JPH08136903A - Liquid crystal display medium - Google Patents

Abstract

PURPOSE: To obtain a liquid crystal display medium having a protective layer with which excellent rewriting durability is obtainable by forming an intermediate layer consisting of a water-soluble resin on a liquid crystal/high polymer combined film (PDLC film) and forming the protective layer thereon. CONSTITUTION: A conductive layer 3, the PDLC film 4, the intermediate layer 5 and the protective layer 6 are successively laminated on a base 2. The PDLC film 4 which constitutes a display part may be formed in a part on the base 2. In such a case, the PDLC film 4 is covered with the intermediate layer 5 up to its side end face and the intermediate layer 5 is covered with the protective layer 6 up to its side end face. The PDLC film 4 is formed by dispersing liquid crystals into a high polymer matrix. For example, smectic liquid crystals are used as the liquid crystal material. The water-soluble resin is preferable in terms of a barrier property as the intermediate layer 5. The same material as the high-polymer matrix material of the PDLC film 4, if used as the water-soluble resin, is preferable in terms of the improvement of the adhesive property and the prevention of the loss of the transmittance in boundary reflection by a refractive index difference.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display medium using a liquid crystal in a rewritable display portion such as a point card capable of displaying the number of points. Particularly, it relates to a liquid crystal display medium having excellent durability.

[0002]

2. Description of the Related Art Conventionally, credit cards such as magnetic cards, IC cards, optical cards, cards such as cash cards, and prepaid cards such as telephone cards have been widely used. By providing a means for displaying and confirming the recorded information of these cards at any time, the function and convenience have been improved, and new uses of the card have been developed. For example, as a usage development of magnetic cards, prepaid cards employ a method of punching a rough information corresponding to a change in the balance in a part of the card as a visual confirmation means of the change in the recorded balance.

However, with a point card, the number of points increases (by gaining points) or decreases (by using points) each time the card is used, so the punch is always the same as the prepaid card. It is not possible to deal with the hole display. Therefore, the point cards, which are widely used at present, cope with this by printing the number of points on a receipt or displaying it on a register.

[0004] However, even if the point card is used, if the card holder can freely check the number of points only by using the card, the convenience will be further improved, and it can be expected that the card issuer will also be motivated to purchase. Thus, if the card itself has a display means for displaying accurate and complicated information according to the recorded information, a magnetic card or an IC having a larger amount of recorded information
With regard to cards and the like, in particular, it is possible to expect new applications and usages of various cards by taking advantage of their functions.

However, if such a display means is used, for example, to print on a card each time, more accurate and complicated information can be displayed, but there is a limit to the printable card area. Further, if a liquid crystal cell is used, the liquid crystal cell which is bulky and manufactured through complicated steps is expensive, and there is a problem that a driving battery is required. Therefore, in recent years, various display media suitable for a card to be carried and capable of repeatedly rewriting by recording and erasing visible information have been proposed, but none of them has satisfactory performance.

[0006] For example, a fatty acid / polymer composite film in which a fatty acid is dispersed in a polymer matrix utilizes cloudiness / transparency due to the phase change of the fatty acid by heating / cooling, but has a problem with stability over time. The erasing energy for making transparent by heating changes depending on the storage conditions, and high-speed erasing (pulse cycle of about 3.0 msec) cannot be performed stably. Further, the contrast between the background glossiness (due to the metal reflection film) and the cloudy display is low, and the visibility is poor.

Further, in the case of utilizing the opening and closing of the lactone ring of the leuco dye by the color-reducing agent, it takes about 1 to 2 seconds for erasing, and high-speed erasing cannot be performed. Further, there is residual erasure, which cannot be completely erased, resulting in poor rewriting durability.

Further, even with a polymer liquid crystal in which a mesogen group is introduced into a polymer, erasing (clouding) takes about 1 to 2 seconds, and high-speed erasing cannot be performed. Then, the contrast between the cloudy state and the transparent display is low, and the visibility is poor.

A magnetic microcapsule type display medium in which magnetic powder is suspended in a microcapsule and written and erased by magnetism has a low contrast between the background color (base color) and the reflection of the magnetic powder, and the visibility is improved. Inferior. Moreover, since the writing of the display is performed by the magnetic pin, the resolution is also rough.

However, the above-mentioned various display media have not yet achieved satisfactory performance. In particular, in a display medium for card use, high-speed rewritability capable of high-speed writing and erasing is a minimum essential performance from the viewpoint of convenience.
In this respect, as a display medium excellent in practicality, a liquid crystal / polymer composite film (PDLC (Polymer Dispersed Liquid Liquid) in which liquid crystal such as smectic liquid crystal is dispersed in a polymer matrix is used.
Various liquid crystal display media using a (d Crystal) film) (hereinafter, also referred to as PDLC film) have been proposed. The PDLC film can be erased at a high speed because it is erased by applying an electric field, and has excellent visibility because color display can be performed using a dichroic dye. Writing can also be performed with a thermal head using a heating element, and thus high resolution is possible.

