Polyimide resin as well as preparation method and application thereof

Abstract

The invention provides polyimide resin as well as a preparation method and application thereof. The polyimide resin comprises a polyimide component A and a polyimide component B; wherein the polyimide component A is polyimide powder of which the imidization degree is greater than or equal to 80%, and the polyimide component B is polyimide powder of which the crosslinking degree is 20-80%; the total weight of the polyimide resin is 100 wt%, the polyimide component A accounts for 85-99 wt%, and the polyimide component B accounts for 1-15 wt%. Compared with the traditional PMR type polyimide resin, the polyimide resin provided by the technical scheme of the invention has the advantages that under the same process conditions, a molded part is uniform and free of bubbles and has excellent heat resistance and melt viscosity, the molding difficulty is reduced, and a better technical effect is achieved.

Description

Technical Field

[0001] The present invention relates to the field of thermosetting resins, and more particularly, to a polyimide resin, a preparation method thereof, and an application thereof. Background Art

[0002] Thermosetting polyimide resins undergo thermal cross-linking and have ultra-high heat resistance temperatures, high specific strength, specific modulus, and excellent thermal-oxidative stability. As matrix materials, when made into composites with carbon fibers or glass fibers, etc., they have outstanding comprehensive properties and can be used as load-bearing components in high-temperature environments, and have extensive applications in the fields of aerospace, electronics, and electrical appliances. Thermosetting polyimides cross-link through a capping agent at high temperatures. The main capping agents include maleic anhydride, nadic anhydride, and phenylacetylene phthalic anhydride, etc. The most representative PMR-type polyimide resin has obvious advantages. Its characteristics are the use of low molecular weight and low viscosity monomers, and the use of low-boiling alcohols as solvents. Therefore, it has broad application prospects and has been successfully applied in the cold-end parts of high-performance aerospace engines, such as the outer casing, blades, vector nozzle adjustment vanes, missile radomes, and missile bodies, etc., which has a significant effect on reducing the structural weight and increasing the thrust-to-weight ratio of the engine. However, due to the relatively high complete imidization temperature of polyimide powder, the commonly used drying temperature of molding powder cannot achieve 100% imidization, resulting in the occurrence of polycondensation reactions during the molding process, releasing water and alcohol gases, and there are easily pores and other defects inside the molded parts, affecting the mechanical strength and reliability of the final product.

[0003] In order to improve the processing performance of polyimide resins, US Patent US7015304B1 discloses a phenylacetylene group-terminated polyimide resin, which has a very low melt viscosity, and the cross-linking temperature is raised to above 370 °C, providing a sufficient temperature range for the resin to release the gases generated during the molding process during the low melt viscosity period, reducing the bubble defects in the product, and is used to prepare carbon fiber-reinforced composites resistant to 288 - 343 °C. However, the temperature of the thermal curing cross-linking reaction of this resin is too high, with high energy consumption and high molding difficulty. For example, a thermosetting polyimide resin and a preparation method thereof disclosed in Patent CN101654518A, after the molding powder removes the solvent and imidizes at a temperature of 230 °C or below, it is immediately subjected to compression molding. Its imidization degree is low, and gas will be further released during the compression molding process, increasing the molding difficulty and possibly affecting the performance of the final product.

[0004] Therefore, it is necessary to study a polyimide resin that can reduce the release of gases and small molecule substances during molding, thereby generating bubbles inside the product and causing product defects, and ensuring the mechanical properties of the product. Summary of the Invention

[0005] In order to solve the technical problems existing in the prior art, the present invention provides a polyimide resin, a preparation method thereof, and an application thereof.

[0006] In the prior art, during the molding process of polyimide resin, due to the release of water and alcohol gases, defects such as bubbles are likely to occur, affecting the mechanical properties and reliability of the final product.

[0007] Through in-depth research, the inventor of the present invention found that by partially cross-linking the polyimide resin and then performing molding, the generation of defects such as bubbles can be surprisingly well overcome. Compared with the traditional PMR-type polyimide resin, the polyimide resin provided by the technical solution of the present invention has a uniform molded part without bubbles and excellent heat resistance and melt viscosity under the same process conditions, reducing the molding difficulty and achieving good technical effects.

