A heat-resistant and pressure-resistant epoxy resin and its preparation method

Abstract

The present invention relates to the technical field of epoxy resins, and particularly relates to a temperature- and pressure-resistant epoxy resin and a preparation method thereof. The preparation method of the epoxy resin comprises the following steps: mixing epichlorohydrin, ethanol and water, adding 4,4'-diaminodiphenylmethane after heating in a water bath to react to obtain a ring-opening intermediate; sequentially adding tea polyphenols, acrylic acid, a crosslinking agent, an initiator and a sodium hydroxide solution, and continuously stirring and reacting to obtain an epoxy resin intermediate; cooling to 30°C or below and slowly adding a sodium hydroxide solution to react again to obtain a crude epoxy resin; finally, extracting with toluene to take the upper resin phase, and obtaining the epoxy resin after solvent removal under reduced pressure and filtration. The epoxy resin of the present invention has both excellent high-temperature resistance and high-pressure resistance at low temperatures, and can be well applied to extreme environments.

Description

Technical Field

[0001] The present invention relates to the technical field of epoxy resins, and more specifically, it relates to a temperature- and pressure-resistant epoxy resin and a preparation method thereof. Background Art

[0002] As a commonly used high molecular compound, epoxy resin has been widely used in many fields such as electronic packaging, coatings, adhesives, etc. due to its excellent dielectric properties, mechanical properties, bonding properties, and the characteristics of small curing shrinkage rate and thermal expansion coefficient.

[0003] In the prior art, in tetrafunctional glycidylamine epoxy resins such as 4,4'-diaminodiphenylmethane tetraglycidylamine, there are multiple epoxy groups and aromatic rings, which can form a relatively high crosslinking density and aromatic density during the curing process, making the cured product exhibit good heat resistance, high mechanical strength, low curing shrinkage rate and other characteristics, and can be used for electrical casting insulation products with better heat resistance requirements.

[0004] However, for some extreme environments, such as low temperature, high pressure, etc., the above epoxy resin is prone to cracking and embrittlement during long-term use in such extreme environments, thereby affecting the normal use of electrical appliances and posing certain potential safety hazards. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a temperature- and pressure-resistant epoxy resin and a preparation method thereof. This epoxy resin has both excellent high-temperature resistance and high-pressure resistance at low temperatures, and can be better applied to extreme environments.

[0006] In the first aspect, the present invention provides a preparation method of a temperature- and pressure-resistant epoxy resin, including the following steps:

[0007] Mix epichlorohydrin, ethanol and water, heat in a water bath to 40 - 45 °C, then add 4,4'-diaminodiphenylmethane, and react at a temperature of 55 - 60 °C for 3 - 4 h to obtain a ring-opening intermediate;

[0008] Sequentially add tea polyphenols, acrylic acid, crosslinking agent, initiator and sodium hydroxide solution to the ring-opening intermediate, and continue to stir and react at a temperature of 75 - 80 °C for 5 - 6 h to obtain an epoxy resin intermediate;

[0009] When the epoxy resin intermediate cools down to 30 °C or below, slowly add sodium hydroxide solution, and control the reaction at a temperature of 30 - 40 °C for 1 - 2 h to obtain a crude epoxy resin;

[0010] Add toluene to the crude epoxy resin for extraction, take the upper resin phase after standing and separating layers, carry out vacuum desolvation, and then obtain the epoxy resin after filtration.

[0011] By adopting the above technical solution, the epoxy resin of the present invention is mainly 4,4'-diaminodiphenylmethane and epichlorohydrin, and 4,4'-diaminodiphenylmethane tetraglycidylamine is prepared by ring opening, cyclization and post-treatment. The present invention uses a mixture of ethanol and water as a promoter and adopts a relatively low temperature to promote more thorough ring opening of epichlorohydrin. Compared with the epoxy resin prepared using ethylene glycol, the present invention has better low temperature and high pressure resistance. The above ring opening and cyclization reaction process can be expressed by the following formula:

[0012]

[0013] On the basis of the above reaction, the present invention further adds tea polyphenol and acrylic acid during the reaction process. The two can be cross-linked under the action of a cross-linking agent, an initiator and a sodium hydroxide solution to generate a tea polyphenol-acrylic acid resin. The tea polyphenol-acrylic acid resin has good weather resistance and can improve the high-pressure resistance of the epoxy resin at low temperatures to a certain extent.

