JPH111688A - Reversible display method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable reversible display to be realized with a display medium excellent in repeatability, display contrast, and storage stability by using a reversible display medium comprising an alignment film and a side-chain-type highmolecular liq. crystal layer formed thereon, heating the liq. crystal layer at a temp. not higher than the phase transition temp. to bring it into a transparent state, and then heating the layer at the phase transition point or higher to bring it into a light-scattering state. SOLUTION: The side-chain-type high-molecular liq. crystal layer is formed from a copolymer comprising repeating units represented by formulas I and II or by formulas III and IV. In the formulas, R<a> and R<b> are each H. methyl, or halogen; A, C, and D are each a liq. crystal molecule residue represented by one of formulas V to VIII (X and Y are each a single bond. -N=N-, -N(O)=N-, -CH=N-, -N=CH-, -COO-, -OCO-, or ethynylene; R<1> is alkoxy, halogen, cyano, carboxyl, or alkyl); and B is OH, halogen, (alkylated or alkenylated) phenyl, heterocyclic, amino, cyano, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversible display method using heat. That is, the present invention provides a resource saving method capable of repeatedly erasing / displaying by controlling heat using a projector display medium such as paper, thermal paper, an overhead projector (OHP) display sheet, or a whiteboard-like large area display medium. The present invention relates to an advantageous reversible display method.

[0002]

2. Description of the Related Art Humans have long used paper as a medium for displaying and storing information. Even in the trend of paperless display accompanying the spread of flat panel displays in recent years, the amount of use has not decreased, but rather increased.
This is probably because paper is a reflective display medium that is easy on the eyes and a display and storage medium that is excellent in flexibility and portability. As a display method other than paper, a method of forming a toner image on a polyester film and using OHP to obtain a large area display is also widely practiced. However, the use of a large amount of paper or plastic in these display methods is regarded as a problem from the viewpoint of resource and environmental problems. Under such circumstances, a technology of a display medium replacing paper is disclosed. For example, a reversible thermosensitive display medium that disperses an organic low-molecular compound in a polymer base material and controls the scattering and transmission of light by controlling the applied heat (Japanese Patent Laid-Open No. 54-119377).
JP-A-55-154198), a film composed of a blend of a plurality of polymers, and performing display by controlling the phase separation by heat (JP-A-60-180872, JP-A-62-116192). JP-A-2-117888 and JP-A-3-53285, which are based on the same principle using a polymer liquid crystal. In addition, a thermal address type projector display device that encloses a smectic liquid crystal between two transparent electrodes and repeatedly forms and erases an image by the action of an electric field and heat is also attracting attention because a high-resolution display can be obtained. ing. (Electronics Let
ters, 11 (4), 73 (1975) and App
l. Phys. Lett. , 22 (3), 111
(Refer to (1973))

[0003]

However, a reversible thermosensitive display medium composed of a film in which an organic low-molecular compound is dispersed in a polymer matrix and a reversible thermosensitive display medium composed of a film in which a plurality of polymers are blended, The compatible state of the mixed two components is controlled by heat, and the light transmitting state and the light scattering state are reversibly repeated. There is a problem that the contrast is reduced due to obscuration of the two states, and the number of repetitions is limited. Further, in a reversible display medium using a known polymer liquid crystal, display contrast is low, and there is a problem in storage stability of recording. Furthermore, the conventionally used OHP sheet is practically used only once, and there is a problem in terms of resource saving, economic efficiency, and environment.

Further, in a projector device of a thermal addressing type using a smectic liquid crystal, an electrode substrate forming a display cell is made of glass, and the accuracy of a cell gap is required. Further, in a projector using a strong light source, there is a problem in display stability against heat generated and the like. It also has the disadvantage of increasing costs.

