Laser-curable epoxy adhesive as well as preparation method and application thereof

Abstract

The invention belongs to the field of adhesives, and particularly relates to a laser-curable epoxy adhesive as well as a preparation method and application thereof. The laser-curable epoxy adhesive is prepared from the following raw materials: low-viscosity epoxy resin, toughened epoxy resin, epoxy acrylate resin, dopamine modified graphene oxide nanosheets, a curing agent and a thermal initiator in a mass ratio of 1: (0.5-2): (0.75-3): (0.05-0.5): (0.75-2.5): (0.05-0.5): (0-1): (0-0.2): (0-0.15): (0-2) as well as optional epoxy diluent, stabilizer, coupling agent and filler. The laser-curable epoxy adhesive provided by the invention has high modulus and high Tg, and can be rapidly cured.

Description

Technical Field

[0001] This invention belongs to the field of adhesives, specifically relating to a laser-curable epoxy adhesive, its preparation method, and its application. Background Technology

[0002] The vibration motor inside a mobile phone provides feedback to the user through vibration. A linear resonant electromagnetic motor uses alternating current passing through a coil to generate an alternating magnetic field. This magnetic field drives a mover (mass block) containing a permanent magnet to move back and forth, generating inertial impact force, thus achieving the vibration effect. Linear resonant electromagnetic motors provide a stronger vibration than eccentric rotor motors, making them popular with users. Space is extremely limited inside a mobile phone, requiring the motor to be as small as possible to achieve a strong vibration. Linear resonant electromagnetic motors use small electromagnetic coils, achieving both small size and strong vibration. The electromagnetic coils need to be bonded and fixed using adhesives. Due to the nature of the motor's operation, the adhesive needs to vibrate at the same frequency as the motor; therefore, the adhesive must have a high modulus and a high glass transition temperature (Tg).

[0003] Currently, production lines for bonding and protecting electronic components are highly automated. However, traditional heat curing methods suffer from long curing times and slow efficiency, severely hindering the production efficiency of electronic products. Laser heat curing achieves heating and curing through the adhesive's own light absorption, offering an energy-saving, environmentally friendly, convenient, efficient, and three-dimensional curing method from the inside out. The light source for laser heat curing is typically a point source emanating from a laser, with adjustable power to customize the curing temperature and time. Lasers are characterized by high brightness and good directionality, with concentrated energy and a small thermal dispersion spot. This allows for rapid and thorough heating of the adhesive, enabling the resin and curing agent to fully react and bond quickly. Laser heating curing offers numerous advantages. Firstly, because the wavelength of the laser is easily absorbed by the adhesive, there is relatively little reflection and scattering of the light source by the adhesive during laser curing, resulting in high curing efficiency. Secondly, the high energy of the laser source leads to a short curing time, enabling the curing of various complex and deep surfaces. Furthermore, laser curing boasts advantages such as simple equipment, ease of implementation, and excellent curing results. In contrast, traditional infrared heating simply utilizes air as a heat conductor, transferring heat to achieve curing. Its essence is heat transfer, resulting in low heat utilization and a long heating time, leading to lower production efficiency. Moreover, infrared heating is ineffective on sharp edges or hidden surfaces due to the difficulty in heat transfer.

[0004] In summary, in order to ensure the normal operation of the motor and improve its production efficiency, there is an urgent need to develop an epoxy adhesive that combines high modulus and high Tg and can achieve rapid curing and positioning. Summary of the Invention

[0005] The first objective of this invention is to provide a laser-curable epoxy adhesive that combines high modulus and high Tg and can achieve rapid curing.

[0006] A second objective of this invention is to provide a method for preparing the aforementioned laser-curable epoxy adhesive.

[0007] A third objective of this invention is to provide the application of the above-mentioned laser-curable epoxy adhesive in the field of consumer electronics.

[0008] The raw materials for preparing the laser-curable epoxy adhesive provided by the present invention contain low-viscosity epoxy resin, toughened epoxy resin, epoxy acrylate resin, dopamine-modified graphene oxide nanosheets, curing agent and thermal initiator, and optional epoxy diluent, stabilizer, coupling agent and filler in a mass ratio of 1:(0.5-2):(0.75-3):(0.05-0.5):(0.75-2.5):(0.05-0.5):(0-1):(0-0.2):(0-0.15):(0-2).

