Polyester resin composition and application thereof in water-resistant matte powder coating

Abstract

The invention discloses a polyester resin composition and application thereof in a water-resistant matte powder coating. The polyester resin composition comprises high-acid-value resin and low-acid-value resin, the acid value of the high acid value resin is 40-60 mgKOH / g; the acid value of the low-acid-value resin is 18 to 30 mgKOH / g; the high-acid-value resin is prepared from the following raw materials: polyol A, polyacid A, an acidolysis agent A, glycidyl ester, a carbodiimide compound, a catalyst A and a curing accelerator A; the low-acid-value resin is prepared from the following raw materials: polyol B, polyacid B, a catalyst B and a curing accelerator B. In the high-acid-value resin A, glycidyl ester is used as a carboxyl sealing agent, and a carbodiimide compound is used as a hydrolysis stabilizer, so that the polyester resin composition is endowed with excellent water resistance and ageing resistance; the low-acid-value resin B is further combined, so that the water-resistant matte powder coating with good leveling property, mechanical property and water resistance can be obtained.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, and particularly relates to a polyester resin composition and its application in water-resistant matte powder coatings. Background Technology

[0002] Matte powder coatings are increasingly used in the coatings industry due to their unique decorative properties. Weather-resistant powder coatings are used in protective applications that require resistance to outdoor sunlight and moisture, placing strict demands on the coating's water resistance. Currently, weather-resistant matte powder coatings typically employ a two-component dry-mix matte coating technology. This technology utilizes the difference in reactivity between resins with high and low acid values ​​to achieve a lower coating gloss level, and because no matting agent is added, the coating exhibits excellent weather resistance. However, in existing technologies, on the one hand, the polyester resin has strong hydrophilicity due to its ester bonds; on the other hand, the cross-linked network distribution within the two-component dry-mix matte coating is uneven, easily forming micropores or voids that become channels for moisture penetration. These factors ultimately lead to changes in gloss and surface color after boiling in water, and even decreased adhesion and blistering of the coating.

[0003] Semi-crystalline polyester resins often exhibit better water resistance due to the regular and compact arrangement of molecular chains in their crystalline regions, making it difficult for water molecules to penetrate. However, existing semi-crystalline polyester resins either have excessively low crystallinity or excessively high melting points, resulting in poor processing performance, or they significantly reduce the glass transition temperature of coatings, affecting storage performance. Summary of the Invention

[0004] In order to overcome at least one of the problems existing in the prior art, one of the objectives of the present invention is to provide a polyester resin composition that can be used to prepare powder coatings with higher water resistance, better processing and storage performance, and superior matte appearance.

[0005] A second objective of this invention is to provide a method for preparing the above-mentioned polyester resin composition.

[0006] A third objective of this invention is to provide the aforementioned powder coating.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A first aspect of the present invention provides a polyester resin composition comprising a high acid value resin and a low acid value resin; The high acid value resin has an acid value of 40~60 mgKOH / g; the low acid value resin has an acid value of 18~30 mgKOH / g. The high acid value resin comprises the following raw materials: polyol A, polyacid A, acid hydrolysis agent A, glycidyl ester, carbodiimide compound, catalyst A, and curing accelerator A. The low acid value resin comprises the following raw materials: polyol B, polyacid B, catalyst B, and curing accelerator B.

[0008] Preferably, the glycidyl ester includes at least one of glycidyl tert-carbonate, diglycidyl adipic acid, glycidyl methacrylate, or diglycidyl dimerate; more preferably, the glycidyl ester is selected from glycidyl tert-carbonate.

[0009] Preferably, the carbodiimide compound includes at least one of polycarbodiimide, N,N'-dicyclohexylcarbodiimide (DCC), N,N'-diisopropylcarbodiimide (DIC), or N-ethyl-N'-(3-dimethylaminopropyl)carbodiimide (EDC); more preferably, the carbodiimide compound is selected from polycarbodiimide.

[0010] Preferably, the high acid value resin comprises the following raw materials in parts by weight: 32-40 parts polyol A, 45-65 parts polyacid A, 8-15 parts acid hydrolysate A, 0.5-3 parts glycidyl ester, 0.2-1 part carbodiimide compound, 0.04-0.15 parts catalyst A, and 0.02-0.2 parts curing accelerator A.

[0011] Preferably, the polyol A includes at least one of neopentyl glycol, 2-methyl-1,3-propanediol, 2-methyl-2,4-pentanediol, 2-butyl-2-ethyl-1,3-propanediol, hydrogenated bisphenol A, 1,4-cyclohexanediol, trimethylolpropane, or pentaerythritol.

[0012] Preferably, the polybasic acid A includes at least one of terephthalic acid, isophthalic acid, 1,2-cyclosuccinic acid, or 1,4-cyclohexanedicarboxylic acid.

