JP2001271069A - High molecular liquid crystal for composition for reversible recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high molecular liquid crystal hardly causing reduction of contrast, hardly causing the change of preservability at high temperature and the change of orientation by printing pressure, capable of allowing display to be rewritten in a short time, and usable for a composition for a reversible recording medium. SOLUTION: This high molecular liquid crystal is the one for the composition for the reversible recording medium, and has a side chain represented by general formula (1) (wherein, rings A, B, C and D are each independently an aromatic or aliphatic 6-membered hydrocarbon ring, a heterocycle or a condensed ring; Z, Z1, Z2 and Z3 are each independently a direct bond, -CH2O-, -OCH2-, -COO-, -OCO-, -CH2-,-CH2CH2-, -CH=CH-, -CF=CF- or -C≡C-; R1 is a hydrogen atom, a 1-8C straight chain or branched alkyl group, an alkoxy group, an alkoxyalkyl group, a fluoroalkyl group, a cyano group, a halogen atom, a carboxy group or a hydroxy group; X1 and X2 are each independently a hydrogen atom, a halogen atom or a cyano group; l is 1-20; m is 0 or 1; n, p, q and r are each independently a number of 0-2; and n+p+q+r>=1).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a polymer liquid crystal for a composition used in a reversible recording medium. In particular, the present invention is a rewritable paper or OHP display sheet,
The present invention relates to a polymer liquid crystal useful for obtaining a composition used for a display portion of a card and the like. The present invention also relates to a composition for a reversible recording medium containing the polymer liquid crystal, and a reversible recording medium having a recording layer containing the polymer liquid crystal or the composition for a reversible recording medium.

[0002]

2. Description of the Related Art In recent years, liquid crystal materials have been used in many devices as display materials, and have been put to practical use as watches, calculators, televisions, and displays. These display elements use a low-molecular nematic liquid crystal, and adopt a display type called a TN type or STN type. This type of display element is composed of a cell in which liquid crystal is sealed between transparent electrodes and a polarizing plate is provided on both sides. However, the viewing angle is narrow and the luminance is insufficient, so a high power consumption backlight is required. . Further, the displayed information disappears with the removal of the applied voltage. On the other hand, as a liquid crystal material that can be used without being enclosed in a cell, a display element using a liquid crystal / polymer composite film in which liquid crystal molecules are present in a polymer matrix has been proposed. By using a smectic liquid crystal, it is possible to add a memory property to the display, and it can be applied as a reflective display medium. However, in this method, it is necessary to uniformly disperse the liquid crystal molecules in the polymer substance, and it is difficult to manufacture. In addition, a large amount of a polymer substance is required to form a liquid crystal recording layer, and when a dichroic dye is added and used in a host-guest method, the dichroic dye diffuses into the polymer substance and the contrast is reduced. was there. As a liquid crystal display medium that can be used without being enclosed in a cell, has display memory properties, and can be applied as a reflective display medium, a method using a polymer liquid crystal has been proposed. The polymer liquid crystal is obtained by chemically imparting a molecule (mesogen) capable of exhibiting liquid crystallinity to a side chain of a polymer skeleton via a flexible group, and the liquid crystal phase can be easily fixed below Tg.

As a technique utilizing a polymer liquid crystal, Japanese Patent Application Laid-Open No. 63-191673 discloses a display by controlling the applied heat to control the scattering of light due to the state of a liquid crystal domain and the transmission due to the state of an isotropic liquid. A reversible recording material is disclosed. However, this reversible recording material has a preservation property at a high temperature because the orientation state of either an isotropic liquid state or a finely dispersed liquid crystal domain state becomes dominant at a temperature higher than the Tg of the polymer liquid crystal. There was a problem. In addition, since the orientation change from the light transmitting state to the light scattering state is slow and an annealing process is required, there is a problem that it takes time for rewriting. Also, JP-A-59-109
Japanese Patent Publication No. 30 discloses an information recording medium that utilizes a difference in alignment between heat and an electric field or heat applied to a polymer liquid crystal. However, the polymer liquid crystal disclosed here has a problem that the alignment speed is very slow by itself, and it is difficult to put it into practical use as an information recording medium. Furthermore, Japanese Patent Application Laid-Open No. 2-219861 discloses a technique for improving the response speed of a liquid crystal display device using a ferroelectric polymer liquid crystal. However, when a ferroelectric liquid crystal is used for a liquid crystal display device or the like, it is necessary to perform an alignment treatment. Further, since it is necessary to introduce a chiral agent into the polymer liquid crystal in order to obtain a ferroelectric polymer liquid crystal, there is a problem that the synthesis is difficult and the material becomes expensive. Japanese Patent Application Laid-Open Nos. 4-110925 and 6-265861 disclose a technique for improving the response speed of a liquid crystal element by adding a nematic liquid crystal to a polymer liquid crystal to form a smectic phase. ing. However, since the orientation of the smectic phase changes depending on the pressure, there is a problem in durability and storage stability of the liquid crystal element. As described above, it can be used for rewritable paper, OHP display sheets, magnetic card display sections, and IC card display sections. There is no decrease in contrast over a long period or repeated use, no change in contrast due to printing pressure, and high temperature. At present, no polymer liquid crystal has been obtained for a composition capable of achieving a reversible recording medium having excellent storage stability, durability and visibility under the following conditions.