[0014] Because tea polyphenols have a large molecular weight and contain a large number of phenolic hydroxyl groups in their structure, they can also react with epichlorohydrin in the reaction system to generate a high molecular weight tea polyphenol bio-based epoxy resin. This resin and the previous two resins form an interwoven network structure in situ, further improving the epoxy resin's resistance to high temperatures and high pressure at low temperatures after curing, thereby effectively extending its service life in extreme environments.

[0015] In order to ensure the effective progress of the reaction, the present invention strictly controls the addition of tea polyphenols, acrylic acid, crosslinking agent, initiator and a portion of sodium hydroxide solution after 4,4'-diaminodiphenylmethane reacts with epichlorohydrin for 3-4 hours. At this time, the system has completed a large amount of ring opening to generate ring-opening intermediates. The added sodium hydroxide solution can, on the one hand, promote the preliminary cyclization of a portion of the ring-opening intermediates, and on the other hand, promote the tea polyphenols to react with excess epichlorohydrin and acrylic acid respectively. The resins generated by the reaction can directly interpenetrate and crosslink with each other, which has a better crosslinking effect than directly mixing the finished products. The polyhydroxy structure of tea polyphenols realizes the hybrid crosslinking of acrylic acid segments and epoxy segments to form partial hybrid segments. The benzene ring structure introduced by the epoxy resin prepared by 4,4'-diaminodiphenylmethane is combined with the benzene ring structure of tea polyphenols to achieve better distribution between molecules, while promoting better segment distribution of molecular segments such as hybrid segments and acrylic acid segments, thereby further improving the high temperature resistance and pressure resistance of the resin. Sufficient sodium hydroxide solution is subsequently added to promote the reaction to proceed fully, and finally obtain an epoxy resin with excellent heat and pressure resistance.

[0016] Among them, the heat generated during the preliminary cyclization of 4,4'-diaminodiphenylmethane and epichlorohydrin can be used to break the covalent bonds before the crosslinking of acrylic acid, thereby making the temperature during the preliminary cyclization of the intermediate tend to be stable, reducing the situation of local overheating in the system that affects the performance of epoxy resin, and at the same time can also improve the utilization rate of the reaction heat of the system to a certain extent. Adding sodium hydroxide in the form of a solution can also dilute the reaction system, facilitating the uniform dispersion of the subsequent added materials.

[0017] Preferably, the molar ratio of the 4,4'-diaminodiphenylmethane to the epichlorohydrin is 1:5 - 6.

[0018] Preferably, the molar ratio of the 4,4'-diaminodiphenylmethane, tea polyphenols and acrylic acid is 1:0.1 - 0.3:0.5 - 0.6.

[0019] Preferably, the molar ratio of the acrylic acid, crosslinking agent and initiator is 1000:0.15 - 0.25:0.30 - 0.40.

[0020] Preferably, the molar ratio of the 4,4'-diaminodiphenylmethane, ethanol and water is 1:0.4 - 0.6:0.2 - 0.4.

[0021] In the process of preparing epoxy resin in the present invention, both the epoxy resin and tea polyphenols need to be appropriately in excess to meet the requirements of each reaction; if the amount of acrylic acid used is too small, the content of the tea polyphenol-acrylic resin prepared correspondingly is insufficient and it is difficult to play an effective role; if the amount of acrylic acid used is too large, the content of the tea polyphenol-acrylic resin prepared correspondingly is relatively large and will affect the water resistance of the epoxy resin to a certain extent; in addition, the amounts of the crosslinking agent and initiator will directly affect the crosslinking effect of acrylic acid and tea polyphenols, and ethanol and water are promoters for the reaction of 4,4'-diaminodiphenylmethane and epichlorohydrin, directly affecting the progress of the reaction; by strictly controlling the above parameters, each reaction can proceed orderly, and then an epoxy resin with high temperature resistance and high pressure resistance at low temperature can be obtained.

[0022] Preferably, the molar ratio of sodium hydroxide to the 4,4'-diaminodiphenylmethane in the first added sodium hydroxide solution is 2 - 4:1.

[0023] Preferably, the molar ratio of sodium hydroxide to the 4,4'-diaminodiphenylmethane in the second added sodium hydroxide solution is 6 - 8:1.

[0024] With the above technical solution, when adding the sodium hydroxide solution for the first time, the sodium hydroxide not only needs to act in the reaction of 4,4'-diaminodiphenylmethane and epichlorohydrin, but also needs to neutralize acrylic acid first. Therefore, if the addition amount of sodium hydroxide is too small, it will be difficult to effectively generate the acrylic resin. If the addition amount of sodium hydroxide is too large, it will promote the excessive cyclization reaction of 4,4'-diaminodiphenylmethane and epichlorohydrin, affecting the subsequent interpenetrating cross-linking effect of the resin.

