A polyimide adhesive for bonding polyimide honeycomb and its preparation method

Abstract

A polyimide adhesive for bonding polyimide honeycomb and its preparation method. The present invention relates to a polyimide adhesive and its preparation method. It solves the problems of poor matching, low adhesive infiltration and climbing, low adhesive strength, and insufficient heat resistance in the integral bonding of existing polyimide adhesives and polyimide honeycomb. The polyimide adhesive is made of polyimide resin, polyfunctional compound, salt-forming compound and solvent; the preparation method: First, prepare polyimide resin; Second, weigh and mix. The present invention is used for the polyimide adhesive for bonding polyimide honeycomb and its preparation.

Description

Technical Field

[0001] The present invention relates to a polyimide adhesive and a preparation method thereof. Background Art

[0002] Honeycomb sandwich structures have a series of advantages that traditional materials do not have, such as high specific strength and specific modulus, good fatigue resistance and vibration resistance, and the ability to effectively absorb impact loads. Since their inception, they have been favored by the aviation and aerospace industries and have become one of the indispensable materials for the development of aviation and aerospace. With the development of aerospace vehicles towards high speed and high performance, their honeycomb sandwich structures currently generally use polyimide resin-based honeycomb sandwiches, and the service temperature can reach 300°C and above. During the forming process of polyimide honeycomb / composite material sandwiches, a special polyimide adhesive is required to achieve the bonding between the honeycomb and the composite material panel.

[0003] It is difficult for polyimide adhesives to melt and flow on the bonded surface and have poor deep infiltration like other small molecule adhesives such as epoxy and bismaleimide. Especially when bonding honeycomb structures, it is difficult to form good adhesive melt climbing at the bottom of the honeycomb structure. The bonding only occurs at the bottom, and the bonding area is too small, resulting in structural defects and adhesive bonding failure at the interface. In recent years, in order to improve the melt infiltration performance of polyimide adhesives for honeycomb structures, introducing isomeric structural monomers into the main chain can effectively increase the rotational radius and reduce the structural regularity in the rigid imide structure, improve the melt movement ability of the chain segments, and maintain a relatively high glass transition temperature (Tg), which has been applied.

[0004] Existing data and literature reports mainly focus on how to improve the molecular structure of polyimide adhesives and test the metal bonding performance at high and low temperatures. This is because although existing polyimide adhesives can bond metals to achieve high bonding strength and cohesive strength, it is difficult to form an interface layer with sufficient strength on the rough surface and difficult-to-wet surface of polyimide honeycombs, resulting in adhesive bonding failure. Therefore, there is poor compatibility between existing polyimide adhesives and polyimide honeycombs in the overall adhesive bonding, so there is little discussion on the bonding performance of polyimide honeycombs, especially less discussion on the adhesive bonding infiltration climbing of polyimide honeycombs. There is no data report on how to improve the adhesive bonding interface with polyimide honeycombs, improve the climbing effect of the adhesive at the bottom of the honeycomb, and obtain high-temperature honeycomb bonding performance. Summary of the Invention

[0005] The present invention aims to solve the problems of poor compatibility, low adhesive bonding infiltration climbing and adhesive bonding strength, and insufficient heat resistance between existing polyimide adhesives and polyimide honeycombs in the overall adhesive bonding, and provides a polyimide adhesive for bonding polyimide honeycombs and a preparation method thereof.

[0006] A polyimide adhesive for bonding polyimide honeycomb, which is made of 100 parts by weight of polyimide resin, 20 to 50 parts of polyfunctional compound, 2 to 15 parts of salt-forming compound and 100 to 200 parts of solvent;

[0007] The polyfunctional compound is a POSS compound with a functionality of 6 to 10;

[0008] The salt-forming compound is an organic ammonium salt;

[0009] The structural general formula of the polyimide resin is:

[0010]

[0011] The n is 9 to 19;

[0012] The Ar1 is -O-, - or

[0013] The Ar2 is

[0014] A preparation method of a polyimide adhesive for bonding polyimide honeycomb, which is carried out according to the following steps:

