Process for laminating rigid polyurethane foam to a gelled polyester resin

#The field of the invention relates to plastic foams, and more particularly, to relatively rigid polyurethane foams which are to be laiminated to a polyester resin formed from the reaction of an unsaturated polyester laiminating resin which contains an unsaturated monomer such as styrene. One process for forming such a lamination is disclosed in an application by Francis Gallap and the present inventor in U.S. Pat. No. 3,859,401 filed on Aug. 9, 1971 which patent is hereby incorporated by reference herein.

#Many useful articles can be made from a laminate having an outer skin of a polyester resin such as fiberglass-reinforced polyester resin and an inner layer of a rigid polyurethane foam. Such laminates have been widely used in the construction of boats. While various processes have been used to form such laminates, a problem common to all prior art processes is poor adhesion at the interface between the polyester layer and the foam.

#While the process disclosed in the above-described U.S. Pat. No. 3,859,401 leads to substantially improved adhesion, still further improvements would permit a further increase in load-bearing ability and thus could permit wider use of such panels as, for instance, in multi-story buildings fabricated from polyester-polyurethane laminates.

#FIG. 1 is a perspective view of a mold apparatus of the type useful to produce a laminate utilizing the formulations of the present invention.

#FIG. 2 is a graph showing a time-temperature profile for a typical curing cycle for a laminate utilizing a formulation of the present invention.

#FIG. 3 is a cross-sectional side elevation of the laminate made using the formulation of the present invention.

#The polyurethane foam formulations of the present invention are advantageously used in a manner so that the foam is expanded and cured against a partially uncured but gelled unsaturated polyester laminating resin which in its uncured state, contained an unsaturated monomer such as styrene. It is believed that this gelling step causes a substantial amount of the styrene (typically a styrene level of about 30% is present with the uncured, unsaturated polyester laminating resin) to either cross-link or volatilize. In this manner, it is believed that the styrene is not present in an amount sufficient to break down or degrade the foaming polyurethane. It is further believed that the curing of the unsaturated polyester and styrene in contact with the curing polyurethane results in some chemical cross-linking which cross-linking is believed greatly enhanced by the formulations of the present invention.

#Turning now to FIG. 1, a molding apparatus is depicted which is of the type described in U.S. Pat. No. 3,809,357 filed Apr. 23, 1970 by Francis Gallap and assigned to the assignee of the present invention. That patent is incorporated by reference herein. Similar molding apparatus is also disclosed in the above-described U.S. Pat. No. 3,859,401. While the present formulation is described as useful in such a molding apparatus, the invention is not limited to use in such apparatus, as improved adhesion may be obtained by the use of any molding apparatus or forming method which permits contact between the reacting polyurethane and polyester.

#The apparatus of FIG. 1 has a stationary mold surface 10 and a movable mold surface 11 which is attached by counterweighted arms 12 and 13 to shaft 14. Shaft 14 is driven by a pair of hydraulic torque motors 15 and 16. When hydraulic fluid is passed through motors 15 and 16, movable mold surface 11 rotates to a closed position where it is parallel to stationary mold surface 10. The four sides 17 through 20 of stationary mold surface 10 closed the cavity between surfaces 10 and 11 and a pair of latches 21 and 22 help to hold mold surface 11 in a closed position. Mold surfaces 10 and 11 are advantageously heated by the passage of heat transfer fluid through tubes 23 through 26. Sides 17 through 20 are advantageously hinged so that they may be moved away from mold surface 10 after the curing step is complete. This movement may be carried out hydraulically through pistons such as piston 30 which is attached to side 20 through arm 31. The sides are hinged to mold surface 10 by hinges such as those shown along side 20 and indicated by reference characters 32 and 33.