FR2478661A1 - Vapour phase stripper for removing organic surface coatings - operates at ambient temp. cheaply, efficiently, safely and is ecologically acceptable - Google Patents

Abstract

Organic coating is removed from surface of a coated article by contacting the surface with a stripping compsn. (I) in gas state, thus destroying the adhesion of coating to the surface, and doing so without the temp. of the surface or the stripper substantially going above ambient temp. Stripper can be used esp. for removing organic resin based compsns. such as paint lacquer, varnish etc. as well as oils and asphalts from articles having large, uneven surfaces such as the interior walls of storage silos and reservoirs ballast tanks, and ships holds, and tanks petrol or oil tanks. Process is cheaper, more efficient, safer, less harmful to the environment and uses less energy than current processes and any additives such as waxes to prevent evapn. do not remain on the cleaned surface to interfere with subsequent fresh coatings. (I) can be recovered for further use.

Description

 The present invention relates to a method. to strip coated objects, organic coatings.

More particularly, it relates to a process for removing or stripping a coating obtained from compositiors based on organic resins and / or prepared with organic vehicles, such as paint, shellac, varnish, lacquer and analogues, as well as various oils and asphalts. The method according to the invention is particularly useful for removing such coatings from objects having irregular surfaces and large areas, including vertical and inclined surfaces inside large constructions, such as silos and storage tanks on land and ballast tanks and holds on ships.

Commonly, the paint is stripped of painted objects on a small scale by application of an organic or inorganic solvent or a mixture, as described in
ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY, Vol. 14, pages 485493, 2nd Edition, John Wiley and Sons, 1967, by Kirk
Othmer.

 Of the chlorinated hydrocarbon solvents employed in many formulas, methylene chloride (dichloromethane) has been found to be particularly effective. Liquid pickling compositions usually contain additives including thickeners, evaporation retarders and detergents.

 The organic solvent formulas for stripping paint and other revolutions can be of the type to be removed by scraping or jet. In general, the pickling composition is applied to the coated or coated object by one of the above methods and allowed to stand for a period of time, and then the swollen and / or softened coating is removed from the surface by scraping in. the case of formulas to scratch or rinse with water and / or wiping with a damp cloth in the case of formulas to rinse.

 The foregoing methods are relatively expensive since the organic solvent, except in the case of immersion application, is not recovered. Moreover, all the known processes are generally dangerous and much too expensive when it comes to supermarkets. In addition, the waxes used as an evaporation retarding agent in such formulations are difficult to remove completely and any residual wax interferes with the adhesion of subsequent coatings on the surfaces.

Processes have also been described in US Pat. Nos. 2,689,198 to Judd No. 3,794,524 to Nogueira et al. And No. 3,832,235 to
Cooper et al., Where the paint is stripped from a relatively small object by contact with the vapors of a composition of a boullant solvent. In these processes, the hot vapors condense in liquids on the painted surface.

 A method of cleaning the tanks has been disclosed in U.S. Patent No. 3,042,553 to Kearney et al., In which a solvent is heated to its boiling point to produce solvent vapors fed to a reservoir where they occur. condense and wash the walls of the tank.

 These methods are not applicable for removing large area organic coatings because the cost of heating a sufficient quantity of the solvent under reflux for a long period of time is prohibitive and, moreover, expensive, high-level waterproofing equipment is required. to perform such a large-scale operation. Moreover, in some constructions, such as large tanks and metal vessels, even a moderate temperature difference from one part of building to another can be harmful.

 It is common practice in the industry to remove paint and most other protective coatings from large tanks and other large constructions by slow, unpleasant, rough and dangerous abrasive jet processes. It is important that a ballast tank of a boat, which usually contains water, is anti-rust. For this purpose, the ballast tanks are coated with a layer of paint. If the paint coating is flaking or defective in some way, it is necessary to remove the paint from the inside of the ballast tank and repaint it, to avoid the possibility of rust and possible holes.

This is particularly important for ships carrying liquefied natural gas. A ballast tank of a ship can have a capacity of up to 3.785.000 liters or more, and it often has a complex configuration in "honeycomb", making difficult and laborious the work of a sandblaster. The removal and disposal of a large amount of abrasive particles or sand that is necessary is difficult.

 At present, even though sanding or abrasive blasting has significant disadvantages, it is practically the only process used to remove paint from large areas; water-blasting and even pounding are sometimes used.

 There is a great demand for more efficient and less laborious processes of cleaning stationary storage tanks as well as tankers of barges and bunkers, tar, pitch, asphalt, oil and vegetable oil residues prior to type change. cargai sound, structural repairs or inspection by government agencies. Some of these tanks and holds may have a capacity exceeding 75,700,000 liters.

 Currently, they are mainly cleaned by high-pressure, hand-held water or water-based solutions or emulsions, often scraping with trowels and other hand tools. It is also possible to use caustic soda solutions.

The prices are very high and the cleanliness obtained is often marginal or unacceptable. Residues are usually lost and disposal is a problem.

 The main subject of the present invention is a process for stripping an organic coating of an object coated or coated by an economical process avoiding the problems associated with a known process, stripping.

