JP2002096564A - Reversible thermal recording material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the dependence of a presented content on a view angle and to improve visibility, in a reversible thermal recording medium provided with a thermal recording layer constituted of a thermotropic cholesteric liquid crystal. SOLUTION: In the reversible thermal recording medium provided with the thermal recording layer 3 constituted of the thermotropic cholesteric liquid crystal, a protective material 2 has a function of diffusing a selectively reflected light from the recording layer 3 by the surface thereof. The function of diffusing the selectively reflected light can be obtained by forming a large number of semispherical or polyhedral minute projections or a large number of minute indentation threads on the protective material 2 or by coating the protective material 2 with a resin solution containing minute particles.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible thermosensitive recording medium, and more particularly to a reversible thermosensitive recording medium having a thermosensitive recording layer made of a thermotropic cholesteric liquid crystal.

[0002]

2. Description of the Related Art In recent years, with the development of the information society, O
With the spread of A, the data amount of various types of information has been steadily increasing, and as a means for outputting such information, a hard copy using paper as a medium has become a representative display means. on the other hand,
As interest in preserving the global environment increases, from the viewpoint of protecting forest resources, hard copy technology for media instead of paper,
Furthermore, a rewritable display technology has attracted attention.

In particular, development and research on a reversible thermosensitive recording medium that can be recorded and erased by a heating means such as a thermal head are being actively conducted. Such a rewritable recording medium is being studied for various applications in addition to the purpose of visualizing internal information as necessary for various prepaid cards such as an IC card and a magnetic card.

Heretofore, as reversible thermosensitive recording materials, leuco dyes / color-reducing agents, organic low molecular weight / polymer resin matrices, and cholesteric liquid crystals have been known. But,
With the leuco dye / developing agent, the displayed color is limited to the color of the leuco dye, and full-color display was impossible. In addition, even with organic low molecular weight / polymer resin matrix, permeation /
Since the display is performed in a scattering state, full-color display is impossible.

On the other hand, in a cholesteric liquid crystal (especially, a thermotropic cholesteric liquid crystal), the cholesteric pitch caused by the helical structure of the liquid crystal layer changes in principle in accordance with the heating temperature, and a selective reflection color corresponding to this is observed. Accordingly, full-color display is possible, and various studies are being made on the application to display media and recording media as well as the development of materials.

When the cholesteric liquid crystal is used as a recording material, the recorded color display information is
Due to the characteristics of the liquid crystal, when viewed from an oblique direction compared to when viewed from a direction perpendicular to the medium surface, a phenomenon occurs in which the color tone changes to the short wavelength side according to the viewing angle. In other words, there is a problem that the display contrast is low in principle because the display content depends on the viewing angle, and the information is difficult to read.

Accordingly, an object of the present invention is to provide a reversible thermosensitive recording medium having reduced viewing angle dependence of display contents and excellent visibility.

[0008]

In order to achieve the above objects, the present invention relates to a reversible thermosensitive recording medium having a thermosensitive recording layer made of a thermotropic cholesteric liquid crystal, which is selected from a surface on which the recorded information is viewed. It has a diffusion layer for diffusing reflected light.

In the reversible thermosensitive recording medium according to the present invention, the thermosensitive recording layer made of a thermotropic cholesteric liquid crystal enables display with an arbitrary color light (that is, full color) in the visible light region, and the thermosensitive recording layer. The light that is selectively reflected in the visual field of the observer is diffused when emitted, and the viewing angle is widened, that is, the viewing angle dependency is reduced, the display contrast is improved, and the visibility is good. Become.

The function of diffusing the selectively reflected light is provided by providing a protective material having a large number of hemispherical or polyhedral fine protrusions on the surface of the heat-sensitive recording layer, or by forming a large number of fine irregularities. This can be realized by providing a protective material. Further, a protective material coated with a resin solution containing fine particles may be provided on the surface of the heat-sensitive recording layer.

In the reversible thermosensitive recording medium according to the present invention, the surface of the thermosensitive recording layer has a glass transition temperature of 80.degree. C. or more to thermally protect the surface of the recording layer. It is preferable to provide a protective material having a function of diffusing selectively reflected light on a surface opposite to a surface in contact with the layer. For this purpose, a single sheet having both functions may be provided, or a sheet having a function of thermally protecting the surface of the heat-sensitive recording layer and a sheet having a function of diffusing selectively reflected light are laminated. You may provide.

