JP2976401B2 - Reversible thermosensitive recording material and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In recent years, a reversible thermosensitive recording material which can form a temporary image and erase the image when it becomes unnecessary has been attracting attention. A typical example is a glass transition temperature (Tg) of 50 to 60 ° C to 8 ° C.
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 base material 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
No. 54198, JP-A-63-39376, JP-A-63
Publications such as -107584).

When a heat roller, a hot pen, or the like is used as a heating method at the time of image formation and erasing, and only heat is applied without applying much pressure, image formation is repeated.
Erasing does not cause a problem in durability. However, when heating is applied simultaneously by applying pressure using a thermal head or the like, the resin base material around the organic low-molecular substance in the heat-sensitive layer is deformed during repeated image formation and The molecular substance particles gradually become larger particles,
The effect of scattering light is lost (the turbidity is reduced),
There is a drawback that the image and the contrast are reduced at last, and a reversible thermosensitive recording material capable of forming a high-contrast image capable of obtaining a sufficient turbidity while maintaining high transparency has not been obtained. Not been.

[0004]

SUMMARY OF THE INVENTION The present invention is directed to a reversible thermosensitive recording material which has solved the above-mentioned drawbacks, has high transparency and high image contrast, and has improved repetition durability. It is intended to provide.

[0005]

According to the present invention, there is provided a reversible thermosensitive layer comprising, on a support, a thermosensitive layer comprising a low-molecular organic substance whose transparency changes reversibly depending on temperature and a resin base material. In a recording material, the organic low-molecular substance has a phase separation structure in a state of being dispersed in the resin matrix, and the structural period of phase separation of the heat-sensitive layer is 1.3 μm or less. A thermosensitive recording material is provided. Also, a method for producing a reversible thermosensitive recording material, in which a solution in which a low-molecular organic 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. Wherein the drying condition is adjusted while measuring the structural period of the heat-sensitive layer by a light scattering method, thereby providing a method for producing the reversible thermosensitive recording material.

That is, the present inventors have found that a reversible thermosensitive recording material having a heat-sensitive layer composed of a resin base material and an organic low-molecular substance whose transparency changes reversibly depending on temperature, the organic low-molecular substance is It has a phase separation structure dispersed in the resin base material, and when the structural period of the phase separation of the heat-sensitive layer is 1.3 μm or less, the above object can be achieved. As a means for obtaining a thermosensitive recording material, a method in which a solution in which an organic low-molecular substance and a resin base material are dissolved is coated on a support to form a coating film, and then dried, is simple. Is that the structural period can be controlled by the drying conditions.However, depending on the conditions, slight differences in the drying conditions can cause the structural period to be significantly different, so the structural period is measured in the process after coating. While drying strips 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 change in transparency (transparent state, cloudy opaque state) as described above. The difference between this transparent state and cloudy opaque state is presumed as follows. . That is, (i) in the case of transparency, the particles of the organic low-molecular substance dispersed in the resin base material are composed of large particles of the organic low-molecular substance, and the light incident from one side is not scattered and is opposite. (Ii) In the case of cloudiness, the particles of the organic low-molecular substance are composed of polycrystals composed of fine crystals of the organic low-molecular substance, and the crystal axes of the individual crystals Is oriented in various directions, so that light incident from one side is refracted many times at the interface between the crystals of the organic low-molecular substance particles, and is scattered, so that it appears white.

In FIG. 1 (which shows the change in transparency due to heat), a heat-sensitive layer mainly composed of a resin base material and an organic low-molecular substance dispersed in the resin base material is, for example, T
_At a room temperature of ₀ or less, it is cloudy and opaque. This is called temperature T ₂
When the temperature is returned to room temperature below T ₀ , the film remains transparent. This is from temperature T ₂ to T ₀
It is considered that the crystal grows from the fine polycrystalline state to the larger single crystal state through the semi-molten state of the organic low-molecular substance until the following. Upon further heating to T ₃ or more temperature becomes translucent state intermediate between the maximum transparency and the maximum opacity. Then, when the temperature is lowered, the state returns to the first cloudy and opaque state, which is again a transparent state. This after low-molecular organic material is melted at a temperature T ₃ or more, presumably because the polycrystals precipitated by being cooled. When this opaque state is heated to a temperature between T _{1 and} T ₂ and then cooled to room temperature, that is, a temperature equal to or lower than T ₀ , an intermediate state between transparent and opaque can be obtained. Also, by returning to room temperature After heating to be again T ₃ or more temperature which became clear at the normal temperature, the flow returns to cloudy opaque state again. That is, both opaque and transparent forms at room temperature and intermediate states thereof can be taken. Therefore, the heat-sensitive layer can be selectively heated by selectively applying heat to form a cloudy image on a transparent ground and a transparent image on a cloudy ground, and the change can be repeated many times. .

