Recovery and utilization of scrap in production of foamed thermoplastic polymeric products

Claim 5

The method as defined in claim 1, wherein at least 80% by weight of the fragments provided by said grinding step have a maximum dimension not more than 0.5 in.

Claim 6

The method as defined in claim 1, wherein the belt is heated, before reaching the end of the heating zone, by applying heat to the surface of the belt opposite said bed; and said bed is heated in said heating zone by directing heat onto said bed.

Claim 7

In the production of meat trays, egg cartons and the like by thermoforming from foam polystyrene sheet, the improved method for recovering scrap foam polystyrene from the thermoforming operation, comprising grinding the scrap into fragments, not more than 20% of said fragments having a maximum particle size which does not exceed the thickness of the foamed sheet being thermoformed, the balance of said fragments having a maximum dimension not greater than 1 in.; continuously depositing said fragments on a moving endless metallic belt to form on the belt a bed of fragments having a depth of 0.25-3.5 in.; continuously advancing the belt, with said bed supported thereon, through a heating zone and thereby heating said fragments to a temperature above the fusion temperature of the polystyrene but below the thermal degradation temperature thereof, said fragments fusing during passage through the heating zone, and the resulting bodies of fused polystyrene joining with the bodies of fused polystyrene from adjacent fragments, the initial depth of said bed of fragments being such that the total fused polystyrene is inadequate to cover the surface area of the belt, and the fused polystyrene therefore forming on the belt as a reticulated layer; then continuously advancing the belt, with the reticulated layer of fused polystyrene thereon, through a cooling zone and thereby cooling the belt and the fused polystyrene to a temperature not exceeding about 55*F., whereby the fused polystyrene is caused to solidify into a thin, brittle, reticulated web; bending the belt away from said reticulated web, whereby said web is separated from the belt and said web is broken into individual pieces; and grinding said pieces to produce particles of solid polystyrene of a size suitable for extrusion.

Claim 8

In the production of meat trays, egg cartons and the like by thermoforming from foam polystyrene sheet, the improved method for recovering scrap foam polystyrene from the thermoforming operation, comprising grinding the scrap into fragments, not more than 20% of said fragments having a maximum particle size which does not exceed the thickness of the foamed sheet being thermoformed, the balance of said fragments having a maximum dimension not greater than 1 in.; continuously depositing said fragments on a moving endless metallic belt to form on the belt a bed of fragments having a depth of 0.25-3.5 in.; continuously advancing the belt, with said bed supported thereon, through a heating zone and thereby heating said fragments to a temperature above the fusion temperature of the polystyrene but below the thermal degradation temperature thereof, said fragments fusing during passage through the heating zone, and the resulting bodies of fused polystyrene joining with the bodies of fused polystyrene from adjacent fragments, the initial depth of said bed of fragments being such that the total fused polystyrene is inadequate to cover the surface area of the belt, and the fused polystyrene therefore forming on the belt as a reticulated layer; then continuously advancing the belt, with the reticulated layer of fused polystyrene thereon, through a cooling zone and thereby cooling the belt and the fused polystyrene to a temperature not exceeding about 55*F., whereby the fused polystyrene is caused to solidify into a thin, brittle, reticulated web; bending the belt away from said reticulated web, whereby said web is separated from the belt and said web is broken into individual pieces; and grinding said pieces to produce particles of solid polystyrene of a size suitable for extrusion.