JPH0777608A - Polarizing plate - Google Patents

Abstract

PURPOSE:To provide the polarizing plate which has excellent wet heat resistance at a high temp. and maintains a high degree of polarization and the high transmittance of the plate alone even when the polarizing plate is used under severe conditions, such as applications in vehicles and various kinds of industrial instruments. CONSTITUTION:This polarizing plate is formed by sticking a protective film to at least one surface of a polyvinyl alcohol film imparted with polarization performance by adsorption orientation of iodine or dichromatic dyes. The degree of polarization of the polarizing plate after resting for 500 hours at 80 deg.C and 90% RH is >=95% and the transmittance of the polarizing plate alone is >=38%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing plate having a high degree of polarization and a high single transmittance, which has excellent resistance to moist heat.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have been used in desk-top electronic calculators, electronic timepieces, word processors, measuring instruments such as automobiles and machines, and the demand for polarizing plates having high polarization performance has increased accordingly. In particular, since instruments are often used under severe conditions, there is a demand for a polarizing plate with a high degree of polarization that retains resistance to moist heat.

However, conventionally, a polyvinyl alcohol-based polarizing film in which iodine or a dichroic dye is adsorbed on a polyvinyl alcohol-based film has been widely used. However, it generally has poor resistance to heat and humidity, and particularly in a hot and humid environment, a polyiodine ion is used. However, discoloration due to dissociation of iodine, desorption of iodine, etc. occurred, and the polarization performance deteriorated, resulting in lack of reliability.

In order to solve such a drawback, Japanese Patent Laid-Open No. 59-15
No. 9109 discloses a protective film in which a polymer compound film (high-density polyethylene or polypropylene) having a water vapor transmission rate of 10 g / m ² · day or less is coated on both sides of a water-absorbing polarizing film, laminated or formed on a sealed bag. Is disclosed.

Further, in JP-A-60-159704, at least one surface of a polarizing polyvinyl alcohol-based film provided with heat resistance so that the shrinkage ratio after heating at 100 ° C. for 30 minutes is 1.0% or less. 80 ℃, 95% R
As a protective film having a moisture permeability at H of 55 g / m ² hr or less, there is disclosed a polarizing plate obtained by laminating films such as polymethyl methacrylate, polyether sulfone, and polycarbonate.

[0006]

However, in the technique disclosed in Japanese Patent Laid-Open No. 59-159109, the temperature is 70 ° C. and the temperature is 90 ° C.
Although the effect of improving the durability performance under high temperature and high humidity of about% RH is recognized, for polarizing plate applications that require a higher degree of polarization, resins such as high-density polyethylene have a large photoelastic coefficient, so it is slightly Phase difference easily occurs due to various stresses, which causes optical spots and it is difficult to satisfy high polarization performance. Further, in JP-A-60-159704,
Although it is intended to reduce discoloration due to wetting of a polyvinyl alcohol-based film having a polarizing property, the film of polymethylmethacrylate, polyethersulfone, polycarbonate, etc. used for the protective film has a high water vapor transmission rate, and the recent high The durability performance of polarizing plates that require polarization performance is not yet satisfactory, and further improvement has been desired.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to improve such a drawback, and as a result, at least one surface of a polyvinyl alcohol-based film provided with polarization performance by adsorption orientation of iodine or a dichroic dye. , 80 ℃, 90%
RH, water vapor permeability 200g / m ² · 24hr · 100μ or less, and by attaching a protective film having a photoelastic coefficient of 1 × 10 ^-11 cm ² / dyne or less at 80 ℃, 9
The inventors have found that a polarizing plate excellent in wet heat resistance having high polarization performance resulting in a polarization degree of 95% or more after standing for 5 hours at 0% RH and a simple substance transmittance of 38% or more was obtained, and the present invention was completed. .

The present invention will be described in detail below. The polarizing film of the present invention is a uniaxially stretched film of polyvinyl alcohol film. Polyvinyl alcohol is generally produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate, but the present invention is not necessarily limited to this, and a small amount of unsaturated carboxylic acid (salt, ester, amide, nitrile, etc. ), Olefins, vinyl ethers, unsaturated sulfonates, vinyl acetate, and other copolymerizable components.

