Abstract:
This invention provides a paint stripping composition comprising N-methyl-2-pyrrolidone and lower alkyl ethers of propylene glycol and dipropylene glycol. The composition does not include any toluene, halogenated hydrocarbons, acids, caustics or waxes and is not harmful to a wide variety of substrates.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to compositions and methods for chemically removing paint and varnish from wood, metal, glass, fiberglass and many plastics surfaces. Prior to the realization of the various health hazards caused by halogenated hydrocarbon chemicals, the cornerstone of the paint stripping industry was methylene chloride. With the discovery of the hazards connected with the use of such materials, many proposals have been made for paint and varnish stripping compositions that do not include halogenated hydrocarbons. Hitherto, the most successful of these developments required the use of acids, thereby creating the problems of neutralization and/or harming the surface to be stripped. A recent patent, U.S. Pat. No. 4,965,010 to Ralph R. Swett, proposes to solve the problem by employing approximately equal parts of methyl ethyl ketone, methyl alcohol, toluene and acetone. The volatile nature of such compositions can create severe ventilation problems when working in confined spaces and further requires the use of large amounts of thickeners to assist in keeping the stripping compositions in place long enough to do a thorough stripping job. 
     U.S. Pat. No. 5,089,164 describes and claims multi-purpose paint and varnish strippers comprising N-methyl-2-pyrrolidone, toluene, lower aliphatic alcohols and ketones, propylene glycol, mineral spirits, surfactants and thickeners. While such compositions are very effective paint and varnish strippers, it has been found that they are not environmentally acceptable due to the suspected carcinogenic activity of toluene. 
     SUMMARY OF THE INVENTION 
     This invention provides an improved composition and method for stripping paint or varnish from a variety of substrates such as, for example, wood, metal, glass, fiberglass and plastics which comprises at least one member of the group consisting of N-methyl-2-pyrrolidone and dipropylene glycol dimethyl ether, ethyl 3-ethoxypropionate, lower alipathic ketones, surfactants and at least one member of the group consisting of lower alkyl ethers of propylene glycol and dipropylene glycol wherein the lower alkyl groups comprise 1 to 4 carbon atoms. Odorants, such as d-limonene and thickeners, may be added if desired. The compositions of this invention have improved stripping efficiency, improved flash points, reduced evaporation and improved environmental safety. They are safe to handle and do not harm the surface to be stripped. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The compositions of this invention are preferably prepared by first blending the desired amounts of N-methyl-2-pyrrolidone or dipropylene glycol dimethyl ether and the lower alkyl ethers of propylene glycol and dipropylene glycol. After blending or thoroughly mixing the N-methyl-2-pyrrolidone and lower alkyl ethers of propylene glycol and dipropylene glycol, the remaining ingredients comprising ethyl 3-ethoxypropionate, acetone, surfactants such as Igepal (Reg. TM) CO-730 (nonylphenoxypoly(ethyleneoxy)ethanol), odorants such as, for example, d-limonene and thickeners, if desired, such as, for example, hydroxypropyl cellulose, and others known in the art, can be added and mixed as desired. When properly mixed, these components remove the paint and/or varnish without the development of air bubbles which serve to prevent the stripping composition from penetrating all layers of the paint or varnish to be removed. As used herein, propylene glycol refers to both the 1,2 and 1,3 hydroxy substitution on the propylene moiety. 
     Compositions in accordance with the present invention advantageously comprise the following materials and amounts, the weight percentages all being based on the total weight of the composition: 
     
         ______________________________________                Wt. %______________________________________Mixture of propylene glycol n-butyl                   2-35ether (80%) and dipropylene glycoldimethyl ether (20%)N-methyl-2-pyrrolidone 10-25Ethyl 3-ethoxypropionate                   5-10Isopropyl alcohol       5-15Lower aliphatic ketones                  10-25Surfactant             1-5Odorant                1-5Thickener              0-5______________________________________ 
    
     A preferred composition in accordance with the present invention comprises the following materials and approximate amounts, the weight percentages all being based on the total weight of the composition: 
     
         ______________________________________                Wt. %______________________________________N-methyl-2-pyrrolidone  20Mixture of propylene glycol n-butyl                   20ether (80%) and dipropylene glycoldimethyl ether (20%)Mixture of 1-Methoxy-2-propanol (98%)                   10and 2-Methoxy-1-propanol (2%)Ethyl 3-ethoxypropionate                   10Isopropyl alcohol       10Acetone                 25Igepal (Reg. TM) CO-730  2Odorant                  4______________________________________ 
    
     If a semi-paste is desired, a thickener may be added in an amount of about 4% and the amount of acetone decreased accordingly. 
     In the most preferred compositions, hydroxypropyl cellulose is employed as the thickener and d-limonene is a preferred odorant. 
     The compositions of this invention are environmentally safe, do not burn the skin, do not raise the grain or fur the wood, do not harm veneers, patina, glue joints, glass, fiberglass, most plastics or metal and do not require neutralizing or a water wash. Because of their reduced volatility, the compositions of this invention have increased effectiveness without requiring excessive amounts of thickeners. Further, a wax sealer is not needed to reduce evaporation. Wax sealers generally leave a residue or film on stripped surfaces and thus interfere with finishes that are to be re-applied. 
     The compositions of the invention can be applied as a liquid or can be thickened sufficiently to form a semi-paste like product. No acids or caustics are employed and no halogenated hydrocarbons. The compositions will soften most paints and varnishes in from 1 to 3 minutes, at which time the residue can be readily removed with a scraper or a rag or brush moistened with further stripping composition. Urethane finishes require a somewhat longer time to soften and the use of the semi-paste formulation rather than the liquid formulation is suggested. These compositions will stay moist for up to 24 hours without leaving an oily residue. 
     Various modifications may be made in the present invention without departing from the spirit or scope thereof, as will be understood by those skilled in the art.