Flexible / heat-conducting / wave-absorbing PVA / NMP organic packaging gel and application thereof

Abstract

The invention discloses a flexible / heat-conducting / wave-absorbing PVA / NMP organic packaging gel and application thereof. The preparation method comprises the following steps: constructing PDA coating layers with different thicknesses on the surface of aluminum oxide / boron nitride in a Tris-HCl buffer solution by adopting an in-situ polymerization method; mixing the PDA-Al2O3 filler with an NMP (N-Methyl Pyrrolidone) solvent, and carrying out probe and ultrasonic dispersion to obtain stably dispersed premixed slurry; adding PVA particles into the slurry, stirring until the PVA particles are completely dissolved, and carrying out vacuum defoaming treatment; and carrying out blade coating forming, low-temperature gelation and temperature returning demolding on a PET (Polyethylene Terephthalate) substrate, so as to prepare the PDA-coated Al2O3 / PVA / NMP or PDA-coated BN / PVA / NMP gel. According to the method, the component-process-structure-life quantitative relation model and the acceleration-practical equivalent method are constructed, the attenuation trajectory of the performance along with the working condition and time can be predicted in the material design stage, a rapid type selection rule and a parameter window are formed, and standardized, verifiable and reliable integration of new materials in a target scene is achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of new materials and electronic packaging technology, and particularly relates to a high-performance organic packaging gel and a preparation method and application thereof, and especially relates to an organic gel composite material for flexible electronic devices, which has high thermal conductivity and strong electromagnetic wave absorption function. BACKGROUND

[0002] Flexible electronics technology is accelerating from wearable to conformable, bendable, mass production, and deeply integrating into key scenarios such as health monitoring and tactical communication, becoming the core carrier of the next generation of information systems. Under the guidance of the "double carbon" target, flexible thermal and wave-absorbing materials are listed as key technology directions to improve energy efficiency and ensure electromagnetic compatibility, becoming an important fulcrum for high-quality development of the electronic information industry.

[0003] However, as devices evolve towards high performance and intelligence, the thermal-electromagnetic-mechanical multi-field coupling problem in the packaging process is increasingly prominent, and has become a key bottleneck for system-level integration. The specific performance is as follows: thermal management challenge - under the conditions of high power density and limited space, insufficient heat dissipation induces local overheating, leading to performance degradation and device aging; electromagnetic compatibility challenge - antenna near-field coupling, reflection interference and signal crosstalk are intensified, communication quality and system stability decline; mechanical reliability and environmental adaptability challenge - bending, stretching and temperature and humidity cycling conditions are prone to interface peeling, filler network damage and parameter drift. In summary, thermal-electromagnetic-mechanical triple coupling has become the last inch problem for flexible electronics to move from the laboratory to large-scale application, and is a core technology that must be overcome for China to achieve high-level packaging and industrialization.

[0004] The development of flexible electronic packaging materials is advancing along two main lines, each with its own advantages and boundary conditions. Path one is a silicon-based polymer, metal / ceramic filler composite system. This system has achieved large-scale production in consumer electronics and communication equipment, relying on stable dielectric properties, temperature resistance / aging resistance, mature process, and perfect supply chain, forming a complete product family of thermal pad, gap filling glue, potting glue, thermal gel, absorbing sheet, and shielding sealing strip. The production consistency and delivery stability are good. Limited by the low polarity of Si-O main chain and the scarcity of interface sites, this system lacks interface anchoring and polarization regulation ability, and the construction of designable structures such as orientation, gradient, and microporous structure is limited. In high deformation and ultra-thin form, it is difficult to simultaneously meet multiple service indicators such as high thermal conductivity, strong wave absorption, and bending resistance, which becomes the performance limit and engineering constraint in the next generation of high-integration packaging. Path two is the engineering route of high polymer flexible composite system (such as PU, PVDF, PVA, etc. and thermal / electromagnetic functional fillers). This route is based on excellent flexibility and designable molecular structure, and generally realizes the comprehensive optimization of thermal-electromagnetic-mechanical properties in thin layer form through the triple synergy of thermal conduction network, electromagnetic loss, and structure design. Existing research and applications show that its thermal conductivity can reach 1-15 Wm -1 K -1 , the wave absorption performance is significantly better than the commercial standard (RL<-10 dB), and can maintain structural stability and performance retention under repeated bending and small curvature radius service conditions, showing the adaptation potential in flexible packaging, conformable devices, and ultra-thin modules. However, the performance of this system is highly dependent on high-filled functional fillers, and the matrix mainly bears flexibility and shaping, which leads to a significant performance trade-off between high-filled heat conduction and impedance matching absorption: too high filling is beneficial to heat path connection, but inevitably raises the modulus and hardens the system, while causing impedance mismatch, increased reflection, and increased risk of crosstalk, making it difficult to balance thermal conductivity, absorption, and flexibility. In the actual packaging space with limited thickness and high integration, how to simultaneously unify efficient heat management, excellent electromagnetic protection, and long-term deformation stability constitutes the key bottleneck of current engineering landing.

