JPH02285303A - Double refractive film and production thereof and phase difference plate and liquid crystal panel - Google Patents

Abstract

PURPOSE:To attain the enlargement of a black and white display and the angle of field thereof by compensation of a phase difference by forming the phase difference plate of the double refractive film which is larger in the refractive index in the thickness direction than the refractive index in the direction perpendicular to the optical axis of double refractions and applying this plate to a double refractive liquid crystal cell. CONSTITUTION:The film is so formed that the refractive index in the thickness direction is larger than the refractive index in the direction perpendicular to the optical axis of the double refractions of the film plane. The production of such double refractive film can be executed by a method for uniaxially stretching the film obtd. by impressing a DC electric film to the film at the time of casting a liquid consisting of, for example, a soln., melt or the like of plastics, to form the film or a method for depositing a crystal, such as cadmium sulfide or rutile, which is anisotropic in refractive index on a film base material by diagonal evaporation. The liquid crystal panel compensated by using the phase difference plate 5 consisting of such double refractive film is decreased in the change in the contrast by the visual angle and is, therefore, greatly improved in the black and white display characteristics of the liquid crystal display.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a birefringent film, a method for manufacturing the same, a retardation plate made of the film, and a birefringent liquid crystal panel using the same with excellent viewing angles.

BACKGROUND OF THE INVENTION Based on the high-speed responsiveness of STN liquid crystals, large-screen liquid crystal panels based on a simple matrix drive system have been realized and are used in displays for personal computers, word processors, and the like. In a birefringent liquid crystal cell, there is a problem in that the display is colored in blue, green, or yellow based on elliptically polarized light through a polarizing plate. Therefore, measures have been taken to return the elliptically polarized light to linearly polarized light to prevent coloring (and to compensate for the phase difference due to birefringence).

As the above means, D-8TN which overlaps liquid crystal cells
A method has been proposed. However, since multiple liquid crystal cells are used, it inevitably becomes bulky and heavy, and the viewing angle of the display is narrow, and the background color changes from blue to red with a slight change in viewing angle. There were problems such as difficulty in realizing a black and white display and poor visibility.

BACKGROUND TECHNOLOGY AND PROBLEMS To overcome the above-mentioned problems, a BFTN system has been proposed in which a retardation plate made of a birefringent film is interposed between a liquid crystal cell and a polarizing plate, thereby making it possible to form a single layer of a liquid crystal cell. There is.

However, although the problem of bulkiness and high weight has been solved by making the liquid crystal cell a single layer, the narrow viewing angle of the display has not been sufficiently solved, and the contrast changes significantly due to changes in the viewing angle in black and white displays. There was a problem with poor visibility.

Means for Solving the Problems The present invention overcomes the above problems by using a birefringent film whose refractive index characteristics in the thickness direction are controlled.

That is, the present invention provides a birefringent film characterized in that the refractive index in the thickness direction is thicker than that in the direction perpendicular to the optical axis of birefringence, and a plastic liquid film. A method for producing a birefringent film as described above, which comprises forming a film under the application of an electric field and stretching the obtained film, and a method comprising the birefringent film as described above. The present invention provides a liquid crystal panel comprising a retardation plate and the retardation plate disposed on at least one side of a birefringent liquid crystal cell.

forming a retardation plate with a birefringent film whose refractive index in the direction of the working thickness is larger than the refractive index in the direction perpendicular to the optical axis of birefringence;
By applying this to a birefringent liquid crystal cell, it is possible to achieve a black-and-white display by compensating the phase difference and an enlarged viewing angle.

Examples of Constituent Elements of the Invention The birefringent film of the present invention is formed so that the refractive index in the thickness direction is larger than the refractive index in the direction perpendicular to the optical axis of birefringence in the plane of the film. be.

Birefringent films can be produced by, for example, applying a direct current electric field when casting a liquid material such as a plastic solution or melt, and uniaxially stretching the resulting film, or This can be done by obliquely depositing a crystal with an anisotropic refractive index such as cadmium or rutile on the film substrate.

There are no particular limitations on the plastic used when forming a birefringent film by applying an electric field. From the viewpoint of electric field responsiveness, plastics having an aromatic ring such as a benzene ring and a polar group such as a hydroxyl group, a carboxyl group, or an amine group in a fallen chain are preferably used. Further, there are no particular limitations on the film base material used when forming a birefringent film by a vapor deposition method. Generally, isotropic materials are used. In any case, a plastic that forms a film with excellent transparency or a film base material with excellent transparency is preferably used.

The retardation plate of the present invention is made of a birefringent film whose refractive index in the thickness direction is larger than the refractive index in the direction perpendicular to the optical axis of birefringence.

The retardation plate may be formed as a laminate of birefringent films, if necessary. By laminating, it is possible to superimpose or adjust the wavelength characteristics of the birefringence index of each birefringent film, thereby controlling the characteristics, and it becomes possible to highly compensate for the retardation in a birefringent liquid crystal cell. FIG. 1 shows an example of a retardation plate formed by laminating birefringent films. 1.
3 is a birefringent film, and 2 is an adhesive layer. The wavelength characteristics of the birefringent index in the retardation plate can be changed by changing the combination of laminated birefringent films, the number of laminated layers, the crossing angle of the optical axes, and the like. Therefore, the number of laminated layers, etc. may be determined to be continuous depending on the wavelength characteristics of the required birefringence, the phase difference to be compensated, etc. f! It is more advantageous to have fewer layers.

Adhesives or pressure-sensitive adhesives are usually used for laminating birefringent films, and in this case, those with good transparency such as acrylic adhesives or pressure-sensitive adhesives are preferably used. In the lamination process, in order to prevent changes in the retardation characteristics of the birefringent film, it is preferable to use a film that does not require high temperatures for curing or drying, such as a solvent-free coating type. A method of transferring an adhesive layer provided on a separator is also preferable from the viewpoint of preventing deterioration of the birefringent film.

In the liquid crystal panel of the present invention, a retardation plate made of a birefringent film whose refractive index in the thickness direction is larger than that in the direction perpendicular to the optical axis of birefringence is installed on one side of a birefringent liquid crystal cell or It is placed on both sides.

Figure 2 shows an example of its configuration. This is a type in which a retardation plate is provided only on one side, and 4 and 7 are polarizing plates, 5 is a retardation plate, and 6 is a birefringent liquid crystal cell.

Note that the polarizing plate 4 is on the viewing side.

A retardation plate used to form a liquid crystal panel compensates for the retardation in a birefringent liquid crystal cell. This prevents coloration and achieves a black and white display.

In that case, a retardation plate that achieves a high degree of compensation, including the wavelength characteristics of the birefringence of the liquid crystal cell, is preferably used.

Example: Place plate electrodes on both sides of the molten layer of polycarbonate,
A 2KV DC electric field was applied to form a film, and the resulting film was uniaxially stretched in an atmosphere of 180°C to a thickness of about 80mm.
A birefringent film was obtained.

The phase difference of the birefringent light for light with a wavelength of 550r++n in the birefringent film, the refractive index in the optical axis direction (n
X), refractive index in the direction perpendicular to the optical axis in the plane (ny)
, and the refractive index (n2) in the thickness direction are shown in the table.

In addition, STN
A black-and-white display liquid crystal panel (Fig. 2) was fabricated on one side of the liquid crystal cell. The viewing angles at which the contrast ratio of the obtained liquid crystal panel in the driving state and non-driving state is 6:1 or more are shown in the table. Note that the front contrast ratio between the driven state and the non-driven state was lO:1.

Comparative Example 1 A birefringent film was obtained according to the example except that a direct current electric field was not applied.

Retardation according to the above-mentioned birefringent film example, n
X s n V and n2 are shown in the table.

In addition, the viewing angle at which the contrast ratio in the driving state and non-driving state of a liquid crystal panel produced by applying the birefringent film as a retardation plate according to the example is 6:1 or more is shown in the table. Note that the front contrast ratio between the driven state and the non-driven state was lO:1.

Comparative Example 2 A birefringent film was obtained in the same manner as in Example, except that no DC electric field was applied and two-wheel stretching was performed.

Retardation according to the above-mentioned birefringent film example, nX
)ny, and n2 are shown in the table.

In addition, the viewing angle at which the contrast ratio in the driving state and non-driving state is 6=1 or more in the liquid crystal panel produced by applying the birefringent film as a retardation plate according to the example is shown in the table. Note that the front contrast ratio between the driven state and the non-driven state was 10:1.

Effects of the Invention The liquid crystal panel compensated using the retardation plate made of the birefringent film of the present invention has a small change in contrast depending on the viewing angle (it has excellent visibility of black and white displays and a large viewing angle). .

Therefore, the black and white display characteristics of the liquid crystal display can be dramatically improved.

Further, the manufacturing method of the present invention is excellent in manufacturing efficiency of birefringent films having such characteristics.

[Brief explanation of drawings]

FIG. 1 is a sectional view illustrating a retardation plate formed by laminating birefringent films, and FIG. 2 is a sectional view illustrating a liquid crystal panel. 1.3:? 3 [Refractive film 2: Adhesive layer 4゜7: Polarizing plate 5: Retardation plate: Liquid crystal cell

Claims (1)

[Claims] 1. A birefringent film, characterized in that the refractive index in the thickness direction is larger than that in the direction perpendicular to the optical axis of birefringence. 2. The method for producing a birefringent film according to claim 1, characterized in that a plastic liquid material is formed into a film under the application of an electric field, and the obtained film is subjected to a stretching treatment. 3. A retardation plate comprising the birefringent film according to claim 1. 4. A liquid crystal panel comprising the retardation plate according to claim 3 disposed on at least one side of a birefringent liquid crystal cell.