JPH0798425B2 - 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, the organic material to the resin base material When the amount of low molecular weight substance is small, the concentration of the opaque portion (white portion) is low, and when the amount of organic low molecular weight substance relative to the resin base material is high, the concentration of the opaque portion (white portion) is high but the transparency is low, Therefore, sufficient contrast cannot be obtained. Further, since the temperature range in which the opaque portion becomes transparent is as narrow as about 2 to 4 ° C., the entire recording material which is at least partially opaque is made transparent, or a colorless (transparent) image is formed on the recording material which is totally opaque. At this time, it is difficult to control the temperature.

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

Structure 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, and has a heat-sensitive layer in which the transparency reversibly changes depending on temperature. The thermal recording material is characterized in that the heat sensitive layer further contains a high boiling point solvent having a boiling point of 200 ° C. or higher.

The recording (and erasing) principle of the recording material of the present invention utilizes the change in transparency depending on the temperature of the heat sensitive layer (or sheet), which will be described with reference to the drawings. In FIG. 1, the heat-sensitive layer containing a resin base material and an organic low-molecular substance dispersed in the resin base material as a main component is in a cloudy opaque state at a room temperature of T ₀ or lower, for example. When it 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, the first cloudy opaque state is restored without taking the transparent state again. Note that this opaque state is T ₀
After heating to a temperature between through T _1, it may take the state between the normal temperature, i.e. when cooled to T ₀ temperature below the transparent and opaque. In addition, the one that became transparent at room temperature again had T ₃
When heated to the above temperature and returned to room temperature, it returns to a cloudy and opaque state 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 roll or the like, it is cooled to a normal temperature of T ₀ or lower to be transparent, and then this is imagewise heated with a thermal head or the like to T ₃ or higher. If the portion is made opaque, a white image is formed on this layer. If a coloring sheet is arranged under the heat-sensitive layer having such a white image, this image can be recognized as a white image with the color of the coloring sheet as the background. 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, and then a thermal head or the like is used to image-form T ₁ to T. If you heat it to a temperature between ₂ and make that part transparent, a transparent image is formed against a white background. If a coloring sheet is arranged under the heat-sensitive layer having such a transparent image, this image can be recognized as an image of the color of the coloring sheet against the white background.

The recording and erasing operations on the heat sensitive layer as described above can be repeated 10 ⁴ times or more.

In order to prepare the heat-sensitive recording material of the present invention, generally, (1) a solution in which three components of a resin base material, an organic low molecular weight substance and a high boiling point solvent are dissolved, or a solution of a resin base material (the organic low molecular weight substance is dissolved as a solvent A low molecular weight substance is dispersed in the form of fine particles, and a high boiling point solvent is further dissolved in the dispersion liquid to apply it to a support such as paper, plastic film, glass plate and metal plate. Or (impregnation)) to form a heat-sensitive layer by drying, or (2) kneading the above-mentioned three components in the presence or absence of a solvent, while heating if necessary, and molding this into a sheet, and then itself. It is made by making a heat sensitive sheet. As the solvent, tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, chloroform,
Examples include carbon tetrachloride, ethanol, toluene, benzene and the like. The organic low molecular weight substance is precipitated as fine particles and exists in a dispersed state in the heat-sensitive sheet obtained not only when the dispersion liquid is used but also when the solution or the kneaded material 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. Examples of such resin include polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-acrylate copolymer. Vinyl chloride-based copolymers such as; polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymers, vinylidene chloride-based 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. Alkanols; alkanediols;
Halogen alkanols or halogen alkane diols; Alkyl amines; Alkanes; Alkenes; Alkynes;
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; thioalcohols And the like. These may be used alone or in admixture of two or more. The carbon number of these compounds is preferably 10 to 30. 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-,
A compound containing —O—, halogen or the like is preferable.

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 ₁₈ 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.

Next, the high boiling point solvent having a boiling point of 200 ° C. or higher as described above is a material mainly contributing to the expansion of the transparentization temperature range, and is usually present in the thermosensitive layer or the thermosensitive sheet in a compatible state with the organic low molecular weight substance or the resin base material. To do. Specific examples of these high-boiling solvents include tributyl phosphate, tri-2-ethylhexyl phosphate, triphenyl phosphate, tricresyl phosphate and other phosphate esters, butyl oleate, dibutyl adipate, and di-n-hexyl adipate. , Di-2-ethylhexyl adipate, alkyl 610 adipate, di-2 azelaate
An aliphatic monobasic acid or dibasic acid ester such as ethylhexyl, dibutyl sebacate, di-2-ethylhexyl sebacate, dimethyl phthalate, diethyl phthalate,
Dibutyl phthalate, diheptyl phthalate, di-phthalate
Phthalates such as n-octyl, di-2-ethylhexyl phthalate, diisononyl phthalate, dioctyldecyl phthalate, diisodecyl phthalate, butylbenzyl phthalate, diethylene glycol dibenzoate, triethylene glycol di-2-ethyl butyrate, etc. And dioxy alcohol esters such as methyl acetylricinoleate, butyl acetylricinoleate, butylphthalylbutyl glycolate and tributyl acetylcitrate.

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: 5. 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 substance is retained in the base material. When the ratio is higher than this, it is difficult to make the opacity because the amount of the organic low molecular weight substance is small. become. On the other hand, the amount of the high boiling point solvent having a boiling point of 200 ° C or higher is 0.01 to 1 with respect to 1 part by weight of the resin base material.
Suitable is parts by weight, preferably 0.05 to 0.5 parts by weight. If the amount used is less than 0.01 part, it is difficult to expand the transparency temperature range, and if it exceeds 1 part, the mechanical strength of the film is lost.

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

Examples 1 to 14 Behenic acid on a 75 μm thick polyester film 10 parts High boiling point solvent shown in the following table 6 parts Vinyl chloride-vinyl acetate copolymer (UCY VYHH) 28 parts Tetrahydrofuran 200 parts And then dry to 15 μm
A white opaque reversible thermosensitive recording material was prepared by providing a thick thermosensitive layer.

Next, each recording material was heated from 50 ° C. to 1 ° 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 was defined as the density of the opaque part (white part), while the maximum value was defined as the density of the transparent part.
The results are shown in the table below.

Effect Since the reversible thermosensitive recording material of the present invention contains the high boiling point solvent as described above, the transparency temperature range is expanded, and as a result, temperature control is performed when the recording material as a whole is transparent or when a transparent image is formed on a white background. There is an advantage that it becomes easier and therefore a uniform transparent image can be obtained as compared with the conventional product.

[Brief description of drawings]

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

Claims (1)

[Claims] 1. A reversible thermosensitive recording material comprising, as a main component, a resin matrix and an organic low molecular weight substance dispersed in the resin matrix and having a thermosensitive layer whose transparency reversibly changes depending on temperature. , A high boiling point solvent having a boiling point of 200 ° C or higher in the heat sensitive layer,
However, polyhydric alcohol higher fatty acid ester, polyhydric alcohol higher alkyl ether, higher alcohol, higher alkylphenol, higher fatty acid higher alkylamine, higher fatty acid amide, lower olefin oxide adduct of oil or polypropylene glycol, acetylene glycol, higher alkylbenzene sulfonic acid Na, Ca, Ba or
Mg salt, higher fatty acid, aromatic carboxylic acid, higher aliphatic sulfonic acid, aromatic sulfonic acid, sulfuric acid monoester or phosphoric acid mono- or di-ester Ca, Ba or Mg salt, except low-sulfated oil, A reversible heat-sensitive recording material comprising: