Thermoplastic polyimide and supporting ring prepared from same

Abstract

The present invention relates to the field of engineering machinery, specifically relates to the field of design and manufacturing of hydraulic oil cylinders, and particularly relates to a thermoplastic polyimide supporting ring and a preparation method therefor. By using a composite application technology of a nano nucleating agent and a two-dimensional transition metal sulfide, the present invention increases the crystallization speed of a polyimide supporting ring on the molecular structure level, shortens the injection molding time, and optimizes the molding effect; and on the macroscopic level, the wear resistance of polyimide is improved, and the service life is prolonged. Upon test verification, the polyimide supporting ring of the present invention has the effects of good forming quality, a high high-temperature compression strength, good wear resistance and a long service life.

Description

A thermoplastic polyimide and a supporting ring prepared therefrom Technical Field

[0001] The present invention relates to the fields of polymer materials and engineering machinery, and in particular to a modified polyimide, a support ring prepared therefrom, and a method for preparing the support ring. Background Art

[0002] A hydraulic cylinder (hydraulic oil cylinder) is an energy conversion device that converts hydraulic energy into mechanical energy and serves as the actuator in a hydraulic transmission system. Due to its simple structure, high reliability, and smooth transmission, it is widely used in construction machinery. Support rings, also known as guide rings, are typically installed between the cylinder piston seal and the piston rod seal, as shown in Figure 1.

[0003] The primary function of a cylinder support ring is to prevent friction and wear between the piston and cylinder barrel, or between the piston rod and the inner wall of the guide sleeve, during movement. Since the cylinder is often subjected to radial loads during operation, the support ring is subjected to repeated radial pressure, which can cause the support material to creep, melt, extrude, or break, ultimately leading to cylinder failure. Therefore, there is an urgent need to develop a high-load, wear-resistant, and high-temperature resistant cylinder support ring.

[0004] Conventional support rings on the market are mostly made of phenolic cloth, polyoxymethylene composite materials, or modified nylon. Phenolic cloth has extremely high compressive strength at room temperature, but its operating temperature is below 150°C. Polyoxymethylene and nylon have slightly higher temperature resistance, but their wear and compressive properties are poor at high temperatures, and neither can meet the high-temperature, high-load, and high-wear requirements.

[0005] Summary of the Invention

[0006] One of the purposes of the present invention is to provide a cylinder support ring that can meet high temperature, high load and high wear resistance working conditions.

[0007] The present invention uses polyimide as the material for the supporting ring. Polyimide (PI) refers to a class of polymers containing an imide ring (-(C=O)-N-(C=O)-) in the main chain. It can be obtained by polymerizing dianhydrides and diamines. Based on the structure of the repeating unit, it can be divided into aliphatic polyimides and aromatic polyimides. Polyimides can be divided into thermoplastic polyimides and thermosetting polyimides based on their reprocessability. Polyimides can withstand temperatures exceeding 400°C and have a long-term operating temperature range of -200 to 300°C, showing excellent high-temperature resistance. However, their wear resistance and high-temperature compressive strength are insufficient and require modification.

[0008] Polyimide has high melt viscosity and is difficult to process. When a large amount of hard reinforcing phase and solid lubricating phase are added, the plastic processing performance of the material deteriorates. Therefore, existing polyimide materials mostly use processing methods similar to thermosetting polyimide. By adding graphene oxide, carbon nanotubes or polytetrafluoroethylene, the wear resistance and load-bearing performance of polyimide can be improved to a certain extent. The thermosetting processing method has simple molds and does not require high processing equipment. However, the processing efficiency is low, turning wastes raw materials, and it cannot be produced and applied in large quantities. In comparison, the thermoplastic processing method is more flexible, more efficient, more precise and complex, and can achieve one-time molding, but it has higher requirements on the processing performance of the material.

[0009] Currently, domestically produced thermoplastic polyimide products generally suffer from poor thermoplastic processing properties. This is especially true when various additives are added to the resin, making it difficult to process and easily leading to surface defects such as burrs and smears. Consequently, the primary challenge hindering the application of thermoplastic polyimide support rings is the selection of modifying agents and the minimum amount of components added to ensure both processability and mechanical properties.

[0010] In order to solve the above problems, the present invention adopts a blend of nano-polyimide powder and nano-tungsten disulfide powder as a nano-composite nucleating agent. Tungsten disulfide, with the molecular formula WS2, is a compound of tungsten and sulfur. It is a transition metal sulfide with a gray-black crystal or powder with a metallic luster, belonging to the hexagonal crystal system. The existing technology lacks effective cases of tungsten disulfide filling and modifying polyimide. At the molecular structure level, nano-scale tungsten disulfide can be used as a polyimide nucleating agent to enable polyimide to rapidly crystallize and nucleate, thereby increasing the glass transition temperature and optimizing the molding effect; at the macro level, due to the lamellar structural characteristics of tungsten disulfide and the characteristics of decreasing friction coefficient with increasing load, it is very suitable for use in high-load, high-frequency, and instantaneous high-temperature environments such as hydraulic cylinders, and is an ideal auxiliary agent for thermoplastic polyimide modification.

[0011] Therefore, the present application provides the following invention:

[0012] In one aspect, the present application provides a modified polyimide, wherein the modified polyimide is prepared from a composition comprising the following components:

[0013] Polyimide, a nanocomposite nucleating agent, a wear-resistant lubricant and an antioxidant, wherein the nanocomposite nucleating agent is a blend of nano-polyimide powder and nano-tungsten disulfide powder with an organic surface treatment;

[0014] Among them, in parts by weight, polyimide is 90 to 94 parts, nanocomposite nucleating agent is 0.5 to 1.5 parts (for example, 0.8 parts), wear-resistant lubricant is 3 to 6 parts (for example, 4 or 5 parts), and antioxidant is 0.1 to 0.8 parts.

[0015] In certain embodiments, the polyimide is a thermoplastic polyimide. Depending on the structure of the organic aromatic tetracarboxylic dianhydride monomer used, the thermoplastic polyimide may include phthalic anhydride-type, ether anhydride-type, ketone anhydride-type, fluoroanhydride-type polyimide, etc. In certain embodiments, the thermoplastic polyimide is a multi-monomer copolymer. In certain embodiments, the number average molecular weight of the thermoplastic polyimide is 35,000 to 40,000. In certain embodiments, the polyimide is a domestically produced thermoplastic polyimide.

[0016] The present invention utilizes a nanocomposite nucleating agent, enabling the polyimide to maintain its original thermoplastic processability while significantly improving its wear resistance and load-bearing properties, while minimizing the additive loading. Furthermore, tungsten disulfide is an inorganic powder, and organic treatment can form an organic coating on the powder's surface, thereby firmly bonding it to the polyimide bulk.

[0017] In certain embodiments, the nanocomposite nucleating agent includes 70 to 100 parts (e.g., 70 to 75, 75 to 80, 80 to 85, 85 to 90, 90 to 95, or 95 to 100 parts) of nano-polyimide powder and 20 to 40 parts (e.g., 20 to 25, 25 to 30, 30 to 35, or 35 to 40 parts) of surface-organically treated nano-tungsten disulfide powder.

[0018] In some embodiments, the nano-polyimide powder is a nano-thermoplastic polyimide powder, which can be selected from the types of thermoplastic polyimides described above, such as multi-monomer copolymerized polyimide. In some embodiments, the number average molecular weight of the polyimide powder is 48,000 to 50,000.

[0019] In certain embodiments, the nanocomposite nucleating agent employed in the present invention is prepared by a method comprising the following steps:

[0020] (1) Weigh 70-100 parts of nano-polyimide powder and 20-40 parts of surface-organized tungsten disulfide powder for later use;

[0021] (2) The two powders are placed in a ball mill and subjected to ball milling treatment.

[0022] In certain embodiments, the purity of the nano-polyimide powder is 99.9-99.999% (eg, 99.99%).

[0023] In certain embodiments, the particle size of the nano-polyimide powder is 1 to 100 nanometers (eg, 1 to 10 nanometers, 10 to 20 nanometers, 20 to 50 nanometers, 50 to 80 nanometers, or 80 to 100 nanometers).

[0024] In certain embodiments, the purity of the nano-tungsten disulfide powder is 99.0-99.9%.

[0025] In certain embodiments, the particle size of the nano-tungsten disulfide powder is 1 to 100 nanometers (eg, 1 to 10 nanometers, 10 to 20 nanometers, 20 to 50 nanometers, 50 to 80 nanometers, or 80 to 100 nanometers).

