Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-10-12
2002-08-06
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S174000, C524S320000, C524S321000, C524S360000, C524S361000
Reexamination Certificate
active
06429242
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates in general to an aerosol solvent weld cement and pertains more particularly to a solvent weld cement composition which comprises at least one polymer resin, at least one welding solvent, and at least one conventional propellant, the solvent weld cement being stable when stored in and dispensed from an aerosol container. The solvent weld cement (SWC) of the present invention is an improvement over conventional SWC since SWC has not previously been successfully stored and dispensed by aerosol means.
Plastic pipe, primarily polyvinyl chloride (PVC) and post chlorinated polyvinyl chloride (CPVC) is commonly used as underground water pipe and for other applications. Plastic pipe is replacing ceramic and metal pipe due to its reduced weight, lower cost, and resistance to cracking under stress. Another advantage of plastic pipe is the capability of forming watertight junctions when attached using SWC in contrast to ceramic pipe interference fittings and metal pipe welded joints. The use of SWC allows joining of the pipes by relatively unskilled workers as compared to the use of welding or soldering equipment with metal pipes.
Unfortunately, application of the adhesive to the pipefittings and joints often takes place within trenches, where there is no convenient location to place the SWC container. SWC is conventionally applied in liquid form with a swab from an open container. The open container releases fumes into the atmosphere, and allows air and moisture to contaminate the remaining SWC. In addition, the open containers are susceptible of being contaminated with dirt or debris, which may affect the performance of the SWC. Further, the container is easily spilled, contaminating the soil with hazardous substances, as well as increasing the time and resources necessary to complete the job.
The application of a liquid SWC by use of a swab or brush does not consistently provide optimum uniformity of application. This can result in incomplete bonding of the joints where too little SWC is applied, and waste as well as environmental concerns where the application is excessive.
Solvent weld cements have not been previously stored and dispensed by aerosol means. Use of an aerosol dispensing system would provide ease of application and the prevention of environmentally unkind spills.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a SWC that can be stored in an aerosol container without gelling of the SWC.
Another object of the present invention is to provide a SWC that can be dispensed by aerosol means.
Still another object of the present invention is to provide a SWC that can easily and uniformly be applied using one hand.
Yet another object of the present invention is to provide a SWC that is dispensed from a container which is not open for solvent evaporation, oxidation or physical contamination of the SWC.
A further object of the present invention is to provide a SWC that cannot be spilled by the user, thereby preventing ground contamination by the SWC.
Still a further object of the present invention is to provide a SWC that can be applied quickly thereby providing additional working time or set up time before the SWC hardens.
Yet a further object of the present invention is to provide a SWC in an aerosol container which complies with current volatile organic compounds (V.O.C.). requirements as mandated by federal and local governments.
To accomplish the foregoing and other objects of this invention there is provided a SWC composition that can be stored in and dispensed from an aerosol container without gelling of the SWC. The SWC composition disclosed herein is easily and uniformly applied, and it allows the user a longer set up time in which to complete the joints as compared to the conventional swab application method. Further, the SWC provided herein is not vulnerable to solvent loss and hence gelling, oxidation or physical contamination, and cannot be spilled during application. It has been discovered that the SWC disclosed herein meets all of the objects of the present invention.
The SWC composition comprises a polymer resin, preferably CPVC or a CPVC/PVC blend, partially dissolved in a solvent mixture including tetrahydrofuran (THF), cyclohexanone, butyrolactone and acetone. The composition further comprises a viscosity modifier/flow control agent, an organotin compound, and an optional dye, utilized to aid in application. The composition is then mixed with a propellant, preferably dimethyl ether, and packaged in a conventional nonferrous aerosol container.
Solvent based adhesives such as SWC work primarily by two means of action. First, the solvent portion of the formulation softens the outer surfaces of the pipe. Then, as the solvent evaporates, the pipe surfaces harden or “cure”. Second, as the solvent evaporates, the resin dissolved in the adhesive dries. The resin acts to fill the small gaps between the pipe and the fittings and to increase the viscosity of the product.
These and other objects and features of the present invention will be better understood and appreciated from the following detailed description of the following embodiments, selected for the purposes of illustration.
DETAILED DESCRIPTION
The presently preferred polymer resin in the SWC composition is CPVC, or a CPVC/PVC blend. Use of a formula including CPVC resin results in the SWC being considered a “universal” pipe cement, as it is suitable for joining PVC, CPVC, Acrylonitrile Butadiene Styrene (ABS) and butyrate pipe. Other polymer resins, including but not limited to PVC, ABS, acrylic resins and blends thereof, may be utilized in the aerosol SWC of the present invention, however, the resulting SWC will not be a universal cement as defined above.
The percent resin utilized is determined by many factors, including the ASTM standards, D-3138-95, F-493, D-2564. (All percentages given herein are wt/wt % based on the total weight of the composition unless otherwise indicated.) In addition, as the percent resin increases, the instability of the product due to premature gelling increases exponentially. The preferred percent of resin in the composition is about 14.5 to 20%, more preferred about 14.5 to 16.0% with about 14.5% being most preferred, resulting in a SWC containing about 10-11% resin solids. This percent meets ASTM standards, provides satisfactory strength of bond, and resists gelling during storage.
The presently preferred solvent system is a mixture of tetrahydrofuran (THF), cyclohexanone, butyrolactone and acetone. This solvent system meets or exceeds current government mandated V.O.C. requirements THF is utilized because it easily dissolves the polymer resin, and instantly softens or etches the surface of the pipe or fittings to be joined, resulting in a more secure attachment. The preferred range of THF is about 20 to 45%, more preferred is about 20 to 30%, and most preferred is about 26%.
Cyclohexanone is utilized to lengthen the working time, or set-up time, of the SWC, as cyclohexanone has a lower vapor pressure than THF. This component is important because by extending the working time the SWC becomes easier to use. The presently preferred range of cyclohexanone is about 0 to 20%, more preferred is about 5 to 10% and most preferred is about 7%.
Another solvent, butyrolactone, is added in the following percentages. The preferred range of butyrolactone is about 1 to 15%, more preferred is about 2 to 8%, and most preferred is about 5%. This solvent is utilized because it has a lower vapor pressure than cyclohexanone, which aids in further lengthening the working time of the SWC. At the same time, butyrolactone dissolves the polymer resin better than cyclohexanone.
Acetone is added to the composition in the following percentages. The preferred range of acetone is about 10 to 40%, more preferred is about 20 to 30%, and most preferred is about 26%. While acetone is a poor solvent for CPVC resins, it is utilized in order to remain compliant with the federal government's maximum volatile organic
Macher Robert J.
Smith Allen L.
Blackwell Sanders Peper Martin LLP
Cain Edward J.
Camie-Campbell, Inc.
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