WO1996040852A1

WO1996040852A1 - Composition for stripping surfaces

Info

Publication number: WO1996040852A1
Application number: PCT/US1996/009968
Authority: WO
Inventors: John Lunsford
Original assignee: Furniture Medic, Inc.
Priority date: 1995-06-07
Filing date: 1996-06-07
Publication date: 1996-12-19

Abstract

A composition for stripping coatings from surfaces, and method for using the composition, are provided. The composition includes 1-methyl-2-pyrrolidone (NMP) or an equivalent thereof, one or more alkylated aromatic hydrocarbons (preferably a mixture of alkyl benzenes and alkyl napthalenes), and alkoxy propionic acid ester, preferably ethyl-3-ethoxypropionate, and dialkyl esters of dibasic acids, preferably dimethyl esters of adipic and glutaric acids, and a cellulose ether, for example, hydroxypropyl methyl cellulose.

Description

COMPOSITION FOR STRIPPING SURFACES

Field of the Invention The invention relates generally to a composition for stripping or otherwise removing one or more layers of cured coatings from a surface. More particularly, the invention relates to water-soluble and environmentally safe compositions for stripping surfaces.

Background of the Invention Chemical paint removers have achieved considerable popularity because they are much easier to use than non-chemical alternatives, such as blow torches and power sanders. There are several known compositions and methods for removing or otherwise chemically stripping coatings, such as paint, varnish, and lacquer, from surfaces such as wood, metal, and Concrete. The most popular type of coating remover incorporates an organic chemical solvent base. Methylene chloride is an organic solvent commonly used to remove coatings. U.S. Patent No. 2,507,983 discloses a paint stripper composition containing 86 percent methylene chloride by weight, with methanol added in a smaller proportion to solubilize a methylcellulose thickener. U.S. Patent Nos. 4,579,627 to Brailsford and 3,950, 185 to Mitsuo Toyama, et al., also disclose paint stripping compositions containing methylene chloride or other chlorinated hydrocarbons.

Paint removers based on methylene chloride are generally very effective on varnish and alkyd paint. They are less effective on lacquer and latex finishes. Unthickened removers that have high concentrations of methanol and benzene are typically used for varnish removal.

A major limitation of such paint removers is their high degree of toxicity, particularly due to the inhalation of vapors and penetration through the skin. Chlorinated hydrocarbons such as methylene chloride are suspected carcinogens, and can burn the skin, causing various degrees of dermatitis, depending on the exposure. Workers handling these substances are advised to wear full protective clothing and breathing equipment when handling these substances, especially when they are used in a confined area.

A further limitation of using chlorinated organic solvents is that these solvents can dissolve certain surfaces, such as polymers commonly reinforced with fiberglass.

Further, chlorinated solvents rapidly evaporate, limiting the time the composition can remain on the surface to be treated. The short residence time can limit the number of coating layers that can be effectively removed in one application. Compositions with high volatility have higher labor and material costs than compositions with low volatility, especially when they are used to remove multiple coating layers.

Wax is sometimes added to restrain the rapid evaporation of highly volatile organic solvents. A major limitation of compositions containing wax is that when they are used to remove a coating from wood, the wax tends to remain in the wood. This can cause fish-eye problems in the final finishing process if the wax is not properly removed.

There are several stripping processes in which it is useful to have water-soluble strippers. For example, when painting vehicles, the parts of the automobiles are typically spray-painted in metal spraying booths. The interior of the booths must be cleaned, usually on a daily basis, and the uncured paint on the (mostly metal) surfaces of the interior of the booth must be removed. In this application, it is highly advantageous to use a water-soluble paint stripping composition, and preferably one that does not contain acidic or basic components. Paint removers or strippers that are water-soluble can more easily wash away the softened paint that, itself, is not water-soluble.

A typical method for cleaning an automobile painting facility is to apply the paint remover, allow it to stand for a sufficient amount of time to soften the paint, and hose down the entire facility. This procedure is much easier to perform when the paint strippers are water-soluble than when they are not water-soluble.

Attempts to produce water-soluble paint removers generally require using highly corrosive materials, including acidic and basic components. Basic components, such as caustic or other strong alkaline bases, are seldom used in home applications because they often require heat for activation and some require dip tanks. Basic compositions often have a deleterious effect on wood and often dissolve the glue holding the furniture together. See, for example, U.S. Patent Nos. 4,426,250 to Michael I.D. Brailsford and

4,581,413 to Raymond M. Yoakam.

Compositions containing acidic and basic components can be effective at stripping paint, but are potentially damaging to the environment and to workers exposed to the compositions. Sodium hydroxide is hazardous because it is strongly basic and can cause serious bums on unprotected skin. Also, since sodium hydroxide is insoluble in organic solvents, its use is limited to water-based systems. Further, compositions containing sodium hydroxide or other strong bases must be neutralized after the surface is stripped.

