A polyester powder coating and a method for its preparation

Abstract

The application provides a polyester powder coating and a preparation method thereof, and belongs to the technical field of coatings and comprises the following components: a polyester resin, a fluorine-containing glycidyl ester curing agent, a filler and an additive; the fluorine-containing glycidyl ester curing agent comprises tetrafluoro-phthalic acid diglycidyl ester and trimesic acid triglycidyl ester. The comprehensive performance of the polyester powder coating is significantly improved by compounding the fluorine-containing glycidyl ester curing agent system.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, specifically relating to a polyester powder coating and its preparation method. Background Technology

[0002] Powder coatings, as solvent-free protective coatings containing 100% solid components, are widely used in metal casings of household appliances, indoor and outdoor metal furniture, highway guardrails, metal building materials, and other metal materials due to their environmental friendliness, high bonding strength, and excellent mechanical properties. Powder coatings primarily use polyester resin as the film-forming substance. Under the action of a curing agent, a ring-opening and cross-linking curing reaction occurs, generating a three-dimensional cross-linked network structure. Therefore, the selection of a suitable curing agent directly affects the application performance of the coating.

[0003] In existing technologies, triglycidyl isocyanurate is the main curing agent in polyester powder coatings. The cured coating exhibits excellent mechanical properties, outdoor weather resistance, chemical solvent resistance, and yellowing resistance, making it the most widely used curing agent in polyester powder coatings. However, triglycidyl isocyanurate also has significant drawbacks. For example, it requires high-temperature baking at 200℃ for curing, resulting in high energy consumption. Furthermore, triglycidyl isocyanurate can cause allergies, skin and respiratory damage, and genotoxicity during production and application. Therefore, it is crucial to develop a green and environmentally friendly powder coating curing agent that can completely replace triglycidyl isocyanurate. Summary of the Invention

[0004] In view of the above situation and to overcome the defects of the prior art, the purpose of the present invention is to provide a polyester powder coating and a method for preparing the same, so as to at least partially solve the problems mentioned in the background art.

[0005] The technical solution adopted in this invention is as follows:

[0006] The first aspect of the present invention provides a polyester powder coating comprising the following components: polyester resin, fluorinated glycidyl ester curing agent, filler and additives; wherein the fluorinated glycidyl ester curing agent comprises diglycidyl tetrafluorophthalate and triglycidyl pyromellitic acid.

[0007] In some embodiments of the present invention, the mass ratio of the polyester resin to the fluorinated glycidyl ester curing agent is 20:(2-5).

[0008] In some embodiments of the present invention, the mass ratio of diglycidyl tetrafluorophthalate to diglycidyl terephthalate in the fluorinated glycidyl ester curing agent is 1:(3-5).

[0009] In some embodiments of the present invention, the mass ratio of the polyester resin to the filler is 50:(1-3), and the filler includes barium sulfate and calcium carbonate, wherein the mass ratio of barium sulfate to calcium carbonate in the filler is 1:(0.8-1.2).

[0010] In some embodiments of the present invention, the mass ratio of the polyester resin to the additives is 100:(0.5-2), and the additives include leveling agents, degassing agents, and antioxidants.

[0011] A second aspect of this invention provides a method for preparing a polyester powder coating, comprising the following steps:

[0012] Premix polyester resin, fluorinated glycidyl ester curing agent, filler, and additives;

[0013] The mixture is melt-blended using a twin-screw extruder at an extrusion temperature of 100-120℃.

[0014] After being compressed and cooled, the powder is crushed and passed through a 200-mesh sieve to obtain polyester powder coating.

[0015] In some embodiments of the present invention, the screw speed of the twin-screw extruder is 300-500 rpm and the vacuum degree is ≥-0.09 MPa.

[0016] In some embodiments of the present invention, the method for preparing the tetrafluorophthalic acid diglycidyl ester in the fluorinated glycidyl ester curing agent includes:

[0017] Tetrafluorophthalic acid and epichlorohydrin were mixed, a catalyst was added, and the mixture was heated to 85-95℃ and reacted for 2-4 hours. Then the temperature was lowered to 35-45℃, NaOH solution was added dropwise, and the mixture was kept at this temperature for 4-6 hours to obtain diglycidyl tetrafluorophthalate.

[0018] In some embodiments of the present invention, the mass ratio of tetrafluorophthalic acid to epichlorohydrin is 1:(0.8-1).

[0019] In some embodiments of the present invention, the catalyst is benzyltriethylammonium chloride, and the amount of catalyst added is 3%-6% of the mass of tetrafluorophthalic acid.

[0020] The beneficial effects achieved by this invention are as follows:

[0021] This invention significantly improves the overall performance of polyester powder coatings by compounding a fluorinated glycidyl ester curing agent system. The highly stable CF bonds formed by the strongly electronegative fluorine atoms in diglycidyl tetrafluorophthalate endow the coating with excellent resistance to UV degradation and chemical corrosion, improving its weather resistance. The multifunctional properties of triglycidyl pyromellitic acid significantly enhance the coating's hardness and abrasion resistance through high-density crosslinking. Through the synergistic effect of the two curing agents, polyester coatings can maintain structural integrity and strong adhesion even in extreme outdoor environments, achieving a dual breakthrough in both weather resistance and mechanical properties. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to this invention. The preferred embodiments and materials described herein are for illustrative purposes only and do not limit the scope of this application.

[0024] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0025] In view of the deficiencies in the prior art mentioned in the background, the first aspect of the present invention provides a polyester powder coating, comprising the following components: polyester resin, fluorinated glycidyl ester curing agent, filler and additives; wherein the fluorinated glycidyl ester curing agent comprises diglycidyl tetrafluorophthalate and triglycidyl pyromellitic acid.

[0026] In the composition, polyester resin is the base resin of powder coating and is the main skeleton of the coating; fillers (such as calcium carbonate and barium sulfate) mainly increase the hardness and wear resistance of the coating; additives contain a variety of functional additives, which are used in small amounts and can improve the workability and leveling performance of the coating; fluorinated glycidyl ester curing agent is the key component for the chemical cross-linking reaction of powder coating.

[0027] In fluorinated glycidyl ester curing agents, diglycidyl tetrafluorophthalate contains highly electronegative fluorine in its molecular structure. Fluorine atoms have a small atomic radius but the highest electronegativity, enabling the formation of very strong and stable CF bonds. The high bond energy of the CF bonds makes them difficult to cleave under ultraviolet light, resulting in excellent resistance to UV degradation and chemical stability. Therefore, the introduction of diglycidyl tetrafluorophthalate significantly improves the overall coating's resistance to environmental factors such as photo-oxidation, salt spray, acid rain, and atmospheric pollutants, effectively preventing chalking, loss of gloss, discoloration, cracking, and blistering, thus significantly extending the coating's weather resistance. Triglycidyl pyromellitic acid contains three epoxy groups in its molecular structure, exhibiting high functionality. Theoretically, one molecule of triglycidyl pyromellitic acid can react with up to three carboxyl groups on the polyester chain during crosslinking reactions. This multifunctional characteristic allows it to act as a crosslinking node in the crosslinking network, effectively increasing the overall crosslinking density of the coating and enhancing its hardness and abrasion resistance.

[0028] In summary, this invention significantly improves the overall performance of polyester powder coatings by using a compounded fluorinated glycidyl ester curing agent system. The highly stable CF bonds formed by the strongly electronegative fluorine atoms in diglycidyl tetrafluorophthalate endow the coating with excellent resistance to UV degradation and chemical corrosion, improving its weather resistance. The multifunctional properties of triglycidyl pyromellitic acid significantly enhance the coating's hardness and abrasion resistance through high-density crosslinking. Through the synergistic effect of the two curing agents, polyester coatings can maintain structural integrity and strong adhesion even in extreme outdoor environments, achieving a dual breakthrough in both weather resistance and mechanical properties.

[0029] In some embodiments, the mass ratio of the polyester resin to the fluorinated glycidyl ester curing agent is 20:(2-5). Since the carboxyl groups of the polyester resin need to undergo a ring-opening esterification reaction with the epoxy groups in the fluorinated glycidyl ester curing agent, setting the mass ratio of the polyester resin to the fluorinated glycidyl ester curing agent to 20:(2-5) ensures that all the carboxyl groups of the polyester resin react fully. At the same time, it avoids excessive epoxy groups leading to excessively high crosslinking density, which would cause the coating to become brittle and reduce its impact resistance.

