JPH1062738A - Reversible display medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reversible recording display medium having high light scatterbility and high strength as the flexible reversible recording display medium which executes turbid/transparent display by impression of heat. SOLUTION: This reversible display medium is obtd. by forming a light scattering body prepd. by dispersing high-polymer liquid crystal materials in a fibrous form into a resin on a base material and executes recording/erasing by reversibly changing the transmittance of the light scattering body by impression of heat thereon. The high-polymer liquid crystal materials are preferably a copolymer of a liquid crystalline monomer and a non-liquid crystalline monomer and the fiber diameter of the high-polymer liquid crystal materials is preferably >=0.1 to <=2μm. The recording/erasing are executed by using the isotropic glass state and liquid crystal phase glass state of the high-polymer liquid crystal material dispersed into the reversible display medium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible display medium capable of recording / erasing reversibly at least by application of heat,
More specifically, the present invention relates to a flexible thermoreversible display medium that performs opaque / transparent display at least by applying heat.

[0002]

2. Description of the Related Art In recent years, reversible recording and display media capable of reversibly recording and erasing images due to light scattering properties have attracted attention.
Above all, many reversible thermosensitive display media capable of easily performing cloudy / transparent display using heat from a thermal head or the like have been reported. As such a cloudy / transparent type recording / display material,
An element for blending two kinds of polymers and performing display by compatibility / incompatibility depending on temperature (Japanese Patent Application Laid-Open No. 60-18087);
An element which disperses microcrystals of an organic low-molecular compound in a resin base material and performs display by changing the crystal size (Japanese Patent Laid-Open No. 54-119).
377) There is known an element for performing display using a liquid crystal polydomain structure of a polymer liquid crystal compound and an isotropic phase glass state. Forms a scattering state due to the refractive index difference at the interface between the two polymers, forms a light scattering state due to the presence of voids when the crystal size of the organic small molecule and microcrystallize, and is based on a liquid crystal group. It is known that a light scattering state is formed by a large birefringence and a liquid crystal polydomain structure.

On the other hand, an element for controlling light scattering by a driving force other than heat has a structure in which a low-molecular liquid crystal is dispersed in a binder polymer, and has a large birefringence of the low-molecular liquid crystal and refraction of the binder polymer. There is known a polymer-dispersed liquid crystal in which a light scattering state is formed by a combination of rate differences and light scattering is controlled by an electric field. Japanese Patent Application Laid-Open No. 3-284988 discloses a device similar to that described above, in which a polymer liquid crystal is dispersed in a binder polymer and light scattering is controlled by heat and an electric field.

[0004]

Is prepared by dissolving an organic low-molecular substance and a resin base material or two kinds of polymers in a common solvent, and applying and drying the same to cause a melt phase separation. In these methods, the material selection is limited due to the use of the melt phase separation method, and two materials having a large difference in refractive index cannot be combined, and the dispersion shape after the phase separation is limited. It is difficult to control the dispersed particle diameter, and it is not easy to improve the light scattering performance (white turbidity). Although a higher light scattering performance (white turbidity) can be obtained as compared with light scattering due to a large birefringence and a liquid crystal polydomain structure, a higher light scattering performance (white turbidity) is required for a display element.

[0005] Polymer-dispersed polymer liquid crystal (Japanese Unexamined Patent Publication No.
284988) is produced by a polymerization phase separation method,
It is difficult to control the particle diameter and particle diameter distribution of the dispersed liquid crystal in the same manner as described above, and it is not easy to obtain sufficient light scattering performance (white turbidity). Further, since is based on electric field driving, a transparent conductive layer is required in the element, and the device configuration becomes complicated. In order to achieve high light scattering performance (cloudiness), a domain diameter of about visible light is required,
It is difficult to drive a low electric field with this domain diameter, and if it is attempted to drive at a low voltage, the dispersed particle size of the liquid crystal must be increased, and the light scattering performance (white turbidity) decreases because the liquid crystal / binder polymer interface decreases. There is a problem that the resolution is reduced and the resolution is also reduced. Furthermore, since a low-molecular liquid crystal, which is a liquid, is used, the gap between the electrodes cannot be kept constant, and there is a problem that application to a flexible element is difficult. However, it is necessary to apply heat and an electric field at the same time, and it is necessary to heat the entire element and address it with an electric field, or address it with a laser etc. with the electric field applied to the whole element, and the recording means becomes large. there were. Further, since the polymer-dispersed liquid crystal is produced by a polymerization phase separation method, a solvent phase separation method, and an emulsification method, the shape of the dispersed liquid crystal cannot be freely controlled.