Further, it is preferable that the thermotropic cholesteric liquid crystal selectively reflects light in a visible light region and is capable of full-color display. A more preferred thermotropic cholesteric liquid crystal has a glass transition temperature of 3
The temperature is 5 ° C. or more, and the isotropic phase transition temperature is 200 ° C. or less.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a thermosensitive recording medium according to the present invention will be described with reference to the accompanying drawings. In the following embodiments, specific substances are shown and described, but these are merely examples, and the heat-sensitive recording medium according to the present invention is not limited to these, and various types of materials using various materials may be used. Recording medium having the configuration described above.

Reversible thermosensitive recording medium 1 as one embodiment
As shown in FIG. 1, a thermosensitive recording layer 3 containing a cholesteric liquid crystal is provided on a base material 4, and a protective material 2 is laminated thereon. Various types of resin sheets and films are used for the protective material 2.

The protective material 2 protects the surface of the heat-sensitive recording layer 3 from physical and chemical loads, especially from a thermal load.
The light which is selectively reflected by the heat-sensitive recording layer 3 and transmitted again through the protective material 2 and emitted is diffused on the surface. By diffusing the selectively reflected light, it is possible to reduce the viewing angle dependence of the display content on the thermosensitive recording layer 3.

As the material used as the protective material 2, various commercially available resin sheets and films can be used. The material is not particularly limited as long as it is excellent in light transmittance and high in heat resistance, but it is desirable that the material be capable of accurately forming a fine structure on the surface. For example, an acrylic resin is preferable for a resin curable by ultraviolet rays or electron beams, and an epoxy resin or a urethane resin is preferable for a thermosetting resin.

If the resin is a thermosetting resin, an acrylic resin and a copolymer thereof, an olefin resin such as a cyclic polyolefin, a polyester resin such as polyethylene terephthalate, polybutylene terephthalate and polyethylene naphthalate, and a copolymer thereof And polycarbonate resins and copolymers thereof.

In order to enlarge the viewing angle characteristics, as a fine structure formed on the surface of the protective material 2, for example, when the viewing angle in only one direction such as the vertical direction or the horizontal direction is increased, FIG. As shown in Fig. 7, a large number of fine ridges 2a having a circular cross section may be arranged in parallel. The height a of the ridge 2a is 20 to 100 μm, and the pitch b is 20 to 100 μm.
m can be exemplified.

Further, as shown in FIG.
A so-called waveform shape in which b and the concave stripes 2c are arranged alternately and in parallel may be used. The height a from the mountain to the valley is 20-100
μm and the pitch b can be exemplified by 20 to 100 μm.

The ridge 2a or the ridge 2b and the ridge 2c
Has an effect of diffusing the selectively reflected light from the heat-sensitive recording layer 3 in the circumferential direction of the cross section, thereby widening the viewing angle.

In order to increase the viewing angle in all directions, a fine polyhedral lens group, a plano-convex lens group, or the like may be formed on the surface of the protective member 2. Regarding the polyhedral lens group, for example, as shown in FIG.
d may be continuously juxtaposed or, as shown in FIG. 5, quadrangular pyramid-shaped fine projections 2e may be juxtaposed continuously. The height a of the projections 2d and 2e is 20 to 100 μm, and the length b of each side is 20 to 100 μm.

Further, as for the plano-convex lens group, as shown in FIG. 6, hemispherical fine projections 2f may be continuously juxtaposed. Its height a is 20 to 100 μm and its diameter b is 20 to
100 μm can be exemplified.

The method of forming the microstructures 2a to 2f is arbitrary, and can be formed by various methods. For example, it can be produced by a press method using a female flat plate mold engraved with a pattern of a desired fine structure or a flat plate made of resin such as polyurethane. Further, when extruding the protective material 2 from a resin material, the protective material 2 may be continuously processed using a metal roll having a desired structure formed on the surface. Alternatively, after filling the female flat mold with an ultraviolet curable resin, a smooth transparent resin sheet is stacked thereon, and the resin is cured by irradiating ultraviolet rays with a high-pressure mercury lamp through the sheet to cure the resin. A fine structure may be formed on the transparent resin sheet by removing.

