ACTEGA Kelstar Technical Bulletin UV Coating Intercoat Adhesion

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ACTEGA Kelstar Technical BulletinUV Coating
Intercoat Adhesion

• Intercoat Adhesion
• As the use of ultraviolet (UV) cured coatings
  increases in the graphic arts industry, so does
  the potential for problems. One subject that
  continues to be misunderstood is adhesion. If
  intercoat adhesion is defined as the binding of a
  layer of material to the next immediate layer in
  contact, then it becomes understandable that true
  intercoat adhesion does not always occur.
• UV coating chemistry has limited compatibility
  with the oils used in conventional sheetfed and
  web offset heatset inks. The UV coating will
  never rewet the inks, and therefore never really
  bind or adhere to them. Since the level of the
  oils present varies with the degree of dryness of
  an ink, including the chemistry of the ink itself
  and even the porosity of the substrate (which
  affects solvent retention and drying), the
  coating / ink interface may always potentially be
  contaminated.
• Scotch Tape Test The use of the Scotch Tape
  Test to measure intercoat adhesion and curing of
  the UV coating is still sometimes used. However,
  the test results from a scientific standpoint are
  inconclusive because the use of additives such as
  waxes and silicones change the surface
  characteristics of UV coatings and inhibit the
  ability of the tape to adhere to the UV coating.
  The Scotch Tape Test results then leave the false
  appearance of providing adhesion between UV
  coating and ink when the tape pulls free from the
  UV coating.

• Fingernail Scratch Adhesion Test The use of the
  Fingernail Scratch Adhesion Test is a good method
  to measure intercoat adhesion. Intercoat
  adhesion chemistry is complex and can be affected
  by VOC level or migration of surface active
  agents in the ink or substrate. However, because
  of the multiple layers and compatibility of the
  chemistry involved, intercoat adhesion is also
  influence by many variables including ink,
  fountain solution, aqueous primer and substrate
  selection.
• The use of current technology can provide good
  intercoat adhesion with the proper selection of
  aqueous primer and UV coating. The use of
  aqueous primer provides several benefits, such as
  the reduction of spray powder while providing a
  surface the UV coating can more efficiently wet
  and bind to. As with the oils used in
  conventional inks, additives found in both inks
  and primers can have a significant role in
  reducing adhesion. The fact the some additives
  are immediately at the surface of the ink or
  primer and cause problems quickly as compared to
  those additives that bloom to the surface later,
  postponing eventual problems only make the
  situation more difficult to anticipate and deal
  with.
• The best and most predictable intercoat adhesion
  occurs when UV coatings are used in conjunction
  with UV inks. The similarities in chemistry
  allow the two products the greatest opportunity
  to bind.
• Contact ACTEGA Kelstar at 856 829 6300 or
  info.actega.kelstar_at_altana.com for additional
  information or technical assistance.