JP3230556B2 - Reversible thermosensitive 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 reversible thermosensitive recording medium for performing recording and erasing by utilizing a reversible change in transparency of a thermosensitive medium depending on temperature.

[0002]

2. Description of the Related Art As recording media capable of reversible recording and erasing, Japanese Patent Laid-Open Publication Nos.
JP-A-154198 discloses a substrate provided with a heat-sensitive recording layer in which a low molecular weight organic compound such as a higher alcohol or a higher fatty acid is dispersed in a resin matrix such as polyester. The transparency of the heat-sensitive recording layer changes depending on the temperature, thereby enabling recording and erasing. However, in a conventional reversible thermosensitive recording medium, when an image is formed by heating with a heating element such as a thermal head, the surface is easily deformed by the heat and pressure of the heating element, so that image formation and erasing are repeated. There has been a problem that the amount of deformation increases and the transparency of a portion that should be transparent decreases.
To solve this problem, Japanese Patent Application Laid-Open No. 63-221087 discloses
In Japanese Patent Application Laid-Open Publication No. Hei 10 (1995) -207, there has been proposed a method of providing an overcoat layer of a silicone resin, a silicone rubber, or the like to reduce the surface friction coefficient. However, since the overcoat layer has insufficient adhesiveness to the heat-sensitive recording layer, there is a problem in that the overcoat layer peels off due to repeated mechanical action, thereby deteriorating the image.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a reversible thermosensitive recording medium which does not deteriorate the image and the transparency of the transparent portion even when the image formation and erasure are repeatedly performed by a heating element such as a thermal head. With the goal.

[0004]

According to the present invention, it has been found that the above object can be achieved by providing an overcoat layer comprising a polysiloxane-urea-polyamide multiblock copolymer on a heat-sensitive recording layer. That is, according to the present invention, a heat-sensitive recording layer having a resin matrix and a low molecular weight organic compound dispersed in the resin matrix as main components and having a transparency that reversibly changes depending on a temperature change is provided on the support. In the provided reversible thermosensitive recording medium, there is provided a reversible thermosensitive recording medium characterized in that an overcoat layer comprising a polysiloxane-urea-polyamide multi-block copolymer is provided on the thermosensitive recording layer. Further, according to the present invention, the polysiloxane-urea-polyamide multi-block copolymer has the following general formula (1):
Wherein the reversible thermosensitive recording medium is a copolymer having a repeating unit represented by the formula:

Embedded image (Wherein, R ₁ represents a divalent organic group having 10 or less carbon atoms, R ₂ and R ₃ each represent a divalent organic group having 2 or more carbon atoms,
L ₁ , L ₂ , L ₃ and L ₄ represent (a) an alkyl group having 1 to 12 carbon atoms, (b) an alkyl group having 1 to 12 carbon atoms substituted with a halogen atom or a CN group, and (c) phenyl Group and
(D) represents a group arbitrarily selected from the group consisting of an alkyl group having 1 to 4 carbon atoms, an alkoxy group or a phenyl group substituted with a halogen atom, x is an integer of 5 to 300, and y is 1
To 50 and n each represent an integer of 2 to 30. )Also,
According to the present invention, the polysiloxane-urea-polyamide multi-block copolymer represented by the general formula (1) has a breaking elongation of 50% or more when formed into a film. A thermosensitive recording medium is provided. Further, according to the present invention, the polysiloxane-urea-polyamide multi-block copolymer represented by the general formula (1) has a glass transition point of 180 ° C. or higher. A medium is provided. Still further, according to the present invention, the polysiloxane-urea-polyamide multiblock copolymer represented by the general formula (1) has a dynamic friction coefficient of 0.20 or less. A recording medium is provided.

The reversible thermosensitive recording medium of the present invention utilizes a change from a transparent state to a cloudy opaque state and a change from a cloudy opaque state to a transparent state due to the temperature dependence of the transparency of the heat-sensitive recording layer. Can be recorded and erased. The difference between the transparent state and the cloudy opaque state is presumed as follows. That is, in the (i) transparent state, the low-molecular-weight organic compound particles dispersed in the resin base material exist as relatively large particles, and light incident from one side is transmitted to the other side without being scattered, so that it is transparent. In addition, (ii) in the cloudy state, the low-molecular organic compound particles are composed of polycrystals in which fine crystals are aggregated, and since each crystal axis is oriented in various directions, light incident from one side is a low-molecular compound. This is because the organic compound particles are refracted and scattered many times at the crystal interface, and appear white because of scattering.

