Preparation method of heat-conducting liquid crystal polymer film and heat-conducting liquid crystal polymer film

Abstract

The embodiment of the present application relates to the technical field of liquid crystal polymer film, and particularly discloses a preparation method of a heat-conducting liquid crystal polymer film, which can be used for heat-conducting lines or substrates in power devices, etc., comprising providing a liquid crystal polymer and a first solvent, adding the liquid crystal polymer into the first solvent to form a liquid crystal polymer solution, providing boron nitride fillers and a dispersing agent, wherein the boron nitride fillers are prepared by mixing a first boron nitride and a second boron nitride according to a preset mass ratio and are modified, the particle diameter of the first boron nitride is smaller than that of the second boron nitride, adding the boron nitride fillers and the dispersing agent into the liquid crystal polymer solution, stirring and mixing to obtain an initial slurry, coating the initial slurry on a substrate, and performing temperature curing after casting the initial slurry into a wet film to obtain the heat-conducting liquid crystal polymer film and stripping it from the surface of the substrate, wherein the boron nitride fillers are prepared by using boron nitride with different particle diameters, so that the performance of the prepared heat-conducting liquid crystal polymer film can be improved.

Description

Technical Field

[0001] This invention relates to the field of liquid crystal polymer film technology, and in particular to a method for preparing a thermally conductive liquid crystal polymer film and the thermally conductive liquid crystal polymer film itself. Background Technology

[0002] Thermally conductive liquid crystal polymer films, as a type of high-performance special engineering plastic film, possess excellent mechanical properties, dimensional stability, and electrical properties, as well as a high in-plane thermal conductivity, making them suitable for fabricating thermally conductive circuits and substrates for electronic devices.

[0003] Currently, there are reports on technologies for preparing thermally conductive films by compositing boron nitride with liquid crystal polymers. For example, by adding boron nitride to liquid crystal polymers through solution blending, the thermal conductivity of the prepared composite thermally conductive film is significantly improved in both the vertical and horizontal directions. However, existing technologies still have the following shortcomings: (1) Thermal conductivity is still insufficient: The highest thermal conductivity of boron nitride and liquid crystal polymer composite films reported so far is only 2.63 W / (m·K). Although this level has improved to some extent, it is still far from the requirement of thermal conductivity ≥5 W / (m·K) or even higher for high-performance thermally conductive substrates (such as power device packaging, 5G base station heat dissipation substrates, etc.).

[0004] (2) Insufficient dispersion of fillers and insufficient construction of thermal conductive networks: It is difficult for single large-diameter or single small-diameter boron nitride fillers to achieve uniform dispersion and effective overlap in liquid crystal polymer matrix at the same time. Although small-diameter fillers are easy to disperse, they are difficult to form long-range thermal conductive pathways. Although large-diameter fillers are conducive to the construction of thermal conductive networks, they are prone to agglomeration and sedimentation. Summary of the Invention

[0005] In view of the above problems, the present invention provides a method for preparing a thermally conductive liquid crystal polymer film and a thermally conductive liquid crystal polymer film, which overcomes the above problems.

[0006] This invention provides a method for preparing a thermally conductive liquid crystal polymer film, comprising providing a liquid crystal polymer and a first solvent, adding the liquid crystal polymer to the first solvent to form a liquid crystal polymer solution, providing boron nitride filler and a dispersant, wherein the boron nitride filler is prepared by mixing and modifying a first boron nitride and a second boron nitride in a preset mass ratio, the particle diameter of the first boron nitride being smaller than the particle diameter of the second boron nitride, adding the boron nitride filler and dispersant to the liquid crystal polymer solution, stirring and mixing to obtain an initial slurry, providing a substrate, coating the initial slurry onto the substrate, and casting the initial slurry into a wet film, heating and curing the wet film to obtain the thermally conductive liquid crystal polymer film, and peeling the thermally conductive liquid crystal polymer film off the surface of the substrate.

[0007] In one alternative embodiment, the step of providing boron nitride filler further includes: A boron nitride solid, a modifier, and a second solvent are provided. The boron nitride solid and the modifier are added to the second solvent to obtain a mixed solution. The mixed solution is stirred and reacted at a preset temperature for a preset time to obtain a modified boron nitride solution. The modified boron nitride solution is filtered to obtain initial modified boron nitride. The initial modified boron nitride is washed and dried to obtain boron nitride filler.

[0008] In one optional embodiment, the boron nitride solid is prepared by mixing a first boron nitride and a second boron nitride in a preset ratio, the modifier is at least one of a silane coupling agent and a titanate coupling agent, the second solvent is an anhydrous solvent, and the particle diameter of the first boron nitride is smaller than the particle diameter of the second boron nitride.

[0009] In one optional embodiment, the step of adding boron nitride filler and dispersant to the liquid crystal polymer solution and stirring to obtain an initial slurry further includes: adding liquid crystal polymer solution, boron nitride filler and dispersant to a container and stirring to obtain a mixture; transferring the mixture to a dispersion plate for dispersion; and placing the dispersed mixture in a vacuum degassing machine for vacuum degassing to obtain the initial slurry.

[0010] In one alternative embodiment, the step of coating the initial slurry onto the substrate and casting the slurry into a wet film further includes: providing a coating machine, the coating machine including a slit coating head, through which the initial slurry is coated onto the substrate.

