CN118496667A - A thermally conductive composite film and a preparation method thereof, and a precursor slurry for manufacturing a thermally conductive composite film and a preparation method thereof - Google Patents

Abstract

The present invention relates to the technical field of polymer composite materials, and in particular to a heat-conducting composite film and a preparation method thereof, and a precursor slurry for manufacturing a heat-conducting composite film and a preparation method thereof, wherein the preparation method of the precursor slurry comprises: adding expanded graphite to a poly(p-phenylene terephthalamide) nanofiber solution to form a mixed solution; freezing the mixed solution to complete freezing, and then stirring the expanded graphite at a speed of more than 1900 rpm to form a dispersion; adding an excess of a proton-donating solvent to the dispersion, stirring and dispersing the dispersion, and filtering to obtain a precursor slurry. The precursor slurry of the present invention is prepared by a one-pot method, and efficient stripping and dispersion of a heat-conducting filler are achieved. At the same time, through the effective assembly of interface interaction and polymer nanofibers, the organic polymer nanofibers adhere to the surface of an inorganic heat-conducting material, and the intermolecular interaction between the chemical structure of the organic fiber and the inorganic heat-conducting filler is relied on to give the composite film a low filler-matrix interface thermal resistance.

Description

A thermally conductive composite film and a preparation method thereof, and a precursor slurry for manufacturing a thermally conductive composite film and a preparation method thereof

Technical Field

The present invention relates to the technical field of polymer composite materials, and in particular to a thermally conductive composite film and a preparation method thereof, as well as a precursor slurry for manufacturing the thermally conductive composite film and a preparation method thereof.

Background Art

At present, electronic components are developing rapidly towards miniaturization and integration. The substantial improvement in performance is accompanied by a large amount of heat generation and heat accumulation, which seriously affects the service life, stability and reliability of electronic components. Therefore, the efficient removal of residual heat or waste heat has become a key issue for the further development of electronic components. For this reason, it is urgent to develop thermal management materials with excellent thermal conductivity.

In recent years, a lot of research has focused on the design and manufacture of polymer-based thermally conductive composite materials with high thermal conductivity. Previous studies have found that thermally conductive micro-sheet fillers with a high crystalline structure (such as graphite, boron nitride, silver, etc.) may be more practical for the thermal conductivity of composite materials, and this high-quality thermally conductive filler is conducive to reducing the production cost of thermally conductive composite materials. At the same time, inorganic thermally conductive fillers with a two-dimensional structure can give composite materials excellent in-plane thermal conductivity, showing good application prospects in the field of thermal management.

As a commonly used high thermal conductivity filler, two-dimensional graphene has a honeycomb lattice that gives it an ultra-high in-plane thermal conductivity. However, the high-quality graphite thermal conductive fillers currently prepared usually use liquid phase to assist exfoliation. The main principle is to use the shear force to overcome the van der Waals force between graphite sheets to prevent lattice defects. The prepared fillers are generally small in size, and the method is relatively complex and costly. At the same time, such small-sized microflakes are usually used in the preparation of composite materials to ensure the dispersibility of the filler in the polymer system. However, such thermal conductive microflakes are prone to produce more filler-filler and filler-matrix interfaces in the matrix, thereby limiting the further improvement of thermal conductivity. On the contrary, the preparation of large-sized thermal conductive microflakes is more conducive to reducing high interface thermal resistance and fundamentally improving in-plane heat conduction. At present, it is difficult to form high-quality large-sized graphite sheets by destroying the van der Waals force between graphite sheets, and chemical vapor deposition requires a high cost. Therefore, it is still necessary to efficiently prepare large-sized graphite microflakes through a simple and energy-saving method to meet the requirements of reducing interface thermal resistance.

Summary of the invention

Based on the above-mentioned technical problems, the present invention provides a thermally conductive composite film and a preparation method thereof, as well as a precursor slurry for manufacturing a thermally conductive composite film and a preparation method thereof, so as to solve the problems that the existing small-sized thermally conductive micro-sheets are limited in their contribution to thermal conductivity, and the large-sized thermally conductive micro-sheets have high preparation costs and difficult operations, as well as high filler-filler interface thermal resistance and high filler-matrix interface thermal resistance.

To achieve the above object, according to one aspect of the present invention, the present invention provides a method for preparing a precursor slurry for manufacturing a thermally conductive composite film, which comprises the following steps:

1) preparing a poly(p-phenylene terephthalamide) nanofiber solution, wherein the solvent is dimethyl sulfoxide and deionized water; adding expanded graphite to the poly(p-phenylene terephthalamide) nanofiber solution to form a mixed solution;

2) freezing the mixed solution of step 1) until it is completely frozen, and then mechanically stirring at a speed of more than 1900 rpm to exfoliate the expanded graphite to obtain a dispersion;

3) Add an excess amount of proton-donating solvent to the dispersion in step 2), fully stir and disperse, and filter to obtain a precursor slurry, wherein the proton-donating solvent is one or a mixture of ethanol, methanol, and deionized water.

