JP2001290119A - Reversible recording material and method for recording using the reversible recording material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reversible recording material in which recording and erasing of color images can be repeated and to provide a method for recording in the material. SOLUTION: The reversible recording material is obtained by forming a beat sensitive recording layer containing microcapsules housing a heat color- developing cholesteric liquid crystal compound (preferably having-<=2,000 mol.wt. and 30 to 150 deg.C glass transition temperature) on a supporting body. The obtained recording material is heated to the temperature at which the liquid crystal compound shows an isotropic or cholesteric liquid crystal phase and then cooled at >=1 deg.C/sec cooling rate to a temperature lower than the glass transition temperature of the compound to fix the color image in the cholesteric phase. If necessary, the recorded image is erased by heating the material to the temperature at which the material transits to a noncholesteric liquid crystal phase or to other temperature to change the color developing phase.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a reversible recording material and a recording method using the reversible recording material.
More specifically, the present invention relates to a reversible recording material that can be repeatedly rewritten by writing and erasing information by displaying images in multiple colors by heating, and a reversible image recording method using the reversible recording material.

[0002]

2. Description of the Related Art Heretofore, as reversible recording materials, heat-sensitive recording materials such as leuco dyes / decolorizers or low-molecular organic compounds / polymer resin matrices and photochromic compounds such as spiropyran derivatives have been used. Optical recording materials used are known.

[0003] In a leuco dye / desensitizer recording material, when heated and then rapidly cooled, the lactone ring in the leuco dye molecular structure is opened to form a color. The ring closes and discolors. In the organic low molecular weight / high molecular weight resin matrix type recording material, for example, in the case of a combination of behenic acid and PVCA (vinyl chloride-vinyl acetate copolymer), the transparency / scattering of a color image can be switched according to the heating temperature.
However, these conventional reversible recording materials are only capable of displaying a single color, and there is no material capable of achieving both multicolor recording characteristics and rewritable characteristics.

[0004] In recent years, a color thermosensitive recording material by a new method using a cholesteric liquid crystalline compound has been announced (N. Tamaoki, et. Al, Advanced).
Materials, 9 (14), 1102 (199
7)). This recording material is a recording material containing a cholesteric liquid crystal compound having a molecular weight of 2000 or less and a glass transition temperature of 35 ° C. or more, as described in JP-A-11-024027. By quenching from a high temperature forming a cholesteric liquid crystal to a temperature below its glass transition temperature,
While maintaining the reflected light based on the helical molecular arrangement in the cholesteric liquid crystal phase, it becomes a glassy solid in this state. For this reason, it has attracted attention as a color recording material that can be repeatedly rewritten.

In a recording material using such a cholesteric liquid crystal compound, when the liquid crystal compound is heated to a temperature at which its isotropic phase or liquid crystal phase is formed, the liquid crystal compound has fluidity. In particular,
When recording and erasing operations are repeatedly performed on the liquid crystal compound-containing heat-sensitive recording layer by a contact-type heating device such as a thermal head, unevenness in the thickness of the recording layer occurs due to pressure stress, or the edge of the recording material There is a problem that a liquid crystal compound leaks out of the device. In addition, the cholesteric liquid crystal compound may be decomposed and oxidized and deteriorated by ultraviolet light or air when used for a long period of time. Furthermore, in a manufacturing process of filling a liquid crystal compound between two substrates, at least one of which is transparent, it is necessary to use an organic solvent or to heat and melt the material to perform the casting, and the manufacturing process is complicated. .

[0006]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, and uses a reversible recording material capable of performing color recording and having repetitive rewritable properties. It is intended to provide a recording method.

[0007]

The reversible recording material of the present invention comprises a support and a thermosensitive recording layer formed thereon, wherein the thermosensitive recording layer is a cholesteric liquid crystal compound having a thermochromic property. And a large number of microcapsules comprising a wall film material enclosing the microcapsules. In the reversible recording material of the present invention, the thermochromic cholesteric liquid crystal compound preferably has a glass transition temperature of 30 to 150 ° C. In the reversible recording material of the present invention, it is preferable that the wall film material is formed of an acid aldehyde resin. In the reversible recording material of the present invention, the thermochromic cholesteric liquid crystalline compound is represented by the following general formula (I): Z—O—CO— (CH ₂ ) _m —R— (CH ₂ ) _n —CO—O— Y (I) [In the formula (I), Z represents a cholesteryl group, Y represents a cholesteryl group, a hydrogen atom or an alkyl group, and R represents p-
Represents a phenylene group, a 4,4'-biphenylene group, a butylene diyne group or a 1,5-hexadienylene group, and m and n each independently represent an integer of 1 to 20. ] Is preferable. In the reversible recording material of the present invention, in a number of microcapsules in the thermosensitive recording layer, the cholesteric liquid crystalline compound has a molecular weight of 2000 or less and a glass transition temperature of 30 to 150 ° C., and the wall film material Is preferably formed of an organic polymer substance. In the reversible recording material of the present invention, the cholesteric liquid crystal compound is represented by the following formula (II): Z—O—CO—R ¹ —CO—O—Y (II) [wherein, in the formula (II), Z and Y Each independently represents a cholesteryl group, a hydrogen atom or an alkyl group, R ¹ represents a divalent hydrocarbon group having 2 to 34 carbon atoms, and at least one of Z and Y is a cholesteryl group Represents Is preferable. In the reversible recording material of the present invention, the formula (II)
In a divalent hydrocarbon group represented by the R is, the following formula (III), (IV) and _{(V): - (CH 2} ) m-C≡C-C≡C- (CH 2) n- (III) wherein, in the formula (III), m and n each independently represent an integer of 1 or more, provided that the sum of m and n is 3
Does not exceed 0. ] _{- (CH 2) m'-CH} = CH-CH 2 -CH 2 -CH = CH- (CH 2) n '- (IV) [where, m of formula (IV)' and n 'are each each other Independently represent an integer of 1 or more, provided that the sum of m ′ and n ′ does not exceed 28. ] _{- (CH 2) m "-} (V) [where, m in the formula (V)" represents an integer of 2 to 34. ]
It is preferable to be selected from cholesteric liquid crystalline compounds represented by In the reversible recording material of the present invention, it is preferable that the organic polymer substance for a wall film material contains at least one selected from polyurea and polyurethane. In the reversible recording material of the present invention, the microcapsules are a cholesteric liquid crystalline compound and a polymer-forming raw material that forms at least one of polyurea and polyurethane by polymerization with a water-insoluble organic solvent having a boiling point of 100 ° C. or less. The organic solvent solution is emulsified and dispersed in an aqueous medium, the emulsified dispersion is heated to volatilize and remove the organic solvent, and then the polymer-forming raw material is polymerized. It is preferably prepared. In the reversible recording material of the present invention, the polymer-forming raw material forming the wall material of the microcapsule is a polyvalent isocyanate compound, an adduct of a polyvalent isocyanate compound with a polyol, a biuret of a polyvalent isocyanate compound, It is preferably selected from the group consisting of an isocyanurate of a polyvalent isocyanate compound and a mixture of a polyvalent isocyanate compound and a polyol.
In the reversible recording material of the present invention, the polymer-forming raw material may further contain a polyamine compound. In the reversible recording material of the present invention, the content of the cholesteric liquid crystal compound in the microcapsules is preferably from 10 to 95% by weight based on the weight of the microcapsules. The recording method (1) of the reversible recording material of the present invention comprises a support and a heat-sensitive recording layer formed thereon, wherein the heat-sensitive recording layer comprises a cholesteric liquid crystalline compound having thermochromic properties. Using a reversible recording material containing a large number of microcapsules encapsulated in the material, the thermosensitive recording layer is heated to a temperature at which the cholesteric liquid crystal compound exhibits a cholesteric liquid crystal phase, according to an image pattern to form a colored image. The color image is erased or its hue is changed by changing the temperature of the color image. The recording method (2) of the reversible recording material of the present invention comprises a support, a support formed thereon, a molecular weight of 2000 or less, and a glass transition temperature of 30 to 150 ° C.
Having a heat-sensitive recording layer containing a cholesteric liquid crystal compound, wherein the cholesteric liquid crystal compound is contained in a large number of microcapsules having an organic polymer material as a wall film material, using a reversible recording material encapsulated therein. Heating the thermosensitive recording layer to a temperature at which the cholesteric liquid crystal compound exhibits an isotropic phase or a cholesteric liquid crystal phase in accordance with an image pattern, and cooling the thermosensitive recording layer at a cooling rate of 1 ° C./sec or more. By cooling to a temperature lower than the glass transition temperature of the compound, the helical molecular arrangement of the cholesteric liquid crystal phase is fixed to form a cholesteric glass phase, and the selection caused by the helical molecular arrangement of the cholesteric liquid crystal compound is caused. It is characterized by recording an image showing a reflection color. In the recording method (2) of the reversible recording material of the present invention, in the heating according to the image pattern of the thermosensitive recording layer, a heating recording head is used as a heating means, and thermal energy given to the thermosensitive recording layer from the recording head is controlled. By setting the image temperature of the heat-sensitive recording layer at the start of the cooling, thereby controlling the pitch of the helical molecular arrangement of the cholesteric liquid crystal phase, to form a multicolor image showing an arbitrary reflection color. Is preferred.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory sectional view of an example of the constitution of the reversible recording material of the present invention. Reversible recording material 1 of the present invention
Is provided with a thermosensitive recording layer 4 including a microcapsule 3 in which an organic polymer substance is used as a capsule wall material and a cholesteric liquid crystal compound is encapsulated therein, on a support 2. It is preferable that the support has a function of absorbing visible light in order to observe a reflection color derived from the pitch of the helical molecular arrangement of the cholesteric liquid crystal phase. Highly transparent protective layer 5 thereon
Is preferably provided.

