A two-component polyurethane thermally conductive structural adhesive based on hydroxyl-terminated hyperbranched polyborosiloxane and its preparation method

Abstract

This invention relates to the field of two-component polyurethane structural adhesives, specifically to a two-component polyurethane thermally conductive structural adhesive based on hydroxyl-terminated hyperbranched polyborosiloxane and its preparation method. Traditional polyurethane structural adhesives suffer from insufficient thermal conductivity and difficulty in simultaneously achieving flame retardant and mechanical properties. To address these issues, this invention provides a two-component polyurethane thermally conductive structural adhesive based on hydroxyl-terminated hyperbranched polyborosiloxane. By introducing hydroxyl-terminated hyperbranched polyborosiloxane, an ordered orientation structure of filler is induced within the polyurethane matrix, thereby improving the thermal conductivity of the structural adhesive. The boron-phosphorus-aluminum ternary synergistic flame retardant system, composed of hydroxyl-terminated hyperbranched polyborosiloxane, aluminum hydroxide, and phosphate ester groups, significantly enhances the flame retardant properties of the structural adhesive. Simultaneously, the hydroxyl-terminated hyperbranched polyborosiloxane, polypropylene triol, and modified castor oil form a hyperbranched-linear interpenetrating network structure, achieving a good balance in mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of two-component polyurethane structural adhesives, specifically to a two-component polyurethane thermally conductive structural adhesive based on hydroxyl-terminated hyperbranched polyborosiloxane and its preparation method. Background Technology

[0002] With the rapid development of the new energy vehicle industry, the integration and power density of power devices are constantly increasing, which places more stringent performance requirements on encapsulation and bonding materials. Structural adhesives, while meeting mechanical bonding strength requirements, must also possess efficient thermal conductivity and reliable flame retardant properties, thereby achieving the integration of structural load-bearing, heat conduction, and safety protection functions.

[0003] Two-component polyurethane structural adhesives are widely used in the field of power batteries due to their high bonding strength, excellent toughness, mild curing conditions, and wide range of adjustable formulations. These applications include bonding cells to cooling plates, fixing battery module end plates, and bonding and potting power electronic module heat sinks.

[0004] However, traditional polyurethane structural adhesives still have the following technical drawbacks in application: First, insufficient thermal conductivity. Polyurethane matrix itself is a poor conductor of heat. To improve its thermal conductivity, the conventional approach is to add high thermal conductivity fillers, such as alumina, boron nitride, or aluminum nitride. However, high filler content often leads to a sharp increase in system viscosity, significantly reducing workability. Simultaneously, the interfacial thermal resistance between the filler and the matrix is ​​relatively high, resulting in a low efficiency in improving thermal conductivity, making it difficult to achieve ideal thermal conductivity while ensuring workability.

[0005] Secondly, it is difficult to simultaneously achieve flame retardancy and mechanical properties. To improve the flame retardancy of polyurethane, halogenated, phosphorus-based, or inorganic flame retardants, such as aluminum hydroxide or magnesium hydroxide, are often added. However, halogenated flame retardants are subject to increasingly stringent environmental regulations; while phosphorus-based flame retardants can exert a flame-retardant effect, they may degrade the mechanical properties of the structural adhesive; and inorganic flame retardants, when added in high amounts, can significantly reduce the tensile strength and elongation at break of the structural adhesive. Therefore, how to maintain or even improve mechanical properties while performing flame retardant modification has become a major challenge in existing technologies.

[0006] Third, poor filler dispersion and interfacial bonding. The uniformity of dispersion of thermally conductive and flame-retardant fillers in the polyurethane matrix and the strength of their interfacial bonding with the matrix directly determine the overall performance of the composite material. Existing technologies mostly use conventional silane coupling agents to surface treat the fillers, but these coupling agents have limited modification effects on common fillers such as alumina and aluminum hydroxide, making it difficult to form strong chemical bonds between the fillers and the matrix. This results in low stress transfer efficiency and high interfacial thermal resistance, further limiting the improvement of the overall material performance.

