Process for the Preparation of Expandable Polystyrene Beads
Expandable monovinylidene aromatic polymer, e.g., polystyrene, beads are prepared by a suspension polymerization process comprising polymerizing monovinylidene aromatic monomer, e.g., styrene, under suspension polymerization conditions with, based on the weight of the monomer: A. 0.05 to 0.60 percent by weight (wt %) of tricalcium phosphate, B. Greater than 0 to 0.1 wt % of calcium carbonate, C. 0.0002 to 0.005 wt % of co-stabilizer, D. 0.0001 to 0.01 wt % of a low molecular weight polyethylene wax, E. 0.4 to 0.9 wt % of a flame retardant, and F. 2 to 10 wt % of a C 3-6 hydrocarbon blowing agent. The expandable beads are converted to foam having a low thermal conductivity by contacting the separated and dried expandable beads at foaming conditions with, based on the weight of the monomer: A. 0.05 to 0.65 wt % of a glyceride comprising units of fatty acids with a C 8-26 chain length, and B. 0.005 to 0.30 wt % of a metal stearate.
1 . A process for preparing expandable monovinylidene aromatic polymer beads, the process comprising polymerizing a monovinylidene aromatic monomer under suspension polymerization conditions with, based on the weight of the monovinylidene aromatic monomer:
A. 0.05 to 0.60 percent by weight (wt %) of tricalcium phosphate,
B. Greater than 0 to 0.1 wt % of calcium carbonate,
C. 0.0002 to 0.005 wt % of a co-stabilizer,
D. 0.0001 to 0.01 wt % of a low molecular weight polyethylene wax with a melting temperature between 100° C. and 120° C., determined by DSC as the maximum of the first scan at a heating rate of 20° K/min,
E. 0.4 to 0.9 wt % of a flame retardant, and
F. 2 to 10 wt % of a C 3-6 hydrocarbon blowing agent.
2 . The process of claim 1 in which the monovinylidene aromatic monomer is of the formula:
in which R′ is hydrogen or methyl, Ar is an aromatic ring structure having from 1 to 3 aromatic rings with or without alkyl, halo, or haloalkyl substitution, wherein any alkyl group contains 1 to 6 carbon atoms and haloalkyl refers to a halo-substituted alkyl group.
3 . The process of claim 2 in which the monovinylidene aromatic monomer is styrene.
4 . The process of claim 3 in which the molecular weight of the polyethylene wax does not exceed 10,000 g/mol.
5 . The process of claim 4 in which the flame retardant is a halogenated organic compound.
6 . The process of claim 5 in which the blowing agent is at least one of butane, pentane, cyclopentane and hexane.
7 . Expandable monovinylidene aromatic polymer beads prepared by the process of claim 1 .
8 . Expandable polystyrene beads prepared by the process of claim 6 .
9 . The beads of claim 8 further comprising at least one of an antioxidant, filler, UV stabilizer, cling additive, light stabilizer, thermal stabilizer, mold release agent, tackifier, processing aid, crosslinking agent, colorant and pigment.
10 . A process for preparing monovinylidene aromatic polymer foam having a low thermal conductivity, the process comprising foaming the expandable monovinylidene aromatic polymer beads of claim 1 under foaming conditions with, based on the weight of the monovinylidene aromatic monomer:
A. 0.05 to 0.65 wt % of a glyceride comprising units of fatty acids with a C 8-26 chain length, and
B. 0.005 to 0.30 wt % of a metal stearate.
11 . The process of claim 10 comprising the further steps of drying and screening the beads of claim 1 before subjecting the beads to the foaming conditions.
12 . The process of claim 11 in which the expandable monovinylidene aromatic polymer beads are polystyrene beads.
13 . The process of claim 12 in which the glyceride is at least one glyceride of eicosanoic acid, octadecanoic acid, hexadecanoic acid and tetradecanoic acid.
14 . The process of claim 13 in which the metal stearate is at least one of calcium stearate, zinc stearate and barium stearate.
15 . Monovinylidene aromatic polymer foam made by the process of claim 10 .
16 . Polystyrene foam made by the process of claim 14 .
17 . Construction or building insulation board comprising the monovinylidene aromatic polymer foam of claim 15 .
18 . Construction or building insulation board comprising the polystyrene foam of claim 17 .