Rubber modified monovinylidene aromatic polymers and thermoformed articles
View Patent ↗The present invention is a rubber modified monovinylidene aromatic polymer composition which can be used in conventional thermoforming or other highly orienting forming or shaping processes to produce tough, cost effective, transparent containers or other packaging materials.
1. A rubber modified monovinylidene aromatic polymer composition comprising:
a) a monovinylidene aromatic polymer matrix;
b) from about 1.5 to about 8 percent by weight rubber (based on total diene content in the composition) dispersed as crosslinked rubber particles having primarily a core/shell morphology, said primarily core shell morphology being produced during polymerization of monovinylidene aromatic monomer in the presence of a blend of rubbers, and a volume average particle size of from about 0.1 to about 1.5 microns; where from about 40 to about 90 volume percent of the rubber particles have diameters of less than about 0.4 microns and from about 10 to about 60 volume percent of the rubber particles have diameters between about 0.4 and about 2.5 microns and wherein the rubber in the blend comprises a blend of (i) a conjugated diene block copolymer rubber comprising from about 15 to about 60 percent by weight monovinylidene aromatic monomer block and (ii) from about 2 to about 25 weight percent of conjugated diene homopolymer rubber based on the total weight of rubber in the composition; and
c) optionally from 0.1 to 4 weight percent mineral oil.
2. A polymer composition according to claim 1 comprising from about 2 to about 6 percent by weight rubber.
3. A polymer composition according to claim 1 where at least about 70 percent of the rubber particles have core/shell morphology and the volume average particle size is from about 0.2 to about 1 micron.
4. A polymer composition according to claim 1 where from about 50 to about 80 volume percent of the rubber particles have diameters of less than about 0.4 microns and from about 20 to 50 volume percent of the rubber particles have diameters of from about 0.4 to about 1.2 microns.
5. A polymer composition according to claim 1 where the monovinylidene aromatic matrix polymer is polystyrene.
6. The polymer composition of claim 1 wherein at least 90 percent of the total rubber particles have core/shell morphology and the volume average particle size of the rubber particles is from 0.2 to 0.6 micron.
7. A sheet suitable for thermoforming produced from the polymer composition of claim 1 having a thickness of from about 0.2 to about 4.5 mm.
8. An improved thermoformed article produced from a sheet, blank or other preformed starting material for a thermoforming application produced from polymer composition of claim 1 .