The principle of recording / erasing the display information of the liquid crystal display medium by the PDLC film is to utilize the birefringence of the liquid crystal. Specifically, the liquid crystal and the polymer are changed by changing the alignment state of the liquid crystal. Light is transmitted and scattered by changing the refractive index difference from the matrix. That is, PDLC
When the film is heated above the liquid crystal phase transition temperature and cooled, the orientation of the liquid crystal becomes random, and the refractive index of the liquid crystal adjusted to match the refractive index of the polymer matrix changes, causing a difference in the refractive index and becoming cloudy. When recording is performed and an electric field of a threshold voltage necessary for liquid crystal alignment is applied to the PDLC film, the alignment of the liquid crystal is vertically aligned (horizontal alignment when the dielectric anisotropy of the liquid crystal is negative) by the electric field, It is erased by making the polymer matrix transparent so that the refractive indexes of the polymer matrix and the polymer matrix are almost the same. Of course, it is possible to use the recording as transparent and the erasing as clouding. Also, two-color display is possible by mixing a dichroic dye in the liquid crystal.

As a specific example of a display medium using a PDLC film, for example, Japanese Patent Laid-Open No. 4-71899 discloses an information recording card having a PDLC film formed on a transparent electrode provided on a base material. In addition, the applicant of the present invention also
A medium using a PDLC film is disclosed in Japanese Patent No. 240992, Japanese Patent Laid-Open No. 5-301489, and the like.

Further, when the PDLC film is put to practical use, the application of the protective layer is particularly important. This is because, for example, when a display medium is written using a thermal head as a writing means while transporting the display medium, heat and pressure are simultaneously applied to the surface of the display medium in contact with the thermal head,
This is because the PDLC film is destroyed when rewriting is repeated. Therefore, a protective layer is laminated on the PDLC film. Therefore, as the protective layer, in addition to transparency, thermal head suitability (heat resistance, pressure resistance, lubricity) is very important.

For example, regarding the protective layer, JP-A-5-29 is known.
Japanese Patent No. 4092 discloses a tough and heat-resistant protective layer made of an ultraviolet curable resin or the like. In addition, JP-A-4-71
Japanese Patent No. 899 discloses a protective layer formed by ultraviolet curing a polyphosphazene solution, or a protective layer obtained by laminating the entire card with a film.

[0015]

However, Japanese Unexamined Patent Publication No.
In the protective layer according to Japanese Patent No. 294092, a coating material such as a monomer penetrates into the liquid crystal in the PDLC film during the formation of the protective layer, which adversely affects reversibility of rewriting, contrast,
This causes a problem that the display memory property is degraded.

The protective layer made of a polyphosphazene solution or the like in JP-A-4-71899 is merely for protecting the PDLC film from an external impact and is referred to as a protective layer having excellent rewriting durability. Not a thing. Further, when the display medium is laminated with a film to form a protective layer, there is a problem that the protective layer becomes too thick and the threshold voltage required for erasing becomes high because of the film.

There is also a method of indirectly forming a protective layer from the transfer foil as a transfer foil, but it is difficult to obtain a protective layer that sufficiently satisfies rewriting durability and other properties. This is because it is difficult to achieve both releasability and performance required for the protective layer.

Therefore, it is desirable that the protective layer is formed by directly laminating it on the PDLC film. Therefore, an object of the present invention is to solve the above-mentioned drawbacks and to provide a liquid crystal display medium having a protective layer capable of obtaining excellent rewriting durability by a method of directly forming on a PDLC film.

[0019]

Therefore, in order to solve the above problems and achieve the object, the liquid crystal display medium of the present invention contains at least a liquid crystal containing a liquid crystal in a polymer matrix.
In a liquid crystal display medium using a polymer composite film, the liquid crystal /
An intermediate layer made of a water-soluble resin and a protective layer formed on the intermediate layer are formed on the polymer composite film. In the above liquid crystal display medium, the liquid crystal / polymer composite film is formed on a part of the liquid crystal display medium, and the intermediate layer is formed so as to cover the side end surface of the liquid crystal / polymer composite film. It is also a thing. Further, in the above liquid crystal display medium, the protective layer is formed so as to cover the side end surface of the intermediate layer. In addition, in the above liquid crystal display medium, the liquid crystal / polymer composite film also has a structure in which liquid crystal microcapsules in which liquid crystal is surrounded by a polymer film wall are held in a water-soluble polymer matrix.

