CN-121975410-A - Low-temperature fast-curing polyester resin for outdoor powder coating and preparation method thereof

Abstract

The application provides a low-temperature rapid-curing polyester resin for outdoor powder coating and a preparation method thereof, belonging to the technical field of polyester resin preparation. The application introduces isophthalic acid-5-sodium sulfonate into a polyester main chain, adopts 1, 4-cyclohexanedicarboxylic acid/hydrogenated bisphenol A to construct a full-alicyclic rigid skeleton, improves the glass transition temperature and outdoor weather resistance of resin, maintains proper melt fluidity, combines the storage stability and leveling effect of powder, ensures that the content of terminal carboxyl groups is matched with the molecular weight of a beta-hydroxyalkylamide system by adjusting the acid value, ensures that the catalyst maintains the latency in the preparation and storage stages by adopting stearic acid modified zinc phosphonate and is easy to coordinate and anchor with sulfonate/carboxyl groups in situ in the polyester, gradually exerts Lewis acid catalysis when the powder coating is cured and heated, and is beneficial to obtaining faster curing, better comprehensive performance at lower curing temperature and further reducing the curing energy consumption.

Inventors

• LI LIEDONG
• ZHANG LIANGWU
• TAN XI
• LI ZHENYU
• TANG KUN
• HE LIN

Assignees

• 衡阳山泰化工有限公司

Dates

Publication Date

20260505

Application Date

20260409

Claims (10)

1. 1. The preparation method of the low-temperature fast-curing polyester resin for the outdoor powder coating is characterized by comprising the following steps of: S1, adding zinc phenylphosphonate into a stearic acid ethanol solution, stirring and refluxing, cooling and filtering after the reaction is finished, washing with hot ethanol, and vacuum drying to obtain a latent modified zinc phosphonate catalyst; S2, mixing an alcohol monomer component and an acid monomer component in a nitrogen atmosphere, adding tetrabutyl titanate to obtain a reaction solution A, reacting to obtain a reaction solution B, heating and carrying out vacuum polycondensation to obtain a polyester prepolymer; s3, releasing vacuum and continuously introducing nitrogen, cooling the polyester prepolymer, adding isophthalic acid to obtain a reaction solution C, and carrying out heat preservation reaction to obtain a carboxyl-terminated polyester matrix; And S4, cooling the carboxyl-terminated polyester matrix under the protection of nitrogen, adding the latent modified zinc phosphonate catalyst and the compound antioxidant, melting, stirring, mixing, discharging, cooling and crushing to obtain the low-temperature rapid-curing polyester resin for the outdoor powder coating.
2. 2. The method for preparing a low-temperature rapid-curing polyester resin for outdoor powder coating according to claim 1, wherein in S1: The concentration of the stearic acid ethanol solution is 0.1-0.3M; The mass volume ratio of the zinc phenylphosphonate to the stearic acid ethanol solution is 1g (10-20) mL.
3. 3. The method for preparing a low-temperature rapid-curing polyester resin for outdoor powder coating according to claim 1, wherein in S1: The temperature of the stirring reflux is 70-80 ℃; After the reaction is finished, the mixture is cooled to 40-50 ℃ and filtered.
4. 4. The method for preparing a low-temperature rapid-curing polyester resin for outdoor powder coating according to claim 1, wherein in S2: The alcohol monomer component consists of neopentyl glycol and hydrogenated bisphenol A; the molar ratio of neopentyl glycol to hydrogenated bisphenol A in the alcohol monomer component is (70-95): 5-30.
5. 5. The method for preparing a low-temperature rapid-curing polyester resin for outdoor powder coating according to claim 1, wherein in S2: The acid monomer component consists of terephthalic acid, 1, 4-cyclohexanedicarboxylic acid and isophthalic acid-5-sodium sulfonate; The molar ratio of terephthalic acid, 1, 4-cyclohexanedicarboxylic acid and isophthalic acid-5-sodium sulfonate in the acid monomer component is (40-70): 20-40): 0.5-2.
6. 6. The method for preparing a low-temperature rapid-curing polyester resin for outdoor powder coating according to claim 1, wherein in S2: the molar ratio of the alcohol monomer component to the acid monomer component is (1.02-1.05): 1; the feeding amount of the tetrabutyl titanate is 0.01-0.05% of the total mass of the alcohol monomer component and the acid monomer component.
7. 7. The method for preparing a low-temperature rapid-curing polyester resin for outdoor powder coating according to claim 1, wherein in S3: the mass ratio of the isophthalic acid to the polyester prepolymer is 1 (8-15); the acid value of the carboxyl-terminated polyester matrix is 30-36mgKOH/g.
8. 8. The method for preparing a low-temperature rapid-curing polyester resin for outdoor powder coating according to claim 1, wherein in S4: The carboxyl-terminated polyester matrix is cooled to 120-135 ℃; the mass ratio of the latent modified zinc phosphonate catalyst to the carboxyl-terminated polyester matrix is (0.1-0.5) 100.
9. 9. The method for preparing a low-temperature rapid-curing polyester resin for outdoor powder coating according to claim 1, wherein in S4: The mass ratio of the compound antioxidant to the carboxyl-terminated polyester matrix is (0.2-0.5): 100; the mass ratio of the antioxidant 1010 to the antioxidant 168 in the compound antioxidant is 1:1.
10. 10. A low temperature fast curing polyester resin for outdoor powder coating prepared by the preparation method of any one of claims 1 to 9.

