Phosphate-based inorganic heat-conducting adhesive and preparation method thereof

Abstract

The invention relates to a phosphate-based inorganic heat-conducting adhesive and a preparation method thereof, and the phosphate-based inorganic heat-conducting adhesive is prepared by taking aluminum dihydrogen phosphate as an adhesive body, aluminum oxide as a curing agent and modified boron nitride and graphene oxide as composite heat-conducting fillers. And through sodium hydroxide assisted mechanical ball milling treatment, particle aggregation is broken, and the specific surface area and the reaction activity are increased. And introducing the modified boron nitride into a modified phosphate resin matrix to prepare the boron nitride reinforced inorganic heat-conducting adhesive. In order to improve the heat conduction and mechanical properties of the adhesive, graphene oxide is introduced. Graphene oxide is pretreated in absolute ethyl alcohol, and uniform and few-layer dispersion of graphene oxide in a solvent is achieved through the ultrasonic technology. The pretreated graphene oxide is added into the boron nitride reinforced inorganic heat-conducting adhesive, the ultrahigh heat conductivity and mechanical strength of the graphene oxide are fully utilized, and the heat-conducting property and adhesive property of the adhesive are improved through the synergistic effect of the graphene oxide and boron nitride.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal conductive adhesives, and particularly relates to a phosphate-based inorganic thermal conductive adhesive and a preparation method thereof. Background Art

[0002] With the continuous progress of micro-encapsulation technology and integration technology in the field of electronics and electrical engineering, electronic devices and electronic components are developing towards the direction of integration, miniaturization, and microminiaturization. As a result, the heat generated by electronic components within a limited volume has increased sharply. If the heat dissipation performance is poor, the excessive accumulated heat will cause the working temperature of the electronic components to rise, affecting the normal operation of the components. When the temperature is too high, the components may even be damaged. Therefore, the heat dissipation problem has become a major technical problem restricting the development of the electronics industry. Currently, electronic components mainly rely on a highly integrated thermal management system including radiators, refrigeration, heat sinks, chips, etc. to achieve heat dissipation. The thermal conductivity and connection performance between the various components of the electronic components in the thermal management system are particularly crucial, which mainly depends on thermal conductive adhesives with thermal conductivity and strong bonding performance.

[0003] Currently, most thermal conductive adhesives are organic thermal conductive adhesives based on organic materials such as epoxy resins and polyurethanes. The thermal conductivity of organic materials is generally low, resulting in limited thermal conductivity of organic adhesives, which greatly restricts their application in high-performance electronic devices. Although some progress has been made in using inorganic materials such as aluminum nitride and boron nitride as thermal conductive fillers for organic adhesives, due to the insufficient intrinsic thermal conductivity of the organic adhesive matrix and the problem of incompatibility between the organic / inorganic interfaces, it is difficult to significantly improve the overall thermal conductivity of organic thermal conductive adhesives. In addition, organic thermal conductive adhesives will generate a certain shrinkage rate during the curing process, which will cause internal stress at the bonding interface, thus affecting the bonding strength and thermal conductivity. Moreover, the thermal stability and chemical stability of organic adhesives are poor, and they are prone to decomposition and thermal chemical reactions in high-temperature environments, resulting in a decrease in bonding strength or even bonding failure.

[0004] Compared with organic thermal conductive adhesives, due to the thermal conductivity of inorganic materials being much higher than that of organic materials, inorganic adhesives based on inorganic materials such as borates, sulfates, silicates, and phosphates have better thermal conductivity than organic adhesives. In addition, inorganic adhesives perform excellently in high-temperature environments and have excellent high-temperature resistance. Moreover, the curing shrinkage rate of inorganic adhesives is small, which helps to improve the bonding strength, maintain the dimensional stability of the bonded objects, and reduce the deformation caused by curing. In addition, inorganic adhesives are inexpensive, easy to use, and have good durability, and can maintain stable performance during long-term use. However, at present, the application of inorganic materials as thermal conductive adhesives is less, and thermal conductive adhesives prepared from pure inorganic materials are relatively scarce. Summary of the Invention

[0005] The object of the present invention is to provide a phosphate-based inorganic thermal conductive adhesive and a preparation method thereof, so as to solve the technical problem that the current organic thermal conductive adhesive with an organic material as the matrix has poor thermal conductivity.

[0006] The technical problem solved by the present invention can be achieved by the following solutions:

[0007] On the one hand, the present invention provides a phosphate-based inorganic thermal conductive adhesive, which comprises: a modified phosphate resin, modified boron nitride, graphene oxide. The modified phosphate resin comprises aluminum dihydrogen phosphate and aluminum oxide. A boron nitride-reinforced inorganic thermal conductive adhesive is made from the modified phosphate resin and the modified boron nitride. The mass ratio of aluminum dihydrogen phosphate to aluminum oxide in the modified phosphate resin is 1:0.5 - 2. The proportion of the modified boron nitride added to the modified phosphate resin is 10wt% - 70wt%. The proportion of the graphene oxide added to the boron nitride-reinforced inorganic thermal conductive adhesive is 10wt% - 70wt%.

[0008] The modified boron nitride is prepared according to the following steps: Dispersing boron nitride powder with a particle size of 10μm in an NaOH solution for ultrasonic treatment, ball-milling the dispersion, and washing, filtering, and drying the ball-milled mixture to obtain the modified boron nitride. The graphene oxide is pretreated according to the following steps: Dispersing the graphene oxide in absolute ethanol for ultrasonic treatment, and filtering to obtain the graphene oxide.

[0009] Further, the mass ratio of aluminum dihydrogen phosphate to aluminum oxide in the modified phosphate resin is 1:0.5, 1:1, 1:1.5, or 1:2. The proportion of the modified boron nitride added to the modified phosphate resin is 10wt%, 20wt%, 30wt%, 40wt%, 50wt%, 60wt%, or 70wt%. The proportion of the graphene oxide added to the boron nitride-reinforced inorganic thermal conductive adhesive is 10wt%, 20wt%, 30wt%, 40wt%, 50wt%, 60wt%, or 70wt%.

[0010] Further: The mass ratio of aluminum dihydrogen phosphate to aluminum oxide in the modified phosphate resin is 1:1. The proportion of the modified boron nitride added to the modified phosphate resin is 60wt%. The proportion of the graphene oxide added to the boron nitride-reinforced inorganic thermal conductive adhesive is 50wt%.

[0011] On the other hand, the present invention provides a preparation method of the above-mentioned phosphate-based inorganic thermal conductive adhesive, and the method comprises the following steps:

[0012] Preparing the modified boron nitride: Dispersing boron nitride powder with a particle size of 10μm in an NaOH solution for ultrasonic treatment, ball-milling the dispersion, and washing, filtering, and drying the ball-milled mixture to obtain the modified boron nitride.

[0013] Preparation of modified phosphate resin: Mix aluminum dihydrogen phosphate with alumina, and obtain the modified phosphate resin after grinding, air drying, tabletting and curing;

[0014] Preparation of boron nitride-reinforced inorganic thermal conductive adhesive: Add modified boron nitride into the modified phosphate resin, and obtain the boron nitride-reinforced inorganic thermal conductive adhesive after grinding and mixing, and tabletting;

[0015] Pretreatment of graphene oxide: Disperse graphene oxide in absolute ethanol for ultrasonic treatment, and obtain graphene oxide after filtration;

[0016] Preparation of phosphate-based inorganic thermal conductive adhesive: Mix the pretreated graphene oxide with the boron nitride-reinforced inorganic thermal conductive adhesive, and after grinding and dispersion, tabletting, heat and cure to obtain the phosphate-based inorganic thermal conductive adhesive.