The present invention will be described in detail below with reference to the drawings. FIG. 1 is a vertical sectional view showing an embodiment of the liquid crystal display medium of the present invention. The liquid crystal display medium 1 of the present invention is one in which a PDLC film is formed as a display portion on the entire surface of the support 2, and the conductive layer 3, the PDLC film 4, the intermediate layer 5, and the protective layer 6 are provided on the support 2 in this order. Are laminated. The PDLC film serving as the display portion may be formed on a part of the support, as shown in FIGS.
Is an example. In FIG. 2, the intermediate layer 5 covers the side end surface of the PDLC film 4, and the protective layer covers the side end surface of the intermediate layer 5. In FIG. 3, the intermediate layer 5 covers the side end surface of the PDLC film 4, but the protective layer 6 is only above the intermediate layer 5 and the side end surface of the intermediate layer 5 is exposed.

The liquid crystal display medium of the present invention has at least a display section using a PDLC film, and if necessary, magnetic recording means such as a magnetic card or IC recording such as an IC card. Means, an optical recording means such as an optical card, or other type of information storage means may be provided. In such a case, by displaying the information held in the information storage means and the information displayed on the display unit in association with each other, more versatile use becomes possible.

As the support 2 of the liquid crystal display medium of the present invention, when it is used as a card, it is possible to use a material used for a conventionally known card having an appropriate rigidity necessary for carrying, for example, polyethylene terephthalate. ,
Polyester resin such as polybutylene terephthalate,
Polymethylmethacrylate, polymethylmethacrylate, acrylic resin such as polyethylmethacrylate, polystyrene, acrylonitrile-butadiene-styrene copolymer, cellulose triacetate, film or sheet such as polycarbonate, the thickness is not particularly limited. , Usually 100 ~
It is about 1000 μm. Further, art paper, coated paper, paper such as high-quality paper, synthetic paper, metal foil, ceramic sheet and the like can be appropriately used according to the application. Also, a composite of these may be used. Further, as a form other than the card, a film, a sheet, a label or the like may be used.

The support 2 is usually an insulating material,
It does not necessarily have to be an insulating material. As long as it is a conductive material having a conductivity higher than that of the PDLC film, a conductive material in a semiconductor region may be used (for example, a resin containing a conductive substance such as carbon black) instead of a so-called conductor. In this case, the liquid crystal display medium can be sandwiched by electrodes from both front and back surfaces, or the front and back surfaces can be charged with different polarities to apply an electric field to the PDLC film. In such a case, the support 2 also serves as the conductive layer 3, and the conductive layer 3 shown in FIGS. 1, 2, and 3 can be omitted.

As the conductive layer 3, a transparent electrode such as an ITO film or a reflective electrode formed of a metal deposition film such as aluminum or a metal foil may be formed on the support by a known method such as vacuum deposition or sputtering. . Alternatively, it may be formed by applying or printing a conductive paint or conductive ink in which a conductive powder such as ITO fine powder is contained in a resin. It is preferable that the conductive layer have good conductivity, but it is sufficient that the conductive layer has conductivity such that an electric field can be applied perpendicularly to the PDLC film. The conductive layer may be on the entire surface of the support, but at least a portion of the PDLC film that carries information display and an electrode portion for applying an electric field to the PDLC film by grounding the conductive layer and the like are provided on the support. It may be provided as a target. In addition, it is necessary that the conductive layer of the portion that carries the information display and the conductive layer of the electrode portion be continuous, that is, electrically conductive. In addition to the function as an electrode, the conductive layer contributes to the improvement of the visibility of the display, and in some cases, the conductive layer also has the function of hiding the support. For example, in terms of visibility, the visual effect can be improved by using the conductive layer as a reflective layer or a colored layer. Further, in terms of the concealing property, if the conductive layer is formed by a white conductive paint, aluminum paste, aluminum vapor deposition or the like, there is no restriction on the color of the support.

The PDLC film 4 is composed of liquid crystal dispersed in a polymer matrix. As the liquid crystal substance used,
For example, a conventionally known smectic liquid crystal can be used. Besides nematic liquid crystals, cholesteric liquid crystals, discholesteric liquid crystals, polymer liquid crystals, and mixed systems thereof can also be used. Further, by mixing an appropriate amount of dichroic dye with the liquid crystal, it is possible to improve the contrast due to the guest-host effect and to perform colored display.

