GB2150587A - Paint remover - Google Patents

Abstract

A solvent-based paint remover is improved by incorporating therein a film forming resin which is a copolymer of a major proportion of vinyl chloride and a minor proportion of an acrylic ester containing free hydroxy groups.

Description

SPECIFICATION Paint remover This invention relates to a paint remover, particularly for domestic use, based on methylene chloride or the like.

The removal of old paint from painted surfaces is a problem which can be met in various ways. One of the simplest solutions has always been the use of heat, for example by using a burner fuelled by spirit or liquid gas, such as a blow lamp. In this method the temperature of the paint coating is raised by direct application of the burner flame and at the point at which the paint softens, the layers blister and bubble and lift from the painted surface. The softened blistered paint must then be removed by scraping. The problems with this method are many.

The danger of fire is probably the most important, particularly where the painted substrate is wood. A considerable amount of skill is necessary in the application of heat to prevent scorching of the substrate or to prevent damage, for example by softening of putty or craking of glass when working on window frames. Another problem is the danger of the use of highly inflammable fuels for the burner.

Paint can also be removed by mechanical means, generally by the use of abrasives such as sand paper or glass paper or by abrasive wheels and discs. This method requires the expenditure of a considerable amount of energy and produces a large amount of fine dust comprising paint, abraded work surface and abrasive material.

Another much used method of removing paint involves the use of caustic materials, in particular sodium hydroxide which is generally applied in some form of paste. Paint removers of this type act by liquifying the paint so that it can be removed by scraping. The alkali requires a fairly long time to produce the required effect and even modern formulations require exposure of several hours. The softened paint is often very messy and contaminated with caustic materials.

As the paint surface has to be exposed to the alkali for several hours it is often desirable to cover the paint remover with a special blanket in order to prevent evaporation and to pick up the degraded paint. In this method the danger of skin burns caused by the caustic material is considerable. The formulations are generally based on a powder which must be mixed with water to form a paste. During this procedure there is a danger off inhaing caustic dust. An added problem is that some surfaces, particularly some woods and metals, cannot be treated because the alkali causes staining or corrosion. Furthermore, these materials are difficult to use around window frames because of damage to the putty. The alkali is also undesirable in contact with plaster and stone.

Another serious problem with the use of sodium hydroxide-based paint removers is that, generally speaking, a large amount of remover is required for a given area of work, which makes the cleaning up of the work piece a difficult task. It is, of course, essential that the substrate is well washed before any new paint is applied.

The other main type of paint remover is based on a solvent which acts by swelling the paint and thus lifting it from the work surface and from other layers of paint. Removers of this type are generally formulated as liquids which vary in viscosity from free flowing to gels. The solvent system used in removers of this type is generally based on a chlorinated hydrocarbon, particularly methylene chloride, in combination with an alcohol such as methanol. The main problem with the use of this kind of paint remover is that the solvent evaporates rapidly, particularly in warm conditions, and thus a fresh application of remover is needed after the first two or three layers of paint have been softened. The solvents are also difficult to handle in that they rapidly de-fat the skin and cause irritation and soreness.Methylene chloride in particular also-gives off an unpleasant vapour which can cause sickness and headache if breathed in high concentration. For this reason good ventilation is essential. As a certain amount of the composition eventually comes into contact with the substrate, it is generally necessary to clean the exposed surface with spirit before repainting. Alternatively, the paint remiver can be formulated with a detergent to facilitate washing of the substrate with water.

The problem of the evaporation and the fluidity of the methylene chloride has been recognised for many years. British patent specification No. 377949 describes a paint stripper comprising methylene chloride containing sufficient dissolved cellulose ester to render it viscous and less volatile. Such a system is not, in fact, a solution and tends to settle out on standing.

The film provided is not particularly tough or coherent. British patent specification 485857 describes the use of various cellulose or polymeric products as thickeners for methylene chloride and also the use of waxes to form a film. It suggests replacing the waxes with scaly filling agents such as mica powder or talc. However, such systems tend to contain substantial quantities of water and are not very stable. The film produced is not particularly successful and strippers of this type have not enjoyed commercial success.

