JPH0459605B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a non-reflective polarizing plate with excellent display clarity and a method for manufacturing the same.

Generally, a polarizing plate is a polarizing element (polarizing film) made by adsorbing iodine or dye to polyvinyl alcohol (PVA) and a protective substrate mainly made of cellulose plastic such as triacetylcellulose, diacetylcetylycellulose, acetate butyrate cellulose, etc. It is configured by pasting it on.

This polarizing plate is mounted on a liquid crystal display device and is widely used in various industrial fields to display numerical values, characters, symbols, patterns, and the like. That is,
The liquid crystal polarizing plate is attached to the upper and lower surfaces of the liquid crystal cell. In general, in the transmission type, the top surface is a surface with good light transmission without unevenness, or a polarizing plate that has been subjected to anti-reflection processing to reduce surface reflection light. The lower polarizing plate is a transmissive type with good transparency like the above, or a polarizing plate with a semi-transparent reflector whose surface has extremely low light transmittance by vapor deposition of fine particles on the surface, whereas a reflective type has a polarizing plate with a semi-transparent reflector that completely transmits light. A polarizing plate is used in combination with a vapor-deposited reflective plate made of aluminum foil or aluminum, etc.

However, most of the cellulose plastic protective substrates currently used for the outer layer of polarizing plates have smooth surfaces, so there is little diffuse reflection on the surface, and external light is specularly reflected, making it difficult to read the display. is the current situation.

Conventionally, methods for preventing the reflection of external light on such transparent optical members include (1) forming an antireflection film by vacuum-depositing particulate inorganic materials such as silicon dioxide (SiO ₂ ), glass, zirconium oxide, etc. on the surface of the member; (2) A method in which a transparent resin mixed with a light-diffusing powder such as silica, titanium oxide, or aluminum oxide is melted or dissolved in a solvent and coated to form a particle film of these inorganic substances on the surface of the member. (3) ) A method using the so-called casting method in which plastic is injected and polymerized into a molded glass whose glass plate surface has been eroded with hydrogen fluoride to form fine irregularities; (4) Powder of diamond sand, silica, glass, etc. is directly applied to the surface of the plastic plate. A method is known in which fine irregularities are formed by a so-called sandblasting method.

However, methods (1) and (2) above have poor durability and resistance to heat and humidity, and the antireflection film or particle film formed on the surface of the base material tends to peel off over time, so the range of use is limited, and the use of polarizing plates is limited. It is unsuitable for processing the protection plate of the protection board. The casting method (3) is limited to plastics that can be polymerized and cast, such as acrylic resin, and cannot be applied to cellulose resins used for the protective substrate of polarizing plates.

In addition, the method (4) of directly sandblasting the plastic surface has the problem that the unevenness formed on the surface is rough and the light is diffused too strongly, reducing the resolution of the display board and making it impossible to obtain the desired antireflection coating. .

In view of the problems of conventional antireflection methods for plastic protective plates, the present inventors developed a method for forming a highly durable antireflection layer on polarizing plates that mainly use cellulose plastic as a protective substrate. We conducted various studies on the following.

As a result, the surface of the metal roll is embossed using a known sandblasting method or other method in which diamond sand, silica powder, etc. are injected to form an irregular, finely uneven surface on the surface.The metal roll is combined with a smooth elastic roll. The embossed surface of the protective substrate formed by contacting the plastic protective substrate surface of the polarizing plate with a metal roll between these two rolls and passing the polarizing plate under pressure under heated and pressurized conditions is durable. We have discovered that this is the most excellent antireflection layer for a certain polarizing plate.

However, a drawback of this embossing method is that even if the degree of meshing of the embossing formed on the surface of the metal roll is varied and a fairly fine embossed surface is formed, light diffusion on the surface of the protective substrate remains. It is strong and has the disadvantage that the display on the display becomes blurry and unclear.

The present inventors conducted further research to solve this problem, and found that the surface of the protective substrate of the polarizing plate, which was embossed using a metal roll with an uneven rough surface, was treated with a solvent to display the display material. The present invention was completed based on the discovery that the sharpness of images can be significantly improved.

That is, the present invention is a polarizing plate that is most often used on the top surface of a liquid crystal cell, especially for use in automobiles, aircraft, agricultural machinery, and other industrial equipment that require durability. The present invention has been made for the purpose of providing a polarizing plate having an external light reflecting surface with excellent heat and humidity resistance and high display clarity, and a method for manufacturing the same.

