Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1998-01-06
2002-04-23
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C524S505000
Reexamination Certificate
active
06376606
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
FEDERALLY SPONSORED RESEARCH
Not applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for the manufacture of a semi-transparent thermoplastic composition of a polyphenylene ether resin and a styrenic block copolymer wherein the processes comprises melt-mixing the polyphenylene ether resin in a powder form with the styrenic block copolymer and wherein the styrene-butadiene copolymer is a linear di-block copolymer, a tri-block copolymer, or a mixture of di-block and tri-block copolymers. The composition of the invention may also contain polystyrene resin.
The invention also relates to articles formed out of the compositions made by the process of the invention.
2. Brief Description of the Related Art
In the food handling area, clamshell styled containers having an opaque bottom and a see-through top are in great demand for prepared foods. Busy consumers desire to purchase entrees at a local store or restaurant and take the meal home for the family meal. Reheating the food in a microwave oven is often the method of choice because of convenience and time and consequently the clamshell styled containers must have sufficient heat resistance to withstand steam and hot greases and oils. Additionally, the containers must have sufficient ductility to not break on handling and use by both the food preparer and the consumer.
In order to achieve great penetration into the clamshell styled container market, a resin needs to be of low cost and have outstanding processability, have sufficient transparency for food to be seen through the container top, have sufficient ductility to withstand breakage, and be able to resist hot greases and oils from foods on heating in a microwave oven.
Polystyrene resins are widely used thermoplastic resins because of their low cost and easy processability. These resins are available as homopolymer polystyrene (often called crystal polystyrene), as block copolymers with elastomeric materials (e.g., S-B-S, S-(EB)-S, S-EP copolymers), and as impact modified graft resins with polybutadiene resin (HIPS). Within these categories, there are flame-retardant, abrasion resistant, super-tough, UV-resistant, expandable, and environmental stress crack resistant grades that enable these resins to be used in a wide variety of everyday consumer goods such as toys, packaging, housewares, construction materials, automobile parts, and disposables.
Polystyrene resins are currently used in many clamshell designed containers, both in foamed opaque clamshells and in containers having see-through lids. Unfortunately, the properties of the various polystyrene resins are insufficient albeit for different reasons for great penetration into the market for clamshell styled containers having an opaque bottom and a see-through top. For example, crystal polystyrene is insufficient in ductility although acceptable in cost, processing, and transparency for the top. Addition of rubbery styrenic copolymers (S-B-S, S-EB-S) to crystal polystyrene improves the ductility but at the expense of the necessary transparency. High impact polystyrene (i.e., HIPS) has good impact strength but is not transparent. Polystyrene-butadiene copolymers containing over fifty percent styrene exhibit good ductility, cost, and transparency but are insufficient in heat resistance.
Poly(phenylene ether) resins (referred to hereafter as “PPE”) are commercially attractive materials because of their unique combination of physical, chemical, and electrical properties. Commercially, most PPE are sold as blends with predominantly high impact polystyrene resins. PPE are miscible with polystyrene resins in all proportions and because of the very high glass transition temperatures of PPE, the blends of PPE with polystyrene resins possess higher heat resistance than that of the polystyrene resins alone. Moreover, the combination of PPE with high impact polystyrene resins results in additional overall properties such as high flow and ductility, however, such blends are not transparent or even semi-transparent. Examples of such blends can be found in U.S. Pat. Nos. 3,383,435; 4,097,550; 4,113,800; 4,101,503, 4,101,504; 4,101,505; 4,128,602; 4,139,574; and 4,154,712 among others. The properties of these blends can be further enhanced by the addition of various additives such as impact modifiers, flame retardants, light stabilizers, processing stabilizers, heat stabilizers, antioxidants and fillers but none of these additives results in transparent or semi-transparent compositions that would be useful for the aforementioned clamshell styled containers having a see-through top. Moreover, the melt blending of styrene-butadiene copolymer, wherein the styrene content in the copolymer is at least 50% by weight based on the weight of the copolymer, with pellets of PPE or PPE blended with high impact polystyrene results in degradation of the styrene-butadiene copolymer and sheet made the composition has an unacceptable surface quality, including unacceptable gels.
It is therefore apparent there continues to be a need for improved compositions as well as processes to manufacture compositions containing polystyrene resins that have acceptable ductility, heat resistance, and transparency for use in clamshell styled containers having a see-through top.
SUMMARY OF THE INVENTION
The needs discussed above have been generally satisfied by the discovery of a process for the manufacture of a semi-transparent thermoplastic composition containing:
a) a polyphenylene ether resin, and
b) a styrene-butadiene copolymer, wherein the styrene content in the copolymer is at least 50% by weight based on the weight of the copolymer, and wherein the butadiene block length and structure results in butadiene domains that are smaller than the wavelength of visible light;
wherein the process comprises melt-mixing the polyphenylene ether resin in a powder form with the styrenic block copolymer and wherein the styrene-butadiene copolymer is a linear di-block block copolymer, a tri-block block copolymer, or a mixture of di-block and tri-block copolymers.
The styrene-butadiene copolymer may also be a tapered di-block or tri-block copolymer as well as various mixtures of any of the foregoing copolymers. The process may optionally include melt mixing crystal polystyrene with the polyphenylene ether resin, and styrene-butadiene copolymer.
The description which follows provides further details regarding this invention.
DESCRIPTION OF THE DRAWINGS
Not applicable.
DETAILED DESCRIPTION OF THE INVENTION
Polyphenylene ether resins are a well known class of compounds sometimes referred to as polyphenylene oxide resins. Examples of suitable PPE and processes for their preparation can be found in, for example, U.S. Pat. Nos. 3,306,874; 3,306,875; 3,257,357; and 3,257,358. Compositions of the present invention will encompass homopolymers, copolymers and graft copolymers obtained by the oxidative coupling of phenolic compounds. The preferred PPE used in compositions of the present invention are derived from 2,6-dimethyl phenol. Also contemplated are PPE copolymers derived from 2,6-dimethyl phenol and 2,3,6-trimethyl phenol.
Useful PPE include poly(2,6-dimethyl-1,4-phenylene ether) resin having an intrinsic viscosity (I.V.) of between about 0.10 and about 0.60 dl/g as measured in toluene at 25° C. and a concentration of 0.6 gram per 100 ml. In a preferred embodiment of the invention, the PPE have an intrinsic viscosity (I.V.) of between about 0.25 and about 0.35 dl/g as measured in toluene at 25° C. and a concentration of 0.6 gram per 100 ml.
The present compositions also contain, as component B, a styrene-butadiene copolymer, wherein the styrene content in the copolymer is at least 50% by weight based on the weight of the copolymer, and wherein the butadiene block length and structure results in butadiene domains that are smaller than the wavelength of visible light. When the butadiene block length and structure results in butadiene domains that are larger than the wavelength of vis
Asinovsky Olga
General Electric Co.
Seidleck James J.
LandOfFree
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