The thickness of the protective material 2 on which a fine structure is formed by the various methods described above can be 1.5 mm or less, preferably 1.0 to 0.05 mm.

The cholesteric liquid crystal material used for the thermosensitive recording layer 3 has a glass transition temperature of 35 ° C. or more,
Those having an isotropic phase transition temperature of 200 ° C. or less are preferable,
After writing desired information in the liquid crystal phase transition temperature region, the recording layer 3 may be rapidly cooled immediately after the writing to fix the recording state. The molecular weight is not particularly limited, but in applications requiring a high writing speed, it is preferable to use a so-called low to medium molecular cholesteric liquid crystal compound having a molecular weight of about 600 to 2,000. Representative examples of such liquid crystal compounds include compounds represented by the following chemical structural formulas (A) to (G).

[0026]

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[0027]

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[0028]

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[0029]

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[0030]

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[0031]

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[0032]

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In addition to the compounds exemplified here, various low- / medium-molecular cholesteric liquid crystal compounds having a cholesterol group can be used. These compounds may be used alone or in combination of plural kinds of liquid crystalline compounds.

The heat-sensitive recording layer 3 may have a constitution in which the cholesteric liquid crystal compound is dispersed alone or as a mixture of plural kinds in a suitable transparent resin binder, for example, polycarbonate, PMMA, polyvinyl alcohol or the like.

At least one of the low-molecular / medium-molecular cholesteric liquid crystal molecules has a molecular weight of 1,000 to 150.
It is desirable to include zero. All molecular weight is 1000
If less than this, the memory property of the selective reflection state will be low,
If the molecular weight exceeds 1500, the transition temperature to the cholesteric liquid crystal phase becomes too high, which may make writing with a thermal head or the like difficult.

The material used for the substrate 4 is not particularly limited as long as it can maintain the mechanical strength of the recording medium 1 and has a heat distortion temperature equal to or higher than the melting point of the material constituting the recording layer 3. Resin-made sheets and films can be used. For example, polycarbonate resin, polypropylene resin, polyvinyl alcohol resin, polyvinylidene chloride resin, polyester resin such as polyethylene terephthalate, polybutylene terephthalate and polyethylene naphthalate, polystyrene resin, polyamide resin, polyether sulfone resin, polyetherimide resin, polyurethane Examples thereof include sheets and films of resin, polybutadiene resin and the like. These materials may be appropriately selected and used depending on the heat source, the thermal characteristics of the constituent materials of the recording layer 3, the use and use form of the recording medium 1, and the like.

The method of forming the heat-sensitive recording layer 3 on the surface of the base material 4 is as follows: the cholesteric liquid crystal composition or a mixture of the cholesteric liquid crystal composition and the transparent resin binder is dissolved in a suitable solvent such as hexane or tetrahydrofuran. The solution may be applied to the surface of the substrate 4 and air-dried or heat-treated to remove the solvent.

As a method of applying the cholesteric solution,
Various methods such as a roll coating method, a dipping method, a knife coating method, a spray coating method, a spin coating method, and a laminating method can be used. Further, the recording layer 3 may be formed by heating the cholesteric liquid crystal material to an isotropic phase temperature region to be in a molten state, applying this solution on the base material 4 by any of the above-mentioned various methods, and cooling the solution. .

When the protective material 2 is formed on the surface of the recording layer 3, after forming the recording layer 3, a resin sheet or film used as the protective material 2 is thermocompression-bonded, The bonding may be performed using an appropriate adhesive, for example, an epoxy-based adhesive.

Further, in constructing the reversible thermosensitive recording medium 1, as shown in FIG.
May be repeated. Each protective material 2 can be selectively combined with the same sheet or a sheet of a different shape or material according to a purpose such as a direction for improving visibility.

Further, one of the protective members 2 has a light diffusing function in which a transparent resin solution in which inorganic fine particles or resin fine particles such as acrylic resin or silicone resin are dispersed is applied to one surface of a transparent resin sheet. Sheets having the same may be used. As this kind of sheet, products of various grades having different light transmittance and light diffusing ability are already on the market.

Further, as shown in FIG. 8A, the commercially available diffusion sheet is laminated on the protective material 2 as a protective material 2 ', or as shown in FIG. The protective material 2 may be laminated on the protective material 2 ′ made of.

