Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Noninterengaged fiber-containing paper-free web or sheet...
Reexamination Certificate
1998-10-16
2001-09-11
Cole, Elizabeth M. (Department: 1771)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Noninterengaged fiber-containing paper-free web or sheet...
C428S300700, C428S317100, C428S318600, C428S319300, C156S228000, C156S324000
Reexamination Certificate
active
06287678
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a composite structural panel including a core of thermoplastic material and outer layers containing natural fibers in a thermoplastic material. The invention further relates to a method and an apparatus for producing such a composite structural panel.
BACKGROUND INFORMATION
It is generally known to use composite structural panels comprising polymer materials as interior trim components in motor vehicles, aircraft, railroad cars, and the like. Such trim components include molded dashboards, interior door panels and inserts, headliners, and the like. Conventional present-day composite panels for use as such trim components are made of a polyurethane foam material reinforced with glass fibers saturated or embedded in epoxy resin. More specifically, one or more layers of glass rovings impregnated with epoxy resin are laminated onto the foam for reinforcing and stiffening the resulting composite panel. As a further alternative, a polypropylene powder material may be incorporated in the glass roving layers as a binder.
Such a conventional composite panel and the method of its manufacture suffer distinct disadvantages, For example, handling of the glass fiber material and handling and application of the epoxy resin in fluid form are difficult and complicated, especially in view of worker safety and environmental concerns. Moreover, this process, for example carried out as a lay-up process, requires substantial handling effort, and also a long curing time for the hardening the resin in a heated compression mold. Since the finished trim components contain a mixture of different non-degradable and incompatible materials, e.g. polyurethane foam, glass fibers and epoxy resin, these trim components are not recyclable by means of separation and reprocessing of the materials. Since at least some of the materials are non-combustible or give off noxious or toxic gases when combusted, the trim components are also not thermo-recyclable, i.e. burnable as a fuel. The recyclability of composite structural panels in general, and especially motor vehicle trim components, is presently a strong driving force in the industry. There is a great need to provide composite materials that can be easily separated, reprocessed for reuse, or combusted as an industrial fuel.
Another type of known composite structural panel, as disclosed in U.S. Pat. No. 5,709,925 (Spengler et al.) is based on a combination of natural fibers and a fibrous thermoplastic material. More particularly, such a composite structural panel includes a laminated composite substrate that comprises a core layer and two cover layers laminated onto the core layer, wherein the core layer comprises natural fibers and a fibrous thermoplastic material, and each cover layer respectively comprises synthetic fibers and a fibrous thermoplastic material. Such a structural panel achieves environmental advantages, because all of the materials of the multi-layer panel are easily broken down or otherwise processed for reuse or recycling. Namely, all of the materials can be burned without producing toxic gases, or the thermoplastic material can be melted down while burning off the natural fibers and/or separating out the fiber materials. These known structural panels also achieve very good impact energy absorption without splintering or shattering, and thus are effective for providing occupant crash protection in motor vehicles and the like.
While these multi-layered composite panels are very suitable and effective for achieving their intended purposes, it is desirable to provide a composite panel having all the environmental advantages, even better impact energy absorption characteristics, and an even simpler structure especially including a foam core, that may be produced by a relatively simple process.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the invention to provide a composite structural panel having a foam core and incorporating natural fibers, that can be easily reprocessed or recycled in an environmentally friendly manner, that can be compression molded into different surface contours and configurations, that has the necessary strength and stiffness for forming large surface trim components such as automobile headliners, and that provides impact energy absorption without splintering, shattering, or breaking. It is a further object of the invention to expressly avoid the use of glass fibers, polyurethane, epoxy resin and other thermosetting or otherwise environmentally non-degradable materials. It is still another object of the invention to provide a simplified process and apparatus for producing such composite structural panels. The invention further aims to avoid or overcome the various disadvantages of the prior art, and to achieve additional advantages, as apparent from the present description.
The above objects have been achieved in a composite structural panel according to the invention, comprising a thermoplastic foam core sandwiched between two outer layers that each respectively comprise natural fibers intermixed with thermoplastic material. Preferably, the thermoplastic material of the outer layers comprises thermoplastic fibers that have been at least partially, or predominantly or entirely melted to form a matrix in which the natural fibers are embedded. The polypropylene fibers and the natural fibers of each outer layer are preferably interneedled together, such that the respective outer layer comprises an intertwined mixture of polypropylene fibers and natural fibers. Alternatively, the polypropylene fibers and the natural fibers can each be provided in respective layers of non-oriented, non-woven fibers, with several thin alternating layers of polypropylene fibers and natural fibers stacked or laid on top of each other to form each respective outer layer. Once the outer layer is heated to about 200° C., the polypropylene fibers are at least partially melted, to become fusion bonded to each other and around the natural fibers, such that each outer layer in the finished composite panel has a structure including polypropylene fibers and natural fibers embedded in a polypropylene matrix or skeleton structure.
The thermoplastic foam core and the thermoplastic fibers of the outer layers preferably both consist of a polyolefin, and particularly polypropylene. The foam core is preferably a substantially rigid sheet or board of expanded polypropylene beads that have been heated and pressed together. Such an expanded cellular polypropylene foam material has a structure, appearance and physical properties generally similar to expanded cellular polystyrene such as “styrofoam” (TM), but is much more environmentally friendly than the polystyrene material of the “styrofoam”.
The natural fibers are generally cellulose fibers from various natural sources. Particularly, the natural fibers may include one or more natural plant fibers such as straw, cotton, flax, hemp, jute, sisal, and kenaf, or natural fibers such as wood product fibers. The preferred natural fiber is a kenaf bast fiber. The ratio of natural fibers to polypropylene fibers in the outer layers is preferably in the range from 30% polypropylene with 70% natural fibers to 70% polypropylene with 30% natural fibers.
The composite structural panel may further comprise any desired cover material such as a decorative fabric or film laminated onto the three-layered substrate. The outer decorative cover sheet may be a synthetic film or a textile, that is coated at least on the interface side with a coating film of polypropylene or polyethylene to achieve fusion bonding onto the respective outer layer, without requiring any adhesive applied therebetween.
The structural panel preferably consists entirely of polypropylene and one or more natural fiber materials, along with the optional cover sheet. For this reason, the structural panel can be easily recycled or thermo-processed for an environmentally friendly reuse or recovery, because the cover sheet can be relatively easily stripped off (or processed along with the composite subs
Cole Elizabeth M.
Fasse W. F.
Fasse W. G.
R + S Technik GmbH
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