Aqueous thinner waste liquid recycling system and aqueous thinner waste liquid recycling method

Abstract

The purpose of the present invention is to provide an aqueous thinner waste liquid recycling system that can generate a recycled thinner having almost no malodor and capable of maintaining cleaning performance. This aqueous thinner waste liquid recycling system 1 comprises a circulation line 10, a filtration membrane module 21, and a recycled thinner generation unit 60. The circulation line 10 circulates an aqueous thinner waste liquid W1 including a paint material discharged from a paint booth. The filtration membrane module 21 is provided on the circulation line 10 and separates the aqueous thinner waste liquid W1 into a concentrated liquid W2 and a filtrate W3. The recycled thinner generation unit 60 stores the filtrate W3 transmitted through the filtration membrane module 21, and mixes a new thinner W4 with the stored filtrate W3 to generate a reusable recycled thinner. Selected drawing: FIG. 1.

Description

Aqueous thinner waste liquid recycling system, aqueous thinner waste liquid recycling method

[0001] The present invention relates to a system and method for recycling aqueous thinner waste liquid, which reuses aqueous thinner discharged from a painting booth.

[0002] Traditionally, when painting substrates such as automobile bodies and bumpers, it is necessary to wash off paint remaining in the sprayer with thinner. While solvent-based paints have traditionally been used for topcoating substrates, the use of water-soluble paints (water-based paints) has been promoted in recent years from the perspective of environmental protection. In the case of solvent-based paints, solvent thinners are used as cleaning thinners, and the waste solvent thinners are recycled by distillation. On the other hand, in the case of water-soluble paints, aqueous thinners are used as cleaning thinners. Because the waste water from aqueous thinners (aqueous thinner waste liquid) contains a high proportion of water, recycling it by distillation requires a great deal of energy. Therefore, currently, aqueous thinner waste liquid is not recycled but is collected and incinerated by waste disposal companies, resulting in a problem of a high environmental impact, as the amount used equals the amount disposed of.

[0003] A membrane filtration system for separating and recovering aqueous thinner waste liquid has also been proposed (see, for example, Patent Document 1). In this membrane filtration system, the aqueous thinner waste liquid is separated into a concentrated liquid and a filtrate using a filtration membrane (e.g., a UF membrane) while maintaining a constant supply pressure for the aqueous thinner waste liquid. Then, by mixing a chemical substance such as an amine with the filtrate, a reusable recycled thinner can be produced.

[0004] JP 2009-247977 A

[0005] However, recycled thinners produced by adding chemical substances have a strong odor, which makes it impossible to use recycled thinners for cleaning.

[0006] The present invention has been made in view of the above-mentioned problems, and its object is to provide an aqueous thinner waste liquid recycling system and an aqueous thinner waste liquid recycling method that can produce recycled thinner that is almost odorless and can maintain its cleaning properties.

[0007] In order to solve the above problems, the invention described in claim 1 is an aqueous thinner waste liquid reuse system characterized by comprising: a circulation line for circulating aqueous thinner waste liquid containing paint components discharged from a painting booth; a filtration membrane module provided on the circulation line for separating the aqueous thinner waste liquid into a concentrated liquid and a filtrate; and a recycled thinner production unit that stores the filtrate that has passed through the filtration membrane module and mixes the stored filtrate with new thinner to produce reusable recycled thinner.

[0008] In the invention described in claim 1, aqueous thinner waste liquid is separated into a concentrate and a filtrate using a filtration membrane module, and then the separated filtrate is mixed with new thinner to produce recycled thinner. Therefore, unlike conventional technologies for producing recycled thinner, no chemicals are mixed, and recycled thinner with almost no unpleasant odor can be obtained. Furthermore, by controlling the concentration of the filtrate and the mixing ratio of the filtrate to new thinner, the cleaning properties of the recycled thinner can be maintained.

[0009] The invention described in claim 2 is characterized in that, in claim 1, the recycled thinner production section includes a mixing tank for adding the new thinner and a filtrate tank for storing the filtrate before mixing.

[0010] In the invention described in claim 2, the filtrate before mixing with new thinner is temporarily stored in the filtrate tank, and then a certain amount of filtrate is transferred to the mixing tank before new thinner is added. This makes it difficult for the mixing ratio of the filtrate and new thinner to fluctuate. This stabilizes the quality of the recycled thinner produced. In addition, the stable mixing ratio makes the mixing process relatively easy.

