Water-based ACF glue and preparation method thereof

Abstract

The invention discloses a water-based ACF adhesive and a preparation method thereof, and relates to the technical field of anisotropic conductive adhesive films, the preparation method comprises the following steps: S1, diisocyanate, polyester polyol and a catalyst are mixed and pre-polymerized; s2, adding a hydrophilic chain extender and other chain extenders into the prepolymer obtained in S1, and carrying out chain extension reaction; s3, after the chain extension reaction is completed, adding 20-200 parts by mass of an acrylate end-capping reagent, and carrying out an end-capping reaction; s4, adding a neutralizer into a reactant obtained in S3, and stirring for 5-45 minutes to form a salt; s5, adding a specific amount of water, and then stirring for 10-60 minutes to finish emulsification, so as to obtain waterborne polyurethane; s6, uniformly mixing 100 parts by mass of waterborne polyurethane, 5-30 parts by mass of an inorganic filler, 2-25 parts by mass of conductive particles and 1-10 parts by mass of an initiator to obtain a target sizing material; and S7, coating and drying the sizing material to obtain the target water-based ACF adhesive. The water-based ACF adhesive provided by the invention is strong in interface bonding force, low in on resistance and good in water resistance, and has extremely high practicability in the aspect of electronic component connection.

Description

Technical Field

[0001] The present invention relates to the technical field of anisotropic conductive film, and particularly relates to an aqueous ACF adhesive and a preparation method thereof. Background Art

[0002] Anisotropic Conductive Film (ACF) is a thin film material with both unidirectional conductivity (insulating in the plane direction of the adhesive film and conductive in the Z-axis direction, i.e., perpendicular to the plane direction of the adhesive film) and adhesive functions. ACF adhesives have gradually become a substitute for traditional tin-lead soldering due to their excellent conductivity, high usability, low curing temperature, and the ability to achieve ultra-narrow pitch conduction. Especially in the connection of precision electronic components, it has an absolute advantage compared with tin-lead soldering.

[0003] Currently, the mainstream ACF adhesives are mainly epoxy-based and acrylic-based, and most of them belong to solvent-based adhesives or solvent-free adhesives, and the application of aqueous systems in this field is very rare. Solvent-based adhesives will produce VOCs (volatile organic compounds) during the preparation / use process, which runs counter to the current green production policy, while solvent-free adhesives mostly have the disadvantages of high colloid viscosity, which is not conducive to filler dispersion and adhesive film production. However, the ACF adhesives produced by these two methods often have high bonding strength and water resistance, and these two aspects are often the disadvantages of aqueous adhesives. Therefore, there are few applications of aqueous ACF at present.

[0004] Aqueous adhesives have the inherent disadvantage of poor water resistance, and poor water resistance will further affect their mechanical properties or bonding properties when the material is used / stored in a high-temperature and high-humidity environment. Therefore, a new solution is needed to solve these problems. Summary of the Invention

[0005] The present invention overcomes the deficiencies of the prior art and provides an aqueous ACF adhesive and a preparation method thereof.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a preparation method of an aqueous ACF adhesive, comprising the following steps:

[0007] S1. Mix 100-150 parts by mass of diisocyanate, 30-300 parts by mass of polyester polyol, and 0.1-5 parts by mass of catalyst, and pre-polymerize at 70-100 °C under nitrogen protection for 0.5-4 h;

[0008] S2. Add 5-65 parts by mass of hydrophilic chain extender and 1-90 parts by mass of other chain extenders to the prepolymer obtained in S1, and carry out a chain extension reaction at 60-100 °C under nitrogen protection for 1-5 h;

[0009] S3. After completing the chain extension reaction, 20 - 200 parts by mass of an acrylate capping agent is added, and the capping reaction is carried out at 60 - 100 °C under nitrogen protection for 1 - 3 h;

[0010] S4. After reducing the reaction temperature to 20 - 60 °C, a neutralizing agent corresponding to the hydrophilic chain extender is added to the reactant obtained through S3, and it is stirred for 5 - 45 min to form a salt;

[0011] S5. At 20 - 60 °C, a specific amount of water is added according to the target solid content, and then it is stirred for 10 - 60 min to complete emulsification to obtain a waterborne polyurethane;

[0012] S6. 100 parts of the waterborne polyurethane, 5 - 30 parts by mass of an inorganic filler, 2 - 25 parts by mass of conductive particles, and 1 - 10 parts by mass of an initiator are mixed uniformly to obtain the target rubber compound;

[0013] S7. The rubber compound is coated and dried to obtain the target waterborne ACF adhesive.

[0014] In a preferred embodiment of the present invention, in step S1, the diisocyanate is one or more of diphenylmethane diisocyanate or dicyclohexylmethane diisocyanate, and the polyester polyol is one or more of poly(1,4 - butanediol adipate) diol with a molecular weight of 2000 - 3000, polycarbonate diol with a molecular weight of 2000 - 3000, and poly(ε - caprolactone) diol with a molecular weight of 2000 - 3000.

