An epoxy resin for high-gloss and high-temperature resistant powder coatings and its preparation method

Abstract

The present invention relates to an epoxy resin for high-gloss and high-temperature-resistant powder coatings, which is obtained by reacting 1,3,5-tris(2-hydroxyethyl) cyanuric acid, xylene, cyclohexanecarboxylic acid, epichlorohydrin, sodium hydroxide, hydrogenated bisphenol A, a catalyst, etc. as main raw materials; in the epoxy resin chain segments finally prepared, there are mainly cyanuric acid rings and hydrogenated bisphenol A chain segments with excellent high-temperature resistance. The obtained epoxy resin has excellent high-temperature resistance. On the one hand, the cyclohexanecarboxylate specially introduced in the chain segment structure has excellent high-temperature resistance. More importantly, during the film-forming process of curing, it has the functions of lubricating the epoxy resin chain segments, promoting leveling and improving gloss. Finally, after the epoxy resin is cured at a low temperature with an acid anhydride curing agent, the obtained coating film has excellent high-temperature resistance, leveling and gloss properties. Moreover, the whole preparation process does not require expensive raw materials and special processes, has a low cost, and has a better market prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical products, and particularly relates to an epoxy resin for high-gloss and high-temperature-resistant powder coatings and a preparation method thereof. Background Art

[0002] With the acceleration of the paint-to-powder conversion speed, powder coatings have become one of the most common metal surface coating paints due to their unique environmental protection characteristics. Epoxy powder coatings are widely used due to their excellent adhesion and other characteristics. In related special fields, such as the coating of high-temperature metal surfaces of gas stoves, heaters, etc., traditional E-12 epoxy resins have insufficient high-temperature resistance due to their ordinary bisphenol A structure, and the coating film is prone to yellowing, cracking, and even peeling, making it difficult to meet the requirement of high-temperature resistance (250 / 48h). Although some studies have prepared high-temperature-resistant coating film products using special raw materials and processes, on the one hand, the cost is too high, and on the other hand, due to the too-hard chain segments of the epoxy resin, the gloss of the coating film is insufficient, making it difficult to achieve a high-gloss coating film of more than 95%. How to obtain a special epoxy resin product with both high-temperature resistance and excellent coating film gloss performance is an urgent problem to be solved in the industry.

[0003] In view of the above problems existing in high-temperature-resistant epoxy powder coatings, the present invention mainly uses 1,3,5-tris(2-hydroxyethyl) cyanuric acid, xylene, cyclohexanecarboxylic acid, epichlorohydrin, sodium hydroxide, hydrogenated bisphenol A, catalysts, etc. as the main raw materials for reaction. Finally, the main chain segments of the prepared epoxy resin are cyanuric acid and hydrogenated bisphenol A chain segments with excellent high-temperature resistance. The finally obtained epoxy resin has excellent high-temperature resistance, and the specially introduced cyclohexanecarboxylate in the chain structure has excellent high-temperature resistance on the one hand, and more importantly, it has the functions of lubricating the epoxy resin chain segments, assisting in leveling, and improving the gloss during the film-forming process. Finally, after the epoxy resin is cured with an acid anhydride curing agent, the obtained coating film has excellent high-temperature resistance, leveling, and gloss performance, and the whole preparation process does not require expensive raw materials and special processes, with a low cost and a good market prospect. Summary of the Invention

[0004] The present invention relates to an epoxy resin for high-gloss and high-temperature-resistant powder coatings, which is prepared by reacting raw materials including 1,3,5-tris(2-hydroxyethyl) cyanuric acid, xylene, cyclohexanecarboxylic acid, epichlorohydrin, sodium hydroxide, hydrogenated bisphenol A, and catalysts.

[0005] An epoxy resin for high-gloss and high-temperature-resistant powder coatings, the raw material composition of which includes, in terms of mole parts:

[0006]

[0007] In addition, the composition further includes catalyst 1, catalyst 2, and catalyst 3.

[0008] Further, Catalyst 1 is p-toluenesulfonic acid, and its dosage is 0.4 - 0.8% of the mass of 1,3,5-tris(2-hydroxyethyl)cyanuric acid; Catalyst 2 is boron trifluoride etherate, and its dosage is 0.8 - 1.2% of the mass of 1,3,5-tris(2-hydroxyethyl)cyanuric acid; Catalyst 3 is ethyltriphenylphosphonium bromide, and its dosage is 0.1 - 0.15% of the mass of 1,3,5-tris(2-hydroxyethyl)cyanuric acid.

[0009] A preparation method of an epoxy resin for high-gloss and high-temperature resistant powder coatings, which comprises the following steps:

[0010] A. Add the formula amount of 1,3,5-tris(2-hydroxyethyl)cyanuric acid, xylene, cyclohexanecarboxylic acid and Catalyst 1 into a reaction kettle, start stirring, and raise the temperature to 135 - 140 °C for reflux water separation esterification reaction;

[0011] B. Sample and detect the acid value of the reaction mixture. When the acid value of the system mixture reaches below 1 mgKOH / g, it indicates that the cyclohexanecarboxylic acid has been basically esterified. At this time, start the vacuum system and continue the vacuum reaction at 135 - 140 °C to remove the xylene solvent in the system;

[0012] C. When the xylene content in the system mixture is lower than 2%, release the vacuum system to obtain Esterification Intermediate 1, cool it to 70 - 75 °C, then add the formula amount of epichlorohydrin, fully dissolve it with epichlorohydrin to form a single phase, add the formula amount of Catalyst 2, and continue the full ring-opening reaction at 70 - 75 °C;

[0013] D. Sample for liquid chromatography detection. When the content of Esterification Intermediate 1 is lower than 1%, it indicates that its ring-opening reaction with epichlorohydrin has been basically completed. Then cool it to 35 - 40 °C, add the formula amount of sodium hydroxide for ring-closing reaction, and continue the heat preservation reaction after adding;

[0014] E. Detect the change of pH value in the system. When the pH value has no obvious change within 30 min, filter the material to remove the by-product solid sodium chloride, obtain the organic phase containing epichlorohydrin, then wash it with water to remove impurities, separate the water phase by stratification, and obtain the washed organic phase; then start the vacuum system, gradually raise the temperature to 75 - 80 °C under negative pressure to remove the residual water and epichlorohydrin in the organic phase;

[0015] F. When the volatile content is < 1%, the vacuum system is released to obtain the cyclization intermediate 2. Then, the formulated amount of hydrogenated bisphenol A is added, the temperature is raised to 100 - 105°C, and after stirring evenly, the formulated amount of catalyst 3 is added. After stirring evenly, the temperature is gradually raised to 155 - 160°C. The epoxy equivalent and softening point are sampled and detected. When the epoxy equivalent reaches 920 - 980 g / mol and the softening point reaches 80 - 86°C, the reaction is stopped, and the product is discharged at high temperature and post-treated to obtain the epoxy resin for high-gloss and high-temperature resistant powder coatings.

[0016] Further, in steps A and B, the reaction temperature is preferably 138 - 140°C.

[0017] Further, in step B, the vacuum degree is controlled at -0.095 to -0.097 Mpa.

[0018] Further, in step D, after cooling, the formulated amount of sodium hydroxide is added in 5 - 7 portions for the ring-closing reaction, with an interval of 8 - 12 min between each addition. After the addition is completed, the reaction is continued under insulation.

[0019] Further, in step E, when the pH value does not change significantly within 30 min, it means the change value ≤ 0.1; the water washing for impurity removal includes washing with water with a mass of 1 / 2 of epichlorohydrin twice for impurity removal, and separating the water phase by stratification to obtain the washed organic phase; the negative pressure of the vacuum system is maintained at -0.098 to -0.099 Mpa.

