Single-component heat-resistant and impact-resistant epoxy structural adhesive

Abstract

The application discloses a single-component heat-curable epoxy structural adhesive with excellent high-temperature resistance and impact resistance and a preparation method. The single-component heat-curable epoxy structural adhesive comprises the following components in parts by weight: 5-10 parts of self-synthesized acid anhydride-silane modified epoxy, 40-60 parts of epoxy resin, 4-6 parts of diluent, 2-4 parts of coupling agent, 2-4 parts of black paste, 45-55 parts of filler, 4-10 parts of curing agent and 2-6 parts of accelerator. The single-component heat-curable epoxy structural adhesive has excellent impact resistance and can fully meet the strength requirement of structural bonding. The single-component heat-curable epoxy structural adhesive has excellent high-temperature shear strength on metal materials and can meet the application requirement under high-temperature conditions, thereby guaranteeing the reliability of bonding parts. The single-component heat-curable epoxy structural adhesive has excellent application prospect in vehicle body structural bonding, motor shell bonding and the like.

Description

Technical Field

[0001] This invention belongs to the field of adhesives, specifically relating to a method for preparing a single-component thermosetting epoxy structural adhesive suitable for bonding vehicle body structures and motor housings. Background Technology

[0002] Epoxy resins, as an important class of thermosetting polymers, possess excellent adhesion, low residual stress, high tensile strength and modulus, low shrinkage during curing, good chemical resistance, and excellent mechanical and dielectric properties. They are widely used in aerospace composite materials, high-strength adhesives, molding materials, biomedical systems, electronic packaging, and coatings. However, cured epoxy resins exhibit certain shortcomings in practical applications due to their inherent brittleness. For example, high crosslinking density leads to poor crack propagation resistance, poor toughness, low fracture energy, brittleness, and low impact resistance. Therefore, optimizing and improving epoxy resins to enhance their toughness and impact resistance has always been a key research topic for researchers.

[0003] Thermosetting one-component epoxy adhesives have been used in automotive structural applications for a considerable period, typically exhibiting good adhesion to metal substrates and excellent mechanical properties. However, in heat-prone components of the automotive structure, such as motors and gearboxes, the applied thermosetting one-component epoxy structural adhesive must possess excellent thermal stability and superior shear strength at high temperatures to ensure the strength and reliability of the bonded joints, thereby reducing risk and ensuring personal safety. Typically, thermosetting one-component epoxy structural adhesives exhibit a high strength decay rate at high temperatures, posing a risk to bonding under these conditions. Therefore, developing a thermosetting one-component epoxy adhesive with excellent thermal stability and a low high-temperature strength decay rate is crucial. Summary of the Invention

[0004] To address the shortcomings of the existing technology, this invention provides a method for preparing a single-component thermosetting epoxy structural adhesive suitable for bonding vehicle body structures and motor housings. The resulting product exhibits excellent impact resistance, outstanding shear strength against metal materials under high-temperature conditions, and superior reliability, thus meeting the requirements for workability, reliability, and strength in structural bonding.

[0005] The specific technical solution is as follows: One objective of this invention is to provide a method for preparing a one-component thermosetting epoxy structural adhesive suitable for bonding vehicle body structures and motor housings, characterized in that it comprises the following components in parts by weight: 5-10 parts of self-synthesized anhydride-silane modified epoxy, 40-60 parts of epoxy resin, 4-6 parts of diluent, 2-4 parts of coupling agent, 2-4 parts of black paste, 45-55 parts of filler, 4-10 parts of curing agent, and 2-6 parts of accelerator.

[0006] The self-synthesized anhydride-silane modified epoxy is synthesized from the following raw materials in parts by weight: maleic anhydride 190-200 parts, 3-cyclohexene-1-methanol 220-235 parts, hydrogen-terminated polydimethylsiloxane 560-600 parts, K855033KARSTEDT catalyst 0.001-0.002 parts, 50% sodium hydroxide aqueous solution 20-25 parts, epichlorohydrin 20-30 parts, and ethanol 315-350 parts.

[0007] Furthermore, the self-synthesized anhydride-silane modified epoxy is prepared by a three-step method. The first step is to esterify maleic anhydride with 3-cyclohexene-1-methanol to obtain an ester compound A containing a double bond and a carboxylic acid group.