[0013] Preferably, the acid hydrolysant A includes at least one of isophthalic acid, trimellitic anhydride, pyromellitic anhydride, hexahydrophthalic anhydride, or hydrogenated dimer acid.

[0014] Preferably, the low acid value resin comprises the following raw materials in parts by weight: 25-45 parts polyol B, 55-75 parts polyacid B, 0.04-0.15 parts catalyst B, and 0.01-0.1 parts curing accelerator B.

[0015] In some embodiments of the present invention, the polyol B includes branched polyols, straight-chain polyols, or combinations thereof; preferably, the polyol B is selected from straight-chain polyols.

[0016] In some embodiments of the present invention, the polyol B includes branched polyols, straight-chain polyols, or combinations thereof; preferably, the polyacid B is selected from straight-chain polyacids.

[0017] In some embodiments of the present invention, the branched polyol includes neopentyl glycol, trimethylolpropane, or combinations thereof.

[0018] In some embodiments of the present invention, the branched polyacid includes isophthalic acid.

[0019] Preferably, the linear polyol includes at least one selected from ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, or 1,6-hexanediol.

[0020] Preferably, the linear polyacid includes at least one selected from terephthalic acid, 1,4-succinic acid, 1,6-adipic acid, azelaic acid, sebacic acid, and dodecanoic acid.

[0021] Preferably, catalyst A and catalyst B each independently comprise a tin-based catalyst, a titanium-based catalyst, or a combination thereof; more preferably, the tin-based catalyst comprises at least one of monobutyltin oxide, dimethyltin oxide, dibutyltin oxide, or stannous oxalate; and the titanium-based catalyst comprises at least one of tetrabutyl titanate, tetraisopropyl titanate, or activated titanium dioxide.

[0022] Preferably, the curing accelerator A and the curing accelerator B each independently comprise an organophosphorus curing accelerator, a quaternary ammonium salt curing accelerator, or a combination thereof; more preferably, the organophosphorus curing accelerator comprises at least one of triphenylphosphine, triphenylethyl phosphorus bromide, benzyltriphenylethyl phosphorus bromide, or tribenzylethyl phosphorus chloride; and the quaternary ammonium salt curing accelerator comprises at least one of tetrabutylammonium bromide, tetrabutylammonium chloride, benzyltrimethylammonium chloride, or benzyltriethylammonium chloride.

[0023] Preferably, the raw materials for preparing the high acid value resin A also include antioxidant A.

[0024] Preferably, antioxidant A comprises hindered phenolic antioxidants, phosphite antioxidants, or combinations thereof; more preferably, antioxidant A comprises at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, triethylene glycol bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate], 2,6-di-tert-butyl-4-methylphenol, triphenyl phosphite, pentaerythritol diisodecyl diphosphite, bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, or bisoctadecyl thiodipropionate.

[0025] Preferably, the raw materials for preparing the low acid value resin B also include antioxidant B.

[0026] Preferably, antioxidant B comprises hindered phenolic antioxidants, phosphite antioxidants, or combinations thereof; more preferably, antioxidant B comprises at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, triethylene glycol bis[3-(3-tert-butyl-5-methyl-4-hydroxyphenyl)propionate], 2,6-di-tert-butyl-4-methylphenol, triphenyl phosphite, pentaerythritol diisodecyl diphosphite, bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, or bisoctadecyl thiodipropionate.

[0027] Preferably, the raw materials for preparing the low acid value resin B further include a nucleating agent; more preferably, the nucleating agent includes at least one of sodium 2,2'-methylene bis(4,6-di-tert-butylphenyl) phosphate, sodium bis(4-tert-butylphenyl) phosphate, or dibenzyl sorbitol.

[0028] In some embodiments of the present invention, the raw materials for preparing the low acid value resin B further include an acid hydrolysant B; further, the acid hydrolysant B includes isophthalic acid, 1,6-adipic acid, or a combination thereof.

[0029] Preferably, the high acid value resin A satisfies at least one of the following characteristics: glass transition temperature of 65~75℃; melt viscosity of 9000~15000mPa.s at 200℃; reactivity of 40~120s at 180℃; and number average molecular weight of 2500~4500g / mol.

[0030] Preferably, the low acid value resin B satisfies at least one of the following characteristics: melting point of 120~240℃; melt viscosity of 100~12000mPa.s at 160℃; reactivity of 400~1000s at 180℃; and number average molecular weight of 3000~5000g / mol.

[0031] More preferably, the low acid value resin B satisfies at least one of the following characteristics: melting point of 120~140℃; melt viscosity of 4000~7000mPa.s at 160℃; reactivity of 400~800s at 180℃; and number average molecular weight of 3000~5000g / mol.

