JP2001272534A - Protective film for polarizing plate and polarizing plate formed by using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a protective film equipped with excellent properties and a polarizing plate using the same. SOLUTION: The protective film for the polarizing plate is composed of a practically nonaligned film formed of a specific cyclic olefin polymer with 5-50 g/m2.24 hr moisture vapor permeation rate and >=90.0% light transmittance and has excellent properties such as transparency, heat resistance, absence of aligning, surface hardness, adhesiveness to a polarizing element or the like. The polarizing plate using the same has excellent initial performance and excellent durability such as moisture and heat resistance or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protective film for a polarizing plate and a polarizing plate using the same. More specifically, the present invention relates to a protective film for a polarizing plate having specific physical properties using a cyclic olefin-based polymer and a polarizing plate using the same.

[0002]

BACKGROUND OF THE INVENTION Cellulose triacetate film has been frequently used as a protective film for a polarizing element comprising a polyvinyl alcohol-iodine system. However, in fields where moisture resistance is particularly required, such as for outdoor use, cellulose triacetate films are unsuitable due to their high water absorption and moisture permeability, and there has been a demand for an alternative film.

Accordingly, cyclic polyolefin films having characteristics such as low water absorption, moisture resistance, and low birefringence have been proposed (JP-A-6-51117, JP-A-7-776).
08, JP-A-11-142645).

However, when the cyclic polyolefin film proposed above is used as a protective film of a polarizing plate,
Since the moisture proof property is good, it is possible to prevent intrusion of water from the front and back surfaces of the polarizing plate, but it is difficult to release the water that has entered the polarizing element from the side surface of the polarizing plate. For this reason, the polarizing plate may be fogged or the protective film and the polarizing element may be separated.

[0005]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned disadvantages, and furthermore, the transparency and the ultraviolet shielding property required for a protective film,
An object of the present invention is to provide a protective film having various properties such as light resistance, heat resistance, non-orientation, surface hardness, and adhesion to a polarizing element. Another object of the present invention is to provide a polarizing plate having excellent initial performance and durability such as moisture resistance and heat resistance.

[0006]

The present invention provides the following (A):
(B), (C) and is formed from at least one cyclic olefin polymer is selected from (D), moisture permeability of ^{5g / m 2 · 24hr~50g / m} 2 · 24hr, light transmittance of 90 Provided is a protective film for a polarizing plate comprising a film of 0.0% or more. (A) a polymer of a vinyl alicyclic hydrocarbon-based compound or a copolymer with a monomer copolymerizable with the compound, and (B) a polymer of a vinyl aromatic hydrocarbon-based compound having at least an aromatic ring. A polymer obtained by hydrogenating at least 30% of an aromatic ring of a copolymer obtained by hydrogenating 30% or a copolymer of the compound and a monomer copolymerizable with the compound; (C) a monocyclic monoolefin (D) a hydrogenated product of a polymer of a monocyclic conjugated diene-based compound, or a copolymer of a polymer of a monocyclic conjugated diene-based compound, A hydrogenated product of a copolymer with a monomer.

Further, the present invention provides a polarizing plate comprising a specific polarizing element and the above protective film.

[0008]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a film useful as a protective film for a polarizing plate. The moisture permeability of the film according to the present invention is 5.0 g / m ² · 24 hrｈ5.
0 g / m ² · 24 hr, preferably 7 g / m ² · 24 h
r to 30 g / m ² · 24 hr, more preferably 10 g
/ M is ^{2 · 24hr~20g / m 2 · 24hr} . If the moisture permeability of the protective film is too large or too small, the moisture resistance of the polarizing plate tends to decrease.

The light transmittance of the film of the present invention is 90.0.
%, Preferably 91.0% or more, more preferably 91.5% or more. When the light transmittance is small, the single light transmittance of the polarizing plate tends to decrease.

The light resistance is, for example, 50 with a fade meter.
It is sufficient that the deterioration of mechanical strength and the change of coloring or the like do not substantially occur for 0 hours or more, preferably 750 hours or more, more preferably 1000 hours or more.

The heat resistance is, for example, a softening temperature of 70 ° C. or higher,
It is preferably 75 ° C. or higher, more preferably 80 ° C. or higher.