[0008] The second step is to react hydrogen-terminated polydimethylsiloxane with the ester compound A obtained in the first step via a hydrosilylation reaction to obtain silane-modified ester compound B with a carboxylic acid group.

[0009] The third step is to react the ester compound B prepared in the second step with epichlorohydrin to obtain anhydride-silane modified epoxy.

[0010] The beneficial effects of adopting the above-mentioned further scheme are as follows: On the one hand, the epoxy groups in the anhydride-silane modified epoxy can improve the compatibility between the anhydride-silane modified epoxy and the epoxy resin, facilitating better dispersion and the formation of a uniform phase; on the other hand, the epoxy groups can participate in the reaction, forming a three-dimensional network with the main epoxy resin, increasing the crosslinking degree of the system, and endowing the material with excellent mechanical strength. The cyclohexene structure of the self-synthesized anhydride-silane modified epoxy can endow the material with outstanding high-temperature modulus and excellent thermal stability. Furthermore, the silicon-oxygen bonds in the anhydride-silane modified epoxy structure play a positive role in enhancing the thermal stability of the material, ensuring its reliability under high-temperature conditions. The silicon-oxygen bonds on the self-synthesized anhydride-silane modified epoxy skeleton and the introduction of anhydride segments improve the flexibility of the material. Simultaneously, the presence of ether bonds in the anhydride-silane modified epoxy is beneficial for enhancing the flexibility of the material and improving the modulus and impact resistance of the single-component epoxy structural adhesive.

[0011] The structural formula of the self-synthesized anhydride-silane modified epoxy is:

[0012] The synthetic route for the self-synthesized anhydride-silane modified epoxy is as follows: .

[0013] Furthermore, the epoxy resin is one or a mixture of two or more of bisphenol A type epoxy resin, bisphenol F type epoxy resin, and bisphenol S type epoxy resin. Preferably, the bisphenol A type epoxy resin is Epikote 828 from Henkel, Inc., USA; the bisphenol F type epoxy resin is preferably DER 354 from Dow Chemical; and the bisphenol S type epoxy resin is preferably YBPS-360 from Nanjing Yuelai New Materials Co., Ltd.

[0014] The beneficial effect of adopting the above-mentioned further scheme is that by selecting different types of epoxy resins, the workability, Tg point, bond strength, tensile strength and modulus of the single-component thermosetting epoxy structural adhesive can reach a balance point, resulting in excellent comprehensive performance.

[0015] Furthermore, the diluent is one or a mixture of two or more of benzyl glycidyl ether, neopentyl glycol diglycidyl ether, and butyl glycidyl ether.

[0016] The beneficial effects of adopting the above-mentioned further solutions are: adjusting the viscosity and fluidity of the system to meet the requirements of different workability, while optimizing the surface smoothness of the cured product.

[0017] Furthermore, the coupling agent is a silane coupling agent, specifically one or a mixture of two or more of 3-(2,3-epoxypropoxy)propylmethyldiethoxysilane, 3-diethylaminopropyltrimethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

[0018] The beneficial effects of adopting the above-mentioned further solutions are: silane coupling agents are beneficial to improving the wetting performance of single-component thermosetting epoxy structural adhesives on substrates, improving the compatibility between resins and fillers; improving the wettability of epoxy structural adhesives on bonding materials, and enhancing bonding strength.

[0019] Furthermore, the black paste is a premix of carbon black and epoxy resin, specifically a premix of MA100 from Mitsubishi Corporation of Japan and 840 from DIC Corporation of Japan, with a ratio of MA100 to 840 of 2:8.

[0020] Furthermore, the curing agent is a latent amine curing agent, preferably a dicyandiamide curing agent, and more preferably Huntsman's OMICURE DDA 10.

[0021] The accelerator is one or a mixture of two or more of substituted urea or modified imidazole, preferably a substituted urea accelerator, preferably Huntsman's OMICURE U-410M.

[0022] The beneficial effect of adopting the above-mentioned further solution is that it meets the requirements of curing temperature and curing speed of single-component thermosetting epoxy structural adhesives for structural bonding.

[0023] Furthermore, the filler is one or a mixture of two or more of the following: talc, kaolin, wollastonite, bentonite, silica, calcium oxide, aluminum hydroxide, calcium carbonate, magnesium oxide, and glass microspheres. Preferably, the filler is a composite combination of calcium carbonate and fumed silica. Furthermore, the calcium carbonate is heavy calcium carbonate with a particle size of 10-15 micrometers, preferably heavy calcium carbonate with a particle size of 10-15 micrometers from Nanning Musen Mining.

[0024] Furthermore, the fumed silica is hydrophobic fumed silica, preferably Evonik Degussa's AEROSIL R202, AEROSIL R805 and AEROSIL R974; or Cabot's TS-720.

[0025] The beneficial effects of adopting the above-mentioned further solutions are: the introduction of heavy calcium carbonate can significantly reduce production costs; at the same time, it can enhance the modulus, tensile strength and hardness of the cured structural adhesive, and improve surface gloss and wear resistance.

[0026] Introducing hydrophobic fumed silica can prevent the sedimentation of heavy calcium carbonate in the system; improve the anti-aging properties of the cured structural adhesive; adjust the viscosity and thixotropy of the system to meet the requirements of processability; and also have a positive promoting effect on the strength and ductility of the cured structural adhesive.

[0027] The beneficial effects of the present invention are: the single-component thermosetting epoxy structural adhesive of the present invention has excellent impact resistance, excellent shear strength against metal materials under high temperature conditions, and excellent reliability, which can meet the requirements of structural bonding workability, reliability and strength. Detailed Implementation

[0028] The principles and features of the present invention are described below with reference to examples. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention. Example 1

[0029] The following steps are taken to prepare a one-component thermosetting epoxy structural adhesive suitable for bonding vehicle body structures and motor housings: (1) Maleic anhydride (196 g) was added to 3-cyclohexene-1-methanol (224 g), and the mixture was stirred at 60°C for 3 hours under nitrogen protection to obtain an ester compound A containing a double bond and a carboxylic acid group.

[0030] Under nitrogen protection, ester compound A (420 g) was dehydrated at 120 °C for 30 minutes, followed by the addition of hydrogen-terminated poly(dimethylsiloxane) (580 g; average). M n~580), K855033 KARSTEDT catalyst (0.001 g; 3000 ppm), reacted at 100 °C for 4 hours, and collected by vacuum distillation to obtain silane-modified ester compound B with carboxylic acid groups.

[0031] Ester compound B (254 g) and epichlorohydrin (22 g) were added separately to anhydrous ethanol (350 g) under N2 atmosphere, and the reaction temperature was raised to 90 °C. A 50% sodium hydroxide aqueous solution (25 g) was added dropwise to the above mixed solution over 2.5 hours. The reaction was stirred at 90 °C for 5 hours, followed by washing three times with deionized water by centrifugation. Anhydrous magnesium sulfate was added to remove the remaining water, the solvent was removed by rotary evaporation, and the product was purified by vacuum distillation to obtain anhydride-silane modified epoxy.

[0032] (2) At room temperature, by weight, 10 parts of the self-synthesized anhydride-silane modified epoxy resin obtained in step (1), 40 parts of bisphenol A type epoxy resin Epikote 828, 4 parts of neopentyl glycol diglycidyl ether, 2 parts of 3-(2,3-epoxypropoxy)propylmethyldiethoxysilane, 2 parts of black paste, 5 parts of AEROSIL R202 hydrophobic fumed silica and 40 parts of heavy calcium carbonate are put into a mixing tank, stirred evenly, and vacuumed to remove bubbles; then 5 parts of OMICURE DDA 10 and 2 parts of OMICURE U-410M are added into the mixing tank in sequence, stirred evenly, and vacuumed to remove bubbles, to obtain the single-component thermosetting epoxy structural adhesive of the present invention suitable for bonding vehicle body structure and motor housing. Example 2

[0033] The following steps are taken to prepare a one-component thermosetting epoxy structural adhesive suitable for bonding vehicle body structures and motor housings: (1) Same as Example 1.

