Polyamide-imide resin, composition and prepared flexible copper-clad plate

Abstract

The invention discloses a polyamideimide resin, a composition and a prepared flexible copper-clad plate, and relates to the technical field of polyamideimide materials, and the preparation method comprises the following steps: in a nitrogen atmosphere, adding trimellitic anhydride into a solvent, stirring at room temperature until the trimellitic anhydride is dissolved, adding aromatic diisocyanate, stirring and dissolving, supplementing the solvent, carrying out programmed heating reaction, and filtering to obtain the polyamideimide resin. The polyamide-imide resin is obtained; the preparation method comprises the following steps: adding epoxy resin, an inorganic filler, a wetting leveling agent and a solvent into polyamide-imide resin, stirring and dispersing at room temperature, standing for defoaming, and filtering to obtain a polyamide-imide resin composition; and coating the polyamide-imide resin composition on the polyimide film, pre-baking, pressing the polyamide-imide resin composition on the rough surface of the electrolytic copper foil at a high temperature, carrying out programmed heating curing, and repeating the steps on the other surface to obtain the flexible copper-clad plate. The flexible copper-clad plate is simple in preparation process and low in cost, and the obtained flexible copper-clad plate is good in heat resistance and adaptability.

Description

Technical Field

[0001] This invention relates to the field of polyamide-imide materials technology, specifically to a polyamide-imide resin, composition, and the prepared flexible copper-clad laminate. Background Technology

[0002] Flexible copper clad laminates are the core substrate of flexible printed circuit boards (PCBs). Based on the lamination method, they can be divided into two categories: two-layer adhesive-free and three-layer adhesive-based. Among them, two-layer adhesive-free PCBs are difficult to meet the growing demand of the flexible PCB consumer market due to high cost, demanding manufacturing process, limited production capacity, and limited application scope. Therefore, three-layer adhesive-based flexible copper clad laminates are often used to make up for the above shortcomings.

[0003] Three-layer adhesive-based flexible copper clad laminates use thermosetting adhesives such as epoxy, acrylic, and polyester resins to bond polyimide films and metal foils together. The polyimide film used is polymerized from inexpensive pyromellitic dianhydride and 4,4'-diaminodiphenyl ether monomers. This type of film has the largest industrial scale and a significant cost advantage. Furthermore, the epoxy, acrylic, and polyester resin adhesives used in three-layer adhesive-based flexible copper clad laminates exhibit excellent initial tack performance, allowing for medium-temperature lamination processes (60-130℃) and high-speed production (≥5m / min). This makes them compatible with most coating production equipment and offers high yield. However, the adhesives used in three-layer adhesive-based flexible copper clad laminates are prone to aging and decomposition under prolonged high temperatures of 200℃, leading to a significant decrease in adhesive strength and eventual failure.

[0004] Therefore, it is of great significance to develop a cost-effective, highly soluble polyamide-imide resin that can be used in the preparation of flexible copper-clad laminate substrates. Summary of the Invention

[0005] The purpose of this invention is to provide a polyamide-imide resin, a composition, and a flexible copper-clad laminate prepared therefrom, in order to solve the problems raised in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A polyamide-imide resin, wherein the structural formula (A) of the polyamide-imide resin is: (A); Where n is an integer between 4 and 50.

[0007] Further, Ar is a compound containing a benzene ring group; the compound is one or more selected from 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 4,4'-dimethyldiphenylmethane, 2,4'-dimethyldiphenylmethane, 2,3'-dimethyldiphenylmethane, 1,5-dimethylnaphthalene, p-xylene, p-diethylbenzene, 1,2-diethylbenzene, 1,3-diethylbenzene, 1,3-di-tert-butylbenzene, 3,3',4,4'-tetramethylbiphenyl, and 3',4,4'-dimethyldiphenylmethane.

