Alignment layer and a liquid crystal display using the same

Details Alignment layer and a liquid crystal display using the same Alignment layer and a liquid crystal display using the same

2000-01-18

2004-02-24

Pyon, Harold (Department: 1772)

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

Alignment layer of specified composition

C349S123000, C349S124000, C349S127000, C349S129000, C349S136000

Reexamination Certificate

active

06696114

ABSTRACT:

BACKGROUND OF THE INVENTION
1. (Field of the Invention)
The present invention relates to an alignment layer capable of conferring alignment functions on liquid crystals by a non-rubbing treating means using a simple optical alignment device and to a liquid crystal display using such alignment layer.
2. (Description of the Related Art)
A liquid crystal cell has a pair of glass substrates confronting to each other and an alignment layer disposed on an inner surface of each substrate to give alignment to liquid crystal molecules charged between the substrates. As conventional typical processes for manufacturing an alignment layer, the following 2 processes are known. In the first process as shown in
FIG. 14
, a photosensitive polymer 52 such as polyimide is applied onto a substrate
51
, and its surface is rubbed with a rubbing drum
53
having. a nylon or polyester fiber-planted cloth wound on it, whereby very fine grooves are formed on the surface of the polymer 52. The second process is a SiO slanting deposition process in which silicon oxide (SiO) is vapor deposited in a slanting direction onto a substrate.
In the first process, however, fine dusts are generated or an electric discharge occurs due to static electricity upon rubbing the surface of polymer 52 with the rubbing drum
53
, thus causing inconvenience in producing liquid crystal panels. In the second process, an angle of deposition to a substrate as well as the uniformity of layer thickness is difficult to maintain, and further a manufacturing device of large scale is required.
Under these circumstances, the present inventors proposed an alignment layer for liquid crystal displays (also referred to hereinafter as LCD) using a polymer whose photo-reaction is selectively induced by irradiation with linear polarized ultraviolet light (also referred to hereinafter as linear polarized light), as well as a process for producing the same (JP-A-10-87859). This polymer makes use of that shown in the following chemical formula C60:
wherein—R
1
=—CnH
2n+1
(n=0 to 5), k=1 to 12, m=1 to 12; R
2
=none, —COO, —OCO—, —N═N—, —CH═CH— or —C
6
H
4
—; and —R
3
to R
7
=—H, halogen group or alkyloxy group such as methoxy group. Further, the portion surrounded by the broken line is a cinnamate group or its derivative.
In the case of the alignment layer described above, however, it is necessary to convert natural light directly into linear polarized light with which the polymer is to be irradiated. As a dichroic polarizer used in such conversion into polarized light, a sheet prepared generally by primarily drawing PVA (polyvinyl alcohol), then impregnated it with I(iodine) and sandwiching it between TAC (triacetyl cellulose) is known. However, this dichroic polarizer is poor not only in transmittance in the UV range but also in thermostability, so it cannot be used as an optical alignment device. For this reason, a birefringence-type prism is used to polarize light in the UV range. However, since the birefringence-type prism makes use of a natural crystal of calcite as the prism, it is difficult to obtain a large prism through which the whole area of a substrate used in LCD is irradiated with light. Furthermore, when this prism is used, a optical alignment device is rendered complicated and large.
SUMMARY OF THE INVENTION
Accordingly, the object of the present invention is to provide an alignment layer capable of conferring alignment functions on liquid crystals by a non-rubbing treating means in a simple optical alignment device without generating fine dusts or causing an electric discharge by static electricity, as well as a liquid crystal display using the same.
To accomplish the object described above, the alignment layer according to the first aspect of the invention is obtained by applying onto a substrate a polymer having side chains with a mesogen structure and irradiating this applied polymer with ultraviolet light. This mesogen structure is a structure having a group capable of forming liquid crystals.
The alignment layer according to the second aspect of the invention is obtained by applying onto a substrate a polymer shown in formula C4 with side chains having at least one of the mesogen structures shown in formulae C1 to C3 and with the main chain being at least one of homopolymers or copolymers of hydrocarbon, acrylate, methacrylate and siloxane, and irradiating this applied polymer with non-polarized ultraviolet light.
In formula C1 to C4, x:y:z=100 to 0:100 to 0:99 to 0 whereupon x+y+z=100; n=1 to 12, m=1 to 12, j=1 to 12, k=1 to 12; X, Y, Z=none, —COO, —OCO—, —N═N—, —C═C— or —C
6
H
4
—; —R
1
to R
10
=—H, halogen group, or alkyloxy group such as methoxy group, and —R
11
=—H, —CN, or alkyloxy group such as methoxy group.
This branched-chain polymer has at least one substituent group such as biphenyl, terphenyl, phenyl benzoate and azobenzene as a mesogen component in the side chains thereof, and hydrocarbons, acrylates, methacrylates and cyclohexane in the main chain. As necessary, the polymer can have a structure having photosensitive groups such as cinnamate group or its derivatives added to the mesogen component in the side chains, or a structure to which side chains having and not having photosensitive groups are added together at a predetermined proportion.
The alignment layer described above is obtained easily by applying the polymer onto a substrate and irradiating it with natural light (also referred to hereinafter as non-polarized light). That is, by irradiating the polymer with natural light, the side chains in the polymer are crosslinked with one another (dimerization) to form an alignment layer indicating a pre-tilt angle when used for liquid crystals. Further, since the alignment layer in the first and second aspects of the present invention is obtained by the use of natural light, a polarizer such as birefringence-type prism is not necessary. Accordingly, the optical alignment device can be simplified to form the alignment layer easily. Then, this alignment layer can be used effectively in liquid crystal displays.
Furthermore, by controlling the direction and amount of irradiation of light, it is possible to arbitrarily set the direction of alignment of liquid crystal molecules and the degree of the pre-tilt angle in the alignment layer. Accordingly, the product can be used as an alignment layer in various liquid crystal displays in e.g. TN, VA and IPS modes.
Furthermore, by partial irradiation through a mask, an alignment layer with different pre-tilt angles and alignment directions can be formed on the same substrate. In particular, the expression of a state of alignment of liquid crystal molecules with low and high pre-tilt angles in 1 picture element or the picture-dividing alignment of inverting the alignment of liquid crystal molecules in 1 picture element is an effective means for enlarging a viewing angle in liquid crystal displays. According to the first and second aspects of the invention described above, the picture-dividing alignment is feasible, thus enlarging the viewing angle of a liquid crystal display. Furthermore, the present invention is advantageous for production of liquid crystal displays because fine dusts or an electric discharge due to static electricity upon physical rubbing of the surface of a polymer with a rubbing drum do not occur, and a large manufacturing device is not necessary.
The alignment layer according to the third aspect of the invention is obtained by applying onto a substrate a polymer having at least one of the photosensitive groups shown in formulae C11 to C14 and irradiating the photosensitive groups shown in formulae C11 to C14 and irradiating this applied polymer with non-polarized, linear polarized or partially polarized ultraviolet light. Here, the term “partially polarized” refers to a state of low degrees of polarization as a whole in which a completely linear polarized component and a non-polarized component are prese

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