JPS62138286A - Thermal recording element - Google Patents

Abstract

PURPOSE:To improve dot reproducibility and enhance saturated color forming density by using paper containing an inorganic pigment which has more than a specific value of oil absorption as a support and providing an intermediate layer containing plastic pigment between a thermal color forming layer and the support. CONSTITUTION:A thermal color forming layer consisting of colorless or pale color leuko compound and a developer which thermally develops a color in the leuko compound as main components is provided on a support. The support is a paper containing an inorganic pigment having 100ml/100g or more of oil absorption. Further an intermediate layer containing a plastic pigment is provided between the support and the thermal color forming layer. As inorganic pigments, for instance, diatom earth, silicic hydride, aluminium silicate hydride and calcium silicate hydride are available. Plastic pigments are almost spherical microparticles of polystyrene, polymethyl methacrylate, polyvinyl chloride or polyvinylidene chloride. The diameter of these particles is 0.05-5mum. Thus superb dot reproducibility required for recording in half tone is assured with high saturated color forming density and wide dynamic range.

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 that has excellent dot reproducibility and a wide dynamic range necessary for halftone recording.

(Prior Art) The thermal 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, there was a method of smoothing the Bekk smoothness of the recording medium surface to 200 to 1000 seconds using a super calender etc. (Japanese Patent Publication No. 52-2
0142), a method of using undercoated paper as a support, a method of using cast coated paper, baryta paper, etc. as seen in JP-A No. 54-83841, a method of using baryta paper, etc. as seen in JP-A-55-86789. A method of providing an intermediate layer containing a glassy pigment, or a method of adjusting the surface roughness and gloss of the recording medium to a specific range (
JP-A-55-156086) is known.

However, with the method of increasing smoothness through surface treatment,
Dot reproducibility in a low concentration range is hardly improved, and on the contrary, the accumulation of hot melt on the head, so-called piling, or adhesion between the recording medium and the head, so-called sticking, tends to occur.

In addition, methods that use undercoated paper as a support, such as cast coated paper, baryta paper, or paper with an intermediate layer of plastic pigment, have the effect of slightly improving dot reproducibility compared to uncoated paper, but still have no effect. It 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.

As an effective alternative to such conventional methods, the present inventors focused on the pigment of the support, and first applied oil absorption t 100 m/
A method was proposed in which a paper containing 1 o o y or more of an inorganic pigment is used as a support and a heat-sensitive coloring layer is provided thereon. (Japanese Patent Application No. 59-220363) Hitherto, wood-free paper has often been used as a support for heat-sensitive recording media, and general wood-free paper has an oil absorption of 20 to 30 m/100 f, such as clay and Merck.
It contains about 10 to 15% by weight of a low oil absorption filler.

However, when these high-quality papers are used as a support for a heat-sensitive recording medium, the dot reproducibility in a low density region is very poor, so the present inventors filed an earlier application.

According to this method, it is possible to obtain a heat-sensitive recording medium with excellent dot reproducibility in the low density region, but it also has a wide dynamic range, which is necessary for recording halftone images in addition to dot reproducibility, that is, saturation color development tλ degree. The height was still insufficient.

(Problems to be Solved by the Invention) The present invention has been researched in view of these conventional drawbacks, and its purpose is to provide excellent dot reproducibility necessary for halftone recording, high saturated color density, and dynamic color development. The purpose is to provide a heat-sensitive recording medium with a wide range.

(Means for Solving the Problems) That is, the present invention provides a heat-sensitive coloring layer on a support, the active ingredients of which are a normally colorless or light-colored leuco compound and a color-developing substance that causes the leuco compound to develop color when heated. The heat-sensitive recording material is characterized in that the support is paper containing an inorganic pigment with an oil absorption of 100 m/1009 or more, and an intermediate layer containing a plastic pigment is provided between the support and the heat-sensitive coloring layer. The gist of this paper is a heat-sensitive recording medium.

Inorganic pigments with an oil absorption i10 (Lm7 of 100 F or higher) used in the present invention include, for example, calcined clay, aluminum oxide, titanium oxide, magnesium carbonate, magnesium silicate, algae, hydrated silicic acid, hydrated aluminum silicate, Calcium silicate etc. or oil absorption 100 m/1
The following pigments may be chemically or physically treated to have an oil absorption of 100 mZ/foot or more, among which silicic acids are preferred.

The silicic acids in the present invention have an oil absorption of 100 m// 1
S10. The content of
The effect is particularly remarkable for those with a rating of 5 or higher.

