Quaternary ammonium salt modified polyester resin, preparation method thereof and antibacterial powder coating

Abstract

The invention discloses quaternary ammonium salt modified polyester resin, a preparation method thereof and an antibacterial powder coating. The invention relates to a quaternary ammonium salt modified polyester resin. The molecular formula of the quaternary ammonium salt modified polyester resin contains the following repetitive units:-[O-CO-Ar-CO-O-R1-O]-and-[O-CO-Ar-CO-O-R2-N + (R3) (R4)-X-]-, wherein Ar is an aryl group derived from an aromatic dicarboxylic acid or a derivative thereof; r1 is an alkylene group from an aliphatic or alicyclic diol; r < 2 > is alkylene of C < 2 > to C < 6 >; r < 3 > and R < 4 > are respectively and independently straight chain or branched chain alkyl of C < 8 > to C < 18 >; x-is an anion; the acid value of the quaternary ammonium salt modified polyester resin is 20-50 mg KOH / g, and the glass transition temperature is 50-70 DEG C. The prepared powder coating does not need to be additionally provided with an antibacterial agent, and also has excellent mechanical properties, chemical resistance and appearance.

Description

Technical Field

[0001] This invention relates to the field of coating technology, specifically to a quaternary ammonium salt modified polyester resin and its preparation method, and an antibacterial powder coating. Background Technology

[0002] Powder coatings, as an environmentally friendly coating, are widely used in home appliances, building materials, furniture, and medical devices due to their advantages such as being solvent-free, highly efficient, and recyclable. However, in humid environments with high-frequency contact (such as hospitals, schools, public transportation, and kitchen equipment), the coating surface can easily become a breeding ground for microorganisms (such as bacteria and mold), causing hygiene and safety problems. Therefore, developing powder coatings with antibacterial properties is of significant practical importance.

[0003] Currently, the mainstream method for imparting antibacterial properties to powder coatings is to add antibacterial agents to the coating formulation. These mainly include: 1) inorganic antibacterial agents, such as silver ions, zinc ions, copper ions, and their oxides / complexes; 2) organic antibacterial agents, such as isothiazolinones and quaternary ammonium salts. While these methods are effective, they have significant drawbacks: added antibacterial agents are prone to migration and leaching from the coating film, resulting in a short antibacterial effective period and potential environmental and health risks (e.g., the leaching of silver ions may cause environmental enrichment and cytotoxicity); at the same time, the addition of antibacterial agents may negatively affect the mechanical properties, leveling, and weather resistance of the coating film, and poor compatibility with the resin matrix can easily lead to agglomeration, affecting the appearance of the coating.

[0004] In the prior art: CN112646159A discloses a method for preparing quaternary ammonium salt modified polyester resin for antibacterial powder coatings. The quaternary ammonium salt modified polyester resin is formed by bulk polymerization of carboxylic acid compounds, tertiary amine compounds, comonomers and esterification catalysts in a heated molten state. The carboxylic acid compounds are carboxylic acid compounds with halomethyl groups, and the comonomers include polybasic acids and / or acid anhydrides and polyols. The entire process is solvent-free, avoiding the use of expensive, highly toxic and volatile solvents.

[0005] CN114524926A discloses a biodegradable antibacterial cationic polyester, its preparation method, and its applications, belonging to the field of biomaterials. The preparation method of the antibacterial cationic polyester provided by this invention includes the following steps: an aliphatic copolyester containing C=C double bonds undergoes bromination and quaternization reactions of the C=C double bonds on its molecular chain to obtain a quaternary ammonium salt cationic copolyester, which is the aforementioned antibacterial cationic polyester. The antibacterial cationic polyester of this invention has advantages such as good biocompatibility, good biodegradability, and excellent antibacterial properties. The antibacterial cationic polyester of this invention can be used for surface antibacterial modification of degradable polyesters, especially for surface modification of 3D-printed degradable polyester materials.

