JP3358002B2 - 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 capable of repeatedly forming and erasing an image by utilizing a reversible change in transparency of a thermosensitive layer depending on the temperature.

[0002]

2. Description of the Related Art In recent years, reversible thermosensitive recording materials having a thermosensitive layer in which a temporary image can be formed and the image can be erased when it becomes unnecessary and the transparency reversibly changes depending on the temperature have been attracting attention. Have been. As a typical example,
A reversible thermosensitive recording material in which an organic low molecular weight substance such as a higher fatty acid is dispersed in a resin base material such as a vinyl chloride-vinyl acetate copolymer is known (JP-A-54-119377).
And Japanese Unexamined Patent Publication No. 55-154198). However, these conventional reversible thermosensitive recording materials have the drawback that the temperature range showing light transmission / transparency is as narrow as 2 to 4 ° C., and an image is formed using light transmission / transparency or light shielding / white turbidity. It was difficult to control the temperature during formation.

In consideration of this point, Japanese Patent Application Laid-Open No. 63-3937
No. 8, No. 63-130380 and the like propose that the temperature range showing light transmission and transparency can be expanded by using a certain higher aliphatic ester as a eutectic agent. However, these have the drawback that the repetition durability due to the thermal head heating element is inferior, and the image erasability (transparency) by short-time heat application by the thermal head is poor. In addition, after long-term image storage, the erasability of the heat-sensitive recording layer over time fluctuates greatly from a preset initial erasure characteristic, and when an image is erased under erasure conditions corresponding to the initial erasure characteristic. However, there is a disadvantage that the erased density value over time is reduced as compared with the initial erased density value, that is, the erasability over time after image storage is poor.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned drawbacks, and provides a reversible thermosensitive recording material in which a transparent state and a cloudy state are reversibly changed depending on the temperature. With the thermal head, the initial image erasability can be reduced to near the background density (transparent state), and the image erasability over time is significantly higher than the initial image erasability even after long-term image storage. It is an object of the present invention to provide a reversible thermosensitive recording material that does not fluctuate.

[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 reversibly dependent on temperature. In a reversible thermosensitive recording material provided with a heat-sensitive layer that changes to an alkanediol having 4 or more carbon atoms,
In the di-fatty acid esters, those having a 35 ° C. or more melting point
Reversible thermosensitive recording material which comprises using at least one or more is provided, and or, the organic low-molecular material is different than the melting point and 10 ° C. of di-fatty acid esters and the esters of the alkane diol A mixture of organic low-molecular substances having a melting point ;
Organic low molecular weight substances used by mixing with all difatty acid esters are aliphatic monocarboxylic acids, aliphatic dicarboxylic acids,
The reversible heat-sensitive material, which is at least one selected from thiodipropionic acid, a fatty acid ester, a ketone having a higher alkyl group, a semicarbazone derived from a ketone having a higher alkyl group, and an α-phosphono fatty acid. A recording material is provided. In addition, a reversible thermosensitive recording material comprising a support and a thermosensitive layer whose main component is a resin base material and an organic low-molecular substance dispersed in the resin base material and whose transparency changes reversibly depending on temperature. In the above, a vinyl chloride polymer or a vinyl chloride copolymer is used as the resin base material, and the vinyl chloride unit content (Y weight%) and the average degree of polymerization (X) of these polymers are represented by the following formula: 1)
The reversible thermosensitive recording material, characterized in that it has a value in a range satisfying the relationship represented by

## EQU00001 ## In particular, the reversible thermosensitive recording material is provided, wherein the average degree of polymerization (X) is 500 or more, wherein -0.68 logX + 3.794 ≤ logY ≤ -0.215 logX + 2.66.

That is, a reversible thermosensitive recording material comprising a resin base material and a low-molecular organic substance dispersed in the resin base material as a main component and having a heat-sensitive layer whose transparency reversibly changes depending on temperature, By using at least one polyhydric alcohol difatty acid ester as an organic low molecular weight substance, repeated durability and image erasability are improved, and a vinyl chloride unit content (Y % By weight) and an average degree of polymerization (X) having a value satisfying the relationship represented by the above formula (Equation 1) by using a vinyl chloride polymer or a vinyl chloride copolymer.
The heat resistance of the resin base material is further improved while maintaining the contrast of the transparent-white turbidity change, and the resin base material is hardly deformed by the heat and pressure of the thermal head, etc. It has been found that the organic low-molecular substance dispersed in fine particles is maintained as fine particles and the image contrast is also maintained, and the present invention has been completed.