The high-definition non-reflective polarizing plate of the present invention is a polarizing plate formed by pasting a protective substrate mainly made of cellulose plastic on one or both sides of a polarizing element.
The protection substrate is characterized in that a rough surface with fine irregularities is formed by embossing, and further, a portion of the surface layer of the rough fine rough surface is dissolved with an organic solvent.

In addition, the manufacturing method includes a polarizing plate in which a protective substrate mainly made of cellulose plastic is attached to one or both sides of a polarizing element, and the protective substrate is heated and pressed with a metal roll having a roughened surface. After transferring the finely uneven surface to the surface of the protective substrate, the protective substrate is immersed for a short time in an organic solvent that dissolves the protective substrate, and then washed with an insoluble agent for the protective substrate and dried.

The present invention will be explained in detail below.

First, the embossing process on the plastic protective substrate of the polarizing plate is carried out as follows.

That is, the so-called sandplast method or photoetching method, in which hard fine inorganic powder such as diamond sand or silica powder is injected at high speed onto the surface of a metal roll made of materials such as difficult steel, semi-hard steel, and hard steel, or other machines. A metal roll (hereinafter also simply referred to as a metal roll) is manufactured by forming an irregular, finely uneven rough surface on the circumferential surface using a conventional method and performing embossing.

Using an embossing device in which this metal roll is combined with a smooth elastic roll such as a rubber roll or a cotton roll, the surface of the protective substrate of the polarizing plate is subjected to embossing treatment under heat and pressure. In this case, the desired antireflection layer cannot be formed by embossing using an engraved roll with a regular uneven pattern.

The heating and pressure conditions for embossing processing vary depending on the type of protective substrate, but when using a protective substrate made of cellulose acetate plastic, the heating temperature of the metal roll is 100 to 150°C.
℃, preferably 125-135℃, press pressure 60-300
2 to 30 kg/cm between the press-welded rolls.
The polarizing plate is passed through the protective substrate surface facing the metal roll surface at a speed of m/min.

In this case, the metal roll is heated by a known means such as an electric heating method, a heating medium circulation heating method, a heating medium closed induction heating method, etc., and the pressure is applied between the metal roll and the metal roll. The distance between the elastic rolls can be adjusted pneumatically or hydraulically.

Through this embossing process, the finely uneven rough surface of the metal roll is transferred onto the protective substrate surface of the polarizing plate.

This forms a durable surface that does not reflect external light on the protective substrate surface, but when reading the display by attaching this non-reflection polarizing plate to a liquid crystal display device, the clarity of the display may be affected. The drawback remains that it is bad.

In the present invention, in order to eliminate this drawback, the embossed polarizing plate is further treated with a solvent to dissolve a part of the surface layer of the finely uneven rough surface formed on the protective substrate surface.

The organic solvent used for this solvent treatment has good solubility for the protective substrate, and it is necessary to perform a cleaning process using a solvent (insoluble solvent) that does not attack the protective substrate as a post-processing process. It is desirable that the organic solvent be compatible with the dissolving solvent. For example, N-methyl-2-pyrrolidone,
Organic solvents such as N,N-dimethylformamide, cyclohexanone, methyl formate, methyl acetate, triacetin, acetone, dioxane, methylene chloride, and tetrachloroethane can be suitably used. or,
These organic solvents can be used alone.

However, in order to slowly progress the dissolution of the protective substrate, it is preferable to use a phase solution of an organic solvent and an insoluble solvent. The blending ratio of the organic solvent and the insoluble solvent can be appropriately selected in the range of 60 to 80:40 to 20 (Vol%).

Water is generally used as an insoluble solvent for the protective substrate, but other alcohols such as methyl alcohol, ethyl alcohol, and isopropyl alcohol,
Examples include organic solvents such as carbon tetrachloride, ethylene tetrachloride, carbon disulfide, ethylene glycol, and freon.

Next, the polarizing plate that has been embossed as described above is subjected to a dipping treatment in the above-mentioned solution containing an organic solvent and an insoluble solvent. The conditions for this immersion treatment can be set in various ways depending on the combination of the type of protective substrate, type of organic solvent or insoluble agent, blending ratio, immersion temperature, immersion time, etc., and cannot be unconditionally specified. When the temperature is 30 to 40°C, good results can be obtained with short immersion of about 20 seconds to 6 minutes.

Next, following the above-mentioned solvent immersion treatment, organic solvent cleaning and drying treatment are performed. As the cleaning liquid, the above-mentioned insoluble agents can be used, but it is especially economical and common to use water as the cleaning liquid.

As a cleaning method, immersion cleaning, shower cleaning, etc. can be used, but in order to prevent excessive dissolution of the protective substrate by the organic solvent, it is necessary to quickly remove the organic solvent adhering to the substrate. Shower cleaning is suitable for this purpose. Drying after washing is accomplished in the case of water washing by passing through a blow dryer at a temperature below about 60°C, preferably about 50°C, for about 10 minutes.