[0005] The present invention has been made in view of the above-mentioned problems in the prior art. That is, an object of the present invention is to provide a reversible display method using a display medium which can be used like paper or a display sheet for OHP, and which has solved repeatability, display contrast and storage stability by controlling heat. Is to do. Another object of the present invention is to
An object of the present invention is to provide a reversible display method using a display sheet for a projector, which can be repeatedly displayed by controlling heat and is excellent in thermal stability, contrast, and economy.

[0006]

According to the reversible display method of the present invention, a copolymer comprising repeating units represented by the following formulas (I) and (II) on an alignment film;
A reversible display medium provided with a side chain type polymer liquid crystal layer having a copolymer composed of the repeating units represented by (III) and (IV) is used. The side chain type polymer liquid crystal layer is made transparent by heating below the transition temperature, and then the side chain type polymer liquid crystal layer is heated above its phase transition temperature to be in a light scattering state. I do.

[0007]

Embedded image [Wherein, R ^a and R ^b each represent a group selected from a hydrogen atom, a methyl group and a halogen atom;
C and D each represent a group selected from the liquid crystal molecule residues represented by the following formulas (a) to (j).

[0008]

Embedded image (Wherein X and Y are each a single bond or -N = N
-, -N (→ O) = N-, -CH = N-, -N = CH
-, - COO -, - represents O-CO- and ethynylene group selected from group, R ¹ represents an alkoxy group, a halogen atom, a cyano group, a carboxylic acid group, a group selected from alkyl groups, p is Represents an integer of 1 to 5, and when p is 2 or more, each R ¹ may be different. ) B represents a hydroxyl group, a halogen atom, an alkyl group or an optionally substituted phenyl group an alkenyl group, a heterocyclic group, an amino group, a cyano group, is selected from -COOR ^2, -OCOR ² and -CONR ² R ³ Represents a group (however,
R ² and R ³ each have 1 carbon atom which may be substituted with a hydrogen atom, a halogen atom or a heterocyclic group;
To 30 alkyl groups, alkenyl groups, alicyclic groups, hydroxyalkyl groups, alkyl groups containing a hetero atom, and optionally substituted phenyl groups. ), K, m and n each represent an integer of 1 to 30. However, A, B, C and D may each be composed of two or more groups. ]

The reversible display medium used in the present invention comprises a side chain type polymer liquid crystal capable of repeatedly realizing a transparent state and a light scattering state by the action of heat on an alignment film. Can be used as a rewritable display sheet for a projector, in which case, the side-chain type polymer liquid crystal is converted into the above formula (III) and (I)
It is preferably a copolymer composed of the repeating unit represented by V).

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. First, the side chain type polymer liquid crystal used in the present invention will be described. The side chain type polymer liquid crystal in the present invention is a copolymer containing as essential components at least two components of a liquid crystal monomer having an acrylic polymerizable group and a specific non-liquid crystal monomer described in detail below, It is composed of a copolymer containing two components of a liquid crystal monomer having an acrylate group as a functional group and a liquid crystal monomer having a methacrylate group as a polymerizable group as essential components. This configuration achieves display thermal stability, high display contrast, repeatability and recording stability that could not be achieved with acrylic liquid crystal homopolymers or methacrylic liquid crystal homopolymers, and as projector display materials and other reversible display media. It has optimal characteristics.

The above-mentioned copolymer in the present invention is prepared by mixing a predetermined amount of each polymerizable monomer, performing ordinary radical polymerization or ionic polymerization, and then purifying the same to remove a poor solvent such as alcohol or ether. And can be produced by purification. The liquid crystalline monomer usable for producing the side chain type polymer liquid crystal in the present invention includes Makromol. Chem. p273, Vo
l. 179 (1978), Eur. Polym. J. ,
p651, Vol. 18 (1982) and Mol. C
ryst. Liq. Cryst. , P167, Vol.
169 (1989) and the like, for example, biphenyl type, phenylbenzoate type,
A rigid molecule such as cyclohexylbenzene, azoxybenzene, azobenzene, azomethine, phenylpyrimidine, diphenylacetylene, biphenylbenzoate, cyclohexylbiphenyl, or terphenyl is interposed through a predetermined length alkyl spacer. hand,
Various compounds to which an acrylate or a methacrylate is bonded are exemplified.

