A halogen-free flame-retardant epoxy resin and its preparation method

Abstract

The present invention relates to the technical field of epoxy resin synthesis, and specifically relates to a halogen-free flame-retardant epoxy resin and a preparation method thereof. In the present invention, a flame retardant is prepared by adding 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, N-tert-butylacrylamide, tetramethylpiperidine nitroxide phosphite, triethylamine, tetrahydrofuran and phenethyltrichlorosilane. Then, using anhydrous magnesium sulfate, aluminum sulfate octadecahydrate, sodium hydroxide, anhydrous sodium carbonate, the flame retardant and deionized water as raw materials, a composite flame retardant is prepared. The epoxy resin and the composite flame retardant are subjected to high-temperature mechanical blending, and then 4,4'-diaminodiphenylmethane is added, and after vacuum degassing and stepwise curing, the finished product is prepared. The finished product prepared by the present invention has good flame retardancy and environmental protection effects, and thus has broad application prospects in the technical field of epoxy resin synthesis.

Description

Technical Field

[0001] The present invention relates to the technical field of epoxy resin synthesis, and specifically to a halogen-free flame-retardant epoxy resin and a preparation method thereof. Background Art

[0002] Epoxy resin is a synthetic material with excellent properties and diverse characteristics, playing an important role in modern industrial and technological fields. First of all, epoxy resin has excellent mechanical properties. Its high strength and high toughness make it an ideal choice for high-strength structural materials. Epoxy resin can achieve different levels of mechanical property adjustment by controlling the formulation and curing process to meet the needs of different applications, which enables epoxy resin to be widely used in fields such as aerospace, automotive industry, and construction. Secondly, epoxy resin has excellent chemical stability and corrosion resistance, which makes it widely used in fields such as chemical industry, petroleum, and electronics. Epoxy resin can also improve its chemical corrosion resistance by adjusting its formulation to meet the requirements of different working environments. In addition, epoxy resin has excellent electrical insulation properties, making it an important material in the electronics and electrical fields. It can be used to manufacture insulating materials, circuit boards, encapsulation materials, etc., to protect electronic components from moisture, pollutants, and electromagnetic interference.

[0003] Epoxy resin is an important synthetic material widely used in various fields. However, the inherent flammability drawback of epoxy resin limits its further application in high-end fields such as aerospace, electronics and electrical, and transportation. Therefore, it is usually necessary to add flame retardants to improve the flame retardant performance of epoxy resin. However, the use of traditional flame retardants has some problems and defects that cannot be ignored: traditional halogen-based flame retardants pose environmental and health hazards. Brominated flame retardants are often used to improve the flame resistance of materials, but the bromine gas in their decomposition products will damage the ozone layer and release toxic bromides at high temperatures. Chlorinated flame retardants also have similar problems, and the chlorine gas in their decomposition products causes non-negligible damage to the environment and human health. While halogen-free flame-retardant epoxy resin can reduce the impact on the environment and human health, has good high-temperature stability, and reduces the release of smoke and toxic substances. Therefore, in order to reduce the adverse effects on the environment and human body, the preparation of halogen-free flame-retardant epoxy resin has become an urgent need.

[0004] In order to overcome the defects of the prior art, the present invention provides a halogen-free flame-retardant epoxy resin and a preparation method thereof. Summary of the Invention

[0005] The purpose of the present invention is to provide a halogen-free flame-retardant epoxy resin and a preparation method thereof to solve the problems in the prior art.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] A preparation method of a halogen-free flame retardant epoxy resin, comprising the following steps:

[0008] Step 1: Under a nitrogen atmosphere, heat 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to melting, then add N-tert-butylacrylamide, and raise the temperature of the reactants to 180 - 190 °C for reaction for 25 - 30 h. After the reaction, wash and dry under vacuum to obtain an intermediate product; mix the intermediate product, tetramethylpiperidine nitroxide free radical phosphite and tetrahydrofuran, stir and dissolve in an ice-water bath, then add triethylamine for reaction for 20 - 30 min. After the reaction, add phenethyltrichlorosilane and stir and react at 45 - 55 °C for 10 - 15 h. After the reaction, filter, wash and dry under vacuum to prepare a flame retardant;

