A method for surface functional modification of powder polyester coating waste paint residue and application thereof

Abstract

The application provides a surface functionalization modification method of powder polyester coating waste paint residue and application thereof, and the modification method comprises the following steps: removing impurities, drying and crushing and then screening the powder polyester coating waste paint residue; performing surface treatment on the paint residue by using a functional silane coupling agent to introduce hydroxyl, amino or sulfhydryl active groups on the surface of the paint residue particles to obtain surface-activated paint residue; reacting diisocyanate with polyether polyol or polyester polyol to obtain an isocyanate-terminated polyurethane prepolymer; adding a blocking agent to obtain a partially blocked polyurethane prepolymer; adding the surface-activated paint residue into the partially blocked polyurethane prepolymer to make the unblocked isocyanate groups in the prepolymer react with the active groups on the surface of the paint residue, and then performing filtration and drying to obtain a polyurethane synergistic surface-functionalized paint residue intermediate. The method has simple process and mild reaction conditions, does not need to use strong acid, strong base or organic solvent, does not need to destroy the three-dimensional crosslinking network of the paint residue, is environmentally friendly and has high industrial value.

Description

Technical Field

[0001] This invention relates to the field of waste resource utilization technology, specifically to a method for surface functionalization modification of waste paint residue from powdered polyester coatings and its application. Background Technology

[0002] Powdered polyester coatings, characterized by stable film performance, good weather resistance, and low volatile organic compound emissions during application, are widely used for electrostatic spraying on the surfaces of household appliances, metal components, automotive parts, and machinery. In continuous spraying production, in addition to depositing on the workpiece surface, powder coatings also adhere to the surfaces of spraying fixtures, hooks, and conductive jigs, forming a thick cross-linked polyester coating during high-temperature curing. With increasing spraying cycles, the cured coating on the fixture surface affects its conductivity and reusability, requiring periodic peeling, thus generating a large amount of waste powdered polyester coating sludge. This waste sludge mainly consists of highly cross-linked polyester resin, barium sulfate, titanium dioxide, pigments, and a small amount of additives. Because the polyester resin has formed a stable three-dimensional cross-linked network structure, the material exhibits insoluble and infusible properties, making it impossible to recover using conventional thermoplastic processing methods. Furthermore, the waste sludge still contains a considerable proportion of polyester resin and inorganic fillers; direct disposal would result in a serious waste of material resources.

[0003] The current methods for disposing of and utilizing such waste paint residue have the following main drawbacks: Incineration and landfill are energy-intensive and highly polluting end-of-pipe treatments that fail to achieve resource recycling. While physically crushing paint sludge and directly incorporating it as a filler into epoxy resin, polyurethane, vinyl ester resin, or thermoplastic resin is a resource-based approach, the low surface activity of waste paint sludge particles leads to poor wettability and compatibility with the polymer matrix. Direct use can easily result in particle agglomeration, interfacial voids, particle pull-out, and stress concentration, causing a decrease in the tensile strength, flexural strength, and impact properties of the composite material, thus limiting its application value.

[0004] While treatment with common silane coupling agents can improve particle surface polarity to some extent, the resulting interfacial layer is thin, with limited flexibility and stress buffering capacity, making it difficult to simultaneously address the issues of dispersibility, interfacial bonding, and material toughness. When using polyurethane physical coating alone, the coating layer does not bond firmly to the particle surface and is prone to detachment during subsequent processing, failing to form stable chemical bonds. Furthermore, the chemical structures and processing conditions of different polymer matrices vary significantly, and a single surface treatment method is typically only applicable to a specific resin system. This makes it difficult to achieve stable application results for waste paint residue in various polymer materials such as epoxy resins, polyurethanes, vinyl ester resins, and thermoplastic resins, greatly limiting its widespread use as a functional filler.

[0005] In summary, existing technologies have failed to fundamentally solve the core problems of poor interfacial compatibility, easy agglomeration, and decreased mechanical properties when cross-linked polyester paint residue is used as a filler, or have introduced new limitations such as narrow applicability and weak interfacial bonding in the process of solving these problems.

[0006] Therefore, there is an urgent need in this field for a surface functionalization method that can firmly bind to the surface of waste paint residue particles and has flexible segments and subsequent reactivity, so as to transform waste paint residue from ordinary inert fillers into functionalized intermediates with interface regulation capabilities, thereby achieving wide compatibility and high-value utilization of various polymer matrices. Summary of the Invention

[0007] The present invention aims to overcome the shortcomings of the prior art and solve the technical problems of easy agglomeration, weak interfacial bonding, and decreased mechanical properties when waste paint residue of existing powder polyester coatings is directly filled, as well as the narrow applicability and difficulty in adapting to various resin matrices of conventional surface treatment methods.