Acidic stripping compositions are also are also commonly used in dip tanks. Major limitations of using acidic compositions include the hazardous nature of the acids, and the inability to use the compositions on-site. Further, acidic stripping compositions tend to dry out wood joints and glue, and neutralize the oil in the wood, making the wood very brittle and hard.

There is an increasing need for on-site wood and furniture repair. compositions that contain acids, bases, and/or highly volatile organic solvents are not well suited for on-site stripping. Several compositions for removing coatings from surfaces do not contain strong bases or chlorinated organic solvents. A component of several of these compositions is N-methyl-2- pyrrolidone. The compositions strip paint without exhibiting the same safety, toxicity, volatility and other problems associated with acidic, basic, or chlorinated stripping compositions. In U.S. Patent No. 4,128,810, which discloses using N-methyl-2-pyrrolidone in combination with a mixture of aromatic hydrocarbons having more than six carbon atoms.

U.S. Patent No. 5,089,164 to Stanley discloses a paint stripper containing N-methyl pyrrolidone (NMP), an aromatic hydrocarbon, ethyl-3- ethoxypropionate, dimethyl esters of adipic and glutaric acids, and hydroxypropyl cellulose, a cellulose ether. U.S. Patent No. 5,332,526 to Stanley discloses a paint stripper composition containing NMP, ethyl-3-ethoxypropionate, and hydroxypropyl cellulose, and a cellulose ether, among other components.

U.S. Patent No. 4,120,810 to Palmer discloses a paint stripper formulation containing NMP, a mixture of alkyl benzene and alkyl napthalene, glycol ethers and hydroxypropyl cellulose.

U.S. Patent No. 5,049,314 to Palmer discloses a paint stripper formulation containing NMP, ethyl-3-ethoxypropionate, dibasic esters of glutaric acid and adipic acid, and cellulose ethers. U.S. Patent No. 4,732,695 to Fransisco discloses a paint stripper formulation containing benzyl alcohol, NMP, aromatic naptha and optionally containing alkyl benzene.

EPO 355,763 to BASF discloses a paint stripper formulation containing NMP, at least one mononuclear aromatic hydrocarbon, a glycol ether, an alkanolamine, and a cellulose ether.

EPO 389,829 to BASF discloses a paint stripper formulation containing NMP, a dibasic ester, a propylene glycol or glycol ether, a hydroxypropyl cellulose thickener and optionally contains water.

A commercially available composition sold by 3M Corporation is a product called "Safest Stripper." This product contains a dibasic ester and aluminum silicate.

Even those compositions that do not contain acidic or basic components, chlorinated organic solvents or other volatile organic substances can still have several problems. The residence time that the composition must remain on the surface of the painted article in order to be effective is an important concern. The effective residence time varies greatly depending on the concentration of the individual components. The cost of the components is an additional concern. Preparing compositions that are cost effective, safe to handle, require a short residence time, and that are relatively odorless remains a significant problem in the paint stripping industry. It is an object of the present invention to provide a stripping composition that can readily and effectively be used on a variety of surfaces to remove cured coatings, such as paint, lacquer and varnish.

It is another object of the present invention to provide a composition that is relatively non-toxic.

It is yet another object of the present invention to provide such a composition that includes solvents that are sufficiently non-volatile that they can be used to remove multiple layers of cured surface coatings with one application. It is yet another object of the present invention to provide such a composition that can be applied consistently and evenly, vertically, horizontally, overhead or the like, without any dripping or sagging.

It is yet a further object of the present invention to provide a composition that is relatively inexpensive and relatively odorless. It is still a further object of the present invention to provide a method for stripping coatings such as paint, varnish and nitrocellulose finishes using the stripping composition.

Summary of the Invention A composition for stripping coatings from surfaces, and method for using the composition, are provided. The composition includes l-methyl-2- pyrrolidone (NMP) or an equivalent thereof, one or more alkylated aromatic hydrocarbons (preferably a mixture of alkyl benzenes and alkyl napthalenes), an alkoxy propionic acid ester, preferably ethyl-3ethoxypropionate, and dialkyl esters of dibasic acids, preferably dimethyl esters of adipic and glutaric acids, and a cellulose ether, for example, hydroxypropyl methyl cellulose.

In one embodiment, the composition includes between approximately 20 and 40 percent l-methyl-2-pyrrolidone (NMP) or its equivalent, 1 and 20 percent of one or more alkylated aromatic hydrocarbons (preferably containing a mixture of alkyl benzenes and alkyl napthalenes), 10 and 30 percent alkoxy propionic acid esters, preferably ethyl-3ethoxypropionate, 20 and 60 percent dialkyl esters of dicarboxylic acids (also known as dibasic acid esters), preferably dimethyl esters of adipic and glutaric acids, and 0.2 and 2.0 percent of a cellulose ether.