The precursor slurry of the present invention has long-term stability, uniformity and easy storage. The main body is expanded graphite with poly(p-phenylene terephthalamide) nanofibers (ANF) attached to the surface, which is obtained by rapidly stirring a mixed solution of poly(p-phenylene terephthalamide) nanofibers (ANF) and expanded graphite after freezing, and then peeling, dispersing the expanded graphite and assembling it with polymer fibers. The precursor slurry of the present invention is a composite of polymer organic nanofibers and expanded graphite as thermal conductive fillers, with thermal conductive fillers as the main structure, and organic polymer nanofibers firmly adhere to the surface thereof through intermolecular interactions, which greatly reduces the filler-matrix interface thermal resistance and is conducive to reducing phonon scattering.

Optionally, the mass concentration of the poly(p-phenylene terephthalamide) nanofiber solution is 0.1% to 5.0%, which can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 1%, 2%, 4% and other typical but non-limiting mass concentrations. If the mass concentration of the poly(p-phenylene terephthalamide) nanofiber solution is too high, the preparation is difficult, and the system viscosity is too large, which is not conducive to stirring and dispersion. Preferably, the mass concentration of the poly(p-phenylene terephthalamide) nanofiber solution is 0.2%, the manufacturing method is mature, and the system viscosity is moderate, which is conducive to the dispersion of the thermal conductive filler.

Optionally, the mass ratio of the solid content of the poly(p-phenylene terephthalamide) nanofiber solution to the amount of expanded graphite is 1:0.01-20, and can be 1:0.01, 1:0.1, 1:1, 1:10, 1:20, etc. Typical but non-limiting weight percentages. If the amount of thermal conductive material added is too small, the thermal conductivity is insufficiently improved, and if it is too much, the overall mechanical properties of the composite material are affected.

Expanded graphite is an inorganic thermally conductive material with a two-dimensional structure. Its layers are bonded by van der Waals forces and are easily destroyed by shear force. Compared with chemical stripping, it is not easy to destroy the intrinsic structure or introduce unnecessary chemical elements. At the same time, the unique aspect ratio of the two-dimensional multilayer filler helps to prepare a thermally conductive composite film oriented in the plane, thereby achieving high in-plane heat transfer efficiency. Expanded graphite has a highly crystalline structure that contributes greatly to thermal conductivity. At the same time, it has stable chemical properties and is non-corrosive, and has good development prospects. At the same time, expanded graphite has a loose stacking structure, and the interaction between layers is easily destroyed by volume expansion, so that it can be easily stripped under the action of shear force, so that it has a large lateral size. Preferably, the average lateral size of the graphite microsheets obtained after stripping is 25-30 μm.

The present invention uses poly(p-phenylene terephthalamide) fiber (PPTA) as the organic polymer fiber matrix. This organic polymer fiber material has high intrinsic thermal conductivity, high thermal stability and excellent mechanical properties. The fiber interconnection network structure can give the thermal conductive composite film a simultaneous improvement in thermal conductivity and mechanical properties.

Furthermore, a poly(p-phenylene terephthalamide) nanofiber (ANF) solution is obtained by dissociating poly(p-phenylene terephthalamide) fibers. The benzene ring structure and abundant surface groups (-OH) of poly(p-phenylene terephthalamide) nanofiber (ANF) can easily form interactions with expanded graphite, such as hydrogen bonds, π-π interactions, etc., thereby improving the interfacial heat transfer efficiency. In the present invention, poly(p-phenylene terephthalamide) nanofiber (ANF) can easily bond with graphite microsheets through π-π interactions through the benzene rings on the molecular chain structure.

Preferably, the poly(p-phenylene terephthalamide) nanofiber solution is prepared by the following steps:

Poly(p-phenylene terephthalamide) fibers and potassium hydroxide are added into a mixed solvent of dimethyl sulfoxide and deionized water, and the poly(p-phenylene terephthalamide) fibers are dissociated by stirring to obtain a poly(p-phenylene terephthalamide) nanofiber solution.

