Process for Molding a Weatherable, Paint-free SMC or Metal/Thermoplastic Film System with Class-A Surface Finish
Publication Date: 2003-Apr-23
The IP.com Prior Art Database
AbstractMolding a cured SMC or stamped metal part and a weatherable thermoplastic film and adhering them with a two component adhesive in such a way as to form a class-A quality part which possesses excellent interlayer adhesion and is resistant to cycle crack testing, thermal cycling and sun load.
SUMMARY OF IDEA
The Idea is to take a cured Sheet Molding Compound (SMC) part (made via injection, compression or injection/compression molding) or metal parts (made via stamping process) and a weatherable thermoplastic film (such as, but not limited to, LEXAN SLXâ), which has been extruded and/or thermoformed to roughly the shape of the SMC
part, and adhere them with an adhesive (such as, but not limited to a two component flexible polyurethane) in such a way as to form a class-A quality part which possesses excellent interlayer adhesion and is resistant to cycle crack testing.
PROBLEM TO BE SOLVED
Thermoset composite materials such as SMC, display excellent toughness, low creep and coefficient of thermal expansion (CTE), which is critical for some structural applications, such as but not limited to, automotive hoods. The SMC part is brittle and also has an issue with “paint popping,” causing higher than desired scrap rate. Addition of a weatherable film eliminates the need for paint.
In Mold Decoration of a glossy, weatherable film such as LEXAN SLXâ with SMC typically has poor interlayer adhesion, likely due to the adhesion mechanism of styrene monomer in the SMC attempting to plasticize the thermoplastic film. In addition, because of the molding temperatures typically used to mold SMC, the final part tends to be less than a class-A quality.
PRIOR ART - CRITICAL FOR VALID PATENTS
US Patent 5,001,000 Process for forming a composite structure of thermoplastic polymer and sheet molding compound describes a method of In Mold Decoration of SMC and polyarylate as the thermoplastic material.
US Patent 6,136,441 Multilayer Plastic Articles describes the invention of a multiplayer plastic composite material (since registered as LEXAN SLXâ).
Patent Disclosure RD-29605 of the GE Global Research Center describes methods for adhering LEXAN SLXâ films to several substrates.
None of the above patents and disclosures mentioned above addresses the process issues of manufacturing large parts such as automotive hood with class-A surface finish from a cured thermoset composites and thermoformed LEXAN SLXâ film.
OBJECT OF INVENTION
The object of the invention is to create a paint-free, weatherable, multi-layer system, which has the rigidity and low CTE required for many structural applications. The method of binding the two materials demonstrates excellent adhesion between the adhered layers both before and after cycle crack testing.
DESCRIPTION OF INVENTION
This invention details a process for adhering a pre-formed thermoplastic weatherable material (LEXAN SLXâ) to a cured thermoset composite substrate (SMC) with an adhesive (A two compon...