Preparation method and application of polyimide material with hierarchical pore structure

Abstract

The invention belongs to the technical field of high polymer materials, and relates to a preparation method and application of a polyimide material with a hierarchical pore structure, and the preparation method comprises the following steps: firstly carrying out esterification reaction on aromatic dianhydride and alcohol, then mixing with aromatic diamine, and sequentially carrying out rotary evaporation and heating to obtain a polyimide foaming agent; and mixing the molding powder with a polyimide foaming agent, performing hot pressing, and sintering to obtain the polyimide material with the hierarchical pore structure. Compared with the prior art, the controllable preparation of the porous polyimide material with the hierarchical pore structure is realized according to the relationship between the gas expansion pore-forming process and the alcohol controllable release gasification pore-forming process and the performance of the multi-component matrix resin. The method is high in pore-forming efficiency, low in equipment requirement and easy to implement, and the obtained porous polyimide has extremely wide pore size distribution while maintaining relatively high mechanical strength, and can be suitable for a use scene at a high rotating speed.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and relates to a preparation method and application of a polyimide material with a multi-level pore structure, and in particular to a preparation method of a polyimide material with a multi-level pore structure and application in a high-speed bearing retainer. Background Art

[0002] Polyimide refers to a class of polymers containing imide rings on the main chain, which have good mechanical properties and thermal stability. The YS20 polyimide material of Shanghai Plastics Research Institute Co., Ltd. is an ether anhydride type polyimide, the monomers of which are diphenyl ether tetracarboxylic dianhydride (ODPA) and diaminodiphenyl ether (ODA), which has the advantages of high tensile strength, low friction coefficient, and wear resistance.

[0003] YS20 molding powder is a common raw material for preparing porous bearing cages. Luoyang Bearing Research Institute Co., Ltd. uses YS20 molding powder as the material matrix in patent CN 112080146 A, blends polytetrafluoroethylene and molybdenum disulfide into it, and prepares porous polyimide blanks through molding and sintering. It has the comprehensive advantages of high mechanical strength, wear resistance, self-lubrication, high and low temperature resistance, and is suitable for use as ultra-low temperature high-speed bearing self-lubricating cages. On this basis, in order to improve the performance of the material at high temperatures, Luoyang Bearing Research Institute Co., Ltd. introduced isophthalic polyimide molding powder and thermal conductive lubricating materials into YS20 molding powder in patent CN 103756313 B, and prepared a porous polyimide material with high high-temperature tensile strength and heat resistance while maintaining tribological properties.

[0004] However, most porous polyimide materials currently have a single pore structure with an average pore size of about 1.0 μm. When the bearing cage prepared therefrom is used at a speed of more than 3000 rpm, the lubricating oil in the porous structure will be thrown out from the inside in a short time, which greatly reduces the service life of the bearing cage. In patent CN113510891 A, the Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, used rigid aromatic diamines, flexible aromatic diamines and aromatic dibasic acid anhydrides for copolymerization to obtain molding powder, and prepared a two-stage porous polyimide material by isostatic pressing, which can realize intelligent oil-containing and oil-discharging regulation according to different rotation speeds. However, the molding powder synthesis process in this patent is complicated, and the sewage treatment involved in the water washing process in industrial production will greatly increase its production cost, and the isostatic pressing equipment is expensive and not easy to implement industrially. Therefore, it is urgent to develop a method that can prepare a porous polyimide material with a two-stage / multi-stage pore structure and is inexpensive and easy to implement. Summary of the invention

[0005] The purpose of the present invention is to provide a preparation method and application of a polyimide material with a multi-level pore structure. In the preparation of polyimide foam, dianhydride is esterified in alcohol and alcohol is released in a controlled manner during heating to achieve the purpose of foaming and forming pores. This method is also of reference significance for porous polyimide materials with a two-level / multi-level pore structure. The polyimide material prepared by the present invention has the advantages of good mechanical properties and extremely wide pore size distribution, can be used in high-speed rotation scenarios, has low production equipment requirements, and is easy to implement.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A first aspect of the present invention provides a method for preparing a polyimide material having a multi-level pore structure, comprising the following steps:

[0008] S1: esterifying an aromatic dianhydride with an alcohol, mixing the mixture with an aromatic diamine, and then subjecting the mixture to rotary evaporation and heating to obtain a polyimide foaming agent;

[0009] S2: The molding powder is mixed with a polyimide type foaming agent, hot pressed, and sintered to obtain a polyimide material with a multi-level pore structure.

