Paint film peeling treatment method

Abstract

To solve the problem in which: upon recycling resin applied with coating, the conventional method of removing a coating film causes the resin to deteriorate, making it impossible to maintain physical properties such as strength, elastic modulus, and impact resistance; accompanied by usage of coating film removing, a concentration of a dissolved coating film component increases in a stripping solution, and as usage count increases, coating film removing ability of the stripping solution decreases, leading to a limit in the usage count; and a disposal cost for a used stripping solution or environmental impact increases.SOLUTION: A sulfuric acid solution is brought into contact with a coating film formed on resin, to strip the coating film from the resin. An organic matter being a component of the coating film dissolved in the sulfuric acid solution is treated by being decomposed into carbon dioxide and water by an electrolytic sulfuric acid solution.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a coating film stripping method for stripping and removing a coating film from a resin having a coating film. [Background technology]

[0002] Polymer materials such as PC / PBT material, which is a mixture of polycarbonate (PC) resin and polybutylene terephthalate (PBT) resin, and ABS material, which is a copolymer synthetic resin of polycarbonate resin and acrylonitrile, butadiene, and styrene, are used for automobile parts, etc. In addition, these parts are painted to improve their appearance and to prevent deterioration due to ultraviolet rays. Due to painting errors during the painting process, some parts are discarded due to poor appearance or part replacement. Most of these painted resin parts are currently discarded. In recent years, there has been a demand to reduce the amount of resin waste from the perspective of reducing the environmental impact, and studies and technological developments are being made on recycling resins that have been discarded up until now. However, in reality, recycling has not yet become commonplace, and various companies, including resin manufacturers and companies that use that resin to mold parts, are still in the process of developing the technology.

[0003] In Patent Document 1, a solution containing tetraalkylammonium hydroxide and a pyrrolidone compound as a solvent component is used for removing the coating film, and in Patent Document 2, a solution mainly containing sodium hydroxide, i.e., an alkaline solution, is used. In Patent Document 3, an organic solvent containing benzyl alcohol and butyl cellosolve is used. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2013-40266 A [Patent Document 2] Patent No. 6188068 [Patent Document 3] JP 2014-69369 A Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, a coating film stripper containing tetraalkylammonium hydroxide and a pyrrolidone-based compound as a solvent component is used, and in Patent Document 2, an aqueous sodium hydroxide solution is used. These conventional techniques focus only on the coating film removal method, and make no mention of maintaining the physical properties such as strength of the resin after stripping, raising concerns about a decrease in physical properties. In addition, Patent Document 3 mentions maintaining the physical properties of the resin after stripping, and describes a method of combining a chemical coating film removal method and a physical coating film removal method to maintain the physical properties, but this results in many processing steps.

[0006] When recycling painted resin, problems occur such as deterioration of the resin when removing the coating and deterioration of physical properties due to contamination by the removed coating. Therefore, a challenge in this field is to completely remove the coating while maintaining physical properties such as strength, elastic modulus, and impact resistance, and to recycle the resin. In addition, the stripping solution used to remove the coating contains dissolved coating components, and the coating removal ability of the stripping solution decreases as the number of times it is used increases, which creates the problem of there being a limit to the number of times it can be used. Furthermore, in disposing of used stripping solution, the following problems can easily be imagined as the number of stripping and removal treatments increases. (1) Increased costs for waste liquid treatment and replacement, and collection and transportation costs (2) Increased wastewater treatment costs due to multiple wastewater treatment processes (3) Increased environmental impact from waste liquid treatment to replacement and regeneration [Means for solving the problem]

[0007] The present invention has been made in consideration of the above-mentioned problems in the prior art, and has an object to provide a coating film stripping method that completely strips and removes a coating film while maintaining the physical properties of the resin.

[0008] That is, the first embodiment of the coating film peeling treatment method of the present invention is a coating film peeling treatment method for peeling and removing a coating film formed on a surface of a resin from the resin, comprising the steps of: The coating film formed on the resin is brought into contact with a sulfuric acid solution to remove the coating film from the resin, and the organic matter that is a component of the coating film dissolved in the sulfuric acid solution is treated by being decomposed into carbon dioxide and water using an electrolytic sulfuric acid solution.

[0009] In another embodiment of the coating film stripping method of the invention, in the above-described embodiment, an electric current is passed through a part or all of the sulfuric acid solution in which the coating film has been dissolved, to generate an electrolytic sulfuric acid solution by electrolysis.

[0010] In another embodiment of the coating film stripping treatment method of the invention, in the above-mentioned embodiment, the sulfuric acid solution brought into contact with the coating film is an electrolytic sulfuric acid solution.

[0011] In another embodiment of the coating film stripping method of the invention, in the above-described embodiment, an electric current is passed through a part or all of the electrolytic sulfuric acid solution in which the coating film has been dissolved, thereby carrying out further electrolysis.

[0012] In another embodiment of the coating film peeling treatment method of the invention, in the above-described embodiment, the temperature of the sulfuric acid solution in which the coating film is dissolved is increased to 60 to 100° C., and the sulfuric acid solution is reacted with an electrolytic sulfuric acid solution for the decomposition.

[0013] In another embodiment of the coating film peeling treatment method of the invention, in the above-mentioned embodiment, the sulfuric acid solution brought into contact with the coating film has a concentration of 85.0 mass % or more and a temperature within the range of 45 to 80°C.

[0014] In another embodiment of the coating film peeling treatment method of the invention, in the above-mentioned embodiment, the electrolytic sulfuric acid solution brought into contact with the coating film has a concentration of 80.0 mass % or more and a temperature within the range of 45 to 80°C.

[0015] In another embodiment of the coating film peeling treatment method of the invention, in the above-mentioned embodiment, the solution temperature during the electrolysis is set to 20 to 60°C.

[0016] Another embodiment of the coating film peeling treatment method according to the above embodiment of the present invention further comprises preparing a plurality of tanks for peeling and removing the coating film, and terminating the coating film peeling and removal in each tank according to a decrease in the decomposition rate of the coating film in each tank; The coating film peeling and removal was completed. The sulfuric acid solution in the tank is regenerated by electrolysis.

[0017] In another embodiment of the coating film peeling treatment method of the invention, in the above-mentioned embodiment, the decomposition rate of the coating film is determined by the electrical conductivity and / or the oxidation-reduction potential of the solution.

[0018] In another embodiment of the coating film stripping method according to the invention, upon completion of the coating film stripping removal, stripping removal of the coating film in another tank is continued or started.

[0019] The contents stipulated in the present invention will be explained below. [Sulfuric acid concentration, solution temperature] In the sulfuric acid solution that is brought into contact with the coating film, if the sulfuric acid concentration is low, the peeling ability of the coating film decreases, and some coating colors cannot be peeled off depending on the set coating color. Since the higher the concentration of the sulfuric acid solution, the stronger the hydrophobicity, the higher the sulfuric acid concentration is for dissolving the coating film, and it is desirable to set the lower limit concentration to 85.0 mass%. However, when an electrolytic sulfuric acid solution is used as the sulfuric acid solution that is brought into contact with the coating film, the peeling ability increases due to the addition of oxidizing power, so it is desirable to set the lower limit concentration to 80 mass%.

[0020] Increasing the temperature of the sulfuric acid solution increases the amount of coating that dissolves, and the coating's peeling ability increases. For this reason, it is desirable to set the temperature of the sulfuric acid solution (including electrolytic sulfuric acid solution) that comes into contact with the coating to 45°C or higher. On the other hand, if the solution temperature is raised too high, the coating's peeling ability will increase, but the resin surface will discolor and deteriorate significantly after the coating is peeled off, which is not desirable for reusing the resin, so it is desirable to set the upper limit temperature to 80°C. However, in the present invention, the sulfuric acid concentration and the solution temperature are not limited to those described above.

[0021] [Decomposition by electrolytic sulfuric acid solution] The electrolytic sulfuric acid solution has a high oxidizing power and can react with the organic matter that is a component of the coating film and decompose it into carbon dioxide and water. The electrolytic sulfuric acid solution can be prepared by electrolyzing a part or all of the sulfuric acid solution in contact with the coating film. In addition, by using an electrolytic sulfuric acid solution as the sulfuric acid solution in contact with the coating film, the dissolved coating film components can be decomposed as they are. The electrolytic sulfuric acid solution in contact with the coating film can be further decomposed by passing electricity to increase the oxidizing power. The sulfuric acid solution in which the coating film has been dissolved can be mixed with an electrolytic sulfuric acid solution to decompose the coating film components. At this time, the sulfuric acid solution in which the coating film has been dissolved can be heated to 60 to 100°C to react with the electrolytic sulfuric acid solution, thereby increasing the oxidizing power.