[0008] Further, the preparation method of the polyamide-imide resin is as follows: Under a nitrogen atmosphere, trimellitic anhydride is added to a solvent and stirred at room temperature until dissolved. Aromatic diisocyanate is added and stirred until dissolved, and solvent is added. The reaction is carried out at 70-90℃ for 4-6 hours, 100-120℃ for 4-6 hours, and 150-170℃ for 2-4 hours. The mixture is then filtered to obtain the polyamide-imide resin. In the preparation of polyamide-imide resin, the molar ratio of trimellitic anhydride to aromatic diisocyanate is 1:(0.8-0.98).

[0009] Furthermore, the structural formula (B) of the aromatic diisocyanate is: (B); Wherein, Ar is a compound containing a benzene ring group; the compound is one or more selected from 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 4,4'-dimethyldiphenylmethane, 2,4'-dimethyldiphenylmethane, 2,3'-dimethyldiphenylmethane, 1,5-dimethylnaphthalene, p-xylene, p-diethylbenzene, 1,2-diethylbenzene, 1,3-diethylbenzene, 1,3-di-tert-butylbenzene, 3,3',4,4'-tetramethylbiphenyl, and 3',4,4'-dimethyldiphenylmethane; Further, the solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, butanone, cyclohexanone, and toluene.

[0010] A polyamide-imide resin composition is obtained by mixing polyamide-imide resin with epoxy resin, inorganic filler, wetting and leveling agent and solvent.

[0011] In the preparation of the polyamide-imide resin composition, the mass ratio of epoxy resin, inorganic filler, wetting and leveling agent, solvent and polyamide-imide resin is (5-50):(5-40):(0.05-0.5):(10-50):100.

[0012] Further, the epoxy resin is one or more of N,N',N,N'-tetracyclooxypropyl-4,4'-diaminodiphenylmethane, N,N',N,N'-tetra(epoxyethylenemethyl)-1,3-phenylenediamine, 2,2-bis-(4-glycyloxyphenyl)propane, and dicyclopentadiene phenol epoxy resin; The inorganic filler is one or more of silicon dioxide, aluminum oxide, titanium dioxide, zirconium oxide, and barium sulfate; The wetting and leveling agent is one or more of BYK333, BYK310, BYK306, Wet410, Wet270 and Evonik 5830.

[0013] A flexible copper-clad laminate prepared from a polyamide-imide resin composition is prepared by the following steps: coating the polyamide-imide resin composition onto a polyimide film, pre-baking, pressing it at high temperature onto the rough surface of an electrolytic copper foil, curing it by programmed temperature rise, and repeating the above steps on the other side to obtain a flexible copper-clad laminate.

[0014] Furthermore, the pre-baking temperature is 140-180℃, and the time is 2-5 min; the high-temperature pressing temperature is 150-180℃, the pressing pressure is 5-20 MPa, and the pressing time is 60-180 s; the programmed temperature rise curing conditions are 100-130℃ for 4-6 h, 140-180℃ for 4-6 h, and 220-280℃ for 4-8 h.

[0015] Furthermore, the coating thickness of the polyamide-imide resin adhesive composition is 5-25 μm; the thickness of the polyimide film is 5-100 μm; and the copper foil is one of rolled copper foil and electrolytic copper foil, with a thickness of 12-75 μm.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. The adhesive composition used in this invention uses polyamide-imide resin as the matrix. On one hand, the polyamide-imide resin is composed of trimellitic anhydride and aromatic diisocyanate. The terminal hydroxyl groups and terminal anhydrides in this structure have active hydrogen, which can undergo crosslinking reactions with the epoxy groups on the epoxy resin, improving the adhesion between the polyamide-imide resin and the copper foil. On the other hand, the polyamide-imide resin has a similar chemical structure to the polyimide film. According to the principle of similar compatibility, the two have good compatibility and intermolecular forces, thereby improving the peel strength between the adhesive composition and the base film. Simultaneously, the polyamide-imide resin has good heat resistance and mechanical strength, increasing the glass transition temperature and ultimate heat resistance temperature of the flexible copper-clad laminate, and enhancing the mechanical strength of the flexible copper-clad laminate.

