JPH05100115A - Polarizing film - Google Patents

Abstract

PURPOSE:To provide the polarizing film having extremely outstanding water resistance, wet heat resistance, durability and optical characteristics. CONSTITUTION:This polarizing film consists of an ethylene/vinyl alcohol copolymer(EVOH) having >=0.1liter/g ultimate viscosity measured at 30 deg.C in a solvent mixture composed of 85wt.% phenol and 15wt.% water and 3 to 24mol% ethylene content. A film consisting of the EVOH having >=0.1liter/g ultimate viscosity and 13 to 24mol% ethylene content is immersed into water kept at >=40 deg.C and is then dyed by an iodine compd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing film which is excellent in heat resistance, wet heat resistance and durability and has optical characteristics of high polarization degree and high transmittance.

[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 clock, a calculator, a word processor, and instrumentation for machinery, and the demand for display quality has not been particularly strict, but in recent years It has been widely used as a display for laptop word processors, laptops and notebooks, displays for automobiles and aircraft instrument panels, and liquid crystal projectors, and is required to be large in size, high in display quality, and improved in durability. ing. Therefore, in order to achieve the above-mentioned problems also regarding the polarizing film which is a component of the liquid crystal display device, in addition to improving the optical characteristics such as a large screen, high polarization degree and high transmittance, water resistance, heat resistance, and moisture resistance are provided. Improvements in heat resistance and durability are required.

Conventionally, as a polarizing film, a uniaxially stretched film of polyvinyl alcohol dyed with iodine or a dichroic substance has been often used. Although this polarizing film has an excellent degree of polarization, it has water resistance and wet heat resistance. And poor in durability. On the other hand, a proposal of using a uniaxially stretched film of polyvinyl alcohol having a high degree of polymerization as a base material of a polarizing film (for example, JP-A-1-105204) or a proposal of using a uniaxially stretched polyester film as a base material of a polarizing film. (For example, JP-A-58-68008). However, in the former, although the effect of the degree of polymerization is recognized, it is not always sufficient, and in the latter, the drawback of the polarizing film using a polyvinyl alcohol-based resin as a base material is improved to some extent, but the polarizing property is insufficient. However, it has not been able to sufficiently meet the above requirements. A polarizing film based on an ethylene-vinyl alcohol copolymer has also been proposed (for example, JP-A-55-7735). However, when an iodine-based compound is used as a dichroic substance, usually using an ethylene-vinyl alcohol-based copolymer as a base material, the dyeability of the iodine-based compound is poor, the color tone does not become neutral gray, and a slightly yellowish tint is obtained. The film became impregnated and could not be obtained in terms of polarization and color tone.

[0004]

Under such circumstances, the present invention has excellent optical characteristics such as high polarization degree and high transmittance, and also has excellent optical characteristics even when left for a long time under high temperature and high humidity. The present invention provides a polarizing film having reduced heat and humidity resistance, heat resistance and durability.

[0005]

Means for Solving the Problems As a result of intensive studies aimed at solving the above problems, the present inventors have found that 85% by weight of phenol is used.
Intrinsic viscosity of 0.1 liter / g or more and ethylene content of 3 to 24 measured in a mixed solvent of 15% by weight of water and 30% by weight
The present invention has been completed by finding a polarizing film composed of an ethylene-vinyl alcohol-based copolymer of mol%.

The present invention will be described in detail below. The ethylene-vinyl alcohol-based copolymer used in the polarizing film of the present invention is an ethylene-vinyl alcohol-based copolymer having an intrinsic viscosity of 0.1 liter / g or more and an ethylene content of 3 to 24 mol%.

The intrinsic viscosity of the ethylene-vinyl alcohol copolymer must be 0.1 liter / g or more, preferably 0.13 liter / g or more, and 0.14 liter / g or more.
L / g or more is more preferable, and 0.15 L /
More than g is more preferable. The upper limit of the intrinsic viscosity is not particularly limited, but 0.36 liter / g or less is preferable from the viewpoint of workability such as film formation and stretching of the ethylene-vinyl alcohol copolymer. When the intrinsic viscosity is less than 0.1 liter / g, the optical properties, water resistance, wet heat resistance, durability, etc. are deteriorated, which is not preferable. Where ethylene
Intrinsic viscosity of vinyl alcohol copolymer (liter /
g) is a value measured at 30 ° C. in a mixed solvent of 85% by weight of phenol and 15% by weight of water.