[0015] I. Under a nitrogen atmosphere, add aromatic dianhydride to N,N-dimethylacetamide and stir, then add aromatic diamine and stir to obtain a mixed solution. Add phthalic anhydride to the mixed solution and stir to react, then add toluene, heat up to 120°C to 130°C, and under the condition of 120°C to 130°C, reflux and react for 1h to 4h to obtain a polyimide solution. After the polyimide solution is cooled to room temperature, precipitate, filter and dry to obtain polyimide resin;

[0016] The molar ratio of the aromatic dianhydride to the aromatic diamine is (0.9 to 0.95):1; the molar ratio of the aromatic diamine to the phthalic anhydride is 1:(0.1 to 0.2); and the total molar of the acid anhydride functional groups of the aromatic dianhydride and the phthalic anhydride is equal to the molar of the amino functional groups of the aromatic diamine;

[0017] The aromatic dianhydride is

[0018]

[0019] The aromatic diamine is

[0020] II. Weigh 100 parts of polyimide resin, 20 - 50 parts of polyfunctional compound, 2 - 15 parts of salt-forming compound, and 100 - 200 parts of solvent by weight. Under the conditions of a temperature of 80°C - 100°C and stirring, stir 100 parts of polyimide resin, 20 - 50 parts of polyfunctional compound, 2 - 15 parts of salt-forming compound, and 100 - 200 parts of solvent for 1 - 4 hours to obtain the adhesive.

[0021] The beneficial effects of the present invention are as follows:

[0022] The polyimide of the present invention adopts an aromatic diamine structure containing a specific carboxylic acid side chain structure. By utilizing its carboxylic acid groups, it can combine with polyfunctional compounds. Unexpectedly, under the action of organic ammonium salts, a climbable gel state can be formed on the surface of three-dimensional structures such as honeycombs by using the formed complex structure.

[0023] Specifically, the polyimide main chain structure composed of aromatic diamines containing carboxylic acid side chain structures not only ensures the heat resistance of the system, but also utilizes the dicarboxylic acids under the dihedral angle brought by its biphenyl structure to form chemical binding interactions with polar groups in different directions. On this basis, polyfunctional compounds are introduced, especially amino compounds and epoxy compounds with 6 - 10 functional groups, which can form chemical bonding and interactions with carboxylic acid groups, further increasing the swelling gelation under the action of aprotic strongly polar amide solvents, thereby achieving effective enrichment and climbing at the bottom of the honeycomb.

[0024] Unexpectedly, by adding salt-forming compounds such as triethylamine, under the action of aprotic strongly polar amide solvents, multi-coordinated salt complexes can be formed with amino terminals and carboxylic acid side chains. Utilizing the synergistic effect of the solvents, the thixotropy of the solution viscosity and the gelation climbing effect on the honeycomb surface are greatly enhanced. At the same time, by adopting the above methods, it is innovatively found that the wettability and contact angle are not affected, thereby improving the interfacial adhesion and bonding effect while maintaining a low contact angle wetting.

[0025] The present invention relates to a polyimide adhesive for bonding polyimide honeycombs and its preparation method. Description of the Drawings

[0026] Figure 1 It is a physical diagram of the honeycomb after room-temperature planar stretching of a polyimide honeycomb sandwich structure bonded with a polyimide adhesive. a is Comparative Experiment 1, and b is Example 1;

[0027] Figure 2 It is a physical diagram of the honeycomb glue climbing in a polyimide honeycomb sandwich structure bonded with the polyimide adhesive prepared in Example 1, where the frame is the climbing height of the glue layer;

[0028] Figure 3 It is the infrared spectrum of the polyimide resin prepared in Example 1. Specific Embodiment

[0029] Specific Embodiment 1: A polyimide adhesive for bonding polyimide honeycomb is prepared from 100 parts by weight of polyimide resin, 20 to 50 parts of polyfunctional compound, 2 to 15 parts of salt-forming compound and 100 to 200 parts of solvent;

[0030] The polyfunctional compound is a POSS compound with a functionality of 6 to 10;

[0031] The salt-forming compound is an organic ammonium salt;

[0032] The structural general formula of the polyimide resin is:

[0033]

[0034] The n is 9 to 19;

[0035] The Ar1 is -O- - or

[0036]

[0037] The Ar2 is

[0038] The beneficial effect of this embodiment is:

[0039] In this embodiment, the polyimide adopts an aromatic diamine structure containing a specific carboxylic acid side chain structure. By using its carboxylic acid groups, it can combine with polyfunctional compounds. Unexpectedly, under the action of organic ammonium salts, a climbable gel state can be formed on the surface of three-dimensional structures such as honeycomb by using the formed complex structure.

