JP3907908B2 - Protective film for polarizing plate and polarizing plate using the same - Google Patents

Description

[0001]
BACKGROUND 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 polymer and a polarizing plate using the same.
[0002]
TECHNICAL BACKGROUND OF THE INVENTION
A 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 inappropriate because of their high water absorption and moisture permeability, and alternative films have been desired.
[0003]
Accordingly, cyclic polyolefin films having characteristics such as low water absorption, moisture resistance, and low birefringence have been proposed (see JP-A-6-511117, JP-A-7-77608, and JP-A-11-142645). ).
[0004]
However, when the cyclic polyolefin film proposed above is used as a protective film for the polarizing plate, moisture penetration is prevented and moisture can be prevented from entering from the front and back surfaces of the polarizing plate. It is difficult to release moisture that has entered the polarizing element. Therefore, the polarizing plate may be clouded or peeled off between the protective film and the polarizing element.
[0005]
[Problems to be solved by the invention]
The present invention eliminates the above-mentioned drawbacks and has a protective film having various properties such as transparency, ultraviolet blocking property, light resistance, heat resistance, non-orientation, surface hardness, and adhesion to a polarizing element required for the protective film. The purpose is to provide.
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]
[Means for Solving the Problems]
The present invention is formed from at least one cyclic olefin polymer selected from a polymer obtained by hydrogenating at least 30% of an aromatic ring of a polymer comprising a vinyl aromatic hydrocarbon compound, and has a moisture permeability of 5 g. The protective film for polarizing plates which consists of a film whose / m < ² > * 24hr-50g / m < ² > * 24hr and light transmittance are 90.0% or more is provided .
[0007]
The present invention also provides a polarizing plate comprising a specific polarizing element and the protective film.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a film useful as a protective film for a polarizing plate. Moisture permeability of the film according to the present invention is ^{5.0g / m 2 · 24hr~50g / m} 2 · 24hr, preferably ^{7g / m 2 · 24hr~30g / m} 2 · 24hr, and more preferably 10g / m ² · 24hr ˜20 g / m ² · 24 hr.
If the moisture permeability of the protective film is too large or too small, the moisture resistance of the polarizing plate tends to decrease.
[0009]
The film according to the present invention has a light transmittance of 90.0% or more, preferably 91.0% or more, and more preferably 91.5% or more. When the light transmittance is small, the single light transmittance of the polarizing plate tends to decrease.
[0010]
The light resistance is not particularly limited as long as it does not cause substantial deterioration in mechanical strength, coloration, or the like in a fade meter of 500 hours or longer, preferably 750 hours or longer, more preferably 1000 hours or longer.
[0011]
The heat resistance may be, for example, a softening temperature of 70 ° C. or higher, preferably 75 ° C. or higher, more preferably 80 ° C. or higher.
[0012]
The protective film is preferably substantially non-oriented. “Substantially non-oriented” means that a step of actively orienting molecules such as a stretching step has not been performed. If it is oriented, it must be aligned with the orientation direction of the polarizing element without any deviation when bonded to the polarizing element.
[0013]
The thickness of the protective film is usually 10 to 150 μm, preferably 15 to 100 μm, and more preferably 20 to 80 μm on one side. In the case where the protective film is provided on both surfaces, a total thickness range of twice the film thickness is exemplified. If the thickness is too thin, it is difficult to handle and it is difficult to ensure moisture permeability. If it is too thick, the cost is increased and the folding resistance tends to be lowered.
[0014]
The polarizing element used in the present invention is not particularly limited, and examples thereof include a film made of polyvinyl alcohol, polyethylene terephthalate, polyamide, or the like, by adsorbing and orienting iodine or a dichroic dye to give polarization performance. . In particular, a polarizing element composed of polyvinyl alcohol-iodine or polyvinyl alcohol-dichroic dye is more preferable from the viewpoint of initial performance.
[0015]
Examples of the dichroic dye include azo, anthraquinone and tetrazine dichroic dyes.
[0016]
The adhesive used for bonding the protective film of the present invention and the polarizing element is not particularly limited. For example, polyvinyl alcohol-based, acrylic-based, urethane-based, polyester-based, epoxy-based adhesives, or curing agents for them. Can be exemplified.