In the present invention, the heat-sensitive recording layer containing the microcapsules encapsulating the cholesteric liquid crystal compound is heated to a temperature at which the cholesteric liquid crystal compound exhibits a cholesteric liquid crystal phase in accordance with an image pattern, and the heated liquid crystal compound is heated to an isotropic phase or an isotropic phase. After the color image is formed in the liquid crystal phase state, the color image can be erased or its hue can be changed by changing the temperature of the color image. Preferably, when the color image is rapidly cooled to a temperature lower than the glass transition temperature of the cholesteric liquid crystalline compound, the cholesteric liquid crystal phase becomes a glassy solid (cholesteric glass phase) while maintaining its helical molecular arrangement, and becomes cholesteric. The reflection color derived from the pitch of the helical molecular arrangement of the liquid crystal phase can be observed from the outside. For example, by controlling the temperature of the thermosensitive recording layer at the start of rapid cooling, the cooling rate, and the area (image area),
A multicolor image or the like having an optional selective reflection color can be formed reversibly (erasably).

[0010] By heating the reversible recording material, when the cholesteric liquid crystalline compound is in an isotropic phase or a liquid crystal phase, it enters a state having fluidity. If the recording and erasing of an image are repeatedly performed using a contact-type heating device such as a thermal head in a state having this fluidity, the above-described problem occurs. However, in the recording material of the present invention, cholesteric Since the liquid crystalline compound is encapsulated in the microcapsules, the thickness stress of the heat-sensitive recording layer does not occur due to the pressure stress at the time of heating for recording and erasing the image, and from the edge of the recording material. Problems such as leakage of the liquid crystal compound do not occur.

Furthermore, in the microcapsules, the cholesteric liquid crystalline compound is surrounded and enclosed by the polymer material wall material, so that direct contact with the outside air is cut off. The cholesteric liquid crystalline compound was hardly oxidized, decomposed and deteriorated by ultraviolet rays, and showed sufficient durability in long-term use as a reversible recording material. Moreover,
The recording material of the present invention is a cholesteric liquid crystal compound,
By encapsulating it in a microcapsule, it is possible to suppress a shift in the selective reflection wavelength caused by viewing the recorded image obliquely with respect to the recording surface, thereby reducing the viewing angle dependence of the recorded image. It has advantages such as being able to.

The cholesteric liquid crystalline compound used in the present invention can be handled as ordinary solid fine particles by encapsulating it in microcapsules. For this reason, there is no need to use an organic solvent or heat-melt and cast for forming the heat-sensitive recording layer, and the heat-sensitive recording layer can be formed by a general coating method using an aqueous paint. Therefore, the manufacturing process of the heat-sensitive recording layer can be significantly simplified.

The type of the cholesteric liquid crystalline compound that can be used in the present invention includes a compound having a molecular weight of 2000 or less, preferably 500 to 15 as long as it can fix the cholesteric reflection color.
00, and the glass transition temperature is 30 to 15
There is no particular limitation as long as it is 0 ° C, preferably 50 to 110 ° C.

In the recording material of the present invention, when the molecular weight of the cholesteric liquid crystalline compound exceeds 2,000, the time required for recording or erasing an image is disadvantageously increased. On the other hand, if the glass transition temperature is lower than 30 ° C., the recorded image may be discolored and faded with time. Is generated.

The chemical structure of the cholesteric liquid crystal compound preferred for use in the present invention is not particularly limited.
When a compound represented by the following formula (I) or (II) is used, a particularly clear color recorded image can be obtained. Z—O—CO— (CH ₂ ) _m —R— (CH ₂ ) _n —CO—O—Y (I) [In the formula (I), Z represents a cholesteryl group, and Y represents a cholesteryl group, a hydrogen atom or Represents an alkyl group, and R is p-
Represents a phenylene group, a 4,4'-biphenylene group, a butylene diyne group or a 1,5-hexadienylene group, and m and n each independently represent an integer of 1 to 20. Z—O—CO—R ¹ —CO—O—Y (II) (In the formula (I), Z and Y each independently represent a cholesteryl group, a hydrogen atom or an alkyl group, and R ¹ represents Represents a divalent hydrocarbon group having 2 to 34 carbon atoms, Z and Y
At least one of which represents a cholesteryl group)

Further, in the compound of the formula (I), the divalent hydrocarbon group represented by R is represented by the following formula (III):
It is preferable that they are represented by (IV) and (V). _{(III) - (CH 2)} m-C≡C-C≡C- (CH 2) n- (m and n in formula (III), each other and independently represent an integer of 1 or more, However, the sum of m and n is 3
Does not exceed 0. ) M in _{(IV) - - (CH 2} ) m'-CH = CH-CH 2 -CH 2 -CH = CH (CH 2) n'- ( formula (IV) 'and n' are mutually respectively independently represents an integer of 1 or more, provided that the sum of m 'and n' does not exceed 28). (V) - ( CH 2) m "- ( formula (V) m in" is Represents an integer of 2 to 34)

Preferred examples of the cholesteric liquid crystalline compound represented by the chemical structural formula (II) include 1
0,12-docosadiyne dicarboxylic acid cholesteryl ester, 8,12-eicosadiene dicarboxylic acid cholesteryl ester, eicosane dicarboxylic acid cholesteryl ester, 10,12-pentacosadiin dicarboxylic acid cholesteryl ester, dodecadicarboxylic acid diester Cholesteryl ester and 12,14-hexacosadiin dicarboxylic acid dicholesteryl ester can be mentioned. The compound of the above formula (I) is prepared by converting the compound of the above formula (II)
[4- (5-cholesteryloxycarbonylpentyloxy) phenoxyhexanoic acid cholesteryl ester], [4- (3-cholesteryloxycarbonylpropyloxy) biphenyloxybutanoic acid cholesteryl ester], [4 -(7-cholesteryloxycarbonylpentyloxy) phenoxyoctanoic acid cholesteryl ester] and 8,12-eicosadiene dicarboxylic acid dicholesteryl ester. The compounds of the above formulas (I) and (II) are disclosed in
It can be obtained by a method described in Japanese Patent Application Laid-Open No. 1-24027, Japanese Patent No. 2936137 or Japanese Patent No. 2946142.

