CN115651582A - Preparation method of heat-conducting toughening insulating epoxy resin structural adhesive - Google Patents
Preparation method of heat-conducting toughening insulating epoxy resin structural adhesive Download PDFInfo
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Abstract
The invention relates to a preparation method of a heat-conducting toughening insulation epoxy resin structural adhesive. The method adopts the method of combining high-temperature activation treatment, modification in a polar mixed solvent and a coupling agent, sanding and high-shear action to obtain organic modified boron nitride nanosheets, and simultaneously prepares a multi-layer structure acrylate polymer toughening modifier through an emulsion polymerization technology, wherein the mass ratio of a rubber phase to a plastic phase of the toughening modifier is less than 1, and two functional monomers are copolymerized in an outermost interface layer to realize chemical compatibilization of the toughening modifier and an epoxy resin interface, so that the strength of thermosetting epoxy resin is retained while the toughening efficiency is improved; the structural adhesive mixture obtained by adopting a specific multi-component mixing process has low viscosity and is beneficial to construction. The invention keeps the insulativity on the basis of improving the thermal conductivity and the bonding performance of the epoxy resin structural adhesive, and achieves unexpected effects on the aspect of the epoxy resin structural adhesive.
Description
Technical Field
The invention relates to a preparation method of an epoxy resin structural adhesive with high thermal conductivity, high bonding strength and good insulating property, in particular to a structural modification method of hexagonal boron nitride, a preparation method of a multilayer structure acrylate polymer and a unique preparation method of the epoxy resin structural adhesive. Belongs to the technical field of adhesive preparation.
Background
The structural adhesive has high bonding strength, good durability, can bear larger load, is aging-resistant and corrosion-resistant, has stable performance in expected life, is suitable for bonding strong structural members, and is widely applied to electronics, electric appliances, automobiles, machinery, civil construction, containers, sports goods and daily necessities. With the rapid development of electronic science and technology, automobile and building industries in recent years, the structural adhesive is widely applied. The twenty-first century is an information age, the electronic industry develops rapidly, and new requirements are put forward on the heat conducting performance of materials, such as prevention of influence on the service life of electronic products caused by overlarge heat productivity and difficulty in dissipation of small-size high-integration components. The traditional high polymer material has low thermal conductivity which is only 0.192W/(m.K), is difficult to meet the requirement of modern electronic products on high heat conduction, and develops a material with excellent adhesive property, high thermal conductivity and high insulating property so as to meet the requirement of industrial development.
The epoxy resin structural adhesive is a three-dimensional network structure thermosetting material formed by the reaction of epoxy resin and a curing agent, has the advantages of good insulation and bonding performance, relatively low price, common bonding process and the like, and is widely applied to the fields of household appliances, electronic devices, automobiles, machinery and the like. However, epoxy resins have low thermal conductivity, high viscosity after mixing with common toughening modifiers and fillers, and poor flowability, which limits the application range thereof. Therefore, how to improve the thermal conductivity and fluidity of the epoxy resin becomes a difficult point and a key point in material development on the premise of ensuring the excellent performance of the epoxy resin. For this reason, a thermally conductive filler is generally added to the epoxy resin to improve its thermal conductivity. The traditional heat conducting filler comprises carbon-based materials, such as carbon nano tubes, graphene and the like, and metal powder and other fillers; however, the adhesive prepared by using the fillers has the defects of high conductivity, poor forming manufacturability and the like, and cannot meet the application of occasions with high insulation performance requirements. The patent CN01831264A adopts the filled carbon nano tube to prepare a high-performance heat-conducting adhesive, and the heat conductivity coefficient is as high as 25.5W/(m.K). However, the carbon nanotube has good conductivity, which causes poor insulation of the adhesive after filling, and is difficult to meet the requirement of the existing electronic product on the insulation performance, and limits the application of the carbon nanotube in the fields of high heat conductivity and insulation performance. The patent CN110205071A discloses a preparation method and application of a quick-drying heat-conducting epoxy resin structural adhesive, wherein a heat-conducting filler is one or more of alumina, aluminum hydroxide, boron nitride and aluminum nitride, and the prepared structural adhesive has a heat conductivity coefficient of 0.5-3W/(m.K); the epoxy resin structural adhesive can be automatically operated, has short curing time and greatly shortens the production period; however, the two-component mixed glue needs to be stored at the temperature of 0-10 ℃, has strict requirements on storage environment, and increases storage steps and production cost.
Hexagonal boron nitride (b)hBN) is a two-dimensional structure inorganic material with the characteristics of high heat conductivity, electric insulation and the like, and can be used as the optimal selection of the heat-conducting modified filler of the epoxy resin structural adhesive. But the hexagonal boron nitride has the defects of low surface activity, few reactive sites, large interfacial tension with matrix resin, easy agglomeration and the like; if unmodified hexagonal boron nitride is added directly to the resin, the adhesion and thermal conductivity properties of the matrix resin are greatly reduced. Therefore, it is necessary to modify the surface of hexagonal boron nitride to improve the dispersibility in the matrix resin and the interfacial adhesion with the resin matrix, thereby improving the thermal conductivity of the epoxy resin structural adhesive.
Disclosure of Invention
The invention aims to provide a preparation method of a heat-conducting toughened insulating epoxy resin structural adhesive, aiming at the defects that the current epoxy resin structural adhesive has low heat-conducting property and high crosslinking density, causes low brittleness, low bonding strength and the like, and cannot simultaneously meet the performance requirements. According to the invention, a method of combining high-temperature activation treatment, modification in a polar mixed solvent and a coupling agent, sanding and high-shear action is adopted to obtain organically modified hexagonal boron nitride nanosheets, meanwhile, a multi-layer structure acrylate polymer toughening modifier is prepared by an emulsion polymerization technology, the mass ratio of a rubber phase to a plastic phase of the toughening modifier is less than 1, two functional monomers are copolymerized in an outermost interface layer to realize chemical compatibilization of the toughening modifier and an epoxy resin interface, and the strength of thermosetting epoxy resin is retained while the toughening efficiency is improved; the structural adhesive mixture obtained by adopting a specific multi-component mixing process has low viscosity and is beneficial to construction. Therefore, the invention keeps the insulativity on the basis of improving the thermal conductivity and the bonding performance of the epoxy resin structural adhesive, and achieves unexpected effects on the aspect of the epoxy resin structural adhesive.