The degree of saponification in polyvinyl alcohol is practically 85 to 100 mol%, preferably 98 to 100 mol%. The average degree of polymerization of the polyvinyl alcohol of the present invention is 110 in order to obtain the effects of the present invention.
0 or more, preferably 1500 or more, more preferably 26
Polyvinyl alcohol having a high degree of polymerization of 00 to 5000 is advantageous.

If the average degree of polymerization is less than 1100, the initial polarization performance (polarization degree, transmittance) is low, and the optical performance is largely deteriorated under high temperature and high humidity conditions, and the effect of the present invention is difficult to obtain.

As a method for producing a polyvinyl alcohol film, a stock solution obtained by dissolving polyvinyl alcohol in water or an organic solvent is cast to form a film, which is then stretched and dyed with iodine or an azo type, anthraquinone type, or tetrazine type two-color film. Examples of the method include dyeing with a sex dyeing, stretching and dyeing at the same time, or dyeing and stretching, and then treating with a boron compound. As the solvent used in preparing the stock solution, water, dimethyl sulfoxide, N-methylpyrrolidone, glycerin, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyhydric alcohols such as trimethylolpropane, ethylenediamine, diethylenetriamine. Amines such as and mixtures thereof.

A small amount, for example, 5 to 30% by weight in the above solvent
There is no problem even if it contains water. The concentration of polyvinyl alcohol in the stock solution is practically about 5 to 20% by weight. The polyvinyl alcohol film-forming stock solution obtained by using the solvent is formed into a film by an arbitrary method such as a casting method or an extrusion method. The film-forming method is a dry / wet film-forming method, that is, the solution is once discharged from the mouth slit into the air or into an inert atmosphere such as nitrogen, helium, or argon, and then introduced into a coagulation bath for unstretching. Form a film. Alternatively, the film-forming solution discharged from the die may be introduced into the coagulation bath after the solvent is partially dried on a roller, a belt conveyor or the like.

The solvent used in the coagulation bath is miscible with the solvent of polyvinyl alcohol, and examples thereof include alcohols such as methanol, ethanol, propanol and butanol, acetone, benzene and toluene. As a method for obtaining a polyvinyl alcohol-based film, a method called a so-called gel stretching method other than the above can be adopted.

That is, polyvinyl alcohol is dissolved in a solvent so that the polymer concentration is 30% or less to prepare a polyvinyl alcohol film-forming stock solution. The solution is discharged into air or an inert atmosphere through a slit-shaped die and then introduced onto a roller or belt conveyor whose surface is cooled or into a coagulating liquid to form a gelled film. The gelled film is desolvated and then stretched. The film forming method is almost the same as the dry / wet film forming method, but there is a difference in that a gelled film is formed so that the polymer concentration does not change from the stock solution.

Examples of the solvent for the polyvinyl alcohol film-forming stock solution in this case include polyhydric alcohols such as glycerin, ethylene glycol, tetraethylene glycol, trimethylolpropane, benzenesulfonamide, and caprolactam.

The polyvinyl alcohol-based unstretched film obtained as described above is then stretched and dyed. Stretching and dyeing may be performed separately or simultaneously.
When they are performed separately, the order of stretching and dyeing is arbitrary. It is desirable that the stretching is 3.5 times or more, preferably 4.5 times or more in the uniaxial direction. At this time, some stretching (stretching to a degree that prevents shrinkage in the width direction or more) may be performed in the direction perpendicular to the above. The temperature condition during stretching is appropriately selected from the range of 50 to 130 ° C.

The dyeing of the film, that is, the adsorption of the polarizing element is performed by bringing the liquid containing the polarizing element into contact with the film. Usually, an aqueous solution of iodine-potassium iodide or an aqueous solution of an azo-based, anthraquinone-based or tetrazine-based dichroic dye is used. Iodine concentration is 0.1-2.0 g / l, potassium iodide concentration is 10-
50 g / l, iodine / potassium iodide weight ratio is 20-
100 is suitable, and the concentration of the dichroic dye is 0.1 to 0.1.
3.0 g / l is suitable. Practical dyeing time is about 30 to 500 seconds. A small amount of an organic solvent compatible with water may be contained in addition to the water solvent.