However, as described above, light scattering and light transmission are used depending on whether the recording / erasing of the reversible thermosensitive recording material is a fine polycrystalline state or a relatively large single crystal state in the crystalline state of the organic low molecular substance. Therefore, the crystal growth for causing light scattering and transmission and the effect thereof naturally depend on the phase separation structure between the organic low-molecular substance and the resin base material.

In describing the state of phase separation, the concept of the structural period becomes important. The structural period may be considered as a quantity representing the size of the phase separation structure. For example, FIG.
In the phase separation 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 above, the composition of the substance A and the substance B can be grasped in a periodically changed form. This period Λ is called a structural period. This structural period is not determined in any phase separation structure, but can be determined when the following factors are comprehensively satisfied, and is a meaningful numerical value. (1) The phase-separated structure has a certain degree of regularity and a characteristic structural period. (2) The volume ratio between the substance A and the substance B in the structure is not 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,
The substance A may be considered as a low-molecular organic substance and the substance B may be considered as a resin base material, and these substances comprehensively satisfy the above factors (1), (2) and (3) in the heat-sensitive layer. In this case, the concept of the 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 analyzing the structure of an organic polymer compound is effective as a method of capturing such a structural period. As shown in FIG. 3 (a), a method of measuring light scattering involves applying light from a light source to a sample and calculating the structural period from the scattering angle of the transmitted light. The relationship between the scattering angle and the structural period Λ Is given by equation (1). [Equation 1] Here, λ is the wavelength [μm] of the light source, D is the refractive index of the sample [−], and σ is the scattering angle [deg]. Generally, laser light is used as a light source for measurement, and He-N
e-lasers are most often used. (1),
When a sample satisfying the conditions (2) and (3) is applied to a light scattering measurement device, the scattered light shows a ring-shaped light intensity distribution as shown in FIG. When the scattered light intensity is plotted against the scattering angle, a curve having a peak value of the intensity 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 above equation (1) becomes the structural period Δm unique 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 (Optical Co., Ltd.) (light source He-
Ne laser wavelength λ = 0.6328 μm) was used.
The measurement sample needs to have a certain degree of light transmittance. Therefore, when the heat-sensitive layer is provided on an opaque support, the support must be removed to obtain a sample. However, when the heat-sensitive layer is provided on a transparent support, this is not the case.
The heat-sensitive layer is in the form of a film, and calculation of the scattering angle requires angle correction in consideration of the refractive index difference between the sample and air. The reason for this is that, as schematically shown in FIG. 4, the scattered light further refracts at the interface between the film and the air, so that the apparent scattering angle θap is smaller than the true scattering angle θ.

Further, the sample according to the present invention changes to a cloudy, transparent, or translucent state depending on the temperature, and therefore, there is a problem in which state the light scattering measurement is performed. Since little scattering occurs in the transparent state, the light scattering measurement is performed in the cloudy or translucent state. In both cases, the shape of the light intensity distribution of scattering is slightly different, but the angle θ at the intensity peak value.
Since m hardly changes, the measurement should be performed in a state where measurement is easy.

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

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 condition. It is effective to use a device having a single thermal head for forming an image and erasing an image. In the former case, the cost of the apparatus increases because two thermal heads are required, but if the energy application conditions for each thermal head are different and the reversible thermosensitive recording material is passed once, the formation and erasing of the image can be performed. Can do it. In the latter case, in order to form and erase an image with one thermal head, the condition for applying energy to the thermal head at one time when the thermal recording material passes is adjusted according to the part where the image is formed and the part to be erased. Although the operation is complicated, the operation is complicated, for example, the image is formed under different energy conditions by changing the thermal recording material in a small direction or by erasing the image on the thermal recording material once and then running the thermal recording material in the opposite direction again. Therefore, the equipment cost is reduced.

