Preparation method of high-resistance flame-retardant two-component epoxy adhesive

Abstract

The invention discloses a method for preparing a high-electrical-resistance flame-retardant two-component epoxy adhesive. The method specifically comprises the following steps: dispersing and mixing a modified epoxy resin, a diluent, a flame retardant, a thixotropic agent, a defoaming agent, and a coupling agent to obtain component A; dispersing and mixing a curing agent, a curing accelerator, a flame retardant, a thixotropic agent, a defoaming agent, and a coupling agent to obtain component B; and mixing component A and component B to obtain the high-electrical-resistance flame-retardant two-component epoxy adhesive. The method for preparing the modified epoxy resin comprises the following steps: placing an epoxy resin in a reactor, adding a phosphorus-containing modifier, and heating the mixture to react to obtain the modified epoxy resin. The two-component epoxy adhesive is prepared by the method provided by the invention. The prepared two-component epoxy adhesive has good flame retardancy and broad application prospects.

Description

Technical Field

[0001] The invention relates to the field of adhesives, and in particular to a method for preparing a high-electrical-resistance flame-retardant two-component epoxy adhesive. Background Art

[0002] Epoxy resin adhesives are primarily composed of epoxy resin, a curing agent, an accelerator, and a modifier. They exhibit excellent compatibility with metals, glass, cement, wood, and polar plastics. Due to their excellent overall performance, epoxy resins are widely used in both industrial and consumer applications. As structural adhesives, epoxy resins are particularly widely used in areas such as building reinforcement and decoration, and airport maintenance.

[0003] However, for different applications, epoxy resin adhesives still have many problems: 1) In terms of curing process, such as the need to lower the curing temperature, increase the curing speed and improve fluidity; 2) In terms of performance, such as the need to improve mechanical properties (reinforcement, hardening and toughening, etc.), improve temperature resistance (such as heat resistance, low temperature resistance), improve adhesion on special parts such as wet surfaces, oily surfaces, underwater (in water), have special properties (such as electrical conductivity, thermal conductivity, damping, flame retardancy, water resistance, corrosion resistance, etc.), and have multifunctionality; 3) Other characteristics, such as the need to reduce toxicity, be environmentally friendly and reduce costs.

[0004] Clearly, epoxy resin adhesives, when used in specific applications, must meet the specific requirements of each field, such as taking into account mechanical, thermal, bonding, and halogen-free flame retardancy. Only in this way can epoxy resin adhesives meet the application needs of rapidly developing industrial fields and develop towards high performance, multifunctionality, and environmental friendliness. Summary of the Invention

[0005] In order to solve the above problems, the present invention provides a method for preparing a high-resistance flame-retardant two-component epoxy adhesive. The two-component epoxy adhesive is prepared by the method provided by the present invention, and the prepared two-component epoxy adhesive has good flame retardancy.

[0006] The technical solution of the present invention is achieved as follows:

[0007] The present invention provides a method for preparing a high-resistance flame-retardant two-component epoxy adhesive, which specifically comprises the following steps:

[0008] Dispersing and mixing the modified epoxy resin, diluent, flame retardant, thixotropic agent, defoaming agent, and coupling agent to obtain component A;

[0009] Dispersing and mixing a curing agent, a curing accelerator, a flame retardant, a thixotropic agent, a defoaming agent, and a coupling agent to obtain component B;

[0010] Mixing the component A and the component B to obtain the high-resistance flame-retardant two-component epoxy adhesive;

[0011] The preparation method of the modified epoxy resin is:

[0012] placing an epoxy resin in a reactor, adding a phosphorus-containing modifier, and heating the reaction to obtain the modified epoxy resin;

[0013] The curing agent is a modified amine curing agent, and the preparation method of the modified amine curing agent is:

[0014] Dissolving 3-hydroxyphenylphosphinoyl propionic acid in deionized water, adding sodium hydroxide solution to adjust to neutrality, adding melamine and heating to react to obtain the modified amine curing agent;

[0015] The flame retardant is preferably boehmite, and the amount used is 1 / 3-1 / 1 of the mass of the modified epoxy resin.

