Paint Remover

This invention relates to a composition of matter suitable for use as a paint remover. The composition is less hazardous to use than conventional paint remover.

A common commercially available class of paint remover contains a high percentage of methylene chloride. Although methylene chloride based paint removers are inexpensive and quite effective, such paint removers may be hazardous to the health of the user if not properly handled. U.S. Pat. No. 2,507,983 discloses methylene chloride based paint removers.

As a less hazardous substitute for methylene chloride based paint removers, N-methyl-2-pyrrolidone based materials have been proposed. Such materials are effective, but also quite expensive. Paint removers based on N-methyl-2-pyrrolidone are disclosed in U.S. Pat. No. 4,120,810.

As another substitute for the more toxic methylene chloride based paint removers, compositions containing dialkyl esters of succinic glutaric and adipic acid have been disclosed. German Pat. No. 3,438,399 (granted Mar. 20, 1986) shows such a paint removing composition.

The present invention is a paint removing composition which comprises (a) at least 20% by weight of, at least one C.sub.1 to C.sub.4 dialkyl ester of a C.sub.4 to C.sub.6 aliphatic dibasic acid, (b) 0.1 to 5% by weight of an activator, (c) an effective amount of a thickener, (d) an effective amount of a compatible surfactant, and (e) from 1 to 80% by weight of at least one nonhalogen-containing-organic solvent.

Activators for the paint removers of this invention are of two different types, i.e., basic activators such as ammonium hydroxide and monoethanolamine, and acidic activators such as formic acid, acetic acid and oxalic acid.

Suitable nonhalogen-containing-organic solvents are preferably those that have high flash points, i.e., above about 140.degree. F. Such solvents include N-methyl-2-pyrrolidone, esters of monoalkyl ethers of dipropylene glycol, and esters of monoalkyl ethers of tripropylene glycol, and blends of hydrocarbons sometimes called "heavy aromatic naptha"--See U.S. Pat. No. 4,120,810, column 3.

The composition of the invention also contains an effective amount of at least one thickener. Suitable thickeners for paint removers are known in the art and include ethylcellulose, hydroxypropyl cellulose, organic modified clay and hydrogenated castor oil. The amount of thickener required depends in part on the other ingredients present in the composition, but in general an amount between about 0.5 and 10% by weight is effective.

The final ingredient required by the composition is an effective amount of a compatible surfactant. The surfactant is primarily included in the composition to enhance the water wash of the substrate to remove the paint residue and the other ingredients from the substrate. Suitable surfactants include potassium oleate, the dioctyl ester of sodium sulfosuccinic acid, sodium alkyl napthalene sulfonate, sodium alkyl benzene sulfonate and the like.

The paint remover of this invention comprises at least 20% and preferably at least 40% by weight of at least one C.sub.1 to C.sub.4 dialkyl ester of at least one C.sub.4 to C.sub.6 aliphatic dibasic acid. The dialkyl ester in most cases will be of a mixture of C.sub.4 to C.sub.6 aliphatic dibasic acid. Mixtures of C.sub.4 to C.sub.6 dibasic acids are a byproduct of the manufacture of adipic acid--an acid that is used commercially on a large scale in the production of some types of nylon. Suitable dialkyl esters for use in the present invention are obtained by the esterification of such a byproduct stream. The composition of such a byproduct stream varies considerably, but in general will contain about 15 to 30 percent succinic acid, 50 to 73 percent glutaric acid, and about 6 to 25 percent adipic acid. The methyl esters of such a mixture of acids is usually the most economically attractive, but ethyl, propyl and butyl esters are also useful.

The other solvent in the paint remover is a nonhalogen-containing-organic solvent. Nonhalogen-containing solvents which may be used in conjunction with the dibasic ester are of two types. One is a functional group-containing solvent which can have the effect of increasing removal effectiveness on a particular type of substrate or can modify the performance of a thickener. This type solvent may make up 1 to 50% by weight of the paint remover composition. Preferred are high flash point solvents such as N-methyl-2-pyrrolidone, and esters of dipropylene and tripropylene glycol ethers. Other nonhalogen-containing solvents which can be used but may be less desirable because of toxicity, cost, odor or volatility are C.sub.1 to C.sub.12 alcohols, including isopropanol and benzyl alcohol; ethers of ethylene and propylene glycols and their esters; C.sub.3 to C.sub.12 ketones including acetone, diacetone alcohol and acetophenone; acetate esters of C.sub.1 to C.sub.12 aliphatic alcohols; organic nitriles including acetonitrile and benzonitrile; nitropropane; propylene carbonate, and ethyl-3-ethoxypropionate. The second type of nonhalogen-containing solvents is a high flash point, highly aromatic blend of hydrocarbons often referred to as "aromatic naphtha" . Examples are Exxon Chemicals' Aromatic 150, Shell Chemicals' Cyclo Sol 63, Amoco's Panasol AN-3N, and Texaco's Aromatic Solvent 400, each of which contain mainly C.sub.8 and higher alkyl benzenes and/or naphthalenes. This second type of solvent may make up 10 to 60% by weight of the paint remover composition. Although these solvents serve primarily to maximize cost-performance of the remover mixture, for certain coatings such as alkyd enamels, the mixture of aromatic solvent and dibasic ester solvent provides enhanced removal action.

The Aromatic 150 solvent is a high purity aromatic mixture of C.sub.9 to C.sub.12 aromatics. The mixture contains about 8% C.sub.9 aromatic compounds, about 74% C.sub.10 aromatic compounds, about 15% C.sub.11 aromatic compounds, and about 1% C.sub.12 aromatic compounds, and about 1% of nonaromatic compounds. This mixture has a flash point of 150.degree. F. (Flash point is defined as the temperature at which a liquid gives off a vapor sufficient to form an ignitable mixture with air near the surface of the liquid.)

The following ingredients were mixed in a closed container:

39.5 parts by weight dibasic ester (containing about 17% by weight dimethyl succinate, 66% by weight dimethyl glutarate, and 17% by weight dimethyl adipate)

5.0 parts by weight N-methyl-2-pyrrolidone

2.5 parts by weight ethyl cellulose

2.0 parts by weight potassium oleate

1.0 parts by weight acetic acid.

The following ingredients were mixed in a closed container:

25.0 parts by weight of the dibasic ester of Example I

5.0 parts by weight of N-methyl-2-pyrrolidone

14.5 parts by weight Aromatic 150

1.0 parts by weight monoethanolamine

2.5 parts by weight ethyl cellulose

2.0 parts by weight potassium oleate.

Paint Removal Results

The compositions obtained from Example I and II were tested for their ability to remove various paints from pineboard surfaces. Eight different painted surfaces were employed in the test. The samples are identified and characterized in Table I below:

As can be seen from Table I each sample had three layers of paint.

The compositions of Example I and II, as well as two different commercially available methylene chloride based paint removers were applied with a brush to different portions of each of the eight panels. After 20 minutes the panels were scraped. The results are tabulated below in Table II. Table II shows the relative results of the paint removers, i.e., a rating of 1 means that on that particular panel this sample removed more paint or more paint layers, or exposed more wood grain than the other paint removers shown, while a rating of 4 means that on that particular panel, the sample removed less paint or less paint layers or exposed less wood grain than the other paint removers shown.