JP4863100B2 - Recording display medium and manufacturing method thereof - Google Patents

Description

  The present invention relates to a recording display medium having a liquid crystal layer that is rewritable and capable of recording and displaying in a heat-sensitive specific color or full color, and a manufacturing method thereof.

  Color photographs and color copies are known as recording materials that can record full color and cannot be rewritten. Rewritable recording materials that are not full color include thermal recording materials containing long-chain alkyl carboxylic acid derivatives such as behenic acid, optical recording materials using photochromic compounds such as spiropyran derivatives, and other memory such as magnetism and magneto-optical. The material is known.

  Until now, recording materials have not been compatible with full color and rewritable characteristics. Certainly, some display materials change the display, such as televisions and liquid crystal displays, and there are full-color ones, but they can be used as thin cards that can fit in a wallet or display images stably without power. It was not possible to use it instead of recording material.

  In recent years, rewritable full-color recording has been achieved by a new method using a liquid crystalline compound (Patent Documents 1 to 3, etc.).

  The recording display medium described in the above publication has a liquid crystal compound sandwiched between substrates, but the liquid crystal layer sandwiched between the substrates is composed of only the liquid crystal compound, so that the strength of the liquid crystal layer is insufficient. When a protective layer made of a resin is provided on a liquid crystal layer, there is a problem that the adhesion with the protective layer is insufficient. In addition, since the liquid crystal compound is generally expensive, the recording display medium in which the liquid crystal layer is formed only by the liquid crystal compound has a problem that the cost is high.

  In order to solve this point, the present applicant has made various studies on the binder resin used in the liquid crystal layer. However, when the binder resin is used, there is a new problem that the color development of the recording display medium is not sufficient.

JP-A-11-24027 Japanese Patent No. 2946042 JP 2000-7613 A

  In view of the above-mentioned conventional problems, the present invention does not impair the metallic luster that is characteristic of the cholesteric reflection color even when the amount of the liquid crystal compound is reduced, and has sufficient strength, An object of the present invention is to provide a recording display medium having a liquid crystal layer having excellent adhesion and excellent color development and a method for producing the same.

That is, the recording display medium of the present invention is a recording display medium in which a liquid crystal layer and a surface layer are sequentially laminated on a substrate, and the liquid crystal layer is colored in a liquid crystal state according to a heating temperature, A cholesteric liquid crystal compound that retains the colored state upon rapid cooling from temperature and a polyether resin, and the surface layer is formed on a liquid crystal layer in which the cholesteric liquid crystal compound is a liquid crystal or a liquid It is characterized by being a layer .

  In addition, the method for producing a recording display medium of the present invention is characterized by having a step of forming a surface layer on the liquid crystal layer in a state where the cholesteric liquid crystal compound of the liquid crystal layer is liquid crystal or liquid.

  According to the present invention, a cholesteric liquid crystal display having vivid color development performance is possible, and the adhesion between the surface layer and the liquid crystal layer can be improved.

  Hereinafter, the present invention will be described in detail.

<Liquid crystal layer>
The liquid crystal layer contains a cholesteric liquid crystal compound that develops color according to the heating temperature in the liquid crystal state, and maintains the color developed state by quenching from the temperature, and a polyether resin.

  Examples of cholesteric liquid crystal compounds that develop color according to the heating temperature in the liquid crystal state and maintain the color developed state by rapidly cooling from the temperature (fix the color) include, for example, the following (a) to (d) The compounds as shown are mentioned.

(I) Dibasic acid dicholesteryl ester Specifically, the dibasic acid dicholesteryl ester represented by the following general formula (I) is mentioned.
_{YO-CO (CH 2) o} -R- (CH 2) p CO-OY ...... (I)
(In the formula, Y represents a cholesterol residue obtained by removing a hydroxyl group bonded to cholesterol from cholesterol, R is any group shown in the following (a) to (k), and o and p are the same or Differently, it represents an integer of 1 to 20. In the following (f), l represents an integer of 2 to 20.)

