For virtually any enclosed structure having one or more walls exposed to weather, it is important that the structure walls retain their watertight integrity. And for many types of structures, maintenance of the appearance of the wall is important. When the wall is part of a static structure, the techniques and materials which provide watertight integrity and attractive, long-lasting appearance are known. But when the wall is part of the driver- and passenger-enclosing body of a type of motor vehicle, the techniques and materials have been found less than satisfactory.
U.S. Pat. No. 4,082,882 (Weinstein et al.), U.S. Pat. No 4,491,362 (Kennedy) and U.S. Pat. No. 4,791,768 (Crean) all disclose products useful in making motor vehicle bodies of one type or another. The Weinstein et al. patent discloses a multi-layer structure said to be useful in making truck walls or the like. In one version of the structure, its layers include, from the exterior inwardly, sheet acrylic, general purpose resin, fiberglass, plywood, general purpose resin, and fiberglass.
The Kennedy patent discloses a fiberglass body for a Jeep vehicle. In an embodiment, only the inner and outer rigid shells are fiberglass. Such shells have what the patent calls "close foam" insulation material, e.g., styrofoam or urethane, between them.
The Crean patent discloses a composite structure for mobile applications such as motorized coaches. The structure includes what the patent calls a second subassembly which, from the exterior inwardly, includes fiberglass exterior sheathing, a glue layer, a first substrate made of foam laminated between paper, another glue layer, and a relatively thick layer of plywood.
Commonly, recreational vehicles have sidewalls made differently than any of the arrangements described in the above-mentioned patents. Such RV sidewalls include a sheet of a fiberglass product, the smooth "finished" surface of which is exposed to weather, road grit and the like. An exemplary product is FILON.TM. gel-coated, semi-rigid fiberglass-reinforced polyester resin material, about 0.045 to 0.06 inches thick, available from Kemlite Company, Joliet, Ill.
A sheet of lauan plywood is bonded to the interior surface of the fiberglass using moisture-cured urethane or polyurethane reactive hotmelt. In lieu of such plywood, the fiberglass may have bonded thereto a particle board made in Europe.
Lengths of rectangular aluminum tube are spaced along and adhere to the plywood or to the particle board, as the case may be. In the finished RV, the tubes are generally vertical and are spaced horizontally. Other tubes are mounted horizontally across the top and bottom of the vertical tubes. In preferred practice, the tubes form a welded frame.
A slab of styrofoam insulation is placed into each space between adjacent pairs of tubes and is also glued to the plywood or particle board. And when considered from the outside inwardly, styrofoam insulation is between the plywood and the interior wall visible to passengers.
A problem with this construction arises from the fact that as the RV moves along the road, it "flexes." Moisture migrates inwardly, both through the wall/seal junction at resilient seals around doors and windows and, perhaps, at the junction of a side wall and another wall structure. Such moisture permeates the plywood layer, causing it to rot. Or, less likely, such moisture causes a failure in the adhesive used to make the plywood.
Significant moisture migration eventually evidences itself in a "wavy" or "bulgy" outer fiberglass surface and/or interior wall. In addition, the cellulosic fibers of the plywood may separate and in any event, the plywood retains moisture for a long period of time.
None of these eventualities is acceptable to the vehicle owner or, for that matter, to the manufacturer. As to the latter, an RV manufacturer may, in a single year, experience very-substantial warranty claims. Attending to such claims detracts from the main production effort and drives up costs.
Yet another characteristic of the aforedescribed vehicle wall construction relates to vehicle weight. Of course, any significant saving in vehicle weight translates into improved fuel economy, reduced tire wear and other advantageous results. As will become apparent, the invention helps achieve further weight reduction in the walls of recreational vehicles.
Yet another concern relating to existing RV wall construction is the diminishing availability of lauan plywood. Lauan is a rain forest product and if its use is not voluntarily diminished, perhaps markedly so, the exhaustion of the forest will force other approaches.
Still another concern relating to existing RV wall construction using the Europe-sourced particle board is that, to be given reasonable consideration by the seller, a buyer must order very substantial quantities. This ties up cash in inventory and, in view of the invention, is unnecessary. And delivery "lead times" are considerable.
A new motor vehicle wall product and related method which address characteristics and disadvantages of earlier products would be an important advance in this field of technology.