CN113234244A

CN113234244A - Low-dielectric high-thermal-conductivity polyimide film and preparation method thereof

Info

Publication number: CN113234244A
Application number: CN202110609229.5A
Authority: CN
Inventors: 朱凌云; 王振宇; 汪英; 任小龙
Original assignee: Guilin Electrical Equipment Scientific Research Institute Co Ltd
Current assignee: Guilin Electrical Equipment Scientific Research Institute Co Ltd
Priority date: 2021-06-01
Filing date: 2021-06-01
Publication date: 2021-08-10

Abstract

The invention discloses a polyimide film with low dielectric constant and high thermal conductivity and a preparation method thereof. The preparation method of the film comprises the following steps: firstly, preparing a polyamic acid resin solution; adding the silver salt dispersion liquid and the heat-conducting filler dispersion slurry into the polyamic acid resin solution, uniformly mixing, and carrying out constant-temperature thermal decomposition, imidization and sizing treatment on the obtained mixed resin solution after casting to form a film; wherein the silver salt dispersion liquid and the heat-conducting filler dispersion slurry are respectively a solution and a slurry formed by respectively dispersing silver salt and heat-conducting filler in a polar aprotic solvent, and the adding amount of the silver salt dispersion liquid and the heat-conducting filler dispersion slurry is respectively 0.1-10 wt% of the solid content of the polyamic acid resin solution and 0.8-1.2 times of the adding amount of the silver salt; the constant temperature thermal decomposition treatment is thermal decomposition at 190-220 ℃, and the decomposition time is more than or equal to 5 min. The method of the invention ensures that the obtained film has low dielectric property and higher heat conductivity coefficient on the premise of adding a small amount of heat-conducting filler.

Description

Low-dielectric high-thermal-conductivity polyimide film and preparation method thereof

Technical Field

The invention relates to a polyimide material, in particular to a low-dielectric high-thermal-conductivity polyimide film and a preparation method thereof.

Background

Polyimide (PI) films have excellent high temperature resistance, chemical resistance, mechanical properties, and electrical properties, and are widely used as dielectric materials in the microelectronics industry. The molecular chain of the common PI film is a polar chain, and the dielectric constant (Dk) is usually 3.2-3.8.

With the rapid development of the microelectronic industry, the functions of microelectronic elements are continuously enhanced, the volume is continuously reduced, the integration level of very large scale integrated circuits is higher and higher, the size is gradually reduced, the parasitic resistance effect and the parasitic capacitance effect in the circuits are more and more serious, and the resistance and capacitance delay of metal interconnection is increased in a nearly quadratic way, so that the capacitance in resistance and wiring is increased, the problems of signal transmission delay and crosstalk, noise interference, power loss increase and the like are caused, and the performance of devices is directly influenced. In order to reduce the increase of power consumption caused by signal transmission delay, crosstalk and dielectric loss, satisfy the requirement of high speed signal transmission, and further improve the function of electronic circuits, a dielectric interlayer insulating material is required to have lower dielectric properties, and usually, a dielectric constant of a polyimide material is required to be reduced from 3.2 to 3.8 to less than 3.0, and a dielectric loss factor (Df) is required to be reduced from 0.4 to 0.01 to less than 0.006, or even lower. On the other hand, because polyimide itself is almost a poor thermal conductor, the thermal conductivity of the conventional polyimide film is about 0.1-0.2W/m.k, the thermal conductivity is poor, heat is easily accumulated, the stability, the service life and the operation safety of electronic components are affected, and the upgrading of related industries is limited. In order to meet the increasing heat conduction (dissipation) requirements of circuit boards and devices, insulation materials with high thermal conductivity must be considered, and therefore, the development and production of polyimide films with high thermal conductivity are promoted. Therefore, it is desirable to obtain a reduced polyimide film having an ultra-low dielectric constant and high thermal conductivity.

In the prior art, the method for reducing the dielectric property of polyimide mainly comprises the following steps: (1) the polyimide is subjected to fluorination modification, and the molecular polarizability is reduced by introducing fluorine-containing groups on the polyimide; (2) by adding bulky structural groups such as fluorene functional groups, poly cage siloxane structural groups; (3) adding fluoroplastic fillers such as polytetrafluoroethylene powder; (4) lowering the dielectricity by introducing a microporous structure in the polyimide molecular structure according to the minimum dielectric constant of air; and so on. Among these methods, the preparation of polyimide porous films by introducing air holes is an effective method for reducing the dielectric constant of polyimide. At present, polyimide porous films are prepared at home and abroad mainly by adopting a chemical solvent method and a thermal degradation method:

a. the chemical solvent method is a method in which a composite material is prepared by adding a pore-forming agent (pore-forming substance), and then the pore-forming agent is removed by a chemical reaction or an extractive dissolution method to generate pores. Such as patent publications CN104910409A, CN1760241A or CN 104211980A.

b. Thermal degradation methods create holes by introducing thermally degradable components. For example, patent publication No. CN110358134A discloses a method for preparing a polyimide film with a low dielectric constant, in which aluminum triacetylacetonate is used as a pore-forming agent, and is dispersed in a polyamic acid resin solution, and the resulting mixed solution is subjected to a high-temperature heat treatment to sublimate and volatilize the aluminum triacetylacetonate in the thermal imidization process, so that holes are left in the polyimide substrate, thereby obtaining a polyimide film with a dielectric constant of 2.0-2.6. Although the polyimide film with a lower dielectric constant can be obtained by the method, the elongation of the obtained film is too low to meet the requirements of certain fields in the actual industry (for example, the elongation of the flexible copper clad laminate to the polyimide film with the thickness of 12.5 mu m is more than or equal to 40 percent and the surface resistivity requirement is more than or equal to 10 percent according to the standard requirement of GB/T13542.6-2006 when the film is used for the flexible copper clad laminate¹⁴Ω) of the measured values.

In order to obtain higher thermal conductivity, the current commercial method is mainly to prepare a composite film by uniformly doping a polyamide acid resin with a thermal conductive filler including alumina, silica, magnesia, zinc oxide, aluminum nitride, silicon nitride, boron nitride, or the like. The polyimide composite film prepared by the method for uniformly doping the heat-conducting filler is difficult to form an effective heat-conducting channel when the doping amount of the heat-conducting filler is lower than 30 wt%, so that the heat-conducting performance of the obtained composite film is improved to a limited extent. Theoretically, the film can be endowed with a high thermal conductivity coefficient by doping a large amount of thermal conductive filler, but it is known in the art that the mechanical property and the insulating property of the film are greatly reduced because the filler is easy to agglomerate in the film.

Disclosure of Invention

The invention aims to solve the technical problem of providing a low-dielectric high-thermal-conductivity polyimide film and a preparation method thereof.

In order to solve the technical problems, the invention adopts the following technical scheme:

a preparation method of a polyimide film with low dielectric and high thermal conductivity comprises the following steps:

1) preparing a polyamic acid resin solution;

2) adding silver salt dispersion liquid and heat-conducting filler dispersion slurry into polyamide acid resin solution, uniformly mixing, and carrying out constant-temperature thermal decomposition, imidization and sizing treatment on the obtained mixed resin solution after casting to form a film so as to obtain a low-dielectric high-heat-conducting polyimide film; wherein the content of the first and second substances,

the silver salt dispersion liquid is a solution formed by dispersing silver salt in a polar aprotic solvent, wherein the silver salt is any one or the combination of more than two of silver nitrate, silver carbonate and silver oxalate;

the adding amount of the silver salt dispersion liquid is controlled to be 0.1-10 wt% of the solid content of the polyamic acid resin solution;

the heat-conducting filler dispersing slurry is formed by dispersing a heat-conducting filler in a polar aprotic solvent, and the adding amount of the heat-conducting filler dispersing slurry is 0.8-1.2 times that of the silver salt;

the constant temperature thermal decomposition treatment is thermal decomposition at 190-220 ℃, and the decomposition time is more than or equal to 5 min.

In step 2) of the method of the present invention, the selection of the polar aprotic solvent for dispersing the silver salt and dispersing the heat conductive filler is the same as that used in the preparation of the polyamide-based resin solution in the art, wherein the amount of the polar aprotic solvent is preferably controlled, and the concentration of the silver salt in the silver salt dispersion liquid or the concentration of the heat conductive filler in the heat conductive filler dispersion slurry is preferably controlled to be 1 to 30 wt%, more preferably 5 to 20 wt%. The silver salt is easy to dissolve in polar aprotic solvent, and the silver salt has excellent compatibility with the polyamic acid resin solution, so that the problem that the introduced silver salt is difficult to disperse is solved. In order to further improve the dissolution or dispersion of the silver salt or the heat conductive filler in the polar aprotic solvent, a dispersing device such as a homogenizer, a grinder, a sand mill, an emulsifying machine, or an ultrasonic dispersing machine may be used to uniformly disperse the silver salt or the heat conductive filler in the polar aprotic solvent. Similarly, the above conventional method and apparatus can be used to further improve the uniform dispersion degree of the silver salt dispersion liquid and the heat conductive filler dispersion slurry in the polyamic acid resin solution.

In step 2) of the method of the present invention, silver nitrate is further preferably used as the silver salt; the addition amount of the silver salt dispersion liquid is further preferably controlled to be 0.5-7.5 wt% of the solid content of the polyamic acid resin solution, and more preferably 1-5 wt% of the solid content of the polyamic acid resin solution. As for the thermally conductive filler, it may be a conventional choice in the art, and is preferably one or a combination of two or more selected from carbon nanotubes, graphene, alumina, aluminum nitride, boron nitride, and the like. For the carbon nanotube, the diameter is preferably 200nm or less and the length is 5 μm or less; for alumina and boron nitride, their particle size is preferably micron, submicron or nanometer, and may be any combination of these particle sizes; the particle size of the aluminum nitride is preferably less than or equal to 300nm, and the particle size is more preferably 25-180 nm; for graphene, graphene with the number of layers less than or equal to 4 is preferable. The addition amount of the heat-conducting filler dispersing slurry is further preferably controlled to be 0.9-1.0 time of that of the silver salt.

In step 2) of the method of the present invention, the self-supporting film (also referred to as polyamic acid film in this application) obtained by casting is thermally decomposed at a specific temperature, so that the silver salt therein is completely decomposed into silver oxide (wherein the generated nitrogen dioxide or carbon monoxide continuously escapes from the self-supporting film, and the heat conductive filler is not decomposed at the above temperature conditions. Because the content of the solvent in the self-supporting film obtained by casting is about 30% (20-40% in general), nitrogen dioxide or carbon monoxide generated in the thermal decomposition process escapes from the self-supporting film and cannot cause the formation of holes), the silver oxide generated by thermal decomposition is heated and further decomposed into nano silver simple substances and oxygen in the subsequent high-temperature imidization treatment, because the generated oxygen is small, in the process of further decomposition by heating, the oxygen generated in the decomposition of the silver oxide positioned in the self-supporting film expands in situ in the polyimide matrix obtained by synchronously heating and imidizing to form bubbles, and the oxygen generated in the decomposition of the silver oxide positioned on the surface or close to the surface of the self-supporting film leaves holes from the surface of the polyimide matrix obtained by heating and imidizing, the obtained film contains the bubbles inside, The existence of the air bubbles and the holes ensures the low dielectric property of the obtained film. On the other hand, since the pores present inside the film are closed bubbles rather than pores communicating with the surface of the film, the degree of deterioration of the mechanical properties of the resulting film can be effectively suppressed.