  (B) A cholesteric liquid crystalline compound having a molecular weight of 2000 or less and a glass transition temperature of 35 ° C. or more.

  The molecular weight of this compound is preferably 500-1500, more preferably 700-1200, and the glass transition temperature is preferably 50 ° C. or higher, more preferably 70-110 ° C.

Particularly preferred cholesteric liquid crystal compounds include compounds represented by the following general formula (II).
Z-O-CO-Q-CO-O-Z '(II)
Wherein Z and Z ′ each independently represent a cholesteryl group, a hydrogen atom or an alkyl group, Q represents a divalent hydrocarbon group having 2 to 20 carbon atoms, and at least one of Z and Z ′ is cholesteryl. Represents a group)

Examples of the divalent hydrocarbon group include groups represented by the following general formula (III).
— (CH ₂ ) _q —C≡C—C≡C— (CH ₂ ) _r — (III)
(Wherein q and r are each independently an integer of 1 or more, provided that the sum of q and r does not exceed 30)

  Preferred examples include 10,12-docosadiin dicarboxylic acid dicholesteryl ester, eicosane dicarboxylic acid dicholesteryl ester, 10,12-pentacosadiin dicarboxylic acid cholesteryl ester, dodecadicarboxylic acid dicholesteryl ester, 12,14-hexacosa. And diindicarboxylic acid dicholesteryl ester.

  (C) A mixture comprising a cholesteryl ester compound which is composed of at least two cholesteryl ester compounds and has a reflection peak in a liquid crystal state other than the visible region or does not take a liquid crystal state.

  Such a mixture exhibits a temperature range that is different from the liquid crystal temperature range exhibited by the cholesteryl ester compound alone, and the fixed reflection wavelength region is also different.By appropriately setting the compound to be mixed and the mixing ratio, the liquid crystal temperature range, The fixed reflection wavelength region can be arbitrarily controlled. As a result, the color can be fixed at a temperature lower than that of the compound alone. In addition, even in the case of a mixture of compounds that cannot fix the color, the temperature range different from the liquid crystal temperature range shown by the single substance is shown, and the fixed reflection wavelength region is also different, so that the color can be fixed. Become.

  Examples of the mixture include a mixture of dicholesteryl ester compounds, a mixture of a dicholesteryl ester compound and a monocholesteryl ester compound, a mixture of a compound that can fix a color and a compound that cannot fix a color, and a mixture of compounds that cannot fix a color. However, at least one compound other than the compound that cannot fix the color develops color according to the heating temperature in the liquid crystal state, and maintains the colored state by rapidly cooling from the temperature, that is, the color is changed. A compound to be immobilized is preferable.

Although it does not specifically limit as a dicholesteryl ester compound, For example, dibasic acid dicholesteryl ester is mentioned, Specifically, the dibasic acid dicholesteryl ester represented with the following general formula (IV) is mentioned, s is When the number is odd, the compound can fix the color, and when s is even, the compound cannot fix the color.
YO—CO (CH ₂ ) _s —O—R′—O— (CH ₂ ) _s CO—OY (IV)
(In the formula, Y represents a cholesteryl group, R ′ represents p-phenylene or 4,4′-biphenylene, and s represents a number of 1 to 20)

Moreover, as a monocholesteryl ester compound, the compound represented by the following general formula (V) is mentioned. This is a compound that cannot fix or hardly fix color.
YO—CO (CH ₂ ) _t —O—R′—OH (V)
(In the formula, Y represents a cholesteryl group, R ′ represents p-phenylene or 4,4′-biphenylene, and t represents a number of 1 to 20)

  Among these, a mixture of dibasic acid dicholesteryl esters represented by the general formula (IV), that is, a mixture of a compound capable of fixing the color and a compound capable of fixing the color, two represented by the general formula (IV) Of the basic acid dicholesteryl ester, a mixture of a compound capable of fixing the color and the monocholesteryl ester represented by the general formula (V) is preferable.

