JP3104141B2 - Reversible thermosensitive recording material - 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 material for recording and erasing by utilizing a reversible change in transparency with temperature.

[0002]

2. Description of the Related Art In recent years, a reversible thermosensitive recording material which can form a temporary image and erase the image when it becomes unnecessary has been attracting attention. As a typical example, a glass transition temperature (Tg) of from 50 to 60 ° C. to less than 80 ° C. on a support such as a polyester film, which can form and erase an image by utilizing a change in transparency with temperature, is used. 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 base material such as a vinyl chloride-vinyl acetate copolymer having a low glass transition temperature is known (Japanese Unexamined Patent Publication No. 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 state of transparency and white turbidity was repeated with good reproducibility in the first 100 or so times. A phenomenon was found in which the printed portion gradually turned red as the layers 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 disadvantages 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 substance dispersed in the resin base material are mainly used on a support, and the transparency is reversible depending on the temperature. Reversible thermosensitive recording material provided with a heat-sensitive layer which changes gradually, characterized in that the thermosensitive layer contains at least one of an organotin compound, an epoxy compound and an inorganic metal salt. Is provided, and the reversible thermosensitive recording material is further characterized in that an organic tin compound is particularly contained in the heat-sensitive layer. Further, at least one of the organic tin compound, the epoxy compound and the inorganic metal salt is provided. The reversible thermosensitive recording material is provided, wherein the seed is contained in an amount of 0.02 to 10 parts by weight based on 100 parts by weight of the resin base material.

As a result of repeated investigations in view of the above problems, the present inventors have found that discoloration has occurred because a polymer containing vinyl chloride as a skeleton is 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 at present to omit it. Therefore, a material capable of preventing discoloration by adding a very small amount to the resin base material was searched, and the present invention was reached.

Hereinafter, the present invention will be described in more detail. The feature of the present invention resides in the addition of a thermo-discoloration preventing material, which was conventionally considered to be unnecessary for resin-coated products, especially thermosensitive recording paper, etc., to a reversible thermosensitive recording material.

It is known to add the above-mentioned additives to a molded article of vinyl chloride resin. When molding the resin, the resin is heated to about 170 to 180 ° C. It is known that the resin discolors red during molding if such a high-temperature state extends for several minutes to several tens of minutes, including residual heat, until it cools down after molding. Add such additives.

On the other hand, the above additives are not added to the coated product of the vinyl chloride resin. This is because the temperature that can be applied by coating and drying is very low as compared to molding at 100 ° C or less,
This is to prevent discoloration. The hot air blown for drying may increase the temperature to 100 ° C. or higher, but the resin being dried remains at a lower temperature than the surrounding hot air until the solvent evaporates. Therefore, in the past, the above additives have been regarded as materials necessary only for the prevention of discoloration during the production of vinyl chloride resin molded products.

The problem in the present invention is not the discoloration at the time of manufacture but the discoloration due to the writing or erasing operation at the time of use.
The writing temperature of the reversible thermosensitive recording material varies depending on the prescription, but is about 100 ° C. According to conventional thinking, discoloration does not occur at such a temperature.
In fact, no discoloration was observed in the conventional repeated printing of several tens or about 100 times. However, for the purpose of improving the number of times printing can be repeated, a study was conducted as a preceding step to increase the number of printings with a conventional reversible thermosensitive recording material. Was. The reason for the discoloration at such a low temperature is not clear at present, but it is presumed that the stress due to repeated heating causes a structural change of the resin base material such as cutting of the polymer.

The degree of discoloration varies greatly depending on the composition of the resin base material. When a plasticizer such as a phthalate is added for the purpose of extending the clearing temperature, discoloration is severe. Further, vinyl chloride and vinyl acetate were further added with vinyl alcohol.
When the original copolymer resin is used as a resin base material, the discoloration is further increased.