[0008] One object of the present invention is to provide a polyimide resin, comprising polyimide component A and polyimide component B; wherein polyimide component A is a polyimide powder with an imidization degree of ≥80%, and polyimide component B is a polyimide powder with a cross-linking degree of 20-80%;

[0009] Based on the total weight of the polyimide resin being 100 wt%, polyimide component A accounts for 85-99 wt%, and polyimide component B accounts for 1-15 wt%.

[0010] In a preferred embodiment of the present invention,

[0011] Based on the total weight of the polyimide resin being 100 wt%, polyimide component A accounts for 90-98 wt%, and polyimide component B accounts for 2-10 wt%.

[0012] In a preferred embodiment of the present invention,

[0013] The polyimide component A is obtained by a preparation method comprising the following steps:

[0014] (1) Mix a capping agent A, an aromatic tetracarboxylic dianhydride A, and a fatty alcohol A to carry out an esterification reaction A to obtain a solution of an aromatic diacid diester A and a capping agent monoacid monoester A;

[0015] (2) Dissolve an aromatic diamine A in the solution obtained in step (1) to obtain a resin solution A;

[0016] (3) Remove the excessive fatty alcohol A from the resin solution A obtained in step (2) to obtain a resin powder A;

[0017] (4) Imidize the resin powder A obtained in step (3) to obtain the polyimide resin component A.

[0018] In a preferred embodiment of the present invention,

[0019] In step (1),

[0020] The capping agent A is at least one of nadic anhydride (norbornene dicarboxylic anhydride, NA), 4-phenylethynylphthalic anhydride (PEPA), 4-ethynylphthalic anhydride (EPA), and methyl ethynylphthalic anhydride (MEPA);

[0021] The aromatic tetracarboxylic dianhydride A is at least one of the structures shown in formula (1):

[0022]

[0023] Among them, Ar1 is a tetravalent aromatic residue containing at least one benzene ring; the aromatic tetracarboxylic dianhydride A is preferably at least one of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), hexafluorodiacid anhydride (6FDA), 4,4'-biphenyl ether dianhydride (ODPA), pyromellitic dianhydride (PMDA), diphenyl sulfide dianhydride (TDPA), and 3,3,4,4-diphenylsulfone tetracarboxylic dianhydride;

[0024] The fatty alcohol A is at least one of methanol, ethanol, propanol, isopropanol, n-butanol, isobutanol, n-pentanol, isopentanol, and tert-butanol;

[0025] The temperature of the esterification reaction A is 60-130°C, preferably 60-90°C;

[0026] The time of the esterification reaction A is 1-10 h, preferably 1-4 h;

[0027] In step (2),

[0028] The aromatic diamine A is at least one of the structures shown in formula (2):

[0029] H2N-Ar2-NH2 Formula (2)

[0030] Among them, Ar2 is a divalent aromatic residue containing at least one benzene ring; the aromatic diamine A is preferably at least one of 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), p-phenylenediamine (PDA), diphenylmethanediamine (MDA), 4,4'-diaminodiphenyl ether, 1,3-bis(4'-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, and 3,4'-diaminodiphenyl ether (3,4'-ODA);

[0031] The temperature for adding diamine can be the usual temperature in the prior art, preferably 20-60°C;

[0032] In step (3),

[0033] The method for removing fatty alcohol can adopt the general methods of the prior art, such as rotary evaporation followed by drying. The drying can be carried out by vacuum drying, with a vacuum degree of 0 to 101 Kpa, and the drying temperature is preferably 180 to 220 °C;

[0034] In step (4),

[0035] The imidization temperature is 220 to 300 °C, preferably 220 to 280 °C;

[0036] The imidization time is 0.1 to 4 h, preferably 0.5 to 1 h;

[0037] The imidization degree ≥ 80%.

[0038] In a preferred embodiment of the present invention,

[0039] The molar ratio of aromatic tetracarboxylic dianhydride A to aromatic diamine A is (n + 1):n, where 1 ≤ n ≤ 100, preferably 1 < n ≤ 20;

[0040] The ratio of the difference in the molar amounts of aromatic diamine A and aromatic tetracarboxylic dianhydride A to the molar amount of the end-capping agent A is 1:(1 to 2); when using a pure end-capping agent for end-capping, the above molar ratio is 1:2;

[0041] The ratio of the sum of the masses of end-capping agent A, aromatic tetracarboxylic dianhydride A, and aromatic diamine A to the mass of fatty alcohol A is 1:(0.6 to 3), preferably 1:(0.6 to 1.6).