Specific structural formulas of these compounds are shown below. CH ₂ ＣC (R ^a ) -COO- (CH ₂ ) _k -OA (where R ^a , A and k have the same meanings as described above)

As the non-liquid crystalline monomer, various general-purpose monomers can be used. Specific examples thereof include: C ₁ -C ₃₀ alkyl esters of (meth) acrylic acid and derivatives thereof, and (meth) acrylic acid. Acid dialkylaminoethyl ester, polyethylene glycol mono (meth) acrylate, (meth) acrylic acid, (meth) acrylamide, styrene and styrene derivatives,
(Meth) acrylonitrile, vinyl chloride, vinylidene chloride and N-vinylpyrrolidone. next,
Each of the copolymers will be described. First, a copolymer containing at least two components of a liquid crystal monomer and a specific non-liquid crystal monomer as an essential component will be described. The copolymerization ratio of these two components can be variously changed depending on desired properties. , The content of the liquid crystalline monomer is 50
To 99% by weight, more preferably 80% by weight.
９８98% by weight.

Further, in a copolymer containing two components of a liquid crystal monomer having an acrylate group and a liquid crystal monomer having a methacrylate group as an essential component, a liquid crystal monomer for producing the copolymer is selected. In this case, only the polymerizable groups, acryl and methacryl, are different, and the other two liquid crystal monomers having the same structure may be used, or two types of liquid crystal monomers having completely different structures may be used. It does not matter. Further, it is also possible to use a plurality of types of acrylic and methacrylic liquid crystal monomers.

The copolymerization ratio of the two components of the liquid crystal monomer having an acrylate group and the liquid crystal monomer having a methacrylate group can be variously changed depending on the desired contrast and thermal stability. The liquid crystalline monomer having an ester group is 5-95.
%, Preferably in the range of 10 to 80% by weight. In addition, the form of copolymerization of each essential component in the above two types of copolymers can take various known forms such as random, graft, and alternating, and is not particularly limited.

The molecular weight of the copolymer is in the range of 1,000 to 500,000 in terms of weight average molecular weight.
From the viewpoints of strength and response speed, a range of 10,000 to 100,000 is particularly preferable. When the weight average molecular weight is smaller than 1000, the film-forming property and self-holding property of the copolymer decrease, and
If it is larger than 10,000, the response and the orientation due to the electric field are reduced.

Among the above two types of copolymers, copolymers containing two components of a liquid crystal monomer having an acrylate group and a liquid crystal monomer having a methacrylate group as essential components are particularly suitable for heat stability of recording. And high contrast in transmitted light, and is useful as a projector display medium such as an OHP display sheet. The side-chain type polymer liquid crystal in the present invention is a copolymer composed of the above two components as essential components, and may be used as a composition obtained by adding other components to this copolymer.

For example, various antioxidants such as hindered amines and hindered phenols may be added for the purpose of improving weather resistance, and anthraquinone-based, styryl-based, and azomethine-based for the purpose of improving display contrast. And various dichroic dyes such as azo dyes.
Furthermore, in order to efficiently perform thermal writing with laser light, various laser light absorbing dyes (780 to 830n) are used.
In the case of using a commonly used semiconductor laser of m, it is preferable to add a near-infrared absorbing dye such as phthalocyanine, squarylium or azurenium). The amounts of the various components described above are preferably in the range of 0.01 to 5% by weight in the liquid crystal composition. In addition to the above, for the purpose of improving display characteristics, low-molecular
You may add in the range of 20 weight%.

Next, the configuration of the reversible display medium used in the present invention and the recording / erasing method will be described. The reversible display medium used in the present invention can adopt various modes depending on the recording method and the erasing method.
FIG. In the figure, 1 is a polymer liquid crystal layer, 2 is a substrate, 3 is an alignment film, and 4 is a protective layer.

