Temperature-resistant and pressure-resistant epoxy resin and preparation method thereof

Abstract

The invention relates to the technical field of epoxy resin, in particular to temperature-resistant and pressure-resistant epoxy resin and a preparation method thereof. The preparation method of the epoxy resin comprises the following steps: uniformly mixing epichlorohydrin, ethanol and water, heating in a water bath, adding 4, 4 '-diaminodiphenylmethane, and reacting to obtain a ring-opening intermediate; sequentially adding tea polyphenol, acrylic acid, a cross-linking agent, an initiator and a sodium hydroxide solution, and continuously stirring and reacting to obtain an epoxy resin intermediate; cooling to 30 DEG C or below, slowly adding a sodium hydroxide solution, and reacting to obtain an epoxy resin coarse material; and finally, extracting by using methylbenzene to take an upper-layer resin phase, desolventizing under reduced pressure, and filtering to obtain the epoxy resin. The epoxy resin provided by the invention has excellent high temperature resistance and high pressure resistance at low temperature, and can be well suitable for extreme environments.

Description

Technical Field

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

[0002] As a commonly used polymer 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, as well as small curing shrinkage and thermal expansion coefficient.

[0003] In the prior art, tetrafunctional glycidylamine epoxy resins such as 4,4'-diaminodiphenylmethane tetraglycidylamine have multiple epoxy group aromatic rings, which can form a higher cross-linking density and aromatic density during the curing process, so that the cured product exhibits good heat resistance, high mechanical strength, low curing shrinkage, etc., and can be used for electrical cast insulation products with good heat resistance requirements.

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

[0005] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a heat-resistant and pressure-resistant epoxy resin and a preparation method thereof. The epoxy resin has excellent high-temperature resistance and high-pressure resistance at low temperatures, and can be well applied in extreme environments.

[0006] In a first aspect, the present invention provides a method for preparing a heat-resistant and pressure-resistant epoxy resin, comprising the following steps:

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

[0008] Adding tea polyphenol, acrylic acid, a crosslinking agent, an initiator and a sodium hydroxide solution to the ring-opening intermediate in sequence, and continuing to stir and react at a temperature of 75-80° C. for 5-6 hours to obtain an epoxy resin intermediate;

[0009] When the epoxy resin intermediate is cooled to 30° C. or below, a sodium hydroxide solution is slowly added, and the reaction is controlled at a temperature of 30-40° C. for 1-2 hours to obtain a crude epoxy resin;

[0010] Toluene is added to the crude epoxy resin for extraction, and after standing for stratification, the upper resin phase is taken out, the solvent is removed under reduced pressure, and then the epoxy resin is obtained after filtration.

[0011] By adopting the above technical scheme, 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, wherein the present invention adopts a mixture of ethanol and water as an accelerator and adopts a relatively low temperature to promote the ring opening of epichlorohydrin more thoroughly. Compared with the epoxy resin prepared by 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 polyphenols and acrylic acid during the reaction process, and 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, and the tea polyphenol-acrylic acid resin has good weather resistance, which can improve the high pressure resistance of epoxy resin at low temperature to a certain extent;

[0014] Since 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 generate an interwoven network structure in situ, further improving the high temperature resistance and high pressure resistance at low temperatures of the epoxy resin 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 part 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 open-ring intermediates. The added sodium hydroxide solution can promote the initial cyclization of a part of the open-ring intermediates on the one hand, and promote the tea polyphenols to react with excess epichlorohydrin and acrylic acid respectively on the other hand. 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, and at the same time promotes the hybrid segments, acrylic acid segments and other molecular segments to achieve better segment distribution, 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 be fully carried out, and finally obtain epoxy resin with excellent heat and pressure resistance.

[0016] The heat generated by the initial cyclization of 4,4'-diaminodiphenylmethane and epichlorohydrin can be used to break the covalent bond before acrylic acid cross-linking, thereby stabilizing the temperature of the intermediate during the initial cyclization, reducing the situation where the system is overheated locally and affects the performance of the epoxy resin, and at the same time, it can also improve the utilization rate of the system reaction heat to a certain extent. The addition of sodium hydroxide in the form of a solution can also dilute the reaction system, making it easier for the subsequent added materials to be evenly dispersed.

