JP2007187789A - Display medium and method for recording on the display medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display medium having simple construction and excellent contrast, and a method for recording on the display medium. <P>SOLUTION: The rewritable display medium is equipped with a display composition layer composed of a composition containing a self-organizing type gelling agent interposed between a pair of substrates and a visible ray absorption layer disposed on the rear side of the display composition layer, and is characterized by being written thereinto with heat. The method for recording is characterized by having data written into the display medium with heat. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a display medium and a recording method on the display medium.

Conventionally, various heat-sensitive recording media have been proposed as rewritable recording media (for example, Patent Documents 1 and 2). In addition, a display medium that has a photoconductive layer and a polymer-dispersed liquid crystal layer and can be written by irradiating light with an alternating electric field applied to the liquid crystal layer has been proposed (for example, Patent Documents). 3). These are not only rewritable many times, but also can be kept light even after being recorded by an external writing device and then separated from the writing device. The use as is expected.
JP 61-257883 A JP 2000-192044 A JP-A-7-199214

  However, the conventional display medium and the recording method on the display medium have a problem that it is difficult to achieve both a bright and easily recognizable display and a high contrast, and a bright and high-contrast monochrome display cannot be performed.

  An object of the present invention is to provide a display medium having a simple configuration and excellent contrast, and a recording method therefor.

  As a result of earnest research to solve the above problems, a composition containing a self-organizing gelling agent is sandwiched between a pair of substrates, and the morphology of the gelling agent is changed by applying heat, thereby I found out that I could write. Further, it has been newly found that this display principle is advantageous for high contrast.

  That is, the present invention comprises a display composition layer made of a composition containing a self-organizing gelling agent sandwiched between a pair of substrates, and a visible light absorbing layer disposed on the back side of the display composition layer. The present invention relates to a rewritable display medium characterized in that writing is performed by heat, and a recording method characterized by performing writing on the display medium by heat.

  The rewritable display medium of the present invention has a simple configuration and can perform display with excellent contrast. Further, the recording method of the present invention can perform display with excellent contrast by a simple method.

FIG. 1 is a schematic view showing a cross-sectional structure of a rewritable display medium according to an embodiment of the present invention. The display medium shown in FIG. 1 has a display composition 10 sandwiched between a pair of substrates (1, 2), and is usually sealed at the periphery by a sealing material 11 and is made of a display composition. A visible light absorbing layer 12 (for example, black) is provided on the back surface side of the composition layer, that is, the outer surface (back surface) of the substrate 2 on the side opposite to the light incident side, as necessary. Instead of providing the visible light absorbing layer 12, a substrate 2 itself having visible light absorption may be used.
Hereinafter, main components in the display medium of the present embodiment will be described in detail.

  The display composition 10 contains at least a self-organizing gelling agent, and usually contains a display material that can be anisotropic in a liquid state, typically a liquid crystal. Although it is possible to use a display material such as an ink exhibiting anisotropy in addition to the liquid crystal, in the following, the case where the display composition 10 contains a self-organizing gelling agent and a liquid crystal will be described in detail. explain.

(Display composition)
The display composition 10 is a liquid crystal composition in which a liquid crystal contains at least a self-organizing gelling agent, and the liquid crystal is usually a cholesteric liquid crystal or a smectic liquid crystal. The cholesteric liquid crystal composition in the case of using cholesteric liquid crystal includes the components and contents of the display composition so that the peak wavelength (25 ° C.) of selective reflection during the planarization of the obtained display medium is in the range of 450 to 700 nm. It is preferable that the ratio is adjusted. When the peak wavelength is less than 450 nm or more than 700 nm, the reflectivity at the time of the planar is lowered, so that a high contrast is achieved between the planar (for example, white) and the focal conic (for example, black). Difficult to do. Further, the smectic liquid crystal composition in the case of using the smectic liquid crystal may be a single compound or a mixture of a plurality of compounds as long as it is a liquid crystal composition showing a smectic phase in the operating temperature range.

  The gelling agent used in the present embodiment belongs to a self-organizing type. Specifically, without adding other means such as UV irradiation, the gelling agent is self-organized by adding and mixing the gelling agent. A structure can be formed. Since such a self-organizing type gelling agent is contained, it is possible to write an image having excellent contrast by heat. The phenomenon that can achieve such an effect is considered to be based on the following mechanism. Since the gelling agent molecules are easily dispersed uniformly at the molecular level in the display composition and form a pseudo network structure by hydrogen bonding, the network structure may have finer density and appropriate flexibility. As will be described in detail later, the pseudo-network structure composed of such gelling agent molecules can change its morphology (for example, a form such as regularity and compactness) depending on the temperature when heated and cooled. Furthermore, by controlling the morphology, the scattering characteristics of incident light can be adjusted. Therefore, using such characteristics, when obtaining a bright state, the incident light is strongly scattered together with the anisotropic liquid material, and when obtaining a dark state, the incident light can be as much as possible with the anisotropic liquid material. A transmission-scattering display medium capable of writing an image with excellent contrast can be obtained by selecting the morphology of the gelling agent so as to be transmitted. In addition, since the display medium of the present embodiment is free from unreacted substances such as residual monomers found in polymer dispersed liquid crystals in principle, the initial display color and excellent contrast can be maintained over a long period of time. . Furthermore, wide viewing angle display is possible compared to a display medium to which no gelling agent is added.

