Photolithographic plate having a composite backing

Claim 1

A SENSITIZED, DIMENSIONALLY STABLE PLATE SUITABLE FOR PHOTOLITHOGRAPHIC PRINTING WHEREIN A MASKING MEDIA IS EMPLOYED TO DETERMINE THE EXPOSURE AREAS, COMPRISING IN COMBINATION (A) A COMPOSITE BACKING SHEET, SAID BACKING SHEET INCLUDING A THIN PLIABLE ANNEALED TEMPER METAL FOIL FIRMLY BONDED TO ONE FACE OF A YIELDABLE CONFORMABLE BASE LAYER AND A WATER RESISTANT SURFACING BONDED TO THE OPPOSITE FACE OF SAID BASE LAYER, SAID COMPOSITE BACKING BEING OF A THICKNESS RANGING FROM ABOUT 5 TO 12 MILS, AND SAID BASE LAYER HAVING A THICKNESS SUBSTANTIALLY GREATER THAN THE THICKNESS OF THE METAL FOIL, (B) THE EXPOSED SURFACE OF SAID METAL FOIL HAVING AN ISOLATING AND BONDING SURFACE TREATMENT, AND (C) OVER AND IN CONTACT WITH SAID SURFACE TREATMENT ON SAID METAL FOIL A THIN COATING OF A LIGHT-SENSITIVE MATERIAL, SAID COMPOSITE BACKING SHEET DURING EXPOSURE OF THE PLATE WITHIN A VACUUM FRAME, CONFORMING TO THE WINDOWS OF THE MASKING MEDIA TO FACILITATE INTIMATE CONTACT BETWEEN THE STENCIL OR IMAGECARRYING TRANSPARENCY AND THE METAL FOIL THROUGHOUT THE OPEN AREAS OF SAID WINDOWS TO THEREBY EFFECTIVELY REDUCE HALATION.