A low-density impact-resistant two-component epoxy adhesive

Abstract

The present application relates to a low-density impact-resistant two-component epoxy adhesive, which comprises two components A and B. By weight percentage, the component A is composed of the following raw materials: 38%-45% of the main epoxy resin, 3%-4% of the reactive diluent, 10%-20% of the modified epoxy resin, 25%-30% of the flame retardant filler, 12%-15% of hollow glass microspheres, and 0.8%-1.0% of other auxiliary agent 1; By weight percentage, the component B is composed of the following raw materials: 67%-70.5% of the amine curing agent, 20%-25% of the flame retardant filler, 9.5%-12.5% of hollow glass microspheres, and 0.1%-0.5% of other auxiliary agents. Among them, the modified epoxy resin has a polybutadiene chain segment covalently bonded via a urethane group and has an epoxy equivalent of 500-600 g / eq.

Description

Technical Field

[0001] The present invention relates to the technical field of adhesives, and particularly to a low-density impact-resistant two-component epoxy adhesive. Background Art

[0002] With the development of new energy vehicles, the cruising range has received increasing attention and has become a very crucial point for new energy vehicles to expand their market share. Before a complete breakthrough in battery technology, the lightweighting of vehicles has become an important direction to solve the cruising range. The current mainstream solution is to make the metal parts of the vehicle body into composite materials such as carbon fiber as much as possible, and then use adhesives to bond and fix them. For the bonding of vehicle body composite materials, not only high bonding strength is required, but also good impact resistance at different temperatures and excellent flame retardant properties. In addition, in order to meet the lightweight requirements, low density is also very crucial. Common epoxy adhesives have excellent mechanical properties and very high bonding strength for composite materials such as carbon fiber. However, their cured products have a high modulus, large brittleness, and poor impact resistance, which limits the further expansion of their application scope. Currently, the main methods to solve the large brittleness of epoxy adhesives are to toughen the system, and there are two paths: one path is to modify the curing agent to synthesize a highly flexible epoxy resin curing agent; the other path is to toughen the epoxy component, and the commonly used toughening methods are rubber elastomer blending modification, core-shell polymer blending modification, flexible chain segment grafting modification, etc.

[0003] Patent Application No. CN202211374244.7 discloses a preparation method of an elastic epoxy adhesive. The mass ratio of the A component to the B component is 1:(0.8 - 1.5). By weight, the A component includes 80 - 89 parts of bisphenol A epoxy resin, 20 - 30 parts of bisphenol F epoxy resin, 10 - 18 parts of polyglycol diglycidyl ether, 8 - 12 parts of ethylene glycol diglycidyl ether, 8 - 12 parts of neopentyl glycol diglycidyl ether, 1 - 3 parts of silane coupling agent, and 0.1 - 0.5 parts of the first silicone defoamer; the B component includes 100 - 120 parts of modified curing agent, 1 - 3 parts of DMP-30 accelerator, and 0.1 - 0.4 parts of the second silicone defoamer. The epoxy adhesive disclosed in this patent uses a variety of small molecule epoxy resin active diluents and is combined with a flexible curing agent to introduce flexible chain segments into the crosslinked three-dimensional network. Although the flexibility has been improved to a certain extent, it greatly reduces the glass transition temperature, damages the bonding strength at the same time, and does not have low density and flame retardancy itself.

[0004] The patent application number CN201410252522.0 discloses an impact-resistant, high-toughness, high-temperature-resistant epoxy adhesive and its preparation process. The adhesive uses polymer particles with a butadiene rubber core and an acrylate shell structure and terminal amino nitrile rubber in component A and component B respectively to improve the toughness of the system, and at the same time uses a high-temperature-resistant curing agent to ensure the temperature resistance of the system. This patent focuses on the toughening problem of high-temperature-resistant adhesives. The obtained structural adhesive is suitable for places that require long-term heating, such as the bonding of motor magnetic steels. However, for body composites, under normal working conditions, they do not need to be heated at high temperature for a long time, but need to be affected by alternating environmental temperatures for a long time. Therefore, while ensuring a certain glass transition temperature, it is more necessary to have good impact performance under low-temperature conditions. The adhesive disclosed in this patent obviously cannot meet the requirements of high impact resistance and high toughness at low temperature, and itself does not have the characteristics of low density and flame retardancy.