The technical scheme of the invention is as follows:
a preparation method of a heat-conducting toughening insulating epoxy resin structural adhesive comprises the following steps:
step 1, stripping and surface modification of hexagonal boron nitride:
(a) Putting the hexagonal boron nitride into a high-temperature tube furnace, and activating for 2-5 hours at 800-1200 ℃; adding the activated hexagonal boron nitride into 5-20 wt% sodium hydroxide solution, carrying out oil bath at 90-120 ℃, stirring, condensing and refluxing for 2-4 h, cooling, filtering and drying to obtain hexagonal boron nitride powder;
wherein, every 100 to 200ml of sodium hydroxide solution is added with 4 to 7g of hexagonal boron nitride;
(b) Adding the hexagonal boron nitride powder obtained in the step (a), N-dimethylformamide and 3- (2-aminoethylamino) propyl trimethoxy silane coupling agent into deionized water, mixing for 20-40 min to obtain a dispersion, then adding the dispersion into a sand mill with zirconia beads, shearing at a high speed of 6000-8000 rpm for 2-4 h, filtering, centrifuging and drying to obtain organically modified hexagonal boron nitride;
wherein the mass ratio of the dispersion liquid is hexagonal boron nitride powder: n, N-dimethylformamide: 280-420 parts of 3- (2-aminoethylamino) propyl trimethoxy silane coupling agent = 2-4, and 280-420 parts of zirconium oxide beads are added into 280-420 parts of dispersion liquid by mass;
the diameter of the zirconia beads is 1-5 mm;
step 2. Preparation of multilayer acrylate Polymer
(a) Preparation of seed layer monomer pre-emulsion
Mass fraction of the components
0.10-0.15% of emulsifier
Deionized water 130
Seed layer acrylate monomer 10-15
0.04-0.10 percent of cross-linking agent
Adding the material components into a container according to the proportion, and uniformly stirring by magnetic force to obtain seed layer monomer pre-emulsion for later use;
(b) Preparation of core layer monomer pre-emulsion
Mass fraction of the components
0.72 to 1.05 percent of emulsifier
70 to 75 percent of nuclear layer acrylate monomer
0.10-0.25 of cross-linking agent
Adding the material components into a container according to the proportion, and uniformly stirring by magnetic force to obtain a core layer monomer pre-emulsion for later use;
(c) Preparation of Shell monomer Pre-emulsion
Mass fraction of the components
Emulsifier 2.55-3.05
120-160 parts of shell acrylic ester monomer
0.28 to 0.52 percent of cross-linking agent
Adding the material components into a container according to a ratio, and uniformly stirring by magnetic force to obtain a shell layer monomer pre-emulsion for later use;
(d) Preparation of the outermost monomer Pre-emulsion
Mass fraction of the components
0.10-0.20 percent of emulsifier
1 to 4 of fluorine-containing acrylate monomer
0.08 to 0.12 percent of cross-linking agent
5 to 8 functional monomers
Adding the material components into a container according to the proportion, and uniformly stirring by magnetic force to obtain an outermost layer monomer pre-emulsion for later use;
(e) Preparation of acrylate polymers having a multilayer Structure
Placing a four-opening reactor provided with a stirrer, a condenser pipe, a thermometer and a nitrogen inlet pipe in a constant-temperature water bath kettle, setting the mechanical stirring speed to be 100-300 r/m, introducing nitrogen into the four-opening reactor for 5-15 minutes to replace air, adding the seed layer monomer pre-emulsion obtained in the step a into the reactor, introducing condensed water into the condenser pipe, heating the reactant to 55-57 ℃ under the stirring state, adding a first initiator aqueous solution into the reactor once after the temperature of the system is constant, and starting reaction timing; after reacting for 25-35 minutes, ending the polymerization stage of the seed layer monomer; uniformly dripping the nuclear layer monomer pre-emulsion prepared in the step b into a reactor, simultaneously continuously dripping 1/2 of second initiator aqueous solution at a constant speed from another feeding port, finishing dripping at a constant speed within 15-20 minutes, finishing dripping the nuclear layer monomer pre-emulsion at a uniform speed within 30-50 minutes, and finishing the polymerization stage of the nuclear layer monomer; then, dropwise adding the shell layer monomer pre-emulsion prepared in the step c into the reactor, simultaneously, continuously and uniformly dropwise adding the rest 1/2 of the second initiator aqueous solution at the other feeding port, uniformly dropwise adding the shell layer monomer pre-emulsion in the reactor within 15-20 minutes, uniformly dropwise adding the shell layer monomer pre-emulsion in the reactor within 60-90 minutes, and finishing the polymerization stage of the shell layer monomer; uniformly dropwise adding the outermost monomer pre-emulsion obtained in the step d, and finishing the polymerization stage of the outermost monomer after the uniform dropwise adding is finished within 10-20 minutes; then keeping the temperature for reaction for 15-45 minutes, stopping stirring, closing the condensed water and the nitrogen, taking out the reactor, and naturally cooling to room temperature; then dropwise adding 1-10 wt% of NaOH aqueous solution until obtaining a multilayer structure acrylate polymer emulsion with a pH value of 7;
the seed layer and the core layer acrylate monomers in the steps a and b are all hexyl acrylate;
the shell acrylic ester monomer in the step c is methyl acrylate;
the outermost layer of the fluorine-containing acrylate monomer in the step d is trifluoroethyl acrylate; the functional monomer is acrylic acid;
the emulsifier used in the steps a, b, c and d is anionic emulsifier sodium dodecyl diphenyl ether disulfonate; all the cross-linking agents used in the steps a, b, c and d are allyl acrylate;
the initiator is potassium persulfate, and is added in a water solution mode, and the specific material ratio is as follows:
mass fraction of potassium persulfate Water
0.40-0.60-50 parts of first initiator aqueous solution
0.20-0.40-50 parts of second initiator aqueous solution
(f) The neutralized emulsion is put into a refrigerator at the temperature of-5 to-30 ℃ for freezing for 3 to 8 hours, and then is dried for 5 to 6 hours in a low-temperature freeze drier with the vacuum degree of 10 to 30 Pa to prepare powdery multi-layer structure acrylate polymer;
the specific quality of the above substances is not limited to the invention, and the actual production is expanded or reduced according to the above quality ratio according to the required product amount.
