CA2012739A1 - Coating removal compositions and method for use thereof - Google Patents

Abstract

Abstract The present invention is a coating removal composition formulated so that the composition is capable of being applied to a coating using conventional spraying equipment and of forming a dry peelable mass which may be removed from a surface as a dry powder or flake material. A process for removing coatings is disclosed wherein the coating removal composition is applied to a surface, preferably by spraying, which dries in less than an hour to form a dry, peelable mass.
The dry mass is then removed as a dry powder or flake material. The composition is also useful for removing labels from substrates.

Description

¦ (? ~O -~j COATING RENOVAL ~OMPO~ITION~
AND MET~OD FOR U~E THEREOF

Backaround of the Invention The present invention relates to coating removal and, more particularly, to the stripping of labels, paint and other finishes from various substrates.
It is well-known to those in the refinishing arts that coatings are removed by sanding and/or with the aid of chemical strippers. When using a chemical stripper, typically a liquid, or more usually, a semi-liquid thin paste containing the active paint stripper is applied to the surface to be stripped and allowed to stand until the coating has been lifted from the surface. This may require several hours or even standing overnight. When the coating is at its loosest, it is removed by scraping. This produces a messy deposit on the floor of the work place consisting of strips or scraps of coating film swollen with the still wet paint remover.
Inasmuch as the active coating removing agents in the remover 201Z7~9 are irritating to the skin and eyes, protective gloves and goggles are preferably worn for this work. In any event, it is a difficult and unpleasant task to clean up and dispose of the wet residue. Furthermore, federal and many local regulations restrict the disposal of wet solvent-containing residue. ~--Another disadvantage of commercially available coatingremovers, particularly for automotive and aircraft use, is that they have varying degrees of effectiveness, removing most of the coating in some cases, but only part of the coating or hardly any of it in others. Previously available wet coating removers are particularly ineffective on epoxy, urethane and lacquer finishes, and some automotive undercoats.
Still another disadvantage of currently available wet chemical coating strippers is that the coating layer tends to re-adhere to the stripped surface if the coating remover is allowed to stand too long. Therefore, the scraping operation must be conducted at the optimum time to avoid the need to re-apply paint remover with consequent loss of time. This presents a scheduling problem and necessarily reduces efficiency.
The deficiencies of presently available chemical coating removers are so great that some shops resort to the more time-consuming and therefore, expensive sand-blasting and grinding techniques. These methods of coating removal also -have the disadvantage of creating a dust problem, requiring the workers to wear protective masks and clothing. Also, as with any operation that creates a dust-laden atmosphere, there is always the possibility of a dust explosion.
A paint stripping formulation for removing paint from a substrate as a dry, frangible mass (a "dry stripper") is disclosed in Canadian Patent No. 1,229,778. Dry strippers differ from wet stripping compositions in that the stripper is permited to dry without substantial re-adherence to the substrate prior to removal of the coa'ing. According to the disclosure, the formulations comprise an inert, absorbent particulate material. These compositions are not well suited for application to a surface by spraying, because the particulate material such as diatomaceous earth is abrasive and also tends to clog conventional spraying equipment with continued use.
Another dry stripper is disclosed in U.S. Patent No.
4,801,397. The compositions disclosed therein purport to be an improvement over the dry stripper containing the particulate material in that they also comprise a resin binder and 1/16" to 5" fibers which permit the coating-stripper mass to dry in 4 to 8 hours and be removed as "flakes". Because of the fibers, these formulations are not at all suited for use as a sprayable coating removal formulations.
Thus, there is a need for a composition which is both a 20~2739 dry stripper and may be applied by conventional spraying equipment. It would also be desirable for a dry stripper to lift the coating and dry in a relatively short period of time.
It is a primary object of the present invention, therefore, to provide an improved method for removing coatings, and particularly paint and labels, and improved chemical compositions for this purpose, which are not subject to the disadvantages of the prior art.
It is another object of the invention to provide an improved method and compositions for coating removal, which reduce labor, increase efficiency, and which permit easy clean up of the stripped coating.
It is another object of the invention to provide a method and compositions for coating removal, which prevent re-adhesion of stripped coating to the treated surface.
It is another object of the invention to provide a method and compositions for coating removal which are not only more efficient and convenient than those of the prior art, but which are also less expensive.
It is another object of the invention to provide a method and compositions capable of completely removing all commercial finishes, including acrylics, synthetics, epoxies, urethanes, certain lacquers and undercoating, down to the bare substrate with minimal effort in the stripping operation.
It is another object of the invention to provide a method and compositions for automotive and aircraft paint removal in which the paint is removed in dry flake form without the need for heavy manual scraping.
It is another object of the invention to provide coating removing compositions which have good flow and adhesion, long shelf life, non-flammability, good color and low odor.
It is yet another object of the invention to provide coating removing compositions which may be readily applied to the coating using hand pump bottles or conventional siphon or pressure spray equipment.
It is still another object of the invention to provide such compositions which are capable of removing multiple coats of paint and/or labels adhered to the surface in a single operation.

