JPH07198939A - Production of polarizing film - Google Patents

Abstract

PURPOSE:To obtain a polarizing plate having excellent optical characteristics, high durability and improved resistance against moisture and heat by including several steps to incorporate a specified amt. of boron atoms into the film so that in each step, the film is dipped in a treating liquid having different concn. of boron compd. CONSTITUTION:This method includes two or more steps of incorporating 4.5-7.0wt.% boron atoms to the total amt. of polyvinylalcohol (PVA) polymer film. In each step, the film is dipped in a treating liquid having different concn. of boron compd. Namely, during the polarizing film is subjected to adsorption treatment with a dichroic material or to orienting treatment by stretching, the film is dipped in a soln. of a boron compd. to incorporate the boron compd. into the film. The film is dipped in two or more kinds of treating liquids having different concn. of boron compd. The concn. of the treating liquid is preferably 0.01-3wt.% boron atoms concn. For example, the film is subjected to stretching and orienting treatment in an aq. soln. containing 3.5 wt.% boric acid and then dipped in a 5.0wt.% boric acid aq. soln.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing plate excellent in heat resistance, wet heat resistance and durability and having a high degree of polarization and a high degree of transmission.

[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 strict. However, in recent years, liquid crystal display devices have been widely used as displays for laptop word processors, laptop computers, notebook computers; displays for instrument panels of automobiles and aircraft; liquid crystal projectors, etc., and have become large in size and high in display quality. And improvement of durability is required. Therefore, regarding the polarizing plate, which is a component of the liquid crystal display device, in order to achieve the above-mentioned problems, in order to achieve the above-mentioned problems, improvement in optical properties such as large screen, high polarization degree and high transmittance, and water resistance, heat resistance, moist heat resistance and durability. It is required to improve the sex.

Conventionally, a uniaxially stretched film of polyvinyl alcohol on which iodine or a dichroic dye is adsorbed is often used as a polarizing plate. Although this polarizing plate has excellent polarizing characteristics, it has water resistance and wet heat resistance. And poor durability, when using an iodine-based compound as a dichroic substance,
In an environment of high temperature and high humidity, discoloration occurs and polarization performance deteriorates. On the other hand, a proposal using a uniaxially stretched film of polyvinyl alcohol having a high degree of polymerization as a substrate (for example, JP-A-1-105204) and a proposal for using a uniaxially stretched polyester film as a substrate (for example, JP-A-58-58). 6
No. 8008) has been issued. However, in the former,
Although the effect of the degree of polymerization is recognized, it is not always sufficient. In the latter, the drawbacks of the polarizing plate using a polyvinyl alcohol-based resin as a base material have been improved to some extent, but the polarization performance is insufficient, and the above requirements are sufficiently satisfied. It was not something that could be done. In general, a film made of a polyvinyl alcohol-based polymer has low moisture resistance, and thus when it is used as a polarizing element, it is usually a transparent film such as cellulose triacetate and has no birefringence (when used as a liquid crystal element. In addition, a film that does not affect the display function) is attached to the surface to form a protective layer (support). On the other hand, moisture resistance of a polyvinyl alcohol-based polarizing film (polyvinyl alcohol-based film) has also been studied. However, in addition to acetalization, formalization, and the like, treatment with a boron-based compound, a phosphorus-based compound, or the like has not sufficiently satisfied both the wet heat resistance and the polarization performance.

[0004]

Under such circumstances, the present invention has excellent optical properties and highly durable polarized light having improved resistance to humidity and heat, that is, deterioration of polarization performance when left under high temperature and high humidity conditions. It provides a board.

[0005]

Means for Solving the Problems As a result of intensive studies aimed at solving the above-mentioned problems, the inventors of the present invention have determined that the boron atom content is 4.5 to 4.5 with respect to the total weight of the polyvinyl alcohol polymer film.
The present invention has been completed to find a method for producing a polarizing film, which has two or more steps of containing 7.0% by weight, and is immersed in a treatment liquid having a different concentration of a boron-based compound in each step. .

The present invention will be described in detail below. The process for producing a polarizing film comprises two steps, and the first step is a film made of a polyvinyl alcohol polymer (hereinafter sometimes abbreviated as PVA polymer) (hereinafter, referred to as an untreated film for polarizing film). A film may be abbreviated as an anti-original film), and the second step is P
Adsorption treatment and stretching of dichroic substances on VA polymer film
This is a step of processing into a polarizing film by carrying out an orientation treatment or the like. The method for producing a polarizing film of the present invention is characterized by the above second step.

There is no particular limitation on the step of producing the raw film in the first step (hereinafter, this step may be abbreviated as film formation), and it is generally as follows. PVA
An aqueous solution or organic solvent solution of the base polymer is formed into a liquid film or a gel film, and then the solvent is removed to obtain a raw film.

