Blow moulding of containers esp. non-circular PET bottles - by blowing pressurised air through porous die forming cushion to avoid first bubble contact with mould and permit uniform stretching and orientation

摘要

To blow mould containers, gaseous, e.g. air, cushions are arranged to hold the bubble expanding from the preform, away from the mould surface where lateral slipping is required. The cushion may be formed by air flow through porous dies in the mould surface. More specifically, blowing pressure rapidly increases until time when thermoplastic deformation starts. The blowing pressure then drops briefly and then increases approximately asymptotically to a maximum. When bubble approaches nearest point on mould at time, cushion air is admitted, increasing rapidly in pressure while bubble continues to expand. When cushion pressure exceeds blowing pressure, radial expansion of bubble at this posiiton ceases, leaving cushion gap. Elsewhere, e.g. lengthwise and into wider regions of mould, expansion continues until the moulding conforms to the shape of the mould. At a suitable intermediate time, the supply of cushion air is shut off. USE/ADVANTAGE - Especially for non-circular, biaxially oriented containers, e.g. PET drinks bottles, including flat or concave sections. Avoids use of lubricants esp. for foodstuffs packaging. Permits lateral stretching of area of bubble which would first touch the mould, giving improved uniformity of wall thickness and distribution of material stretching (orientation). Increases permissible average extension near to limit for material, improving stability. Improves thermal insulation of bubble from mould, ensuring sufficient extensibility, esp. for biaxial orientation