Preparation method of polyimide film, high-thermal-conductivity graphite sheet and application thereof

Abstract

The application discloses a preparation method of a polyimide film, a high-thermal-conductivity graphite sheet and application of the polyimide film. A diamine, a dianhydride monomer, a large-aromatic-ring monomer and an end-capping agent are added in batches in a solvent, and a polyamide acid resin is obtained through reaction. An inorganic particle dispersion liquid and a chemical flow casting method promoter are prepared respectively. The three are continuously and on-line instantaneously mixed uniformly in a needle mixer, and then a polyimide film is obtained through slushing and imidization. The planar orientation degree and mechanical properties of the film are improved, and the carbon density is improved through the large-aromatic-ring structure and the cross-linking type end-capping agent. The problem of uneven dispersion of the inorganic particles in the resin system due to agglomeration and sedimentation is solved through the continuous on-line instantaneously mixing technology, and the ratio of the resin, the dispersion liquid and the promoter can be on-line flexibly adjusted, which opens up a new way for continuous and stable engineering preparation of the inorganic particle functionalized polyimide film. The graphite sheet prepared from the polyimide film has a thermal conductivity of 2000 W / m*K.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of high polymer materials, and particularly relates to a polyimide film, a graphite sheet and a preparation method and application thereof. BACKGROUND

[0002] With the continuous iteration and upgrading of new technologies represented by AI, electronic product design is developing towards lightness, intelligence and multi-functionality. The rapid growth of big data, cloud computing and parallel computing leads to an increase in data transmission speed and data volume, resulting in a sharp increase in power consumption of data centers. Heat dissipation of components has become a bottleneck problem faced by electronic terminal devices.

[0003] According to different needs of terminals, new heat dissipation schemes can be divided into two directions. The first is to increase the thickness of the heat dissipation material to obtain higher heat conduction flux in the plane direction. The second is to improve the thermal conductivity of the material as much as possible to improve the heat conduction speed. High-performance polyimide (PI) film can obtain heat-conducting graphite sheet with several times the thermal conductivity of copper after high-temperature carbonization and graphitization, which is the core material for solving the heat dissipation problem of electronic products at present. Chinese patent application file CN110423467A discloses a preparation method of a 90 μm or more ultra-thick polyimide film. The thickness of the graphite sheet obtained by high-temperature sintering can reach 45-130 μm, which solves the problem of insufficient heat flux in the plane direction caused by insufficient thickness of the existing polyimide-based artificial graphite. However, the thermal conductivity of polyimide-based artificial graphite in the industry cannot reach 2000 W / m·K, which cannot meet the latest heat dissipation needs of the electronic industry, and breakthroughs are urgently needed.

[0004] There are two main methods to improve the thermal conductivity of artificial graphite in the industry. One is to introduce rigid coplanar structures to improve the planar orientation of the precursor polyimide film. The molecular structure can form more continuous carbon layers during graphitization, thereby providing a better heat conduction path. However, the introduction of rigid segments will inevitably reduce the flexibility of the film, affecting the forming processing yield, and the thermal conductivity of the graphite sheet prepared by relying solely on the PI molecular structure is difficult to break through 2000 W / m·K. Chinese patent application CN114014657A discloses a polyimide-based high-thermal-conductivity graphite film. A dianhydride monomer containing 1,4,5,8-naphthalene tetracarboxylic anhydride is condensed with a diamine monomer in a polar solvent to obtain a polyamide acid, and then cast, vertically and horizontally stretched, and heated to obtain a 30-50 μm polyimide film. Naphthalene tetracarboxylic anhydride with a regular molecular structure is used to induce graphitization transformation, without the need to add inorganic additives as in traditional technology, avoiding appearance defects caused by uneven dispersion and large particle size of inorganic additives. However, the thickness range of the precursor polyimide film prepared by this technology is too narrow, and the maximum elongation at break is only 20%. The film is prone to breakage during winding or processing, resulting in low yield and difficulty in large-scale production. The planar thermal conductivity of the graphite film prepared is not more than 900 W / m·K, which is far from meeting the heat dissipation needs of electronic terminals.

[0005] Another method to improve the thermal conductivity of artificial graphite is to introduce nanoparticles into the precursor polyimide film, such as graphene or carbon nanotube doped nanohybrid films. During graphitization, the above nanoparticles and artificial graphite sheets form a more continuous thermal conduction network, reducing phonon scattering and improving graphite thermal conductivity. However, how to achieve uniform distribution of nanoparticles in the system has been a problem in the industry. Chinese patent application CN118439878A discloses a high-thermal-conductivity polyimide composite graphite film and a preparation method thereof. Surface-modified carbon nanotubes are dispersed in an organic solvent, and then diamine and dianhydride are added for polycondensation reaction for more than 12 hours to obtain a polyamide acid / carbon nanotube mixture. Then, a catalyst pyridine / propionic anhydride mixture is added, stirred, and then poured onto a glass plate. After heating treatment, the film is separated from the glass plate and treated at 150-230°C for 5-30min to obtain a polyimide film. Further high-temperature sintering obtains a graphite film with a thermal conductivity of at most 1115.7 W / (m·K). Moreover, the residence time of nanoparticles in the resin system exceeds 12 hours, which inevitably leads to sedimentation and secondary agglomeration, affecting product performance and consistency, and making it impossible to achieve stable engineering production.

[0006] To reduce the residence time of nanoparticles in the resin system, Chinese patent application file CN116375016A proposes a method for preparing high-thermal-conductivity polyimide graphene film by doping graphene, first preparing a polyamide acid resin solution, then adding graphene oxide, carbon nanotubes, and swelling starch ether as reinforcing phases into the imidization reagent to obtain a dispersion liquid, ultrasonic dispersion for about 2h, then mixing with the polyamide acid resin, centrifugal defoaming, casting imidization to obtain a film, and then high-temperature graphitization to obtain a high-thermal-conductivity graphene film. Although the agglomeration of graphene during the synthesis of polyamide acid resin is avoided, the ultrasonic, centrifugal and defoaming time is as long as several hours, and the nanomaterials will still have sedimentation and secondary agglomeration. Moreover, once the dispersion liquid is prepared, the amount of graphene and imidization reagent cannot be adjusted online, and the ratio of the dispersion liquid to the polyamide acid resin cannot be adjusted online, which cannot adjust the product performance according to the actual production situation, and is not suitable for industrial continuous production. After the dispersion liquid is mixed with the polyamide acid resin, the imidization reagent will promote the rapid dehydration of the resin, and a large amount of gel and impurities will be formed during the centrifugal and defoaming process, which does not have industrial value. The thermal conductivity coefficient of the final graphene material is only 1658W / (m·K), which is difficult to meet the latest application requirements. SUMMARY

[0007] To overcome the problems in the prior art, the present application provides a preparation method of a polyimide film, a high-thermal-conductivity graphite sheet and its application. The instant online mixing technology is used to reduce the residence time of nanoparticles in the resin system, solve the problem of uneven dispersion of inorganic particles in the prior art, and flexibly adjust the ratio of resin, dispersion liquid and casting accelerator online to obtain a high-performance polyimide film. The thermal conductivity coefficient of the graphite sheet prepared from the film can reach 2000W / m·K, which opens up a new way for the continuous and stable engineering preparation of inorganic particle functionalized polyimide film.

[0008] To solve the above technical problems, the technical scheme provided by the present application is as follows:

[0009] The present application provides a preparation method of a polyimide film, comprising the following steps:

[0010] S1, preparing raw materials of a polyamide acid resin solution, an inorganic particle dispersion liquid and a chemical casting method accelerator; the polyamide acid resin solution is prepared by polycondensation reaction of diamine, dianhydride, large aromatic ring monomer and crosslinking type blocking agent; the large aromatic ring monomer is an aromatic ring containing one or more of naphthalene ring, anthracene ring or anthraquinone.

[0011] S2, instantaneously mixing the raw materials prepared in S1 uniformly in a needle mixer.

[0012] S3, after mixing, immediately casting, imidizing to obtain a polyimide film without defoaming.

[0013] The present application introduces the unique large aromatic ring structure containing naphthalene ring, anthracene ring and anthraquinone into the polyimide structure, which can improve the molecular orientation degree, ensure good mechanical properties and excellent dimensional stability, and the graphite sheet made of the film has better thermal conductivity. The needle-type mixer instantaneous online mixing technology reduces the residence time of inorganic nanoparticles in the resin system, solves the problem of uneven dispersion of inorganic particles caused by agglomeration and sedimentation in the prior art, and the instantaneous online mixing technology can also flexibly adjust the ratio of resin, dispersion liquid and casting accelerator online, so as to control the product performance according to the actual production situation, and is more suitable for industrial continuous production. The film prepared by the present application technology is sintered into a graphite sheet, and the thermal conductivity can reach 2000 W / m·K or more.

[0014] As an optional embodiment, in the preparation method provided by the present application, the time for instantaneous online mixing in the needle-type mixer is 10-50 s, the mixing temperature is-15-10℃, and the mixer rotation speed is 1000-4000 rpm.