[0011] The invention described in claim 3 is based on claim 2 and is characterized in that it includes a backwash pump that cleans the filtration membrane provided in the filtration membrane module by supplying the filtrate stored in the filtrate tank from the downstream side to the upstream side of the filtration membrane module.

[0012] When the aqueous thinner wastewater is separated into a concentrated solution and a filtrate using a filtration membrane module, impurities contained in the aqueous thinner wastewater accumulate on the upstream surface of the filtration membrane, which can cause the filtration membrane to become clogged. Therefore, in the invention described in claim 3, a backwash pump is driven to supply the filtrate stored in the filtrate tank from the downstream side of the filtration membrane module (filtration membrane). This allows the impurities accumulated on the upstream surface of the filtration membrane to be washed away, making it easy to regenerate the filtration membrane.

[0013] The invention described in claim 4 is based on claim 2 or 3 and is characterized in that it further comprises a filtrate concentration sensor that measures the concentration of the filtrate stored in the filtrate tank, and a control device that performs control to determine the amount of new thinner to be added to the mixing tank based on the concentration of the filtrate measured by the filtrate concentration sensor.

[0014] In the invention described in claim 4, the control device determines the amount of new thinner to be added to the mixing tank based on the measured concentration of the filtrate, making it possible to add an appropriate amount of new thinner based on the determined amount. This makes it less likely that the mixing ratio of the filtrate and the new thinner will fluctuate, thereby stabilizing the quality of the recycled thinner produced.

[0015] The invention described in claim 5 is based on claim 1 and further comprises a waste liquid tank that is provided on the circulation line and stores the aqueous thinner waste liquid and the concentrated liquid, a waste liquid concentration sensor that measures the concentration of the aqueous thinner waste liquid stored in the waste liquid tank, a concentrated liquid concentration sensor that measures the concentration of the concentrated liquid stored in the waste liquid tank, and a control device that performs control to detect abnormalities in the filtration membrane module based on the concentration of the aqueous thinner waste liquid measured by the waste liquid concentration sensor and the concentration of the concentrated liquid measured by the concentrated liquid concentration sensor.

[0016] In the invention described in claim 5, for example, when the concentration of the aqueous thinner waste liquid or the concentration of the concentrated liquid is high, the control device can detect that an abnormality has occurred in the filtration membrane module, specifically, an abnormality such as a tear in the filtration membrane of the filtration membrane module.

[0017] Examples of filtration membranes included in the filtration membrane module include UF membranes (ultrafiltration membranes), NF membranes (nanofiltration membranes), RO membranes (reverse osmosis membranes), and MF membranes (microfiltration membranes). The pore sizes of nanofiltration membranes and reverse osmosis membranes are smaller than those of ultrafiltration membranes, making them more likely to clog immediately after the aqueous thinner waste liquid passes through, resulting in the difficulty of securing the filtrate volume. Furthermore, the pore sizes of microfiltration membranes are larger than those of ultrafiltration membranes, resulting in problems such as paint pigments passing through and coloring the filtrate, or resin components (polymer regions) passing through. Therefore, it is preferable that the filtration membrane included in the filtration membrane module be an ultrafiltration membrane (claim 6).

[0018] The invention described in claim 7 is a method for reusing aqueous thinner waste liquid, characterized by comprising a separation step of separating aqueous thinner waste liquid containing paint components discharged from a painting booth into a concentrated liquid and a filtrate, and a recycled thinner production step of storing the filtrate and mixing the stored filtrate with new thinner to produce reusable recycled thinner.

[0019] In the invention described in claim 7, the aqueous thinner waste liquid is separated into a concentrated liquid and a filtrate in the separation step, and then the recycled thinner is produced by mixing the separated filtrate with new thinner in the recycled thinner production step. This, unlike conventional techniques for producing recycled thinner, does not involve mixing chemical substances, so recycled thinner with almost no unpleasant odor can be obtained. Furthermore, by controlling the concentration of the filtrate and the mixing ratio of the filtrate to new thinner, the cleaning properties of the recycled thinner can be maintained.

[0020] As described above in detail, according to the inventions described in claims 1 to 7, recycled thinners that are almost odorless and can maintain their cleaning properties can be produced.

[0021] The present invention relates to a system for reusing aqueous thinner waste liquid, a method for reusing the ...

[0022] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

[0023] As shown in Figure 1, the aqueous thinner waste liquid recycling system 1 is a system that reuses aqueous thinner waste liquid W1 containing paint components discharged from a painting booth. The aqueous thinner waste liquid recycling system 1 includes a circulation line 10 that circulates the aqueous thinner waste liquid W1 and three filtration membrane modules 21. Each filtration membrane module 21 is provided on the circulation line 10 and separates the aqueous thinner waste liquid W1 into a concentrate W2 and a filtrate W3. The aqueous thinner waste liquid recycling system 1 also includes a waste liquid tank 31. The waste liquid tank 31 is provided on the circulation line 10 and stores the aqueous thinner waste liquid W1 and the concentrate W2.