 An important object of the present invention is a process for stripping organic coatings on large surfaces, for example the interior of large constructions such as storage tanks, ballast tanks and ship holds and all-complex surfaces of complex shapes. or inclined, by a more economical, str str and less environmentally damaging process and using less energy than current processes, while avoiding additives interfering with a subsequent coating of the surface.

 Another object of the present invention is a method for removing organic coatings and residues remaining after draining a tank from a petroleum product or a vegetable oil.

 Other objects and advantages of the invention will become more obvious upon reading the description which follows.

 In view of the foregoing and still other objects of the invention, stripping of an organic coating of a coated or coated surface is provided by contacting the surface with a rphase stripping composition. Since the gaseous mixture can destroy the adhesion between the coating and the surface, in this process neither the etching composition nor the surface to be etched is substantially above room temperature. In a preferred embodiment of the invention, the gaseous pickling composition is contacted with the surface to be etched approximately at room temperature, substantially: the absence of a liquid pickling composition condensate at In another preferred embodiment of the invention, either the gaseous stripping composition or the surface to be etched is below ambient temperature.

It has been discovered that organic coatings may be substantially detached, and in many cases, completely etched from surfaces merely by the action of the vapors of a pickling composition. The term organic coating refers to any coating based on an organic resin or an organic carrier, such as a paint, shellac, varnish, lacquer and the like, which may be applied to a metal or wood surface. The method may be used to remove organic protective coatings applied to a surface for its protection and / or improvement. In addition, the process can be used to remove residual coatings that are not usually called protectors, and which are incorporated in the sense of coatings according to the invention. Residual revolutions include crude oils, heavy fuels
Bunker C (N $, crude oil with a high paraffin content, asphalt such as blown asphalt or bitumen and vacuum tar residues, among other residues of high vacuum distillation of certain crude oils, tars, vegetable oils and the like withdrawn from the surfaces of the holds or tanks for a change of cargo or when it is necessary to clean them for repairs, inspection by the coast guards and the like.

 In accordance with the present invention, a surface which is to be further etched is contacted with the vapors of a stripping composition until adhesion between the coating and the surface is destroyed or until the coating forms a coating. solution that flows to the ground.

 In one embodiment of the process according to the invention, the gaseous stripping composition is introduced in contact with the coated surface at a concentration, a pressure and a temperature such that there is substantially no condensation of the gaseous composition. on the coated surface, and thus the process takes place substantially in the absence of liquid condensate. Adsorption and / or vapor absorption occurs in the coating during the process. Vapors can usually be recovered at a very good efficiency. There is no lower theoretical temperature limit in the process, as long as the pickling chemicals have a low vapor pressure. Preferably, the process is carried out at about room temperature for economic reasons.

 Depending on the particular conditions, the time required to remove or destroy the adhesion of the coating is between a few minutes and a few days. It has been found that organic coatings generally decapitate much more rapidly by contact with a gaseous stripping composition at room temperature than would be expected by reference to the time required at higher temperatures, considering the higher concentration of gaseous stripping composition and the faster rate expected of any chemical reaction at higher temperatures.

 What is even more surprising is the discovery that petroleum products such as asphalt and oil and some paints were more quickly scoured if the gaseous stripping compound or the surface to be stripped was at a lower temperature than a higher temperature. For example, asphalt scrapers faster at 220C than at 320C or 360C at constant concentrations of the vapors of a pickling composition, and oil # 6 is more easily removed when the substrate or vapor is cooled.

 The method according to the invention has a particular advantage which is the utility of heating the etching composition at reflux and in many cases it is not at all useful or desirable to heat the gaseous stripping composition, since this process is preferably is performed substantially at or below the environment temperature.

 When the process according to the invention is carried out at about room temperature, it is generally preferable that it be at least about 0 ° C, otherwise this process may be slow for some coatings; but even at a room temperature lower than OOC, the process according to the invention is usually preferable to all other processes currently available.

 In some cases, it is preferable to contact the coating with the gaseous stripping composition while neither the etching composition nor the coated surface is above the amine temperature and one of the two is cooled down. below the ambient temperature.

 When a painted surface which has been treated according to the steam stripping process of the present invention is released from the gaseous stripping composition, by air drying or other practical means, it is found that in many cases the coating paint is either totally dropped or can easily be removed by brushing it, leaving only small spots of paint.

In most cases, the surface that has been contacted by the gaseous stripping composition is free from 75 to 100% of visible paint residues.

However, even if a troublesome amount of coating remains, the surface can be cleaned with an abrasive jet in order to be 100% clean, in a substantially shorter time than that required to obtain a 100% clean surface. by an abrasive jet or abrasive sandblasting alone.

 When cleaning surfaces of oily or gassy substances, a removal of 95 to 100% is normally obtained.

 During the process according to the invention, think that the vapor is adsorbed and / or absorbed on the coating, forcing the coating to undergo physical and sometimes chemical changes and to break free from the substrate. Many epoxy, alkyd, polyurethane and polyester coatings form dry flakes that can easily and economically be removed or even sold, which is still an unexpected benefit of treating with a stripping composition substantially within the absence of liquid condensate according to the present invention. When a surface is treated with a liquid or a condensate of vapors of a composition at reflux, the liquid pickling composition can extract the soluble components of the coating; with many returns it results in a sticky mass, whose cleaning is difficult and significantly less economical than the removal of dry flakes.