Furthermore, in the present invention, oil absorption! If a certain amount or more of an inorganic pigment with an oil absorption of 100 m/1009 or more is contained, a pigment with an oil absorption of 1004100 f or less, such as clay, talc, calcium carbonate, aluminum hydroxide, zinc oxide, etc., may be used together with the inorganic pigment. It is possible.

The content of the inorganic pigment of the present invention having an oil absorption of 100 m/1 o y or more is 5% by weight or more, preferably 10% by weight or more based on the weight of the support. The upper limit is limited by the required strength of the paper, etc.

On the other hand, the plastic pigment used in the intermediate layer in the present invention is approximately spherical fine particles of polystyrene, polymethyl methacrylate, polyvinyl chloride, polyvinylidene chloride, etc., and has a particle size of 0.05 to 5 μm.

In the intermediate layer of the present invention, these m-lipid fine particles need to maintain a fine particle state without being completely formed into a film, so the Tg point thereof is preferably 80° C. or higher.

To form the intermediate layer, these plastic pigments are mixed with a water-soluble resin such as polyvinyl alcohol, starch, or casein, or a latex such as SBR or MBR as a binder, and the mixture is coated on the support.

The amount of application of the middle layer is the highest in the world of plastic pigments.
12 or more, preferably 3 f, hawk or more.

If the amount of plastic pigment applied is less than 122, the effect will not be sufficient. There is no particular upper limit, but even if too much is applied, an effect proportional to the amount applied will not be obtained.

Each component used in the heat-sensitive coloring layer of the heat-sensitive recording material of the present invention, namely, a normally colorless or light-colored leuco compound, a color developing substance that causes the leuco compound to develop color when heated, a binder, a sensitizer, and various other additives. All conventionally known substances can be used.

In the heat-sensitive recording material of the present invention, an overcoat layer of a water-soluble polymer such as PVA or casein, an ultraviolet curable resin, an electron beam curable resin, or the like can be further provided on the heat-sensitive coloring layer. By providing an overcoat layer, it becomes possible to produce a heat-sensitive recording material that is suitable for halftone recording, has excellent chemical resistance, and generates little residue.

In producing the heat-sensitive recording material of the present invention, all known methods can be used to provide the intermediate layer, heat-sensitive recording layer, and overcoat layer.

(Example) The present invention will be explained below according to examples.

Example 1 Oil absorption amount a OOll was added to a pulp slurry consisting of 50 parts by weight of LBKP of C, S, FP Suisan 300- and 50 parts by weight of NBKP of C, S, FF Suisan 300-.
00? 20 parts by weight of water-containing calcium RL/1 (Thyroid 244 manufactured by Fuji Depison Co., Ltd.), a neutral sizing agent ()-con W
, manufactured by Dick Vercules Co., Ltd.), 3 parts by weight of cationized starch (l! IA Starch Chemical), and 0.2 parts by weight of anionic polyacrylamide (Polymethron 117, manufactured by Arayo Kagaku). In addition, 60 yen tsubo? /lr? The paper was made into a paper and lightly calendered to a thickness of 70 μm, a surface smoothness of 250 seconds, a size of 5 seconds, and a pigment-containing group of 15 weight i%.
got the paper.

Next, 208 parts by weight of a polystyrene plastic pigment 48 liquid (L-880I manufactured by Asahi Kasei) was mixed with 150 parts of a 12% polyvinyl alcohol solution in a homomixer for 10 minutes.
The mixture was dispersed for minutes to obtain a coating liquid for forming an intermediate layer.

Is the coating amount of this coating liquid on the paper mentioned above 6 f/l? It was coated 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 of solution C, 20 parts by weight of zinc stearate 30% dispersion, and 12% polyvinyl alcohol. A heat-sensitive coating liquid was prepared by mixing 125 parts by weight of the aqueous solution.

This coating solution was coated on the intermediate layer at a coating amount of 6 f/lri, dried, and calendered to give a Beck smoothness of about 600 seconds to obtain a heat-sensitive recording material.

A liquid black coloring dye S-205 (manufactured by Yamada Chemical Co., Ltd.) 7 parts by weight m-
Terphenyl 10 l Polyvinyl alcohol 12% aqueous solution 15 1 Polystyrene ammonium acrylate 20 l Aqueous solution 2.51 Water
17.5 #
Disperse the paint conditioner for 16 hours.