[0032] A second aspect of the present invention provides a method for preparing a polyester resin composition as described in the first aspect of the present invention, comprising the following steps: mixing polyol A, polyacid A, and catalyst A, and performing an esterification reaction to obtain esterified product A; adding acidolytic agent A to the esterified product A and performing an acidolytic reaction to obtain acidolytic product A; performing a vacuum polycondensation reaction on the acidolytic product A under vacuum to obtain polycondensation product A; adding glycidyl ester to the polycondensation product A and reacting to obtain a partially carboxyl-blocked product; and adding curing accelerator A and carbodiimide compound to the partially carboxyl-blocked product and reacting to obtain a high acid value resin A. Polyol B, polyacid B, and catalyst B are mixed and subjected to esterification to obtain esterified product B; then acid hydrolysis is performed to obtain acid hydrolysis product B; the acid hydrolysis product B is subjected to vacuum polycondensation to obtain polycondensation product B; curing accelerator B is added to the polycondensation product B and reacted to obtain low acid value resin B.

[0033] Preferably, in the step of preparing high acid value resin A, the esterification reaction process is as follows: the raw materials and catalyst in the specified proportions are added to the reaction vessel, nitrogen gas is introduced for protection, and the mixture is heated under oxygen-free conditions. The temperature is raised to 180~200℃ within 2 hours, and then gradually raised to 220~230℃ within 5~10 hours. The reaction is maintained at this temperature for 2~6 hours until the reaction solution is completely clear.

[0034] Preferably, in the step of preparing high acid value resin A, the esterification reaction is carried out until the acid value of the esterification product is 5~20 mgKOH / g.

[0035] Preferably, in the step of preparing high acid value resin A, the acid hydrolysis reaction temperature is 230~240℃; and the acid hydrolysis reaction time is 1~3h.

[0036] Preferably, in the step of preparing high acid value resin A, the acid hydrolysis reaction is carried out until the acid value of the acid hydrolysis product is 60~80 mgKOH / g.

[0037] Preferably, in the step of preparing high acid value resin A, the vacuum degree of the vacuum polycondensation is -0.090 ~ -0.010 MPa.

[0038] Preferably, in the step of preparing high acid value resin A, the temperature of the vacuum polycondensation reaction is 210-220°C, and the time of the vacuum polycondensation reaction is 1-5 hours.

[0039] Preferably, in the step of preparing high acid value resin A, the vacuum polycondensation reaction is carried out until the acid value of the polycondensation product is 50-70 mgKOH / g, the hydroxyl value is less than 8 mgKOH / g, and the melt viscosity at 200°C is 9000-15000 mPa·s; Preferably, in the step of preparing high acid value resin A, the temperature when adding glycidyl ester is 220~230℃, the reaction time is 1~2h, and the reaction proceeds until the acid value of the partially carboxyl-blocked product is 40~60mgKOH / g.

[0040] Preferably, in the step of preparing high acid value resin A, the temperature when adding curing accelerator A and carbodiimide compound is 190~210℃, and the stirring and dispersion time is 0.5~1h.

[0041] Preferably, in the step of preparing high acid value resin A, when the raw materials for preparing high acid value resin A also include antioxidant A, curing accelerator A, carbodiimide compound and antioxidant A are added to the partially carboxyl-blocked product to react and obtain high acid value resin A; more preferably, the temperature when adding curing accelerator A, carbodiimide compound and antioxidant A is 190~210℃ and the stirring and dispersion time is 0.5~1h.

[0042] Preferably, the steps for preparing low-acid-value resin B are as follows: First, a portion of polyol B, a portion of polyacid B, and a portion of catalyst B are mixed and subjected to esterification reaction 1 to obtain esterification product B1; then, the remaining polyol B, the remaining polyacid B, and the remaining catalyst B are mixed and subjected to esterification reaction 2 to obtain esterification product B2; the esterification product B1 and the esterification product B2 are mixed and subjected to acid hydrolysis reaction to obtain acid hydrolysis product B; the acid hydrolysis product B is subjected to vacuum polycondensation reaction until the acid value of the polycondensation product B is 18~30 mgKOH / g; curing accelerator B is added to react and obtain low-acid-value resin B.

[0043] Preferably, in the step of preparing low acid value resin B, the esterification reaction 1 process is as follows: the raw materials and catalyst in the specified proportions are added to the reaction vessel, nitrogen gas is introduced for protection, and the mixture is heated under oxygen-free conditions. The temperature is raised to 180~190℃ within 4 hours, and then gradually raised to 200~210℃ within 5~10 hours. The reaction is maintained at this temperature for 2~6 hours until the reaction solution is completely clear.

[0044] Preferably, in the step of preparing low acid value resin B, the esterification reaction 1 is carried out until the hydroxyl value of the esterification product 1 is 60~90 mgKOH / g.