[0042] In a preferred embodiment of the present invention,

[0043] The polyimide component B is obtained by a preparation method including the following steps:

[0044] (i) Mix end-capping agent B, aromatic tetracarboxylic dianhydride B with fatty alcohol B to carry out esterification reaction B to obtain a solution of aromatic diacid diester B and end-capping agent monoacid monoester B;

[0045] (ii) Dissolve aromatic diamine B in the solution obtained in step (1) to obtain resin solution B;

[0046] (iii) Remove fatty alcohol B from the resin solution B obtained in step (2) to obtain resin powder B;

[0047] (iv) Carry out crosslinking reaction on the obtained resin powder B to obtain the polyimide resin component B.

[0048] In a preferred embodiment of the present invention,

[0049] In step (i),

[0050] The capping agent B is at least one of dicyclic anhydride (norbornene dicarboxylic anhydride, NA), 4-phenylethynyl phthalic anhydride (PEPA), 4-ethynyl phthalic anhydride (EPA), and methyl ethynyl phthalic anhydride (MEPA);

[0051] The aromatic tetracarboxylic dianhydride B is at least one of the structures shown in formula (1):

[0052]

[0053] Wherein, Ar1 is a tetravalent aromatic residue containing at least one benzene ring; the aromatic tetracarboxylic dianhydride B is preferably at least one of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), hexafluorodiacid anhydride (6FDA), 4,4'-biphenyl ether dianhydride (ODPA), pyromellitic dianhydride (PMDA), diphenyl sulfide dianhydride (TDPA), and 3,3,4,4-diphenylsulfone tetracarboxylic dianhydride;

[0054] The fatty alcohol B is at least one of methanol, ethanol, propanol, isopropanol, n-butanol, isobutanol, n-pentanol, isopentanol, and tert-butanol;

[0055] The temperature of the esterification reaction B is 60-130°C, preferably 60-90°C;

[0056] The time of the esterification reaction B is 1-10 h, preferably 1-4 h;

[0057] In step (ii),

[0058] The aromatic diamine B is at least one of the structures shown in formula (2):

[0059] H2N-Ar2-NH2 Formula (2)

[0060] Wherein, Ar2 is a divalent aromatic residue containing at least one carbon six-membered ring; the aromatic diamine B is preferably at least one of 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), p-phenylenediamine (PDA), diphenylmethanediamine (MDA), 4,4'-diaminodiphenyl ether, 1,3-bis(4'-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, and 3,4'-diaminodiphenyl ether (3,4'-ODA);

[0061] The temperature for adding diamine can be the usual temperature in the prior art, preferably 20-60°C;

[0062] In step (iii),

[0063] The method for removing fatty alcohol can adopt the general methods of the prior art, such as rotary evaporation followed by drying. The drying can be carried out by vacuum drying, with a vacuum degree of 0 - 101 Kpa, and the drying temperature is preferably 180 - 220 °C;

[0064] In step (ⅳ),

[0065] The temperature of the crosslinking reaction is 310 - 400 °C, preferably 320 - 390 °C;

[0066] The time of the crosslinking reaction is 1 - 120 min, preferably 5 - 60 min;

[0067] The degree of crosslinking is 20 - 80%.

[0068] In a preferred embodiment of the present invention,

[0069] The molar ratio of aromatic tetracarboxylic dianhydride B to aromatic diamine B is (n + 1) : n, where 1 ≤ n ≤ 100, preferably 1 < n ≤ 20;

[0070] The ratio of the difference in the molar amounts of aromatic diamine B and aromatic tetracarboxylic dianhydride B to the molar amount of capping agent B is 1 : (1 - 2); when using a pure capping agent for capping, the above molar ratio is 1 : 2;

[0071] The ratio of the sum of the masses of capping agent B, aromatic tetracarboxylic dianhydride B and aromatic diamine B to the mass of fatty alcohol B is 1 : (0.6 - 3), preferably 1 : (0.6 - 1.6).

[0072] The second object of the present invention is to provide a method for preparing a polyimide resin, including:

[0073] Preparing polyimide component A and polyimide component B respectively, and then mixing them evenly according to the said mass percentage to obtain the polyimide resin.