The polymer serving as a matrix for holding the liquid crystal in a dispersed state has film-forming properties, good transparency, and good heat resistance.
Those that are tough and have excellent bending strength during film formation are preferred. For example, vinyl chloride resin, vinyl chloride resin such as vinyl chloride-vinyl acetate copolymer, vinylidene chloride, polyvinyl alcohol resin, epoxy resin, polycarbonate resin,
Examples thereof include polyester resins, polyamide resins, polyacrylates, polymethacrylates, acrylic resins such as acrylate-methacrylate copolymers, polythiol resins, polyurethane resins and the like. Further, an ionizing radiation curable resin composed of an acrylic monomer, a polymerizable prepolymer or the like may be cured by ionizing radiation such as ultraviolet rays or electron beams. In the case of polyvinyl alcohol, various properties such as bending strength are realized by appropriately adjusting the saponification degree and the polymerization degree.

In order to disperse the liquid crystal in the polymer, a phase separation method, an emulsion method, a microcapsule method, a solvent evaporation method, a suspension polymerization method or the like can be used. Among them, the liquid crystal and the polymer are made incompatible. The emulsion method, which has the effect of preventing the exudation of liquid crystals, is excellent, and more preferably, the microcapsule method in which liquid crystal microcapsules in which liquid crystals are surrounded by microcapsules is excellent in terms of the effect of improving durability.

PDLC by the microcapsule method
Regarding the membrane, JP-A-5-301489 by the applicant of the present invention
Japanese Patent Application, Japanese Patent Application No. 6-33283, Japanese Patent Application No. 6-4473.
No. 5, Japanese Patent Application No. 6-119702 can be applied.

The thickness of the PDLC film is usually about 3 to 23 μm when the PDLC film is used alone. If it is less than 3 μm, the display contrast is lowered, and if it exceeds 23 μm, the electric field necessary for the liquid crystal alignment becomes excessive. Too much. In the liquid crystal display medium of the present invention, since the intermediate layer and the protective layer are laminated on the PDLC film, these layers are included in the range of 4 to 30.
μm, and from the realistic layer thickness of the intermediate layer and the protective layer, P
The thickness of the DLC film is more preferably about 3 to 15 μm. In order to suppress the thickness of the PDL film to a maximum of 15 μm, the particle size of the liquid crystal dispersed in the PDLC film is 10 μm.
The following is preferable, and by doing so, the unevenness of the film surface of PDLC can be reduced.

PD in which the particle size of liquid crystal is suppressed to 10 μm or less
Although various dispersion methods described above can be used to form an LC film, when a liquid crystal is made into an emulsion using a dispersant,
For example, by appropriately adjusting the saponification degree of polyvinyl alcohol, which is a nonionic surfactant, it is possible to control the liquid crystal to 10 μm or less. In addition to this, it is preferable to further adjust the particle size distribution of the dispersed liquid crystal by a method such as a film emulsification method. Further, as a method for emulsifying and dispersing the liquid crystal using a dispersant, a mechanical dispersion method such as a dissolver, an ultrasonic dispersion method using ultrasonic waves, or the like can be used. In the method of ultrasonically dispersing or encapsulating the liquid crystal by heating, it is preferable to select a material such as a dispersant that does not reduce the dispersibility by the heat generated. When the liquid crystal is microencapsulated to prevent exudation of the liquid crystal, the in-liquid crystal microcapsule should have a particle size of 10 μm or less without becoming too large.
It is preferable to use the in situ polymerization method. in-situ
In the polymerization method, a monomer such as methyl methacrylate can be used for the membrane wall of the microcapsule. When the microcapsules are formed by the coacervation method using gelatin or gum arabic, the particle size of the liquid crystal microcapsules becomes as large as 20 μm or more, which is not preferable because the PDLC film becomes too thick.

Further, in the case of utilizing the phase separation by the solvent evaporation method as used in the above-mentioned JP-A-4-71899, the volatilization rate of the solvent and the compatibility between the liquid crystal and the solvent are appropriately adjusted, Controls the particle size of the liquid crystal. However, this method has a drawback that the liquid crystal seeps out because the liquid crystal is not completely surrounded by the polymer matrix, but it can be prevented by completely covering the PDLC film including the side end faces with the intermediate layer and the protective layer. it can. However, the liquid crystal exudes from the side end face exposed.

