Preparation method and application of oriented polyurethane composite material with high thermal conductivity

Abstract

The invention discloses a preparation method and application of a high-thermal-conductivity oriented polyurethane composite material. The preparation method comprises the following steps: introducing hydroxylated boron nitride into a polyurethane matrix to obtain a polyurethane mixture solution; and then the vertically-oriented high-thermal-conductivity composite material is obtained through the processes of layer-by-layer blade coating, curing, hot pressing and re-hot pressing. The filler is oriented in a film coating, hot pressing and re-hot pressing manner, so that the filler constructs an efficient oriented heat-conducting network in a matrix, and the heat conductivity coefficient of the material is remarkably improved without increasing the content of the heat-conducting filler. By utilizing reversible dissociation of dynamic oxime ammonia ester bonds and through a hot pressing process, composite material layer sheets can realize molecular-level fusion. In addition, the dissociation of oxime carbamate bonds improves the fluidity of the material and the wettability with a heterogeneous interface; the dissociated isocyanate group reacts with reactive hydrogen, so that the adhesion to a heterogeneous interface is enhanced, the interface thermal resistance is reduced, the overall heat conduction performance is improved, and the preparation method has a wide application prospect.

Description

Technical Field

[0001] This invention belongs to the field of thermally conductive composite materials technology, and specifically relates to a method for preparing a high thermal conductivity oriented polyurethane composite material and its application. Background Technology

[0002] As semiconductor devices evolve towards miniaturization, high integration, and high power density, their heat generation increases dramatically. Thermal failure has become the primary problem hindering the performance and lifespan of microelectronic packaged devices. The development of thermal interface materials has become a technological bottleneck restricting the improvement of computing speed, functionality, and reliability of electronic chips, as well as the extension of their service life.

[0003] Traditional thermal interface materials are mainly composed of a polymer matrix and thermally conductive fillers. Commercially available thermal interface materials typically have a thermal conductivity of no more than 5-10 W / m·K, which is insufficient to meet the heat dissipation requirements of rapidly developing high-power electronic devices. Researchers have discovered a strategy to achieve high thermal conductivity in the orientation direction of composite materials by controlling the orientation of anisotropic fillers. Orientation maximizes the advantages of anisotropic fillers in high thermal conductivity directions, enabling the composite material to achieve ultra-high thermal conductivity in a specific direction. While the orientation-guided thermal network can effectively improve the material's thermal conductivity, the material's modulus also increases, resulting in lower adhesion strength to the heterogeneous interface, hindering interfacial contact and leading to high interfacial thermal resistance. Furthermore, traditional hot-pressed orientation materials cannot establish molecular-level connections between layers, preventing the formation of a cohesive thermal pathway and affecting thermal conductivity. In addition, traditional thermal interface materials are cross-linked by chemical bonds, making them infusible and insoluble, difficult to process and recycle, negatively impacting the environment and economy. Therefore, in practical applications, how to endow thermal interface materials with high thermal conductivity, low interfacial thermal resistance, and reprocessable characteristics is an important problem that urgently needs to be solved. Summary of the Invention

[0004] To address the aforementioned problems, the present invention aims to provide a method for preparing a high thermal conductivity oriented polyurethane composite material and its application. The method achieves the construction of an outward-oriented heat-conducting network under hot-pressing conditions. Furthermore, in practical applications, the reversible bonds impart reprocessing properties to the material, and the reduced contact thermal resistance at the interface improves heat transfer efficiency.

[0005] To address the problems in the existing technology, the technical solution adopted by this invention is as follows:

[0006] A method for preparing a high thermal conductivity oriented polyurethane composite material, wherein the high thermal conductivity oriented polyurethane composite material comprises polycaprolactone, isophorone diisocyanate, dimethylene diphenyl isocyanate, dimethylglyoxime, boron nitride, and a ball milling modifier; the preparation method includes the following steps:

[0007] S1. Preparation of hydroxylated boron nitride:

[0008] Boron nitride and ball milling modifier are placed in a ball mill and ball milled at a speed of 500-1500 r / min for 6-12 h. The ball-milled boron nitride powder is then washed with deionized water and anhydrous ethanol and dried to obtain hydroxylated boron nitride.

