MXPA99003698A

MXPA99003698A - Compositions and method for removing paint from a substrate

Info

Publication number: MXPA99003698A
Application number: MXPA/A/1999/003698A
Authority: MX
Inventors: Mary Lawlor Angela; May Braley Joanna; Alfred Whitton Colin
Original assignee: Brent International Plc
Priority date: 1996-10-22
Filing date: 1999-04-21
Publication date: 1999-10-14

Abstract

A paint stripper for use by immersion of a painted substrate in a bath of the composition or application in place comprises two phases, one aqueous and the other of partially water soluble organic solvent. The aqueous phase is saturated with organic solvent. The organic solvent is preferably benzyl alcohol, dibasic ester or ethyl-3-ethoxypropionate. The total amount of organic solvent in the bath is suitably in the range 2 to 20%. The stripper may be acid or alkali activated. The application stripper is thickened to avoid separation during storage.

Description

COMPOSITIONS AND METHOD FOR PIT.TMTWRR PAINTING OF SUBSTRATE DESCRIPTION OF INVENTION The present invention relates to a method for extracting paint from a painted substrate, especially a metal substrate. The extractor comprises an aqueous phase and an organic phase. An ample range of organic solvents has been used in extract formulations of paints. The most successful solvents are chlorinated hydrocarbons, especially methylene chloride. For environmental reasons, however, it is desirable that the levels of organic solvents, especially chlorinated solvents, be reduced. The present invention allows reduced levels of chlorinated solvents to be used or even allows the use of such solvents to be avoided all together. It is well known to use water as an activating compound in paint extractors based on organic solvent. Such compositions tend to have low water levels, for example less than 10%. Other paint extraction compositions comprising both water and organic solvents which are immiscible with water have been described. Emulsifiers are generally added in amounts such that an emulsion of one phase is formed in another phase. Such emulsions are storage stable and do not need to be separated before use. Alternatively they can be added cosolvents for " create a homogeneous individual phase system. Some examples are described for example in DE-A-3325166, GB 1114220, EP-A-0611214 and US-A-4619706 *. It has now been surprisingly found that paint-extracting compositions comprising immiscible organic solvent (ie only partially soluble) and water, but which are not in the form of an emulsion, can not be used as "paint extractors". with very useful properties. In a new method for extracting paint from a painted substrate surface according to the invention, the surfaces are contacted with the aqueous phase of a two phase liquid extracting composition comprising an aqueous phase which comprises water, soluble activator compound in dissolved water and an organic solvent which has a solubility in water in the range of 0.1 to 10% by weight at 20 ° C, the organic solvent that is present in the aqueous phase at a concentration of approximately the saturation level (as in ambient conditions for the method) and also comprising an organic phase comprising the organic solvent, in which the organic phase is in interfacial contact with the aqueous phase. In the present it is believed that it is the aqueous phase of the extracting composition which provides the primary extraction function, ie which attacks the paint in the surface of the substrate, so it allows its elimination. It has been found that some thermal or mechanical agitation can increase the extraction. This increase may be due to the provision of some solvent in contact with the substrate. The solvent phase essentially provides a reserve for the solvent dissolved in the aqueous phase. In view of the continuous interfacial contact, as soon as the solvent is exhausted from the aqueous phase by contact with the paint surfaces, it is regenerated from the solvent phase. The solvent therefore remains dissolved in the aqueous phase at the saturation level.