[0017] Furthermore: When preparing modified boron nitride, disperse 1 g of boron nitride powder in 30 ml of NaOH solution, after ultrasonic treatment for 30 minutes, transfer the dispersion liquid to a grinding bowl containing zirconia balls for ball milling for 6 hours, use 60 g of zirconia balls for every 1 g of boron nitride powder, wash the ball-milled mixture, filter it to neutrality, and vacuum dry it for 24 hours to obtain modified boron nitride.

[0018] Furthermore: When pretreating graphene oxide, disperse 1 g of graphene oxide in 100 ml of absolute ethanol, ultrasonic treatment for 8 hours, and obtain graphene oxide after vacuum filtration.

[0019] Furthermore: When preparing the phosphate-based inorganic thermal conductive adhesive, mix the pretreated graphene oxide with the boron nitride-reinforced inorganic thermal conductive adhesive, after grinding and dispersion, tabletting, cure at 170 °C for 2 hours to obtain the phosphate-based inorganic thermal conductive adhesive.

[0020] The present invention uses aluminum dihydrogen phosphate as the main body of the inorganic thermal conductive adhesive, alumina as the curing agent, and modified boron nitride and pretreated graphene oxide as the composite thermal conductive fillers to prepare a phosphate-based inorganic thermal conductive adhesive. First, a chemical and mechanical composite treatment method is used to modify boron nitride. The boron nitride powder is dispersed in a sodium hydroxide solution, and through ultrasonic and ball milling technologies, particle agglomeration is effectively broken, increasing its specific surface area and reactivity. Subsequently, modified phosphate resin serving as the adhesive matrix is prepared using aluminum dihydrogen phosphate and alumina, and the modified boron nitride is introduced into the modified phosphate resin matrix. Through grinding and mixing, a boron nitride-reinforced inorganic thermal conductive adhesive is prepared. The combination of modified boron nitride and modified phosphate resin not only improves the thermal conductivity of the adhesive but also enhances the overall strength of the adhesive through the excellent mechanical properties of boron nitride. To further improve the thermal and mechanical properties of the adhesive, graphene oxide, a high-performance nanomaterial, is introduced. First, graphene oxide is pretreated in absolute ethanol, and the ultrasonic technology can achieve its uniform and few-layer dispersion in the solvent. Subsequently, the pretreated graphene oxide is added to the boron nitride-reinforced inorganic thermal conductive adhesive, and through the grinding process, the uniform dispersion of graphene oxide in the thermal conductive adhesive is ensured. This composite process not only makes full use of the ultra-high thermal conductivity and mechanical strength of graphene oxide but also further improves the comprehensive performance of the adhesive through its synergistic effect with boron nitride. Boron nitride and graphene oxide, as efficient thermal conductive fillers, construct an efficient thermal conductive network in the modified phosphate resin matrix, significantly improving the thermal conductivity of the adhesive. The addition of boron nitride and graphene oxide not only improves the bonding strength of the adhesive but also enhances its toughness and wear resistance, enabling the thermal conductive adhesive to exhibit higher stability and reliability when subjected to complex mechanical environments. Aluminum dihydrogen phosphate itself has excellent chemical stability, and its combination with boron nitride and graphene oxide further enhances the corrosion resistance and high-temperature resistance of the adhesive, broadening its application range. Description of the Drawings

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0022] Figure 1 It is a flowchart of a preparation method of a phosphate-based inorganic thermal conductive adhesive of the present invention;

[0023] Figure 2 They are SEM morphology diagrams of BN-1 and m-BN. (a)(b) are SEM morphology diagrams of BN-1, and (c)(d) are SEM morphology diagrams of m-BN;

[0024] Figure 3 SEM morphology diagrams of BN-10 and M-BN, (a)(b) are SEM morphology diagrams of BN-10, and (c)(d) are SEM morphology diagrams of M-BN;

[0025] Figure 4 Infrared spectra of BN-1 and m-BN;

[0026] Figure 5 Infrared spectra of BN-10 and M-BN;

[0027] Figure 6 Dispersion of BN-1, m-BN, BN-10 and M-BN in deionized water. a is after ultrasonic treatment, b is after standing for 24 h, and c is the agglomeration and sedimentation at the bottom of the glass bottle after standing for 24 h;

[0028] Figure 7 Graph of the change rule of the shear strength of boron nitride-reinforced inorganic thermal conductive adhesive with different M-BN addition amounts. a is Comparative Example 1, b is Comparative Example 2, c is Comparative Example 3, d is Comparative Example 4, e is Comparative Example 5, f is Comparative Example 6, and g is Comparative Example 7;

[0029] Figure 8 Graph of the change rule of the thermal conductivity coefficient of boron nitride-reinforced inorganic thermal conductive adhesive with different M-BN addition amounts. a is Comparative Example 1, b is Comparative Example 2, c is Comparative Example 3, d is Comparative Example 4, e is Comparative Example 5, f is Comparative Example 6, and g is Comparative Example 7;

[0030] Figure 9 Cross-sectional views of phosphate-based inorganic thermal conductive adhesives with different graphene oxide addition amounts. (a) is the phosphate-based inorganic thermal conductive adhesive of Example 1 with a graphene oxide addition amount of 10%, (b) is the phosphate-based inorganic thermal conductive adhesive of Example 5 with a graphene oxide addition amount of 50%, (c) is the phosphate-based inorganic thermal conductive adhesive of Example 7 with a graphene oxide addition amount of 70%, and (d) is a partial enlarged view of (c);

[0031] Figure 10 X-ray diffraction analysis image of the phosphate-based inorganic thermal conductive adhesive of Example 5;

[0032] Figure 11 Graph of the change rule of the shear strength of phosphate-based inorganic thermal conductive adhesives with different graphene oxide addition amounts. a is Example 1, b is Example 2, c is Example 3, d is Example 4, e is Example 5, f is Example 6, and g is Example 7;

[0033] Figure 12Variation law diagram of the thermal conductivity of the phosphate-based inorganic thermal conductive adhesive with different addition amounts of graphene oxide. a is Example 1, b is Example 2, c is Example 3, d is Example 4, e is Example 5, f is Example 6, and g is Example 7. Detailed implementation manners

[0034] To clearly demonstrate the objectives, technical solutions, and advantages of the present invention, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0035] This embodiment provides a phosphate-based inorganic thermal conductive adhesive, which comprises: a modified phosphate resin, modified boron nitride, and graphene oxide. The modified phosphate resin comprises aluminum dihydrogen phosphate and aluminum oxide. A boron nitride-reinforced inorganic thermal conductive adhesive is made from the modified phosphate resin and the modified boron nitride. The mass ratio of aluminum dihydrogen phosphate to aluminum oxide in the modified phosphate resin is 1:0.5 - 2. The proportion of the modified boron nitride added to the modified phosphate resin is 10wt% - 70wt%. The proportion of the graphene oxide added to the boron nitride-reinforced inorganic thermal conductive adhesive is 10wt% - 60wt%.

[0036] The modified boron nitride is prepared according to the following steps: Boron nitride powder with a particle size of 10 μm is dispersed in a NaOH solution and subjected to ultrasonic treatment to promote the full dispersion of boron nitride particles in the NaOH solution. Ultrasonic treatment can effectively break the agglomeration of boron nitride particles and increase the contact area between boron nitride particles and the NaOH solution. Subsequently, the dispersion is ball-milled. Ball milling can further refine the boron nitride particles through the action of mechanical force, increase the specific surface area and reaction activity of boron nitride, and promote the chemical reaction between boron nitride and NaOH. The mixture after ball milling is washed and filtered to neutrality. This step ensures the purity and chemical stability of the product. Finally, the product after washing and filtering is dried to obtain the modified boron nitride. The drying process can effectively remove the residual moisture in the product and ensure the dryness and stability of the modified boron nitride. In this embodiment, the NaOH solution uses a concentrated NaOH solution.

