JPH0752555A - Reversible thermal recording material - Google Patents

Abstract

PURPOSE:To obtain a reversible thermal recording material having a good repetition durability and a superior image erasablity even if an image is repeatedly formed and erased using a heating means, such as a thermal head, simultaneously applying heat and pressure. CONSTITUTION:In a reversible thermal recording material provided with a heat-sensitive layer mainly composed of a resin matrix and an organic low- molecular substance dispersed in the resin matrix and reversibly changed in transparency dependently on a temperature on a substrate, at least one or more kinds of polyhydric alcohol difatty arid ester (preferably having a melting point of 35 deg.C or higher) are used as the organic low-molecular substance.

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 reversible transparency change with temperature of a thermosensitive layer.

[0002]

2. Description of the Related Art In recent years, a reversible thermosensitive recording material having a thermosensitive layer capable of temporarily forming an image and erasing the image when it is no longer needed and having a thermosensitive layer whose transparency reversibly changes depending on temperature has been attracting attention. Has been done. As a typical one,
A reversible thermosensitive recording material 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 is known (Japanese Patent Laid-Open No. 54-119377).
No. 55-154198). However, these conventional reversible thermosensitive recording materials have a drawback that the width of the temperature range showing light transmission / transparency is as narrow as 2 to 4 ° C., and images are formed by utilizing light transmission / transparency or light shielding / cloudiness. There was a difficulty in controlling the temperature during formation.

In consideration of this point, JP-A-63-3937
Nos. 8 and 63-130380 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 drawbacks that the repeated durability due to the heating element of the thermal head is inferior and the image erasability (transparency) when heat is applied for a short time by the thermal head is poor. In addition, after the image is stored for a long time, the erasability of the thermosensitive recording layer with time greatly changes from the preset initial erasing characteristic, and if the image is erased under the erasing condition corresponding to the initial erasing characteristic, However, there is a drawback that the erasing density value with time is lower than the initial erasing density value, that is, the erasability after storage of the image is poor.

[0004]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned drawbacks and provides a reversible thermosensitive recording material in which the transparent state and the cloudy state reversibly change depending on the temperature, and has good repeated durability. Therefore, the initial image erasability by the thermal head can be erased to near the background density (transparent state), and even after storing the image for a long time, the image erasability over time is significantly different from the initial image erasability. The object is to provide a reversible thermosensitive recording material which does not fluctuate.

[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. In a reversible thermosensitive recording material provided with a thermosensitive layer that changes to, there is provided a reversible thermosensitive recording material characterized by using at least one polyhydric alcohol difatty acid ester as the organic low molecular weight substance, In particular, the polyhydric alcohol difatty acid ester has a melting point of 35 ° C. or higher, and the organic low molecular weight substance has a melting point of 1 or more with the polyhydric alcohol difatty acid ester and the ester.
It is a mixture of organic low molecular weight substances having different melting points of 0 ° C. or more, and the organic low molecular weight substance used by mixing with a polyhydric alcohol difatty acid ester is an aliphatic monocarboxylic acid, an aliphatic dicarboxylic acid, or thiodipropion. Acids, fatty acid esters, ketones having higher alkyl groups, semicarbazones derived from ketones having higher alkyl groups, α
-The above reversible thermosensitive recording material is provided, which is characterized in that it is at least one selected from phosphono fatty acids. 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 reversibly changes depending on temperature. In, a vinyl chloride polymer or a vinyl chloride copolymer is used as the resin base material, and
Vinyl chloride unit content (Y% by weight) and average degree of polymerization (X)
The above-mentioned reversible thermosensitive recording material is provided, wherein and have a value in a range satisfying the relationship represented by the following formula (Equation 1):

[Equation 1] -0.68logX + 3.794 ≤ logY ≤ -0.215log
X + 2.66 In particular, the reversible thermosensitive recording material is provided, wherein the average degree of polymerization (X) is 500 or more.