The reversible display method of the present invention is referred to as a thermal alignment initialization method, and is a simple form in which initialization is performed only by heat treatment without using an electric field. A reversible display medium having a typical configuration used in this method has a schematic sectional view shown in FIG. A structure in which an alignment film 3 is formed on a base material 2 and a polymer liquid crystal layer 1 is laminated has a basic structure, and a protective layer 4 may be provided for the purpose of improving surface strength or heat resistance, if desired. Further, a light reflecting layer, a light absorbing layer, or a colored layer can be provided. Further, another alignment film may be formed between the protective layer and the polymer liquid crystal layer. Furthermore, a layer for the purpose of improving adhesiveness or the like may be provided between the transparent substrate and the alignment film. Examples of the orientation film that can be used here include, in the case of horizontal orientation, a rubbing treatment of a polyvinyl alcohol film, a polyimide film, a nylon-epoxy-organotitanium-based film or a SiO ₂ film, and in the case of vertical orientation, lecithin,
Organic silane, hexadecylamine, and the like can be generally used. Further, since the stretched polymer film becomes a good horizontal alignment film, for example, when a stretched PET film or the like is used as a base material, the alignment film can be omitted.

Next, a recording / erasing method will be described.
In the initialization, the reversible display medium is heated (annealed) in a temperature range in which a liquid crystal is displayed, preferably at a temperature just below a phase transition point.
By doing so, the polymer liquid crystal layer becomes transparent. In this case, the liquid crystal molecules become optically transparent in both cases of horizontal alignment and vertical alignment. However, when a dichroic dye is added, the liquid crystal molecules need to be vertically aligned. In the recording, the transparent part is changed to a light scattering state (white turbidity) by partially heating to a temperature equal to or higher than the phase transition point of the liquid crystal and then cooling. In this case, it is possible to give a cloudy display on a transparent background. As the heating means,
A thermal head or a laser can be used. Erasing is performed by repeating the above initialization.

In the reversible display medium used in the above method, the thickness of the polymer liquid crystal layer is not particularly limited, but varies depending on the desired contrast. It is preferably selected from the range of 1 to 100 μm, and particularly preferably selected from the range of 5 to 50 μm.

The protective layer (dielectric layer) formed on the above-mentioned polymer liquid crystal layer as desired is desirably high in heat resistance, and is made of a fluorine-based polymer, a silicone-based polymer, or various thermosetting polymers. It is possible. A plurality of protective layers may be laminated, and the thickness of the protective layer is preferably selected from the range of 0.1 to 20 μm.

The thickness of the alignment film is 0.001 to 5 μm.
It is generally selected from the range of m. The material and thickness of the substrate are not particularly limited, but in the case of a film, generally, 1 to
It is desirable that the projector display medium is optically transparent, such as an OHP display sheet that is selected from the range of 1000 μm and performs display using transmitted light.

In order to improve the contrast,
It is also practiced to provide a reflective layer or a colored layer as one constituent layer. Generally, a metal film can be used as the reflective layer, and a polymer film containing a dye can be generally used as the colored layer.

[0026]

EXAMPLES Next, examples will be described, but the present invention is not limited to these examples. (Contrast evaluation) The contrast described in each of the following Examples and Comparative Examples was calculated by the following method. 1) Transmitted light contrast: Halogen light is incident on a sample having a transparent portion and an opaque portion perpendicularly to the sample surface as parallel rays, and the maximum spread angle is about ± 1 using a transparent light using a lens.
The light was collected as 0 degree transmitted light, converted into a current by a photodiode, read as light intensity, and calculated as a ratio of (transmitted light intensity of transparent portion) / (transmitted light intensity of opaque portion). 2) Reflected light contrast: A sample having a transparent part and an opaque part was measured using a spectrophotometer (Hitachi U-4000) to reflect light of each of the transparent part and the opaque part (λ = 500 n).
m) The strength was measured and calculated as the ratio. Example 1 A 30 wt% trichloroethane solution of a polymer liquid crystal represented by the following structural formula (1) was applied on a PET film (stretched) having a thickness of 100 μm (stretched) using a blade coater, dried, and dried. A polymer liquid crystal layer of about 20 μm was formed. Further, a butyl alcohol solution of a melamine-based thermosetting polymer (trade name: Uvan, manufactured by Mitsui Toatsu Co., Ltd.) is applied, and cured at 130 ° C. for 1 hour to obtain a film thickness of about 3 μm
Was formed to produce a reversible display medium.

