A method for recycling waste paint residues generated in a powder polyester paint spraying process and application thereof

Abstract

The application provides a recycling method of waste paint residues generated in a powder polyester paint spraying process and application thereof, and the recycling method comprises the following steps: drying and crushing the paint residues; mixing the paint residues, polylactic acid or polylactic acid copolymer, polyol additives and catalysts, and performing internal mixing under high temperature and shearing conditions to make the polylactic acid or polylactic acid copolymer degrade, the degradation product reacts with the crosslinked polyester molecular chain of the paint residues to obtain a mixture after de-crosslinking; adding an epoxy compound into the mixture to continue the internal mixing, so that the epoxy compound and the carboxyl generated in the reaction system undergo ring-opening reaction to obtain a grafted modified mixture; and then the mixture is subjected to melt extrusion, cooling and granulation to obtain modified recycled plastic particles which can be reprocessed. The method realizes de-crosslinking and modified utilization of the crosslinked polyester paint residues, and the obtained recycled material has good processing performance and can be used for reprocessing application of plastic products.

Description

Technical Field

[0001] This invention relates to the field of polymer material waste resource utilization technology, specifically to a method for recycling waste paint residue generated during powder polyester paint spraying and its application. Background Technology

[0002] Powdered polyester paint is widely used in metal surface treatment due to its excellent performance, but the effective treatment of the resulting solid waste—paint sludge—has always been a technical challenge in the industry. This paint sludge originates from the periodic peeling off of the accumulated coating on the spray hook, and its chemical nature is cured unsaturated polyester resin. During the curing process, the resin molecules form a stable three-dimensional cross-linked network structure, which directly results in the paint sludge having the stubborn characteristic of being "insoluble and infusible," making it impossible to recycle and reuse through conventional thermoplastic processing methods (such as melt extrusion and injection molding).

[0003] Currently, the methods for disposing of this type of paint residue generally have environmental or economic drawbacks:

[0004] Incineration and landfill (end-of-life disposal): Both methods are passive disposal methods and fail to achieve resource recycling. Incineration is energy-intensive and releases greenhouse gases and toxic substances, causing secondary air pollution. Landfilling requires long-term occupation of land resources, and cross-linked polymers are extremely difficult to degrade in the natural environment, posing a potential risk of soil and groundwater pollution.

[0005] Physical crushing and reuse (low-value recycling): This method attempts to crush paint sludge and use it as a cheap filler in other materials (such as plastics, rubber, or asphalt). However, due to the chemical inertness of the paint sludge and the lack of effective interfacial bonding between it and the matrix material, the composite material exhibits significant performance defects. It not only fails to provide reinforcement but also significantly reduces the mechanical strength and toughness of the product due to poor compatibility, resulting in extremely low application value.

[0006] Chemical dissolution method (high cost and high risk): This approach attempts to disrupt the cross-linked structure of paint residue using strong acids, strong bases, or high-temperature organic solvents. While theoretically feasible, it faces significant challenges in practical application: the required chemical reagents are highly corrosive and toxic, demanding high-quality equipment materials, and require stringent reaction conditions (such as high temperature and pressure). Furthermore, the waste liquid and residue generated after the reaction are costly to treat and prone to secondary pollution; these safety and environmental risks make it difficult to scale up industrial applications.

[0007] In summary, existing technologies have failed to fundamentally solve the core obstacle of "insoluble and infusible" cross-linked polyester paint residue, or have introduced new problems such as high energy consumption, heavy pollution, high cost, or low product value in the process of solving the problem. Therefore, there is an urgent need in this field for an environmentally friendly, process-feasible, and high-value-added method for the recycling of powdered polyester paint residue. Summary of the Invention

[0008] The present invention aims to overcome the shortcomings of the prior art and solve the technical problem of how to transform the powdered polyester paint residue generated by electrostatic spraying, which is "insoluble and infusible" due to its cross-linked structure, into plasticized recycled materials through green chemical methods, thereby solving the problems of high pollution, high cost or low value of existing treatment methods.

[0009] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0010] In a first aspect, the present invention provides a method for recycling waste paint residue generated during the powder polyester paint spraying process, comprising the following steps:

[0011] S1. Pretreatment: Drying and crushing the paint residue;

[0012] S2, Decrosslinking: The pretreated paint sludge, polylactic acid or polylactic acid copolymer, polyol additives and catalyst are mixed and kneaded under high temperature and shear conditions to degrade the polylactic acid or polylactic acid copolymer. The degradation products undergo transesterification with the crosslinked polyester molecular chains of the paint sludge to achieve partial decrosslinking of the paint sludge, and a decrosslinked mixture is obtained.

