This invention relates generally to the production of decorative plastic laminates, which are extensively used in making furniture, counter tops, paneling and other decorative or functional surfaces.
The art of making such laminates is well known. A plurality of sheets of resin impregnated kraft paper are stacked together to form a core or backing. The resin employed is a heat curable type such as phenol formaldehyde. A decorative sheet of paper having a printed design or solid color and impregnated with a melamine resin is laid over the core, and an overlay sheet, usually melamine impregnated alpha cellulose paper, is superimposed over the decorative sheet. In some instances, especially where the final product is of solid color, the overlay sheet may be omitted. A panel of particle board may be substituted for the core sheets.
The foregoing assembly of resin impregnated sheets is subjected to heat and compression by confining the same between heated press plates or molding cauls such that the sheets become firmly adhered to one another as the resin cures. A release sheet composed of relatively non-adhereable paper, plastic film or aluminum foil is interposed between the decorative surface and the caul to prevent adhesion between the caul and the decorative surface.
Various techniques have been developed for applying a textured surface to the decorative surface of such laminates. U.S. Pat. No. 1,742,516 describes a process wherein a design or letter is embossed in a laminate by using an engraved caul having the design debossed therein. U.S. Pat. No. 1,997,358 and No. 2,133,081 describe the texturizing of plastic laminates utilizing an embossed metal caul.
Inasmuch as engraved or embossed metal cauls are expensive to produce and have a short life span, subsequent efforts have been directed primarily toward substitute methods. U.S. Pat. No. 2,606,855 discloses a process of using a master to make a number of textured caul plates from a stack of resin impregnated paper. Similar techniques utilizing embossed or debossed plastic laminates as molding cauls are described in U.S. Pat. No. 3,303,081 and No. 3,311,520. U.S. Pat. No. 3,373,068 describes the use of particulate matter on the decorative sheet to impart texture thereto.
In my U.S. Pat. No. 3,616,011 there is described another method for making a textured molding caul wherein a textured original is sandwiched between a pair of thin flexible resin impregnated sheets. The sheets are forced intimately into the surface recesses of the original and the resin is cured. Thereafter, the resin-set sandwich of the original and the sheets are used as a master molding caul.
Often it is desirable to produce a laminate that simulates another product, a good example being a wood grained surface. In such a case, it has been possible to use a decorative sheet having a colored wood grain printed thereon, and the decorative surface may also be textured during the subsequent molding process. It is not usually possible or convenient, however, to impart a texture conforming to the print pattern, and the resulting product does not have the combined texture and appearance of a naturally stained wood wherein the grain is highlighted by differential absorption of the stain into the grain, saw marks or depressed areas of the wood.