PVAc / PS rigid core-shell particle modified epoxy resin adhesive and preparation method thereof

Abstract

The invention relates to a PVAc / PS rigid core-shell particle modified epoxy resin adhesive and a preparation method thereof, and belongs to the technical field of modified epoxy resin adhesives. In order to solve the problem that an existing modified epoxy resin adhesive cannot give consideration to material toughness, rigidity and heat resistance, the invention provides a preparation method of a PVAc / PS rigid core-shell particle modified epoxy resin adhesive, and the preparation method comprises the following steps: preparing a PVAc / PS rigid core-shell emulsion and core-shell particles, PVAc / PS rigid core-shell particle modified epoxy resin and a modified epoxy resin adhesive. The PVAc / PS rigid core-shell particle modified epoxy resin adhesive provided by the invention has remarkable comprehensive performance advantages, and has positive effects on the strength, rigidity and heat resistance of epoxy resin while improving the toughness of the epoxy resin. The characteristic breakthrough of rigidity-toughness balance provides a bonding solution with more excellent performance for the field of high-end equipment manufacturing, and has important engineering application value.

Description

Technical Field

[0001] This invention belongs to the field of modified epoxy resin adhesive technology, and particularly relates to a PVAc / PS rigid core-shell particle modified epoxy resin adhesive and its preparation method. Background Technology

[0002] Epoxy resins are widely used in adhesives, coatings, insulating materials, and advanced composite materials due to their excellent bonding, mechanical, electrical insulation, and chemical stability. However, cured epoxy resins have inherent defects such as high brittleness, low toughness, and poor impact resistance, which limit their application in a wider range of fields. Toughening modification is usually necessary to meet practical requirements.

[0003] Currently, toughening modification methods for epoxy resins mainly include rubber elastomers, thermoplastic resins, core-shell polymers, thermotropic liquid crystal polymers, and nanoparticles. Among these, core-shell polymer toughening agents have gained widespread application in the preparation of high-performance adhesives due to their significant toughening effect. However, currently commercially available and most researched core-shell polymer toughening agents are mainly soft-core, hard-shell particles, which have significant limitations in application.

[0004] First, soft-core, hard-shell core-shell particles have a low modulus. While they can effectively improve the toughness of epoxy resin, they often reduce its modulus and strength. Second, this structural design leads to a decrease in the heat resistance of epoxy resin, making it unsuitable for high-temperature applications. Most importantly, when used as a modifier, soft-core, hard-shell particles struggle to simultaneously achieve the three key performance indicators of epoxy resin: toughness, rigidity, and heat resistance.

[0005] The reason for this is that the design concept of a soft-core, hard-shell structure determines its performance limitations: while the soft core can absorb energy through plastic deformation to improve toughness, it sacrifices the material's rigidity; and while the hard shell can provide a certain degree of rigidity, it cannot effectively improve heat resistance. This inherent contradiction in the structure makes it difficult for traditional core-shell particles to achieve a synergistic improvement in the overall performance of epoxy resins, which is a key problem that urgently needs to be solved in the current field of epoxy resin modification. Summary of the Invention

[0006] To address the issue that existing soft-core and hard-shell core-shell particles cannot simultaneously achieve the desired toughness, rigidity, and heat resistance in the preparation of modified epoxy resin adhesives, this invention provides a PVAc / PS (polyvinyl acetate / polystyrene) rigid core-shell particle modified epoxy resin adhesive and its preparation method.

[0007] The technical solution of the present invention:

[0008] A method for preparing a PVAc / PS rigid core-shell particle modified epoxy resin adhesive, comprising the following steps:

[0009] Step 1: Preparation of PVAc / PS rigid core-shell particle emulsion:

[0010] Mix 8-10 parts of composite emulsifier, 125-130 parts of deionized water, and 0.4-0.6 parts of pH buffer by weight until homogeneous. Heat the resulting reaction system to 60-65°C, and add 8.5-12 parts of vinyl acetate monomer and 10-12 parts of an initiator aqueous solution with a concentration of 2.0-2.5 wt%, stirring until the reaction system turns milky blue. Heat the reaction system to 80-85°C, and add 41.5-58 parts of vinyl acetate monomer and 15-18 parts of an initiator aqueous solution with a concentration of 0.6-0.8 wt% again. After all the vinyl acetate monomer has been added, start adding 1.3-1.5 parts of grafted monomer to the reaction system, and then immediately start adding 30-50 parts of styrene monomer. After the styrene monomer is added, keep the temperature for 30-40 minutes, and then cool to room temperature to discharge the material to obtain PVAc / PS rigid core-shell particle emulsion.