The protective film is preferably substantially non-oriented. “Substantially non-oriented” means that a step of actively molecular orientation such as a stretching step has not been performed. This is because if they are oriented, they need to be aligned with the orientation direction of the polarizing element without any deviation when bonding to the polarizing element.

The thickness of the protective film is one side, usually 10 to 150
μm, preferably 15 to 100 μm, and more preferably 20 to 80 μm. In the case where the protective film is provided on both sides, a range of a thickness twice as large as the total thickness is exemplified. If the thickness is too thin, it tends to be difficult to handle and it is difficult to ensure moisture permeability. If the thickness is too thick, the cost increases and the folding resistance tends to decrease.

The polarizing element used in the present invention is not particularly limited. For example, a polarizing element obtained by adsorbing and orienting iodine or a dichroic dye on a film made of polyvinyl alcohol, polyethylene terephthalate, polyamide or the like to have a polarizing property. Can be exemplified. In particular, a polarizing element comprising a polyvinyl alcohol-iodine system or a polyvinyl alcohol-dichroic dye system is more preferable from the viewpoint of initial performance.

Examples of the dichroic dye include azo, anthraquinone and tetrazine dichroic dyes.

The adhesive used for bonding the protective film of the present invention and the polarizing element is not particularly limited.
Examples thereof include polyvinyl alcohol-based, acrylic-based, urethane-based, polyester-based, and epoxy-based adhesives and those obtained by adding a curing agent thereto.

The protective film of the present invention is a protective film for a polarizing plate having an excellent ultraviolet light transmittance of 10% or less and excellent light resistance. In order to impart light resistance to the polarizing element and prevent deterioration of the liquid crystal due to ultraviolet rays, it is desirable that the protective film has ultraviolet absorbing performance. For that purpose, an ultraviolet absorber may be added to the protective film. The UV absorber may be a known one such as a benzophenone type or a benzotriazole type, but in order to further enhance the effect, it is more preferable to use at least two types of mixtures based on the UV absorption wavelength. In order to impart light resistance to the polarizing element and prevent deterioration of the liquid crystal, the protective film must have an ultraviolet transmittance of 10%.
%, Preferably 3% or less, more preferably 1% or less.

In this way, the deterioration of the liquid crystal due to ultraviolet rays is prevented, and the degree of polarization retention of the polarizing plate after the light resistance test is 95% or more, usually 99% or more.

The present invention also relates to a polarizing plate comprising a specific polarizing element and a protective film.

The polarizing element is made of a polyvinyl alcohol-iodine system or a polyvinyl alcohol-dichroic dye system, and the protective film is as described above.

The polarizing element is manufactured by immersing a film made of polyvinyl alcohol or a derivative thereof in an aqueous solution of iodine to adsorb iodine, and then performing uniaxial stretching orientation in boric acid water. Alternatively, it can be obtained by uniaxially stretching a film made of polyvinyl alcohol or a derivative thereof, adsorbing iodine, and treating with boric acid water. A polarizing element using a dichroic dye instead of iodine is similarly manufactured.

The adhesive used for adhering the protective film and the polarizing element is not particularly limited. For example, an adhesive of polyvinyl alcohol type, acrylic type, urethane type, polyester type, epoxy type or the like or a curing agent therefor Can be exemplified. In particular, aqueous solutions and emulsions are more preferable from the viewpoint of durability.

As described above, the initial performance is such that the single transmittance is 42.0% or more, the degree of polarization is 99.9% or more, and the durability is the degree of polarization after the moisture resistance test, the heat resistance test, and the light resistance test. Each has a retention of 95% or more, usually 99% or more, and a polarizing plate excellent in both initial performance and durability can be easily obtained. By changing the manufacturing conditions of the polarizing element, the initial performance polarization degree may be appropriately manufactured according to the field of use from a general-purpose polarization degree of about 90% to a high polarization degree of 99.9% or more depending on the field of use. It goes without saying.