[0011] In one optional embodiment, the step of heating and curing the wet film to obtain a thermally conductive liquid crystal polymer film further includes: placing the wet film in an oven, heating the wet film to a first preset temperature at a first preset heating rate, and holding it at that temperature for a first preset time to obtain an initially cured liquid crystal polymer film, and heating the initially cured liquid crystal polymer film to a second preset temperature at a second preset heating rate, and holding it at that temperature for a second preset time to obtain the thermally conductive liquid crystal polymer film.

[0012] In one alternative embodiment, the first solvent is a polar aprotic solvent, and / or the polar aprotic solvent is at least one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, or γ-butyrolactone.

[0013] In one alternative embodiment, the dispersant is at least one of a silane coupling agent and a titanate coupling agent.

[0014] In one alternative embodiment, the step of peeling the thermally conductive liquid crystal polymer film from the surface of the substrate further includes: peeling the thermally conductive liquid crystal polymer film from the surface of the substrate, and winding up the substrate and the thermally conductive liquid crystal polymer film respectively.

[0015] According to another aspect of the present invention, a thermally conductive liquid crystal polymer film is also provided, which is prepared by the above method.

[0016] The beneficial effects of this invention's embodiments: Unlike existing technologies, this invention provides a method for preparing a thermally conductive liquid crystal polymer film, comprising providing a liquid crystal polymer and a first solvent, adding the liquid crystal polymer to the first solvent to form a liquid crystal polymer solution, providing boron nitride filler and a dispersant, wherein the boron nitride filler is prepared by mixing and modifying a first boron nitride and a second boron nitride in a preset mass ratio, the particle diameter of the first boron nitride being smaller than the particle diameter of the second boron nitride, adding the boron nitride filler and dispersant to the liquid crystal polymer solution, stirring and mixing to obtain an initial slurry, providing a substrate, and then... A slurry is applied to a substrate and cast into a wet film. The wet film is then heated and cured to obtain the thermally conductive liquid crystal polymer film. The thermally conductive liquid crystal polymer film is then peeled off from the surface of the substrate. The boron nitride filler is prepared and modified using a first boron nitride and a second boron nitride in a predetermined ratio. The particle diameter of the first boron nitride is smaller than that of the second boron nitride. By using boron nitride with different particle diameters to prepare the boron nitride filler, the first boron nitride can fill the gaps between the second boron nitrides, making the thermally conductive liquid crystal polymer film more dense and improving its performance. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0018] Figure 1 This is a flowchart of a method for preparing a thermally conductive liquid crystal polymer film according to an embodiment of the present invention; Figure 2 This is a flowchart of the preparation of boron nitride filler in the preparation method of thermally conductive liquid crystal polymer film according to an embodiment of the present invention; Figure 3 This is a flowchart of the preparation of the initial slurry in the method for preparing a thermally conductive liquid crystal polymer film according to an embodiment of the present invention.

[0019] Figure 4This is a flowchart of the initial slurry coating process in the preparation method of the thermally conductive liquid crystal polymer film according to an embodiment of the present invention; Figure 5 This is a flowchart of the process of heating and curing a wet film in the preparation method of a thermally conductive liquid crystal polymer film according to an embodiment of the present invention; Figure 6 These are test graphs of the thermal diffusivity and thermal conductivity of the thermally conductive liquid crystal polymer film according to an embodiment of the present invention; Figure 7 These are test diagrams of the tensile strength and elongation at break of the thermally conductive liquid crystal polymer film according to an embodiment of the present invention. Figure 8 This is a test diagram of the linear thermal expansion coefficient of the thermally conductive liquid crystal polymer film according to an embodiment of the present invention; Figure 9 These are test graphs of the dielectric constant and dielectric loss of the thermally conductive liquid crystal polymer film according to an embodiment of the present invention; Figure 10 These are the thermal expansion coefficient test results of the thermally conductive liquid crystal polymer films in comparative experiments one, two, and three of the present invention. Figure 11 These are the thermal expansion coefficient test results of thermally conductive liquid crystal polymer films in Experiments 1, 2, and 3 of this invention. Detailed Implementation

[0020] To facilitate understanding of the present invention, a more detailed description is provided below with reference to the accompanying drawings and specific embodiments. It should be noted that when an element is described as being "fixed to" another element, it can be directly on the other element, or one or more intermediate elements may exist between them. When an element is described as being "connected to" another element, it can be directly connected to the other element, or one or more intermediate elements may exist between them. The terms "vertical," "horizontal," "left," "right," and similar expressions used in this specification are for illustrative purposes only.

[0021] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "and / or" as used in this specification includes any and all combinations of one or more of the associated listed items.

[0022] Thermally conductive liquid crystal polymer (LCP) films are used to fabricate thermally conductive circuits and substrates for electronic devices. However, current methods for preparing LCP films typically use boron nitride fillers with only one particle diameter. LCP films prepared using a single boron nitride filler have numerous interface defects, affecting various properties of the LCP film. To improve the performance of LCP films, this invention provides a method for preparing thermally conductive LCP films by using boron nitride fillers formulated with boron nitride of different particle diameters, resulting in LCP films with better performance.