[0009] Step 2: Mix anhydrous magnesium sulfate, aluminum sulfate octadecahydrate and 1 / 4 part by mass of deionized water to obtain Solution 1; mix sodium hydroxide, anhydrous sodium carbonate and 1 / 4 part by mass of deionized water to obtain Solution 2; mix the flame retardant and 1 / 2 part by mass of deionized water, stir until dissolved at 90 - 100 °C, then lower the temperature to 70 - 80 °C, and add Solution 1 and Solution 2 and continue to stir and react for 3 - 4 h. After the reaction, carry out suction filtration, washing and drying to prepare a composite flame retardant;

[0010] Step 3: Mechanically stir and blend epoxy resin and the composite flame retardant at 100 - 120 °C, then add 4,4'-diaminodiphenylmethane, and continue to stir for 15 - 20 min to prepare a mixed solution; degas the mixed solution under vacuum for 10 - 15 min and then transfer it to a mold, and prepare a finished product by gradient curing.

[0011] Preferably, in Step 1, when preparing the intermediate product, the reaction molar ratio of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to N-tert-butylacrylamide is 1:(1.3 - 1.5).

[0012] Preferably, in Step 1, when preparing the flame retardant, the reaction molar ratio of the intermediate product, tetramethylpiperidine nitroxide free radical phosphite, triethylamine and phenethyltrichlorosilane is (3 - 5):1:3:2.

[0013] Preferably, in Step 1, when preparing the intermediate product, the temperature of vacuum drying is 100 - 110 °C.

[0014] Preferably, in Step 1, when preparing the flame retardant, the temperature of vacuum drying is 140 - 150 °C.

[0015] Preferably, in Step 1, when preparing the intermediate product, the washing parameters are: washing at 70 - 80 °C for 40 - 50 min.

[0016] Preferably, in step one, when preparing the flame retardant, the washing parameters are: washing at 80 - 90°C for 40 - 50 min.

[0017] Preferably, in step two, the contents of the components of the composite flame retardant are: by mass parts, 8 - 10 parts of anhydrous magnesium sulfate, 12 - 15 parts of aluminum sulfate octadecahydrate, 2 - 4 parts of sodium hydroxide, 7.5 - 10 parts of anhydrous sodium carbonate, 12 - 15 parts of flame retardant, and 200 - 240 parts of deionized water.

[0018] Preferably, in step three, the gradient curing parameters are: successively curing at 120 - 125°C for 2 - 3 h, 140 - 145°C for 2 - 3 h, 160 - 165°C for 2 - 3 h, and 180 - 185°C for 2 - 3 h.

[0019] Preferably, in step three, the contents of the components of the finished product are: by mass parts, 100 - 120 parts of epoxy resin, 15 - 30 parts of composite flame retardant, and 25 - 35 parts of 4,4'-diaminodiphenylmethane.

[0020] The beneficial effects of the present invention:

[0021] The present invention prepares a flame retardant by adding 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, N-tert-butylacrylamide, tetramethylpiperidine nitroxide phosphite, triethylamine, tetrahydrofuran, and phenethyltrichlorosilane. Then, using anhydrous magnesium sulfate, aluminum sulfate octadecahydrate, sodium hydroxide, anhydrous sodium carbonate, the flame retardant, and deionized water as raw materials, a composite flame retardant is prepared. The epoxy resin and the composite flame retardant are mechanically blended at high temperature, and then 4,4'-diaminodiphenylmethane is added. After vacuum degassing and stepwise curing, the finished product is prepared.

[0022] The characteristics of the present invention are as follows. In step one, an intermediate product is prepared by adding 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and N-tert-butylacrylamide. The reaction principle is that the P-H bond in 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide can undergo an addition reaction with the carbon-carbon double bond in N-tert-butylacrylamide. The intermediate product obtained through this reaction contains relatively more flame-retardant elements P and N. Then, using the intermediate product, tetramethylpiperidine nitroxide phosphite, tetrahydrofuran, triethylamine, and phenethyltrichlorosilane as raw materials, a flame retardant is prepared. The reaction principle is that the hydroxyl groups in the intermediate product and tetramethylpiperidine nitroxide phosphite can undergo an etherification reaction with the chlorine atoms in phenethyltrichlorosilane, and finally a flame retardant is prepared. In this step, by compounding and adjusting these three substances, namely the intermediate product, tetramethylpiperidine nitroxide phosphite, and phenethyltrichlorosilane, within a certain proportion range, it is determined that the reaction efficiency reaches the optimum within the reaction molar ratio range of (3-5):1:2. Within this range, the flame-retardant performance of the flame retardant can be effectively improved.