[0017] Preferably, the molar ratio of 4,4'-diaminodiphenylmethane to 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, the crosslinking agent and the initiator is 1000:0.15-0.25:0.30-0.40.

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

[0021] In the process of preparing epoxy resin of the present invention, both epoxy resin and tea polyphenol need to be appropriately excessive to meet the requirements of each reaction; if the amount of acrylic acid used is too little, the content of the corresponding tea polyphenol-acrylic resin prepared is insufficient and it is difficult to play an effective role; if the amount of acrylic acid used is too much, the content of the corresponding tea polyphenol-acrylic resin prepared is relatively high and will affect the water resistance of the epoxy resin to a certain extent; in addition, the amount of crosslinking agent and initiator used will directly affect the crosslinking effect of acrylic acid and tea polyphenol, and ethanol and water are accelerators for the reaction of 4,4'-diaminodiphenylmethane and epichlorohydrin, which directly affect the progress of the reaction; by strictly controlling the above parameters, each reaction can be carried out in an orderly manner, thereby obtaining an epoxy resin that is resistant to high temperature and high pressure at low temperature.

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

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

[0024] When the above technical solution is adopted, when the sodium hydroxide solution is added for the first time, the sodium hydroxide not only needs to act on the reaction between 4,4'-diaminodiphenylmethane and epichlorohydrin, but also needs to neutralize the acrylic acid first. Therefore, if the amount of sodium hydroxide added is too little, it will cause the acrylic resin to be difficult to effectively generate. If the amount of sodium hydroxide added is too much, it will promote the excessive cyclization reaction of 4,4'-diaminodiphenylmethane and epichlorohydrin, which will subsequently affect the interlaced cross-linking effect of the resin.

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

[0026] By adopting the above technical scheme, 4,4'-diaminodiphenylmethane and epichlorohydrin react to release heat, and adding them several times at certain intervals is helpful to control the reaction temperature, thereby obtaining an epoxy resin with better performance.

[0027] Preferably, during the desolventizing, the upper resin phase is kept at a vacuum degree of ≥750 mmHg and a temperature of 120-130° C. for 40-60 min, and filtered while hot.

[0028] After the cyclization reaction is completed, the reactants produce a certain amount of sodium chloride and residual alkali. Therefore, the present invention uses toluene for extraction. By adopting the above technical scheme, toluene can be effectively recovered for utilization, thereby improving the utilization rate of toluene; and hot filtration helps the epoxy resin to further remove toluene by utilizing the residual temperature during filtration, thereby reducing the toluene content in the epoxy resin.

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

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

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

[0032] 2. The present invention controls the timing of adding tea polyphenols, acrylic acid, crosslinking agent and initiator and adds sodium hydroxide solution twice, so that the resins generated by the reaction can be directly crosslinked with each other, which has a better crosslinking effect than directly mixing the finished products, and finally obtains an epoxy resin with excellent heat and pressure resistance;

[0033] 3. The present invention strictly controls the amounts of 4,4'-diaminodiphenylmethane, epichlorohydrin, tea polyphenols, acrylic acid, crosslinking agent, initiator, ethanol and water, as well as the amounts of sodium hydroxide solution added twice, so that each reaction can proceed in an orderly manner. DETAILED DESCRIPTION

[0034] In order to make the above-mentioned purpose, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below. In the following description, many specific details are set forth to facilitate a full understanding of 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 violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0035] raw material

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

[0037] The crosslinking agent and initiator in the present invention are mainly used to promote the reaction of tea polyphenols and acrylic acid, wherein the crosslinking agent is illustrated by taking N,N'-methylenebisacrylamide as an example, and 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 the environment and production safety, this application takes potassium persulfate as an example for illustration.

[0038] The mass concentration of the sodium hydroxide solution used in the present invention can fluctuate within the range of 15-30% as required, but 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 is further described in detail below with reference to Examples and Comparative Examples.