Optionally, a uniform mixed dispersion containing poly(p-phenylene terephthalamide) nanofibers (ANF) and large-sized graphite microsheets is prepared, and the time of rapid stirring (above 1900 rpm) is adjusted to be above 20 minutes, which can be typical but non-limiting rapid stirring times such as 20 min, 30 min, 40 min, 50 min and 60 min. The stirring speed can be a typical but non-limiting mechanical stirring speed such as 1900 rpm, 2000 rpm, 2300 rpm, 2500 rpm. During stirring, the frozen multi-layer expanded graphite is peeled off by rapid shear force, the interlayer van der Waals force is destroyed, and the intrinsic structure of the thermally conductive microsheet is maintained to the greatest extent during the peeling process. The graphite thermally conductive microsheets with larger lateral dimensions prepared in the present invention are conducive to constructing in-plane orientation and promoting mutual overlap between fillers in the composite material, forming an effective thermal conduction path, and realizing high in-plane heat transfer.

Optionally, the freezing temperature is below -20 °C, which may be typical but non-limiting freezing temperatures such as -20 °C, -25 °C, and -30 °C. Similarly, the freezing time is more than 2 h, which may be typical but non-limiting freezing time such as 2 h, 3 h, and 4 h.

Optionally, when preparing a solid composite of a transversely sized graphite thermally conductive microsheet adhered to poly(p-phenylene terephthalamide) nanofibers (ANF), the fiber structure can be restored by adding a protonated solvent (i.e., a proton-donating solvent), wherein the protonated solvent includes a mixture of one or more of ethanol, methanol, and deionized water, preferably deionized water. Poly(p-phenylene terephthalamide) fibers (PPTA) are chemically inert and structurally stable. The hydrogen bonding interactions between the fiber molecular chains can be destroyed by the action of a strong base, and the protonated hydrogen atoms are lost to dissociate and obtain a nanofiber solution. After the protonated solvent is added, hydrogen atoms can be obtained and the original molecular chain structure can be restored. In the present invention, the effective adhesion of the fiber to the thermally conductive microsheet requires the integration of a protonated solvent to construct a complete assembly of the fiber and the filler.

Optionally, the preparation of a precursor slurry with a complete fiber network requires adjusting the protonation recovery time, and the mechanical stirring time can be adjusted to more than 1 hour, and can be a typical but non-limiting mechanical stirring time of 1 hour, 2 hours, 3 hours, etc. Considering that a complete fiber network is required in the present invention to ensure effective improvement of thermal conductivity and mechanical properties, excess protonation solvent and sufficient protonation time help to ensure that the poly(p-phenylene terephthalamide) nanofibers obtain hydrogen atoms and restore hydrogen bonds at the same time, so as to achieve the recovery of the original chemical structure of the specialty fiber.

According to another aspect of the present invention, the present invention further provides a precursor slurry, which is prepared by the above method.

According to another aspect of the present invention, the present invention also provides a method for preparing a thermally conductive composite film, which comprises the following steps:

The precursor slurry prepared above is dispersed in a solvent, stirred and dispersed evenly, then vacuum filtered and dried to obtain a thermally conductive composite film; the solvent is ethanol, methanol, deionized water or a mixture of several thereof.

The present invention utilizes the negative pressure of the filtration process to promote the horizontal arrangement of the precursor slurry and to design a layered orientation structure, and finally performs drying and cold pressing treatment, retaining the layered structure constructed by the inorganic thermal conductive microsheet material and the poly(p-phenylene terephthalamide) nanofiber (ANF) matrix material, and preparing a thermally conductive composite film material. The precursor slurry is added and evenly dispersed in deionized water to obtain a precursor aqueous dispersion, and the precursor aqueous dispersion is vacuum filtered, dried, and cold pressed to obtain a thermally conductive composite film material. The thermally conductive composite film material has a layered orientation structure, can achieve a good anisotropic in-plane heat transfer effect, and has high thermal conductivity and excellent mechanical properties. It is used in electronic equipment to achieve efficient electronic equipment thermal management.

The composite film material containing a small amount of deionized water obtained by vacuum filtration is placed in a vacuum oven and the solvent is evaporated at 40-80 °C, which can be typical but non-limiting volatilization temperatures such as 40 °C, 50 °C, 60 °C, 70 °C and 80 °C, so as to completely remove the solvent. The drying time is 8 h to 12 h, which can be typical but non-limiting drying times such as 8 h, 9 h, 10 h, 11 h and 12 h. The longer the drying time, the more complete removal of the solvent in the composite film can be ensured.

Preferably, the solvent used to prepare the thermally conductive composite film is the same as the proton-donating solvent used to prepare the precursor slurry.

According to another aspect of the present invention, the present invention also provides a thermally conductive composite film, which is prepared by the above method. Preferably, the thickness of the obtained thermally conductive composite film is 30-35 μm.