[0015] As an optional embodiment, in the preparation method provided by the present application, the top of the needle-type mixer is provided with a polyamide acid resin feeding port, and the same height of the needle-type mixer is provided with a dispersion liquid feeding port and a chemical casting method accelerator feeding port; the polyamide acid resin is fed first, and then the dispersion liquid and the chemical casting method accelerator are fed simultaneously.

[0016] In the present application, the polyamide acid resin first fills the cavity of the needle-type mixer, and is rapidly sheared and thinned under the action of the high rotation speed of the stirring paddle, which is more beneficial to uniform mixing with the inorganic particle dispersion liquid and the chemical casting method accelerator. After the chemical casting method accelerator is added, the viscosity of the solution in the mixer is further reduced, which is beneficial to uniform mixing of the inorganic particle dispersion liquid in the resin. The inorganic particle dispersion liquid and the chemical casting method accelerator are added simultaneously, which can avoid the premature gelation of the resin in contact with the accelerator.

[0017] As an optional embodiment, in the preparation method provided by the present application, the molar amount of the large aromatic ring monomer accounts for 5-30% of the total molar amount of diamine and dianhydride.

[0018] In the present application, the molar amount of the large aromatic ring monomer is controlled to account for 5-30% of the total molar amount of diamine and dianhydride, the addition amount of the large aromatic ring monomer is reduced, the improvement of the orientation structure is small, and the performance is not obviously affected. If the addition amount is too large, the film rigidity is too large, the film is too brittle, and it is difficult to be industrialized.

[0019] As an optional embodiment, in the preparation method provided by the application, the large aromatic ring monomer is selected from one or more of 1,4,5,8-naphthalene tetracarboxylic dianhydride, 2,3,6,7-naphthalene tetracarboxylic dianhydride, 2,3,6,7-anthracene tetracarboxylic dianhydride, anthracene-2,6-diamine, 1.5-naphthalene diamine, 1,4-diaminonaphthalene and 1,8-dihydroxy-2,4,5,7-tetraaminanthraquinone (4NADA).

[0020] As an optional embodiment, in the preparation method provided by the application, the cross-linking type end-capping agent is selected from one or more of 4-phenylacetylene phthalic anhydride (4-PEPA), 4-ethynyl phthalic anhydride (EPA) and 4-ethynyl aniline.

[0021] As an optional embodiment, in the preparation method provided by the application, the addition amount of the cross-linking type end-capping agent is 0.05% to 0.5% of the mass of the polyamic acid resin.

[0022] As an optional embodiment, in the preparation method provided by the application, the solid content of the inorganic particle dispersion liquid is 10% to 25%, and the inorganic particle is selected from one or more of silicon oxide, silicon carbide, aluminum nitride, silicon nitride, boron nitride, calcium phosphate, calcium hydrogen phosphate, calcium pyrophosphate, calcium carbonate, calcium bicarbonate, aluminum oxide, carbon nanotube and graphene.

[0023] As an optional embodiment, in the preparation method provided by the application, the particle size of the inorganic particle is 50 nm to 5 μm, and the addition amount of the inorganic particle is 0.03% to 20% of the mass of the polyimide film.

[0024] Further, the particle size of the inorganic particle is preferably 500 nm to 3 μm, and the addition amount of the inorganic particle is preferably 0.2% to 10% of the mass of the polyimide film.

[0025] As an optional embodiment, in the preparation method provided by the application, in S3, the casting temperature is 60 to 180 ℃, the imidization temperature is 200 to 600 ℃, and the casting speed is 10 to 35 m / min.

[0026] In the application, the in-line mixing time is 5 to 60 s, the casting temperature is 60 to 180 ℃, the solvent is rapidly volatilized by heating, the polyamic acid gel film is obtained, and the polyamic acid gel film is peeled off from the steel belt to enter the imidization stage; the imidization temperature is 200 to 600 ℃, the gel film completes imidization, and the end-capping agent realizes chemical cross-linking, further improving the performance of the film, thereby obtaining a polyimide film with ultra-high planar orientation.

[0027] As an optional embodiment, in the preparation method provided by the present application, the organic solvent is selected from one or more of dimethylformamide (DMF), dimethylacetamide (DMAc) and N-methyl pyrrolidone (NMP).

[0028] As an optional embodiment, in the preparation method provided by the present application, the diamine is an aromatic diamine and the dianhydride is an aromatic dianhydride.

