Print quality


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Print Quality

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Print quality

  1. 1. Print quality
  2. 2. Print quality Light <ul><li>Illumination conditions </li></ul><ul><li>inside / outside </li></ul><ul><li>sunny / cloudy </li></ul><ul><li>light bulb / fluorescent light </li></ul><ul><li>Print quality </li></ul><ul><li>reproduction of colour </li></ul><ul><li>reproduction of details </li></ul><ul><li>visual impression of gloss </li></ul><ul><li>print defects </li></ul><ul><li>Reader </li></ul><ul><li>vision sets limits </li></ul><ul><li>likings differ </li></ul><ul><li>culture affects </li></ul>
  3. 3. Reproduction of colour and details <ul><li>Reproduction of colour </li></ul><ul><ul><li>“ how large colour space can be reproduced” </li></ul></ul><ul><ul><li>“ how well does the print match the original colours” </li></ul></ul><ul><ul><li>affected by </li></ul></ul><ul><ul><ul><li>paper surface properties </li></ul></ul></ul><ul><ul><ul><ul><li>achievable print densities </li></ul></ul></ul></ul><ul><ul><ul><ul><li>dot gain </li></ul></ul></ul></ul><ul><ul><ul><li>paper brightness and hue </li></ul></ul></ul><ul><ul><ul><li>ink properties and trapping </li></ul></ul></ul><ul><li>Reproduction of details </li></ul><ul><ul><li>“ how small details can be reproduced” </li></ul></ul><ul><ul><li>“ number of shades i.e. tone steps inside colour gamut” </li></ul></ul><ul><ul><li>affected by </li></ul></ul><ul><ul><ul><li>screen ruling </li></ul></ul></ul><ul><ul><ul><li>paper surface properties </li></ul></ul></ul><ul><ul><ul><ul><li>dot gain </li></ul></ul></ul></ul>INK DEMAND INK DEMAND
  4. 4. Reproduction of color Original Coated paper's colour gamut Uncoated paper's colour gamut Correct dot gain Dot gain too high
  5. 5. Colour gamuts - an example
  6. 6. Colour impression <ul><li>Measured print density values = darkness </li></ul><ul><li>Measure lab-values = darkness and colour </li></ul>white light print gloss = surface reflection of white light print-trough print density = coloured light base paper coating layer ink layer
  7. 7. Ink demand <ul><li>Roughness is the main limiting factor in colour gamut together with porosity </li></ul><ul><li>Smoother paper can achieve higher print densities than rougher paper with same ink amount </li></ul><ul><li>This means also higher colour gamut </li></ul>
  8. 8. Ink demand vs. roughness <ul><li>Ink demand is mostly controlled by roughness </li></ul><ul><ul><li>glossy coated grades </li></ul></ul><ul><li>And also by porosity </li></ul><ul><ul><li>uncoated and rougher papers </li></ul></ul>matt silk grades
  9. 9. Dot gain <ul><li>Dot gain is an increase in the diameter of the halftone dot </li></ul><ul><li>Limiting factor when choosing screen ruling </li></ul>40% dot on plate 60% dot on paper  20% dot gain
  10. 10. Dot gain vs screen ruling - an example
  11. 11. Dot gain <ul><li>Dot gain can be divided into </li></ul><ul><ul><li>mechanical dot gain (ink flows in xy-direction in the printing nip) </li></ul></ul><ul><ul><ul><li>nip pressure </li></ul></ul></ul><ul><ul><ul><li>ink amount (paper roughness) </li></ul></ul></ul><ul><ul><ul><li>absorption in xy-direction </li></ul></ul></ul><ul><ul><li>optical dot gain (light scattering) </li></ul></ul><ul><ul><ul><li>some of the light is trapped under the dot  shadow </li></ul></ul></ul>
  12. 12. Dot gain - an example Galerie Fine Gloss 115 g Galerie Brite 70 g Galerie Lite 45 g
  13. 13. Trapping <ul><li>Trapping is a measure how much ink printed on top of another ink transfers </li></ul><ul><li>Important from when choosing ink sequence </li></ul><ul><li>Influences to colour gamut through secondary colours </li></ul>+ = + = + = Ideal situation ~70% of magenta is transferring ~70% of cyan is transferring
  14. 14. Trapping - an example (50x magnification) + = Offset Cyan 100% Magenta 100% Cyan + Magenta 200% + = Gravure Cyan 100% Magenta 100% Cyan + Magenta 200%
  15. 15. Print gloss <ul><li>Very many printed products require high print gloss for visual appearance </li></ul>
  16. 16. Formation of print gloss <ul><li>Macro-roughness (flock-size) causes poor ink transfer </li></ul><ul><ul><li>high print gloss variation and low print gloss </li></ul></ul><ul><li>Micro-roughness (fibre-size) affects to gloss level </li></ul>uncoated single coated
  17. 17. Formation of print gloss <ul><li>Ink layer can cover optical roughness (pigment-size) </li></ul><ul><ul><li>high print gloss and low paper gloss </li></ul></ul><ul><li>Smooth and glossy paper gives highest print gloss </li></ul>double coated silk double coated gloss
  18. 18. Effect of ink on print gloss <ul><li>Printing ink has major influence on print gloss </li></ul><ul><ul><li>in this example over 15 units </li></ul></ul>10 commercial heatset inks printed on double coated gloss paper (laboratory)
  19. 19. Visual impression of gloss <ul><li>Our reader studies have shown that </li></ul><ul><ul><li>consumers don't pay attention to small gloss differencies </li></ul></ul><ul><ul><li>e.g. a reader study, where </li></ul></ul><ul><ul><ul><li>30 consumers evaluated printed samples with different paper gloss (from 65% to 75%) </li></ul></ul></ul><ul><ul><ul><ul><li>approx. half of the consumers did not have any preference </li></ul></ul></ul></ul><ul><ul><ul><ul><li>~15% preferred lower gloss paper </li></ul></ul></ul></ul><ul><ul><ul><ul><li>~30% preferred higher gloss paper </li></ul></ul></ul></ul><ul><li>However print buyers still pay attention to gloss and it can have impact on the brand of the magazine in question </li></ul>
  20. 20. Print quality - a summary <ul><li>Print quality level according to purpose </li></ul><ul><ul><li>colour gamut </li></ul></ul><ul><ul><ul><li>choice of paper, ink </li></ul></ul></ul><ul><ul><ul><li>printing method </li></ul></ul></ul><ul><ul><li>colour reproduction </li></ul></ul><ul><ul><ul><li>understanding of the role of paper and ink on colour reproduction </li></ul></ul></ul><ul><ul><ul><li>using that understanding in prepress and printing </li></ul></ul></ul><ul><ul><li>gloss </li></ul></ul><ul><ul><ul><li>has influnce on colour gamut </li></ul></ul></ul><ul><ul><ul><li>influences also through visual impression </li></ul></ul></ul>