JPS6144683A - Thermosensitive recording body - Google Patents

Abstract

PURPOSE:To obtain a thermosensitive body which is suitable to half-tone recording and has high dot reproducibility by providing an intermediate layer containing an amorphous silica having BET specific surface area and oil absorption within a specific range between a thermosensitive color-forming agent containing leuco compound and a developer, and a support. CONSTITUTION:An intermediate layer containing an amorphous silica having BET specific surface area of less than 150m<2>/g and oil absorption of less than 100ml/100g, is provided between a thermosensitive color-forming layer containing normally clear or pale leuco compound and a developer, and a support, thus making a thermosensitive recording body intended for. A pigment may be added to said intermediate layer. In addition, normally casein, starch, PVA, etc. are used as an adhesive.

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 various printer/tar 7 axis, 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 thermal recording medium is required to have dot reproducibility of K and dot reproducibility in a low density region.

Conventionally, in order to improve such dot reproducibility, there was a method of smoothing the Beck smoothness of the recording medium surface to 200 to 1000 seconds using a super calender, etc. (% Kosho 52-2).
0142), 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
-156086), but the method of increasing the smoothness by surface treatment hardly improves the dot reproducibility in the low concentration range, and conversely, the deposition of hot melt on the head, so-called piling. In this case, adhesion between the recording medium and the head, that is, so-called sticking, is likely to occur. Also, a method using undercoated paper as a support, especially JP-A-54-
Cast-coated paper, baryta paper, etc., such as 83841, have the effect of slightly improving dot reproducibility compared to non-coated paper, but the redness is insufficient. In addition, the method of adjusting the surface roughness and glossiness of the recording material within a specific range is subject to limitations on the heat-sensitive color forming layer, 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 provides a heat-sensitive recording material in which a heat-sensitive color-forming layer is provided on a support, the heat-sensitive color forming layer mainly consisting of a usually colorless or light-colored leuco compound, the leuco compound, and a color developing substance that develops color when heated. The BET specific surface area between the coloring layer and the coloring layer is 1.
The gist of the present invention is a heat-sensitive recording material characterized by providing an intermediate layer containing amorphous silica with an oil absorption of 11007 d/100.S1 or more with an oil absorption of 7 g or less.

The present invention will be explained in detail below.

The present invention has a BET specific surface area of 1 between the support and the thermosensitive coloring layer.
It is less than 50m2/g and has an oil absorption of 10011! j
The feature is that an intermediate layer containing amorphous silica of /1009 or more is provided, and those that deviate from these conditions are
The purpose of the present invention cannot be achieved. That is, when amorphous silica having a specific surface area of 150 nt2/9 or more is used, the whiteness of the surface of the heat-sensitive recording material is significantly reduced, especially when exposed to high temperature or high humidity. Also, the oil absorption amount is 1
00m/100. li! When the following amorphous silica is used, the effect of improving dot reproducibility is insufficient.

It is also possible to further add conventionally known pigments to the intermediate layer, in which case aluminum hydroxide and calcium carbonate are particularly preferred.

The intermediate layer contains amorphous silica and water-soluble resins such as starch, PVA, and SB as binders for the pigments.
Latex such as R and MBR is used, and the amount used is determined by considering the strength of the coating layer, dot reproducibility, etc.
When the amount of binder is large, the strength of the coating layer increases, but dot reproducibility tends to decrease. The coating amount of the intermediate layer is not particularly limited and may be changed as appropriate to obtain the required performance.

In the present invention, the heat-sensitive color-forming layer provided on the intermediate layer is not particularly limited as long as it mainly contains a normally colorless or light-colored leuco compound and a color-developing substance that causes the leuco compound to develop color when heated. .

As the support used in the present invention, paper is generally used, but synthetic resin films, woven fabric sheets, etc. can also be used.

〔Example〕

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

Example 1 Amorphous silica (specific surface area 40 m2//i, oil absorption 160
m/100. li + volume average particle diameter 1.7 μm) 100I
was poured into 425 g of a 7% casei/aqueous solution, dispersed for 5 minutes using a homomixer, and coated on base paper with a basis weight of 52:i/m2 to a coating amount of 61! /m'' and dried.

Next, the following solutions A, B, and C were prepared respectively: 52 parts by weight of solution A, 90 parts by weight of solution B, 56 parts by weight of solution C, 20 parts by weight of 30% zinc stearate dispersion, 12% aqueous polyvinyl alcohol solution, 125 parts by weight were mixed to prepare a heat-sensitive coating liquid. This coating liquid was applied onto the intermediate layer at a coating amount of 69/m.
It was coated and dried so that the Bekk smoothness was about 60.
A heat-sensitive recording material was obtained by carrying out rolling/dabbing so that the time was 0 seconds.

A liquid black coloring dye S-205 (Yamada Chemical) 7 parts by weight Stearamide 10 1 Polyvinyl alcohol 12% aqueous solution ts z Polystyrene acrylic acid a/monium 2.51 μm 20% aqueous solution Water 1
Disperse 7.5 parts by weight or more in paint conditioner for 16 hours.

Part B Bisphenol A 20 parts by weight Stearamide 10 1 Polyvinyl alcohol 12% aqueous solution i 25 #Polystyrene acrylic acid a/monium 2,51 mm 20% aqueous solution water 32
．． Disperse 5# or more with paint conditioner for 16 hours.

Liquid C light calcium carbonate (particle size 2 μm) 100 parts by weight Sodium polyacrylate 40% aqueous solution 41 water
Disperse 96 1 or more in a homomixer for 10 minutes.

Examples 2 and 3 Instead of the amorphous silica of Example 1, specific surface area 95 m''/,
9. Oil absorption amount 185 m1/100 g, volume Example 2 manufactured in the same manner as in Example 1, specific surface area 130 m2
/9, oil absorption 255mA! /100I, volume average particle size 2
, 0 μm amorphous silica was used, and Example 3 was produced in the same manner as in Example 1 except for the following.

Comparative Examples 1, 2, 3.4 In place of the amorphous silica of Example 1, a specific surface area of 300 m
2/jj, oil absorption 3101d/Zoo, 9, amorphous silica with a volume average particle diameter of 3.5 μm or specific surface area 700
m”/9, oil absorption 75Kg/100g, volume average particle size 1
Amorphous silica of 0.0 μm or specific surface fa, 300
m2/ji, oil absorption 210 mj/100y1 Amorphous silica with volume average particle diameter 7.0 μm or specific surface area 700 m
27g, oil absorption fk85m7/100y, volume average particle size 4
．． Comparative Examples 1, 2, and 3.4 were manufactured in the same manner as in Example 1 except that 0 μm amorphous silica was used.

Comparative Example 5 Specific surface area 10.5 m instead of amorphous silica of Example 1
2/9, oil absorption 99d/100g, volume average particle size 4.
Comparative Example 5 was prepared in the same manner as in Example 1 except that 0 μm light calcium carbonate was used.

〔Effect of the invention〕

Table 1 shows evaluations of dot reproducibility and background density for Examples and Comparative Examples. As is clear from the table, according to the present invention, it is possible to obtain a heat-sensitive recording material with good dot reproducibility in a low density region and with little background fog.

Table 1 Luxury malt Note 1) Specific surface area is BET specific surface area.

2) Oil absorption is based on JISK5101.

3) Evaluation of dot reproducibility is dot density 6 dots/IR1
! Using a No. L facsimile machine, solid recording was performed at an image density of 0.1 to 0.8 by varying the width of the applied pulse, and the results were visually determined.

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

Claims (1)

[Claims] In a heat-sensitive recording material in which a heat-sensitive color-forming layer is provided on a support, the heat-sensitive color-forming 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, between the support and the heat-sensitive color-forming layer. and an intermediate layer containing amorphous silica having a BET specific surface area of 150 m^2/g or less and an oil absorption of 100 ml/100 g or more.