[0022] The present invention will now be described chemically. The process in which the coating film dissolves in the sulfuric acid solution is a phenomenon in which the hydrophobic coating film dissolves and diffuses in the hydrophobic sulfuric acid solution, that is, it is a physical phenomenon, and there is no chemical reaction formula. The chemical reaction formula when sulfuric acid solution is electrolyzed is shown below. From formula (1), when sulfuric acid solution is electrolyzed, hydrogen sulfate ions (HSO4 - ) reacts with peroxodisulfate (SO8 2― ) is produced. Peroxodisulfate is unstable, so it is converted to peroxomonosulfate (HSO5 ― ) and hydrogen peroxide (H2O2) (equations (2) and (3)), and there are three types of oxidants in the electrolytic sulfuric acid solution. 2HSO4 - → 2H + + S2O8 2- + 2e - (1) S2O8 2- + H2O → HSO5 - + HSO4 - (2) HSO5 - + H2O → HSO4 - + H2O2(3)

[0023] Next, the reaction in which the coating film, which is an organic substance, reacts with an oxidizing agent such as peroxodisulfuric acid and decomposes into carbon dioxide and water will be described. By generating an electrolytic sulfuric acid solution, the resin is decomposed into sulfate radicals and hydroxyl radicals as shown in formulas (4) to (5). The generated sulfate radicals and hydroxyl radicals completely oxidize and decompose the resin components in the stripping solution as shown in formulas (6) to (7). S2O8 2- → 2SO4 - (4) 2SO4 - + 2H2O → 2HSO4 - + 2OH· (5) C, H + 2SO4 - · → 2HSO4 - + xCO2+ yH2O (6) C, H + 2OH· → xCO2+ yH2O (7)

[0024] [Solution temperature during electrolysis] When electrolyzing a sulfuric acid solution (including an electrolytic sulfuric acid solution), it is desirable to set the temperature of the solution to 20 to 60°C. If the solution temperature during electrolysis is less than 20°C, the oxidant generation reaction at the anode will be slow. On the other hand, if the temperature during electrolysis is more than 60°C, the self-decomposition rate of the oxidant will increase and the oxidant will be reduced at the cathode. Therefore, it is desirable to set the temperature range to 20 to 60°C.

[0025] [Reduction in the rate of decomposition of coating film] The decomposition rate of the coating film in the electrolytic sulfuric acid solution decreases as the oxidizing agent concentration decreases. Therefore, the amount (concentration) of the coating film in the solution in which the coating film is dissolved can be grasped by electrical conductivity, and the decomposition rate can be judged. In addition, the amount (concentration) of the oxidizing agent can be grasped from the oxidation-reduction potential of the solution, and the decomposition rate of the coating film can be judged. When the organic coating dissolves, the electrical conductivity decreases and the redox potential decreases as the concentration of the organic insulator increases. The decomposition rate of the coating can be estimated from these values. There are methods to directly analyze the organic concentration, but it would be too expensive to incorporate such a device, so this method makes it easy to judge. Effect of the Invention

[0026] According to the present invention, by contacting the resin with a sulfuric acid solution, it is possible to suppress deterioration of the resin and completely peel off and remove the coating film. The coating film dissolved in the sulfuric acid solution is decomposed by an electrolytic sulfuric acid solution, and the sulfuric acid can be reused without being discarded. [Brief description of the drawings]

[0027] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of an apparatus used in an embodiment of the present invention. [Diagram 2] FIG. 1 is a process flow diagram illustrating an embodiment of a resin stripping method and a stripping solution regenerating method of the present invention. [Diagram 3] FIG. 13 is a flow diagram illustrating an embodiment in which an electrolytic sulfuric acid solution is used as the solution to be brought into contact with the coating film. [Figure 4] This is a process flow when multiple sulfuric acid tanks are prepared. [Diagram 5] Photographs of the appearance before and after the stripping solution regeneration process are shown. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] (Embodiment 1) FIG. 1 is a schematic cross-sectional view showing an example of an apparatus used in an embodiment of the present invention, and shows a treatment apparatus applicable to a method for stripping a resin coating film and a method for regenerating a stripping solution after the film has been stripped. The treatment device 1 has a treatment tank 5 and is a treatment device for removing the coating film of the applied resin 2, and also has an electrolytic sulfuric acid device 6 and is a treatment device for regenerating the stripping solution. In addition, in the treatment tank 5, stirring means such as an external air pump 4 and an air bubble generator 3 connected thereto may be provided in order to stir the inside of the tank as necessary.

