Heatset Offset Lithography

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Heatset Offset Lithography

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Heatset Offset Lithography

  1. 1. Heatset Offset Lithography
  2. 2. Heatset Web OffsetHeatset offset is very versatile printing method both from product and paper point of view • Products • magazines, catalogues, direct mail, newspapers, inserts, brochures, illustrated books and manuals • Papers • WFC, MWC, LWC, MFC, SC, UWF, newsprint • Grammages from 35 ~150 gsmHeatset printing has global market of ~80 billion €Paper consumption over 8 million tons of paper in Western Europe (2008)
  3. 3. Reality checkGlobal advertising is down ~10% and in magazines ~18%Deliveries of coated mechanical reels were down ~20% in 2009 compared to 2008Low operating rates are reflected on prices, which are also going downCustomers are shifting to lower qualities and lower grammages • How to maintain printed quality?Paper manufacturers are turning every stone to cut cost in paper manufacturing • Runnability issues will increase
  4. 4. Basic design of heatset press siliconization unitreelstand dryer printing units infeed chill rolls folder Web widths: ~50 - 280 cm Web speed: ~4 - 15 m/s Web tension: ~600 - 800 N/m Drying (web temp): ~110 - 140 °C Folding: usually on-line
  5. 5. Press layoutsMajority of presses (>80%) are long grainBenefits of long grain • more variety in folding • last fold in grain direction in A4 production • important for perfect bindingBenefits of short grain • ribbon folder higher productivity • page flexibility (height of page)
  6. 6. Heatset presses - different designsAdditional units additional colour varnishing unit (offset varnish) • extra colours • varnishingTwin webs • productivity • versatilitySheet cutter • for heavier grammages • for off-line varnishingOn-line finishing Twin web • direct mail
  7. 7. Heatset web offset printing unitKBA Compacta618 Blanket to blanket nip Ink system • high number of rollers to ensure thin and even ink layer • 3-4 ink form rollers to ensure even ink transfer to plate Fountain system • 3-4 rollers • water form roller in contact with ink rollers and plate • ensures fast emulsification ink duct Courtesy of KBA
  8. 8. Heatset dryerWeb 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 dryerExhaust air is either circulated back or is let to atmosphere through treatment (e.g. afterburner)Together with solvent also moisture is evaporated coated grades: ~4-5% 1-2% uncoated grades: ~5-8% 2-3% ~240°C ~200°C ~150°C ~120-140°C
  9. 9. Chill rolls and SiliconizationChill rolls Siliconization • Thermoplastic ink binder is in • Usually one roller rotating soft form after the dryer in pan • chill rolls cools down the web and • to protect printed area from solidifies the binder (better rub smearing resistance) • also functions as a • Steel cylinders (3 - 6) with cold remoistening device water pumped through • Web tension has to be high enough to ensure good contact
  10. 10. FoldersUsually former folders • former fold followed by 1-2 jaw foldsWith high pagination the use of ribbon folding is increasing • web is slitted into ribbons (typical in gravure) • also choice for short-grain presses Courtesy of KBA
  11. 11. Folding: 16-page, long-grain Former fold Jaw fold880 mm Chopper/ jaw fold 630 mm
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