Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1998-06-03
2001-10-16
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C428S411100, C428S421000, C428S500000, C428S521000, C428S522000
Reexamination Certificate
active
06303224
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable
STATEMENT REGARDING FEDERALLY FUNDED RESEARCH
Not Applicable
FIELD OF THE INVENTION
This invention relates generally to polyphenylene ether and polystyrene polymers, and related articles. More particularly, it concerns the use of protective layers for polyphenylene ether or polystyrene-based articles, and to methods for attaching such layers.
BACKGROUND OF THE INVENTION
Polymer compositions based on polystyrene resins or polyphenylene ether (PPE) resins are commercially attractive materials. Many polystyrenes, for example, are characterized by high strength, impact resistance, and insulating capacity—both thermal and electrical. They are used for appliances, food containers, packaging, and for many other products.
PPE resins also have a wide variety of desirable attributes. They possess good chemical and physical properties, such as impact strength, hydrolytic stability, and high temperature-resistance. Moreover, they can be easily formed into films, fibers, and molded articles. One of the most popular compositions of this type is based on a blend of PPE with various types of styrene resins, such as rubber-modified, “high impact styrene”.
Despite their many attributes, PPE compositions and polystyrene compositions are sometimes unsuitable for exterior applications, such as an outdoor environment. The “weatherability” of articles based on these materials is not always at an acceptable level, since the materials tend to exhibit yellowing when exposed to ultraviolet light. In addition to the discoloration, the yellowing can in turn act as the source of cracks which can weaken or permanently damage the article. PPE articles are therefore sometimes painted to shield them from UV sources.
Other techniques could be used to provide weatherability for PPE or polystyrene articles. For example, a thin layer of a weatherable material such as poly(vinylidene fluoride) (PVDF) could be applied to the surface of the article. In this manner, the article would continue to possess the desirable properties of the base material (i.e., the PPE or polystyrene), while also exhibiting the characteristics often required for an outdoor environment. As an example, U.S. Pat. No. 4,563,393 (Kitigawa et al) describes the use of a layer of a vinylidene fluoride resin to protect a layer of a thermoplastic resin such as PPE or polycarbonate from the forces of an outdoor environment. Similarly, it may sometimes be desirable to apply a layer of a PVDF-type material to a base layer of polystyrene, for weatherability or some other purpose.
It is usually critical that the protective layer adhere very tightly to the base layer. In the case of layers formed from chemically dissimilar polymers like PVDF with either PPE or polystyrene, satisfactory adhesion between the layers is not easily obtained. The Kitigawa et al invention relies on the use of polymerized units of an ethylenic unsaturated carboxylic acid ester to improve adhesion between the vinylidene resin and the thermoplastic base layer. The carboxylic acid ester units can be in the form of a copolymer-constituent of the base layer polymer, as an example.
There continues to be a need for additional techniques for improving the adhesion between a base layer of a PPE-based or polystyrene-based material, and an overlying layer (e.g., a protective layer) made from a material which is normally incompatible with PPE and polystyrene, such as a fluoride-based polymer. The adhesion should be strong enough to prevent any substantial peeling of the protective layer during rigorous conditions of use, e.g., in an outdoor environment exposed to a considerable amount of UV light. Moreover, the technique should be cost-effective and relatively simple to utilize in a larger-scale, industrial fabrication setting, such as a commercial molding facility. Furthermore, the adhesion technique should not adversely affect any of the desired properties for the completed article, e.g., the impact strength of a PPE/styrene base layer composition, or the weatherability of the protective layer.
SUMMARY OF THE INVENTION
The needs cited above have been met by the discoveries upon which the present invention is based. One embodiment of this invention is directed to a tie layer for improving the adhesion of a layer of a fluoride-based polymeric material to a layer of a polyphenylene ether-based material or a polystyrene-based material. The tie layer comprises a copolymer of a styrenic material like high impact polystyrene, and an acrylic material which is compatible with the fluoride-based polymer, such as poly(methyl methacrylate) (PMMA). In preferred embodiments, the copolymer is of the graft- or block-type, and comprises at least about 40% by weight styrenic material.
In some of the preferred embodiments, the tie layer composition further comprises at least one flexibilizing agent which is compatible with the fluoride-based polymeric material or the PPE/polystyrene-based material. Exemplary flexibilizing agents are blends or copolymers which comprise rubber and polystyrene, or core-shell impact modifiers, or combinations of these types of materials.
The tie layer can be coextruded with the other two layers by conventional methods. The resulting adhesion of the fluoride-based layer to the PPE or polystyrene layer (through the tie layer) is very high, as demonstrated by peel-strength evaluation. Moreover, these multi-layer articles continue to display all of the desirable attributes of both the base layer material and the fluoride-based material.
Another aspect of the present invention relates to a method for improving the adhesion of a fluoride-based polymer layer to a PPE or polystyrene-based polymer layer. The method comprises situating a tie layer between the two primary layers, wherein the tie layer comprises a copolymer of a styrenic material like high impact polystyrene, and an acrylic material such as poly(methyl methacrylate) (PMMA). The tie layer composition often contains at least one flexibilizing agent, as mentioned above. In preferred embodiments, all of the layers are coextruded or laminated together by conventional techniques.
Still another embodiment of the invention is directed to an article which comprises:
a) a fluoride-based polymer layer;
b) a polyphenylene ether-based or polystyrene-based polymer layer; and
c) a tie layer disposed between layer (a) and layer (b), having a composition as described herein.
Exemplary articles include various types of roofing panels, shingles, and similar types of structures used outdoors, such as canopies.
Other details regarding this invention are comprehensively provided in the sections which follow.
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