High-initial-strength heat-conducting polyurethane adhesive with thick adhesive glue layer

Abstract

The invention provides a high-initial-strength heat-conducting polyurethane adhesive with a thick adhesive layer, which is characterized in that an adhesion accelerant is prepared by taking alkyl acrylate, glycidyl acrylate, acrylonitrile and styrene as reaction monomers and phosphate as an end-capping reagent; the heat-conducting polyurethane adhesive is matched with latent curing agents such as aldimine and the like to be applied to a heat-conducting polyurethane adhesive requiring a thick adhesive layer, so that the defect that bubbles are generated due to water vapor and the like in the curing process is effectively avoided, and high initial strength and relatively rapid strength improvement are provided. The heat-conducting polyurethane adhesive prepared by the invention is suitable for occasions with relatively high heat conductivity, heat dissipation, adhesion, sealing and the like, such as new energy power batteries, electrical components, electric control components and the like, and provides excellent mechanical properties and good heat-conducting property.

Description

Technical Field

[0001] This invention relates to the field of polyurethane adhesive technology, specifically to a thick adhesive layer polyurethane adhesive with high initial strength and thermal conductivity. More specifically, this invention relates to a two-component polyurethane adhesive that achieves high initial bond strength, maintains excellent thermal conductivity, and effectively eliminates air bubbles during the curing process through the synergistic effect of a specific structured adhesive accelerator and a latent curing agent. Background Technology

[0002] Two-component thermally conductive polyurethane adhesives possess advantages such as excellent thermal conductivity, high cohesive strength, wide compatibility with bonding substrates, and a large range of performance adjustments, making them a focus of research in application fields with high requirements for thermal management and structural reliability, such as new energy vehicle battery modules, energy storage systems, and electronic material packaging. In applications such as bonding cells to cold plates and modules to shells in new energy vehicle battery packs, and battery modules to heat sinks in energy storage battery cabinets, adhesives are required to possess both good thermal conductivity and the ability to achieve thick-layer bonding with good adhesive strength. The curing mechanism of two-component polyurethane adhesives involves a cross-linking reaction through the mixing of polyols or hydroxyl-containing prepolymers, which provide active -OH groups, with isocyanate-containing prepolymers or polyisocyanate monomers at a specific molar ratio. This process satisfies the final requirements for mechanical and thermal conductivity properties. To ensure these properties, the molar number of isocyanate groups is usually greater than the molar number of hydroxyl groups. The reaction between isocyanate and water is one of the most important chemical reactions involved in polyurethane, especially in polyurethane adhesives. Due to the presence of moisture, isocyanate reacts with water during storage, leading to increased viscosity, "can swelling," and other problems, affecting the storage stability of the adhesive. During the bonding and curing process, while isocyanate reacts with hydroxyl groups, moisture on the surface of the bonding substrate may also react with isocyanate groups to produce carbon dioxide, forming a gas film layer on the substrate surface. This causes non-cohesive failure of the bond, affecting the bonding effect. At the same time, as the gelation process proceeds, the viscosity of the system rises rapidly, and the generated carbon dioxide gas forms bubbles inside and on the surface of the colloid, affecting the bulk strength and appearance of the colloid.

[0003] Existing technologies aim to address the aforementioned problems by introducing polyols with strong adsorption groups, adding tackifying resins, and introducing aldehyde-imine latent curing agents. Patent CN 118126283 A, "A Polyurethane Composition with Stable Thermal Conductivity and its Preparation Method and Application," introduces terminal hydroxyl-containing polyacrylate diols and hyperbranched polyester polyols into the original system, achieving good stability and thermal conductivity of the polyurethane composition through the combination of components. The introduction of polyacrylate diols with strong polar groups and hyperbranched polyester polyols significantly improves the adhesive's adsorption force on the substrate, effectively improving bonding performance, but the initial strength of the colloid is not significantly improved. Patent CN 109593507 A, "A Polyurethane Adhesive for Bonding Soft-Pack Battery Cells," improves the initial tack of the adhesive by adding tackifying resins, giving the adhesive excellent bonding performance to PET, aluminum alloys, etc. Tackifying resins lack active groups and are not chemically bonded to the resin matrix. They improve adhesion to the substrate through physical adsorption. However, their introduction into the system significantly reduces the Tg of the matrix resin, negatively impacting the adhesive's performance at higher temperatures. Patent CN 116490493 A, "Moisture-Curing Polyurethane Compositions," introduces aldehyde imides, which react with isocyanate groups upon contact with moisture, improving the curing properties of moisture-curing polyurethane compositions, particularly by preventing bubble formation caused by excessive carbon dioxide release during the reaction of water with isocyanate groups. The addition of aldehyde imides effectively reduces carbon dioxide release, showing good results in preparing elastic materials with low surface tack and good mechanical properties, and also providing positive guidance for other applications.

[0004] The application of thermally conductive polyurethane adhesives in thick layers presents a complex set of challenges, including air bubbles within the colloid, at the bonding interface, and on the surface during curing; low initial bond strength; and slow strength gain. Conventional techniques often only address one or some of these issues, and may introduce other problems while solving one, creating a technical obstacle to synergistic optimization. Therefore, there is an urgent need in the field for an innovative solution that can systematically address all of these problems. To address this, this invention prepares an adhesion promoter, combined with latent curing agents such as aldehyde imides. This effectively eliminates air bubbles at the colloid bonding interface, within the colloid, and on its surface, while providing the colloid with good adhesion and high initial strength. Furthermore, the rate of strength gain during curing is significantly higher than with conventional methods, representing a reliable path to solve the problems inherent in conventional techniques. Summary of the Invention

[0005] The present invention aims to overcome the shortcomings of existing technologies, including: while introducing resins containing strongly polar groups can improve the adsorption of the colloid to the substrate, it cannot significantly improve the initial strength of the colloid; while adding tackifying resins helps improve the adsorption to the bonding substrate, it weakens the bulk strength and bond strength at higher temperatures; and while adding aldehyde imines can solve the bubble problem caused by the reaction of isocyanates with water, it does not significantly improve other properties. Therefore, the present invention provides a high initial strength thermally conductive polyurethane adhesive for thick adhesive layers. Through the synergistic effect of a bonding promoter with a specific molecular structure and a latent curing agent, it simultaneously solves three major problems in thick adhesive layer applications: first, effectively eliminating bubbles at the bonding interface and inside the colloid; second, providing significantly higher initial bond strength than conventional solutions; and third, achieving rapid strength improvement during the curing process.

[0006] To achieve the objectives of the invention described above, the specific technical solution is as follows:

[0007] A thick adhesive layer with high initial strength and thermal conductivity polyurethane adhesive, characterized in that it is obtained by mixing component A and component B in a volume ratio of 1:1, and its raw material composition by mass percentage includes: component A: 5-58% polyester polyol, 1-15% adhesion promoter, 40-70% thermally conductive powder, and 1-10% anti-settling agent. Component B: 7-58.4% isocyanate-terminated polyurethane prepolymer, 40-70% thermally conductive powder, 1-10% anti-settling agent, and 0.5-5.0% latent curing agent; The adhesion promoter has the following structural formula: Where n is a positive integer from 2 to 100, and the number average molecular weight of the adhesive promoter is 5000-100000, and the viscosity is 200 mPa*s-5000 mPa*s; R2 is H or CH3; when R2 is H, R1 is one of -CH2-O-CH2-, -C6H5-O-CH2-, -C6H5-CH2-O-CH2-, and -CHO-O-CH2-; when R2 is CH3, R1 is -CHO-O-CH2-; R3 is a linear or branched alkane with 1 to 18 carbon atoms; R4 is methyl, ethyl, or phenyl.

[0008] The adhesive bonding accelerator is prepared as follows: dry nitrogen gas is introduced into a dry reaction vessel. After the air is purged, solvent is added, stirred, and heated to 40-60°C. The functional unit monomer, end-capping agent, and free radical initiator are mixed evenly and continuously added dropwise to the reaction vessel. The mixture is refluxed at 50-100°C for 1-5 hours. After the reaction is completed, the unreacted monomer and solvent are distilled off under low pressure to obtain the adhesive bonding accelerator. The reaction equation is as follows (in words): The amount of solvent used is 100% to 300% of the total mass of the functional unit monomer, capping agent, and free radical. To ensure uniform dispersion of the reactants and avoid explosive polymerization during the reaction, the reactants need to be dispersed in the solvent.

