阅读说明：本技术 一种低介电性能的热塑性聚酰亚胺树脂复合薄膜及其制备方法 (Thermoplastic polyimide resin composite film with low dielectric property and preparation method thereof ) 是由 刘洋 初金军 辛乐民 徐伟杰 丰佩川 于 2021-08-31 设计创作，主要内容包括：本发明涉及一种低介电性能的热塑性聚酰亚胺树脂复合薄膜,属于复合薄膜材料技术领域,所述的聚酰亚胺树脂复合薄膜由聚酰亚胺树脂与LCP树脂共混改性制得,按照重量份数计,所述聚酰亚胺树脂由以下组分制成：对-亚苯基-双苯偏三酸酯二酐单体20～100份,其他共聚二酐单体0～80份,含氟基团的二胺单体20～80份,含大侧基的二胺单体20～80份。聚酰亚胺树脂具有溶解性好、熔融加工性好的特点,降低聚酰亚胺加工成本,并且分子结构中含有酯基,与LCP树脂共混改性可以提高相容性,改善LCP树脂由于结晶取向导致的各向异性问题,制备复合薄膜,进一步提升介电性能和降低吸水率。(The invention relates to a thermoplastic polyimide resin composite film with low dielectric property, belonging to the technical field of composite film materials, wherein the polyimide resin composite film is prepared by blending and modifying polyimide resin and LCP resin, and the polyimide resin is prepared from the following components in parts by weight: 20-100 parts of p-phenylene-ditrimellitic dianhydride monomer, 0-80 parts of other copolymerized dianhydride monomer, 20-80 parts of diamine monomer containing fluorine groups and 20-80 parts of diamine monomer containing large side groups. The polyimide resin has the characteristics of good solubility and good melt processability, reduces the processing cost of polyimide, contains ester groups in the molecular structure, can improve the compatibility by blending modification with the LCP resin, improves the anisotropy problem of the LCP resin caused by crystal orientation, prepares a composite film, further improves the dielectric property and reduces the water absorption rate.)

1. The thermoplastic polyimide resin composite film with low dielectric property is characterized in that the polyimide resin composite film is prepared by blending and modifying polyimide resin and LCP resin, and the polyimide resin is prepared from the following components in parts by weight: 20-100 parts of p-phenylene-ditrimellitic dianhydride monomer, 0-80 parts of other copolymerized dianhydride monomer, 20-80 parts of diamine monomer containing fluorine groups and 20-80 parts of diamine monomer containing large side groups.

2. The thermoplastic polyimide resin composite film with low dielectric property as claimed in claim 1, wherein the mole ratio of the structural unit with benzene ring number greater than 2 in the molecular unit of other copolymerized dianhydride monomer is 50-100%.

3. The thermoplastic polyimide resin composite film with low dielectric constant of claim 2, characterized in that the other co-dianhydride monomer is selected from one or more of pyromellitic dianhydride, 3,3 ', 4,4' -biphenyl tetracarboxylic dianhydride, 2,3 ', 3, 4' -triphendiether tetracarboxylic dianhydride, 3,3 ', 4,4' -triphendiether tetracarboxylic dianhydride, 2', 3,3 ' -triphendiether tetracarboxylic dianhydride, 3,3 ', 4,4' -benzophenone tetracarboxylic dianhydride, bisphenol A type diether dianhydride, diphenyl ether tetracarboxylic dianhydride, cyclobutane tetracarboxylic dianhydride, hydrogenated pyromellitic dianhydride, 3,3 ', 4,4' -diphenylsulfone tetracarboxylic dianhydride, 4,4' - (hexafluoroisopropyl) diphthalic anhydride.

4. The low dielectric thermoplastic polyimide resin composite film according to claim 1, wherein the fluorine-containing group-containing diamine monomer is selected from one or more combinations of 2, 2-bis [4- (4-aminophenoxy) phenyl ] -1,1,1,3,3, 3-hexafluoropropane, 1, 4-bis (4-amino-2-trifluoromethylphenoxy) benzene, 2 '-bis (trifluoromethyl) -4,4' -diaminobiphenyl, and 2,2 '-bis (trifluoromethyl) -4,4' -diaminophenyl ether.

5. The thermoplastic polyimide resin composite film with low dielectric constant of claim 1, wherein the diamine monomer containing large side groups is selected from one or more of 9, 9-bis (4-amino-3-fluorophenyl) fluorene, 9-bis (4-aminophenyl) fluorene, and 9, 9-bis [4- (4-amino-phenoxy) phenyl ] fluorene.