[0030] In some embodiments, the mass ratio of diglycidyl tetrafluorophthalate to diglycidyl terephthalate in the fluorinated glycidyl ester curing agent is 1:(3-5). Since diglycidyl tetrafluorophthalate is the source of weather resistance and self-cleaning properties, its strong CF bonds need to reach the surface enrichment threshold; however, excessive amounts can lead to coating embrittlement due to molecular rigidity and are too costly. Diglycidyl terephthalate is the main crosslinking backbone, and its epoxy groups are key to building a dense network and maintaining the hardness of the polyester coating. Therefore, the mass ratio of diglycidyl tetrafluorophthalate to diglycidyl terephthalate needs to be set to 1:(3-5).

[0031] In some embodiments, the mass ratio of polyester resin to filler is 50:(1-3), and the filler includes barium sulfate and calcium carbonate, wherein the mass ratio of barium sulfate to calcium carbonate in the filler is 1:(0.8-1.2). Excessive filler can disrupt the continuous enrichment layer of fluorine monomers on the coating surface, leading to a decrease in the weather resistance of the polyester coating. However, insufficient filler can result in excessively low hardness of the polyester coating. Therefore, the mass ratio of polyester resin to filler needs to be set to 50:(1-3). Among the fillers, barium sulfate can enhance density and improve the hardness of the cured coating, while the lamellar structure of calcium carbonate can enhance the wear resistance of the cured coating. Therefore, the combination of barium sulfate and calcium carbonate can achieve both hardness and wear resistance.

[0032] In some embodiments, the mass ratio of the polyester resin to the additives is 100:(0.5-2), and the additives include leveling agents, degassing agents, and antioxidants. The leveling agent promotes uniform flow of the molten powder before curing, forming a smooth and flat surface; the degassing agent helps eliminate volatiles or small molecule byproducts (such as CO2) generated during coating curing, preventing defects such as pinholes and fisheyes; the antioxidant prevents photo-oxidation chain reactions of the coating molecular chains, preventing oxidative deterioration of the coating.

[0033] A second aspect of this invention provides a method for preparing a polyester powder coating, comprising the following steps:

[0034] Premix polyester resin, fluorinated glycidyl ester curing agent, filler, and additives;

[0035] The mixture is melt-blended using a twin-screw extruder at an extrusion temperature of 100-120℃.

[0036] After being compressed and cooled, the powder is crushed and passed through a 200-mesh sieve to obtain polyester powder coating.

[0037] The extrusion temperature of 100-120℃ can melt the polyester coating while avoiding excessive temperature that could cause the curing agent to pre-react; passing through a 200-mesh sieve can remove coarse powder >74μm, avoiding poor leveling properties of the coating due to excessively large particles.

[0038] In some embodiments, the twin-screw extruder has a screw speed of 300-500 rpm and a vacuum degree of ≥-0.09 MPa. The high screw speed of 300-500 rpm promotes full dispersion of the polyester coating and prevents localized fluorine accumulation in the coating; the vacuum degree of ≥-0.09 MPa facilitates rapid gas escape, avoiding the retention of a large number of residual bubbles.

[0039] In some embodiments, the method for preparing the tetrafluorophthalic acid diglycidyl ester in the fluorinated glycidyl ester curing agent includes:

[0040] Tetrafluorophthalic acid and epichlorohydrin were mixed, a catalyst was added, and the mixture was heated to 85-95℃ and reacted for 2-4 hours. Then the temperature was lowered to 35-45℃, NaOH solution was added dropwise, and the mixture was kept at this temperature for 4-6 hours to obtain diglycidyl tetrafluorophthalate.

[0041] Among them, high-temperature esterification at 85-95℃ enhances molecular kinetic energy, overcomes the steric hindrance effect of the tetrafluorobenzene ring, improves the esterification rate, and ensures high reactivity of the product; low-temperature alkali dropping at 35-45℃ can avoid the risk of hydrolysis of epichlorohydrin under alkaline conditions and improve the ring-closing rate of the reaction.

[0042] In some embodiments, the mass ratio of tetrafluorophthalic acid to epichlorohydrin is 1:(0.8-1). Excessive addition of epichlorohydrin can trigger ring-opening self-polymerization of the epoxy resin during the high-temperature esterification stage, forming a dimer. Insufficient addition of epichlorohydrin will prevent the esterification reaction from proceeding sufficiently. Therefore, the mass ratio of tetrafluorophthalic acid to epichlorohydrin is set to 1:(0.8-1).

