Extrusion stretch blow molding

Extrusion stretch blow molding (ESBM) is a one-stage or two-stage process using two mold/mandrel sets where one is for preblow and the other for final blow. An extruded parison is first pinched off and blown... 

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. 

Biaxially stretched oriented PVC (OPVC) pressure bottles have been used as an alternative to PET for packaging some carbonated drinks. In this application, the level of carbon dioxide inside the bottle and the temperature at which the bottles are kept are important. Producing OPVC by extrusion stretch blow molding results in greater clarity, increases impact resistance, and reduces cost by up to 14% compared to ordinary PVC. Fruit, squashes, and edible oils are commonly packed in PVC bottles. 

Two-Stage Injection Stretch Blow Molding Extrusion Stretch Blow Molding... 

Extrusion stretch blow molding is a two-stage process using two mold/mandrel sets — one for pre-blow and the other for final blow. An extruded parison is first pinched off and blown conventionally in a relatively small pre-blow mold to produce a closed-end preform. The preform is then transferred to the final blow mold where an extending stretch rod within the blowing mandrel bears on the closed preform end to stretch it axially. The stretched preform is then blown to impart circumferential stretch. Standard blow molding machines can be converted for extrasion stretch blow molding. 

Standard Extrusion Blow-molding 2-Parison Head 4-Fold Stretch Blow Molding PVC (2) Single-parison Heads 4-Fold Stretch Blow Molding PET... 

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

The multilayer film is formed by injection molding, co-injection blow molding, co-injection stretch-blow molding or co-extrusion blow molding techniques. 

Figure 6.1 Examples of extrusion, injection, and stretch blow molding techniques...

Two basic methods are used in this process to deliver material to the processing units. These are extrusion and injection. In the next step, the preformed material is expanded to form parison. There are many commercial variations on this basic technique some of which include continuous-extrusion-blow-molding, coextrusion-and-sequential-blow-molding, and injection-stretch-blow-molding. Both extrusion and injection molding are the subjects of later discussions below, we will concentrate here on the parison formation, its processing, and the related effects. 

Films can be produced using chill roll casting. Injection blow molding and stretch blow molding are used to produce bottles. PET is also used in extrusion coating, and PET sheet is often thermoformed. 

In either extrusion or injection blow molding, the polymers in the containers are oriented because of the radial stretching that takes place in the blowing step. If desired, the mechanical or barrier properties of the material can be maximized by producing biaxial orientation, stretching the preform vertically as well as horizontally, using stretch blow molding. 

Stretch blow molding begins with the production of a preform, either by injection molding or extrusion blow molding (or rarely, extrusion alone). The container finish is formed in this step. The preform is shorter than the final height of the container. Next, the body of the preform, on a stretch rod, is conditioned to an accurate, consistent temperature, usually just above its Tg, while the bottle finish is kept cool to avoid distortion. Then, the preform is placed in the container mold and is stretched by a vertical movement of the stretch rod while air is blown through the rod to expand the bottle into its final shape, stretching it axially (Fig. 12.13). 

Technology to successfully produce multilayer injection blow molded bottles is much newer than that to produce multilayer extrusion blow molded bottles. Heinz Inc. s ketchup bottle was the first U.S. example (Fig. 12.22). The use of PET bottles made by coinjection blow molding has grown rapidly. As is the case for coextrusion blow molding, the key is production of the parison. Once the multilayer parison is produced, the remainder of the process is essentially the same as for single layer materials. Even stretch blow molding can be used. 

In-mold labeling is used most often with extrusion blow molded HDPE bottles. It has also been used on PET and PP stretch blow molded bottles, as well as on injection molded tubs. The technique also finds applications outside packaging, such as in labels that are applied directly to electronics and other consumer goods. 

In contrast, PEN meets the requirements, but more complex forming techniques are needed. PEN bottles cannot be produced by simple extrusion blow molding. PEN requires the use of the more complex two-step injection stretch blow molding process. In this process, a preform is first injection molded and then stretch blow molded to produce the final bottle. This is the same process used to produce bottles of the related polyester, PET. 

Injection vs. extrusion/blow-molding For clarity, processmg factors go hand-in-hand with the choice of a clarifier. Relatively thick-walled, injection-molded cPP homopolymer or random copolymer parts have hmits on the clarity they can achieve, perhaps down to 7%-10% haze. Only thin extruded or injection-stretch blow-molded (ISBM) cPP may achieve lower haze levels (l%-2%) that allow it to compete with PET. For one-stage ISBM of random copolymer PP, for example, newer clarifiers may work better than sorbitol-based agents... 

The intermittent extrusion blow molding process is generally used in the fabrication of large volume articles (e.g., > 20 liter bottles). An accumulator is employed to increase the parison extrusion speed (see diagram below). After the mold closes there is no additional mold movement. Refer to Injection Stretch Blow Molding. 

This is the primaiy processing technique used to fabricate hollow plastic objects, particularly bottles, which do not need a very uniform distribution of wall thickness. It is a secondary shaping technique that inflates the preprocessed plastic (usually extruded) against the inside walls of the mold with a blow pin. In addition to extrusion blow molding, injection blow molding and stretch blow molding are commonly employed. With most polymers, especially when the product size is... 

In stretch blow molding, a heated pre-formed melt is positioned in the blow mold (Figure 1.5). A center rod extends which stretches the preform with axial orientation. Blown air then expands the preform in the mold, fcwming a bottle with radial orientation. The stretch process takes advantage of the crystallization behavior of the resin and requires the pre-form to be temperature conditioned and then rapidly stretched and cooled. PET soft drink bottles are formed using the stretch method. PET bottles are also formed using extrusion blow molding. 

Processing methods extrusion, injection molding, blow molding, thin-wall injection molding, injection stretch blow molding, sheet extrusion, blown fihn, cast film, rotomolding, and thermo-forming... 

In blow molding, bottles or jars are produced by blowing, with air, a molten previously formed part. There are three types of blow molding extrusion blow molding (EBM), injection blow molding (IBM), and injection stretch blow molding (ISBM). 

Extrusion blow molding Injection blow molding Stretch blow molding... 

There are three main processes used by the blow-molding industry to supply containers and hollow products to the blow-molding market injection blow molding, extrusion blow molding, and stretch blow molding. 

Stretch blow molding is the most significant development since the development of the two piece can. This process improves produce performance, such as bottle-impact strength, cold strength, transparency, surface gloss, stiffness, and gas barrier. The bottles are lighter and less costly, and products that otherwise would not be suitable can be packaged. The process uses injection-molded, extruded, or extrusion blow-molded parisons in one or two steps. 

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