JPH04194902A - Phase difference film - Google Patents

Abstract

PURPOSE:To decrease dependence on view field angle and to widen a visible range by specifying the polymer material of a mixture which constitutes a film comprising two or more polymer components. CONSTITUTION:A film comprising a mixture of polymer materials is uniaxially oriented. Each polymer material used has positive or negative double refraction DELTAni when each single polymer material is uniaxially oriented. DELTAni is defined as formula I, wherein nalphai and nbetai are the refractive indices of the film of single polymer in the orientation direction and perpendicular to the orientation, respectively. Thereby, dependence on view field angle is decreased and visibility can be improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a retardation system with low viewing angle dependence.
This invention relates to a novel retardation film for liquid crystal displays.

[Prior Art] In recent years, the use of black and white liquid crystal displays in word processors has progressed, and color liquid crystal displays have been put into practical use in personal computers and portable televisions. 5T is the mainstream used for such black and white or color display.
It is an N (super twisted nematic) type liquid crystal display.

The STN method has made it possible to increase the capacity of high-order time-division driving, but because the twist angle of the liquid crystal molecules is large, the external hue of the liquid crystal cell when no voltage is applied is not white but green to yellow-red. It has become. Further, the hue when the selection voltage is applied is not black but blue. Therefore, it was difficult to see the color and it was also difficult to colorize it. Currently, as methods for such achromatization, color correction using dyes, a two-layer liquid crystal cell system, and a method using a retardation compensation element made of a birefringent film are proposed. Among them, a method using a retardation compensation element, that is, a retardation film is advantageous because it reduces the weight and cost of the liquid crystal display, and its practical use is progressing.

[Problems to be Solved by the Invention] The retardation film used for the above-mentioned STN method achromatization has the ability to achromatize not only when viewed from a direction perpendicular to the surface of the liquid crystal display but also when viewed from an angle. Characteristics are also required. Furthermore, this characteristic is greatly influenced by the angle dependence (viewing angle dependence) of the tarpsion of the retardation film when viewed obliquely.

However, conventional retardation films have a large viewing angle dependence, and no film has been obtained that satisfies the achromatic properties when viewing an STN liquid crystal display obliquely. On the other hand, some attempts have been made to improve the viewing angle dependence by controlling the orientation state of the molecules of the polymeric material that constitutes the retardation film (Japanese Patent Application Laid-open No. 2-1.60204). It is thought that there are problems with productivity and productivity.

An object of the present invention is to solve these problems and provide a retardation film that has low viewing angle dependence and can widen the viewing angle range when incorporated into an STN liquid crystal display.

[Means for Solving the Problems] In order to achieve the above object, the present inventors have developed a three-dimensional refractive index characteristic of the first polymer material constituting the retardation film, and the angular dependence of the tarpaulin. After careful consideration of the relationship between The inventors have discovered that a retardation film with excellent viewing angle dependence can be obtained by stretching and orienting the film, leading to the present invention.

That is, the present invention is an optically anisotropic film having birefringence formed by uniaxially stretching and orienting a film composed of a mixture of two or more polymeric materials,
The present invention relates to a retardation film characterized in that the mixture contains at least one polymeric material in which 8n is positive and one polymeric material in which 8n is negative.

80 in the present invention is the birefringence of a film that is uniaxially stretched and oriented using each polymeric material that is a component of the mixture, and is defined by the formula (1).

Δni=n, , -nB, (1)(
In formula (1), n n l, n4. represents the refractive index in the direction of the stretching axis in the plane of the film and in the direction perpendicular to the stretching axis of a film using the polymer material alone. ) That is, a polymer material in which Δni is positive has a large refractive index n + in the direction of the stretching axis, whereas a polymer material in which Δni is negative has a large refractive index n + in the direction perpendicular to the stretching axis. .

Δni may be substantially positive or negative within the stretching ratio range of the retardation film finally obtained from the polymer material mixture, and the size of Δni is not limited.

The above polymer materials are not particularly limited, but examples of polymer materials with positive 8n1 include polyolefin polymers such as polyethylene, polypropylene, and polyisoprene, polyvinyl chloride, polyvinyl fluoride, and polyfluorinated polymers. Halogen-containing polymers such as vinylidene and polytetrafluoroethylene, polyvinyl acetate polymers, polyester polymers such as polyethylene terephthalate, polyamide polymers such as nylon 6 and nylon 6.6, and polyacrylic acid ester polymers. molecules, polymethacrylic acid ester polymers,
Polycarbonate polymer, poly(2゜6 dimethyl 1,
Examples include polyether polymers such as 4-phenylene oxide) and modified products thereof. On the other hand, examples of polymeric materials having a negative Δnl include polystyrene polymers, polyacrylonitrile, triacetylcellulose, trinitrocellulose, polymethylmethacrylate, polyα-fluoromethylmethacrylate, polybenzylmethacrylate, and the like.