[0007] The organic low molecular weight substance used in the present invention, 35 ° C
Having an above-mentioned melting point and having 4 or more carbon atoms
The difatty acid ester is represented by the following general formula
Things. CH_Three(CH_Two)_m-2COO (CH_Two)_nOOC (CH_Two)_m-2CH_Three (Where n is4~ 40, GoodPreferably an integer from 4 to 22
You. m is 2 to 40, preferably 3 to 30, more preferably
Is an integer of 4 to 22. The following are specific examples:You. 1,4 Butanediol dialkanate1,5 Pentanediol dialkanate 1,6 hexanediol dialkanate 1,7 heptanediol dialkanate 1,8 octanediol dialkanate 1,9 nonanediol dialkanate 1,10 decanediol dialkanic acid Ester 1,11 undecanediol dialkanate 1,12 dodecanediol dialkanate 1,13 tridecanediol dialkanate 1,14 tetradecanediol dialkanate 1,15 pentadecanediol dialkanate 1,16 Hexadecanediol dialkanate 1,17 heptadecanediol dialkanate 1,18 octadecanediol dialkanate 1,19 nonadecanediol dialkane Ester 1,20 Icosandiol dialkanate 1,21 Henicosandiol dialkanate 1,22 Docosandiol dialkanate 1,23 Tricosandiol dialkanate 1,24 Tetracosandiol dialkane Acid ester 1,25 pentacosanediol dialkanate 1,26 hexacosanediol dialkanate 1,27 heptacosanediol dialkanate 1,28 octacosanediol dialkanate 1,29 nonacosandiol dialkane Acid esters 1,30 triacontandiol dialkanate 1,31 Hentriacontandiol dialkanate S
Ter 1,32 dotriacontandiol dialkanate
1,33-tritriacontandiol dialkanic acid
Ter 1,34 tetratriacontandiol dialkanic acid
Steal

Further , it has a melting point of 35 ° C. or more and a carbon number of 4 or less.
Examples of the above- mentioned difatty acid ester of alkanediol include the following. As having 4 or more Arukanjio Lumpur carbon, 1,4-butanediol, 1,5-pentanediol, 1,
6-hexanediol, 1,7 heptanediol, 1,8
Octanediol, 1,9 nonanediol, 1,10 decanediol, 1,11 undecanediol, 1,12
Dodecanediol, 1,13 tridecanediol, 1,
14 tetradecanediol, 1,15 pentadecanediol, 1,16 hexadecanediol, 1,17 heptadecanediol, 1,18 octadecanediol, 1,
19 nonadecanediol, 1,20 icosanediol,
1,21 henicosandiol, 1,22 docosandiol, 1,23 trichosandiol, 1,24 tetracosandiol, 1,25 pentacosandiol, 1,2
6 hexacosanediol, 1,27 heptacosanediol, 1,28 octacosanediol, 1,29 nonacosandiol, 1,30 triacontandiol, 1,3
1 Hentriacontandiol, 1,32 Dotriacontandiol, 1,33 Tritriacontandiol,
And a diol selected from 1,34 tetratriacontandiol, dilaurate, ditridecate,
Dimyristate, dipentadecate, dipalmitate,
Examples include dimalgalate, distearate, dinonadecate, diarachicade, dihenicosate and dibehenate.

The polyhydric alcohol difatty acid ester has the characteristic that it has a lower melting point than fatty acids when compared at the same carbon number, and conversely has more carbon atoms than fatty acid when compared at the same melting point. The repetition durability of printing with the thermal head is considered to be due to the compatibility of the resin and the organic low-molecular substance at the time of heating,
It is considered that the compatibility between the resin and the organic low-molecular substance decreases as the number of carbon atoms in the organic low-molecular substance increases. Furthermore, the turbidity also tends to increase in proportion to the number of carbon atoms. Therefore, by using a polyhydric alcohol difatty acid ester, compared with a fatty acid in a reversible thermosensitive recording material having the same clearing temperature (near the melting point), It is thought that the durability is improved repeatedly.

Also, polyhydric alcohol difatty acid esters have low melting points, and have the same characteristics as fatty acids having higher melting points in terms of cloudiness and repetition durability. When mixing and expanding the clarifying temperature range, the clarifying temperature range can be expanded while having the same degree of white turbidity and repetitive durability as in the case of using a fatty acid. Image erasing (transparency) by heating in a short time can be improved, and even if the image erasing energy fluctuates over time due to an increase in the margin for image erasing, there is no practical problem and erasing with a thermal head Is also possible.

As the organic low molecular weight substance, a mixture of the polyhydric alcohol difatty acid ester and the organic low molecular weight substance having a melting point different from that of the polyhydric alcohol diester by 10 ° C. or more may be used. Examples of organic low molecular weight substances used in combination with polyhydric alcohol difatty acid esters include aliphatic monocarboxylic acids, aliphatic dicarboxylic acids, thiodipropionic acids, fatty acid esters, ketones having higher alkyl groups, and higher alkyl groups Semicarbazones derived from ketones, α-phosphono fatty acids, and the like.

