JPH02191904A - Phase difference film and its production - Google Patents

Abstract

PURPOSE:To obtain a phase difference film of good visual angle characteristic by setting a ratio of retardation values, which are obtained at the time of setting the angle formed between a plane orthogonal to the stretching direction of a polarized film, which is formed by stretching a high polymer film, and the normal and the angle formed between the axis of stretching of this film and the normal to 40 deg. and 0 deg. respectively, to a prescribed value. CONSTITUTION:When an incident monochromatic light beam having 632.8nm wavelength is on a plane orthogonal to the stretching direction of the polarized film, Re(40)/Re(O) is expressed with an inequality I where Re(40) is the retardation value of this film for 40 deg. incidence angle and Re(O) is the retardation value for perpendicular incidence to the film surface at the time of setting the angle formed between the incident monochromatic light beam and the normal of the polarized film surface to 40 deg.. When the incident light is on an orthogonal plane including the axis of stretching of the film, Re(40)/Re(O) is expressed with an inequality II at the time of setting the angle formed between the incident monochromatic light beam and the normal of the film to 40 deg.. This phase difference film has these characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a novel retardation film used in optical applications and a method for producing the same.

[Conventional technology]

Films or sheets with light transmittance and birefringence are increasingly being used as anti-glare applications to cut reflected light from the surfaces of television cathode ray tubes and cathode ray tubes, and as materials for the purpose of sharpening liquid crystal displays. .

Retardation, which is one of the optical properties of a film, is defined as the product of birefringence value and film thickness, and its required value varies depending on the purpose.For example, a retardation film for anti-glare function is , circularly polarizing plate, 1/4λ
This is called a (lambda) plate, and the retardation is set to 1/4λ by uniaxial stretching. As this type of technology, methods are already known in which materials such as cellulose resins, vinyl chloride resins, polycarbonate resins, acrylonitrile resins, styrene resins, and polyolefin resins are produced by uniaxial stretching.

In recent years, as the applications of liquid crystal displays have expanded, there has been a desire to improve various problems caused by the birefringence of liquid crystals. Initially, coloring was removed in the direction perpendicular to the surface of the liquid crystal display, but when viewing the display from an angle, a slight change in angle caused a significant change in coloring or the content displayed on the screen disappeared due to viewing angle characteristics. The problems have been exposed and have become a serious issue regarding the use of retardation films.

[Problem to be solved by the invention]

Therefore, an object of the present invention is to provide a retardation film that can improve viewing angle characteristics and a method for manufacturing the same.

[Means to solve the problem]

The present invention was completed as a result of repeated research in order to eliminate the above problems and obtain a new retardation film.

More specifically, the present invention focuses on the fact that the cause of the above problem lies in the viewing angle dependence of retarded silane, and as a result of extensive research, the present invention has developed a birefringent film formed by stretching a polymer film. If the incident monochromatic light beam with a wavelength of 632.8 nm is on a plane perpendicular to the stretching direction of the birefringent film (referred to as the α direction), the relationship between the incident monochromatic light beam and the normal to the birefringent film surface is The angle is 40°, and the retardage gin value of the film at an incident angle of 40°C is R
e (40), and when the retardation value when incident perpendicularly to the film surface is Re (0), if the incident light is on the orthogonal plane containing the stretching axis of the film (referred to as the β direction), the incident light When the angle between the monochromatic light beam and the normal line of the film is 40°, and the retardation value of the film at an incident angle of 40@ is Re (40), the objective can be achieved with 0.85≦retardation film. There was found.

In addition, we have found that by allowing some shrinkage in the width direction during the uniaxial stretching process of the above film, we have found that the viewing angle can be significantly improved compared to a film that has excellent surface quality and does not allow shrinkage in the width direction. This led to the completion of the invention.

More specifically, the present invention relates to a method for producing a retardation film characterized by a width in a direction orthogonal to the stretching axis and before stretching, when the stretching ratio is a in uniaxial stretching. If the ratio is greater than the ratio of the width after stretching to the width before stretching, the effect of increasing the viewing angle will be reduced. Means for stretching the film and simultaneously applying uniform shrinkage in the width direction can be achieved by a two-wheeled stretching device capable of shrinking the film at a constant rate in the width direction. or,
It can also be achieved under specific conditions by longitudinal uniaxial stretching using rolls with different circumferential speeds. For example, if both sides are not fixed and allowed to completely shrink freely, the film becomes corrugated in the width direction. Furthermore, if the ratio between the distance between the rolls and the width of the film is small, the birefringence value in the width direction tends to become non-uniform. Therefore, the preferable am is a ratio of the distance between the rolls and the width of the film of 5 or more. More preferably, the number is 10 or more. In addition, although the influence cannot be easily determined by the stretching temperature before and after stretching, the molecular weight of the film, etc., it can be easily controlled by providing an intermediate roll that does not nip between the rolls that determine the stretching ratio in addition to the above conditions. becomes.