[0017] 2. This invention introduces inorganic fillers such as silica and wetting and leveling agents into the adhesive composition. The inorganic fillers not only adjust the coefficient of thermal expansion of the adhesive composition, preventing edge warping of the flexible copper-clad laminate, but also reduce raw material costs. The wetting and leveling agents promote uniform coating of the adhesive composition onto the base film, which helps to ensure uniform pressure distribution during lamination, improving the stability and yield of the flexible copper-clad laminate.

[0018] 3. Compared with the traditional two-layer adhesive-free substrate, the flexible copper clad laminate prepared by the present invention is a three-layer adhesive-based substrate. Its heat resistance is close to that of the traditional two-layer adhesive-free substrate. Moreover, it has low raw material cost, simple production process, high yield, and good adaptability. It can be widely used in new energy storage, consumer electronics, automotive electronics and aerospace fields. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of a single-sided copper-clad laminate as shown in this invention; Figure 2 This is a schematic diagram of the structure of a double-sided copper-clad laminate according to the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] The following are examples: trimellitic anhydride has a CAS number of 552-30-7; N,N-dimethylacetamide has a CAS number of 127-19-5; 4,4′-diphenylmethane diisocyanate has a CAS number of 101-68-8; 2,4-toluene diisocyanate has a CAS number of 584-84-9; cyclohexanone has a CAS number of 108-94-1; N,N,N',N'-tetracyclooxypropyl-4,4'-diaminodiphenylmethane has a CAS number of 28768-32-3; 1,5-naphthalene diisocyanate has a CAS number of 3173-72-6; N-methylpyrrolidone has a CAS number of 872-50-4; and 2,2-bis-(4-glycyloxyphenyl)propane has a CAS number of 1675-54-3.

[0022] Example 1: Flexible copper-clad laminate prepared from a polyamide-imide resin composition: S1: Under a nitrogen atmosphere, 192.12 g of trimellitic anhydride was added to 300 g of N,N-dimethylacetamide and stirred at 25 °C until dissolved. Then, 125.13 g of 4,4′-diphenylmethane diisocyanate, 73.14 g of 2,4-toluene diisocyanate and 110 g of cyclohexanone were added sequentially. The mixture was stirred at 80 °C for 6 h, at 120 °C for 6 h, and at 160 °C for 4 h. After filtration, polyamide-imide resin was obtained. S2: 16.5g N,N,N',N'-tetracyclooxypropyl-4,4'-diaminodiphenylmethane, 25.5g silica, 0.5g wetting and leveling agent BYK333 and 20g cyclohexanone were added to 200g polyamide-imide resin. The mixture was stirred and dispersed at 1100rpm / min for 6h at room temperature, allowed to stand for defoaming for 8h, and filtered to obtain the polyamide-imide resin composition. S3: The polyamide-imide resin composition is coated with a 15μm thick layer onto a 25μm polyimide film, pre-baked at 160℃ for 3min, and then pressed onto the rough surface of a 36μm electrolytic copper foil at 180℃ and 10MPa for 90s. After pressing, it is cured sequentially at 120℃ for 6h, 160℃ for 4h, and 280℃ for 6h to obtain a single-sided flexible copper-clad laminate. S4: The polyamide-imide resin composition is coated onto a single-sided flexible copper clad laminate with a thickness of 15 μm. The pre-baking, pressing, and curing processes are the same as in step S3 to obtain a double-sided flexible copper clad laminate.

[0023] Example 2: Flexible copper-clad laminate prepared from a polyamide-imide resin composition: S1: Under a nitrogen atmosphere, 192.12 g of trimellitic anhydride was added to 300 g of N-methylpyrrolidone and stirred at 25 °C until dissolved. Then, 125.13 g of 4,4′-diphenylmethane diisocyanate, 73.14 g of 2,4-toluene diisocyanate and 150 g of butanone were added sequentially. The mixture was stirred at 80 °C for 6 h, at 120 °C for 6 h, and at 160 °C for 4 h. After filtration, polyamide-imide resin was obtained. S2: 22.35g of dicyclopentadiene phenol epoxy resin, 30.55g of titanium dioxide, 0.6g of wetting and leveling agent Wet410 and 20g of toluene were added to 200g of polyamide-imide resin. The mixture was stirred and dispersed at 1100rpm / min for 6h at room temperature, allowed to stand for defoaming for 8h, and filtered to obtain the polyamide-imide resin composition. S3: The polyamide-imide resin composition is coated with a 25μm thick layer onto a 50μm polyimide film, pre-baked at 160℃ for 5min, and then pressed onto the rough surface of a 36μm electrolytic copper foil at 180℃ and 10MPa for 90s. After pressing, it is cured sequentially at 120℃ for 6h, 160℃ for 4h, and 280℃ for 6h to obtain a single-sided flexible copper-clad laminate. S4: The polyamide-imide resin composition is coated onto a single-sided flexible copper clad laminate with a thickness of 25 μm. The pre-baking, pressing, and curing processes are the same as in step S3 to obtain a double-sided flexible copper clad laminate.

