A low temperature curing polyester resin for QM1260 system powder coating and a preparation method thereof

Abstract

The application provides a low-temperature curing QM1260 system polyester resin for powder coating and a preparation method thereof, and belongs to the technical field of powder coating. The polyester resin is prepared by using 3-methyl-1,5-pentanediol, 2,3-dimethyl-2,3-butanediol, 4,4'-diphenyl ether dicarboxylic acid, hexadecanedioic acid, 2,2-difluoro-1,3-propanediol, dimer acid and the like as raw materials for step-by-step polymerization. The polyester resin is prepared by using a special raw material combination and process. The polyester resin is matched with a QM1260 curing agent, low-temperature curing at 140 DEG C / 20 min is realized, and the coating film after curing has no obvious pinholes, and the gloss, leveling and boiling water resistance are also relatively good.

Description

Technical Field

[0001] This invention belongs to the field of powder coating technology, specifically relating to a low-temperature curing QM1260 system polyester resin for powder coating and its preparation method. Background Technology

[0002] QM1260, short for N,N,N',N'-tetra(2-hydroxypropyl)hexamethylenediamide, is a tetrahydroxy powder coating curing agent. Like N,N,N',N'-tetra(2-hydroxyethyl)hexamethylenediamide curing agent, it belongs to the hydroxyalkylamide curing agent series. However, compared to N,N,N',N'-tetra(2-hydroxyethyl)hexamethylenediamide curing agent, it has advantages such as a lower melting point, better low-temperature fluidity, and better resistance to yellowing. However, its hydroxyl functional groups have high steric hindrance and low reactivity, requiring highly reactive carboxyl polyester resins for curing. Furthermore, QM1260 hydroxyl curing agent requires specific curing conditions at low temperatures. At low temperatures, the moisture generated during curing is difficult to escape from the coating quickly, making it more prone to pinholes compared to high-temperature curing. Therefore, polyester resin products with lower softening points and excellent melt flowability are needed to solve this problem. More importantly, the resins used for low-temperature curing generally have insufficient water resistance, resulting in defects in the water resistance of the coating. This is because the polyester resins used, in order to lower the softening point and increase low-temperature flowability, often use liquid diols with insufficient water resistance, such as diethylene glycol and triethylene glycol. How to solve these defects is a problem that the industry needs to address.

[0003] In patent ZL201911182351.8, straight-chain linear diols such as diethylene glycol, diethanolamine, and 1,6-hexanediol are used as the main raw materials, combined with octadecanoic acid as a capping agent, which achieves the effect of reducing the softening point of polyester resin. Finally, it achieves rapid curing and film formation with QM1260 curing agent at 180℃ / 10min. However, when this polyester resin is used for low-temperature curing, such as at 140℃, it still cannot be fully cured, resulting in poor impact performance. Furthermore, the pinholes, leveling, and water resistance of the coating film cannot meet the application requirements. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a low-temperature curing polyester resin for QM1260 system powder coatings, prepared using a special combination of raw materials and process. This polyester resin is matched with QM1260 curing agent to achieve low-temperature curing at 140℃ / 20min. Moreover, the cured coating film not only has no obvious pinholes, but also has superior gloss, leveling and water resistance.

[0005] One of the objectives of this invention is to provide a polyester resin for low-temperature curing QM1260 system powder coatings.

[0006] The second objective of this invention is to provide a method for preparing the polyester resin.

[0007] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In a first aspect, the present invention provides a polyester resin for low-temperature curing QM1260 system powder coatings. It is prepared from raw materials comprising the following molar amounts: 8-13 parts of 3-methyl-1,5-pentanediol; 17-23 parts of 2,3-dimethyl-2,3-butanediol; 7-11 parts of 4,4'-diphenyl ether dicarboxylic acid; 4-6 parts of hexadecanoic acid; 5-9 parts of 2,2-difluoro-1,3-propanediol; 18-27 parts of dimer acid; The raw materials also include a catalyst and an antioxidant; the catalyst is stannous octoate, and the amount used is 0.1-0.12% of the total mass of the raw materials; the antioxidant is antioxidant 1010, and the amount used is 0.3-0.4% of the total mass of the raw materials.

[0008] Typical, but not limiting, molar amounts of 3-methyl-1,5-pentanediol are, for example, 8, 9, 10, 11, 12, or 13 parts. Typical, but not limiting, molar amounts of 2,3-dimethyl-2,3-butanediol are, for example, 17, 18, 19, 20, 21, 22, or 23 parts. Typical, but not limiting, molar amounts of 4,4'-diphenyl ether dicarboxylic acid are, for example, 7, 8, 9, 10, or 11 parts. Typical, but not limiting, molar amounts of hexadecanoic acid are, for example, 4, 5, or 6 parts. Typical, but not limiting, molar amounts of 2,2-difluoro-1,3-propanediol are, for example, 5, 6, 7, 8, or 9 parts. Typical, but not limiting, molar amounts of dimer acids are, for example, 18, 19, 20, 21, 22, 23, 24, 25, 26, and 27 parts.

[0009] Secondly, the present invention provides a method for preparing the polyester resin for the above-mentioned low-temperature curing QM1260 system powder coating, comprising the following steps: A. Add the prescribed amounts of 3-methyl-1,5-pentanediol and 2,3-dimethyl-2,3-butanediol to the reactor, start stirring, and heat to 130-135℃; then add the prescribed amounts of catalyst, 4,4'-diphenyl ether dicarboxylic acid, and 1 / 3 to 1 / 2 of the prescribed amount of dimer acid, turn on nitrogen protection, and gradually heat to 190-195℃ at a heating rate of 8-11℃ to carry out the heat-holding polymerization reaction; B. Take samples to test the acid value range of the polymer. When the acid value of the polyester resin reaches 30-40 mg KOH / g, add the formula amount of hexadecanoic acid, 2,2-difluoro-1,3-propanediol and the remaining 1 / 2 formula amount of dimer acid, and gradually raise the temperature to 225-230℃ at a heating rate of 6-8℃ / h, and continue to keep the temperature for reaction. C. Sample and test the acid value range of the polymer. When the acid value of the polymer reaches 25-30 mgKOH / g, add the prescribed amount of antioxidant, stir evenly, and start the vacuum system to carry out vacuum polycondensation reaction. Stop the vacuum system when the acid value drops to 8-12 mgKOH / g. Then add the remaining prescribed amount of dimer acid and continue the carboxyl end-capping reaction at 225-230℃. Stop the reaction when the acid value of the reactant is 22-28 mgKOH / g. Discharge the material at high temperature and cool it with a rapid cooling steel belt. Then crush and granulate to obtain polyester resin.

[0010] In some implementations, in step C, the vacuum system controls the negative pressure to be between -0.095 and -0.098 MPa.

[0011] The polyester resin obtained by this invention is a light yellow transparent granule with an acid value of 22-28 mgKOH / g and a softening point of 78-88℃.

[0012] Beneficial effects: This invention primarily uses 3-methyl-1,5-pentanediol, 2,3-dimethyl-2,3-butanediol, 4,4'-diphenyl ether dicarboxylic acid, hexadecanoic acid, 2,2-difluoro-1,3-propanediol, and dimer acid as raw materials for stepwise polymerization. The final polyester resin product has a low acid value, controlled at 22-28 mg KOH / g, to reduce the amount of water released during curing. The stannous octoate catalyst used has good low-temperature catalytic esterification reaction capability. In the polyester resin, combined with the highly active terminal carboxyl groups of dimer acid, it can achieve sufficient curing at a low temperature (140℃ / 20min) with QM1260. 4,4'-Diphenyl ether dicarboxylic acid and dimeric acid provide excellent water resistance to polyester resins. Meanwhile, the stepwise polymerization of hexadecanoic acid and dimeric acid introduces polyester segments, significantly reducing the softening point of the polyester resin product. Furthermore, the polymerization of 3-methyl-1,5-pentanediol, 2,3-dimethyl-2,3-butanediol, and 2,2-difluoro-1,3-propanediol as diols not only lowers the softening point of the polyester and enhances melt flow properties, but the introduction of multiple branched methyl groups and fluorine elements also improves the product's water resistance and leveling properties. Ultimately, the softening point of the polyester resin product is reduced to below 88℃, and it exhibits excellent flowability during low-temperature curing at 140℃, ensuring good low-temperature leveling, moisture escape, and curing activity.

