GC 444 Notes_ Gravure Cylinders
GC 444 Notes_ Gravure Cylinders GC 4440
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This 10 page Class Notes was uploaded by Allie S on Sunday March 27, 2016. The Class Notes belongs to GC 4440 at Clemson University taught by Dr. O'Hara in Fall 2015. Since its upload, it has received 44 views. For similar materials see Current Trends and Deviations in Graphic Communications at Clemson University.
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Date Created: 03/27/16
Gravure Cylinders • Overview: – Base Cylinder – Copper Electroplating – Engraving – Chrome Plating • cylinders designCylindersree common traits . . . – A base to support the engraving medium – the medium for receiving the engraving, typically copper for electromechanical engraving and chemical etching, and zinc for laser engraving – chrome plating over the engraved copper to provide long life Base Cylinders • Integral – Mounted on permanent shaft • Mandrel – Removable shaft – Lighter, easier to store • Sleeve – No shafts, mount directly in press – Very light, easy to change, store 1 Base Composition • Steel Core – Integral cylinders, most mandrel • Aluminum – Sleeves • Alloys – Some mandrels and sleeves • Composite plastics Base Quality Checks • Balance – Static, distribution of weight across the cylinder – Dynamic, deals with centrifugal forces of high-speed rotation • Surface and internal integrity – Pits and cavities, examine with X-Ray Electroplating • Cylinder base is rotated in a bath of copper and sulfuric acid • Anode/Cathode system to electroplate copper to the cylinder base – Copper is the anode, cylinder acts as cathode • Build layer of copper approximately 400 microns thick. 2 Surface Finishing • to ensure uniform surfaceer • Grind and polish surface – Polish after lathe –electromechanical engraving – Polish after corrections • Surface must be uniform and smooth prior to chroming DisCop • Dissolved solution of copper ions • More controlled plating process • Less polishing required Chroming • Similar process to copper plating, but the anode is insoluble, a chrome solution is used • Chrome layer very thin, 6 microns, just enough to protect engraving from wear • Final polishing of chrome 3 Reclaiming Cylinders • Dechrome the cylinder • Cut away image layer with lathe – Can cut away a few layers without re- electroplating • Degreasing • Polish, re-image and chrome Ballard Shell • After initial copper layer is built up and polished, coat with special release layer • After production, can cut in and strip away the shell, reduces turn-around time • Used primarily in publication Proofing/Corrections • Prior to chroming, a proof is pulled from the engraved copper • Positive corrections – Staging and etching • Negative corrections – Lacquers and burnishing • Digital proofing increasingly standard 4 Engraving Technologies • Chemical Etching • Electromechanical Engraving • Laser Engraving Carbon Tissue—1st Exposure • Clear areas are exposed and become the land between cells. • Black areas remain unexposed. 2nd Exposure • 2nd exposure through film positive • Gelatin turns hard as it is exposed (black is exposed, white is not). • Gelatin is inverted and applied to cylinder; backing material removed and unexposed gelatin washed away. • Cylinder is immersed in acid. Where there is little resist, the acid etches deep cells; where the resist for highlights.etches shallow cells 5 Direct Transfer • THINK technologies—1960’s • Photo-sensitive material applied directly to cylinder • Film wrapped around the cylinder and exposed • Unexposed material washed away to bare copper underneath. • Cells of varying size, equal depth Electromechanical Engraving • Developed in 1980’s • Primary method of engraving cylinders • Diamond stylus cuts into cylinder • Depth and size variable, but fixed ratio • Direct to cylinder, digital input Electromechanical • As cylinder turns, diamond cutting tool enters the cylinder and removes copper to create cell 6 Electromechanical • Depth of cutting tool sets cell size as well Electromechanical • Speed of cylinder rotation along with speed of cutting sets angles. Question: • If we engrave cylinders at fixed angles, 30˚, 45˚, 60˚, how do we avoid moiré? 7 Electromechanical • Engraving head can produce 6,000– 7,000 cells/second • Array of up to 14 engraving heads to produce 84,000 cells/second Electromechanical Innovations • Xtreme Engraving—Hell Gravure Systems • tranScribe—Max Daetwyler Corp. • Use multiple passes with fine engraving heads to create type and linework without the “jagged” edges. Xtreme 8 Conventional Engraving Xtreme Engraving Laser Engraving • Developed in mid-90’s • Uses zinc engraving medium • Can engrave up to 70,000 cells/second • Two lasers on a single mounting for up to 140,000 cells/second CoVariable in deVariable in depth and size 9 Laser Engraving • Improved ink release – Less ink consumption • Greater resolutions • Faster turnaround • Greater repeatability • Greater continuous tone Indirect Laser • Coat cylinder in resist • Use laser to ablate cells – Can create cells of varying shape – Can image line work with very little “jagged” edge • Chemically etch, uniform depth Questions??? 10
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