JPS61148403A - Circular polarizing plate and its preparation - Google Patents

Abstract

PURPOSE:To improve efficiency for prepn. and to reduce the cost for prepn. of a circular polarizing plate by pasting a biaxially stretched thermoplastic resin film having a specified angle between an optical orientation direction and a longitudinal stretching direction of the film and a specified retardation value to a plate for linear polarization. CONSTITUTION:For example, a 1/4 wavelength plate comprising a biaxially stretched thermoplastic resin film consisting of polyethleni terephthalate resin having 30-60%o or 120-150 deg. angle between the optical orientation direction and the longitudinal stretching direction and 80-200mmu retardation value is laid on a plate for linear polarization comprising, for example, polyvinyl alcohol linear polarizing film so as to arrange the longitudinal stretching direction of the biaxially stretched film to cross orthogonally or to be arranged parallely to the optical orientation direction of the linear polarization plate, thus forming a circular polarization plate by adhering the both. By this method, a continuous and long sized product is prepd., so the preparation efficiency is improved and the preparation cost is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a circularly polarizing plate, and more particularly to a surface antireflection filter for a display such as a cathode ray tube.

[Prior Art] A circularly polarizing plate is made up of a combination of a quarter-wave plate and a linear polarizing plate, and a large number of quarter-wave plates are known. Specifically, homopolymers and copolymers such as vinyl chloride resins, polycarbonate resins, and polystyrene resins are uniaxially stretched (for example,
-149008) and biaxially stretched polypropylene (for example, JP-A-49-128741) are known.

[Problems to be Solved by the Invention] However, in these conventional circularly polarizing plates, the direction of the stretching axis of the film, which is a quarter-wave plate, is 45 degrees
Because they are pasted together in a criss-cross pattern, it is not possible to produce long, continuous pieces, which is the biggest cause of increased costs. Moreover, those stretched along the -axis have the disadvantage of being susceptible to tearing.

The present invention has excellent mechanical properties and high production efficiency.
Another object of the present invention is to provide an inexpensive circularly polarizing plate and a method for manufacturing the same.

[Means for Solving the Problems] The present invention provides: (1) The angle between the optical orientation direction and the longitudinal stretching direction of the film is 30' to 60°, or the retardation value is 80 mμ or more from 120° to 1500°. 200mμ
A linear polarizing plate is laminated on the following biaxially stretched thermoplastic resin film, and the longitudinal stretching direction of the biaxially stretched thermoplastic resin film and the optical orientation direction of the linear polarizing plate are perpendicular or the same direction. Circularly polarizing plates stacked in different positions. and (2) the sequentially biaxially stretched and heat-treated film is cut in the longitudinal direction of the film so that the angle between the optical orientation direction and the longitudinal stretching direction is 30' to 60°, or 120° to 150°. , the retardation value is 8
A method for manufacturing a circularly polarizing plate, which comprises taking out a portion of 0 mμ or more and 200 mμ or less, and continuously bonding the taken out film with the length direction of the linearly polarizing plate so that the length direction of the film matches the length direction of the linearly polarizing plate.

It is characterized by

The thermoplastic resin in the present invention may be any resin that can be melt-extruded and biaxially stretched, such as polyester resins such as polyethylene terephthalate and polyethylene naphthalate, polyamide resins such as nylon 6 and nylon 66, Examples include polyolefin resins such as polypropylene, but from the viewpoint of production efficiency, polyether resins and polyamide resins are particularly preferred, and polyethylene terephthalate resin is most preferred.

The biaxially stretched thermoplastic resin film (hereinafter simply referred to as biaxially stretched film) used as the quarter-wave plate of the circularly polarizing plate of the present invention is a film made of the above-mentioned thermoplastic resin. The angle between the stretching direction (longitudinal stretching axis of the film) and the optical orientation direction of the film (
(hereinafter referred to as optical deviation angle) is 30' to 60°, or; 120° to 150°, preferably 35° to 5
5°, or 125° to 145°, preferably 40° to 50°, or 130° to 140°
Must be 0.゛Optical deviation angle is 30° to 6
If the angle is outside the range of 0° or 120° to 150°, the function as a circularly polarizing plate may be small when bonded so that the optical orientation direction of the linearly polarizing plate matches the stretching axis direction of the film. Or it's lost altogether.
In addition, the retardation value of the biaxially stretched film is 80m.
μ or more and 200 mμ or less, preferably 90 mμ or more and 180
Must be less than mμ.

Retardation value is smaller than 80mμ or 2
If it is larger than 00 mμ, the function as a quarter wavelength plate will be reduced or completely lost. The value of this retardation is expressed as the product of film thickness and birefringence (Δn). The biaxially stretched film preferably used in the present invention has a thickness of 10 μm or more and 300 μm, and a value of Δn of about 0.27 to 20×10′.

Conventionally known linear polarizing plates can be used as the linear polarizing plate used for lamination with the biaxially stretched film, such as polyvinyl alcohol-iodine, polyvinyl alcohol-2
Examples include a polyvinyl alcohol polarizing film made of a chromatic dye, a polyene polarizing film made of a vinyl halide dichroic dye, and a polyester polarizing film made of a polyester dichroic dye. Linear polarizing plates are usually obtained by uniaxially stretching these films in the longitudinal direction or the width direction, but either may be used for this purpose.

A circularly polarizing plate is made by laminating the above-mentioned biaxially stretched film and a linearly polarizing plate, and conventionally known laminating agents can be used as the laminating agent, such as ethylene-vinyl acetate copolymer, Thermoplastic resins such as polyethylene terephthalate-isophthalate copolymers can be used as adhesives.

Note that the bonded surfaces may be subjected to a known discharge treatment. Alternatively, dry lamination may be used without using adhesive.

Next, an example of the method for manufacturing the circularly polarizing plate of the present invention will be described.

After sufficiently drying polyethylene terephthalate, the biaxially stretched film is supplied to an extruder, melt-extruded through a T-die at a temperature of 260 to 310°C, and solidified by cooling at a temperature of 20 to 90°C to produce an unstretched sheet.

In this case, electrostatic casting is effective for uniformly cooling the film.

Next, this unstretched sheet is treated at a stretching temperature, stretching ratio, and heat treatment temperature within a conventionally known range, and after edge cutting, it is wound up as an intermediate spool.

The optical alignment direction was examined for the entire width of the film, and the optical deviation angle was found to be within the range of the present invention, that is, 30° to 60°.
Alternatively, a portion in the range of 120° to 150′ is slit and rolled up into a roll.

A film with such an optical deviation angle can be
When successive biaxial stretching is performed by the transverse stretching method, the portions at both ends corresponding to 20 to 30% of the total width from the clip gripping portions at both ends respectively.

This is due to the fact that in the tenter method, in which the transverse stretching and heat treatment of the film are carried out continuously, there is a large temperature gap between the stretching chamber and the heat treatment chamber, and the heat treatment chamber is at a much higher temperature. This stress is greater than the thermal acid stress of the film in the longitudinal direction of the film in the heat treatment chamber, and is thought to occur because it is pulled toward the stretched palm side in the longitudinal direction.

Therefore, in order to increase production efficiency, the difference between the stretching temperature and the heat treatment temperature is preferably 50°C or more, preferably 70°C or more. If the difference between the stretching temperature and the heat treatment temperature is less than 50'C, the width of the portion having the optical deviation angle of the present invention becomes narrow, leading to a decrease in production efficiency.

A linearly polarizing plate is obtained by stretching a polyvinyl alcohol film 3 to 7 times in the length direction by a known method, followed by immersing it in a periodine solution and drying it. Note that a triacetate film, a diacetate film, or the like may be provided as a protective film on the linearly polarizing plate.

A circularly polarizing plate is obtained by laminating the thus obtained biaxially stretched film and a linearly polarizing plate in the longitudinal direction via an adhesive resin or the like.

Alternatively, the biaxially stretched film can be laminated with a linear polarizing plate supplied from another roll as it is after slitting.

Furthermore, the resin may be blended with other polymers to the extent that it does not impede the purpose of the present invention, or may contain antioxidants, heat stabilizers, lubricants, ultraviolet absorbers, nucleating agents, surface protrusion forming agents, etc. Inorganic and organic additives may be added to the extent that they are normally added.

The characteristic values of the present invention are determined by the following measurement method.