[0025] Preferably, the 4,4'-diaminodiphenylmethane is added in multiple portions, with an interval of 20 - 30 minutes each time.

[0026] With the above technical solution, the reaction of 4,4'-diaminodiphenylmethane and epichlorohydrin is exothermic. Adding in multiple portions at certain intervals helps to control the reaction temperature, thereby obtaining an epoxy resin with more excellent performance.

[0027] Preferably, during the solvent removal under reduced pressure, the upper resin phase is kept at a vacuum degree of ≥750 mmHg and a temperature of 120 - 130 °C for 40 - 60 minutes, and then filtered while it is hot.

[0028] After the cyclization reaction ends, a certain amount of sodium chloride and the remaining alkali are generated in the reactants. Therefore, in the present invention, toluene is used for extraction. With the above technical solution, toluene can be effectively recovered and utilized, improving the utilization rate of toluene; and filtering while it is hot helps the epoxy resin to further remove toluene using the remaining heat during filtration, reducing the toluene content in the epoxy resin.

[0029] In the second aspect, the present invention provides a temperature and pressure resistant epoxy resin, which is prepared by the above preparation method, and has excellent high-temperature resistance and low-temperature high-pressure resistance, and can be well applied to extreme environments.

[0030] In summary, the present invention has the following beneficial effects:

[0031] 1. During the reaction of 4,4'-diaminodiphenylmethane and epichlorohydrin, tea polyphenols and acrylic acid are also added in the present invention, thereby obtaining a composite epoxy resin cross-linked by three resins, which has excellent high-temperature resistance and low-temperature high-pressure resistance, and thus effectively extends its service life in extreme environments.

[0032] 2. By controlling the addition timing of tea polyphenols, acrylic acid, cross-linking agent and initiator and adding the sodium hydroxide solution in two portions, the present invention can promote the direct interpenetrating cross-linking of the generated resins, which has a better cross-linking effect compared to directly mixing the finished products, and finally obtains an epoxy resin with excellent temperature and pressure resistance;

[0033] 3. By strictly controlling the dosages of 4,4'-diaminodiphenylmethane, epichlorohydrin, tea polyphenols, acrylic acid, crosslinking agent, initiator, ethanol and water, as well as the two addition amounts of sodium hydroxide solution, the reactions proceed in an orderly manner in the present invention. Detailed implementation manners

[0034] To make the above objects, features and advantages of the present invention more obvious and understandable, the following provides a detailed description of the specific implementation manners of the present invention. Many specific details are set forth in the following description in order to fully understand the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0035] Raw materials

[0036] The raw materials used in the present invention hereinafter are all commercially available products. Among them, the purities of 4,4'-diaminodiphenylmethane, epichlorohydrin and ethanol are all ≥99%, deionized water is used for water, tea polyphenols with a CAS number of 84650-60-2 and a purity of ≥98% are selected, and acrylic acid with a CAS number of 79-10-7 and a purity of ≥99% is selected.

[0037] The crosslinking agent and initiator in the present invention are mainly used to promote the reaction between tea polyphenols and acrylic acid. Among them, N,N'-methylenebisacrylamide is taken as an example to illustrate the crosslinking agent. The initiator is further preferably an initiator that can act at a relatively low temperature (≤85°C), such as potassium persulfate, azobisisobutyronitrile, benzoyl peroxide, etc. However, considering environmental and production safety, potassium persulfate is taken as an example in this application for illustration.

[0038] The mass concentration of the sodium hydroxide solution used in the present invention can fluctuate within the range of 15-30% according to needs. However, considering comprehensive factors such as the viscosity of the reaction system and side reactions, a sodium hydroxide solution with a mass concentration of 25% is preferably used.

[0039] The present invention will be further described in detail below with reference to examples and comparative examples.

