JPH05104857A - Reversible thermal recording material - Google Patents

Abstract

PURPOSE:To provide a reversible thermal recording material generating no discoloration even when printing and erasure are repeated many times. CONSTITUTION:In a reversible thermal recording material wherein a thermal layer based on a resin matrix and the org. low-molecular substance dispersed in the resin matrix and reversibly changing in transparency in dependence on temp. is provided on a support, at least one kind of an organotin compound, an epoxy compound and an inorg. metal salt (especially, the organotin compound) is added to the thermal layer in an amount of 0.02-10 pts.wt. per 100 pts.wt. of the resin matrix.

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 for recording and erasing by utilizing reversible change in transparency with temperature.

[0002]

2. Description of the Related Art In recent years, reversible thermosensitive recording materials have been attracting attention because they enable temporary image formation and can erase the image when it is no longer needed. A typical example thereof is a glass transition temperature (Tg) of 50 to 60 ° C to less than 80 ° C on a support such as a polyester film capable of forming and erasing an image by utilizing a change in transparency with temperature. A reversible thermosensitive recording material having a thermosensitive layer in which an organic low molecular weight substance such as a higher fatty acid is dispersed in a resin matrix such as a vinyl chloride-vinyl acetate copolymer having a low glass transition temperature is known. JP-A-54-119377 and JP-A-55-154198).

When a reversible thermosensitive recording material was provided on a transparent PET film and printing and erasing were repeated with a hot stamp, the transparent and opaque states were repeated with good reproducibility in the first 100 times or so. It was discovered that the printed parts gradually turned red as they were stacked.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a reversible thermosensitive recording material which solves the above-mentioned drawbacks and does not cause discoloration even when printing and erasing are repeated.

[0005]

According to the present invention, a resin base material and an organic low molecular weight substance dispersed in the resin base material are used as main components on a support, and the transparency is reversible depending on temperature. A reversible heat-sensitive recording material provided with a heat-sensitive layer that changes dynamically, wherein the heat-sensitive layer contains at least one of an organic tin compound, an epoxy compound and an inorganic metal salt. The present invention also provides the reversible thermosensitive recording material characterized by containing an organic tin compound in the thermosensitive layer. Further, at least one of the organotin compound, the epoxy compound and the inorganic metal salt is provided. The reversible thermosensitive recording material is characterized in that 0.02 to 10 parts by weight of the seed is contained in 100 parts by weight of the resin base material.

As a result of repeated studies in view of the above problems, the present inventors discovered that discoloration occurred because a polymer containing vinyl chloride as a skeleton was used as a resin base material. .. However, since it is necessary to obtain a good reversible change, polyvinyl chloride is an excellent resin base material as a resin base material, and it is difficult to omit it at present. Therefore, the inventors have searched for a material that can prevent discoloration by adding a very small amount to the resin base material, and arrived at the present invention.

The present invention will be described in more detail below. The feature of the present invention resides in that a reversible thermosensitive recording material is added with a thermal discoloration preventing material which is conventionally considered not necessary for a resin coated product, particularly a thermosensitive recording paper.

It is known to add the above-mentioned additives to a molded product of vinyl chloride resin. When molding the resin, it is heated to about 170 to 180 ° C. It is known that the resin will turn red during molding if such a high temperature state including residual heat for several minutes to several tens of minutes until the molding is finished and it is cooled. Such additives are added.

On the other hand, the above additives are not added to the coated product of vinyl chloride resin. This is because the temperature applied by coating and drying is 100 ° C or less, which is much lower than molding.
This is to prevent discoloration. The warm air blown for drying may raise the temperature to 100 ° C. or more, but the resin being dried remains at a temperature lower than the surrounding hot air until the solvent evaporates. Therefore, conventionally, the above additives have been regarded as materials necessary only for preventing discoloration during the production of vinyl chloride resin molded products.

The problem of the present invention is not the discoloration at the time of manufacture but the discoloration due to the writing or erasing work at the time of use.
The writing temperature of the reversible thermosensitive recording material is about 100 ° C., although it varies depending on the formulation. It was considered that discoloration does not occur at such a temperature according to conventional thinking.
In fact, discoloration was not recognized in the conventional repeated printing of several tens or 100 times. However, for the purpose of improving the repeatable number of times of printing, a study was conducted to increase the number of times of printing with a conventional reversible thermosensitive recording material as a preceding step. As a result, discoloration of the printed part was confirmed after about 500 times of repetition. It was The reason for such discoloration at low temperature is not clear at present, but it is presumed that the stress caused by repeated heating causes structural changes in the resin base material such as cutting of the polymer.