6. A method for preparing a thermoplastic polyimide resin composite film with low dielectric property according to any one of claims 1 to 5, comprising the steps of:

(1) under the protection of inert gas, carrying out polymerization reaction on a diamine monomer containing a fluorine group, a diamine monomer containing a large side group, a p-phenylene-ditrimellitic dianhydride monomer and other copolymerized dianhydride monomers in an organic solvent, adding a capping agent to seal end after the polymerization is finished, and carrying out polymerization reaction to obtain a polyamic acid solution with the solid content of 10-30%;

(2) adding a dehydrating agent and a catalyst into the polyamic acid solution prepared in the step (1) to perform normal-temperature chemical imidization; or adding a catalyst into the polyamic acid solution prepared in the step (1) and heating for performing dehydration and imidization;

(3) directly or diluting the polyimide solution prepared in the step (2), pouring the diluted polyimide solution into a poor solvent to obtain a solid polyimide resin, filtering the solid polyimide resin, washing the solid polyimide resin with the poor solvent for a plurality of times, filtering, and drying;

(4) dissolving the polyimide resin prepared in the step (3) with an organic solvent to prepare a film by tape casting, or extruding and granulating the film by an extruder and then preparing the film by a blow molding or melt extrusion double-drawing mode; or blending and modifying the polyimide resin prepared in the step (3) and the LCP resin to prepare the composite film.

7. The method for preparing a thermoplastic polyimide resin composite film with low dielectric constant according to claim 6, wherein in the step (1), the organic solvent is a polar aprotic solvent, and the organic solvent is one or more selected from the group consisting of N, N '-dimethylformamide, N' -dimethylacetamide, N-methylpyrrolidone, tetrahydrofuran, dimethylsulfoxide, sulfolane and diphenylsulfone.

8. The method for preparing a thermoplastic polyimide resin composite film with low dielectric property according to claim 6, wherein in the step (1), the end-capping agent is selected from one or more of phthalic anhydride and aniline; in the step (2), the dehydrating agent is one or more selected from the group consisting of trifluoroacetic anhydride and acetic anhydride; the catalyst is selected from one or more of carbonate, bicarbonate, hydroxide, organic base, alkali metal salt of alcohol, metal hydride, pyridine, isoquinoline and triethylamine; in the step (3), the poor solvent is one or more selected from the group consisting of ethanol, acetone, butanone and deionized water.

9. The preparation method of the thermoplastic polyimide resin composite film with low dielectric property as claimed in claim 6, wherein the mass ratio of the polyimide resin to the LCP resin is 0.1-3: 7 to 9.9.

10. The method for preparing the thermoplastic polyimide resin composite film with low dielectric property as claimed in claim 6, wherein the operation method for preparing the composite film by blending and modifying the polyimide resin and the LCP resin in the step (4) comprises the following steps:

after dissolving the polyimide resin in an organic solvent, blending the polyimide resin with a solution of LCP resin dissolved in the organic solvent, coating the mixture on a support, and drying to remove the organic solvent to obtain a composite film;

or after extruding and granulating the polyimide resin, blending the polyimide resin with the LCP resin, mixing the mixture by a double-screw extruder, exhausting, cooling by side blowing, drafting, winding and carrying out heat treatment to obtain a finished product of the composite film.

Technical Field

The invention relates to a thermoplastic polyimide resin composite film with low dielectric property and a preparation method thereof, belonging to the technical field of composite film materials.

Background

In the big data age, information processing of electronic products is continuously developing towards high frequency and high speed digitization of signal transmission. In order to ensure that an electronic product has good signal transmission quality under the condition of high-frequency signal transmission, impedance matching between a transmission line in a conductive copper foil of a circuit board and an electronic component connected with the transmission line needs to be achieved, so that phenomena such as signal reflection, scattering, attenuation and delay are avoided. The dielectric constant of the insulating layer material in contact with the conductive traces in the circuit board is one of the factors that affect impedance matching for high frequency transmission. In order to achieve impedance matching for high frequency signal transmission, the insulating layer generally needs to be made of a material with a low dielectric constant.

