JPH06171228A - Reversible thermosensible recording material and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve the repeat-durability together with the transparency and the contrast of an image respectively by a method wherein a phase separation structure under a condition being dispersed in a resin base material is formed for an organic low molecular substance in the thermosensible layer, and the structural cycle of the phase separation is set to be a specified numerical value (mum). CONSTITUTION:For the reversible thermosensible recording material, on the upper surface of a substrate, a thermosensible layer, consisting of an organic low molecular substance the transparency of which reversibly changes depending on the temperature, and a resin base material is arranged. In this case, for the organic low molecular substance, a phase separation structure under a condition being dispersed in the resin base material is formed. Then, the structural cycle of the phase separation in the thermosensible layer is set to be not more than 1.3mum. The structural cycle can be observed by a form that in a cross section of the phase separation structure in which, e.g. a substance A forms a doman in a substance B, the composition of both substances A, B periodically changes. In the meantime, at the time of manufacture, a drying condition of a film which is coated on the substrate is adjusted while the structural cycle is being measured by the light confusion method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible heat-sensitive material for recording and erasing by utilizing reversible change in transparency with temperature of a heat-sensitive layer.

[0002]

2. Description of the Related Art In recent years, reversible heat-sensitive recording materials have been attracting attention because they can form images temporarily and can erase the images when they are no longer needed. As a typical example, the glass transition temperature (Tg) is from 50 to 60 ° C. to 8
A reversible thermosensitive recording material is known in which an organic low molecular weight substance such as a higher fatty acid is dispersed in a resin matrix such as a vinyl chloride-vinyl acetate copolymer having a low glass transition temperature of less than 0 ° C. JP-A-54-119377, JP-A-55-1
54198, JP-A-63-39376, and JP-A-63.
-107584, etc.).

When a heat roller, a hot pen or the like is used as a heating method for image formation and erasing, and only heat is applied without applying much pressure, repeated image formation-
Even if it is erased, there is no problem in durability. However, when pressure is applied using a thermal head or the like and heating is performed at the same time, the resin base material around the organic low molecular weight substance in the heat sensitive layer deforms during repeated image formation and deletion, and the finely dispersed organic low molecular weight substance is deformed. Molecular substance particles gradually become larger in size,
The effect of scattering light is lost (white turbidity decreases),
Finally, there is a drawback that the image and the contrast are deteriorated, and a reversible thermosensitive recording material capable of forming a high-contrast image with sufficient transparency while still having high transparency is obtained. Has not been done.

[0004]

SUMMARY OF THE INVENTION The present invention provides a reversible thermosensitive recording material which solves the above-mentioned drawbacks, has high transparency and high image contrast, and has improved repeated durability, and a method for producing the same. It is intended to be provided.

[0005]

According to the present invention, a reversible thermosensitive material comprising a support and a thermosensitive layer comprising a resin base material and an organic low molecular weight substance whose transparency reversibly changes depending on temperature are provided on the support. In the recording material, the organic low-molecular substance has a phase-separated structure in a state of being dispersed in the resin base material, and the structural period of the phase-separation of the heat-sensitive layer is 1.3 μm or less. A heat-sensitive recording material is provided. Further, a method for producing a reversible thermosensitive recording material, in which a solution in which an organic low molecular weight substance and a resin base material are dissolved is applied to a support, a coating film is formed and then dried to form a thermosensitive layer having a phase separation structure. In the method for producing a reversible thermosensitive recording material described above, the drying condition is adjusted while measuring the structural period of the thermosensitive layer by a light scattering method.

That is, the present inventors have found that in a reversible thermosensitive recording material having a heat sensitive layer composed of an organic low molecular weight substance whose transparency reversibly changes depending on temperature and a resin matrix, the organic low molecular weight substance is When the heat-sensitive layer has a phase-separated structure dispersed in the resin matrix and the structural period of the phase separation of the heat-sensitive layer is 1.3 μm or less, the above object can be achieved, and further, such reversible As a means for obtaining a thermosensitive recording material, a method in which a solution in which an organic low molecular weight substance and a resin base material are dissolved is applied onto a support to form a coating film and then dried is simple. The structural cycle can be controlled by the drying conditions, but the structural cycle is considerably different depending on the drying conditions, so the structural cycle is measured in the process after coating. While dry strip Method of modulating the found to be very effective means for manufacturing the stable structure period, and have completed the present invention.