Further, a sheet having a function of thermally protecting the surface of the heat-sensitive recording layer 3 is used as one protective material 2, and a sheet having a function of diffusing selectively reflected light is used as the other protective material 2 '. Can be used. If the functions are differentiated in this way, it is possible to combine sheets having characteristics that can optimally guarantee each function.

When information is recorded on the thermosensitive recording layer 3, first, the temperature of the recording layer 3 is heated to a temperature equal to or higher than the phase transition temperature of the cholesteric liquid crystal. In the cholesteric liquid crystal, a selective reflection color corresponding to the pitch of the layer structure is observed.
Since the cholesteric pitch changes continuously with an increase in temperature, and the selective reflection color changes continuously from red to blue in response to this, the recording layer 3 is heated to a predetermined temperature and the desired color information is obtained. After the formation, the information can be stored by rapidly cooling the recording layer 3.

As a means for heating the recording layer 3, a method of partially heating the recording layer 3 to a predetermined temperature using a conventionally known thermal head or heating roller, or a method using a laser beam such as a YAG laser or a carbon dioxide gas laser. A method of controlling the output energy and the spot diameter and heating in a non-contact state can be adopted.

(Method for Producing Protective Material and Method for Producing Recording Medium) Next, the method for producing the protective material 2 and the method for producing the reversible thermosensitive recording medium 1 will be specifically described. It should be noted that it is needless to say that it can be manufactured by a method other than the method described below, and that the numerical values and shapes are optional.

(Method of Manufacturing Protective Material) First, the protective material 2
Will be described.

Manufacturing Method 1 A flat metal mold 11 (see FIG. 9) in which the fine structures (projections 2b and recesses 2c) shown in FIG. These fine structures are transferred to one surface of the resin sheet by hot pressing. The height a from the peak to the valley is set to 20 μm, and the pitch b is set to 50 μm.

Manufacturing Method 2 A roll-shaped mold 12 (see FIG. 10) engraved on the outer peripheral surface so that the triangular pyramid-shaped fine projections 2d shown in FIG. 4 are continuously connected, and a roll having a smooth outer peripheral surface are prepared. I do. A transparent thermoplastic sheet is sandwiched between these two rolls, and the mold 12 is rotationally driven while the sheet is heated by a heating mechanism built in the roll-shaped mold 12, thereby transferring the fine projections 2d. The projection 2d has an equilateral triangle as a bottom surface, and the other surface is an isosceles triangle. The height a is 40 μm, and the side length b is 80
Set to μm.

Manufacturing Method 3 A roll-shaped mold 13 (see FIG. 11) engraved on the outer peripheral surface so that the square pyramidal fine projections 2e shown in FIG. 5 are continuously connected, and a roll having a smooth outer peripheral surface are prepared. I do. While extruding a transparent thermoplastic resin from a die, it is pressed and cooled by two rolls to form a sheet having fine projections 2e on one surface. The projection 2e has an isosceles triangle on the other surface with the square as the bottom surface. The height a is 40 μm and the side length b is 80 μm
Set to m.

Manufacturing Method 4 A female flat plate mold 14 (see FIG. 12) is prepared by engraving the square pyramid-shaped fine projections 2e shown in FIG. 5 so as to be continuously connected. After filling the concave portion of the mold 14 with an ultraviolet curable resin, a smooth transparent resin sheet is stacked thereon. next,
Ultraviolet rays are irradiated through a transparent resin sheet by a high-pressure mercury lamp to cure the resin, thereby forming fine projections 2e on the transparent resin sheet. The projection 2e has an isosceles triangle on the other surface with the square as the bottom surface. The height a is set to 40 μm, and the side length b is set to 80 μm.

(Manufacturing Method of Recording Medium) Next, manufacturing methods 1 to 7 of the reversible thermosensitive recording medium 1 and a comparative example will be described.

Production method 1 (see FIG. 13) The following structural formula (A ₁ ) was added to 100 parts by weight of tetrahydrofuran.
Was dissolved in 5 parts by weight of a cholesteric liquid crystalline compound represented by the following formula, and the solution was applied to a 100 μm-thick black polyethylene terephthalate sheet 4 with a wire bar and dried to form a 5 μm-thick thermosensitive recording layer 3.