[0009] The functional unit monomers are alkyl acrylate, acrylonitrile, glycidyl acrylate / ester, and styrene. Alkyl acrylate and acrylonitrile provide good adsorption to the substrate, ensuring adhesion; glycidyl acrylate / ester provides high initial cohesive strength; and styrene ensures the bulk rigidity of the adhesion promoter, preventing a decrease in glass transition temperature due to the introduction of polar segments.

[0010] The composition of each raw material in the adhesion accelerator, by mass percentage, is as follows:

[0011] The alkyl acrylate is linear or branched, with 1 to 18 carbon atoms, preferably linear or branched, with 1 to 18 carbon atoms, preferably one of methyl acrylate, ethyl acrylate, butyl acrylate, octyl acrylate, isobutyl acrylate, etc.

[0012] The glycidyl acrylate ether / ester is one of allyl glycidyl ether, 4-vinylbenzyl glycidyl ether, 4-vinylphenyl glycidyl ether, glycidyl acrylate, and glycidyl methacrylate.

[0013] The free radical initiator is a peroxide initiator and a redox initiator, wherein the peroxide initiator is preferably one of tert-hexylperoxy-2-ethylhexanoate, benzoyl peroxide, tert-butyl permaleate, azobisisobutyronitrile, and azobisisoheptanenitrile; the redox initiator is preferably one of organic peroxide / vanadium compound and naphthenic acid metal salt / butyraldehyde.

[0014] The capping agent is one or more of trimethylphosphonate, triethylphosphonate, and triphenylphosphonate.

[0015] The solvent is one or more of ethyl acetate, butyl acetate, and butanone.

[0016] According to claim 1, the thick adhesive layer high initial strength thermally conductive polyurethane adhesive is characterized in that the thermally conductive powder is one or more of alumina, magnesium oxide, zinc oxide, magnesium hydroxide, calcium carbonate, aluminum hydroxide, silicon micro powder, boron nitride, aluminum nitride, silicon carbide, and diamond, and its morphology is one or more of flake, quasi-spherical, spherical, and amorphous, and its particle size D50 is 0.01 to 120 μm.

[0017] The latent curing agent is one or more of ketimine, aldolimine, monooxazolidine, and bisoxazolidine. The latent curing agent has higher activity than isocyanate and can act as a dehydrating agent for the isocyanate component, coexisting with it.

[0018] The polyester polyol is one or more of the following: oxalic acid polyester polyol, adipic acid polyester polyol, azelaic acid polyester polyol, sebacic acid polyester polyol, phthalic acid polyester polyol, dimer acid modified polyester polyol, castor oil modified polyester polyol, polycaprolactone polyol, and polycarbonate polyol, with a hydroxyl value range of 40–400 mg KOH / g and a viscosity range of 300–15000 mPa*s.

[0019] The anti-settling agent is one or more of the following: organobentonite, oleophilic fumed silica, modified hydrogenated castor oil, nano-activated calcium carbonate, polyamide wax, and polyethylene oxide wax.

[0020] The isocyanate content of the terminal isocyanate-based polyurethane prepolymer is 5% to 30%; the terminal isocyanate-based polyurethane prepolymer is prepared from polyester polyol and MDI.

[0021] A method for preparing a thick-layer high initial strength thermally conductive polyurethane adhesive as described in any one of claims 1-8, characterized by comprising the following steps: (1) Preparation of component A: Polyester polyol, adhesion promoter, thermally conductive powder and anti-settling agent are added to a planetary mixer according to the metering ratio. The mixture is stirred for 1 to 5 hours at a temperature of 100 to 150°C, a vacuum degree of 0.093 to 0.099 MPa and a speed of 10 to 50 Hz. After cooling to room temperature, component A is obtained. (2) Preparation of component B: The isocyanate-terminated polyurethane prepolymer, the thermally conductive powder dried at 100-130℃ for 2-6h, the anti-settling agent, and the latent curing agent are added to a planetary mixer in proportion. The mixture is stirred for 0.5-5h at a temperature of 50-80℃, a vacuum of 0.093-0.099MPa, and a rotation speed of 10-50Hz. After cooling to room temperature, the component B powder is obtained. (3) Preparation of thick adhesive layer high initial strength thermally conductive polyurethane adhesive: Mix component A and component B in a volume ratio of 1:1 to obtain the adhesive.

[0022] To verify the effects of the prepared additives on the elimination of bubbles in thermally conductive polyurethane adhesives and the tensile shear strength test during the curing process of thick adhesive layers, the following method can be used for verification: Prepare test samples for thermal conductivity, mechanical properties, etc., according to the corresponding test standard requirements by mixing the above-mentioned components A and B in a volume ratio of 1:1, and conduct corresponding performance tests.

[0023] Compared with the prior art, the advantages of this invention are as follows: (1) The adhesive accelerator with a specific structure prepared in this invention produces a significant synergistic effect with the latent curing agent. The amine group generated by the hydrolysis of the latent curing agent inhibits the reaction between isocyanate and water, avoiding the formation of carbon dioxide bubbles. In addition, the amine group can also react with active sites such as epoxy groups on the molecular chain of the adhesive accelerator, which is the key to rapid strength development and effectively improves the initial strength. (2) The adhesive promoter prepared in this invention integrates alkyl acrylate and acrylonitrile functional segments that have good adsorption properties to the substrate, glycidyl acrylate / ester functional segments that improve the initial cohesive strength of the adhesive, and styrene segments that improve the rigidity of the bulk. Furthermore, the good wettability and stability of the adhesive with the polyurethane system are ensured by phosphonate end-capping, thereby achieving designability and reliability of the performance. Detailed Implementation

[0024] To provide a more detailed description of the objectives and advantages of the present invention, the following embodiments are provided for further explanation and illustration.

[0025] The test methods for the examples and comparative examples are described below: Thermal conductivity: The thermal conductivity of the material was tested using a thermal conductivity meter according to the ASTM-D5470 standard. The test sample, which was dispersed in a vacuum disperser, was evenly coated onto the inside of a polytetrafluoroethylene mold ring with an inner diameter of 30 mm. The material thickness was 2 mm, and the coating was smooth. The ambient temperature was 23±2℃, the test pressure was 10 psi, the upper heat conduction column temperature was 65℃, and the lower heat conduction column temperature was 30℃. Mechanical properties: The tensile strength of dumbbell-shaped specimens was tested for 24h, 48h, 72h and 168h under the standard test environment of GB / T528-2009; and the tensile strength of the specimens was tested under the condition of curing for 168h and 60℃. The samples need to be placed in the test environment for more than 0.5h before testing. Tensile shear strength: Following standard GB / T 7124-2021, components A and B were mixed uniformly at a volume ratio of 1:1, and then applied to a 3003 aluminum sheet wiped with alcohol. The application area was 25mm*12.5mm*2mm. The applied area was then bonded and fixed, unlike the 0.25mm adhesive layer thickness used in conventional bonding tests. The tensile shear strength of the test specimens after curing at standard conditions (23±2℃) for 24h, 48h, 72h, and 168h, and the tensile shear strength of the test strips after curing for 168h at 60℃, were measured. Samples needed to be placed in the test environment for >0.5h before testing. The testing speed was 5mm / min. Failure modes: AF represents adhesive failure, CF represents cohesive failure, and AF / CF represents a mixed failure mode (both adhesive and cohesive failure).

[0026] Preparation of isocyanate-terminated prepolymers: High hydrolysis-resistant polyester polyol BY-3020 (hydroxyl value: 50-60 mg KOH / g) produced by Beijing Baiyuan Chemical Co., Ltd., and [other prepolymers] produced by Yantai Wanhua Chemical Group [were used]. MDI-100 (NCO content: 33.5%) and MDI-100LL (NCO content: 28.0-30.0%) was prepared according to conventional polyurethane prepolymer production processes well known in the art.