 With oils, asphalts, and certain paints, the resulting solution is distilled to recover the pickling composition and the coating material.

 In another preferred embodiment of the invention, the surface to be treated is substantially sealed with respect to the atmosphere to form a stripping zone.

A stream of the gaseous pickling composition near ambient temperature or, in some cases below, is introduced into the pickling zone in contact with the coated surface. If the pickling composition is liquid at ambient temperature, the gaseous stream may advantageously produce another product by blowing air on the surface of the liquid in an evaporator with a conduit to the pickling zone. The stripping zone is preferably provided with a return duct to the gas blower depression, which allows the recirculating air and gaseous stripping composition to be circulated. Gaseous stripping composition increases in the stripping zone, air can purge the stripping zone; normally, the density of the gaseous pickling composition is higher than that of the air, the air can usually be purged near the top of the pickling zone. This achieves high concentrations of the gaseous stripping composition and can be used to pocket a significant increase in pressure.

 The evaporators must be heated to replace the heat of vaporization of the liquid pickling composition in order to pocket this composition to cool excessively. But it is generally preferable for the gaseous pickling composition to be at ambient temperature or below-in the conduit and stripping zone.

In the case where the coating decays more rapidly at low temperatures, the evaporation heat may not have completely replaced; the vapors will be colder and there will be energy saving.

 It is also possible to evaporate the liquid pickling composition within the stripping zone of the paint, in which case a special evaporation zone can be removed.

 Means for the circulation of the gaseous pickling composition are desirable, such as a gas pump or a blower or blower. The efficiency of the process according to the invention is increased and the time required to destroy the adhesion of the coating and the surface is decreased if the gaseous pickling composition is fully circulated throughout the pickling zone.

 In the pickling zone, the coating absorbs and / or adsorbs the gaseous pickling composition and thus undergoes physical and / or chemical changes, and is released from the substrate. The gaseous stripping composition is then pumped from the stripping zone and is desorbed from the coating.

Air is blown into the paint stripping zone by a vacuum relief valve, during the removal of the gaseous stripping composition to avoid the creation of a potentially dangerous depression and to make the tanks safer for get in there.

 The gaseous pickling composition can be continuously introduced into the pickling zone and it is also preferable, with compositons with high vapor pressure, to continuously remove air from the top of the pickling zone, which can be accomplished by a expansion valve set at approximately 0.07 - 0.14 kg / cm2, until air has been substantially removed and the highly concentrated vapors of the denser stripping compounds are stale. Stale chemical vapors can other easily recovered by condensation and / or adsorption on charcoal for reuse, avoiding air pollution.

The gaseous stripping composition may also be continuously removed from the stripping zone and recovered and maintained in the gaseous state and recycled to the paint stripping zone or, in the case where two or more zones are etched, the gaseous composition of Pickling removed from one area may be put into circulation to another pickling area. In large-scale operations, fans are used to distribute the vapors over the entire structure in a reasonable time.

 No single gaseous compound or admixture ideally suited for organic revolutions has yet been found. Normally, a few simple experiments will allow a person of ordinary skill to determine an effective compound or mixture. Organic and inorganic compounds known to be useful for stripping paint, shellac, varnish and the like, which have a partial pressure of at least about 2 mm Hg at room temperature, may be used in the process according to the invention. . In practice it is preferred to use mixtures containing a relatively high percentage of lower chlorocarbons, in particular chlorocarbons containing 1 to 3 carbon atoms and 1 to 4 chlorine atoms. Methylene chloride is a particularly effective scouring agent, as well as safety and economy. However, other chloroalkanes such as 1,2-dichloroalkane and chloroform are also advantageous. Not only these mixtures are usually effective and economical, but also allow to reduce damage from fire and explosion. Stripping compositions containing methylene chloride in an amount of the order of 25 to 100% by volume, and better Compositions containing methylene chloride as a main ingredient and even better, especially for economy and safety, compositions containing about 70, 100 or 85 to 100 methylene chloride are used.

 The compounds which have been found to increase the effectiveness of methylene chloride and other lower chloroalkanes with various coatings are the following: aliphatic hydrocarbons containing up to about 8 carbon atoms, water, lower carboxylic acids such as formic acid, ammonia, lower alkylamines, lower alkanols, and lower alkyl ethers, esters, ketones, nitriles, amines, arenes such as benzene and benzene substituted with halogen and lower alkyl, and inorganic acids volatile. The term "lower" indicates a compound having 1 to 4 carbon atoms. In general, vapor phase compositions which contain about 70 to 95% methylene chloride, about 1% water, and about 4 to 29% methylene chloride. other compounds such as those just mentioned are very effective. Alkyl amines and lower dialkyl amines were also found to be potent activators of the gas phase methylene chloride compositions containing about 70 to 90% by volume of methylene chloride and 10 to 30% of 33 to 75% aqueous ethylamine. are particularly useful. In general, small molecules with dipole moments and of acidic or basic character seem to be generally useful, alone or with methylene chloride for paint stripping.

