A polyester resin for high-hardness powder coating and a method for preparing the same

Abstract

The present application relates to a kind of high-hardness polyester resin for powder coating and its preparation method, which is obtained by polymerization using alkaline lignin, 1,4-dioxane, glutaric anhydride, dimethylbenzene, terephthalic acid, neopentyl glycol, triethylene glycol, adipic acid, etc. as main raw materials. The polyester resin contains high-functionality alkaline lignin structure in its molecule, which is rigid and has high hardness and excellent scratch resistance after curing with TGIC. The polyester resin comprehensively utilizes the effective components of alkaline lignin, a by-product of papermaking, providing an effective way for the high-value-added comprehensive utilization of alkaline lignin, a by-product of papermaking.

Description

Technical Field

[0001] This invention relates to the field of powder coating technology, specifically to a high-hardness polyester resin for powder coatings and its preparation method, as well as its application in TG IC-cured powder coating systems. Background Technology

[0002] Powder coatings boast significant advantages such as solvent-free emissions, environmental friendliness, and excellent overall performance, leading to rapid growth in the current coating industry. They are widely used in applications such as highways, railway facilities, air conditioning, and refrigerators. As the industry expands, downstream manufacturers aim to reduce the cost and price of polyester resins, thereby lowering the cost of powder coatings and further promoting their widespread application. Alkaline lignin, commonly known as xylose powder, is an industrial byproduct produced by separating and spray-drying wastewater from alkaline pulping processes. Approximately 10 million tons are produced annually. Due to its pronounced alkalinity, it is currently mainly used as a low-end additive in industries such as cement and concrete, or burned directly as a pollutant. This not only fails to generate effective added value but also pollutes the environment. Therefore, its effective and comprehensive utilization is an important research direction. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a high-hardness polyester resin for powder coatings and its preparation method, which comprehensively utilizes alkaline lignin with high added value. This polyester resin is obtained by polymerization using alkaline lignin, 1,4-dioxane, glutaric anhydride, xylene, terephthalic acid, neopentyl glycol, triethylene glycol, and adipic acid as main raw materials. First, the alkaline lignin is purified using solvents such as 1,4-dioxane. Then, it undergoes a grafting reaction with glutaric anhydride, and finally, it is copolymerized with terephthalic acid, neopentyl glycol, triethylene glycol, and adipic acid to obtain the polyester resin product. This polyester resin molecule contains a highly functional alkaline lignin structure, exhibiting high rigidity. The resulting coating after curing with TGIC exhibits high hardness and excellent scratch resistance. This polyester resin comprehensively utilizes the effective components of alkaline lignin, a byproduct of papermaking, providing a pathway for the high-value-added comprehensive utilization of this byproduct.

[0004] A high-hardness powder coating polyester resin, said polyester resin comprising the following raw materials in parts by weight:

[0005]

[0006] The raw materials also include hydrochloric acid, catalysts, and antioxidants.

[0007] Furthermore, alkaline lignin, with an effective ingredient content of over 98%, can be a byproduct of papermaking; for example, it can be purchased from Wuhan Huaxiang Kejie Biotechnology Co., Ltd.

[0008] Furthermore, the hydrochloric acid has a mass fraction of 30-32%; the catalyst is tetrabutyl titanate, used in an amount of 0.01-0.04% of the total mass of the raw materials; and the antioxidant is antioxidant 1010, namely pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], used in an amount of 0.1-0.2% of the total mass of the main raw materials.

[0009] The method for preparing the high-hardness powder coating polyester resin involves first purifying alkaline lignin with 1,4-dioxane, then grafting it with glutaric anhydride, and finally copolymerizing it with terephthalic acid, neopentyl glycol, triethylene glycol, and adipic acid to obtain the polyester resin product.

[0010] The method for preparing the high-hardness powder coating polyester resin includes the following steps:

[0011] A. Add the prescribed amount of 1,4-dioxane to the reaction vessel, then add alkaline lignin powder, start stirring, and heat to 95-98℃ for heat preservation and dissolution reaction, and add hydrochloric acid to adjust the pH value of the solution to between 6.0 and 6.5.

