Room temperature curing polyurethane toughened low temperature resistant epoxy adhesive containing six hydrogen bonds

Abstract

This invention provides a room-temperature curing, hexahydrogen-bonded polyurethane toughened low-temperature resistant epoxy adhesive, comprising the following components: isocyanate, polyol, chain extender, glycidyl ether, epoxy resin, catalyst, and curing agent. A polyurethane prepolymer is synthesized via isocyanate and polyol, hydrogen bonds are provided by the chain extender, and finally, glycidyl ether is used for end-capping to obtain an epoxy-terminated polyurethane containing hexahydrogen bonds. The epoxy resin is then modified to prepare a modified epoxy adhesive. Adipate dihydrazide, as a chain extender, can form hexahydrogen bonds and introduce this dynamic bond into the epoxy-terminated polyurethane, structurally improving the poor compatibility between the toughening agent and the epoxy resin, and providing an energy dissipation pathway to increase the toughness of the epoxy resin at -196°C. This invention cures at room temperature and exhibits excellent mechanical strength and good toughness, strong adhesion to substrates, and reduced brittle fracture under low-temperature conditions.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, and more specifically, to a room-temperature curing polyurethane toughened low-temperature resistant epoxy adhesive containing six hydrogen bonds. Background Technology

[0002] Epoxy resins, due to their polar groups such as hydroxyl and ether bonds, can form strong adhesion to various substrates such as metals, glass, and ceramics. However, the rigid three-dimensional cross-linked network of pure epoxy resin results in low elongation at break and poor peel and impact resistance when untoughened. Highly cross-linked thermosetting epoxy resins exhibit greater brittleness at low temperatures, affecting their application in ultra-low temperature environments. In recent years, numerous research results have been achieved on toughened low-temperature epoxy resin adhesives. Among them, polyurethane, due to its flexible molecular chains containing urethane groups (—NH—COO—), has received widespread attention for its use in toughening epoxy resins. However, several shortcomings remain: firstly, there are compatibility issues between polyurethane and epoxy resins; secondly, energy dissipation pathways are limited at low temperatures; thirdly, curing conditions are cumbersome, making it unsuitable for use in harsh environments; and fourthly, most research on low-temperature toughening is limited to the temperature range of -40℃ to -60℃, with insufficient research on ultra-low temperatures. Furthermore, at low temperatures, these flexible segments can freeze to some extent, significantly reducing the toughening effect. Introducing dynamic bonds into epoxy resins offers a new pathway for low-temperature toughening and energy dissipation. Therefore, it is crucial to explore how to modify epoxy resins by introducing dynamic bonds into polyurethane through rational structural design, thereby enhancing toughness and bond strength and improving the material's mechanical properties at extreme low temperatures.

[0003] Patent application CN121950229A reports an amine curing agent (2EG) with dynamic β-amino ester bonds, which, when cured with bisphenol A epoxy resin, forms a network containing β-amino ester bonds and abundant hydrogen bonds, providing an effective pathway for energy dissipation at low temperatures. After liquid nitrogen treatment at extreme temperatures (-196℃), the strength increases instead of decreasing, reaching 23.51 MPa. The lap shear strength of stainless steel is 15.93 MPa. However, its curing process is cumbersome, requiring curing at 80℃ under normal pressure for 4 hours, followed by curing under vacuum at 100℃ for 6 hours. Such curing conditions cannot meet the requirements for large-area applications under harsh conditions. Patent application CN121362550A reports a polyurethane with glycerol carbonate end-capping as an epoxy resin modifier. Samples were tested and compared after immersion and drying in boiling water and cold water, respectively. The peeling rate of the cold water group was higher than that of the boiling water group, indicating insufficient low-temperature mechanical properties. Although this patent uses glycerol carbonate end-capping and subsequent curing reaction to covalently link to the epoxy network to improve compatibility... However, at low temperatures, polyurethane segments freeze to some extent, lacking effective energy dissipation pathways, leading to a decline in low-temperature mechanical properties. The adhesive materials disclosed in the above patents are limited in high-load applications, such as aerospace and polar regions, due to stringent curing conditions or insufficient low-temperature mechanical properties. These applications require materials to not only withstand extreme temperatures but also significant stress and deformation. Therefore, developing epoxy adhesive materials with high mechanical strength and ease of application is crucial. This not only improves the reliability and durability of engineering materials but also broadens their application range, providing new solutions for the development of high-performance materials. Summary of the Invention

[0004] In view of this, the present invention aims to provide a room temperature curing polyurethane toughened low-temperature resistant epoxy adhesive containing six hydrogen bonds, in order to solve the problem that the curing conditions of the adhesives in the prior art are harsh and cannot maintain good toughness and bonding strength at low temperatures.

[0005] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0006] A room-temperature curing, low-temperature resistant epoxy adhesive comprises the following components: isocyanate, polyol, chain extender, glycidyl ether, epoxy resin, catalyst, and curing agent. A polyurethane prepolymer is synthesized by isocyanate and polyol, and hydrogen bonds are provided by the chain extender. Finally, glycidyl ether is used for end-capping to obtain an epoxy-terminated polyurethane containing six hydrogen bonds. Then, the epoxy resin is modified to prepare a modified epoxy adhesive.

[0007] Optionally, the isocyanate is selected from at least one of toluene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, and diphenylmethane diisocyanate, and the polyol is selected from at least one of polycaprolactone diol, polypropylene glycol, polytetrahydrofuran ether diol, 1,4-butanediol, and hydroxyl-terminated polybutadiene, and the molar ratio of isocyanate to polyol is 2:0.3-1.

[0008] Optionally, the molar ratio of glycidyl ether to isocyanate is 1:1.

[0009] Optionally, the chain extender is adipic dihydrazide, and the ratio of the molar amount of the chain extender to the sum of the molar amounts of the chain extender and the polyol is 0.1-0.7.

[0010] Optionally, the epoxy resin is selected from at least one of E51, E44, E55, E20, G1302, G1605, and EP-410, and the glycidyl-terminated polyurethane accounts for 1%-20% of the weight of the epoxy resin.

[0011] Optionally, the catalyst is selected from at least one of dibutyltin dilaurate, stannous octoate, and dibutyltin oxide, and the amount of catalyst used accounts for 0.01%-0.1% of the total weight of polyurethane.

[0012] Optionally, the curing agent is selected from at least one of diethylenetriamine, polyetheramine D-230, polyamide (650), T-31, 593, and 4,4'-diaminodiphenylmethane, and the amount of curing agent is 10 to 40% of the amount of epoxy resin.

[0013] Optionally, the ratio of the molar amount of the chain extender to the sum of the molar amounts of the chain extender and the polyol is 0.3-0.5.

[0014] This invention also proposes a method for preparing the above-mentioned room temperature curing, low-temperature resistant epoxy adhesive, comprising the following steps:

[0015] Step 1: Dry the polyol and isocyanate;

[0016] Step 2: Add the catalyst to the dried polyol and isocyanate, and stir.

[0017] Step 3: Dissolve the chain extender in a solvent. After it is completely dissolved, add it to the mixture from Step 2 and stir overnight.

[0018] Step 4: Next, add glycidol and continue stirring;

[0019] Step 5: Slowly add epoxy resin to the product from Step 4 and stir.

[0020] Step 6: Finally, add the curing agent and stir.

[0021] Step 7: Pour the solution obtained in Step 6 into a mold and cure it at room temperature to obtain polyurethane toughened epoxy resin adhesive.

[0022] Optionally, in step three, the solvent is selected from at least one of acetone, dichloromethane, ethyl acetate, N,N-dimethylformamide, N,N-dimethylacetamide, and butyl acetate.

[0023] Compared with existing technologies, the room-temperature curing, low-temperature resistant epoxy adhesive and its preparation method described in this invention have the following advantages:

[0024] (1) The present invention uses adipic dihydrazide as a chain extender, which can form a six-fold hydrogen bond and introduce this dynamic bond into the epoxy-terminated polyurethane, thereby structurally improving the problem of poor compatibility between the toughening agent and the epoxy resin, and providing an energy dissipation path for increasing the toughness of the epoxy resin at a low temperature of -196℃.

[0025] (2) The room temperature curing low temperature resistant epoxy adhesive prepared by the present invention can achieve room temperature curing without complicated equipment, and has excellent mechanical strength and good toughness. It can adhere strongly to the substrate. When applied under low temperature conditions, it can reduce safety problems caused by brittle fracture, save manpower and material resources, and extend service life. Attached Figure Description

[0026] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0027] Figure 1 The FTIR spectra of PUADHX prepared in Examples 1-4 and Comparative Example 2 of this invention are shown below.

