JP2000347006A - Diffusing adhesive layer, optical member and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diffusion type adhesive layer having excellent balance between the transmittance of light and diffusion property while satisfying the adhesion treatment with excellent reliability so that a liquid crystal display device having excellent visibility such as brightness can be obtained. SOLUTION: The diffusion adhesive layer 1 consists of a light-transmitting adhesion layer 1 having dispersion of light-transmitting colorless particles and showing light- diffusing property. The light-diffusing property gives <=10% light diffusion rate which is defined by 100×I30/I10, wherein I30 and I10 are the intensity of transmitted light in the direction inclined by 10 deg. and 30 deg. from the perpendicular transmission direction when light enters perpendicular to the layer. The optical member is produced by forming the aforementioned diffusion adhesive layer on an optical material 2 having at least a polarizing plate or a phase difference plate. The liquid crystal display device is a reflection type having the diffusion adhesive layer between a liquid crystal cell and a polarizing plate. Thereby, the obtained light diffusion type adhesive layer has an excellent balance between the transmittance for light and diffusing property and can be subjected to adhesion treatment with high reliability, and the obtained reflection type liquid crystal display device has excellent brightness in the front direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diffusion adhesive layer suitable for forming a liquid crystal display device having an excellent balance between light transmittance and diffusivity and excellent visibility such as brightness, and an optical member thereof.

[0002]

2. Description of the Related Art Conventionally, there has been known a light-diffusion-type pressure-sensitive adhesive layer in which particles having different refractive indices are contained to impart light-diffusing properties so that the viewing angle of a liquid crystal display can be increased. However, when the diffusion angle is increased to increase the viewing angle while satisfying the bonding property that is excellent in reliability, the transmittance decreases due to an increase in backscattering, and the transmittance decreases when the transmittance increases. There is a problem in that it is difficult to balance the transmittance and the diffusivity.

[0003]

SUMMARY OF THE INVENTION The present invention provides a liquid crystal display device which can form a liquid crystal display device which is excellent in balance between light transmittance and diffusivity and excellent in visibility such as brightness while satisfying bonding processability which is excellent in reliability. The task is to develop a mold adhesive layer.

[0004]

The present invention comprises a light-transmitting pressure-sensitive adhesive layer having light-transmitting non-colored particles dispersed therein and exhibiting light-diffusing property, and the light-diffusing property of the light-transmitting pressure-sensitive adhesive layer in the vertical transmission direction of vertically incident light. On the other hand, when the intensity of the transmitted light in the direction inclined by 10 degrees or 30 degrees is the former I ₁₀ and the latter I ₃₀ , 100 × I ₃₀ / I
A diffusion pressure-sensitive adhesive layer characterized by being 10% or less based on the light diffusion rate defined by ₁₀ , and the diffusion pressure-sensitive adhesive layer provided on an optical material having at least a polarizing plate or a retardation plate. And a reflection type liquid crystal display device having the diffusion adhesive layer between the liquid crystal cell and the polarizing plate.

[0005]

According to the present invention, it is possible to obtain a light diffusion type pressure-sensitive adhesive layer which is excellent in balance between light transmittance and light diffusion based on the light diffusion rate and which can be bonded with high reliability. By using the liquid crystal display device, a liquid crystal display device having excellent visibility such as brightness, particularly a reflective liquid crystal display device having excellent brightness in the front direction can be obtained. Further, since the adhesive layer also serves as the light diffusion layer, the necessity of disposing a separate light diffusion plate can be avoided, and the members of the liquid crystal display device can be omitted to achieve a reduction in thickness and weight.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION A diffusion adhesive layer according to the present invention has a light transmitting property.
Light-transmitting material that exhibits light-diffusing properties by containing non-colored particles dispersed
And its light diffusing property is perpendicular to normal incident light.
In a direction inclined by 10 or 30 degrees to the transmission direction
The intensity of transmitted light is the former I₁₀, The latter I ₃₀And 10
0 × I₃₀/ I₁₀1 based on the light diffusion rate defined by
0% or less.

[0007] For forming the diffusion adhesive layer, an appropriate adhesive substance exhibiting light transmissivity can be used, and the type thereof is not particularly limited. Incidentally, examples of the adhesive substance include a rubber-based adhesive and an acrylic-based adhesive, a silicone-based adhesive and a vinylalkyl ether-based adhesive, a polyvinyl alcohol-based adhesive and a polyvinylpyrrolidone-based adhesive, a polyacrylamide-based adhesive and the like. Cellulose-based adhesives and the like can be mentioned.

