JPH0452622A - Optical panel - Google Patents

Abstract

PURPOSE:To obtain the optical panel which is excellent in light scatterability by dispersing polymer fine particles of specific grain sizes into a medium of changing refractive indices and clamping such medium between two sheets of substrates. CONSTITUTION:This optical panel is formed by dispersing the polymer fine particles having 0.2 to 2mum average particle size into the medium of the changing refractive index and clamping such medium between two sheets of the substrates 4, at least one of which is transparent. The polymer contg. >=1wt.% crosslinkable monomer, such as divinyl benzene or ethylene glycol dimethacrylate, is preferable as the polymer as this polymer hardly absorbs and swells the material (medium) to constitute the matrix. The light scattering of the polymer fine particles themselves dispersed in a liquid crystal is effectively utilized in this way and, therefore, there is no need for making the orientation treatment of the liquid crystal like heretofore and there is no need for exactly controlling the liquid crystal layer.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an optical panel, and more particularly, to an optical panel suitable for an optical display material that utilizes changes in optical properties caused by a difference in refractive index between particles and a medium. Regarding optical panels.

[Prior Art] Conventionally, a liquid crystal panel using a polarizing plate has been used as an optical display material, but since the polarizing plate is used, there is a drawback that a bright white display cannot be obtained. Recently, a display method using a backlight has been adopted to overcome this drawback. However, this method has disadvantages in that it loses the inherent advantage of liquid crystals, such as low power consumption, and is disadvantageous in terms of thinness and weight reduction.

In order to eliminate this drawback, we developed a reflective black-and-white display method that does not use a polarizing plate. A method that utilizes the effect of becoming transparent when the case is different, and becoming a scattering state when there is a mismatch (Published Patent Publication No. 58-501631, Published Patent Publication No. 61
-502128, JP-A No. 62-2231, etc.), (2
) A method in which transparent particles such as silica particles or polymer particles are dispersed in a nematic liquid crystal medium, and the particles disturb the orientation of the liquid crystal molecules, making use of the light scattering phenomenon of the liquid crystal itself, rather than the scattering of light by the particles ( Japanese Patent Publication No. 54-21859
No. 63-96629, JP-A-1-3
12527, etc.) have been developed.

However, all of these methods lack scattering ability, so significant improvement in bulk was required for use as a reflective paper white display.

[Problem to be solved by the invention]

An object of the present invention is to solve the problems of the prior art described above and to provide an optical panel with excellent light scattering ability that can be used as a reflective paper white display without using a polarizing plate.

(Means for Solving the Problems) In view of the above-mentioned problems, the inventors of the present invention have made extensive studies and have discovered that by dispersing polymer fine particles of an appropriate particle size in a medium, the scattering of light by the polymer fine particles themselves can be efficiently reduced. The present invention has been achieved based on the discovery that by utilizing this method and controlling the refractive index of the medium, it is possible to obtain an excellent scattering ability that can be sufficiently used as a reflective paper white display.

That is, the optical panel of the present invention has an average particle diameter of 0.2
It is characterized in that polymer fine particles having a diameter of ~2 μm are dispersed in a medium with a variable refractive index, and this is sandwiched between two substrates, at least one of which is transparent.

The polymer fine particles used in the present invention have a diameter of 0.2 to 2 μm.
, preferably has an average particle size in the range of 0.3 to 1 μm. If the particle diameter of the polymer is less than 0.2 μm, visible light on the longer wavelength side will not be scattered, resulting in insufficient scattering ability and a bright white color will not be obtained. Moreover, if the thickness exceeds 2 μm, visible light of all wavelengths will be scattered, but the number of times of scattering will be significantly reduced, resulting in insufficient scattering ability, and a sufficient white color will not be obtained unless the layer thickness is increased. It is preferable that the particle size distribution of the polymer is as narrow as possible, and specifically, it is preferable that the particle size variation coefficient is 10% or less.

Polymer fine particles can be obtained, for example, by synthesis using an emulsion polymerization method, or by seed polymerization using a polymer obtained by an emulsion polymerization method as a seed, followed by coagulation, washing, drying, and pulverization. There are no particular restrictions on the monomers constituting the polymer particles, such as monomers commonly used in emulsion polymerization, styrene, α-methylstyrene,
Aromatic vinyl compounds such as fluorostyrene, vinylpyridine, divinylbenzene, vinyl cyanide compounds such as acrylonitrile and methacrylonitrile, butyl acrylate, 2-ethylhexyl acrylate, methyl acrylate, 2-hydroxyethyl acrylate, glycidyl acrylate, N .

