Coextruded layers

Some packaging applications may be particularly sensitive to styrene or other volatile components. SBC and crystal polystyrene blends, even with low residual monomer levels in the polystyrene, may be unacceptable for these applications. In this case one possible solution may be to co-extrude a thin food contact layer on the surface of the blended sheet. Studies have indicated that by co-extruding a thin layer of crystal polystyrene on the surface of an SBC and crystal polystyrene blend, the styrenic volatiles and the odor can be significantly reduced. However, the downside is that the added layer of crystal polystyrene can serve to make the blended part more brittle. Another option that could reduce odor, but not have a deleterious effect on impact, is a thin coextruded layer of PETG [20]. 

PP has inherent good barrier properties and high clarity, in addition to proper radiation resistance. Properties which made PP one of the best candidates in medical devices and packaging applications (parenteral nutrition and dialysis films, blister packaging and flexible pouches, syringes, tubing, hospital disposables, test tubes, beakers and pipettes). Medical grade PP is used mostly as blown, cast films and also as coextruded layered structures. 

The versatility of the feedblock has made it the most popular flat-die coextrusion method. Large nmnbers of layers may be coextruded, layer structure may be readily altered with interchangeable modules, and thermally sensitive... 

Point 2 on the flowchart represents the second area for assessment, a full scale trial. The full scale assessment is essentially a confirmation trial, that may immediately precede the production run. Minor changes in blends or coextruded layer ratios may be made at this stage. Sensory quality and extrusion performance should not be an issue unless there is a significant variance within a lot of material. 

Polybutene is incorporated into polyolefines (frequently octene LLDPE) for these products. The film may have up to three coextruded layers with polybutene in two of them. This process has been well established for some years and data on such properties as the influence of polybutene on ultimate bond and rate of generation of tack properties have been produced by a polybutene supplier [3]. 

Low transfer to material in contact migration to coextruded layers S Y Y... 

Recently, a novel method to prepare multilayers and nanolayers from a sequential coextrusion process has been introduced. In this method, the number of layers can be largely increased at the expense of reducing the thickness of the coextruded layers. It is also possible to obtain nanodroplet dispersions by annealing such multilayer coextruded ensemble. The following systems have been studied employing this method polyethylene/ polystyrene (PE/PS), polypropylene/polystyrene (PP/ PS), polycarbonate/poly(ethylene terephtalate) (PC/ PET), and poly(ethylene oxide)/ethylene acrilic acid copolymer (PEO/EAA). The crystallization behavior within the nanolayers and within the spheres that are obtained after heating and coalescence of the nanolayers has also been studied [18,33,66,94,104, 111, 140-143]. 

For samples that underwent mechanical and thermal testing, the PP nanocomposite layers were separated Ifom the coextrudate layer. Samples had the outermost 1.5 mm of each edge removed and the sample was gently flexed to initiate delamination of the layers. The partially delaminated layers were then slowly peeled apart, making sure to keep track of the layer number of each. Individual layers were soaked in toluene solvent and then air dried to ensure removal of any residual PS. 

A typical coextruded sheet has a total thickness of 1270 p.m (50 mil). After the container is formed by one of several methods, the sheet might then yield a wall thickness of 510 p.m. The barrier layer in the container is typically in the range of 25 to 75 p.m. 

Thermoformed chassis and body panels are featured on the car. The products were made initially in the USA for assembly in China. The car will weigh less than 2000 lb (900 kg). Automotive Design Composites, Inc of San Antonio, TX, designed the vehicle to have body panels and trunk formed from coextruded sheet of ABS with an ASA cap layer that will hang on a pultruded composite frame. Ceramic tooling is used to thermoform plastic products. 

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. 

A number of techniques are available for coextrusion, some of them patented and available only under license. Basically, three types exist feedblock, multiple manifolds, and a combination of these two (Table 9-18). Productions of coextruded products are able to meet product requirements that range from flat to complex profiles. Figure 8-35 (a) shows a typical 3-layer coextrusion die and (b) examples of rather complex profiles that are routinely extruded. 

The recycled plastic will also have a degree of different contaminants that would eliminate its use in certain devices or products, such as in medicine, electronics, and food packaging. However, within these market applications there are acceptable designs with three-layer coextruded, coinjected, or laminated structures having the contaminated plastic as the center layer, isolated by clean plastics around it and no migration occurring. 

