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Basics of offset printing and other printing techniques

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Basics of offset printing and other printing techniques

  1. 1. Basics of offset printing & other printing methods1
  2. 2. Products Offset Sheet- Heatset Coldset Gravure Flexo Digi fed Magazines, catalogues X X X Brochures, annual reports etc. X X Direct marketing X X X X X Books X X X Newspapers X X Packages, wrappers X X X2
  3. 3. Why ? A better understanding of the first end use of our products (to be printed) will allow you to better advise your customers and thus give added value to your sales3
  4. 4. Summary Offset printing What is colour ? Principle of offset printing Sheet-fed offset printing Heat-set web offset printing Other printing methods Conventional methods Gravure Flexography Silk screen Digital printing methods Laser (electro photography) Ink jet Conclusion4
  5. 5. High Placement of printing methods Ink-jet Sheet-fed offset Heatset offset GravureQuality Medium Electro photo- graphy Low 100 1 000 10 000 100 000 1 000 000 10 000 000 Run length 5
  6. 6. Summary Offset printing What is colour ? Principle of offset printing Sheet-fed offset printing Heat-set web offset printing Other printing methods Conventional methods Gravure Flexography Silk screen Digital printing methods Laser (electro photography) Ink jet Conclusion6
  7. 7. What is colour ? Colour Without light, no object has a colour7
  8. 8. What do we need to see colours ? A light source (Sunlight, Light Bulb, Candle) A receiver and processor (eye + brain) An object to interact with the light source8
  9. 9. Human eye • light enters the eye through the lens and is focused on the retina There, an array of photoreceptor cells respond to light and pass the signals on to the brain which translates into colour sensation There are 2 types of cells : -> rods = black & white -> cones = colours 3 different types of cone cells sensitive to the wavelength of => red light => green light => blue light Cells light stimulates the eye three dimensionally!!9
  10. 10. Spectrum of electromagnetic radiation waves Gamma X-ray UV IR Radio Radar Wavelength 0,001 0,01 0,1 1,0 10 100 10³ 10 4 10 5 10 6 1010 1011 10 12 10 13 nm Spectrum of the visible light photon violet blue green yellow orange red nm 400 500 600 700 different wavelengths = different colours400 - 500 nm = blue 500 - 600 nm = green 600 - 700 nm = red10
  11. 11. How to create colours ? : 2 methods Additive Subtractive Yellow Cyan Magenta11
  12. 12. How to create colours : additive method Additive Lights : Red + Blue + Green = White For example a Television or a Computer Monitor12
  13. 13. How to create colours? Based on this (Green + Blue = CYAN, Green + Red = YELLOW, Blue + Red = MAGENTA), we can reproduce every colour based on 3 selected colorants Each colorant will have to act on a primary colour of the spectrum (Red, Green or Blue) For example to act on Red, we need a colorant which absorbs only Red and not Green and not Blue. This is the CYAN Ink which absorbs red light reflects blue light blue + green = cyan ink reflects green light13
  14. 14. How to create colours : subtractive method Selective absorption of certain wavelength by the ink layer. Magenta ink Cyan ink Yellow ink reflects red absorbs red reflects red reflects blue reflects blue absorbs blue absorbs green reflects green reflects green14
  15. 15. Primary colours in printing Mixing the 3 primary colours theoretically results in black. => In practice the result is brown! => To remedy this, blacK is used as the fourth primary colour. CMY blacK CMYK CMY Black CMYK + =15
  16. 16. Summary Offset printing What is colour ? Principle of offset printing Sheet-fed offset printing Heat-set web offset printing Other printing methods Conventional methods Gravure Flexography Silk screen Digital printing methods Laser (electro photography) Ink jet Conclusion16
  17. 17. Principle of offset printing On a printing plate there are two areas: • Areas accepting ink and being repellent to water = Image areas (= hydrophobic) • Areas accepting water = Non-Image areas (= hydrophilic). The areas are occupied by water. Due to the different surface tension water and ink do not mix. The behaviour of the image and non-image areas is caused by a complex chemistry.17