[0013] The present invention has been described in detail above; however, the above embodiments are merely illustrative in nature and are not intended to limit the invention. Furthermore, this document is not limited to the foregoing prior art or the invention itself, or to any theory described in the following embodiments. Detailed Implementation

[0014] The present invention will be further described below with reference to the embodiments. It should be noted that the following embodiments are provided for illustrative purposes only and do not constitute a limitation on the scope of protection of the present invention.

[0015] Unless otherwise specified, the raw materials, reagents, and methods used in the embodiments are all conventional raw materials, reagents, and methods in the art.

[0016] Dimeric acid, model YF1002, acid value 198mgKOH / g, Yichun Yongfeng Chemical Co., Ltd.; The acid value test method is based on HG / T 2708-1995 "Determination of Acid Value in Polyester Polyols"; The softening point test method is based on GB / T 15332-1994 "Determination of softening point of hot melt adhesives - Ring and Ball method"; Example 1 A low-temperature curing QM1260 system powder coating polyester resin, comprising the following raw materials in molar amounts: 11 parts of 3-methyl-1,5-pentanediol; 19 parts of 2,3-dimethyl-2,3-butanediol; 8 parts of 4,4'-diphenyl ether dicarboxylic acid; 4 parts hexadecanoic acid; 7 parts of 2,2-difluoro-1,3-propanediol; 24 parts of dimer acid; Stannous octoate, used at a rate of 0.1% of the total mass of the raw materials; Antioxidant 1010 is used at a rate of 0.4% of the total mass of the raw materials.

[0017] The method for preparing the polyester resin for low-temperature curing QM1260 system powder coatings includes the following steps: A. Add the prescribed amounts of 3-methyl-1,5-pentanediol and 2,3-dimethyl-2,3-butanediol to the reactor, start stirring, and heat to 130°C; then add the prescribed amounts of catalyst stannous octoate and 4,4'-diphenyl ether dicarboxylic acid and 1 / 2 of the prescribed amount (1 / 2 of the molar amount) of dimer acid, turn on nitrogen protection, and gradually heat to 190°C at a heating rate of 10°C to carry out the heat-holding polymerization reaction; B. Take samples to test the acid value range of the polymer. When the acid value of the polyester resin reaches 30-40 mg KOH / g, add the formula amount of hexadecanoic acid, 2,2-difluoro-1,3-propanediol and the remaining 1 / 2 formula amount (i.e., 1 / 2 of the remaining formula amount) of dimer acid, and gradually raise the temperature to 230℃ at a heating rate of 8℃ / h, and continue to keep the temperature for reaction. C. Sample and test the acid value range of the polymer. When the acid value of the polymer reaches 25-30 mgKOH / g, add the prescribed amount of antioxidant 1010, stir evenly, and start the vacuum system to carry out vacuum polycondensation reaction. The vacuum system controls the negative pressure at -0.098 MPa. Stop the vacuum system when the acid value drops to 8-12 mgKOH / g. Then add the remaining prescribed amount of dimer acid and continue the carboxyl end-capping reaction at 230℃. Stop the reaction when the acid value of the reactant is 22-28 mgKOH / g. Discharge the material at high temperature and cool it with a rapid cooling steel belt. After crushing and granulation, obtain polyester resin.

[0018] The prepared polyester resin has an acid value of 27 mg KOH / g and a softening point of 79℃.

[0019] Example 2 A low-temperature curing QM1260 system powder coating polyester resin, comprising the following raw materials in molar amounts: 8 parts of 3-methyl-1,5-pentanediol; 21 parts of 2,3-dimethyl-2,3-butanediol; 7 parts of 4,4'-diphenyl ether dicarboxylic acid; 6 parts of hexadecanoic acid; 5 parts of 2,2-difluoro-1,3-propanediol; 18 parts of dimer acid; Stannous octoate, used at a rate of 0.11% of the total mass of the raw materials; Antioxidant 1010 is used at a rate of 0.3% of the total mass of the raw materials.

[0020] The preparation method is the same as in Example 1.

[0021] The prepared polyester resin has an acid value of 22 mg KOH / g and a softening point of 87℃.