[0028] Figure 2 The stress-strain response curves of EPPUADHX finally prepared in Examples 1-4 and Comparative Example 2, and E51593 prepared in Comparative Example 1, under room temperature conditions;

[0029] Figure 3 b is a comparison diagram of tensile stress and elongation at break of EPUADHX finally prepared in Examples 1-4 and Comparative Example 2, and E51593 prepared in Comparative Example 1 under room temperature conditions. Figure 3 c is a comparison diagram of the Young's modulus and toughness of EPUADHX finally prepared in Examples 1-4 and Comparative Example 2, and E51593 prepared in Comparative Example 1 at room temperature.

[0030] Figure 4The stress-strain response curves of EPPUADHX finally prepared in Examples 1-4 and Comparative Example 2, and E51593 prepared in Comparative Example 1, under the condition of -196℃ (immersed in liquid nitrogen);

[0031] Figure 5 e is a comparison of the tensile stress and elongation at break of EPPUADHX finally prepared in Examples 1-4 and Comparative Example 2, and E51593 prepared in Comparative Example 1, under the condition of -196℃ (immersed in liquid nitrogen). Figure 5 f is a comparison chart of Young's modulus and toughness of EPUADHX finally prepared in Examples 1-4 and Comparative Example 2, and E51593 prepared in Comparative Example 1 at -196℃ (immersed in liquid nitrogen).

[0032] Figure 6 a is a comparison diagram of the lap shear strength of EPPUADHX finally prepared in Examples 1-4 and Comparative Example 2, and E51593 prepared in Comparative Example 1 under room temperature conditions. Figure 6 b is a comparison of the peeling work of EPPUADHX finally prepared in Examples 1-4 and Comparative Example 2, and E51593 prepared in Comparative Example 1 at room temperature.

[0033] Figure 7 d is a comparison diagram of the lap shear strength of EPPUADHX finally prepared in Examples 1-4 and Comparative Example 2, and E51593 prepared in Comparative Example 1 at -196°C (immersed in liquid nitrogen). Figure 7 e is a comparison of the peeling work of EPPUADHX finally prepared in Examples 1-4 and Comparative Example 2, and E51593 prepared in Comparative Example 1 at -196°C (immersed in liquid nitrogen).

[0034] Figure 8 This is a schematic diagram of EPPUADH0.3 prepared in Example 1 of the present invention being attached to a substrate and then immersed in liquid nitrogen.

[0035] Figure 9 The bar chart shows the shear strength of EPPUADH0.3 prepared in Example 1 of this invention after being immersed in liquid nitrogen for different times. Detailed Implementation

[0036] The present invention will be further described below with reference to specific embodiments. First, it should be noted that the data in the following experimental examples were obtained by the inventors through numerous experiments. Due to space limitations, only a portion of these data is shown in the specification, and those skilled in the art can understand and implement the present invention based on this data. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the contents of this invention, those skilled in the art can make various modifications or alterations to the invention, and these modifications or alterations also fall within the scope of protection of this application.

[0037] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0038] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0039] This invention proposes a room-temperature curing polyurethane toughened low-temperature resistant epoxy adhesive containing six hydrogen bonds, comprising the following components: isocyanate, polyol, chain extender, glycidyl ether, epoxy resin, catalyst, and curing agent. A polyurethane prepolymer is synthesized via isocyanate and polyol, and hydrogen bonds are provided by the chain extender. Finally, glycidyl ether is used for end-capping to obtain an epoxy-end-capped polyurethane containing six hydrogen bonds. The epoxy resin is then modified to prepare a modified epoxy adhesive.

[0040] The isocyanate is selected from at least one of toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), and diphenylmethane diisocyanate (MDI), and the polyol is selected from at least one of polycaprolactone diol (PCL), polypropylene glycol (PPG), polytetrahydrofuran ether diol (PTMEG), 1,4-butanediol (BDO), and hydroxyl-terminated polybutadiene (HTPB). The molar ratio of isocyanate to polyol is 2:0.3-1. The molar ratio of glycidyl ether to isocyanate is 1:1.

[0041] The chain extender is adipic dihydrazide (ADH).

[0042] The epoxy resin is selected from at least one of E51, E44, E55, E20, G1302, G1605, and EP-410. The glycidyl-terminated polyurethane accounts for 1%-20% of the epoxy resin by weight.