 In the case where one chooses a gaseous pickling composition which contains two or more components which do not form a homogeneous solution in the liquid phase, it is preferable to have separate evaporators for each of these compounds.

 The particular amount of pickling composition used varies greatly, depending on the nature and thickness of the coating, the ambient temperature and the particular pickling composition chosen, as well as the volume of the pickling zone and the surface area of the coated surface. treat. In general terms, the ratio of the weight of the pickling composition used to that of the removed coating may be in the range of about 0.5 to about 4: 1.

 Provided that the area to be etched can be substantially sealed with respect to the atmosphere, there is no practical upper limit to the size or complexity of the coated structures that can be treated with gaseous pickling compositions according to the invention. 'invention. The fact that the process according to the invention does not endanger or damage the structure by a change in pressure or temperature, is an important advantage of the method according to the invention. Moreover, no corrosion problem has been observed, with respect to the metal surfaces using the preferred pickling compositions disclosed above.

 The process according to the invention is very economical because the price of the chemicals is currently low and moreover, most of these chemicals can be recovered for reuse. The necessary equipment is marketed at a reasonable price and the necessary human force is weak.

 Another important advantage of the stripping process according to the invention is that the personnel do not have to be exposed to chemical stripping agents or remodels, some of which, like certain petroleum products, are dangerous; chemicals can be transferred from shipping containers to the pickling system with little or no exposure to the atmosphere, so operators do not have to enter the pickling zone until the vapors have been replaced by air.

 The following examples will better illustrate the present invention, but should in no way limit the scope.

In the examples which follow, as well as in the general description, all the proportions of the etching components are by volume unless otherwise indicated the relative proportions of the solvents to the paint coating are by weight
Example 1

 Offset painting.

A 16 cm2 area of a steel plate which had been subjected to an abrasive jet and spray painted with two coats (0.3 mm) of paint n01 (see Table 1) was subjected to sand or sandstone blasting. 'to a condition of a nearly white metal by means of a pistol "5andblasting
Gun "Speedaire (4.8 mm internal diameter of the tubing) using abrasive particles or sandstone" Stanblast "(oven residues) and a pressure of 5.6 kg / cm 2. The required time was 85 seconds.

 Another portion of the painted surface is placed on a plastic beaker containing methylene chloride (9 ml) and 90% formic acid (1 ml), i.e. a solvent ratio of MC: FA: H 2 O of 9: 0.9: 0.1 after 14 hours of exposure to 230C vapors, most of the exposed epoxy coating had delaminated and dropped into the beaker. The plate was left standing in air at 230 ° C. for 4 hours.

A 16 cm 2 area of the treated surface was then blasted to a white metal using the equipment and conditions above. This took only a few sweeps not exceeding 5 seconds, only 6% of the time required for the untreated coating.

 Examples 2 to 15

 Stripping of various paints.

 Test panels coated with various painted paints exposed to a gaseous stripping composition by placing a test panel coated at the top of a container with a liquid pickling composition or inside a closed container such as a closed tank, a desiccator or a thin layer chromatography (TLC) chamber containing a mass of liquid pickling composition with the exception of example No. 15. In all cases, the test panel was not not in contact with the liquid pickling composition, and the removal of the coating was only due to the action of the pickling composition in the gaseous state.

 In Example 15, a coated steel panel was placed inside a 4 liter receptacle provided with steam supply and withdrawal lines, and sealed with respect to the atmosphere; a stripping composition in the gaseous state was continuously circulating therein.

 All test panels were metal except for examples 8 and 9, where wooden test panels were used. Also, all examples were run at the specified ambient temperature except for Examples 7a and 7b where a TLC chamber containing a mass of the pickling composition was placed in a crushed ice bed and the chamber cooled to 0 ° C; Blotting papers were used to accelerate the balance between the vapor and liquid phases in the chamber.

 The stripping conditions and results of Examples 2 to 15 are shown in Table 2. The paint reference number in Table 2 is the paint number of Table 1, or the stripped paint in all examples is identified. When measured, the paint thickness is shown in parentheses below the paint reference number in Table 2.

The abbreviations that follow were used for the components of the pickling compositions in all the examples:
MC methylene chloride PCE perchlorethylene
FA formic acid DMF dimethylformamide MEK methyl ethyl ketone CLF chloroform
EA ethylamine HEX hexane
Table 1.

PAINT COATINGS WITHDRAWN BY THE GASEOUS COMPOSITIONS
DETACHING.

