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

Accumulation problems

• Image area problems

• Linting

• typical with uncoated grades

• newsprint, SC

• Fibre picking

• with LWC papers

• connected to shives

• better screening helps

• coating layer strength

• binder amount

• optimatization between cost of binder and high enough surface strength

Linting

Fibre picking

Accumulation 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

• ink tack, ink setting speed, water amount on blanket etc...

• but also to coating strength of the paper

• not much a problem nowadays

Coating picking

Carry-over piling

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

Dusting

Vanishing dots and ghosting

ghosting varnishing dots

Vanishing dots and ghosting – ink build-up