated on the same high-quality paper as in Example 1 so that the coating amount was 7 g/II2. Dry.

FIG. 2 is a microscopic photograph of the cross section of the product with the undercoat layer formed at a magnification of 2000 times. The flaky talc was blended in the coating direction corresponding to the lateral direction of the photograph, and the coating layer was thinner than in the case of Example 1 shown in FIG.

In other words, in the case of Fig. 1, the thickness of the undercoat layer is 2
The surface of the undercoat layer, which is thicker than 5 to 30%, has high smoothness due to the talc, but it is observed that there are few voids.

After forming the undercoat layer, a heat-sensitive coloring layer was formed in the same manner as in Example 1, and the same treatment was performed to obtain a heat-sensitive recording paper.

Comparative example 4 water
100 parts heavy calcium carbonate (Softon 1800° Bihoku Funka 5 particle size 1.3 μs) too part 10
After dispersing 10 parts of % polyvinyl alcohol for 5 minutes using a homogenizer, a coating solution for an undercoat layer was prepared in the same manner as in Example 1. The same support and heat-sensitive coloring layer coating solution as in Example 1 were obtained, and the same treatments as in Example 1 were carried out to obtain heat-sensitive recording paper.

Comparative example 5 water
100 parts talc (Micro Ace P-4)
50 parts fired clay (Sachinton Whitex, manufactured by Engelhard, oil absorption 45-1/100y)
) 50 copies 102
≦10 parts of polyvinyl alcohol were dispersed using a homogenizer for 5 minutes, and then an undercoat layer coating solution was prepared in the same manner as in Example 1. The same support and heat-sensitive coloring layer coating solution as in Example 1 were obtained, and the same treatments as in Example 1 were carried out to obtain heat-sensitive recording paper.

Table 1 shows the results of measuring the sensitivity and degree of lees adhesion for the thermal recording papers obtained in Examples 1 to 2 and Comparative Examples 1 to 5.

Table 1 Note that the above measurements were performed as follows.

(1) Sensitivity Measured using an actual thermal facsimile machine modified for testing purposes. 1 line recording time 10+5sec/line,
The pulse width was modulated under the conditions of a scanning line density of 8.times.8 dots/dot, the applied energy per dot was adjusted to 0.44 mJ, and 64 lines were printed.

The color density at that time was measured using a Macbeth densitometer RD-514, and was taken as a value representative of recording sensitivity.

(2) Degree of lees adhesion The state of lees adhesion on the thermal head was visually inspected. It is clear from these measurement results that O indicates that there is almost no residue adhering and is good for practical use, Δ indicates that there is adhesion of residue but there is almost no problem in practical use, and × indicates that there is a large amount of residue adhesion that is practically impossible. Furthermore, the sensitivity and degree of lees adhesion of the thermal recording paper of the present invention using a combination of talc and heavy calcium carbonate in forming the undercoat layer are higher and better than those using an undercoat solution containing only one of them. It showed a good degree of lees adhesion.

[Effects of the Invention] The present invention has made it possible to provide a thermal recording paper that has good thermal response and high sensitivity, and has almost no amount of lees adhering to the thermal head.

[Brief explanation of drawings]

Figure 1 shows the cross section m of the thermosensitive recording paper of Example 1 at a magnification of 2000 times with an undercoat layer formed on the support.
This is a microscopic photograph. Figure 2 shows the cross section m of the thermal recording paper of Comparative Example 3 at a magnification of 2000 times with an undercoat layer formed on the support.
This is a microscopic photograph. Patent applicant: Oji Paper Co., Ltd. (1 other person) Atsushi/

Claims (1)

[Claims] 1. A thermosensitive recording paper comprising an undercoat layer and a thermosensitive coloring layer laminated in this order on a support, characterized in that the pigment contained in the undercoat layer consists of talc and heavy calcium carbonate.