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

Examples of the polyhydric alcohol difatty acid ester of an organic low molecular weight substance used in the present invention include those represented by the following general formula. CH ₃ (CH ₂ ) m- ₂ COO (CH ₂ ) nOOC (CH ₂ ) m- ₂ CH ₃ (In the formula, n is 2 to 40, preferably 3 to 30, and more preferably 4 to 22 is an integer. M is an integer of 2 to 40, preferably 3 to 30, and more preferably 4 to 22.)
Specific examples include the following. 1,2 ethanediol dialkanoic acid ester 1,3 propanediol dialkanoic acid ester 1.4 butanediol dialkanoic acid ester 1.5 pentanediol dialkanoic acid ester 1,6 hexanediol dialkanoic acid ester 1,7 heptanediol Dialkanate 1,8 Octanediol dialkanate 1,9 Nonanediol dialkanate 1,10 Decanediol dialkanate 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, 7 Heptadecanediol dialkanate 1,18 Octadecanediol dialkanate 1,19 Nonadecanediol dialkanate 1,20 Icosandiol dialkanate 1,21 Henicosandiol dialkanate 1, 22 Docosanediol dialkanoic acid ester 1,23 Tricosanediol dialkanoic acid ester 1,24 Tetracosanediol dialkanoic acid ester 1,25 Pentacosanediol dialkanoic acid ester 1,26 Hexacosanediol dialkanoic acid ester 1,2 27 Heptacosandiol dialkanoic acid ester 1,28 Octacosandiol dialkanoic acid ester 1,29 Nonacosandiol dialkanoic acid ester 1,30 Triacontanediol dialkanoic acid ester 1 , 31 Hentriacontanediol dialkanate 1,32 Dotriacontanediol dialkanate 1,33 Tritriacontanediol dialkanate 1,34 Tetratriacontanediol dialkanate

The alcohol difatty acid ester having a temperature of 35 ° C. or higher includes the following. As the polyhydric alcohol, 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 heptadecane diol, 1,18 octadecane diol, 1,19 nonadecane diol, 1,20 icosane diol, 1,21 hen icosane diol, 1,2
2 docosanediol, 1,23 tricosanediol,
1,24 tetracosane diol, 1,25 pentacosane diol, 1,26 hexacosane diol, 1,27 heptacosane diol, 1,28 octacosane diol,
1,29 Nonacosandiol, 1,30 Triacontanediol, 1,31 Hentriacontanediol, 1,
Dilaurate using a diol selected from 32 dotriacontanediol, 1,33 tritriacontanediol, and 1,34 tetratriacontanediol,
Ditridecate, dimyristate, dipentadecate,
Examples thereof include dipalmitate, dimalgallate, distearate, dinonadecate, diarachicade, dihen icosate and dibehenate.

The polyhydric alcohol difatty acid ester is characterized in that it has a lower melting point than the fatty acid when compared at the same carbon number, and conversely has a higher carbon number than the fatty acid when compared at the same melting point. The repeated durability of printing with the thermal head is considered to be due to the compatibility of the resin and the organic low molecular weight substance during heating,
It is considered that the compatibility between the resin and the organic low molecular weight substance decreases as the carbon number of the organic low molecular weight substance increases. Further, the white turbidity also tends to increase in proportion to the number of carbon atoms. Therefore, by using a polyhydric alcohol difatty acid ester, as compared with a fatty acid in a reversible thermosensitive recording material having the same clearing temperature (which is near the melting point), Repeated durability seems to be improved.

Further, since the polyhydric alcohol difatty acid ester has a low melting point and has the same characteristics as the fatty acid having a higher melting point in terms of white turbidity and repeated durability, it is different from the organic low molecular weight substances having a higher melting point. When mixed and widened the clearing temperature range, the clearing temperature range can be expanded while having the same white turbidity as when a fatty acid is used and performance such as repeated durability. 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 increased image erasing margin, there is no practical problem and erasing with a thermal head is possible. Will also be possible.