[0023] The characteristics of the present invention are as follows. In step two, a composite flame retardant is prepared by adding anhydrous magnesium sulfate, aluminum sulfate octadecahydrate, sodium hydroxide, anhydrous sodium carbonate, a flame retardant, and deionized water. The reaction mechanism of this step is to intercalate the flame retardant prepared in step one into the structure of hydrotalcite by the coprecipitation method to prepare a composite flame retardant. On the one hand, this composite flame retardant contains relatively more flame-retardant elements phosphorus, nitrogen, and silicon at the same time. Therefore, the flame retardant prepared by bonding the phosphorus-containing group, nitrogen-containing group, and siloxane molecule through chemical bonds can utilize the phosphorus-nitrogen-silicon synergistic effect to achieve excellent flame-retardant performance. On the other hand, the lamellar structure of hydrotalcite contains a large amount of bound water and anions, which will gradually escape when heated and decomposed, releasing a large amount of water and CO2, which can dilute the concentration of oxygen and other combustion gases, thus playing a flame-retardant effect. Therefore, intercalating the flame retardant into the hydrotalcite structure through the intercalation reaction to obtain a composite flame retardant can achieve the effect of synergistic flame retardancy by combining inorganic and organic multiple flame-retardant elements, and significantly improve the flame retardancy. Specific embodiments

[0024] The following will clearly and completely describe the technical solutions in the present invention in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0025] Source of raw materials:

[0026] Epoxy resin, provided by Guangzhou Ruihua Trading Co., Ltd., with the model number AV170. By mass fraction, one part is 1 g.

[0027] Example 1: Step 1: Under a nitrogen atmosphere, 1 mol of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide was heated to melting, then 1.3 mol of N-tert-butylacrylamide was added, and the reactants were heated to 190 °C and reacted for 30 h. After the reaction, it was washed at 80 °C for 50 min and dried under vacuum at 110 °C to obtain an intermediate product; 3 mol of the intermediate product, 1 mol of tetramethylpiperidine nitroxide phosphite, and 150 ml of tetrahydrofuran were mixed and stirred to dissolve in an ice-water bath, then 3 mol of triethylamine was added for reaction for 30 min. After the reaction, 2 mol of phenethyltrichlorosilane was added, and the mixture was stirred and reacted at 55 °C for 15 h. After the reaction, it was filtered, washed at 90 °C for 50 min, and dried under vacuum at 150 °C to prepare a flame retardant;

[0028] Step 2: 8 g of anhydrous magnesium sulfate, 12 g of aluminum sulfate octadecahydrate, and 50 g of deionized water were mixed to obtain Solution 1; 2 g of sodium hydroxide, 7.5 g of anhydrous sodium carbonate, and 50 g of deionized water were mixed to obtain Solution 2; 12 g of the flame retardant and 100 g of deionized water were mixed and stirred to dissolve at 100 °C, then the temperature was lowered to 80 °C, and Solution 1 and Solution 2 were added and stirring reaction continued for 4 h. After the reaction, it was filtered, washed, and dried to prepare a composite flame retardant;

[0029] Step 3: 100 g of epoxy resin and 15 g of the composite flame retardant were mechanically stirred and blended at 120 °C, then 25 g of 4,4'-diaminodiphenylmethane was added, and stirring continued for 20 min to obtain a mixed solution; the mixed solution was degassed under vacuum for 15 min and then transferred to a mold, and cured at 125 °C for 3 h, 145 °C for 3 h, 165 °C for 3 h, and 185 °C for 3 h in sequence to prepare the finished product.