[0023] Please see Figure 1 This invention provides a method for preparing a thermally conductive liquid crystal polymer film, comprising: Step S1: Provide the liquid crystal polymer and the first solvent; Liquid crystal polymers are high-performance special engineering plastics that combine the fluidity of liquids with the orderliness of crystals. Liquid crystal polymers have good heat resistance, mechanical properties and dielectric properties. The first solvent is a polar aprotic solvent. Polar aprotic solvents refer to a class of organic solvents with strong polarity but without hydrogen atoms directly bonded to oxygen or nitrogen in their molecular structure. The polar aprotic solvent is at least one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide or γ-butyrolactone. The polar aprotic solvent is used to dissolve the soluble liquid crystal polymer.

[0024] Step S2: Add the liquid crystal polymer to the first solvent to form a liquid crystal polymer solution; When the liquid crystal polymer is added to the first solvent, the molecular chains of the liquid crystal polymer will be broken down under the action of the first solvent and evenly distributed in the first solvent.

[0025] Step S3: Provide boron nitride filler and dispersant, wherein the boron nitride filler is prepared and modified by mixing first boron nitride and second boron nitride in a preset mass ratio, and the particle diameter of the first boron nitride is smaller than the particle diameter of the second boron nitride. Boron nitride filler is used to enhance the thermal conductivity of liquid crystal polymer films. Boron nitride filler itself has high thermal conductivity and excellent electrical insulation properties. The dispersant is at least one of silane coupling agent and titanate coupling agent. The dispersant is used to improve the compatibility between boron nitride filler and liquid crystal polymer, and can also prevent the agglomeration of boron nitride particles in boron nitride filler, so that the boron nitride particles are uniformly dispersed in the liquid crystal polymer solution. Agglomeration of boron nitride particles will affect the performance of the prepared liquid crystal polymer film.

[0026] Step S4: Add boron nitride filler and dispersant to the liquid crystal polymer solution, and stir to mix to obtain an initial slurry; Step S5: Provide a substrate, apply the initial slurry onto the substrate, and cast the initial slurry into a wet film; The substrate is used to support the initial slurry and usually needs to be able to withstand the subsequent drying temperature and be easy to separate from the film after curing. The substrate can be a polymer film, such as PET (polyethylene terephthalate), polyimide film, etc., or a glass plate or steel strip, as well as a metal plate, foil or ceramic substrate. Casting refers to the process of spreading liquid slurry into a uniform thin layer on the surface of the substrate. Relying on the gravity and fluidity of the slurry itself, it automatically spreads into a continuous and uniform liquid film on the surface of the substrate. Under stable slurry supply and substrate movement conditions, a wet film with a relatively uniform thickness can be obtained. Furthermore, by controlling parameters such as casting speed and slurry viscosity, the orientation degree of molecular chains and fillers can be adjusted.

[0027] Step S6: The wet film is heated and cured to obtain the thermally conductive liquid crystal polymer film; During the formation of a wet film, the molecular chains of liquid crystal polymers arrange themselves in an orderly manner. However, these chains are still mobile, and this ordered structure is unstable. Heating and curing initiate a cross-linking reaction in the liquid crystal polymers, forming chemical bonds between the molecular chains. The reactive groups of the liquid crystal polymers are gradually consumed during curing, which can be monitored using equipment such as differential scanning calorimetry. Curing is considered complete when the reaction conversion rate reaches a predetermined value. However, in actual production, curing is usually set with preset temperatures and preset times.

[0028] Step S7: Peel the thermally conductive liquid crystal polymer film from the surface of the substrate.

[0029] Depending on the production scale and process requirements, different peeling methods can be used. For example, manual peeling involves using a blade or tweezers to lift a corner of the film and then manually peeling it off the substrate. Mechanical peeling can also be used, where the substrate with the film is placed on a peeling device, and the film is separated from the substrate under tension by the traction force and angle change of the peeling roller. Alternatively, continuous peeling (such as etching processes) can be used, where, on a roll-to-roll production line, the cured film and the substrate pass through a peeling unit, and the film and substrate are automatically separated by precisely controlled winding tension and then wound up separately.

[0030] Please see Figure 2 In some embodiments, the step of providing boron nitride filler further includes: Step S31: Provide boron nitride solid, modifier, and second solvent; The boron nitride solid is prepared by mixing a first boron nitride and a second boron nitride in a preset ratio, wherein the particle diameter of the first boron nitride is smaller than that of the second boron nitride. Large-diameter boron nitride layers inevitably leave gaps, which the small-diameter boron nitride can fill, increasing the contact points between filler particles. Mixing boron nitride particles of different sizes and morphologies in the formulation can improve the fluidity of the slurry, making it easier to coat. A reasonable particle size distribution helps the filler disperse more evenly in the matrix, reducing interface defects and voids caused by poor compatibility between large-diameter fillers and the liquid crystal polymer matrix, thereby helping to maintain or even improve the mechanical properties of the film. The modifier is at least one of a silane coupling agent and a titanate coupling agent. The second solvent is an anhydrous solvent. In some water-sensitive polymer systems or reactions, trace amounts of water may participate in the reaction as impurities, leading to the formation of byproducts or a decrease in the performance of the target product. Using an anhydrous solvent ensures that the reaction proceeds as expected.

