A METHOD FOR REMOVING A POLYMER COATING FROM A CARRIER PART

Abstract: The invention relates to a method and a device for dissolving a polymer coating from a carrier part (10), comprising the steps of: a) storing the solvent (11) in a first container (1) in the absence of air, at a temperature which is approximately equal to or higher than the temperature at which the carrier part (10) is to be immersed in the solvent (11), b) introducing the carrier part (10) into a closed reactor (2), c) purging the reactor (2) with an inert gas, d) supplying the heated solvent (11) to the reactor (2) and immersing the carrier part (10) in the solvent (11) for a predetermined period of time, e) removing the solvent (11) from the reactor (2) and returning the solvent (11) to the first container (1) and f) rinsing the reactor (2) and the carrier part (10) with a liquid rinsing agent (12) and removing the carrier part (10) from the reactor (2).

Description: A method for removing a polymer coating from a carrier part. The present invention relates to a method for removing a polymer from a carrier part by immersing the carrier part in a solvent for the polymer. From the art, a method for removing a polymer from a carrier part is known wherein the carrier part is immersed in a solvent for the polymer, in an autoclave. The solvent and the carrier part are supplied to the autoclave at environmental temperature. After the carrier part has been immersed in the solvent, the autoclave is heated to a temperature of approximately 230JC, at high pressure in case triethyleneglycol is used as a solvent. After the polymer coating has been dissolved to a sufficient extent, the solvent is cooled down in the autoclave, the autoclave is opened and the carrier part is lifted out of the autoclave. Thereafter the carrier part is rinsed with water outside the autoclave so as to remove any remaining solvent. This known method however has the disadvantage that it is a batch process, which requires long processing times. It has namely been found that it may take 2 to 3 hours to heat the solvent to the required temperature, and 2 to 3 hours to cool the solvent down before the carrier part can be removed. It is the aim of the present invention to provide a method with a shorter processing time. This is achieved in the present invention with the measures described in the characterising part of the first claim. The storing of the solvent in a container at a temperature which is equal to or somewhat higher than the temperature at which the carrier part is to be treated, and the use of this pre-heated solvent in the reactor for dissolving the polymer coating, allows to save on the time needed for heating the reactor to the required temperature. Namely, the dissolution of the polymer coating is mostly carried out at a temperature of between 150-300°C depending on the type of solvent used. It appears that the heating of a volume of a few m 3 to those temperatures takes a substantial period of time, and may take a few hours or even more. The solvent is preferably stored at a temperature somewhat above the temperature at which the carrier part is to be treated so as to allow to compensate for the temperature decrease that may occur when transporting the solvent from the first container to the reactor. Examples of factors that may co-operate in decreasing the temperature of the solvent are a loss of heat occurring during transport, the use of a cold reactor and immersing cold carrier parts into the solvent. If so desired, the reactor may be re-heated to the temperature at which the carrier part is to be immersed in the solvent, to compensate for the above described heat loss. A storing of the hot solvent in a closed container allows to prevent that solvent is lost due to evaporation thereof. In that way not only a more economically favourable process can be obtained, but also the environmental safety of the process can be improved. The purging of the reactor with an inert gas before it is filled with solvent, the absence of air in the reactor and in the first container where the solvent is stored, all co-operate in preventing that the solvent degenerates or can be decomposed or oxidised by the air. In that way the loss of solvent during the dissolution of the polymer coating can be further reduced. Besides this, in case use is made of a flammable solvent, the safety of the process can be improved when avoiding contact with the open air. In the method of this invention also, the reactor is emptied of solvent before the carrier part is subjected to a rinsing step. By removing substantially all of the solvent from the reactor before the liquid rinsing agent is supplied to the reactor, it is possible to reduce the amount of solvent that is mixed with the rinsing agent, so that the same volume of rinsing agent can be re-used several times without necessitating a purification of the rinsing agent after each rinsing step. Because in the method of this invention use is made of a closed system, it may either be operated at atmospheric pressure, or a pressure slightly above atmospheric pressure for example