The intermediate layer 5 acts as a barrier layer so that the constituents of the composition for forming the protective layer formed thereon do not reach the PDLC film and adversely affect the liquid crystal, and the transparency and the film are formed. Properties, adhesion to the PDLC film and the protective layer, and the like. Since the liquid crystal is insoluble in water, a water-soluble resin as an intermediate layer is particularly advantageous in terms of barrier properties. Further, it is preferable to use the same material system as the polymer matrix material of the PDLC film as the water-soluble resin, from the viewpoints of improving the adhesiveness and preventing the loss of the transmittance due to the interface reflection due to the refractive index difference. In particular, when the PDLC film is formed by the emulsion method or the microcapsule method, a water-soluble resin such as polyvinyl alcohol is usually used for the polymer matrix, so that the intermediate layer is also a water-soluble resin of the same material system. It is advantageous. Therefore, when using an intermediate layer made of a water-soluble resin,
Also as the PDLC film, it is particularly advantageous to use a water-soluble resin as the polymer matrix.

As such a water-soluble resin, for example,
Synthetic resin such as polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, water-soluble acrylic resin,
Semi-synthetic resins such as carboxymethyl cellulose and hydroxyethyl cellulose, natural resins such as starch, casein, glue, gelatin, gum arabic and the like are mentioned, and one kind or a mixture of two or more kinds thereof is used.

The intermediate layer may be formed by applying a coating solution or ink in which a water-soluble resin is dissolved in water by a conventionally known coating and printing means such as gravure coating and silk screen printing. Further, various additives may be appropriately mixed with the coating liquid or the ink in order to improve coating suitability, print suitability and the like. Incidentally. After coating or printing, the water solvent is preferably dried and removed sufficiently. Middle layer, and sometimes PD
This is because if it remains in the polymer matrix of the LC film, the fluidity of the liquid crystal increases and the alignment memory property of the liquid crystal deteriorates. This is because liquid crystal and water are incompatible, but P
When water remains in the DLC film, water molecules penetrate into the liquid crystal dispersed in the PDLC film, which adversely affects the interaction between the liquid crystal molecules and, as a result, the alignment memory of the liquid crystal. This will reduce the sex.

The thickness of the intermediate layer may be such that, when the protective layer is formed on the intermediate layer, the PDLC film does not adversely affect the alignment of the liquid crystal and the barrier property is obtained.
If it is too thick, the threshold voltage for orienting the liquid crystal of the PDLC film becomes too high, and if it is too thin, the barrier property is not sufficiently obtained and the liquid crystal is adversely affected. The thickness may be appropriately adjusted depending on the constituent components forming the protective layer, the intermediate layer component, the PDLC film component, and the like. Specifically, for example, 0.5 to 10 μm.
m, and more preferably about 1 to 5 μm. If it is too thick, these effects are deteriorated when an electrode is pressed against the outside to apply an electric field or a heating roller or the like is pressed against to heat. It is not preferable to use the intermediate layer as the outermost layer also as the protective layer from the viewpoint of water resistance since it is water-soluble.

At least the intermediate layer is PDLC immediately below the protective layer.
Form on the film. However, when the PDLC film is formed on a part of the liquid crystal display medium, a cross section (side end face) can be formed around the PDCL film, so that a protective layer is formed on the side end face portion.
When the step around the LC film is reduced or the PDLC film is shielded from the outside, it is preferable to cover the side end face portion with the intermediate layer as shown in FIG.

The protective layer 6 is transparent and has PDLC.
It is sufficient that the film is protected from pressure and external force and has heat resistance and the like in consideration of writing with a thermal head. Further, it is more preferable that the display portion has abrasion resistance and scratch resistance so that the display is not scratched and the display is difficult to see. As such a protective layer, since the intermediate layer is formed on the underlayer, the material can be freely selected without considering the influence on the PDLC film. Various curable resins such as resins or UV curable resins or ionizing radiation curable resins as electron beam curable resins can be used, and various additives such as waxes and powders for imparting lubricity, and lubricants. Can be added. The resin used is, among other things, heat resistant, abrasion resistant, and scratch resistant.
Curable resins are preferred. Further, the thermosetting resin may adversely affect the PDLC film by heat during curing, and thus an ionizing radiation curable resin that does not require heat is preferable.

As the ionizing radiation curable resin, conventionally known ultraviolet curable resin and electron beam curable resin can be used. Examples thereof include polyene-thiols, urethane acrylate,
Known ionizing radiation curable resins composed of polymerizable acrylate prepolymers having a (meth) acryloyl group in the molecule such as epoxy acrylate and silicone acrylate, and monofunctional or polyfunctional monomers such as methyl methacrylate can be used. Of these, soft urethane acrylate is a preferable example in terms of appropriate head touch properties for the thermal head, cushioning properties, and the like. In addition, in the present invention, since the intermediate layer can prevent the influence of the monomer component on the liquid crystal, a monomer component that contributes largely to improving the surface strength such as scratch resistance and the like of the protective layer is hard to be selected among the components of the ionizing radiation curable resin. The advantage is that you can choose freely.