[0006] In summary, intrinsic antibacterial polymers, by covalently bonding antibacterial functional groups (such as quaternary ammonium salts) to the polymer backbone or side chains, fundamentally overcome the aforementioned shortcomings. The antibacterial groups are firmly fixed to the coating surface, providing durable and safe contact-based antibacterial activity without the risk of leaching. Polyester resins are one of the most important film-forming resins for powder coatings, but research on polyester resins with intrinsic antibacterial functions is currently limited, and they generally face the following challenges: a) High synthesis difficulty: Monomers with quaternary ammonium salt functional groups often have poor thermal stability and are incompatible with the high-temperature (>200°C) polycondensation process of polyester, and are prone to decomposition or discoloration.

[0007] b) Difficulty in balancing performance: Introducing hydrophilic quaternary ammonium salt groups may significantly reduce the hydrophobicity and hydrolysis resistance of polyester resin, affecting coating durability.

[0008] c) Antibacterial efficiency and cost: How to achieve a broad-spectrum and rapid antibacterial effect comparable to highly efficient silver-based antibacterial agents at a reasonable cost is a technical challenge.

[0009] d) Formulation compatibility: The modified resin must maintain good compatibility with traditional powder coating formulations (such as leveling agents, curing agents, and pigments), and the curing process should not be significantly changed.

[0010] Therefore, there is an urgent need for a quaternary ammonium salt modified polyester resin and its powder coating that has a feasible synthesis process, excellent comprehensive performance, and long-lasting and highly effective intrinsic antibacterial function. Summary of the Invention

[0011] The purpose of this invention is to provide a quaternary ammonium salt modified polyester resin and its preparation method, as well as an antibacterial powder coating.

[0012] The quaternary ammonium salt modified polyester resin has high thermal stability and long alkyl chain quaternary ammonium salt structural units introduced into the polyester backbone in the form of covalent bonds, so that the resin has both excellent film-forming properties and antibacterial properties.

[0013] The resulting powder coating does not require the addition of antibacterial agents and can also achieve excellent mechanical properties, chemical resistance, and appearance.

[0014] To achieve the above objectives, the following technical solutions are used: A quaternary ammonium salt modified polyester resin, The molecular formula of quaternary ammonium salt modified polyester resin contains the following repeating units: -[O-CO-Ar-CO-O-R1-O]- and -[O-CO-Ar-CO-O-R2-N+(R3)(R4)-X-]-; Wherein, Ar is an aryl group derived from an aromatic dicarboxylic acid or its derivative; R1 is an alkylene derivative from aliphatic or alicyclic diols; R2 is a C2-C6 alkylene group; R3 and R4 are each independently a C8-C18 straight-chain or branched alkyl group; X- is an anion; Furthermore, the quaternary ammonium salt modified polyester resin has an acid value of 20-50 mg KOH / g and a glass transition temperature of 50-70℃.

[0015] As a further improvement to this scheme, R3 and R4 are C12-C16 straight-chain alkyl groups.

[0016] As a further improvement to this scheme, X- is Cl-, Br-, BF4- or TFSI-; The Ar is derived from terephthalic acid, isophthalic acid, or naphthalenedicarboxylic acid; the R1 is derived from neopentyl glycol, ethylene glycol, or cyclohexanediethanol.

[0017] A method for preparing quaternary ammonium salt modified polyester resin includes the following steps: (1) A long-chain alkyl tertiary amine is reacted with an excess of epoxy compound to generate an epoxy end-group intermediate, which is then subjected to a ring-opening esterification reaction with an excess of dibasic organic acid or anhydride to obtain a diol monomer containing a tertiary amine group. (2) An aromatic dicarboxylic acid or its derivative, a diol, and a diol monomer containing a tertiary amine group obtained in step (1) are subjected to esterification / ester exchange and polycondensation reaction to obtain a copolyester prepolymer containing a tertiary amine group; the comonomer also includes isosorbide, long-chain dicarboxylic acid and / or branched acid anhydride. (3) The copolyester prepolymer obtained in step (2) is reacted with a quaternizing agent in a solvent to quaternize, and then the solvent is removed to obtain the quaternary ammonium salt modified polyester resin.