<Tb>

<SEP> Reference of <SEP><SEPName> and / or <SEP><SEP> Type of <SEP> Paint <SEP> Manufacturer
<tb> the <SEP> painting
<tb><SEP> n0
<tb><SEP> 1 <SEP> Epoxy <SEP> Carboline <SEP> Co.
<Tb>

<SEP> 2 <SEP> Arylamine <SEP> Epoxy <SEP> 1204 <SEP> Southern <SEP> Imperial
<tb><SEP> Coatings, <SEP> INC.
<Tb>

<SEP> 3 <SEP> Polyurethane <SEP> 4311 <SEP> Southern <SEP> Imperial
<tb><SEP> Coatings, <SEP> INC.
<Tb>

<SEP> 4 <SEP> Alkyde <SEP> Unknown
<tb><SEP> 5 <SEP> Epoxy <SEP> Amine <SEP> Aromatic <SEP> Carboline <SEP> Co.
<Tb>

<SEP> 6 <SEP> Polyamide <SEP> Epoxy <SEP> 1201 <SEP> Southerm <SEP> Imperial
<tb><SEP> Coatings, <SEP> INC.
<Tb>

<SEP> 7 <SEP> Phenicon <SEP> 980-Epoxy <SEP> Cook <SEP> Paint <SEP>& BR <
<tb><SEP> Varnish
<tb><SEP> 8 <SEP><SEP> Flow-Loc Varnish <SEP> Sherwin-Williams <SEP>
<tb><SEP> 9 <SEP> Rustoleum-Linseed- <SEP> Rust-Oleum <SEP> Corp.
<Tb>

<SEP> Menhaden, <SEP> Resin
<tb><SEP> Alkyde
<tb><SEP> 10 <SEP> Internal <SEP> Layer
<tb><SEP> tank <SEP> epoxy <SEP> 343 <SEP> Pan-American
<tb><SEP> Coatings
<tb><SEP> 11 <SEP> Polyamide <SEP> Epoxy <SEP> 313 <SEP> Pan-American
<tb><SEP> Coatings
<tb><SEP> 12 <SEP> Permachlor <SEP> 890, <SE> Southern <SEP> Imperial
<tb><SEP> base <SEP> Rubber <SEP> Chlorinated <SEP> Coatings, <SEP> INC.
<Tb>

 Table 2.

PAINT COATING PAINT REMOVAL

Paint <SEP> Composition <SEP> of <SEP> Temperature <SEP> Time <SEP> Quantity <SEP> Remarks
<tb> reference <SEP> stripping <SEP> (report) <SEP> C <SEP> expo- <SEP> from <SEP> defecation
Ex.
<Tb>

n <SEP> (thick- <SEP> sition <SEP>
<tb> n <SEP> seur, <SEP> mm) <SEP> h
<tb> 2 <SEP> 2 <SEP> MC: H2O <SEP> 23 <SEP> 47 <SEP> sensitive <SEP> 72% <SEP> of <SEP> reduction <SEP> of
<tb> time <SEP> of <SEP> jet <SEP> for <SEP> on (99: <SEP> 1) <SEP> face <SEP> own <SEP> at <SEP> 100%
<tb> 3 <SEP> 2 <SEP> MC: FA: H2O <SEP> 22 <SEP> 1 <SEP> almost <SEP> Coating <SEP> falls <SEP> from
<tb> complete <SEP> panel <SEP> in <SEP> fragments
<tb> (0.20- <SEP> (100: 5: 4) <SEP> 48 <SEP> 100% <SEP> solids
<tb> 0.23)
<tb> 4 <SEP> 3 <SEP> MC: MEK: H2O <SEP> 22 <SEP> 48 <SEP> 100% <SEP> Coating <SEP> falls <SEP> into
<tb> (94: 5: 1) <SEP> a <SEP> piece
<tb> 5 <SEP> 4 <SEP> MC: EA: H2O <SEP> 22 <SEP> 8.5 <SEP> 90%
<tb> (0.15) <SEP> (90: 3: 7) <SEP> 48 <SEP> 100%
<tb> 6 <SEP> 2 <SEP> MC: FA :: H2O <SEP> 17 <SEP> 16 <SEP> sensitive- <SEP> Coating <SEP> falls,
<tb> ment <SEP> any <SEP> leaving <SEP> a few
<tb> (0.25) <SEP> (95: 4.5: 0.5) <SEP> fragments <SEP> of primer
<tb> 7a <SEP> 7 <SEP> MC: FA: H2O <SEP> 0 <SEP> 6 <SEP># 80% <SEP> Large <SEP> blisters
<tb> torn
<tb> (0.13) <SEP> (90: 8.5: 1.5)
<tb> More <SEP> big <SEP> part <SEP> of
<tb> 7b <SEP> 7 <SEP> MC: FA: H2O <SEP> 0 <SEP> 22 <SEP> almost <SEP> the <SEP> painting <SEP> fell,
<tb> 100% <SEP> a few <SEP><SEP> stains removed
<tb> (0.13) <SEP> (90: 8.5: 1.5) <SEP> to <SEP> the <SEP> brush
<tb> Table 2 (continued)

Painting <SEP> Time
<tb> Quantity
<tb> Ex. <SEP> reference <SEP> Composition <SEP> of <SEP> Temperature <SEP> of expode <SEP> def <SEP> stripping <SEP> (report) <SEP> C <SEP> sition <SEP> Remarks
<tb> n <SEP> (Thickness
<tb> seur, <SEP> mm) <SEP> h
<tb> 7c <SEP> 7 <SEP> MC: FA: H2O <SEP> 22 <SEP> 3 <SEP> 99%
<tb> (90: 8.5: 1.5)
<tb> 8 <SEP> 8 <SEP> MC: EA: H2O <SEP> 22 <SEP> 48 <SEP> 100% <SEP><SEP> Casting <SEP> Coating of
<tb> wood, <SEP> leaving <SEP>
<tb> (86 <SEP>: 9.8 <SEP>: <SEP> 4.2) <SEP> marks <SEP> brown <SEP> -wood
<tb> no <SEP> damaged
<tb> 9 <SEP> 9 <SEP> MC: EA: H2O <SEP> 22 <SEP> 48 <SEP> 100% <SEP> Blistered <SEP> coating
<tb> and <SEP> poured <SEP> from <SEP> wood, <SEP> the
<tb> (86: 9,8: 4,2) <SEP> leaving <SEP> clean <SEP> and <SEP> no
<tb> damaged <SEP> but <SEP> slightly <SEP> tinted
<tb> 10 <SEP> 10 <SEP> PCE: DMF <SEP> 22 <SEP> 24 <SEP> 99-100%
<tb> (0.23-0.25) <SEP> (93: 7)
<tb> 11 <SEP> 10 <SEP> MC: FA: H2O <SEP> 22 <SEP> 1/2 <SEP> 99-100%
<tb> (0.25) <SEP> (90: 9: 1)
<tb> 12 <SEP> 11 <SEP> MC: FA: H2O <SEP> 22 <SEP> 1.75 <SEP> 99-100%
<tb> (90: 9: 1)
<tb> 13 <SEP> 12 <SEP> MC <SEP> 22 <SEP> 1 <SEP> 95%
<tb> Table 2 (Continued)

Painting <SEP> Time
<tb> Quantity <SEP> of
<tb> Composition <SEP> of <SEP> Temperature <SEP> of expo
Ex. <SEP> Reference <SEP> File <SEP> Remarks
<tb> stripping <SEP> (report) <SEP> C <SEP> sition
<tb> n <SEP> n <SEP> (thick- <SEP> tage
<tb> seur, <SEP> mm) <SEP> h
<tb> 14 <SEP> 6 <SEP> MC: EA: H2O <SEP> 22 <SEP> 30 <SEP> sensitive <SEP> Swollen <SEP> Coating,
<tb> (65:25:10) <SEP> during <SEP> of the <SEP> panel <SEP> 86% <SEP> of <SEP><SEP> reduction of
<tb> time <SEP> of <SEP> jet <SEP> for
<tb> get <SEP> clean <SEP> surface
<tb> to <SEP> 100%
<tb> 15 <SEP> 5 <SEP> MC: FA: H2O <SEP> 20.5 <SEP> 6 <SEP> 100%
<tb> (93: 4: 3)
<Tb>
Example 16

 Stripping paint from the inside of a tank.

A 1.85 x 1.85 x 1.85 m steel tank was sandblasted, and the interior was spray painted with # 07 paint to a dry film thickness of 0 , 23 mm. Several months later, the paint was stripped as follows
At the outer side of a GM 3-53 gas pump, two steel evaporators, vessels A and B, were connected in series, using a 2.5 cm steel tube and a flexible plastic hose. chemical products. The evaporators were cylindrical steel vessels equipped with sighting glasses and provided at the top with 2.5 cm inlet and outlet tubes and were placed in hot water baths. The outlet pipe was connected to the bottom of the test tank. At the top of the tank, piping led to the opposite fan inlet. At the outlet of the tank, T-fittings led to a vent pipe. Pickling reagents MC (16 1) and MA (31) were introduced into the containers A and B, respectively; the blower turned on, forcing about 280 l / min of air from the tank onto the surfaces of the pickling reagents, which were sufficiently heated to maintain the vapor stream at about room temperature, ranging from 1 to 210 ° C during the test . The pump ran for 8 hours and at that moment the tank walls were almost bare and the paint flakes were falling from the ceiling. The tank was closed in relation to the atmosphere and left to rest for one night, then only a few fragments of paint were visible on the walls and ceiling.

 The vent was opened, the containers A and B were cooled with a jet of water and ice and the direction of rotation of the gas pump was reversed. This replaced the stripping vapors with air and allowed the recovery of most of the reagents used. The tank hatches were opened and the dried flakes of paint (11.5 kg) were quickly removed with a vacuum cleaner.

An accurate inspection of the internal surfaces showed some small spots of paint remaining in the pattern, and in solder holes at the corners. Over 99% of the paint had been removed, and it was determined that the surface was clean enough for repainting without an abrasive jet.

 Examples 17 to 24 and Comparative Examples 17C to 21C

Asphalt and oil coating stripping at various
substrate temperatures.

 Tested weighed 12.5 cm x 0.9 cm were coated with a substrate and suspended in the vapor phase above the specified liquid pickling composition at room temperature in a chamber covered with metal foils.

 To illustrate the practice of the invention, one of the tabs was allowed to remain at room temperature 220 ° C, or held at about 210 ° C. by cooling with tap water.

 For comparison, a second test-tube coated and suspended in a manner analogous to the first, was heated by passing a stream of hot water through it.

 The amount of substrate removed from the outer surface of each test piece was measured after exposure to the vapor phase in the glass chamber either by drying and weighing the tubes after a given time or by weighing the dropped coating of the tube after evaporation of the samples. absorbed and / or adsorbed gases.