[0037] Specifically, when preparing the modified boron nitride, 1 g of boron nitride powder is dispersed in 30 ml of the NaOH solution and ultrasonically treated for 30 minutes. Subsequently, the dispersion is transferred to a grinding bowl containing zirconia balls and ball-milled for 6 hours. 60 g of zirconia balls are used for every 1 g of boron nitride powder. After ball milling, the dispersion is washed and filtered to neutrality and dried in vacuum for 24 hours to obtain the modified boron nitride.

[0038] As a thermal conductive filler, boron nitride has excellent thermal conductivity. However, the surface inertness of boron nitride and its tendency to agglomerate make it difficult to disperse uniformly in the phosphate matrix, which becomes a key problem restricting the improvement of the thermal conductivity of thermal conductive adhesives. In this embodiment, a method of NaOH-assisted mechanical ball milling is used to modify boron nitride. During the ball milling process, the NaOH solution serves as an effective liquid control agent, creating defects on the surface of boron nitride through mechanical shear force, and then promoting the bonding of hydroxyl groups to these defect sites, thereby modifying boron nitride.

[0039] In this embodiment, the boron nitride with a particle size of 10 μm before modification is named BN-10, and the boron nitride after being modified by NaOH-assisted mechanical ball milling is named M-BN. The NaOH-assisted mechanical ball milling treatment can effectively roughen and glassify the relatively smooth surface of boron nitride, and some massive particles are peeled into flakes, thus improving the agglomeration phenomenon of BN-10 and enhancing the dispersion ability of M-BN. Due to the relatively large particle size of BN-10, the grinding balls can fully contact and act on the particle surface during the ball milling process, thereby forming defects on the surface. These defects provide effective sites for the grafting of hydroxyl groups, enabling the hydroxyl groups to successfully graft onto the surface of M-BN particles. The grafting of hydroxyl groups can change the surface chemical properties of M-BN and also have a positive impact on its dispersibility and interfacial compatibility in the phosphate matrix. The grafted hydroxyl groups can enhance the interaction between M-BN and the phosphate matrix, thereby improving its dispersibility in the matrix. At the same time, the introduction of hydroxyl groups also helps to construct effective thermal conduction pathways and improve the thermal conductivity of thermal conductive adhesives. The modification process in this embodiment increases the active sites on the surface of M-BN, improves the interaction ability between boron nitride as a thermal conductive filler and the phosphate matrix material using it, enhances its dispersion performance in the phosphate matrix, and plays a positive role in improving the thermal conductivity of thermal conductive adhesives.

[0040] As the matrix, aluminum dihydrogen phosphate has a significantly higher thermal conductivity than traditional organic polymer materials, thus effectively overcoming the problem of low intrinsic thermal conductivity of the matrix. However, aluminum dihydrogen phosphate has a high curing temperature and a fast rate, which easily leads to the formation of pores inside the colloid and affects the thermal enhancement efficiency. Therefore, in this embodiment, alumina is introduced as a curing agent to prepare a modified phosphate resin, which not only optimizes the properties of the aluminum dihydrogen phosphate matrix but also helps to construct effective thermal conduction channels. The introduction of alumina as a curing agent can not only effectively control the rate and temperature of the curing reaction and achieve a more controllable curing process, but also helps to optimize the internal structure of the colloid, reduce the formation of micropores, and thus enhance its bonding strength and overall performance.

[0041] Aluminum oxide, as a curing agent for the aluminum dihydrogen phosphate matrix, plays a crucial role in its addition amount during the curing process. An appropriate amount of aluminum oxide can provide sufficient reactive sites, effectively promoting the chemical reaction between phosphate ions in the aluminum dihydrogen phosphate matrix and hydroxyl or oxygen ions on the surface of aluminum oxide, thereby accelerating the curing process. This is because the active sites on the surface of aluminum oxide can form chemical bonds with the functional groups in the aluminum dihydrogen phosphate matrix, forming a stable network structure, and thus realizing the curing of the adhesive.

[0042] Preferably, in this embodiment, the aluminum dihydrogen phosphate and aluminum oxide are mixed in a preset ratio, and the mass ratio of aluminum dihydrogen phosphate to aluminum oxide is 1:0.5, 1:1, 1:1.5 or 1:2. Preferably, the mass ratio of aluminum dihydrogen phosphate to aluminum oxide is 1:1.

[0043] In addition to acting as a thermal conductive filler, the modified boron nitride in this embodiment also acts as a reinforcing particle to bond with the matrix, and can effectively improve the bonding strength of the thermal conductive adhesive. This is because the addition of boron nitride can enhance the mechanical locking effect inside the adhesive and increase the interface area, thereby improving the tensile shear strength of the adhesive. As a thermal conductive filler and a reinforcing filler, the addition amount of the modified boron nitride is crucial for improving the bonding strength and thermal conductivity of the inorganic thermal conductive adhesive. Preferably, in this embodiment, the modified boron nitride is added to the modified phosphate resin in proportions of 10wt%, 20wt%, 30wt%, 40wt%, 50wt%, 60wt%, 70wt% to prepare a boron nitride-reinforced inorganic thermal conductive adhesive. That is, the weight percentage of the modified boron nitride in the mixture of the modified boron nitride and the modified phosphate resin is 10%, 20%, 30%, 40%, 50%, 60%, 70%. Preferably, the modified boron nitride is added to the modified phosphate resin in a proportion of 60wt%.

[0044] In this embodiment, the graphene oxide is pretreated according to the following steps: The graphene oxide is dispersed in absolute ethanol and subjected to ultrasonic treatment, and then the graphene oxide is obtained after filtration. Absolute ethanol has good polarity and solubility, which enables it to interact with the oxides on the surface of graphene oxide, thus facilitating the dispersion of graphene oxide. At the same time, the molecular weight of absolute ethanol is small, and it can penetrate into the interlayer voids of graphene oxide better, helping to form a more stable dispersion state. Ultrasonic treatment can generate a large number of tiny bubbles. These bubbles expand and burst rapidly in the liquid, generating high-speed eddies and impact forces, which can make graphene oxide reach a more uniform and stable few-layer dispersion state in absolute ethanol. When ultrasonic waves propagate in the liquid, a series of complex physical effects will be generated, including phenomena such as instantaneous high pressure and microjets. When these ultrasonic waves act on graphene oxide, large pieces of graphene oxide will be effectively ultrasonically broken into flaky layers of different sizes. Specifically, the instantaneous high pressure generated by ultrasonic waves will form strong shock waves in the liquid, and these shock waves will generate strong impact and shear forces on the surface and internal structure of graphene oxide. Under the action of this impact force, the interlayer binding force of graphene oxide is weakened, and the interaction between layers is broken, so that large pieces of graphene oxide are peeled off and broken. At the same time, effects such as microjets and eddies generated by ultrasonic waves in the liquid also contribute to the fragmentation and peeling of graphene oxide. These effects can promote the uniform dispersion of graphene oxide in the liquid and further accelerate the fragmentation process of graphene oxide. Ultrasonic treatment can endow graphene oxide with an excellent few-layer structure, and this structural feature helps to form effective heat conduction channels in the thermal conductive adhesive, improving the overall thermal conductivity.

[0045] Specifically, 1 g of graphene oxide is dispersed in 100 ml of absolute ethanol, ultrasonically treated for 8 hours, and then the graphene oxide is obtained after vacuum filtration.