More preferably, the composition includes between approximately 25 and 35 percent l-methyl-2-pyrrolidone (NMP) or its equivalent, 5 and 15 percent of one or more alkylated aromatic hydrocarbons (preferably containing a mixture of alkyl benzenes and alkyl napthalenes), 15 and 25 percent alkoxy propionic acid esters, preferably ethyl-3ethoxypropionate, 30 and 50 percent dialkyl esters of dicarboxylic acids (also known as dibasic acid esters), preferably dimethyl esters of adipic and glutaric acids, and 0.5 and 1.5 percent of a cellulose ether.

The most preferred composition includes between approximately 28 and 32 percent l-methyl-2pyrrolidone (NMP) or its equivalent, 8 and 12 percent of one or more alkylated aromatic hydrocarbons (preferably containing a mixture of alkyl benzenes and alkl-1 napthalenes), 16 and 20 percent alkoxy propionic acid esters, preferably ethyl-3ethoxypropionate, 35 and 45 percent dialkyl esters of dicarboxylic acids (also known as dibasic acid esters preferably dimethyl esters of adipic and glutaric acids, and 0.7 and 1.0 percent of a cellulose ether. The preferred cellulose ether is hydroxypropyl methyl cellulose. The composition can be in the form of a gel, paste, or liquid.

The composition is effective in removing most conventional coatings from surfaces. The most preferred use of the composition is to remove nitrocellulose lacquer from the surface of wood. Because of the relatively high amount of dibasic esters, the composition is very effective at quickly removing nitrocellulose coati!~Ts from wood. The composition is adapted to remain on the coated surface for a relatively long period of time (as compared to compositions containing highly volatile organic solvents) to decompose the cured coating, facilitating removal of the coating.

The time required to strip coatings completely is similar to that of conventional strippers containing chlorinated solvents, and ranges from about 5 minutes to about 80 minutes, with a typical range of about 5 to about 35 minutes. Multiple layers of coatings can be stripped by exposing the surface to the composition for periods ranging from 5 minutes to more than 24 hours.

The composition can optionally include water and a surfactant. Typical surfactants are anionic, cationic, zwitterionic, and nonionic surfactants. Preferred surfactants are anionic surfactants, more preferably sodium tallate or potassium tallate. The most preferred surfactant is potassium tallate. The composition can also include an extender, a corrosion inhibitor, dyes, and fragrances.

Conventional methods, such as brushing, rolling, and spraying, can be used to apply the composition to a surface. The composition can be sprayed using a conventional airless paint sprayer, a hopper gun or other spraying unit driven by compressed air or other mechanical means.

After the composition is applied to a surface, it can be covered with a laminated cover or cover means. The cover or at least a portion thereof sticks to the decomposed coat of a coating, such as paint, lacquer and varnish, on the surface to be treated.. The decomposed coat sticks to the laminated paper cover when the paper cover is pulled from the surface.

Detailed Description of the Invention

A composition for stripping surfaces, and method for using the composition, is provided. The composition is effective in removing most conventional coatings from surfaces. The most preferred use of the composition is to remove nitrocellulose lacquer from the surface of wood. Moreover, the composition is adapted to react on the coated surface for a long period of time, relative to compositions containing highly volatile organic solvents, to decompose the cured coating, facilitating the removal of the coating.

Surfaces that can be treated with the composition include, but are not limited to, paint brushes and pads, wood, glass, acrylic-type plastics, brick, concrete, plaster, stucco, metals such as aluminum, galvanized steel, stainless steel, and automotive grade and quality steels. Coatings that can be removed from these surfaces include, but are not limited to, lacquers, such as nitrocellulose lacquer, varnishes, enamels, paints, such as epoxy paints, oil-based alkyd resins, polyurethane coatings, epoxy esters, epoxy amides and acrylics, among other polymeric coatings. The time required to strip coatings completely is competitive with that of conventional strippers containing chlorinated solvents, and ranges from about 5 minutes to about 80 minutes, with a preferred range of about 5 to about 35 minutes.

Certain embodiments of the present invention can be used to strip multiple layers of coatings off of surfaces by exposing the surface to the composition for periods ranging from between approximately 5 minutes and more than 24 hours.

Composition The composition includes l-methyl-2pyrrolidone (NMP) or an equivalent thereof, one or more alkylated aromatic hydrocarbons (preferably a mixture of alkyl benzenes and alkyl napthalenes), an alkoxy propionic acid ester, preferably ethyl-3ethoxypropionate, and dialkyl esters of dicarboxylic acids (also known as dibasic esters), preferably dimethyl esters of adipic and glutaric acids, and a cellulose ether, for example, hydroxypropyl methyl cellulose. The composition can be in the form of a gel, paste, or liquid.

