High-adhesion thermoplastic polyimide slurry as well as preparation method and application thereof

Abstract

The invention discloses high-adhesion thermoplastic polyimide slurry and a preparation method and application thereof, and belongs to the technical field of high polymer materials, and the preparation method comprises the following steps: under the protection of inert gas, adding o-bitoluidine and bisphenol A type diether dianhydride into a polar aprotic solvent to prepare a polyamide acid solution; adding a dehydrating agent and a catalyst into the polyamide acid solution, and carrying out chemical imidization reaction to prepare thermoplastic polyimide reaction slurry; dropwise adding the reaction slurry into absolute ethyl alcohol for settling, washing, drying and crushing to obtain thermoplastic polyimide powder; the thermoplastic polyimide powder is re-dissolved in the polar aprotic solvent, and the thermoplastic polyimide slurry is prepared through ultrasonic dispersion and filtration. The glass-transition temperature Tg of the slurry is greater than or equal to 300 DEG C, the stripping force with a copper foil is greater than or equal to 1.1 N / mm, the slurry can be directly used for preparing a non-adhesive two-layer flexible copper-clad plate, and the problem that the traditional TPI is insufficient in adhesive property and difficult to consider the heat resistance at the same time is solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high polymer materials, and particularly relates to a high-adhesion thermoplastic polyimide paste as well as a preparation method and application thereof. BACKGROUND

[0002] Thermoplastic polyimide (TPI) is one of the special engineering plastics developed on the basis of traditional thermosetting polyimide (PI) and has good thermoplastic processing performance. It can be molded by all processing methods of thermosetting PI and can also be molded by extrusion and injection molding methods suitable for thermoplastic plastics. Therefore, it is particularly suitable for one-time molding of complex products and does not need secondary processing, thus solving the problems of traditional thermosetting PI, such as difficult molding and processing, and single product form. TPI has excellent high-temperature resistance, mechanical properties and processability, and becomes one of the core substrates of flexible copper-clad laminates (FCCL). In particular, in the non-adhesive two-layer flexible copper-clad laminate (2L-FCCL), TPI needs to meet the dual requirements of high-temperature resistance and high interfacial adhesion. It not only needs to withstand the high-temperature environment (such as welding and packaging process) in the process of electronic device processing and service, but also needs to form a stable interfacial bond with the copper foil to avoid delamination failure after repeated bending.

[0003] At present, the synthesis of TPI mostly adopts thermal imidization or chemical imidization process, but there are significant technical pain points. Firstly, traditional thermal imidization needs high-temperature (200-350℃) staged heating, which has high energy consumption and easily leads to excessive crosslinking of molecular chains, reducing the thermoplasticity and processability of TPI. Secondly, the existing chemical imidization process mostly selects ordinary diamines (such as 4,4'-diamino diphenyl ether) and dianhydride monomers, and the synthesized TPI has a low proportion of polar groups in the molecular chain, which is insufficient for the interfacial adhesion strength with the copper foil, and the peeling force is often lower than 0.8N / mm, which is difficult to meet the long-term reliability requirements of 2L-FCCL. Thirdly, some processes introduce additional adhesives to improve adhesion, which may improve the short-term peeling force, but will reduce the high-temperature resistance of TPI, and the Tg is reduced to below 280℃. In addition, the adhesive layer is easily hygroscopic and swells at high temperature, which leads to the degradation of the dimensional stability of the copper-clad laminate. SUMMARY

[0004] In order to overcome the problems of high energy consumption, easy crosslinking of molecular chains, reduction of thermoplasticity and processability, low adhesion strength with copper foil, and sacrifice of heat resistance and dimensional stability by introducing adhesives to improve adhesion in the prior art, the application provides a high-adhesion thermoplastic polyimide paste as well as a preparation method and application thereof, which are as follows.

[0005] A preparation method of a high-adhesion thermoplastic polyimide paste, comprising the following steps:

[0006] S1, under the protection of inert gas, o-dianisidine and bisphenol A diether dianhydride were added in a polar aprotic solvent successively, and a polyamic acid solution was prepared by reaction at 0-5℃;

[0007] S2, a dehydrating agent and a catalyst were added to the polyamic acid solution, and a chemical imidization reaction was carried out at a temperature of 23-27℃ to prepare a thermoplastic polyimide reaction slurry;

[0008] S3, the reaction slurry was slowly added into excess anhydrous ethanol for sedimentation, and after multiple ethanol washing, drying and crushing, a thermoplastic polyimide powder with a particle size of 50-100μm was prepared;

[0009] S4, the thermoplastic polyimide powder was redissolved in a polar aprotic solvent, and a high-adhesion thermoplastic polyimide slurry with a solid content of 15-20wt% and a viscosity of 12000-18000cPs was prepared by ultrasonic dispersion and filtration.

[0010] Further, in step S1, the molar ratio of o-dianisidine to bisphenol A diether dianhydride was 1:1, and the error range was ±0.02.

[0011] Further, in step S1, o-dianisidine was first added in the polar aprotic solvent and stirred until completely dissolved, then the system temperature was controlled at 0-5℃, bisphenol A diether dianhydride was slowly added, the stirring rate was maintained at 300-500r / min during the adding process, and after the adding was completed, the reaction was continued at 0-5℃ for 24h to obtain a transparent and uniform polyamic acid solution.

[0012] Further, in step S1, the polar aprotic solvent was N,N-dimethylacetamide, and the addition amount of the polar aprotic solvent should make the solid content of the polyamic acid solution be 10-15wt%.

[0013] Further, in step S2, the dehydrating agent was acetic anhydride, the molar ratio of acetic anhydride to carboxyl in polyamic acid was (1-1.5):1; the catalyst was pyridine, and the molar ratio of pyridine to acetic anhydride was 1:1.

[0014] Further, in step S3, the drying conditions were as follows: temperature was 80-100℃, vacuum degree was <0.1kPa, and time was 8-12h.

[0015] Further, in step S4, ultrasonic assisted dispersion was adopted, the ultrasonic power was 300-500W, and the ultrasonic time was 30-60min.

