Effect of Painting on the Mechanical Properties of Injection-Molded Plastics
Paint can have significant effects on the mechanical properties of plastic substrates. The selection of a paint system that is not properly matched to a given plastic substrate can lead to premature failure. While anecdotal accounts are plentiful, quantitative data regarding effects of coating on plastics is relatively scarce. This paper describes the effect of a high-solids acrylic topcoat paint, with either of two different adhesion promoters or no adhesion promoter, on the mechanical properties of four different plastic substrates: general-purpose acrylonitrile-butadiene-styrene (ABS), high-impact ABS, weather-resistant acrylonitrile-styrene-acrylate (ASA), and mineral-filled polyethylene ionomer/polyamide-6 blend.
Paint and plastics
QUESTION: Why paint plastics?
Color/effect not available in resin
Resin lacks UV resistance
Paint and plastics
QUESTION: What are the effects of painting on
the mechanical properties of plastics?
• Elastic mismatch
• Interfacial strength
• Film thickness
M.S. Hu and A.G. Evans,
"The cracking and
decohesion of thin films
on ductile substrates,"
• For four (4) different substrates, measure
mechanical properties in each of these six (6)
promoter 1 only
promoter 2 only
promoter 1 with
promoter 2 with
• General purpose ABS
• High impact ABS
• Weather-resistant ASA
• 10% mineral filled polyethylene
• Black topcoat:
45 µm dry film build
Cure at 93°C for 20 minutes
• Clear adhesion promoter:
5 µm dry film build
Cure at 77°C for 20 minutes
• Black adhesion promoter:
20 µm dry film build
Cure at 71°C for 20 minutes
• Notched Izod impact
ASTM D256-10 Method A
• Tension testing
Polyethylene ionomer/PA-6 blend: 50 mm/min
All other substrates: 5 mm/min
Rank ordering of effects:
Strain at break
Strain at yield
Coating effect on substrates:
For ABS and ASA substrates, strain at break
and impact strength decreased with coating.
For mineral-filled PE ionomer/PA-6 blend,
strain at break and impact strength increased
Effects of adhesion promoters/topcoat:
The effects of the topcoat and the two adhesion
promoters were different on different substrates.
When the adhesion promoters were used
together with the topcoat, the effects were not
Matching a paint system to a plastic substrate
should be done with great care.
Published data is scarce.
Testing is the best way to ensure a successful
PolyOne – Richard Baril
SABIC – Dennis Yon
LTL Color Compounders – Don Hone
PPG Industries – Ron Kalski, Dave Nale, Cari Stein
Polymer Diagnostics – Keith Mathews, Jill Moran, Katlyn Hoffman
BRP US, Inc. – Bill Barth, Rich Smock, Mike Davenport, Ben Jones,