[0040] Examples

[0041] Example 1

[0042] This example provides a heat-resistant and pressure-resistant epoxy resin, and its preparation method includes the following steps:

[0043] (1) Ring opening: Mix 518.11 g of epichlorohydrin, 23.04 g of absolute ethanol, and 5.40 g of deionized water. After heating in a water bath to 42 °C, add 198.26 g of 4,4'-diaminodiphenylmethane, and react at a temperature of 52 ± 2 °C for 3.5 h. The 4,4'-diaminodiphenylmethane is added in 4 equal portions at intervals of 25 min to obtain a ring-opening intermediate;

[0044] (2) Crosslinking: Sequentially add 70.34 g of tea polyphenols, 39.63 g of acrylic acid, 0.019 g of N,N'-methylenebisacrylamide, 0.054 g of potassium persulfate, and 480 mL of a 25 wt% sodium hydroxide solution to the ring-opening intermediate obtained in step (1). Continue to stir and react at a temperature of 78 ± 2 °C for 5.5 h to obtain an epoxy resin intermediate;

[0045] (3) Cyclization and re-crosslinking: After the epoxy resin intermediate obtained in step (3) is cooled to 30 °C, slowly add 1120 mL of a 25 wt% sodium hydroxide solution, and react at a temperature of 35 ± 2 °C for 1.5 h to obtain a crude epoxy resin;

[0046] (4) Purification: Add 500 mL of toluene to the crude epoxy resin for extraction. After standing and separating layers, take the upper resin phase. Vacuum the upper resin phase to ≥750 mmHg and keep it at a temperature of 125 ± 2 °C for 60 min for solvent removal under reduced pressure. Filter while it is hot, and cool to room temperature to obtain an epoxy resin.

[0047] Example 2

[0048] This example provides a temperature- and pressure-resistant epoxy resin, and its preparation method includes the following steps:

[0049] (1) Ring opening: Mix 462.60 g of epichlorohydrin, 18.43 g of absolute ethanol, and 3.60 g of deionized water. After heating in a water bath to 45 °C, add 198.26 g of 4,4'-diaminodiphenylmethane, and react at a temperature of 53 ± 2 °C for 5 h. The 4,4'-diaminodiphenylmethane is added in 4 equal portions at intervals of 20 min to obtain a ring-opening intermediate;

[0050] (2) Crosslinking: Sequentially add 28.14 g of tea polyphenols, 36.03 g of acrylic acid, 0.012 g of N,N'-methylenebisacrylamide, 0.041 g of potassium persulfate, and 320 mL of a 25 wt% sodium hydroxide solution to the ring-opening intermediate obtained in step (1). Continue to stir and react at a temperature of 78 ± 2 °C for 5 h to obtain an epoxy resin intermediate;

[0051] (3) Cyclization and re-crosslinking: When the epoxy resin intermediate obtained in step (3) is cooled to 30 °C, slowly add 960 mL of sodium hydroxide solution with a concentration of 25 wt%, and react at a temperature of 32 ± 2 °C for 1 h to obtain crude epoxy resin;

[0052] (4) Purification: Add 400 mL of toluene to the crude epoxy resin for extraction. After standing for layer separation, take the upper resin phase. Vacuum the upper resin phase to ≥750 mmHg and keep it at a temperature of 122 ± 2 °C for 40 min for solvent removal under reduced pressure. Filter while it is hot, and cool to room temperature to obtain epoxy resin.

[0053] Example 3

[0054] This example provides a heat-resistant and pressure-resistant epoxy resin, and its preparation method includes the following steps:

[0055] (1) Ring opening: Mix 555.12 g of epichlorohydrin, 27.64 g of absolute ethanol, and 7.21 g of deionized water, heat in a water bath to 45 °C, then add 198.26 g of 4,4'-diaminodiphenylmethane, and react at a temperature of 53 ± 2 °C for 4 h. 4,4'-diaminodiphenylmethane is added in 4 equal portions at intervals of 30 min to obtain a ring-opening intermediate;

[0056] (2) Crosslinking: Sequentially add 84.41 g of tea polyphenols, 43.24 g of acrylic acid, 0.023 g of N,N'-methylenebisacrylamide, 0.065 g of potassium persulfate, and 640 mL of sodium hydroxide solution with a concentration of 25 wt% to the ring-opening intermediate obtained in step (1), and continue to stir and react at a temperature of 77 ± 2 °C for 6 h to obtain an epoxy resin intermediate;

[0057] (3) Cyclization and re-crosslinking: After the epoxy resin intermediate obtained in step (3) is cooled to 30 °C, slowly add 1280 mL of sodium hydroxide solution with a concentration of 25 wt%, and react at a temperature of 38 ± 2 °C for 2 h to obtain crude epoxy resin;

[0058] (4) Purification: Add 600 mL of toluene to the crude epoxy resin for extraction. After standing for layer separation, take the upper resin phase. Vacuum the upper resin phase to ≥750 mmHg and keep it at a temperature of 128 ± 2 °C for 60 min for solvent removal under reduced pressure. Filter while it is hot, and cool to room temperature to obtain epoxy resin.