[0004]

SUMMARY OF THE INVENTION Accordingly, the present invention is directed to a rewritable paper or OHP for rewritable paper or the like which does not cause a decrease in contrast, has no storability at high temperatures, does not change orientation due to printing pressure, and can rewrite display in a short time. Polymer liquid crystal for a reversible recording medium composition usable for a display sheet, a display portion of a magnetic card, a display portion of an IC card, and the like;
And a composition for a reversible recording medium comprising the polymer liquid crystal. The present invention also provides a reversible recording medium excellent in responsiveness, high-temperature storage property, light resistance, durability, visibility, and tamper resistance.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, by employing a polymer liquid crystal having a specific molecular structure, especially a side chain structure,
It has been found that the above problems can be solved. That is, the present invention provides a polymer liquid crystal for a composition for a reversible recording medium, which has the following general formula (1):

[0006]

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Wherein the rings A, B, C and D are each independently
Aromatic or aliphatic hydrocarbon 6-membered ring, heterocyclic ring or
Represents a condensed ring, Z, Z¹, Z^TwoAnd Z^ThreeAre directly independent of each other
Bond, -CH_TwoO-, -OCH_Two-, -COO-, -OC
O-, -CH_Two-, -CH_TwoCH _Two-, -CH = CH-,
-CF = CF- or -C≡C-, and R¹Is hydrogen field
, A linear or branched alkyl group having 1 to 8 carbon atoms,
Coxy group, alkoxyalkyl group, fluoroalkyl
Group, cyano group, halogen atom, carboxyl group or hydroxyl
X represents a group¹And X^TwoAre each independently a hydrogen atom or a halogen
Represents an atom or a cyano group, 1 is 1 to 20, m is 0 or
1, n, p, q and r are each independently a number of 0 to 2,
n + p + q + r ≧ 1. Has a side chain represented by)
The polymer liquid crystal. In addition, the present invention
A polymer liquid crystal, and a low-molecular compound compatible with the polymer liquid crystal;
A composition for a reversible recording medium, comprising: further,
The present invention provides a recording layer containing the polymer liquid crystal or the composition.
The present invention provides a reversible recording medium having:

[0008]

Next, embodiments of the present invention will be described in more detail. The polymer liquid crystal according to the present invention has the following general formula (1):

[0009]

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It has a side chain represented by the formula: In the general formula (1), the rings A, B, C and D are each independently a 6-membered aromatic or aliphatic hydrocarbon ring, heterocycle or fused ring. These rings are a 6-membered hydrocarbon ring or a heterocyclic 6-membered ring.
Examples of a membered ring include 1,4-phenylene,
Examples include 1,4-cyclohexylene, 1,4-cyclohexenylene, dioxanylene, pyridylene, pyrimidine and the like. Examples of the fused ring include naphthylene and the like. As ring A, B, C or D,
1,4-phenylene or 1,4-cyclohexylene is preferred. Z, Z ¹ , Z ² and Z ³ are each independently a direct bond;
_{-CH 2 O -, - OCH 2} -, - COO -, - OCO-,
_{-CH 2 -, - CH 2 CH} 2 -, - CH = CH -, - CF
= CF- or -C≡C-. Of these groups,-
_{CH 2 O -, - OCH 2} -, - COO- or -CH ₂ - are preferred.

R ¹ is a hydrogen atom, a linear or branched alkyl group having 1 to 8 carbon atoms, an alkoxy group, an alkoxyalkyl group, a fluoroalkyl group, a cyano group, a halogen atom, a carboxyl group or a hydroxyl group. Examples of the alkyl group include methyl, ethyl, propyl, butyl, isobutyl, pentyl, and the like.Examples of the alkoxy group include an alkoxy group corresponding to the above-described alkyl group. ,
Examples include methoxyethyl, methoxypropyl, ethoxymethyl and the like. Examples of the fluoroalkyl group include a fluoroalkyl group corresponding to the above-mentioned alkyl group, for example, trifluoromethyl, pentafluoroethyl and the like.
Examples of the halogen atom include fluorine, chlorine, and bromine, and fluorine is preferable because of its excellent stability. X ¹ and X ² are each independently a hydrogen atom, a halogen atom or a cyano group. Examples of the halogen atom include fluorine, chlorine, and bromine, and fluorine is preferred because of its excellent stability. When the ring D is at the terminal, X
Preferably, ¹ and X ² are ortho to R ¹ .
l is a number of 1 to 20, and is preferably 1 to 14, and more preferably 2 to 12, from the viewpoint of imparting sufficient alignment stability to the polymer liquid crystal. In addition, l methylene groups are
Does not impair the effects of the present invention, -CH ₂ O -, - O
It may be blocked by a group such as CH ₂ —, —COO— or —OCO—. m is a number of 0 or 1, and is preferably 1. n, p, q and r are each independently a number from 0 to 2, and preferably 0 or 1. Also, n + p + q
+ R ≧ 1, and preferably 4 ≧ n + p + q + r ≧ 1, more preferably 4 ≧ n + p + q + r ≧ 2, from the viewpoint of the liquid crystallinity and rigidity of the polymer liquid crystal.
The polymer liquid crystal of the present invention may have a single type having the side chain represented by the above general formula (1), or may have two or more different general formulas ( It may have a side chain represented by 1).

In the specification of the present application, "reversible recording medium"
The term "medium" generally refers to a medium capable of repeatedly recording and erasing information. As an example of the reversible recording medium, there is a recording medium capable of recording information such as an image by applying heat and erasing the recorded information by applying an electric field while applying heat. In such a reversible recording medium, the recorded information is retained even after the heat is removed and the medium is left at room temperature. As described above, a polymer liquid crystal is generally obtained by chemically adding a molecule (mesogen) capable of exhibiting liquid crystallinity to a polymer skeleton via a flexible group as a side chain. Polymer liquid crystal is T
g or less, the liquid crystal phase can be easily fixed. However, since the viscosity at the temperature indicating the liquid crystal phase (hereinafter, referred to as the liquid crystal phase temperature) is very high, the conventional recording layer for recording information on a reversible recording medium has a low viscosity. Even when a polymer liquid crystal is used, the response to an electric field or heat is generally low. In contrast, the polymer liquid crystal of the present invention can provide a reversible recording medium having good electric field response by having the side chain represented by the general formula (1) as a mesogen. By having two or more different side chains represented by the above general formula (1), the liquid crystal phase temperature and the isotropic liquid temperature can be arbitrarily adjusted. Can provide an excellent reversible recording medium.

The polymer liquid crystal of the present invention preferably has a main chain obtained by addition polymerization of an unsaturated compound. Examples of such a main chain include a polyacrylate main chain, a polymethacrylate main chain, a polychloroacrylate main chain,
Examples thereof include a polyvinyl alcohol main chain and a polyvinyl ether main chain. Further, the main chain of the polymer liquid crystal of the present invention is:
For example, it may be composed of two or more different repeating units such as a poly (acrylate / methacrylate) main chain. The main chain of the polymer liquid crystal of the present invention is preferably a polyacrylate main chain or a polymethacrylate main chain from the viewpoint of the glass transition temperature (Tg) of the polymer liquid crystal, simplicity of polymerization, and the like. The number average molecular weight of the polymer liquid crystal of the present invention is desirably 2,000 or more from the viewpoint of the mechanical strength of the recording layer of the reversible recording medium having the recording layer formed using the polymer liquid crystal. In addition, when the polymer liquid crystal is dissolved in a solvent to form a composition for a reversible recording medium, the viscosity is preferably 500,000 or less from the viewpoint of solubility in the solvent and viscosity of the solution. Preferably, the number average molecular weight of the polymer liquid crystal of the present invention is from 5,000 to 100,000.

The polymer liquid crystal of the present invention comprises one or more monomers having a molecular portion represented by the general formula (1), if necessary, as long as the effects of the present invention are not impaired. Obtained by polymerizing with a monomer of Specific examples of monomers that can be used to produce the polymer liquid crystal of the present invention include the following compounds, but are not limited to these compounds.

[0015]

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A polymerizable liquid crystal obtained by using the above-mentioned compound is introduced with a crosslinking-reactive site to form a compound having a hydroxyl group, a carboxyl group, a mercaptan group or an epoxy group, or an amine such as an amine. By polymerizing with a polymerizable compound having a functional group capable of undergoing an addition reaction with a crosslinking agent, the polymer liquid crystal of the present invention can also be obtained. When a recording layer of a reversible recording medium is formed using such a polymer liquid crystal, a layer having a three-dimensional network structure is obtained, so that a robust recording layer having no fluidity even at high temperatures can be formed. It is.

The polymer liquid crystal of the present invention can be used alone to form a recording layer of a reversible recording medium. On the other hand, from the viewpoint of the response of the formed recording layer, it is desirable to use a low-molecular compound compatible with the high-molecular liquid crystal. Thus, the composition for a reversible recording medium according to the present invention contains the above-mentioned liquid crystal polymer and a low-molecular compound compatible with the liquid crystal. The low-molecular compound that can be used in the composition of the present invention is a compound that is compatible with the high-molecular liquid crystal,
Those which are stable even at low temperatures and do not cause phase separation are desirable. Generally, a low-molecular compound having a structure similar to the mesogen skeleton of a high-molecular liquid crystal has high compatibility. Further, as the low-molecular compound, a compound that lowers the viscosity of the liquid crystal phase state of the high-molecular liquid crystal is desirable from the viewpoint of further improving the response of the formed recording layer. As such a low-molecular compound, a single compound may be used, or two or more different compounds are used in combination to adjust the isotropic liquid temperature or the liquid crystal phase temperature to a desired range. It may be that.