[0009] S2. Preparation of reversible polyurethane blends:

[0010] Polycaprolactone at 100-120 o After dehydration treatment at temperature C, the temperature is lowered to 60-80°C. o C, then add isophorone diisocyanate and dimethylene diphenyl isocyanate, react for 60-120 min to obtain polyurethane prepolymer; disperse hydroxylated boron nitride into polyurethane prepolymer, then add dimethylglyoxime dissolved in anhydrous tetrahydrofuran, vacuum mix and disperse, and degas to obtain polyurethane mixture.

[0011] S3. Preparation of Oriented Polyurethane Composites:

[0012] The polyurethane mixture was placed in a coating machine, and a layer was uniformly coated at 80°C and cured. Another layer was coated and cured again. This process was repeated until the mixture was completely coated into a thin sheet. The sheet was then placed in a vacuum drying oven at 80°C for 24 hours to obtain a reversible polyurethane composite material based on dynamic oxime ester bonds. The reversible polyurethane composite material based on dynamic oxime ester bonds was cut, stacked, and placed between two PET films. It was then hot-pressed into a pre-oriented polyurethane sheet with a thickness of 2 mm. The pre-oriented polyurethane sheet was then cut into square sheets with a side length of 50 mm and stacked. The sheets were then placed in a tablet press and pressure was applied. The sheets were hot-pressed for 5-10 minutes to obtain a high thermal conductivity oriented polyurethane composite material with a thickness of 50 mm.

[0013] Preferably, the ball milling modifier in S1 is one or more of sodium hydroxide, sucrose, and boric acid; under mechanical ball milling, hydroxyl groups are introduced onto the surface of boron nitride, enabling the boron nitride powder to react with the isocyanate groups in the polyurethane to form urethane bonds.

[0014] Preferably, the boron nitride in S1 has a particle size range of 1-30 μm.

[0015] Preferably, the mass ratio of soft segments to hard segments of the polyurethane prepolymer in S2 is (50-80):(20-50).

[0016] Preferably, the pressure of the tablet press in S3 is 5-15 MPa.

[0017] Preferably, the concentration of the polyurethane mixture in S2 ranges from 1 to 1.2 g / cm³. 3 .

[0018] Preferably, the coating machine in S2 applies the coating 5-10 times.

[0019] Preferably, the curing temperature in S3 is 80℃, the curing time is 30min, the hot pressing temperature is 70-100℃, and the tableting time is 5-10min.

[0020] Beneficial effects:

[0021] This invention achieves simultaneous exfoliation and surface hydroxylation of boron nitride through mechanical ball milling and a ball milling modifier, improving the interfacial compatibility between the filler and the matrix. By introducing oxime ester bonds, molecular-level connections can be formed between the stacked materials during hot pressing, creating a complete thermal conductivity pathway, increasing the in-plane thermal conductivity from 2.11 W / (m·K) to 3.82 W / (m·K). The introduction of dynamic bonds enhances the adhesion between the material and the heterogeneous interface, increasing the adhesion strength from 1.21 MPa to 2.15 MPa, resulting in a tighter connection and effectively reducing interfacial thermal resistance. An oriented boron nitride thermally conductive network is constructed under simple hot pressing conditions. Furthermore, in practical applications, the reversible bonds impart reprocessing properties to the material, allowing the bonding of two substrates without any external pressure, effectively filling interfacial voids and improving heat transfer efficiency. The dynamic oxime ester bonds endow the thermal interface material with reusability, improving its utilization efficiency. Attached Figure Description

[0022] Figure 1 This is a flowchart of sucrose-assisted ball milling modification of boron nitride;

[0023] Figure 2 This is a diagram of the self-healing properties of reversible polyurethane materials. Detailed Implementation

[0024] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough understanding of the disclosure of the present invention.

[0025] Example 1

[0026] (1) Place 10g of boron nitride and 32g of sucrose in a ball mill. The ball milling speed is 1200r / min, and the ball milling time is 12h. The ball-milled boron nitride powder is washed three times with deionized water and three times with anhydrous ethanol. o Drying at C for 24 h yields hydroxylated boron nitride.

[0027] (2) Place 18.48 g of polycaprolactone diol in a three-necked flask and heat at 120 °C. o Vacuum stirring at C for 2 hours to remove water; temperature reduced to 50°C. oAfter step C, add 8.45g IPDI and 0.5g PM200, with a soft-to-hard segment mass ratio of 67:33, and then heat to 80°C. o React at C for 2 hours to synthesize isocyanate-terminated polyurethane prepolymers. Weigh 4g of hydroxylated boron nitride and 16g of polyurethane prepolymer into a mixing bottle and disperse evenly. Then add 1.21g of dimethylglyoxime dissolved in 8.48ml of anhydrous tetrahydrofuran, mix and disperse under vacuum, and degas for half an hour to obtain a polyurethane mixture.

[0028] (3) The polyurethane mixture was placed in a scraper and coated at 80°C at a uniform speed, followed by curing. Another layer was then coated and cured at 80°C for 30 minutes. This process was repeated until the mixture was completely coated into a thin sheet. The sheet was then placed in a vacuum drying oven at 80°C for 24 hours to obtain a reversible polyurethane composite material based on dynamic oxime ester bonds. The reversible polyurethane composite material based on dynamic oxime ester bonds was cut, stacked, and placed between two PET films. It was then placed at 100°C. o Preheat in a tablet press for 5 minutes, then hot-press at 10 MPa for 15 minutes to obtain a 2 mm thick composite sheet. Cut the sheet into small square sheets with a side length of 50 mm, stack 20 layers of oriented sheets, and hot-press again to obtain a 50 mm thick high thermal conductivity oriented composite material.

[0029] A 50mm thick high thermal conductivity oriented composite material was stretched at a speed of 20mm / min until it broke. Figure 2 As shown, after 12 hours at room temperature, the fracture surface almost completely disappeared, indicating that the composite material has excellent self-healing properties. This is because the complexation rate of hydroxyl and boric acid groups on adjacent polymer chains is extremely fast. When a large number of hydroxyl groups complex with boric acid groups, the hydrogel heals, allowing the material to be perfectly repaired within seconds of contact. These results demonstrate that the composite material possesses excellent self-healing properties.

[0030] Example 2:

[0031] (1) Place 10g of boron nitride and 32g of sucrose in a ball mill. The ball milling speed is 1200r / min, and the milling time is 12h. The ball-milled boron nitride powder is washed three times with deionized water and anhydrous ethanol. o Drying at C for 24 h yields hydroxylated boron nitride.

[0032] (2) Place 18.48 g of polycaprolactone diol in a three-necked flask and heat at 120 °C. o Vacuum stirring to remove water for 2 hours; temperature reduced to 50°C. o After step C, add 8.45g IPDI and 0.5g PM200, with a soft-to-hard segment mass ratio of 67:33, and then heat to 80°C. oReact at C for 2 hours to synthesize a polyurethane prepolymer with terminal isocyanates. Weigh 6g of hydroxylated boron nitride and 14g of polyurethane prepolymer into a mixing bottle and disperse evenly. Then add 1.06g of dimethylglyoxime dissolved in 7.42ml of anhydrous tetrahydrofuran, mix and disperse under vacuum, and degas for half an hour to obtain a polyurethane mixture.

[0033] (3) The polyurethane mixture was placed in a scraper and coated at 80°C at a uniform speed, followed by curing. Another layer was then coated and cured at 80°C for 30 minutes. This process was repeated until the mixture was completely coated into a thin sheet. The sheet was then placed in a vacuum drying oven at 80°C for 24 hours to obtain a reversible polyurethane composite material based on dynamic oxime ester bonds. The reversible polyurethane composite material based on dynamic oxime ester bonds was cut, stacked, and placed between two PET films. It was then placed at 100°C. o Preheat in a tablet press for 5 minutes, then hot-press at 10 MPa for 15 minutes to obtain a 2 mm thick composite sheet. Cut the sheet into small square sheets with a side length of 50 mm, stack 20 layers of oriented sheets, and hot-press again to obtain a 50 mm thick high thermal conductivity oriented composite material.

[0034] Example 3:

[0035] (1) Place 5g of graphene and 16g of sucrose in a ball mill. The ball milling speed is 1200r / min, and the ball milling time is 12h. The ball-milled boron nitride powder is washed three times with deionized water and three times with anhydrous ethanol. o Hydroxy-based graphene was obtained by drying at C for 24 hours.

[0036] (2) Place 18.48 g of polycaprolactone diol in a three-necked flask and heat at 120 °C. o Vacuum stirring to remove water for 2 hours; temperature reduced to 50°C. o After step C, add 8.45g IPDI and 0.5g PM200, with a soft-to-hard segment mass ratio of 67:33, and then heat to 80°C. o React at C for 2 hours to synthesize a polyurethane prepolymer with terminal isocyanates. Weigh 4g of hydroxylated graphene and 16g of polyurethane prepolymer into a mixing bottle and disperse evenly. Then add 1.21g of dimethylglyoxime dissolved in 8.48ml of anhydrous tetrahydrofuran, mix and disperse under vacuum, and degas for half an hour to obtain a polyurethane mixture.

[0037] (3) The polyurethane mixture was placed in a scraper and coated at 80°C at a uniform speed, followed by curing. Another layer was then coated and cured at 80°C for 30 minutes. This process was repeated until the mixture was completely coated into a thin sheet. The sheet was then placed in a vacuum drying oven at 80°C for 24 hours to obtain a reversible polyurethane composite material based on dynamic oxime ester bonds. The reversible polyurethane composite material based on dynamic oxime ester bonds was cut, stacked, and placed between two PET films. It was then placed at 100°C. o Preheat in a tablet press for 5 minutes, then hot-press at 10 MPa for 15 minutes to obtain a 2 mm thick composite sheet. Cut the sheet into small square sheets with a side length of 50 mm, stack 20 layers of oriented sheets, and hot-press again to obtain a 50 mm thick high thermal conductivity oriented composite material.

[0038] Comparative Example 1

[0039] (1) Place 5g of boron nitride powder and 16g of sucrose in a ball mill. The ball milling speed is 1200r / min, and the milling time is 12h. The ball-milled boron nitride powder is washed three times with deionized water and three times with anhydrous ethanol. o Drying at C for 24 h yields hydroxylated boron nitride.

[0040] (2) Place 18.48 g of polycaprolactone diol in a three-necked flask and heat at 120 °C. o Vacuum stirring to remove water for 2 hours; temperature reduced to 50°C. o After step C, add 8.45g IPDI and 0.5g PM200, with a soft-to-hard segment mass ratio of 67:33, and then heat to 80°C. o React at C for 2 hours to synthesize a polyurethane prepolymer with terminal isocyanates. Weigh 4 g of hydroxylated boron nitride and 16 g of polyurethane prepolymer into a mixing bottle and disperse evenly. Then add 1.21 g of dimethylglyoxime dissolved in 8.48 ml of anhydrous tetrahydrofuran, mix and disperse under vacuum, and place the reaction mixture into a polytetrafluoroethylene mold and vacuum dry at 80 °C for 24 hours to obtain a reversible polyurethane composite material based on dynamic oxime urethane bonds.

[0041] Comparative Example 2

[0042] (1) Place 5g of boron nitride powder and 16g of sucrose in a ball mill. The ball milling speed is 1200r / min, and the milling time is 12h. The ball-milled boron nitride powder is washed three times with deionized water and anhydrous ethanol. o Drying at C for 24 h yields hydroxylated boron nitride.

[0043] (2) Place 18.48 g of polycaprolactone diol in a three-necked flask and heat at 120 °C. o Vacuum stirring to remove water for 2 hours; temperature reduced to 50°C. oAfter step C, add 8.45g IPDI and 0.5g PM200, with a soft-to-hard segment mass ratio of 67:33, and then heat to 80°C. o Reacting at C for 2 hours, a polyurethane prepolymer with terminal isocyanates was synthesized. 4g of hydroxylated boron nitride and 16g of the polyurethane prepolymer were weighed into a mixing bottle and dispersed evenly. Butylene glycol and polycaprolactone triol were then added, and the mixture was vacuum-mixed and dispersed. The reaction mixture was placed in a doctor blade coater and pre-oriented by layer-by-layer coating at 80°C. After the mixture was completely coated into a film, it was placed in a vacuum drying oven and vacuum-dried at 80°C for 24 hours to obtain the polyurethane composite material.