The cholesteric liquid crystal compounds used in the present invention include, in addition to the compounds of the above formulas (I) and (II), main chain liquid crystals such as polypeptides, polyesters and polyamides, polyacrylates and polysiloxanes. And a rigid main chain type liquid crystal such as a cellulose derivative. Further, the cholesteric liquid crystalline compound used in the present invention may be used singly, or two or more kinds may be appropriately mixed and used.

In the present invention, a microcapsule formed by enclosing the cholesteric liquid crystal compound in a microcapsule wall film material is used.

The microcapsules used in the present invention can be prepared by various known methods. For example, the cholesteric liquid crystal compound described above, or a core substance (oil-based liquid) obtained by dissolving the cholesteric liquid crystal compound in an organic solvent as needed, is emulsified and dispersed in an aqueous medium, and the liquid around the core substance droplets is dispersed. Microcapsules are prepared by a method of forming a wall film made of an organic polymer substance. Specific examples of the organic polymer substance forming the wall film of the microcapsule include, for example, polyurethane resin, polyurea resin, polyurethane-polyurea resin,
Examples include polyamide resin, polyester resin, polycarbonate resin, aminoaldehyde resin, melamine resin, polystyrene resin, styrene-methacrylate copolymer resin, styrene-acrylate resin, gelatin, and polyvinyl alcohol. Among them, microcapsules having a wall film made of polyurethane-polyurea resin or aminoaldehyde resin are particularly preferably used because of their excellent heat resistance. More preferably, microcapsules having a wall film made of a polyurethane-polyurea resin are used.

In order to prepare a microcapsule containing at least one polymer selected from the polyurea-polyurethane resins used in the present invention as a wall material and encapsulating a cholesteric liquid crystal compound, for example, a cholesteric liquid crystal compound is prepared. It is dissolved in a low-boiling water-insoluble organic solvent having a boiling point of 100 ° C. or less, and a polymer-forming raw material, for example, a polyisocyanate compound alone, or a mixture of a polyvalent isocyanate and a polyol that reacts with the same, or a polyvalent isocyanate , A mixture of a polyol, biuret, or an adduct with isocyanuric acid is emulsified and dispersed in an aqueous medium containing and dissolving a protective colloidal substance such as polyvinyl alcohol, and further mixed with a reactive substance such as polyamine if necessary. The emulsified dispersion is heated and Volatile removal, and then polymerizing the polymer-forming material on the surface of the droplet particles to form a polyurea, a wall film material made of polyurethane, and a microcapsule in which a cholesteric liquid crystal compound is encapsulated. Form.

A microcapsule having a wall film made of an aminoaldehyde resin can be obtained by adding a wall film agent after emulsification of a core substance. Capsules having an aminoaldehyde resin membrane used in the present invention are generally urea, thiourea, alkyl urea, ethylene urea, acetoguanamine,
At least one amine such as benzoguanamine, melamine, guanidine, biuret, cyanamide and at least one aldehyde such as formaldehyde, acetaldehyde, paraformaldehyde, glutaraldehyde, glyoxal, furfural or an initial condensate obtained by condensing them In-si using
It is manufactured by a tu polymerization method.

In the microcapsule preparation step,
In order to adequately volatilize and remove the organic solvent from the dispersion, it is necessary to experimentally set the volatilization and removal conditions in consideration of the type of the solvent, the emulsification and dispersion conditions, the mixing ratio of the cholesteric liquid crystal compound and the solvent, and the like. Good.

The polymer-forming raw materials used for forming the microcapsules include a mixture of a polyamine compound and a polyvalent isocyanate compound for forming polyurea.
A mixture of a polyamine compound and a carbonate compound, a mixture of a polyamine compound and bisurethane, and / or a mixture of a polyamine and urea, and a compound of a polyvalent isocyanate compound and a polyol for forming a polyurethane; An adduct with a polyol and / or an isocyanurate of a polyvalent isocyanate can be used.

Examples of the polyvalent isocyanate compound used as a polymer-forming raw material include m-phenylene diisocyanate, p-phenylene diisocyanate,
2,6-tolylene diisocyanate, 2,4-tolylene diisocyanate, naphthalene-1,4-diisocyanate, diphenylmethane-4,4'-diisocyanate, 3,3'-dimethyldiphenylmethane-4,4'-
Diisocyanate, xylylene-1,4-diisocyanate, 4,4'-diphenylpropane diisocyanate, trimethylene diisocyanate, hexamethylene diisocyanate, propylene-1,2-diisocyanate, butylene-1,2-diisocyanate, cyclohexylene-1,2- Diisocyanates such as diisocyanate and cyclohexylene-1,4-diisocyanate;
Triisocyanates such as 4,4 ', 4 "-triphenylmethane triisocyanate and toluene-2,4,6-triisocyanate; 4,4'-dimethyldiphenylmethane-2,2', 5,5'-tetraisocyanate And the like.

Examples of the adduct of a polyvalent isocyanate and a polyol include a trimethylolpropane adduct of hexamethylene diisocyanate, a trimethylolpropane adduct of 2,4-tolylenediisocyanate, and a trimethylolpropane adduct of xylylenediisocyanate. And an isocyanate prepolymer such as a hexanetriol adduct of tolylene diisocyanate. A polyvalent isocyanate compound, for example, an adduct of hexamethylene diisocyanate with biuret,
Polyvalent isocyanate compounds, for example, adducts of hexamethylene diisocyanate with isocyanuric acid and the like can also be used as the polymer-forming raw material of the present invention.

As the polyol compound used for the polymer-forming raw material, for example, ethylene glycol,
1,3-propanediol, 1,4-butanediol,
1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, propylene glycol, 2,3-dihydroxybutane, 1,2-dihydroxybutane, 1,3-dihydroxy Butane, 2,2-dimethyl-1,3-propanediol, 2,4-pentanediol, 2,5-hexanediol, 3-methyl-1,5-pentanediol, 1,
4-cyclohexanedimethanol, dihydroxycyclohexane, diethylene glycol, 1,2,6-trihydroxyhexane, phenylethylene glycol, 1,
Aliphatic polyols such as 1,1-trimethylolpropane, hexanetriol, pentaerythritol, and glycerin; aromatics such as 1,4-di (2-hydroxyethoxy) benzene and 1,3-di (2-hydroxyethoxy) benzene Condensation product of polyhydric alcohol and alkylene oxide, p-xylylene glycol, m-xylylene glycol, α, α′-dihydroxy-p-diisopropylbenzene, 4,4′-dihydroxydiphenylmethane, 2- (p, p '-Dihydroxydiphenylmethyl)
Benzyl alcohol, 4,4'-isopropylidene diphenol, 4,4'-dihydroxydiphenyl sulfone, 4,4'-dihydroxydiphenyl sulfide,
Examples thereof include ethylene oxide adducts of 4,4'-isopropylidene diphenol, propylene oxide adducts of 4,4'-isopropylidene diphenol, and acrylates having a hydroxy group in the molecule such as 2-hydroxyacrylate.

