JP2827610B2 - Rewritable thermal recording medium - Google Patents

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 an improvement in contrast between an image area and a non-image area. The present invention relates to an improvement in a thermosensitive recording medium which can maintain an initial clearing temperature range and can improve repetitive rewriting resistance.

[0002]

2. Description of the Related Art Japanese Patent Application Laid-Open No. 55-154198 and U.S. Pat.
As described in JP-A No. 3 (1993) -1991, a recording layer mainly composed of a thermoplastic resin such as polyvinyl chloride and a low-molecular organic substance such as a higher fatty acid dispersed in the resin is provided on a support. A structure having such a structure is known.

[0003] In this thermosensitive recording medium, the optical absorption characteristic (light scattering characteristic) of the recording layer is skillfully utilized by reversibly changing depending on temperature. In other words, the recording layer has a specific temperature T near room temperature.
_The recording layer has two state transition temperatures T ₁ and T ₂ (where T ₁ <T ₂ ) at a temperature higher than _{0. When} the recording layer is heated to and maintained at T ₂ or higher and then cooled to T ₀ or lower, it becomes cloudy. Meanwhile the light scattering becomes maximum shielding state increases, the cooling of the recording layer in this opaque state above T ₁ is heated to less than T ₂ and after holding the T ₀ following the light scattering property decreases It becomes a transparent state. Moreover, the maximum light-shielding state and the transparent state of the recording layer can be stably maintained under the temperature condition of T ₀ or less, and these states can be reversibly changed. By setting to, the recording medium can be differentiated from the other state and can be used as a rewritable recording medium.

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

Since a heating means such as a thermal head is applied as a printing means for the recording medium, a mark formed by the printing means (formed upon contact with the thermal head or the like) is formed on the surface of the recording layer every time a printing operation is repeated. There is a drawback that the image quality deteriorates as a recording image is formed repeatedly because the minute unevenness is likely to remain, and the recording layer surface is partially shaved and becomes a scum and adheres to printing means such as a thermal head. There was an easy defect.

In JP-A-63-221087, a protective layer made of a fluorine-based resin or a silicone-based resin is provided on the recording layer to reduce the friction on the surface to improve the printing suitability. There has been proposed a method for preventing the accompanying deterioration of image quality and adhesion of scum to printing means such as a thermal head. However, even if this method is applied, if the printing operation is repeated, the adhesive force between the recording layer and the protective layer is reduced, and the protective layer is peeled off with time to deteriorate the image quality. Japanese Patent Application Laid-Open Publication No. H11-15083 proposes a method in which an intermediate layer made of a thermoplastic resin or a thermosetting resin is provided between a recording layer and a protective layer, and the protective layer is made of a heat resistant resin.

[0007]

By applying this means, the rewriting durability and the deterioration of the image quality are surely reduced, but on the other hand, when forming the intermediate layer and the protective layer on the recording layer, these layers are required. The resin monomer and the solvent such as methyl ethyl ketone and toluene are easy to penetrate into the recording layer, and the dispersion state of the organic low-molecular substance in the recording layer changes slightly with the intrusion of these solutions, and its transparency This has the disadvantage of adversely affecting the properties and affecting the above clearing temperature range.

That is, since the surface of the resin constituting the recording layer partially swells or dissolves due to the infiltration of the above-mentioned monomer or solvent, the dispersion state of the organic low-molecular substance in the resin is slightly changed. There is a problem that the transparency of the layer is reduced and adversely affects the contrast between the image part and the non-image part.
In addition, the initial clearing temperature range set before the formation of the protective layer and the like is slightly influenced by the clearing temperature range, so the recording set temperature of the thermal head etc. is set in accordance with 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 method of applying a wire bar or the like. There is still a problem that the rewriting resistance is deteriorated due to deterioration over time due to insufficient repetition, and furthermore, the thermal conductivity to the recording layer is also deteriorated as the thickness of the protective layer is increased. There was a problem that the sensitivity was lowered.

The present invention has been made in view of such a problem, and it is an object of the present invention to improve the contrast between an image portion and a non-image portion and to maintain an initial clearing temperature range. Another object of the present invention is to provide a heat-sensitive recording medium capable of improving the rewriting durability.