[0040] Specifically, the polyimide main chain structure composed of aromatic diamines containing carboxylic acid side chain structures not only ensures the heat resistance of the system, but also uses the dicarboxylic acids under the dihedral angle brought by its biphenyl structure to form chemical binding with polar groups in different directions. On this basis, polyfunctional compounds are introduced, especially amino compounds and epoxy compounds with 6-10 functional groups, which can form chemical bonding and interaction with carboxylic acid groups, further increasing the swelling gelation under the action of aprotic strongly polar amide solvents, so as to form effective enrichment and climb at the bottom of the honeycomb.

[0041] Surprisingly, by adding a salt-forming compound such as triethylamine, in the presence of a strongly polar aprotic amide solvent, a multi-coordinated salt complex can be formed with the amino-terminated group and the carboxylic acid side chain. With the synergistic effect of the solvent, the thixotropy of the solution viscosity and the gel climbing effect on the honeycomb surface are greatly enhanced. At the same time, by adopting the above method, it is innovatively found that the wettability and contact angle are not affected, thus improving the interfacial adhesion and bonding effect while maintaining low contact angle wetting.

[0042] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that: the polyfunctional compound is octakis(aminophenyl)-T8-silsesquioxane or epoxycyclohexyl-cage polyhedral oligomeric silsesquioxane. Others are the same as Specific Embodiment 1.

[0043] The CAS number of octakis(aminophenyl)-T8-silsesquioxane in this specific embodiment is 518359-82-5, and its structural formula is

[0044] The CAS number of epoxycyclohexyl-cage polyhedral oligomeric silsesquioxane in this specific embodiment is 187333-74-0, and its structural formula is R is

[0045] Specific Embodiment 3: The difference between this embodiment and one of Specific Embodiments 1 or 2 is that: the salt-forming compound is one or a mixture of several of triethylamine, trialkyl tertiary amine, octadecyl dimethyl tertiary amine, and dodecyl dimethyl tertiary amine. Others are the same as Specific Embodiment 1 or 2.

[0046] Specific Embodiment 4: The difference between this embodiment and one of Specific Embodiments 1 to 3 is that: the solvent is an amide polar solvent. Others are the same as Specific Embodiments 1 to 3.

[0047] Specific Embodiment 5: The difference between this embodiment and one of Specific Embodiments 1 to 4 is that: the solvent is N,N-dimethylformamide or N,N-dimethylacetamide. Others are the same as Specific Embodiments 1 to 4.

[0048] Specific Embodiment 6: A preparation method of a polyimide adhesive for bonding polyimide honeycomb, which is carried out according to the following steps:

[0049] 1. Under a nitrogen atmosphere, add aromatic dianhydride to N,N-dimethylacetamide and stir, then add aromatic diamine and stir to obtain a mixed solution. Add phthalic anhydride to the mixed solution and stir for reaction, then add toluene, heat up to a temperature of 120°C to 130°C, and under the condition of a temperature of 120°C to 130°C, reflux and react for 1h to 4h to obtain a polyimide solution. After the polyimide solution is cooled to room temperature, precipitate, filter and dry to obtain a polyimide resin;

[0050] The molar ratio of the aromatic dianhydride to the aromatic diamine is (0.9 to 0.95):1; the molar ratio of the aromatic diamine to phthalic anhydride is 1:(0.1 to 0.2); and the total moles of the anhydride functional groups of the aromatic dianhydride and phthalic anhydride are equal to the moles of the amino functional groups of the aromatic diamine.