Embedded image (Weight average molecular weight (polystyrene conversion by GPC):
35000, Tg (glass transition point): 34 ° C., phase transition point: 89 ° C.) The above-mentioned reversible display medium was heated (annealed) at a temperature of 85 ° C. for 10 minutes to be initialized to a transparent state. A thermal head (about 200 dp) is applied to the transparent reversible display medium.
By printing using i), white characters could be written on a transparent background. When the transmitted light contrast was measured using a halogen light, it was confirmed to be about 40. Further, the written characters could be erased by repeating the initialization. 100 for printing and erasing
After the repetition, the contrast was the same as the initial value, and no deterioration was observed.

Example 2 A 100 μm-thick PET film (stretched) having a reflective layer formed by evaporating aluminum on one side was prepared.
A polymer liquid crystal layer (about 20 μm) composed of the polymer liquid crystal represented by the above structural formula (1) and a protective layer were formed on the PET surface side in the same manner as in Example 1 to produce a reversible display medium. Printing was performed on this reversible display medium using a thermal head in the same manner as in Example 1. At this time, the reflected light contrast of the printed portion was about 60, which was an improved value as compared with Example 1. This is probably because the formation of the reflective layer improved the light scattering property of the light scattering portion (printed portion). That is, it is considered that the incident light transmitted without being scattered by the light scattering portion is reflected by the reflection layer and scattered again, so that the scattering efficiency is improved.

Example 3 A polymer liquid crystal copolymer represented by the following structural formula (2) was dissolved in toluene on a 100 μm-thick PET film (stretched) to form a 40% solution. This solution was applied on the PET film using a blade coater and dried to form a polymer liquid crystal layer having a thickness of about 30 μm.

Embedded image (Weight average molecular weight (polystyrene conversion by GPC):
20000, Tg (glass transition point): 40 ° C., phase transition point: 109 ° C.) Next, a silicone-based polymer (trade name: Cymac US-350, manufactured by Toa Gosei Chemical Co., Ltd.) was formed on the polymer liquid crystal layer. Apply methyl ethyl ketone solution,
After drying for a time, a reversible display medium in which a heat-resistant layer having a thickness of about 2 μm was laminated as a protective layer was produced.

This reversible display medium is heated at 105 ° C. for 1 hour.
Heating (annealing) was performed for 0 minutes to initialize and set to a transparent state. By printing on a transparent reversible display medium using a thermal head (about 200 dpi), white characters could be written on a transparent background. When the transmitted light contrast was measured using a halogen light, it was confirmed to be about 40. Further, the written characters could be erased by repeating the initialization. Even after printing and erasing were repeated 100 times, the contrast was the same as the initial value, and no deterioration was observed.

An example of the synthesis of the high-molecular liquid crystal copolymer represented by the structural formula (2) is shown below. (Synthesis of Polymer Liquid Crystal Copolymer) 2.0 g of each of the liquid crystal monomers represented by the following structural formulas (A) and (B) was dissolved in 20 ml of tetrahydrofuran (THF), and azoisobutyronitrile (AIBN) was used as an initiator. After adding 0.01 g), polymerization was carried out at 60 ° C. for 48 hours under a nitrogen atmosphere. After completion of the polymerization, the resultant was purified by reprecipitation using ethanol as a precipitation solvent, and dried to obtain 3.7 g of a liquid crystal polymer as a white solid. This liquid crystal polymer has a temperature range showing a liquid crystallinity of 40 ° by observation with a polarizing microscope and thermal analysis.
It was confirmed that the temperature was in the range of C to 109 ° C.

