Blow molding preforms

Stretch blow molding that employs an injection molded, extrusion blow-molded preform, or extruded tube preform... 

Extrusion stretch blow molding begins with an extrusion blow molded preform injection stretch blow molding begins with an injection molded preform. Injection stretch blow molding is the method of choice for most PET bottles, including all soft drink bottles. It is also used for PEN bottles and some PP bottles. Extrusion stretch blow molding is used for some PVC bottles. 

Polylactic acid resin pellets should be dried 4-6 hours to less than 400 ppm prior to blow molding into bottles. Blow molded preforms are injection molded with standard PLA injection molding conditions. 

Figure 2.14 Blow molding preforms, being transferred to the blow molding station. DegtiarovaViktoriia/Shutterstock.com.

Fig. 14. The H.E. IS blow-and-blow machine (85). The gob is deUvered into a blank mold, setded with compressed air, and then preformed with a counter-blow. The parison or preform is then inverted and transferred into the blow mold where it is finished by blowing.

Soft-drink bottles made from poly(ethylene terephthalate) (PET) are usuady made by stretch-blow mol ding in a two-step process. Eirst, a test-tube-shaped preform is molded, which is then reheated to just above its glass-transition temperature, stretched, and blown. Stretching the PET produces biaxial orientation, which improves transparency, strength, and toughness of the botde (54,56). A one-step process is used for many custom containers that are injection stretch-blow molded. 

When a parison or preform is inflated, it displaces the air around it within the mold. If no provision is made to vent the mold, compression of the air around the parison or preform can raise its temperature to such an extent that it can scorch the surface of the product. To avoid this problem, we equip blow molds with vents. These can consist of slit vents at the parting line between mold halves, porous plugs of sintered metal, or small holes drilled into the cavity walls. 

Injection blow molding that employs injection molded test-tube shaped preforms or parisons... 

Extrusion blow molding that uses an extruded tube preform or parison... 

The major difference between injection and extrusion blow molding is the way the soft hollow tube (called a preform or parison) is made. In injection blow molding, two different molds are used. One mold forms the preform and the other mold is used in the actual blow-molding operation to give the final shaped article. In the molding process, the softened material preform, from the preform mold, is introduced into the blowing mold and blow-molded to... 

In continuous extrusion blow molding, the preform is continuously produced at the same rate as the article is molded, cooled, and released. To avoid interference with the preform formation, the mold-clamping step must be rapid to capture the preform and move it to the blow mold station. There are various modifications of this that allow essentially continuous operation. 

Multilayered articles can be made by coinjection blow-molding or coextrusion methods. A three-layer system generally contains a barrier layer sandwiched between two exterior layers. These are actually laminar products. In the coextrusion sequence, several extruders can be used to place the material into the mold. The multilayer container is then produced from blowing air into the preform. 

Secondary shaping operation - Here a preform such as a parison or sheet is transformed into a final product using thermoforming or blow molding. 

A process that greatly improves blow molded product properties is that of injection stretch blow molding, which introduces biaxial orientation in crystallizable polymers. There are two variants of this process involving the molding of a preform as the first step. The thermomechanical paths of the two process variants are shown in Fig. 14.19. In the... 

Fig. 14.20 Schematic representation of the injection stretch blow-molding process. Step (1) producing preforms may be carried out in different location from the stretch blow molding process. [Reprinted by permission from Schmidt et al., Experimental Study and Numerical Simulation of the Injection Stretch/Blow Molding Process, Polym. Eng. Sci., 38, 1399 (1998).]...

Fig. 14.21 Schematic representation of the crystallization behavior of PET relative to the stretch blow molding process. [J. S. Schaul, Drying and Injection Molding PET for Beverage Bottle Preform, SPE ANTEC Tech. Papers, 26, 534 (1980).]...

Blow molding—A process used in the fabrication of plastic bottles and other hollow shapes a heated tube of plastic (a preform or parison) is forced against the sides of a mold by air pressure. 

Parison (preform) for blow molding, 162, 162-163,260 Parkes, Alexander, 53, 150 Patrick, J. C., 64 PC. See Polycarbonate PDMS (poly[dimethyl-siloxane]), 135-136, 138,155 Pectin, 122,130... 

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