[0013] S3. Grafting modification: Add an epoxy compound to the mixture obtained in step S2 and continue to knead, so that the epoxy compound and the carboxyl group generated in the reaction system undergo a ring-opening esterification reaction to achieve grafting modification of the molecular chain and obtain the grafted modified mixture.

[0014] S4. Granulation: The mixture after the reaction in step S3 is melt-extruded, cooled, and granulated to obtain reprocessable modified recycled plastic particles.

[0015] Based on the above technical solution, the present invention can be further improved as follows.

[0016] Furthermore, in step S2, the mass ratio of the paint residue to the polylactic acid or polylactic acid copolymer is 100:(50~200).

[0017] Furthermore, in step S2, the amount of the polyol additive added is 1% to 10% of the mass of the paint sludge; the amount of the catalyst added is 0.1% to 3% of the mass of the paint sludge.

[0018] Furthermore, in step S2, the mixing temperature is 180℃~230℃, the rotation speed is 20rpm~50rpm, and the time is 10 minutes~30 minutes.

[0019] Furthermore, in step S3, the amount of epoxy compound added is 1% to 5% of the mass of the paint residue, and the mixing time is 5 to 15 minutes.

[0020] Furthermore, in step S2, the polyol is one or more of glycerol, pentaerythritol, diethylene glycol, and diethanolamine;

[0021] And / or, the catalyst is one or more of stannous octoate, tetrabutyl titanate, and zinc acetate;

[0022] And / or, the polylactic acid copolymer is a polylactic acid-hydroxyacetic acid copolymer.

[0023] Furthermore, in step S3, the epoxy compound is one or more of 1,4-butanediol diglycidyl ether, ethylene glycol diglycidyl ether, and bisphenol A diglycidyl ether.

[0024] In a second aspect, the present invention provides modified recycled plastic particles prepared by the method described in the first aspect.

[0025] Based on the above technical solution, the present invention can be further improved as follows.

[0026] Furthermore, the modified recycled plastic particles have a tensile strength of not less than 25 MPa and a melt index of 1.0 g / 10min to 5.0 g / 10min under the conditions of 210℃ temperature and 2.16 kg load.

[0027] Furthermore, the modified recycled plastic particles are used as functional fillers in blends with thermoplastic resins;

[0028] The thermoplastic resin is polylactic acid and its copolymers, polyethylene terephthalate, polystyrene, ABS, nylon 6 or nylon 66.

[0029] Compared with existing technologies, the method for recycling waste paint residue generated during powder polyester paint spraying provided by this invention achieves a comprehensive improvement in technical performance through a unique chemical modification pathway, specifically in the following aspects:

[0030] 1. Environmental friendliness and process safety

[0031] This invention eliminates the use of strong acids, strong alkalis, or hazardous organic solvents required by traditional chemical dissolution methods. Its core reaction medium is biodegradable polylactic acid (PLA), and the entire process is carried out in a high-temperature molten state, requiring no additional solvents. This eliminates the use of toxic and harmful chemicals and the subsequent waste treatment problems at the source. This significantly reduces the environmental burden and safety risks, making the production process meet the requirements of green chemistry.

[0032] 2. Decrosslinking efficiency and controllability

[0033] The key to this invention lies in utilizing the controllable thermal degradation products of PLA as "chemical scissors." Under the action of a specific catalyst, the small-molecule carboxylic acids and other active substances generated by PLA degradation can precisely attack the ester bonds in the crosslinked network of paint residue, achieving partial decrosslinking through transesterification. This method differs from the mechanical destruction of physical crushing and the indiscriminate erosion of strong chemical reagents; it is a gentle and controllable chemical tailoring that effectively overcomes the core obstacle of "insolubility and infusibility" in crosslinked polyesters, laying the foundation for its subsequent plasticizing processing. Its reaction pathway is clear and specific, with few side reactions and high efficiency.

[0034] 3. Product performance and high-value applications

[0035] Through subsequent epoxy grafting modification, PLA molecular chains are chemically bonded to the decrosslinked polyester chains of paint slag, fundamentally solving the interfacial problem of poor compatibility between the two. This transforms the originally immiscible system into a homogeneous and stable plasticizable material. The resulting modified recycled plastic particles not only possess good mechanical strength (tensile strength ≥25MPa) and processing fluidity (melt index 1.0-5.0 g / 10min), but also, due to their rich content of original inorganic fillers such as barium sulfate and titanium dioxide, additionally possess functional properties such as reinforcement, stiffness enhancement, and high hiding power. The resulting products are dense and uniform, and can be used as high-performance functional fillers in high-end plastic products, realizing an upgrade from waste to high-value resources.

[0036] 4. Technological economics and industrialization prospects

[0037] The mixing and extrusion processes used in this invention are all general-purpose polymer processing equipment, resulting in a short process flow that does not require complex or expensive specialized equipment. PLA, the raw material, is a readily available and relatively cost-controllable biodegradable plastic. The overall process is smooth and simple, easily adaptable to existing plastic processing enterprises for large-scale production, with low industrialization barriers and significant economic benefits.

[0038] In summary, this invention systematically addresses the three core pain points that have long plagued the field of powdered polyester paint residue recycling: high pollution, low efficiency, and poor product value, through a synergistic innovative technical route of "PLA degradation-induced decrosslinking" and "epoxy grafting for modification." Compared with traditional technologies, it has achieved significant progress in environmental benefits, technological advancement, product added value, and economic feasibility, providing a new and practical green path for the resource utilization of solid waste in the coatings industry. Attached Figure Description

[0039] Figure 1The diagram shown is an overall process flow chart of the method for recycling powdered polyester paint residue according to the present invention.

[0040] Figure 2 The diagram shown illustrates the core mechanism of the decrosslinking and grafting modification reaction described in this invention.

[0041] Figure 3 The image shown is the Fourier Transform Infrared Spectrum (FT-IR) of the regenerated particle A obtained in Example 1 of this invention;

[0042] Figure 4 The image shown is a photograph of the recycled particle B obtained in Example 2 of this invention and its injection-molded standard sample.

[0043] Figure 5 The image shown is a cross-sectional scanning electron microscope (SEM) image of the regenerated particle C obtained in Example 3 of the present invention;

[0044] Figure 6 The image shown is a photograph of the blend product obtained in the comparative example (without the addition of catalyst and epoxide). Detailed Implementation

[0045] The implementation methods of this solution will be described in further detail below. Obviously, the described embodiments are only a part of the embodiments of this solution, and not an exhaustive list of all embodiments. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of this solution can be combined with each other.

[0046] The contents disclosed in this invention can be improved simultaneously in terms of materials, methods, and reaction conditions, and all such improvements should fall within the spirit and scope of this invention. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art. Reagents and biological materials, unless otherwise specified, are commercially available; the databases used are all publicly available online databases.

[0047] The method for recycling waste paint residue generated during powder polyester paint spraying provided in this embodiment of the invention includes the following steps:

[0048] S1. Pretreatment: The paint residue is dried and crushed.

[0049] Specifically, the paint residue stripped from the home appliance spraying production line is pre-treated. After being screened to remove metal scraps, dust and other impurities, the paint residue is dried at 80°C for 4 hours to control the moisture content to below 0.5%. The dried paint residue is then crushed to a particle size of less than 2 mm for later use.

[0050] S2. Decrosslinking: The pretreated paint sludge, polylactic acid or polylactic acid copolymer, polyol additives and catalyst are mixed and kneaded under high temperature and shear to degrade the polylactic acid or polylactic acid copolymer. The degradation products undergo transesterification with the crosslinked polyester molecular chains of the paint sludge to achieve partial decrosslinking of the paint sludge, and a decrosslinked mixture is obtained.

[0051] Preferably, the mass ratio of paint residue to polylactic acid or polylactic acid copolymer is 100:(50~200).

[0052] Preferably, the amount of polyol additive added is 1% to 10% of the mass of paint sludge; the amount of catalyst added is 0.1% to 3% of the mass of paint sludge.

[0053] Preferably, the mixing temperature is 180℃~230℃, the speed is 20rpm~50rpm, and the time is 10 minutes~30 minutes.

[0054] The polyol may be selected from one or more of glycerol, pentaerythritol, diethylene glycol, and diethanolamine; the catalyst may be selected from one or more of stannous octoate, tetrabutyl titanate, and zinc acetate; and the polylactic acid copolymer may be selected from polylactic acid-glycolic acid copolymer.

[0055] Specifically, paint sludge is mixed with polylactic acid (PLA) or a PLA copolymer in a preferred ratio of 100 parts paint sludge to 150 parts PLA, along with approximately 5 parts polyol (such as glycerol, pentaerythritol, diethylene glycol, or diethanolamine) and a suitable catalyst (such as stannous octoate, tetrabutyl titanate, or 0.5 parts zinc acetate). All the above raw materials are added to a Banbury mixer and mixed at 190-220°C for approximately 20 minutes. During this process, PLA undergoes thermal degradation under the action of the catalyst, and the generated carboxylic acid groups can attack the ester bonds in the paint sludge, causing some cross-linking bonds to break. The paint sludge transforms from its original insoluble and infusible state into a structure with plasticity. The reaction principle is as follows: Figure 2 As shown.

[0056] S3. Grafting modification: Add an epoxy compound to the mixture obtained in step S2 and continue to knead. This allows the epoxy compound to undergo a ring-opening esterification reaction with the carboxyl groups generated in the reaction system, thereby achieving grafting modification of the molecular chain and obtaining the grafted modified mixture.

[0057] The amount of epoxy compound added is 1% to 5% of the mass of the paint residue, and the mixing time is 5 to 15 minutes.

[0058] The epoxy compound may be selected from one or more of 1,4-butanediol diglycidyl ether, ethylene glycol diglycidyl ether, and bisphenol A diglycidyl ether.

[0059] Specifically, after the reaction has lasted for about 20 minutes, an epoxy compound (such as 1,4-butanediol diglycidyl ether, ethylene glycol diglycidyl ether, or bisphenol A diglycidyl ether) is added, and the mixture is stirred for another 5 to 10 minutes. The epoxy groups react with the carboxyl groups to form ester bonds, which chemically grafts polylactic acid segments onto the polyester chains of the paint residue, further improving the compatibility and uniformity of the system.

[0060] S4. Granulation: The mixture after the reaction in step S3 is melt-extruded, cooled, and granulated to obtain reprocessable modified recycled plastic particles.

[0061] Specifically, after the reaction is complete, the mixture is cooled and crushed, then melt-extruded at 180~190℃ using a twin-screw extruder, and finally water-cooled and pelletized to obtain modified recycled plastic particles.

[0062] The modified recycled plastic particles obtained by the above method are light gray or milky white, with high density, firm feel, and good thermoplasticity. Their tensile strength is not less than 25 MPa, and their melt index is 1.0 g / 10min ~ 5.0 g / 10min under the conditions of 210℃ and 2.16 kg load. They can be used as functional fillers for blending with thermoplastic resins. The thermoplastic resins are polylactic acid and its copolymers, polyethylene terephthalate, polystyrene, ABS, nylon 6 or nylon 66.

[0063] The following embodiments and comparative examples further illustrate the technical effects of the method for recycling waste paint residue generated during the powder polyester paint spraying process provided by the present invention.

[0064] Example 1

[0065] This embodiment provides a method for recycling waste paint residue generated during the powder polyester paint spraying process, specifically as follows:

[0066] 100 parts of polyester paint residue with a particle size of less than 2 mm, 150 parts of polylactic acid, 5 parts of glycerol, and 0.5 parts of stannous octoate were added to a mixer and mixed at 205°C and 30 rpm for 20 minutes. Then, 2 parts of 1,4-butanediol diglycidyl ether were added, and the reaction was continued for 5 minutes.

[0067] After the reaction is complete, the mixture is cooled and crushed, and then extruded into strips at 195°C using a twin-screw extruder. After cooling and pelletizing, recycled particles A are obtained.

[0068] The infrared spectrum of regenerated particle A is as follows Figure 3 As shown, its tensile strength is 32 MPa, elongation at break is 1.8%, and melt flow index is 1.8 g / 10min, indicating that the material has excellent mechanical properties and processing fluidity.

[0069] It should be noted that, unless otherwise specified, the melt flow index (MFR) mentioned above is determined according to ASTM D1238 standard, under conditions of 210°C and 2.16 kg load.

[0070] Example 2

[0071] This embodiment provides a method for recycling waste paint residue generated during the spraying of powder polyester paint. Specifically, 100 parts of paint residue with a particle size of less than 2 mm, 100 parts of polylactic acid, 4 parts of diethanolamine, and 0.5 parts of tetrabutyl titanate are added to a mixer and mixed at 200°C and 30 rpm for 20 minutes. Then, 2 parts of ethylene glycol diglycidyl ether are added, and the reaction is continued for 5 minutes.