[0009] The key to this invention lies in introducing epoxy acrylate resin and a thermal initiator into an epoxy photocurable adhesive system, along with dopamine-modified graphene oxide nanosheets. The resulting laser-curable epoxy adhesive exhibits high modulus, high Tg, and rapid curing properties. The reason for this is speculated to be that the thermal initiator is activated under near-infrared light irradiation, undergoing thermal decomposition to generate free radicals. These free radicals then initiate a carbon-carbon double bond reaction in the epoxy acrylate resin for rapid localization. Once initiated, this free radical reaction continues by generating secondary free radicals, exhibiting a cascade amplification effect similar to nuclear fission, making it difficult to stop automatically. Free radical reactions release a large amount of heat, causing the entire reaction system to heat up. The addition of dopamine-modified graphene oxide nanosheets not only allows the graphene oxide nanosheets to be better dispersed in the epoxy resin system, but also, due to the high thermal conductivity and large specific surface area of ​​the graphene oxide nanosheets, greatly facilitates the rapid transfer of heat released by the free radical reaction, thus enabling the entire system to heat up uniformly to the curing temperature. When the temperature reaches the active reaction temperature of the curing agent, it will activate the reactivity of the curing agent, causing it to initiate epoxy ring-opening to obtain a polymer network structure, thereby increasing the modulus and Tg in the first step. At the same time, the primary amine group (-NH2) in dopamine has strong nucleophilicity and can attack the methylene carbon atom in the epoxy group to undergo a ring-opening addition reaction, thereby uniformly dispersing the graphene oxide nanosheets in the polymer network structure, preventing polymer chain movement and playing a reinforcing role, thus further increasing the modulus and Tg, enabling it to effectively match the bonding of linear motor coils and improve production efficiency. Detailed Implementation

[0010] The laser-curable epoxy adhesive provided by this invention comprises low-viscosity epoxy resin, toughened epoxy resin, epoxy acrylate resin, dopamine-modified graphene oxide nanosheets, curing agent, thermal initiator, and optionally epoxy diluent, stabilizer, coupling agent, and filler. The laser-curable epoxy adhesive can be cured using an infrared laser, preferably with a wavelength of 800nm-1100nm, more preferably 900nm-1100nm.

[0011] The mass ratio of the toughening epoxy resin to the low-viscosity epoxy resin is (0.5-2):1, specifically 0.5:1, 0.8:1, 1:1, 1.2:1, 1.4:1, 1.6:1, 1.8:1, 2:1, or any value between them. The mass ratio of the epoxy acrylate resin to the low-viscosity epoxy resin is (0.75-3):1, such as 0.75:1, 1:1, 1.25:1, 1.5:1, 1.75:1, 2:1, 2.25:1, 2.5:1, 2.75:1, 3:1, or any value between them. The mass ratio of the dopamine-modified graphene oxide nanosheets to the low-viscosity epoxy resin is (0.05-0.5):1, such as 0.05:1, 0.1:1, 0.15:1, 0.2:1, 0.25:1, 0.3:1, 0.35:1, 0.4:1, 0.45:1, 0.5:1, or any value between them. The mass ratio of the curing agent to the low-viscosity epoxy resin is (0.75-2.5):1, such as 0.75:1, 1:1, 1.25:1, 1.5:1, 1.75:1, 2:1, 2.25:1, 2.5:1, or any value between them. The mass ratio of the thermal initiator to the low-viscosity epoxy resin is (0.05-0.5):1, such as 0.05:1, 0.1:1, 0.15:1, 0.2:1, 0.25:1, 0.3:1, 0.35:1, 0.4:1, 0.45:1, 0.5:1, or any value between them. The mass ratio of the epoxy diluent to the low-viscosity epoxy resin is (0-1):1, such as 0, 0.01:1, 0.05:1, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, or any value between them. The mass ratio of the stabilizer to the low-viscosity epoxy resin is (0-0.2):1, such as 0, 0.01:1, 0.02:1, 0.04:1, 0.06:1, 0.08:1, 0.1:1, 0.12:1, 0.14:1, 0.16:1, 0.18:1, 0.2:1, or any value between them. The mass ratio of the coupling agent to the low-viscosity epoxy resin is (0-0.15):1, such as 0, 0.01:1, 0.02:1, 0.04:1, 0.06:1, 0.08:1, 0.1:1, 0.12:1, 0.14:1, 0.15:1, or any value between them. The mass ratio of the filler to the low-viscosity epoxy resin is (0-0.2):1, such as 0, 0.01:1, 0.02:1, 0.04:1, 0.06:1, 0.08:1, 0.1:1, 0.12:1, 0.14:1, 0.16:1, 0.18:1, 0.2:1, or any value between them.