The present invention has been made in view of the above problems, and has as its object to provide a reversible display medium having high light scattering properties and high strength and capable of performing opaque / transparent display at least by application of heat. I do.

[0007]

SUMMARY OF THE INVENTION The present invention provides a reversible display medium in which a light-scattering layer in which a high-molecular liquid crystal material is dispersed in a resin in a fibrous form is formed on a base material. A reversible display medium characterized by being configured to be capable of reversibly recording / displaying by changing the ratio at least reversibly by application of heat. In the case of performing recording / display by applying only heat, a polymer liquid crystal is used. Recording / display can be performed using the isotropic glass state (transparent state) and the liquid crystal phase glass state (white turbid state) of the material.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. One preferred embodiment of the present invention is shown in FIG. The embodiment shown in FIG. 1A has a configuration in which a light scattering layer 2 and a surface protection layer 3 are sequentially laminated on a support substrate 1. In the embodiment shown in FIG. 1B, a light reflection layer 4 is provided between the support substrate 1 and the light scattering layer 2.
In the embodiment shown in (c), a light absorption layer 5 is provided between the support substrate 1 and the light scattering layer 2. Further, FIG.
In the embodiment shown in FIG. 1, the light absorbing layer 5 and the air layer 6 are provided between the support substrate 1 and the light scattering layer 2, and the light reflecting layer composed of the light absorbing layer 5 and the air layer 6 is combined. The configuration is preferably used because display characteristics are improved.

First, a "polymer liquid crystal material" which is used in the present invention and forms a light scattering layer and which is dispersed in a fibrous form in a resin will be described, and then a "binder resin" in which a polymer liquid crystal will be dispersed will be described. . As the polymer liquid crystal, a main chain type and a side chain type polymer liquid crystal having a mesogen (molecule exhibiting liquid crystallinity) bonded to a main chain or a side chain are known. Is preferably used. Further, a copolymer having a liquid crystal side chain and a non-liquid crystal side chain in a polymer side chain is also preferably used. Such a polymer liquid crystal is disclosed in JP-A-4-218024 and JP-A-6-18866, and makes it possible to greatly improve the recorded image contrast and optimize the heat-sensitive characteristics.

Usually, a side chain type polymer liquid crystal is formed by polymerization of a polymerizable mesogen compound (hereinafter, referred to as a mesogen monomer).
Alternatively, it can be produced by adding a mesogen compound capable of undergoing an addition reaction to a reactive polymer such as hydrogenated polysilicone. Such a technique is described in Makromol. Che
m. , P273-179 (1978), Eur-Pol
ym. J. 18, p651 (1982), Mol. Cr
yst. Liq. Cryst. 169, p167 (19
89).

The polymer liquid crystal of the present invention can be produced by a similar method. The above-mentioned mesogenic monomers and mesogenic compounds capable of addition reaction include biphenyl, phenylbenzoate, cyclohexylbenzene, azoxybenzene, azobenzene, azomethine, phenylpyrimidine, diphenylacetylene, p-phenyl (phenylbenzoate). ), Cyclohexylbiphenyl, terphenyl and other rigid molecules (mesogens)
Typical examples include various compounds in which an acrylate, methacrylate or vinyl group is bonded via an alkyl spacer having a predetermined length.