[0029] An electrolytic sulfuric acid device 6 for regenerating the stripping solution is connected to the treatment tank 5. As a connection state to the treatment tank 5, a solution inlet path 9A and one end of a solution outlet path 9B are arranged, so that the solution can be introduced into the treatment tank 5 and discharged from the treatment tank 5. The other ends of the solution inlet path 9A and the outlet path 9B are connected to the liquid passage of the electrolytic cell 10, and a circulation pump 8 is provided in the solution outlet path 9B. By operating the circulation pump 8 to send the solution to the electrolytic cell side, the solution is sent to the outlet path 9B, the electrolytic cell 10, the inlet path 9A, and the treatment tank 5, enabling the solution to circulate.

[0030] In the electrolysis cell 10, a solution outlet path 9B is connected to the lower end of the cell, and a solution inlet path 9A is connected to the upper end of the cell, with an anode 10A and a cathode 10B installed in the flow path between them, and a bipolar electrode 10C installed between the anode 10A and the cathode 10B, so that the solution moves from bottom to top in the flow path between the electrodes. A DC power supply 7 for electrolysis is provided between the anode 10A and the cathode 10B. In this embodiment, a device having a bipolar electrode has been described, but the present embodiment is not particularly limited to the presence or absence of a bipolar electrode.

[0031] In this embodiment, the device shown in FIG. 1 is used. However, the method of electrolysis is not particularly limited, and is not limited to the device shown in FIG.

[0032] FIG. 2 is a flow chart showing the steps of the resin stripping method and the stripping solution regeneration method of the present invention, which will be described below. The method mainly comprises a coating film stripping process as a first step, in which the coating film is stripped and removed from the resin surface using a sulfuric acid solution, which is an acidic stripping liquid, and a stripping solution regeneration process as a second step, in which the sulfuric acid solution is electrolyzed to generate peroxodisulfuric acid through electrolysis, and peroxomonosulfuric acid and other oxidizing agents generated by the self-decomposition of peroxodisulfuric acid react with organic matter, which is a component of the coating film, and the organic matter is decomposed into carbon dioxide and water.

[0033] In the initial stripping step (step s1), a sulfuric acid solution is placed in a treatment tank 5. The sulfuric acid solution is adjusted to have a sulfuric acid concentration of 85 mass % or more and a temperature within a range of 45 to 80° C. The temperature of the sulfuric acid solution can be adjusted by heating it using a heater (not shown) installed in the tank. Resin 2 made of PC (polycarbonate) or PBT (polybutylene terephthalate) material on which a coating film (not shown) is formed is immersed in this sulfuric acid solution to bring the resin coating film into contact with the sulfuric acid solution. The coating film can be brought into contact with the sulfuric acid solution by immersing the resin in the sulfuric acid solution, but the coating film can also be brought into contact with the sulfuric acid solution by any other suitable method, such as spraying the sulfuric acid solution.

[0034] In the present invention, the resin may be either a natural resin or a synthetic resin, and may be either a thermoplastic resin or a thermosetting resin, and is not limited to a specific resin. The coating film formed on the surface of the resin is not limited to a specific one, and may be, for example, an acrylic resin, an acrylic urethane resin, or a polyurethane resin. The coating film color may be a solid color such as white, red, blue, or yellow, or a metallic or pearl coating color containing a glittering pigment such as metallic or pearl, and the paint composition and number of coats may vary depending on the coating color, but any coating color can be peeled off. The method of forming the coating film is not particularly limited.

[0035] When the resin 2 is immersed, air can be sent from an external air pump 4 to the air bubble generator 3 to appropriately agitate the sulfuric acid solution. When the resin 2 is immersed in the sulfuric acid solution, the coating film gradually peels off and is removed from the resin 2, and the coating film components dissolve in the sulfuric acid solution. When the coating film is removed, the process proceeds to a washing and drying step (step s2) for the resin 2.

[0036] In the washing and drying step (step s2), the resin 2 is taken out of the treatment tank 5, washed with a washing liquid, and dried. The washed and dried resin can be recycled.

[0037] The sulfuric acid solution in which the coating film has been dissolved is electrolyzed by an electrolytic sulfuric acid device 6 in an electrolytic sulfuric acid solution generating step (step s3). In the electrolytic sulfuric acid solution generating process, the circulation pump 8 is operated to circulate the sulfuric acid solution in the treatment tank 5 through the delivery line 9B, the electrolytic cell 10, the introduction line 9A, and the treatment tank 5. In the delivery line 9B, a cooler (not shown) or the like is provided to adjust the temperature of the sulfuric acid solution to 20 to 60° C. as a desirable electrolysis condition. In the electrolysis cell 10, a voltage is applied between the anode 10A and the cathode 10B by the DC power supply for electrolysis 7 to pass a current, and the sulfuric acid solution flowing through the flow path is electrolyzed by the anode 10A, the cathode 10B, and the bipolar electrode 10C to produce an electrolytic sulfuric acid solution such as peroxodisulfuric acid. The generated electrolytic sulfuric acid solution can be supplied to the treatment tank 5 via the treatment bath inlet 9A, and the process can proceed to the sulfuric acid solution regeneration step (step s4).