[0007] In summary, developing a two-component polyurethane thermally conductive structural adhesive that combines high thermal conductivity, high flame retardancy, and high mechanical strength has become an urgent technical problem to be solved in this field. Summary of the Invention

[0008] The existing technology has the following problems: traditional polyurethane structural adhesives have insufficient thermal conductivity and it is difficult to achieve both flame retardancy and mechanical properties. To address the above problems, this invention provides a two-component polyurethane thermally conductive structural adhesive based on hydroxyl-terminated hyperbranched polyborosiloxane, which is composed of a mixture of component A and component B, with a mass ratio of component A to component B of 1:0.9~1.1; Component A, by mass parts, includes the following raw material components: 10-15 parts of modified castor oil; 28-32 parts of polyoxypropylene triol; 4-6 parts of reactive diluent; 2-5 parts of coupling agent; 45-55 parts of thermally conductive and flame-retardant filler; 2-4 parts of hydrophobic fumed silica; 3-5 parts of hydroxyl-terminated hyperbranched polyborosiloxane; Component B, by mass parts, includes the following raw material components: 25-27 parts isocyanate; 45-55 parts of thermally conductive and flame-retardant filler; 2-4 parts of hydrophobic fumed silica; 0.5-1 part of dehydrating agent; The terminal hydroxyl hyperbranched polyborosiloxane has a number average molecular weight of 2000~4000 g / mol, a hydroxyl value of 120~180 mg KOH / g, and a branching degree of 0.54~0.62.

[0009] Preferably, the modified castor oil is epoxy-modified castor oil or silane-modified castor oil.

[0010] Preferably, the active diluent is one or more of C8-C14 alkyl glycidyl ether, butyl glycidyl ether, and allyl glycidyl ether.

[0011] Preferably, the coupling agent is composed of a phosphate coupling agent, a silane coupling agent, and a titanate coupling agent. Specifically, it is a complex formed by N,N-bis(2-hydroxyethyl)aminomethylenephosphonate diethyl ester (flame retardant FRC-6), KH-560, and isopropyltris(dioctylpyrophosphonooxy) titanate. The mass ratio of flame retardant FRC-6 to KH-560 is 1:(1-3), and the amount of isopropyltris(dioctylpyrophosphonooxy) titanate is 10% to 30% of the total mass of flame retardant FRC-6 and KH-560.

[0012] Preferably, the thermally conductive and flame-retardant filler is a composite filler modified with a coupling agent. The composite filler, by mass percentage, consists of 60-80 wt% spherical alumina, 15-30 wt% aluminum hydroxide, and 5-15 wt% nano boron nitride. The spherical alumina is obtained by uniformly mixing spherical alumina with a particle size D50 of 5-15 μm and a particle size D50 of 30-50 μm at a mass ratio of (2-4):(6-8). The D50 of the aluminum hydroxide is 1-10 μm, and the D50 of the nano boron nitride is 50-200 nm.

[0013] Preferably, the preparation method of the thermally conductive and flame-retardant filler is as follows: (1) According to the formula, spherical alumina, aluminum hydroxide and nano boron nitride are mixed evenly to obtain a mixed filler; (2) By mass, 100 parts of mixed filler, 1.5 parts of flame retardant FRC-6 and 1.0 parts of KH560 are mixed evenly, dried and then the thermally conductive flame retardant filler is obtained. After cooling, it is sealed for later use.

[0014] Preferably, the dehydrating agent is composed of vinyltrimethoxysilane and 3A molecular sieve in a mass ratio of 1:(10-12).

[0015] Preferably, the isocyanate is composed of liquefied MDI and polymeric MDI in a mass ratio of (10-12):15.

[0016] Preferably, the polyoxypropylene triol has a molecular weight of 3000~5000 g / mol and a functionality of 2.5~3.0.