[0011] Step 2: Preparation of PVAc / PS rigid core-shell particle modified epoxy resin:

[0012] Weigh 30-50 parts of the PVAc / PS rigid core-shell particle emulsion obtained in step one, add 40-60 parts of 28-32wt% calcium chloride aqueous solution to it, stir evenly to break the emulsion into flocculent material, let it stand and separate into layers, pour out the supernatant, and test the pH value of the supernatant. If the pH value does not reach 6.5-7.5, add the calcium chloride aqueous solution to the precipitate again, and repeat the operation of stirring to break the emulsion, letting it stand and separate into layers, and testing the pH value of the supernatant until the pH value of the supernatant is 6.5-7.5.

[0013] The precipitate was frozen into a solid by liquid nitrogen and then freeze-dried to obtain PVAc / PS rigid core-shell particle powder. 2-10 parts of PVAc / PS rigid core-shell particle powder were added to 90-98 parts of epoxy resin and homogenized until the mixture was semi-transparent to obtain PVAc / PS rigid core-shell particle modified epoxy resin.

[0014] Step 3: Preparation of PVAc / PS rigid core-shell particle modified epoxy resin adhesive:

[0015] The PVAc / PS rigid core-shell particle modified epoxy resin obtained in step two is mixed with the curing agent in an equimolar ratio of reactive groups until homogeneous, thus obtaining the PVAc / PS rigid core-shell particle modified epoxy resin adhesive.

[0016] Furthermore, the composite emulsifier in step one is an equal mass mixture of disodium alkyl ethoxysulfosuccinate and sodium dodecyl ether sulfate; the pH buffer is sodium bicarbonate; the initiator is ammonium persulfate; and the grafting monomer is acrylonitrile or maleic anhydride.

[0017] Furthermore, in step one, the rate of the first addition of vinyl acetate monomer is 4-6 mL / min, the rate of the second addition of vinyl acetate monomer is 0.4-0.6 mL / min, the rate of the first addition of the initiator aqueous solution is 3-5 mL / min, the rate of the second addition of the initiator aqueous solution is 0.1-0.2 mL / min, the rate of the addition of the grafted monomer is 1.0-1.5 mL / min, and the rate of the addition of the styrene monomer is 0.2-0.8 mL / min.

[0018] Furthermore, in the PVAc / PS rigid core-shell particle emulsion prepared in step one, the core-shell mass ratio of the PVAc / PS rigid core-shell particles is 5:5, 6:4, or 7:3.

[0019] Furthermore, the epoxy resin mentioned in step two is one or a combination of several of the following: bisphenol A type epoxy resin E-51, bisphenol A type epoxy resin E-54, bisphenol F type epoxy resin BFE-170, or phenolic epoxy resin F-51.

[0020] Furthermore, the freeze-drying temperature of the freeze-drying process described in step two is -30~-35℃, the vacuum degree is 10~20Pa, and the freeze-drying time is 24~30h.

[0021] Furthermore, the dispersion speed of the homogenization process described in step two is 8000~12000 rpm.

[0022] Furthermore, the curing agent mentioned in step three is one or a combination of several of the following: polyetheramine D230, hexamethylenediamine, triethylenetetramine, polyethylenepolyamine, isophorone diamine, m-phenylenediamine, and 1,4-bis(3-aminopropyl)piperazine.

[0023] A PVAc / PS rigid core-shell particle modified epoxy resin adhesive prepared by the preparation method provided by the present invention.

[0024] Furthermore, the curing temperature of the PVAc / PS rigid core-shell particle modified epoxy resin adhesive is ≤80℃.

[0025] The beneficial effects of this invention are:

[0026] The rigid core-shell particle-modified epoxy resin adhesive provided by this invention has significant comprehensive performance advantages. Due to the high elastic modulus of the rigid core-shell particles, when modifying epoxy resin, they reinforce low-modulus matrix resins and toughen high-modulus matrix resins. Therefore, by using a curing agent to adjust the modulus of the epoxy resin matrix in combination with high-modulus rigid core-shell particles, through the adjustment, matching, and synergistic effect of the rigid core-shell particles and the curing agent, the material's toughness and strength are improved while having minimal or even positive impacts on its rigidity and heat resistance. This demonstrates a composite effect of toughening and reinforcement, achieving a "rigid-toughness balance" effect in the modified epoxy resin, thus significantly improving the overall performance of the epoxy resin adhesive.