The ethylene content of the ethylene-vinyl alcohol copolymer must be 3 to 24 mol%, preferably 5 to 24 mol%, more preferably 8 to 20 mol%. When the ethylene content is less than 5 mol%, the water resistance, wet heat resistance and durability of the polarizing film are deteriorated, which is not preferable. When the ethylene content exceeds 24 mol%, the water resistance and heat resistance of the polarizing film are improved,
This is not preferable because it causes problems in the steps such as dyeing and orientation with a dichroic substance, and when an iodine-based compound is used as the dichroic substance, the optical characteristics deteriorate.

The degree of saponification of the vinyl ester unit of the ethylene-vinyl alcohol copolymer is preferably 90 mol% or more, more preferably 95 mol% or more, even more preferably 98 mol% or more.

The method for producing the ethylene-vinyl alcohol copolymer used in the present invention is not particularly limited, but the ethylene-vinyl ester copolymer obtained by copolymerizing ethylene with a vinyl ester monomer such as vinyl acetate. The method of saponifying the copolymer is preferred.

In copolymerizing ethylene and vinyl ester, monomers other than these may be copolymerized to the extent that the gist of the present invention is not impaired. Examples of such comonomers include olefins such as propylene, 1-butene, and isobutene, acrylic acid and salts thereof, methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, and n-acrylic acid. -Butyl,
Acrylic esters such as i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate, methacrylic acid and its salts, methyl methacrylate, ethyl methacrylate, n-methacrylic acid Propyl, methacrylic acid i-
Propyl, n-butyl methacrylate, i-methacrylic acid
Butyl, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, and other methacrylate esters, acrylamide, N-methyl acrylamide, N-ethyl acrylamide, N, N-dimethyl acrylamide, diacetone acrylamide , Acrylamidopropanesulfonic acid and its salts, acrylamidopropyldimethylamine and its salts or quaternary salts thereof, acrylamide derivatives such as N-methylolacrylamide and its derivatives, methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacryl Amidopropanesulfonic acid and salts thereof, methacrylamidopropyldimethylamine and salts thereof or quaternary salts thereof, N-methylolmethacrylamide and And methacrylamide derivatives such as derivatives thereof, methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, and other vinyl ethers, acrylonitrile , Nitriles such as methacrylonitrile, vinyl chloride, vinylidene chloride, vinyl fluoride,
Vinyl halide such as vinylidene fluoride, allyl acetate,
Examples thereof include allyl compounds such as allyl chloride, maleic acid and salts or esters thereof, vinylsilyl compounds such as vinyltrimethoxysilane, and isopropenyl acetate.

As the dichroic substance used in the polarizing film of the present invention, not only iodine compounds but also so-called dichroic substances are used alone or in combination. Examples of dichroic dyes include Direct black 17, 19, 154, Direct brown 44, 10
6, 195, 210, 223, Direct red2, 23, 28, 31, 37, 3
9, 79, 81, 240, 242, 247, Direct blue 1, 15, 22, 7,
8, 90, 98, 151, 168, 202, 236, 249, 270, Direct vi
olet 9, 12, 51, 98, Direct green 1, 85, Direct yel
low 8, 12, 44, 86, 87, Direct orange 26, 39, 106,
107 etc. are mentioned.

The polarizing film of the present invention is manufactured, for example, by the following method. One is a method of producing a film of an ethylene-vinyl alcohol-based copolymer, followed by dyeing with a dichroic substance such as an iodine compound or a dye and uniaxial stretching. The order is arbitrary. The other is a method of uniaxially stretching a film containing a dichroic substance obtained by adding a dichroic substance during the production of the film, and the polarizing film of the present invention can be produced by either method. ..

Film formation of the ethylene-vinyl alcohol copolymer film can be obtained by melt film formation or film formation from a solution. Film formation from ethylene-vinyl alcohol copolymer solution is cast film formation, dry film formation (extrusion into air or inert gas such as nitrogen), wet film formation (ethylene-
(Extrusion of vinyl alcohol-based copolymer into poor solvent), dry-wet film formation, gel film formation (method of once gelating ethylene-vinyl alcohol-based polymer solution to obtain film). .. Solvents used during film formation include dimethyl sulfoxide, dimethylformamide, dimethylacetamide, ethylene glycol,
Glycerin, methanol, n-propanol, i-propanol, phenol, water and the like are used alone or as a mixture. Further, an aqueous solution of an inorganic salt such as lithium chloride or calcium chloride may be used alone or as a mixture with the organic solvent. Among these solvents, water, dimethyl sulfoxide, a mixed solvent of dimethyl sulfoxide and water, and a mixed solvent of n-propanol and water are preferably used.

