JPH0692035A - Thermal recording material - Google Patents

Abstract

PURPOSE:To mainly eliminate the fading or erasure of an image by adding a granular resin opaque at normal temp. or lower, melted by heating to become transparent, having a particle size within a specific numerical value range and having gaps therein to a recording medium layer. CONSTITUTION:A thermal recording material is constituted of a support and a recording medium layer. In this case, a specific granular resin is added to the recording madium layer. The specific granular resin is opaque at normal temp. and melted by the thermal head of a thermal printer to become transparent and has a particle size of 0.1-3.0mum and has one or more gaps therein. One or more core particles are allowed to present in the gaps. The granaular resin is based on a polymerizable vinyl monomer and produced by emulsion polymerization. The granular resin and a binder such as a water-soluble resin are together mixed with the recording medium layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel heat-sensitive recording material and heat-sensitive recording method suitable for recording images, characters and the like by heat.

Specific examples of such a thermal recording material include, for example, facsimiles, printers, data communications,
Labels, tickets, commuter passes, etc.

[0003]

2. Description of the Related Art A heat-sensitive recording material is a material which develops color when heated by a thermal head or a thermal pen and easily obtains an image recording. It is used in a wide range of fields such as terminals, labels, tickets, and commuter passes.

In recent years, the information equipment as described above has been used more and more widely with the progress of hardware.
As a result, the applications of thermal recording materials are rapidly expanding.
A conventional heat-sensitive recording material can be obtained by dispersing a colorless or light-colored dye and a color developer as a color-developing agent in a binder, coating the base material, and drying. However, the conventional heat-sensitive recording material has a drawback that the image to be colored by heating is caused by a chemical reaction, so that the image is easily discolored by a plasticizer, oil, water, humidity, etc., and the stability and storability of the image are not good.
Also, these conventional methods use expensive materials, and
Since a complicated process is essential, it also has a drawback that the manufacturing cost is very high.

Further, in Japanese Patent Laid-Open No. 3-51186, a recording medium layer containing a particulate resin which is opaque at 50 ° C. or lower and melts at 50 ° C. or higher to be transparent is formed on a colored support. It is disclosed that the recording medium layer in a predetermined portion is made transparent by heating with a head or a hot pen, and the colored support can be perceived as an image. However,
In this method, the opacity of the above-mentioned particulate resin is not sufficient, so a large amount of the particulate resin must be used to hide the color of the support, and the recording medium layer must be thickened. . Therefore, there is a drawback that a large amount of heat energy is required to melt these large amounts of particulate resin and the coloring sensitivity is reduced.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an inexpensive, simple, and highly sensitive method in the field of heat-sensitive recording, which is free from image fading and disappearance.

[0007]

In order to solve the above-mentioned problems, the invention utilizing the fact that a coating film containing a particulate resin is opaque below the temperature at which the particles soften and melt, and becomes transparent when heated above that temperature Had a defect in color development sensitivity, although it achieved the purpose of fading and disappearance of the image.

The present inventor has paid attention to the fact that a particulate resin having one or more voids inside shows extremely excellent opacity at a temperature below the temperature at which the particles soften and melt, and becomes transparent when heated above that temperature. The present invention has been completed. That is, the present invention is a heat-sensitive recording material comprising a support and a recording medium, the recording medium layer is opaque at room temperature or lower, and is melted to be transparent by being heated by a thermal head of a thermal printer, Is in the range of 0.1 to 3.0 μ,
The present invention relates to a thermal recording material containing a particulate resin having one or more voids inside.

In the present invention, a particulate resin having one or more voids inside is introduced into the recording medium layer. The particulate resin exhibits extremely excellent opacity due to the voids inside the particles at a temperature below the temperature at which the particles soften and melt. Therefore, the particulate resin in the recording medium layer for the purpose of hiding the color of the support can be significantly reduced, and the thickness of the recording medium layer can be greatly reduced. Therefore, in order to print the color of the heat-sensitive recording material, it is sufficient to melt a smaller amount of the particulate resin, the heat energy required for the color development of the print is less, and the color development sensitivity is significantly improved. Further, as described in JP-A-4-211411, one or more core particles are present inside the voids of the particulate resin, and in the case of cored multilayer structure particles, the hiding power of the recording medium layer is further improved, and the color development sensitivity is further improved. It is more preferable because it improves.

As these particulate resins, commercially available resins can be used and they can be easily prepared by the method disclosed in the above-mentioned Japanese Patent Laid-Open Publication. The kind of the monomer used for producing the synthetic resin emulsion and the composition thereof in the recording medium layer have a glass transition temperature of room temperature or higher, preferably 40 ° C. or higher in order to maintain the recording medium layer in an opaque state at room temperature. To be selected.

The material constituting the recording medium layer, which is coated on the support of the present invention, is dried while maintaining the particle form of the particulate resin to form a coating film for the recording layer. To this end, the drying is performed at room temperature or when the particulate resin is fused to each other.
It is carried out at a forced heating temperature within a range where coalescence and particle morphology are not lost. This condition is usually satisfied by setting the temperature of the forced heating below the glass transition point of the particulate resin and evaporating and removing the dispersion medium at a temperature within this range. Therefore, the glass transition point of the resin is desired to be 40 ° C. or higher, preferably 50 ° C. or higher in view of the above requirement for the drying temperature, and the monomer should be selected in consideration of this point.

The average particle size of the particulate resin which is a component of the recording medium layer of the present invention is 0.1 to 3.0 μ, preferably 0.3 to 1.0 μ. When the average particle size of this particulate resin is less than 0.1 μ, sufficient opacity of the recording medium layer cannot be obtained, while the average particle size is 3.
When it exceeds 0 μ, aggregation of the synthetic resin emulsion is likely to occur, and emulsion separation phenomenon due to sedimentation of particles is likely to occur during storage, which makes it difficult to form a uniform recording layer, which is not preferable.

In order to improve the adhesion between the particulate resins of the recording medium layer of the present invention and the adhesion between the support and the recording medium layer, a resin capable of forming a uniform layer in the recording layer is used as a binder. desirable. The binder used in that case is not particularly limited, and any of a commonly used water-soluble type or water-dispersed type can be used, but the purpose is to melt and make transparent the particulate resin in the recording medium layer by heat. Since a heat-sensitive recording material can be obtained, as a binder for binding the particulate resin onto the support,
A material having heat resistance is preferable, and generally, various known binders used in conventional heat-sensitive recording materials can be mentioned.

Specific examples of such binders include various polyvinyl alcohols, starches, and modified products thereof, casein, gelatin, soybean protein, cellulose esters such as hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, and polyacrylamide. , Water-soluble substances such as sodium acrylate, alkali modified styrene / maleic anhydride copolymer, styrene / butadiene copolymer, ethylene / vinyl acetate copolymer, acrylonitrile / acrylic acid ester copolymer, Water-dispersible resins such as vinyl acetate resins, which are used alone or in combination.

Alternatively, the water-soluble resin may be used as a dispersion stabilizer and may be used when the particulate resin is produced by emulsion polymerization. In this case, addition of a binder is unnecessary. However, when the content of the particulate resin becomes low, the transparency at room temperature comes out, and therefore the amount of the uniform layer resin component is limited, and in order to obtain the desired opacity, the particulate resin component is required. The content of is preferably 50% by volume or more, and particularly preferably 60% by volume or more in the recording layer.

Next, as the support used in the present invention, it is suitable that all or at least one layer of the support is colored, but it may be colorless and transparent depending on the use. As the support, for example, a plastic film or sheet such as polyester resin, methacrylic resin, polycarbonate resin, styrene copolymer resin, vinyl chloride resin, polypropylene resin, or the like, or paper is used.

Further, as a method of coloring the support, for example, at the time of molding the above-mentioned plastic film or sheet, a colorant is mixed with a resin for molding, or the molded plastic film, sheet or paper. A suitable method is such that a colored coating material in which a binder is mixed with a coloring agent is applied to a support and dried. The colorant is not particularly limited to the colorant as long as it can identify the image forming portion of the present invention.

Examples of such colorants include carbon-based colorants such as carbon black and graphite powder, metal oxides such as titanium oxide, iron oxide, zinc oxide, chromium oxide, molybdenum oxide, tellurium oxide, alumina and silica. Things,
Metal salts such as yellow lead, barium sulfate, calcium carbonate, ultramarine, cadmium sulfate, fine metal powders such as iron, chromium, manganese, cobalt, aluminum, copper and zinc, organic pigments such as phthalocyanine blue and phthalocyanine green, acid dyes Suitable dyes are basic dyes, disperse dyes and fluorescent dyes.