[0012] In a preferred embodiment, the low-viscosity epoxy resin comprises 10-20 parts by weight, the toughening epoxy resin comprises 10-20 parts by weight, the epoxy acrylate resin comprises 15-30 parts, the dopamine-modified graphene oxide nanosheet comprises 1-3 parts, the curing agent comprises 15-25 parts, the thermal initiator comprises 1-3 parts, the epoxy diluent comprises 5-10 parts, the stabilizer comprises 0.5-2 parts, the coupling agent comprises 0.1-1.5 parts, and the filler comprises 10-20 parts. In this embodiment, the components can achieve better synergistic effects, which is more conducive to improving the modulus and Tg and achieving rapid positioning. The content of the low-viscosity epoxy resin can be 10, 12, 14, 16, 18, 20 parts by weight or any value between them. The content of the toughening epoxy resin can be 10, 12, 14, 16, 18, 20 parts by weight or any value between them. The content of the epoxy acrylate resin can be 15, 18, 20, 22, 25, 28, 30 parts by weight or any value between them. The content of the dopamine-modified graphene oxide nanosheets can be 1, 1.5, 2, 2.5, 3 parts by weight or any value between them. The content of the curing agent can be 15, 18, 20, 22, 25 parts by weight or any value between them. The content of the thermal initiator can be 1, 1.5, 2, 2.5, 3 parts by weight or any value between them. The content of the epoxy diluent can be 5, 6, 7, 8, 9, 10 parts by weight or any value between them. The content of the stabilizer can be 0.5, 0.8, 1, 1.2, 1.4, 1.6, 1.8, 2 parts by weight or any value between them. The content of the coupling agent can be 0.1, 0.3, 0.5, 0.8, 1, 1.2, 1.5 parts by weight or any value between them. The content of the filler can be 10, 12, 14, 16, 18, 20 parts by weight or any value between them.

[0013] In this invention, the low-viscosity epoxy resin can be bisphenol A epoxy resin, bisphenol F epoxy resin, or a mixture of the two. The viscosity of the low-viscosity epoxy resin is preferably 1000-5000 mPa·s, specifically 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, 5000 mPa·s or any value between them. When the viscosity of the low-viscosity epoxy resin is controlled within the above preferred range, the molecular weight of the low-viscosity epoxy resin is relatively small, and the epoxy group content is high, which is beneficial to improving the reactivity of the final product.

[0014] In this invention, the toughening epoxy resin is a nano-core-shell styrene-butadiene rubber modified epoxy resin and / or a nano-core-shell polybutadiene rubber modified epoxy resin, more preferably a nano-core-shell styrene-butadiene rubber modified epoxy resin. Specifically, the nano-core-shell styrene-butadiene rubber modified epoxy resin can be a product manufactured by KANEKA with model numbers MX-113, MX-125, or MX-135, and the nano-core-shell polybutadiene rubber modified epoxy resin can be a product manufactured by KANEKA with model numbers MX-136, MX-139, MX-153, MX-154, or MX-158.

[0015] In this invention, the epoxy acrylate resin can be any existing compound obtained by ring-opening esterification of epoxy resin and acrylic acid, including unmodified epoxy acrylate resin and / or modified epoxy acrylate resin, such as at least one of 2-hydroxy-3-phenoxypropyl acrylate, bisphenol A epoxy acrylate, fatty acid epoxy acrylate, phenolic epoxy acrylate, epoxy soybean oil acrylate, and epoxy diacrylate. Specifically, the epoxy acrylate resin can be Changxing Materials' 6270 or 6278, or Zhanxin Resin's... 600 600 / 20DP, 600 / 30OT At least one of 605 / 20. Furthermore, the viscosity of the epoxy acrylate resin at 25°C is preferably 500–20000 mPa·s, such as 500, 800, 1000, 2000, 5000, 8000, 10000, 12000, 15000, 18000, 20000 mPa·s or any value between them. In addition, the epoxy acrylate resin is liquid at room temperature. Controlling the viscosity of the epoxy acrylate resin within the above-mentioned preferred range is more conducive to the dispersion of each component in the epoxy adhesive system, thereby imparting a higher modulus and Tg to the laser-curable epoxy adhesive.

[0016] Graphene nanosheets are highly lipophilic "pure carbon," easily aggregated, and have difficulty interacting with the surrounding matrix, making them difficult to disperse in epoxy resin systems. Graphene oxide, an oxide of graphene, is usually obtained by reacting graphite with strong acids. The oxidation process enriches graphene with oxygen functional groups, thus endowing it with higher chemical activity. This can improve the solubility of graphene in water, but it is still not easily compatible with epoxy resins. This invention modifies graphene oxide nanosheets with dopamine. Dopamine adheres to the outer layer of the graphene oxide nanosheets, promoting interfacial bonding between the graphene oxide sheets and epoxy resin, reducing defects, and improving the compatibility of the graphene oxide nanosheets in epoxy resin. Furthermore, the primary amine group (-NH2) of dopamine has strong nucleophilicity, which can attack the methylene carbon atom in the epoxy group, causing a ring-opening addition reaction. This uniformly disperses the graphene oxide nanosheets in the polymer network structure, preventing polymer chain movement and providing reinforcement, thereby increasing the modulus and Tg. At the same time, the high thermal conductivity and large specific surface area of ​​the graphene oxide nanosheets greatly facilitate rapid heat transfer, improving the heat transfer efficiency of the system. This allows the entire system to uniformly heat up to the curing temperature, thereby stimulating the curing agent to initiate epoxy ring-opening to obtain the polymer network structure.