Of course, the polyvalent isocyanate compound, the adduct of the polyvalent isocyanate and the polyol, and the polyol compound are not limited to the above compounds.
These may be used alone or in combination of two or more as needed. It is particularly preferable to use a polyvalent isocyanate compound or an adduct of a polyvalent isocyanate compound and a polyol compound having at least three isocyanate groups in the molecule.

The polyamine compound used in the polymer-forming raw material of the present invention includes, for example, ethylenediamine, trimethylenediamine, tetramethylenediamine,
Pentamethylenediamine, hexamethylenediamine, p
-Phenylenediamine, m-phenylenediamine, piperazine, 2-methylpiperazine, 2,5-dimethylpiperazine, 2-hydroxytrimethylenediamine, diethylenetriamine, triethylenetriamine, triethylenetetramine, diethylaminopropylamine, tetraethylenepentamine, epoxy Examples include amine adducts of compounds. Also, within a range that does not impair the purpose of the present invention,
Other polymer substances may be included.

As the organic solvent used for preparing the microcapsules, it is preferable to use a hydrophobic solvent having a boiling point of 100 ° C. or lower, more preferably 80 ° C. or lower. For example, such low-boiling hydrophobic (water-insoluble) organic solvents include butyl chloride (boiling point 78 ° C.), ethylidene chloride (57 ° C.), propyl chloride (46 ° C.), and methylene chloride (42 ° C.). , Ethyl acetate (77 ° C), methyl acetate (57 ° C) and the like. Acetone (56 ° C.), methanol (65 ° C.) and the like are not preferable because they have high compatibility with water and the resulting emulsion may become unstable.

The amount of the organic solvent used in the preparation of the microcapsules should be appropriately set according to the type and amount of the cholesteric liquid crystal compound to be used, the type of the organic solvent, etc., and is not particularly limited. Since it is preferable that the emulsified and dispersed droplets be in a sufficiently stable state, in the case of polyurethane and polyurea resin, an organic solvent,
The ratio of the organic solvent to the total weight of the liquid crystal compound and the microcapsule wall film material is generally 10 to 95%.
It is preferably within the range of about% by weight.

In the microcapsule for a recording material of the present invention, the weight ratio of the cholesteric liquid crystal compound to the polymer material wall film is set so as not to lower the storage stability of the cholesteric liquid crystal compound in the microcapsule due to long-term storage. In order to prevent deformation of the shape of the reversible recording material during repeated use, it is preferable that the weight ratio of the large amount of wall film material is higher than that of ordinary microcapsules.
From these points, based on the total weight of the microcapsules,
The content of the cholesteric liquid crystal compound is preferably from 10 to 95% by weight, and more preferably from 50 to 95% by weight.

In the present invention, emulsifiers (protective colloid agents) used for preparing microcapsules include modified polyvinyl alcohol such as polyacrylamide, polyvinylpyrrolidone, polyvinyl alcohol, and sulfonated polyvinyl alcohol, methylcellulose, carboxymethylcellulose, and styrene. Water-soluble synthetic high molecular compounds such as maleic anhydride copolymer salts and derivatives thereof can be used. At the same time, a surfactant, an antifoaming agent and the like may be used. The amount of the emulsifier used in preparing the microcapsules is not particularly limited, but generally,
It is preferably 1 to 50% by weight, more preferably about 3 to 30% by weight, based on the weight of the microcapsules.

In the inclusion of the microcapsules used in the present invention, in addition to the cholesteric liquid crystal compound, if necessary, an ultraviolet absorber, an antioxidant, an oil-soluble fluorescent dye,
A release agent or the like may be added. In addition, when polymerizing the microcapsules, a tin compound, a polyamide compound, an epoxy compound, a polyamine compound, or the like may be used in combination as a reaction accelerator. When a polyamine compound is used in the material for forming a wall film, it is preferable to use an aliphatic polyamine compound from the viewpoint of not deteriorating the light resistance of the obtained microcapsules.

The particle size of the liquid crystal microcapsules used in the present invention is preferably about 0.5 to 100 μm, more preferably 5 to 50 μm. The smaller the average particle diameter, the higher the color-forming sensitivity.On the other hand, if the average particle size is too small, it may not be possible to form a sufficient helical molecular arrangement in the cholesteric liquid crystal phase. The purity may be reduced.

The heat-sensitive recording layer of the recording material of the present invention contains a binder in addition to the above-mentioned microcapsules containing a cholesteric liquid crystal compound, and furthermore, organic and inorganic pigments and spacer particles as long as the effects of the present invention are not impaired. ,
It may contain an additive composed of one or more of a crosslinking agent, a wax, a metal soap, an organic dye, a colored pigment, a fluorescent dye, an oil repellent, a defoamer, a viscosity modifier, an antioxidant, and the like. However, it is desirable that these materials have no absorption in the wavelength region of the selectively reflected light to be recorded. The content of the microcapsules containing the cholesteric liquid crystal compound in the heat-sensitive recording layer is preferably 50% by weight or more, more preferably 60 to 95% by weight. When the content of the microcapsules containing the cholesteric liquid crystal compound is less than 50% by weight, the reflectance of the recorded image may be reduced.

In order to obtain a clear recorded image, the coating amount of the heat-sensitive recording layer is preferably about 5 to 50 g / m ² , more preferably 10 to 30 g / m ² . When the coating amount of the recording layer is less than 5 g / m ² , sufficient selective reflection cannot be obtained, so that the sharpness of the recorded image may be insufficient. On the other hand, if the coating amount exceeds 50 g / m ² , the recording layer becomes more cloudy, and the recorded image may be blurred and turbid.

There are no particular restrictions on the type, shape, dimensions, etc., of the material forming the support used in the present invention. For example, paper, polyolefin-based synthetic paper, synthetic fiber paper, non-woven fabric, PET, PES, or A film made of a synthetic resin such as polyetherimide, or a sheet or plate of glass or the like can be used. The surface of the support may be flat or curved, and may be flexible or rigid. However, by using a flexible sheet material, it is hard to break when bent, and can be bound to multiple files and can be easily carried, such as paper-like handling. Is more preferably used.

In the present invention, in order to more clearly observe the reflected color derived from the pitch of the helical molecular arrangement of the cholesteric liquid crystal phase, the function of absorbing visible light transmitted through the recording layer is provided on the back of the heat-sensitive recording layer. Is effective. This effect can be achieved, for example, by applying a black paint between the heat-sensitive recording layer and the support to provide a light absorbing layer. When a transparent support is used, a light-absorbing layer can be formed on the surface (back surface) of the support opposite to the heat-sensitive recording layer. Further, a black pigment or the like may be mixed in the support to give the support itself a light absorbing function.

By using, for example, a thermosensitive coloring material formed of a combination of a leuco dye / developing agent as such a light absorbing layer, a cholesteric reflection color of the recording layer can be obtained by a thermosensitive recording device, and at the same time, a visible color can be obtained. The function of absorbing light can be provided on the back of the recorded image. That is, it is possible to form a recording image of any color on a white background. In particular, by using a reversible thermosensitive coloring type leuco dye / dispersible colorant capable of repeating coloring and decoloring as the light absorbing layer, the versatility as a reversible recording material is broadened.

