JP3458236B2 - Reversible thermosensitive recording material - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible thermosensitive recording material capable of repeatedly forming and erasing an image by utilizing reversible transparency change with temperature of a thermosensitive layer.

[0002]

2. Description of the Related Art In recent years, reversible heat-sensitive recording materials have been attracting attention because they can form images temporarily and can erase the images when they are no longer needed. A typical example thereof is a heat-sensitive material in which an organic low-molecular substance such as a higher fatty acid is dispersed in a resin matrix such as a vinyl chloride-vinyl acetate copolymer, and the transparency reversibly changes depending on the temperature. A reversible thermosensitive recording material provided with a layer is known (JP-A-54).
No. 119377, JP-A No. 55-154198, etc.), the width of the temperature range showing light transmission / transparency is 2 to 4 ° C.
However, there is a drawback that it is narrow, and it is difficult to control the temperature when forming an image by utilizing light transmission / transparency or light shielding / cloudiness.

In consideration of this point, JP-A-63-3937
Nos. 8 and 63-130380 propose that the temperature range showing light transmission and transparency can be expanded by using a certain higher fatty acid ester as an organic low molecular weight substance as a eutectic agent. However, the repeated durability by the thermal head is poor, and the erasability (transparency) is poor,
After storage for a longer period of time, the erasing characteristics of the thermal recording layer over time significantly fluctuate with the preset initial erasing characteristics.If the image is erased under the erasing conditions corresponding to the initial erasing characteristics, the initial erasing characteristics will change. In some cases, the difference in concentration was large and the erasability with time was poor.

[0004]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned drawbacks and provides a reversible thermosensitive recording material in which the transparent state changes from the cloudy state to the reversible state depending on the temperature, and the repeated durability is good. The image erasability of the thermal head can be erased to near the background density (transparent state), and the image erasability of the recording layer does not significantly change from the initial erasability even after long-term storage. An object is to provide a reversible thermosensitive recording material.

[0005]

According to the present invention, a resin base material and an organic low molecular weight substance dispersed in the resin base material are contained as a main component on a support, and transparency is reversible depending on temperature. In a reversible thermosensitive recording material provided with a thermosensitive layer that changes dynamically , at least the dibasic acid dial is used as the organic low molecular substance.
Provided reversible thermosensitive recording material which comprises using Kill ester one or more, in particular the dibasic acid di
As alkyl esters, mp 40 ° C. or more dibasic acid di
An alkyl ester is used, or the dibasic acid dialkyl ester and the dibasic acid dialkyl ester differ in melting point by 10 ° C. or more as the organic low molecular weight substance.
A small amount selected from monocarboxylic acid and saturated dicarboxylic acid
The reversible thermosensitive recording material and the concomitant child and one of low-molecular organic material and it <br/> respectively, wherein there is provided even without.
Further, a vinyl chloride polymer or a vinyl chloride copolymer is used as the resin base material, and the vinyl chloride unit content (Y% by weight) and the average degree of polymerization (X) of these polymers are represented by the following formula (number: Have a value in a range satisfying the relationship represented by 1),

## EQU1 ## The reversible thermosensitive recording material is provided, characterized in that the average degree of polymerization (X) is 500 or more, in particular, -0.68logX + 3.794≤logY≤-0.215logX + 2.66. Furthermore, the reversible thermosensitive recording material is provided with an adhesive layer provided between the support and the thermosensitive layer.

The present invention will be described in more detail below. The dibasic acid dialkyl ester used in the present invention has a characteristic that it has a lower melting point than a fatty acid (association state) having the same carbon number, and conversely has a higher carbon number than a fatty acid having the same melting point. Degradation due to repeated printing-erasing of the image with the thermal head is considered to be due to the change in the dispersion state of the organic low-molecular substance particles due to the compatibility of the resin base material and the organic low-molecular substance during heating.
It is considered that the compatibility between the resin base material and the organic low-molecular weight substance decreases as the carbon number of the organic low-molecular weight substance increases, and the deterioration in printing and erasing of an image is small. Furthermore, the turbidity is proportional to the carbon number,
It tends to increase. Therefore, in the same reversible thermosensitive recording material of the clearing temperature (in the vicinity melting point), dibasic acid di
It is considered that the use of the alkyl ester improves the repeated durability as compared with the case of using the fatty acid.

Further, dibasic acid dialkyl esters have a low melting point, and have the same characteristics as the fatty acids having a higher melting point in terms of white turbidity and repeated durability, so that they are organic low molecular weight substances having a higher melting point than these compounds. Even when the mixture is mixed with and the transparentization temperature range is widened, the transparentization temperature range can be widened while maintaining the same white turbidity and repeated durability as when using a fatty acid. It is possible to improve the image erasing (transparency) by heating in a short time, and even if the image erasing energy fluctuates over time due to the increase of the image erasing margin, there is no practical problem in erasing with the thermal head. Will also be possible.

[0008] As a dibasic acid dialkyl ester <br/> Le used in the present invention are those represented by the following following general formula (I) (Formula 1).

[Chemical 1] (Wherein, R, R 'represents an alkyl group having a carbon number of 1~30, R, R' is but it may also be optionally substituted by one or more identical. N
Represents an integer of 0 to 40. ) In the dibasic acid dialkyl ester represented by the above general formula (I), R, R '
The number of carbon atoms of the alkyl group is preferably 1 to 22, and n is 1 to
30 is preferable and 2-20 is more preferable. The melting point is preferably 40 ° C or higher.