The low dielectric materials commonly used at present are mainly Modified Polyimide (MPI) and Liquid Crystal Polymer (LCP), but the MPI film has the characteristics of high dielectric constant, dielectric loss factor and water absorption rate, and does not meet the requirement of using under high frequency. LCP resin has the problem of difficult processing due to high crystal orientation, and the existing improvement scheme is to add PPO into the LCP resin for blending modification, but the compatibility is poor, or add PEI into the LCP resin for blending modification, but the compatibility is poor, the dielectric property is reduced, and the PEI heat resistance is poor.

In order to obtain low dielectric polyimide materials, a great deal of research work has been done: CN109942815B discloses a low dielectric polyimide resin, and provides a polyimide composite resin obtained by uniformly copolymerizing polyimide and polyimide, wherein the dielectric constant of the polyimide composite resin is reduced by introducing polyimide units, the polyimide composite resin has a branched chain structure, so that not only is the space between molecular chains increased and the dielectric constant further reduced, but also the mechanical properties of the introduced polyimide resin can be improved, but high-temperature thermal imidization is adopted, and the addition of the polyimide can lead to stronger rigidity of the molecular chains and influence the solubility and processability of the polyimide resin.

CN105837819B discloses a hybrid polyimide containing trifluoromethyl and oligomeric silsesquioxane structures and a preparation method thereof, wherein a matrix polyimide is prepared by polycondensation of 4,4' -diphenyl ether tetracarboxylic dianhydride and an aromatic diamine monomer containing the trifluoromethyl structures, the dissolving and film-forming properties, the dielectric properties and the optical transparency of a polymer are improved to a certain extent, oligomeric silsesquioxane needs to be added under the condition of certain viscosity after high-temperature polymerization, and the uniform dispersion has certain difficulty.

CN109228586B discloses a low dielectric polyimide multilayer composite film, which introduces cage polysilsesquioxane through a thermosetting polyimide layer and a thermoplastic polyimide glue layer, and after the cage polysilsesquioxane is dispersed in polyimide, the cage polysilsesquioxane introduces holes with molecular size into the polyimide, so that the dielectric constant of the polyimide film can be effectively reduced.

CN106750435B discloses a method for preparing a low dielectric constant ordered porous polyimide film, wherein polyimide is grafted on the surface of a silica microsphere modified by amino groups in a chemical bond form to prepare a polyimide composite film, and the low dielectric constant ordered porous polyimide film is prepared.

As described above, the above improvements have been made, but the polyimide matrix still has problems such as poor solubility and difficulty in controlling the uniformity of the added inorganic filler. And no relevant data is mentioned about the melt processing method of low dielectric polyimide and the modification problem of blending with LCP resin.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a thermoplastic polyimide resin composite film with low dielectric property and a preparation method thereof, wherein a long-chain ester group-containing dianhydride monomer, a large side group monomer and a fluorine-containing monomer are introduced into a main chain of polyimide in the thermoplastic polyimide resin composite film, so that the space free volume of polyimide molecules is increased, the molecular molar polarizability is reduced, and the prepared film has the characteristics of low dielectric constant Dk, low dielectric loss factor Df, low water absorption and the like; in addition, the polyimide resin has the characteristics of good solubility and good melt processability, is suitable for film forming by means of blow molding, melt extrusion double-drawing and solution casting, effectively reduces the processing cost of the polyimide, can improve the compatibility by blending modification with the LCP resin due to ester groups in the molecular structure, improves the anisotropy problem of the LCP resin caused by crystal orientation, prepares a composite film, further improves the dielectric property and reduces the water absorption rate, and is suitable for the fields of circuit substrates for high-frequency flexibility, covering film materials, communication materials for high-frequency high-speed use and the like.

The technical scheme for solving the technical problems is as follows: the thermoplastic polyimide resin composite film with low dielectric property is prepared by blending and modifying polyimide resin and LCP resin, wherein the polyimide resin is prepared from the following components in parts by weight: 20-100 parts of p-phenylene-ditrimellitic dianhydride (TAHQ) monomer, 0-80 parts of other copolymerized dianhydride monomer, 20-80 parts of diamine monomer containing fluorine groups and 20-80 parts of diamine monomer containing large side groups.

The structural formula of the p-phenylene-ditrimellic acid ester dianhydride (TAHQ) monomer is as follows:

furthermore, the molar ratio of the structural units with the benzene ring number more than 2 in the polyimide molecular units is 50-100%.

Furthermore, the molar ratio of the structural unit with the benzene ring number more than 2 in the polyimide molecular unit is preferably 60-90%.