  A self-organizing gelling agent is an organic compound capable of forming a hydrogen bond between self molecules, for example, an organic compound having at least an intermolecular hydrogen bonding group, preferably an organic compound having an intermolecular hydrogen bonding group and an alkylene group. Compounds. When an organic compound having an alkylene group together with an intermolecular hydrogen bonding group is used as a gelling agent, the formation of a pseudo-network structure is promoted by the intermolecular force between the alkylene groups.

The intermolecular hydrogen-bonding group is not particularly limited as long as it is a group that can form a hydrogen bond between molecules containing the group, and examples thereof include an amide bond group (—NHCO—).
It is desirable that one or more, preferably two or more intermolecular hydrogen bonding groups are contained in the molecule.

The alkylene group is a long-chain alkylene group (hereinafter sometimes referred to as Re), specifically a divalent saturated hydrocarbon group having 4 or more carbon atoms, preferably 6 to 20 carbon atoms, preferably a linear polymethylene group (- is a _(CH 2) n-).
It is desirable that one or more, preferably two or more alkylene groups are contained in the molecule.

  As long as the gelling agent is an organic compound having at least an intermolecular hydrogen-bonding group, preferably an intermolecular hydrogen-bonding group and an alkylene group, the structure is not particularly limited, and the heating temperature during writing on a display medium is reduced. In addition, from the viewpoint of obtaining an image with high contrast, a sol-gel transition temperature (Tsg) of 40 to 100 ° C., particularly 40 to 80 ° C. is preferable. Examples of such gelling agents include alicyclic amide compounds represented by the following general formula (I), aliphatic amide compounds represented by the following general formulas (II) to (IV), and And aliphatic urea compounds represented by the formula (V).

In formula (I), R ¹ is an alkyl group, an aryloxy group or an arylalkoxy group, and these groups may have a substituent such as a cyano group.
The alkyl group is an alkyl group having 1 to 3 carbon atoms, and examples thereof include a methyl group, an ethyl group, an n-propyl group, and a sec-propyl group.
The aryloxy group is an aryloxy group having 6 to 14 carbon atoms, and examples thereof include a phenyloxy group, a biphenylyloxy group, and a naphthyloxy group.
The arylalkoxy group is a monovalent group in which 1 to 2 aryl groups having 6 to 14 carbon atoms are substituted with alkoxy groups having 1 to 3 carbon atoms, such as a phenylmethoxy group, a phenylethoxy group, and a phenylpropoxy group. Group, biphenylylmethoxy group, biphenylylethoxy group, biphenylylpropoxy group and the like.
Preferred R ¹ is an alkyl group or an aryloxy group.

Re is the same group as the long-chain alkylene group (Re), and a preferred group is the same as Re.
m is an integer of 1 to 3, preferably 2.
When there are a plurality of the same groups in one formula, these groups may be independently selected from a predetermined range (the same applies hereinafter).

Preferable specific examples of such alicyclic amide compounds (I) include the following compounds.

In formulas (II) to (IV), a common group means the same group.
R ² is the same group as R ¹ described above. Preferred R ² is an arylalkoxy group.
R ³ is a C 1-3 divalent alkylene group, and examples thereof include a methylene group, a dimethylene group, and a trimethylene group. R ³ may have a substituent, and examples of the substituent include the following groups, among which a branched alkyl group having 3 to 5 carbon atoms is preferable.

Re is the same group as the long-chain alkylene group (Re), and a preferred group is the same as Re.
R ⁴ is the same group as R ¹ described above. Preferred R ⁴ is an alkyl group.
R ⁵ is the same group as R ³ described above. Preferred R ⁵ is an alkylene group having no substituent.
n is an integer of 0 to 3, preferably 0 to 1.

Preferable specific examples of such aliphatic amide compounds (II) to (IV) include the following compounds.

In formula (V), R ⁶ is the same as R ⁴ described above, and preferred groups are also the same as R ⁴ described above.
Re is the same group as the long-chain alkylene group (Re), and a preferred group is the same as Re.
R ⁷ is the same as R ⁵ , and a preferred group is the same as R ⁵ .

Preferable specific examples of the aliphatic urea compound (V) include the following compounds.

  These compounds can be synthesized according to a known synthesis method.

  The content of the gelling agent is not particularly limited as long as the object of the present invention can be achieved, and can be, for example, 1.0 to 4.0% by weight with respect to the total amount of the display composition. 0 to 3.0% by weight is suitable. When set within the above range, the Y value during focal conic (for example, black) can be reduced, and as a result, the contrast can be improved more effectively.

  The liquid crystal phase-isotropic phase transition temperature of the liquid crystal used together with the gelling agent may be 60 to 120 ° C., particularly 80 to 120 ° C. in the case of cholesteric liquid crystal, from the viewpoint of forming a higher contrast image on the display medium. In the case of a smectic liquid crystal, it is preferably 50 to 80 ° C., particularly 55 to 80 ° C.