As the organic low molecular weight substance, the polyhydric alcohol difatty acid ester may be mixed with an organic low molecular weight substance having a melting point different by 10 ° C. or more. Examples of the organic low molecular weight substance used by mixing with the polyhydric alcohol difatty acid ester include an aliphatic monocarboxylic acid, an aliphatic dicarboxylic acid, thiodipropionic acid, a fatty acid ester, a ketone having a higher alkyl group, and a higher alkyl group. Examples thereof include semicarbazones derived from ketones and α-phosphono fatty acids.

Specific examples of the aliphatic monocarboxylic acid used in the present invention include, for example, palmitic acid, margaric acid,
Stearic acid, nonadecyl acid, arachidic acid, heneicosanoic acid, hepbic acid, tricosanoic acid, tetracosanoic acid, pentacosanoic acid, hexacosanoic acid, peptacosanoic acid, octacosanoic acid, nonacosanoic acid, triacontanoic acid, hentriacontanoic acid, dotriacontanoic acid, Examples thereof include tritriacontanoic acid, tetratriacontanoic acid, pentatriacontanoic acid, hexatriacontanoic acid, heptatriacontanoic acid, octatriacontanoic acid, and hexatetracontanoic acid.

Specific examples of the aliphatic dicarboxylic acid used in the present invention include succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid and tridecanedioic acid. acid,
Examples thereof include tetradecanedioic acid, pentadecanedioic acid, hexadecanedioic acid, heptadecanedioic acid, octadecanedioic acid, nonadecanedioic acid, eicosanedioic acid, heneicosanedioic acid, and docosanedioic acid.

Specific examples of the fatty acid ester used in the present invention include behenyl laurate docosyl palmitate dodecyl palmitate tetradecyl palmitate pentadecyl palmitate hexadecyl palmitate octadecyl palmitate triaconyl palmitate octadecyl palmitate docosyl stearate stearate. Propyl isopropyl stearate Butyl stearate Amyl stearate Heptyl stearate Octyl stearate Octadecyl stearate Hexadecyl stearate Heptadecyl stearate Octadecyl stearate Dodecyl stearate Hexacosyl stearate Triaconyl stearate Dodecyl behenate Octadecyl behenate Dodecyl lignoceri Tetracosyl acid acid myricin melicinate and the like can be mentioned.

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 primed ring. The total number of carbon atoms in 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. Examples of ketones and semicarbazones used in the present invention include 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. V. Kaurer et al. Ak. Oil Che
Fatty acids were converted to Hell-Volhard-Zel according to the method of kist's Soc, 41, 205 (1964).
Bromination by inskin reaction to α-brominated acid bromide, then ethanol was added to obtain α-bromo fatty acid ester, which was further reacted with triethyl phosphite by heating to obtain α-phosphono fatty acid ester, which was hydrolyzed with concentrated hydrochloric acid. It can be obtained by recrystallizing the product 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 ℃) α-phosphonomyristylic acid CH ₃ (CH ₂ ) ₁₁ CH [PO (OH) ₂ ] COOH (mp 132-3 ℃, 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 ℃). It should be noted that it has two mps (melting points) other than α-phosphonoberargonic acid.

