Moldable silane-crosslinked polyolefin foam beads

DETAILED DESCRIPTION OF THE INVENTION In accordance with the present invention, moldable expanded crosslinked polyolefin foam beads are produced using conventional extruder apparatus having suitable means for heating and cooling, with a blowing agent injected into the polymer melt or introduced in solid form.
Crosslinking of the polyolefin resin is carried out after extrusion when the polyolefin is brought into contact with moisture.
A silane-modified polyolefin resin is used, such as a polyethylene which contains carbon-bonded silyl groups.
This silated or silane-grafted resin is melt mixed in the extruder with the proper amount of a silanol condensation catalyst.
A plastic product made in this manner will crosslink when contacted with water, such as moisture in the atmosphere.
In making the novel beads of this invention, the silane-grafted polyolefin resin, the condensation catalyst, talc or other nucleating agent for cell size control, and any other desired additives typically are added to the hopper of an extruder.
The ingredients are melted, mixed and forwarded through the extruder.
At a point in the extruder where all of the ingredients are well mixed and fully melted, a blowing agent, preferably comprising a volatile organic compound, an inert gas or a mixture thereof, is injected under pressure into the molten polymer mix.
The blowing agent and polymer are sufficiently mixed and cooled to the proper foaming temperature.
The foamable melt is then extruded through a die plate containing a number of small holes.
The resultant foam strands are cut as they emerge from the die so that they are cut while the foam is still expanding.
In this manner, beads are produced, forming substantially closed cells with a thin skin present on the entire surface of each bead.
The crosslinking of the polyolefin then commences with exposure to the moisture present in the ambient atmosphere.
The beads can be collected after cutting and conveyed to a suitable storage area, such as a porous bag, and held until the crosslinking reaction has proceeded to the extent that the crosslinked polyolefin beads are heat stable enough to be molded