Specifically, oxalic acid dialkyl ester malonic acid dialkyl ester succinic acid dialkyl ester glutaric acid dialkyl ester adipic acid dialkyl ester pimelic acid dialkyl ester suberic acid dialkyl ester azelaic acid dialkyl ester sebacic acid dialkyl ester 1-, 9-nona Methylenedicarboxylic acid dialkyl ester 1-, 10-decamethylenedicarboxylic acid dialkyl ester 1-, 11-undecamethylenedicarboxylic acid dialkyl ester 1-, 12-dodecamethylenedicarboxylic acid dialkyl et <br/> ester 1, 13-tridecamethylene dicarboxylic acid dialkyl <br/> ester 1, 14-tetradecamethylene dicarboxylic acid dialkyl
Ester 1, 15 pentadecamethylene dicarboxylic acid dialkyl
Ester 1, 16 hexamethylene decamethylene dicarboxylic acid dialkyl
Ester 1, 17-heptadecamethylene dicarboxylic acid dialkyl
Ester 1, 18-octadecamethylene dicarboxylic acid dialkyl
Ester 1, 19 nonadecamethylene dicarboxylic acid dialkyl <br/> ester 1, 20-eicosyl shark Chi dicarboxylic acid dialkyl <br/> ester 1, 21-Heng Eiko shark Chi dicarboxylic acid dialkyl
Kill ester 1, 22-docosapentaenoic methylene dicarboxylic acid dialkyl et <br/> ester 1-, 24- tetra drizzle Chi dicarboxylic acid dialkyl
Ester 1-, 28- octa drizzle Chi dicarboxylic acid dialkyl
Ester 1, 32 de triacontyl Tan methylene dicarboxylic acid di
Examples thereof include alkyl esters.

Further, as the above 40 ° C. dibasic acid dialkyl et <br/> ester, include the following. Sebacate Diundecal Suberate Dilauryl Azelate Dilauryl Sebacate Dilauryl Oxalate Ditridecyl Succinate Ditridecyl Glutarate Ditridecyl Adipic Acid Ditridecyl Pimelic Acid Ditridecyl Suberate Ditridecyl Azelaic Acid Ditridecyl Sebacic Acid Ditridecyl

Dimyristyl malonic acid dimyristyl succinic acid dimyristyl glutarate dimyristyl adipate dimyristyl pimelic acid dimyristyl suberate dimyristyl azelate dimyristyl sebacate dimyristyl 1-, 9-nonamethylene dicarboxylic acid dimyristyl 1 Dimyristyl 1-, 11-undecamethylenedicarboxylic acid dimyristyl 1-, 10-decamethylenedicarboxylic acid dimyristyl 1-, 13-tridecamethylenedicarboxylic acid dimyristyl 1-, 14-tetradecamethylenedicarboxylic acid Acid dimyristyl 1-, 15-pentadecamethylene dicarboxylic acid dimyristyl 1-, 16-hexadecamethylene dicarboxylic acid dimyristyl 1-, 17-heptadecamethylene dicarboxylic acid dimyristyl 1-, 18-octadecamethylene dicarboxylic acid dimyristyl 1-, 19-nonadecamethylene dicarboxylic acid dimyristyl 1-, 20-eicosamethylene dicarboxylic acid dimyristyl 1-, 21-hen eicosamethylene dicarboxylic acid dimyristyl 1-, 22 -Dimyristyl docosamethylene dicarboxylic acid 1-, 24-Dimyristyl tetracosamethylene dicarboxylic acid 1-, 28-Dimyristyl octacosamethylene dicarboxylic acid 1-, 32-Dotriacontamethylene dicarboxylic acid dimyristyl

Oxalic acid dipentadecal malonic acid dipentadecal succinic acid dipentadecal glutaric acid dipentadecal adipic acid dipentadecal pimelic acid dipentadecal suberate dipentadecal azelaic acid dipentadecal sebacic acid dipentadecal 1-, 9-nonamethylene dicarboxylic acid dipentadecal 1-, 10-decamethylene dicarboxylic acid dipentadecal 1-, 11-undecamethylene dicarboxylic acid dipentadecal 1-, 12-dodecamethylene dicarboxylic acid dipentadecal 1-, 13-tridecamethylene dicarboxylic acid dipentadecal 1 -, 14-Tetradecamethylenedicarboxylic acid dipentadecal 1-, 15-pentadecamethylenedicarboxylic acid dipentadecal 1-, 16-hexadecamethylenedicarboxylic acid dipentadecal 1-, 17-hep Decamethylene dicarboxylic acid dipentadecal 1-, 18-octadecamethylene dicarboxylic acid dipentadecal 1-, 19-nonadecamethylene dicarboxylic acid dipentadecal 1-, 20-eicosamethylene dicarboxylic acid dipentadecal 1-, 21-heneicosamethylene dicarboxylic acid dipentadecal 1-, 22-docosamethylene dicarboxylic acid dipentadecal 1-, 24-tetracosamethylene dicarboxylic acid dipentadecal 1-, 28-octacosamethylene dicarboxylic acid dipentadecal 1-, 32-dotoacontamethylene dicarboxylic acid dipentadecal

Dipalmityl malonate Dipalmityl succinate Dipalmityl glutarate Dipalmityl adipate Dipalmityl pimelic acid Dipalmityl Suberate dipalmityl Azelate dipalmityl Sebacate dipalmityl 1-, 9-nonamethylene dicarboxylate dipalmityl 1-, 10-decamethylene dicarboxylic acid dipalmityl 1-, 11-undecamethylene dicarboxylic acid dipalmityl 1-, 12-dodecamethylene dicarboxylic acid dipalmityl 1-, 13-tridecamethylene dicarboxylic acid dipalmityl 1 Dipalmityl 1-, 14-tetradecamethylenedicarboxylic acid Dipalmityl 1-, 15-pentadecamethylenedicarboxylic acid dipalmityl 1-, 16-hexadecamethylenedicarboxylic acid dipalmityl 1-, 17-heptadecamethylenedicarboxylic acid dipalmi 1-, 18-octadecamethylenedicarboxylate dipalmityl 1-, 19-nonadecamethylenedicarboxylate dipalmityl 1-, 20-eicosamethylenedicarboxylate dipalmityl 1-, 21-heneicosamethylenedicarboxylate dipalmityl 1-, 22 -Dicosamethylene dicarboxylate dipalmityl 1-, 24-Tetracosamethylene dicarboxylate dipalmityl 1-, 28-octacosamethylene dicarboxylate dipalmityl 1-, 32-Dotriacontamethylene dicarboxylate dipalmityl