The additive used in the present invention is at least one of an organic tin compound, an epoxy compound and an inorganic metal salt. Among them, organotin compounds are particularly excellent in terms of safety and transparency. As an organic tin compound, di-
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 include di-n-butyltin compounds and dimethyltin compounds such as dimethyltin bis (isooctylmercaptoacetate).

Epoxy compounds include epoxidized soybean oil, epoxy allyl phthalate, epoxidized fatty acids and metal salts thereof, epoxidized polyester containing tetrahydrophthalic acid, polyethylene glycol mono (epoxystearyl ether), bisepoxyalkyl phthalate , 1-benzyloxy-2,6-epoxypropane, 2,3-epoxycyclopentanol ester or ether. Epoxy compounds can also be used as plasticizers and help extend the clearing temperature range of reversible thermosensitive recording materials.

As the inorganic metal salt, tribasic lead sulfate, 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, 0.02-1 to 100 parts by weight of the resin base material.
0 parts by weight is good. 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 based on parts by weight.

Materials for preventing discoloration of the vinyl chloride resin include:
In addition to the materials described in claim 1, typical examples include metal soaps such as zinc stearate and barium stearate. It is known that these metal soaps are mixed into a recording layer for the purpose of improving contrast (Japanese Patent Laid-Open No.
No. 3-41186). However, metal soaps
For example, when added to a reversible thermosensitive recording material of a type in which an organic low-molecular substance is dispersed in a resin base material, segregation is more likely to occur on the organic low-molecular substance side than the resin base material, so that discoloration cannot be prevented unless a large amount is added. Originally, metal soap had poor solubility in organic solvents and could not be added in large quantities.However, even if it was forcibly added in large quantities, the amount in organic low-molecular substances became too large, and metal soap precipitated,
On the contrary, the basic characteristics of the reversible thermosensitive recording material are impaired, such as a decrease in contrast. For the above reasons, metal soap is not suitable for being added for the purpose of preventing discoloration.

In the present invention, the reversible thermosensitive recording material is
It is a material that reversibly causes a visible change due to a temperature change. Visible changes can be divided into color changes and shape changes, and the present invention mainly uses materials that cause color changes. Changes in color tone include changes in transmittance, reflectance, absorption wavelength, scattering degree, and the like, and an actual reversible thermosensitive recording material performs display by a combination of these changes. More specifically, it is a material that changes reversibly between a transparent state and a cloudy state . As such a material, as described in the related art, a material in which a heat-sensitive layer in which a low-molecular organic substance such as a higher alcohol or a higher fatty acid is dispersed in a resin base material such as a polyester is exemplified.

The reversible thermosensitive recording material of the present invention utilizes the change in transparency (transparent state, cloudy opaque state) as described above. The difference between this transparent state and cloudy opaque state is presumed as follows. . That is, in the case of (I) transparent, the particles of the organic low-molecular substance dispersed in the resin base material are composed of large particles of the organic low-molecular substance, and the light incident from one side is not scattered and is opposite. (II) In the case of white turbidity, the particles of the organic low molecular weight substance are composed of polycrystals in which fine crystals of the organic low molecular weight substance are aggregated, and the crystal axis of each crystal Is oriented in various directions, so that light incident from one side is refracted many times at the interface between the crystals of the organic low-molecular substance particles, and is scattered, so that it appears white.

In FIG. 1 (representing a change in transparency due to heat), a heat-sensitive layer mainly composed of a resin base material and an organic low-molecular substance dispersed in the resin base material is, for example, T _0.
At the following room temperature, it is cloudy and opaque. This became clear when heated to a temperature T _2, which remains also clear again returned to the normal temperature of T ₀ or less in this state. This may be because the crystalline low-molecular organic material before reaching the T ₀ or less from the temperature T ₂ is between the single crystal from a polycrystalline via a semi-molten state grows. Further T ₃
Heating to the above temperature results in a 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, presumably because the polycrystals precipitated by being cooled. 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 equal to or lower than T ₀ , an intermediate state between transparent and opaque can be obtained. Also, by returning to room temperature After heating to be again T ₃ or more temperature which became clear at the normal temperature, the flow returns to cloudy opaque state again. That is, both opaque and transparent forms at room temperature and intermediate states thereof can be taken.

