JPH0585045A - Rewritable thermal recording medium - Google Patents

Abstract

PURPOSE:To provide the title recording medium enhanced in the contrast of an image part and a non-image part and rewriting resistance and capable of keeping an initial transparentizing temp. range. CONSTITUTION:In a rewritable thermal recording medium wherein a recording layer 2 based on a resin matrix and the org. low-molecular substance dispersed in the resin matrix and reversibly changed in its transparency in dependence on temp. is provided on a support 1, the resin matrix is constituted of a thermosetting resin consisting of a hydroxyl modified vinyl chloride/vinyl acetate copolymer and an isocyanate compound. Since this thermosetting resin is more excellent in heat resistance and mechanical strength as compared with a conventional resin matrix and also excellent in the adhesiveness to the support 1, it has good rewriting resistance and requires no protective layer and, therefore, there is no passibility such that a monomer or org. solvent for the resin penetrates in the recording layer and the dispersed state of the org. low- molecular substance in the recording layer can be held to an initial state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rewritable thermosensitive recording medium having a recording layer whose transparency reversibly changes depending on temperature, and more particularly to improving the contrast between an image portion and a non-image portion. The present invention relates to an improvement in a heat-sensitive recording medium which can be maintained in the initial clearing temperature range and can be improved in repeated rewriting resistance.

[0002]

2. Description of the Related Art As a thermal recording medium of this type, Japanese Patent Laid-Open No. 55-154198 and US Pat.
As described in Japanese Patent Publication No. 3, a recording layer mainly composed of a thermoplastic resin such as polyvinyl chloride and an organic low molecular weight substance such as a higher fatty acid dispersed in the resin is provided on a support. It is known to have a structure consisting of:

This heat-sensitive recording medium is constructed by skillfully utilizing the property that the light absorption property (light scattering property) of the recording layer reversibly changes depending on temperature. That is, this recording layer has a specific temperature T near room temperature.
_It has two state transition temperatures T ₁ and T ₂ (provided that T ₁ <T ₂ ) at a temperature higher than ₀ , and becomes cloudy when the recording layer is heated to T ₂ or higher and held and then cooled to T ₀ or lower. When the recording layer in the cloudy state is heated to T ₁ or more and less than T ₂ and then held and then cooled to T ₀ or less, the light scattering property is decreased. It becomes transparent. Moreover, since the maximum light-shielding state and the transparent state of the recording layer can be stably maintained under a temperature condition of T ₀ or lower, and these states can be reversibly changed, either one of the states is the base state. When set to, it can be used as a rewritable recording medium that can be differentiated from the other state.

Since the recording layer can be made transparent in the temperature range from T ₁ to T ₂ , this temperature range is referred to as a transparentization temperature range.

By the way, since a heating means such as a thermal head is applied as a printing means for the recording medium, a trace of the printing means (formed when the thermal head or the like is contacted is formed on the surface of the recording layer every time the printing operation is repeated. Has a drawback that the image quality deteriorates as a recorded image is repeatedly formed, and the surface of the recording layer is partially scraped off to form debris that adheres to the printing means such as a thermal head. There was an easy drawback.

Therefore, in Japanese Patent Laid-Open No. 63-221087, a print layer is provided with a protective layer made of a fluorine-based resin or a silicone-based resin to reduce the friction on the surface, thereby improving the printability and repeatedly rewriting. There has been proposed a method of preventing deterioration of image quality and adhesion of dust to a printing means such as a thermal head. However, even if this method is applied, the adhesive force between the recording layer and the protective layer decreases with repeated printing operations, and the protective layer peels off over time, resulting in deterioration of image quality, and therefore, JP-A-1-133781. The official gazette proposes a means in which an intermediate layer made of a thermoplastic resin or a thermosetting resin is provided between the recording layer and the protective layer, and the protective layer is made of a heat-resistant resin.

[0007]

By applying this means, repeated rewriting resistance and deterioration of image quality are certainly reduced, but on the other hand, when forming an intermediate layer or a protective layer on the recording layer, each of these layers is reduced. The monomer for resin and solvent such as methyl ethyl ketone, toluene, etc. that compose the layer easily penetrate into the recording layer, and the dispersion state of the organic low-molecular substance in the recording layer changes subtly as the solution invades. There is a drawback that it adversely affects the transparency and influences the above-mentioned clearing temperature range.

That is, since the surface of the resin constituting the recording layer partially swells or dissolves due to the penetration of the above-mentioned monomer or solvent, the dispersion state of the organic low-molecular substance in the resin changes subtly, so that recording There is a problem that the transparency of the layer decreases and the contrast between the image part and the non-image part is adversely affected.
Moreover, since the transparency temperature range is also affected and the initial transparency temperature range set before the formation of the protective layer, etc. slightly changes, the recording setting temperature of the thermal head etc. is set according to this change. There was a problem that had to be redone.

Although the protective layer is made of a heat resistant resin, the material applicable to the protective layer is limited to a resin material suitable for a coating method such as a wire bar, so that the heat resistance of the protective layer is high. There is a problem that the resistance to repeated rewriting is deteriorated due to deterioration over time without sufficient ejection, and further, the thermal conductivity to the recording layer is deteriorated as the film thickness of the protective layer is increased. However, there is a problem that causes a decrease in sensitivity.

The present invention has been made by paying attention to such a problem, and the problem is that the contrast between the image portion and the non-image portion can be improved and the initial transparentization temperature range can be maintained. At the same time, another object of the present invention is to provide a heat-sensitive recording medium capable of improving repeated rewriting resistance.

[0011]

That is, the invention according to claim 1 has a resin base material and an organic low-molecular substance dispersed in the resin base material as a main component, and its transparency is reversible depending on temperature. Assuming a rewritable heat-sensitive recording medium having a changing recording layer on a support, the resin matrix is composed of a thermosetting resin composed of a hydroxyl-modified vinyl chloride-vinyl acetate copolymer and an isocyanate compound. On the other hand, the invention according to claim 2 is based on the invention according to claim 1, wherein the hydroxyl-modified vinyl chloride-vinyl acetate copolymer is a vinyl chloride-vinyl acetate-vinyl alcohol copolymer. It is characterized by being either a polymer or an alkyl acrylate copolymer having a vinyl chloride-vinyl acetate-hydroxyl group.

In such a technical means, the thermosetting resin which constitutes the resin base material of the recording layer is, as described above, composed mainly of the hydroxyl-modified vinyl chloride-vinyl acetate copolymer and the isocyanate compound. It is something.

The above hydroxyl-modified vinyl chloride-
The vinyl acetate copolymer means a vinyl chloride-vinyl acetate copolymer in which a hydroxyl group (-OH) is introduced in an amount of about 0.5 to 10% by weight, and for example, vinyl chloride-vinyl acetate-vinyl alcohol copolymer. Polymer and vinyl chloride
Examples thereof include vinyl chloride-vinyl acetate-hydroxyl group-containing alkyl acrylate copolymers such as vinyl acetate-hydroxyalkyl acrylate copolymers.

Table 1 below shows specific examples applicable to this means.

[0015]

[Table 1]

On the other hand, the above hydroxyl-modified vinyl chloride-
The isocyanate compound that reacts with the hydroxyl group of the vinyl acetate copolymer to form the curable resin that is the resin matrix has an isocyanate group (-N = C = O) and is widely used as a crosslinking agent. The isocyanate compound that is used is applicable, and an example thereof is toluylene diisocyanate, a dimer of 2,4 toluylene diisocyanate,
Naphthylene-1,5-diisocyanate, o-toluylene diisocyanate, diphenylmethane diisocyanate, triphenylmethane triisocyanate, tris-
(P-isocyanatophenyl) thiophosphite, polymethylene polyphenyl isocyanate, polyfunctional aromatic isocyanate, aromatic polyisocyanate, polyfunctional aliphatic isocyanate, hexamethylene diisocyanate, trimethyl hexamethylene diisocyanate , Isophorone diisocyanate, xylylene diisocyanate and the like.

The amount of the isocyanate compound added to the hydroxyl-modified vinyl chloride-vinyl acetate copolymer is such that the isocyanate group is 0.5 to 0.5 with respect to the hydroxyl group of the hydroxyl-modified vinyl chloride-vinyl acetate copolymer.
About 3 times equivalent is preferable. Further, as a catalyst for promoting the curing reaction between the hydroxyl-modified vinyl chloride-vinyl acetate copolymer and the isocyanate compound, triethylenediamine, cobalt naphthenate, stannous chloride, tetra-
n-Butyltin, stannic chloride, trimethyltin hydroxide, dimethyl stannic chloride, di-n-butyltin dilaurate, etc. can be applied, and the addition ratio thereof is preferably about 0.5 to 2% by weight based on the resin solid content. ..