[0005] In summary, aiming at the deficiencies of current epoxy adhesives in bonding composites, it is very necessary to develop a two-component epoxy resin adhesive with high bonding strength, good impact resistance, especially excellent impact resistance under low-temperature conditions, and at the same time having low density and good flame retardancy. Summary of the Invention

[0006] To solve the deficiencies of the prior art, the present invention provides a low-density impact-resistant two-component epoxy resin adhesive. This adhesive has a very high bonding strength for composites, and at the same time has excellent impact resistance at different temperatures, especially under low-temperature conditions. The low-density feature meets the lightweight requirements and has excellent flame retardancy.

[0007] Technical Solution of the Present Invention

[0008] A low-density impact-resistant two-component epoxy resin adhesive, which comprises two components A and B. By weight percentage, component A is composed of the following raw materials:

[0009]

[0010] By weight percentage, component B is composed of the following raw materials:

[0011]

[0012] Wherein, the modified epoxy resin has a polybutadiene chain segment covalently bonded via urethane and has an epoxy equivalent of 500-600 g / eq; and wherein, the amine curing agent comprises a modified flexible curing agent with a polyether segment.

[0013] In an embodiment of the present invention, the viscosity of the modified epoxy resin at 25 °C is in the range of 15000-30000 mPa·s.

[0014] In one embodiment according to the present invention, the weight-average molecular weight of the polybutadiene segment is in the range of 2000-3500.

[0015] In another embodiment according to the present invention, the polybutadiene segment has a 1,2-vinyl content of 20%-50%.

[0016] In some embodiments according to the present invention, the main epoxy resin includes bisphenol A epoxy resin, bisphenol F epoxy resin and heat-resistant epoxy resin or a combination thereof. As an illustrative example, the main epoxy resin is prepared by mixing bisphenol A epoxy resin, bisphenol F epoxy resin and heat-resistant epoxy resin in a mass ratio of 5 / 3 / 2.

[0017] Furthermore, the bisphenol A epoxy resin is Nanya NPEL-128 epoxy resin; the bisphenol F epoxy resin is Nanya NPEF-170 epoxy resin; the heat-resistant epoxy resin is at least one of phenolic epoxy resin and triglycidylamine epoxy resin.

[0018] The active diluent is one or more of 1,4-butanediol diglycidyl ether and glycidyl versatate.

[0019] In one embodiment according to the present invention, the modified epoxy resin is self-made. As an illustrative example, the modified epoxy resin is prepared through the following steps:

[0020] i) Provide a hydroxyl-terminated liquid polybutadiene resin; ii) React the hydroxyl-terminated liquid polybutadiene resin with a polyisocyanate to form an isocyanate-terminated prepolymer, wherein the isocyanate group content is not less than 14.5%; iii) React the isocyanate-terminated prepolymer with a hydroxyl-functionalized epoxy resin to form the modified epoxy resin, wherein the formed modified epoxy resin has an epoxy equivalent in the range of 500-600 g / eq.

[0021] In one embodiment according to the present invention, the hollow glass microspheres include a mixture of hollow glass microspheres with a particle size in the range of 5-10 μm, hollow glass microspheres with a particle size in the range of 20-40 μm and hollow glass microspheres with a particle size in the range of 50-60 μm. In a specific embodiment according to the present invention, the hollow glass microspheres are compounded from hollow glass microspheres with particle sizes in the ranges of 5-10 μm, 20-40 μm and 50-60 μm respectively in a mass ratio of (1-5) / (60-80) / (15-31).

[0022] The flame retardant filler is a compound of ammonium polyphosphate and aluminum hydroxide in a mass ratio of 3 / 1 to 4 / 1.

[0023] The other auxiliary agent 1 includes fumed silica, carbon black, and silane coupling agent.

