Compositions – Liquid crystal compositions
Reexamination Certificate
2002-08-09
2004-11-16
Wu, Shean C. (Department: 1756)
Compositions
Liquid crystal compositions
C522S006000
Reexamination Certificate
active
06818152
ABSTRACT:
The invention relates to a stratified phase-separated composite, a method of manufacturing such a composite and photo-chemically reactive compositions for use in such a method.
In Science vol.283 (1999) page 1903, Kumar et al (see also U.S. Pat. No. 5,949, 508) disclose a phase-separated composite and a method of manufacturing such. The known composite is manufactured by providing, between a pair of opposed substrates, a layer of a photo-polymerizable monomer (prepolymer) dissolved in an organic liquid, in particular a liquid crystal. The organic liquid and monomer are selected such that the liquid is poorly miscible with the photo-polymerized monomer. If so selected, phase-separation of the liquid and the photo-polymer takes place during photo-polymerization, a process known in the art as polymerization-induced phase separation (PIPS). In the composite of Kumar et al. the organic liquid is furthermore adapted to absorb the UV light used for photo-polymerizing the monomer. Therefore, according to Kumar et al, upon subjecting the layer to UV light, a light intensity gradient is set up in the layer in directions normal to the layer, the highest intensity occurring at the side layer facing the UV light source. Since the rate at which photo-polymerization takes place scales with the intensity of UV light, photo-polymerization and therefore phase-separation preferentially takes place at the side of the layer facing the light source. As a result the phase-separation takes place in a stratified manner, producing composite comprising a predominantly polymeric layer formed at the UV light source side and a predominantly liquid layer at the side facing away from the UV light source.
The range of liquid crystals which can be suitably used to form a stratified-phase-separated composite is limited to those which absorb the radiation used to bring about phase-separation. However, for many applications, the use of other liquid crystals would be desirable. In particular, liquid crystal used by Kumar, E7, a cyanobiphenyl LC is not suitable for use in AMLCD. A further disadvantage of the known composite may be that the phase-separation is not perfect. In particular, small amounts of LC material are still present in the polymeric layer. For many applications such inclusions of LC material may be undesirable. For example, the liquid crystal inclusions may give rise to spurious switching effects and if LC inclusions during the useful lifetime migrate to and merge with the liquid layer the properties, such as retardation or orientation, may be affected.
It is an object of the invention, inter alia, to provide a stratified phase-separated composite which does not have these drawbacks. In particular, it is an object to extend the range of stratified-phase-separated composites by extending the range of fluids suitable for use in a such a composite. A further object may be to provide a composite which may have an improved phase-separation.
In accordance with the invention, these objectives are achieved by a stratified phase-separated composite a stratified phase-separated composite comprising a photo-polymeric layer and a liquid layer, the composite being obtainable by photo-polymerizing a layer of a photo-polymerizable stratified-phase-separable composition, the composition comprising:
a photo-polymerizable monomer;
a photo-polymerization dye which, during photo-polymerization, selectively accumulates in the photo-polymeric layer being formed; and
a liquid.
The stratified-phase-separated composite in accordance with the invention is, like the known composite, obtainable by photo-polymerization induced phase-separation. It differs from the known composite in that the stratified-phase-separated composite in accordance with the invention comprises a photo-polymerization dye which is selectively accumulated in the polymeric layer, where in the context of the invention, the term “photo-polymerization dye” refers to a compound which is adapted to at least partially absorb the actinic radiation used for photo-polymerizing the monomeric material.
Since the required intensity gradient is provided by the photo-reactive photo-polymerization dye, the liquid (crystal) may but need not be light-absorbing. The range of liquids which can be suitably used in the composite in accordance with the invention is thus significantly increased. Also, having the photo-polymerization dye as a separate component gives more flexibility in selecting the desired light intensity gradient. After all, in case the absorption is predominantly determined by the liquid crystal, as is the case in the prior art composite, selecting the desired thickness of the liquid layer in the composite already fixes the light intensity gradient and thus the stratification process.
The addition of a dye which selectively accumulates in the polymeric layer may improve the phase-separation. In particular, the improved phase separation may take the form of a reduction of the amount of liquid enclosed in the polymeric layer and/or an improvement in the uniformity of the interface between the liquid and polymeric layer. Although not wishing to be bound by any theory it is noted that adding a photo-polymerization dye (as a component separate from the liquid) changes the absorption of the stratified-phase-separable layer and thus the intensity gradient set up in that layer both at the beginning and during photo-polymerization compared to the known composite in which the liquid serves as the absorbing material. In particular, adding such a dye renders the layer significantly more absorptive and/or the transition from high to low intensity significantly more steep. Moreover, since the dye selectively accumulates in the polymeric layer being formed an intensity gradient is obtained which is different from the gradient obtained using a dye which is either uniformly distributed in the phase-separable layer or a dye which selectively accumulates in the liquid layer such as the light absorbing liquid crystal used by Kumar.
Furthermore, if the composite is used in a device in which the liquid layer is an active layer, such as an LC device, it may be of disadvantage that the photo-polymerization dye is present in such an active layer. After all, generally, the dye serves a purpose during manufacture of the composite but after that, so during use or further manufacture, it has served this purpose and there is—for this purpose—no longer a need for it to be present. Instead during use or further manufacture the dye may in fact have an adverse effect. For example, if a UV photo-polymerization dye is used the liquid may photo-degrade more easily over time. The dye may also influence the electro-optical properties of the liquid such as in particular its dielectric constant and birefringence. By selectively accumulating the dye in the polymeric layer, these adverse effects are avoided. In addition, the amount of dye can be selected freely without having to consider its effect on the liquid layer.
In a broad sense, the invention relates to any stratified-phase-separated composite which comprises a photo-polymerization dye as a component separate from the liquid as long as the dye, at least partially, absorbs the radiation used to photo-polymerize the monomers. However, in general the dyes have a tendency to selectively accumulate in the liquid layer instead of in the polymeric layer.
Generally, dyes which selectively accumulate in the polymeric layer may be found by selecting a dye which dissolves better in the (partially polymerized) monomer than in the liquid. A difference in solubility can be obtained by combining a liquid with a monomer or (partially) polymerized forms thereof having a polarity substantially different from the liquid. For example if the liquid is an apolar liquid the polymer may be polar or rendered polar by functionalizing with polar substituents or even ionic groups. If the dye is selected to be polar or similarly rendered polar selective accumulation in the polymeric layer is obtained.
A further means to promote selective accumulation in the polymeric l
Broer Dirk Jan
Penterman Roel
Koninklijke Philips Electronics , N.V.
Sadula Jennifer R.
Wu Shean C.
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