[0059] Example 4

[0060] This example provides a heat-resistant and pressure-resistant epoxy resin, and its preparation method includes the following steps:

[0061] (1) Open-loop: Mix 490.36 g of epichlorohydrin, 25.34 g of absolute ethanol, and 4.50 g of deionized water. After heating in a water bath to 42 °C, add 198.26 g of 4,4'-diaminodiphenylmethane, and react at a temperature of 52 ± 2 °C for 3.5 h. The 4,4'-diaminodiphenylmethane is added in 4 equal portions at intervals of 25 min to obtain an open-loop intermediate;

[0062] (2) Crosslinking: Sequentially add 56.27 g of tea polyphenols, 41.07 g of acrylic acid, 0.015 g of N,N'-methylenebisacrylamide, 0.059 g of potassium persulfate, and 480 mL of a 25 wt% sodium hydroxide solution to the open-loop intermediate obtained in step (1). Continue to stir and react at a temperature of 78 ± 2 °C for 5.5 h to obtain an epoxy resin intermediate;

[0063] (3) Cyclization and re-crosslinking: After the epoxy resin intermediate obtained in step (3) cools to 30 °C, slowly add 1120 mL of a 25 wt% sodium hydroxide solution, and react at a temperature of 35 ± 2 °C for 1.5 h to obtain a crude epoxy resin;

[0064] (4) Purification: Add 500 mL of toluene to the crude epoxy resin for extraction. After standing and separating layers, take the upper resin phase. Vacuum the upper resin phase to a vacuum degree of ≥ 750 mmHg and keep it at a temperature of 125 ± 2 °C for 60 min for solvent removal under reduced pressure. Filter while it is hot, and cool to room temperature to obtain the epoxy resin.

[0065] Example 5

[0066] In this example, based on the method of Example 1, the amount of epichlorohydrin is adjusted to 416.34 g, that is, the molar ratio of 4,4'-diaminodiphenylmethane to epichlorohydrin is 1:4.5.

[0067] Example 6

[0068] In this example, based on the method of Example 1, the amount of tea polyphenols is adjusted to 98.48 g, that is, the molar ratio of 4,4'-diaminodiphenylmethane, tea polyphenols, and acrylic acid is 1:0.35:0.55.

[0069] Example 7

[0070] In this example, based on the method of Example 1, the amount of acrylic acid is adjusted to 45.40 g, that is, the molar ratio of 4,4'-diaminodiphenylmethane, tea polyphenols, and acrylic acid is 1:0.25:0.63.

[0071] Example 8

[0072] Based on the method of Example 1, in this example, the dosages of N,N'-methylenebisacrylamide and potassium persulfate are adjusted. The dosage of N,N'-methylenebisacrylamide is 0.09 g, and the dosage of potassium persulfate is 0.070 g. That is, the molar ratio of acrylic acid, 3.85 g of N,N'-methylenebisacrylamide and potassium persulfate is approximately 1000:0.11:0.47.

[0073] Example 9

[0074] Based on the method of Example 1, in this example, the dosages of ethanol and deionized water are adjusted. The dosage of ethanol is 13.82 g, and the dosage of deionized water is 9.01 g. That is, the molar ratio of 4,4'-diaminodiphenylmethane, ethanol and water is 1:0.3:0.5.

[0075] Example 10

[0076] Based on the method of Example 1, in this example, the dosages of the two sodium hydroxide solutions are adjusted. The dosage added for the first time is 560 mL, and the dosage added for the second time is 1040 mL.

[0077] Example 11

[0078] Based on the method of Example 1, in this example, the dosage of the sodium hydroxide solution added for the first time is adjusted to 160 mL.

[0079] Example 12

[0080] Based on the method of Example 1, in this example, the dosage of the sodium hydroxide solution added for the second time is adjusted to 1440 mL.

[0081] Example 13

[0082] Based on the method of Example 1, in this example, 4,4'-diaminodiphenylmethane is added in one portion.

[0083] Comparative Example

[0084] Comparative Example 1

[0085] This comparative example is commercially available epoxy resin AG-80.

[0086] Comparative Example 2

[0087] This comparative example is prepared by stirring and mixing 614.60 g of commercially available epoxy resin AG-80 with the following self-made tea polyphenol bio-based epoxy resin and tea polyphenol-acrylic resin.