[0015] In a preferred embodiment of the present invention, in step S1, the catalyst is dibutyltin dilaurate or bismuth isooctanoate.

[0016] In a preferred embodiment of the present invention, the hydrophilic chain extender is 2,2 - bis(hydroxymethyl)propionic acid and / or 2,2 - bis(hydroxymethyl)butyric acid, and the other chain extender is a compound combination of one or more of ethylene glycol, 1,4 - butanediol, or diethanolamine and bisphenol A glycerol diacrylate.

[0017] In a preferred embodiment of the present invention, the acrylate capping agent is one or more of pentaerythritol triacrylate, 2 - hydroxyethyl methacrylate, or 2 - hydroxy - 3 - phenoxypropyl acrylate.

[0018] In a preferred embodiment of the present invention, the neutralizing agent is one or more of triethylamine, triethanolamine, diethanolamine, or N,N - dimethylethanolamine.

[0019] In a preferred embodiment of the present invention, the inorganic filler is one or more of silica, magnesium oxide, or alumina.

[0020] In a preferred embodiment of the present invention, the conductive particles are one or more of nickel-plated polystyrene microspheres and gold-plated polystyrene microspheres, and the particle size is 1-10 μm.

[0021] In a preferred embodiment of the present invention, the initiator is one or more of azobisisobutyronitrile, benzoyl peroxide or methyl ethyl ketone peroxide.

[0022] The present invention solves the defects existing in the background technology, and the present invention has the following beneficial effects:

[0023] (1) The present invention provides an aqueous base material with good bonding strength and water resistance. Selecting aqueous polyurethane as the film-forming base material has the advantage of flexible adjustable structure. The isocyanate is selected as diphenylmethane diisocyanate and dicyclohexylmethane diisocyanate with a highly symmetric structure, which can promote the crystallization of molecular chains, thereby improving the water resistance of the film; combined with crystalline polyester polyol (such as PBA) or polyester polyol with excellent water resistance and solvent resistance (such as PCD), the water resistance of the material is improved, and polyfunctional polyacrylate is added to increase the crosslinking density of the film, thereby improving its adhesion and water resistance.

[0024] (2) In the chain extension stage and the capping stage of the present invention, high molecular compounds containing double bonds are introduced. Using the double bond structure to increase more crosslinking sites, a relatively dense crosslinked structure is formed to reduce the water molecule penetration channels. While enhancing the water resistance of the target ACF, the double bonds between the chain extension stage and the capping stage form mutual crosslinking, thereby enhancing the three-dimensional network structure, greatly improving the bonding force and water resistance of the target ACF adhesive, and thus overcoming the problem that poor water resistance will affect its mechanical properties or bonding properties when the material is used / stored in a high temperature and high humidity environment.

[0025] (3) The aqueous ACF adhesive prepared by the present invention forms an aqueous polyurethane with appropriate crosslinking degree through the control of the raw material parts and types. When this kind of aqueous polyurethane is mixed with inorganic fillers and conductive particles, its appropriate bonding force and fluidity can ensure the uniform dispersion of conductive particles and inorganic fillers, avoiding the problem of inconsistent electrical conduction performance between two electronic components caused by uneven dispersion resulting in inconsistent local resistance, and the strength problem caused by uneven distribution of inorganic fillers resulting in uneven material strength. The aqueous ACF adhesive provided by the present invention application has extremely high practicality in the connection between electronic components. In addition, during the production process of the aqueous ACF adhesive of the present invention, no volatile organic compounds are generated, meeting the requirements of green production. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments recorded in the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on these drawings;

[0027] Figure 1 It is a flowchart of the implementation steps of the preferred embodiment of the present invention. Specific implementation manners

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0029] Many specific details are set forth in the following description in order to fully understand the present invention, but the present invention can also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited by the specific embodiments disclosed below.

[0030] A water-based ACF adhesive provided by the present invention is mainly applied to the connection of precision electronic components. The raw materials involved in the present invention can be obtained through commercial purchase without special declaration, or can also be prepared by the preparation methods well-known to those skilled in the art.

[0031] The present application provides a water-based ACF adhesive, which comprises the following components in parts by mass:

[0032] Diisocyanate 100 - 150 parts;

[0033] Polyester polyol 30 - 300 parts;

[0034] Catalyst 0.1 - 5 parts;

[0035] Hydrophilic chain extender 5 - 65 parts;

[0036] Other chain extenders 1 - 90 parts;

[0037] Acrylate capping agent 20 - 200 parts;

[0038] Neutralizer 10 - 30 parts;

[0039] Inorganic filler 5 - 30 parts;

[0040] Conductive particles 2 - 25 parts;

[0041] 1 - 10 parts of initiator.

[0042] Specifically, 100 - 150 parts by mass of diisocyanate and 30 - 300 parts by mass of polyester polyol are used to prepare waterborne polyurethane through prepolymerization, chain extension, capping and neutralization reactions; the inorganic filler includes one or more of silica, magnesium oxide or aluminum oxide; the conductive particles include one or more of nickel - plated polystyrene microspheres and gold - plated polystyrene microspheres.

[0043] The diisocyanate is selected as diphenylmethane diisocyanate (MDI) and dicyclohexylmethane diisocyanate (HMDI) with a highly symmetric structure, which can promote the crystallization of molecular chains, thereby improving the water resistance of the adhesive film; further combined with polyester polyol, a prepolymer with a certain molecular weight is obtained, and at the same time, multifunctional polyacrylate is added to increase the cross - link density of the adhesive film, and then improve its adhesiveness and water resistance; under the action of the initiator, the double bonds in the molecular chain are cured and cross - linked.

[0044] As Figure 1 shown, the present invention provides a preparation method of a waterborne ACF adhesive as described in the above technical solution, including the following steps:

[0045] S1. Mix 100 - 150 parts by mass of diisocyanate, 30 - 300 parts by mass of polyester polyol, and 0.1 - 5 parts by mass of catalyst, and carry out prepolymerization at 70 - 100 °C under nitrogen protection for 0.5 - 4 h;

[0046] S2. Add 5 - 65 parts by mass of hydrophilic chain extender and 1 - 90 parts by mass of other chain extenders to the prepolymer obtained in S1, and carry out chain extension reaction at 60 - 100 °C under nitrogen protection for 1 - 5 h;

[0047] S3. After the chain extension reaction is completed, add 20 - 200 parts by mass of acrylate capping agent, and carry out capping reaction at 60 - 100 °C under nitrogen protection for 1 - 3 h;

[0048] S4. After reducing the reaction temperature to 20 - 60 °C, add the neutralizer corresponding to the hydrophilic chain extender to the reactant obtained in step S3, and stir for 5 - 45 min to form a salt;

[0049] S5. Add a specific amount of water at 20 - 60 °C according to the target solid content, and then stir for 10 - 60 min to complete emulsification to obtain waterborne polyurethane;

[0050] S6. Mix 100 parts of waterborne polyurethane, 5 - 30 parts by mass of inorganic filler, 2 - 25 parts by mass of conductive particles and 1 - 10 parts by mass of initiator uniformly to obtain the target adhesive;

[0051] S7. Coat and dry the adhesive to obtain the target waterborne ACF adhesive.

[0052] Preferably, in step S1, the diisocyanate is one or more of diphenylmethane diisocyanate (MDI) or dicyclohexylmethane diisocyanate (HMDI), and the polyester polyol is one or more of poly(butylene adipate) diol (PBA) with a molecular weight of 2000 - 3000, polycarbonate diol (PCD) with a molecular weight of 2000 - 3000, and poly(ε-caprolactone) diol (PCL) with a molecular weight of 2000 - 3000. By combining the diisocyanate with the polyester polyol, taking advantage of the highly symmetric molecular structures of MDI and HMDI, the crystallization of molecular chains is promoted, thereby improving the water resistance of the adhesive film, ensuring the stability of molecular chains, reducing the possibility of thermal decomposition of the material, and thus enhancing the heat resistance of the material; then combining with the crystalline polyester polyol PBA or PCL to form a crystalline structure, thereby restricting the movement of molecular chains and ensuring that the material has excellent mechanical properties such as strength and modulus, or improving the corresponding properties of the waterborne polyurethane by utilizing the excellent solvent resistance and water resistance of PCD itself.

[0053] Preferably, in step S1, the catalyst is dibutyltin dilaurate or bismuth isooctanoate.

[0054] Preferably, the hydrophilic chain extender is 2,2 - bis(hydroxymethyl)propionic acid (DMPA) and / or 2,2 - bis(hydroxymethyl)butyric acid (DMBA), and the other chain extenders are a compound combination of one or more of ethylene glycol (EG), 1,4 - butanediol (BDO), or diethanolamine (DEA) and bisphenol A glycerol diacrylate, and the combination ratio has no range limitation; specifically, both 2,2 - bis(hydroxymethyl)propionic acid (DMPA) and 2,2 - bis(hydroxymethyl)butyric acid (DMBA) have a structure with 2 hydroxyl groups and 1 carboxyl group. Their two hydroxyl groups can react with isocyanate groups to achieve the purpose of chain extension, and the carboxyl group is used to form a salt with a neutralizing agent in the later stage, thereby enabling the polyurethane molecular chain to be emulsified in water to obtain a waterborne polyurethane emulsion; while bisphenol A glycerol diacrylate (BGDA) contains 2 double bonds and 2 hydroxyl groups per molecule. Introducing double bonds in the chain - extending stage can serve as cross - linking sites, thus providing more cross - linking sites, increasing the cross - linking density, and preparing for the cross - linking with another group of double bonds in the capping stage.

