Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Patent
1996-04-24
1997-12-09
Rosasco, S.
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
430321, G03F 900
Patent
active
056958951
DESCRIPTION:
BRIEF SUMMARY
THIS INVENTION relates to the manufacture of a diffusing screen, for example a rear-projection or depixelating screen, by exposure of a sheet or layer of a transparent photopolymerisable monomer to polymerising light through an opaque mask having light transmitting apertures, and thereby producing selective polymerisation of the photopolymerisable material in the regions thus exposed. More particularly, the invention is concerned with the manufacture of such a mask for use in the manufacture of such a diffusion screen. European Patent EP0294122B discloses a technique for manufacturing a rear-projection screen in the form of a transparent sheet of photopolymer bearing an array of microlenses which are in the form of graded refractive index lenses, the diffusing screen comprising an integral sheet of the transparent photopolymer with each of said lenses being formed by a respective region of said sheet extending between the surfaces of the sheet, with the refractive index, in said region, varying gradually with radial distance from the optical axis of each said lens.
In the technique described in European Patent EP0294122B the graded refractive index lenses are formed by selective exposure of a photopolymerisable monomer to a pattern of dots, such exposure being in ultra-violet light or suitable visible polymerising light and being effected by "contact" exposure through a mask having an array of circular holes formed therein.
It has been found that if, in a technique similar to that disclosed in EP0294122B, at least one surface of the monomer is left free to deform during polymerisation, e.g. by stripping from said surface any covering layer of other material, a surface relief pattern is produced which enhances the graded refractive index effect and may even predominate. For example, it has been found that in such circumstances a domed region tends to be produced where the monomer has been exposed to a circular patch of light and a concave hollow tends to be produced where the monomer has been masked from the photopolymerising light by a circular opaque area of the mask surrounded by a light transmitting region.
International Patent Publication WO92/16075, in the name of the present applicants, discloses the use of a microlens screen of the kind described in EP0294122B in conjunction with an LCD pixelated video display, for example of the kind used in hand-held or "pocket" television receivers, hand-held video games, etc. and in which the primary function of the microlens screen is to "de-pixelate" the LCD screen, that is to say, to render the individual pixels unnoticeable to the eye, particularly when the LCD screen is viewed under magnification. In particular, when used in conjunction with a pixelated colour video screen, having red, blue and green pixels, such a microlens screen prevents the individual pixels from being distinguished visually and ensures that the viewer has the impression, from the area of each set of three pixels, (red, blue and green), representing a particular "point" in the picture, of a corresponding area of a substantially uniform hue represented by a combination of the light intensities from the respective red, blue and green pixels.
Whilst the arrangement disclosed in WO92/16075 does, indeed, give significantly improved visual impression, compared with that obtained using a pixelated LCD screen alone, it has been found that, under certain conditions, where the microlens screen comprises an entirely regular array of microlenses, (for example where each microlens is of the same size and the microlenses are arranged in regularly spaced rows and columns), disturbing interference effects are perceptible, both "colour fringing" diffraction effects and Moire effects resulting from apparent interaction of the regularly spaced pixels in the LCD array and the regularly spaced microlenses in the microlens screen. Similar Moire effects can arise when such a screen is used in conjunction with, for example, a colour CRT display of the shadow-mask type having regularly spaced phosphor dots or b
REFERENCES:
patent: 3625686 (1971-12-01), Kitano
patent: 4360372 (1982-11-01), Maciejko
patent: 4674834 (1987-06-01), Margolin
Johnson William Nevil Heaton
Phillips Nicholas John
Nashua Corporation
Nashua Photo Limited
Rosasco S.
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