What are the best rollers to use for UV printing?
UV inks for commercial offset printing have been in the spotlight in recent months with a growing number of dedicated UV offset presses entering the market.
These include new sheetfed presses, such as the Komori H-UV technology, which give printers to ability to use UV inks without many of the drawbacks often associated with UV printing such as excessive heat and ozone generation.
As a result, press operators get all the benefits of using UV inks, such as instant drying, vibrant colours and the ability to print on a wide range of substrates, without having to deal with the unwanted by-products of the process.
Locally, too, there is a greater use of UV inks on newspaper presses as printers attempt to improve the quality of their coldset production and compete for a slice of the commercial heatset market.
UV inks are not new. They have been used in narrow web and packaging applications for many years, particularly on plastics and non-absorbent substrates. What is new though is the take-up of UV in day-to-day commercial applications as a replacement for conventional offset inks.
What challenges does this pose for the management of a press’s rollers?
In part this depends on how the press is used. If it is used purely for UV inks and nothing else then it makes sense to use rollers that are specifically designed for this purpose.
Typically these are covered with EPDM (Ethylene-Propylene-Diene-Caoutchouc) which is chemically resistant to UV inks.
For UV specific printing, Böttcher offers the Stabilo UV 725 40 and 726 40 compounds, both of which are used in UV printing applications the world over and by leading press manufacturers as original equipment on their UV presses.
For the dampening forme roller, Böttcher recommends the special 134 25 compound roller which combines good dampening characteristics with chemical stability against UV inks.
The situation is different, however, if the press is used to switch between UV and conventional ink printing.
This is because the two types of ink use very different chemistries. If you use conventional inks on an EPDM covered UV roller, the effect can be catastrophic with severe swelling.
Alternating between UV and conventional inks can have a cumulative effect on rollers, causing both swelling and shrinkage at the same time. This might seem like an ideal situation with one cancelling out the other but it’s not as neat as that. In fact the end result is double the trouble and can quickly create an unmanageable maintenance problem.
The goal then is to use a rubber compound that is resistant to both swelling and shrinkage for both types of chemistry used.
In this regard, Böttcher has led the industry with its award-winning Chameleon series rollers available as 471 38 in 38 Shore A durometer and as 171 25 in 25 Shore A durometer.
For dampening rollers in dual purpose applications, the 134 25 compound, which can also be used in 100% UV printing, is recommended.
When changing from UV to conventional inks with dual compound rollers, the correct wash-up procedure is vital. Your local Böttcher representative has all the information about the necessary steps to take.
As with all offset processes, regular preventative maintenance will help to maintain the surface of the rollers and reduce any tackiness caused by the UV inks.
UV inks offer a number of attractive benefits for offset printers looking to improve the productivity, quality and versatility of their print output but, as ever, there are technical challenges too.
Using the right rollers for the job from a reputable manufacturer will go a long way towards addressing those challenges.
For more information about rollers for UV print, check out the product specifications here.SHARE THIS: