TWO-STEP PROCESS FOR PRODUCING SOLID SURFACE MATERIAL WITH FOAM BACKING

Abstract: A process of producing solid surface material is provided with a thin layer of filled polymer integrally formed with a backing of bubble-filled polymer, without an interface or transition zone in the polymer mix, using two-steps wet-on-wet casting.

Description: UI E TWO-STEP PROCESS FOR PRODUCING SOLID SURFACE MATERIAL WITH FOAM BACKING BACKGROUND OF THE INVENTION This invention relates to a process of producing a composite cast article having a polymeric solid surface with added filler and a backing of similar material also filled with hollow bubbles, with no transition zone of unfilled polymer between the layers. Solid surface materials are known in the art including those based on polymethyl methacrylate and alumina trihydrate. Basic technology for these products is disclosed in U.S. Patents 3,847,865 - Duggins (1974), 4,085,246 - Buser, Roedel and Vassiliou (1978), and published PCT patent application US88/14322 - Frank, Otremba, Pohl and Schlier (1988). Prior attempts to laminate such solid surface materials with bubble-filled backing material and fiberglass-reinforcement have led to expensive multi-step processes and to laminar products which had distinctly different layers with their own properties. Laminar products generally are more prone to delamination and other weaknesses due to the interface under certain conditions than integral products. Among the multi-layer, laminated products of this type is that of EP 285,046 - Schock (1993). All of the above-mentioned documents are incorporated herein by reference for their teachings of methods and materials for making solid surface filled polymeric materials. It would be desirable to be able to provide lighter weight sheet material with the surface characteristics of this solid surface material in integral form without laminar transitions between layers, and to be able to prepare such products by less expensive processes. SUMMARY OF THE INVENTION The present invention provides a process of producing the cast composite article comprising a polymer matrix and two zones of different filler, said article being substantially flat with two opposing faces, a first zone of such article including one face of the article having filler at a level in the range of 10 to 80% by weight of the filler plus matrix, and a second zone including the second face opposing said first face having filler of 5 to 60% and 3 to 30% of bubbles, both by weight of the filler and bubbles plus matrix, said first and second zones forming a continuum with essentially no layer of unfilled matrix between the two zones. Said process comprising the steps of forming a multi-layer composite article by casting on a flat surface a first mix comprising the polymerizable monomer(s) and a filler which will cure to give the composition of said first zone, and, before said first mix cures substantially, casting on the first mix a second mix comprising polymerizable monomer(s). filler, and bubbles which will cure to give the composition of said second zone, under conditions that will cause the second mix and the first mix to interpenetrate, so that there is essentially no interface in the matrix and no resulting layer of unfilled polymer, and curing the resulting composite article. In other embodiments, a third layer is added to the second layer, having a composition in the limits of the first layer. Also, a hard face can be added by applying it before the first layer with a filler harder than ATH. such as alumina, silica, calcium carbonate, or natural stone material such as granite. Furthermore, ground particles of filled or unfilled resin can be added to the first layer in accordance with the ground particles taught in US 4,085,246. DETAILED DESCRIPTION An advantage of the invention is that it provides a light weight, more economical solid surface material without any transition zone of polymer which could create a zone of brittleness or cause other mechanical difficulties. Parts, proportions and percentages herein are by weight except where indicated otherwise. "WET-ON-WET" CASTING PROCEDURE Two mixtures are prepared so they can be cast sequentially, into a mold, one on top of the other. Mixture (A) consists of a filler, such as alumina trihydrate. dispersed in a liquid phase consisting of a syrup containing approximately 20% polymethylmethacrylate in methyl methacrylate monomer along with an initiator. Additional monomer may be added to adjust the mix viscosity. Colored pigments and/or particles may be added to get a desired color and pattern. A typical composition for mixture (A) comprises: Wt % Methyl methacrylate 4.0 Syrup 36.0 Alumina trihydrate 42.0 Colored particles (30-150 mesh U.S. Standard 18.0 Sieve= 100-600μm) 100.0 Mixture (B) consists of a filler, usually lightweight, such as hollow glass microspheres along with calcium acarbonate. dispersed in a liquid phase consisting of a syrup containing approximately 20% polymethylmethacrylate in methvl methacrvlate monomer and an initiator. Additional monomer may be added to adjust casting viscosity. A typical composition for mixture (B) comprises: Wt % Methyl methacrylate 44.0 Syrup 1 1.0 Alumina trihydrate 37.0 "Scotchlite" K-l glass bubbles 8.0 (20-120μm, median 70μm, sp.gr. 0.125) 100.0 Mixture (A) is evacuated to remove air. then poured into a mold to form a 0.5cm layer in the bottom of the mold. Mixture (B), also evacuated, is then poured on top of the layer from mixture (A) in the mold while it is still wet and uncured. to form a second layer which is 1.4cm thick. After the structure has cured, the polymerized form of mixture (A) is the face layer and that of mixture (B) is the back foam layer. Although there appears to be two separate layers there is no interface between them. They are integral, with the polymer matrix continuous throughout the structure.

Claims: I CLAIM: 1. A process of producing a cast composite article comprising a polymer matrix and two zones of different filler, said article being substantially flat with two opposing faces, a first zone of such article including one face of the article having filler at a level in the range of 10 to 80% by weight of the filler plus matrix, and a second zone including the second face opposing said first face having filler of 5 to 60% and 3 to 30% of bubbles, both by weight of the filler and bubbles plus matrix, said first and second zones forming a continuum with essentially no layer of unfilled matrix between the two zones, said process comprising the steps of forming a multi-layer composite article by casting on a flat surface a first mix comprising polymerizable monomer and filler which will cure to give the composition of said first zone. and. before said first mix cures substantially, casting on the first mix a second mix comprising polymerizable monomer, filler, and bubbles which will cure to give the composition of said second zone, under conditions that will cause the second mix and the first mix to interpenetrate, so that there is essentially no interface in the matrix and no resulting layer of unfilled polymer, and curing the resulting composite article. 2. The process of claim 1 in which a third mix is cast on the second mix. said third mix being within the composition limits of said first mix under conditions that will cause the third mix and second mix to interpenetrate, so there is no interface in the matrix and no resulting layer of unfilled polymer, and curing the resulting three zone composite article. 3. The process of producing a hard-faced article by applying a base layer of polymerizable monomer with filler harder than alumina trihydrate to a flat surface, then forming a multi-layer composite article on said base layer and curing the resulting composite article in accordance with claim 1. 4. The process of claim 3 in which the harder filler is selected from the group consisting of alumina, silica, calcium carbonate and natural stone materials..

Inventors: SWARTS DONALD EUGENE, SWARTS, DONALD, EUGENE
Applicants: DU PONT, E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1996
Main classification: B29C39
IPC codes: B29C39, B29C41, B32B5, C04B14, C04B26, C08J9