Oxalic acid diheptadecyl malonic acid diheptadecyl succinic acid diheptadecyl glutaric acid diheptadecyl adipate diheptadecyl pimelic acid diheptadecyl suberate diheptadecyl azelate diheptadecyl sebacic acid diheptadecyl 1-, 9-nonamethylene dicarboxylic acid diheptadecyl 1-, 10-decamethylene dicarboxylic acid diheptadecyl 1-, 11-undecamethylene dicarboxylic acid diheptadecyl 1-, 12-dodecamethylene dicarboxylic acid diheptadecyl 1-, 13-tridecamethylene dicarboxylic acid diheptadecyl 1 Diheptadecyl 1-, 14-tetradecamethylene dicarboxylic acid 1-, 15-Pentadecamethylene dicarboxylic acid diheptadecyl 1-, 16-hexadecamethylene dicarboxylic acid diheptadecyl 1-, 17-hep Decamethylene dicarboxylic acid diheptadecyl 1-, 18-octadecamethylene dicarboxylic acid diheptadecyl 1-, 19-nonadecamethylene dicarboxylic acid diheptadecyl 1-, 20-eicosamethylene dicarboxylic acid diheptadecyl 1-, 21-heneicosamethylene dicarboxylic acid diheptadecyl 1-, 22-docosamethylene dicarboxylic acid diheptadecyl 1-, 24-tetracosamethylene dicarboxylic acid diheptadecyl 1-, 28-octacosamethylene dicarboxylic acid diheptadecyl 1-, 32-dotriacontane methylene dicarboxylic acid diheptadecyl

Distearyl malonate, distearyl malonate, distearyl succinate, distearyl adipate, distearyl adipate, distearyl submerate, distearyl azelate, distearyl sebacate, distearyl 1,9-nonamethylene dicarboxylic acid diester Stearyl 1-, 10-decamethylene dicarboxylic acid distearyl 1-, 11-undecamethylene dicarboxylic acid distearyl 1-, 12-dodecamethylene dicarboxylic acid distearyl 1-, 13-tridecamethylene dicarboxylic acid distearyl 1-, Distearyl 1-, 15-pentadecamethylenedicarboxylic acid distearyl 1-, 15-pentadecamethylenedicarboxylic acid distearyl 1-, 17-heptadecamethylenedicarboxylic acid disteare 14-tetradecamethylenedicarboxylic acid 1-, 18-octadecamethylenedicarboxylic acid distearyl 1-, 19-nonadecamethylenedicarboxylic acid distearyl 1-, 20-eicosamethylenedicarboxylic acid distearyl 1-, 21-heneicosamethylenedicarboxylic acid distearyl 1-, 22-docosamethylenedicarboxylic acid distearyl 1-, 24-tetracosamethylenedicarboxylic acid distearyl 1-, 28-octacosamethylenedicarboxylic acid distearyl 1-, 32-dotriacontamethylenedicarboxylic acid distearyl

Oxalate dibehenylmalonic acid dibehenyl succinic acid dibehenyl glutaric acid dibehenyl adipate dibehenyl pimelic acid dibehenyl suberate dibehenyl azelaic acid dibehenyl sebacate dibehenyl 1-, 9-nonamethylene dicarboxylic acid dibehenyl 1 -, 10-Decamethylenedicarboxylic acid dibehenyl 1-, 11-undecamethylenedicarboxylic acid dibehenyl 1-, 12-dodecamethylenedicarboxylic acid dibehenyl 1-, 13-tridecamethylenedicarboxylic acid dibehenyl 1-, 14-tetradecamethylenedicarboxylic acid Acid dibehenyl 1-, 15-pentadecamethylene dicarboxylic acid dibehenyl 1-, 16-hexadecamethylene dicarboxylic acid dibehenyl 1-, 17-heptadecamethylene dicarboxylic acid dibehenyl 1-, 18-octadecamethylene di Dibehenyl 1-, 19-dibehenyl 1-, 19-nonadecamethylene dicarboxylic acid Dibehenyl 1-, 20-eicosamethylene dicarboxylic acid dibehenyl 1-, 21-hen eicosamethylene dicarboxylic acid dibehenyl 1-, 22-docosamethylene dicarboxylic acid dibehenyl 1-, Dibehenyl 24-tetracosamethylene dicarboxylate 1-, 28-octacosamethylene dicarboxylate dibehenyl 1-, 32-Dotriacontane methylene dicarboxylate dibehenyl

Dimethyl 1-, 12-dodecamethylenedicarboxylic acid 1-, 13-Dimethyl dimethyl 1-tridecamethylenedicarboxylic acid 1-, 14-Dimethyl 1-tetradecamethylenedicarboxylic acid 1-, 15-Dimethyl 1-pentadecamethylenedicarboxylic acid 1-, 16 Dimethyl 1-, 17-heptadecamethylene dicarboxylic acid dimethyl 1-, 18-octadecamethylene dicarboxylic acid dimethyl 1-, 19-nonadecamethylene dicarboxylic acid dimethyl 1-, 20-eicosamethylene dicarboxylic acid Dimethyl 1-, 21-heneicosamethylenedicarboxylic acid dimethyl 1-, 22-docosamethylenedicarboxylic acid dimethyl 1-, 24-tetracosamethylenedicarboxylic acid dimethyl 1-, 28-octacosamethylenedicarboxylic acid dimethyl 1-, 32- Doto Acon Tan methylene dicarboxylic acid dimethyl