[0054]

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Separately, a protective material 2 having fine ridges 2b and concave ridges 2c was formed on the surface of a smooth transparent polyester sheet having a thickness of 100 μm by the above-mentioned manufacturing method 1, and this was formed on the heat-sensitive recording layer 3. After being superposed, they were heated to 120 ° C. and bonded to obtain a reversible thermosensitive recording medium 1 shown in FIG.

The heat-sensitive recording layer 3 of the recording medium 1 is
Heat to above the isotropic phase transition temperature using a thermal head,
When the temperature was lowered to 60 to 110 ° C., the liquid crystal compound showed a cholesteric liquid crystal phase, and selectively reflected light of a specific wavelength according to the temperature. Red at about 65 ° C, green at about 80 ° C, about 10
It showed a blue color at 0 ° C., and was rapidly cooled from those temperatures to become a solid state while maintaining its reflection color.

Production method 2 (see FIG. 14) The above-mentioned structural formula (A ₁ ) was added to 100 parts by weight of tetrahydrofuran.
5 parts by weight of the cholesteric liquid crystal compound represented by the formula ( ₁ ) and the cholesteric liquid crystal compound 1 represented by the following structural formula (B ₁ )
The solution was applied to a 100 μm-thick black polyethylene terephthalate sheet 4 with a wire bar and dried to form a 5 μm-thick thermosensitive recording layer 3.

[0058]

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Separately, a protective material 2 having fine protrusions 2d on the surface of a smooth transparent polyester sheet having a thickness of 100 μm.
Was produced by the above-mentioned production method 2, and this was superimposed on the thermosensitive recording layer 3 and then heated to 120 ° C. and bonded to obtain a reversible thermosensitive recording medium 1 shown in FIG.

The thermosensitive recording layer 3 of the recording medium 1 is
Heat to above the isotropic phase transition temperature using a thermal head,
When the temperature was lowered to 60 to 110 ° C., the liquid crystal compound showed a cholesteric liquid crystal phase, and selectively reflected light of a specific wavelength according to the temperature. Red at about 63 ° C, green at about 85 ° C, about 10
It showed a blue color at 5 ° C. and rapidly cooled from those temperatures, and became a solid state while maintaining its reflection color.

Production method 3 (see FIG. 15) The following structural formula (F ₁ ) was added to 100 parts by weight of tetrahydrofuran.
Was dissolved on a 100 μm-thick black polyethylene terephthalate sheet 4 with a wire bar and dried to form a 3 μm-thick thermosensitive recording layer 3.

[0062]

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Separately, a protective material 2 having fine protrusions 2d on the surface of a smooth transparent polyester sheet having a thickness of 100 μm.
Was produced by the above-mentioned production method 2, and this was superimposed on the thermosensitive recording layer 3 and then heated to 120 ° C. and bonded to obtain a reversible thermosensitive recording medium 1 shown in FIG.

The heat-sensitive recording layer 3 of the recording medium 1 is
Heat to above the isotropic phase transition temperature using a thermal head,
When the temperature was lowered to 60 to 110 ° C., the liquid crystal compound showed a cholesteric liquid crystal phase, and selectively reflected light of a specific wavelength according to the temperature. Red at about 60 ° C, green at about 75 ° C, about 95
It showed a blue color at ℃ and rapidly solidified from those temperatures to become a solid state while maintaining its reflection color.

Manufacturing method 4 (see FIG. 16) Using a polycarbonate resin, a protective material 2 having a thickness of 80 μm and having fine projections 2e on the surface was manufactured by the above-described manufacturing method 3. Other than that, the reversible thermosensitive recording medium 1 shown in FIG.

The thermosensitive recording layer 3 of the recording medium 1 is
Heat to above the isotropic phase transition temperature using a thermal head,
When the temperature was lowered to 60 to 110 ° C., the liquid crystal compound showed a cholesteric liquid crystal phase, and selectively reflected light of a specific wavelength according to the temperature. Red at about 65 ° C, green at about 80 ° C, about 10
It showed a blue color at 0 ° C., and was rapidly cooled from those temperatures to become a solid state while maintaining its reflection color.

Production method 5 (see FIG. 17) The following structural formula (C ₁ ) was added to 100 parts by weight of tetrahydrofuran.
Was dissolved in 5 parts by weight of a cholesteric liquid crystalline compound represented by the following formula, and the solution was applied to a 100 μm-thick black polyethylene terephthalate sheet 4 with a wire bar and dried to form a 5 μm-thick thermosensitive recording layer 3.