[0016] Further, in step S4, polytetrafluoroethylene filter membrane was used for filtration, and the filter membrane pore size was 1.0-2.0μm.

[0017] The application also provides a thermoplastic polyimide paste prepared by the above method, wherein the thermoplastic polyimide paste has a glass transition temperature Tg≥300℃, a peel strength with a copper foil ≥1.1 N / mm, a tensile strength ≥220 MPa, and an elongation at break ≥20%.

[0018] Further, the thermoplastic polyimide paste is applied to the preparation of a glue-free two-layer flexible copper-clad plate.

[0019] Compared with the prior art, the application has the following beneficial effects:

[0020] (1) The application selects o-tolidine as a diamine monomer, adopts bisphenol A type diether dianhydride (BPADA) to match the o-tolidine, synthesizes a polyamic acid precursor at a low temperature of 0-5℃ to control the molecular weight, and then performs efficient chemical ring closure imidization through an acetic anhydride-pyridine system at a normal temperature of 25℃, so that the destruction of the molecular structure caused by a high temperature process is completely avoided, and thus the high glass transition temperature of the TPI and the high peel strength with the copper foil are simultaneously realized without introducing any adhesive, and the harsh requirements of the glue-free two-layer flexible copper-clad plate on the heat resistance of the substrate and the interface reliability are met.

[0021] (2) Through ethanol sedimentation precipitation, combined with multiple washing and optimized low-temperature vacuum drying, the process can effectively remove residual solvents, catalysts and by-products, avoid the potential corrosion of impurities to the copper foil and the weakening of the interface bonding strength, and prevent the TPI from being pre-crosslinked during the purification process, and the thermoplastic nature of the TPI is perfectly retained.

[0022] (3) The application successfully solves the problems of insufficient adhesion and poor heat resistance of the traditional TPI by optimizing the monomer o-tolidine and BPADA, precisely controlling the process, synthesizing the PAA at a low temperature, performing the imidization at a normal temperature, performing the ethanol sedimentation purification, performing the ultrasonic dispersion, and optimizing the parameters such as the molar ratio, the solid content, and the proportion of the dehydrating agent, and thus the high-performance TPI paste suitable for the glue-free two-layer flexible copper-clad plate (2L-FCCL) is prepared. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the application, and therefore should not be regarded as a limitation to the scope, and other related drawings can also be obtained by the drawings without paying creative labor for those skilled in the art.

[0024] Figure 1 The viscosity-temperature change curve of the TPI paste prepared in the embodiment 1 of the application;

[0025] Figure 2DSC curve (Tg test result) of the TPI film prepared in Example 1 of the present application;

[0026] Figure 3 Peeling force test curve of the 2L-FCCL prepared in Example 1 of the present application.

[0027] Figure 4 Peeling force test curve of the 2L-FCCL prepared in Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0028] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0029] The present embodiment successfully synthesizes the TPI slurry with high Tg, high adhesion, high thermal stability and good processability through monomer selection, process optimization and purification and preparation parameter control, and solves the problems of insufficient adhesion and poor temperature resistance of traditional thermoplastic polyimide (TPI) in 2L-FCCL applications. The specific implementation is as follows:

[0030] A preparation method of a high-adhesion thermoplastic polyimide slurry, comprising the following steps:

[0031] S1. Under the protection of inert gas, o-tolidine and bisphenol A type diether dianhydride (BPADA) are sequentially added in a polar aprotic solvent, and a polyamide acid solution is prepared by reaction at 0-5℃;

[0032] S2. Dehydrating agent and catalyst are added to the polyamide acid solution, and chemical imidization reaction is carried out at a temperature of 23-27℃ to prepare a thermoplastic polyimide reaction slurry;

[0033] S3. The reaction slurry is slowly added to excess anhydrous ethanol for sedimentation, and after multiple ethanol washing, drying and crushing, a thermoplastic polyimide powder with a particle size of 50-100μm is prepared;

[0034] S4. The thermoplastic polyimide powder is redissolved in a polar aprotic solvent, ultrasonically dispersed and filtered to prepare a high-adhesion thermoplastic polyimide slurry with a solid content of 15-20wt% and a viscosity of 12000-18000cPs.

[0035] By low-temperature synthesis of polyamic acid (PAA), room temperature chemical imidization, ethanol precipitation purification and ultrasonic dispersion to prepare slurry, the balance of high glass transition temperature and high adhesion is realized, the crosslinking and performance decline caused by traditional high-temperature imidization are avoided, and the purity and thermal stability of thermoplastic polyimide (TPI) are ensured without introducing adhesive.

[0036] As a preferred embodiment, the molar ratio of o-tolidine to bisphenol A diether dianhydride in step S1 is 1:1, and the error range is ±0.02.

[0037] By strictly controlling the monomer ratio, end group defects can be avoided, ensuring the integrity of the molecular chain and the completeness of the reaction, thereby improving the thermal stability and adhesion performance of TPI and avoiding performance fluctuations caused by ratio deviation.

[0038] As a preferred embodiment, in step S1, o-tolidine is first added to the polar aprotic solvent and stirred until completely dissolved, then the system temperature is controlled at 0-5℃, bisphenol A diether dianhydride is slowly added dropwise, the stirring rate is maintained at 300-500r / min during the dropwise addition, and after the dropwise addition is completed, the reaction is continued at 0-5℃ for 24h to obtain a transparent and uniform polyamic acid solution.

[0039] As a preferred embodiment, in step S1, the polar aprotic solvent is N,N-dimethylacetamide (DMAC), and the addition amount of the polar aprotic solvent should make the solid content of the polyamic acid solution 10-15wt%.

[0040] Because DMAC has good solubility and stability, it can effectively dissolve o-tolidine and BPADA, promote uniform synthesis of PAA, ensure uniformity of the reaction system and no precipitation, and provide a good foundation for subsequent imidization. The solid content range of 10-15wt% can ensure that the PAA solution has appropriate fluidity for subsequent operation, and can avoid too high viscosity caused by too high concentration, or insufficient film thickness caused by too low concentration.