[0024] The amine curing agent also includes a modified alicyclic amine heat-resistant curing agent, preferably a mixture formed by compounding a modified alicyclic amine heat-resistant curing agent and a modified flexible curing agent with a polyether segment in a weight ratio of 4 / 6.

[0025] The other auxiliary agent 2 includes fumed silica and titanium dioxide.

[0026] The mixing ratio of components A and B is 1:(0.6 - 1.0) in terms of mass ratio.

[0027] In one embodiment according to the present invention, the density of the two-component epoxy resin adhesive is 1.0 g / ml or lower.

[0028] In one embodiment according to the present invention, the low-density impact-resistant two-component epoxy resin adhesive has a glass transition temperature of 60 °C or higher, preferably 65 °C or higher, and more preferably 70 °C or higher.

[0029] According to the present invention, a preparation method of a low-density impact-resistant two-component epoxy resin adhesive is also provided. The method includes the following steps:

[0030] The preparation method of component A: First, add the main epoxy resin and the self-made modified epoxy resin into the stirring kettle in proportion, start the star stirring, with a rotation speed of 1800 rpm, control the temperature below 60 °C, and stir for 20 min; then cool down to 30 - 40 °C, add the reactive diluent and the flame retardant filler in proportion, start the dispersion and star stirring, with a rotation speed of 2400 rpm, control the temperature below 50 °C, keep the vacuum degree at -0.07 MPa to -0.08 MPa, stir for 10 min, clean the kettle once, and then stir for another 30 min; finally, add the other auxiliary agent 1 in proportion, start the dispersion and star stirring, with a rotation speed of 2700 rpm - 3000 rpm, control the temperature below 60 °C, keep the vacuum degree at -0.07 MPa to -0.08 MPa, stir for 5 min and clean the kettle once, and then continue to stir for 30 min; finally, add hollow glass microspheres, start the dispersion and star stirring, stir for a certain time at an appropriate rotation speed and vacuum degree, turn off the dispersion, adjust the rotation speed of the star stirring to 600 rpm, control the temperature below 40 °C, keep the vacuum degree at -0.09 MPa to -0.1 MPa, and defoam for 10 - 15 min, then take out of the kettle to obtain component A.

[0031] Preparation of Component B: First, add the amine-based high-temperature resistant modified curing agent and the flexible curing agent into the reaction kettle according to the ratio of 4 / 6, start the star-shaped stirring, with a rotation speed of 600 rpm, and stir for 10 min; then add the flame retardant filler and other additives 2 into the reaction kettle according to the ratio, start the dispersion and star-shaped stirring, with a rotation speed of 2400 rpm, control the temperature below 50°C, keep the vacuum degree at -0.07 MPa to -0.08 MPa, stir for 10 min, clean the kettle once, and then stir for another 50 min; finally, add hollow glass microspheres, start the dispersion and star-shaped stirring, stir for a certain time at an appropriate rotation speed and vacuum degree, then turn off the dispersion, adjust the speed of the star-shaped stirring to 600 rpm, control the temperature below 35°C, keep the vacuum degree at -0.09 MPa to -0.1 MPa, and defoam for 10 - 15 min, then take out of the kettle to obtain Component B.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The synthesized modified epoxy resin is used to toughen the main epoxy resin. First, the modified epoxy resin has good compatibility with the main resin and can react with the curing agent together. The modified epoxy is embedded in the main epoxy resin to form an interpenetrating network or semi-interpenetrating network structure, achieving the purpose of toughening the epoxy cured product; second, since the polybutadiene resin segment is introduced into the synthesized modified epoxy resin, it has the characteristics of rubber particles itself, so it can toughen the epoxy cured product through the toughening mechanism of the rubber elastomer. The combination of the two toughening methods enables the toughness of the prepared epoxy adhesive, especially the low-temperature toughness, to be greatly improved, enhancing the impact resistance. 2. The hollow glass microspheres with different particle size combinations added to the system not only ensure low density but also make the system have good fluidity and are not easy to float; at the same time, when the cured product containing hollow glass microspheres is subjected to external stress impact, the hollow glass microspheres can absorb part of the stress of the system, reducing the impact of the impact stress on the system, and macroscopically showing an increase in the toughness of the system, the material is not easy to crack, and the impact resistance is further enhanced, which was difficult to foresee before this application. 3. The curing agent used in the system includes a highly flexible curing agent. The use of the highly flexible curing agent introduces flexible chain segments into the system, thereby improving the toughness of the system and further enhancing the impact resistance. 4. In the two-component epoxy resin adhesive according to the present invention, there are a polyurethane-epoxy system interpenetrating network toughening system, a rubber particle toughening system, a hollow glass microsphere toughening system, and a flexible curing agent chain segment toughening system. The four toughening systems are used in combination to improve the toughness of the cured product, especially to improve the low-temperature toughness, thereby greatly enhancing the impact resistance of the cured product. 5. The obtained adhesive has a high bonding strength to composite materials such as carbon fiber, the flame retardancy can reach the 3 mm V-0 level, and at the same time, the density is below 1.0 g / ml, meeting the requirements of high strength, lightweight, and flame retardancy. Detailed implementation mode