1-, 15-Pentadecamethylenedicarboxylic acid diethyl 1-, 16-Hexadecamethylenedicarboxylic acid diethyl 1-, 17-Heptadecamethylenedicarboxylic acid diethyl 1-, 18-Octadecamethylenedicarboxylic acid diethyl 1-, 19-Nonadecamethylenedicarboxylic acid diethyl 1-, 20-eicosamethylenedicarboxylic acid diethyl 1-, 21-heneicosamethylenedicarboxylic acid diethyl 1-, 22-docosamethylenedicarboxylic acid diethyl 1-, 24-tetracosamethylenedicarboxylic acid Diethyl acid 1-, 28-octacosamethylenedicarboxylic acid diethyl 1-, 32-dotriacontamethylenedicarboxylic acid diethyl In addition, dimethyl oxalate and the like are used.

As the organic low molecular weight substance, the above dibasic acid dialkyl ester may be mixed with an organic low molecular weight substance having a melting point different by 10 ° C. or more. Dibasic acid
Examples of the organic low-molecular substance used by mixing with the dialkyl ester include aliphatic monocarboxylic acid and aliphatic dicarboxylic acid.
An acid is mentioned.

Specific examples of the aliphatic monocarboxylic acid include:
For example, palmitic acid, margaric acid, stearic acid,
Nonadecyl acid, arachidic acid, heneicosanoic acid, behenic acid, tricosanoic acid, tetracosanoic acid, pentacosanoic acid,
Hexacosanoic acid, peptacosanoic acid, octacosanoic acid, nonacosanoic acid, triacontanoic acid, hentriacontanoic acid, dotriacontanoic acid, tritriacontanoic acid, tetratriacontanoic acid, pentatriacontanoic acid, hexatriacontanoic acid, heptatriacontanoic acid , Octatriacontanoic acid, hexatetracontanoic acid and the like.

Specific examples of the aliphatic dicarboxylic acid include succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid and tetradecanedioic acid. Acid, pentadecanedioic acid, hexadecanedioic acid, heptadecanedioic acid, octadecanedioic acid, nonadecanedioic acid, eicosanedioic acid, heneicosanodioic acid, docosanedioic acid and the like can be mentioned.

[0022] In the present invention, the two base-dialkyl S. <br/> ether, the dibasic acid dialkyl ester and a melting point of 10 ° C.
The ratio of use with different organic low molecular weight substances is 9 by weight.
5: 5 to 5:95 are preferable, and 90:10 to 10:90.
Is more preferable, and 80:20 to 20:80 is particularly preferable.

The reversible thermosensitive recording material of the present invention utilizes the transparency change (transparent state, cloudy opaque state) as described above, and the difference between the transparent state and the cloudy opaque state is presumed as follows. . That is, (i) in the case of transparency, the particles of the organic low-molecular substance dispersed in the resin matrix are composed of large particles of the organic low-molecular substance, and the light incident from one side is not scattered and is opposite. It appears to be transparent because it is transmitted to the side, and (ii) in the case of turbidity, the particles of the organic low-molecular substance are composed of polycrystals of fine crystals of the organic low-molecular substance, and the crystal axis of each crystal Since the light is directed in various directions, the light incident from one side is refracted many times at the interface of the crystal of the organic low molecular weight substance particles, and is scattered and thus appears white.

In FIG. 1 (representing the change in transparency due to heat), a thermosensitive layer mainly composed of a resin base material and an organic low molecular weight substance dispersed in the resin base material is, for example, T
It is cloudy and opaque at room temperature below ₀ . This is the temperature T ₂
When it is heated to ₀ , it becomes transparent, and even if it is returned to room temperature below T _{0 in} this state, it remains transparent. This is the temperature T ₂ to T ₀
It is considered that the organic low molecular weight substance is in a semi-molten state until the following and the crystal grows from a polycrystal to a single crystal.
Upon further heating to T ₃ or more temperature becomes translucent state intermediate between the maximum transparency and the maximum opacity. Next, when this temperature is lowered, the first cloudy opaque state is restored without taking the transparent state again. It is considered that this is because when the organic low molecular weight substance is melted at a temperature of T ₃ or higher, the polycrystal is deposited by being cooled. When this opaque state is heated to a temperature between T _{1 and} T ₂ and then cooled to room temperature, that is, a temperature of T ₀ or lower, an intermediate state between transparent and opaque can be obtained. Also, the transparent material that has become transparent at room temperature returns to the cloudy and opaque state again when heated to a temperature of T ₃ or higher and then returned to room temperature. That is, both opaque and transparent forms at room temperature and intermediate forms thereof can be obtained.

Therefore, the heat-sensitive layer can be selectively heated by selectively applying heat to form a cloudy image on a transparent background and a transparent image on a cloudy background, and the change can be repeated many times. It is possible. By arranging a coloring sheet on the back surface of such a heat-sensitive body, it is possible to form an image of the color of the coloring sheet on a white background or a white image on the background of the color of the coloring sheet. Further, when projected by an OHP (overhead projector) or the like, the cloudy portion becomes a dark portion, the transparent portion transmits light and becomes a bright portion on the screen.

In order to prepare the reversible thermosensitive recording material used in the present invention, generally, (1) a resin matrix and an organic low molecular weight substance are used.
A solution in which the components are dissolved, or (2) a dispersion liquid in which an organic low molecular weight substance is dispersed in fine particles in a solution of a resin base material (a solvent that does not dissolve at least one of the organic low molecular weight substances is used as a solvent) It may be applied on a support such as a plastic film, a glass plate or a metal plate and dried to form a laminated heat-sensitive layer. The solvent for forming the heat-sensitive layer or the heat-sensitive recording material can be variously selected depending on the type of the resin base material and the organic low molecular weight substance, for example, tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, chloroform, carbon tetrachloride, ethanol, toluene, benzene and the like. Can be mentioned. The organic low molecular weight substance is precipitated as fine particles and exists in a dispersed state in the heat-sensitive layer obtained not only when the dispersion liquid is used but also when the solution is used.