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20~2739 Summary of the Invention The foregoing and other objects of the invention which will become apparent below are achieved by formulating ingredients in a paint stripping composition which permits the primary active paint removing agent, such as methylene chloride, to achieve complete paint removal and to convert the stripped paint and paint remover to a dry, peelable mass, which is easily removed from the treated surface to leave bare substrate.
According to the present invention, a coating removal composition is formulated so that the composition is capable of being applied to a coating using conventional spraying equipment and of forming a dry, peelable mass which may be removed from a surface as a dry powder or flake material. A
process for removing coatings is disclosed wherein the coating removal composition is applied to a surface, preferably by spraying, which dries in less than an hour to form a dry, peelable mass. The dry mass is then removed as a dry powder or flake material. The composition is also useful for removing labels from substrates.
A coating remover of the present invention consists essentially of methylene chloride in the range of from 50 to 90%, preferably 65 to 85%, by weight; a penetrating agent such as aqua ammonia in the range of from O to 8%, preferably 2 to 8%, by weight; an evaporation retarder such as paraffin wax or tlle equivalellt ln t~le xange ~ from ~.5 to 2.5~ by weight: a solve~t for tl~e evaporatlon retarder, for example ~
wax solvent such as mineral splrits or the equlvalent ln the range of from 1 to 20% by welgllt; an alcohol or mlxture of alcollols ln tlle range of from ~ to 22~, preferably 9 to 13~, by weigh~ (preferably a mix~ure of denatured ethyl alcollol ln tlle range of from o to 11% by welght and methanol in tlle range of from o to 11% by weigh~ of the total compositlon): and a thickening agent such as hydroxypropyl-metllylcellulose or tlle equivalent in the range o from 0.5 to 3.0%, pre~erably ~.8 to 2.~%, by weight.
~ ccording to a fur~ller aspect of the lnvention tllere ls provided a method o~ ma1cing sucll preeerred coating remover comprising dissolving tlle paraffln wax or equlvalent ln the mlneral spirits with heatlng, slowly adding the dissolved wax-mineral splrlts mixture to the methylene chloride or equivalent, witll s~irring, slowly adding the hydroxyproplymethyl cellulose, or equlvalent, eollowed by, wltll s~irring, adding tl~e ammonla,.addlng a mlxture of denatured ethyl alcohol or equlvalen~, and the methanol.

Description Oe the_Inve~ntion More speclflcally, the preferred coating removers havQ

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20~27:~9 the following compositions:

