GB2205107A - Paint stripper composition - Google Patents

Abstract

A paint stripper composition, of particular utility for the removal of plastisol coatings from fixed structures, comprises a liquid haloalkanoic acid, usually 2-chloropropionic acid, and a chlorine substituted hydrocarbon. It usually also contains a thickener.

Description

PAINT STRIPPER COMPOSITION The present invention relates to solvent-based stripper compositions accelerated by organic acids.

There are many disclosures in the literature of paint stripper compositions comprising an organic solvent, usually a chlorinated hydrocarbon solvent and most often methylene chloride, which are activated by organic acids. US3356614 lists formic, acetic, propionic, salicylic, butyric, carbolic, benzoic and cinnamic acids as examples of activators which have been used with methylene chloride. However, for many paints, these acids are not efficient enough as activators. The invention in the above mentioned specification is the use of a mixture of acetic and trichloroacetic acids as activator for trichloro-ethylene based compositions. One problem with trichloro-acetic acid is that it is hazardous for the user and furthermore is a solid at room temperature and is insufficiently soluble or dissolves slowly in the liquid stripper.The solution produced is unstable, the acid coming out of solution on storage. Acetic acid is insufficiently aggressive as an activator on many paint surfaces.

In US3075923 methylene chloride strippers are activated by benzene sulphonic acid or alkyl benzene sulphonic acids. Such acids are insufficiently aggresive, particularly where it is desired to remove aged plastisol paints from external structures. These tend to become badly degraded, probably as a result of being exposed over long periods to ultra violet radiation which makes them extremely difficult to rembve. Furthermore the acid has limited solubility in the stripper composition so that it may be necessary to add a co-solvent, such as a glycol or an alcohol.

In US 3072579 there are disclosed organic solvent based compositions comprising orthocresol and trichloroacetic acid. The problems with trichloroacetic acid have been enumerated above. In US5418518 there is disclosed a chlorinated hydrocarbon based stripper composition containing chloroacetic acid. The chloroacetic acid may be mono-chloroacetic acid or a mixture of chloroacetic acids. Although it is stated that the concentrate may contain up to 25% chloroacetic acid, in practice it is difficult to achieve a stable composition containing such high amounts of the acid which has limited solubility.

Furthermore the acid dissolves slowly so that manufacture of the compositions is difficult It is possible to improve the solubility of the solid chloroacetic acid mentioned in the citations, by incorporating co-solvents. Thus glycols and/or aliphatic alcohols may be incorporated in the composition, but, as stated above, this reduces the concentration of the active stripping compounds in the composition and thereby reduces the stripping efficiency. The incorporation of water also helps solubilise the acid but the amount of water that can be incorporated may be limited. For instance, a thickened composition which is intended for use by brushing or otherwise coating onto a painted structure, may contain only a limited amount of water since above a certain value the gel-like properties of the composition deteriorate.

According to the invention a new paint stripper composition comprises a chlorine-substituted hydrocarbon and an organic acid activaor in which the organic activator is a haloalkanic acid which is a liquid at room temperature.

The use of a liquid activator allows the amount of the activator to be increased whilst retaining the stability of the composition. Thus the stripper preferably contains at least 5% by weight activator.

Particularly advantageous results are achieved when the concentration is between 10% and 15% by weight.

Haloalkaonic acid which is a liquid at room temperature may be used. Usually the acid is a C35 alkanoic acid, suitably having two or, preferably one halogen substituent at the 2-position, and/or the 3- or higher (if present) positions. The carbon chain can be branched but is usually straight. Preferably it is a C3 or C4 alkanoic acid. The halogen can be any halogen, preferably bromine or chlorine, most preferably chlorine.

Examples of acids which are useful are 2-chloropropionic acid, 2,2-dichloropropionic acid, 2-chlorobutyric acid and 2-bromobutyric acid, the most preferred acid being 2-chloropropionic acid. Usually the liquid acid is the sole acid used as the activator, but in some cases it may be desirable to use a mixture of that acid with another organic acid activator, for instance a chloro-acetic acid or a benzene sulphonic acid.

By the use of the liquid acid in the composition of the invention, compositions containing higher amounts of activator and which therefore have more efficient stripping properties, may be prepared quicklv and simply at room temperature without requiring excessive mixing and are stable in storage so do not require excessive mixing before use. The further benefit of the use of the liquid acid is that there is no longer a need to dissolve a solid activator which is a time and energy consuming part of the manufacturing process. Thus by effectively replacing a solid acid with a liquid acid having comparable activator properties, savings in production and storage costs may be achieved and a more-storage stable composition is formed while at the same time maintaining the stripping efficiency of the compositions.

The above-mentioned acids have activator properties of the same order of magnitude as chloroacetic acid.

The composition may be an immersion-type composition in which case it does not contain a thickener.

Immersion-type systems are for instance similar to those described in US 3075923 and US4518518.

The composition is most preferably a thickened composition which is for use by brushing, spraying or coating by other means onto a painted substrate. The thickener may be an organic thickener or an inorganic thickener. The 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. Additionally 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.