The resin base material used for the heat-sensitive layer is a material that forms a layer in which an organic low molecular weight substance is uniformly dispersed and held, and has an effect on the transparency at maximum transparency. Therefore, the resin base material is preferably a resin having good transparency, mechanical stability, and good film forming property. Such resins include polyvinyl chloride; vinyl chloride-vinyl acetate copolymer, vinyl chloride-
Vinyl acetate-vinyl alcohol copolymer, vinyl chloride-
Vinyl chloride-based copolymers such as vinyl acetate-maleic acid copolymers and vinyl chloride-acrylate copolymers; polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymers, vinylidene chloride-based vinylidene chloride-acrylonitrile copolymers, etc. Copolymer; Polyester; Polyamide; Polyacrylate or polymethacrylate or acrylate-
Methacrylate copolymers; silicone resins and the like can be mentioned. Needless to say, these resins may be used alone or in combination of two or more.

In the present invention, a vinyl chloride polymer or a vinyl chloride copolymer is used as the resin base material, and the vinyl chloride unit content (Y% by weight) and the average degree of polymerization (X) of these polymers are By repeating the use of a polymer having a value within the range satisfying the relationship represented by the following formula (Formula 1), particularly one having an average degree of polymerization (X) of 500 or more in the following formula (Formula 1), repeated The durability can be improved.

[Equation 1]       -0.68logX + 3.794 ≤ logY ≤ -0.215logX + 2.66

That is, as the resin base material, a vinyl chloride polymer having a vinyl chloride unit content (Y% by weight) and an average degree of polymerization (X) within a range satisfying the relationship represented by the above formula (Equation 1). By using a polymer or a vinyl chloride copolymer, the heat resistance of the resin base material is improved while maintaining the contrast of transparent-white turbidity change, and the resin base material is less likely to be deformed by the heat and pressure of the thermal head, etc. Even if this is repeated many times, the organic low molecular weight substance dispersed in the resin base material is maintained as fine particles, and the image contrast is maintained.

In the vinyl chloride polymer or vinyl chloride copolymer used as the resin matrix in the present invention, the relationship between the vinyl chloride unit content (Y% by weight) and the average degree of polymerization (X) is represented by the above formula (Formula 1). Has a value in the range satisfying the condition (hatched portion and grid-like portion in FIG. 2). Here, the formula has a low average degree of polymerization (X) and a vinyl chloride unit content (Y
(% By weight), the average degree of polymerization (X) is high, and the ratio of vinyl chloride unit content (Y% by weight) is high, problems occur, and when the degree of polymerization (X) is low, vinyl chloride units are contained. It has been shown that it is preferable that the vinyl chloride unit content (Y wt%) becomes lower as the amount (Y wt%) becomes higher and the polymerization degree (X) becomes higher. In the resin base material of the present invention, when the average degree of polymerization (X) is high and the proportion of vinyl chloride unit content (Y wt%) is high, the following formula (Equation 2) (upper right of FIG. 2) Those in the range of values are preferable,

[Formula 2] logY ≤ -0.215logX + 2.636 When the average degree of polymerization (X) is low and the proportion of vinyl chloride unit content (Y wt%) is low, the average degree of polymerization (X) is 600 or more. A value within the range of the following formula (Equation 3) (lower left of FIG. 2) is preferable.

## EQU00003 ## logY.gtoreq.-0.215logX + 2.49 Note that the preferable range is shown in a lattice form in FIG.
Further, the average degree of polymerization (X) of the resin base material of the present invention is preferably 500 or more, more preferably 600 or more, particularly preferably 700 or more.

It is not clear why the use of the specific vinyl chloride polymer or vinyl chloride copolymer as the resin matrix improves the durability against repeated image formation and erasure by a heating means such as a thermal head, but these are not clear. When the average degree of polymerization of the polymer is high or the proportion of vinyl chloride units is high, the melt viscosity when heated is high, and image formation is performed using a heating means such as a thermal head that simultaneously applies heat and pressure. Even after repeated erasing, there is little deformation of the resin base material around the fine particles of organic low molecular weight substances,
Because the organic low-molecular substance is maintained as fine particles,
It is estimated that the durability will be improved.

If the average degree of polymerization and the vinyl chloride ratio are too high, the solubility in the solvent is lowered and the viscosity of the solution becomes high, and the organic low molecular weight substance and the resin base material are dissolved in the solvent and then dried. It is thought that the white turbidity is lowered because it is difficult to separate and the organic low molecular weight substance particles are difficult to form. The logarithm (logY) of the vinyl chloride unit (Y) of the resin base material is (-0.68logX + 3.794: X).
If it is smaller than (average degree of polymerization), the durability against repeated image formation and erasure is reduced, and (logY) is (-0.21).
5logX + 2.66), the initial white turbidity decreases.

The polyvinyl chloride or vinyl chloride copolymer used as the resin matrix is usually polymerized by various methods such as bulk polymerization, emulsion polymerization, suspension polymerization, and modifications thereof.

Specific examples of the polymerization method will be described below. First, in the suspension polymerization method, a vinyl chloride monomer is dispersed and suspended in minute liquid droplets in a water phase containing a small amount of a hydrophilic protective colloid dispersant by vigorous shear agitation to form a monomer-soluble organic peroxide. It is used as a polymerization initiator to carry out radical polymerization in a monomer droplet to obtain a polymer slurry having a particle size of several tens to several hundreds μ, which is filtered, washed, dried, and sieved to obtain a product. Suspension polymerization has few impurities, it is easy to control the reaction temperature, the resin quality is excellent, the equipment cost and production cost are low, the production control is easy, and it is easy to maintain the quality uniformity. Has become the mainstream of the PVC resin manufacturing method.