The low molecular compound used in the composition of the present invention includes the following general formula (2):

[0019]

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The following is preferred. In the general formula (2), as described above, Y ¹ represents a hydrogen atom, a linear or branched alkyl group having 1 to 8 carbon atoms, an alkoxy group, an alkenyl group, an alkenyloxy group, an alkoxyalkyl group, an alkanoyloxy group. Or, the ring E and F are each independently a benzene ring, a cyclohexane ring, a cyclohexene ring, a pyrimidine ring or a dioxane ring. W ¹ and W ² are each independently a direct _{bond, -CH 2 O -, - OCH} 2 -, - COO-,
_{-OCO -, - CH 2 -,} - CH 2 CH 2 -, - CH = C
H- or -C≡C-. As W ¹ or W ² , a direct bond, —CH ₂ O—, —OCH ₂ —, —COO— or —C
≡C- is preferred. In addition, as described above, Y is a hydrogen atom or a halogen atom, and Y ² is a cyano group, a halogen atom,
A linear or branched alkyl group, an alkoxy group, an alkenyl group, an alkenyloxy group, an alkoxyalkyl group,
It is an alkanoyloxy group or a cyano group, and Y ³ is a hydrogen atom, a halogen atom or a cyano group. further,
m is a number from 0 to 2, preferably 0 or 1.

Specific examples of the low molecular weight compound that can be used in the composition of the present invention include compounds represented by the following general formulas, but are not limited to these compounds.

[0022]

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(Wherein Y ¹ , Y, Y ² and Y ³ are as defined for the above general formula (2).) In the composition of the present invention, a liquid crystal polymer and a low molecular compound are used in combination. In this case, the amount of the high-molecular liquid crystal or the low-molecular compound used can be appropriately determined according to the type of the high-molecular liquid crystal and the low-molecular compound to be used, and the high compatibility thereof, but generally, the composition Based on the mass of the whole object,
It is preferable that the amount of the high-molecular liquid crystal used is 99 to 60% by mass and the amount of the low-molecular compound is 40 to 1% by mass. It is preferable to use 30 to 5% by mass.

Further, the composition for a reversible recording medium of the present invention may contain a dichroic dye. By using a composition containing a dichroic dye, a reversible recording medium capable of performing colored display can be obtained. The dichroic dye used in the composition of the present invention may be either an azo type or an anthraquinone type. As dichroic dyes,
Only a single dye component may be used, or the color tone of the display of the reversible recording medium may be adjusted by mixing multiple dyes. Examples of the dichroic dye that can be used in the composition of the present invention include, for example, Mitsui Chemicals, Inc.
M-361, SI-484, M-1 commercially available from
41, M-484, M-34, SI-497, M-40
3, S-409, M-412, S-428, NKX-1366, G-2 which are commercially available from Nippon Kosaku Dyestuffs Co., Ltd.
02, G-205, G-206, G-207, G-23
2, G-239, G-241, G-254, G-25
6, G-289, G-470, G-471, G-47
2. KRD-201 commercially available from Showa Kako Co., Ltd.
KRD-901, KRD-902, KPD-503, K
PD-906, KBD-401, KBD-701, KK
D-602, KKD-604 and the like. The amount of the dichroic dye in the composition of the present invention can be appropriately determined according to the type of the dye to be used and the like.In general, from the viewpoint of solubility of the dye in liquid crystal, the composition It is desirable that the content be 20% by mass or less based on the total mass. Incidentally, the composition for a reversible recording medium of the present invention, in addition to the dichroic dye, a solvent, a surfactant, a filler, a resin, etc., those commonly used when forming a recording layer of a reversible recording medium May be included.