  The cholesteric liquid crystal that can be used in the present embodiment exhibits a cholesteric phase at room temperature. For example, a chiral nematic liquid crystal composed of a nematic liquid crystal and a chiral agent can be used. When a chiral nematic liquid crystal is used, the liquid crystal phase-isotropic phase transition temperature of the chiral nematic liquid crystal is preferably within the above range.

  The nematic liquid crystal is not particularly limited, and a nematic liquid crystal conventionally known in the field of liquid crystal display elements can be used. Examples of such nematic liquid crystal materials include liquid crystal ester compounds, liquid crystal pyrimidine compounds, liquid crystal cyanobiphenyl compounds, liquid crystal tolan compounds, liquid crystal phenyl cyclohexane compounds, liquid crystal terphenyl compounds, fluorine atoms, and fluoroalkyls. Other liquid crystalline compounds having a polar group such as a cyano group and a cyano group, and mixtures thereof.

  The content of the nematic liquid crystal in the chiral nematic liquid crystal is not particularly limited, and is usually 60 to 97% by weight with respect to the total of the nematic liquid crystal and the chiral agent.

  As the chiral agent, various materials conventionally known in the field of liquid crystal display elements can be used. For example, a cholesteric compound having a cholesteric ring, a biphenyl compound having a biphenyl skeleton, a terphenyl compound having a terphenyl skeleton, an ester compound having a skeleton in which two benzene rings are connected by an ester bond, and a cyclohexane ring directly on the benzene ring A cyclohexane compound having a skeleton formed by linking a ring, a pyrimidine compound having a skeleton formed by directly linking a pyrimidine ring to a benzene ring, and an azoxy having a skeleton formed by linking two benzene rings by an azoxy bond or an azo bond Or an azo compound etc. are mentioned.

  The content of the chiral agent in the chiral nematic liquid crystal is not particularly limited, and is usually 3 to 40% by weight based on the total of the nematic liquid crystal and the chiral agent.

  Further, the smectic liquid crystal is not particularly limited, and a smectic liquid crystal conventionally known in the field of liquid crystal display elements can be used. Examples of such smectic liquid crystal materials include biphenyl compounds, terphenyl compounds, ester compounds, cyclohexane compounds, pyrimidine compounds, and the like.

You may further add additives, such as a ultraviolet absorber, to a display composition.
The ultraviolet absorber is for preventing ultraviolet deterioration of the liquid crystal, for example, fading or responsive change with time. For example, materials such as a benzophenone compound, a benzotriazole compound, and a salicylate compound can be used. The addition amount is 5% by weight or less, preferably 3% by weight or less, based on the total amount of the display composition.

Such a display composition is obtained by mixing each material at a predetermined ratio.
If desired, the display composition may be purified by contact with an ion exchange resin, an adsorbent, etc. to remove moisture and impurities, and then used for manufacturing a display medium.

(substrate)
In FIG. 1, the substrates 1 and 2 are both translucent, but the pair of substrates that can be used for the display medium of this embodiment is at least one substrate (at least the substrate on which light is incident). 1) should just have translucency. As the light-transmitting substrate, a glass substrate and a flexible substrate such as polycarbonate, polyethersulfone, polyarylate, and polyethylene terephthalate can be used. From the viewpoint of reducing the weight of the display medium, it is preferable to use a flexible substrate. When a flexible substrate is used as at least one of the pair of substrates, preferably both substrates, a lightweight and thin display medium can be manufactured and damage (cracking) can be suppressed. From the viewpoint of maintaining the flexibility of the display medium and improving the coloration of the display medium, the thickness of the substrate is preferably 0.1 to 0.5 mm, particularly preferably 0.1 to 0.3 mm.

(Seal material)
The sealing material 11 is used to enclose the display composition 10 so as not to leak from between the substrates 1 and 2, and includes a thermosetting resin such as an epoxy resin or an acrylic resin, or a photocurable adhesive. Can be used.

(Visible light absorption layer)
The visible light absorbing layer 12 is not particularly limited as long as it is a sheet that can absorb visible light, and for example, a black paint can be used.

  The display medium may be provided with other members. As other members, those conventionally used as members constituting liquid crystal display elements can be used, and examples thereof include electrodes, insulating thin films, alignment films, polymer structures, and spacers.

FIG. 2 is a schematic view showing a cross-sectional structure of a display medium according to another embodiment of the present invention. The display medium shown in FIG. 2 has a structure in which the display composition 10 is sandwiched between a pair of substrates 1 and 2, and is formed on each surface of the substrates 1 and 2 in a plurality of parallel strips. Transparent electrodes 3 and 4 are provided. The transparent electrode 3 and the transparent electrode 4 are arranged to face each other so as to cross each other. The facing portions of the electrodes 3 and 4 are pixels, and a plurality of pixels are arranged in a matrix. An insulating thin film 5 is coated on the electrodes 3 and 4. Further, an alignment film 7 is formed on the insulating thin film 5. 6 is a polymer structure as a space holding member, and 8 is a spacer as a space holding member.
Hereinafter, main components in the display medium of the present embodiment will be described in detail. 2, the same reference numerals as those in FIG. 1 indicate the same members as those in FIG. 1, and thus description of those members will be omitted.

