Optical recording film and process for production thereof

A process for producing the optical holographic film which comprises a silicon dioxide or metal oxide porous gel having a network structure and pores in which gases are present, said porous gel containing a network portion having a high porosity, a network portion having a low porosity and porosity differences in the network structure, said network portion having a high porosity having been formed by exposure to light having high intensity and has a low refractive index, and said network portion having a low porosity and having been formed by exposure to light having low intensity and has a high refractive index, said film being substantially free from organic compounds, said process comprising:

• (1) the step of applying a composition containing a photopolymerizable compound (A), a photoinitiator (B), a metal compound (C) which is crosslinkable by self-hydrolysis when in contact with water and the subsequent polycondensation, a solvent (D) for the metal compound, water (E) and a catalyst (F) for the hydrolysis of the metal compound, the content of the metal compound being 5 to 90 wt %, to a substrate and removing a volatile component contained in the coating by evaporation to form a film for optical recording in which the photopolymerizable compound is retained in the network structure of an oxide of the metal formed by the hydrolysis and polycondensation of the metal compound on the substrate;
• (2) the step of irradiating the film for optical recording with actinic radiation to form an area rich with an organic polymer formed by the polymerization of the photopolymerizable compound in a portion exposed to light having high intensity and an area rich with the oxide of the metal in a portion exposed to light having low intensity of the film;
• and
• (3) the step of removing an organic component contained in the area rich with the organic polymer and the area rich with the oxide of the metal in the exposed film to form a film-like network of a metal oxide having a large number of pores which are the marks of the removed organic component.

A process for producing an optical holographic film which comprises a silicon dioxide or metal oxide porous gel having a network structure and pores in which gases are present, the porous gel having a concavo-convex form on the surface thereof in which the concave portion has been formed by exposure to light having a high intensity and the convex portion has been formed by exposure to light having a low intensity, said film being substantially free from organic compounds, comprising:

• (1) the step of applying a composition containing a photopolymerizable compound (A), a photoinitiator (B), a metal compound (C) which is crosslinkable by self-hydrolysis when in contact with water and the subsequent polycondensation, a solvent (D) for the metal compound, water (E) and a catalyst (F) for the hydrolysis of the metal compound, the content of the metal compound being 5 to 90 wt. %, to a substrate and removing a volatile component contained in the coating by evaporation to form a film for optical recording in which the photopolymerizable compound is retained in the network structure of an oxide of the metal formed by the hydrolysis and polycondensation of the metal compound on the substrate;
• (2) the step of irradiating the film for optical recording with actinic radiation to form an area rich with an organic polymer formed by the polymerization of the photopolymerizable compound in a portion exposed to light having high intensity and an area rich with the oxide of the metal in a portion exposed to light having low intensity of the film;
• and
• (3) the step of removing an organic component contained in the area rich with the organic polymer and the area rich with the oxide of the metal in the exposed film to form a film-like network of a metal oxide having a large number of pores which are the marks of the removed organic component, wherein
• the organic component is removed at a temperature at which the metal oxide can deform to form a controlled concavo-convex surface on the optical recording film.