[0046] In the thermal conductive adhesive system, the granular morphology of the modified boron nitride enables it to be dispersed in the matrix to form a dense thermal conduction network, while the two-dimensional sheet structure of graphene oxide can construct continuous heat conduction channels in this network, making up for the heat conduction path defects of a single filler, and then improving the heat transfer efficiency. In this embodiment, the construction of the dual-filler system of modified boron nitride and graphene oxide not only makes full use of the differences in shape and properties between boron nitride and graphene oxide, but also can achieve the synergistic effect between the two. This synergistic effect makes the inorganic thermal conductive adhesive system more likely to form a complete and efficient heat conduction path, thus significantly improving the thermal conductivity.

[0047] Preferably, in this embodiment, the pretreated graphene oxide is added to the boron nitride-reinforced inorganic thermal conductive adhesive in proportions of 10wt%, 20wt%, 30wt%, 40wt%, 50wt%, 60wt%, and 70wt% to prepare the phosphate-based inorganic thermal conductive adhesive. That is, the weight percentage of graphene oxide in the phosphate-based inorganic thermal conductive adhesive is 10%, 20%, 30%, 40%, 50%, 60%, and 70%. Preferably, the pretreated graphene oxide is added to the boron nitride-reinforced inorganic thermal conductive adhesive in a proportion of 50wt%.

[0048] As Figure 1 shown, the phosphate-based inorganic thermal conductive adhesive of this embodiment is prepared according to the following steps:

[0049] S101. Prepare modified boron nitride: Disperse boron nitride powder with a particle size of 10 μm in NaOH solution for ultrasonic treatment, ball-mill the dispersion, and obtain modified boron nitride after washing, filtering, and drying the ball-milled mixture;

[0050] S102. Prepare modified phosphate resin: Mix aluminum dihydrogen phosphate and alumina, and obtain modified phosphate resin after grinding, air-drying, tabletting, and curing;

[0051] S103. Prepare boron nitride-reinforced inorganic thermal conductive adhesive: Add the modified boron nitride to the modified phosphate resin, and obtain boron nitride-reinforced inorganic thermal conductive adhesive after grinding and mixing, and tabletting;

[0052] S104. Pretreat graphene oxide: Disperse graphene oxide in absolute ethanol for ultrasonic treatment, and obtain graphene oxide after filtration;

[0053] S105. Prepare phosphate-based inorganic thermal conductive adhesive: Mix the pretreated graphene oxide with the boron nitride-reinforced inorganic thermal conductive adhesive, and obtain the phosphate-based inorganic thermal conductive adhesive after grinding and dispersion, tabletting, and heating and curing.

[0054] Specifically, in step S101, when preparing the modified boron nitride, every 1 g of boron nitride powder is dispersed in 30 ml of NaOH solution. After ultrasonic treatment for 30 minutes, transfer the dispersion to a grinding bowl containing zirconia balls and ball-mill for 6 hours. Use 60 g of zirconia balls for every 1 g of boron nitride powder. After filtration and washing of the ball-milled mixture until neutral, vacuum-dry for 24 hours to obtain the modified boron nitride.

[0055] Specifically, in step S104, when pretreating graphene oxide, every 1 g of graphene oxide is dispersed in 100 ml of absolute ethanol, ultrasonic-treated for 8 hours, and graphene oxide is obtained after vacuum filtration.

[0056] Specifically, in the step S105, when preparing the phosphate-based inorganic thermal conductive adhesive, the pretreated graphene oxide is mixed with the boron nitride-reinforced inorganic thermal conductive adhesive. After grinding and dispersing, and pressing into tablets, it is cured at 170°C for 2 hours to obtain the phosphate-based inorganic thermal conductive adhesive.

[0057] Example 1: A phosphate-based inorganic thermal conductive adhesive, comprising a modified phosphate resin, modified boron nitride, and graphene oxide. The modified phosphate resin comprises aluminum dihydrogen phosphate and alumina. The boron nitride-reinforced inorganic thermal conductive adhesive is made from the modified phosphate resin and modified boron nitride. The mass ratio of aluminum dihydrogen phosphate to alumina in the modified phosphate resin is 1:1. The proportion of the modified boron nitride added to the modified phosphate resin is 60 wt%, and the proportion of the graphene oxide added to the boron nitride-reinforced inorganic thermal conductive adhesive is 10 wt%.

[0058] The phosphate-based inorganic thermal conductive adhesive is prepared according to the following steps:

[0059] Prepare modified boron nitride: Disperse boron nitride powder with a particle size of 10 μm in NaOH solution and perform ultrasonic treatment. The boron nitride used is hexagonal boron nitride. For every 1 g of boron nitride powder, it is dispersed in 30 ml of NaOH solution. After ultrasonic treatment for 30 minutes, transfer the dispersion to a grinding bowl containing zirconia balls, seal it, and place it in a ball mill. Ball mill at a rotation speed of 400 r / min for 6 hours. For every 1 g of boron nitride powder, 60 g of zirconia balls are used. After ball milling, the mixture is washed and filtered to neutral, and then placed in a vacuum oven at 70°C for vacuum drying for 24 hours to obtain modified boron nitride.

[0060] Prepare modified phosphate resin: Mix aluminum dihydrogen phosphate and alumina, and after grinding, air drying, and pressing into tablets, cure at 170°C for 2 hours to obtain the modified phosphate resin. When pressing into tablets, press them into cylinders with a diameter of 25 mm and a thickness of 1 - 2 mm.

[0061] Prepare boron nitride-reinforced inorganic thermal conductive adhesive: Add the modified boron nitride to the modified phosphate resin, and after grinding and mixing, and pressing into tablets, obtain the boron nitride-reinforced inorganic thermal conductive adhesive.

[0062] Pretreat graphene oxide: Disperse graphene oxide in absolute ethanol and perform ultrasonic treatment. For every 1 g of graphene oxide, it is dispersed in 100 ml of absolute ethanol. After ultrasonic treatment for 8 hours, obtain graphene oxide through vacuum filtration.

[0063] Prepare phosphate-based inorganic thermal conductive adhesive: Mix the pretreated graphene oxide with the boron nitride-reinforced inorganic thermal conductive adhesive, grind and disperse, and then press into a cylinder, and cure at 170°C for 2 hours to obtain the phosphate-based inorganic thermal conductive adhesive.

[0064] Example 2: The difference between this example and Example 1 is that the proportion of graphene oxide added to the boron nitride-reinforced inorganic thermal conductive adhesive is 20 wt%, and the others are the same as in Example 1.

[0065] Example 3: The difference between this example and Example 1 is that the proportion of graphene oxide added to the boron nitride-reinforced inorganic thermal conductive adhesive is 30 wt%, and the others are the same as in Example 1.

[0066] Example 4: The difference between this example and Example 1 is that the proportion of graphene oxide added to the boron nitride-reinforced inorganic thermal conductive adhesive is 40 wt%, and the others are the same as in Example 1.

[0067] Example 5: The difference between this example and Example 1 is that the proportion of graphene oxide added to the boron nitride-reinforced inorganic thermal conductive adhesive is 50 wt%. The others are the same as in Example 1.

[0068] Example 6: The difference between this example and Example 1 is that the proportion of graphene oxide added to the boron nitride-reinforced inorganic thermal conductive adhesive is 60 wt%, and the others are the same as in Example 1.

[0069] Example 7: The difference between this example and Example 1 is that the proportion of graphene oxide added to the boron nitride-reinforced inorganic thermal conductive adhesive is 70 wt%, and the others are the same as in Example 1.