[0041] As a preferred embodiment, in step S2, the dehydrating agent is acetic anhydride, the molar ratio of acetic anhydride to carboxyl in polyamic acid is (1-1.5):1; the catalyst is pyridine, and the molar ratio of pyridine to acetic anhydride is 1:1.

[0042] The combination of acetic anhydride and pyridine can efficiently catalyze the dehydration and ring closure of carboxyl, avoid molecular chain degradation caused by high-temperature imidization, ensure efficient imidization reaction at room temperature, and improve the molecular weight and performance of TPI.

[0043] As a preferred embodiment, in step S3, the drying conditions are temperature 80-100℃, vacuum degree <0.1kPa, and time 8-12 hours.

[0044] The above drying conditions can completely remove residual solvents and small molecular impurities, while avoiding thermal crosslinking of the TPI at high temperatures to maintain its thermoplasticity and ensure subsequent slurry preparation and film formation quality.

[0045] In step S3, ethanol sedimentation purification: the thermoplastic polyimide reaction slurry is slowly added to an excess of anhydrous ethanol (the volume ratio of the reaction slurry to the anhydrous ethanol is 1: (5-8)), and the stirring rate is maintained at 200-300 r / min during the addition process. The TPI will form a light yellow flocculent precipitate in the ethanol. After standing for 1-2 h, the precipitate is collected by filtration and washed repeatedly with anhydrous ethanol for 3-5 times (each time, the volume of the ethanol used is 3-5 times the wet weight of the precipitate) to remove residual DMAC, acetic anhydride, pyridine and unreacted monomers. The washed precipitate is placed in a vacuum drying oven for subsequent drying.

[0046] As a preferred embodiment, in step S4, ultrasonic-assisted dispersion is used, the ultrasonic power is 300-500 W, and the ultrasonic time is 30-60 min.

[0047] The ultrasonic treatment can effectively break the agglomeration of the TPI powder, improve the dispersibility and solubility in DMAC, thereby obtaining a uniform and stable TPI slurry and avoiding defects in the coating process.

[0048] As a preferred embodiment, in step S4, a polytetrafluoroethylene filter membrane is used for filtration, and the pore size of the filter membrane is 1.0-2.0 μm.

[0049] The filtration can remove trace amounts of undissolved impurities and agglomerates, improve the purity and film formation quality of the slurry, avoid defects in the coating process, and ensure the interfacial bonding strength and reliability during subsequent compounding with a copper foil.

[0050] The embodiment also provides a thermoplastic polyimide slurry prepared by the above method. The thermoplastic polyimide slurry has a glass transition temperature Tg≥300 ℃, a peel strength with a copper foil ≥1.1 N / mm, a tensile strength ≥220 MPa, and an elongation at break ≥20%.

[0051] The slurry has excellent thermal properties, mechanical properties and bonding properties, and meets the requirements of high-end flexible electronic materials (such as 2L-FCCL) for high temperature resistance, high reliability and high flexibility.

[0052] The embodiment also provides an application of the thermoplastic polyimide slurry in the preparation of a glue-free two-layer flexible copper-clad plate.

[0053] Here, the high-adhesion TPI slurry synthesized by the present application can be directly used for the preparation of a glue-free two-layer flexible copper-clad plate (2L-FCCL): the TPI slurry is coated on the surface of a copper foil, and after pre-drying at 120-150°C and hot-pressing at 200-250°C, a TPI / copper foil composite substrate is prepared, which has high high-temperature resistance (long-term use temperature ≥ 280°C), high flexibility (peeling force retention rate ≥ 90% after 180° bending 1000 times), and low dielectric loss, and can be widely used in high-end flexible electronic fields such as 5G communication equipment, flexible OLED display, wearable medical electronics, and new energy vehicle electronics.

[0054] Example 1

[0055] A method for synthesizing a high-adhesion thermoplastic polyimide, the specific steps being as follows:

[0056] S1. A 500 mL three-necked flask was purged with high-purity nitrogen (purity ≥ 99.999%), 200 mL of N,N-dimethylacetamide (DMAC) was added, then 10.81 g (0.05 mol) of o-dianisidine was added, and mechanical stirring (speed 300 r / min) was started until complete dissolution; the three-necked flask was placed in an ice water bath, and when the temperature of the system dropped to 3°C, 22.21 g (0.05 mol) of BPADA was slowly added, the dropwise addition time was controlled for 30 min, and after the dropwise addition was completed, the system was continuously incubated at 3°C for 24 h to prepare a transparent PAA solution with a solid content of 12 wt%.

[0057] S2. To the above PAA solution, 10.21 g (0.1 mol) of acetic anhydride and 7.91 g (0.1 mol) of pyridine were added in sequence, stirred for 10 min until uniform, the ice water bath was removed, the temperature of the system was raised to 25°C, and the reaction was carried out at this temperature for 24 h to prepare a light yellow TPI reaction slurry.

[0058] S3. The TPI reaction slurry was slowly added to 1000 mL of anhydrous ethanol (stirring speed 400 r / min) to form a light yellow flocculent precipitate; after standing for 1.5 h, the precipitate was collected by suction filtration and washed with anhydrous ethanol 4 times (50 mL of ethanol each time); the washed precipitate was placed in a vacuum drying oven at 85°C and a vacuum degree of 0.08 kPa for drying for 10 h, and after drying, it was crushed with a pulverizer to prepare TPI powder with a particle size of 80 μm.

[0059] S4. 15 g of TPI powder was added to 75 mL of DMAC, stirred at 25°C at 400 r / min for 3 h, and during this period, 400 W ultrasonic assistance was used for dispersion for 45 min; after stirring was completed, the TPI slurry was filtered with a 1.2 μm polytetrafluoroethylene filter membrane.

[0060] Example 2

[0061] A method for synthesizing a high-adhesion thermoplastic polyimide, the main difference from Example 1 being the ice-water bath temperature during PAA synthesis and the TPI slurry solid content, the specific steps being as follows:

[0062] S1, nitrogen was introduced into a three-necked flask, 180 mL of DMAC was added, 11.93 g (0.05 mol) of o-dianisidine was added, mechanical stirring (400 r / min) was started to dissolve, and then the flask was placed in an ice-water bath to control the temperature at 5°C. 22.21 g (0.05 mol) of BPADA was slowly added, and after the addition was completed, the system was kept at 5°C for 24 hours to prepare a PAA solution with a solid content of 13 wt%.