[0008] The adhesive substance forming the adhesive layer is preferably one having excellent light transmittance, and in consideration of weather resistance and the like, an acrylic adhesive is particularly preferably used. The diffusion pressure-sensitive adhesive layer may be formed in a form superimposed on a transparent pressure-sensitive adhesive layer containing no uncolored particles for the purpose of adjusting the adhesive force, if necessary.

As the light-transmitting non-colored particles dispersed and contained in the diffusion adhesive layer, colorless and transparent appropriate ones can be used. Incidentally, examples thereof include silica, alumina, titania, zirconia, tin-based oxides, indium oxide, cadmium oxide, antimony oxide, and other conductive inorganic particles, and organic particles made of various crosslinked or uncrosslinked polymers. And so on.

The diffusion pressure-sensitive adhesive layer is formed by an appropriate method such as a method of rolling a mixture of a pressure-sensitive adhesive substance and light-transmissive uncolored particles by a calender roll method or a coating method by a doctor blade method or a gravure roll coater method. A method of attaching to a supporting base made of an optical element or the like by a method, or using a separator as the supporting base and forming a diffusion adhesive layer on the separator in accordance with the above and forming it on another supporting base made of an optical element or the like. An appropriate method such as a method of transferring to a material can be used.

In the above, in the present invention, it is necessary to form a diffusion adhesive layer having a light diffusivity of 10% or less by containing non-colored particles. When the light diffusivity exceeds 10%, the light diffusivity becomes excessive, and the front (vertical) when the reflective liquid crystal display device is visually recognized under illumination.
Poor brightness in direction. A preferable light diffusivity is from 1 to 9%, especially from 1.5 to 9 in view of the balance between the expansion of the viewing angle for good visibility due to the diffusivity of light and the brightness in the front direction.
8%, especially 2-7%.

[0012] Note that the light diffusivity, when is incident perpendicular light H to as diffusing adhesive layer 1 illustrated in FIG. 1, a direction inclined 10 degrees with respect to the vertical permeability direction I ₀ of the normally incident light H The intensity of the transmitted light at I _{10 is} 30 with _respect to I _0.
When the intensity of the transmitted light in degrees inclined direction is _{I 30,} is defined at _{100 × I 30 / I 10 (} %).

The non-colored particles which can be preferably used in view of the above-mentioned achievable light diffusivity and controllability of adhesive strength have an average particle diameter of 1 to 10 μm, preferably 9 μm or less, particularly 2 to 8 μm.
belongs to. Further, when the refractive index of the non-colored particles is n ¹ and the refractive index of the adhesive layer is n ² , the formula is 0.01 from the viewpoint of suppressing the backscattering and giving good diffusivity in the transmission direction.
^{<┃n 1 -n 2 ┃ <0.1} , especially ┃n ¹ -n ² ┃ <0.
09, in particular, a combination satisfying −0.08 <n ¹ −n ² <−0.01 is preferable.

The amount of the light-transmitting uncolored particles dispersedly contained in the diffusion adhesive layer is appropriately determined based on the above-mentioned light diffusivity and the like. (Solid content) 5 to 200 parts per 100 parts by weight
Parts by weight, in particular 10 to 150 parts by weight, in particular 15 to 100 parts by weight, of uncolored particles are used. The thickness of the diffusion pressure-sensitive adhesive layer can be determined according to the desired light diffusion rate or adhesive strength, but is generally 300 μm or less, preferably 1 to 200 μm, particularly 5 to 100 μm.

An optical member can be obtained as shown in FIG. 2 in which a diffusion adhesive layer 1 according to the present invention is provided on an optical material 2. In that case, one or two or more layers of the diffusion adhesive layer can be provided at one or both surfaces of the optical material, or at an appropriate position in the middle of the optical material composed of a laminate of a plurality of optical layers.

The optical material used for forming the optical member is not particularly limited, and for example, an appropriate material such as an optical material for forming a final object such as a liquid crystal display device can be used. Incidentally, examples of the optical material include a polarizing plate, a retardation plate, a backlight such as an elliptically polarizing plate or a light guide plate made of a laminate of the polarizing plate and the retardation plate, a reflection plate, a polarization separation plate, a liquid crystal cell or an anti-glare plate. And an optical path control plate such as a prism sheet or a lens sheet. Also, there is no particular limitation on the optical layers forming the above-mentioned laminate and the combination thereof, and examples thereof include a laminate of the above-described optical material.