The film of the ethylene-vinyl alcohol copolymer obtained by the above film forming method is dyed with a dichroic material and subjected to orientation treatment by uniaxial stretching, or a dichroic material is added at the time of film formation. Only uniaxial stretching is performed on the formed film. The above dyeing treatment and orientation treatment may be performed simultaneously or separately, and the order thereof is arbitrary.

The dyeing of the base film with the dichroic material is
Usually, it is carried out by immersing the substrate film in a liquid containing a dichroic substance, but there are no particular restrictions on the processing conditions, method, etc. As a liquid containing a dichroic substance,
For example, when an iodine compound is used as the dichroic substance, an aqueous solution of iodine-potassium iodide is used, and when a dye is used as the dichroic substance, an aqueous dye solution is used. Further, a boron compound such as boric acid or borax may be added to the liquid containing these dichroic substances.

Before the base film is dyed (or oriented) with a dichroic substance, the base film is preferably swollen with water or the like. By swelling the base film, optical properties such as polarization properties and color tone are improved. The temperature of the liquid during the swelling treatment of the base film varies depending on the ethylene content, the intrinsic viscosity and the crystallinity of the base film, but an ethylene-vinyl alcohol copolymer having an ethylene content of 13 mol% or less is used. In this case, it is preferable to swell the base film at a temperature of 5 to 55 ° C. Further, in order to obtain a polarizing film having sufficient wet heat resistance and excellent optical properties, an ethylene-vinyl alcohol copolymer having an ethylene content of 13 to 24 mol% is used, and 40 ° C. or higher (preferably Is 60 ° C
As mentioned above, it is preferable to dye with an iodine compound after immersing in water of preferably 98 ° C. or lower). By swelling the base film by immersing the base film in water at 40 ° C. or higher prior to dyeing with an iodine compound, the color tone is close to neutral gray and the optical characteristics and durability are improved.

The stretching is carried out by wet stretching or dry heat type stretching, preferably uniaxially at least 3 times, more preferably at least 5 times. The temperature during stretching varies depending on the stretching conditions, but is usually between 20 and 250 ° C. In the case of dry heat stretching, it is preferable to perform stretching in an inert gas. The film thickness after stretching is not particularly limited, but is preferably 3 to 100 μm, particularly preferably 5 to 40 μm. The adsorbed and stretched film is dried in air or an inert gas under a fixed length. The dried film may be further heat-treated at a temperature of 80 to 230 ° C. in order to impart water resistance and moist heat resistance. Further, a boron-based compound such as boric acid or borax may be added for the purpose of strengthening the adsorption of the dichroic material to the base film, and the addition of the boron-based compound is not limited to dyeing and stretching. It may be carried out at the same time, and may be carried out before or after dyeing or stretching, or at any point during that time.

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.

[0020]

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, the degree of polarization, and the hue were measured according to the Japan Electronic Machinery Manufacturers Association Standard (EIAJ) LD-201-1983, and were calculated using a spectrophotometer with a C light source and a double visual field.

Example 1 An ethylene-vinyl alcohol copolymer having an ethylene content of 9.2 mol%, an intrinsic viscosity of 0.16 liter / g, and a saponification degree of 99.8 mol% was added to water / n-propanol = 8/2.
The liquid film of the solution dissolved in the mixed solvent (weight ratio) was dried at 70 ° C. to obtain a film of the copolymer. The obtained film was swollen by immersing it in water at 30 ° C. for 10 minutes, and then the film was swelled with iodine (0.063% by weight) and potassium iodide (0.
(042% by weight) and then dipped in an aqueous solution containing 4% by weight of boric acid at a rate of 100% / min.
The film was stretched up to 5 times and dried at 50 ° C. to obtain a polarizing film. The optical properties of the obtained polarizing film are a transmittance of 45.2% and a polarization degree of 97.4%, and the optical properties after leaving for 10 days in an atmosphere of 40 ° C. and 90% RH are the transmittance of 46.8%. The polarization degree was 94.2%.

