JP2002011951A - Reversible recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reversible recording medium, in which the uneven thickness of a heart sensitive recording layer is prevented from developing by keeping the thickness of the recording layer uniform even when pressure or the like is applied from outside through the suppression of the flowing of a cholesteric liquid crystal compound during a recording action by making the heat sensitive recording layer out of a high- molecular dispersing type liquid crystal. SOLUTION: The reversible recording medium has a heat sensitive recording layer including a thermotropic liquid crystalline compound having a molecular weight of 2,000 or less and capable of forming a cholesteric liquid crystal phase and a recording means for recording an image showing a selective reflection color caused by a spiral molecular arrangement, so as to form a cholesteric glass phase made by solidifying spiral molecular arrangement of the cholesteric liquid crystal phase by heating the heat sensitive recording layer up to a temperature showing an isotropy phase or a cholesteric liquid crystal phase and the cooling the same at a specified cooling speed on a supporting substrate. At least part of the heat sensitive recording layer is made of a high-molecular dispersing type liquid crystal layer made through the photopolymerization of the mixture of the thermotropic liquid crystalline compound and a polymerizable monomer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible recording medium, and more particularly, to a reversible recording medium capable of repeatedly writing and erasing information by heating, and in particular, a color display or rewritable information.

[0002]

2. Description of the Related Art JP-A-5-69672, JP-A-5-69672
273707 “Rewritable thermosensitive recording medium” (topographic printing) relates to a thermosensitive recording medium using cholesteric polymer liquid crystal. In the present invention, when the entire recording layer is heated to a recording set temperature equal to or lower than the isotropic phase transition temperature and equal to or higher than the glass transition temperature to appropriately form a color liquid crystal state, and when it is cooled to a temperature equal to or lower than the glass transition temperature, a suitable pressing means is used. For example, this liquid crystal state can be fixed by adjusting the pressure at the time of insertion between a pair of heating rollers. 2. JP-A-11-24027 "Rewritable color image recording medium and image forming method using the same" (Technical Institute) At least one of two transparent substrates has a molecular weight of 2,000 or less and a glass transition temperature of 35. A cholesteric liquid crystal compound having a temperature of at least ℃ is provided.

[0003]

Problems to be Solved by the Invention
7, a rewritable color image in which a heat-sensitive layer containing a cholesteric liquid crystal compound having a molecular weight of 2,000 or less and a glass transition temperature of 35 ° C. or more is provided between two substrates at least one of which is transparent. The temperature of the recording medium is changed from a first temperature to a second temperature (at least one of the first and second temperatures, the cholesteric liquid crystalline compound forms a cholesteric liquid crystal phase) according to a desired image. An image forming method is known in which an image is formed by cooling the recording medium, and then the recording medium is rapidly cooled to cool the heat-sensitive layer to a temperature equal to or lower than a glass transition temperature to fix the image.

This method has a promising feature that rewritable full-color recording is possible only by changing the recording conditions for a single material system. However, when a stress such as pressure is applied in a state of isotropic phase or liquid crystal phase, a flow occurs in a liquid crystal material as a recording layer, and if it is fixed as it is, there is a problem that thickness unevenness occurs in the recording layer. In particular, this phenomenon becomes remarkable when recording and erasing are repeatedly performed by a contact-type heating device such as a thermal head on a film-shaped recording medium using a sheet in which at least one of the substrates is flexible. . Further, as the heating area of the recording section is larger, the thickness unevenness of the recording layer is more likely to occur in that area.

[0005] The present invention has solved the above problems by employing the following technical means. A first aspect of the present invention is to provide a thermosensitive recording layer containing a thermotropic liquid crystalline compound having a molecular weight of 2,000 or less on a supporting substrate to form a cholesteric liquid crystal phase, and the thermosensitive recording layer is heated to a temperature at which the thermosensitive recording layer exhibits an isotropic phase or a cholesteric liquid crystal phase. After the heating operation of heating, a cooling operation of cooling at a specific cooling rate causes a cholesteric liquid crystal phase to form a cholesteric glass phase in which the helical molecular arrangement is solidified, and exhibits a selective reflection color due to the helical molecular arrangement In a reversible recording medium having a recording means for recording an image, at least a part of the heat-sensitive recording layer is composed of a polymer-dispersed liquid crystal layer produced by photopolymerizing a mixture of a thermotropic liquid crystalline compound and a polymerizable monomer. Reversible recording medium.