When the optical material is an elliptically polarizing plate comprising a laminate of a polarizing plate and a retardation plate, the diffusion adhesive layer is provided on the side of the retardation plate to prevent variations in the optical characteristics of transmitted light. It is preferable to provide an adhesive layer having no diffusivity for lamination of the polarizing plate and the retardation plate. For forming the adhesive layer, an appropriate adhesive such as the above-mentioned tacky substance can be used.

In the above, an appropriate polarizing plate can be used. By the way, as examples, polyvinyl alcohol-based and partially formalized polyvinyl alcohol-based,
A film of a hydrophilic polymer such as a partially saponified ethylene-vinyl acetate copolymer, which is drawn by adsorbing iodine and / or a dichroic dye, dehydrated polyvinyl alcohol or dehydrochlorinated polyvinyl chloride A polarizing film made of a polyene oriented film or the like, such as a processed product, may be used.

Also, there can be mentioned a polarizing plate obtained by covering one or both sides of the above-mentioned polarizing film with a transparent protective layer or the like.
Such a transparent protective layer or the like may have various purposes such as reinforcing the polarizing film, improving heat resistance, and protecting the polarizing film from humidity and the like. The transparent protective layer can be formed as a resin coating layer, a resin film laminate layer, or the like.

On the other hand, any suitable retardation plate or retardation layer can be used, such as a quarter-wave plate, a half-wave plate, or a compensating retardation plate exhibiting other retardation characteristics. It may show an appropriate phase difference. The compensating retardation plate aims at compensating the wavelength dependence of birefringence and improving the visibility of the liquid crystal display device. The retardation plate may have an appropriate layer form such as a single-layered product or a multilayered product obtained by superposing two or more retardation layers.

The retardation plate and the like include, for example, carbonates, esters, imides and ethersulfones, sulfones and styrenes, vinyl alcohols and allylates, vinyl chlorides and vinylidene chlorides, acrylics and amides, It may be made of a suitable material such as a stretched film of a plastic such as an epoxy-based or cellulosic, polyolefin-based such as polyethylene or polypropylene, or an oriented film of a liquid crystal polymer.

The thickness of the retardation plate or the like can be appropriately determined according to the intended retardation or the like, but is generally from 1 to 500 μm, particularly from 5 to 400 μm, particularly from the viewpoint of flexibility and thinness. It is 10 to 300 μm. The retardation plate may be one in which the refractive index in the thickness direction is controlled, such as a film obtained by stretching or / and shrinking a polymer film while being bonded to a heat shrinkable film.

As a backlight such as a light guide plate, an appropriate one such as a sidelight type backlight known for a liquid crystal display device or the like can be used. The light guide plate is generally formed of a plate having a light incident side surface including an upper surface, a lower surface opposed thereto, and at least one end surface between upper and lower surfaces, and diffusing while transmitting incident light from the side surface in the plate. The light is emitted from one of the upper and lower surfaces of the plate due to reflection, diffraction, interference, or the like.

The light guide plate may be formed by, for example, providing a diffuser in the form of dots or stripes on the upper or lower surface of a transparent or translucent plastic plate made of an appropriate plastic as exemplified by the above retardation plate, It can be performed by a method of providing a structure, in particular, a concavo-convex structure composed of a prism array.

As the reflection plate or the reflection layer, an appropriate one can be used. By the way, as an example, a metal foil, a coating layer holding a metal powder with a binder, a reflection plate having the coating layer provided on a support substrate, a metal vapor deposition layer or the metal vapor deposition layer on the support substrate. And a reflection plate provided. Such a reflection plate or reflection layer may be integrated with the above-mentioned polarizing plate and formed as a reflection-type polarizing plate or the like.

As the polarization separation plate or the polarization separation layer, an appropriate one can be used. By the way, as an example, a device that separates natural light into reflected light and transmitted light consisting of linearly polarized light by Brewster angle through a multilayer film on which a dielectric thin film is superimposed, or a birefringent dielectric thin film Natural light is separated into reflected light and transmitted light consisting of linearly polarized light through a superposed multilayer film, or natural light is composed of left and right circularly polarized light by superimposing cholesteric liquid crystal layers and combinations of them with different reflection characteristics One that separates reflected light and transmitted light can be used.

