Halogen-free flame-retardant epoxy resin and preparation method thereof

Abstract

The invention relates to the technical field of epoxy resin synthesis, in particular to halogen-free flame-retardant epoxy resin and a preparation method thereof. According to the invention, the 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, the N-tert-butyl acrylamide, the tetramethylpiperidine nitroxide free radical phosphorous acid triester, the triethylamine, the tetrahydrofuran and the phenethyl trichlorosilane are added, so that the flame retardant is prepared. Anhydrous magnesium sulfate, aluminum sulfate octadecahydrate, sodium hydroxide, anhydrous sodium carbonate, a flame retardant and deionized water are used as raw materials, and the composite flame retardant is prepared. The preparation method comprises the following steps: carrying out high-temperature mechanical blending on epoxy resin and the composite flame retardant, then adding 4, 4 '-diaminodiphenylmethane, and carrying out vacuum degassing and stepped curing to prepare a finished product. The finished product prepared by the invention has good flame retardance and environment-friendly effect, so that the finished product has a wide application prospect in the technical field of epoxy resin synthesis.

Description

Technical Field

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

[0002] Epoxy resin is a synthetic material with excellent performance and diverse characteristics, playing an important role in modern industry and technology. 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 makes epoxy resin widely used in aerospace, automotive industry, construction and other fields. Secondly, epoxy resin has excellent chemical stability and corrosion resistance, which makes it widely used in chemical, petroleum, electronics and other fields. 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 also has excellent electrical insulation properties, making it an important material in the electronic and electrical fields. It can be used to manufacture insulating materials, circuit boards, packaging 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 of epoxy resin limits its further application in high-end fields such as aerospace, electronics and electrical, transportation, etc. Therefore, flame retardants are usually added to improve the flame retardant properties of epoxy resin. However, the use of traditional flame retardants has some problems and defects that cannot be ignored: traditional halogen flame retardants have environmental and health risks, and brominated flame retardants are often used to improve the flame retardancy of materials, but the bromine gas in its 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 its decomposition products causes significant damage to the environment and human health. 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 object of the present invention is to provide a halogen-free flame-retardant epoxy resin and a preparation method thereof, so as 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 method for preparing a halogen-free flame-retardant epoxy resin comprises the following steps:

[0008] Step 1: In a nitrogen environment, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is heated to melt, and then N-tert-butyl acrylamide is added, and the reactants are heated to 180-190°C for reaction for 25-30 hours. After the reaction is completed, the reactants are washed and vacuum dried to obtain an intermediate product; the intermediate product, tetramethylpiperidinium nitroxide free radical phosphite and tetrahydrofuran are mixed, stirred and dissolved in an ice water bath, and triethylamine is added to react for 20-30 minutes. After the reaction is completed, phenethyltrichlorosilane is added, and the reaction is stirred at 45-55°C for 10-15 hours. After the reaction is completed, the flame retardant is prepared by filtering, washing and vacuum drying;

[0009] Step 2: Mix anhydrous magnesium sulfate, aluminum sulfate 18hydrate and 1 / 4 mass part of deionized water to obtain solution 1; mix sodium hydroxide, anhydrous sodium carbonate and 1 / 4 mass part of deionized water to obtain solution 2; mix the flame retardant and 1 / 2 mass part of deionized water, stir at 90-100°C until dissolved, then lower the temperature to 70-80°C, add solution 1 and solution 2, continue stirring and reacting for 3-4h, and after the reaction is completed, filter, wash and dry to prepare a composite flame retardant;

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

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

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

[0013] More optimally, in step 1, when preparing the intermediate product, the vacuum drying temperature is 100-110°C.

[0014] More optimally, in step 1, when preparing the flame retardant, the vacuum drying temperature is 140-150°C.

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

[0016] More optimally, in step 1, when preparing the flame retardant, the washing parameters are: washing at 80-90°C for 40-50 minutes.

[0017] More optimally, in step 2, the contents of the components of the composite flame retardant are: by mass, 8-10 parts of anhydrous magnesium sulfate, 12-15 parts of aluminum sulfate 18-hydrate, 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] More optimally, in step three, the gradient curing parameters are: curing at 120-125°C for 2-3h, curing at 140-145°C for 2-3h, curing at 160-165°C for 2-3h, and curing at 180-185°C for 2-3h.