[0010] Furthermore, in step S1, the aromatic dianhydride is selected from one of 4,4'-biphenyl ether dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride or 4,4'-(hexafluoroisopropylene) diphthalic anhydride.

[0011] Furthermore, in step S1, the alcohol is selected from one of methanol, ethanol or propanol, and the amount used is not less than the minimum amount required for sufficient esterification reaction with the aromatic dianhydride.

[0012] Furthermore, in step S1, the mass ratio of the aromatic dianhydride to the alcohol is 60-90:500-600.

[0013] Furthermore, in step S1, after the reaction product mixture of the esterification reaction is mixed with the aromatic diamine, the solid content of the obtained mixture is 15-40%.

[0014] Furthermore, in step S1, in the esterification reaction, the reaction temperature is 80°C.

[0015] Furthermore, in step S1, the aromatic diamine is selected from one of m-phenylenediamine, 4,4'-biphenyl ether diamine, 3,4'-biphenyl ether diamine, 3-amino-6-(4-aminophenoxy)biphenyl or 2,2'-bis(trifluoromethyl)diaminobiphenyl.

[0016] Furthermore, in step S1, the molar ratio of the aromatic diamine to the aromatic dianhydride is 0.90 to 1:1.

[0017] Furthermore, in step S1, during the rotary evaporation, the rotary evaporation temperature is 60-80° C., which is used to remove the alcohol solvent.

[0018] Furthermore, in step S1, during the heating, the heating temperature is 160-280° C., and the insulation time is 4-12 hours.

[0019] Furthermore, in step S2, the mixing includes: adding molding powder and polyimide foaming agent into a mixer according to a prescribed ratio, and mixing to obtain a porous polyimide molding powder premix.

[0020] Furthermore, in step S2, during the mixing, the mixing speed is 800 to 1500 rpm, the mixing times are 3 to 10 times, and the mixing time for each time is 1 to 3 minutes.

[0021] Furthermore, in step S2, after each mixing, the obtained mixture is observed using an optical microscope at 50 times. When it is observed that the molding powder has a uniform color without abnormal spots or color differences, the mixing is completed to obtain a porous polyimide molding powder premix.

[0022] Furthermore, in step S2, the molding powder is a mixture of at least one of polytetrafluoroethylene molding powder and molybdenum disulfide and YS20 molding powder.

[0023] Furthermore, in step S2, when the molding powder includes polytetrafluoroethylene molding powder and molybdenum disulfide, the mass ratio of the YS20 molding powder, the polyimide foaming agent, the polytetrafluoroethylene molding powder and / or the molybdenum disulfide is 65-90:1-5:5-35.

[0024] Furthermore, in step S2, during the mixing, the particle size of each mixed material does not exceed 200 mesh.

[0025] Furthermore, in step S2, the hot pressing includes: adding the porous polyimide molding powder premix into the mold and ensuring that it is densely stacked, loading it into the molding press and heating it to the insulation temperature according to the program to apply pressure, and maintaining the temperature and pressure, and cooling and demolding after the insulation is completed.

[0026] Furthermore, in step S2, during the hot pressing, the hot pressing temperature is 150-200°C, and the hot pressing pressure is 300-700 kg / cm 2 , the hot pressing time is 5 to 50 minutes.

[0027] Furthermore, in step S2, during the hot pressing, the heating rate is 2-6°C / min.

[0028] Furthermore, in step S2, after the hot pressing, air cooling is adopted to reduce the temperature, and the mold is removed after the temperature is below 50°C.

[0029] Furthermore, in step S2, during the sintering, the sintering temperature is 240-300° C., the sintering time is 60-240 min, and the sintering atmosphere is nitrogen or an inert gas.

[0030] Furthermore, the inert gas is selected from argon or helium.

[0031] Furthermore, in step S2, during the sintering, the heating rate is 0.2-1.0°C / min.

[0032] Furthermore, in step S2, the sintering includes: placing the porous polyimide molded blank in a sintering furnace, heating it to a holding temperature under an inert gas atmosphere, then cooling it along with the furnace, and taking it out of the furnace when the temperature drops below 50°C.