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 being transparent, the particles of the organic low-molecular substance dispersed in the resin base material are composed of large particles of the organic low-molecular substance, and the light incident from one side is not scattered and is opposite. 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 (which shows the change in transparency due to heat), a thermosensitive layer containing a resin base material and an organic low molecular weight substance dispersed in the resin base material as main components 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 conceivable that the organic low-molecular-weight substance goes through a semi-molten state until the following and the crystal grows from a fine polycrystalline state to a larger single crystalline state. 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 first cloudy opaque state, which is a 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 the opaque material 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 less, 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. .

However, as described above, light scattering and light transmission are utilized depending on whether the recording / erasing of the reversible thermosensitive recording material is a fine polycrystal state or a relatively large single crystal state in the crystalline state of the organic low molecular weight substance. Since it is a process for producing light, crystal growth and its effect for causing light scattering / transmission naturally depend on the phase separation structure of the organic low molecular weight substance and the resin base material.

In describing the state of phase separation, the concept of structural period is important. The structural period can be considered as an amount representing the size of the phase separation structure. For example, in FIG.
In the phase-separated structure in which the substance A forms a spherical domain in the substance B as schematically shown in FIG.
Considering the cross section at the position of the dotted line in (a), FIG.
As shown in, the composition of the substances A and B can be seen in a form that changes periodically. This period Λ is called a structural period. This structural period cannot be captured in any phase-separated structure, and can be captured when the following factors are comprehensively satisfied, and is a meaningful numerical value. (1) The phase-separated structure has regularity with some order and has a characteristic structural period. (2) The volume ratio of substance A and substance B in the structure should not be extremely large or small. (3) Substance A and substance B in the structure are clearly separated to some extent.

In the case of the reversible thermosensitive recording material according to the present invention,
It can be considered that the substance A is an organic low molecular weight substance and the substance B is a resin base material, and these substances in the thermosensitive layer comprehensively satisfy the factors (1), (2) and (3). In this case, the concept of structural period becomes effective. However, the above (1),
It is not clear how much each of the factors (2) and (3) should be satisfied. A light scattering measurement method used for structural analysis of organic polymer compounds is effective as a method of capturing such a structural period. As for the method of measuring light scattering, as schematically shown in FIG. 3A, light is emitted from a light source to a sample and the structural period is calculated from the scattering angle of the transmitted light. The relationship between the scattering angle and the structural period Λ Is given by Expression (1). [Equation 1] Here, λ is the wavelength of the light source [μm], D is the refractive index of the sample [−], and σ is the scattering angle [deg]. Laser light is generally used as a light source for measurement, and He-N
The e-laser is most often used. (1),
When a sample satisfying the conditions of (2) and (3) is applied to the light scattering measurement device, the scattered light exhibits a ring-shaped light intensity distribution as shown in FIG. 3 (a). When the scattered light intensity is plotted against the scattering angle, a curve having an intensity peak value at a certain angle as shown in FIG. 3B is shown. Angle θ at this peak value
The value obtained by substituting m into the equation (1) is the structural period Λm peculiar to the sample.

In the reversible thermosensitive recording material according to the present invention, a specific method for measuring the structural period of the thermosensitive layer by a light scattering measurement method will be described as an example. As a light scattering measuring device, GP-7 (light source He-) manufactured by Optec Co., Ltd.
Ne laser wavelength λ = 0.6328 μm) was used.
The measurement sample needs to have a certain degree of light transmission. Therefore, when the heat-sensitive layer is provided on an opaque support, this support must be removed to form a sample, but this is not the case when it is provided on a transparent support.
Further, the heat-sensitive layer is in the form of a film, and the angle correction in consideration of the difference in refractive index between the sample and air is necessary for calculating the scattering angle. This is because the scattered light further refracts at the interface between the film and the air, as shown schematically in FIG. 4, so that the apparent scattering angle θap becomes smaller than the true scattering angle θ.