[0005] To address the above bottleneck, polar organic gel systems provide an underestimated path with both theoretical potential and engineering feasibility. The three-dimensional gel network and polar solvent system have high designability and rich interface sites, which can maintain flexibility and achieve a synergistic balance of thermal conductivity / absorption under high filling conditions: on the one hand, the polar environment and network structure can amplify dipole polarization and interfacial polarization, achieve low reflection of electromagnetic energy dissipation dominated by absorption; on the other hand, the functional groups on the gel molecular chain can significantly improve the dispersion and interfacial coupling strength of the filler, stabilize the thermal / electric conduction channel, and maintain structural integrity in multiple deformation cycles. In addition, polar organic gel systems have good environmental stability in humid heat and oxidation environment, providing a material basis for long-term service of flexible electronics. To avoid the loss mismatch caused by the superposition of high filling thermal / electric conductive fillers and solvent polarization loss, high thermal conductivity / low dielectric fillers should be selected to obtain high thermal conductivity and inhibit excessive electrical loss under high filling. Typical materials include alpha phase aluminum oxide (alpha-Al2O3), silicon nitride (Si3N4), silicon carbide (SiC), aluminum nitride (AlN), hexagonal boron nitride (h-BN) and diamond.

[0006] At the interface and structure design level, enhancing the interfacial coupling between the reinforcing filler and the organic gel matrix is the key to reducing the interfacial thermal resistance, reducing the critical filling amount and avoiding material embrittlement. Inspired by the adhesion of mussels, polydopamine (PDA) modification method has the advantages of green and environmental protection and high efficiency and universality. The PDA surface is rich in hydroxyl and amino groups, which can form dynamic hydrogen bonds with the hydroxyl groups on the PVA molecular chain. Therefore, the thermal / electrically conductive material modified by PDA is equivalent to a molecular rivet of polymer chains to inhibit polymer crosslinking, while providing excellent flexible thermal conductivity and wave absorption performance. At the same time, the dynamic hydrogen bonds formed between PDA and PVA and NMP are beneficial to the excellent steady-state service performance of the polymer under bending, stretching, cold and hot impact. The excellent encapsulation gel can be applied in the packaging of flexible intelligent devices to solve the problems of heat dissipation, electromagnetic interference and deformation. SUMMARY

[0007] The purpose of the present application is to provide an organic gel composite material with high thermal conductivity and strong electromagnetic wave absorption function for flexible electronic devices, and a preparation method and application thereof.

[0008] The present application is realized by the following technical solutions: An organic gel composite material with high thermal conductivity and strong electromagnetic wave absorption function for flexible electronic devices, the preparation stage follows the process of surface modification-slurry homogenization-scratching forming-low temperature gelation, establishing a controllable preparation path of the material.

[0009] (1) Surface modification and dispersion: In situ polymerization was used to construct PDA coating layers of different thicknesses (20-50 nm) on the surfaces of alumina (Al2O3) and boron nitride (BN) in Tris-HCl buffer at pH=8.5 by controlling the dopamine concentration (0.5-2.0 mg / mL) and reaction time (4-12 h). Subsequently, PDA@Al2O3 filler was mixed with NMP solvent at a solid content of 0-50 wt% (the proportion in the gel), and subjected to high-speed shear emulsification (5000-10000 rpm, 10-30 min) and ultrasonic dispersion (600W, 15-30 min) to obtain a stable premixed slurry.

