Low-density polyimide foam material and preparation method thereof

Abstract

The invention relates to the technical field of polyimide foam materials, in particular to a low-density polyimide foam material and a preparation method thereof. The main raw materials are dianhydride, a polar solvent, fatty alcohol, a foaming agent, a catalyst, a surfactant, a curing agent and the like. The preparation method comprises the following steps: firstly, preparing a material A: mixing binary anhydride, fatty alcohol and a solvent according to a certain proportion, completely esterifying at 30-70 DEG C, then cooling to obtain an esterified cooling liquid, then adding a catalyst, a foaming agent and a surfactant into the prepared esterified cooling liquid according to a certain proportion, and fully stirring to obtain a foaming precursor; and adding isocyanate (black material) into the foaming precursor, quickly transferring into a forming mold, and finally feeding foam into a drying oven for curing and demolding to obtain the polyimide foam material. The curing agent with the functionality of 2 is introduced and reacts with functional groups in a polyimide chain to form a long-chain structure, so that the toughening purpose is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of polyimide foam materials, in particular to a low-density polyimide foam material and a preparation method thereof. Background Art

[0002] Polyimide foam is a high-performance foam based on polyimide materials, which has excellent thermal stability, mechanical properties, chemical stability and electrical insulation properties. These properties make polyimide foam widely used in aerospace, electronics, automobiles and energy. Polyimide foam materials not only retain the inherent properties of polyimide, but also have light weight, radiation resistance, corrosion resistance and excellent heat insulation and sound insulation properties.

[0003] As early as 1965, DuPont launched the Kapton series of products, marking the beginning of commercial mass production of polyimide materials. Polyimide was first used as an insulation material for aircraft cabins. Later, the U.S. Department of Defense designated polyimide foam materials as thermal insulation materials for naval ships to improve the safety and environmental adaptability of warships. Today, polyimide foam materials have been extended to vehicles, shelters, energy, and civil buildings. With the continuous expansion of application fields, the development of green and environmentally friendly foaming agents and multifunctional foam materials has become a research hotspot for polyimide foam materials.

[0004] At present, the preparation of polyimide foam is generally divided into a one-step method and a two-step method. The one-step method, also known as the direct foaming method, refers to directly adding a foaming agent and a cross-linking agent to a polyimide precursor, and completing polymerization and foaming simultaneously through a single reaction process. The one-step method has a simple process flow, convenient operation, low production cost, easy control, high production efficiency, easy industrial mass production, and good consistency in the performance of the prepared material. However, in the one-step method, foaming polymerization and foaming are carried out simultaneously, and it is difficult to accurately control the pore size, and some foaming agents may be harmful to the environment and have a low degree of imidization. The two-step method, also known as the indirect foaming method, refers to first preparing a polyimide prepolymer powder by reacting a dianhydride and a diamine, and then adding a foaming agent, a cross-linking agent, etc. to complete the secondary reaction foaming. The two-step method can better control the performance of the material as well as the pore size and distribution of the pores, and can introduce modifiers to achieve multifunctional materials. However, the process operation is complicated, with many steps, difficult to control, poor consistency in material performance, and low production efficiency, making it difficult to achieve industrial mass production and produce low-density foam materials.

[0005] US3483144 discloses a method for preparing polyimide foam using dianhydride and diamine by ball milling. However, the polyimide foam prepared by this method has a poor pore structure and can only be prepared with a density of about 430 kg / m 3High-density polyimide foam material. US7541393B2 discloses a method for preparing flexible polyimide foam, but the foaming agent used therein, an organic foaming agent, will volatilize VOCs, which has a certain impact on the environment and is not conducive to the concept of green development. CN106751826A discloses a supercritical foaming treatment method for preparing polyimide foam. The strength and toughness of the product are improved by adding modifiers such as glass microspheres, but it also makes the production process more complicated and difficult to control.