[0070] Comparative Example 1: A boron nitride-reinforced inorganic thermal conductive adhesive contains a modified phosphate resin and modified boron nitride. The modified phosphate resin contains aluminum dihydrogen phosphate and alumina. The boron nitride-reinforced inorganic thermal conductive adhesive is made from the modified phosphate resin and modified boron nitride. The mass ratio of aluminum dihydrogen phosphate to alumina in the modified phosphate resin is 1:1, and the proportion of modified boron nitride added to the modified phosphate resin is 10 wt%.

[0071] The boron nitride-reinforced inorganic thermal conductive adhesive is prepared according to the following steps:

[0072] Prepare modified boron nitride: Disperse boron nitride powder with a particle size of 10 μm in NaOH solution and perform ultrasonic treatment. The boron nitride used is hexagonal boron nitride. Every 1 g of boron nitride powder is dispersed in 30 ml of NaOH solution. After ultrasonic treatment for 30 minutes, transfer the dispersion to a grinding bowl containing zirconia balls, seal it, and place it in a ball mill. Ball mill at a rotation speed of 400 r / min for 6 hours. Every 1 g of boron nitride powder uses 60 g of zirconia balls. The ball-milled mixture is washed and filtered to neutral, and then placed in a vacuum oven at 70 °C for vacuum drying for 24 hours to obtain modified boron nitride.

[0073] Preparation of modified phosphate resin: Mix aluminum dihydrogen phosphate with alumina, grind, dry in air, and press into tablets. Then cure at 170 °C for 2 hours to obtain the modified phosphate resin. When pressing tablets, make the tablets into cylinders with a diameter of 25 mm and a thickness of 1 - 2 mm.

[0074] Preparation of boron nitride reinforced inorganic thermal conductive adhesive: Add modified boron nitride to the modified phosphate resin, grind and mix, press into tablets, and then cure at 170 °C for 2 hours to obtain the boron nitride reinforced inorganic thermal conductive adhesive.

[0075] Comparative Example 2: The difference between this comparative example and Comparative Example 1 is that the proportion of modified boron nitride added to the modified phosphate resin is 20 wt%, and the others are the same as those in Comparative Example 1.

[0076] Comparative Example 3: The difference between this comparative example and Comparative Example 1 is that the proportion of modified boron nitride added to the modified phosphate resin is 30 wt%, and the others are the same as those in Comparative Example 1.

[0077] Comparative Example 4: The difference between this comparative example and Comparative Example 1 is that the proportion of modified boron nitride added to the modified phosphate resin is 40 wt%, and the others are the same as those in Comparative Example 1.

[0078] Comparative Example 5: The difference between this comparative example and Comparative Example 1 is that the proportion of modified boron nitride added to the modified phosphate resin is 50 wt%, and the others are the same as those in Comparative Example 1.

[0079] Comparative Example 6: The difference between this comparative example and Comparative Example 1 is that the proportion of modified boron nitride added to the modified phosphate resin is 60 wt%, and the others are the same as those in Comparative Example 1.

[0080] Comparative Example 7: The difference between this comparative example and Comparative Example 1 is that the proportion of modified boron nitride added to the modified phosphate resin is 70 wt%, and the others are the same as those in Comparative Example 1.

[0081] Effect Example:

[0082] Analysis of the Properties of Modified Boron Nitride

[0083] To evaluate the modification effect of boron nitride, hexagonal boron nitride (h-BN) samples with different particle sizes, including two specifications of 1 μm and 10 μm, were selected and named BN-1 and BN-10 respectively. After the modification treatment, these samples were marked as m-BN and M-BN respectively. For BN-10, the modification steps of boron nitride in Example 1 were adopted for modification. Boron nitride powder with a particle size of 10 μm was dispersed in NaOH solution and subjected to ultrasonic treatment. Hexagonal boron nitride was used as the boron nitride. Every 1 g of boron nitride powder was dispersed in 30 ml of NaOH solution. After ultrasonic treatment for 30 minutes, the dispersion was transferred to a grinding bowl containing zirconia balls, sealed and placed in a ball mill, and ball milled at a speed of 400 r / min for 6 hours. 60 g of zirconia balls were used for every 1 g of boron nitride powder. The ball-milled mixture was washed and filtered to neutrality, and then placed in a vacuum oven at 70 °C for vacuum drying for 24 hours to obtain modified boron nitride. The modification method of BN-1 was basically the same as that of BN-10, only replacing the 10-μm boron nitride powder with 1-μm boron nitride powder.

[0084] Figure 2 are the SEM morphology diagrams of BN-1 and m-BN. (a)(b) are the SEM morphology diagrams of BN-1, and (c)(d) are the SEM morphology diagrams of m-BN. It can be seen from Figure 2 the figure that both BN-1 and m-BN exhibit irregular blocky morphologies, and the agglomeration phenomenon is quite significant. The main reason for this phenomenon is that the particle size of the BN-1 crystal particles is relatively small, resulting in a relatively high specific surface energy and a relatively large specific surface area of the BN-1 particles. This high specific surface energy makes the particles easily attract each other, thus forming aggregates. However, even after the modification treatment, the agglomeration phenomenon of m-BN is still serious. For the particle size of BN-1, due to its small size, it is difficult for the grinding balls to form an effective impact on the particle surface during the ball milling process. The lack of this impact force makes it difficult to generate sufficient defects on the particle surface, thereby limiting the grafting of hydroxyl groups on the surface of m-BN particles. Due to the lack of sufficient grafting points, the hydroxyl groups cannot effectively improve its interfacial compatibility, resulting in a still serious agglomeration phenomenon. The existence of this agglomeration phenomenon is extremely unfavorable for the improvement of the thermal conductivity. The agglomerated m-BN particles cannot form an effective heat conduction path in the modified phosphate resin, which will limit the heat transfer efficiency. Through the observation and analysis of the scanning electron microscope (SEM) images, it can be seen that the modification treatment has not produced a significant improvement effect on the agglomeration phenomenon of BN-1.

[0085] Figure 3 are the SEM morphology diagrams of BN-10 and M-BN. (a)(b) are the SEM morphology diagrams of BN-10, and (c)(d) are the SEM morphology diagrams of M-BN. It can be seen from Figure 3It can be seen that the untreated BN-10 exhibits a regular block structure with clear edges and no impurities, and the surface is relatively smooth. However, after the treatment of sodium hydroxide-assisted mechanical ball milling, the morphology of M-BN has changed significantly. Specifically, the irregularity of the edges of the treated M-BN particles has increased significantly, and a large number of scaly protrusions have appeared on the surface, indicating that the particle surface has been effectively peeled and roughened. More importantly, some of the massive particles have been peeled into boron nitride nanosheets with a relatively thin thickness. This significant change in morphology is mainly attributed to the combined action of mechanical force and sodium hydroxide. Due to the relatively large particle size of BN-10, the grinding balls can fully contact and act on the particle surface during the ball milling process, thus forming defects on the surface. These defects provide effective sites for the grafting of hydroxyl groups, enabling the hydroxyl groups to successfully graft onto the surface of M-BN particles. After the modification treatment, the agglomeration phenomenon of BN-10 has been significantly improved.

[0086] Fourier transform infrared spectroscopy (FT-IR) was performed on BN-1, m-BN, BN-10, and M-BN. Figure 4 Figures for the infrared spectra of BN-1 and m-BN, where the upper curve is the infrared spectrum of BN-1 and the lower curve is the infrared spectrum of m-BN. As Figure 4 can be seen, BN-1 shows obvious characteristic absorption peaks at wavelengths of 1349 cm -1 and 770 cm -1 respectively. Among them, the vibration peak at 1349 cm -1 is attributed to the in-plane stretching vibration peak of the B-N bond of h-BN after analysis, and the vibration peak at 770 cm -1 is attributed to the out-of-plane bending vibration peak of the B-N-B bond of h-BN after analysis. At the same time, it can be found from the infrared spectrum that a small absorption peak appears at a wavelength of 3500 cm -1 . After analysis, this absorption peak is the vibration peak of the hydroxyl group. The appearance of the hydroxyl group may be due to BN-1 absorbing water in the air during the tablet pressing process, or there may be residual hydroxyl groups at the edges of BN-1 during the preparation of BN-1. The results of infrared spectroscopy analysis show that the number of hydroxyl groups introduced on the surface of m-BN is very small.

