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Question and Answer

UV Coatings and Inks

by Staff

May-June, 2006
As with other printing and finishing processes, the performance level of UV inks and coatings has continued to improve over the past few years. Both can run at much higher speeds than ever before and there are now an array of choices available that can complement a variety of printed materials.

InsideFinishing called upon a few industry experts in the field of UV coatings and inks to help catch us up on what is available and to answer questions on working with these processes in relation to foil stamping.

1. What specific steps should be taken when foil stamping over UV inks and coatings?
In regard to UV coatings, it is generally better to foil stamp prior to the final UV coating, thereby eliminating the chemical bonding issues related to the foil adhesion coat, and the possibility of it not stamping to the surface of the UV coating whatsoever. However, this is not always the desired look the customer wants to achieve. Foil stamping over UV coatings is very difficult and at times, impossible. However, if you work very closely with your foil supplier and UV coating supplier, a measure of success can be obtained. Most foil suppliers will have a foil series formulated specifically for UV or aqueous coatings. The success of the foil product depends on the dyne level (surface energy) of the UV coating. For the very best results, a dyne level of 38 dyne/cm or higher will yield acceptable results (the dyne level is one decisive criterion for measuring the adhesion quality of foil, printing inks, and glue when applying it to plastic, coatings, film, and paper). UV coatings are available that can provide the dyne level necessary to foil stamp over them. However, in most cases, you will give up some of the high-sheen associated with UV coatings by using a coating that is formulated to accept foil.

The brilliant decorative look of a foil product applied to UV inks can have a dramatic impact on the printed page. The key to success is making sure the UV inks are fully cured on the sheet before a successful foil stamping run can be accomplished. The following simple guidelines can ensure that the inks properly dry:

  • Utilizing UV plates that are grained with HNO3 (Nitric Acid) will provide a better ink to water balance than the plate that is grained with HCL (Hydrochloric Acid). The HNO3 plate has a very fine porous structure to carry more fountain solution.
  • A non-polar blanket made of EPDM or Butyl Rubber material will provide better print quality.
  • Compressible blankets also can provide a smoother stripping action as the blanket separates from the sheet or web.
  • Temperature-controlled ink rollers and ink fountain agitators offer a good solution for premature photo-initiator reaction.

The true measure of success comes from the ink being fully cured. So a good maintenance program is a plus – one that includes photo-initiator curing lamp replacement.

Stamping over UV coatings and inks can at times be like swimming in a deep dark abyss. It is recommended to set up in-house print trials to qualify the best ink, coating, and foil. Generally, a good rule of thumb for quality stamping when stamping over UV coatings or inks is to remember that medium to fine line type fonts will stamp with greater success than medium to solid coverage designs. Very large image areas can cause more gassing and picking problems and may not provide a quality stamp even at a higher dyne level.

2. Are there special UV coatings that will accept hot stamping foils?
Yes. Like most foil companies, ink and coating suppliers will have a proprietary formulation that is supplied for the purpose of foil compatibility. For UV ink applications, there is a very good product formulated as a film prep coat. This prep coat is an excellent tool in the rotary foil environment for problem films when using UV inks. When the substrate surface is improved for printing, it also is improved for foil stamping, so the prep coat can improve the ability to apply the foil as well. Most suppliers will have a formulation for this purpose.

However, it is always a good idea to remember that the success of this process depends on formulation parameters and the experience of the foil stamping operator. Even if the dyne level is above 38, adhesion must be accomplished through the correct temperature, pressure, and dwell time on press.

3. Are UV inks the best choice for overprinting foil?
UV ink technology is an excellent choice because it removes the cure time associated with conventional inks. Most overprinting jobs involve a medium to large solid area to be overprinted (especially with a refractive overprinting job). The ability to dry the UV inks quickly in a UV dryer in-line provides less possibilities that the ink will smear or not dry properly over the foil stamped area. Most commercial printers would love to stage a sheet run for 48 hours before completing the final run. In today’s competitive world, excessive time for staging and waiting for ink to dry is not a possibility. Because of this, the UV process is gaining popularity for all types of printing and finishing situations.

4. What are the advantages of using UV coatings and UV inks today?
UV coatings provide a gloss level that is substantially higher than conventional coatings and also offer abrasion and chemical resistant properties. When a high-gloss, protective coating is of utmost importance, UV is usually the best choice. The quality of the coatings and the speed and safety of applying UV coatings has continued to improve while the cost of the machinery and the application of the process has decreased. In addition, UV technologies now have been declared by the Environmental Protection Agency (EPA) as a ‘Best Available Control Technology’, a designation for processes that reduce emissions the most when compared to other similar processes.

UV inks provide the commercial printer many advantages over conventional inks. Because UV inks do not evaporate like conventional inks, 100 percent of the ink that is applied remains after the ink is cured. This helps create very crisp, fine line work with excellent opacity. UV inks also have great resistance to rub, chemicals, and provide excellent gloss qualities, which work very well with foil stamping. However, UV inks are not the answer to every application and do have some drawbacks. Because the ink will not dry without curing, it does create a mess for the pressroom and other areas. UV inks also can cause skin irritations and allergic reactions in some cases. Direct contact with the skin should be avoided.

InsideFinishing would like to provide a special thanks to Jim Kingsby of ITW Foilmark (816-564-3527) for his assistance with this article, and also to David Samide of Prime UV Curing (630-681-2100) and Lee Bradley of Amalgamated International (631-391-4577) for their assistance.