[0024] The circulation line 10 is made up of a supply flow path 11 and a return flow path 12. The supply flow path 11 is a flow path that supplies the aqueous thinner waste liquid W1 from the waste liquid tank 31 to each filtration membrane module 21, and the return flow path 12 is a flow path that returns the concentrated liquid W2 from each filtration membrane module 21 to the waste liquid tank 31.

[0025] 1, the waste liquid tank 31 is provided with a liquid level sensor 32 and a waste liquid concentration sensor 33. The liquid level sensor 32 is a sensor that measures the liquid levels of the aqueous thinner waste liquid W1 and concentrated liquid W2 stored in the waste liquid tank 31. The waste liquid concentration sensor 33 is an insertion-type refraction concentration sensor that measures the concentration of the aqueous thinner waste liquid W1 stored in the waste liquid tank 31.

[0026] Also installed on the supply flow path 11 are a circulation pump 41, a temperature sensor 42, a fluid concentration sensor 43, a paint filter 44, a pressure gauge 45, a flow rate sensor 46, a pressure sensor 47, and an automatic valve 48. The circulation pump 41 supplies the aqueous thinner waste liquid W1 and the concentrated liquid W2 from the waste liquid tank 31 to each filtration membrane module 21. The temperature sensor 42 is located downstream of the circulation pump 41 and measures the temperature of the fluid (specifically, the aqueous thinner waste liquid W1 and the concentrated liquid W2) flowing through the supply flow path 11. The fluid concentration sensor 43 is a water-passing type refraction concentration sensor located downstream of the temperature sensor 42 and measures the concentration of the fluid flowing through the supply flow path 11 and outputs a fluid concentration measurement signal to the CPU of the control device 101. The paint filter 44 is located downstream of the fluid concentration sensor 43 and serves to separate foreign matter (debris, particles) from the fluid flowing through the supply flow path 11. The pressure gauges 45 are disposed upstream and downstream of the paint filter 44, respectively, and measure the pressures in the supply passage 11 on the upstream and downstream sides. The pressure loss in the paint filter 44 can be obtained by calculating the differential pressure between the two. This pressure loss enables detection of abnormalities such as filter clogging. The flow rate sensor 46 is disposed downstream of the paint filter 44 and measures the flow rate of the fluid flowing through the supply passage 11 and outputs a fluid flow rate measurement signal to the CPU. The pressure sensor 47 is disposed downstream of the flow rate sensor 46 and measures the pressure of the fluid flowing through the supply passage 11 and outputs a fluid pressure measurement signal to the CPU. The automatic valve 48 is disposed downstream of the pressure sensor 47 and switches the supply passage 11 between an open state and a closed state. In this embodiment, the automatic valve 48 is an electrically operated valve operated by a motor.

[0027] As shown in FIG. 1 , a pressure sensor 51, a concentrate concentration sensor 52, and a flow rate sensor 53 are installed on the return flow path 12. The pressure sensor 51 measures the pressure of the concentrate W2 flowing through the return flow path 12 and outputs a concentrate pressure measurement signal to the CPU of the control device 101. The concentrate concentration sensor 52 is a water-passing type refraction concentration sensor located downstream of the pressure sensor 51 and measures the concentration of the concentrate W2 flowing through the return flow path 12 and stored in the waste tank 31 and outputs a concentrate concentration measurement signal to the CPU. The flow rate sensor 53 is located downstream of the concentrate concentration sensor 52 and measures the flow rate of the concentrate W2 passing through the filtration membrane module 21 and flowing through the return flow path 12 and outputs a concentrate flow rate measurement signal to the CPU.

[0028] The supply flow path 11 branches into three first flow paths 13 downstream (toward the filtration membrane module 21), and each first flow path 13 is connected to the inlet of one of the three filtration membrane modules 21. Each filtration membrane module 21 is located downstream of the automatic valve 48 and includes a filtration membrane that separates the aqueous thinner waste liquid W1 into a concentrate W2 and a filtrate W3. The filtration membrane module 21 of this embodiment is a cross-flow module that is applicable to internal pressure filtration. The filtration membrane of this embodiment is a UF membrane (ultrafiltration membrane). The concentrate outlet of each filtration membrane module 21 is connected to the return flow path 12 via the second flow path 14. The filtrate outlet 22 of each filtration membrane module 21 is connected to the filtrate recovery flow path 15.

