Bottle blowing

The principles of thermoplastic melt processing can perhaps best be illustrated by reference to Figure 8.1 illustrating extrusion, injection moulding, bottle blowing and calendering operations. In order to realise the full potential of the process it is necessary to consider the following factors ... 

One unfortunate characteristic property of polypropylene is the dominating transition point which occurs at about 0°C with the result that the polymer becomes brittle as this temperature is approached. Even at room temperature the impact strength of some grades leaves something to be desired. Products of improved strength and lower brittle points may be obtained by block copolymerisation of propylene with small amounts (4-15%) of ethylene. Such materials are widely used (known variously as polyallomers or just as propylene copolymers) and are often preferred to the homopolymer in injection moulding and bottle blowing applications. 

Due consideration of these principles has made it possible to process unplasticised PVC by all the standard melt processes, including injection moulding and bottle blowing, a state of affairs hardly conceivable in the 1950s. 

Since the last edition several new materials have been aimounced. Many of these are based on metallocene catalyst technology. Besides the more obvious materials such as metallocene-catalysed polyethylene and polypropylene these also include syndiotactic polystyrenes, ethylene-styrene copolymers and cycloolefin polymers. Developments also continue with condensation polymers with several new polyester-type materials of interest for bottle-blowing and/or degradable plastics. New phenolic-type resins have also been announced. As with previous editions I have tried to explain the properties of these new materials in terms of their structure and morphology involving the principles laid down in the earlier chapters. 

Molding includes bottle blow molding, and the continued move toward PET for use in soft drink and water bottles depresses growth slightly, although the trend remains positive. 

Chain orientation enhanees the rate of crystallisation, because every volume element in which a few ehain parts lie parallel forms a nueleus. This is the ease in fibre spitming, film stretehing and bottle blowing. 

VC/Polyepichlorohydrin and VC/Poly(epichlorohydrin-co-ethylene oxide) Graft Copolymers. Alloys of PVC and graft copolymers of this type with high backbone-polymer content give interesting results in the field of bottle blowing (12). The combination of transparency and impact strength that can be realized with these compositions should enable them to penetrate into the field covered at present by PVC-MBS mixtures. 

Polystyrene was the first synthetic polymer used for blow molding during World War II and polyethylene was the first material to be implemented in commercial applications. Until the late 1950s, the main application for blow molding was the manufacture of PE-LD articles such as squeeze bottles. Blow molding produces hollow articles that do not require a homogeneous thickness distribution. Today, PE-HD, PE-LD, PP, PET, and PVC are the most common materials used for blow molding. 

FEM is the only practical tool to handle the problem. Not surprisingly, this method was first applied to membranes or thin shells in the field of structural analysis, a field where, in fact, FEM was pioneered, with a much later penetration to fluid mechanics and polymer processing. Indeed, Oden and Sato (81) were the first to apply FEM to examine the three-dimensional membrane inflation problem. Two other engineering fields that apply a similar FEM approach are metal sheet forming and glass bottle blowing (82). 

Form/Fill/Seal Machine Targets Bottle Blow Molding, MP, June 2003. 

In the starch sector for example, Stanelco is understood to be developing a new starch-based biopolymer that it claims will undercut PET and PP prices, while offering a similar ease of processing in both bottle blowing and thermoforming processes. 

Both employ a preprinted transfer (up to six colours). In the in-mould process the transfer is placed within the mould prior to bottle blowing or injection moulding. During the moulding cycle the printed transfer becomes fused to the container. The printing can be produced by either screen or gravure and can be line or half tone. 

An increase in extensional flow viscosity in film blowing, fiber spinning, and bottle blowing, etc., is usually advantageous, but the change in viscosity will depend very much on the polymer structure [17]. 

The laminated resin blend technology using Du Pout s barrier resins, trade-named Selar, has been employed to produce barrier bottles. Blow-mocan Limited has used the Selar RB polyamide barrier resin in a one-step process that blends with polyethylene to form overlapping discontinuous plates within the wall system. The container can be used for many cleaning chemicals and agricultural products. 

Example of injection molding production bottle blow molding plant... 

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