Specific examples of the aliphatic monocarboxylic acid used in the present invention include, for example, palmitic acid, margaric acid,
Stearic acid, nonadecylic acid, arachinic acid, heneicosanoic acid, hebenic acid, tricosanoic acid, tetracosanoic acid, pentacosanoic acid, hexacosanoic acid, peptacosanoic acid, octacosanoic acid, nonakosanoic acid, triacontanic acid, hentriacontanic acid, dotriacontanic acid, Examples include tritriacontanic acid, tetratriacontanic acid, pentatriacontanic acid, hexatriacontanic acid, heptatriacontanic acid, octatriacontanic acid, and hexatetracontanic acid.

Specific examples of the aliphatic dicarboxylic acid used in the present invention include, for example, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecandioic acid, dodecandioic acid, and tridecanedioic acid. acid,
Tetradecandioic acid, pentadecandioic acid, hexadecandioic acid, heptadecandioic acid, octadecandioic acid, nonadecandioic acid, eicosantioic acid, heneicosandioic acid, docosandioic acid, and the like.

Specific examples of the fatty acid ester used in the present invention include: behenyl laurate docosyl myristate dodecyl palmitate tetradecyl palmitate pentadecyl palmitate hexadecyl palmitate octadecyl palmitate tricontyl octadecyl palmitate docosyl stearate stearate Propyl isopropyl stearate butyl stearate amyl stearate heptyl stearate octyl stearate detradecyl stearate hexadecyl stearate heptadecyl stearate octadecyl stearate docosyl stearate hexacosyl stearate tricontyl behenate dodecyl behenate octadecyl behenate And tetrachosyl myrislate.

The ketone used in the present invention contains a ketone group and a higher alkyl group as essential constituent groups, and may also contain an unsubstituted or substituted aromatic ring or a substituted ring. The total carbon number of the ketone is preferably 16 or more, more preferably 21 or more. The semicarbazone used in the present invention is derived from the above ketone. Ketones and semicarbazones used in the present invention include, for example, those shown in Table 1 below.

[0015]

[Table 1- (1)]

[Table 1- (2)]

[Table 1- (3)]

The α-phosphono fatty acid used in the present invention is, for example, E. coli. V. Kaurer et al. Ak. Oil Che
According to the method of Kist's Soc, 41, 205 (1964), the fatty acid is converted to the value of the value of "Hell-Volhard-Zel".
α-brominated acid bromide by bromination by an inskin reaction, followed by addition of ethanol to obtain an α-bromo fatty acid ester, and furthermore, a heating reaction with triethyl phosphite to form an α-phosphono fatty acid ester, followed by hydrolysis with concentrated hydrochloric acid. The product can be obtained by recrystallization from toluene. Specific examples of the phosphono fatty acid used in the present invention are shown below.

Α-phosphonopelargonic acid CH ₃ (CH ₂ ) ₆ CH [PO (OH) ₂ ] COOH (mp 130-1 ° C.) α-phosphonocaprylic acid CH ₃ (CH ₂ ) ₇ CH [PO (OH ) ₂ ) COOH (mp 131-2 ℃, mp 16
2-4 ° C) α-phosphonolauric acid CH ₃ (CH ₂ ) ₉ CH [PO (OH) ₂ ] COOH (mp 131-2 ° C, mp 16
2-3 ° C) α-phosphonomyristylic acid CH ₃ (CH ₂ ) ₁₁ CH [PO (OH) ₂ ] COOH (mp 132-3 ° C, mp 15
3-6 ° C) α-phosphonopalmitic acid CH ₃ (CH ₂ ) ₁₃ CH [PO (OH) ₂ ] COOH (mp 132-3 ° C, mp 15
6-65 ° C) α-phosphonostearic acid CH ₃ (CH ₂ ) ₁₅ CH [PO (OH) ₂ ] COOH (mp 130-1 ° C, mp 15
7-65 ° C). Except for α-phosphonoberalgonic acid, it has two mps (melting points).

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, a polyvinyl chloride copolymer, and polyvinyl chloride;
Vinyl chloride copolymers such as vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-acrylate copolymer; poly Vinylidene chloride-based copolymers such as vinylidene chloride, vinylidene chloride-vinyl chloride copolymer, vinylidene chloride-acrylonitrile copolymer; polyester; polyamide; polyacrylate or polymethacrylate or acrylate-methacrylate copolymer; Can be Of course, these resins may be used alone or in combination of two or more.