As the contact means, any means such as dipping, coating and spraying can be applied. The stretched and dyed film is then treated with a boron compound. Boric acid and borax are practical as the boron compound. The boron compound has a concentration of 0.5 in the form of an aqueous solution or a water-organic solvent mixture.
It is used at about 2.0 mol / l.

The treatment method is preferably dipping, but of course the coating method and the spraying method are also practical. The processing temperature is 50 to 70 ° C,
The treatment time is preferably about 5 to 20 minutes, and if necessary, a stretching operation may be performed during the treatment or after the treatment.

The polarizing plate of the present invention is obtained by laminating a specific protective film on at least one surface of the polyvinyl alcohol-based film having the above-mentioned polarizing performance. As the above-mentioned protective film, one having low moisture permeability and optical characteristics that does not impair the performance as a polarizing plate is used. Specifically, the moisture permeability is 200 g / m ² · 24 hr · 100μ or less under the measurement conditions of 80 ° C. and 90% RH,
If the water vapor transmission rate is more than 200 g / m ² · 24 hr · 100μ, the effect in terms of optical durability decreases, and preferably 100
g / m ² · 24 hr · 100μ or less, photoelastic coefficient is 1 × 10 ^-11 cm ² / dyne or less, and photoelastic coefficient is 1 × 1
When it is larger than 0 ^-11 cm ² / dyne, optical distortion is apt to occur due to external stress and causes optical spots, preferably 1 ×.
It is necessary that it is 10 ^-12 cm ² / dyne or less and is substantially transparent as an optical property, and a light transmittance of 90% or more in a 100 μ film. The photoelastic coefficient is a value indicating the degree of optical strain with respect to external stress. The smaller the value, the better the optical property as a protective film for a polarizing plate, and the measurement was performed using an ellipsometer at a wavelength of 633 nm. .

The protective film used in the present invention can be used as long as it satisfies the above-mentioned conditions, and polymers such as amorphous nylon and cyclic olefin can be used. In particular, a thermoplastic resin which is a cyclic olefin polymer can be used. Saturated norbornene resin has excellent acid resistance and chemical resistance, and its photoelastic coefficient is 3
~ 9 × 10 ^-13 cm ² / dyne, small and water vapor transmission rate is 80
40 to 70 g / m ² · 24 hr · 1 at 90 ° C and 90% RH
It shows a low value of 00μ and is a material suitable as a protective film.

Examples of the thermoplastic saturated norbornene-based resin include (a) ring-opening (co) of norbornene-based monomers.
The polymer is optionally subjected to modification such as maleic acid addition or cyclopentadiene addition, and then hydrogenated resin, (b) resin obtained by addition polymerization of norbornene-based monomer, (ha) norbornene-based monomer and ethylene, Resins that are addition-polymerized with olefin-based monomers such as α-olefins, (d) Norbornene-based monomers and resins that are addition-polymerized with cyclic olefin-based monomers such as cyclopentene, cyclooctene, and 5,6-dihydrodicyclopentadiene To be The polymerization is carried out by using I as a polymerization catalyst.
Hydrochloride of trichloride of r, Os and Ru, MoCl ₅ , WC
l ₆ , ReCl ₅ , (C ₂ H ₅ ) ₃ Al, (C ₂ H ₅ ) ₃
Al / TiCl ₄ , (π-C ₄ H ₇ ) ₄ Mo / TiCl
₄ , (π-C ₄ H ₇ ) ₄ W / TiCl ₄ , (π-C ₃ H ₅
) ₃ Cr / WCl ₆ or the like can be used in a conventional manner, and hydrogenation can be carried out in a conventional manner.