Step 3, the preparation of the heat-conducting toughened insulating epoxy resin structural adhesive comprises the following steps:
the material proportion and the preparation steps of the epoxy resin structural adhesive are as follows:
the mass portions of the components
50-70 parts of epoxy resin
10 to 25 portions of liquid rubber
Dicyandiamide 3-10
1 to 10 portions of organic modified hexagonal boron nitride
Acrylate polymer 2 to 8 having a multilayer structure
10-20 parts of fumed silica
Cyanate ester resin 1-5
2 to 7 portions of iron oxide red pigment
Mixing materials: the materials are stirred according to a certain mass ratio until no dry powder exists, and then the materials are rolled on a three-roller machine for four times, wherein the first time of loose rolling (the roller spacing is 1.5-2.0 mm) is carried out for 0.5-1.5 minutes, the second time to third time of tight rolling (the roller spacing is 0.5-0.8 mm) is carried out for 2-5 minutes, and the fourth time of loose rolling (the roller spacing is 1.5-2.0 mm) is carried out for 0.5-1.5 minutes.
Finally obtaining the heat-conducting toughening insulating epoxy resin structural adhesive.
The epoxy resin is bisphenol F type epoxy resin; the liquid rubber is liquid nitrile rubber. The iron oxide red pigment is specifically ferric oxide, and the iron oxide red pigment is 600-800 meshes;
the application method of the heat-conducting toughening insulating epoxy resin structural adhesive prepared by the method comprises the following steps:
coating: respectively coating the two cleaned metal materials with a structural adhesive layer with the thickness of 0.08-0.15 mm, and then clamping the two metal materials together;
and (3) curing: and (3) placing the clamped bonding piece in an oven with a blowing function at 170-190 ℃ for 10-40 min, taking out, and placing at room temperature for 12-24h to finish bonding.
The application method of the heat-conducting toughening insulating epoxy resin structural adhesive is characterized in that the metal material is specifically stainless steel, aluminum alloy or cast iron.
The units of the mass parts are the same.
The invention has the substantive characteristics that:
the hexagonal boron nitride is a two-dimensional inorganic material, and after high-temperature treatment, interlayer loosening occurs, so that subsequent stripping is easy to perform; the hexagonal boron nitride with the micron thickness is stripped into nanosheets by alkali solution treatment and high-speed shearing treatment in a polar solvent and a silane coupling agent in a sand mill, organic modification is simultaneously realized on the surfaces of the novel high-surface-energy nanosheets, the organically modified hexagonal boron nitride nanosheets are easily dispersed in an epoxy resin matrix, the interfacial tension is reduced, and the bonding performance and the thermal conductivity of the epoxy resin structural adhesive are improved simultaneously. In addition, the invention adopts emulsion polymerization technology to prepare the multi-layer structure acrylate polymer, and controls the monomer composition and the addition, the emulsifier structure and the addition, and the dropping speed of the mixed monomer to obtain the final multi-layer structure acrylate polymer with controllable emulsion particle size and radial composition. The current patent of the invention is a three-layer structure, and the mass ratio of the rubber phase mass of the sum of the seed layer and the core layer to the shell layer plastic phase is more than 1; the ratio of the mass of the rubber phase of the seed layer and the core layer to the mass of the shell layer and the outermost layer plastic is less than 1, so that the strength of the thermosetting epoxy resin matrix can be maintained, and the fluorine acrylate monomer and the functional monomer acrylic acid are independently added into the outermost layer, so that the formed outermost layer polymer can remarkably reduce the viscosity of the mixture with the epoxy resin matrix and other components, and is favorable for coating construction on the adhered surface. In the prior art, a plastic phase hard monomer and a functional monomer are copolymers in a shell layer plastic phase, and the copolymer is used as an outermost layer to form a single polymer, so that the content of a functional polymer is increased, the addition of a toughening modifier is reduced, the toughness of epoxy resin is improved, and the bonding strength between an epoxy resin structural adhesive and metal is improved.
The addition of the organically modified hexagonal boron nitride nanosheets can form a heat conduction path in a structural adhesive system of an epoxy resin matrix more easily, and the brittleness of the epoxy resin is improved by the multi-layer structure acrylate polymer, so that the heat conduction performance and the bonding performance of the epoxy resin structural adhesive are effectively improved. Therefore, the surface organic modified hexagonal boron nitride nanosheet, the multi-layer structure acrylate polymer, the epoxy resin and other components are mixed by a specific process, and the toughened insulating epoxy resin structural adhesive with excellent heat conductivity is prepared after heating and crosslinking.
The invention has the beneficial effects that:
the common epoxy resin has poor heat-conducting property, belongs to a brittle material after being cured, has the defects of poor mechanical property, flammability and the like, and limits the application of the epoxy resin in the fields of electronic device bonding, aerospace, machinery and the like. In order to make up for the performance defect of the epoxy resin structural adhesive and the defects in the prior art, the invention carries out high-temperature activation treatment and surface modification on the hexagonal boron nitride to obtain the organically modified hexagonal boron nitride nanosheet,the heat conductivity of the epoxy resin structural adhesive is improved; the multi-layer structure acrylate polymer is prepared by adopting an emulsion polymerization technology, so that the bonding property of the epoxy resin structural adhesive is improved. The invention provides a preparation method of a heat-conducting toughened insulating epoxy resin structural adhesive, which is used for further improving the bonding strength of the structural adhesive and expanding the application range of the epoxy resin structural adhesive on the basis of improving the heat-conducting property. High heat-conducting performance and excellent bonding performance, and expands the application of the adhesive in the fields of electronic device bonding and aerospace. The organic modified hexagonal boron nitride nanosheet obtained by high-temperature activation treatment, surface modification of a silane coupling agent and a sand grinding technology has good interface cohesiveness in an epoxy resin matrix, reduces phonon scattering and forms a heat conduction path; the multilayer structure acrylate polymer modifier emulsion prepared by the emulsion polymerization method has the advantages that the total conversion rate of monomers is 99.68%, the content of coalescents is only 0.34%, the particle size of final emulsion particles is 348 nm, the particle size distribution index is only 0.023, and the mass ratio of the mass of a rubber phase of the sum of the seed layer and the core layer to the mass of shell layer and outermost layer plastic is 0.6. When the addition amount of the organically modified hexagonal boron nitride nanosheet is 2 parts and the addition amount of the multi-layer structure acrylate polymer is 5 parts, the outflow volume of the epoxy resin structural adhesive per minute is increased from 4.19 g to 12.57 g, the two times are increased, and the coating workability of the structural adhesive is improved; the tensile shear strength of the steel sheet-steel sheet is improved to 37.45 MPa from 15.75 MPa, and is doubled; the compressive strength is improved to 70.98 MPa from 58.03 MPa, and the impact peel strength is improved to 28.52 kN/m from 12.17 kN/m; the T peeling strength is improved from 4.98 kN/m to 10.89 kN/m; the thermal conductivity coefficient is increased from 0.22W/(m.K) to 1.72W/(m.K), the improvement is 6.8 times, and the resistivity is kept at 10 16 On the order of (omega or omega cm), the insulating performance of the structural adhesive is still very good. The results show that the organic modified hexagonal boron nitride nanosheet and the multi-layer structure acrylate polymer toughening modifier are jointly added, so that the epoxy resin structural adhesive mixture is low in viscosity, convenient to construct, environment-friendly and safe, the dispersing time is shortened, and the organic modified hexagonal boron nitride nanosheet and the multi-layer structure acrylate polymer toughening modifier have a very positive effect on improving the thermal conductivity, the bonding performance and the insulating performance of the epoxy resin structural adhesive.