  Although it does not specifically limit as a mixing ratio, When mixing 2 types of compounds, it is preferable that both weight ratio is 1: 0.8-1.2. Moreover, it is preferable to contain 20% by weight or more, more preferably 40% to 60% by weight of a compound capable of fixing the color. By setting such a mixing ratio, the liquid crystal temperature range and the reflection wavelength range can be widened.

  As a mixing method, a conventionally known method can be used. For example, a compound to be mixed is dissolved in a solvent that dissolves such as methylene chloride, and the solvent is distilled off, followed by vacuum drying. A powdery mixture can be obtained.

  Polyether-based resin has a hydrophilic part, so the compatibility with the cholesteric liquid crystal compound is inhibited, the inside of the liquid crystal layer has a sea-island structure, and the cholesteric liquid crystal compound becomes the island part. Becomes vivid. In addition, as will be described later, the separation of the liquid crystal compound and the polyether resin is further promoted by forming a surface layer on the liquid crystal layer in a state where the cholesteric liquid crystal compound of the liquid crystal layer is liquid crystal or liquid. .

  The polyether-based resin may have other hydrophilic sites such as a carboxyl group, a hydroxyl group, a sulfonic acid group, an amino group, a heterocyclic group, and a sugar chain in order to increase hydrophilicity. In order to improve the adhesion to the surface layer, reactivity such as carboxyl group, hydroxyl group, isocyanate group, sulfone group, amino group, vinyl group, acrylic group, methacryl group is added to the main chain or side chain including the terminal. It preferably has a group.

The polyether-based resin is a resin obtained by polymerizing or copolymerizing ethylene glycol, propylene glycol, tetramethylene glycol, or the like, preferably a resin having a reactive group, and more preferably a polyether polyol. The polyether-based resin may be a polymer obtained by reacting ethylene glycol, propylene glycol, or the like with a polycondensation agent in the liquid crystal layer, but a resin polymerized in advance is preferable.

  When the polyether-based resin has a reactive group, by further containing a reactive compound having a reactive group that can be covalently bonded by a chemical reaction with the reactive group of the polyether-based resin, A liquid crystal layer and a surface layer can be laminated without providing an adhesive layer.

  Examples of combinations of reactive groups of polyether resins and reactive groups of reactive compounds include carboxyl groups and isocyanate groups, carboxyl groups and hydroxyl groups, carboxyl groups and amino groups, amino groups and epoxy groups, isocyanate groups and hydroxyl groups. Groups, isocyanate groups, amino groups, and the like, and combinations of two or more of these may be used. Low-molecular diols, diamines and the like can be used as chain extenders and crosslink density modifiers.

  The reactive compound may be appropriately selected in accordance with the reactive group of the polyether resin, but when the polyether resin is a polyether polyol, an isocyanate resin, particularly tolylene diisocyanate, diphenylmethane diisocyanate, Isocyanate resins obtained from 1,5-naphthalene diisocyanate, hexamethylene isocyanate and the like are preferred.

  The content of the reactive compound is preferably 150 parts by weight or less with respect to 100 parts by weight of the polyether resin. If it exceeds 150 parts by weight, there is a possibility that the color of the liquid crystal will be hindered.

  In addition, the liquid crystal layer can contain additives such as a dye and an antioxidant, and the content of the additive is preferably 10% by weight or less.

  The content of compounds other than cholesteric liquid crystal compounds such as polyether resins, reactive compounds, and other additives is preferably 10 to 150 parts by weight, and 25 to 100 parts by weight with respect to 100 parts by weight of cholesteric liquid crystal compound. Part by weight is more preferred. If it is less than 10 parts by weight, the strength of the liquid crystal layer may be insufficient. If the amount exceeds 150 parts by weight, the characteristics of the cholesteric liquid crystal compound may change, such as no color development, the state cannot be fixed even after color development, the color changes, and the relationship between temperature and color shifts.

  The thickness of the liquid crystal layer is not particularly limited, but is preferably 3 μm to 50 μm, more preferably 3 μm to 10 μm.

