Irish Printer article from JJ Stafford
Coatings for the Printing Industry
Save Money and Increase Productivity
The printing environment presents many challenges that can sap the printer's ability to remain productive and to cut costs. There are mechanical issues with the flow of materials at various stages of completion through conveyor systems and chutes, against sliding plates etc. The environment is full of chemicals that are not only difficult and costly to clean, but sometimes corrosive and harmful to machinery and equipment.
However a vast range of coatings has been developed to deal with these issues. These coatings include polymers, ceramic and metal coatings that provide a choice of properties that can help to reduce costs and increase productivity.
The increase of water-based technology and the variety of substrates, inks, coatings, and adhesives that form today’s packaging place great demands on press drying and cooling systems. Should press tolerances be exceeded, even momentarily, undried inks and coatings form deposits on roller surfaces, causing print defects and costly cleaning stoppages. The excellent release properties of plasma coatings have proved invaluable for increasing wear resistance minimizing deposits on print contact rollers.
Special Coatings For Metallic Inks
Metallic inks such as gold or silver are easier to clean off a coated surface than a bare metal surface, but might still leave a residue. Often this residue requires the use of solvent to remove it; not much solvent perhaps, but in an environmentally friendly factory the use of even small quantities of solvent will be avoided if possible. Fortunately there are available special coatings that avoid residues from metallic inks for a small price premium that pays for itself in savings of labour, materials and waste disposal.
Improved Colour Print Quality
A colour change is a major source of downtime. The ink dries on the pans, then the pans must be scraped and washed before a different colour ink can be used. This can take hours. The process can be reduced to minutes by coating the ink pans; thereafter, drain the pan of all ink, and simply wipe the residue with a damp rag. Not only is the pan cleaning time reduced, but so also is the surface tension, and this helps the ink to stay dissolved more easily for a more homogeneous colour and a better print product.
A Swedish label printer achieved “Zero Defects” by having a plasma coating applied to the idler and waste rewind rollers on their label printing machines. Now label stock which has adhesive on the edges can no longer stick to the rollers. The tolerances for applying the ink have become much tighter, and the improved ink registration and printing process have led to a higher label quality. Costly downtime due to labels jamming has been eliminated and the equipment is also more durable thanks to its hard release surface.
Quicker Ink Changes
In a sheet-fed offset press, ink is poured into the ink duct at the top of the inking system and flows from there into the inking system. Every time the ink is changed, the ink duct has to be cleaned. Sheet-fed offset ink is tough to remove. Even very small traces of the old ink cause waste because when the new ink is mixed with the old, the printing quality is affected. By applying the appropriate coating to the duct, less time is needed for ink changes and the risk of cross-contamination is minimised. Employees can change the ink quickly and with little effort, and the reduction in downtime increases productivity.
Hardness and Durability
Laminating rollers require non-stick properties and good traction attuned to the film to ensure safe and reliable web transport. It is also important that the surface structure of the roller does not damage the delicate film, and must also be resistant to wear even when very abrasive substrates are processed. Plasma coating can lend all of these properties.
Its outstanding non-stick properties prevent deposits of sticky substances. There is no residue on the laminating roll, even when it comes into direct contact with the adhesive. Product deposits around the edges can be removed with a damp cloth. The spherical surface structure of the coating ensures that the film material is guided precisely but is not scratched. The high degree of hardness (70 HRc) ensures a long operational lifetime.
Because of the fragility of tissue paper, perfect traction is required on both the draw and winding rolls. These pull the tissue from the stock roll and feed it onto the cardboard core to create the final product. These two rolls are very high-wear areas due to the stop/start nature of the process. They also become less effective from the build up of hot melt adhesive within the traction area. Plasma coatings can solve the three requirements of perfect traction, high-wear, and hot melt non-stick.
Reduce Damage to Rollers
Ink and varnish builds up on idler rollers, and normally can be removed only by scratching it off. This leaves grooves on the roller surfaces. A high quality polymer coating can prevent such build-up almost completely. It is easy to clean the roller surfaces from time to time with a rag soaked in solvent, without scratching the surfaces.
Cleaning/Maintenance of Ink Pumps, Cross Contamination
Ink pumps tend to become clogged up with dried ink and the printer cannot strip off the dried ink to carry out maintenance. By coating the pump the ink doesn’t stick to it, which means no clogging up. This means a cost saving to the printer because any maintenance is easy to carry out and can be completed in house. Also, the ink can easily be hosed off with water, which means the pumps can readily be swapped from one colour to another without cross contamination.
Increase Up-Time on Varnishing Equipment
The cleaning of varnishing stations takes a lot of time and labour, and is not a popular task. To minimise this costly downtime one manufacturer opted for a polymer coating. The coating creates a wax-like surface, which prevents the build-up of residue on the surface of the varnish tray. This cuts down greatly on the time and effort needed for cleaning and therefore returns the equipment to production more quickly.
Reduce/Eliminate Cutting/Abrasion Damage, Increase Safety
A plasma coating can increase the hardness of roller surfaces, reducing abrasion damage and facilitating the use of cutter knives and other sharp instruments against the face of the roller. Use of these coatings for the production of plastic film can eliminate the need for costly renovations caused by knife scratches on the rolls. Production runs more smoothly as the occurrence of scratches used to cause the plastic film to twist and curl, resulting in operational interruptions. Prevention of injuries due to abrasions on the rolls has also lead to greater safety for the machine operators.
Increase the Efficiency of Conveyor Systems
An area not often thought about is the equipment used to convey the product around the factory. Polymer coatings are excellent for the conveyor side guides and rails for low friction, and plasma coatings are ideal for the driven conveyor rolls for traction without damaging the conveyed material.