Suitable thickeners for many compositions are inorganic particulate materials, especially inorganic silicate materials. Fumed silica can be used but where a large amount is needed for thickening it tends to absorb too much of the solvent preventing it from evaporating but not allowing it to act upon the coating to be stripped. Inorganic particulate materials such as clay and calcium carbonate can be used although they need to be added in relatively high amounts which can make the composition difficult to apply, particularly using mechanical spray devices. The thickener of preference 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 stripper compositions containing inorganic thickener 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 aids subsequent removal of the composition from the surface to which it has been applied.

In many instances organic thickener is preferred for compositions which require to be left in contact with the surface from which the coating is to be stripped for long periods, for instance several hours. Compositions containing inorganic thickeners tend to dry to a composition which is difficult to remove by rinsing, whereas compositions in which the thickener is organic.

remain relatively easy to remove.

Suitable organic thickeners are polymeric and may be synthetic or natural. Preferred natural polymers are cellulose and derivatives, for instance ether derivatives, usually C14-alKvl ethers, in which the alkyl group may be substituted, for instance with hydroxyl groups. Examples of suitable thickeners include methyl-, ethyl-, hydroxyethyl-, propyl- and hydroxypropyl- cellulose. Mixtures can be used. We have found that degradation of these polymeric thickeners is minimised if the composition is substantially free of water.

vhe compositions generally contain one or more surfactants, which help stabilize the composition and aid the subsequent removal of the composition. Suitable surfactants are usually anionic surfactants, for example an alkylbenzensulphonic acid, e.g. dodecylbenzensulphonic 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. Preferably the composition is free of such cosolvents. The compositions may additionally 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. A thickened composition usually contains 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 858 by weight and preferably between w0 and 80% by weight. Where water is present it is generally present in an amount of between 1 and 5 by weight, usually between 2 and 4% by weight. Any 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 thickener is present in an amount of at least 0.1% by weight, generally less than 10% by weight.

Inorganic thickener is usually required in higher amounts than organic thickeners, for the same degree of thickening. inorganic thickener is usually present in an amount of at least 0.5% preferably in the range 1 to 5% by weight. Any activator for the inorganic thickener is present in an amount of from 20% to 200% of the weight of the thickener, generally about 50 to 100% of the weight of the thickener. Organic thickener is generally present in-an amount in the range 0.1 to 5%, preferably 0.5 to 2% by weight. A thickened composition preferably contains 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.

A thickened composition may be used in a method of removing paint from a substrate that can not be immersed in a stripper bath by applying the new composition to the substrate. The substrate is for instance the surface of a fixed structure, and is generally plastisol coated building cladding. The compositions are most useful where the plastisol is a degraded plastisol coating.

In the method 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 or 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 some cases, particularly where the composition has been left in contact with the substrate for a long period of time, it may be necessary to use an 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 a stripped surface with a new protective coating. The surface of building cladding 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.

The stripper of the invention can be provided in with reconditioner for the stripped surface comprising a conversion coating composition, usually a thickened conversion coating composition, that is one which is suitable for application to the surface in situ, for instance by brush, roller or spray.

The following examples illustrate the invention.

Example 1 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 2-chloropropionic 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. The stripper is left in contact with the coating for 20-25 mins. and is then removed by a water rinse.

EXAMPLE 2 A similar composition to that provided in example 1 is made up, but the Bentone 27 and glycol are replaced by 1 part by weight of a mixture of Celacol PR5 (Courtaulds), which is a methyl cellulose (high substitution/high viscosity) and Klucel H (Hercules) (high substitution/high viscosity) in a ratio of 4:1 The water is omitted.

The composition is a stable gel and is suitable for application by spray or brush. It was found to be effective for the removal of a plastisol finish after being left in contact with these coated surface for a period of 30 mins. after which it was easily removed by rinsing with water. This composition was more easily removable by the water rinse than that of Example 1.

Claims (11)

1. A paint stripper composition comprising a chlorine-substituted hydrocarbon and an organic acid activator in which the organic activator is a haloalkanoic acid which is a liquid at room temperature.

2. A paint stripper according to claim 1 in which the haloalkanoic acid is selected from 2-chloropropionic acid, 2,2-dichloropropionic acid, 2-chlorobutyric acid and 2-bromobutyric acid.

3. A paint stripper according to claim 1 in which the haloalkanoic acid is 2-chloropropionic acid.

4. A paint stripper according to any preceding claim which contains a thickener.

5. A paint stripper according to claim 4 in which the thickener comprises an organic polymer.

6. A paint stripper according to claim 5 which is substantially free of water.

7. A paint stripper according to claim 4 in which the thickener comprises an inorganic thickener.

8. A paint stripper according to claim 7 in which the thickener comprises bentonite.

9. A paint stripper according to any preceding claim in which the chlorine substituted hydrocarbon is present in the composition in an amount of at least 50% by weight.

10. A paint stripper according to any preceding claim in which the haloalkanoic acid is present in an amount of at least 5% by weight.

11. Process for the removal of paint from a surface, in which a paint stripper composition according to claim 1 is applied to the surface.