In one embodiment, the composition includes between approximately 20 and 40 percent l-methyl-2-p-yrroIidone (NMP) or its equivalent, 1 and 20 percent of one or more alkylated aromatic hydrocarbons (preferably containing a mixture of alkyl benzenes and alkyl napthalenes), 10 and 30 percent alkoxy propionic acid esters, preferably ethyl-3-ethoxypropionate, 20 and 60 percent dialkyl esters of dicarboxylic acids, preferably dimethyl esters of adipic and glutaric acids, and 0.2 and 2.0 percent of a cellulose ether. All percentages are by weight unless otherwise specified. More preferably, the composition includes between approximately 25 and 35 percent l-methyl-2-pyrrolidone (NMP) or its equivalent, 5 and 15 percent of one or more alkylated aromatic hydrocarbons (preferably containing a mixture of alkyl benzenes and alkyl napthalenes), 15 and 25 percent alkoxy propionic acid esters, preferably ethyl- 1-ethoxypropionate, 30 and 50 percent dialkyl esters of dicarboxylic acids, preferably dimethyl esters of adipic and glutaric acids, and 0.5 and i.5 percent of a cellulose ether. The most preferred composition includes between approximately 28 and 32 percent l-methyl-2-p-yrrolidone (UMP) or its equivalent, 8 and 12 percent of one or more alkylated aromatic hydrocarbons (preferably containing a mixture of alkyl benzenes and alkyl napthalenes), 16 and 20 percent alkoxy propionic acid esters, preferably ethyl-3-ethoxypropionate, 35 and 45 percent dialkyl esters of dicarboxylic acids, preferably dimethyl esters of adipic and glutaric acids, and 0.7 and 1.0 percent of a cellulose ether.

The amount of each of the components in the composition can vary within the defined ranges. It is important, however, that each be present in an amount sufficient to provide the composition with effectiveness for stripping and cleaning coatings such as paint, nitrocellulose, urethane, polyester and epoxy compounds off of surfaces such as wood, metal, tools, molds, etc., before or after the cure is complete. Therefore, the combination of the components is selected according to the solvating capacities of the respective components, individually and in combination, in order to obtain a composition with low volatility and relatively low environmental impact, and with a 1981 National Paint and Coating Association H.M.I.S. rating equal to or less than 1 for health, 1 for flammability, 0 for reactivity, and C or better for personal protection.

NKP and its Equivalent

A primary component in the composition is N-methyl-2-pyrrolidone (NMP) , (CsHgNO) , or its equivalent. NMP has a vapor pressure of about 1 mm Hg at 400C, and is a highly polar, water-miscible solvent that is also miscible with almost all conventional organic solvents. It is also soluble in a wide range of polymers used in the coatings industry. NMP is typically used as an industrial solvent for natural and synthetic plastics, waxes, resins and various types of paints. NMP can dissolve polyethylene glycol, nylon, polyesters, polystyrene, polyacrylonitrile, polyvinyl chloride, polyvinyl acetate, cellulose derivatives, polyurethanes, polycarbonates and many copolymers. NMP chemically attacks coatings by dissolving or lifting the coatings from a surface.

Compositions containing as little as 20 percent N-methylpyrrolidone can be used, but compositions containing higher weight percentages of N- methylpyrrolidone strip surfaces more rapidly.

Those of ordinary skill in the art will recognize that a number of variations can be made to the structure of N-methylpyrrolidone without significantly affecting the physicochemical properties of the underlying stripping composition. Where required, one of ordinary skill in the art will know to vary the amounts and types of the other components within the stripping composition to produce an efficient composition. For example, the nitrogen of the pyrrolidone ring can be unsubstituted or substituted with alkyl groups other than methyl. However, as the number of carbon atoms within the pyrrolidone compound increases beyond 3 (propyl), the watermiscibility decreases, thus affecting the ability of stripping compositions to accommodate water for microgel formation or for removal of the stripping composition from surfaces. In addition, such substitution can affect the solvent power of the pyrrolidone compound used, thus necessitating adjustments in the other components of the stripping composition.

Suitable NMP equivalents for use in the present invention include, but are not limited to, N-ethyl-2-pyrrolidone, N-isopropyl-2-pyrrolidone, N- propyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, N-propylpyrrolidone, 2- hydroxyethyl-2-pyrrolidone, N-dimethylaminopropyl-2-pyrrolidone, vinylpyrrolidone, 2-pyrτolidone, N,N-dimethyl 2-pyrrolidone, 3,3-dimethyl 2- pyrrolidone, and mixtures thereof.

In addition to nitrogen substitution, the carbon atoms of the pyrrolidone ring can also be substituted, but such compositions are less preferred because of the cost and the reduced polarity that often results from such substitution. The 2-keto group of N-methylpyrrolidone is not a requirement for the pyrrolidone compound of the present invention. Suitable pyrrolidine analogs for use in the present invention include, but are not limited to, N,N- dimethylpyrrolidine, 2,4-dimethylpyrrolidine, 2,5-dimethylpyrrolidine and N- methylpyrrolidine.