[0008] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: In a first aspect, the present invention provides a method for surface functionalization modification of waste paint residue from powdered polyester coatings, comprising the following steps: S1. Pretreatment: Screen the waste paint residue of powder polyester coating to remove impurities, dry it at 80℃~100℃ for 2 hours to 6 hours, and then screen it after mechanical crushing. S2. Surface activation modification: The paint sludge after the pretreatment in step S1 is surface-treated with a functional silane coupling agent to introduce hydroxyl, amino, or mercapto active groups on the surface of the paint sludge particles, thereby obtaining surface-activated paint sludge; the functional silane coupling agent is one or more of 3-[bis(2-hydroxyethyl)amino]propyltriethoxysilane, γ-aminopropyltriethoxysilane, and γ-mercaptopropyltrimethoxysilane; S3. Preparation of partially blocked polyurethane prepolymer: Diisocyanate is reacted with polyether polyol or polyester polyol, and the molar ratio of isocyanate groups to hydroxyl groups is controlled at (2.0~2.5):1 to obtain isocyanate-terminated polyurethane prepolymer; then a blocking agent is added to block some of the isocyanate groups, and the molar ratio of blocking agent to isocyanate groups is controlled at (0.4~0.7):1 to obtain partially blocked polyurethane prepolymer; S4. Surface grafting reaction: The surface-activated paint sludge obtained in step S2 is added to the partially closed polyurethane prepolymer obtained in step S3, so that the unclosed isocyanate groups in the prepolymer react with the active groups on the surface of the paint sludge. After the reaction, the mixture is filtered and dried to obtain a polyurethane synergistic surface functionalized paint sludge intermediate.

[0009] Based on the above technical solution, the present invention can be further improved as follows.

[0010] Furthermore, in step S3, the number average molecular weight of the polyether polyol or polyester polyol is 500-2000; the diisocyanate is 4,4'-diphenylmethane diisocyanate or isophorone diisocyanate; and the blocking agent is butanone oxime, ε-caprolactam, or phenol.

[0011] Furthermore, step S3 also includes adding a small molecule diol as a chain extender, the amount of which accounts for 5% to 15% of the total molar amount of hydroxyl groups.

[0012] Furthermore, in step S4, the amount of the partially closed polyurethane prepolymer added is 8% to 12% of the mass of the surface-activated paint sludge; the reaction temperature is 60℃ to 80℃, and the reaction time is 1 hour to 3 hours.

[0013] Further, in step S2, the specific operation of the surface treatment is as follows: mix silane coupling agent, ethanol and water, adjust the pH to 4.5~5.5, hydrolyze for 20 minutes~40 minutes, then add the pretreated paint residue, stir for 0.5 hours~1.5 hours, keep warm at 50℃~70℃ for 0.5 hours~1.5 hours, filter and dry.

[0014] Furthermore, in step S1, the sieving control particle size is less than 500 μm.

[0015] Secondly, the present invention provides a polyurethane synergistic surface functionalized paint residue intermediate, which is prepared by the method described in the first aspect.

[0016] Based on the above technical solution, the present invention can be further improved as follows.

[0017] Furthermore, the intermediate is used as a functional filler in blending with the polymer matrix; The polymer matrix is ​​epoxy resin, polyurethane, vinyl ester resin, thermoplastic resin or thermosetting resin.

[0018] Furthermore, the thermoplastic resin is polystyrene, polycarbonate, or polyvinyl chloride; And / or, the thermosetting resin is an unsaturated polyester resin or a phenolic resin.

[0019] The surface functionalization modification method for waste paint residue with powdered polyester coating provided by this invention effectively solves the technical problems of low surface activity, poor interfacial compatibility, easy agglomeration, and narrow applicability of single surface treatment methods when waste paint residue is directly used as a filler. Through the synergistic combination of pretreatment, surface activation modification, preparation of partially closed polyurethane prepolymer, and surface grafting reaction, it realizes the transformation of waste paint residue from an inert filler to a functionalized intermediate with interfacial regulation capability.

[0020] 1. Impurities are removed by sieving, and the product is dried at 80℃~100℃ for 2 to 6 hours to control the moisture content. Then, it is mechanically crushed and sieved to control the particle size to below 500μm, providing clean, dry, and uniform particles with suitable specific surface area for subsequent surface activation modification. This physically ensures that the activating groups and prepolymers can uniformly contact the paint residue surface, avoiding interference from moisture or impurities in subsequent chemical reactions.

