This study exemplifies the two major problems with adhesion in IPIT (Instrument Panel & Interior Trimm) composite parts: (a) Adhesion to PP containing materials such as TPO and LGFPP; and (b) maximizing cohesive bond strength at the PU foam interphase. Our formulation development for adhesion to dissimilar materials and maximum cohesive peel strength continues. However, the findings from this study were used to create a processing guide for the molder to optimize adhesion in soft IP's. The primary conclusions pertaining to bonding PU foam to skin and substrate are: Adhesion failure only occurred for surfaces with a percent polar component of total surface energy less than 3%. Only the non-flame-treated TPO and LGFPP surfaces had low enough polar components to have adhesive failure. Always when the percent polarity was greater than 3% the peels resulted in cohesive failure. According to our results the polar component of surface energy is more important than the total surface energy. Surface material does not appreciably affect cohesive peel strength. However, peels from flexible skins resulted in peel strengths that were on average one third of those from rigid substrate peels. When there is adhesion, and the failure mode is cohesive, the cohesive peel strength is correlated to the physicalmechanical properties of the foam, with the strongest correlation to the foam's tensile strength. PU chemistry and PU foam density both affect the physical-mechanical properties of the foam, therefore, also indirectly affect the cohesive peel strength of the foam. Polylol P and isocyanate Blend both improved the cohesive peel strength of the foam because they improved the foam's physical-mechanical properties. Greater molded PU foam density improves the cohesive strength of the foam, and thus promotes separation in the interphase region. Heat aging reduces cohesive peel strength because it reduces the physical-mechanical properties of the foam, and thus promotes separation in the bulk foam region. PU foam surface energy and PU liquid surface tension may affect the wetting of surfaces but they do not affect the cohesive peel strength because neither affects the physical-mechanical properties of the foam. Peels from foam made with Formulation W, designed for maximum wet-out capability, resulted in the lowest cohesive peel strengths, because it had the weakest physical-mechanical property performance.
Adhesion of polyurethane foam with skin and substrate materials in automotive composite instrument panels
Die Haftfestigkeit von Polyurethanschaumstoffen mit Randschicht- und Substratwerkstoffen in den Werkstoffverbunden von Automobil Instrumententafeln
2008
15 Seiten, 9 Bilder, 8 Tabellen, 16 Quellen
Conference paper
English
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