JPS6198585A - Thermal recording medium - Google Patents

Abstract

PURPOSE:To raise the reproductivity of dots in low-density region by using a paper containing precipitated calcium carbonate in an amount of more than a specific % as a supporter. CONSTITUTION:A paper containing 30wt% or more precipitated calcium carbonate is used as a supporter to greatly improve the reproductivity of dots. The addition of 70wt% or more precipitated calcium carbonate greatly lowers the strength of the paper, although the upper limit of the calcium carbonate content is governed by the required strength of paper and also by manufacturing methods. The grain size of the precipitated calcium carbonate, obtained which is produced from reaction of line milk, carbon dioxide gas, and sodium carbonate, is usually 0.01-10mum. Any type of the conventional trigonal crystal (calcite) and orthorhombic crystal form (aragonite) as used at present time of precipitated calcium carbonate can be used for thermal recording materials.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a heat-sensitive recording medium, and particularly to a heat-sensitive recording medium with excellent dot reproducibility and suitable for halftone recording.

[Conventional technology]

The heat-sensitive recording method does not require a developing and fixing process and has easy hardware maintenance, so it is widely used for recording in various printers, facsimile machines, measuring instruments, etc. Furthermore, recently, devices have appeared that apply the thermal recording method to record halftones of television images and the like.

In order to perform such halftone recording, the heat-sensitive recording medium is required to have good dot reproducibility, especially in a low density region.

Conventionally, in order to improve such dot reproducibility, a method such as a super calender was used to smooth the Bekk flatness of the surface of the recording medium to 200 to 1000 seconds (Japanese Patent Publication No. 1973-
20142), a method of using undercoated paper as a support (Japanese Patent Laid-Open No. 54-83841), a method of adjusting the surface roughness and gloss of the recording medium to a specific range (Japanese Patent Laid-Open No. 54-83841),
5-156086), etc., but the method of increasing the smoothness by surface treatment hardly improves the dot reproducibility in the low concentration range, and on the contrary, it causes the accumulation of hot melt on the head, so-called piling. In other words, adhesion between the recording medium and the head, so-called sticking, is likely to occur. Also, a method of using undercoated paper as a support, especially JP-A-54
-G3841, cast coated paper, baryta paper, etc. have a slight effect of improving dot reproducibility compared to non-coated paper, but it is still insufficient. Furthermore, in the method of setting the surface roughness and glossiness of the recording medium within a specific range, there are restrictions on the heat-sensitive color forming layer, the coating method, etc., and dot reproducibility in the low density region is not necessarily satisfactory.

[Problem that the invention seeks to solve]

The present invention has been researched in view of these conventional drawbacks, and its purpose is to provide a thermal recording medium with excellent dot reproducibility and suitable for halftone recording.

[Means for solving problems]

That is, the present invention relates to a heat-sensitive recording material in which a heat-sensitive coloring layer is provided on a support, the heat-sensitive color forming layer mainly comprising a usually colorless or light-colored leuco compound and a color-developing substance that causes the leuco compound to develop color when heated. The object of the present invention is to provide a heat-sensitive recording material characterized by being a paper containing 30% by weight or more of calcium carbonate.

Hitherto, wood-free paper has often been used as a support for heat-sensitive recording materials, and general wood-free paper contains about 10 to 15% by weight of fillers such as clay and talc. However, when these high-quality papers are used as a support for a thermal recording medium, the dot reproducibility in the low density range is very poor, and even if the filler content is increased, the dot reproducibility is almost constant. No improvement.

Furthermore, in JP-A-55-156087, there is a description of adding 20 grams of calcium carbonate to the pulp when making a support for thermal paper. The objective of the present invention is to improve the storage stability of the dots, but it is not possible to achieve satisfactory dot reproducibility in the low concentration range, which is the objective of the present invention. Therefore, precipitated calcium carbonate is used as a filler, and its content is 30% by weight.
It was unexpected that the dot reproducibility in the low concentration range could be significantly improved by using the above method compared to the lower method.

The precipitated charcoal calcium used in the present invention is a synthetic product produced by reacting milk of lime with charcoal gas or soda carbonate, and can be obtained in various particle sizes and shapes depending on the manufacturing conditions. For example, particle sizes of 0°01 to 10 μm are usually obtained.

Furthermore, although trigonal system (calzite) has conventionally been the mainstream crystal system, in recent years, orthorhombic system (aragonite) systems have also been commercially available, and any of these can be used in the thermosensitive recording medium of the present invention.

In the present invention, paper containing 30 weight ke4 or more of precipitated carbonized calcium is used as a support.

If the content is less than 30% by weight, the significant improvement in dot reproducibility, which is the object of the present invention, cannot be achieved. The upper limit of the content is determined by the required paper strength and manufacturing method, but if it exceeds 70% by weight, the paper strength will drop significantly and the thermosensitive recording material of the present invention cannot be rolled.

The support used in the heat-sensitive recording material of the present invention may be prepared by adding precipitated calcium carbonate, a sizing agent, and other additives to a pulp slurry and then making the paper using a paper machine, and then using the support as it is for the heat-sensitive recording material. Alternatively, it is used as a support after increasing the surface smoothness by calendering, but it is not necessary to increase the smoothness by intensive calendering.

Each component used in the heat-sensitive recording layer of the heat-sensitive recording material of the present invention, namely, a usually colorless or light-colored leuco compound, a color developing substance that causes the leuco compound to develop color when heated, various additives including a binder and a sensitizer. All conventionally known substances can be used. [Example] The present invention will be described below with reference to Examples.