[0029] As shown in FIG. 1 , the aqueous thinner waste liquid reuse system 1 includes a recycled thinner production unit 60. The recycled thinner production unit 60 stores filtrate W3 that has permeated the filtration membrane module 21 and mixes the stored filtrate W3 with new thinner W4 to produce reusable recycled thinner. Specifically, the recycled thinner production unit 60 includes a mixing tank 61 and a filtrate tank 62. The filtrate tank 62 is connected to the filtrate recovery flow path 15 and stores the filtrate W3 before mixing with the new thinner W4. The mixing tank 61 is connected to the filtrate tank 62 via the filtrate transfer flow path 16, and new thinner W4 is added to the filtrate W3. In this embodiment, the new thinner W4 is an aqueous thinner containing, but not limited to, diisopropanolamine, propylene glycol, a surfactant, an ethylene oxide adduct of an acetylenic diol, a polyether-modified siloxane, potassium oxide, and silicon dioxide.

[0030] Additionally, a pressure sensor 71, a filtrate concentration sensor 72, a flow rate sensor 73, and an automatic valve 74 are installed on the filtrate recovery channel 15. The pressure sensor 71 measures the pressure of the filtrate W3 flowing through the filtrate recovery channel 15 and outputs a filtrate pressure measurement signal to the CPU of the control device 101. The filtrate concentration sensor 72 is a water-passing type refraction concentration sensor located downstream of the pressure sensor 71. It measures the concentration of the filtrate W3 flowing through the filtrate recovery channel 15 and stored in the filtrate tank 62 and outputs a filtrate concentration measurement signal to the CPU. The flow rate sensor 73 is located downstream of the filtrate concentration sensor 72 and measures the flow rate of the filtrate W3 flowing through the filtrate recovery channel 15 and outputs a first filtrate flow rate measurement signal to the CPU. The automatic valve 74 is located downstream of the flow rate sensor 73 and switches the filtrate recovery channel 15 between an open state and a closed state. In this embodiment, the automatic valve 74 is an electrically operated valve operated by a motor.

[0031] 1 , a backwash pump 81, a pressure gauge 82, a flow rate sensor 83, and an automatic valve 84 are installed on the filtrate transfer flow path 16. The pressure gauge 82 is located downstream of the backwash pump 81 and is an instrument that measures the pressure in the filtrate transfer flow path 16. The flow rate sensor 83 is located downstream of the pressure gauge 82 and is configured to measure the flow rate of filtrate W3 flowing through the filtrate transfer flow path 16 and output a second filtrate flow rate measurement signal to the CPU of the control device 101. The automatic valve 84 is located downstream of the flow rate sensor 83 and is configured to switch the filtrate transfer flow path 16 between an open state and a closed state. Note that the automatic valve 84 in this embodiment is an electrically operated valve operated by a motor.

[0032] The aqueous thinner waste liquid reuse system 1 also includes a backwash flow path 17 that connects the filtrate recovery flow path 15 and the filtrate transfer flow path 16. The upstream end of the backwash flow path 17 is connected between the pressure gauge 82 and the flow rate sensor 83 in the filtrate transfer flow path 16, and the downstream end of the backwash flow path 17 is connected between the flow rate sensor 73 and the automatic valve 74 in the filtrate recovery flow path 15. An automatic valve 91 is also installed on the backwash flow path 17. The automatic valve 91 is located downstream of the pressure gauge 82 and switches the backwash flow path 17 between an open state and a closed state. The automatic valve 91 in this embodiment is an electrically operated valve operated by a motor.

[0033] When the backwash flow path 17 is closed and the filtrate transfer flow path 16 is open, the backwash pump 81 flows the filtrate W3 stored in the filtrate tank 62 through the filtrate transfer flow path 16 and then through the mixing tank 61. On the other hand, when the backwash flow path 17 is open and the filtrate transfer flow path 16 is closed, the backwash pump 81 flows the filtrate W3 stored in the filtrate tank 62 through the filtrate transfer flow path 16, then through the backwash flow path 17, then through the filtrate recovery flow path 15, and then through the filtrate outlet 22 of the filtration membrane module 21. In this case, the backwash pump 81 supplies the filtrate W3 from the downstream side to the upstream side of the filtration membrane module 21, thereby cleaning the filtration membrane provided in the filtration membrane module 21.

