JPH02125202A - Polarizing film - Google Patents

Abstract

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

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a novel polarizing film for color liquid crystal displays that has excellent heat and humidity resistance.

[Prior Art] In recent years, liquid crystal display elements in word processors have become increasingly monochrome, and color liquid crystal display elements have been put into practical use in personal computers and portable televisions. Such black and white or color displays have high transmittance and degree of polarization;
A polarizing film with a neutral gray hue is required. In addition, these liquid crystal display elements are expected to be used in vehicles and outdoors under high temperature and humidity conditions, and there is a strong demand for polarizing films with excellent moisture and heat resistance in order to maintain reliability. .

Conventional polarizing films for color LCD displays are generally made by adsorbing iodine to a stretched polyvinyl alcohol film, treating it with a fixed aqueous solution containing boric acid, and then laminating it with a protective film made of cellulose ester resin. . (Applications of polarizing film, p135.1986
, CMC Corporation). This is because a polarizing film in which iodine is adsorbed onto a polyvinyl alcohol film is the most excellent in terms of transmittance and degree of polarization, and can increase the contrast of a liquid crystal display element.

[Problems to be Solved by the Invention] However, the above-mentioned polarizing film generally does not have good heat and humidity resistance. For example, when a heat and humidity resistance test is performed in an atmosphere of 60°C and 90% relative humidity (RH), the degree of polarization decreases significantly. do. Therefore, as a means to improve heat and humidity resistance, there is a method of using a protective film with low moisture permeability such as polyester or polysulfone. This is a practical problem because problems such as curling occur due to the difference in the moisture absorption swelling rate of the film.

An object of the present invention is to solve these problems and provide a polarizing film for color liquid crystal displays that has excellent heat and humidity resistance.

[Means for Solving the Problems] In order to achieve the above object, the present inventors conducted intensive studies on the heat and humidity resistance of polarizing films and the color reproducibility when used in color liquid crystal displays, and found that polyvinyl alcohol-based b in the density of the material film and the color coordinates of the Lab system
It has been discovered that by controlling the value, a polarizing film for color liquid crystal displays with improved heat and humidity resistance can be obtained, leading to the present invention.

That is, the present invention provides a polarizing film in which iodine is adsorbed and oriented on a polyvinyl alcohol base film, and the base film has a density of 1.2980-1 and 3140.
g/cm3 and a b value in Lab color coordinates of -2.0 to 4.0.

The polyvinyl alcohol base film used in the present invention has at least 8 acetyl groups in the resin constituting the film.
It is desirable that 5 mol % or more, preferably 90 to 100 mol %, be saponified and converted into hydroxyl groups. For example, polyvinyl alcohol derivative films such as polyvinyl alcohol film, polyvinyl formal film, polyvinyl acecool film, polyvinyl butyral film, and saponified ethylene-vinyl acetate copolymer film can be used.

Here, in the polyvinyl alcohol base film, if the degree of saponification of the resin constituting the film is 85 mol % or less, a sufficient degree of polarization cannot be obtained, which is not preferable.

This is thought to be due to insufficient iodine adsorption due to the small number of hydroxyl groups that serve as iodine adsorption sites.

The density of the polyvinyl alcohol base film is preferably 1.2980 to 1.3140 g/cm3, more preferably 1.3020 to 1.3130 g/cm3.
It is 3. The density ρ2 of the base film is determined by equation (1).

ρ2=(ρ, −φ1×ρ1)/(1−φI) where, ρ; the density of the polyvinyl alcohol base film at 30°C.

ρ: Density of polarizing film at 30°C.

ρ: Density of iodine at 30°C. Here it is 4.93
g/cm3. (United States, National Research, Riki Rancil, ed., International Critical Tables, Vol.

■, p20.1928) φ1: Weight fraction of iodine in the polarizing film.