[0043] The catalyst is selected from at least one of dibutyltin dilaurate, stannous octoate, and dibutyltin oxide. The amount of catalyst used is 0.01%-0.1% of the total weight of polyurethane.

[0044] The curing agent is selected from at least one of diethylenetriamine, polyetheramine D-230, polyamide (650), T-31, 593, and 4,4'-diaminodiphenylmethane (DDM). The amount of curing agent used is 10-40% of the amount of epoxy resin.

[0045] It should be noted that the amounts of isocyanate and polyol mentioned in this invention refer to their amounts after drying.

[0046] This invention also proposes a method for preparing a room-temperature curing, low-temperature resistant epoxy adhesive, which includes the following steps:

[0047] Step 1: Dry the polyol and isocyanate;

[0048] Specifically, in step one, polyol is added to a three-necked flask and stirred at 90℃-120℃ for 1-3 hours. One end of the three-necked flask is connected to a circulating water vacuum pump with a vacuum level of 0.096MPa-0.1MPa. Isocyanate is dehydrated using activated molecular sieves and left to stand for at least one week. Since using activated molecular sieves for dehydration is a conventional technique, it will not be described in detail here.

[0049] Step 2: Add the dried polyol, isocyanate and catalyst, and stir for 1-3 hours at a speed of 90-200 rpm.

[0050] Step 3: Dissolve the chain extender in a solvent. After it is completely dissolved, add it to the mixture from Step 2 and stir overnight at a speed of 90-200 rpm.

[0051] Step 4: Next, add glycidyl glycerol and continue stirring for 40-90 minutes at a speed of 90-200 rpm. The resulting product, glycerol-terminated polyurethane, is labeled as PUADHX, where X represents the ratio of the molar amount of the chain extender to the sum of the molar amounts of the chain extender and the polyol.

[0052] Step 5: Slowly add epoxy resin to the product from Step 4 and stir for 1-3 minutes at a speed of 90-200 rpm.

[0053] Step 6: Finally, add the curing agent and stir for 1-3 minutes at a speed of 90-200 rpm.

[0054] Step 7: Pour the solution obtained in Step 6 into a mold and cure it at room temperature to obtain a polyurethane toughened epoxy resin adhesive, labeled as EPPUADHX.

[0055] It should be noted that steps two through six are all carried out under nitrogen atmosphere, and the reaction temperature in steps two through four is 50℃-60℃.

[0056] In step three, the solvent is selected from at least one of acetone, dichloromethane, ethyl acetate, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and butyl acetate.

[0057] In step six, after stirring is complete, connect the container containing the reaction system to a vacuum pump and stir thoroughly to eliminate air bubbles.

[0058] The epoxy adhesive obtained by this invention needs to be stored under conditions where the relative humidity is less than 80%.

[0059] The ADH molecule has a primary amino group (-NH2) at each end. During synthesis, these primary amino groups react with the isocyanate group (-NCO) at the end of the prepolymer to generate a urea group (-NHCONH-). This reaction integrates ADH as a chain extender into the polymer backbone, forming six hydrogen bonds between chain segments. It also introduces a large number of hydrogen-bonding urethane and urea groups into the material, providing a chemical basis for constructing a high-density hydrogen bond network. The structure of the six hydrogen bonds is shown in Equation 1 below.

[0060] Formula 1

[0061] The epoxy-terminated polyurethane toughened room temperature curing low temperature resistant epoxy adhesive synthesized in this invention, containing six hydrogen bonds, has high mechanical strength and toughness, and can still maintain excellent mechanical properties at -196℃, thus improving safety in use.

[0062] Example 1

[0063] Polyurethane:

[0064] Polycaprolactone diol (molecular weight 2000) 7g

[0065] Isophorone diisocyanate (molecular weight 222.28) 4.4456g

[0066] Polytetrahydrofuran ether diol (molecular weight 1000) 3.5g

[0067] Adipic acid dihydrazide 0.5226g

[0068] Glycerin 1.4816g

[0069] 0.00897g of dibutyltin dilaurate

[0070] Modified epoxy resin:

[0071] Epoxy Resin E51 100g

[0072] 10g of the above polyurethane

[0073] 593 curing agent 27g

[0074] Step 1: Add polycaprolactone diol and polytetrahydrofuran ether diol to a three-necked flask and stir at 120°C for 2 hours. Connect one end of the three-necked flask to a circulating water vacuum pump with a vacuum degree of 0.096MPa-0.1MPa. Use activated molecular sieves to remove water from isophorone diisocyanate and let it stand for at least one week.

