Polyester resin for TGIC (triglycidyl isocyanurate) curing coiled material powder coating and preparation method of polyester resin

Abstract

The invention discloses polyester resin for a TGIC (triglycidyl isocyanurate) curing coiled material powder coating and a preparation method of the polyester resin. The polyester resin for the TGIC curing coiled material powder coating is prepared from the following main components in percentage by mass through melt polymerization: 30.0-50.0% of polyhydric alcohols, 0.1-0.5% of a curing agent, 0.1-0.5% of an antioxidant, 0.1-0.5% of a cross-linking agent and the balance of a solvent. 40.0% to 60.0% of a polybasic acid; 0.1%-0.3% of a catalyst; 4.0%-10.0% of an acidolysis agent; 6 to 10.0 percent of modified copolyester; 0.2%-1% of an antioxidant; 0.1%-0.5% of a curing accelerator; the acid value of the prepared polyester resin for the TGIC cured coiled material powder coating is 30.0-36.0 mgKOH / g, the hydroxyl value is 2.0-5.0 mgKOH / g, the melting rotary viscosity is 2500-3500 mPa.s / 200 DEG C, and the glass transition temperature is 62-68 DEG C. The invention further discloses a preparation method of the polyester resin for the TGIC cured coiled material powder coating. The coiled material powder coating prepared from the polyester disclosed by the invention can be rapidly cured for 60-90 seconds at 250 DEG C, has excellent storage stability, and also can consider that a coating film has excellent leveling property, excellent mechanical property and excellent weather resistance.

Description

Technical Field

[0001] The invention relates to the technical field of polyester resins, in particular to a polyester resin for TGIC-cured coil powder coatings, and also to a preparation method of the polyester resin. Background Art

[0002] Compared with traditional coating, pre-coated coils can simplify the production process, improve production efficiency, and save costs. They have broad prospects in the industries of building interior and exterior wall panels, home appliances, automobiles, metal furniture, etc. For a long time, almost all pre-coated steel coils have been coated with liquid coil coatings, which are accompanied by VOC emissions during use, wasting resources and polluting the environment. However, powder coatings have no VOC emissions during use and are one of the best choices to replace traditional liquid coil coatings. Rapid curing of coil powder coatings is one of the key technical challenges to promote the development of this field. As the core film-forming component of powder coatings, the performance of polyester resins is directly related to whether the coating can achieve rapid curing. During the rapid curing process, the flow time of the coating is shortened, which may lead to poor leveling of the coating. In order to improve the leveling at low temperatures, polyester resins with low glass transition temperatures (Tg) are usually used, but this may sacrifice the storage stability of the powder coating. In addition, during the rapid curing process, if the curing is not thorough, the key properties of the coating such as weather resistance and bending resistance may be affected. Therefore, how to ensure the leveling, storage stability and comprehensive performance of the coating while ensuring rapid curing is a difficult problem that needs to be solved in the development of coil powder coating technology.

[0003] In the prior art, there are also relevant literature reports on polyester resins for coil coatings:

[0004] Chinese patent CN112552495B discloses that a fast-curing polyester resin is obtained by polymerization of 3,3-dimethylglutaric acid, terephthalic acid, acrylic polymer, 1,6-diglycidyl adipate, neopentyl glycol, 1,4-naphthalenedimethanol, 1,10-decanediamine, and ethylenediamine-N,N'-diacetic acid as raw materials. The fast-curing polyester resin product contains active amino groups, amide groups of different structures, and a small amount of carboxyl groups. However, the above polyester curing system is different from the mainstream powder coating curing system in the existing market, and it is easy to interfere with each other during the powder production process, which is not conducive to the production of powder manufacturers.

[0005] Chinese patent CN105218795B discloses a pure polyester resin for HAA-cured coil powder coating, which is a terminal saturated polyester resin. The polyester resin has high reactivity and short curing time, and is suitable for the fast curing system required by coil coating. The powder coating obtained has excellent comprehensive performance and can be cured at 280℃ / 60s. However, the HAA curing system has the defects of difficulty in powdering and the coating is prone to yellowing.