[0010] Coating and Low-Temperature Gelation: PVA particles were added to the above slurry and mechanically stirred in an oil bath at 120 °C for 2–4 h until completely dissolved, followed by vacuum degassing. A doctor blade was used to coat the slurry onto a PET substrate, with the doctor blade gap optimized (100–500 μm) to control the wet film thickness. Subsequently, the wet film was frozen in a low-temperature environment (-40 to 20 °C) for 4–12 h to complete low-temperature confined gelation. Finally, the film was thawed, demolded, and cut to the target size to prepare PDA@Al2O3 / PVA / NMP gel. Al2O3 / PVA / NMP, BN / PVA / NMP, and PDA@BN / PVA / NMP gels were also prepared using a similar process.

[0011] The gel prepared above is used as a packaging material for flexible electronics to solve the problems of thermal buildup, electromagnetic interference, and service deformation in flexible smart devices.

[0012] Beneficial effects (1) Thin-layer material thermal conductivity / wave absorption / flexibility integration: The present invention constructs a molecular rivet-dynamic hydrogen bond composite interface system, and conducts synergistic design around three key channels: phonon conduction, dielectric polarization and stress dissipation. It simultaneously achieves the same direction of improvement of high thermal conductivity, strong wave absorption and excellent flexibility within the scale of thin-layer material, and solves the traditional problem of mutual restraint of performance.

[0013] (2) Simplified preparation process of coating-low temperature gelation: This invention abandons the traditional multi-stage high-energy-consuming process and adopts a two-step method to achieve direct forming of functional slurry into structured gel film on general-purpose equipment. By precisely controlling the rheological parameters and thermodynamic path through windowing, a general scale-up criterion is established to ensure batch-to-batch consistency and quality stability from laboratory to kilogram-level pilot-scale, breaking through the key bottleneck of large-scale preparation.

[0014] (3) Quantitative design and prediction of in-service steady state: In view of the industry pain point that flexible electronics are prone to failure under complex working conditions, the present application takes the service steady state as the starting point, constructs the component-process-structure-life quantitative relationship model and acceleration-practical equivalent method, can predict the performance decay trajectory with working conditions and time in the material design stage, form the rapid selection rule and parameter window, realize the standardized, verifiable and reliable integration of new materials in the target scene. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 Performance graph of PDA@Al2O3 / PVA / NMP gel with different mass fractions of Al2O3 with a size of 200 nm; Figure 2 Performance graph of PDA@Al2O3 / PVA / NMP gel with different mass fractions of Al2O3 with a size of 5 μm; Figure 3 Microwave absorption performance of different molding temperatures; Figure 4 Real object graph of large size PDA@Al2O3 / PVA / NMP gel sheet; Figure 5 PDA@Al2O3 / PVA / NMP gel multi-variation and bearing graph. DETAILED DESCRIPTION

[0016] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the following will be further illustrated by combining specific examples, but these examples are not used to limit the present application.

[0017] Example 1 (1) Surface modification and dispersion: using in-situ polymerization method, in Tris-HCl buffer solution with pH=8.5, the concentration of dopamine is 0.1 mg / mL, a 20 nm PDA coating layer is constructed on the surface of aluminum oxide, and the reaction time is 12 h. Subsequently, the PDA@Al2O3 filler is mixed with 20 ml NMP solvent at a solid content of 0-50wt% (proportion in the gel), treated by high-speed shearing emulsification (8000 rpm, 3 min) and ultrasonic dispersion (600 W, 10 min), to obtain a stable dispersed premix slurry.

[0018] (2) Doctor blading and low-temperature gelation: 5.14 g PVA particles were added into the above slurry, and the mixture was mechanically stirred at 120 °C for 2 h until the PVA was completely dissolved, and then vacuum degassing was performed. Doctor blading was performed on a PET substrate, and the doctor blade gap (100-500 pm) was optimized to control the wet film thickness. Subsequently, the wet film was frozen at -40 °C for 4-12 h to complete the low-temperature confined gelation, and finally the gel was demolded after warming up, and the PDA@Al2O3 / PVA / NMP gel was prepared by cutting to the target size.