Further, since the sample according to the present invention changes to cloudy, transparent and translucent states depending on the temperature, there is a problem in which state the light scattering measurement is performed. Since scattering hardly occurs in the transparent state, the light scattering measurement is performed in the cloudy or semi-transparent state. Although the shape of the scattered light intensity distribution is slightly different in both cases, the angle θ at the intensity peak value
Since m does not change much, it suffices to carry out the measurement in the condition that is easier to measure.

By arranging a coloring sheet on the back surface of such a heat sensitive member, an image of the color of the coloring sheet or a white image of the background of the coloring sheet can be formed on a white background.
Further, when projected by an OHP (overhead projector) or the like, the cloudy portion becomes a dark portion, the transparent portion transmits light and becomes a bright portion on the screen.

In order to form and erase an image using such a reversible thermosensitive recording material, it is necessary to have two thermal heads for image formation and image erasure, or to change the applied energy conditions. Therefore, it is effective to use a thermal head having a single thermal head for image formation and image deletion. In the former case, the cost of the apparatus increases because two thermal heads are required, but if the reversible thermosensitive recording material is passed once with different energy application conditions for each thermal head, image formation and erasure can be performed. Can be done. In the latter case, since the image is formed and erased by one thermal head, the conditions for applying energy to the thermal head at one time when the thermal recording material passes should be adjusted according to the image forming portion and the erasing portion. The operation is complicated, but the operation is complicated, such as changing finely, or erasing the image on the thermal recording material once and then running the thermal recording material again in the opposite direction to form an image under different energy conditions. Therefore, the equipment cost is reduced.

In order to prepare the reversible thermosensitive recording material according to the present invention, generally, a solution in which two components of a resin base material and an organic low molecular weight substance are dissolved is applied onto a support such as a plastic sheet, a glass plate or a metal plate. It may be dried to form.

The structural period of the present invention is 1.3 μm.
The method for producing a heat-sensitive layer having the following phase separation structure can be obtained depending on the solvent concentration of the coating liquid and the drying conditions. That is,
The structural period of the heat-sensitive layer can be controlled depending on the drying conditions, and the stronger the drying strength, that is, the faster the drying, the smaller the structure period of the heat-sensitive layer. However, if the dry strength is simply increased in order to obtain a heat-sensitive layer having a small phase separation structure as in the present invention,
The solvent is boiled by rapid heating and bubbles are generated. As a result, defects such as cissing and pinholes were formed on the film, and a uniform film could not be obtained.

Therefore, it was found that the object of the present invention can be achieved by selecting the solvent concentration and the drying conditions. That is, the weight concentration of the resin base material and the organic low molecular weight substance in the coating liquid is set to 25% or more. Alternatively, 90% or more of the solvent is evaporated within 40 seconds after starting to dry after applying the coating solution. More preferably, it is carried out in combination with both. This is a concentration of 25%
It is considered that when the above-mentioned coating liquid is used, the interaction between the solvent and the resin base material or the organic low-molecular-weight substance becomes strong to make it difficult to boil, and at the same time, the cissing is suppressed by the increase in the viscosity of the coating liquid. However, even after evaporating the solvent by 90% or more, it is necessary to continue drying in order to remove the residual solvent, but unless extremely heated, the strength of the drying here has almost no effect on the structural cycle. .

Further, in order to obtain a thermoreversible thermosensitive recording material of the present invention having a smaller structural period of 1.0 μm or less, for example, the coating liquid is applied twice or more and laminated. The method is effective. This is because under the same drying conditions, the thin film dries faster than the thick film, and extremely rapid heating is required to obtain a thermoreversible thermosensitive recording material with a smaller structural period. The method can easily obtain a uniform film with less boiling of the solvent, as compared with the case of performing and drying.

Furthermore, when such a drying condition is applied by an actual coating machine, as described above, the structural period changes depending on the strength of the drying condition. It is necessary to adjust the drying conditions for the purpose of keeping the contrast and the like at a constant level. Therefore, the online measurement in the coating process by the light scattering method and the method of adjusting the drying condition according to the result are very effective means.