Further, the other dianhydride monomers are selected from the group consisting of pyromellitic dianhydride (PMDA), 3,3 ', 4,4' -biphenyltetracarboxylic dianhydride (BPDA), 2,3 ', 3, 4' -biphenyltetracarboxylic dianhydride (3, 4' -BPDA), 2,3 ', 3, 4' -triphenyldiether tetracarboxylic dianhydride (3, 4' -HQDPA), 3,3 ', 4,4' -triphenyldiether tetracarboxylic dianhydride (4, 4' -HQDPA), 2', 3,3 ' -triphenyldiether tetracarboxylic dianhydride (3,3 ' -HQDPA), 3,3 ', 4,4' -benzophenonetetracarboxylic dianhydride (BTDA), bisphenol a type diether dianhydride (BPADA), diphenylether tetracarboxylic dianhydride (ODPA), cyclobutane tetracarboxylic dianhydride (CBDA), hydrogenated pyromellitic dianhydride (HPMDA), 3,3 ' 4,4 '-diphenyl sulfone tetracarboxylic dianhydride (DSDA), 4' - (hexafluoroisopropyl) diphthalic anhydride (6 FDA).

Further, the fluorine-containing diamine monomer is one or more selected from the group consisting of 2, 2-bis [4- (4-aminophenoxy) phenyl ] -1,1,1,3,3, 3-Hexafluoropropane (HFBAPP), 1, 4-bis (4-amino-2-trifluoromethylphenoxy) benzene (6FAPB), 2 '-bis (trifluoromethyl) -4,4' -diaminobiphenyl (TFMB), and 2,2 '-bis (trifluoromethyl) -4,4' -diaminophenyl ether (FODA).

Further, the diamine monomer containing the large side group is one or more selected from the group consisting of 9, 9-bis (4-amino-3-fluorophenyl) fluorene (BFAF), 9-bis (4-aminophenyl) fluorene (BAFL), and 9, 9-bis [4- (4-amino-phenoxy) phenyl ] fluorene (BAOFL).

The invention also discloses a preparation method of the thermoplastic polyimide resin composite film with low dielectric property, which comprises the following steps:

(1) under the protection of inert gas, carrying out polymerization reaction on a diamine monomer containing a fluorine group, a diamine monomer containing a large side group, a p-phenylene-ditrimellitic dianhydride monomer and other copolymerized dianhydride monomers in an organic solvent, and specifically operating as follows:

dissolving a diamine monomer containing a fluorine group, a diamine monomer containing a large side group, a p-phenylene-ditrimellitic dianhydride monomer and other copolymerized dianhydride monomers in an organic solvent in sequence; or dissolving diamine monomer containing fluorine group and diamine monomer containing large side group in organic solvent, and adding p-phenylene-ditrimellitic dianhydride monomer and other copolymerized dianhydride monomer in batches;

after the polymerization is finished, adding an end-capping agent for end capping, and carrying out polymerization reaction to obtain a polyamic acid solution with the solid content of 10-30%;

(2) adding a dehydrating agent and a catalyst into the polyamic acid solution prepared in the step (1) to perform normal-temperature chemical imidization; or adding a catalyst into the polyamic acid solution prepared in the step (1) and heating for performing dehydration and imidization;

(3) directly or diluting the polyimide solution prepared in the step (2), pouring the diluted polyimide solution into a poor solvent to obtain a solid polyimide resin, filtering the solid polyimide resin, washing the solid polyimide resin with the poor solvent for a plurality of times, filtering, and drying;

(4) dissolving the polyimide resin prepared in the step (3) with an organic solvent to prepare a film by tape casting, or extruding and granulating the film by an extruder and then preparing the film by a blow molding or melt extrusion double-drawing mode; or blending and modifying the polyimide resin prepared in the step (3) and the LCP resin to prepare the composite film.

Further, the organic solvent is a polar aprotic solvent.

Further, the organic solvent is one or more selected from the group consisting of N, N '-Dimethylformamide (DMF), N' -Dimethylacetamide (DMAC), N-methylpyrrolidone (NMP), Tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), sulfolane, and diphenylsulfone.

Further, the organic solvent is preferably N, N' -Dimethylacetamide (DMAC) or N-methylpyrrolidone (NMP).

Further, the blocking agents are respectively selected from one or more of the group consisting of phthalic anhydride and aniline.

Further, the dehydrating agents are respectively selected from one or more of trifluoroacetic anhydride and acetic anhydride.