The protective film having the above excellent properties is formed of at least one type of cyclic olefin polymer selected from the following (A), (B), (C) and (D). (A) a polymer of a vinyl alicyclic hydrocarbon-based compound or a copolymer with a monomer copolymerizable with the compound, and (B) a polymer of a vinyl aromatic hydrocarbon-based compound having at least an aromatic ring. A polymer obtained by hydrogenating at least 30% of an aromatic ring of a copolymer obtained by hydrogenating 30% or a copolymer of the compound and a monomer copolymerizable with the compound; (C) a monocyclic monoolefin (D) a hydrogenated product of a polymer of a monocyclic conjugated diene-based compound, or a copolymer of a polymer of a monocyclic conjugated diene-based compound, A hydrogenated product of a copolymer with a monomer.

Vinyl alicyclic hydrocarbon-based (co) polymer (A) The vinyl alicyclic hydrocarbon-based compound which is a monomer of the vinyl alicyclic hydrocarbon-based (co) polymer (A) includes: Vinyl group or α
-An alkyl-substituted vinyl group, a monocyclic cycloalkyl group,
Alkyl-substituted cycloalkyl group, cycloalkenyl group,
Or a compound having a structure in which an alkyl-substituted cycloalkenyl group is bonded.

Examples of such compounds include vinylcyclobutane, vinylcyclopentane, vinylcyclohexane, vinylcycloheptane, vinylcyclooctane, and those compounds in which the vinyl group has an α-position with an alkyl group such as methyl, ethyl or propyl. Examples include substituted compounds. Also, 4-vinylcyclohexene, 4-isopropenylhexene, 1-methyl-4-vinylcyclohexene, 1-methyl-4-isopropenylcyclohexene, 2-methyl-4-vinylcyclohexene, 2-methyl-4-isopropenylhexene And vinylcyclohexene derivatives.

The above compounds can be polymerized singly or in a combination of two or more. Further, other monomers copolymerizable with the above compounds can be combined and copolymerized within a range not to impair the purpose of the present invention.

Other monomers copolymerizable with the vinyl alicyclic hydrocarbon compound include α-olefins having 3 or more carbon atoms such as propylene and butene, conjugated dienes such as butadiene and isoprene, and ethylidene. Non-conjugated dienes such as norbornene, acrylonitrile, acrylic acid, methacrylic acid, maleic anhydride, acrylates,
Examples include methacrylic acid ester, maleimide, vinyl acetate, vinyl chloride and the like. Of these, α-olefins are preferably used, and particularly when they are combined with monomers such as propylene and butene, flexibility and impact resistance can be imparted. Other monomers copolymerizable with such a vinyl alicyclic hydrocarbon-based compound are 0 to 9 based on the total amount of the monomers.
It is desirable to use 5 mol%, more preferably 0 to 90 mol%.

The polymerization method for obtaining the vinyl alicyclic hydrocarbon-based (co) polymer (A) is not particularly limited, and includes known radical polymerization, coordination anion polymerization (Ziegler polymerization), cationic polymerization, and anionic polymerization. Can be applied.

Vinyl aromatic hydrocarbon (co) polymer (B) The vinyl aromatic hydrocarbon compound as a monomer of the vinyl aromatic hydrocarbon (co) polymer (B) is a vinyl group or a vinyl group. A compound in which an aromatic hydrocarbon substituent is bonded to an α-alkyl-substituted vinyl group.

Such compounds include styrene, α
-Methylstyrene, α-ethylstyrene, α-propylstyrene, α-isopropylstyrene, α-t-butylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2,4-diisopropylstyrene, 2, 4-dimethylstyrene, 4-t-butylstyrene, 5-t-butyl-2-methylstyrene, monochlorostyrene, dichlorostyrene,
Monofluorostyrene, 4-phenylstyrene, vinylnaphthalene, vinylanthracene and the like can be exemplified.

The above compounds can be polymerized alone or in combination of two or more. Further, other monomers copolymerizable with the above compounds can be combined and copolymerized within a range not to impair the purpose of the present invention.

Other monomers copolymerizable with the vinyl alicyclic hydrocarbon compound include α-olefins having 3 or more carbon atoms such as propylene and butene, conjugated dienes such as butadiene and isoprene, and ethylidene. Examples include non-conjugated dienes such as norbornene, acrylonitrile, acrylic acid, methacrylic acid, maleic anhydride, acrylate, methacrylate, maleimide, vinyl acetate, vinyl chloride, and the like. Of these, α-olefins are preferably used, and in particular, a combination with a monomer such as propylene or butene is preferred because flexibility and impact resistance can be imparted.