[0075] Step 2: At 60°C, nitrogen gas is introduced into the container to purge the air. Then, under the nitrogen atmosphere, dried polycaprolactone diol, polytetrahydrofuran ether diol, and isophorone diisocyanate are added, followed by dibutyltin dilaurate. The mixture is stirred for 2 hours at a speed of 200 rpm.

[0076] Step 3: Dissolve adipic dihydrazide in 30mL-40mL of N,N-dimethylformamide (DMF) solvent. After complete dissolution, add it to the mixture from Step 2 under nitrogen purging and stir for 24 hours at 200rpm and 60℃.

[0077] Step 4: Next, add glycidol to the container and continue stirring for 1 hour at a speed of 200 rpm and a temperature of 60°C. Label the resulting product as PUADH0.3.

[0078] Step 5: Slowly add epoxy resin E51 to 10g of the product from Step 4 and stir for 1 minute at a speed of 200 rpm.

[0079] Step 6: Finally, add the curing agent and stir for 1 minute at a speed of 200 rpm. After stirring, connect the container containing the reaction system to a vacuum pump and stir thoroughly to eliminate air bubbles.

[0080] Step 7: Pour the solution obtained in Step 6 into a mold and cure at room temperature for 24 hours to obtain polyurethane toughened epoxy resin adhesive, labeled as EPPUADH0.3.

[0081] Steps two through six are all carried out in an environment where nitrogen gas is introduced.

[0082] Example 2

[0083] Polyurethane:

[0084] Polycaprolactone diol (molecular weight 2000) 5g

[0085] Isophorone diisocyanate (molecular weight 222.28) 4.4456g

[0086] Polytetrahydrofuran ether diol (molecular weight 1000) 2.5g

[0087] Adipic acid dihydrazide 0.871g

[0088] Glycerin 1.4816g

[0089] 0.00717g dibutyltin dilaurate

[0090] Modified epoxy resin:

[0091] Epoxy Resin E51 100g

[0092] 10g of the above polyurethane

[0093] 593 curing agent 27g

[0094] The preparation method of Example 2 is the same as that of Example 1. The product obtained in step four of Example 2 is labeled as PUADH0.5, and the product obtained in step seven is labeled as EPPUADH0.5.

[0095] Example 3

[0096] Polyurethane:

[0097] Polycaprolactone diol (molecular weight 2000) 9g

[0098] Isophorone diisocyanate (molecular weight 222.28) 4.4456g

[0099] Polytetrahydrofuran ether diol (molecular weight 1000) 4.5g

[0100] Adipic acid dihydrazide 0.1742g

[0101] Glycerin 1.4816g

[0102] 0.01176g of dibutyltin dilaurate

[0103] Modified epoxy resin:

[0104] Epoxy Resin E51 100g

[0105] 10g of the above polyurethane

[0106] 593 curing agent 27g

[0107] The preparation method of Example 3 is the same as that of Example 1. The product obtained in step four of Example 3 is labeled as PUADH0.1, ​​and the product obtained in step seven is labeled as EPPUADH0.1.

[0108] Example 4

[0109] Polyurethane:

[0110] Polycaprolactone diol (molecular weight 2000) 3g

[0111] Isophorone diisocyanate (molecular weight 222.28) 4.4456g

[0112] Polytetrahydrofuran ether diol (molecular weight 1000) 1.5g

[0113] Adipic acid dihydrazide 1.2194g

[0114] Glycerin 1.4816g

[0115] 0.00699g of dibutyltin dilaurate

[0116] Modified epoxy resin:

[0117] Epoxy Resin E51 100g

[0118] 10g of the above polyurethane

[0119] 593 curing agent 27g

[0120] The preparation method of Example 4 is the same as that of Example 1. The product obtained in step four of Example 4 is labeled as PUADH0.7, and the product obtained in step seven is labeled as EPPUADH0.7.

[0121] Comparative Example 1

[0122] Epoxy Resin E51 100g

[0123] 593 curing agent 27g

[0124] 100g of epoxy resin E51 and 27g of 593 curing agent were stirred at room temperature. After the mixture was stirred evenly, it was cured at room temperature for 24 hours to obtain an adhesive, which was denoted as E51593.