Here, the principle of displaying information using the liquid crystal composition of the present invention will be described with reference to FIGS. 1 and 2 are diagrams showing the phase states of the polymer liquid crystal, respectively. FIGS. 1A and 1B are diagrams showing the respective phase states of a liquid crystal composition in which a polymer liquid crystal and a low molecular component are mixed. FIG. 1A shows an isotropic liquid state, FIG. 1B shows a domain state, and FIG. The tropic alignment state is shown. In the figure, 1a indicates the main chain of the polymer liquid crystal, 1b indicates the mesogen of the polymer liquid crystal, 2 indicates a low molecular component, and 3 indicates the direction of application of the electric field. The polymer liquid crystal 1 changes its orientation by the electric field at the liquid crystal phase temperature, shows a glassy state at the liquid crystal phase temperature or lower, and can fix the liquid crystal phase. Fig. 2 shows that P has a transition moment of light absorption in the molecular long axis direction.
FIG. 4 is a diagram showing a phase state when a dichroic dye of a type is mixed in a liquid crystal layer. In this case, the homeotropic alignment state shows colorless, and the domain state and the isotropic liquid state show color. 2, (d) shows an isotropic liquid state, (e) shows a domain state, and (f) shows a homeotropic alignment state. In the figure, 1a, 1b, 2 and 3 indicate the same ones as in FIG. 1, and 4 indicates a dichroic dye. The dichroic dye is held between the side chain molecules of the electric field responsive side chain type liquid crystal polymer, takes an alignment state similar to the alignment between the side chain molecules, and performs the same optical function as the liquid crystal polymer. . When a polymer liquid crystal having a positive dielectric anisotropy (Δε> 0) is heated to a liquid crystal phase temperature and an electric field higher than a threshold voltage is applied, the liquid crystal is aligned parallel to the electric field (homeotropic alignment). The liquid crystal recording layer in the homeotropic alignment state is colorless. Also, when heat is applied and cooled above the temperature of the isotropic liquid, the orientation of the domain or the isotropic liquid state is frozen. The orientation state changes depending on the cooling temperature. In the case of rapid cooling, an isotropic liquid state (colorless) as shown in FIG. 1 is formed, and in the case of slow cooling, domains (white turbidity) as shown in FIG. 2 are formed. An image can be formed and erased using this orientation, and colorless and white turbidity can be displayed. The layer stability is different between the homeotropic alignment state (transparent) and the isotropic liquid state (colorless). The isotropic liquid state gradually changes to the domain state even below the liquid crystal phase temperature. Is maintained up to the liquid crystal phase temperature.
Therefore, it is preferable to form an image using the domain state and the homeotropic alignment state.

Further, the present invention relates to a reversible recording medium having a recording layer containing the above polymer liquid crystal or composition. An embodiment of a reversible recording medium according to the present invention will be described with reference to FIG. FIG. 3 shows that a recording layer 33 is formed on a conductive layer 32 on
FIG. 3 is a diagram schematically illustrating an embodiment of the reversible recording medium of the present invention, in which a protective layer 34 is formed on the recording medium 3. Recording layer 33
Is prepared by dissolving the polymer liquid crystal of the present invention or a composition containing the polymer liquid crystal and a low-molecular compound in an organic solvent, if necessary, to prepare a paint, and applying the paint by any known coating method. It can be formed by: Base material 31
May be any sheet having the rigidity required for carrying a reversible recording medium. Examples of materials that can be used for the substrate 31 include, for example, polyethylene terephthalate films, polyester films such as polybutylene terephthalate films, polymethyl methacrylate, polymethyl acrylate, and acrylic resin-based films such as polyethyl methacrylate, and the like. Examples thereof include a polystyrene film, an acrylonitrile-butadiene-styrene copolymer, a cellulose triacetate film, a polycarbonate film, and a polyimide film. Also, art paper,
General papers such as coated paper, high-quality paper, synthetic paper, metal foil,
It is also possible to use a ceramic sheet or the like as the base material 31. The thickness of the substrate 31 can be about 25 to 1000 μm.

The conductive layer 32 formed on the surface of the substrate 31 may be any material having a literal conductivity. Examples of a material that can be used for the conductive layer 32 include a conductive organic material such as carbon black, a metal such as aluminum, chromium, nickel, cobalt, copper, silver, gold, tin, zinc, brass, and stainless steel; Oxide, nitride, ZnOx, In-Sn-Ox, and the like. The conductive layer 32 is formed on the surface of the base material 31,
A layer containing these materials can be formed and provided by a technique such as vapor deposition, sputtering, electroless plating, or thermal plating. Further, it can be formed as a foil layer of the above material. Furthermore, it is also possible to prepare a coating agent in which the above-mentioned material is made into a powder and this is dispersed in a resin, and to form a coating layer by a general coating method.
The thickness of the conductive layer 32 can be about 0.01 to 50 μm. When the conductive layer 32 is formed on the surface of the base material 31 by vacuum evaporation or sputtering, an anchor coat layer (not shown) is formed on the surface of the base material 31 in order to measure the uniformity of the conductive layer 32. ) After forming
Preferably, a conductive layer 32 is formed. When a material having metallic luster is used as the conductive layer 32,
The conductive layer 32 also functions as a reflective layer for forming a high-contrast image. Further, the conductive layer 32 can also be used as a reflective layer. In this case,
When the surface of the conductive layer 32 is a mirror surface, the specular reflection component is strong and the viewing angle is narrow, and therefore, it is preferable that the surface of the conductive layer 32 is appropriately roughened. The surface roughness of the conductive layer 32 may be adjusted by the amount of filler added to the base material 31 or the amount of filler added to the coating liquid when forming the anchor coat layer on the surface of the base material 31. It is possible. Conductive layer 3
If the base material 2 is transparent, the color of the base material 31 can be seen through the base material 31. The base material 31 is made of a milky white polyethylene terephthalate film or the like, or the base material 31 is coated with a white coating agent. It is possible to obtain a dichroic dye color character print. Further, when the conductive layer 32 is transparent, using a highly transparent sheet for the base material,
When a reflective layer and a white layer are formed on the back surface of the sheet via an air layer, it is possible to reduce the coloring of the background portion due to the dichroic dye. The conductive layer 32 may be formed on the entire surface of the base material 31 of the reversible recording medium, or may be formed partially.