[0030] Example 2: Step 1: Under a nitrogen atmosphere, 1 mol of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide was heated to melting, then 1.3 mol of N-tert-butylacrylamide was added, and the reactants were heated to 187 °C and reacted for 29 h. After the reaction, it was washed at 77 °C for 47 min and dried under vacuum at 107 °C to obtain an intermediate product; 3 mol of the intermediate product, 1 mol of tetramethylpiperidine nitroxide phosphite, and 150 ml of tetrahydrofuran were mixed and stirred to dissolve in an ice-water bath, then 3 mol of triethylamine was added for reaction for 27 min. After the reaction, 2 mol of phenethyltrichlorosilane was added, and the mixture was stirred and reacted at 53 °C for 14 h. After the reaction, it was filtered, washed at 87 °C for 47 min, and dried under vacuum at 147 °C to prepare a flame retardant;

[0031] Step 2: Mix 8 g of anhydrous magnesium sulfate, 12 g of aluminum sulfate octadecahydrate and 50 g of deionized water to obtain Solution 1; mix 2 g of sodium hydroxide, 7.5 g of anhydrous sodium carbonate and 50 g of deionized water to obtain Solution 2; mix 12 g of the flame retardant and 100 g of deionized water, stir until dissolved at 97 °C, then lower the temperature to 77 °C, and add Solution 1 and Solution 2 and continue stirring and reacting for 3.7 h. After the reaction is completed, carry out suction filtration, washing and drying to prepare a composite flame retardant;

[0032] Step 3: Mechanically stir and blend 100 g of epoxy resin and 15 g of the composite flame retardant at 115 °C, then add 25 g of 4,4'-diaminodiphenylmethane, and continue stirring for 18 min to prepare a mixed solution; degas the mixed solution under vacuum for 14 min and then transfer it to a mold, and carry out curing at 124 °C for 2.7 h, 144 °C for 2.7 h, 164 °C for 2.7 h, and 184 °C for 2.7 h in sequence to prepare the finished product.

[0033] Example 3: Step 1: Under a nitrogen atmosphere, heat 1 mol of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to melting, then add 1.3 mol of N-tert-butylacrylamide, and raise the temperature of the reactants to 185 °C and react for 27 h. After the reaction is completed, wash at 75 °C for 45 min and dry under vacuum at 105 °C to obtain an intermediate product; mix 3 mol of the intermediate product, 1 mol of tetramethylpiperidine nitroxide phosphite and 150 ml of tetrahydrofuran, stir and dissolve in an ice-water bath, then add 3 mol of triethylamine and react for 25 min. After the reaction is completed, add 2 mol of phenethyltrichlorosilane and stir and react at 50 °C for 13 h. After the reaction is completed, carry out filtration, wash at 85 °C for 45 min and dry under vacuum at 145 °C to prepare a flame retardant;

[0034] Step 2: Mix 8 g of anhydrous magnesium sulfate, 12 g of aluminum sulfate octadecahydrate and 50 g of deionized water to obtain Solution 1; mix 2 g of sodium hydroxide, 7.5 g of anhydrous sodium carbonate and 50 g of deionized water to obtain Solution 2; mix 12 g of the flame retardant and 100 g of deionized water, stir until dissolved at 95 °C, then lower the temperature to 75 °C, and add Solution 1 and Solution 2 and continue stirring and reacting for 3.5 h. After the reaction is completed, carry out suction filtration, washing and drying to prepare a composite flame retardant;

[0035] Step 3: Mechanically stir and blend 100 g of epoxy resin and 15 g of composite flame retardant at 110 °C, then add 25 g of 4,4'-diaminodiphenylmethane, and continue stirring for 17 min to prepare a mixed solution; degas the mixed solution under vacuum for 13 min and then transfer it to a mold, and cure it at 123 °C for 2.5 h, 143 °C for 2.5 h, 163 °C for 2.5 h, and 183 °C for 2.5 h in sequence to prepare the finished product.