[0043] In some embodiments, the catalyst is benzyltriethylammonium chloride, and the amount of catalyst added is 3%-6% of the mass of tetrafluorophthalic acid. If the amount of catalyst added is too small, the reaction time will be too long, and the unreacted tetrafluoroic acid residue will result in an excessively high acid value in the final product; if the amount of catalyst added is too large, the enrichment of quaternary ammonium salt cations will trigger side reactions. Therefore, the amount of catalyst added is set to 3%-6% of the mass of tetrafluorophthalic acid.

[0044] The present invention will be further described below by way of specific embodiments.

[0045] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods already existing in the art; unless otherwise specified, the experimental materials used in the following embodiments are all purchased from commercial channels.

[0046] Example 1:

[0047] Tetrafluorophthalic acid and epichlorohydrin were mixed at a mass ratio of 1:0.8, and 3% (by mass) of benzyltriethylammonium chloride catalyst was added. The mixture was heated to 85°C and reacted for 2 hours. Then the temperature was lowered to 35°C, and NaOH solution was added dropwise. The mixture was kept at this temperature for 4 hours to obtain diglycidyl tetrafluorophthalic acid.

[0048] A fluorinated glycidyl ester curing agent is obtained by compounding diglycidyl tetrafluorophthalate and triglycidyl pyromellitic acid in a mass ratio of 1:3.

[0049] By weight, 100 parts polyester resin, 10 parts fluorinated glycidyl ester curing agent, 2 parts filler, and 0.5 parts additives are premixed.

[0050] The material is melt-blended using a twin-screw extruder at an extrusion temperature of 100℃, a rotation speed of 300rpm, and a vacuum degree of ≥-0.09MPa.

[0051] After being compressed and cooled, the powder is crushed and passed through a 200-mesh sieve to obtain polyester powder coating.

[0052] Example 2:

[0053] Tetrafluorophthalic acid and epichlorohydrin were mixed in a mass ratio of 1:1, and then 6% (by mass) of benzyltriethylammonium chloride catalyst was added. The mixture was heated to 95°C and reacted for 4 hours. Then the temperature was lowered to 45°C, and NaOH solution was added dropwise. The mixture was kept at this temperature for 6 hours to obtain diglycidyl tetrafluorophthalic acid.

[0054] A fluorinated glycidyl ester curing agent is obtained by compounding diglycidyl tetrafluorophthalate and triglycidyl pyromellitic acid in a mass ratio of 1:5.

[0055] By weight, 100 parts polyester resin, 25 parts fluorinated glycidyl ester curing agent, 6 parts filler, and 2 parts additives are premixed.

[0056] The material is melt-blended using a twin-screw extruder at an extrusion temperature of 120℃, a rotation speed of 500rpm, and a vacuum degree of ≥-0.09MPa.

[0057] After being compressed and cooled, the powder is crushed and passed through a 200-mesh sieve to obtain polyester powder coating.

[0058] Example 3:

[0059] Consistent with Example 1, except that the amount of fluorinated glycidyl ester curing agent added to the polyester powder coating is 15 parts.

[0060] Example 4:

[0061] Consistent with Example 1, except that the amount of fluorinated glycidyl ester curing agent added to the polyester powder coating is 20 parts.

[0062] Example 5:

[0063] Consistent with Example 1, except that in the fluorinated glycidyl ester curing agent, the mass ratio of diglycidyl tetrafluorophthalate and triglycidyl pyromellitic acid is 1:4.

[0064] Comparative Example 1:

[0065] Consistent with Example 1, except that diglycidyl tetrafluorophthalate is used instead of fluorinated glycidyl ester curing agent.

[0066] Comparative Example 2:

[0067] Consistent with Example 1, except that triglycidyl pyromellitic acid is used instead of fluorinated glycidyl ester curing agent.

[0068] Tests were conducted on Examples 1-5 and Comparative Examples 1 and 2. The specific test contents are as follows:

[0069] Polyester powder coating was sprayed onto the sample plate and cured at 200℃ for 10 minutes to obtain the coating test plate.

