High Pressure Laminates

FIG. 1 is a transverse cross-sectional view of a laminate designed for use as a facing for a wallboard made in accordance with the invention;

FIG. 2 is a perspective view showing the various layers of the laminate of FIG. 1;

FIG. 3 is a transverse cross-section of a laminate in accordance with the invention having two spaced metal foil sheets;

FIG. 4 is a perspective view showing the various layers of the laminate of FIG. 3;

FIG. 5 is a transverse cross-section of an alternate laminate in accordance with the invention wherein the spaced sheet metal layers are in the form of wire screens;

FIG. 6 is a perspective view showing the various layers of the laminate of FIG. 5;

FIG. 7 is a transverse cross-sectional view of a first wallboard in accordance with the invention;

FIG. 8 is a transverse cross-sectional view of a second wallboard in accordance with the invention;

FIG. 9 is an elevation of a foraminous steel sheet of the type used in the laminate of FIGS. 1 and 3;

FIG. 10 is an elevational view of a wire screen of the kind used in the laminate of FIG. 5;

FIG. 11 is a perspective view showing the details of the wire screen of FIG. 10; and

FIG. 12 is a perspective view showing the manner in which faced wallboards of the prior art tend to split when subjected to conditions of low humidity.

In FIGS. 1 and 2 a wallboard facing is shown comprising a two-ply decorative layer consisting of a sheet 14 of melamine-impregnated alpha cellulose tissue over a melamine-impregnated alpha cellulose ply 16, the latter being printed to provide the desired decorative pattern or color. Located next to ply 16 is a sheet 18 of phenolic-impregnated kraft paper.

On the opposite side of sheet 18, a metal foil layer 20 is provided. The metal foil layer is preferably steel, and is also preferably foraminous, both for lightness in weight, and also for the purpose of allowing bridges of resin to secure the phenolic layers on the opposite sides of the foil layer together. Desirably, a pattern of holes is punched in sheet 20, as seen in FIG. 2.

Additional phenolic-impregnated kraft paper layers are provided at 22, 24, 26, 28 and 30. When these layers are subjected to pressure and heat in a press, a laminate 32 is formed which can be used as a wallboard facing, as will be described.

FIGS. 3 and 4 show a laminate 38 which can be used either as a wallboard facing, or by itself in applications such as headliners or wainscots of busses and other vehicles used for public transportation. The laminate of FIGS. 3 and 4 is similar to that shown in FIGS. 1 and 2 in all respects except that phenolic sheet 28 is replaced by a second metal foil layer 34. In this laminate, therefore, there are two metal foil sheets 34 and 36. These metal foil layers are preferably foraminous sheets of steel. As shown, they are both located on the same side of the two-ply decorative melamine layer comprising sheets 37 and 39, but are spaced from each other by three phenolic layers 40, 42 and 44. An additional phenolic layer 46 is located between melamine sheet 39 and metal foil layer 36, and another phenolic layer 48 is located on the side of the laminate which is opposite the melamine layer. Preferably, the two metal foil layers 34 and 36 are separated from each other by as great a distance as possible, using additional phenolic layers as required. However, phenolic layer 48 is desirably provided to cover metal layer 34, and phenolic layer 46 is likewise provided in order to prevent the pattern of perforations in metal foil layer 36 from affecting the texture of the outer melamine layer 37.

FIG. 9 shows a type of foraminous steel foil sheet suitable for use in layer 20 of FIG. 1 and in layers 34 and 36 of FIG. 3. The steel foil sheet designated 50 is provided with round openings 52 arranged in a uniform pattern. The round shape was chosen because it represents the most common shape available in metal punches. However, the shape of the openings is of little consequence provided that the foil is flat (without burrs or bumps), and possesses in the perforated form, sufficient compressive strength in the plane of the foil to resist the shrinkage stresses imposed on the laminate by the melamine layer. Preferably, in order to provide sufficient compressive strength, the metal foil layers are each at least approximately 0.002 inch in thickness.

While foraminous metal foil sheets provide better adhesion between the phenolic layers because bridges of resin extend through the openings and secure the phenolic sheets together, unperforated steel foil can be used provided that suitable precautions are taken to insure adhesion of the phenolic layers to the foil. The steel foil can be prepared, for example, by treatment with a 10% solution of Butvar B-90 (Monsanto Company) in denatured alcohol. Butvar B-90 is a well-known polyvinyl butyral adhesive, and is used in this instance as a metal primer to secure the unperforated steel foil to the adjacent phenolic layers. The steel foil is air dried in an inclined position for about ten minutes, and then is oven dried for five minutes at 250.degree. F. and allowed to cool. Other suitable metal adhesives can be used instead of Butvar B-90. In addition, in some instances it is desirable to use Butvar B-90 or another suitable adhesive even when foraminous metal foil sheets are used.

FIGS. 5 and 6 show another laminate which is suitable for use either as a wallboard facing, or by itself as a headliner or wainscot for a transportation vehicle. The laminate of FIGS. 5 and 6 is similar to that of FIGS. 3 and 4 in all respects except that foraminous layers 34 and 36 are replaced respectively by foraminous layers 54 and 56, which are flattened steel wire screens. The construction of these screens is illustrated in FIGS. 10 and 11. In FIG. 10, the screen is shown as comprising a first array of generally parallel steel wires 58, 60, 62, 64, 66 and 68, and a second array of generally parallel steel wires 70, 72, 74, 76 and 78. The wires of the second array are superimposed upon those of the first array and arranged in substantially perpendicular relationship to the wires of the first array to form a foraminous layer.

The wires of the screen are flattened, as illustrated in FIG. 11, the flattening being accomplished by compression of the screen between a pair of rollers. Flattening by compression causes the perpendicular wires of the screen to merge together where they cross, forming what is essentially a metal foil layer similar to the one shown in FIG. 9. If desired, heat may be applied in order to forge the wires together. Flattening of the wires reduces the tendency of the pattern of the screen to appear on the melamine surface of the laminate. In addition, the flattening process makes it possible to form a screen without the need for weaving. Instead, the second array of parallel wires is placed on top of the first array of parallel wires, and the arrays are then compressed to produce a screen. The perpendicular wires of the screen are held together with sufficient strength by the compression to enable the screen to be handled in the process of forming the laminate. After the laminate is formed, the perpendicular wires of the screen are held together by virtue of the elements of phenolic resin which extend through the openings of the screen between opposed layers of phenolic-impregnated kraft paper.

The melamine layers of ordinary melamine-faced wallboards tend to shrink under conditions of low humidity, producing the condition illustrated in FIG. 12. FIG. 12 shows a gypsum wallboard 80 partially split at locations 82 and 84 as a result of shrinkage of a synthetic resin containing facing. It is this type of splitting which the invention is intended to avoid. FIG. 7 illustrates a gypsum wallboard faced on both sides with laminates of the type illustrated in FIG. 1. This wallboard comprises a gypsum core 86 having paper layers 88 and 90 on its opposite sides, and being provided with identical melamine-faced laminates 92 and 94 on its opposite sides. The melamine laminates are secured to their respective paper layers by a suitable adhesive. Each melamine laminate has a single foraminous metal foil layer, as shown in FIG. 1, and the single metal foil layer is sufficient to prevent splitting of the gypsum core even when the wallboard is exposed to very low humidity for extended periods of time. It is possible, of course, to use facing laminates having two metal foil layers, of the kind shown in FIGS. 3 and 5, but normally it is unnecessary to do so. It is desirable, however, to provide facings on both sides of the gypsum wallboard, as the facings on opposite side of the wallboard tend to balance each other and prevent bowing of the wallboard.

Often, it is not practical to provide facings on both sides, as one side of the wallboard is hidden. When this is the case, a wallboard of the kind shown in FIG. 8 may be used. The wallboard comprises a gypsum core 96 having paper faces 98 and 100 on its opposite sides. A laminate 102, of the kind shown in FIG. 1, is secured to paper layer 98 by a suitable adhesive. On the opposite side of the core, a metal sheet 104 is secured by adhesive to paper layer 100 to provide the necessary balance in order to prevent bowing of the wallboard.

A wallboard made up in accordance with the structure of FIG. 7 or 8 is an entirely new product in that it has not been practical, heretofore, to use a melamine facing on a low-strength wallboard core without subjecting the core to the kind of splitting illustrated in FIG. 12. Various low-strength core materials other than gypsum may be used, for example calcium silicate, mineral wool, ceramic fiber, perlite, sodium silica or silicate, or cement asbestos. The invention enables any of these materials to be faced with a decorative melamine laminate on one or both sides without being subject to splitting in a low humidity environment. The improved physical strength imparted to the wallboard by reason of the presence of the metal foil layers also makes it possible to use wider and taller panels and to use fewer supports.

The wallboard in accordance with the invention has certain advantages from the standpoint of fire protection. In the first place, the combustion products of melamine-formaldehyde and phenolic resins are comparatively less toxic than those of some so-called "fire-resistant" laminates. Secondly, the presence of the metal foil layer or layers reinforce the laminate, making it possible to use a minimum amount of flammable material. Third, the metal foil layer or layers in the facing act as heat sinks, improving the fire resistance of the wallboards.

The use of two spaced metal foil layers in the laminate, as shown in FIGS. 3 and 5 produces a laminate which is greatly improved from the standpoint of dimensional stability. The laminate also exhibits improved impact strength by reason of the ductility of the metal foil layers. The dimensional stability and high impact strength of the laminate makes it especially suitable for use in vehicle interiors.

The laminates in accordance with the invention may, of course, be used either by themselves, or as facings for low-strength wallboards, or even as facings for high-strength wallboard cores, including aluminum honeycombs and the like.