Compared with the prior art, the present invention has the following beneficial effects:

The thermally conductive composite film material with high thermal conductivity and excellent mechanical properties provided by the present invention has a layered oriented structure and can achieve a good in-plane heat transfer effect. The thermally conductive composite film material is obtained by vacuum filtration and drying of a precursor slurry containing an organic polymer nanofiber matrix (poly(p-phenylene terephthalamide) nanofiber) material and an expanded graphite material. The preparation method is simple, the material is readily available, the price is low, and it can be produced under mild conditions, and the industrial production of the thermally conductive composite film material is easy to achieve.

The precursor slurry provided by the present invention is prepared by a one-pot method, which realizes efficient exfoliation and dispersion of expanded graphite, and at the same time effectively assembles with polymer nanofibers through interface interaction. The exfoliated and dispersed graphite microsheets are used as thermally conductive fillers, and organic polymer nanofibers adhere to the surface of the thermally conductive filler, relying on the intermolecular interaction between the chemical structure of the organic fiber and the thermally conductive filler to give the composite film a low filler-matrix interface thermal resistance. The thermally conductive filler is effectively overlapped into an in-plane oriented structure, and the homogeneous interconnected heat conduction path greatly reduces the interface thermal resistance between the filler and the filler. Heat is rapidly transmitted in the network with an inherent high phonon transmission efficiency, thereby greatly improving the thermal conductivity of the composite material and reducing the filler-filler interface thermal barrier. Combining the two aspects, the thermal conductivity and mechanical properties of the composite material are simultaneously improved, and it can be applied to achieve efficient thermal management of electronic equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

FIG1 is a macroscopic morphology of the precursor slurry of Example 1 of the present invention;

FIG2 is a schematic structural diagram and a principle diagram of a precursor slurry dispersion provided in Example 1 of the present invention;

FIG3 is a microscopic morphology of expanded graphite, a two-dimensional heat-conducting filler used in the present invention;

FIG4 is a microscopic morphology of large-sized graphite flakes prepared in Example 1 of the present invention;

FIG5 is a cross-sectional electron micrograph of the thermally conductive composite film prepared in Example 6 of the present invention;

FIG6 shows the long-term stability of the thermally conductive composite film prepared by the precursor slurry of Example 1 of the present invention, and the existence time days are 1, 7 and 14 respectively;

FIG7 is a comparison of the thermal conductivity of the thermally conductive composite films prepared in Example 2 of the present invention and Comparative Example 2;

FIG8 is a comparison of the mechanical properties of the thermally conductive composite films prepared in Example 2 of the present invention and Comparative Example 2;

FIG. 9 is a comparison of the thermal conductivity of the thermally conductive composite films prepared in Example 2 of the present invention and Comparative Example 8.

The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings in conjunction with the embodiments.

DETAILED DESCRIPTION

The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described herein is only used to illustrate and explain the present invention, and is not used to limit the present invention.

Unless otherwise defined, the technical terms used in the following examples have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. The test reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the experimental methods, unless otherwise specified, are all conventional methods.

Example 1

The preparation method of the precursor slurry for manufacturing the thermally conductive composite film is as follows:

First, 0.3 g poly (p-phenylene terephthalamide) fiber (PPTA) and 0.45 g potassium hydroxide (KOH) were weighed into a 250 mL round-bottom flask, and 150 mL dimethyl sulfoxide (DMSO) and 6 mL deionized water were added. The mixture was rapidly stirred at 1000 rpm for 4 h to dissociate PPTA to obtain a poly (p-phenylene terephthalamide) nanofiber (ANF) solution with a mass percentage concentration of 0.2%.

Weigh 0.7 g of expanded graphite (EG) and add it to the above poly(p-phenylene terephthalamide) nanofiber (ANF) solution, and place it in a refrigerator for freezing treatment to ensure that the solution is completely frozen. Then, in an icing environment, quickly stir at a speed of 1900 rpm for 20 min to obtain a mixed solution of large-sized graphite microplatelets (GMP) and poly(p-phenylene terephthalamide) nanofibers (ANF).

Deionized water was added in a volume ratio of 1:9 relative to the mixed solution to provide ANF with sufficient protons. The mixture was stirred at room temperature for 1 h to obtain a precursor solution that was evenly dispersed. The stirred precursor solution was filtered to remove a large amount of deionized water to obtain a precursor slurry.

The appearance of the precursor slurry sample prepared in this example is shown in FIG1 . The slurry particles form a certain network structure due to interaction and steric hindrance, which is convenient for storage and transportation.

Figure 2 is a schematic diagram and principle diagram of the structure of the precursor slurry dispersion provided in Example 1. The benzene ring groups in the poly(p-phenylene terephthalamide) nanofibers form a π-π stacking effect with the hexagonal rings of large-sized graphite, so that the fibers are tightly adhered to both sides of the thermally conductive filler.