[0063] S2, 10.21 g (0.1 mol) of acetic anhydride and 7.91 g (0.1 mol) of pyridine were added to the above PAA solution in sequence, stirred until uniform, the ice-water bath was removed, and the system temperature was raised to 25°C. The reaction was carried out at this temperature for 24 hours to prepare a light yellow TPI reaction slurry.

[0064] S3, the TPI reaction slurry was slowly added to 1000 mL of anhydrous ethanol (stirring speed 500 r / min), forming a light yellow flocculent precipitate; after standing for 1.5 h, the precipitate was collected by suction filtration and washed with anhydrous ethanol 4 times (50 mL of ethanol each time); the washed precipitate was placed in a vacuum drying oven, dried at 90°C and a vacuum degree of 0.07 kPa for 8 h, and then crushed with a pulverizer to prepare TPI powder with a particle size of 70 μm.

[0065] S4, 18 g of TPI powder was added to 72 mL of DMAC, stirred at 28°C for 3 h, and ultrasonically dispersed at 500 W for 40 min; filtration through a 1.5 μm filter membrane to prepare a TPI slurry.

[0066] Example 3

[0067] A method for synthesizing a high-adhesion thermoplastic polyimide, the main difference from Example 1 being the amount of acetic anhydride used during chemical imidization, the specific steps being as follows:

[0068] S1, high-purity nitrogen (purity ≥ 99.999%) was introduced into a 500 mL three-necked flask, 220 mL of DMAC was added, followed by 9.81 g (0.05 mol) of o-dianisidine, and mechanical stirring (500 r / min) was started until complete dissolution; the three-necked flask was placed in an ice-water bath, and when the system temperature dropped to 3°C, 18.25 g (0.05 mol) of BPADA was slowly added, the dropwise addition time was controlled to be 30 min, and after the addition was completed, the system was kept at 3°C for 24 hours to prepare a transparent PAA solution with a solid content of 10 wt%.

[0069] S2, 12.25 g (0.12 mol) of acetic anhydride and 9.49 g (0.12 mol) of pyridine were sequentially added to the above PAA solution, stirred for 15 min until uniform, the ice water bath was removed, the temperature of the system was raised to 25 °C, and the reaction was carried out at this temperature for 24 h to prepare a light yellow TPI reaction slurry.

[0070] S3, the TPI reaction slurry was slowly added to 1000 mL of anhydrous ethanol (stirring speed 500 r / min), forming a light yellow flocculent precipitate; after standing for 1.5 h, the precipitate was collected by suction filtration and washed with anhydrous ethanol 5 times (50 mL of ethanol each time); the washed precipitate was placed in a vacuum drying oven at a temperature of 85 °C and a vacuum degree of 0.06 kPa for drying for 8 h, and after drying, it was crushed by a crusher to prepare TPI powder with a particle size of 60 μm.

[0071] S4, 15 g of TPI powder was added to 75 mL of DMAC, stirred at 25 °C at 600 r / min for 3 h, and during the stirring, 400 W ultrasonic assisted dispersion was carried out for 45 min; after stirring, a TPI slurry with a solid content was prepared by filtering with a 2 μm polytetrafluoroethylene filter membrane.

[0072] Example 4

[0073] A method for synthesizing a high-adhesion thermoplastic polyimide, the specific steps are as follows:

[0074] S1, a 500 mL three-necked flask was purged with high-purity nitrogen (purity ≥ 99.999%), 200 mL of DMAC was added, then 20.81 g (0.05 mol) of o-tolidine was added, and mechanical stirring (speed 300 r / min) was started until complete dissolution; the three-necked flask was placed in an ice water bath, and when the temperature of the system dropped to 0 °C, 19.25 g (0.05 mol) of BPADA was slowly added, the dropwise addition time was controlled for 30 min, and after the dropwise addition was completed, the reaction was continued at 0 °C for 24 h to prepare a transparent PAA solution with a solid content of 15 wt%.

[0075] S2, 10.21 g (0.1 mol) of acetic anhydride and 7.91 g (0.1 mol) of pyridine were sequentially added to the above PAA solution, stirred until uniform, the ice water bath was removed, the temperature of the system was raised to 25 °C, and the reaction was carried out at this temperature for 24 h to prepare a light yellow TPI reaction slurry.

[0076] S3, slowly drop the TPI reaction slurry into 1000 mL of anhydrous ethanol (stirring speed 300 r / min), form a light yellow flocculent precipitate; after standing for 1.5 h, collect the precipitate by suction filtration, wash with anhydrous ethanol 4 times (50 mL of ethanol each time); place the washed precipitate in a vacuum drying oven, dry at 80℃, vacuum degree 0.08 kPa for 12 h, after drying, crush with a crusher, to obtain TPI powder with a particle size of 80 μm.

[0077] S4, add 15 g of TPI powder to 75 mL of DMAC, stir at 25℃ for 3 h at 400 r / min, and assist dispersion with 300 W ultrasound for 45 min during the stirring; after the stirring is completed, filter with a 1.0 μm polytetrafluoroethylene filter membrane to obtain a TPI slurry.

[0078] Example 5

[0079] A method for synthesizing a high-adhesion thermoplastic polyimide, the specific steps are as follows:

[0080] S1, introduce high-purity nitrogen (purity ≥ 99.999%) into a 500 mL three-necked flask, add 200 mL of DMAC, then add 10.81 g (0.05 mol) of o-dianisidine, start mechanical stirring (speed 300 r / min) until completely dissolved; place the three-necked flask in an ice water bath, when the temperature of the system drops to 5℃, slowly add 22.21 g (0.05 mol) of BPADA, control the dropwise addition time to be 30 min, after the dropwise addition is completed, continue to incubate at 5℃ for 24 h, to obtain a transparent PAA solution with a solid content of 12 wt%.