[0034] 1 , the mixing tank 61 is provided with a liquid level sensor 63 and a thinner concentration sensor 64. The liquid level sensor 63 is a sensor that measures the liquid level of the recycled thinner (filtrate W3 and new thinner W4) stored in the mixing tank 61. The thinner concentration sensor 64 is an insertion-type refraction concentration sensor that measures the concentration of the recycled thinner stored in the mixing tank 61.

[0035] The mixing tank 61 is connected to a thinner supply passage 18. A thinner supply pump 92 is installed on the thinner supply passage 18. The thinner supply pump 92 supplies the recycled thinner produced in the mixing tank 61 to the painting booth.

[0036] Next, the electrical configuration of the aqueous thinner waste liquid reuse system 1 will be described.

[0037] As shown in FIG. 1 , the aqueous thinner waste liquid reuse system 1 includes a control device 101 for overall control of the entire system. The control device 101 is composed of a CPU, ROM, RAM, input / output circuits, etc. Automatic valves 48, 74, 84, and 91 are electrically connected to the CPU via their respective driver circuits (not shown). The CPU is also electrically connected to liquid level sensors 32 and 63, waste liquid concentration sensor 33, fluid concentration sensor 43, flow rate sensors 46, 53, 73, and 83, pressure sensors 47, 51, and 71, thinner concentration sensor 64, concentrated liquid concentration sensor 52, and filtrate concentration sensor 72 via a relay board 102. The ROM stores a program for controlling the aqueous thinner waste liquid reuse system 1.

[0038] The CPU of the control device 101 performs control to detect an abnormality in the filtration membrane module 21 based on the concentration of the aqueous thinner waste liquid W1 measured by the waste liquid concentration sensor 33 and the concentration of the concentrated liquid W2 measured by the concentrated liquid concentration sensor 52. For example, if the concentration of the aqueous thinner waste liquid W1 or the concentration of the concentrated liquid W2 is high, the CPU can detect that an abnormality such as a break has occurred in the filtration membrane of the filtration membrane module 21.

[0039] Next, a method for reusing aqueous thinner waste liquid using the aqueous thinner waste liquid reusing system 1 will be described.

[0040] First, a painting process is carried out in a painting booth to paint objects such as automobile bodies and bumpers. The painting process includes a primer coating process and a top coat coating process, and the top coat coating process includes a base coating process and a clear coating process. In this embodiment, the base coating process is described. In this case, paint remaining in the paint sprayer or the like after painting the object is washed away with aqueous thinner. As a result, the aqueous thinner becomes aqueous thinner waste liquid W1 containing paint components. The aqueous thinner waste liquid W1 is discharged from the painting booth and charged into a waste liquid tank 31.

[0041] In the subsequent separation step, the aqueous thinner waste liquid W1 is separated into a concentrated liquid W2 and a filtrate W3. Specifically, the CPU of the control device 101 first controls the supply flow path 11 to be open by driving the automatic valve 48. As a result, the aqueous thinner waste liquid W1 in the waste liquid tank 31 is passed through the supply flow path 11 and the first flow path 13 by the circulation pump 41 and supplied to the filtration membrane module 21.

[0042] The aqueous thinner waste liquid W1 is separated into a concentrated liquid W2 and a filtrate W3 when passing through the filtration membrane in the filtration membrane module 21. More specifically, the aqueous thinner waste liquid W1 becomes the filtrate W3 when passing through the filtration membrane.

[0043] The filtrate W3 is then discharged from the filtrate outlet 22 of the filtration membrane module 21. The CPU also controls the automatic valve 74 to switch the filtrate recovery flow path 15 to an open state. As a result, the filtrate W3 discharged from the filtrate outlet 22 passes through the filtrate recovery flow path 15 and is stored in the filtrate tank 62. The filtrate concentration sensor 72 measures the concentration of the filtrate W3 flowing through the filtrate recovery flow path 15 and outputs a filtrate concentration measurement signal to the CPU. Meanwhile, the remaining aqueous thinner waste liquid W1 that did not become filtrate W3 is concentrated to become concentrated liquid W2, which is discharged from the outlet of the filtration membrane module 21 without passing through the filtration membrane. The concentrated liquid W2 discharged from the outlet of the filtration membrane module 21 passes through the second flow path 14 and the return flow path 12 and is returned to the waste liquid tank 31.