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

Also, the structure period of the present invention is 1.3 μm.
The following production method for obtaining a thermosensitive layer having a phase separation structure can be obtained depending on the solvent concentration of the coating solution and drying conditions. That is,
The structure cycle of the heat-sensitive layer can be controlled by its drying condition, and the larger the drying strength, that is, the faster the drying, the smaller the heat-sensitive layer having a smaller structure cycle. However, when simply increasing the drying strength to obtain a thermosensitive layer having a small phase separation structure as in the present invention,
Rapid heating causes the solvent to boil and generate air bubbles. As a result, defects such as repelling and pinholes were formed in the film, and a uniform film could not be obtained.

Thus, it has been 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 substance in the coating liquid is set to 25% or more. Alternatively, 90% or more of the solvent is evaporated within 40 seconds from the start of drying after the application of the coating liquid. More preferably, the method is carried out in combination with the both. This is a 25% concentration
It is considered that the use of the above-mentioned coating solution strengthens the interaction between the solvent and the resin base material or the organic low-molecular substance to make it difficult to boil, and at the same time suppresses cissing due to an increase in the viscosity of the coating solution. However, even after evaporating the solvent by 90% or more, it is necessary to continue drying in order to remove the residual solvent, but the intensity of the drying hardly affects the structural period unless extreme heating is performed. .

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

Further, when such drying conditions are carried out in an actual coating machine, as described above, the structural period changes depending on the strength of the drying conditions. For the purpose of keeping the contrast and the like at a constant level, it is necessary to adjust the drying conditions. For this reason, on-line measurement in a coating process by a light scattering method and a method of adjusting drying conditions based on the results are very effective means.

FIG. 5 shows an example of a basic configuration of an apparatus for implementing 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 magnitude of the period is used to control the strength of the drying conditions. It is preferable to use a photodiode array or a CCD image sensor for the light scattering light detector in order to increase the measurement speed, and to measure the entire width of the coating, the light scattering measuring device must be used. It is desirable to scan in the width direction of the coating.

When measuring the structural period of a reversible thermosensitive recording material, the scattering peak angle is most easily measured when the thermosensitive layer is in a translucent state. . For this reason, it is desirable that the positions of the light source and the detector shown in FIG. 5 be installed near or inside the outlet of the dryer, or in another part whose temperature is controlled.

Further, as means used to achieve such drying conditions, there are a heater roll dryer, a hot air dryer and an infrared heater which contact-heats the support from the back surface. A heater roll dryer having a good heat effect is particularly preferred.

Further, in the present invention, there is a method in which at least two or more kinds of organic solvents having different vapor pressures are used for dissolving the two components of the resin base material and the organic low molecular weight substance. These can be variously selected depending on the type of the resin base material and the organic low-molecular substance, and examples thereof include tetrahydrofuran, methyl ethyl ketone, methine isobutyl ketone, chloroform, carbon tetrachloride, ethanol, toluene, and benzene.

In the present invention, the resin used as the resin base material of the thermosensitive layer of the reversible thermosensitive recording material is preferably a resin which can form a film or sheet, has good transparency, and is mechanically stable. Examples of such a resin include polyvinyl chloride; vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, and vinyl chloride-acrylate copolymer. Vinylidene chloride copolymers such as polyvinylidene chloride, vinylidene chloride-vinyl chloride copolymer, vinylidene chloride-acrylonitrile copolymer; polyester; polyamide; polyacrylate or polymethacrylate or acrylate -Methacrylate copolymers; silicone resins and the like. These may be used alone or as a mixture of two or more.