[0036] Example 4: Step 1: Under a nitrogen atmosphere, heat 1 mol of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to melting, then add 1.3 mol of N-tert-butylacrylamide, and raise the temperature of the reactants to 183 °C and react for 26 h. After the reaction, wash at 73 °C for 43 min and dry under vacuum at 103 °C to obtain an intermediate product; mix 3 mol of the intermediate product, 1 mol of tetramethylpiperidine nitroxide phosphite, and 150 ml of tetrahydrofuran, stir and dissolve in an ice-water bath, then add 3 mol of triethylamine and react for 23 min. After the reaction, add 2 mol of phenethyltrichlorosilane and stir and react at 47 °C for 11 h. After the reaction, filter, wash at 83 °C for 43 min, and dry under vacuum at 143 °C to prepare the flame retardant;

[0037] Step 2: Mix 8 g of anhydrous magnesium sulfate, 12 g of aluminum sulfate octadecahydrate, and 50 g of deionized water to obtain Solution 1; mix 2 g of sodium hydroxide, 7.5 g of anhydrous sodium carbonate, and 50 g of deionized water to obtain Solution 2; mix 12 g of the flame retardant and 100 g of deionized water, stir until dissolved at 93 °C, then lower the temperature to 73 °C, and add Solution 1 and Solution 2 and continue stirring and reacting for 3.3 h. After the reaction, filter, wash, and dry to prepare the composite flame retardant;

[0038] Step 3: Mechanically stir and blend 100 g of epoxy resin and 15 g of composite flame retardant at 105 °C, then add 25 g of 4,4'-diaminodiphenylmethane, and continue stirring for 16 min to prepare a mixed solution; degas the mixed solution under vacuum for 11 min and then transfer it to a mold, and cure it at 121 °C for 2.3 h, 141 °C for 2.3 h, 161 °C for 2.3 h, and 181 °C for 2.3 h in sequence to prepare the finished product.

[0039] Example 5: Step 1: Under a nitrogen atmosphere, 1 mol of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide was heated to melting, then 1.3 mol of N-tert-butylacrylamide was added, and the reactants were heated to 180 °C and reacted for 25 h. After the reaction, it was washed at 70 °C for 40 min and dried under vacuum at 100 °C to obtain an intermediate product; 3 mol of the intermediate product, 1 mol of tetramethylpiperidine nitroxide phosphite, and 150 ml of tetrahydrofuran were mixed and stirred to dissolve in an ice-water bath, then 3 mol of triethylamine was added for reaction for 20 min. After the reaction, 2 mol of phenethyltrichlorosilane was added, and the mixture was stirred and reacted at 45 °C for 10 h. After the reaction, it was filtered, washed at 80 °C for 40 min, and dried under vacuum at 140 °C to prepare a flame retardant;

[0040] Step 2: 8 g of anhydrous magnesium sulfate, 12 g of aluminum sulfate octadecahydrate, and 50 g of deionized water were mixed to obtain Solution 1; 2 g of sodium hydroxide, 7.5 g of anhydrous sodium carbonate, and 50 g of deionized water were mixed to obtain Solution 2; 12 g of the flame retardant and 100 g of deionized water were mixed and stirred to dissolve at 90 °C, then the temperature was lowered to 70 °C, and Solution 1 and Solution 2 were added and stirring reaction continued for 3 h. After the reaction, it was filtered, washed, and dried to prepare a composite flame retardant;

[0041] Step 3: 100 g of epoxy resin and 15 g of the composite flame retardant were mechanically stirred and blended at 100 °C, then 25 g of 4,4'-diaminodiphenylmethane was added, and stirring continued for 15 min to prepare a mixed solution; the mixed solution was degassed under vacuum for 10 min and then transferred to a mold, and cured at 120 °C for 2 h, 140 °C for 2 h, 160 °C for 2 h, and 180 °C for 2 h in sequence to prepare a finished product.

[0042] Comparative Example 1: The step of the composite flame retardant was removed, and the rest was the same as in Example 1. The specific steps were as follows: Step 1: Under a nitrogen atmosphere, 1 mol of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide was heated to melting, then 1.3 mol of N-tert-butylacrylamide was added, and the reactants were heated to 190 °C and reacted for 30 h. After the reaction, it was washed at 80 °C for 50 min and dried under vacuum at 110 °C to obtain an intermediate product; 3 mol of the intermediate product, 1 mol of tetramethylpiperidine nitroxide phosphite, and 150 ml of tetrahydrofuran were mixed and stirred to dissolve in an ice-water bath, then 3 mol of triethylamine was added for reaction for 30 min. After the reaction, 2 mol of phenethyltrichlorosilane was added, and the mixture was stirred and reacted at 55 °C for 15 h. After the reaction, it was filtered, washed at 90 °C for 50 min, and dried under vacuum at 150 °C to prepare a flame retardant;

[0043] Step 2: Mechanically stir and blend 100 g of epoxy resin and 15 g of flame retardant at 120 °C, then add 25 g of 4,4'-diaminodiphenylmethane, and continue stirring for 20 min to prepare a mixed solution; degas the mixed solution under vacuum for 15 min and then transfer it to a mold, and cure it at 125 °C for 3 h, 145 °C for 3 h, 165 °C for 3 h, and 185 °C for 3 h in sequence to prepare a finished product.

