JP2934071B2 - Polymer-dispersed liquid crystal display device and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polymer dispersed liquid crystal display device and a method for manufacturing the same.

[0002]

2. Description of the Related Art A polymer-dispersed liquid crystal display device utilizes the fact that liquid crystals have a refractive index anisotropy, and uses a liquid crystal impregnated in a porous polymer to determine whether or not a voltage is applied. This is a display element that controls transmission and scattering by changing the refractive index and adjusting the refractive index with the polymer. The characteristics of this display element include the conventional Twisted Nema
Compared to tic type liquid crystal display devices, a very high transmission state is possible because a polarizing plate is unnecessary, a wide viewing angle, a large area, a free shape, good responsiveness, etc. Is mentioned.

Conventionally, methods for producing a polymer matrix containing liquid crystals include (1) phase separation by polymerization (Polymer
Preprint, Japan, Vol. 38, No. 7 (1989)), (2) Phase separation by solvent evaporation (Polymer Preprint, Japan, Vol. 37, No.
8 (1988)), (3) Solvent evaporation from the emulsified state (JP-A-60-25
No. 2687) and the like. However, in these production methods, the structure cannot be controlled, the productivity is poor, and even the control of the monodispersion of the pore diameter for impregnating the liquid crystal, which has the greatest influence on the response speed, cannot be expected at all. Was.

[0004]

Means for Solving the Problems The inventors of the present invention have made intensive studies to improve such a drawback, and as a result, by using a polymer bead having a large number of fine holes as a matrix for fixing a liquid crystal. It has been found that a very suitable liquid crystal display element can be obtained, and the present invention has been completed.
That is, the present invention relates to a polymer-dispersed liquid crystal display device in which a porous polymer bead having a large number of fine holes and a liquid crystal layer formed of a liquid crystal substance filled in the holes are sandwiched between electrodes, and a liquid crystal. Disclosed is a method for producing a polymer-dispersed liquid crystal display device, comprising dispersing porous polymer beads impregnated with a substance in a photocurable resin, curing the film, and sandwiching the film between electrodes. Things.

[0005] The driving principle of the polymer dispersed liquid crystal display element is as follows.
Using the refractive index anisotropy of the liquid crystal, the refractive index of the liquid crystal is changed depending on whether or not a voltage is applied between the electrodes. When the refractive index of the liquid crystal matches the refractive index of the resin matrix, the liquid crystal enters a transmission state, and when the refractive index is different, Is in a scattering state. More specifically, in the case of a polymer-dispersed liquid crystal display device in which the ordinary light refractive index or the extraordinary light refractive index of the liquid crystal matches the refractive index of the resin matrix, the liquid crystal is oriented with respect to an electric field when a voltage is applied. In a state where no voltage is applied, the arrangement of the liquid crystal becomes random, so that a scattering state occurs. Conversely, in a polymer-dispersed liquid crystal display device in which the refractive index of the liquid crystal is the same as the refractive index of the resin matrix when the liquid crystal is randomly arranged, the state is a scattering state when a voltage is applied, and the voltage is applied. If not, it is in a transmission state. However, the random alignment of the liquid crystal in the polymer-dispersed liquid crystal display element is caused by the interaction between the resin matrix wall and the liquid crystal. However, since the alignment state is slightly different microscopically, the latter polymer-dispersed liquid crystal display element is not preferable because unevenness of the refractive index may occur due to a partial difference in the alignment state.

According to the driving principle of the polymer-dispersed liquid crystal display device described above, the liquid crystal and the porous polymer beads used in the polymer-dispersed liquid crystal display device of the present invention must be selected in consideration of the respective refractive indexes. . When the liquid crystal impregnated porous polymer beads are formed into a film using a medium,
It is necessary to select a medium for forming a film in consideration of such a refractive index. Specifically, when a liquid crystal impregnated porous polymer bead is used in the form of a film, it is necessary to use a porous polymer bead and a medium forming the film that have substantially the same refractive index. In addition, the refractive index of the matrix composed of the porous polymer beads or the medium forming the film with the porous polymer beads has a refractive index of at least one of a state in which a voltage is applied and a state in which the voltage is not applied. It is preferable to use a material having a refractive index, an extraordinary light refractive index, or a refractive index that matches any of the refractive indexes when the liquid crystal is randomly aligned. However, when the matrix is swollen by the liquid crystal, the refractive index of the matrix swollen by the liquid crystal is closer to the refractive index of the liquid crystal than the refractive index of the matrix alone. No problem. In particular, it is desirable that the refractive index of the matrix and the ordinary light refractive index or the extraordinary light refractive index of the liquid crystal match.