It is preferred that organic solvents be used which have a solubility in water at 20 ° C in the range of 0.5 to 6.0% by weight. The level of the solvent dissolved in the aqueous phase during the paint removal method may be greater than at the end of that range, since it is possible that the methods are carried out under conditions in which the solubility of the solvent in water is higher. In this way where the method is carried out at elevated temperatures, the level of the organic solvent in the aqueous phase can be at least 50% higher than the saturation level at 20 ° C, for example at least 100% higher or higher. The organic solvent may include chlorinated hydrocarbons, for example in combination with other organic solvents. In this way the invention allows lower levels of chlorinated solvents to be used when a combination of such a solvent and another organic solvent with which the chlorinated solvent is miscible. Preferably, however, the extractant composition is free of chlorinated organic solvents. Suitable organic solvents are, for example, benzyl alcohol, methylene chloride, dibasic ester, which is an oxygenated solvent composed of a mixture of methyldiesters of glutaric, succinic and adipic acids, or ethyl-3-ethoxypropionate. The solubility of these solvents in water are 3.3% benzyl alcohol, 5..32% methylene chloride, 5.6% dibasic ester and 2.9% ethyl ethoxypropionate. The dissolved activator compound present in the aqueous phase of the composition used in the invention can be any compound which increases the paint extracting activity. Such compounds can be selected for the specific paint which will be removed and / or the substrate from which the paint will be removed, in order to provide "optimum paint removal characteristics and / or minimize damage to the treated substrate. often be a pH modifying compound Such pH modifiers can be acids and considerable benefits have been observed with such acid activated systems The acid activators are usually organic acids, for example trichloroacetic, alkylbenzenesulfonic, benzoic or lactic acid. Preferably a pH modifying compound is a alkali Suitable alkalis are, for example, alkali metal hydroxides, alkali metal hydroxides, silicates, for example alkali metals and basic organic compounds such as amines or ammonium compounds. Another category of activating compound is an oxidizing agent. It has been found that such oxidizing agents improve the behavior of the aqueous phase. An example of an oxidizing agent is hydrogen peroxide. Another example is permanganate, usually potassium permanganate. The composition may contain, in addition to one of the activating compounds mentioned above, a secondary activator, such as an alcohol, for example C3-4 alcohol, preferably methanol. The paint-extracting composition may optionally contain surfactants, generally in low amounts such that the surfactant does not lead to the formation of an emulsion between the immiscible aqueous and organic phases. The inclusion of such surfactants can increase the wetting of the substrate surface. Suitable surfactants are, for example, alkylbenzenesulfonic acids, and fluorosurfactants. The surfactant is generally present in an amount of less than 2% by weight, more preferably less than 1% by weight, based on the weight of the total extracting composition. Where the activating compound is a modifier of pH, the pH is preferably above 9, more preferably above 10, or below 5, preferably below 4. The present invention is of particular value where the extraction method uses an immersion technique, in which the vehicle of the which the paint will be extracted is immersed in a bath containing the extracting composition. In such embodiments, the extractor composition is generally present as a two-phase system with upper and lower continuous layers. Preferably the lower layer is the organic solvent layer, i.e. the organic solvent preferably has a higher density than water. In this mode, the article is dipped from which the paint will be extracted in the upper aqueous phase only and not in the lower organic phase. After immersion for an adequate period of time, the article is removed from the bath. The bathroom is reused to extract the paint of additional items. Where the bath is reused, it is generally necessary to regenerate the bath to maintain an appropriate mixture of ingredient in the upper aqueous phase. It is found that both solvent and water are depleted from the bath while the activating compound and the solvent are also consumed. The regeneration of the bath is without difficulty in the invention which is convenient for the user. In this way since the lower organic phase provides a reserve of the solvent for dissolution in the upper aqueous phase, as soon as the volume of the lower phase comes to decrease, this can be regenerated by simply adding water. The aqueous phase maintains its level of saturation of the solvent since the solvent can pass from the organic phase to the aqueous phase between the interfacial layer. The level of the activating compound is maintained at the desired level by a continuous monitoring system and addition of the activating compound either in the pure form or in the form of a concentrated regenerated solution, usually in water. It is possible to use automated regeneration to control the total volume and concentration of the activating compound of the aqueous phase. The total level of water in the extracting composition as a whole is generally in the range of 50 to 99.5% by weight, preferably in the range of 60 to 98% by weight, more preferably in the range of 70 to 95%, especially 80 to 90% by weight. An alternative embodiment of the extraction method of the invention, for non-immersion purposes, uses an on-site application system, in which the extracting composition is generally brushed, sprayed or otherwise applied to the painted surface of a large substrate. . Since such surfaces will include non-horizontal surfaces, in order to ensure that adequate levels of the extracting composition are retained in contact with the painted substrate over sufficient periods of time, it is generally desirable to use a thick composition. The thick compositions may comprise a continuous aqueous phase and a dispersed organic phase. The organic solvent may cross the interface between the phases, thereby providing a reserve for the solvent in the aqueous phase as in the first embodiment of the invention. The dispersion may be storage stable by virtue of the provision of a thick continuous aqueous phase (as opposed to an organic phase emulsion dispersed in continuous aqueous phase).