The other monomer copolymerizable with the vinyl alicyclic hydrocarbon-based compound is 0 to 0 based on the total amount of the monomer.
It is desirable to use 95 mol%, more preferably 0 to 90 mol%. As the polymerization method, the same method as the polymerization method (A) can be applied.

The polymer thus obtained can be hydrogenated with an aromatic ring by a known method to obtain a desired vinyl aromatic hydrocarbon (co) polymer (B). A conventionally known method can be applied to the method of hydrogenation, for example,
JP-A-7-247321, U.S. Pat. No. 5,612,4
For example, a method described in JP-A No. 22 can be exemplified.
Hydrogenation rate of aromatic ring in polymer (measured by NMR)
Is at least 30%, preferably at least 60%, more preferably at least 90%.

Monocyclic cyclic monoolefin-based (co) polymer (C) Monocyclic cyclic monoolefin-based compound (C) is a monomer of monocyclic cyclic monoolefin-based (co) polymer. The monocyclic monoolefin which may be possessed, for example, cyclobutene, cyclopentene, cyclohexene, cyclooctene and the like.

The above compounds can be polymerized alone or in combination of two or more. Further, other monomers copolymerizable with the above compounds can be combined and copolymerized within a range not to impair the purpose of the present invention.

Other monomers copolymerizable with the monocyclic monoolefin compound include ethylene, propylene, butene; conjugated dienes such as butadiene and isoprene; non-conjugated dienes such as ethylidene norbornene; acrylonitrile and acrylic. Examples thereof include acids, methacrylic acid, maleic anhydride, acrylic esters, methacrylic esters, maleimides, vinyl acetate, and vinyl chloride. Such other monomer copolymerizable with the monocyclic monoolefin compound is 0 to 95 mol% based on the total amount of the monomer,
More preferably, it is used in a ratio of 0 to 90 mol%.

Monocyclic cyclic monoolefin (co) polymer (C)
The polymerization method for obtaining is not particularly limited, and a known method of addition-polymerizing a monomer containing a cyclic monoolefin-based compound can be employed.

Monocyclic conjugated diene (co) polymer (D) Monocyclic conjugated diene compound as a monomer of monocyclic conjugated diene (co) polymer (D) has a substituent. Monocyclic conjugated dienes which may be mentioned, for example, cyclopentadiene, cyclohexadiene, cycloheptadiene, cyclooctadiene and the like.

The above compounds can be polymerized alone or in combination of two or more. Further, other monomers copolymerizable with the above compounds can be combined and copolymerized within a range not to impair the purpose of the present invention.

Other monomers copolymerizable with the monocyclic conjugated diene compound include ethylene, propylene, butene; conjugated dienes such as butadiene and isoprene; non-conjugated dienes such as ethylidene norbornene; acrylonitrile and acrylic. Examples thereof include acids, methacrylic acid, maleic anhydride, acrylic esters, methacrylic esters, maleimides, vinyl acetate, and vinyl chloride. Such a monomer copolymerizable with the monocyclic conjugated diene-based compound is used at a ratio of 0 to 95 mol%, more preferably 0 to 90 mol%, based on the total amount of the monomers. It is desirable.

The polymerization method is not particularly limited, and a known method for addition-polymerizing a monomer containing a cyclic conjugated diene compound can be employed.

The polymer thus obtained can be hydrogenated by a known method to obtain a desired monocyclic conjugated diene (co) polymer (D). In particular,
For example, polycyclohexadiene and a hydrogenated product thereof can be obtained by using the method disclosed in JP-A-11-106571. The hydrogenation rate (measured by NMR) of the double bond in the hydrocarbon ring contained in the (co) polymer is desirably 30% or more, preferably 60% or more, and more preferably 90% or more.