The degree of discoloration greatly changes depending on the composition of the resin base material. If a plasticizer such as phthalate ester is added to increase the clearing temperature, discoloration is severe. In addition, vinyl alcohol was added to vinyl chloride and vinyl acetate.
When the original copolymer resin is used as the resin base material, the discoloration becomes worse.

The additive used in the present invention is at least one of an organic tin compound, an epoxy compound and an inorganic metal salt. Of these, organotin compounds are particularly excellent in terms of safety and transparency. Di- as an organotin compound
di-n-octyltin-based compounds such as n-octyltin maleate and di-n-octyltin laurate, di-n-butyltin bismaleate and di-n-butyltin laurate Examples thereof include di-n-butyltin compounds and dimethyltin compounds such as dimethyltin bis (isooctylmercaptoacetate).

Examples of the epoxy compound include epoxidized soybean oil, epoxyallyl phthalate, epoxidized fatty acid and its metal salt, epoxidized polyester containing tetrahydrophthalic acid, polyethylene glycol mono (epoxy stearyl ether), and bisepoxyalkyl phthalate. , 1-benzyloxy-2,6-epoxypropane, 2,3-epoxycyclopentanol ester or ether, and the like. The epoxy compound can also be used as a plasticizer and serves to extend the clearing temperature range of the reversible thermosensitive recording material.

Inorganic metal salts include tribasic lead sulfate and 2
There are basic lead phosphite and basic lead sulfite.
In the present invention, at least one of these is added.

In the present invention, the additive may be added in an amount of 0.001 to 50 parts by weight based on 100 parts by weight of the resin base material. Preferably, it is 0.02-1 with respect to 100 parts by weight of the resin base material.
Addition of 0 parts by weight is preferred. However, when an epoxy compound-based additive is added as a plasticizer, the resin base material 100
It is preferable to add 1 to 50 parts by weight with respect to parts by weight.

The material for preventing discoloration of vinyl chloride resin is
In addition to the materials listed in claim 1, there is a typical metal soap such as zinc stearate or barium stearate. It is known to mix these metal soaps into the recording layer for the purpose of improving the contrast (Japanese Patent Laid-Open Publication No. Sho 6-62).
3-41186). However, metal soap is
For example, when an organic low molecular weight substance is added to a reversible thermosensitive recording material of a type in which it is dispersed in a resin base material, segregation tends to occur on the organic low molecular weight substance side rather than the resin base material, and discoloration cannot be prevented unless a large amount is added. Originally, metal soap has poor solubility in organic solvents and cannot be added in a large amount, but even if it is forcibly added in a large amount, the amount in the organic low-molecular-weight substance is too large, and the metal soap is deposited,
On the contrary, the contrast decreases and the basic properties of the reversible thermosensitive recording material are impaired. For the above reasons, metal soap is not suitable for addition for the purpose of preventing discoloration.

The reversible thermosensitive recording material in the present invention means
It is a material that reversibly causes visible changes due to temperature changes. Although the visible change can be divided into a change in color tone and a change in shape, the present invention mainly uses a material that causes a change in color tone. Changes in color tone include changes in transmittance, reflectance, absorption wavelength, scattering degree, etc., and in actual reversible thermosensitive recording materials, display is performed by a combination of these changes. More specifically, (a) a material in which the transparent state and the cloudy state reversibly change. (B) A material whose color such as dye changes reversibly. Currently, it can be classified into two types of systems. As (a), as described in the prior art, a typical example is a resin base material such as polyester provided with a heat-sensitive layer in which an organic low-molecular substance such as higher alcohol or higher fatty acid is dispersed. As (b), the reversibility of conventional leuco thermal recording materials is enhanced (eg, Yoshihiro Hino, Jiro Watanabe Ja.
pan Hardcopy '90 papers, P147).

The reversible thermosensitive recording material of the present invention utilizes the change in transparency (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, in the case of (I) transparent, the particles of the organic low molecular weight substance dispersed in the resin base material are composed of large particles of the organic low molecular weight substance, and the light incident from one side is not scattered and is opposite. When it is cloudy, the particles of the organic low molecular weight substance are composed of polycrystals of fine crystals of the organic low molecular weight 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 crystals of the organic low molecular weight substance particles, and the light appears white because it is scattered.

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 ₀
It is cloudy and opaque at room temperature below. When it is heated to a temperature T ₂ , it becomes transparent, and even if it is returned to room temperature below T _{0 in} this state, it remains transparent. It is considered that this is because the organic low-molecular-weight substance undergoes a semi-molten state from the temperature T ₂ to T ₀ or lower and the crystal grows from a polycrystal to a single crystal. Further T ₃
When heated to the above temperature, a semi-transparent state intermediate between maximum transparency and maximum opacity is obtained. Next, when this temperature is lowered, the initial cloudy opaque state is restored without taking the transparent state again. It is considered that this is because the organic low-molecular-weight substance melts at a temperature of T ₃ or higher and is then cooled to precipitate polycrystals. 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, it can take both opaque and transparent forms at room temperature and intermediate forms thereof.