[0016] Furthermore, in the component A, the mass percentages of the substances are: modified epoxy resin 50-85%, flame retardant 10-30%, diluent 2-4%, thixotropic agent 1-10%, defoaming agent 0.1-1%, and coupling agent 0.5-2%.

[0017] Furthermore, in the B component, the mass percentages of the various substances are: curing agent 50-80%, curing accelerator 2-10%, flame retardant 10-30%, thixotropic agent 1-10%, defoaming agent 0.1-1%, and coupling agent 0.5-2%.

[0018] Furthermore, the epoxy resin is one or more of bisphenol A epoxy resin, bisphenol F epoxy resin and hydrogenated bisphenol A epoxy resin.

[0019] Furthermore, the epoxy resin has an epoxy value of 0.09-0.56 eq / 100 g and a viscosity of 1000-4000 mPa·s.

[0020] Epoxy resins are products that contain two or more epoxy groups in their molecular structure and, when reacted with appropriate reagents, can form a network-like structure. Common epoxy resins are primarily bisphenol A glycidyl epoxy resins, commonly referred to as bisphenol A epoxy resins.

[0021] Furthermore, the preparation method of the phosphorus-containing modifier is: vinyl triethoxysilane, azobisisobutyronitrile and 3-hydroxyphenylphosphinopropionic acid are placed in a reaction container and nitrogen is introduced, and the reaction is carried out at 80° C. for 5 hours to obtain the phosphorus-containing modifier.

[0022] Furthermore, the mass ratio of the vinyltriethoxysilane to 3-hydroxyphenylphosphinoyl propionic acid is (0.5-2):1, and the amount of azobisisobutyronitrile is 0.2 of the mass of 3-hydroxyphenylphosphinoyl propionic acid.

[0023] Furthermore, the amount of the phosphorus-containing modifier is 1-5% of the mass of the epoxy resin, and the reaction conditions are 100-120° C. and 0.5-1.5 h.

[0024] There are two methods to introduce phosphorus into epoxy resin adhesives: additive and reactive. Using phosphorus-based flame retardants with active functional groups to react with epoxy resins and bond the phosphorus element to the molecular skeleton of the epoxy resin can achieve the purpose of permanent flame retardancy. Moreover, reactive flame retardants do not have compatibility issues with epoxy resins.

[0025] At high temperatures, polysiloxane produces a cracking layer, which can effectively improve the oxidation resistance of the carbon layer to achieve its flame retardant effect.

[0026] Furthermore, polysiloxanes exhibit good compatibility with polymers. During combustion, they migrate to the polymer surface, forming a polymer gradient material with a polysiloxane-rich layer on the surface. This effectively addresses the issue of decreased thermal stability of phosphorus-containing flame retardants when heated and volatilized. When the material burns, it produces an inorganic, oxygen-isolating, and heat-insulating char layer unique to polysiloxanes (containing -Si-O- or -Si-C- bonds). This layer not only prevents the escape of combustion (decomposition) products but also inhibits the thermal decomposition (decomposition) of the polymer, thereby achieving a low-smoke, low-toxicity flame retardant effect.

[0027] Furthermore, the diluent is one or more of dodecyl glycidyl ether, 1,4-butanediol glycidyl ether, phenyl glycidyl ether and polyhydroxy polyether.

[0028] Furthermore, the defoaming agent is one or more of 6201, BYK-141 and BYK-053.

[0029] Furthermore, the thixotropic agent is one or more of hydrogenated castor oil, polyamide wax, and fumed silica.

[0030] Because boehmite is similar to metal hydroxides, it absorbs a large amount of heat during the combustion process of the material. During the thermal decomposition process, the water formed by the decomposition of boehmite will gradually evaporate, absorbing heat. At the same time, the water vapor formed can also dilute the combustible gas. In addition, after the decomposition of boehmite during the combustion process, it will form dense aluminum oxide on the surface of the material, which will hinder the transmission of heat and combustible gases into the interior of the material, slowing the combustion rate of the material and achieving a good flame retardant effect.