[0088] The preparation method of the above tea polyphenol bio-based epoxy resin is as follows:

[0089] Add 70 g of tea polyphenols and 101.77 g of epichlorohydrin to a reaction kettle. Under the protection of nitrogen, stir and mix evenly at a rotation speed of 250 r / min. During the stirring process, add 9.6 g of sodium hydroxide, and control the continuous reaction at a temperature of 65 °C for 4 h. Filter while it is hot to obtain the crude resin. Dissolve the crude resin thoroughly with 130 mL of toluene, then add 100 mL of a 5 wt% suspension of porous nano-calcium carbonate (prepared by dispersing 5 g of commercially available porous nano-calcium carbonate in 100 mL of deionized water). While stirring, control the temperature at 65 °C and react for 4 h. Subsequently, adjust the pH of the system to 6.5 with a 2 wt% phosphoric acid solution, let it stand to separate the resin layer and the water layer, and then take the resin layer. Finally, keep the harvested resin layer under a vacuum of ≥750 mmHg and at a temperature of 125 ± 2 °C for 60 min to carry out solvent decompression removal, and thus obtain the tea polyphenol bio-based epoxy resin;

[0090] The preparation method of the above-mentioned tea polyphenol-acrylic resin is as follows:

[0091] Under the conditions of ice-water bath and stirring, take 100 mL of a 25 wt% sodium hydroxide solution and carry out a neutralization reaction with 39.63 g of acrylic acid. Add 20 mL of an aqueous solution of N,N'-methylenebisacrylamide (containing 0.019 g of N,N'-methylenebisacrylamide) and stir for 5 min, then add 0.054 g of potassium persulfate and stir until it is completely dissolved. Then add 10 mL of an aqueous solution containing 0.34 g of tea polyphenols to the reaction system, stir and mix evenly. Place the obtained mixed solution in an oven at a temperature of 80 °C for a polymerization reaction for 2 h. After obtaining a transparent gel, carry out cooling, shearing, drying and pulverization in sequence, and thus obtain the tea polyphenol-acrylic resin.

[0092] Comparative Example 3

[0093] Based on the method of Example 1, this comparative example adjusts "directly carry out cyclization after ring opening", and the specific preparation method is as follows:

[0094] (1) Ring opening: Mix 518.11 g of epichlorohydrin, 23.04 g of absolute ethanol and 5.40 g of deionized water, heat in a water bath to 42 °C, then add 198.26 g of 4,4'-diaminodiphenylmethane, and keep the reaction at a temperature of 52 ± 2 °C for 3.5 h. Divide 4,4'-diaminodiphenylmethane into 4 equal portions and add them at intervals of 25 min to obtain a ring-opening intermediate;

[0095] (2) Cyclization: After cooling the ring-opening intermediate obtained in step (1) to 30 °C, slowly add 1120 mL of a 25 wt% sodium hydroxide solution, and control the reaction at a temperature of 35 ± 2 °C for 1.5 h to obtain the crude epoxy resin;

[0096] (3) Crosslinking: 70.34 g of tea polyphenols, 39.63 g of acrylic acid, 0.019 g of N,N'-methylenebisacrylamide, 0.054 g of potassium persulfate and 480 mL of sodium hydroxide solution with a concentration of 25 wt% were successively added to the crude epoxy resin obtained in step (2), and the mixture was continuously stirred and reacted at a temperature of 78 ± 2 °C for 5.5 h to obtain a crosslinked epoxy resin material;

[0097] (4) Purification: 500 mL of toluene was added to the crosslinked epoxy resin material for extraction. After standing for stratification, the upper resin phase was taken. The upper resin phase was kept under reduced pressure to remove the solvent at a vacuum degree of ≥ 750 mmHg and a temperature of 125 ± 2 °C for 60 min, filtered while it was hot, and cooled to room temperature to obtain epoxy resin.

[0098] Comparative Example 4

[0099] In this comparative example, based on the method of Example 1, ethanol was replaced with the same molar amount of ethylene glycol.

[0100] Comparative Example 5

[0101] In this comparative example, based on the method of Example 1, tea polyphenols were replaced with the same molar amount of hydroquinone.

[0102] Comparative Example 6

[0103] In this comparative example, based on the method of Example 1, 4,4'-diaminodiphenylmethane was replaced with the same molar amount of 4,4'-diaminodicyclohexylmethane.