[0044] Comparative Example 2: Replace the composite flame retardant with the conventional flame retardant 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and the rest is the same as in Example 1. The specific steps are as follows: Step 1: Mechanically stir and blend 100 g of epoxy resin and 15 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide at 120 °C, then add 25 g of 4,4'-diaminodiphenylmethane, and continue stirring for 20 min to prepare a mixed solution; degas the mixed solution under vacuum for 15 min and then transfer it to a mold, and cure it at 125 °C for 3 h, 145 °C for 3 h, 165 °C for 3 h, and 185 °C for 3 h in sequence to prepare a finished product.

[0045] Detection test:

[0046] Limiting oxygen index test: Take the finished product prepared by the present invention as a sample, cut the sample into specimens with dimensions of 130×7×3 mm, and perform in accordance with the ASTM D2836-2017 standard. Test by using an oxygen index instrument, adjust the oxygen concentration so that the resin spline can still maintain stable combustion after removing the ignition source, and record the oxygen concentration at this time as the limiting oxygen index. Repeat the test 3 times for each sample and take the average value.

[0047] Impact strength: Take the finished product prepared by the present invention as a sample, cut the sample into specimens with dimensions of 80×10×4 mm, and perform in accordance with the GB / T 1843-2008 standard. Adopt the pendulum impact method, repeat the test 3 times for each group of samples and take the average value. The results are shown in the following table:

[0048] Oxygen index / % Impact strength / MPa Example 1 33 28.7 Example 2 33 28.6 Example 3 32 28.5 Example 4 32 28.4 Example 5 31 28.3 Comparative Example 1 27 27.1 Comparative Example 2 22 27.8

[0049] Conclusion: The dosages in Examples 1 to 5 remain unchanged, and only some reaction parameters are modified. It can be seen from the experimental data that there are no obvious fluctuations in the performance of the specimens. Comparative Example 1: The step of the composite flame retardant is removed, and the rest is the same as in Example 1. It can be seen from the experimental data that compared with Example 1, the oxygen index is reduced to 27%, and the impact strength is reduced to 27.1 MPa. The reason for the analysis is that after removing the step of the composite flame retardant, only the flame retardant is added to the epoxy resin. Compared with Example 1, the hydrotalcite structure is removed. Therefore, the flame retardant performance related to the hydrotalcite structure will be correspondingly removed, so the flame retardant performance of the prepared specimen will be reduced and the oxygen index will be reduced; in addition, the hydrotalcite has a layered structure and can absorb and disperse energy by interlayer slip when subjected to impact force, thereby reducing the impact pressure of the impact load on the epoxy resin and improving the impact resistance of the material. Therefore, the impact strength will also be reduced after removing the hydrotalcite structure.

[0050] Comparative Example 2: The composite flame retardant is replaced with the conventional flame retardant 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and the rest is the same as in Example 1. It can be seen from the experimental data that compared with Example 1, the oxygen index is reduced to 22%, and the impact strength is reduced to 27.8 MPa. The reason for the analysis is that the flame retardant prepared in the present invention simultaneously contains three flame retardant elements for synergistic flame retardancy. In addition, by intercalating the flame retardant into the hydrotalcite structure, the flame retardant performance of the hydrotalcite can be compounded and increased, achieving the effect of synergistic flame retardancy of multiple flame retardant elements combined with inorganic-organic. Therefore, after replacing the composite flame retardant with the conventional flame retardant 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, the flame retardant effect will be significantly reduced and the oxygen index will be reduced; in addition, since the silicon element in the composite flame retardant can improve the toughness and impact resistance of the epoxy resin, the impact strength will also be reduced after replacing the composite flame retardant with the conventional flame retardant 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide.