[0017] In a preferred embodiment, the dopamine-modified graphene nanosheets are prepared by the following method: dispersing graphene oxide nanosheets and dopamine hydrochloride in a buffer solution, heat-treating the resulting dispersion to adsorb dopamine onto the surface of the graphene oxide nanosheets, and then separating the solid and liquid components of the heat-treated product and drying it to obtain the dopamine-modified graphene nanosheets. The amount of dopamine hydrochloride added is preferably 0.5 to 1 times the mass of the graphene oxide nanosheets, such as 0.5 times, 0.6 times, 0.7 times, 0.8 times, 0.9 times, 1 times, or any value between these values. The heat treatment conditions preferably include a temperature of 40℃ to 60℃, such as 40℃, 42℃, 45℃, 48℃, 50℃, 52℃, 55℃, 58℃, 60℃, or any value between them; and a time of 24h to 48h, such as 24h, 26h, 28h, 30h, 32h, 34h, 36h, 38h, 40h, 42h, 44h, 46h, 48h, or any value between them. The drying conditions include a temperature of 60℃ to 80℃, such as 60℃, 62℃, 65℃, 68℃, 70℃, 72℃, 75℃, 78℃, 80℃, or any value between them; and a time of 10min to 40min, such as 10min, 20min, 30min, 40min, or any value between them. The buffer solution can be a Tris buffer solution (tris(hydroxymethyl)aminomethane) hydrochloride. The pH value of the buffer solution is preferably 8 to 9.

[0018] In this invention, the type and source of the curing agent can be any of the existing options, for example, imidazole curing agents are particularly preferred. Examples of imidazole curing agents include imidazole, 2-methylimidazolium, 2-ethylimidazolium, 1-isobutyl-2-methylimidazolium, 2-ethyl-4-methylimidazolium, 2-phenylimidazolium, 2-phenyl-4-methylimidazolium, 1-benzyl-2-methylimidazolium, 1-benzyl-2-phenylimidazolium, 1,2-dimethylimidazolium, 1-cyanoethyl-2-methylimidazolium, 1-cyanoethyl-2-ethyl-4-methylimidazolium, 1-cyanoethyl-2-undecylimidazolium, 1-cyanoethyl-2-phenylimidazolium and other 2-substituted imidazole compounds, 1-cyanoethyl-2-undecyltrimethylimidazolium salt, 1-cyanoethyl-2-phenyltrimethylimidazolium salt and other trimellitates, 2... At least one of the following: 4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct, 2-phenylimidazolium isocyanuric acid adduct, 2-methylimidazolium isocyanuric acid adduct, 2-phenyl-4,5-dihydroxymethylimidazolium, and 2-phenyl-4-methyl-5-dihydroxymethylimidazolium.

[0019] In this invention, the thermal initiator is a compound capable of generating free radicals via thermal decomposition to initiate a polymerization reaction, and can be a peroxide initiator and / or an azo initiator. Examples of peroxide initiators include at least one selected from: benzoyl peroxide, lauroyl peroxide, cumene hydroperoxide, 1,1-di(tert-hexylperoxy)cyclohexane, cumene hydroperoxide, tert-butyl hydroperoxide, di-tert-butyl peroxide, dicumyl peroxide, tert-butyl peroxybenzoate, tert-butyl peroxyvalerate, methyl ethyl ketone peroxide, cyclohexanone peroxide, diisopropyl peroxide, and dicyclohexyl peroxide. Examples of azo initiators include at least one selected from: azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, and azobiscyclohexylformitrile.

[0020] In this invention, the epoxy diluent is used to reduce the viscosity of the adhesive and extend its pot life. It can be an active diluent or a non-active diluent, preferably an active diluent, in which case it can participate in the curing reaction and become part of the cross-linked network of the cured product. The active diluent can be an aliphatic epoxy diluent and / or an aromatic epoxy diluent. Examples of aliphatic epoxy diluents include at least one selected from allyl glycidyl ether, butyl glycidyl ether, octyl glycidyl ether, decanyl glycidyl ether, dodecyl glycidyl ether, tridecyl glycidyl ether, tetradecyl glycidyl ether, ethylene glycol diglycidyl ether, butanediol diglycidyl ether, hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and trimethylolpropane triglycidyl ether. The aromatic epoxy diluent may include at least one of cashew phenol glycidyl ether, propylene oxide o-tolyl ether, phenyl glycidyl ether, benzyl glycidyl ether, o-tolyl glycidyl ether, and p-tert-butylphenyl glycidyl ether. The epoxy diluent is preferably a monofunctional epoxy diluent, more preferably an aromatic epoxy diluent, because the benzene ring structure can increase the glass transition temperature of the epoxy adhesive after curing, thereby improving its heat resistance.