[0087] Figure 5 Figures for the infrared spectra of BN-10 and M-BN, where the upper curve is the infrared spectrum of BN-10 and the lower curve is the infrared spectrum of M-BN. As Figure 5It can be seen that compared with BN-10, the modified M-BN still retains two significant characteristic absorption peaks, indicating that the ball-milling modification process assisted by sodium hydroxide solution mainly acts on the surface of the sample, introducing some defects and leaving hydroxyl groups at its edges. However, this treatment process does not destroy the original crystal structure of BN-10 and maintains its basic physical and chemical properties. It is worth noting that the characteristic absorption peaks of the modified M-BN have shifted slightly. Specifically, the in-plane stretching vibration peak of the B-N bond has shifted from 1349 cm -1 to 1381 cm -1 , while the out-of-plane bending vibration peak of the B-N-B bond has shifted from 770 cm -1 to 799 cm -1 . This slight shift phenomenon can be attributed to the successful grafting of hydroxyl groups onto the surface of M-BN under the combined action of sodium hydroxide and ball milling. The interaction between the hydroxyl group and BN-10 affects the inherent vibration characteristics of the BN-10 lattice, which is manifested as a slight shift of the characteristic absorption peak in the infrared spectrum. As can be Figure 5 also seen, compared with BN-10, a more obvious characteristic absorption peak of hydroxyl groups appears in the infrared spectrum of M-BN at a wavelength of 3467 cm -1 , while only a small hydroxyl absorption peak appears in the infrared spectrum of the BN-10 powder sample at 3500 cm -1 . The obvious characteristic absorption peak of hydroxyl groups at a wavelength of 3467 cm -1 indicates that the hydroxyl groups have been successfully grafted onto the surface of M-BN. The hydroxyl group and M-BN are stably connected by forming a B-O bond, thus realizing the hydroxylation of the M-BN surface.

[0088] The modified phosphate resin needs to be dissolved in water during use. To further compare the modification effects of two different particle sizes of boron nitride under the same experimental conditions, BN-1, m-BN, BN-10, and M-BN were respectively dispersed in deionized water and subjected to ultrasonic treatment, and the concentration of the dispersion liquid was 1 mg / mL. The results are as Figure 6 shown.

[0089] As Figure 6It can be seen that the dispersions of BN-1, m-BN, BN-10, and M-BN initially appear milky white, but after standing for 24 h, the color significantly fades. This phenomenon is due to the agglomeration of some boron nitride particles and their sedimentation to the bottom of the bottle, resulting in a decrease in the concentration of boron nitride in the upper liquid. The agglomeration occurs because the interaction forces between boron nitride particles are relatively strong, causing them to easily aggregate together during standing. In contrast, the M-BN and BN-10 dispersions exhibit different characteristics. The BN-10 dispersion becomes nearly transparent after standing, and a large amount of precipitation appears at the bottom of the bottle. This indicates that the dispersion of BN-10 in deionized water is poor and it is prone to agglomeration. However, the M-BN dispersion shows almost no change after standing for 24 h, with only a small amount of white precipitation at the bottom of the bottle. This shows that the dispersion of the modified M-BN in deionized water has been significantly improved, and the interaction forces between its particles have been weakened, thus reducing the occurrence of agglomeration. This good dispersion helps to achieve the preparation of a more uniform and stable phosphate-based inorganic thermal conductive adhesive. It can be seen that the sodium hydroxide-assisted mechanical ball milling treatment has a significant effect on improving the dispersion of boron nitride, and M-BN exhibits excellent dispersion.

[0090] Analysis of the Properties of Boron Nitride Reinforced Inorganic Thermal Conductive Adhesive

[0091] To evaluate the bonding strength of the boron nitride-reinforced inorganic thermal conductive adhesive, the test was carried out in accordance with the adhesive tensile shear strength test method of GB / T7124-2008 and using an electronic universal testing machine. 6061 aluminum alloy was used as the standard specimen, with its dimensions of length×width×thickness: 100×25×2 mm, and the lap length was 12.5 mm. Then, the thermal conductive adhesive was evenly applied to the lap part of the specimen. After airing to remove the solvent, the specimens were closed and appropriate pressure was applied for curing to ensure good bonding between the colloid and the specimen. The samples were tested three times on the electronic universal testing machine at a tensile speed of 20 mm / min, and the average value was taken to reduce errors.

[0092] Figure 7 Shows the shear strength changes of the boron nitride-reinforced inorganic thermal conductive adhesives of Comparative Example 1 to Comparative Example 7 at different M-BN contents. Figure 7It can be seen that the tensile shear strength of the thermal conductive adhesive first increases and then decreases with the increase of the M-BN content. When the mass fraction of the M-BN filler increases to about 50 wt%, the tensile shear strength reaches the maximum value, about 3.76 MPa. However, when the M-BN content continues to increase to 60-70 wt%, the tensile shear strength of the thermal conductive adhesive decreases rapidly. The reasons for this phenomenon can be explained from the following aspects: First, when the M-BN content is low, the modified phosphate resin matrix and the M-BN filler can be effectively combined. The M-BN filler as the reinforcing particles combines with the matrix, which can effectively improve the strength of the thermal conductive adhesive. With the increase of the filler filling amount, the strengthening effect becomes more significant, and the bonding performance of the thermal conductive adhesive gradually improves. This is because the addition of the filler can enhance the mechanical locking effect inside the thermal conductive adhesive and increase the interface area, thereby improving the tensile shear strength of the thermal conductive adhesive. However, when the filler content reaches a certain critical value, continuing to increase the filler will cause the tensile shear strength of the thermal conductive adhesive to decrease. This is because with the increase of the filler content, the content of the modified phosphate resin matrix relatively decreases. When the content of the matrix becomes small, it becomes difficult to effectively combine the filler and the matrix. Excessive fillers will damage the continuity of the matrix, resulting in the formation of a large number of gaps inside the thermal conductive adhesive system. These gaps not only reduce the contact area between the filler and the matrix, but also increase the interfacial thermal resistance, thus affecting the thermal conductivity and tensile shear strength of the thermal conductive adhesive. In addition, excessive fillers may also lead to uneven stress distribution inside the thermal conductive adhesive, making the thermal conductive adhesive prone to stress concentration and fracture when subjected to external forces. Therefore, although increasing the M-BN filler content can improve the bonding performance of the thermal conductive adhesive to a certain extent, too high a filler content will instead lead to a decrease in the bonding performance.

[0093] The Hot Disk thermal constant analyzer was used to test the thermal conductivity of the boron nitride-reinforced inorganic thermal conductive adhesive to understand its thermal conductivity characteristics. During the test, a flat plate module and a 7577 probe were used to ensure the accuracy and reliability of the test. And the probe output power was set to 50 mW, and the test temperature was set to 29 °C.