[0022] Example 3 A low-temperature curing QM1260 system powder coating polyester resin, comprising the following raw materials in molar amounts: 13 parts of 3-methyl-1,5-pentanediol; 23 parts of 2,3-dimethyl-2,3-butanediol; 11 parts of 4,4'-diphenyl ether dicarboxylic acid; 4 parts hexadecanoic acid; 9 parts of 2,2-difluoro-1,3-propanediol; 27 parts of dimer acid; Stannous octoate, used at a rate of 0.12% of the total mass of the raw materials; Antioxidant 1010 is used at a rate of 0.4% of the total mass of the raw materials.

[0023] The preparation method is the same as in Example 1.

[0024] The prepared polyester resin has an acid value of 24 mg KOH / g and a softening point of 82℃.

[0025] Example 4 A low-temperature curing QM1260 system powder coating polyester resin, comprising the following raw materials in molar amounts: 10 parts of 3-methyl-1,5-pentanediol; 20 parts of 2,3-dimethyl-2,3-butanediol; 9 parts of 4,4'-diphenyl ether dicarboxylic acid; 5 parts hexadecanoic acid; 7 parts of 2,2-difluoro-1,3-propanediol; 22 parts of dimer acid; Stannous octoate, used at a rate of 0.12% of the total mass of the raw materials; Antioxidant 1010 is used at a rate of 0.35% of the total mass of the raw materials.

[0026] The preparation method is the same as in Example 1.

[0027] The prepared polyester resin has an acid value of 26 mg KOH / g and a softening point of 85℃.

[0028] Example 5 A low-temperature curing QM1260 system powder coating polyester resin, comprising the following raw materials in molar amounts: 8 parts of 3-methyl-1,5-pentanediol; 17 parts of 2,3-dimethyl-2,3-butanediol; 8 parts of 4,4'-diphenyl ether dicarboxylic acid; 4 parts hexadecanoic acid; 9 parts of 2,2-difluoro-1,3-propanediol; 20 parts of dimer acid; Stannous octoate, used at a rate of 0.1% of the total mass of the raw materials; Antioxidant 1010 is used at a rate of 0.35% of the total mass of the raw materials.

[0029] The preparation method is the same as in Example 1.

[0030] The prepared polyester resin has an acid value of 23 mg KOH / g and a softening point of 80℃.

[0031] Comparative Example 1 Everything else is the same as in Example 1, except that the dimer acid is replaced with an equimolar amount of adipic acid; The prepared polyester resin has an acid value of 26 mg KOH / g and a softening point of 98℃.

[0032] Comparative Example 2 The rest is the same as in Example 1, except that 2,2-difluoro-1,3-propanediol is replaced with an equimolar amount of 1,3-propanediol; and 2,3-dimethyl-2,3-butanediol is replaced with an equimolar amount of diethylene glycol. The prepared polyester resin has an acid value of 24 mg KOH / g and a softening point of 75℃.

[0033] Performance testing Powder coating formulations using the QM1260 curing system typically have the following formulation by weight: Examples and comparative examples: 550 parts of polyester resin; 32 parts of QM1260 curing agent; 200 parts of titanium dioxide; 150 parts of barium sulfate; 10 parts leveling agent; 10 parts of wetting accelerator; Three portions of benzoin.

[0034] All of the above raw materials are commercially available common raw materials. Among them, QM1260 curing agent is a product of EMS Company; leveling agent is GLP588 and wetting accelerator is BLC701, both of which are products of Ningbo Nanhai Chemical Co., Ltd.

[0035] Coating preparation: After thoroughly mixing all materials according to the above formula, high-temperature melt extrusion is performed using a twin-screw extruder, followed by tableting and crushing. The pulverized material is then ground and sieved (160 mesh) to produce a powder coating. The powder coating is electrostatically sprayed onto a surface-treated test-specific aluminum substrate, with a film thickness controlled at approximately 80 μm. After curing at 140℃ for 20 min, the cured coating is obtained.

[0036] Performance Comparison The coating performance was tested according to GB / T 5237.4-2017 "Aluminum Alloy Building Profiles Part 4: Spray-coated Profiles". Specifically, boiling water resistance (5 hours) was tested according to the method in Part 5.4.6, and the dry adhesion grade of the coating was tested according to the method in Part 5.4.5.1 (using adhesive tape with a peel strength of 11.5 N / 25 mm). The leveling grade was determined using the PCI leveling grade method: the prepared coating was compared with a PCI leveling grade control panel (grades 0-10).