[0033] To more comprehensively demonstrate the technical solutions and advantages of this invention, the following specific embodiments are provided for further illustration.

[0034] The present invention uses a composite system of bisphenol A epoxy resin, bisphenol F resin, and heat-resistant resin as the main epoxy resin, a self-made urethane-modified epoxy resin containing polybutadiene segments as the modified epoxy resin, a composite system of heat-resistant epoxy curing agent and high-flexibility curing agent as the curing agent, introduces hollow glass microspheres, and simultaneously adds flame-retardant fillers, thereby preparing a low-density flame-retardant two-component epoxy adhesive with excellent impact resistance at different temperatures, especially at low temperatures, and good adhesion to composites.

[0035] The ways for the present invention to improve the impact resistance are: urethane-epoxy interpenetrating network toughening system, rubber particle toughening system, hollow glass microsphere toughening system, and flexible curing agent segment toughening system. The four toughening systems are used in combination to improve the toughness of the cured product, especially the low-temperature toughness, thus greatly enhancing the impact resistance of the cured product.

[0036] Synthesis Examples

[0037] Preparation of Modified Epoxy Resin

[0038] The preparation method of the modified epoxy resin is as follows: 20 parts of hydroxyl-terminated liquid polybutadiene resin and 1 part of plasticizer alkyl sulfonic acid phenyl ester are added to the reaction equipment, heated to 120 °C, the vacuum degree is maintained at -0.07 MPa to -0.10 MPa, the stirring speed is 1800 rpm, and stirring and dehydration are carried out for 4 h. Then the temperature is lowered to 50 °C - 60 °C, and 20 parts of diphenylmethane diisocyanate (MDI) are quickly added, the rotation speed is adjusted to 800 rpm, and under nitrogen protection, stirring is carried out for 20 min. Then the temperature is raised to 75 - 80 °C, the rotation speed is 1800 rpm, and stirring and reaction are continued for 2 h to obtain a prepolymer with an isocyanate group (NCO) content of 14.5% and a viscosity of 2000 - 3000 mPa·s. In this article, the isocyanate group content is titrated by a potentiometric titrator and determined by calculation based on the principle of the reaction between the isocyanate group and excessive dibutylamine.

[0039] Then the system is cooled to 50 °C, 40 parts of dehydrated bisphenol A epoxy resin are added to the system, and the reaction is carried out at 130 °C for 2 h. Then the temperature is lowered to 60 °C, 3 parts of C12 - 14 alkyl glycidyl ether are added to the system, and stirring is carried out for 10 min to obtain a modified epoxy resin containing polybutadiene segments with an epoxy equivalent of 500 - 600 g / eq and a viscosity of 15000 - 30000 mPa·s. The molecular weight of the used hydroxyl-terminated liquid polybutadiene resin is 2000 - 3500 g / mol, and the 1,2-vinyl content is 20% - 50%, which is provided by the supplier.