[0034] (2) At room temperature, by weight, 5 parts of the self-synthesized anhydride-silane modified epoxy resin obtained in step (1), 45 parts of bisphenol A type epoxy resin Epikote 828, 4 parts of neopentyl glycol diglycidyl ether, 2 parts of 3-(2,3-epoxypropoxy)propylmethyldiethoxysilane, 2 parts of black paste, 5 parts of AEROSIL R202 hydrophobic fumed silica and 40 parts of heavy calcium carbonate are put into a mixing tank, stirred evenly, and vacuumed to remove bubbles; then 5 parts of OMICURE DDA 10 and 2 parts of OMICURE U-410M are added into the mixing tank in sequence, stirred evenly, and vacuumed to remove bubbles, to obtain the single-component thermosetting epoxy structural adhesive of the present invention suitable for bonding vehicle body structure and motor housing. Example 3

[0035] The following steps are taken to prepare a one-component thermosetting epoxy structural adhesive suitable for bonding vehicle body structures and motor housings: (1) Same as Example 1.

[0036] (2) At room temperature, by weight, 10 parts of the self-synthesized anhydride-silane modified epoxy resin obtained in step (1), 20 parts of bisphenol A type epoxy resin Epikote 828, 20 parts of bisphenol F type epoxy resin DER354, 4 parts of neopentyl glycol diglycidyl ether, 2 parts of 3-(2,3-epoxypropoxy)propylmethyldiethoxysilane, 2 parts of black paste, 5 parts of AEROSIL R202 hydrophobic fumed silica and 40 parts of heavy calcium carbonate are put into a mixing tank, stirred evenly, and vacuumed to remove bubbles; then 5 parts of OMICURE DDA 10 and 2 parts of OMICURE U-410M are added into the mixing tank in sequence, stirred evenly, and vacuumed to remove bubbles, to obtain the single-component thermosetting epoxy structural adhesive of the present invention suitable for bonding vehicle body structure and motor housing. Example 4

[0037] The following steps are taken to prepare a one-component thermosetting epoxy structural adhesive suitable for bonding vehicle body structures and motor housings: (1) Same as Example 1.

[0038] (2) At room temperature, by weight, 5 parts of the self-synthesized anhydride-silane modified epoxy resin obtained in step (1), 22.5 parts of bisphenol A type epoxy resin Epikote828, 22.5 parts of bisphenol F type epoxy resin DER354, 4 parts of neopentyl glycol diglycidyl ether, 2 parts of 3-(2,3-epoxypropoxy)propylmethyldiethoxysilane, 2 parts of black paste, 5 parts of AEROSIL R202 hydrophobic fumed silica and 40 parts of heavy calcium carbonate are put into a mixing tank, stirred evenly, and vacuumed to remove bubbles; then 5 parts of OMICURE DDA 10 and 2 parts of OMICURE U-410M are added into the mixing tank in sequence, stirred evenly, and vacuumed to remove bubbles, to obtain the single-component thermosetting epoxy structural adhesive of the present invention suitable for bonding vehicle body structure and motor housing. Example 5

[0039] The following steps are taken to prepare a one-component thermosetting epoxy structural adhesive suitable for bonding vehicle body structures and motor housings: (1) Same as Example 1.

[0040] (2) At room temperature, by weight, 10 parts of the self-synthesized anhydride-silane modified epoxy resin obtained in step (1), 40 parts of bisphenol F type epoxy resin DER354, 4 parts of neopentyl glycol diglycidyl ether, 2 parts of 3-(2,3-epoxypropoxy)propylmethyldiethoxysilane, 2 parts of black paste, 5 parts of AEROSIL R202 hydrophobic fumed silica and 40 parts of heavy calcium carbonate are put into a mixing tank, stirred evenly, and vacuumed to remove bubbles; then 5 parts of OMICURE DDA 10 and 2 parts of OMICURE U-410M are added into the mixing tank in sequence, stirred evenly, and vacuumed to remove bubbles, to obtain the single-component thermosetting epoxy structural adhesive of the present invention suitable for bonding vehicle body structure and motor housing. Comparative Example 1

[0041] Preparation of epoxy structural adhesive: 50 parts of bisphenol A type epoxy resin Epikote 828, 4 parts of neopentyl glycol diglycidyl ether, 2 parts of 3-(2,3-epoxypropoxy)propylmethyldiethoxysilane, 2 parts of black paste, 5 parts of AEROSIL R202 hydrophobic fumed silica, and 40 parts of heavy calcium carbonate were added to a mixing tank, stirred evenly, and then degassed under vacuum. Subsequently, 5 parts of OMICURE DDA 10 and 2 parts of OMICURE U-410M were added to the mixing tank in sequence, stirred evenly, and then degassed under vacuum to obtain epoxy structural adhesive. Comparative Example 2

