Multi-layer blow mouldings

Multi-layer blow mouldings, give the process added versatility by allowing the use of layers of different materials that can be tailored for purpose and economy. Multi-layers also provide a means of incorporating recyclates and masking the inherent colour of the recyclate itself. For example, consider a two-layer bottle structure that used blue virgin material as the outer visible layer and black recyclate as the inner layer. If you actually looked into the bottle you would see the black recyclate material, but all of the outer surface would be blue. 

The multi-layer article is made using moulds between which a cavity clearance is freely set. A skin material lined with foam is placed between the upper and lower moulds and molten PP containing a chemical blowing agent is supplied through a resin melt conduit in the lower mould when the cavity clearance is between (C plus 15) mm and (C plus 50) mm, where C is the thickness of the skin material lined with the foam. The upper mould is lowered at a specific rate and the molten resin is pressed at a specific pressure to fill the cavity ends with the molten resin to complete the moulding of the resin body. The body is pressed for a certain time to form a skin layer, the upper mould is lifted up to decrease the compression pressure of the skin material lined with the foam to a pressure lower than the blowing pressure of the PP resin to form and solidify the foamed body, the upper mould is lowered to apply pressure to the moulded article and finally the article is cooled in the mould. 

Polypropylene (PP) bottles have the advantage that they are inherently hot-fillable (at 85°C) and retortable to 120°C. The bottles are normally extrusion blow-moulded, and can also be made with multi-layering to include barriers against oxygen permeability. This technology is commonly used for sauce bottles and juice products. Since most of the bottles are of an oval shape, product contraction resulting in volume reduction is countered by allowing die bottle to become more oval under the effects of vacuum. 

Among the latest techniques is the Japanese Cuius blow moulding process which produces a preclosed tube from an extrusion process. It is argued that the absence of a base pinch off eliminates the weakest part of a conventionally moulded bottle. The process is suitable for single layer and multi-layer bottles with a wide variety of shapes. 

Any recyclate derived from multi-layer mouldings will consist of a combination of the materials used to make up the individual layers. This does not usually present a problem as the layers are all of suitable properties for blow moulding and compatibilised with each other. 

Multi-layer extrusion blow moulding Complex Inflation Closed Single layers Very low... 

Injection blow moulding is commonly used to produee eontainers sueh as PET earbonated drinks bottles. In this method, preforms are injection moulded and then inflated in a separate operation. Core bars are used to transfer mouldings from the moulding station to the inflation station. Multi-layer for extrusion blow moulding has been practised for some time with nine or even more distinct layer configurations possible. Multi-layer with injection blow moulding is a newer development. 

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