[0094] Figure 8 Shows the change of the thermal conductivity of the boron nitride-reinforced inorganic thermal conductive adhesive of Comparative Example 1 to Comparative Example 7 at different M-BN contents. Figure 8It can be seen that as the content of M-BN filler increases, the thermal conductivity of the colloid shows an obvious upward trend. When the filler content reaches 60wt%, the thermal conductivity of the system is significantly increased to 5.24W / (m·K). This result fully demonstrates that the content of M-BN has a significant impact on the thermal conductivity of the system. When the filling amount of M-BN is small, these fillers can be evenly dispersed in the system. However, due to their limited quantity, there is no effective contact and interaction between them. At this time, the main part of the thermal conductive adhesive is still occupied by the modified phosphate resin matrix, and it is difficult to construct an effective thermal conduction path between the fillers. Therefore, in this case, the contribution of the fillers to the thermal conductivity of the whole system is relatively small. However, as the content of M-BN filler further increases, the contact points between them and the modified phosphate resin matrix also increase, and a structure similar to a network or chain is gradually formed inside the thermal conductive adhesive system, that is, an effective thermal conduction chain is formed, constituting a continuous heat flow channel. These channels provide convenient conditions for the transmission of phonons, thus significantly increasing the thermal conductivity of the thermal conductive adhesive system. Especially in the range of 30-50wt% of the filler content, due to the formation of thermal conduction chains and the improvement of heat flow channels, the increase rate of the thermal conductivity is particularly rapid. When the content of M-BN filler increases to the range of 30-50wt%, the thermal conductivity shows a more significant increase. This is because in this stage, a large number of thermal conduction networks begin to form inside the thermal conductive adhesive, and these networks provide a more efficient path for heat transmission. But as the filler content continues to increase, although the thermal conduction network is continuously improved, due to the gradual decrease in the content of the modified phosphate resin matrix, it is difficult to completely fill all the voids between the fillers. This results in a large number of air gaps inside the thermal conductive adhesive, and these air gaps will increase the thermal resistance, thus affecting the heat transmission efficiency. In addition, as the filler content increases, the number of interfaces between the fillers also increases, and these interfaces will become obstacles to heat transmission, that is, the interface thermal resistance will increase. When the influence of the interface thermal resistance exceeds the positive effect of the formation of the thermal conduction network, the thermal conductivity will begin to decrease. Therefore, although increasing the filler content can improve the thermal conductivity to a certain extent, too high a filler content will instead lead to a decrease in the thermal conductivity. It can be seen that in order to obtain the best thermal conductivity, it is necessary to select an appropriate content of M-BN filler. While ensuring the formation of the thermal conduction network, it is also necessary to avoid the generation of excessive air gaps and interface thermal resistance.

[0095] Analysis of the Properties of Phosphate-based Inorganic Thermal Conductive Adhesive

[0096] Figure 9Cross-sectional views of phosphate-based inorganic thermal conductive adhesives with different graphene oxide addition amounts. (a) Phosphate-based inorganic thermal conductive adhesive of Example 1 with a graphene oxide addition amount of 10%. (b) Phosphate-based inorganic thermal conductive adhesive of Example 5 with a graphene oxide addition amount of 50%. (c) Phosphate-based inorganic thermal conductive adhesive of Example 7 with a graphene oxide addition amount of 70%. (d) Partial enlarged view of (c).

[0097] It can be seen from Figure 9 that at low filling amounts (Example 1), the reinforcing effect of graphene oxide on the M-BN reinforced inorganic adhesive is limited. This is because the addition amount of graphene oxide is small and its dispersion degree in the colloid is not high. Therefore, its improvement effect on the overall structure of the colloid is not significant. At this time, the colloid mainly consists of massive M-BN particles, and it is difficult to observe the layered graphene oxide. When the addition amount of graphene oxide gradually increases to 50% (Example 5), it can be clearly observed that the density of the colloid is greatly improved, and the dispersion of graphene oxide in the colloid is also more obvious. This is because as the addition amount of graphene oxide increases, its dispersion in the colloid is improved, so that it can effectively fill the voids between M-BN particles, improving the density and thermal conductivity of the colloid. However, when the addition amount of graphene oxide continues to increase to 70% (Example 7), it can be seen from Figure 9 (c) and 9(d) that graphene oxide has agglomerated. This is because the interaction force between the graphene oxide sheets is enhanced, resulting in poor dispersion of it in the colloid, and then forming aggregates. This agglomeration phenomenon not only destroys the continuity of the colloid but also affects the thermal conductivity and mechanical properties of the colloid. It can be seen that the addition amount of graphene oxide has a significant impact on the structure and properties of the M-BN reinforced inorganic adhesive. At an appropriate addition amount, graphene oxide can effectively improve the density and thermal conductivity of the colloid; but too high an addition amount may lead to the agglomeration of graphene oxide, thus destroying the structural continuity of the colloid.

[0098] Figure 10The X-ray diffraction image of the phosphate-based inorganic thermal conductive adhesive in Example 5 is analyzed, and the following conclusions can be drawn: First, at the diffraction angle of 11.56°, a sharp and narrow crystal peak appears, which is a typical characteristic peak of graphene oxide. The presence of this characteristic peak conclusively proves that graphene oxide has been successfully incorporated into the thermal conductive colloid as a filler. The introduction of graphene oxide can improve the thermal conductivity of the thermal conductive adhesive and effectively enhance the mechanical strength and structural stability of the thermal conductive adhesive through its unique two-dimensional structure. Second, in the low-angle region of the diffraction pattern, an obvious "broad peak" is observed, indicating that the modified phosphate resin matrix has good crystallinity. The morphology and intensity of this "broad peak" are closely related to the crystallinity and lattice structure of the matrix. Its presence indicates that an ordered and stable crystal structure is formed in the matrix during the preparation process, which helps to improve the overall performance of the thermal conductive adhesive. In addition, it is worth noting that at an appropriate addition amount of graphene oxide, graphene oxide does not participate in the curing reaction of the matrix. This finding is crucial because it shows that the addition of graphene oxide does not interfere with the curing process of the matrix and does not have a negative impact on the curing rate or other key properties. This ensures the stable performance of the thermal conductive adhesive during preparation and use. In addition, Figure 10 it can also be seen that there is a diffraction peak at the position of 22.1°, which corresponds to the unreacted phosphate matrix. The high peak at 26.5° is the characteristic peak of M-BN, which further confirms the presence of boron nitride in the thermal conductive adhesive.

[0099] The shear strength of the phosphate-based inorganic thermal conductive adhesive is tested using the same bonding strength test method as that of the boron nitride-reinforced inorganic thermal conductive adhesive. Figure 11 The shear strength changes of the phosphate-based inorganic thermal conductive adhesives in Examples 1 to 7 at different graphene oxide contents are shown, revealing the important influence of graphene oxide on the performance of the thermal conductive adhesive. From Figure 11It can be seen that: First of all, the introduction of graphene oxide has a positive impact on the shear strength of the phosphate-based inorganic thermal conductive adhesive. When the content of graphene oxide is 10-20 wt%, there is a slight increase in the shear strength. This is because a small amount of graphene oxide can fill the tiny voids between M-BN and the matrix in the thermal conductive adhesive, thereby enhancing the interfacial bonding force and the overall toughness of the material. This enhancement enables the thermal conductive adhesive to better resist deformation when subjected to tension, thus increasing the shear strength. As the content of graphene oxide further increases (20 wt%-50 wt%), the shear strength shows an upward trend. This is because within this range, the dispersion of graphene oxide is relatively uniform, and an effective reinforcement network can be formed, further improving the mechanical properties of the thermal conductive adhesive. In addition, graphene oxide itself has high strength and toughness, so as its content increases, the overall mechanical properties of the thermal conductive adhesive are also improved. However, when the content of graphene oxide reaches 50 wt%, the shear strength reaches the maximum value. Subsequently, when the content of graphene oxide continues to increase to 60 wt%-70 wt%, the shear strength decreases instead. This is due to the aggregation of excessive graphene oxide in the thermal conductive adhesive, forming larger aggregates. These aggregates are prone to becoming stress concentration areas when subjected to shear force, resulting in local damage of the thermal conductive adhesive and thus reducing the overall shear strength. In addition, the maximum shear force strength of the phosphate-based inorganic thermal conductive adhesive reaches 4.56 MPa, which is 21.2% higher than that of the pure boron nitride-reinforced inorganic thermal conductive adhesive with a boron nitride addition of 50 wt% (Comparative Example Five). This significant improvement indicates that the introduction of graphene oxide has a significant impact on the shear strength of the thermal conductive adhesive.