[0024] Example 3: Flexible copper-clad laminate prepared from a polyamide-imide resin composition: S1: Under a nitrogen atmosphere, 192.12 g of trimellitic anhydride was added to 300 g of N-methylpyrrolidone and stirred at 25 °C until dissolved. Then, 125.13 g of 4,4′-diphenylmethane diisocyanate, 92.48 g of 1,5-naphthalene diisocyanate and 120 g of butanone were added sequentially. The mixture was stirred at 80 °C for 6 h, at 120 °C for 6 h, and at 160 °C for 4 h. After filtration, polyamide-imide resin was obtained. S2: 18.5g N,N,N',N'-tetracyclooxypropyl-4,4'-diaminodiphenylmethane, 25.5g silica, 0.4g wetting and leveling agent Wet410 and 20g cyclohexanone were added to 200g polyamide-imide resin. The mixture was stirred and dispersed at 1100rpm / min for 6h at room temperature, allowed to stand for defoaming for 8h, and filtered to obtain the polyamide-imide resin composition. S3: The polyamide-imide resin composition is coated with a 20μm thick layer onto a 50μm polyimide film, pre-baked at 160℃ for 4min, and then pressed onto the rough surface of a 36μm electrolytic copper foil at 180℃ and 10MPa for 90s. After pressing, it is cured sequentially at 120℃ for 6h, 160℃ for 4h, and 280℃ for 6h to obtain a single-sided flexible copper-clad laminate. S4: The polyamide-imide resin composition is coated onto a single-sided flexible copper clad laminate with a thickness of 20 μm. The pre-baking, pressing, and curing processes are the same as in step S3 to obtain a double-sided flexible copper clad laminate.

[0025] Example 4: Flexible copper-clad laminate prepared from a polyamide-imide resin composition: S1: Under a nitrogen atmosphere, 192.12 g of trimellitic anhydride was added to 300 g of N-methylpyrrolidone and stirred at 25 °C until dissolved. Then, 225.23 g of 4,4′-diphenylmethane diisocyanate and 140 g of butanone were added sequentially. The mixture was stirred at 80 °C for 6 h, at 120 °C for 6 h, and at 160 °C for 4 h. After filtration, polyamide-imide resin was obtained. S2: 20.5g N,N,N',N'-tetracyclooxypropyl-4,4'-diaminodiphenylmethane, 19.5g silica, 0.5g wetting and leveling agent Wet270 and 20g cyclohexanone were added to 200g polyamide-imide resin. The mixture was stirred and dispersed at 1100rpm / min for 6h at room temperature, allowed to stand for defoaming for 8h, and filtered to obtain the polyamide-imide resin composition. S3: The polyamide-imide resin composition is coated with a 15μm thick layer onto a 50μm polyimide film, pre-baked at 160℃ for 3min, and then pressed onto the rough surface of a 36μm electrolytic copper foil at 180℃ and 10MPa for 90s. After pressing, it is cured sequentially at 120℃ for 6h, 160℃ for 4h, and 280℃ for 6h to obtain a single-sided flexible copper-clad laminate. S4: The polyamide-imide resin composition is coated onto a single-sided flexible copper clad laminate with a thickness of 15 μm. The pre-baking, pressing, and curing processes are the same as in step S3 to obtain a double-sided flexible copper clad laminate.