[0044] In the subsequent recycled thinner production step, the filtrate W3 is stored in the mixing tank 61, and new thinner W4 is mixed with the stored filtrate W3 to produce a reusable recycled thinner. More specifically, the CPU of the control device 101 controls the automatic valve 84 to switch the filtrate transfer flow path 16 to an open state. As a result, the filtrate W3 stored in the filtrate tank 62 is discharged from the storage tank 62, passes through the filtrate transfer flow path 16, and is stored in the mixing tank 61.

[0045] Next, the CPU controls the amount of new thinner W4 to be added to the mixing tank 61 based on the concentration of the filtrate W3 indicated by the filtrate concentration measurement signal from the filtrate concentration sensor 72. Specifically, the CPU determines whether the concentration of the filtrate W3 is equal to or lower than a predetermined concentration (%). If the CPU determines that the concentration of the filtrate W3 is equal to or lower than the predetermined concentration, the CPU executes a process to add new thinner W4 to the mixing tank 61 based on the determined amount. Specifically, for example, a tank (not shown) storing new thinner W4 is connected to the mixing tank 61 via piping (not shown). The CPU then adds a certain amount of new thinner W4 to the mixing tank 61 by controlling the operation of a pump installed on the piping or by switching a valve installed on the piping to an open state. In this embodiment, new thinner W4 is added so that the volume of the new thinner W4 is 60% and the volume of the filtrate W3 is 40%. As a result, the filtrate W3 and the new thinner W4 are mixed to produce recycled thinner. In this embodiment, a certain amount of filtrate W3 is stored in the mixing tank 61, and then the new thinner W4 is added. However, the new thinner W4 may be added while the filtrate W3 is continuously stored in the mixing tank 61.

[0046] The produced recycled thinner is then discharged from the mixing tank 61 by the thinner supply pump 92 and supplied to the painting booth through the thinner supply passage 18. This allows the recycled thinner to be used in the painting booth to wash off paint remaining in the painting machine, etc.

[0047] Next, the evaluation method and results of the recycled thinner will be described.

[0048] First, measurement samples were prepared as follows. A recycled thinner containing 50% new thinner by volume and 50% filtrate by volume was prepared, and designated Sample 1 (see Figures 2 and 3). A recycled thinner containing 60% new thinner by volume and 40% filtrate by volume was prepared, and designated Sample 2 (see Figures 2 and 3). A recycled thinner containing 70% new thinner by volume and 30% filtrate by volume was prepared, and designated Sample 3 (see Figures 2 and 3). A recycled thinner containing 80% new thinner by volume and 20% filtrate by volume was prepared, and designated Sample 4 (see Figures 2 and 3).

[0049] Next, the coating object (automobile body and bumper) was painted using a sprayer. Then, after cleaning the sprayer using each measurement sample (Samples 1 to 4), the cleaning condition was visually confirmed. Specifically, after a primer (white) was applied as a base coat, the sprayer was cleaned using each measurement sample, and the cleaning condition was confirmed. In this embodiment, the automobile body was painted using Primer A, and the bumper was painted using Primer B, which was different from Primer A. After a base coat was applied using a water-based solid paint (red), the sprayer was cleaned using each measurement sample, and the cleaning condition was confirmed. Furthermore, after a base coat was applied using a water-based metallic paint (silver), the sprayer was cleaned using each measurement sample, and the cleaning condition was confirmed. Furthermore, after a base coat was applied using a water-based solid paint (black), the sprayer was cleaned using each measurement sample, and the cleaning condition was confirmed. The painting → cleaning → confirmation steps were each performed multiple times (three times in this embodiment).

[0050] As a result, Sample 4 was confirmed to have good washability, because no paint remained on the various parts of the sprayer (external parts such as the rim, inner wall, and feed tube insertion port, and internal parts such as the dam, paint hole, and center cone) whether it was used to base coat an automobile body (see Figure 2) or a bumper (see Figure 3) (see "O" for Sample 4 in Figures 2 and 3). On the other hand, Sample 3 was confirmed to have poor washability when used to base coat a bumper using a water-based solid paint (red), because paint remained on parts of the sprayer (see "X" for Sample 3 in Figure 3). Furthermore, Sample 2 was confirmed to have good washability when used to base coat an automobile body (see "O" for Sample 2 in Figure 2), but poor washability when used to base coat a bumper (see "X" for Sample 2 in Figure 3). Furthermore, it was confirmed that Sample 1 did not have good washability, whether it was used to paint the base coat of an automobile body or a bumper (see "X" for Sample 1 in Figures 2 and 3). It was also confirmed that when an undercoat paint using a primer was used, Samples 1 to 4 did not have good washability (see "X" in the Primer column in Figures 2 and 3). Primers dry quickly and are completely dry by the time of cleaning, which is thought to be why washability deteriorates.