[0104] Performance testing

[0105] The epoxy resins of the above Examples 1 - 12 and Comparative Examples 1 - 3 were used as Specimen 1, and the epoxy value, total chlorine content, viscosity and yield were measured. Among them, the epoxy value was measured by Method A of GB / T 1677 - 2008, the total chlorine content of the epoxy resin was measured according to the standard of EN 14582 - 2016, and the viscosity was measured according to the standard of GB / T 22314 - 2008.

[0106] Specimen 1 was mixed with the curing agent DDM in a molar ratio of epoxy to NH of 1:1, heated to 110 °C in an oven for curing, and cooled to room temperature after complete curing to obtain a cured epoxy resin material as Specimen 2, and the high-temperature resistance and high-pressure resistance at low temperature were measured.

[0107] Among them, the high-temperature resistance is reflected by the glass transition temperature, and it is specifically measured by a DSC instrument. The high-pressure resistance at low temperature is reflected by the breakdown voltage, shear strength, and peel strength detected under the conditions of a temperature of -70°C and a humidity of 65%. The breakdown voltage is measured with reference to the GB / T 1408.1-2016 standard; when measuring the shear strength and peel strength, Specimen II is first coated on the test plate before curing and then the test plate is placed in an oven for curing. The shear strength is specifically measured with reference to the GB / T 7124-2008 standard (the test plate is 45# steel), and the peel strength is specifically measured with reference to the GJB 94-1986 standard (both the test plate and the test block are 45# steel).

[0108] The test results are shown in Table 1 below.

[0109] Table 1 Test Results of Epoxy Resins of Examples 1-12 and Comparative Examples 1-3

[0110]

[0111]

[0112] Referring to Table 1, by comparing the test results of Example 1 with those of Comparative Examples 1-3, it can be obtained that the epoxy resin of the present invention has a lower total chlorine content, a higher glass transition temperature, and more excellent breakdown voltage, shear strength, and peel strength at low temperature (-70°C) compared with conventional tetrafunctional glycidylamine epoxy resins (AG-80), a composite epoxy resin obtained by directly stirring and mixing three resins (tetrafunctional glycidylamine epoxy resin, tea polyphenol bio-based epoxy resin, and tea polyphenol-acrylic resin), and an epoxy resin obtained by "directly cyclizing after ring opening". Therefore, the epoxy resin of the present invention has both excellent high-temperature resistance and high-pressure resistance at low temperature, and can effectively reduce its corrosive effect on electrical components, and can be well applicable to extreme environments for a long time.

[0113] From the test results of Examples 1-12, it can be seen that different dosage ratios of raw materials and process parameters in the present invention will have a certain impact on the performance of the epoxy resin. Among them, by comparing the test results of Example 1 with those of Example 4, it can be obtained that there is a more preferable ratio within the range of raw material dosages. Although the dosage of Example 4 is relatively close to that of Example 1, from the test results, the total chlorine content, yield, glass transition temperature, and breakdown voltage, shear strength, and peel strength at low temperature (-70°C) of Example 1 are all better than those of Example 4. Therefore, Example 1 in the present invention is a further preferred example.

[0114] Comparing the test results of Example 1 with those of Examples 5-7, it can be obtained that adjusting the dosage of any one of epichlorohydrin, tea polyphenols, and acrylic acid in the present invention will have a great impact on the performance of the epoxy resin. This is because there are three resin forming and interpenetrating cross-linkings during the reaction to prepare the epoxy resin in the present invention. Adjusting the above raw materials will directly lead to the reaction process. Therefore, the present invention further limits that "the molar ratio of 4,4'-diaminodiphenylmethane to epichlorohydrin is 1:5-6" and "the molar ratio of 4,4'-diaminodiphenylmethane, tea polyphenols, and acrylic acid is 1:0.1-0.3:0.5-0.6", and the epoxy resin obtained thereby has more excellent performance.

[0115] Comparing the test results of Example 1 with those of Example 8, it can be obtained that the performance of the epoxy resin of the present invention will also be indirectly affected by the cross-linking agent and the initiator. This is because the cross-linking agent and the initiator are one of the key factors promoting the cross-linking of acrylic acid and tea polyphenols. Therefore, the present invention further limits that the molar ratio of acrylic acid, cross-linking agent to initiator is 1000:0.15-0.25:0.30-0.40, thereby ensuring the excellent high-temperature resistance and high-pressure resistance at low temperature of the epoxy resin.

