FR2785571A1 - Method for stripping paint from wooden involves heating article and submerging it in solvent bath - Google Patents

Abstract

The paint stripping commences with immersion (2) of the item in a fluid raised to a temperature of round 40 degrees Centigrade, and this fluid is subject to permanent agitation created by injection of compressed air bubbles into the fluid, below the item to be stripped. The fluid is water with a wetting agent, an anti-oxidant and a solvent. The item is then cooled sharply by rinsing (3) with a liquid below 25 degrees.

Description

 The present invention relates to a new method of stripping painted wooden objects, as well as a device for implementing this method.

 It is known that painted wooden objects, such as shutters, doors, windows, components of furniture or frames, etc., must be regularly stripped with a view to their renovation. This stripping operation aims to clean the object on the surface to remove the layer of dirt and used paint that covers it. The object is thus prepared for a new protective treatment and in particular for the application of a new layer of paint. The term painting is also taken here in its widest expression, covering any material capable of covering the surface of objects to form an adherent protective film, colored or not. It will in particular include varnishes and all other translucent or colored protective films.

 Currently, two methods are commonly used for pickling wood.

 First of all, there is a first method of manual pickling which can be described as artisanal insofar as it is essentially used on a small scale by craftsmen. According to this method, the paint is softened by a flame or by a flow of hot air, before being mechanically removed by scraping using a suitable tool such as a spatula, a brush, etc. This first process has two major drawbacks: on the one hand, it is limited to artisanal use and cannot be reliably and economically subjected to industrial adaptation, and on the other hand it causes, during the heating of painting, release of fumes harmful to the operator (and to the environment if it could be used on a large scale).

 Another process, much more widespread, especially in an industrial context, consists in carrying out a chemical pickling. Alkaline strippers (soda, potash) or based on methylene chloride are applied by brushing or by dipping on the surface to be treated. In contact with these strippers, the disintegrated paint is then removed by a simple rinsing. This simple and economical process however has serious drawbacks. First of all, from a qualitative point of view, it can prove to be penalizing for subsequent renovation operations, in particular with regard to the application of a new coat of paint if the object thus stripped is not not thoroughly and thoroughly rinsed in order to remove not only the disintegrated paint, but also the stripper which can also impregnate the wood and which risks thwarting the adhesion or polymerization of the new coating layer. This is a particularly acute problem, since it conditions the final quality and the longevity of the overall renovation operation. On the other hand, the use of chemical strippers constitutes a source of pollution which is particularly dangerous for the environment and operators.

 It therefore appeared useful to design a process for pickling painted wooden objects and a device for its implementation, usable on an industrial scale and non-polluting for the environment and operators.

 To this end, the subject of the invention is a pickling process which comprises at least the step of immersing the objects in a hot fluid brought to a temperature of at least 40 C, this hot fluid being subjected to permanent agitation obtained by injecting compressed air bubbles into the fluid, below the objects to be stripped.

 The immersion of the objects in the hot fluid causes embrittlement and detachment of the used paint layer by promoting the rupture of the adhesive bonds between this layer and the wood. The paint is therefore not or little dissolved, so that the process causes no emission of volatile organic compounds.

The agitation created by the air bubbles allows homogenization of the fluid and in particular of its temperature.

Air bubbles also promote the detachment of the paint, not only by the mechanical action resulting from the agitation they create, but also by the mechanical action resulting from their direct contact with objects.

According to a first advantageous characteristic of the invention, the method further comprises the following steps of:
- remove the objects from the fluid, and
-immediately leaving the fluid, subject the objects to brutal cooling by spraying at least one rinsing product sprayed on them at a maximum temperature of 25 C.

 The cold rinsing of the objects, immediately out of the fluid, not only ensures the evacuation of the weakened and detached paint residues, but also makes them undergo a thermal "shock" which makes them brittle and prevents them from restoring their adhesion to the wood. This second rinsing step is also carried out without any harm to the environment and the health of personnel in the vicinity, since it proceeds from a simple brutal cooling by means of a projection of a cold product.

In practice, the process can be optimized when the temperature of the hot fluid is between 70 and 90 C and the time of immersion of the objects to be stripped in the hot fluid is between 10 and 20 minutes depending on the type and thickness. of used paint covering the objects.
according to another advantageous characteristic of the invention, the hot fluid comprises at least 60 W of water.