[0019] Example 2 (1) Surface modification and dispersion: A 20-nm PDA coating layer was constructed on the BN surface in a Tris-HCl buffer solution at pH 8.5 using an in-situ polymerization method, and the dopamine concentration was 0.1 mg / mL. The reaction time was 12 h. Subsequently, the PDA@BN filler was mixed with 20 ml of NMP solvent at a solid content (proportion in the gel) of 0-50 wt%, and then treated by high-speed shearing emulsification (8000 rpm, 3 min) and ultrasonic dispersion (600 W, 10 min) to obtain a stable pre-mixed slurry.

[0020] (2) Doctor blading and low-temperature gelation: 5.14 g PVA particles were added into the above slurry, and the mixture was mechanically stirred at 120 °C for 2 h until the PVA was completely dissolved, and then vacuum degassing was performed. Doctor blading was performed on a PET substrate, and the doctor blade gap (100-500 pm) was optimized to control the wet film thickness. Subsequently, the wet film was frozen at -40 °C for 4-12 h to complete the low-temperature confined gelation, and finally the gel was demolded after warming up, and the PDA@BN / PVA / NMP gel was prepared by cutting to the target size.

[0021] The above-prepared gel was subjected to performance testing: (1) As can be seen from Figure 1 , when the mass ratio of PDA to Al2O3 is 1:20, the mass fraction (proportion in the gel) of PDA@Al2O3 is 30%, 40%, and 50%, respectively, and the size is 200 nm, the microwave absorption performance is good, and the reflection loss is -17.03 dB, -22.37 dB, and -54.77 dB, respectively, and the thermal conductivity is 0.3889 W m -1 K -1 , 0.476 W m -1 K -1 , and 0.5582 W m -1 K -1 . Moreover, it has good flexibility and can be repeatedly bent and stretched.

[0022] (2) As can be seen from Figure 2As can be seen, when the mass ratio of PDA to Al2O3 is 1:20, and the mass fraction of PDA@Al2O3 (as a percentage in the gel) is 30%, 40%, and 50%, respectively, and the size is 5 μm, it exhibits microwave absorption properties with reflection losses of -18.94 dB, -27.35 dB, and -47.85 dB, respectively, and a thermal conductivity of 0.442 W / m². -1 K -1 0.531 W m -1 K -1 0.701 W m -1 K -1 It also has excellent flexibility and can be repeatedly bent and stretched.

[0023] (3) From Figure 3 As can be seen, when the mass ratio of PDA to BN is 1:20, the mass fraction of BN (in the gel) is 5%, the size is 200 nm, and the molding temperatures are 20 ℃, 5 ℃, -5 ℃, and -10 ℃, respectively, exhibiting microwave absorption properties. The reflection losses are -20.21 dB, -21.25 dB, -51.28 dB, and -19.10 dB, respectively. The thermal conductivity is 4.15 W / m². -1 K -1 4.81 Wm -1 K -1 5.12 W m -1 K -1 5.23 W m -1 K -1 .

[0024] Figure 4 and Figure 5 As can be seen, the prepared gel has excellent flexibility and can be repeatedly bent and stretched.

[0025] The material prepared by this invention exhibits excellent comprehensive properties: First, it has good formability and scalability, and the process is suitable for subsequent large-scale preparation; Second, it has outstanding flexibility and durability, and can withstand 1,000 repeated bending without damage, and can still fully rebound after 1,000 cycles of stretching at 200% tensile rate, showing stable cyclic reversible elasticity; Third, it has reliable mechanical toughness, and can support a 1 kg weight without breaking at a thickness of 2 mm.

[0026] use: 1. Thermally conductive and electromagnetic shielding pads for flexible electronic devices Application scenario: In the narrow space of folding phones, wearable devices (such as smartwatches, health monitoring patches), high-density integrated chips and circuits are both heat sources and electromagnetic interference sources. Make such a gel into a film or gasket, paste it between the chip and the shell, or as the bottom layer of the circuit board. It can not only efficiently conduct the heat of the chip to the metal shell or a larger area heat sink, preventing the device from overheating, but also absorb the electromagnetic clutter inside and outside the device, improving signal integrity and anti-interference capability. In the laboratory prototype of a flexible heart rate monitoring patch, a similar gel is used as the interface layer between the sensor and the skin, which not only solves the problem of local overheating during long-term wear, but also shields external electromagnetic signals from interfering with weak bioelectric signals.