  The method for forming the liquid crystal layer is not particularly limited, and examples thereof include a method in which a mixture containing a cholesteric liquid crystal compound and a polyether resin is heated to a molten state and cast onto a substrate. Further, as a method that does not require heating to a molten state, there is a method of forming a liquid crystal layer by dissolving the mixture in an organic solvent, applying the mixture on a substrate, and then drying to remove the organic solvent. .

  The application method is not particularly limited, and general methods such as spin coating, bar coating, reverse roll coating, and gravure coating can be used. The organic solvent is not particularly limited as long as it can dissolve the above mixture, and examples thereof include toluene, xylene, tetrahydrofuran, and methylene chloride.

  The organic solvent only needs to use at least an amount capable of dissolving the above mixture, and differs depending on the combination of the cholesteric liquid crystal compound, polyether resin and the like used with the organic solvent, but in general, with respect to 100 parts by weight of the cholesteric liquid crystal compound. In the range of 100 to 1500 parts by weight, the above mixture can be dissolved. However, it is not limited to this range.

<Adhesive layer>
The recording display medium of the present invention has, between the liquid crystal layer and the surface layer, an adhesive layer containing a reactive compound having a reactive group that can be covalently bonded by a chemical reaction with the reactive group of the polyether resin. Thus, the lamination strength of the liquid crystal layer and the surface layer can be improved.

  Examples of the reactive compound contained in the adhesive layer include those similar to the reactive compound that may be contained in the liquid crystal layer. Similarly, when the polyether resin is a polyether polyol, an isocyanate compound is used. Resins are preferred. The adhesive layer may contain a low-molecular diol, diamine, or the like as a chain extender or a crosslinking density adjuster.

  The thickness of the adhesive layer is not particularly limited, but is preferably 0.1 μm to 20 μm, more preferably 0.5 μm to 5 μm.

<Surface layer>
The surface layer is laminated on the liquid crystal layer and functions as, for example, a protective layer for the liquid crystal layer. In order to enable display, it is desirable to have transparency that allows at least part of light to pass therethrough. Surface layer materials include acrylic resins, polyamide resins, polyimide resins, polyethersulfone resins, polyetherimide resins, acrylic urethane resins, polyester resins, polyolefin resins, and UV curable resins. Resins, inorganic materials such as siloxane compounds, organic / inorganic hybrid materials such as organosiloxane, glass plates, and the like can be used, and those having excellent heat resistance, flexibility, and adhesion to the liquid crystal layer may be appropriately selected.

  Although the thickness of a surface layer is not specifically limited, Preferably it is 1 micrometer-2 mm, More preferably, it is 1 micrometer-50 micrometers.

  The surface layer is preferably formed in a state where the cholesteric liquid crystal compound in the liquid crystal layer is in a liquid crystal or liquid state by heating the liquid crystal layer. By doing so, separation of the liquid crystal compound and the polyether resin is promoted, and the color developability becomes clear. Specifically, for example, it is formed by heat sealing, extrusion lamination, or the like. Although heating temperature changes with cholesteric liquid crystal compounds, Preferably it is 120 to 150 degreeC.

<Base material>
As the substrate, a polymer film, a thin glass plate, a metal plate, or the like is used. In particular, when light is used for writing or erasing a record as described later, it is desirable that the substrate absorbs light. Further, when the surface layer is not transparent, it is desirable that the substrate is transparent.

  Although the thickness of a base material is not specifically limited, Preferably it is 50 micrometers-5 mm, More preferably, it is 50 micrometers-500 micrometers.

  The recording display medium of the present invention can perform recording (writing) and recording display by partial or total heating. For the heating, various methods such as a thermal head, a heating roll, and a laser beam are possible. Heating that requires temperature control to the liquid crystal temperature range is controlled by controlling the temperature of the thermal head, heating roll, etc., adjusting the laser beam intensity and spot diameter, or heating the whole to a certain temperature. This is possible by lowering the temperature to the required temperature with a flat metal plate or rubber plate.

