This rubber coverings used on Offset inking rollers where UV inks are used exclusively. The chemistry of UV inks creates a unique set of conditions making conventional Offset roller coverings questionable in performance at best. While some UV inks are very mild in their effect on conventional coverings, most attack these covering severely, causing swelling and softening. Consequently it was necessary to find roll covering compositions compatible with UV printing inks. The specific chemistry used in UV printing inks is based on acrylates. Acrylates react to UV energy causing them to cross link or cure, or in the terms of the printer to dry. Acrylates are very polar, whereby conventional inks are based on vehicles which are non polar in nature. Thus Nitrile or Nitrile/PVC compositions which work very well conventional inks are unsatisfactory for continuous use with most UV inks. These compositions swell and soften quickly and severely.
Until now EPDM type coverings have been used with UV inks with mixed success. As long as the coverings are harder in nature, e.g. 40 durometer, EPDM coverings are satisfactory. However, printers want softer rollers to achieve better performance or better printing. When softer EPDM compositions are used they prove to be unstable due the high amount of plasticizers that must be incorporated into these type of polymers to reduce the hardness. While the EPDM resists the UV inks, the plasticizers in the composition are readily extracted, causing the rollers to get harder and to shrink, and usually uneven across the face of the roll. The softer the EPDM compound the worse this problem becomes.
We have developed a unique blend of polymers designed specifically to work in conjunction with UV inks, which does not exhibit the phenomena of plasticizer extraction encountered with EPDM based polymers. The result is a material which resists UV inks, prints well, and is stable in its working environment.
This new UV roller covering material is not suitable for conventional inks or roller washes used on conventional inks. In fact it is only suitable for presses using UV inks exclusively.
For printers who are switching back and forth between UV and conventional inks the selection of a covering becomes more difficult. However, our NB-Series compounds based on Nitrile rubber and PVC resin are an excellent compromise and have been very successful in this dual environment. The NB-Series compounds are excellent in conventional inks, but not particularly well suited for continuous exposure to certain UV inks.
To highlight the advantages of this new material are as follows:
· Dimensional stability in a straight UV ink environment
· Hardness stability in UV inks
· Excellent resiliency
· Excellent ink transfer characteristics and printability