Epoxy resin for halogen-free flame-retardant self-leveling powder coating and preparation method thereof

Abstract

The invention provides epoxy resin for halogen-free flame-retardant self-leveling powder coating and a preparation method of the epoxy resin, and belongs to the technical field of powder coating. The flame retardant is mainly prepared from anhydrous piperazine, bisphenol A diglycidyl ether, trihydroxymethyl phosphorus oxide, triethyl phosphite, epoxy chloropropane, sodium hydroxide, N-methyl iminodiacetic acid, ethylene glycol diglycidyl ether and other main raw materials through polymerization. The prepared epoxy resin and 2-phenylimidazoline are subjected to low-temperature curing (135 DEG C / 20 min) on the premise that an additional flatting agent does not need to be used, the flexibility of a coating film is good, the impact resistance grade is high, the impact performance reaches the condition that no cracking phenomenon exists in the front and back 60cm, the leveling grade reaches the grade 7 or above, the gloss is high and reaches 95% or above, the oxygen index reaches 34% or above, and the halogen-free flame retardant performance is excellent.

Description

Technical Field

[0001] This invention belongs to the field of powder coating technology, specifically relating to a halogen-free flame-retardant, self-leveling epoxy resin for powder coating and its preparation method. Background Technology

[0002] Powder coatings offer advantages such as recyclability, energy saving, and zero VOC emissions, making them widely used in everyday industrial coating applications. Epoxy resin powder coatings are primarily used for indoor coatings. With increasingly stringent environmental and flame-retardant requirements, there's a gradual shift from halogen-based flame retardants to halogen-free flame retardants. Currently, indoor coatings require good halogen-free flame-retardant properties. Simultaneously, indoor furniture coatings, to enhance aesthetics and decorative properties as well as impact resistance, require coatings with excellent leveling and impact resistance.

[0003] Currently, the industry mainly uses external small-molecule polyacrylate leveling agents to improve the leveling grade of coatings through compounding. Polyacrylate substances themselves do not have flame retardant properties, and their migration to the coating surface will reduce the flame retardant properties of the coating surface. Moreover, since leveling agents are external substances, their compatibility with epoxy resins is generally poor, and epoxy resins themselves have insufficient lubrication and leveling ability. Relying solely on external leveling agents, especially under the condition of low-temperature curing at 135℃, it is difficult to achieve a leveling grade of 6 or higher. Furthermore, the impact resistance of the coating can generally only reach 50cm, making it difficult to achieve higher impact resistance.

[0004] The industry has also conducted relevant research on the above-mentioned problems. For example, CN202110859213.X introduces methacrylate to improve the lubricity of chain segments. Although it achieves a high leveling grade for 50 / 50 mixed powder coatings, it requires a large amount of 50 / 50 polyester resin for compounding, resulting in a low proportion of epoxy resin in the powder coating formulation, and it does not have flame retardant properties. Moreover, it requires a large amount of hydrogen peroxide for oxidation preparation, which is costly and generates a large amount of wastewater. CN202011219253.X achieves halogen-free flame retardancy in powder coatings, but its high functionality leads to low gloss and leveling grades of the coating film, and it is difficult to achieve a high impact resistance of 60cm. Summary of the Invention

[0005] One of the objectives of this invention is to provide a halogen-free flame-retardant, self-leveling epoxy resin for powder coatings, which is mainly polymerized from anhydrous piperazine, bisphenol A diglycidyl ether, trimethylolphosphine oxide, triethyl phosphite, epichlorohydrin, sodium hydroxide, N-methyliminodiacetic acid, ethylene glycol diglycidyl ether, and other main raw materials.

[0006] The second objective of this invention is to provide a method for preparing the epoxy resin for halogen-free flame retardant and self-leveling powder coatings.