The weight average molecular weight (Mw) of the cyclic olefin polymers (A) to (D) measured by gel permeation chromatography (GPC) used in the present invention is from 5,000 to 5,000 in terms of polystyrene molecular weight. One,
00000, preferably 10,000 to 500,00
0, more preferably 50,000 to 300,000. The molecular weight distribution (Mw / Mn; Mn is a number average molecular weight measured by GPC) is 10 or less, preferably 5.0 or less, more preferably 3.0 or less.

The glass transition temperature (Tg; measured by DSC) is in the range of 50 to 300 ° C, preferably 60 to 280 ° C, more preferably 70 to 250 ° C. The glass transition temperature can be adjusted by adding a plasticizer. As the plasticizer added for the purpose of adjusting the glass transition temperature of the polymer, any compound which can be added to the polymer to lower the glass transition temperature can be used without any limitation. Examples of such compounds include liquid paraffin, spindle oil, process oils such as naphthenic oils, squalane, terpene compounds such as limonene, stearic acid, oleic acid, palmitic acid, myristic acid, higher fatty acids such as erucic acid, The higher fatty acids and monohydric alcohols such as methanol, ethanol, propanol and butanol, dihydric alcohols such as ethylene glycol, propylene glycol, tetramethylene glycol and 2-butene-1.4-diol, trihydric alcohols such as glycerin, and pentaerythritol And esters of polyhydric alcohols such as sorbitol, and amides formed by the higher fatty acids and amines or hydroxyamines.

The cyclic olefin polymers (A) to (D) used in the present invention may optionally contain other resins and additives as long as the objects of the present invention are not impaired. Such resins and additives include rubber components, other resin components, petroleum resins, waxes, heat stabilizers, weather stabilizers, light stabilizers, antistatic agents, slip agents, antiblocking agents, antifogging agents, Examples include nucleating agents, lubricants, dyes and pigments that absorb only light of a specific wavelength, natural oils, synthetic oils, waxes, and translucent fillers.

The method for obtaining the protective film from the cyclic olefin polymer used in the present invention is not particularly limited. For example, a method utilizing thermoplasticity such as an extrusion method or a calendering method may be used. In view of this, the production method by the solution casting method is more desirable.

The solvent used for the casting solution is not particularly limited. For example, aliphatic hydrocarbons such as hexane, heptane, octane, nonane, decane, undecane, dodecane and derivatives thereof, cyclohexane, cyclohexene, decalin, etc. Alicyclic hydrocarbons and their derivatives, aromatic hydrocarbons such as toluene, xylene and ethylbenzene and their derivatives, etc .; halogenated hydrocarbons such as chloroform, carbon tetrachloride, dichloroethane, trichloroethane, tetrachloroethane and the like Can be exemplified.

The solvent may be one kind, but it may be difficult to obtain a smooth film depending on the solution viscosity and drying conditions. At that time, a desirable film can be obtained by adding a leveling agent or the like to the solution or by using at least two kinds of mixed solvents having a difference in boiling point of 10 ° C. or more.

An ultraviolet absorber may be added to the casting solution in order to prevent the liquid crystal from being deteriorated by ultraviolet rays.

The thickness of the protective film is usually 10 to 150 μm, preferably 15 to 100 μm, more preferably 20 to 8 μm.
0 μm. If the thickness is too thin, it is difficult to handle,
Also, it tends to be difficult to secure moisture permeability, and if it is too thick, cost tends to increase, and it tends to be difficult to secure folding resistance.

In order to improve the adhesiveness to the polarizing element and the adhesive to be described later, the surface of the protective film is subjected to corona discharge treatment, ozone spraying, ultraviolet irradiation, electron beam irradiation, gamma ray irradiation, plasma irradiation, Microwave irradiation, flame treatment, chemical treatment, and other known surface treatments may be performed. The treatment degree is such that the wetting tension is 30 dyn / cm or more, preferably 40 dyn / cm or more, and more preferably 45 dyn / cm or more.
yn / cm or more.

