Liquid crystalline film with broadened reflection bandwidth and process for preparation thereof
First Claim
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1. A polymer film comprising a helical molecular structure which contains, in a direction transverse to the film, at least three sequences of helical molecular structure:
- a first sequence having a first helical pitch;
a second sequence having a second helical pitch; and
a third sequence having a third helical pitch, in the same order as listed, each of said first, second, and third sequences comprising at least three turns of helical molecular structure, the first helical pitch being shorter than the second helical pitch, and the third helical pitch being intermediate the first and second helical pitches, the change in helical pitch between the first helical pitch and the second helical pitch taking place in less then 10 turns of the helical structure, the helical pitches calculated based on reflection wavelength/average refractive index, the film comprising a single layer of a polymerized mixture of polymerizable liquid-crystalline material.
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Abstract
Reflective liquid crystalline polymer films having increased bandwidth have a single layer of liquid crystalline material with short, long, and medium pitch of the helical molecular structure of the liquid crystalline polymer. The films are easily produced by a readily reproducible and economic process of low complexity.
15 Citations
21 Claims
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1. A polymer film comprising a helical molecular structure which contains, in a direction transverse to the film, at least three sequences of helical molecular structure:
- a first sequence having a first helical pitch;
a second sequence having a second helical pitch; and
a third sequence having a third helical pitch, in the same order as listed, each of said first, second, and third sequences comprising at least three turns of helical molecular structure, the first helical pitch being shorter than the second helical pitch, and the third helical pitch being intermediate the first and second helical pitches, the change in helical pitch between the first helical pitch and the second helical pitch taking place in less then 10 turns of the helical structure, the helical pitches calculated based on reflection wavelength/average refractive index, the film comprising a single layer of a polymerized mixture of polymerizable liquid-crystalline material. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
- a first sequence having a first helical pitch;
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17. A process for producing a polymer film having an adjustable pitch gradient of a helical molecular structure, comprising the steps of:
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a) applying in a layer on a substrate, a mixture of polymerizable liquid-crystalline material which comprises a) i) at least one monomer or oligomer, each of which has at least one mesogenic group and at least one polymerizable functional group, and a) ii) at least one chiral compound, b) aligning the material such that the mesogenic groups become arranged in a helical structure whose axis is transverse to the layer, c) partially polymerizing the layer by the action of actinic radiation in an environment which has an inhibiting action on the polymerization, and d) after the material has become newly aligned in a semi-polymerized structure, final fixing by fully polymerizing the film or cooling the film into the glass state, wherein the final polymer film comprises a helical molecular structure which contains, in a direction transverse to the film, at least three sequences of helical molecular structure;
a first sequence having a first helical pitch;
a second sequence having a second helical pitch; and
a third sequence having a third helical pitch, in the same order as listed, each of said first, second, and third sequences comprising at least three turns of helical molecular structure, the first helical pitch being shorter than the second helical pitch, and the third helical pitch being intermediate the first and second helical pitches, the change in helical pitch between the first helical pitch and the second helical pitch taking place in less then 10 turns of the helical structure, the helical pitches calculated based on reflection wavelength/average refractive index. - View Dependent Claims (18, 19, 20, 21)
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Specification