(electrode)
Examples of the electrodes 3 and 4 include transparent conductive films such as ITO (Indium Tin Oxide) and IZO (Indium Zinc Oxide), metal electrodes such as aluminum and silicon, or amorphous silicon, A photoconductive film such as BSO (Bismuth Silicon Oxide) can be used. In the display medium shown in FIG. 2, as described above, a plurality of strip-like transparent electrodes 3 and 4 parallel to each other are formed on the surfaces of the transparent substrates 1 and 2, and these electrodes 3 and 4 intersect each other. Are facing each other. In order to form the electrode in this manner, for example, an ITO film may be deposited on the substrate by a masking method using a sputtering method or the like, or an ITO film may be formed on the entire surface and then patterned by a photolithography method.

(Insulating thin film)
Although not essential in principle, an insulating thin film 5 is formed on at least one of the electrodes 3 and 4 in order to prevent a short circuit between the electrodes and to improve the reliability of the gas barrier property of the display medium. Preferably it is. Examples of the insulating thin film 5 include inorganic films made of silicon oxide, titanium oxide, zirconium oxide, alkoxides thereof, and the like, and organic films such as polyimide resin, epoxy resin, acrylic resin, and urethane resin. It can form by well-known methods, such as a vapor deposition method, a spin coat method, and a roll coat method, using such materials. Furthermore, the insulating thin film can be formed using the same material as the polymer resin used for the polymer structure.

(Polymer structure)
The polymer structure 6 may have any shape such as a columnar body, an elliptical columnar body, a quadrangular columnar body, the arrangement may be random, and has regularity such as a lattice shape. It may be a thing. By providing such a polymer structure, it becomes easy to keep the gap between the substrates constant, and the self-maintaining characteristic of the display medium itself can be improved. In particular, when dot-shaped polymer structures are arranged at regular intervals, the display performance is easily uniformed. The height of the polymer structure corresponds to the thickness of the cell gap, that is, the thickness of the layer made of the display composition. It is particularly effective to provide a polymer structure when a flexible resin substrate is used as a substrate for sandwiching the display composition layer.

  To form a polymer structure, a photocurable resin material such as a photoresist material made of an ultraviolet curable monomer is used and applied to the outermost surface film (insulating thin film, alignment film) of the substrate with a desired thickness. A so-called photolithography method can be used in which pattern exposure is performed by irradiating ultraviolet rays through a mask to remove uncured portions.

  Alternatively, a polymer structure made of a thermoplastic resin may be formed using a resin material in which a thermoplastic resin is dissolved in an appropriate solvent. In this case, a resin material such as a printing method in which printing is performed on the substrate by extruding a thermoplastic resin material with a squeegee using a screen plate or a metal mask, a dispenser method, an ink jet method, etc. is applied onto the substrate from the tip of the nozzle The polymer structure can be arranged by a method of forming by discharging, or a transfer method in which a resin material is supplied onto a flat plate or a roller and then transferred to the substrate surface.

(Alignment film)
The alignment film 7 is not essential in principle, but is preferably provided for the purpose of stabilizing the display medium. When the alignment film is formed, it is formed on the insulating thin film when the insulating thin film is formed on the electrode, and on the electrode when the insulating thin film is not formed on the electrode. Examples of the alignment film 7 include organic films such as polyimide resin, silicon resin, polyamideimide resin, polyetherimide resin, polyvinyl butyral resin, and acrylic resin, and inorganic films such as silicon oxide and aluminum oxide. The alignment film formed using these materials may be subjected to a rubbing treatment or the like. Further, the alignment film can be formed using the same material as the polymer resin used for the polymer structure.

(spacer)
A spacer 8 may be provided between the pair of substrates to keep the gap between the substrates uniform. Examples of the spacer include a sphere made of resin or inorganic oxide. For example, ball-shaped glass, ceramic powder, or spherical particles made of an organic material can be used. Further, a fixed spacer having a surface coated with a thermoplastic resin is also preferably used. In order to keep the gap between the substrates more uniform, it is preferable to provide both the spacer 8 and the polymer structure 6 as shown in FIG. 2, but only one of them may be provided. . When the polymer structure is formed, the diameter of the spacer is equal to or less than the height, preferably equal to the height. When the polymer structure is not formed, the diameter of the spacer corresponds to the thickness of the cell gap, that is, the thickness of the layer made of the display composition.

(Scattering layer)
A scattering layer (not shown) may be provided on the surface (upper surface in the drawing) of the substrate 1 and / or between the substrate 2 and the visible light absorbing layer 12. By providing the scattering layer, the degree of scattering during white display increases, and the whiteness improves. Examples of the scattering layer include product name FT-014 (manufactured by Polatechno).

  As the thickness of the cell gap in the display medium, that is, the thickness of the layer made of the display composition increases, the reflectance during white display increases, but the reflectance during black display also increases. Therefore, the thickness of the cell gap may be 2 to 50 μm, but 3 to 15 μm is preferable. This is because a high contrast can be achieved more effectively by setting such a preferable range.

(Production method)
The display medium of this embodiment can be obtained by injecting the display composition into a vacuum cell in a heated state and then gradually cooling it. Moreover, you may apply a voltage simultaneously in slow cooling.