[0031] Step S32: Add the boron nitride solid and the modifier to the second solvent to obtain a mixed solution; Dissolve silane coupling agents or titanate coupling agents in an anhydrous solvent to disperse them in a molecular state, which facilitates subsequent reactions.

[0032] Step S33: Stir the mixed solution and react the mixed solution at a preset temperature for a preset time to obtain a modified boron nitride solution; Modification involves introducing active groups onto the surface of boron nitride. The alkoxy groups at the ends of silane coupling agents hydrolyze in the system with trace amounts of water or under heating conditions to generate reactive silanol groups. The hydrolyzed silanol groups undergo a dehydration condensation reaction with the hydroxyl groups on the surface of boron nitride, firmly grafting organic functional groups onto the surface of boron nitride. The mechanism of action of titanate coupling agents is similar, introducing active groups onto the surface of boron nitride through chemical reactions.

[0033] Step S34: Filter the modified boron nitride solution to obtain initial modified boron nitride; At this point, the modified boron nitride solution still contains unreacted coupling agent molecules, oligomers generated by the self-condensation of the coupling agent, a second solvent, and possible byproducts. The filtration operation utilizes the size difference between the boron nitride solid particles and the liquid components, using filter media to retain the solids while allowing the liquid to pass through, thereby achieving solid-liquid separation.

[0034] Step S35: Wash and dry the initially modified boron nitride to obtain boron nitride filler.

[0035] Washing is to remove residual coupling agents and other substances from the surface of the initially modified boron nitride. The washing solvent can be ethanol or deionized water, and the washing can be performed multiple times.

[0036] Please see Figure 3 In some embodiments, the step of adding boron nitride filler and dispersant to the liquid crystal polymer solution and stirring to obtain an initial slurry further includes: Step S41: Add liquid crystal polymer solution, boron nitride filler and dispersant to a container and stir to mix to obtain a mixture; Under the shear force of stirring, the boron nitride filler will undergo initial orientation along the flow direction, laying the foundation for a more ordered arrangement structure during subsequent casting and film formation. This is beneficial for constructing in-plane thermal conductivity pathways. The coupling agent can connect the boron nitride filler and the liquid crystal polymer, effectively reducing interfacial thermal resistance and allowing heat to be transferred more smoothly from the liquid crystal polymer to the highly thermally conductive boron nitride filler, fully leveraging the thermal conductivity enhancement effect of boron nitride.

[0037] Step S42: Transfer the mixture to a dispersion disc for dispersion; After the mixture enters the dispersion disk area, the dispersion disk rotates at high speed, and the mixture is efficiently dispersed under the strong shear force, impact force and turbulence generated by the high speed rotation.

[0038] Step S43: Place the dispersed mixture in a vacuum degassing machine for vacuum degassing to obtain the initial slurry.

[0039] Vacuum degassing is used to remove air bubbles from the slurry, preventing them from forming surface defects such as pinholes and pits after subsequent coating and curing. Vacuum degassing ensures the density and appearance quality of the film. The presence of air bubbles can cause local dielectric instability in the prepared thermally conductive liquid crystal polymer film, affecting high-frequency signal transmission. Vacuum degassing ensures the uniformity of dielectric properties. Air bubbles, as stress concentration points, reduce the mechanical strength of the film. Removing air bubbles helps improve the tensile strength and toughness of the film. Air bubbles can also cause changes in the volume of the slurry, resulting in uneven wet film thickness during coating. After degassing, the slurry density is uniform, which can better control the thickness consistency of the final film.

[0040] Please see Figure 4 In some embodiments, the step of coating the initial slurry onto a substrate and casting the slurry into a wet film further includes: Step S51: Provide a coating machine, the coating machine including a slit coating head; The slit coating head, through a precise slit gap, can stably extrude various slurries ranging from low to high viscosity. The slit coating head can coat a wet film with uniform thickness, and the thickness deviation can be controlled within a very small range. Furthermore, due to the closed liquid supply system and precise flow channel design of the coating machine, coating with a slit coating head can effectively reduce the mixing of impurities and avoid the generation of air bubbles, resulting in a smoother surface of the coated wet film.

[0041] Step S52: Apply the initial slurry onto the substrate through the slit coating head.

[0042] The degassed and homogenized composite precursor slurry is quantitatively and uniformly transferred to the substrate surface using a coating machine to form a liquid wet film with precisely controllable thickness. Under constant pressure, the initial slurry flows out uniformly through a slit-type coating head, while the substrate moves at a uniform speed and smoothly under the drive system, allowing the flowing slurry to spread on the substrate surface. During the process of the slurry flowing out of the slit and being dragged to form a film, the slurry is subjected to a continuous and controllable shear force. This shear force causes the molecular chains of the liquid crystal polymer and the boron nitride filler inside the initial slurry to align in an orderly manner along the extension direction, which is beneficial for building a more regular thermal conductivity path.

[0043] Please see Figure 5 In some embodiments, the step of heating and curing the wet film to obtain a thermally conductive liquid crystal polymer film further includes: Step S61: Place the wet film in an oven; Heating initiates the curing and cross-linking reaction of the liquid crystal polymer, ultimately forming a solid liquid crystal polymer film. Heating in an oven allows the solvent to evaporate fully, preventing residues in the final film and avoiding defects such as bubbles and pinholes, thus ensuring the film's density and performance stability.

[0044] Step S62: Heat the wet film to a first preset temperature at a first preset heating rate and keep it at that temperature for a first preset time to obtain an initially cured thermally conductive liquid crystal polymer film; In the first stage, a temperature typically lower than the melting point or crosslinking initiation temperature of the liquid crystal polymer is used to allow the polar aprotic solvent in the wet film to evaporate slowly. The first preset temperature holding time can prevent the solvent from rapidly vaporizing, which could cause defects such as bubbling and pinholes in the film, thus ensuring the film's density.

[0045] Step S63: The initially cured liquid crystal polymer film is heated to a second preset temperature at a second preset heating rate and held at that temperature for a second preset time to obtain the thermally conductive liquid crystal polymer film.

[0046] The second preset temperature usually reaches or exceeds the curing temperature of the liquid crystal polymer, which promotes the full reaction of the reactive groups on the liquid crystal polymer molecular chain to form a highly cross-linked three-dimensional network structure, which can give the film excellent heat resistance, mechanical strength and dimensional stability. The second preset temperature is maintained to ensure that the polymerization reaction is complete.

[0047] In some implementations, the step of peeling the thermally conductive liquid crystal polymer film from the substrate surface further includes: The thermally conductive liquid crystal polymer film is peeled off from the surface of the substrate, the substrate is removed by an etching process, and the thermally conductive liquid crystal polymer film is wound up and collected.

[0048] To facilitate understanding of the inventive concept of this invention, the inventors conducted experimental comparisons on the preparation of thermally conductive liquid crystal polymer films, as detailed below: Experiment 1: Provide liquid crystal polymer and first solvent; The liquid crystal polymer is added to the first solvent to form a liquid crystal polymer solution, wherein the liquid crystal polymer solution is; 50g of boron nitride filler and 2.5g of dispersant silane coupling agent are provided, wherein the particle diameter of the first boron nitride is 0.5μm, the particle diameter of the second boron nitride is 10μm, and the mass ratio of the first boron nitride to the second boron nitride is 3:7.

[0049] 50g of boron nitride filler was added to 1000g of the liquid crystal polymer solution, and the mixture was stirred and mixed in a stirred tank and then transferred to a dispersion plate to disperse the solution. The stirring speed was set to 1200 rpm, the dispersion plate speed was set to 1500 rpm, and the stirring time was 90 min. The dispersed mixture was placed in a vacuum degassing machine for vacuum degassing. The air bubbles in the mixture were removed by degassing under reduced pressure (-85 kPa) for 40 min. A substrate is provided, the initial slurry is coated onto the substrate, and the initial slurry is cast into a wet film with a thickness of 50 μm. The wet film is heated and cured to obtain the liquid crystal polymer film, wherein the first heating rate is 0.5℃ / min, the heating termination temperature is 150℃, the first holding time is 1 hour, the second heating rate is 2℃ / min, the heating termination temperature is 290℃, the second holding time is 1 hour, and the film is cooled at a rate of 1℃ / min, with a cooling termination temperature of 60℃. The liquid crystal polymer film is peeled off from the surface of the substrate to obtain a thermally conductive liquid crystal polymer film.

[0050] Experiment 2: Provide liquid crystal polymer and first solvent; The liquid crystal polymer is added to the first solvent to form a liquid crystal polymer solution, wherein the liquid crystal polymer solution is; 50g of boron nitride filler and 2.5g of dispersant silane coupling agent are provided, wherein the particle diameter of the first boron nitride is 0.5μm, the particle diameter of the second boron nitride is 10μm, and the mass ratio of the first boron nitride to the second boron nitride is 4:6.

[0051] 50g of boron nitride filler was added to 1000g of the liquid crystal polymer solution, and the mixture was stirred and mixed in a stirred tank and then transferred to a dispersion plate to disperse the solution. The stirring speed was set to 1200 rpm, the dispersion plate speed was set to 1500 rpm, and the stirring time was 90 min. The dispersed mixture was placed in a vacuum degassing machine for vacuum degassing. The air bubbles in the mixture were removed by degassing under reduced pressure (-85 kPa) for 40 min. A substrate is provided, the initial slurry is coated onto the substrate, and the initial slurry is cast into a wet film with a thickness of 50 μm. The wet film is heated and cured to obtain the liquid crystal polymer film, wherein the first heating rate is 0.5℃ / min, the heating termination temperature is 150℃, the first holding time is 1 hour, the second heating rate is 2℃ / min, the heating termination temperature is 290℃, the second holding time is 1 hour, and the film is cooled at a rate of 1℃ / min, with a cooling termination temperature of 60℃. The liquid crystal polymer film is peeled off from the surface of the substrate to obtain a thermally conductive liquid crystal polymer film.

[0052] Experiment 3: Provide liquid crystal polymer and first solvent; The liquid crystal polymer is added to the first solvent to form a liquid crystal polymer solution, wherein the liquid crystal polymer solution is; 50g of boron nitride filler and 2.5g of dispersant silane coupling agent are provided, wherein the particle diameter of the first boron nitride is 0.5μm, the particle diameter of the second boron nitride is 10μm, and the mass ratio of the first boron nitride to the second boron nitride is 5:5.

