Ah, the marriage of plastic and metal — it’s always a challenge, not the least because of the need to pre-treat the metal part in order for it to bond with the plastic part. But marrying these two materials is almost always necessary at some point in the manufacture of plastic automotive parts and plastic electrical components.
Why? Because the characteristics of the two materials are perfectly complementary: metal has great rigidity and high electrical conductivity; plastic has low density and zero conductivity. It’s a match made in parts-heaven.
In the classic process, metal inserts and plastics are securely bonded via the introduction of molten plastic through injection molding to metal inserts which have already received some type of surface treatment. Numerous factors, however, such as the specific type of metal inserts, specific plastics, the mold structure, or injection molding parameters, etc., all can have deleterious effects and interfere with stable bonding.
A new technical development, however, has just simplified combining those two materials. The Quick-10 process uses super-fast heating and cooling of metal inserts to actualize direct metal-plastic bonding through the plastic injection molding process alone, without any added surface treatment of the metal. The plastics used, however must have properties such as:
- interface affinity
- surface transferability (flowability)
- low shrinkage
… to realize good bonding. Appropriate polyphenylene sulfide (PPS) and polybutylene terephthalate (PBT) grades have been developed for this exact purpose.
One of the key factors of the Quick-10 process is an “affinity-improvement” substance that gives the metal-plastic interface enhanced compatibility while promoting maximum adhesion to the metal surface. These metal adhesion grades include 1135MF1 and 940MA for PPS and PBT, respectively. Two more metal adhesion grades, 1150MF1 and 930MA, provide added functionality.
There’s one more critical factor: mold temperature can have a dramatic impact on bonding. It’s vital that optimum molding conditions be attained such as excellent surface transferability and minimal mold shrinkage with a linear expansion rate nearly like metal.