[0081] S2, to the above PAA solution, add 10.0 g (0.1 mol) of acetic anhydride and 7.91 g (0.1 mol) of pyridine in sequence, stir until uniform, remove the ice water bath, raise the temperature of the system to 25℃, react at this temperature for 24 h, to obtain a light yellow TPI reaction slurry.

[0082] S3, slowly drop the TPI reaction slurry into 1000 mL of anhydrous ethanol (stirring speed 300 r / min), form a light yellow flocculent precipitate; after standing for 1.5 h, collect the precipitate by suction filtration, wash with anhydrous ethanol 4 times (50 mL of ethanol each time); place the washed precipitate in a vacuum drying oven, dry at 85℃, vacuum degree 0.08 kPa for 10 h, after drying, crush with a crusher, to obtain TPI powder with a particle size of 100 μm.

[0083] S4, add 15 g of TPI powder to 75 mL of DMAC, stir at 25℃ for 3 h at 400 r / min, and assist dispersion with 400 W ultrasound for 45 min during the stirring; after the stirring is completed, filter with a 2.0 μm polytetrafluoroethylene filter membrane, to obtain a TPI slurry.

[0084] Comparative Example 1

[0085] A method for synthesizing a polyimide, the main difference from Example 1 is that the diamine monomer is replaced by 4,4'-diaminodiphenyl ether (ODA), the specific steps are as follows:

[0086] S1, add 200 mL of DMAC to a three-necked flask, add 9.91 g (0.05 mol) of ODA, stir to dissolve, then ice water bath at 3°C, add 22.21 g (0.05 mol) of BPADA, react at 0-5°C for 24 h to prepare a PAA solution.

[0087] S2, to the above PAA solution, add 10.21 g (0.1 mol) of acetic anhydride and 7.91 g (0.1 mol) of pyridine in turn, stir for 10 min until uniform, remove the ice water bath, and raise the temperature of the system to 25°C, react at this temperature for 24 h to prepare a light yellow TPI reaction slurry.

[0088] S3, slowly add the TPI reaction slurry to 1000 mL of anhydrous ethanol (stirring speed 200 r / min), form a light yellow flocculent precipitate; after standing for 1.5 h, collect the precipitate by suction filtration, wash with anhydrous ethanol 4 times (each time with 50 mL of ethanol); place the washed precipitate in a vacuum drying oven, dry at 85°C under a vacuum of 0.08 kPa for 10 h, after drying, crush with a pulverizer to prepare TPI powder with a particle size of about 80 μm.

[0089] Comparative Example 2

[0090] A method for synthesizing a polyimide, the main difference from Example 1 is that the amount of dehydrating agent acetic anhydride is increased to 0.18 mol, so that the molar ratio of it to the carboxyl groups in the polyamic acid deviates from the recommended 1.8:1, the specific steps are as follows:

[0091] S1, introduce high-purity nitrogen (purity ≥ 99.999%) into a 500 mL three-necked flask, then add 200 mL of DMAC, and then add 10.8 g (0.05 mol) of o-tolidine, start mechanical stirring (speed 350 r / min) until completely dissolved; place the three-necked flask in an ice water bath, when the temperature of the system drops to 3°C, slowly add 22.2 g (0.05 mol) of BPADA, the dropwise addition time is controlled for 30 min, after the dropwise addition is completed, continue to incubate at 3°C for 24 h to prepare a transparent PAA solution with a solid content of 13 wt%.

[0092] S2, 18.73 g (0.18 mol) of acetic anhydride and 14.24 g (0.1 mol) of pyridine were sequentially added to the above PAA solution, stirred for 10 min until uniform, the ice water bath was removed, the temperature of the system was raised to 25 °C, and the reaction was carried out at this temperature for 24 h to prepare a light yellow TPI reaction slurry.

[0093] S3, the TPI reaction slurry was slowly added to 1000 mL of anhydrous ethanol (stirring speed 200 r / min), forming a light yellow flocculent precipitate; after standing for 1.5 h, the precipitate was collected by suction filtration and washed with anhydrous ethanol 4 times (50 mL of ethanol each time); the washed precipitate was placed in a vacuum drying oven, dried at 85 °C under a vacuum of 0.08 kPa for 10 h, and then crushed by a crusher to prepare TPI powder with a particle size of about 80 μm.

[0094] S4, 15 g of TPI powder was added to 75 mL of DMAC, stirred at 25 °C at 400 r / min for 3 h, and dispersed for 45 min with the aid of 400 W ultrasonic during the stirring; after stirring, it was filtered with a 1.2 μm polytetrafluoroethylene filter membrane to prepare a TPI slurry.

[0095] Comparative Example 3

[0096] A method for synthesizing a polyimide, the main difference from Example 1 is that the synthesis starting temperature of polyamide acid is increased to 10 °C, and the specific steps are as follows:

[0097] S1, high-purity nitrogen (purity ≥ 99.999%) was introduced into a 500 mL three-necked flask, 200 mL of DMAC was added, then 10.8 g (0.05 mol) of o-tolidine was added, and mechanical stirring (speed 300 r / min) was started until completely dissolved; the three-necked flask was placed in an ice water bath, and when the temperature of the system dropped to 10 °C, 22.2 g (0.05 mol) of BPADA was slowly added, the dropwise addition time was controlled for 30 min, and after the dropwise addition was completed, the reaction was continued at 3 °C for 24 h to prepare a transparent PAA solution with a solid content of 13 wt%.

[0098] S2, 10.21 g (0.1 mol) of acetic anhydride and 7.91 g (0.1 mol) of pyridine were sequentially added to the above PAA solution, stirred for 10 min until uniform, the ice water bath was removed, the temperature of the system was raised to 25 °C, and the reaction was carried out at this temperature for 24 h to prepare a light yellow TPI reaction slurry.

[0099] S3, slowly drop the TPI reaction slurry into 1000 mL of anhydrous ethanol (stirring speed 200 r / min), form light yellow flocculent precipitate; after standing for 1.5 h, collect the precipitate by suction filtration, wash with anhydrous ethanol 4 times (50 mL of ethanol each time); place the washed precipitate in a vacuum drying oven at 85°C, vacuum degree 0.08 kPa, dry for 8 h, after drying, crush with a pulverizer, to obtain TPI powder with a particle size of 80 μm.