Next, the emulsion polymerization method is emulsified and dispersed in an aqueous phase with the aid of an anionic surfactant, and a water-soluble polymerization initiator such as persulfate is used to obtain a particle size of 0.1 to several. Take a polymer latex of μ, salt out, filter, wash, dry,
The product is obtained by grinding or by spray-drying the latex directly. Emulsion polymer is a fine powder that is difficult to handle, and contains a large amount of emulsifiers and other impurities.
Poor properties such as thermal stability, transparency, and electrical insulation.

The bulk polymerization method is also regarded as precipitation type solution polymerization (precipitation polymerization) using a monomer as a solvent. That is, a soluble initiator is added to a monomer to carry out radical polymerization, the polymerization reaction is stopped at an appropriate reaction rate to recover unreacted monomer, and the obtained precipitated polymer is pulverized and classified to obtain a product. Since it does not contain a dispersant or emulsifier, it has high polymer purity, and since it does not use water, it does not require filtration or drying, and is expected to have advantages such as simple equipment and low production costs. However, industrialization was delayed due to difficulty in removing heat of reaction and controlling particle shape, but recently, two-stage bulk polymerization method of Pescine Saint-Gobain was developed due to improvement of reactor.

The homogeneous solution polymerization method uses an expensive organic solvent and requires solvent recovery, so that the production cost is high, and it is difficult to obtain a polymer having a high degree of polymerization due to the chain transfer action of the solvent. There is a drawback that it becomes small and it is difficult to increase the reaction yield.

Among them, the suspension polymerization method is preferably used,
Any average degree of polymerization can be obtained by controlling the polymerization temperature (a high polymerization resin can be obtained when the polymerization temperature is low and the polymerization time is long). In the case of a copolymer, it can be produced by adding the monomer of the material desired to be copolymerized with vinyl chloride from the beginning or during the polymerization. The vinyl chloride ratio is mostly determined by the initial monomer addition ratio.

As such a vinyl chloride copolymer,
Vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinyl acetate-vinyl alcohol copolymers, vinyl chloride-vinyl acetate-maleic acid copolymers, vinyl chloride-acrylate copolymers, and other vinyl chloride-based copolymers Can be mentioned. These may be used alone or in admixture of two or more.

The degree of polymerization (molecular weight) of this resin base material is GPC.
It is measured by (gel permeation chromatography). This GPC
(Gel permeation chromatography) means that when a sample solution of resin dissolved in a solvent is injected into a column packed with a particulate gel having pores, a sample with a molecular size larger than the gel pore enters the pores. Therefore, the time that the molecules that pass through the outside of the gel and enter the pores stay in the gel pores differs depending on their size. The smaller the molecular size, the longer the elution time from the column. Therefore, in the eluate from the column, the sample is gradually separated from the high molecular weight to the low molecular weight. A method of measuring the difference in refractive index (differential refractive index) between the liquid that elutes and the solvent in which the resin is dissolved, and calculating the molecular weight distribution and average molecular weight of the measurement sample from the calibration curve of the standard sample whose molecular weight is known. Is.

The average degree of polymerization (X) is calculated from the measured number average molecular weight (Mn) by the following formula (Equation 4).

[Equation 4] Here, VD and VE are not specific ones, and in the case of a vinyl chloride-vinyl acetate copolymer, VD becomes vinyl acetate and VE does not exist. Further, here, the calculation formulas up to the terpolymer of vinyl chloride and the other two types are shown.
The calculation is performed in the same manner in the case of a copolymer of two or more species. The unit molecular weight is defined as follows (Table
1 ).

[Table 1]

The weight ratio of the organic low molecular weight substance to the resin base material in the heat sensitive layer is preferably about 2: 1 to 1:16, and more preferably 1: 2 to 1: 8. If the ratio of the resin base material is below this range, it will be difficult to form a film in which the organic low molecular weight material is retained in the resin base material. Becomes difficult.

In addition to the above components, additives such as a surfactant and a high boiling point solvent may be added to the heat-sensitive layer in order to facilitate the formation of a transparent image. Specific examples of these additives are as follows. Examples of high boiling point solvents: tributyl phosphate, tri-2-ethylhexyl phosphate,
Triphenyl phosphate, tricresyl phosphate, butyl oleate, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diheptyl phthalate, di-n-octyl phthalate, di-2-ethylhexyl phthalate, diisononyl phthalate, phthalate. Acid dioctyldecyl, diisodecyl phthalate, butylbenzyl phthalate, dibutyl adipate, di-n-hexyl adipate, di-2-adipate
Ethylhexyl, di-2-ethylhexyl azelate, dibutyl sebacate, di-2-ethylhexyl sebacate, diethylene glycol dibenzoate, triethylene glycol di-2-ethylbutyrate, methyl acetylricinoleate, butyl acetylricinoleate, butylphthalyl Butyl glycolate, tributyl acetyl citrate.

Examples of surfactants and other additives: polyhydric alcohol higher fatty acid ester; polyhydric alcohol higher alkyl ether; polyhydric alcohol higher fatty acid ester, higher alcohol, higher alkylphenol, higher fatty acid higher alkylamine, higher fatty acid amide , Lower olefin oxide adducts of fats and oils or polypropylene glycol; acetylene glycol; Na, Ca, Ba or Mg salt of higher alkylbenzene sulfonic acid; higher fatty acid, aromatic carboxylic acid, higher fatty acid sulfonic acid, aromatic sulfonic acid, sulfuric acid monoester Or Ca, Ba or Mg salts of phosphoric acid mono- or di-esters; low-sulfated oils; poly long-chain alkyl acrylates; acrylic orgomers;
Poly long-chain alkyl methacrylate; long-chain alkyl methacrylate-amine-containing monomer copolymer; styrene-maleic anhydride copolymer; olefin-maleic anhydride copolymer.