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 layer, an image of the color of the coloring sheet or a white image of the background of the coloring sheet can be formed on a white background. Also, when projected with an OHP (overhead projector) or the like, the cloudy part becomes a dark part, and the transparent part transmits light and becomes a bright part on the screen.

To prepare the reversible thermosensitive recording material according to the present invention, generally, (1) a solution in which two components of a resin base material and an organic low molecular weight substance are dissolved, or (2) a solution of a resin base material (the solvent is an organic solvent) A low-molecular substance that does not dissolve at least one of them is used as a fine particle dispersion of an organic low-molecular substance on a support such as a plastic film, glass plate, metal plate, etc. Should be formed.

The solvent for preparing the heat-sensitive layer or the heat-sensitive recording material can be variously selected depending on the kind of the resin base material and the organic low molecular weight substance, and for example, tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, chloroform, carbon tetrachloride, ethanol, toluene, Examples thereof include benzene. Of course, when using the dispersion,
Even when a solution is used, the organic low molecular weight substance is precipitated as fine particles and exists in a dispersed state in the obtained heat-sensitive layer.

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.

Examples of such resins include polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride- Vinyl chloride-based copolymers such as acrylate copolymers are preferable, but polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymers, vinylidene chloride-copolymers such as vinylidene chloride-acrylonitrile copolymers; polyesters; polyamides Polyacrylate or polymethacrylate or acrylate-methacrylate copolymer; silicone resin and the like. These may be used alone or in admixture of two or more.

On the other hand, as the organic low molecular weight substance, any substance which changes from polycrystal to single crystal due to heat in the recording layer may be used, and generally, one having a melting point of 30 to 200 ° C., preferably 50 to 150 ° C. is used. .. Such organic low molecular weight substances include alkanols; alkane diols; halogen alkanols or halogen alkane diols; alkylamines; alkanes; alkenes; alkynes; halogen alkanes; halogen alkenes; halogen alkynes; cycloalkanes; cycloalkenes; cycloalkynes; 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; halogenallylcarboxylic acids or Of their esters, amides or ammonium salts; thioalcohols; thiocarboxylic acids or their esters, amines or ammonium salts; of thioalcohols Carboxylic acid esters, 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, and particularly 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 -, - SS -, - O-, 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, aragic acid and oleic acid; methyl stearate. Ester of higher fatty acid such as tetradecyl stearate, octadecyl stearate, octadecyl laurate, tetradecyl palmitate, dodecyl behenate; C ₁₆ H ₃₃ -OC ₁₆ H ₃₃ , C ₁₆ H ₃₃ -SC ₁₆ H ₃₃ , C ₁₈ H ₃₇ -SC ₁₈ H ₃₇ , C ₁₂ H ₂₅ -SC ₁₂ H ₂₅ , C ₁₉ H ₃₉ -SC ₁₉ H ₃₉ , C ₁₂ H ₂₅ -SSC ₁₂ H ₂₅ , Etc., such as ether or thioether. Among them, 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 preferable in the present invention, and higher fatty acids having 16 to 24 carbon atoms are more preferable.

In order to widen the range of temperatures at which the material can be made transparent, the organic low molecular weight substances described in this specification may be appropriately combined, or such organic low molecular weight substances may be combined with other materials having different melting points. .. These are, for example, JP-A-63-3
Publications such as 9378 and JP-A-63-130380, and Japanese Patent Application No. 63-14
No. 754, Japanese Patent Application No. 1-140109 and the like are disclosed, but the invention is not limited thereto. The ratio of the organic low molecular weight substance and the resin base material in the heat sensitive layer is 2: 2 by weight.
It is preferably about 1 to 1:16, more preferably 1: 1 to 1: 3. When the ratio of the resin 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 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, diphthalate. -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-ethylbutyrate, methyl acetylricinoleate, butyl acetylricinoleate, butyl Phthalyl 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 adduct 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 phosphoric acid mono- or di-ester Ca,
Ba or Mg salt; low-sulfated oil; poly long-chain alkyl acrylate; acrylic orgomer; poly long-chain alkyl methacrylate; long-chain alkyl methacrylate-amine-containing monomer copolymer; styrene-maleic anhydride copolymer;
Olefin-maleic anhydride copolymer.

When an image of this recording material is used as a reflection image, if a layer that reflects light is provided on the back surface of the recording layer, the contrast can be increased even if the thickness of the recording layer is reduced. Specifically, vapor deposition of Al, Ni, Sn and the like can be mentioned (described in JP-A-64-14079).