[0020] Further, in step F, the temperature is gradually raised to 155 - 160°C at a heating rate of 10 - 12°C / h; the post-treatment includes cooling the resin with a steel belt with condensed water, and then crushing and granulating.

[0021] The present invention also relates to the application of the epoxy resin for high-gloss and high-temperature resistant powder coatings as described above or the epoxy resin for high-gloss and high-temperature resistant powder coatings obtained by the preparation method as described above in powder coatings, wherein the powder coatings are sprayed on a substrate by an electrostatic spray gun and cured to obtain a coating film.

[0022] For example, the preparation method of the epoxy resin for high-gloss and high-temperature resistant powder coatings includes the following steps:

[0023] A. Add the formulated amounts of 1,3,5-tris(2-hydroxyethyl) cyanuric acid, xylene, cyclohexanecarboxylic acid, and catalyst 1 into a reaction kettle, start stirring, and raise the temperature to 138 - 140°C for reflux water separation esterification reaction;

[0024] B. Sample and detect the acid value of the reaction mixture. When the acid value of the system mixture reaches below 1 mg KOH / g, it indicates that the cyclohexanecarboxylic acid has been basically esterified. At this time, start the vacuum system, control the vacuum degree at -0.095 to -0.097 Mpa, and continue to carry out vacuum distillation to remove the xylene solvent in the system at 138 - 140 °C;

[0025] C. When the xylene content in the system mixture is lower than 2%, release the vacuum system to obtain the esterification intermediate 1, and cool it to 70 - 75 °C. Then add the formulated amount of epichlorohydrin, and after it is fully dissolved into one phase with epichlorohydrin, add the formulated amount of catalyst 2 and continue to carry out a full ring-opening reaction at 70 - 75 °C;

[0026] D. Take a sample for liquid chromatography detection. When the content of the esterification intermediate 1 is lower than 1%, it indicates that its ring-opening reaction with epichlorohydrin has been basically completed. Then cool it to 35 - 40 °C, and add the formulated amount of sodium hydroxide in 5 - 7 portions for the ring-closure reaction, with an interval of 8 - 12 minutes each time. After adding, continue the heat preservation reaction;

[0027] E. Detect the change of the pH value in the system. When the pH value does not change significantly within 30 minutes (the change value ≤ 0.1), it indicates that the ring-closure reaction has been completed. Filter the material to remove the by-product solid sodium chloride to obtain the organic phase containing epichlorohydrin. Then wash it twice with water with a mass of 1 / 2 of that of epichlorohydrin for impurity removal, and separate the layers to remove the aqueous phase to obtain the washed organic phase. Then start the vacuum system, and gradually raise the temperature to 75 - 80 °C under negative pressure (maintaining -0.098 to -0.099 Mpa) to remove the residual water and epichlorohydrin in the organic phase;

[0028] F. When the volatile content is < 1%, release the vacuum system to obtain the cyclization intermediate 2. Then add the formulated amount of hydrogenated bisphenol A, raise the temperature to 100 - 105 °C, and stir evenly. Then add the formulated amount of catalyst 3, stir evenly, and gradually raise the temperature at a rate of 10 - 12 °C / h to 155 - 160 °C. Take a sample to detect the epoxy equivalent and softening point. When the epoxy equivalent reaches 920 - 980 g / mol and the softening point reaches 80 - 86 °C, stop the reaction. Discharge the material at high temperature and cool the resin with a steel belt with condensed water, and then crush and granulate to obtain the high-gloss, high-temperature resistant epoxy resin for powder coatings.

[0029] Among them, the structure of the esterification intermediate 1:

[0030]

[0031] The structure of the cyclization intermediate 2:

[0032]

[0033] The obtained epoxy resin has a colorless or light yellow transparent granular appearance, an epoxy equivalent of 920 - 980 g / mol, and a softening point of 80 - 86 °C.

[0034] The formulation of the epoxy powder coating of the present invention can be obtained from the epoxy resin prepared above, and filler aids such as 1,2,4 - cyclohexanetricarboxylic anhydride, barium sulfate, and titanium dioxide. The powder coating is sprayed on the surface - treated tinplate substrate using an electrostatic spray gun, and the coating film is obtained after curing.

[0035] The beneficial effects of the present invention:

[0036] The present invention mainly uses 1,3,5 - tris(2 - hydroxyethyl) cyanuric acid, xylene, cyclohexanecarboxylic acid, epichlorohydrin, sodium hydroxide, hydrogenated bisphenol A, catalysts, etc. as the main raw materials for reaction. The epoxy resin segments finally prepared mainly contain cyanuric acid and hydrogenated bisphenol A segments with excellent high - temperature resistance. The finally obtained epoxy resin has excellent high - temperature resistance. On the one hand, the specially introduced cyclohexanecarboxylate in the segment structure has excellent high - temperature resistance. More importantly, during the film - forming process of curing, it has the functions of lubricating the epoxy resin segments, assisting in leveling, and improving the gloss. Finally, after the epoxy resin is cured with an acid anhydride curing agent, the obtained coating film has excellent high - temperature resistance, leveling, and gloss properties. Moreover, the whole preparation process does not require expensive raw materials and special processes, has a low cost, and has a good market prospect. Detailed implementation manners

[0037] To facilitate the understanding of the present invention, various exemplary implementation manners of the present invention are described in detail below. This detailed description should not be regarded as a specific limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0038] The raw materials are all commercially available ordinary industrial - grade raw materials.

[0039] Example 1

[0040] An epoxy resin for a high - gloss and high - temperature - resistant powder coating, the raw material composition in terms of mole parts includes:

[0041]

[0042] Catalyst 1 is p - toluenesulfonic acid, and the dosage is 0.6% of the mass of 1,3,5 - tris(2 - hydroxyethyl) cyanuric acid; Catalyst 2 is boron trifluoride diethyl ether, and the dosage is 1% of the mass of 1,3,5 - tris(2 - hydroxyethyl) cyanuric acid; Catalyst 3 is ethyltriphenylphosphonium bromide, and the dosage is 0.12% of the mass of 1,3,5 - tris(2 - hydroxyethyl) cyanuric acid.

[0043] The preparation method of the epoxy resin for the high - gloss and high - temperature - resistant powder coating includes the following steps:

[0044] A. Add the formulated amount of 1,3,5-tris(2-hydroxyethyl) cyanuric acid, xylene, cyclohexanecarboxylic acid, and catalyst 1 into a reaction kettle, start stirring, and raise the temperature to 140 °C for reflux water separation esterification reaction;

[0045] B. Sample and detect the acid value of the reaction mixture. When the acid value of the system mixture reaches below 1 mg KOH / g, it indicates that the cyclohexanecarboxylic acid has been basically esterified. At this time, start the vacuum system, control the vacuum degree at -0.097 Mpa, and continue to carry out vacuum removal of the xylene solvent in the system at 140 °C;

[0046] C. When the xylene content in the system mixture is lower than 2%, release the vacuum system to obtain esterification intermediate 1, cool it to 75 °C, then add the formulated amount of epichlorohydrin. After it is fully dissolved with epichlorohydrin into one phase, add the formulated amount of catalyst 2 and continue to carry out a full ring-opening reaction at 75 °C;

[0047] D. Sample for liquid chromatography detection. When the content of esterification intermediate 1 is lower than 1%, it indicates that its ring-opening reaction with epichlorohydrin has been basically completed. Then cool it to 40 °C and add the formulated amount of sodium hydroxide in 7 portions for ring-closure reaction, with an interval of 10 min each time. After adding, continue to carry out heat preservation reaction;

[0048] E. Detect the change of pH value in the system. When the pH value does not change significantly (the change value ≤ 0.1) within 30 min, it indicates that the ring-closure reaction has been completed. Filter the material to remove the by-product solid sodium chloride to obtain an organic phase containing epichlorohydrin. Then wash it 2 times with water with a mass of 1 / 2 of epichlorohydrin for impurity removal, and separate the water phase by stratification to obtain the washed organic phase. Then start the vacuum system and gradually raise the temperature to 80 °C under negative pressure (maintaining -0.098 Mpa) to remove the residual water and epichlorohydrin in the organic phase;

[0049] F. When the volatile content < 1%, release the vacuum system to obtain cyclization intermediate 2. Then add the formulated amount of hydrogenated bisphenol A, raise the temperature to 105 °C, stir evenly, add the formulated amount of catalyst 3, stir evenly, and gradually raise the temperature to 160 °C at a heating rate of 12 °C / h. Sample and detect the epoxy equivalent and softening point. When the epoxy equivalent and softening point reach the expected values, stop the reaction, discharge the material at high temperature, and cool the resin with a steel belt with condensed water, then crush and granulate to obtain the epoxy resin for high-gloss and high-temperature-resistant powder coatings.

[0050] The obtained epoxy resin has a light yellow transparent granular appearance, an epoxy equivalent of 930 / mol, and a softening point of 81 °C.

[0051] Example 2

[0052] An epoxy resin for high-gloss and high-temperature resistant powder coatings, the raw material composition includes, in terms of mole parts:

[0053]

[0054] Catalyst 1 is p-toluenesulfonic acid, and its dosage is 0.8% of the mass of 1,3,5-tris(2-hydroxyethyl) cyanuric acid; Catalyst 2 is boron trifluoride diethyl ether, and its dosage is 1.2% of the mass of 1,3,5-tris(2-hydroxyethyl) cyanuric acid; Catalyst 3 is ethyltriphenylphosphonium bromide, and its dosage is 0.15% of the mass of 1,3,5-tris(2-hydroxyethyl) cyanuric acid.

[0055] The preparation method is the same as that in Example 1.

[0056] The obtained epoxy resin has a light yellow transparent granular appearance, an epoxy equivalent of 974 g / mol, and a softening point of 85 °C.

[0057] Example 3

[0058] An epoxy resin for high-gloss and high-temperature resistant powder coatings, the raw material composition includes, in terms of mole parts:

[0059]

[0060]

[0061] Catalyst 1 is p-toluenesulfonic acid, and its dosage is 0.4% of the mass of 1,3,5-tris(2-hydroxyethyl) cyanuric acid; Catalyst 2 is boron trifluoride diethyl ether, and its dosage is 0.8% of the mass of 1,3,5-tris(2-hydroxyethyl) cyanuric acid; Catalyst 3 is ethyltriphenylphosphonium bromide, and its dosage is 0.1% of the mass of 1,3,5-tris(2-hydroxyethyl) cyanuric acid.

[0062] The preparation method is the same as that in Example 1.

[0063] The obtained epoxy resin has a light yellow transparent granular appearance, an epoxy equivalent of 961 g / mol, and a softening point of 84 °C.

[0064] Example 4

[0065] An epoxy resin for high-gloss and high-temperature resistant powder coatings, the raw material composition includes, in terms of mole parts:

[0066]

[0067] Catalyst 1 is p-toluenesulfonic acid, and its dosage is 0.8% of the mass of 1,3,5-tris(2-hydroxyethyl)cyanuric acid; Catalyst 2 is boron trifluoride ethyl ether, and its dosage is 1.2% of the mass of 1,3,5-tris(2-hydroxyethyl)cyanuric acid; Catalyst 3 is ethyltriphenylphosphonium bromide, and its dosage is 0.15% of the mass of 1,3,5-tris(2-hydroxyethyl)cyanuric acid.

[0068] The preparation method is the same as that of Example 1.