[0017] Preferably, the two-component polyurethane thermally conductive structural adhesive based on hydroxyl-terminated hyperbranched polyborosiloxane is prepared by the following steps: (1) Preparation of component A: According to the formula amount, the modified castor oil, polyoxypropylene triol, reactive diluent, coupling agent, and hydroxyl-terminated hyperbranched polyborosiloxane are mixed evenly at 40~60℃, and then thermally conductive and flame-retardant filler and hydrophobic fumed silica are added. After vacuum degassing, component A is obtained. (2) Preparation of component B: According to the formula, the isocyanate and dehydrating agent are mixed evenly at room temperature, and then thermally conductive flame retardant filler and hydrophobic fumed silica are added, mixed evenly, and degassed under vacuum to obtain component B. (3) Mix component A and component B at a mass ratio of 1: (0.9~1.1) to obtain a two-component polyurethane thermally conductive structural adhesive.

[0018] Beneficial effects: (1) This invention introduces terminally hydroxyl hyperbranched polyborosiloxane into component A of a two-component polyurethane thermally conductive structural adhesive. Utilizing the electron-deficient properties of boron atoms in its molecular structure, it forms Lewis acid-base pairs with the surface of the thermally conductive filler, thereby inducing the filler to form an ordered orientation structure within the polyurethane matrix. This orientation structure helps reduce the interfacial thermal resistance between the filler and the matrix, further improving the thermal conductivity of the structural adhesive.

[0019] (2) This invention constructs a boron-phosphorus-aluminum ternary synergistic flame retardant system composed of hydroxyl-terminated hyperbranched polyborosiloxane, aluminum hydroxide, and a coupling agent containing phosphate groups. During combustion, the hydroxyl-terminated hyperbranched polyborosiloxane catalyzes char formation, forming a hybrid char layer containing boron, oxygen, and silicon; aluminum hydroxide decomposes under heat and generates an alumina protective layer; the phosphate component simultaneously plays a role in capturing gaseous free radicals and promoting char formation. The three components synergistically form a dense, continuous, and high-strength char layer, which can effectively isolate heat and oxygen, significantly improving the flame retardant performance of the structural adhesive.

[0020] (3) This invention uses terminal hydroxyl hyperbranched polyborosiloxanes with specific molecular weight and hydroxyl value ranges to form a hyperbranched-linear interpenetrating network structure together with polypropylene triol and modified castor oil. This network structure can further improve the elongation at break while maintaining the excellent tensile strength of the structural adhesive, thus achieving a good balance of mechanical properties. Detailed Implementation

[0021] The present invention will be described in detail below with reference to embodiments. However, it should be understood that the following embodiments are merely illustrative examples of implementation of the present invention and are not intended to limit the scope of the present invention.

[0022] The hydroxyl-terminated hyperbranched polyborosiloxanes used in the following embodiments and comparative examples of this invention were prepared by the following method: (1) Add boric acid (6.18 g, 0.10 mol), phenyltrimethoxysilane (13.88 g, 0.07 mol), dimethyldimethoxysilane (3.60 g, 0.03 mol), and 40 mL of isopropanol to a 250 mL three-necked flask in sequence, and stir to dissolve; (2) Slowly add 5.4 g of deionized water (containing 0.1 g of p-toluenesulfonic acid) to the reaction system of step (1), control the system temperature to ≤40℃, and complete the addition within 30 min; (3) Heat the reaction system obtained in step (2) to 70°C, reflux for 3 h, and collect the low-boiling substances by distillation until no liquid is obviously distilled out, to obtain borosilicate oligomers; (4) Add trimethylolpropane (6.70 g, 0.05 mol) and 20 mL isopropanol to the reaction system obtained in step (3), heat to 110 °C, and stir under nitrogen protection for 4 h. (5) After the reaction in step (4) is completed, the solvent is removed by vacuum distillation to obtain a light yellow transparent viscous liquid, which is the terminal hydroxyl hyperbranched polyborosiloxane, denoted as HBPSi.

[0023] GPC testing revealed that the number-average molecular weight (Mn) of the obtained hydroxyl-terminated hyperbranched polyborosiloxane was 2800 g / mol, and the hydroxyl value was 156 mg KOH / g. Quantitative analysis confirmed this. 13 12C NMR analysis showed that its branching degree (DB) was 0.56, consistent with the characteristics of hyperbranched polymers (DB > 0.5). Meanwhile, GPC-MALLS analysis showed a Mark-Houwink index α = 0.48, confirming its spherical hyperbranched structure.

[0024] The thermally conductive and flame-retardant filler used in the following embodiments of the present invention is prepared according to the following steps: (1) Mix spherical alumina (D50=5μm and D50=40μm at a mass ratio of 3:7), aluminum hydroxide (D50=5μm), and nano boron nitride (D50=80nm) at a mass ratio of 70:20:10 to obtain a mixed filler; (2) By mass, 100 parts of mixed filler, 1.5 parts of flame retardant FRC-6 and 1.0 parts of KH560 are mixed in a high-speed mixer at 80°C. Then the material is placed in a vacuum drying oven at 80°C for 2 hours to remove residual small molecules and obtain thermally conductive flame retardant filler. After cooling, it is sealed for later use.

[0025] The hydrophobic fumed silica used in the following embodiments of the present invention is CAB-O-SIL. ® TS-720.

[0026] The 3A molecular sieve used in the following embodiments of the present invention is a commercially available product, CAS No. 308080-99-1, purchased from Shandong Nengteyi Energy Technology Co., Ltd.

[0027] The liquefied MDI used in the following embodiments of the present invention is carbodiimide-urea ketimide modified MDI, purchased from Wanhua Chemical Group Co., Ltd., brand name WANNATE. ® CDMDI-100L.

[0028] The polymeric MDI used in the following embodiments of the present invention was purchased from Wanhua Chemical Group Co., Ltd., and the product brand name is WANNATE. ® PM-200.

[0029] Example 1 A two-component polyurethane thermally conductive structural adhesive based on hydroxyl-terminated hyperbranched polyborosiloxane is composed of a mixture of component A and component B, with a mass ratio of component A to component B of 1:1. Component A, by mass parts, consists of the following raw material components: 12 parts modified castor oil; 28 parts of polyoxypropylene triol; 4 parts reactive diluent; 2 parts coupling agent; 45 parts of thermally conductive and flame-retardant filler; Two parts of hydrophobic fumed silica; Three parts of hydroxyl-terminated hyperbranched polyborosiloxane; Component B, by mass parts, consists of the following raw material components: 27 parts isocyanate; 45 parts of thermally conductive and flame-retardant filler; Two parts of hydrophobic fumed silica; 0.5 parts of dehydrating agent; The modified castor oil is epoxy-modified castor oil, and its preparation method is as follows: 100.0 g of castor oil and 3.5 g of SiO2-Al2O3 solid acid catalyst were added to a 250 mL flask equipped with a thermometer, stirrer, and distillation head. The mixture was heated to 230 °C under vacuum of 1 mmHg for a dehydration reaction for 2.5 h. Then the temperature was lowered to 45 °C, and 46.0 g of peracetic acid was added dropwise for 1.5 h. After the addition was completed, an epoxidation reaction was carried out at 55 °C for 3.0 h. After the reaction was completed, particulate matter was filtered off, and vacuum distillation was carried out at 55 °C under vacuum of 1 mmHg. When the distillation outlet temperature dropped to 40 °C, the vacuum distillation was stopped to obtain epoxidized castor oil.

[0030] The active diluent is butyl glycidyl ether.

[0031] The coupling agent is a complex formed by flame retardant FRC-6, KH-560 and isopropyl tris(dioctyl pyrophosphoryloxy) titanate, with the mass ratio of flame retardant FRC-6 to KH-560 and isopropyl tris(dioctyl pyrophosphoryloxy) titanate being 1:2:0.5.