[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 halogen-free flame-retardant, self-leveling epoxy resin for powder coatings, wherein the halogen-free flame-retardant, self-leveling epoxy resin comprises the following raw materials in molar amounts: 8-11 parts of trimethylolphosphine oxide; 9-12 parts of triethyl phosphite; 28-35 parts of epichlorohydrin; 16-22 parts sodium hydroxide; 20-26 parts of anhydrous piperazine; 5-8 parts of N-methyliminodiacetic acid; 12-16 parts of bisphenol A diglycidyl ether; 6-8 parts of ethylene glycol diglycidyl ether; The raw materials also include catalyst A, catalyst B, and phase transfer catalyst; Catalyst A is sodium methoxide, and its dosage is 0.03-0.05% of the mass of trimethylolphosphine oxide. Catalyst B is a boron trifluoride diethyl ether solution, used in an amount of 0.5-0.8% of the mass of trimethylolphosphine oxide; The phase transfer catalyst is triphenylmethylphosphorus chloride, and the amount used is 0.1-0.2% of the mass of trihydroxymethylphosphorus oxide.

[0008] Typical, but not limiting, molar amounts of trimethylolphosphine oxide are, for example, 8, 9, 10, or 11 parts. Typical, but not limiting, molar amounts of triethyl phosphite are, for example, 9, 10, 11, or 12 parts. Typical, but not limiting, molar amounts of epichlorohydrin are, for example, 28, 29, 30, 31, 32, 33, 34, or 35 parts. Typical, but not limiting, molar amounts of sodium hydroxide are, for example, 16, 17, 18, 19, 20, 21, or 22 parts. Typical, but not limiting, molar fractions of anhydrous piperazine are, for example, 20, 21, 22, 23, 24, 25, or 26 parts. Typical, but not limiting, molar amounts of N-methyliminodiacetic acid are, for example, 5, 6, 7, or 8 parts; Typical, but not limiting, molar amounts of bisphenol A diglycidyl ether are, for example, 12, 13, 14, 15, or 16 parts. Typical, but not limiting, molar amounts of ethylene glycol diglycidyl ether are, for example, 6, 7, or 8 parts.

[0009] Secondly, the present invention provides a method for preparing the above-mentioned halogen-free flame-retardant, self-leveling epoxy resin for powder coatings, comprising the following steps: A. Add the prescribed amounts of tris(hydroxymethyl)phosphine oxide, triethyl phosphite, and catalyst A to the synthesis reactor A, stir until homogeneous, and carry out the transesterification reaction. At the same time, collect the byproduct ethanol produced by the reaction. B. When the conversion rate of triethyl phosphite reaches 98% or more, intermediate 1 after transesterification of triethyl phosphite is obtained. The reaction temperature is lowered, and then the prescribed amount of epichlorohydrin, catalyst B and phase transfer catalyst are added to carry out the ring-opening reaction. C. When the conversion rate of intermediate 1 is greater than 95%, cool down and add sodium hydroxide in three equal portions (each addition is 1 / 3 of the formula amount). After all the sodium hydroxide has been added, continue to keep the temperature to achieve full ring closure. D. When no obvious byproduct sodium chloride is generated (i.e., the increase in the mass of newly generated sodium chloride within 10 minutes is less than 1% of the mass of sodium chloride already generated), the mixture is cooled to room temperature. The filtrate after filtration of the reaction mixture is pumped to polymerization reactor B. The temperature is raised, and the vacuum system is started to remove excess epichlorohydrin by vacuum distillation. When the volatile content is less than 2%, intermediate 2 of glycidyl etherification is obtained. At this time, the formulated amount of bisphenol A diglycidyl ether and anhydrous piperazine are added to the reactor. After thorough stirring, the temperature is gradually raised to carry out the chain extension polymerization reaction. E. When the conversion rate of piperazine reaches 65-70%, add the prescribed amount of N-methyliminodiacetic acid to participate in the copolymerization chain extension reaction to adjust the flexibility of epoxy resin segments. F. When the epoxy equivalent of the polymer reaches 3000-3200 g / mol, add the prescribed amount of ethylene glycol diglycidyl ether to carry out the end-capping reaction. G. When the acid value of the polymer is lower than 1 mg KOH / g, stop the reaction, cool down, add 10-15% of the polymer mass of boiling water into the reactor for stirring and washing to remove residual sodium chloride, catalyst and impurities. Stir thoroughly and separate the aqueous phase. H. Heat the washed polymer and simultaneously start the high vacuum system to depressurize and remove volatiles. When the volatile content is less than 1%, discharge the material while it is still hot and at high temperature. After cooling by a steel belt with cooling water, crush it to obtain epoxy resin product.