The monomer constituting the liquid crystal-impregnated porous polymer beads used in the polymer-dispersed liquid crystal display element of the present invention is such that the polymer beads obtained by using the polymer beads satisfy the above-mentioned refractive index condition, and It is not particularly limited as long as it does not dissolve in, for example, styrene,
p-methylstyrene, p-chlorostyrene, p-chloromethylstyrene, pt-butoxystyrene, mt-
Styrene monomers such as butoxystyrene, α-methyl-pt-amyloxystyrene, pt-amyloxystyrene; ethyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate Acrylate-based monomers such as methyl methacrylate, ethyl methacrylate, lauryl methacrylate, dimethylaminoethyl methacrylate, and diethylaminoethyl methacrylate; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and maleic acid -Based monomers; polyethylene glycol mono (meth) acrylate; alkyl vinyl ethers such as methyl vinyl ether and ethyl vinyl ether; vinyl esters such as vinyl acetate and vinyl butyrate N-alkyl-substituted (meth) acrylamides such as N-ethylacrylamide, N-methylmethacrylamide and N-ethylmethacrylamide; nitrile monomers such as acrylonitrile and methacrylonitrile; divinylbenzene, ethylene glycol di (meth) ) Polyfunctional monomers such as acrylate, polyethylene glycol di (meth) acrylate, trimethylolpropane triacrylate, and 1,4-divinyloxybutane; these monomers may be used alone or in a range of 2 or A mixture of more than one species can be used.
In addition, its production method is also a general method of synthesizing a porous polymer bead, that is, a hydrophobic organic solvent which is inactive to polymerize a monomer,
For example, toluene, xylene, diethylbenzene, n-dodecane and the like are present in a polymerization reaction system, and after suspension polymerization, seed polymerization, etc., are polymerized by a method usually used for producing polymer beads, and then diluted with a liquid crystal alone or an appropriate solvent. The immersion in the liquid crystal, the lifting and drying may be repeated several times, and the liquid crystal may be filled in the porous polymer beads, or the porous polymer beads may be filled in the liquid crystal by immersion in a reduced pressure drier. Alternatively, the liquid crystal may be directly dissolved in the monomer and polymerized using the above method. However, the responsiveness of the liquid crystal to the application of voltage is greatly affected by the size of the pores impregnated with the liquid crystal, and if there is a distribution in the size between the liquid crystal domains, the responsiveness differs between the domains. As a result, the contrast deteriorates, and therefore, it is necessary to increase the driving voltage. Therefore, in order to increase the contrast under the same driving voltage, that is, to make the response uniform among the liquid crystal domains, it is necessary to monodisperse the pore size. The size of the pore size of the porous polymer beads depends on the particle size of the polymer beads. Therefore, the particle diameter of the porous polymer beads is preferably 1 to 200 μm. The particle size distribution is preferably monodisperse, and the standard deviation of the particle size distribution is preferably 20% or less, and most preferably 10% or less of the particle size. Therefore, when the particle size distribution of the obtained porous polymer beads is wide, it is preferable to classify by the elutriation method or the wind method.

In the present invention, the pore volume of the porous polymer beads before filling with liquid crystal is preferably 0.5 to 5.0 ml / g. The pore volume of the porous polymer beads is
If it is less than 0.5 ml / g, the impregnation amount of the liquid crystal becomes insufficient,
When this is used for a liquid crystal display element, the contrast becomes poor, which is not preferable. On the other hand, if the pore volume of the porous polymer beads exceeds 5.0 ml / g, the strength of the polymer beads is remarkably reduced, and cracks or the like are generated in the liquid crystal display element assembling step, which is not preferable.

The liquid crystal used in the present invention includes a nematic liquid crystal and a smectic liquid crystal. These liquid crystals may be used alone or as a mixture, but it is particularly preferable to use a nematic liquid crystal having a large dielectric anisotropy. It is preferable to obtain good characteristics.