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. Such resins include polyvinyl chloride, vinyl chloride copolymer, polyvinyl chloride;
Vinyl chloride copolymers such as vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinyl acetate-vinyl alcohol copolymers, vinyl chloride-vinyl acetate-maleic acid copolymers, vinyl chloride-acrylate copolymers; poly Vinylidene chloride, vinylidene chloride-vinyl chloride copolymer, vinylidene chloride-acrylonitrile copolymer and other vinylidene chloride-based copolymers; polyester; polyamide; polyacrylate or polymethacrylate or acrylate-methacrylate copolymer; silicone resin, etc. To be Needless to say, 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% by weight) and the average degree of polymerization (X) is represented by the above formula ( Those having a value in the range satisfying the expression 1) are preferable (FIG. 2, hatched portions and grid-like portions). here,
The formula has a low average degree of polymerization (X) and a low vinyl chloride unit content (Y% by weight), and a high average degree of polymerization (X) and a salt or vinyl unit content (Y% by weight). When the degree of polymerization (X) is low, the vinyl chloride unit content (Y wt%) is high, and as the degree of polymerization (X) is high, the vinyl chloride unit content (Y wt%) is high. It is shown that it is preferable that it becomes low. In the resin base material of the present invention, when the average degree of polymerization (X) is high and the proportion of vinyl chloride unit content (Y% by weight) is high,
A value within the range of the following formula (Equation 2) (upper right of FIG. 2) is more preferable,

[Formula 2] logY ≤ -0.215logX + 2.636 When the average degree of polymerization (X) is low and the proportion of vinyl chloride unit content (Y wt%) is low, the average degree of polymerization (X) is 600 or more. A value within the range of the following formula (Equation 3) (lower left of FIG. 2) is more preferable.

## EQU00003 ## logY.gtoreq.-0.215logX + 2.49 Note that the preferable range is shown in a lattice form in FIG.
Further, the average degree of polymerization (X) of the resin base material of the present invention is preferably 500 or more, more preferably 600 or more, 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 matrix improves the durability against repeated image formation and erasure by heating means such as a thermal head, but these are not clear. When the average degree of polymerization of the polymer is high or the proportion of vinyl chloride units is high, the melt viscosity when heated is high, and image formation is performed using a heating means such as a thermal head that simultaneously applies heat and pressure. Even after repeated erasing, there is little deformation of the resin base material around the fine particles of the organic low molecular weight substance,
Because the organic low-molecular substance is maintained as fine particles,
It is estimated that the durability will be improved.

Further, if the average degree of polymerization and the vinyl chloride ratio are too high, the solubility in the solvent is lowered and the viscosity of the solution becomes high, and the organic low molecular weight substance and the resin base material are dissolved in the solvent and then dried. It is thought that the white turbidity is lowered because it is difficult to separate and the organic low molecular weight substance particles are difficult to form. The logarithm (logY) of the vinyl chloride unit (Y) of the resin base material is (-0.68logX + 3.794: X).
If it is smaller than (average degree of polymerization), the durability against repeated image formation and erasure is reduced, and (logY) is (-0.21).
5logX + 2.66), the initial white turbidity decreases.

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

Specific examples of the polymerization method will be described below. First, in the suspension polymerization method, a vinyl chloride monomer is dispersed and suspended in minute liquid droplets in a water phase containing a small amount of a hydrophilic protective colloid dispersant by vigorous shear agitation to form a monomer-soluble organic peroxide. It is used as a polymerization initiator to carry out radical polymerization in a monomer droplet to obtain a polymer slurry having a particle size of several tens to several hundreds μ, which is filtered, washed, dried, and sieved to obtain a product. Suspension polymerization has few impurities, it is easy to control the reaction temperature, the resin quality is excellent, the equipment cost and production cost are low, the production control is easy, and it is easy to maintain the quality uniformity. Has become the mainstream of the PVC resin manufacturing method.

Next, the emulsion polymerization method is emulsified and dispersed in an aqueous phase with the aid of an anionic surfactant, and a water-soluble polymerization initiator such as persulfate is used to obtain a particle size of 0.1 to several. Take a polymer latex of μ, salt out, filter, wash, dry,
The product is obtained by grinding or by spray-drying the latex directly. Emulsion polymer is a fine powder that is difficult to handle, and contains a large amount of 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, a soluble initiator is added to a monomer to carry out radical polymerization, the polymerization reaction is stopped at an appropriate reaction rate to recover unreacted monomer, and the obtained precipitated polymer is pulverized and classified to obtain a product. Since it does not contain a dispersant or emulsifier, it has high polymer purity, and since it does not use water, it does not require filtration or drying, and is expected to have advantages such as simple equipment and low production costs. However, industrialization was delayed due to difficulty in removing heat of reaction and controlling particle shape, but recently, two-stage bulk polymerization method of Pescine Saint-Gobain was developed due to improvement of reactor.