Description of the drawings:
fig. 1 is a Transmission Electron Micrograph (TEM) of the final organically modified hexagonal boron nitride nanosheets of example 1;
FIG. 2 is a thermogravimetric curve of the finally organically modified hexagonal boron nitride nanosheet in example 1 under a nitrogen atmosphere;
FIG. 3 is a graph of monomer conversion versus reaction time for the preparation of the multi-layer acrylate polymer of example 1;
FIG. 4 is a graph showing the relationship between the particle size of latex particles and the reaction time in the preparation of the acrylate polymer having a multi-layer structure according to example 1;
FIG. 5 is a graph showing a distribution of Particle Diameters (PDI) of latex particles at the end of the production of the multi-layer acrylate polymer in example 1;
the present invention will be further explained with reference to the following examples and the accompanying drawings. It should be noted that the following examples of the present invention are only illustrative and exemplary of technical aspects.
Detailed Description
Example 1
1.1 Modification of hexagonal boron nitride
(a) Putting hexagonal boron nitride into a high-temperature tube furnace, activating at the high temperature of 1000 ℃ for 3 hours, adding 5 grams of activated hexagonal boron nitride into a 200mL 15wt% sodium hydroxide solution four-neck flask, carrying out oil bath at the temperature of 110 ℃, stirring, condensing, refluxing for 4 hours, cooling, filtering and drying to obtain hexagonal boron nitride powder for later use;
(b) Uniformly mixing 4 g of hexagonal boron nitride powder treated in the step (a), 0.45 g of 3- (2-aminoethylamino) propyl trimethoxy silane coupling agent and 320ml of N, N-dimethylformamide, adding the mixture into a 1.5-liter sand mill, adding 260 g of zirconia beads with the diameter of 2 mm, shearing at a high speed of 7000 r/min for 2 hours, and then filtering, centrifuging and drying to obtain the organically modified hexagonal boron nitride.
And (3) putting a small amount of sample powder into deionized water for ultrasonic dispersion for 30 minutes, taking five droplets, putting the five droplets on a copper net for natural air drying, and observing the morphology of the hexagonal boron nitride nanosheet under a JEM 2100F type Transmission Electron Microscope (TEM). Fig. 1 is a transmission electron micrograph of the final hexagonal boron nitride nanosheet of example 1, and fig. 2 is a thermogravimetric plot under nitrogen atmosphere of the final organically modified hexagonal boron nitride nanosheet of example 1.
1.2 Preparation of acrylate polymers having a multilayer Structure
(a) Preparation of seed layer monomer pre-emulsion
0.12 g of anionic emulsifier sodium dodecyl diphenyl ether disulfonate and 130 g of deionized water are added into a 250ml beaker, magnetic stirring is carried out for 10 min at 80 r/min, then 12 g of hexyl acrylate and 0.06 g of allyl acrylate are added, stirring is continued for 10 min, and seed layer monomer pre-emulsion is obtained for standby.
(b) Preparation of core layer monomer pre-emulsion
0.975 g of anionic emulsifier sodium dodecyl diphenyl ether disulfonate, 72 g of hexyl acrylate and 0.125 g of allyl acrylate are added into a 250ml beaker and magnetically stirred for 20 min at 80 rpm to obtain a core layer monomer pre-emulsion for later use.
(c) Preparation of shell monomer pre-emulsion
2.65 g of anionic emulsifier sodium dodecyl diphenyl ether disulfonate, 128 g of methyl acrylate and 0.32 g of allyl acrylate are added into a 250ml beaker, and are magnetically stirred for 20 min at 80 r/min, and are uniformly mixed to obtain a shell layer monomer pre-emulsion for later use.
(d) Preparation of outermost monomer Pre-emulsion
0.12 g of anionic emulsifier sodium dodecyl diphenyl ether disulfonate, 4 g of trifluoroethyl acrylate and 8 g of acrylic acid are added into a 100ml beaker, and are magnetically stirred for 10 min at 80 revolutions per minute, and are uniformly mixed to obtain the outermost monomer pre-emulsion for later use.
(e) Preparation of acrylate polymers having a multilayer Structure
Placing a four-opening reactor provided with a stirrer, a condenser pipe, a thermometer and a nitrogen inlet pipe in a constant-temperature water bath kettle, setting the mechanical stirring speed to be 158 revolutions per minute, introducing nitrogen into the four-opening reactor for 12 minutes to replace air, adding the seed monomer pre-emulsion obtained in the step a into the reactor, introducing condensed water into the condenser pipe, heating the reactant to 56.5 ℃ under the stirring state, simultaneously increasing the introduction amount of the nitrogen to 2.85 liters per minute, and starting reaction timing after a first initiator aqueous solution is added into the reactor once after the temperature of the system is constant; after reacting for 30 minutes, ending the polymerization stage of the seed layer monomer; uniformly dripping the nuclear layer monomer pre-emulsion prepared in the step b into a reactor, simultaneously continuously dripping 1/2 of second initiator aqueous solution at a constant speed from the other feeding port, finishing dripping at a constant speed within 20 minutes, finishing dripping the nuclear layer monomer pre-emulsion at a uniform speed within 30 minutes, and finishing the polymerization stage of the nuclear layer monomer; then, dropwise adding the shell monomer pre-emulsion prepared in the step c into the reactor, and simultaneously, continuously and uniformly dropwise adding the rest 1/2 of the second initiator aqueous solution at another feeding port, wherein after the uniform dropwise adding is finished in 20 minutes, the uniform dropwise adding of the shell monomer pre-emulsion is finished in 75 minutes, and the polymerization stage of the shell monomer is finished; uniformly dropwise adding the outermost monomer pre-emulsion obtained in the step d, finishing the uniform dropwise adding within 15 minutes, and finishing the polymerization stage of the outermost monomer; then keeping the temperature for reaction for 30 minutes, stopping stirring, closing the condensed water and the nitrogen, taking out the reactor, and naturally cooling to room temperature; then 5wt% of NaOH aqueous solution is dripped until multilayer structure acrylic ester polymer emulsion with the pH value of 7 is obtained;
the initiator is potassium persulfate, and is added in a water solution mode, and the specific material ratio is as follows:
mass of potassium persulfate per gram of water per gram
First aqueous initiator solution 0.45
Second aqueous initiator solution 0.25.35
(f) Emulsion post-treatment
And (3) freezing the neutralized emulsion in a refrigerator at the temperature of-20 ℃ for 6 hours, and then drying the emulsion in a low-temperature freeze dryer with the vacuum degree of 10 Pa for 5 hours to prepare the powdery multi-layer structure acrylate polymer.