[0011]

That is, the invention according to claim 1 comprises a resin base material and an organic low-molecular substance dispersed in the resin base material as main components, and its transparency is reversibly dependent on temperature. Assuming a rewritable thermosensitive recording medium having a changing recording layer on a support, the resin base material is composed of a thermosetting resin composed of a hydroxyl-modified vinyl chloride-vinyl acetate copolymer and an isocyanate compound, And above
Hydroxyl-modified vinyl chloride-vinyl acetate copolymer is salt
Alkyl having vinyl chloride-vinyl acetate-hydroxyl group
It is a acrylate copolymer .

In such technical means, the main part of the thermosetting resin constituting the resin base material of the recording layer is composed of the hydroxyl-modified vinyl chloride-vinyl acetate copolymer and the isocyanate compound as described above. Things.

The hydroxyl-modified vinyl chloride-
The vinyl acetate copolymer means a vinyl chloride-vinyl acetate copolymer into which a hydroxyl group (-OH) has been introduced, and specifically, vinyl chloride-vinyl acetate-hydroxya.
Vinyl chloride-vinyl acetate such as alkyl acrylate copolymer
Alkyl acrylate having ru-hydroxyl group
And particularly preferably a hydroxyl group (—O
H) vinyl chloride-acetic acid in which 0.5 to 10% by weight is introduced
Vinyl-hydroxyalkyl acrylate copolymer
Vinyl chloride-vinyl acetate-alcohol with hydroxyl group
It is a kill acrylate copolymer .

Table 1 below shows specific examples applicable to this means.

[0015]

[Table 1]

On the other hand, the hydroxyl-modified vinyl chloride-
As an isocyanate compound constituting a curable resin as a resin base material by reacting with a hydroxyl group of a vinyl acetate copolymer, it has an isocyanate group (-N = C = O) and is generally widely used as a crosslinking agent. The isocyanate compound which can be applied, for example, 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, trimethylhexamethylene 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 preferably such that the isocyanate group is 0.5 to 0.5 to the hydroxyl group of the hydroxyl-modified vinyl chloride-vinyl acetate copolymer.
About three equivalents are preferred. Examples of the catalyst for promoting the curing reaction between the hydroxyl-modified vinyl chloride-vinyl acetate copolymer and the isocyanate compound include triethylenediamine, cobalt naphthenate, stannous chloride, and tetra-
N-butyltin, stannic chloride, trimethyltin hydroxide, dimethyl stannic chloride, di-n-butyltin dilaurate and the like can be applied, and the addition ratio is preferably about 0.5 to 2% by weight based on the resin solid content. .

Next, the organic low-molecular substance dispersed in the resin matrix 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 the melting point is 50-
Organic compounds in the range of 150 ° C. are mentioned, and specific examples thereof include higher alcohols such as alkanols, alkanediols, halogen alkanols, and halogen alkane diols; higher aliphatic amines; alkanes, alkenes, alkynes and halogen-substituted products thereof. Cyclic compounds such as cycloalkanes, cycloalkenes and cycloalkynes; saturated carboxylic acids, unsaturated monocarboxylic acids, dicarboxylic acids or their esters, amides and ammonium salts; saturated or unsaturated halogen fatty acids or their esters and amides Acrylic acid or their esters, amides, ammonium salts; halogen allyl carboxylic acids or their esters, amides, ammonium salts; thioalcohols or their carboxylic esters;
There are thiocarboxylic acids or their esters, amides, ammonium salts and the like, and these can be used alone or in combination of two or more.

Then, methyl ethyl ketone, methyl isobutyl ketone, chloroform, ethanol, benzene, and toluene in which a resin material such as the above-mentioned hydroxyl-modified vinyl chloride-vinyl acetate copolymer, isocyanate compound, and curing accelerator and a low-molecular organic substance are dissolved. An organic solution of tetrahydrofuran, carbon tetrachloride or the like, or a dispersion in which an organic low-molecular substance is dispersed in fine particles in a solution in which the above resin material is dissolved is coated on a support described below and dried. After curing, the recording layer whose transparency reversibly changes depending on the temperature is formed.