FIG3 is a microscopic morphology of expanded graphite, a two-dimensional structure thermal conductive filler. It can be clearly seen that the expanded graphite sheets are loosely stacked, which is conducive to being peeled off by shearing.

FIG4 is a microscopic morphology of the prepared large-sized graphite microsheets, from which it can be clearly seen that the graphite has been completely peeled off from the expanded graphite and presents an independent large-sheet structure, which can meet the requirements of the invention.

Example 2

Take an appropriate amount of the precursor slurry in Example 1, add deionized water to disperse, and stir at room temperature for 20 min. Remove moisture by vacuum filtration, and place the filter membrane in a vacuum oven at 60 ° C for 12 hours to obtain a thermally conductive composite film with a GMP/ANF mass ratio of 7:3 and a thickness of 30-35 μm.

The thermal diffusion coefficient of the film in the in-plane direction (consistent with the orientation direction) was tested by a flash thermal conductivity instrument and was found to be 75.83 mm ² /s. The mechanical properties of the film were tested by a universal tensile machine, with a tensile strength of 14.99 MPa and an elongation at break of 2.61 %.

Example 3

First, 0.3 g poly (p-phenylene terephthalamide) fiber (PPTA) and 0.45 g potassium hydroxide (KOH) were weighed into a 250 mL round-bottom flask, and 150 mL dimethyl sulfoxide (DMSO) and 6 mL deionized water were added. The mixture was rapidly stirred at 1000 rpm for 4 h to dissociate PPTA to obtain a poly (p-phenylene terephthalamide) nanofiber (ANF) solution with a mass percentage concentration of 0.2%.

Weigh 0.3 g of expanded graphite (EG) and add it to the above poly(p-phenylene terephthalamide) nanofiber (ANF) solution, and place it in a refrigerator for freezing treatment to ensure that the solution is completely frozen. Then, in an icing environment, quickly stir at a speed of 1900 rpm for 20 min to obtain a mixed solution of large-sized graphite microsheets (GMP) and poly(p-phenylene terephthalamide) nanofibers (ANF). Add deionized water with a volume ratio of 1:9 relative to the mixed solution to provide ANF with sufficient protons, stir at room temperature for 1 h to obtain a precursor solution that is evenly dispersed, and filter the stirred precursor solution to remove a large amount of deionized water to obtain a precursor slurry.

Example 4

Take an appropriate amount of the precursor slurry in Example 3, add deionized water to disperse, and stir at room temperature for 20 min. Remove moisture by vacuum filtration, and place the filter membrane in a vacuum oven at 60 ° C for 12 hours to obtain a thermally conductive composite film with a GMP/ANF mass ratio of 5:5 and a thickness of 30-35 μm.

The thermal diffusion coefficient of the film in the in-plane direction (consistent with the orientation direction) was tested by a flash thermal conductivity instrument and was found to be 52.26 mm ² /s. The mechanical properties of the film were tested by a universal testing machine and the tensile strength was 47.88 MPa and the elongation at break was 4.56 %.

Example 5

First, 0.3 g poly (p-phenylene terephthalamide) fiber (PPTA) and 0.45 g potassium hydroxide (KOH) were weighed into a 250 mL round-bottom flask, and 150 mL dimethyl sulfoxide (DMSO) and 6 mL deionized water were added. The mixture was rapidly stirred at 1000 rpm for 4 h to dissociate PPTA to obtain a poly (p-phenylene terephthalamide) nanofiber (ANF) solution with a concentration of 0.2%.

Weigh 0.1285 g of expanded graphite (EG) and add it to the above poly(p-phenylene terephthalamide) nanofiber (ANF) solution, and place it in a refrigerator for freezing treatment to ensure that the solution is completely frozen. Then, in an icing environment, quickly stir at a speed of 1900 rpm for 20 min to obtain a mixed solution of large-sized graphite microsheets (GMP) and poly(p-phenylene terephthalamide) nanofibers (ANF). Add deionized water with a volume ratio of 1:9 relative to the mixed solution to provide ANF with sufficient protons, stir at room temperature for 1 h to obtain a precursor solution that is evenly dispersed, and filter the stirred precursor solution to remove a large amount of deionized water to obtain a precursor slurry.

Example 6

Take an appropriate amount of the precursor slurry in Example 5, add deionized water to disperse, and stir at room temperature for 20 min. Remove moisture by vacuum filtration, and place the filter membrane in a vacuum oven at 60 ° C for 12 hours to obtain a thermally conductive composite film with a GMP/ANF mass ratio of 3:7 and a thickness of 30-35 μm.