[0018] As a further improvement to this plan, In step (1), the long-chain alkyl tertiary amine is N,N-bisdodecylethanolamine or N,N-bistetradecylethanolamine; the epoxy compound is epichlorohydrin or dodecyl glycidyl ether. The dibasic organic acid or anhydride is itaconic acid, fumaric acid, or maleic anhydride.

[0019] As a further improvement to this scheme, in step (2), the amount of isosorbide in the comonomer accounts for 5%-25% of the total molar amount of the diol; The long-chain dicarboxylic acid is a straight-chain dicarboxylic acid with 12-20 carbon atoms, and its feed amount accounts for 2%-10% of the total molar number of dicarboxylic acids; The branched acid anhydride is trimellitic anhydride or pyromellitic dianhydride, and its feed amount accounts for 0.5%-3% of the total molar amount of the dicarboxylic acid.

[0020] As a further improvement to this scheme, in step (3), the quaternizing agent is a halogenated C8-C18 alkane or a long-chain alkyl glycidyl ether halogenated hydrochloric acid ring-opening adduct. The solvent is a mixture of at least two of N-methylpyrrolidone, xylene, or n-butanol; The reaction temperature is 70-100°C, and the reaction time is 6-12 hours.

[0021] An antibacterial powder coating comprising the following components: 50-70 parts of the quaternary ammonium salt modified polyester resin according to claims 1-3; 10-25 parts of curing agent; Leveling agent 0.5-2 parts; 0.5-1.5 parts of degassing agent; 10-30 parts pigment; 10-25 parts of filler.

[0022] As a further improvement to this solution, the curing agent is any one or more of triglycidyl isocyanurate (TGIC), hydroxyalkylamide (HAA), or epoxy resin.

[0023] As a further improvement to this scheme, 50-70 parts of quaternary ammonium salt modified polyester resin of 1-3; 10-25 parts of curing agent; 0.5-2 parts of leveling agent; 0.5-1.5 parts of degassing agent; 10-30 parts of pigment; and 10-25 parts of filler are premixed, and then melt-extruded, cooled and pressed into sheets, crushed, and sieved to obtain powder coating.

[0024] The quaternary ammonium salt modified polyester resin, its preparation method, and antibacterial powder coating of the present invention have the following beneficial effects: 1) The powder coating prepared by this invention has an antibacterial rate of more than 99.9% (even >99.99%) against Staphylococcus aureus (Gram-positive bacteria) and Escherichia coli (Gram-negative bacteria) within 24 hours, which is comparable to the control sample with 1.5% nano-silver antibacterial agent added. The specific mechanism of action is as follows: The quaternary ammonium cations (N+) on the coating surface strongly bind to the negatively charged bacterial cell membrane (phospholipid bilayer and lipopolysaccharide) through electrostatic adsorption. Long alkyl chains (R3, R4, C12-C16) can contact the hydrophobic regions of the bacterial cell membrane, disrupting the membrane structure and causing leakage of cell contents (such as K+, DNA, RNA, and proteins), thereby killing bacteria. Covalent bonding ensures that the antibacterial groups are permanently fixed to the coating surface, forming a "contact-kill" antibacterial surface with no risk of leaching and a lifespan equivalent to that of the coating itself. The key role of long alkyl chains: Compared to short-chain quaternary ammonium salts (such as those below C8), the C12-C16 long-chain alkyl groups used in this invention have stronger hydrophobicity and membrane-disrupting ability. Long chains can more effectively penetrate the lipid bilayer of bacterial cell membranes, causing irreversible physical damage, thus giving the coating highly efficient antibacterial properties.

[0025] 2) In the preparation method of this invention: a polyester prepolymer containing tertiary amine groups with relatively good thermal stability is first synthesized, and then quaternization is carried out under relatively mild conditions. This avoids the decomposition and discoloration problems caused by directly involving quaternary ammonium salt monomers in high-temperature polycondensation.

