Process for vertical alignment of rod-like liquid crystal...

Details Process for vertical alignment of rod-like liquid crystal... Process for vertical alignment of rod-like liquid crystal...

2002-03-29

2004-04-27

Dawson, Robert (Department: 1712)

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

Alignment layer of specified composition

C428S001200, C252S299400, C252S299600, C252S299610, C252S299620, C252S299630

Reexamination Certificate

active

06726966

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a process for alignment of rod-like liquid crystal molecules at an average inclined angle of 50° to 90°. The invention also relates to an optically anisotropic element in which rod-like liquid crystal molecules are aligned at an average inclined angle of 50° to 90°.
BACKGROUND OF THE INVENTION
A liquid crystal display of transmission type comprises a liquid crystal cell provided between two polarizing plates. A liquid crystal display of reflection type comprises a reflection plate, a liquid crystal cell and a polarizing plate in this order.
The liquid crystal cell comprises rod-like liquid crystal molecules provided between a pair of substrates. The liquid crystal cell further comprises an electrode layer, which has a function of applying a voltage to the rod-like liquid crystal molecules. Each of the substrates has an orientation layer by which the rod-like liquid crystal molecules are aligned. The rod-like liquid crystal molecules are placed between two orientation layers. It is relatively easy to control alignment of the liquid crystal molecules by using the two orientation layers.
The liquid crystal display preferably further comprises an optical compensatory sheet (phase retarder) between the liquid crystal cell and the polarizing plate. The optical compensatory sheet has a function of preventing the displayed image from undesirable coloring. The optical compensatory sheet has another function of enlarging a viewing angle of the liquid crystal cell.
A stretched birefringent polymer film has been conventionally used as the optical compensatory sheet. An optically anisotropic element using liquid crystal molecules has recently been used as the optical compensatory sheet in place of the stretched birefringent polymer film. The optically anisotropic element comprises a transparent support and an optically anisotropic layer, which is formed from liquid crystal molecules.
The liquid crystal molecules are aligned in the optically anisotropic element, and alignment is fixed to form the optically anisotropic layer. An orientation layer is provided between the transparent support and the optically anisotropic layer to align the liquid crystal molecules.
SUMMERY OF THE INVENTION
It is difficult for only one orientation layer to align rod-like liquid crystal molecules evenly and essentially vertically from the interface with the orientation layer to the interface with air.
An object of the present invention is to align rodlike liquid crystal molecules evenly and essentially vertically from the interface with the orientation layer to the interface with air
Another object of the invention is to provide an optically anisotropic element in which rod-like liquid crystal molecules are evenly and essentially vertically aligned.
The present invention provides a process for alignment of rod-like liquid crystal molecules, which comprises the steps of: forming an orientation layer for vertical alignment on a support; and forming a liquid crystal layer containing rod-like liquid crystal molecules and a compound represented by the formula (I) on the orientation layer to align the rod-like liquid crystal molecules at an average inclined angle of 50 to 90°:
(Hb—L
1
—Cy
1
—L
2
—)
n
Cy
2
  (I)
in which Hb is an aliphatic group having 6 to 40 carbon atoms or an siloxanoxy group substituted with an aliphatic group having 6 to 40 carbon atoms; L
1
is a single bond or a divalent linking group selected from the group consisting of an alkylene group, a fluorine-substituted alkylene group, —O—, —S—, —CO—, —NR—, —SO
2
— and a combination thereof, wherein R is hydrogen or an alkyl group having 1 to 30 carbon atoms; Cy
1
is a divalent aromatic group or a divalent heterocyclic group; L
2
is a single bond or a divalent linking group selected from the group consisting of an alkylene group, an alkenylene group, an alkynylene group, —O—, —S—, —CO—, —NR—, —SO
2
— and a combination thereof, wherein R is hydrogen or an alkyl group having 1 to 30 carbon atoms; n is 2, 3 or 4; and Cy
2
is an n-valent aromatic group or an n-valent heterocyclic group.
The invention also provides an optically anisotropic element comprising a transparent support and a liquid crystal layer containing rod-like liquid crystal molecules, wherein the rod-like liquid crystal molecules are aligned at an average inclined angle of 50 to 90°, and the liquid crystal layer further contains a compound represented by the formula (I) in an amount of 0.01 to 20 wt. % based on the amount of the liquid crystal molecules.
In the present specification, the term “average inclined angle” of the rod-like liquid crystal molecules means an average angle between the long axes of the molecules and the surface of the support (or the surface of the orientation layer). Further, the essentially vertical alignment (homeotropic alignment) of the rod-like liquid crystal molecules means that the molecules are aligned at an average inclined angle of 50 to 90°.
The term “orientation layer for vertical alignment” means an orientation layer that has a function of essentially vertically aligning the rod-like liquid crystal molecules placed near the orientation layer.
In the case where rod-like liquid crystal molecules are placed between two orientation layers (for example, in a liquid crystal cell), the liquid crystal molecules do not have a free interface (interface with air). Therefore, it is easy to control the alignment of the liquid crystal molecules by the two orientation layers. In contrast, various alignment defects are often observed on the free interface where only one orientation layer is used. Since the liquid crystal molecules near the free interface are not forced to align, it is very difficult to evenly align the molecules without causing any alignment defects. Further, the alignment of the rod-like liquid crystal molecules near the free interface is often perturbed to form aligning defects, since the free interface is exposed to outer stimuli such as uneven solvent evaporation or air blow for drying.
The applicants have found that a compound represented by the formula (I) can control the alignment of rod-like liquid crystal molecules near the free interface even if there is only one orientation layer. The compound of the formula (I) comprises a hydrophobic group (Hb) connecting to plural cyclic structures (Cy
1
and Cy
2
) showing excluded volume effect.
The compound represented by the formula (I) is mixed with rod-like liquid crystal molecules to prepare a coating solution, which is then applied on the orientation layer (on the support). After that, the compound of the formula (I) can be thickly placed near the free interface. The compound of the formula (I) is not incompatible the rod-like liquid crystal molecules. Therefore, the compound and the rod-like liquid crystal molecules cause a phase separation. The separated compound is placed near the free interface. The hydrophobic group (Hb) in the compound causes the phase separation with the liquid crystal molecules. The phase separation is clearly observed where the hydrophobic group (Hb) is a fluorine-substituted aliphatic group.
Further, the compound must have a relatively rigid part whose polarization is similar to that of the rod-like liquid crystal molecules to promote vertical alignment of rod-like liquid crystal molecules. The plural cyclic structures (Cy
1
and Cy
2
) showing excluded volume effect play the role of that part.
Accordingly, the compound represented by the formula (I) is used as an alignment promoter in the present invention. Therefore, the rod-like liquid crystal molecules are evenly and essentially vertically aligned even near the free interface, where an orientation layer is not provided.
DETAILED DESCRIPTION OF THE INVENTION
[Alignment Promoter]
In the present invention, the compound represented by the formula (I) is used as an alignment promoter for liquid crystal.
(Hb—L
1
—Cy
1
—L
2
—)
n
Cy
2
  (I)
In the formula (I), Hb is an aliphatic group having 6 to 40 carbon atoms or a siloxanoxy group sub

Affiliated with

Also associated with

Rating

Process for vertical alignment of rod-like liquid crystal... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Process for vertical alignment of rod-like liquid crystal..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for vertical alignment of rod-like liquid crystal... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3203533