In the present invention, the resin base material is a vinyl chloride polymer or a vinyl chloride copolymer, and the relationship between the vinyl chloride unit content (Y weight%) and the average degree of polymerization (X) is represented by the above formula (X). Those having a value satisfying Formula 1) are preferable (FIG. 2, hatched portions and lattice portions). here,
The formula shows that the average degree of polymerization (X) is low and the vinyl chloride unit content (Y% by weight) is low, and that the average degree of polymerization (X) is high and the salt or vinyl unit content (Y% by weight) is high. When the degree of polymerization (X) is low, a problem arises. When the degree of polymerization (X) is low, the vinyl chloride unit content (Y% by weight) is high. As the degree of polymerization (X) increases, the vinyl chloride unit content (Y% by weight) increases. Is preferably lower. In the resin matrix of the present invention, when the average degree of polymerization (X) is high and the ratio of the vinyl chloride unit content (Y weight%) is high,
A value in the range of the following expression (Equation 2) (upper right in FIG. 2) is more preferable.

## EQU2 ## When the average degree of polymerization (X) is low and the ratio of the vinyl chloride unit content (Y wt%) is low, the average degree of polymerization (X) is 600 or more. A value in the range of the following equation (Equation 3) (lower left of FIG. 2) is more preferable.

[Mathematical formula-see original document] logY≥-0.215 logX + 2.49 The preferred range is shown in a lattice form in FIG.
Furthermore, the average polymerization degree (X) of the resin base material of the present invention is preferably 500 or more, more preferably 600 or more, and particularly preferably 700 or more.

It is not clear why the use of the above-mentioned specific vinyl chloride polymer or vinyl chloride copolymer as the resin base material improves the repetition durability of image formation and erasure by heating means such as a thermal head. When the average degree of polymerization of the polymer is high or the proportion of vinyl chloride units is increased, the melt viscosity when heated is increased, and image formation is performed using a heating means such as a thermal head that simultaneously applies heat and pressure. Even if erasure is repeated, the deformation of the resin matrix around the fine particles of the organic low molecular substance is small,
Because organic low-molecular substances are maintained as fine particles,
It is assumed that the durability is improved.

If the average degree of polymerization and the vinyl chloride ratio are too high, the solubility in a solvent is reduced, the viscosity of the solution is increased, and the organic low-molecular substance and the resin base material are dissolved in the solvent, and then dried. It is considered that separation is difficult and low-molecular organic material particles are hard to form, resulting in a decrease in turbidity. The logarithm (logY) of the vinyl chloride unit (Y) of the resin base material is (-0.68 logX + 3.794: X
(Average degree of polymerization), the durability of repeated image formation and erasure decreases, and (logY) becomes (-0.21).
If it exceeds 5 logX + 2.66), the initial turbidity decreases.

The polyvinyl chloride or vinyl chloride copolymer used as the resin base material is usually polymerized by various methods such as bulk polymerization, emulsion polymerization, suspension polymerization, and modifications thereof.

Hereinafter, specific examples of the polymerization method will be described. First, in the suspension polymerization method, a vinyl chloride monomer is dispersed and suspended in minute droplets by vigorous shear stirring in an aqueous phase containing a small amount of a hydrophilic protective colloid dispersant, and the monomer-soluble organic peroxide is dissolved. Radical polymerization is performed in a monomer droplet using a polymerization initiator to obtain a polymer slurry having a particle size of several tens to several hundreds of microns, which is filtered, washed, dried and sieved to obtain a product. Polymers produced by the suspension polymerization method are low in impurities, easy to control the reaction temperature, excellent in resin quality, low in equipment and production costs, easy to control production, and easy to maintain uniform quality. Has become the mainstream of the PVC resin manufacturing method.

In the emulsion polymerization method, the emulsion is dispersed in an aqueous phase with the aid of an anionic surfactant, and a water-soluble polymerization initiator such as persulfate is used. μ polymer latex, salting out, filtration, washing, drying,
The product is obtained by grinding or by directly spray drying the latex. Emulsion polymerization method polymer is a fine powder that is difficult to handle and contains many emulsifiers and other impurities,
Poor properties such as thermal stability, transparency, and electrical insulation.

The bulk polymerization method is also regarded as precipitation-type solution polymerization (precipitation polymerization) using a monomer as a solvent. That is, radical polymerization is performed by adding a soluble initiator to the monomer, the polymerization reaction is stopped at an appropriate reaction rate, the unreacted monomer is recovered, and the resulting precipitated polymer is pulverized and classified to obtain a product. It has high polymer purity because it does not contain dispersants or emulsifiers, and does not require filtration and drying because it does not use water. However, industrialization has been delayed due to difficulties in removing the heat of reaction and controlling the particle shape. Recently, improvement of the reaction apparatus has led to the development of a two-stage bulk polymerization method of Pesine Saint-Gobain.

In the homogeneous solution polymerization method, an expensive organic solvent is used, and the production cost is high because the solvent is required to be recovered. It is difficult to obtain a polymer having a high degree of polymerization by the chain transfer action of the solvent. There is a disadvantage in that the reaction yield is small and it is difficult to increase the reaction yield.

