Blow molding development

Further Blow Molding Developments of PET/PEN Blends Bottles, by Luc Desoutter, Group Sidel. Presented at Bev-Pak America 95. 

Polymer scientists and engineers have developed a wide variety of processes by which to convert polypropylene into useable articles. These processes include fiber-spinning, production of melt blown and spun bond non-woven fabrics, film production, blow molding, and injection molding. The following sections describe these processes and the resulting properties of the product as a function of the process. 

Blow molding uses compressed air to blow and expand a hot plastic tube ( rubbery melt ) in a female mold cavity, until the plastic conforms to the walls of the mold. This has developed into a major way to produce plastic bottles, and also more specialized hollow shapes such as fuel tanks, seat backs, tricycles, surfboards, and so on. The leading material is HDPE for milk, water, and household chemicals. Second largest is PET for carbonated beverages. A number of other thermoplastics are blow molded in smaller amounts for more specialized uses. 

An important development in screw design was the barrier screw. The primary reason for a barrier screw is to eliminate the problem of solids bed breakup for more efficient melting. They have been around for over a quarter century. Original developments were for extrusion, but latter they were used to solve problems in injection and blow molding. There are many different patented barrier screw designs that under the broad claims of the Geyer or Uniroyal U.S. Patent No. 3,375,549 that expired in 1985.3>143... 

Many grades of polyethylene are used in food packaging, e.g., blow molded bottles for milk and blown film for wrapping meat and poultry. In the EU, the USA and other developed countries, the resin must satisfy governmental regulations for food contact. In the USA, the resin (including additives see Chapter 8)... 

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