Dibasic Esters Dibasic esters are dialkyl esters of aliphatic dicarboxylic acids. Examples of aliphatic dicarboxylic acids that can be esterified include, but are not limited to, oxalic, malonic, succinic, glutaric, and adipic acid. The term "alkyl", as used herein, unless otherwise specified, refers to a saturated straight, branched, or cyclic hydrocarbon of CI to C6, and specifically includes methyl, ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, pentyl, cyclopentyl, isopentyl, neopentyl, hexyl, isohexyl, cyclohexyl, 3-methylpentyl, 2,2-dimethylbutyl, and 2,3-dimethylbutyl. Any dibasic ester can be used that achieves a desired result. Dibasic esters are an important component of the composition. When used on nitrocellulose lacquer finishes, the dibasic esters are particularly active, resulting in compositions that effectively remove the nitrocellulose lacquers in as little as 5 minutes. The ability to quickly remove nitrocellulose lacquers is particularly important in furniture repair, because the majority of furniture is coated with nitrocellulose lacquer. However, the concentration of the dibasic esters is preferably kept within the prescribed range, and not exceeded, to minimize the odor associated with the dibasic esters.

Suitable dibasic esters for use in the present invention include, but are not limited to, dimethyl glutarate, dimethyl adipate and dimethyl succinate. The most preferred mixture is Dibasic Ester DBE II, a commercially available blend of dimethyl adipate and dimethyl glutarate, sold by Dupont.

Alkoxy Propionic Acid Esters An alkoxy propionic acid ester is any C„ straight, branched or cyclic ester of an alkoxy propionic acid. The alkoxy (0-alkyl) group can be at either the 2 or 3 position on the propionic acid, where the alkyl group is as defined above. Suitable alkoxy,propionic acid esters for use in the present invention include, but are not limited to, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, 3-methylbutyl, pentyl, hexyl, heptyl, and octyl esters of 3-ethoxy propionic acid, and mixtures thereof. Particularly preferred is ethyl-3- ethoxypropionate. These materials are commercially available or can be prepared by procedures known to those skilled in the art.

Other oxygenated solvents useful in the present invention that can be used in mixture with or as a substitution for the alkoxy propionic acid esters include, but are not limited to aliphatic alcohols such as butyl alcohol, amyl alcohol, hexyl alcohol, heptyl alcohol, furfuryl alcohol, tetrahydrofurfuryl alcohol, 2-butoxy ethanol; 2 or 3 carbon atom; alkylene glycol ethers such as propylene glycol mono-t-butyl ether, dipropylene glycol monomethyl ether, and dipropylene glycol mono-n-butyl ether; and aliphatic ketones, such as diisobutyl ketones. While such other solvents provide a formulation that is relatively non-toxic, the resulting compositions do not strip surfaces, particularly nitrocellulose lacquer, surfaces, as quickly as when the composition includes ethyl-,3ethyoxypropionate or another alkoxy propionic acid ester.

Alkylated Aromatics

Alkylated aromatic compounds are defined as benzene or naphthalene rings containing one or more CI-20 straight, branched or cyclic alkyl groups. The composition can contain one or more alkyl aromatics, and preferably contains a mixture of alkyl benzenes and alkyl napthalenes.

Suitable alkylated aromatic compounds for use in the present invention include, but are not limited to, toluene, xylene (all isomers), hemimellitene, pseudocumene, mesitylene, ethylbenzene, n-propylbenzene, cumene, n-butylbenzene, isobutylbenzene, sec-butylbenzene, tert- butylbenzene, and paracymene. Preferably, C8-10 alkyl-substituted benzenes and/or napthalenes are used. A particularly preferred mixture of alkyl benzenes and alkyl napthalenes is Hisol 15Tm, a proprietary mixture of alkyl benzenes and alkyl napthalenes, sold by Exxon Chemicals. Substantially equivalent mixtures are commercially.available from other sources.

Cellulose Ethers

The composition includes one or more cellulose ethers. Cellulose ethers impart adequate thickening and film-forming properties. Cellulose ethers are soluble in both water and organic solvents. Those cellulose ethers that have substantially similar viscosity in organic solvents and aqueous solutions are particularly preferred for use as gelling agents. Compositions including cellulose ethers can form substantially transparent gels, depending on the other components.

Preferred cellulose ethers have etherifying groups such as hydroxyalkyl groups and groups derived therefrom. Etherifying groups consisting of or derived from hydroxyalkyl groups containing up to 5 carbon atoms, particularly 2, 3 or 4 carbon atoms, are preferred. Hydroxypropyl celluloses are preferred hydroxyalkyl cellulose ethers. Preferred hydroxypropyl cellulose ethers are derived from isopropanol rather than propanol, and have molecular weights in the range from about 50,000 to about 1,000,000, preferably from about 800,000 to 1,000,000.

Suitable cellulose ethers for use in the present invention include, but are not limited to, methylcellulose, such as Methocel 311, available from Dow Chemical Corp. Midland, Michigan, hydroxypropyl cellulose, such as Klucel™, available from Hercules, Inc., Wilmington, Del., and ethyl cellulose, such as Bermocol PR™, available from Seaboard Sales, New Jersey). Methocel 31 1 is the most preferred cellulose ether.

