JP2000075134A - Light diffusion polarizing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a polarizing plate which allows the formation of a liquid crystal display device making it possible to lower bulk in spite of omission of a light diffusion sheet and substantially preventing the generation of interference fringes in spite of control of the optical path via a condenser sheet, does not damage the device in site of the arrangement thereof on the condenser sheet and does give rise to a sticking problem. SOLUTION: This light diffusion polarizing plate has a light diffusion layer 1 formed in tight contact with the one surface of the polarizing plate 2 and has a cloud value >=60%. The light diffusion layer 1 consists of a resin layer which contains porous amorphous particles and spherical particles dispersed therein, has a thickness above the average diameter of these particles and has a fine rugged structure on the outside surface. As a result, the display device of good visibility which is of a thin type and substantially prevents the generation of the interference fringes may be formed. The porous amorphous particles are preferably silica particles having a grain size of 1 to 10 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light diffusing polarizing plate suitable for forming a thin liquid crystal display device with good visibility by preventing the occurrence of interference fringes by a light-collecting sheet.

[0002]

2. Description of the Related Art There is known a liquid crystal display device in which liquid crystal cells are sequentially disposed on a side light type light guide plate via a light condensing sheet, a light diffusion sheet, a polarizing plate or an elliptically polarizing plate. Such an arrangement structure controls the optical path of light emitted from the light guide plate by a single-layer or multilayer light-condensing sheet made of a prism sheet or the like, and the optical path control light interferes with the pixels of the liquid crystal cell to generate interference fringes such as moire. In this case, the light is diffused by a light diffusion sheet and introduced into a polarizing plate, and the object is to improve the viewing angle characteristics of a liquid crystal display device. However, in such a configuration, the number of stacked sheets and the like is large, and there is a problem that the display device is bulky due to the interposition of an adhesive layer for fixing the sheets and the like, and a reduction in thickness is required.

The present inventors believe that the method of reducing the thickness of a sheet or the like has a limit from the point of strength and the like, and cannot achieve the above-mentioned reduction in thickness. The antiglare polarizing plate to be arranged was arranged on the light source side of the liquid crystal cell, and an attempt was made to reduce the thickness essentially by omitting the light diffusion sheet on the condensing sheet.

However, it has been found that when such an anti-glare polarizing plate is arranged on a light-collecting sheet, there is a problem that the light-collecting sheet is damaged due to surface irregularities of the anti-glare polarizing plate. As described above, the light-collecting sheet is intended to control the optical path, and damage such as surface flaws becomes a scattering point and the like, which makes the optical path control impossible and is fatal. Simply preventing damage can be achieved by smoothing the surface of the anti-glare polarizing plate, but in that case, it causes problems such as insufficient diffusion ability and sticking due to close contact with the light-collecting sheet. Problems are also induced.

[0005]

According to the present invention, it is possible to form a liquid crystal display device which can reduce the bulk by omitting a light diffusing sheet and hardly cause interference fringes even when an optical path is controlled via a light condensing sheet. It is an object of the present invention to develop a polarizing plate that does not damage the light-collecting sheet even when it is arranged on the light-collecting sheet and does not cause sticking.

[0006]

According to the present invention, there is provided a polarizing plate having a light diffusion layer adhered to one side of a polarizing plate and having a haze value of 60% or more, wherein the light diffusion layer contains porous amorphous particles and spherical particles dispersedly. In addition, the present invention provides a light-diffusing polarizing plate comprising a resin layer having a thickness not less than the average diameter of these particles and having a fine uneven structure on the outer surface.