Therefore, the heat-sensitive layer can be selectively heated by selectively applying heat to form a cloudy image on a transparent ground and a transparent image on a cloudy ground, and the change can be repeated many times. It is possible. If a colored sheet is arranged on the back of such a heat-sensitive layer, a color image of the colored sheet on a white background or a white image on a colored background of the colored sheet can be formed. Further, when projected by an OHP (overhead projector) or the like, the cloudy portion becomes a dark portion, the transparent portion transmits light, and becomes a bright portion on the screen.

In order 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 substance are dissolved, or (2) a solution of the resin base material (an organic solvent is used as a solvent) A dispersion in which at least one of the low-molecular substances is not dissolved) is applied to a support such as a plastic film, a glass plate, or a metal plate, and dried by applying a dispersion liquid in which organic low-molecular substances are dispersed in fine particles. May be formed.

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

The resin base material used for the heat-sensitive layer is a material that forms a layer in which organic low-molecular substances are uniformly dispersed and held, and that affects the transparency at the time of maximum transparency. For this reason, the resin base material is preferably a resin having good transparency, mechanical stability, and good film formability.

Examples of such a resin include polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, and vinyl chloride-vinyl chloride. Vinyl chloride copolymers such as acrylate copolymers are preferred, but in addition, polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymer, vinylidene chloride-based copolymers such as vinylidene chloride-acrylonitrile copolymer; polyester; polyamide A polyacrylate or polymethacrylate or an acrylate-methacrylate copolymer; and a silicone resin. These may be used alone or as a mixture of two or more.

On the other hand, any organic low-molecular substance may be used as long as it changes from polycrystalline to single-crystal by heat in the recording layer, and generally has a melting point of 30 to 200 ° C., 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 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; Esters, amides or ammonium salts thereof; thioalcohols; thiocarboxylic acids or their esters, amines or ammonium salts; 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, particularly preferably 10 to 30. The alcohol group in the ester may be saturated or non-saturated, and may be halogen-substituted. In any case, the organic low-molecular 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, araginic acid and oleic acid; methyl stearate Esters of higher fatty acids 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 , And ether or thioether. Among them, in the present invention, 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, and higher fatty acids having 16 to 24 carbon atoms are more preferable.

In order to widen the range of temperatures at which transparency can be achieved, the organic low-molecular substance described in this specification may be appropriately combined, or such an organic low-molecular substance may be combined with another material having a different melting point. . These are disclosed, for example, in JP-A-63-3
No. 9378, JP-A-63-130380 and Japanese Patent Application No. 63-14
No. 754, Japanese Patent Application No. 1-140109, and the like, but are not limited thereto. The ratio between the organic low-molecular substance and the resin base material in the heat-sensitive layer was 2: 2 by weight.
About 1 to 1:16 is preferable, and 1: 1 to 1: 3 is more preferable. 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 substance is held in the resin base material, and when the ratio is higher, the amount of the organic low-molecular substance is small, so that the opacity is increased. Becomes difficult.

In addition to the above components, additives such as a surfactant and a high-boiling solvent can be added to the heat-sensitive layer in order to facilitate formation of a transparent image. Specific examples of these additives are as follows. Examples of high boiling solvents: tributyl phosphate, tri-2-ethylhexyl phosphate, triphenyl phosphate, tricresyl phosphate, butyl oleate, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diheptyl phthalate, diphthalic 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, butyl acetyl ricinoleate, 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 alkyl phenol, higher fatty acid higher alkyl amine, higher fatty acid amide Lower olefin oxide adducts of fats and oils or polypropylene glycol; acetylene glycol; Na, Ca, Ba or Mg salts of higher alkylbenzene sulfonic acids; higher fatty acids, aromatic carboxylic acids, higher fatty acid sulfonic acids, aromatic sulfonic acids, sulfuric acid monoesters Or phosphoric acid mono- or di-ester Ca,
Ba or Mg salt; 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 to maleic anhydride copolymer.