  18. 18. How do we get printed and unprinted areas? Ink = hydrophobic Water = hydrophilic IMAGE NON-IMAGE Function of the offset plate18
  19. 19. How do we get printed and unprinted areas?Image Non-Image Magnified (15x) of an offset plate19
  20. 20. How do we get printed and unprinted areas? Non- ImageImage Magnified (1000X) picture of an offset plate20
  21. 21. How do we get printed and unprinted areas? Substrate = direct transfer IMAGE NON-IMAGE Function of the offset plate21
  22. 22. How do we get printed and unprinted areas? Rubber Rubber 1st transfer 2nd transfer Substrate IMAGE IMAGE NON-IMAGE NON- IMAGE Function of Rubber blanket = indirect transfer22
  23. 23. Offset printing unit23
  24. 24. The printing plate Light sensitive coating Aluminium oxide coating Grained aluminium base24
  25. 25. The printing plate25
  26. 26. Basic composition of offset ink Pigments ~10-20 % organic and inorganic Binders ~30-50 % Hard resins Alkyds Vegetable oils Solvents ~20-30 % Mineral oils Vegetable oils Additives ~0-5 % waxes, rheology modifiers, antioxidants, fillers...26
  27. 27. Offset blankets Oil-resistant synthetic elastomers attached to textile fabrics Reproduction properties Release properties27
  28. 28. The fountain solution Surface tension of liquid has to be lower than surface energy of solid to ensure quick spreading •Water 85-98 % •IPA (Isopropanol) 0-20 % •Additives 2-4 % weak organic acid(s), buffers, film formers, surfactants, chelating (sequestering) agents, biocides, anti-foams, humectants, glycols, corrosion inhibitors pure water, 72 mN/m water + 6% IPA, 45 mN/m surface energy of non-image area, 50 mJ/m 228
  29. 29. Screening One half-tone image may contain thousands of different shades………29
  30. 30. Different screening Conventional screening Stochastic screening  distance between the centers of  tone is formed by altering dot position the dots is constant and spacing, number of dots30
  31. 31. Stochastic screen Standard dot size, Dot size and but the amount of amount of dots them vary. vary.31
  32. 32. Screen ruling – conventional screening Light tones ~ small dots The dots are so small that the human eye Dark tones ~ bigger dots sees them as a single colour. Tonal value 75% Tonal value 25% 40l/cm Tonal value 50% 60l/cm 80l/cm Tonal value 100% Screening ruling (L/cm or L/inch)32
  33. 33. Human eye In case of the 4-colour printing the colours are mixed in the eye when looking at them, as the eye cannot differ between the small, close picture elements. Normal screen surface Strongly magnified screen surface33
  34. 34. Print density  Print density (darkness) is created by increasing the inked area (halftone percentage) Black 20% Black 40% Black 60% Black 80%34
  35. 35. Print colour  Print colour (tone) is created by mixing halftone percentages of process colours C80%/M20% C60%/M40% C40%/M60% C20%/M80%35
  36. 36. Examples of screening methods Staccato 25µm Conventional 60 l/cm36
  37. 37. Summary Offset printing What is colour ? Principle of offset printing Sheet-fed offset printing Heat-set web offset printing Other printing methods Conventional methods Gravure Flexography Silk screen Digital printing methods Laser (electro photography) Ink jet Conclusion37
  38. 38. Sheet fed offset press Margin - Ink rollers & Damping rolls Feeder Anti set-off powder systemDelivery ofthe printed sheets Settings of pressure and register 38
  39. 39. After the 4 printing units39
  40. 40. Sheet fed presses 5 colour units + 1 varnish unit Delivery Varnish Ink units Feeder  4/4 colour units, change of the printing side of the sheet in the perfecting system40
  41. 41. Different formats41
  42. 42. Feeder42
  43. 43. Ink Rollers43
  44. 44. Sheet Transfer Transfer cylinder44
  45. 45. Spray powder to avoid ink set-off distance holder between the sheets. increases the amount of oxygen to improve the oxidative drying process. Spray 10 to 80 microns calcium carbonate organic, vegetable based powder of natural starch 300x - CaCo345
  46. 46. Varnish Why ? More gloss Protect Less drying time before converting Sometimes two varnish units High gloss and matt varnish at the same run Premier and UV- varnish when using conventional inks Better gloss than one unit applying46