Protective layer 34 formed on recording layer 33
Is the force, heat, light,
It is intended to protect from water and the like, and needs to have an action with excellent robustness. Examples of the material that can be used for the protective layer 34 include a silicone resin and a mixed resin composition of a prepolymer, an oligomer, a monomer, and the like having a polymerizable unsaturated bond or an epoxy group in a molecule. Further, the protective layer 34 may be provided with an ultraviolet absorbing ability. In this case, the inorganic ultraviolet absorbing particles may be dispersed in the material. The protective layer 34 can be provided by forming a layer containing these materials on the recording layer by a usual coating method or the like. The thickness of the protective layer 34 can be about 0.5 to 10 μm.

Next, a method of forming and erasing image information on a reversible recording medium according to an embodiment of the present invention will be described. The application of heat to the reversible recording medium can be performed with a hot plate, a heating roller, a thermal head, optical means, or the like. Also,
The cooling rate such as rapid cooling or slow cooling can be controlled by a heating temperature, a heating time or a cooling device. The application of an electric field to the reversible recording medium should be performed by a corona charger, an ion flow, an electrostatic roller, an electrostatic head, an electric field applying roller or an electric field applying plate as shown in FIGS. 4 (g) and 4 (h). Is possible. The recording of image information on a reversible recording medium can be performed by applying heat to the colorless state by the above-described method or the like to form a transparent coloring state and a concealing coloring state. Erasing image information from a reversible recording medium
After applying heat to the reversible recording medium by the above method or the like, while the recording layer is in the liquid crystal phase temperature range, applying an electric field by the above method or the like to make the recording layer colorless. Can be. When the entire surface of the reversible recording medium is heated and an electric field is applied to the entire surface, recorded information can be erased over the entire surface. On the other hand, the recorded information can be partially erased by partially heating the reversible recording medium and applying a voltage to the entire surface, or by heating the entire surface and partially applying an electric field. . Although it is possible to form a colored image on a colorless background by the above method,
By performing erasure and image formation in the reverse manner, a colorless image can be formed on a colored background. Thus, information can be recorded and erased freely by repeating the operation of applying heat and heat and an electric field. In the above-described embodiment of the present invention, the laminated type reversible recording medium has been described. However, a polymer liquid crystal or a composition containing the liquid crystal is sealed between the electrodes to form a cell, and the liquid crystal display has a form like a liquid crystal display. It is also possible to use Also, by introducing a light-to-heat conversion layer into the layer structure of the reversible recording medium or by introducing an infrared absorbing dye into the recording layer, recording and erasing of image information by light and an electric field can be performed. It is also possible.

[0030]

EXAMPLES Example 1 Formula I-1:

[0031]

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Polymer liquid crystal having a structure represented by the following formula (number average molecular weight: 9,000) was injected into a cell having a cell thickness of 10 μm. When the ni point (isotropic liquid temperature) of this polymer liquid crystal was measured and found to be 125 ° C., the cell was cooled to 125 ° C.
After heating to 50 Hz, an electric field of 50 V and 25 V was applied to a part of the cell, and the cell was cooled in that state. As a result, it was confirmed that the electric field application portion was in a homeotropic alignment state. Furthermore, when the cell was heated again to 125 ° C. and cooled, it was found that the portion that had been in the homeotropic alignment state was now in the domain state. In addition, the cell was left at 60 ° C. for 24 hours, and the change over time in the alignment state was observed with a transmission microscope and a polarizing microscope. As for the homeotropic alignment state and the domain state,
No change was found in the orientation state. From the results, it is clear that the polymer liquid crystal of the present invention is useful for a reversible recording medium using a thermal electric field. Example 2 As the high-molecular liquid crystal, the one represented by the above-mentioned I-1 was used, and the low-molecular compound represented by the following formula II-1 was used at the ratio (% by mass) shown in Table 1. By mixing, compositions a to c for reversible recording media were prepared.

[0033]

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Each of the obtained compositions a to c was injected into a cell having a cell thickness of 10 μm, and the ni point and the threshold voltage were measured. The results are shown in Table 1.

[0035]

[Table 1] Table 1 Composition I-1 II-1 ni Threshold voltage a 90% 10% 110 ° C. 50 Hz, 5 Vb 70% 30% 107 ° C. 50 Hz, 3 V c 50% 50% 105 ° C. 50 Hz, 3 V

From the results, it is apparent that the response is improved by adding a low molecular compound to the polymer liquid crystal of the present invention. The mixture was left at room temperature for 48 hours to observe the phase stability. Although mixture c underwent phase separation, a and b were stable. In the case where the homeotropic and liquid crystal domain states of a and b were left at 60 ° C. for 24 hours, no change was observed in the transmittance and the alignment state observed by a deflection microscope. From these results, it is clear that by adding a low molecular compound to the polymer liquid crystal of the present invention, it is possible to improve the response speed and at the same time maintain the preservability.