The PVA polymer used for the PVA polymer film and the method for producing the film are not particularly limited, but the degree of polymerization of the PVA polymer is preferably 1000 or more, more preferably 1500 or more, and saponification. The degree is preferably 95 mol% or more, more preferably 98 mol% or more. The PVA-based polymer can be copolymerized with other vinyl-based monomers without any problem, and examples of the copolymerizable comonomer include olefins such as ethylene, propylene, 1-butene and isobutene, acrylic acid and salts thereof, Methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-acrylate
Acrylic esters such as butyl, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate, methacrylic acid and its salts, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, methacrylic acid i-propyl, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate,
Methacrylic acid esters such as dodecyl methacrylate and octadecyl methacrylate, 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,
Methacrylamide derivatives such as N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid and its salts, methacrylamideamidopropyldimethylamine and its salts or quaternary salts thereof, N-methylolmethacrylamide and its derivatives, 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, methacrylonitrile and other nitriles, vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride and other vinyl halides, allyl acetate and allyl chloride Examples thereof include compounds, maleic acid and its salts or esters, vinylsilyl compounds such as vinyltrimethoxysilane, and isopropenyl acetate.

The method for producing the PVA-based polymer film in the present invention is not particularly limited, and generally a method of forming a liquid film or a gel film from an aqueous PVA solution and drying it to obtain a film is adopted. Film formation from PVA polymer solution is cast film formation, dry film formation (extrusion into air or inert gas such as nitrogen), wet film formation (extrusion of PVA polymer into poor solvent), dry and wet. It is carried out by a formula film formation or a gel film formation (a method of once gelating a PVA polymer solution to obtain a film), and the solvent used at this time is dimethyl sulfoxide, dimethylformamide, dimethylacetamide, ethylene glycol. , Glycerin and water are used alone or as a mixture. Further, an aqueous solution of an inorganic salt such as lithium chloride or calcium chloride can be used alone or as a mixture with the organic solvent. Of these, water, dimethyl sulfoxide, and a mixed solvent of dimethyl sulfoxide and water are preferably used. Further, a film may be formed by mixing a dichroic dye with this solution.

Next, the step of obtaining the polarizing film by the above second step will be described. The PVA-based polymer film is subjected to an alignment treatment by adsorption of a dichroic substance and uniaxial stretching, or the PVA-based polymer film to which the dichroic substance is added at the time of film formation is uniaxially stretched. There is no problem whether the adsorption treatment and the orientation treatment are performed simultaneously or separately, and the order thereof is arbitrary. Adsorption of the dichroic substance to the substrate film is usually carried out by immersing it in a liquid containing a dichroic substance, and there is no particular limitation on the treatment conditions or method thereof, and for example when an iodine compound is used. Is an aqueous solution of iodine-potassium iodide, and when a dye is used, an aqueous dye solution is used. The orientation treatment by stretching is carried out by wet stretching or dry heat stretching, and it is preferable to stretch the film uniaxially by 3 times or more, more preferably 5 times or more. The temperature during stretching varies depending on the stretching method and other conditions, but is usually between 20 and 250 ° C. Further, the dry heat drawing is preferably performed in an inert gas. 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.

A feature of the present invention is a method of incorporating a boron-based compound in the above-mentioned second step (step of processing a raw film into a polarizing film), and the step of incorporating this boron-based compound is the performance of the polarizing film. Greatly affect the.

Generally, a polarizing film is manufactured through steps such as an adsorption treatment of a dichroic substance, an orientation treatment such as stretching, a water resistance (moisture resistance) treatment with a boron compound and the like, and a drying process. A solution of boron compound is used
The VA-based film is dipped to contain the boron-based compound. In the present invention, it is necessary to pass two or more treatment liquids containing different concentrations of boron compounds, and the concentration of the boron compound in the treatment liquid is preferably 0.01 to 3% by weight in terms of boron atom conversion concentration. . As an example, the boron compound is stretched and oriented in an aqueous solution containing 3.5% by weight of boric acid, and then immersed in an aqueous solution of 5.0% by weight of boric acid so that the boron-based compound is treated with PVA.
It is contained in the polymer film. When there is only one treatment liquid containing a boron compound, that is, when there is only one step of incorporating the boron compound into the PVA polymer film, the polarization performance and wet heat resistance of the polarizing film decrease. Further, even if there are two or more steps of incorporating the boron-based compound, when the concentration of the boron-based compound in the treatment liquid of each step is the same, the polarizing performance and the wet heat resistance of the obtained polarizing film are insufficient, Particularly, when the concentration of the boron-based compound in the treatment liquid is high, the polarization performance is significantly deteriorated.

The content of the boron-based compound in the PVA-based polymer film has a great influence on the resistance to moist heat, and it is necessary to contain the boron-based compound in the range of 4.5 to 7.0% by weight in terms of boron atom. It is preferably 4.6 to 6.5% by weight.
If it is less than 4.5% by weight, the wet heat resistance is remarkably reduced to 7.0.
When the content is more than 10% by weight, the wet heat resistance is improved but the polarization performance is deteriorated or the polarizing film becomes brittle.

The stretching / orientation treatment step has a great influence on the polarizing performance of the polarizing film, and the content of the boron-based compound in the PVA-based polymer film in this step has a great influence on the stretchability and the polarizing property of the polarizing film. give. If the content of the boron-based compound is large during the stretching / orienting treatment, the elongation of the film will be low (the stretching ratio will be low), and sufficient orientation treatment cannot be performed. In the stretching step, the content of the boron-based compound in the PVA-based polymer film is preferably 5 wt% or less in terms of boron atom based on the dry weight of the film. Further, in order to sufficiently improve the moist heat resistance, after the stretching / orienting treatment, the boron-based compound is further added to the above-mentioned range by P
It is contained in the VA polymer film.

The polarizing film of the present invention is used as a polarizing plate by laminating an optically transparent protective film (support) having mechanical strength on both sides or one side. As the protective film, a cellulose acetate film, an acrylic film, a polyester film or the like is usually used, and among them, a cellulose acetate film such as cellulose triacetate is generally used in view of optical characteristics and the like. The polarizing plate may be formed by laminating compounds of the same kind or different kinds in order to further add performance and function. For example, an adhesive, a hard coat layer, an anti-reflection layer, etc. are generally laminated.

[0016]

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 were measured in accordance with Japanese Electronic Machinery Industry Standard (EIAJ) LD-201-1983, using a spectrophotometer with a C light source and a 2 degree visual field.

Example 1 A polyvinyl alcohol polymer film, vinylon film (Kuraray Co., Ltd.) was immersed in an iodine / potassium iodide solution (iodine concentration 0.025% by weight, potassium iodide concentration 0.03% by weight). Then, it was uniaxially stretched 5 times in boric acid / potassium iodide aqueous solution (boric acid concentration 3.5% by weight, potassium iodide concentration 1.5% by weight), and further in boric acid / potassium iodide aqueous solution (boric acid The film was immersed in a concentration of 6% by weight and a potassium iodide concentration of 1.5% by weight for 5 minutes and then dried at 50 ° C. to obtain a polarizing film. The boron atom content in the obtained polarizing film was 5.3% by weight. An 80 μm thick cellulose triacetate film was attached to this polarizing film using an adhesive to obtain a polarizing plate.
Optical properties and durability of the obtained polarizing plate (80 ° C, 90% R
Table 1 shows the optical characteristics when left under H).

Comparative Example 1 A polyvinylon polymer film, vinylon film (Kuraray Co., Ltd.) was immersed in an iodine / potassium iodide solution (iodine concentration 0.025% by weight, potassium iodide concentration 0.03% by weight). After that, the film was uniaxially stretched 5 times in boric acid / potassium iodide aqueous solution (boric acid concentration 3% by weight, potassium iodide concentration 1.5% by weight) and then dried at 50 ° C. to obtain a polarizing film. The boron atom content in the obtained polarizing film was 3.8% by weight. An 80 μm thick cellulose triacetate film was attached to this polarizing film using an adhesive to obtain a polarizing plate. Table 1 shows the optical characteristics and durability (optical characteristics when left at 80 ° C. and 90% RH) of the obtained polarizing plate.

Comparative Example 2 A polyvinylon polymer film, vinylon film (Kuraray Co., Ltd.) was immersed in an iodine / potassium iodide solution (iodine concentration 0.025% by weight, potassium iodide concentration 0.03% by weight). Then, after uniaxially stretching 4.1 times in a boric acid / potassium iodide aqueous solution (boric acid concentration 6.2% by weight, potassium iodide concentration 1.5% by weight), 5
A polarizing film was obtained by drying at 0 ° C. The boron atom content in the obtained polarizing film was 5.6% by weight. An 80 μm thick cellulose triacetate film was attached to this polarizing film using an adhesive to obtain a polarizing plate. Table 1 shows the optical characteristics and durability (optical characteristics when left at 80 ° C. and 90% RH) of the obtained polarizing plate.

[0020]

[Table 1]

[0021]

As is clear from the above examples, the polarizing film of the present invention is
It is excellent in water resistance, wet heat resistance and durability, and also excellent in optical characteristics. Taking advantage of the above characteristics, the polarizing film obtained in the present invention is a liquid crystal display having high performance and high durability, such as a liquid crystal television, a liquid crystal projector, a word processor display, a personal computer display, an OA equipment terminal display, an aircraft or an automobile display. It is used for instrument panel displays, other filters, sunglasses, window glass, antiglare for various lights, and various sensors.

Claims (1)

[Claims] 1. A treatment comprising two or more steps of containing 4.5 to 7.0% by weight of boron atom with respect to the total weight of the polyvinyl alcohol-based polymer film, each step having a different concentration of boron-based compound. A method for producing a polarizing film, which comprises immersing in a liquid.