[0031] During the combustion process, the modified amine curing agent decomposes into phosphoric acid at high temperature. Metaphosphoric acid or polymetaphosphoric acid covers the surface of the material, forming a phosphorus-rich organic carbon layer, which can effectively slow down the combustion rate of the polymer material; at the same time, the gases such as N2, NH3 and water vapor produced during its decomposition can also isolate oxygen, further improving the flame retardant properties.

[0032] Furthermore, the molar ratio of melamine to 3-hydroxyphenylphosphinopropionic acid is greater than 1:1.

[0033] Furthermore, the curing accelerator is one or more of triethanolamine, 2-ethyl-4-methylimidazole, and 2,4,6-tris(dimethylaminomethyl)phenol.

[0034] Furthermore, the coupling agent is KH550 and / or KH560.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. There are two methods for introducing phosphorus into epoxy resin adhesives: additive and reactive. Phosphorus-based flame retardants with active functional groups are used to react with epoxy resins to bond phosphorus to the molecular skeleton of epoxy resins, thereby achieving permanent flame retardancy. Moreover, reactive flame retardants do not have compatibility issues with epoxy resins. Polysiloxanes have good compatibility with polymers and can migrate appropriately to the polymer surface during combustion to form a polymer gradient material with a polysiloxane-rich layer on the surface. This can effectively solve the problem of decreased thermal stability of phosphorus-containing flame retardants when they volatilize due to heat.

[0037] 2. Boehmite absorbs a large amount of heat during the combustion process of the material, and the water formed by the decomposition of boehmite will gradually evaporate during the thermal decomposition process, absorbing heat. At the same time, the water vapor formed can also dilute the combustible gas. In addition, after the decomposition of boehmite during the combustion process, dense aluminum oxide will be formed on the surface of the material, which will hinder the spread of heat and combustible gases into the interior of the material, slow down the combustion rate of the material, and achieve a good flame retardant effect.

[0038] 3. During the combustion process, the modified amine curing agent decomposes into phosphoric acid at high temperature. Metaphosphoric acid or polymetaphosphoric acid covers the surface of the material, forming a phosphorus-rich organic carbon layer, which can effectively slow down the combustion rate of the polymer material. Due to the adsorption effect between phosphorus and alumina, the phosphorus-rich organic carbon layer can be more stably attached to the dense alumina surface, enhancing the flame retardant effect. At the same time, the gases such as N2, NH3 and water vapor produced during its decomposition can also isolate oxygen, further improving the flame retardant performance. DETAILED DESCRIPTION

[0039] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the embodiments described are part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0040] Reagent Description:

[0041] Bisphenol A epoxy resin, industrial grade, Wuxi Resin Factory; vinyl triethoxysilane, azobisisobutyronitrile, dodecyl glycidyl ether, 3-hydroxyphenylphosphinopropionic acid, sodium hydroxide, melamine, polyamide wax, triethanolamine, analytical grade, Sinopharm Chemical Reagent Co., Ltd.; BYK-141, analytical grade, Shanghai Buding Chemical Co., Ltd.; boehmite, Zibo Shuochuang Alumina Co., Ltd.

[0042] Preparation Example 1

[0043] Preparation of modified epoxy resin:

[0044] 10 g of vinyltriethoxysilane, 0.2 g of azobisisobutyronitrile, and 10 g of 3-hydroxyphenylphosphinopropionic acid were placed in a reactor, introduced with nitrogen, and heated to 80° C. for reaction for 5 h to obtain the phosphorus-containing modifier.

[0045] 100g of bisphenol A epoxy resin and 3g of phosphorus-containing modifier were placed in a reactor and heated at 10℃·min -1 The temperature was raised to 100° C., reacted for 1 hour, and then cooled to room temperature to obtain the modified epoxy resin.