[0012] B. Sampling and testing: When the solubility of 1,4-dioxane solution in alkaline lignin does not change significantly, stop the reaction, then centrifuge to remove unreacted dissolved solid residue and obtain filtrate.

[0013] C. Add the filtrate back into the reaction vessel, heat to 100-105℃, start the vacuum system, and remove the 1,4-dioxane solvent under reduced pressure to obtain purified alkaline lignin.

[0014] D. When the residual amount of 1,4-dioxane solvent in the alkaline lignin is <1wt%, add the amount of xylene solvent as specified in the formula, heat to 120-125℃, add the amount of catalyst and glutaric anhydride as specified in the formula, and carry out the grafting modification reaction on the purified alkaline lignin.

[0015] E. Take samples for testing. When the acid value of the polymer in the system no longer decreases significantly, the grafting reaction ends. Add the formulated amounts of terephthalic acid, neopentyl glycol and triethylene glycol, gradually raise the temperature to 210-215℃ and keep the temperature for reaction. During the heating process, remove the xylene solvent at the same time.

[0016] F. Sampling and testing: When the acid value of the polymer in the system reaches 36-43 mgKOH / g, raise the temperature to 225-230℃, then add the prescribed amount of antioxidant and start the vacuum system.

[0017] G. Take samples to test the acid value of the polymer. When the acid value of the polymer reaches 10-15 mg KOH / g, stop the vacuum system, add the prescribed amount of adipic acid as a capping agent, and continue the carboxyl capping reaction at 225-230℃.

[0018] H. When the acid value of the polymer reaches 27-35 mg KOH / g, stop the reaction, discharge the material while it is still hot, cool it, granulate it, and the polyester resin is obtained.

[0019] Preferably, in steps C and F, the vacuum degree is controlled between -0.096 MPa and -0.098 MPa; in step E, the temperature is gradually increased to 210-215°C at a heating rate of 10-13°C / h; in step H, the polyester resin is cooled with a steel belt containing condensate, and then crushed and granulated.

[0020] For example, the method for preparing the polyester resin for high-hardness powder coating includes the following steps:

[0021] A. Add the prescribed amount of 1,4-dioxane to the reaction vessel, then add alkaline lignin powder, start stirring, and heat to 95-98℃ for heat preservation and dissolution reaction, and add an appropriate amount of hydrochloric acid to adjust the pH value of the solution to between 6.0 and 6.5 (weakly acidic).

[0022] B. Sampling and testing: When the solubility of 1,4-dioxane solution in alkaline lignin does not change significantly (the solid content in the solution increases by <1% in 10 min), the reaction is stopped, and then the unreacted dissolved solid residue is removed by centrifugation to obtain the filtrate.

[0023] C. Add the filtrate back into the reactor, heat to 100-105℃, start the vacuum system, control the vacuum degree at -0.096Mpa to -0.098Mpa, remove the 1,4-dioxane solvent under reduced pressure to obtain purified alkaline lignin.

[0024] D. When the residual amount of 1,4-dioxane solvent in the alkaline lignin is <1wt%, add the amount of xylene solvent as specified in the formula, heat to 120-125℃, add the amount of catalyst and glutaric anhydride as specified in the formula, and carry out the grafting modification reaction on the purified alkaline lignin.

[0025] E. Sampling and testing: When the acid value of the polymer in the system no longer decreases significantly (sampling every 10 minutes, the decrease in acid value is less than 1 mg KOH / g), the grafting reaction ends. Add the prescribed amounts of terephthalic acid, neopentyl glycol and triethylene glycol, and gradually raise the temperature to 210-215℃ at a heating rate of 10-13℃ / h, and keep the temperature for reaction. During the heating process, remove the xylene solvent at the same time.

[0026] F. Sampling and testing: When the acid value of the polymer in the system reaches 36-43 mgKOH / g, the temperature is raised to 225-230℃, then the amount of antioxidant in the formula is added, the vacuum system is started, and the vacuum degree is controlled at -0.096Mpa to -0.098Mpa.

[0027] G. Take samples to test the acid value of the polymer. When the acid value of the polymer reaches 10-15 mg KOH / g, stop the vacuum system and add the prescribed amount of adipic acid as a capping agent to continue the carboxyl capping reaction at 225-230℃.