In formula (1), the density ρ2 of the base film is 1°29
If it is less than 80 g/cm 3 , the heat and humidity resistance will be poor, and when it is incorporated into a liquid crystal display device and used under a high temperature and high humidity atmosphere, the degree of polarization will be significantly lowered and the contrast will be lowered. This is considered to be because the effect of improving heat and humidity resistance is not sufficient due to the low crystallinity of the base film. 1
．． If it exceeds 3140 g/cm3, the moisture and heat resistance will decrease, which is not preferable. This is thought to be because the base film deteriorates due to heat treatment to increase density.

The polarizing film of the present invention preferably has a b value of -2.0 to 4.0, more preferably -1.0 to 2.0 in Lab color steric coordinates. When used in a color liquid crystal display, if the value is less than -2.0, the blue color becomes stronger, and if it is 4.0 or more, the yellow color becomes stronger, so that natural color reproducibility cannot be obtained in either case.

The polarizing film of the present invention can be produced, for example, by the following method, but the method is not limited thereto.

That is, an unstretched polyvinyl alcohol film with a thickness of 50 μm is stretched 4 to 6 times along the longitudinal axis at 80 to 150°C, and then immersed in an aqueous solution consisting of iodine and potassium iodide while keeping it in a tensioned state. , then 5
Polyiodine, which is a polarizing element, is formed by immersing it in an aqueous solution containing ~15% boric acid as a main component. Furthermore, this film is heat-treated at 150 to 240°C to increase its density and improve its resistance to heat and humidity. At this time, the b value of the polarizing film increases and becomes yellow. 5 to 15 pieces of film in this state
% boric acid-based aqueous solution or treated under a humid heat atmosphere of 70-95% relative humidity (RH) at 50-80 °C to bring the b-value close to 0 and give it a neutral gray hue. do. Finally, a protective film layer is formed on one or both sides of the obtained film to obtain the polarizing film of the present invention.

[Effects of the Invention] According to the present invention, a polarizing film having excellent heat and humidity resistance and suitable for color liquid crystal display devices can be obtained. Therefore, the polarizing film of the present invention not only improves the reliability of word processors, personal computers, portable TV displays, etc., but also can be used in various applications such as sunglasses and light control devices.

[Example] The present invention will be explained below with reference to Examples.

The transmittance (Y) in the present invention is calculated by the following formula from the spectral transmittance τo determined every 10 nm in the wavelength range of 400 to 700 nm in accordance with the Japan Electronics Industry Standard LD-201.

fPλ°yλ゛τλdλ fPλ“yλdλ Here, Po is the spectral distribution of standard light (D65 light source), and yo is the isochromatic number based on the 2-degree visual field X, Y, Z system.

The transmittance of one polarizing film is the single transmittance Y, the parallel transmittance YP is the case when two polarizing films are stacked so that their orientation directions are the same, and the parallel transmittance is YP when the orientation directions of the two polarizing films are orthogonal. The orthogonal transmittance Y is the case where they are stacked so that

respectively.

The polarization degree V is the parallel transmittance Y2 and the orthogonal transmittance Y2, and the spectral transmittance τ is the spectrophotometer (manufactured by Hitachi, U-340).
0 type).

The b value of the color three-dimensional coordinates was measured using a spectrophotometer (manufactured by Suga Test Instruments, S M
-, Type 3) was used to measure the spectral transmittance according to JIS-Z8722, and determined based on JIS-Z8730. If the b value is positive, it tends to be yellow; if it is negative, it tends to be blue.

In addition, a commercially available LCD color television (manufactured by Matsushita Electric, TR-
After removing the polarizing film from the liquid crystal display section of the 3LT4 model, the polarizing film of the present invention was attached to the front and rear surfaces of the liquid crystal display section, and color reproducibility was visually confirmed.

Example 1 A 50 μIn thick film made of a polyvinyl alcohol resin with a degree of saponification of 99.5 mol % was stretched 4.5 times along the contraction axis at 130° C. to obtain a polarizing film base material. The stretched polyvinyl alcohol film was immersed in a 40'C aqueous solution containing 0.2 parts by weight of iodine and 20 parts by weight of potassium iodide for 20 seconds while maintaining tension to adsorb iodine.

