Akulon (PA6 and PA66)
The relatively high heat deflection temperature
and solvent resistance of
Akulon PA6 and PA66 make them excellent resins for paint applications.
However, the ability of polyamides to withstand the required curing
temperature of the paint should be checked. Acceptable mold release-agents and
moisture levels should be ascertained.
Stanyl (PA46)
Stanyl
does not usually require any form of pretreatment. Primers applied for
polyamides used for outdoor applications and for those cases where high gloss
and/or extremely good adhesion is required, are generally based on
two-component isocyanate systems. Coating the Stanyl part in the dry-as-molded
state increases the adhesion of the lacquer to the substrate. Suitable
paints/lacquers for Stanyl are based on:
- nitrocellulose
-
vinyl chloride copolymers
- polyisocyanate resins
-
polyurethane resins
- formaldehyde/alkyd resins
These coatings are recommended for Stanyl, provided that the temperature
resistance of the lacquers is similar to that of the base material.
Reinforcements and flame retardants used for Stanyl can influence the adhesion
behavior of the lacquer to the substrate, which can necessitate a primer step.
Arnite (PBT and PET)
Arnite can be coated with practically all known coating
systems. The chemical resistance of polyester is so good however, that these
coatings generally have a poor adhesion to the surface of the part. A primer
should be used for all standard coatings.
Standard coatings for metals normally have a low elasticity compared to
plastics, which may lead to reduced impact strength. An elastic primer that
serves as a buffer between the part and the topcoat can help to reduce
premature failure. Highly elastic PUR coatings are especially suitable for
retention of properties of elastomer-modified Arnite.
The high heat resistance of many Arnite types makes them suitable for on-line
top-coating of automobile bodies with standard coatings.
Surface preparations, like sanding or filling are normally not necessary, but
cleaning of molded parts is generally necessary.
Arnitel (TPE)
Arnitel is easily coated, provided that no silicone
containing mold releases agent or other products with an adverse effect on
adhesion are used during the injection molding process. No special adhesion
promoters are necessary. Most paints are based on a two-component PUR system
as manufactured by Mankiewitz, ISL, Herberts, Peter Lacke, Wörwag, Beckers etc.
Xantar (PC), Xantar C (PC + ABS) and Stapron E (PC + PET)
If no mold-release is used and the parts are not touched with bare hands, the
only necessary cleaning operation might be blowing with clean air.
Cleaning with a compatible solvent is necessary if parts have been
contaminated with oil, grease, mold-release and other foreign materials.
A variety of conventional as well as waterborne paints has been developed for
Xantar PC and blends. Common types include:
- Acrylic
-
Epoxy
- Polyester
- Polysiloxane
- Polyurethane
It should always be checked that the paint system is not too aggressive.
Organic solvents may cause stress cracking. Chlorinated and aromatic solvents,
as well as ketones, should generally be avoided, although they may sometimes
be used in other solvent systems as adhesion promoters to etch the surface.
Solvents should evaporate easily and leave the painted part completely.
Waterborne paints and paints based on aliphatic hydrocarbons (mineral spirits,
heptane, hexane and alcohols) are generally compatible with PC.
Second-surface painting of transparent parts is a way to protect the paint
layer with a clear layer of tough PC. The front side of the part is covered
with a mask and the reverse side(second-surface) is painted.
Special coatings with glass-like optical properties have been developed. These
offer a significant improvement in chemical and/or scratch resistance, or
reduce yellowing under the influence of UV light. Hard coats can also be
applied on opaque parts to give them a wet-glossy appearance. Silicone and
acrylic hard coats are most widely used. The hard coat system commonly
consists of a primer and a topcoat.
Hot curing temperatures up to 120ºC (250ºF) are commonly used for Xantar and
its blends.
