Stock material or miscellaneous articles – Composite – Of addition polymer from unsaturated monomers
Reexamination Certificate
2003-02-19
2004-11-23
Seidleck, James J. (Department: 1711)
Stock material or miscellaneous articles
Composite
Of addition polymer from unsaturated monomers
C428S515000, C428S521000, C525S071000, C525S086000, C525S095000
Reexamination Certificate
active
06821635
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to blends of rubber modified monovinylidene aromatic polymers.
Rubber modified monovinylidene aromatic polymers, such as high impact polystyrene (HIPS), have found numerous applications which require high impact strength. One application wherein HIPS is typically used is food packaging products which specifically require good impact strength and transparent properties. Although toughness is achieved by HIPS resins, the transparency of thermoformed articles, such as thermoformed cups, is achieved using an expensive HIPS product having rubber particles with a specific capsule morphology.
Numerous attempts have been made to acquire the necessary balance of toughness and transparency in thermoformed articles using various materials and techniques. Transparent resins, such as polystyrene, polyethylene terephthalate and polypropylene have been used to produce transparent packaging via in-line thermoforming. However, each of these materials have certain drawbacks: polystyrene is too brittle, polyethylene terephthalate is relatively expensive and difficult to process requiring relatively long cycle time, and polypropylene has limited processability in that thermoformed articles therefrom demonstrate poor dimensional stability.
Transparent packaging has also been made using optical grade general purpose polystyrene (GPPS) which is oriented to obtain a balance of clarity and toughness. However, such products can only be obtained to a maximum sheet thickness of 0.75 mm due to process constraints, which is not thick enough for some thermoforming applications. Polyvinylchloride has also been used to produce transparent packaging, but is thermally unstable and undesirable for food packaging.
Blends of a GPPS and a styrene-butadiene (S-B) copolymer generally offer a good balance of clarity and toughness, however, such blends have certain limitations, because S-B copolymer is relatively expensive and forms gels when extruded at temperatures in excess of 215° C. Maintaining the extrusion temperature below 215° C. typically results in lower output rates and higher conversion costs. In addition, GPPS and S-B copolymer blends are often associated with poor taste and odor properties when used in food packaging.
A good balance of clarity and toughness can also be obtained by blends of a GPPS having molecular weight from about 260,000 to 400,000 and a HIPS, when sheet or film made from such blends are used to form certain articles, such as a drinking cup, at a forming temperature below 144° C. and draw ratios of 0.4 to 1.5. However, lower forming temperature often results in final articles having poor geometric definition resulting in poor handling thereof, such as stacking and lip rolling during the fabrication of drinking cups.
Therefore, there remains a need for polymers which can produce cost effective transparent packaging, which can be used in food packaging and non-food packaging markets, and can be produced by conventional thermoforming lines.
SUMMARY OF THE INVENTION
The present invention is a blend of a monovinylidene aromatic polymer, a rubber modified monovinylidene aromatic polymer, and monovinyl aromatic-conjugated diene copolymer which can be used to produce cost effective, transparent packaging that can be used in food packaging and non-food packaging markets, and can be produced using conventional thermoforming equipment. The blend (blend A) comprises:
a) from 49 to 70, preferably 60, weight percent based on the total weight of the blend, of a monovinylidene aromatic polymer having a weight average molecular weight (Mw) of from 210,000 to 400,000 and a melt flow rate of less than 12.0 g/10 min.;
b) from 20 to 50, preferably 36, weight percent based on the total weight of the blend, of a rubber modified monovinylidene aromatic polymer comprising a monovinylidene aromatic polymer matrix having rubber particles dispersed therein, wherein the rubber particles comprise, based on the total weight of the rubber particles, from 25 to 100 weight percent rubber particles having a capsule morphology and a volume average particle size of from 0.1 to 0.4 microns; and from 75 to 0 weight percent rubber particles having an entanglement morphology having a volume average particle size of from 0.25 to 1 micron; and
c) a monovinyl aromatic-conjugated diene copolymer,
wherein:
i) the rubber and rubbery component in the rubber modified monovinylidene aromatic polymer and the monovinyl aromatic-conjugated diene copolymer range from 3 to 10 weight percent, preferably 5.4 weight percent, based on the total weight of the blend A; and
ii) the amount of the monovinyl aromatic-conjugated diene copolymer is less than 7 weight percent, based on the total weight of the blend A.
In a preferred embodiment of the present invention, a multilayer sheet or film has two layers comprising a layer of one polymer blend (A) and a second layer of another polymer blend (B), or three layers comprising a core or middle layer of one polymer blend (A) and an outer or capping layer (B) located on each side of the core or middle layer. More specifically, the two-layer film or sheet comprises:
a) from 2 to 30, preferably 5, percent of the total thickness of the film or sheet, of two outer layers of a blend (blend B) comprising:
1) from 0 to 50, preferably 0, weight percent based on the total weight of the blend B, of a monovinylidene aromatic polymer having a weight average molecular weight (Mw) of from 170,000 to 325,000 and a melt flow of less than 18.0 g/10 min.;
2) from 50 to 100, preferably 96, weight percent based on the total weight of the blend B, of a rubber modified monovinylidene aromatic polymer comprising a monovinylidene aromatic polymer matrix having rubber particles dispersed therein, wherein the rubber particles comprise, based on the total weight of the rubber particles, from 25 to 100 weight percent rubber particles having a capsule morphology and a volume average particle size of from 0.1 to 0.4 microns; and from 75 to 0 weight percent rubber particles having an entanglement morphology having a volume average particle size of from 0.25 to 1 micron; and
3) from 0 to 10, preferably 4, weight percent based on the total weight of the blend B, of a monovinyl aromatic-conjugated diene copolymer; and
b) from 70 to 98, preferably 95, percent of the total thickness of the film or sheet of a blend (blend A) comprising:
1) from 49 to 70, preferably 60, weight percent based on the total weight of the blend A, of a monovinylidene aromatic polymer having a weight average molecular weight (Mw) of from 210,000 to 400,000 and a melt flow of less than 12.0 g/10 min.;
2) from 10 to 50, preferably 36, weight percent based on the total weight of the blend A, of a rubber modified monovinylidene aromatic polymer comprising a monovinylidene aromatic polymer matrix having rubber particles dispersed therein, wherein the rubber particles comprise, based on the total weight of the rubber particles, from 25 to 100 weight percent rubber particles having a capsule morphology and a volume average particle size of from 0.1 to 0.4 microns; and from 75 to 0 weight percent rubber particles having an entanglement morphology having a volume average particle size of from 0.25 to 1 micron; and
3) from 1 to 10, preferably 4, weight percent based on the total weight of the blend A, of a monovinyl aromatic-conjugated diene copolymer;
wherein:
i) the rubber and rubbery component in the rubber modified monovinylidene aromatic polymer and the monovinyl aromatic-conjugated diene copolymer range from 3 to 10 weight percent, preferably 5.4 weight percent, based on the total weight of the two-layer film or sheet;
ii) the amount of the monovinyl aromatic-conjugated diene copolymer is less than 7 weight percent, based on the total weight of the two-layer film or sheet; and
iii) the amount of the monovinylidene aromatic polymer having a weight average molecular weight (Mw) of from 210,000 to 400,000 and a melt flow rate of less than 12.0 g/10 min. is at least 34 weight percent, based on the total weight of
Sugden John L.
Wagner Phillip A.
Dow Global Technologoies Inc.
Seidleck James J.
Tran Thao
LandOfFree
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