Compositions – Liquid crystal compositions
Reexamination Certificate
2002-05-14
2004-10-05
Wu, Shean C. (Department: 1756)
Compositions
Liquid crystal compositions
C252S299500, C252S299610, C252S299620, C252S299670, C252S299700, C528S403000, C528S406000, C528S190000, C528S192000, C528S193000, C528S194000, C430S020000, C430S270110, C430S627000, C349S002000, C349S106000, C428S001330
Reexamination Certificate
active
06800220
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optically active polyester having photosensitivity; a photoreactive chiral agent which causes a change in liquid crystal structure; a liquid crystal composition, an optical film, a liquid crystal color filter and a recording medium containing this agent; and a method of changing or fixing the helical structure of a liquid crystal.
2. Description of the Related Art
In recent years, attention has been paid to liquid crystal materials. For example, a cholesteric liquid crystal compound, which has a helical structure and exhibits various selective reflected colors by the pitch of the helix, and the like compounds are superior in selective reflectivity and color purity in the range of the visible region. Therefore, these compounds are widely used as an optical film, a liquid crystal color filter, a recording medium and so on.
As a specific example thereof, a color filter will be described hereinafter.
For example, a color filter used in a color liquid crystal display or the like is generally composed of pixels in red (R), green (G) and blue (B), and a black matrix for improving display contrast, which is formed between the pixels. Conventionally, the main current of such a color filter is a filter comprising a pigment dispersed in a resin or a dyed colorant. The method of producing the color filter is in general a method of applying a color-resin solution to a glass substrate by spin coating or the like to form a colored resist layer, and patterning the layer by photolithography to form color filter pixels, or a method of printing colored pixels directly onto a substrate.
However, for example, the production method based on printing has drawbacks that color filters obtained by this method has a low resolution of pixels and does not cope easily with the formation of an highly-minute image pattern. The production method based on spin-coating has drawbacks that a loss of raw material is large and unevenness of coating is large in the case that this method is applied to a substrate having a large area. According to a production method based electrodeposition, it is possible to obtain a color filter having a relatively high resolution and a little unevenness of a colored layer. However, this method has drawbacks that producing steps therein are complicated and control of the solution is also difficult.
For the above-mentioned reasons, it has been demanded to develop, as a method of producing a color filter, a method which causes little loss in raw materials and which makes it possible to produce a color filter with high efficiency and ease.
As the performance of a color filter, high transmittance and high color purity are demanded. In recent years, the demands have been satisfied by optimizing, in the method using a colorant, the kind of the colorant or a resin to be dyed, or by making, in the method using a pigment, the pigment into particles dispersed into very fine particles. However, in recent liquid crystal display (LCD) panels, the transmittance and color purity of their color filter have been requested to be very high. Particularly in a reflection type color filter for LCD, it is difficult to satisfy all of white display corresponding to white paper, contrast, and color reproducibility. All color filters produced by dying a colorant in a resin or dispersing a pigment therein in the conventional production methods are light-absorbing type color filters; therefore, an improvement in color purity based on a more improvement in the transmittance thereof substantially reaches the upper limit.
In light of situation as described above, a color filter using polarized light, which is made mainly of cholesteric liquid crystal, is known. In the color filter using polarized light, light rays of a given quantity are reflected and light rays of a quantity other than the given quantity are transmitted to display images. Therefore, the color filter has a high efficiency of using light and is superior in transmittance and color purity to the light-absorbing type color filter. The production method thereof is in general a method of forming a film on a substrate by spin coating or the like in order to make the thickness of the film uniform. However, this method has a problem that a loss in raw materials is large and is disadvantageous from the viewpoint of costs.
As a method for solving the above-mentioned problems and making it possible to ensure the uniformity of the color purity or the like of a color filter film and realize a reduction in the number of the producing steps thereof, a method of using a photoreactive chiral compound is useful. This method is a principle as follows: when a liquid crystal composition containing a photoreactive chiral compound is irradiated patternwise with light having a reaction wavelength of the chiral compound, reaction of the chiral compound advances correspondingly to the intensity of irradiation energy so that the helical pitch (twisting angle) of the liquid crystal compound changes; therefore, selective reflected colors are formed in respective pixels only by pattern-exposure having a distribution in light energy. Thus, this method has an advantage that patterning at the time of forming a color filter is finished by carrying out mask-exposure using a mask having a distribution in transmitted light quantity only one time.
Accordingly, a film functioning as a color filter can be formed by irradiating a cholesteric liquid crystal compound imagewise with light to pattern the compound and then fixing the compound. This can be applied to an optical film, image-recording, and so on.
Particularly in the case that a color filter is produced by subjecting a liquid crystal to mask-exposure one time, it is desired that three primary colors of blue (B), green (G) and red (R) can be produced with high color purity by the one-time exposure. However, when a rate of change in the twist of the liquid crystal is small, sufficient color purity cannot be obtained. Therefore, in order to display the three primary colors having high color purity by one-time exposure, it is necessary to use, as a photoreactive chiral compound, a chiral compound (chiral agent) having a high rate of change in twisting so as to change the twisting power of its helical structure largely. That is, by using a chiral compound having a high rate of change in twisting, the light quantity thereof is changed, whereby the range of selective reflected colors can be enlarged.
As such a chiral agent, the Applicant filed a Japanese Patent Application about a low molecular-weight photoreactive chiral agent having an isosorbide skeleton (Japanese Patent Application No. 2001-5740). Moreover, WO 00/34808 discloses a low molecular-weight photoreactive chiral agent having a benzylidene menthone skeleton.
In the case that a cholesteric liquid crystal compound is irradiated imagewise with light to pattern the compound and then the patterned compound is fixed, an image having a high resolution cannot be obtained if the pattern is not maintained during the time from the patterning to the fixation.
However, these chiral agents have a problem that images having good resolution cannot be obtained.
As described above, in the case of a cholesteric liquid crystal phase which has a photoreactivity capable of changing orientation structures of a liquid crystal (for example, the helical pitch (the twisting power, or the twisting angle of the helix) of a liquid crystal) by the quantity of irradiation with light and which contains, for example, a nematic liquid crystal compound, a photoreactive chiral agent capable of changing the helical pitch (twisting power) thereof largely has not yet been provided in the present situation. That is, there has not yet been provided a photoreactive chiral agent which has a wide range of light wavelengths which can be selectively reflected and gives a wide selective reflection range and which can display three primary colors (B, G and R) with high color purity and good resolution.
SUMMARY OF THE INVENTION
Object
Ichihashi Mitsuyoshi
Kawabata Kouya
Yumoto Masatoshi
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