[0029] As an optional embodiment, in the preparation method provided by the present application, the diamine monomer is selected from one or more of 4,4'-oxydianiline (ODA), 1,3-bis(4'-aminophenoxy)benzene (TPE-R), 1,4-bis(4'-aminophenoxy)benzene (TPE-Q), p-phenylenediamine (PDA) and 2,2-bis(4-aminophenoxy)benzene (BAPP).

[0030] As an optional embodiment, in the preparation method provided by the present application, the dianhydride monomer is selected from one or more of pyromellitic dianhydride (PMDA), 3,3',4,4'-diphenyltetracarboxylic dianhydride (s-BPDA), 2,3,3',4-biphenyltetracarboxylic dianhydride (a-BPDA), 3,3',4,4-benzophenonetetracarboxylic dianhydride (BTDA) and 4,4'-oxydiphthalic dianhydride (ODPA).

[0031] As an optional embodiment, in the preparation method provided by the present application, the solid content of the prepared polyamic acid resin is 12% to 30%, the reaction temperature is 20 to 55°C, and the viscosity is 1200P to 5000P.

[0032] Further, the viscosity is preferably 1800 to 2500P.

[0033] As an optional embodiment, in the preparation method provided by the present application, the chemical flow casting method promoter comprises a catalyst and a dehydrating agent.

[0034] As an optional embodiment, in the preparation method provided by the present application, the dehydrating agent is selected from at least one of acetic anhydride, propionic anhydride and benzoic anhydride, and the addition amount is 15 to 35% of the mass of the polyamic acid resin; further, the addition amount is 20 to 30% of the mass of the polyamic acid resin.

[0035] As an optional embodiment, in the preparation method provided by the present application, the catalyst is selected from at least one of pyridine and its derivatives, imidazole, quinoline and isoquinoline, and the catalyst addition amount is 1 to 8% of the mass of the polyamic acid resin.

[0036] Based on the same technical concept, the application further provides a high-thermal-conductivity graphite sheet, wherein the polyimide film prepared by the preparation method is subjected to carbonization, graphitization and calendering treatment.

[0037] As an optional embodiment, in the high-thermal-conductivity graphite sheet provided by the application, the single-layer thickness of the graphite sheet is 17-130 μm.

[0038] As an optional embodiment, in the high-thermal-conductivity graphite sheet provided by the application, the thermal conductivity of the graphite sheet is ≥2000 W / m·K.

[0039] Based on the same technical concept, the application further provides the polyimide film prepared by the preparation method or the graphite sheet in the application in the application of electronic device heat dissipation materials.

[0040] Based on the same technical concept, the application further provides the polyimide film prepared by the preparation method in the application in the fields of electronic information, flexible display, aerospace, chip semiconductor or national defense.

[0041] Compared with the prior art, the application has the following beneficial effects:

[0042] (1) The application designs a continuous online instantaneous mixing technology, wherein the nano-particle dispersion liquid and the catalytic system are synchronously and continuously added to the resin solution in the flow film stage, and the film can be directly cast without defoaming. On the one hand, the diffusion efficiency is improved by high-speed and high-flow shearing dispersion, the instantaneous uniform mixing of the resin and the catalytic system is realized, the local gel defect problem caused by the uneven mixing of the catalytic system and the resin is solved, and the large-scale stable and efficient production of the film can be realized.

[0043] On the other hand, since the mixing time of the nano-particles and the resin only needs several seconds to several tens of seconds, the film is rapidly cast on the steel belt immediately, the imidization is rapidly carried out under the action of the catalytic system, and then the distribution state of the nano-particles is locked. Compared with the traditional doping mode, the residence time of the nano-particles in the resin solution system is shortened from more than ten hours to several seconds, not only the secondary agglomeration and sedimentation are effectively avoided, the mechanical properties, application performance and consistency of the functional film are improved, but also the ratio and type of the polyamide acid resin, the accelerator and the nano-particles can be online controlled according to the actual production situation, which is a more flexible common technology, has great development potential and industrialization value, and opens up a new way for the continuous and stable engineering preparation of the inorganic particle functional polyimide film.

[0044] (2) The application introduces large aromatic ring structures containing naphthalene rings, anthracene rings and anthraquinone to improve the molecular orientation degree, and regulates the hard and soft segment structures to ensure good mechanical properties and excellent dimensional stability. When applied in the field of heat dissipation, not only the carbon density of graphite can be increased, but also the difficulty of forming ordered graphite crystal from disordered carbon atoms in the graphitization process can be reduced, forming more uniform graphite crystal structure, providing better heat conduction path, and forming synergistic effect with uniformly dispersed inorganic particles, better inducing graphitization transformation, and the prepared graphite sheet thermal conductivity can break through 2000W / m·K. BRIEF DESCRIPTION OF DRAWINGS

[0045] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0046] Figure 1 The schematic diagram of the pin-type mixer and the continuous online doping process used in the embodiments of the present application. DETAILED DESCRIPTION

[0047] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the accompanying drawings and preferred embodiments. However, the scope of protection of the present application is not limited to the following specific embodiments.