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

[0020] 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-butyl acrylamide, tetramethyl piperidine nitroxide free radical phosphite triester, triethylamine, tetrahydrofuran and phenylethyl trichlorosilane. Then, anhydrous magnesium sulfate, octahydrate aluminum sulfate, sodium hydroxide, anhydrous sodium carbonate, flame retardant and deionized water are used as raw materials to prepare a composite flame retardant. The epoxy resin and the composite flame retardant are mechanically blended at high temperature, and then 4,4'-diaminodiphenylmethane is added, and vacuum degassing and step curing are performed to prepare a finished product.

[0022] The present invention is characterized in that, in step 1, an intermediate product is prepared by adding 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and N-tert-butyl acrylamide; the reaction principle is that the PH bond in 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide can undergo addition reaction with the carbon-carbon double bond in N-tert-butyl acrylamide, and the intermediate product obtained by the reaction contains more flame retardant elements P and N. Then, the intermediate product, tetramethylpiperidine nitroxide phosphite triester, tetrahydrofuran, triethylamine, and phenethyl trichlorosilane are used as raw materials to prepare a flame retardant; the reaction principle is that the hydroxyl groups in the intermediate product and tetramethylpiperidine nitroxide phosphite triester can undergo etherification reaction with the chlorine atoms in phenethyl trichlorosilane, and finally the flame retardant is prepared. In this step, the intermediate product, tetramethylpiperidinium nitroxide phosphite triester and phenethyl trichlorosilane are compounded and adjusted within a certain ratio range to determine that the reaction efficiency is optimized within the reaction molar ratio of (3-5):1:2. Within this range, the flame retardant properties of the flame retardant can be effectively improved.

[0023] The feature of the present invention is that in step 2, a composite flame retardant is prepared by adding anhydrous magnesium sulfate, aluminum sulfate 18hydrate, 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 1 into the structure of hydrotalcite by coprecipitation to prepare a composite flame retardant; on the one hand, the composite flame retardant contains a large amount of flame retardant elements such as phosphorus, nitrogen and silicon at the same time, so the flame retardant prepared by bonding the phosphorus-containing group, the nitrogen-containing group and the siloxane molecule by chemical bonds can utilize the phosphorus-nitrogen-silicon synergistic effect to achieve excellent flame retardant properties. On the other hand, the layered structure of hydrotalcite contains a large amount of bound water and anions, which will gradually escape when thermally decomposed, releasing a large amount of water and CO 2 , which can dilute the concentration of oxygen and other combustion gases, thus achieving a flame retardant effect. Therefore, the composite flame retardant obtained by intercalating the flame retardant into the hydrotalcite structure through an intercalation reaction can achieve the effect of inorganic-organic combination of multiple flame retardant elements to synergistically enhance flame retardancy, which has a significant improvement in flame retardancy. DETAILED DESCRIPTION

[0024] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] Source of raw materials:

[0026] Epoxy resin, provided by Guangzhou Ruihua Trading Co., Ltd., model AV170. In terms of mass parts, one part is 1 g.

[0027] Example 1: Step 1: Under a nitrogen environment, 1 mol of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide was heated to melt, and then 1.3 mol of N-tert-butyl acrylamide was added, and the reactants were heated to 190°C for reaction for 30 hours. After the reaction, the mixture was washed at 80°C for 50 minutes and vacuum dried at 110°C to obtain an intermediate product; 3 mol of the intermediate product, 1 mol of tetramethylpiperidinium nitroxide free radical phosphite and 150 ml of tetrahydrofuran were mixed, stirred and dissolved in an ice-water bath, and then 3 mol of triethylamine was added to react for 30 minutes. After the reaction, 2 mol of phenethyltrichlorosilane was added, and the mixture was stirred at 55°C for reaction for 15 hours. After the reaction, the mixture was filtered, washed at 90°C for 50 minutes, and vacuum dried at 150°C to prepare a flame retardant;

[0028] Step 2: 8 g of anhydrous magnesium sulfate, 12 g of aluminum sulfate 18hydrate and 50 g of deionized water are mixed to obtain solution 1; 2 g of sodium hydroxide, 7.5 g of anhydrous sodium carbonate and 50 g of deionized water are mixed to obtain solution 2; 12 g of flame retardant and 100 g of deionized water are mixed, stirred at 100° C. until dissolved, then the temperature is lowered to 80° C., and solution 1 and solution 2 are added and stirred to react for 4 hours. After the reaction is completed, the composite flame retardant is prepared by suction filtration, washing and drying;

[0029] Step 3: Blend 100g of epoxy resin and 15g of composite flame retardant at 120°C with mechanical stirring, add 25g of 4,4'-diaminodiphenylmethane, and continue stirring for 20min to prepare a mixed solution; degas the mixed solution under vacuum for 15min and then transfer it to a mold, and cure it at 125°C for 3h, 145°C for 3h, 165°C for 3h, and 185°C for 3h in sequence to prepare a finished product.

