JP2005309219A - Polarizer protection film and polarizing plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarizer protection film which is free from the occurrence of cracking due to deformation stress of a polarizer and has excellent durability and dimensional stability, and a polarizing plate. <P>SOLUTION: The polarizer protection film is constituted by laminating at least one layers shrunk by drying or curing on the surface on one side and is composed of a cyclic olefinic resin of ≥3 cm in curling height. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a polarizer protective film and a polarizing plate excellent in durability that can be suitably used for a liquid crystal display (LCD).

  In recent years, LCDs are used in mobile phones and personal digital assistants, and optical films for LCDs are often required to be thin and highly durable. Optical films for LCDs that require thinning include, for example, protective films for polarizers.

  Thinning and high durability of the protective film for a polarizer are contradictory, and it is difficult to satisfy both at the same time with a conventionally used material such as triacetyl cellulose (hereinafter abbreviated as TAC). I came. When this TAC is thinned, the moisture permeability of TAC is high, so that moisture penetrates into the polarizing plate, resulting in a durability problem that the polarizer is faded.

  Further, in the polarizing plate using the TAC protective film, since the photoelastic coefficient of TAC is large, there is another problem related to durability that light leaks in a frame shape around the polarizing plate when a heat resistance test is performed. . In order to solve these problems, Patent Document 1 discloses a polarizing plate using a norbornene resin, which is one of cyclic olefin resins, as a protective film. The norbornene resin has transparency, heat resistance, and moisture resistance. It has been proposed that it is suitable as an optical film for LCDs because of its excellent properties and low birefringence and photoelastic coefficient.

  On the other hand, Patent Document 2 discloses an injection-molded product that is a synthetic resin tableware made of a cyclic olefin resin containing a norbornene resin, and shows excellent stress crack resistance.

JP-A-6-511117 Japanese Patent Laid-Open No. 11-178690

  Conventionally, it has not been known that cracks occur in a polarizer protective film with low residual stress, but when a durability test of a polarizing plate using the norbornene-based resin as a protective film for a polarizer was performed, a liquid crystal cell And found a problem that cracks occur in the protective film on the opposite side. That is, in the durability test of the polarizing plate under high temperature and humidity conditions, deformation stress accompanying the contraction of the polarizer is added, so that cracks are generated even in a thin film having a thickness of 0.1 mm or less after removing residual stress. It is considered a thing. In addition, when the cracks generated in this way are observed using a laser microscope, the heat shrinkage stress of the polarizer is applied to the protective film on the surface side, so the protective film curls on the polarizer side and is bent. In this state, it can be seen that cracks are generated and grown from the outermost surface.

  Specifically, a polarizing plate prepared by laminating a cyclic olefin resin film as a protective film on both sides of a uniaxially stretched polarizer obtained by adsorbing iodine to a polyvinyl alcohol (PVA) film is a cyclic olefin resin film. When laminated with glass of a liquid crystal cell so as to be on the surface, exposed to high temperature and humidity conditions, and left to stand at normal temperature and humidity, cracks occurred in the surface of the cyclic olefin resin film due to the deformation stress of the polarizer.

In addition, cracks did not occur in the polarizing plate using the TAC protective film, but when the load was applied for a long time, the TAC protective film was subjected to creep deformation, so the deformation of the polarizing plate was large and the dimensional stability was poor. Therefore, it can be said that it is preferable to use a cyclic olefin resin as a protective film in view of dimensional stability.
Therefore, in view of the above problems, an object of the present invention is to provide a polarizer protective film and a polarizing plate which are excellent in durability and free of cracks due to deformation stress of the polarizer and excellent in dimensional stability. is there.

The polarizer protective film according to the first aspect of the present invention is made of a cyclic olefin-based resin in which at least one layer dried or cured and shrunk on one surface is laminated, and the curl height is 3 cm or more.
The polarizer protective film according to the second aspect of the present invention is characterized in that the cyclic olefin resin of the first aspect is a norbornene resin.
Furthermore, the polarizing plate according to the third aspect of the present invention according to the third aspect is obtained by laminating the polarizer protective film of the first or second aspect on the surface side opposite to the liquid crystal cell side of the polarizer.

The curl height according to the present invention refers to the height at which the four corners of the rectangle observed when the polarizer protective film is cut into A4-size rectangular sheets are curled. It is limited to 3 cm or more. In the present invention, when the polarizer protective film is cut out to A4 size, the curl is severe, and the one that becomes a roll shape with the upper surface facing inward is the curl height regardless of the positions of the four corners. Was 3 cm or more.
That is, in the present invention, when at least one layer dried or cured and contracted by shrinkage is laminated on one surface of the polarizer protective film made of the above cyclic olefin resin, a curl height of 3 cm or more is easily obtained. This can be achieved, and the occurrence of the cracks can be effectively suppressed. This is because the shrinkage stress that causes curling on the surface side of the polarizer protective film balances with the shrinkage stress on the polarizer side of the polarizer protective film, and the protective film does not buckle.