[0040] Example

[0041] Example 1

[0042] This embodiment provides a heat-resistant and pressure-resistant epoxy resin, and a preparation method thereof comprises the following steps:

[0043] (1) Ring opening: 518.11 g of epichlorohydrin, 23.04 g of anhydrous ethanol and 5.40 g of deionized water were mixed, heated to 42°C in a water bath, and then 198.26 g of 4,4'-diaminodiphenylmethane was added. The temperature was maintained at 52±2°C and the reaction was continued for 3.5 h. 4,4'-diaminodiphenylmethane was added in 4 portions, each time with an interval of 25 min, to obtain a ring-opening intermediate.

[0044] (2) Cross-linking: 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 were added to the ring-opening intermediate obtained in step (1) in sequence, and the reaction was continued under stirring at 78±2°C for 5.5 h to obtain an epoxy resin intermediate;

[0045] (3) Cyclization and cross-linking: After the epoxy resin intermediate obtained in step (3) is cooled to 30° C., 1120 mL of a 25 wt % sodium hydroxide solution is slowly added, and the reaction is controlled 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 for stratification, take the upper resin phase, and keep the upper resin phase at a vacuum degree of ≥750 mmHg and a temperature of 125±2°C for 60 min to remove the solvent under reduced pressure. Filter while hot and cool to room temperature to obtain the epoxy resin.

[0047] Example 2

[0048] This embodiment provides a heat-resistant and pressure-resistant epoxy resin, and a preparation method thereof comprises the following steps:

[0049] (1) Ring opening: 462.60 g of epichlorohydrin, 18.43 g of anhydrous ethanol and 3.60 g of deionized water were mixed, heated in a water bath to 45°C, and then 198.26 g of 4,4'-diaminodiphenylmethane was added. The temperature was maintained at 53±2°C and the reaction was continued for 5 h. 4,4'-diaminodiphenylmethane was added in 4 portions, each time with an interval of 20 min, to obtain a ring-opening intermediate.

[0050] (2) Cross-linking: 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 were added to the ring-opening intermediate obtained in step (1) in sequence, and the reaction was continued under stirring at 78±2°C for 5 h to obtain an epoxy resin intermediate;

[0051] (3) Cyclization and cross-linking: When the epoxy resin intermediate obtained in step (3) is cooled to 30° C., 960 mL of a 25 wt % sodium hydroxide solution is slowly added, and the reaction is controlled at a temperature of 32±2° C. for 1 h to obtain a crude epoxy resin;

[0052] (4) Purification: 400 mL of toluene was added to the crude epoxy resin for extraction. After standing for stratification, the upper resin phase was taken out, and the upper resin phase was kept at a vacuum degree of ≥750 mmHg and a temperature of 122±2°C for 40 min for decompression and solvent removal. The upper resin phase was filtered while hot and cooled to room temperature to obtain epoxy resin.

[0053] Example 3

[0054] This embodiment provides a heat-resistant and pressure-resistant epoxy resin, and a preparation method thereof comprises the following steps:

[0055] (1) Ring opening: 555.12 g of epichlorohydrin, 27.64 g of anhydrous ethanol and 7.21 g of deionized water were mixed, heated to 45°C in a water bath, and then 198.26 g of 4,4'-diaminodiphenylmethane was added. The temperature was maintained at 53±2°C and the reaction was continued for 4 h. 4,4'-diaminodiphenylmethane was added in 4 portions, each time with an interval of 30 min, to obtain a ring-opening intermediate.

[0056] (2) Cross-linking: 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 a 25 wt% sodium hydroxide solution were added to the ring-opening intermediate obtained in step (1) in sequence, and the reaction was continued under stirring at 77±2°C for 6 h to obtain an epoxy resin intermediate;

[0057] (3) Cyclization and cross-linking: After the epoxy resin intermediate obtained in step (3) is cooled to 30° C., 1280 mL of a 25 wt % sodium hydroxide solution is slowly added, and the reaction is controlled at a temperature of 38±2° C. for 2 h to obtain a crude epoxy resin;

[0058] (4) Purification: 600 mL of toluene was added to the crude epoxy resin for extraction. After standing for stratification, the upper resin phase was taken out, and the upper resin phase was kept at a vacuum degree of ≥750 mmHg and a temperature of 128±2°C for 60 min for decompression and solvent removal. The upper resin phase was filtered while hot and cooled to room temperature to obtain epoxy resin.

