JPS61193880A - Thermal recording material - Google Patents

Abstract

PURPOSE:To ensure that dot reproduction property in a low density region is favorable, ground fogging is little and an excellent effect is displayed in the case of intermediate gradation recording or the like, by sequentially providing on a base a layer comprising an inorganic pigment having an oil absorption not less than a specified value, a film-forming high molecular weight material layer and a thermal color forming layer. CONSTITUTION:A layer comprising an inorganic pigment having an oil absorption of not less than 100ml/100g, a film-forming high molecular weight material layer and a thermal color forming layer are sequentially providing on the base. The pigment is, for example, fired clay, aluminum oxide or titanium oxide, and a binder for the pigment may be an ordinary one, e.g., casein, starch, a water-soluble resin such as PVA or a latex such as SBR and MBR. A film- forming high molecular weight material is, for example, PVA, casein, MC or HEC. The thermal color forming layer comprises a normally colorless or light- colored leuco compound, a color developing substance for developing the color of the leuco compound when being heated and a binder as main constituents, each constituent being a conventional one.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a heat-sensitive recording medium, and in particular, a heat-sensitive recording medium suitable for halftone recording.
This invention relates to a heat-sensitive recording material with excellent dot reproducibility.

[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 dot reproducibility, especially dot reproducibility in a low density region.

Conventionally, in order to improve such dot reproducibility, a method such as a super calendarer was used to increase the Beck smoothness of the recording medium surface to 200 to 1000 seconds (Japanese Patent Publication No. 52-2014).
No. 2), 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. 55-15)
6086), etc., but the method of increasing the smoothness by surface treatment does not always improve the dot reproducibility in the low concentration range, and on the contrary, the deposition of hot bath melt on the head does not improve the new pile method. When this occurs, adhesion between the recording medium and the head, so-called sticking, is likely to occur. In addition, it is also possible to use undercoated paper as a support.
Cast-coated paper, baryta paper, etc., such as those shown in No. 841, have the effect of slightly improving dot reproducibility compared to non-coated paper, but are still insufficient. Furthermore, in the method of adjusting the surface roughness and glossiness of the recording medium to 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.

Therefore, the present inventors conducted research to improve the dot reproducibility of thermosensitive recording paper in the low density range, and found that the oil absorption between the support and the thermosensitive coloring layer was xooml/lo.

It has been found that by providing an intermediate layer containing an inorganic pigment of more than or equal to
The application was filed earlier (Japanese Patent Application No. 166500, 1983). However, although the heat-sensitive recording material with such a structure improves dot reproducibility, the intermediate layer is porous, so the binder of the heat-sensitive recording layer penetrates into the intermediate layer, making it difficult to smooth it using a calender or the like. When stored under high temperature and high humidity, the background density tends to increase when stored under high temperature and high humidity.

[Problem that the invention seeks to solve]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a heat-sensitive recording material which has good dot reproducibility and does not have the above-mentioned drawbacks.

[Means for solving problems]

That is, in the present invention, the oil absorption amount is 100 mg/10 on the support.
This is a heat-sensitive recording material in which a layer containing 0 or more inorganic pigments (hereinafter referred to as an inorganic pigment layer), a film-forming polymer layer, and a heat-sensitive coloring layer are sequentially provided.

Oil absorption used in the inorganic pigment layer of the present invention: 100 m/10
Examples of inorganic pigments having a value of 0 or more include calcined seaweed, aluminum oxide, titanium oxide, magnesium carbonate, diatomaceous earth, hydrous silicic acid, anhydrous silicic acid, aluminum silicate,
Magnesium silicate, calcium silicate, magnesium aluminosilicate, sodium aluminosilicate, etc., or pigments with an oil absorption of less than xooml/xoor can be chemically or physically treated to have an oil absorption of 1ook/1oot or more.

Further, the binder used as a binder for the pigment in the inorganic pigment layer is not particularly limited and may be any binder that is normally used as a binder for pigments, but examples include casein, starch, PVA, etc. Water-soluble resins and latexes such as SBR and MBR are used.

Film-forming polymers used in the film-forming polymer layer of the present invention include PVA, casein, and MC1HEC.

Water-soluble resins such as polyacrylate, polyacrylamide, and sodium alginate, latex such as SBR and MBR, or solvent-soluble resins are used alone or in combination.