Further, the basic catalyst is selected from one or more of the group consisting of carbonate, bicarbonate, hydroxide, organic base, alkali metal salt of alcohol, metal hydride, pyridine, isoquinoline, triethylamine.

Further, the poor solvent is selected from one or more of the group consisting of ethanol, acetone, butanone and deionized water.

Further, the polyimide and liquid crystal polymer composite film has a mass ratio of polyimide to liquid crystal polymer of 0.1-3: 7 to 9.9.

Further, in the polyimide and liquid crystal polymer composite film, the mass ratio of the polyimide to the liquid crystal polymer is preferably 0.3-2: 8 to 9.7.

Further, the casting process is that the polyimide resin is dissolved in an organic solvent and then directly coated on a support (such as a clean glass plate), or the polyimide resin is dissolved in an organic solvent and then coated on a support (such as a clean glass plate) after being blended with an LCP resin solution, and the solvent is removed through a heating plate and an oven to obtain a polyimide film or a composite film;

polyimide resin is dissolved in an organic solvent and then coated on a clean glass plate, the drying temperature and the drying time of a heating plate are respectively 50-120 ℃ and 20-90min, the temperature of an oven is 260-350 ℃, and the heating time is 0.2-5 h.

The blow molding processing mode is that the polyimide resin is extruded and pelletized, directly or mixed with LCP resin particles and then mixed by a double-screw extruder, exhausted, cooled by side blowing through a metering pump and a component, drawn and wound to obtain a polyimide film or a composite film, and the polyimide film or the composite film is subjected to heat treatment to obtain a polyimide finished film or a composite film finished film.

The viscosity of the polyimide resin provided by the invention is 0.4-1.8 dL/g, preferably 0.6-1.5 dL/g, measured in N-methylpyrrolidone with the concentration of 0.5dL/g at 30 ℃ by an Ubbelohde viscometer. The melt index of the polyimide resin is 0.1-50 g/10min, preferably 1-30 g/10 min. The melt index of the polyimide is determined by a melt indexer.

The dielectric constant Dk of the polyimide film is less than or equal to 3.2, the dielectric loss factor Df is less than or equal to 0.005, and the water absorption rate is less than or equal to 0.8%. The glass transition temperature of the polyimide film is more than or equal to 240 ℃. The mechanical properties of the polyimide film are that the Transverse Direction (TD) tensile strength is 80-180 MPa, and the longitudinal direction (MD) tensile strength is 80-180 MPa.

The dielectric constant Dk of the composite film is less than or equal to 3.0, the dielectric loss factor Df is less than or equal to 0.002, and the water absorption rate is less than or equal to 0.2%. The mechanical properties of the composite film are that the Transverse Direction (TD) tensile strength is 100-180 MPa, and the longitudinal direction (MD) tensile strength is 140-220 MPa.

The invention has the beneficial effects that:

the long-chain ester group-containing dianhydride monomer, the large side group monomer and the fluorine-containing monomer are introduced into the main chain of the polyimide, the space free volume of polyimide molecules is increased, the molecular molar polarizability is reduced, and the prepared film has the characteristics of low dielectric constant Dk, low dielectric loss factor Df, low water absorption and the like. In addition, the resin has the characteristics of good solubility and good melt processability, is suitable for film forming by means of blow molding, melt extrusion double drawing and solution casting, effectively reduces the processing cost of polyimide, can be blended and modified with a liquid crystal polymer due to ester groups in a molecular structure, improves the anisotropy problem of the liquid crystal polymer caused by crystal orientation, prepares a composite film, and further improves the dielectric property and reduces the water absorption rate. The method is suitable for the fields of circuit substrates for high-frequency flexibility, covering film materials, communication materials for high frequency and high speed and the like;

(1) the prepared polyimide film and the prepared film have low dielectric constant Dk, low dielectric loss factor Df and low water absorption;

(2) the polyimide resin has the characteristics of good solubility and good melt processability, and effectively reduces the processing cost;

(3) because the molecular structure contains ester group and good processing property, the modified LCP resin can be blended and modified with LCP resin to prepare a composite film, further improve dielectric property and reduce water absorption.