[0051] The aromatic dianhydride is

[0052]

[0053] The aromatic diamine is

[0054] Second, weigh 100 parts of polyimide resin, 20 to 50 parts of polyfunctional compound, 2 to 15 parts of salt-forming compound, and 100 to 200 parts of solvent by weight. Under the conditions of a temperature of 80°C to 100°C and stirring, stir 100 parts of polyimide resin, 20 to 50 parts of polyfunctional compound, 2 to 15 parts of salt-forming compound, and 100 to 200 parts of solvent for 1 h to 4 h to obtain an adhesive.

[0055] Specific Embodiment Seven: The difference between this embodiment and Specific Embodiment Six is that: in Step One, the mass ratio of N,N-dimethylacetamide to toluene is 1:(0.2 to 0.5). Others are the same as Specific Embodiment Six.

[0056] Specific Embodiment Eight: The difference between this embodiment and one of Specific Embodiments Six or Seven is that: in Step One, the total mass of N,N-dimethylacetamide and toluene and the total mass of phthalic anhydride, aromatic dianhydride, and aromatic diamine have a mass ratio of (1 to 3):1. Others are the same as Specific Embodiment Six or Seven.

[0057] Specific Embodiment Nine: The difference between this embodiment and one of Specific Embodiments Six to Eight is that: in Step One, under a nitrogen atmosphere, add the aromatic dianhydride to N,N-dimethylacetamide and stir for 1 h to 2 h, then add the aromatic diamine and stir for 1 h to 5 h to obtain a mixed solution, and add phthalic anhydride to the mixed solution and stir and react for 1 h to 5 h. Others are the same as Specific Embodiments Six to Eight.

[0058] Specific Embodiment Ten: The difference between this embodiment and one of Specific Embodiments Six to Nine is that: after the polyimide solution is cooled to room temperature in Step One, it is dropped into distilled water, precipitated for 1 h to 2 h and then filtered, and finally dried under the condition of a temperature of 130°C to 140°C. Others are the same as Specific Embodiments Six to Nine.

[0059] The following examples are used to verify the beneficial effects of the present invention:

[0060] Example One:

[0061] A polyimide adhesive for bonding polyimide honeycomb is prepared from 100 parts by weight of polyimide resin, 30 parts of polyfunctional compound, 5 parts of salt-forming compound and 200 parts of solvent;

[0062] The polyfunctional compound is octakis(aminophenyl)-T8-silsesquioxane;

[0063] The salt-forming compound is triethylamine;

[0064] The structural formula of the polyimide resin is:

[0065]

[0066] The n is 9;

[0067] The Ar1 is

[0068] The Ar2 is

[0069] The solvent is N,N-dimethylformamide.

[0070] The preparation method of the above polyimide adhesive for bonding polyimide honeycomb is carried out according to the following steps:

[0071] I. Under a nitrogen atmosphere, add aromatic dianhydride to N,N-dimethylacetamide, stir for 1 h, then add aromatic diamine and stir for 2 h to obtain a mixed solution. Add phthalic anhydride to the mixed solution, stir and react for 5 h, then add toluene, raise the temperature to 120 °C, and reflux and react for 1 h at 120 °C to obtain a polyimide solution. After cooling the polyimide solution to room temperature, drop it into distilled water, carry out precipitation for 1 h and then filter, and finally dry it at 140 °C to obtain polyimide resin;

[0072] The molar ratio of the aromatic dianhydride to the aromatic diamine is 0.9:1; the molar ratio of the aromatic diamine to phthalic anhydride is 1:0.2; and the total molar amount of the acid anhydride functional groups of the aromatic dianhydride and phthalic anhydride is equal to the molar amount of the amino functional groups of the aromatic diamine; the mass ratio of N,N-dimethylacetamide to toluene is 1:0.2; the total mass ratio of N,N-dimethylacetamide and toluene to the total mass of phthalic anhydride, aromatic dianhydride and aromatic diamine is 2:1;

[0073] The aromatic dianhydride is

[0074] The aromatic diamine is

[0075] II. Weigh 100 parts of polyimide resin, 30 parts of polyfunctional compound, 5 parts of salt-forming compound and 200 parts of solvent by weight. At a temperature of 100 °C and under stirring conditions, stir 100 parts of polyimide resin, 30 parts of polyfunctional compound, 5 parts of salt-forming compound and 200 parts of solvent for 2 h to obtain an adhesive.