The homogeneous solution polymerization method uses an expensive organic solvent and requires solvent recovery, so that the production cost is high, and it is difficult to obtain a polymer having a high degree of polymerization due to the chain transfer action of the solvent. There is a drawback that it becomes small and it is difficult to increase the reaction yield.

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

As such a vinyl chloride copolymer,
Vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinyl acetate-vinyl alcohol copolymers, vinyl chloride-vinyl acetate-maleic acid copolymers, vinyl chloride-acrylate copolymers, and other vinyl chloride-based copolymers Can be mentioned. These may be used alone or in admixture of two or more.

The degree of polymerization (molecular weight) of this resin base material is GPC.
It is measured by (gel permeation chromatography). This GPC
(Gel permeation chromatography) means that when a sample solution of resin dissolved in a solvent is injected into a column packed with a particulate gel having pores, a sample with a molecular size larger than the gel pore enters the pores. Therefore, the time that the molecules that pass through the outside of the gel and enter the pores stay in the gel pores differs depending on their size. 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 molecular weight to the low molecular weight. A method of measuring the difference in refractive index (differential refractive index) between the liquid that elutes and the solvent in which the resin is dissolved, and calculating the molecular weight distribution and average molecular weight of the measurement sample from the calibration curve of the standard sample whose molecular weight is known. Is.

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

[Equation 4] Here, VD and VE are not specific ones, and in the case of a vinyl chloride-vinyl acetate copolymer, VD becomes vinyl acetate and VE does not exist. Further, here, the calculation formulas up to the terpolymer of vinyl chloride and the other two types are shown.
The calculation is performed in the same manner in the case of a copolymer of two or more species. 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
Then, 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 weight ratio of the organic low molecular weight substance to the resin base material in the heat sensitive layer is preferably about 2: 1 to 1:16, and more preferably 1: 2 to 1: 8. If the ratio of the resin base material is below this range, it will be difficult to form a film in which the organic low molecular weight material is retained in the resin base material. Becomes difficult.

The reversible thermosensitive recording material of the present invention utilizes the transparency change (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, (i) in the case of transparency, the particles of the organic low-molecular substance dispersed in the resin matrix are composed of large particles of the organic low-molecular substance, and the light incident from one side is not scattered and is opposite. It appears to be transparent because it is transmitted to the side, and (ii) in the case of turbidity, the particles of the organic low-molecular substance are composed of polycrystals of fine crystals of the organic low-molecular 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 crystal of the organic low molecular weight substance particles, and is scattered and thus appears white.

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
It is cloudy and opaque at room temperature below ₀ . This is the temperature T ₂
When it is heated to ₀ , it becomes transparent, and even if it is returned to room temperature below T _{0 in} this state, it remains transparent. This is the temperature T ₂ to T ₀
It is considered that the organic low molecular weight substance is in a semi-molten state until the following and the crystal grows from a polycrystal to a single crystal.
Upon further heating to T ₃ or more temperature becomes translucent state intermediate between the maximum transparency and the maximum opacity. Next, when this temperature is lowered, the first cloudy opaque state is restored without taking the transparent state again. It is considered that this is because when the organic low molecular weight substance is melted at a temperature of T ₃ or higher, the polycrystal is deposited 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 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, both opaque and transparent forms at room temperature and intermediate forms thereof can be obtained.

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 body, it is possible to form an image of the color of the coloring sheet on a white background or a white image on the background of the color of the coloring sheet. Further, when projected by an OHP (overhead projector) or the like, the cloudy portion becomes a dark portion, and the transparency becomes a light portion on the screen because light is transmitted therethrough.

