Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-12-15
2002-07-09
Yao, Sam Chuan (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S078000, C156S245000, C156S272200, C264S122000, C264S257000
Reexamination Certificate
active
06416614
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns a composite material consisting essentially of a particle foam made from expanded polypropylene (EPP), at least one fiber layer, and a layer introduced thereon made from a polymer, as well as a method for producing a molded component comprising such a composite material.
Thermoplastic polymers and foams produced through expansion thereof have many applications. Disadvantageously, the material is not well suited for the manufacture of intimately joined composite materials. This is primarily due to the very poor surface bonding properties. This is especially the case for all polyolefines and, in particular, for the widely used polypropylene. Expanded polymers are normally used as an insulating layer to provide acoustical insulation, heat insulation or shock insulation. They can, however, only accept limited forces and are neither diffusion tight nor resistant to abrasion. In most applications, the foam material must therefore be coated at one side or completely encased, wherein the coating or casing material provides e.g. a smooth, rigid surface and imparts the required strength to the molded component. This layer therefore comprises reinforcement fibers upon which e.g. a duroplastic material is impregnated, sprayed, or applied in a similar fashion.
With a composite material of this kind, the foam is first produced, shaped and joined to the fiber reinforced layer, whereupon the duroplastic layer is applied. Alternatively, the prefabricated, impregnated fiber layer is joined to the foam body. This is done using glue, solvents or the like. To the extent that the molded component has a closed jacket, this jacket is conventionally prefabricated and subsequently expanded. The former method is difficult and generally not particularly acceptable from an environmental point of view. Disjoining of laminations can occur in response to loads. The second method produces articles which do not have an intimate connection between the cover layer and the foam body, in consequence of which, associated loading of the cover layer causes the foam body to tear and, under certain circumstances, the foam structure is destroyed.
DE-OS 14 79 995 describes a method for producing a laminate with which the surface of a layer made from a thermoplastic polymer material is bound to a fabric containing glass fibers as well as fibers comprising a thermoplastic polymer material in such a fashion that the polymer material of the thermoplastic layer is melted together with thermoplastic polymer fibers of the fabric. The layered body thereby produced can be reinforced through incorporation of resins on the fabric side, strengthened by fiber glass layers. Towards this end, neither the use of a particle foam as a layer made from a thermoplastic polymer material nor the application to the fabric of a layer made from a rigid polymer, cured or cross-linked from the fluid phase, is envisioned.
DE 41 41 113 A1 discloses a composite body in the form of a cover member for inside use in motor vehicles having a support member made from polyolefine particle foam, a decorative layer preferentially substantially made from a polyolefine polymer on a multi-layer weave or fabric primarily made from polyolefine polymer threads, as well as foils laminated on one or both sides of the fabric made from a polyolefine material. With this composite body, the particle foam is not welded to the fabric and there is no layer made from a rigidly curing or cross-linking polymer introduced in the liquid phase.
SUMMARY OF THE INVENTION
It is the underlying purpose of the invention to create a composite material with the above mentioned structure with which a firm connection is guaranteed both between the EPP particle foam and the fiber reinforced layer as well as between that layer and the polymer layer applied thereto without the assistance of additives such as glues, solvents or the like. The invention is also directed to a method for manufacturing a molded component using a composite material of this type.
The first purpose is achieved in accordance with the invention using a composite material of the above mentioned kind in that the fiber layer comprises mixed fibers having a fraction of fibers made from polypropylene (PP) which are welded to the particle foam and an additional amount of reinforcing fibers, which can be sufficiently wet by the rigidly curing or cross-linking polymer applied to the free surface of the fiber layer in the liquid phase.
The mixed fiber layer in accordance with the invention serves two purposes within the composite material. It provides the conventional reinforcement function with regard to pressure and tensile strength and also effects bonding between the fiber layer and the PP particle foam, since it contains PP fibers which, during melting of the particle foam, undergo an intimate welding connection thereto. In this manner, a strong connection is effected between the mixed fiber layer and the particle foam made from EPP. In addition, the free surface of the fiber layer has sufficient wetability for impregnation with a rigidly curing or cross-linking polymer, so that a layer having the required properties (e.g. smooth surface, abrasion resistance, proper spray behavior and scratch resistance and the like) is introduced onto the compound comprising the mixed fiber layer and the EPP particle foam. The layer introduced on the free surface of the fiber layer made from the hardening, curing or cross linking polymer can, for its part, have a plurality of layers (e.g. a sandwich-type structure). The compound material in accordance with the invention can be produced in plates or as a three dimensional molded component, optionally even as a hollow component e.g. through forming and shaping of the composite material on a core.
The EPP/fiber compound has extremely high tensile and shear strength. Compared to other particle foams, in particular the commonly used polystyrene foam, the composite material in accordance with the invention is characterized by a very high restoring capability to avoid pressed-in locations. The ability to withstand high temperatures is also advantageous in many applications.
The composite material in accordance with the invention is therefore particularly well suited for surfboards, wave gliders, hulls, skies of various types and other kinds of sporting equipment, planes, insulated containers, housings, motor vehicle inner coverings and chassis components such as bumpers and front hoods etc.
The particle foam can be a compound foam comprising EPP and an additional expanded polymer e.g. EPS (expanded polystyrene) and/or EPE (expanded polyethylene). In this case as well, the mixed fiber layer has a fraction of PP fibers forming an intimate connection with the EPP particles in the particle foam.
The polymer introduced in the liquid phase on the free outer surface of the fiber layer can e.g. be a thermoplastic applied to the mixed fiber layer using arbitrary conventional methods such as injection molding or low pressure injection molding, through pressing, extruding or co-extruding, thermoplastic foam molding, heat molding, flame spraying, using continuous casting techniques or swell-flow procedures. The thermoplastic applied in a heat-melted liquid phase, e.g. polyolefine, PVC, polystyrene, polyacrylic etc., becomes rigid on the mixed fiber layer when cooled to thereby function not only as a bonding agent and for reinforcement, rather, in particular, to also effect heat insulation so that the particle foam is not damaged during spray application, extrusion application or the like. Use of the mixed fiber layer in accordance with the invention between the particle layer and the applied liquid phase thermoplastic makes the production of such a compound material possible, since the heat energy of the melted liquid thermoplastic when introduced onto the particle foam, would otherwise lead to a freeing of the gases enclosed therein and to a collapse of the particle foam and a smooth surface could not be obtained. When, for example, the thermoplastic introd
Fraunhofer-Gesellschaft zur Förderung der angewandten Gesellscha
Vincent Paul
Yao Sam Chuan
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