The protective layer may be formed by applying a coating liquid or ink containing the above resin by a conventionally known coating or printing means such as gravure coating or silk screen printing. In addition, the coating liquid or ink has coating suitability, printability, lubricity,
In order to improve stain resistance, antistatic property, writing suitability, etc.,
You may mix various additives suitably. The thickness of the protective layer is
It is about 0.5 to 10 μm, more preferably about 1 to 5 μm. If it is too thick, these effects are deteriorated when an electrode is pressed against the outside to apply an electric field or a heating roller or the like is pressed against to heat.

At least the protective layer is formed on the PDLC film (with an intermediate layer interposed therebetween). However, when the PDLC film is formed on a part of the liquid crystal display medium, a cross section (side end face) can be formed around the PDCL film, so that a protective layer is also formed on the side end face portion to reduce the step difference in the periphery of the PDLC film. Or
Further, it is preferable to shield the PDLC film from the outside. Further, when the intermediate layer is formed on a part of the liquid crystal display medium, in order to improve water resistance and moisture resistance of the water-soluble resin intermediate layer, as shown in FIG. Is preferred.

Thus, the liquid crystal display medium of the present invention is obtained. Next, an example of the operation of the display unit will be described. When the PDLC film is initially formed, the liquid crystal orientation is nonuniform and the entire surface is clouded. By applying an electric field to this, the alignment is aligned with the homeotropic alignment that is vertical to the film surface, and a transparent erased state is obtained. This alignment state is maintained even when the electric field is removed.

There are various methods for aligning liquid crystals by applying an electric field. In addition to the methods disclosed in the above publications, these methods include, for example, Japanese Patent Application No. 6-103249 filed by the present applicant.
And the methods and devices disclosed in “Non-contact liquid crystal alignment method and liquid crystal alignment device for liquid crystal display medium” and “Liquid crystal alignment method and liquid crystal alignment device for liquid crystal display medium” of the same application as the present application. it can. These methods are roughly classified into a contact method in which an electrode is brought into contact with the display portion and a non-contact method in which the display portion is charged with static electricity.

For example, as a contact method, assuming that the PDLC film is formed in a part, an external electrode is brought into contact with the PDLC film, and one electrode is brought into contact with the conductive layer of the liquid crystal display medium other than the PDLC film. Then, a predetermined electric field is applied to the PDLC film. These electrodes may be rolled on the liquid crystal display medium as rollers. In the non-contact method, corona chargers having different polarities are used to charge different surfaces of the PDLC on different surfaces to apply an electric field. The electric field may be directly applied by contacting the electrostatic roller, and in this case, a relatively strong electric field can be applied at high speed. Further, as a method employing both the contact type and the non-contact type, a liquid crystal aligning device 11 as shown in FIG.
Thus, the surface may be charged by the charger 12 and the roller electrode 13 made of a grounded conductive member may be brought into contact with the surface to apply an electric field to the PDLC film.

In writing information, the writing portion is locally heated up to a predetermined temperature or higher by a heating means such as a thermal head or a laser to a temperature above the phase transition temperature at which the liquid crystal changes from a smectic phase to an isotropic phase or a nematic phase. It is carried out by heating the liquid crystal to disturb the alignment of the liquid crystal to make it cloudy.
This cloudy state is maintained even when cooled. In the description, the erased state is transparent and the recorded state is cloudy, but they may be reversed. At this time, the writing and erasing means are also reversed. When a dichroic dye is mixed with the liquid crystal, the coloring becomes dark in the cloudy state and thin in the transparent state.

[0045]

As described above, in the liquid crystal display medium of the present invention, since the protective layer on the PDLC film is formed via the intermediate layer made of a water-soluble resin, the water-soluble resin of the intermediate layer serves as a barrier layer. When the protective layer is formed, the components of the coating liquid for forming or the ink penetrates into the liquid crystal in the PDLC film,
There is no adverse effect on the liquid crystal which causes a deterioration in display performance. If the intermediate layer is a water-soluble resin, the coating and printing of the intermediate layer can be first performed with a water solvent, while the liquid crystal is insoluble in water, so that the liquid crystal is not affected. Further, even when the protective layer is formed, most of the constituent materials are usually not water-soluble, so that the intermediate layer acts as a barrier layer. As a result, the constituents of the protective layer can be selected almost freely without being constrained by the influence on the PDLC film, so that a material superior in thermal head suitability and durability can be used. As a result, a liquid crystal display medium having excellent rewriting durability and visibility can be obtained.