[0010] In some embodiments, the transesterification reaction temperature in step A is 100-105°C.

[0011] In some implementations, in step B, the ring-opening reaction temperature is 80-85°C and the time is 2-3 hours.

[0012] In some implementations, in step C, the temperature is lowered to 35-40°C; the interval between each step is 20-30 minutes. In some embodiments, in step D, the temperature is raised to 90-95°C; the vacuum degree is maintained at -0.092 to -0.095 MPa; and the temperature of the chain extension polymerization reaction is 110-115°C. In some embodiments, in step E, the polymerization temperature is increased to 118-123°C.

[0013] In some implementations, in step G, the temperature is lowered to 100-105°C; and the mixture is stirred thoroughly for 20-30 minutes.

[0014] In some implementations, in step H, the temperature is raised to 135-140°C; the vacuum degree is controlled between -0.098 MPa and -0.099 MPa.

[0015] In one specific embodiment, the preparation method of epoxy resin for halogen-free flame retardant and self-leveling powder coating includes the following steps: A. Add the prescribed amounts of trimethylolphosphine oxide, triethyl phosphite, and catalyst A to the synthesis reactor A. After stirring evenly, heat the mixture to 100-105℃ and maintain the temperature to carry out the transesterification reaction. At the same time, collect the byproduct ethanol produced by the reaction. B. Sampling and gas chromatography detection: When the conversion rate of triethyl phosphite reaches 98% or more, it indicates that the transesterification reaction is basically completed and intermediate 1 after transesterification of triethyl phosphite is obtained. At this time, the reaction temperature is reduced to 80-85℃, and then the formula amount of epichlorohydrin, catalyst B and phase transfer catalyst are added, and the ring-opening reaction is carried out at the temperature for 2-3 hours. C. Take samples and use liquid chromatography to detect the content of intermediate 1. When the conversion rate of intermediate 1 is greater than 95%, it indicates that the ring-opening reaction is basically completed. Cool down to 35-40℃ and add sodium hydroxide in three equal portions, each time adding 1 / 3 of the formula amount, with an interval of 20-30 minutes between each addition. After all the sodium hydroxide has been added, continue to keep the reaction at 35-40℃ to achieve complete ring closure. D. When no obvious byproduct sodium chloride is generated, it indicates that the ring-closing reaction is basically complete. At this time, the temperature is lowered to room temperature, and the reaction mixture is filtered to remove the solid byproduct sodium chloride in the system. The obtained filtrate is pumped to polymerization reactor B. When the temperature is raised to 90-95℃, the vacuum system is started to remove excess epichlorohydrin by vacuum distillation. The vacuum degree is maintained at -0.092 to -0.095 MPa. When the volatile content is less than 2%, it indicates that epichlorohydrin has been basically removed, and glycidyl etherified intermediate 2 is obtained. At this time, the formulated amount of bisphenol A diglycidyl ether and anhydrous piperazine are added to the reactor. After being stirred evenly, the temperature is gradually raised to 110-115℃ to carry out chain extension polymerization reaction. E. The content of anhydrous piperazine was detected by gas chromatography. When the conversion rate of piperazine reached 65-70%, the amount of N-methyliminodiacetic acid in the formulation was added to participate in the copolymerization chain extension reaction to adjust the flexibility of the epoxy resin chain segments. The polymerization reaction temperature was increased to 118-123℃. F. Take samples to test the epoxy equivalent of the polymer. When the epoxy equivalent of the polymer reaches 3000-3200 g / mol, it indicates that the epoxy monomer raw material in the reactor has basically reacted completely. At this time, add the formula amount of ethylene glycol diglycidyl ether for end-capping reaction. G. Take a sample to test the acid value of the polymer. When the acid value of the polymer is lower than 1 mg KOH / g, it indicates that the end-capping reaction has been completed. At this time, stop the reaction, cool down to 100-105℃, add 10-15% of the polymer mass of boiling water into the reactor and stir and wash to remove residual sodium chloride, catalyst and impurities. After stirring thoroughly for 20-30 minutes, separate the aqueous phase. H. Heat the washed polymer to 135-140℃, and simultaneously start the high vacuum system to remove volatiles by depressurization. The vacuum degree is controlled between -0.098Mpa and -0.099Mpa. When the volatile content is less than 1%, discharge the material while it is still hot and at high temperature. After cooling by a steel belt with cooling water, crush it to obtain epoxy resin product.

[0016] The resulting epoxy resin is a pale yellow transparent resin particle with an epoxy equivalent of 705-750 g / mol and a softening point of 78-85℃.

[0017] The molecular structure of intermediate 1 after transesterification of triethyl phosphite is as follows: ; The molecular structure of intermediate 2, which is a glycidyl etherified compound, is as follows: .

[0018] Beneficial effects: This invention primarily uses anhydrous piperazine, bisphenol A diglycidyl ether, trimethylolphosphine oxide, triethyl phosphite, epichlorohydrin, sodium hydroxide, N-methyliminodiacetic acid, and ethylene glycol diglycidyl ether as main raw materials for polymerization. The final epoxy resin segments are polymerized using a segmental polymerization method to adjust the flexibility and water resistance of the epoxy resin segments. Furthermore, both components have a high nitrogen content, providing halogen-free flame retardant elements for the epoxy resin product. The nitrogen content in the segments also enhances the adhesion between the coating and the metal substrate. Meanwhile, the phosphite intermediate formed by the transesterification of trimethylolphosphite and triethyl phosphite has excellent lubrication and leveling properties. The epoxy resin products prepared by the polymerization of the glycidyl ether segments formed therefrom not only have high content of flame-retardant elements such as phosphorus and nitrogen and good flame-retardant properties, but also have excellent lubrication and self-leveling properties. The epoxy resin end groups use highly active ethylene glycol diglycidyl ether to improve its high-temperature melt flowability and low-temperature curing ability. Without the use of external leveling agents, the coating film after low-temperature curing (135℃ / 20min) with 2-phenylimidazoline has good flexibility, high impact resistance, and no cracking phenomenon at 60cm on both sides. The leveling grade reaches level 7 or above, and the gloss is high, reaching over 95%. The oxygen index reaches over 34%, and the halogen-free flame retardant properties are excellent.

[0019] 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

[0020] 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.

[0021] Unless otherwise specified, the raw materials, reagents, and methods used in the embodiments are all conventional raw materials, reagents, and methods in the art.

[0022] The boron trifluoride diethyl ether solution was obtained from Nanjing Chemical Reagent Co., Ltd., and the boron trifluoride content was ≥47%. Determination of softening point: according to the method in GB / T 15332-1994 "Determination of softening point of hot melt adhesives - Ring and Ball Method"; Determination of epoxy equivalent: according to the method in GB / T 4612-2008 "Determination of epoxy equivalent in epoxide compounds for plastics"; Acid value determination: according to the method in HG / T2708 "Determination of Acid Value in Polyester Polyols".

[0023] The method for testing volatile matter is as follows: accurately weigh 10g of sample, place it in an oven, and weigh the sample again at 130℃ for 30min. The volatile matter is [(10-W) / 10]×100%.

[0024] Example 1 A halogen-free flame-retardant, self-leveling epoxy resin for powder coatings comprises the following raw materials in molar amounts: 10 parts of trimethylolphosphine oxide; 11 parts of triethyl phosphite; 30 parts of epichlorohydrin; 21 parts sodium hydroxide; 20 parts of anhydrous piperazine; 8 parts of N-methyliminodiacetic acid; 12 parts of bisphenol A diglycidyl ether; 8 parts of ethylene glycol diglycidyl ether; The raw materials also include catalyst A, catalyst B, and phase transfer catalyst; Catalyst A is sodium methoxide, and its dosage is 0.05% of the mass of trimethylolphosphine oxide. Catalyst B is a boron trifluoride diethyl ether solution, used in an amount of 0.6% of the mass of tris(hydroxymethyl)phosphine oxide; The phase transfer catalyst was triphenylmethylphosphorus chloride, and the amount used was 0.1% of the mass of trihydroxymethylphosphorus oxide.

