Coextruded Bottles

For some applications, no single polymer can best deliver the desired combination of price and performance, so there is a need or desire to combine one or more resin streams in production of the finished bottle. Use of such coextruded bottles has grown rapidly. Applications range from inclusion of a layer of recycled content in laundry detergent bottles to provision of oxygen barrier in mayonnaise containers. 

A coextruded bottle is made by melting each type of resin in a separate extruder, feeding the melts into a die where they are formed into a multilayer tubular parison, and then blowing the container as usual. As with coextruded film, the combining must be done carefully to avoid blending, with attention paid to melt viscosities and other factors. When dissimilar resins are used, a tie (adhesive) layer is often required to obtain adequate adhesion between the layers. 

A very different type of coextrusion is used to produce opaque bottles with clear viewing stripes, so that the consumer can see the product level in the container (see Eig. 12.5). In this case, the separate layer, rather than extending around the container, occupies the whole wall thickness in a defined portion of the container. Typically, unpigmented resin is used, which is processed in a small satellite extruder and introduced into the die as a separate vertical stripe in the parison. Since the resin is the same type as the pigmented resin found in the rest of the bottle, no tie layer is needed. Such containers are used for motor oil, liquid laundry detergent, and other products. 

Some cosmetics containers are using HDPE/EVOH/HDPE/EVOIVHDPE coextruded bottles for better barrier performance. Others are using nylon exterior layers on ffDPE containers for added gloss. 

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Figure 12.8 Typical coextruded bottle structures, (a) for oxygen sensitive foods, (b) for laundry...

A similar problem is presented by vehicle tires and certain blow molded bottles, which must be virtually impermeable to air and other gases. An example of the use of a very impermeable elastomers is butyl rubber. Because of its impermeability to gases, butyl rubber is used as a roof coating. With plastic bottles, different layers of both coinjected and coextruded plastics (Chapter 8) can be used to fabricate the bottle to make it impermeable to different vapors and gases depending on the barrier plastic included. 

Collation trays, as used in supermarkets to transport and display products, remain one possibility for mechanical recycling but this depends on a system to identify the polymer, linked to a suitable collection system. One outlet for this material is a foam layer in coextruded cladding (439). PVC water bottle scrap has also been incorporated into the foam core of coextruded pipe. Another outlet is moulding of rainwater fittings. 

Coextrusion, e.g. a process incorporating two or more plies of a plastic, will undoubtedly find more use in flexible pharmaceutical packs. Coextrudates can also be moulded into rigid containers, bottles, tubes, tubs, etc. subject to the quantities justifying the costs. 

Figure 4. SEM Micrograph of Extrusion Direction Cross-Section of Coextruded Blow Molded Bottle Showing "Sine Wave" Pattern of Mica Platelets.

Table VII. Effect of Platelet Orientation on Barrier Enhancement - Coextruded Blow Molded Bottles...

In order to tap the commercial applications of LCP in packaging, processing must achieve efficient use of the high-performance polymer. There are many high value polymers and other materials that are used in thin layers. A prime example is ethylene vinyl alcohol (EVOH), a super barrier material used as a thin layer in coextruded film and multilayer containers such as ketchup bottles. Other examples are coatings, such as metal, glass, and polymeric coatings. LCP used in thin multilayer constructions should compete well with these other materials. 

Oriented LCP layers can be coextruded with other thermoplastics such as polyethylene terephthalate, nylon, polycarbonate, and high-density polyethylene. The primary benefit of the LCP layer is to improve the barrier properties of the container, especially under conditions of high heat and humidity, such as retorted bottles and trays. Eor example, using an LCP layer comprising 5% of the wall thickness of a container along with PET and tie layer in the other 95% will increase the oxygen barrier by more than 20 times compared with a pure PET container. A further example, below, compares the barrier properties of LCP with another barrier material, EVOH. 

Once the coextruded LCP-thermoplastic multilayer parison is formed, it can be blow molded into bottles and other containers. The orientation in the LCP layer is controlled by the counter-rotating action of the cylinders in the die, and the LCP orientation remains in the finished bottle because of the very long relaxation time of LCP. While other polymers being coextruded with LCP may... 

While many processes for using commingled plastics look at collection of bottles from curbside as the primary source of materials, they frequently combine these materials with industrial waste stream plastics, including coextruded scrap and other examples of multiresin, perhaps contaminated, materials. Other companies focus entirely on these types of waste streams. For example. Northern Telecom Ltd., based in Toronto, has a recycling facility for plastic reclaimed from wire and cable, along with materials from phone, fax, business machine, and pager equipment. The material, which contains small amounts of residual copper and aluminum, is used for truck mud flaps, flower pots, traffic stops, reflective bibs for construction workers, and other applications where high purity is not required,... 

Some years of experience also clearly show that a sound policy must necessarily combine several approaches, whereas in the field only well defined and realistic objectives must be selected. This work describes the mechanical recycling of PVC bottles and/or pipes to non-pressure coextruded three-layer pipes. In a first step the material (bottles or pipes) must be regenerated and in the second step, re-used. The coextrusion process also describes the modification of the production equipment required by multilayer coextrusion. 

Some modifications of the standard production line of coextruded pipes have been necessary to process the PVC bottle scraps under optimal conditions. 

In addition to bottles, a rapidly growing application for blow molding is the production of technical parts, such as automotive components—bumpers, ducts, and other fluid containers. For fuel tanks, a coextruded parison has polyethylene as the structural material and special barrier layers to prevent escape of polluting fumes. 

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