[0017]
The protective film of the present invention is preferably a protective film for a polarizing plate having an ultraviolet transmittance of 10% or less and excellent light resistance. In order to impart light resistance to the polarizing element and to prevent deterioration of the liquid crystal due to ultraviolet rays, it is desirable that the protective film has ultraviolet absorption performance. For this purpose, an ultraviolet absorber may be added to the protective film. The ultraviolet absorber may be a known one such as benzophenone or benzotriazole, but it is more desirable to use at least two types of mixtures based on the ultraviolet absorption wavelength in order to enhance the effect. In order to impart light resistance to the polarizing element and prevent deterioration of the liquid crystal, the ultraviolet transmittance of the protective film is 10% or less, preferably 3% or less, more preferably 1% or less.
[0018]
In this way, deterioration of the liquid crystal due to ultraviolet rays is prevented, and the polarization degree retention after the light resistance test of the polarizing plate is 95% or more, usually 99% or more.
[0019]
The present invention also relates to a polarizing plate comprising a specific polarizing element and a protective film.
[0020]
The polarizing element is made of polyvinyl alcohol-iodine or polyvinyl alcohol-dichroic dye, and the protective film is as described above.
[0021]
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 uniaxially stretching in boric acid water. Alternatively, it can also 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 produced in the same manner.
[0022]
The adhesive used for bonding the protective film and the polarizing element is not particularly limited. For example, a polyvinyl alcohol-based, acrylic-based, urethane-based, polyester-based, epoxy-based adhesive, or a curing agent is added to them. The thing can be illustrated. In particular, aqueous solutions and emulsions are more preferable from the viewpoint of durability.
[0023]
In this way, the initial performance is a single transmittance of 42.0% or more, the polarization degree is 99.9% or more, the durability is the polarization degree retention after the moisture resistance test, the heat test, and the light resistance test. Both are 95% or more, usually 99% or more, and a polarizing plate excellent in initial performance and durability can be easily obtained. In addition, by changing the manufacturing conditions of the polarizing element, the degree of polarization of the initial performance may be appropriately manufactured according to the field of use, from a general-purpose one with a degree of 90% to a high degree of polarization of 99.9% or more. It goes without saying that there is nothing.
[0024]
The protective film having excellent properties as described above includes at least one cyclic olefinic polymer selected from a polymer obtained by hydrogenating at least 30% of an aromatic ring of a polymer comprising a vinyl aromatic hydrocarbon compound. Formed from coalescence .
[0025]
The vinyl aromatic hydrocarbon compound as a monomer of a polymer comprising a vinyl aromatic consisting of hydrocarbon-based compound polymer vinyl aromatic hydrocarbon compound, a vinyl group or an α- alkyl-substituted vinyl group, aromatic Is a compound to which an aromatic hydrocarbon substituent is bonded.
[0026]
Such compounds include styrene, α-methyl styrene, α-ethyl styrene, α-propyl styrene, α-isopropyl styrene, α-t-butyl styrene, 2-methyl styrene, 3-methyl styrene, 4-methyl styrene. 2,4-diisopropylstyrene, 2,4-dimethylstyrene, 4-t-butylstyrene, 5-t-butyl-2-methylstyrene, monochlorostyrene, dichlorostyrene, monofluorostyrene, 4-phenylstyrene, vinyl Examples include naphthalene and vinyl anthracene.
[0027]
Said compound can also superpose | polymerize independently and can also copolymerize combining 2 or more types .
[0028]
There is no particular limitation on the polymerization method for obtaining a polymer comprising a vinyl aromatic hydrocarbon-based compound, and a known polymerization method such as radical polymerization, coordination anion polymerization (Ziegler polymerization), cationic polymerization, or anionic polymerization can be applied.
[0029]
The thus obtained polymer can be obtained a polymer consisting of the desired vinyl aromatic hydrocarbon compound by hydrogenating an aromatic ring in a known manner. A conventionally known method can be applied as the hydrogenation method, and examples thereof include methods described in JP-A-7-247321, US Pat. No. 5,612,422, and the like. The hydrogenation rate (measured by NMR) of the aromatic ring in the polymer is 30% or more, preferably 60% or more, more preferably 90% or more .
[0030]
Used in the present invention, the weight-average molecular weight measured by the cyclic olefin polymer of the gel permeation chromatography (GPC) (Mw) is 5,000 to 1,000,000 in polystyrene equivalent value of molecular weight, preferably 10, 000 to 500,000, more preferably 50,000 to 300,000. The molecular weight distribution (Mw / Mn; Mn is the number average molecular weight measured by GPC) is 10 or less, preferably 5.0 or less, more preferably 3.0 or less.
