JP3031014B2 - Phase difference plate and liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel retardation plate used for a liquid crystal display or the like.

[0002]

2. Description of the Related Art A retardation plate is disclosed in JP-A-63-189804 and JP-A-1-9662.
3. A polymer film having optical homogeneity and durability and having uniaxial orientation as shown in JP-A-1-118805, etc., and optical compensation for improving display quality of a liquid crystal display device. It is commonly used as a plate. An STN-type liquid crystal display device using a retardation plate has two liquid crystal cells.
Lighter than a two-layer STN liquid crystal display device
Although it has the advantages of being thin and inexpensive, it has disadvantages such as poor viewing angle characteristics and inferior black and white levels. These disadvantages have been considerably improved by a method such as laminating two retardation plates, but the viewing angle characteristics have not yet reached a satisfactory level.

The viewing angle characteristic of a liquid crystal display device largely depends not only on the angle dependence of the birefringence of a liquid crystal cell but also on the birefringence of a retardation plate, that is, the angle dependence of retardation. It is known that the smaller the change in retardation angle of the plate, the better. In recent years, as shown in JP-A-2-191904 and JP-A-2-285303, a method of shrinking a film in a direction perpendicular to a stretching axis at the time of uniaxial stretching or forming a film of a polymer liquid under an electric field is applied. Methods for controlling the birefringence characteristics by stretching the formed film, and various methods such as laminating a film formed under application of an electric field on a conventional retardation plate as shown in JP-A-3-85519. In order to improve the viewing angle characteristics by reducing the angle change of the retardation of the retardation plate, the use of these methods has many problems in mass productivity.

[0004] To evaluate the viewing angle characteristics of such a biaxially birefringent film having a uniaxial orientation, a polarizing microscope equipped with a Senarmon compensator is used to evaluate the birefringent film having a positive refractive index anisotropy. Is measured with the retardation (R) measured in a state in which the biaxial film has a slow axis and, in the case of a birefringent film having a negative refractive index anisotropy, the fast axis as a rotation axis, and in a horizontal state. using the retardation inclination angle when the ratio of _{(R 0) (R / R} 0) is _1.10 (θ 1.10), referred to the value as the viewing angle of the film. The smaller the change in retardation angle, the larger the inclination angle (θ _1.10 ), that is, the better the viewing angle characteristics.

In a retardation plate obtained by stretching a conventional thermoplastic resin, even a retardation plate obtained by a longitudinal uniaxial stretching method can obtain a viewing angle of only up to 42 degrees.

In order to improve the display characteristics of a liquid crystal display, T
Various display methods other than the N method and the STN method have been devised. In these display systems, not only the conventional uniaxially oriented birefringent film but also no anisotropy of the refractive index in the film plane, that is, R ₀ = 0, the refractive index in the film plane and the film There is also a need for a retardation plate made of a birefringent film having a different refractive index in the thickness direction.

An object of the present invention is to provide a retardation plate having an unprecedented good viewing angle characteristic, and a retardation plate having a different refractive index in a film plane and a refractive index in a thickness direction.

[0008]

As a result of intensive studies to solve the above problems, it has been found that the use of the microphase-separated structure of the AB type or ABA type block copolymer makes it effective. The film has an orientation structure in the thickness direction of the film, and the film has a different in-plane refractive index and a different refractive index in the thickness direction, and has a good viewing angle characteristic by laminating this film on a conventional retardation plate. The present inventors have discovered that a suitable retardation plate can be obtained, and have completed the present invention.

That is, the present invention provides a retardation plate comprising a block copolymer having a lamellar structure, and a field of view wherein the block copolymer having a lamellar structure is laminated on a retardation plate comprising a thermoplastic resin. This is a phase difference plate having good angular characteristics.

The ratio of the A part to the B part of the AB type or ABA type block copolymer forming the lamellar structure of the present invention is preferably in the range of 0.66 to 1.5 in volume ratio. Preferably
More preferably, it is 0.9 to 1.1.

The AB type or ABA type block copolymer of the present invention is not particularly limited as long as it has an intrinsic birefringence, but those having excellent optical properties such as transparency. It is preferably used. For example, styrene-2-
Examples thereof include a vinylpyridine copolymer, a styrene-isoprene copolymer, a styrene-butadiene copolymer, and an α-methylstyrene-isoprene-α-methylstyrene copolymer.