[0026] In some embodiments, the mixed powder is ball-milled for 2 to 10 hours. In some embodiments, high-energy ball milling is used for the treatment.

[0027] In certain embodiments, the composite nucleating agent has an average particle size of 1 to 100 nm (eg, 1 to 10 nm, 10 to 20 nm, 20 to 50 nm, 50 to 80 nm, or 80 to 100 nm, such as 15 nm).

[0028] In certain embodiments, the surface organic treatment refers to treatment with C8-C22 alkyl chain fatty acids (eg, stearic acid) and C8-C22 alkyl chain fatty amines (eg, octadecylamine).

[0029] In certain embodiments, the organic treatment of the tungsten disulfide powder includes: mixing an organic solvent (such as chloroform) with the tungsten disulfide powder and heating it, adding C8-C22 alkyl chain fatty acids and C8-C22 alkyl chain fatty amines to the solution, and then adding an amidation dehydrating agent (such as N'N-dicyclohexylcarbodiimide) dropwise, performing solid-liquid separation after the reaction, and collecting the solid.

[0030] In certain embodiments, the organic treatment of the tungsten disulfide powder includes: taking 100 parts of tungsten disulfide powder, placing it in 1000 ml of chloroform, stirring and heating it to 70° C., sequentially adding 25 g of stearic acid and 30 g of octadecylamine to the solution, and then adding N'N-dicyclohexylcarbodiimide dropwise, reacting for 10 hours, separating the solid and the liquid, and collecting the solid.

[0031] Furthermore, the present invention adds a wear-resistant lubricant to the polyimide to improve the wear resistance of the support ring. In some embodiments, the wear-resistant lubricant is a micron tungsten disulfide powder with an organic surface treatment. The micron tungsten disulfide that has been organically treated can better bond with the matrix, is not easy to fall off the matrix, and can better exert good wear resistance. In some embodiments, the purity of the micron tungsten disulfide powder is 99.0-99.9%. In some embodiments, the particle size of the micron tungsten disulfide powder is 20-100 microns (for example, 20-40 microns, 40-60 microns, 60-80 microns or 80-100 microns). In some embodiments, the micron tungsten disulfide powder has been subjected to the organic treatment described above.

[0032] The present invention adds an antioxidant to the polyimide to improve the antioxidant properties of the support ring. In certain embodiments, the antioxidant used is a nitrogen-containing hindered phenolic antioxidant, such as Anti-1098, which is N,N'-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hexanediamine.

[0033] The modified polyimide of the present invention can be prepared by blending the above composition. In some embodiments, the modified polyimide of the present invention can be prepared by mixing the above composition in a high-speed mixer at high speed.

[0034] In one aspect, the present application also provides a method for preparing a support ring, comprising extruding and granulating the modified polyimide of the present invention and injection molding the granulated modified polyimide into a support ring.

[0035] In certain embodiments, the method comprises the steps of:

[0036] (1) Weighing polyimide, nanocomposite nucleating agent, wear-resistant lubricant and antioxidant according to a certain proportion for use, and placing polyimide and nanocomposite nucleating agent in an oven for drying;

[0037] (2) placing the raw materials in step (1) into a high-speed mixer and mixing them uniformly at high speed;

[0038] (3) placing the mixed material in step (2) into a twin-screw extruder for extrusion granulation;

[0039] (4) The granules in step (3) are added into an injection molding machine and injection molded into a supporting ring sample.

[0040] In certain embodiments, the high-speed mixing speed in step (2) is 1500-2000 rpm (eg, 1800 rpm) and the time is 1-3 h (eg, 2 h).

[0041] In certain embodiments, the melt extrusion temperature of the twin-screw extruder in step (3) is 345-385° C. (eg, 360° C., 365° C.), and the screw speed is 60-100 rpm (eg, 75 rpm).

[0042] In certain embodiments, the injection temperature of the injection molding machine in step (4) is 360-400°C (eg, 380°C, 385°C), and the mold temperature is 180-220°C (eg, 185°C).

[0043] In one aspect, the present application provides a support ring, which is prepared from the modified polyimide of the present invention or the method for preparing a support ring of the present invention.

[0044] In one aspect, the present application provides a hydraulic cylinder or a gas cylinder comprising the support ring of the present invention.