Among them, a suspension polymerization method is preferably used,
The average degree of polymerization can be arbitrarily obtained by controlling the polymerization temperature (a high polymerization resin is obtained by lowering the polymerization temperature and lengthening the polymerization time). In the case of a copolymer, it can be produced by adding a monomer of the material to be copolymerized with vinyl chloride from the beginning or during the polymerization. The ratio of vinyl chloride is mostly determined by the initial monomer addition ratio.

As such a vinyl chloride copolymer,
Vinyl chloride copolymers such as vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-acrylate copolymer, etc. No. These may be used alone or as a mixture of two or more.

The degree of polymerization (molecular weight) of this resin base material is determined by GPC
(Gel permeation chromatography). This GPC
(Gel permeation chromatography) means that when a sample solution of a resin dissolved in a solvent is injected into a column filled with a particulate gel having pores, a sample with a molecular size larger than the gel pores enters the pores. Therefore, the molecules passing through the outside of the gel and entering the pores stay in the gel pores depending on their size, and the smaller the molecular size, the longer the elution time from the column. Therefore, in the eluate from the column, the sample is gradually separated from the high molecule into the low molecule and comes out. A method of measuring the difference in refractive index between the eluted liquid and the solvent in which the resin is dissolved (differential refractive index), and calculating the molecular weight distribution and average molecular weight of the measurement sample from a calibration curve of a standard sample whose molecular weight is known. It is.

The average degree of polymerization (X) is calculated from the measured number average molecular weight (Mn) by the following equation (Equation 4).

(Equation 4) Here, VD and VE are not specified, and in the case of a vinyl chloride-vinyl acetate copolymer, VD becomes vinyl acetate, and VE does not exist. Further, the calculation formula up to the terpolymer of vinyl chloride and the other two types is shown here.
In the case of copolymers of more than one kind, calculation is performed in the same manner. The unit molecular weight is defined as follows. Unit molecular vinyl chloride - (CH ₂ -CHCl) - a and this mass is the sum of the mass of each atom. Examples of other units molecule, vinyl acetate, - [CH ₂ -CH (C
OOH)] -, PVA is _{- [CH 2 CH (OH)} ] -, maleic acid - [CH (COOH) -CH ( COOH)] -, vinylidene chloride - [CH ₂ -CClCl] - a. Table 2 below
In the calculation, the unit molecular weight (Vc) of vinyl chloride is 63, vinyl acetate is 72, PVA is 44, maleic acid is 116, and vinylidene chloride is 98.

The ratio between the organic low-molecular substance and the resin base material in the heat-sensitive layer is preferably about 2: 1 to 1:16 by weight, more preferably 1: 2 to 1: 8. When the ratio of the resin base material is less than this, it becomes difficult to form an organic low-molecular substance in a film held in the resin base material. Becomes difficult.

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, (i) in the case of transparency, 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 cloudiness, the particles of the organic low-molecular substance are composed of polycrystals composed of fine crystals of the organic low-molecular substance, and the crystal axes of the individual crystals 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
_At a room temperature of ₀ or less, it is cloudy and opaque. This is called temperature T ₂
When the temperature is returned to room temperature below T ₀ , the film remains transparent. This is from temperature T ₂ to T ₀
It is considered that the crystal grows from a polycrystal to a single crystal through the semi-molten state of the organic low-molecular substance until the following.
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, presumably because the polycrystals precipitated by being cooled. When the opaque state is heated to a temperature between T _{1 and} T ₂ and then cooled to room temperature, that is, a temperature 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 side of such a heat sensitive body, 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, and the transparency transmits light and becomes a bright portion on the screen.

The reversible thermosensitive recording material used in the present invention can be formed as a film on a supporting member or formed into a sheet by the following method, for example. 1) A method of dissolving a resin base material and an organic low-molecular substance in a solvent, applying this on a support member, and evaporating the solvent to form a film or sheet. 2) The resin base material is dissolved in a solvent in which only the resin base material is dissolved, and the organic low-molecular substance is pulverized or dispersed therein by various methods, applied to a support member, and the solvent is evaporated to form a film. Or a method of forming a sheet. 3) A method in which a resin base material and an organic low-molecular substance are heated and melted and mixed without using a solvent, and the resulting mixture is formed into a film or a sheet and cooled. The solvent for the heat-sensitive layer or the heat-sensitive recording material can be variously selected depending on the type of the resin base material and the organic low-molecular substance.
Examples include tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, chloroform, carbon tetrachloride, ethanol, toluene, benzene and the like. In addition, not only when a dispersion is used, but also when a solution is used, in a heat-sensitive layer obtained, organic low-molecular substances are precipitated as fine particles and exist in a dispersed state.

In addition to the above components, additives such as a surfactant and a high boiling point 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 point solvents; tributyl phosphate, tri-2-phosphate
Ethylhexyl, triphenyl phosphate, tricresyl phosphate, 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 azelate
-Ethylhexyl, 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, acetyl citric acid Tributyl.