In this case, the thermosetting resin comprising the hydroxyl-modified vinyl chloride-vinyl acetate copolymer and the isocyanate compound constituting the resin base material of the recording layer is different from the conventional vinyl chloride-vinyl acetate copolymer resin and the like. The recording layer is excellent in heat resistance and mechanical strength, and has good adhesiveness to a support, so that the recording layer has a sufficient rewriting resistance without forming a protective layer. Therefore, since the protective layer is not required, there is no possibility that the monomer or organic solvent for the protective layer may permeate into the recording layer, so that the dispersion state of the organic low-molecular substance in the recording layer is determined when the recording layer is formed. It is possible to maintain the initial state, and since the printing operation is performed directly on the recording layer, there is an advantage that the recording sensitivity can be improved.

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

[0022]

According to the first aspect of the present invention, a thermosetting resin comprising a hydroxyl-modified vinyl chloride-vinyl acetate copolymer and an isocyanate compound constituting a resin base material of a recording layer is replaced with a conventional vinyl chloride-acetic acid. Compared with vinyl copolymer resin, etc., the recording layer is excellent in heat resistance and mechanical strength, and has good adhesion to supports such as plastic sheets and paper, so that the recording layer has sufficient rewriting resistance without forming a protective layer. Have.

Further, since the protective layer is not required, there is no danger of the protective layer monomer or organic solvent penetrating into the recording layer. It is possible to maintain the initial state at the time of formation, and since the printing operation is performed directly on the recording layer, the recording sensitivity can be improved.

[0024]

Embodiments of the present invention will be described below in detail.

The parts and percentages of the 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 includes a support 1 made of transparent polyethylene terephthalate as shown in FIG.
The recording layer 2 provided on the support 1 constitutes a main part thereof.

This thermosensitive recording medium is manufactured through the following steps.

That is, the following uniformly dissolved recording layer composition is coated on a support 1 made of transparent polyethylene terephthalate having a thickness of 150 μm using a wire bar, dried at 90 ° C. for 5 minutes, and The recording layer 2 having a cured film thickness of 10 μm was formed by heat curing 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-hydroxyalkyl acrylate copolymer 30 parts (VYES manufactured by Union Carbide Co., Ltd.) Isocyanate 3 parts (Nippon Polyurethane Curing agent (brand name: Coronate HL) Dibutyltin acetate (curing accelerator) 0.5 parts Toluene 30 parts Tetrahydrofuran 120 parts

Example 2 The heat-sensitive recording medium according to Example 1 was substantially the same as that of Example 1, except that the following composition was used as the recording layer composition.

(Composition for recording layer) Behenic acid 8 parts Stearic acid 2 parts Vinyl chloride-vinyl acetate-alkyl acrylate copolymer containing hydroxyl 30 parts (product name: VROH, manufactured by Union Carbite Co.) 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 The following composition for a recording layer, which was uniformly dissolved, was coated on a 150 μm-thick transparent polyethylene terephthalate support using a wire bar, and dried at 90 ° C. for 3 minutes. Then, a recording layer having a dry film thickness of 10 μm was formed 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 (trade name: SREC C, manufactured by Sekisui Chemical Co., Ltd.) Isocyanate 3 parts Toluene 30 parts Tetrahydrofuran 120 parts

Comparative Example 2 An intermediate layer composition having the following composition was applied on the recording layer of the recording medium according to Comparative Example 1 by a solvent coating method (wire bar) so that the dry film thickness was 1 μm. An intermediate layer is formed by coating and drying, and a protective layer composition having the following composition having a dry film thickness of 2.0 μm is formed on the intermediate layer.
Thus, a heat-sensitive recording medium according to Comparative Example 2 was obtained by coating and drying with a wire bar to form a protective layer.

(Composition for Intermediate Layer) 10 parts of vinyl chloride-vinyl acetate copolymer (VYHH manufactured by Union Carbide Co., Ltd.) 90 parts of 2-butanone / toluene (composition for protective layer) Polysiloxane graft polymer 25 Part (Nippon Shokubai Chemical Co., Ltd. product name R-41) Hardener (for same as above) 0.2 part Dioxane 50 parts

[0036] "Comparison Test" Next, compared with the thermal recording media of Examples 1-2 cases 1-2
For the thermosensitive recording medium according to (1), a comparison test described below was performed to compare the contrast between the image portion (white turbid portion) and the non-image portion (transparent portion), the transparency temperature range, and the rewriting durability. .

The recording layers of the thermosensitive recording media according to the examples and the comparative examples obtained as described above were all formed in a cloudy state.

First, with respect to each of the obtained thermosensitive recording media, the temperature was gradually increased from 50 ° C. to 100 ° C. once at a rate of 200 g / g.
cm ² for 2 seconds, cooled to room temperature after thermocompression bonding, and treated as a standard plate (optical density = 1.
79), and the reflection densities (optical densities) thereof were measured from above with an optical reflection densitometer (Macbeth optical densitometer RD-517) to determine the transparency temperature range.

Next, with respect to all the heat-sensitive recording media, the entire surface is heated to within a clearing temperature range (referred to a temperature range in which the reflection density becomes 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), and white turbidity printing was performed 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.

Table 2 shows the results.

Next, for all the thermosensitive recording media, 6
After the recording layer was returned to a transparent state by passing between the heat rollers set at 2 ° C., the same portion was printed again in white turbidity at 0.4 mJ / dot using the above-mentioned thermal head, and this was printed. After 100 repetitions, the reflection densities of the image portion (white turbid portion) and the non-image portion (transparent portion) were measured, and the deterioration due to the repetition was measured. The results are also shown in Table 2.

In the case of the heat-sensitive 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 deteriorated significantly in 20 repetitive tests and did not function as a recording medium. .

[0043]

[Table 2]

[Evaluation] From the results shown in Table 2, the heat-sensitive recording media according to Comparative Example 1 and Examples 1 and 2 in which only the recording layer was provided were more transparent than the heat-sensitive recording media according to Comparative Example 2. Temperature range is wide, and
It was confirmed that the difference in reflection density between the transparent state formed in this temperature range and the other cloudy state was large, and therefore, the contrast between the image area and the non-image area was excellent.

Further, the transparency temperature range of the recording layer according to each example is equal to that of Comparative Example 1, and there is almost no difference in transparency. It was also confirmed that the initial dispersion state did not change.

Further, it was also confirmed that the rewriting resistance of each of the examples was several times better than that of the heat-sensitive recording medium according to the comparative example.

[0047]

According to the first aspect of the present invention, a thermosetting resin comprising a hydroxyl-modified vinyl chloride-vinyl acetate copolymer and an isocyanate compound constituting a resin base material of a recording layer is a conventional vinyl chloride. -The recording layer is rewritten sufficiently without forming a protective layer because it has better heat resistance and mechanical strength than vinyl acetate copolymer resin, etc., and has good adhesion to a support such as a plastic sheet or paper. Has resistance.

Further, since a protective layer is not required, there is no danger that a monomer or an organic solvent for the protective layer infiltrates into the recording layer. It is possible to maintain the initial state at the time of formation, and since the printing operation is performed directly on the recording layer, the recording sensitivity can be improved.

Accordingly, the recording layer has improved repetition rewriting resistance, and the transparency of the initial recording layer can be maintained, and the sensitivity is good, so that the contrast between the image area and the non-image area can be improved, and the initial transparency can be improved. This has the effect of simplifying the adjustment of the recording set temperature of the printing means because the temperature range for the printing can be maintained.

[Brief description of the drawings]

FIG. 1 is a configuration sectional view of a thermosensitive recording medium according to an embodiment.

[Explanation of symbols]

 Reference Signs List 1 support 2 recording layer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B41M 5/36

Claims (1)

(57) [Claims] 1. A rewritable substrate comprising a resin base material and a recording layer mainly composed of an organic low-molecular substance dispersed in the resin base material and having a reversibly changing transparency depending on temperature on a support. in the thermosensitive recording medium, the resin base material, a hydroxyl modified vinyl chloride - is constituted by a thermosetting resin comprising a vinyl acetate copolymer and an isocyanate compound, and the hydroxyl-modified chloroplatinic
Vinyl-vinyl acetate copolymer is vinyl chloride-vinyl acetate
-Alkyl acrylate copolymer having hydroxyl group
A rewritable thermosensitive recording medium characterized by being a body .