[0021] 2. One or more functional silane coupling agents selected from 3-[bis(2-hydroxyethyl)amino]propyltriethoxysilane, γ-aminopropyltriethoxysilane, and γ-mercaptopropyltrimethoxysilane are used to treat the surface of the pretreated paint sludge. This introduces active groups such as hydroxyl, amino, or mercapto groups onto the particle surface, providing sufficient chemical bonding sites for the subsequent fixation of the polyurethane prepolymer. This enables the originally inert paint sludge surface to react with isocyanate groups, ensuring that the prepolymer can be firmly bonded to the paint sludge surface through chemical bonds, fundamentally avoiding the problem of easy detachment of simple physical coating.

[0022] 3. By reacting diisocyanate with polyether polyol or polyester polyol, controlling the molar ratio of isocyanate groups to hydroxyl groups to be (2.0~2.5):1, the prepolymer retains terminal isocyanate groups, enabling grafting reactions with active groups on the surface of paint residue. Simultaneously, a blocking agent is added to block some of the isocyanate groups. This ensures the stability of the prepolymer during storage and initial mixing, preventing unblocked prepolymers from sticking together due to excessive crosslinking. Furthermore, the blocked isocyanate groups remain latently within the polyurethane functional layer on the surface of the intermediate particles. When subsequent processing or post-treatment temperatures reach the appropriate deblocking conditions, the blocked isocyanate groups are deblocked, regenerating reactive NCO groups. Because these NCO groups are fixed in the functional layer on the particle surface, their subsequent effects occur at the interface between the intermediate particles and the polymer matrix, rather than relying on the long-distance migration of NCO groups throughout the polymer matrix. In addition, the polyurethane prepolymer segments composed of diisocyanate and polyether / polyester polyol have good flexibility and can form a flexible transition layer between rigid paint residue particles and polymer matrix, effectively buffering interfacial stress concentration.

[0023] 4. Surface-activated paint sludge is added to a partially closed polyurethane prepolymer, allowing the unclosed isocyanate groups in the prepolymer to react with the hydroxyl, amino, or mercapto groups on the paint sludge surface, thereby forming a chemically bonded polyurethane functional layer on the paint sludge particle surface. After the reaction, the mixture is filtered and dried to obtain a polyurethane-synergistically surface-functionalized paint sludge intermediate. This intermediate fully retains the original three-dimensional cross-linked structure and inorganic filler components of the paint sludge, while simultaneously constructing a polyurethane functional layer on its surface that combines flexible buffering capacity and latent reactivity. This successfully transforms it from a common inert filler into a functionalized intermediate with interface regulation capabilities, making it widely adaptable to various polymer matrices.

[0024] In summary, the method described in this invention is simple in process and mild in reaction conditions. It does not require strong acids, strong alkalis, or organic solvents, nor does it disrupt the three-dimensional cross-linked network of the paint sludge. It is environmentally friendly and easy to implement industrially. The resulting polyurethane-synergistic surface-functionalized paint sludge intermediate can significantly improve the dispersibility and interfacial bonding of waste paint sludge in various polymer matrices, effectively enhancing the mechanical properties of composite materials. This provides a practical and feasible green technology path for the resource utilization and high-value utilization of waste paint sludge from powder polyester coatings. Attached Figure Description

[0025] Figure 1 The diagram shown is a schematic representation of the core mechanism of the surface functionalization modification method for waste paint residue from powdered polyester coatings according to an embodiment of the present invention. Figure 2 The diagram shown is an overall process flow chart of the surface functionalization modification method for waste paint residue from powdered polyester coatings according to an embodiment of the present invention. Figure 3 The image shows the infrared spectra of paint residue before and after treatment with KH550 in Example 1 of this invention. Figure 4 The image shown is the infrared spectrum of polyurethane synergistic surface functionalized paint residue intermediate A in Embodiment 1 of the present invention; Figure 5 The image shown is a scanning electron microscope image of the paint residue intermediate A obtained in Example 1 of the present invention. Detailed Implementation

[0026] 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.

[0027] 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; all databases used are publicly available online databases.

[0028] The surface functionalization modification method for waste paint residue from powdered polyester coatings provided in this embodiment of the invention includes the following steps: Step S1, Pretreatment: Screen the waste paint residue of powder polyester coating to remove impurities, dry it at 80℃~100℃ for 2 hours to 6 hours, and then screen it after mechanical crushing.

[0029] The sieving process controls the particle size to be less than 500 μm; after this treatment, the waste particles can meet the requirements for subsequent modification and compound use.

[0030] Step S2, Surface activation modification: The paint sludge after the pretreatment in step S1 is surface treated with a functional silane coupling agent to introduce hydroxyl, amino or thiol active groups on the surface of the paint sludge particles, thus obtaining surface-activated paint sludge.