[0069] The obtained epoxy resin has the appearance of colorless or light yellow transparent particles, an epoxy equivalent of 947 g / mol, and a softening point of 83°C.

[0070] Comparative Example 1

[0071] As Comparative Example 1, the epoxy resin in Example 1 was replaced with common commercially available E-12 epoxy resin.

[0072] Purchased from Huangshan Wuhuan Technology Co., Ltd., epoxy equivalent 842g / mol, softening point 93℃.

[0073] The amount of curing agent 1,2,4-cyclohexanetricarboxylic anhydride was increased from 40 g to 43 g.

[0074] Comparative Example 2

[0075] The other conditions were the same as those in Comparative Example 1, except that the curing conditions were changed to 180° C. / 15 min.

[0076] Application Examples

[0077] The formula of epoxy powder coating is usually as follows in parts by weight:

[0078]

[0079]

[0080] Preparation of powder coating: Mix all materials according to the formula of the above powder coating, use a twin-screw extruder to melt and extrude at high temperature (the screw temperature is controlled at 125-135°C), and then press and crush the flakes, and then crush and sieve them to make powder coating (160-180 mesh). The powder coating is sprayed on the surface treated tinplate substrate with an electrostatic spray gun, and cured at 155°C / 20min to obtain a coating with a film thickness of 80-90μm.

[0081] Performance comparison:

[0082] The coating index test is carried out according to GB / T 21776-2008 "Guide to the Testing Standards of Powder Coatings and Their Coatings"; the leveling grade is based on JB-T 3998-1999 "Scrape-coat Determination of Coating Leveling".

[0083] The coating performance results of the powder coatings in the above examples and comparative examples are shown in Table 1 below.

[0084] Table 1 Coating Film Performance

[0085]

[0086]

[0087] From the comparison between Examples 1-4 and Comparative Examples 1-2 in Table 1, it can be seen that the product of the present invention uses a special cyanuric acid ring as the main chain segment of the epoxy resin. The ester groups in its structure realize the lubricating ability of the product chain segment, improve the gloss and leveling grade of the coating film, and obtain a high-temperature resistant powder coating under the condition of achieving low-temperature curing (155°C / 20 min). The appearance of its coating film is flat and smooth, with a very high gloss, basically above 95%, and the leveling grades are all above 7. Especially, the high-temperature resistance performance test is excellent. After 250°C / 50 h, the coating film has almost no obvious change, and the comprehensive performance is excellent.

[0088] For Comparative Examples 1-2, the coating films cured with ordinary E-12 epoxy resin and 1,2,4-cyclohexanetricarboxylic anhydride were used. In Comparative Example 1, it could not be fully cured at 155°C / 20 min, so the coating film was not good; Comparative Example 2 used normal high-temperature curing conditions (180°C / 15 min), which could be fully cured, but the appearance, gloss, and leveling performance of the coating film were average, and the high-temperature resistance performance was significantly worse than that of the product of the present invention. After 250°C / 50 h, the coating film turned yellow significantly and began to show very slight cracks.