[0033] The polyimide material prepared by the invention has the advantages of good mechanical properties and extremely wide pore size distribution, a ring tensile strength of 15-90 MPa, a porosity of 5-30%, a pore size distribution range of 0.02-3.00 μm, and an average pore size of 0.1-1.0 μm.

[0034] A second aspect of the present invention provides an application of a polyimide material having a multi-level pore structure, including using the polyimide material to prepare a bearing retainer.

[0035] Compared with the prior art, the present invention has the following characteristics:

[0036] The present invention provides a method for preparing a porous polyimide material with a multi-level pore structure. The method uses molding powder (YS20) as a main structural raw material, and adds a small amount of polyimide type foaming agent therein, and prepares the porous polyimide material with a multi-level pore structure through low-temperature compression molding and high-temperature program temperature-controlled free sintering.

[0037] The present invention realizes the controllable preparation of porous polyimide materials with multi-level pore structures based on the relationship between gas expansion pore-forming and alcohol controlled release gasification pore-forming processes and the performance of multi-component matrix resins. The YS20 molding powder used therein has stable performance and low price. The molding equipment used is low in price and easy to purchase compared with similar equipment such as isostatic pressing. Free sintering avoids the use of complex limiting tooling and sealed packaging, and is easy to implement industrially. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is an adsorption-desorption curve diagram of a porous polyimide material with a multi-level pore structure prepared in Example 1.

[0039] Figure 2 This is a pore size distribution curve diagram of a porous polyimide material with a multi-level pore structure prepared in Example 1.

[0040] Figure 3 This is an adsorption-desorption curve diagram of a porous polyimide material with a multi-level pore structure prepared in Example 2.

[0041] Figure 4 This is a pore size distribution curve diagram of a porous polyimide material with a multi-level pore structure prepared in Example 2. DETAILED DESCRIPTION

[0042] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0043] The following are more detailed implementation cases, which further illustrate the technical solutions of the present invention and the technical effects that can be obtained.

[0044] In the following examples, unless otherwise specified, raw materials, reagents or processing techniques are all conventional commercial products or conventional processing techniques in the art.

[0045] In the following examples, polytetrafluoroethylene molding powder was purchased from Shanghai Huayi Sanaifu New Materials Co., Ltd. with a brand name of DF102.

[0046] Example 1

[0047] A porous polyimide material with a multi-level pore structure, the preparation method of which comprises the following steps:

[0048] S1: Add 62.00 g of 4,4'-biphenyl ether dianhydride to 500 g of ethanol, heat to 80°C and reflux until the solvent is clear, cool to room temperature, add 38.05 g of 4,4'-biphenyl ether diamine, evaporate the solvent at 60°C using a rotary evaporator, put the obtained solid into an oven, keep it warm at 250°C for 8 hours, take out the crushed solid, and pass it through 200 mesh to obtain a polyimide type foaming agent.

[0049] S2: Take 160g of YS20 molding powder, 36g of polytetrafluoroethylene molding powder and 4g of polyimide foaming agent respectively, which have been sieved through a 200-mesh sieve, add them to a mixer, set the speed to 1000rpm, mix 5 times, and mix for 3 minutes each time to obtain a porous polyimide molding powder premix. Put the molding powder premix into the mold, tap the mold to make the powder dense. Then put it into the molding press, set the heating rate to 3℃ / min and heat it to 170℃, press it at 400kg / cm 2, keep the temperature and pressure for 50 minutes. After the program is completed, blow the air to cool down, and remove the mold at 42°C to obtain a porous polyimide molded blank. Place the porous polyimide molded blank in a sintering furnace and protect it with nitrogen. Set the heating rate to 0.3°C / min, the insulation temperature to 285°C, and the insulation time to 120 minutes. After the program is completed, cool down with the furnace and remove it at 50°C to obtain a porous polyimide material with a multi-level pore structure.

[0050] The blank obtained above was machined to prepare a specimen for testing. The specimen preparation was referred to GJB 9288-2017. The test results obtained were: ring tensile strength of 58MPa, porosity of 22%, average pore size of 0.138μm, and the adsorption-desorption curve was as shown in the figure. Figure 1 As shown, the pore size distribution curve is as follows Figure 2 shown.