Next, the liquid crystal-impregnated porous polymer beads thus obtained are sandwiched between substrates. As the sandwiching method, liquid crystal-impregnated porous polymer beads may be dispersed in liquid crystal and used, but it is particularly preferable to form a film using an appropriate medium. The medium is not particularly limited as long as it satisfies the above-mentioned refractive index conditions, and a film forming method is also a method in which liquid crystal-impregnated porous polymer beads are dispersed in a monomer and polymerized by heat, light, or the like, or a medium. Can be produced by a usual method such as dissolving a polymer to be used in an appropriate solvent, dispersing the liquid crystal-impregnated porous polymer beads in the solvent, and evaporating the solvent. It is preferable to use a photocurable resin as the material. The photocurable resin is composed of a prepolymer, a monomer and a photoinitiator, and further, if necessary, a photosensitizer, and the composition thereof is not particularly limited as long as the above refractive index condition is satisfied. For example, polyester acrylates as a prepolymer,
Monofunctional monomers such as epoxy acrylates, polyester urethane acrylates, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, and 2-hydroxypropyl acrylate as monomers; 1,3-
Butanediol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, diethylene glycol diacrylate, neopentyl glycol diacrylate, polyethylene glycol
(400) Bifunctional monomers such as diacrylate and hydroxypivalate neopentyl glycol diacrylate; trifunctional or higher functional monomers such as trimethylolpropane triacrylate, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, triallyl isocyanurate , Acetophenone, benzophenone, Michler's ketone (4,
4'-bisdimethylaminobenzophenone), benzyl,
Benzoin, benzoin isobutyl ether, benzyldimethyl ketal, 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-dimethyl-1-phenylpropan-1-one, 1- (4-isopropylphenyl) -2-hydroxy-2-methyl Examples of propane-1-one, azobisisobutyronitrile, benzoyl peroxide, di-t-butyl peroxide, and photosensitizers include n-butylamine, di-n-butylamine, triethylamine, and diethylaminoethyl methacrylate. . As a specific production method using such a photocurable resin, a liquid crystal impregnated porous polymer bead is dispersed in a photocurable resin, and this is dispersed in an ITO (indium tin oxide) which is used in a normal liquid crystal panel. ) Or Sn
Apply it on a glass substrate or plastic film substrate on which a vapor-deposited film such as O ₂ has been formed, cover it with another substrate, and irradiate it with light to cure the resin, or use ordinary liquid crystal. In the same way as in the panel manufacturing method, an empty panel is prepared using two substrates in advance using a sealant and a spacer having an appropriate size, and liquid crystal-impregnated porous polymer beads are dispersed under vacuum in this photocuring. The resin may be filled and light reflected to cure the resin.

The amount of the photocurable resin including the liquid crystal-impregnated porous polymer beads is determined by the following equation.
5/95 to 75/25 by weight of the photocurable resin, preferably 30
/ 70 to 70/30. The thickness of the photocurable resin film containing the liquid crystal-impregnated porous polymer beads is 1 to 300 μm,
Particularly, it is preferably 1 to 200 μm. In this case, the thickness of the resin film between the substrates may be controlled by liquid crystal-impregnated porous polymer beads, but the photocurable resin may be provided with another gap retaining agent having a particle size corresponding to a target film thickness. It may be mixed.

[0012]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples. The parts in the examples are on a weight basis.

Example 1 (1) Synthesis of porous polymer beads 50 parts of styrene, 50 parts of ethylene glycol dimethacrylate
Part, benzoyl peroxide (Niper BW, NOF Corporation)
1 part) and 150 parts of isoamyl acetate were mixed with 800 parts of a 3% aqueous solution of polyvinyl alcohol (GH-17, manufactured by Nippon Synthetic Chemical Industry Co., Ltd .; saponification degree: 86.5 to 89 mol%), and stirred. Polymerization was performed at 80 ° C. for 10 hours under a nitrogen stream. The obtained crosslinked polymer fine particles were subjected to a classification operation to obtain crosslinked polymer fine particles having an average particle size of 50 μm and a standard deviation of 4.5 μm. When the pore volume of the particles was determined by a mercury intrusion method, it was 3.5 ml / g. (2) Liquid crystal impregnation treatment 100 parts of Logic's liquid crystal (STN-203) and 10 parts of the above porous cross-linked polymer beads are mixed and dispersed under reduced pressure (0.1 mmHg or less), and the liquid crystal is returned to normal pressure. Was impregnated.

(3) Preparation of display panel The polymer beads obtained by the above operation were isolated, and 10 parts of photomer 4028 (aromatic acrylate resin, manufactured by San Nopco Co., Ltd.) as a photocurable resin was added. Irga as sensitizer
Cure 651 (manufactured by Ciba Geigy) was mixed with 0.3 part and sufficiently dispersed. This mixture was placed on a glass plate (300 mm
× 300 mm, thickness 1 mm), glass plates with ITO electrodes are superposed, and cured with a high-pressure UV lamp (UVLa
mp 150 W / cm ² , 150 sec). An AC voltage (AC 100 V, 200 Hz) is applied to the obtained liquid crystal display panel (cell thickness 50 μm).
Is applied, the part where the voltage is applied becomes transparent, but the other parts become cloudy, and the rising response time
It was confirmed that the contrast was good in 30 ms.

