New Advances in UV-Curable Soft-Touch Coatings
August 2016 www.coatingsworld.com Coatings World | 55
Experimental
Table 1 shows a base soft-touch coating
formulation. Silica was added as both a
surface additive to impart soft feel and as
a matting agent. The acrylate resin was
dissolved in solvent to reduce the viscosity and to provide enough shrinkage to
allow for the migration of silica to the
film’s surface, which is necessary to reduce friction and impart a soft feel. 5
After applying the formulations, the
panels were dried for 15 minutes at 60 °C
to remove the solvent. The coatings were
then cured with two mercury arc lamps at
400 W/in and a belt speed of 50 fpm resulting in a final film thickness of 2 mils.
The panels were allowed to stand overnight before testing for abrasion, solvent,
food stain, sunscreen, and insect-repellent
resistance, pencil hardness, and adhesion.
Experienced observers rated the feel
of the panels by type and quality. We
divided the range of observed feel into
three regions: rubbery, velvety, and silky.
Rubbery describes a coating close to rubber, which has more grip (less slip) than
a silky (silk-like feel) coating. A velvety
coating has a slip/grip feel between that
of rubbery and silky. The observers also
rated the quality of the soft touch on a
scale of one to five, with one being a poor
match and five being an exact match to
the coating’s respective feel type.
Results And Discussion
In our initial screening, we used difunctional urethane acrylate oligomers (UA)
to mimic the softer polyol regions in the
traditional two-part systems and trifunctional acrylate crosslinkers (M) for the
harder isocyanate regions. 4 We found
that UA5:M1 at 60: 40 created a good
silky feel with improved durability over
the conventional two-part urethane system tested. By reducing the amount of
crosslinker, we were able to achieve a velvety feel, but the durability of the coating
decreased significantly (Table 2). Since a
reduction of crosslinker alone cannot be
used to change the feel type while maintaining durability, we set out to design
new urethane acrylates and crosslinkers.
The new difunctional urethane acrylates UA6 and UA7 were evaluated
in the same way as UA5 by varying the
Table 2: Adjusting feel type with crosslinker concentration.
Figure 2: Properties of UA6 and UA7 as a function of crosslinker content.
Figure 3: Properties of UA6 as a function of crosslinker content.