[0055] Specifically, ethylene glycol (EG), 1,4-butanediol (BDO), or diethanolamine (DEA) all contain hydroxyl groups, and the hydroxyl groups will react with isocyanate groups to form urethane bonds; at the same time, they are compounded with bisphenol A glycerol diacrylate. The hydroxyl groups in bisphenol A glycerol diacrylate can react with the isocyanate groups in the prepolymer to form new polyurethane chains, thereby increasing the molecular weight of the polyurethane; at the same time, bisphenol A glycerol diacrylate contains two double bonds. Introducing double bonds in the chain extension stage can increase the crosslinking density of the polymer, thereby enhancing the intermolecular force, reducing the exposure of hydrophilic groups, and improving the water resistance and adhesion of the waterborne polyurethane.

[0056] Preferably, the acrylate end-capping agent is one or more of pentaerythritol triacrylate, 2-hydroxyethyl methacrylate, or 2-hydroxy-3-phenoxypropyl acrylate;

[0057] Among them, pentaerythritol triacrylate (PETA) contains 1 hydroxyl group and 3 double bonds; 2-hydroxyethyl methacrylate contains 1 hydroxyl group and 1 double bond; 2-hydroxy-3-phenoxypropyl acrylate contains 1 hydroxyl group and 1 double bond;

[0058] The above three types of end-capping agents all have different numbers of double bonds. Double bonds are important functional groups in these compounds, and they play a key role in free radical polymerization reactions, enabling these compounds to form long-chain polymers. The number and position of double bonds will affect the properties of the polymer, such as hardness, flexibility, and reactivity.

[0059] Specifically, in the present invention application, the double bonds of bisphenol A glycerol diacrylate introduced in the chain extension stage will crosslink with the double bonds in pentaerythritol triacrylate (PETA), 2-hydroxyethyl methacrylate (HEMA), or 2-hydroxy-3-phenoxypropyl acrylate introduced in the end-capping stage. Crosslinking will also occur between bisphenol A glycerol diacrylate and bisphenol A glycerol diacrylate, and between end-capping agents and end-capping agents, forming a dense crosslinked structure, thereby enhancing the intermolecular force. The dense structure with high crosslinking density reduces the water molecule penetration channels, thereby improving the water resistance of the target product. Finally, while ensuring that the formed waterborne ACF adhesive has high adhesiveness, the problem of poor water resistance of traditional waterborne adhesives is overcome.

[0060] Preferably, the neutralizing agent is one or more of triethylamine, triethanolamine, diethanolamine, or N,N-dimethylethanolamine; using a weak base can effectively neutralize the carboxyl groups in the polyurethane, avoid affecting the product performance, and control the proportion and type of the neutralizing agent to achieve the purpose of precisely controlling the ionic concentration and particle surface charge of the polyurethane emulsion, thereby optimizing the stability of the emulsion and the performance of the final product.

[0061] Preferably, the inorganic filler is one or more of silica, magnesium oxide or alumina; based on the differences in electronic components, selecting the above three different types of inorganic fillers can improve the various properties of the ACF adhesive. Specifically, using silica as the reinforcing filler can significantly improve the mechanical strength and hardness of the ACF adhesive while ensuring the thermal stability of the adhesive; filling with magnesium oxide can increase the thermal conductivity of the target aqueous ACF adhesive, so that the aqueous ACF adhesive can be used in applications requiring good heat conduction; filling with alumina can utilize the high melting point of alumina to improve the heat resistance of the adhesive, and utilize the chemical stability of alumina to improve the resistance of the aqueous ACF adhesive to chemicals (such as acids, alkalis, solvents).

[0062] Preferably, the conductive particles specifically include one or more of nickel-plated polystyrene microspheres and gold-plated polystyrene microspheres. Specifically, they are polystyrene microspheres with a conductive metal coating on the surface, and have excellent electrical conductivity. The particle size of the conductive particles is 1-10 μm. Limiting the particle size of the conductive particles is beneficial to the full dispersion of the conductive particles in the aqueous ACF adhesive, and can avoid the uneven local dispersion of the conductive particles resulting in different conduction rates of each part of the aqueous ACF adhesive in this application, which affects the use of the product.

[0063] The initiator is one or more of azobisisobutyronitrile, benzoyl peroxide or methyl ethyl ketone peroxide. These initiators can decompose to generate free radicals under heating conditions. These free radicals can undergo a chain reaction with acrylate end-capping agents or other polymerizable components, thereby promoting the formation of a crosslinked network. When mixing aqueous polyurethane with conductive particles and inorganic fillers, adding the initiator and reaching a certain temperature can quickly initiate the polymerization reaction of double bonds in the molecular chain, forming a more stable three-dimensional crosslinked structure, thereby significantly improving the bonding strength and water resistance of the adhesive film.

