JPH03103801A - Polarizing film - Google Patents

Abstract

PURPOSE:To improve the resistance to moist heat of the polarizing film by incorporating polyhalogen ions contg. iodine into an adhesive. CONSTITUTION:The polarizing film formed by laminating transparent bases via the adhesive on both surfaces of the polarizing film consisting of a polyvinyl alcohol (PVA) film contains the polyhalogen ions contg. the iodine into the adhesive. The polarizing film consists of a film formed by absorbing the iodine or dichromatic dye as a polarizing element on the unstetched film of the PVA system, then stretching the film in the longitudinal direction or a film formed by stretching the film of the PVA system in the longitudinal direction, then absorbing the iodine or the dichromatic dye as the polarizing element thereon. The polarizing film having the excellent resistance to moist heat is obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a polarizing film. More specifically, the present invention relates to a polarizing film having excellent heat and humidity resistance.

[Prior art] In recent years, with the expansion of the use of liquid crystal elements, the demand for polarizing films has also increased, and the ways in which they are used have expanded to include a wide variety of applications, especially under high temperature and humidity conditions, such as in automotive applications. It is used in many cases, so a polarizing film with excellent heat and humidity resistance is essential. As methods for improving the heat-and-moisture resistance of polarizing films, methods have been proposed such as using a dichroic dye in the polarizing element of a polyvinyl alcohol film, and using a transparent support with low moisture permeability as a transparent support.

[Problems to be Solved by the Invention] However, while the method of using a dichroic dye in the polarizing element of the conventional polyvinyl alcohol film described above has excellent heat and humidity resistance, the degree of polarization is insufficient, and it is not transparent. In the method of using a transparent support with low moisture permeability, the transmittance is low, interference fringes occur due to the difference in birefringence between the polarizing film and the transparent support, and curling occurs due to the difference in hygroscopic swelling between the polarizing film and the transparent support. There were problems such as heat and humidity generation, and there were limits to the improvement of the heat and humidity resistance of polarizing films.

An object of the present invention is to improve such problems and provide a polarizing film with excellent heat and humidity resistance.

[Means for Solving the Problems] In order to achieve the above object, the present inventors have intensively studied methods for improving the heat and humidity resistance of polarizing films, and found that the adhesive used to bond the transparent support to the polarizing film contains It was discovered that a polarizing film with excellent heat and humidity resistance can be obtained by incorporating polyhalogen ions including iodine.
This led to the present invention.

That is, the present invention provides a polarizing film in which transparent supports are laminated on both sides of a polyvinyl alcohol-based polarizing film via an adhesive, the adhesive containing polyhalogen ions containing iodine. It is made of a polarizing film characterized by the following.

The polarizing film in the present invention is a polyvinyl alcohol-based unstretched film on which iodine or dichroic dye is adsorbed as a polarizing element and then stretched in the longitudinal direction, or a polyvinyl alcohol-based film stretched in the longitudinal direction. The rear polarizing element is made of something to which iodine or dichroic dye is adsorbed. More preferably, a polarizing element containing at least 60% iodine is preferable since a high degree of polarization can be obtained.

As the polyvinyl alcohol film in the present invention, polyvinyl alcohol derivative films such as polyvinyl alcohol film, polyvinyl formal film, polyvinyl acetal film, and saponified ethylene-vinyl acetate copolymer film can be used.

Transparent supports include cellulose acetate butyrate films such as cellulose triacetate and cellulose diacetate, cellulose nitrate films, polycarbonate films, polymethyl methacrylate films, and polyvinyl chloride in terms of transparency, hygroscopic dimensional stability, and strong properties. A polyester film is preferred, and a cellulose acetate film having a thickness of 25 to 200 μm is particularly preferred from the viewpoints of transparency, moisture absorption dimensional stability, and strength properties.

The adhesive for bonding the polarizing film and the transparent support must have optical transparency in addition to adhesive properties, and must not eliminate or reduce the polarizing properties of the polarizing film.
Preferred are polyester adhesives, polyacrylic adhesives, epoxy adhesives, and 3? Anoacrylate adhesive, polyurethane adhesive,
Examples include subilane adhesive, phenolic adhesive, urea adhesive, melamine adhesive, vinyl acetate adhesive, polyvinyl alcohol adhesive, cellulose nitrate adhesive, and the like.

In the present invention, it is necessary that the adhesive for bonding the transparent support to the polarizing film contains polyhalogen ions containing iodine. Any material containing at least one atom may be used.

As such a polyhalogen ion containing iodine, I-
I3- I5- ICI2- IBr2-,
Examples include I2Cl- I'2Br-, IBrC1-, and the like. Moreover, these compounds can also be used in combination. Further, the content of polyhalogen ions including iodine in the adhesive is preferably 0.02 to 0.02 per gram of adhesive.
It is good to contain 1.20 g, more preferably 0.1 to 0.8 g. If it is less than 0.02 g, the effect of improving heat and humidity resistance may be insufficient, and if it is more than 1.2 g, adhesiveness may deteriorate. Further, a polarizing film obtained by bonding a transparent support to a polarizing film using an adhesive containing multi-halogen ions including iodine is heated at 80 to 180°C, preferably at 120°C.
Heat treatment at a temperature of ~160° C. for 30 to 120 seconds can further improve the heat-and-moisture resistance effect.