[0038] In the sulfuric acid solution regeneration step, the electrolytic sulfuric acid solution supplied to the treatment tank 5 is desirably heated to 60 to 100° C. by a heater provided in the introduction path or a heater provided in the treatment tank 5 to enhance the oxidizing power. In the treatment tank 5 where the electrolytic sulfuric acid solution is introduced, peroxodisulfuric acid (SO2O8 2― ) and peroxomonosulfuric acid (HSO5 ―) or hydrogen peroxide (H2O2) reacts with the organic matter that is a component of the coating dissolved in the sulfuric acid solution, breaking it down into carbon dioxide and water, and the sulfuric acid solution is regenerated. The regenerated sulfuric acid solution can be used again to peel off and remove the coating from another resin that has been coated with the coating.

[0039] (Embodiment 2) In the above-mentioned embodiment 1, the embodiment having one treatment tank has been described, but it may have a plurality of treatment tanks. The embodiment 2 will be described with reference to FIG. In this embodiment, there are two treatment tanks, a first treatment tank 5A and a second treatment tank 5B, and one electrolytic sulfuric acid device 6. The first treatment tank 5A and the second treatment tank 5B are each connected to the electrolytic sulfuric acid device 6 via an inlet path and an outlet path, and the first treatment tank 5A and the second treatment tank 5B can be connected to the electrolytic sulfuric acid device 6 by switching the inlet path and the outlet path. The electrolytic sulfuric acid device 6 is provided with an anode, a cathode, a bipolar electrode, and a DC power supply for electrolysis, as in the first embodiment.

[0040] In this embodiment, one treatment tank, for example, the first treatment tank 5A, is used to immerse the resin having the coating film in a sulfuric acid solution to peel off and remove the coating film (Figure A). When the decomposition rate of the coating film in the first treatment tank 5A decreases, it is determined that the peeling and removal capacity is insufficient, and the resin is removed. The sulfuric acid solution is circulated between the resin and the electrolytic sulfuric acid device 6, and electrolytic sulfuric acid is generated in the electrolytic sulfuric acid device 6, thereby decomposing the coating film components and regenerating sulfuric acid.

[0041] Meanwhile, in the other second treatment tank 5B, a sulfuric acid solution is stored in the treatment tank, and another resin having a coating film is immersed in the sulfuric acid solution to peel off and remove the coating film (Figure B). When the solubility in the second treatment tank 5B decreases in this state, the resin is removed, and the coating components are decomposed and sulfuric acid is regenerated while the solution is circulated between the second treatment tank 5B and the electrolytic sulfuric acid device 6. In the other first treatment tank 5A, the resin is immersed in the regenerated sulfuric acid solution to peel off the coating (Figure C). By repeating the above procedure, multiple resins can be continuously treated without interrupting the process. In this embodiment, the description has been given of a case in which two treatment tanks are provided, but the number of treatment tanks is not particularly limited.

[0042] In the above-mentioned first and second embodiments, the electrolytic sulfuric acid solution is generated by electrolyzing the sulfuric acid solution in which the coating film is dissolved. However, the electrolytic sulfuric acid solution may be prepared by reacting the sulfuric acid solution with a separately prepared electrolytic sulfuric acid solution. In this case, it is preferable to increase the temperature of the sulfuric acid solution to 60 to 100°C and react it with the electrolytic sulfuric acid solution. This increases the generation rate of sulfate radicals and / or hydroxyl radicals, and increases the decomposition rate of the coating film.

[0043] (Embodiment 3) In the above embodiments 1 and 2, a sulfuric acid solution other than an electrolytic sulfuric acid solution is initially prepared for peeling and removal of the coating film, but the coating film can also be peeled and removed using an electrolytic sulfuric acid solution. In the embodiment 3, the processing apparatus 1 used in the embodiment 1 can be used. The procedure will be described with reference to the flow chart of FIG.

