Composite Polymeric Panel and Process for Making Same

My present invention relates to a composite panel made from various polymeric materials and to a process for producing such a panel.

In my prior U.S. Pat. No. 4,305,982 I have described a shatterproof laminate adapted to serve as an insulator of light-transmissive character usable, for example, in a skylight or in a greenhouse. The laminate comprises a synthetic-resin panel of skeletal type, with two parallel plates interconnected by spaced-apart webs, bonded onto a glass sheet. Suitable polymeric materials mentioned in the patent include polymethylmethacrylate, polyvinylchloride and polyethylene, which are thermoplastic resins, as well as polycarbonates which could be of either thermoplastic or thermosetting character. A structurally improved skeletal panel is the subject matter of my copending application Ser. No. 541,672 filed Oct. 13, 1983.

Panels or layers of such a skeletal structure are generally produced by extrusion. In some instances several such layers are extruded jointly to form a composite panel.

An important object of my present invention is to provide an insulating panel of the general type referred to which can be used for a variety of purposes without necessarily being bonded to an inorganic support such as a glass plate.

A more particular object is to provide a composite polymeric panel of this nature capable of being deformed into a nonplanar shape which it subsequently retains.

Another object is to provide a transparent or translucent panel of this type with a wear-resistant surface in order to prevent a diminution of its light transmissivity by scratches due to hailstones or other falling objects.

A further object is to provide a process for making such composite panels.

A composite panel according to my present invention comprises, essentially, a basic skeletal layer of the aforedescribed type, consisting of a first polymeric material, and a reinforcing layer of a protective second polymeric material overlying at least one of the plates of the skeletal layer.

When the composite panel is to be transparent or translucent, e.g. for use as a roof of a greenhouse, the skeletal layer may consist of a polycarbonate while the reinforcing layer is made of a polyacrylate such as the polymethylmethacrylate mentioned in my prior patent. In that case it will be advantageous to interpose an intermediate layer of a third polymeric material between the skeletal layer and the reinforcing layer to equalize level differences; the third polymeric material could be polyethylene, for example.

In other instances, in which scratch resistance is less of a consideration, the resinous material of the skeletal layer may be softer than the protective material of the reinforcing layer which in that case advantageously consists of a polycarbonate. Thus, the first polymer may then be a thermoplastic resin such as polystyrene, low-pressure polyethylene, an acrylonitrile-butadiene-styrene copolymer (ABS) or polypropylene. The scratch-prone polycarbonate layer is advantageously provided with a covering such as a textile fabric which can be bonded thereto with the aid of an adhesive layer of a further polymeric material whose melting point is significantly lower than those of the other polymeric materials. Such a heat-softenable material may be an ethylene-vinylacetate copolymer (EVA), for example.

In all these instances the presence of a layer of polycarbonate confers a high degree of structural stability to the composite panel. The combination of a basic polycarbonate layer with a protective polyacrylate layer is particularly useful in greenhouses or the like since the polyacrylate is not only scratchproof but also stable against ultraviolet radiation and thereby minimizes discoloration and aging phenomena in the polycarbonate structure.

The several layers of my improved composite panel are advantageously formed by concurrent extrusion, followed by a slicing of the resulting laminate into sections of the desired dimensions. Such a section, pursuant to a further feature of my invention, can be deformed under heat and pressure to produce a shaped body such as, for example, a domed roof. When light transmissivity is not required, as where the ultimate article is to be covered with a textile fabric or the like, the same technique can be used to shape the laminate into a part of a piece of furniture, for example, such as a seat or a back of a chair or the like. With or without such subsequent deformation, the voids existing between the webs and the plates of a skeletal layer of a non-light-transmissive laminate are advantageously filled with a highly porous polymer, preferably a foam plastic such as polystyrene or polyurethane foam; thus, a foaming agent introduced along with a polymeric substance into these voids during extrusion will expand in that substance on exiting from the extrusion nozzle.

The above and other features of my invention will now be described in detail with reference to the accompanying drawing in which:

FIG. 1 is a cross-sectional view of part of a composite panel embodying the present invention; and

FIG. 2 is a perspective view of part of a similar panel in the process of extrusion and subsequent deformation.

FIG. 1 shows a representative portion of a composite panel according to my invention comprising a basic skeletal layer 1, preferably of a polycarbonate, with a lower plate 1a, an upper plate 1b and spaced-apart webs 1c forming intervening voids 1d. A reinforcing layer 2 of polymethylmethacrylate overlies the upper plate 1b with interposition of an equalizing layer 3. The light-transmissive panel of FIG. 1 can be produced by joint extrusion of the several layers and can be subsequently deformed, with the aid of a heated die, to serve for example as a domed roof of a greenhouse. It should be understood, however, that this panel can also be laminated onto an underlying glass plate in the manner disclosed in my prior U.S. Pat. No. 4,305,982 or my copending application Ser. No. 541,672.

In FIG. 2 I have illustrated a generally similar panel with a basic skeletal layer 1, a reinforcing layer 2 and an adhesive layer 4 all coming from an extruder (not shown) in which these layers are jointly produced and laminated together. The same extruder introduces a foaming agent 6 into the voids 1d (FIG. 1) of the skeletal layer 1 along with polymeric material which may or may not be the same as the resin forming the plates and the webs of that layer. Thus, for example, layers 1, 2 and 4 may respectively consist of polystyrene, polycarbonate and EVA, with the voids of layer 1 occupied by foamed polystyrene.

The laminate exiting from the extruder is cut into sections of predetermined dimensions which, as further shown in FIG. 2, are then deformed under heat and pressure to produce a shaped article such as, for example, the back of an easychair. The adhesive layer 4, softened by the applied heat, can be used to bond a textile fabric 5 to the reinforcing layer 2 under the pressure of the heated die in which the article is being shaped.

Reinforcing layer 2 along with equalizing and/or adhesive layers 3, 4 could also be provided on the lower plate 1a of the skeletal layer 1 shown in FIGS. 1 and 2. The webs 1c need not be perpendicular to the plates 1a, 1b and, furthermore, could be curved instead of straight.