[0045] In one aspect, the present application provides a hydraulic system comprising the hydraulic cylinder of the present invention.

[0046] In one aspect, the present application provides a pneumatic system comprising the pneumatic cylinder of the present invention.

[0047] In one aspect, the present application provides a construction machine comprising the hydraulic system or pneumatic system of the present invention.

[0048] Definition of terms

[0049] Support ring - also called guide ring or guide support ring, is a part used on the piston or guide sleeve of a hydraulic cylinder or air cylinder to support the movement of the piston or piston rod. It can prevent the piston or piston rod from direct contact and friction with the cylinder during movement, and protect the cylinder and the piston or piston rod from damage.

[0050] Advantageous Effects of the Invention

[0051] The polyimide cylinder support ring of this invention utilizes a nano-nucleating agent and two-dimensional transition metal sulfide composite technology to accelerate the crystallization rate of the polyimide support ring at the molecular level, shortening the injection molding time and optimizing the molding effect. At the macro level, it also improves the polyimide's wear resistance and extends its service life. Experiments have confirmed that the support ring of this invention offers advantages such as high molding quality, high high-temperature compressive strength, excellent wear resistance, and a long service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 is a schematic diagram of an exemplary oil cylinder structure, wherein the numerical symbols represent: 1. Guide ring 2. Piston 3. Cylinder barrel 4. Guide sleeve 5. Piston rod. DETAILED DESCRIPTION

[0053] The embodiments of the present invention will be described in detail below with reference to the examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present invention and should not be construed as limiting the scope of the invention. Where specific conditions are not specified in the examples, the methods were performed according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be obtained commercially.

[0054] Organic treatment of tungsten disulfide powder: Take 100 parts of tungsten disulfide powder, put it into 1000 ml of chloroform, stir and heat to 70 ° C, add 25 g of stearic acid and 30 g of octadecylamine to the solution in sequence, and then add N'N-dicyclohexylcarbodiimide dropwise. React for 10 hours, separate the solid and liquid, and collect the solid.

[0055] Preparation of nanocomposite nucleating agent:

[0056] (1) Weigh a certain amount of nano-polyimide powder (number average molecular weight 48,000-50,000) and surface-organized tungsten disulfide powder for later use;

[0057] (2) Place the two powders in a ball mill and subject them to high-energy ball milling for 2 to 10 hours.

[0058] The antioxidant used in the following examples and comparative examples is ANTI-1098.

[0059] Example 1:

[0060] Weigh 90 parts by weight of thermoplastic polyimide (phthalic anhydride type, number average molecular weight 35,000-40,000), 0.8 parts of nanocomposite nucleating agent (organized tungsten disulfide nanoparticles: polyimide powder mass ratio of 7:3), 4 parts of organically treated micronized tungsten disulfide powder, and 0.3 parts of antioxidant; wherein the average particle size of the composite nucleating agent is 15 nanometers, and the particle size of the tungsten disulfide powder is 20 microns;

[0061] Add the above raw materials into a high-speed mixer and mix them evenly at a speed of 1800 rpm for 2 hours;

[0062] The mixed material was added into a twin-screw extruder for extrusion and pelletization, with a melt extrusion temperature of 360°C and a screw speed of 75 rpm;

[0063] The extruded granules were placed in an injection molding machine and injection molded into supporting ring samples at an injection temperature of 380°C and a mold temperature of 185°C.

[0064] Example 2:

[0065] Weigh 94 parts of thermoplastic polyimide (phthalic anhydride type, number average molecular weight 35000-40000), 1.5 parts of nanocomposite nucleating agent (mass ratio of organically treated tungsten disulfide nanoparticles to polyimide powder is 7:3), 6 parts of organically treated micronized tungsten disulfide powder, and 0.8 parts of antioxidant according to weight;

[0066] Add the above raw materials into a high-speed mixer and mix them evenly at a speed of 2000 rpm for 3 hours;

[0067] The mixed material was added into a twin-screw extruder for extrusion and granulation, with a melt extrusion temperature of 365°C and a screw speed of 100 rpm;

[0068] The extruded granules were placed in an injection molding machine and injection molded into supporting ring samples at an injection temperature of 385°C and a mold temperature of 185°C.

