JPS60159704A - Polarizing plate - Google Patents

Abstract

PURPOSE:To obtain a polarizing plate having superior heat resistance and moisture resistance by sticking a heat resistant protective film having low moisture permeability to the surface of a polarizing PVA film provided with polarizing performance by the adsorption and orientation of a dichroic dye and with heat resistance by specified heat treatment. CONSTITUTION:A dichroic dye such as Direct Black 17 is adsorbed on a polyvinyl alcohol film, and the dyed film is uniaxially stretched about 3-4 times with hot air. The stretched film is heat treated under tension so that it has <=1% rate of shrinkage in a direction perpendicular to the stretching axis after heating at 100 deg.C for 30min. A transparent protective film is stuck to the surface of the resulting polarizing PVA film provided with heat resistance to obtain the desired polarizing plate. The protective film has <=55gr/m<2>hr moisture permeability at 80 deg.C and 95% RH, -0.3-0% rate of dimensional change after heating at 100 deg.C for 30min and <=100nm retardation value.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to a polarizing plate made from PVA, particularly with improved heat and moisture resistance.

Prior art PVA (polyvinyl alcohol) films have been widely used to adsorb iodine, but they generally have poor heat resistance and moisture resistance, and iodine tends to be easily desorbed, especially in high-temperature and humid environments. This resulted in poor polarization performance and lacked reliability.

A polarizing film using a dichroic dye has been proposed to compensate for such drawbacks of the iodine-based polarizing plate, and at least a decrease in the degree of polarization due to detachment of the polarizer has been prevented. However, since PVA film itself has low moisture resistance, a transparent film such as cellulose triacetate that does not have birefringence, that is, does not affect the display function when used as a liquid crystal element, is usually attached to the surface. It also serves as a protective layer.

This protective layer is required to have many functions, such as 1) preventing the shrinkage of the PVA film at high temperatures, and 2) suppressing the permeation of water vapor into the PVA layer under high temperature and high humidity conditions, and preventing discoloration of PTA. However, cellulose triacetate, which is commonly used, has a high moisture permeability, and for example, an 80P film can be heated at 80℃ at 9
It shows a value of 108 gr/-.hr under 5%R1'10 conditions, and the PVA film tends to swell and discolor under high temperature and high humidity conditions.

For this reason, it has been proposed to use a protective film with a lower moisture permeability. For example, JP-A No. 57-30808 uses a thermoplastic polycarbonate film, and JP-A No. 57-62011 uses polysulfone, The use of films of polyethersulfone, polyester, polyamide, etc. has been disclosed. However, in reality, even if these protective films are laminated to polarized PVA stretched films, it is difficult to completely suppress discoloration due to moisture, and furthermore, when exposed to high temperatures, PVA
There are problems such as sharp cracks forming in the VA film. In other words, when applying a polarizing plate to a liquid crystal element, small pieces are punched out from a large size film and attached to the liquid crystal cell via adhesive, but the PVA layer is exposed on the cut surface.
Therefore, discoloration of the cut end is likely to occur due to moisture intrusion from the cut surface, and in a heat resistance test (100°C), PV
It is difficult for cracks to occur in the A layer along the stretching axis direction.O Purpose of the InventionThe present invention is based on the above-mentioned current situation. The reason why such discoloration and cracks occur is that the PVA layer itself lacks moisture resistance, and that the PVA layer is damaged during heating.
This is due to the generation of shrinkage stress in the direction perpendicular to the stretching axis of the layer and PVAji! This was made based on the knowledge that the above-mentioned drawbacks can be overcome by imparting heat resistance to the material by orienting and crystallizing it so that the shrinkage ratio in the direction perpendicular to the stretching axis is below a certain value.

Summary and Structure of the Invention Namely, the summary of the present invention is that polarization performance is imparted by adsorption and orientation of dichroic dye, and the iOO in the direction perpendicular to the stretching axis is
At least one side of the polarized PVA film is heat resistant so that the shrinkage rate after heating for 30 minutes at 80°C and 95% RH is 55 gr/n.
f-hr or less, the dimensional change rate after heating at 100°C for 30 minutes is 1 CLmo% to O%, and the protective film is attached with a substantially transparent protective film and a retardation value r of 1100n or less. A polarizing plate characterized by:

The polarized PVA film used in the present invention is made of dichroic dyes such as azo, anthraquinone, and tetrazine, such as one or two of Direct Black 17, 19°22, Direct Blue 1.6, Direct Red 28, etc. The above film is adsorbed and oriented to give polarizing properties due to K, but the film is also heat resistant so that the shrinkage rate after heating at 100°C for 30 minutes in the direction perpendicular to the stretching axis is 1% or less. It is necessary that gender is given.

In order to obtain a polarized PVA film that satisfies this requirement, the PVA film dyed with the dichroic dye is single-stretched 3 to 4 times by dry heat stretching, and then stretched under tension at 160°C or higher, preferably at 160°C to 180°C. A heat treatment is performed in which the PVA film is heated to a temperature of
A film with stabilized heat resistance can be obtained due to thermal stress, but the heat shrinkage rate of the film thus obtained varies somewhat depending on the processing conditions such as temperature and time during the heat treatment. It is preferable to adjust the heat treatment conditions so that the shrinkage rate of the film falls within the range specified in the present invention.

The polarizing plate of the present invention comprises at least one side K of the heat-resistant polarized PVA film prepared as described above.

The above protective film should have low moisture permeability, an extremely small dimensional change rate upon heating, and optical properties that do not impair its performance as a polarizing plate. Specifically, the moisture permeability is 55 g under the measurement conditions of 80°C and 95% RH.
r/l# h Below, it is dimensionally transparent and means the retardation value F. Also, the retardation value F is also called the retardation value, and indicates the degree of birefringence of the film. The value can be determined by the usual method of measurement using a Pavinefunpensator. Since the smaller the F value is, the better the film is optically as a protective film for a polarizing plate, it is preferable that the value is 50 nm or less. By the way, the r value of a commonly used cellulose triacetate film having a thickness of about 80P is about 50 nm.

The protective film used in the present invention can be used as long as it satisfies the above conditions; for example, films made of polymethyl methacrylate, polyether nalphone, polycarbonate, etc. can be used; At the time of production, care must be taken so that the produced film satisfies the above conditions, for example by employing a casting method to minimize dimensional change and birefringence.

Further, the button for bonding the protective film to at least one surface of the polarizing PTA film is usually made of an adhesive, and a flexible adhesive is preferably used as the adhesive.

The polarizing plate of the present invention thus obtained has excellent heat resistance and moisture resistance, and for example, even when subjected to a heat resistance test at 100°C for 500 hours or a humidity resistance test for 500 hours at 80°C and 95% RH. PVA11K does not have fine particles or discoloration at the edges, so there is no risk of deterioration in quality or performance.

If the polarized PVA film does not have sufficient heat resistance due to oriented crystallization as in the past, 11! While the heat shrinkage of the protective layer is small, the PVA layer is affected by the force of #1llllf water release and shrinkage of rain crystals, causing a shrinkage gap between the two layers, resulting in structural KHr horizontal When the shrinkage force acts in this direction, fine cracks may occur in the vertical direction of the PVA layer, which is thought to be due to
Discoloration occurs at the edge of the polarizing plate, which is thought to be caused by deorientation of the A layer, but as described above, in the present invention, P
By using a material with sufficient heat resistance as the VA layer and using a film with low permeability and extremely small dimensional change rate upon heating as the protective layer, the above drawbacks are eliminated.
It has excellent heat resistance and moisture resistance.

Example Hereinafter, the present invention will be explained based on examples.

Example L An unstretched PVA film with a degree of saponification of 99.8% was washed with water at room temperature, and then immersed for 5 minutes in a 40'CO aqueous solution containing the dichroic dye Direct Black 11 with aOS weight % to remove the dye. Let it absorb.

