Week 9 Notes
Week 9 Notes GC 4440
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This 4 page Class Notes was uploaded by Allie S on Monday March 28, 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 24 views. For similar materials see Current Trends and Deviations in Graphic Communications at Clemson University.
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Date Created: 03/28/16
Press Components • Engraved Cylinder The Gravure Press • Ink Fountain • Doctor Blade • Impression Roll eir Print Issues Unwind Station • Web Handling • Reel sizes from 24–120 inches wide, • Registration 12–84 inches diameter, 5–6,000 • Print Defects pounds. –Hazing – Mottle • Unwind station must be rigid to avoid – Whiskers – Snowflakes vibration – Volcanoes! Tension Control and Substrate Issues Registration • Cylinders are the main pull on the web • Foil—expands under heat • Unwind and rewind systems follow the • Film—stretches under tension, heat cylinders • Paper—shrinks in heat • Increase tension at each unit to maintain control • Cylinder Progression 1 The Flying Splice! Ink Fountain • Pan that moves vertically to accommodate various cylinder sizes • Inks are very low viscosity for flow in and out of cells • Temperature control is critical to ink performance • Viscosity control critical to color strength, printability, drying time, etc. Ink Components Ink Classification • Pigment • Publication • Vehicle – Group VI: SWOP, similar to heatset web offset, –Resin coated – Group I: newsprint and supercalendared – Solvent • Packaging and Product • Additives – C-Type: foil, paper, films, most used – E-Type: alcohols, low residual odor – D, M, T, V, W, and X-Type inks • Resin/Solvent capability with substrate Solvent vs. Water Doctor Blades Issues: • Blade profile • Saturation and luster • Composition • Drying time, energy consumption • Contact angle • pH control • Wear 2 Blade Profiles Blade wear • Square blades • Blade profile affects • Beveled blades contact area • Lamella tip – Lamella is uniform over life of blade New 1/2 Life Worn • Rounded blades – Requires less pressure – More sensitive to pressure, affecting contact angle New 2 Life Worn Contact Angle Deflection Correct Doctor Blade • Preferred 60˚ Pressure Pressure • Deflection Doctor Blade • Pressure Pressure Doctor Blade Angle Doctor Blade Angle Incorrect Pressure Deflection Blade Wear • Blade Holder • Where do the coatings and metal particles go? • Blade Extension • Filters and Magnets in Ink Sump • Back-Up Blade • Blade Oscillation • Lubrication • Beveled cylinder ends 3 Blade Composition Impression Roll • Carbon Steel • Rubber coated metal cylinder • Stainless Steel – 60–100 Shore A durometer – Water based inks – Film 60-80, Paper 80-90, Board 90+ • Subject to deflection • Ceramic Coated Blades – Back up roller for support – Cambered impression roller • Impression at 30–100 psi – Not “kiss” impression! Print Issues Electrostatic Assist • Mottle • Impression roll takes an electric charge, – viscosity, surface treatment building an electrostatic field at the nip. •ae – Doctor blade pressure, contact angle • Ink and engraved cylinder is given • Whiskers opposite charge – Solvent, viscosity • Ink is repelled from cylinder and • Volcanoes attracted toward substrate – Solvent, drying • Skips, snowflakes – Electrostatic Assist (ESA) Factors Affecting Print RR Donnelley Tour • Cylinder • Wednesday, January 30 •Ik • Meet behind Godfrey, depart 7:00 • Doctor Blade Wipe • Call your lab partner! • Impression Roll • Wear shoes, appropriate dress • Web Tension • Safety Glasses • Drying/Curing Conditions • Environmental Conditions 4
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