JPH07102744B2 - Reversible thermosensitive recording material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a reversible thermosensitive recording material for performing image formation and erasing by utilizing reversible transparency change of a thermosensitive layer with temperature.

RELATED ART JP-A-54-119377 and JP-A-55-154198 disclose a reversible thermosensitive recording material having a thermosensitive layer in which an organic low molecular substance such as a higher fatty acid is dispersed in a resin matrix such as a vinyl chloride resin. Is proposed. Image formation and erasing by this type of recording material utilize reversible transparency change of the heat-sensitive layer due to temperature. However, when these recording materials are actually made transparent or opaque by heating, they become opaque (white part). ), And therefore the contrast is low, and the temperature range in which the opaque part becomes transparent is as narrow as 2 to 4 ° C., the entire recording material that is at least partly opaque or the entire opaque white background is transparent. It is difficult to control the temperature when forming a transparent (colorless) image on the recording material.

Aim of the Invention It is an object of the present invention to provide a reversible thermosensitive recording material capable of forming a high-contrast image and having easy temperature control.

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 main components,
A reversible thermosensitive recording material having a thermosensitive layer whose transparency reversibly changes depending on temperature is characterized by further containing a higher fatty acid metal salt in the thermosensitive layer.

The recording, that is, image forming and erasing principle of the recording material of the present invention is as follows. In FIG. 1, the resin base material and the heat-sensitive layer whose main component is an organic low molecular weight substance dispersed in this resin base material are white and opaque due to crystallization of the organic low molecular weight substance at room temperature below T _0, for example. . When this is heated to a temperature between T _{1 and} T ₂ , it becomes transparent, and even if it is returned to room temperature below T ₀ in this state, it remains transparent. Further heating to a temperature of T ₃ or higher results in a semi-transparent state intermediate between maximum transparency and maximum opacity. Next, when this temperature is lowered, it moves from the temperature T ₃ to T ₁ on the bottom of the trapezoidal hysteresis curve in FIG. 1 without taking the transparent state again, and when it returns to room temperature below T ₀ , the first Return to opaque state. When this opaque state is heated to a temperature between T _{0 and} T ₁ and then cooled to room temperature, that is, a temperature of T ₀ or lower, a state between transparent and opaque can be obtained. In addition, the above-mentioned transparent material that has become transparent at normal temperature is heated again to a temperature of T ₃ or higher, and when it is returned to normal temperature, it becomes cloudy and opaque again. That is, both opaque and transparent forms at room temperature and intermediate states thereof can be obtained.

Therefore, after heating the entire heat-sensitive layer to a temperature between T _{1 and} T ₂ with a heat roller or the like, it is cooled to room temperature below T ₀ to make it transparent, and then this is heated in an image with a thermal head etc. When opaque, a white image is formed on this layer. On the other hand, after heating the entire partially opaque heat-sensitive layer to a temperature of T ₃ or higher, the temperature is returned to room temperature of T ₀ or lower to make the whole cloudy and opaque,
If a thermal head is imagewise heated to a temperature between T _{1 and} T ₂ to make the portion transparent, a transparent image is formed against a white background. The recording and erasing operations on the heat sensitive layer as described above can be repeated 10 ⁴ times or more.

When a higher fatty acid metal salt is added to the heat-sensitive layer, the organic low-molecular-weight substance dispersed in the resin base material causes a eutectic phenomenon during heating, and the transparentization temperature range T _{1 to} T _{2 of the} heat-sensitive layer may be expanded. Was found.

Furthermore, when the heat-sensitive layer is heated to a temperature of T ₃ or higher and cooled to a normal temperature of T ₀ or lower to make it opaque, the presence of higher fatty acid metal salts suppresses the growth of crystals of organic low molecular weight substances and reduces It has been found that as a result of the aggregated state of crystals, the light scattering at that portion increases, which increases the whiteness and improves the contrast.

The heat-sensitive recording material of the present invention is generally prepared by coating or impregnating and drying a heat-sensitive layer-forming liquid containing a resin base material, an organic low molecular weight substance and a higher fatty acid metal salt on a support such as paper, plastic film, glass plate, metal plate or the like. Alternatively, it can be prepared by kneading the above three components in the presence or absence of a solvent while heating, if necessary, and molding this into a film or sheet. The heat-sensitive layer forming liquid used here is usually a solution in which both components of the resin base material and the organic low molecular weight substance are dissolved, or a base material solution (in this case, a solvent that does not dissolve the organic low molecular weight substance is used. (2) A low-molecular weight organic substance is dispersed in a fine particle form and a higher fatty acid metal salt solution to obtain a mixture. Examples of the solvent include tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, chloroform, carbon tetrachloride, ethanol, toluene, benzene and the like. The organic low-molecular weight substance is precipitated in the form of 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 substance is uniformly dispersed and held, and has an effect on the transparency at maximum transparency. For this reason, the base material is preferably a resin having good transparency, mechanical stability, and good film forming properties. Such resins include polyvinyl chloride; vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinyl acetate-vinyl alcohol copolymers, vinyl chloride-vinyl acetate-maleic acid copolymers, vinyl chloride-acrylate copolymers. Vinyl chloride-based copolymers such as; polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymers, vinylidene chloride-copolymers such as vinylidene chloride-acrylonitrile copolymers; polyesters; polyamides; polyacrylates or polymethacrylates or acrylates Methacrylate copolymers, silicone resins, etc. may be mentioned. These may be used alone or in admixture of two or more.

On the other hand, the organic low molecular weight substance may be appropriately selected according to the temperature T _{0 to} T ₃ shown in FIG. 1, but has a melting point of 30 to 200 ° C.
Particularly, a temperature of about 50 to 150 ° C. is preferable. Such organic low molecular weight substances include alkanols; alkanediols;
Halogen alkanols or halogen alkane diols; Alkyl amines; Alkanes; Alkenes; Alkyl;
Halogen alkanes; halogen alkenes, halogen alkynes; cycloalkanes; cycloalkenes; cycloalkynes; saturated or unsaturated mono- or dicarboxylic 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; halogen allylcarboxylic acids or their esters, amides, or ammonium salts; thioalcohols; thiocarboxylic acids or their esters, amines, or ammonium salts; Examples thereof include carboxylic acid esters of thioalcohol. These may be used alone or in admixture of two or more. The carbon number of these compounds is 10 to 60, preferably 10
~ 38, especially 10-30 are preferred. The alcohol group moiety in the ester may be saturated or unsaturated, and may be halogen-substituted. In any case, the organic low molecular weight substance is at least one kind of oxygen, nitrogen, sulfur and halogen in the molecule, for example, -OH, -COOH, -CONH, -COOR, -NH.
_{-, - NH 2, -S -} , - S-S -, - O-, it is preferably a compound containing a halogen and the like.

More specifically, these compounds include higher fatty acids such as lauric acid, dodecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, stearic acid, behenic acid, nonadecanoic acid, arachidic acid and oleic acid; methyl stearate, tetradecyl stearate. , Esters of higher fatty acids such as octadecyl stearate, octadecyl laurate, tetradecyl palmitate and docosyl behenate; C ₁₆ H ₃₃ -O-C ₁₆ H ₃₃ , C ₁₆ H ₃₃ -S-C ₁₆ H ₃₃ , C ₁₆ H _37- S-C ₁₈ H ₃₇ , C ₁₂ H ₂₅ -S-C ₁₂ H ₂₅ , C ₁₉ H ₃₉ -S-C ₁₉ H ₃₉ , C ₁₂ H ₂₅ -S-S-C ₁₂ H ₂₅ , Etc., such as ether or thioether. Of these, higher fatty acids, particularly higher fatty acids having 16 or more carbon atoms, such as palmitic acid, stearic acid, behenic acid, and lignoceric acid, are preferred in the present invention, and higher fatty acids having 16 to 24 carbon atoms are more preferred.

On the other hand, the higher fatty acid metal salt is a material that contributes to the widening of the transparency temperature range and the improvement of whiteness as described above, and is usually present in a compatible state with the organic low molecular weight substance in the heat sensitive layer. Examples of the higher fatty acid metal salt include stearic acid metal salt and palmitic acid metal salt. More specifically, those shown in the following table can be mentioned.

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, more preferably 2: 1 to 1: 3. When the ratio of the base material is less than this, it becomes difficult to form a film in which the organic low-molecular weight material is retained in the base material, while when it exceeds the ratio, the amount of the organic low-molecular weight material is small, and the opacity is reduced. It will be difficult.

On the other hand, the amount of the higher fatty acid metal salt used is preferably 0.05 to 0.5 parts by weight per 1 part by weight of the organic low molecular weight substance. When the amount of the metal salt used is less than this, the effect of eutecticization and whitening is small, and when it is more than this, the solubility in the solvent decreases and it becomes difficult to be compatible with the organic low molecular weight substance.

Hereinafter, the present invention will be described in more detail with reference to Examples. All parts are parts by weight.

Example 1 A solution of behenic acid 10 parts Vinyl chloride-vinyl acetate copolymer (VYHH manufactured by UCC Co., Ltd.) 40 parts A solution of tetrahydrofuran 200 parts and a solution B of calcium stearate 1.5 parts Toluene 25 parts were mixed. , This is coated on a 75μm thick polyester film with a wire bar and dried at 100 ° C for 1
A reversible thermosensitive recording material of the present invention was prepared by forming a thermosensitive layer having a thickness of 3 μm. This is white and opaque.

Example 2 A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that a solution containing 1 part of barium stearate and 20 parts of toluene was used as the solution B.

Examples 3 to 4 and Comparative Example Same as Example 1 except that 1.5 parts of calcium stearate in the liquid B was changed to 3 parts (Example 3), 5 parts (Example 4) and 8 parts (Comparative Example), respectively. The method produced a white opaque reversible thermosensitive recording material.

Next, each recording material was heated from 50 ° C to 2 ° C in increments of 80 ° C, allowed to cool to room temperature, placed on black drawing paper, and the reflection density was measured with a Macbeth densitometer RD514. At this time, the temperature when the reflection density exceeded 1.0 was defined as the clearing temperature, and the range (width) was shown. The minimum value of this density is the density of the opaque part (white part), and the maximum value is the density of the transparent part. The results are shown in the table below.

As described above, since the reversible thermosensitive recording material of the present invention contains the higher fatty acid metal in the thermosensitive layer, the light scattering in the white part is increased, the contrast can be improved, and the transparentization temperature range is widened. There is an advantage that temperature control becomes easy when the entire recording material is made transparent or when a transparent image is formed on a white background.

[Brief description of drawings]

FIG. 1 is an explanatory view of the principle of image formation and erasing in the heat-sensitive layer of the recording material of the present invention.

Claims (1)

[Claims] 1. A reversible thermosensitive recording material comprising a resin base material and an organic low molecular weight substance dispersed in the resin base material as a main component and having a thermosensitive layer whose transparency reversibly changes depending on temperature. 2. A reversible thermosensitive recording material characterized in that the thermosensitive layer further contains a higher fatty acid metal salt.