The processing of the present invention described above is not limited to polarizing plates formed by pasting polarizing elements on a protective substrate. The polarizing plate of the present invention may be manufactured by attaching the above to a polarizing element as an outer layer.

As explained above, according to the present invention, there is no difficulty in reading the display due to specular reflection of external light.
A non-reflective polarizing plate with excellent durability and heat-and-moisture resistance can be obtained. Furthermore, the blurring of the display accompanying the non-reflective polarizing plate is removed, and a highly clear non-reflecting polarizing plate can be provided. Furthermore, the method for manufacturing a high-definition non-reflective polarizing plate of the present invention includes heating and press-bonding the protective substrate of the polarizing plate with a metal roll having a rough surface with fine irregularities,
After transferring the finely uneven rough surface to the surface of the protective substrate, immersing the protective substrate in an organic solvent for a short time to dissolve it;
This method is then washed and dried using a solvent that does not dissolve the protective substrate, so it has the advantage of being able to continuously mass-produce durable, high-definition, non-reflective polarizing plates with relatively simple processing operations. have

Example 1 An embossed roll was manufactured by spraying 180 mesh of Diamond Sand onto a metal roll made of semi-hard steel (diameter 180 mmφ x width 675 mm) to form a fine irregular roughened surface on its surface. Using an embossing device that combines an embossing roll and an elastic hard rubber roll (diameter 300 mmφ x width 650 mm), the surface temperature of the metal roll was heated to 120°C, and the press pressure between the rollers was adjusted to 100 kg/cm. Back, width 525mm, thickness 180μ,
The sample was passed through a polarizing plate (manufactured by Sanritsu Electric Co., Ltd.) whose protective substrate was made of triacetyl cellulose at a speed of 10 m/min. As a result, the protective air was uniformly transferred to the surface of the embossing roll having fine irregularities and roughness, and a non-reflective polarizing plate with excellent appearance and quality was obtained.

When this was installed in a liquid crystal display device, the diffusivity of externally reflected light was extremely good and the antireflection effect against the polarizing plate was sufficient, but the display lacked sharpness and appeared a little blurry. was undesirable.

Therefore, the obtained non-reflective polarizing plate was mixed with N-methyl-2-pyrrolidone as an organic solvent and water as an insoluble solvent at a temperature of 70:30 (Vol%).
After being passed through a solution at 25°C for 3 minutes, it was washed with water under a shower, drained, and then passed through a blow dryer at 50°C for 10 minutes to dry. As a result, a beautiful non-reflection polarizing plate having a very fine uneven surface on the protective plate surface was obtained.

When this non-reflective polarizing plate was attached to a liquid crystal display device in the same manner as described above, it was verified that the non-reflective polarizing plate was excellent in the diffusion of reflected light and the clarity of the display.

Example 2 The embossed non-reflective polarizing plate obtained in Example 1 was mixed with N,N-dimethylformamide as an organic solvent and water as an insoluble solvent in a ratio of 60:40, respectively.
After passing through a solution at a temperature of 40° C. mixed with (Vol%) for 2 minutes, it was washed with water and dried under the same conditions as in Example 1. As a result, a non-reflective polarizing plate excellent in both the diffusivity of externally reflected light and the clarity of display was obtained.

Claims (1)

[Scope of Claims] 1. In a polarizing plate formed by pasting a protective substrate mainly made of cellulose plastic on one or both sides of a polarizing element, a finely uneven rough surface is formed on the surface of the protective substrate by embossing, Furthermore, a high definition non-reflective polarizing plate characterized in that the surface layer of the finely uneven rough surface is partially dissolved by an organic solvent. 2 A polarizing plate formed by pasting a protective substrate mainly made of cellulose plastic on one or both sides of a polarizing element, which is protected by heating and pressing the protective substrate with a metal roll having a rough surface with fine irregularities. A high-definition, non-reflective method characterized by transferring a finely uneven surface onto a substrate surface, immersing the protective substrate in an organic solvent for a short period of time, and then cleaning and drying the protective substrate using a solvent that does not dissolve the protective substrate. A method of manufacturing a polarizing plate. 3. The manufacturing method according to claim 2, which is carried out using a phase solution in which a solvent that does not dissolve the protective substrate is mixed with an organic solvent that dissolves the protective substrate. 4. Mixing ratio of organic solvent and insoluble solvent is 60~
80:40-20 (Vol%) manufacturing method according to claim 3.