On the other hand, any organic low-molecular substance may be used as long as it changes from polycrystal to single crystal by heat in the heat-sensitive part (a substance that changes in the temperature range of T _{1 to} T ₃ shown in FIG. 1).
Generally, those having a melting point of about 30 to 200 ° C, preferably about 50 to 150 ° C are used. Such organic low molecular weight substances include alkanol; alkane diol; halogen alkanol or halogen alkane diol; alkylamine; alkane; alkene; alkyne; halogen alkane; halogen alkene; halogen alkyne; cycloalkane; cycloalkene; cycloalkyne; Unsaturated mono- or dicarboxylic acids or their esters, amides or ammonium salts; saturated or unsaturated halogen fatty acids or their esters, amides or ammonium salts; allylcarboxylic acids or their esters, amides or ammonium salts; Esters, amides or ammonium salts thereof; thioalcohols; thiocarboxylic acids or esters, amides or ammonium salts thereof; Carboxylic acid esters, and the like. These may be used alone or in combination of two or more. These compounds have 10 to 10 carbon atoms.
60, preferably 10 to 38, particularly preferably 10 to 30. The alcohol group in the ester may be saturated, may not be saturated, and may be halogen-substituted. In any case, the organic low molecular weight substance contains at least one kind 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, these compounds include
Uric acid, dodecanoic acid, myristic acid, pentadecane
Acid, palmitic acid, henicosanoic acid, tricosanoic acid,
Gnocellic acid, pentacosanoic acid, cerotic acid, montan
Acid, melicic acid, stearic acid, behenic acid, nonadecane
Higher fatty acids such as acid, araginic acid and oleic acid;
Methylate, tetradecyl stearate, stearic acid
Octadecyl, octadecyl laurate, palmitic acid
S of 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} , And ether or thioether. In particular, the present invention
Higher fatty acids, especially palmitic acid and heneicosane
Acid, trichosanoic acid, lignoceric acid, pentadecanoic acid,
Nonadecanoic acid, arachiic acid, stearic acid, behenic acid, etc.
Are preferably higher fatty acids having 16 or more carbon atoms,
~ 24 higher fatty acids are more preferred.

Further, in order to widen the range of temperatures at which transparency can be obtained, the organic low-molecular substance described in this specification is appropriately combined, or such an organic low-molecular substance is combined with another material having a different melting point. I just need. These are disclosed in, for example, JP-A-63-39378 and JP-A-63-130380, and Japanese Patent Application Nos. 1-140109, 2-
Although disclosed in the specification such as No. 1363, the present invention is not limited thereto.

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

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

In addition to the above components, additives such as a surfactant and a high boiling point solvent can be added to the heat-sensitive layer in order to facilitate formation of a transparent image. Specific examples of these additives are as follows. Examples of high boiling point solvents; tributyl phosphate, tri-2-phosphate
Ethylhexyl, triphenyl phosphate, tricresyl phosphate, butyl oleate, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diheptyl phthalate, di-n-octyl phthalate, di-2-ethylhexyl phthalate, diisononyl phthalate , Dioctyldecyl phthalate, diisodecyl phthalate, butylbenzyl phthalate,
Dibutyl adipate, di-n-hexyl adipate, di-2-ethylhexyl adipate, di-2 azelate
-Ethylhexyl, dibutyl sebacate, di-2-ethylhexyl sebacate, diethylene glycol dibenzoate, triethylene glycol di-2-ethyl butyrate, methyl acetyl ricinoleate, butyl acetyl ricinoleate, butyl phthalyl butyl glycolate, acetyl citric acid Tributyl.

Examples of surfactants and other additives: polyhydric alcohol higher fatty acid ester; polyhydric alcohol higher alkyl ether; polyhydric alcohol higher fatty acid ester, higher alcohol, higher alkyl phenol, higher fatty acid higher alkyl amine, higher fatty acid amide Lower olefin oxide adducts of fats and oils or polypropylene glycol; acetylene glycol; Na, Ca, Ba or Mg salts of higher alkylbenzene sulfonic acids; higher fatty acids, aromatic carboxylic acids, higher fatty acid sulfonic acids, aromatic sulfonic acids, monoesters of sulfuric acid Or Ca, Ba or Mg salts of phosphoric acid mono- or di-esters; low sulfated oils; poly long chain alkyl acrylates; acrylic oligomers; poly long chain alkyl methacrylates; Chromatography copolymers; styrene-maleic anhydride copolymer; olefin-maleic anhydride copolymer.

In the present invention, as the support of the reversible thermosensitive recording material, as described above, a plastic film,
A glass plate, a metal plate, or the like is used. In order to improve the image contrast of the recording material, a light reflection layer can be provided 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. Specific examples include vapor deposition of Al, Ni, Sn, Au, Ag, and the like (described in JP-A-64-14079). When the support is made of a material having poor adhesion to a resin, such as an Al vapor-deposited layer, an adhesive layer may be provided between the support and the heat-sensitive layer (JP-A-3-7377). Alternatively, 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 to improve the contrast may be used.