[0072] After the reaction is complete, the mixture is cooled and crushed, and then extruded into strips at 195°C using a twin-screw extruder. After cooling and pelletizing, regenerated particles B are obtained.

[0073] Regenerated particles B and injection-molded dumbbell-shaped splines, such as Figure 4 As shown. Its tensile strength is 27 MPa, elongation at break is 1.6%, and melt flow index is 1.3 g / 10min (210℃ / 2.16 kg).

[0074] Example 3

[0075] This embodiment provides a method for recycling waste paint residue generated during the powder polyester paint spraying process, specifically as follows:

[0076] 100 parts of paint residue with a particle size of less than 2 mm, 100 parts of polylactic acid-glycolic acid copolymer (lactic acid to glycolic acid ratio of 75:25), 5 parts of glycerol, and 0.5 parts of zinc acetate were added to a mixer and mixed at 200°C and 30 rpm for 20 minutes. Then, 2 parts of ethylene glycol diglycidyl ether were added, and the reaction was continued for 5 minutes.

[0077] After the reaction is complete, the mixture is cooled and crushed, and then extruded into strips and pellets at 195°C using a twin-screw extruder to obtain regenerated particles C.

[0078] Scanning electron microscope images of particle cross sections, such as Figure 5 The results showed that the material was uniformly mixed internally and had good compatibility. The tensile strength of the recycled particles C was 31 MPa, the elongation at break was 2.5%, and the melt flow index was 1.4 g / 10min (210℃ / 2.16 kg).

[0079] Example 4

[0080] This embodiment provides an application of the blending of regenerated particles A obtained in Example 1:

[0081] Recycled particles A and PLA were blended in a ratio of 30 parts recycled particles A and 70 parts PLA. After mixing in the ratio, the mixture was added to an internal mixer and kneaded at 190°C and 30 rpm for 20 minutes. The mixture was then cooled, crushed, and sent to an injection molding machine to be injection molded into dumbbell-shaped test specimens at 210°C.

[0082] The test results showed that the tensile strength of the sample was 41 MPa, the elongation at break was 4.5%, and the melt flow index was 4.1 g / 10min (210℃ / 2.16 kg), indicating that the blended material has good mechanical properties and processability.

[0083] Example 5

[0084] This embodiment provides the application of the blend of regenerated particles B obtained in Example 2:

[0085] Recycled particles B were blended with PET in a ratio of 25 parts recycled particles B to 75 parts PET. After mixing in the specified ratio, the mixture was added to an internal mixer and kneaded at 250°C and 30 rpm for 20 minutes. The mixture was then cooled, crushed, and injection molded into dumbbell-shaped samples at 280°C.

[0086] Test results show that the material has a tensile strength of 55 MPa, an elongation at break of 5.0%, and a melt flow index of 1.5 g / 10min (250℃ / 2.16 kg), exhibiting excellent thermal stability and processing performance.

[0087] Example 6

[0088] This embodiment provides the application of the blend of the regenerated particles C obtained in Example 3:

[0089] Recycled particles C were blended with nylon-66 in a ratio of 20 parts recycled particles C to 80 parts nylon-66. After mixing in the specified ratio, the mixture was added to an internal mixer and kneaded at 280°C and 30 rpm for 15 minutes. The mixture was then cooled, crushed, and injection molded into dumbbell-shaped test specimens at 285°C.

[0090] Test results show that the tensile strength of the sample is 70 MPa, the elongation at break is 5.5%, and the melt flow index is 3.0 g / 10min (275℃ / 2.16 kg), indicating that the material has high strength, toughness and processing adaptability.

[0091] Example 7

[0092] This embodiment provides an application of the blending of regenerated particles A obtained in Example 1:

[0093] Recycled particles A were blended with general-purpose polystyrene (GPPS) in a ratio of 10 parts recycled particles A to 90 parts GPPS. After mixing in the ratio, the mixture was added to an internal mixer and kneaded at 200°C and 30 rpm for 20 minutes. The mixture was then cooled and crushed and sent to an injection molding machine to be injection molded into dumbbell-shaped test specimens at 205°C.

[0094] The test results showed that the tensile strength of the sample was 57 MPa, the elongation at break was 3.4%, and the melt flow index was 2.9 g / 10min (200℃ / 5 kg), indicating that the blended material has good mechanical properties and processability.

