Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1997-10-01
2002-05-21
Gallagher, John J. (Department: 1733)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C156S308600, C156S001000, C156S331600, C285S285100, C285S288100, C285S290100, C525S084000
Reexamination Certificate
active
06391950
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to solvent-based cements for bonding joints of polyvinyl chloride (PVC) pipe and fittings. This invention also relates to adhesives or sealants useful for bonding or welding two polymeric surfaces, at least one of which is PVC.
BACKGROUND OF THE INVENTION
Nearly half of the PVC manufactured today is used to form pipes, conduits, and fittings. PVC pipes and fittings are used extensively in the construction industry for both homes and businesses. For example, PVC pipes are used to transport potable water and water for household uses; for drain, waste, and vent (DWV) piping; for outdoor plumbing such as for irrigation and sprinkler systems; for hot tubs, spas, and bathtubs; and for electrical conduits.
Cements, or adhesives, used to form PVC pipe joints must meet both a lap shear bond strength standard and a hydrostatic burst strength standard, both set forth in ASTM D 2564-88, incorporated herein by reference. A strong bond between two pieces, at least one of which is thermoplastic PVC, is obtained by softening the PVC with the solvent in the cement so that the thermoplastic resin at the interface of the pieces to be joined flow together to bond the pieces when they are pressed together. The PVC resin in the cement serves to fill any voids between the pieces, thereby strengthening the bond. Conventional PVC pipe cements consist of from 10 weight percent to about 14 weight percent PVC resin in one or more organic solvents.
In recent years, environmental concerns have prompted efforts aimed toward reducing the volatile organic compounds (VOC) in industrial materials, including plastic pipe cements. Initial efforts typically involved increasing the resin content of the cement. It was discovered, however, that when the amount of PVC was increased from 10 weight percent up to more than about 14 weight percent, the cement displayed the consistency of a gel and was difficult to handle. Further, in order to comply with ASTM D 2564-88 specifications, the cement must be capable of dissolving an additional 3 weight percent of PVC resin without gelation. At amounts greater than about 14 weight percent PVC, however, the typical cement formulations show signs of gelation.
Alternatively, the art-provides compositions that include inert fillers, for example the hollow ceramic spheres and thixotropic agents such as fumed silica and bentonite clay disclosed by Patel et al., U.S. Pat. No. 5,252,634, and by Bush et al., U.S. Pat. No. 5,416,142, both patents being incorporated herein by reference. The cements contain a resin selected from polyvinyl chloride, chlorinated polyvinyl chloride, and acrylonitrile-butadiene-styrene copolymer. The cements produced according to these patents are relatively expensive because of the cost of the hollow ceramic spheres.
King, Sr. discloses in U.S. Pat. No. 4,788,002 compositions comprising 5- or 6-member lactam rings with a cosolvent selected from mono-alcohols having up to four carbon atoms; lower alkyl esters (up to four carbon atoms) of lower alkanoic acids (also up to four carbon atoms); and PVC or ABS polymer. The cosolvents disclosed by King, Sr. are volatile organic compounds that contribute to the VOC content of the cement.
It would be desirable to formulate a low VOC cement with a polymer that could contribute to the ultimate bond strength of the bond or weld formed by the cement.
SUMMARY OF THE INVENTION
It has now been discovered that a solvent-based cement containing a polymeric material of a rigid methyl methacrylate polymer, a rigid styrene-acrylonitrile polymer, and a flexible copolymer of an alkyl methacrylate grafted onto an unsaturated rubber works exceptionally well in certain bonding applications. Thus, according to the present invention, there is provided a cement composition comprising at least about 10% by weight of a polymeric material of a rigid methyl methacrylate polymer, a rigid styrene-acrylonitrile polymer, and a flexible copolymer of an alkyl methacrylate grafted onto an unsaturated rubber. The grafted rubber is preferably a copolymer of styrene butadiene rubber (SBR) that is grafted with an alkyl methacrylate and, optionally, styrene.
The cement composition of the invention further comprises at least about 10% by weight of a solvent or a mixture of solvents. The cement may optionally contain other thermoplastic resins or polymers, such as polyvinyl chloride, chlorinated polyvinyl chloride, acrylonitrile-butadiene-styrene copolymer, acrylic, polycarbonate, cellulose acetate, polyacrylamide, polyamide, or polystyrene. The invention also provides a method of joining two pieces of thermoplastic material, such as poly(vinyl chloride) piping and fittings, and the product piece having one or more joints formed thereby.
The cement compositions of the invention have reduced volatile organic content as compared to conventional PVC pipe cements, at workable viscosities. Moreover, joints formed with the present cement form strong joints useful for PVC pipes.
DETAILED DESCRIPTION
The cements or adhesives of the invention comprise a polymeric material and one or more organic solvents. The polymeric material of the invention contains a polymer of predominantly methyl methacrylate, a styrene-acrylonitrile copolymer, an unsaturated rubber grafted with an alkyl methacrylate, and, optionally styrene. The cements or adhesives of the invention also comprise one or more solvents and, optionally, one or more additional resins. The solvent is preferably N-methyl pyrrolidone or a mixture of solvents that includes N-methyl pyrrolidone.
The polymeric material of the invention comprises at least about 15 parts by weight, preferably at least about 30 parts by weight, of the polymer of predominantly methyl methacrylate and comprises and up to about 70 parts by weight, preferably up to about 60 parts by weight, of the polymer of predominantly methyl methacrylate. In addition, the polymeric material of the invention comprises at least about 10 parts by weight of the styrene-acrylonitrile copolymer and comprises up to about 50 parts by weight, preferably up to about 40 parts by weight, of the styrene-acrylonitrile copolymer. The polymeric material of the invention also comprises at least about 20 parts by weight, preferably at least about 25 part by weight, of the unsaturated rubber grafted with an alkyl methacrylate and comprises up to about 50 parts by weight, preferably up to about 40 parts by weight of the unsaturated rubber grafted with an alkyl methacrylate. Finally, the polymeric material of the invention optionally comprises styrene. (It will be appreciated that each of the foregoing weight percent limitations, as well as each of the other quantitative limitations provided for the invention that follow, may be employed alone or in combination with other limitations.) The polymeric material preferably comprises a rigid component that is a homopolymer or copolymer of methyl methacrylate, a rigid styrene-acrylonitrile polymer, and a styrene butadiene rubber grafted with methyl methacrylate. Such polymeric materials are commonly referred to as methacrylate acrylonitrile butadiene styrene polymers (MABS).
The preferred copolymer of the invention and its preparation is described in U.S. Pat. No. 4,393,164, incorporated herein by reference. The rigid methyl methacrylate component may be a homopolymer of methyl methacrylate or a copolymer of methyl methacrylate with at least about 0.5 by weight of an alkyl acrylate having from 1 to 8 carbon atoms in the alkyl radical and up to about 10 percent, preferably up to about 7.0 percent, by weight of the alkyl acrylate having from 1 to 8 carbon atoms in the alkyl radical. Examples of such acrylates include ethyl acrylate, propyl acrylate, and butyl acrylate. The rigid methyl methacrylate component preferably has a weight average molecular weight of at least about 60,000 and up to about 300,000 as measured by light scattering in chloroform.
The styrene-acrylonitrile polymer component of the polymeric materials of the invention is preferably a copolymer of at least abou
BASF Corporation
Borrego Fernando
Cameron Mary K.
Gallagher John J.
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