A second aspect of the present invention is the first reversible recording medium, wherein at least a part of the polymer-dispersed liquid crystal layer is obtained by removing a residual polymerizable monomer after photopolymerization. . A third aspect of the present invention is that at least a part of the thermosensitive recording layer has a thickness of 30 to 7 with respect to the thermotropic liquid crystalline compound.
The first and second reversible recording media are characterized by comprising a polymer-dispersed liquid crystal layer produced by photopolymerizing a mixture containing 0% by weight of a polymerizable monomer. A fourth aspect of the present invention is that at least a part of the heat-sensitive recording layer photopolymerizes a mixture of a thermotropic liquid crystalline compound and a polymerizable monomer between the crystallization temperature of the mixture and 10 ° C. higher than the crystallization temperature. The first to third reversible recording media are characterized by comprising a polymer-dispersed liquid crystal layer produced by the above method.

A fifth aspect of the present invention is that at least a part of the heat-sensitive recording layer cools a mixture of the thermotropic liquid crystalline compound and the polymerizable monomer at a specific rate from a temperature showing an isotropic phase to a temperature lower than a crystallization temperature. 3. The liquid crystal display device according to claim 3, wherein the liquid crystal droplets are uniformly dispersed in a glass state obtained by photopolymerization at a crystallization temperature or lower. It is on a reversible recording medium. A sixth aspect of the present invention is that at least a part of the heat-sensitive recording layer changes a cooling rate of a dispersion obtained by uniformly dispersing liquid crystal droplets in a glass state from a temperature at which an isotropic phase is exhibited to a temperature below a crystallization temperature. The fifth reversible recording medium according to the fifth aspect, comprising a polymer-dispersed liquid crystal layer formed by controlling the size of a liquid crystal droplet in a glassy state by a photo-polymerization at a crystallization temperature or lower. .

A seventh aspect of the present invention is the reversible recording medium according to any one of the first to sixth aspects, characterized in that a rubbed crystalline resin film is provided between the supporting substrate and the heat-sensitive recording layer. An eighth aspect of the present invention is the reversible recording medium according to any one of the first to seventh aspects, wherein the thermotropic liquid crystalline compound is a compound represented by the following formula (a).

Embedded image Z—O—CO— (CH ₂ ) m—CR ＝ CH—CH ₂ —CH ₂ —CH ＝ CR —— (CH ₂ ) n—CO—O—Y (a) Y independently represents a cholesteryl group, a hydrogen atom or an alkyl group, R represents a hydrogen atom or an alkyl group, wherein m and n each independently represent an integer of 1 or more, and at least one of Z and Y Represents a cholesteryl group.)

[0009]

FIG. 1 shows an example of the structure of a reversible recording medium according to the present invention. A heat-sensitive recording layer and a transparent surface substrate are formed on a support substrate provided with a light absorption layer for observing a cholesteric reflection color. Of these, the surface substrate may not be present, but is preferably present to protect the heat-sensitive recording layer. The thermosensitive recording layer contains a polymer-dispersed liquid crystal (having a structure in which a thermotropic cholesteric liquid crystal compound is dispersed in a droplet form in a polymer compound). Glass, PET, PC,
A plastic film such as PES is used, but is not limited thereto. In order to obtain a sheet-shaped recording medium, the thickness of the supporting substrate is preferably about 10 μm to 0.5 mm.

As the light absorbing layer, a material in which a black paint or the like is applied to the back side of the medium substrate or a material in which a black pigment is dispersed in the medium substrate are used. As the surface substrate, a plastic film such as PES or PEI which is excellent in transparency and heat resistance is preferable, but is not limited thereto. After the heat-sensitive recording layer is formed, a UV-curable resin layer may be coated and cured. When recording is performed from the front side of the recording medium with a contact heating device such as a thermal head, the thickness of the front substrate is preferably about 1 μm to 30 μm.