between 200 - 1500 mbar, preferably 350-900 mbar above atmospheric pressure, without thereby involving a risk to explosion. The use of an over pressure allows that the solvent can be maintained at a higher temperature, i.e. its boiling temperature or somewhat higher, without involving the formation of a vapour phase. Because the temperature of the solvent can be increased with approximately 50°C, the dissolution rate of the polymer can be increased with a factor of 3 or 4 or even more. The process of this invention may despite the slight over pressure, be carried out in a light reactor. It appeared that there is no necessity to use a heavy, dedicated, pressure resistant and expensive autoclave. Because contact of the solvent with air is avoided, oxidation of the solvent can be prevented. In the method of this invention it is preferred to agitate the solvent while the carrier is immersed therein. In that way not only the dissolution rate of the polymer coating can be increased, but also polymer coating present in small holes and interstecies can be dissolved. The method of this invention appeared to be particularly suitable for dissolving a polymer coating from a filter, the orifices of which are obstructed by the polymer, especially in case the holes are rather small in the range of 0.1 mm or less. The method of this invention appeared also to be particularly suitable for dissolving a polymer coating from an in depth filter, which may for example be made of sintered metal particles, wire cloth, random wire fibre etc. An in depth filter element is made up of a porous structure with thickness and voids which allow particles to be trapped in the interstecies. By agitating the solvent it appeared to be possible to dissolve polymer particles that are stuck in the above-described interstecies. In order to allow the temperature in the reactor to be kept sufficiently high, the solvent is preferably continuously circulated between the first container where it is heated, and the reactor. In that way also the solvent can be continuously re-freshened. In the method of this invention it is preferred to store the liquid rinsing agent at low temperature, for example room temperature, and to supply the rinsing agent to the reactor at this low temperature. The use of a relatively cold rinsing agent as compared to the temperature of the carrier parts, allows the carrier parts to be simultaneously rinsed and cooled. Thus, the carrier parts can be removed from the reactor after the rinsing has been terminated, without necessitating an additional cooling step. Agitation of the rinsing agent when rinsing, and preferably also continuously circulating the rinsing agent between the reactor and the second container during the rinsing step, allows to improve the efficiency of the rinsing step and to save on the time needed for rinsing the carrier part and the reactor. The preferred solvent in the method of this invention is triethyleneglycol, which is stored in the container at a temperature of approximately 250-290°C, preferably approximately 280°C. It has namely been found that a storing of the solvent at this temperature allows to obtain in the reactor the optimum temperature for dissolving the polymer coating from the carrier parts, i.e. a temperature of approximately 280°C, without necessitating a re-heating of the reactor. It has namely been found that triethyleneglycol is a very suitable solvent for removing a polymer coating, such as for example a varnish, paint, polymer, resin from carrier parts that may easily be deformed when subjected to a too high temperature, without thereby affecting the carrier part. Namely, because of its high boiling temperature approximately 284-294°C, triethyleneglycol can be used at high temperature, so that even hardly soluble polymers will dissolve and the dissolution rate of the polymer can be increased. Thereby mostly an over pressure of 350-850 mbar will be maintained. Examples of parts that are sensitive to high temperature include painted metal car parts, painted aluminium parts, coated aluminium parts, filters of sintered metal particles, spinnerets for producing polymer fibres or yarns, woven or non-woven fibrous materials, filter elements used in spin pack filtration, or filter grids that cannot be cleaned otherwise in a fluidised bed because the fluidised bed particles would obstruct the filter holes. The method of this invention allows that the polymer coating of such parts be removed without thereby involving a mechanical deformation of the carrier part. It has for example been found that aluminium car parts are easily deformed, and that the particles of a sintered metal filter come loose from each other, when subjected to a temperature of 450°C needed for removing the coating in a fluidised bed or pyrolysis oven. Above a temperature of 290°C the dissolution rate of the polymer coating does not improve, so that the use of a higher temperature only involves larger energy costs. Below a temperature of approximately 250°C, the dissolution rate of the polymer is becoming low, thus rendering the process less economically