[0025] The method for preparing the above-mentioned halogen-free flame-retardant, self-leveling epoxy resin for powder coatings includes the following steps: A. Add the prescribed amounts of tris(hydroxymethyl)phosphine oxide, triethyl phosphite, and catalyst A to the synthesis reactor A. After stirring evenly, heat the reactor to 100°C and maintain the temperature to carry out the transesterification reaction. At the same time, collect the byproduct ethanol produced by the reaction. B. Sampling and gas chromatography detection: when the conversion rate of triethyl phosphite reaches 98% or more, it indicates that the transesterification reaction is basically completed and intermediate 1 after transesterification of triethyl phosphite is obtained. At this time, the reaction temperature is reduced to 80℃, and then the formula amount of epichlorohydrin, catalyst B and phase transfer catalyst are added, and the ring-opening reaction is carried out at the temperature for 2 hours. C. Take samples and use liquid chromatography to detect the content of intermediate 1. When the conversion rate of intermediate 1 is greater than 95%, it indicates that the ring-opening reaction is basically completed. Cool down to 40℃ and add sodium hydroxide solid in three equal portions, each time adding 1 / 3 of the formula amount, with an interval of 30 minutes between each addition. After all the sodium hydroxide solid has been added, continue to keep the reaction at 40℃ to achieve complete ring closure. D. When no obvious byproduct sodium chloride is generated (i.e., the increase in the mass of newly generated sodium chloride within 10 minutes is less than 1% of the mass of sodium chloride already generated), it indicates that the closed-loop reaction is basically completed. At this time, the temperature is lowered to room temperature, and the reaction mixture is filtered to remove the solid byproduct sodium chloride in the system. The filtrate is pumped to polymerization reactor B, and the temperature is raised to 90°C. Then, the vacuum system is started to remove excess epichlorohydrin by vacuum distillation. The vacuum degree is maintained at -0.095 MPa. When the volatile content is less than 2%, it indicates that epichlorohydrin has been basically removed, and glycidyl etherified intermediate 2 is obtained. At this time, the formulated amount of bisphenol A diglycidyl ether and anhydrous piperazine are added to the reactor. After thorough stirring, the temperature is gradually raised to 110°C to carry out the chain extension polymerization reaction. E. The content of anhydrous piperazine was detected by gas chromatography. When the conversion rate of piperazine reached 65-70%, the amount of N-methyliminodiacetic acid in the formulation was added to participate in the copolymerization chain extension reaction to adjust the flexibility of the epoxy resin chain segments. The polymerization reaction temperature was increased to 120℃. F. Take samples to test the epoxy equivalent of the polymer. When the epoxy equivalent of the polymer reaches 3000-3200 g / mol, it indicates that the epoxy monomer raw material in the reactor has basically reacted completely. At this time, add the formula amount of ethylene glycol diglycidyl ether for end-capping reaction. G. Take a sample to test the acid value of the polymer. When the acid value of the polymer is lower than 1 mg KOH / g, it indicates that the end-capping reaction has been completed. At this time, stop the reaction, cool down to 100℃, add 10-15% of the polymer mass of boiling water into the reactor for stirring and washing to remove residual sodium chloride, catalyst and impurities. After stirring thoroughly for 30 minutes, separate the aqueous phase. H. Heat the washed polymer to 140°C and simultaneously start the high vacuum system to remove volatiles by depressurization. Control the vacuum degree at -0.099 MPa. When the volatile content is less than 1%, discharge the material while it is still hot and cool it with a steel belt with cooling water. Then crush it to obtain epoxy resin product.

[0026] The epoxy equivalent of the obtained epoxy resin is 735 g / mol, and the softening point is 79℃.