Representative structural examples of these compounds are shown below. _{CH 2 = C (Ra) -COO-} (CH 2) n -Z-A CH 2 = CH- (CH 2) in _n -Z-A (the formulas, Ra represents a hydrogen or a methyl radical, n is 1 to 3
It represents an integer selected from 0, and A represents mesogen A. Z is a single bond, -O-, -COO-, -OOC-,-
Represents a group selected from CH = N- and -N = CH-. Examples of the mesogen A include the following compounds (a) to (k).

[0013]

Embedded image

(Wherein X and Y are each a single bond,-
N = N-, -N (→ O) = N-, -CH = N-, -N =
CH -, - COO -, - OOC-, represents a group selected from a thienylene group, R ¹ is an alkoxy group, a halogen group,
Represents a group selected from a cyano group, a carboxy group and an alkyl group, p represents an integer selected from 1 to 5,
Is 2 or more, each R ¹ may be different. )

Examples of various non-mesogenic monomers and compounds which are preferably copolymerized or co-added with mesogenic monomers or mesogenic compounds include alkyl (meth) acrylate and its derivatives, styrene and its derivatives, vinyl acetate, (meth) Acrylonitrile, vinyl chloride, vinylidene chloride, vinylpyrrolidone, 1-hexene, 1-octene and the like, and compounds having a reactive group for crosslinking (meth) acrylic acid, ω-carboxy-polycaprolactone-mono (meth) Acrylate, vinyl sulfonate, hydroxyethyl (meth) acrylate,
Hydroxypropyl (meth) acrylate, 2- (meth) acryloxyethyl acid phosphate, 2-
Hydroxy-3-phenoxypropyl (meth) acrylate, 2- (meth) acryloxyethyl succinate,
Mono (meth) acrylate phthalate, 2- (meth) acryloxyethyl (2-hydroxyethyl) phthalate,
4- (meth) acryloxyalkyloxy-benzoic acid, glyceryl (meth) acrylate, hydroxy-substituted styrene, meth (acryl) amide, N, N
-Dimethylaminoethyl (meth) acrylate, N, N
-Diethylaminoethyl (meth) acrylate, glycidyl (meth) acrylate, 2-propen-1-ol, 5-hexen-1-ol and the like. What is illustrated here is an example, and there is no particular limitation.

The copolymerization or co-addition amount of the above compound into the polymer liquid crystal is 0.1 mol% to 70 mol% as a monomer unit.
Mol% is preferable, and more preferably 0.5 mol% to 50 mol%. If the copolymerization or co-addition amount of the non-liquid crystalline compound is smaller than this, the intended copolymerization or co-addition effect is less likely to appear, and if it is larger than this, the liquid crystal phase disappears in the copolymer or co-adduct. Resulting in. Further, two or more non-mesogenic monomers may be used at the same time.

The polymer liquid crystal of the present invention is synthesized by homopolymerization (addition) or copolymerization (addition) by using the above-mentioned monomer or reactive compound and adding it to radical polymerization, ionic polymerization or reactive polymer. can do. The molecular weight of the polymer liquid crystal is 5000 to 10
It is in the range of 100,000, particularly preferably in the range of 10,000 to 500,000. The form of copolymerization is random, block,
Various forms such as grafting and alternating are possible.

To the polymer liquid crystal used in the present invention, various antioxidants such as hindered amine and hindered phenol may be added for the purpose of improving weather resistance. In addition, various fillers may be added to strengthen the structure. The added amounts of the various components listed above are 0.1% in the composition.
The range of 01 to 5% by weight is preferred.

Next, a method for forming a polymer liquid crystal material into a fibrous form will be described. Wet spinning and dry spinning, which extrude a solution in which a polymer is dissolved from a spinneret with fine holes and form into a fibrous form, and melt spinning, which extrude a molten polymer from a spinneret and form into a fibrous form. Etc. In addition, the polymer liquid crystal material used in the present invention can form fibers by an emulsion / suspension spinning method or a reaction spinning method.