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

That is, a polyvinyl alcohol-based unstretched film with a thickness of 50 μm is mixed with potassium iodide containing 0.05 to 0.3
% by weight in an aqueous iodine solution at a temperature of 30 to 45°C for 10 to 120 seconds, and then immersed vertically in an aqueous solution containing boric acid at a temperature of 30 to 60°C for 3. After stretching 0 to 6.0 times, it is dried to obtain a polarizing film. Next, a film serving as a transparent support is placed on both sides of the polarizing film through an adhesive containing polyhalogen ions including iodine, and heated.
In a laminator equipped with a pressure device, the temperature is 20 to 90.
℃ and a pressure of 3.0 to 30 kg/cm2.

Although there are no particular limitations on the method of incorporating polyhalogen ions containing iodine into the adhesive, it is more effective to uniformly contain polyhalogen ions containing iodine into the adhesive.

The method of measuring and evaluating the characteristic values of the present invention is as follows.

(1) Transmittance and degree of polarization A polarizing film is attached to an adhesive sheet with a release film, and a glass plate with a thickness of 1 mm is further attached to the adhesive sheet side. This was used as a measurement sample.

Measured every 10 nm in the wavelength range of 400 nm to 700 nm using a spectrophotometer, and calculated the average transmittance (T) of the polarizing plate alone.
Find this and use it as the transmittance of the polarizing film. Furthermore, 2
Average transmittance when two polarizing plates are arranged parallel to the same axis (T2
), and the average transmittance (T3) when arranged perpendicularly to the coaxial
was calculated, and the degree of polarization (V) was calculated from the following calculation formula.

Degree of polarization (%) − [(T2 T3)/(T2+T3)l”2×100 (2) Average transmittance (T) and degree of polarization after placing the heat-and-moisture resistant polarizing film in a 90% atmosphere at 60°C for 300 hours (V) and calculate the difference from each initial value and display it as a change in transmittance (ΔT) and a change in polarization degree (Δ■).Of course, the smaller these changes, the better the heat and humidity resistance of the polarizing film. It will be excellent.

[Example] The invention will be explained in further detail by the following examples.

Example 1 An unstretched polyvinyl alcohol film with a thickness of 50 μm was immersed in a 0.1% by weight aqueous iodine solution (coexisting with 0.6% potassium iodide) at a temperature of 35°C for 15 seconds, and then immersed in a 0.1% by weight aqueous solution of iodine (coexisting with 0.6% by weight of potassium iodide) at a temperature of 35°C, and then immersed in a 0.1% by weight aqueous iodine solution (coexisting with 0.6% by weight of potassium iodide) at a temperature of 40°C. 4. lengthwise in an aqueous solution of 3.0% by weight of boric acid. After stretching 0 times, the aqueous solution adhering to the film surface was removed and dried at 70° C. for 60 seconds to obtain a polarizing film.

Next, a cellulose triacetate film with a thickness of 80 μm was placed on both sides of this polarizing film in a 5.0% by weight aqueous solution of polyvinyl 7-alcohol (“Poval” manufactured by Kuraray) as an adhesive, per 1 g of the adhesive. A solution containing 0.02, 0.1, 0.4, 0.8, and 1.2 g of KI added as iodine ions was heated at a pressure of 5.0 kg/c using a laminator.
m2 at a temperature of 50°C and dried at 70°C for 30 seconds to obtain a polarizing film.

Example 2 The polarizing film obtained in Example 1 was heat-treated at 150° C. for 60 seconds.

Example 3 Cellulose triacetate films with a thickness of 80 μm were placed on both sides of the polarizing film obtained in Example 1, and 1 g of the adhesive was added to a 5.0% by weight aqueous solution of polyvinyl alcohol (“Bovar” manufactured by Kuraray) as an adhesive. For, NH4■, CoI2, Ni■
2. A solution in which 0.4g of znI2 was added as an iodine ion, and the pressure was 5.0kg/c using a laminator.
m2 at a temperature of 50°C and dried at 70°C for 30 seconds to obtain a polarizing film.

8 Example 4 A polyester film with a thickness of 50 μm was placed on both sides of the polarizing film obtained in Example 1, and 0.4 g of KI was added in the form of iodine ion to 1 g of polyester urethane adhesive, and a solvent (
dimethylformamide) to create a 30% by weight solution, and use a laminator with this solution at a pressure of 5.0 kg/cm2.
They were laminated at a temperature of 50°C and dried at 70°C for 30 seconds to obtain a polarizing film.

Comparative Example 1 Cellulose triacetate films with a thickness of 80 μm were placed on both sides of the polarizing film obtained in Example 1 using a laminator with a 5% by weight aqueous solution of polyvinyl alcohol (“Poval” manufactured by Kuraray) as an adhesive under a pressure of 560 kg. /Cm2, temperature 50℃
The films were bonded together and dried at 70° C. for 30 seconds to obtain a polarizing film.

Table 1 shows the results of heat and humidity resistance of Examples and Comparative Examples. It can be seen that the polarizing plate in which the adhesive of the present invention contains multi-halogen ions including iodine has excellent heat and humidity resistance.

[Effects of the Invention] According to the structure of the present invention, a polarizing film having excellent heat and humidity resistance can be obtained, and can sufficiently contribute to improving the performance of liquid crystal elements for use in a wide variety of liquid crystal elements.

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Claims (1)

[Claims] A polarizing film formed by laminating transparent supports on both sides of a polyvinyl alcohol-based polarizing film via an adhesive, characterized in that the adhesive contains polyhalogen ions containing iodine. film.