The polyacrylate emulsion prepared was characterized as follows:
in the preparation process of the multi-layer acrylate polymer emulsion, 2 ml of the multi-layer acrylate polymer emulsion is sampled every 30 minutes, and 1.95 ml of the multi-layer acrylate polymer emulsion is used for measuring the instantaneous conversion rate and the total conversion rate of monomer polymerization, and the reference figure 3 shows. After weighing (weight of the beaker was recorded), the mixture was dried in an oven at 80 ℃ for 24 hours until the mass was not changed, and then weighed (weight of the beaker was recorded).
Calculation of monomer conversion:
overall conversionOC：
Instantaneous conversionIC：
In the formula:M i is a firstiThe total mass of the emulsion during the secondary sampling,S i is as followsiThe solid content at the time of sub-sampling,
to be underiTotal mass of initiator added, delta, at subsamplingmTo be at the firstiThe total mass of the emulsifier and the cross-linking agent is added during the secondary sampling,M 0 in order to add the total mass of the monomers,Mto be underiThe mass of monomer added at the time of subsampling.
The agglomerate content calculation formula is as follows:
in the formula:
the total mass of the agglomerates and beaker before drying,wfor the total mass of the agglomerates and beaker after drying,w 0 is the total mass of the acrylate monomers used in the formulation.
Diluting the rest 0.05 ml of the solution with deionized water, and detecting latex particles in a Malvern Zetasizer Nano-ZS90 dynamic laser particle size analyzerParticle size at different reaction times; and the theoretical value of the particle size of the latex particles (d t ) The calculation formula of (a) is as follows:
in the formulaM t RepresentstThe total amount of monomer added at any time;I t is represented intInstantaneous conversion of monomer at the moment;M s represents the total mass of the monomers added at the seed stage;d s represents the calculated particle size of the latex particles at the end of the 30 minute seed stage.
Actual particle size measurement of latex Particles and Distribution Index (PDI): the z-average particle size (dz) and the distribution index PDI of the latex particles were measured at a test temperature of 25. + -. 0.5 ℃ using a Zetasizer model ZS90 dynamic light scattering analyzer from Malvern, UK. The change of the particle size of the latex particle with the reaction time in the polymerization reaction process is shown in FIG. 4, and the final particle size of the multi-layer acrylate polymer latex particle is 348 nm; and the particle size distribution of the latex particles of the final emulsion is shown in figure 5.
1.3 Preparation of epoxy resin structural adhesive
55 g of bisphenol F epoxy resin, 16 g of liquid nitrile rubber, 2 g of organically modified hexagonal boron nitride nanosheet, 5 g of multi-layer structure acrylate polymer, 13 g of fumed silica and 3 g of 600-mesh iron oxide red pigment (ferric oxide) are mechanically stirred for 20 min and uniformly mixed, then 5 g of dicyandiamide and 2 g of cyanate resin are added, the mixture is stirred until the mixture is dry powder-free and then rolled on a three-roll machine for four times, wherein the first time of loose rolling (roll spacing of 1.8 mm) is carried out for 1min, the second time to third times of tight rolling (roll spacing of 0.6 mm) is carried out for 4 min, and the fourth time of loose rolling (roll spacing of 1.6 mm) is carried out for 1 min.
Coating: the surface of the stainless steel metal material is kept clean, and two stainless steel metal surfaces are uniformly coated with glue by a blade. Two adherends coated with glue samples are directly overlapped and overlapped, the thickness of a glue layer is controlled to be 0.10 mm, redundant glue on the edges is scraped off, and the two edges are clamped by clamps.
And (3) curing: and (3) placing the bonding piece in an oven with a blowing function at 170 ℃ for baking for 20 min, taking out, placing at room temperature for 24h, and testing.
Examples 2 to 5
The other steps are the same as example 1, except that in the preparation of the epoxy resin structural adhesive, the addition amount of the multi-layer structure acrylate polymer is 5 g, but the addition amounts of the organically modified hexagonal boron nitride nanosheets are respectively as follows: 2.5 grams, 3 grams, 3.5 grams, and 4 grams.
Comparative example 1
The method comprises the steps of mechanically stirring 55 g of bisphenol F epoxy resin, 16 g of liquid nitrile rubber, 13 g of fumed silica and 3 g of 600-mesh iron oxide red pigment for 20 min, uniformly mixing, adding 5 g of dicyandiamide and 2 g of cyanate ester resin, stirring until the mixture is dry powder-free, rolling on a three-roll machine for four times, wherein the first time of loose rolling (roll spacing of 1.8 mm) is carried out for 1min, the second time to third time of tight rolling (roll spacing of 0.6 mm) is carried out for 4 min, and the fourth time of loose rolling (roll spacing of 1.6 mm) is carried out for 1 min.
Coating: keeping the surface of the stainless steel metal material clean, and uniformly gluing the two stainless steel metal surfaces by using a blade. Two adherends coated with glue samples are directly overlapped and overlapped, the thickness of a glue layer is controlled to be 0.10 mm, redundant glue on the edges is scraped off, and the two edges are clamped by clamps.
And (3) curing: and (3) placing the bonding piece in an oven with a blowing function at 170 ℃ for baking for 20 min, taking out, placing at room temperature for 24h, and testing.