More recently, U.K. patent application GB 2031447A has described an aqueous-based emulsion of methylene chloride with a system containg a solvent-soluble film-forming polymer, in particular a vinyl acetate a-olefine copolymer for emulsion paints sold by Vinyl Products, under the product number 6705. An emulsion is necessary, because the hydrophobic cellulose derivative used as thickner are incompatible in a single-phase system. Aqueous systems have uses in some fields, but are of limited use against modern high gloss paints and tend to be unstable.

Because of the inherent instability of mixed-phase systems containing film-forming polymers and methylene chloride, there remains a need for a stable single-phase paint stripper containing methylene chloride and a film-forming resin and being of the required consistency for application to vertical surfaces without run-off.

Research has shown that the majority of resins available for use, simply do not dissolve in methylene chloride-based solvent systems, or else provide unsatisfactory films or unsuitable viscosities. For example, vinyl chloride homopolymers provide completely the wrong type of viscosity characteristics and are not easily soluble. Vinyl chloride/acetate copolymers are of some slight use as film-formers, but must be present at very high concentrations and need the presence of large amounts of thickeners to maintain dispersion, resulting in an undesirably concentrated gel. Many acrylic acid-based resins are unsuccessful because they tend to be incompatible with the thickener component and cause breakdown of the system. They are also, in general, not sufficiently soluble.

However, we have now found a partuclar type of resin which can be used in a single phase paint stripper of the type mentioned above and can provide good film-forming characteristics and solubility and compatability with thickness.

According to the present invention there is provided a paint remover of the type based on a chlorinated hydrocarbon such as methylene chloride, in combination with an alcohol such as methanol, to which has been added a resin capable of forming a relatively impervious film by evaporation, characterised in that the resin is a copolymer of a major proportion of vinyl chloride and a minor proportion of an acrylic ester containing free hydroxy groups.

The paint remover according to the present invention can be simply applied to the painted material, for example by brushing or spraying as in the case of conventional methylene chloridebased removers. Shortly after the paint remover has been spread on the painted surface, the resin present in the formulation acts to form a substantially impervious coat or skin which then serves to retard evaporation of the solvent system. Thus, the solvent system can go on softening and disrupting the paint surface to which it has been applied for a much longer time than was hitherto possible. In practice, we find that an exposure of from, say, 30 to 60 minutes is sufficient to soften and lift several coats of paint which can then easily be peeled off. A particular advantage of this system is that the material which can be removed is coated with a film which prevents irritation of the skin.Thus, even though a proportion of the solvent remains, the removed paint layers can be handled. Furthermore, the film suppresses the unpleasant vapours, thus rendering the atmosphere far more pleasant in which to work.

We also found that the film which forms holds the solvents in place to such an extent that the substrate can be directly sanded down and painted, without need for washing or treatment with white spirits.

We have found, in particular, that these requirements are met by certain vinyl chloride copolymers which are soluble in methylene chloride/methanol mixtures, namely vinyl chloride copolymers containing a major proportion of vinyl chloride and a minor proportion of an acrylic ester containing free hydroxy groups.

The copolymer is preferably a copolymer of vinyl chloride and a hydroxyalkyl acrylate containing 1 to 5 carbon atoms in the hydroxyalkyl moiety. Hydroxypropyl acrylate copolymers are especially useful. The major proportion of vinyl chloride may comprise from 70 to 90%, preferably 75 to 85%, by weight of the total copolymer and the minor proportion of acrylate may comprise 10 to 30%, preferably 1 2 to 25% by weight. The hydroxyl content may be about 1.3 to 4%, preferably 2 to 3%, by weight. Other components may be present in the copolymer, in particular C16 dialkyl esters of dicarboxylic acids, especially unsaturated acids, which are desirably present at up to 10% by weight. A particularly useful combination includes dibutyl maleate at about 7% by weight. Components of this type improve the film strength and adhesion.

A resin of choice is that marketed by Wacker-Chemie GmbH, Burghausen, West Germany under the code name VCO 401/48 or E22/48A. This resin is stated to be a vinyl chloride/acrylate copolymer containing free hydroxy groups, the hydroxyl content being about 2% and the K value being about 48. The viscosity of this resin is stated to be as follows: (25% solution in methyl ethyl ketone, DIN cup 4 mm) 28 seconds, or alternatively (20% solution in methyl ethyl ketone at 20 ) = 50 + 10% mPa.s.