[0006] Therefore, finding a method for preparing a high-density polyimide foam material with strong adaptability, low cost, high degree of imidization, high production efficiency and easy industrial mass production is the current key research direction. Summary of the invention

[0007] In order to solve the above technical problems existing in the prior art, the present invention provides a low-density polyimide foam material and a preparation method thereof. Specifically, the present invention is achieved through the following technical solutions:

[0008] A method for preparing a low-density polyimide foam material comprises the following steps:

[0009] (1) Preparation of esterification liquid: dibasic anhydride, polar solvent and fatty alcohol are mixed, and esterification reaction is completed at 50-90° C. to obtain esterification liquid, which is cooled for standby use;

[0010] (2) Preparation of a foaming precursor: The esterification liquid in step (1) is mixed with a dibasic anhydride, an initiator, a catalyst, and a surfactant and stirred until fully mixed to obtain a foaming precursor;

[0011] (3) Foaming: adding isocyanate and curing agent to the foaming precursor in step (2), mixing and stirring, and then quickly transferring to a mold for molding;

[0012] (4) Curing: The foamed product in step (3) is demoulded and then heated to obtain a polyimide foam material.

[0013] Furthermore, the dibasic anhydride in step (1) is one or more of 1,2,4,5-pyromellitic dianhydride (PMDA), 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 4,4'-(hexafluoroethylene)phthalic anhydride (6FDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA), 2,3',4,4'-biphenyltetracarboxylic dianhydride (α-BPDA), maleic anhydride (MAH), 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride (ODPA), bisphenol A diphenyl ether dianhydride (BPADA), and 3,3',4,4'-biphenyl sulfone tetracarboxylic dianhydride (DSDA), mixed in any proportion.

[0014] Furthermore, the polar solvent in step (1) is one or more of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N,N-dimethylacetamide (DMAc), tetrahydrofuran (THF), N-methylmorpholine (NMM), N-ethylpyrrolidone (NEP), 1,3-dimethyl-2-imidazolidinone (DMI), isopropyl alcohol (IPA), and 2,6-dichloropyridine, mixed in any proportion.

[0015] Furthermore, the fatty alcohol in step (1) is one or more of methanol, ethanol, propylene glycol, glycerol, 1,4-butanediol, neopentyl glycol, n-butanol, hexadecanol, cyclohexanol, and phenylethyl alcohol mixed in any proportion.

[0016] Furthermore, the mass ratio of the dibasic anhydride, the polar solvent and the fatty alcohol in the step (1) is (2-12): (2-12): (1-6).

[0017] Furthermore, the catalyst in step (2) is one or more of stannous octoate, dibutyltin dilaurate, triethylenediamine, triethylamine, organotin, dibutyltin dichloride, dibutyltin diacetate, stannous isooctanoate, and dioctyltin dichloride mixed in any proportion.

[0018] Furthermore, the foaming agent in step (2) is one or more of water, carbon dioxide and nitrogen mixed in any proportion.

[0019] Furthermore, the surfactant in step (2) is one or more of AK series silicone oil (including but not limited to AK8803, AK8805), siloxane-based surfactant, polypropylene glycol, polyethylene glycol, polyether sulfone, silicone, and sodium dodecyl sulfate mixed in any proportion.

[0020] Furthermore, the mass ratio of the esterification liquid, catalyst, foaming agent and surfactant in step (2) is (50-100): (1-10): (5-20): (5-20).

[0021] Furthermore, the curing agent in step (3) is a mixture of one or more of toluene diisocyanate (TDI), polyphenyl polymethylene polyisocyanate, diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), 1,6-diisocyanato-2,2,4-trimethylhexane, diethylenetriamine (DETA), methyl cyclohexane diisocyanate, cyclohexyl dimethylene diisocyanate, methyl formate pentamethylene diisocyanate, triethylenetetramine (TETA), 4,4'-dicyclohexylmethane diisocyanate and 3,3'-dimethoxy-4,4'-diphenyl diisocyanate.

[0022] Furthermore, the injection ratio of the high-pressure foaming machine in step (4) is the injection ratio of foaming precursor: black material = (50-100): (15-60).

[0023] Furthermore, the curing in step (5) is a step-by-step temperature curing: in the first step, the system temperature is 100°C to 200°C, and the time is 30min to 120min; in the second step, the system temperature is 200°C to 300°C, and the time is 150min to 300min.

[0024] The low-density polyimide foam material is prepared by the above preparation method.

[0025] Compared with the prior art, the technical effects created by the present invention are embodied in:

[0026] (1) The present invention introduces a curing agent with difunctionality to react with the functional groups in the polyimide chain to form a long chain structure, thereby reducing crosslinking points and achieving the purpose of toughening.