[0021] In this invention, the stabilizer is used to improve the stability of the system and extend the shelf life. The stabilizer can be any existing stabilizer based on epoxy resin. From the perspective of improving storage stability, the stabilizer is preferably selected from at least one of lactic acid, boric acid, benzoic acid, phenylacetic acid, fumaric acid, salicylic acid, citric acid, stearic acid, benzoic acid, and barbituric acid.

[0022] In this invention, the coupling agent is used to improve the dispersion performance of inorganic substances in the adhesive within the resin matrix. From the perspective of raw material availability, the coupling agent is preferably at least one selected from methyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, γ-mercaptopropyltriethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, γ-glycidyletheroxypropyltrimethoxysilane, γ-(2,3-epoxypropoxy)-propyltrimethoxysilane, 3-glycidyletheroxypropyltrimethoxysilane, and bis(γ-triethoxysilylpropyl)-tetrasulfide.

[0023] In this invention, the filler is used to improve the mechanical strength of the system and reduce its coefficient of thermal expansion. The filler is preferably an inorganic filler, specifically including at least one of the following: silica, alumina, talc, calcium carbonate, barium sulfate, mica, quartz powder, glass powder, aluminum hydroxide, zinc oxide, aluminum nitride, silicon carbide, silicon nitride, boron nitride, titanium nitride, dolomite, titanium dioxide, aluminum silicate, calcium silicate, bentonite, magnesium oxide, magnesium hydroxide, magnesium silicate, cobalt silicate, zirconium oxide, and barium titanate. Furthermore, the surface of the inorganic filler is preferably treated with a silane coupling agent, which improves the compatibility between the inorganic filler and the epoxy adhesive system, further enhancing the performance of the epoxy adhesive. Specific treatment methods can be various existing conventional options, which are well known to those skilled in the art and will not be elaborated upon here.

[0024] The method for preparing the laser-curable epoxy adhesive provided by this invention includes uniformly mixing a low-viscosity epoxy resin, a toughened epoxy resin, an epoxy acrylate resin, dopamine-modified graphene oxide nanosheets, a curing agent, a thermal initiator, and optionally an epoxy diluent, stabilizer, coupling agent, and filler. The mixing method is not particularly limited and can be implemented using various existing methods. In one specific embodiment, the mixing method includes adding the low-viscosity epoxy resin, toughened epoxy resin, epoxy acrylate resin, curing agent, thermal initiator, and optionally an epoxy diluent, stabilizer, and coupling agent to a dual planetary hybrid reactor and stirring under vacuum until uniformly mixed. Then, dopamine-modified graphene oxide nanosheets and filler are added, and vacuum stirring continues until uniformly mixed. The temperature for each step of vacuum mixing is independently 20-30℃, such as 20℃, 22℃, 24℃, 26℃, 28℃, 30℃ or any value between them; the vacuum degree is below 0.098MPa, such as 0.098MPa, 0.095MPa, 0.09MPa, 0.08MPa, 0.07MPa, 0.06MPa, 0.05MPa, 0.04MPa, 0.03MPa, 0.02MPa, 0.01MPa, 0MPa or any value between them.

[0025] This invention also provides the application of the above-mentioned laser-curable epoxy adhesive in the field of consumer electronics.

[0026] The present invention will be described in detail below through embodiments.

[0027] In the following examples and comparative examples, the graphene oxide nanosheets were purchased from Nanjing Xianfeng Nanomaterials Technology Co., Ltd., with the grade XF002-1, a sheet diameter of 0.5-5 μm, a thickness of 0.8-1.2 nm, and a purity of approximately 99%.

[0028] Preparation Example 1: Dopamine-Modified Graphene Oxide Nanosheets

[0029] Graphene oxide nanosheets were dispersed in Tris buffer solution (pH 8.5) to obtain a GO dispersion with a concentration of 0.1 g / L. Dopamine hydrochloride was added to the resulting dispersion and the mixture was stirred at 40 °C for 48 h. The amount of dopamine hydrochloride added was 0.5 times the mass of graphene oxide. After the reaction was completed, the mixture was filtered through a microporous membrane, the solid product was collected and washed with deionized water, and then the product was dried in a vacuum oven at 60 °C for 40 min to obtain dopamine-modified graphene oxide nanosheets, denoted as DOP-GO-1.

[0030] Preparation Example 2: Dopamine-Modified Graphene Oxide Nanosheets

[0031] Graphene oxide nanosheets were dispersed in Tris buffer solution (pH 8) to obtain a GO dispersion with a concentration of 0.5 g / L. Dopamine hydrochloride was added to the resulting dispersion and the mixture was stirred at 60 °C for 24 h. The amount of dopamine hydrochloride added was 1 times the mass of graphene oxide. After the reaction was completed, the solid product was collected by microporous membrane filtration and washed with deionized water. The product was then dried in a vacuum oven at 80 °C for 10 min to obtain dopamine-modified graphene oxide nanosheets, denoted as DOP-GO-2.

[0032] Preparation Example 3: Dopamine-Modified Graphene Oxide Nanosheets

[0033] Graphene oxide nanosheets were dispersed in Tris buffer solution (pH 9) to obtain a GO dispersion with a concentration of 0.3 g / L. Dopamine hydrochloride was added to the resulting dispersion and the mixture was stirred at 50 °C for 36 h. The amount of dopamine hydrochloride added was 0.8 times the mass of graphene oxide. After the reaction was completed, the solid product was collected by microporous membrane filtration and washed with deionized water. The product was then dried in a vacuum oven at 70 °C for 30 min to obtain dopamine-modified graphene oxide nanosheets, denoted as DOP-GO-3.

[0034] Example 1

[0035] This embodiment illustrates the preparation of the laser-curable epoxy adhesive provided by the present invention.

[0036] (1) The raw materials are as follows:

[0037] Low viscosity epoxy resin (Dai Nippon Ink Co., Ltd. EXA-830LV) 10 parts by weight

[0038] Toughened epoxy resin (KANEKA's MX-135) 20 parts by weight

[0039] Epoxy acrylate resin (Changxing Materials' 6278) 25 parts by weight Dopamine-modified graphene oxide nanosheets (DOP-GO-1) 2 parts by weight

[0040]

[0041] (2) The preparation process of epoxy adhesive is as follows:

[0042] EXA-830LV, MX-135, 6278, PN-23J, benzoyl peroxide, cashew phenol glycidyl ether, fumaric acid, and γ-methacryloyloxypropyltrimethoxysilane were sequentially added to a dual planetary hybrid reactor and stirred under vacuum until homogeneous. Then, alumina and dopamine-modified graphene oxide nanosheets were added to the resulting mixture and stirred under vacuum until homogeneous to obtain a laser-curable epoxy adhesive, denoted as A1.

[0043] Example 2

[0044] This embodiment illustrates the preparation of the laser-curable epoxy adhesive provided by the present invention.

[0045] (1) The raw materials are as follows:

[0046]

[0047] (2) The preparation process of low-temperature thermosetting epoxy adhesive is as follows:

[0048] EPON 872, MX-125, and Zhanxin resin 605 / 20, propylene oxide o-tolyl ether, EH-5011S, 2,2'-azobisisobutyronitrile, barbituric acid and γ-mercaptopropyltriethoxysilane were sequentially added to a dual planetary hybrid reactor and stirred under vacuum until homogeneous. Then, magnesium oxide and dopamine-modified graphene oxide nanosheets were added to the resulting mixture and stirred under vacuum until homogeneous to obtain a laser-curable epoxy adhesive, denoted as A2.

[0049] Example 3

[0050] This embodiment illustrates the preparation of the laser-curable epoxy adhesive provided by the present invention.

[0051] (1) The raw materials are as follows:

[0052]

[0053] (2) The preparation process of epoxy adhesive is as follows:

[0054] NPEF-170, MX-136 600, cashew phenol glycidyl ether, MC120D, tert-butyl hydroperoxide, salicylic acid and γ-mercaptopropyltriethoxysilane were sequentially added to a dual planetary hybrid reactor and stirred under vacuum until homogeneous. Then aluminum hydroxide and dopamine-modified graphene oxide nanosheets were added to the resulting mixture and stirred under vacuum until homogeneous to obtain laser-cured epoxy adhesive, denoted as A3.

[0055] Example 4

[0056] A laser-curable epoxy adhesive was prepared according to the method of Example 1, except that cashew phenol glycidyl ether was replaced with the same amount of allyl glycidyl ether by weight, and the other conditions were the same as in Example 1. The resulting laser-curable epoxy adhesive was denoted as A4.

[0057] Comparative Example 1

[0058] A laser-cured epoxy adhesive was prepared according to the method of Example 1, except that the epoxy acrylate resin was replaced with the same amount of low-viscosity epoxy resin and the benzoyl peroxide was replaced with the same amount of curing agent. The other conditions were the same as in Example 1, and a reference laser-cured epoxy adhesive, denoted as DA1, was obtained.