We have found that the content of the film forming resin in the compoition should generally be up to 15% by weight, particularly 5 to 15% and especially 7 to 12%.

The composition should also contain the normal components of a solvent paint remover.

Thus, the main component should be a solvent system based on a chlorinated hydrocarbon solvent and an alcohol, in particular methylene chloride and methanol or, optionally, ethanol.

When a mixture of methylene chloride and methanol is used, the ratio of the two solvents is preferably about 2 to 1 by weight, but higher proportion of methylene chloride may be adopted if desirable. The solvent system should, in general, comprise from about 70 to about 95% by weight of the composition, especially 80 to 90%. In addition to methylene chloride, it may be useful to include another chlorinated hydrocarbon solvent such as trichloroethene (e.g Triklone A, trade mark). Solvent mixtures of this type have a lower volatility and a more thorough softening action on the paint.

The composition should also contain a thickener system to provide the correct viscosity and cling. A thickener system based on a hydrated polysaccharide may be used. In general, such a mixture may contain from 1 to 3% of a polysaccharide, particularly a hydroxyalkyl cellulose, for example that sold under the trade mark CELLACOL. The polysaccharide may be solvated by the alcohol component, but it is desirable that a small proportion of water should also be present.

The hydroxyalkyl cellulose of choice is hydroxypropyl cellulose, especially that sold under the trade mark Klucel H. Thickeners of this type have the greatest affinity, among the polysaccharides, for the resin solution. However, even the best hydroxyalkyl cellulose thickener is not ideal as it is difficult to prevent separation of the mixture into two phases.

We have now found that the thickener is advantageously a saccharide-linked acrylic acid polymer of the type sold by B.F. Goodrich under the trade mark Carbopol, particularly Carbopol 940, 941 and 934 and their technical equivalents in the so-called 800 series. Thickeners of this type are used in conjunction with a neutralising amine, generally an aliphatic amine with 6 to 20 carbon atoms in one aliphatic group. The amine is advantageously a liquid at ambient temperature. The amine may be a primary, secondary or tertiary amine and may comprise a mixed amine, for example one derived from natural sources. An example of a mixed amine is one of the amines sold under the trade mark Armeen by Akzo Chemie, e.g. Armeen CD, a cocoamine containing 53% of saturated C,2 amines together with a small distribution of saturated C8 ,8 amines.Other particularly useful amines include N,N-dimethyl long chain amines, e.g. N,N-dimethyl CB -C14 amines such as N,N-dimethyl-tetradecylamine.

We have found that a thickener system of this type is completely compatible with the vinyl chloride/hydroxyalkyl acrylate copolymer and with the methylene chloride/methanol (or other solvent) system used for the paint remover, yielding a single phase, stable solution with good viscosity and adhesion characteristics.

A conventional solvent-based paint remover generally comprise a proportion of wax in order to retard evaporation. A wax content of about 1% is usual. We have found that in the compositions according to the present invention, the wax content must be considerably reduced, but wax is still necessary for a good result. In general, we find that wax should be present at about 0.05 to 0. 1% in the composition, preferably about 0.055 to 0.075%. The wax may desirably be a long chain paraffin hydrocarbon. As the wax is preferably incorporated in the composition in a liquid form, it is particularly desirable to choose a paraffin having a melting point below the boiling point of methylene chloride. Alternatively the wax can be added as a solution in another solvent, for example trichloroethylene.

The remaining components in the composition are a small amount of water, necessary to hydrate the polysaccharide thickener, or to provide sufficient hydrogen bonding for the carbopoltype thickener, which may be present at a level of about 0.3 to 1%, e.g. 0.5 to 0.6%; and any required dyestuff in order to improve the appearance of the applied coating.

The composition may be produced by dissolving the resin in the solvent mixture, adding the melted wax or a wax solution, optionally together with an additional amount of methylene chloride, then incorporating the polysaccharide thickener and water and dyestuff. Alternatively, the methylene chloride and trichloroethene are mixed and the wax dissolved therein. The Carbopol-type thickener is then added and neutralised with the amine.