[0059] Example 4

[0060] This embodiment provides a heat-resistant and pressure-resistant epoxy resin, and a preparation method thereof comprises the following steps:

[0061] (1) Ring opening: 490.36 g of epichlorohydrin, 25.34 g of anhydrous ethanol and 4.50 g of deionized water were mixed, heated in a water bath to 42°C, and then 198.26 g of 4,4'-diaminodiphenylmethane was added. The temperature was maintained at 52±2°C and the reaction was continued for 3.5 h. 4,4'-diaminodiphenylmethane was added in 4 portions, each time with an interval of 25 min, to obtain a ring-opening intermediate;

[0062] (2) Cross-linking: 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 25 wt% sodium hydroxide solution were added to the ring-opening intermediate obtained in step (1) in sequence, and the reaction was continued under stirring at 78±2°C for 5.5 h to obtain an epoxy resin intermediate;

[0063] (3) Cyclization and cross-linking: After the epoxy resin intermediate obtained in step (3) is cooled to 30° C., 1120 mL of a 25 wt % sodium hydroxide solution is slowly added, and the reaction is controlled 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 for stratification, take the upper resin phase, and keep the upper resin phase at a vacuum degree of ≥750 mmHg and a temperature of 125±2°C for 60 min to remove the solvent under reduced pressure. Filter while 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 used 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 used 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 used 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] In this example, based on the method of Example 1, the amounts of N,N'-methylenebisacrylamide and potassium persulfate were adjusted, wherein the amount of N,N'-methylenebisacrylamide was 0.09 g, and the amount of potassium persulfate was 0.070 g, that is, the molar ratio of acrylic acid, 3.85 g of N,N'-methylenebisacrylamide and potassium persulfate was approximately 1000:0.11:0.47.

[0073] Example 9

[0074] In this embodiment, based on the method of embodiment 1, the amounts of ethanol and deionized water are adjusted, wherein the amount of ethanol is 13.82 g, and the amount 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] In this embodiment, based on the method of embodiment 1, the dosage of the two sodium hydroxide solutions is adjusted, wherein the dosage of the first addition is 560 mL, and the dosage of the second addition is 1040 mL.

[0077] Embodiment 11

[0078] In this embodiment, based on the method of embodiment 1, the amount of the first addition of sodium hydroxide solution is adjusted to 160 mL.

[0079] Example 12

[0080] In this embodiment, based on the method of embodiment 1, the amount of the second addition of sodium hydroxide solution is adjusted to 1440 mL.

[0081] Example 13

[0082] In this embodiment, based on the method of embodiment 1, 4,4'-diaminodiphenylmethane is added at one time.

[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 mixing 614.60 g of commercially available epoxy resin AG-80 with the following homemade tea polyphenol bio-based epoxy resin and tea polyphenol-acrylic resin by stirring.

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

[0089] 70g of tea polyphenols and 101.77g of epichlorohydrin are added to a reactor, and under the protection of nitrogen, the mixture is stirred and mixed at a speed of 250r / min, 9.6g of sodium hydroxide is added during the stirring process, and the reaction is continuously carried out at a temperature of 65°C for 4h, and the crude resin is filtered while hot; the crude resin is fully dissolved with 130mL of toluene, and then 100mL of a 5wt% porous nano calcium carbonate suspension (obtained by dispersing 5g of commercially available porous nano calcium carbonate in 100mL of deionized water) is added, and the temperature is controlled to react at 65°C for 4h while stirring, and then the pH of the system is adjusted to 6.5 with a 2wt% phosphoric acid solution, and the resin layer is taken after standing to separate the resin layer and the water layer; finally, the harvested resin layer is decompressed and desolventized at a vacuum degree of ≥750mmHg and a temperature of 125±2°C for 60min to obtain a tea polyphenol bio-based epoxy resin;

