The present invention relates to dielectrically positive liquid-crystalline media comprising one or more compounds of the formula I, ##STR00001##
and one or more compounds selected from the group of the compounds of the formulae II and III and/or IV, ##STR00002##
in which the parameters have the respective meanings indicated in the specification, and optionally one or more further dielectrically positive compounds and optionally one or more further dielectrically neutral compounds, and to liquid-crystal displays, especially active-matrix displays and in particular TN, IPS and FFS displays, containing these media.

The present invention relates to liquid-crystalline media comprising one or more compounds of formula T ##STR00001##
and one or more compounds selected from the group of compounds of formulae I, II and III, ##STR00002##
in which the parameters have the meaning indicated in Claim 1, and to components comprising these media for high-frequency technology, in particular phase shifters and microwave array antennas.

The present invention is related to the filed of optically variable security elements comprising a region based on a single cured ink comprising a cholesteric liquid crystal polymer, said region having at least two, preferably at least three, patterns exhibiting, at at least one viewing angle, a different CIE (1976) color index parameter and/or a different position of the selective reflection band for protecting security documents against counterfeiting and/or illegal reproduction. In particular, the present invention relates to processes for manufacturing said features, when the processes comprises the steps of a) applying on a substrate by a rotogravure process with the use of a gravure cylinder having at least two, preferably at least three, different engravings a single cholesteric liquid crystal precursor composition, b) heating the applied composition to bring said composition to a cholesteric liquid crystal state, and c) curing the composition so as to form the region based on a single cured ink comprising a cholesteric liquid crystal polymer.

Provided are a liquid crystal composition satisfying at least one of characteristics such as high maximum temperature, low minimum temperature, small viscosity, suitable optical anisotropy, large dielectric anisotropy and a short helical pitch, or the liquid crystal composition having a suitable balance regarding at least two of the characteristics; and an AM device including the composition. The liquid crystal composition contains a specific optically active compound as an additive, and a specific compound having high maximum temperature or small viscosity as a first component, and may contain a specific compound having positive dielectric anisotropy as a second component, or a specific compound having negative dielectric anisotropy as a third component.

Provided are a liquid-crystal-medium having stability to heat, light and so forth, a wide liquid-crystal-phase temperature-range and significantly large dielectric-anisotropy and developing an optically isotropic liquid-crystal-phase; and various optical-devices used in a wide temperature-range, having short response-time, a large contrast-ratio and low drive-voltage and suppressing decrease in an effective dielectric-constant in a high-frequency range. A Liquid-crystal composition contains achiral-component T containing at least one compound selected from a first component represented by formula (1) and at least one compound selected from a second component represented by formula (2) or (3) and a chiral-agent to develop optically-isotropic liquid-crystal-phase: ##STR00001##
In formula (1), R.sup.1: alkyl, ring A.sup.1: 1,4-cyclohexylene, ring B.sup.1: 1,4-phenylene, L.sup.11 to L.sup.14: fluorine, Y.sup.1: fluorine, n.sup.1: 1 or 2, R.sup.2: alkyl, Z.sup.21 and Z.sup.22: single-bond or CF.sub.2O, L.sup.21 to L.sup.23: fluorine, Y.sup.2: fluorine, R.sup.3: alkyl, Z.sup.31 and Z.sup.32: single-bond or CF.sub.2O, L.sup.31 to L.sup.34: fluorine, Y.sup.3: fluorine, for example.

An object of the present invention is to provide a method for producing a reflective layer having an excellent diffuse reflectivity and a wide reflection wavelength range. Another object of the present invention is to provide a reflective layer having an excellent diffuse reflectivity and a wide reflection wavelength range.

The method for producing a reflective layer of the present invention includes: a step 1 of applying a composition selected from the group consisting of the following composition X and the following composition Y onto a substrate to form a composition layer; a step 2 of heating the composition layer to align a liquid crystal compound in the composition layer into a cholesteric liquid crystalline phase state; a step 3 of cooling or heating the composition layer in a cholesteric liquid crystalline phase state to reduce a helical pitch; and a step 4 of irradiating at least a partial region of the composition layer with light, between the step 1 and the step 2, between the step 2 and the step 3, or after the step 3, to photosensitize a chiral agent A or a chiral agent C in the composition layer. Composition X: a composition including a liquid crystal compound, a chiral agent A whose helical twisting power is changed upon light irradiation, and a chiral agent B whose helical twisting power is increased upon cooling or heating. Composition Y: a composition including a liquid crystal compound and a chiral agent C whose helical twisting power is changed upon light irradiation and whose helical twisting power is increased upon cooling or heating.

Disclosed is a substrate which has thereon a marking or layer comprising a salt-free cured chiral liquid crystal precursor composition which comprises one or more nematic compounds A and one or more chiral dopant compounds B which are capable of giving rise to a cholesteric state of the chiral liquid crystal precursor composition and are of formula (I) as set forth herein. A modifying resin made from one or more polymerizable monomers comprising an average of at least one ether functionality per polymerizable group is disposed between the substrate and the marking or layer and in contact with the marking or layer in one or more areas thereof. The modifying resin changes the position of a selective reflection band exhibited by the cured chiral liquid crystal precursor composition on the substrate in the one or more areas.

A first object of the present invention is to provide a liquid crystal composition capable of forming a reflective layer having excellent diffuse reflectivity. A second object of the present invention is to provide a method for producing a reflective layer having excellent diffuse reflectivity and a reflective layer having excellent diffuse reflectivity. A third object of the present invention is to provide a cured product and an optically anisotropic body, each of which is formed of the liquid crystal composition.

The present invention relates to a liquid crystal composition including a liquid crystal compound; a chiral agent A whose helical twisting power is reduced upon light irradiation; and a chiral agent B which induces a helix in a direction opposite to that of the chiral agent A, in which the liquid crystal compound is cholesterically aligned in the direction of the helix induced by the chiral agent B in a case where the liquid crystal compound is aligned into a cholesteric liquid crystalline phase state.

An optical film includes a cholesteric liquid crystal layer formed in a stripe-shaped pattern in which an optically anisotropic region having optical anisotropy and an optically isotropic region having optical isotropy are alternately disposed, a helical axis of a cholesteric liquid crystal in the optically anisotropic region is oriented in one axial direction tin a plane of the optical film, and the helical axis is oriented in a normal direction t of a boundary surface between the optically anisotropic region and the optically isotropic region.

A liquid-crystalline medium which comprises at least one compound selected from the group of compounds of the formulae IA to IH, ##STR00001##
in which Z.sup.1 denotes a single bond, CH.sub.2CH.sub.2, CH?CH, CH.sub.2O, OCH.sub.2, CF.sub.2O, OCF.sub.2, COO, OCO, C.sub.2F.sub.4, (CH.sub.2).sub.4, CHFCHF, CF.sub.2CH.sub.2, CH.sub.2CF.sub.2, C?C, CF?CF, CH?CHCHO or CH.sub.2CF.sub.2O,
and the use thereof for an active-matrix display, in particular based on the VA, PSA, PS-VA, PALC, FFS, PS-FFS, SA-VA, PS-IPS or IPS effect.