We have found that a composition of this type can be painted on to a painted substrate and left for, say 45 minutes. After a few seconds the applied material forms a dry, waxy film. After a few minutes the coating bubbles and lifts as the solvent action begins to work on the underlying paint. After 40 to 45 minutes the various underlying paint layers have been softened and lifted and also have begun to separate from each other. The whole mass can then be simply lifted off with a knife or scraper. The removed material has a soft plastic consistency and can be handled without undue irritation to the skin. While the material is working on the paint, there is very little smell of methylene chloride.

The following examples are provided to illistrate particular embodiments of the invention.

Example 1 A paint remover was mixed to the following composition (% values are by weight): Methylene chloride 283.00 ml 377.309 58.30X Methanol 175.00 ml 138.409 21.38X Water 3.25 ml 3.259 O.5X Resin E22/48A (Wacker) 50.00 g 50.009 7-73s Trlchloroethene 39.00 ml 56.80g 8.78; Wax 0.45 g 0.459 0.07X Carbopol 940 7.00 9 7.009 1.08X 2-Ethyl hexylamine 17.50 ml 14.00g 2.16X 647.20g 100.00X colourant ad lib.

To make up the mixture, the methylene chloride and trichloroethene were mixed and the wax was dissolved. The Carbopol was then added, followed by the amine. The mixture was stirred for a few minutes and then the resin was added and the mixture stirred until clear. The methanol was then gradually added with constant stirring, followed by the water and a small amount of green colourant. The mixture was stirred and stored in sealed containers. It remained a stable clear solution and could be brushed onto paintwork with ease.

Example 2 The following mixture was made up: Resin E22/48A (Wacker) 12.94X by weight Methylkene chloride 56.30% Methanol 28.10% Hydroxy propyl cellulose (Klucel H) 2.00X Wax 0.06% Water 0.60X 100.00 Colourant ad lib.

The resin was dissolved in the mixed methylene chloride and methanol. Wax was then added (if necessary in solution in some of the methylene chloride). The cellulose thickener was hydrated with the water and then stirred into the solution followed by colourants. The mixture was stirred and stored in sealed containers. This mixture needed shaking before use.

Claims (16)

1. A paint remover of the type based on a chlorinated hydrocarbon in combination with an alcohol, to which has been added a resin capable of forming a relatively impervious film by evaporation, characterised in that the resin is a copolymer of a major proportion of vinyl chloride and a minor proportion of an acrylic ester containing free hydroxy groups.

2. A paint remover according to claim 1, in which the resin is a copolymer of vinyl chloride and a hydroxide alkyl acrylate containing 1 to 5 carbon atoms in the hydroxy alkyl moiety.

3. A paint remover according to claim 2, in which the resin contains hydroxy propyl acrylate.

4. A paint remover according to any of claims 1 to 3, in which the resin contains 70-90% by weight of vinyl chloride and 10-30% by weight of acrylate.

5. A paint remover according to claim 4, in which the resin contains 75-85% by weight of vinyl chloride and 12-25% by weight of acrylate.

6. A paint remover according to any of claims 1 to 5, in which the resin further contains a C1 ,6 dialkyl ester of a dicarboxylic acid.

7. A paint remover according to claim 6, in which the resin contains up to 10% by weight of said ester.

8. A paint remover according to any of claims 1 to 7, in which the resin has a hydroxyl content of 1.3 to 4% by weight.

9. A paint remover according to any of claims 1 to 8, containing up to 15% by weight of said resin.

10. A paint remover according to claim 9 containing 7 to 12% by weight of said resin.

11. A paint remover according to any of claims 1 to 10 containing a thickener system comprising a saccharide-linked acrylic acid polymer and a neutralising amine.

1 2. A paint remover according to claim 11, in which the amine is an aliphatic amine having 6 to 20 carbon atoms in one aliphatic group.

1 3. A paint remover according to claim 12, in which the amine is a liquid at ambient temperature.

14. A paint remover according to claim 1 2 or claim 13, in which the amine is a cocoamine or an N,N-dimethyl long chain amine.

1 5. A paint remover according to any of claims 1 to 14, containing containing a wax at a concentration of from 0.05 to 0. 1% by weight.

16. A paint remover according to any of claims 1 to 15, containing 0.3 to 1% water.

1 7. A method of removing paint from a substrate by applying thereto a remover composition according to any of claims 1 to 1 6.