To prepare the reversible thermosensitive recording material used in the present invention, it can be formed as a film on a supporting member or formed into a sheet by the following method, for example. 1) A method in which a resin base material and an organic low molecular weight substance are dissolved in a solvent, which is applied onto a support member, and the solvent is evaporated to form a film or sheet. 2) The resin base material is dissolved in a solvent that dissolves only the resin base material, and the organic low molecular weight substance is pulverized or dispersed therein by various methods, and this is applied onto a support member, and the solvent is evaporated to form a film. Or the method of making 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 this is molded into a film or sheet and cooled. As the solvent for forming the heat-sensitive layer or the heat-sensitive recording material, various selections can be made according to 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, benzene and the like. The organic low molecular weight substance is precipitated as fine particles and exists in a dispersed state in the heat-sensitive layer obtained not only when the dispersion liquid is used but also when the solution is used.

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-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 azelaate
-Ethylhexyl, dibutyl sebacate, di-2-ethylhexyl sebacate, diethylene glycol dibenzoate, triethylene glycol di-2-ethyl butyrate, methyl acetylricinoleate, butyl acetylricinoleate, butylphthalylbutyl glycolate, acetylcitric acid Tributyl.

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 adducts 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 Ca, Ba or Mg salt of phosphoric acid mono- or di-ester; low degree of sulfated oil; poly long chain alkyl acrylate; acrylic orgomer; poly long chain alkyl methacrylate; long chain alkyl methacrylate to amine-containing mono Chromatography copolymers; styrene-maleic anhydride copolymer; olefin-maleic anhydride copolymer.

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

The resin used as the resin base material may have weak adhesion to the support when it is applied on a support such as a plastic film, glass or metal and dried to form a laminated heat-sensitive layer. It is also possible to provide an adhesive layer between the heat sensitive layer and the heat sensitive layer so that the heat sensitive layer does not come off. The resin of 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 thermosensitive recording layer, and examples thereof include vinyl chloride resin, polyester resin,
An acrylic resin, a polyamide resin, etc. are mentioned. In particular, the adhesiveness is poor on a metal or a metal thin film, and a copolymer containing vinyl chloride and a phosphoric acid ester as a main component is preferably used as an adhesive layer material. The thickness of the adhesive layer is 0.1
It is preferably about 5 μm, more preferably about 0.3 to 2 μm.

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 (as described in JP-A No. 64-14079). It is also possible to create a card that combines the magnetic recording layer and the reversible thermosensitive layer. In particular, when a reversible heat-sensitive layer is provided on the magnetic recording layer, a smoothing layer containing a resin as a main component is provided to make the surface slippery, a light reflecting layer is provided thereon, and further on that. In some cases, a heat-sensitive layer may be provided via an adhesive layer (Jpn. Pat. Appln. KOKAI No. 2-3876).

Further, a protective layer may be provided on the heat-sensitive layer of the present invention in order to prevent the transparency of the transparent portion from being lowered by the deformation of the surface due to the heat and pressure of the heating means such as a thermal head by the writing method. good. A protective layer (thickness: 0.
1 to 5 μm), silicone rubber, silicone resin (described in JP-A-63-221087),
Polysiloxane graft polymer (JP-A-63-317)
No. 385), an ultraviolet curable resin, an electron beam curable resin (described in JP-A-2-566), 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. Examples of the solvent that hardly dissolves the resin and the organic low molecular weight substance in the heat-sensitive layer include n-hexane, methyl alcohol, ethyl alcohol, isopropyl alcohol and the like, and the alcohol solvent is particularly preferable from the viewpoint of cost.