It is briefly reported that PP foam sheet from Convenience Food Systems in thickness from 500 to 1800 micron is thermoformable into chilled food packaging trays. Trays made in TiroPak XPP, which is coextruded with an EVOH barrier layer, can be taken from the freezer and heated to 90C in a microwave oven without loss of shape or properties. 

GE introduced, in 2000, a new polyester carbonate based on resorcinol arylates called W-4. It is now marketed as Sollx. Sollx does not need to be painted, it offers good weather, chip, scratch, and chemical resistance and is being used as the fenders for the new Segway Human Transporter. It is also aimed at automotive uses including body panels. Sollx is coextruded into two layers clear and colored, to simulate automotive paint. It is then thermoformed and molded into the finished product. 

Attempts to substitute PVC containers have shown, however, that non-PVC containers may also contain plasticizer components resulting in the release of some DEFIP into the preparation. A study conducted by Sautou-Miranda and co-workers showed that [65] leaches rapidly from coextruded and triple-layered IV tubing into etoposide infusion solution (see details of the results under Section 9.1.3.3). 

Sautou-Miranda et al. [77] showed that DEHP is rapidly leached from PVC, coextruded, and also triple-layered IV tubing by action of an etoposide infusion... 

Phase contrast-Thin sections (100-200 nm) in thickness (and having refractive indices which differ by approximately. 005) are supported on glass slides and examined "as is" or with oil to remove microtoming artifacts, e.g., determination of the number of layers in coextruded films, dispersion of fillers, and polymer domain size. (Figures 2 and 3)... 

Viscoelastic flow effects in polymer coextrusion. In this example we will present work done by Dooley [7, 8] on the viscoelastic flow in multilayer polymer extrusion. Dooley performed extensive experimental work where he coextruded multilayer systems through various non-circular dies such as the teardrop channel presented in Fig. 9.39. For the specific example shown, 165 layers were coextruded through a feedblock to form a single multiple-layer structure inside the channel. 

PVDF can be coextruded and laminated, but the process has its technical challenges in matching the coefficients of thermal expansion, melt viscosities, and layer adhesion. Special tie-layers, often from blends of polymers compatible with PVDF, are used to achieve bonding.26-27... 

In chapter 7, section 7.2.8 an example of permeation through a functional barrier is described. Three-layered coextruded PET films were produced in which the core layer (P) was contaminated with chlorobenzene and the outer barrier layers (B) were made with virgin material. During the coextrusion process a partial contamination of the virgin layer occurred. The symmetrical structure of this film leads to a simplified treatment of it as a two layer laminate with the thickness d = a + b = 160 + 40 = 200 pm. For the modeling of this problem with numerical mathematics all parameters given in Section 7.2.8 are used. 

Extrusion is the process of heating practically only TPs that may be in the shape of powders, beads, flakes, pellets, or combinations of these forms. This plastic enters the extruder s hopper. The extruder utilizes a plasticator [spiral screw that rotates within a heated barrel (cylinder)] to melt the plastic (Chapter 3). The melted plastic is then forced through a die to produce the desired continuous product shape. Figure 5.1 shows a very simplified schematic of the extrusion process. Information on dies (mono-layer and coextruded) used in extrusion is in Chapter 17. 

Melt flow instabilities, such as interfacial instability, melt fracture, surging, and/or layer nonuniformity, can become problems that could cause quality problems with the coextruded product.200 There are several options to correct these problems. The key to success is to select... 

Technologies, such as coextrusion and coinjection, allow PET and other plastics to package foods and other products.225 226> 227 Care must be taken to control the process so that the melt when blown will not have micro-voids in the container walls or will delaminate. Coextrusion and coinjection (or multilayer processes) are essential technique in the production of high performance BM products (Chapters 4 and 5). The parison or preform is coextruded with a number of different layers, each of which contributes an important property to the finished product. Increasingly, a mid layer may consist of recycled material which is encapsulated between inner and outer layers of virgin plastics. 

The following TPs are the main thermoforming materials processed high-impact and high-heat PS, HDPE, PP, PVC, ABS, CPET, PET, and PMMA. Other plastics of lesser usage are transparent styrene-butadiene block copolymers, acrylics, polycarbonates, cellulosics, thermoplastic elastomers (TPE), and ethylene-propylene thermoplastic vulcanizates. Coextruded structures of up to seven layers include barriers of EVAL, Saran, or nylon, with polyolefins, and/or styreneics for functional properties and decorative aesthetics at reasonable costs.239-241... 

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