(Only on coated papers)
- Too high moisture content in the paper
- Too low z-strength
- Basis weight (higher is more critical)
- Porosity of the coating, not letting the moisture to escape
Occurs when water vapour can not evaporate fast enough through the coating layer in the dryer section of the heat-set press.
- Try reducing the dryer temperature
- Try to reduce press speed. This will slow the moisture vaporisation and permit the water vapour to escape through the pores in the coating.
- Increase the press speed without increasing the dryer temperature as this allows the paper to be in the oven for a shorter period of time.
Build-up on rubber blanket (Piling)
(Piling is a general term for all kinds of build-up)
Piling; material gradually builds up on the press blanket or plate.
- Ink is too tacky
- Ink is too unstable
- Paper absorbency is too high
- Too acid fount
- Over heating of the press
Burst web inside the reel is caused by too high web tension between a hard and soft section of the reel during winding, and results in a machine direction shearing force that exceeds the web strength.
This is an unusual problem and very difficult to find.
Occurs at the machine calender or super calender. It results from excess paper that accumulates as a blister at the entrance of a nip. The cut happens when the blister passes through the nip.
There are many types of coating faults.
A plugged nozzle have given a 1 cm wide streak with no coating.
To little coating have put on which leaves spots in the surface with no coating.
The core gets worn out by the core chuck in the reel stand. Either to weak core have been used or there was a fault with the core.
Edge tears fold over during the winding operation.
A dull or nicked slitter that nicks the edge after which the stress of winding will cause the tear to open up or
If the reel is bumped on the edge.
Felt hairs can be transferred to the paper in the paper machines press section.
The felt hairs will be stuck in the printing press where they prevent ink transfer. Often only one side of the sheet is affected.
Part of black printed are to the left and a press felt to the right.
Glue on reel end
Blue – green glue is used to glue the layers of wrapping together.
In the wrapping line it can happen that pieces of loose paper move the glue to places where it should not be.
"Hair" of any species that infiltrates the pulping process. The cuts occur during calendering and are caused by either hair or synthetic thread that is caught on the web.
"Fish eye", usually nut-shaped white spots surrounding a small coloured spot are caused by hard particles of dried ink, dryer skin, dirt, plaster or other foreign material in the ink. The particle is preventing the closest part of the rubber blanket to transfer the ink and a white area around the particle can be seen.
White spots in solids that are not nut-shaped can be caused by paper dust or particles picked up from the paper.
Inner shield missing
The wrapping on a reel shall have double end shields. When the inner end shield is missing the outer end shield will be glued directly on to the reel end. A typical pattern can be seen on the reel end when this happens in wrapping line 5.
Linting (fibre)/Dusting (pigment)
Lint or dust can give different patterns in printed areas.
Low surface strength on the paper or tacky ink
The ink-water balance will effect linting/dusting
Too high tack on ink is used. (In some cases to low tack on the ink)
See the top of the big black letters where lint have started to affect print quality.
Low surface strength on the paper or tacky ink.
When the lint from rubber blankets is analysed we always find so called parenchyma cells (square shaped particles), fibre fragments, pigments (round particles in this case) and printing ink.
A very long print run will always cause some kind of build-up.
More build-up is normally found on non printing areas.
Oil or grease marks
Oil have leaked on to the paper giving a yellow –brown greasy surface. There is often more than one layer involved as on the picture.
Grease marks can look similar but there is often more dirt in the grease that make the spots darker.
Piping is moisture wrinkles. Normally parallel to machine direction and are caused by moisture absorption from the air into the paper and thereby expansion in the cross direction. Occurs when the moisture in the paper and the relative humidity in the surrounding air are not in balance.
Poor mill joint
Defect mill joint
The joint tape is not set in a properly place and therefore sticks to the paper underneath
Protruding mill joint
The two webs are not put in line with each other and the paper is therefore protruding at the end of the reel
Stuck mill joint
The joint tape is not covered by the paper or the cover tape. The tape sticks to the paper layer and causes a break
Poor slitter cut
A defect slitter edge may appear nicked or torn, irregular or rough edge on the paper. Slitter dust sometimes is present. The cause is usually a dull slitter. It gives the reel end a wavy or shaggy appearance.
The result of non-uniform thickness and moisture across the web. Will cause misregister problems and web breaks in severe cases.
Caused by lower calliper and greater stretching of the web under high tension during winding and calendering.
A dirty drop of slime with bacteria has dropped onto the sheet. The mist from the hot furnish can build up as slime on the paper machine frame.
The crushing occurs when the wet slime on the paper passes a press nip.
Step in winding
A defect which manifests itself as an abrupt change in the position of the edge of the paper. It can be caused by:
Abrupt change in tension or web draw control at winder
Webs are not aligned when spliced
The web have moved over a slitter during a stop in the winder
Winder wrinkles/Drum puckers
Occur when outer layers in a reel is wound with higher tension than inner layers. The outer layers will press so hard that the web tension on inner layers will be under zero, giving a compression force.
Reels wound soft close to the core will be sensitive
An abrupt change in hardness during winding
Large calliper variations will contribute to this problem