[0027] Example 2 A halogen-free flame-retardant, self-leveling epoxy resin for powder coatings comprises the following raw materials in molar amounts: 8 parts of trimethylolphosphine oxide; 9 parts of triethyl phosphite; 35 parts of epichlorohydrin; 17 parts sodium hydroxide; 25 parts of anhydrous piperazine; 6 parts of N-methyliminodiacetic acid; 14 parts of bisphenol A diglycidyl ether; 7 parts of ethylene glycol diglycidyl ether; The raw materials also include catalyst A, catalyst B, and phase transfer catalyst; Catalyst A is sodium methoxide, used at a rate of 0.03% of the mass of trimethylolphosphine oxide; Catalyst B is a boron trifluoride diethyl ether solution, used in an amount of 0.6% of the mass of tris(hydroxymethyl)phosphine oxide; The phase transfer catalyst was triphenylmethylphosphorus chloride, and the amount used was 0.2% of the mass of trihydroxymethylphosphorus oxide.

[0028] The preparation method is the same as in Example 1.

[0029] The resulting epoxy resin has an epoxy equivalent of 720 g / mol and a softening point of 82℃.

[0030] Example 3 A halogen-free flame-retardant, self-leveling epoxy resin for powder coatings comprises the following raw materials in molar amounts: 11 parts of trimethylolphosphine oxide; 12 parts of triethyl phosphite; 28 parts of epichlorohydrin; 22 parts sodium hydroxide; 24 portions of anhydrous piperazine; 7 parts of N-methyliminodiacetic acid; 16 parts of bisphenol A diglycidyl ether; 6 parts of ethylene glycol diglycidyl ether; The raw materials also include catalyst A, catalyst B, and phase transfer catalyst; Catalyst A is sodium methoxide, used at a rate of 0.04% of the mass of trimethylolphosphine oxide; Catalyst B is a boron trifluoride diethyl ether solution, used in an amount of 0.5% of the mass of tris(hydroxymethyl)phosphine oxide; The phase transfer catalyst was triphenylmethylphosphorus chloride, and the amount used was 0.15% of the mass of trihydroxymethylphosphorus oxide.

[0031] The preparation method is the same as in Example 1.

[0032] The epoxy equivalent of the obtained epoxy resin is 742 g / mol, and the softening point is 81℃.

[0033] Example 4 A halogen-free flame-retardant, self-leveling epoxy resin for powder coatings comprises the following raw materials in molar amounts: Nine parts of trimethylolphosphine oxide; 9 parts of triethyl phosphite; 32 parts of epichlorohydrin; 19 parts sodium hydroxide; 26 portions of anhydrous piperazine; 5 parts of N-methyliminodiacetic acid; 15 parts of bisphenol A diglycidyl ether; 7 parts of ethylene glycol diglycidyl ether; The raw materials also include catalyst A, catalyst B, and phase transfer catalyst; Catalyst A is sodium methoxide, used at a rate of 0.04% of the mass of trimethylolphosphine oxide; Catalyst B is a boron trifluoride diethyl ether solution, used in an amount of 0.7% of the mass of tris(hydroxymethyl)phosphine oxide. The phase transfer catalyst was triphenylmethylphosphorus chloride, and the amount used was 0.15% of the mass of trihydroxymethylphosphorus oxide.

[0034] The preparation method is the same as in Example 1.

[0035] The epoxy equivalent of the obtained epoxy resin is 711 g / mol, and the softening point is 84℃.

[0036] Comparative Example 1 The rest is the same as in Example 1, except that anhydrous piperazine is replaced with an equimolar amount of bisphenol A.

[0037] Comparative Example 2 The rest is the same as in Example 1, except that trimethylolphosphine oxide is replaced with an equimolar amount of glycerol.

[0038] Comparative Example 3 The product of Example 1 in CN202110859213.X was used as Comparative Example 3.

[0039] Comparative Example 4 The product of Example 1 in CN202011219253.X was used as Comparative Example 4.