[0100] S4, add 15 g of TPI powder into 75 mL of DMAC, stir at 25°C at 400 r / min for 3 h, during which time, use 400 W ultrasonic to assist dispersion for 45 min; after stirring is completed, filter with a 1.2 μm polytetrafluoroethylene filter membrane, to obtain TPI slurry.

[0101] Comparative Example 4

[0102] A method for synthesizing a thermoplastic polyimide, the main difference from Example 1 is that the dianhydride monomer is replaced from bisphenol A type diether dianhydride (BPADA) to hexafluoro dianhydride (6FDA), the specific steps are as follows:

[0103] S1, introduce high-purity nitrogen (purity ≥ 99.999%) into a 500 mL three-necked flask, add 200 mL of DMAC, then add 10.8 g (0.05 mol) of o-dianisidine, start mechanical stirring (speed 300 r / min) until completely dissolved; place the three-necked flask in an ice water bath, when the system temperature drops to 3°C, slowly add 22.2 g (0.05 mol) of hexafluoro dianhydride (6FDA), the dropwise addition time is controlled for 30 min, after dropwise addition is completed, continue to incubate at 3°C for 24 h, to obtain a transparent PAA solution with a solid content of 13 wt%.

[0104] S2, to the above PAA solution, add 10.21 g (0.1 mol) of acetic anhydride and 7.91 g (0.1 mol) of pyridine in sequence, stir for 10 min until uniform, remove the ice water bath, raise the system temperature to 25°C, react at this temperature for 24 h, to obtain light yellow TPI reaction slurry.

[0105] S3, slowly drop the TPI reaction slurry into 1000 mL of anhydrous ethanol (stirring speed 200 r / min), form light yellow flocculent precipitate; after standing for 1.5 h, collect the precipitate by suction filtration, wash with anhydrous ethanol 4 times (50 mL of ethanol each time); place the washed precipitate in a vacuum drying oven at 85°C, vacuum degree 0.08 kPa, dry for 12 h, after drying, crush with a pulverizer, to obtain TPI powder with a particle size of 80 μm.

[0106] S4, 15 g of TPI powder was added into 75 mL of DMAC, stirred at 400 r / min for 3 h at 25 °C, and dispersed with 400 W ultrasound for 45 min during the stirring; after the stirring was completed, it was filtered with a 1.2 μm polytetrafluoroethylene filter membrane to prepare a TPI slurry.

[0107] Comparative Example 5

[0108] A method for synthesizing a thermoplastic polyimide, the main difference from Example 1 being that the solid content of the polyamic acid solution was reduced to 8 wt%, and the specific steps were as follows:

[0109] S1, high-purity nitrogen (purity ≥ 99.999%) was introduced into a 500 mL three-necked flask, 400 mL of DMAC was added, then 10.81 g (0.05 mol) of o-dianisidine was added, and mechanical stirring (speed 300 r / min) was started until complete dissolution; the three-necked flask was placed in an ice water bath, and when the temperature of the system dropped to 15 °C, 22.21 g (0.05 mol) of BPADA was slowly added, the dropwise addition time was controlled for 30 min, and after the dropwise addition was completed, the system was continuously incubated at 3 °C for 24 h to prepare a transparent PAA solution with a solid content of 8 wt%.

[0110] S2, 10.21 g (0.1 mol) of acetic anhydride and 7.91 g (0.1 mol) of pyridine were sequentially added to the above PAA solution, stirred for 10 min until uniform, the ice water bath was removed, the temperature of the system was raised to 25 °C, and the reaction was carried out at this temperature for 24 h to prepare a light yellow TPI reaction slurry.

[0111] S3, the TPI reaction slurry was slowly added to 1000 mL of anhydrous ethanol (stirring speed 200 r / min) to form a light yellow flocculent precipitate; after standing for 1.5 h, the precipitate was collected by suction filtration and washed with anhydrous ethanol 4 times (50 mL of ethanol each time); the washed precipitate was placed in a vacuum drying oven, dried at 85 °C and a vacuum degree of 0.08 kPa for 10 h, and then crushed with a pulverizer to prepare TPI powder with a particle size of 80 μm.

[0112] S4, 15 g of TPI powder was added into 75 mL of DMAC, stirred at 400 r / min for 3 h at 25 °C, and dispersed with 400 W ultrasound for 45 min during the stirring; after the stirring was completed, it was filtered with a 1.2 μm polytetrafluoroethylene filter membrane to prepare a TPI slurry.

[0113] Comparative Example 6

[0114] A method for synthesizing a thermoplastic polyimide with high adhesion, the main difference from Example 1 being that the molar ratio of o-dianisidine to BPADA was 1:2, and the specific steps were as follows:

[0115] S1, high purity nitrogen (purity ≥ 99.999%) was introduced into a 500 mL three-necked flask, 200 mL DMAC was added, then 10.8 g (0.05 mol) of o-tolidine was added, and mechanical stirring (speed 300 r / min) was started until complete dissolution; the three-necked flask was placed in an ice water bath, and when the temperature of the system dropped to 3°C, 22.2 g (0.1 mol) of BPADA was slowly added, the dropwise addition time was controlled for 30 min, and after the dropwise addition was completed, the reaction was continued at 3°C for 24 h, and a transparent PAA solution with a solid content of 13 wt% was prepared.

[0116] S2, to the above PAA solution, 10.21 g (0.1 mol) of acetic anhydride and 7.91 g (0.1 mol) of pyridine were added in sequence, stirred for 10 min until uniform, the ice water bath was removed, the temperature of the system was raised to 25°C, and the reaction was carried out at this temperature for 24 h, and a light yellow TPI reaction slurry was prepared.

[0117] S3, the TPI reaction slurry was slowly added to 1000 mL of anhydrous ethanol (stirring speed 200 r / min), forming a light yellow flocculent precipitate; after standing for 1.5 h, the precipitate was collected by suction filtration and washed with anhydrous ethanol 4 times (50 mL of ethanol each time); the washed precipitate was placed in a vacuum drying oven at 85°C, 0.08 kPa vacuum, and dried for 10 h, then crushed with a pulverizer to prepare TPI powder with a particle size of about 80 μm.