[0044] First, the electrolytic sulfuric acid solution generating step (step s10) is carried out. The treatment tank 5 contains a sulfuric acid solution. The sulfuric acid solution in this case preferably has a sulfuric acid concentration of 80 mass % or more. Since the sulfuric acid solution is used as an electrolytic sulfuric acid solution, the oxidation-reduction potential is high, and it is possible to use a sulfuric acid solution with a lower concentration than a sulfuric acid solution that is not an electrolytic sulfuric acid solution. In the electrolytic sulfuric acid solution generating process, the circulation pump 8 is operated to circulate the sulfuric acid solution in the treatment tank 5 through the discharge line 9B, the electrolytic cell 10, the introduction line 9A, and the treatment tank 5. In the discharge line 9B, a cooler (not shown) or the like is provided to adjust the temperature of the sulfuric acid solution being sent to a temperature of 20 to 60° C. The temperature of the solution contained in the treatment tank 5 may be adjusted to this temperature. In the electrolysis cell 10, a voltage is applied between the anode 10A and the cathode 10B by the DC power supply for electrolysis 7 to pass a current, and the sulfuric acid solution flowing through the flow path is electrolyzed by the anode 10A, the cathode 10B, and the bipolar electrode 10C to produce an electrolytic sulfuric acid solution such as peroxodisulfuric acid. The produced electrolytic sulfuric acid solution is supplied to the treatment tank 5 via the treatment bath inlet 9A. When the sulfuric acid solution in the treatment tank 5 is produced as an electrolytic sulfuric acid solution, the process proceeds to a resin peeling step (step s11). Electrolysis by the electrolytic sulfuric acid device 6 is continued even during the resin peeling step.

[0045] In the resin peeling step (step s11), the resin 2 having the coating is immersed in an electrolytic sulfuric acid solution. The electrolytic sulfuric acid solution is preferably heated to a temperature in the range of 45 to 80°C. The electrolytic sulfuric acid solution comes into contact with the coating film, and effectively strips and removes the coating film. The electrolytic sulfuric acid solution has a stronger oxidizing power than a sulfuric acid solution that does not contain an oxidizing agent, so it oxidizes the surface of the coating film and makes it hydrophilic, thereby improving the strippability of the coating film. Furthermore, the coating film that has been peeled off from the resin dissolves in an electrolytic sulfuric acid solution.

[0046] The resin from which the coating film has been peeled off is transferred to a washing and drying step as in the previous embodiment (resin washing and drying step; step s12). At the same time, in the electrolytic sulfuric acid solution, the coating components are decomposed by the oxidizing agent in the electrolytic sulfuric acid solution, and the sulfuric acid solution is regenerated (sulfuric acid solution regeneration step; step s13). According to this embodiment, the coating film can be peeled off from the resin and the coating film components dissolved in the electrolytic sulfuric acid solution can be decomposed at the same time, so that the treatment can be carried out efficiently.

[0047] In relation to the above-mentioned embodiments 1 to 3, the decrease in the decomposition rate of the coating film can be measured by various methods, and can be judged by measuring the electrical conductivity of the solution. In addition, whether the organic matter in the treatment solution has been decomposed and the treatment solution has been regenerated can be judged by measuring the electrical conductivity and / or the redox potential. The electrical conductivity and the oxidation-reduction potential can be measured by a conventional method. The degree of decrease in the solubility of the coating film is determined based on a predetermined reference value, and the completion of peeling and removal can be judged based on this value.

[0048] Although the present invention has been described based on the above embodiment, appropriate modifications can be made without departing from the scope of the present invention. EXAMPLES

[0049] An embodiment of the present invention was carried out using a processing apparatus 1 shown in FIG. [Conditions for peeling test pieces] The effectiveness of the paint film removal using a sulfuric acid solution was evaluated. Test pieces were PC / PBT materials cut into 100 mm squares with paint films of the paint colors with different pigment concentrations shown in Table 1. In the embodiment, a PC / PBT material is used as the resin, but the resin is not limited to the PC / PBT material.

[0050] [Specifications of the peeling tank] -Volume of treatment tank 5: 25L PC / PBT material dimensions: 100mm x 100mm x thickness 4mm [Peeling conditions and results for PC / PBT materials with different paint colors] The peeling conditions for the coating were variously changed as shown in Table 1, and the state of the coating after the peeling treatment was visually observed.

[0051] [Table 1]

[0052] For the tensile strength and elastic modulus tests, dumbbell test pieces molded into the test piece shape 1A specified in JIS K 7161-1 and -2 were prepared by painting the test pieces in the same color for Example 1, Example 2, Comparative Example 1, and Comparative Example 2 shown in Table 1. In addition, for the Izod impact test, a parallel portion was cut out from the dumbbell test pieces prepared for the tensile strength and elastic modulus tests to prepare a bar-type test piece with a length of 80 mm, a width of 10 mm, and a thickness of 4 mm.

