Manufacture of printing plates

Claim 1

A METHOD OF PRODUCING A PRINTING PLATE OR LIKE MEMBER HAVING A PRECISION DIFFERENTIAL RELIEF PATTERN IN A BASE, CMPRISING: COATING A BASE WITH AN EXTREMELY THIN, IMPERMEABLE, CONTINUOUS FILM OF SUBSTANTIALLY PURE ELEMENTAL PHOTOCONDUCTOR MATERIAL; PRODUCING AN ELECTROSTATIC CHARGE IMAGE ON THE SURFACE OF SAIDFILM BY SELECTIVELY EXPOSING SAID FILM IN ACCORDANCE WITH A DESIRED IMAGE PATTERN; DEVELOPING SAID CHARGE IMAGE BY CONTACTING SAID FILM WITH A SUSPENSION OFFINE DEVELOPER PARTICLLES A ND A BINDER IN AN INSULATING FLUID TO DEPOSIT SAID DEVELOPER PARTICLES ELECTROSTATICALLY ON SAID IMAGE, SAID DEVELOPER PARTICLES BEING SUBSTNTIALLY INSOLUBLE IN A GIVEN SOLVENT FOR SAID ELEMENTL PHOTOCONDUCTOR, TO AFFORT A DENSE COATING FOR SAID CHARGE IMAGE THAT ADHERES TO BUT DOES NOT PENETRATE SAID FILM; PRE-ETCHING THE PHOTOCONDUCTOR FILM BY DISSOLVING AWAY THE PHOTOCONDUCTOR FILM IN SAID SOLVENT, AREAS NOT PROTECTED BY SAID DEVELOPER, LEAVING A PHOTOCONDUCTOR IMAGE ON SAID BASE, SAID DEVELOPER REMAINING ON THE SURFACE OF SAID PHOTOCONDUCTOR FILM AS DEPOSITED BY ELECTROSTATIC ATTRACTION AND WITHOUT ANY ADDITIONAL BONDING OF A NATURE TENDING TO INCREASE TTCHMENT OF THE DEVELOPER IMAGE TO THE PHOTOCONDUCTOR OR THE BASE, DURING PRE-ETCHING; AND ETCHING SAID BASE, USING AN ETCHANT TO WHICH SAAID PHOTOCONDUCTOR IS SUBSTANTIALLY RESISTANT, TO PRODUCE A DIFFERENTIAL RELIEF PATTERN IN SAID BASE THAT IS A PRECISE REPRODUCTION OF SAID IMAGE PATTERN.

Claim 2

A METHOD OF PRODUCING A PRINTING PLATE OR LIKE MEMBER HAVING A PRECISION DIFFERENTIAL PATTERN ON BASE, COMPRISING: COATING A BASE WITH A THIN, CONTINUOUS FILM OF AMORPHOUS PHOTOCONDUCTIVE SELENIUM; PRODUCING AN ELECTROSTATIC CHARGE IMAGE ON THE SURFACE OF SAID FILM BY SELECTIVELY EXPOSING SAID FILM IN ACCORDANCE WITH A DESIRED IMAGE PATTERN; DEVELOPING SAID CHARGE IMAGE WITH A DEVELOPER HAVING A SUBSTANTIALLY DIFFERENT ABSORPTION CHARACTERISTIC WITH RESPECT TO INFRA-RED RADIATION THAN SAIDSLENIUM FILM; IRRADIATING THE DEVELOPED IMAGE WITH INFRA-RED RADIATION TO HEAT THE DEVELOPED AND UNDEVELOPED PORTIONS OF THE SELENIUM FILM DIFFERENTIALLY IN ACCORDANCE WITH THEIR DIFFERING ABSORPTION CHARACTERISTIC, AND MAINTAINING SUCH IRRADIATION UNTIL THE MORE ABSORPTIVE OF THE DEVELOPED AND UNDEVELOPED PORTIONS IS HEATED TO THE CRYSTALLINE TEMPERATURE OF SELENIUM AND CONVERTED TO CRYSTALLINE FORM; DISCONTINUING SAID IRRADIATION BEFORE THE LESS ABSORPTIVE PORTION OF THE FILM IS CRYSTALLIZED; SAID DEVELOPER REMAINING ON THE SURFACE OF SAID SELENIUM FILM AS DEPOSITED, BY ELECTROSTATIC ATTRCTION AND WITHOUT ANY ADDITIONAL BONDING OF A NATURE TENDING TO INCREASE ATTACHMENT OF THE DEVELOPER IMAGE TO THE SELENIUM OR TO THE BASE THROUGHOUTTHE FOREGOING STEPS; AND THEREAFTER TREATING THE DEVELOPED FILM WITH AN AGENT THAT ATTACKS AND REMOVES ONE OF THE CRYSTALLINE ND AMORPHOUS FORMS OF SELENIUM BUT THAT DOES NOT ATTACK THE OTHER FORM OF SELENIUM, LEAVING A SELENIUM IMAGE ON SAID BASE THAT IS A PRECISE REPRODUCTION OF SAID IMAGE PATTERN.