Solving dirt problems when painting plastics: Andy Thomas of CT Supplies looks at solving contamination problems

摘要

Most paint shops suffer from a small number of rejects due to "dirt" problems. Plastic finishing shops are particularly prone to defects due to the tribo-charging effect on plastic components. Tribo-charging is the build-up of electro-static charge due to friction. Most people have tried the school boy test of rubbing a balloon on a jumper to generate sufficient electrostatic charge to hold the balloon to that jumper. Unfortunately air movement over a plastic automotive bumper can generate a similar effect. Thus any airborne particles in the paint shop have a high degree of probability of being attracted to the parts to be painted. The electrostatic attraction can hold on to the particle even through an "air curtain". Automotive manufacturing paint shops go to extreme lengths to avoid dirt contamination on vehicle bodies and typically get the reject rate down below '2%. Plastic finishing plants, presumably because of these electrostatic issues can have much higher reject rates, more than 10% is not that unusual. The cost of rejects and rework cannot be over emphasised. An analysis of the rejects gives further clues to the problem. Typically more than 70% plus of the inclusions that causes rejects are fibres, which are light and prone to the effect of electrostatic attraction.