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

[0091] In an ice-water bath and under stirring conditions, 100 mL of 25 wt% sodium hydroxide solution was taken to neutralize 39.63 g of acrylic acid, and 20 mL of N, N'-methylenebisacrylamide aqueous solution (containing 0.019 g of N, N'-methylenebisacrylamide) was added and stirred for 5 min, and then 0.054 g of potassium persulfate was added and stirred until it was completely dissolved. Then 10 mL of 0.34 g of tea polyphenols aqueous solution was added to the reaction system and stirred and mixed, and the obtained mixed solution was placed in an oven at a temperature of 80°C for polymerization reaction for 2 h, and after obtaining a transparent gel, it was cooled, sheared, dried and crushed in sequence to obtain tea polyphenols-acrylic resin.

[0092] Comparative Example 3

[0093] This comparative example is based on the method of Example 1, and the adjustment is made to "directly perform cyclization after ring opening". The specific preparation method is as follows:

[0094] (1) Ring opening: 518.11 g of epichlorohydrin, 23.04 g of anhydrous ethanol and 5.40 g of deionized water were mixed, heated to 42°C in a water bath, and then 198.26 g of 4,4'-diaminodiphenylmethane was added. The temperature was maintained at 52±2°C and the reaction was continued for 3.5 h. 4,4'-diaminodiphenylmethane was added in 4 portions, each time with an interval 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., 1120 mL of a 25 wt % sodium hydroxide solution was slowly added, and the reaction was controlled at a temperature of 35±2° C. for 1.5 h to obtain a crude epoxy resin;

[0096] (3) Cross-linking: 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 25 wt% sodium hydroxide solution were added to the epoxy resin crude material obtained in step (2) in sequence, and the reaction was continued under stirring at 78±2°C for 5.5 h to obtain an epoxy resin cross-linked material;

[0097] (4) Purification: Add 500 mL of toluene to the epoxy resin crosslinking material for extraction. After standing for stratification, take the upper resin phase, and keep the upper resin phase at a vacuum degree of ≥750 mmHg and a temperature of 125±2°C for 60 min to remove the solvent under reduced pressure. Filter while hot and cool 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 ethylene glycol of the same molar amount.

[0100] Comparative Example 5

[0101] In this comparative example, based on the method of Example 1, tea polyphenols were replaced with an equal 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 an equal molar amount of 4,4'-diaminodicyclohexylmethane.

[0104] Performance Testing

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

[0106] Sample 1 was mixed with curing agent DDM in a molar ratio of epoxy to NH:1, and cured in an oven at 110°C. After complete curing, it was cooled to room temperature to obtain epoxy resin curing material as sample 2, and its resistance to high temperature and high pressure at low temperature was tested.

[0107] Among them, the high temperature resistance is reflected by the glass transition temperature, which is specifically measured by a DSC instrument. The high pressure resistance at low temperature is reflected by the breakdown voltage, shear strength and tear strength tested at 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 tear strength, the sample 2 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 tear 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 a better breakdown voltage, shear strength, and tear strength at low temperature (-70°C) than the conventional tetrafunctional glycidylamine epoxy resin (AG-80), the 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 the 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 voltage resistance at low temperature, and can effectively reduce its corrosion to electrical devices, and can be well applied in extreme environments for a long time.

[0113] It can be seen from the test results of Examples 1-12 that the different ratios of the raw materials used and the 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 that of Example 4, it can be obtained that there is a more preferred ratio within the range of the raw material dosage, wherein the dosage of Example 4 is relatively close to that of Example 1, but it can be seen from the test results that the total chlorine content, yield, glass transition temperature, and breakdown voltage, shear strength and tear strength at low temperature (-70°C) of Example 1 are all better than those of Example 4, so Example 1 in the present invention is a further preferred embodiment.