[0051] Example 2

[0052] A porous polyimide material with a multi-level pore structure, the preparation method of which comprises the following steps:

[0053] S1: Add 64.45 g of 3,3',4,4'-benzophenonetetracarboxylic dianhydride to 600 g of ethanol, heat to 80°C and reflux until the solvent is clear, cool to room temperature, add 38.05 g of 4,4'-biphenyl ether diamine, evaporate the solvent at 60°C using a rotary evaporator, put the obtained solid into an oven, keep it warm at 280°C for 6 hours, take out the crushed solid, and pass it through 200 mesh to obtain a polyimide type foaming agent.

[0054] S2: Take 170g of YS20 molding powder, 26g of polytetrafluoroethylene molding powder, 2g of molybdenum disulfide and 2g of polyimide foaming agent through a 200-mesh sieve, add them to a mixer, set the speed to 1100rpm, mix 7 times, and mix for 1 minute each time to obtain a porous polyimide molding powder premix. Put the molding powder premix into the mold, tap the mold to make the powder dense. Then put it into the molding press, set the heating rate to 3℃ / min and heat it to 200℃, press it at 650kg / cm 2 , heat preservation and pressure preservation for 40 minutes. After the program is completed, the temperature is blown down, and the mold is removed at 36°C to obtain a porous polyimide molded blank. The porous polyimide molded blank is placed in a sintering furnace and protected by nitrogen. The heating rate is set to 0.6°C / min, the insulation temperature is 300°C, and the insulation time is 90 minutes. After the program is completed, the temperature is lowered with the furnace and removed from the furnace at 50°C to obtain a porous polyimide material with a multi-level pore structure.

[0055] The blank obtained above was machined to prepare a specimen for testing. The specimen preparation was referred to GJB 9288-2017. The test results obtained were: the ring tensile strength was 71MPa, the porosity was 19%, the average pore size was 0.081μm, and the adsorption-desorption curve was as shown in the figure. Figure 3As shown, the pore size distribution curve is as follows Figure 4 shown.

[0056] Example 3

[0057] A porous polyimide material with a multi-level pore structure, the preparation method of which comprises the following steps:

[0058] S1: Add 62.00 g of 4,4'-biphenyl ether dianhydride to 600 g of propanol, heat to 80°C and reflux until the solvent is clear, cool to room temperature, add 38.05 g of 4,4'-biphenyl ether diamine, evaporate the solvent at 60°C using a rotary evaporator, put the obtained solid into an oven, keep it warm at 230°C for 10 hours, take out the crushed solid, and pass it through 200 mesh to obtain a polyimide type foaming agent.

[0059] S2: Take 185g of YS20 molding powder, 8g of polytetrafluoroethylene molding powder, 4g of molybdenum disulfide and 3g of polyimide foaming agent through a 200-mesh sieve, add them to a mixer, set the speed to 900rpm, mix 5 times, and mix for 2 minutes each time to obtain a porous polyimide molding powder premix. Put the molding powder premix into the mold, tap the mold to make the powder dense. Then put it into the molding press, set the heating rate to 2℃ / min to 200℃, and press at 350kg / cm 2 , heat preservation and pressure preservation for 40 minutes. After the program is completed, the temperature is blown down, and the mold is removed at 47°C to obtain a porous polyimide molded blank. The porous polyimide molded blank is placed in a sintering furnace and protected by nitrogen. The heating rate is set to 0.6°C / min, the insulation temperature is 300°C, and the insulation time is 180 minutes. After the program is completed, the temperature is lowered with the furnace and removed from the furnace at 50°C to obtain a porous polyimide material with a multi-level pore structure.

[0060] The blank obtained above was machined to prepare a specimen for testing. The specimen preparation referred to GJB 9288-2017. The test results obtained were: ring tensile strength of 88 MPa, porosity of 23%, and average pore size of 0.253 μm.

[0061] Example 4

[0062] A porous polyimide material with a multi-level pore structure, the preparation method of which comprises the following steps:

[0063] S1: Add 88.85 g of 2,2'-bis(trifluoromethyl)diaminobiphenyl to 600 g of methanol, heat to 80°C and reflux until the solvent is clear, cool to room temperature, add 20.55 g of m-phenylenediamine, evaporate the solvent at 60°C using a rotary evaporator, put the obtained solid into an oven, keep it warm at 200°C for 10 hours, take out the crushed solid, and pass it through a 200 mesh to obtain a polyimide type foaming agent.