The thickness of the heat sensitive layer is preferably 1 to 30 μm,
2 to 20 μm is more preferable. If the heat-sensitive layer is too thick, heat distribution will occur in the layer and it will be difficult to achieve uniform transparency. On the other hand, if the heat-sensitive layer is too thin, the white turbidity is lowered and the contrast is lowered. Further, the white turbidity can be increased by increasing the amount of the organic low molecular weight substance in the heat sensitive layer.

A protective layer may be provided on the heat-sensitive layer to protect the heat-sensitive layer. Materials for the protective layer (thickness: 0.1 to 5 μm) to be laminated on the heat-sensitive layer include silicone rubber, silicone resin (described in JP-A-63-221087), and polysiloxane graft polymer (Japanese Patent Application No. 62-62). 152550) or UV curable resin or electron beam curable resin (described in Japanese Patent Application No. 63-310600).
Etc. In any case, a solvent is used at the time of coating, but it is desirable that the solvent is difficult to dissolve the resin of the heat sensitive layer and the organic low molecular weight substance. Examples of the solvent that hardly dissolves the resin and the organic low molecular weight substance in the heat-sensitive layer include n-hexane, methyl alcohol, ethyl alcohol, isopropyl alcohol and the like, and the alcohol solvent is particularly preferable from the viewpoint of cost.

Furthermore, an intermediate layer may be provided between the protective layer and the heat-sensitive layer in order to protect the heat-sensitive layer from the solvent, monomer components and the like of the protective-layer forming liquid (JP-A-1-133).
781). As the material for the intermediate layer, the following thermosetting resins and thermoplastic resins can be used in addition to those listed as the resin base material in the heat sensitive layer. That is, polyethylene, polypropylene, polystyrene, polyvinyl alcohol, polyvinyl butyral, polyurethane, saturated polyester, unsaturated polyester, epoxy resin, phenol resin, polycarbonate, polyamide and the like can be mentioned. The thickness of the intermediate layer is preferably about 0.1 to 2 μm. If it is less than this, the protective effect is lowered, and if it is more than this, the thermal sensitivity is lowered.

[0048]

EXAMPLES The present invention will be described in more detail by way of examples, which should not be construed as limiting the invention thereto. All parts and% herein are by weight.

EXAMPLE 1 r-Fe ₂ O ₃ 10 parts Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 10 parts (UCC: VAGH) Isocyanate (Nippon Polyurethane Coronate) on white PET having a thickness of about 188 μm. L 50% toluene solution) 2 parts Methyl ethyl ketone 40 parts Toluene 40 parts is applied with a wire bar and dried by heating to about 1
A magnetic recording layer having a thickness of 0 μm was provided. A special acrylic UV-curable resin (Dainippon Ink and Chemicals, Inc., Unidick C7-164, 49% butyl acetate solution) 10 parts Toluene 4 parts was applied with a wire bar, and after heating and drying 80 W
Approximately 1.
A 5 μm thick smooth layer was provided. Al about 400Å on it
It was vacuum-deposited so as to have a thickness, and a light reflection layer was provided. Further thereon, vinyl chloride-vinyl acetate-phosphate ester copolymer (Denka Vinyl # 1000P manufactured by Denki Kagaku Kogyo Co., Ltd.) 10 parts T.I. H. A solution consisting of 90 parts of F (tetrahydrofuran) was applied and dried by heating to provide an adhesive layer having a thickness of about 0.5 μm. Furthermore, dilauryl adipate 5 parts, eicosane diacid 5 parts, diisodecyl phthalate 3 parts, vinyl chloride-vinyl acetate copolymer (manufactured by Kaneka Corporation: 20-1621 vinyl chloride 80%, vinyl acetate 20%, Polymerization degree 3000) Prototype 39 parts T.I. H. A solution of 100 parts of F (tetrahydrofuran) and 65 parts of toluene was applied, and dried by heat to provide a heating layer (reversible thermosensitive recording layer) having a thickness of about 5 μm. Furthermore, a 75% butyl acetate solution of urethane acrylate UV curable resin (manufactured by Dainippon Ink and Chemicals, Inc .: Unidic C7-157) 10 parts A solution consisting of 10 parts isopropyl alcohol was applied with a wire bar and heated and dried. After 8
A reversible thermosensitive recording medium was prepared by curing with a 0 w / cm ultraviolet lamp and providing a protective layer having a thickness of about 2 μm.

Example 2 A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that dilauryl sebacate was used instead of dilauryl adipate in the thermosensitive layer.

Example 3 A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that distearyl succinate was used instead of dilauryl adipate in the thermosensitive layer.

Example 4 A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that distearyl sebacate was used instead of dilauryl adipate in the thermosensitive layer.

Example 5 A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that dibehenyl succinate was used instead of dilauryl adipate in the thermosensitive layer.

Example 6 As heat-sensitive layer Dimethyl eicosane diacid 2.5 parts Stearic acid 2.5 parts Eicosane diacid 5 parts Diisodecyl phthalate 3 parts Vinyl chloride-vinyl acetate copolymer (manufactured by Kaneka Corporation: 20 -1621 Vinyl chloride 80%, vinyl acetate 20%, degree of polymerization 3000) Prototype 39 parts T.I. H. A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that 100 parts of F (tetrahydrofuran) and 65 parts of toluene were used.

Example 7 A reversible thermosensitive recording material was prepared in the same manner as in Example 6 except that dimethyl sebacate was used instead of dimethyl eicosane diacid in the thermosensitive layer.