[0116] Comparing the test results of Example 1 with those of Example 9 and Comparative Example 4, it can be obtained that, compared with using ethylene glycol and water as the accelerator, the scheme of using ethanol and water as the accelerator in the present invention can obtain an epoxy resin with more excellent high-temperature resistance and high-pressure resistance at low temperature. Among them, the scheme of "the molar ratio of 4,4'-diaminodiphenylmethane, ethanol and water is 1:0.4-0.6:0.2-0.4" is further preferred.

[0117] Comparing the test results of Example 1 with those of Examples 10-12, it can be obtained that the two addition amounts of the sodium hydroxide solution in the present invention both need to be limited. Among them, the epoxy resin obtained when "the molar ratio of sodium hydroxide to 4,4'-diaminodiphenylmethane in the first added sodium hydroxide solution is 2-4:1, and the molar ratio of sodium hydroxide to 4,4'-diaminodiphenylmethane in the second added sodium hydroxide solution is 6-8:1" is preferred.

[0118] Comparing the test results of Example 1 with those of Example 13, it can be obtained that the method of adding 4,4'-diaminodiphenylmethane in several portions at intervals of a certain time in the present invention is helpful for controlling the reaction temperature, and thereby an epoxy resin with more excellent performance is obtained.

[0119] Comparing the test results of Example 1 with those of Comparative Examples 5-6, it can be obtained that the present invention uses tea polyphenols and 4,4'-diaminodiphenylmethane in the cross-linking step, and the epoxy resin obtained thereby has a higher glass transition temperature, breakdown voltage and mechanical strength. In addition, the total chlorine content can also be reduced.

[0120] This specific embodiment is only an interpretation of the present invention and is not a limitation thereof. After reading this specification, those skilled in the art may make modifications to this embodiment that do not contribute creatively as needed, but as long as they are within the scope of the claims of the present invention, they are protected by the patent law.

Claims

1. A preparation method of a temperature and pressure resistant epoxy resin, characterized in that, It includes the following steps: Mix epichlorohydrin, ethanol and water, heat them in a water bath to 40 - 45°C, then add 4,4'-diaminodiphenylmethane, and react at a temperature of 50 - 55°C for 3 - 4 h to obtain a ring-opening intermediate; Sequentially add tea polyphenols, acrylic acid, crosslinking agent, initiator and sodium hydroxide solution to the ring-opening intermediate, and continue to stir and react at a temperature of 75 - 80°C for 5 - 6 h to obtain an epoxy resin intermediate; Wait for the epoxy resin intermediate to cool down to 30°C or below, slowly add sodium hydroxide solution, and control the reaction at a temperature of 30 - 40°C for 1 - 2 h to obtain crude epoxy resin; Add toluene to the crude epoxy resin for extraction, take the upper resin phase after standing and separating layers, carry out solvent removal under reduced pressure, and then obtain the epoxy resin after filtration; The molar ratio of 4,4'-diaminodiphenylmethane, tea polyphenols and acrylic acid is 1:0.1 - 0.3:0.5 - 0.

6.

2. The preparation method according to claim 1, wherein: The molar ratio of 4,4'-diaminodiphenylmethane and epichlorohydrin is 1:5 - 6.

3. The preparation method according to claim 1, characterized in that: The molar ratio of acrylic acid, crosslinking agent and initiator is 1000:0.15 - 0.25:0.30 - 0.

40.

4. The preparation method according to claim 1, characterized in that: The molar ratio of 4,4'-diaminodiphenylmethane, ethanol and water is 1:0.4 - 0.6:0.2 - 0.

4.

5. The preparation method according to claim 1, wherein: In the sodium hydroxide solution added for the first time, the molar ratio of sodium hydroxide to 4,4'-diaminodiphenylmethane is 2 - 4:

1.

6. The preparation method according to claim 5, characterized in that: In the sodium hydroxide solution added for the second time, the molar ratio of sodium hydroxide to 4,4'-diaminodiphenylmethane is 6 - 8:

1.

7. The preparation method according to claim 1, characterized in that: The 4,4'-diaminodiphenylmethane is added in multiple times, with an interval of 20 - 30 min each time.

8. The preparation method according to claim 1, characterized in that: During solvent removal under reduced pressure, keep the upper resin phase at a vacuum degree of ≥750 mmHg and a temperature of 120 - 130°C for 40 - 60 min, and filter while it is hot.

9. A temperature and pressure resistant epoxy resin, characterized in that, It is prepared by using the preparation method described in any one of claims 1 - 8.

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