[0031]

Embedded image

EXAMPLE 4 Octadecyldimethyl [3- (trimethoxysilyl) propyl] ammonium chloride (manufactured by Chisso Corporation), a vertical alignment agent, was placed on a PET film having a thickness of 50 μm.
% Methanol solution using a blade coater,
After drying, a vertical alignment film having a thickness of about 0.5 μm was provided.
Subsequently, a polymer liquid crystal layer (about 30 μm) was formed in the same manner as in Example 2 using the polymer liquid crystal of Example 1. In this state, the reversible display medium was cloudy. When this reversible display medium was heated at 105 ° C. to 110 ° C. for 20 minutes, the cloudy state changed to a transparent state. At this time, the halogen light transmittance was 70%. Using a thermal head as in Example 3, white turbid characters could be written on a transparent background. Further, when this reversible display medium was projected using OHP, the written portion was displayed in black characters and was clearly displayed. Erasing can be performed again by heating at 105 ° C. to 110 ° C. for 20 minutes, thereby returning the written portion to a transparent state. Therefore, repeated writing / erasing was possible.

[0033]

The reversible display method of the present invention uses a reversible display medium having a recording layer of a high-molecular liquid crystal copolymer having the above-mentioned specific structure. Excellent in contrast and workability.
Further, the present invention can repeatedly realize transmission / scattering of light by the action of heat, and is thin as paper,
It is a reversible display method that provides a reflection-type display that is easy on the eyes and is also useful in saving resources. Further, the reversible display medium used in the present invention can be applied as a sheet for a whiteboard-like large-area display device because there is no restriction on the enlargement of the area. Furthermore, since a material having a high transmitted light contrast can be obtained, it is useful as a projector display medium such as an OHP display sheet.

[Brief description of the drawings]

FIG. 1 is a sectional view of one embodiment of a reversible display medium used in the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Polymer liquid crystal layer, 2 ... Base material, 3 ... Orientation film, 4 ... Protective layer (dielectric layer).

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI G09F 13/04 G09F 13/04 U

Claims (1)

[Claims] 1. The method according to claim 1, wherein the following formulas (I) and (II)
Reversible display provided with a side chain type polymer liquid crystal layer having a copolymer composed of a repeating unit represented by the following or a copolymer composed of the repeating units represented by the following formulas (III) and (IV): The side chain type polymer liquid crystal layer is made transparent by heating the side chain type polymer liquid crystal layer below its phase transition temperature using a medium. A reversible display method characterized by heating to a light-scattering state by heating above a transition temperature. Embedded image [Wherein, R ^a and R ^b each represent a group selected from a hydrogen atom, a methyl group and a halogen atom;
C and D each represent a group selected from liquid crystal molecule residues represented by the following formulas (a) to (j): (Wherein X and Y are each a single bond or -N = N
-, -N (→ O) = N-, -CH = N-, -N = CH
-, - COO -, - represents O-CO- and ethynylene group selected from group, R ¹ represents an alkoxy group, a halogen atom, a cyano group, a carboxylic acid group, a group selected from alkyl groups, p is Represents an integer of 1 to 5, and when p is 2 or more, each R ¹ may be different. ) B represents a hydroxyl group, a halogen atom, an alkyl group or an optionally substituted phenyl group an alkenyl group, a heterocyclic group, an amino group, a cyano group, is selected from -COOR ^2, -OCOR ² and -CONR ² R ³ Represents a group (however,
R ² and R ³ each have 1 carbon atom which may be substituted with a hydrogen atom, a halogen atom or a heterocyclic group;
To 30 alkyl groups, alkenyl groups, alicyclic groups, hydroxyalkyl groups, alkyl groups containing a hetero atom, and optionally substituted phenyl groups. ), K, m and n each represent an integer of 1 to 30. However, A, B, C and D may each be composed of two or more groups. ]