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Runnability

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Good runnability is usually connected to accumulations on the blanket vs. washing interval.

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Runnability

  1. 1. Runnability• Good runnability is usually connected to accumulations on blanket vs. washing interval• There is always something accumulating on blankets • washing interval can be from 20 000 copies up to hundreds of thousends copies • accumulation can be said to affect runnability if • washing interval is reduced significantly • print quality detoriates • risk of blanket damage
  2. 2. Accumulation problems Linting• Image area problems • Linting • typical with uncoated grades • newsprint, SC • Fibre picking • with LWC papers • connected to shives Fibre picking • better screening helps • coating layer strength • binder amount • optimatization between cost of binder and high enough surface strength
  3. 3. Coating pickingAccumulation problems• Image area problems • Coating picking • usually not surface strength problem but connected to papermaking process • different precipitations on paper machine or dirt • does not bind well to paper easily removed in printing • Carry-over piling • printing ink printed in previous unit gets tackier in following units and starts to pick coating surface • connected to several factors like Carry-over piling • ink tack, ink setting speed, water amount on blanket etc... • but also to coating strength of the paper • not much a problem nowadays
  4. 4. Dusting Accumulation problems• Non-image area problems • Dusting • accumulation of pigment particles on non-image area of the blanket • uncoated paper with high filler amount • coated papers with low amount of calandering (matt, silk) • accumulation usually purely coating/filler pigment • Milking • calcium/fountain solution problems • transparent white film (calcium precipitate, for example calcium citrate) on blanket • not seen very often • Ghosting / Vanishing dots • the most current problem in heatset printing! • main mechanism still unsolved • a lot of studies in recent years
  5. 5. Vanishing dots and ghosting ghosting varnishing dots
  6. 6. Vanishing dots and ghosting – ink build-up

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