favourable. Triethyleneglycol appears to be an environmental friendly, biodegradable solvent, which is water soluble and can thus be rinsed from the carrier parts by means of water. The triethyleneglycol can be purified from dissolved impurities, such as for example dissolved polymer coating or paint, through distillation. In the method of this invention, the preferred rinsing agent is water that is stored in the second container at approximately environmental temperature. After a first charge of carrier parts have been subjected to the above described dissolution process and have been rinsed with water, they can be removed from the reactor. Thereafter the reactor is immediately available for receiving a second charge of carrier parts and starting a new dissolution cycle, without necessitating that the reactor is first cooled down before solvent can be supplied. With the present invention thus a process for dissolving a coating from carrier parts is provided, which can be carried out in an almost continuous manner. The present invention also relates to a device for dissolving a polymer coating from a carrier part. The device of this invention comprises (1 ) a first container with a heating, for storing and heating a solvent for the polymer coating to the required temperature, (2) a reactor which is connected to the first container for immersing a carrier part in the solvent, (3) a third container, which is connected to the reactor and is provided for storing a liquid rinsing agent (4) means for purging the reactor with an inert gas, means for transporting the solvent from the first container to the reactor and back, and means for transporting the rinsing agent from the third container to the reactor. If so desired, the reactor can be provided with an insulation so as to prevent that the reactor cools down to quickly due to contact with the atmosphere, or with a heating so as to allow the solvent to be re-heated in case its temperature may have dropped too low, because for example of heat loss occurring during transport from the first container to the reactor, the reactor was cold or the carrier parts had a low temperature. The third container may contain a heat exchanger so as to make profitable use of the heat contained in the rinsing agent after it has been contacted with the hot carrier parts. The invention is further illustrated in the attached figure of a preferred embodiment of this invention, and the description of the figure. The device shown in figure 1 comprises a first container 1 for the solvent 11 for dissolving a polymer coating from a carrier part 10. The first container 1 contains a heating 6 for heating the solvent to the required temperature. Suitable solvents 11 for use in the method and device of this invention include the usual organic solvents generally known to the man skilled in the art, such as for example mono and poly-alcohols, glycols, ethers, ketones, for example acetone, etc. The preferred solvent for use in the present invention is triethyleneglycol, since it has been found to be capable of dissolving a wide variety of polymer coatings and is environmentally friendly. The device shown in figure 1 contains a reactor 2 for immersing a carrier part 10 in the solvent 11 at the desired temperature. In order to allow the reactor 2 to maintain approximately a constant required temperature, the reactor 2 is preferably provided with a thermal insulation 7. To maintain the desired temperature and simultaneously increase the dissolution rate of the polymer coating, means 13, 14 may be provided for continuously circulating the solvent 11 from the first container 1 to the reactor 2 and back. The means for circulating the solvent may comprise a pump, electro-pneumatic valves or other devices well known to the man skilled in the art. The reactor 2 preferably also contains means for agitating the solvent 11 especially while the carrier part 10 is immersed therein, so as to improve the dissolution of the polymer coating. A suitable example of means for agitating the solvent is a stirrer or means for circulating the solvent. The reactor 2 further comprises at its bottom an inlet 8 for the solvent 11 and an inlet 9 for the rinsing agent 12. The solvent 11 is transported from the first container 1 to the reactor 2 through a pipe 13. The pipes 13 and 14 allow a continuous circulation of the solvent 11 to and from the reactor 1. In the reactor 2, an over pressure valve 18 may be provided so as to allow solvent vapour to escape from the reactor 2, to be condensed in a condenser 22 and to be returned to the first container 1 through a pipe 23. Examples of carrier parts 10 that may be treated with the method of this invention include painted metal car parts, painted aluminium parts, coated aluminium parts, filters of sintered metal particles, spinnerets for producing polymer fibres or yarns, woven or non-woven fibrous materials, filter elements used in spin pack filtration, or filter grids that cannot be cleaned otherwise in a fluidised bed because the fluidised bed particles would obstruct the filter holes. The device of this invention further comprises