GB2199337A - Paint stripper composition - Google Patents

Abstract

A paint stripper of particular use for removing aged plastisol paints from building exteriors comprises an organic acid accelerator, usually a chloroacetic acid, a chlorine-substituted hydrocarbon, usually methylene chloride, and an inorganic thickener, usually bentonite.

Description

PAINT STRIPPER COMPOSITION The present invention relates to a thickened paint stripper composition that is suitable for stripping plastisol paints, particularly paint coatings which are old and degraded, for instance following exposure to ultra violet light, and which are difficult to remove.

Plastisol paints or coatings comprising vinyl chloride polymers are often used to protect metallic surfaces on large external structures, for example on roofs or walls of buildings. The coatings have a limited life and must thus be replaced. Before recoating the surfaces it is necessary to remove the old coating which may have become uneven, cracked and lost its adhesiveness to the surface and may have allowed corrosion of the surface to occur. Although these types of paints are not difficult to remove when they have been applied relatively recently, after several years they tend to age and degrade badly, probably as a result of being exposed over long periods to ultra violet radiation, and become extremely difficult to remove.Conventional paint strippers have until now not been capable of stripping these coatings or have required extremely long stripping time, e.g. several-weeks or have required a large amount of physical work.

In US3075923 there is described a paint stripper composition which comprises methylene chloride and is accelerated by a benzene sulphonic acid. The compositions maybe thickened e.g. by cellulosic thickeners, bentonite or casein. The compositions are used to remove a wide range of coatings, including vinyl coatings however these are newly applied coatings and probably solvent-based coatings which are not difficult to remove. The compositions are insufficiently aggressive to remove degraded plastisol paints.

In US3356614 stripping compositions for removal of paint, enamel, varnish and lacquer are described. The compositions are based on trichloroethylene and a combined activator (accelerator) comprising acetic acid and trichloroacetic acid and may additionally contain viscosity increasing agents. The only thickeners disclosed are cellulosic thickeners, of the type conventionally used in organic mixtures. The compositions described are insufficiently aggressive to remove degraded plastisol coatings.

In US4518518 paint stripping compositions containing methylene chloride, chloroacetic acid and water are described. Articles from which paint is to be removed are immersed in a bath of the composition. There is no disclosure of the use of the compositions other than as immersion type compositions and no disclosure of the use of thickeners. In addition the compositions have insufficient amounts of methylene chloride so that the compositions are not aggressive enough to remove degraded plastisol coatings.

A new stripper compsition according to the invention comprises an organic acid accelerator, a chlorine subsituted hydro carbon solvent and an inorganic thickener.

Stripper compositions suitable for removing degraded plastisol type coatings comprise a chloroacetic acid as the accelerator, methylene chloride as the solvent and a bentonite, preferably a modified bentonite, as the thickener.

The stripper compositions will usually contain low amounts of water which has an accelerating effect on the composition, probably by interacting with the acid accelerator, it helps solubilise the acid and a ids subsequent removal of the composition from the surface to which it has been applied.

The compositions generally contain one or more surfactants, which help stablize the composition and aid the subsequent removal of the composition. Suitable surfactants are usually anionic surfactants, for example an alkylbenzensulphonic acid, e.g. dodecyl benzensulphonic acid, or, more preferably, an ethersulphate, for example an ethoxylated alcohol ester of sulphuric acid (an alcohol ethoxy sulphate).

The composition may also contain small amounts cosolvents, for example low molecular weight alcohols such as ethanol or methanol. The compositions may additonally contain corrosion inhibitors, any of the conventional inhibitors which are stable in the compositions being suitable.

The compositions may contain fillers or extenders, usually in minor amounts, although it is preferable for the compositions to be substantially free of such additional components, since in general they merely dilute the effect of the solvent and the accelerator on the film.

The organic acid accelerator usually comprises a haloacetic acid, preferably a chloroacetic acid.

Bromoacetic acids may also be used although they are less readily available. The most prefered chloroacetic acid is monochloroacetic acid although di- and tri- chloro derivatives maybe used. The monochloro derivative is most readily available, most effective and least hazardous to the operator.

The inorganic thickener should be stable within the composition so that the composition remains thickened even after a period of storage. It should be effective in amounts at which the composition is not rendered difficult to apply. Additonally the thickener should not accelerate evaporation of the solvent, nor should it absorb so much solvent as to render the solvent in the composition incapable of acting on the coating to which it is applied. For compositions based on methylene chloride and chloroacetic acid we have found that many of the conventional thickeners that might be expected to work are unsatisfactory. For instance cellulosic type thickeners and xanthan gum and polyacryeates are unstable, becoming ineffective after storage. Fumed silica tends to absorb too much of the solvent allowing it to evaporate but not to act upon the coating to be stripped.Most other inorganic particulate materials such as clay and calcium carbonate need to be added in relatively high amounts which makes the composition difficult to apply, particularly using mechanical spray devices. The thickener that is used in methylene chloride, chloroacetic acid based compositions is modified bentonite.

The modified bentonite thickener is preferably used in combination with an activator. Any of the conventionally used activators maybe used, such as glycols. Preferably the glycol has a relatively low evaporation rate. A suitable glycol is tripropylene glycol. The modified bentonite and activator are generally premixed to form a paste before combination with the other components of the composition.

The compositions usually contain an evaporation retarder, which retards the evaporation of the solvent from the composition and retaining it within the coating of stripper applied to a surface. A suitable example is paraffin wax.

The amount of methylene chloride in the stripper compositions is generally at least 50% by weight, generally between 60 and 85% by weight and preferably between 70 and 80% by weight. The acid accelerator is preferably present in an amount of at least 3% by weight, preferably in an amount of between 5% by weight upto the saturation point. The saturation level depends upon the amounts of other components present, particularly the amount of water present. Usually the acid is present in an amount in the range of 8 to 15%. The thickener is present in an amount of at least 0.58 by weight, generally less than 10% by weight and preferably in the range 1 to 5% by weight. Water is generally present in an- amount of between 1 and 58 by weight, usually between 2 and 4% by weight.Surfactant is generally present in an amount in the range 0.2 to 5% by weight, for example between 1 and 4% by weight. Any activator for the filler is present in an amount of from 20% to 200% of the weight of the filler, generally about 50 to 100% of the weight of the filler.

The compositions preferably contain a colour, e.g. a pigment or, usually, a dye in order that the operator can identify the areas that have been coated with the stripper.

According to a further aspect of the invention a new method of removing paint from a substrate comprises applying the new composition to the substrate. The substrate is for instance the surface of a fixed structure, and is generally building cladding.

-We believe that this is the first time that a chlorinated hydro carbon-based stripper accelerated by a chloroacetic acid has been used to remove plastisol coatings and therefore a further aspect of the invention is a method of removing a plastisol coating from a surface by applying to the surface a composition containing a chloroacetic acid accelerator and a chlorinated hydro carbon solvent. Generally the composition is one of the new compositions, i.e. is thickened with an inorganic thickener. The method is most useful where the plastisol is a degraded plastisol coating.

In the new methods the composition is applied to the surface by brushing or, more conveniently, especially for larger surface areas, by spraying. Any of the conventional devices for applying paint stripper compositions by airless spray and that are not corroded by the composition may be used.

The composition is applied to a thickness of about 100 to 2000 microns, conviently about 500 microns. The composition is left in contact with the surface for a sufficient time for the coating to be stripped. This period depends upon the thickness and state of the coating and may be for instance only a few minutes or maybe up to one or two days in order for the stripping process to be as economic as possible. It is preferred for the composition to be in contact with the surface for a period in the range 10 minutes to 2 hours, usually for between 20 and 60 minutes. It may sometimes be necessary to repeat application of the stripper, for particularly badly degraded or thick coatings.

The composition is removed by water. In sometime cases, particularly where the composition has been left in contact for a long period of time, it may be necessary to use aqueous detergent solution to remove the film of stripper composition. The compositions are most conveniently removed by a high pressure water jet and any of the commercially available apparatus maybe used for this removal.

It is usually desired to coat the stripped surface with a new protective coating. The surface is usually of steel, aluminium or galvanised steel and it is often preferred to apply a conversion coating on to the stripped surface immediately following removal of the stripper, usually after drying. The composition may for instance be a phosphating solution e.g. an iron phosphating solution or a chromating composition or any other composition suitable for local application to the surface.

According to a further aspect of the invention there is provided a pack of two compositions the first of which is stripper composition according to the present invention and the second of which is a reconditioner for the stripped surface comprising a thickened conversion coating solution.

The following is an example of the composition according to the invention.

Example A stripper composition that is stable and is capable of removing plastisol finishes at least 15 years old, from fixed structures comprises the following components in the amounts stated (parts by weights;) Bentone 27 2.4 Tri-propylene glycol 1.9 Methylene chloride 76.4 Monochloroacetic acid 12 Water 2.6 Refined paraffin wax 0.9 Ethoxylated alcohol sulphate surfactant 3.8 Colour (fat yellow ggn) 0.015 The stripper comprised a stable thixotropic gel that was capable of being applied by brush or by a portable spray paint stripper device.

Claims (19)

Claims

1) A stripper composition comprising an organic acid accelerator, a chlorine subsituted hydrocarbon solvent and an inorganic thickener.

2) A composition according to claim 1 in which the acid comprises a chloroacetic acid, the solvent comprises methylene chloride and the inorganic thickener comprises a bentonite.

3) A composition according to claim 2 in which the acid is monochloroacetic acid and the thickener is modified bentonite.

4) A composition according to claim 2 or claim 3 in which the methylene chloride is present in an amount of at least 50% by weight, the chloroacetic acid is present in an amount of at least 3% by weight and the bentonite is present in amount of at least 0.5% by weight.

5) A composition according to claim 4 in which methylene chloride is present in an amount in the range of 60 to 85% by weight, preferably 70 to 80% by weight, the chloroacetic acid is present in an amount in the range 5% up to the saturation point, preferably 8 to 15% by weight, and the thickener is present in an amount in the range 0.5 to 10%, preferably 1 to 5% by weight.

6) A composition according to any preceding claim which also comprises water, preferably in an amount in the range of 1 to 5% by weight, and a surfactant, preferably in an amount in the range of 0.2 to 5% by weight.

7) A composition according to claim 6 in which the surfactant is an anionic surfactant, preferably selected from alkylbenzenesulphonic acids and ether sulphates, and is preferably an ethoxylated alcohol sulphate ester.

8) A composition according to any preceding claim, in which the thickener is a modified bentonite, which additionally contains an activator for the modified bentonite, preferably a glycol, most preferably tri propylene glycol.

9) A composition according to any preceding claim, comprising an evaporation retarder, preferably in an amount in the range 0.2 to 2% by weight, usually about 1% by weight, preferably comprising paraffin wax.

10) A pack of two compositions, the first of which is a stripper composition according to any preceding claim and the second of which is a surface reconditioning composition, comprising a thickened conversion coating composition.

11) A method of removing paint from a surface by applying to the surface a thickened stripper composition containing organic acid accelerator, chlorine substituted hydrocarbon and an inorganic thickener.

12) A method according to claim 11 in which the paint is a plastisol paint, preferably a degraded plastisol paint.

13) A method of removing a plastisol paint from a surface by applying to the surface a stripper composition containing a chloroacetic acid accelerator and a chlorine subsituted hydrocarbon solvent.

14) A method according to claim 13 in which the composition is thickened with an inorganic thickener.

15) A method according to any of claims 11 to 14 in which the composition is a composition according to any of claims 1 to 9.

16) A method according to any of claims 11 to 15 in which the composition is left in contact with the surface for a period in the range of 5 minutes to 2 days, usually 10 minutes to 2 hours, and is then removed by water, optionally containing detergent, usually applied under pressure.

17) A method according to any of claims 11 to 16 in which the stripper composition is applied by brush or airless spray.

18) A method according to any of claims 11 to 17 in which the surface is a steel, galvanised steel or aluminium surface.

19) A method according to claim 18 in which, following removal of the stripper composition from the surface, the stripper surface is reconditioned using a composition, which is a reconditioning composition as defined in claim 10.