[0064] S2: Take 140g of YS20 molding powder, 55g of polytetrafluoroethylene molding powder and 5g of polyimide foaming agent respectively, which have been sieved through a 200-mesh sieve, add them to a mixer, set the speed to 1500rpm, mix 8 times, and mix for 3 minutes each time to obtain a porous polyimide molding powder premix. Put the molding powder premix into the mold, tap the mold to make the powder dense. Then put it into the molding press, set the heating rate to 5℃ / min and heat it to 150℃, and press it at 550kg / cm 2 , heat preservation and pressure preservation for 25 minutes. After the program is completed, the temperature is blown down, and the mold is removed at 50°C to obtain a porous polyimide molded blank. The porous polyimide molded blank is placed in a sintering furnace and protected by nitrogen. The heating rate is set to 0.3°C / min, the insulation temperature is 265°C, and the insulation time is 150 minutes. After the program is completed, the temperature is lowered with the furnace and removed from the furnace at 50°C to obtain a porous polyimide material with a multi-level pore structure.

[0065] The blank obtained above was machined to prepare a specimen for testing. The specimen preparation referred to GJB 9288-2017. The test results obtained were: ring tensile strength of 39 MPa, porosity of 13%, and average pore size of 0.046 μm.

[0066] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for preparing a polyimide material having a multi-level pore structure, characterized in that: The following steps are involved: S1: esterifying an aromatic dianhydride with an alcohol, mixing the mixture with an aromatic diamine, and then subjecting the mixture to rotary evaporation and heating to obtain a polyimide foaming agent; S2: Mixing with a polyimide foaming agent, hot pressing, and sintering to obtain a polyimide material with a multi-level pore structure.

2. The method for preparing a polyimide material having a multi-level pore structure according to claim 1, characterized in that: In step S1, the aromatic dianhydride is selected from one of 4,4'-biphenyl ether dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride or 4,4'-(hexafluoroisopropylene) diphthalic anhydride; The alcohol is selected from one of methanol, ethanol or propanol; In the esterification reaction, the reaction temperature is 80°C.

3. The method for preparing a polyimide material having a multi-level pore structure according to claim 1, characterized in that: In step S1, the aromatic diamine is selected from one of m-phenylenediamine, 4,4'-biphenyl ether diamine, 3,4'-biphenyl ether diamine, 3-amino-6-(4-aminophenoxy)biphenyl or 2,2'-bis(trifluoromethyl)diaminobiphenyl; The molar ratio of the aromatic diamine to the aromatic dianhydride is 0.95:

1.

4. The method for preparing a polyimide material having a multi-level pore structure according to claim 1, characterized in that: In step S1, during the rotary evaporation, the rotary evaporation temperature is 60-80°C.

5. The method for preparing a polyimide material having a multi-level pore structure according to claim 1, characterized in that: In step S1, during the heating, the heating temperature is 160-280° C. and the insulation time is 4-12 hours.

6. The method for preparing a polyimide material having a multi-level pore structure according to claim 1, characterized in that: In step S2, the molding powder is a mixture of at least one of polytetrafluoroethylene molding powder and molybdenum disulfide and YS20 molding powder; The mass ratio of the YS20 molding powder, the polyimide foaming agent, the polytetrafluoroethylene molding powder and / or molybdenum disulfide is 65-90:1-5:5-35.

7. The method for preparing a polyimide material having a multi-level pore structure according to claim 6, characterized in that: In step S2, when the molding powder includes polytetrafluoroethylene molding powder and molybdenum disulfide, the mass content of molybdenum disulfide in YS20 molding powder, polyimide foaming agent, polytetrafluoroethylene molding powder and molybdenum disulfide is not higher than 5%.

8. The method for preparing a polyimide material having a multi-level pore structure according to claim 1, characterized in that: In step S2, the hot pressing temperature is 150-200°C and the hot pressing pressure is 300-700kg / cm 2 , the hot pressing time is 5 to 50 minutes.

9. The method for preparing a polyimide material having a multi-level pore structure according to claim 1, characterized in that: In step S2, during the sintering, the sintering temperature is 240-300° C. and the sintering time is 60-240 min.

10. An application of the polyimide material with a multi-level pore structure as claimed in any one of claims 1 to 9, characterized in that: The polyimide material is used to prepare a bearing retainer.

Images