JPH11119022A - Phase difference film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high durability phase difference film having improved water and wet heat resistances by using a specified ethylene-vinyl alcohol copolymer. SOLUTION: A film of an ethylene-vinyl alcohol copolymer having 1-25 mol.% ethylene content is uniaxially stretched and heat-treated to obtain an objective phase difference film. The ethylene-vinyl alcohol copolymer is obtd. by copolymerizing ethylene with a vinyl ester monomer such as vinyl acetate and saponifying the resultant ethylene-vinyl ester copolymer to convert the vinyl ester units to vinyl alcohol units. The ethylene content of the ethylene-vinyl alcohol copolymer largely affects the durability of the phase difference film. Since the water and wet heat resistances and durability of the film are deteriorated by a lowered ethylene content, the min. ethylene content of the copolymer is >=1 mol.%. Since the optical performance of the film is deteriorated by an excessively increased ethylene content, the max. ethylene content is <=25%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a retardation film. More specifically, the present invention relates to a retardation film having excellent wet heat resistance.

[0002]

2. Description of the Related Art A retardation film or a retardation plate is a film or a sheet having birefringence. Light passing through the retardation plate has different refractive indexes in two directions orthogonal to each other. A phase difference is generated between electric field vectors of orthogonal light beams. There is a λλ plate as a retardation plate which is currently commercially available and practically used. The ４λ plate produces a phase difference of １ ／ λ with respect to the wavelength λ of the incident light, and becomes a circularly polarizing plate when stuck at 45 ° to the optical principal axis of the linearly polarizing plate. Circularly polarizing plates have an anti-glare function of cutting reflected light and are therefore used for various anti-glare materials including VDT filters. On the other hand, in a conventional liquid crystal display device, the twist angle of liquid crystal molecules is 90 degrees, a pair of polarizing plates are provided above and below a liquid crystal cell, and the polarizing plates are arranged so that their absorption axes are orthogonal or parallel. It has been used for clocks and calculators (generally T
It is called an N-type liquid crystal display device). Attempts have been made to improve the display quality by applying a retardation plate to this TN type liquid crystal display device (for example, Japanese Patent Application Laid-Open Nos. 61-186937 and 60-26322). In recent years, a liquid crystal display device having a twist angle of liquid crystal molecules of 90 degrees or more, specifically, 180 to 270 degrees has been developed with an increase in display capacity and an enlargement of a liquid crystal screen (generally called an STN type liquid crystal display device). Is). However, there has been a problem that black and white display, which was possible with the conventional TN type liquid crystal display device, cannot be performed with the STN type liquid crystal display device due to coloring caused by birefringence of liquid crystal molecules. As an example, the background color is yellow-green and the display color is dark blue. When the display device has such a hue, there are many restrictions when performing color display such as multi-color and full-color. In order to solve this problem, there is disclosed a method of adding another achromatizing liquid crystal cell as an optical compensator to the STN type liquid crystal cell to eliminate coloration and enable monochrome display. However, although black-and-white display is possible in the above-described method, since a liquid crystal cell is used as an optical compensator,
There are problems such as being expensive, heavy, and thick.

Accordingly, organic polymer films having an anisotropic refractive index, that is, a birefringent index, have been developed as optical compensators. Examples of these organic high-molecular polymers include polycarbonate resins, polyacrylates, polyvinyl alcohol resins, polyacrylonitrile resins, polystyrene resins, polyolefin resins, and cellulosic resins. Is used. Above all, polyvinyl alcohol-based resins are extremely promising polymer compounds because of their excellent optical transparency and good workability. However, a film made of a conventional polyvinyl alcohol-based polymer has a drawback in that it has poor water resistance, moisture resistance, or dimensional stability and phase stability under high temperature and high humidity, and shrinks when left under high temperature and high humidity. Or the phase difference changes.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a highly durable retardation film having improved water resistance and heat and moisture resistance (stability under high temperature and high humidity).