[0027] This invention achieves precise matching and synergistic effect between the modulus of the core-shell particles and the epoxy resin matrix through a hard-core, hard-shell structure design of PVAc / PS core-shell particles. This structure exhibits a distinct heterogeneous morphology and layering effect, endowing the material with anisotropic rigidity and toughness properties. While improving the toughness of the epoxy resin, it also positively impacts its strength, rigidity, and heat resistance. Experimental data show that the room temperature shear strength of the 10% PVAc / PS (7:3) modified adhesive reaches 38.32 MPa, an increase of 27.3% compared to the unmodified sample, and the 90° peel strength increases by 176% to 4.94 N / mm, achieving a "rigidity-toughness balance" effect in the modified adhesive. Simultaneously, the 80° shear strength also increases by 8.4%, indicating a positive effect on heat resistance.

[0028] The toughening and strengthening mechanism of this invention exhibits multiple energy dissipation characteristics. When the PVAc / PS rigid core-shell particle modified epoxy resin adhesive is subjected to external forces during application, the rigid core-shell particles generate voids and microcracks within the adhesive layer, inducing ductile shear yielding and causing plastic deformation to absorb energy. Simultaneously, the core-shell particles can deflect, pin, and bifurcate cracks, effectively terminating crack propagation. This unique toughening mechanism not only significantly improves the fracture toughness of the material but also maintains the high strength properties of the matrix. The preparation method of the PVAc / PS rigid core-shell particle modified epoxy resin adhesive provided by this invention demonstrates broad application adaptability. By adjusting the core-shell ratio (5:5 to 7:3) and the addition amount (2%-10%), it can be adapted to different epoxy resin systems (bisphenol A type epoxy resin, bisphenol F type epoxy resin, etc.) and curing agent systems. Taking the 10% PVAc / PS (6:4) modified adhesive as an example, its room temperature shear strength reaches 34.69 MPa, its 80° shear strength is 31.25 MPa, and its 90° peel strength is 4.37 N / mm, demonstrating excellent and balanced performance across all indicators. This adjustability allows it to meet the application needs of various fields such as aviation, aerospace, automotive, and electronics.

[0029] Compared to traditional toughening technologies, this invention offers groundbreaking technical advantages. Compared to commercially available elastic core-shell particle modified products, rigid core-shell particles maintain excellent toughening effects without sacrificing the material's rigidity and heat resistance. The 8% PVAc / PS (5:5) modified adhesive maintains a room temperature shear strength of 34.08 MPa while achieving a 90° peel strength of 2.84 N / mm. This breakthrough in "rigidity-toughness balance" provides a superior bonding solution for high-end equipment manufacturing, possessing significant engineering application value. Attached Figure Description

[0030] Figure 1 SEM and TEM images of the PVAc / PS rigid core-shell particles prepared in Example 1, with the TEM image in the upper left corner;

[0031] Figure 2 SEM image of the fracture surface of the cured PVAc / PS rigid core-shell particle modified epoxy resin adhesive prepared in Example 1.

[0032] Figure 3 SEM image of the fracture surface of the cured unmodified epoxy resin adhesive prepared for Comparative Example 1. Detailed Implementation

[0033] The technical solution of the present invention will be further described below with reference to embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention. In the following embodiments, the process equipment or apparatus not specifically specified are all conventional equipment or apparatus in the art. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commercially available; unless otherwise specified, the technical means used in the embodiments of the present invention are all conventional means well known to those skilled in the art.

[0034] Example 1

[0035] This embodiment provides a method for preparing a PVAc / PS rigid core-shell particle modified epoxy resin adhesive, the steps of which are as follows:

[0036] Step 1: Preparation of PVAc / PS rigid core-shell particle emulsion:

[0037] A composite emulsifier was prepared by mixing equal masses of disodium alkyl ethoxysulfosuccinate and sodium dodecyl ether sulfate. 10 parts by weight of the composite emulsifier, 128 parts by weight of deionized water, and 0.5 parts by weight of sodium bicarbonate (pH buffer) were added to a reaction vessel and stirred thoroughly. The resulting reaction system was heated to 65°C, and 12 parts by weight of vinyl acetate monomer were added dropwise at a rate of 5 mL / min. 10.5 parts by weight of a 2.4 wt% ammonium persulfate aqueous solution (initiator) were added dropwise at a rate of 4 mL / min. The mixture was stirred until the reaction system turned milky blue. The reaction system was then heated to 80°C, and the mixture was added again at a rate of 0.4 mL / min. Add 58 parts of vinyl acetate monomer at a rate of mL / min, and add 15.5 parts of 0.7wt% ammonium persulfate aqueous solution as initiator at a rate of 0.15 mL / min. After all the vinyl acetate monomer has been added, add 1.5 parts of grafted monomer acrylonitrile to the reaction system at a rate of 1.0 mL / min, and then immediately add 30 parts of styrene monomer at a rate of 0.2 mL / min. After the styrene monomer is added, keep the mixture at the temperature for 35 min, and then cool it to room temperature before discharging to obtain a PVAc / PS rigid core-shell particle emulsion with a core-shell mass ratio of 7:3.

