Stretch-blow-molding

PLA bottles are formed by injection stretch blow molding (ISBM). This process induces biaxial orientation of PLA bottle in the axial and hoop directions, which results in much improved mechanical and barrier properties compared to injection molded PLA. The molecular orientation induced during the ISBM process decreases the effect of aging by stabilizing the polymer free volume [21]. The crystallites 

FIGURE 14.14 Injection stretch blow molding of PLA bottle. 

PLA exhibits strain hardening when stretched beyond its natural stretch ratio. This self-leveling phenomenon is desirable for blow molding of preforms to minimize wall thickness variation. To exploit the self-leveling effect, the preform must be designed to match the target bottle size and 

Since the stretching behavior of PLA is similar to PET but not entirely identical, conversion of materials using existing PET preform designs may be feasible, although design modifications are often required to achieve an optimized bottle thickness distribution. For example, PLA preforms have a tendency to shrink much more during reheat than PET 

FIGURE 14.15 Thermal history of PLA polymer during single-stage and two-stage PLA bottle manufacturing. 

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. 

With the increase in the recent environmental awareness, there is an improved interest from the food industry to replace the existing non-biodegradable thermoplastics with PLA for certain beverage products. PLA bottles are predominantly used for beverage containers, which are not sensitive to oxygen. While barrier properties of PLA bottles may be improved by various technologies, their implementation is currently limited due to higher production costs. 

Injection stretch blow molding (ISBM) is an extension of injection blow molding with two modifications (a) the preform is significantly shorter than the bottle and (b) a stretch rod is used to stretch the preform in the axial direction. This process became known in the blow molding industry with the introduction of plastic or PET soft drink bottles. 

Many of today s plastics may be suitable for only one or for just a few of the above-listed processing methods. 

The type of product contemplated will play a large role in determining the method of manufacturing. The following discussion will describe some of the advantages and disadvantages of the various methods. 

Processing Ais csttegm p mdudes compress transfer, or injection molding of H nK is orth raieitl stic.  

This book will be concerned mostly with designing products for injection molding, but, before continuing,we should etminder some of the other plastic processing method used. 

In extrusion blow wMchiS atiihible Only for e lJl t DE iplasticS, cutlangtbs 

Thermal conditioning is the next step of the multilayer preform production. The purpose of thermal conditioning of a given preform is to provide the necessary temperature distribution in a preform. After leaving the injection mold and undergoing cooling process, the preform has a cross-sectional temperature distribution of an upside-down U-shape, which means that the middle of the preform wall shows higher temperatures than the two outside skin-layers. 

Since PET stretch properties are influenced by the temperature level above the glass transition point of PET, the preform requires more even temperature distribution, otherwise the middle layer will stretch at a different rate from the skin-layers. Thermal conditioning can be carried out by allowing the preform to equilibrate before stretch-blow-molding or by applying thermal energy from the 

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Injection stretch-blow molding may be performed on a single one-stage machine in sequence or on two independent sequential two-stage machines. PET carbonated beverage botties are usually produced by injection stretch blow molding. 

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. 

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

Figure 14.4 Schematic diagram of stretch blow molding ...

Injection-production wells, in soil and ground water treatment, 25 835 Injection stretch blow molding, of food packaging, 18 50-51 Injection wells, 18 613... 

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

Single-screw extmsion in general is the most important conversion process for biodegradable plastics. Only injection-molded and injection-stretch blow molded rigid containers like closures and bottles are not produced by a continuous extmsion process. 

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

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... 

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