In FIG. 1 (change in transparency due to heat),
Thermosensitive layer mainly composed of the particle matrix and low-molecular organic compound dispersed in this, for example, the cloudy opaque state at T ₀ or lower. This became clear when heated to a temperature T _2, also maintains the transparent state returning to a normal temperature of T ₀ or less from this state. This may be because the crystalline low molecular organic compounds down to T ₀ or less from the temperature T ₂ is between the single crystal from a polycrystalline via a semi-molten state grows. Upon further heating to T ₃ or more temperature, it becomes an intermediate state of the maximum transparent state and the maximum opaque state. Next, when the temperature is lowered from this state,
It returns to the original cloudy and opaque state again without becoming transparent.
This is believed to be due to multi crystals precipitate by low-molecular organic compound at a temperature T ₃ or more is melted, cooled. The opaque state is heated to a temperature of T _{1 to} T ₂ , and then cooled to room temperature, that is, a temperature equal to or lower than T _0, to be in an intermediate state between transparent and opaque. Further Returning to room temperature after heating what became transparent at the room temperature to again T ₃ or more temperature returns to cloudy opaque state again. That is, at room temperature, it can be made into an opaque and transparent state and an intermediate state. Therefore, by selectively applying heat, the heat-sensitive layer can selectively form a cloudy image on a transparent ground and a transparent image on a cloudy ground, and the change can be repeated many times.

Hereinafter, the present invention will be described in more detail. As described above, the reversible thermosensitive recording medium of the present invention is characterized in that an overcoat layer made of a polysiloxane-urea-polyamide multiblock copolymer is provided on the upper surface of the reversible recording layer. The polysiloxane-urea-polyamide multi-block copolymer used in the present invention is represented by the following general formula (1), particularly in terms of preventing a decrease in transparency due to repeated image formation and erasure of 100 times or more. Polysiloxane-urea-polyamide multiblock copolymers having repeating units are preferred.

Embedded image (In the formula, R _{1 to} R ₃ , L _{1 to} L ₄ , x, y, and n are the same as described above.)

[0008] The polysiloxane-urea-polyamide multiblock copolymer of the present invention is obtained by reacting one or more dicarboxylic acid compounds with one or more diisocyanate compounds in the presence of lithium chloride to form an isocyanate group at both ends. Is obtained by synthesizing a polyamide oligomer having the following formula, and reacting the obtained oligomer with one or more kinds of diaminosiloxane oligomers.

In this case, as the dicarboxylic acid compound,
It has a carboxylic acid residue R ₃ (R ₃ is the same as above), and specifically includes oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacin Aliphatic dicarboxylic acids such as acid, maleic acid and fumaric acid or derivatives thereof, benzophenol-2,4'-dicarboxylic acid, 2,2'-biphenyldicarboxylic acid, 4,4'-biphenyldicarboxylic acid, 5-t -Butylisophthalic acid, 2,5-dichloroterephthalic acid, isophthalic acid, phthalic acid, tetrabromophthalic acid, tetrabromoterephthalic acid, tetrachlorophthalic acid, tetrachlorophthalic acid, tetrafluorophthalic acid, tetrafluoroisophthalic acid, tetra Fluoroterephthalic acid, 4 '-(2-thiazolesulfamyl) phthalic acid, 1,1,3 Trimethyl-3-phenyl indene-4 ', 5-dicarboxylic acid, 2,3-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid and 1,1,
Aromatic dicarboxylic acids such as 3-trimethyl-3-phenylindane-4 ', 5-dicarboxylic acid, or imidazole-4,5-dicarboxylic acid, pyrazine-2,3-dicarboxylic acid, pyridine-2,3-dicarboxylic acid Pyridine-2,4-dicarboxylic acid, pyridine-2,5-dicarboxylic acid, pyridine-2,6-dicarboxylic acid, pyridine 3,4
And heterocyclic aromatic dicarboxylic acids such as -dicarboxylic acid, pyridine-3,5-dicarboxylic acid and thiazolidine-2,4-dicarboxylic acid.

The isocyanate compound has an isocyanate residue R ₂ (R ₂ is the same as described above). Specifically, 1,6-hexamethylene diisocyanate, 2,2,4-trimethyl Hexamethylene diisocyanate, 1,12-diisocyanate dodecane, isophorone diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, toluene-2,4-diisocyanate, toluene-2,6
-Diisocyanate, 4-isopropyl-1,3-phenylene diisocyanate, 4-chloro-1,3-phenylene diisocyanate, 4-butoxy-1,3-phenylene diisocyanate, m-xylylene diisocyanate, 4,4'-diphenylmethane diisocyanate,
4,4'-diisocyanate-3,3'dimethyldiphenylmethane, 4,4'-diisocyanate diphenyl ether, 3,4'-diisocyanate diphenyl ether, 4,4-diisocyanate biphenyl, 4,4'-
The diisocyanates 3,3'-dimethylbisphenyl and 3,3'-dichlorodiphenyl-4,4'-diisocyanate are used.

On the other hand, as the diaminosiloxane oligomer, R ₁ in the general formula (1) (R ₁ is the same as above),
It has each group of L ₁ , L ₂ , L ₃ and L ₄ and has an amino group at both terminals. Specific examples of the group represented by R ₁ include, for example, the following formula (2): The groups represented by (3), (4), (5) and (6) are mentioned.

Embedded image (N1 is an integer of ₁ to 10)

Embedded image (N ₂ is 0-4 integer)

Embedded image (N ₃ is an integer of 1 to 3)

Embedded image (Integer of n ₄ is 0 to 4)

Embedded image (N ₅ is an integer of 1 to 3)

L ₁ , L ₂ , L ₃ and L ₄ are the following 4
It is a group arbitrarily selected from the group consisting of types of groups, and may be the same or different. (A) a linear or branched alkyl group having 1 to 12 carbon atoms; (B) A linear or branched alkyl group having 1 to 12 carbon atoms and substituted with one or more halogen atoms or CN groups.
In this case, the halogen atom includes Cl, Br, F and the like. (C) phenyl group. (D) a phenyl group substituted with an alkyl group or alkoxy group having 1 to 4 carbon atoms or a halogen atom.

In the general formula (1), x represents the average degree of polymerization of the siloxane monomer constituting the diaminosiloxane oligomer, and is an integer of 5 to 300. Y represents the average degree of polymerization of the polyamide oligomer, and is an integer of 1 to 50. Further, n represents an average degree of polymerization of a repeating unit composed of a diaminokiloxane oligomer and a polyamide oligomer, and is an integer of 2 to 30.

In the present invention, for example, in order to prevent a decrease in transparency due to repeated image formation and erasure of 300 times or more, it is preferable to use a multi-block copolymer having a glass transition point of 180 ° C. or more. For this purpose, it is preferable to use the following materials as the raw materials for the dicarboxylic acid compound and the isocyanate compound.

That is, dicarboxylic acid compounds include benzophenone-2,4'-dicarboxylic acid, 2,2'-bisphenyldicarboxylic acid, 4,4'-biphenyldicarboxylic acid, 5-t-butylisophthalic acid, 5-dichloroterephthalic acid, isophthalic acid, phthalic acid, tetrabromophthalic acid, tetrabromoterephthalic acid, tetrachlorophthalic acid, tetrachloroterephthalic acid, tetrafluorophthalic acid, tetrafluoroisophthalic acid, tetrafluoroterephthalic acid, 4'- (2-thiazolesulfamyl)
Phthalic acid, 1,1,3-trimethyl-3-phenylindene-4 ', 5-dicarboxylic acid, 2,3-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid and 1,
1,3-trimethyl-3-phenylindane-4 ', 5
Aromatic dicarboxylic acids such as dicarboxylic acids, or imidazole-4,5-dicarboxylic acids, pyrazine-2,3-
Dicarboxylic acid, pyridine-2,3-dicarboxylic acid, pyridine-2,4-dicarboxylic acid, pyridine-2,5-dicarboxylic acid, pyridine-2,6-dicarboxylic acid, pyridine-3,4-dicarboxylic acid, pyridine- Heterocyclic aromatic dicarboxylic acids such as 3,5-dicarboxylic acid and thiazolidine-2,4-dicarboxylic acid are exemplified.

Examples of the diisocyanate include p-phenylene diisocyanate, m-phenylene diisocyanate, toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, and 4-isopropyl-isocyanate.
1,3-phenylene diisocyanate, 4-chloro-
1,3-phenylene diisocyanate, 4-butoxy-
1,3-phenylene diisocyanate, m-xylylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-diisocyanate-3,3'-
Dimethyldiphenylmethane, 4,4'-diisocyanate diphenyl ether, 3,4'-diisocyanate diphenyl ether, 4,4'-diisocyanate biphenyl, 4,4'-diisocyanate-3,3'-dimethylbiphenyl and 3,3'-dichlorophenyl-4 ,
4'-diisocyanate and the like.

Further, the overcoat layer may be scraped off by frictional force with the thermal head, so that the components of the overcoat layer are fused or adhered to the heat generating portion of the thermal head and its vicinity, thereby deteriorating the image quality. Or a phenomenon that erasing is not performed completely occurs. In order to suppress this phenomenon, it is preferable to use a multi-block copolymer having a film elongation at break of 50% or more, and a polysiloxane-urea-polyamide multi-block copolymer having such mechanical properties is desired. To obtain it, it is preferable to use a polyamide oligomer having an average molecular weight lower than the average molecular weight of the diaminosiloxane oligomer.

Further, in order to prevent a decrease in transparency due to repetition of image formation and erasure 500 times or more, it is desirable to reduce a frictional force generated between a heating element such as a thermal head and an overcoat layer. It is preferable to use a multi-block copolymer having a dynamic friction coefficient of 0.20 or less.

The polysiloxane-urea-polyamide multi-block copolymer of the present invention does not cause a problem of performance deterioration even when two or more copolymers are mixed and used. You can also. The polysiloxane-urea-polyamide multi-block copolymer may be a mixture of conventionally used materials such as silicone resin and silicone rubber. However, since the advantages of mixed use are small except in special cases, generally, the copolymer of the present invention produced from a dicarboxylic acid compound, a diisocyanate compound, and an aminosiloxane oligomer according to the purpose as described above is used. May be used for the overcoat layer. The overcoat layer of the present invention has a thickness of about 0.1 to 7.5 μm, preferably 0.5 to 3.5 μm.

The heat-sensitive recording layer can be formed by a method in which a solution in which a matrix resin and a low molecular weight organic compound or the like are dispersed or dissolved in a solvent is coated on a support and dried. Can be variously selected depending on the type of matrix resin and low molecular weight organic compound,
For example, ethyl acetate, butyl acetate, tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, methylene chloride, chloroform, carbon tetrachloride, methanol,
Examples include ethanol, toluene, xylene, and benzene. The low-molecular-weight organic compound precipitates as fine particles in the heat-sensitive layer obtained when the solution is used, as well as when the dispersion is used, and exists in a dispersed state.

In the present invention, the matrix resin in the thermosensitive recording layer of the reversible thermosensitive recording medium can form a film,
It is preferable that the film has excellent transparency and is mechanically stable. As such a resin, polyvinyl chloride; vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-
Vinyl alcohol copolymer, vinyl chloride-vinyl acetate-
Vinyl chloride copolymers such as maleic acid copolymer and vinyl chloride-acrylate copolymer; polyvinylidene chloride; vinylidene chloride copolymers such as vinylidene chloride-vinyl chloride copolymer and vinylidene chloride-acrylonitrile copolymer Polyester; polyamide; polyacrylate; polymethacrylate; polyacrylate-polymethacrylate copolymer; and silicone resin. These may be used alone or as a mixture of two or more.

On the other hand, the low molecular weight organic compound may be any compound that changes from polycrystal to single crystal by heat in the recording layer, and generally has a melting point of 30 to 200 ° C., preferably 50 to 200 ° C.
Low molecular organic compounds having a melting point of 150 ° C. are used. Such low molecular organic compounds include alkanols; alkanediols; halogenated alkanols; halogenated alkanediols; alkylamines;
Alkenes; alkynes; halogenated alkanes; halogenated alkenes; halogenated alkynes; cycloalkanes; cycloalkenes; cycloalkynes; saturated or unsaturated mono- or dicarboxylic acids or their esters, amides or salts; These esters,
Amides or salts; allylcarboxylic acids or their esters, amides or salts; halogenated allylcarboxylic acids or their esters, amides or salts; thioalcohols; thiocarboxylic acids or their esters, amides or salts; carboxylic esters of thioalcohols And the like. These may be used alone or as a mixture of two or more. These compounds have 10 to 60 carbon atoms, preferably 10 to 3 carbon atoms.
8, particularly preferably 10 to 30. The alcohol group in the ester may be saturated, may not be saturated, and may be halogen-substituted. In any case, the low molecular weight organic compound contains at least one oxygen,
Groups containing nitrogen, sulfur or halogen, such as -OH
-, -COOH, -CONH, -COOR, -NH-,
It is preferably a compound having -S-, -SS- or -O-.

More specifically, these compounds
Is lauric acid, dodecanoic acid, myristic acid, pentade
Canoic acid, palmitic acid, stearic acid, behenic acid, nona
Decanoic acid, arachiic acid, heneicosanoic acid, trichosan
Acid, lignoceric acid, pentacosanoic acid, cerotic acid,
Butacosanoic acid, montanic acid, melicic acid and oleic acid
Higher fatty acids such as methyl stearate, stearic acid
Tetradecyl, octadecyl stearate, lauric acid
Octadecyl, tetradecyl palmitate and behenic acid
Esters of higher fatty acids such as dodecyl; C₁₆H₃₃-OC₁₆H₃₃, C₁₆H₃₃-SC₁₆H₃₃ C₁₈H₃₇-SC₁₈H₃₇, C₁₂H_{twenty five}-SC₁₂H_{twenty five} C₁₉H₃₉-SC₁₉H₃₉, C₁₂H_{twenty five}-S-S-C₁₂H_{twenty five}   And ethers and thioethers. During ~
However, in the present invention, higher fatty acids, especially palmitic acid,
Decanoic acid, nonadecanoic acid, arachidic acid, heneicosane
Acid, trichosanoic acid, stearic acid, behenic acid, lignose
Higher fatty acids having 16 or more carbon atoms such as phosphoric acid
Preferably, higher fatty acids having 16 to 24 carbon atoms are further added.
Preferred.

Further, in order to widen the range of the temperature at which the liquid crystal can be made transparent, the above-mentioned low molecular weight organic compound may be appropriately combined, or such a low molecular weight organic compound may be combined with another material having a different melting point. . These are described, for example, in JP-A-63-39378, JP-A-63-130380, Japanese Patent Application No. 63-14754 and Japanese Patent Application No. 1-1.
It is described in, for example, Japanese Patent No. 40109, but is not limited thereto.

The ratio between the low molecular weight organic compound and the resin matrix in the heat sensitive layer is preferably about 2: 1 to 1:16, more preferably 1: 2 to 1: 6 by weight. When the ratio of the resin base material is less than this, it becomes difficult to form a film holding the low molecular weight organic compound in the resin base material, and when the ratio is more than this, it is difficult to make the film opaque because the amount of the low molecular weight organic compound is small. Become.

The thickness of the heat-sensitive layer is preferably 1 to 30 μm,
2-20 μm is more preferred. When the heat-sensitive layer is too thick, the heat sensitivity is lowered, and it is difficult to make the heat-sensitive layer transparent uniformly. On the other hand, if the heat-sensitive layer is too thin, the turbidity decreases and the contrast decreases. Further, the turbidity can be increased by increasing the amount of the low molecular organic compound in the heat-sensitive layer.

In addition to the above components, additives such as a high melting point solvent and a surfactant can be added to the heat-sensitive layer in order to facilitate formation of a transparent image. As a high melting point solvent, tributyl phosphate, tri-2-ethylhexyl phosphate, triphenyl phosphate, tricresyl phosphate, butyl oleate, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diheptyl phthalate, di-phthalate n
-Octyl, di-2-ethylhexyl phthalate, diisononyl phthalate, dioctyldecyl phthalate, diisodecyl phthalate, butylbenzyl phthalate, dibutyl adipate, di-n-hexyl adipate, di-adipate-
2-ethylhexyl, di-2-ethylhexyl azelate, dibutyl sebacate, di-2-ethylhexyl sebacate, diethylene glycol dibenzoate, triethylene glycol di-2-ethyl butyrate, methyl acetyl ricinoleate, methyl acetyl ricinoleate,
Butyl phthalyl butyl glycolate and acetyl tributyl citrate are included.

As a surfactant 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 oils and fats or polypropylene glycol; acetylene glycol; Na, Ba, Ca or Mg salts of higher alkylbenzene sulfonic acids; higher fatty acids, aromatic carboxylic acids, higher aliphatic sulfonic acids, aromatic sulfonic acids, monoesters of sulfuric acid Or Ca, Ba or Mg salts of phosphoric acid mono- or diesters; low-sulfated oils; poly-long-chain alkyl acrylates; acrylic oligomers; poly-long-chain alkyl methacrylates; Over copolymer; a styrene - maleic acid copolymer and olefin anhydride - like maleic anhydride copolymer.

In the present invention, as the support of the reversible thermosensitive recording material, a plastic film, a glass plate, a metal plate and the like are used as described above.

In order to improve the image contrast of the recording material, a light reflection layer can be provided on the back surface of the recording layer. In this case, high contrast can be obtained even if the thickness of the recording layer is reduced. Specifically, JP-A-64-140
No. 79 describes a method of depositing Al, Ni, Sn, Au, Ag and the like.

For a material having a poor adhesion to a resin such as an Al vapor-deposited layer, a method of providing an adhesive layer between the support and a heat-sensitive layer described in JP-A-64-14079 may be used. Good. Further, an intermediate layer is provided between the overcoat layer and the reversible recording material described in JP-A-1-1337981 in order to protect the reversible recording material from a solvent, a monomer component, and the like of the overcoat layer forming liquid. A method may be used. As the material of 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 thermosensitive layer. That is, specific examples include polyethylene, polypropylene, polystyrene, polyvinyl alcohol, polyvinyl butyral, polyurethane, saturated polyester, unsaturated polyester, epoxy resin, phenol resin, polycarbonate, polyamide, and the like. The thickness of the intermediate layer varies depending on the application, but is preferably about 0.1 to 2 μm. Below this, the protective effect decreases, and above that, the thermal sensitivity decreases.

Further, as described in JP-A-2-3876, a magnetic recording layer can be provided and used as a magnetic reversible thermosensitive recording medium capable of recording by magnetism and heat.

[0033]

Next, examples and comparative examples will be described. All parts and percentages shown below are based on weight.

Example 1 On a 75 μm thick polyethylene terephthalate (RET) film, 8 parts of stearyl stearate, 3 parts of di (2-ethylhexyl) phthalate and 28 parts of vinyl chloride-vinyl acetate copolymer (UCC) VYHH) and 2
A solution consisting of 00 parts of tetrahydrofuran was applied with a wire bar and dried at 80 ° C. for 3 minutes to provide a 15 μm thick thermosensitive recording layer. A solution consisting of 10 parts of a polyamide resin (manufactured by Toray Industries, Inc., CM8000) and 90 parts of methyl alcohol was coated on this recording layer with a wire bar,
After drying for an minute, an intermediate layer having a thickness of 0.5 μm was provided. On this intermediate layer, an α, ω-bis (3
-Aminopropyl) poly (dimethylsiloxane), and 4,4'-diisocyanate-3,3'-dimethyldiphenylmethane and azelaic acid / isophthalic acid (50/5
0) derived from a polysiloxane-urea-polyamide copolymer (elongation at break, 20%, glass transition point 160 ° C) consisting of 4% N, N
-Applying a dimethylacetamide solution with a wire bar,
After drying at 120 ° C. for 10 minutes, a 2.5 μm thick overcoat layer was provided to obtain a reversible thermosensitive recording medium. The dynamic friction coefficient of the overcoat layer was 0.25.

Example 2 After providing a recording layer and an intermediate layer in the same manner as in Example 1,
Α, ω-bis (3-aminopropyl) poly (dimethylsiloxane) having an average molecular weight of 00, and a di-isocyanate polyamide oligomer having both ends terminated with an average molecular weight of 1500 derived from 1,6-diisocyanatohexane and adipic acid; , A 4% N, N-dimethylacetamide solution of a polysiloxane-urea-polyamide copolymer (55% elongation at break, glass transition point 120 ° C) is coated with a wire bar and dried at 120 ° C for 10 minutes. Thus, an overcoat layer having a thickness of 2.5 μm was provided to obtain a reversible thermosensitive recording medium. The dynamic friction coefficient of the overcoat layer was 0.23.

Example 3 After providing a recording layer and an intermediate layer in the same manner as in Example 1,
Α, ω-bis (3-aminopropyl) poly (dimethylsiloxane) having an average molecular weight of 00, and 4,4′-
A polysiloxane-urea-polyamide copolymer (85% elongation at break, glass transition) consisting of diphenylmethane diisocyanate and a di-isocyanate polyamide oligomer having both ends terminated with an average molecular weight of 1400 derived from azelaic acid / isophthalic acid (50/50) Point 130
C) with a 4% N, N-dimethylacetamide solution with a wire bar and dried at 120C for 10 minutes.
An overcoat layer having a thickness of 5 μm was provided to obtain a reversible thermosensitive recording medium. The dynamic friction coefficient of the overcoat layer was 0.19.

Example 4 After a recording layer was provided in the same manner as in Example 1, α, ω-bis (3-aminopropyl) having an average molecular weight of 3500
Polysiloxane-urea-polyamide comprising poly (dimethylsiloxane) and di-isocyanate polyamide oligomers with both ends terminated with 4,4'-diphenylmethane diisocyanate and azelaic acid / isophthalic acid (50/50) and having an average molecular weight of 15050 4 of copolymer (elongation at break: 20%, glass transition point: 185 ° C)
% N, N-dimethylacetamide solution was applied with a wire bar, and dried at 120 ° C. for 10 minutes to provide a 2.5 μm thick overcoat layer to obtain a reversible thermosensitive recording medium. The dynamic friction coefficient of the overcoat layer was 0.20.

Example 5 After a recording layer was formed in the same manner as in Example 1, α, ω-bis (3-aminopropyl) having an average molecular weight of 3500
Poly (dimethylsiloxane) and polysiloxane comprising 4,4'-diphenylmethane diisocyanate and a di-isocyanate polyamide oligomer having both ends terminated with an average molecular weight of 3500 derived from isophthalic acid.
A 4% N, N-dimethylacetamide solution of a urea-polyamide copolymer (elongation at break: 60%, glass transition point: 190 ° C.) is applied with a wire bar, dried at 120 ° C. for 10 minutes, and dried at 2.5 μm. A thick overcoat layer was provided to obtain a reversible thermosensitive recording medium. The dynamic friction coefficient of the overcoat layer was 0.18.

Comparative Example 1 A reversible thermosensitive recording medium was obtained in the same manner as in Example 1, except that an intermediate layer and an overcoat layer were not provided.

Comparative Example 2 A reversible thermosensitive recording layer and an intermediate layer were provided in the same manner as in Example 1. On the intermediate layer, 3 parts of organopolysiloxane (KS-779H, manufactured by Shin-Etsu Silicon Co., Ltd.) and 0.01 part were used. A solution consisting of a catalyst (PL-8, manufactured by Shin-Etsu Silicon Co., Ltd.) and 92 parts of toluene was applied with a wire bar, dried at 80 ° C. for 1 minute, provided with an overcoat layer having a thickness of 0.12 μm, and reversible thermosensitive recording. I got the medium.

(Evaluation method) The reversible thermosensitive recording medium prepared as described above was subjected to 0.5 μJ using a thin film thermal head.
After forming an image with a printing energy of / dot, 65 ° C.
The operation of reheating until erasing the image was repeated 500 times. The density of the image portion and the non-image portion at the first, 100th, 300th, and 500th times was measured with a Macbeth densitometer RD514 with black paper on the back surface. The results are shown in Table 1.

[0041]

[Table 1]

[0042]

As described above, the reversible thermosensitive recording medium of the present invention is provided with an overcoat layer comprising the polysiloxane-urea-polyamide multi-block copolymer having the above-mentioned specific structure on the upper surface of the reversible thermosensitive recording layer. It is possible to suppress a decrease in the transparency of the non-image portion due to the repetition of image formation and erasing by the heating element. Further, by using a diisocyanate compound and / or a dicarboxylic acid compound having at least one aromatic group in the diisocyanate compound and / or the dicarboxylic acid compound as a raw material for the polymer, the above-mentioned decrease in transparency is further suppressed. It is possible to do. The polymer has a breaking elongation of 50% when formed into a film.
By using the above polysiloxane-urea-polyamide multi-block copolymer, the overcoat layer composition is fused or adhered to a heating element such as a thermal head or the vicinity thereof, thereby deteriorating image quality or incompletely forming the image. Erasure can be prevented. Further, as the polymer,
Polysiloxane having a glass transition point of 180 ° C. or higher
By using the urea-polyamide multi-block copolymer, it is possible to further suppress the above-mentioned decrease in transparency. Furthermore, by using a polysiloxane-urea-polyamide multi-block copolymer having a dynamic friction coefficient of 0.20 or less as the polymer,
The frictional force generated between the heating element such as a thermal head and the overcoat layer is reduced, and the deformation of the overcoat layer is suppressed, so that the above-described decrease in transparency can be further prevented.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram in a case where an image is formed / erased by a heat-sensitive layer according to the present invention.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B41M 5/36 B41M 5/28-5/34

Claims (6)

(57) [Claims] 1. A reversible thermosensitive recording layer comprising, as a main component, a resin matrix and a low molecular weight organic compound dispersed in the resin matrix, and having a transparency that reversibly changes depending on a temperature change. A reversible thermosensitive recording medium, characterized in that an overcoat layer comprising a polysiloxane-urea-polyamide multiblock copolymer is provided on the thermosensitive recording layer. 2. The reversible feeling according to claim 1, wherein the polysiloxane-urea-polyamide multiblock copolymer is a copolymer having a repeating unit represented by the following general formula (1). Thermal recording medium. Embedded image (Wherein, R ₁ represents a divalent organic group having 10 or less carbon atoms, R ₂ and R ₃ each represent a divalent organic group having 2 or more carbon atoms,
L ₁ , L ₂ , L ₃ and L ₄ represent (a) an alkyl group having 1 to 12 carbon atoms, (b) an alkyl group having 1 to 12 carbon atoms substituted with a halogen atom or a CN group, and (c) phenyl Group and
(D) represents a group arbitrarily selected from the group consisting of an alkyl group having 1 to 4 carbon atoms, an alkoxy group or a phenyl group substituted with a halogen atom, x is an integer of 5 to 300, and y is 1
To 50 and n each represent an integer of 2 to 30. ) 3. R ₂ and / or R in the general formula (1)
_3. The reversible thermosensitive recording medium according to claim 2, wherein ₃ is a divalent group containing at least one aromatic group. 4. The polysiloxane-urea-polyamide multiblock copolymer represented by the general formula (1),
The reversible thermosensitive recording medium according to claim 2, wherein the recording medium has a breaking elongation of 50% or more when formed into a film. 5. The polysiloxane-urea-polyamide multiblock copolymer represented by the general formula (1),
3. The reversible thermosensitive recording medium according to claim 2, having a glass transition point of 180 [deg.] C. or higher. 6. The reversible heat-sensitive material according to claim 2, wherein the polysiloxane-urea-polyamide multi-block copolymer represented by the general formula (1) has a dynamic friction coefficient of 0.20 or less. recoding media.