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present application.

[0049] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or can be prepared by existing methods.

[0050] Embodiment 1

[0051] A preparation method of high-thermal-conductivity graphite sheet, comprising the following steps:

[0052] (1) Resin preparation: 70.64 kg of ODA, 4.239 kg of PDA, 72.67 kg of PMDA and 12.61 kg of 1,4,5,8-naphthalene tetracarboxylic dianhydride are added in batches in 840 kg of DMAc, and the polycondensation reaction is carried out at 45℃. After completion, 1 kg of 4-PEPA is added for end-capping, and after defoaming, a polyamic acid resin with a viscosity of 2100P is obtained.

[0053] (2) Dispersion preparation: 0.32 kg of calcium carbonate with a particle size of 1 μm was first added to 1.28 kg of DMAc, and then stirred at high speed for dispersion, and used after stirring.

[0054] (3) Preparation of a chemical flow casting method promoter: 280 kg of acetic anhydride and 20 kg of imidazole were dissolved in 100 kg of DMAc, and then stirred for dissolution and uniformity, and used after stirring.

[0055] (4) PI film preparation: the above three were mixed in a needle mixer for 50 s, the mixing temperature was -10°C, the mixer speed was 1200 rpm, and the slurry temperature was 100°C, to obtain a polyamic acid gel film, which was then peeled off from a steel belt and imidized at 200-600°C, and the casting speed was 33 m / min, to obtain a PI film with a thickness of 43 μm.

[0056] (5) Graphite sheet preparation: the PI film was sequentially subjected to high-temperature treatment in a carbonization furnace and a graphitization furnace, and then calendered, to obtain a high-thermal-conductivity graphite sheet.

[0057] Example 2

[0058] A method for preparing a high-thermal-conductivity graphite sheet, comprising the following steps:

[0059] (1) Resin preparation: 92.91 kg of ODA, 75.90 kg of PMDA, and 31.10 kg of 2,3,6,7-naphthalene tetracarboxylic dianhydride were added to 800 kg of DMF in batches, and subjected to polycondensation reaction at 30°C, and then 4 kg of EPA was added for end-capping, and defoaming was performed to obtain a polyamic acid resin with a viscosity of 2450 P.

[0060] (2) Dispersion preparation: 2 kg of carbon nanotubes with a particle size of 2 μm and 0.4 kg of calcium bicarbonate with a particle size of 0.8 μm were first added to 11.2 kg of DMF, and then stirred at high speed for dispersion, and used after stirring.

[0061] (3) Preparation of a chemical flow casting method promoter: 240 kg of propionic anhydride and 30 kg of quinoline were dissolved in 130 kg of DMF, and then stirred for dissolution and uniformity, and used after stirring.

[0062] (4) PI film preparation: the above three were mixed in a needle mixer for 40 s, the mixing temperature was -5°C, the mixer speed was 1800 rpm, and the slurry temperature was 90°C, to obtain a polyamic acid gel film, which was then peeled off from a steel belt and imidized at 200-600°C, and the casting speed was 28 m / min, to obtain a PI film with a thickness of 90 μm.

[0063] (5) Graphite sheet preparation: the PI film was sequentially subjected to high-temperature treatment in a carbonization furnace and a graphitization furnace, and then calendered, to obtain a high-thermal-conductivity graphite sheet.

[0064] Example 3

[0065] A method for preparing a high-thermal-conductivity graphite sheet, comprising the following steps:

[0066] (1) Resin preparation: 79.29 kg of ODA, 10.16 kg of BAPP, 8.02 kg of PDA, 91.77 kg of PMDA, 14.56 kg of BPDA, and 10.40 kg of 4NADA were added in batches to 760 kg of NMP, and a polycondensation reaction was performed at 35°C. After completion, 2 kg of 4-ethynylaniline was added for end-capping, and after defoaming, a polyamic acid resin with a viscosity of 2350P was obtained.

[0067] (2) Dispersion liquid preparation: 21.42 kg of graphene with a particle size of 3 μm and 4.28 kg of dicalcium phosphate with a particle size of 1.2 μm were first added to 77.2 kg of NMP, and after high-speed dispersion stirring, they were used.

[0068] (3) Chemical flow casting method accelerator preparation: 200 kg of propionic anhydride and 40 kg of pyridine were dissolved in 160 kg of NMP, and after uniform dissolution and stirring, they were used.

[0069] (4) PI film preparation: The above three were mixed in a needle mixer for 30 s online, the mixing temperature was 0°C, the mixer speed was 2500 rpm, and the slurry temperature was 110°C, to obtain a polyamic acid gel film. Then, the film was peeled off from the steel belt, and imidization was completed at 200-600°C, the casting speed was 23 m / min, and a PI film with a thickness of 115 μm was obtained.

[0070] (5) Graphite sheet preparation: The PI film was sequentially placed in a carbonization furnace and a graphitization furnace for high-temperature treatment, and then calendered to obtain a high-thermal-conductivity graphite sheet.

[0071] Example 4

[0072] A method for preparing a high-thermal-conductivity graphite sheet, comprising the following steps:

[0073] (1) Resin preparation: 98.90 kg of ODA, 12.01 kg of TPE-R, 12.60 kg of anthracene-2,6-diamine, 115.42 kg of PMDA, 9.12 kg of ODPA, and 18.71 kg of 2,3,6,7-anthracene tetra-carboxylic dianhydride were added in batches to 720 kg of NMP, and a polycondensation reaction was performed at 25°C. After completion, 3 kg of 4-PEPA was added for end-capping, and after defoaming, a polyamic acid resin with a viscosity of 2050P was obtained.

[0074] (2) Dispersion liquid preparation: 13.33 kg of carbon nanotubes with a particle size of 0.6 μm were first added to 77.2 kg of DMF, and after high-speed dispersion stirring, they were used.

[0075] (3) Chemical flow method promoter preparation: 260 kg of propionic anhydride and 50 kg of 2-methylpyridine were dissolved in 90 kg of NMP, and after uniform dissolution and stirring, were used.

[0076] (4) PI film preparation: the above three were mixed in a needle mixer for 20 s, the mixing temperature was 5°C, the mixer speed was 3200 rpm, and the slurry temperature was 130°C to obtain a polyamic acid gel film, which was then peeled off from the steel belt and imidized at 200-600°C, the casting speed was 16 m / min, and a PI film with a thickness of 170 μm was obtained.

[0077] (5) Graphite sheet preparation: the PI film was sequentially placed in a carbonization furnace and a graphitization furnace for high temperature treatment, and then calendered to obtain a high thermal conductivity graphite sheet.

[0078] Example 5

[0079] A method for preparing a high thermal conductivity graphite sheet, comprising the following steps:

[0080] (1) Resin preparation: 85.78 kg of ODA, 11.96 kg of 1.5-naphthalene diamine, 87.94 kg of PMDA, 9.74 kg of BTDA, and 20.27 kg of 1,4,5,8-naphthalene tetracarboxylic dianhydride were added in batches in 780 kg of DMF, and a polycondensation reaction was carried out at 28°C. After completion, 2.5 kg of EPA was added for end capping, and after defoaming, a polyamic acid resin with a viscosity of 1850P was obtained.

[0081] (2) Dispersion liquid preparation: 4.31 kg of boron nitride with a particle size of 2.5 μm was first added to 11.2 kg of DMF, and after high-speed dispersion and stirring, was used.

[0082] (3) Chemical flow method promoter preparation: 300 kg of acetic anhydride and 60 kg of isoquinoline were dissolved in 40 kg of NMP, and after uniform dissolution and stirring, were used.

[0083] (4) PI film preparation: the above three were mixed in a needle mixer for 10 s, the mixing temperature was 6°C, the mixer speed was 3800 rpm, and the slurry temperature was 150°C to obtain a polyamic acid gel film, which was then peeled off from the steel belt and imidized at 200-600°C, the casting speed was 12 m / min, and a PI film with a thickness of 190 μm was obtained.

[0084] (5) Graphite sheet preparation: the PI film was sequentially placed in a carbonization furnace and a graphitization furnace for high temperature treatment, and then calendered to obtain a high thermal conductivity graphite sheet.

[0085] The schematic diagram of the needle mixer and the continuous online doping process used in the example is shown in Figure 1 .

[0086] Comparative Example 1

[0087] A method for preparing a graphite sheet, comprising the following steps:

[0088] (1) Resin preparation: 69.74 kg of ODA, 4.19 kg of PDA and 86.1 kg of PMDA were added in batches in 840 kg of DMAc, and a polycondensation reaction was carried out at 45°C. After completion, 1 kg of 4-PEPA was added for end capping, and after defoaming, a polyamic acid resin with a viscosity of 2100P was obtained.