Acrylic acid ester monomers such as N'-dimethylaminoethyl acrylate, butyl methacrylate, 2-ethylhexyl methacrylate, methyl methacrylate,
methacrylic acid ester monomers such as 2-hydroxyethyl methacrylate glycidyl methacrylate, N,N' dimethylaminoethyl methacrylate, acrylic acid,
Mono- or dicarboxylic acids and dicarboxylic acid anhydrides such as methacrylic acid, maleic acid, and itaconic acid; amide monomers such as acrylamide and methacrylamide;
Furthermore, ionic monomers such as sodium styrene sulfonate and sulfonated isoprene, ethylene glycol di(
Meth)acrylate, trimethylolpropane di(meth)acrylate, etc. can be used. In addition, within the allowable range in terms of polymerization rate and polymerization stability,
Conjugated double bond compounds such as butadiene and isoprene, vinyl ester compounds such as vinyl acetate, 4-methyl-1-
Pentene and other α-olefin compounds can also be used.

The polymer used in the present invention is preferably one containing 1% by weight or more of a crosslinkable monomer such as divinylbenzene or ethylene glycol dimethacrylate because it absorbs and swells the substance (medium) that becomes the matrix.

In addition, when producing polymer fine particles, the polymer composition is appropriately selected so that the difference in refractive index from the medium under specific electric field or temperature conditions is usually 0.01 or less, preferably 0.0.
It is preferable to control it so that it is 0.05 or less.

The medium for dispersing the polymer fine particles used in the present invention is not particularly limited as long as the refractive index changes depending on electric field, temperature, etc., but a medium in which the refractive index changes by 0.01 or more is preferable, and more preferably. is 0.02 or more.

A liquid crystal is an example of a medium whose refractive index changes depending on an electric field. Liquid crystal is preferable because its molecular arrangement can be reversibly changed relatively easily in response to an external electric field, and the refractive index can thereby change by about 0.1. Examples of the liquid crystal include nematic liquid crystal and cholesteric liquid crystal. Nematic type liquid crystals include ship base type, azo type, azoxy type, benzoic acid ester type, biphenyl type, terphenyl type, cyclohexylcarboxylic acid ester type, phenylcyclohexane type, biphenylcyclohexane type, pyrimidine type, and dioxane type. Examples of cholesteric liquid crystals include cholesteryl halide, cholesteryl benzoate, and cholesteryl acetate.

Further, a dichroic dye or the like may be added to the liquid crystal.

Examples of media whose refractive index changes with temperature include polymers such as polystyrene and polyester. For example, the refractive index of polystyrene with a molecular weight of 3600 decreases by 0.02 when the temperature is increased by 100'C (edited by the Society of Polymer Science and Technology, Optical Fiber Optical Materials, p. 8, Imori Publishing (1987)).
), this is a sufficient change to obtain a white display due to light scattering.

A film made by kneading into this polystyrene polymer particles such as polydivinylhenzen, whose refractive index has little temperature dependence, can be suitably used as a display material when it is desired to visualize large temperature changes. can.

The blending ratio of the polymer fine particles is 5 to 50% by volume of the medium.
is preferred. If this proportion is less than 5% by volume, the scattering ability of incident light is insufficient, and if it exceeds 50% by volume, it is difficult to uniformly disperse the polymer particles in the medium and the change in refractive index is also small, which is preferable. do not have. The thickness of this layer consisting of polymer particles and medium is 3 to 500 μm, in particular 6 μm.
~100 μm is preferred.

The substrates used in the present invention may be made of glass, polycarbonate, polymethyl methacrylate, polystyrene, nylon, polyethylene terephthalate, or the like, as long as at least one of the two substrates is transparent. When using a medium whose refractive index changes depending on an electric field, indium oxide, ITO, etc. are added to the surface in contact with the substrate.
Transparent electrodes such as tin dioxide doped with fluorine or antimony, zinc oxide doped with indium, aluminum, silicon, etc. are installed.

FIG. 1 is a sectional view of an optical panel using liquid crystal as a medium, showing one embodiment of the present invention. This panel consists of a layer in which polymer fine particles 7 are dispersed in a liquid crystal made up of liquid crystal molecules 6, a transparent electrode 5 placed above and below this layer and connected to a power source 8, and a layer provided on each surface of the transparent electrode 5. It consists of a glass substrate 4 made of

On the left side of FIG. 1, a state in which a voltage is applied to the transparent electrode 5 (
ON state). In this ON state, the liquid crystal molecules 6 are aligned in the vertical direction, and the apparent refractive index with respect to the incident light 1 from above matches the refractive index of the polymer particles 6, so that light is transmitted and the transmitted light 2 is obtained. Therefore, if a blackboard is placed on the transparent side, black will be displayed due to the transmission of light.