[0040] Example 1

[0041] The A component is composed of the following raw materials by weight percentage:

[0042]

[0043] The B component is composed of the following raw materials by weight percentage:

[0044]

[0045]

[0046] In the above examples, 301 is a triglycidylamine type epoxy resin, the modified IPDA is a heat-resistant curing agent, 910 is a flexible curing agent, and the hollow glass microspheres are composed of those with particle sizes of 5 - 10μm, 20 - 40μm, and 50 - 60μm compounded according to a mass ratio of 5 / 70 / 25.

[0047] Example 2

[0048] The A component is composed of the following raw materials by weight percentage:

[0049]

[0050] The B component is composed of the following raw materials by weight percentage:

[0051]

[0052]

[0053] In the above examples, the modified 1,3 - BAC is a heat-resistant curing agent, R - 3403 is a flexible curing agent, 301 is a triglycidylamine type epoxy resin, 8240 is a phenolic epoxy resin, and the hollow glass microspheres are composed of those with particle sizes of 5 - 10μm, 20 - 40μm, and 50 - 60μm compounded according to a mass ratio of 3 / 75 / 22.

[0054] Example 3

[0055] The A component is composed of the following raw materials by weight percentage:

[0056]

[0057] The B component is composed of the following raw materials by weight percentage:

[0058]

[0059] In the above embodiments, the modified 1,3-BAC is a temperature-resistant curing agent, R-3403 is a flexible curing agent, 301 is a triglycidylamine-type epoxy resin, 8240 is a phenolic epoxy resin, and the hollow glass microspheres are compounded by mixing those with particle sizes of 5 - 10μm, 20 - 40μm, and 50 - 60μm in a mass ratio of 2 / 67 / 31.

[0060] The most significant difference among the above three embodiments lies in the different amounts of the self-made modified epoxy resin added, and the other components are correspondingly changed and slightly adjusted according to the change in the amount of the modified epoxy resin added.

[0061] Comparative Example 1

[0062] Replace the self-made modified epoxy resin with the polybutadiene core - acrylate shell toughening agent XH-154 used in Patent Application No. CN201410252522.0, remove the hollow glass microspheres, and the rest is the same as in Example 3.

[0063] Comparative Example 2

[0064] Replace the self-made modified epoxy resin with a urethane-modified epoxy resin without polybutadiene segments, and the rest is the same as in Example 1.

[0065] Comparative Example 3

[0066] Remove the hollow glass microspheres, and the rest is the same as in Example 2.

[0067] Comparative Example 4

[0068] Remove the flexible curing agent, and the rest is the same as in Example 2.

[0069] Comparative Example 5

[0070] Remove the self-made modified epoxy resin, the hollow glass microspheres, and the flexible curing agent, and the rest is the same as in Example 2.

[0071] Mix the epoxy adhesives prepared in the above embodiments and comparative examples in a specific proportion, cure them at room temperature for 7 days, and then conduct corresponding tests.

[0072] The shear strength of the present invention is tested in accordance with GB / T7124 - 2008, and the substrate is carbon fiber.

[0073] The flame retardancy of the present invention is tested according to the UL-94 standard.

[0074] The impact strength of the present invention is tested in accordance with GB / 6328 - 1999.

[0075] The density of the present invention is tested in accordance with GB / T13354.

[0076] The T-peel strength of the present invention is tested in accordance with GB / T2791, and the substrate is 5-series aluminum with a sandblasted surface.

[0077] The tensile strength and elongation at break of the present invention were tested in accordance with GB / T 1040.

[0078] The glass transition temperature of the present invention was tested using DMA.

