Coextrusion foam core

In the early 1980s, a multitude of patents and patent applications were registered in the field of coextrusion of multi-layer pipes. Meanwhile, a number of pipe products representing a composite of several layers are established products on the market. The technology of the coextruded foam core pipe builds on these developments. The foam core type of PVC plastic pipe today takes the largest volume share of all coextruded foam core products. This product has developed into an important and very competitive alternative for non-pressure applications such as drain pipes, sewer pipes and cable ducts. France has played the role of a pacesetter in this development. Today, over 80% of all pipes for non-pressure applications are produced in the form of foam core pipes in that country. Since the common market realised within the EU is connected with a strong market equalisation tendency, other European countries are following. 

Counter-rotating twin screw extruders are used almost exclusively for the production of uPVC pipes, profiles and sheet because they treat material more gently than single screws. Parallel screw and conical twin screw extruders are compared. Cincinnati Milacron Austria introduced its Argos parallel twin screw extruders last year. These machines are intended to complement the company s Titan conical screw range. Coextrusion of foamed core pipes is also described. 

With sheet or pipe, multilayer coextrusion can be used. Solid outer-solid core coextrusion can place an ABS grade on the outside that has special attributes such as color, dullness, chemical resistance, static dissipation, or fire-retardancy over a core ABS that is less expensive or even regrind. Composites can be created in which the core optimizes desired physical properties such as modulus, whereas the outer layer optimizes surface considerations not inherent in the core material. Solid outer-foam core can provide composites with significant reductions in specific gravity (0.7). Dry blowing agents can be dusted onto the pellets or liquid agents injected into the first transition section of the extruder. 

U.S. Pat No. 6,827,995 [53] discloses a single coextrusion process of making a WPG as a hollow profile comprising a weatherable outer layer made of a first polymeric material, a core layer made of a thermoplastic polymeric foamed composition including a wood component, and an inner layer made of a third thermoplastic material. The first and second polymeric materials are PVC or acrylonitrile-styrene-acrylic polymer or a combination thereof. The third polymeric material is PVC. 

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