[0068]

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Separately, a protective material 2 having fine projections 2 e was formed on a smooth transparent polyester sheet having a thickness of 70 μm using an acrylic ultraviolet curable resin by the above-mentioned manufacturing method 4. After superimposing on
By heating to 120 ° C. and bonding, a reversible thermosensitive recording medium 1 shown in FIG. 17 was obtained.

The heat-sensitive recording layer 3 of the recording medium 1 is
Heat to above the isotropic phase transition temperature using a thermal head,
When the temperature was lowered to 60 to 110 ° C., the liquid crystal compound showed a cholesteric liquid crystal phase, and selectively reflected light of a specific wavelength according to the temperature. Red at about 60 ° C, green at about 75 ° C, about 95
It showed a blue color at ℃ and rapidly solidified from those temperatures to become a solid state while maintaining its reflection color.

Production method 6 (see FIG. 18) The above-mentioned structural formula (A ₁ ) was added to 100 parts by weight of tetrahydrofuran.
Was dissolved in 5 parts by weight of the cholesteric liquid crystalline compound shown in the above, and the solution was applied to a 100 μm-thick black polyethylene terephthalate sheet 4 with a wire bar and dried to form a 5 μm-thick thermosensitive recording layer 3.

Separately, a protective material 2 having fine convex stripes 2b and concave stripes 2c was formed on the surface of a smooth transparent polyester sheet having a thickness of 100 μm by the above-mentioned production method 1, and this was formed on the heat-sensitive recording layer 3. Superimposed. Further, a diffusion sheet 2 ′ (manufactured by Kimoto Co., Ltd.) was superimposed thereon, and the ends of the respective sheets were heat-melted and stuck to obtain a reversible thermosensitive recording medium 1 shown in FIG.

The heat-sensitive recording layer 3 of the recording medium 1 is
Heat to above the isotropic phase transition temperature using a thermal head,
When the temperature was lowered to 60 to 110 ° C., the liquid crystal compound showed a cholesteric liquid crystal phase, and selectively reflected light of a specific wavelength according to the temperature. Red at about 65 ° C, green at about 80 ° C, about 10
It showed a blue color at 0 ° C., and was rapidly cooled from those temperatures to become a solid state while maintaining its reflection color.

Production method 7 (see FIG. 19) The above-mentioned structural formula (F ₁ ) was added to 100 parts by weight of tetrahydrofuran.
Was dissolved in 5 parts by weight of the cholesteric liquid crystal compound shown in the above, and the solution was applied to a 100 μm-thick black polyethylene terephthalate sheet 4 with a wire bar and dried to form a 3 μm-thick thermosensitive recording layer 3.

Separately, a protective material 2 having fine projections 2d on the surface of a smooth transparent polyester sheet having a thickness of 100 μm.
A was produced by the above-mentioned production method 2, and this was overlaid on the thermosensitive recording layer 3. Further, using a transparent polyester sheet, a protective member 2B having a thickness of 80 μm and having fine protrusions 2e on the surface is prepared by the above-described preparation method 3 and superimposed on the protective member 2A, and the end of each sheet is thermally melted. To obtain a reversible thermosensitive recording medium 1 shown in FIG.

The heat-sensitive recording layer 3 of the recording medium 1 is
Heat to above the isotropic phase transition temperature using a thermal head,
When the temperature was lowered to 60 to 110 ° C., the liquid crystal compound showed a cholesteric liquid crystal phase, and selectively reflected light of a specific wavelength according to the temperature. Red at about 60 ° C, green at about 75 ° C, about 95
It showed a blue color at ℃ and rapidly solidified from those temperatures to become a solid state while maintaining its reflection color.

Comparative Example A transparent polyester sheet having a smooth surface and a thickness of 100 μm was used as a protective material.
A reversible thermosensitive recording medium was obtained by the same process.

(Evaluation of Reversible Thermosensitive Recording Medium) Recording was performed on the reversible thermosensitive recording media obtained in the above Production Methods 1 to 7 and Comparative Examples using a thermal head, and the normal direction of the recording display surface and all directions. The recorded contents were observed and evaluated under indoor lighting, which is a normal use environment, in a state of being tilted up to 60 °.