Not all of the free hydroxy groups of the cellulose need to be etherified and, if desired, the hydroxy groups of certain hydroxypropyl groups can, in turn, be substituted by a further hydroxypropyl group (as for example, in the Klucel materials described above).

The amount of gelling agent required in the compositions in order to give good gels depends in part on the molecular weight of the gelling agent used. Higher molecular weight materials can be used in lower concentrations than lower molecular weight materials, to produce a gel of an appropriate viscosity. It is preferable to use less of a higher molecular weight cellulose ether than more of a smaller molecular weight cellulose ether. Both the type and amount of cellulose ether are important to afford an effective, substantially stable water-based composition. "Substantially stable" compositions are those that remain substantially homogenous and do not separate into visible or visually observable layers for at least 48 hours upon standing undisturbed and, should layering occur, readily return to a homogenous state with gentle shaking by hand. This stability is, of course, one measure of the shelf life of a coating remover.

The amount of cellulose thickener present in the concentrate of the present invention is preferably within the ranges discussed above. When the cellulose ether is present in the concentrate above or below these levels, significant loss of stability can occur in the water-based composition.

Organoclays modified with quaternary compounds (high medium and low polar) can be used in place of or in addition to the cellulose ethers. Examples of these organoclays include, but are not limited to, Bentone 27 and stearalkonium hectorites, and'other Bentones including Bentone E and Bentone LT™, products of NL Industries, New Jersey, USA.

Water-soluble Compositions

The composition can optionally contain water. In one embodiment, the composition includes between 1 and 50 percent water. Water-soluble compositions are easy to work with and/or apply to the surface to be treated. Specifically, water can thin down a coat or layer of the composition should the layer be too thick. Further, water-soluble compositions are water- washable and water-miscible. Compositions containing water should also contain a surfactant in order to maintain the composition as an emulsion or as a single phase. Any surfactant that achieves the desired result can be used. T pical surfactants are anionic, cationic, zwitterionic, and nonionic surfactants.

Surfactants

Surfactants (also known as surface-active agents) are soluble compounds that reduce the surface tension of liquid, or reduce the interfacial tension between two liquids or a liquid and a solid.

Surfactants contain both a hydrophobic (or lyophobic) end and a hydrophilic (or lyophilic) end.

Surfactants are preferably selected for solubility in the composition, low toxicity, and the ability to form a useful emulsion of the composition with water. Normally, if surfactants are included in the composition, they are included in an amount of between approximately 1 and 8 weight percent, and preferably between approximately 3 and 6 weight percent.

The surfactant composition preferably includes an oil-soluble nonionic surfactant to improve the ability of the composition to wet surfaces to be stripped. A preferred oil-soluble nonionic surfactant is the 6-mole ethoxylate of tridecyl alcohol, commercially available from GAF under the tradename Emulphogene 610, and from Stepan under the tradename Makon TD-6. Also, a watersoluble nonionic surfactant is preferably included to facilitate rinsing the composition and loosened paint from the surface.

The characteristics of surfactants are described by Rosen in Surfactants and Interfacial Phenomena. 2nd Edition (John Wiley and Sons, NY), incorporated herein by reference. In general, the desired chemical structures of the hydrophilic and hydrophobic portions of the surfactant will vary with the nature of the solvent and the conditions of use. Methods to select the surfactant for a given composition are well known to those of skill in the art, and are described in a large number of textbooks, for example, Surfactants and Interfacial Phenomena.

Any surfactant can be used with the composition that achieves the desired result. Suitable surfactants for use in practicing the present invention include, but are not limited to, anionic, cationic, zwitterionic and nonionic surfactants. The most preferred surfactant is triethanolamine.

Surfactants are typically characterized by the nature of their hydrophilic portion. Anionic surfactants have a negatively charged moiety in the hydrophilic end of the molecule, such as a carboxylate or sulfonate salt.

Cationic surfactants have a positive charge in the hydrophilic portion of the molecule, provided by, for example, an ammonium salt or a quaternary amine.

A zwitterionic surfactant has both positive and negative charges in the hydrophilic portion. Examples of zwitterions are long chain amino acids and sulfobetaines. Nonionic surfactants do not have a formalized charge.

Examples include the monoglycerides of long chain fatty acids and polyoxyethylenated alkyl phenol.

Optional Components

The composition can also include an extender, a corrosion inhibitor, dyes, and fragrances.

Extenders

Any extender can be used that achieves the desired result. Suitable extenders for use in the present invention include, but are not limited to, acrylic polymers, titanium dioxide, calcined clay, attapulgite clay, fumed silica, silica, mineral wool, mica, man-made fibers, such as nylon, polyester, and polyethylene, ceramic microspheres, and wood flour. Preferred extenders are acrylic polymers, titanium dioxide, calcined clay, silica, mica, and ceramic microspheres. The most preferred extender is an acrylic polymer.