The method for stretching the film obtained from the above polymer material mixture is not particularly limited as long as it can orient molecules in one direction and exhibit birefringence.

Any of the uniaxial or biaxial stretching methods using rolls and/or a tenter, or the inflation method may be used, but the uniaxial stretching method using rolls and/or a tenter is particularly preferred.

The retardation film of the present invention preferably has a refractive index in a three-dimensional direction that satisfies the relationships of formulas (2) to (5) below.

nβ<n, ≦n n (2) nβ ≦n7 <n, (
3) Mouth β 〉na ≧n,
(4) nβ ≧n7 >n,
(5) (In formulas (2) to (5), n, , n
, respectively, represent the refractive index in the direction of the stretching axis in the plane of the film and in the direction perpendicular to the stretching axis, and n, ≠ mouth. n7
indicates the refractive index in the thickness direction of the film. ), that is, n
If 7 is larger than the larger value of n or n, and if it is smaller than the smaller value of n6 or n, the viewing angle dependence of the tarpaulin is large and the STN liquid crystal display is The viewing angle range cannot be expanded sufficiently.

The thickness range of the retardation film of the present invention is preferably]
- to 500μ, more preferably 4 to 250μ. If it is thinner than this range, it is unfavorable for handling, such as wrinkles, breakage, and uneven retardation due to uneven tension. In addition, if the thickness exceeds this range, the thickness of the liquid crystal display may be reduced.
This is not preferable because it causes problems such as continuous processability.

The retardation film of the present invention can be produced, for example, by the following method, but is not limited thereto.

Poly(2,6
A polymer material mixture is prepared using dimethyl 1,4 phenylene oxide) and polystyrene and formed into a film, for example, by the following method.

The polymer material mixture is dissolved in a solvent such as chloroform so that the concentration of the polymer material mixture is 3 to 20% by weight, and the mixture is cast onto a smooth plate made of glass, stainless steel, etc., and coated with an applicator to a predetermined thickness. Let's do it.

Next, it is dried at 20 to 80° C. until the solvent is sufficiently volatilized, and further vacuum dried to remove the solvent almost completely to obtain an amorphous film. Alternatively, an amorphous film can be obtained by drying, melting, and extruding the polymer + a material mixture.

Next, this amorphous film is heated to 50 to 250°C and stretched 1.2 to 4.0 times to obtain a retardation film. Furthermore, surface treatments such as heat treatment, corona treatment, and plasma treatment may be performed as necessary. The heating temperature during stretching varies depending on the characteristics of the polymer material mixture and cannot be unambiguously determined, but it is usually preferably selected between the glass transition temperature and melting point of the polymer material mixture. The stretching ratio can be arbitrarily set as long as a predetermined adhesive tapering is obtained. The thus obtained retardation film is finally made into a product by applying an adhesive for ease of use.

[Example] The present invention will be explained below with reference to Examples.

The retardation in the present invention is determined by measuring the value at 570 nm using Nippon Kogaku's phase difference measuring device N I) DM-1,
Measured using OOO type. Also, the refractive index is ASTM D5
41-50 using an Atsube refractometer model 1-T manufactured by Atago Co., Ltd.

Viewing angle dependence can be measured from the normal direction of the film surface, from the normal direction of the tarp John, or from an oblique direction tilted by 40° on the axis of the tarp John. is R41,1, the ratio R4Ll/R
It was evaluated using o.

Example 1 Poly(2,6 dimethyl 1,4 phenylene oxide) (
(manufactured by Aldrich) in chloroform to a raw resin concentration of 10% by weight to prepare a film-forming stock solution. Next, this film-forming stock solution was cast onto a glass plate and dried at 40° C. for 48 hours to produce a film. Next, the film was uniaxially stretched under the conditions shown in Table 1. A film was similarly made of polystyrene (Styron 600 manufactured by Asahi Kasei),
Uniaxial stretching was carried out under the conditions shown in Table 1. As shown in Table 1, 8n was positive for poly(2,6 dimethyl 1,4 phenylene oxide), and Δni was negative for polystyrene.