The AB type or ABA type block copolymer of the present invention is formed into a film, and used alone or bonded to a retardation plate. Although there is no particular limitation on the film forming method, a solution casting method, a press molding method, or the like is preferably used, and the formed film becomes a retardation plate having a different refractive index in a plane and a refractive index in a thickness direction. Further, the formed film may be stretched in a uniaxial direction to have in-plane birefringence, and used as a retardation plate having biaxial refractive index anisotropy. When laminating on a retardation plate made of a thermoplastic resin, the method is not limited, and a method of applying from a solution state or laminating via a pressure-sensitive adhesive after film formation is used.

The thickness of these retardation plates depends on the birefringence and thickness of the laminated liquid crystal cell or conventional retardation plate, and needs to be set for each individual case. Angle dependence of birefringence when liquid crystal molecules having anisotropy are oriented vertically to the glass substrate of the liquid crystal cell (when no electric field is applied to a vertically aligned nematic liquid crystal cell, when an electric field is applied to a twisted nematic liquid crystal cell, etc.) When the layers are laminated in order to compensate for the property, generally, the difference between the in-plane refractive index of the retardation plate made of the block copolymer and the refractive index in the thickness direction is multiplied by the retardation plate made of the block copolymer. 0-2 × (intrinsic birefringence of liquid crystal molecules)
The thickness of the retardation plate made of a block copolymer is set so as to be in the range of x (thickness of the liquid crystal layer), and a uniaxially stretched film made of a thermoplastic resin having a negative refractive index anisotropy is used. In order to improve the viewing angle of the retardation plate of (1), generally, the difference between the in-plane refractive index of the retardation plate made of a block copolymer and the refractive index in the thickness direction × (block weight) The thickness of the retardation plate made of the block copolymer is set so that the thickness of the retardation plate made of the united product is in the range of 0 to (birefringence of the uniaxially stretched film) × (the thickness of the uniaxially stretched film). And so on.

The retardation plate made of a thermoplastic resin for laminating the block copolymer having a lamellar structure of the present invention may be a positive retardation plate when the block copolymer having a lamellar structure has a positive intrinsic birefringence. When the thermoplastic resin having an intrinsic birefringence has a negative intrinsic birefringence in a block copolymer having a lamellar structure, a thermoplastic resin having a negative intrinsic birefringence is used. For example, thermoplastic resins having a positive intrinsic birefringence include polycarbonate and polysulfone, and negative ones include polystyrene, poly-α-methylstyrene, poly2-vinylpyridine, polyvinylnaphthalene, and polymethylmethacrylate. Can be

The AB type or ABA type block copolymer of the present invention can be generally produced by the following method. That is, New Experimental Chemistry Course 19, Polymer Chemistry I,
111-116 (Chemical Society of Japan, 1978 Maruzen)
As described in, a method of synthesizing a terminal functional prepolymer and coupling the terminal functional group with another prepolymer, and a method of sequentially adding monomers using the terminal functional group of the prepolymer as an initiator. can give.

The film having a lamellar structure used in the present invention and the retardation plate laminated on the film having the lamellar structure may be stretched by a tenter stretching method as long as the retardation film has uniform retardation. Any of known methods such as an inter-roll stretching method and an inter-roll compression stretching method may be used.

The method for mounting the retardation plate of the present invention to a liquid crystal display device is not particularly limited. One or both sides of the retardation plate are provided with an adhesive and bonded to a liquid crystal cell and / or a polarizing plate. And the like. Either of the retardation plates may be disposed on the liquid crystal cell side, or may be disposed between the upper polarizing plate and the liquid crystal cell or between the lower polarizing plate and the liquid crystal cell.

[0018]

In the AB type or ABA type block copolymer, the phase separation structure changes depending on the composition ratio of the A monomer and the B monomer at the time of polymerization, so that one phase is spherical and the other is spherical. , One phase is dispersed in the form of a rod in the other phase, and a lamellar structure in which the A and B phases are alternately stacked in layers. (For example, Polymer Alloy Fundamentals and Applications (edited by the Society of Polymer Science, 1981, Tokyo Kagaku Dojin) 196-200
page). Among them, in order to form a lamellar structure, the ratio between the A part and the B part of the AB type or ABA type block copolymer is preferably in the range of 0.66 to 1.5 in volume ratio. , More preferably 0.9 to 1.1. In the case of lamellar structure, polymer processing Vol. 39, No. 10 (1990)
As described on pages 489 to 496, it is known that the main chains of the polymers A and B extend vertically in the lamella layer and contract in the lamella in-plane direction. If the film is formed so as to have a microphase-separated structure by a method having a small shearing force such as a cast film forming method, the lamella surface is oriented in a direction parallel to the film surface, and the AB type or ABA type block co-loads. The main chains of the coalescence will be oriented perpendicular to the film plane.