[0038] Step 2: Preparation of PVAc / PS rigid core-shell particle modified epoxy resin:

[0039] Weigh 30 parts of the PVAc / PS rigid core-shell particle emulsion obtained in step one, add 40 parts of a 28wt% calcium chloride aqueous solution to it, stir evenly to break the emulsion into flocculent material, let it stand and separate into layers, pour off the supernatant, and test the pH value of the supernatant. If the pH does not reach 6.5~7.5, add the above calcium chloride aqueous solution to the precipitate again, and repeat the operation of stirring to break the emulsion, letting it stand and separate into layers, and testing the pH value of the supernatant until the pH value of the supernatant is 7.0.

[0040] The precipitate was removed and placed in an evaporating dish. The precipitate was rapidly frozen into a solid using liquid nitrogen, and then placed in a freeze dryer. The freeze-drying temperature was set to -32℃, the vacuum degree to 15Pa, and the freeze-drying time was 24 hours to obtain PVAc / PS rigid core-shell particle powder. Ten parts of the PVAc / PS rigid core-shell particle powder were weighed and added to 90 parts of epoxy resin E-51. The mixture was homogenized using a high-speed dispersant at a dispersion speed of 10000 rpm until the mixture became translucent, yielding a modified epoxy resin with a PVAc / PS rigid core-shell particle content of 10 wt%.

[0041] Step 3: Preparation of PVAc / PS rigid core-shell particle modified epoxy resin adhesive:

[0042] Mix 10 parts of the PVAc / PS rigid core-shell particle modified epoxy resin obtained in step two with 2.3 parts of 1,4-bis(3-aminopropyl)piperazine curing agent until homogeneous to obtain the PVAc / PS rigid core-shell particle modified epoxy resin adhesive.

[0043] Example 2

[0044] This embodiment provides a method for preparing a PVAc / PS rigid core-shell particle modified epoxy resin adhesive, the steps of which are as follows:

[0045] Step 1: Preparation of PVAc / PS rigid core-shell particle emulsion:

[0046] A composite emulsifier was prepared by mixing equal masses of disodium alkyl ethoxysulfosuccinate and sodium dodecyl ether sulfate. 10 parts by weight of the composite emulsifier, 125 parts by weight of deionized water, and 0.5 parts by weight of sodium bicarbonate pH buffer were added to a reaction vessel and stirred thoroughly. The resulting reaction system was heated to 60°C, and 10 parts by weight of vinyl acetate monomer were added dropwise at a rate of 5 mL / min. 11.0 parts by weight of a 2.4 wt% ammonium persulfate aqueous solution was added dropwise at a rate of 4 mL / min. The mixture was stirred until the reaction system turned milky blue. The reaction system was then heated to 85°C, and the mixture was added again at a rate of 0.4 mL / min. Add 50 parts of vinyl acetate monomer at a rate of mL / min, and add 15.5 parts of 0.7wt% ammonium persulfate aqueous solution as initiator at a rate of 0.15 mL / min. After all the vinyl acetate monomer has been added, start adding 1.5 parts of grafted monomer acrylonitrile to the reaction system at a rate of 1.0 mL / min, and then immediately start adding 40 parts of styrene monomer at a rate of 0.4 mL / min. After the styrene monomer is added, keep warm for 30 min, and then cool to room temperature to discharge, to obtain a PVAc / PS rigid core-shell particle emulsion with a core-shell mass ratio of 6:4.

[0047] Step 2: Preparation of PVAc / PS rigid core-shell particle modified epoxy resin:

[0048] Weigh 40 parts of the PVAc / PS rigid core-shell particle emulsion obtained in step one, add 50 parts of a 30wt% calcium chloride aqueous solution to it, stir evenly to break the emulsion into flocculent material, let it stand and separate into layers, pour off the supernatant, and test the pH value of the supernatant. If the pH does not reach 6.5~7.5, add the above calcium chloride aqueous solution to the precipitate again, and repeat the operation of stirring to break the emulsion, letting it stand and separate into layers and testing the pH value of the supernatant until the pH value of the supernatant is 7.2.