[0026] 3) The role of other components in the formulation of this invention: Isosorbide: Its rigid bicyclic five-membered ring structure (the 1,4:3,6-didehydrohexitol structure of isosorbide) effectively restricts the free rotation of polyester segments, significantly increasing the glass transition temperature (Tg) of the resin. This compensates for the Tg decrease caused by the long alkyl chain quaternary ammonium salt units (which have an internal plasticizing effect), ensuring that the powder resin has sufficient storage stability and anti-caking properties. Its intramolecular ether bonds also contribute a certain degree of flexibility.

[0027] Dodecanedioic acid / behenic acid: As a long-chain dicarboxylic acid, it introduces soft -(CH2)10-20- segments into the polyester backbone. This effectively increases the chain's flexibility and impact strength, avoids material embrittlement caused by the introduction of a large number of rigid aromatic units and isosorbide, and gives the coating good flexibility (excellent forward and reverse impact performance).

[0028] Long-chain alkyl glycidyl ether derivatives: When used in the synthesis of quaternizing reagents or tertiary amine monomers, it not only introduces quaternization sites, but its long-chain alkoxy structure also further enhances the hydrophobicity of the resin and its compatibility with other components in the coating film.

[0029] Technical effects: By combining rigid monomers (isosorbide, aromatic acids) and flexible long-chain monomers (long-chain dicarboxylic acids, alkyl chains of long alkyl quaternary ammonium salts), the high Tg of the resin (ensuring powder stability) and good flexibility (ensuring the mechanical properties of the coating) are balanced.

[0030] Adhesion (cross-cut test) grade 0, bending test (≤2mm) passed, impact resistance (kg·cm) front / back 50 / 50, pencil hardness 1-2H, salt spray resistance (500h) scratches spread on one side <2mm, resistance to 5% NaOH (168h) no change, storage stability (40°C, 30 days) no clumping.

[0031] 4) The present invention relates to an intrinsic antibacterial polyester resin with a long alkyl chain quaternary ammonium salt structure. Highly efficient antibacterial units are introduced into the resin molecular chain. The prepared powder coating requires no external antibacterial agent while maintaining the physical and mechanical properties of the coating, solving the technical problems of short antibacterial lifespan and easy impact on coating performance in traditional externally applied antibacterial coatings. Attached Figure Description

[0032] Figure 1 This is a product image of the quaternary ammonium salt modified polyester resin from Example 1 of the present invention; Figure 2 This is an antibacterial test chart of the coating made from the quaternary ammonium salt modified polyester resin product of Example 1 of the present invention (one week, 30°C, 50% humidity). Figure 3 This is an antibacterial test chart of the quaternary ammonium salt modified polyester resin product of Example 2 of the present invention after it was made into a coating (one week, 30°C, 50% humidity). Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described below in conjunction with embodiments and accompanying drawings: Example 1 Preparation of a monomer containing a tertiary amine group (itaconic acid ester of N,N-bisdodecyl-N-(2-hydroxyethyl)amine): In a four-necked flask equipped with a stirrer, thermometer, and condenser, 100 g of N,N-bisdodecylethanolamine and 50 g of epichlorohydrin (excess) were added. Tetrabutylammonium bromide (1 g) was added as a catalyst, and the mixture was heated to 80°C and reacted for 4 hours to obtain an epoxy-terminated intermediate. The temperature was lowered to 60°C, and 70 g of itaconic acid and a small amount of hydroquinone as a polymerization inhibitor were added. The mixture was then heated to 100°C and reacted for 6 hours. After the reaction was complete, the mixture was washed with a dilute alkaline aqueous solution, and the organic layer was removed under reduced pressure to remove unreacted material, yielding a pale yellow viscous liquid, denoted as monomer A. (2) Synthesis of copolyester prepolymer: In a reactor equipped with a fractionating column, stirrer, and nitrogen inlet pipe, terephthalic acid (PTA, 200g), isophthalic acid (IPA, 40g), neopentyl glycol (NPG, 150g), isosorbide (IS, 30g), dodecanoic acid (DDDA, 20g), and monomer A (60g, containing approximately 0.08mol of tertiary amine) obtained in step (1) were added. Monobutyltin oxide catalyst (0.5g) was added. Under nitrogen protection, the temperature was slowly raised to 210°C for esterification until the water content reached more than 95% of the theoretical value. Then, trimellitic anhydride (TMA, 5g) was added for slight branching. The temperature was raised to 240°C, and the system pressure was gradually evacuated until it was below 300Pa. The polycondensation reaction was carried out for about 2 hours. The acid value was monitored and dropped to about 35 mg KOH / g, and the viscosity was moderate (melt viscosity at 200°C was about 5000 mPa·s). The reaction was stopped, the pressure was released, and a pale yellow transparent prepolymer B was obtained. (3) Quaternization reaction: Prepolymer B was dissolved in 400g of N-methylpyrrolidone (NMP), and bromododecane (45g) was added. The temperature was raised to 90°C and the reaction was stirred for 10 hours. After the reaction was completed, most of the NMP and unreacted bromododecane were recovered by distillation at 120°C / reduced pressure. The product was vacuum devolatilized at 180°C for 2 hours to obtain quaternary ammonium salt modified polyester resin C1. Its performance indicators are: acid value 35mgKOH / g, Tg 63°C, Mn4200.

[0034] Example 2 The same as step (1) in Example 1.

[0035] In step (2), the monomer ratios were adjusted as follows: PTA, 210g; IPA, 30g; NPG, 140g; IS, 40g; DDDA, 15g; monomer A, 70g; TMA, 8g. The catalyst dosage remained the same. In step (3), iodotetradecane (52g) was used as the quaternizing agent. Quaternary ammonium salt modified polyester resin C2 was obtained. Its performance indicators were: acid value 41mgKOH / g, Tg 64°C, Mn 3800.

[0036] In step (1) of Example 3, N,N-bistetradecylethanolamine and dodecyl glycidyl ether were reacted, followed by ring-opening with maleic anhydride to prepare monomer A+. In step (2), dimethyl terephthalate (DMT) was used for transesterification synthesis, and a small amount of behenic acid (eicosanoic acid, 10g) was added. The amount of isosorbide was increased to 50g. In step (3), the dodecyl glycidyl ether hydrochloric acid ring-opening adduct was used as the quaternizing agent (prepared by reacting dodecyl glycidyl ether with concentrated hydrochloric acid). Quaternary ammonium salt modified polyester resin C3 was obtained. Its performance indicators are: acid value 30mgKOH / g, Tg 65°C, Mn 5000.

[0037] Comparative Example 1: Conventional Carboxylated Polyester Resin A conventional polyester resin without any tertiary amine or quaternary ammonium salt monomers was synthesized. Formulation: PTA, 250g; IPA, 50g; NPG, 180g; ethylene glycol (EG), 20g; TMA, 5g. The catalyst and process were the same as in Example 1. Resin D1 was obtained, with an acid value of 34 mgKOH / g, Tg 62°C, and Mn 4500.

[0038] Comparative Example 2: Powder coating with added silver ion antibacterial agent. Using resin D1 of Comparative Example 1, 1.5 wt% of nano-silver-loaded zirconium phosphate antibacterial agent (average particle size <1μm) was added to the powder coating formulation.

[0039] Comparative Example 3: Short-chain quaternary ammonium salt modified polyester resin. Referring to Example 1, but in step (1) N,N-dimethylethanolamine (short-chain tertiary amine) was used instead of N,N-bisdodecylethanolamine, and in step (3) quaternization was performed using bromomethane. Resin D3 containing short-chain (-N+(CH3)3) quaternary ammonium salt was obtained.

[0040] Comparative Example 4: Polyester resin modified with high tertiary amine content was prepared according to Example 1, but the amount of monomer A was increased to 150 g (approximately 2.5 times that of Example 1), and other acids and alcohols were reduced proportionally to maintain functional group balance. Resin D4 was obtained, with Tg decreasing to 54°C.