[0064] Example 1:

[0065] Taking the preparation of ACF adhesive with aqueous polyurethane with a solid content of 40% as the base material as an example, the specific implementation steps are as follows:

[0066] S1. Add 100 parts by mass of diphenylmethane diisocyanate, 160 parts by mass of polycarbonate diol (PCD) with a molecular weight of 2000, and 1 part by mass of dibutyltin dilaurate into a four-necked flask equipped with a stirrer, a thermometer and a condenser, and pre-polymerize at 80 °C under a nitrogen atmosphere for 2 h;

[0067] S2. Add 18 parts by mass of 2,2-dimethylolpropionic acid, 6 parts by mass of 1,4-butanediol and 16 parts by mass of bisphenol A glycerol diacrylate into the four-necked flask, and carry out chain extension at 70 °C under a nitrogen atmosphere for 3 h;

[0068] S3. After the chain extension is completed, add 50 parts by mass of pentaerythritol triacrylate to the four-necked flask, and carry out the end-capping reaction at 70 °C under a nitrogen atmosphere for 1 h;

[0069] S4. After the end-capping reaction is completed, lower the system temperature to 25 °C, then add 13.5 parts by mass of triethylamine to neutralize for 15 min, and then keep the temperature at 25 °C and add 546.5 parts by mass of water to the four-necked flask. Stir vigorously for 30 min to complete the emulsification of the product to obtain an aqueous polyurethane substrate with a solid content of 40%;

[0070] S5. Take 100 parts by mass of the above-mentioned aqueous polyurethane, 8 parts by mass of fumed silica, 6 parts by mass of nickel-plated polystyrene conductive microspheres, and 3 parts by mass of BPO. Mix them and carry out ultrasonic water bath for 30 min, and then further mix them evenly with a vortex mixer to obtain the required rubber compound;

[0071] S6. Coating the above rubber compound into a film and drying it at 50 °C for 5 min to obtain the target aqueous ACF adhesive.

[0072] Example 2:

[0073] Taking the preparation of ACF adhesive with an aqueous polyurethane with a solid content of 40% as the substrate as an example, the specific implementation steps are as follows:

[0074] S1. Add 100 parts by mass of diphenylmethane diisocyanate, 160 parts by mass of poly(1,4-butylene adipate) glycol (PBA, molecular weight 2000), and 1.5 parts by mass of bismuth isooctanoate to a four-necked flask equipped with a stirrer, a thermometer, and a condenser, and carry out prepolymerization at 75 °C under a nitrogen atmosphere for 2.5 h;

[0075] S2. Add 18 parts by mass of 2,2-dimethylolbutanoic acid, 4 parts by mass of ethylene glycol, and 22 parts by mass of bisphenol A glycerol diacrylate to the four-necked flask, and carry out chain extension at 75 °C under a nitrogen atmosphere for 2.5 h;

[0076] S3. After the chain extension is completed, add 23.5 parts by mass of 2-hydroxyethyl methacrylate to the four-necked flask, and carry out the end-capping reaction at 70 °C under a nitrogen atmosphere for 1 h;

[0077] S4. After the end-capping reaction is completed, lower the system temperature to 20 °C, then add 12.5 parts by mass of triethylamine to neutralize for 10 min, and then keep the temperature at 20 °C and add 512 parts by mass of water to the four-necked flask. Stir vigorously for 30 min to complete the emulsification of the product to obtain an aqueous polyurethane substrate with a solid content of 40%;

[0078] S5. Take 100 parts by mass of the above-mentioned aqueous polyurethane, 8 parts by mass of fumed silica, 6 parts by mass of nickel-plated polystyrene conductive microspheres, and 3 parts by mass of AIBN. Mix them and ultrasonically bath in water for 30 min, and then further mix evenly using a vortex mixer to obtain the required rubber compound;

[0079] S6. Coat the above rubber compound into a film and dry it at 50 °C for 5 min to obtain the target aqueous ACF adhesive.

[0080] Example 3:

[0081] Taking the aqueous polyurethane with a solid content of 40% as the base material to prepare the ACF adhesive as an example, the specific implementation steps are as follows:

[0082] S1. Add 100 parts by mass of dicyclohexylmethane diisocyanate, 160 parts by mass of poly(ε-caprolactone)diol (PCL2000), and 1.5 parts by mass of dibutyltin dilaurate into a four-necked flask equipped with a stirring paddle, a thermometer, and a condenser. Prepolymerize them at 85 °C under a nitrogen atmosphere for 2 h;

[0083] S2. Add 20 parts by mass of 2,2-dimethylolbutanoic acid, 2.5 parts by mass of 1,4-butanediol, 1.5 parts by mass of ethylene glycol, and 12.5 parts by mass of bisphenol A glycerol diacrylate into the four-necked flask. Chain-extend them at 85 °C under a nitrogen atmosphere for 2 h;

[0084] S3. After the chain extension is completed, add 39 parts by mass of 2-hydroxy-3-phenoxypropyl acrylate into the four-necked flask and carry out a capping reaction at 75 °C under a nitrogen atmosphere for 1 h;

[0085] S4. After the capping reaction is completed, lower the system temperature to 25 °C, then add 13.5 parts by mass of triethylamine and neutralize for 15 min. Then, while maintaining 25 °C, add 526 parts by mass of water into the four-necked flask and stir vigorously for 30 min to complete the emulsification of the product to obtain an aqueous polyurethane base material with a solid content of 40%;

[0086] S5. Take 100 parts by mass of the obtained aqueous polyurethane, 8 parts by mass of fumed silica, 6 parts by mass of nickel-plated polystyrene conductive microspheres, and 3 parts by mass of MEKP. Mix them and ultrasonically bath in water for 30 min, and then further mix evenly using a vortex mixer to obtain the required rubber compound;

[0087] S6. Coat the above rubber compound into a film and dry it at 50 °C for 5 min to obtain the target aqueous ACF adhesive.