[0040] Performance testing Epoxy resin powder coatings comprise the following components in parts by weight: 560 parts epoxy resin, 40 parts 2-phenylimidazoline, 110 parts titanium dioxide, 60 parts barium sulfate, and 6 parts gloss enhancer were used. 2-phenylimidazoline was used as a curing agent, model WK31, and the gloss enhancer was model WK701. Both were purchased from Ningbo Weikai Chemical Co., Ltd.

[0041] The epoxy resins from Examples 1-4 and Comparative Examples 1-4 were mixed in a mixer according to the formulations of the epoxy resin powder coatings described above. Then, they were melt-extruded at high temperature using a twin-screw extruder (screw temperature controlled at 100-105℃), followed by tableting, cooling, crushing, grinding, and sieving to produce a powder coating (160 mesh). The powder coating was then sprayed onto a surface-treated tinplate substrate using an electrostatic spray gun and cured at a low temperature of 135℃ for 20 minutes to obtain a coating with a film thickness of 80 μm.

[0042] The epoxy resin powder coatings prepared in Examples 1-4 and Comparative Examples 1-4 were subjected to performance tests. The test standards are as follows: Coating index testing was conducted in accordance with GB / T 21776-2008 "Guidelines for Testing Powder Coatings and Their Coatings"; Flame retardant performance testing of epoxy resin products was conducted according to GB / T2406.2-2009 "Determination of Combustion Behavior by Oxygen Index Method for Plastics", using Type I specimens and Method B-Diffusion Ignition Method 8.2.3; The leveling rating is tested according to the PCI leveling rating, from 1 to 10. The higher the number, the better the leveling.

[0043] The performance test results are shown in Table 1.

[0044] Table 1. Coating properties of powder coatings prepared from the products of Examples 1-4 and Comparative Examples 1-4

[0045] As can be seen from the test results in Table 1, the powder coating prepared by mixing the epoxy resin and 2-phenylimidazoline curing agent produced by this invention has a smooth and even coating film after low-temperature curing (135℃ / 20min) with a gloss of over 96%. Moreover, in terms of impact resistance (60cm), it passes both positive and negative impact tests, demonstrating high impact resistance. Furthermore, the leveling grade reaches level 7 or above, and the oxygen index of the epoxy resin reaches over 35%, exhibiting excellent halogen-free flame retardant properties. The coating film shows no change after boiling in water for 2 hours, demonstrating superior overall performance.

[0046] In Comparative Example 1, replacing anhydrous piperazine with an equimolar amount of bisphenol A resulted in a significant increase in chain segment hardness, a decrease in nitrogen content in the epoxy resin, and a significant reduction in the final coating gloss, leveling grade, and oxygen index.

[0047] In Comparative Example 2, replacing trimethylolphosphine oxide with an equimolar amount of glycerol resulted in a decrease in phosphorus content in the epoxy resin chain segments, ultimately leading to a slight decrease in coating gloss and a significant decrease in the oxygen index.

[0048] In Comparative Example 3, the coating film prepared from the product of Example 1 in CN202110859213.X and 2-phenylimidazoline, under curing conditions of 135℃ / 20min, passed through a 60cm high impact test with a forward impact but cracked significantly with a reverse impact. At the same time, the leveling grade also decreased, and the oxygen index was only 24.4%. After boiling in water for 2 hours, the coating film showed slight blistering, indicating obvious defects in overall performance.

[0049] The coating prepared from the product of Example 1 in CN202011219253.X in Comparative Example 4 and 2-phenylimidazoline has significant deficiencies in terms of high impact resistance (60cm), coating gloss, leveling grade, and boiling water resistance.

[0050] 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 halogen-free flame-retardant, self-leveling epoxy resin for powder coating, characterized in that, The halogen-free flame-retardant, self-leveling powder coating epoxy resin comprises the following raw materials by mole fraction: Trimethylol phosphate 8-11 parts; Triethyl phosphite 9-12 parts; Epichlorohydrin 28-35 parts; Sodium hydroxide 16-22 parts; Anhydrous piperazine 20-26 parts; N-methyl iminodiacetic acid 5-8 parts; Bisphenol A diglycidyl ether 12-16 parts; Ethylene glycol diglycidyl ether 6-8 parts; The raw materials further comprise catalyst A, catalyst B and a phase transfer catalyst; Catalyst A is sodium methoxide, and the amount is 0.03-0.05% of the mass of trimethylol phosphate; Catalyst B is boron trifluoride ether solution, and the amount is 0.5-0.8% of the mass of trimethylol phosphate; The phase transfer catalyst is triphenylmethyl phosphonium chloride, and the amount is 0.1-0.2% of the mass of trimethylol phosphate.