[0076] Example 2: The difference between this example and Example 1 is that: the amount of the salt-forming compound is 10 parts. Others are the same as in Example 1.

[0077] Example 3: The difference between this example and Example 1 is that: the amount of the polyfunctional compound is 20 parts. Others are the same as in Example 1.

[0078] Example 4: The difference between this example and Example 1 is that: the aromatic dianhydride is The Ar1 is -. Others are the same as in Example 1.

[0079] Example 5: The difference between this example and Example 1 is that: the solvent is N,N-dimethylacetamide. Others are the same as in Example 1.

[0080] Example 6: The difference between this example and Example 1 is that: the amount of the polyfunctional compound is 40 parts. Others are the same as in Example 1.

[0081] Example 7: The difference between this example and Example 1 is that: the polyfunctional compound is epoxycyclohexyl-caged polyhedral oligomeric silsesquioxane. Others are the same as in Example 1.

[0082] Example 8: The difference between this example and Example 1 is that: the salt-forming compound is octadecyl dimethyl tertiary amine. Others are the same as in Example 1.

[0083] Comparative Experiment 1: The difference between this example and Example 1 is that: the salt-forming compound is not added. Others are the same as in Example 1.

[0084] Comparative Experiment 2: The difference between this example and Example 1 is that: the polyfunctional compound is not added. Others are the same as in Example 1.

[0085] Comparative Experiment 3: The difference between this example and Example 1 is that: the polyfunctional compound is tetrafunctional epoxy AG80. Others are the same as in Example 1.

[0086] Comparative Experiment 4: The difference between this example and Example 1 is that: the amount of the salt-forming compound is 1 part. Others are the same as in Example 1.

[0087] Place the polyimide adhesives prepared in Examples 1 to 8 and Comparative Experiments 1 to 4 on the polyimide honeycomb (a high-temperature resistant polyimide honeycomb produced by Suzhou Fanglei Honeycomb Co., with a surface density of 80 g / cm 2) and the panel (titanium alloy) are bonded. The curing process is as follows: First, heat at a temperature of 80 °C and a pressure of 0.2 MPa for 1 h, then heat at a temperature of 150 °C and a pressure of 0.2 MPa for 1 h, and then heat at a temperature of 300 °C and a pressure of 0.2 MPa for 4 h to obtain a polyimide honeycomb sandwich structure. The polyimide honeycomb sandwich structure was subjected to flatwise compression strength testing, flatwise tensile testing, and honeycomb adhesive bond climb height measurement (as shown in Table 1). The test conditions for each property refer to the following standards (methods):

[0088] 1. Flatwise compression test: Use GJB 130.5-1986 to test the flatwise compression performance test method of the polyimide honeycomb sandwich structure. The flatwise compression strength at room temperature after high and low temperature cycling is specifically tested by heating and cooling rates of 50 °C / min, cycling the temperature from -55 °C to 250 °C 1000 times, and then testing the flatwise compression performance at room temperature.

[0089] 2. Flatwise tensile test: Use GJB 130.4-1986 to test the flatwise tensile test method of the polyimide honeycomb sandwich structure.

[0090] 3. Contact angle measurement: Use a contact angle measuring instrument to measure the water contact angle on the surface of the adhesive coating.

[0091] Table 1

[0092]

[0093]

[0094] Figure 1 It is a physical diagram of the honeycomb after room temperature flatwise tensile of the polyimide honeycomb sandwich structure bonded with polyimide adhesive. a is Comparative Experiment 1, and b is Example 1. As can be seen from the figure, the adhesive layer debonded after flatwise tensile in Comparative Experiment 1; the honeycomb was damaged after flatwise tensile in Example 1.

[0095] Figure 2 It is a physical diagram of the honeycomb adhesive bond climb in the polyimide honeycomb sandwich structure bonded with the polyimide adhesive prepared in Example 1. The frame is the climb height of the adhesive layer. As can be seen from the figure, the adhesive climbed at the bottom of the honeycomb during the curing process, forming more stacking effects and areas, and improving the bonding strength.