[0051] Therefore, it was confirmed that when base painting an automobile body, good cleaning properties are achieved if the volume of new thinner contained in the recycled thinner is 60% or more. On the other hand, when base painting a bumper, good cleaning properties are achieved if the volume of new thinner contained in the recycled thinner is 80% or more.

[0052] In addition, after base coating of the substrates using the water-based metallic paint (silver), the coating machine was cleaned using each measurement sample. Next, a base coating was applied to a substrate other than the one coated with the water-based metallic paint (silver) using the water-based solid paint (black). At this time, it was visually confirmed whether or not the water-based metallic paint was mixed in with the paint sprayed onto the substrate.

[0053] As a result, it was confirmed that when painting car bodies, if the sprayer is washed with recycled thinner that is 60% new thinner by volume and 40% filtrate by volume, the water-based metallic paint will not be mixed in. On the other hand, when painting bumpers, if the sprayer is washed with recycled thinner that is 80% new thinner by volume and filtrate by volume, the water-based metallic paint will not be mixed in.

[0054] Therefore, according to this embodiment, the following effects can be obtained.

[0055] (1) In the aqueous thinner waste liquid recycling system 1 of this embodiment, aqueous thinner waste liquid W1 is separated into a concentrated liquid W2 and a filtrate W3 using a filtration membrane module 21, and then the separated filtrate W3 is mixed with new thinner W4 to produce recycled thinner. Therefore, unlike conventional techniques for producing recycled thinner, this system does not involve the mixing of chemicals such as amines, and therefore produces recycled thinner with almost no unpleasant odor. Furthermore, by controlling the concentration of the filtrate W3 to ensure its quality, for example, when painting an automobile body, the mixing ratio of the filtrate W3 to new thinner W4 can be controlled to 40% filtrate W3 and 60% new thinner W4, thereby maintaining the cleaning properties of the recycled thinner. This is thought to be because metal ion components such as barium and iron, which are detrimental to cleaning, are kept at low concentrations.

[0056] (2) In this embodiment, instead of using only new thinner W4 to clean paint remaining in a sprayer, etc., the paint is cleaned using recycled thinner obtained by mixing new thinner W4 and filtrate W3. This reduces the amount of new thinner W4 used for cleaning, and therefore the amount of new thinner W4 purchased can be reduced.

[0057] (3) In this embodiment, the aqueous thinner waste liquid W1 is separated into a concentrated liquid W2 and a filtrate W3 by the filtration membrane module 21. The filtrate W3 is then mixed with new thinner W4 to become recycled thinner and be reused. The concentrated liquid W2 is returned to the waste liquid tank 31, mixed with the aqueous thinner waste liquid W1, and supplied again to the filtration membrane module 21. As a result, the amount of concentrated liquid W2 discarded is significantly reduced, thereby reducing the cost of disposal and the CO2 generated in the disposal process. ２ can be reduced.

[0058] (4) In this embodiment, three filtration membrane modules 21 are used to separate the aqueous thinner waste liquid W1 into a concentrated liquid W2 and a filtrate W3. This allows a larger amount of filtrate W3 to be obtained in a shorter time than when using, for example, only one or two filtration membrane modules 21. Therefore, by mixing the obtained filtrate W3 with new thinner W4, recycled thinner can be efficiently produced. Furthermore, even if the filtration membrane of one filtration membrane module 21 becomes clogged, the remaining filtration membrane modules 21 can be used to continue the separation process.

[0059] The above embodiment may be modified as follows.

[0060] The aqueous thinner waste liquid reuse system 1 in the above embodiment includes three filtration membrane modules 21. However, the aqueous thinner waste liquid reuse system 1 may include one or two filtration membrane modules 21, or may include four or more filtration membrane modules 21.

[0061] The filtration membrane module 21 in the above embodiment is a module that is applicable to internal pressure filtration, but may be a module that is applicable to external pressure filtration.

[0062] In the above embodiment, the CPU of the control device 101 automatically performs the process of adding new thinner W4 to the mixing tank 61, but the operator may also perform the task of adding new thinner W4 to the mixing tank 61.

[0063] The aqueous thinner waste liquid recycling system 1 in the above embodiment includes the mixing tank 61 for charging new thinner W4 and the filtrate tank 62 for storing the unmixed filtrate W3. However, the filtrate tank 62 may be omitted, and the unmixed filtrate W3 may be directly supplied to the mixing tank 61.