[0041] Comparative Example 5: Quaternary ammonium salt modified polyester resin without isosorbide was prepared according to Example 1, but without the addition of isosorbide (IS), and its molar amount was supplemented by an equimolar amount of NPG. Resin D5 was obtained with a Tg of 52°C.

[0042] Powder Coating Preparation and Film Performance Testing: Powder coatings were prepared using the resins from Examples 1-3 and Comparative Examples 1-5 according to the following basic formulations: Polyester resin: 60 parts; curing agent (TGIC): 11 parts (adjusted according to resin acid value); leveling agent (GLP588): 1 part; benzoin: 0.5 parts; titanium dioxide (R902): 25 parts; barium sulfate: 15 parts. The components are premixed, melt-extruded (extrusion temperature 90-120°C), tableted, pulverized, and sieved (200 mesh) to obtain a powder coating. Electrostatic spraying is applied to phosphated cold-rolled steel sheets and cured at 200°C for 15 minutes, resulting in a film thickness of 60-80 μm.

[0043] Performance test results *Note: The granular texture of Comparative Example 2 originates from the slight agglomeration of the silver nanoparticles; its decreased salt spray resistance may be related to the formation of electrochemical corrosion microcells by the silver particles. Comparative Example 4 exhibits decreased chemical resistance due to its excessively high content of hydrophilic quaternary ammonium salts, and its high proportion of soft segments also resulted in slight powder agglomeration. Comparative Example 5 suffers from poor storage stability due to its lower Tg.

[0044] Comparison of antibacterial effects: Examples 1-3 exhibited antibacterial rates equal to or even better than those of added silver ions (Comparative Example 2), confirming their intrinsic antibacterial efficiency. Comparative Example 3 (short-chain quaternary ammonium salt) showed a significantly lower antibacterial rate than the examples, directly demonstrating the decisive role of long alkyl chains (C12 vs. C1) in disrupting bacterial cell membranes and achieving highly efficient sterilization. Although short-chain quaternary ammonium salts can adsorb onto bacterial surfaces, their membrane penetration and disruption capabilities are weak.

[0045] Mechanical properties and Tg: Examples 1-3 achieved a balance between high Tg and good flexibility through the synergistic effect of isosorbide (rigidity) and long-chain dicarboxylic acid / long alkyl chain (flexibility). Comparative Example 5 (without isosorbide) showed a significantly lower Tg (52°C), resulting in poorer powder storage stability (severe clumping) and a decrease in pencil hardness, demonstrating the crucial role of isosorbide in maintaining resin rigidity and ensuring powder application performance.

[0046] Overall performance and content relationship: Comparative Example 4 (high tertiary amine content): Although antibacterial properties were maintained, the Tg decreased to 54°C, leading to slight agglomeration; at the same time, excessive hydrophilic groups significantly reduced alkali resistance and salt spray resistance. This indicates that the introduction of antibacterial groups needs to be moderate, and its negative effects can be offset by molecular structure design (such as introducing hydrophobic long chains and rigid units).

[0047] Advantages of the synthesis process: The "post-functionalization" route adopted in this invention (first polymerizing into a prepolymer containing a tertiary amine, then quaternizing) successfully avoids the decomposition of the quaternary ammonium salt structure during high-temperature polycondensation, resulting in lighter resin colors in all embodiments. Attempting to directly involve the quaternary ammonium salt monomer in polycondensation would lead to severe charring and discoloration of the resin.

[0048] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent modifications made using the present invention are within the patent protection scope of the present invention.

Claims

1. A quaternary ammonium salt modified polyester resin, characterized in that, The molecular formula of quaternary ammonium salt modified polyester resin contains the following repeating units: -[O-CO-Ar-CO-O-R1-O]- and -[O-CO-Ar-CO-O-R2-N+(R3)(R4)-X-]-; Wherein, Ar is an aryl group derived from an aromatic dicarboxylic acid or its derivative; R1 is an alkylene derivative from aliphatic or alicyclic diols; R2 is a C2-C6 alkylene group; R3 and R4 are each independently a C8-C18 straight-chain or branched alkyl group; X- is an anion; Furthermore, the quaternary ammonium salt modified polyester resin has an acid value of 20-50 mg KOH / g and a glass transition temperature of 50-70℃.