[0051] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device.

[0052] Finally, it should be noted that the above are only preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a flame-retardant epoxy resin, characterized in that: It includes the following steps: Step 1: Under a nitrogen atmosphere, heat 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to melting, then add N-tert-butylacrylamide, and raise the temperature of the reactants to 180 - 190 °C for reaction for 25 - 30 h. After the reaction, wash and dry under vacuum to obtain an intermediate product; mix the intermediate product, tetramethylpiperidine-nitroxyl free radical phosphite, and tetrahydrofuran, stir and dissolve in an ice-water bath, then add triethylamine for reaction for 20 - 30 min. After the reaction, add phenethyltrichlorosilane and stir and react at 45 - 55 °C for 10 - 15 h. After the reaction, filter, wash, and dry under vacuum to prepare a flame retardant; when preparing the intermediate product, the reaction molar ratio of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to N-tert-butylacrylamide is 1:(1.3 - 1.5); Step 2: Mix anhydrous magnesium sulfate, aluminum sulfate octadecahydrate, and 1 / 4 part by mass of deionized water to obtain Solution 1; mix sodium hydroxide, anhydrous sodium carbonate, and 1 / 4 part by mass of deionized water to obtain Solution 2; mix the flame retardant and 1 / 2 part by mass of deionized water, stir to dissolve at 90 - 100 °C, then lower the temperature to 70 - 80 °C, and add Solution 1 and Solution 2 and continue to stir and react for 3 - 4 h. After the reaction, carry out suction filtration, washing, and drying to prepare a composite flame retardant; Step 3: Mechanically stir and blend epoxy resin and the composite flame retardant at 100 - 120 °C, then add 4,4'-diaminodiphenylmethane, and continue to stir for 15 - 20 min to prepare a mixed solution; degas the mixed solution under vacuum for 10 - 15 min and then transfer it to a mold, and prepare the finished product by gradient curing.

2. The preparation method of a flame-retardant epoxy resin according to claim 1, characterized in that: In Step 1, when preparing the flame retardant, the reaction molar ratio of the intermediate product, tetramethylpiperidine-nitroxyl free radical phosphite, triethylamine, and phenethyltrichlorosilane is (3 - 5):1:3:

2.

3. The preparation method of a flame-retardant epoxy resin according to claim 1, characterized in that: In Step 1, when preparing the intermediate product, the temperature for vacuum drying is 100 - 110 °C.

4. The preparation method of a flame-retardant epoxy resin according to claim 1, characterized in that: In Step 1, when preparing the flame retardant, the temperature for vacuum drying is 140 - 150 °C.

5. The preparation method of a flame-retardant epoxy resin according to claim 1, characterized in that: In Step 1, when preparing the intermediate product, the washing parameters are: wash at 70 - 80 °C for 40 - 50 min.

6. The preparation method of a flame-retardant epoxy resin according to claim 1, characterized in that: In Step 1, when preparing the flame retardant, the washing parameters are: wash at 80 - 90 °C for 40 - 50 min.

7. The preparation method of a flame-retardant epoxy resin according to claim 1, characterized in that: In Step 2, the content of each component of the composite flame retardant is: by mass parts, 8 - 10 parts of anhydrous magnesium sulfate, 12 - 15 parts of aluminum sulfate octadecahydrate, 2 - 4 parts of sodium hydroxide, 7.5 - 10 parts of anhydrous sodium carbonate, 12 - 15 parts of the flame retardant, 200 - 240 parts of deionized water.

8. The preparation method of a flame-retardant epoxy resin according to claim 1, characterized in that: In Step 3, the gradient curing parameters are: cure at 120 - 125 °C for 2 - 3 h, 140 - 145 °C for 2 - 3 h, 160 - 165 °C for 2 - 3 h, 180 - 185 °C for 2 - 3 h in sequence.

9. The preparation method of a flame-retardant epoxy resin according to claim 1, characterized in that: In Step 3, the content of each component of the finished product is: by mass parts, 100 - 120 parts of epoxy resin, 15 - 30 parts of the composite flame retardant, 25 - 35 parts of 4,4'-diaminodiphenylmethane.