[0064] The aqueous thinner waste liquid recycling system 1 in the above embodiment is a system that produces recycled thinner from the aqueous thinner waste liquid W1 generated during the base coating process. However, if the clear paint used in the clear coating process is an aqueous paint, the aqueous thinner waste liquid recycling system 1 may also produce recycled thinner from the aqueous thinner waste liquid W1 generated during the clear coating process.

[0065] Next, in addition to the technical ideas set forth in the claims, the technical ideas grasped by the above-described embodiments will be listed below.

[0066] (1) In claim 2, the aqueous thinner waste liquid recycling system comprises: a waste liquid tank provided on the circulation line for storing the aqueous thinner waste liquid and the concentrated liquid; a filtrate concentration sensor for measuring the concentration of the filtrate, which is the liquid stored in the filtrate tank; a waste liquid concentration sensor for measuring the concentration of the aqueous thinner waste liquid, which is the liquid stored in the waste liquid tank; and a concentrated liquid concentration sensor for measuring the concentration of the concentrated liquid, which is the liquid stored in the waste liquid tank, wherein the filtrate concentration sensor, the waste liquid concentration sensor, and the concentrated liquid concentration sensor each have a prism and are refractive concentration sensors that measure low concentrations when the refractive index difference between the prism and the liquid is large and light is reflected at the interface between the prism and the liquid, and measure high concentrations when the refractive index difference between the prism and the liquid is small and light at a predetermined angle transmits from the prism into the liquid.

[0067] (2) In claim 7, a method for recycling waste aqueous thinner liquid, characterized in that a painting process is carried out in the painting booth before the separation step, in which the object to be painted is painted, the painting process including a middle coat painting process and a top coat painting process, and the top coat painting process including a base coat painting process and a clear coat painting process.

[0068] REFERENCE SIGNS LIST 1...Aqueous thinner waste liquid recycling system 10...Circulation line 21...Filtration membrane module 31...Waste liquid tank 33...Waste liquid concentration sensor 52...Concentrated liquid concentration sensor 60...Recycled thinner production section 61...Mixing tank 62...Filtrate tank 72...Filtrate concentration sensor 81...Backwash pump 101...Control device W1...Aqueous thinner waste liquid W2...Concentrated liquid W3...Filtrate W4...New thinner

Claims

1. A water-based thinner waste liquid recycling system comprising: a circulation line for circulating water-based thinner waste liquid containing paint components discharged from a painting booth; a filtration membrane module installed on the circulation line for separating the water-based thinner waste liquid into a concentrated liquid and a filtrate; and a recycled thinner production unit for storing the filtrate that has passed through the filtration membrane module and mixing the stored filtrate with new thinner to produce reusable recycled thinner.

2. The aqueous thinner waste liquid reuse system described in claim 1, characterized in that the recycled thinner production section includes a mixing tank for adding the new thinner and a filtrate tank for storing the filtrate before mixing.

3. The aqueous thinner waste liquid recycling system described in claim 2, characterized in that it is equipped with a backwash pump that cleans the filtration membrane of the filtration membrane module by supplying the filtrate stored in the filtrate tank from the downstream side to the upstream side of the filtration membrane module.

4. The aqueous thinner waste liquid recycling system described in claim 2 or 3, characterized in that it comprises: a filtrate concentration sensor that measures the concentration of the filtrate stored in the filtrate tank; and a control device that performs control to determine the amount of new thinner to be added to the mixing tank based on the concentration of the filtrate measured by the filtrate concentration sensor.

5. The aqueous thinner waste liquid recycling system described in claim 1, characterized in that it comprises: a waste liquid tank that is provided on the circulation line and that stores the aqueous thinner waste liquid and the concentrated liquid; a waste liquid concentration sensor that measures the concentration of the aqueous thinner waste liquid stored in the waste liquid tank; a concentrated liquid concentration sensor that measures the concentration of the concentrated liquid stored in the waste liquid tank; and a control device that performs control to detect abnormalities in the filtration membrane module based on the concentration of the aqueous thinner waste liquid measured by the waste liquid concentration sensor and the concentration of the concentrated liquid measured by the concentrated liquid concentration sensor.

6. The aqueous thinner waste liquid recycling system according to claim 1, wherein the filtration membrane provided in the filtration membrane module is an ultrafiltration membrane.

7. A method for reusing aqueous thinner waste liquid, comprising: a separation step of separating aqueous thinner waste liquid containing paint components discharged from a painting booth into a concentrated liquid and a filtrate; and a recycled thinner production step of storing the filtrate and mixing the stored filtrate with new thinner to produce reusable recycled thinner.

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