Date post: | 12-Aug-2015 |
Category: |
Education |
Upload: | sappihouston |
View: | 1,989 times |
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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