2. The quaternary ammonium salt modified polyester resin according to claim 1, characterized in that, R3 and R4 are C12-C16 straight-chain alkyl groups.

3. The quaternary ammonium salt modified polyester resin according to claim 1, characterized in that, The X- is Cl-, Br-, BF4- or TFSI-; The Ar is derived from terephthalic acid, isophthalic acid, or naphthalenedicarboxylic acid; the R1 is derived from neopentyl glycol, ethylene glycol, or cyclohexanediethanol.

4. A method for preparing the quaternary ammonium salt modified polyester resin according to any one of claims 1 to 3, Its features are, Includes the following steps: (1) A long-chain alkyl tertiary amine is reacted with an excess of epoxy compound to generate an epoxy end-group intermediate, which is then subjected to a ring-opening esterification reaction with an excess of dibasic organic acid or anhydride to obtain a diol monomer containing a tertiary amine group. (2) An aromatic dicarboxylic acid or its derivative, a diol, and a diol monomer containing a tertiary amine group obtained in step (1) are subjected to esterification / ester exchange and polycondensation reaction to obtain a copolyester prepolymer containing a tertiary amine group; the comonomer also includes isosorbide, long-chain dicarboxylic acid and / or branched acid anhydride. (3) The copolyester prepolymer obtained in step (2) is reacted with a quaternizing agent in a solvent to quaternize, and then the solvent is removed to obtain the quaternary ammonium salt modified polyester resin.

5. The method for modifying polyester resin with quaternary ammonium salt according to claim 4, characterized in that, In step (1), the long-chain alkyl tertiary amine is N,N-bisdodecylethanolamine or N,N-bistetradecylethanolamine; the epoxy compound is epichlorohydrin or dodecyl glycidyl ether. The dibasic organic acid or anhydride is itaconic acid, fumaric acid, or maleic anhydride.

6. The method for modifying polyester resin with quaternary ammonium salt according to claim 5, characterized in that, In step (2), isosorbide accounts for 5%-25% of the total molar amount of the diols in the comonomer. The long-chain dicarboxylic acid is a straight-chain dicarboxylic acid with 12-20 carbon atoms, and its feed amount accounts for 2%-10% of the total molar number of dicarboxylic acids; The branched acid anhydride is trimellitic anhydride or pyromellitic dianhydride, and its feed amount accounts for 0.5%-3% of the total molar amount of the dicarboxylic acid.

7. The method for modifying polyester resin with quaternary ammonium salt according to claim 4, characterized in that, In step (3), the quaternizing agent is a cyclization adduct of a halocyanate of a halogenated C8-C18 alkane or a long-chain alkyl glycidyl ether; The solvent is a mixture of at least two of N-methylpyrrolidone, xylene, or n-butanol; The reaction temperature is 70-100°C, and the reaction time is 6-12 hours.

8. An antibacterial powder coating, characterized in that, Includes the following components: 50-70 parts of the quaternary ammonium salt modified polyester resin according to claims 1-3; 10-25 parts of curing agent; Leveling agent 0.5-2 parts; 0.5-1.5 parts of degassing agent; 10-30 parts pigment; 10-25 parts of filler.

9. The antibacterial powder coating according to claim 8, characterized in that, The curing agent is any one or more of triglycidyl isocyanurate (TGIC), hydroxyalkylamide (HAA), or epoxy resin.

10. A method for preparing an antibacterial powder coating as described in claim 9 or 10, characterized in that, 50-70 parts of quaternary ammonium salt modified polyester resin (1-3%); 10-25 parts of curing agent; 0.5-2 parts of leveling agent; 0.5-1.5 parts of degassing agent; After premixing 10-30 parts of pigment and 10-25 parts of filler, the mixture is melt-extruded, cooled and pressed into sheets, crushed and sieved to obtain powder coating.

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