Preferred Compositions Percent By Weiaht Ingredients Min. Preferred Max.
Methylene chloride 50 77.1 90 Paraffin refined wax 0.5 o.g 2.5 Mineral Spirits 1 5.8 20 Ethyl alcohol, 0 5.5 11 denatured Aqua ammonia 2 4 8 Hydroxypropyl 0.5 1.2 3.0 methylcellulose Methanol 0 5.5 11 It should be understood that the foregoing proportions are approximate and that they are based on the weight of the total composition.
While not intending to be bound by a particular theory, it is believed that the present compositions have the ability to encapsulate active coating-removing solvent and penetrating agent for a temporary yet sufficient time to inhibit evaporation and permit the loosening of the coating without re-adherence to the substrate before complete drying of the loosened coating. This feature results in short drying periods, the gradual release of solvent into the air and low odor in the working environment.
The preferred active stripping agent, methylene chloride, 9- ;~012739 is commonly used for this purpose in chemical coating removers. While less than about 50% methylene chloride may be used, if desired, there is a consequent loss of paint stripping effectiveness. It is preferred to use about 65 to 85% to provide a composition which will have the desired effectiveness. While more than 90% methylene chloride could be used, it has not been found necessary to do so, and such large amounts increase the rate o~ evaporation from the composition, and consequently its odor.
A penetrating agent is desirable to enhance the effectiveness of the solvents in removing durable coatings such as polyurethane- and epoxy-based coatings. The penetrating agent may be omitted when, for example, the composition is to be used to remove less durable coatings such as ~arnishes, laquers and enamels or when the penetrating agent would otherwise damage a substra~e such as wood. The preferred penetrating agent is aqua ammonia. Any suitable concentration of aqua ammonia, which is typically an aqueous solution containing up to about 30% ammonia, by weight, may be used. While somewhat more than about 8~ aqua ammonia may be employed, it has not been found to be necessary and it is undesirable to add more water to the composition than is contained in that amount of aqua ammonia. Other suitable penetrating agents include organic amines such as isopropylamine, monoethanolamine, triethanolamine and triethyl ':

amine; organic acids such as formic acid, crysilic acid, polyacrylic acids, acetic acids and other carboxylic acids;
phenols and cresols. When using acids such as formic or acetic acids, a corrosion inhibitor such as sodium dichromate should be used. When a corrosion inhibitor is employed, it may be present in amounts of from O.l to 3% by weight of the total composition. Certain penetrating agents such as phenol may be less desirable because of their flammability.
A thickening agent is added to lend body to the composition, not only in holding it in place on the surface to be treated, but to aid in the formation of the dry, peelable mass. Any suitable thickening agent known to the art may be employed. Modified cellulose available under the tradenames "Methocel" (Registered Trademark) and "Cellosize" (Registered Trademark) are suitable. Carboxymethylcellulose, methyl cellulose and hydroyxethylcellulose are also very effective.
~he preferred thickening agent is hydroypropyl -methylcellulose, such as Methocel F4M-PRG available from Dow Chemicals, Midland, Michigan. While less than 0.5% thickening agent may be employed the resulting compositions are thin and difficult to use~ More than 3.0% by weight of the thickening agent may be used, but the sprayability of the composition may be impaired.
Other suitable thickening agents include cellulose derivatives such as Methocel 311 available from Dow Chemicals, :
, Midland, Michigan; ethylcellulose derivatives such as K-5000 and HG available from Hercules, Inc., Wilmington, Delaware;
polyvinyl chloride and polyvinyl acetate polymers or co-polymers such as UCAR solution vinyl VYHH and VYNS
available from Union Carbide, Danbury, Connecticut; polyvinyl alcohol.s as Vinyl 205 available from Air Products and Chemicals, Inc., Allentown, Pennsylvania; a methyl styrene/vinyl toluene copolymer such as PICOT~C LC available from Hercules, Inc., Wilmington, Delaware; bentonite clays such as Bentone LT available from N.L. Industries; sodium silicates such as those available from PQ Company, Philadelphia, Pennsylvania; potassium silicates such as those available from E.I. Dupont De Nemours, Inc., Wilmington, Delaware; colloidal and fumed amorphous silica such as Aerosil 200 available from Degussa Corp., Teterboro, New Jersey; and precipitated silica such as Zeothix 177 and 265 available from Huber Chemicals, Haver De Grace, Maryland.
An alcohol component is present in the range of from 4 to 22%, preferably 9 to 13%, by weight. Suitable alcohols are methanol, ethanol, denatured ethyl alcohol, isopropyl alcohol and the like. The methanol is a desirable ingredient, since it swells the modified cellulose thickening agent and enhances its thickening properties. More than about 4% methanol may be used, but would require labeling the composition as a poison.
Methanol may be added up to 11% by weight of the total ~ :~

20~2739 compositlon. The ethyl alcohol is desirable, since it aids in the penetration of various paint surfaces. It is preferred that the combined amount of methanol and ethanol or their equivalents i8 in the range of from 4 to 22%, preferably 9 to 13%, by weight o~ total composition.
Optionally, ketone 601vents such as acetone, methyl ethyl ketone, methyl isobutyl ~etone and the like may be added up to 50% by weight of the composition. However, the coating removal compositions will become increasingly flammable upon the addition of such ketone solvents.
Any suitable evaporation retarder may be employed in amounts from about 0.5 to about 2.5% by weight. Examples of commonly used evaporation retarders are paraffin wax, beeswax, vegetable wax, montan and petroleum wax. Paraffin waxes are preferred for most paint removers. The wax serves several functlons, i.e., it reduces evaporation of the volatile ingredients and for this reason also reduces the odor of ammonia. The wax al~o forms a film on the surface to be treated. ThQ wax film aids in holding the other ingredients in place while the composition is working. While less than about 0.5% wax may be employed, such small amounts reduce control o~ evaporation. More than about 2.5% wax is undesirable, since it reduces the effectiveness and sprayability o the composition.

A solvent employed to dissolve the evaporation retarder for addition to the liquid or semi-liquid composition. Typical wax solvents are aromatic and aliphatic solvents such as toluene, xylene, mineral spirits and aromatic blends. The preferred wax solvent is mineral spirits. The preferred mineral spirits are a hydrocarbon cut having a--boiling point in the range from about 200F to about 400F. From about 1 to about 20% wax solvent may be employed depending on the amount of wax used. The solid wax is placed in the solvent in a container and the solvent is heated sufficiently to dissolve the wax: typically to about 132F.
A preferred method of making new compositions is as follows: The methylene chloride is stirred in a suitable container with conventional blending equipment. In a separate container, the wax is dissolved in the mineral spirits or other wax solvent by heating and melting the wax in the solvent. The solution of wax and solvent is then added to the methylene chloride, slowly with continued stirring. Next, while the stirring continues, the hydroxypropylmethyl cellulose is slowly added. The aqua ammonia is added next, followed by the ethyl alcohol and methanol mixture.
In this way a coating removal composition is made which has long shelf life, is non-flammable, has good color and a low odor, and which is capable of completely removing paint finishes and labels to the bare substrate.

~!739 The new compositions may be applied to the surface to be treated by techniques known in the art, such as by brushing, rolling, or spraying. However, a primary advantage of the present compositions is that they are formulated such that they may be applied using a hand spray bottle or conventional siphon or pressure spray-equipment. In this manner, the compositions may be conveniently and quickly applied to the coating in a substantially uniform layer. This greatly reduces the labor required in a paint or label removing operation, and particularly in an operation where paint and labels are removed in an assembly-line fashion, such as in the recycling of oil drums. The compositions of the present invention may also be applied as an aerosol spray. An aerosol spray may be obtained by placing the composition in an aerosol can with any suitable propellant such as carbon dioxide.
In addition to being sprayable using conventional equipment, the compositions of the present invention have a very low odor, even when sprayed on the surface to be treated.
Typically, no extraordinary ventilation is required as is usually necessary when solvent-based coating removers are used. The compositions may be used to remove a variety of coatings such as varnishes, epoxies, urethane and nitro-cellulose lacquers, acrylics, grease, adhesives and the like from a variety of substrates such as metal, glass, wood, urethane and other plastics, fiberglass, tile, concrete, 20~2739 masonry and the like. The compositions may also conviently be used to remove plastic, paper and plastic coated paper labels and the underlying adhesives from substrates.
The coating removing compositions may be applied to vertical and even overhead surfaces without dripping away or impairing the effectiveness of the compositions. Since the compositions typically dry in less than about thirty minutes at ambient temperature, problems with running or dripping away are obviated. Because one object of the invention is to provide a coating remover that dries quickly without running, the use of wetting agents or surfactants should be avoided.
The new compositions lift the paint from the substrate in about 7 to 15 minutes and dry in about one half to one hour at ambient temperatures in most cases. If desired, the compositions may be removed by scraping or wiping while still wet after the paint has been lifted. This is not preferred however, since a primary advantages of dry stripping and clean up are lost. It is preferred to wait until the coating and coating remover mixture has fully dried to a peelable, dry mass. This mass is then very easily peeled from the surface by any suitable mechanical method with minimal effort, as by scraping or brushing, either manually or by the use of a power tool. The easiest method of all is to use compressed air from commercially available hand held air guns, which direct a jet of air at the peelable mass to swiftly and fully remove it --16- ~01~739 from the bare substrate. The dry mass containing the removed paint is then simply swept up and discarded as clean dry, easily handled loose material.
The invention will now be described in greater detail in the following examples.