Examples of the norbornene-based monomer include norbornene and 5-methyl-2-norbornene,
Alkyl and / or alkylidene substituents such as 5-dimethyl-2-norbornene, 5-ethyl-2-norbornene, 5-butyl-2-norbornene and 5-ethylidene-2-norbornene, and polar group substituents thereof such as halogen ;
6-methyl-1,4: 5,8-dimethano-1,4,4
a, 5,6,7,8,8a-octahydronaphthalene,
6-ethyl-1,4: 5,8-dimethano-1,4,4
a, 5,6,7,8,8a-octahydronaphthalene,
6-Ethylidene-1,4: 5,8-dimethano-1,4,4
4a, 5,6,7,8,8a-octahydronaphthalene, 6-chloro-1,4: 5,8-dimethano-1,4
4a, 5,6,7,8,8a-octahydronaphthalene, 6-cyano-1,4: 5,8-dimethano-1,4
4a, 5,6,7,8,8a-octahydronaphthalene, 6-pyridyl-1,4: 5,8-dimethano-1,
4,4a, 5,6,7,8,8a-octahydronaphthalene, 6-methoxycarbonyl-1,4: 5,8-dimethano-1,4,4a, 5,6,7,8,8a-octa Dimethanooctahydronaphthalene such as hydronaphthalene,
Its alkyl and / or alkylidene substituents, and polar substituents such as halogens; dicyclopentadiene, 2,3-
Dihydrodicyclopentadiene and the like; 4,9: 5,8-dimethano-3a, 4,4a, 5,8,8a, 9,9a-octahydro-1H-benzoindene, 4,11: 5,1
0: 6,9-trimethano-3a, 4,4a, 5,5a,
Examples include cyclopentadiene trimer and tetramer such as 6,9,9a, 10,10a, 11,11a-dodecahydro-1H-cyclopentaanthracene.

The above cyclic olefin polymer or the like can be used as a protective film for a polarizing plate by using a known film forming method such as a solvent casting method or an extrusion method.

An adhesive is usually used to bond the protective film to at least one surface of the polyvinyl alcohol-based film having a polarizing property. Examples of the adhesive include an acrylic adhesive and a polyester-isocyanate adhesive. Agents and the like are used. If desired, various additives such as phenol-based or phosphorus-based antioxidants, antistatic agents, and ultraviolet stabilizers may be added to the polymer compound forming the protective film.

A pressure-sensitive adhesive layer and a release film can be further added to the polarizing plate thus obtained.

[0027]

The polarizing plate of the present invention has excellent resistance to moisture and heat at high temperatures and maintains a high degree of polarization and a high single substance transmittance even after being left for a long time. It is also very useful when used under various conditions.

[0028]

EXAMPLES The present invention will be described in more detail below with reference to examples. The degree of polarization referred to in the present invention is expressed by the equation 1.

[0029]

[Equation 1] Here H ₁₁ at the time of superposition of two polarizing film sample, transmittance orientation direction was measured using a spectrophotometer in a state superimposed so as to become the same direction of the polarizing film (%), H ₁ Is the transmittance (%) measured in a state in which the two polarizing plates were superposed so that the orientation directions of the polarizing films were orthogonal to each other.

Example 1 100 parts of polyvinyl alcohol having an average degree of polymerization of 3800 and a saponification degree of 99.5 mol% was dissolved in water to obtain a solution having a concentration of 5.0% by weight. The liquid was cast on polyethylene terephthalate and dried to obtain a raw film. This film was attached to the chuck and iodine 0.2 g / l, potassium iodide 6
Immerse in an aqueous solution of 0 g / l at 30 ° C. for 240 seconds, then boric acid 70 g / l, potassium iodide 30 g / l
While being dipped in an aqueous solution having a composition of 1 and simultaneously uniaxially stretched 6.0 times, the boric acid treatment was performed for 5 minutes. Finally, it was dried at room temperature for 24 hours. Using an acrylic adhesive on both sides of the film, 6-methyl-1, 4, 5, 8-
Dimethano-1,4,4a, 5,6,7,8,8a Ring-opening polymerization of octahydronaphthalene, thermoplastic saturated norbornene-based resin (80 ° C, 90
A film (thickness 100 μm) produced by a casting method having a moisture permeability of 50 g / m ² · 24 hr · 100 μm and a photoelastic coefficient of 6.3 × 10 ⁻¹³ cm ² / dyne at% RH was used as a laminated polarizing plate.