[0070] Hardness test: A standard pencil lead of known hardness is used to scratch a flat coating film under a certain load. After the test, the hardness grade of the test pencil is used as the result according to the degree of damage to the coating film (indentation, scratch, abrasion).

[0071] Weather resistance: The coating was tested using a deuterium lamp artificial accelerated climate tester, with 8 hours of drying, 0.25 hours of water spraying, and 3.75 hours of condensation. It was also subjected to 500 hours of ultraviolet aging, in accordance with the national standard GB / T14522-2008 "Artificial Climate Aging Test Method for Plastics, Coatings and Rubber Materials for Mechanical Industry Products".

[0072] Impact resistance test: A heavy hammer (8mm diameter, 1kg) is dropped freely from a certain height to impact the coating test panel, causing the panel to deform rapidly between the instrument's punch and concave die. The impact strength is then recorded, and the measurement is performed according to the national standard GB / T1732-93 "Test Method for Impact Resistance of Coatings".

[0073] The test results are shown in Table 1.

[0074]

[0075] Referring to the hardness test results in Table 1, the hardness of Examples 1-5 is 3H, which is a significant improvement compared to Comparative Examples 1-3. The hardness of Comparative Example 1 is significantly lower, indicating that the addition of triglycidyl pyromellitic acid can improve the hardness of polyester resin coatings.

[0076] Referring to the weather resistance test results in Table 1, the gloss retention rate (60°) of Comparative Example 2 decreased significantly, indicating that the use of diglycidyl tetrafluorophthalate can improve the weather resistance of polyester coatings.

[0077] Referring to the impact resistance test results in Table 1, the impact resistance of Comparative Example 1 decreased significantly, indicating that the addition of triglycidyl pyromellitic acid can improve the impact resistance of polyester resin coatings.

[0078] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0079] The above embodiments are only used to illustrate 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 preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the protection scope of the present invention.

Claims

1. A polyester powder coating, characterized in that, The product comprises the following components: polyester resin, fluorinated glycidyl ester curing agent, filler, and additives; the fluorinated glycidyl ester curing agent includes diglycidyl tetrafluorophthalate and triglycidyl pyromellitic acid; the mass ratio of the polyester resin to the fluorinated glycidyl ester curing agent is 20:(2-5); and the mass ratio of diglycidyl tetrafluorophthalate to triglycidyl pyromellitic acid in the fluorinated glycidyl ester curing agent is 1:(3-5).

2. The polyester powder coating according to claim 1, characterized in that, The mass ratio of the polyester resin to the filler is 50:(1-3), and the filler includes barium sulfate and calcium carbonate, wherein the mass ratio of barium sulfate to calcium carbonate in the filler is 1:(0.8-1.2).

3. The polyester powder coating according to claim 1, characterized in that, The mass ratio of the polyester resin to the additives is 100:(0.5-2), and the additives include leveling agents, degassing agents, and antioxidants.

4. A method for preparing a polyester powder coating according to any one of claims 1-3, characterized in that, Includes the following steps: Premix polyester resin, fluorinated glycidyl ester curing agent, filler, and additives; The mixture is melt-blended using a twin-screw extruder at an extrusion temperature of 100-120℃. After being compressed and cooled, the powder is crushed and passed through a 200-mesh sieve to obtain polyester powder coating.

5. The method for preparing polyester powder coating according to claim 4, characterized in that, The twin-screw extruder has a screw speed of 300-500 rpm and a vacuum degree of ≥-0.09 MPa.

6. The method for preparing polyester powder coating according to claim 4, characterized in that, The method for preparing the tetrafluorophthalic acid diglycidyl ester in the fluorinated glycidyl ester curing agent includes: Tetrafluorophthalic acid and epichlorohydrin were mixed, a catalyst was added, and the mixture was heated to 85-95℃ and reacted for 2-4 hours. Then the temperature was lowered to 35-45℃, NaOH solution was added dropwise, and the mixture was kept at this temperature for 4-6 hours to obtain diglycidyl tetrafluorophthalate.

7. The method for preparing polyester powder coating according to claim 6, characterized in that, The mass ratio of tetrafluorophthalic acid to epichlorohydrin is 1:(0.8-1).

8. The method for preparing polyester powder coating according to claim 6, characterized in that, The catalyst is benzyltriethylammonium chloride, and the amount of catalyst added is 3%-6% of the mass of tetrafluorophthalic acid.

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