The present invention relates to a retardation film obtained by subjecting a film formed from a cellulose derivative to an orientation treatment, wherein a hydroxyl group of cellulose is substituted by at least one kind of aliphatic acyl group having 5 to 20 carbon atoms, and a degree of substitution by said hydroxyl group is 1 to 3. According to the present invention, a retardation film having various wavelength dispersion characteristics, positiveness or negativeness in birefringence and viewing angle characteristics, in particular, an achromatic retardation film and a retardation film having a high birefringent property and the like can be obtained by preparing a retardation film using a properly selected said cellulose derivative as a raw material of the film.

The invention provides an optical film prepared by laminating at least one of a first retardation film (2), having a mean in-plane refractive index of n.sub.0 and refractive index in the thickness direction of n.sub.e wherein n.sub.e-n.sub.o>0, and at least one of a second retardation film (3) having an in-plane refractive index of n.sub.x in the direction showing the maximum refractive index, refractive index of n.sub.y in the direction perpendicular to the direction described just before, and refractive index in the thickness direction of n.sub.z wherein n.sub.x>n.sub.y.gtoreq.n.sub.z. The light leakage occurred as the observation point is tilted from the front direction to a direction different from the direction of each absorption axis can be reduced when a polarizing film is arranged so that the absorption axes will be perpendicular to each other.

A compensator element for a liquid crystal display is provided comprising at least one layer of negative biaxial burefringement material formed by at least one polycyclic organic compound.

The invention reports on the use of multi-reactive polymerizable surfactants in mixtures of polymerizable mesogenic materials. The polymerizable surfactants are readily polymerized into the liquid crystal film and build a protective topcoat layer. The invention also relates to a method of producing polymeric optical films with improved stability by using the surfactants. Uses of these films are given for various applications including security applications and displays.

Presently described are (e.g. brightness enhancing film) optical articles comprising the reaction product of a polymerizable resin and surface modified inorganic nanoparticles, methods of surface modifying inorganic nanoparticles, and surface modified inorganic nanoparticles. The surface treatment comprises at least one monocarboxylic acid having a refractive index of at least 1.50 and/or at least one monocarboxylic acid having a Mn of at least 200 g/mole and an ethylenically unsaturated group and/or at least one dicarboxylic acid.