In this manner, the moisture permeability is 5 g / m ² · 2
4 hr to 50 g / m ² · 24 hr, preferably 7 g / m ²
· 24hr~30g / m ² · 24hr, and more preferably ^{10g / m 2 · 24hr~20g / m} 2 · 24hr, light transmittance of 90.0% or more, preferably 91.0% or more, more preferably 91. When the content is 5% or more, a protective film made of a substantially non-oriented film having excellent heat resistance and light resistance can be easily obtained. The present invention relates to a polarizing plate comprising a polarizing element and the above-mentioned cyclic olefin polymer protective film. As a method of bonding the protective film and the polarizing element, any known method may be used. In the case of bonding using an adhesive, for example, an adhesive of a polyvinyl alcohol type, an acrylic type, a urethane type, a polyester type, an epoxy type or the like or a material obtained by adding a curing agent thereto can be exemplified. In particular, aqueous solutions and emulsions are more desirable from the viewpoint of durability. In this case, it is desirable that the surface of the protective film be treated as described above. The treatment degree is 37 dyn / cm or more in terms of wet tension, preferably 40 dyn / cm, and more preferably 45 dyn / c.
m, the contact angle with water is 90 degrees or less, preferably 75 degrees
Degrees or less.

The initial performance of the polarizing plate thus obtained was such that the single transmittance was 42.0% or more and the degree of polarization was 99.9%.
Above, as the durability, after the moisture resistance test, after the heat resistance test,
And the degree of polarization retention after light resistance test is 95% or more,
Usually, it is 99% or more, and both initial performance and durability are excellent.

The polarizing plate is usually coated on one side with an adhesive for adhering to a liquid crystal substrate, a separator is attached, and a protective film is attached on the other side. The thus manufactured one is used as a transmission type, but a reflection layer may be provided on one side to be used as a reflection type or a semi-transmission type.

The surface of the protective film may be subjected to various processes conventionally applied to a polarizing plate such as a hard coat layer, an antireflection layer, and an antiglare layer.

[0058]

According to the present invention, there is provided a protective film having various properties required for the protective film, such as transparency, heat resistance, non-orientation, surface hardness, and adhesion to a polarizing element. Further, the polarizing plate of the present invention is excellent in initial performance and durability such as moisture resistance and heat resistance.

[0059]

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

The methods for measuring and evaluating the physical properties used in the present invention are as follows.

Moisture permeability: PERMARTRAN manufactured by Mocon
-40 ° C, relative humidity 90% with W600 type moisture permeability measuring device
It measured on condition of.

Light transmittance: measured in accordance with ASTM D1003.

[0063] polarizer degree of polarization: by overlapping two polarizing plates such that the orientation direction is in the same direction, the light transmittance is measured, and this number and T _1. Next, two polarizing plates were superimposed so that the orientation directions were orthogonal to each other, and the light transmittance was measured in the same manner. The value was T ₂ and the degree of polarization was calculated by the following equation. Degree of polarization = {(T ₁ −T ₂ ) / (T ₁ + T ₂ )} ^1/2

The humidity test of the polarizing plate was carried out at 80 ° C. × 90% RH.
After leaving for 200 hours in a thermo-hygrostat at 23 ° C x 50
% RH for 200 hours and then again at 80 ° C x 90%
After leaving in a RH constant temperature and humidity chamber for 200 hours, 23 ° C x
It was left at 50% RH for 200 hours.

The degree of polarization retention (the same applies hereinafter) is a value obtained by multiplying the value obtained by dividing the degree of polarization after the test by the degree of polarization before the test and multiplying by 100. The higher the value, the better the durability.

Reference Example 1 A stainless steel autoclave having an internal volume of 5 liters had a number average molecular weight (Mn) of 110,
Mw / Mn with a weight average molecular weight of 130,000
Is 1.18 polystyrene 240g, cyclohexane 1
000 g and 36 g of a hydrogenation catalyst (manufactured by Nippon Chemical Industry Co., Ltd., 40% nickel-supported silica, alumina carrier) are charged, and the system is purged with nitrogen. Next, while stirring the inside of the system at a speed of 1000 rpm, the system was heated at 230 ° C. and a hydrogen pressure of 45 Kg / cm ² at 8
Perform the hydrogenation reaction for hours. After the completion of the hydrogenation reaction, the reaction solution was filtered through Celite, and after adding 4000 g of cyclohexane, the mixture was added to a large excess of methanol to precipitate a polymer.
Physical properties of the obtained polymer were as follows: Mn: 43,000, Mw:
87,000, Mw / Mn: 1.85, hydrogenation rate: 10
0%, Tg: 140 ° C., density: 0.95 g / cm ³ . The light transmittance measured using a 3 mm-thick test piece was 92%.