a second container 3 for containing a liquid rinsing agent 12 for rinsing the carrier part 10 after the coating has been dissolved and the reactor 2 has been emptied of the solvent 11. The first 1 and second container 3 preferably have the same volume, so as to provide the best economically feasible process. The preferred rinsing agent is water. The rinsing agent is preferably stored in the second container 3 at environment temperature. The second container 3 is connected to the reactor 2 through a first pipe 15 along which the rinsing agent 12 is transported to the reactor 2 by means of a liquid pump. Water vapour is allowed to escape from the reactor 2 through a pipe 16, whereafter it is condensed. The first container 1 is preferably also provided with a third over pressure valve 20 so as to allow solvent vapour to escape and to be transported through a pipe 21 towards the condenser 22 in the second container 12. Due to the lower temperature remaining in the second container 3, the solvent vapour will condense arid can be returned to the first container 1 through the pipe 23. The first container 1 can also be coupled to a vacuum destination device, so as to allow a continuous purification of the solvent. The reactor 2 used in the method and device of this invention preferably has a rounded bottom, wherein at least one bulge is provided for collecting the last traces of solvent or rinsing agent that may remain in the reactor 2 after the majority of the solvent or rinsing agent have been removed from the reactor 2. Any liquid remaining in the bulge may be removed for example by means of pressurised air, so as to allow a complete removal of liquid from the reactor and to avoid that the solvent is mixed with the rinsing agent and vice versa. In the method of this invention, a carrier part 10 is inserted in the reactor 2, whereafter the reactor 2 is closed and purged with an inert gas, preferably nitrogen so as to remove virtually all air from the reactor 2. Then, the solvent which is preferably triethyleneglycol 11 which has been stored at a temperature of approximately 280°C is transported from the container 1 to the reactor 2, so as to immerse a polymer coated carrier part 10 therein. The triethyleneglycol is stirred and is continuously circulated between the container 1 and the reactor 2. After the carrier part 10 has been immersed in the triethyleneglycol 11 for 20 minutes at a temperature of approximately 280°C while stirring, the triethyleneglycol is removed from the reactor 2 and the reactor 2 is filled with water for 10 minutes, while stirring so as to rinse the carrier part 10. The water 12 is removed from the reactor 2 and returned to the second container 3, the carrier part 10 is removed from the reactor 2. When making use of a first container with a volume of approximately 1.2 m 3 , which can be heated from room temperature to a temperature of approximately 280°C in approximately 100 minutes, and a reactor with a volume of approximately 0.25 m 3 , approximately 100 parts of 1 m length, 6.5 cm diameter can be treated, requiring 220 kWh per day. This in contrast to the method known from the art with which only 25 can be treated when using the same volume of solvent. With the method and device of the present invention products such as for example paint, varnish, resin, polyester coatings, plastics etc can be removed from a carrier part.

Claims: CLAIMS. 1. A method for dissolving a polymer coating from a carrier part (10), by immersing the carrier part (10) in a solvent (11 ) for the polymer, characterised in that the method comprises the steps of (a) storing the solvent (11 ) in a first container (1 ) in the absence of air, at a temperature which is approximately equal to or higher than the temperature at which the carrier part (10) is to be immersed in the solvent (11), (b) introducing the carrier part (10) into a closed reactor (2), (c) purging the reactor (2) with an inert gas, (d) supplying the heated solvent (11) to the reactor (2) and immersing the carrier part (10) in the solvent (11) for a predetermined period of time, (e) removing the solvent (11) from the reactor (2) and returning the solvent (11 ) to the first container (1 ) and (f) rinsing the reactor (2) and the carrier part (10) with a liquid rinsing agent (12) and removing the carrier part (10) from the reactor (2). 2. A method as claimed in claim 1 , characterised in that the solvent (11 ) is agitated while the carrier part (10) is immersed therein. 3. A method as claimed in claim 1 or 2, characterised in that during the immersing of the carrier part (10) in the solvent (11), the solvent (11 ) is continuously circulated between the container (1 ) and the reactor (2), and the container (1 ) is heated. 4. A method as claimed in any one of claims 1 to 3, characterised in that the rinsing agent (12) is stored and supplied to the reactor (2) at a temperature below the temperature of the solvent (1 1 ). 5. A method as claimed in any one of claims 1 to 4, characterised in that the rinsing agent (12) is continuously circulated between the second container (3) and the reactor (2). 