Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-06-30
2001-11-20
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S115000, C349S098000
Reexamination Certificate
active
06320632
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a color reflection type polarizer and a liquid crystal display provided with said polarizer.
BACKGROUND OF THE INVENTION
Recently, the liquid crystal display has spread in quick tempo and at the same time has come to be used also in the fields requiring an excellent design such as the fields of game machines, watches and portable telephones. In these fields there is a gradually increasing demand for the colorization of a polarizer, but a colored polarizer capable of satisfying a required design is not available yet at present.
The polarizer generally adopted widely in liquid crystal displays utilizes a linear dichroism obtained by impregnating a plastic material such as a polyvinyl alcohol with iodine or a colorant and by subsequent stretching or the like, thereby allowing the iodine molecules or the colorant molecules to be oriented in a certain direction (see “How to use Cptical Parts and Points to be Noted,” Optonics. Co., page 51, ISBN4-900474-03-7). In such a polarizer, a component of an incident light which component is parallel to the orienting direction of the molecules is absorbed. In colorization, therefore, a colorant molecule is needed which absorbs only the light of a desired zone selectively. Besides, a colorant molecule is required to exhibit a highly efficient linear dichroism and a high stability under high temperature and humidity. Thus, there arises the problem that the number of utilizable colorants is limited. In the manufacturing process, moreover, a process for the impregnation of colorant molecules is needed, thus giving rise to the problem that the impregnation process becomes complicated in order to produce different colors.
As one of methods for obtaining a colored polarizer in an optical manner without using such a colorant as mentioned above, there is known a method which utilizes the circular polarization selectivity of a cholesteric liquid crystal.
The cholesteric liquid crystal has a property of reflecting only the light of a specific wavelength selectively, and a colored polarizer which utilizes this property has also been proposed (see, for example, JP1-133003A).
However, the ordinary cholesteric liquid crystal involves the problem that it possesses the property of specular reflection and that therefore it is inferior in visibility. The method which utilizes a cholesteric liquid crystal is advantageous in that the color purity of reflected light is high, but involves a basic problem such that the mass production of a uniform cholesteric liquid crystal free of any defect or orientation disorder is difficult. Thus, it cannot be said that the method in question is a simple method.
OBJECTS OF THE INVENTION
It is an object of the present invention to solve the above-mentioned problems of the prior art.
Having made earnest studies about optical characteristics of optically anisotropic mediums, the present inventors succeeded in developing a novel and effective color reflection type polarizer.
It is widely known that in the interior of an optically anisotropic medium there occurs a phase difference between incident light and exit light because of different refractive indices depending on the direction of propagation (birefringence phenomena). If a linearly polarized light is introduced into such a medium, the light will usually emerge as an elliptically polarized light, but in the case where an intra-plane phase difference of an optically anisotropic medium is 90°, a linearly polarized light when introduced into the medium will be changed into a circularly polarized light, while a circularly polarized light when introduced into the medium will be changed into a linearly polarized light. If the phase difference of such a medium is 180°, the incidence of a circularly polarized light will result in output of a circularly polarized light whose rotational direction is inverted, although no influence is exerted on a linearly polarized light.
The phase difference which occurs in the optically anisotropic medium depends also on the wavelength of incident light. More specifically, even in the case where a phase difference of 90° occurs at a certain wavelength, the phase difference may not become 90° at another wavelength. The relation between wavelength and phase difference is determined by both retardation (birefringence×actual film thickness) of the optically anisotropic medium and birefringence wavelength dispersion.
By utilizing such optical properties of an optically anisotropic medium as mentioned above the present inventor has invented a color reflection type polarizing plate.
SUMMARY OF THE INVENTION
The present invention, in the first aspect thereof, relates to a color reflection type polarizer characterized in that at least one layer of an optically anisotropic medium having a retardation in a plane thereof is disposed between a reflector and a polarizer.
The present invention, in the second aspect thereof, relates to the above color reflection type polarizer, characterized by using an optically anisotropic medium having an intra-plane retardation in the range of 100 to 2,000 nm.
The present invention, in the third aspect thereof, relates to the above color reflection type polarizer, characterized by using an optically anisotropic medium having a birefringence value at 450 nm in the range of 0.8 to 1.3 times the birefringence value at 590 nm.
The present invention, in the fourth aspect thereof, relates to the above color reflection type polarizer, characterized in that a polarizer and an optically anisotropic medium are disposed so that a combination angle between an absorption axis of the polarizing plate and a slow axis of the optically anisotropic medium is within the range of 30° to 60°.
The present invention, in the fifth aspect thereof, relates to a liquid crystal display characterized by being provided with the color reflection type polarizer mentioned in the above first aspect.
REFERENCES:
patent: 3972587 (1976-08-01), Scheffer
patent: 4025164 (1977-05-01), Doriguzzi et al.
patent: 4032218 (1977-06-01), Scheffer et al.
patent: 4239349 (1980-12-01), Scheffer et al.
patent: 5548422 (1996-08-01), Conner et al.
patent: 5808713 (1998-09-01), Broer et al.
Nippon Mitsubishi Oil Corporation
Scully Scott Murphy & Presser
Ton Toan
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