[0046] Preparation Example 2

[0047] Preparation of a modified amine curing agent: Dissolve 21.4 g of 3-hydroxyphenylphosphinopropionic acid in 200 mL of deionized water. Add sodium hydroxide solution to adjust the solution pH to neutral. Then, add 18.9 g of melamine. Heat to 90°C and reflux with stirring for 24 hours. Filter to remove unreacted melamine. Place in an ice-water bath. The product precipitates in the aqueous phase, filters, and washes with deionized water to obtain the modified amine curing agent. Example 1

[0048] 60 g of the modified epoxy resin described in Preparation Example 1, 20 g of boehmite, 3 g of dodecyl glycidyl ether, 5 g of polyamide wax, 0.5 g of BYK-141, and 1 g of KH550 were placed in a reaction kettle, stirred at 400 rpm at 50° C. for 60 min, then vacuumed and discharged, and allowed to stand in a sealed, dry environment at 10° C. to obtain component A;

[0049] 60 g of the modified amine curing agent described in Preparation Example 2, 5 g of triethanolamine, 20 g of boehmite, 5 g of polyamide wax, 0.5 g of BYK-141, and 1 g of KH550 were placed in a reaction kettle and stirred at 400 rpm at 40° C. for 60 min. The mixture was then vacuumed and discharged, and allowed to stand in a sealed, dry environment at 10° C. to obtain the B component. Example 2

[0050] The difference between this embodiment and embodiment 1 is that the amount of the phosphorus-containing modifier used in the preparation example 1 is 1 g.

[0051] The other parts are exactly the same as in Example 1. Example 3

[0052] The difference between this embodiment and embodiment 1 is that the amount of the phosphorus-containing modifier used in the preparation example 1 is 5 g.

[0053] The other parts are exactly the same as in Example 1. Example 4

[0054] The difference between this embodiment and embodiment 1 is that the amount of boehmite used is 10 g.

[0055] The other parts are exactly the same as in Example 1. Example 5

[0056] The difference between this embodiment and embodiment 1 is that the amount of boehmite used is 30 g.

[0057] The other parts are exactly the same as in Example 1. Example 6

[0058] The difference between this embodiment and embodiment 1 is that the amount of the modified amine curing agent used is 50 g.

[0059] The other parts are exactly the same as in Example 1. Example 7

[0060] The difference between this embodiment and embodiment 1 is that the amount of the modified amine curing agent used is 80 g.

[0061] The other parts are exactly the same as in Example 1. Example 8

[0062] The difference between this embodiment and embodiment 1 is that the amount of vinyltriethoxysilane used in the preparation example 1 is 5 g.

[0063] The other parts are exactly the same as in Example 1. Example 9

[0064] The difference between this embodiment and embodiment 1 is that the amount of vinyltriethoxysilane used in the preparation example 1 is 20 g.

[0065] The other parts are exactly the same as in Example 1.

[0066] Comparative Example 1

[0067] The difference between this comparative example and Example 1 is that the modified epoxy resin is not modified, the amount of boehmite used is 0 g, and the modified amine curing agent is not modified.

[0068] The other parts are exactly the same as in Example 1.

[0069] Comparative Example 2

[0070] The difference between this comparative example and Example 1 is that the amount of boehmite used is 0 g.

[0071] The other parts are exactly the same as in Example 1.

[0072] Comparative Example 3

[0073] The difference between this comparative example and Example 1 is that the modified amine curing agent is not modified.

[0074] The other parts are exactly the same as in Example 1.

[0075] Tests and results

[0076] The component A and the component B were mixed in a volume ratio of 1:1, and the flame retardant properties of the prepared flame retardant epoxy structural adhesive were evaluated by limiting oxygen index and vertical burning tests.

[0077] Limiting oxygen index test: The test conditions are in accordance with GB2406-93 Plastics combustion performance test method - oxygen index method.

[0078] And test the resistance value of its rubber block (3cm*3cm*4cm).

[0079] The results are shown in Table 1.