[0026] Example 5: Flexible copper-clad laminate prepared from a polyamide-imide resin composition: S1: Under a nitrogen atmosphere, 192.12 g of trimellitic anhydride was added to 300 g of N-methylpyrrolidone and stirred at 25 °C until dissolved. Then, 125.13 g of 4,4′-diphenylmethane diisocyanate, 105.71 g of 3,3′-dimethyl-4,4′-biphenyl diisocyanate and 140 g of butanone were added sequentially. The mixture was stirred at 80 °C for 6 h, at 120 °C for 6 h, and at 160 °C for 4 h. After filtration, polyamide-imide resin was obtained. S2: 25.5g N,N,N',N'-tetracyclooxypropyl-4,4'-diaminodiphenylmethane, 28.5g silica, 0.5g wetting and leveling agent Wet270 and 25g cyclohexanone were added to 200g polyamide-imide resin. The mixture was stirred and dispersed at 1100rpm / min for 6h at room temperature, allowed to stand for defoaming for 8h, and filtered to obtain the polyamide-imide resin composition. S3: The polyamide-imide resin composition is coated onto a 25μm polyimide film with a thickness of 20μm, pre-baked at 160℃ for 4min, and then pressed onto the rough surface of a 36μm electrolytic copper foil at 180℃ and 10MPa for 90s. After pressing, it is cured sequentially at 120℃ for 6h, 160℃ for 4h, and 280℃ for 6h to obtain a single-sided flexible copper-clad laminate. S4: The polyamide-imide resin composition is coated onto a single-sided flexible copper clad laminate with a thickness of 20 μm. The pre-baking, pressing, and curing processes are the same as in step S3 to obtain a double-sided flexible copper clad laminate.

[0027] Example 6: Flexible copper-clad laminate prepared from a polyamide-imide resin composition: S1: Under a nitrogen atmosphere, 192.12 g of trimellitic anhydride was added to 300 g of N,N-dimethylacetamide and stirred at 25 °C until dissolved. Then, 125.13 g of 4,4′-diphenylmethane diisocyanate, 73.14 g of 2,4-toluene diisocyanate and 100 g of cyclohexanone were added sequentially. The mixture was stirred at 80 °C for 6 h, at 120 °C for 6 h, and at 160 °C for 4 h. After filtration, polyamide-imide resin was obtained. S2: Add 28.5g of 2,2-bis-(4-glycyloxyphenyl)propane, 20.5g of silica, 0.4g of wetting and leveling agent Wet270 and 20g of cyclohexanone to 200g of polyamide-imide resin, stir and disperse at 1100rpm / min for 6h at room temperature, let stand to defoam for 8h, filter to obtain polyamide-imide resin composition; S3: The polyamide-imide resin composition is coated with a 25μm thick layer onto a 50μm polyimide film, pre-baked at 160℃ for 5min, and then pressed onto the rough surface of a 36μm electrolytic copper foil at 180℃ and 10MPa for 90s. After pressing, it is cured sequentially at 120℃ for 6h, 160℃ for 4h, and 280℃ for 6h to obtain a single-sided flexible copper-clad laminate. S4: The polyamide-imide resin composition is coated onto a single-sided flexible copper clad laminate with a thickness of 25 μm. The pre-baking, pressing, and curing processes are the same as in step S3 to obtain a double-sided flexible copper clad laminate.