FIG. 5 shows a basic configuration example of an apparatus for carrying out this method. The coating liquid applied by the coating head is dried in a dryer to form a phase separation structure. At the outlet of the dryer, the structural period of the reversible thermosensitive recording material is measured by a light scattering method, and the strength of the drying condition is controlled depending on its size. It is desirable to use a photodiode array, a CCD image sensor, or the like for the detector of the light scattering light in order to increase the speed of measurement, and to measure the entire width of the coating, the entire light scattering measuring device is used. It is desirable to scan in the width direction of the coating.

Further, when measuring the structural period of the reversible thermosensitive recording material, the scattering peak angle is most accurately measured when the thermosensitive layer is in a semitransparent state. Therefore, it is desirable to measure in a heated state to some extent. . For this reason, it is desirable that the positions of the light source and the detector shown in FIG. 5 be installed near the outlet of the dryer, inside the dryer, or at another temperature-controlled portion.

Further, as means used for achieving such drying conditions, there are a heater roll dryer for contact-heating the support from the back surface, a hot air dryer, an infrared heater, etc. A heater roll dryer having a good heat effect is particularly preferable.

In the present invention, there is also a method of using at least two kinds of organic solvents having different vapor pressures when dissolving two components of a resin base material and an organic low molecular weight substance. These can be variously selected depending on the type of resin base material and organic low molecular weight substance, and examples thereof include tetrahydrofuran, methyl ethyl ketone, methine isobutyl ketone, chloroform, carbon tetrachloride, ethanol, toluene, benzene and the like.

In the present invention, the resin used as the resin base material of the heat-sensitive layer of the reversible heat-sensitive recording material is preferably a resin which can form a film or a sheet, has good transparency and is mechanically stable. Examples of such resins include polyvinyl chloride; vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-acrylate copolymer. Vinyl chloride-based copolymers such as polymers; polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymers, vinylidene chloride-based copolymers such as vinylidene chloride-acrylonitrile copolymers; polyesters; polyamides; polyacrylates or polymethacrylates or acrylates -Methacrylate copolymer; silicone resin and the like can be mentioned. These may be used alone or in admixture of two or more.

On the other hand, as the organic low molecular weight substance, any substance that changes from polycrystal to single crystal due to heat in the heat sensitive portion (changes within the temperature range of T _{1 to} T ₃ shown in FIG. 1) may be used.
Generally, those having a melting point of 30 to 200 ° C., preferably about 50 to 150 ° C. are used. Such organic low-molecular substances include alkanols; alkane diols; halogen alkanols or halogen alkane diols; alkylamines; alkanes; alkenes; alkynes; halogen alkanes; halogen alkenes; halogen alkynes; cycloalkanes; cycloalkenes; cycloalkynes; saturated or Unsaturated mono- or dicarboxylic acids or their esters, amides or ammonium salts; saturated or unsaturated halogen fatty acids or their esters, amides or ammonium salts; allylcarboxylic acids or their esters, amides or ammonium salts; halogenallylcarboxylic acids or Of their esters, amides or ammonium salts; thioalcohols; thiocarboxylic acids or their esters, amides or ammonium salts; of thioalcohols Carboxylic acid esters, and the like. These may be used alone or in admixture of two or more. The carbon number of these compounds is 10
60, preferably 10-38, particularly 10-30 are preferred. The alcohol group moiety in the ester may be saturated or unsaturated, and may be halogen-substituted. In any case, the organic low molecular weight substance is at least one of oxygen, nitrogen, sulfur and halogen in the molecule, for example, -OH, -COOH, -CONH, -COOR, -N.
_{H, -NH 2, -S -,} - S-S -, - O-, is preferably a compound containing a halogen and the like.

More specifically, as these compounds,
Uric acid, dodecanoic acid, myristic acid, pentadecane
Acid, palmitic acid, henicosanoic acid, tricosanoic acid,
Gnoceric acid, pentacosanoic acid, cerotic acid, montan
Acid, melissic acid, stearic acid, behenic acid, nonadecane
Higher fatty acids such as acids, araginic acid, oleic acid; steari
Methyl acid salt, tetradecyl stearate, stearic acid
Octadecyl, octadecyl laurate, palmitic acid
Higher fatty acids such as tetradecyl and dodecyl behenate
Tell; C₁₆H₃₃-OC₁₆H₃₃ , C₁₆H₃₃-SC
₁₆H₃₃ , C₁₈H₃₇-SC₁₈H₃₇ , C₁₂H_{twenty five}-S
-C₁₂H_{twenty five} , C₁₉H₃₉-SC₁₉H₃₉ , C₁₂H_{twenty five}
-S-S-C₁₂H_{twenty five} ， Etc., such as ether or thioether. Above all, the present invention
Then higher fatty acids, especially palmitic acid, heneicosane
Acid, tricosanoic acid, lignoceric acid, pentadecanoic acid,
Nonadecanoic acid, arachidic acid, stearic acid, behenic acid, etc.
Is preferably a higher fatty acid having 16 or more carbon atoms, and has 16 carbon atoms.
-24 higher fatty acids are more preferred.

In order to increase the range of temperatures at which the material can be made transparent, the organic low molecular weight substances described in this specification may be combined appropriately, or such organic low molecular weight substances may be combined with other materials having different melting points. Good. These are disclosed in, for example, JP-A-63-39378 and JP-A-63-130380, Japanese Patent Application No. 1-140109, and JP-A-2-14093.
However, the present invention is not limited thereto.

The weight ratio of the organic low molecular weight substance to the resin base material in the heat sensitive layer is preferably about 2: 1 to 1:16, more preferably 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 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 heat-sensitive 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.

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.

In the present invention, as the support of the reversible thermosensitive recording material, a plastic film as described above,
A glass plate, a metal plate or the like is used. In order to improve the image contrast of this recording material, it is possible to provide a light reflecting layer on the back surface of the recording layer. In this case, high contrast can be obtained even if the thickness of the recording layer is reduced. Specifically, vapor deposition of Al, Ni, Sn, Au, Ag and the like can be mentioned (described in JP-A No. 64-14079). When the support is made of a material such as Al vapor-deposited layer that has poor adhesion to the resin, an adhesive layer may be provided between the support and the heat-sensitive layer (JP-A-3-7377). In addition, in order to improve the contrast, a method of providing a low refractive index layer such as air between the heat sensitive layer and the coloring layer or the light reflecting layer may be used.

A protective layer may be provided on the heat-sensitive portion of the present invention in order to prevent the transparency of the transparent portion from being lowered due to 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 10 μm), silicone rubber, silicone resin (described in JP-A-63-221087), polysiloxane graft polymer (JP-A-63-210).
No. 317385), an ultraviolet curable resin, an electron beam curable resin (described in JP-A-2-566), and the like.
Further, the surface may be roughened by a method such as adding an inorganic or organic filler to the protective layer in order to prevent dust and dirt from adhering to the thermal head (Japanese Patent Laid-Open No. 4-8).
No. 5077). In any case, a solvent is used at the time of application, but it is desirable that the solvent is difficult to dissolve the resin of the heat sensitive part and the organic low molecular weight substance. Examples of the solvent that hardly dissolves the resin of the heat-sensitive part and the organic low-molecular substance 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 heat-sensitive layer in order to protect the heat-sensitive layer from the solvent, monomer components and the like of the protective layer-forming liquid (JP-A-1-13378).
No. publication). 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, epoxy resin, phenol resin, polycarbonate, polyamide and the like can be mentioned. The thickness of the intermediate layer varies depending on the use, but is preferably about 0.1 to 2 μm. Below this,
The protective effect decreases, and if it exceeds this, the thermal sensitivity decreases. It is also possible to provide a magnetic recording layer and use it as a card (Japanese Utility Model Laid-Open No. 2-3876, JP-A-3-130).
188).

