Screen E-Book (.PDF) - MacDermid Autotype

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Colour shifts54high-frequency (non-flooding) Rz of 4µmas this has consistently proved to be anexcellent balance of stencil properties forhigh-quality printing. We found no skipping,our mono dot gain was under goodcontrol and the job was easy to print. Thestencil also has a proven high fidelity fromfilm to print so we were reducing stencilinducedcolour shifts to a minimum.2. - Use a “thin”meshIn addition to choosing a thin stencil, youneed to use the thinnest practical meshwhich holds, and therefore prints, the leastamount of ink.3.- Choose an ink with a thin depositObviously solvent-based inks can give youa thinner ink deposit. With UV inks theonly relevant “solvent” is water and we allknow that water-based UV gives less doton-dotgain than standard UV. However,water-based UV has its own challenges.We deliberately chose a standard UV inkas this would maximise the print sequenceeffects in which we were interested.4.- Make sure you have the rightCMYK intensities from your inksWe have to admit to making an error herethat is all too common. We printed our solidinks onto our chosen substrate (a mattcoated paper) then “based” the inks till theyreached the required ISO density standardsfor 4-colour screen. What was our error?We forgot that the paper absorbed a smallamount of the ink so the intensity of thefirst ink down is higher than that of subsequentprints. With hindsight we shouldhave based the inks to a compromise valuebased on, e.g. densities obtained by printingonto a non-absorbent plastic substrate.However, we found that we are not alone.Many printers make this error and ascribethe reduced colour of subsequent inks tosome mythical “trapping” effect. Simpleexperiments on non-absorbent substratesshow that such “trapping” is a myth. We’velearned from our mistake, we hope you willlearn from it too.5.- Choose a mesh/lpi combinationwhich will give zero mesh moiréAs we are not expert printers and were usinga single-colour press we didn’t wantto be too ambitious so we chose to printat 80lpi. Using the <strong>MacDermid</strong> <strong>Autotype</strong>Mesh Moiré Calculator we were able to determinethat our C,Y and M screens at 37.5,82.5 and 7.5° would be free of mesh moiréon a 150/31 mesh but that there wouldbe a strong moiré with the K at 67.5°. Wetherefore printed the K on a 180/27 meshwhich the Calculator showed to be moiréfree. See Steve’s moiré section for an explanation.6.- Make sure you have good registrationand fitAs this was a complex job done over manyweeks it was not realistic for us to havesubstrates all stabilized perfectly to thesame extent. So registration and fit were
not perfect. However, careful inspectionshowed that this in no way affected theconclusions about the print sequence.7.- Always have a definition of“truth”We used a high quality colour proof as ourdefinition of truth. The definition of goodcolour, good shadows, grey balance etc.was taken to be the proof.The test imagesIt was important to have a good range oftest images as the different print sequenceswill show different effects on differentimages. We therefore chose (a) a child’sface with lots of difficult skin tone, (b) abeautiful lily for aesthetic reasons [but thischoice turned out to be important as wewill see later on], (c) a fiendishly difficultgrey image, (d) some pretty tulips includinga duotone for educational purposes.In addition we printed standard test stripsfrom Linotype-Hell including the all-importantgrey-balance test area.The test sequencesThere are 24 possible CMYK print sequences.Our mentors narrowed the choicedown to 6 plus the two Caza sequences.This gave us1 CYMK2 KCMY (Caza b)3 YMCK4 MCYK5 MYCK6 YCMK7 CMYK8 CMKY (Caza a)The resultsNeedless to say, we found large differencesbetween the various sequences, and someof the prints were appallingly bad. Dot-ondotgain is not a pretty thing to see! Youcan get some idea of the variations fromthis view of four of the eight sequences.The Caza sequencesWe are very grateful for Michel Caza’s activeintervention in our work. Caza has strongviews, based on his years of printing andteaching, that his “Yellow-last” sequencesare highly effective so we were keen to seehow they compared to more conventionalsequences.55
Page 1 and 2:
HowHow to be agreat ScreenprinterEd
Page 3: About this eBookI’m passionate ab
Page 6: 06Table ofContents07 The Theory Bit
Page 11 and 12: The wrong way: a strong-deep flood.
Page 13 and 14: why a light flood is recommended so
Page 15: This is the single most important f
Page 18 and 19: When I first pointed this out to my
Page 20 and 21: The Theory Bit20Why is the 1-2-3 so
Page 22 and 23: The mesh does the meteringThe 1-2-3
Page 24 and 25: This gives us the ‘real’ TIV fo
Page 26 and 27: simple, in-control process.Years of
Page 28 and 29: The Optional Theory28At the shear r
Page 30 and 31: I’ve come across examples in all
Page 32 and 33: The Optional TheoryOur 50µm line b
Page 34 and 35: oughness can slow slumping; it prob
Page 36 and 37: The Optional TheoryThe exact part o
Page 38 and 39: atches of the ‘same’ mesh. My f
Page 40 and 41: The Optional Theory40The industry r
Page 42 and 43: the screen frame itself to compensa
Page 44 and 45: Print Faults - Making and fixing th
Page 46 and 47: Print FaultsThey include tape marks
Page 48 and 49: Wrong ink - Too much viscous drag (
Page 50 and 51: DustPrint FaultsWe threw some dust
Page 52 and 53: What’s the best order to print yo
Page 56 and 57: We formed our own (subjective) opin
Page 58 and 59: And the winner is...Colour shifts58
Page 60 and 61: Getting the right exposureAnna Harr
Page 62 and 63: Getting the right exposureThe light
Page 64 and 65: 3/4 full exposureEFFECTS: Emulsion
Page 66 and 67: Getting the right exposureThere is
Page 68 and 69: Undercutting from a rough stencilSo
Page 70 and 71: Getting the right exposure(or numbe
Page 72 and 73: Solving problems in the real worldA
Page 74 and 75: Solving problemsThe simple act of r
Page 76 and 77: Emulsion coatingThe advice about cl
Page 78 and 79: Solving problemsA quick tip to help
Page 80 and 81: stencil causes a thick edge needed
Page 82 and 83: Solving problemsThis screen-shot fr
Page 84 and 85: A modest Rz gives amodest absolute
Page 86 and 87: Solving problemsThe root cause of n
Page 88 and 89: Now the ink fully fills the extra s
Page 90 and 91: Solving problems90Stencil X gives b
Page 92 and 93: Moiré, causes and curesSteven Abbo
Page 94 and 95: Moire, causes and cures94fluential
Page 96 and 97: Figure ii. The overlayedpattern fro
Page 98 and 99: Moire, causes and cures98Causes and
Page 100 and 101: 2 15° moiréIt’s an unfortunate
Page 102 and 103: Moire, causes and cureson top of an
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Ideal. Find a RIP with an option fo
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Moire, causes and curescan’t pick
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frequency tend to have a lower ampl
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Moire, causes and curesis a half-tr
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Incidentally, note that the ratio o
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Moire, causes and cures114So, surpr
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grid) in a conventional set that wa
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Moire, causes and cures118what this
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Arguably the skipping takes place p
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Moire, causes and curesSummaryAs Ma
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MoiréDescriptionAn unexpected patt
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Problem solving GuideCause1. The mo
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Dark spots / HickiesDescriptionDark
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Problem solving GuideTechnical refe
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6. Substrate unstable.7. Changes in
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Glossary of terms used in this eBoo
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Glossary136Moiré amplitudeThe ampl
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A Macdermid Autotype HowTo eBookEdi
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