Further, an intermediate layer may be provided between the protective layer and the reversible recording material in order to protect the reversible recording material from the solvent of the protective layer forming liquid, the monomer component and the like (JP-A-1-133781). issue). As the material for 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,
Examples thereof include epoxy resin, phenol resin, polycarbonate, polyamide and the like. The thickness of the intermediate layer varies depending on the use, but is preferably about 0.1 to 2 μm. If it is less than this, the protective effect is lowered, and if it is more than this, the thermal sensitivity is lowered. It is also possible to improve contrast by providing 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.

Further, 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 polydispersity and represents the width of the molecular weight distribution. When the polydispersity is 1, it means that the polymer 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. Further, 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. Resin 1
Nos. 22 to 22 are preferable resins as the resin base material satisfying the above formula 1. The relationship between the average degree of polymerization (X) and the vinyl chloride unit content is shown in FIG. The specific measurement conditions are shown below. (1) Pretreatment THF is added to the sample to a concentration of about 0.2 (wt / vol%), which is filtered with a 0.45 μm fluoropore filter to obtain a sample solution. (2) GPC measurement conditions [Device] 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 polystyrene standard molecular weight calibration curve was used.

[0045]

[Table 2- (1)]

[Table 2- (2)]

[0046]

EXAMPLES The present invention will be described in more detail by way of examples, which should not be construed as limiting the invention thereto. In addition, both parts and% are based on weight.

Example 1 r-Fe ₂ O ₃ 10 parts Vinyl chloride-vinyl acetate-vinyl alcohol copolymer 10 parts (UCC: VAGH) Isocyanate 2 parts (Nippon Polyurethane Company) on white PET having a thickness of about 188 μm. Manufactured by Coronate L, 50% toluene solution) 40 parts of methyl ethyl ketone A solution of 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 special acrylic UV curable resin 10 parts (Dainippon Ink and Chemicals Co., Ltd., Unidec C7-164, 49% butyl acetate solution) toluene 4 parts was applied with a wire bar and heated and dried to 80 W.
Approximately 1.
A 5 μm thick smooth layer was provided. Al about 400Å on it
It was vacuum-deposited so as to have a thickness, and a light reflection layer was provided. Further thereon, 10 parts of vinyl chloride-vinyl acetate-phosphate ester copolymer (Denka Vinyl # 1000P manufactured by Denki Kagaku Kogyo Co., Ltd.) H. A solution of 90 parts of F (tetrahydrofuran) was applied and heated and dried to form an adhesive layer having a thickness of about 0.5 μm. Furthermore, 1,4 butanediol dilaurate 5 parts Eicosane diacid 5 parts Diisodecyl phthalate 3 parts Vinyl chloride-vinyl acetate copolymer 39 parts (Kanebuchi Chemical Industry Co., Ltd .: 20-1621 vinyl chloride 80%, Vinyl acetate 20%, degree of polymerization 3000) Prototype T.P. H. A solution of 100 parts of F (tetrahydrofuran) and 65 parts of toluene was applied and dried by heating to provide a heat sensitive layer (reversible heat sensitive recording layer) having a thickness of about 5 μm. Furthermore, a solution of urethane acrylate-based UV-curable resin 75% bityl acetate solution 10 parts (Dainippon Ink and Chemicals, Unidec C7-157) isopropyl alcohol 10 parts was applied with a wire bar, and after heating and drying. , 8
A reversible thermosensitive recording material was prepared by curing with a 0 W / cm ultraviolet lamp and providing a protective layer having a thickness of about 2 μm.

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 thermosensitive 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 dilaurate constituting the thermosensitive 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 instead of 1,4 butanediol dilaurate constituting the thermosensitive layer. did.

Example 5 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 Combined 39 parts (Kanefuchi Chemical Co., Ltd .: 20-1621 vinyl chloride 80%, vinyl acetate 20%, polymerization degree 3000) Trial product T.I. 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 thermosensitive layer. .