Example 8 A reversible thermosensitive recording material was prepared in the same manner as in Example 6 except that diethyl eicosane diacid was used instead of dimethyl eicosane diacid in the heat-sensitive layer.

Example 9 A reversible thermosensitive recording material was prepared in the same manner as in Example 6 except that dilauryl adipate was used instead of dimethyl eicosane diacid in the thermosensitive layer.

Example 10 A reversible thermosensitive recording material was prepared in the same manner as in Example 6 except that dilauryl sebacate was used instead of dimethyl eicosane diacid in the thermosensitive layer.

Example 11 A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that dilauryl adipate and eicosane diacid in the thermosensitive layer were changed to distearyl sebacate.

Example 12 A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that dilauryl adipate and eicosane diacid were replaced with dibehenyl succinate in the thermosensitive layer.

Example 13 A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that dilauryl adipate and eicosane diacid in the thermosensitive layer were changed to distearyl eicosane diate.

Example 14 A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that dilauryl adipate and eicosane diacid were replaced with dibehenyl eicosane diacid in the thermosensitive layer.

Comparative Example 1 A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that palmitic acid was used instead of dilauryl adipate in the thermosensitive layer.

Comparative Example 2 A reversible thermosensitive recording material was prepared in the same manner as in Example 6 except that palmitic acid was used instead of dimethyl eicosane diacid in the thermosensitive layer.

Comparative Example 3 A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that dilauryl adipate and eicosane diacid in the thermosensitive layer were changed to stearic acid.

The reversible thermosensitive recording materials of Examples and Comparative Examples thus obtained were subjected to image formation, image erasability and repeated durability tests as follows. The results are shown in Table 3. A thermal head printing tester manufactured by Yashiro Denki Co., Ltd. was used as a thermal recording / printing apparatus, and a Ricoh 8 dot / mm thermal head was used as a thermal head, and it became cloudy under the conditions of a pulse width of 1 msec and an applied voltage of 18.5V. An image was formed, and the applied voltage was changed to the optimum erasing voltage to erase the cloudy image (initial erasing, erasing over time). The initial erasure density when the image is erased after image formation and the image formation 40
The difference (△ value) between the background density (transparent state) and the erasing density when erasing with the same erasing voltage after storing for 24 hours at ℃
2 shows. Further, the cloudiness image formation was repeated 40 times and the durability test was conducted. Regarding the cloudiness image density in the repeated durability test, the cloudiness density at the 1st and 40th times was measured by a Macbeth densitometer (RD914), and the Δ at the 1st and 40th times was measured.
The values are shown in Table 2.

[0067]

[Table 2]

As is clear from the examples and comparative examples, the reversible thermosensitive recording material of the present invention was prepared by using a dibasic acid dial as an organic low-molecular substance dispersed in the resin matrix forming the thermosensitive layer.
By using the kill ester, there is an effect that the repeating durability is improved, and the initial erasability and the erasability with time are improved. Further, the organic low molecular weight substance is selected from monocarboxylic acids and saturated dicarboxylic acids whose melting points differ from that of the dihydrochloric acid dialkyl ester by 10 ° C. or more .
By using at least one kind of organic low molecular weight substance in combination, the transparentization temperature range can be widened and the erasability can be further improved. Furthermore, as a resin base material constituting the heat sensitive layer,
By using the specific vinyl chloride polymer, the durability is further improved even when the image is formed and erased by using a heating means such as a thermal head that applies heat and pressure at the same time.

[Brief description of drawings]

FIG. 1 is a diagram showing a change in transparency of a reversible thermosensitive recording material according to the present invention due to heat.

FIG. 2 is a diagram showing the range of the resin base material of the present invention in the relationship between the vinyl chloride unit content and the degree of polymerization of the resin base material.

[Explanation of symbols] ○ …… The initial white turbidity is very good and the repeating durability is very good △ …… The initial white turbidity is good and the repeating durability is very good ▽ …… The initial white turbidity Is very good, and the repeatability is good ▲ …… The initial white turbidity is poor ▼ …… The initial white turbidity is very good and the repeat durability is poor

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-2-1363 (JP, A) JP-A-5-85047 (JP, A) JP-A-4-299181 (JP, A) JP-A-4- 347684 (JP, A) US Patent 5283220 (US, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B41M 5/36 B41M 5/28-5/34

Claims (6)

(57) [Claims] 1. A reversible device comprising a support and a heat-sensitive layer containing a resin base material and an organic low-molecular substance dispersed in the resin base material as a main component and having a transparency reversibly changing depending on temperature. A reversible thermosensitive recording material comprising at least one dibasic acid dialkyl ester as the organic low-molecular substance in the thermosensitive recording material. 2. The reversible thermosensitive recording material according to claim 1, wherein a dibasic acid dialkyl ester having a melting point of 40 ° C. or higher is used as the dibasic acid dialkyl ester. As claimed in claim 3, wherein said organic low-molecular material, the two base-acid dialkyl ester, the dibasic acid dialkyl ester <br/> Le and different melting points monocarboxylic acids and saturated 10 ° C. or higher
The reversible thermosensitive recording material according to claim 1 or 2, which is used in combination with at least one organic low molecular weight substance selected from dicarboxylic acids . 4. A vinyl chloride polymer or a vinyl chloride copolymer is used as the resin base material, and the vinyl chloride unit content (Y% by weight) and the average degree of polymerization (X) of these polymers are as follows. The reversible thermosensitive recording material according to claim 1, which has a value in a range satisfying the relationship represented by the formula (Formula 1). [Equation 1] -0.68logX + 3.794 ≤ logY ≤ -0.215logX + 2.66 5. The reversible thermosensitive recording material according to claim 4, wherein the average degree of polymerization (X) is 500 or more. 6. The reversible thermosensitive recording material according to claim 1, 2, 3, 4 or 5, wherein the provision of the adhesive layer between the support and the heat-sensitive layer.