The thickness of the heat-sensitive recording layer is 3 μm or more and 40 μm or more.
Is preferably in the range of less than 5 μm to 25 μm.
m is more preferable. That is, when the thickness of the recording layer is less than 3 μm, a sufficient selective reflectance cannot be obtained. When the thickness is more than 40 μm, the heating and cooling conditions in the recording layer depend on the printing temperature of the thermal head. In some cases, the color becomes non-uniform, resulting in uneven reflection color or cloudiness. In the range of 5 μm or more and 25 μm or less, there is a large margin in the printing conditions of the thermal head for obtaining an arbitrary selective reflection color, and a uniform selective reflection color that does not cause a visual observation problem with a film thickness variation of about several μm. Is obtained.

The thermotropic cholesteric liquid crystal compound used in the present invention has a molecular weight of 2,000 or less, a glass transition temperature of 35 ° C. or more, shows a cholesteric liquid crystal phase at a glass transition temperature or more, and shows an isotropic phase at a temperature higher than that. Are preferred. When the cholesteric liquid crystal phase at a high temperature is rapidly cooled to room temperature, it becomes a glassy solid (cholesteric glass phase) retaining the helical molecular arrangement of the cholesteric liquid crystal phase, and a selective reflection color depending on the helical pitch is observed. By arbitrarily setting the temperature of the heat-sensitive recording layer at the time of the start of rapid cooling and the area thereof, a multicolor image or the like having an arbitrary reflection color can be formed. FIG. 2 shows an example of a cholesteric liquid crystal compound, but is not limited to this compound.

When a reversible recording medium is heated and recorded by a thermal head device, the thermotropic cholesteric liquid crystal compound transitions to an isotropic phase or a liquid crystal phase to cause fluidity. At this time, in a medium in which the heat-sensitive recording layer is formed only of the thermotropic cholesteric liquid crystal compound, when the printing pressure applied to the recording layer fluctuates, the heat-sensitive recording layer is fixed to the cholesteric glass phase while the thickness unevenness occurs. . In order to prevent a change in film thickness due to the flow of the heat-sensitive recording layer, there is a method of sandwiching the heat-sensitive recording layer between a surface substrate and a supporting substrate, and further providing a spacer in the heat-sensitive recording layer. In this case, as the spacer, a general spacer for a liquid crystal display such as a spherical plastic bead such as a copolymer of divinylbenzene and styrene or a spherical metal oxide such as SiO ₂ and Al ₂ O ₃ is used. It is possible.

However, when the above-described spherical spacer particles are used, when heating and recording while applying pressure as in a thermal head device, printing pressure is also applied to the spacers in the recording layer having fluidity, and the thermal pressure is increased. The spacer may move along the moving direction of the head. In the part where the spacer has moved, the cooling condition is slightly changed by the presence of the spacer, and appears as a change in the selective reflection color that is finally fixed. The length of the moving trace varies depending on the printing pressure of the thermal head, the surface properties of the spacer and the substrate, and may be as long as about 100 μm. Further, the movement of the spacer may damage not only the movement trace on the image but also the inside of the substrate.

Therefore, one of the features of the present invention is to use a thermotropic cholesteric liquid crystal compound dispersed in a polymer compound in order to solve the above-mentioned problems. Compared with conventionally used spherical spacer particles, the polymer compound has better adhesion to the support substrate and does not flow even when the printing pressure of the thermal head is applied. Further, by adopting a structure in which the cholesteric liquid crystal compound is dispersed in the polymer compound, the flow of the cholesteric liquid crystal compound can be prevented, and the necessity of using a surface substrate is eliminated (corresponding to claim 1).