Comparative Example 1 A liquid film of an aqueous solution of a polyvinyl alcohol copolymer having an intrinsic viscosity of 0.16 liter / g and a saponification degree of 99.9 mol% was dried at 70 ° C. to obtain a film of the polymer. The obtained polarizing film was treated in the same manner as in Example 1 to obtain a polarizing film. The optical property of the obtained polarizing film is a transmittance of 45.6.
%, The degree of polarization is 98.1%, and the optical characteristics after being left for 10 days in an atmosphere of 40 ° C. and 90% RH have a transmittance of 70.
The degree of polarization was 2% and the degree of polarization was 22.4%.

Comparative Example 2 Intrinsic viscosity 0.086 liter / g, ethylene content 9.
A polarizing film was obtained in the same manner as in Example 1 except that an ethylene-vinyl alcohol-based copolymer having 6 mol% and a saponification degree of 99.8 mol was used. The optical properties of the obtained polarizing film are a transmittance of 42.4% and a polarization of 91.5%, and the optical properties after leaving it for 10 days in an atmosphere of 40 ° C. and 90% RH are 60.8%. , Polarization degree 32.6%
Met.

Example 2 Intrinsic viscosity 0.168 liter / g, ethylene content 1
A film was obtained in the same manner as in Example 1 except that an ethylene-vinyl alcohol copolymer having a saponification degree of 9.8 mol% and a saponification degree of 99.8 mol was used. The obtained film was immersed in water at 80 ° C. for 10 minutes to be swollen, and the film was treated in the same manner as in Example 1 to obtain a polarizing film. The optical properties of the obtained polarizing film are such that the transmittance is 43.7% and the polarization degree is 98.
3%, and the hue has an a value of -0.02 and a b value of 1.
It was 3. The optical property of the polarizing film left for 10 days in an atmosphere of 40 ° C. and 90% RH has a transmittance of 44.
The degree of polarization was 9% and the degree of polarization was 97.1%.

Example 3 Intrinsic viscosity 0.168 liter / g, ethylene content 1
Example 1 except that an ethylene-vinyl alcohol copolymer having a saponification degree of 9.8 mol% and a saponification degree of 99.8 mol% was used.
A film was obtained by the same method as described above. The obtained film was immersed in water at 30 ° C. for 10 minutes to be swollen, and the film was treated in the same manner as in Example 1 to obtain a polarizing film. The optical properties of the obtained polarizing film are as follows: transmittance 42.3%, polarization degree 8
The hue was 0.1%, and the hue was a value -10.2 and b value 31.4. The polarizing film at 40 ° C, 90% R
The optical characteristics after leaving it to stand in an atmosphere of H for 10 days were such that the transmittance was 46.5% and the polarization degree was 75.3%.

[0026]

As is apparent from the above examples, the polarizing film of the present invention has a higher degree of polarization and a higher degree of transmittance than the conventional polarizing film even when left for a long time under high temperature and high humidity. It is excellent in water resistance, wet heat resistance, and durability with little deterioration in optical characteristics. That is, the polarizing film of the present invention solves the deterioration of optical properties due to water, humidity and heat, which are the biggest drawbacks of the conventional polarizing films based on polyvinyl alcohol-based polymers, and the conventional ethylene-vinyl. The color tone, which was a defect of the polarizing film obtained by dyeing an alcohol-based copolymer film with an iodine-based compound, was improved to a color tone close to a neutral gray color, and the optical characteristics were improved. The polarizing film obtained in the present invention makes use of the above characteristics, and is a high-performance, highly durable liquid crystal display, for example, a liquid crystal television, a liquid crystal projector,
Display for word processor, display for PC, O
A device terminal display, aircraft and car instrument panel display, other filters,
Used for sunglasses, window glass, anti-glare of various lights, various sensors, etc.

Claims (2)

[Claims] 1. An intrinsic viscosity of 0.1 liter / measured at 30 ° C. in a mixed solvent of 85% by weight of phenol and 15% by weight of water.
A polarizing film comprising an ethylene-vinyl alcohol-based copolymer having an amount of g or more and an ethylene content of 3 to 24 mol%. 2. An intrinsic viscosity of 0.1 liter / measured at 30 ° C. in a mixed solvent of 85% by weight of phenol and 15% by weight of water.
a film made of an ethylene-vinyl alcohol copolymer having a content of g or more and an ethylene content of 13 to 24 mol% is 4
A method for producing a polarizing film, comprising immersing in water at 0 ° C. or higher and then dyeing with an iodine compound.