Example I
Place 7.5 lbs of solid, refined paraffin wax into a metal pot containing 48 lbs of mineral spirits, the wax should be cut or chopped into small pieces to facilitate melting and solution. The pot is heated with occasional mild stirring, until the mineral spirits reach the melting point of the wax, i.e., about 132F., and stirring is continued until all of the wax has melted and dissolved.
The mineral spirits - wax solution is added very 510wly to 643.5 lbs of methylene chloride in a vessel fitted with a conventional stirrer. The mixture is stirred slowly, during the gradual addition of the wax solution, until all of the wax has been added and the solution in the vessel is homogeneous.
While continuing mild stirring, 10 lbs of hydroxypropylmethyl cellulose is added. Then, while continuing mild stirring, 34 lbs of aqua ammonia is added followed by a mixture of 58.4 lbs of denatured ethyl alcohol and 33.4 lbs of methanol. Stirring is continued until the mixture is homogeneous. Stirring is continued while filling the finished paint stripper into drums or cans in order to insure the uniformity of the composition.

Example II
The stripping composition of Example I is sprayed onto the surface of an oil drum having a label affixed thereto.
The stripper is allowed to stand in contact with the oil drum for about half an hour, until the lifted label, adhesive, paint and stripper is thoroughly dry to the touch.
The dry, peelable label is then removed from the oil drum by hand or by any suitable mechanical means, such as a scraper or a common scrub brush. The dislodged residue is swept up and disposed of as clean fill.

Example III
The stripping composition of Example I is sprayed from a hand held pump spray bottle to form a uniform layer of the composition on an automobile fender painted with acrylic enamel base coat, urethane clear coat and acrylic primer.
After 7 to 14 minutes the paint composition lifts from the metal surface and does not re-adhere to the metal. In approximately one hour the paint composition and stripper is dry and easily peeled away as a dry powder or flake material using a scraper.

Example IV
The stripping composition of Example I is sprayed from an ordinary siphon-type spray gun assembly onto a polyurethane bumper coated with a urethane paint, primer and flex agent additive. After 14 minutes the paint/remover composition lifts from the surface^and drys in approximately one hour.
The dry flake material is easily peeled away from the surface by brushing the surface. The stripping composition did not cause swelling on the surface of the urethane bumper which can occur with certain other strippers.

It will be apparent to those skilled in the art that the foregoing description and examples are merely illustrative, and that other compositions, and other methods of making and using them are included in the scope of the invention. For example, and without limitation, any known active paint stripping ingredient other than the preferred methylene chloride may be used. The ammonia may be supplied from any known source. Thickeners other than the preferred, hydroxypropylmethyl cellulose, may be employed. Indeed, functional equivalents of any of the ingredients may be used, and any other ingredients commonly employed in such compositions may also be added as long as they do not alter the character of the claimed compositions.