[0044] (3) Place the dried and cured polyurethane composite material between two PET films and place it at 100°C. o A pressure of 10 MPa is applied in a tablet press of C, and hot-pressed for 10 min to obtain a composite sheet with a thickness of 2 mm. The sheet is then cut into small square sheets with a side length of 50 mm. 20 layers of oriented sheets are stacked and hot-pressed again to obtain a 50 mm thick high thermal conductivity oriented composite material.

[0045] Comparative Example 3

[0046] (1) Place 18.48 g of polycaprolactone diol in a three-necked flask and heat at 120 °C. o Vacuum stirring to remove water for 2 hours; temperature reduced to 50°C. o After step C, add 8.45g IPDI and 0.5g PM200, with a soft-to-hard segment mass ratio of 67:33, and then heat to 80°C. o React at C for 2 hours to synthesize isocyanate-terminated polyurethane prepolymer. Weigh 4g of hydroxylated boron nitride and 16g of polyurethane prepolymer into a mixing bottle and disperse evenly. Then add 1.21g of dimethylglyoxime dissolved in 8.48ml of anhydrous tetrahydrofuran, mix and disperse under vacuum, and degas for half an hour to obtain a polyurethane filler mixture.

[0047] (2) The polyurethane mixture was placed in a coater and coated at 80°C at a uniform speed, followed by curing. Another layer was then coated and cured at 80°C for 30 minutes. This process was repeated until the mixture was completely coated into a thin sheet. The sheet was then placed in a vacuum drying oven at 80°C for 24 hours to obtain a reversible polyurethane composite material based on dynamic oxime ester bonds. The reversible polyurethane composite material based on dynamic oxime ester bonds was cut, stacked, and placed between two PET films. It was then placed in a 100°C container. o Preheat in a tablet press for 5 minutes, then hot-press at 10 MPa for 15 minutes to obtain a 2 mm thick composite sheet. Cut the sheet into small square sheets with a side length of 50 mm, stack 20 layers of oriented sheets, and hot-press again to obtain a 50 mm thick high thermal conductivity oriented composite material.

[0048] Performance testing

[0049] In-plane thermal conductivity test:

[0050] The in-plane thermal conductivity of composite materials is determined by the equation Calculate, where α, C and C represent the thermal diffusivity, density, and specific heat capacity of the composite film, respectively. The in-plane thermal diffusivity (α) of the composite material was measured using the laser flash method. C is calculated according to the equation... Sure, Corresponding to the volume content of boron nitride filler, C h-BN and C PU Differential scanning calorimetry was used for determination.

[0051] Test methods and calculation formulas for self-healing efficiency:

[0052] The self-healing efficiency of composite materials is based on the equation Calculate, where η and ε r and ε o These correspond to self-healing efficiency, elongation at break after repair, and elongation at break before repair, respectively. The elongation at break (ε) of the composite material was measured using the axial tensile method.

[0053] Test methods and calculation formulas for bond strength:

[0054] The bond strength of composite materials is based on the equation The calculations are performed, where τ, σ, and S correspond to the bonding strength, shear force, and bonding area of ​​the composite material to the aluminum plate, respectively. σ and S are determined using the single-lap bonding strength test method.

[0055] Various performance tests were conducted on Examples 1-3 and Comparative Examples 1-3, and the test results are shown in Table 1.

[0056] Table 1. Statistical table of performance test results for Examples 1-3 and Comparative Examples 1-3

[0057]

[0058] As shown in Table 1, Example 2 increased the mass ratio of boron hydroxynitride filler compared to Example 1. It was found that the higher the mass ratio of boron hydroxynitride filler, the more complete the thermal conductivity pathway was constructed and the higher the thermal conductivity. However, a higher filler ratio would lead to filler agglomeration, which would reduce the self-healing efficiency and bonding strength.

[0059] In Example 3, the filler was changed from boron hydroxynitride to hydroxylated graphene. It was found that the composite material with hydroxylated graphene as filler had a higher thermal conductivity than the composite material with boron hydroxynitride as filler at the same mass ratio of boron hydroxynitride, but the bond strength was reduced.

[0060] Compared with the unmodified Example 1, it was found that the composite material with modified hydroxylated boron nitride as filler had higher thermal conductivity than the unmodified boron nitride at the same mass ratio, and the bonding strength was higher due to the introduction of dynamic bonds.

