1. Field of the Invention
The invention relates to a cholesteric liquid crystal composition which reflects light of a specific wavelength in the vicinity of room temperature and body temperature and uses thereof.
2. Description of the Related Art
A cholesteric liquid crystal molecule has a spiral structure in a liquid crystal state. Accordingly, when a cholesteric liquid crystal phase is irradiated with light, it reflects a circular polarizing light of a specific wavelength corresponding to a spiral rotational direction of the liquid crystal molecule and a length of the pitch. For example, when irradiated with a visible light, it reflects selectively lights having wavelengths of blue, green, yellow and red corresponding to a length of a pitch in the liquid crystal. The color tones thereof are different from those of pigments and dyes which take on colors by absorption of lights and have a visual dependency in which a color tone changes according to viewing angles. Further, a length of a pitch in cholesteric liquid crystal can be controlled by temperature and the kind of compounds, and therefore it can selectively reflect not only visible lights but also lights of near infrared and ultraviolet regions.
There have been materials which selectively reflect lights of various wavelengths in a broad wavelength region making use of the characteristics of the cholesteric liquid crystal. They are, for example, liquid crystal pigments, coating materials, spray inks, print inks, cosmetics, printed matters for preventing counterfeit, ornamental articles and the like. Further, they are proposed as well for polarizing plates in optical devices such as liquid crystal displays and holographic devices, compensation plates, optical films such as color filters and the like. In the case of a cholesteric liquid crystal pigment which is an existing material, flake-shaped cholesteric liquid crystal polymers and microencapsulated cholesteric liquid crystal are used. The uses thereof include coating materials for cars, cosmetic ingredients and the like.
JP S61-1015 B/1986 (Patent Document 1; JP S56-92836 A/1981) describes that an optically active menthol compound is used as an additive for shortening a pitch of a liquid crystal composition without extremely reducing a clearing point of the composition. Further, the uses of such cholesteric liquid crystal material include display parts of thermometers, wrist watches and calculators.
JP S63-34918 B/1988 (Patent Document 2; JP S57-40581 A/1982) describes that an L-menthol compound is used for a component of a guest-host liquid crystal display as a pitch controlling agent.
JP H16-137158 A/2004 (Patent Document 3) describes that an optically active menthol compound as a chiral dopant for a liquid crystal composition which is used as a liquid crystal display unit is a material maintaining a lower viscosity as compared with those of other chiral agents such as cholesterol derivatives and the like.
Examples of applications of liquid crystal materials in which a color of the material is changed irreversibly by temperature to inks are described in GB2280681A (Patent Document 4; U.S. Pat. No. 5,705,093), and a thermochromic liquid crystal material including an optically active menthol derivative and a nematic liquid crystal material is disclosed therein as the above liquid crystal material. Further, the possibility of application thereof to cosmetics such as lip rouges, eye shadows and the like making use of such thermochromic characteristics is indicated as well in Patent Document 4.
When a cholesteric material is used for application particularly in cosmetic ingredients coated on lips and skins in the cosmetic field, a material showing a cholesteric reflection color in the vicinity of room temperature and body temperature is required. Red to purple, preferably red to yellow colors are required to be developed in a temperature range in the vicinity of 0 to 60° C., particularly preferably 20 to 40° C. As described above, a range of developed color versus temperature is required to be controlled in order to allow a cholesteric liquid crystal material to exhibit an effect of aesthetic decoration in cosmetic use.
A mixing example of Mixture B of three components which has a clearing point of 91.1° C. and a menthol derivative is shown in Example 3 of Patent Document 4, and a composition example of nine components including two kinds of menthol derivatives is shown in Example 5. However, a range of developed color versus a cholesteric liquid crystal phase area and temperature is not described, and informations which can be applied to materials for cosmetic ingredients are not disclosed.