[0088] Comparative Example 1:

[0089] Taking the aqueous polyurethane with a solid content of 40% as the base material to prepare the ACF adhesive as an example, the specific implementation steps are as follows:

[0090] S1. Add 100 parts by mass of diphenylmethane diisocyanate, 160 parts by mass of polycarbonate diol (PCD2000), and 1 part by mass of dibutyltin dilaurate into a four-necked flask equipped with a stirrer, a thermometer, and a condenser. Prepolymerize them at 80 °C under a nitrogen atmosphere for 2 h.

[0091] S2. Add 18 parts by mass of 2,2-dimethylolpropionic acid and 9 parts by mass of 1,4-butanediol into the four-necked flask, and carry out chain extension at 70 °C under a nitrogen atmosphere for 3 h.

[0092] S3. After the chain extension is completed, add 50 parts by mass of pentaerythritol triacrylate into the four-necked flask, and carry out capping reaction at 70 °C under a nitrogen atmosphere for 1 h.

[0093] S4. After the reaction is completed, lower the temperature of the system to 25 °C, then add 13.5 parts by mass of triethylamine to neutralize for 15 min. Then, while maintaining 25 °C, add 527 parts by mass of water into the four-necked flask, and vigorously stir for 30 min to complete the emulsification of the product to obtain an aqueous polyurethane substrate with a solid content of 40%.

[0094] S5. Take 100 parts by mass of the above-mentioned aqueous polyurethane, 8 parts by mass of fumed silica, 6 parts by mass of nickel-plated polystyrene conductive microspheres, and 3 parts by mass of BPO. Mix them and carry out ultrasonic water bath for 30 min, and then further mix them evenly using a vortex mixer to obtain the required rubber compound.

[0095] S6. Coat the above rubber compound into a film and dry it at 50 °C for 5 min to obtain the target ACF adhesive.

[0096] Comparative Example 2:

[0097] Taking the preparation of ACF adhesive with an aqueous polyurethane with a solid content of 40% as the substrate as an example, the specific implementation steps are as follows:

[0098] S1. Add 100 parts by mass of diphenylmethane diisocyanate, 160 parts by mass of polycarbonate diol (PCD2000), and 1 part by mass of dibutyltin dilaurate into a four-necked flask equipped with a stirrer, a thermometer, and a condenser. Prepolymerize them at 80 °C under a nitrogen atmosphere for 2 h.

[0099] S2. Then add 18 parts by mass of 2,2-dimethylolpropionic acid, 6 parts by mass of 1,4-butanediol, and 16 parts by mass of bisphenol A glycerol diacrylate into the four-necked flask, and carry out chain extension at 70 °C under a nitrogen atmosphere for 3 h.

[0100] S3. After the chain extension is completed, add 15 parts by mass of neopentyl alcohol into the four-necked flask, and carry out capping reaction at 70 °C under a nitrogen atmosphere for 1 h.

[0101] S4. After the reaction is completed, cool the system temperature to 25 °C, then add 13.5 parts by mass of triethylamine and neutralize for 15 min. Then, while maintaining 25 °C, add 494 parts by mass of water into the four-necked flask, and stir vigorously for 30 min to complete the emulsification of the product to obtain an aqueous polyurethane substrate with a solid content of 40%.

[0102] S5. Take 100 parts by mass of the above-obtained aqueous polyurethane, 8 parts by mass of fumed silica, 6 parts by mass of nickel-plated polystyrene conductive microspheres, and 3 parts by mass of BPO. Mix them and perform ultrasonic water bath for 30 min, and then further mix evenly using a vortex mixer to obtain the required rubber compound.

[0103] S6. Coating the above rubber compound into a film and drying at 50 °C for 5 min to obtain the target ACF adhesive.

[0104] Comparative Example 3:

[0105] Taking the preparation of ACF adhesive with aqueous polyurethane with a solid content of 40% as the substrate as an example, the specific implementation steps are as follows:

[0106] S1. Add 100 parts by mass of diphenylmethane diisocyanate, 160 parts by mass of polycarbonate diol (PCD2000), and 1 part by mass of dibutyltin dilaurate into a four-necked flask equipped with a stirring paddle, a thermometer, and a condenser tube, and pre-polymerize at 80 °C under a nitrogen atmosphere for 2 h.

[0107] S2. Then add 18 parts by mass of 2,2-dimethylolpropionic acid and 9 parts by mass of 1,4-butanediol into the four-necked flask, and carry out chain extension at 70 °C under a nitrogen atmosphere for 3 h.

[0108] S3. After the chain extension is completed, add 15 parts by mass of neopentyl alcohol into the four-necked flask, and carry out capping reaction at 70 °C under a nitrogen atmosphere for 1 h.