Further, if necessary, a light reflecting layer, a heat reflecting layer, and / or a light (laser beam) absorbing layer may be provided between the heat-sensitive recording layer and the support.

In the present invention, a magnetic recording layer may be provided on the surface (back surface) of the support on which the heat-sensitive recording layer is not provided, or between the support and the heat-sensitive recording layer. As the magnetic recording layer, a magnetic recording layer conventionally used for a magnetic ticket, a prepaid card, a magnetic commuter pass, or the like can be used. Further, the reversible recording material of the present invention is also suitable for use as a display medium of a card in which an IC chip or the like is embedded.

In the present invention, an undercoat layer used in a conventional heat-sensitive recording material can be used. In particular, when paper is used as the support, it is preferable to provide an undercoat layer on the paper support. By using a pigment having a high porosity, such as silica or calcined kaolin, for the undercoat layer, the heat insulating property of the undercoat layer can be increased, and the coloring sensitivity of the heat-sensitive recording layer can be increased. Including a plastic pigment, hollow particles, foam, or the like in the undercoat layer is also effective in improving the color sensitivity of the heat-sensitive recording layer formed thereon.

In the recording material of the present invention, it is preferable to provide a protective layer on the heat-sensitive recording layer. Such a protective layer has high transparency and can be formed of a material appropriately selected from materials which do not impair the storage stability of the heat-sensitive layer,
This protective layer is provided on the heat-sensitive recording layer so that its thickness is 0.5 to 30 μm. A more preferred thickness is 1 to 1.
0 μm.

In the present invention, a resin layer cured by an electron beam or ultraviolet rays may be further provided on the heat-sensitive recording layer or on the protective layer. Examples of the resin cured by an electron beam include JP-A-58-177392 and JP-A-58-177392.
Japanese Patent Application Laid-Open No. 177392/1992. In such a resin, a non-electron beam curable resin, a pigment, and additives such as an antifoaming agent, a leveling agent, a lubricant, a surfactant, and a plasticizer can be appropriately added. The resin layer cured by electron beams or ultraviolet rays has a coating amount after drying of 0.5 to 30 g / m.
It is coated to be ^2. More preferably 1 to 10 g
/ M ² .

Further, the protective layer of the recording material of the present invention is formed by laminating a plastic film having excellent transparency and heat resistance, such as PET, PES, polyetherimide, etc. on the heat-sensitive recording layer. Can also be used. In this case, the thickness of the protective layer plastic film is preferably about 1 to 30 μm. If a thicker film is used, the efficiency of heat transfer to the heat-sensitive recording layer may deteriorate.

For the recording material of the present invention, a UV ink,
Printing can be performed using flexographic ink or the like.
In this case, printing may be performed on any layer such as a thermosensitive recording layer, a protective layer, an electron beam curable resin layer, an ultraviolet curable resin layer, and a plastic film.

The reversible recording material obtained as described above changes the temperature of the heat-sensitive recording layer to a temperature range in which the cholesteric liquid crystal compound encapsulated in the microcapsules forms a cholesteric liquid crystal phase.
A color image is formed. A cholesteric liquid crystal compound is transparent or colorless when in a non-cholesteric liquid crystal phase (glass phase, crystal phase, isotropic phase, etc.), but develops color when changed to a cholesteric liquid crystal phase by heating. When this is in the cholesteric liquid crystal phase, the color of the cholesteric liquid crystal compound changes in a spiral molecular arrangement according to the temperature, and the color changes accordingly. When the temperature is changed so as to change from a cholesteric liquid crystal phase to a non-cholesteric liquid crystal phase, the color of the thermosensitive recording layer changes from a colored state to a colorless state. When the temperature of the heat-sensitive recording layer is changed while maintaining the cholesteric liquid crystal phase, the color of the heat-sensitive recording layer changes depending on the temperature.

The reversible recording material on which a desired color image has been formed as described above is rapidly cooled to lower the temperature of the heat-sensitive recording layer below the glass transition temperature of the cholesteric liquid crystalline compound, thereby fixing the color image. . This fixation of the image seems to be due to the phase transition from the cholesteric liquid crystal phase to the glass phase.

The method for recording an arbitrary selective reflection color on the reversible recording material of the present invention is roughly classified into the following two methods.

<First Image Forming Method: Image Formation by Cooling Operation from Cholesteric Liquid Crystal Phase> Using a heating means, the cholesteric liquid crystal compound in the recording portion is heated to a temperature higher than the temperature at which the compound changes to an isotropic phase. After the liquid crystal phase is rapidly cooled from a temperature exhibiting an isotropic phase to a temperature at which a liquid crystal phase exhibiting a desired selective reflection color is formed by cooling means, the liquid crystal phase is rapidly cooled to a temperature lower than the glass transition temperature by other cooling means. Thus, a cholesteric glass phase exhibiting a desired selective reflection color is fixed. In general, a cholesteric liquid crystalline compound shows a short-wavelength reflected color on a high-temperature side and a long-wavelength reflected color on a low-temperature side. For this reason, rapid recording from a relatively high temperature is required when recording blue, and rapid cooling from a relatively low temperature is required when recording red.

<Second Image Forming Method: Image Formation by Cooling Operation from Isotropic Phase> Using a heating means, the recording portion is heated to a temperature higher than the temperature at which the cholesteric liquid crystalline compound transitions to the isotropic phase. The cholesteric liquid crystalline compound is rapidly cooled from the temperature of the isotropic phase to about room temperature by a cooling means to fix the cholesteric liquid crystal compound to a cholesteric glass phase exhibiting a desired selective reflection color. Generally, a cholesteric liquid crystal compound is
When the cooling rate is high, a blue color image is formed, and when it is low, a red color image is formed.

As a heating means which can be used in the recording method of the present invention, any heating means can be used as long as the temperature of the heat-sensitive recording layer can be heated to a temperature higher than the temperature at which the cholesteric liquid crystal compound transitions to the isotropic phase. Can be used. For example, various known heating means such as a thermal head, a heating roll, a heating stamp, a hot plate, and a laser beam can be used. On the other hand, any cooling means may be used as long as it can contact the recording material immediately after heating and release heat. For example, in a coolant,
Alternatively, immersion in a cooling gas atmosphere, cooling gas flow,
Alternatively, cooling can be performed by contacting the surface of a cooled solid. However, the heating means and the cooling means are not limited to those described above.

The cooling rate for fixing the image is preferably at least 1 ° C./sec, more preferably at least 10 ° C./sec, and even more preferably at least 50 ° C./sec. If the cooling rate is less than 1 ° C./sec, the color of the image may easily change during the immobilization stage. For the same reason, it is preferable to shorten the time from image formation to fixation as much as possible. Depending on the ambient temperature and the type of the cholesteric liquid crystalline compound used, if left at room temperature for 10 seconds or more, the color of the image may partially change before immobilization.

In the second image forming method, for example, by adjusting the output of the thermal head, the thermal energy given to the thermosensitive recording layer is controlled, and the temperature of the thermosensitive recording layer at the start of cooling is set; Conditions for rapid cooling from the isotropic phase to room temperature can be set. In this case, if the thermal energy from the thermal head is increased, the cooling rate becomes slower, so that the color may shift to the longer wavelength side.

[0056]

The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto. Unless otherwise specified, “parts” and “%” indicate “parts by weight” and “% by weight”, respectively.