[0074] The third object of the present invention is to provide an application of the polyimide resin in a composite material.

[0075] Compared with the prior art, the beneficial effects of the present invention are:

[0076] In the prior art, polyamic acid is generally imidized and then subjected to molding processing and curing crosslinking. Since 100% imidization cannot be achieved, polycondensation reactions often occur, releasing water and alcohol gases, and it is easy to produce defects such as bubbles, which affect the mechanical properties and reliability of the final product.

[0077] The present invention combines partially crosslinked polyimide and imidized polyimide. The two components match and cooperate with each other, featuring low melt viscosity, low gas release during the molding process, reducing the possibility of bubbles in the final product, thus achieving a high product yield, stable performance, and excellent heat resistance. Compared with traditional PMR-type polyimide resins, the polyimide resin provided by the technical solution of the present invention has uniform and bubble-free molded parts, excellent heat resistance and melt viscosity under the same process conditions, reducing the molding difficulty and achieving good technical effects. Detailed Embodiments

[0078] The present invention will be specifically described below in conjunction with specific embodiments. It is necessary to point out here that the following embodiments are only for further illustration of the present invention and cannot be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention still fall within the protection scope of the present invention.

[0079] The raw materials used in the embodiments are all conventional commercially available raw materials.

[0080] The testing equipment and testing conditions used in the present invention are as follows:

[0081] Glass transition temperature: The Q800 of TA Instruments in the United States is used for DMA testing. Under nitrogen conditions, the temperature is raised at a rate of 10 °C / min to 500 °C, and the peak temperature of the change curve of the loss tangent value of the sample is the glass transition temperature of the product.

[0082] For the internal defects of the molded parts, a non-destructive testing method is used. Using an ultrasonic flaw detector (plastic product type), the surface of the sample is contacted to observe the reflected wave signal. If the reflected bottom wave is clear and stable, it means there are no obvious defects; if there are abnormalities such as a sharp increase in the reflected wave signal, it indicates that there are bubble or crack defects on the surface of the sample.

[0083]

Example 1

[0084] 3,3',4,4'-Benzophenone tetracarboxylic dianhydride (hereinafter referred to as BTDA) powder and nadic anhydride (hereinafter referred to as NA) were added to ethanol, and esterification was carried out at 80 °C for 2.5 h to obtain diethyl benzophenone dicarboxylate (hereinafter referred to as BTDE) and monoethyl 5-norbornene-2,3-dicarboxylate (hereinafter referred to as NE) (the solution of the diacid diester of the dianhydride and the monoacid monoester of the end-capping agent). Then, 2,2-bis[4-(4-aminophenoxy)phenyl]propane (hereinafter referred to as BAPP) powder was added to the solution. The molar ratio of BAPP to BTDA was 1.38, and the difference in the molar amounts of BAPP and BTDA: the molar amount of NA was 1:2. The mass ratio of the sum of the masses of NA, BTDA, and BAPP to the mass of ethanol was 1:1. Stir well at 45 °C until BAPP was completely dissolved to obtain a polyimide resin solution. After most of the ethanol solvent in the solution was removed by rotary evaporation, it was placed in a vacuum oven and gradually heated to 200 °C to obtain a preform molding powder.

[0085] The obtained preform molding powder was imidized at 220 °C for 1 h to obtain polyimide component A, and the imidization degree was 80%.

[0086] The obtained preform molding powder was subjected to a cross-linking reaction at 320 °C for 10 min to obtain polyimide component B, and the cross-linking degree was 20%.

[0087] Component A and component B were mixed, and component B accounted for 10 wt% of the total amount of the mixed molding powder to obtain a polyimide resin.

[0088] The obtained polyimide resin was placed in a mold and molded by compression molding to obtain a polyimide molded part. The glass transition temperature of the obtained molded part was 330 °C. Ten samples were detected by an ultrasonic flaw detector, and no ultrasonic abnormal signals were found, indicating that the interior of the molded part was uniform and there were no bubble defects.