[0007]

According to the present invention, the light diffusion layer adhered to the polarizing plate shows the necessary diffusion effect of incident light such as light path control light by the light-collecting sheet without greatly changing the control light path by the light-collecting sheet. Therefore, the arrangement of a separate light diffusing sheet can be omitted by preventing the occurrence of interference fringes, and the adhesive layer can be omitted because it is in close contact with the polarizing plate, so that the bulk can be reduced. It is possible to form a display device that is difficult and has good visibility. Further, even if it is arranged on the light-collecting sheet, it is not damaged and the sticking problem does not occur in the fine uneven structure on the surface.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION A light-diffusing polarizing plate according to the present invention has a light-diffusing layer adhered to one side of a polarizing plate and has a haze value of 60% or more. Having a thickness equal to or greater than the average diameter of the particles containing dispersed spherical particles,
In addition, it is made of a resin layer having a fine uneven structure on the outer surface. Examples thereof are shown in FIGS. Reference numerals 1 and 3 are light diffusion layers, and 2 is a polarizing plate.

Any suitable polarizing plate can be used as a supporting base of the light diffusion layer, and the type thereof is not particularly limited. By the way, for example, hydrophilic polymer films such as polyvinyl alcohol-based films, partially formalized polyvinyl alcohol-based films, ethylene-vinyl acetate copolymer-based partially saponified films, and dichroic dyes such as iodine and dichroic dyes Stretched by adsorbing substances,
Examples of the polarizing film include dehydration products of polyvinyl alcohol and dehydrochlorination products of polyvinyl chloride. The thickness of the polarizing film is generally 5 to 80 μm,
It is not limited to this.

Further, as shown in FIG.
A transparent protective layer 2 comprising a polymer coating layer or a film laminating layer on one or both sides for the purpose of protection such as water resistance.
There are also those provided with 1, 23 and the like. For forming the transparent protective layer, an appropriate material such as a transparent polymer can be used, but a material having excellent transparency, mechanical strength, heat stability, moisture shielding property and the like can be preferably used. In many cases, the transparent protective layer is preferably as small as possible in optical anisotropy such as retardation. The thickness of the transparent protective layer is generally from 10 to 300 μm, but is not limited thereto.

The polymer forming the transparent protective layer is, for example, a polyester polymer such as polyethylene terephthalate or polyethylene naphthalate, a cellulose polymer such as cellulose diacetate or cellulose triacetate, a polycarbonate polymer or a PMM.
Examples include acrylic polymers such as A, and styrene polymers such as polystyrene and acrylonitrile / styrene copolymer (AS resin).

Further, olefin polymers such as polyethylene and polypropylene, polyolefins having a cyclo or norbornene structure, and ethylene / propylene copolymers, vinyl chloride polymers, amide polymers such as nylon and aromatic polyamide, imide polymers, and the like. Sulfone polymer, polyether sulfone polymer, polyether ether ketone polymer, polyphenylene sulfide polymer, vinyl alcohol polymer, vinylidene chloride polymer, vinyl butyral polymer, arylate polymer, polyoxymethylene polymer, epoxy polymer And a blend of the above-mentioned polymers are also examples of the polymer forming the transparent protective layer.

The light-diffusing polarizing plate according to the present invention has a light-diffusing layer on one side of the polarizing plate, and has a haze value of 60% or more based on the light transmission side when perpendicular light is incident on the reference plane. It shows the characteristics. If the haze value is less than 60%, the diffusion effect is poor, and it is difficult to prevent the occurrence of interference fringes when the optical path control light is incident on the light-collecting sheet.

Therefore, in the light diffusion layer of the present invention, the light path control light by the light-collecting sheet is not diffused at a large angle, and its directivity is maintained as much as possible, and the generation of interference fringes is effectively prevented. Characteristics are required. From this point, the haze value is preferably 65% or more, more preferably 70% or more, especially 75%.
That is all.

In the above, it is assumed that a degree of polarization of 80% or more, especially 85% or more, especially 90% or more based on a polarizing plate is achieved, rather than achieving a bright display in a liquid crystal display device or the like. It is preferable that the light-diffusing polarizing plate exhibit as high a light transmittance as possible. In particular, it is preferable that the transmittance of light incident perpendicular to the reference plane be 35% or more, particularly 40% or more.

The reference plane is assumed based on the entire light-diffusing polarizing plate in which the uneven structure on the surface of the light-diffusing layer and the variation in the layer thickness are leveled, as exemplified by the imaginary line H in FIG. Means the plane to be set. In addition, the haze value is defined as Tt (total light transmittance) of the ratio of the transmitted light of the polarizing plate to the incident light, and Tp (parallel light transmittance) of the transmitted light, which is parallel to the incident light. ), The ratio of diffused light is defined as Td / Tt, where Td is the diffused light transmittance = Tt−Tp.

The light diffusion layer for imparting the above-mentioned diffusion properties such as haze value is provided on one side of the polarizing plate for the purpose of eliminating the necessity of providing a separately arranged light diffusion sheet as described above and achieving a thin thickness. For example, a method of coating and forming a resin layer containing porous irregular particles and spherical particles dispersedly on the transparent protective layer 21 of the polarizing plate 2 as shown in FIG. Can be performed.

The light diffusion layer provided in close contact can be formed as a resin layer instead of the transparent protective layer or as a transparent protective layer, as in the light diffusion layer 3 illustrated in FIG. In this case, a resin film in which porous amorphous particles and spherical particles are dispersed and contained in advance may be bonded to a polarizing film or the like via an adhesive layer. The light diffusion layer may be formed as an overlapping layer of a resin layer by two or more types of formation methods.

The method of forming the light diffusion layer, which is preferable from the viewpoints of the above-mentioned properties of imparting diffusion characteristics, adhesion and ease of thin film processing, is a method using the above-mentioned coating resin layer, that is, for example, a method in which a resin solution is made of a porous amorphous material. In this method, particles and spherical particles are dispersed and contained, and the resulting mixture is coated on a polarizing plate by an appropriate method such as a doctor blade method or a gravure roll coater method to form a coating film.

The light diffusing layer to be formed is a resin layer containing dispersed and irregular porous particles and spherical particles, having a layer thickness not less than the average diameter of the particles used, and having a fine uneven structure on the outer surface. It consists of Thereby, the object of the present invention can be achieved comprehensively. When the porous irregular shaped particles or the spherical particles are used alone, the layer thickness is smaller than the average diameter of the particles used, or the outer surface is smooth, the haze (prevention of interference fringes) or damage to the light-collecting sheet is prevented. Prevention of sticking cannot be achieved.

The fine uneven structure on the outer surface of the resin layer may be based on the contained particles, may be a structure reflecting the uneven structure on the surface of the polarizing plate, or may be a combination thereof. Irregularities on the polarizing plate surface include, for example, sandblasting or embossing of the transparent protective layer, surface roughening treatment by chemical etching, craze generation treatment by applying mechanical stress or solvent treatment, and shape transfer treatment by an irregular mold. It can be performed by an appropriate method.

As the resin forming the resin layer, an appropriate resin such as the polymer exemplified in the above-mentioned transparent protective layer can be used, but an ultraviolet curing resin is preferably used. According to this, the light diffusion layer composed of the particle-containing ultraviolet-curable resin layer can be efficiently formed by a simple processing operation in the curing treatment of the coating layer by ultraviolet irradiation.
It is also easy to form an ultraviolet-curable resin layer on the surface of the roughened transparent protective layer and reflect the surface irregularities of the transparent protective layer on the surface.

Examples of the UV-curable resin include polyester-based, acrylic-based, urethane-based and amide-based resins.
An appropriate compound such as a compound obtained by compounding an ultraviolet polymerization initiator with a monomer, oligomer, or polymer capable of forming a resin such as a silicone-based or epoxy-based resin and forming a resin layer by a curing treatment by ultraviolet irradiation is used. sell.

The UV-curable resin which can be preferably used is, for example, an acrylic monomer or oligomer having 3 to 6 UV-polymerizable functional groups as a component, such as adhesion and transparency to a polarizing plate surface to be provided. In the case where particles are contained, they have excellent dispersibility and the like.

The particles contained in the resin layer as described above include:
At least two kinds of porous irregular-shaped particles and spherical particles are used. As the porous amorphous particles, for example, appropriate particles such as inorganic particles such as porous silica and porous alumina obtained by a treatment such as pulverization and reaggregation can be used. Porous amorphous particles that can be preferably used from the viewpoint of imparting the above-mentioned diffusion characteristics are silica particles having a particle diameter of 1 to 10 μm.

Examples of the spherical particles include inorganic particles which may be conductive, such as titania, zirconia, calcium oxide, tin oxide, indium oxide, cadmium oxide, antimony oxide, and polymethyl methacrylate (PMM).
Appropriate materials such as crosslinked or uncrosslinked organic particles composed of various polymers such as A) and polyurethane can be used.

The spherical particles which can be preferably used are those which have excellent sphericity and transparency and do not dissolve in a UV-curable resin before forming a cured film. Spherical particles that can be preferably used from the viewpoint of imparting property and dispersibility of the above-described diffusion properties,
It is a spherical particle having an average particle diameter of 30 μm or less, preferably 0.1 to 15 μm, particularly 0.5 to 10 μm, particularly an organic spherical particle.

The proportion of the porous irregular-shaped particles to the spherical particles can be determined as appropriate.
5 to 45 parts by weight, preferably 10 to 40 parts by weight, particularly 15 to 35 parts by weight, per 0 parts by weight of the porous amorphous particles are used.

The thickness of the light diffusion layer composed of the resin layer is set to be equal to or larger than the average diameter of the particles used. Thus, it is possible to prevent the optical layers, such as the light-collecting sheet, which are superposed, from being damaged, while achieving the above-described diffusion characteristics and the like. The thickness of the light diffusion layer is
Although it may be appropriately determined in the range of the average diameter or more, generally 100 μm or less, particularly 50 μm or less for the purpose of thinning,
In particular, it is 30 μm or less.

As shown in FIG. 2, the light diffusion polarizing plate may be provided with an adhesive layer 4 on one side or both sides as needed. The purpose of such an adhesive layer is to adhere the light diffusion polarizing plate to another member such as a liquid crystal cell or a light condensing sheet. The adhesive layer can be formed with an appropriate adhesive such as an acrylic-based, rubber-based, or silicone-based adhesive or a hot-melt-based adhesive, and preferably has excellent transparency and weather resistance.

The light-diffusing polarizing plate according to the present invention can be used for various conventional applications such as display devices. In particular, as in a liquid crystal display device, pixels are arranged at predetermined intervals, and interference fringes such as moiré are easily generated by light path control light or the like through a light-collecting sheet. Therefore, it can be preferably used for a display device in which an increase in thickness is not desirable.

[0032]

EXAMPLE 1 20 parts of spherical resin particles having an average particle diameter of 4 μm were added to an ultraviolet-curable resin composed of 100 parts (parts by weight, the same applies hereinafter) of an ultraviolet-curable urethane acrylate monomer and 3 parts of a benzophenone-based photopolymerization initiator. And 5 parts of porous amorphous silica particles having a particle size of 1 to 10 μm, and adding a solvent for adjusting the viscosity to a solid content concentration of 50% by weight, followed by mixing with a high-speed stirrer,
The mixture was applied to one side of a polarizing plate having a 50 μm-thick triacetylcellulose film bonded to both sides of an iodine-based polyvinyl alcohol-type polarizing film via a polyvinyl alcohol-based adhesive layer with a bar coater, and the solvent was evaporated. Irradiation and curing treatment were performed to form a light diffusion layer having a fine surface unevenness composed of a resin layer having a thickness of 10 μm to obtain a light diffusion polarizing plate.