[0031] The functional silane coupling agent is one or more of 3-[bis(2-hydroxyethyl)amino]propyltriethoxysilane, γ-aminopropyltriethoxysilane, and γ-mercaptopropyltrimethoxysilane.

[0032] The specific operation of the surface treatment is as follows: mix silane coupling agent, ethanol and water, adjust the pH to 4.5~5.5, hydrolyze for 20 minutes~40 minutes, then add the pretreated paint residue, stir for 0.5 hours~1.5 hours, keep warm at 50℃~70℃ for 0.5 hours~1.5 hours, filter and dry.

[0033] The purpose of this step is to provide reaction sites for the subsequent fixation of the polyurethane prepolymer onto the surface of the waste paint residue particles. The active groups are selected from hydroxyl, amino, or mercapto groups that can react with isocyanate groups. The surface of the waste paint residue is modified using appropriate functional silane coupling agents.

[0034] Step S3: Preparation of partially blocked polyurethane prepolymer: The diisocyanate used to introduce reaction sites in paint sludge is reacted with polyether polyol or polyester polyol, and the molar ratio of isocyanate groups to hydroxyl groups is controlled at (2.0~2.5):1 to obtain a polyurethane prepolymer with terminal isocyanate groups; then a blocking agent is added to block some of the isocyanate groups, and the molar ratio of blocking agent to isocyanate groups is controlled at (0.4~0.7):1 to obtain a partially blocked polyurethane prepolymer.

[0035] This step also includes adding a small molecule diol as a chain extender, which accounts for 5% to 15% of the total molar amount of hydroxyl groups, to adjust the molecular weight and chain segment structure of the prepolymer. By controlling the molar ratio of isocyanate groups to hydroxyl groups to be (2.0 to 2.5):1, the prepolymer retains some isocyanate end groups.

[0036] The number average molecular weight of the polyether polyol or polyester polyol is 500-2000; the diisocyanate is 4,4'-diphenylmethane diisocyanate or isophorone diisocyanate; the blocking agent is butanone oxime, ε-caprolactam or phenol.

[0037] S4. Surface grafting reaction: The surface-activated paint sludge obtained in step S2 is added to the partially closed polyurethane prepolymer obtained in step S3, so that the unclosed isocyanate groups in the prepolymer react with the active groups on the surface of the paint sludge. After the reaction, the mixture is filtered and dried to obtain a polyurethane synergistic surface functionalized paint sludge intermediate.

[0038] Specifically, the amount of the partially closed polyurethane prepolymer added is 8% to 12% of the mass of the surface-activated paint sludge; the reaction temperature is 60℃ to 80℃, and the reaction time is 1 hour to 3 hours.

[0039] In this process, such as Figure 1 As shown, the corresponding principle is as follows: hydroxyl, amino, or mercapto groups on the surface of paint sludge can react with unblocked isocyanate groups in the prepolymer, causing polyurethane segments to be chemically bonded to the surface of the waste paint sludge particles, obtaining a polyurethane-co-functionalized paint sludge intermediate. The blocked isocyanate groups remain latently in the polyurethane functional layer on the surface of the intermediate particles. When the subsequent processing or post-treatment temperature reaches the corresponding deblocking conditions, the blocked isocyanate groups are deblocked, regenerating reactive NCO groups. Because these NCO groups are fixed in the functional layer on the particle surface, their subsequent effects occur at the interface between the intermediate particles and the polymer matrix, rather than relying on the long-distance migration of NCO groups throughout the polymer matrix. Therefore, the intermediate can further participate in interfacial reactions during subsequent blending, co-curing, or post-treatment with different polymer matrices, playing a role in improving interfacial compatibility, enhancing dispersibility, and buffering interfacial stress.

[0040] The following embodiments further illustrate the corresponding technical effects of the surface functionalization modification method for waste paint residue of powdered polyester coating provided by the present invention.

[0041] Example 1 This embodiment illustrates a method for surface functionalization of waste paint residue from powder polyester coatings using amination treatment and partially blocked polyurethane prepolymers.

[0042] Waste paint residue from the peeling of powdered polyester coating from the surface of the spraying rack was sieved to remove metal shavings, dust, and other impurities, and then dried in a 90℃ oven for 4 hours. The dried waste paint residue was then mechanically crushed and sieved, and particles with a diameter of less than 200 μm were collected for later use.

[0043] Preparation of the amination treatment solution: 2 parts of γ-aminopropyltriethoxysilane (KH550), 95 parts of ethanol, and 5 parts of deionized water were mixed. The pH was adjusted to 4.5-5.5 with acetic acid, and the mixture was stirred and hydrolyzed for 30 minutes at room temperature. Then, 100 parts of pretreated paint sludge were added, and stirring continued for 1 hour, followed by heat treatment at 60℃ for 1 hour. After treatment, the mixture was filtered, and the resulting particles were dried at 80℃ for 3 hours to obtain waste paint sludge particles with amino groups on their surface. The infrared spectra of the paint sludge before and after treatment are shown in Figure 3.