In the wet spinning, fibers are formed by extruding a polymer liquid crystal solution prepared in advance from a spinneret in a poor solvent for the polymer liquid crystal material to precipitate. The formed fiber is taken up after a washing / drying step via a driving roll. Also, if necessary, various kinds of catalysts and additives are added to the spinning tank for surface treatment, and a polymer liquid crystal material having a reactive group or a polymer liquid crystal material containing a reactive substance is spun. The fiber surface can be made into a cured fiber by heat treatment.

In dry spinning, a polymer liquid crystal solution prepared in advance is extruded from a spinneret, and the solvent is rapidly evaporated to form fibers. In melt spinning, a polymer liquid crystal material once melted by heating is extruded from a spinneret via an extruder or a gear pump, and is passed through cooling air to form fibers. The molded fiber is taken up via a driving roll. It is also preferable to form a web directly on a net as a sheet without passing through a winding step. At this time, by vibrating the fiber group in the direction perpendicular to the winding direction of the web or vibrating the fiber group in the direction perpendicular to the winding direction and the winding direction, the fibers have anisotropy in strength by making the fibers orthogonal to each other. It is desirable to have no random web. The produced web is heat-sealed by heating, and can have sufficient strength.
Furthermore, in order to harden the surface, a web molded from a polymer liquid crystal material having a reactive group or a polymer liquid crystal solution containing a reactive substance is immersed in a poor solvent to which various catalysts and additives are added, and then heat-treated. Thereby, the fiber surface can be cured.

In the emulsification / suspension spinning method, a polymer liquid crystal material prepared in advance by heating and melting a solid polymer liquid crystal material or dissolved in a solvent is used as a poor solvent for the polymer liquid crystal material. Dropping / stirring is performed inside to adjust the viscosity according to the molecular weight and concentration of the polymer liquid crystal material, and to control the shear stress by adjusting parameters such as the shape and rotation speed of the stirring blade to form fibers. At this time, if necessary, an emulsifier may be added to the poor solvent to improve the dispersibility of the polymer liquid crystal material. In the reactive spinning method, a polymer liquid crystal material having a reactive group or a polymer liquid crystal solution containing a reactive substance is used as necessary, and various catalysts and additives are added to a poor solvent for surface hardening, followed by heating. By treating, the fiber surface can be hardened. The suspension containing the produced polymer liquid crystal fibers can be sprayed onto a net through a nozzle and dewatered to form a sheet-like web directly.

In the case where the light scatterer of the present invention is used as a cloudy / transparent display element, the fiber diameter is more preferably 0.1 to 2.0 μm at the maximum of the distribution number. Is preferably in the range of 0.3 to 1.0 μm, since light is most strongly scattered. Also,
Since the tensile strength of the produced reversible display medium has a correlation with the aspect ratio of the fiber, the aspect ratio is desirably 10 or more.

Next, the "binder resin" in which the fibrous polymer liquid crystal is dispersed will be described. As the binder resin, thermoplastic resins such as polyvinyl alcohol, polyacrylate, polymethacrylate, polystyrene, polyester, polyamide, polymethyl acrylate, polyethyl acrylate, polymethyl acrylate, polyethyl acrylate, and polyolefin can be used. In addition, various binder resins can be selected depending on the purpose. For example, for the purpose of increasing the refractive index difference from the polymer liquid crystal, it is preferable to use a binder resin having a low refractive index. Specifically, a thermoplastic low refractive index binder resin such as polyvinylidene fluoride, polytetrafluoroethylene, polytrifluoroethyl methacrylate, polyvinyl isobutyl ether, polyvinyl isopropyl ether, or the like is preferably used.

For the purpose of improving the durability, an ultraviolet curable resin, an electron beam curable resin or a thermosetting resin having a high glass transition temperature can be selected. Specifically, resins such as epoxy acrylate (bisphenol A type, bisphenol F type, novolac type acrylate), urethane acrylate, polycarbonate, polyester acrylate and the like can be used.

