1. Printing Technology
Printing Problems Sheetfed Offset
Technical Support
1 | [Printing problems Sheetfed Offset] Sappi Fine paper Europe

2. Content
- Questions and check list in case of complaints
- Doubling effects
- Misregister
- Ghosting effects / Yellowing effects
- Rub resistance / Pick outs
- Mottling
- Scuff resistance / Carbonize
- Ink drying
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3. Important questions in case of complaints
What is the problem?
Is printing still carried out or was the paper completely processed?
Was the printing process interrupted and another job taken into the
machine?
Is a further printing possible:
With a less good printing result?
With a lower production speed and/or more interruptions?
What are the estimated costs?
Is the entire job processed at once?
Is the supply of additional paper necessary?
In connection with the visit: how long is printing still carried out?
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4. Doubling
Doubling characteristics:
The question is of doubling if an unintentional, shadow-shaped
colour point with small dimensions can be found at the artificial
printed screen point. Doubling is generated by the non-congruent
re-transfer of colour through the following rubber blanket.
Doubling:
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5. Passer differences
Passer differences are caused by:
– Hygro-expansion of the printed stock
– Lack of plane position of the printed stock
– Technical error or failures of the printing machine
– Unfavourable climatic conditions
Printed stock
expansion
1. Printing colour
2. Printing colour
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6. Passer differences
The following points should be checked:
– Longitudinal direction of the paper (use small web)
– Check fountain solution and reduce it, if possible
– Check the paper run of the printing machine (feeding)
– Check the winding-off
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7. Ghost effect
Characteristics of the ghost effect:
A ghost effect is caused by an interaction of paper, printing colour
and production conditions. The printing pictures distinguish
themselves by released cleave products on the back of the sheet
lying above in the stack. We differ between matt-glossy-effect and
contact yellowing.
Paper Cleave
products
Printing colour
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8. Matt-glossy-effect
Characteristics of the matt-glossy-effect:
The cleave products change the back of the sheet lying above in
the stack. If this back is now printed the colour drying is changed
at this point. By the different colour dryings, the matt-glossy-
effect is generated.
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9. Contact yellowing
Characteristics of the contact yellowing:
The cleave products taken from the back react with the paper.
Strongly brightened papers are especially sensitive to contact
yellowing.
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10. Ghost effect
The ghost effect appears completely accidental and
unexpected. A ghost effect may be avoided by the following
processes:
– Printing of bigger colour surfaces in the second form
printing
– Run of smaller stacks and provision of sufficient
aeration during drying (manual, stack changer)
– Use of concentrated colour to keep the colour
guidance as low as possible
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11. Picking / parts breaking off
“Picking” is a tearing-out of coating particles or fibres from the
paper surface due to too high forces during colour cleaving.
Rubber blanket cylinder
Bulb formation
Printing colour before cleaving Colour cleaving
Printed Printed sheet tear-off angle
sheet Impression cylinder gripper
Printing zone width
Impression cylinder
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12. Picking / parts breaking off
Reasons for the “picking” are:
– Poorly sized paper
– Too quick absorption of the printing colour
– Too continuous printing colour
– Printing room and machine too cold
– Too high printing speed
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13. Irregular printing / mottling
This error appearance in the printing is caused by a non-uniform
absorption of the printing colour in the paper surface and, thus, a
non-uniform re-cleaving of the following printing material to the
rubber blanket (backtrap mottling).
Printing
colour
Coating
Basis paper
By changing the colour sequence, the printer may reduce or
prevent the mottling effect.
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14. Scuffing / carbonising
Definition of the “scuff strength”:
Scuff strength is the resistance of a printing colour layer against
the mechanical stress due to pressure load and friction.
– Scuffing: colour soiling due to mechanical abrasion of
the printing colour film
– Carbonising: colour soiling due to the pressure load onto
the unprinted back of a printing object
in the stack or during cutting
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15. Scuffing / carbonising
Difference:
Scuffing Carbonising
Average pressure with High pressure with very small
relatively long scuffing path strokes
(e.g. collating machine, folding (e.g. guillotine-type cutter, three cutter
machine, gather-stitcher) machine)
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16. Scuffing / carbonising
Scuffing
Silk Matt
Carbonising
Silk Matt
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17. Scuffing / carbonising
Especially in case of matt papers, the scuff strength is
influenced by the following factors:
Colours Fountain solution Paper
 Oxidative drying  Optimal 5-8% ISO  Smooth surface
colours ph 5.5
 Acid water, much ISO  Coarse surface
 Fresh colours
Powder Time
 Starch powder  Drying time, incl.
Scuff strength aeration
 Mineral powder
 Quick processing
Printing conditions Repro Book bindery
 Stable continuous printing  UCR  Upright sheet feeder
without many stops good
 400 % colour  Horizontally laying
climate
sheet, pulled from the
 Drying e.g. with IR at 1 point
bottom
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18. Scuffing / carbonising
“Scuff strength” What is the printer capable to do?
Little or not influenced :
1. Placing of single-coloured and multicoloured figures.
2. Use and arrangement of special colours.
3. Realisation of an enamelling.
4. Realisation of a laminating.
5. Planning of a bigger paper size for co-printed colour bars.
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19. Scuffing / carbonising
“Scuff strength” What is the printer capable to do?
1. Selection of the printing colour
– Use of so-called „scuff-resistant“colours
– No use of “box-fresh” printing colours
2. Determination of the colour sequence
– The colour printed last should always be yellow (function as lacquer printing)
3. Selection and dosing of printing auxiliaries
– Principally, no printing auxiliaries (oils, pastes, etc.) should be used
– The use of paint driers could be useful (dosing according to the manufacturer’s
recommendation)
4. Regulation of the fountain solution
– Alcohol share 8 - 10 %
– pH - value 5.3
5. Optimisation of the colour-water balance
– Damping adjustment slightly above the “lubrication limit”
– Perfect condition of colour and damping rolls
– Precise adjustment of colour and damping rolls
– Stabilisation of the colour-water balance by co-printed colour bars in case of poor
printing forms
6. “Correct” printing-dry-spraying
– Graining of the powder analogue to the basis weight of the paper
– No powder with “edged” structures (mineral powder)
– Use of powder with “round” structures” (starch powder)
– No powder on sugar basis
– The less powder, the better the scuff strength
7. Drying time
– The drying time between printing and further processing should amount to at least
48 hours
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20. Drying of the colour
The drying of the printing colour is a criterion of the printability. In the sheet
offset printing drying colours are mostly used in an absorbing or oxidative
way.
The most important parameters are:
– The penetration or the physical absorption behaviour of the paper.
In this first phase, the coating of the paper shall provide the absorption of
the liquid parts of the colour binding agents in the paper, similar to the
function of a screen.
– The acidity or the alkalinity of the paper surface (expressed as pH-value),
which influences the chemical drying process of the binding agent
(oxidative drying).
The surface pH-value should be in the neutral or slightly alkali range in
case of coated paper ( 6.0).
– The relative stack humidity of the paper (approx. 50 % rel.).
– The topographic nature of the paper surface
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21. Drying of the colour
The printing colour drying depends on the interaction with the humidity in the
offset printing.
Critical are:
– Too high fountain solution guidance
– Printing forms with poor colour consumption
– Wrongly dosed fountain solution binding agents
The colour absorption behaviour of the paper should not be adjusted too
quickly or too slowly.
In case of printing machines operating at a high speed, a deposit in the stack
should not occur, on the other hand, the colour absorption should not run too
quickly in view of 10 and 12 colour offset machines (danger of accumulation
and picking).
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