Suitable thickeners for use in this embodiment of the invention should provide a thickener capacity for the aqueous phase in the presence of the organic solvent at saturation levels and in the presence of the activating compound. Although naturally derived thickeners such as cellulose and starch derivatives may be used, in the present invention it has been found that improved performance and stability can be achieved by using synthetic thickeners, for example associative thickeners based on acrylics as are available under the brand Rheox. or Rheovis. Alternatively, inorganic thickeners, such as clays, for example bentonite, especially surface treated with bentonite, can be used. In the extraction method of the present invention, the substrate must be rinsed, after it has been put in contact with the extracting composition for a suitable time to loosen the paint, to remove the extracting composition and the loosened paint. Where the submerged substrate in a bath of the extractant composition, the article is removed from the bath and rinsed, for example by immersion and / or by spraying with water or an aqueous rinse solution. It may be desirable to use a pressurized water spray or apply other mechanical assistance to remove the loosened paint from the substrate. Where the extractor composition is applied in place, it is rinsed by a spray of water or aqueous rinse solution, for example using a pressurized water spray. The method of the present invention can be carried out under ambient, room temperature conditions. Alternatively, the temperature of the extraction composition can be increased, for example, where the composition is applied by immersion. In this way * a bath of an extracting composition can be heated to a temperature at which the extraction rate is improved. In the present invention it has been found that temperatures in the range of 40 to 90 ° C can be used. It is generally found that improved results can be found when the temperature is increased above 50 ° C, or even above 60 ° C although it is generally not necessary to use temperatures above 80 ° C. Thick compositions are generally applied at room temperature. Where the composition is contacted with the substrate by immersion, it may be desirable that the body of the Extractor is mechanically stirred. Such agitation should generally be inadequate to provide some stability to the two phase mixture against separation. In this way such agitation can result in the temporary creation of a dispersed phase, this dispersed phase mixture will separate rapidly into two phases after the elimination of mechanical agitation. The present invention is illustrated in the following worked examples. EXAMPLE 1 The following ingredients are mixed together. Benzyl alcohol 20% in ~ weight. Water 79.21% by weight. Potassium silicate 0.79% by weight. The ingredients form a two-phase system with benzyl alcohol in the lower phase and with the potassium silicate in the aqueous phase, which also contains benzyl alcohol at the limit of solubility at room temperature. Non-dried (uncured) epoxy paint test substrates are used on an aluminum substrate. Appropriate removal is achieved at room temperature, when the substrates are submerged in the aqueous layer, after seven hours of contact. Where the bath is used continuously, it can be charged with water while the benzyl alcohol is still present in the lower phase. The level of alkali (potassium silicate) can be monitored by appropriate means and the levels regenerated as necessary. Two adaptations of the above formulation are made in one of which the hydrogen peroxide is incorporated in a volume of 40 in an amount of 10% by weight, and in the other of which 5.00% by weight of potassium permanganate (and a 5% additional weight of water) is added as activators. The resulting compositions give improved performance. Example 12 This example represents a composition which contains methylene chloride, but at lower concentrations than the methylene chloride-based extractors of the prior art. The following ingredients are mixed together in the amounts shown: Water 90% by weight. Alkylbenzenesulfonic acid 0.5% by weight. Methanol 2.0% by weight. Methylene chloride 6.0% by weight. Trichloroacetic acid - 1.5% by weight. The formulation provides a two phase composition. The composition allows acrylic paint to be extracted from steel substrates in six hours at room temperature (from the room).

E-i emplo 3 This example is from an application extractor in the thick place. The following ingredients are mixed together: Benzyl alcohol 35.0% by weight. Water 62.31% by weight. Wax 1.0% by weight. Reolato 101 1.0% by weight. Sodium silicate 0.69% by weight. This composition is applied by "brush to painted substrates." It has been found that the above composition "extracts-polyurethane paint from aluminum substrates in two to three hours, acrylic paint from aluminum substrates in about two hours and epoxy paint from substrates of aluminum in about two hours. The above extracting compositions are removed from each of the substrate after a specified period of time and rinsed using water spray. It is not found that the extractors damage the treated metal surface which can be subsequently painted.

Claims

CLAIMS 1. A method for extracting paint from a surface of a substrate wherein the surface is contacted with the aqueous phase of a two-phase liquid extracting composition comprising an aqueous phase which comprises water, soluble water-soluble activator compound and an organic solvent comprising benzyl alcohol, the organic solvent that is present in the aqueous phase at a concentration of approximately the saturation level (as in environmental conditions for the method) and which also comprises an organic phase comprising the organic solvent , in which the organic phase is in interfacial contact with the aqueous phase. 2. A method according to claim 1 characterized in that the temperature of the composition is greater than 20 ° C in which the organic solvent is present in the composition at a level above the saturation level at 20 ° C. 3. A method according to any preceding claim characterized in that the composition is free of the chlorinated solvent. . A method according to any preceding claim characterized in that the activator is a pH modifier. 5. A method according to any preceding claim characterized in that the pE ** is above 9. 6. A method according to claim 5 characterized in that the activator is selected from alkali metal hydroxides, alkaline earth metal hydroxides, silicates, for example alkali metals and basic organic compounds such as amines or ammonium compounds. according to any of claims 1 to 4 characterized in that the pH is below 5. 8. A method according to claim 7 characterized in that the activator is an organic acid selected from trichloroacetic acid, dobamic acid, benzoic acid and lactic acid 9. A method according to any one of claims 1 to 3 characterized in that the activator is an oxidizing agent, preferably hydrogen peroxide or potassium permanganate 10. A method according to any preceding claim characterized in that the Substrate is submerged in a bath containing the composition, the bath that has two liquid layers, the upper layer consisting of the specified composition and the lower layer "comprising the organic solvent. 11. A method according to claim 10, characterized in that the bath is regenerated after use by addition of water and activator.

1 . A method according to claim 11, characterized in that the composition in the bath is at a temperature in the range of 40-80 ° C. 13. A method according to any of claims 1 to 9, characterized in that the composition contains a thickener and is applied as a coating to a substrate. 14. A method according to any preceding claim characterized in that the treated substrate is rinsed with water to remove the smoothed paint.