JP2739992B2 - Reversible thermosensitive recording material - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a reversible thermosensitive recording material that performs recording and erasing by utilizing a reversible change in transparency of a thermosensitive material depending on temperature.

BACKGROUND ART As a heat-sensitive recording material capable of reversible recording and erasing, a heat-sensitive recording material having a heat-sensitive layer in which an organic low-molecular substance such as a higher alcohol or a higher fatty acid is dispersed in a resin such as polyester on a support is disclosed in, for example, These are known from JP-A-54-119377 and JP-A-55-154198. Recording with this type of recording material, that is, image formation and erasing, utilizes a change in transparency due to the temperature of the heat-sensitive layer.

However, these reversible thermosensitive recording materials have a drawback that the contrast is remarkably lowered when a support colored in black or the like is used as a support in order to make the image easy to see. Therefore, the present inventors have previously proposed in Japanese Patent Application No. 62-171629 to provide a metal light reflecting layer in order to eliminate such a defect.

However, this reversible thermosensitive recording material was also inferior in durability when the thermosensitive layer was provided directly on the metal surface serving as the light reflecting layer, because of poor adhesion between the two layers.

An object of the present invention is to provide a reversible thermosensitive recording material having high contrast and excellent durability.

The reversible thermosensitive recording material of the present invention comprises a resin base material and an organic low-molecular substance dispersed in the resin base material as a main component on a support having at least a part of the surface made of metal, and is dependent on temperature. In a reversible thermosensitive recording material provided with a thermosensitive layer whose transparency reversibly changes, a main component of the resin base material is a copolymer containing mainly vinyl chloride, a vinyl group-containing phosphate ester and another vinyl monomer. It is characterized by being united.

The recording principle of the recording material of the present invention utilizes a change in transparency due to the temperature of the heat-sensitive layer, that is, a change from transparent to cloudy and opaque or vice versa. Note that the transparent portion looks transparent because the organic low-molecular substance particles dispersed in the resin base material of this portion are composed of large crystals, so that light incident from one side is not scattered, and the other It is considered that the light is transmitted to the side of. The opaque part looks white because it is composed of polycrystals in which fine crystals of organic low-molecular substance particles dispersed in the resin base material are gathered, and the crystal axes of the individual crystals are oriented in various directions. Therefore, it is considered that the light incident from one side is refracted and scattered many times at the interface of each crystal.

The above-described change in transparency due to temperature will be described with reference to the drawings. In cloudy opaque state in the heat-sensitive layer, for example T ₀ or less at room temperature in the first view. When this is heated to a temperature between T _{1 and} T ₂ , it becomes transparent, and in this state, it remains transparent even if it is returned to room temperature of T ₀ or lower. This is believed to low-molecular organic material before reaching the temperature T ₀ or less from between the temperature T ₁ through T ₂ is because the crystal to a single crystal from a polycrystalline via a semi-molten state grows. Upon further heating to T ₃ or more temperature becomes translucent state intermediate between the maximum transparency and the maximum opacity. Next, when the temperature is lowered, the state returns to the original cloudy and opaque state without taking the transparent state again. This after low-molecular organic material is melted at a temperature T ₃ or more, is considered to be because polycrystalline precipitates by being cooled. In this opaque state, T ₀
After heating to a temperature between through T _1, ambient temperature, that is, when cooled to T ₀ temperature below it can take an intermediate state between the opaque and transparent. The above things became clear at room temperature also again heated to T ₃ or higher, by returning to room temperature, return to the cloudy opaque state again. That is, both opaque and transparent forms at room temperature and intermediate states thereof can be taken.

Therefore, if the recording material is selectively heated by selectively applying heat to the surface of the heat-sensitive recording material having the above-described heat-sensitive layer, a cloudy image can be formed on a transparent ground, or a transparent image can be formed on a cloudy ground. This image formation can be repeated many times. If a colored sheet is arranged on the back of the thermosensitive recording material having such an image, an image of the color of the colored sheet on a white background or an image of a white background on the colored background of the colored sheet can be formed. Further, when this heat-sensitive recording material is projected by a projection device such as an overhead projector, the white turbid portions appear as dark portions, and the transparent portions appear as bright portions due to light transmission on the screen.

Here, if a metal light reflecting layer is provided below the heat-sensitive layer as described above, light that has once passed through the heat-sensitive layer is reflected by the reflection layer and enters the heat-sensitive layer again, so that the contrast, particularly the cloudy opaque state Although the turbidity is improved, if a heat-sensitive layer is provided directly on the metal surface as the light reflection layer, the heat-sensitive layer is easily peeled off because of poor adhesion between the metal and the heat-sensitive layer, and there is a problem in durability. Was. Therefore, the present inventors focused on a vinyl chloride copolymer having good adhesion to metal as a resin base material in the heat-sensitive layer, and as a result of various studies, found that vinyl chloride, a vinyl group-containing phosphoric ester and another vinyl-based copolymer were used. The present inventors have found that a copolymer with a monomer can greatly improve the adhesion to a metal, and have reached the present invention.

In order to prepare the reversible thermosensitive recording material of the present invention, a method of forming a thermosensitive layer on a support by the following method is generally employed.

That is, a solution in which a resin base material and an organic low-molecular substance are dissolved,
Alternatively, a heat-sensitive layer is formed by applying a dispersion of a low-molecular-weight organic substance in the form of fine particles in a solution of a resin base material (a solvent that does not dissolve the low-molecular-weight organic substance as a solvent) on a support and drying. . In the heat-sensitive layer thus formed, the organic low-molecular substance exists in a dispersed state as fine particles in the resin base material.

The thickness of the heat-sensitive layer is 1 to 30 μm, preferably 3 to 20 μm.
About m is appropriate.

If necessary, a protective layer can be further provided on the heat-sensitive layer. The thickness of the protective layer is preferably 10 μm or less.

Next, materials and the like used for the above-described thermosensitive recording material will be described.

First, a support whose surface is at least partially made of metal is used. Specifically, a thin metal film formed on a plastic film, paper, or the like by a vacuum evaporation method, an ion plating method, a sputtering method, or the like; similarly, a thin metal film adhered to a plastic film, paper, or the like; a metal film or sheet, etc. Is mentioned. Any metal may be used as long as it reflects light, for example,
Al, Ge, Au, Ag, Cu and their alloys are mentioned. In order to form an image that can be easily viewed from any angle by suppressing the specular reflection of extra light on the metal surface, an appropriate method (for example, Japanese Patent Application No.
-252767, 63-306855). A magnetic recording layer may be provided between a plastic film, paper, or the like and a metal thin film. When such a support is used, image formation and magnetic recording can be performed on the same surface. For example, a limited area for small size can be effectively used. However, in this case, reading of magnetic recording by the magnetic head must be performed from above the heat-sensitive layer, and the thickness of the heat-sensitive layer is suppressed to 8 μm or less, preferably 5 μm or less.

 Next, the materials used for the heat-sensitive layer are as follows.

First, a vinyl group-containing phosphate ester constituting a copolymer of vinyl chloride, a vinyl group-containing phosphate ester, and another vinyl monomer used as a main component of the resin base material is represented by the following general formula.

General formula I; (However, R ₁ is -H or -CH ₃ , R ₂ is -H, -CH ₃ or -CH ₂ C
l and R ₃ are —H, an alkyl group having 8 or less carbon atoms, or a phenyl group, and n is an integer of 1 to 10. ) General formula II; (However, R ₁ , R _2, and n are the same as those in the general formula I.) Specific examples of the compounds of the general formulas I and II are as follows.

As other vinyl monomers constituting the copolymer, vinyl carboxylate such as vinyl acetate, vinylidene chloride,
Acrylonitrile, acrylic acid ester, methacrylic acid ester, vinyl ether, maleic acid, maleic acid ester, styrene, propylene, ethylene and the like can be mentioned. These may be used alone or in combination of two or more.

Next, a general method for producing the copolymer used in the present invention will be described.

The production of this copolymer can be carried out by a usual solution polymerization method, suspension polymerization method, bulk polymerization method, or emulsion polymerization method, but practical methods are a solution polymerization method and a suspension polymerization method. Here, a production method by a solution polymerization method will be described. In this method, vinyl chloride, a phosphoric ester having a vinyl group and another vinyl monomer may be heated and reacted in a solvent in the presence of a polymerization initiator. Here, rather than adding the vinyl group-containing phosphate at once from the beginning, a copolymer having a uniform composition can be obtained by continuously adding the vinyl chloride and the other vinyl-based monomer as the copolymerization reaction proceeds, It is preferable in terms of the dispersibility of the organic low-molecular substance and the physical properties of the coating film when forming the heat-sensitive layer. If necessary, the obtained copolymer can be subjected to a saponification reaction in the presence of alcohol using hydrochloric acid as a catalyst. In any case, the amounts of vinyl chloride, vinyl group-containing phosphoric acid ester and other vinyl monomers used are 50 to 95% (weight, the same applies hereinafter), 0.1 to 10%, 0.1 to 10%, respectively.
45% is appropriate.

In the present invention, the copolymer obtained as described above can be used as a resin base material by mixing with other resins such as polyvinyl chloride, a vinyl chloride-vinyl acetate copolymer, and polyester.

On the other hand, the organic low-molecular substance may be appropriately selected in accordance with the selection of the temperatures T _{0 to} T ₃ in FIG.
° C, particularly preferably about 50 to 150 ° C. Such organic low molecular weight substances include alkanol; alkane diol; halogen alkanol or halogen alkane diol; alkylamine; alkane; alkene; alkyne; halogen alkane; halogen alkene, halogen alkyne; cycloalkane; cycloalkene; cycloalkyne; Unsaturated or monocarboxylic acids or their esters, amides or ammonium salts; saturated or unsaturated halogen fatty acids or their esters, amides or ammonium salts; allylcarboxylic acids or their esters, amides or ammonium salts; Acids or their esters, amides or ammonium salts; thioalcohols;
Thiocarboxylic acids or their esters, amines, or ammonium salts; carboxylic acid esters of thioalcohols, and the like. These may be used alone or in combination of two or more. The carbon number of these compounds is 10 to 60, preferably 10 to 38, particularly preferably 10 to 30. The alcohol group in the ester may be saturated or unsaturated, and may be halogen-substituted. In any case, the organic low molecular weight substance contains at least one of oxygen, nitrogen, sulfur and halogen in the molecule, for example, -OH, -COOH, -CONH, -C
_{OOR, -NH -, - NH 2} , -S -, - S-S -, - O-, is preferably a compound containing a halogen and the like.

More specifically, these compounds include lauric acid, dodecanoic acid, myristic acid, pentadecanoic acid, palmitic acid,
Stearic acid, behenic acid, nonadecanoic acid, arachiic acid,
Higher fatty acids such as oleic acid; esters of higher fatty acids such as methyl stearate, tetradecyl stearate, octadecyl stearate, octadecyl laurate, tetradecyl palmitate, docosyl behenate; And ether or thioether.

The ratio between the organic low-molecular substance and the resin base material in the heat-sensitive layer is preferably about 1: 0.5 to 1:16, particularly preferably 1: 1 to 1: 3 by weight.
When the ratio of the resin base material is less than this, it becomes difficult to form a film holding the organic low-molecular substance in the resin base material,
On the other hand, if it is more than this, the amount of the organic low-molecular substance is small, so that it is difficult to make the material opaque.

In the present invention, a substance that controls the crystal growth of an organic low-molecular substance can be used in combination. Such a substance can be eutectic with an organic low-molecular substance and expand the temperature range in which the organic low-molecular substance is in a semi-molten state,
One that promotes the movement of the crystal may be used. For example, those commonly used as surfactants, higher fatty acid esters of polyhydric alcohols; higher alkyl ethers of polyhydric alcohols; higher fatty acid esters of polyhydric alcohols, higher alcohols, higher alkyl phenols, higher fatty acid higher alkyl amines, higher fatty acids A lower olefin oxide adduct of amide, fat or polypropylene glycol;
Acetylene glycol; Na, Ca, Ba or Mg salt of higher alkylbenzene sulfonic acid; Ca, Ba or Mg salt of aromatic carboxylic acid, higher aliphatic sulfonic acid, aromatic monosulfonic acid monoester or diester phosphate; Low-sulfated oil; poly long-chain alkyl acrylate; acrylic oligomer; poly long-chain alkyl methacrylate; long-chain alkyl methacrylate-amine-containing monomer copolymer;
Styrene-maleic anhydride copolymer; olefin-maleic anhydride copolymer; olefin-maleic anhydride copolymer. Tributyl phosphate, tri-2-ethylhexyl phosphate, triphenyl phosphate, tricresyl phosphate used as a plasticizer for the film,
Butyl oleate, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diheptyl phthalate, di-n-octyl phthalate, di-2-ethylhexyl phthalate,
Diisononyl phthalate, dioctyldecyl phthalate, diisodecyl phthalate, butylbenzyl phthalate, dibutyl adipate, di-n-hexyl adipate, di-2-ethylhexyl adipate, di-2-ethylhexyl azelate, dibutyl sebacate, Di-2-sebacic acid
Examples include ethylhexyl, diethylene glycol dibenzoate, triethylene glycol di-2-ethyl butyrate, methyl acetyl ricinoleate, butyl acetyl ricinoleate, butyl phthalyl butyl glycolate, and tributyl acetyl citrate.

In addition, one of the above-mentioned organic low-molecular substances can be used as an organic low-molecular substance, and another type of organic low-molecular substances can be used as a substance for controlling crystal growth. For example, stearic acid is used as a low-molecular organic substance, and stearyl alcohol is used as a substance for controlling crystal growth.

The weight ratio of the organic low-molecular substance and the substance controlling the crystal growth of the organic low-molecular substance is preferably about 1: 0.01 to 1: 0.8.
If the substance controlling the crystal growth of the organic low-molecular substance is less than this, the temperature range or energy range in which it becomes transparent cannot be widened, and if it exceeds this, the opacity decreases.

As the solvent for forming the heat-sensitive layer, various solvents can be used depending on the type of the organic low-molecular substance and the resin base material. Examples include organic solvents such as tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, chloroform, carbon tetrachloride, ethanol, toluene and benzene. As a material of the protective layer, a transparent material is preferable,
For example, silicone rubber, silicone resin (for example,
63-221087), polysiloxane graft polymers (for example, those described in JP-A-62-317385), and ultraviolet or electron beam curable resins.

Hereinafter, the present invention will be described with reference to examples. "Department"
And “%” are based on weight.

Example 1 Behenic acid 8 parts Stearyl stearate 2 parts Di (2-ethylhexyl) phthalate 2 parts Vinyl chloride-vinyl acetate-vinyl group-containing phosphoric acid ester on the Al-deposited surface of a support made of an Al-deposited polyester film having a thickness of 50 μm Copolymer (ratio 85: 14: 1, phosphoric acid ester is acid phosphooxyethyl methacrylate) 20 parts Tetrahydrofuran 150 parts Toluene 15 parts A solution composed of a wire bar is applied, dried by heating and dried.
A heat-sensitive layer having a thickness of μm was provided, and then reheated to 65 ° C. to prepare a reversible heat-sensitive recording material in which the heat-sensitive layer became transparent.

Example 2 As a support, a 10 μm-thick Al foil and a 25 μm-thick polyester film were bonded together, and a vinyl chloride-vinyl acetate-vinyl group-containing phosphoric acid ester copolymer was converted from vinyl chloride-vinyl acetate-vinyl alcohol- Heat-sensitive in the same manner as in Example 1 except that the vinyl group-containing phosphate ester copolymer (ratio 91: 2: 6: 1, the phosphate ester was acid phosphooxypropyl methacrylate) and the thickness of the heat-sensitive layer was 10 μm. A reversible thermosensitive recording material having a transparent layer was prepared.

Example 3 Ge was vacuum-deposited on a glass plate to form a support, and 8 parts of behenic acid 1,2 parts of 10-decanedicarboxylic acid 2 parts of di (2-ethylhexyl) phthalate 2 parts of vinyl chloride to vinylidene chloride -Vinyl group-containing phosphate copolymer (ratio 82: 15: 3, phosphate ester is 3-chloro-2-acid phosphooxypropyl methacrylate)
Apply a solution consisting of 20 parts of tetrahydrofuran 150 parts of toluene 15 parts with a wire bar, and heat and dry.
A heat-sensitive layer having a thickness of μm was provided, and then reheated to 75 ° C. to prepare a reversible heat-sensitive recording material in which the heat-sensitive layer became transparent.

Comparative Example 1 A vinyl chloride-vinyl acetate-vinyl group-containing phosphate copolymer was converted to a vinyl chloride-vinyl acetate copolymer (ratio 86: 1).
A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that the method was changed to 4).

Comparative Example 2 Same as Example 2 except that the vinyl chloride-vinyl acetate-vinyl alcohol-vinyl group-containing phosphate copolymer was changed to a vinyl chloride-vinyl acetate-vinyl alcohol copolymer (ratio 91: 2: 7). A reversible thermosensitive recording material was prepared by the method.

Comparative Example 3 A reversible thermosensitive recording material was prepared in the same manner as in Example 3 except that the vinyl chloride-vinylidene chloride-vinyl group-containing phosphate copolymer was changed to a vinyl chloride-vinylidene chloride copolymer (ratio 80:20). Created.

Comparative Example 4 A reversible thermosensitive recording material was produced in the same manner as in Example 1 except that the Al-deposited polyester film support was changed to a black film support having a thickness of 100 μm into which carbon was kneaded.

The surface of the reversible thermosensitive recording material prepared as described above was partially heated to 100 ° C. to make it turbid. The transparent portion and the cloudy portion of the heat-sensitive layer were measured with a Macbeth reflection densitometer RD514. In addition, a cut line (25 squares) was inserted into the heat-sensitive layer using an Eriksen model 295 type multi-cross cutter,
After sticking the mending tape, it was peeled off and the adhesiveness was evaluated.

 The results are shown in the table.

[Effects of the Invention] As described above, the reversible thermosensitive recording material of the present invention uses vinyl chloride, a vinyl group-containing phosphate ester, and other vinyl monomer copolymers as a resin base material. And thus durability can be improved while maintaining high contrast.

[Brief description of the drawings]

FIG. 1 is an explanatory view of the principle of recording and erasing of the reversible thermosensitive recording material of the present invention.

Claims (1)

(57) [Claims] 1. A resin base material and an organic low-molecular substance dispersed in the resin base material as a main component on a support having at least a part of the surface made of metal, and the transparency depends on the temperature. In a reversible thermosensitive recording material provided with a reversibly changing thermosensitive layer, the main component of the resin base material is a copolymer mainly composed of vinyl chloride, a vinyl group-containing phosphate ester, and another vinyl monomer. A reversible thermosensitive recording material characterized by the following.