The coating amount of the inorganic pigment layer and the film-forming polymer layer varies depending on the basis paper weight and web characteristics, but the inorganic pigment layer has a coating amount of 1 to 10 f.
/wl, film-forming polymer layer is 0.5~a, o y/vt
The purpose of the present invention can be achieved with this method.

In addition, the ratio of the pigment to the binder in the inorganic pigment layer can be changed as appropriate to obtain the required performance. The main components are a sensitizer and a binder, and various substances including a sensitizer may be added as necessary, and all conventionally known components can be used as these components.

〔Example〕

Hereinafter, the present invention will be explained according to examples.

Example 1゜ Amorphous silica (oil absorption a1oml/1oor.

100 tons of 796 casein aqueous solution (3.5 μfi) was poured into 425 f of 796 casein aqueous solution, dispersed for 5 minutes using a homomixer, coated on base paper with a basis weight of 52 ψ, and dried so that the coating amount was 6. An inorganic pigment layer was provided.

Next, casein was applied onto the inorganic pigment layer at a rate of 1.5 f/rrl to provide a film-forming polymer layer.

Next, prepare the following solutions A, B, and C, respectively, and
A heat-sensitive coating liquid was prepared by mixing 90 parts by weight of liquid B, 56 parts by weight of liquid C, 20 parts by weight of a 30% zinc stearate dispersion, and 125 parts by weight of polyvinyl alcohol 129b water ffi liquid. This coating solution was applied and dried on the film-forming polymer layer so that the coating amount was 6 acids, and the Peck smoothness was about 6.
After 00 seconds, calendering was performed to obtain a heat-sensitive recording material.

A liquid black coloring dye S-205 (Yamada Chemical System) 7 parts by weight Stearamide 10 I polyvinyl alcohol 124711 liquid 15 g Polystyrene ammonium acrylate 265120T4 aqueous solution 17.51
Disperse the above in a paint conditioner for 16 hours.Part B Bisphenol A 20 Parts by weight Stearamide 10 I Polyvinyl alcohol 12 Aqueous solution 25 I Polystyrene ammonium acrylate 2.5120 Aqueous solution water 32.5
Disperse with 1 or more paint conditioners for 16 hours.

Liquid C Light calcium carbonate (particle size 2 μs) 100 parts by weight Sodium polyacrylate 40% aqueous solution 4 parts by weight Water 96
1 or more are dispersed for 10 minutes using a homomixer.

Example 2 Instead of the amorphous silica used in the inorganic pigment layer of Example 1, a pigment obtained by acid treatment of acidic white i& (oil absorption 220d/100F volume average particle diameter 1.8 μWL) was used. Example 2. was manufactured in the same manner as in Example 1 except for Example 2. shall be.

Example 3゜Example 1. Example 3 was prepared in the same manner as in Example 1 except that PEA was used instead of casemine for the film-forming polymer layer.

Comparative Example 1.2 Comparisons were made in the same manner as in Example 1, except that the film-forming polymer layer of Examples 1 and 2 was not provided, and a heat-sensitive coloring layer was provided on the inorganic pigment layer. Example 1.2.

Comparative Example 3 Comparative Example 3 was prepared in the same manner as in Example 1, except that the heat-sensitive coloring layer of Example 1 was placed directly on a base paper having a basis weight of 5297 M.

Dot reproducibility and background density were measured for the samples prepared as described above (Table 1). The measurement method was as follows.

l) Evaluation of dot reproducibility was performed using a dot density of 6 dots/...
Using a facsimile machine, solid recording was performed at an image density of 0.1 to 0.8 by changing the width of the applied pulse, and the results were visually judged.

2) The skin density was measured using a Macbeth reflection densitometer RD-514 (using a visual filter).

Immediately after preparing the sample, after leaving it at 40℃ and 901RH for 24 hours,
Testing was carried out under three conditions after being left standing for 24 hours in a 60°C room temperature.

〔Effect of the invention〕

As is clear from the test results, the heat-sensitive recording material of the present invention has good dot reproducibility in the low density region and has the characteristics of less background fogging, and is particularly useful when recording halftones. Features excellent effects

Claims (1)

[Claims] A heat-sensitive recording material comprising a layer containing an inorganic pigment having an oil absorption of 100 ml/100 g or more, a film-forming polymer layer, and a heat-sensitive coloring layer, which are sequentially provided on a support.