[0079] The specific test results are shown in Table 1:

[0080] Table 1

[0081]

[0082]

[0083]

[0084] As can be seen from the results of the above examples and comparative examples, with the increase in the amount of the self-made modified epoxy resin added, the toughness of the system is significantly improved, the impact performance is significantly improved, and the toughness at low temperature is also very significantly enhanced. Although the glass transition temperature decreases slightly with the increase in the modified epoxy resin, it does not affect the use under normal working conditions. In addition, from the comparison results of the examples of the present invention, especially Example 2 and Comparative Example 3, it can be seen that the application of hollow glass microspheres not only reduces the density of the epoxy resin adhesive, but also significantly improves the toughness of the adhesive system.

[0085] In summary, in the present invention, the urethane-epoxy system interpenetrating network toughening system, the rubber particle toughening system, the glass microsphere toughening system, and the flexible curing agent segment toughening system are used in combination, thereby greatly improving the impact resistance of the cured product, especially the low-temperature impact resistance. The self-made urethane-modified epoxy resin containing polybutadiene segments has both toughening mechanisms, so the improvement effect on the system is the most obvious. Glass microspheres and flexible curing agents each improve the system by one toughening mechanism. From the results of the examples and comparative examples, it can be seen that although the degrees of action of several toughening methods are different, the best toughening effect cannot be obtained by removing any one toughening measure.

[0086] The above are only the preferred embodiments of the present invention. The present invention is not limited to the above specific embodiments. Any modifications, equivalent replacements, improvements, etc. made by those skilled in the art on the basis of the present invention shall be included within the protection scope of the present invention.

Claims

1. A low-density impact-resistant two-component epoxy adhesive, which comprises two components A and B. By weight percentage, The component A is composed of the following raw materials: ， By weight percentage, the component B is composed of the following raw materials: ， Wherein, the modified epoxy resin has a polybutadiene segment covalently bonded via a urethane bond and has an epoxy equivalent of 500-600 g / eq; and wherein, the amine curing agent comprises a modified flexible curing agent with a polyether segment.

2. The low-density impact-resistant two-component epoxy adhesive according to claim 1, wherein, The viscosity of the modified epoxy resin at 25 °C is in the range of 15000-30000 mPa·s.

3. The low-density impact-resistant two-component epoxy adhesive according to claim 1 or 2, wherein, The weight-average molecular weight of the polybutadiene segment is in the range of 2000-3500.

4. The low-density impact-resistant two-component epoxy adhesive according to claim 3, wherein, The polybutadiene segment has a 1,2-vinyl content of 20%-50%.

5. The low-density impact-resistant two-component epoxy adhesive according to claim 4, wherein, The modified epoxy resin is prepared by the following steps: i) providing a hydroxyl-terminated liquid polybutadiene resin; ii) reacting the hydroxyl-terminated liquid polybutadiene resin with a polyisocyanate to form an isocyanate-terminated prepolymer, wherein the isocyanate group content is not less than 14.5%; and iii) reacting the isocyanate-terminated prepolymer with the hydroxyl group of the epoxy resin to form the modified epoxy resin.

6. The low-density impact-resistant two-component epoxy adhesive according to claim 5, wherein, The hollow glass microspheres are compounded by hollow glass microspheres with particle sizes in the ranges of 5-10 μm, 20-40 μm, and 50-60 μm respectively according to the mass ratio of (1-5) / (60-80) / (15-31).

7. The low-density impact-resistant two-component epoxy adhesive according to claim 6, wherein the amine curing agent is a mixture formed by compounding a modified alicyclic amine heat-resistant curing agent and a modified flexible curing agent with a polyether segment according to a weight ratio of 4 / 6.

8. The low-density flame-retardant impact-resistant two-component epoxy adhesive according to claim 7, wherein, The main epoxy resin comprises bisphenol A epoxy resin, bisphenol F epoxy resin and heat-resistant epoxy resin or a combination thereof.

9. The low-density flame-retardant impact-resistant two-component epoxy adhesive as described in claim 8, wherein, The flame retardant filler is a mixture compounded by ammonium polyphosphate and aluminum hydroxide according to a mass ratio of 3 / 1-4 / 1.

10. The low-density flame-retardant and impact-resistant two-component epoxy adhesive according to claim 9, wherein, The density of the epoxy adhesive is 1.0 g / ml or lower.

Images