  On the other hand, in order to fix the coloration of the cholesteric liquid crystal compound, it is necessary to rapidly cool the liquid crystal below its glass transition temperature. For this purpose, the entire liquid is immersed in a refrigerant or a cooled atmosphere. A method, a method of bringing a part into contact with a cooled head, or the like is employed.

  The recording display medium of the present invention can be used, for example, as a card, a sheet for an overhead project, a label, a ticket, and the like, and a back layer or the like may be further provided as necessary. For example, in the case of a label, a mount is provided on the back surface of the recording display medium via an adhesive layer. In the case of a magnetic ticket, a magnetic recording layer made of a binder and a ferromagnetic powder is provided instead of the mount.

<Example 1, comparative example 1>
Using a bar coater, a coating liquid prepared by dissolving the following liquid crystal compound (Y represents a cholesterol residue) and polyether polyol in a toluene solvent at a weight ratio of 1: 1 to a black PET film (base material) having a thickness of 188 μm. This was applied to form a liquid crystal layer having a thickness of 10 μm.
Y—O—CO— (CH ₂ ) ₈ —C≡C—C≡C— (CH ₂ ) ₈ —CO—O—Y

  On the other hand, an isocyanate resin and a polyether polyol are dissolved in a toluene solvent at a weight ratio of 1: 1, and applied to a transparent PET film (surface layer) having a thickness of 12 μm using a bar coater, and an adhesive layer having a thickness of 1 μm is formed. Formed.

Then, on the liquid crystal layer, the surface layer to the adhesive layer side facing combined weight, through a roll heated to Example 1, 140 ° C., through a roll which is not heated in Comparative Example 1, subjected to lamination, recording and displaying A medium was made.

  The recording display medium of Example 1 showed a bright cholesteric interference color as compared with the recording display medium of Comparative Example 1.

<Example 2>
The same liquid crystal compound, polyether polyol, and isocyanate resin as in Example 1 were dissolved in a toluene solvent at a weight ratio of 2: 1: 1. A gravure coater was applied to the same black PET film (base material) as in Example 1. Was applied to form a liquid crystal layer having a thickness of 10 μm.

  Next, polypropylene was extruded from the extruder onto the liquid crystal layer to form a surface layer having a thickness of 30 μm, thereby producing a recording display medium. At this time, the liquid crystal compound in the liquid crystal layer was heated by being in contact with the heated polypropylene, and the liquid crystal compound was in a dissolved state (liquid crystal or liquid state).

  The recording display medium of Example 2 showed a bright cholesteric interference color compared to the recording display medium of Comparative Example 1.

Claims (7)

A recording display medium in which a liquid crystal layer and a surface layer are sequentially laminated on a base material, wherein the liquid crystal layer is colored in a liquid crystal state according to a heating temperature, and is colored by being rapidly cooled from the temperature. A recording medium comprising: a cholesteric liquid crystal compound that retains a liquid crystal and a polyether-based resin , wherein the surface layer is a layer formed on a liquid crystal layer in which the cholesteric liquid crystal compound is a liquid crystal or a liquid Display medium.   The recording display medium according to claim 1, wherein the polyether-based resin has a reactive group.   An adhesive layer containing a reactive compound having a reactive group capable of being covalently bonded by a chemical reaction with a reactive group of the polyether resin is provided between the liquid crystal layer and the surface layer. Item 3. The recording display medium according to Item 2.   The recording display medium according to claim 2, wherein the liquid crystal layer contains a reactive compound having a reactive group capable of being covalently bonded by a chemical reaction with the reactive group of the polyether resin. The recording display medium according to any one of claims 1 to 4 , wherein the cholesteric liquid crystal compound becomes liquid crystal or liquid by heating. In a state in which the cholesteric liquid crystal compound of the liquid crystal layer is in the liquid crystal or liquid, record display according to any one of claims 1 to 5, characterized in that a step of forming a surface layer on the liquid crystal layer A method for producing a medium. The method for producing a recording display medium according to claim 6 , wherein the liquid crystal layer is heated to change the cholesteric liquid crystal compound into a liquid crystal or a liquid.