Example 1 Preparation of Cholesteric Liquid Crystal Compound Dispersion Ethylene-maleic anhydride copolymer (trade name: EMA-
31, a 20% aqueous solution of caustic soda added to 20 parts by weight of a 3% aqueous solution of Monsanto Co., Ltd. so that the pH becomes 6.0, and 1 a cholesteric liquid crystal compound.
A composition comprising 2 parts by weight of cholesteryl ester of 0,12-docosadiindicarboxylate was pulverized by a sand mill so as to have an average particle diameter of 10 μm to obtain a cholesteric liquid crystal compound dispersion.

Preparation of Microcapsule Dispersion Into 11 parts by weight of this cholesteric liquid crystal compound dispersion, 10 parts of a 30% aqueous solution of melamine-formaldehyde prepolymer was added dropwise with stirring, and the pH was adjusted to 5.3.
1N-hydrochloric acid was added dropwise to the mixture, and the mixture was heated at 80 ° C. for 1 hour. 20% concentration
To obtain a microcapsule dispersion having an average particle size of about 10 μm.

Preparation of Thermosensitive Recording Material A black 188 μm white PET film was coated on one side with a black coating liquid for an anchor coat layer and dried so that the coating amount after drying was 2 g / m ² to form an undercoat layer. 20 parts of the microcapsule dispersion and styrene-
The coating amount after drying of the coating solution for the heat-sensitive recording layer consisting of 3 parts of butadiene latex (solid concentration: 50%) is 25 g / m ^2.
Was applied and dried to form a thermosensitive coloring layer. Further, a UV curable varnish was applied on the thermosensitive coloring layer in an amount of 3 g /
m ^2, and a protective layer was formed by irradiating ultraviolet rays to form a cured protective layer.

[0060] exhibits a green where the thermosensitive recording layer surface side of the heat-sensitive recording material obtained evaluation was adhered 5 seconds hot plate maintained at 95 ° C., 115
When it was brought into close contact with a hot plate kept at 5 ° C. for 5 seconds, it turned blue. When the recording portion (colored portion) was rapidly cooled (0 ° C.) and stored at room temperature for 3 months, each recording portion was stable without any color change. The surface of the heat-sensitive recording layer side of the obtained heat-sensitive recording material was adhered to a hot plate kept at 120 ° C. for 5 seconds, and then gradually cooled to a colorless state, and further adhered to a hot plate kept at 115 ° C. for 5 seconds. After quenching, it turned blue.

Example 2 In the preparation of the cholesteric liquid crystal compound dispersion of Example 1, [4- (5-cholesteryloxycarbonylpentyloxy) phenoxyhexanoic acid was used in place of 10,12-docosadiynedicarboxylic acid dicholesteryl ester. [Cholesteryl ester] was used to produce a thermosensitive recording material in the same manner as in Example 1 except that cholesteryl ester was used.

[0062] turned red where the thermosensitive recording layer surface side of the heat-sensitive recording material obtained evaluation was adhered 5 seconds hot plate kept at 126 ° C., 14
When it was brought into close contact with the hot plate kept at 0 ° C. for 5 seconds, it exhibited green, and when it was brought into close contact with the hot plate kept at 180 ° C. for 5 seconds, it exhibited blue. The recording part (coloring part) is rapidly cooled (0 ° C.).
When stored at room temperature for 3 months, each recording portion was stable without any color change.

Example 3 In the preparation of the cholesteric liquid crystal compound dispersion of Example 1, 4- (3-cholesteryloxycarbonylpropyloxy) biphenoxybutanoic acid was used instead of 10,12-docosadiynedicarboxylic acid dicholesteryl ester. A heat-sensitive recording material was produced in the same manner as in Example 1 except that cholesteryl ester was used.

[0064] turned red where the thermosensitive recording layer surface side of the heat-sensitive recording material obtained evaluation was adhered 5 seconds hot plate kept at 250 ° C., The recording unit (color generation) and quenched (0 ° C.) After storage at room temperature for 3 months, each recording portion was stable without any color change.

Example 4 In the preparation of the cholesteric liquid crystalline compound dispersion of Example 1, 8,12-eicosadiene dicarboxylic acid dicholesteryl ester was used in place of 10,12-docosadiyne dicarboxylic acid dicholesteryl ester. A heat-sensitive recording material was produced in the same manner as in Example 1 except for the above.

[0066] turned red where the thermosensitive recording layer surface side of the heat-sensitive recording material obtained evaluation was adhered 5 seconds hot plate maintained at 110 ° C., 12
When it was brought into close contact with the hot plate kept at 0 ° C. for 5 seconds, it exhibited green, and when it was brought into close contact with the hot plate kept at 132 ° C. for 5 seconds, it exhibited blue. The recording part (coloring part) is rapidly cooled (0 ° C.).
When stored at room temperature for 3 months, each recording portion was stable without any color change. The thermal recording layer side of the obtained thermal recording material is recorded by a thermal head (applied energy 4.
(0 mJ / dot), a blue recording portion was obtained.

Example 5 A microcapsule containing a cholesteric liquid crystalline compound
Preparation of Dispersion (A) As a cholesteric liquid crystalline compound, 50 parts by weight of 10,12-docosadiyne dicarboxylic acid cholesteryl ester (molecular weight: 1099.8, glass transition temperature: 80 ° C.) was used, and methylene chloride 2
To the solution, and 10 parts by weight of a 3: 1 adduct of trimethylolpropane of xylene diisocyanate (Takenate D-110N, manufactured by Takeda Pharmaceutical Co., Ltd.) as a polymer material for forming a wall film material was added to the solution. Then, this solution was gradually added to 500 parts by weight of a 3% aqueous solution of polyvinyl alcohol, and this mixture was emulsified and dispersed by a homomixer by stirring at 1,000 rpm. Subsequently, the obtained emulsion was heated to a temperature of 45 ° C.
After holding for a time, the methylene chloride was evaporated off. Next, the temperature of the emulsion was raised to 60 ° C. to cause the organic polymer substance to undergo a curing reaction for 4 hours, thereby dispersing a microcapsule containing a cholesteric liquid crystal compound having an average particle diameter of 14 μm (A). Was prepared.

In order to observe the shape of the microcapsules (A) containing the cholesteric liquid crystal compound thus obtained, the microcapsule dispersion (A) was applied on an aluminum foil and dried. The surface of this sample was subjected to an observation test. For this observation, an accelerating voltage of 20 kV and a scanning electron microscope S-510 manufactured by Hitachi, Ltd. were used.
The measurement was performed under the condition of 2000 times magnification.

FIG. 2 shows the obtained electron micrograph. As is clear from FIG. 2, the presence of dents, dents, and pores on the particle surface of the microcapsule (A) was not recognized,
It was confirmed that the particles were almost spherical.

Preparation of Reversible Recording Material As a support, a black pigment was kneaded, and the thickness was 75 μm.
Polyetherimide (PEI) film (Sumilite FS-1401B, manufactured by Sumitomo Bakelite Co., Ltd.) was used. The microcapsule dispersion (A) (solid concentration 1
5%) 80 parts and 6 parts of styrene-butadiene-based latex (solid content 50%) were coated on the surface of the support such that the coating amount after drying was 20 g / m ^2. And dried to form a heat-sensitive recording layer. Further, an ultraviolet-curable varnish was applied on the heat-sensitive recording layer so that the coating amount was 3 g / m ^2, and this was irradiated with ultraviolet rays to form a protective layer. Since the cholesteric liquid crystalline compound in the microcapsules was translucent, a reversible recording material (A) having a black base color of the PEI film as the support was obtained.