The preferred content of the polymer liquid crystal fibers in the polymer liquid crystal dispersion composition is in the range of 20% by weight to 90% by weight, more preferably in the range of 40% by weight to 80% by weight. If the content of the polymer liquid crystal fiber is less than this range, the desired optical properties, for example, light scattering properties, cannot be obtained.If the content is too large, the binding effect of the binder resin is reduced, and the mechanical strength is reduced. May be caused.

As a support substrate for the thermoreversible display medium, a plastic film such as polyester, acetate, polycarbonate, polysulfone, polyimide, polyethylene, polypropylene, polystyrene, polyvinyl chloride, etc. is used, and its thickness is selected from the range of 10 to 1000 μm. And more preferably in the range of 25 to 200 μm. Further, it is also possible to color the plastic film of the above material or to form a reflective layer or a colored layer of aluminum or the like according to the display mode. The preferred thickness of the reflective layer and the colored layer is in the range of 10 nm to 100 μm.

Next, the surface protective layer will be described. The characteristics required for the surface protective layer are abrasion resistance, heat resistance, pressure resistance,
Surface friction and surface lubricity. One of the materials satisfying these is a thermosetting resin such as an ultraviolet curable resin and an electron beam curable resin. Since the ultraviolet curable resin and the electron beam curable resin form a film by a polymerization reaction of a polyfunctional monomer or a polyfunctional oligomer, they form a tough surface protective layer having high mechanical strength. Specific materials of such a resin include polyester acrylate, polyester methacrylate, polyether acrylate, polystyrene methacrylate, polyether methacrylate, urethane acrylate, epoxy acrylate (particularly bisphenol A type, bisphenol F type, bisphenol S
A polyfunctional oligomer having 1 to 10 functional groups, such as an epoxy acrylate or a phenol novolac type epoxy acrylate having a skeleton of each type, polycarbonate, polybutadiene acrylate, silicone acrylate, and melamine acrylate, is preferably used.
Also, 2-ethylhexyl acrylate, cyclohexyl acrylate, phenoxyethyl acrylate, 1,
Monofunctional monomers such as 6 hexadiol acrylate are also preferably used.

Next, a method for producing a thermoreversible display medium will be described. Fibers of a polymer liquid crystal material prepared in advance are collected by spreading / diffusing them by an electrostatic charging method, an air jet diffusion method using an air jet, an impingement plate method, or an emulsification / suspension spinning method. The suspension of molecular liquid crystal fibers is collected by passing through a furnace. A method of mixing / dispersing the collected fibers and a binder resin solution dissolved in a poor solvent for a polymer liquid crystal to form a coating solution, and applying and drying the coating solution on a substrate film to form a light scattering layer; Alternatively, a method is employed in which a binder and a polymer liquid crystal fiber which are substantially incompatible with the polymer liquid crystal are heated and mixed at a temperature at which the binder softens, dispersed, molded into a predetermined film thickness, and then cooled. At this time, when a curable resin is used as the binder resin,
After forming a film to a predetermined thickness, a method of applying a UV / electron beam or heat to cure the resin to form a light scattering layer is applied. When using a web made of fibers of a polymer liquid crystal material, impregnate the prepared web into a binder resin solution dissolved in a poor solvent for the polymer liquid crystal while applying ultrasonic waves without bubbles. A method of laminating and drying a light scattering layer by laminating on a substrate film, or impregnating a curable resin oligomer substantially incompatible with a polymer liquid crystal so as to avoid bubbles while applying ultrasonic waves to a curable resin oligomer,
A method of applying a UV / electron beam or heat to the substrate film to cure the resin and form a light scattering layer is applied. The thickness of the light-scattering layer is variously set depending on the desired optical characteristics, but from the range of 0.1 to 50 μm,
Particularly preferably, it is selected from the range of 1 to 20 μm.

After forming the light-scattering layer, the surface-protecting layer is coated with a material for the surface-protecting layer on the light-scattering layer, dried, and exposed to ultraviolet light, electron beam,
A thermoreversible display medium is produced by applying heat to cure and form. The thickness of the surface protective layer is preferably 0.1
It is selected from the range of ２０20 μm.

