JPH08190017A - Production of polarizing film - Google Patents

Abstract

PURPOSE: To provide a polarizing film having excellent optical characteristics and durability against humidity and heat by forming a film of specified thickness from a soln. containing a specified polyvinylalcohol polymer and specified amt. of iodine and uniaxially stretching the film by specified times. CONSTITUTION: A soln. containing polyvinylalcohol polymer (PVA) having >=55% of sydiotacticity and iodine is formed into a film, which is then uniaxially stretched into a size three or more times as large. The syndiotacticity of PVA is >=55% and preferably >=57%, and its upper limit is <=75%. The amt. of iodine is controlled to 0.001-1wt.% of PVA, preferably 0.001-1wt.%. The thickness of the source film is 50-150μm, and preferably 30-100μm. The times of stretching is preferably >5. By this method, stable PVA-iodine complex can be formed and highly oriented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polarizing film having excellent optical properties and resistance to moist heat.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal display device has been used as a display device having a relatively small screen such as a timepiece, a calculator, a word processor, and instrumentation for machinery, and the demand for display quality has not been particularly severe. However, in recent years, liquid crystal display devices have come to be widely used as displays for laptop word processors, laptop computers, notebook computers, displays for instrument panels of automobiles, aircrafts, liquid crystal projectors, etc., and are large in size and high in display quality. And improved durability are required. Therefore, regarding the polarizing film which is a component of the liquid crystal display device, in order to achieve the above-mentioned problems, a large screen, improvement in optical characteristics such as high polarization degree and high transmittance and water resistance, heat resistance, wet heat resistance, etc. Improved durability is required.

Conventionally, a uniaxially stretched film of a polyvinyl alcohol polymer having adsorbed iodine or a dichroic dye is often used as a polarizing film. This polarizing film has an excellent degree of polarization, but is water resistant. , Poor in moist heat resistance and durability. On the other hand, a proposal using a uniaxially stretched film of a polyvinyl alcohol-based polymer having a high degree of polymerization as a base material (for example, JP-A-1-105204, etc.) and a polarizing film using a uniaxially stretched polyester film as a base material ( For example, JP-A-58-68008). However, in the former, the effect of the degree of polymerization is not necessarily sufficient although it is recognized, and in the latter, the drawback of the polarizing film of the polyvinyl alcohol-based polymer substrate is improved to some extent, but the degree of polarization is insufficient. The above requirements cannot be fully answered.

Therefore, in order to obtain a polarizing film made of a polyvinyl alcohol-based polymer having high optical characteristics and high humidity and heat resistance, a polarizing film is produced by using a polyvinyl alcohol-based polymer film having enhanced syndiotacticity. Have been proposed (JP-A-3-206402 and JP-A-3-274508). However, since a polyvinyl alcohol-based polymer film having high syndiotacticity has high crystallinity, crystallization of the polyvinyl alcohol-based polymer occurs preferentially depending on the production method, and a stable polyvinyl alcohol-based polymer-iodine complex is obtained. However, there was a problem in that the optical characteristics could not be obtained as expected, because it was not possible to form

[0005]

Under such circumstances, the present invention provides a method for producing a polarizing film having excellent optical characteristics and resistance to moist heat.

[0006]

Means for Solving the Problems As a result of intensive studies aimed at solving the above-mentioned problems, the present inventors have found that a polyvinyl alcohol polymer having a syndiotacticity of 55% or more and the polyvinyl alcohol polymer. Thickness of 5 to 150 μm formed by forming a solution containing 0.001 to 1% by weight of iodine
The present invention has been completed by finding out a method for producing a polarizing film, which comprises stretching the film (1) in the uniaxial direction three times or more.

Hereinafter, the present invention will be described in detail. The method for producing a polarizing film of the present invention, by adopting the above method,
It is characterized in that a stable polyvinyl alcohol polymer-iodine complex is formed and highly oriented.

It is important that the polyvinyl alcohol polymer of the present invention has high syndiotacticity.
Since the polyvinyl alcohol-based polymer-iodine complex is stabilized as the syndiotacticity becomes higher, specifically, the syndiotacticity value is preferably 55% or more.
% Or more is more preferable, and 60% or more is even more preferable. Further, the upper limit of syndiotacticity is 75% or less, preferably 70% or less, due to the restrictions on the production of the polyvinyl alcohol polymer. The syndiotacticity here means that a polyvinyl alcohol-based polymer is dissolved in deuterated dimethylsulfoxide, and a peak of a hydroxyl group (T. Moritanieta) in proton NMR measurement is obtained.
l. , Macromolecules, 5, 577,
(1972). It is syndiotacticity by the dyad display obtained from.

The molecular weight of the polyvinyl alcohol polymer used in the present invention also affects the performance of the polarizing film of the present invention. The molecular weight is 0.3 to 7 in terms of the intrinsic viscosity of polyvinyl acetate obtained by completely saponifying a polyvinyl alcohol-based polymer and then acetylating it at 30 ° C in acetone.
0 dl / g is preferable, 0.4 to 6.0 dl / g is more preferable, and 0.5 to 5.0 dl / g is even more preferable. Optical properties when the intrinsic viscosity is less than 0.3 dl / g,
Performances such as water resistance, wet heat resistance, and durability are deteriorated. When the intrinsic viscosity is more than 7.0 dl / g, processing properties such as film formation and stretching are deteriorated.

The degree of saponification of the polyvinyl alcohol polymer of the present invention also affects the performance of the polarizing film of the present invention. In order to improve optical properties and mechanical properties, the saponification degree is preferably 95 mol% or more, more preferably 99 mol% or more,
Even more preferably, it is 9.9 mol% or more.

The polyvinyl alcohol polymer of the present invention may contain units other than the vinyl alcohol unit and the vinyl ester unit as long as the effects of the present invention are not impaired. Examples of such units include olefins such as ethylene, propylene, 1-butene, and isobutene; acrylic acid and salts thereof; acrylic acid such as methyl acrylate, ethyl acrylate, n-propyl acrylate, and i-propyl acrylate. Methacrylic acid and its salts; Methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate; acrylamide; N
-Acrylamido derivatives such as methyl acrylamide and N-ethyl acrylamide; methacrylamides; Methacrylamide derivatives such as N-methyl methacrylamide and N-ethyl methacrylamide; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-
Vinyl ethers such as propyl vinyl ether; Nitriles such as acrylonitrile and methacrylonitrile; Vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid, Examples thereof include salts or esters thereof; itaconic acid, salts or esters thereof; vinylsilyl compounds such as vinyltrimethoxysilane; and isopropenyl acetate. The content of these units is preferably 10 mol% or less, more preferably 5 mol% or less, still more preferably 3 mol% or less.

The method for producing the polyvinyl alcohol-based polymer of the present invention is not particularly limited, but is, for example, JP-A-3-686.
No. 04 and JP-A-3-121102 (the method of polymerizing a vinyl ester and then saponifying in the absence of oxygen in the presence of an alkali catalyst).

A method for producing a film by forming a solution containing the polyvinyl alcohol polymer and iodine is, for example, to dissolve the polyvinyl alcohol polymer and iodine in water, an organic solvent or a mixed solution of water and an organic solvent. Then, the obtained polyvinyl alcohol polymer solution may be molded on a resin film, a drying drum or a drying belt by a cast casting method or a die casting method, dried, and optionally heat treated. Examples of the organic solvent used at this time include dimethyl sulfoxide, dimethylformamide, dimethylacetamide, ethylene glycol, glycerin, methanol, n-propanol, i-propanol and phenol. Here, if necessary, inorganic salts such as potassium iodide and lithium chloride, inorganic substances such as boric acid, plasticizers, surfactants and the like can be added to the polyvinyl alcohol-based solution.

If the amount of iodine contained in the raw material film thus produced is too small, the optical properties of the polarizing film cannot be exhibited, and if it is too large, the optical properties, water resistance and heat resistance are deteriorated. Therefore, the amount is usually adjusted to 0.001% by weight to 1% by weight, preferably 0.001 to 0.5% by weight, based on the polyvinyl alcohol polymer. The thickness of the raw material film is 5 to 150 μm.
m can be used, and is preferably 30 to 100 μm.

In order to manufacture a polarizing film from the raw material film obtained by the above film forming method, an alignment treatment by uniaxial stretching is performed. As the uniaxial stretching, a wet stretching method and a dry stretching method, that is, a stretching method in warm water and a stretching method in water after absorbing water can be used. The draw ratio is 3 in the uniaxial direction.
It is preferable to carry out stretching twice or more, and it is more preferable to carry out stretching five times or more. The stretching temperature is 30 to 90 in the wet method.
C., and preferably 50 to 180.degree. C. in the dry method.