[0089]

Example 2

[0090] Hexafluorodiacid dianhydride (hereinafter referred to as 6FDA) powder and NA were added to methanol, and esterification was carried out at 60 °C for 1 h to obtain a solution of the diacid diester of the dianhydride and the monoacid monoester of the end-capping agent. Then, p-phenylenediamine (hereinafter referred to as PDA) powder was added to the solution. The molar ratio of diamine PDA to dianhydride 6FDA was 1.1, and the difference in the molar amounts of diamine PDA and dianhydride 6FDA: the molar amount of the end-capping agent NA was 1:1. The mass ratio of the sum of the masses of NA, 6FDA, and PDA to the mass of methanol was 1:1.5. Stir well at 40 °C until PDA was completely dissolved to obtain a polyimide resin solution. After most of the methanol solvent in the solution was removed by rotary evaporation, it was placed in a vacuum oven and gradually heated to 200 °C to obtain a preform molding powder.

[0091] The obtained preform molding powder was imidized at 280 °C for 0.5 h to obtain polyimide component A, and the imidization degree was 95%.

[0092] The obtained preformed molding powder was subjected to a cross-linking reaction at 330 °C for 30 min to obtain polyimide component B, with a cross-linking degree of 50%.

[0093] Component A and component B were mixed, with component B accounting for 2 wt% of the total amount of the mixed molding powder, to obtain a polyimide resin.

[0094] The obtained polyimide resin was put into a mold and molded by compression to obtain a polyimide molded part. The glass transition temperature of the obtained molded part was 380 °C. Ten samples were detected by an ultrasonic flaw detector, and no abnormal ultrasonic signals were found, indicating that the interior of the parts was uniform and there were no bubble defects.

[0095]

Example 3

[0096] Powder of diphenyl sulfide dianhydride (hereinafter referred to as TDPA) and 4-ethynylphthalic anhydride (hereinafter referred to as EPA) were added to ethanol, and esterification was carried out at 85 °C for 2.5 h to obtain a solution of diacid diester of dianhydride and monoacid monoester of the end-capping agent. Powder of PDA and BAPP were added to the solution. The molar ratio of PDA to BAPP was 1:1, where the molar ratio of diamine to dianhydride was 1.9, and the molar quantity difference between diamine and dianhydride: the molar quantity of the end-capping agent was 1:1.5. The mass ratio of the sum of the masses of TDPA, EPA, PDA, and BAPP to the mass of ethanol was 1:1. Stir thoroughly at 50 °C until the diamine was completely dissolved to obtain a polyimide resin solution. After most of the ethanol solvent in the solution was removed by rotary evaporation, it was put into a vacuum oven and gradually heated to 200 °C to obtain a preformed molding powder.

[0097] The obtained preformed molding powder was imidized at 250 °C for 45 min to obtain polyimide component A, with an imidization degree of 90%.

[0098] The obtained preformed molding powder was subjected to a cross-linking reaction at 340 °C for 60 min to obtain polyimide component B, with a cross-linking degree of 80%.

[0099] Component A and component B were mixed, with component B accounting for 6 wt% of the total amount of the mixed molding powder, to obtain a polyimide resin.

[0100] The obtained polyimide resin was put into a mold and molded by compression to obtain a polyimide molded part. The glass transition temperature of the obtained molded part was 362 °C. Ten samples were detected by an ultrasonic flaw detector, and no abnormal ultrasonic signals were found, indicating that the interior of the parts was uniform and there were no bubble defects.

[0101]

Example 4

[0102] BTDA powder and 4-phenylethynylphthalic anhydride (hereinafter referred to as PEPA) were added to ethanol, and esterification was carried out at 80 °C for 4 h to obtain a solution of diacid diester of dianhydride and monoacid monoester of capping agent. MDA powder (hereinafter referred to as MDA) was added to the solution, where the molar ratio of diamine to dianhydride was 1.05, and the difference in the molar amounts of diamine and dianhydride: the molar amount of capping agent was 1:2. The mass ratio of the sum of the masses of PEPA, BTDA, and MDA to the mass of methanol was 1:0.7. Stir well at 40 °C until the diamine was completely dissolved to obtain a polyimide resin solution. After most of the ethanol solvent in the solution was removed by rotary evaporation, it was placed in a vacuum oven and gradually heated to 200 °C to obtain preformed molding powder.

[0103] The obtained preformed molding powder was imidized at 280 °C for 60 min to obtain polyimide component A, and the imidization degree was 98%.

[0104] The obtained preformed molding powder was subjected to a cross-linking reaction at 390 °C for 5 min to obtain polyimide component B, and the cross-linking degree was 30%.

