GRA 324 Study Guide - Quiz Guide: Grammage, Pantone, Hydrometer
5 May 2013
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Lab tests: tempurature/relative humidity (rh) of paper. Paper is hydroscopic absorbs and releases moisture. Rh level 35-50% = good pressroom conditions. Ink dries it absorbs and oxidizes creating film. When moisture is in the air, there is no static charge. Sheets of paper don"t separate properly: folding endurance test. Determine grain direction 5 long, 5 short, then discuss the average and range: ink drying time. Dries in 2 stages: absorption setting (metal solvants) cobalt manganese metal. Varnish is absorbed into paper, while pigment sits on top. Varnish sits on top of paper , white pigment is on top of coat. Set-off discuss in report, usually a powder to drink ink, leaves scuff marks of ink btw/ sheets: oxidative polymerization exposed to oxygen. Coated polymerizes faster, more varnish exposed to oxygen solidifying of ink (the ink thickens and dries) hydroperoxide (oils + oxygen) hydroperoxide + driers = polymerization (chemical reaction to start drying itself)