An appropriate liquid crystal cell can be used. For example, liquid crystal cells using twisted nematic liquid crystal or super twisted nematic liquid crystal,
A non-twist type liquid crystal, a guest-host type liquid crystal in which a dichroic dye is dispersed in a liquid crystal, a liquid crystal cell using a ferroelectric liquid crystal, or the like may be used, and the driving method may be an appropriate method.

The above-mentioned optical path control plate is intended to control the direction of emitted light, and includes a lens sheet having a light condensing property in the front direction, a prism sheet for converting an oblique light path in the front direction, and the like. An appropriate one can be used.

The above-described diffusion adhesive layer and optical member according to the present invention can be preferably used for forming various devices such as a reflection type, a transmission type, and a reflection / transmission type liquid crystal display device.
In the application, one or two or more diffusion adhesive layers according to the present invention can be arranged. When forming a device or the like, a diffusion layer other than the diffusion adhesive layer according to the present invention may be provided.

When the above-mentioned reflection type liquid crystal display device is formed, the diffusion adhesive layer and the optical member according to the present invention are preferably arranged on the viewing side of the liquid crystal cell. It is preferable that the optical layers are arranged as a structure in which adjacent optical layers are bonded between the plates.

As shown in FIG. 2, when the diffusion adhesive layer 1 is exposed on the surface, it may be temporarily coated with a separator 3 or the like as shown in the drawing until it is adhered to the adherend. preferable. The separator can be obtained, for example, by a method in which a thin sheet made of paper, a plastic film, or the like is subjected to a surface treatment with an appropriate release agent such as a silicone-based or long-chain acrylic-based material, if necessary.

[0032]

Example 1 A light-transmitting uncolored particle having a refractive index (n ¹ ) of 1.43 and an average particle size of 4 μm was mixed with an acrylic pressure-sensitive adhesive and applied on a separator to obtain a refractive index. (N ² ) A diffusion adhesive layer containing the above-mentioned non-colored particles dispersed in a ratio of 30% by weight in a transparent acrylic adhesive layer having a thickness of 1.47 and a thickness of 25 μm was obtained.

Comparative Example According to Example 1, light-transmissive uncolored particles having a refractive index (n ¹ ) of 1.63 and an average particle diameter of 6 μm were converted to a refractive index (n ² ).
A diffusion adhesive layer having a dispersion of 15% by weight was obtained in a transparent acrylic adhesive layer having a thickness of 1.47 and a thickness of 25 μm.

Evaluation Test The light diffusivity defined in the present invention of the diffusion adhesive layer obtained in Example 1 and Comparative Example was examined, and the diffusion adhesive layer was adhered to a specular reflection plate and diffused light was incident. , Its front (normal)
The brightness in the direction was compared with the reflection intensity of the standard white plate. The diffusion adhesive layer was strongly adhered to the specular reflection plate.

The results are shown in the following table. Light diffusion ratio (%) to standard white plate ratio Example 13 2.2 times Comparative example 12 1.5 times

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of calculating a light diffusivity.

FIG. 2 is a cross-sectional view of an example of an optical member.

[Explanation of symbols]

 1: diffusion adhesive layer 2: optical material 3: separator

Claims (4)

[Claims] 1. A light-transmissive pressure-sensitive adhesive layer that exhibits light-diffusing properties by dispersing and containing light-transmissive uncolored particles, and has a light-diffusing property of 10 degrees or 30 degrees with respect to the vertical transmission direction of vertically incident light. Wherein the intensity of transmitted light in the direction inclined at an angle of ₁₀ degrees is 10% or less based on the light diffusivity defined by 100 × I ₃₀ / I ₁₀ when the intensity of the transmitted light is the former I ₁₀ and the latter I _30. . 2. The diffusion pressure-sensitive adhesive layer according to claim 1, wherein the light diffusivity is 2% or more and the average particle size of the uncolored particles is 1 to 10 μm. 3. An optical member comprising the diffusion adhesive layer according to claim 1 or 2 provided on an optical material having at least a polarizing plate or a retardation plate. 4. A reflective liquid crystal display device comprising the diffusion adhesive layer according to claim 1 between a liquid crystal cell and a polarizing plate.