Detailed Description

The present invention will be described in detail with reference to the following embodiments in order to make the aforementioned objects, features and advantages of the invention more comprehensible. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

The polyimide resin and the composite film prepared in the examples were subjected to a performance test according to the following method:

(1) inherent viscosity: the inherent viscosity of the polyimide was measured at a concentration of 0.5g/dL in N-methylpyrrolidone at 30 ℃ by an Ubbelohde viscometer. When the inherent viscosity of the resin is large, the mechanical property of the material is improved, but the processability of the material is affected if the inherent viscosity of the resin is too large. The greater the inherent viscosity, the greater the molecular weight.

(2) Dielectric constant Dk and dielectric loss factor Df: the test method is a coaxial resonant cavity method, the instrument is a high-frequency dielectric constant analyzer developed by AET of Japan, and the test is carried out at the frequency of 10 GHz.

(3) Water absorption: the test method was performed according to ASTM D57098, and the water absorption was calculated by accurately measuring the change in mass of the film before and after soaking in deionized water at 23 ℃ for 24 hours.

(4) Glass transition temperature Tg: the temperature rise rate was 20 ℃/min under nitrogen, as determined by differential scanning calorimetry. In theory, a higher glass transition temperature of the resin is better, but generally, a higher glass transition temperature results in a stronger structure, which is disadvantageous for processing.

(5) Mechanical properties: the test was carried out using GB/T1040.1 "determination of tensile Properties of plastics", INSTRON Universal materials tester, available from Instron, USA, at a tensile rate of 5 mm/min.

(6) Melt index: the measurement is carried out by a melt index meter under the conditions of 12.5Kg of pressure, 340 ℃ of temperature and 2 minutes of plasticizing time. Theoretically, the higher the melt index, the better the subsequent melt processing, but generally, after the structure is determined, the melt index of the resin needs to be increased by lowering the molecular weight, which leads to loss of mechanical properties of the material.

Example 1

8.0058g (0.025mol) of 4,4 '-diamino-2, 2' -bistrifluoromethylbiphenyl monomer, 9.6105g (0.025mol) of 9, 9-bis (4-amino-3-fluorophenyl) fluorene monomer and 180mL of N, N-dimethylacetamide are added into a dry and clean 500mL three-necked flask, stirred at normal temperature under nitrogen protection, and after the diamine monomer is completely dissolved, 4.5833g (0.01mol) of p-phenylene-bistrimellitic dianhydride monomer is added: 20.7155g (0.0398mol) bisphenol A type diether dianhydride monomer, 50mL of N, N-dimethylacetamide; after 22 hours of reaction at ordinary temperature, 0.1185g (0.0008mol) of phthalic anhydride monomer was added and reaction was carried out at ordinary temperature for 4 hours to obtain a polyamic acid solution.

Adding 34mL of mixed solution of acetic anhydride and pyridine (30 mL of acetic anhydride and 4mL of pyridine), continuing to react for 6 hours at normal temperature, slowly pouring the reaction solution into 3L of deionized water for precipitation, filtering, boiling and washing the obtained filter cake for 2 times by using the deionized water, and then placing the filter cake in a vacuum oven at 120 ℃ for drying for 5 hours to obtain 38.71g of polyimide resin powder with the yield of 90.2 percent.

Dissolving the polyimide powder in N, N-dimethylacetamide, coating on a dry and clean glass plate to form a film, drying on a heating plate at 100 ℃ for 40min, drying in a vacuum oven at 300 ℃ for 1h, cooling, taking out, boiling with boiling water until the polyimide film is taken off from the glass plate, and obtaining the polyimide film with the thickness of 25 microns. The performance test results of the polyimide film are shown in Table 1.

Example 2

336.23g (1mol) of 2,2 '-bis (trifluoromethyl) -4,4' -diaminophenyl ether monomer, 1567.98g (4mol) of 9, 9-bis (4-aminophenyl) fluorene monomer and 17L N, N-dimethylacetamide are added into a dry and clean 50L double-layer glass reaction kettle, stirred at normal temperature under the protection of nitrogen, and after the diamine monomer is completely dissolved, 458.33g (1mol) of p-phenylene-bis (trimellitate) dianhydride monomer is slowly added: 1601.19g (3.98mol)4, 4' -triphendiethanetetracarboxylic dianhydride monomer, 1L N, N-dimethylacetamide; after reacting at room temperature for 18 hours, 11.85g (0.08mol) of a phthalic anhydride monomer was added and reacted at room temperature for 4 hours to obtain a polyamic acid solution.