The polymer compound used in the present invention has a high viscosity even at a temperature higher than the thermal recording temperature, and preferably has a glass transition temperature higher than the thermal recording temperature. If the viscosity is low, the fluid flows due to the printing pressure of the thermal head. In consideration of recording by a contact-type heating device such as a thermal head, it is preferable that the polymer compound does not have a rigid and brittle structure. Further, it is preferable that the selective reflection light to be recorded has no absorption in the wavelength range. As a method of dispersing a cholesteric liquid crystal in a polymer compound in a uniform droplet shape, a photopolymerization method of irradiating a mixture of a cholesteric liquid crystal compound, a polymerizable monomer, and a photopolymerization initiator with light to polymerize the polymerizable monomer is known. Used. The mixture is coated on a supporting substrate, heated and dissolved, and then irradiated with light in any of an isotropic state, a liquid crystal state, and a glass state to solidify by polymerizing the polymerizable monomer. When a front substrate is used, the mixture before polymerization may be irradiated with light after being sandwiched between two substrates, or may be bonded by using a method such as lamination after the light irradiation.

Examples of the polymerizable monomer include, but are not limited to, acrylate, methacrylate, and vinyl compounds. However, since the mixture of the cholesteric liquid crystal compound, the polymerizable monomer, and the photopolymerization initiator must be heated and dissolved, the boiling point of the polymerizable monomer is preferably higher than the heating and dissolving temperature of the mixture. The polymerizable monomer has one double bond
There is a monofunctional compound having one and a polyfunctional compound having two or more double bonds, and either may be used,
In order to obtain a compound having a high glass transition temperature, it is preferable to use a polyfunctional compound. Further, two or more kinds of polymerizable monomers may be used as a mixture.

The structure of the photopolymerization initiator is not limited as long as it causes a polymerization reaction by light irradiation. The wavelength, intensity, and time of the irradiation light may be optimized so as to promote the polymerization reaction by the combination of the polymerizable monomer and the photopolymerization initiator used. When a polymer-dispersed liquid crystal is prepared by a photopolymerization method, it is difficult for all the polymerizable monomers in the system to react. Therefore, there is a high possibility that a portion of the polymerizable monomer remains even after irradiation with sufficient light. Since the polymerizable monomer is present as an impurity and affects physical properties such as the liquid crystallinity of the cholesteric liquid crystal compound, the amount thereof is as small as possible, preferably not present at all (corresponding to claim 2). As a method of removing the polymerizable monomer, a method of heating after polymerization to volatilize the remaining polymerizable monomer, or the like can be considered. If the polymerizable monomer can be removed,
The liquid crystal phase temperature range of the cholesteric liquid crystal compound is wider than that in the case where it is not removed, and the color range that can be fixed by rapid cooling is wider.

The mixing ratio between the cholesteric liquid crystal compound and the polymerizable monomer is not particularly limited, but a medium containing the polymerizable monomer in an amount of 30% by weight to 70% by weight based on the cholesteric liquid crystal compound is preferable. If the amount of the polymerizable monomer is less than 30% by weight, the mechanical strength as a spacer is weak, and the spacer cannot be sufficiently effective for a contact-type thermal recording apparatus, and the recording layer may be crushed. When the amount of the polymerizable monomer is more than 70% by weight, the area of the liquid crystal portion is reduced, so that when the recording medium is viewed macroscopically, there is a possibility that a sufficient reflectance cannot be obtained. ).

When a polymer-dispersed liquid crystal is prepared by a photopolymerization method, temperature conditions during polymerization are important parameters. In the present invention, the crystallization temperature and 10 ° C. from the crystallization temperature,
Preferably, the temperature range showing the cholesteric liquid crystal phase when irradiated with light at a temperature higher by 5 ° C. is the widest.
Corresponding to). This is considered to be due to the fact that the compatibility between the cholesteric liquid crystal compound and the polymerizable monomer changes depending on the temperature. That is, it is considered that the lower the temperature, the easier the phase separation of the cholesteric liquid crystal compound and the polymerizable monomer is, and the more easily the polymerization reaction of the monomer is promoted. However, since a polymerization reaction does not occur in a crystalline state, a temperature that is higher by about 5 ° C. to 10 ° C. than the crystallization temperature is optimal.