[0006] In summary, in order to solve the above-mentioned defects of the prior art, the present invention proposes a polyester resin for TGIC-cured coil powder coating and a preparation method thereof. Summary of the invention

[0007] The object of the present invention is to provide a polyester resin for TGIC-cured coil powder coating and a preparation method thereof. The polyester resin coating for TGIC-cured coil powder coating prepared by the method can achieve rapid curing of 60-90s under 250° C. and has excellent storage stability, and the coating film thereof can have excellent leveling, excellent mechanical properties, and excellent weather resistance.

[0008] To achieve the above object, the present invention is implemented by the following technical solutions:

[0009] A polyester resin for TGIC-cured coil powder coatings,

[0010] The polyester resin for TGIC curing coil powder coating is prepared by melt polymerization of the following main components in percentage by mass:

[0011] Polyol 30.0~50.0%;

[0012] Polyacid 40.0~60.0%;

[0013] Catalyst 0.1~0.3%;

[0014] Acid dissolution agent 4.0~10.0%;

[0015] Modified copolyester 6~10.0%

[0016] Antioxidant 0.2-1%;

[0017] Curing accelerator 0.1~0.5%;

[0018] The polyester resin for TGIC-cured coil powder coating has an acid value of 30.0-36.0 mgKOH / g, a hydroxyl value of 2.0-5.0 mgKOH / g, a melt rotation viscosity of 2500-3500 mPa.s / 200°C, and a glass transition temperature of 62-68°C.

[0019] As a further improvement of the present solution, the polyol is any one or more of neopentyl glycol, 2-methyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, trimethylolpropane, and trihydroxyethyl isocyanurate.

[0020] As a further improvement of this solution, the polyacid is any one or more of 1,6-hexanediol, terephthalic acid, and isophthalic acid.

[0021] As a further improvement of this solution, the esterification catalyst is any one or more of monobutyltin oxide, stannous oxalate, and antimony glycol.

[0022] As a further improvement of this solution, the acidolysis agent is any one or more of 1,6-hexanediol and isophthalic acid.

[0023] As a further improvement of this scheme,

[0024] The modified copolyester is a modified PBT type copolyester;

[0025] The modified copolyester has a number average molecular weight of 24,000 to 26,000, a melting point of 100 to 120° C., a melt index of 40 to 50 g / 10 min, 180° C., a hydroxyl value of less than 1.0 mgKOH / g, and an acid value of 6 to 10 mgKOH / g;

[0026] The modified copolyester is prepared by polycondensation reaction of the following raw materials in molar percentage:

[0027] Terephthalic acid 15.0-25.0%;

[0028] Isophthalic acid 15.0-25.0%;

[0029] The molar percentage of docosane diacid is a, satisfying the quantitative relationship: 0.0<a≤8.0%;

[0030] The molar percentage of octadecane dioic acid is b, which satisfies the quantitative relationship: 0.0<b≤10.0%;

[0031] 1,4-Butanediol 40.0~60.0%;

[0032] The percentage of 2,2,4,4-tetramethyl-1,3-cyclobutanediol is c, which satisfies the quantitative relationship: 0.0<c≤8.0%;

[0033] Trimellitic anhydride 0.5-1%;

[0034] The polycondensation reaction catalyst is any one or more of tetrabutyl titanate, zinc acetate, and germanium dioxide; the amount of the catalyst is 50 to 100 ppm;

[0035] The heat stabilizer is phosphoric acid; the usage of the heat stabilizer is 30 to 50 ppm.

[0036] As a further improvement of this solution, the modified copolyester is prepared according to the following steps:

[0037] Put terephthalic acid, isophthalic acid, docosane dioic acid, octadecane dioic acid, 1,4-butanediol, and 2,2,4,4-tetramethyl-1,3-cyclobutanediol into the S1 reactor, slowly raise the temperature to the final esterification temperature of 230°C at a rate of 10°C / hour, maintain the temperature at 230°C and continue the reaction, control the column top temperature below 102°C, and when the column top temperature drops and the water output rate reaches more than 90%, the esterification is considered to be completed;

[0038] After the S2 esterification reaction was completed, the reactor was sealed and vacuumed to reduce the pressure to below 100 Pa. The total time from low vacuum to high vacuum (100 Pa) was 60 min, during which the reaction temperature slowly increased from 230 ° C to 240 ° C;

[0039] S3 maintains vacuum degree below 100Pa and temperature at 240℃ for continuous reaction. After the molecular weight reaches 24000-26000 by observing the torque and current of the stirring motor, the vacuum is stopped.