6. A method as claimed in anyone of claims 1 -5, characterised in that an over pressure of between approximately 200-1500 mbar, preferably approximately 350-900 mbar is maintained in the reactor (2) while the carrier part (10) is immersed in the solvent (11 ). 7. A method as claimed in any one of claims 1 to 6, characterised in that as a solvent (11 ) use is made of triethyleneglycol, which is stored in the container (1 ) at a temperature of approximately 250-290°C, preferably approximately 280°C, and as a rinsing agent (12) use is made of water which is stored in the second container (3) at environmental temperature. 8. A device for removing a polymer coating from a carrier part, characterised in that the device comprises a first container (1 ) with a heating (6) for storing and heating a solvent (11 ) for the polymer coating, a reactor (2) which is connected to the first container (1 ) for immersing a carrier part (10) in the solvent (11), a third container (3) for storing a liquid rinsing agent (12), which third container (3) is connected to the reactor (2), means (4) for purging the reactor (2) with an inert gas, means (5) for transporting the solvent (11 ) from the first container to the reactor (1 ) and back, and means (6) for transporting the rinsing agent (12) from the third container (3) to the reactor (2). 9. A device as claimed in claim 8, characterised in that the reactor (2) comprises a thermal insulation (7). _ . -._ AMENDED CLAIMS [received by the International Bureau on 12 September (12.09.00); original claims 1-9 replaced by new claims 1-10 (2 pages)] 1. A method for dissolving a polymer coating from a carrier part (10), by immersing the carrier part (10) in a solvent (11 ) for the polymer, characterised in that the method comprises the steps of (a) storing the solvent (11 ) in a first container (1 ) in the absence of air, at a temperature which is approximately equal to or higher than the temperature at which the carrier part (10) is to be immersed in the solvent (11 ), (b) introducing the carrier part (10) into a closed reactor (2), (c) purging the reactor (2) with an inert gas, (d) supplying the heated solvent (11 ) to the reactor (2) and immersing the carrier part (10) in the solvent (11 ) for a predetermined period of time, (e) removing the solvent (11 ) from the reactor (2) and returning the solvent (11 ) to the first container (1 ) and (f) rinsing the reactor (2) and the carrier part (10) with water as a liquid rinsing agent (12) which is stored in a second container (3) at a temperature below the temperature of the solvent (11 ) and removing the carrier part (10) from the reactor (2). 2. A method as claimed in claim 1 , characterised in that the solvent (11 ) is agitated while the carrier part (10) is immersed therein. 3. A method as claimed in claim 1 or 2, characterised in that during the immersing of the carrier part (10) in the solvent (11 ), the solvent (11 ) is continuously circulated between the container (1 ) and the reactor (2), and the container (1 ) is heated. 4. A method as claimed in any one of claims 1 to 3, characterised in that the rinsing agent (12) is stored and supplied to the reactor (2) at environmental temperature. 5. A method as claimed in any one of claims 1 to 4, characterised in that the rinsing agent (12) is continuously circulated between the second container (3) and the reactor (2). 6. A method as claimed in anyone of claims 1-5, characterised in that an over pressure of between approximately 200-1500 mbar, preferably approximately 350-900 mbar is maintained in the reactor (2) while the carrier part (10) is immersed in the solvent (11 ). 7. A method as claimed in any one of claims 1 to 6, characterised in that as a solvent (11 ) use is made of triethyleneglycol, which is stored in the container (1 ) at a temperature of approximately 250-290°C, preferably approximately 280°C. 8. A device for removing a polymer coating from a carrier part, characterised in that the device comprises a first container (1 ) with a heating (6) for storing and heating a solvent (11 ) for the polymer coating, a reactor (2) which is connected to the first container (1 ) for immersing a carrier part (10) in the solvent (11 ), a third container (3) for storing a liquid rinsing agent (12), which third container (3) is connected to the reactor (2), means (4) for purging the reactor (2) with an inert gas, means (5) for transporting the solvent (11) from the first container to the reactor (1) and back, and means (6) for transporting the rinsing agent (12) from the third container (3) to the reactor (2). 9. A device as claimed in claim 8, characterised in that the reactor (2) comprises a thermal insulation (7). 10. A device as claimed in claim 8 or 9, characterised in that the reactor (2) comprises a rounded bottom with at least one bulge for collecting remaining traces of solvent or rinsing agent.

Inventors: GEEROMS ANDRE, GEEROMS, ANDRE
Applicants: GEEROMS ANDRE, SEGHERS BETTER TECHNOLOGY FOR, GEEROMS, ANDRE, SEGHERS BETTER TECHNOLOGY FOR SERVICES+MACHINERY,
Application year: 1999
Main classification: B08B3
IPC codes: B08B3