Comparative example 2
55 g of bisphenol F epoxy resin, 16 g of liquid nitrile rubber, 2 g of organically modified hexagonal boron nitride nanosheet, 13 g of fumed silica and 3 g of 600-mesh iron oxide red pigment are mechanically stirred for 20 min and uniformly mixed, then 5 g of dicyandiamide and 2 g of cyanate ester resin are added, the mixture is stirred until the mixture is dry powder-free and then rolled on a three-roll machine for four times, the first time of loose rolling (roll spacing 1.8 mm) is carried out for 1min, the second to third times of tight rolling (roll spacing 0.6 mm) are carried out for 4 min, and the fourth time of loose rolling (roll spacing 1.6 mm) is carried out for 1 min.
Coating: the surface of the stainless steel metal material is kept clean, and two stainless steel metal surfaces are uniformly coated with glue by a blade. Two adherends coated with glue samples are directly overlapped and overlapped, the thickness of a glue layer is controlled to be 0.10 mm, redundant glue on the edges is scraped off, and the two edges are clamped by clamps.
And (3) curing: and (3) placing the bonding piece in an oven with a blowing function at 170 ℃ for baking for 20 min, taking out, placing at room temperature for 24h, and testing.
Comparative example 3
The method comprises the steps of mechanically stirring 55 g of bisphenol F epoxy resin, 16 g of liquid nitrile rubber, 5 g of multi-layer structure acrylate polymer, 13 g of fumed silica and 3 g of 600-mesh iron oxide red pigment for 20 min, uniformly mixing, adding 5 g of dicyandiamide and 2 g of cyanate ester resin, stirring until the mixture is dry powder-free, rolling on a three-roll machine for four times, wherein the first time is loose-rolled (the roll spacing is 1.8 mm) for 1min, the second time is tight-rolled to the third time (the roll spacing is 0.6 mm) for 4 min, and the fourth time is loose-rolled (the roll spacing is 1.6 mm) for 1 min.
Coating: the surface of the stainless steel metal material is kept clean, and two stainless steel metal surfaces are uniformly coated with glue by a blade. Two adherends coated with glue samples are directly overlapped and overlapped, the thickness of a glue layer is controlled to be 0.10 mm, redundant glue on the edges is scraped off, and the two edges are clamped by clamps.
And (3) curing: and (3) placing the bonding piece in an oven with a blowing function at 170 ℃ for baking for 20 min, taking out, placing at room temperature for 24h, and testing.
Table 1 shows the parts by mass of the raw materials of the epoxy resin structural adhesives of examples 1 to 5 and comparative examples 1 to 3. Table 2 shows the parameters of the emulsion polymerization process for the acrylate polymer having a multi-layer structure.
And (3) testing the performance of the obtained epoxy resin structural adhesive:
and (3) testing the pressure flow viscosity of the epoxy resin structural adhesive: the experiments were performed according to SAE J1524-1995 standard on a model pressure-flow viscometer available from the Tianjin Hengpril precision die manufacturer. And (3) testing temperature: 23 ± 2 ℃, relative humidity: RH50% +/-5%. The test procedure is as follows: a glue outlet with a diameter of 2 mm was mounted on a cylinder, a glue sample thermostated to room temperature was injected into the cylinder to prevent air from being mixed into the sample, and the piston was placed from above. The cylinder port was attached to the vent port of the pressure flow viscometer and tightened, taking care not to leak gas. Starting an air pump, adjusting the pressure to 0.5 MPa, releasing the glue, timing for 1min, and taking the extruded weight as the pressure-flow viscosity value of the glue, wherein the unit is g/min. The measurement was carried out in triplicate, and the average of triplicates was taken as the measurement of the pressure flow viscosity.
And (3) testing the tensile shear strength of the steel sheet-steel sheet of the epoxy resin structural adhesive: the experiment is tested according to the standard of GB/T7124-2008, 25 × 12.5 mm epoxy resin structural glue samples are coated on a 100 × 25 × 0.8mm steel plate, two test pieces (two are a group) coated with the glue samples are directly lapped and overlapped, excess glue on the edges is scraped, the two test pieces are clamped by a clamp, the coating glue of a bonding part is placed in a German Bingde oven with the model of FD53 and baked at 170 ℃ for 20 min, the bonding part is taken out and placed at room temperature for more than 24h, the shearing strength of the bonding part is measured by an electronic universal testing machine of Shenzhen Wan testing machine equipment Limited with the model of 204C, the stretching speed is 50 mm/min, the average value of five groups of data is the steel plate-steel plate stretching shearing strength of the glue samples, and the unit is MPa.
And (3) testing the compressive strength of the cured epoxy resin structural adhesive: the test is carried out by preparing sample strips according to the standard of GB/T2567-2008, bending the cured material sample strips in a CMT6104 type microcomputer controlled electronic universal tester, testing the sample strips to be 25 mm × 10 mm × 10 mm, placing the sample strips in a constant temperature environment with the humidity of 50 +/-5% and the temperature of 23 +/-1 ℃ for 24h to eliminate the internal stress, then carrying out compression test at the compression speed of 5 mm/min, similarly selecting at least 6 sample strips from each group for testing, and taking the average value of six groups of data, namely the compression strength of the adhesive, wherein the unit is MPa.
And (3) testing the impact peel strength of the epoxy resin structural adhesive: the test is carried out according to the standard of GB/T36877-2018, a steel plate of 90X 20X 0.8mm is coated with a layer of 30X 20 mm glue sample, two test pieces (two are in a group) coated with the glue sample are overlapped, the excessive glue on the edges is scraped off, the two test pieces are clamped by a clamp, the adhered test pieces are placed in an oven at 170 ℃ for baking for 20 min, and the adhered test pieces are taken out and placed at room temperature for 24h. And inserting the bonding test piece into a wedge-shaped test fixture of model number 302E Shenzhen Wan test testing machine equipment Limited, assembling the test fixture and starting testing. The impact speed is 2 m/s, the average value of five groups of data is taken, namely the impact peel strength of the adhesive, and the unit is kN/m.
And (3) testing the T peel strength of the cured epoxy resin structural adhesive: the test is carried out by coating a layer of 150 × 25 mm glue sample on a steel plate of 200 × 25 × 0.8mm, overlapping two test pieces (two are a group) coated with the glue sample, scraping off the excessive glue on the edges, clamping with a clamp, baking the bonding piece in an oven at 170 ℃ for 20 min, taking out, standing at room temperature for more than 24h, testing the peel strength on a CMT6104 microcomputer controlled electronic universal testing machine, wherein the stretching speed is 200 mm/min, and taking the average value of five groups of data, namely the peel strength of the glue, and the unit is kN/m.