[0045] Preferably, in the step of preparing low acid value resin B, the esterification reaction 2 process is as follows: the raw materials and catalyst in the specified proportions are added to the reaction vessel, nitrogen gas is introduced for protection, and the mixture is heated under oxygen-free conditions. The temperature is raised to 170~180℃ within 2 hours, and then gradually raised to 220~230℃ within 5~10 hours. The reaction is maintained at this temperature for 2~6 hours until the reaction solution is completely clear.

[0046] Preferably, in the step of preparing low acid value resin B, the esterification reaction 2 is carried out until the acid value of the esterification product 2 is 70~100mgKOH / g.

[0047] Preferably, in the step of preparing low acid value resin B, the acid hydrolysis reaction temperature is 230~240℃; and the acid hydrolysis reaction time is 1~3h.

[0048] Preferably, in the step of preparing low acid value resin B, the acid hydrolysis reaction is carried out until the acid value of the acid hydrolysis product B is 30~36 mgKOH / g.

[0049] Preferably, in the step of preparing low acid value resin B, the vacuum degree of the vacuum polycondensation is -0.090 ~ -0.010 MPa.

[0050] Preferably, in the step of preparing low acid value resin B, the vacuum polycondensation reaction takes 1 to 5 hours.

[0051] Preferably, in the step of preparing high acid value resin B, the vacuum polycondensation reaction is carried out until the acid value of the polycondensation product is 18~30 mgKOH / g, the hydroxyl value is less than 10 mgKOH / g, and the melt viscosity at 160℃ is 4000~7000 mPa.s.

[0052] Preferably, in the step of preparing high acid value resin B, the temperature when adding curing accelerator B is 190~210℃ and the stirring and dispersion time is 0.5~1h.

[0053] Preferably, in the step of preparing high acid value resin B, when the raw materials for preparing high acid value resin B further include antioxidant B and / or nucleating agent, curing accelerator B, antioxidant B and / or nucleating agent are added to the polycondensation product B to react and obtain low acid value resin B; more preferably, the temperature when adding curing accelerator B, antioxidant B and / or nucleating agent is 190~210℃, and the stirring and dispersion time is 0.5~1h.

[0054] A third aspect of the present invention provides a powder coating comprising the polyester resin composition described in the first aspect of the present invention.

[0055] Preferably, the powder coating comprises component I and component II; component I comprises the high acid value resin A; component II comprises the low acid value resin B; and the mass ratio of component I to component II is (1~5):1.

[0056] Preferably, the high acid value resin A has a mass percentage of 40-70% in component I.

[0057] Preferably, the high acid value resin B has a mass percentage of 40-70% in the Ⅱ component.

[0058] Preferably, component I further includes curing agent I, pigment and filler I, and additive I; component II further includes curing agent II, pigment and filler II, and additive II.

[0059] Preferably, curing agent I and curing agent II each independently comprise triglycidyl isocyanurate (TGIC), hydroxyalkylamide (HAA), or glycidyl polybenzoate.

[0060] Preferably, pigment I and pigment II each independently comprise titanium dioxide, barium sulfate, or a combination thereof.

[0061] Preferably, additive I and additive II each independently include leveling agents, defoamers, charge regulators, etc.

[0062] Preferably, the powder coating is prepared by a method comprising the following steps: synthesized high acid value resin A and low acid value resin B are weighed and mixed with equivalent amounts of curing agent, pigments, fillers, and additives in proportion, and then melt-extruded, pressed, crushed, and sieved through a twin-screw extruder to produce powder coating component I and powder coating component II; then powder coating component I and powder coating component II are mixed at a mass ratio of (1~5):1 to obtain the finished powder coating.

[0063] This invention also provides the application of the above-mentioned powder coating in surface coating of electrical appliances, automobiles, office supplies, metal materials, outdoor buildings, engineering machinery, etc.

[0064] The beneficial effects of this invention are as follows: In the high acid value resin A of this invention, glycidyl ester is used as a carboxyl group blocking agent, which partially blocks the free carboxyl groups, and carbodiimide compound is used as a hydrolysis stabilizer, which can capture the carboxylic acid generated by hydrolysis, thus giving the polyester resin composition excellent water resistance and anti-aging properties; further combined with low acid value resin B, a water-resistant matte powder coating with good leveling properties, mechanical properties and water resistance can be obtained. Detailed Implementation

[0065] The following specific embodiments further illustrate the content of the present invention in detail. It should also be understood that the following embodiments are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made by those skilled in the art based on the principles described herein are all within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make selections within a suitable range based on the description herein, and are not intended to be limited to the specific data in the examples below. Unless otherwise specified, the raw materials, reagents, or apparatus used in the following embodiments and comparative examples can be obtained from conventional commercial sources or by existing known methods.