[0040] After S4 is cooled to 200°C, trimellitic anhydride is added, and the reaction is continued for 30 minutes before cooling and discharging.

[0041] As a further improvement of this solution, the antioxidant is AT-215, which is a mixture of antioxidant 1010 (pentaerythritol tetrakis(3,5-di-tert-butyl-4-hydroxy)phenylpropionate) and antioxidant 168 (tris(2,4-tert-butylphenyl)phosphite) in a mass ratio of 1:2.

[0042] As a further improvement of this solution, the curing accelerator is any one or two of ethyltriphenylphosphine bromide and 2-aminoimidazole.

[0043] A method for preparing a polyester resin for TGIC-cured coil powder coating comprises the following preparation steps:

[0044] S1: Put the raw materials polyol, polyacid and catalyst into the reactor according to the formula, fill with nitrogen for protection, and when the temperature rises to 165-175℃, esterification and water production begins. Continue to heat up to 243±2℃ and keep warm for reaction. When there is no esterification water, a colorless and transparent resin is obtained.

[0045] S2 is sampled and tested. When the acid value is 8-10 mgKOH / g, an acidolysis agent is added and the reaction is kept at 238°C-240°C for 90-120 minutes.

[0046] S3 sampling and testing, when the acid value is 45-47 mgKOH / g, start vacuuming, gradually control the vacuum to -0.097-0.099 MPa, and react at 230-235°C under vacuum conditions for 90-120 minutes.

[0047] S4 sampling and testing, when the acid value is 32-38 mgKOH / g, cool to 200°C, add modified copolyester, antioxidant, curing accelerator and stir to react for 15-30 minutes, discharge, cool and crush to obtain a colorless or light yellow transparent granular material.

[0048] A polyester resin for TGIC-cured coil powder coating and a preparation method thereof of the present invention have the following characteristics:

[0049] Beneficial effects:

[0050] 1) The polyols in the formula of the present invention: neopentyl glycol does not contain β-H and its branched structure can shield the ester bond, which can improve the weather resistance of the resin; 2-methyl-1,3-propanediol and 2-butyl-2-ethyl-1,3-propanediol are flexible monomers, which can improve the flexibility of the molecular chain and enhance the mechanical properties of the coating, and the branched structure can protect the ester bond and provide certain weather resistance; trimethylolpropane and trihydroxyethyl isocyanurate are triols, which can increase the branching degree of polyester resin molecules, thereby increasing the glass transition temperature of the polyester resin and the mechanical properties of the coating film, wherein the stable structure of the triazine ring of trihydroxyethyl isocyanurate can further increase the glass transition temperature of the polyester resin and the mechanical properties of the coating film.

[0051] 2) The polyacid in the formula of the present invention: the polyacid is 1,6-adipic acid, terephthalic acid, and isophthalic acid, wherein the mass ratio of terephthalic acid to other polyacids is (6-7):1. The aliphatic long carbon chain structure of 1,6-adipic acid can increase the degree of freedom of the main chain of the polyester resin molecule, thereby improving the flexibility of the powder coating; terephthalic acid is the main structure of the polyester skeleton, and the benzene ring structure can effectively increase the glass transition temperature of the polyester and improve the storage stability of the powder coating; the steric hindrance formed by the meta structure of isophthalic acid can shield the ester bonds in the polyester resin, and at the same time can reduce the transmittance of water molecules, effectively inhibit the hydrolysis of polyester, and improve the weather resistance of the powder coating.

[0052] 3) The composite catalyst system in the formula of the present invention can effectively increase the reaction speed and improve the polyester synthesis efficiency.

[0053] 4) Acidolysis agent in the formula of the present invention: The acidolysis agents isophthalic acid and 1,6-adipic acid have high reactivity and can ensure the acidolysis and end-capping reaction. At the same time, the long carbon chain structure of 1,6-adipic acid can improve the mechanical properties of the prepared coating.