Evaluation of Image Formation by Hot Stage The reversible recording material (A) obtained by the above operation was heated to 130 ° C. on a hot stage to convert the cholesteric liquid crystalline compound in the microcapsules into an isotropic phase. When the set temperature is lowered and the recording material is cooled,
In the temperature range described above, a selective reflection color due to the cholesteric liquid crystal phase was exhibited. From this state, when the recording material was quenched by immersing it in ice water, the cholesteric reflection color of the recording layer could be fixed. The reflection wavelength (λmax) of the recorded image changed from 400 to 600 nm according to the temperature of the recording material at the start of rapid cooling and the cooling rate. Table 1 shows the results.

[0072]

[Table 1]

Evaluation of Image Formation by Thermal Head Using the reversible recording material (A) obtained by the above operation, a thermosensitive color recording test was carried out by a printer equipped with the following thermal head. Thermal color recording was performed using a thermal printing tester (TH-PMD, manufactured by Okura Electric Co., Ltd.), recording time per line: 2.0 msec, sub-scanning line density: 8 lines /
mm, applied energy per dot: 0.30 to 0.6
The printing was performed by solid printing under the condition of 0 mJ. As a result, the cholesteric reflection color of the recording layer shifted to the longer wavelength side as the energy applied from the thermal head increased. Table 2 shows the results.

[0074]

[Table 2]

Evaluation of repetitive durability When the printing test and the erasing operation using the thermal head described above were repeated 30 times, the surface of the reversible recording material was hardly damaged by damage such as large damage or roughness, and the thickness of the recording material was reduced. There was almost no change. In addition, no deterioration in coloring was observed.

Example 6 Microcapsule containing a cholesteric liquid crystal compound
Of dispersion liquid (B) and preparation of reversible recording material (B)
Dispersion (B) was prepared in manufacturing the microcapsule dispersion dispersion (A) and a similar operation. However, as the cholesteric liquid crystalline compound, instead of 50 parts by weight of cholesteric dicholesteryl dicarboxylate,
8,12-eicosadiene dicarboxylic acid dicholesteryl ester (molecular weight: 1075.8, glass transition temperature; 3
(5 ° C.) 50 parts by weight. A microcapsule dispersion liquid (B) containing a cholesteric liquid crystal compound having an average particle diameter of 13 μm was obtained. Subsequently, in the same procedure as for the reversible recording material (A), the dispersion (B) is used instead of the microcapsule dispersion (A) to obtain the reversible recording material (B).
Was prepared.

Evaluation of Image Formation with Thermal Head A thermosensitive color recording test was performed on the reversible recording material (B) using a thermal head under the same conditions as in the recording method using the reversible recording material (A). Table 3 shows the results.

[0078]

[Table 3]

Evaluation of repetitive durability When the printing test and the erasing operation using the thermal head described above were repeated 30 times, little damage such as large damage or roughness was observed on the surface of the reversible recording material, and the thickness of the recording material was reduced. No change in color was observed, and no deterioration in coloring was observed.

Example 7 Microcapsule containing a cholesteric liquid crystal compound
Preparation of dispersion liquid (C) and production of reversible recording material (C)
To prepare a dispersion (C) by manufacturing the microcapsule dispersion dispersion (A) and a similar operation. However, as the cholesteric liquid crystal compound, eicosandicarboxylic acid cholesteryl ester (molecular weight: 1079.8, glass transition temperature: 45 ° C.) was used instead of 50 parts by weight of 10,12-docosadiin dicarboxylic acid cholesteryl ester.
0 parts by weight were used. A microcapsule dispersion (C) containing a cholesteric liquid crystal compound having an average particle size of 15 μm was obtained. Subsequently, a reversible recording material (C) was prepared in the same procedure as the reversible recording material (A), except that the dispersion liquid (C) was used instead of the microcapsule dispersion liquid (A).

Evaluation of Image Formation by Thermal Head A thermosensitive color recording test was performed on the reversible recording material (C) using a thermal head under the same conditions as those for the reversible recording material (A). Table 4 shows the results.

[0082]

[Table 4]

Evaluation of repetition durability When the printing test and the erasing operation with the above-mentioned thermal head were repeated 30 times, the surface of the reversible recording material was hardly damaged by damage such as large damage and roughness.
Almost no change in the thickness of the recording material was observed, and no deterioration in coloring was observed.

Example 8 Microcapsules containing a cholesteric liquid crystal compound
Preparation of dispersion liquid (D) and production of reversible recording material (D)
Dispersion (D) was prepared in manufacturing the microcapsule dispersion dispersion (A) and a similar operation. However, as the cholesteric liquid crystalline compound, instead of 50 parts by weight of cholesteric dicholesteryl dicarboxylate, 1
A mixture of 40 parts by weight of cholesteryl ester of 0,12-docosadiyne dicarboxylic acid and 10 parts by weight of cholesteryl ester of 8,12-eicosadiene dicarboxylic acid was used. A microcapsule dispersion (D) containing a cholesteric liquid crystal compound having an average particle size of 16 μm was obtained. Subsequently, a reversible recording material (D) was produced in the same procedure as the reversible recording material (A), except that the dispersion liquid (D) was used instead of the microcapsule dispersion liquid (A).

Evaluation of Image Formation with Thermal Head A thermosensitive color recording test was performed on the reversible recording material (D) using a thermal head under the same conditions as those for the reversible recording material (A). Table 5 shows the results.

[0086]

[Table 5]

Evaluation of repetitive durability When the printing test and the erasing operation using the thermal head described above were repeated 30 times, no significant damage such as large damage or roughness was observed on the surface of the reversible recording material, and the thickness of the recording material was reduced. No change in color was observed, and no deterioration in coloring was observed.

Example 9 Microcapsule containing a cholesteric liquid crystal compound
Preparation of dispersion liquid (E) and production of reversible recording material (E)
Dispersion (E) was prepared in manufacturing the microcapsule dispersion dispersion (A) and a similar operation. However, as an isocyanate compound, 10 parts by weight of dicyclohexylmethane-4,4′-diisocyanate was used instead of 10 parts by weight of a 3: 1 adduct of xylene diisocyanate with trimethylolpropane (D-110N, manufactured by Takeda Pharmaceutical Company Limited). And
After the temperature of the emulsified dispersion was raised to 45 ° C. and kept for 2 hours, 10 parts by weight of a 5% aqueous solution of an aliphatic polyamine (Epicure T, manufactured by Yuka Shell Epoxy) was added, and the temperature was raised to 85 ° C. for 6 hours. A curing reaction was performed. A microcapsule dispersion liquid (E) containing a cholesteric liquid crystal compound having an average particle diameter of 16 μm was obtained. Subsequently, a reversible recording material (E) was produced in the same procedure as the reversible recording material (A), except that the dispersion liquid (E) was used instead of the microcapsule dispersion liquid (A).

Evaluation of Image Formation by Thermal Head A thermosensitive color recording test of the reversible recording material (E) was performed by using a thermal head under the same conditions as those for the reversible recording material (A). Table 6 shows the results.

[0090]

[Table 6]

Evaluation of repetitive durability When the printing test and the erasing operation with the above-mentioned thermal head were repeated 30 times, the surface of the reversible recording material was hardly damaged by damage such as large scratches and roughness. No change in color development was observed, and no deterioration in coloring was observed.