When vertical light was incident on the light diffusing polarizing plate, the total light transmittance was 41%, and the haze value on the light transmitting side was 81%. The light-diffusing polarizing plate is placed on the sidelight type light guide plate via two light-condensing sheets made of a prism sheet, and a liquid crystal cell and a polarizing plate are placed on the light-diffusing polarizing plate. When the display panel was formed, it was possible to obtain a panel which was excellent in the clarity and brightness of the screen and thinner than the conventional panel. Also, no damage occurred to the light-collecting sheet.

Comparative Example 1 A light-diffusing polarizing plate was obtained by forming a light-diffusing layer having a fine surface unevenness according to Example 1 except that the amount of the spherical resin particles used was changed to 10 parts. When perpendicular light was incident on the polarizing plate, the total light transmittance was 42% and the haze value on the light transmission side was 53%. When a liquid crystal color display panel without a light diffusing sheet was formed using the light diffusing polarizing plate according to Example 1, the light collecting sheet was not damaged, but the sharpness of the screen was inferior and it was difficult to see. .

Comparative Example 2 The amount of the spherical resin particles used was 10 parts, and the solid content concentration was 20 parts.
A light-diffusing polarizing plate was obtained by forming a light-diffusing layer having a surface unevenness composed of a resin layer having a thickness of 3 μm in the same manner as in Example 1 except that the content was changed to wt%. When perpendicular light was made incident on this light diffusing polarizing plate, its total light transmittance was 43%, and the haze value on the light transmission side was 7%.
It was 0%. However, when a liquid crystal color display panel without a light diffusion sheet was formed using the light diffusion polarizing plate according to Example 1, the sharpness of the screen was good, but the light collection sheet was damaged.

Comparative Example 3 A light-diffusing polarizing plate was obtained by forming a light-diffusing layer having a fine irregular surface structure according to Example 1, except that 25 parts of spherical resin particles were used and no porous amorphous silica particles were added. Was. When perpendicular light was incident on this light diffusing polarizing plate, the total light transmittance was 42% and the haze value on the light transmitting side was 44%. When a liquid crystal color display panel without a light diffusing sheet was formed using the light diffusing polarizing plate according to Example 1, the light-collecting sheet was not damaged, but the sharpness of the screen was poor and it was difficult to see. .

Comparative Example 4 A light-diffusing polarizing plate was obtained by forming a light-diffusing layer having a fine irregular surface structure according to Example 1, except that 25 parts of porous amorphous silica particles were used and no spherical resin particles were added. Was. When perpendicular light was incident on this light diffusing polarizing plate, the total light transmittance was 43% and the haze value on the light transmitting side was 67%. When a liquid crystal color display panel without a light diffusion sheet was formed using the light diffusion polarizing plate according to Example 1, the sharpness of the screen was good, but the light collection sheet was damaged.

[Brief description of the drawings]

FIG. 1 is a sectional view of an embodiment.

FIG. 2 is a cross-sectional view of another embodiment.

[Explanation of symbols]

 1,3: light diffusion layer 2: polarizing plate 21, 23: transparent protective layer 22: polarizing film 4: adhesive layer

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masamori Masada 1-2-1, Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation F-term (reference) 2H042 BA02 BA20 2H049 BA02 BB23 BB43 BB63 BC22 2H091 FA08X FA08Z FA31X FA31Z FD14 GA16 GA17 LA02 LA16 LA21 4F100 AA20B AJ06 AK01B AK21 AK21G AK25 AK51 BA02 CA02 DD07B DE01B DE04B DJ00B EH46 EJ08 EJ54 GB41 JB14 JN02B JN10A JN30B

Claims (2)

[Claims] 1. A polarizing plate having a light diffusion layer in close contact with one side thereof and having a haze value of 60% or more, wherein said light diffusion layer contains porous irregular particles and spherical particles dispersedly and comprises A light-diffusing polarizing plate comprising a resin layer having a thickness not less than the average diameter and having a fine uneven structure on an outer surface. 2. The light diffusing polarizing plate according to claim 1, wherein the porous irregular shaped particles are silica particles having a particle size of 1 to 10 μm.