[0049] The precipitate was removed and placed in an evaporating dish. The precipitate was rapidly frozen into a solid using liquid nitrogen, and then placed in a freeze dryer. The freeze-drying temperature was set to -35℃, the vacuum degree to 15Pa, and the freeze-drying time was 25 hours to obtain PVAc / PS rigid core-shell particle powder. Ten parts of the PVAc / PS rigid core-shell particle powder were weighed and added to 90 parts of epoxy resin E-54. The mixture was homogenized using a high-speed dispersant at a dispersion speed of 10,000 rpm until the mixture became translucent, yielding a modified epoxy resin with a PVAc / PS rigid core-shell particle content of 10 wt%.

[0050] Step 3: Preparation of PVAc / PS rigid core-shell particle modified epoxy resin adhesive:

[0051] Mix 10 parts of the PVAc / PS rigid core-shell particle modified epoxy resin obtained in step two with 2.43 parts of 1,4-bis(3-aminopropyl)piperazine curing agent until homogeneous to obtain the PVAc / PS rigid core-shell particle modified epoxy resin adhesive.

[0052] Example 3

[0053] This embodiment provides a method for preparing a PVAc / PS rigid core-shell particle modified epoxy resin adhesive, the steps of which are as follows:

[0054] Step 1: Preparation of PVAc / PS rigid core-shell particle emulsion:

[0055] A composite emulsifier was prepared by mixing equal masses of disodium alkyl ethoxysulfosuccinate and sodium dodecyl ether sulfate. 10 parts by weight of the composite emulsifier, 125 parts by weight of deionized water, and 0.5 parts by weight of sodium bicarbonate (pH buffer) were added to a reaction vessel and stirred thoroughly. The resulting reaction system was heated to 60°C, and 8.5 parts by weight of vinyl acetate monomer were added dropwise at a rate of 5 mL / min. 10.5 parts by weight of a 2.5 wt% ammonium persulfate aqueous solution (initiator) were added dropwise at a rate of 4 mL / min. The mixture was stirred until the reaction system turned milky blue. The reaction system was then heated to 80°C, and the mixture was added again at a rate of 0.4 mL / min. Add 41.5 parts of vinyl acetate monomer at a rate of L / min, and add 15.5 parts of 0.68wt% ammonium persulfate aqueous solution as initiator at a rate of 0.2 mL / min. After all the vinyl acetate monomer has been added, add 1.5 parts of grafted monomer acrylonitrile to the reaction system at a rate of 1.5 mL / min, and then immediately add 50 parts of styrene monomer at a rate of 0.6 mL / min. After the styrene monomer is added, keep the mixture at the temperature for 40 min, and then cool it to room temperature before discharging to obtain a PVAc / PS rigid core-shell particle emulsion with a core-shell mass ratio of 5:5.

[0056] Step 2: Preparation of PVAc / PS rigid core-shell particle modified epoxy resin:

[0057] Weigh 50 parts of the PVAc / PS rigid core-shell particle emulsion obtained in step one, add 60 parts of a 32wt% calcium chloride aqueous solution to it, stir evenly to break the emulsion into flocculent material, let it stand and separate into layers, pour off the supernatant, and test the pH value of the supernatant. If the pH does not reach 6.5~7.5, add the above calcium chloride aqueous solution to the precipitate again, and repeat the operation of stirring to break the emulsion, letting it stand and separate into layers, and testing the pH value of the supernatant until the pH value of the supernatant is 7.0.

[0058] The precipitate was removed and placed in an evaporating dish. The precipitate was rapidly frozen into a solid using liquid nitrogen, and then placed in a freeze dryer. The freeze-drying temperature was set to -35℃, the vacuum degree to 15Pa, and the freeze-drying time was 30 hours to obtain PVAc / PS rigid core-shell particle powder. Eight parts of the PVAc / PS rigid core-shell particle powder were weighed and added to 92 parts of epoxy resin E-54. The mixture was homogenized using a high-speed dispersant at a dispersion speed of 12000 rpm until the mixture became translucent, yielding a modified epoxy resin with a PVAc / PS rigid core-shell particle content of 8 wt%.

[0059] Step 3: Preparation of PVAc / PS rigid core-shell particle modified epoxy resin adhesive:

[0060] Mix 10 parts of the PVAc / PS rigid core-shell particle modified epoxy resin obtained in step two with 3.03 parts of polyetheramine D230 curing agent until homogeneous to obtain the PVAc / PS rigid core-shell particle modified epoxy resin adhesive.

[0061] Comparative Example 1

[0062] This comparative example provides a method for preparing unmodified epoxy resin E-51 adhesive. 10 parts of epoxy resin E-51 and 2.55 parts of 1,4-bis(3-aminopropyl)piperazine curing agent are weighed and mixed evenly to obtain unmodified epoxy resin E-51 adhesive.

[0063] Comparative Example 2

[0064] This comparative example provides a method for preparing unmodified epoxy resin E-54 adhesive. 10 parts of epoxy resin E-54 and 2.7 parts of 1,4-bis(3-aminopropyl)piperazine curing agent are weighed and mixed evenly to obtain unmodified epoxy resin E-54 adhesive.

[0065] Comparative Example 3

[0066] This comparative example provides a method for preparing unmodified epoxy resin E-54 adhesive. 10 parts of epoxy resin E-54 and 3.29 parts of polyetheramine D230 curing agent are weighed and mixed evenly to obtain unmodified epoxy resin E-54 adhesive.

[0067] Comparative Example 4

[0068] This comparative example provides a method for preparing a modified epoxy resin adhesive using commercially available elastic core-shell particles. 10 parts of commercially available elastic core-shell particles are weighed and added to 90 parts of epoxy resin E-51. The mixture is homogenized using a high-speed disperser at a dispersion speed of 10,000 rpm until the resulting mixture is semi-transparent, thus obtaining a modified epoxy resin with a commercially available elastic core-shell particle content of 10 wt%.

[0069] Mix 10 parts of the commercially available elastic core-shell particle modified epoxy resin obtained above with 2.79 parts of polyetheramine D230 curing agent until homogeneous to obtain the commercially available elastic core-shell particle modified epoxy resin adhesive.

[0070] The commercially available flexible core-shell particles used in this comparative example were purchased from Rohm and Haas Corporation, USA, product model EXL2691.

[0071] Comparative Example 5

[0072] This comparative example provides a prior art method for preparing rigid core-shell particle modified epoxy resin adhesives.

[0073] Step 1: Preparation of PVAc / PS rigid core-shell particle emulsion:

[0074] A composite emulsifier was prepared by mixing equal masses of disodium alkyl ethoxysulfosuccinate and sodium dodecyl ether sulfate. 10 parts by weight of the composite emulsifier, 128 parts by weight of deionized water, and 0.5 parts by weight of sodium bicarbonate (pH buffer) were added to a reaction vessel and stirred thoroughly. The resulting reaction system was heated to 65°C, and 12 parts by weight of vinyl acetate monomer were added dropwise at a rate of 5 mL / min. 10.5 parts by weight of a 2.4 wt% ammonium persulfate aqueous solution (initiator) were added dropwise at a rate of 4 mL / min. The mixture was stirred until the reaction system turned milky blue. The reaction system was then heated to 80°C, and the mixture was added again at a rate of 0.4 mL / min. Add 58 parts of vinyl acetate monomer at a rate of mL / min, and add 15.5 parts of 0.7wt% ammonium persulfate aqueous solution as initiator at a rate of 0.15 mL / min. After all the vinyl acetate monomer has been added, add 1.5 parts of grafted monomer acrylonitrile to the reaction system at a rate of 1.0 mL / min, and then immediately add 30 parts of styrene monomer at a rate of 0.2 mL / min. After the styrene monomer is added, keep the mixture at the temperature for 35 min, and then cool it to room temperature before discharging to obtain a PVAc / PS rigid core-shell particle emulsion with a core-shell mass ratio of 7:3.

[0075] Step 2: Preparation of PVAc / PS rigid core-shell particle modified epoxy resin:

[0076] The actual solid content of the core-shell particles in the core-shell emulsion prepared in step one is 36%. 27.8 parts of the core-shell emulsion were weighed and added to 90 parts of epoxy resin E-51. After stirring evenly, the mixture was placed in a rotary evaporator and the water in the mixture was evaporated under the conditions of 60℃ water bath and vacuum degree -0.1MPa until no distillate dripped out at the collection bottle, thus obtaining a modified epoxy resin with a PVAc / PS rigid core-shell particle content of 10wt%.