 Blots immersed in the liquid helped to keep the vapor phase close to saturation, however the concentration of the vapor in all these examples and comparison examples is much lower than the maximum possible amount, about 50% in the case of methylene chloride .

 The coating, its amount, the gaseous pickling composition and the percent removal of the coating at different temperatures are shown in Table 3, where the letters RG and AB respectively indicate sealing asphalt and blown asphalt.

 Table 3.

STRIPPING OF ASPHALT AND OIL COATINGS.

Ex. <SEP> Coating <SEP> Agent <SEP> Gaseous <SEP> Time <SEP> of <SEP> Quantity <SEP> d <SEP>
<tb> of <SEP> stripping
<tb> n <SEP> Tempe <SEP> treatment <SEP> coating
<tb><SEP> Composi
Tempe <SEP> removed <SEP>%
<tb> tion <SEP> rature <SEP> Compo (quantity <SEP> C
<tb> g)
<tb> 17 <SEP> Asphalt <SEP> 21 <SEP> MC <SEP> Amb. <SEP> 45mn <SEP> 63.5
<tb><SEP> RG <SEP> (3,5)
<tb> 17c <SEP> Asphalt <SEP> 36 <SEP> MC <SEP> Amb. <SEP> 45mn <SEP> 3,5
<tb><SEP> RG <SEP> (3,5)
<tb> 18 <SEP> Asphalt <SEP> 22 <SEP> HEX <SEP> Amb. <SEP> 18mn <SEP> 11.3
<tb><SEP> AS <SEP> (4,5)
<tb> 18c <SEP> Asphalt <SEP> 32 <SEP> HEX <SEP> Amb. <SEP> 18mn <SEP> 0.5
<tb><SEP> AB <SEP> (4,5)
<tb> 19 <SEP> Asphalt <SEP> 22 <SEP> HEX <SEP> Amb. <SEP> 53mn <SEP> 77
<tb><SEP> AB <SEP> (4,5)
<tb> 19c <SEP> Asphalt <SEP> 32 <SEP> HEX <SEP> Amb. <SEP> 53mn <SEP> 35.5
<tb><SEP> AB <SEP> (4,5)
<tb> 20 <SEP> Asphalt <SEP> 22 <SEP> HEX- <SEP> Amb. <SEP> 4 <SEP> h <SEP> 99.7
<tb><SEP> AB <SEP> (4,5)
<tb> 20c <SEP> Asphalt <SEP> 32 <SEP> HEX <SEP> Amb. <SEP> 4 <SEP> h <SEP> 96
<tb><SEP> AB <SEP> (4,5)
<tb> 21 <SEP> Oil <SEP> n06 <SEP> 22 <SEP> CHF <SEP> Amb. <SEP> 5mn <SEP> 87.5
<tb> 21c <SEP> Oil <SEP> n06 <SEP> 33 <SEP> CHF <SEP> Amb. <SEP> 5mn <SEP> 70.2
<tb> 22 <SEP> Oil <SEP> of <SEP> 22 <SEP> MC <SEP> Amb. <SEP> 60 <SEP> 99-100
<tb><SEP> flax <SEP> dried
<tb> 23 <SEP> Oil <SEP> of <SEP> 22 <SEP> MC <SEP> Amb. <SEP> 60 <SEP> 99-100
<tb><SEP> cotton
<tb><SEP> dried
<tb> 24 <SEP> Oil <SEP> 22 <SEP> MC <SEP> Amb. <SEP> 60 <SEP> 99-100
<tb><SEP> fratche
<tb><SEP> of <SEP> soybean
<Tb>
Examples 25 and 26.

Stripping oil at various temperatures from the
gaseous stripping composition.

 The temperature of the coating was kept constant in these examples by running water through the coated tubes and the temperature of the pickling vapor was changed while its concentration in the air was constant. Coated test pieces were suspended in a small, non-bermetically clogged reservoir by means of aluminum foil. Tap water was poured into the tubes of these examples. A stream of air containing 30% MC was produced by bubbling 13 l / min of air into liquid MC held at a constant level and temperature, and passed through a copper coil heater at 780C, then in the center of the tank.

In Example 26, the tank was cooled in a water bath at 120C while in Example 25 it was totally exposed to the atmosphere.

 When one of the coatings on the tube was so thin that a red cross on a white background could be seen through it, stripping was interrupted and the amount of coating remaining on the nearly transparent test piece was determined. The results are shown in Table 4.

Table 4

<tb> Ex. <SEP> Coating <SEP> Agent <SEP> Gaseous <SEP> of
<tb> Composition <SEP> Tempe <SEP> stripping
<tb> n
<tb> (quantity, g) <SEP> eradication
<tb><SEP> Compo- <SEP> Tempera- <SEP> Time <SEP> of <SEP> Quantity
<tb> C.
<Tb>

<SEP> sition <SEP> ture <SEP> C. <SEP><SEP>SEP> processing
<SEP> mistreated,
<tb><SEP>%
<tb><SEP> 25 <SEP> Oil <SEP> n <SEP> 6 <SEP> 23.6 <SEP> MC <SEP> 78 <SEP> 52 <SEP> mn <SEP> 73
<tb><SEP> 26 <SEP> Oil <SEP> n <SEP> 6 <SEP> 26 <SEP> MC <SEP> 16 <SEP> 35 <SEP> mn <SEP> 73
<tb><SEP> (0.285)
<Tb>
Examples 27 to 30.