[0066] Examples 1-2 and Comparative Examples 1-2 each provide a high acid value resin A, and Examples 3-9 each provide a low acid value resin B. The main difference between Comparative Examples 1-2 and Examples 1-2 is that the raw materials do not contain glycidyl tert-carbonate or polycarbodiimide. The main difference between Example 5 and Examples 3-4 is that the raw materials are not limited to linear polyacids or polyols, and the resin is a common amorphous polyester. The main difference between Examples 6-9 and Examples 3-4 is that the resin synthesis process is a one-step feeding process.

[0067] Examples 1-2 Examples 1 and 2 each provide a high acid value resin A, which is synthesized by condensation polymerization of the raw materials shown in Table 1. The specific preparation method is as follows: 1) Add the polyols in the proportions listed in Table 1 to a 10L reactor, heat until the material melts, add polyacids and catalysts, and purge with nitrogen to isolate oxygen, and carry out the esterification reaction. Raise the temperature to 180℃ within 2 hours, and then continue to raise the temperature to 225℃ at a rate of 5℃ / h, and hold for 2 hours. Continue the esterification reaction until the acid value of the product is 5-20 mgKOH / g, and obtain the esterified product. 2) Under the condition of purging nitrogen to isolate oxygen, add an acid hydrolysate to the esterification product to carry out the acid hydrolysis reaction, and then heat to about 230℃ and react for 3 hours until the acid value is 65-75 mgKOH / g to obtain the acid hydrolysis product. 3) Cool the acid hydrolysis product to 220℃ and carry out a vacuum polycondensation reaction (vacuum degree -0.098MPa) for 3h until the acid value of the product is 50~70mgKOH / g and the melt viscosity at 200℃ is 9000~15000mPa.s, and the polycondensation product is obtained. 4) Add a carboxyl blocking agent to the polycondensation product and react at 220°C for 1.5 h until the acid value is 40-60 mg KOH / g to obtain a partially carboxyl-blocked product; 5) Cool down to 200℃, add antioxidant, curing accelerator and hydrolysis stabilizer, stir and disperse for 0.5h to obtain high acid value polyester resin, which are respectively labeled A1~A2.

[0068] Comparative Example 1 Comparative Example 1 provides a high acid value resin A, which is synthesized by condensation polymerization of the raw materials shown in Table 1. The specific preparation method is as follows: 1) Add the polyols in the proportions listed in Table 1 to a 10L reactor, heat until the material melts, add polyacids and catalysts, and purge with nitrogen to isolate oxygen, and carry out the esterification reaction. Raise the temperature to 180℃ within 2 hours, and then continue to raise the temperature to 225℃ at a rate of 5℃ / h, and hold for 2 hours. Continue the esterification reaction until the acid value of the product is 5-20 mgKOH / g, and obtain the esterified product. 2) Under the condition of purging nitrogen to isolate oxygen, add an acid hydrolysate to the esterification product to carry out the acid hydrolysis reaction, and then heat to about 230℃ and react for 3 hours until the acid value is 55-65 mgKOH / g to obtain the acid hydrolysis product; 3) Cool the acid hydrolysis product to 220℃ and carry out a vacuum polycondensation reaction (vacuum degree -0.098MPa) for 3h until the acid value of the product is 40~60mgKOH / g and the melt viscosity at 200℃ is 9000~15000mPa.s, and the polycondensation product is obtained. 4) Cool down to 200℃, add antioxidant, curing accelerator and hydrolysis stabilizer, stir and disperse for 0.5h to obtain high acid value polyester resin, denoted as A3.

[0069] Comparative Example 2 Comparative Example 2 provides a high acid value resin A, which is synthesized by condensation polymerization of the raw materials shown in Table 1. The specific preparation method is as follows: 1) Add the polyols in the proportions listed in Table 1 to a 10L reactor, heat until the material melts, add polyacids and catalysts, and purge with nitrogen to isolate oxygen, and carry out the esterification reaction. Raise the temperature to 180℃ within 2 hours, and then continue to raise the temperature to 225℃ at a rate of 5℃ / h, and hold for 2 hours. Continue the esterification reaction until the acid value of the product is 5-20 mgKOH / g, and obtain the esterified product. 2) Under the condition of purging nitrogen to isolate oxygen, add an acid hydrolysate to the esterification product to carry out the acid hydrolysis reaction, and then heat to about 230℃ and react for 3 hours until the acid value is 65-75 mgKOH / g to obtain the acid hydrolysis product. 3) Cool the acid hydrolysis product to 220℃ and carry out a vacuum polycondensation reaction (vacuum degree -0.098MPa) for 3h until the acid value of the product is 50~70mgKOH / g and the melt viscosity at 200℃ is 9000~15000mPa.s, and the polycondensation product is obtained. 4) Add a carboxyl blocking agent to the polycondensation product and react at 220°C for 1.5 h until the acid value is 40-60 mg KOH / g to obtain a partially carboxyl-blocked product; 5) Cool down to 200℃, add antioxidant and curing accelerator, stir and disperse for 0.5h to obtain high acid value polyester resin, denoted as A4.