This fluid is therefore by its nature very little (or not) polluting or toxic.

 To improve the efficiency of the hot fluid in its function of weakening and detachment of the paint, and to avoid corrosion of any metal parts incorporated into the wooden object, provision may be made for the hot fluid to contain, in addition to the water, a wetting agent, an antioxidant, and at least one solvent. For example, the or at least one of the solvents is Dimethylsulfoxide (DMSO).

 According to another advantageous characteristic of the invention, the or at least one of the cold rinse products consists of a liquid solution containing at least 90% water, sprayed at a temperature below 20 C. This product rinsing is thus particularly economical and low pollution. In addition, its neutrality preserves the wood from any aggressiveness and makes it possible to remove not only the paint residues, but also any trace of the components of the hot fluid which is not itself necessarily clean and neutral.

 As an alternative or in combination with such a rinse aid, ice beads can also be used as another rinse aid. These ice balls not only reinforce the thermal shock undergone by the objects leaving the hot fluid, but also improve by their mechanical action the evacuation of the paint residues. In addition, when melting, the ice balls freeze the paint residues, cause an effect of rinsing and washing of the objects and fall back into liquid form, entraining the residues in the hot fluid.

 An optimum effect is obtained when the ice balls are sprayed at a temperature below minus 40 C and at a pressure above 10 bars.

 Other characteristics and advantages of the invention will appear on reading the following description of a particular mode of operation of the method, given by way of nonlimiting example.

Reference will be made to the attached drawings, among which:
FIG. 1 is a plan view of a device for implementing the process of stripping painted wooden objects according to the invention;
FIG. 2 is a front elevation view of the device of FIG. 1;
FIG. 3 is a side view of the device, according to arrow III in FIG. 2.

 With reference to the figures, the device for implementing the method according to the invention comprises a closed cabin 1. This cabin comprises a lower soaking part 2 and an upper rinsing part 3.

 The lower part 2 incorporates a heating tank 4. This tank has a bottom 5 which forms a channel having a V-shaped profile and having a longitudinal direction inclined relative to the horizontal. At its lowest end, this channel leads to an evacuation orifice 6 which is connected to an evacuation circuit 7. This evacuation circuit which continues with a buried portion (not visible in the figures) leads to its opposite end in a decanter 8, itself connected by means of a pump 9 to a compacting filter press 10.

 The upper part 3 of the cabin 1 is located vertically above the tank 4 and is internally equipped with a series of nozzles 11 mounted on ramps 12 which provide the common supply. The ramps 12 are arranged to form an inverted U (that is to say whose branches are substantially vertical and point downwards). The nozzles 11 for supplying the nozzles 11 are themselves supplied by a pressurized circuit (not shown in the figures) with a rinsing product, as will be better explained later.

 The upper part 3 of the cabin 1 is further provided with portholes 13 which allow observation of the interior of the cabin. To facilitate access to these portholes, which are located in height, a monitoring bridge 14 is provided along the lower part 2 of the cabin at a height adapted so that the head of an observer being on this bridge is located substantially at the height of the portholes 13.

 For handling the objects to be treated, the device comprises a motorized traveling crane 15 provided with two hoists 16, the cables 17 of which are provided with hooks 18 below for attachment to a basket 19 for loading objects O to be stripped.

 The hoists 16 are slidably mounted on an upper rail 21 of the deck 15 extending horizontally at a height greater than that of the cabin 1. This rail 21 is disposed substantially along the median vertical plane of the cabin 1 which, seen in plan (as in Figure 1), is rectangular. The upper part 3 of the cabin 1 has a ceiling 22 which has a longitudinal upper opening 23 allowing the passage of the cables 17. The upper part 3 of the cabin also has a lateral opening 24 allowing the introduction and removal of the basket 19 in a displacement in the horizontal direction 51.

 The basket 19 carrying the objects to be stripped can thus be moved in a vertical direction 50 and a horizontal direction 51, in the median vertical plane of the cabin 1 to be introduced into and out of the upper part 3 of the cabin 1 and for, inside the cabin 1, be moved vertically between the upper 3 and lower 2 parts of this cabin. There are shown in Figures 2 and 3 the three main positions that can occupy the basket 19 carrying objects to be stripped. In FIG. 2, the basket 19, shown in solid lines, is in the standby position (for loading or unloading) and rests on the ground S next to the cabin. In FIGS. 2 and 3, the basket 19 is shown in dotted lines, on the one hand in the upper rinsing and draining position where it is located in the upper part 3 of the cabin, and on the other hand in the lower position 2 soaking in the tank 4 of the lower part 2 of the cabin. The corresponding position of the hoists 16 and their cables 17 has also been shown in dotted lines.