[0054] 5) Modified PBT in the formula of the present invention: The main synthetic monomers of the modified PBT copolyester are terephthalic acid, isophthalic acid, docosane dioic acid, octadecane dioic acid, 1,4-butanediol, and 2,2,4,4-tetramethyl-1,3-cyclobutanediol. Terephthalic acid and isophthalic acid have a benzene ring structure, which can improve the strength of the copolyester. At the same time, the meta structure of isophthalic acid can adjust the symmetry of the molecular chain, adjust the crystallinity, and balance the toughness and strength of the copolyester; the ultra-long carbon chain structure of docosane dioic acid and octadecane dioic acid can greatly improve the flexibility of the copolyester. 1,4-Butanediol and 2,2,4,4-tetramethyl-1,3-cyclobutanediol, as relatively flexible monomers, can also improve the flexibility of the copolyester. Trimellitic anhydride, as an acidolysis agent, can make the synthetic copolyester a carboxyl-terminated polyester, which can form a cross-linked network-like stable structure with the entire coating. The role of the modified PBT copolyester in the present invention is to form an island structure in the coating, so that the stress field in the coating is no longer uniform, thereby inducing a large number of silver streaks and shear bands, absorbing a large amount of impact energy, and greatly improving the mechanical properties of the coating. At the same time, the structure of the long fatty chain can effectively reduce the viscosity of the system and improve the leveling performance of the coating.

[0055] 6) Antioxidant and curing accelerator in the synthesis of modified PBT in the formula of the present invention: the antioxidant is AT-215, which is a mixture of antioxidant 1010 (pentaerythritol tetrakis(3,5-di-tert-butyl-4-hydroxy)benzene propionate) and antioxidant 168 (tris(2,4-tert-butylphenyl)phosphite) in a mass ratio of 1:2, which can effectively improve the thermal stability and anti-yellowing performance of the coating; the curing accelerator is a mixture of one or two of ethyltriphenylphosphonium bromide and 2-aminoimidazole in any mass ratio, which can effectively reduce the activation energy of the powder coating curing reaction, reduce the energy required for the reaction, and realize the rapid curing of the coil powder coating.

[0056] 7) The polycondensation reaction catalyst and heat stabilizer in the formula of the present invention: the composite catalyst system can effectively increase the reaction speed, reduce the occurrence of side reactions, and improve the chromaticity of the copolyester; the heat stabilizer is phosphoric acid, which can effectively protect the copolyester from being oxidized during the synthesis process, and the amount of the heat stabilizer is 30 to 50 ppm.

[0057] 8) The powder coating made from the polyester of the present invention can achieve rapid curing of 60-90s at 250°C and has excellent storage stability. On this basis, the addition of the modified copolyester enables the coating film to have extremely excellent leveling properties and mechanical properties, while ensuring excellent weather resistance. DETAILED DESCRIPTION

[0058] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is further described below in conjunction with embodiments:

[0059] In the following embodiments of the present invention, the modified PBT copolyester is prepared by the following method. 650 parts of terephthalic acid, 650 parts of isophthalic acid, 175 parts of docosane diacid, 205 parts of octadecane diacid, 900 parts of 1,4-butanediol, and 495 parts of 2,2,4,4-tetramethyl-1,3-cyclobutanediol are added to the reactor. 50ppm of tetrabutyl titanate, 20ppm of zinc acetate, and 10ppm of germanium dioxide are added. The temperature is slowly raised to the final esterification temperature of 230°C at a rate of 10°C / hour, and the temperature is maintained at 230°C to continue the reaction. The column top temperature is controlled below 102°C. When the column top temperature drops and the water output rate reaches more than 90%, 50ppm of phosphoric acid is added, and the reactor is evacuated to reduce its pressure to below 100Pa. The total time from low vacuum to high vacuum (100Pa) is 60min, during which the reaction temperature slowly rises from 230°C to 240°C. The vacuum was maintained below 100 Pa and the temperature was kept at 240°C for continuous reaction. After the molecular weight reached 24,000 to 26,000 by observing the torque and current of the stirring motor, the vacuum was stopped. After cooling to 200°C, 30 parts of trimellitic anhydride were added, and the reaction was continued for 30 minutes before cooling and discharging. The above synthesis was completed in a nitrogen atmosphere.