[0092]

According to the reversible recording material of the present invention, a color image is recorded by giving a change in temperature.
The image can be rewritten repeatedly. In particular, by encapsulating the cholesteric liquid crystal compound in microcapsules, it is possible to control the fluidity of the cholesteric liquid crystal compound, and even if pressure or the like is repeatedly applied from the outside during the recording operation, the thickness of the heat-sensitive recording layer can be reduced. Can be kept uniform. In addition, since the cholesteric liquid crystal compound can be handled as ordinary solid fine particles by microencapsulation, the recording layer can be formed by a coating method used in a general water-based paint. The manufacturing process can be greatly simplified.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view showing an example of the configuration of a reversible recording material of the present invention.

FIG. 2 is an electron micrograph of an example of a microcapsule dispersion containing a cholesteric liquid crystal compound contained in a heat-sensitive recording layer of the reversible recording material of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Reversible recording material 2 ... Support 3 ... Microcapsule encapsulating cholesteric liquid crystal compound 4 ... Thermal recording layer 5 ... Protective layer

 ──────────────────────────────────────────────────の Continuing from the front page (71) Applicant 597072464 Hiroo Matsuda 1966-8 Uenomuro, Tsukuba City, Ibaraki Prefecture (72) Inventor Yasuyuki Aoki 1-10-6 Shinonome, Koto-ku, Tokyo Inside the Oji Paper Shinonome Research Center (72) Inventor Nobuyuki Tamaki 1-1-1, Higashi, Tsukuba, Ibaraki Pref., National Institute of Advanced Industrial Science and Technology, Materials Science and Technology Research Institute (72) Inventor Hiroo Matsuda 1-1-1, Higashi, Tsukuba, Ibaraki, Japan Research Laboratory Material Engineering Industrial Technology Laboratory

Claims (15)

[Claims] 1. A thermosensitive recording layer comprising: a support; and a thermosensitive recording layer formed thereon. The thermosensitive recording layer comprises a cholesteric liquid crystalline compound having thermochromic properties and a wall film material containing the same. A reversible recording material comprising a large number of microcapsules. 2. The thermochromic cholesteric liquid crystalline compound has a glass transition temperature of 30 to 150 ° C.
4. The reversible recording material according to item 1. 3. The reversible recording material according to claim 1, wherein the wall film material is formed of an acid aldehyde resin. 4. The thermochromic cholesteric liquid crystal compound according to the following general formula (I): Z—O—CO— (CH ₂ ) _m —R— (CH ₂ ) _n —CO—O—Y (I [In the formula (I), Z represents a cholesteryl group, Y represents a cholesteryl group, a hydrogen atom or an alkyl group, and R represents p-
Represents a phenylene group, a 4,4'-biphenylene group, a butylene diyne group or a 1,5-hexadienylene group, and m and n each independently represent an integer of 1 to 20. The reversible recording material according to any one of claims 1 to 3, which is a compound represented by the formula: 5. The method according to claim 1, wherein the cholesteric liquid crystal compound comprises two or more microcapsules in the thermosensitive recording layer.
The reversible recording material according to claim 1, wherein the reversible recording material has a molecular weight of 000 or less and a glass transition temperature of 30 to 150 ° C, and the wall film material is formed of an organic polymer substance. 6. The cholesteric liquid crystal compound represented by the following formula (II): Z—O—CO—R ¹ —CO—O—Y (II) [wherein, in the formula (II), Z and Y each represent Each independently represents a cholesteryl group, a hydrogen atom or an alkyl group; R ¹ represents a divalent hydrocarbon group having 2 to 34 carbon atoms; and at least one of Z and Y represents a cholesteryl group. The reversible recording material according to claim 5, which is a compound represented by the following formula: 7. In the formula (II), the divalent hydrocarbon group represented by R is represented by the following formulas (III), (IV) and (V): — (CH ₂ ) m—C≡C —C≡C— (CH ₂ ) n— (III) [wherein, in the formula (III), m and n each independently represent an integer of 1 or more, provided that the total of m and n is 3
Does not exceed 0. ] _{- (CH 2) m'-CH} = CH-CH 2 -CH 2 -CH = CH- (CH 2) n '- (IV) [where, m of formula (IV)' and n 'are each each other Independently represent an integer of 1 or more, provided that the sum of m ′ and n ′ does not exceed 28. ] _{- (CH 2) m "-} (V) [where, m in the formula (V)" represents an integer of 2 to 34. ]
Selected from cholesteric liquid crystal compounds represented by
The reversible recording material according to claim 6. 8. The reversible recording material according to claim 5, wherein the organic polymer substance for a wall film material includes at least one selected from polyurea and polyurethane. 9. The microcapsule is prepared by dissolving and mixing a cholesteric liquid crystal compound and a polymer-forming material that forms at least one of polyurea and polyurethane by polymerization in a water-insoluble organic solvent having a boiling point of 100 ° C. or less. Then, the organic solvent solution was emulsified and dispersed in an aqueous medium, the emulsified dispersion was heated to volatilize and remove the organic solvent, and then the polymer-forming raw material was polymerized. The reversible recording material according to claim 8, which is a material. 10. The polymer-forming raw material forming the wall material of the microcapsules is a polyvalent isocyanate compound, an adduct of a polyvalent isocyanate compound and a polyol, a biuret of a polyvalent isocyanate compound, or a polyvalent isocyanate compound. The reversible recording material according to claim 9, which is selected from the group consisting of an isocyanurate compound of formula (I) and a mixture of a polyvalent isocyanate compound and a polyol. 11. The reversible recording material according to claim 10, wherein the polymer-forming raw material further contains a polyamine compound. 12. The reversible recording material according to claim 1, wherein the content of the cholesteric liquid crystal compound in the microcapsules is 10 to 95% by weight based on the weight of the microcapsules. 13. A microcapsule comprising a support and a thermosensitive recording layer formed thereon, wherein said thermosensitive recording layer includes a cholesteric liquid crystalline compound having thermochromic properties in a wall material. Using a reversible recording material containing, the heat-sensitive recording layer is heated to a temperature at which the cholesteric liquid crystal compound exhibits a cholesteric liquid crystal phase, according to an image pattern to form a color-formed image, and the temperature of the color-formed image is changed. A method for recording a reversible recording material, wherein the color image is erased or its hue is changed. 14. A support, formed thereon, having a molecular weight of 2,000 or less, and a glass transition temperature of 30 to 1
A thermosensitive recording layer containing a cholesteric liquid crystal compound at 50 ° C., wherein said cholesteric liquid crystal compound is encapsulated in a number of microcapsules having an organic polymer substance as a wall film material. And heating the heat-sensitive recording layer to a temperature at which the cholesteric liquid crystal compound exhibits an isotropic phase or a cholesteric liquid crystal phase according to an image pattern, and cooling the heat-sensitive recording layer at a cooling rate of 1 ° C./second or more. By cooling to a temperature lower than the glass transition temperature of the liquid crystal compound, the helical molecular arrangement of the cholesteric liquid crystal phase is fixed to form a cholesteric glass phase, which is caused by the helical molecular arrangement of the cholesteric liquid crystal compound. A method for recording a reversible recording material, comprising recording an image showing a selective reflection color. 15. In the heating according to the image pattern of the thermosensitive recording layer, a heating recording head is used as a heating means, and by controlling heat energy given to the thermosensitive recording layer from the recording head, the heating at the start of the cooling is performed. 2. A multicolor image showing an arbitrary reflection color by setting an image temperature of the heat-sensitive recording layer, thereby controlling a pitch of a helical molecular arrangement of a cholesteric liquid crystal phase.
5. The recording method of the reversible recording material according to item 4.