With the recording media obtained by the above-mentioned production methods 1 to 7, the display of the same color tone was obtained, and the readability of the display contents to the naked eye was good. On the other hand, in the recording medium obtained in the comparative example, the display color becomes shorter in wavelength as the viewing angle becomes larger. For example, when the red display portion is observed from a direction inclined by 40 °, the color changes to yellowish. The entire displayed content is difficult to read with the naked eye.

(Other Embodiments) The reversible thermosensitive recording medium according to the present invention is not limited to the above embodiment, but can be variously modified within the scope of the invention.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing an embodiment of a reversible thermosensitive recording medium according to the present invention.

FIG. 2 is a perspective view showing a first example of a fine structure formed on a protective material.

FIG. 3 is a perspective view showing a second example of the fine structure formed on the protective material.

FIG. 4 is a perspective view showing a third example of the fine structure formed on the protective material.

FIG. 5 is a perspective view showing a fourth example of the fine structure formed on the protective material.

FIG. 6 is a perspective view showing a fifth example of the fine structure formed on the protective material.

FIG. 7 is a cross-sectional view showing a loading state of a protective material.

FIG. 8 is a cross-sectional view showing another loading form of the protection member.

FIG. 9 is a perspective view showing a method 1 of manufacturing a protective material.

FIG. 10 is a perspective view showing a method 2 for manufacturing a protective material.

FIG. 11 is a perspective view showing a method 3 for manufacturing a protective material.

FIG. 12 is a perspective view showing a method 4 for manufacturing a protective material.

FIG. 13 is a perspective view illustrating a recording medium manufacturing method 1;

FIG. 14 is a perspective view showing a recording medium manufacturing method 2;

FIG. 15 is a perspective view showing a recording medium manufacturing method 3;

FIG. 16 is a perspective view showing a recording medium manufacturing method 4;

FIG. 17 is a perspective view illustrating a recording medium manufacturing method 5;

FIG. 18 is a perspective view showing a recording medium manufacturing method 6;

FIG. 19 is a perspective view showing a recording medium manufacturing method 7;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Reversible thermosensitive recording medium 2, 2 ', 2A, 2B ... Protective material 2a-2f ... Microstructure 3 ... Thermosensitive recording layer 4 ... Substrate

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideaki Ueda 2-13-13 Azuchicho, Chuo-ku, Osaka-shi, Osaka F-term in Osaka International Building Minolta Co., Ltd. (reference) 2C005 HB04 JA02 JA26 JC02 KA06 KA48 LB06 LB25 2H111 HA07 HA23 HA35

Claims (8)

[Claims] 1. A reversible thermosensitive recording medium provided with a thermosensitive recording layer composed of a thermotropic cholesteric liquid crystal, comprising a diffusion layer for diffusing selectively reflected light on a surface on which recorded information is viewed. Thermal recording medium. 2. The heat-sensitive recording layer has a glass transition temperature of 80 ° C. or more on its surface to thermally protect the surface of the recording layer, and has a function of selecting a surface opposite to the surface in contact with the recording layer. The reversible thermosensitive recording medium according to claim 1, further comprising a protective material having a function of diffusing reflected light. 3. The reversible thermosensitive recording according to claim 2, further comprising a sheet having a function of thermally protecting the surface of the thermosensitive recording layer and a sheet having a function of diffusing selectively reflected light. Medium. 4. The reversible thermosensitive recording medium according to claim 1, wherein a protective material having a large number of hemispherical or polyhedral fine protrusions is provided on the surface of the thermosensitive recording layer. 5. The reversible thermosensitive recording medium according to claim 1, wherein a protective material having a number of fine irregularities formed thereon is provided on the surface of the thermosensitive recording layer. 6. The reversible thermosensitive recording medium according to claim 1, wherein a protective material coated with a resin solution containing fine particles is provided on the surface of the thermosensitive recording layer. 7. The reversible thermosensitive recording medium according to claim 1, wherein the thermotropic cholesteric liquid crystal selectively reflects light in a visible light region and can perform full-color display. 8. The reversible thermosensitive recording medium according to claim 7, wherein the thermotropic cholesteric liquid crystal has a glass transition temperature of 35 ° C. or more and an isotropic phase transition temperature of 200 ° C. or less.