[0060] Example A

[0061] The specific implementation of the synthesis process is to add 1065 parts of polyol (including 1045 parts of neopentyl glycol and 20 parts of trimethylolpropane) of the formula amount, 1605 parts of polyacid (including 300 parts of isophthalic acid and 1305 parts of terephthalic acid) and 2 parts of esterification catalyst (including 2 parts of monobutyltin oxide) in a 3000mL reactor equipped with a heating device, a stirrer and a distillation column, fill with nitrogen protection, gradually heat up while stirring, and when the temperature rises to 165-175°C, esterification water begins to be produced, continue to heat up to 248±2°C, and heat to react until there is no esterification water, a colorless transparent resin is obtained. Add 180 parts of acidolysis agent (including 120 parts of isophthalic acid and 60 parts of 1,6-hexanodioic acid), and heat at 245°C to 250°C for 90-120 minutes. After the reaction is completed, gradually evacuate to -0.097~-0.099Mpa, and react for 90~120 minutes under vacuum conditions of 235~240℃. Cool down to 200℃, add 7 parts by weight of antioxidant AT-215 and 6 parts by weight of curing accelerator (including 6 parts of ethyl triphenylphosphine bromide), stir and react for 15~30 minutes, discharging, cooling and crushing to obtain a colorless or light yellow transparent granular material. The above synthesis process is carried out in a nitrogen protection atmosphere. The physical and chemical indicators of the obtained polyester resin are shown in Example A shown in Table 1.

[0062] Example B

[0063] The specific implementation of the synthesis process is as follows: in a 3000mL reactor equipped with a heating device, a stirrer and a distillation column, 1125 parts by weight of a polyol (including 120 parts of 2-methyl-1,3-propanediol, 865 parts of neopentyl glycol, 120 parts of 2-butyl-2-ethyl-1,3-propanediol, and 20 parts of trimethylolpropane), 1645 parts by weight of a polyacid (including 200 parts of isophthalic acid, 130 parts of 1,6-hexanodioic acid, and 1315 parts of terephthalic acid) and 2 parts by weight of an esterification catalyst (including 1 part of monobutyl tin oxide and 1 part of ethylene glycol antimony) are added, nitrogen is filled for protection, the temperature is gradually increased while stirring, and when the temperature is increased to 165-175°C, esterification water begins to be produced, the temperature is continued to be increased to 248±2°C, and the reaction is carried out by heat preservation. When the reaction is carried out until there is no esterification water, a colorless and transparent resin is obtained. Add 180 parts by weight of an acidolysis agent (60 parts of isophthalic acid and 120 parts of 1,6-hexanediol) and keep warm for 90-120 minutes at 245°C to 250°C. After the reaction is completed, gradually evacuate to -0.097 to -0.099Mpa and react for 90 to 120 minutes at 235 to 240°C. Cool to 200°C, add 7 parts by weight of an antioxidant AT-215 and 7 parts by weight of a curing accelerator (5 parts of ethyl triphenylphosphine bromide and 2 parts of 2-aminoimidazole), stir and react for 15 to 30 minutes, discharging, cooling and crushing to obtain a colorless or light yellow transparent granular material. The above synthesis process is carried out in a nitrogen protection atmosphere. The physical and chemical indicators of the obtained polyester resin are shown in Example B shown in Table 1.

[0064] Example C

[0065] The specific implementation of the synthesis process is as follows: in a 3000mL reactor equipped with a heating device, a stirrer and a distillation column, add 1065 parts of polyol (including 1045 parts of neopentyl glycol and 20 parts of trimethylolpropane), 1605 parts of polyacid (including 300 parts of isophthalic acid and 1305 parts of terephthalic acid) and 2 parts of esterification catalyst (including 2 parts of monobutyltin oxide), fill with nitrogen for protection, gradually heat up while stirring, and when the temperature rises to 165-175°C, esterification begins to produce water, continue to heat up to 248±2°C, and carry out heat preservation reaction. When there is no esterification water, a colorless transparent resin is obtained. Add 185 parts of acidolysis agent (including 125 parts of isophthalic acid and 60 parts of 1,6-hexanodioic acid), and keep the temperature at 245°C to 250°C for 90-120 minutes. After the reaction is completed, gradually evacuate to -0.097~-0.099Mpa, and react for 90~120 minutes under vacuum conditions of 235~240℃. Cool down to 200℃, add 7 parts by weight of antioxidant AT-215, 200 parts by weight of copolyester, and 7 parts by weight of curing accelerator (including 4 parts of ethyl triphenylphosphine bromide and 3 parts of 2-aminoimidazole), stir and react for 15~30 minutes, discharging, cooling and crushing to obtain a colorless or light yellow transparent granular material. The above synthesis process is carried out in a nitrogen protection atmosphere. The physical and chemical indicators of the obtained polyester resin are shown in Example C shown in Table 1.