[0036]

According to the present invention, by setting the structural period of the phase-separated structure of the heat-sensitive layer to 1.3 μm or less, high transparency and high contrast are obtained in the transparent state, and high repetitive durability is achieved even in thermal head printing. A thermosensitive recording material is obtained. Although the reason for this is not clear, as described above, the crystal state of the organic low molecular weight substance and the magnitude of the interaction between the organic low molecular weight substance and the resin base material, which influences the effect on the light scattering of the substance, depend on the phase separation. It is thought that it changes depending on the structural cycle of. That is, it is not clear why a structural period of 1.3 μm or less can form a high-contrast image showing sufficient white turbidity while maintaining high transparency, but it can be interpreted as follows. The light-transmitting ability or light-scattering ability of the heat-sensitive layer can be understood as a comprehensive result of the following two factors. (1) Whether the crystalline state of each organic low molecular weight substance is a single crystalline state in which light easily passes or a polycrystalline state in which light easily diffuses. (2) Whether the structure of a large number of domains and the resin base material that covers them is in a state in which light is easily transmitted or in a state in which light is easily scattered. The former (1) is the result of the interaction between the organic low molecular weight substance and the resin base material with respect to the change of the crystalline state in the domain, and the latter (2) is the result of the organic low molecular weight substance and the resin base material with respect to the light scattering ability or the light transmission ability. It is an optical interaction, and it is presumed that each interaction has a causal relationship with the phase-separated structure. It is considered that the influence of these two interactions changes with the structural period, and when the structural period is 1.3 μm or less, it leads to high transparency.

The reason why the heat-sensitive recording material of the present invention exhibits high durability in thermal head printing is considered to be as follows. It is considered that the process of decreasing the white turbidity due to repeated printing of the thermal head is due to destruction of the phase-separated structure of the heat-sensitive layer by heat and pressure during printing. In other words, those that formed a clear domain in the initial state and showed a relatively small structural period showed a sufficient cloudiness concentration, but the domain became unclear due to domain destruction and coalescence during repeated printing. Become
The structural period increases and the cloudiness decreases. However, since the reversible thermosensitive recording material of the present invention exhibits a sufficiently small structural period at the initial stage, the decrease in white turbidity due to domain destruction or coalescence is less than that at the initial stage, and the durability is low. It is considered to be excellent. Further, among the thermal recording materials of the present invention, those having a smaller structural period, for example, 1.0 μm or less, are more remarkably effective in improving the durability.

[0038]

EXAMPLES All parts and percentages herein are by weight.

Example 1 Behenic acid 6 parts Eicosane diacid 4 parts Vinyl chloride-vinyl acetate copolymer 40 parts (Denka vinyl # 1000GK manufactured by Denki Kagaku Kogyo Co.) Diisodecyl phthalate on a transparent polyester film having a thickness of about 50 μm. 3 parts Tetrahydrofuran 60 parts Toluene 20 parts A solution consisting of 20 parts is applied with a wire bar and the surface temperature is 90 ° C.
After contacting the polyester film backside for 40 seconds with the heater roll (the surface is a mirror surface made of stainless steel) of 100,
After drying for 60 seconds in a hot air dryer at ℃, a heat-sensitive layer having a thickness of 10 μm is provided, and a 75% butyl acetate solution of a urethane acrylate UV-curable resin (Unidick C7-manufactured by Dainippon Ink and Chemicals, Inc.) 157) 10 parts A solution consisting of 10 parts of isopropyl alcohol is applied with a wire bar, dried in a hot air dryer at 100 ° C. for 60 seconds, and then cured with an ultraviolet lamp of 80 w / cm to provide an overcoat layer of about 2 μm thickness. A reversible thermosensitive recording material was prepared.

Example 2 Behenic acid 6 parts Eicosane diacid 4 parts Vinyl chloride-vinyl acetate copolymer 40 parts (Denka vinyl # 1000GK manufactured by Denki Kagaku Kogyo KK) Diisodecyl phthalate 3 parts Tetrahydrofuran 110 parts Toluene 37 parts The surface temperature of the heat roll is 80 ° C.
A reversible thermosensitive recording material was prepared in the same manner as in Example 1 except for the above.

Example 3 A heat roller having a surface temperature of 90 ° C. has a thickness of about 100 μm.
A reversible biosensitive recording material was prepared in the same manner as in Example 2 except that the cloth was used.

