Expandable polypropylene interpolymer particles
First Claim
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1. A process for producing expandable polypropylene particles comprising (a) suspending in an aqueous medium, a copolymer of propylene and sufficient olefin comonomers to give said copolymer a melting peak of less than 140°
- C., with the aid of a suitable suspending agent system;
(b) adding to said suspension vinyl aromatic monomer and a catalyst system such that the amount of monomer is 40 to 80% by weight based on copolymer plus monomer;
(c) polymerizing said monomer in the interior of said copolymer to form a polypropylene-polyvinylaromatic monomer interpolymer;
(d) separating said interpolymer from said suspension by acidifying, filtering, washing with water and drying in air;
(e) extruding said interpolymer in admixture with a lubricant and cell control agent and a peroxide, if used, to viscbreak said interpolymer to a melt flow (condition L) of at least 10, under conditions to minimize orientation stress in the final extrudate;
(f) impregnating said extrudate with a blowing agent to give expandable polypropylene-polyvinyl aromatic monomer interpolymers which can be expanded at 100°
C. to fine cell structure foams of density less than 2.0 pounds per cubic foot.
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Abstract
A process for producing a polypropylenepolystyrene interpolymer which can be impregnated with a blowing agent and can then be expanded under normal conditions for polystyrene particles to low density, fine cell structure foams. The interpolymer must be viscbroken, lubricated and stress relaxed in order to foam at 100° C. to densities less than 2.0 pcf.
33 Citations
12 Claims
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1. A process for producing expandable polypropylene particles comprising (a) suspending in an aqueous medium, a copolymer of propylene and sufficient olefin comonomers to give said copolymer a melting peak of less than 140°
- C., with the aid of a suitable suspending agent system;
(b) adding to said suspension vinyl aromatic monomer and a catalyst system such that the amount of monomer is 40 to 80% by weight based on copolymer plus monomer; (c) polymerizing said monomer in the interior of said copolymer to form a polypropylene-polyvinylaromatic monomer interpolymer; (d) separating said interpolymer from said suspension by acidifying, filtering, washing with water and drying in air; (e) extruding said interpolymer in admixture with a lubricant and cell control agent and a peroxide, if used, to viscbreak said interpolymer to a melt flow (condition L) of at least 10, under conditions to minimize orientation stress in the final extrudate; (f) impregnating said extrudate with a blowing agent to give expandable polypropylene-polyvinyl aromatic monomer interpolymers which can be expanded at 100°
C. to fine cell structure foams of density less than 2.0 pounds per cubic foot. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
- C., with the aid of a suitable suspending agent system;
Specification