ASK JOE POWDER
The “Ask an Expert” Column Kevin Biller
kbiller@chemquest.com
Hey Richard, Thanks for reading my article and I am glad that it helped. UV durability is mainly influenced by the primary resin in the powder coating formulation. Both polyester-HAA and polyurethane chemistries rely on a polyester polymer as the main binder component. Polyester polymers can be standard outdoor grade (1-2 years Florida durability) or “superdurable” grade (about 5 years Florida durability). For your products, you’ll want to specify the superdurable grade. Even better yet, require an AAMA 2604 (American Architectural Manufacturers Association) grade (or Qualicoat Class 2) powder. The 2604 spec requires 5 years Florida durability and the Qualicoat Class 2 requires 3 years Florida durability. I have attached copies of these specifications. As for formulators using special additives to enhance outdoor durability, the inherent performance is based on two things - using only UV durable ingredients (raw materials) in the powder formula and not incorporating any weak links or bad actors (e.g., waxes or fillers). Special
Our powder coating expert is back to answer increasingly challenging
additives don’t make a big difference especially in pigmented powder
questions from readers.
coatings. The ole adage, “You can’t make a silk purse out of a sow’s ear”. I hope that this helps. Please let me know if you have any other
Hey Joe,
questions.
My name is Richard Stange and I’m a Mechanical Engineer at
Kind regards, Joe
major fabricator in California. I just read your 2017 article, “Technology Interchange: Choosing an Outdoor Durable Powder
Hi Joe,
Coating”. I found your article very informative and feel like
We have been developing new polymers for powder coatings.
I have a better understanding on the subject. Our company
One of the most critical properties is impact resistance. Our test
designs and manufactures irrigation equipment, which includes
results have been inconsistent and vary significantly depending
metal chassis and pedestals that get powder coated for the
on substrate used. In some cases the coating passes 160 inch-
outdoor environment, which is sold all over the world. We have
lbs. and with other conditions only gets 80 inch-lbs. What could
multiple sheet metal vendors who use different powder coaters.
be the cause of this variation? And how can we eliminate these
We recently discovered that the different powder coaters don’t
variations? Thank you!
all use the same chemistry type. Some use a polyurethane-based
Rebekah
chemistry, where others use a polyester-HAA based chemistry.
Philadelphia
From your article, it looks like the Industrial and HighPerformance chemistries are what we are looking for in our
Hi Rebekah,
product for UV durability resistance. My question is this – Is the
First of all, kudos to you and your colleagues for developing new
UV resistance in powder coating based solely on the polyester-
polymers. Most advancements in powder coating technology are based
HAA or polyurethane, or is an additional “UV inhibitor” added to
on new and improved polymer chemistry. It’s tough for us formulators
the chemistry? I’m trying to determine how to best call out UV
to create new coatings without innovative polymers.
resistance for the powder coating in my drawings.
The most common impact resistance test method is described in ASTM
Appreciate your help and look forward to hearing from you.
D-2794 Standard Test Method for the Rapid Deformation of Organic
Best regards,
Coatings (Impact). The ISO-6272-1 standard covers the same test
Richard Stange
method. The values typically quoted in impact resistance are inch-
San Marcos, California
pounds (the metric centric folks use Newton-meters) and refer to the
18
N. 76 - JULY/AUGUST 2022 - international PAINT&COATING magazine