Now, the reason why the viewing angle increases by allowing contraction in the direction perpendicular to the stretching axis is thought to be due to differences in the orientation of molecules depending on the stretching conditions. In ideal uniaxial stretching that allows necking freely, the birefringence value is constant from any direction perpendicular to the stretching direction of the film, but when shrinkage in the width direction is restricted, pure uniaxial stretching occurs. Planar orientation of molecules occurs due to thickness contraction rather than stretching. Due to this plane orientation, the birefringence value from the edge of the film increases compared to the birefringence value from the plane direction. Therefore, it is thought that the retardation tan at oblique incidence is caused not only by an increase in thickness but also by an increase in birefringence value, causing a sudden change in retardation tan, resulting in a narrowing of the viewing angle.

In addition, the polymer film in the present invention refers to any material that is substantially transparent with a light transmittance of 70% or more, and whose molecular stiffness has an absolute value of birefringence of 0.02 or more. These include, but are not limited to, polycarbonate, polyethylene terephthalate, polyacrylate, polyether sulfone, polyphenylene sulfide, polyphenylene oxide, polyallyl sulfone, polyamideimide, polyimide, polystyrene, polyolefin, polyacrylonitrile, cellulose, among others. , polyester, etc. are preferred, and polycarbonate-based polymer films are particularly preferred, and polymer blends between these polymers and polymer blends containing at least one selected from these polymers are also objects of the present invention.

Example 1 The present invention will be described in detail below with reference to Examples.

Example A polycarbonate having a molecular weight of 80,000 obtained by condensation of phosgene and bisphenol A was dissolved in methylene dichloride to form a 10% solution. The solution was cast onto a steel drum and continuously peeled off to obtain a film with a thickness of 50 μm and a width of 500 μm. The film is T, M, Long
The film was stretched by 35% at a temperature of 165°C using a two-wheel stretching machine manufactured by Co., Ltd.
In the direction perpendicular to this, a contraction of 13% was performed. The angular dependence of the retardation value of the stretched film was measured using a birefringence meter ARP-100 manufactured by Shimadzu Corporation.
A result similar to 1 was obtained. When the film was used as a retardation film for a liquid crystal device, the viewing angle characteristics were good and images could be observed satisfactorily even when viewed at an angle of 40 degrees.

Example 2 A polycarbonate film having a width of 500 cm obtained in Example 1 was stretched with a distance of 10 m between two sets of nip rolls that determined the stretching ratio, and two sets of free rolls that did not nip were placed in the middle. The stretching temperature was 175°C, the film feeding speed was 2 m/sin, and the winding speed was 2.5 m/w.
It was set as in. At this time, the width of the film was 445 square meters. Table 1 shows the results of determining the angular dependence of the retardation cylindrical value and the standard deviation of the retardation tan in the width direction using the same method as in Example 1. When used as a film, the viewing angle characteristics were good and the image could be observed satisfactorily even when viewed at an angle of 40''.

Comparative Example 1 The film obtained by casting in Example 1 was
When the retardation tan value of the 1% stretched film was measured in the same manner as in Example 1, the results shown in Table 1 were obtained. When the film was used as a retardation film for a liquid crystal device, the image became difficult to see when tilted at an angle of about 20 degrees.

Comparative Example 2 Between two sets of nip rolls in Example 2 (7) M F
When i was set to 200- and everything else was carried out in the same manner as in Example 2, the variation in the retardation tongue width direction was large, making it unsuitable for optical use.

Comparative Example 3 When the intermediate free roll was removed in Example 2, the winding width of the film was 430-, and
The film was corrugated, and the retardation varied widely in the width direction, making it unsuitable for optical applications.

Example 1.2 has Re(40)/R in both α and β directions.
Although the ratio of e (0) is close to 1, in Comparative Example 1, it deviates from l and the difference becomes large. In Comparative Examples 2.3, the standard difference in Re is large, that is, the variation is large.

Claims (4)

[Claims] (1) In a birefringent film formed by stretching a polymer film, when an incident monochromatic light beam with a wavelength of 632.8 nm is on a plane perpendicular to the stretching direction of the birefringent film, the incident monochromatic light beam and The angle formed with the normal to the birefringent film surface is 40°C, the retardation value of the film at an incident angle of 40°C is Re (40), and the retardation value when the film is incident perpendicularly to the film surface is Re (0 )
When 0.98≦Re(40)/Re(0)≦1
．． 15 and the incident light is on an orthogonal plane containing the stretching axis of the film, the angle between the incident monochromatic light beam and the normal to the film is 40°, and the letter of the film at the incident angle of 40° is When the dation value is Re(40), 0.85≦Re(40)/Re(0)≦1.0
A retardation film characterized by being 2. (2) A method for producing a retardation film, which is characterized by shrinking in a direction perpendicular to the stretching axis during uniaxial stretching. (3) When the stretching ratio in uniaxial stretching is a, the ratio of the length in the direction perpendicular to the stretching axis and the length before stretching is 1/√a
3. The method for producing a retardation film according to claim 2, wherein the retardation film is controlled to be .about.1/2√a. (4) In the longitudinal uniaxial stretching method using rolls with different circumferential speeds, the distance between the rolls is determined so that the ratio of the distance between the rolls and the film width is 5 or more.
) to (3), the method for producing a retardation film.