[0032] The dehydrating agent is composed of vinyltrimethoxysilane and 3A molecular sieve at a mass ratio of 1:10.

[0033] Isocyanate is composed of liquefied MDI and polymeric MDI in a mass ratio of 12:15.

[0034] The polyoxypropylene triol is PPG-4000, Mn=4000, functionality=2.8.

[0035] A method for preparing a two-component polyurethane thermally conductive structural adhesive based on hydroxyl-terminated hyperbranched polyborosiloxane is as follows: (1) Preparation of component A: According to the formula amount, the modified castor oil, polyoxypropylene triol, reactive diluent, coupling agent, and hydroxyl-terminated hyperbranched polyborosiloxane were mixed evenly at 50°C, and then thermally conductive and flame-retardant filler and hydrophobic fumed silica were added. After vacuum degassing for 30 min, component A was obtained. (2) Preparation of component B: According to the formula, the isocyanate and dehydrating agent are mixed evenly at room temperature, and then thermally conductive and flame-retardant filler and hydrophobic fumed silica are added. The mixture is dispersed evenly at high speed and vacuum degassed for 30 minutes to obtain component B. (3) Mix component A and component B at a mass ratio of 1:1 to obtain a two-component polyurethane thermally conductive structural adhesive.

[0036] Example 2 A two-component polyurethane thermally conductive structural adhesive based on hydroxyl-terminated hyperbranched polyborosiloxane is composed of a mixture of component A and component B, with a mass ratio of component A to component B of 1:1.1. Component A, by mass parts, consists of the following raw material components: 15 parts modified castor oil; 30 parts of polyoxypropylene triol; 5 parts reactive diluent; 4 parts coupling agent; 50 parts of thermally conductive and flame-retardant filler; Three parts of hydrophobic fumed silica; 4 parts of hydroxyl-terminated hyperbranched polyborosiloxane; Component B, by mass parts, consists of the following raw material components: 27 parts isocyanate; 50 parts of thermally conductive and flame-retardant filler; Three parts of hydrophobic fumed silica; 0.8 parts of dehydrating agent; The modified castor oil is silane-modified castor oil, and its preparation method is as follows: By weight, 10 parts of trimethoxysilane and 46 parts of xylene were added sequentially to an oil bath reactor equipped with a thermometer, a constant pressure dropping funnel, a stirrer, and a condenser. The temperature of the material inside the reactor was controlled at 80°C. A mixture of 70 parts of castor oil and 0.0030 parts of chloroplatinic acid was added dropwise to the reactor over 120 min. The temperature of the material inside the reactor was adjusted to 90°C and the reaction was continued for 300 min. Finally, the temperature was adjusted to 120°C and the vacuum was reduced to below -0.09 MPa to remove the solvent for 190 min, thus obtaining silane-modified castor oil.

[0037] The reactive diluent is alkyl glycidyl ether (AGE, CAS 68609-97-2).

[0038] The coupling agent is a complex formed by flame retardant FRC-6, KH-560 and isopropyl tris(dioctyl pyrophosphoryloxy) titanate, with the mass ratio of flame retardant FRC-6 to KH-560 and isopropyl tris(dioctyl pyrophosphoryloxy) titanate being 1:2:0.6.

[0039] The dehydrating agent is composed of vinyltrimethoxysilane and 3A molecular sieve at a mass ratio of 1:11.

[0040] Isocyanate is composed of liquefied MDI and polymeric MDI in a mass ratio of 12:15.

[0041] The polyoxypropylene triol is PPG-4000, Mn=4000, functionality=2.8.

[0042] A method for preparing a two-component polyurethane thermally conductive structural adhesive based on hydroxyl-terminated hyperbranched polyborosiloxane is as follows: (1) Preparation of component A: According to the formula amount, the modified castor oil, polyoxypropylene triol, reactive diluent, coupling agent, and hydroxyl-terminated hyperbranched polyborosiloxane were mixed evenly at 50°C, and then thermally conductive and flame-retardant filler and hydrophobic fumed silica were added. After vacuum degassing for 30 min, component A was obtained. (2) Preparation of component B: According to the formula, the isocyanate and dehydrating agent are mixed evenly at room temperature, and then thermally conductive and flame-retardant filler and hydrophobic fumed silica are added. The mixture is dispersed evenly at high speed and vacuum degassed for 30 minutes to obtain component B. (3) Mix component A and component B at a mass ratio of 1:1.1 to obtain a two-component polyurethane thermally conductive structural adhesive.

[0043] Example 3 A two-component polyurethane thermally conductive structural adhesive based on hydroxyl-terminated hyperbranched polyborosiloxane is composed of a mixture of component A and component B, with a mass ratio of component A to component B of 1:0.9. Component A, by mass parts, consists of the following raw material components: 10 parts modified castor oil; 32 parts of polyoxypropylene triol; 6 parts reactive diluent; 5 parts coupling agent; 55 parts of thermally conductive and flame-retardant filler; 4 parts of hydrophobic fumed silica; 5 parts of hydroxyl-terminated hyperbranched polyborosiloxane; Component B, by mass parts, consists of the following raw material components: 25 parts isocyanate; 55 parts of thermally conductive and flame-retardant filler; 4 parts of hydrophobic fumed silica; 1 part dehydrating agent; The modified castor oil is epoxy-modified castor oil, and its preparation method is as follows: 100.0 g of castor oil and 3.5 g of SiO2-Al2O3 solid acid catalyst were added to a 250 mL flask equipped with a thermometer, stirrer, and distillation head. The mixture was heated to 230 °C under vacuum of 1 mmHg for a dehydration reaction for 2.5 h. Then the temperature was lowered to 45 °C, and 46.0 g of peracetic acid was added dropwise for 1.5 h. After the addition was completed, an epoxidation reaction was carried out at 55 °C for 3.0 h. After the reaction was completed, particulate matter was filtered off, and vacuum distillation was carried out at 55 °C under vacuum of 1 mmHg. When the distillation outlet temperature dropped to 40 °C, the vacuum distillation was stopped to obtain epoxidized castor oil.

[0044] The active diluent is allyl glycidyl ether.

[0045] The coupling agent is a complex formed by flame retardant FRC-6, KH-560 and isopropyl tris(dioctyl pyrophosphoryloxy) titanate, with the mass ratio of flame retardant FRC-6 to KH-560 and isopropyl tris(dioctyl pyrophosphoryloxy) titanate being 1:2:0.4.

[0046] The dehydrating agent is composed of vinyltrimethoxysilane and 3A molecular sieve at a mass ratio of 1:12.

[0047] Isocyanate is composed of liquefied MDI and polymeric MDI in a mass ratio of 10:15.

[0048] The polyoxypropylene triol is PPG-4000, Mn=4000, functionality=2.8.

[0049] A method for preparing a two-component polyurethane thermally conductive structural adhesive based on hydroxyl-terminated hyperbranched polyborosiloxane is as follows: (1) Preparation of component A: According to the formula amount, the modified castor oil, polyoxypropylene triol, reactive diluent, coupling agent, and hydroxyl-terminated hyperbranched polyborosiloxane were mixed evenly at 50°C, and then thermally conductive and flame-retardant filler and hydrophobic fumed silica were added. After vacuum degassing for 30 min, component A was obtained. (2) Preparation of component B: According to the formula, the isocyanate and dehydrating agent are mixed evenly at room temperature, and then thermally conductive and flame-retardant filler and hydrophobic fumed silica are added. The mixture is dispersed evenly at high speed and vacuum degassed for 30 minutes to obtain component B. (3) Mix component A and component B at a mass ratio of 1:0.9 to obtain a two-component polyurethane thermally conductive structural adhesive.

[0050] Comparative Example 1 is the same as Example 1, except that hydroxyl-terminated hyperbranched polyborosiloxane was not added to component A of Comparative Example 1.