The thermal diffusion coefficient in the film in the in-plane direction (consistent with the orientation direction) was tested by a flash method thermal conductivity instrument and was found to be 38.86 mm ² /s. The mechanical properties of the film were tested by a universal testing machine, where the tensile strength was 78.06 MPa and the elongation at break was 5.98%. FIG5 is a cross-sectional electron microscope image of the thermally conductive composite film prepared in this embodiment. It can be seen that the film forms a highly in-plane oriented dense structure, and large-sized graphite microsheets directly overlap the heat conduction path of high heat transfer in the material, and the nanofibers form a tight connection on both sides of the filler, thereby reducing the thermal resistance between the filler and the matrix.

Comparative Example 1

As a comparative experiment of Example 1, during the preparation of the precursor slurry, the mixed dispersion was not frozen, and the specific steps were as follows:

First, 0.3 g poly (p-phenylene terephthalamide) fiber (PPTA) and 0.45 g potassium hydroxide (KOH) were weighed into a 250 mL round-bottom flask, and 150 mL dimethyl sulfoxide (DMSO) and 6 mL deionized water were added. The mixture was rapidly stirred at 1000 rpm for 4 h to dissociate PPTA to obtain poly (p-phenylene terephthalamide) nanofiber (ANF) solution with a mass concentration of 0.2%.

Weigh 0.7 g of expanded graphite (EG) and add it to the above poly(p-phenylene terephthalamide) nanofiber (ANF) solution. Then stir rapidly at 1900 rpm for 20 min to obtain a mixed solution of large-sized graphite microplatelets (GMP) and poly(p-phenylene terephthalamide) nanofiber (ANF). Add deionized water at a volume ratio of 1:9 to the mixed solution to provide ANF with sufficient protons, stir at room temperature for 1 h to obtain a precursor solution that is evenly dispersed, and filter the stirred precursor solution to remove a large amount of deionized water to obtain a precursor slurry.

Since it has not been frozen, the precursor slurry prepared in Comparative Example 1 has poor dispersibility, is easy to agglomerate, and has poor long-term stability. The long-term stability of the precursor slurries prepared in Example 1 and Comparative Example 1 and their effects on thermal conductivity were compared and tested. Three groups of each sample were taken to compare the dispersion degree at storage time of 1, 7, and 14. It can be seen that the precursor slurry of Example 1 can show uniformity and redispersibility after storage for 7 days and 14 days, and the thermal conductivity of the film formed after vacuum filtration remains the same as that at storage for 1 day (as shown in Figure 6); while Comparative Example 1 has already seriously agglomerated after long-term storage (no more than 7 days) and cannot be uniformly dispersed again, and thus cannot form a complete film through vacuum filtration, so the thermal conductivity test cannot be carried out normally.

Comparative Example 2

Take an appropriate amount of the precursor slurry of Comparative Example 1 (stored for no more than 1 day), add deionized water to disperse, stir at room temperature for 20 min, remove moisture by vacuum filtration, and place the filter membrane in a 60 ° C vacuum oven for drying for 12 hours to obtain a thermally conductive composite film with a GMP/ANF mass ratio of 7:3 and a thickness of about 30-35 μm. The thermal diffusion coefficient of the film in the in-plane direction (consistent with the orientation direction) tested by a flash thermal conductivity instrument is 45.90 mm ² /s, and the mechanical properties of the film are tested by a universal testing machine, wherein the tensile strength is 8.14 MPa and the elongation at break is 2.13%.

From the difference in thermal conductivity of the thermally conductive composite film materials prepared in Example 2 and Comparative Example 2 in Figure 7, it can be seen that since the large-sized graphite flakes prepared without freezing treatment cannot be completely peeled off and have poor dispersion, the thermal conductivity is much lower than that of the thermally conductive composite film obtained by freezing treatment.

From the difference in mechanical properties of the thermally conductive composite film materials prepared by Example 2 and Comparative Example 2 in Figure 8, it can be seen that since the large-sized graphite flakes prepared without freezing treatment have poor dispersion and too many interlayer gaps, their mechanical strength is worse than that of the thermally conductive composite film obtained by freezing treatment.

In summary, the precursor slurry can be prepared by freezing and non-freezing treatments, so as to prepare two composite films with different thermal conductivity and mechanical properties. Moreover, it can be seen from Example 1 and Comparative Example 1 that the uniformity and long-term storage properties of the precursor slurry prepared by freezing treatment and the precursor slurry prepared by non-freezing treatment are significantly different. The precursor slurry is prepared by assembling organic polymer nanofibers and large-sized thermally conductive microsheets. The efficient and high-quality preparation of large-sized microsheets helps to give the slurry uniformity, and it is not easy to aggregate under long-term storage conditions and has repeatable dispersion. The composite of organic polymer nanofibers further promotes the improvement of the mechanical properties of the thermally conductive composite film; and enhances the interfacial interaction between the microsheets and the substrate, further improving the thermal conductivity of the thermally conductive composite film.