Next, a raw material resin containing poly(2,6 dimethyl 1,4 phenylene oxide) and polystyrene mixed at a weight ratio of 20:80 was formed into a film and stretched under the same conditions, and a retardation of 308 nm was obtained. A retardation film was obtained. As shown in Table 2, there was almost no change in tarpaulin when measured from an oblique direction, indicating good viewing angle dependence. Furthermore, when incorporated into a liquid crystal display, the dependence on the viewing angle became extremely small, and the screen was clear even from a 40° direction.

Example 2 In the same manner as in Example 1, poly(2,6
A film was prepared by mixing dimethyl 1,4 phenylene oxide) and negative polystyrene at a weight ratio of 40:60.

Next, this film was uniaxially stretched to 1.5 times at 190°C,
A retardation film with a retardation of 315 nm was obtained. As shown in Table 2, there was almost no change in tarpaulin when measured from an oblique direction, indicating good viewing angle dependence.

Example 3 A film was prepared by adding 10% by weight of dioctyl phthalate 1. to polyvinyl chloride (manufactured by Aldrich) and pressing it on a hot plate, followed by uniaxial stretching. Further, a film was prepared by pressing polymethyl methacrylate (manufactured by Mitsubishi Rayon ■) with a hot plate, and uniaxially stretched under the conditions shown in Table 1. As shown in Table 1, polyvinyl chloride has 8n1 positive,
Polymethyl methacrylate was negative.

Next, a raw resin prepared by mixing polyvinyl chloride with 10% by weight of dioctyl phthalate and polymethyl methacrylate at a weight ratio of 10:90 was pressed on a hot plate to produce a film. did.

Next, this film was uniaxially stretched 3.5 times at 90° C. to obtain a retardation film with a retardation of 321° C.m.

As shown in Table 1, when measured from an oblique direction, there was almost no change in tarpaulin, indicating good viewing angle dependence.

Comparative Example 1 - A commercially available polycarbonate film (manufactured by General Electric Co., Ltd., Lexan) was uniaxially stretched by 1°5 times at 170°C to obtain a retardation film with a retardation of 4200 m. As shown in Table 1, Δn was positive. Table 2
As shown in Figure 2, when measured from an oblique direction, the tarpaulin changes are large, and the viewing angle dependence is not good.

Comparative Example 2 As shown in Table 1, a polystyrene having negative 8n1 (Styron 600 manufactured by Fukasei Co., Ltd.) was formed into a film in the same manner as in Example 1, and uniaxially stretched to 1.5 times at 150°C. A retardation film having a retardation of 562° C.m was obtained.

As shown in Table 2, when measured from an oblique direction, the tarpaulin changes are large, and the viewing angle dependence is not good.

Comparative Example 3 As shown in Table 1, poly(2,6 dimethyl), 4-phenylene oxide (manufactured by Aldrich) having a positive Δni was pressed on a hot plate in the same manner as in Example 3 to form a film. It was filmed and uniaxially stretched to 1.2 times at 200°C to obtain a retardation film with a retardation of 1.85 nm. Table 2
As shown in the figure, when measured from an oblique direction, the tarpsion change is large, and the viewing angle dependence is not good.

From the above results, it can be seen that the retardation film of the present invention is excellent in viewing angle characteristics.

[Effects of the Invention] The present invention industrially provides a retardation film suitable for liquid crystal display devices with excellent viewing angle characteristics, and the retardation film of the present invention can be used in word processors, personal computers, portable TVs, etc. The visibility of personal displays, etc. can be improved.

Claims (1)

[Scope of Claims] An optically anisotropic film having birefringence formed by uniaxially stretching and orienting a film composed of a mixture of one or more polymeric materials, the film comprising: 1. A retardation film comprising at least one component each of a polymeric material whose Δn_i is positive and a polymeric material whose Δn_i is negative. However, Δn_i is the birefringence of a film that is uniaxially stretched and oriented using each polymeric material that is a component of the mixture, and is defined by equation (1). Δn_i=n_α_i−n_β_i (1) (In formula 1, n_α_i and n_β_i respectively represent the refractive index in the stretching axis direction and in the direction perpendicular to the stretching axis in the film plane of a film using the polymer material alone.) 2 The retardation film according to claim 1, characterized in that the refractive index in three-dimensional directions satisfies the relationships of the following formulas (2) to (5). n_β<n_γ≦n_α (2) n_β≦n_γ<n_α (3) n_β>n_γ≧n_α (4) n_β≧n_γ>n_α (5) (In formulas (2) to (5), n_α and n_β are each within the film plane It shows the refractive index in the stretching axis direction and the direction perpendicular to the stretching axis, and n_β≠n_α. n_γ shows the refractive index in the thickness direction of the film.)