2. The halogen-free, flame-retardant, epoxy resin for a self-leveling powder paint according to claim 1, characterized by, The content of boron trifluoride in the boron trifluoride ether solution is 47-47.8%.

3. A process for the preparation of a halogen-free flame-retardant, self-levelling epoxy resin for powder coatings according to claim 1 or 2, characterized in that, The steps comprise: A. The formula amount of trimethylol phosphate, triethyl phosphite and catalyst A are added to a synthesis reaction kettle A, stirred uniformly, then ester exchange reaction is carried out, and the by-product ethanol generated in the reaction is collected; B. When the conversion rate of triethyl phosphite reaches more than 98%, the intermediate 1 after ester exchange of triethyl phosphite is obtained, the reaction temperature is lowered, then the formula amount of epichlorohydrin, catalyst B and a phase transfer catalyst are added, and ring-opening reaction is carried out; C. When the conversion rate of the intermediate 1 is more than 95%, the temperature is lowered, the formula amount of sodium hydroxide is added uniformly in three times (the amount of each time is 1 / 3 of the formula amount), after the addition is completed, the reaction is continuously kept warm to realize complete ring closure; D. When no obvious by-product sodium chloride is generated, the reaction mixture is filtered, the filtrate is pumped into a polymerization reaction kettle B, the temperature is raised, the vacuum system is started to remove the excess epichlorohydrin by reduced pressure distillation, when the volatile content is less than 2%, the glycidyl etherized intermediate 2 is obtained, at this time, the formula amount of bisphenol A diglycidyl ether and anhydrous piperazine is added to the reaction kettle, stirred uniformly, then the temperature is gradually raised to carry out chain extension polymerization reaction; E. When the conversion rate of piperazine reaches 65-70%, the formula amount of N-methyl iminodiacetic acid is added to participate in copolymerization chain extension reaction to adjust the flexibility of the epoxy resin segment; F. When the epoxy equivalent weight of the polymer reaches 3000-3200 g / mol, the formula amount of ethylene glycol diglycidyl ether is added to carry out end-capping reaction; G. When the acid value of the polymer is less than 1 mgKOH / g, the reaction is stopped, the temperature is lowered, and 10-15% of boiling water of the mass of the polymer is added to the kettle to stir and wash to remove the residual sodium chloride, catalyst and impurities, the water phase is separated after sufficient stirring; H. The polymer after water washing is heated, the high vacuum system is started to remove the volatile matter under reduced pressure, when the volatile content is less than 1%, the product is discharged while hot, and cooled on a steel belt with cooling water, then broken to obtain the epoxy resin product.

4. The production method according to claim 3, characterized by, In step A, the ester exchange reaction temperature is 100-105°C.

5. The production method according to claim 3, wherein In step B, the ring-opening reaction temperature is 80-85°C, and the time is 2-3 h.

6. The preparation method according to claim 3, characterized in that, In Step C, the temperature is lowered to 35-40°C; the interval time is 20-30 min.

7. The preparation method according to claim 3, characterized in that, In Step D, the temperature is raised to 90-95°C; the vacuum degree is kept at -0.092 to -0.095 Mpa; the temperature of chain extension polymerization is 110-115°C.

8. The preparation method according to claim 3, characterized in that, In Step E, the temperature of polymerization is raised to 118-123°C.

9. The preparation method according to claim 3, characterized in that, In Step G, the temperature is lowered to 100-105°C; the stirring is kept for 20-30 min.

10. The method of claim 3, wherein, In Step H, the temperature is raised to 135-140°C; the vacuum degree is controlled at -0.098 Mpa to -0.099 Mpa.

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