[0095] Comparative example:

[0096] To verify the modification effect of the solution provided in this embodiment of the invention, paint residue and polylactic acid were mixed at a ratio of 100:150, but without adding a catalyst or epoxy compound, and then kneaded at 200°C and 30 rpm for 20 minutes. The kneaded paint residue and polylactic acid are incompatible, resulting in a mixture with a rough surface that cannot be extruded, exhibiting an appearance similar to... Figure 6 As shown, the unmodified architecture exhibits poor stability and insufficient processing performance, thus verifying the effectiveness of this technical solution.

[0097] As can be seen from the test data of the above embodiments, the modified system achieves effective linkage between polylactic acid and the polyester chains of paint slag through chemical reaction, transforming the system from a physical mixture to a partially chemical copolymer structure, significantly improving interfacial compatibility, and enhancing plasticizing effect and thermal fluidity. The results show that this invention not only enables powdered polyester paint slag to achieve reprocessability but also endows it with reinforcing and filling functions to a certain extent, realizing the transformation from solid waste to functional materials.

[0098] In summary, the powdered polyester paint residue regeneration method proposed in this embodiment is simple, safe, reliable, and uses readily available raw materials. The equipment is highly versatile, and the resulting product has stable performance. It is suitable for widespread application in the plastics industry and has significant economic and environmental value.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for recycling waste paint residue generated during powder polyester paint spraying, characterized in that, Includes the following steps: S1. Pretreatment: Drying and crushing the paint residue; S2. Decrosslinking: The pretreated paint sludge, polylactic acid or polylactic acid copolymer, polyol additives, and catalyst are mixed and kneaded under shear conditions at 180℃~230℃ to degrade the polylactic acid or polylactic acid copolymer. The degradation products undergo transesterification with the crosslinked polyester molecular chains of the paint sludge, achieving partial decrosslinking of the paint sludge and obtaining a decrosslinked mixture. The catalyst is one or more of stannous octoate, tetrabutyl titanate, and zinc acetate. S3. Grafting modification: Add an epoxy compound to the mixture obtained in step S2 and continue to knead, so that the epoxy compound reacts with the carboxyl group generated in the reaction system to undergo a ring-opening reaction, thereby achieving grafting modification of the molecular chain and obtaining a grafted modified mixture; the epoxy compound is one or more of 1,4-butanediol diglycidyl ether, ethylene glycol diglycidyl ether, and bisphenol A diglycidyl ether. S4. Granulation: The mixture after the reaction in step S3 is melt-extruded, cooled, and granulated to obtain reprocessable modified recycled plastic particles.

2. The method for recycling waste paint residue generated during the powder polyester paint spraying process according to claim 1, characterized in that, In step S2, the mass ratio of the paint residue to the polylactic acid or polylactic acid copolymer is 100:(50~200).

3. The method for recycling waste paint residue generated during the powder polyester paint spraying process according to claim 1, characterized in that, In step S2, the amount of polyol additive added is 1% to 10% of the mass of paint sludge; the amount of catalyst added is 0.1% to 3% of the mass of paint sludge.

4. The method for recycling waste paint residue generated during the powder polyester paint spraying process according to claim 1, characterized in that, In step S2, the shearing conditions are a rotation speed of 20 rpm to 50 rpm and a time of 10 minutes to 30 minutes.

5. The method for recycling waste paint residue generated during the powder polyester paint spraying process according to claim 1, characterized in that, In step S3, the amount of epoxy compound added is 1% to 5% of the mass of the paint residue, and the mixing time is 5 to 15 minutes.

6. The method for recycling waste paint residue generated during powder polyester paint spraying according to claim 1, characterized in that, In step S2, the polyol is one or more of glycerol, pentaerythritol, diethylene glycol, and diethanolamine; And / or, the polylactic acid copolymer is a polylactic acid-hydroxyacetic acid copolymer.

7. A modified recycled plastic particle, characterized in that, Prepared by the method according to any one of claims 1 to 6.

8. The modified recycled plastic particles according to claim 7, characterized in that, The modified recycled plastic particles have a tensile strength of not less than 25 MPa and a melt index of 1.0 g / 10min to 5.0 g / 10min under the conditions of 210℃ temperature and 2.16 kg load.

9. The modified recycled plastic particles according to claim 7, characterized in that, The modified recycled plastic particles are used as functional fillers in blends with thermoplastic resins. The thermoplastic resin is polylactic acid and its copolymers, polyethylene terephthalate, polystyrene, ABS, nylon 6 or nylon 66.

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