Causes of static on plastic molded parts

[carfreak01]

Plastic molded parts have a lot of static electricity when coming out of the molding machine. Is the static electricity generated in the molding process? or do the resin has it or generates it when stored (in a box or a silo)?

Thanks,

Jose Luis Walters

 

[patprimmer]

Static can only build up after the last time the article was earthed.

I would think a moulding machine and mould should be well earthed.

Regards

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[Compositepro]

Static is generated by the process of removing the part from the mold. When two different materials come into contact, one will have a stronger affinity for electrons than the other. Upon separation one material will end up with more than its share of electrons so it is now electrically charged. The intimate contact between the plastic and the mold surface accentuates this effect. The type of plastic has a strong influence and the conductivity of the plastic determine how long it takes for the charge to bleed-off.
There are numerous products on the market to neutralize static electricity. Some are very sophisticated and expensive. The one that I have found to be very effective and inexpensive is Ion Cord.

http://www.fibraplex.com/IonCord.htm

You can also put additives into the plastic that make it slightly conductive. Carbon black is used, and also humectants that will absorb moisture from the air to make the surface slightly conductive.

 

[carfreak01]

Thanks, this information has been very useful.

 

[Demon3]

Antistatic additives are commonly added to plastics (organic additives) see for example Handbook of Plastics Additives by H. Zweifel.

Some types need some days/weeks to diffuse to the part surface after molding so that type won'tr help you. You need the kind that works right away. They work by making a polar surface that attracts water and conducts electricity well enough to dissipate static.


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