Reference Example 2 A polyvinyl alcohol film (manufactured by Kuraray Co., Ltd., thickness: 75 μm) was immersed in an aqueous solution consisting of 1,000 parts by weight of water, 7 parts by weight of iodine, and 105 parts by weight of potassium iodide for 5 minutes to remove iodine. Adsorbed. Then, the film was heated at 40 ° C. in a 4% by weight aqueous solution of boric acid.
The film was monoaxially stretched 4.4 times in the machine direction, taken out in a tension state, and dried to obtain a polarizing element.

Example 1 After 30 parts by weight of the polymer obtained in Reference Example 1 were dissolved in 70 parts by weight of cyclohexane, a film having a thickness of 30 μm was prepared by a casting method. When the moisture permeability of this film was measured, it was 10 g / m
² · 24 hr or, light transmittance was 91.5%. Next, the surface of this film was subjected to corona treatment, and a polyvinyl alcohol was adhered to both surfaces of the polarizing element of Reference Example 2 using an aqueous solution as an adhesive to obtain a polarizing plate. Table 1 shows the initial performance and results of the moisture resistance test of this polarizing plate.

<Comparative Example 1> Instead of the polymer of Reference Example 1 used in Example 1, the glass transition temperature was 140 ° C and the MFR (2
60 ° C., 2.16 Kg): 30 μm film according to the method of Example 1 using a random copolymer of ethylene and tetracyclo [4.4.0.1 2,5.1 1 ^7,10 ] -3-dodecene at ⁷ g / 10 min ^. I got The moisture permeability of this film is 3.0 g / m
Was ² · 24hr. Example 1 using this film
A polarizing plate was prepared in the same manner as described above. Table 1 shows the initial performance and results of the moisture resistance test of this polarizing plate.

[0070]

[Table 1]

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08F 32/06 C08F 32/06 C08J 5/18 CER C08J 5/18 CER G02F 1/1335 510 G02F 1/1335 510 // C08L 23:18 C08L 23:18 F term (reference) 2H049 BA02 BA26 BA27 BB13 BB22 BB39 BB43 2H091 FA08X FA08Z FC25 FD06 GA16 LA04 LA06 4F071 AA20 AA21 AA22 AA39 AA78 AF08 AF11 A02A01A01A01A02A01 AB00P AB02P AB03P AB04P AB07P AB08P AB10P AC03Q AG04Q AJ02Q AK32Q AL02Q AM02Q AM43Q AR16P AR17P AR18P AS02Q AS03Q AS15Q BC04H BC43P CA01 CA04 CA31 DA37 DA41 DA62 HA04 HA05 HB02 HB17 JA32

Claims (3)

[Claims] 1. The following (A), (B), (C) and (D)
Is formed from at least one cyclic olefin polymer is more selective, moisture permeability 5g / m ² · 24hr~50
g / m ² · 24 hr, a protective film for a polarizing plate comprising a film having a light transmittance of 90.0% or more. (A) a polymer of a vinyl alicyclic hydrocarbon-based compound or a copolymer with a monomer copolymerizable with the compound, and (B) a polymer of a vinyl aromatic hydrocarbon-based compound having at least an aromatic ring. A polymer obtained by hydrogenating at least 30% of an aromatic ring of a copolymer obtained by hydrogenating 30% or a copolymer of the compound and a monomer copolymerizable with the compound; (C) a monocyclic monoolefin (D) a hydrogenated product of a polymer of a monocyclic conjugated diene-based compound, or a copolymer of a polymer of a monocyclic conjugated diene-based compound, A hydrogenated product of a copolymer with a monomer. 2. The protective film for a polarizing plate according to claim 1, wherein the cyclic olefin-based polymer is substantially non-oriented. 3. A polarizing plate comprising a polarizing element comprising iodine or a dichroic dye and a polyvinyl alcohol-based film, and the protective film according to claim 1 attached to at least one surface of the polarizing element.