[0109] S4. After the reaction is completed, cool the system temperature to 25 °C, then add 13.5 parts by mass of triethylamine and neutralize for 15 min. Then, while maintaining 25 °C, add 475 parts by mass of water into the four-necked flask, and stir vigorously for 30 min to complete the emulsification of the product to obtain an aqueous polyurethane substrate with a solid content of 40%.

[0110] S5. Take 100 parts by mass of the above-obtained aqueous polyurethane, 8 parts by mass of fumed silica, 6 parts by mass of nickel-plated polystyrene conductive microspheres, and 3 parts by mass of BPO. Mix them and perform ultrasonic water bath for 30 min, and then further mix evenly using a vortex mixer to obtain the required rubber compound.

[0111] S6. Coating the above rubber compound into a film and drying at 50 °C for 5 min to obtain the target ACF adhesive.

[0112] Performance test:

[0113] The ACF adhesives obtained in Examples 1-3 and Comparative Examples 1-3 were hot-pressed and cured, and then the interfacial adhesion, conduction resistance, and water absorption of each sample were tested.

[0114] Among them, the interfacial adhesion was measured using a welding thrust machine, the conduction resistance was measured by the four-probe method, and the water absorption was obtained by calculating the ratio of the weight gain to the initial mass (dry weight) after placing the sample in a test chamber at T = 85°C and RH = 85% for 24 h.

[0115] The test data of each sample are shown in Table 1.

[0116] Table 1 Test data of each sample

[0117]

[0118] The results show that Examples 1-3 obtained by the method of the present invention all have good interfacial adhesion, electrical conductivity, and water resistance.

[0119] Due to the different material properties, some environmental conditions in the above Examples 1-3 and Comparative Examples 1-3 were appropriately adjusted to adapt to the material changes. The ultimate goal was to obtain waterborne polyurethane with a solid content of 40% and the subsequent ACF adhesive.

[0120] In addition, according to the knowledge in the relevant field and the description of this application, it can be predicted that when the double bonds in the target product are continuously increased to a certain content according to the technical solution given in this application, there is a threshold value of the crosslinking density. Beyond this threshold, continuing to increase the number of double bonds will not significantly improve the adhesion, and may even become fragile due to excessive crosslinking of the adhesive film. At the same time, too high a crosslinking density will affect the crosslinking and dispersion of conductive particles, inorganic fillers, and waterborne polyurethane, increasing the dispersion difficulty, thereby affecting the electrical conductivity. In addition, the formation of too high a crosslinking density also increases the time and cost of product preparation. The reason for not giving this threshold value in this experiment is that the waterborne ACF adhesive prepared in this application is mainly used for the connection between electronic components, and the adhesion, electrical conductivity, mechanical strength, and water resistance need to reach a balance, so as to prepare a product with low cost, high practicability, and easy production that can be put into actual production and application.

[0121] Comparing Example 1 with Comparative Example 1, it can be seen from the experimental data that the interfacial adhesion and water resistance of Comparative Example 1 are significantly lower than those of Example 1. The reason for this is that in the chain extension stage of Comparative Example 1, bisphenol A glycerol diacrylate with two double bonds was not added, but was replaced by 1,4-butanediol with an equal amount of substance. Therefore, its double bond content is much lower than that of Example 1, and the crosslinking density after curing is lower than that of Example 1, resulting in relatively poor water resistance of the formed ACF adhesive; while the electrical conductivity is mainly determined by the number, type, and dispersion of conductive particles, and the influence of the double bond content is small, so the on-resistance gap is not large.

[0122] Comparing Example 1 with Comparative Example 2, it can be seen from the experimental data that the interfacial adhesion and water resistance of Comparative Example 2 are also significantly lower than those of Example 1. The reason for this is that in the capping stage, pentaerythritol triacrylate with three double bonds was not used, but was replaced by neopentyl alcohol with an equal amount of substance. Neopentyl alcohol does not contain double bonds, and the double bond content in the waterborne polyurethane is low, so its adhesion and water resistance are also worse than those of Example 1; the dosage of pentaerythritol triacrylate in Example 1 is more than that of bisphenol A glycerol diacrylate, and the double bond content of the former is also higher than that of the latter. Therefore, Comparative Example 2 without pentaerythritol triacrylate also has worse performance than Comparative Example 1 without bisphenol A glycerol diacrylate.

[0123] In Comparative Example 3, bisphenol A glycerol diacrylate and pentaerythritol triacrylate were respectively replaced by 1,4-butanediol and neopentyl alcohol with an equal amount of substance on the basis of Example 1. Therefore, in fact, after the film was prepared by the method of Comparative Example 3, it no longer has groups that can participate in the curing reaction, that is, it has no adhesiveness or very poor adhesion strength. Therefore, it does not have the basic function of the ACF adhesive, so there is no data on its adhesiveness and on-resistance. In addition, since it does not form a crosslinked structure, its water absorption rate is much higher than that of other samples, that is, its water resistance is worse, which is also an inherent disadvantage of the waterborne substrate. The adhesive film with poor water resistance is likely to reduce its strength due to water absorption when stored / used in a high-temperature and high-humidity environment, which will affect the service life of the material and may even lead to the failure of adhesion.

[0124] In summary, the waterborne ACF adhesive provided by the present invention application introduces high-molecular compounds containing double bond structures (bisphenol A glycerol diacrylate, pentaerythritol triacrylate, 2-hydroxyethyl methacrylate or 2-hydroxy-3-phenoxypropyl acrylate) in the chain extension and capping stages of preparing the waterborne ACF adhesive, respectively. The double bonds form a crosslinked network through free radical polymerization during the curing process, enhancing the intermolecular interaction force. Furthermore, a dense structure formed by a high crosslinking density is used to reduce the water molecule penetration channels, improving the water resistance of the target ACF adhesive of the present application. In addition, the three-dimensional network structure formed by the synergistic effect of the double bonds in the chain extension and capping is used to improve the mechanical strength and water resistance of the ACF adhesive, making it highly practical in actual applications.

[0125] Based on the inspiration of the ideal embodiments of the present invention, through the above description, relevant personnel can completely make various changes and modifications without departing from the technical idea of this invention. The technical scope of this invention is not limited to the content in the specification, and the technical scope must be determined according to the scope of the claims.

Claims

1. A preparation method of an aqueous ACF adhesive, characterized in that, It includes the following steps: S1. Mix 100 - 150 parts by mass of diisocyanate, 30 - 300 parts by mass of polyester polyol, and 0.1 - 5 parts by mass of catalyst, and pre-polymerize for 0.5 - 4 h at 70 - 100 °C under nitrogen protection; S2. Add 5 - 65 parts by mass of hydrophilic chain extender and 1 - 90 parts by mass of other chain extenders to the prepolymer obtained in S1, and carry out a chain extension reaction for 1 - 5 h at 60 - 100 °C under nitrogen protection; S3. After completing the chain extension reaction, add 20 - 200 parts by mass of acrylate capping agent, and carry out a capping reaction at 60 - 100 °C under nitrogen protection for 1 - 3 h; S4. Lower the reaction temperature to 20 - 60 °C, then add a neutralizing agent corresponding to the hydrophilic chain extender to the reactant obtained through S3, and stir for 5 - 45 min to form a salt; S5. Add a specific amount of water at 20 - 60 °C according to the target solid content, and then stir for 10 - 60 min to complete emulsification to obtain waterborne polyurethane; S6. Mix 100 parts of waterborne polyurethane, 5 - 30 parts by mass of inorganic filler, 2 - 25 parts by mass of conductive particles, and 1 - 10 parts by mass of initiator evenly to obtain the target rubber compound; S7. Coating and drying the rubber compound to obtain the target waterborne ACF adhesive.

2. The preparation method of an aqueous ACF adhesive according to claim 1, characterized in that: In step S1, the diisocyanate is one or more of diphenylmethane diisocyanate or dicyclohexylmethane diisocyanate, and the polyester polyol is one or more of poly(1,4 - butanediol adipate) diol with a molecular weight of 2000 - 3000, polycarbonate diol with a molecular weight of 2000 - 3000, and poly(ε - caprolactone) diol with a molecular weight of 2000 - 3000.

3. The preparation method of an aqueous ACF adhesive according to claim 1, characterized in that: In step S1, the catalyst is dibutyltin dilaurate or bismuth isooctanoate.

4. The preparation method of an aqueous ACF adhesive according to claim 1, characterized in that: The hydrophilic chain extender is 2,2 - bis(hydroxymethyl)propionic acid and / or 2,2 - bis(hydroxymethyl)butyric acid, and the other chain extender is a compound combination of one or more of ethylene glycol, 1,4 - butanediol, or diethanolamine and bisphenol A glycerol diacrylate.

5. The preparation method of an aqueous ACF adhesive according to claim 1, wherein: The acrylate capping agent is one or more of pentaerythritol triacrylate, 2 - hydroxyethyl methacrylate, or 2 - hydroxy - 3 - phenoxypropyl acrylate.

6. The preparation method of an aqueous ACF adhesive according to claim 1, characterized in that: The neutralizing agent is one or more of triethylamine, triethanolamine, diethanolamine, or N,N - dimethylethanolamine.

7. The preparation method of an aqueous ACF adhesive according to claim 1, characterized in that: The inorganic filler is one or more of silica, magnesium oxide, or alumina.

8. The preparation method of a water-based ACF adhesive according to claim 1, characterized in that: The conductive particles are one or more of nickel - plated polystyrene microspheres, gold - plated polystyrene microspheres, with a particle size of 1 - 10 μm.

9. The preparation method of an aqueous ACF adhesive according to claim 1, wherein: The initiator is one or more of azobisisobutyronitrile, benzoyl peroxide, or methyl ethyl ketone peroxide.

10. An aqueous ACF adhesive, characterized in that, It is prepared by the preparation method of a waterborne ACF adhesive according to any one of claims 1 - 9.

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