And (3) testing the heat conductivity coefficient: the test was carried out according to ASTM D-5470 test method, with an ambient temperature of 25. + -. 2 ℃.
Testing the electrical insulation performance: the surface resistivity and the volume resistivity of the epoxy resin structural adhesive are tested by adopting a ZC36 type high-resistance meter of a sixth electric meter factory in Shanghai. Temperature: normal temperature, test voltage: 250 And V.
Table 3 shows the amount of different organically modified hexagonal boron nitride nanosheets used in examples 1-5 and the performance parameters of the epoxy resin structural adhesive obtained in comparative examples 1-3. As can be seen from fig. 1, after the hexagonal boron nitride is organically modified and sanded, it shows a low contrast under a transmission electron microscope and is a transparent sheet, indicating that the hexagonal boron nitride is successfully exfoliated into few layers of boron nitride nanosheets. The upper right corner of fig. 1 is its six-fold lattice structure, consistent with that of hexagonal boron nitride, indicating that hexagonal boron nitride retains its structural integrity before and after exfoliation. Fig. 2 is a thermal weight loss curve of organically modified hexagonal boron nitride under nitrogen atmosphere, the high-temperature weight loss rate reaches 6.31%, the content of organic matters on the surface of the hexagonal boron nitride is shown, namely the organic modification effect is shown, and the surface organic modification effect is obvious. The thermal conductivity of the unmodified epoxy resin structural adhesive in comparative example 1 is only 0.22W/(m.K), the thermal conductivity of the epoxy resin structural adhesive is obviously improved after the organically modified hexagonal boron nitride nanosheets are added, the thermal conductivity of the epoxy resin structural adhesive is improved to 4.04W/(m.K) when the addition amount of the organically modified hexagonal boron nitride nanosheets is 4 grams in example 5, and the thermal conductivity of the structural adhesive is in an ascending trend along with the increase of the addition amount. The organically modified hexagonal boron nitride nanosheets have good dispersibility and interfacial force in the epoxy resin structural adhesive, and are beneficial to uniformly dispersing the organically modified hexagonal boron nitride nanosheets in an epoxy resin matrix, and a heat conduction path is formed after the additive amount reaches a certain degree, so that the mutual force of the organically modified hexagonal boron nitride nanosheets in the epoxy resin matrix is increased, the interface phonon scattering is reduced, and the heat conduction performance of the epoxy resin structural adhesive is improved. The research results of the prior literature show that: in the toughening system of the epoxy resin, the mass ratio of a core layer elastomer phase to a shell layer plastic phase of the polyacrylate core/shell structure modifier is required to be more than 1, and the required addition ratio is high, so that the tensile strength and the compressive strength of an epoxy resin matrix are remarkably reduced, because the strength of a rubber elastomer phase is obviously lower than that of a plastic phase. The principle of toughening the brittle matrix by the polyacrylate with the core-shell structure is realized by utilizing the phase separation effect of a rubber elastomer dispersed phase and a plastic phase and improving the deformation capacity of a continuous phase matrix through silver line formation or shear yield of a stress concentration point generated by external force. The mass ratio of the seed layer and the core layer elastomer phase to the shell layer plastic phase and the outermost layer functional polymer layer is less than 1 and 0.6, so that the bonding strength of the epoxy resin structural adhesive is obviously improved even if a small amount of added mass is added, the epoxy resin matrix generates crazing and shear yielding due to stress concentration at the equator of the rubber phase, the deformation capacity of the epoxy resin matrix is improved, the tensile shear strength, the impact peel strength and the T-shaped peel strength of the structural adhesive are improved, and the application range of the epoxy resin structure is greatly expanded. The outermost layer of the functional monomer of acrylate trifluoroethyl methacrylate has relatively low surface energy, and shows low viscosity after being mixed with organically modified hexagonal boron nitride, epoxy resin and matching components thereof, but forms chemical crosslinking with epoxy groups of the epoxy resin by virtue of carboxyl contained in acrylic acid, so that the rubber phase can still achieve the purpose of toughening and modifying.
The results show that the addition of the organically modified hexagonal boron nitride nanosheet and the multi-layer structure acrylate polymer toughening modifier has a positive effect on the bonding performance of the epoxy resin structural adhesive, so that the thermal conductivity of the material is improved, the excellent bonding performance and flowability are ensured, and the use field of the material is expanded; meanwhile, the embodiments 1 to 5 achieve the technical effects of the present invention.
The invention is not the best known technology.