Further, a protective layer may be provided on the heat-sensitive portion of the present invention in order to prevent the surface from being deformed by the heat and pressure of the heating means by a writing method such as a thermal head and the transparency of the transparent portion from being lowered. good. A protective layer (thickness of 0. 0) laminated on the heat sensitive part.
Materials of silicone rubber, silicone resin (described in JP-A-63-221087), and polysiloxane graft polymer (JP-A-63-210 μm)
317385), an ultraviolet curable resin or an electron beam curable resin (described in JP-A-2-566).
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, dirt and the like 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 coating, and it is preferable that the solvent does not easily dissolve the resin of the heat-sensitive part and the organic low-molecular substance. Examples of the solvent that hardly dissolves the resin and the organic low-molecular substance in the heat-sensitive portion include n-hexane, methyl alcohol, ethyl alcohol, and isopropyl alcohol, and an alcohol-based solvent is particularly desirable in terms of cost.

Further, an intermediate layer can be provided between the protective layer and the heat-sensitive layer in order to protect the heat-sensitive layer from a solvent, a monomer component and the like of the protective layer forming solution (Japanese Patent Laid-Open No. 1-1378).
No. Gazette). As the material of the intermediate layer, the following thermosetting resins and thermoreversible resins can be used in addition to those listed as the resin base material in the thermosensitive layer. That is, specific examples include polyethylene, polypropylene, polystyrene, polyvinyl alcohol, polyvinyl butyral, polyurethane, saturated polyester, unsaturated polyester, epoxy resin, phenol resin, polycarbonate, polyamide, and the like. The thickness of the intermediate layer varies depending on the application, but is preferably about 0.1 to 2 μm. Below this,
The protective effect is reduced, and above this, the thermal sensitivity is reduced. Furthermore, it is also possible to provide a magnetic recording layer and use it as a card (Japanese Utility Model Laid-Open No. 2-3876, Japanese Unexamined Patent Publication No. 3-130).
188).

[0036]

According to the present invention, by setting the structural period of the phase separation structure of the heat-sensitive layer to 1.3 μm or less, it has high transparency and high contrast in a transparent state, and has high repetition durability even in thermal head printing. A heat-sensitive recording material is obtained. Although the reason for this is not clear, as described above, the crystal state of the organic low-molecular substance and the magnitude of the interaction between the organic low-molecular substance and the resin base material, which affect the effect on light scattering, depend on the phase separation. It is thought that it has been changed by the structural period of. That is, if the structural period is 1.3 μm or less, the reason why a high-contrast image showing sufficient white turbidity can be formed while maintaining high transparency is not clear, but can be interpreted as follows. The light transmitting ability and scattering ability of the heat-sensitive layer can be considered as a comprehensive result of the following two factors. (1) Whether the crystal state of each domain of the organic low-molecular substance is a single crystal state that easily transmits light or a polycrystalline state that is easily scattered. (2) Whether the structure of a large number of domains and the resin base material covering the domains is in a state where light is easily transmitted or scattered. The former (1) is the result of the interaction of the organic low-molecular substance and the resin base material with respect to the change of the crystal state in the domain, and the latter (2) is the result of the interaction between the organic low-molecular substance and the resin base material with respect to the light scattering ability or transmission ability. It is an optical interaction, and a causal relationship between each interaction and the phase separation structure is presumed. 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.

Next, 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 lowering the turbidity due to the repetition of printing by the thermal head is due to the phase separation structure of the thermosensitive layer being destroyed 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 white turbid density, but the domain became unclear due to the destruction and coalescence of the domains during repeated printing. Becoming
The structural period increases and the turbidity also decreases. However, since the reversible thermosensitive recording material of the present invention shows a sufficiently small structural period at the initial stage, the decrease in cloudiness due to domain destruction or coalescence is smaller than that at the initial stage showing a large structural period. It is considered to be excellent. Among the heat-sensitive recording materials of the present invention, those having a smaller structural period, for example, 1.0 μm or less, have the more remarkable effect of improving the durability as described above.