[0037] The coating performance results are shown in Table 1 below.

[0038] Table 1. Performance of the prepared powder coatings

[0039] As can be seen from the comparison of Comparative Examples 1-5 and Example 1 in Table 1, the polyester resin prepared using the specific formulation and process of the product of this invention has the characteristics of low acid value, high end carboxyl group activity, and low softening point. It can achieve full curing with QM1260 curing agent under low-temperature curing conditions of 140℃ / 20min, effectively allowing moisture to escape during the curing process and avoiding pinholes. At the same time, the product exhibits good dry adhesion and boiling water resistance (5h), with a leveling grade of 7, demonstrating excellent overall performance. It is a superior low-temperature curing polyester resin product that is well-matched with QM1260 curing agent.

[0040] In Comparative Example 1, when the dimer acid was replaced with an equimolar amount of adipic acid, the softening point of the prepared polyester resin increased significantly. At 140℃, the melt flow and end carboxyl group activity of the polyester were poor, which led to insufficient final curing and difficulty in the rapid escape of moisture. The final surface pinholes were obvious, and the dry adhesion grade and boiling water resistance were defective, with the leveling grade being only 5. In Comparative Example 2, 2,2-difluoro-1,3-propanediol was replaced with an equimolar amount of 1,3-propanediol; and 2,3-dimethyl-2,3-butanediol was replaced with an equimolar amount of diethylene glycol. The gloss and water resistance of the polyester resin were significantly reduced, resulting in significant loss of gloss after boiling water resistance (5h).

[0041] The above embodiments are merely illustrative of the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and substance defined by the claims of the present invention; and such modifications or substitutions are still within the scope defined by the claims of the present invention.

Claims

1. A low-temperature curing polyester resin for QM1260 system powder coatings, characterized in that, It is prepared from raw materials comprising the following molar amounts: 8-13 parts of 3-methyl-1,5-pentanediol; 17-23 parts of 2,3-dimethyl-2,3-butanediol; 7-11 parts of 4,4'-diphenyl ether dicarboxylic acid; 4-6 parts of hexadecanoic acid; 5-9 parts of 2,2-difluoro-1,3-propanediol; 18-27 parts of dimer acid.

2. The low-temperature curing QM1260 system powder coating polyester resin according to claim 1, characterized in that, The raw materials also include a catalyst and an antioxidant; the catalyst is stannous octoate, and the amount used is 0.1-0.12% of the total mass of the raw materials; the antioxidant is antioxidant 1010, and the amount used is 0.3-0.4% of the total mass of the raw materials.

3. A method for preparing the polyester resin for low-temperature curing QM1260 system powder coating as described in claim 1 or 2, characterized in that, Includes the following steps: A. Add the prescribed amounts of 3-methyl-1,5-pentanediol and 2,3-dimethyl-2,3-butanediol to the reactor, start stirring, and heat to 130-135℃; then add the prescribed amounts of catalyst, 4,4'-diphenyl ether dicarboxylic acid, and 1 / 3 to 1 / 2 of the prescribed amount of dimer acid, turn on nitrogen protection, and gradually heat to 190-195℃ at a heating rate of 8-11℃ to carry out the heat-holding polymerization reaction; B. When the acid value of the polyester resin reaches 30-40 mg KOH / g, add the formula amount of hexadecanoic acid, 2,2-difluoro-1,3-propanediol and the remaining 1 / 2 formula amount of dimer acid, and gradually raise the temperature to 225-230℃ at a heating rate of 6-8℃ / h, and continue to keep the temperature for reaction. C. When the acid value of the polymer reaches 25-30 mgKOH / g, add the prescribed amount of antioxidant, stir evenly, and start the vacuum system to carry out the vacuum polycondensation reaction. Stop the vacuum system when the acid value drops to 8-12 mgKOH / g. Then add the remaining prescribed amount of dimer acid and continue the carboxyl end-capping reaction at 225-230℃. Stop the reaction when the acid value of the reactant is 22-28 mgKOH / g. Discharge the material at high temperature and cool it with a rapid cooling steel belt. Then crush and granulate to obtain polyester resin.

4. The preparation method according to claim 3, characterized in that, In step C, the vacuum system controls the negative pressure to be between -0.095 and -0.098 MPa.

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