[0051] Comparative Example 2 is the same as Example 1, except that the spherical alumina used in the preparation of the thermally conductive filler in Comparative Example 2 has a single particle size (D50=40μm).

[0052] Comparative Example 3 is the same as Example 1, except that the coupling agent in Comparative Example 3 is only KH-560, and the flame retardant FRC-6 and isopropyl tris(dioctyl pyrophosphate) titanate are not added to the coupling agent.

[0053] Performance testing The two-component polyurethane thermally conductive structural adhesives obtained in the examples and comparative examples were heat-cured at 80°C for 1.5 h, and then heat-cured at 100°C for 1 h to obtain structural adhesive samples. Relevant performance tests were conducted on the structural adhesive samples obtained in the examples and comparative examples of this invention, and the test results are shown in Table 1. Tensile strength and elongation at break tests: The tests were conducted in accordance with GB / T 528-2009 standard, with 5 samples tested per group and the arithmetic mean was taken.

[0054] Thermal conductivity test: The test was conducted according to ASTM D5470-2017 standard, with 3 samples tested in each group and the arithmetic mean was taken.

[0055] Flame retardancy rating test: Vertical burning test is conducted according to UL 94 standard, with 5 samples tested in each group, and the worst result is taken as the final rating.

[0056] Shear strength test: conducted according to GB / T 7124-2008 standard. Structural adhesive was uniformly applied to the overlapping surface of an aluminum plate (grade 6061, dimensions 100mm × 25mm × 2mm) cleaned with acetone. The overlap length was 12.5 mm, the adhesive thickness was controlled at 0.2 mm, and the overlap area was approximately 312.5 mm². 2 After curing at 80℃ for 1.5 h, it was then cured at 100℃ for 1 h, and cooled to room temperature. A universal testing machine was used to test the tensile strength at a rate of 10 mm / min, and the maximum breaking load was recorded. The shear strength (MPa) was calculated using the formula: maximum breaking load (N) / overlap area (mm²). 2 Calculate the shear strength. Test 5 specimens in each group and take the arithmetic mean.

[0057] Table 1 Test Items Tensile strength (MPa) Elongation at break (%) Thermal conductivity (W / (m·K)) UL94 flame retardant rating (0.8mm) Shear strength (aluminum-aluminum, MPa) Example 1 23.8 142 2.15 V-0 16.5 Example 2 25.2 128 2.38 V-0 17.9 Example 3 24.5 136 2.26 V-0 17.1 Comparative Example 1 14.8 140 1.72 V-1 10.8 Comparative Example 2 21.5 135 1.48 V-1 15.2 Comparative Example 3 18.2 143 2.02 V-1 12.6 .

[0058] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A two-component polyurethane thermal conductive structural adhesive based on hydroxyl-terminated hyperbranched polysiloxaboranes, characterized in that, It is composed of a mixture of component A and component B, with a mass ratio of component A to component B of 1:0.9~1.1; Component A, by mass parts, includes the following raw material components: 10-15 parts of modified castor oil; 28-32 parts of polyoxypropylene triol; 4-6 parts of reactive diluent; 2-5 parts of coupling agent; 45-55 parts of thermally conductive and flame-retardant filler; 2-4 parts of hydrophobic fumed silica; 3-5 parts of hydroxyl-terminated hyperbranched polyborosiloxane; Component B, by mass parts, includes the following raw material components: 25-27 parts isocyanate; 45-55 parts of thermally conductive and flame-retardant filler; 2-4 parts of hydrophobic fumed silica; 0.5-1 part of dehydrating agent; The terminal hydroxyl hyperbranched polyborosiloxane has a number average molecular weight of 2000~4000 g / mol, a hydroxyl value of 120~180 mgKOH / g, and a branching degree of 0.54~0.

62.

2. The two-component polyurethane thermal conductive structural adhesive based on hydroxyl-terminated hyperbranched polysiloxane-boron of claim 1, characterized in that, The modified castor oil is either epoxy-modified castor oil or silane-modified castor oil.