[0028] Example 7: Flexible copper-clad laminate prepared from a polyamide-imide resin composition: S1: Under a nitrogen atmosphere, 192.12 g of trimellitic anhydride was added to 300 g of N-methylpyrrolidone and stirred at 25 °C until dissolved. Then, 230.28 g of 4,4′-diphenylmethane diisocyanate and 120 g of butanone were added sequentially. The mixture was stirred at 80 °C for 6 h, at 120 °C for 6 h, and at 160 °C for 4 h. After filtration, polyamide-imide resin was obtained. S2: 15.8g N,N,N',N'-tetracyclooxypropyl-4,4'-diaminodiphenylmethane, 20.1g silica, 0.5g wetting and leveling agent Wet270 and 20g cyclohexanone were added to 200g polyamide-imide resin. The mixture was stirred and dispersed at 1100rpm / min for 6h at room temperature, allowed to stand for defoaming for 8h, and filtered to obtain the polyamide-imide resin composition. S3: The polyamide-imide resin composition is coated with a 10μm thick layer onto a 25μm polyimide film, pre-baked at 160℃ for 2min, and then pressed onto the rough surface of a 36μm electrolytic copper foil at 180℃ and 10MPa for 90s. After pressing, it is cured sequentially at 120℃ for 6h, 160℃ for 4h, and 280℃ for 6h to obtain a single-sided flexible copper-clad laminate. S4: The polyamide-imide resin composition is coated onto a single-sided flexible copper clad laminate with a thickness of 10 μm. The pre-baking, pressing, and curing processes are the same as in step S3 to obtain a double-sided flexible copper clad laminate.

[0029] Comparative Example 1: Flexible copper-clad laminate prepared from a polyamide-imide resin composition: S1: Under a nitrogen atmosphere, 192.12 g of trimellitic anhydride was added to 300 g of N-methylpyrrolidone and stirred at 25 °C until dissolved. Then, 250.3 g of 4,4′-diphenylmethane diisocyanate and 450 g of cyclohexanone were added sequentially. The mixture was stirred at 80 °C for 6 h, at 120 °C for 6 h, and at 160 °C for 4 h. After filtration, polyamide-imide resin was obtained. S2: 20.5g N,N,N',N'-tetracyclooxypropyl-4,4'-diaminodiphenylmethane, 25.2g silica, 0.4g wetting and leveling agent Wet270 and 50g cyclohexanone were added to 200g polyamide-imide resin. The mixture was stirred and dispersed at 1200rpm / min for 6h at room temperature, allowed to stand for defoaming for 8h, and filtered to obtain the polyamide-imide resin composition. S3: The polyamide-imide resin composition is coated with a 15μm thick adhesive onto a 25μm polyimide film, pre-baked at 160℃ for 4min, and then pressed onto the rough surface of an 18μm electrolytic copper foil at 180℃ and 10MPa for 90s. After pressing, it is cured sequentially at 120℃ for 6h, 160℃ for 4h, and 280℃ for 6h to obtain a single-sided flexible copper-clad laminate. S4: The polyamide-imide resin composition is coated onto a single-sided flexible copper clad laminate with a thickness of 15 μm. The pre-baking, pressing, and curing processes are the same as in step S3 to obtain a double-sided flexible copper clad laminate.

[0030] Comparative Example 2: Flexible copper-clad laminate prepared from a polyamide-imide resin composition: S1: Under a nitrogen atmosphere, 192.12 g trimellitic anhydride was added to 300 g N,N-dimethylacetamide and stirred at 25 °C until dissolved. Then, 156.4 g hexamethylene diisocyanate and 100 g cyclohexanone were added sequentially, and the mixture was stirred at 80 °C for 6 h, at 120 °C for 6 h, and at 160 °C for 4 h. The mixture was then filtered to obtain the polyamide-imide resin. S2: 16g of N,N,N',N'-tetracyclooxypropyl-4,4'-diaminodiphenylmethane, 20.9g of silica, 0.5g of wetting and leveling agent Wet270 and 20g of cyclohexanone were added to 200g of polyamide-imide resin. The mixture was stirred and dispersed at 1100rpm / min for 6h at room temperature, allowed to stand for defoaming for 8h, and filtered to obtain the polyamide-imide resin composition. S3: The polyamide-imide resin composition is coated with a 15μm thick layer onto a 25μm polyimide film, pre-baked at 160℃ for 2min, and then pressed onto the rough surface of an 18μm electrolytic copper foil at 180℃ and 10MPa for 90s. After pressing, it is cured sequentially at 120℃ for 6h, 160℃ for 4h, and 280℃ for 6h to obtain a single-sided flexible copper-clad laminate. S4: The polyamide-imide resin composition is coated onto a single-sided flexible copper clad laminate with a thickness of 15 μm. The pre-baking, pressing, and curing processes are the same as in step S3 to obtain a double-sided flexible copper clad laminate.