A protective layer may be provided on the heat-sensitive layer to protect the heat-sensitive layer. As a material for the protective layer (thickness of 0.1 to 5 μm) laminated on the heat-sensitive layer, silicone rubber, silicone resin (described in JP-A-63-221087),
Polysiloxane graft polymer (described in Japanese Patent Application No. 62-152550), UV curable resin or electron beam curable resin (Japanese Patent Application No. 63-3
No. 10600) and the like. 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. As a solvent in which it is difficult to dissolve the resin and the organic low molecular weight substance of the heat sensitive layer, n-hexane, methyl alcohol, ethyl alcohol,
Examples include isopropyl alcohol and the like, and an 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 and monomer components of the protective layer-forming liquid (Japanese Patent Laid-Open No. 1-133781). Description). As the material of the intermediate layer, in addition to those listed as the resin base material in the heat-sensitive layer, the following thermosetting resin,
Thermoplastic resins can be used. That is, polyethylene,
Examples thereof include polypropylene, polystyrene, polyvinyl alcohol, polyvinyl butyral, polyurethane, saturated polyester, unsaturated polyester, epoxy resin, phenol resin, polycarbonate and polyamide. The thickness of the intermediate layer is preferably about 0.1 to 2 μm.

[0033]

EXAMPLES The present invention will be described in more detail by way of examples, but the present invention is not limited thereto. In addition, both parts and% are based on weight. Example 1 First, a liquid A having the following composition was prepared. Behenic acid 7 parts Eicosane diacid 3 parts Diisodecyl phthalate 2 parts Vinyl chloride / vinyl acetate copolymer resin (VYHH manufactured by UCC) 40 parts THF 150 parts Toluene 15 parts Next, liquid A is octyl tin laurate 100 parts 0.5 parts to 0.5 parts of the reversible thermosensitive recording material having a thickness of about 15 μm was coated on a transparent PET film having a thickness of 50 μm and dried by heating with hot air at 110 ° C. for 3 minutes. Layers were formed. The formed layer was white and no discoloration was observed.

Example 2 First, a liquid B having the following composition was prepared. Behenic acid 7 parts Eicosane diacid 3 parts Diisodecyl phthalate 2 parts Vinyl chloride / vinyl acetate / vinyl alcohol copolymer resin 40 parts (Denka # 1000GK manufactured by Denki Kagaku Kogyo KK) THF 150 parts Toluene 15 parts Next, in solution B The epoxidized soybean oil was added at a ratio of 1 part of the epoxidized soybean oil to 100 parts of the resin, and the thickness was adjusted to 50
It was applied to a transparent PET film having a thickness of μ and dried by heating with hot air at 110 ° C. for 3 minutes to form a layer of a reversible thermosensitive recording material having a thickness of about 15 μm. The formed layer was white and no discoloration was observed.

Comparative Example 1 Liquid A of Example 1 was applied to a transparent PET film having a thickness of 50 μm, and dried by heating with hot air at 110 ° C. for 3 minutes to give a thickness of about 15 μm.
A thick layer of reversible thermosensitive recording material was formed. The formed layer was white and no discoloration was observed.

Comparative Example 2 Solution B of Example 2 was applied to a transparent PET film having a thickness of 50 μm, and dried by heating with hot air at 110 ° C. for 3 minutes to give a thickness of about 15 μm.
A thick layer of reversible thermosensitive recording material was formed. The formed layer was white and no discoloration was observed.

The films of the above-mentioned Examples and Comparative Examples were repeatedly printed and erased by hot stamping (printing 105 ° C., erasing 90 ° C.), and the density value after printing was measured by a Macbeth RD914 using a red filter to change the color. I examined the degree of. The results are shown in Table 1.

[0038]

[Table 1]

[0039]

As is clear from the above examples and comparative examples, according to the present invention, no color change occurs even after repeated printing,
It is possible to obtain a reversible thermosensitive recording material which maintains good printing and erasing repetition.

[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.

Claims (3)

[Claims] 1. A reversible device comprising a support and a heat-sensitive layer which comprises a resin base material and an organic low-molecular substance dispersed in the resin base material as a main component, and whose transparency reversibly changes depending on temperature. In a thermosensitive recording material, an organotin compound,
A reversible heat-sensitive recording material containing at least one of an epoxy compound and an inorganic metal salt. 2. The reversible thermosensitive recording material according to claim 1, wherein the thermosensitive layer contains an organic tin compound. 3. An organic tin compound, an epoxy compound, and at least one kind of inorganic metal salt are contained in an amount of 0.02 to 10 parts by weight with respect to 100 parts by weight of the resin base material. Reversible thermosensitive recording material.