[0118] S4, 15 g of TPI powder was added to 75 mL of DMAC, stirred at 25°C at 400 r / min for 3 h, and during this time, 400 W ultrasonic assisted dispersion was performed for 45 min; after stirring was completed, filtration was performed with a 1.2 μm polytetrafluoroethylene filter membrane to prepare a TPI slurry.

[0119] Comparative Example 7

[0120] A method for synthesizing a polyimide, the main difference between Example 1 is that in step S1, the amount of substance of BPADA is 0.055 mol, and the molar ratio of o-tolidine to BPADA is 1:1.1, and the specific steps are the same as Example 1.

[0121] Comparative Example 8

[0122] A method for synthesizing a polyimide, the main difference between Example 1 is that in step S1, the solid content of the polyamic acid solution is reduced to 22 wt%, and the specific steps are as follows:

[0123] S1, high purity nitrogen was introduced into a 500 mL three-necked flask, 200 mL of N,N-dimethylacetamide (DMAC) was added, then 10.81 g (0.05 mol) of o-tolidine was added, and mechanical stirring (speed 300 r / min) was started until complete dissolution; the three-necked flask was placed in an ice water bath, and when the temperature of the system dropped to 3℃, 22.21 g (0.05 mol) of BPADA was slowly added, the dropwise addition time was controlled for 30 min, and after the dropwise addition was completed, the reaction was continued at 3℃ for 24 h, a transparent PAA solution with a solid content of 22 wt% was prepared, and the remaining steps were the same as in Example 1.

[0124] Comparative Example 9

[0125] A synthesis method of a polyimide, the main difference from Example 1 is that the amount of dehydrating agent acetic anhydride in step S2 is increased to 0.18 mol, so that the molar ratio of it to the carboxyl group in polyamic acid deviates from 1:1.9, and the specific steps are the same as in Example 1.

[0126] Comparative Example 10

[0127] A synthesis method of a thermoplastic polyimide, the main difference from Example 1 is that the particle size of the TPI powder in step S3 is 120 μm, and the specific steps are the same as in Example 1.

[0128] Comparative Example 11

[0129] A synthesis method of a thermoplastic polyimide, the main difference from Example 1 is that the particle size of the TPI powder in step S3 is 30 μm, and the specific steps are the same as in Example 1.

[0130] The thermoplastic polyimides prepared in the above Examples 1-5 and Comparative Examples 1-11 were tested for performance, and the test data are shown in Table 1:

[0131] Table 1 Performance parameters of thermoplastic polyimides Item Glass transition temperature - Tg (°C) 5% thermal weight loss temperature (°C) Coefficient of thermal expansion - CTE (ppm / °C) Tensile strength (MPa) Elongation at break (%) Peel force (with copper foil) (N / mm) Sizing viscosity at 26°C (cPs) Sizing viscosity change rate after 30 days (%) Example 1 364 472 15 235 22 5 15200 3.2 Example 2 318 468 16 228 21 1.2 17800 4.5 Example 3 330 475 14 242 20 1.4 14800 2.8 Example 4 344 454 18 224 21.5 2.2 14500 2.7 Example 5 351 460 17 230 21 1.7 16500 3.0 Comparative Example 1 302 407 26 205 19 0.5 10000 6.5 Comparative Example 2 280 442 22 210 17 0.6 8000 6.9 Comparative Example 3 290 430 20 195 15 0.7 8600 8 Comparative Example 4 280 435 24 205 18 0.8 9000 8.4 Comparative Example 5 303 441 19 209 14 0.3 12000 4.1 Comparative Example 6 324 417 20 221 19 0.9 16000 6.2 Comparative Example 7 260 411 22 195 16 0.7 7400 7.7 Comparative Example 8 270 414 24 190 14 0.6 12500 11.1 Comparative Example 9 265 420 28 186 17 0.65 10600 8.4 Comparative Example 10 275 419 41 204 18 0.8 10700 6.5 Comparative Example 11 270 404 36 216 15 0.55 13000 9.1

[0132] The present application successfully prepared a thermoplastic polyimide (TPI) slurry with high glass transition temperature, high adhesion, good mechanical properties, good thermal stability and stability by selecting o-tolidine as a diamine monomer, pairing with bisphenol A type diether dianhydride (BPADA), combining low-temperature polyamic acid (PAA) synthesis and normal temperature chemical imidization process.

[0133] The peel force of the TPI slurry prepared in Example 1 from the copper foil is more prominent because the adhesion of TPI to copper is essentially a synergistic effect of chemical bonding force, mechanical bonding force and Van der Waals force, and the molecular structure of BPADA and o-tolidine and the suitable synthesis conditions maximize the three types of forces. The BPADA molecule contains ether bonds (-O-) and imide rings (-CO-N-CO-), and the o-tolidine molecule contains amino groups (-NH2, which are converted into N-H bonds of imide rings after polymerization) and methyl groups. In the TPI molecular chain formed by the polymerization of the two, the oxygen atoms of the imide rings and the hydrogen atoms of the N-H bonds can form strong interactions with the oxide layer on the surface of copper. When the synthesis conditions are optimal, BPADA and o-tolidine can completely polymerize to form TPI with high molecular weight and narrow distribution.

[0134] The TPI molecular chain contains a large number of aromatic rings (the benzene rings of bisphenol A in BPADA and the benzene rings in o-tolidine), and the π-electron clouds of the aromatic rings can form π-metal coordination with the free electrons on the surface of copper, and at the same time the distance between the molecular chain and the surface of copper is extremely close, and the Van der Waals force is significantly enhanced, further supplementing the adhesion.