Description

Low-temperature fast-curing polyester resin for outdoor powder coating and preparation method thereof Technical Field The invention belongs to the technical field of preparation of polyester resin, and relates to low-temperature rapid-curing polyester resin for outdoor powder coating and a preparation method thereof. Background At present, low-temperature curing polyester powder coating used in the fields of outdoor building aluminum profiles, steel structures and the like mostly adopts linear carboxyl-terminated polyester mainly comprising terephthalic acid/neopentyl glycol and is matched with triglycidyl isocyanurate or beta-hydroxyalkylamide curing system. In order to realize solidification at about 130 ℃, the conventional technology mainly comprises two means, namely, reducing the molecular weight of polyester, introducing flexible diacid/diol to reduce the melt viscosity, and improving the dosage of a catalyst or selecting a metal catalyst with stronger activity and an imidazole accelerator. However, the former tends to cause a decrease in the glass transition temperature (Tg) of the resin, a tendency of caking of the powder during storage and transportation, and a decrease in the weather resistance and mechanical properties of the coating film, while the latter tends to cause a pre-reaction during extrusion, an increase in yellowing during curing, and a deterioration in the storage stability of the powder, and the contradiction between low-temperature curing and high Tg and outdoor weather resistance is difficult to be compatible. Meanwhile, in order to improve weather resistance, the existing outdoor polyester is mostly dependent on improving aromatic structure content or simply introducing alicyclic diacid/diol, and has the problems of higher melt viscosity and insufficient 130 ℃ lower leveling in a low-temperature curing system although yellowing resistance is improved to a certain extent. The existing zinc catalyst is directly and physically mixed into resin in the form of simple inorganic salt or organic zinc salt, and the space distribution and coordination environment of the zinc catalyst in the resin are lack of regulation, so that the catalytic activity is difficult to realize effective distinction between a preparation/storage stage and a curing stage, and the powder storage stability and the film color stability are easily sacrificed while the low-temperature curability is obtained. Disclosure of Invention In view of the above problems, the present application aims to provide a low-temperature fast-curing polyester resin for outdoor powder coating and a method for preparing the same. According to the application, the isophthalic acid-5-sodium sulfonate is introduced into the main chain, and the 1, 4-cyclohexanedicarboxylic acid/hydrogenated bisphenol A is adopted to construct the full-alicyclic rigid skeleton, so that the glass transition temperature and outdoor weather resistance of the resin are improved, and meanwhile, the proper melt fluidity is maintained, thereby being beneficial to the comprehensive balance of stable powder storage and construction leveling. The acid value is regulated in a mode of high molecular weight polycondensation and isophthalic acid acidolysis, so that the content of carboxyl end groups and the molecular weight are in a proper range, and the reaction activity meeting the low-temperature curing requirement is facilitated. The stearic acid modified zinc phosphonate is further adopted and is easy to coordinate and anchor with sulfonate/carboxyl groups in situ in the polyester, so that the catalyst keeps lower activity in the preparation and storage stages, and the Lewis acid catalysis effect is gradually exerted along with the temperature rise in the powder coating curing stage, thereby being beneficial to realizing faster curing at lower curing temperature and reducing energy consumption. In the whole, the scheme of the application forms a relatively balanced comprehensive technical effect among low-temperature curing performance, powder storage stability and outdoor weather resistance. In order to achieve the purpose, the invention adopts the following technical scheme: In a first aspect, the present invention provides a method for preparing a low-temperature fast-curing polyester resin for outdoor powder coating, the method comprising: S1, adding zinc phenylphosphonate into a stearic acid ethanol solution, stirring and refluxing, cooling and filtering after the reaction is finished, washing with hot ethanol, and vacuum drying to obtain a latent modified zinc phosphonate catalyst; S2, mixing an alcohol monomer component and an acid monomer component in a nitrogen atmosphere, adding tetrabutyl titanate to obtain a reaction solution A, wherein the alcohol monomer component consists of neopentyl glycol and hydrogenated bisphenol A, and the acid monomer component consists of terephthalic acid, 1, 4-cyclohexanedicarboxylic acid and isophthalic acid-5-sodium sulfona