[0027] Example 1: (1) Preparation of novel adhesion promoter 1#: Dry nitrogen gas was introduced into a 1L dry reaction vessel to purge air. After the air was completely removed, 250ml of ethyl acetate was added, stirred, and heated to 50℃. Under a dry nitrogen atmosphere, 99.75g of isooctyl acrylate, 12.5g of glycidyl methacrylate, 6.25g of acrylonitrile, 6.25g of styrene, 0.25g of trimethylphosphonate, and 0.07g of tert-hexylperoxy-2-ethylhexanoate were mixed evenly and continuously added dropwise to the reaction vessel for reflux reaction at a temperature of 75℃ for 3.5h to obtain novel adhesion promoter 1#. The molecular weight and viscosity of novel adhesion promoter 1# were determined to be 52000 and 1100mPa*s (25℃). (2) Preparation of component A: 750g of polyester polyol with a hydroxyl value of 280mgKOH / g and a viscosity of 900mPa*s (25℃), 2110g of aluminum hydroxide (D50: 40 microns), 50g of organic bentonite, and 90g of novel adhesion promoter 1# were added to a planetary mixer. The temperature was 125℃, the vacuum degree was 0.097, the speed was 40Hz, and the mixture was stirred for 3.0h. After the temperature was cooled to 30℃, component A was obtained. (3) Preparation of component B: 750g of polyurethane prepolymer with isocyanate content of 20.5%, 2150g of aluminum hydroxide (D50: 40 microns) dried in a forced-air drying oven at 105℃ for 4h, 50g of organic bentonite, and 50g of latent curing agent aldehyde imide were added to a planetary mixer. The temperature was 65℃, the vacuum degree was 0.097, the speed was 40Hz, and the mixture was stirred for 2.5h. After the temperature was cooled to 30℃, component B was obtained.

[0028] Example 2: (1) Preparation of novel adhesion promoter 2#: Dry nitrogen gas was introduced into a 1L dry reaction vessel to purge air. After the air was completely purged, 200ml of butyl acetate was added, stirred, and heated to 50℃. Under a dry nitrogen atmosphere, 72.7g of butyl acrylate, 12g of 4-vinylphenyl glycidyl ether, 7.5g of acrylonitrile, 7.5g of styrene, 0.3g of triethylphosphonate, and 0.09g of tert-butyl permaleate were mixed evenly and continuously added dropwise to the reaction vessel for reflux reaction at 80℃ for 3.0h to obtain novel adhesion promoter 2#. The molecular weight of novel adhesion promoter 2# was determined to be 80000, and the viscosity was 2100mPa*s (25℃). (2) Preparation of component A: 1549g of polyester polyol with hydroxyl value of 160mgKOH / g and viscosity of 2500mPa*s (25℃), 1256g of silica powder (D50: 18 microns), 120g of nano-active calcium carbonate, and 75g of novel adhesion promoter 2# were added to a planetary mixer. The temperature was 115℃, the vacuum degree was 0.098, the speed was 42Hz, and the mixture was stirred for 3.5h. After the temperature cooled to 80℃, the mixture was then cooled to 30℃ to obtain component A. (3) Preparation of component B: 1448g of polyurethane prepolymer with 12% isocyanate content, 1357g of silica powder (D50: 18 microns) dried in a forced-air drying oven at 115℃ for 5h, 120g of nano-activated calcium carbonate, and 75g of latent curing agent ketimine were added to a planetary mixer. The temperature was 65℃, the vacuum degree was 0.098, the speed was 42Hz, and the mixture was stirred for 3.0h. When the temperature was cooled to 35℃, component B was obtained.

[0029] Example 3: (1) Preparation of novel adhesion promoter 3#: Dry nitrogen gas was introduced into a 1L dry reaction vessel to purge air. After the air was completely removed, 250ml of ethyl acetate was added, stirred, and heated to 55℃. Under a dry nitrogen atmosphere, 72.4g of butyl acrylate, 7.5g of 4-vinylbenzyl glycidyl ether, 10g of acrylonitrile, 10g of styrene, 0.1g of triphenylphosphonate, and 0.09g of azobisisobutyronitrile were mixed evenly and continuously added dropwise to the reaction vessel for reflux reaction at 85℃ for 3.0h to obtain novel adhesion promoter 3#. The molecular weight of novel adhesion promoter 3# was determined to be 45000, and the viscosity was 1050mPa*s (25℃). (2) Preparation of component A: 700g of polyester polyol with a hydroxyl value of 220mgKOH / g and a viscosity of 1200mPa*s (25℃), 2030g of alumina (D50:20μ), 70g of oleophilic fumed silica, and 200g of novel adhesion promoter 3# were added to a planetary mixer. The temperature was 110℃, the vacuum degree was 0.095, the speed was 35Hz, and the mixture was stirred for 3h. After the temperature was cooled to 30℃, component A was obtained. (3) Preparation of component B: 698g of polyurethane prepolymer with isocyanate content of 16.2%, 2032g of alumina (D50:20μ) dried in a forced-air drying oven at 120℃ for 3h, 70g of oleophilic fumed silica, and 200g of latent curing agent ketimine were added to a planetary mixer. The temperature was 60℃, the vacuum degree was 0.095, the speed was 35Hz, and the mixture was stirred for 3h. When the temperature was cooled to 35℃, component B was obtained.