Example 7 A reversible thermosensitive recording material was prepared in the same manner as in Example 5 except that 1,4 butanediol dislaurate was used instead of 1,4 butanediol dilaurate which constitutes the thermosensitive 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 thermosensitive layer. 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 thermosensitive 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 in place of 1,4 butanediol dilaurate constituting the thermosensitive 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 thermosensitive 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 forming the thermosensitive layer were replaced with 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 thermosensitive 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 a time-erasability test as follows. First, in the repeated durability test, a thermal head printing test device manufactured by Yashiro Denki Co., Ltd. was used as a thermal recording printing device, and Ricoh 8 Co., Ltd. was used as the thermal head.
1mse pulse width using dot / mm thermal head
The cloudiness image was formed under the conditions of c and applied voltage of 18.5 V, and the durability test was repeated under the same conditions until the cloudiness image formation reached 40 times in total. Regarding the cloudiness image density in the repeated durability test, the cloudiness density at the 1st and 40th times was measured with a Macbeth reflection densitometer (RD914).
The Δ values of the white turbidity density values of the second time and the 40th time, the initial erasability in image erasing, and the erasability with time were performed as follows for Examples 1 to 8 and Comparative Examples 1 and 2. The same apparatus as described above was used as the thermal recording / printing apparatus, the image forming voltage was also set under the same conditions as described above, and the image erasing voltage was set to the optimum erasing voltage (voltage at which the erasing density value becomes maximum) to erase the image. . The initial erase density is the erase density when the image is erased immediately after the image is formed.
Table 3 shows the erasure density when erased at the same erasure voltage as the initial one after 24 Hr storage, and the difference (Δ value) from the background density (transparent state).

[0061]

[Table 3]

[0062]

As is clear from the description of Examples and Comparative Examples, the reversible thermosensitive recording material of the present invention has a polyhydric alcohol difatty acid ester as the organic low molecular weight substance of the thermosensitive recording layer.
In particular, by using a polyhydric alcohol difatty acid ester having a melting point of 35 ° C. or higher, the repeating durability can be improved, and the initial erasability and the erasability upon erasing the image of the thermal head can be improved.

[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.

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 white turbidity and very good repeated durability △ …… Good initial white turbidity and very good repeated durability ▽ …… Very good initial white turbidity, And repeat durability is good ▲ …… Initial cloudiness is poor ▼ …… Initial cloudiness is very good and repeat durability is poor

Claims (6)

[Claims] 1. A reversible sensation comprising, on a support, a thermosensitive layer containing a resin base material and an organic low-molecular substance dispersed in the resin base material as a main component, and the transparency of which reversibly changes depending on temperature. A reversible thermosensitive recording material comprising at least one polyhydric alcohol difatty acid ester as the organic low-molecular substance in the thermal recording material. 2. The reversible thermosensitive recording material according to claim 1, wherein the polyhydric alcohol difatty acid ester has a melting point of 35 ° C. or higher. 3. The organic low molecular weight substance is a mixture of the polyhydric alcohol difatty acid ester and an organic low molecular weight substance having a melting point different by 10 ° C. or more from the melting point of the ester. The reversible thermosensitive recording material described. 4. An organic low-molecular substance used in a mixture with a polyhydric alcohol difatty acid ester is an aliphatic monocarboxylic acid,
At least one kind selected from aliphatic dicarboxylic acid, thiodipropionic acid, fatty acid ester, ketone having a higher alkyl group, semicarbazone derived from a ketone having a higher alkyl group, and α-phosphono fatty acid The reversible thermosensitive recording material according to claim 3. 5. A reversible sensation comprising, on a support, a thermosensitive layer comprising a resin base material and an organic low-molecular substance dispersed in the resin base material as a main component, and the 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% by weight) and average degree of polymerization (X)
The reversible thermosensitive recording material according to claim 1, wherein and have a value in a range satisfying the relationship represented by the following formula (Equation 1). [Equation 1] -0.68logX + 3.794 ≤ logY ≤ -0.215log
X + 2.66 6. The reversible thermosensitive recording material according to claim 5, wherein the average degree of polymerization (X) is 500 or more.