Example 16 Precipitated calcium carbonate (manufactured by Shiroishi Kogyo Co., Ltd. 80 parts by weight of PC), cationized starch (
(manufactured by Arayo Kagaku Co., Ltd.) 6-layer needle part, anionic polyacrylamide (Polystron 117, manufactured by Arayo Kagaku Co., Ltd.) 0.5-layer needle part, neutral sizing agent (bar: ffn W, Dick Bercules) Company ff) Add 1 part by weight, 60 t/n?
Paper is made from paper and lightly calendered to a thickness of 6.
A paper with a surface smoothness of 6 μm, a size of 18 seconds, and a filler content of 400 parts by weight was obtained.

Next, the following liquids A, B, and C were prepared respectively: 52 parts by weight of liquid A, 90 parts by weight of liquid B, 56 parts by weight of liquid C, 20 parts by weight of a 30% zinc stearate dispersion, a 12% polyvinyl alcohol aqueous solution, 125 parts by weight were mixed to prepare a heat-sensitive coating liquid.

This coating liquid was applied on the paper in an amount of 6 'i'/n? The coating was coated and dried to obtain a heat-sensitive recording material, and calendering was performed to obtain a Bekk smoothness of approximately 600 seconds.

A liquid black coloring dye S-205 (manufactured by Yamada Chemical Co., Ltd.) 7 Parts by weight Stearamide 10 #Polyvinyl alcohol 12% aqueous solution 15 I Polystyrene ammonium acrylate 2.5 II2O3 aqueous solution 17.5 parts by weight or more was dispersed between 1f3R with paint conditioner do.

Part B Bisphenol A 20 Parts by weight Stearamide 10 I Polyvinyl alcohol 12% water soluble? ffl 25' polystyrene ammonium acrylate 2.5IM 20
Aqueous solution water 32.5
1 or more with paint conditioner for 16 hours.

C liquid light calcium carbonate (particle size 2 μm) Zoo Part by weight Sodium polyacrylate 40% Aqueous solution 41 Water 96 ・
Disperse the above with a homomixer for 10 minutes.

Example 2 Precipitated calcium carbonate (TP manufactured by Okutama Kogyo Co., Ltd.) was used as a filler.
Example 2 is a heat-sensitive recording material manufactured in the same manner as in Example 1 except that 121) was used.

Comparative Example 1 Comparative Example 1 is a heat-sensitive recording material produced in the same manner as in Example 1 except that heavy calcium carbonate (Softon 2200, manufactured by Bihoku Funka Co., Ltd.) was used as a filler.

Comparative Example 2 Merck (manufactured by Paper Talc Co., Ltd. 1) was added to a pulp slurry consisting of 50 parts by weight of LBKP of C, S, FF Suisan 300- and 50 parts by weight of NBKP of C, S, F Suisan 300-. Parts by weight, 4 parts by weight of sulfuric acid-dry soil, 4 parts by weight of cationized starch (manufactured by 8 Star Chemical Co., Ltd.), 0 parts by weight of anionic polyacrylamide (Polystron 117, Buyou Kagaku Co., Ltd. ff)
．． 3 parts by weight, acidic paper sizing agent (Sizevine E50
, manufactured by Buyou Kagaku Co., Ltd.) to form a paper with a weight of 602 m² or more, and lightly calendered it to a thickness of 60 μm.
m, surface smoothness of 39 () seconds, sizing degree of 3 seconds, and filler content of 400 parts by weight. Next, apply the heat-sensitive coating liquid used in Example 1 to 6 W/lr? Apply and dry so that the following results are obtained. Further, calendering was performed to obtain a Bekk smoothness of approximately 600 seconds to obtain a heat-sensitive recording material.

Comparative Example 3: Clay (AT, manufactured by Zikrite Chemical Industry Co., Ltd.) as a filler
Comparative Example 3 is a heat-sensitive recording material manufactured in the same manner as in Comparative Example 1 except for using the following.

Table 1 shows the evaluation results of the dot reproducibility of Example 1.2 and Comparative Example 1.2.3.

Table 1 * Solid coloring was performed using a thermal printer with a fixed head of 6 dots/meter at an energy of 16 mJ/m171', and visually judged.

With this amount of energy, the print density is 0.3 to 0.4.

Examples 3 to 5 Comparative Examples 4 to 7 Based on Example 1, the additive gold of precipitated calcium carbonate was changed and the content R of the filler was changed to produce Ml of 6o2/R and calendered under the same conditions. The heat-sensitive paint used in Example 1 was coated on the coated support, and calendering was performed under the same conditions to obtain a heat-sensitive recording material. The dot reproducibility of this thermosensitive recording material was evaluated.Examples 3 to 5, Comparative Example 4
~7.

Table 2 [Effects of the Invention] As is clear from the examples and drawing photographs, the heat-sensitive recording material using as a support paper containing precipitated carbonized calcium as an IcQ material in an amount of 30"iIL or more did not produce dots in the low concentration range. The reproducibility is very good (0).

[Brief explanation of the drawing]

Figures 1 to 3 are electron micrographs of the surfaces of heat-sensitive recording materials of the present invention and for comparison, on which images have been recorded, Figure 1 is Example 1, Figure 2 is Comparative Example 1, Figure 3 is 3 is a photograph of the surface of a heat-sensitive recording material of Comparative Example 7. Patent application included Honshu Paper Co., Ltd. Procedural Amendments March 7, 1985

Claims (1)

[Claims] In a heat-sensitive recording material in which a heat-sensitive coloring layer is provided on a support, the heat-sensitive coloring layer is mainly composed of a usually colorless or light-colored leuco compound and a color-developing substance that causes the leuco compound to develop color when heated. A heat-sensitive recording material characterized by being paper containing 30% by weight or more.