When enclosing the display composition, the following method may be employed.
The heated display composition is vacuum-injected into an empty cell of the display medium, and then the injection hole is closed. The display composition is thermoreversible.
An empty cell of the display medium can be produced by heating or / and pressurizing two substrates on which the above-mentioned predetermined constituent members of the display medium are formed so as to oppose each other with a sealant at the periphery. It is.
Since the display composition increases fluidity by heating, injection between the substrates and formation of the display composition layer on the substrates can be easily performed in a short time.

(Recording method)
In the recording method of the present embodiment, writing is performed on the display medium by heat.
The application of heat to the display medium is achieved by external writing means, and the written display is maintained without applying energy. Therefore, the display medium can be handled separately from the means after writing, and is portable. Excellent.

  The external writing means is means that can be written to the display medium from the outside, and is not particularly limited as long as it can heat the display composition of the display medium. Examples of such external writing means include a heat generating means and a light generating means, and these means may be used alone or in combination.

The heat generating means heats the display composition by generating heat in itself and bringing the means into contact with the display medium. For example, a thermal head, a hot stamp, or the like is used.
The light generating means generates light but does not generate heat in itself, and heats the display composition by irradiating the display composition with the light, for example, a He-Ne laser or the like. Laser.

  Thermal writing is accomplished by controlling the composition temperature as the display composition is heated and cooled. That is, in the display medium of the present embodiment, the display composition contains a gelling agent. Therefore, by controlling the composition temperature during heating and cooling, the morphology of the pseudo-network structure formed by the gelling agent (for example, , Forms such as regularity and denseness). Furthermore, the scattering characteristics of incident light can be adjusted by controlling the regularity and density of such a network structure. That is, when obtaining a white display state, select a morphology that strongly scatters incident light together with liquid crystal that is an anisotropic liquid material, and when obtaining a colored display state, liquid crystal that is an anisotropic liquid material is incident. It is possible to select a morphology that does not hinder the light transmitting state as much as possible. Therefore, it is possible to write an image with excellent contrast by controlling such scattering characteristics.

  Specifically, in the recording method of the present embodiment, the display composition of the display medium is heated to a temperature at which the display composition is in an isotropic liquid state, and the subsequent cooling is controlled to control image display. Write. More specifically, color display is performed by heating and slow cooling, while white display is performed by heating and quenching. When the display composition is a cholesteric liquid crystal composition, the colored display achieved by heating and slow cooling is based on the focal conic state as will be described in detail later. It is a colored display by the hue of the absorption layer 12 or the lower substrate 2. When the display composition is a smectic liquid crystal composition, the colored display achieved by heating and slow cooling is based on the homeotropic alignment by slow cooling, and therefore, similar to the cholesteric liquid crystal composition, FIG. 1 and FIG. The colored display by the hue of the visible light absorbing layer 12 or the lower substrate 2 in FIG.

  When the display composition is a cholesteric liquid crystal composition after heating and slow cooling, the gelling agent network structure is formed in a relatively regular and dense network size, and the cholesteric liquid crystal molecules in each network structure. Since the helical axis is oriented parallel to the substrate, the display composition is in a focal conic state. As a result, since the display composition transmits incident light, the hue of the visible light absorbing layer or the lower substrate is displayed, and a colored image is formed. In addition, when the display composition is a smectic liquid crystal composition, the smectic liquid crystal molecules are homeotropically aligned in the direction perpendicular to the substrate in each network structure, and as a result, the display composition transmits incident light. The hue of the visible light absorbing layer or the lower substrate is displayed, and a colored image is formed.

  In the heating and gradual cooling, after heating to a temperature higher than the sol-gel transition temperature of the gelling agent, the cooling is performed for a longer time than that of allowing to cool so that a colored display state can be realized. Although the temperature of the heating member may be gradually lowered and gradually cooled, as a simpler method, for example, to a temperature higher than the sol-gel transition temperature of the gelling agent (hereinafter simply referred to as “Tx”). Two-stage heating consisting of high-temperature heating and low-temperature heating to a temperature lower than the sol-gel transition temperature (hereinafter simply referred to as “Ty”) may be performed continuously. Specifically, from the viewpoint of making the contrast as high as possible, Tx and Ty preferably satisfy the following relationship with respect to the sol-gel transition temperature of the gelling agent (hereinafter simply referred to as “Tsg”).

Tx;
Preferably Tsg <Tx ≦ Tsg + 30;
More preferably, Tsg + 5 ≦ Tx ≦ Tsg + 25;
Most preferably, Tsg + 8 ≦ Tx ≦ Tsg + 25.

Ty;
Preferably Tsg-30 ≦ Ty ≦ Tsg-5;
More preferably Tsg-25 ≦ Ty ≦ Tsg-10;
Most preferably, Tsg-23 ≦ Ty ≦ Tsg-10.

  After heating and gradual cooling, that is, after performing low temperature heating, it may be allowed to cool. The term “cooling” refers to cooling by leaving it as it is after heating. In any case, by performing heating and slow cooling, the liquid crystal, which is an anisotropic liquid material, takes a regular alignment state that transmits incident light, while the gelling agent is a relatively weak molecule. It is considered that a network structure is formed by interbonding so as not to disturb the orientation of the anisotropic liquid material. For this reason, a favorable colored display state can be realized, leading to an improvement in contrast. In this way, the polymer network in the polymer-dispersed liquid crystal is fixed, and in contrast to inhibiting the orientation of the liquid crystal, the network structure by the self-organizing gelling agent changes flexibly. It is considered that high contrast can be achieved because the orientation of the anisotropic liquid material is not hindered.

