Patent CA-1197406-A (CA)
Inventor: SULLIVAN DONALD F
IPC: G03F7/20
Filed: 1983-11-15
Granted: 1985-12-03
Abstract: Abstract Improved resolution in a low cost non-critical photopolymer printing process is achieved by an image quality photopolymer layer disposed with air free surfaces sandwiched between two carrier surfaces, one being transparent and carrying a transparency image adjacent to the photopolymer surface to be exposed by radiation to cure the layer changing its solubility characteristics thereby to produce the image pattern.          In a typical example, a paste-consistency negative photopolymer layer is coated onto printed wiring boards and the photographic film is positioned over the board in register and off-contact.  A resilient blade is pressed against the phototool at one end of the board and traverses across the surface, thus forcing the photographic film into intimate contact with the photopolymer and purging all air therebetween.  Mounted on the resilient blade aft of leading edge is a shuttered tubular lamp which hardens the potopolymer where the photographic film is clear, so that is a single pass the photographic film is sequentially mated and photo-polymer exposed, to produce high resolutions unmatched by prior art photopolymer film systems and at speeds of .15 m per second.  Film thickness from .006 mm to .05 mm can give resolutions for line widths and spacings as fine as .076 mm.          Higher resolution photo images are produced in the photopolymer arts by intimate contact of a photo image bearing surface of a phototransparency phototool and the surface of a photopolymer layer preferably liquid, to expose the photopolymer layer to curing radiation in that relationship.  When phototools are to be reused over and over in production they are subject to wear and corresponding loss of resolution.  Also the cured and hardened photopolymer tends to stick to the phototool surface.  This invention resolves these problems by forming an image through a thin polyolefin film that wets with the liquid photopolmyer and does not stick to photopolymer cured and hardened thereon.  Any scratching from wear, etc. causes little loss of resolution because of the through-the-film image, formed by exposing a dye and solvent solution to the porous film through an image forming stencil pattern.           Imaging phototools are prepared with reduced heat generation and improved scratch resistance and longer term non-contaminating structure for reuse in production over many cycles even though they are in contact with photopolymer surfaces.  Thus, longwear low heating aluminum film photo image patterns or dyed through polypropylene release film patterns are provided by this invention.  Heat problems are resolved by faster exposure time and dissipation of heat with liquid coolants.  In one embodiment the photopolymer is cured underwater to keep out air and increase curing speed while serving as a collant. A photopolymer film pack sandwich is provided with a photopolymer layer between two surfaces, one constituting a transparent sheet with a photo pattern thereon adjacent the photopolymer layer.  One preferred embodiment provides high resolution, inexpensive material and processing costs and flexibility of processing by means of two thin photopolymer layers laminated over a printed wiring board having an irregular surface pattern.