Compositions – Liquid crystal compositions
Reexamination Certificate
2001-01-12
2004-06-15
Huff, Mark F. (Department: 1756)
Compositions
Liquid crystal compositions
C428S001100, C524S731000
Reexamination Certificate
active
06749771
ABSTRACT:
The present invention relates to the use of a component of a polymerisable liquid crystalline mixture in the production of orientated liquid crystalline polymers; compounds used as components in polymerisable liquid crystalline mixtures; liquid crystalline mixtures comprising these components, liquid crystalline polymers prepared from such components and liquid crystalline devices comprising those compounds.
Liquid crystal polymers (LCPs) are used in the manufacture of optical components such as waveguides, optical gratings, filters, retarders, piezoelectric cells and non-linear optical cells and films. The choice of LCP for use in any one of the aforementioned optical components depends upon its associated optical properties such as the optical anisotropy, refractive index, transparency and dispersion. Optical filters, for example, contain LCPs having a large anisotropy (&Dgr;n) and a low dispersion (n=f(&lgr;)).
In some applications there is a requirement to produce LCPs in which the component molecules adopt a specific tilt angle with respect to the plane of the substrate. These LCP materials can be used as optical components such as compensation layers and retarders. Such optical components may be used in the production of liquid crystal devices (LCDs) with improved viewing angles, for example.
LCPs are manufactured by orientating a layer of a polymerisable liquid crystal single compound or mixture on an orientated substrate and cross-linking the mesogenic layer to form a liquid crystal polymer (LCP) network. Polymerisable LC compounds used in the manufacture of the LCPs need to be chemically and thermally stable, stable to electromagnetic radiation, soluble in standard solvents, miscible with other LC components and exhibit liquid crystalline properties over the range 25 to 150° C., preferably 25 to 80° C. The configuration imposed by the orientation layer on the polymerisable LC single compound or mixture becomes fixed or frozen into the LCP network formed upon cross-linking. The resulting LCP films have a high viscosity and are stable to mechanical stresses, temperature and light exposure.
The tilt angle adopted by the polymerisable LC single compound or mixture prior to cross-linking depends in part upon the nature of the LC components comprising that single compound or mixture. Previous strategies employed in generating a tilt angle in a given LC single compound or mixture prior to cross-linking have, for example, relied upon the introduction of one or more lateral substituents into the meosogen, such as a short aliphatic alkyl chain. However, such substitution is accompanied by a decrease in the mechanical properties of the LC material or, depending upon the molecular architecture of the mesogen, is associated with a small or vanishing tilt angle. In each case the reproducibility of the initial tilt is readily lost before the mixture is cross-linked to give the LCP network due to thermal and mechanical effects.
There is therefore a need for a liquid crystalline single compound or mixture that can be orientated on a substrate prior to cross-linking in such a way that the orientation of the LC single compound or mixture on the substrate remains stable over the period required for manufacturing the LCP network. There is also a need for a LC component with the ability to facilitate the generation of and maintain a wide range of predetermined tilt angles prior to and during the manufacture of the LCP film. The present invention addresses those needs.
A first aspect of the present invention provides the use of a component of a LC mixture in the manufacture of a LCP network comprising the mixture, characterised in that the component induces a stable tilt angle in the LCP network. By the word stable it is to be understood to mean that there is no substantial change in the value of the tilt angle over the period necessary for manufacturing the LCP network. The LCP network obtained by cross-linking the polymerisable LC mixture can be a nematic, smectic A or discotic film, but is preferably a nematic film. These films are characterised by good orientation of the film components relative to the substrate.
The component used to induce a stable tilt angle is preferably mesogenic in nature or is compatible with a mesogenic molecular architecture and may contain polymerisable or non-polymerisable substituents. It is preferably miscible with the other components of the liquid crystal mixture. Without wishing to limit the scope of the invention, it is believed that the component must contain a sterically bulky group that has the ability to form a strong association with the substrate or with the orientation layer. The component should also contain a sterically less bulky group that is compatible with a mesogenic molecular architecture and which extends into the bulk of the LC single compound or mixture as a whole. It is believed that this mesogenically compatible group is able to assume an angle in which it is tilted relative to the plane of the substrate. Unlike the LCP mixtures of the prior art, LCPs including these components are less susceptible to thermal effects and the polymerisable LC single compound or mixture comprising or including a component of the present invention is able to retain its initial orientation over the period necessary for manufacturing the LCP network. Judicious choice of the substrate associating and mesogenic extending groups allows this angle to be varied. It will be appreciated that the components of the invention can therefore be used in the manufacture of polymerisable LC single compounds or mixtures having a stable orientation or tilt angle relative to the plane of the substrate.
By sterically bulky it is to be understood that the lateral dimensions of the substrate associating group are at least half as large again as the lateral dimensions of the less bulky group, preferably two or more times the dimensions of the less bulky group.
The substrate associating or more bulky groups preferably comprise organosiloxane groups and the mesogenic extending or less bulky groups preferably contain aromatic or non-aromatic carbocyclic or heterocyclic ring systems. It is believed that the organosiloxane containing components used in the first aspect of the invention include compounds that are new per se and a second aspect of the invention provides an organosiloxane compound of formula I
wherein
B
1
to B
4
each individually represent a spacer group selected from the group comprising optionally substituted saturated or unsaturated, straight chain or branched chain C
1-80
alkyl group, one or more of the non-adjacent alkyl CH
2
groups being optionally replaced by one or more heteroatoms;
B
5
represents a hydrogen atom or spacer group as defined above,
A
1
and A
2
each individually represent a single bond or a spacer group as defined above,
MG
1
to MG
3
each individually represent a mesogenic group comprising at least one optionally substituted aromatic or non aromatic carbocyclic or heterocyclic ring systems; and
n1 and n2 are each independently 0 or a positive integer with the proviso that, firstly, when n2 is 0 both B
1
and B
2
include a polymerisable group and at least one of A
1
, B
1
and B
2
includes a group selected from an organosiloxane, an organogermanium, an organotin and an organo-perfluoro residue and secondly, when n2 >0 at least one of B
1
, B
2
, B
3
and B
4
includes a polymerisable group and at least one of A
1
, A
2
, B
1
, B
2
, B
3
and B
4
includes an organosiloxane group.
By the term ‘heteroatom’ it should be understood to include nitrogen, oxygen and sulphur. Replacement nitrogen atoms may be further substituted with groups such as alkyl, aryl and cycloalkyl. These compounds have been found to be particularly useful in the preparation of liquid crystalline polymer networks (LCPs) in which the molecules are tilted with respect to the orientation layer. These LCPs can be used in a range of different optical and electrical applications. LCP networks having nematic, smectic A and surprisingly discotic properties may be
Benecke Carsten
Cherkaoui Zoubair
Huff Mark F.
Rolic AG
Sadula Jennifer R
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