When an image of this recording material is used as a reflection image, providing a light reflecting layer on the back of the recording layer can increase the contrast even if the thickness of the recording layer is reduced. Specific examples include vapor deposition of Al, Ni, Sn and the like (described in JP-A-64-14079).

A protective layer can be provided on the heat-sensitive layer to protect the heat-sensitive layer. Materials for the protective layer (thickness 0.1 to 5 μm) laminated on the heat-sensitive layer include silicone rubber and silicone resin (described in JP-A-63-221087).
Polysiloxane graft polymers (described in Japanese Patent Application No. 62-152550) and ultraviolet curable resins or electron beam curable resins (Japanese Patent Application No. 63-3152)
No. 10600). In any case, a solvent is used at the time of coating, and it is preferable that the solvent does not easily dissolve the resin of the thermosensitive layer and the organic low-molecular substance. N-Hexane, methyl alcohol, ethyl alcohol,
Examples thereof include isopropyl alcohol, and alcohol-based solvents are particularly desirable in terms of cost.

Further, an intermediate layer can be provided between the protective layer and the heat-sensitive layer in order to protect the heat-sensitive layer from a solvent, a monomer component and the like of the protective layer-forming solution (see JP-A-1-33781). Described). As the material of the intermediate layer, in addition to those listed as the resin base material in the thermosensitive layer, the following thermosetting resin,
Thermoplastic resins can be used. That is, polyethylene,
Examples 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 with reference to examples, but the present invention is not limited to these examples. The parts and percentages 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, octyltin laurate is added to liquid A in 100 parts of resin. Of a reversible thermosensitive recording material having a thickness of about 15 μm, 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. A layer was 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 Co., Ltd.) THF 150 parts Toluene 15 parts Epoxidized soybean oil was added at a ratio of 1 part of epoxidized soybean oil to 100 parts of resin, and this was added to a thickness of 50 parts.
A transparent PET film having a thickness of about 15 μm was coated on the transparent PET film having a thickness of about 15 μm and dried by heating with hot air at 110 ° C. for 3 minutes. The formed layer was white and no discoloration was observed.

Comparative Example 1 The liquid A of Example 1 was applied to a transparent PET film having a thickness of 50 μm, dried by heating with hot air at 110 ° C. for 3 minutes, and dried to 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 The solution B of Example 2 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 to obtain 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 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 Macbeth RD914 using a red filter to change the color. Was examined. Table 1 shows the results.

[0038]

[Table 1]

[0039]

As is clear from the above Examples and Comparative Examples, according to the present invention, the color does not change even by repeated printing.
It is possible to obtain a reversible thermosensitive recording material that maintains good repetition of printing and erasing.

[Brief description of the 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.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-41186 (JP, A) JP-A-4-189177 (JP, A) JP-A-5-38872 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) B41M 5/36

Claims (3)

(57) [Claims] 1. A reversible heat-sensitive layer comprising, as a main component, a resin base material and an organic low-molecular substance dispersed in the resin base material and having a transparency reversibly changing with temperature on a support. In the thermosensitive recording material, in the thermosensitive layer, an organotin compound,
A reversible thermosensitive recording material characterized by containing at least one of an epoxy compound and an inorganic metal salt. 2. The reversible thermosensitive recording material according to claim 1, wherein an organic tin compound is contained in the thermosensitive layer. 3. The resin according to claim 1, wherein at least one of the organic tin compound, the epoxy compound and the inorganic metal salt is contained in an amount of 0.02 to 10 parts by weight based on 100 parts by weight of the resin base material. Reversible thermosensitive recording material.