Based on the good compatibility of silver salt and polar aprotic solvent, silver salt is uniformly distributed in the self-supporting film, and the subsequent thermal decomposition is carried out at a specific temperature, so that the particles of the obtained silver oxide are tiny, the silver oxide can be decomposed in the subsequent imidization to obtain nano-scale silver simple substance particles with the particle size of 10-150 nm, and the oxygen obtained by the decomposition is limited, therefore, the silver oxide positioned in the self-supporting film only expands in situ in a polyimide matrix to form bubbles, but not directly escapes from the polyimide matrix to form holes. Moreover, the existence of simple substance silver nanoparticles in the film can play a synergistic role in the technical effect of high heat conduction by adding a small amount of heat-conducting filler: the heat-conducting filler is connected in the PI matrix through functional bonding force such as hydrogen bond, Van der Waals force and the like under the assistance of the simple substance silver nanoparticles to form a heat-conducting connecting structure, a conjugated system is formed through PI-PI action, and a (two-dimensional laminated layer structure or a specific three-dimensional topological structure) multidimensional heat-conducting pore channel is formed at the same time, so that the obtained film can obtain the technical effect of high heat conductivity coefficient under the condition of adding a small amount of the heat-conducting filler, and the technical balance between dielectric constant and heat conductivity in the existing low dielectric material is overcome.

The time for constant-temperature thermal decomposition can be determined according to the thickness of the low-dielectric-property polyimide film to be prepared actually, and when the thickness of the film to be prepared is 7.5-12.5 mu m, the time for thermal decomposition is preferably controlled to be 5-10 min; when the thickness of the film to be prepared is 12.5 to 50 μm, the thermal decomposition time is preferably controlled to 10 to 30 min. For thicker films, such as 75-150 μm films, 35-60 min is usually required.

In order to improve the dimensional stability of the silver/polyimide composite film, a stretching treatment is preferably added after the constant-temperature thermal decomposition treatment and before the imidization treatment, the operation of the stretching treatment is the same as that of the prior art, specifically, the stretching treatment comprises longitudinal stretching and/or transverse stretching of the self-supporting film obtained by casting, preferably, the longitudinal stretching and the transverse stretching are both carried out at 225-280 ℃, the time is controlled at 0.1-6.0 h, and the stretching ratio is preferably 0.8-2.5.

In step 2) of the method of the present invention, in actual production, the mixed resin solution obtained by mixing the polyamic acid resin solution and the silver salt dispersion liquid usually needs to be defoamed and then salivated to form a film. In the step, the operations of the salivation film forming, the imidization and the sizing treatment are the same as those of the prior art, specifically, the salivation film forming can be carried out at the temperature of between room temperature and 175 ℃, and the salivation drying treatment time is usually controlled to be between 0.1 and 3.0 hours; the thermal imidization is preferably carried out at 350-600 ℃, and the imidization time is controlled to be 0.1-9.0 h; the setting treatment is carried out at 180-360 ℃, and the time of the setting treatment is controlled to be 0.1-7.0 h.

The polyamic acid resin solution in step 1) of the present invention, also referred to as polyamic acid resin, polyamic acid solution, polyamic acid or polyimide precursor, is prepared by conventional in situ polymerization, such as known polycondensation reaction of diamine and dianhydride in polar aprotic solvent. Wherein, the selection and the dosage of the diamine, the dianhydride and the polar aprotic solvent are the same as those of the prior art, and the temperature and the time of the polycondensation reaction are also the same as those of the prior art. Specifically, the method comprises the following steps:

the diamine is preferably an aromatic diamine selected from the group consisting of 3,4' -diaminodiphenyl ether (3,4' -ODA), 4' -diaminodiphenyl ether (4,4' -ODA), 2' -bis (trifluoromethyl) -4,4' -diaminobiphenyl (2,2' -TFDB), 3' -bis (trifluoromethyl) -4,4' -diaminobiphenyl (3,3' -TFDB), 4' -diaminobiphenyl, m-phenylenediamine (m-PDA), p-phenylenediamine (p-PDA), 2' -bis (trifluoromethyl) -4,4' -diaminodiphenyl ether (TFODA), 3' -diamino-5, 5 ' -bis (trifluoromethyl) biphenyl (s-TFDB), 2, 2-bis (trifluoromethyl) -4,4 '-diaminophenylsulfone (SFTA), 4' -bis (2-trifluoromethyl-4-aminophenoxy) diphenylsulfone, 2- (4-aminophenyl) -5-aminobenzimidazole (APBIA), 4 '-bis (3-aminophenoxy) diphenylsulfone (M-BAPS), bis (3-aminophenyl) sulfone (3-DDS), bis (4-aminophenyl) sulfone (4-DDS), 4' -bis (4-aminophenoxy) biphenyl (BAPB), 1, 3-bis (3-aminophenoxy) benzene (TPE-M), 1, 3-bis (4-aminophenoxy) benzene (TPE-R), 1, 4-bis (4-aminophenoxy) benzene (TPE-Q), 2,2' -bis [4- (4-aminophenoxy phenyl) ] propane (BAPP), 2-bis [4- (4-aminophenoxy) phenyl ] Hexafluoropropane (HFBAPP), 9-bis (3-fluoro-4-aminophenyl) fluorene (FFDA), 9-bis (3-methyl-4-aminophenyl) fluorene (BMAPF), 9-bis (4-aminophenyl) Fluorene (FDA), 1, 3-cyclohexanediamine, 1, 3-cyclobutanediamine, and the like. Further preferred are compounds selected from the group consisting of 2,2' -bis (trifluoromethyl) -4,4' -diaminobiphenyl (2,2' -TFDB), 3' -bis (trifluoromethyl) -4,4' -diaminobiphenyl (3,3' -TFDB), 2' -bis (trifluoromethyl) -4,4' -diaminodiphenyl ether (TFODA), 3' -diamino-5, 5 ' -bis (trifluoromethyl) biphenyl (s-TFDB), 2-bis (trifluoromethyl) -4,4' -diaminophenylsulfone (SFTA), 4' -bis (2-trifluoromethyl-4-aminophenoxy) diphenylsulfone, 2' -bis [4- (4-aminophenoxyphenyl) ] propane (BAPP), 2, 2-bis [4- (4-aminophenoxy) phenyl ] Hexafluoropropane (HFBAPP), 9-bis (3-fluoro-4-aminophenyl) fluorene (FFDA), 9-bis (3-methyl-4-aminophenyl) fluorene (BMAPF), 9-bis (4-aminophenyl) Fluorene (FDA), 1, 3-cyclohexanediamine, 1, 3-cyclobutanediamine, and the like.

The dianhydride is preferably an aromatic dianhydride selected from the group consisting of 2, 2-bis (3, 4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA), 3,4 '-hexafluoroisopropylphthalic anhydride (a-6FDA), 4- (2, 5-dioxotetrahydrofuran-3-yl) -1,2, 3, 4-tetrahydronaphthalene-1, 2-dicarboxylic anhydride (TDA), 4' - (4,4 '-isopropyldiphenoxy) bis (phthalic anhydride) (HBDA), 2,3,3',4 '-biphenyltetracarboxylic dianhydride (a-BPDA), 4' -triphendiether tetracarboxylic dianhydride (HQDPA), diphenylsulfide tetracarboxylic dianhydride (3,4,3',4' -TDPA, 2,3,2',3' -TDPA, 2,3,3',4' -TDPA), 2,3,3',4' -diphenylether tetracarboxylic dianhydride (a-ODPA), 2-bis [4- (3, 4-dicarboxyphenoxy) phenyl ] propane dianhydride (BPADA), 3,3',4,4' -diphenylsulfone tetracarboxylic dianhydride, 2,3',4' -diphenylsulfone tetracarboxylic dianhydride, pyromellitic acid (PMDA), 3,3',4,4' -biphenyltetracarboxylic dianhydride (BPDA), 2',3,3' -biphenyltetracarboxylic dianhydride (BPDA), 2,3,3',4' -benzophenonetetracarboxylic dianhydride (a-BTDA), benzophenonetetracarboxylic dianhydride (BTDA), 4,4' -oxydiphthalic anhydride (ODPA), 1,2,3, 4-cyclobutanetetracarboxylic dianhydride (CBDA), 1,2,3, 4-cyclopentanetetracarboxylic dianhydride (CPDA) and 1,2,4, 5-cyclohexanetetracarboxylic dianhydride (HPMDA). More preferably, it is any one or a combination of two or more selected from 2, 2-bis (3, 4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA), 3,4' -hexafluoroisopropylphthalic anhydride (a-6FDA), 1,2,3, 4-cyclobutanetetracarboxylic dianhydride (CBDA), 1,2,3, 4-cyclopentanetetracarboxylic dianhydride (CPDA), 1,2,4, 5-cyclohexanetetracarboxylic dianhydride (HPMDA), and the like.

The polar aprotic solvent may be specifically selected from the group consisting of N, N '-Dimethylacetamide (DMAC), N' -Dimethylformamide (DMF), N-methylpyrrolidone (NMP), N-ethyl-2-pyrrolidone, 1, 3-dimethyl-2-imidazolidinone, N-methylcaprolactam, hexamethylphosphoric triamide, 1, 2-dimethoxyethane, bis (2-methoxyethyl) ether, 1, 2-bis (2-methoxyethoxy) ethane, tetrahydrofuran, bis [2- (2-methoxyethoxy) ethyl ] ether, 1, 4-dioxane, dimethyl sulfoxide (DMSO), tetramethylsulfoxide, N '-dimethyl-N, N' -propyleneurea (DMPU), cyclopentanone, cyclohexanone, N-Dimethylolmethane (DMF), N-methylpyrrolidone (DMF), N-methylethyl, N-Dimethylolmethane (DMF), N-methylethyl-Dimethylolmethane (DMF), N-2-Dimethylolmethane (DMF), hexamethylolmethane (DMF), N-2-Dimethoxyethane (DMPU), tetrahydrofuran (DMPU), Dimethylolmethane (DMP), or Dimethylolmethane (DMP) or, Dichloromethane, monochlorobenzene, dichlorobenzene, chloroform, tetrahydrofuran, 3-methyl-N, N-dimethylpropionamide, N dialkyl carboxyl amide, dimethyl sulfone, diphenyl ether, sulfolane, diphenyl sulfone, tetramethylurea, phenol m-cresol and gamma-butyrolactone. Further preferred is N '-Dimethylacetamide (DMAC), N' -Dimethylformamide (DMF), N-methylpyrrolidone (NMP) or γ -butyrolactone.

The polycondensation reaction of diamine and dianhydride is preferably carried out in an inert atmosphere (such as nitrogen, and the like) at the temperature of 10-80 ℃ under stirring, the dianhydride is preferably added in batches, and the molar ratio of the diamine to the dianhydride is generally controlled to be 0.9-1.1: 1, the reaction time is usually controlled to be 4-8 h. The solid content of the polyamic acid resin solution obtained by polymerization is preferably controlled to be 5 to 40 wt%, more preferably 10 to 30 wt%, and particularly preferably 12 to 22 wt%.

Compared with the prior art, the invention is characterized in that:

the invention also comprises the polyimide film with low dielectric constant and high thermal conductivity prepared by the method, the dielectric loss factor of the film is less than or equal to 0.003, the dielectric constant is less than or equal to 2.8 (under the test frequency of 10 GHz), and the surface resistivity is more than or equal to 3.5 multiplied by 10¹⁴Omega, the out-of-plane thermal conductivity coefficient is more than 0.58W/m.K, the tensile strength is more than or equal to 240MPa, the elongation is more than or equal to 42 percent, and the water absorption is less than or equal to 2.0 percent.

Compared with the prior art, the invention is characterized in that:

1. the obtained film is a polyimide film which contains bubbles inside and has holes on the surface, so that the film has lower dielectricity compared with the conventional nonporous film; secondly, by introducing soluble silver salt into the PAA resin, the introduction of silver salt (particularly silver nitrate) inhibits the deformation effect of a specific framework in the process of forming polyimide, namely, the relative displacement among atoms in a main chain structure is greatly reduced, and the atom polarization is inhibited; moreover, nanoscale simple substance silver particles obtained after imidization are uniformly dispersed in the PI matrix, and due to the fact that the simple substance silver particles are small in size, an effective dielectric network is not easily formed inside the composite film, and the inhibition on the interface polarization of polyimide molecules around the silver particles is more obvious (due to the uniform dispersion of the simple substance silver particles, the quantum coulomb blocking effect of the simple substance silver particles is effectively promoted to block the migration of electrons in a system); the combination of these two effects further results in a reduction in the dielectric properties of the resulting film; the combined action of the three actions realizes the great reduction of the overall dielectric property of the obtained film.

2. Based on the polyimide with covalent bond connection as a main chain structure, in the presence of lone pair electrons of silver atoms (metal) and nitrogen atoms in silver salts, through chemical bond actions such as metal-carboxylic acid coordination bonds, hydrogen bonds and the like, the crystallization and orientation of polyimide molecules with a conjugated structure are greatly improved, so that the stacking among the polyimide molecular chains is further enhanced under the influence of van der Waals force, and the interlayer distance of the polyimide molecular chains is reduced; in addition, the simple substance silver nanoparticles obtained by reduction are uniformly dispersed in the polyimide matrix and are not separated from the inside of the film (at least, the simple substance silver nanoparticles in the film are not separated from the inside of the film), and because the simple substance silver particles are small in size and uniform in distribution, a supporting framework in the polyimide matrix is effectively formed, so that the obtained polyimide film has good mechanical properties; on the other hand, since the pores present inside the film are bubbles rather than pores communicating with the surface of the film, the degree of deterioration of the mechanical properties of the resulting film can be effectively suppressed. Meanwhile, silver nitrate and nano-scale decomposition products thereof effectively inhibit molecular chain distortion in the imidization process of the polyamic acid, so that the arrangement of polyimide molecular chains is more linear, and in addition, simple substance silver particles reduced in situ are uniformly dispersed in a polyimide substrate, so that the obtained polyimide film keeps lower water absorption under the comprehensive action.

3. The existence of the simple substance silver nano particles in the film enables the obtained film to obtain the technical effect of higher heat conductivity coefficient on the basis of adding a small amount of heat-conducting filler.

4. Dielectric loss of films produced according to the method of the inventionThe factor is less than or equal to 0.003, the dielectric constant is less than or equal to 2.8 (at the test frequency of 10 GHz), and the surface resistivity is more than or equal to 3.5 multiplied by 10¹⁴Omega, the out-of-plane thermal conductivity coefficient is more than 0.58W/m.K, the tensile strength is more than or equal to 240MPa, the elongation is more than or equal to 42 percent, and the water absorption is less than or equal to 2.0 percent.

Drawings

FIGS. 1 and 2 are electron micrographs of a polyimide composite film obtained in example 1 of the present invention, wherein FIG. 1 is a surface and FIG. 2 is a cross section (thickness direction).

FIG. 3 is a DTA curve of the polyamic acid resin solution obtained in step 1) and the mixed resin solution obtained in step 2) in example 1, wherein curve A represents the polyamic acid resin solution and curve B represents the mixed resin solution.

FIG. 4 is an XRD pattern of the self-supporting film obtained in step 2) in example 1 of the present invention.

FIG. 5 is an electron micrograph of a film of a pure polyimide obtained in comparative example 1 of the present invention.

FIG. 6 is an electron micrograph of a polyimide film obtained in comparative example 2 of the present invention.

Detailed Description

In order to better explain the technical solution of the present invention, the present invention is further described in detail with reference to the following examples, but the embodiments of the present invention are not limited thereto.

When a polyimide film is produced by using the process described in the following examples, the thickness of the polyimide film is not limited, and may be various thicknesses such as 12.5 μm, 25 μm, 38 μm, 50 μm, 75 μm, 100 μm, 125 μm, or 150 μm.

In the following examples and comparative examples, the purity of the monomer is 99.5% or more, and the solvent for forming the silver salt dispersion and the heat conductive filler dispersion slurry in each example is the same as the solvent for preparing the polyamic acid resin solution in the examples.

The dielectric loss factor and dielectric constant of the films in Table 1 were tested according to the Standard GB/T13542.2-2006 "film for Electrical insulation part 6: polyimide film for electrical insulation "6.1 properties independent of thickness were tested.

The mechanical properties (tensile strength and elongation) of the film in table 1 are tested by using an electronic universal tensile machine (model KD111-0.2, qian li test instrument ltd, shenzhen), specifically referring to standard GB/T13542.2-2009 part 2 of film for electrical insulation: test methods.

In Table 1, the water absorption properties are as described in GB/T13542.6-2006 part 6 of film for electrical insulation: polyimide film for electrical insulation "6.1 properties independent of thickness were tested.

The Thermal conductivity (out-of-plane) in Table 1 was measured by using an interface material Thermal resistance and Thermal conductivity measuring apparatus (model LW-9389, Taiwan, science and technology Co., Ltd., China) in accordance with ASTM D5470-2017 Standard Test Method for Thermal Transmission Properties of Thermal Conductive insulating Materials.

The test of the surface resistivity of the film in the table 1 refers to the GB/T1410-.

Example 1

1) 656.00kg of N-methyl-2-pyrrolidone (NMP) is added into a reaction kettle under the nitrogen atmosphere and the temperature of a synthesis system is controlled to be 18 ℃, then 58.315kg of 4,4 '-diaminodiphenyl ether (4,4' -ODA) is added, after stirring and dissolving, dianhydride 3,3',4,4' -biphenyltetracarboxylic acid dianhydride (s-BPDA, 85.685kg, added by 18 times) with the molar ratio of 1:1 to diamine is added, and stirring and reacting are carried out for 24 hours, so that a polyamic acid resin solution with the solid content of 18 wt% is obtained (the solid content in the solution (M, the same below) is 144.0 kg);

2) keeping the polyamic acid resin solution at 10 ℃, adding silver nitrate dispersion liquid (the concentration of silver nitrate is 8 wt%) and carbon nano tube dispersion slurry (the concentration of carbon nano tube is 10 wt%), wherein the addition amount of the silver nitrate dispersion liquid is 3.0 wt% of the solid content of the polyamic acid resin solution, the addition amount of the carbon nano tube dispersion slurry is 3.0 wt% of the solid content of the polyamic acid resin solution (1.0 time of the addition amount of silver nitrate), and stirring and mixing uniformly to obtain a mixed resin solution; coating the obtained mixed resin solution on an annular steel belt through an extrusion molding die, controlling the thickness of a liquid film on the steel belt to be 280 mu m, and then drying and curing at 200 ℃ to remove 75 wt% of solvent to obtain a self-supporting film; and (3) the obtained self-supporting film is sent to an environment at 200 ℃ for heat preservation and decomposition for 18min, then sent to a longitudinal and transverse biaxial stretching machine for longitudinal stretching at 250 ℃ and 1.3 times of stretching for 0.2h and transverse stretching at 280 ℃ and 1.25 times of stretching for 0.5h in sequence, then imidized for 1.5h at 550 ℃, finally shaped for 1.0h at 300 ℃, and rolled to obtain the polyimide film with the thickness of 25 mu m. The surface and cross-section of the obtained polyimide film are shown in fig. 1 and 2, respectively, and it can be seen from fig. 1 and 2 that the obtained film has nano-silver simple substance particles and carbon nanotubes dispersed therein, and the film contains bubbles inside and has pores on the surface.

The polyamic acid resin solution obtained in step 1) and the mixed resin solution obtained in step 2) were subjected to DTA (Differential Thermal Analysis) Analysis, respectively, and their DTA curves are shown in fig. 3. As can be seen from fig. 3, the mixed resin solution has an endothermic peak (the second endothermic peak in the B curve) at 190.2 ℃, which is significantly different from that of the pure polyamic acid resin, and the endothermic peak at 190.2 ℃ of the mixed resin solution can be resolved into the reaction process of decomposing silver nitrate into silver oxide by comparing with the pure silver nitrate DTA curve.

Sampling from the self-supporting film obtained in the step 2), and carrying out XRD analysis on the sample by using an X-ray diffractometer, wherein an X-ray diffraction pattern is shown in figure 4. As can be seen from fig. 4, the diffraction peaks of the self-supporting film sample appeared at 26.4 ° and 38.5 °, which are characteristic diffraction peaks of the carbon nanotube (26.4 °) and the silver oxide (38.5 °), respectively, indicating that the silver nitrate decomposed to form the silver oxide (nitrogen dioxide, a gas product, was released from the matrix) after the mixed resin solution was coated with the film and heat-treated at 200 ℃.

Comparative example 1

The difference between the comparative example and the example 1 is that the silver nitrate dispersion liquid and the carbon nanotube dispersion slurry are not added in the step 2), and the polyamic acid resin solution obtained in the step 1) is directly coated on the ring-shaped steel belt through the extrusion molding die. Finally, a pure (intrinsic) polyimide film with a thickness of 25 μm was obtained, and an electron micrograph thereof is shown in FIG. 5.

Comparative example 2

The difference between the comparative example and the example 1 is that the self-supporting film obtained in the step 2) is directly sent to a longitudinal and transverse biaxial stretching machine for subsequent operation (i.e. the process of thermal decomposition at 200 ℃ for 18min is not carried out). Finally, a polyimide film having a thickness of 25 μm was obtained, and an electron micrograph thereof is shown in FIG. 6. The polyimide film obtained also contains nano-scale silver simple substance particles and carbon nanotubes, but no pores are formed.

Comparative example 3

The difference between the comparative example and the example 1 is that in the step 2), the addition amount of the silver nitrate dispersion liquid is controlled to be 0.05 wt% of the solid content of the polyamic acid resin solution; the addition amount of the carbon nanotube dispersion slurry was controlled to be 0.065 wt% of the solid content of the polyamic acid resin solution (1.3 times of the addition amount of silver nitrate).

Comparative example 4

The difference between the comparative example and the example 1 is that in the step 2), the addition amount of the silver nitrate dispersion liquid is controlled to be 12.0 wt% of the solid content of the polyamic acid resin solution; the addition amount of the carbon nanotube dispersion slurry was controlled to be 8.4 wt% of the solid content of the polyamic acid resin solution (0.7 times the addition amount of silver nitrate).

Comparative example 5

The comparative example is different from example 1 in that the amount of the carbon nanotube dispersion paste was controlled to be 3.9 wt% of the solid content of the polyamic acid resin solution (1.3 times the amount of silver nitrate added).

Comparative example 6

The comparative example is different from example 1 in that the amount of the carbon nanotube dispersion paste was controlled to be 2.1 wt% of the solid content of the polyamic acid resin solution (0.7 times the amount of silver nitrate added).

Comparative example 7

This comparative example differs from example 1 in that no silver nitrate dispersion was added in step 2).

Example 2

This example is different from example 1 in that, in step 2), the amount of silver nitrate dispersion was controlled to be 10.0 wt% of the solid content of the polyamic acid resin solution; the addition amount of the carbon nanotube dispersion slurry was controlled to be 8.0 wt% of the solid content of the polyamic acid resin solution (0.8 times the addition amount of silver nitrate).

Example 3

This example is different from example 1 in that, in step 2), the amount of silver nitrate dispersion was controlled to be 1.0 wt% of the solid content of the polyamic acid resin solution; the addition amount of the carbon nanotube dispersion slurry was controlled to be 1.2 wt% of the solid content of the polyamic acid resin solution (1.2 times of the addition amount of silver nitrate).

Example 4

1) 425.00kg of N, N-Dimethylformamide (DMF) is added into a reaction kettle under the nitrogen atmosphere and at the temperature of a synthesis system controlled to be 35 ℃, 35.897kg of 4,4 '-diaminodiphenyl ether (4,4' -ODA) is added, stirring is carried out to dissolve the DMF, dianhydride pyromellitic diacid (PMDA, 39.103kg, added by 9 times) with the molar ratio of 1:1 to diamine is added into the mixture, stirring is carried out for 36 hours, and polyamic acid resin solution with the solid content of 15 weight percent is obtained (M is 75.0 kg);

2) maintaining 23 ℃ of the polyamic acid resin solution, adding a silver salt dispersion (specifically, a dispersion of silver nitrate and silver carbonate, wherein the concentration of silver nitrate is 15 wt%, and the concentration of silver carbonate is 15 wt%), and a graphene dispersion slurry (the concentration of graphene is 8 wt%), wherein the addition of the silver salt dispersion is controlled to be 3.0 wt% of the solid content of the polyamic acid resin solution, the addition of silver carbonate is 4.5 wt% of the solid content of the polyamic acid resin solution, and the addition of the graphene dispersion slurry is controlled to be 6.75 wt% of the solid content of the polyamic acid resin solution (0.9 times of the addition of silver salt), and uniformly stirring and mixing to obtain a mixed resin solution; coating the obtained mixed resin solution on an annular steel belt through an extrusion molding die, controlling the thickness of a liquid film on the steel belt to be 380 mu m, and then drying and curing at 155 ℃ to remove 85 wt% of solvent to obtain a self-supporting film; and (3) putting the obtained self-supporting film into an environment with the temperature of 190 ℃ for heat preservation and decomposition for 30min, then carrying out imidization treatment for 2.2h at the temperature of 480 ℃, finally carrying out setting treatment for 0.8h at the temperature of 320 ℃, and rolling to obtain a polyimide film with the thickness of 25 mu m. The obtained film contains bubbles inside and holes on the surface.

Example 5

1) 820.00kg of N, N '-Dimethylacetamide (DMAC) is added into a reaction kettle under the nitrogen atmosphere and the temperature of a synthesis system is controlled to be 25 ℃, then 74.96kg of 2,2' -bis (trifluoromethyl) -4,4 '-diaminobiphenyl (2,2' -TFDB) is added, after stirring and dissolving, dianhydride 2, 2-bis (3, 4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA, 105.04 kg) with the molar ratio of 1:0.99 to diamine is added in 12 times, and stirring reaction is carried out for 48 hours to obtain a polyamic acid resin solution (M is 180.0kg) with the solid content of 18 wt%;

2) keeping the polyamic acid resin solution at 10 ℃, adding silver nitrate dispersion liquid (the concentration of silver nitrate is 5 wt%) and alumina dispersion slurry (the concentration of alumina is 6 wt%), wherein the addition amount of the silver nitrate dispersion liquid is 0.1 wt% of the solid content of the polyamic acid resin solution, and the addition amount of the alumina dispersion slurry is 0.12 wt% of the solid content of the polyamic acid resin solution (1.2 times of the addition amount of silver nitrate), and stirring and mixing uniformly to obtain a mixed resin solution; coating the obtained mixed resin solution on an annular steel belt through an extrusion molding die, controlling the thickness of a liquid film on the steel belt to be 365 mu m, and then drying and curing at 168 ℃ to remove 78 wt% of solvent to obtain a self-supporting film; and (3) the obtained self-supporting film is sent to a 220 ℃ environment for heat preservation and decomposition for 10min, the obtained self-supporting film is sent to a longitudinal and transverse biaxial stretching machine for longitudinal stretching at 265 ℃ for 3.0h by 1.2 times and transverse stretching at 300 ℃ for 1.2h by 1.1 times, imidization treatment is carried out for 0.5h at 500 ℃, finally setting treatment is carried out for 1.0h at 320 ℃, and rolling is carried out to obtain the polyimide film with the thickness of 25 mu m.

Comparative example 8

The difference between this example and example 5 is that the self-supporting film in step 2) is decomposed for 3min under the condition of 220 ℃.

Comparative example 9

The difference between this example and example 5 is that the self-supporting film in step 2) is decomposed for 30min under the condition of 230 ℃.

Although the finally prepared polyimide film also contains nano-scale silver elementary substance particles and aluminum oxide, due to the fact that the thermal decomposition temperature is too high, most silver oxide in the constant-temperature thermal decomposition process of silver nitrate is further decomposed into silver elementary substances, only a small part of silver oxide is further decomposed in the subsequent imidization process, and therefore bubbles in the obtained polyimide film are few and are not uniformly distributed, and the dielectric property of the obtained film is not ideal.

Example 6

1) 1125.00kg of N, N '-Dimethylacetamide (DMAC) is added into a reaction kettle under the nitrogen atmosphere and the temperature of a synthesis system is controlled to be 40 ℃, then 99.989kg of 2,2' -bis (trifluoromethyl) -4,4 '-diaminobiphenyl (2,2' -TFDB) and 91.277kg of 1, 3-bis (4-aminophenoxy) benzene (TPE-R) are added, after stirring and dissolving, dianhydride 3,3',4,4' -biphenyltetracarboxylic dianhydride (s-BPDA, 183.734kg, added in 12 times) with the molar ratio of 1:1 to diamine is added into the reaction kettle, and stirring reaction is carried out for 24 hours to obtain a polyamic acid resin solution (M is 375.0kg) with the solid content of 25 wt%;

2) keeping the polyamic acid resin solution at 10 ℃, adding a silver oxalate dispersion liquid (the concentration of silver oxalate is 5 wt%) and an aluminum nitride dispersion slurry (the concentration of aluminum nitride is 6 wt%), wherein the adding amount of the silver oxalate dispersion liquid is 5.0 wt% of the solid content of the polyamic acid resin solution, the adding amount of the aluminum nitride dispersion slurry is 5.0 wt% of the solid content of the polyamic acid resin solution (1.0 time of the adding amount of silver oxalate), and stirring and mixing uniformly to obtain a mixed resin solution; coating the obtained mixed resin solution on an annular steel belt through an extrusion molding die, controlling the thickness of a liquid film on the steel belt to be 680 mu m, and then drying and curing at 100 ℃ to remove 80 wt% of solvent to obtain a self-supporting film; and (3) the obtained self-supporting film is sent to an environment at 210 ℃ for heat preservation and decomposition for 45min, then sent to a longitudinal and transverse biaxial stretching machine for longitudinal stretching at 250 ℃ and 1.12 times of stretching for 0.2h and transverse stretching at 280 ℃ and 1.25 times of stretching for 0.6h in sequence, then imidized in a high-temperature imidization oven at 600 ℃ for 3.0h, finally shaped at 180 ℃ for 0.8h, and rolled to obtain the polyimide film with the thickness of 75 microns.

Example 7

This example is different from example 6 in that, in step 2), the amount of the silver oxalate dispersion was controlled to be 0.5 wt% of the solid content of the polyamic acid resin solution; the aluminum nitride dispersion slurry was replaced with a boron nitride dispersion slurry in which the amount of boron nitride added was controlled to be 0.55 wt% of the solid content of the polyamic acid resin solution (1.1 times the amount of silver oxalate added).

Table 1:

as shown in table 1, the low dielectric property and high thermal conductivity polyimide composite films prepared in examples 1 to 7 have relatively low dielectric constant and dielectric loss, good surface resistance, and low water absorption property, and also exhibit high mechanical properties (such as high tensile strength and high elongation) and excellent thermal conductivity (high out-of-plane thermal conductivity). When a film with a thicker thickness is prepared, a high-thermal conductivity polyimide composite film with low dielectric property can be obtained by increasing the time of constant-temperature thermal decomposition treatment (such as example 6 and example 7); furthermore, by selecting different silver salt compounds (examples 4 and 6 to 7, such as silver carbonate and silver oxalate), a polyimide composite film with low dielectric property and high thermal conductivity can be prepared.

On the other hand, the polyimide film prepared in comparative example 1 without adding silver salt compound silver nitrate as shown in table 1 did not have the desired dielectric properties and thermal conductivity; the polyimide film prepared in comparative example 2, in which silver salt compound, silver nitrate, and the heat conductive filler, carbon nanotubes, were added, but were not subjected to the constant temperature thermal decomposition treatment, also did not have the desired dielectric properties and thermal conductivity, whereas in comparative examples 3 to 9, when the amount of silver salt added and/or the amount of heat conductive filler added and/or the constant temperature thermal decomposition treatment process were not within the range defined in the present application, the polyimide composite film prepared had inferior dielectric properties and/or thermal conductivity and/or mechanical properties.

Although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A preparation method of a polyimide film with low dielectric and high thermal conductivity comprises the following steps:

1) preparing a polyamic acid resin solution;

2. The method according to claim 1, wherein in the step 2), the decomposition time is 10 to 30min in the isothermal thermal decomposition treatment.

3. The method according to claim 1, wherein in step 2), the thermally conductive filler is one or a combination of two or more selected from the group consisting of carbon nanotubes, graphene and alumina.

4. The method according to any one of claims 1 to 3, wherein the silver salt dispersion is added in the step 2) in an amount of 0.5 to 7.5 wt% based on the solid content of the polyamic acid resin solution.

5. The method according to any one of claims 1 to 3, wherein in the step 2), the amount of the heat conductive filler dispersed slurry is controlled to be 0.9 to 1.0 time the amount of the silver salt.

6. The process according to any one of claims 1 to 3, wherein in the step 2), the stretching treatment is performed after the constant-temperature thermal decomposition treatment and before the imidization treatment.

7. The low-dielectric high-thermal-conductivity polyimide film prepared by the method according to any one of claims 1 to 6.