[0070] Table 1. Raw materials and amounts used in the preparation of Examples 1-2 and Comparative Examples 1-2 (amount in g).

[0071] Examples 3-4 Examples 3 and 4 each provide a low acid value resin B, which is synthesized by condensation polymerization of the raw materials shown in Table 2. The specific preparation methods are as follows: 1) Add the linear polyol 1 in the proportions listed in Table 2 to a 10L reactor, heat until the material melts, add linear polyacid 1 and catalyst, and purge with nitrogen to isolate oxygen, and carry out the esterification reaction. Raise the temperature to 180℃ within 4 hours, and then continue to raise the temperature to 210℃ at a rate of 5℃ / h, and hold for 2 hours. Continue the esterification reaction until the hydroxyl value of the product is 60-90 mgKOH / g, and obtain esterified product 1. 2) Add the linear polyol 2 in the proportions listed in Table 2 to another 10L reactor, heat until the material melts, add linear polyacid 2 and catalyst, and purge with nitrogen to isolate oxygen, and carry out esterification reaction. Raise the temperature to 180℃ within 2 hours, and then continue to raise the temperature to 230℃ at a rate of 5℃ / h, and hold for 4 hours. The esterification reaction is carried out until the acid value of the product is 70-100mgKOH / g, and esterified product 2 is obtained. 3) Under oxygen-free conditions, the esterification product 1 is added to the esterification product 2, stirred and mixed, and heated to 230°C to carry out an acid hydrolysis reaction. The reaction is carried out at 230°C for 3 hours until the acid value is 30-36 mgKOH / g, and the acid hydrolysis product is obtained. 4) Vacuum the acid hydrolysis product (vacuum degree -0.098MPa) for 3 hours and react until the acid value of the product is 18-30 mgKOH / g and the melt viscosity at 160℃ is 4000-7000 mPa.s, to obtain the polycondensation product; 5) Cool down to 190℃, add curing accelerator, nucleating agent, antioxidant, stir and disperse for 0.5h to obtain low acid value polyester resin, which are respectively labeled as B1~B2.

[0072] Example 5 Example 5 provides a low acid value resin B, which is synthesized by condensation polymerization of the raw materials shown in Table 2. The specific preparation method is as follows: 1) Add the polyol and polyacid in the proportions listed in Table 2 to a 10L reactor, heat until the materials melt, add polyacid 1 and polyacid 2 and catalyst, and purge with nitrogen to isolate oxygen and carry out esterification reaction. Raise the temperature to 180℃ within 2 hours, and then continue to raise the temperature to 225℃ at a rate of 5℃ / h, and hold for 2 hours. Continue esterification reaction until the acid value of the product is 5-20 mgKOH / g to obtain the esterified product. 3) Under the condition of purging nitrogen to isolate oxygen, add an acid hydrolysate to the esterification product to carry out the acid hydrolysis reaction, and then heat to about 230℃ and react for 3 hours until the acid value is 20-40 mgKOH / g to obtain the acid hydrolysis product; 4) Vacuum the acid hydrolysis product (vacuum degree -0.098MPa) for 3 hours and react until the acid value of the product is 18-30 mgKOH / g and the melt viscosity at 160℃ is 4000-7000 mPa.s, to obtain the polycondensation product; 5) Cool down to 190℃, add curing accelerator and antioxidant, stir and disperse for 0.5h to obtain low acid value polyester resin, denoted as B3.

[0073] Examples 6-9 Examples 6-9 each provide a low acid value resin B, which is synthesized by condensation polymerization of the raw materials shown in Table 2. The specific preparation method is as follows: 1) Add the linear polyol 1 and linear polyol 2 in the proportions listed in Table 2 to a 10L reactor, heat until the materials melt, add linear polyacid 1 and linear polyacid 2 and catalyst, and purge with nitrogen to isolate oxygen and carry out esterification reaction. Raise the temperature to 180℃ within 2 hours, and then continue to raise the temperature to 230℃ at a rate of 5℃ / h, and hold for 2 hours. Continue esterification reaction until the acid value of the product is 20-40 mgKOH / g to obtain the esterified product. 2) The esterification product is evacuated (vacuum degree -0.098MPa) for 3 hours and reacted until the acid value of the product is 18-30 mgKOH / g and the melt viscosity at 160℃ is 4000-7000 mPa.s, thus obtaining the polycondensation product; 3) Cool down to 200℃, add curing accelerator, nucleating agent, antioxidant, stir and disperse for 0.5h to obtain low acid value polyester resin, which are designated as B4~B7 respectively.

[0074] Table 2. Raw materials and dosages for the preparation of Examples 3-9 (dosage unit is g).