[0077] Step 3: Preparation of PVAc / PS rigid core-shell particle modified epoxy resin adhesive:

[0078] Mix 10 parts of the PVAc / PS rigid core-shell particle modified epoxy resin obtained in step two with 6.3 parts of polyamide curing agent until homogeneous to obtain the PVAc / PS rigid core-shell particle modified epoxy resin adhesive.

[0079] Comparative Example 6

[0080] The only difference between this comparative example and Comparative Example 5 is that step two involves preparing the PVAc / PS rigid core-shell particle modified epoxy resin:

[0081] The actual solid content of the core-shell particles in the core-shell emulsion prepared in step one is 36%. 13.9 parts of the core-shell emulsion were weighed and added to 95 parts of epoxy resin E-51. After stirring evenly, the mixture was placed in a rotary evaporator and the water in the mixture was evaporated under the conditions of a 60°C water bath and a vacuum of -0.1MPa until no distillate dripped out at the collection bottle, thus obtaining a modified epoxy resin with a PVAc / PS rigid core-shell particle content of 5wt%.

[0082] Step 3: Preparation of PVAc / PS rigid core-shell particle modified epoxy resin adhesive:

[0083] Mix 10 parts of the PVAc / PS rigid core-shell particle modified epoxy resin obtained in step two with 6.7 parts of polyamide curing agent until homogeneous to obtain the PVAc / PS rigid core-shell particle modified epoxy resin adhesive.

[0084] Figure 1 SEM and TEM images of the PVAc / PS rigid core-shell particles prepared in Example 1 are shown below. Figure 1 As shown, PVAc / PS rigid core-shell particles exhibit a bilayered structure with a core-shell heterogeneity.

[0085] Figure 2 SEM images of the fracture surfaces of the cured PVAc / PS rigid core-shell particle modified epoxy resin adhesive prepared in Example 1; as shown. Figure 2 As shown, the fracture surface exhibits obvious ductile fracture characteristics.

[0086] Figure 3SEM images of the fracture surface of the cured unmodified epoxy resin adhesive prepared in Comparative Example 1 are shown below. Figure 3 As shown, the fracture surface exhibits obvious brittle fracture characteristics.

[0087] The adhesives prepared in Examples 1-3 and Comparative Examples 1-6 were subjected to performance tests, and the specific methods are as follows:

[0088] Aluminum alloy specimens treated according to GB / T 21526-2008 were bonded with adhesives prepared in Examples 1-3 and Comparative Examples 1-6, respectively. After curing at 80°C for 2 hours, the room temperature shear strength was tested according to GB 7124-2008, and the 80°C shear strength was tested according to GJB444-88.

[0089] Aluminum alloy specimens treated according to the HB / Z 197-91 method were bonded with adhesives prepared in Examples 1-3 and Comparative Examples 1-6, respectively. After curing at 80°C for 2 hours, the 90° peel strength was tested according to the GJB 446-88 method.

[0090] The performance test results of each adhesive are shown in Table 1.

[0091] Table 1

[0092]

[0093] As shown in Table 1, none of the epoxy resin adhesives in the comparative examples could simultaneously achieve toughness, rigidity, and heat resistance. However, this invention, through the adjustment, matching, and synergistic effect of PVAc / PS rigid core-shell particles and curing agent, improves the toughness and strength of the material while having a minimal or even positive impact on the rigidity and heat resistance. This demonstrates a composite effect of toughening and strengthening, achieving a "rigid-toughness balance" effect in modified epoxy resin, and significantly improving the overall performance of the epoxy resin adhesive.

Claims

1. A method for preparing a PVAc / PS rigid core-shell particle modified epoxy resin adhesive, characterized in that, The steps are as follows: Step 1: Preparation of PVAc / PS rigid core-shell particle emulsion: Mix 8-10 parts of composite emulsifier, 125-130 parts of deionized water, and 0.4-0.6 parts of pH buffer by weight until homogeneous. Heat the resulting reaction system to 60-65°C, and add 8.5-12 parts of vinyl acetate monomer and 10-12 parts of an initiator aqueous solution with a concentration of 2.0-2.5 wt%, stirring until the reaction system turns milky blue. Heat the reaction system to 80-85°C, and add 41.5-58 parts of vinyl acetate monomer and 15-18 parts of an initiator aqueous solution with a concentration of 0.6-0.8 wt% again. After all the vinyl acetate monomer has been added, start adding 1.3-1.5 parts of grafted monomer to the reaction system, and then immediately start adding 30-50 parts of styrene monomer. After the styrene monomer is added, keep the temperature for 30-40 minutes, and then cool to room temperature to discharge the material to obtain PVAc / PS rigid core-shell particle emulsion. Step 2: Preparation of PVAc / PS rigid core-shell particle modified epoxy resin: Weigh 30-50 parts of the PVAc / PS rigid core-shell particle emulsion obtained in step one, add 40-60 parts of 28-32wt% calcium chloride aqueous solution to it, stir evenly to break the emulsion into flocculent material, let it stand and separate into layers, pour out the supernatant, and test the pH value of the supernatant. If the pH value does not reach 6.5-7.5, add the calcium chloride aqueous solution to the precipitate again, and repeat the operation of stirring to break the emulsion, letting it stand and separate into layers, and testing the pH value of the supernatant until the pH value of the supernatant is 6.5-7.

