Tips for high quality results
To minimise show through, it is preferable when designing your document, to put heavy coverage and dark colours back to back.
For the design, try, if possible, to avoid solids, high ink loads and a reverse on UV varnish in the fold areas. There will be no scaling of the ink film on the fold.
Also when designing your document, do not place high ink loads in bleed-off areas to avoid smudging when cutting. The blade of the guillotine picks up ink particles and deposits them on the edge of the stack.
Finally, when printing, be careful when using Reflex blue and warm red inks which cause abrasion problems. The use of process colours is preferable.
Matt coated papers
Satimat is a slightly calendered silk-coated paper. As well as surface smoothness, this calendering gives good resistance to ink abrasion. Chromomat is a true matt paper and is not calendered at all. This provides its unique aspect, its deep matt finish and touch, but it is, however, a little more fragile and certain precautions need to be taken when printing and finishing.
When designing the artwork, the images or any other areas with heavy ink coverages should be ideally placed opposite each other (and not placed opposite areas of text or non-printed areas), in order to restrict marking.
During reprography, in order to avoid excessive ink loads and reduce set off, it is recommended to lower the strength of the three process colours and compensate with an increase in the black.
When printing: it is recommended not to work in high stacks to avoid risks of set off. The best results are obtained with inks specially made for matt coated papers. It is recommended to apply a protective overvarnish to reduce risks of marking. Make sure that the ink and varnish are compatible.
|Print interference, especially at the edges||Cutting debris||When cutting paper in half prior to printing, it is necessary to back knife trim the edge cut from the front of the guillotine blade.|
|Set off marking during finishing||Slow ink drying||Ink incompatible with stock. Ph and / or conductivity of fount solution incorrect. Fount levels too high.|
|Smudging||Excessive driers||Check the temperature of the IR oven (if too high the ink softens due to the rise in the stack’s temperature).|
|Ink refusal||Poor trapping when printing screen over solid areas||Change colour sequence to print screen areas under solids.|
|Ink becoming too thick||Damping defect||Check the damping level (not high enough).|
|Yellowing of paper on reverse of print Gloss or matt image from 1st side printed appears on reverse||Ghosting||There
are few solutions to this problem after printing. In some cases an
acrylic overvarnish can help disguise the ghost. If printing text and
screen on one side and solids on reverse, always print solid side
first. Leave plenty of time for drying between passes and keep stacks small. Avoid duct fresh or stay open inks.
Back Knife Trimming
When cutting coated papers in half, it is essential to trim the edge cut from the front of the blade. This will avoid debris problems during printing. Make first cut slightly undersize. Turn oversize stack and trim off edge from front of blade. Stacks will now have one mill cut edge and one guillotine trimmed edge.
(especially with multi-passes through 1 and 2 colour machines)
|Wrong fibre direction||Always use long grain paper for multi-colour printing.|
|Paper not flat
Wavy edges or tight edges
|Ensure the temperature of the paper and the pressroom are in equilibrium before opening pallets.|
|Paper not flat.
Rapid distortion of paper after opening
|Relative Humidity (RH)
|If the pressroom is too dry (RH below 35%) the fibres dry out and tight edges occur. To avoid the problem, increase humidity. If the pressroom is too damp (RH above 60%) the fibres take on moisture and the edges become wavy. Warm up the pressroom to dry the air.|
|Creasing during printing||Paper not flat||See above.
Check the presentation of the sheets at the lays as well as the adjustment of the transfer grippers.
|Static||RH too low /air too dry||Humidify the air.
Check the machine’s earth.
Install anti- static bars.
Recommended times for conditioning unopened pallets
||Temperature difference between pallet and pressroom
Effects of high humidity
Effects of low humidity
In dry conditions, the fibres shed moisture into the atmosphere, causing the edges of the stack to contract and the centre to become baggy. The corners of the stack curl upwards. In extreme cases, creasing can occur on press, specially
during backup. This is a particular problem during the winter months when the air is cold and dry. Keep the paper covered prior to printing and protect between passe
|Cracking on the fold||Splitting of the coating||It is recommended to precrease all substances 150 g and above using a rule and matrix system. The fold must always be made into the bead, never into the groove.|
|Marking during finishing and transportation
(matt coated papers).
|Ink rub.||Use inks with a high resistance to abrasion, particularly those formulated for matt coated papers, or adjust the hardness of the ink. Overprint with a compatible acrylic sealer to ensure complete protection.|
To ensure a good crack-free fold on coated papers it is recommended that all substances 150 gsm and over are pre-creased prior to folding. The crease should be made with a rule and matrix system. Once creased, the fold should always be made into the bead. Wherever possible, always put the fold in the machine direction.
This information is supplied in good faith; it is only intended as a general guide and Arjowiggins shall not be held liable for loss of damage arising from actions based on these tips.