Example 4 A heat roll having a surface temperature of 80 ° C. has a thickness of about 100 μm.
A reversible biosensitive recording material was prepared in the same manner as in Example 2 except that the cloth was used.

Example 5 Behenic acid 6 parts Eicosane diacid 4 parts Vinyl chloride-vinyl acetate copolymer 30 parts (Denka vinyl # 1000GK manufactured by Denki Kagaku Kogyo KK) Diisodecyl phthalate 2 parts Tetrahydrofuran 89 parts Toluene 29 parts Solution A reversible thermosensitive recording material was prepared in the same manner as in Example 2 except that was used.

Example 6 A reversible thermosensitive recording material was prepared in the same manner as in Example 3 except that the same solution as in Example 5 was used.

Example 7 A reversible thermosensitive recording material was prepared in the same manner as in Example 4 except that the same solution as in Example 5 was used.

Example 8 A transparent polyester film having a thickness of about 50 μm was coated with the same solution as in Example 2 using a wire bar, heated in a hot air dryer at 130 ° C. for 30 seconds, and then dried at 100 ° C. in a hot air dryer. And heat-dried for 60 seconds to form a heat-sensitive layer having a thickness of 15 μm.
Further, an overcoat layer similar to that of Example 1 was provided thereon to prepare a reversible thermosensitive recording material.

Example 9 Two thermosensitive layers each having a thickness of 5 μm were formed under the same solution and drying conditions as in Example 2.
A reversible thermosensitive recording material was obtained in the same manner as in Example 1 except that the thermosensitive layer having a thickness of 10 μm was laminated.

Comparative Example 1 Behenic acid 6 parts Eicosane diacid 4 parts Vinyl chloride-vinyl acetate copolymer 40 parts (Denka vinyl # 1000GK manufactured by Denki Kagaku Kogyo Co., Ltd.) Diisodecyl phthalate on a transparent polyester film having a thickness of about 50 μm. 3 parts Tetrahydrofuran 148 parts Toluene 49 parts A solution consisting of 49 parts was applied with a wire bar and dried in a hot air dryer at 100 ° C. for 90 seconds to provide a heat-sensitive layer having a thickness of 15 μm. An overcoat layer was provided to make a reversible thermosensitive material.

Comparative Example 2 In the same manner as in Comparative Example 1, a reversible thermosensitive recording material provided with a thermosensitive layer having a thickness of 10 μm was prepared.

Comparative Example 3 A reversible thermosensitive recording material provided with a thermosensitive layer having a thickness of 10 μm was prepared in the same manner as in Example 2 except that the same solution as in Comparative Example 1 was used.

Comparative Example 4 A reversible thermosensitive recording material was obtained in the same manner as in Comparative Example 2 except that the same solution as in Example 5 was used.

Comparative Example 5 A solution of behenic acid 6 parts eicosane diacid 4 parts vinyl chloride-vinyl acetate copolymer 40 parts diisodecyl phthalate 3 parts tetrahydrofuran 210 parts toluene 70 parts on a transparent polyester film having a thickness of about 50 μm. Is applied with a wire bar and dried for 90 seconds in a hot air dryer at 90 ° C. to provide a heat-sensitive layer having a thickness of 10 μm, and an overcoat layer similar to that of Example 1 is further provided thereon to form a reversible heat-sensitive material. Obtained.