[0053] 50g of boron nitride filler was added to 1000g of the liquid crystal polymer solution, and the mixture was stirred and mixed in a stirred tank and then transferred to a dispersion plate to disperse the solution. The stirring speed was set to 1200 rpm, the dispersion plate speed was set to 1500 rpm, and the stirring time was 90 min. The dispersed mixture was placed in a vacuum degassing machine for vacuum degassing. The air bubbles in the mixture were removed by degassing under reduced pressure (-85 kPa) for 40 min. A substrate is provided, the initial slurry is coated onto the substrate, and the initial slurry is cast into a wet film with a thickness of 50 μm. The wet film is heated and cured to obtain the liquid crystal polymer film, wherein the first heating rate is 0.5℃ / min, the heating termination temperature is 150℃, the first holding time is 1 hour, the second heating rate is 2℃ / min, the heating termination temperature is 290℃, the second holding time is 1 hour, and the film is cooled at a rate of 1℃ / min, with a cooling termination temperature of 60℃. The liquid crystal polymer film is peeled off from the surface of the substrate to obtain a thermally conductive liquid crystal polymer film.

[0054] Comparative Experiment 1: The liquid crystal polymer is added to the first solvent to form a liquid crystal polymer solution, wherein the liquid crystal polymer solution is; The liquid crystal polymer solution was stirred and mixed in a stirred tank and then transferred to a dispersion plate to disperse it to obtain an initial solution. The stirring speed was set to 1200 rpm, the dispersion plate speed was set to 1500 rpm, and the stirring time was 90 min. The dispersed initial solution was placed in a vacuum degassing machine for vacuum degassing. The air bubbles in the mixed solution were removed by degassing under reduced pressure (-85 kPa) for 40 min. A substrate is provided, the initial slurry is coated onto the substrate, and the initial slurry is cast into a wet film with a thickness of 50 μm. The wet film is heated and cured to obtain the liquid crystal polymer film, wherein the first heating rate is 0.5℃ / min, the heating termination temperature is 150℃, the first holding time is 1 hour, the second heating rate is 2℃ / min, the heating termination temperature is 290℃, the second holding time is 1 hour, and the film is cooled at a rate of 1℃ / min, with a cooling termination temperature of 60℃. The liquid crystal polymer film is peeled off from the surface of the substrate to obtain a thermally conductive liquid crystal polymer film.

[0055] Comparative Experiment 2: Provide liquid crystal polymer and first solvent; The liquid crystal polymer is added to the first solvent to form a liquid crystal polymer solution, wherein the liquid crystal polymer solution is; The product contains 50g of boron nitride filler and 2.5g of dispersant silane coupling agent, wherein the boron nitride filler contains only boron nitride with a particle diameter of 10μm.

[0056] 50g of boron nitride filler was added to 1000g of the liquid crystal polymer solution, and the mixture was stirred and mixed in a stirred tank and then transferred to a dispersion plate to disperse the solution. The stirring speed was set to 1200 rpm, the dispersion plate speed was set to 1500 rpm, and the stirring time was 90 min. The dispersed mixture was placed in a vacuum degassing machine for vacuum degassing. The air bubbles in the mixture were removed by degassing under reduced pressure (-85 kPa) for 40 min. A substrate is provided, the initial slurry is coated onto the substrate, and the initial slurry is cast into a wet film with a thickness of 50 μm. The wet film is heated and cured to obtain the liquid crystal polymer film, wherein the first heating rate is 0.5℃ / min, the heating termination temperature is 150℃, the first holding time is 1 hour, the second heating rate is 2℃ / min, the heating termination temperature is 290℃, the second holding time is 1 hour, and the film is cooled at a rate of 1℃ / min, with a cooling termination temperature of 60℃. The liquid crystal polymer film is peeled off from the surface of the substrate to obtain a thermally conductive liquid crystal polymer film.

[0057] Comparative Experiment 3: Provide liquid crystal polymer and first solvent; The liquid crystal polymer is added to the first solvent to form a liquid crystal polymer solution, wherein the liquid crystal polymer solution is; 50g of boron nitride filler and 2.5g of dispersant silane coupling agent are provided, wherein the boron nitride filler contains only first boron nitride with a particle diameter of 0.5μm.

[0058] 50g of boron nitride filler was added to 1000g of the liquid crystal polymer solution, and the mixture was stirred and mixed in a stirred tank and then transferred to a dispersion plate to disperse the solution. The stirring speed was set to 1200 rpm, the dispersion plate speed was set to 1500 rpm, and the stirring time was 90 min. The dispersed mixture was placed in a vacuum degassing machine for vacuum degassing. The air bubbles in the mixture were removed by degassing under reduced pressure (-85 kPa) for 40 min. A substrate is provided, the initial slurry is coated onto the substrate, and the initial slurry is cast into a wet film with a thickness of 50 μm. The wet film is heated and cured to obtain the liquid crystal polymer film, wherein the first heating rate is 0.5℃ / min, the heating termination temperature is 150℃, the first holding time is 1 hour, the second heating rate is 2℃ / min, the heating termination temperature is 290℃, the second holding time is 1 hour, and the film is cooled at a rate of 1℃ / min, with a cooling termination temperature of 60℃. The liquid crystal polymer film is peeled off from the surface of the substrate to obtain a thermally conductive liquid crystal polymer film.