[0030] Example 2: Step 1: Under a nitrogen environment, 1 mol of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide was heated to melt, and then 1.3 mol of N-tert-butyl acrylamide was added, and the reactants were heated to 187°C for reaction for 29 hours. After the reaction, the mixture was washed at 77°C for 47 minutes and vacuum dried at 107°C to obtain an intermediate product; 3 mol of the intermediate product, 1 mol of tetramethylpiperidinium nitroxide free radical phosphite and 150 ml of tetrahydrofuran were mixed, stirred and dissolved in an ice-water bath, and then 3 mol of triethylamine was added to react for 27 minutes. After the reaction, 2 mol of phenethyltrichlorosilane was added, and the mixture was stirred at 53°C for reaction for 14 hours. After the reaction, the mixture was filtered, washed at 87°C for 47 minutes, and vacuum dried at 147°C to prepare a flame retardant;

[0031] Step 2: 8 g of anhydrous magnesium sulfate, 12 g of aluminum sulfate 18hydrate and 50 g of deionized water are mixed to obtain solution 1; 2 g of sodium hydroxide, 7.5 g of anhydrous sodium carbonate and 50 g of deionized water are mixed to obtain solution 2; 12 g of flame retardant and 100 g of deionized water are mixed, stirred at 97° C. until dissolved, then the temperature is lowered to 77° C., and solution 1 and solution 2 are added and stirred to react for 3.7 hours. After the reaction is completed, the composite flame retardant is prepared by suction filtration, washing and drying;

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

[0033] Example 3: Step 1: Under a nitrogen environment, 1 mol of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide was heated to melt, and then 1.3 mol of N-tert-butyl acrylamide was added, and the reactants were heated to 185°C for reaction for 27 hours. After the reaction, the mixture was washed at 75°C for 45 minutes and vacuum dried at 105°C to obtain an intermediate product; 3 mol of the intermediate product, 1 mol of tetramethylpiperidinium nitroxide free radical phosphite and 150 ml of tetrahydrofuran were mixed, stirred and dissolved in an ice-water bath, and then 3 mol of triethylamine was added to react for 25 minutes. After the reaction, 2 mol of phenethyltrichlorosilane was added, and the mixture was stirred at 50°C for reaction for 13 hours. After the reaction, the mixture was filtered, washed at 85°C for 45 minutes, and vacuum dried at 145°C to prepare a flame retardant;

[0034] Step 2: 8 g of anhydrous magnesium sulfate, 12 g of aluminum sulfate 18hydrate and 50 g of deionized water are mixed to obtain solution 1; 2 g of sodium hydroxide, 7.5 g of anhydrous sodium carbonate and 50 g of deionized water are mixed to obtain solution 2; 12 g of flame retardant and 100 g of deionized water are mixed, stirred at 95° C. until dissolved, then the temperature is lowered to 75° C., and solution 1 and solution 2 are added and stirred to react for 3.5 hours. After the reaction is completed, the composite flame retardant is prepared by suction filtration, washing and drying;

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

[0036] Example 4: Step 1: Under a nitrogen environment, 1 mol of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide was heated to melt, and then 1.3 mol of N-tert-butyl acrylamide was added, and the reactants were heated to 183°C for reaction for 26 hours. After the reaction, the mixture was washed at 73°C for 43 minutes and vacuum dried at 103°C to obtain an intermediate product; 3 mol of the intermediate product, 1 mol of tetramethylpiperidinium nitroxide free radical phosphite and 150 ml of tetrahydrofuran were mixed, stirred and dissolved in an ice-water bath, and then 3 mol of triethylamine was added to react for 23 minutes. After the reaction, 2 mol of phenethyltrichlorosilane was added, and the mixture was stirred at 47°C for reaction for 11 hours. After the reaction, the mixture was filtered, washed at 83°C for 43 minutes, and vacuum dried at 143°C to prepare a flame retardant;