The thermoreversible display medium thus manufactured can display and record information with a laser or a thermal head. When the medium is partially heated to above the isotropic phase-liquid crystal phase transition temperature of the polymer liquid crystal material using a laser or thermal head, and rapidly cooled to below the glass phase transition temperature of the polymer liquid crystal material, The optically isotropic state above the isotropic phase-liquid crystal phase transition temperature of the molecular liquid crystal material is fixed to the glass state below the glass phase transition temperature to form a region showing a transparent isotropic glass state. it can. The region not heated by the laser or the thermal head is a region showing a cloudy liquid crystal phase glass state below the isotropic phase-liquid crystal phase transition temperature and below the glass phase transition temperature of the polymer liquid crystal material. By forming the transparent isotropic phase glass state and the cloudy liquid crystal phase glass state on the reversible display medium, information can be displayed and recorded.

When erasing the recorded information, the entire reversible display medium is heated to a temperature equal to or higher than the isotropic phase-liquid crystal phase transition temperature of the polymer liquid crystal material using a heat roller or a hot stamper. By gradually cooling the liquid crystal material to a temperature lower than the glass transition temperature, the entire thermoreversible display medium becomes a cloudy liquid crystal phase glass state, and information can be erased.

The reason why the reversible thermosensitive display medium of the present invention has a high light scattering property is not clear, but the light scattering interface between the liquid crystal polymer and the binder resin increases due to the structure in which the fibers are complicatedly entangled inside the recording layer. High turbidity. Furthermore, high strength is realized by this structure.

[0034]

【Example】

Synthesis of Polymer Liquid Crystal (I) 285 g of 4-acryloxyhexyloxy-4′-cyano-biphenyl was used as a mesogenic monomer, 15 g of butyl methacrylate was used as a non-mesogenic monomer, and AIBN (azoisobutylnitrile) was used as a polymerization initiator.
2 g and MEK (methyl ethyl ketone) 300 g as a solvent were copolymerized at 60 ° C. for 24 hours, and reprecipitated and purified in methanol to obtain a polymer liquid crystal 290 represented by the following structural formula (I).
g was obtained.

[0035]

Embedded image (Weight average molecular weight (polystyrene conversion by GPC):
300,000)

Example 1 A 23 wt% THF solution of the polymer liquid crystal (I) was mixed with a 10 wt% PVA stirred at a peripheral speed of 70 m / sec.
(Polyvinyl alcohol) was dropped into an aqueous solution to prepare a suspension in which polymer liquid crystals were dispersed in a PVA aqueous solution in a fibrous form, and THF was removed at a low temperature. The size of the prepared fibrous polymer liquid crystal was 600 nm in average diameter and 120 aspect ratio.
Met. The above suspension was applied on a transparent PET film having a thickness of 100 μm using a bar coater, and dried,
A light scattering layer having a thickness of about 6 μm was formed. Further, as a surface protective layer, an ultraviolet curable composition (trade name: ARONIX UV3700) in which a filler of 1% calcium carbonate is dispersed.
N: manufactured by Toa Gosei Co., Ltd.), and ultraviolet curing using a metal halide lamp to form a surface protective layer of about 1 μm on the light scattering layer, thereby producing a reversible display medium.