[0027] (2) The present invention adopts an environmentally friendly foaming agent to reduce the impact of chemical foaming agents on the environment.

[0028] (3) The present invention adopts a staged temperature rise curing technology, which can make the heat distribution more uniform and reduce the risk of material deformation and cracking due to the generation of thermal stress. In addition, low-temperature desolventization and pre-curing are performed first, and then high-temperature curing and imidization are performed, which can improve the imidization degree of the product.

[0029] (4) The polyimide foam prepared by the present invention has the characteristics of excellent flame retardancy, good temperature resistance and low moisture absorption rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the test report of the permanent deformation of the polyimide foam obtained in Example 1.

[0031] Figure 2 This is a test report on the thermal conductivity of the polyimide foam prepared in Example 1.

[0032] Figure 3 This is a test report on the temperature resistance of the polyimide foam prepared in Example 1. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is further defined below in conjunction with specific implementation methods, but the scope of protection required is not limited to the description.

[0034] In the present invention, the thermal conductivity of the sample is measured by using a DRL-2A thermal conductivity tester at 100°C and 50N; the oxygen index is measured by using an oxygen index meter BS ISO 4589-2. 2 The concentration starts from 22% and increases until the sample burns. The O 2 The critical concentration value is the limiting oxygen index of the fabric; the apparent density is analyzed by a high-density electronic analytical balance for the apparent density of the polyimide foam material.

[0035] Example 1

[0036] This embodiment provides a method for preparing low-density polyimide foam, which specifically includes the following steps:

[0037] (1) Preparation of esterification liquid: 1,2,4,5-pyromellitic dianhydride, tetrahydrofuran and methanol are uniformly mixed in a ratio of 5:4:1, and the mixture is completely reacted and esterified at 60° C. to obtain an esterification liquid.

[0038] (2) Preparation of a foaming precursor: The esterification liquid in step (1) is mixed with stannous octoate, water, and a silicone surfactant in a ratio of 100:1:9:7, and stirred until uniform to obtain a foaming precursor.

[0039] (3) Preparation of black material: isocyanate such as toluene diisocyanate, polyphenyl polymethylene polyisocyanate and diethylene triamine are mixed in a ratio of 4:4:2 to obtain black material.

[0040] (4) Foaming: The foaming precursor in step (2) and the black material in step (3) are mixed in a ratio of 100:50, stirred, and then quickly injected into a mold for foaming molding.

[0041] (5) Curing: demoulding the foamed object in step (4) and curing it to obtain a polyimide foam material. The curing system temperature is 180°C for 90 minutes in the first stage and 220°C for 300 minutes in the second stage.

[0042] Example 2

[0043] (1) Preparation of esterification liquid: 3,3',4,4'-benzophenonetetracarboxylic dianhydride, N,N-dimethylformamide, methanol and ethanol are uniformly mixed in a ratio of 9:7:2:1, and the mixture is completely reacted and esterified at 60°C to obtain an esterification liquid.

[0044] (2) Preparation of foaming precursor: The esterification liquid in step (1) is mixed with stannous octoate, water and AK8803 silicone oil in a ratio of 100:1:8:6, and stirred until uniform to obtain a foaming precursor.

[0045] (3) Preparation of black material: polyphenyl polymethylene polyisocyanate and triethylenetetramine are mixed in a ratio of 5:2 to obtain a black material.

[0046] (4) Foaming: The foaming precursor in step (2) and the black material in step (3) are mixed in a ratio of 100:55, stirred, and then quickly injected into a mold for foaming molding.

[0047] (5) Curing: demoulding the foamed object in step (4) and curing it to obtain a polyimide foam material. The curing system temperature is 190°C for 60 minutes in the first stage and 220°C for 300 minutes in the second stage.

[0048] Finally, it should be pointed out that the above embodiments are only representative examples of the present invention. Obviously, the technical solution of the present invention is not limited to the above embodiments, and there are many variations. All variations that can be directly derived or associated with the content disclosed by ordinary technicians in this field should be considered as the protection scope of the present invention.