[0059] In the comparative experiments, no boron nitride filler was added during the preparation process of Comparative Experiment 1, only boron nitride filler modified with boron nitride particles with a diameter of 10 μm was added in Comparative Experiment 2, and only boron nitride filler modified with boron nitride particles with a diameter of 0.5 μm was added in Comparative Experiment 3. To illustrate the performance of the liquid crystal polymer films prepared by different preparation methods, the applicant tested the relevant performance parameters of the liquid crystal polymer films prepared by Experiments 1, 2, and 3 and Comparative Experiments 1, 2, and 3.

[0060] Please see Figure 6 , Figure 6 The graphs show the thermal diffusivity and thermal conductivity of the thermally conductive liquid crystal polymer film in this invention embodiment. Thermal diffusivity measures the rate at which a material transmits temperature changes, while thermal conductivity measures a material's ability to conduct heat; it reflects how much heat can pass through per unit time under a stable temperature difference. Figure 6 It can be seen that the thermal diffusivity and thermal conductivity of liquid crystal polymer films prepared with boron nitride filler are greater than those prepared without boron nitride filler. Furthermore, the thermal conductivity and thermal diffusivity of liquid crystal polymer films prepared with boron nitride filler prepared by modifying boron nitride with different particle diameters according to a preset ratio are greater than those prepared with boron nitride filler prepared by modifying boron nitride with a single particle diameter. The thermal conductivity can be increased by up to 12.5 times, and the thermal diffusivity can be increased by up to 17.5 times.

[0061] Please see Figure 7 , Figure 7 This diagram shows the tensile strength and elongation at break test results of the thermally conductive liquid crystal polymer film according to an embodiment of the present invention. Tensile strength is the maximum tensile force that a material can withstand per unit area before breaking; it measures the strength of the material. A higher tensile strength value indicates a stronger material that is more difficult to break. Elongation at break is the percentage of total elongation relative to the original length when the material breaks; it measures the plasticity of the material. A higher elongation at break value indicates a more flexible material with better ductility during stretching. Figure 7 It can be seen that the tensile strength and elongation at break of the thermally conductive liquid crystal polymer film prepared by adding boron nitride with different particle diameters and preparing it according to a preset ratio are reduced to a certain extent, but the tensile strength can be maintained above 80 MPa. That is, while maintaining a high thermal conductivity, it has a high tensile strength, which can meet the requirements of roll-to-roll production.

[0062] Please see Figure 8 , Figure 8This is a test graph of the linear thermal expansion coefficient of the thermally conductive liquid crystal polymer film according to an embodiment of the present invention. The thermal expansion coefficient is a physical parameter that measures the expansion and contraction of a material's length or volume when the temperature changes. A large thermal expansion coefficient indicates that the material's length and volume change drastically when the temperature changes, while a small thermal expansion coefficient indicates that the material's length and volume change only slightly when the temperature changes. Figure 8 It can be seen that the thermal expansion coefficient of the thermally conductive liquid crystal polymer film prepared by adding boron nitride with different particle diameters and preparing it according to a preset ratio is reduced to a certain extent and can be kept below 18 ppm / ℃. This indicates that the volume or length of the prepared thermally conductive liquid crystal polymer film changes little when the temperature changes.

[0063] Please see Figure 9 , Figure 9 This diagram shows the dielectric constant and dielectric loss test results of the thermally conductive liquid crystal polymer film according to an embodiment of the present invention. The dielectric constant measures the material's ability to store charge in an electric field; the dielectric loss measures the degree to which the material loses energy due to heat generation in an alternating electric field. A smaller value indicates more ideal insulation performance and higher signal transmission fidelity. Figure 9 It can be seen that the dielectric constant and dielectric loss of the thermally conductive liquid crystal polymer film prepared by modifying boron nitride filler with different particle diameters according to a preset ratio are significantly reduced. This indicates that when the thermally conductive liquid crystal polymer film prepared by modifying boron nitride filler with different particle diameters according to a preset ratio is used in electronic devices, it can achieve better signal integrity.

[0064] Please see Figure 10 and Figure 11 , Figure 10 The graph shows the test results of the thermal expansion coefficient of the liquid crystal polymer film in comparative experiments one, two, and three of this invention. Figure 10 The slope of the line represents the coefficient of thermal expansion of the thermally conductive liquid crystal polymer films prepared in comparative experiments one, two, and three. Figure 11 The graphs show the test results of the thermal expansion coefficient of the thermally conductive liquid crystal polymer film in Experiments 1, 2, and 3 of this invention. Figure 11 The slope of the line represents the coefficient of thermal expansion of the thermally conductive liquid crystal polymer films prepared in experiments one, two, and three. The coefficient of thermal expansion is used to measure the degree to which a material expands or contracts in size when its temperature changes. Figure 10 and Figure 11The thermally conductive liquid crystal polymer film prepared by modifying boron nitride fillers with different particle diameters according to a preset ratio has a smaller coefficient of thermal expansion. This indicates that the degree of expansion or contraction of its size when the temperature changes is less than that of the thermally conductive liquid crystal polymer film prepared without boron nitride fillers or the thermally conductive liquid crystal polymer film prepared by modifying boron nitride fillers with a single particle diameter. It also indicates that its dimensional stability is better.