(1) Using a polarizing microscope equipped with an optical deviation angle scale of the film, place the film in the orthogonal Nicol state and mark the vertical stretching direction in advance, read the extinction angle, and measure the vertical stretching direction. Find the deviation from.

(2) Film retardation value Obtained using a polarizing microscope using the compensator method.

[Operations and Effects of the Invention] The present invention achieves the following effects by laminating a film whose optical orientation direction has a specific angular distribution with respect to the vertical stretching direction of the film to a linear polarizing plate as a 1/4 wavelength plate. That's what I got. In other words, (1) since the 1/4 wavelength plate and the linear polarizing plate are made by stacking each other in continuous rolls, long, continuous plates can be manufactured, increasing production efficiency, and as a result, manufacturing costs are significantly reduced. decreases,
We can supply inexpensive circularly polarizing plates.

(2) Since a biaxially stretched film is used, various mechanical properties such as tear resistance are easily achieved.

The circularly polarizing plate obtained by the present invention can be applied to surface antireflection filters in various displays including cathode ray tubes for televisions. Further, by using it in the window of a self-luminous display such as a fluorescent display, LED, or plasma display, it is possible to obtain an effect of increasing contrast by cutting off external light.

Note that the effects of the present invention were evaluated based on the following criteria.

Place the circularly polarizing plate on a smooth reflector and observe under illumination.
The quality was determined based on the degree of blackening.

A perfect circularly polarizing plate is determined by the fact that the reflected light is absorbed by the film, resulting in a black color.

[Example] Next, embodiments of the present invention will be described based on Examples.

Example 1 Polyethylene terephthalate was fed into an extruder and a thickness of 1
An unstretched sheet of 50 μm was obtained.

The unstretched sheet was longitudinally stretched at a stretching temperature of 90° C. and a stretching ratio of 3° to 4 times, and subsequently stretched at a stretching temperature of 95° C. and a stretching ratio of 3.
It was laterally stretched 5 times. After that, it was roughly heat-treated at 220°C for 15 seconds to obtain a biaxially stretched film with a thickness of 15 μm.

When the angular distribution between the optical orientation direction of the film and the longitudinal stretching direction of the film was examined for the entire width of the film in the width direction, it was found to be 30° to 60' at each 1.2 m portion from both ends of the 4 m full width of the intermediate spool. Further, the retardation value was 130 mμ.

After slitting this part to form a roll-shaped film, a linear polarizing plate also made of rolled polyvinyl alcohol-iodine was aligned in the length direction, and the film was made of polyethylene terephthalate (75)/isophthalate (25> (mol% each)). It was thermally bonded via an adhesive resin to form a circularly polarizing plate.

The performance of the obtained circularly polarizing plate was extremely good.

In addition, since it was made into a continuous long circularly polarizing plate, it was possible to manufacture products of the required length, and production efficiency was also dramatically improved compared to conventional methods.

Comparative Example 1 When the distribution of the angle formed between the optical orientation direction and the longitudinal stretching direction of the film obtained in Example 1 with width cut near the center was investigated, it was between 80' and 90°, indicating that the retardation The value was 130 mμ.

A circularly polarizing plate was prepared by laminating the anchor film in the same manner as in Example 1, but its performance was poor.

Claims (2)

[Claims] (1) The angle between the optical orientation direction and the longitudinal stretching direction of the film is 30° to 60°, or 120° to 15°
0°, a linear polarizing plate is laminated on a biaxially stretched thermoplastic resin film having a retardation value of 80 mμ or more and 200 mμ or less, and the longitudinal stretching direction of the biaxially stretched thermoplastic resin film and the linear polarizing plate are A circularly polarizing plate that is laminated in a position where the optical alignment direction is perpendicular or in the same direction. (2) The sequentially biaxially stretched and heat-treated film is cut in the longitudinal direction of the film, and the angle between the optical orientation direction and the longitudinal stretching direction is 30° to 60°, or 120°.
or 150°, retardation value of 80 mμ or more2
1. A method for manufacturing a circularly polarizing plate, which comprises taking out a portion having a diameter of 00 mμ or less, and continuously bonding the two together by aligning the length direction of the taken out film with the length direction of the linearly polarizing plate.