Claims

1. A method for preparing a low-density polyimide foam material, characterized in that: The steps include: (1) Preparation of esterification liquid: dibasic anhydride, polar solvent and fatty alcohol are mixed, and esterification reaction is completed at 50-90° C. to obtain esterification liquid, which is cooled for standby use; (2) Preparation of a foaming precursor: The esterification liquid in step (1) is mixed with a dibasic anhydride, an initiator, a catalyst, and a surfactant and stirred until fully mixed to obtain a foaming precursor; (3) Foaming: adding isocyanate and curing agent to the foaming precursor in step (2), mixing and stirring, and then quickly transferring to a mold for molding; (4) Curing: The foamed product in step (3) is demoulded and then heated to obtain a polyimide foam material.

2. The preparation method according to claim 1, characterized in that: The dibasic anhydride in step (1) is one or more of 1,2,4,5-pyromellitic dianhydride (PMDA), 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 4,4'-(hexafluoroethylene)phthalic anhydride (6FDA), 3,3',4,4'-biphenyl tetracarboxylic dianhydride (s-BPDA), 2,3',4,4'-biphenyl tetracarboxylic dianhydride (α-BPDA), maleic anhydride (MAH), 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride (ODPA), bisphenol A diphenyl ether dianhydride (BPADA), and 3,3',4,4'-biphenyl sulfone tetracarboxylic dianhydride (DSDA), mixed in any proportion.

3. The preparation method according to claim 1, characterized in that: The polar solvent in step (1) is one or more of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N,N-dimethylacetamide (DMAc), tetrahydrofuran (THF), N-methylmorpholine (NMM), N-ethylpyrrolidone (NEP), 1,3-dimethyl-2-imidazolidinone (DMI), isopropyl alcohol (IPA), and 2,6-dichloropyridine, mixed in any proportion.

4. The preparation method according to claim 1, characterized in that: The fatty alcohol in step (1) is one or more of methanol, ethanol, propylene glycol, glycerol, 1,4-butanediol, neopentyl glycol, n-butanol, hexadecanol, cyclohexanol, and phenylethyl alcohol mixed in any proportion.

5. The preparation method according to claim 1, characterized in that: The mass ratio of the dibasic anhydride, the polar solvent and the fatty alcohol in the step (1) is (2-12): (2-12): (1-6).

6. The preparation method according to claim 1, characterized in that: The catalyst in step (2) is one or more of stannous octoate, dibutyltin dilaurate, triethylenediamine, triethylamine, organotin, dibutyltin dichloride, dibutyltin diacetate, stannous isooctanoate, and dioctyltin dichloride, mixed in any proportion.

7. The preparation method according to claim 1, characterized in that: The foaming agent in step (2) is one or more of water, carbon dioxide and nitrogen mixed in any proportion.

8. The preparation method according to claim 1, characterized in that: The surfactant in step (2) is one or more of AK series silicone oil, siloxane-based surfactant, polypropylene glycol, polyethylene glycol, polyether sulfone, silicone, and sodium lauryl sulfate mixed in any proportion.

9. The preparation method according to claim 1, characterized in that: The mass ratio of the esterification liquid, catalyst, foaming agent and surfactant in the step (2) is (50-100): (1-10): (5-20): (5-20).

10. The preparation method according to claim 1, characterized in that: The curing agent in the step (3) is a mixture of one or more of toluene diisocyanate (TDI), polyphenyl polymethylene polyisocyanate, diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), 1,6-diisocyanato-2,2,4-trimethylhexane, diethylenetriamine (DETA), methyl cyclohexane diisocyanate, cyclohexyl dimethylene diisocyanate, methyl formate pentamethylene diisocyanate, triethylenetetramine (TETA), 4,4'-dicyclohexylmethane diisocyanate and 3,3'-dimethoxy-4,4'-diphenyl diisocyanate.

11. The preparation method according to claim 1, characterized in that: The injection ratio of the high-pressure foaming machine in the step (4) is the injection ratio of the foaming precursor: the black material = (50-100): (15-60).

12. The preparation method according to claim 1, characterized in that: The curing in step (5) is a step-by-step temperature curing: in the first step, the system temperature is 100°C to 200°C, and the time is 30min to 120min; in the second step, the system temperature is 200°C to 300°C, and the time is 150min to 300min.

13. A low-density polyimide foam material prepared by the preparation method according to any one of claims 1 to 12.

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