[0031]
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 a plasticizer to be added for the purpose of adjusting the glass transition temperature of the polymer, any compound that can be added to the polymer to lower the glass transition temperature can be used without limitation. Such compounds include process oils such as liquid paraffin, spindle oil, naphthenic oil, terpene compounds such as squalane and limonene, higher fatty acids such as stearic acid, oleic acid, palmitic acid, myristic acid, erucic acid, 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, pentaerythritol Examples thereof include esters with polyhydric alcohols such as sorbitol and amides formed by the higher fatty acids and amines or hydroxyamines.
[0032]
The cyclic olefin polymer used in the present invention, if necessary, within a range that does not impair the object of the present invention, other resins, additives may be blended. 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 that absorb only light of a specific wavelength, pigments, natural oils, synthetic oils, waxes, or translucent fillers.
[0033]
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 using thermoplasticity such as an extrusion method or a calender method may be used. A production method by a solution casting method is more desirable.
[0034]
The solvent used in the casting solution is not particularly limited. For example, aliphatic hydrocarbons such as hexane, heptane, octane, nonane, decane, undecane, and dodecane, and derivatives thereof, alicyclic rings such as cyclohexane, cyclohexene, and decalin. Formula hydrocarbons and derivatives thereof, aromatic hydrocarbons such as toluene, xylene, ethylbenzene and derivatives thereof, halogenated hydrocarbons such as chloroform, carbon tetrachloride, dichloroethane, trichloroethane, tetrachloroethane and derivatives thereof It can be illustrated.
[0035]
One type of solvent may be used, but a smooth film may be difficult to obtain depending on the solution viscosity and drying conditions. In that case, a desired 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.
[0036]
An ultraviolet absorber may be added to the casting solution in order to prevent deterioration of the liquid crystal due to ultraviolet rays.
[0037]
The thickness of the protective film is usually 10 to 150 μm, preferably 15 to 100 μm, and more preferably 20 to 80 μm. When the thickness is too thin, it tends to be difficult to handle and it is difficult to ensure moisture permeability, and when it is too thick, the cost is increased and it is difficult to ensure folding resistance.
[0038]
Corona discharge treatment, ozone spraying, ultraviolet irradiation, electron beam irradiation, gamma ray irradiation, plasma irradiation, microwave irradiation on the surface of the protective film in order to improve the adhesion to the polarizing element and the adhesive to be described later Flame treatment, chemical treatment, and other known surface treatments may be performed. The degree of treatment is such that the wetting tension is 30 dyn / cm or more, preferably 40 dyn / cm or more, more preferably 45 dyn / cm or more.
[0039]
In this way, moisture permeability ^{5g / m 2 · 24hr~50g / m} 2 · 24hr, preferably ^{7g / m 2 · 24hr~30g / m} 2 · 24hr, and more preferably 10g / m ² · 24hr~20g / m ² · 24 hr, light transmittance of 90.0% or more, preferably 91.0% or more, more preferably 91.5% or more, and consists of a substantially non-oriented film excellent in heat resistance and light resistance. A protective film can be obtained easily. The present invention relates to a polarizing plate comprising a polarizing element and the above-mentioned cyclic olefin polymer protective film. Any known method may be used for attaching the protective film and the polarizing element. In the case of bonding using an adhesive, for example, polyvinyl alcohol-based, acrylic-based, urethane-based, polyester-based, and epoxy-based adhesives or those 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 to subject the protective film to surface treatment as described above. The treatment degree is 37 dyn / cm or more in terms of wet tension, preferably 40 dyn / cm, more preferably 45 dyn / cm, and 90 degrees or less, preferably 75 degrees or less in terms of the contact angle with water.
[0040]
The initial performance of the polarizing plate thus obtained has a single transmittance of 42.0% or more and a degree of polarization of 99.9% or more. The durability is after the moisture resistance test, after the heat resistance test, and the light resistance test. The subsequent degree of polarization retention is 95% or more, usually 99% or more, and both initial performance and durability are excellent.
[0041]
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 opposite side. The product manufactured in this way is used as a transmission type, but it may be used as a reflection type or a semi-transmission type by providing a reflective layer on one side.
[0042]
In addition, the surface of the protective film may be subjected to various processes conventionally added to the polarizing plate such as a hard coat layer, an antireflection layer, and an antiglare layer.
[0043]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the protective film provided with various performances, such as transparency required for a protective film, heat resistance, non-orientation, surface hardness, adhesiveness with a polarizing element, is provided.
The polarizing plate of the present invention is excellent in initial performance, durability such as moisture resistance and heat resistance.
[0044]
【Example】
Next, the present invention will be described in more detail with reference to representative examples. The present invention is not limited by these examples.
[0045]
The measurement method and evaluation method of the physical property values used in the present invention are as follows.