[0059] Comparative Example 2

[0060] A laser-cured epoxy adhesive was prepared according to the method of Example 2, except that 2,2ˋ-azobisisobutyronitrile was replaced with the same amount of curing agent by weight, and the other conditions were the same as in Example 1, to obtain a reference laser-cured epoxy adhesive, denoted as DA2.

[0061] Comparative Example 3

[0062] A photocurable epoxy adhesive was prepared according to the method of Example 4, except that the dopamine-modified graphene oxide nanosheets were replaced with the same amount of aluminum hydroxide by weight, and the other conditions were the same as in Example 4, to obtain a reference laser-curable epoxy adhesive, denoted as DA3.

[0063] Comparative Example 4

[0064] A photocurable epoxy adhesive was prepared according to the method of Example 4, except that the dopamine-modified graphene oxide nanosheets were replaced with graphene oxide nanosheets of the same weight, and the other conditions were the same as in Example 4, to obtain a reference laser-curable epoxy adhesive, denoted as DA4.

[0065] Test case

[0066] (1) Laser curing shear strength: Using the laser curing epoxy adhesives obtained in the above embodiments and the reference laser curing epoxy adhesives obtained in the comparative examples, a shear sheet of stainless steel to anodized aluminum with an overlap area of ​​25.4 mm × 12.7 mm was prepared. The adhesive layer thickness was controlled at 0.1 mm. The sample was irradiated with a 980 nm laser using a laser device. The laser heating temperature was 160 °C and the duration was 6-10 s. The shear strength of the obtained cured sample was tested using a universal tensile testing machine.

[0067] (2) Thermosetting shear strength: Using the laser-cured epoxy adhesives obtained in the above embodiments and the reference laser-cured epoxy adhesives obtained in the comparative examples, stainless steel to anodized aluminum shear plates with an overlap area of ​​25.4 mm × 12.7 mm were prepared. The adhesive layer thickness was controlled at 0.1 mm. The plates were cured at 90 °C for 1 h. The shear strength of the cured samples was tested using a universal tensile testing machine.

[0068] (3) Tg: The sample was prepared as follows: a cylindrical sample with a height of 5 mm and a diameter of 6 mm was prepared using a Teflon mold and cured at 90 °C for 1 h. Dynamic thermomechanical analysis (TMA) was performed on the sample using a TA DiscoveryTMA450 analyzer under a nitrogen inlet flow rate of 100 mL / min. The sample was brought into contact with a bending probe under a force of 0.20 N, and then heated from 0 °C to 250 °C at a rate of 5 °C / min. During the test cycle, the force was adjusted to ±0.08 N at a frequency of 0.10 Hz to measure the Tg of the epoxy adhesive. The data is the average of three independent runs. The test results are shown in Table 1.

[0069] (4) Tensile modulus: A type 4 dumbbell film with a thickness of 0.4 mm was prepared according to the standard GB / T 528-2009 "Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber". The tensile modulus of the dumbbell film was then tested using an Inström universal tensile testing machine. The test results are shown in Table 1.

[0070] Table 1

[0071]

[0072] As can be seen from the results in Table 1, the laser-curable epoxy adhesive provided by this invention possesses both high modulus and high Tg, and can achieve rapid curing. The data on laser-cured shear strength and thermosetting shear strength show that the laser-curable epoxy adhesive provided by this invention can be cured by both infrared laser and thermosetting. A comparison between Example 1 and Example 4 shows that when an aromatic epoxy diluent is used, the laser-curable epoxy adhesive can be given a higher glass transition temperature, thereby improving heat resistance. A comparison between Example 1 and Comparative Example 1 shows that when no epoxy acrylate resin and curing agent are added to the laser-curable epoxy adhesive, it cannot react under laser irradiation, and the curing agent cannot react quickly, resulting in no initial bond strength and inability to achieve rapid positioning. A comparison between Example 2 and Comparative Example 2 shows that when epoxy acrylate resin is added to the laser-curable epoxy adhesive but no curing agent is added, it also cannot react under laser irradiation, resulting in no initial bond strength and inability to achieve rapid positioning. As can be seen from the comparison between Example 4 and Comparative Examples 3 and 4, when dopamine-modified graphene oxide nanosheets are not added, not only will the initial bonding strength decrease slightly, but the Tg and tensile modulus will also decrease.