[0066] Example D

[0067] The specific implementation of the synthesis process is as follows: in a 3000mL reactor equipped with a heating device, a stirrer and a distillation column, 1095 parts of a polyol (including 60 parts of 2-methyl-1,3-propanediol, 935 parts of neopentyl glycol, 60 parts of 2-butyl-2-ethyl-1,3-propanediol, and 40 parts of trihydroxyethyl isocyanurate) and 1605 parts of a polyacid (including 20 parts of isophthalic acid) are added. 50 parts, 30 parts of 1,6-hexanedioic acid, 1325 parts of terephthalic acid) and 2.5 parts of esterification catalyst (including 1 part of monobutyltin oxide, 0.5 parts of stannous oxalate, and 1 part of ethylene glycol antimony), nitrogen protection, stirring and gradually heating, when the temperature rises to 165-175℃, esterification water begins to be produced, continue to heat to 248±2℃, and heat to react until there is no esterification water, a colorless and transparent resin is obtained. Add 175 parts of acidolysis agent (including 135 parts of isophthalic acid and 40 parts of 1,6-hexanedioic acid), heat at 245℃~250℃ for 90-120 minutes. After the reaction is completed, gradually evacuate to -0.097~-0.099Mpa, and react at 235~240℃ for 90~120 minutes. The temperature is lowered to 200°C, 7 parts by weight of antioxidant AT-215, 200 parts by weight of copolyester, and 6 parts by weight of curing accelerator (including 3 parts of ethyl triphenylphosphine bromide and 3 parts of 2-aminoimidazole) are added, stirred and reacted for 15 to 30 minutes, and a colorless or light yellow transparent granular material is obtained after discharging, cooling and crushing. The above synthesis process is carried out in a nitrogen protection atmosphere. The physical and chemical indicators of the obtained polyester resin are shown in Example D shown in Table 1.

[0068] Example E

[0069] The specific implementation of the synthesis process is as follows: in a 3000mL reactor equipped with a heating device, a stirrer and a distillation column, 1055 parts by weight of a polyol (including 60 parts of 2-methyl-1,3-propanediol, 915 parts of neopentyl glycol, 80 parts of 2-butyl-2-ethyl-1,3-propanediol, and 40 parts of trihydroxyethyl isocyanurate), 1585 parts by weight of a polyacid (including 240 parts of isophthalic acid and 1345 parts of terephthalic acid) and 2.5 parts by weight of an esterification catalyst (including 1 part of monobutyltin oxide, 0.5 parts of stannous oxalate, and 1 part of ethylene glycol antimony) are added, nitrogen is filled for protection, the temperature is gradually increased while stirring, and when the temperature is increased to 165-175°C, esterification water begins to be produced, the temperature is continued to be increased to 248±2°C, and the reaction is carried out by heat preservation. When the reaction is carried out until there is no esterification water, a colorless and transparent resin is obtained. Add 175 parts by weight of an acidolysis agent (including 135 parts of isophthalic acid and 40 parts of 1,6-hexanediol) and keep warm for 90-120 minutes at 245°C to 250°C. After the reaction is completed, gradually evacuate to -0.097 to -0.099Mpa and react for 90 to 120 minutes at 235 to 240°C. Cool down to 200°C, add 7 parts by weight of an antioxidant AT-215, 260 parts by weight of a copolyester, and 6 parts by weight of a curing accelerator (including 2 parts of ethyltriphenylphosphine bromide and 4 parts of 2-aminoimidazole), stir and react for 15 to 30 minutes, and after discharging, cooling and crushing, a colorless or light yellow transparent granular material is obtained. The above synthesis process is carried out in a nitrogen protection atmosphere. The physical and chemical indicators of the obtained polyester resin are shown in Example E shown in Table 1.