[0089] Obviously, the above examples are only examples clearly described and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. An epoxy resin for high-gloss and high-temperature resistant powder coatings, characterized in that, The raw materials including 1,3,5-tris(2-hydroxyethyl)cyanuric acid, xylene, cyclohexanecarboxylic acid, epichlorohydrin, sodium hydroxide, hydrogenated bisphenol A and a catalyst are used to prepare the product through reaction; The raw material composition includes, by mole: In addition, the components also include catalyst 1, catalyst 2 and catalyst 3; the catalyst 1 is p-toluenesulfonic acid, and the amount used is 0.4-0.8% of the mass of 1,3,5-tris(2-hydroxyethyl)cyanuric acid; the catalyst 2 is boron trifluoride ethyl ether, and the amount used is 0.8-1.2% of the mass of 1,3,5-tris(2-hydroxyethyl)cyanuric acid; the catalyst 3 is ethyl triphenylphosphonium bromide, and the amount used is 0.1-0.15% of the mass of 1,3,5-tris(2-hydroxyethyl)cyanuric acid; The preparation method of the epoxy resin comprises the following steps: A. Add the formulated amount of 1,3,5-tris(2-hydroxyethyl)cyanuric acid, xylene, cyclohexanecarboxylic acid and catalyst 1 into a reaction kettle, start stirring, and heat to 135-140° C. to perform reflux water separation esterification reaction; B. Take a sample to detect the acid value of the reaction mixture. When the acid value of the system mixture reaches below 1 mgKOH / g, start the vacuum system and continue to perform a reduced pressure reaction at 135-140° C. to remove the xylene solvent in the system; C. When the xylene content of the system mixture is less than 2%, the vacuum system is released to obtain the esterification intermediate 1, and the temperature is lowered to 70-75° C., and then the formulated amount of epichlorohydrin is added to fully dissolve the epichlorohydrin into one phase, and then the formulated amount of catalyst 2 is added to continue the ring-opening reaction at 70-75° C.; D. Take a sample for liquid chromatography detection. When the content of the esterified intermediate 1 is less than 1%, cool it to 35-40° C., add a formula amount of sodium hydroxide to carry out a ring-closing reaction, and continue to keep warm after the addition is completed; E. Detect the change of pH value in the system. When there is no obvious change in pH value within 30 minutes, filter the material to remove by-products to obtain an organic phase containing epichlorohydrin, then wash with water to remove impurities, and remove the aqueous phase by layer to obtain an organic phase after washing; start the vacuum system, gradually raise the temperature to 75-80° C. under negative pressure to remove residual water and epichlorohydrin in the organic phase; F. When the volatile content is less than 1%, release the vacuum system to obtain the cyclized intermediate 2, then add the formulated amount of hydrogenated bisphenol A, raise the temperature to 100-105°C, stir evenly, add the formulated amount of catalyst 3, stir evenly, gradually raise the temperature to 155-160°C, take samples to detect the epoxy equivalent and softening point, stop the reaction when the epoxy equivalent reaches 920-980g / mol and the softening point reaches 80-86°C, discharge at high temperature and post-process, and the high-gloss, high-temperature resistant epoxy resin for powder coatings can be obtained.

2. The epoxy resin for high-gloss and high-temperature resistant powder coatings according to claim 1, characterized in that, In steps A and B, the reaction temperature is 138-140°C.

3. The epoxy resin for high-gloss and high-temperature resistant powder coatings according to claim 1, characterized in that, In step B, the vacuum degree is controlled at -0.095 to -0.097 MPa.

4. The epoxy resin for high-gloss and high-temperature resistant powder coatings according to claim 1, wherein, In step D, after cooling, the sodium hydroxide in the formula amount is added in 5-7 times for ring-closing reaction, each time interval is 8-12 minutes, and the reaction is continued after the addition is completed.

5. The epoxy resin for high-gloss and high-temperature resistant powder coatings according to claim 1, characterized in that, In step E, no obvious change in pH value within 30 min means that the change value ≤ 0.1; the water washing for impurity removal includes washing with water with a mass of 1 / 2 of epichlorohydrin twice for impurity removal, and separating the layers to remove the aqueous phase to obtain the washed organic phase; the negative pressure of the vacuum system is maintained at -0.098 to -0.099 Mpa.

6. The epoxy resin for high-gloss and high-temperature resistant powder coatings according to claim 1, further characterized in that in step F, the temperature is gradually increased to 155-160 °C at a heating rate of 10-12 °C / h; the post-treatment includes cooling the resin with a steel belt with condensed water, and then crushing and granulating.

7. Use of the epoxy resin for high-gloss and high-temperature resistant powder coatings according to any one of claims 1-6 in powder coatings, characterized in that, The powder coating is sprayed on the substrate by an electrostatic spray gun and cured to obtain a coating film.

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