Page 305 - Engineering Plastics Handbook

Polyamide-imide (PAI) 265

have great strength-to-weight ratio, and polyamide-imide compounds
are often used for metal replacements. Some of the unique areas where
polyamide-imides are used are illustrated below.

Coatings
Fluorosurfacing. How do you answer the question, “If nothing sticks to
polytetrafluoroethylene (PTFE), how does PTFE stick to the metal of your
nonstick frying pan.” The answer is often polyamide-imide. While other
lower-cost, lower-performing high-temperature polymers such as poly-
phenylsulfide (PPS) and polyethersulfone (PES) are often used as fluo-
ropolymer binders, polyamide-imides are recognized as the best-performing
polymeric adhesive used in the high-temperature fluorosurfacing market.
Cookware and bakeware coatings are well-known high-temperature
nonstick applications. In addition, many other low-friction, abrasion-
resistant, and high-temperature industrial coating applications use fluo-
ropolymers in conjunction with high-temperature polymer binders. The
polyamide-imide is formulated into the primer or first layer of a fluo-
ropolymer coating. This layer provides the adherence to the metal sub-
strate and to the subsequent fluoropolymer layers or to itself in a
single-coat system. With a glass transition temperature of 280°C (536°F)
and a decomposition onset temperature of over 450°C (842°F), it can read-
ily handle the typical cookware temperatures. The high adhesive strength
and high modulus of polyamide-imides resist scratching and gouging often
seen with lower-priced nonstick cookware.

Friction and wear applications
A prime example of where polyamide-imides enjoy prominence is in fric-
tion and wear applications. This means not only in a system where the
polymer components are meant to operate with low-friction and low-
wear characteristics, but also in new applications such as brake pads and
abrasion wheels, where the operating conditions require low wear with
high friction, a truly demanding scenario. Polyamide-imides can achieve
this due to their high softening temperature and retention of strength,
stiffness, and compression properties at elevated temperatures.

High-speed bobbins. The critical component in today’s commercial lock-
stitch sewing machine is the rotary hook and bobbin (Fig. 12.11). These
parts traditionally have been manufactured out of stainless steel, which
requires constant lubrication and stitch tension adjustments. Both can
play havoc with operator productivity and stitch consistency, particularly
with lighter-weight or delicate fabrics. Hooks and bobbin baskets made