 The stripping of painted wooden objects O in accordance with the method of the present invention and with the device which has just been described takes place in the following manner.

 The objects O to be stripped are first loaded onto the basket 19 which is in the standby position on the floor S on the side of the cabin 1 where the lateral opening 24 of its upper part is located. This basket 19 is coupled by the hooks 18 to the cables 17 of the hoists (16) of the traveling crane 15. The hoists 16 are actuated to lift the basket 19 in the vertical direction 50 until this basket reaches the level of the upper part 3 of the cabin 1. The basket being held at this height, the hoists 16 are driven on the rail 21 of the traveling crane 15 towards the cabin 1. The basket 19 enters the upper part 3 of this cabin through the lateral opening 24 provided at this effect. When the basket 19 reaches the center of the upper part 3, the sliding of the hoists 16 on the rail 21 is stopped and the hoists 16 are immobilized in this position. The hoists 16 are then actuated to lower the basket 19 from its upper position to its lower position (both shown in dotted lines in FIGS. 2 and 3) to be immersed in a hot fluid contained by the tank 4.

 This hot fluid is maintained by heating means incorporated in the tank 4 (for example electrical resistors, submerged gas burners, etc.) at a temperature of at least 40 C. However, for better efficiency, the temperature of this fluid may be raised to 70 ° C. or more. However, it should not exceed 90 ° C, the temperature above which the wood may be damaged.

 The hot fluid is also subjected to permanent agitation. This agitation promotes weakening and detachment of the paint. It can for example be obtained by injecting compressed air bubbles into the hot fluid below the objects to be stripped. These air bubbles promote the detachment of the paint, not only by the agitation they create, but also by their direct contact with objects.

 The composition of the hot fluid may be variable. However, so that the hot fluid does not constitute a too significant source of pollution, difficult to reprocess in the event of emptying, and so that this fluid remains neutral with respect to the wood to be stripped, provision will preferably be made that it comprises at least 60% water.

 The hot fluid can also comprise, in addition to water, a wetting agent, an antioxidant and one or more solvents. The addition of one or more solvents makes it possible to strengthen the weakening and detachment function of the paint exerted by the hot fluid. We can for example use a biochemical solvent with low toxicity such as Dimethyl-sulfoxide (DMSO). The antioxidant, on the other hand, prevents corrosion of any metal parts incorporated into wooden objects.

Finally, the wetting agent facilitates the penetration of the components of the hot fluid between the paint to be eliminated and the wood.

 The time for immersion of the objects to be stripped in the hot fluid can vary depending on the type and thickness of the layer of paint to be removed. In practice, immersion of the objects in the hot fluid for 10 to 20 minutes will most often give complete satisfaction.

 At the end of the predetermined immersion time, the basket 19 carrying the objects 0 is raised in the vertical direction 50 by the hoists 16 which are actuated for this purpose. The basket 19 is immobilized when it reaches the high position inside the U formed by the ramps 12.

 These ramps 12 of nozzles 11 are then supplied with pressurized rinsing product, so that the nozzles 11 project this product onto the objects to be scoured, as illustrated in FIG. 3. This rinsing is carried out cold so as to subjecting still hot objects emerging from the fluid to a thermal "shock". For this thermal "shock" to be effective, rinsing must take place immediately after the objects have been removed from the fluid.

 By "immediately" is meant that this rinsing must take place at the latest within a few minutes following the exit of the objects from the hot fluid. In practice, for optimum efficiency, it will be preferable that between the exit of the objects from the hot fluid and their cold rinsing, a maximum interval of 30 seconds elapses.

 The temperature of the cold rinse aid must of course be significantly lower than that of the hot fluid: the rinse aid must be sprayed onto the objects O at a maximum temperature of approximately 25 C.

 The rinsing can be carried out with a single product or with several distinct products.