  On the other hand, when the display composition is a cholesteric liquid crystal composition when heated and rapidly cooled, the network structure of the gelling agent is relatively random and coarse, and cholesteric liquid crystal molecules are formed in each network structure. Since the helical axes of the layers are randomly oriented, the display composition is in an intermediate state between the planar state and the focal conic state. As a result, since the display composition scatters incident light, white display is performed and a white image is formed. Further, when the display composition is a smectic liquid crystal composition, the smectic liquid crystal molecules are randomly oriented in each network structure. As a result, incident light is scattered, so that white display is performed and a white image is formed.

  The heating and quenching may be performed by, for example, high-temperature heating and cooling to a temperature higher than the sol-gel transition temperature of the gelling agent (hereinafter simply referred to as “Tz”). Specifically, from the viewpoint of making the contrast as high as possible, Tz preferably satisfies the following relationship with respect to the sol-gel transition temperature (Tsg) of the gelling agent;

Tz;
Preferably Tsg <Tz ≦ Tsg + 30;
More preferably, Tsg + 1 ≦ Tz ≦ Tsg + 25;
Most preferably, Tsg + 2 ≦ Tz ≦ Tsg + 25.

  Tx and Tz are preferably higher than the liquid crystal phase-isotropic phase transition temperature of the cholesteric liquid crystal or smectic liquid crystal contained in the display composition from the viewpoint of more effectively improving the contrast. At such temperatures, the liquid crystal molecules can behave relatively freely. As a result, the cholesteric liquid crystal molecules are aligned so that the helical axis is more effectively parallel to the substrate by slow cooling, and are aligned so that the helical axis becomes more random by rapid cooling. Smectic liquid crystal molecules are aligned perpendicular to the substrate by slow cooling and are randomly oriented by rapid cooling.

  The temperature control as described above can be easily achieved by bringing the heat generating means that generates heat at each predetermined temperature, particularly the thermal head, into contact with a desired portion on the surface of the display medium. Specifically, the heating time in high temperature heating and low temperature heating when performing heating and slow cooling, and the heating time in high temperature heating when performing heating and quenching, that is, the contact time depends on the thermal conductivity of the substrate, In the case of use, it is usually sufficient to select each independently within a range of 1 to 60 seconds, particularly 1 to 10 seconds.

  The temperature control may be achieved by light generation means. That is, high-temperature heating and low-temperature heating during heating and slow cooling, and high-temperature heating during heating and quenching may each be achieved independently by heat generation means, or by light generation means, particularly a laser. May be.

  When employing the light generating means, the light generating means, particularly the laser output and irradiation time, depends on the heating temperature, the Tsg of the gelling agent and the type of laser, but the Tsg is 60 to 80 ° C., particularly 65 to 75 ° C. In addition, when a He—Ne laser is used, it is preferably selected as appropriate within the following range.

  High temperature heating during heating and slow cooling, low temperature heating during heating and slow cooling, and high temperature heating during heating and quenching are 1 to 30 at an output of 10 to 50 (mW), particularly 10 to 40 (mW). It can be achieved by laser irradiation for a second, in particular 1 to 10 seconds. The low temperature heating can be realized by weakening the output or shortening the irradiation time than the high temperature heating.

  In particular, when a display medium having electrodes as shown in FIG. 2 is used, after writing by performing heating and cooling as described above, the writing is further electrically performed to further improve the contrast. Can be made. In particular, when the display composition is a cholesteric liquid crystal composition, when writing is performed by applying a specific voltage to an image portion that has been displayed white by heating and quenching, the helical axis of the liquid crystal molecules is ideal for the substrate. Therefore, an ideal white display in the display composition can be achieved. In addition, when writing is performed by applying a specific voltage to an image portion that is colored and displayed by heating and slow cooling, the light transmittance of the display composition at the time of colored display can be further increased, and the Y value and contrast ratio can be increased. Can be improved. As a voltage to be applied to the display composition, a voltage that is in a planar state is applied when white display is performed, and a voltage that is in a focal conic state is applied when colored display is performed. Specifically, a pulse voltage having an amplitude of 30 to 80 V and 5 to 30 ms is applied.

  In the case where the display composition is a cholesteric liquid crystal composition, the control to the focal conic state by heating and slow cooling performed in the present invention is particularly effective. This is because the helical axis of the liquid crystal molecules is aligned more effectively parallel to the substrate as compared with the conventional control to the focal conic state by applying a specific voltage to the liquid crystal composition. Even when other anisotropic liquid materials are used such as when the display composition is a smectic liquid crystal composition, the contrast can be further improved by applying a specific voltage after writing by heating and cooling. it can.

  In the recording method of the present invention, the written image can be erased by performing the above-mentioned “heating and slow cooling” or “heating and rapid cooling” on the entire surface of the display medium on which writing is performed as described above. Thereafter, repeated rewriting is possible by performing writing and erasing as described above again. Since the image previously written is erased by heating before rapid cooling or slow cooling, it is possible to directly write the portion to be rewritten without the step of erasing the image entirely.