When a coloring agent such as carbon, pigment or dye is applied to form a colored layer on the support, the thickness of the coating layer can be arbitrarily selected depending on the intended use, but it is usually 1 to 50 μ (dry base). And preferably 3 to
It is 20μ. At that time, the binder to be used is not particularly limited, and any of the commonly used solvent type, water-soluble and water-dispersed types can be used. The coloring paint can be applied by a known method such as a roll coater, knife coater, spin coating, spray coating, dipping or the like which is commonly used, and dried to obtain a colored layer.

For the recording medium layer used in the present invention, the above-mentioned synthetic resin emulsion having one or more voids inside is well-known on the support by roll coater, knife coater, spin coat, spray coat, dipping and the like. It can be formed by applying the above method. The thickness of the recording medium layer can be arbitrarily selected depending on the intended use, but is usually 1 μ to 100 μ (dry base), and preferably 5 to 50 μ.

The image formation of the heat-sensitive recording material of the present invention can be obtained by passing it through a thermal head used for a thermal recording paper such as a facsimile or a thermal pen. A heated head or a hot pen heats and melts the heated portion to make it transparent, so that the colored support layer can be visually recognized and sensed as an image.

[0022]

[Preparation of particulate resin]

Polymerization Example 1 Based on Example 1 of JP-A-2-173101, particle diameter D = 0.
Synthetic resin emulsion particles having a glass transition temperature of 45 ° C., having 53 μm and one void having a diameter d = 0.28 μ in the particles, were prepared. The nonvolatile content of the obtained emulsion is 42
%Met.

Polymerization Example 2 Based on Polymerization Example 20 of JP-A-4-211411, particle diameter D =
0.69μ, core particle diameter φ = 0.18μ, diameter d of void
= 0.50μ, glass transition temperature 60 ℃, cored multilayer structure particle emulsion was prepared. The nonvolatile content of the obtained emulsion was 42%.

Polymerization Comparative Example 3 Based on Example 1 of JP-A-3-51186, particle diameter D = 0.
20μ, glass transition temperature 5 with no voids inside the particles
Synthetic resin emulsion particles at 0 ° C were prepared. The nonvolatile content of the obtained emulsion was 40%.

Polymerization Comparative Example 4 Polymerization Example 1 was changed except that the monomer components of Polymerization Example 1 were changed.
In the same manner as in the above method, the glass transition temperature is 1 with an outer diameter of 0.46μ and one void with a diameter d = 0.26μ in the particle.
5 ° C. synthetic resin emulsion particles were prepared. The nonvolatile content of the obtained emulsion was 42%.

Polymerization Comparative Example 5 In the same manner as in Polymerization Example 1 except that the amount of the polymerization initiator in Polymerization Example 1 was changed, the particle outer diameter was 0.08 μm, and the particle diameter d was 0.04 μm. Synthetic resin emulsion particles having one void and a glass transition temperature of 45 ° C. were prepared.
The nonvolatile content of the obtained emulsion was 42%.

[Examples as Thermal Recording Material] Example 1 100 parts by weight of the synthetic resin emulsion obtained in Polymerization Example 1 was mixed with styrene (40% by weight) and butyl acrylate (45%).
Wt%) and ammonium methacrylate (15 wt%)
Of water-soluble acrylic resin prepared by copolymerizing
50 parts by weight of a 0% by weight aqueous solution and 10 parts by weight of a 5% by weight aqueous solution of hydroxyethyl cellulose as a thickener were added and mixed to obtain a coating liquid for a recording medium layer. This coating liquid for a recording medium layer was applied on a polyester film having a thickness of 75 μm using a knife coater so that the thickness after drying would be 10 μm, and was applied at room temperature for 12 hours in a vacuum dryer (internal pressure,
The recording medium of the present invention was obtained by drying at 10 mmHg) for 1 hour.

The characteristics of the recording medium obtained in this example were evaluated with respect to the light transmittance in the normal state, the temperature for making the recording medium layer transparent, and the light transmittance after making transparent. In the evaluation of the above items, the light transmittance was measured using a spectrophotometer with monochromatic light having a wavelength of 800 nm.