Comparative Example 3

First, 0.3 g poly (p-phenylene terephthalamide) fiber (PPTA) and 0.45 g potassium hydroxide (KOH) were weighed into a 250 mL round-bottom flask, and 150 mL dimethyl sulfoxide (DMSO) and 6 mL deionized water were added. The mixture was rapidly stirred at 1000 rpm for 4 h to dissociate PPTA to obtain a poly (p-phenylene terephthalamide) nanofiber (ANF) solution with a concentration of 0.2%.

Weigh 0.3 g of expanded graphite (EG) and add it to the above poly(p-phenylene terephthalamide) nanofiber (ANF) solution. Then stir rapidly at 1900 rpm for 20 min to obtain a mixed solution of large-sized graphite microplatelets (GMP) and poly(p-phenylene terephthalamide) nanofiber (ANF). Add deionized water at a volume ratio of 1:9 to the mixed solution to provide ANF with sufficient protons, stir at room temperature for 1 h to obtain a precursor solution that is evenly dispersed, and filter the stirred precursor solution to remove a large amount of deionized water to obtain a precursor slurry.

Comparative Example 4

Take an appropriate amount of the precursor slurry in Comparative Example 3, add deionized water to disperse, and stir at room temperature for 20 min. Remove moisture by vacuum filtration, and place the filter membrane in a 60 ° C vacuum oven for drying for 12 hours to obtain a thermally conductive composite film with a GMP/ANF mass ratio of 5:5 and a thickness of 30-35 μm. The thermal diffusion coefficient of the film in the in-plane direction (consistent with the orientation direction) tested by a flash thermal conductivity instrument is 38.11 mm ² /s, and the mechanical properties of the film are tested by a universal testing machine, wherein the tensile strength is 30.47 MPa and the elongation at break is 3.96%.

Comparative Example 5

First, 0.3 g poly (p-phenylene terephthalamide) fiber (PPTA) and 0.45 g potassium hydroxide (KOH) were weighed into a 250 mL round-bottom flask, and 150 mL dimethyl sulfoxide (DMSO) and 6 mL deionized water were added. The mixture was rapidly stirred at 1000 rpm for 4 h to dissociate PPTA to obtain a poly (p-phenylene terephthalamide) nanofiber (ANF) solution with a concentration of 0.2%.

Weigh 0.1285 g of expanded graphite (EG) and add it to the above poly(p-phenylene terephthalamide) nanofiber (ANF) solution. Then stir rapidly at 1900 rpm for 20 min to obtain a mixed solution of large-sized graphite microplatelets (GMP) and poly(p-phenylene terephthalamide) nanofiber (ANF). Add deionized water at a volume ratio of 1:9 to the mixed solution to provide ANF with sufficient protons, stir at room temperature for 1 h to obtain a precursor solution that is evenly dispersed, and filter the stirred precursor solution to remove a large amount of deionized water to obtain a precursor slurry.

Comparative Example 6

Take an appropriate amount of the precursor slurry in comparative example 5, add deionized water to disperse, and stir at room temperature for 20 min. Remove moisture by vacuum filtration, and place the filter membrane in a 60 ° C vacuum oven for drying for 12 hours to obtain a thermally conductive composite film with a GMP/ANF mass ratio of 3:7 and a thickness of 30-35 μm. The thermal diffusion coefficient of the film in the in-plane direction (consistent with the orientation direction) tested by a flash thermal conductivity instrument is 15.45 mm ² /s. The mechanical properties of the film are tested by a universal testing machine, wherein the tensile strength is 37.23 MPa and the elongation at break is 5.25%.

Table 1 Performance test results of thermal conductive composite films

Comparative Example 7

As a comparative experiment of Example 1, the only difference from Example 1 is that the rotation speed of stirring and peeling is reduced.

First, 0.3 g poly (p-phenylene terephthalamide) fiber (PPTA) and 0.45 g potassium hydroxide (KOH) were weighed into a 250 mL round-bottom flask, and 150 mL dimethyl sulfoxide (DMSO) and 6 mL deionized water were added. The mixture was rapidly stirred at 1000 rpm for 4 h to dissociate PPTA to obtain a poly (p-phenylene terephthalamide) nanofiber (ANF) solution with a concentration of 0.2%.

Weigh 0.7 g of expanded graphite (EG) and add it to the above poly(p-phenylene terephthalamide) nanofiber (ANF) solution. Then stir rapidly at 1600 rpm for 20 min to obtain a mixed solution of large-sized graphite microplatelets (GMP) and poly(p-phenylene terephthalamide) nanofiber (ANF). Add deionized water at a volume ratio of 1:9 to the mixed solution to provide ANF with sufficient protons, stir at room temperature for 1 h to obtain a precursor solution that is evenly dispersed, and filter the stirred precursor solution to remove a large amount of deionized water to obtain a precursor slurry.

Comparative Example 8

Take an appropriate amount of the precursor slurry in Comparative Example 7, add deionized water to disperse, and stir at room temperature for 20 min. Remove moisture by vacuum filtration, and place the filter membrane in a 60 ° C vacuum oven for drying for 12 hours to obtain a thermally conductive composite film with a GMP/ANF mass ratio of 7:3 and a thickness of 30-35 μm. The thermal diffusion coefficient of the film in the in-plane direction (consistent with the orientation direction) is 73.60 mm ² /s as measured by a flash thermal conductivity instrument.

Figure 9 is a comparison of the thermal conductivity of the thermally conductive composite film materials prepared in Example 2 and Comparative Example 8. Since the degree of exfoliation of the graphite microsheets in Comparative Example 8 is worse than that in Example 2, the thermal diffusion coefficient of the composite film is reduced. Further experimental tests show that when the speed of stirring and exfoliating is further reduced on the basis of Comparative Example 7, the thermal diffusion coefficient of the obtained precursor slurry decreases more significantly.

Although specific embodiments of the present invention are described above, those skilled in the art should understand that these are merely examples and that various changes or modifications may be made to the embodiments without departing from the principles and essence of the present invention. The scope of protection of the present invention is limited only by the appended claims.

Claims (10)

1. A method for preparing a precursor slurry for manufacturing a thermally conductive composite film, characterized in that it comprises the following steps: 1) preparing a poly(p-phenylene terephthalamide) nanofiber solution, wherein the solvent is dimethyl sulfoxide and deionized water; adding expanded graphite to the poly(p-phenylene terephthalamide) nanofiber solution to form a mixed solution; 2) freezing the mixed solution of step 1) until it is completely frozen, and then mechanically stirring at a speed of more than 1900 rpm to exfoliate the expanded graphite to obtain a dispersion; 3) Adding an excess amount of proton-donating solvent to the dispersion in step 2), fully stirring and dispersing, and filtering to obtain a precursor slurry, wherein the proton-donating solvent is at least one of ethanol, methanol, and deionized water. 2. The method for preparing a precursor slurry for manufacturing a thermally conductive composite film according to claim 1, characterized in that the mass percentage concentration of the poly(p-phenylene terephthalamide) nanofiber solution is 0.1%~5.0%; and/or the mass ratio of the solid content of the poly(p-phenylene terephthalamide) nanofiber solution to the feed amount of the expanded graphite is 1:0.01~20. 3. The method for preparing a precursor slurry for manufacturing a thermally conductive composite film according to claim 1, wherein the poly(p-phenylene terephthalamide) nanofiber solution is prepared by the following steps: Poly(p-phenylene terephthalamide) fibers and potassium hydroxide are added into a mixed solvent of dimethyl sulfoxide and deionized water, and the poly(p-phenylene terephthalamide) fibers are dissociated by stirring to obtain a poly(p-phenylene terephthalamide) nanofiber solution. 4. The method for preparing a precursor slurry for manufacturing a thermally conductive composite film according to claim 1, characterized in that the freezing temperature in step 2) is below -20 °C and the freezing time is more than 2 h; and/or the mechanical stirring time in step 2) is more than 20 min. 5. The method for preparing a precursor slurry for manufacturing a thermally conductive composite film according to claim 1, wherein the average lateral size of the graphite flakes obtained after the peeling is 25-30 μm. 6. A precursor slurry, characterized in that it is prepared by the method described in any one of claims 1 to 5. 7. A method for preparing a thermally conductive composite film, characterized in that it comprises the following steps: Dispersing the precursor slurry according to claim 6 in a solvent, stirring and dispersing it evenly, and then vacuum filtering and drying to obtain a thermally conductive composite film; The solvent is at least one of ethanol, methanol and deionized water. 8 . The method for preparing a thermally conductive composite film according to claim 7 , wherein the thermally conductive composite film has a thickness of 30-35 μm. 9. The method for preparing a thermally conductive composite film according to claim 7, wherein the drying temperature is 40 to 80 °C. 10. A thermally conductive composite film, characterized in that it is prepared by the method according to any one of claims 7 to 9.