Reducing oxygen@= diffusion by plasma-coating extruded plastics pipe - comprises polymerising gaseous monomer, e.g. ethylene@ by microwaves onto pipe surface within quartz tube in vacuum space near die for pore-free coating

摘要

Extruded plastics pipe has surface coating to reduce diffusion esp. of atmospheric O2. The coating is a void-free deposited plasma polymerisation layer. The gaseous monomer (10) is fed into a vacuum space adjoining the extrusion die (2), where a high energy electromagnetic field (8) produces free radicals and short-chain oligomers which are deposited or condensed on the cooling pipe surface, where they are fully polymerised to an adherent coating a few micrometres thick. USE/ADVANTAGE - Avoiding equipment corrosion e.g. heating pipes and vehicle brakes, and product contamination, e.g. foodstuffs esp. beer, wine, milk, and pharmaceuticals due to gas, esp. atmospheric O2, diffusion through plastics pipes and containers. Avoiding diffusion out of pipes by refrigerants and dangerous chemicals. Avoiding attack by prods., e.g. acidic fruit juices, on pipe material, leading to product contamination. Lower cost, weight and handling and problems w.r.t. stainless steel. Improved resistance to gas diffusion w.r.t. wound film, co-extrusion, lacquer or chemical deposition. Improved resistance to mechanical damage, e.g. in underfloor heating systems; not penetrated or flaked-off by impact. Negligible change in pipe dia. permits usual jointing methods.