Adding 2.83L of mixed solution of acetic anhydride and pyridine (2.04L of acetic anhydride and 0.79L of pyridine), continuing to react for 6 hours at normal temperature, diluting the reaction solution with 54L of N, N-dimethylacetamide, slowly pouring into 360L of deionized water for precipitation, filtering, boiling and washing the obtained filter cake for 2 times with deionized water, and then drying in a vacuum oven at 120 ℃ for 5 hours to obtain 3614.26g of polyimide resin with the yield of 91.2%.

14g of the polyimide resin was dissolved in 64g N N-dimethylacetamide, and the resulting solution was coated on a dry and clean glass plate to form a film, which was then dried on a hot plate at 100 ℃ for 40min, dried in a vacuum oven at 300 ℃ for 1h, cooled and taken out, and then boiled in boiling water until the polyimide film was taken off the glass plate, thereby obtaining a polyimide film having a thickness of 25 μm. The performance test results of the polyimide film are shown in Table 1.

Examples 3 to 14 and comparative examples 1 to 2

Replacing diamine and dianhydride with the proportions shown in the following tables 1 and 2, respectively carrying out resin polymerization, and carrying out heat preservation reaction at the temperature of 0-50 ℃ for 1-24 h to polymerize to obtain a polyamide acid solution with the solid content of 10-30%.

Then, a polyimide film having a thickness of 25 μm was prepared in the same manner as in example 1.

The properties of the polyimide films obtained in examples and comparative examples were measured in the manner described above, and the results are shown in tables 1 and 2.

Example 15

3500g of the polyimide resin of example 2 was dried in a vacuum oven at 200 ℃ for 5 hours, naturally cooled to room temperature under vacuum, and then put into a single-screw extruder to be extruded and pelletized, wherein the temperature of the extruder was set once from a feed port to an extrusion die at 255 ℃, 280 ℃, 320 ℃ and 300 ℃ to obtain 2633g of a polyimide pellet, which was designated as PI-M2.

1500g of the polyimide particle PI-M2 resin and 3500g of liquid crystal polymer resin (A950 RX, produced by Baoli plastics Co., Ltd.) are mechanically blended to form a mixture, the mixture is placed in a double-screw extruder for melting plasticization and mixing, the temperature of the mixture in the double-screw extruder is 100-300 ℃, the temperature of a die head is 290-300 ℃, a metering pump and a component are used for metering the flow of the pump by a metering pump and the component, the lateral blowing temperature is 60 ℃, the drawing speed is 5M/min, and a composite film of the polyimide and the liquid crystal polymer is obtained after winding, and the performance test result of the composite film is shown in Table 3.

Examples 16 to 18 and comparative example 3

Resin blend modification was performed by replacing the PI-M2 and the liquid crystal polymer resin with the proportions shown in table 3 below, respectively, and a composite film of polyimide and a liquid crystal polymer was prepared by an extrusion molding apparatus according to the processing method of example 15, and the characteristics of the prepared composite film were measured as described above, and the results are summarized in table 3.

TABLE 1, table of formulations and Property parameters for polyimide films prepared in examples 1-8

TABLE 2, EXAMPLES 9-14 AND COMPARATIVE EXAMPLES 1-2

Table 3, examples 15-18 and comparative example 3, the formula and property parameter table of the polyimide and liquid crystal polymer composite film

As can be seen from examples 1 to 14 and comparative examples 1 to 2: the polyimide film materials obtained in examples 1 to 14 have low dielectric constant Dk, low dielectric dissipation factor Df, and low water absorption. In addition, the polyimide resin has the characteristics of good solubility and good melt processability, is suitable for film forming in modes of blow molding, melt extrusion double drawing and solution casting, and effectively reduces the processing cost of polyimide. From examples 15 to 18 and comparative example 3, it can be seen that: the polyimide resin and the liquid crystal polymer are blended and modified, so that the strong orientation of the molecular chain in the melting processing film-forming process of the LCP molecular chain is improved, the film-forming property and the toughness of the film are improved, and the prepared composite film has more consistent mechanical properties in the Transverse Direction (TD) and the longitudinal direction (MD). In conclusion, the melt index of the product is more than 8 in the example 1/2/3/4/5/9/11, the product has relatively good processing performance, the dielectric performance is relatively good in the example 11/12, and the comprehensive performance is excellent in the example 16/17. The method is suitable for the fields of circuit substrates for high-frequency flexibility, covering film materials, communication materials for high-frequency high-speed use and the like.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.