The adsorbed and stretched film is dried in air or an inert gas under a fixed length. The dried film has water resistance, moist heat resistance, etc.
You may heat-process at the temperature of 0 to 150 degreeC. Further, a boron compound such as boric acid or borax may be added for the purpose of strengthening the adsorption of the dichroic substance on the base film, but this may be carried out at the same time as adsorption or stretching. It may be performed at any point before, after, or during these processes.

The polarizing film thus obtained is used as a polarizing plate by laminating an optically transparent protective film having mechanical strength on both sides or one side thereof. As the protective film, a cellulose acetate film, an acrylic film, a polyester film or the like is usually used.

[0018]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the examples. The transmittance and the degree of polarization are measured in accordance with the Japan Electronic Machinery Manufacturers Association Standard (EIAJ) LD-201-1983,
Calculation was performed using a spectrophotometer in a C light source and a double visual field.

Example 1 Syndiotacticity obtained from vinyl pivalate 61.
5%, saponification degree 99.9 mol%, intrinsic viscosity (value of polyvinyl acetate obtained by acetylation in acetone at 30 ° C.)
0.79 dl / g of polyvinyl alcohol-based polymer, 100 parts by weight of iodine and potassium iodide, 0.0
3 parts by weight and 0.02 parts by weight were dissolved in 900 parts by weight of water, and the liquid film was dried at 50 ° C. to obtain a film of the polyvinyl alcohol polymer. 4% by weight of the swollen film obtained by swelling the obtained film in water at 50 ° C. for 10 minutes
Was stretched up to 4.7 times at a rate of 100% / min in the boric acid aqueous solution and dried at 50 ° C. to obtain a polarizing film. The transmittance and the polarization degree of the obtained polarizing film are respectively 44.5.
%, The degree of polarization was 99.2%, and the transmittance and the degree of polarization after standing for 10 days in an atmosphere of 40 ° C. and 90% RH were respectively 48.6% and 90.9%. .

Example 2 Syndiotacticity obtained from vinyl pivalate 61.
3%, saponification degree 99.9 mol%, intrinsic viscosity (value of acetylated polyvinyl acetate in acetone at 30 ° C.)
1.41 dl / g of polyvinyl alcohol-based polymer, iodine and potassium iodide 50 parts by weight, respectively 0.01
5 parts by weight and 0.010 parts by weight were dissolved in 950 parts by weight of water, and a polarizing film was prepared in the same manner as in Example 1. The stretch ratio was 4.5 times, and the transmittance and the polarization degree of the obtained polarizing film were respectively 44.9% and 98.7%.
And the transmittance and the polarization degree after standing for 10 days in an atmosphere of 40 ° C. and 90% RH are respectively 48.8%.
The polarization degree was 91.2%.

Comparative Example 1 Syndiotacticity 53.6% obtained from vinyl acetate,
Saponification degree 99.6 mol%, intrinsic viscosity (value of polyvinyl acetate obtained by acetylation at 30 ° C. in acetone) 0.81
A polarizing film was produced in the same manner as in Example 1 using a polyvinyl alcohol polymer having a dl / g. The stretching ratio was 4.7 times, the transmittance and the polarization degree of the obtained polarizing film were 44.6% and 98.5%, respectively, and the transmittance was 10 at 40 ° C. and 90% RH. The transmittance and the polarization degree after leaving for one day were 62.7% and 63.7%, respectively.

[0022]

As is apparent from the above examples, the polarizing film of the present invention is excellent in optical characteristics and resistance to moist heat as compared with conventional polarizing films. This was achieved for the first time by uniaxially stretching a film obtained by forming a solution containing a polyvinyl alcohol polymer having 55% or more of syndiotacticity and iodine. The polarizing film obtained by the present invention makes use of the above characteristics, and is a high-performance and highly durable liquid crystal display, such as a liquid crystal television, a liquid crystal projector, a word processor display, a personal computer display, an office equipment terminal display, and an instrument panel of an aircraft or automobile. It is used for displays, other filters, sunglasses, window glass, anti-glare for various lights, and various sensors.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Toshiaki Sato 1621 Sakata, Kurashiki City, Okayama Prefecture Kuraray Co., Ltd.

Claims (1)

[Claims] 1. A thickness 5 formed by forming a film containing a polyvinyl alcohol-based polymer having a syndiotacticity of 55% or more and 0.001 to 1% by weight of iodine with respect to the polyvinyl alcohol-based polymer. A method for producing a polarizing film, which comprises stretching a film having a thickness of ˜150 μm three times or more in a uniaxial direction.