Next, a fixing treatment was performed by immersing it in an aqueous solution of 10 parts by weight of potassium iodide and 10 parts by weight of boric acid at 65°C for 90 seconds to obtain a polarizing film. Further, this polarizing film was heat-treated in a hot air oven at 180°C for 60 seconds, and then immersed in an aqueous solution at 70°C containing 10 parts by weight of boric acid for 15 seconds to obtain a polarizing film with a monochromatic hue of New 1 to Largre. . After FL, a commercially available triacedelcellulose film (manufactured by Fuji Photo Film Co., Ltd., Fujitac) with a thickness of 80 μm was bonded to both sides of this polarizing film using a polyvinyl alcohol resin adhesive. After leaving the polarizing film thus obtained in a constant temperature chamber at 60'C and 90% relative humidity (RH) for 300 hours, the transmission speed and polarization degree were measured, and the degree of decrease from the initial value was measured. The rate change ΔY and the polarization degree change were evaluated as ■.The results are shown in Table 1.

Example 2 Stretching, iodine adsorption, and fixing treatments were carried out in exactly the same manner as in Example 1, and after heat treatment in a hot air oven at 150°C for 60 seconds, 60°C in an atmosphere of 60°C and 90% relative humidity (RH). A polarizing film was obtained by heat treatment for seconds. Furthermore, this polarizing film was subjected to a heat-and-moisture resistance test in exactly the same manner as in Example 1. The results are also shown in Table 1.

Example 3 After stretching and iodine adsorption in exactly the same manner as in Example 1, a film was prepared at 65°C consisting of 15 parts by weight of boric acid and 5 parts by weight of borax.
A polarizing film was obtained by immersing the film in an aqueous solution for 90 seconds for fixation. Next, this polarizing film was heat-treated in a hot air oven at 180°C for 60 seconds, and then immersed in a 65°C aqueous solution containing 10 parts by weight of boric acid for 10 seconds. The obtained polarizing film was subjected to a heat-and-moisture resistance test in exactly the same manner as in Example 1. The results are also shown in Table 1.

Example 4 After heat treatment at 180°C for 60 seconds, the porcelain vi1
A polarizing film was obtained in exactly the same manner as in Example 1, except that it was immersed for 5 seconds in a 70° C. aqueous solution containing 2 parts by weight. Furthermore, this polarizing film was subjected to a heat-and-moisture resistance test in exactly the same manner as in Example 1. The results are also shown in Table 1.

Comparative Example 1 After stretching, iodine adsorption, and fixing treatments were performed in exactly the same manner as in Example 1, a conventional polarizing film was obtained by drying at 50° C. for 300 seconds. Furthermore, this polarizing film was subjected to a heat-and-moisture resistance test in exactly the same manner as in Example 1. The results are also shown in Table 1.

Comparative Example 2 After stretching, iodine adsorption, and fixing treatments were carried out in exactly the same manner as in Example 1, heat treatment was performed at 250°C for 15 seconds, and then Hoi! A polarizing film was obtained by immersing it in a 65° C. aqueous solution containing 11,210 parts by weight for 5 seconds. Furthermore, this polarizing film was subjected to a heat-and-moisture resistance test in exactly the same manner as in Example 1. The results are also shown in Table 1.

Comparative Example 3 After heat treatment, 3 parts of boric acid was added to a 65°C aqueous solution containing 5 parts by weight of boric acid
A polarizing film was obtained in exactly the same manner as in Example 1 except that the film was immersed for 0 seconds. Furthermore, this polarizing film was subjected to a heat-and-moisture resistance test in exactly the same manner as in Example 1. The results are also shown in Table 1.

Claims (2)

[Claims] (1) In a polarizing film in which iodine is adsorbed and oriented on a polyvinyl alcohol base film, the density of the base film is 1.2980 to 1.3140 g/cm^3, and b in Lab color 3D coordinates. The value is -2.0
A polarizing film characterized in that it has a polarization ratio of 4.0 to 4.0. (2) The polarizing film according to claim 1, wherein the polyvinyl alcohol base film is a polyvinyl alcohol film having a degree of saponification of 85 to 100 mol%.