The purpose of the extender is to turn the composition into a paint- like product. Specifically, the extender makes the composition have roughly the same rheology as a latex paint. The extender can also be used to make the composition provide an easily observable coating over the surface to be treated.

Corrosion Inhibitors

Corrosion inhibitors are well known to those of skill in the art. Any corrosion inhibitor can be used that achieves a desired result. Suitable corrosion inhibitors for use in the present invention include, but are not limited to, mono-, di-, and trialkanolamines, such as diethylethanolazine, monoisopropanolamine, and triisopropanolamine; mono-, di and trialkylamines, such as diisopropylamine, ethylamine, ethylenediamine, isopropylamine; morpholine; triethylenetetramine; and mixtures thereof. A preferred corrosion inhibitor is Rodine® from Amchem, Ambler, Pa.

Typical concentrations of corrosion inhibitors, if included at all, range from between approximately 0.5 and 2 weight percent, and preferably, from between approximately 0.9 and 1.1 weight percent. However, for stripping coatings from wood and. other non-metal surfaces, corrosion inhibitors are not preferred.

Dyes and Fragrances

Any dye or fragrance can be used that achieves a desired result. Dyes and fragrances can be selected according to the needs of product identification as well as aesthetics. The appropriate dye or fragrance should be chemically stable in the composition, as well as having little or no effect on the ability of the composition to remove the coating from the surface. Furthermore, the dye or fragrance should have little to no effect on the ability of the surfactant, if present in the composition, to create an emulsion so that the composition remains rinsable. Preferably, the amount of the dye or fragrance is between approximately 0.001 percent and 0.1 percent of the composition. Any dye or fragrance that achieves a desired,result can be used. An example of a suitable dye is Pylaklor LX-1911 A Orange, which is commercially available from Pylam.

Methods of Use Conventional methods can be used to apply the composition to a surface to be treated. Suitable methods for applying the composition to a surface include, but are not limited to, brushing, rolling, and spraying. The composition can be sprayed using a conventional airless paint sprayer, a hopper gun or other spraying unit driven by compressed air or other mechanical means. A particularly preferred means of application is brushing. The coating on the surface is softened by reaction with the composition. After the coating is softened, the stripper and loosened coating can be rinsed from the surface with water or manually scraped or sanded from the surface. The composition typically requires between approximately 5 and 20 minutes to soften the coating. The relatively 'long work life allows the coating to be completely removed with a single application, regardless of the thickness of the coating, in most instances, since the composition can be left n until all or substantially all of the coating is loosened or dissolved.

In one embodiment, the compositions are kept in contact with the surface for a period of time sufficient to produce a blistering of the coating. The blistered coating can be removed, for example, by contacting the coating with an abrasive pad. Alternatively, the coating can be removed by simply lifting the blistered coating off of the surface or by spraying the blistered coating with water. The continuity or evenness of the thickness of the single layer of the composition applied to the surface can be important to the success of the composition at stripping coatings. Preferably, the composition is applied in a uniform and continuous manner over the entire surface to be treated. When applied in this manner, the composition is effective in removing all layers of coatings from surfaces with a single application. Cover means for the composition

In one embodiment, after the composition is applied to a surface, it is covered with a laminated cover or cover means. The cover means covers the composition for at least a portion of the time the composition remains on and treats the surface.

The cover means is adapted to enhance the decomposition of the cured coats on the surface to be stripped, as well as to facilitate removal of at least a portion of the stripper composition and the decomposed surface coating.

Preferred cover means are laminated covers. Preferred laminated covers include paper tissue coated with polyethylene or wax. The combined weight of the coated paper should be between approximately 25 and 150 grams/m². The preferred combined weight is between approximately 30 and 50 grams/M².

The paper or at least a portion thereof sticks to the decomposed coating on the surface to be treated, and sticks to the laminated paper when the paper is pulled from the surface.

Generally, a non-woven, highly absorbent fabric, without chemical binders, is used. Any fabric or paper that absorbs the composition and is stable to the composition can be used. Examples of suitable fabrics for use in the present invention include, but are not limited to, thermally bonded composite blends of cellulose and propylene (cellulose/propylene), typically a 50/50 percent blend of each component, fabrics based upon polyester, rayon/polyester blends and woodpulp/polyester blends (the Sontara7m fabrics from DuPont). The fabric can range in thickness and abrasive quality, but typically, preferred fabrics range in thickness from between approximately 0.28 mm up and 1.02 mm.

Generally, cloth having a basis weight of approximately 2 ounces/yard is satisfactory for use in the present invention, but the basis weight can vary without impacting the stripping efficiency of the composition. Fabric to which compositions are absorbed are generally packaged in a barrier bag to prevent the transmission of vapor. Generally, the barrier bag is made of aluminum foil or another material that does not transmit vapor from the composition.