[0105] Component A and component B were mixed, where component B accounted for 4 wt% of the total amount of the mixed molding powder to obtain a polyimide resin.

[0106] The obtained polyimide resin was put into a mold and molded by compression to obtain a polyimide molded part. The glass transition temperature of the obtained molded part was 345 °C. Ten samples were detected by an ultrasonic flaw detector, and no ultrasonic abnormal signals were found, indicating that the interior of the parts was uniform and there were no bubble defects.

[0107]

Example 5

[0108] BTDA and pyromellitic dianhydride (hereinafter referred to as PMDA) powder (the molar ratio of BTDA to PMDA was 2:1) and NA were added to ethanol, and esterification was carried out at 80 °C for 2.5 h to obtain a solution of diacid diester of dianhydride and monoacid monoester of capping agent. BAPP powder was added to the solution, where the molar ratio of diamine to dianhydride was 1.34, and the difference in the molar amounts of diamine and dianhydride: the molar amount of capping agent was 1:1.8. The mass ratio of the sum of the masses of BTDA, PMDA, and BAPP to the mass of methanol was 1:1. Stir well at 40 °C until the diamine was completely dissolved to obtain a polyimide resin solution. After most of the ethanol solvent in the solution was removed by rotary evaporation, it was placed in a vacuum oven and gradually heated to 200 °C to obtain preformed molding powder.

[0109] The obtained preformed molding powder was imidized at 240 °C for 35 min to obtain polyimide component A, and the imidization degree was 85%.

[0110] The obtained preformed molding powder was subjected to a cross-linking reaction at 350 °C for 10 min to obtain polyimide component B, and the cross-linking degree was 75%.

[0111] Mix component A and component B, where component B accounts for 8 wt% of the total amount of the mixed molding powder, to obtain a polyimide resin.

[0112] Put the obtained polyimide resin into a mold and perform compression molding to obtain a polyimide molded part. The glass transition temperature of the obtained molded part is 358 °C. 10 samples are detected by an ultrasonic flaw detector, and there are no abnormal ultrasonic signals, indicating that the interior of the part is uniform and there are no bubble defects.

[0113]

Example 6

[0114] Add 4,4'-oxydiphthalic anhydride (hereinafter referred to as ODPA) powder and NA to ethanol, and esterify at 80 °C for 2.5 h to obtain a solution of the diacid diester of the dianhydride and the monoacid monoester of the end-capping agent. Add 3,4'-oxydianiline (hereinafter referred to as 3,4'-ODA) powder to the solution, where the molar ratio of diamine to dianhydride is 1.07, and the difference in the molar amounts of diamine and dianhydride: the molar amount of the end-capping agent is 1:1.2. The mass ratio of the sum of the masses of ODPA, NA, and 3,4'-ODA to the mass of methanol is 1:1. Stir well at 40 °C until the diamine is completely dissolved to obtain a polyimide resin solution. After rotary evaporation to remove most of the ethanol solvent in the solution, put it into a vacuum oven and gradually heat up to 200 °C to obtain a preformed molding powder.

[0115] Imidize the obtained preformed molding powder at 260 °C for 40 min to obtain polyimide component A, and the imidization degree is 90%.

[0116] Carry out a cross-linking reaction on the obtained preformed molding powder at 320 °C for 20 min to obtain polyimide component B, and the cross-linking degree is 40%.

[0117] Mix component A and component B, where component B accounts for 5 wt% of the total amount of the mixed molding powder, to obtain a polyimide resin.

[0118] Put the obtained polyimide resin into a mold and perform compression molding to obtain a polyimide molded part. The glass transition temperature of the obtained molded part is 341 °C. 10 samples are detected by an ultrasonic flaw detector, and there are no abnormal ultrasonic signals, indicating that the interior of the part is uniform and there are no bubble defects.

[0119]

Comparative Example 1

[0120] The difference from Example 1 is that after obtaining the polyimide resin solution, rotary evaporation is used to remove most of the ethanol solvent in the solution, and then it is put into a vacuum oven and gradually heated up to 220 °C to obtain a polyimide molding powder with an imidization degree of 78%; directly put the obtained polyimide molding powder into a mold and perform compression molding;

[0121] Except for the above differences, other conditions of Comparative Example 1 were the same as those of Example 1. After molding, a polyimide molded part was obtained. The glass transition temperature of the obtained molded part was 323 °C. Ten samples were detected by an ultrasonic flaw detector, and ultrasonic abnormal signals were found in 2 of them, indicating that there were defects such as air bubbles inside.