[0061] Comparative Example 2, which did not undergo an orientation step, showed that the thermal conductivity of the oriented composite material was significantly higher than that of the unoriented composite material at the same mass ratio.

[0062] In Comparative Example 3, the chain extender was changed from dimethylglyoxime to butanediol. It was found that the composite material with introduced oxime ester bonds had higher thermal conductivity and significantly improved bonding strength compared with the material without introduced oxime ester bonds at the same mass ratio.

[0063] The above description is merely a preferred embodiment of the present invention. It should be noted that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. Moreover, after reading the contents of the present invention, those skilled in the art can make various modifications or alterations to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A method for preparing a high thermal conductivity oriented polyurethane composite material, characterized in that, The high thermal conductivity oriented polyurethane composite material comprises polycaprolactone, isophorone diisocyanate, dimethylene diphenyl isocyanate, dimethylglyoxime, boron nitride, and a ball milling modifier; the preparation method includes the following steps: S1. Preparation of hydroxylated boron nitride: Boron nitride and ball milling modifier are placed in a ball mill and ball milled at a speed of 500-1500 r / min for 6-12 h. The ball-milled boron nitride powder is then washed with deionized water and anhydrous ethanol and dried to obtain hydroxylated boron nitride. S2. Preparation of reversible polyurethane blends: Polycaprolactone at 100-120 o After dehydration treatment at temperature C, the temperature is lowered to 60-80°C. o C, then add isophorone diisocyanate and dimethylene diphenyl isocyanate, react for 60-120 min to obtain polyurethane prepolymer; disperse hydroxylated boron nitride into polyurethane prepolymer, then add dimethylglyoxime dissolved in anhydrous tetrahydrofuran, vacuum mix and disperse, and degas to obtain polyurethane mixture. S3. Preparation of Oriented Polyurethane Composites: The polyurethane mixture was placed in a coating machine, and a layer was uniformly coated at 80°C and cured. Another layer was coated and cured again. This process was repeated until the mixture was completely coated into a thin sheet. The sheet was then placed in a vacuum drying oven at 80°C for 24 hours to obtain a reversible polyurethane composite material based on dynamic oxime ester bonds. The reversible polyurethane composite material based on dynamic oxime ester bonds was cut, stacked, and placed between two PET films. It was then hot-pressed into a pre-oriented polyurethane sheet with a thickness of 2 mm. The pre-oriented polyurethane sheet was then cut into square sheets with a side length of 50 mm and stacked. The sheets were then placed in a tablet press and pressure was applied. The sheets were hot-pressed for 5-10 minutes to obtain a high thermal conductivity oriented polyurethane composite material with a thickness of 50 mm.

2. The method for preparing a high thermal conductivity oriented polyurethane composite material according to claim 1, characterized in that: In S1, the ball milling modifier is one or more of sodium hydroxide, sucrose, and boric acid. Under mechanical ball milling, hydroxyl groups are introduced onto the surface of boron nitride, enabling the boron nitride powder to react with the isocyanate groups in the polyurethane to form urethane bonds.

3. The method for preparing a high thermal conductivity oriented polyurethane composite material according to claim 1, characterized in that: The boron nitride particle size range described in S1 is 1-30 mm.

4. The method for preparing a high thermal conductivity oriented polyurethane composite material according to claim 1, characterized in that: The mass ratio of soft segments to hard segments in the polyurethane prepolymer in S2 is (50-80):(20-50).

5. The method for preparing a high thermal conductivity oriented polyurethane composite material according to claim 1, characterized in that: The pressure of the tablet press in S3 is 5-15 MPa.

6. The method for preparing a high thermal conductivity oriented polyurethane composite material according to claim 1, characterized in that: The concentration range of the polyurethane mixture in S2 is 1-1.2 g / cm³. 3 .

7. The method for preparing a high thermal conductivity oriented polyurethane composite material according to claim 1, characterized in that: The S3 coating machine requires 5-10 coats.

8. The method for preparing a high thermal conductivity oriented polyurethane composite material according to claim 1, characterized in that: The curing temperature in S3 is 80℃, the curing time is 30min, the hot pressing temperature is 70-100℃, and the tableting time is 5-10min.

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