[0089] The rest was the same as Example 1.

[0090] Comparative Example 2

[0091] A method for preparing a graphite sheet, comprising the following steps:

[0092] (1) Resin preparation: 64.33 kg of ODA, 3.86 kg of PDA, 58.40 kg of PMDA and 33.51 kg of 1,4,5,8-naphthalene tetracarboxylic dianhydride were added in batches in 840 kg of DMAc, and a polycondensation reaction was carried out at 45°C. After completion, 1 kg of 4-PEPA was added for end capping, and after defoaming, a polyamic acid resin with a viscosity of 2100P was obtained.

[0093]

[0094] The rest was the same as Example 1.

[0095] Comparative Example 3

[0096] A method for preparing a graphite sheet, comprising the following steps:

[0097] (1) Resin preparation: 70.65 kg of ODA, 4.24 kg of PDA, 72.67 kg of PMDA and 12.61 kg of 1,4,5,8-naphthalene tetracarboxylic dianhydride were added in batches in 840 kg of DMAc, and a polycondensation reaction was carried out at 45°C. After defoaming, a polyamic acid resin with a viscosity of 2100P was obtained.

[0098] The rest was the same as Example 1.

[0099] Comparative Example 4

[0100] A method for preparing a graphite sheet, without dispersing liquid in the preparation process, and the rest was the same as Example 1.

[0101] Comparative Example 5

[0102] A method for preparing a graphite sheet, comprising the following steps

[0103] ​(1) Hybrid resin preparation: 0.32 kg of calcium carbonate with a particle size of 1 μm was dissolved in 1.28 kg of DMAc, and uniformly dispersed by high-speed stirring to obtain a dispersion liquid, which was then added in batches to 840 kg of DMAc, 70.65 kg of ODA, 4.24 kg of PDA, 72.67 kg of PMDA and 12.61 kg of 1,4,5,8-naphthalene tetracarboxylic dianhydride, and a polyamide acid resin with a viscosity of 2100 P was obtained by performing a polycondensation reaction at 45°C, followed by addition of 1 kg of 4-PEPA for end capping and defoaming.

[0104] The preparation of the chemical flow casting method promoter, the PI film and the graphite sheet was the same as in Example 1.

[0105] Comparative Example 6

[0106] A method for preparing a graphite sheet, wherein the preparation process is performed in a pin mixer with an online mixing time of 75 s, and the rest is the same as in Example 1.

[0107] Comparative Example 7

[0108] A method for preparing a graphite sheet, wherein the preparation process is performed in a pin mixer with an online mixing temperature of 15°C in step (4), and the rest is the same as in Example 1.

[0109] Performance detection

[0110] The mechanical properties of the PI film are characterized by tensile strength and elongation at break, the planar orientation degree of the PI film is characterized by birefringence, and the thermal conductivity of the graphite is characterized by carbon density and thermal conductivity coefficient. The properties of the polyimide films and graphite sheets prepared in Examples 1-5 and Comparative Examples 1-7 are shown in Table 1.

[0111] Table 1: Comparison of properties of PI films and graphite sheets prepared in examples and comparative examples

[0112]

[0113] *Note: The symbol " / " indicates that the mechanical properties of the PI film are low and the texture is too brittle, and continuous production is not possible.

[0114] From the results of Table 1, it can be analyzed that the PI film in Comparative Example 1 without inorganic particles of large aromatic ring structure cannot obtain high thermal conductivity graphite due to low carbon density or poor induced orientation effect. In Comparative Example 2, the content of large aromatic ring structure is too high, and the rigidity of the molecular chain is too large, which can significantly reduce the mechanical properties of the PI film, and the graphite sheet with good appearance cannot be obtained. In Comparative Example 3, the PI film without introducing a cross-linking type end-capping agent has a decreased orientation degree, and the thermal conductivity cannot reach 2000 W / m·K. In Comparative Example 4, no specific filler is added, and it is difficult to form a continuous thermal conduction network during graphitization, which affects the thermal conductivity of graphite. In Comparative Example 5, the hybrid resin is prepared by in-situ polymerization, and the inorganic particles stay in the resin system for a long time, which causes secondary agglomeration and sedimentation, resulting in uneven distribution of the inorganic particles in the film, which affects the performance of the PI film and its graphite sheet. In Comparative Examples 6 and 7, the online mixing time of the imidization promoter, the resin and the inorganic particle dispersion liquid is too long or the temperature is too high, and a large amount of gel impurities is formed in the system, which can cause a sharp decrease in the mechanical properties of the PI film, and the PI film cannot be smoothly wound to obtain a PI film with good appearance. In the present application, by introducing a certain amount of large aromatic ring structure of naphthalene ring, anthracene ring and anthraquinone into the PI molecular structure and cross-linking type end-capping agent, the planar orientation degree of the PI film can be improved, the carbon density can be increased, and the inorganic particles introduced by the online hybrid technology can form a synergistic effect, and then induce graphitization transformation during high-temperature sintering, and the thermal conductivity of the prepared graphite sheet can reach 2000 W / m·K.