[0005]

As a result of intensive studies to solve the above problems, the ethylene content was found to be 1 to 25 mol%.
The present inventors have found a retardation film composed of an ethylene-vinyl alcohol-based copolymer, and completed the present invention. An object of the present invention is to provide a retardation film having high durability performance by performing a heat treatment after uniaxially stretching a film made of an ethylene-vinyl alcohol copolymer having an ethylene content of 1 to 25 mol%. It is.

Hereinafter, the present invention will be described in detail. Conventionally, a polymer used as a base film of a polyvinyl alcohol-based retardation film is an unmodified polyvinyl alcohol-based polymer. The retardation film of the present invention uses a uniaxially stretched film of an ethylene-vinyl alcohol-based copolymer having an ethylene content of 1 to 25 mol%,
It is characterized by providing a highly durable retardation film having excellent stability under high temperature and high humidity.

[0007] The ethylene content of the ethylene-vinyl alcohol copolymer is also a feature of the retardation film of the present invention, and greatly affects the durability of the retardation film. Since the decrease in the ethylene content lowers the water resistance, wet heat resistance and durability of the retardation film, the ethylene content must be 1 mol% or more in order to sufficiently exert the effect of the ethylene-vinyl alcohol copolymer. It is important that the content is preferably at least 2 mol%, more preferably at least 5 mol%. An increase in the ethylene content improves the water resistance and heat resistance of the retardation film. However, if the ethylene content is too high, the optical performance is reduced.
It is necessary to be less than 5 mol%, preferably 10 mol%.
Mol% or less.

[0008] The degree of polymerization of the ethylene-vinyl alcohol copolymer also affects the performance of the retardation film of the present invention.
When the degree of polymerization is smaller than 300, the optical properties, water resistance, resistance to moist heat and durability are deteriorated. Therefore, it is important that the degree of polymerization is 300 or more, preferably 500 or more, more preferably 1000 or more. is there. From the viewpoint of processing characteristics such as film formation and stretching, it is preferably 30,000 or less. The polymerization degree (P) of the ethylene-vinyl alcohol copolymer is measured according to JIS-K6726. That is, after the ethylene-vinyl alcohol copolymer is re-saponified and purified, it can be obtained from the intrinsic viscosity [η] (unit: dl / g) measured in water at 30 ° C. by the following formula. P = ([η] × 10 ³ /8.29) ^{(1 / 0.62)}

The ethylene-vinyl alcohol copolymer is obtained by saponifying an ethylene-vinyl ester copolymer obtained by copolymerizing ethylene with a vinyl ester monomer such as vinyl acetate, and converting the vinyl ester unit into a vinyl alcohol unit. It is obtained by doing. The degree of saponification of the ethylene-vinyl alcohol polymer in the vinyl alcohol unit also affects the durability of the retardation film of the present invention. Here, the degree of saponification indicates the ratio of units actually saponified to vinyl alcohol units among units that can be converted to vinyl alcohol units by saponification, and the residue is a vinyl ester unit. Saponification degree at least 9
It is at least 0 mol%, preferably at least 95 mol%, more preferably at least 98 mol%.

When ethylene and vinyl ester are copolymerized, monomers other than these may be copolymerized to such an 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 its salts, and methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, and n-butyl acrylate. , I-butyl acrylate, t-butyl acrylate, acrylic acid 2
-Acrylates such as ethylhexyl, dodecyl acrylate, octadecyl acrylate, methacrylic acid and salts thereof, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, methacryl Methacrylates such as i-butyl acrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, acrylamide,
N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetone acrylamide, acrylamidopropanesulfonic acid and its salts, acrylamidopropyldimethylamine and its salts or quaternary salts, N-methylolacrylamide and its derivatives, etc. Acrylamide derivatives, methacrylamide, N-methyl methacrylamide, N-ethyl methacrylamide, methacrylamide propanesulfonic acid and its salts, methacrylamidopropyl dimethylamine and its salts or quaternary salts thereof, N-methylol methacrylamide and its derivatives Methacrylamide derivatives, such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl Vinyl ethers such as nyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether and stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride. And allyl compounds such as allyl acetate and allyl chloride; maleic acid and its salts or esters; vinylsilyl compounds such as vinyltrimethoxysilane; and isopropenyl acetate.