Examples of surfactants and other additives: polyhydric alcohol higher fatty acid esters; polyhydric alcohol higher alkyl ethers; polyhydric alcohol higher fatty acid esters, higher alcohols, higher alkyl phenols, higher fatty acid higher alkyl amines, higher fatty acid amides 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, monoesters of sulfuric acid Or Ca, Ba or Mg salts of phosphoric acid mono- or di-esters; low sulfated oils; poly long chain alkyl acrylates; acrylic oligomers; poly long chain alkyl methacrylates; Chromatography copolymers; styrene-maleic anhydride copolymer; olefin-maleic anhydride copolymer.

The thickness of the heat-sensitive layer is preferably 1 to 30 μm,
2-20 μm is more preferred. If the heat-sensitive layer is too thick, heat distribution within the layer will occur, making it difficult to achieve uniform transparency. On the other hand, if the heat-sensitive layer is too thin, the turbidity decreases and the contrast decreases. Further, the turbidity can be increased by increasing the amount of the organic low-molecular substance in the heat-sensitive layer.

When a resin used as a resin base material is coated and dried on a support such as a plastic film, glass, or metal to form a laminated heat-sensitive layer, some of the resins have poor adhesion to the support. It is also possible to provide an adhesive layer between the thermosensitive layer and the thermosensitive layer so that the thermosensitive layer does not peel off. The resin for the adhesive layer is not particularly limited as long as it has good adhesiveness to the support and does not adversely affect the components of the heat-sensitive recording layer. For example, vinyl chloride resins, polyester resins,
Acrylic resins, polyamide resins, and the like are listed. In particular, a metal or a metal thin film has poor adhesion, and a copolymer or the like containing vinyl chloride and a phosphate ester as main components is suitably used as a material for the adhesive layer. The thickness of the adhesive layer is 0.1
About 5 μm, more preferably about 0.3 to 2 μm.

When an image of the recording material is used as a reflection image, providing a layer that reflects light on the back surface 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). It is also possible to create a card combining a magnetic recording layer and a reversible thermosensitive layer. Especially when a reversible thermosensitive layer is provided on the magnetic recording layer, a smooth layer mainly composed of resin is provided to make the surface smooth, a light reflecting layer is provided thereon, and further thereon. In some cases, a heat-sensitive layer may be provided via an adhesive layer (Japanese Utility Model Application Laid-Open No. 2-3876).

Further, a protective layer may be provided on the heat-sensitive layer of the present invention in order to prevent the surface from being deformed by the heat and pressure of the heating means by a writing method such as a thermal head and the transparency of the transparent portion being reduced. good. A protective layer (having a thickness of 0.1 mm) laminated on the heat-sensitive layer.
1-5 μm) as silicone rubber, silicone resin (described in JP-A-63-221087),
Polysiloxane graft polymer (JP-A-63-317)
385), an ultraviolet curable resin or an electron beam curable resin (described in JP-A-2-566). 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. Examples of the solvent that hardly dissolves the resin and the organic low-molecular substance in the heat-sensitive layer include n-hexane, methyl alcohol, ethyl alcohol, and isopropyl alcohol, and an alcohol-based solvent is particularly desirable in terms of cost.

Further, an intermediate layer can be provided between the protective layer and the reversible recording material in order to protect the reversible recording material from a solvent, a monomer component and the like of the protective layer forming solution (Japanese Patent Laid-Open No. 1-133781). issue). As the material of the intermediate layer, the following thermosetting resins and thermoreversible resins can be used in addition to those listed as the resin base material in the thermosensitive layer. That is, specifically, polyethylene, polypropylene, polystyrene, polyvinyl alcohol, polyvinyl butyral, polyurethane, saturated polyester, unsaturated polyester,
Epoxy resins, phenolic resins, polycarbonates, polyamides and the like are mentioned. The thickness of the intermediate layer varies depending on the application, but is preferably about 0.1 to 2 μm. Below this, the protection effect decreases, and above this, the thermal sensitivity decreases. It is also possible to provide a low-refractive-index layer such as air between the heat-sensitive layer and the support or between the heat-sensitive layer and the coloring layer or the light-reflecting layer to improve the contrast.

Table 2 shows the analysis results (number-average molecular weight Mn, weight-average molecular weight Mw) of the resins used as individual resin base materials. Here, Mw / Mn is the degree of polydispersity and represents the width of the molecular weight distribution. When the polydispersity is 1, it is composed of a single molecular weight, and when it is larger than 1, it is composed of various molecular weights. Actually, the polydispersity is in the range of 1.5 to 3.0 as shown in Table 2. The average degree of polymerization (X) was calculated from the number average molecular weight Mn by the above-described calculation method, and is shown in Table 2. In addition, resin 1
To 22 are preferable resins as the resin base material satisfying the above formula (1). FIG. 2 shows the relationship between the average polymerization degree (X) and the vinyl chloride unit content. Specific measurement conditions are shown below. (1) Pretreatment THF was added to the sample to make it a concentration of about 0.2 (wt / vol%), and the solution was filtered through a 0.45 μm fluoropore filter to obtain a sample liquid. (2) GPC measurement conditions [Apparatus] Waters liquid chromatograph SIC lab chart 180 [Column] Shodex K-80M [Sample amount] 80 µl [Eluent] THF [Flow amount] 1.0 ml / min [Detector] RI (differential refractometer) (3) Calibration A molecular weight calibration curve based on polystyrene was used.