Next, the organic low molecular weight substance dispersed in the resin base material contains at least one atom of oxygen, sulfur, nitrogen and halogen, has 10 to 40 carbon atoms, and has a molecular weight of 100 to 100. 700 and a melting point of 50-
Organic compounds in the range of 150 ° C. are mentioned, and specific examples thereof include higher alcohols such as alkanols, carkanediols, halogenalkanols and halogenalkanediols; higher aliphatic amines; alkanes, alkenes, alkynes and halogen-substituted products thereof. Cyclic compounds such as cycloalkanes, cycloalkenes, cycloalkynes; saturated carboxylic acids, unsaturated monocarboxylic acids, dicarboxylic acids or their esters, amides, ammonium salts; saturated or unsaturated halogen fatty acids or their esters, amides , Ammonium salts; acrylic carboxylic acids or their esters, amides, ammonium salts; halogenallyl carboxylic acids or their esters, amides, ammonium salts; thioalcohols or their carboxylic acid esters;
There are thiocarboxylic acids or their esters, amides, ammonium salts and the like, and these can be used alone or in admixture of two or more.

Then, methyl ethyl ketone, methyl isobutyl ketone, chloroform, ethanol, benzene, and toluene in which the resin material such as the hydroxyl-modified vinyl chloride-vinyl acetate copolymer, the isocyanate compound, the curing accelerator and the organic low molecular weight substance are dissolved. , An organic solution such as tetrahydrofuran, carbon tetrachloride, or a solution prepared by dissolving the above resin material in the form of fine particles of an organic low-molecular substance is applied onto a support described below and dried, and then the above resin material is heated. The recording layer is formed by curing and the transparency thereof reversibly changes depending on the temperature.

In this case, the thermosetting resin comprising the hydroxyl-modified vinyl chloride-vinyl acetate copolymer and the isocyanate compound, which constitutes the resin base material of the recording layer, is the same as the conventional vinyl chloride-vinyl acetate copolymer resin. In comparison, the recording layer has excellent heat resistance and mechanical strength, and also has good adhesiveness to the support, so that the recording layer has sufficient repeated rewriting resistance without forming a protective layer or the like. Therefore, since a protective layer or the like is not necessary, there is no risk that the protective layer monomer or organic solvent will penetrate into the recording layer. It is possible to maintain the initial state of (1), and since the printing operation is directly performed on the recording layer, there is an advantage that the recording sensitivity can be improved.

In this technical means, the same support as the conventional one can be used as it is as the support for supporting the recording layer. For example, a transparent plastic film or sheet,
A plastic film or sheet in which a coloring agent such as a dye or a pigment is mixed, a plastic film or sheet in which a colored layer composed of a paint or an ink colored with a dye or a pigment is laminated, and further, aluminum, tin, silver or magnesium A plastic film, sheet, paper or the like provided with a light-reflecting metal layer of chromium, nickel, or the like can be used. And as specific examples of plastic films and sheets,
Examples of the material group include polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyparabanic acid, and the like, which are excellent in heat resistance, transparency, and mechanical strength.

[0022]

According to the first and second aspects of the invention, the thermosetting resin comprising the hydroxyl-modified vinyl chloride-vinyl acetate copolymer and the isocyanate compound, which constitutes the resin base material of the recording layer, is a conventional vinyl chloride. -It is excellent in heat resistance and mechanical strength as compared with vinyl acetate copolymer resin and has good adhesiveness to a support such as a plastic sheet or paper, so that the above recording layer is sufficiently repeated without forming a protective layer or the like. It has rewriting resistance.

Further, since a protective layer or the like is not necessary, there is no possibility that a monomer for the protective layer, an organic solvent or the like will penetrate into the recording layer, so that the dispersion state of the organic low molecular weight substance in the recording layer is recorded. It is possible to maintain the initial state at the time of layer formation, and since the printing operation is directly performed on the recording layer, the recording sensitivity can be improved.

[0024]

EXAMPLES Examples of the present invention will be described in detail below.

The parts and percentages of the blending components described in Examples and Comparative Examples are all parts by weight and% by weight.

