Finishing for Rigid Polyurethane Elements
March 2002
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A new finishing process for rigid polyurethane elements combines aesthetics and design. GMP S.p.A.'s patented process and equipment molds together the rigid polyurethane element with a pigmented thermoformed sheet, conveying to the final molded element a particular format and an external finishing touch. In this manner, the phases involved in preparation and execution of the varnishing process can be completely eliminated.

The traditional PUR-RlM process is the mixture of two liquids, polyol and isocyanate, at high pressure (150-200 bar). The result of this process is an element in rigid polyurethane with integral surfacing. Until the mid 90s, the material was formed using CFCs, which were later eliminated and replaced by water. The change in composition has shown to be a significant improvement for the environment, but has slightly lengthened the preparation of the pieces for the varnishing stage, according to the supplier. As a consequence, there was a reduction in the productive potential because the manufacturing process was essentially manual. A search was divided into two phases: transforming the PUR (Rigid Polyurethane) varnishing into varnishing made of a compact thermoplastic material (this was the preliminary stage before the film technology); and completely eliminating the varnishing process. In light of the experience gained during the first phase, new finishing films were created, which completely eliminated the need for a varnishing stage. The surface characteristics displayed by these films are said to make them suitable both for indoor (i.e., refrigerator door) and outdoor use.

The new process can be summarized as follows: pre-heating-during this stage, the mold is brought to the desired temperature, differentiating each area according to the pre-set requirements; preparation and cut of the aesthetic film; vacuum creation and partial molding of the thermoplastic film; injection of the polyurethane and completion of the molding; and extraction of the piece and trimming of the film. Since there is no varnishing process, there are no runs, blows, or dust particles, according to the company. The thermoplastic sheet is said to have a uniform surface, both in terms of color, shade, and gloss (up to 95 gloss), and the color reportedly remains constant throughout the various series produced.


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