Example 2 (1) Synthesis of porous polymer beads 40 parts of methyl methacrylate, divinylbenzene (purity of 55)
%), 1 part of benzoyl peroxide (Niper BW, manufactured by NOF CORPORATION), 40 parts of isoamyl acetate, and 110 parts of isoamyl alcohol in a mixed solution of polyvinyl alcohol (GH-1).
7, Nippon Synthetic Chemical Industry Co., Ltd .; saponification degree 86.5-89 mol
%) Of a 3% aqueous solution was added, and polymerization was carried out at 80 ° C. for 10 hours under a nitrogen stream while stirring. The obtained crosslinked polymer fine particles were subjected to a classification operation to obtain crosslinked polymer fine particles having an average particle size of 14 μm and a standard deviation of 1.4 μm. When the pore volume of the particles was determined by a mercury intrusion method, it was 4.8 ml / g. (2) Liquid crystal impregnation treatment 10 parts of the above porous cross-linked polymer beads were dispersed in 100 parts of Logic's liquid crystal (STN-202), and centrifuged (10,000 rp)
m./15 min) to impregnate the liquid crystal.

(3) Preparation of Display Panel The polymer beads obtained by the above operation were isolated, and 7 parts of a photocurable resin, Photomer 4028 (aromatic acrylate resin, manufactured by San Nopco Co., Ltd.) was added. Irga as sensitizer
Cure 651 (manufactured by Ciba Geigy) 0.2 part and polymer beads having a particle size of 30 μm 0.5 part were mixed and sufficiently dispersed. A glass plate with an ITO electrode (300 mm × 300 mm, thickness 1)
mm), glass plates with ITO electrodes are superimposed, and cured with a high-pressure UV lamp (UV Lamp 150W / cm ² ,
120 sec). When an AC voltage (100 V AC, 200 Hz) was applied to the obtained liquid crystal display panel (cell thickness 30 μm), the part where the voltage was applied became transparent, but the other parts became cloudy, and the rise response time was 25 ms. It was confirmed that the contrast was good.

Example 3 (1) Synthesis of porous polymer beads Ethyl methacrylate 50 parts, divinylbenzene (purity 55
%), 50 parts of benzoyl peroxide (Niper BW, manufactured by Nippon Oil & Fats Co., Ltd.) and 5 parts of toluene in a mixed solution of polyvinyl alcohol (GH-17, manufactured by Nippon Synthetic Chemical Industry Co., Ltd .; (89 mol%) of a 3% aqueous solution was added, and polymerization was carried out at 80 ° C. for 10 hours under a nitrogen stream while stirring. The obtained crosslinked polymer fine particles were subjected to a classification operation to obtain crosslinked polymer fine particles having an average particle size of 8 μm and a standard deviation of 0.7 μm. When the pore volume of the particles was determined by a mercury intrusion method, it was 0.8 ml / g. (2) Liquid crystal impregnation treatment 15 parts of Merck liquid crystal (ZLI-1132) are mixed with 100 parts of acetone, and 10 parts of the above porous crosslinked polymer beads are dispersed.
Thereafter, the solvent was distilled off under reduced pressure at room temperature to impregnate the liquid crystal.

(3) Manufacture of a display panel The polymer beads obtained by the above-mentioned operation were combined with 10 parts of Aronix UV-3033 (manufactured by Toa Gosei Chemical Co., Ltd.) as an ultraviolet-curable adhesive, and polymer beads having a particle size of 50 μm. The mixture was mixed with 0.5 part and sufficiently dispersed. This mixture was supplied onto a glass plate (300 mm × 300 mm, thickness 1 mm) with an ITO electrode,
Glass plates with TO electrodes were stacked and cured with a high-pressure UV lamp (UV Lamp 150 W / cm ² , 120 sec). When an AC voltage (AC 100 V, 200 Hz) was applied to the obtained liquid crystal display panel (cell thickness 50 μm), the portion where the voltage was applied became transparent, but the other portions became cloudy,
It was confirmed that the contrast was good with a rise response time of 25 ms.

[0019]

As is clear from the examples, it was found that the panel using the liquid crystal display device of the present invention can provide an extremely good liquid crystal display such as good contrast and quick response.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-280123 (JP, A) JP-A-2-280120 (JP, A) JP-A-3-46621 (JP, A) JP-A-3-28021 43714 (JP, A) JP-A-3-59515 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G02F 1/1333 610

Claims (4)

(57) [Claims] 1. A polymer-dispersed liquid crystal display device comprising a porous polymer bead having a large number of fine holes and a liquid crystal layer formed of a liquid crystal substance filled in the holes, sandwiched between electrodes. 2. The porous polymer beads having a particle size of 1 to 200.
μm and the standard deviation of the particle size distribution is
2. The polymer-dispersed liquid crystal display device according to claim 1, wherein the content of the polymer particles is not more than 10%. 3. The porous polymer beads having a pore volume of 0.5
The polymer-dispersed liquid crystal display device according to claim 1 or 2, wherein the polymer particles are from 5.0 to 5.0 ml / g. 4. The method according to claim 1, wherein the porous polymer beads impregnated with a liquid crystal material are dispersed in a photocurable resin and cured to form a film, and the film is sandwiched between electrodes. The method for producing a polymer-dispersed liquid crystal display device according to claim 1.