[0069] Comparative Example 1:

[0070] Weigh 94 parts of thermoplastic polyimide (number average molecular weight 35,000-40,000) and 0.8 parts of antioxidant according to weight;

[0071] Add the above raw materials into a high-speed mixer and mix them evenly at a speed of 1500 rpm for 3 hours;

[0072] The mixed material was added into a twin-screw extruder for extrusion and granulation, with a melt extrusion temperature of 365°C and a screw speed of 100 rpm;

[0073] The extruded granules were placed in an injection molding machine and injection molded into supporting ring samples at an injection temperature of 385°C and a mold temperature of 185°C.

[0074] Comparative Example 2:

[0075] Weigh 90 parts by weight of thermoplastic polyimide (number average molecular weight 35,000-40,000), 4 parts of organically treated micronized tungsten disulfide powder, and 0.3 parts of antioxidant;

[0076] Add the above raw materials into a high-speed mixer and mix them evenly at a speed of 1800 rpm for 2 hours;

[0077] The mixed material was added into a twin-screw extruder for extrusion and pelletization, with a melt extrusion temperature of 360°C and a screw speed of 75 rpm;

[0078] The extruded granules were placed in an injection molding machine and injection molded into supporting ring samples at an injection temperature of 380°C and a mold temperature of 185°C.

[0079] Comparative Example 3:

[0080] Weigh 90 parts of thermoplastic polyimide (number average molecular weight 35,000-40,000), 0.8 parts of nano-polyimide powder, 4 parts of organically treated micronized tungsten disulfide powder, and 0.3 parts of antioxidant according to weight;

[0081] Add the above raw materials into a high-speed mixer and mix them evenly at a speed of 1800 rpm for 2 hours;

[0082] The mixed material was added into a twin-screw extruder for extrusion and pelletization, with a melt extrusion temperature of 360°C and a screw speed of 75 rpm;

[0083] The extruded granules were placed in an injection molding machine and injection molded into supporting ring samples at an injection temperature of 380°C and a mold temperature of 185°C.

[0084] Comparative Example 4:

[0085] Weigh 90 parts by weight of thermoplastic polyimide (number average molecular weight 35,000-40,000), 0.8 parts of nanocomposite nucleating agent (mass ratio of organically treated tungsten disulfide nanoparticles to polyimide powder is 7:3), 4 parts of unorganized micronized tungsten disulfide powder, and 0.3 parts of antioxidant;

[0086] Add the above raw materials into a high-speed mixer and mix them evenly at a speed of 1800 rpm for 2 hours;

[0087] The mixed material was added into a twin-screw extruder for extrusion and pelletization, with a melt extrusion temperature of 360°C and a screw speed of 75 rpm;

[0088] The extruded granules were placed in an injection molding machine and injection molded into supporting ring samples at an injection temperature of 380°C and a mold temperature of 185°C.

[0089] The supporting rings prepared in the above examples and comparative examples were subjected to performance tests, and the specific test results are shown in the following table.

[0090] Table 1 Performance test results of support rings prepared in Examples of the present invention and Comparative Examples

[0091] It can be seen from the above table that after the various materials in the embodiments of the present invention are injection molded, the performance of the support rings extremely well reflects the expected level of the materials, reflecting that the thermoplastic polyimide support rings prepared by the present invention meet the molding process and cylinder application requirements. The high yield rate of injection molded parts also well reflects that after injection molding, the density and texture of the parts are uniform, the surface is smooth, and there are no burrs or scratches. Compared with Examples 1 and 2, it can be seen that in Comparative Examples 1, 2, 3, and 4, the heat deformation temperature, glass transition temperature, and compressive strength at 150°C are all lower when nano-composite nucleating agents and micron-sized tungsten disulfide powder are not used at the same time, indicating that the nano-composite nucleating agents and micron-sized tungsten disulfide powder significantly improve the temperature resistance of polyimide. At the same time, it can be seen that the friction coefficient of the support ring in the embodiment of the present invention is significantly lower than that of the comparative example, and the final performance is that the service life far exceeds that of comparative examples 1, 2, 3, and 4.

[0092] It can be concluded from the data in the examples that the polyimide cylinder support ring prepared in the examples of the present invention has the advantages of high strength, outstanding wear resistance, high temperature resistance, low friction coefficient, etc. It can be applied to high wear-resistant, high temperature, and high load-bearing hydraulic cylinders, and can solve the shortcomings of the existing technology.

[0093] