JPH1172749A - Irradiation optical system of liquid crystal molecule alignment substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to irradiate a wide area with high irradiation intensity at a short optical path length and to impart alignment and pretilt angle to liquid crystal molecules at a low cost by arranging a plane mirror perpendicularly to the light obtd. by irradiating a liquid crystal molecule alignment substrate diagonally with light source light from a light paralleling means and reflecting this light from the liquid crystal molecule alignment substrate. SOLUTION: The light source 10 consists of a super-high pressure mercury lamp 11, an elliptic mirror 2, a rod 13 and a lens 14. The light paralleling means 20 which forms a secondary light source 15 and consists of a concave mirror aligning its focus to this secondary light source 15 forms parallel light beams. The liquid crystal molecule alignment substrate 40 coated with polyimide on glass is irradiated with these parallel light beams diagonally from a direction A. The beams are partly reflected by the substrate 40. The substrate 40 is again irradiated with the light reflected by the plane mirror 30 arranged perpendicularly to the reflected light from a direction B. The S wave of the irradiation light contributes to the alignment of the liquid crystal molecules. The P wave thereof contributes to the formation of the pretilt angle. Namely, the light cast from the direction A is nearly equal in the intensity of the S wave and the P wave and the light cast from the direction B is polarized to the direction S.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for aligning liquid crystal molecules, and more particularly to a light irradiation apparatus used for alignment using light (including ultraviolet light; the same applies hereinafter).

[0002]

2. Description of the Related Art As a method for aligning liquid crystal molecules in parallel with a substrate surface, a so-called rubbing method in which a substrate is mechanically rubbed with a cloth in one direction is frequently used. However, since the orientation treatment by rubbing generally uses a cloth, there is a problem that the cloth is cut off as dust and static electricity is generated. Therefore, a method of aligning liquid crystal molecules using light, a so-called photo-alignment method, has attracted attention in recent years. By the way, when a liquid crystal is used as a display element, disclination due to reverse tilt occurs unless a pretilt angle is given to each liquid crystal molecule, and the contrast of the liquid crystal display element decreases due to light leakage and scattering. Therefore, in the conventional photo-alignment method, an alignment film is formed by irradiating polarized light obliquely to a glass substrate coated with polyimide. The irradiation optical system used for this has a configuration as shown in FIG. That is, the light collimating means 20 includes the light source 10, the light collimating means 20, and the polarizing element 50.
The liquid crystal molecule alignment substrate 40 is irradiated with polarized light obliquely.

[0003]

However, the conventional irradiation optical system has the following disadvantages. The first disadvantage is that the light irradiation intensity is weak. Since the transmittance of the polarizing element is less than half, the conventional irradiation optical system has a low irradiation intensity. The second disadvantage is that the irradiation area cannot be increased. This is because large-area polarizing elements are extremely difficult to produce. A third disadvantage is that the optical path length is long. In many cases, the incident angle of light is specified for the polarizing element, and in many cases, the optical path length of the irradiation optical system is considerably long in order to install a polarizing element having a required area. A fourth disadvantage is high cost. It is necessary to irradiate polyimide with ultraviolet light. However, since a polarizing element that can be used in the ultraviolet region is extremely expensive, the cost of the conventional irradiation optical system cannot be reduced. Accordingly, it is an object of the present invention to provide an irradiation optical system which has a high irradiation intensity, can irradiate a wide area with a short optical path length, and can give an alignment and a pretilt angle to liquid crystal molecules at low cost.

[0004]

The light source 10, the light collimating means 20, and the plane mirror 30 irradiate the light from the light collimating means 20 to the liquid crystal molecule alignment substrate 40 obliquely. The plane mirror 30 is arranged perpendicularly to the light reflected from.

[0005]

FIG. 1 shows an embodiment of the present invention. 10 is a light source, 20 is a light collimating means, and 30 is a plane mirror. Reference numeral 40 denotes a liquid crystal molecular alignment substrate (hereinafter, referred to as a substrate) in which polyimide is applied on glass. Light source 10
Comprises an ultra-high pressure mercury lamp 11, an elliptical mirror 12, a rod 13, and a lens 14, and forms a secondary light source 15. The light collimating means 20 is a concave mirror whose focal point matches the secondary light source 15, and creates parallel light. As the light collimating means 20, a condenser lens or a Fresnel lens other than a concave mirror can be applied.

The parallel light irradiates the substrate 40 obliquely from the direction A, and a part of the light is reflected by the substrate 40. Since the plane mirror 30 is arranged perpendicularly to the reflected light, the reflected light travels backward in the original optical path and irradiates the substrate 40 again from the B direction.
For this reason, the substrate 40 is irradiated with light from both the left and right sides (A direction and B direction in FIG. 1). When the substrate is irradiated with light obliquely, the S wave of the irradiated light contributes to the alignment of the liquid crystal molecules, and the P wave contributes to the formation of the pretilt angle.

Here, since the orientation of the liquid crystal molecules is in the direction parallel to the substrate, light irradiation from either the A direction or the B direction in FIG. 1 contributes to the alignment in the same direction. Therefore, the S wave is A
Irradiation may be performed from any of the directions B and B. On the other hand, since the pretilt angle is formed in a direction non-parallel to the substrate, the direction of forming the pretilt angle is reversed depending on whether light is irradiated from the direction A or the direction B in FIG. Therefore, the P wave must be irradiated only from one of the A direction and the B direction.

By the way, when light is obliquely incident on an object, its Fresnel reflectance is generally as shown in FIG. That is, the reflectivity of the P wave is relatively low, such as the reflectance becomes 0 when the incident angle of light becomes the Brewster angle, whereas the reflectivity of the S wave increases monotonically as the incident angle increases. At all angles of incidence, the reflectance of the S-wave exceeds that of the P-wave. In other words, after obliquely incident light is reflected,
Light is strongly polarized in the S direction.

That is, in this optical system, the light reflected by the substrate 40 is strongly polarized in the S direction, and the light reflected by the plane mirror 30 and irradiated on the substrate 40 from the B direction is also polarized in the S direction. Will be. As a result, the light irradiated from the direction A in the irradiation optical system has almost the same intensity of the S wave and the P wave, whereas the light irradiated from the direction B is strongly polarized in the S direction. For this reason, the P wave is irradiated almost only from the direction A, and the formation of the pretilt angle is not hindered. In addition, the S wave is irradiated not only from the A direction but also from the B direction, and contributes to the alignment of the liquid crystal molecules.

[0010]

According to the present invention, it is possible to provide an irradiation optical system which has a high irradiation intensity, can irradiate a wide area with a short optical path length, and can give an alignment and a pretilt angle to liquid crystal molecules at low cost.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an irradiation optical system according to the present invention.

FIG. 2 is a graph showing the reflectance of an S wave and a P wave with respect to an incident angle.

FIG. 3 is an overall configuration diagram of a conventional irradiation optical system.

[Explanation of symbols]

 Reference Signs List 10 light source 20 light collimating means 30 plane mirror 40 liquid crystal molecule alignment substrate 50 polarizing element

Claims (1)

[Claims] A light source, a light collimating means, and a plane mirror, which irradiate light obliquely from the light collimating means to a liquid crystal molecule alignment substrate and reflect light reflected from the liquid crystal molecule alignment substrate. An optical system for irradiating a liquid crystal molecule alignment substrate, wherein a plane mirror 30 is arranged perpendicularly to the substrate.