[0044] Preparation of partially blocked polyurethane prepolymer: Polypropylene glycol diol (PPG1000) was vacuum dehydrated at 110°C for 1.5 hours. After cooling to 80°C, 4,4'-diphenylmethane diisocyanate (MDI) was added, controlling the molar ratio of isocyanate groups to hydroxyl groups at 2.3:1. 1,4-Butanediol was added as a chain extender, accounting for 10% of the total molar amount of hydroxyl groups. Subsequently, 0.05 parts of dibutyltin dilaurate were added, and the reaction was carried out at 80°C for 2 hours under nitrogen protection to obtain isocyanate-terminated polyurethane prepolymer. Then, caprolactam was added as a blocking agent, controlling the molar ratio of isocyanate groups to caprolactam at 1:0.6, and the reaction was continued at 75°C for 1.5 hours to obtain a partially blocked polyurethane prepolymer.

[0045] 100 parts of the above-mentioned amination-treated waste paint residue were added to a partially closed polyurethane prepolymer, with the prepolymer accounting for 10% of the mass of the waste paint residue. The mixture was stirred and reacted at 70°C for 2 hours to fix the polyurethane segments onto the surface of the solidified waste paint residue. After the reaction was completed, the mixture was filtered and dried at 80°C to obtain polyurethane-synergistic surface-functionalized paint residue intermediate A, whose infrared spectrum is as follows. Figure 4 As shown in Figure 5, the morphology is illustrated by a scanning electron microscope.

[0046] Example 2 This embodiment illustrates a method for surface functionalization of waste paint residue from powdered polyester coatings using hydroxylation treatment and partially blocked polyurethane prepolymers.

[0047] Preparation of the hydroxylation treatment solution: Mix 2 parts of 3-[bis(2-hydroxyethyl)amino]propyltriethoxysilane, 90 parts of ethanol, and 10 parts of deionized water. Adjust the pH to 4.5-5.5 with glacial acetic acid and hydrolyze for 30 minutes at room temperature. Then add 100 parts of pretreated waste paint residue with a particle size of less than 200 μm, stir for 1 hour, and keep at 60℃ for 1 hour. After treatment, filter and dry at 80℃ for 3 hours to obtain waste paint residue particles with hydroxyl groups on the surface.

[0048] Preparation of partially blocked polyurethane prepolymer: Polycaprolactone diol (PCL1000) with a number average molecular weight of 1000 was vacuum dehydrated at 110°C for 2 hours. After cooling to 80°C, MDI was added, controlling the molar ratio of isocyanate groups to hydroxyl groups at 2.2:1. 1,4-Butanediol was added as a chain extender, accounting for 8% of the total molar amount of hydroxyl groups. Subsequently, 0.05 parts of dibutyltin dilaurate were added, and the reaction was carried out at 80°C for 2.5 hours under nitrogen protection to obtain an isocyanate-terminated polyurethane prepolymer. Then, butanone oxime was added as a blocking agent, controlling the molar ratio of isocyanate groups to butanone oxime at 1:0.6, and the reaction was carried out at 70°C for 1.5 hours to obtain a partially blocked polyurethane prepolymer.

[0049] 100 parts of the above-mentioned hydroxylated waste paint residue were added to a partially closed polyurethane prepolymer, with the prepolymer accounting for 12% of the mass of the waste paint residue. The mixture was stirred and reacted at 75°C for 2 hours. After the reaction was completed, the mixture was filtered and dried to obtain polyurethane synergistic surface functionalized waste paint residue intermediate B.

[0050] Example 3 This embodiment illustrates a method for surface functionalization of waste paint residue from powdered polyester coatings using mercaptolation treatment and partially blocked polyurethane prepolymers.

[0051] Preparation of the thiolization treatment solution: Mix 1.8 parts of γ-mercaptopropyltrimethoxysilane KH590, 95 parts of ethanol, and 5 parts of deionized water. Adjust the pH to 4.5-5.5 with glacial acetic acid and stir for 30 minutes at room temperature. Then add 100 parts of pretreated waste paint residue with a particle size of less than 200 μm, continue stirring for 1 hour, and keep at 60℃ for 1 hour. After treatment, filter and dry at 80℃ for 3 hours to obtain waste paint residue particles with thiol groups on the surface.