If the polymerization reaction is favorably promoted, (1) the molecular weight of the polymer is increased to cause phase separation from the cholesteric liquid crystal compound, and (2) the amount of the remaining polymerizable monomer is reduced. It is considered that the liquid crystal properties of the liquid crystal compound are improved, and the color range that can be fixed by rapid cooling is widened. In a mixture containing a polymerizable monomer in an amount of 30% by weight or more with respect to the cholesteric liquid crystal compound, when the mixture is cooled from a isotropic state to a room temperature which is a crystallization temperature or lower at a specific rate or more, a glass state is formed without crystallization,
A structure in which the cholesteric liquid crystal compound is dispersed in a droplet shape appears. When light is irradiated in this state, a polymerization reaction occurs, and the droplet is solidified while maintaining the droplet structure (corresponding to claim 5).

When the amount of the polymerizable monomer is less than 30% by weight,
Similarly, the droplet structure does not appear when cooled. This is a phenomenon that is observed because the cholesteric liquid crystal compound used in the present invention and the polymerizable monomer have greatly different crystallinity, so that phase separation is likely to occur when the mixing ratio approaches 1: 1. Therefore, 3 polymerizable monomers
When it is used in an amount of 0% by weight or more, a polymer-dispersed liquid crystal having a uniform liquid crystal droplet structure can be obtained, and since light irradiation can be performed at room temperature, there is no need to control the temperature during light irradiation. Furthermore, when the cooling rate from the isotropic state to about room temperature is changed, the individual liquid crystal droplets decrease as the cooling rate increases, and the size of the liquid crystal droplet can be controlled by the cooling rate. Here, when the diameter of the droplet is small, the shift of the selective reflection wavelength caused by oblique viewing to a short wavelength can be suppressed, but the selective reflection wavelength width becomes broad when viewed directly above. Therefore, the viewing angle characteristics of the recording medium can be controlled by controlling the size of the liquid crystal droplet (corresponding to claim 6).

It is considered that the size of the liquid crystal droplet affects light reflection characteristics such as viewing angle characteristics.
Therefore, by controlling the cooling rate, the reflection characteristics can be changed easily and with high accuracy. By cooling the same recording surface at a plurality of speeds, a recording medium having a plurality of portions having different reflection characteristics can be created. The selective reflectance of the cholesteric liquid crystal increases as the orientation of the liquid crystal is aligned in a uniaxial direction. Therefore, after applying and rubbing a crystalline resin film on a supporting substrate, a thermosensitive recording layer composed of a polymer-dispersed liquid crystal was created.
The reflectance was improved (corresponding to claim 7).

[0024]

Examples of the present invention will be described below.

Example 1 As a cholesteric liquid crystal compound, 8,12-eicosadiene diacid dicholester ester (n = 6 in FIG.
R = H; hereinafter abbreviated as III-6), and divinyl adipate (manufactured by Shin-Etsu vinyl acetate) as a polymerizable monomer in a ratio of 8: 2, and Irgacure 3 as a photopolymerization initiator.
69 (manufactured by Ciba Geigy) was added in an amount of 3% by weight based on divinyl adipate. This mixture was dissolved in dichloromethane, and the mixture was stirred, the solvent was removed, and dried under vacuum to obtain a solid sample.
The support substrate has a thickness of 75 μm with black paint on the back surface.
m of polyetherimide film (Sumilite FS1401 manufactured by Sumitomo Bakelite) was used. As the surface substrate, a 25 μm-thick polyether sulfone film (Sumilite FS1300 manufactured by Sumitomo Bakelite) was used. On a hot plate heated to 135 ° C., an appropriate amount of the solid sample was sandwiched between a supporting substrate and a surface substrate, and was heated and dissolved in an isotropic phase. After gradually cooling to 110 ° C., light of a high pressure mercury lamp (350 nm or more, 10 mW / c
m ² ) for 5 minutes. The thickness of the formed heat-sensitive recording layer was about 20 μm, and the structure was such that cholesteric liquid crystal droplets having a diameter of about 50 μm were dispersed in polymerized divinyl adipate (FIG. 3). The polymer-dispersed liquid crystal showed a cholesteric liquid crystal phase in a temperature range from 124 ° C. to 90 ° C. A solid image was recorded on the film sample by heating the film sample to a temperature equal to or higher than the isotropic phase transition temperature using a thermal head device modified from a commercially available thermal recording printer (TA Printer NC3D manufactured by Fuji Photo Film Co., Ltd.) and then cooling. After repeating this operation 30 times,
The change in the thickness of the heat-sensitive recording layer was about 1 μm. However, when a stronger external pressure was applied in the isotropic phase temperature range, the polymer wall collapsed.