[0030] Comparative Example 1: (1) Preparation of component A: 900g of polyester polyol with a hydroxyl value of 220mgKOH / g and a viscosity of 1200mPa*s (25℃), 2030g of alumina (D50: 20 microns), and 70g of oleophilic fumed silica were added to a planetary mixer. The temperature was 110℃, the vacuum degree was 0.095, the speed was 35Hz, and the mixture was stirred for 3h. After the temperature was cooled to 30℃, component A was obtained. (2) Preparation of component B: 898g of polyurethane prepolymer with isocyanate content of 16.2%, 2042g of alumina (D50: 20 microns) dried in a forced-air drying oven at 120℃ for 3h, and 60g of oleophilic fumed silica were added to a planetary mixer. The temperature was 60℃, the vacuum degree was 0.095, the speed was 35Hz, and the mixture was stirred for 3h. When the temperature was cooled to 35℃, component B was obtained.

[0031] Comparative Example 2: (1) Preparation of component A: 900g of polyester polyol with a hydroxyl value of 220mgKOH / g and a viscosity of 1200mPa*s (25℃), 1970g of alumina (D50: 20 microns), 70g of oleophilic fumed silica, and 60g of C9 hydrogenated petroleum resin were added to a planetary mixer. The temperature was 110℃, the vacuum degree was 0.095, and the speed was 35Hz. The mixture was stirred for 3h to obtain component A. (2) Preparation of component B: 898g of polyurethane prepolymer with isocyanate content of 16.2%, 2012g of alumina (D50: 20 microns) dried in a forced-air drying oven at 120℃ for 3h, 60g of oleophilic fumed silica, and 30g of latent curing agent aldehyde imide were added to a planetary mixer. The temperature was 60℃, the vacuum degree was 0.095, the speed was 35Hz, and the mixture was stirred for 3h. When the temperature was cooled to 35℃, component B was obtained.

[0032] Comparative Example 3: (1) Preparation of component A: 900g of polyester polyol with a hydroxyl value of 220mgKOH / g and a viscosity of 1200mPa*s (25℃), 2030g of alumina (D50: 20 microns), and 70g of oleophilic fumed silica were added to a planetary mixer. The temperature was 110℃, the vacuum degree was 0.095, the speed was 35Hz, and the mixture was stirred for 3h to obtain component A. (2) Preparation of component B: 898g of polyurethane prepolymer with an isocyanate content of 16.2%, 2012g of alumina (D50: 20 microns) dried in a forced-air drying oven at 120℃ for 3h, 60g of oleophilic fumed silica, and 30g of latent curing agent aldehyde imide were added to a planetary mixer. The temperature was 60℃, the vacuum degree was 0.095, the speed was 35Hz, and the mixture was stirred for 3h. When the temperature was cooled to 35℃, component B was obtained.

[0033] Comparative Example 4: (1) Preparation of component A: 900g of polyester polyol with a hydroxyl value of 220mgKOH / g and a viscosity of 1200mPa*s (25℃), 1970g of alumina (D50: 20 microns), 70g of oleophilic fumed silica, and 60g of novel adhesion promoter 3# were added to a planetary mixer. The temperature was 110℃, the vacuum degree was 0.095, the speed was 35Hz, and the mixture was stirred for 3h to obtain component A. Preparation of Component B: 898g of polyurethane prepolymer with isocyanate content of 16.2%, 2042g of alumina (D50: 20 microns) dried in a forced-air drying oven at 120℃ for 3h, and 60g of oleophilic fumed silica were added to a planetary mixer. The temperature was 60℃, the vacuum degree was 0.095, the speed was 35Hz, and the mixture was stirred for 3h. When the temperature was cooled to 35℃, Component B was obtained.

[0034] Comparative Example 5: (1) Preparation of component A: 900g of polyester polyol with a hydroxyl value of 220mgKOH / g and a viscosity of 1200mPa*s (25℃), 1970g of alumina (D50: 20 microns), 70g of oleophilic fumed silica, and 60g of novel adhesion promoter 3# were added to a planetary mixer. The temperature was 110℃, the vacuum degree was 0.095, the speed was 35Hz, and the mixture was stirred for 3h to obtain component A. Preparation of Component B: 898g of polyurethane prepolymer with 16.2% isocyanate content, 2039g of alumina (D50: 20 microns) dried in a forced-air drying oven at 120℃ for 3h, 60g of oleophilic fumed silica, and 3g of dibutyltin dilaurate were added to a planetary mixer. The temperature was 60℃, the vacuum degree was 0.095, the speed was 35Hz, and the mixture was stirred for 3h. When the temperature cooled to 35℃, Component B was obtained.

[0035] The performance test results of the embodiments and comparative examples are shown in Tables 1 and 2.

[0036] Table 1: Test results of thermal conductivity and tensile strength

[0037] Table 2: Results of tensile-shear strength test

[0038] As shown in Tables 1 and 2, compared to Comparative Examples 1-5 which used conventional adhesives, adhesives with conventional C9 petroleum resin added individually, adhesives with only latent curing agents added, adhesives with only the adhesive accelerator prepared in this invention, and adhesives with the adhesive accelerator prepared in this invention combined with a conventional polyurethane catalyst dibutyltin dilaurate, the adhesives in Examples 1-3, which added the adhesive accelerator prepared in this invention and synergistically enhanced the latent curing agent, showed a significant increase in strength under the same curing conditions. Furthermore, the adhesive exhibited no bubbles in its appearance or internal structure, and showed cohesive failure in bonding to the substrate, demonstrating excellent physical and adhesive properties. The tensile shear strength at 60°C highlights the adhesive reliability under thermal load conditions, especially the heat resistance and interfacial stability of the adhesive under these conditions.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A thick adhesive layer, high initial strength, and thermally conductive polyurethane adhesive, characterized in that, It is obtained by mixing component A and component B in a mass ratio of 1:

1. Its raw material composition, by mass percentage, includes: Component A: 5-58% polyester polyol, 1-15% adhesion promoter, 40-70% thermally conductive powder, 1-10% anti-settling agent; Component B: 7-58.4% isocyanate-terminated polyurethane prepolymer, 40-70% thermally conductive powder, 1-10% anti-settling agent, and 0.5-5.0% latent curing agent; The adhesion promoter has the following structural formula: Where n is a positive integer from 10 to 200, and the number average molecular weight of the adhesive promoter is 5000-100000, and the viscosity is 200 mPa*s-5000 mPa*s; R2 is H or CH3; when R2 is H, R1 is one of -CH2-O-CH2-, -C6H5-O-CH2-, -C6H5-CH2-O-CH2-, and -CHO-O-CH2-; when R2 is CH3, R1 is -CHO-O-CH2-; R3 is a linear or branched alkane with 1 to 18 carbon atoms; R4 is methyl, ethyl, or phenyl.

2. The thick adhesive layer high initial strength thermally conductive polyurethane adhesive according to claim 1, characterized in that, The adhesive bonding accelerator is prepared as follows: dry nitrogen gas is introduced into a dry reaction vessel. After the air is purged, solvent is added, stirred, and heated to 40-60°C. The functional unit monomer, end-capping agent, and free radical initiator are mixed evenly and continuously added dropwise to the reaction vessel. The mixture is refluxed at 50-100°C for 1-5 hours. After the reaction is completed, the unreacted monomer and solvent are distilled off under low pressure to obtain the adhesive bonding accelerator. The functional unit monomers are alkyl acrylate, acrylonitrile, glycidyl acrylate / ester, and styrene; the composition of each raw material of the adhesion promoter is as follows by mass percentage: alkyl acrylate 49.8-96.89%, glycidyl acrylate / ester 1-15%, acrylonitrile 1-15%, styrene 1-15%, free radical initiator 0.01-0.2%, and end-capping agent 0.1-5%; The amount of solvent used is 100% to 300% of the total mass of the functional unit monomer, end-capping agent, and free radical.