Example 3 The polymer liquid crystal I-1 used in Example 1 and the compositions a and b prepared in Example 2 were combined with NKX-1366 (manufactured by Nippon Kosoku Dye Co., Ltd.) as a dichroic dye. Addition of 1% based on the entire mass, injection into a cell having a cell thickness of 10 μm, change in the homeotropic alignment formed by applying a thermal electric field and the change in the transmittance of the isotropic liquid state formed by heating to the ni point. It was measured. The transmittance was measured at 67.
This was performed using light having a wavelength of 0 nm. For comparison, the same measurement was performed on a low-molecular liquid crystal (ZLI-4792 manufactured by Merck) to which a dichroic dye was added as described above. Table 2 shows the results.

[0038]

[Table 2] Table 2 Composition Homeotropic Orientation Isotropic Liquid State or Domain I-1 69.83% 11.47% b 68.98% 11.58% c 69.63% 39.07% Low Molecular Liquid Crystal 68.52 % 38. 30%

From the results, regarding the transmittance in the case of homeotropic alignment, all the mixtures show the same value,
It is also clear that the high-molecular liquid crystal takes on the same degree of orientation as the low-molecular liquid crystal. As for the transmittance in the isotropic liquid state, the polymer liquid crystal exhibited a lower value than the low molecular liquid crystal. This is because the polymer liquid crystal forms a liquid crystal domain structure and diffusely reflects.

Example 4 In 240 parts by weight of tetrahydrofuran (THF), 100 parts by weight of the composition a prepared in Example 2 and 3 parts by weight of NKX-1366 (manufactured by Nippon Kosoku Dye Co., Ltd.) as a dichroic dye were mixed. Thus, a coating solution for a recording layer of a reversible recording medium was prepared. This coating liquid was applied using a bar coater on a polyethylene terephthalate (PET) film having an Al layer formed on the upper surface so that the film thickness after drying was 5 μm. Next, a 50 mass% ethanol solution of a mixture of 100 parts by weight of UV curing resin NK-OLIGO U-6HA manufactured by Shin-Nakamura Chemical Co., Ltd. and 5 parts by weight of a cross-linking agent Irgacure 907 manufactured by Ciba Geigy was prepared. . This solution was coated on the recording layer with a thickness of 2.5 μm after drying.
m was applied using a bar coater to form a protective layer. The reversible recording medium thus manufactured was heated to 130 ° C., and a thermal electric field was applied at 50 Hz and 50 V using electrodes as shown in FIG. 4 (h). Could be formed. When the reflection density of this display was measured with a Macbeth reflection densitometer,
0.6. When printing was performed on the display section of the reversible recording medium with an energy of 0.34 mJ / dot using a thermal head, the printed section was colored black. The measured reflection density of the printed portion was 1.2. The reversible recording medium was held at 80 ° C. for 96 hours, and the change over time in the reflection density of the unprinted portion of the printing portion and the display portion was observed.
No change was noted. Furthermore, when a thermal electric field was applied to the reversible recording medium held at a high temperature to erase the print, there was no difference in the reflection density between the erased portion and the portion where printing was not performed from the beginning. Did not.

Example 5 A polymer liquid crystal having a structure represented by the following formula I-2 (a monomer corresponding to a repeating unit having a side chain A of 90 mol%, and a polymer corresponding to a repeating unit having a side chain B) Polymerized using 10 mol% of a monomer having a number average molecular weight of 12,000).
Using the compound represented by Formula-2 or the compound represented by the following formula II-3, the composition was mixed at a ratio (% by mass) shown in Table 3 to prepare compositions df for a reversible recording medium. .

[0042]

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[0043]

[Table 3] Table 3

Into 240 parts by weight of tetrahydrofuran (THF), 100 parts by weight of these compositions, and 3 parts by weight of NKX-1366 manufactured by Nippon Kosaku Dye Co., Ltd. as a dichroic dye were mixed to obtain a reversible recording medium. Three types of coating solutions for the recording layer were prepared. These coating solutions were applied using a bar coater on a polyethylene terephthalate (PET) film having an Al layer formed on the upper surface so that the film thickness after drying was 5 μm. Next, 100 parts by weight of UV curing resin NK-OLIGOU-6H manufactured by Shin-Nakamura Chemical Co., Ltd.
A 50 mass% ethanol solution of a mixture of A and 5 parts by weight of a cross-linking agent Irgacure 907 manufactured by Ciba Geigy was prepared. This solution was applied using a bar coater on the above-mentioned recording layer so that the film thickness after drying was 2.5 μm, to form a protective layer. The reversible recording medium thus manufactured was heated to 130 ° C., and a thermal electric field was applied at 50 Hz and 50 V using electrodes as shown in FIG. 4 (h). Could be formed.
The reflection density of the display section was measured by a Macbeth reflection densitometer and was found to be 0.6. On the display of the reversible recording medium,
When printing was performed using a thermal head at an energy of 0.34 mJ / dot, the printed portion was colored black. The measured reflection density of the printed portion was 1.2. When this reversible recording medium was kept at 90 ° C. for 96 hours, the change in reflection density over time of the printed portion and the display portion where no printing was performed was observed. Did not. Furthermore, when a thermal electric field was applied to the reversible recording medium held at a high temperature to erase the print, there was no difference in the reflection density between the erased portion and the portion where printing was not performed from the beginning. Did not.