Claims (20)

1, A coating removal composition consisting essentially of:
50 to 90 percent by weight methylene chloride;
0 to 8 percent by weight a penetrating agent;
0.5 to 2.5 percent by weight an evaporation retarder, 1 to 20 percent by weight an evaporation retarder solvent;
4 to 22 percent by weight an alcohol; and 0.5 to 3.0 percent by weight a thickening agent.

2. A coating removal composition according to claim 1, wherein the penetrating agent is selected from the group consisting of aqua ammonia, an organic amine, an acid, a phenol and a cresol.

3. A coating removal composition according to claim 1, wherein the penetrating agent is aqua ammonia.

4. A coating removal composition according to claim 3, wherein the aqua ammonia is 2 to 8 percent by weight of the total composition.

5. A coating removal composition according to claim 1, wherein the evaporation retarder is selected from the group consisting of paraffin wax, beeswax, vegetable wax, petroleum wax and mixtures thereof.

6. A coating removal composition according to claim 1, wherein the evaporation retarder is paraffin wax.

7. A coating removal composition according to claim 5, wherein the evaporation retarder solvent is selected from the group consisting of mineral spirits, toluene, xylene, an aromatic blend and mixtures thereof.

8. A coating removal composition according to claim 5, wherein the evaporation retarder solvent is mineral spirits.

9. A coating removal composition according to claim 1, wherein the alcohol is selected from the group consisting of methanol, ethanol, denatured ethyl alcohol, isopropyl alcohol, and mixtures thereof.

10. A coating removal composition according to claim 1, wherein the alcohol is a mixture of methanol and denatured ethyl alcohol.

11. A coating removal composition according to claim 1, wherein the thickening agent is selected from the group consisting of hydroxypropyl methylcellulose, carboxymethylcellulose, methylcellulose, hydroxyethylcellulose, a polyvinyl chloride polymer, a polyvinyl acetate polymer, a polyvinyl alcohol, a copolymer resin, bentonite clay, potassium silicate, and silica.

12. A coating removal composition according to claim 1, wherein the thickening agent is hydroxypropyl-methylcellulose.

13. A coating removal composition according to claim 1, said composition further comprising 0.1 to 50 percent by weight a ketone solvent.

14. A coating removal composition according to claim 1, wherein said composition is capable of being applied to a coating using conventional spraying equipment and of forming a dry peelable mass which may be removed from a surface as a dry powder or flake material.

15. A coating removal composition consisting essentially of:
50 to 90 percent by weight methylene chloride;
0 to 8 percent by weight a penetrating agent 0.5 to 2.5 percent by weight a wax evaporation retarder;

1 to 20 percent by weight a wax solvent;
0 to 11 percent by weight methanol;
0 to 11 percent by weight an alcohol selected from the group consisting of ethanol, denatured ethyl alcohol, isopropyl alcohol and mixtures thereof; and 0.5 to 3.0 percent by weight a thickening agent;
the total amount of said methanol and said alcohol components being 4 to 22 percent by weight of said total composition.

16. A coating removal composition according to claim 15, wherein said methylene chloride is present in an amount of from 65 to 85 percent by weight of the total composition;
said penetrating agent is aqua ammonia present in an amount of 2 to 8 percent by weight of the total composition; said evaporation retarder is paraffin wax; said wax solvent is mineral spirits; said alcohol is denatured ethyl alcohol; and said thickening agent is a modified cellulose thickener present in an amount of 0.8 to 2.4% by weight of the total composition.

17. A process for removing a coating from a coated substrate comprising: applying the coating removal composition of claim 1 to the coated substrate in an amount sufficient to lift the coating from the substrate; allowing the lifted coating to dry; and removing the coating from the substrate as a dry powder or flake material.

18. A process according to claim 17, wherein said coating removal composition is applied using conventional spraying equipment.

19. A process according to claim 17, wherein said lifted coating drys at ambient temperature in less than about an hour.

20. A process according to claim 19, wherein said lifted coating drys at ambient temperature in less than about an hour.