[0042] Preparation of epoxy structural adhesive: 25 parts of bisphenol A type epoxy resin Epikote 828, 25 parts of bisphenol F type epoxy resin DER354, 4 parts of neopentyl glycol diglycidyl ether, 2 parts of 3-(2,3-epoxypropoxy)propylmethyldiethoxysilane, 2 parts of black paste, 5 parts of AEROSIL R202 hydrophobic fumed silica, and 40 parts of heavy calcium carbonate were added to a stirred tank, stirred evenly, and degassed under vacuum. Then, 5 parts of OMICURE DDA 10 and 2 parts of OMICURE U-410M were added to the stirred tank in sequence, stirred evenly, and degassed under vacuum to obtain epoxy structural adhesive.

[0043] test

[0044] The performance of the single-component epoxy structural adhesives of Examples 1-5 and Comparative Examples 1-2 of the present invention was tested through the following experiments.

[0045] Test 1: Modulus test at 150℃

[0046] The high-temperature modulus of the cured one-component epoxy structural adhesive was evaluated using DMA (Q800, TA). Samples measuring 60 mm × 12 mm × 3 mm were prepared, and the temperature was increased from 25 °C to 250 °C at a heating rate of 5 °C / min using a double cantilever measurement mode, with an oscillation frequency of 1 Hz and an amplitude of 7.5 μm.

[0047] Test 2: Glass transition temperature (Tg) test

[0048] Dynamic thermomechanical analysis (TMA) of the samples was performed using a TA Instruments Q400-0537 analyzer under an N2 inlet flow rate of 100 mL / min. The samples were brought into contact with a bending probe under a force of 0.20 N, and then heated from 0°C to 330°C at a rate of 5°C / min. The force was adjusted by ±0.08 N at a frequency of 0.10 Hz during the test cycle. The glass transition temperature (Tg) of the epoxy-amine network was thus measured, and the data are the average of three independent runs.

[0049] Test 3: Shear Strength Test

[0050] The tensile shear strength was determined in accordance with the ASTM D1002-10 test standard. The tensile shear strength was measured using the following dimensions: bonded area (10mm × 20mm), adhesive layer thickness (0.2mm), curing process (20min / 150℃), test temperature (25℃ and 150℃), and test speed (10mm / min).

[0051] Test 4: K 1C test K 1C The test was conducted according to ASTM D5045 standard, using the single-sided notch bending technique on a universal testing machine, employing a 3-point bending fixture at a speed of 10 mm / min. -1 The crosshead speed test sample.

[0052] The results of tests 1 to 4 are shown in Table 1.

[0053] Table 1. Comparison of test performance between samples from Examples 1-5 and Comparative Examples 1-2