Example 2 After a film sample was prepared in the same manner as in Example 1, the surface substrate was peeled off, and placed on a hot plate at 150 ° C. for 3 minutes to volatilize unreacted divinyl adipate. Pasted. The temperature range showing the cholesteric phase was 134 ° C. to 90 ° C., which was wider than that of the film sample of Example 1, and the color range that could be fixed was widened.

Example 3 In order to increase the polymer portion, a film sample similar to that of Example 1 was prepared by changing the mixing ratio of 8,12-eicosadiene diacid dicholester ester and divinyl adipate to 1: 1 ( (The thickness of the heat-sensitive recording layer is about 20 μm). When the solid image printing was repeatedly rewritten 30 times by the thermal recording printer, the change in the thickness of the thermal recording layer was 1 μm or less, which was a practically acceptable level. When the same external pressure as in Example 1 was applied in the isotropic phase temperature range, the polymer wall did not collapse, and the durability against the external pressure was improved (corresponding to claim 3).

Comparative Example 1 The same apparatus as in Examples 1 and 3 was used, using a film sample in which the thermosensitive recording layer was composed only of 8,12-eicosadiene diacid dicholester ester (the thickness of the thermosensitive recording layer was about 20 μm). And the rewriting operation was repeated. From the second time, the thickness of the heat-sensitive recording layer began to become uneven, and after 30 rewrites, the change in the thickness of the heat-sensitive recording layer was 15 μm or more.

Example 4 In the same manner as in Example 1, a sample in which 8,12-eicosadiene diacid diester ester and divinyl adipate were mixed at a ratio of 8: 2 to 90 ° C., which is 5 ° C. higher than the crystallization temperature of 85 ° C.
Was irradiated with light to produce a polymer-dispersed liquid crystal. This polymer-dispersed liquid crystal exhibits a cholesteric liquid crystal phase in a temperature range of 130 ° C. to 91 ° C., and has a wider liquid crystal phase temperature range than that of Example 1 irradiated with light at 110 ° C., and has a wider color range that can be fixed. (Corresponding to claim 4).

Example 5 FA129A (a diacrylate monomer manufactured by Hitachi Chemical Co., Ltd.) was used as a polymerizable monomer and mixed with 8,12-eicosadiene diacid diester ester in a ratio of 1: 1. Irgacure 369 (manufactured by Ciba Geigy) was added to FA129A in an amount of 3% by weight. This mixture was dissolved in dichloromethane, stirred, solvent-removed, and vacuum-dried to obtain a sample. On a hot plate heated to 135 ° C., an appropriate amount of a sample was sandwiched between a supporting substrate and a surface substrate and heated and dissolved in an isotropic phase, and then the film sample was separated from the hot plate and rapidly cooled to room temperature. Observation with a polarizing microscope revealed that FA129A had a structure in which 8,12-eicosadiene diacid dicholester ester was uniformly dispersed in a droplet having a diameter of about 20 μm. In addition, the size of the droplet was reduced by reducing the speed of separating from the hot plate, and the diameter became about 10 μm. When irradiated with light from a high-pressure mercury lamp (350 nm or more, 10 mW / cm ² ) at room temperature for 10 minutes, the solidified state was maintained, and polymer dispersed liquid crystals having different droplet sizes could be produced. (Corresponding to claims 5 and 6)

Example 6 A polyimide solution (JSR Optmer AL3046) was spin-coated on a 75 μm-thick polyetherimide film substrate having a black paint on the back surface, and dried to form a resin thin film. The spin coating conditions were 500 rpm for the first 5 seconds and 1600 rpm for the next 30 seconds. The drying conditions were 90 ° C. for 5 minutes for primary drying and 120 ° C. for 60 minutes for secondary drying. The thickness of the target resin thin film was 0.1 to 0.2 μm. Rubbing treatment was performed on the resin thin film, and this film was used as a support substrate. When a polymer-dispersed liquid crystal was prepared in the same manner as in Example 1, the selective reflectance of the cholesteric phase was improved by about 10% (corresponding to claim 7).

[0032]

[Effect] 1. Claim 1 By using a polymer-dispersed liquid crystal for the heat-sensitive recording layer, the flow of the cholesteric liquid crystal compound during recording operation is suppressed, and the thickness of the recording layer is kept uniform even when pressure is applied from the outside. There has been provided a reversible recording medium capable of preventing the thickness unevenness of the heat-sensitive recording layer from occurring. 2. (2) Since the unreacted polymerizable monomer which inhibits the selective reflection characteristic of the cholesteric liquid crystal is removed, the temperature range showing the cholesteric phase is widened in addition to the effect of the first aspect, and the color range that can be fixed is widened. A reversible recording medium was provided. 3. According to a third aspect of the present invention, it is possible to prevent the thickness unevenness of the recording layer from being generated even in a contact-type thermal recording apparatus, and to maintain the thickness of the recording layer more firmly and to have a selective reflection sufficient for a recording medium. A reversible recording medium capable of ensuring a high efficiency has been provided. 4. 4. A temperature at which the cholesteric liquid crystal and the polymer compound are favorably phase-separated and the amount of unreacted polymerizable monomer is small, so that the occurrence of thickness unevenness of the recording layer is prevented and the cholesteric phase exhibits a selective reflection color. A reversible recording medium having a wider range and a wider color range that can be fixed has been provided. 5. Claim 5 Since a polymer-dispersed liquid crystal having a uniform dispersion distribution can be produced, a reversible recording medium having excellent viewing angle characteristics while preventing occurrence of unevenness in the thickness of the recording layer has been provided. 6. Claim 6 Since the size of the liquid crystal droplet of the polymer dispersed liquid crystal can be controlled, the occurrence of thickness unevenness of the recording layer is prevented.
There has been provided a reversible recording medium capable of producing a reversible recording medium having various viewing angle characteristics. 7. 7. A rubbing-treated crystalline resin film on a support substrate can improve the orientation of liquid crystal molecules, prevent the occurrence of unevenness in the thickness of the recording layer, and selectively reflect the cholesteric phase. A reversible recording medium is provided that improves the recording quality. 8. In another aspect of the invention, a reversible recording material having a high cholesteric phase selective reflectance and a wide liquid crystal temperature range is produced while preventing the occurrence of thickness unevenness of the recording layer.

[Brief description of the drawings]

FIG. 1 is a diagram showing one configuration example of a reversible recording medium of the present invention.

FIG. 2 is a diagram showing a structure of a cholesteric liquid crystal compound used in the present invention. a chol-n-diyne-n-chol b chol-n-diene-n-chol

FIG. 3 is a diagram showing a polymer-dispersed liquid crystal having a structure in which cholesteric liquid crystal droplets of the reversible recording medium of Example 1 are dispersed.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) G02F 1/13 505 B41M 5/18 102 1/1334 (71) Applicant 000006747 Ricoh Co., Ltd. 1-3-6, Magome (71) Applicant 391010471 Okamura Oil Co., Ltd. 4-5, Kawaramachi, Kashiwara-shi, Osaka (74) The above four agents 100094466 Patent Attorney Eiji Tomomatsu (72) Inventor Shigenobu Hirano Tokyo 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Ero Nimura 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Hiroyuki Sugimoto Naka, Ota-ku, Tokyo 1-3-6 Magome, Ricoh Co., Ltd. (72) Inventor Nobuyuki Tamaki 1-1, Higashi, Tsukuba, Ibaraki Pref. Person Hiroo Matsuda 1-1 Higashi, Tsukuba, Ibaraki Pref., National Institute of Advanced Industrial Science and Technology (72) Inventor Yoshishige Kida 4-5 Kawaramachi, Kashiwara-shi, Osaka Okamura Oil Company F-term (reference) 2H026 AA09 DD48 FF01 2H088 EA62 FA09 GA03 GA10 HA01 JA22 JA23 MA17 MA20 2H089 HA04 KA08 QA14 QA16 4H027 BA02 BA11 BB07 BB11 BC08