[0053] [Apparatus and method for measuring tensile strength and elastic modulus] The measuring device for tensile strength and elastic modulus was a 5-strand tensile tester 2005X-5 manufactured by Intesco Co., Ltd. The measuring method was in accordance with the provisions of JIS K 7161-1 and -2, and a tensile test was performed under the conditions of a test piece shape of 1A, a test environment temperature and humidity of 23°C and 50% RH, a chuck distance of 115 mm, and a tensile speed of 50 mm / min, to measure the tensile strength and elastic modulus.

[0054] [Measurement device and method for Izod impact test] The measuring device for the Izod impact test was a thermostatic chamber equipped impact tester DG-UB manufactured by Toyo Seiki Seisakusho Co., Ltd. The measurement method was in accordance with the provisions of JIS K 7110, and the Izod impact test was performed under the conditions of a test piece shape of length 80 mm x width 10 mm x thickness 4 mm, a test environment temperature of 23°C, notch processing, a hammer capacity of 2.75 J, and an impact direction of edgewise, to measure the impact strength.

[0055] Table 2 shows the measurement results of the tensile strength, elastic modulus, and Izod impact strength of Examples 1 and 2 and Reference Examples 1 and 2.

[0056] [Table 2]

[0057] As shown in Table 2, it was confirmed that both Examples 1 and 2 were almost equivalent to the virgin material (retention rate of 90% or more). Furthermore, the tensile strength, elastic modulus, and Izod impact strength of Reference Examples 1 and 2 all had retention rates of less than 90%. This is thought to be due to the high sulfuric acid concentration, which caused the PC / PBT material to deteriorate. However, the Reference Examples also obtained better results than the conventional method.

[0058] [Production of electrolytic sulfuric acid solution] The treatment conditions for electrolyzing the sulfuric acid solution are shown below. Volume of electrolysis cell 10: 0.5L Material of anode 10A and cathode 10B: Diamond electrode (diameter 150 mm) Bipolar electrode 10C material: Diamond electrode (diameter 150mm) ·Current density: 1~3A / dm 2 ·Solution circulation flow rate: 2~3L / min From the results before and after the regeneration process shown in Fig. 5, it was confirmed that the black solutions obtained in Examples 1 to 6 were completely decomposed and colorless by electrolyzing the solutions, as the resin in the stripping solutions was completely decomposed. The photograph in Fig. 5 shows the appearance of a solution before the regeneration process, which was a mixture of all the solutions before the regeneration process carried out in the examples, and a solution after the regeneration process, which was a mixture of all the solutions after the regeneration process carried out in the examples.

[0059] Example 2 [Conditions for peeling test pieces] The effectiveness of the electrolytic sulfuric acid solution in removing the paint film was evaluated. The test pieces used were PC / PBT materials cut into 100 mm squares with paint films of the paint colors with different pigment concentrations shown in Table 3. In the embodiment, a PC / PBT material is used as the resin, but the resin is not limited to the PC / PBT material.

[0060] [Specifications of the peeling tank] -Volume of treatment tank 5: 25L PC / PBT material dimensions: 100mm x 100mm x thickness 4mm [Peeling conditions and results for PC / PBT materials with different paint colors] The peeling conditions for the coating were variously changed as shown in Table 3, and the state of the coating after the peeling treatment was visually observed.

[0061] [Table 3]

[0062] For the tensile strength and elastic modulus tests, dumbbell test pieces molded into the test piece shape 1A specified in JIS K 7161-1 and -2 were prepared by painting the test pieces in the same color for Examples 10 and 11 and Comparative Examples 10 and 11 shown in Table 1. In addition, for the Izod impact test, a parallel portion was cut out from the dumbbell test pieces prepared for the tensile strength and elastic modulus tests to prepare a bar-type test piece with a length of 80 mm, a width of 10 mm, and a thickness of 4 mm.

[0063] [Apparatus and method for measuring tensile strength and elastic modulus] The measuring device for tensile strength and elastic modulus was a 5-strand tensile tester 2005X-5 manufactured by Intesco Co., Ltd. The measuring method was in accordance with the provisions of JIS K 7161-1 and -2, and a tensile test was performed under the conditions of a test piece shape of 1A, a test environment temperature and humidity of 23°C and 50% RH, a chuck distance of 115 mm, and a tensile speed of 50 mm / min, to measure the tensile strength and elastic modulus. [Measurement device and method for Izod impact test] The measuring device for the Izod impact test was a thermostatic chamber equipped impact tester DG-UB manufactured by Toyo Seiki Seisakusho Co., Ltd. The measurement method was in accordance with the provisions of JIS K 7110, and the Izod impact test was performed under the conditions of a test piece shape of length 80 mm x width 10 mm x thickness 4 mm, a test environment temperature of 23°C, notch processing, a hammer capacity of 2.75 J, and an impact direction of edgewise, to measure the impact strength.