[0075] The acid value, viscosity, glass transition temperature, and reactivity of the resins in the above examples and comparative examples were tested according to T / GDTL004-2019. The properties of high acid value resin A in Examples 1-2 and Comparative Examples 1-2 are shown in Table 3, and the properties of polyester resin B in Examples 3-9 are shown in Table 4.

[0076] Table 3. Performance of high acid value resin A in Examples 1-2 and Comparative Examples 1-2

[0077] Table 4. Properties of polyester resin B in Examples 3-9

[0078] The processing of powder coatings involves melt extrusion, tableting, and crushing. Table 4 shows that Example 6, using a one-step feeding method, ultimately produced an amorphous resin. Example 7 had a low melting point, and both had excessively good flow properties, resulting in softening during pre-crushing, making normal application difficult using conventional processes. Example 8 had a too high melting point, exceeding the operating temperature of the screw extruder, making it difficult to prepare into a powder coating under conventional processes; its melting point was above 200°C, making viscosity unmeasurable at 200°C. Examples 7 and 8 could not be crushed into powder, and their reactivity was difficult to measure. Other unmeasured data were due to exceeding the laboratory viscosity measurement range, or the resins being structurally nonexistent or unmeasurable. Therefore, the resins from Examples 1-5 and 9, and Comparative Examples 1-2, were subsequently prepared into powder coatings using conventional processes.

[0079] Examples 10-15 and Comparative Examples 3-8 The high-acid-value resins A1-A4 and low-acid-value resins B1-B3 and B7 of the above examples and comparative examples were weighed and mixed with curing agent TGIC, titanium dioxide, barium sulfate 228, leveling agent GLP588, benzoin, carbon black and wax powder according to the components in Table 5. The mixture was then melt-extruded, sheeted, and crushed using a screw extruder (extruder parameters are as follows: zone 1 temperature 140℃, zone 2 temperature 150℃; feed speed 5Hz; screw speed 35Hz; sheeting speed 50Hz). The sheet material was then pulverized and sieved to obtain component I and component II of the powder coating, denoted as IA1-IA4, IIB1-IIB3, and IIB7, respectively. The different component I and component II powder coatings were then mixed according to the weight ratios in Table 6 to prepare the matte powder coatings of Examples 10-15 and Comparative Examples 3-8.

[0080] Next, the powder coatings prepared in Examples 10-15 and Comparative Examples 3-8 were electrostatically sprayed onto the surface-treated iron plate and cured at 200°C for 15 minutes to obtain a powder coating with a thickness of approximately 80 μm. The following performance tests were then conducted, and the results are shown in Table 7. The appearance of the coating was determined visually, while gloss, impact resistance, water boiling resistance, and xenon lamp aging resistance were tested according to T / GDTL004-2019.

[0081] Table 5. Components and dosage of powder coatings (dosage unit is g)

[0082] Table 6. Components and dosages of powder coatings in Examples 10-15 and Comparative Examples 3-8 (dosage unit is g).

[0083] Table 7 Performance of powder coatings in Examples 10-15 and Comparative Examples 3-8

[0084] As can be seen from Table 7, compared with Comparative Examples 3-8 synthesized according to conventional polyester schemes, the high acid value resin A in Examples 10-15 of this invention has excellent water resistance because the glycidyl tert-carbonate partially blocks the free carboxyl groups and polycarbodiimide is added, which can capture the carboxylic acid generated by hydrolysis. When combined with low acid value resin B, the finished powder coating has excellent matte properties, leveling properties, mechanical properties, anti-aging properties and outstanding water resistance.

[0085] Furthermore, by employing a specific low-acid-value resin B, which possesses a block copolymer structure with both soft and hard segments, the suitable melting point and good processing performance are achieved, thus solving the processing problem of semi-crystalline resins in powder coating applications. Compared to Examples 14-15, Examples 10-11, which use a specific structure of low-acid-value resin B, achieve superior matte finish, leveling properties, mechanical properties, and water resistance.

[0086] Furthermore, the high-acid-value resin A and low-acid-value resin B in the embodiments and comparative examples of this invention have different acid values, viscosities, reactivity, and structural compositions. Mixing component I and component II of the powder coating at different mass ratios can control the gloss of the finished water-resistant matte powder coating. Compared to Examples 12-13, the mass ratio of component I to component II in Examples 10-11 achieves better matte performance, leveling performance, mechanical properties, and water resistance.

[0087] In summary, the high acid value resin A of this invention uses glycidyl ester as a carboxyl group blocker to partially block free carboxyl groups, and uses carbodiimide compound as a hydrolysis stabilizer to capture the carboxylic acid generated by hydrolysis, thus endowing the polyester resin composition with excellent water resistance and anti-aging properties. Furthermore, by combining it with low acid value resin B, a water-resistant matte powder coating with good leveling properties, mechanical properties, and water resistance can be obtained.