The structure period of the reversible thermosensitive recording material prepared as described above was measured by the above-mentioned light scattering measuring method. The measurement was performed in an intermediate state (85 ° C.) between cloudiness and transparency. Also,
The structural period was calculated assuming that the refractive index D is 1.5. The relationship between the scattering angle and the scattering intensity is shown in FIGS. 6, 7 and 8 for Examples 1 and 3 and Comparative Example 2, respectively. Next, each of the prepared reversible thermosensitive recording materials was heated at 52 ° C. to 132 by a thermal tilt tester (Type HG-100, Toyo Seiki Seisakusho Co., Ltd.).
The sample was heated in the temperature range of ° C at 2 ° C intervals, the image density of each heated part was measured, and the most transparent part was taken as the transparent density, and the more clouded part was taken as the clouding temperature. The image density was measured using Macbeth reflection densitometer RD-914. At that time, the density was measured with the (O.D. 1.9) printed in black as the back surface.
Moreover, the repeating durability by the thermal head was evaluated as follows. Using a thermal head of 8 dots / mm, white turbidity was printed and transparent erasing was performed with a heat roller. Printing and erasing were repeated 100 times under the same conditions. Further, some samples were repeated 300 times. The above results are summarized in Table 1. Further, FIG. 9 is a graph showing the relationship between the structural period and the transparent density. Further, FIG. 10 is a graph showing the relationship between the structural period and the contrast. In FIG. 9, the transparent density decreases with the structural period, and the smaller the structural period, the more transparent. Further, the reversible thermosensitive recording material of the present invention has a smaller structural period and is more transparent than the conventional one. Further, the white turbidity does not depend on the structural period as long as the composition and thickness of the heat-sensitive layer are the same, so that a high contrast is realized as shown in FIG. Further, also in terms of repeated durability by a thermal head, the reversible thermosensitive recording material of the present invention shows less change in the density of the cloudy part after 100 times printing than that of the comparative example, and shows high durability. FIG. 11 shows the relationship between the number of prints and the cloudiness density. The reversible thermosensitive recording material of the present invention is more excellent in durability of 100 times or more as compared with the conventional one.

[0054]

[Table 1]

[0055]

As is clear from the examples and comparative examples, the reversible thermosensitive recording material of the present invention has a phase-separated structure in which the organic low molecular weight substance in the thermosensitive layer is dispersed in the resin matrix. By having the structural period of the phase separation of the heat-sensitive layer of 1.3 μm or less, it is excellent in high transparency in a transparent state and repeated durability. Further, those having a smaller structural period, for example, those having a structure period of 1.0 μm or less are more excellent in durability. Furthermore, the reversible thermosensitive recording material having the excellent performance can be stably provided by the structure method of the present invention.

[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. 2A is a diagram schematically showing a phase-separated structure. (B) is the figure which represented typically the relationship of a phase separation structure and a structural period.

FIG. 3 is a diagram schematically showing the concept of light scattering measurement.

FIG. 4 is a diagram schematically showing a relationship between an apparent scattering angle and a true scattering angle.

FIG. 5 is a diagram showing a configuration example of an apparatus for producing a reversible thermosensitive recording material of the present invention.

FIG. 6 is a diagram showing the result of light scattering measurement in Example 1.

7 is a diagram showing the result of light scattering measurement in Example 3. FIG.

FIG. 8 is a diagram showing a result of light scattering measurement of Comparative Example 2.

FIG. 9 is a diagram showing a relationship between a structural period and a transparent density.

FIG. 10 is a diagram showing a relationship between a structural period and contrast.

FIG. 11 is a diagram showing a change in white turbidity depending on the number of prints.

Front page continuation (72) Inventor Tsutomu Kagawa 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd.

Claims (5)

[Claims] 1. A reversible thermosensitive recording material comprising a support and a heat-sensitive layer comprising a resin base material and an organic low-molecular substance whose transparency reversibly changes depending on temperature. A reversible thermosensitive recording material having a phase-separated structure dispersed in the resin base material, wherein the thermosensitive layer has a phase separation structural period of 1.3 μm or less. 2. The structural period of the phase separation of the heat sensitive layer is 1.0.
The reversible thermosensitive recording material according to claim 1, wherein the reversible thermosensitive recording material has a thickness of not more than μm. 3. The reversible thermosensitive recording material according to claim 1, wherein the mixing ratio of the organic low molecular weight substance and the resin base material is 1: 2 to 1: 8 by weight. 4. A solution in which an organic low molecular weight substance and a resin base material are dissolved is applied to a support to form a coating film and then dried.
2. The method for producing a reversible thermosensitive recording material which forms a thermosensitive layer having a phase-separated structure, wherein the drying conditions are adjusted while the structural period of the thermosensitive layer is measured by a light scattering method. A method for producing a reversible thermosensitive recording material. 5. The heat-sensitive layer whose structural period is measured by a light scattering method is in a semitransparent state.
A method for producing the reversible thermosensitive recording material described.