5. The precipitate was frozen into a solid by liquid nitrogen and then freeze-dried to obtain PVAc / PS rigid core-shell particle powder. 2-10 parts of PVAc / PS rigid core-shell particle powder were added to 90-98 parts of epoxy resin and homogenized until the mixture was semi-transparent to obtain PVAc / PS rigid core-shell particle modified epoxy resin. Step 3: Preparation of PVAc / PS rigid core-shell particle modified epoxy resin adhesive: The PVAc / PS rigid core-shell particle modified epoxy resin obtained in step two is mixed with the curing agent in an equimolar ratio of reactive groups until homogeneous, thus obtaining the PVAc / PS rigid core-shell particle modified epoxy resin adhesive.

2. The preparation method of the PVAc / PS rigid core-shell particle modified epoxy resin adhesive according to claim 1, characterized in that, The composite emulsifier in step one is a mixture of equal masses of disodium alkyl ethoxysulfosuccinate and sodium dodecyl ether sulfate; the pH buffer is sodium bicarbonate; the initiator is ammonium persulfate; and the grafting monomer is acrylonitrile or maleic anhydride.

3. The preparation method of the PVAc / PS rigid core-shell particle modified epoxy resin adhesive according to claim 1 or 2, characterized in that, In step one, the rate of adding vinyl acetate monomer for the first time is 4~6 mL / min, the rate of adding vinyl acetate monomer for the second time is 0.4~0.6 mL / min, the rate of adding initiator aqueous solution for the first time is 3~5 mL / min, the rate of adding initiator aqueous solution for the second time is 0.1~0.2 mL / min, the rate of adding grafted monomer is 1.0~1.5 mL / min, and the rate of adding styrene monomer is 0.2~0.8 mL / min.

4. The preparation method of the PVAc / PS rigid core-shell particle modified epoxy resin adhesive according to claim 3, characterized in that, In the PVAc / PS rigid core-shell particle emulsion prepared in step one, the core-shell mass ratio of the PVAc / PS rigid core-shell particles is 5:5, 6:4, or 7:

3.

5. The preparation method of the PVAc / PS rigid core-shell particle modified epoxy resin adhesive according to claim 4, characterized in that, The epoxy resin mentioned in step two is one or a combination of several of the following: bisphenol A type epoxy resin E-51, bisphenol A type epoxy resin E-54, bisphenol F type epoxy resin BFE-170, or phenolic epoxy resin F-51.

6. The preparation method of the PVAc / PS rigid core-shell particle modified epoxy resin adhesive according to claim 5, characterized in that, The freeze-drying process described in step two involves a freeze-drying temperature of -30 to -35°C, a vacuum degree of 10 to 20 Pa, and a freeze-drying time of 24 to 30 hours.

7. The preparation method of the PVAc / PS rigid core-shell particle modified epoxy resin adhesive according to claim 6, characterized in that, The dispersion rate of the homogenization process in step two is 8000~12000 rpm.

8. The preparation method of the PVAc / PS rigid core-shell particle modified epoxy resin adhesive according to claim 7, characterized in that, The curing agent mentioned in step three is one or a combination of several of the following: polyetheramine D230, hexamethylenediamine, triethylenetetramine, polyethylenepolyamine, isophorone diamine, m-phenylenediamine, and 1,4-bis(3-aminopropyl)piperazine.

9. A PVAc / PS rigid core-shell particle modified epoxy resin adhesive prepared by the method according to any one of claims 1-8.

10. The PVAc / PS rigid core-shell particle modified epoxy resin adhesive according to claim 9, characterized in that, The curing temperature of the PVAc / PS rigid core-shell particle modified epoxy resin adhesive is ≤80℃.

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