Claims

1. A polyester resin composition, characterized by comprising: Including high acid value resins and low acid value resins; The high acid value resin has an acid value of 40~60 mgKOH / g; the low acid value resin has an acid value of 18~30 mgKOH / g. The high acid value resin comprises the following raw materials: polyol A, polyacid A, acid hydrolysis agent A, glycidyl ester, carbodiimide compound, catalyst A, and curing accelerator A. The low acid value resin comprises the following raw materials: polyol B, polyacid B, catalyst B, and curing accelerator B.

2. The polyester resin composition according to claim 1, characterized by The glycidyl ester includes at least one of glycidyl tert-carbonate, diglycidyl adipic acid, glycidyl methacrylate, or diglycidyl dimerate. And / or, the carbodiimide compound includes at least one of polycarbodiimide, N,N'-dicyclohexylcarbodiimide, N,N'-diisopropylcarbodiimide or N-ethyl-N'-(3-dimethylaminopropyl)carbodiimide.

3. The polyester resin composition according to claim 1, characterized in that, The high acid value resin comprises the following raw materials in parts by weight: 32-40 parts polyol A, 45-65 parts polyacid A, 8-15 parts acid hydrolysate A, 0.5-3 parts glycidyl ester, 0.2-1 part carbodiimide compound, 0.04-0.15 parts catalyst A, and 0.02-0.2 parts curing accelerator A; And / or, the low acid value resin comprises the following raw materials in parts by weight: 25-45 parts polyol B, 55-75 parts polyacid B, 0.04-0.15 parts catalyst B, and 0.01-0.1 parts curing accelerator B.

4. The polyester resin composition according to claim 1, characterized in that, The polyol B is selected from straight-chain polyols; the polyacid B is selected from straight-chain polyacids.

5. The polyester resin composition according to claim 4, characterized in that, The linear polyol includes at least one of ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, or 1,6-hexanediol. And / or, the linear polyacid includes at least one of terephthalic acid, 1,4-succinic acid, 1,6-adipic acid, azelaic acid, sebacic acid, and dodecanoic acid.

6. The polyester resin composition according to claim 1, characterized in that, The polyol A includes at least one of neopentyl glycol, 2-methyl-1,3-propanediol, 2-methyl-2,4-pentanediol, 2-butyl-2-ethyl-1,3-propanediol, hydrogenated bisphenol A, 1,4-cyclohexanediol, trimethylolpropane or pentaerythritol. And / or, the polyacid A includes at least one of terephthalic acid, isophthalic acid, 1,2-cyclosuccinic acid or 1,4-cyclohexanedicarboxylic acid; And / or, the acid hydrolysant A includes at least one of isophthalic acid, trimellitic anhydride, pyromellitic anhydride, hexahydrophthalic anhydride, or hydrogenated dimer acid; And / or, catalyst A and catalyst B each independently comprise a tin-based catalyst, a titanium-based catalyst, or a combination thereof; And / or, the curing accelerator A and the curing accelerator B each independently comprise organophosphorus curing accelerators, quaternary ammonium salt curing accelerators, or combinations thereof.

7. The polyester resin composition according to claim 1, characterized in that, The high acid value resin A satisfies at least one of the following characteristics: glass transition temperature of 65~75℃; melt viscosity of 9000~15000 mPa.s at 200℃; reactivity of 40~120s at 180℃; and number average molecular weight of 2500~4500 g / mol. And / or, the low acid value resin B satisfies at least one of the following characteristics: melting point of 120~240℃; melt viscosity of 100~12000mPa.s at 160℃; reactivity of 400~1000s at 180℃; number average molecular weight of 3000~5000g / mol.

8. A method for preparing a polyester resin composition according to any one of claims 1 to 7, characterized in that, The process includes the following steps: mixing polyol A, polyacid A, and catalyst A, and performing an esterification reaction to obtain esterified product A; adding acidolytic agent A to the esterified product A and performing an acidolytic reaction to obtain acidolytic product A; subjecting the acidolytic product A to a vacuum polycondensation reaction under vacuum to obtain polycondensation product A; adding glycidyl ester to the polycondensation product A and reacting to obtain a partially carboxyl-blocked product; and adding curing accelerator A and carbodiimide compound to the partially carboxyl-blocked product and reacting to obtain a high acid value resin A. Polyol B, polyacid B, and catalyst B are mixed and subjected to esterification to obtain esterified product B; then acid hydrolysis is performed to obtain acid hydrolysis product B; the acid hydrolysis product B is subjected to vacuum polycondensation to obtain polycondensation product B; curing accelerator B is added to the polycondensation product B and reacted to obtain low acid value resin B.

9. A powder coating, characterized in that, The polyester resin composition comprising any one of claims 1 to 7.

10. The powder coating according to claim 9, characterized in that, The powder coating comprises component I and component II; component I comprises high acid value resin A; component II comprises low acid value resin B; the mass ratio of component I to component II is (1~5):1.

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