[0070] Table 1 Raw material ratio and physical and chemical indexes of polyester resin

[0071]

[0072]

[0073] Note: The acid value test of polyester is carried out in accordance with the standard of GB / T 6743-2008

[0074] The melt rotation viscosity test of polyester is carried out according to the standard of GB / T 9751.1-2008.

[0075] The glass transition temperature of polyester is tested according to GB / T 19466.2-2004.

[0076] The softening point of polyester is tested according to the standard of GB / T27808-2011.

[0077] The colorimetry of polyester is tested according to the standard GB / T9282.1-2008

[0078] The performance of the polyester resin synthesized by the present invention needs to be reflected by the performance of the powder coating made. The polyester resin prepared by the method provided by the present invention is weighed and mixed evenly with TGIC, pigments and fillers, and various auxiliary additives according to the proportions in Table 2, and then melted, extruded, tableted, crushed, and sieved by a screw extruder to form a powder coating. The powder coating is sprayed on a metal plate with a phosphating surface by an electrostatic spray gun, cured at 250°C / 90s, and then various performance tests are performed. The performance test results are shown in Table 2.

[0079] Table 2 Composition and properties of powder coatings

[0080]

[0081]

[0082] Note: Curing agent TGIC: triglycidyl isocyanurate (Huangshan Huahui Technology Co., Ltd.);

[0083] GLP588: Leveling agent for powder coating (Ningbo Nanhai Chemical Co., Ltd.);

[0084] GLP701: Brightener for powder coatings (Ningbo Nanhai Chemical Co., Ltd.);

[0085] Titanium dioxide R902: Pigment for powder coatings (DuPont, USA);

[0086] Precipitated barium sulfate: filler for powder coatings (Shaanxi Fuhua Company);

[0087] Benzoin: degassing agent for powder coatings (Wuhan Yincai Technology Co., Ltd.);

[0088] The weather resistance test was carried out in accordance with ISO 16474-2:2013. Table 2 records the gloss retention rate after 1000 hours.

[0089] Powder storage stability test:

[0090] The test is carried out in accordance with GB / T21782.8-2008, ISO8130-8:1994 standards

[0091] Level 0: No change;

[0092] Level 1: Slight compression occurs, and the clumped powder can be easily broken;

[0093] Level 2: Obvious compaction occurs, so that some force is required to disperse the powder coating, and pressure applied by hand can break up the clumps;

[0094] Level 3: There is obvious compaction, making it difficult or impossible to disperse the powder coating, and the agglomerates are so strong that mechanical means are required to break up the agglomerates;

[0095] The coating thickness test is carried out in accordance with the standard of GB / T 13452.2-2008;

[0096] The gloss test of the coating film is carried out in accordance with the standard of GB / T1743-1979;

[0097] The impact performance test of the coating film is carried out in accordance with the standard of GB / T 1732-1993.

[0098] 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 changes made using the present invention are within the patent protection scope of the present invention.

Claims

1. A polyester resin for TGIC-cured coil powder coating, characterized in that: The polyester resin for TGIC curing coil powder coating is prepared by melt polymerization of the following main components in percentage by mass: The polyester resin for TGIC-cured coil powder coating has an acid value of 30.0-36.0 mgKOH / g, a hydroxyl value of 2.0-5.0 mgKOH / g, a melt rotation viscosity of 2500-3500 mPa.s / 200°C, and a glass transition temperature of 62-68°C.

2. The polyester resin for TGIC curing coil powder coating according to claim 1, characterized in that: The polyol is any one or more of neopentyl glycol, 2-methyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, trimethylolpropane, and trishydroxyethyl isocyanurate.

3. The polyester resin for TGIC curing coil powder coating according to claim 1, characterized in that: The polyacid is any one or more of 1,6-adipic acid, terephthalic acid, and isophthalic acid.

4. The polyester resin for TGIC curing coil powder coating according to claim 1, characterized in that: The esterification catalyst is any one or more of monobutyltin oxide, stannous oxalate, and antimony glycolate.

5. The polyester resin for TGIC curing coil powder coating according to claim 1, characterized in that: The acidolysis agent is any one or more of 1,6-hexanediol and isophthalic acid.