[Example 1] A thermosensitive recording medium according to this example comprises a transparent support 1 made of polyethylene terephthalate and a recording layer 2 provided on the support 1, as shown in FIG. The main part is composed.

The thermal recording medium is manufactured through the following steps.

That is, the following recording layer composition which had been uniformly dissolved was coated on a support 1 made of transparent polyethylene terephthalate having a thickness of 150 μm with a wire bar and dried at 90 ° C. for 5 minutes, and The recording layer 2 having a cured film thickness of 10 μm was formed by thermosetting to obtain the thermosensitive recording medium shown in FIG.

(Composition for recording layer) Behenic acid 8 parts Stearic acid 2 parts Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 30 parts (Sekisui Chemical Co., Ltd. trade name Eslec A) Isocyanate 3 parts (Asahi Kasei Corp. Curing agent Trade name Duranate 24A-100) Triethylenediamine (curing accelerator) 0.3 parts Toluene 30 parts Tetrahydrofuran 120 parts [Example 2] In Example 1 except that the following composition was applied as the composition for the recording layer. It is substantially the same as the thermal recording medium.

(Composition for Recording Layer) Behenic Acid 8 parts Stearic Acid 2 parts Vinyl Chloride-Vinyl Acetate-Hydroxyalkyl Acrylate Copolymer 30 parts (Union Carbide Co., trade name VYES) Isocyanate 3 parts (Japan Polyurethane) Curing agent manufactured by the company: Coronate HL) Dibutyltin diacetate (curing accelerator) 0.5 part Toluene 30 parts Tetrahydrofuran 120 parts [Example 3] Examples except that the following composition was applied as the composition for the recording layer It is substantially the same as the thermal recording medium according to No. 1.

(Composition for Recording Layer) Behenic Acid 8 parts Stearic Acid 2 parts Vinyl Chloride-Vinyl Acetate-Hydroxyl-Containing Alkyl Acrylate Copolymer 30 Parts (Union Carbide Co., Ltd. Product Name VROH) Isocyanate 2 Parts ( Asahi Kasei Co., Ltd. curing agent Duranate 24A-100) Triethylenediamine (curing accelerator) 0.3 parts Toluene 30 parts Tetrahydrofuran 120 parts [Comparative Example 1] On a support made of transparent polyethylene terephthalate having a thickness of 150 μm, The composition for recording layer, which is uniformly dissolved, is applied with a wire bar, and the temperature is 90 ° C.
The recording layer was dried for 3 minutes to form a recording layer having a dry film thickness of 10 μm to obtain a thermosensitive recording medium according to Comparative Example 1.

(Composition for recording layer) Behenic acid 8 parts Stearic acid 2 parts Vinyl chloride-vinyl acetate copolymer 30 parts (Sekisui Chemical Co., Ltd. trade name Eslec C) Isocyanate 3 parts Toluene 30 parts Tetrahydrofuran 120 parts [ Comparative Example 2] On the recording layer of the recording medium according to Comparative Example 1, a composition for an intermediate layer having the following composition was applied by a solvent coating method (wire bar) so that the dry film thickness was 1 μm.
Is coated and dried to form an intermediate layer, and a protective layer composition having the following composition is further coated and dried on the intermediate layer with a wire bar so that the dry film thickness is 2.0 μm. A thermal recording medium according to Comparative Example 2 was obtained by forming a protective layer.

(Composition for intermediate layer) Vinyl chloride-vinyl acetate copolymer 10 parts (trade name VYHH manufactured by Union Carbide Co.) 2-butanone / toluene 90 parts (composition for protective layer) Polysiloxane graft polymer 25 Part (trade name R-41 manufactured by Nippon Shokubai Kagaku Kogyo Co., Ltd.) curing agent (for the same as above) 0.2 part dioxane 50 parts "comparative test" Next, the thermal recording media according to Examples 1 to 3 and Comparative Examples 1 and 2 For the heat-sensitive recording medium according to (1), a comparison test as described below was performed in order to compare the contrast between the image part (white turbid part) and the non-image part (transparent part), the transparentization temperature range, and the repeated rewriting resistance. ..

The recording layers of the thermal recording media of Examples and Comparative Examples obtained as described above were all formed in a cloudy state.