 We can for example use as rinse aid a neutral liquid solution containing at least 90% water, sprayed by the nozzles 11 at a temperature between 0 C and 20 C. In practice, a temperature of 10 to 15 C will give whole satisfaction. This rinsing product is therefore particularly economical and not very polluting. In addition, its neutrality preserves the wood from any aggressiveness and allows to evacuate not only the paint residues, but also any trace of the components of the hot fluid which is not itself necessarily clean and neutral.

 It is also possible to use, in isolation or in combination with such a liquid solution, ice balls projected by suitable nozzles. These beads can, for example, consist of frozen water. It has been determined in tests that optimum efficiency is obtained when these ice balls are sprayed at a temperature below minus 40 C and at a pressure above 10 bars.

 These ice balls not only reinforce the thermal shock undergone by the objects leaving the hot fluid, but also improve by their mechanical action the evacuation of the paint residues. In addition, when melting, the ice balls freeze the paint residues, cause an effect of rinsing and washing of the objects and fall back in liquid form in the hot fluid by entraining there the paint residues as well as the traces of hot fluids.

 During these cold rinses, the basket 19 of objects to be stripped is kept vertical to the tank 4, so that the rinsing product (s) sprayed on the objects fall directly into the tank 4 with the paint detritus evacuated. The tank 4 thus centralizes all the waste resulting from the pickling.

 This waste falls into the bottom 5 of the tank 4 where they pile up to form kinds of sludge. This sludge, due to the inclination of the channel formed by the bottom, migrates, by gravity to the discharge orifice 10 to be sucked, by a pump 25, into the discharge circuit 7. The sludge is thus conveyed, via the evacuation circuit 7, to the decanter 8. In this decanter, the mixture of water and detritus forming the sludge undergoes a first separation, the solid or pasty detritus falling by gravity into the bottom of the decanter 8 and the liquid solution being pumped into the upper part of the decanter to be re-injected, via a return circuit (not shown), into the tank 4. Thicker sludge is thus recovered in the lower part of the decanter 8 where they are sucked up by the pump 9, to be injected in successive and constant doses into the compacting filter press 10. This filter press is essentially constituted by a sort of press whose piston is perforated to let the liquids pass and compress the solid detritus so as to compact them in the form of a "pancake". The "wafer" of waste thus recovered can then be conveniently stored, then transported to its place of reprocessing.

 After the rinsing step, which can last a few minutes, the objects can undergo a fourth and final drip step in which they are kept stationary above the tank 4, so that the drops of rinsing product remaining on the objects fall directly into the tank 4. To be effective, this draining step will last at least 10 minutes and preferably about 15 minutes.

 During this step, the objects may be subjected to ventilation aimed at promoting drainage and even drying of the pickled objects. To this end, the upper part 3 of the cabin 1 will be provided with air circulation means such as ventilation ramps connected to electric fans.

Claims (9)

 1. A method of stripping painted wooden objects, characterized in that it comprises at least the steps of immersing the objects in a hot fluid brought to a temperature of at least 40 C, this hot fluid being subjected to permanent agitation obtained by injecting compressed air bubbles into the fluid, below the objects to be stripped.  2. pickling method according to claim 1, characterized in that the subsequent steps of:  - remove the objects from the fluid, and  -immediately leaving the fluid, subject the objects to brutal cooling by spraying at least one rinsing product sprayed on them at a maximum temperature of 25 C.  3. Method according to one of the preceding claims, characterized in that the temperature of the hot fluid is between 70 and 90 C and in that the time of immersion of the objects to be stripped in the hot fluid is between 10 and 20 minutes depending on the type and thickness of paint covering the objects.  4. Method according to one of the preceding claims, characterized in that the hot fluid comprises at least 60% water.  5. Method according to claim 4, characterized in that the hot fluid comprises, in addition to water, a wetting agent, an antioxidant, and at least one solvent.  6. Method according to claim 5, characterized in that the or at least one of the solvents is Dimethylsulfoxide (DMSO).  7. Method according to one of the press claims, characterized in that the or at least one of the cold rinse products consists of a liquid solution containing at least 90% water, sprayed at a lower temperature at 20 C.  8. Method according to one of the preceding claims, characterized in that the or at least one of the cold rinse products comprises ice balls.  9. Method according to claim 9, characterized in that the ice balls are sprayed at a lower temperature minus 40 C at a pressure greater than 10 bars.