[0037] Step 2: 8 g of anhydrous magnesium sulfate, 12 g of aluminum sulfate 18hydrate and 50 g of deionized water are mixed to obtain solution 1; 2 g of sodium hydroxide, 7.5 g of anhydrous sodium carbonate and 50 g of deionized water are mixed to obtain solution 2; 12 g of flame retardant and 100 g of deionized water are mixed, stirred at 93° C. until dissolved, then the temperature is lowered to 73° C., and solution 1 and solution 2 are added and stirred to react for 3.3 hours. After the reaction is completed, the composite flame retardant is prepared by suction filtration, washing and drying;

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

[0039] Example 5: Step 1: Under a nitrogen environment, 1 mol of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide was heated to melt, and then 1.3 mol of N-tert-butyl acrylamide was added, and the reactants were heated to 180°C for reaction for 25 hours. After the reaction, they were washed at 70°C for 40 minutes and vacuum dried at 100°C to obtain an intermediate product; 3 mol of the intermediate product, 1 mol of tetramethylpiperidinium nitroxide free radical phosphite and 150 ml of tetrahydrofuran were mixed, stirred and dissolved in an ice-water bath, and then 3 mol of triethylamine was added to react for 20 minutes. After the reaction, 2 mol of phenethyltrichlorosilane was added, and the mixture was stirred at 45°C for reaction for 10 hours. After the reaction, it was filtered, washed at 80°C for 40 minutes, and vacuum dried at 140°C to prepare a flame retardant;

[0040] Step 2: 8 g of anhydrous magnesium sulfate, 12 g of aluminum sulfate 18hydrate and 50 g of deionized water are mixed to obtain solution 1; 2 g of sodium hydroxide, 7.5 g of anhydrous sodium carbonate and 50 g of deionized water are mixed to obtain solution 2; 12 g of flame retardant and 100 g of deionized water are mixed, stirred at 90° C. until dissolved, then the temperature is lowered to 70° C., and solution 1 and solution 2 are added and stirred to react for 3 hours. After the reaction is completed, the composite flame retardant is prepared by suction filtration, washing and drying;

[0041] Step 3: Blend 100g of epoxy resin and 15g of composite flame retardant at 100°C with mechanical stirring, add 25g of 4,4'-diaminodiphenylmethane, and continue stirring for 15min to prepare a mixed solution; degas the mixed solution under vacuum for 10min and then transfer it to a mold, and cure it at 120°C for 2h, 140°C for 2h, 160°C for 2h, and 180°C for 2h in sequence to prepare a finished product.

[0042] Comparative Example 1: The step of preparing the composite flame retardant is removed, and the rest is the same as Example 1, and the specific steps are as follows: Step 1: In a nitrogen environment, 1 mol of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is heated to melt, and then 1.3 mol of N-tert-butyl acrylamide is added, and the reactant is heated to 190° C. for reaction for 30 hours. After the reaction is completed, it is washed at 80° C. for 50 minutes and vacuum dried at 110° C. to obtain an intermediate product; 3 mol of the intermediate product, 1 mol of tetramethylpiperidinium nitroxide free radical phosphite triester and 150 ml of tetrahydrofuran are mixed, stirred and dissolved in an ice water bath, and then 3 mol of triethylamine is added to react for 30 minutes. After the reaction is completed, 2 mol of phenethyltrichlorosilane is added, and the reaction is stirred at 55° C. for 15 hours. After the reaction is completed, it is filtered, washed at 90° C. for 50 minutes, and vacuum dried at 150° C. to prepare a flame retardant;

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

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

[0045] Detection test:

[0046] Limiting oxygen index test: The finished product prepared by the present invention is used as a sample, and the sample is cut into a specimen with a size of 130×7×3 mm, and the test is performed according to ASTMD2836-2017 standard. The test is performed by using an oxygen index instrument, and the oxygen concentration is adjusted so that the resin sample can still maintain stable combustion after the fire source is removed. The oxygen concentration at this time is recorded as the limiting oxygen index, and each sample is tested 3 times and the average value is taken.

[0047] Impact strength: The finished product prepared by the present invention is used as a sample, and the sample is cut into a sample with a size of 80×10×4 mm, and the test is carried out according to GB / T1843-2008 standard. The pendulum impact method is used, and each group of samples is tested 3 times to obtain the average value. The results are as follows:

[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 dosage of Examples 1 to 5 remains unchanged, and only some reaction parameters are modified. It can be seen from the experimental data that there is no obvious fluctuation in the various properties of the sample. Comparative Example 1: The step of compounding the flame retardant is removed, and the rest is the same as 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 27.1MPa. The reason for the analysis is: after removing the step of compounding the flame retardant, only the flame retardant is added to the epoxy resin. Compared with Example 1, the hydrotalcite structure is removed, so the flame retardant properties related to the hydrotalcite structure will be removed accordingly, so the flame retardant properties of the prepared sample will be reduced, and the oxygen index will be reduced; in addition, the hydrotalcite has a layered structure that 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 the hydrotalcite structure is removed.

[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 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 reasons are analyzed as follows: the flame retardant prepared by the present invention contains three flame retardant elements at the same time for synergistic flame retardancy. In addition, by intercalating the flame retardant into the hydrotalcite structure, the flame retardant properties of the hydrotalcite can be compounded to increase, thereby achieving the synergistic flame retardant effect of inorganic-organic combination of multiple flame retardant elements. 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, after replacing the composite flame retardant with the conventional flame retardant 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, the impact strength will also be reduced.

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

[0052] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a halogen-free flame-retardant epoxy resin, characterized in that: The following steps are involved: Step 1: In a nitrogen environment, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is heated to melt, and then N-tert-butyl acrylamide is added, and the reactants are heated to 180-190°C for reaction for 25-30 hours. After the reaction is completed, the reactants are washed and vacuum dried to obtain an intermediate product; the intermediate product, tetramethylpiperidinium nitroxide free radical phosphite and tetrahydrofuran are mixed, stirred and dissolved in an ice water bath, and triethylamine is added to react for 20-30 minutes. After the reaction is completed, phenethyltrichlorosilane is added, and the reaction is stirred at 45-55°C for 10-15 hours. After the reaction is completed, the flame retardant is prepared by filtering, washing and vacuum drying; Step 2: Mix anhydrous magnesium sulfate, aluminum sulfate 18hydrate and 1 / 4 mass part of deionized water to obtain solution 1; mix sodium hydroxide, anhydrous sodium carbonate and 1 / 4 mass part of deionized water to obtain solution 2; mix the flame retardant and 1 / 2 mass part of deionized water, stir at 90-100°C until dissolved, then lower the temperature to 70-80°C, add solution 1 and solution 2, continue stirring and reacting for 3-4h, and after the reaction is completed, filter, wash and dry to prepare a composite flame retardant; Step 3: mechanically stir and blend the epoxy resin and the composite flame retardant at 100-120° C., add 4,4'-diaminodiphenylmethane, and continue stirring for 15-20 minutes to prepare a mixed solution; degas the mixed solution under vacuum for 10-15 minutes and then transfer it to a mold, and prepare a finished product through gradient curing.

2. The method for preparing a halogen-free flame-retardant epoxy resin according to claim 1, characterized in that: In step 1, when preparing the intermediate product, the reaction molar ratio of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and N-tert-butylacrylamide is 1:(1.3-1.5).

3. The method for preparing a halogen-free 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, tetramethylpiperidinium nitroxide free radical phosphite, triethylamine and phenethyltrichlorosilane is (3-5): 1:3:

2.

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

5. The method for preparing a halogen-free flame-retardant epoxy resin according to claim 1, characterized in that: In step 1, when preparing the flame retardant, the vacuum drying temperature is 140-150°C.

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

7. The method for preparing a halogen-free flame-retardant epoxy resin according to claim 1, characterized in that: In step 1, when preparing the flame retardant, the washing parameters are: washing at 80-90°C for 40-50 minutes.

8. The method for preparing a halogen-free flame-retardant epoxy resin according to claim 1, characterized in that: In step 2, the contents of the components of the composite flame retardant are as follows: by mass: 8-10 parts of anhydrous magnesium sulfate, 12-15 parts of aluminum sulfate 18-hydrate, 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.

9. The method for preparing a halogen-free flame-retardant epoxy resin according to claim 1, characterized in that: In step three, the gradient curing parameters are: curing at 120-125°C for 2-3h, curing at 140-145°C for 2-3h, curing at 160-165°C for 2-3h, and curing at 180-185°C for 2-3h.

10. The method for preparing a halogen-free flame-retardant epoxy resin according to claim 1, characterized in that: In step three, the contents of the components of the finished product are: by mass, 100-120 parts of epoxy resin, 15-30 parts of composite flame retardant, and 25-35 parts of 4,4'-diaminodiphenylmethane.