First, with respect to each of the obtained thermal recording media, 200 g / stepwise, once at 50 ° C. to 100 ° C.
cm ² for 2 seconds, after thermocompression bonding, cooled to room temperature, and treated with a standard plate (optical density = 1.7).
9) and placed on it, the reflection density (optical density) of each was measured with an optical reflection densitometer (Macbeth optical densitometer RD-517) to determine the clearing temperature range.

Next, with respect to all of the thermal recording media, the entire surface thereof is heated within a transparentization temperature range (which means a temperature range where the reflection density is 1.2 or more) and cooled to room temperature to make the entire recording layer transparent. After setting to the state, the thermal head (8 /
m, resistance 420 Ω) was used for white turbid printing under the condition of 0.4 mJ / dot, and the reflection densities of the image part (white turbid part) and the non-image part (transparent part) were measured to obtain initial density data.

The results are shown in Table 2.

Then, for all the thermal recording media, 6
The recording layer was returned to the transparent state by passing it between the heat rollers set at 2 ° C., and then the same portion was clouded again under the condition of 0.4 mJ / dot using the thermal head, and The reflection densities of the image part (white turbid part) and the non-image part (transparent part) after 100 times of repetition were measured respectively, and deterioration due to the repetition was measured. The results are also shown in Table 2.

Regarding the thermosensitive recording medium according to Comparative Example 1 in which the protective layer was not provided, the data was blank because the surface of the recording layer was significantly deteriorated in 20 times of repeated tests and the recording medium did not function. ..

[0040]

[Table 2]

"Evaluation" From the results shown in Table 2, the thermal recording media according to Comparative Example 1 and Examples 1 to 3 having only the recording layer are transparent as compared with the thermal recording media according to Comparative Example 2. The temperature range is wide, and the difference in reflection density between the transparent state and the other cloudy states formed within this temperature range is large,
Therefore, it was confirmed that the contrast between the image area and the non-image area was excellent.

Further, the transparentization temperature range of the recording layer according to each example is the same value as that of Comparative Example 1, and there is almost no difference in transparency, and therefore both of the organic low molecular weight substances in the recording layer are present. It was also confirmed that the initial dispersion state did not change.

Further, it was also confirmed that the repeated rewriting resistance of each example was several times superior to the thermal recording medium of the comparative example.

[0044]

According to the first and second aspects of the present invention, the hydroxyl-modified vinyl chloride-forming resin base material of the recording layer
Thermosetting resin consisting of vinyl acetate copolymer and isocyanate compound is superior in heat resistance and mechanical strength as compared with conventional vinyl chloride-vinyl acetate copolymer resin, etc. Since the adhesiveness is also good, the recording layer has sufficient repetitive rewriting resistance without forming a protective layer or the like.

Further, since a protective layer is not required, there is no possibility that a monomer for the protective layer, an organic solvent or the like will penetrate into the recording layer, so that the dispersion state of the organic low molecular weight substance in this recording layer is recorded. It is possible to maintain the initial state at the time of layer formation, and since the printing operation is directly performed on the recording layer, the recording sensitivity can be improved.

Therefore, the repeated rewriting resistance of the recording layer is improved, the initial transparency of the recording layer can be maintained, and the sensitivity is also good, so that the contrast between the image area and the non-image area can be improved and the initial transparency can be improved. Since the conversion temperature range can be maintained, it has the effect of simplifying the adjustment of the recording set temperature of the printing means.

[Brief description of drawings]

FIG. 1 is a structural cross-sectional view of a thermosensitive recording medium according to an example.

[Explanation of symbols]

 1 support 2 recording layer

Claims (2)

[Claims] 1. A rewritable recording medium comprising a resin base material and an organic low-molecular substance dispersed in the resin base material as a main component, the recording layer of which transparency reversibly changes depending on temperature, provided on a support. In the heat-sensitive recording medium, the rewritable heat-sensitive recording medium is characterized in that the resin base material is composed of a thermosetting resin composed of a hydroxyl-modified vinyl chloride-vinyl acetate copolymer and an isocyanate compound. 2. The hydroxyl-modified vinyl chloride-vinyl acetate copolymer is a vinyl chloride-vinyl acetate-vinyl alcohol copolymer or a vinyl chloride-vinyl acetate-alkyl acrylate copolymer having a hydroxyl group. The rewritable heat-sensitive recording medium according to claim 1, wherein