Claims (6)
1. A preparation method of a heat-conducting toughening insulating epoxy resin structural adhesive is characterized by comprising the following steps:
step 1, stripping and surface modification of hexagonal boron nitride:
(a) Putting the hexagonal boron nitride into a high-temperature tube furnace, and activating for 2-5 hours at 800-1200 ℃; adding the activated hexagonal boron nitride into 5-20 wt% sodium hydroxide solution, carrying out oil bath at 90-120 ℃, stirring, condensing and refluxing for 2-4 h, cooling, filtering and drying to obtain hexagonal boron nitride powder;
wherein, every 100 to 200ml of sodium hydroxide solution is added with 4 to 7g of hexagonal boron nitride;
(b) Adding the hexagonal boron nitride powder obtained in the step (a), N-dimethylformamide and 3- (2-aminoethylamino) propyl trimethoxy silane coupling agent into deionized water, mixing for 20-40 min to obtain a dispersion, then adding the dispersion into a sand mill with zirconia beads, shearing at a high speed of 6000-8000 rpm for 2-4 h, filtering, centrifuging and drying to obtain organically modified hexagonal boron nitride;
wherein the mass ratio of the dispersion liquid is as follows: n, N-dimethylformamide: 280-420 parts of 3- (2-aminoethylamino) propyl trimethoxy silane coupling agent = 2-4, and 280-420 parts of zirconium oxide beads are added into 280-420 parts of dispersion liquid by mass;
step 2. Preparation of multilayer acrylate Polymer
(a) Preparation of seed layer monomer pre-emulsion
Mass fraction of the components
0.10 to 0.15 percent of emulsifier
Deionized water 130
Seed layer acrylate monomer 10-15
0.04 to 0.10 percent of cross-linking agent
Adding the material components into a container according to the proportion, and magnetically stirring to obtain a seed layer monomer pre-emulsion for later use;
(b) Preparation of core layer monomer pre-emulsion
Mass fraction of the components
0.72 to 1.05 percent of emulsifier
70 to 75 percent of nuclear layer acrylate monomer
0.10-0.25 of cross-linking agent
Adding the material components into a container according to the proportion, and magnetically stirring to obtain a core layer monomer pre-emulsion for later use;
(c) Preparation of Shell monomer Pre-emulsion
Mass fraction of the components
Emulsifier 2.55-3.05
120-160 parts of shell acrylic ester monomer
0.28 to 0.52 percent of cross-linking agent
Adding the material components into a container according to the proportion, and magnetically stirring to obtain a shell layer monomer pre-emulsion for later use;
(d) Preparation of the outermost monomer Pre-emulsion
Mass fraction of the components
0.10 to 0.20 percent of emulsifier
1 to 4 of fluorine-containing acrylate monomer
0.08 to 0.12 percent of cross-linking agent
5 to 8 functional monomers
Adding the material components into a container according to the proportion, and magnetically stirring to obtain an outermost layer monomer pre-emulsion for later use;
(e) Preparation of acrylate polymers having a multilayer Structure
Placing a four-opening reactor provided with a stirrer, a condenser pipe, a thermometer and a nitrogen inlet pipe in a constant-temperature water bath kettle, setting the mechanical stirring speed to be 100-300 r/m, introducing nitrogen into the four-opening reactor for 5-15 minutes to replace air, adding the seed layer monomer pre-emulsion obtained in the step a into the reactor, introducing condensed water into the condenser pipe, heating the reactant to 55-57 ℃ under the stirring state, adding a first initiator aqueous solution into the reactor once after the temperature of the system is constant, and starting reaction timing; after reacting for 25-35 minutes, ending the polymerization stage of the seed layer monomer; uniformly dripping the nuclear layer monomer pre-emulsion prepared in the step b into a reactor, simultaneously continuously dripping 1/2 of second initiator aqueous solution at a constant speed from another feeding port, finishing dripping at a constant speed within 15-20 minutes, finishing dripping the nuclear layer monomer pre-emulsion at a uniform speed within 30-50 minutes, and finishing the polymerization stage of the nuclear layer monomer; then, dropwise adding the shell layer monomer pre-emulsion prepared in the step c into the reactor, simultaneously, continuously and uniformly dropwise adding the rest 1/2 of the second initiator aqueous solution at the other feeding port, uniformly dropwise adding the shell layer monomer pre-emulsion in the reactor within 15-20 minutes, uniformly dropwise adding the shell layer monomer pre-emulsion in the reactor within 60-90 minutes, and finishing the polymerization stage of the shell layer monomer; uniformly dropwise adding the outermost monomer pre-emulsion obtained in the step d, and finishing the polymerization stage of the outermost monomer after the uniform dropwise adding is finished within 10-20 minutes; then keeping the temperature for reaction for 15-45 minutes, stopping stirring, closing the condensed water and the nitrogen, taking out the reactor, and naturally cooling to room temperature; then dropwise adding NaOH aqueous solution until obtaining the multi-layer structure acrylate polymer emulsion with the pH value of 7;
the seed layer and the core layer acrylate monomers in the steps a and b are all hexyl acrylate;
the shell acrylic ester monomer in the step c is methyl acrylate;
the outermost layer of the fluorine-containing acrylate monomer in the step d is trifluoroethyl acrylate; the functional monomer is acrylic acid;
the emulsifier used in the steps a, b, c and d is anionic emulsifier sodium dodecyl diphenyl ether disulfonate; all the cross-linking agents used in the steps a, b, c and d are allyl acrylate;
the initiator is potassium persulfate, and is added in a water solution mode, and the specific material ratio is as follows:
mass fraction of potassium persulfate Water
0.40-0.60-50 parts of first initiator aqueous solution
0.20-0.40-50 parts of second initiator aqueous solution
(f) The neutralized emulsion is put into a refrigerator at the temperature of-5 to-30 ℃ for freezing for 3 to 8 hours, and then is dried for 5 to 6 hours in a low-temperature freeze dryer with the vacuum degree of 10 to 30 Pa to prepare powdery multi-layer structure acrylate polymer;
step 3, the preparation of the heat-conducting toughened insulating epoxy resin structural adhesive comprises the following steps:
the material proportion and the preparation steps of the epoxy resin structural adhesive are as follows:
mass fraction of the components
50-70 parts of epoxy resin
10 to 25 portions of liquid rubber
Dicyandiamide 3-10
1 to 10 portions of organic modified hexagonal boron nitride
Acrylate polymer 2 to 8 having a multilayer structure
10-20 parts of fumed silica
Cyanate ester resin 1-5
Iron oxide red pigment 2-7
Mixing materials: the components of the materials are stirred according to the proportion until no dry powder exists, and then the materials are rolled on a three-roller machine for four times, wherein the first loose rolling is carried out for 1.5-2.0 mm of roller spacing and 0.5-1.5 minutes, the second tight rolling is carried out for three times, the roller spacing is 0.5-0.8 mm and 2-5 minutes, the fourth loose rolling is carried out for 1.5-2.0 mm, and 0.5-1.5 minutes;
finally obtaining the heat-conducting toughening insulating epoxy resin structural adhesive.
2. The method for preparing a heat conducting toughened insulating epoxy resin structural adhesive as claimed in claim 1, wherein the diameter of the zirconia beads in step 1 (b) is 1-5 mm.
3. The method for preparing a heat-conducting toughened insulating epoxy resin structural adhesive as claimed in claim 1, wherein the concentration of the aqueous solution of NaOH in the step 2 (e) is 1-10 wt%.
4. The method for preparing the heat-conducting toughening insulating epoxy resin structural adhesive according to claim 1, wherein the epoxy resin is bisphenol F type epoxy resin; the liquid rubber is liquid nitrile rubber; the iron oxide red pigment is ferric oxide with 600-800 meshes.
5. The application method of the heat-conducting toughening insulating epoxy resin structural adhesive prepared by the method of claim 1, which is characterized by comprising the following steps:
coating: respectively coating the two cleaned metal materials with a structural adhesive layer with the thickness of 0.08-0.15 mm, and then clamping the two metal materials together;
and (3) curing: and (3) placing the clamped bonding piece in an oven with a blowing function at 170-190 ℃ for 10-40 min, taking out, and placing at room temperature for 12-24h to finish bonding.
6. The method of claim 5, wherein the metal material is stainless steel, aluminum alloy or cast iron.
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