[0031] Table 1. Raw material ratios and flexible copper clad laminate specifications in the examples and comparative examples. Testing and Experiment Glass transition temperature detection: The polyamide-imide resin compositions prepared in the above examples and comparative examples were coated onto a glass plate with a thickness of 25 μm. The films were then baked at 200°C for 2 hours, then at 280°C for 2 hours to cure. After demolding, the films were boiled in water at 70°C for 30 minutes and dried at 160°C for 30 minutes to obtain a 20 cm × 2.5 cm polyamide-imide resin composition film. The polyamide-imide resin composition film was tested using a differential scanning calorimeter under a nitrogen atmosphere at a heating rate of 10°C / min.

[0032] Tensile strength, tensile modulus, and elongation at break testing: The polyamide-imide resin compositions prepared in the above examples and comparative examples were coated onto a glass plate with a thickness of 25 μm. The films were then baked at 200℃ for 2 hours, then at 280℃ for 2 hours to cure. After curing, the films were demolded by boiling in water at 70℃ for 30 minutes and then dried at 160℃ for 30 minutes to produce 20 cm × 2.5 cm polyamide-imide resin composition films. The samples were tested using a universal testing machine with a gauge length of 100 mm and a testing rate of 5 mm / min.

[0033] Peel strength test: The flexible copper-clad laminates prepared in the above examples and comparative examples were cut into 10cm × 1cm samples. The samples were tested using a peel tester at a test rate of 50mm / min.

[0034] Extreme heat resistance test: Take the flexible copper-clad laminates prepared in the above examples and comparative examples, cut them into 50mm×50mm samples. Bake the samples at 135℃ for 1 hour, then immerse them in a 340℃ solder bath for 10 seconds. Repeat this process 3 times and observe whether there are any abnormalities in the appearance of the samples.

[0035] Peel strength test after thermal aging: The flexible copper-clad laminates prepared in the above examples and comparative examples were cut into 10cm×1cm samples. The samples were baked at 200℃ for 240h, and then the samples after thermal aging were tested with a peel tester at a test rate of 50mm / min.

[0036] The experimental results are shown in Table 2 below.

[0037] Table 2 Performance test data of polyamide-imide resin composition and flexible copper clad laminate Conclusion: By adjusting the component ratios of the polyamide-imide resin and its binder composition, not only can the flexible copper clad laminate exhibit good heat resistance, but its mechanical properties can also be improved.

[0038] In Comparative Example 1, a polyamide-imide resin was synthesized using trimellitic anhydride and aromatic diisocyanate in a 1:1 molar ratio. On one hand, the resin product lacks carboxyl and anhydride groups at the ends, preventing the polyamide-imide resin from forming chemical crosslinks with the epoxy resin. On the other hand, the polyamide-imide resin has a large molecular weight, resulting in poor flowability of the resin composition and difficulty in fully anchoring it to the rough surface of the copper foil during lamination. For these reasons, the peel strength and thermal aging properties of the flexible copper-clad laminate prepared in this comparative example are significantly lower than those in Examples 1-7.

[0039] In Comparative Example 2, aliphatic diisocyanate was used instead of aromatic diisocyanate to synthesize polyamide-imide resin. The flexible aliphatic segments on it are easily rotated, which not only reduces the mechanical strength and heat resistance of the adhesive composition, but also reduces the adhesion between the adhesive composition and the matrix. At the same time, the raw material cost of aliphatic diisocyanate is high, increasing the production cost of flexible copper-clad laminate.

[0040] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A polyamide-imide resin, characterized in that: The structural formula (A) of the polyamide-imide resin is: (A)； Where n is an integer between 4 and 50.