[0122] After the polyimide resin of Comparative Example 1 was imidized at 220 °C, only 78% of the imidization degree was achieved. During its molding process, polycondensation reaction was likely to occur, releasing water and alcohol gases, and defects such as air bubbles were easily generated. The test results proved that 20% of the samples were unqualified, and there were defects such as air bubbles inside. The internal defects would affect the mechanical properties and reliability of the final product. However, in Example 1, a polyimide molded part was obtained by mixing polyimide component A with an imidization degree of 80% and polyimide component B with a crosslinking degree of 20% at a mass ratio of 9:1. After ultrasonic detection, all the samples were uniform inside and had no air bubble defects.

[0123] Through the combination of partially crosslinked polyimide and imidized polyimide in Examples 1 to 6, the two components matched and cooperated with each other, had the characteristics of low melt viscosity, low gas release amount during the molding process, reduced the possibility of air bubbles in the final product, had a high product yield, stable product performance and excellent heat resistance.

Claims

1. A polyimide resin, comprising polyimide component A and polyimide component B; wherein polyimide component A is a polyimide powder with an imidization degree of ≥80%, and polyimide component B is a polyimide powder with a crosslinking degree of 20-80%. Based on the total weight of the polyimide resin being 100 wt%, polyimide component A accounts for 85-99 wt%, and polyimide component B accounts for 1-15 wt%.

2. The polyimide resin according to claim 1, wherein: Based on the total weight of the polyimide resin being 100 wt%, polyimide component A accounts for 90-98 wt%, and polyimide component B accounts for 2-10 wt%.

3. The polyimide resin according to claim 1 or 2, wherein: The polyimide component A is obtained by a preparation method comprising the following steps: (1) Mix a capping agent A, an aromatic tetracarboxylic dianhydride A, and an aliphatic alcohol A to carry out an esterification reaction A to obtain a solution of an aromatic diacid diester A and a capping agent monoacid monoester A; (2) Dissolve an aromatic diamine A in the solution obtained in step (1) to obtain a resin solution A; (3) Remove the excess aliphatic alcohol A from the resin solution A obtained in step (2) to obtain a resin powder A; (4) Imidize the resin powder A obtained in step (3) to obtain the polyimide resin component A.

4. The polyimide resin according to claim 3, wherein: In step (1), The capping agent A is at least one of nadic anhydride, 4-phenylethynylphthalic anhydride, 4-ethynylphthalic anhydride, and methyl ethynylphthalic anhydride; and / or, The aromatic tetracarboxylic dianhydride A is at least one of the structures shown in formula (1): wherein, Ar1 is a tetravalent aromatic residue containing at least one benzene ring; the aromatic tetracarboxylic dianhydride A is preferably at least one of 3,3',4,4'-benzophenone tetracarboxylic dianhydride, hexafluorodiacid anhydride, 4,4'-biphenyl ether dianhydride, pyromellitic dianhydride, diphenyl sulfide dianhydride, and 3,3,4,4-diphenylsulfone tetracarboxylic dianhydride; and / or, The aliphatic alcohol A is at least one of methanol, ethanol, propanol, isopropanol, n-butanol, isobutanol, n-pentanol, isopentanol, and tert-butanol; and / or, The temperature of the esterification reaction A is 60-130 °C, preferably 60-90 °C; and / or, The time of the esterification reaction A is 1-10 h, preferably 1-4 h; and / or, In step (2), The aromatic diamine A is at least one of the structures shown in formula (2): H2N-Ar2-NH2 Formula (2) wherein, Ar2 is a divalent aromatic residue containing at least one benzene ring; the aromatic diamine A is preferably at least one of 2,2-bis[4-(4-aminophenoxy)phenyl]propane, p-phenylenediamine, diphenylmethane diamine, 4,4'-diaminodiphenyl ether, 1,3-bis(4'-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, and 3,4'-diaminodiphenyl ether; and / or, In step (4), The imidization temperature is 220-300 °C, preferably 220-280 °C; and / or, The imidization time is 0.1 to 4 h, preferably 0.5 to 1 h; and / or, The imidization degree is ≥80%.

