Plastic product processing technology-pre-treatment of coating!

Unveil groundbreaking advancements in plastic processing technology, emphasizing coating pre-treatment that enhances manufacturing efficiency and elevates product quality. Discover innovative techniques designed to optimize surface preparation for superior adhesion. Stay at the forefront of the industry with our expert insights and elevate your operational standards! Read more to explore!

Pretreatment includes degreasing of the plastic surface, that is, cleaning the oil and release agent on the surface, and activating the plastic surface, the purpose is to improve the adhesion of the coating.

Degreasing

Degreasing of plastic products. Similar to degreasing of metal products, degreasing of plastic products can be done by cleaning with organic solvents or degreasing with alkaline aqueous solutions containing surfactants. Degreasing with organic solvents is suitable for cleaning paraffin, beeswax, fat and other organic dirt from the plastic surface. The organic solvent used should not dissolve, swell or crack the plastic. It has a low boiling point, is volatile, non-toxic and non-flammable.
 

Alkaline aqueous solutions are suitable for degreasing alkali-resistant plastics. The solution contains caustic soda, alkaline salts and various surfactants. The most commonly used surfactant is the OP series, i.e. alkylphenol polyoxyethylene ether, which does not form foam and does not remain on the plastic surface.
 

Surface activation

This activation is to improve the surface properties of the plastic, that is, to generate some polar groups on the plastic surface or to roughen it so that the coating can be more easily wetted and adsorbed on the surface of the part. There are many methods for surface activation treatment, such as chemical oxidation, flame oxidation, solvent vapor etching and corona discharge oxidation. The most widely used one is chemical oxidation treatment, which often uses chromic acid treatment solution, and its typical formula is 4.5% potassium dichromate, 8.0% water, and 87.5% concentrated sulfuric acid (above 96%).

Some plastic products, such as polystyrene and ABS plastics, can be directly coated without chemical oxidation treatment. In order to obtain high-quality coating, chemical oxidation treatment is also used. For example, after degreasing, ABS plastic can be etched with a relatively dilute chromic acid treatment solution. Its typical treatment formula is 420g/L chromic acid and 200ml/L sulfuric acid (specific gravity 1.83). The typical treatment process is 65℃70℃/5min10min, water washing, and drying. The advantage of etching with chromic acid treatment solution is that no matter how complex the shape of the plastic product is, it can be treated evenly. The disadvantage is that the operation is dangerous and there is a pollution problem.