In the production of the retardation film of the present invention, a film obtained by forming an ethylene-vinyl alcohol copolymer is used as a raw material film. In order to produce an ethylene-vinyl alcohol-based copolymer film, for example, the raw material ethylene-vinyl alcohol-based copolymer is
It is dissolved in an organic solvent or a mixture of water and an organic solvent, and the resulting ethylene-vinyl alcohol copolymer solution is formed on a resin film, a drying drum or a drying belt by a casting method or a die casting method. And dry,
Further, heat treatment may be performed if necessary. The concentration of the ethylene-vinyl alcohol copolymer at the time of film formation varies depending on the ethylene-vinyl alcohol copolymer used, but is usually 1 to 60% by weight, preferably 10 to 55% by weight, and more preferably 30 to 50% by weight. %. Where ethylene
In the vinyl alcohol-based copolymer solution, if necessary,
Plasticizers, surfactants, dichroic dyes, inorganic salts and the like can be added. The thickness of the film before stretching is 5 to 150
μm can be used, and preferably 30 to 100 μm.

The method for producing the retardation film of the present invention is not particularly limited, but for example, it is produced by the following method. The ethylene-vinyl alcohol copolymer film is uniaxially or biaxially stretched. The stretching can be performed by a wet stretching method, a dry heat stretching method, a wet heat stretching method, or a combination of these methods, and is performed by free-width uniaxial stretching, fixed width uniaxial stretching, or biaxial stretching. The stretching ratio is controlled by the desired retardation and the thickness of the film.
It is preferably from 1 to 3.0 times. The stretching speed is preferably from 10 to 5000% / min based on the original length of the film. The temperature at the time of stretching varies depending on the stretching conditions, but is usually between 10 and 250 ° C. Further, it is preferable to perform the dry heat stretching in an inert gas. The stretched film is dried and heat-treated in air or an inert gas such as nitrogen under a fixed length or under contraction. water resistant,
For the purpose of heat resistance and moist heat resistance, stretched film
It is preferable to perform the heat treatment in the air at 00 to 250 ° C or in an inert gas. The thickness after stretching is not particularly limited, but is preferably 3 to 100 µm, and particularly preferably 5 to 80 µm.

Further, during or after stretching, the film after stretching is immersed in a crosslinking agent for the ethylene-vinyl alcohol-based copolymer, for example, an aqueous solution of boric acid, borax, or isocyanates, or is subjected to formalization.
Water resistance and durability can be further imparted by performing a water resistance treatment such as acetalization. The retardation film of the present invention thus obtained can be used alone or as a retardation plate by bonding a protective film that is optically transparent and has mechanical strength to both surfaces or one surface thereof. Can also be used. As the protective film, a cellulose acetate film, an acrylic film, a polyester film or the like is usually used.

[0014]

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. In the examples, “%” and “parts” are “% by weight” and “parts by weight” unless otherwise specified.
Represents The retardation film is usually used in a state in which a protective film is laminated, but in the following Examples and Comparative Examples, the measurement was performed on the retardation film alone without the protective film. The phase difference is a value measured using a polarizing microscope and a Berek compensator.