  If the curl height is less than 3 cm, the polarizing plate is laminated with glass, exposed to high temperature and high humidity, and then left to stand at normal temperature and humidity. The balance of force is lost and cracks due to buckling occur on the surface side.

  In the present invention, at least one layer on the surface of one side only needs to be laminated on one surface of a polarizer protective film made of a cyclic olefin resin, and one or more layers are provided between the layer and the protective film. It may be formed.

  In the present invention, the layer shrunk after drying or curing is not particularly limited, and examples thereof include an undercoat layer, a hard coat layer, an antistatic layer, and an antireflection layer, and these materials are also particularly limited. As long as the optical properties including transparency as a polarizing plate are not impaired, various resins and inorganic materials may be contained in these resins.

  Further, in the present invention, the method for laminating at least one layer dried or cured and contracted on one surface on the polarizer protective film is not particularly limited, for example, coating with a coater, After drying, it can be cured by active energy rays or heat, and other coating methods, lamination, co-extrusion with a protective film, or the like may be used.

Among these methods, one of methods that are particularly effective is a method of providing the above-described hard coat layer.
The hard coat is not particularly limited, and examples thereof include a clear hard coat, a hard coat having antiglare properties, a hard coat having antireflection properties, and a hard coat having antistatic properties.

  The hard coat layer may be composed of two or more layers, and an antistatic layer or an undercoat layer (binder layer) may be formed between the base coat protective film and the hard coat layer.

The material for forming the hard coat layer contains at least an organic material, and may be an organic material alone or a hybrid material containing an inorganic material (for example, inorganic ultrafine particles).
Examples of the resin that is the organic material include an ionizing radiation curable resin, a thermosetting resin, and a thermoplastic resin. Examples of the ionizing radiation curable resin include a photocationic system, an inorganic fine particle dispersed acrylic radical system, and an acrylic radical system. Thermosetting resins include melamine, urethane, alkyd, acrylic silicon, fluorine-containing resin, inorganic fine particle dispersed acrylic radical, inorganic fine particle dispersed organic polymer, inorganic fine particle dispersed organoalkoxysilane, organic high There are molecular dispersion silica type, silicate / organic polymer type and so on.

The hard coat layer may contain resin beads or an inorganic filler for imparting antiglare properties.
Further, a low refractive index layer or a high refractive index layer may be coated on the hard coat layer by a dry method or a wet method to impart an antireflection function. In addition, an antistatic function or an antifouling function may be provided by lamination, or a function may be imparted to the hard coat layer single layer. As the above wet method, a coating solution prepared in an aqueous or solvent system is applied using a coater (for example, a known method such as roll coating, gravure coating, bar coating, extrusion coating) and then dried to form a coating film. Examples of the dry method include a method of forming by vacuum vapor deposition, sputtering, CVD (chemical deposition method), or the like.
Further, the surface of the polymer film forming the hard coat layer may be subjected to hydrophilic treatment such as corona discharge treatment or ultraviolet irradiation treatment, or these may be used in combination.
Furthermore, you may add stabilizers, such as another ultraviolet absorber and antioxidant, to the said hard-coat layer.
Moreover, the hard-coat layer provided with the function mentioned above may be laminated | stacked, and may become two or more layers, and may combine two or more functions mentioned above in the single layer.

  The cyclic olefin-based resin according to the present invention is not particularly limited. For example, a norbornene-based resin is preferable from the viewpoint of optical properties and heat resistance, and the norbornene-based resin is preferably a thermoplastic saturated norbornene-based resin. Resins obtained by hydrogenating ring-opening (co) polymers of norbornene monomers, resins obtained by addition polymerization of norbornene monomers, resins obtained by addition copolymerization with norbornene monomers and olefin monomers such as ethylene and α-olefin Can be mentioned.

The norbornene-based monomer is not particularly limited as long as it has a norbornene ring, but since a molded product excellent in heat resistance, low linear expansion coefficient, etc. is obtained, a tricyclic or higher polycyclic norbornene-based monomer It is preferable to use a body.
Specific examples of these norbornene-based monomers include bicyclics such as norbornene and norbornadiene; tricyclics such as dicyclopentadiene and dihydroxypentadiene; tetracyclics such as tetracyclododecene; pentacycles such as cyclopentadiene trimer. Such as tetracyclopentadiene, etc .; alkyl such as methyl, ethyl, propyl and butyl; alkenyl such as vinyl; alkylidene such as ethylidene; substituted aryl such as phenyl, tolyl and naphthyl; Ester group, ether group, cyano group, halogen atom alkoxycarbonyl group, pyridyl group, hydroxyl group, carboxylic acid group, amino group, hydroxyl group-free, silyl group, epoxy group, acrylic group, methacryl group and other elements other than carbon and hydrogen Examples include substituted groups having so-called polar groups. . These monomers are used alone or in combination of two or more. Tricyclic, tetracyclic and pentacyclic monomers are particularly preferred because they are easily available, excellent in reaction, and excellent in heat resistance of the resulting resin molded product.