[0096] Figure 3 It is the infrared spectrum of the polyimide resin prepared in Example 1; as can be seen from the figure, from 1780 cm -1 and 1720 cm -1 There are carbonyl symmetric absorption peaks, proving that imidization is complete. Through 1300 cm -1 ~1400 cm -1The left and right absorption peaks prove the existence of C-F.

Claims

1. A polyimide adhesive for bonding polyimide honeycomb, characterized in that It is made of 100 parts by weight of polyimide resin, 20 to 50 parts of polyfunctional compound, 2 to 15 parts of salt-forming compound and 100 to 200 parts of solvent; The polyfunctional compound is a POSS compound with a functionality of 6 to 10; The salt-forming compound is one or a mixture of triethylamine, octadecyl dimethyl tertiary amine and dodecyl dimethyl tertiary amine; The structural general formula of the polyimide resin is: ； The n is 9 to 19; The described Ar1 is , , , or ; The aforementioned Ar2 is .

2. The polyimide adhesive for bonding polyimide honeycomb according to claim 1, characterized in that The polyfunctional compound is octa(aminophenyl)-T8-silsesquioxane or epoxycyclohexyl-cage polyhedral oligomeric silsesquioxane.

3. The polyimide adhesive for bonding polyimide honeycomb according to claim 1, characterized in that The solvent is an amide polar solvent.

4. The polyimide adhesive for bonding polyimide honeycomb according to claim 3, characterized in that The solvent is N,N-dimethylformamide or N,N-dimethylacetamide.

5. The preparation method of a polyimide adhesive for bonding polyimide honeycomb according to claim 1, characterized in that It is carried out according to the following steps: I. Under a nitrogen atmosphere, add aromatic dianhydride to N,N-dimethylacetamide and stir, then add aromatic diamine and stir to obtain a mixed solution. Add phthalic anhydride to the mixed solution and stir to react, then add toluene, heat up to 120°C to 130°C, and under the condition of 120°C to 130°C, reflux and react for 1h to 4h to obtain a polyimide solution. After cooling the polyimide solution to room temperature, precipitate, filter and dry to obtain polyimide resin; The molar ratio of the aromatic dianhydride to the aromatic diamine is (0.9 to 0.95):1; the molar ratio of the aromatic diamine to phthalic anhydride is 1:(0.1 to 0.2); and the total molar amount of the acid anhydride functional groups of the aromatic dianhydride and phthalic anhydride is equal to the molar amount of the amino functional groups of the aromatic diamine; The aromatic dianhydride is , , , or ; The aromatic diamine described is ; II. Weigh 100 parts by weight of polyimide resin, 20 to 50 parts of polyfunctional compound, 2 to 15 parts of salt-forming compound and 100 to 200 parts of solvent. Under the conditions of a temperature of 80°C to 100°C and stirring, stir 100 parts by weight of polyimide resin, 20 to 50 parts of polyfunctional compound, 2 to 15 parts of salt-forming compound and 100 to 200 parts of solvent for 1h to 4h to obtain an adhesive.

6. The preparation method of a polyimide adhesive for bonding polyimide honeycomb according to claim 5, characterized in that In step I, the mass ratio of N,N-dimethylacetamide to toluene is 1:(0.2 to 0.5).

7. The preparation method of a polyimide adhesive for bonding polyimide honeycomb according to claim 5, characterized in that In step I, the total mass ratio of N,N-dimethylacetamide and toluene to the total mass of phthalic anhydride, aromatic dianhydride and aromatic diamine is (1 to 3):

1.

8. The preparation method of a polyimide adhesive for bonding polyimide honeycomb according to claim 5, characterized in that In step I, under a nitrogen atmosphere, add aromatic dianhydride to N,N-dimethylacetamide and stir for 1h to 2h, then add aromatic diamine and stir for 1h to 5h to obtain a mixed solution. Add phthalic anhydride to the mixed solution and stir to react for 1h to 5h.

9. The preparation method of a polyimide adhesive for bonding polyimide honeycomb according to claim 5, characterized in that In step I, after cooling the polyimide solution to room temperature, drop it into distilled water, precipitate for 1h to 2h and then filter, and finally dry it under the condition of a temperature of 130°C to 140°C.

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