[0045]

[Table 2- (1)]

[Table 2- (2)]

[0046]

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 here are on a weight basis.

Example 1 r-Fe ₂ O ₃ 10 parts Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 10 parts (UCC: VAGH) isocyanate 2 parts (Nihon Polyurethane Co., Ltd.) on about 188 μm thick white PET A liquid consisting of 40 parts of methyl ethyl ketone and 40 parts of toluene was applied with a wire bar and dried by heating to form a magnetic recording layer having a thickness of about 10 μm. A solution consisting of 10 parts of a special acrylic ultraviolet curing resin (4 parts of Unidec C7-164, 49% butyl acetate solution manufactured by Dainippon Ink and Chemicals, Inc.) and toluene was coated with a wire bar and dried by heating to 80 W.
UV light for 5 seconds with a UV lamp of about 1 / cm.
A smooth layer having a thickness of 5 μm was provided. Al on it is about 400 約
Vacuum evaporation was performed so as to be thick, and a light reflecting layer was provided. Further, 10 parts of a vinyl chloride-vinyl acetate-phosphate ester copolymer (manufactured by Denki Kagaku Kogyo Co., Ltd .: Denka Vinyl # 1000P) H. A solution consisting of 90 parts of F (tetrahydrofuran) was applied and dried by heating to form an adhesive layer having a thickness of about 0.5 μm. Further, 1,4 butanediol dilaurate 5 parts Eicosane diacid 5 parts Diisodecyl phthalate 3 parts Vinyl chloride-vinyl acetate copolymer 39 parts (Kanebuchi Chemical Co., Ltd .: 20-1621 80% vinyl chloride, 20% vinyl acetate, degree of polymerization 3000) H. A solution consisting of 100 parts of F (tetrahydrofuran) and 65 parts of toluene was applied and dried by heating to form a thermosensitive layer (reversible thermosensitive recording layer) having a thickness of about 5 μm. Furthermore, a solution consisting of 10 parts of a 75% bityl acetate solution of a urethane acrylate-based UV-curable resin (manufactured by Dainippon Ink and Chemicals, UNIDEC C7-157) is coated with a isopropyl alcohol 10 parts by a wire bar, and heated and dried. , 8
The composition was cured with an ultraviolet lamp of 0 W / cm, and a protective layer having a thickness of about 2 μm was provided to prepare a reversible thermosensitive recording material.

Example 2 A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that 1,6 hexanediol dilaurate was used instead of 1,4 butanediol dilaurate constituting the heat-sensitive layer.

Example 3 A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that 1,4 butanediol distearate was used instead of 1,4 butanediol distearate constituting the heat sensitive layer. did.

Example 4 A reversible thermosensitive recording material was prepared in the same manner as in Example 1, except that 1,6 hexanediol distearate was used in place of 1,4 butanediol dilaurate constituting the heat-sensitive layer. did.

Example 5 In Example 1, 1,4-butanediol dilaurate 2.5 parts Stearic acid 2.5 parts Eicosane diacid 5 parts Diisodecyl phthalate 3 parts Vinyl chloride-vinyl acetate copolymer 39 parts (Kanebuchi Chemical Industry Co., Ltd .: 20-1621 80% vinyl chloride, 20% vinyl acetate, degree of polymerization 3000) H. A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that 100 parts of F (tetrahydrofuran) and 65 parts of toluene were used.

Example 6 A reversible thermosensitive recording material was prepared in the same manner as in Example 5, except that 1,6-hexanediol laurate was used instead of 1,4-butanediol dilaurate constituting the heat-sensitive layer. .

Example 7 A reversible thermosensitive recording material was prepared in the same manner as in Example 5 except that 1,4-butanediol disularate was used instead of 1,4-butanediol dilaurate constituting the heat-sensitive layer. did.

Example 8 A reversible thermosensitive recording material was prepared in the same manner as in Example 5 except that 1,6 hexanediol distearate was used instead of 1,4 butanediol dilaurate constituting the heat-sensitive layer in Example 5. did.

Comparative Example 1 A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that palmitic acid was used instead of 1,4-butanediol dilaurate constituting the heat-sensitive layer.

Comparative Example 2 A reversible thermosensitive recording material was prepared in the same manner as in Example 5 except that palmitic acid was used instead of 1,4-butanediol dilaurate constituting the heat-sensitive layer.

Example 9 A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that 1,4-butanediol dilaurate and eicosane diacid constituting the heat-sensitive layer were changed to 1,4-butanediol distearate. It was created.

Example 10 A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that 1,4 butanediol dilaurate and eicosane diacid constituting the heat sensitive layer were changed to 1,6 hexanediol distearate. It was created.

Comparative Example 3 A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except that 1,4-butanediol dilaurate and eicosane diacid constituting the heat-sensitive layer were changed to stearic acid.

The reversible thermosensitive recording materials of Examples and Comparative Examples thus obtained were subjected to a repeated durability test, an initial erasability test for image erasure, and an erasure test with time as follows. First, in the repetition durability test, a thermal head printing test device manufactured by Yashiro Electric Co., Ltd. was used as a thermal recording printing device.
Using a dot / mm thermal head, pulse width 1 ms
c, An opaque image was formed under the conditions of an applied voltage of 18.5 V, and a durability test was repeatedly performed under the same direction until the opaque image was formed 40 times in total. Further, regarding the cloudiness image density in the repetitive durability test, the cloudiness densities at the first and forty times were measured with a Macbeth reflection densitometer (RD914), and 1
The Δ value of the cloudiness density value at the 40th and 40th tests, and the initial erasability in image erasing and the erasure over time, were carried out in Examples 1 to 8 and Comparative Examples 1 and 2 as follows. The same apparatus as described above was used as the thermal recording and printing apparatus, the image forming voltage was also set under the same conditions as above, and the image erasing voltage was set to the optimum erasing voltage (the voltage at which the erasing density value becomes maximum). . Then, the erasing density at the time of erasing immediately after the image formation is defined as the initial erasing density.
Table 3 shows the erasure densities at the time of erasing at the same initial erasing voltage after storage for 24 hours as the erasure densities over time, and the difference (Δ value) from the background density (transparent state).

[0061]

[Table 3]

[0062]

Example according to the present invention and is apparent from the description of the comparative example, the reversible thermosensitive recording material of the present invention as the organic low-molecular material of the heat-sensitive recording layer, in melting point 35 ° C. or higher, the number 4 or more carbon
By using a difatty acid ester of an alkanediol , the durability against repetition can be improved, and the initial erasability and the erasure over time in erasing a thermal head image can be improved.

[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.

FIG. 2 is a view showing a preferable range as a resin base material of the present invention in a relationship between a polymerization degree (X) and a vinyl chloride unit content (Y) of the resin base material.

[Explanation of symbols]

…: Very good initial turbidity and very good repetition durability △: good initial turbidity and very good repetition durability ▽: very good initial turbidity And good repetition durability ▲: Initial turbidity is poor ▼: Initial turbidity is very good and repetition durability is poor

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-169807 (JP, A) JP-A-5-169809 (JP, A) JP-A-63-104879 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) B41M 5/36

Claims (5)

(57) [Claims] 1. A reversible sensor comprising, on a support, a heat-sensitive layer having a resin base material and an organic low-molecular substance dispersed in the resin base material as main components and having a transparency reversibly changing depending on temperature. In a thermal recording material, the organic low-molecular substance has a carbon number of 4 or less.
In di-fatty acid esters of alkanediols above, 35 ° C. or more
A reversible thermosensitive recording material characterized by using at least one kind or two or more kinds having the above melting point . 2. The method according to claim 1, wherein the organic low-molecular substance is an alkane
All difatty acid esters and their melting points and 10
The reversible thermosensitive recording material according to claim 1 Symbol mounting, characterized in that ℃ is a mixture of low-molecular organic material having the above different melting points. 3. The organic low molecular weight substance used by mixing with the difatty acid ester of alkanediol is aliphatic monocarboxylic acid, aliphatic dicarboxylic acid, thiodipropionic acid, fatty acid ester, ketone having higher alkyl group, 3. The reversible thermosensitive recording material according to claim 2 , wherein the thermoreversible recording material is at least one selected from semicarbazones derived from ketones having an alkyl group and α-phosphono fatty acids. 4. A reversible sensor comprising, on a support, a heat-sensitive layer having a resin base material and an organic low-molecular substance dispersed in the resin base material as main components, and having a transparency reversibly changing depending on temperature. In the thermal recording material, a vinyl chloride polymer or a vinyl chloride copolymer is used as the resin base material,
Vinyl chloride unit content (Y weight%) and average degree of polymerization (X)
Has a value in a range satisfying a relationship represented by the following equation (Equation 1). [Expression 1] -0.68 logX + 3.794 ≤ logY ≤ -0.215 logX + 2.66 5. The reversible thermosensitive recording material according to claim 4, wherein said average degree of polymerization (X) is 500 or more.