[0028] H. When the acid value of the polymer reaches 27-35 mgKOH / g, stop the reaction, discharge the material while it is still hot, and cool the polyester resin with a steel belt with condensate. Then crush and granulate to obtain the polyester resin.

[0029] The resulting product is a light yellow transparent resin granule with an acid value of 27-35 mgKOH / g and a softening point of 119-130℃.

[0030] The application of a high-hardness powder coating polyester resin in a TGIC curing system, as described above.

[0031] As an example, the TGIC system powder coating formulation may include polyester resin, TGIC, titanium dioxide, barium titanate, leveling agent, brightening agent, benzoin, etc. The coating preparation method is as follows: All materials are mixed according to the requirements of the TGIC system powder coating formulation, extruded, sheeted, and crushed using a twin-screw extruder, and then the sheet is pulverized and sieved to produce powder coating. The powder coating is sprayed onto a surface-treated tinplate substrate using an electrostatic spray gun, and baked to a certain film thickness to obtain the coating layer.

[0032] Beneficial effects:

[0033] The polyester resin of this invention is obtained by polymerization using alkaline lignin, 1,4-dioxane, glutaric anhydride, xylene, terephthalic acid, neopentyl glycol, triethylene glycol, and adipic acid as main raw materials. Firstly, the polyester resin molecule contains a highly functional alkaline lignin structure, exhibiting high rigidity. The resulting coating after curing with TGIC exhibits high hardness and excellent scratch resistance. Simultaneously, this polyester resin comprehensively utilizes the effective components of alkaline lignin, a byproduct of papermaking, providing a pathway for the high-value-added comprehensive utilization of this byproduct. Detailed Implementation

[0034] The present invention will be further described below with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and technical features described in this application can be combined with each other. It should also be pointed out that, unless otherwise specified, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The terms "comprising" or "including" and similar words used in this invention refer to elements or objects preceding the word that encompass the elements or objects listed following the word and their equivalents, without excluding other elements or objects.

[0035] All raw materials used in this invention are commercially available. For example, alkaline lignin, with an effective ingredient content of over 98%, was purchased from Wuhan Huaxiang Kejie Biotechnology Co., Ltd.

[0036] Preparation Example 1

[0037] A high-hardness powder coating polyester resin, said polyester resin comprising the following raw materials in parts by weight:

[0038]

[0039] The catalyst is tetrabutyl titanate, and its dosage is 0.02% of the total mass of the raw materials;

[0040] The antioxidant is antioxidant 1010, and its dosage is 0.1% of the total mass of the main raw materials.

[0041] The preparation method of the polyester resin for high-hardness powder coating includes the following steps:

[0042] A. Add the prescribed amount of 1,4-dioxane to the reactor, then add alkaline lignin powder, start stirring, and heat to 95℃ for heat preservation and dissolution reaction, and add hydrochloric acid (hydrochloric acid mass fraction of 30%) to adjust the pH value of the solution to between 6.0 (weakly acidic).

[0043] B. Sampling and testing: When the solubility of 1,4-dioxane solution in alkaline lignin does not change significantly (the solid content in the solution increases by <1% in 10 min), the reaction is stopped, and then the unreacted dissolved solid residue is removed by centrifugation to obtain the filtrate.

[0044] C. Add the filtrate back into the reactor, heat to 100°C, start the vacuum system, control the vacuum degree at -0.096 MPa, remove the 1,4-dioxane solvent under reduced pressure, and obtain the purified alkaline lignin.

[0045] D. When the residual amount of 1,4-dioxane solvent in the alkaline lignin is <1wt%, add the amount of xylene solvent specified in the formula, heat to 120℃, add the amount of catalyst and glutaric anhydride specified in the formula, and carry out the grafting modification reaction on the purified alkaline lignin.

[0046] E. Sampling and testing: When the acid value of the polymer in the system no longer decreases significantly (sampling every 10 minutes, the decrease in acid value is less than 1 mg KOH / g), the grafting reaction ends. Add the prescribed amounts of terephthalic acid, neopentyl glycol and triethylene glycol, and gradually raise the temperature to 210°C at a rate of 10°C / h, and keep the temperature for reaction. During the heating process, remove the xylene solvent at the same time.