3. The two-component polyurethane thermal conductive structural adhesive based on hydroxyl-terminated hyperbranched polysiloxane-boron of claim 1, characterized in that, The active diluent is one or more of C8~C14 alkyl glycidyl ether, butyl glycidyl ether, and allyl glycidyl ether.

4. The two-component polyurethane thermal conductive structural adhesive based on hydroxyl-terminated hyperbranched polysiloxane-boron of claim 1, characterized in that, The coupling agent is a complex formed by flame retardant FRC-6, KH-560 and isopropyl tris(dioctyl pyrophosphoryloxy) titanate, with the mass ratio of flame retardant FRC-6 to KH-560 being 1:(1-3), and the amount of isopropyl tris(dioctyl pyrophosphoryloxy) titanate being 10% to 30% of the total mass of flame retardant FRC-6 and KH-560.

5. The two-component polyurethane thermal conductive structural adhesive based on hydroxyl-terminated hyperbranched polysiloxane-boron of claim 1, characterized in that, The thermally conductive and flame-retardant filler is a composite filler modified with a coupling agent. The composite filler is composed of 60-80 wt% spherical alumina, 15-30 wt% aluminum hydroxide, and 5-15 wt% nano boron nitride by mass percentage. The spherical alumina is obtained by mixing spherical alumina with a particle size of D50=5-15μm and D50=30-50μm in a mass ratio of (2-4):(6-8). The D50 of aluminum hydroxide is 1-10μm, and the D50 of nano boron nitride is 50-200nm.

6. The two-component polyurethane thermal conductive structural adhesive based on hydroxyl-terminated hyperbranched polysiloxane-boron of claim 5, characterized in that, The preparation method of thermally conductive and flame-retardant filler is as follows: (1) According to the formula, spherical alumina, aluminum hydroxide and nano boron nitride are mixed evenly to obtain a mixed filler; (2) By mass, 100 parts of mixed filler, 1.5 parts of flame retardant FRC-6 and 1.0 parts of KH560 are mixed evenly, dried and then the thermally conductive flame retardant filler is obtained. After cooling, it is sealed for later use.

7. The two-component polyurethane thermal conductive structural adhesive based on hydroxyl-terminated hyperbranched polysiloxane-boron of claim 1, characterized in that, The dehydrating agent is composed of vinyltrimethoxysilane and 3A molecular sieve in a mass ratio of 1:(10-12).

8. The two-component polyurethane thermal conductive structural adhesive based on hydroxyl-terminated hyperbranched polysiloxane-boron of claim 1, characterized in that, Isocyanate is composed of liquefied MDI and polymeric MDI in a mass ratio of (10-12):

15.

9. The two-component polyurethane thermal conductive structural adhesive based on hydroxyl-terminated hyperbranched polysiloxane-boron of claim 1, characterized in that, The molecular weight of polyoxypropylene triol is 3000~5000 g / mol, and the functionality is 2.5~3.

0.

10. The two-component polyurethane thermal conductive structural adhesive based on hydroxyl-terminated hyperbranched polysiloxane-boron of claim 1, characterized in that, The preparation method includes the following steps: (1) Preparation of component A: According to the formula amount, the modified castor oil, polyoxypropylene triol, reactive diluent, coupling agent, and hydroxyl-terminated hyperbranched polyborosiloxane are mixed evenly at 40~60℃, and then thermally conductive and flame-retardant filler and hydrophobic fumed silica are added. After vacuum degassing, component A is obtained. (2) Preparation of component B: According to the formula, the isocyanate and dehydrating agent are mixed evenly at room temperature, and then thermally conductive and flame-retardant filler and hydrophobic fumed silica are added, mixed evenly, and degassed under vacuum to obtain component B. (3) Mix component A and component B at a mass ratio of 1: (0.9~1.1) to obtain a two-component polyurethane thermally conductive structural adhesive.