[0052] Preparation of partially blocked polyurethane prepolymer: Polytetrahydrofuran diol (PTMEG1000) was vacuum dehydrated at 110°C for 2 hours. After cooling to 75°C, isophorone diisocyanate (IPDI) was added, controlling the molar ratio of isocyanate groups to hydroxyl groups at 2.2:1. 1,4-Butanediol was added as a chain extender, accounting for 10% of the total molar amount of hydroxyl groups. Subsequently, 0.04 parts of dibutyltin dilaurate were added, and the reaction was carried out at 75°C for 2.5 hours under nitrogen protection to obtain an isocyanate-terminated polyurethane prepolymer. Then, butanone oxime was added as a blocking agent, controlling the molar ratio of isocyanate groups to butanone oxime at 1:0.5, and the reaction was carried out at 70°C for 1.5 hours to obtain a partially blocked polyurethane prepolymer.

[0053] 100 parts of the above-mentioned mercapto-modified waste paint residue were added to a partially closed polyurethane prepolymer, with the amount of prepolymer being 8% of the mass of the waste paint residue. The mixture was stirred and reacted at 70°C for 1.5 hours. After the reaction was completed, the mixture was filtered and dried to obtain polyurethane synergistic surface functionalized waste paint residue intermediate C.

[0054] Example 4 This embodiment provides application verification of intermediate A obtained in Example 1: 100 parts of E51 epoxy resin were taken, and 20 parts of intermediate A obtained in Example 1 were added. The mixture was mechanically stirred at 60°C for 20 minutes, followed by high-speed dispersion for 10 minutes to ensure that intermediate A was uniformly dispersed in the epoxy resin. Subsequently, 50 parts of polyamide curing agent and 0.5 parts of 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30) accelerator were added, and the mixture was stirred evenly before vacuum degassing. The degassed mixture was poured into a mold and cured at 60°C for 2 hours, followed by curing at 120°C for 3 hours. After curing, the mixture was cooled and demolded. The resulting sample was then heated to 160°C for post-treatment for 2 hours, followed by natural cooling to room temperature to obtain the epoxy resin composite material.

[0055] Comparative samples were prepared using the same formulation ratios, dispersion methods, and curing conditions. The only difference was that 20 parts of intermediate A were replaced with 20 parts of untreated waste paint residue, while the amounts of other raw materials and preparation conditions remained unchanged. Intermediate A was uniformly dispersed in the epoxy resin matrix, and the interfacial bonding between the particles and the resin matrix in the cross-section was relatively tight.

[0056] Tests showed that the epoxy resin sample with untreated waste paint residue had a tensile strength of 25 MPa and a flexural strength of 53 MPa. After adding 20 parts of intermediate A, the tensile strength of the resulting epoxy resin composite material increased to 51 MPa and the flexural strength increased to 77 MPa.

[0057] Example 5 This embodiment provides application verification of intermediate B obtained in Example 2: 100 parts of polyether polyol PPG1000 were taken, and 15 parts of intermediate B obtained in Example 2 were added. The mixture was dispersed at high speed for 15 minutes to ensure that intermediate B was uniformly dispersed in PPG1000. Subsequently, 26 parts of MDI were added, and the mixture was rapidly stirred until homogeneous. Vacuum degassing was then performed, and the mixture was poured into a mold.

[0058] After casting, the sample was pre-cured at room temperature for 24 hours, and then post-cured at 120°C for 4 hours. After curing, the sample was cooled and demolded, and then heated to 160°C for post-treatment for 2 hours, followed by natural cooling to room temperature to obtain the polyurethane composite material.

[0059] Comparative samples were prepared using the same formulation ratio, dispersion method, and curing conditions. The only difference was that 15 parts of intermediate B were replaced with 15 parts of untreated waste paint residue, while the amounts of other raw materials and preparation conditions remained unchanged. The polyurethane composite material prepared by adding intermediate B had a smooth surface, with no obvious particle precipitation or agglomeration. The material cross-section was relatively dense, and the interfacial bonding between the particles and the polyurethane matrix was relatively tight.

[0060] Performance tests showed that the tensile strength of the control sample containing untreated waste paint residue was 13.4 MPa and the elongation at break was 186%. After adding 15 parts of intermediate B, the tensile strength of the resulting polyurethane composite material increased to 28.7 MPa and the elongation at break increased to 348%.

[0061] Example 6 This embodiment provides application verification of intermediate C obtained in Example 3: 100 parts of Shangwei 901 bisphenol A type epoxy vinyl ester resin were taken, and 25 parts of intermediate C obtained in Example 3 were added. After mechanical stirring for 20 minutes, the mixture was dispersed at high speed for 10 minutes to ensure that intermediate C was uniformly dispersed in the vinyl resin. Subsequently, 0.3 parts of cobalt isooctanoate accelerator with a cobalt content of 6% were added, and after stirring evenly, 1.5 parts of methyl ethyl ketone peroxide initiator were added. Stirring was continued until the mixture was uniform, and vacuum degassing was performed.