6. The polyester resin for TGIC curing coil powder coating according to claim 1, characterized in that: The modified copolyester is a modified PBT type copolyester; The modified copolyester has a number average molecular weight of 24,000 to 26,000, a melting point of 100 to 120° C., a melt index of 40 to 50 g / 10 min, 180° C., a hydroxyl value of less than 1.0 mgKOH / g, and an acid value of 6 to 10 mgKOH / g; The modified copolyester is prepared by polycondensation reaction of the following raw materials in molar percentage: Terephthalic acid 15.0-25.0%; Isophthalic acid 15.0-25.0%; The molar percentage of docosane diacid is a, satisfying the quantitative relationship: 0.0<a≤8.0%; The molar percentage of octadecane dioic acid is b, which satisfies the quantitative relationship: 0.0<b≤10.0%; 1,4-Butanediol 40.0~60.0%; The percentage of 2,2,4,4-tetramethyl-1,3-cyclobutanediol is c, which satisfies the quantitative relationship: 0.0<c≤8.0%; Trimellitic anhydride 0.5-1%; The polycondensation reaction catalyst is any one or more of tetrabutyl titanate, zinc acetate, and germanium dioxide; the amount of the catalyst is 50 to 100 ppm; The heat stabilizer is phosphoric acid; the usage of the heat stabilizer is 30 to 50 ppm.

7. The polyester resin for TGIC-cured coil powder coating according to claim 6, characterized in that: The modified copolyester is prepared according to the following steps: Put terephthalic acid, isophthalic acid, docosane dioic acid, octadecane dioic acid, 1,4-butanediol, and 2,2,4,4-tetramethyl-1,3-cyclobutanediol into the S1 reactor, slowly raise the temperature to the final esterification temperature of 230°C at a rate of 10°C / hour, maintain the temperature at 230°C and continue the reaction, control the column top temperature below 102°C, and when the column top temperature drops and the water output rate reaches more than 90%, the esterification is considered to be completed; After the S2 esterification reaction was completed, the reactor was sealed and vacuumed to reduce the pressure to below 100 Pa. The total time from low vacuum to high vacuum (100 Pa) was 60 min, during which the reaction temperature slowly increased from 230 ° C to 240 ° C; S3 maintains vacuum degree below 100Pa and temperature at 240℃ for continuous reaction. After the molecular weight reaches 24000-26000 by observing the torque and current of the stirring motor, the vacuum is stopped. After S4 is cooled to 200°C, trimellitic anhydride is added, and the reaction is continued for 30 minutes before cooling and discharging.

8. The polyester resin for TGIC curing coil powder coating according to claim 1, characterized in that: The antioxidant is AT-215, which is prepared by mixing antioxidant 1010 (pentaerythritol tetrakis(3,5-di-tert-butyl-4-hydroxy)phenylpropionate) and antioxidant 168 (tris(2,4-tert-butylphenyl)phosphite) in a mass ratio of 1:

2.

9. The polyester resin for TGIC-cured coil powder coating according to claim 1, characterized in that: The curing accelerator is any one or two of ethyltriphenylphosphine bromide and 2-aminoimidazole.

10. A method for preparing a polyester resin for TGIC-cured coil powder coating according to any one of claims 1 to 9, characterized in that: The method comprises the following preparation steps: S1: Put the raw materials polyol, polyacid and catalyst into the reactor according to the formula, fill with nitrogen for protection, and when the temperature rises to 165-175℃, esterification and water production begins. Continue to heat up to 243±2℃ and keep warm for reaction. When there is no esterification water, a colorless and transparent resin is obtained. S2 is sampled and tested. When the acid value is 8-10 mgKOH / g, an acidolysis agent is added and the reaction is kept at 238°C-240°C for 90-120 minutes. S3 sampling and testing, when the acid value is 45-47 mgKOH / g, start vacuuming, gradually control the vacuum to -0.097-0.099 MPa, and react at 230-235°C under vacuum conditions for 90-120 minutes. S4 sampling and testing, when the acid value is 32-38 mgKOH / g, cool to 200°C, add modified copolyester, antioxidant, curing accelerator and stir to react for 15-30 minutes, discharge, cool and crush to obtain a colorless or light yellow transparent granular material.

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