[0054] As can be seen from the data in Table 1, the single-component thermosetting epoxy structural adhesive of this invention possesses excellent toughness and modulus, thus giving the material outstanding impact resistance and fully meeting the strength requirements of structural bonding. It also exhibits excellent high-temperature shear strength against metal materials, meeting application requirements under high-temperature conditions and ensuring the reliability of the bonded parts. It shows excellent application prospects in areas such as vehicle body structural bonding and motor housing bonding.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A one-component thermosetting epoxy structural adhesive with excellent high-temperature resistance and impact resistance, characterized in that, It comprises the following components in parts by weight: Self-synthesized anhydride-silane modified epoxy resin 5-10 parts, epoxy resin 40-60 parts, diluent 4-6 parts, coupling agent 2-4 parts, black paste 2-4 parts, filler 45-55 parts, curing agent 4-10 parts, accelerator 2-6 parts. The epoxy resin is one or a mixture of two or more of bisphenol A type epoxy resin, bisphenol F type epoxy resin and bisphenol S type epoxy resin; The self-synthesized anhydride-silane modified epoxy is synthesized from the following raw materials in parts by weight: maleic anhydride 190-200 parts, 3-cyclohexene-1-methanol 220-235 parts, hydrogen-terminated polydimethylsiloxane 560-600 parts, K855033KARSTEDT catalyst 0.001-0.002 parts, 50% sodium hydroxide aqueous solution 20-25 parts, epichlorohydrin 20-30 parts, and ethanol 315-350 parts. The method for preparing self-synthesized anhydride-silane modified epoxy includes the following steps: (1) Under nitrogen protection, maleic anhydride and 3-cyclohexene-1-methanol were reacted at 60°C for 3 hours to prepare ester compound A containing double bond and carboxylic acid group; (2) Under nitrogen protection, the ester compound A obtained in step (1) was dehydrated at 60°C for 30 minutes, and then average M was added. n Hydrogen-terminated polydimethylsiloxane with a concentration of 580 ppm and K855033KARSTEDT catalyst with a concentration of 3000 ppm were reacted at 100°C for 4 hours, and silane-modified ester compound B with a carboxylic acid group was obtained by vacuum distillation. (3) Under nitrogen protection, the ester compound B obtained in step (2), epichlorohydrin and ethanol were mixed, and sodium hydroxide aqueous solution was added dropwise to the mixture. The reaction temperature was raised to 90°C and stirred for 5 hours. Then, the mixture was washed three times by centrifugation with deionized water, and anhydrous magnesium sulfate was added to remove the remaining water. The solvent was removed by rotary evaporation and purified by vacuum distillation to obtain the self-synthesized anhydride-silane modified epoxy.

2. The single-component thermosetting epoxy structural adhesive according to claim 1, characterized in that, The diluent is one or a mixture of two or more of benzyl glycidyl ether, neopentyl glycol diglycidyl ether, and butyl glycidyl ether; the coupling agent is a silane coupling agent, specifically one or a mixture of two or more of 3-(2,3-epoxypropoxy)propylmethyldiethoxysilane, 3-diethylaminopropyltrimethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; the black paste is a premix of carbon black and epoxy resin; the curing agent is a latent amine curing agent; and the accelerator is one or a mixture of two or more of substituted urea or modified imidazole.

3. The single-component thermosetting epoxy structural adhesive according to claim 1, characterized in that, The filler is one or a mixture of two or more of the following: talc, kaolin, wollastonite, bentonite, silica, calcium oxide, aluminum hydroxide, calcium carbonate, magnesium oxide, and glass microspheres.

4. The single-component thermosetting epoxy structural adhesive according to claim 1, characterized in that, The filler is a compound combination of calcium carbonate and fumed silica; the calcium carbonate is heavy calcium carbonate with a particle size of 10-15 micrometers; and the fumed silica is hydrophobic fumed silica.

5. A method for preparing a one-component thermosetting epoxy structural adhesive as described in any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Under nitrogen protection, maleic anhydride and 3-cyclohexene-1-methanol were reacted at 60°C for 3 hours to prepare ester compound A containing double bonds and carboxylic acid groups; (2) Under nitrogen protection, the ester compound A obtained in step (1) was dehydrated at 60°C for 30 minutes, and then average M was added. n Hydrogen-terminated polydimethylsiloxane with a concentration of 580 ppm and K855033KARSTEDT catalyst with a concentration of 3000 ppm were reacted at 100°C for 4 hours, and silane-modified ester compound B with a carboxylic acid group was obtained by vacuum distillation. (3) Under nitrogen protection, the ester compound B obtained in step (2), epichlorohydrin and ethanol were mixed, and sodium hydroxide aqueous solution was added dropwise to the mixture. The reaction temperature was raised to 90°C and stirred for 5 hours. Then, the mixture was washed three times by centrifugation with deionized water, and anhydrous magnesium sulfate was added to remove the remaining water. The solvent was removed by rotary evaporation and purified by vacuum distillation to obtain the self-synthesized anhydride-silane modified epoxy. (4) The self-synthesized anhydride-silane modified epoxy, epoxy resin, diluent, coupling agent, black paste and filler obtained in step (3) are put into a mixing tank, stirred evenly, and vacuumed to remove bubbles; then the curing agent and accelerator are put into the above mixing tank, stirred evenly, and vacuumed to remove bubbles to obtain a single-component thermosetting epoxy structural adhesive.

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