[0062] The degassed mixture was poured into a mold and cured at room temperature for 24 hours, followed by a post-curing at 80°C for 3 hours. After curing, the mixture was cooled and demolded. The resulting sample was then heated to 160°C for post-treatment for 2 hours, and subsequently cooled naturally to room temperature to obtain the vinyl resin composite material.

[0063] Comparative samples were prepared using the same formulation ratio, dispersion method, and curing conditions. The only difference was that 25 parts of intermediate C were replaced with 25 parts of waste paint residue that had not undergone surface functionalization treatment. The amounts of other raw materials and preparation conditions remained unchanged.

[0064] The vinyl resin composite material prepared by adding intermediate C has complete molding and relatively dense internal structure. Intermediate C is relatively uniformly dispersed in the resin matrix, and the interfacial bonding between the particles and the vinyl resin matrix is ​​relatively tight.

[0065] Performance tests showed that the tensile strength of the control sample containing 25 parts of untreated waste paint residue was 38 MPa and the flexural strength was 66 MPa. After adding 25 parts of intermediate C, the tensile strength of the resulting vinyl resin composite material increased to 45 MPa and the flexural strength increased to 73 MPa.

[0066] Example 7 This embodiment provides application verification of intermediate B obtained in Example 2: Covestro Makrolon 2405 polycarbonate (PC) resin was dried in a vacuum drying oven at 120°C for 4 hours. 100 parts of the dried PC resin were taken, and 20 parts of intermediate B were added. The mixture was then mixed in a high-speed mixer for 10 minutes to ensure sufficient pre-dispersion of intermediate B in the PC resin particles. The mixture was then added to a twin-screw extruder for melt blending. The temperatures of each zone of the extruder were sequentially controlled at 250°C, 260°C, 270°C, 280°C, and 285°C, with the die head temperature controlled at 285°C and the screw speed at 120 rpm. After cooling, traction, and pelletizing, PC composite granules were obtained. The obtained PC composite granules were dried again at 120°C for 4 hours, and then injection molded using an injection molding machine. The injection temperature was controlled at 280~295°C, and the mold temperature at 80~100°C, resulting in PC composite test specimens.

[0067] Comparative samples were prepared using the same formulation ratios and processing conditions, with the only difference being that 20 parts of intermediate B were replaced with 20 parts of untreated powdered polyester coating waste paint residue. All other raw material amounts, drying conditions, mixing methods, extrusion conditions, and injection molding conditions remained unchanged. The PC composite material obtained by adding intermediate B had a smoother surface, and the particles were more uniformly dispersed in the PC resin matrix.

[0068] Performance tests showed that the tensile strength of the control sample containing 20 parts of untreated waste paint residue was 33 MPa and the flexural strength was 65 MPa. After adding 20 parts of intermediate B, the tensile strength of the resulting vinyl resin composite material increased to 47 MPa and the flexural strength increased to 88 MPa.

[0069] Furthermore, the overall process flow diagram of the surface functionalization modification method for waste paint residue of powder polyester coating provided in the above embodiments is shown in Figure 2. The polyurethane synergistic surface functionalization paint residue intermediate can be introduced into different polymer matrices such as epoxy resin, polyurethane, thermoplastic polymer and thermosetting polymer to prepare corresponding composite materials. In combination with the above embodiments, it can be seen that it has the following advantages: (1) The intermediate can be mixed with epoxy resin, curing agent and accelerator, and after dispersion, degassing, casting or molding, cured and post-treated at a set temperature to obtain epoxy resin composite material. Since the polyurethane functional layer and latent reaction sites on the surface of the intermediate can improve the interfacial bonding between waste paint residue particles and epoxy resin, the resulting material has good mechanical properties and interfacial stability.

[0070] (2) The intermediate can be mixed with polyether polyols, isocyanates and other components, and polyurethane composites can be prepared by casting, foaming or molding. Because the polyurethane segments on the surface of the intermediate have good compatibility with the polyurethane matrix, its dispersion state and interfacial stability in the system are also good.

[0071] (3) The intermediate can be mixed with thermoplastic resins (PS, PC, PVC, etc.) and then the composite material can be prepared by melt extrusion and injection molding. Since the functional layer on the surface of the intermediate improves the interfacial wetting and compatibility between the particles and the matrix, it is more conducive to obtaining a composite product with uniform dispersion and stable performance than directly filling untreated paint residue.

[0072] (4) The intermediate can be mixed with thermosetting resins (vinyl resin, unsaturated polyester resin, phenolic resin, etc.) and the composite material can be obtained by casting, molding, curing and post-treatment. Since the surface of the intermediate retains latent reactive activity, it helps to strengthen the interfacial bonding with the thermosetting matrix during heating curing and post-treatment.