[0047] F. Sampling and testing: When the acid value of the polymer in the system reaches 36 mg KOH / g, the temperature is raised to 225℃, then the amount of antioxidant in the formula is added, and the vacuum system is started, with the vacuum degree controlled at -0.096 MPa.

[0048] G. Take samples to test the acid value of the polymer. When the acid value of the polymer reaches 10 mg KOH / g, stop the vacuum system and add the prescribed amount of adipic acid as a capping agent to continue the carboxyl capping reaction at 225℃.

[0049] H. When the acid value of the polymer reaches the expected value, stop the reaction, discharge the material while it is still hot, and cool the polyester resin with a steel belt containing condensate. Then crush and granulate to obtain the polyester resin.

[0050] The obtained polyester resin appears as pale yellow transparent granules, with an acid value of 28 mg KOH / g and a softening point of 121℃.

[0051] Preparation Example 2

[0052] A high-hardness powder coating polyester resin, said polyester resin comprising the following raw materials in parts by weight:

[0053]

[0054]

[0055] The catalyst is tetrabutyl titanate, and its dosage is 0.04% of the total mass of the raw materials.

[0056] The antioxidant is antioxidant 1010, and its dosage is 0.2% of the total mass of the main raw materials.

[0057] The preparation method is the same as in Preparation Example 1.

[0058] The obtained polyester resin appears as pale yellow transparent granules, with an acid value of 34 mgKOH / g and a softening point of 128℃.

[0059] Preparation Example 3

[0060] A high-hardness powder coating polyester resin, said polyester resin comprising the following raw materials in parts by weight:

[0061]

[0062] The catalyst is tetrabutyl titanate, and its dosage is 0.03% of the total mass of the raw materials;

[0063] The antioxidant is antioxidant 1010, and its dosage is 0.2% of the total mass of the main raw materials.

[0064] The preparation method is the same as in Preparation Example 1.

[0065] The obtained polyester resin appears as light yellow transparent resin granules, with an acid value of 32 mg KOH / g and a softening point of 124℃.

[0066] Preparation Example 4

[0067] A high-hardness powder coating polyester resin, said polyester resin comprising the following raw materials in parts by weight:

[0068]

[0069] The catalyst is tetrabutyl titanate, and its dosage is 0.01% of the total mass of the raw materials.

[0070] The antioxidant is antioxidant 1010, and its dosage is 0.2% of the total mass of the main raw materials.

[0071] The preparation method is the same as in Preparation Example 1.

[0072] The obtained polyester resin appears as light yellow transparent resin granules, with an acid value of 31 mgKOH / g and a softening point of 127℃.

[0073] Comparative Preparation Example 1: Commercially available polyester resin for ordinary TGIC curing systems, acid value: 33 mg KOH / g, softening point 116℃, model GH-2200, purchased from Zhejiang Guanghua New Material Co., Ltd.

[0074] Examples 1-4 (the polyester resins were obtained from Preparation Examples 1-4 above):

[0075] The TGIC system powder coating formulation, by weight, is as follows:

[0076]

[0077] Coating preparation: Following the requirements of the TGIC system powder coating formulation, all materials were mixed thoroughly, extruded, sheeted, and crushed using a twin-screw extruder. The sheeted material was then pulverized and sieved to produce the powder coating. The powder coating was then sprayed onto a surface-treated tinplate substrate using an electrostatic spray gun, achieving a film thickness of approximately 80 μm. The coating was then cured by baking at 200℃ for 10 minutes to obtain the final coating layer.

[0078] Coating index testing was conducted in accordance with GB / T 21776-2008 "Guidelines for Testing Standards of Powder Coatings and Their Coatings"; film hardness testing was conducted in accordance with GB / T6739-2006 "Determination of Hardness of Paint Film by Pencil Method for Paints and Varnishes"; and scratch resistance testing was conducted in accordance with GB / T 9279-2007 "Scratch Test for Paints and Varnishes".

[0079] Table 1. Basic performance test results of the embodiments and comparative examples.