Further, the right side of FIG. 1 shows a state in which no voltage is applied to the transparent electrode 5 (OFF state). In this OFF state, the liquid crystal molecules 6 exist randomly, so there is a difference in refractive index between the particles and the liquid crystal molecules, and as a result, visible light of all wavelengths is scattered and white is displayed. be done.

This optical panel can efficiently utilize the light scattering of the polymer particles dispersed in the liquid crystal, so there is no need to align the liquid crystal as in conventional methods, and there is no need to accurately control the liquid crystal layer. .

Furthermore, since there is no major difference in the manufacturing process of liquid crystal display materials using conventional polarizing plates, it is easy to switch the manufacturing process.

〔Example〕

The present invention will be explained in more detail by examples below.
The present invention is not limited to these examples. Note that "parts" in the examples mean "parts by weight."

Example 1 Polymer fine particles made of methyl methacrylate and divinyl hanzene with an average particle diameter of 0.50 am (coefficient of variation 5%) (methyl methacrylate/divinyl hensen (weight ratio) = 83/17, refractive index -1°508) 30 parts of liquid crystal ZLI 2144 (manufactured by Merck Japan Co., Ltd.,
It was well dispersed in 60 parts of refractive index (-1,594) using an ultrasonic homogenizer.

This mixture was placed on a glass substrate with a transparent electrode at a thickness of 10 μm.
An optical panel having the same structure as that shown in FIG. 1 was produced by sandwiching the two pieces to a thickness of . At this time, polyimide coating and rubbing treatment, which is performed on conventional liquid crystal panels, was not performed.

A voltage was applied to the reflective liquid crystal display panel thus obtained, and the transmittance at that time was examined. The results are shown by the solid line in FIG. 2, and it was found that excellent display characteristics were exhibited.

Comparative Example 1 A liquid crystal display panel identical to that of Example 1 was produced except that polymer fine particles having a particle diameter of 3 μm were used in Example 1, and the transmittance thereof was examined.

The results are shown by the broken line in Figure 2. Although the transmittance in the ON state is high, the transmittance in the OFF state is close to 50%, so the scattering ability is low and a bright white display cannot be obtained, making it difficult to use as a display material. Couldn't use it.

Example 2 Fine polymer particles consisting of methyl methacrylate, styrene, and dihinylbenzene with an average particle diameter of 0.6 μm (coefficient of variation 6%) (methyl methacrylate/styrene/divinylbenzene (weight 1 ratio) -25150/25, refractive index =
1.570) was dispersed in 80 parts of polystyrene having a molecular weight of 3600 (refractive index = 1.590) using a twin-screw press ratio machine.

This mixture was sandwiched between two glass plates so as to have a thickness of 31 TI [[l] to prepare a temperature-sensitive display material. At room temperature, the difference in refractive index between the polymer fine particles and the medium polystyrene is 0.02, so the display material displayed white due to light scattering, but when heated to 60°C, the polymer fine particles The refractive index of the medium and the medium matched and became transparent. As a result, it was found that this display material can be used for optical display boards, window panel materials, etc. that utilize temperature changes.

(Effects of the Invention) The optical panel of the present invention can efficiently utilize the light scattering of the polymer particles themselves by dispersing specific polymer particles in a medium whose refractive index changes depending on an electric field or temperature. Excellent light scattering ability can be obtained without using panels, without panel orientation treatment, and without precise control of panel thickness, allowing use as a reflective paper white display. It is.

In addition, when manufacturing the optical panel of the present invention, conventional manufacturing processes can be used as is, and manufacturing is much easier than conventional optical display materials, so it is possible to significantly reduce costs. can.

Furthermore, the optical panel of the present invention can be used not only as a display material but also as a window panel, wall surface material, ceiling material, etc. whose light transmittance is controlled by an electric field, temperature, etc.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an optical panel using liquid crystal as a medium, showing an example of the present invention, and FIG. 2 is an applied voltage-transmittance characteristic of the panels obtained in Example 1 and Comparative Example 1. FIG. 1... Incident light, 2... Transmitted light, 3... Scattered light, 4
...Glass substrate, 5.Transparent electrode, 6.Liquid crystal molecules, 7.Polymer fine particles, 8.Power supply.

Claims (1)

[Claims] (1) An optical panel characterized in that polymer fine particles having an average particle diameter of 0.2 to 2 μm are dispersed in a medium with a variable refractive index, and the resultant is sandwiched between two substrates, at least one of which is transparent. .