[0073] In summary, the surface functionalization modification method for waste paint residue from powdered polyester coatings described in this invention is simple in process and mild in reaction conditions. It does not require strong acids, strong alkalis, or organic solvents, nor does it disrupt the three-dimensional cross-linked network of the paint residue. It is environmentally friendly and easy to implement industrially. The resulting polyurethane-synergistic surface functionalized paint residue intermediate can significantly improve the dispersibility and interfacial bonding of waste paint residue in various polymer matrices, effectively enhancing the mechanical properties of the composite material. This provides a practical and feasible green technology path for the resource utilization and high-value utilization of waste paint residue from powdered polyester coatings.

[0074] 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 surface functionalization modification of waste paint residue from powdered polyester coatings, characterized in that, Includes the following steps: S1. Pretreatment: Screen the waste paint residue of powder polyester coating to remove impurities, dry it at 80℃~100℃ for 2 hours to 6 hours, and then screen it after mechanical crushing. S2. Surface activation modification: The paint sludge after the pretreatment in step S1 is surface-treated with a functional silane coupling agent to introduce hydroxyl, amino, or mercapto active groups on the surface of the paint sludge particles, thereby obtaining surface-activated paint sludge; the functional silane coupling agent is one or more of 3-[bis(2-hydroxyethyl)amino]propyltriethoxysilane, γ-aminopropyltriethoxysilane, and γ-mercaptopropyltrimethoxysilane; S3. Preparation of partially blocked polyurethane prepolymer: Diisocyanate is reacted with polyether polyol or polyester polyol, and the molar ratio of isocyanate groups to hydroxyl groups is controlled at (2.0~2.5):1 to obtain isocyanate-terminated polyurethane prepolymer; then a blocking agent is added to block some of the isocyanate groups, and the molar ratio of blocking agent to isocyanate groups is controlled at (0.4~0.7):1 to obtain partially blocked polyurethane prepolymer; S4. Surface grafting reaction: The surface-activated paint sludge obtained in step S2 is added to the partially closed polyurethane prepolymer obtained in step S3, so that the unclosed isocyanate groups in the prepolymer react with the active groups on the surface of the paint sludge. After the reaction, the mixture is filtered and dried to obtain a polyurethane synergistic surface functionalized paint sludge intermediate.

2. The method for surface functionalization modification of waste paint residue from powdered polyester coatings according to claim 1, characterized in that, In step S3, the number average molecular weight of the polyether polyol or polyester polyol is 500-2000; the diisocyanate is 4,4'-diphenylmethane diisocyanate or isophorone diisocyanate; and the blocking agent is butanone oxime, ε-caprolactam, or phenol.

3. The method for surface functionalization modification of waste paint residue from powdered polyester coatings according to claim 1, characterized in that, Step S3 also includes adding a small molecule diol as a chain extender, the amount of which accounts for 5% to 15% of the total molar amount of hydroxyl groups.

4. The method for surface functionalization modification of waste paint residue from powdered polyester coatings according to claim 1, characterized in that, In step S4, the amount of the partially closed polyurethane prepolymer added is 8% to 12% of the mass of the surface-activated paint sludge; the reaction temperature is 60℃ to 80℃, and the reaction time is 1 hour to 3 hours.

5. The method for surface functionalization modification of waste paint residue from powdered polyester coatings according to claim 1, characterized in that, In step S2, the specific operation of the surface treatment is as follows: mix silane coupling agent, ethanol and water, adjust the pH to 4.5~5.5, hydrolyze for 20 minutes~40 minutes, then add the pretreated paint residue, stir for 0.5 hours~1.5 hours, keep warm at 50℃~70℃ for 0.5 hours~1.5 hours, filter and dry.

6. The method for surface functionalization modification of waste paint residue from powdered polyester coatings according to claim 1, characterized in that, In step S1, the sieving control particle size is less than 500 μm.

7. A polyurethane-synergistically surface-functionalized paint residue intermediate, characterized in that, Prepared by the method according to any one of claims 1 to 6.

8. The polyurethane synergistic surface functionalized paint residue intermediate according to claim 7, characterized in that, The intermediate is used as a functional filler in blending with the polymer matrix; The polymer matrix is ​​epoxy resin, polyurethane, vinyl ester resin, thermoplastic resin or thermosetting resin.

9. The polyurethane synergistic surface functionalized paint residue intermediate according to claim 8, characterized in that, The thermoplastic resin is polystyrene, polycarbonate, or polyvinyl chloride; And / or, the thermosetting resin is an unsaturated polyester resin or a phenolic resin.

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