Liquid crystal shutter

#The present invention relates to a liquid crystal shutter or, in particular, to a liquid shutter in which the peripheral circuit or especially the drive circuit can be simplified and the cost and power consumption can be reduced by realizing a low-voltage drive, a high-speed shutter on-off response, a high contrast, etc. The liquid crystal shutter according to this invention has the various advantages as described above, and therefore can find application in various fields such as battery-driven portable equipment, liquid crystal photoprinters and liquid crystal optical elements.

#Conventionally, various liquid crystal shutters have been proposed. Their performance, however, is not yet satisfactory, and market demand is high for a liquid crystal shutter for a liquid crystal printer or a liquid crystal optical element high in response speed, bright, high in contrast, drivable by a simple method and capable of a gradated display.

#The liquid crystal shutters under development are roughly classified, according to the type of the liquid crystal material used, into (1) a liquid crystal shutter using an ordinary nematic liquid crystal, (2) a liquid crystal shutter using a two-frequency drive nematic liquid crystal having positive or negative dielectric constant depending on the frequency, and (3) a liquid crystal shutter using a ferroelectric liquid crystal having a spontaneous polarization.

#FIG. 1 is a plan view showing the positional relation between the alignment directions of the molecules, etc. of the liquid crystal shutter according to a first embodiment of the present invention.

#FIG. 2 is a sectional view showing a configuration of a liquid crystal shutter according to the first embodiment of the present invention.

#FIG. 3 is a plan view showing the positional relations between the alignment directions of molecules, etc. of the liquid crystal shutter according to a second embodiment of the present invention.

#The operation of a liquid crystal shutter according to the first aspect of the invention (the case in which one optical compensator is used and corresponding to claims 1 to 5 and the first and third embodiments) and the second aspect (the case in which two optical compensators are used and corresponding to claims 6 to 12 and the second and fourth embodiments) will be explained in detail below while at the same time explaining the problem points of the conventional structure, with reference to the drawings.

#In the description that follows, the generic concept is defined as the optical compensator (13, 15, 16 in the drawings) and the more limitative concept of the optical compensator is defined as the retardation film and the discotic film. The optical compensator has a lag axis (13a, 15a, 16a) in the same direction as the lag axis (13b, 15b, 16b) of the retardation film and in the direction orthogonal to the direction (13c, 15c, 16c) of orientation of the discotic film.

#FIG. 1 is a plan view showing an example of the relative positions of the polarizing plates, the optical compensator or the retardation film of a liquid crystal shutter according to this invention. Also, FIG. 2 is a diagram showing the structure of an example of a liquid crystal shutter according to this invention. As shown in FIG. 2, the liquid crystal shutter comprises a liquid crystal element 11, an optical compensator (or a retardation film) having a retardation value of 0.03 μm, an upper polarizing plate 9 and a lower polarizing plate 8. The absorption axes of the upper and lower polarizing plates 9, 8 are orthogonal to each other. As shown in FIG. 1, the absorption axis 8a of the lower polarizing plate is arranged at an angle of 45° counterclockwise to the direction 12 of the central liquid crystal molecule, and the delay axis 13a of the optical compensator (or the lag axis 13b of the retardation film) is arranged parallel to the direction 12 of the central liquid crystal molecule.