[0100] The thermal conductivity of the phosphate-based inorganic thermal conductive adhesive was measured using the same thermal conductivity measurement method as that of the boron nitride-reinforced inorganic thermal conductive adhesive. Figure 12 The changes in the thermal conductivity of the phosphate-based inorganic thermal conductive adhesives of Examples 1 to 7 at different graphene oxide contents are shown. Figure 12It can be seen that in the initial stage when the amount of graphene oxide added is low, the thermal conductivity of the thermally conductive adhesive increases relatively slowly. This is because although the addition of graphene oxide improves the thermal conductivity of the thermally conductive adhesive to a certain extent, the dispersion of graphene oxide is relatively high at this time, and it has not yet formed an effective thermal network with M-BN. However, since the dispersion of graphene oxide in the thermally conductive adhesive is relatively high at this time, it has not yet formed an effective thermal network with modified boron nitride (M-BN), so the improvement of thermal conductivity is not significant. However, as the amount of graphene oxide added gradually increases to the range of 20wt%-50wt%, the situation has changed significantly. At this stage, the amount of graphene oxide added gradually approaches the optimal ratio, so that graphene oxide and M-BN can fully contact and interact with each other, thereby forming a tight and efficient thermal network. The formation of this thermal network greatly promotes the efficiency of heat transfer in the thermally conductive adhesive, resulting in a rapid increase in thermal conductivity. It is particularly noteworthy that when the mass fraction of graphene oxide reaches 50wt%, the thermal conductivity of the thermally conductive adhesive reaches its peak. At this time, the thermal conductivity is as high as 6.29W / (m·K), which is about 4.19 times that of the original modified phosphate resin (the original modified phosphate resin is the modified phosphate resin obtained in Example 1. After measurement, the thermal conductivity of the modified phosphate resin is 1.5W / (m·K)). At the same time, the thermal conductivity is also higher than that of the boron nitride reinforced inorganic thermal conductive adhesive (Comparative Example 6) using only 60wt% M-BN as a single filler. This fully demonstrates that at an appropriate addition amount, graphene oxide plays a positive role in improving the thermal conductivity of the thermally conductive adhesive. However, with the further increase in the amount of graphene oxide added, the thermal conductivity of the thermally conductive adhesive began to show a downward trend. This is because when the graphene oxide content is too high, the graphene oxide hinders the modified phosphate resin matrix from filling the micro-vacancies and destroys the continuity of the thermally conductive adhesive, which in turn hinders the transfer of heat and leads to a decrease in thermal conductivity.

[0101] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A phosphate-based inorganic thermally conductive adhesive, characterized in that: The phosphate-based inorganic thermally conductive adhesive comprises: a modified phosphate resin, a modified boron nitride, and graphene oxide, wherein the modified phosphate resin comprises aluminum dihydrogen phosphate and aluminum oxide, and a boron nitride-enhanced inorganic thermally conductive adhesive is prepared from the modified phosphate resin and the modified boron nitride, wherein the mass ratio of aluminum dihydrogen phosphate to aluminum oxide in the modified phosphate resin is 1:0.5-2, the proportion of the modified boron nitride added to the modified phosphate resin is 10wt%-70wt%, and the proportion of the graphene oxide added to the boron nitride-enhanced inorganic thermally conductive adhesive is 10wt%-70wt%; The modified boron nitride is prepared according to the following steps: boron nitride powder with a particle size of 10 μm is dispersed in a NaOH solution and subjected to ultrasonic treatment, the dispersion is ball-milled, and the mixture after ball milling is washed, filtered, and dried to obtain the modified boron nitride; the graphene oxide is pretreated according to the following steps: the graphene oxide is dispersed in anhydrous ethanol and subjected to ultrasonic treatment, and the graphene oxide is obtained after filtering.

2. The phosphate-based inorganic thermally conductive adhesive according to claim 1, characterized in that: The mass ratio of aluminum dihydrogen phosphate to aluminum oxide in the modified phosphate resin is 1:0.5, 1:1, 1:1.5 or 1:2, the ratio of modified boron nitride added to the modified phosphate resin is 10wt%, 20wt%, 30wt%, 40wt%, 50wt%, 60wt% or 70wt%, and the ratio of graphene oxide added to the boron nitride enhanced inorganic thermal conductive adhesive is 10wt%, 20wt%, 30wt%, 40wt%, 50wt%, 60wt% or 70wt%.

3. The phosphate-based inorganic thermally conductive adhesive according to claim 1, characterized in that: The mass ratio of aluminum dihydrogen phosphate to aluminum oxide in the modified phosphate resin is 1:1, the ratio of modified boron nitride added to the modified phosphate resin is 60wt%, and the ratio of graphene oxide added to the boron nitride enhanced inorganic thermal conductive adhesive is 50wt%.

4. A method for preparing a phosphate-based inorganic thermally conductive adhesive according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: Preparation of modified boron nitride: dispersing boron nitride powder with a particle size of 10 μm in a NaOH solution and performing ultrasonic treatment, ball milling the dispersion, and washing, filtering and drying the ball-milled mixture to obtain modified boron nitride; Preparation of modified phosphate resin: mixing aluminum dihydrogen phosphate and aluminum oxide, grinding, drying, tableting and curing to obtain modified phosphate resin; Preparation of boron nitride enhanced inorganic thermal conductive adhesive: adding modified boron nitride to modified phosphate resin, grinding, mixing and tableting to obtain boron nitride enhanced inorganic thermal conductive adhesive; Pre-treating graphene oxide: dispersing graphene oxide in anhydrous ethanol and performing ultrasonic treatment, and obtaining graphene oxide after filtering; Preparation of phosphate-based inorganic thermally conductive adhesive: pre-treated graphene oxide is mixed with boron nitride-enhanced inorganic thermally conductive adhesive, and after grinding, dispersion and tableting, the phosphate-based inorganic thermally conductive adhesive is obtained by heating and curing.

5. The method for preparing a phosphate-based inorganic thermally conductive adhesive according to claim 4, characterized in that: When preparing modified boron nitride, every 1g of boron nitride powder is dispersed in 30ml of NaOH solution. After ultrasonic treatment for 30 minutes, the dispersion is transferred to a grinding bowl containing zirconium oxide balls and ball-milled for 6 hours. 60g of zirconium oxide balls are used for every 1g of boron nitride powder. The ball-milled mixture is washed, filtered to neutrality, and vacuum dried for 24 hours to obtain modified boron nitride.

6. The method for preparing a phosphate-based inorganic thermally conductive adhesive according to claim 4, characterized in that: When pretreating graphene oxide, 1 g of graphene oxide is dispersed in 100 ml of anhydrous ethanol, ultrasonically treated for 8 hours, and graphene oxide is obtained after vacuum filtration.

7. The method for preparing a phosphate-based inorganic thermally conductive adhesive according to claim 4, characterized in that: When preparing the phosphate-based inorganic thermally conductive adhesive, the pretreated graphene oxide is mixed with the boron nitride-enhanced inorganic thermally conductive adhesive, and after grinding, dispersion and tableting, the phosphate-based inorganic thermally conductive adhesive is cured at 170° C. for 2 hours.

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