JPH10332938A - Transparent film having double refraction and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a film having excellent heat resistance which causes little deformation by heat and little changes in double refraction by heat by constituting the film of an amorphous aromatic polycarbonate film and controlling the transmittance for all rays to a specified value or higher. SOLUTION: This transparent film consists of an amorphous aromatic polycarbonate film, and the film shows double refraction with >=80% transmittance for all rays. The film is preferably a transparent film with 500 to 15000 nm retardation. When the double refraction film is used, it is subjected to high temp. in the fabricating processes. However, because aromatic polycarbonate has high heat resistance and causes little deformation by heat and changes in double refraction by heat, it is preferable. The amorphous aromatic polycarbonate film as prepared hardly shows double refraction, especially when the film is obtd. by casting. Therefore, the film is subjected to, for example, uniaxial stretching so as to give higher double refraction to the film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a birefringent transparent film, and more particularly, to a birefringent, amorphous aromatic optical system having an optical total light transmittance of 80% or more. The present invention relates to a transparent plastic film made of polycarbonate and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, as an optical film used in the field of optoelectronics, a film having high birefringence and extremely high transparency has been required. The use of polyethylene terephthalate (PET) has been considered for these applications.

[0003]

The birefringence of a PET film is small without stretching, but the birefringence is generated by stretching the PET film in one direction. This film has good heat resistance and high surface hardness, but there is a problem that PET is crystallized in the film by stretching and transparency is reduced due to light scattering of the crystallized domains. In addition, micro birefringence non-uniformity is unavoidable, and the fact is that the optical film cannot be used.

On the other hand, Japanese Patent Application Laid-Open No. 56-130703 discloses a quarter-wave film having a retardation of 95 to 170 nm made of a polycarbonate polymer.
This film is bonded to a polarizing plate, and a cathode ray tube (C
(RT), etc., which are used for the purpose of preventing reflection of external light, and have a problem that they are unsuitable for a color compensation film of an STN type liquid crystal display device, for example.

[0005]

Means for Solving the Problems In view of such circumstances, the present inventors have studied various materials and their processing methods. As a result, they have been made of an amorphous aromatic polycarbonate film and have a total light transmittance of 80%. The present inventors have found that the above-mentioned film has no problem as described above, has excellent heat resistance, and has little deformation due to heating and little change in birefringence due to heating.

That is, a first aspect of the present invention is that the film is made of an amorphous aromatic polycarbonate film and has a total light transmittance of 80%.
% Or more of a transparent film having birefringence. In a preferred embodiment, the transparent film has a retardation of 500 to 15000 nm. Further, a preferred embodiment is a transparent film formed by forming an amorphous aromatic polycarbonate film by a solvent casting method. A second aspect of the present invention relates to a method for producing a birefringent transparent film having a total light transmittance of 80% or more, characterized by uniaxially stretching a film made of an amorphous aromatic polycarbonate. Is what you do. In a preferred embodiment, the transparent film has a retardation of 500 to 15000 nm. Further, a preferred embodiment is a transparent film formed by forming an amorphous aromatic polycarbonate film by a solvent casting method.

[0007] Birefringent films are subjected to high temperatures during the processing process when applied, but aromatic polycarbonates are suitable because they have high heat resistance and little deformation due to heating and little change in birefringence due to heating. The film made of the amorphous aromatic polycarbonate is obtained by extrusion or casting from a dope solution. The thickness of the film is usually several μm to several hundred μm, more preferably 10 to 300 μm.

A film of an amorphous aromatic polycarbonate rarely exhibits birefringence as it is, especially when obtained by casting. Even in the case of extrusion molding, the birefringence is not so high unless strong tension is applied in the machine direction in the film forming process. As a means for imparting higher birefringence to these films, there is a method of stretching in a uniaxial direction or a method of stretching in a biaxial direction, and a method of giving a difference in the degree of biaxial stretching. The stretching conditions vary depending on the resin of the material or the thickness of the film before stretching, and the stretching temperature is from room temperature to the glass transition temperature (Tg) of the material resin.
Preferably from a temperature lower than the Tg by 10 ° C. or more to 80 ° C.
About high temperature. The stretching ratio is 1.05 to 10 times, preferably 1.1 to 2.0 times, and is appropriately selected depending on the desired degree of birefringence. Stretching just before the film breaks gives the greatest birefringence. When birefringence is obtained by giving a difference in the degree of stretching in the biaxial direction, the difference (Δn) in the refractive index in the direction perpendicular to the in-plane measured by a polarization microscope method or an ellipsometry method is 0.003-0. 05, a retardation of 30 to 15000 nm (for example, a thickness of 10
μm × Δn 0.03 × 10 ³ to thickness 300 μm × Δn
0.05 × 10 ³ ), preferably 500-15000 nm
A film having a thickness of, for example, 10 μm × Δn 0.05 × 10 ³ to 300 μm × Δn 0.05 × 10 ³ can be obtained. Although the transparency varies depending on the thickness of the film, the total light transmittance is 80% or more. The transparent film of the present invention may have a normal transparent hard coat layer on one or both sides for the purpose of surface protection.

[0009]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Examples Polycarbonate resin (Teijin Chemical C-1400, Tg
= 149 ° C) in methylene chloride at a concentration of 20% by weight.
Was produced. The dope was cast on a glass plate, left at room temperature for 60 minutes, peeled off the film, sandwiched between four fixing jigs, dried at 100 ° C. × 10 minutes, and further at 155 ° C. for 10 minutes to obtain a film with a thickness of about A 100 μm film was obtained. Make a 5cm x 10cm sample from this film,
The film was stretched 1.3 times in the machine direction at 165 ° C., and cooled to room temperature. When the properties of this uniaxially stretched film (thickness = 87 μm) were evaluated, the refractive index difference in the in-plane perpendicular direction was 0.0
063, that is, the retardation was 548 nm.
The total light transmittance was 91%.

[0011]

As described above, according to the present invention, there is provided a plastic film having birefringence, high heat resistance and high transparency, which is useful as a color compensation film of an STN type liquid crystal display device. be able to.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI B29K 69:00 105: 32 B29L 7:00

Claims (6)

[Claims] 1. A birefringent transparent film comprising an amorphous aromatic polycarbonate film and having a total light transmittance of 80% or more. 2. The retardation is from 500 to 15,000.
2. The transparent film according to claim 1, which has a nm. 3. The transparent film according to claim 1, wherein the amorphous aromatic polycarbonate film is formed by a solvent casting method. 4. A method for producing a birefringent transparent film having a total light transmittance of 80% or more, comprising uniaxially stretching a film made of an amorphous aromatic polycarbonate. 5. The retardation is from 500 to 15,000.
The production method according to claim 4, wherein the molecular weight is nm. 6. The method according to claim 4, wherein the amorphous aromatic polycarbonate film is formed by a solvent casting method.