[0115] The above is a further detailed description of the present application in combination with specific preferred embodiments, and cannot be regarded as limiting the specific implementation of the present application to these descriptions. For ordinary skilled persons in the art to which the present application belongs, a number of simple deductions or substitutions can be made without departing from the concept of the present application, and all of them should be regarded as falling within the protection scope of the present application.

Claims

1. A method for producing a polyimide film, characterized by, The preparation method comprises the following steps: S1, preparing raw material polyamide acid resin solution, inorganic particle dispersion liquid and chemical flow casting method accelerator; the polyamide acid resin solution is prepared by polycondensation reaction of diamine, dianhydride, large aromatic ring monomer and crosslinking type blocking agent, the large aromatic ring monomer is aromatic ring containing one or more of naphthalene ring, anthracene ring or anthraquinone; the molar amount of the large aromatic ring monomer accounts for 5-30% of the total molar amount of diamine and dianhydride; the crosslinking type blocking agent is selected from one or more of 4-phenylacetylene phthalic anhydride, 4-ethynyl phthalic anhydride and 4-ethynyl aniline; S2, the raw materials prepared in S1 are instantaneously mixed uniformly in a needle mixer, the time of instantaneously mixing online is 10-50s, and the mixing temperature is-15-10℃; S3, after mixing, the polyimide film is obtained by casting and imidization without defoaming.

2. The method for producing a polyimide film according to claim 1, characterized by, The rotating speed of the mixer in S2 is 1000-4000rpm.

3. The method for producing a polyimide film according to claim 2, characterized by, The top of the needle mixer is provided with a polyamide acid resin feeding port, and the same height of the needle mixer is provided with a dispersion liquid feeding port and a chemical flow casting method accelerator feeding port; the polyamide acid resin is fed first, and then the dispersion liquid and the chemical flow casting method accelerator are fed simultaneously.

4. The method for producing a polyimide film according to any one of claims 1 to 3, characterized by, The large aromatic ring monomer is selected from one or more of 1,4,5,8-naphthalene tetracarboxylic dianhydride, 2,3,6,7-naphthalene tetracarboxylic dianhydride, 2,3,6,7-anthracene tetracarboxylic dianhydride, anthra-2,6-diamine, 1.5-naphthalene diamine, 1,4-diaminonaphthalene and 1,8-dihydroxy-2,4,5,7-tetraaminanthraquinone.

5. The method of producing a polyimide film according to any one of claims 1 to 3, characterized by, The addition amount of the crosslinking type blocking agent is 0.05%-0.5% of the mass of the polyamide acid resin.

6. The method of producing a polyimide film according to claim 1, characterized by, The solid content of the inorganic particle dispersion liquid is 10%-25%, and the inorganic particles are selected from one or more of silicon oxide, silicon carbide, aluminum nitride, silicon nitride, boron nitride, calcium phosphate, calcium hydrogen phosphate, calcium pyrophosphate, calcium carbonate, calcium bicarbonate, aluminum oxide, carbon nanotube and graphene; the particle size of the inorganic particles is 50nm-5μm; and the addition amount of the inorganic particles is 0.03%-20% of the mass of the polyimide film.

7. The method of producing a polyimide film according to claim 1, characterized by, In S3, the casting temperature is 60-180℃, the imidization temperature is 200-600℃, and the casting speed is 10-35m / min.

8. A high thermal conductivity graphite sheet, characterized by, The polyimide film prepared by the preparation method in any one of claims 1-7 is subjected to carbonization, graphitization and calendering treatment, and the thermal conductivity coefficient of the graphite sheet is ≥2000W / m·K.

9. The polyimide film prepared by the preparation method in any one of claims 1-7 or the graphite sheet in claim 8 is applied to electronic device heat dissipation materials.

10. The polyimide film prepared by the preparation method in any one of claims 1-7 is applied to the fields of electronic information, flexible display, aerospace, chip semiconductor or national defense.

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