JPH01227103A - Production of polarizing film - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing a polarizing film having excellent polarizing ability and moist heat resistance.

[Prior Art] In recent years, as the range of use of liquid crystal display devices such as word processors, personal computers, and liquid crystal televisions has expanded and their areas have become larger, the demand for i) polarizing films has increased significantly. Furthermore, demand for liquid crystal display devices for automobile panels is expected to grow significantly. Polarizing films used in these liquid crystal display devices are required to have a higher degree of polarization and higher durability than ever before.

[Problem B to be Solved by the Invention] A polarizing film using a polyvinyl alcohol (hereinafter abbreviated as PVA) film includes (1) an iodine film in which iodine is adsorbed and oriented in the film; A dye-based film in which a dichroic dye is adsorbed and oriented, and (3) a polyene-based film in which the film is partially dehydrated are known. Among these, the iodine-based film (1) has better polarizing ability than the others and is most commonly used, but it has a problem in heat and humidity resistance.

A method to solve this problem is to make iodine i-oriented and impregnate it with cobalt ions (Japanese Unexamined Patent Publication No. 56/1989).
-48601) and a method of impregnation with nickel ions (Japanese Patent Application Laid-Open No. 180303/1983), but even these improved methods are insufficiently effective and the problem has not been completely solved. Not yet.

As mentioned above, although the iodine-based polarizing film has high polarizing ability, it has poor heat and humidity resistance, so its application fields have been limited.

In view of these conventional drawbacks, the present inventors have made extensive studies and have arrived at the present invention.

An object of the present invention is to obtain a polarizing film that has both excellent polarizing ability and heat-and-moisture resistance.

[Means for Solving the Problem] In order to achieve the object, the present invention has the following configuration. 1. A method for producing a polarizing film, which comprises immersing a polyvinyl alcohol film made of iodine adsorbed and oriented in an aqueous solution containing boric acid, potassium iodide, and an iron compound.

The present invention will be explained in detail below.

The PVA film used in the present invention includes PVA
Examples include P'VA derivative films such as polyvinyl formal film, polyvinyl acetal film, saponified poly(ethylene-vinyl acetate) copolymer film, and partially polyenated PVA film.

Ordinary methods can be applied to adsorb and orient iodine on these PVA films.

For example, a method in which the unstretched PVA film is immersed in an aqueous solution of iodine and potassium iodide and then stretched in the -axis direction;
- A method in which the axially stretched PVA film is immersed in an aqueous solution of iodine and potassium iodide.

Law, etc. - In the present invention, the stretched P in which iodine is adsorbed and oriented
It is necessary to immerse the VA film in an aqueous solution in which boric acid, potassium iodide, and an iron compound are dissolved.

Since most of the adsorption, orientation, and fixation of iodine (crosslinking of PVA, etc.) is carried out in an aqueous solution, it is easy to understand that a method of incorporating iron ions in the final step is more effective. This is because iodine adsorption will be inhibited if iron ions are impregnated before iodine adsorption orientation due to the strong coordination bond of iron ions.

The iron compounds used here include iron halides such as ferrous chloride, ferrous bromide, and ferrous iodide, and inorganic iron compounds such as ferrous acetate, ferrous sulfate, and ferrous nitrate. An example is salt.

The concentration of the iron compound in the aqueous solution is preferably 0.1 to 20% by weight (hereinafter abbreviated as wt%), particularly 0.5 to 10% by weight.

In addition, boric acid in the aqueous solution is used to stabilize PVA and iodine in the aqueous solution and during thermal treatment by crosslinking PVA, and is used in an amount of 1 to 10 wt%, especially 2 to 4.5 wt%. Preferably, it is added at a concentration.

The addition of potassium iodide prevents the "blue drop" seen in the low wavelength range, and prevents the iodine ions contained during the iodine adsorption and orientation treatment from being extracted during immersion in the aqueous solution. It is for the purpose of The amount of potassium iodide added is preferably 2 to 20 wt%, particularly 5 to 15 wt%.

[Function] The present inventors investigated the iodine concentration in the polarizing film before and after heat treatment with respect to a conventional iodine-based film with poor heat and humidity resistance, and confirmed that there was no change in concentration. In other words, the iodine concentration in the film, which became almost transparent through heat treatment and lost its polarizing ability, remained unchanged. As a result of further studies, we found that polyiodine ions I3- and l have absorption in the visible light region and exhibit polarizing ability.
This is because 5- dissociates into transparent I-, which has no absorption in the visible light region, by the moist heat treatment. Regarding the effect of potassium iodide, it is known that increasing the concentration of 1-ions in the polarizing film suppresses the dissociation equilibrium in the opposite direction from polyiodine ions, but the effect of iron ions is still unknown. No clear answer has been obtained. This is thought to be due to the fact that it can form chelates with PVA and polyiodine ions with many coordination bonds, and also because it inhibits the dissociation equilibrium of polyiodine ions in the same way as potassium iodide.

[Examples] The present invention will be explained in more detail below using Examples and Comparative Examples.

In the Examples and Comparative Examples, the transmittance was measured using a spectrophotometer (manufactured by Hitachi Seisakusho, U-3400).

Single transmittance Y, parallel transmittance (Y//: 2 films,
(light transmittance when two films are stacked so that their molecular orientations are parallel to each other), orthogonal transmittance (Y top: light transmittance when two films are stacked so that their molecular orientations are perpendicular to each other) ) are average values in the visible light region of 400 to 700 nm.

The degree of polarization V was determined by the following formula.

Example 1 Cellulose triacetate (hereinafter abbreviated as CTA) was applied to a pvA film stretched 4.5 times in the uniaxial direction at 130°C.
The film was laminated to obtain a PVA single-sided laminated (semi-laminated) film.

This semi-laminated film was immersed for 15 seconds in an aqueous solution (iodine adsorption bath) at 35°C containing 0.3 wt% iodine and 5.0 wt% potassium iodide, and then washed with water.
%, potassium iodide 3 wt %, and ferrous chloride 4 wt % aqueous solution (fixed bath) at 65° C. for 30 seconds, washed with water, and dried.

Next, a heat treatment was performed at 150° C. for 1 minute under tension, and then a CTA film was laminated on the PVA side to obtain a polarizing film.

Initial performance of this film and moist heat treatment at 75°C19
The performance changes after 18 hours of 0% RH were as shown in Table 1.

Example 2 A polarizing film was obtained by performing the same treatment as in Example 1, except that the potassium iodide concentrations in the iodine adsorption bath and the fixed bath were each set to 10 wt%.

Comparative Example 1 A polarizing film was obtained by performing the same treatment as in Example 1 except that ferrous chloride was not used in the fixing bath.

Comparative Example 2 A polarizing film was obtained by carrying out the same treatment as in Example 1, except that 6 wt % of ferrous chloride was added to the iodine adsorption bath and ferrous chloride was not used in the fixing bath.

Comparative Example 3 Example 1 except that potassium iodide was not used in the fixed bath.
A polarizing film was obtained by performing the same treatment as above.

Comparative Example 4 The same treatment as in Example 1 was carried out except that boric acid was not used in the fixing bath, but PVA film and CTA were used in the fixing bath.
The film peeled off (ζ, no polarizing film was obtained).

[Effects of the Invention] Since the present invention uses an iron compound as a fixation source, iodine is stably fixed.

The polarizing film obtained by the present invention has excellent optical properties (transmittance, degree of polarization) as well as moisture and heat resistance. For this reason, it can be used in a variety of fields, from applications that require harsh usage environments to word processors used in general homes, as well as all types of liquid crystal display devices, various optical instruments, sunglasses, automobile windshields, and windows. Can be done.

Patent applicant: Toshi Co., Ltd.

Claims (3)

[Claims] (1) A method for producing a polarizing film, which comprises immersing a polarizing film made by adsorbing and orienting iodine on a polyvinyl alcohol film in an aqueous solution containing boric acid, potassium iodide, and an iron compound. (2) The method for producing a polarizing film according to claim (1), wherein the iron compound is at least one of an iron halide and an inorganic iron salt. (3) The concentration of iron compounds in the aqueous solution is 0.1 to 20% by weight
The method for producing a polarizing film according to claim (1).