[0045]

[Brief description of the drawings]

FIG. 1 is a view showing an alignment state of a composition comprising a high-molecular liquid crystal and a low-molecular compound.

FIG. 2 is a view showing an alignment state of a composition comprising a high-molecular liquid crystal, a low-molecular compound, and a dichroic dye.

FIG. 3 is a schematic diagram of a layer configuration of a reversible recording medium according to an embodiment of the present invention.

FIG. 4 is a diagram showing an example of an electric field application head for recording and erasing information on a reversible recording medium according to an embodiment of the present invention.

[Explanation of symbols]

 31 base material 32 conductive layer 33 recording layer 34 protective layer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 33/04 C08L 33/04 C09K 19/10 C09K 19/10 19/32 19/32 19/34 19 / 34 19/42 19/42 G02F 1/13 500 G02F 1/13 500 F term (reference) 4H027 BA13 BD01 BD08 BD12 BD20 BD21 BE04 CF04 CL04 CN03 4J002 BE041 BG071 EA046 EB106 ED056 EH126 ET006 GP00 GQ00 4J100 AE26P AL03P BA02P04 BA15P BA16P BA40P BB07P BC04P BC43P CA01 JA39

Claims (10)

[Claims] 1. A polymer for a composition for a reversible recording medium.
A liquid crystal having the following general formula (1):(Wherein rings A, B, C and D are each independently aromatic or
Represents an aliphatic hydrocarbon 6-membered ring, a heterocyclic ring or a condensed ring.
And Z, Z¹, Z^TwoAnd Z^ThreeAre each independently a direct bond, -C
H_TwoO-, -OCH_Two-, -COO-, -OCO-, -C
H_Two-, -CH_TwoCH _Two-, -CH = CH-, -CF = C
F- or -C≡C-;¹Is hydrogen atom, carbon number 1
To 8 linear or branched alkyl groups, alkoxy groups,
Alkoxyalkyl group, fluoroalkyl group, cyano group,
X represents a halogen atom, a carboxyl group or a hydroxyl group;¹
And X^TwoAre each independently a hydrogen atom, a halogen atom or a shea
L represents 1 to 20, m represents 0 or 1, n, p, q
And r are each independently a number from 0 to 2, and n + p + q + r
≧ 1. The polymer liquid having a side chain represented by the formula:
Akira. 2. The polymer liquid crystal according to claim 1, which has a main chain obtained by addition polymerization of an unsaturated compound. 3. A composition for a reversible recording medium, comprising the polymer liquid crystal according to claim 1. 4. The composition according to claim 3, further comprising a low-molecular compound compatible with the high-molecular liquid crystal. 5. The low molecular weight compound represented by the following general formula (2): (Wherein, Y ¹ represents a hydrogen atom, a linear or branched alkyl group having 1 to 8 carbon atoms, an alkoxy group, an alkenyl group, an alkenyloxy group, an alkoxyalkyl group, an alkanoyloxy group or an alkoxycarbonyl group; E and F
Each independently a benzene ring, cyclohexane ring, cyclohexene ring, indicates a pyrimidine ring or a dioxane ring, W ¹
And W ² are each independently a direct bond, —CH ₂ O—, —OCH
_{2 -, - COO -, -} OCO -, - CH 2 -, - CH 2 C
H ₂ —, —CH ＝ CH— or —C≡C—, Y represents a hydrogen atom or a halogen atom, and Y ² is a cyano group, a halogen atom, a linear or branched alkyl having 1 to 8 carbon atoms. Represents a group, an alkoxy group, an alkenyl group, an alkenyloxy group, an alkoxyalkyl group, an alkanoyloxy group or a cyano group, Y ³ represents a hydrogen atom, a halogen atom or a cyano group, and m is a number of 0 to 2. The composition according to claim 4, which is represented by the formula: 6. The method according to claim 3, further comprising a dichroic dye.
A composition according to any one of the preceding claims. 7. A reversible recording medium having a recording layer containing the liquid crystal polymer according to claim 1. Description: 8. A reversible recording medium, comprising a recording layer containing the composition according to claim 4. Description: 9. The recording medium according to claim 7, wherein the recording layer is formed on a layer having conductivity. 10. The recording medium according to claim 7, wherein a protective layer is formed on the recording layer.