[0065] This invention provides a method for preparing a thermally conductive liquid crystal polymer film, comprising providing a liquid crystal polymer and a first solvent, adding the liquid crystal polymer to the first solvent to form a liquid crystal polymer solution, providing boron nitride filler and a dispersant, wherein the boron nitride filler is prepared by mixing and modifying a first boron nitride and a second boron nitride in a preset mass ratio, the particle diameter of the first boron nitride being smaller than the particle diameter of the second boron nitride, adding the boron nitride filler and dispersant to the liquid crystal polymer solution, stirring and mixing to obtain an initial slurry, providing a substrate, and coating the initial slurry onto the substrate, and... The initial slurry is cast into a wet film, and the wet film is heated and cured to obtain the thermally conductive liquid crystal polymer film. The thermally conductive liquid crystal polymer film is then peeled off from the surface of the substrate. The boron nitride filler is prepared and modified using a first boron nitride and a second boron nitride in a preset ratio. The particle diameter of the first boron nitride is smaller than that of the second boron nitride. By using boron nitride with different particle diameters to prepare the boron nitride filler, the first boron nitride can fill the gaps between the second boron nitrides, making the thermally conductive liquid crystal polymer film more dense and improving its performance.

[0066] This invention provides an embodiment of a thermally conductive liquid crystal polymer film, which is prepared by the method described above. The structure and function of the method described above can be found in the above embodiments, and will not be repeated here.

[0067] It should be noted that while the preferred embodiments of the present invention are given in the specification and accompanying drawings, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are not intended to impose additional limitations on the content of the present invention; their purpose is to provide a more thorough and comprehensive understanding of the disclosure of the present invention. Furthermore, the above-described technical features can be combined with each other to form various embodiments not listed above, all of which are considered to be within the scope of the present invention specification. Moreover, those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a thermally conductive liquid crystal polymer film, characterized in that, include: Provide liquid crystal polymer and first solvent; The liquid crystal polymer is added to the first solvent to form a liquid crystal polymer solution; Boron nitride filler and dispersant are provided, wherein the boron nitride filler is prepared and modified by mixing first boron nitride and second boron nitride in a preset mass ratio, and the particle diameter of the first boron nitride is smaller than the particle diameter of the second boron nitride. Boron nitride filler and dispersant are added to the liquid crystal polymer solution and stirred to obtain an initial slurry; Provide a substrate, apply the initial slurry onto the substrate, and cast the initial slurry into a wet film; The wet film is heated and cured to obtain the thermally conductive liquid crystal polymer film; The thermally conductive liquid crystal polymer film is peeled off from the surface of the substrate.

2. The method according to claim 1, characterized in that, The step of providing boron nitride filler further includes: Provides boron nitride solid, modifier, and second solvent; The boron nitride solid and the modifier are added to the second solvent to obtain a mixed solution; The mixed solution is stirred and reacted at a preset temperature for a preset time to obtain a modified boron nitride solution; The modified boron nitride solution was filtered to obtain the initial modified boron nitride. The initially modified boron nitride was washed and dried to obtain boron nitride filler.

3. The method according to claim 2, characterized in that, The modifier is at least one of a silane coupling agent and a titanate coupling agent, and the second solvent is an anhydrous solvent.

4. The method according to claim 1, characterized in that, The step of adding boron nitride filler and dispersant to the liquid crystal polymer solution and stirring to obtain an initial slurry further includes: A liquid crystal polymer solution, boron nitride filler, and dispersant were added to a container and stirred to obtain a mixture. The mixture is transferred to a dispersion disc for dispersion. The dispersed mixture is placed in a vacuum degassing machine for vacuum degassing to obtain the initial slurry.

5. The method according to claim 1, characterized in that, The step of coating the initial slurry onto the substrate and casting the slurry into a wet film further includes: A coating machine is provided, the coating machine including a slit coating head; The initial slurry is applied to the substrate through the slit-type coating head.

6. The method according to claim 1, characterized in that, The step of heating and curing the wet film to obtain a thermally conductive liquid crystal polymer film further includes: Place the wet film in an oven; The wet film is heated to a first preset temperature at a first preset heating rate and held at that temperature for a first preset time to obtain an initially cured thermally conductive liquid crystal polymer film. The initially cured liquid crystal polymer film is heated to a second preset temperature at a second preset heating rate and held at that temperature for a second preset time to obtain the thermally conductive liquid crystal polymer film.

7. The method according to claim 1, characterized in that, The first solvent is a polar aprotic solvent, and / or the polar aprotic solvent is at least one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide or γ-butyrolactone.

8. The method according to claim 4, characterized in that, The dispersant is at least one of a silane coupling agent and a titanate coupling agent.

9. The method according to claim 1, characterized in that, The step of peeling the thermally conductive liquid crystal polymer film from the surface of the substrate further includes: The thermally conductive liquid crystal polymer film is peeled off from the surface of the substrate, and the substrate and the thermally conductive liquid crystal polymer film are wound up separately.

10. A thermally conductive liquid crystal polymer film, characterized in that, It is made by the method described in any one of claims 1-9.

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