Stripping with a gaseous stripping comPosition
room temperature and below.

 Substrate-coated tubes were exposed to the vapors of a pickling composition in a chamber, a tube was left at room temperature (A) and a drum cooled to a specified temperature. The conditions and results of each example are shown in Table 5.

 Table 5.

STRIPPING AT AMBIENT TEMPERATURE AND BELOW.

<Tb>

Coating <SEP> Composition <SEP> Temperature <SEP> Duration
<tb> Ex. <SEP>%
<tb> (quantity, g) <SEP> gaseous <SEP> of <SEP> C <SEP> of expon <SEP> Removal
<tb><SEP> stripping <SEP> sition
<tb> 27 <SEP> Asphalt <SEP> RG <SEP> MC <SEP> (A) 22 <SEP> 4 <SEP> h <SEP> 99.7
<tb><SEP> (4,5)
<tb> 28 <SEP> Asphalt <SEP> RG <SEP> MC <SEP> 8 <SEP> 10 <SEP> mn <SEP> 100
<tb> 29 <SEP> Paint <SEP> MC: FA: H2O <SEP> (A) 21 <SEP> 70 <SEP> mn <SEP> 99
<tb><SEP> n <SEP> 10 <SEP> 90: 9: 1
<tb> (1,8)
<tb> 30 <SEP> Paint <SEP> MC: FA: H2O <SEP> 0-2 <SEP> 16 <SEP> mn <SEP> 99
<tb><SEP> n <SEP> 10 <SEP> 90: 9:: 1
<tb> (1,8)
<Tb>
Thus, in one embodiment of the present process, it is particularly advantageous to cool the stripping composition or surface to be stripped at about 70 to about 700 ° C below ambient temperature and more preferably at about 20 to about 500 ° C below this temperature.

Therefore, in a preferred embodiment of the invention, the process is preferably carried out between a temperature of from -40 to about 80 ° C. and better between about -20 and about OOC.

 Of course, the invention is not limited to the embodiments described which have been given by way of example. In particular, it includes all means constituting technical equivalents of the means described and their combinations if they are executed according to its spirit and implemented in the context of the protection as claimed.

Claims (9)

 A method for etching an organic coating from the coated surface characterized by contacting said surface with a pickling composition in the gaseous state, which can destroy adhesion between said coating and said surface, the temperature said surface and gaseous stripping composition during said contact, and the pressure not being substantially greater than the ambient temperature and pressure.  2. Method according to claim 1, characterized in that the aforesaid contact is made substantially in the absence of a liquid condensate on the surface of the coated article.  3. Method according to claim 1, characterized in that said contact is made while said surface or pickling composition is cooled below ambient temperature.  4. Method according to claim 1, characterized in that the above-mentioned pickling composition contains a chlorocarbon as the main ingredient.  5. Process according to claim 1, characterized in that the aforementioned pickling composition consists essentially of a mixture of a chlorocarbon as main ingredient and at least one additional component selected from the group consisting of water, ammonia, hydrocarbon aliphatic, alkylamine, carboxylic acid, alkanol, alkyl ether, alkyl ester, alkyl nitrile, carboxylic acid amide, alkyl ketone, benzene, benzene substituted with halogen and lower alkyl, heteroaromatic compounds containing up to 8 carbon atoms and inorganic volatile acids, said component having a vapor pressure of at least about 2 mm Hg at room temperature.  6. A method according to claim 1, characterized in that the above pickling composition is normally liquid at room temperature and a current of said gas phase pickling composition is formed by passing a stream of air at above said pickling composition, without heating said composition to the reflux temperature.  7. Method according to any one of the preceding claims, characterized in that the aforementioned organic coating consists of paint, asphalt or oil.  8. Method according to any one of claims 6, characterized in that it further comprises the steps of sealing the surface to be etched with respect to the atmosphere in a stripping zone to put the stripping composition in the aforementioned gas phase in circulating in said zone, and maintaining said gas phase pickling composition in contact with said surface, until adhesion between the coating and the surface is substantially destroyed.  9. A method according to any one of claims 1 to 6, of the type where the organic coating is etched from an inner surface coated with a large construction, in particular the interior of a storage tank on land or of a shim or a ballast tank on a ship or barge, characterized in that it further comprises the steps of: sealing said inner surface with respect to the atmosphere to form a stripping zone, forming a current of a gas phase pickling composition capable of destroying the adhesion between said coating and said inner surface at a temperature and pressure not substantially greater than the ambient temperature and pressure, introducing said gas phase pickling composition into said pickling zone in contact with said inner surface, circulating said pickling composition in said etching area, and maintaining said pickling composition in a gaseous phase in contact with said coated surface at a temperature and pressure not substantially above ambient temperature and pressure until adhesion between the coating and the surface is substantially destroyed.