[0038]

EXAMPLES All parts and percentages herein are by weight.

Example 1 On a transparent polyester film having a thickness of about 50 μm, 6 parts of behenic acid 4 parts of eicosane diacid 40 parts of vinyl chloride-vinyl acetate copolymer (Denka Vinyl # 1000GK manufactured by Denki Kagaku Kogyo KK) diisodecyl phthalate A solution consisting of 3 parts of 60 parts of tetrahydrofuran and 20 parts of toluene was applied with a wire bar, and the surface temperature was 90 ° C.
After contacting the back of the polyester film for 40 seconds with a heater roll (the front surface of which is a mirror surface made of stainless steel),
After drying in a hot air dryer at 60 ° C. for 60 seconds, a 10 μm thick heat-sensitive layer was provided, and a 75% butyl acetate solution of urethane acrylate-based UV-curable resin (Unidic C7-, manufactured by Dainippon Ink and Chemicals, Inc.) 157) 10 parts Isopropyl alcohol A solution consisting of 10 parts was applied with a wire bar, dried in a hot air drier at 100 ° C. for 60 seconds, and cured with an ultraviolet lamp of 80 w / cm to form an overcoat layer having a thickness of about 2 μm. Thus, a reversible thermosensitive recording material was prepared.

Example 2 6 parts of behenic acid 4 parts of eicosane diacid 40 parts of vinyl chloride-vinyl acetate copolymer (Denka Vinyl # 1000GK manufactured by Denki Kagaku Kogyo KK) Diisodecyl phthalate 3 parts Tetrahydrofuran 110 parts Toluene 37 parts And 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 that

Example 3 A heat roll having a surface temperature of 90.degree.
A reversible thermosensitive 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.degree.
A reversible thermosensitive recording material was prepared in the same manner as in Example 2 except that the cloth was used.

Example 5 6 parts of behenic acid 4 parts of eicosane diacid 30 parts of vinyl chloride-vinyl acetate copolymer (Denka Vinyl # 1000GK manufactured by Denki Kagaku Kogyo Co., Ltd.) 2 parts of diisodecyl phthalate 89 parts of tetrahydrofuran 29 parts of a solution composed of 29 parts of toluene A reversible thermosensitive recording material was prepared in the same manner as in Example 2 except that the above 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 The same solution as in Example 2 was coated on a transparent polyester film having a thickness of about 50 μm with a wire bar, heated in a 130 ° C. hot air drier for 30 seconds, and then heated at 100 ° C. hot air drier. Drying in the inside for 60 seconds to provide a heat-sensitive layer having a thickness of 15 μm,
Further, a reversible thermosensitive recording material was formed thereon by providing the same overcoat layer as in Example 1.

Example 9 A heat-sensitive layer having a thickness of 5 μm was 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 layers were laminated one after another to form a thermosensitive layer having a thickness of 10 μm.

Comparative Example 1 6 parts of behenic acid 4 parts of eicosane diacid 4 parts of vinyl chloride-vinyl acetate copolymer 40 parts (Denka Vinyl # 1000GK manufactured by Denki Kagaku Kogyo KK) diisodecyl phthalate on a transparent polyester film having a thickness of about 50 μm A solution consisting of 3 parts tetrahydrofuran 148 parts toluene 49 parts was applied with a wire bar and dried in a hot air drier at 100 ° C. for 90 seconds to form a heat-sensitive layer having a thickness of 15 μm. An overcoat layer was provided to produce 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 10 μm thick thermosensitive layer 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 consisting of 6 parts of behenic acid, 4 parts of eicosane diacid, 40 parts of a vinyl chloride-vinyl acetate copolymer, 40 parts of diisodecyl phthalate, 3 parts of tetrahydrofuran and 210 parts of toluene on a transparent polyester film having a thickness of about 50 μm Was applied with a wire bar, and dried in a hot air drier at 90 ° C. for 90 seconds to provide a 10 μm-thick heat-sensitive layer, and further provided an overcoat layer similar to that in Example 1 to form a reversible heat-sensitive material. Obtained.