5. The polyimide resin according to claim 3, characterized in that: The molar ratio of the aromatic tetracarboxylic dianhydride A to the aromatic diamine A is (n + 1):n, where 1 ≤ n ≤ 100, preferably 1 < n ≤ 20; and / or, The ratio of the difference in the molar amounts of the aromatic diamine A and the aromatic tetracarboxylic dianhydride A to the molar amount of the end-capping agent A is 1:(1 to 2); and / or, The ratio of the sum of the masses of the end-capping agent A, the aromatic tetracarboxylic dianhydride A, and the aromatic diamine A to the mass of the fatty alcohol A is 1:(0.6 to 3), preferably 1:(0.6 to 1.6).

6. The polyimide resin according to claim 1 or 2, characterized in that: The polyimide component B is obtained by a preparation method including the following steps: (i) Mix the end-capping agent B, the aromatic tetracarboxylic dianhydride B, and the fatty alcohol B to carry out the esterification reaction B to obtain a solution of the aromatic diacid diester B and the end-capping agent monoacid monoester B; (ii) Dissolve the aromatic diamine B in the solution obtained in step (1) to obtain the resin solution B; (iii) Remove the fatty alcohol B from the resin solution B obtained in step (2) to obtain the resin powder B; (iv) Carry out a crosslinking reaction on the obtained resin powder B to obtain the polyimide resin component B.

7. The polyimide resin according to claim 6, characterized in that: In step (i), The end-capping agent B is at least one of nadic anhydride, 4-phenylethynylphthalic anhydride, 4-ethynylphthalic anhydride, and methyl ethynylphthalic anhydride; and / or, The aromatic tetracarboxylic dianhydride B is at least one of the structures shown in formula (1): Among them, Ar1 is a tetravalent aromatic residue containing at least one benzene ring; the aromatic tetracarboxylic dianhydride B is preferably at least one of 3,3',4,4'-benzophenone tetracarboxylic dianhydride, hexafluorodiacid anhydride, 4,4'-biphenylether dianhydride, pyromellitic dianhydride, diphenyl sulfide dianhydride, and 3,3,4,4-diphenylsulfone tetracarboxylic dianhydride; and / or, The fatty alcohol B is at least one of methanol, ethanol, propanol, isopropanol, n-butanol, isobutanol, n-pentanol, isopentanol, and tert-butanol; and / or, The temperature of the esterification reaction B is 60 to 130 °C, preferably 60 to 90 °C; and / or, The time of the esterification reaction B is 1 to 10 h, preferably 1 to 4 h; and / or, In step (ii), The aromatic diamine B is at least one of the structures shown in formula (2): H2N-Ar2-NH2 Formula (2) Among them, Ar2 is a divalent aromatic residue containing at least one benzene ring; the aromatic diamine B is preferably at least one of 2,2-bis[4-(4-aminophenoxy)phenyl]propane, p-phenylenediamine, diphenylmethanediamine, 4,4'-diaminodiphenyl ether, 1,3-bis(4'-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, and 3,4'-diaminodiphenyl ether; and / or, In step (iv), The temperature of the crosslinking reaction is 310 to 400 °C, preferably 320 to 390 °C; and / or, The time of the cross-linking reaction is 1 to 120 min, preferably 5 to 60 min; and / or, The degree of cross-linking is 20 to 80%.

8. The polyimide resin according to claim 6, wherein: The molar ratio of aromatic tetracarboxylic dianhydride B to aromatic diamine B is (n + 1):n, 1 ≤ n ≤ 100, preferably 1 < n ≤ 20; and / or, The ratio of the difference in the molar amounts of aromatic diamine B and aromatic tetracarboxylic dianhydride B to the molar amount of capping agent B is 1:(1 to 2); and / or, The ratio of the sum of the masses of capping agent B, aromatic tetracarboxylic dianhydride B and aromatic diamine B to the mass of fatty alcohol B is 1:(0.6 to 3), preferably 1:(0.6 to 1.6).

9. A method for preparing the polyimide resin according to any one of claims 1 to 8, comprising: Preparing polyimide component A and polyimide component B separately, and then mixing them evenly according to the said mass percentages to obtain the polyimide resin.

10. An application of the polyimide resin according to any one of claims 1 to 8 or the polyimide resin obtained by the preparation method according to claim 9 in a composite material.

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