Claims (8)

[Claims] 1. A thermosensitive recording layer containing a thermotropic liquid crystalline compound which forms a cholesteric liquid crystal phase having a molecular weight of 2,000 or less on a supporting substrate, and the thermosensitive recording layer is heated to a temperature showing an isotropic phase or a cholesteric liquid crystal phase. After the heating operation, the cholesteric liquid crystal phase is formed into a cholesteric glass phase in which the helical molecular arrangement is solidified by a cooling operation of cooling at a specific cooling rate, and an image showing selective reflection color caused by the helical molecular arrangement In a reversible recording medium having a recording means for recording, at least a part of the thermosensitive recording layer is composed of a polymer dispersed liquid crystal layer produced by photopolymerizing a mixture of a thermotropic liquid crystalline compound and a polymerizable monomer. A reversible recording medium. 2. The reversible recording medium according to claim 1, wherein at least a part of the polymer-dispersed liquid crystal layer is obtained by removing a residual polymerizable monomer after photopolymerization. 3. A polymer-dispersed liquid crystal layer produced by photopolymerizing a mixture containing a polymerizable monomer in an amount of 30 to 70% by weight with respect to a thermotropic liquid crystal compound. 3. The reversible recording medium according to claim 1, wherein the reversible recording medium is formed. 4. At least a part of the heat-sensitive recording layer is produced by photopolymerizing a mixture of a thermotropic liquid crystalline compound and a polymerizable monomer between the crystallization temperature of the mixture and a temperature higher by 10 ° C. than the crystallization temperature. The reversible recording medium according to any one of claims 1 to 3, comprising a polymer dispersed liquid crystal layer formed as described above. 5. A method according to claim 1, wherein at least a part of the heat-sensitive recording layer comprises a mixture of a thermotropic liquid crystalline compound and a polymerizable monomer.
A polymer prepared by photopolymerizing a dispersion in which liquid crystal droplets are uniformly dispersed in a glass state obtained by cooling at a specific rate from a temperature showing an isotropic phase to a temperature below the crystallization temperature below the crystallization temperature 5. The reversible recording medium according to claim 3, wherein the recording medium is made of a dispersion type liquid crystal. 6. A method in which at least a part of a heat-sensitive recording layer is formed by changing a cooling rate of a dispersion obtained by uniformly dispersing liquid crystal droplets in a glass state from a temperature at which an isotropic phase is exhibited to a crystallization temperature or lower. 6. The reversible recording medium according to claim 5, comprising a polymer-dispersed liquid crystal layer prepared by controlling the size of the liquid crystal droplet in the state and then performing photopolymerization at a crystallization temperature or lower. 7. The reversible recording medium according to claim 1, further comprising a rubbed crystalline resin film between the support substrate and the heat-sensitive recording layer. 8. The reversible recording medium according to claim 1, wherein the thermotropic liquid crystalline compound is a compound represented by the following formula (a). Embedded image Z—O—CO— (CH ₂ ) m-CR ＝ CH—CH ₂ —CH ₂ —CH ＝ CR —— (CH ₂ ) n—CO—O—Y (a) Y independently represents a cholesteryl group, a hydrogen atom or an alkyl group, R represents a hydrogen atom or an alkyl group, wherein m and n each independently represent an integer of 1 or more, and at least one of Z and Y Represents a cholesteryl group.)