[0073] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A laser-curable epoxy adhesive, characterized in that, The raw materials for preparing the laser-curable epoxy adhesive contain low-viscosity epoxy resin, toughened epoxy resin, epoxy acrylate resin, dopamine-modified graphene oxide nanosheets, curing agent, and thermal initiator in a mass ratio of 1:(0.5-2):(0.75-3):(0.05-0.5):(0.75-2.5):(0.05-0.5):(0-1):(0-0.2):(0-0.15):(0-2), as well as optional epoxy diluent, stabilizer, coupling agent, and filler.

2. The laser-curable epoxy adhesive according to claim 1, characterized in that, The content of the low-viscosity epoxy resin is 10-20 parts by weight, the content of the toughened epoxy resin is 10-20 parts by weight, the content of the epoxy acrylate resin is 15-30 parts, the content of the dopamine-modified graphene oxide nanosheets is 1-3 parts, the content of the curing agent is 15-25 parts, the content of the thermal initiator is 1-3 parts, the content of the epoxy diluent is 5-10 parts, the content of the stabilizer is 0.5-2 parts, the content of the coupling agent is 0.1-1.5 parts, and the content of the filler is 10-20 parts.

3. The laser-curable epoxy adhesive according to claim 1, characterized in that, The low-viscosity epoxy resin is bisphenol A epoxy resin and / or bisphenol F epoxy resin; the viscosity of the low-viscosity epoxy resin is 1000-5000 mPa·s.

4. The laser-curable epoxy adhesive according to claim 1, characterized in that, The toughening epoxy resin is a nano-core-shell styrene-butadiene rubber modified epoxy resin and / or a nano-core-shell polybutadiene rubber modified epoxy resin.

5. The laser-curable epoxy adhesive according to claim 1, characterized in that, The viscosity of the epoxy acrylate resin at 25°C is 500–20000 mPa·s; Preferably, the epoxy acrylate resin is in a liquid state at room temperature; Preferably, the epoxy acrylate resin is selected from at least one of 2-hydroxy-3-phenoxypropyl acrylate, bisphenol A epoxy acrylate, fatty acid epoxy acrylate, phenolic epoxy acrylate, epoxy soybean oil acrylate, and epoxy diacrylate.

6. The laser-curable epoxy adhesive according to claim 1, characterized in that, The dopamine-modified graphene nanosheets were prepared by the following method: graphene oxide nanosheets and dopamine hydrochloride were dispersed in a buffer solution, the resulting dispersion was heat-treated to allow dopamine to be adsorbed on the surface of the graphene oxide nanosheets, and the heat-treated product was separated into solid and liquid and dried to obtain dopamine-modified graphene nanosheets. Preferably, the amount of dopamine hydrochloride added is 0.5 to 1 times the mass of the graphene oxide nanosheets; Preferably, the heat treatment conditions include a temperature of 40℃ to 60℃ and a time of 24h to 48h.

7. The laser-curable epoxy adhesive according to claim 1, characterized in that, The curing agent is an imidazole-based curing agent; Preferably, the thermal initiator is a peroxide initiator and / or an azo initiator; Preferably, the epoxy diluent is an aromatic epoxy diluent; Preferably, the stabilizer is selected from at least one of lactic acid, boric acid, benzoic acid, phenylacetic acid, fumaric acid, salicylic acid, citric acid, stearic acid, benzoic acid, and barbituric acid; Preferably, the coupling agent is selected from at least one of methyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, γ-mercaptopropyltriethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, γ-glycidyl etheroxypropyltrimethoxysilane, γ-(2,3-epoxypropoxy)-propyltrimethoxysilane, 3-glycidyl etheroxypropyltrimethoxysilane, and bis(γ-triethoxysilylpropyl)-tetrasulfide; Preferably, the filler is selected from at least one of silicon dioxide, alumina, talc, calcium carbonate, barium sulfate, mica, quartz powder, glass powder, aluminum hydroxide, zinc oxide, aluminum nitride, silicon carbide, silicon nitride, boron nitride, titanium nitride, dolomite, titanium dioxide, aluminum silicate, calcium silicate, bentonite, magnesium oxide, magnesium hydroxide, magnesium silicate, cobalt silicate, zirconium oxide, and barium titanate.

8. A method for preparing the laser-curable epoxy adhesive according to any one of claims 1-7, characterized in that, The method involves uniformly mixing a low-viscosity epoxy resin, a toughened epoxy resin, an epoxy acrylate resin, dopamine-modified graphene oxide nanosheets, a curing agent and a thermal initiator, as well as optional epoxy diluents, stabilizers, coupling agents and fillers.

9. The method for preparing the laser-curable epoxy adhesive according to claim 8, characterized in that, The mixing temperature is 20-30℃, and the vacuum degree is below 0.098MPa.

10. The application of the laser-curable epoxy adhesive according to any one of claims 1-7 in the field of consumer electronics.

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