Compositions – Liquid crystal compositions – Containing nonchiral aligning agents
Reexamination Certificate
2000-03-31
2002-01-15
Wu, Shean C. (Department: 1756)
Compositions
Liquid crystal compositions
Containing nonchiral aligning agents
C428S001200
Reexamination Certificate
active
06338808
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a liquid crystal composition comprising liquid crystal molecules and an alignment promoter. The invention also relates to an optically anisotropic element.
BACKGROUND OF THE INVENTION
A liquid crystal display of transmission type comprises a liquid crystal cell and two polarizing elements placed on both sides of the cell. A display of reflection type comprises a reflection board, a liquid crystal cell and one polarizing element in this order.
The liquid crystal cell comprises a pair of substrates, rod-like liquid crystal molecules and an electrode layer. The rod-like liquid crystal molecules are provided between the substrates. The electrode layer has a function of applying a voltage to the rod-like liquid crystal molecules. Each of the substrates has an orientation layer, which has a function of aligning the rod-like liquid crystal molecules. Since the rod-like liquid crystal molecules are placed between the orientation layers, the alignment of the liquid crystal is easily controlled by the orientation layers.
An optical compensatory sheet (phase retarder) is often provided between the cell and the polarizing element to enlarge a viewing angle of the display. The optical compensatory sheet has another function of removing undesirable color from a displayed image. A stretched birefringent film has been usually used as the optical compensatory sheet. An optically anisotropic element has recently been proposed as an optical compensatory sheet in place of the stretched birefringent film. The optically anisotropic element comprises a transparent support and an optically anisotropic layer.
The optically anisotropic layer comprises aligned liquid crystal molecules that are aligned and polymerized while keeping alignment. The liquid crystal molecules are aligned by one orientation layer provided between the transparent support and the optically anisotropic layer.
SUMMARY OF THE INVENTION
It is difficult to align liquid crystal molecules uniformly (i.e., to orient the molecules in monodomain alignment) from an interface facing the orientation layer to the opposite interface facing air by using only one orientation layer. If the liquid crystal molecules are not uniformly aligned, disclination arises to scatter light.
An object of the present invention is to provide a liquid crystal composition in which liquid crystal molecules can easily be aligned uniformly.
Another object of the invention is to provide an optically anisotropic element in which liquid crystal molecules are uniformly aligned near an interface having no orientation layer.
A further object of the present invention is to provide a fluorine compound which can be used as an alignment promoter effectively controlling the alignment of liquid crystal molecules.
The present invention provides a liquid crystal composition comprising liquid crystal molecules and an alignment promoter represented by the formula (I) in an amount of 0.01 to 20 wt. % based on the amount of the liquid crystal molecules:
(Hb—)
m
L(—Bu)
n
(I)
in which Hb is a hydrophobic group selected from the group consisting of a fluorine-substituted alkyl group having 1 to 40 carbon atoms, a fluorine-substituted aryl group having 6 to 40 carbon atoms, an alkyl group having 6 to 60 carbon atoms and an alkyl-substituted oligosiloxanoxy group having 1 to 60 carbon atoms; Bu is a bulky group showing an excluded volume effect and comprising at least two rings; L is an (m+n)-valent linking group; and each of m and n is independently an integer of 1 to 12.
The invention also provides an optically anisotropic element which comprises a liquid crystal layer comprising liquid crystal molecules and an orientation layer provided on only one side of the liquid crystal layer, wherein the liquid crystal layer further contains an alignment promoter represented by the formula (I) in an amount of 0.005 to 0.5 g/m
2
.
The invention further provides a fluorine compound represented by the formula (Ia):
Hb—L—Bu (Ia)
in which Hb is a fluorine-substituted alkyl group having 1 to 40 carbon atoms or a fluorine-substituted aryl group having 6 to 40 carbon atoms; Bu is a bulky group showing an excluded volume effect and comprising a tricyclic condensed ring, a tetracyclic condensed ring or at least two rings combined by a single bond, a vinylene bond or an ethynylene bond; L is a divalent linking group selected from the group consisting of an alkylene group, —O—, —CO—, —NR—, —SO
2
— and a combination thereof; and R is hydrogen or an alkyl group.
In the present specification, the term “average inclined angle” means an average of angles between discotic planes of discotic liquid crystal molecules and a surface of the support (or a surface of the orientation layer), or an average of angles between major axes of rod-like liquid crystal molecules and a surface of the support (or a surface of the orientation layer).
The present specification refers to alignment of liquid crystal molecules at an average inclined angle in the range of 50° to 90° as essentially vertical alignment. The specification also refers to alignment of liquid crystal molecules at an average inclined angle in the range of 0° to 50° as horizontal alignment.
In other words, the term “essentially vertical alignment” means homogeneous alignment of discotic liquid crystal molecules or homeotropic alignment of rod-like liquid crystal molecules. In contrast, the term “essentially horizontal alignment” in the specification means homeotropic alignment of discotic liquid crystal molecules or homogeneous alignment of rod-like liquid crystal molecules.
If liquid crystal molecules are placed between a pair of orientation layers (for example, in a liquid crystal cell), the layer of the liquid crystal molecules has no free interface (an interface facing air). In that case, the alignment of the liquid crystal molecules can be controlled relatively with ease. On the other hand, however, if only one orientation layer is used, various alignment defects often appear near the free interface (having no orientation layer). Since force for controlling the alignment is not given near the free interface, it is very difficult to align the liquid crystal molecules uniformly without defects. Further, the alignment near the free interface is often perturbed by influence from outside. For example, solvent of the coating liquid unevenly evaporates from the free interface, or the free interface is blown by air for drying. Consequently, defects of the alignment are liable to appear on the free interface. Dual domain alignment is often observed on the free interface when discotic liquid crystal molecules are aligned vertically (homogeneously). The dual domain alignment comprises two aligning forms in which the discotic planes in one aligning form reversely face to those in the other aligning form though the optical axes are parallel.
The study of the present applicants revealed that the compound defined by the formula (I) has a function of controlling the alignment of liquid crystal molecules, particularly liquid crystal molecules near the free interface when only one orientation layer is used. As shown in the formula (I), the compound comprises a hydrophobic group (Hb) and a bulky group (Bu) showing an excluded volume effect.
The compound of the formula (I) is mixed with liquid crystal, applied on the orientation layer, and thickly distributed near the free interface. For thickly distributing near the free interface, the compound must be incompatible with the liquid crystal so that the phase of the compound may be separated from that of the liquid crystal. The hydrophobic group (Hb) has a function of separating the compound from the liquid crystal phase.
Further, for promoting the alignment of the liquid crystal molecules, the compound must comprise a relatively rigid part having molecular polarization property similar to that of the liquid crystal. The bulky group (Bu) functions as that part.
The applicant considers that the hydrophobic group (Hb) faces the air side while t
Ichihashi Mitsuyoshi
Kawata Ken
Matsuoka Koushin
Takeuchi Hiroshi
Yokoyama Shigeki
LandOfFree
Liquid crystal composition comprising 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 Liquid crystal composition comprising liquid crystal..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Liquid crystal composition comprising liquid crystal... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2850804