2. The polyamide-imide resin according to claim 1, characterized in that: The Ar is a compound containing a benzene ring group; the compound is one or more selected from 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 4,4'-dimethyldiphenylmethane, 2,4'-dimethyldiphenylmethane, 2,3'-dimethyldiphenylmethane, 1,5-dimethylnaphthalene, p-xylene, p-diethylbenzene, 1,2-diethylbenzene, 1,3-diethylbenzene, 1,3-di-tert-butylbenzene, 3,3',4,4'-tetramethylbiphenyl, and 3',4,4'-dimethyldiphenylmethane.

3. The polyamide-imide resin according to claim 1, characterized in that: The preparation method of the polyamide-imide resin is as follows: Under a nitrogen atmosphere, trimellitic anhydride is added to a solvent and stirred at room temperature until dissolved. Aromatic diisocyanate is added and stirred until dissolved. The solvent is replenished, and the reaction is carried out at 70-90℃ for 4-6 hours, 100-120℃ for 4-6 hours, and 150-170℃ for 2-4 hours. The mixture is then filtered to obtain the polyamide-imide resin. In the preparation of polyamide-imide resin, the molar ratio of trimellitic anhydride to aromatic diisocyanate is 1:(0.8-0.98).

4. The polyamide-imide resin according to claim 3, characterized in that: The structural formula (B) of the aromatic diisocyanate is: (B)； Wherein, Ar is a compound containing a benzene ring group; the compound is one or more selected from 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 4,4'-dimethyldiphenylmethane, 2,4'-dimethyldiphenylmethane, 2,3'-dimethyldiphenylmethane, 1,5-dimethylnaphthalene, p-xylene, p-diethylbenzene, 1,2-diethylbenzene, 1,3-diethylbenzene, 1,3-di-tert-butylbenzene, 3,3',4,4'-tetramethylbiphenyl, and 3',4,4'-dimethyldiphenylmethane; The solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, butanone, cyclohexanone, and toluene.

5. A polyamide-imide resin composition, characterized in that: The polyamide-imide resin according to any one of claims 1-4 is mixed with epoxy resin, inorganic filler, wetting and leveling agent and solvent to obtain a polyamide-imide resin composition.

6. The polyamide-imide resin composition according to claim 5, characterized in that: In the preparation of the polyamide-imide resin composition, the mass ratio of epoxy resin, inorganic filler, wetting and leveling agent, solvent and polyamide-imide resin is (5-50):(5-40):(0.05-0.5):(10-50):

100.

7. The polyamide-imide resin composition according to claim 5, characterized in that: The epoxy resin is one or more of N,N',N,N'-tetracyclooxypropyl-4,4'-diaminodiphenylmethane, N,N',N,N'-tetra(epoxyethylenemethyl)-1,3-phenylenediamine, 2,2-bis-(4-glycyloxyphenyl)propane, and dicyclopentadiene phenol epoxy resin; The inorganic filler is one or more of silicon dioxide, aluminum oxide, titanium dioxide, zirconium oxide, and barium sulfate; The wetting and leveling agent is one or more of BYK333, BYK310, BYK306, Wet410, Wet270 and Evonik 5830.

8. A flexible copper-clad laminate prepared from a polyamide-imide resin composition, characterized in that: The preparation method includes the following steps: coating the polyamide-imide resin composition of claim 5 onto a polyimide film, pre-baking, high-temperature pressing onto the rough surface of an electrolytic copper foil, programmed temperature rise for curing, and repeating the above steps on the other side to obtain a flexible copper-clad laminate.

9. The flexible copper-clad laminate prepared according to the polyamide-imide resin composition of claim 8, characterized in that: The pre-baking temperature is 140-180℃, and the time is 2-5 min; the high-temperature pressing temperature is 150-180℃, the pressing pressure is 5-20 MPa, and the pressing time is 60-180 s; the programmed temperature rise curing conditions are 100-130℃ for 4-6 h, 140-180℃ for 4-6 h, and 220-280℃ for 4-8 h.

10. The flexible copper-clad laminate prepared according to the polyamide-imide resin composition of claim 8, characterized in that: The coating thickness of the polyamide-imide resin adhesive composition is 5-25 μm; the thickness of the polyimide film is 5-100 μm; the copper foil is one of rolled copper foil and electrolytic copper foil, and the copper foil thickness is 12-75 μm.

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