[0080] Table 1

[0081] project Limiting oxygen index% (LOI) UL-94 vertical burning rating <![CDATA[Resistance (1*10 13 Ω)]]> Example 1 60 V-0 1.3 Example 2 37 V-1 1.8 Example 3 62 V-0 1.7 Example 4 32 V-1 0.9 Example 5 67 V-0 20.4 Example 6 34 V-1 1.2 Example 7 58 V-0 1.3 Example 8 64 V-0 1.1 Example 9 30 V-1 1.5 Comparative Example 1 19 Not flame retardant 0.00006 Comparative Example 2 20 V-2 0.3 Comparative Example 3 27 V-1 1.0

[0082] It can be seen from Examples 1-3 and Comparative Example 1 that the introduction of a modifier into the epoxy resin has a significant effect on its flame retardancy. The two-component epoxy adhesive in Comparative Example 1 has basically no flame retardancy. As the amount of phosphorus-containing modifier increases, the flame retardancy of the two-component epoxy adhesive continues to improve.

[0083] It can be seen from Examples 4-5 and Comparative Example 1 that when the amount of boehmite in the filler is 20 g, the UL-94 vertical burning rating of the two-component epoxy adhesive can reach V-0, and further increasing the amount slightly increases the limiting oxygen index.

[0084] It can be seen from Examples 6-7 and Comparative Example 1 that when the amount of modified amine curing agent increases from 50g to 60g, the flame retardancy of the two-component epoxy adhesive is improved. However, when the amount of modified amine curing agent is 80g, due to its large molecules, it cannot react completely with the epoxy resin and will exist in the system as an impurity, hindering the decomposition reaction of the curing agent that has been combined with the epoxy resin molecules, thereby reducing the flame retardant effect.

[0085] As can be seen from Example 1 and Comparative Examples 1-3, changes in the usage of boehmite and modified amine curing agents will affect the flame retardancy of the adhesive. However, when changing the amount of boehmite, in addition to the impact of its own flame retardancy, the adsorption of aluminum oxide and phosphorus-containing substances produced after its combustion will also be affected. Therefore, changes in the amount of boehmite have the greatest impact on the flame retardancy of the adhesive.

[0086] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing a high-resistance flame-retardant two-component epoxy adhesive, characterized in that: The specific steps include: Preparation of modified epoxy resin: 10 g of vinyl triethoxysilane, 0.2 g of azobisisobutyronitrile, and 10 g of 3-hydroxyphenylphosphinopropionic acid were placed in a reactor, introduced with nitrogen, and heated to 80° C. for 5 h to obtain a phosphorus-containing modifier; 100g of bisphenol A epoxy resin and 3g of phosphorus-containing modifier were placed in a reactor and heated at 10℃·min -1 Heating to 100° C., reacting for 1 hour, and then cooling to room temperature to obtain the modified epoxy resin; Preparation of a modified amine curing agent: 21.4 g of 3-hydroxyphenylphosphinoyl propionic acid was dissolved in 200 mL of deionized water, sodium hydroxide solution was added to adjust the pH of the solution to neutral, and then 18.9 g of melamine was added. The temperature was raised to 90° C. and refluxed with stirring for 24 hours. Unreacted melamine was removed by filtration, and the mixture was placed in an ice-water bath. The product precipitated in the aqueous phase, filtered, and washed with deionized water to obtain the modified amine curing agent. 60 g of the modified epoxy resin, 20 g of boehmite, 3 g of dodecyl glycidyl ether, 5 g of polyamide wax, 0.5 g of BYK-141, and 1 g of KH550 were placed in a reaction kettle, stirred at 400 rpm at 50° C. for 60 min, then vacuumed and discharged, and allowed to stand in a sealed, dry environment at 10° C. to obtain component A; 60 g of the modified amine curing agent, 5 g of triethanolamine, 20 g of boehmite, 5 g of polyamide wax, 0.5 g of BYK-141, and 1 g of KH550 were placed in a reaction kettle, stirred at 400 rpm at 40° C. for 60 min, then vacuumed and discharged, and allowed to stand in a sealed, dry environment at 10° C. to obtain component B; The high-resistance flame-retardant two-component epoxy adhesive is obtained by mixing the component A and the component B.