JPH0535402B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a polarizing plate that is used for applications such as liquid crystal displays, and particularly has improved water resistance and moisture resistance. PRIOR ART Recently, liquid crystal displays using polarizing plates have begun to be used in a variety of fields, including applications that require durability under high temperature and high humidity conditions, such as automobile display panels. As attempts have been made, the demand for polarizing plates with better heat resistance and moisture resistance is increasing. Polyvinyl alcohol (hereinafter referred to as PVA) based polarizing films are commonly used as polarizing plates, but these films have poor moisture resistance, and particularly in high temperature and high humidity environments, the polarizing performance is significantly reduced. This is thought to be due to orientation relaxation due to water absorption of the PVA film. For this reason, PVA
It is common practice to protect the polarizing film by laminating a transparent film such as cellulose diacetate that does not have birefringence on the surface of the polarizing film, but the PVA film itself has poor moisture resistance.
Due to the poor moisture permeability of cellulose triacetate, it does not provide sufficient protection. For example, in an environment of 80° C. and 95% RH, even if the above-mentioned protective layer is provided, discoloration and a decrease in the degree of polarization occur due to orientation relaxation due to water absorption of PVA, resulting in insufficient moisture resistance. In addition, in order to eliminate such drawbacks, for example, in Japanese Patent Application Laid-open No. 12050/1983, an oxide layer such as SiO ₂ or TiO ₂ or a nitride layer such as Si ₃ N ₄ is directly provided on the surface of the polarizing film. , a method for improving moisture resistance is disclosed in JP-A-55-114563, in which an oxide layer such as SiO ₂ , TiO ₂ , ZrO ₂ , etc. is provided on the surface of cellulose triacetate as a protective film via an anchor layer. A method has been proposed to improve moisture resistance by
It is not sufficient to prevent discoloration and decrease in polarization degree under high temperature and high humidity conditions, and further improvements in heat resistance and moisture resistance are required. Purpose of the Invention In view of the above-mentioned current situation, the present invention was developed with the aim of providing a polarizing plate with excellent heat resistance and moisture resistance. The thin film layer is made of the conventionally known SiO, SiO ₂
This was made based on the knowledge that it has particularly excellent moisture permeability compared to other layers, and that by applying it to the protective film of a polarizing plate, a polarizing plate with excellent performance could be obtained. SUMMARY AND STRUCTURE OF THE INVENTION The gist of the present invention is to provide a polarizing plate in which a cellulose acetate film is adhered to at least one surface of a polarizing film in which a polarizing element is adsorbed and oriented on a hydrophilic polymer film. contains SiO ₂ , B ₂ O ₃ , BaO and A
The molar ratio of ₂ O ₃ is SiO ₂ :B ₂ O ₃ :(BaO+A ₂ O ₃ )=2~4:1~
A polarizing plate characterized in that a transparent thin film layer made of a composition having a ratio of 2:0.3 to 1 is formed in close contact with the polarizing plate. The polarizing film used in the present invention is made by adsorbing polarizing elements such as iodine or dichroic dyes such as Direct Black 17, 19, 20, Direct Blue 1, 6, Direct Red 28, etc. to a hydrophilic polymer film such as PVA. , polarizing properties are imparted by orienting a polarizing element by stretching an adsorption film or the like. Cellulose acetate films include cellulose diacetate and cellulose triacetate, and cellulose triacetate is preferably used. The cellulose acetate film used in the present invention has a transparent thin film layer made of a composition of SiO ₂ , B ₂ O ₃ , BaO and A ₂ O ₃ in the above-mentioned molar ratio formed in close contact on at least one surface thereof. However,
Regarding BaO and A ₂ O ₃ , as long as the total number of moles of these two satisfies the above formula, one of the two does not need to be substantially contained. However, when an alkali metal oxide such as Na ₂ O is added to the above composition of the transparent thin film layer, moisture permeation resistance tends to be impaired due to its hydrophilic nature. Furthermore, if the molar ratio of the transparent thin film layer is out of the above range, layer separation tends to occur and moisture permeation resistance decreases. And S ₂
As the amount of O ₃ increases, moisture permeability tends to deteriorate due to its reactivity with water, and as the amount of (BaO+A ₂ O ₃ ) decreases, water resistance tends to deteriorate. The most preferable method for forming the above transparent thin film layer on the surface of a cellulose acetate film is sputtering, and by setting the sputtering target to the above composition, a transparent thin film layer having almost the same composition can be formed. . Further, a transparent thin film layer having the above composition can also be formed by a vacuum evaporation method or an ion plating method. In the case of vacuum evaporation, it is said to be difficult to form a thin film layer using mixed substances having different vapor pressures with the same composition. However, the present inventors have confirmed that if the above composition is melted in advance in an electric furnace and vitrified, then used as an evaporator and evaporated using an electron gun heating method, a deposited film with approximately the same composition can be obtained. did. Further, a deposited film having the above composition can also be formed by a flash deposition method which is generally used when vacuum depositing a mixture. In any of the vacuum evaporation methods, ion plating methods, sputtering methods, etc., the adhesion of the transparent thin film layer to the cellulose acetate film base material is good, and the transparency is also good. Another feature of the present invention is that curling of the film formed by the vacuum evaporation method or the like does not pose a major problem. This is thought to be because the transparent thin film layer has less residual stress in the system of the present invention (SiO ₂ , B ₂ O ₃ , BaO, A ₂ O ₃ ) compared to conventional vapor deposited layers such as silicon oxide. . When forming a transparent thin film layer by a vacuum evaporation method, an ion plating method, or a sputtering method, it is usually preferable to perform the process under a vacuum atmosphere of 2×10 ⁻³ torr or less. The thickness of the transparent thin film layer is preferably in the range of 100 to 5,000 Å, more preferably in the range of 500 to 2,500 Å in order to have good flexibility and adhesion. Even if the thickness of the transparent thin film layer exceeds 5000 Å, the transparency will not be impaired, but the curling property of the cellulose acetate film may become a problem, and cracks and peeling may easily occur. Also, the thickness of the transparent thin film layer is
When the thickness is less than 100 Å, the film may form an island-like structure, resulting in insufficient moisture permeation resistance. In the present invention, sufficient moisture permeation resistance can be achieved by simply providing the borosilicate glass transparent thin film layer on one side of the cellulose acetate film, but it may of course be formed on both sides if necessary. The polarizing plate of the present invention is made by adhering to at least one surface of the polarizing film a cellulose acetate film on which the transparent thin film layer is closely formed, and the adhesive material used for this adhesion is urethane. adhesives, acrylic adhesives, epoxy adhesives, etc. can be used. When a cellulose acetate film with a transparent thin film layer formed on only one side is adhered to a polarizing film, the thin film layer may be placed in contact with the polarizing film, or the thin film layer may be placed in contact with the polarizing film. You can place it opposite to the film side, but
Adhesion is carried out by placing the thin film layer in contact with the polarizing film in order to prevent the transparent thin film layer from being damaged by contact with other objects, etc., and because the thin film layer has excellent adhesion with adhesives. is preferable. The polarizing plate of the present invention has the structure as described above, and the borosilicate glass transparent thin film layer of a specific composition closely formed on at least one surface of the cellulose acetate film used therein provides excellent performance under high temperature and high humidity conditions. Since it is endowed with moisture resistance, it can be used in applications that require moisture resistance under severe conditions, such as automobile liquid crystal display panels, and can exhibit excellent effects. EXAMPLES The present invention will be described below based on examples. Example 1 An unstretched PVA film with a degree of saponification of 99.8% was washed with water at room temperature and then dyed by passing it through an aqueous dyeing solution at about 40°C containing dichroic dye Direct Blue 15. Dry with hot air at ℃. This film was dry-heat stretched approximately 4 times in the uniaxial direction at 140°C, and then stretched at 170°C for 5 times while maintaining tension.
The film was heated for 1 minute, and then immersed in a 3% by weight boric acid aqueous solution at 55°C for 10 minutes while maintaining tension to prepare a PVA polarizing film. On the other hand, a borosilicate glass-like transparent thin film with a thickness of 990 Å was formed on a cellulose triacetate film with a thickness of 80 μm by vacuum evaporation under the following conditions. The composition of the vapor deposited layer formed on the surface of the cellulose triacetate film was analyzed using an X-ray microanalyzer, and was found to have approximately the same composition as the oxide mixture used as the evaporation source. Film formation method: Vacuum deposition method (electron gun heating method) Evaporation source: An oxide mixture of SiO ₂ , B ₂ O ₃ , BaO, and A ₂ O ₃ in a molar ratio of 3:1:0.6:0.3 was prepared in an electric furnace. Melted and vitrified product Vacuum degree: 2 × 10 ^-4 Thor film Thickness: 990 Å (measured with a crystal oscillation monitor) Film formation side: One side of the film Next, the transparent thin film layer of the vapor-deposited film created above is PVA polarized Apply the appropriate amount so that it is in contact with the film surface.
A vapor-deposited film was attached to both sides of the PVA polarizing film using a urethane adhesive. The adhesion between the PVA polarizing film and the thin film layer deposition surface of the vapor-deposited film was extremely good. Regarding the polarizing plate prepared in this way, 80℃,
A humidity test was conducted under the condition of 95RH for 500 hours, and the single plate transmittance T% at a wavelength of 610nm and the degree of polarization P% at a wavelength of 610nm were measured before and after the test, and the results are shown in Table 1. Obtained. Note that the degree of polarization P was determined based on the following formula. T ₁ : Parallel transmittance (λ = 610 nm) when two polarizing plates are stacked with their polarization axes parallel to each other T ₂ : Orthogonal transmittance (λ = 610 nm) when two polarizing plates are stacked with their polarization axes perpendicular to each other Example 2 Instead of the evaporation source used in Example 1, SiO ₂ , B ₂
The molar ratio of O ₃ , BaO, A ₂ O ₃ is 4:2:0.75:
A polarizing plate was prepared in the same manner as in Example 1, except that a 1950 Å thick evaporated layer was formed by using an oxide mixture of 0.25 and vitrified by melting it in an electric furnace. The test was conducted. The results were as shown in Table 1. Comparative Example 1 Instead of the evaporation source of Example 1, SiO ₂ , B ₂ O ₃ ,
Example except that an oxide mixture with a molar ratio of BaO and A ₂ O ₃ of 1:1:0.75:0.25 was melted and vitrified in an electric furnace, and a vapor deposited layer with a thickness of 1020 Å was formed. Create a polarizing plate in the same manner as 1,
A test similar to Example 1 was conducted. The result is the first
It was as shown in the table. Comparative Examples 2 to 3 In the same manner as in Example 1 except that SiO ₂ , TiO ₂ , and ZrO ₂ were used as evaporation sources, they were each vapor-deposited on one side of a cellulose triacetate film (thickness: 80 μm), and then deposited on one side of the film. SiO ₂ thin film with a thickness of 980 Å (Comparative Example 2),
TiO ₂ thin film with a thickness of 1015 Å (comparative example 3) and thickness
Cellulose triacetate films each provided with a 1080 Å ZrO ₂ thin film (Comparative Example 4) were prepared. These vapor-deposited films were applied to both sides of the same PVA polarizing film prepared in Example 1.
Three types of polarizing plates were created by bonding in the same manner as above. The three types of polarizing plates thus prepared were subjected to the same moisture resistance test as in Example 1, and the results shown in Table 1 were obtained. 【table】

Claims (1)

[Scope of Claims] 1. A polarizing plate in which a cellulose acetate film is adhered to at least one surface of a polarizing film in which a polarizing element is adsorbed and oriented on a hydrophilic polymer film, and the cellulose acetate film is attached to at least one surface of the polarizing film. , SiO ₂ , B ₂ O ₃ , BaO and A ₂ O ₃ in a molar ratio, SiO ₂ :B ₂ O ₃ :(BaO+A ₂ O ₃ )=2-4:1-
A polarizing plate characterized in that a transparent thin film layer made of a composition having a ratio of 2:0.3 to 1 is formed in close contact with the composition. 2. The polarizing plate according to claim 1, wherein the hydrophilic polymer film is a polyvinyl alcohol film.