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Graphic Communications
GRA 324

LAB TESTS 1. TEMPURATURE/RELATIVE HUMIDITY (RH) OF PAPER Degrees Celsius Relative Humidity %  increases  positive  decrease  negative Paper is hydroscopic  absorbs and releases moisture Wavy Edges Tight Edges Hydrometer  make/model # RH Level  35-50% = good pressroom conditions Ink dries – it absorbs and oxidizes creating film Build up of Static Electricity when moisture is in the air, there is no static charge  sheets of paper don’t separate properly 2. FOLDING ENDURANCE TEST Determine grain direction  5 long, 5 short, then discuss the average and range 4. INK DRYING TIME Use Sheetfed Offset Inks Pigment  colours Varnish cavius pigment, sets drying properties Vehicle: Resin Oils Dryers vegetable (metal solvants) mineral oils cobalt drying oils manganese metal soybean oil Dries in 2 Stages 1) ABSORPTION  “setting” Uncoated varnish is absorbed into paper, while pigment sits on top Coated 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 2) OXIDATIVE POLYMERIZATION  exposed to oxygen Uncoated  absorbs faster 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) Discuss for Report:  Use Black/Cyan/Magenta colours for lab test  Porosity of paper  Viscosity of ink  Humidity/temp of press room  pH level of paper or fountain solution 5. INK MIXING Write down pantone # Mixing Inks use scales, 50g/2 or 25%, Quickpeek Kit print on coated and uncoated 7. BASIS WEIGHT TEST Calculate: Lumiart Gloss Text 17.5x23 59M  Does this paper weight what the label says it weighs? 1. Nominal Basis Weight 2. Actual Basis Weight M Wt  Basis Wt = Area Basic Size x M Wt
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