After drying the film with hot air at 80°C for 3 minutes,
Dry heat stretching is performed uniaxially at 40° C. by a factor of 4. Next, heat treatment was performed at 170°C for 5 minutes while maintaining the tension at 11°C, followed by further immersion in an aqueous solution at 55°C containing 3% by weight of boric acid for 10 minutes while maintaining the % tension, and heating at 100°C for 130 minutes. A film with a heat shrinkage rate of α7% in the transverse direction was obtained.

%MDI-based polyclekne adhesive was used on both sides of the film, and the moisture permeability at 80°C and 95% RH was 17 gr/l.
ri/hr polycarbonate film (thickness 80μ)
were pasted together to form a polarizing plate.

Furthermore, this polycarbonate film r@ke, 38 n
m% Dimensional change after heating at 100'C for 30 minutes was 0%.

Example 2 PVA film AK%MD created under the same conditions as Example 1
80°C, 95% R using I″A polyclekne adhesive
Polyether sulfone (thickness 75P) having a water vapor permeability of 51 gr/rrl-hr at H was laminated to form a polarizing plate.

In addition, the F value of this polyether sulfone film is 53
nm, the dimensional change rate after heating at 100°C for 30 minutes is -(1
It was 1%.

Example 3 A PVA film made under the same conditions as Example 1 was coated with M
80℃, 95%R using DI polycrethane adhesive
A polymethyl methacrylate film (thickness: 60p) prepared by a casting method and having a moisture permeability of 45 gr/m'·hr in H was laminated to form a polarizing plate.

In addition, the F value of this polymethyl methacrylate film is
The dimensional change rate after heating at 100° C. for 30 minutes was -112%.

Comparative Example 1 A PVA film made under the same conditions as Example 1 was coated with MD.
80℃, 95%RH using I-based polyclekne adhesive
A polymethyl methacrylate film (thickness 25P) made by a casting method with a moisture permeability of 70 gr/ld/br
) were pasted together to form a polarizing plate.

In addition, this polymethyl methacrylate film comparative example 2 MD
80℃, 95% RH using I-type Borikrekun adhesive
A cellulose triacetate film (thickness: 80 μm) with a moisture permeability of 108 gr/m′·hr was bonded to the film to form a polarizing plate.

The r value of the cellulose triacetate film used was 50 nm.
, the dimensional change rate after heating at 100℃ for 30 minutes is -(L6%
Met.

Comparative Example 3 In the same manner as in Example 1, after dry heat stretching was performed 4 times, the sample was immersed in an aqueous solution at 55°C containing 3% by weight of horic acid for 27.5 minutes under tension, and then stretched at 80°C. Dry with hot air,
A film having a transverse shrinkage rate of 13% after heating at 00°C for 30 minutes was obtained.

The same polycarbonate film used in Example 1 was laminated on both sides of the film using an MDI-based polyclekne adhesive to form a polarizing plate.

The polarizing plate obtained above was subjected to a heat resistance test at IOO°C for 500 hours and a humidity test at 80°C, 95% RH for 500 hours, and changes in single plate light transmittance and degree of polarization were measured using a spectrophotometer. It was measured.

The results are shown in Table 1. As is clear from this result,
It can be seen that the combination K of the PVA film whose oriented crystallization was promoted by heat treatment and the low temperature transmittance @y film has improved the problems in the heat resistance and moisture resistance tests.

Margin below Table 1

Claims (1)

[Claims] 1 Second polarization performance is imparted by the adsorption orientation of the dichroic dye,
9596 at 180°C on at least one side of a polarized PVA film that has been given heat resistance so that the shrinkage rate after heating at 100°C for 30 minutes in the direction perpendicular to the stretching axis is 4o% or less.
Moisture permeability at RII is less than 55gr/11fhr, ioo
℃, the dimensional change rate after heating for 30 minutes is -α 1,%~0%
So, practically! 1. A polarizing plate, characterized in that it is laminated with a 11E film which is male and has a letter gougeon value r of 1100n or less.