[0080]

[0081] As can be seen from the test results of Examples 1-4 and Comparative Example 1 in Table 1, the products and processes of the present invention, through the synergistic effect of each component, produce coatings with better appearance, gloss, and boiling water resistance after curing with polyester resin and TGIC, while the coatings have better hardness and scratch resistance, all of which are higher than those prepared by commercially available polyester resin products cured with ordinary TGIC.

[0082] This invention patent not only yields high-performance, high-hardness polyester resin products for powder coatings, but also realizes the comprehensive utilization of alkaline lignin raw materials with high added value, possessing significant economic and environmental value.

[0083] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above description is illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A polyester resin for high-hardness powder coatings, characterized in that, The polyester resin comprises the following raw materials in parts by weight: 12-15 parts of alkaline lignin; 38-45 parts of 1,4-dioxane; 11-15 parts of glutaric anhydride; 25-30 parts xylene; 16-20 parts of terephthalic acid; 14-18 parts of neopentyl glycol; 15-20 parts of triethylene glycol; 7-10 parts adipic acid; The raw materials also include hydrochloric acid, catalysts, and antioxidants; The preparation method of the high-hardness powder coating polyester resin is as follows: A. Add the prescribed amount of 1,4-dioxane to the reaction vessel, then add alkaline lignin powder, start stirring, and heat to 95-98℃ for heat preservation and dissolution reaction, and add hydrochloric acid to adjust the pH value of the solution to between 6.0 and 6.

5. B. Sampling and testing: When the solubility of 1,4-dioxane solution in alkaline lignin does not change significantly, stop the reaction, then centrifuge to remove unreacted dissolved solid residue and obtain filtrate. C. Add the filtrate back into the reaction vessel, heat to 100-105℃, start the vacuum system, and remove the 1,4-dioxane solvent under reduced pressure to obtain purified alkaline lignin. D. When the residual 1,4-dioxane solvent in the alkaline lignin is <1wt%, add the prescribed amount of xylene solvent, heat to 120-125℃, add the prescribed amount of catalyst and glutaric anhydride, and carry out graft modification reaction on the purified alkaline lignin. E. Take samples for testing. When the acid value of the polymer in the system no longer decreases significantly, the grafting reaction ends. Add the formulated amounts of terephthalic acid, neopentyl glycol and triethylene glycol, gradually raise the temperature to 210-215℃ and keep the temperature for reaction. During the heating process, remove the xylene solvent at the same time. F. Sampling and testing: When the acid value of the polymer in the system reaches 36-43 mgKOH / g, raise the temperature to 225-230℃, then add the prescribed amount of antioxidant and start the vacuum system. G. Take samples to test the acid value of the polymer. When the acid value of the polymer reaches 10-15 mg KOH / g, stop the vacuum system, add the prescribed amount of adipic acid as a capping agent, and continue the carboxyl capping reaction at 225-230℃. H. When the acid value of the polymer reaches 27-35 mgKOH / g, stop the reaction, discharge the material while it is still hot, cool it, granulate it, and the polyester resin is obtained.

2. The polyester resin for high-hardness powder coating as described in claim 1, characterized in that, The hydrochloric acid mass fraction is 30-32%; the content of effective alkaline lignin components is over 98%.

3. The polyester resin for high-hardness powder coating as described in claim 1, characterized in that, The catalyst is tetrabutyl titanate, and the amount used is 0.01-0.04% of the total mass of the raw materials.

4. The polyester resin for high-hardness powder coating as described in claim 1, characterized in that, The antioxidant is antioxidant 1010.

5. The polyester resin for high-hardness powder coating as described in claim 1, characterized in that, In steps C and F of the preparation method, the vacuum degree is controlled between -0.096 MPa and -0.098 MPa.

6. The polyester resin for high-hardness powder coating as described in claim 1, characterized in that, In step E of the preparation method, the temperature is gradually increased to 210-215℃ at a heating rate of 10-13℃ / h.

7. The polyester resin for high-hardness powder coating as described in claim 1, characterized in that, In step H of the preparation method, the polyester resin is cooled with a steel belt containing condensate, and then crushed and granulated.

8. The application of a high-hardness powder coating polyester resin as described in any one of claims 1-7 in a TGIC curing system.

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