Hereinafter, “parts” means “parts by weight”.
(Measurement of Y value)
The Y value of the writing portion was measured by applying a spectrocolorimeter (CM3700d; manufactured by Konica Minolta Sensing Co., Ltd.) directly to the surface of the display medium. The Y value of the white display portion is represented as a Y value (white), and the Y value of the black display portion is represented as a Y value (black).
The contrast ratio is expressed by “Y value (white) / Y value (black)”.

(Measurement of sol-gel transition temperature (Tsg) of gelling agent)
The sol-gel transition temperature was measured using a differential thermal analyzer (EXSTAR6000 / DSC6200; manufactured by Seiko Instruments Inc.) at a temperature decreasing rate of 5 ° C / min in a temperature range of 150 ° C to 25 ° C. The transition temperature was measured by examining the position of the peak derived from the phase transition.

(Measurement of liquid crystal phase-isotropic phase transition temperature (Tc) of liquid crystal)
About the chiral nematic liquid crystal obtained by mixing the nematic liquid crystal and the chiral agent at a predetermined ratio, or the smectic liquid crystal alone, using a differential thermal analyzer (EXSTAR6000 / DSC6200; manufactured by Seiko Instruments Inc.), the temperature is 150 ° C. to 25 ° C. The temperature range was measured at a temperature decrease rate of 5 ° C./min. The transition temperature was measured by examining the position of the peak derived from the phase transition.

Example 1
60 parts of nematic liquid crystal (BL035; manufactured by Merck & Co., Inc.), 38 parts of chiral agent (MLC6427; manufactured by Merck & Co., Ltd.) and 2 parts of a gelling agent represented by the chemical formula (2) were mixed to obtain liquid crystal composition A. It was. The cholesteric liquid crystal obtained by mixing the nematic liquid crystal and the chiral agent had a Tc of 85 ° C., and the gelling agent had a Tsg of 71 ° C.

  The selective reflection wavelength (peak reflection wavelength) of the liquid crystal composition A was 600 nm. The obtained liquid crystal composition A was dropped on a film substrate provided with an alignment film, and the other film substrate on which a 5.5 μm resin spacer was dispersed on the alignment film was bonded from above. (However, the polymer structure and the insulating thin film are omitted).

(Black display)
The writing portion (1 cm × 1 cm) of the display medium was heated to 95 ° C. for 1 second with a thermal head (TH-CPS manufactured by Okura Electric Co., Ltd.), and then the portion was heated at 60 ° C. for 1 second. Then, it stood to cool. The Y value (black) of the written portion was 4.0.
(White display)
Subsequently, the writing portion (1 cm × 1 cm) was heated to 95 ° C. for 1 second by the thermal head by the same thermal head operation method as that during black display, and then the portion was allowed to cool. The Y value (white) of the written portion was 12.6.
The contrast ratio was 3.1.
A white-black display medium showing good display characteristics could be produced.

Here, the member used when producing a liquid crystal cell is as follows.
・ Substrate: Film substrate (flexible substrate) made of polyethersulfone, 0.1 mm thick ・ ITO sheet resistance: 100Ω / □
Alignment film: Soluble polyimide AL-2022 manufactured by JSR Corporation
-Orientation wrinkle thickness: 60 nm
-Spacer: Sekisui Fine Chemical Co., Ltd. Micropearl 5.5 μm
・ Sealant: Sumitomo Bakelite Co., Ltd. Sumilite ERS-2400 (main agent), ERS-2840 (curing agent)

(Example 2)
The same display medium as in Example 1 was used.
(Black display)
Black display was performed by the same black display method as in Example 1.
(White display)
After white display was performed by the same white display method as in Example 1, a pulse voltage of 5 ms was applied to the written pixels at ± 40V. The Y value (white) of the written portion was 15.6.
The contrast ratio was 3.9.
A white-black display medium having a better contrast ratio than that of writing by heat could be produced.

(Example 3)
The same display medium as in Example 1 was used.
(Black display)
Black display was performed by the same black display method as in Example 1.
(White display)
The display medium was irradiated with a He—Ne laser (small He-Ne laser manufactured by Showa Optronics) at an output of 20 mW for 3 seconds, and then allowed to cool. Only the laser irradiated part became cloudy. The Y value (white) of the cloudy part was 13.2.
The contrast ratio was 3.3.
A white-black display medium showing good display characteristics could be produced.

Example 4
58 parts of nematic liquid crystal (BL035; manufactured by Merck & Co., Inc.), 40 parts of chiral agent (CB15; manufactured by Merck & Co., Ltd.) and 2 parts of gelling agent represented by the chemical formula (1) were mixed to obtain liquid crystal composition B. It was. The cholesteric liquid crystal obtained by mixing the nematic liquid crystal and the chiral agent had a Tc of 65 ° C., and the gelling agent had a Tsg of 72 ° C.
The selective reflection wavelength (peak reflection wavelength) of the liquid crystal composition B was 600 nm. Thereafter, a display medium was produced in the same procedure as in Example 1.