  Examples of commercially available norbornene-based resins include “ZEONOR series”, “ZEONEX series” manufactured by Nippon Zeon, and “ARTON series” manufactured by JSR.

  The method for forming a polarizer protective film made of the cyclic olefin resin of the present invention is not particularly limited, and a solution casting method, an extrusion method, or the like is used.

  The polarizer in the present invention refers to a PVA film or sheet having the function of a polarizer. For example, a PVA / iodine-based polarizer or PVA film that is uniaxially stretched in a boric acid bath after adsorbing iodine to the PVA film. And a uniaxially stretched PVA / dye-based polarizing film after a direct dye having high dichroism is diffused and adsorbed on the substrate.

  The polarizing plate in this invention refers to what laminated | stacked the protective film on the polarizer, and the protective film of this invention should just be used one sheet | seat at the surface side of a polarizer.

  By using a polarizer protective film comprising a cyclic olefin-based resin having at least one layer dried or cured and shrunk on one side surface and having a curl height of 3 cm or more according to the present invention, this polarizer protection is achieved. The polarizer deformation stress and the curl deformation stress applied to the film are balanced, and generation of cracks due to buckling of the protective film can be suppressed.

  The polarizer protective film and the polarizing plate of the present invention are configured as described above, have no occurrence of cracks due to the deformation stress of the polarizer, have excellent durability, and have excellent dimensional stability.

  The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

(Example 1)
A norbornene-based resin (manufactured by JSR, trade name: ARTON D4650) was melt-extruded into a film with a thickness of 40 μm using a single-screw extruder equipped with a T-die. A corona treatment was performed on one surface of this film. At this time, the contact angle with water was 48 °. On this corona-treated surface, a silicone-modified acrylic hard coating agent (manufactured by GE Toshiba Silicone, trade name: UVHC1105) is diluted with isopropyl alcohol to a solid content of 50%, and microgravure with a # 70 microgravure coater. Protect the polarizer by applying at a rotation speed of 30 rpm and a line speed of 10 m / min, removing the solvent in a drying oven set at 80 ° C., and then curing it by irradiating it with 1.0 J / cm ² of ultraviolet light in an air atmosphere with a high-pressure mercury lamp. A film was obtained. The thickness of the hard coat layer of this film was 10 μm.
Next, wet-lamination was performed using the above-described norbornene-based polarizer protective film with a hard coat on the surface side of the PVA-based polarizer, and an unprocessed norbornene-based polarizer protective film on the liquid crystal cell side. Then, it dried continuously at 60 degreeC for 5 minutes, 70 degreeC for 5 minutes, and 80 degreeC for 5 minutes, and obtained the polarizing plate.

(Example 2)
A polarizer protective film and a polarizing plate were obtained in the same manner as in Example 1 except that a product name: TOPAS 6013 manufactured by Ticona was used as the norbornene-based resin.

(Comparative Example 1)
A polarizer protective film and a polarizing plate were obtained in the same manner as in Example 1 except that the surface of the norbornene-based resin film was not subjected to corona treatment and no hard coat layer was provided.

(Comparative Example 2)
A polarizer protective film in the same manner as in Example 1 except that a polarizer protective film of norbornene resin with a hard coat on the surface side is used and a polarizer protective film of norbornene resin with a hard coat on the liquid crystal cell side is used. And a polarizing plate were obtained.

(Comparative Example 3)
A polarizing plate was obtained in the same manner as in Example 1 except that a 40 μm TAC film formed by the solution casting method was used as a polarizer protective film.

(Evaluation methods)
Durability-1: The obtained polarizing plate was cut into a size of 16 cm × 9 cm with the absorption axis direction of the polarizer at an angle of 90 degrees with respect to the long side, and acrylic on the protective film surface on the liquid crystal cell side A glass-based polarizing plate was prepared by applying a PSA adhesive and laminating a non-alkali glass plate having a thickness of 1 mm. This was heated at 90 ° C. for 500 hours and then allowed to stand at 23 ° C. for 1000 hours to visually evaluate the occurrence of cracks. As the evaluation scale, ◯ indicates that there is no crack, Δ indicates that there are 1 to 5 cracks, and × indicates that there are 5 or more.

Durability-2: A polarizing plate with glass was prepared in the same manner as Durability-1, and the color fading was visually evaluated by heating and humidifying at 60 ° C. and 95% RH for 500 hours. As the evaluation scale, after heating and humidification, no change was observed, and ○, a discoloration or other change was observed, and x.

  The performance of the polarizing plates obtained in Examples 1-2 and Comparative Examples 1-3 was evaluated. The results are shown in Table 1.

Claims (3)

  A polarizer protective film comprising a cyclic olefin-based resin having a curled height of 3 cm or more in which at least one layer dried or cured and contracted is laminated on one surface.   The polarizer protective film according to claim 1, wherein the cyclic olefin-based resin is a norbornene-based resin. The polarizing plate for liquid crystal display devices which laminated | stacked the convex surface side of the polarizer protective film of Claim 1 or 2 on the surface side opposite to the liquid crystal cell side of a polarizer.