Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-08-30
2002-04-16
Niland, Patrick D. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S099000, C524S356000, C524S527000, C524S567000
Reexamination Certificate
active
06372821
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to thermoplastic pipe adhesive and primer compositions, and, more particularly, to adhesives and primers used for joining PCV (polyvinyl chloride) and CPVC (chlorinated PVC) pipe. Specifically, the PVC and CPVC pipe adhesives and primers disclosed and claimed herein are solvent-based, having an environmentally-acceptable VOC (volatile organic compounds) content.
BACKGROUND ART
Solvent-based adhesives, or cements, have been in use for joining thermoplastic pipe for over 30 years. The development of these adhesives is largely responsible for growth of the thermoplastic pipe industry. Several billion pounds of plastic pipe are produced each year in North America. Rapid-setting, solvent-based adhesives weld the pipes together in a timely manner. These rapid-setting adhesives allow for the testing and trouble-shooting of piping systems in a matter of hours while maintaining the long-term durability of the pipe itself. These characteristics, rapid set, ease of use, long-term durability along with low-cost, have made the joining of plastic pipe by solvent-based adhesives a practical and economic system.
The solvent-based adhesives work primarily by two means of action. First, the solvent portion of the formulation softens the outer surfaces of the pipe through solvation of the plastic. Subsequently, the adhesive joint “cures” (hardens) by means of the solvents evaporating to the surrounding atmosphere from the pipe. Secondly, the resin dissolved in the adhesive dries through solvent evaporation and provides continuity between the welded pipe surfaces which aid in preserving the integrity of the entire pipe system.
These adhesives cure rapidly (within a matter of hours), often allowing piping systems to be tested the same day as constructed. However, perhaps the most important benefit of these solvent-based adhesives is the maintenance of the integrity of the pipe itself. The resin is the same as the plastic pipe and/or fitting material. This provides a high degree of long-term durability for the piping system, often up to 30 to 40 years of useful life. This is essential for these systems which are built into the structures of homes and buildings, or are buried underground.
Thousands of miles of thermoplastic piping systems are constructed each day throughout the world, primarily by the means previously described. These systems are used in the transfer of potable water for drinking; residential hot and cold water systems; drain, waste, and vent (DWV) applications in home and industry; turf and agricultural sprinkler systems; jacuzzi, spa and tub connections, residential and commercial fire sprinkler systems; etc. These systems are crucial to the maintenance of safe and healthy means of transport of water and other chemicals throughout the world.
Evaporation of solvents from adhesives is a concern to an environmentally-concerned world, along with all other potential sources of air pollution. Typical solids (non-volatile) contents of plastic pipe adhesives are 10 to 20% for both PVC and CPVC. The balance of the formulation is solvent. By definition, the solvents normally used, e.g., tetrahydrofuran (THF), methyl ethyl ketone (MEK), and acetone are considered to be VOCs. That is, they are volatile compounds which contain the element carbon excluding methane, carbon monoxide, carbon dioxide, carbonic acid, metallic carbides and carbonates, ammonium carbonate, and exempt compounds, such as methylene chloride and 1,1,1-trichlorethane. While other solvents, such as cyclohexanone and dimethyl formamide (in the case of PVC) and cyclohexanone (in the case of CPVC), may also be used in such adhesives, the amount of such solvents are typically minor, considerably less than 15 wt % (in the case of PVC) and 10 wt % (in the case of CPVC) of the total adhesive concentration. Typical VOC values of present commercial PVC solvent adhesives range from 750 to 850 grams/liter and for CPVC solvent adhesives range from 775 to 850 g/l.
Regulations are being created throughout North America regarding allowable VOC levels in adhesive formulations. Federal, state, and local agencies are beginning to adopt strict measures to drastically reduce these levels. The South Coast Air Quality Management District (SCAQMD) in the Los Angeles area has been a leader of the establishment of rules governing VOCs, such as SCAQMD Rule 1168.
SCAQMD Rule 1168 specifies a VOC level for PVC adhesives of 510 g/l or less and for CPVC adhesives of 490 g/l or less, as determined by Method 316-A. All PVC and CPVC adhesives used after Jan. 24, 1994, are required to meet that maximum allowed level.
More recently, acetone has been removed from the list of solvents and placed on the list of exempt solvents. Consequently, there is, at the present time, no legal limit to the amount of acetone that can be added to adhesive compositions.
Further, tetrahydrofuran (THF), which has been a major component of PVC and CPVC adhesive compositions (typically, 25 to 75 wt %), has been found by the National Toxicology Board to have a slight carcinogenicity in animal testing. As a result, THF is under extensive investigation, both with regard to worker health (exposure during pipe assembly) and potable water issues. Furthermore, THF is a high vapor pressure, fast-evaporating solvent that heavily contributes to the VOC level. It is highly desirable to reduce THF levels, but still maintain the adhesive-contributing properties that THF offers, i.e., fast-setting, durable pipe joints.
Also, many PVC and CPVC pipe adhesives are formulated with N-methyl pyrrolidone (NMP), a very effective solvent for PVC and CPVC resins. However, the hygroscopicity of this solvent results in milky white cured film joints, even in pigmented blue and gray formulas, and this is undesirable in many applications.
Other thermoplastic pipe adhesives are formulated with large amounts of low vapor pressure solvents blends, such as di-methyladipate (available from E. I. DuPont de Nemours as DBE-6) and NMP and/or alkyl-substituted naphthalene (U.S. Pat. No. 5,821,289, issued to C. D. Congelio et al) to reduce VOC levels, but generally these type of adhesives require longer set times before water pressure testing of the system can be made. Also, these slower setting adhesives are less effective in colder environments.
Still another method to formulate low VOC cements for thermoplastic pipe and other PVC and CPVC extruded articles is to incorporate higher amounts of resin(s). This does indeed reduces VOC levels, but is less cost effective and generally slower than cements containing lower weight percent of resin.
Thus, adhesives for joining PVC and CPVC pipes having a maximum VOC level of 510 g/l (for PVC) or 490 g/l (for CPVC) are required. Yet, such adhesive must also meet the required hydrostatic burst strength and other performance criteria set forth in ASTM F-493 and D-2846 and lap shear strength set forth in ASTM D-2564. (Test method 316A has been revised and the new acceptable VOC levels are shown above.)
DISCLOSURE OF INVENTION
In accordance with the present invention, novel low VOC solvent-based adhesives are provided, comprising a mixture of low vapor pressure isomeric dimethyl-2-piperidones (DMPD) blended with (1) a non-solvent diluent, specifically, acetone (a VOC-exempt compound), or with mixtures of acetone and other known ketonic solvents such as methyl ethyl ketone (MEK), diethyl ketone (DEK), methyl propyl ketone (MPK), and methyl iso-butyl ketone (MIBK), cyclohexanone, and (2) thermoplastic PVC or CPVC resins. Primers are also provided in accordance with the present invention by omitting the inclusion of the thermoplastic resin.
The novel adhesives described herein overcome the deficiencies described above for the prior art adhesives without compromising adhesive performance. The adhesives of the present invention comprise (for joining PVC pipes and components):
(a) about 5 to 25 wt % PVC resin and 0 to about 25 wt % acrylic resin, the total of PVC resin and acrylic resin ranging from about 10 to 35 wt %;
(b) about 5 t
Otremba Edward D.
Patel Naresh D.
Siddiqi Rashid H.
Collins David W.
IPS Corporation
Niland Patrick D.
LandOfFree
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