[0046]
Moisture permeability: Measured with a PERMARTRAN-W600 type moisture permeability measuring apparatus manufactured by Mocon under the conditions of 40 ° C. and relative humidity of 90%.
[0047]
Light transmittance: measured in accordance with ASTM D1003.
[0048]
Polarization degree of polarizing plate: Two polarizing plates are overlapped so that the alignment directions are the same direction, the light transmittance is measured, and this value is defined as T ₁ . Next, the two polarizing plates were overlapped so that the orientation directions were orthogonal to each other, and the light transmittance was measured in the same manner. This value was T ₂ and the degree of polarization was calculated by the following equation.
Polarization degree = {(T ₁ −T ₂ ) / (T ₁ + T ₂ )} ^1/2
[0049]
The humidity resistance test of the polarizing plate was carried out in a constant temperature and humidity chamber at 80 ° C. × 90% RH for 200 hours, then left at 23 ° C. × 50% RH for 200 hours, and then again at a constant temperature and humidity at 80 ° C. × 90% RH. After leaving in the vessel for 200 hours, it was left at 23 ° C. × 50% RH for 200 hours.
[0050]
The degree of polarization retention (hereinafter the same) 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, by 100. The larger the value, the better the durability.
[0051]
<Reference Example 1>
In a stainless steel autoclave with an internal volume of 5 liters, 240 g of polystyrene having a number average molecular weight (Mn) of 110,000, a weight average molecular weight of 130,000 and an Mw / Mn of 1.18, 1000 g of cyclohexane, a hydrogenation catalyst (Nippon Chemical Industry Co., Ltd.) 36 g (silica, alumina carrier, made of 40% nickel), and the inside of the system is purged with nitrogen. Next, while stirring the system at a speed of 1000 rpm, a hydrogenation reaction is performed at 230 ° C. and a hydrogen pressure of 45 kg / cm ² for 8 hours. After completion of the hydrogenation reaction, the reaction solution was filtered through celite, 4000 g of cyclohexane was added, and the polymer was precipitated in addition to a large excess of methanol.
The physical properties of the polymer obtained were: Mn: 43,000, Mw: 87,000, Mw / Mn: 1.85, hydrogenation rate: 100%, Tg: 140 ° C., density: 0.95 g / cm ³ is there. The light transmittance measured using a 3 mm-thickness test piece was 92%.
[0052]
<Reference Example 2>
A polyvinyl alcohol film (manufactured by Kuraray Co., Ltd., thickness: 75 μm) was immersed in an aqueous solution consisting of 1000 parts by weight of water, 7 parts by weight of iodine, and 105 parts by weight of potassium iodide to adsorb iodine. Next, this film was uniaxially stretched 4.4 times in a 4 wt% boric acid aqueous solution at 40 ° C., taken out in a tension state, and dried as it was to obtain a polarizing element.
[0053]
<Example 1>
After dissolving 30 parts by weight of the polymer obtained in Reference Example 1 with respect to 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, and the light transmittance was 91.5%. Next, the surface of this film was subjected to corona treatment, and a polarizing plate was obtained by pasting polyvinyl alcohol on both surfaces of the polarizing element of Reference Example 2 using an aqueous solution as an adhesive.
Table 1 shows the initial performance and humidity resistance test results of this polarizing plate.
[0054]
<Comparative Example 1>
Glass transition temperature 140 ° C. instead of the polymer of Reference Example 1 used in Example 1, MFR (260 ℃, 2.16Kg ):. Of 7 g / 10min ethylene and tetracyclo [4.4.0.1 ^{2, 5} 1 ^7,10 A 30 μm film was obtained by the method of Example 1 using a random copolymer with] -3-dodecene. The moisture permeability of this film was 3.0 g / m ² · 24 hr. Using this film, a polarizing plate was prepared in the same manner as in Example 1.
Table 1 shows the initial performance and humidity resistance test results of this polarizing plate.
[0055]
[Table 1]

Claims (3)

It is formed from at least one cyclic olefin polymer selected from polymers obtained by hydrogenating at least 30% of an aromatic ring of a polymer comprising a vinyl aromatic hydrocarbon compound, and has a moisture permeability of 5 g / m ² · A protective film for a polarizing plate comprising a film of 24 hr to 50 g / m ² · 24 hr and a light transmittance of 90.0% or more .   The protective film for a polarizing plate according to claim 1, wherein the cyclic olefin polymer is substantially non-oriented.   A polarizing plate comprising a protective film according to claim 1 or 2 bonded to at least one surface of a polarizing element comprising iodine or a dichroic dye and a polyvinyl alcohol film.