[0125] Comparative Example 2

[0126] Polyurethane:

[0127] Polycaprolactone diol (molecular weight 2000) 10g

[0128] Isophorone diisocyanate (molecular weight 222.28) 4.4456g

[0129] Polytetrahydrofuran ether diol (molecular weight 1000) 5g

[0130] Glycerin 1.4816g

[0131] 0.1167g dibutyltin dilaurate

[0132] Modified epoxy resin:

[0133] Epoxy Resin E51 100g

[0134] 10g of the above polyurethane

[0135] 593 curing agent 27g

[0136] The preparation method of Comparative Example 2 is the same as that of Example 1, but without the addition of adipic dihydrazide. The product obtained in step four of Comparative Example 2 is labeled as PUADH0, and the product obtained in step seven is labeled as EPPUADH0.

[0137] It should be noted that in the formulations of the above embodiments and Comparative Example 2, polycaprolactone diol, isophorone diisocyanate, and polytetrahydrofuran ether diol refer to their weight after drying.

[0138] Performance testing

[0139] FTIR tests were performed on PUADH0.3 of Example 1, PUADH0.5 of Example 2, PUADH0.1 of Example 3, PUADH0.7 of Example 4, and PUADH0 of Comparative Example 2, respectively. Figure 1 As shown, in each sample, 2260cm -1 The disappearance of the -NCO absorption peak at 1721 cm⁻¹ indicates that all isocyanate groups have completely reacted. -1 The absorption peak at 3322 cm⁻¹ represents the carbonyl group (C=O) of the carbamate. -1 The absorption peak at 1535 cm⁻¹ is attributed to the stretching vibration of NH₃. -1 The absorption peak at 1655 cm⁻¹ is attributed to the bending vibration of NH₄⁺. -1 The presence of the C=O group at the urea group indicates that ADH reacts with -NCO to form a urea bond during the chain extension reaction. As the content of the chain extender increases, the 1655cm² bond... -1 The peak becomes increasingly pronounced at 913 cm⁻¹. It can be observed at this point. -1 The presence of characteristic absorption peaks of epoxy groups indicates that the polyurethane is epoxy-terminated.

[0140] pass Figure 3As shown in b and 5e, in Examples 1-4, the tensile strength gradually increased with increasing ADH content, regardless of whether it was at room temperature or low temperature. However, when the ADH content was increased to the level of Example 3, the tensile strength was lower than that of Comparative Example 1. This may be because the addition of the chain extender ADH diluted the original three-dimensional cross-linked network structure of the epoxy resin, leading to a decrease in stress and poor tensile strength. However, despite the increase in ADH content, the six-fold hydrogen bonds formed after the introduction of ADH played a role in enhancing cohesion, improving tensile strength while increasing toughness and adhesive adhesion. Figure 3 c and Figure 5 As can be seen from f, compared with the unmodified epoxy resin of Comparative Example 1, the toughness of Examples 1-4 is improved under both room temperature and low temperature conditions. However, when the amount of ADH is increased to that of Example 4, the improvement effect on toughness under low temperature conditions is limited. Therefore, the preferred ratio of the molar amount of the chain extender to the sum of the molar amounts of the chain extender and the polyol in this invention is 0.3-0.5.

[0141] from Figure 6 and Figure 7 It can be seen that, in Examples 1-4, with the increase of ADH addition, the shear strength and peel work showed a trend of first increasing and then decreasing, regardless of whether it was at room temperature or low temperature. However, the room temperature shear strength and peel work, as well as the low temperature shear strength and peel work of EPPUADHX in Examples 1 and 2, were higher than those in Comparative Examples 1 and 2.

[0142] After the EPPUADH0.3 prepared in Example 1 was attached to the substrate, it was immersed in liquid nitrogen. Figure 8 As shown in the bar chart, the slab shear strength at different times is as follows: Figure 9 As shown, the shear strength decreases with time due to the stress mismatch between the adhesive and the substrate, but gradually stabilizes at 30 minutes, indicating that the adhesive can adhere strongly to the substrate.

[0143] The performance test results of EPUADHX prepared in Examples 1-2 and Comparative Example 2, and E51593 prepared in Comparative Example 1 are shown in Table 1. The toughness test standard adopts GB / T2567-2008, and the lap shear strength test standard adopts GB / T7124-2008.