[0027] 2. "Three-in-one" functional layer of UAV / robot FPC Application scenario: There are a large number of flexible printed circuits (FPC) that need to be repeatedly bent inside the joints and gimbals of UAVs and robots, and the main control chip and motor drive chip on them generate a lot of heat, and the entire system is in a complex electromagnetic environment. Coating or molding the gel directly on specific areas of the FPC, it can play three roles at the same time: flexible support layer, heat conducting layer and wave absorbing layer. This simplifies the design, reduces the weight, and improves the reliability of the FPC during dynamic bending. Such a gel gasket is used between the flight control mainboard of a quadcopter UAV and the carbon fiber fuselage, effectively reducing the temperature of the main processor during high-speed operation, and reducing the electromagnetic noise of the video transmission system, improving the video transmission quality.

[0028] 3. Interface management and safety protection of high-power-density battery pack Application scenario: In the battery pack of new energy vehicles and energy storage systems, the cells will generate a lot of heat and electromagnetic interference during charging and discharging. Fill the gel in the gap between cylindrical or square cells. Its flexibility can buffer the volume expansion of the cells during charging and discharging; its heat conductivity helps to balance the temperature between cells and prevent thermal runaway; its wave absorption can absorb high-frequency switching noise inside the battery pack to prevent interference with the BMS (Battery Management System). In the laboratory battery module test, compared with the traditional silicone heat-conducting pad, the gel used as a gap-filling material reduces the maximum temperature difference inside the module, and significantly improves the stability of BMS signal acquisition.

[0029] The gel of the present application is used for packaging flexible electronics, which realizes the reduction of device operating temperature, effective suppression of electromagnetic interference, and overall packaging consistency meets the requirements of engineering application. This scheme effectively solves the key technical problems of flexible electronic heat accumulation, electromagnetic interference and service deformation performance decay.

[0030] It should be noted that the above examples are only used as enumeration of embodiments of the present application, and are not used to limit the present application, and equivalent replacements without creative labor can fall into the protection scope of the present application without deviating from the spirit and scope of the present application.

Claims

1. A method for preparing an organic gel composite material for flexible electronic devices, possessing both high thermal conductivity and strong electromagnetic wave absorption capabilities, characterized in that, Includes the following steps: (1) Surface modification and dispersion: PDA coating layers of different thicknesses were constructed on the surface of alumina / boron nitride in Tris-HCl buffer using in-situ polymerization. PDA@Al2O3 filler was mixed with NMP solvent and then emulsified and ultrasonically dispersed to obtain a stable premixed slurry. (2) Coating and low-temperature gelation: PVA particles are added to the above slurry and stirred until completely dissolved. Vacuum degassing treatment is performed. Coating is performed on a PET substrate, followed by freeze gelation and demolding at room temperature to prepare PDA@Al2O3 / PVA / NMP or PDA@BN / PVA / NMP gel.

2. The preparation method according to claim 1, characterized in that, In step (1), the pH of the Tris-HCl buffer is 8.

5.

3. The preparation method according to claim 1, characterized in that, In step (1), the dopamine concentration is 0.5-2.0 mg / mL, the construction reaction time is 4-12 h, and the thickness of the PDA coating layer is 20-50 nm.

4. The preparation method according to claim 1, characterized in that, In step (1), the content of PDA@Al2O3 filler in the gel is 0-50 wt%.

5. The preparation method according to claim 1, characterized in that, In step (1), the high-speed shear emulsification speed is 5000-10000 rpm and the time is 10-30 min; the ultrasonic power is 600 W and the time is 15-30 min.

6. The preparation method according to claim 1, characterized in that, In step (2), the ratio of the amount of PVA particles added to NMP is 1:

4.

7. The preparation method according to claim 1, characterized in that, In step (2), the wet film thickness is 100-500 μm.

8. The preparation method according to claim 1, characterized in that, In step (2), the temperature for cryogelation is -40℃ to 20℃, and the time is 4-12 h.

9. A PDA@Al2O3 / PVA / NMP or PDA@BN / PVA / NMP gel prepared by the preparation method according to any one of claims 1-8.

10. The application of the PDA@Al2O3 / PVA / NMP or PDA@BN / PVA / NMP gel of claim 9 in the preparation of electronic packaging materials.

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