Moisture and heat resistance test (80 ° C.,
90% RH, left for 500 hours) to measure the transmittance and the degree of polarization of a single substance with a spectrophotometer (Nippon Denshoku Industries Co., Ltd. SZS-
Σ80) was measured to evaluate the amount of change before and after the test. The results are shown in Table 1.

Example 2 The same experiment as in Example 1 was conducted except that polyvinyl alcohol having an average degree of polymerization of 1700 and a saponification degree of 99.7 mol% was used. The results are shown in Table 1.

Comparative Example 1 80 ° C., 90% RH, moisture permeability 320 g / m ² · 24 h
r · 100μ, photoelastic coefficient 6.0 × 10 ⁻¹³ cm ² / d
The same experiment as in Example 1 was performed, except that a polymethylmethacrylate film (thickness 100 μm) prepared by a casting method of yne was used as the protective film. The results are shown in Table 1.

Comparative Example 2 80 ° C., 90% RH, moisture permeability 620 g / m ² · 24 h
r · 100μ, photoelastic coefficient 7.2 × 10 ⁻¹² cm ² / d
Polycarbonate film that is yne (thickness 100
The same experiment as in Example 1 was carried out except that μ) was used as a protective film. The results are shown in Table 1.

Comparative Example 3 At 80 ° C. and 90% RH, the moisture vapor transmission rate is 23 g / m ² · 24 hr.
・ 100μ, photoelastic coefficient 2.7 × 10 ^-11 cm ² / dy
ne high density polyethylene film (thickness 100
The same experiment as in Example 1 was carried out except that μ) was used as a protective film. The results are shown in Table 1.

[0036]

[Table 1]Polarizing ability Immediately after production After moist heat resistance test  Single transmittance, polarization degree Single transmittance, polarization degree(%) (%) Change amount Change amount Example 1 40.0 100.0 +0.3 -1.7 Example 2 39.8 100.0 +3.3 -2.1 Comparative Example 1 40.1 100.0 +7.8 -14.8 Comparative Example 239.5 100.0 +9.1 -15.1Comparative Example 3 39.9 100.0 +8.8 -17.3

[0037]

EFFECTS OF THE INVENTION According to the present invention, a polarizing plate excellent in moisture and heat resistance at high temperature and having a high degree of polarization and a high single substance transmittance even after being left for a long time can be obtained. It is also very useful when used under severe conditions such as display.

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] November 11, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction content]

The degree of saponification in polyvinyl alcohol is practically 85 to 100 mol%, preferably 98 to 100 mol%. The average degree of polymerization of the polyvinyl alcohol of the present invention is 110 in order to obtain the effects of the present invention.
0 or more, preferably 1500 or more, more preferably 26
Highly polymerized polyvinyl alcohol having a degree of polymerization of from 00 to 5000 , particularly preferably from 3500 to 5000 , is advantageous.

Claims (4)

[Claims] 1. A protective film is laminated on at least one surface of a polyvinyl alcohol-based film having polarization performance imparted by adsorption orientation of iodine or a dichroic dye,
Polarization degree is 95 after standing at 80 ° C, 90% RH for 500 hours.
%, And a simple substance transmittance of 38% or more. 2. The moisture permeability of the protective film is 80 ° C., 90%
^2. The polarizing plate according to claim 1, which has an RH of 200 g / m ² · 24 hr · 100 μ or less and a photoelastic coefficient of 1 × 10 ⁻¹¹ cm ² / dyne or less. 3. The polarizing plate according to claim 1, wherein the protective film is a thermoplastic saturated norbornene resin. 4. The polyvinyl alcohol film has an average degree of polymerization of 2600 or more.
<3> The polarizing plate according to any one of <3> to <3>.