[0064] Table 4 shows the measurement results of the tensile strength, elastic modulus, and Izod impact strength of Examples 10 and 11 and Reference Examples 10 and 11.

[0065] [Table 4]

[0066] As shown in Table 4, it was confirmed that both Examples 10 and 11 were almost equivalent to the virgin material (retention rate of 90% or more). Furthermore, the tensile strength, elastic modulus, and Izod impact strength of Reference Examples 10 and 11 all had retention rates of less than 90%. This is thought to be due to the high sulfuric acid concentration, which caused the PC / PBT material to deteriorate. However, the Reference Examples also obtained better results than the conventional method.

[0067] [Production of electrolytic sulfuric acid solution] The treatment conditions for electrolyzing the sulfuric acid solution are shown below. Volume of electrolysis cell 10: 0.5L Material of anode 10A and cathode 10B: Diamond electrode (diameter 150 mm) Bipolar electrode 10C material: Diamond electrode (diameter 150mm) ·Current density: 1~3A / dm2 ·Solution circulation flow rate: 2~3L / min

[0068] As in Figure 5, from the results before and after the regeneration treatment, it was confirmed that the black solutions obtained in Examples 10 to 15 had become colorless by electrolyzing the solutions, as the resin in the stripping solutions was completely decomposed. [Explanation of symbols]

[0069] 1 Processing equipment 2. Resin 3. Bubble Generator 4. Air pump 5 Treatment tank 5A First treatment tank 5B Second treatment tank 6 Electrolytic sulfuric acid equipment 7 DC power supply for electrolysis 8 Circulation Pump 9A Treatment bath inlet 9B Processing bath delivery path 10 Electrolysis Cell 10A anode 10B Cathode 10C Bipolar Electrode

Claims

1. A coating film peeling treatment method for peeling and removing a coating film formed on a surface of a resin from the resin, comprising the steps of: A coating film stripping treatment method comprising contacting a coating film formed on a resin with a sulfuric acid solution to strip and remove the coating film from the resin, and decomposing organic matter, which is a component of the coating film, dissolved in the sulfuric acid solution into carbon dioxide and water using an electrolytic sulfuric acid solution.

2. 2. The coating film stripping method according to claim 1, wherein an electrolytic sulfuric acid solution is produced by electrolysis by passing an electric current through a part or all of the sulfuric acid solution in which the coating film has been dissolved.

3. 2. The coating film stripping method according to claim 1, wherein the sulfuric acid solution brought into contact with the coating film is an electrolytic sulfuric acid solution.

4. 4. The coating film stripping method according to claim 3, further comprising passing an electric current through a part or all of the electrolytic sulfuric acid solution in which the coating film has been dissolved, thereby carrying out electrolysis.

5. 2. The coating film stripping method according to claim 1, wherein the temperature of the sulfuric acid solution in which the coating film is dissolved is raised to 60 to 100° C., and the sulfuric acid solution is reacted with the electrolytic sulfuric acid solution for the decomposition.

6. The coating film stripping method according to any one of claims 1 to 5, wherein the sulfuric acid solution brought into contact with the coating film has a concentration of 85.0 mass % or more and a temperature within the range of 45 to 80°C.

7. The coating film peeling treatment method according to claim 3 or 4, wherein the electrolytic sulfuric acid solution to be brought into contact with the coating film has a concentration of 80.0 mass% or more and a temperature within the range of 45 to 80 ° C.

8. The coating film stripping method according to claim 2 or 4, wherein the solution temperature during the electrolysis is set to 20 to 60°C.

9. The coating film stripping method according to claim 1, further comprising the steps of: preparing a plurality of tanks for stripping and removing the coating film; terminating the coating film stripping and removal in a given tank according to a decrease in the decomposition rate of the coating film in the given tank; and electrolyzing the sulfuric acid solution in the given tank after the coating film stripping and removal has been completed.

10. 10. The coating film stripping method according to claim 9, wherein, upon completion of the coating film stripping and removal, stripping and removal of the coating film in another tank is continued or started.

11. 11. The coating film stripping method according to claim 1, 9 or 10, wherein the decomposition rate of the coating film is judged by the electrical conductivity and / or the oxidation-reduction potential of the solution.

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