[0114] By comparing the test results of Example 1 with those of Examples 5-7, it can be obtained that in the present invention, adjusting the amount of any one of epichlorohydrin, tea polyphenols and acrylic acid will have a significant impact on the performance of the epoxy resin. This is based on the fact that when preparing the epoxy resin by reaction, the three resins are formed and cross-linked, and adjusting the above raw materials will directly lead to the progress of the reaction. For this reason, the present invention further defines "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] By 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 is also indirectly affected by the crosslinking agent and the initiator. This is because the crosslinking agent and the initiator are one of the key factors to promote the crosslinking of acrylic acid and tea polyphenols. For this reason, the present invention further limits the molar ratio of acrylic acid, crosslinking agent and initiator to 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] By comparing the test results of Example 1 with Example 9 and Comparative Example 4, it can be obtained that, compared with using ethylene glycol and water as promoters, the scheme of using ethanol and water as promoters in the present invention can obtain epoxy resins with better high temperature resistance and high pressure resistance at low temperatures, among which 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] By comparing the test results of Example 1 with those of Examples 10-12, it can be obtained that the amounts of the sodium hydroxide solution added twice in the present invention need to be limited to a certain extent, wherein the epoxy resin obtained when "the molar ratio of sodium hydroxide to 4,4'-diaminodiphenylmethane in the sodium hydroxide solution added for the first time is 2-4:1, and the molar ratio of sodium hydroxide to 4,4'-diaminodiphenylmethane in the sodium hydroxide solution added for the second time is 6-8:1" is preferred.

[0118] By comparing the test results of Example 1 with those of Example 13, it can be concluded that the method of adding 4,4'-diaminodiphenylmethane in multiple times at certain intervals in the present invention is helpful for controlling the reaction temperature, thereby obtaining an epoxy resin with better performance.

[0119] By 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 crosslinking step, and the epoxy resin obtained thereby has a higher glass transition temperature, breakdown voltage and mechanical strength, and can also reduce the total chlorine content.

[0120] This specific embodiment is merely an explanation of the present invention and is not a limitation of the present invention. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed. However, 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 method for preparing a heat-resistant and pressure-resistant epoxy resin, characterized in that: The following steps are involved: Mix epichlorohydrin, ethanol and water, heat in a water bath to 40-45°C, add 4,4'-diaminodiphenylmethane, and keep the temperature at 50-55°C for 3-4 hours to obtain a ring-opening intermediate; Adding tea polyphenol, acrylic acid, a crosslinking agent, an initiator and a sodium hydroxide solution to the ring-opening intermediate in sequence, and continuing to stir and react at a temperature of 75-80° C. for 5-6 hours to obtain an epoxy resin intermediate; When the epoxy resin intermediate is cooled to 30° C. or below, a sodium hydroxide solution is slowly added, and the reaction is controlled at a temperature of 30-40° C. for 1-2 hours to obtain a crude epoxy resin; Toluene is added to the crude epoxy resin for extraction, and after standing for stratification, the upper resin phase is taken out, the solvent is removed under reduced pressure, and then the epoxy resin is obtained after filtration.

2. The preparation method according to claim 1, characterized in that: The molar ratio of the 4,4'-diaminodiphenylmethane to epichlorohydrin is 1:5-6.

3. The preparation method according to claim 1, characterized in that: The molar ratio of the 4,4'-diaminodiphenylmethane, tea polyphenols and acrylic acid is 1:0.1-0.3:0.5-0.

6.

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

40.

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

4.

6. The preparation method according to claim 1, characterized in that: The molar ratio of sodium hydroxide to 4,4'-diaminodiphenylmethane in the sodium hydroxide solution added for the first time is 2-4:

1.

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

1.

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

9. The preparation method according to claim 1, characterized in that: When desolventizing, the upper resin phase is kept at a vacuum degree of ≥750 mmHg and a temperature of 120-130° C. for 40-60 min, and filtered while hot.

10. A heat-resistant and pressure-resistant epoxy resin, characterized in that: The preparation method is described in any one of claims 1 to 9.

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