Multilayer molding

Multilayer molded (MM) package, an Intel PQFP package with improved high-speed operation due to separate power and ground planes, which reduces device capacitance. 

To enhance water-vapor- or gas-barrier properties, layers of different plastics may be injected together or sequentially. Multilayer injection-molded pieces may be prepared as packaging or for blowing into bottle or jar shapes. 

Thermoforming of extmded sheet is achieved by warming the sheet to its glass-transition poiat and coUapsiag it over a mold shape (21). The coUapse can be effected by vacuum suction or pressures appHed on the sheet above the mold. This technique is used to make trays and profiled advertisiag signs. Both single- and multilayer sheets can be used. 

Bag molding Hinterspritzen This patented process allows virgin or recycled TPs such as PP, PC/ABS, etc. to thermally bond with the backing of multilayer PP based fabrics providing good elasticity. This one step molding technique provides a low cost approach for in-mold fabric lamination that range from simple to complex shapes. 

Jiang and Zhu (2000) and Qiu and Zhu (2001) have reported the fabrication of multilayered devices composed of stacks of compression-molded disks of alternating compositions. One type of disk is either P(SA-EG) or P[SA-co-TMAgly)-Z>-EG] and the other is a pH-sensitive, protein-loaded blend of, for example, poly(methacrylic acid) and polyethoxazoline. The release of model proteins, myoglobin, bovine serum albumin, and FITC-dextran, and compounds such as brilliant blue have been studied and pulsatile release profiles have been demonstrated (Jiang and Zhu, 2000 Qiu and Zhu, 2001). 

Laminar materials are produced by a variety of techniques. Coextrusion blow-molding produces a number of common food containers that consist of multilayers such as layers consisting of PP-adhesive-PVA-adhesive-adhesive-PP. 

Multilayered articles can be made by coinjection blow-molding or coextrusion methods. A three-layer system generally contains a barrier layer sandwiched between two exterior layers. These are actually laminar products. In the coextrusion sequence, several extruders can be used to place the material into the mold. The multilayer container is then produced from blowing air into the preform. 

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

Extrusion. Sheet, film, and profiled articles are made by extrusion (20). The resin is melted and forced through a die plate or head. Variations include multilayer and blown film applications. In multilayer coextrusions, different combinations of plastics are separately but concurrently extruded to form layered sheet or film. In the packaging industry, specialty resins such as high barrier ethylene—vinyl alcohol copolymers are combined with heat- and impact-resistant thermoplastics for food packages. The properties of each resin layer are additive, as opposed to the "averaging of property" in blends. Multilayers are also used for blow-molded containers, films, and sheet products (see also Film AND sheeting materials). 

In the past few years, we have seen trends where more complex manufacturing systems are developed that manufacture parts using various materials and components such as coextrusion of multilayer films and sheets, multi-component injection molding, sandwiched parts or hollow products. 

Tubes and blown Aims can be produced as multilayer structures by employing multiple extruders and coextrusion manifolds and dies. Figure 12.44 is a schematic representative of a conventional and new spiral coextrusion die. The designs can be used for both blown-film and blown-molding parison dies. In the extrusion of tubes, such as rigid PVC or PE pipe, the extrudate passes over a water-cooled mandrel and enters a cold-water bath whose length depends on the tube thickness the tube leaves the bath well below its Tm (if it is crystalline) or Tg (if it is amorphous) and is sectioned to the desired lengths. 

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