[0135] In Comparative Example 1, ODA is used instead of o-tolidine, resulting in a decrease in Tg and peel force, indicating that the methyl substituent of o-tolidine is crucial for enhancing adhesion. In Comparative Example 2, the amount of acetic anhydride is not appropriate, causing a decrease in Tg and peel force, indicating that the proportion of the dehydrating agent needs to be strictly controlled. In Comparative Example 3, the synthesis temperature is increased to 10°C, resulting in a decrease in Tg and peel force, verifying the protective effect of low-temperature (0-5°C) synthesis on the molecular chain structure. In Comparative Example 4, 6FDA is used instead of BPADA, and both Tg and peel force are significantly reduced, indicating the key role of BPADA in improving adhesion and heat resistance. In Comparative Example 5, the solid content is too low, resulting in extremely low peel force, although the Tg is not low, the film-forming property and adhesion are poor, so the solid content needs to be controlled at 10-15 wt%. In Comparative Example 6, the excessive amount of BPADA results in a decrease in peel force and abnormal viscosity, indicating that strict reaction according to the 1:1 molar ratio is the basis for ensuring performance. In Comparative Example 7, BPADA is excessively large (molar ratio 1:3), Tg is significantly reduced, and peel force is reduced, indicating that a serious imbalance in monomer ratio can destroy the regularity of the molecular chain structure, resulting in uneven molecular weight distribution and an increase in end group defects, thereby seriously damaging the heat resistance and adhesion performance of TPI. This proves from the negative side that it is crucial to strictly control the monomer molar ratio to 1:1 (±0.02). In Comparative Example 8, the solid content is 22 wt%, resulting in a decrease in Tg and a high rate of change in viscosity, indicating that high solid content affects the stability of the solution and the film-forming property. In Comparative Examples 10-11, the particle size of the TPI powder is too large or too small (30-120 μm), resulting in a decrease in adhesion and slurry stability, indicating that controlling the particle size to 60-100 μm is beneficial to dispersion and film formation.

[0136] It can be found by system comparison of Comparative Examples 1-11 that the accurate selection and ratio of monomers (o-tolidine: BPADA = 1:1), strict control of synthesis temperature (0-5℃ in PAA stage), appropriate use of dehydrating agent (acetic anhydride: carboxyl = (1-1.5):1) and optimization of PAA solution solid content (10-15wt%) are the four most critical factors for the successful preparation of high-performance TPI slurry. Deviation of any parameter will cause significant decrease in heat resistance, bonding strength or processing stability of the product.

[0137] The present application successfully solves the problems of insufficient adhesion and poor heat resistance of traditional TPI by optimizing o-tolidine and BPADA, precise process control, low-temperature PAA synthesis, room-temperature imidization, ethanol precipitation purification, ultrasonic dispersion and parameter optimization such as molar ratio, solid content and dehydrating agent ratio, and prepares high-performance TPI slurry suitable for glue-free two-layer flexible copper-clad laminate (2L-FCCL) with high reliability, high heat resistance and excellent processability, meeting the needs of high-end electronic fields such as 5G communication and flexible display.

[0138] The present application is further described above with the aid of specific examples, but it should be understood that the specific description herein should not be construed as limiting the spirit and scope of the present application. Various modifications made by those skilled in the art after reading the present specification belong to the scope of protection of the present application.

Claims

1. A method for preparing a highly adhesive thermoplastic polyimide slurry, characterized in that, Includes the following steps: S1. Under inert gas protection, o-toluidine and bisphenol A diether dianhydride are added sequentially to a polar aprotic solvent, and the reaction is carried out at 0~5℃ to prepare a polyamic acid solution. S2. Add a dehydrating agent and a catalyst to the polyamic acid solution, and carry out a chemical imidization reaction at a temperature of 23~27℃ to obtain a thermoplastic polyimide reaction slurry; S3. The reaction slurry is slowly added dropwise to excess anhydrous ethanol to settle. After repeated washing with ethanol, drying and pulverizing, thermoplastic polyimide powder with a particle size of 50~100μm is obtained. S4. The thermoplastic polyimide powder is redissolved in a polar aprotic solvent, and then ultrasonically dispersed and filtered to obtain a high-adhesion thermoplastic polyimide slurry with a solid content of 15~20wt% and a viscosity of 12000~18000cPs.

2. The preparation method according to claim 1, characterized in that, In step S1, the molar ratio of o-toluidine to bisphenol A diether dianhydride is 1:1, and the error range is ±0.

02.

3. The preparation method according to claim 1, characterized in that, In step S1, o-toluidine is first added to the polar aprotic solvent and stirred until completely dissolved. Then, the system temperature is controlled at 0~5℃, and bisphenol A type diether dianhydride is slowly added dropwise. During the dropwise addition, the stirring rate is maintained at 300~500 r / min. After the dropwise addition is completed, the reaction is continued at 0~5℃ for 24h to obtain a transparent and homogeneous polyamic acid solution.

4. The preparation method according to claim 1, characterized in that, In step S1, the polar aprotic solvent is N,N-dimethylacetamide, and the amount of polar aprotic solvent added is required to make the solid content of the polyamic acid solution 10~15wt%.

5. The preparation method according to claim 1, characterized in that, In step S2, the dehydrating agent is acetic anhydride, and the molar ratio of acetic anhydride to carboxyl groups in polyamic acid is (1~1.5):1; the catalyst is pyridine, and the molar ratio of pyridine to acetic anhydride is 1:

1.

6. The preparation method according to claim 1, characterized in that, In step S3, the drying conditions are: temperature 80~100℃, vacuum degree <0.1kPa, and time 8~12 hours.

7. The preparation method according to claim 1, characterized in that, In step S4, ultrasonic-assisted dispersion is used, with an ultrasonic power of 300~500W and an ultrasonic time of 30~60 minutes.

8. The preparation method according to claim 1, characterized in that, In step S4, a polytetrafluoroethylene (PTFE) filter membrane is used for filtration, with a pore size of 1.0~2.0 μm.

9. A thermoplastic polyimide slurry, prepared by the method according to any one of claims 1 to 8, characterized in that, The thermoplastic polyimide slurry has a glass transition temperature (Tg) ≥ 300℃, a peel force to copper foil ≥ 1.1 N / mm, a tensile strength ≥ 220 MPa, and an elongation at break ≥ 20%.

10. The application of the thermoplastic polyimide slurry according to claim 9 in the preparation of adhesive-free two-layer flexible copper-clad laminates.

Images