The dissolving of polyvinyl chloride resin is well-known process. Usually the PVC is produced by either bulk, suspension polymerization, or emulsion polymerization techniques. The polymerization step is carried out in a reactor vessel and PVC resin scale is normally formed on the internal surface wall of the reactor surface. The need to periodically remove the PVC deposit has been a challenge for the industry for many years. Among other dissolving, different organic solvents have been used, for example tetrahydrofuran (HEF), as described in U.S. Pat. No. 3,475,218. The use of pure THF has not been accepted by the industry, however, due to its danger and toxicity.
The above problems led to the use of other solvents, such as methyl ethyl ketone (MEK) or toxic solvent such as dimethylsulfoxide (DMSO), or their mixtures. MEK is readily available material with a convenient boiling point of 76.6° C.
Macromol, Chem, 1486. 787-799(1985) describes the solution properties of PVC copolymer in various organic solvents like Cyclohexanone, MEK, THF, Acetylacetone and other, This publication shows the viscosity results of 8% PVC in the different media.
DD 81223 describes a process for obtaining low concentrations of PVC in Chloroform or in Dichloroethylene, at high temperatures (80-95° C.), with the need for steam bubbling during the process.
JP 59162564 teaches the use of Xylen/THF mixtures to form 10% PVC solution.
However, according to this patent, a gel and not a clear solution is formed.
U.S. Pat. No. 5,675,914 describes regenerating PVC from waste and similarly in JP 06279614 the recovery of PVC from PVC-coated waste electric wires is described. Multi-component stabilizers are extensively utilized to protect the resins against oxidative, thermal and photochemical degradation. Usually polyhydric alcohols and metals of carboxylic acid, are used.
U.S. Pat. No. 3,928,267 teaches the formation of PVC blends comprising organic phosphates, epoxidized soybean oil and dioctylazelate. The patent describes the formation of PVC paste, which is not a suitable form for spray application. The above blending process requires high temperature of 177° C.
U.S. Pat. No. 4,369,273 teaches the formulation of a powder mixture of PVC blended with alpha and beta-naphthindoles, epoxy soybean oil and trinonyl-phenyl phosphite as stabilizers. According to this patent soft PVC is formed, which is suitable for film and for injection molding articles. The process temperature of this patent is greater than 100° C.
All the above reference deals either with the use of PVC copolymer or requires the use of high temperatures and toxic solvents. Prior art procedures result either in low-concentration PVC solution, which is unsuitable for spray applications.
The usual application of PVC copolymer is in inks, as paints and as adhesives. However PVC homopolymer solution is advantageous as compared to PVC
copolymer solutions, because of its lower price and its better chemical, heat and UV resistance.
Furthermore, it exhibits mechanical properties (e.g. impact & tensile strength), which enables its use as both a flexible and rigid building material.