[0144] As shown in the accompanying drawings and Table 1, Examples 1 and 2 formed six-fold hydrogen bonds, and this dynamic bond was introduced into the epoxy-terminated polyurethane. This structurally improved the poor compatibility between the toughening agent and the epoxy resin, and provided an energy dissipation pathway to increase the toughness of the epoxy resin at a low temperature of -196°C. Epoxy termination enhances compatibility with the epoxy resin, and the polyurethane is introduced through covalent bonding via the curing agent. High toughness and bond strength are observed at both room temperature and ultra-low temperature (-196°C).

[0145] Table 1

[0146]

[0147] The room temperature curing, low-temperature resistant epoxy adhesive prepared by this invention can achieve room temperature curing without complicated equipment, and has excellent mechanical strength and good toughness. It can adhere strongly to the substrate. When applied under low temperature conditions, it can reduce safety problems caused by brittle fracture, save manpower and resources, and extend service life.

[0148] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various alterations and modifications without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A room-temperature curing polyurethane toughened low-temperature resistant epoxy adhesive containing six hydrogen bonds, characterized in that, It includes the following components: isocyanate, polyol, chain extender, glycidyl ether, epoxy resin, catalyst, and curing agent.

2. The room-temperature curing polyurethane toughened low-temperature resistant epoxy adhesive containing six hydrogen bonds according to claim 1, characterized in that, The isocyanate is selected from at least one of toluene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, and diphenylmethane diisocyanate; the polyol is selected from at least one of polycaprolactone diol, polypropylene glycol, polytetrahydrofuran ether diol, 1,4-butanediol, and hydroxyl-terminated polybutadiene; and the molar ratio of isocyanate to polyol is 2:0.3-1.

3. The room-temperature curing, hexa-hydrogen-bonded, toughened, low-temperature resistant polyurethane epoxy adhesive according to claim 1, characterized in that, The molar ratio of glycidyl ether to isocyanate is 1:

1.

4. The room-temperature curing polyurethane toughened low-temperature resistant epoxy adhesive containing six hydrogen bonds according to claim 1, characterized in that, The chain extender is adipic acid dihydrazide, and the ratio of the molar amount of the chain extender to the sum of the molar amounts of the chain extender and the polyol is 0.1-0.

7.

5. The room-temperature curing, hexa-hydrogen-bonded, toughened, low-temperature resistant polyurethane epoxy adhesive according to claim 1, characterized in that, The epoxy resin is selected from at least one of E51, E44, E55, E20, G1302, G1605, and EP-410, and the glycidyl-terminated polyurethane accounts for 1%-20% of the weight of the epoxy resin.

6. The room-temperature curing polyurethane toughened low-temperature resistant epoxy adhesive containing six hydrogen bonds according to claim 1, characterized in that, The catalyst is selected from at least one of dibutyltin dilaurate, stannous octoate, and dibutyltin oxide, and the amount of catalyst used accounts for 0.01%-0.1% of the total weight of polyurethane.

7. The room-temperature curing, hexa-hydrogen-bonded, toughened, low-temperature resistant polyurethane epoxy adhesive according to claim 1, characterized in that, The curing agent is selected from at least one of diethylenetriamine, polyetheramine D-230, polyamide (650), T-31, 593, and 4,4'-diaminodiphenylmethane, and the amount of curing agent is 10-40% of the amount of epoxy resin.

8. The room-temperature curing polyurethane toughened low-temperature resistant epoxy adhesive containing six hydrogen bonds according to claim 4, characterized in that, The ratio of the molar amount of the chain extender to the sum of the molar amounts of the chain extender and the polyol is 0.3-0.

5.

9. A method for preparing a room-temperature curing, hexa-hydrogen-bonded, toughened, low-temperature resistant polyurethane epoxy adhesive as described in any one of claims 1-8, characterized in that, Includes the following steps: Step 1: Dry the polyol and isocyanate; Step 2: Add the catalyst to the dried polyol and isocyanate, and stir. Step 3: Dissolve the chain extender in a solvent. After it is completely dissolved, add it to the mixture from Step 2 and stir overnight. Step 4: Next, add glycidol and continue stirring; Step 5: Slowly add epoxy resin to the product from Step 4 and stir. Step 6: Finally, add the curing agent and stir. Step 7: Pour the solution obtained in Step 6 into a mold and cure it at room temperature to obtain polyurethane toughened epoxy resin adhesive.

10. The preparation method according to claim 9, characterized in that, In step three, the solvent is selected from at least one of acetone, dichloromethane, ethyl acetate, N,N-dimethylformamide, N,N-dimethylacetamide, and butyl acetate.

Images