The structural period of the reversible thermosensitive recording material prepared as described above was measured by the light scattering measurement method described above. The measurement was performed in an intermediate state (85 ° C.) between cloudy and transparent. Also,
The refractive index D was 1.5, and the structural period was calculated. 6, 7, and 8 show the relationship between the scattering angle and the scattering intensity for Examples 1 and 3 and Comparative Example 2, respectively. Next, each reversible thermosensitive recording material thus prepared was subjected to a temperature gradient tester (type HG-100, manufactured by Toyo Seiki Seisaku-sho, Ltd.) at 52 ° C. to 132 ° C.
The image was heated at 2 ° C. in the temperature range of 2 ° C., and the image density of each heated portion was measured. The transparent portion was defined as the transparent density, and the more cloudy portion was defined as the cloudiness temperature. The image density was measured using a Macbeth reflection densitometer RD-914. At that time, the density measurement was performed with black (OD 1.9) printed on the back side.
Further, the repetition durability by the thermal head was evaluated as follows. Using an 8 dot / mm thermal head, the print was made cloudy and erased transparently with a heat roller. Printing / erasing was repeated 100 times under the same conditions. Some samples were further repeated 300 times. The above results are summarized in Table 1. FIG. 9 is a graph showing the relationship between the structural period and the transparent density. FIG. 10 is a graph showing the relationship between the structural period and the contrast. FIG. 9 shows that the transparency 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 conventional ones. Further, as for the cloudiness density, as long as the composition and thickness of the heat-sensitive layer are the same, the contrast does not depend on the structural period, and thus a high contrast is realized as shown in FIG. In addition, the reversible thermosensitive recording material of the present invention has a small change in the density of the white turbid portion after printing 100 times as compared with 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 than 100 times 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 separation structure in which the organic low-molecular substance in the thermosensitive layer is dispersed in a resin matrix. By setting the structural period of the phase separation of the heat-sensitive layer to 1.3 μm or less, the heat-sensitive layer has high transparency in a transparent state and excellent repetition durability. Further, those having a smaller structural period, for example, those having a structure period of 1.0 μm or less have better durability. Further, according to the structure method of the present invention, a reversible thermosensitive recording material having excellent performance can be stably provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing a change in transparency of a reversible thermosensitive recording material according to the present invention due to heat.

FIG. 2A is a diagram schematically illustrating a phase separation structure. (B) is a diagram schematically showing the relationship between the phase separation structure and the structural period.

FIG. 3 is a diagram schematically illustrating 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 illustrating a configuration example of an apparatus for manufacturing a reversible thermosensitive recording material of the present invention.

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

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

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

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

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

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

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tsutomu Kagawa 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company, Ltd. (56) References JP-A-54-119377 (JP, A) JP-A Sho 55-154198 (JP, A) Japanese Utility Model 1-165286 (JP, U) (58) Fields surveyed (Int. Cl. ⁶ , DB name) B41M 5/36

Claims (6)

(57) [Claims] 1. A reversible thermosensitive recording material comprising a support and a reversible thermosensitive layer comprising a thermosensitive layer comprising a low-molecular organic substance whose transparency changes reversibly depending on temperature and a resin base material. Wherein the organic low-molecular substance has a phase-separated structure in a state of being dispersed in the resin matrix, and the structural cycle of phase separation of the heat-sensitive layer is 1.3 μm or less. Recording material. 2. The heat-sensitive layer according to claim 1, wherein the structure period of phase separation is 1.0 μm.
2. The reversible thermosensitive recording material according to claim 1, wherein m is equal to or less than m. 3. The reversible thermosensitive recording material according to claim 1, wherein the mixing ratio of the organic low-molecular substance and the resin base material is from 1: 2 to 1: 8 by weight. 4. The method according to claim 1, further comprising providing a magnetic recording layer.
The reversible thermosensitive recording material according to claim 1. 5. A solution in which a low-molecular organic substance and a resin base material are dissolved is applied to a support, a coating film is formed, and then dried,
5. A method for producing a reversible thermosensitive recording material for forming a thermosensitive layer having a phase-separated structure, wherein drying conditions are adjusted while measuring the structural period of the thermosensitive layer by a light scattering method. The method for producing the reversible thermosensitive recording material according to any one of the above. 6. The heat-sensitive layer for measuring a structural period by a light scattering method is in a translucent state.
A method for producing the reversible thermosensitive recording material described above.