(Black display)
The writing part (1 cm × 1 cm) was heated to 85 ° C. for 1 second with the thermal head by the same thermal head operation method as that for displaying black in Example 1, and then the part was heated at 50 ° C. for 1 second. Then, it stood to cool. The Y value (black) of the written portion was 4.0.
(White display)
Subsequently, by the same thermal head operation method as in black display of Example 1, 1 cm × 1 cm of the entire surface was heated to 85 ° C. for 3 seconds with the thermal head and then allowed to cool. The Y value (white) of the written portion was 12.2.
The contrast ratio was 3.
A white-and-black display medium showing good display characteristics could be produced.

(Example 5)
The same display medium as in Example 1 was used.
(Black display)
Black display was performed by the same black display method as in Example 1.
(White display)
The writing part (1 cm × 1 cm) was heated to 75 ° C. for 1 second by the thermal head in the same manner as in the black display of Example 1, and then the part was allowed to cool. The Y value (white) of the written portion was 11.2.
The contrast ratio was 2.8.
A white-black display medium showing good display characteristics could be produced.

(Example 6)
98 parts of a smectic liquid crystal (S3; manufactured by Merck & Co., Inc.) and 2 parts of a gelling agent represented by the chemical formula (2) were mixed to obtain a liquid crystal composition C. The smectic liquid crystal had a Tc of 58 ° C. and the gelling agent had a Tsg of 71 ° C.
Thereafter, a display medium was produced in the same procedure as in Example 1.
(Black display)
The writing part (1 cm × 1 cm) was heated to 80 ° C. for 1 second with the thermal head by the same thermal head operation method as that for displaying black in Example 1, and then the part was heated at 55 ° C. for 1 second. Then, it stood to cool. The Y value (black) of the written portion was 3.5.
(White display)
Subsequently, the writing portion (1 cm × 1 cm) was heated to 80 ° C. for 1 second with the thermal head by the same thermal head operation method as that for displaying black in Example 1, and then the portion was allowed to cool. The Y value (white) of the writing portion was 11.5. The contrast ratio was 3.3.
A white-black display medium showing good display characteristics could be produced.

It is a schematic sectional drawing of the display medium which is one Embodiment of this invention. It is a schematic sectional drawing of the display medium which is one Embodiment of this invention.

Explanation of symbols

1: 2: substrate, 3: 4: electrode, 5: insulating thin film, 6: polymer structure, 7: alignment film, 8: spacer, 10: display composition (display composition layer), 11: sealant 12: Visible light absorbing layer.

Claims (16)

  A display composition layer comprising a composition containing a self-organizing gelling agent sandwiched between a pair of substrates, and a visible light absorption layer disposed on the back side of the display composition layer, and writing by heat A rewritable display medium characterized in that   The display medium according to claim 1, wherein the composition contains a self-organizing gelling agent and a liquid crystal.   The display medium according to claim 2, wherein the liquid crystal is a chiral nematic liquid crystal.   The display medium according to claim 2, wherein the liquid crystal is a smectic liquid crystal.   The display medium according to claim 1, wherein an electrode for applying a voltage to each pixel arranged in a matrix is formed on each of the substrates.   The display medium according to claim 1, wherein the gelling agent content in the composition is 1 to 4% by weight.   A recording method, wherein writing is performed on the display medium according to claim 1 by heat.   The recording method according to claim 7, wherein writing is performed by heating to a temperature at which the display composition of the display medium is in an isotropic liquid state, and controlling a cooling condition after the heating.   9. The recording method according to claim 7, wherein the writing is further performed electrically after writing by heat.   Writing by heat is achieved by controlling the heating and cooling temperature of the composition in the display medium, colored display is performed by heating and slow cooling, and white display is performed by heating and quenching. The recording method according to claim 7. Heating and slow cooling is achieved by high temperature heating to a temperature (Tx) above the sol-gel transition temperature of the gelling agent and low temperature heating to a temperature (Ty) below the sol-gel transition temperature;
The recording method according to claim 10, wherein the heating and the rapid cooling are achieved by high-temperature heating and cooling to a temperature (Tz) higher than the sol-gel transition temperature of the gelling agent.   The recording method according to claim 11, wherein Tx and Tz are higher than a liquid crystal phase-isotropic phase transition temperature of the liquid crystal. The recording method according to claim 11 or 12, wherein Tx, Ty, and Tz satisfy the following relationship with respect to a sol-gel transition temperature (Tsg) of the gelling agent;
Tsg <Tx ≦ Tsg + 30
Tsg-30 ≦ Ty ≦ Tsg-5
Tsg <Tz ≦ Tsg + 30.   The high temperature heating and low temperature heating during heating and slow cooling, and the high temperature heating during heating and quenching are each independently achieved by a heat generation means or a light generation means. The recording method according to the above.   15. The recording method according to claim 14, wherein when the heat generating means is employed, heating is achieved by bringing a thermal head that generates heat at a predetermined temperature into contact with a desired portion of the display medium surface. When adopting light generation means, high temperature heating during heating and slow cooling, low temperature heating during heating and slow cooling, and high temperature heating during heating and quenching can be achieved by irradiation with a He-Ne laser. 16. The recording method according to claim 14 or 15, characterized in that

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