The procedure for making the fabric applicator of the present invention is straightforward. In one embodiment, fabric is cut or slit to an appropriate size, folded and inserted into the barrier bag, which is then sealed on three of four sides. Then, a metered volume of the composition is injected into the open end of the barrier bag, which is then sealed. After injecting the composition and during storage, the composition impregnates the fabric applicator.

The fabric applicator is designed to blister and remove coatings from surfaces. It is especially useful when applied to vertical surfaces because it adheres when applied. The fabric applicator and composition are designed so that there is sufficient tension between the applicator and the applied surface to retain it on the surface. In one embodiment, the applicator continuously applies composition to the surface to be stripped until the coating has lifted. A particularly advantageous feature of this aspect of the present invention is the fact that paint stripper composition will evaporate even less rapidly than when the composition is applied without a coating. When the composition is applied and is covered, the composition can be used to remove particularly difficult coatings and/or multiple coating layers, in which the contact time between the composition and the coated surface needs to be longer than in less rigorous applications.

The fabric applicator containing the composition is placed on a coated surface. The applicator remains in contact with the coated surface for a period sufficient to blister the underlying coating. Such period can be relatively short, perhaps as little as 5 minutes, or as long as 24 hours or longer for particularly difficult coatings. Once the coating blisters, the applicator is simply peeled off, usually with the underlying coating fixed to the applicator. Often there is no need to scrape or abrade the coating.

Modifications and variations of the present invention will be obvious to those skilled in the art from the foregoing detailed description of the invention. Such modifications and variations are intended to come within the scope of the appended claims.

Claims

1. A composition for stripping a coating from a surface comprising between approximately 20 and 40 percent l-methyl-2-pyrrolidone (NMP) or its equivalent, 1 and 20 percent of one or more alkylated aromatic hydrocarbons, 10 and 30 percent of one or more alkoxy propionic acid esters, 20 and 60 percent of one or more dialkyl esters of dicarboxylic acids, and 0.2 and 2.0 percent of a cellulose ether.

2. The composition of claim 1, further comprising an extender.

3. The composition of claim 2, wherein the extender, is selected from the group consisting of acrylic polymers, titanium dioxide, calcined clay, attapulgite clay, fumed silica, silica, mineral wool, mica, man-made fibers, ceramic microspheres, and wood flour.

4. The composition of claim 1, further comprising a surfactant selected from the group consisting of anionic, cationic, nonionic and zwitterionic surfactants.

5. The composition of claim 4, wherein the surfactant is selected from the group consisting of sodium and potassium tallate.

6. The composition of claim 1, wherein the concentration of 1- methyl-2-pyrrolidone (NMP) or its equivalent is between approximately 25 and 35 percent.

7. The composition of claim 1, wherein the concentration of alkylated aromatic hydrocarbons is between approximately 5 and 15 percent.

8. The composition of claim 1, wherein the concentration of alkoxy propionic acid esters is between approximately 15 and 25 percent.

9. The composition of claim 1, wherein the concentration of dialkyl esters of dicarboxylic acids is between approximately 30 and 50 percent.

10. The composition of claim 1, wherein the concentration of the cellulose ether is between approximately 0.5 and 1.5 percent.

11. The composition of claim 1, wherein the concentration of dialkyl esters of dicarboxylic acids is between approximately 35 and 45 percent.

12. The composition of claim 1, wherein the concentration of 1- methyl-2-pyrrolidone (NMP) or its equivalent is between approximately 28 and 32 percent.

13. The composition of claim 1, wherein the concentration of alkylated aromatic hydrocarbons is between approximately 8 and 12 percent.

14. The composition of claim 1, wherein the concentration of alkoxy propionic acid esters is between approximately 16 and 20 percent.

15. The composition of claim 1, wherein the concentration of cellulose ether is between approximately 0.7 and 1.0 percent.

16. The composition of claim 1, wherein the alkylated aromatic hydrocarbons are a mixture of alkyl benzenes and alkyl napthalenes.

17. The composition of claim.1, wherein the alkox'y propionic acid ester is ethyl-3 -ethoxypropionate.

18. The composition of claim 1, wherein the dibasic esters are a mixture of dimethyl esters of adipic and glutaric acids.

19. The composition of claim 1, wherein the cellulose ether is hydroxypropyl methyl cellulose.

20. A method for removing coatings from surfaces comprising a) applying an effective amount of the composition of claim 1; b) waiting for an effective amount of time for the composition to remove the coating from the surface; and c) removing the composition.

21. The method of claim 20, wherein the surface is wood.

22. The method of claim 20, wherein the coating is nitrocellulose lacquer.

23. A composition for stripping surfaces comprising between approximately 28 and 32 percent l-methyl-2-pyrrolidone (NMP) or its equivalent, 8 and 12 percent of a mixture of alkyl benzenes and alkyl napthalenes, 16 and 20 percent ethyl-3 ethoxypropionate, 35 and 45 percent of a mixture of dimethyl esters of adipic and glutaric acids, and 0.7 and 1.0 percent of hydroxypropyl methyl cellulose.