Next, as a paint for the colored layer of the colored support, 100 parts by weight of an acrylic emulsion (manufactured by Mitsui Toatsu Chemicals, Inc .; trade name Almatex E-208; solid content 45%) was used as a binder. , 10 parts by weight of carbon black was placed in a sand mill and dispersed for 8 hours to form a colored paste. Further, the weight ratio of the resin solid content to the carbon black was 100: 5, respectively, Almatex E-20.
After adding 8 and mixing, it filtered by the cartridge type filter and each colored water-dispersed coating material was obtained. After diluting this water-dispersed paint with water and adjusting the viscosity to 200 to 400 cps, it is applied on a polyester film of 75 μm so that the dry coating film thickness is about 10 μm, and it is heated in a hot air drying oven at 80 ° C. for 20 minutes. After drying, the water was removed by evaporation to form a black opaque (that is, completely light-shielding) support on the polyester support substrate.

On the black opaque support, a mixed solution of a particulate resin emulsion obtained by emulsion polymerization of the above-mentioned monomer composition was dried using a bar coater to give a film thickness of about 10
It was coated so as to have a thickness of μ and dried at a drying temperature of 40 ° C. for 30 minutes to obtain a heat-sensitive recording material of the present invention. This heat-sensitive recording material was used as a heat-sensitive printing device (TH-PMD manufactured by Okura Electric Co., Ltd.).
Was used to print color under the following conditions, and its density was measured using a Macbeth densitometer.

Applied voltage 24 V, pulse width 1.74 ms, applied energy 0.73 mJ / dot This was taken as Example 1 and the results are shown in Table 1.

Example 2 The synthetic resin emulsion obtained in Polymerization Example 2 was used in Example 1
It processed similarly to and evaluated. This is referred to as Example 2, and the results are shown in Table-1.

Comparative Example 1 Polymerization The synthetic resin emulsion obtained in Comparative Example 3 was treated and evaluated in the same manner as in Example 1. The recording medium of this comparative example had a good light transmittance at room temperature, and when treated in the same manner as in Example 1, the underlying colored layer was seen through and the hiding property was insufficient. This is set as Comparative Example 1, and the results are shown in Table-1.

Comparative Example 2 Polymerization The synthetic resin emulsion obtained in Comparative Example 3 was treated and evaluated in the same manner as in Example 1. However, on the support,
The thickness of the synthetic resin emulsion compounded liquid after drying is about 5
It was applied so as to be 0 μ. When the heat-sensitive recording material of this comparative example was treated in the same manner as in Example 1, the hiding property of the recording medium layer remained even after the printing treatment and the printing density was low. This is set as Comparative Example 2, and the results are shown in Table-1.

Comparative Example 3 Polymerization The synthetic resin emulsion obtained in Comparative Example 4 was treated and evaluated in the same manner as in Example 1. This is Comparative Example 3,
The results are shown in Table-1. The recording medium of this comparative example is transparent because the glass transition temperature of the particulate resin is as low as 15 ° C. and the resin already fuses and deforms (looses voids) at room temperature. No print test was performed.

Comparative Example 4 Polymerization The synthetic resin emulsion obtained in Comparative Example 5 was treated and evaluated in the same manner as in Example 1. The recording medium of this comparative example had a good light transmittance at room temperature, and when treated in the same manner as in Example 1, the underlying colored layer was seen through and the hiding property was insufficient. This is Comparative Example 4, and the results are shown in Table 1.

[0037]

It is clear from the examples that the heat-sensitive recording material of the present invention is transparent at the portion heated by the thermal head, and the support layer can be perceived as an image.

[0038]

[Table 1]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Yanagi Hara, Mitsui Toatsu Chemical Co., Ltd., 1190 Kasama-cho, Sakae-ku, Yokohama-shi, Kanagawa

Claims (5)

[Claims] 1. A heat-sensitive recording material comprising a support and a recording medium, wherein the recording medium layer is opaque at room temperature or lower and melts and becomes transparent when heated by a thermal head of a thermal printer, and has a particle size of A heat-sensitive recording material comprising a particulate resin having one or more voids inside, in the range of 0.1 to 3.0 µ. 2. The heat-sensitive recording material according to claim 1, wherein one or more core particles are present inside the voids of the particulate resin. 3. The heat-sensitive recording material according to claim 1, wherein the particulate resin contains a vinyl-polymerizable monomer as a main component and is produced by an emulsion polymerization method. 4. The heat-sensitive recording material according to claim 1, wherein the recording medium layer is a mixture of the particulate resin according to claim 1 and a binder. 5. The heat-sensitive recording material according to claim 4, wherein the binder is a water-soluble resin or a synthetic resin emulsion.