  47. 47. Summary Offset printing What is colour ? Principle of offset printing Sheet-fed offset printing Heat-set web offset printing Other printing methods Conventional methods Gravure Flexography Silk screen Digital printing methods Laser (electro photography) Ink jet Conclusion47
  48. 48. Basic design of heatset press Web widths: ~50- (over) 200 cm Web speed: ~4-15 m/s Web tension: ~600-800 N/m Drying (web temp): ~110-140 °C Folding: usually on-line siliconization unit reelstand dryer printing units infeed chill rolls folder48
  49. 49. Heatset presses - different designs additional colour varnishing unit (offset varnish)49
  50. 50. Operating press Driving the press50
  51. 51. Infeed51
  52. 52. Heatset press – an example52
  53. 53. Paper web in one unit Plate cylinder Blanket cylinder Paper web Blanket cylinder Plate cylinder53
  54. 54. Oven54
  55. 55. Oven55
  56. 56. Heatset dryer Web delay in the dryer is ~1 s dryer length is determined by the press speed (10 m/s  10 m) Dryer has multiple modules Hot air from the nozzles carries the web through the dryer Exhaust air is either circulated back or is let to atmosphere through treatment (e.g. afterburner)56
  57. 57. Temperature profiles in the dryer Web exit temp. usually 100-140 C (90-180) Usually declining temperature profile web temperature rises faster and solvent evaporation starts earlier °C 300 255°C 195°C 200 165°C 130°C 100 drying air temp web temp 1st 2nd 3rd 4th57
  58. 58. Chill rolls Thermoplastic ink binder is in soft form after the dryer chill rolls cools down the web and solidifies the binder (better rub resistance) Steel cylinders (3 - 6) with cold water pumped through Web tension has to be high enough to ensure good contact58
  59. 59. Silicone application59
  60. 60. Center Cut60
  61. 61. Aligning ribbons61
  62. 62. Different kind of folders Cylinder/Jaw folder Former fold62 Chopper folder
  63. 63. Example of fold 16 pages Former fold Jaw fold880 mm Chopper/ jaw fold 630 mm63
  64. 64. Folding possibilities 310 x 440 mm 310 x 220 mm 155 x 110 mm64
  65. 65. Imposition and plate making Imposition Done usually at the printer Depends on what press is used 16/32/48/64 pages Special software used Plate making From imposition layout65
  66. 66. Press layouts 72/80-page 48/64-pagePagination 32-page Double perimeter Single perimeter 24-page 16-page 8-page66 Run length
  67. 67. Manual delivery67
  68. 68. Post-press68
  69. 69. Perfect binding Operations  signatures are collated together in conveyor belt  signatures travels down the belt to the saw  saw trims off of the bind edge of so the binding glue can be applied between the individual pages  magazine travels to the covering station  magazine is trimmed with 3-knife cutting Separate cover is needed Long grain =MD69
  70. 70. Saddle stitcher Operations  signatures are pulled open and dropped in proper order onto a moving "saddle".  assembled signatures receive a cover in the same manner and then pass under the stitching heads where wire staples are applied  magazine is trimmed with 3-knife cutting Usually used only product with pagination under 96 pages70
  71. 71. Summary Offset printing What is colour ? Principle of offset printing Sheet-fed offset printing Heat-set web offset printing Other printing methods Conventional methods Gravure Flexography Silk screen Digital printing methods Laser (electro photography) Ink jet Conclusion71
  72. 72. Gravure72
  73. 73. Gravure73
  74. 74. Gravure - applications Packaging & converting Flexible packaging Labels & wrappers Gift wraps Wall coverings Vinyl Decorative laminates Floor coverings Tissue products Stamps74
  75. 75. Summary Offset printing What is colour ? Principle of offset printing Sheet-fed offset printing Heat-set web offset printing Other printing methods Conventional methods Gravure Flexography Silk screen Digital printing methods Laser (electro photography) Ink jet Conclusion75
  76. 76. Flexography paper plate Double face tapeCounter pressure cylinder ink sleeve blade 76
  77. 77. Applications • Paper sacks • Milk carton • Pocket Books • Plastic bags • Labels • Aluminium • Corrugated Board • Carton cups • Napkins • Tissue • Envelope • Bussinessforms • News Papers • Flexible packaging • Pocket Books77
  78. 78. Summary Offset printing What is colour ? Principle of offset printing Sheet-fed offset printing Heat-set web offset printing Other printing methods Conventional methods Gravure Flexography Silk screen Digital printing methods Laser (electro photography) Ink jet Conclusion78
  79. 79. Silk screen79
  80. 80. Summary Offset printing What is colour ? Principle of offset printing Sheet-fed offset printing Heat-set web offset printing Other printing methods Conventional methods Gravure Flexography Silk screen Digital printing methods Laser (electro photography) Ink jet Conclusion80
  81. 81. What is digital printing ? DIGITAL printing means printing directly from digital data original is in digital form no films are needed no plates are neededSlide 8181
  82. 82. Pro or Contra digital printing ? Pro easily changeable info design and colours text no make-ready -> small runs with reasonable costs personalisation versioning on-demand printing decentralised printing easy to operate vs. offset ”unlimited” repeat length Contra  Print quality still lower than in offset  Low printing speed compared to conventional presses  Format limitations (small reels/sheets)  Limited or non-existing spot colours and metallic  Conventional further converting  Costs (toners etc)82
  83. 83. Applications Production variable data  direct marketing  individualized statements  customized catalogues, brochures etc Commercial printing  on-demand and short run books  short run brochures83
  84. 84. Summary Offset printing What is colour ? Principle of offset printing Sheet-fed offset printing Heat-set web offset printing Other printing methods Conventional methods Gravure Flexography Silk screen Digital printing methods Laser (electro photography) Ink jet Conclusion84
  85. 85. Electro photographic principle 1. Photoconductor is charged 2. Latent image is formed by discharging - - - - - - -- - - - - the drum by laser or -- -- LED + ++ 6. Remaining toner -- - + - -+ is wiped off -- - 3. Latent image is developed by toner 5. Toner is fixed to the paper by heat = fusing + ++ + 4. Toner (image) is transferred to the paper in electric field, opposite charge attracts85
  86. 86. Summary Offset printing What is colour ? Principle of offset printing Sheet-fed offset printing Heat-set web offset printing Other printing methods Conventional methods Gravure Flexography Silk screen Digital printing methods Laser (electro photography) Ink jet Conclusion86
  87. 87. Ink jet : continuous 1. Continuous stream, CS, CIJ printing droplets are selected from the continuous stream by charging them selectively droplets have similar size high speed e.g. Scitex VersaMark87
  88. 88. Ink jet : drop on demand 2. Drop-on-demand, DOD every drop is printing high resolution lower speed e.g. Aprion88
  89. 89. Summary Offset printing What is colour ? Principle of offset printing Sheet-fed offset printing Heat-set web offset printing Other printing methods Conventional methods Gravure Flexography Silk screen Digital printing methods Laser (electro photography) Ink jet Conclusion89
  90. 90. Print definition depends on paper quality LWC, Newsprint, 60l/cm 48l/cm Coated Fine, SC, 70l/cm 54l/cm90
  91. 91. Different printing process, different results Offset Flexography Gravure (20%, 75 l/cm) (20%, 60 l/cm) (~20%, 100 l/cm) • Dots are uniformly • Ink is pressed to • Broken shape of dots and covered with ink edges, print density missing dots are typical for • Edges are ragged inside dot varies light tones (uncoated papers) • Edges are smooth • Doughnut shaped dots • Uniform text • Shadow in the edge • Text is screened, serrated of text edge91
  92. 92. Examples of halftone dots and text Inkjet (20%) Electrophotography • Dots are quite uniformly (~20%) • Dots are quite uniformly covered with ink • Dot is formed by using several covered with toner • Edges are ragged droplets • Edges are ragged or even • Separate toner particles depending on paper (dry toner methods) • Satellites, escaped droplets • Uniform text92
  93. 93. ? Will be happy to answer your technical questions : Questions ? Françoise Accou, +32 492.582.287, francoise.accou@sappi.com93

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