Co-injection, sandwich or two-component molding, is the technique of injecting two materials, one solid and one with chemical foaming agent, into a mold in a programmed manner through the same injection nozzle in order to produce a thick molding with a solid outer skin of regular plastic and an inner core of structural foam. This technique substantially overcomes warping, cracking, shrinkage and much of the built-in-stress found in conventionally molded thick components. Co-injection or bi-component molding represents the best system of producing thermoplastic items having a section of 5 mm. or more (O.2 in.or more), but requiring a smooth glossy surface.
Considering that the first quality material is needed only on the outside, and that second quality material can serve as a filler, there can be important savings.
Furthermore, in making colored items, color concentrate is needed only for the outer component thus reducing also coloring costs. Co-injection is performed with the “Presma” patented injection head by engulfing first quality material with less costly material.
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