Since the AB type or ABA type block copolymer has an intrinsic birefringence, the present film has no anisotropy of the refractive index in the plane of the film, that is, R ₀ = 0. However, they exhibit the performance as a retardation plate in which the refractive index in the film plane and the refractive index in the thickness direction of the film are different. Further, when laminated on a retardation plate made of a thermoplastic resin, the change in retardation angle is small, and the performance of the present invention as a retardation plate having unprecedented good viewing angle characteristics is exhibited.

[0020]

According to the present invention, it is possible to easily obtain a retardation plate having a good viewing angle characteristic in which θ _1.10 is 42 degrees or more. Further, it is possible to easily obtain a retardation plate having no in-plane birefringence and an in-plane refractive index larger than a thickness direction refractive index. By using these as a compensator, the display characteristics of the liquid crystal display device can be significantly improved.

[0021]

EXAMPLES The present invention will be described in detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto.

Example 1 Polymer Journal (Polymer Journal)
l) Styrene-2-vinylpyridine block copolymer (molecular weight: 108000 (number average), volume ratio: 0.51 / 1) synthesized by the method described in Vol. 18, p. 493 (1986).
0.49) was cast into a film using pyridine as a solvent to obtain a film having a thickness of 110 μm. This film had a difference between the in-plane refractive index and the refractive index in the thickness direction of 1.52 × 10 ⁻³ , and the product of the difference between the refractive index and the thickness was 167 nm. Further, a polystyrene film (HR sheet, manufactured by Dainippon Ink and Chemicals, Inc.) was pulverized to prepare a 15% dichloroethane solution, and the film formed by the casting method was stretched 2.8 times at 135 ° C. by the tenter stretching method. R ₀ = 549n
m, θ _1.10 = 35 °, a birefringent film having a thickness of 28 μm was obtained. A retardation plate obtained by laminating the block copolymer film on this polystyrene film has a R ₀ = 549 nm.
_Exhibited good viewing angle characteristics of θ _1.10 = 51 degrees.

Example 2 The styrene-2-vinylpyridine block copolymer used in Example 1 was cast into a film with pyridine as a solvent to obtain a film having a thickness of 118 μm. This film had a difference between the in-plane refractive index and the refractive index in the thickness direction of 1.52 × 10 ⁻³ , and was a retardation plate having no in-plane birefringence.

Example 3 Macromolecules
s) Styrene-isoprene block copolymer (molecular weight 1) synthesized by the method described in Vol. 2, page 453 (1969).
(00000 (number average), volume ratio 0.50 / 0.50) was pressed at 180 ° C. to obtain a 200 μm thick film. This film had a difference between the in-plane refractive index and the refractive index in the thickness direction of 2.37 × 10 ⁻³ , and the product of the refractive index difference and the thickness was 474 nm. R ₀ obtained in the same manner as in Example 1.
A retardation plate obtained by laminating the above block copolymer film on a polystyrene film having a thickness of 515 nm, θ _1.10 = 35 ° and a thickness of 28 μm exhibited good viewing angle characteristics of θ _1.10 = 59 ° at R ₀ = 515 nm.

Example 4 The styrene-isoprene block copolymer used in Example 3 was press-formed at 180 ° C. to obtain a 200 μm thick film. This film had a difference between the in-plane refractive index and the refractive index in the thickness direction of 2.37 × 10 ⁻³ , and was a retardation plate having no in-plane birefringence.

Comparative Example 1 A polystyrene film formed in the same manner as in Example 1 was used.
Stretched 2.8 times at 135 ° C by tenter stretching method
The birefringent film is R₀= Θ at 515 nm _1.10= 3
5 degrees.

────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Tadashi Shindo 2-1-1 Tsukahara, Takatsuki-shi, Osaka Sumitomo Chemical Co., Ltd. 72) Inventor Ichiro Noda 4-505 Kurosawadai, Midori-ku, Nagoya-shi, Aichi (56) References JP-A-56-125703 (JP, A) JP-A-2-282725 (JP, A) JP-A-3 -23404 (JP, A) JP-A-3-194503 (JP, A) JP-A-61-146301 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 5/30 G02F 1/1335 510

Claims (4)

(57) [Claims] 1. A retardation plate using a block copolymer having a lamellar structure. 2. The retardation plate according to claim 1, wherein a block copolymer having a lamellar structure is laminated on a retardation film made of a thermoplastic resin. 3. The retardation plate according to claim 2, wherein both the retardation film comprising a block copolymer having a lamellar structure and a thermoplastic resin have a negative refractive index anisotropy. 4. A liquid crystal display device comprising the retardation plate according to claim 1, 2 or 3.