When the PDLC film is formed on a part of the liquid crystal display medium, if the side end face of the PDLC film is also covered with the intermediate layer, the constituent components of the protective layer can be prevented from entering from the side end face of the PDLC film. . Further, when the side layer is also covered with the protective layer on the intermediate layer, the protective layer functions as a moisture barrier layer and a waterproof layer of the intermediate layer made of a water-soluble resin. Also, if the liquid crystal / polymer composite film is a microcapsule type and the polymer matrix is a water-soluble resin, the liquid crystal does not seep out and the same water-soluble resin as the intermediate layer is used, so that the adhesiveness etc. But it is reliable.

[0047]

EXAMPLES Next, the present invention will be described more specifically by way of Examples and Comparative Examples. In the text, “part” or “%” is based on weight unless otherwise specified.

Example 1 Formation of Conductive Layer and PDLC Film A milk-white polyethylene terephthalate film (thickness: 188 μm) was used as a support, and a conductive coating in which ITO fine powder was dispersed in an acrylic resin was applied to the entire surface by a bar coating method. The coating was applied to form a conductive layer having a thickness of 2 μm. The sheet resistance of the conductive layer was 10 ⁵ [Ω / sq]. The reflection density of the conductive layer was 0.40 as measured by a reflection densitometer (RD-918 manufactured by Macbeth Co.). Then, a PDLC film having a thickness of 10 μm was formed on the entire surface of the conductive layer by applying a coating solution by a bar coating method and then leaving it at room temperature for 24 hours.

The PDLC film is a dispersion coating liquid prepared by dispersing the liquid crystal (and the dichroic dye mixed with the liquid crystal) by ultrasonic dispersion and using the in-situ polymerization method as the microcapsule method. The liquid crystal microcapsules were formed with a particle size distribution of 7 μm or less. The main components of the PDLC film are as follows.

Smectic liquid crystal (S-6 manufactured by Merck Japan Co., Ltd.) Dichroic dye: 2 wt% based on liquid crystal (Mitsui Toatsu Kagaku Co., Ltd. S-428: black coloring / transparent two colors) Properties: ・ Microcapsule wall film component: (liquid crystal + dye) 10 wt% methyl methacrylate in-situ polymer ・ Protective colloid (dispersant) and polymer matrix component 5% aqueous solution of polyvinyl alcohol (Nippon Synthetic Chemical Industry) KP-06 manufactured by K.K.-Thickener and polymer matrix component 10% aqueous solution of polyvinyl alcohol (KH-20 manufactured by Nippon Synthetic Chemical Industry Co., Ltd.)-Liquid crystal / polymer matrix ratio = 1/1 [(liquid crystal + Pigment) / (PMMA + PVA) = 1/1]

Formation of Intermediate Layer Furthermore, a 10% aqueous solution of polyvinyl alcohol (KH-2 manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) was formed on the entire surface of the PDLC film.
0) was applied by a bar coating method, dried at 60 ° C. for 30 seconds, and then left at room temperature to sufficiently dry residual water, to obtain a thickness of 4
The intermediate layer has a thickness of μm.

Formation of Protective Layer Next, an ultraviolet curable resin (soft uretene acrylate) was applied to the entire surface of the intermediate layer by a bar coating method, and then irradiated with ultraviolet rays from a high pressure mercury lamp (output 120 W / cm) to cure the resin. And a protective layer having a thickness of 4 μm.

Formation of Liquid Crystal Display Medium Then, it was punched into a size of 85 × 54 mm to obtain a card-like liquid crystal display medium having a liquid crystal display portion. For the display, the liquid crystal orientation was random and the vertical orientation was used as the erased state.

Example 2 Formation of PDLC Film A conductive layer was formed on the entire surface in the same manner as in Example 1. Then, in the coating liquid used in Example 1, octyl alcohol was further added as a defoaming agent in an amount of 1% based on the total amount of the coating liquid. After printing to a size of 40 mm in width, it was left to dry at room temperature for 24 hours to obtain a PDLC film having a thickness of 10 μm.

Formation of Intermediate Layer Further, a defoaming agent was added to a 10% aqueous solution of polyvinyl alcohol (KH-20 manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) so as to cover the entire surface of the PDLC film and the side end surface of the PDLC film. As an ink, 1% of octyl alcohol was added to the total amount of coating liquid by silk screen printing.
After drying at 0 ° C. for 30 seconds, it was allowed to stand at room temperature to thoroughly dry residual water to form an intermediate layer having a length of 35 mm, a width of 45 mm and a thickness of 4 μm.