Example 1 A polymerization apparatus having a degree of polymerization of 1530 and a degree of saponification of 99.degree. A pellet consisting of 42 parts by weight of an ethylene-vinyl alcohol copolymer modified with 6 mol% and 5 mol of ethylene, 53 parts by weight of water and 5 parts by weight of glycerin was charged into an extruder, cast on a belt surface from a die, and heated with a hot air temperature of 70%. C. and dried at a hot air temperature of 120.degree. C. to produce a 75 .mu.m-thick ethylene-vinyl alcohol copolymer film. Next, this film was processed in the order of uniaxial stretching, fixing, and drying to prepare a retardation film. At this time, the stretching ratio (bath outlet speed / bath inlet speed) of the uniaxial stretching was 1.5 times, the boric acid concentration in the stretching bath water was 4% by weight, and the boric acid concentration in the fixed treatment bath water was 6% by weight. The water temperature of each of the stretching bath and the fixing bath was 35 ° C, and the drying of the retardation film was performed with hot air at 50 ° C. The thickness of the obtained retardation film was 52 μm, and the retardation was 518 nm. When this retardation film was allowed to stand at 40 ° C. and 90% RH for 10 days, the rate of change of the retardation was 4.0%.

Example 2 Using the same film-forming machine as in Example 1, a polymerization degree of 2000, a saponification degree of 99.2 mol%, and ethylene-modified ethylene of 2 mol were used.
A pellet consisting of 37 parts by weight of a vinyl alcohol copolymer, 59 parts by weight of water and 4 parts by weight of glycerin was charged into an extruder, cast on a belt surface from a die, and heated to a hot air temperature of 8%.
After drying at 0 ° C and heat-treating at a hot air temperature of 120 ° C,
An ethylene-vinyl alcohol copolymer film having a thickness of 3 μm was prepared. Next, this film was uniaxially stretched 1.4 times, fixed, and dried in the same manner as in Example 1 to prepare a retardation film. The thickness of the obtained retardation film was 54 μm, and the retardation was 516 nm. When this retardation film was allowed to stand at 40 ° C. and 90% RH for 10 days, the rate of change of the retardation was 4.2%.

Comparative Example 1 A pellet comprising 41 parts by weight of a polyvinyl alcohol resin having a degree of polymerization of 1750 and a saponification degree of 99.9 mol%, 54 parts by weight of water and 5 parts by weight of glycerin was prepared using the same film forming machine as in Example 1. Was charged into an extruder, cast on a belt surface from a die, dried at a hot air temperature of 70 ° C., and heat-treated at a hot air temperature of 120 ° C. to form a 75 μm-thick polyvinyl alcohol film. Next, this film was uniaxially stretched 1.5 times, fixed, and dried in the same manner as in Example 1 to prepare a retardation film. The thickness of the obtained retardation film was 54 μm, and the retardation was 503 nm. When this retardation film was allowed to stand at 40 ° C. and 90% RH for 10 days, the rate of change of the retardation was 8.2%.

Comparative Example 2 A pellet comprising 36 parts by weight of a polyvinyl alcohol resin having a degree of polymerization of 2400 and a saponification degree of 99.7 mol%, 58 parts by weight of water and 5 parts by weight of glycerin was prepared using the same film forming machine as in Example 1. Was charged into an extruder, cast on a belt surface from a die, dried at a hot air temperature of 80 ° C., and heat-treated at a hot air temperature of 120 ° C. to form a 75 μm-thick polyvinyl alcohol film. Next, this film was uniaxially stretched 1.4 times, fixed, and dried in the same manner as in Example 1 to prepare a retardation film. The thickness of the obtained retardation film was 54 μm, and the retardation was 524 nm. When this retardation film was left at 40 ° C. and 90% RH for 10 days, the rate of change of the retardation was 9.0%.

[0019]

As is clear from the above examples, the retardation film of the present invention has better wet heat resistance than the conventional retardation film comprising a polyvinyl alcohol film. The retardation film of the present invention takes advantage of the above-mentioned features, for example, an LCD navigation system or an LC navigation system.
This is effective as a phase difference plate for an in-vehicle LCD having a large change in temperature and humidity such as a D monitor.

Claims (1)

[Claims] 1. A retardation film comprising an ethylene-vinyl alcohol copolymer having an ethylene content of 1 to 25 mol%.