3. The method for preparing the adhesion promoter according to claim 2, characterized in that, The alkyl acrylate is linear or branched, with 1 to 18 carbon atoms, and is preferably one of methyl acrylate, ethyl acrylate, butyl acrylate, octyl acrylate, and isobutyl acrylate. The glycidyl acrylate / ester is one of allyl glycidyl ether, 4-vinylbenzyl glycidyl ether, 4-vinylphenyl glycidyl ether, glycidyl acrylate, and glycidyl methacrylate; the free radical initiator is a peroxide initiator and a redox initiator, wherein the peroxide initiator is preferably one of tert-hexylperoxy-2-ethylhexanoate, benzoyl peroxide, tert-butyl permaleate, azobisisobutyronitrile, and azobisisoheptanenitrile; the redox initiator is preferably one of organic peroxide / vanadium compound and naphthenic acid metal salt / butyraldehyde. The terminator is one or more of trimethylphosphonate, triethylphosphonate, and triphenylphosphonate; The solvent is one or more of ethyl acetate, butyl acetate, and butanone.

4. The thick adhesive layer high initial strength thermally conductive polyurethane adhesive according to claim 1, characterized in that, The thermally conductive powder is one or more of the following: aluminum oxide, magnesium oxide, zinc oxide, magnesium hydroxide, calcium carbonate, aluminum hydroxide, silicon micro powder, boron nitride, aluminum nitride, silicon carbide, and diamond. Its morphology is one or more of the following: flake-like, quasi-spherical, spherical, and amorphous. Its particle size D50 is 0.01–120 μm.

5. The thick adhesive layer high initial strength thermally conductive polyurethane adhesive according to claim 1, characterized in that, The latent curing agent is one or more of ketimine, aldolimine, monooxazolidine, and bisoxazolidine.

6. The thick adhesive layer high initial strength thermally conductive polyurethane adhesive according to claim 1, characterized in that, The polyester polyol is one or more of the following: oxalic acid polyester polyol, adipic acid polyester polyol, azelaic acid polyester polyol, sebacic acid polyester polyol, phthalic acid polyester polyol, dimer acid modified polyester polyol, castor oil modified polyester polyol, polycaprolactone polyol, and polycarbonate polyol, with a hydroxyl value range of 40–400 mg KOH / g and a viscosity range of 300–15000 mPa*s.

7. The thick adhesive layer high initial strength thermally conductive polyurethane adhesive according to claim 1, characterized in that, The anti-settling agent is one or more of the following: organobentonite, oleophilic fumed silica, modified hydrogenated castor oil, nano-activated calcium carbonate, polyamide wax, and polyethylene oxide wax.

8. The thick adhesive layer high initial strength thermally conductive polyurethane adhesive according to claim 1, characterized in that, The isocyanate content of the terminal isocyanate-based polyurethane prepolymer is 5% to 30%; the terminal isocyanate-based polyurethane prepolymer is prepared from polyester polyol and MDI.

9. A method for preparing a thick-layer, high-initial-strength, thermally conductive polyurethane adhesive as described in any one of claims 1-8, characterized in that, Includes the following steps: (1) Preparation of component A: Polyester polyol, adhesion promoter, thermally conductive powder and anti-settling agent are added to a planetary mixer according to the metering ratio. The mixture is stirred for 1 to 5 hours at a temperature of 100 to 150°C, a vacuum degree of 0.093 to 0.099 MPa and a speed of 10 to 50 Hz. After cooling to room temperature, component A is obtained. (2) Preparation of component B: The isocyanate-terminated polyurethane prepolymer, the thermally conductive powder dried at 100-130℃ for 2-6h, the anti-settling agent, and the latent curing agent are added to a planetary mixer in proportion. The mixture is stirred for 0.5-5h at a temperature of 50-80℃, a vacuum of 0.093-0.099MPa, and a rotation speed of 10-50Hz. After cooling to room temperature, the component B powder is obtained. (3) Preparation of thick adhesive layer high initial strength thermally conductive polyurethane adhesive: Mix component A and component B in a volume ratio of 1:1 to obtain the adhesive.

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