Example 2 In the same manner as in Example 1, a suspension in which a polymer liquid crystal was dispersed in a fibrous form in an aqueous PVA solution was prepared, and THF was removed at a low temperature.
The suspension was filtered under pressure using a metal filter having a mesh diameter of 2 μm in a pressure filter while maintaining the low temperature, washed three times with distilled water to wash away PVA, and polymer liquid crystal fibers were placed on the metal mesh. Collected. After drying at a low temperature, the polymer liquid crystal fiber was converted to a 60 wt% polyfunctional monomer (trade name: DPCA6).
0: Nippon Kayaku Co., Ltd.) isopropyl alcohol solution ｛ultraviolet polymerization initiator (Vicure 55: AKZO Ja)
Ultrasonic wave was applied to the｝ containing 4 wt% (manufactured by Span Co., Ltd.) to redisperse, thereby preparing a coating solution. Apply this coating solution to a thickness of 100
applied on a μm PET film using a bar coater,
It was dried and cured with an ultraviolet ray using a metal halide lamp to form a 6 μm light scattering layer. Further, a surface protective layer was formed in the same manner as in Example 1 to produce a reversible display medium.

Example 3 1 part of MDI was added to 20 parts of a 23 wt% THF solution of the above polymer liquid crystal (I), and an aqueous solution obtained by dissolving 10 parts of PVA as an aqueous phase and 3 parts of diethylenetriamine in water was used. While stirring at a peripheral speed of 70 m / sec, the polymer liquid crystal solution was dropped to prepare a suspension in which the polymer liquid crystal material was dispersed in a fibrous form. While stirring the polymer liquid crystal suspension at room temperature at a peripheral speed of 50 m / sec for 8 hours, THF was removed, and an interfacial polymerization reaction between MDI and diethylenetriamine was performed. Then 60 ° C
While stirring at a peripheral speed of 50 m / sec for 3 hours.
The reaction between DI and diethylenetriamine was terminated. This polymer liquid crystal suspension was filtered under pressure and washed three times with distilled water to collect polymer liquid crystal fibers on a metal mesh. The size of the prepared fibrous polymer liquid crystal has an average diameter of 800 n.
m, and the aspect ratio was 80. Binder resin [XE
ONEX280: Olefin resin, manufactured by Zeon Corporation]
The fibrous polymer liquid crystal in which toluene was recovered in a solution was redispersed, and a light scattering layer was formed in the same manner as in Example 2 to produce a reversible display medium.

Example 4 Using a 30 wt% THF solution of the above polymer liquid crystal (I),
The solution was gradually dropped into a PVA aqueous solution being stirred at a peripheral speed of 50 m / sec, and a suspension in which the polymer liquid crystal was dispersed in a fibrous form in the PVA aqueous solution was prepared in the same manner as in Example 1. The size of the produced fibrous polymer liquid crystal was 1.4 μm in diameter on average, and the aspect ratio was about 50. A light-scattering layer was formed in the same manner as in Example 1, and a surface protective layer was formed to produce a reversible display medium.

Example 5 Using a 30 wt% THF solution of the above polymer liquid crystal (I),
In the same manner as in Example 1 except that the stirring speed was reduced to a peripheral speed of 10 m / sec, a suspension in which a polymer liquid crystal was dispersed in a PVA aqueous solution in a fibrous form was prepared. The size of the prepared fibrous polymer liquid crystal was 2.6 μm in diameter on average, and the aspect ratio was about 20. The same suspension as in Example 1
It was coated on an ET film and dried to form a light scattering layer having a thickness of about 6 μm, and a surface protective layer was further formed to produce a reversible display medium.

Example 6 A reversible display medium was produced in the same manner as in Example 1 except that a polymer liquid crystal having a repeating unit represented by the following structural formula (II) was used. The size of the prepared fibrous polymer liquid crystal had an average diameter of 700 nm and an aspect ratio of about 100.

[0042]

Embedded image

Comparative Example 1 A polymer liquid crystal (I) was coated on a PET film having a thickness of 100 μm, and dried to form a light scattering layer composed of a single layer of a polymer liquid crystal having a thickness of about 5 μm. A surface protective layer was formed on the light scattering layer in the same manner as in Example 1 to produce a reversible display medium.

Evaluation of Thermoreversible Display Medium The thermoreversible display medium produced as described above was printed by a thermal head printer (8 dots / mm, 0.
3 mJ / dot) to provide a cloudy part and a transparent part in the thermoreversible display medium. After that, the print sample is made of aluminum evaporated PET.
X on the film, and set the reflection optical density of the cloudy area and the transparent area to X
-Rite404 (manufactured by X-rite). Table 1 shows the results.

[0045]

[Table 1]

Table 1 shows that Examples 1 to 4 and 6 are compared with Comparative Example 1, and that the thermoreversible display medium using the fibrous polymer liquid crystal of the present invention is more light scattering than the reversible display medium using only the polymer liquid crystal. It can be seen that the properties are improved (the lower the optical density, the whiter, preferably 0.3 or less). Comparative Example 1 has relatively high white turbidity but is bluish white and has poor visibility. Further, comparing Examples 1 to 5 with Example 6, the transparency of the printed portion is improved when the “copolymer of liquid crystal monomer and non-liquid crystal monomer” is used as the polymer liquid crystal material (optical The higher the concentration, the higher the transparency, preferably at least 1.2). It can be seen that a reversible display medium with high contrast can be produced. Further, when Examples 1 to 4 are compared with Comparative Example 1, the transparency of the printed portion is higher in Comparative Example 1, but Examples 1 to 4 have higher white turbidity and higher visibility in the printed portion. Further, in comparison with Examples 1 to 4 and Example 5, in light scattering performance, it is found that the fiber diameter of the polymer liquid crystal fiber used in the present invention is preferably 2 μm or less, more preferably 1.0 μm or less. . On the other hand, when the fiber diameter is smaller than the visible light wavelength range, the light scattering performance in the visible light region is reduced. Therefore, the fiber diameter is particularly preferably 0.3 μm or more and 1.0 μm. Furthermore, in Example 3, since the surface of the polymer liquid crystal fiber is covered, it is possible to use a resin that is soluble only in a good solvent for the polymer liquid crystal.

[0047]

By dispersing the liquid crystal polymer in the form of fibers in the binder polymer, a structure in which the fibers are intricately entangled inside the recording layer is formed, and the light scattering interface between the polymer liquid crystal and the binder is increased, resulting in high white turbidity. It is possible to obtain a reversible display medium having a certain degree. Further, since the fiber structure inside the recording layer enables the supply of a reversible recording medium having high strength, the thickness of the light scattering layer can be reduced to obtain the same contrast as that of the conventional polymer liquid crystal system. Costs can be reduced. Further, according to the present invention, since the transmittance of the light scatterer is controlled by the applied heat, the apparatus is compared with other systems in which two or more external forces such as heat and electric field, heat and magnetic field, etc. must be controlled simultaneously. There is an advantage that the size can be reduced and printing control is simple. Furthermore, according to the present invention, in order to prepare a reversible display medium after preparing fibers of the polymer liquid crystal compound in advance,
Various binders can be suitably used, and an optimum light scattering state can be easily realized, thereby increasing productivity.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a preferred embodiment of a reversible display medium of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 support substrate 2 light scattering layer 3 surface protection layer 4 light reflection layer 5 light absorption layer 6 air layer

Claims (5)

[Claims] 1. A reversible display medium in which a light-scattering layer in which a polymer liquid crystal material is dispersed in a fibrous form in a resin is formed on a substrate, and the transmittance of the light-scattering layer is reversibly at least by application of heat. A reversible display medium characterized in that it is configured to be recordable / erasable by changing to a medium. 2. The recording / display device according to claim 1, wherein recording / display is performed using an isotropic glass state and a liquid crystal glass state of a polymer liquid crystal material dispersed in the reversible display medium. Reversible display medium. 3. The reversible display medium according to claim 1, wherein the polymer liquid crystal material is a copolymer of a liquid crystal monomer and a non-liquid crystal monomer. 4. The reversible material according to claim 1, wherein the fiber diameter of the polymer liquid crystal material dispersed in the light scattering layer is 0.1 μm or more and 2 μm or less. Display medium. 5. An apparatus according to claim 1, wherein said fibrous liquid crystal polymer has an aspect ratio of 10 or more.
A reversible display medium according to any one of the above.