Formation of Protective Layer Then, soft uretene acrylate as an ultraviolet curable resin is printed on the entire surface of the intermediate layer by silk screen printing method, and then is irradiated with ultraviolet rays by a high pressure mercury lamp (output 120 W / cm) to be cured. , Length 35mm, width 45mm, thickness 4
The protective layer has a thickness of μm.

Formation of Liquid Crystal Display Medium Then, it was punched out in the same manner as in Example 1 to obtain a liquid crystal display medium.

Comparative Example 1 The liquid crystal display medium of Comparative Example 1 was prepared by removing the intermediate layer from Example 1.

Comparative Example 2 The liquid crystal display medium of Comparative Example 1 was prepared by removing the intermediate layer from Example 2.

<< Performance Evaluation >> A writing head with a thermal head printer of 6 dot / mm is used.
Heat quantity of 0.4 mJ / dot, pulse period 3.0 mse
The PDLC film was heated at a duty ratio of 50% to write a display. Immediately after forming the liquid crystal display medium, the liquid crystal alignment state of the PDLC film was random, and the entire surface was black due to the dichroic dye.

Erasing (Liquid Crystal Alignment) Treatment In the liquid crystal aligning apparatus as shown in FIG. 4, the surface of the protective layer was charged by a corotron charger at an output of 5 kV, and the grounded roller electrode was brought into contact with the surface of the liquid crystal display medium to obtain a treatment speed ( It was erased at a conveyance speed of the liquid crystal display medium) of 500 mm / sec.

<Evaluation Results> In Examples 1 and 2, the visibility was good, the surface was peeled off, and the film was not broken such as cracks even when the number of rewriting was 1000 times. By the way, the contrast at that time was the reflection density (OD) = 1.0 / 0.4 (writing / erasing) and there was no change at the first time. Comparative Examples 1 and 2
When the protective layer is formed, the UV curable resin monomer is PDL.
The film C was adversely affected, the contrast was lowered from the first time, and the liquid crystal alignment memory property was also lowered. By the way,
The contrast at the first time is the reflection density (OD) = 1.0 /
0.7 (writing / erasing), and memory (1 after erasing
Reflection density (optical density)
= 1.0 / 0.7 was 1.0 / 0.9.

[0063]

According to the liquid crystal display medium of the present invention, unnecessary information displayed on the display section made of the PDLC film can be erased and new information can be repeatedly written. For this reason, since the conventional display unit is full and cannot be reused, the card can be recycled without being thrown away, and the effect of preventing environmental damage can be expected. In particular, since the protective layer can be formed without adversely affecting the PDLC film, an excellent protective layer can be obtained and thermal head suitability (heat resistance, pressure resistance,
It is possible to obtain a practical liquid crystal display medium which is excellent in lubricity and the like, and is excellent in rewriting durability, high-speed rewriting property, holding property, visibility, storage property, and safety. Further, by covering the side end surface of the PDLC film and the side end surface of the intermediate layer with a layer laminated thereon, deterioration from the side end surface can be obtained, and the one having excellent performance such as reliability can be obtained. Further, a combination of a polymer matrix of a water-soluble resin and a PDLC film composed of liquid crystal microcapsules can provide a liquid crystal display medium having more excellent adhesion and reliability.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of a liquid crystal display medium of the present invention.

FIG. 2 is a vertical cross-sectional view showing an embodiment of the liquid crystal display medium of the present invention.

FIG. 3 is a vertical sectional view showing another embodiment of the liquid crystal display medium of the present invention.

FIG. 4 is a conceptual diagram showing an erasing (liquid crystal alignment) method using a charger.

[Explanation of symbols]

 1 Liquid Crystal Display Medium 2 Support 3 Conductive Layer 4 PDLC Film (Liquid Crystal / Polymer Composite Film) 5 Intermediate Layer 6 Protective Layer 11 Eraser 12 Charger 13 Roller Electrode

Claims (4)

[Claims] 1. A liquid crystal display medium using at least a liquid crystal / polymer composite film containing a liquid crystal in a polymer matrix, an intermediate layer comprising a water-soluble resin on the liquid crystal / polymer composite film, and the intermediate layer. A liquid crystal display medium having a protective layer formed thereon. 2. A liquid crystal / polymer composite film is formed on a part of a liquid crystal display medium, and an intermediate layer is formed so as to cover a side end surface of the liquid crystal / polymer composite film. Item 3. A liquid crystal display medium according to item 1. 3. The liquid crystal display medium according to claim 2, wherein the protective layer is formed so as to cover the side end surface of the intermediate layer. 4. A liquid crystal / polymer composite film, wherein liquid crystal microcapsules in which liquid crystal is surrounded by polymer film walls are held in a water-soluble polymer matrix. , 2 or 3 liquid crystal display medium.