B liquid bisphenol A 20 parts by weight m-terphenyl 10 I polyvinyl alcohol 1
2% aqueous solution 25 I polystyrene ammonium acrylate 204 aqueous solution 2.51 water
Disperse 32.5 parts by weight or more in 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.

Example 2゜ Oil absorption 1i1240ffL as a pigment to be contained in the support
Example 2 is a heat-sensitive recording material manufactured in the same manner as in Example 1 except that 100% silicate (Silton LP-105F, manufactured by Mizusawa Chemical Co., Ltd., 94%) was used.

Example 3゜OP as a plastic pigment to be included in the intermediate layer
-42-M30 liquid (manufactured by Rohm & Haas),
Example 3 is a thermosensitive recording material manufactured in the same manner as in Example 1 except for the following.

Example 4 The coating amount of the intermediate layer of Example 3 was 15t//rr? The test was conducted in the same manner as in Example 3 except that the paper was closed.

Comparative Example 1 Comparative Example 1 is a heat-sensitive recording material produced in the same manner as in Example 1 except that the intermediate layer of Example 1 was omitted.

Comparative Example 2 Comparative Example 2 is a heat-sensitive recording material manufactured in the same manner as in Example 1 except that light calcium carbonate Pz (Shiraishi Industrial Committee) was used instead of the plastic pigment contained in the intermediate layer of Example 1. .

Comparative Example 3 Oil absorption t30rn/! as a pigment contained in the support. /x
The test was conducted in exactly the same manner as in Example 1 except that oof talc was used.

Example 56 The steps up to the formation of the support and intermediate layer were carried out in the same manner as in Example 1,
Next, the following A liquid and B liquid were prepared respectively, 87 parts by weight of liquid A, and 87 parts by weight of liquid B.
A heat-sensitive coating liquid was prepared by mixing 167 parts by weight of the liquid and 75 parts by weight of an aqueous solution of Flucor 12-bin with polyvinyl vinyl.

This coating liquid was applied onto the intermediate layer in a coating amount of 5179 ml and dried.

Next, prepare the following liquid C, and coat it on the heat-sensitive coloring layer at a coating amount of 2.5 f/rr? The coating was coated and dried, and further calendering was carried out to obtain a Peck smoothness of about 800 seconds to obtain a heat-sensitive recording material.

A liquid black coloring dye S-205 (manufactured by Yamada Chemical Co., Ltd.) 9 parts by weight m-
Terphenyl 18 # Polyvinyl alcohol 12 ml aqueous solution 25 I Polystyrene ammonium acrylate 20 ml aqueous solution 2,5 I water
32.5 1
Disperse the above with paint conditioner for 16 hours.

B liquid Bisphenol A 33 parts Light calcium carbonate PZ (Shiraishi Kogyo) 20 l Polyvinyl alcohol 12 parts aqueous solution 50 parts by weight Polystyrene ammonium acrylate 20 parts aqueous solution 51 water
59 -C liquid 12% polyvinyl alcohol aqueous solution 600 parts by weight Mizukasil P-527 (silica manufactured by Mizusawa Chemical Co., Ltd.) 20 I
Zinc stearate 30mm dispersion 20I Sodium dioctyl sulfosuccinate II Water
Disperse 1601 or more in a homomixer for 10 minutes.

Comparative Example 4 Comparative Example 4 is a heat-sensitive recording material manufactured in the same manner as in Example 4 except that the intermediate layer of Example 5 was omitted.

Dot reproducibility type color saturation #change measurements and evaluations were carried out for the samples & of Examples 1 to 5 and Comparative Examples 1 to 4 above. The results are shown in the table.

Solid coloring was performed using a thermal printer with a fixed head of 16 dots/gourd at an energy of 16 rrLJ/-, and visually judged.

$2 40 trtJ/ with the same thermal printer as the first year of junior high school
A solid color was developed using energy of -, and the color density was measured using a reflection densitometer (Macbeth RD-514).

Umbrella 3 Umbrella 1 and Ne2 were evaluated together.

(Effect of the invention) As is clear from the examples and comparative examples, the oil absorption amount is 100 m
The heat-sensitive recording material of the present invention uses paper containing an inorganic pigment of l/Ao o y or more as a support, and further provides an intermediate layer containing a plastic pigment between the heat-sensitive coloring layer and the support. It has excellent dot reproducibility and high saturated color density, making it suitable for halftone recording.

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, and the support has an oil absorption of 100ml/100g. A heat-sensitive recording material comprising a paper containing the above inorganic pigment, further comprising an intermediate layer containing a plastic pigment between the support and the heat-sensitive coloring layer.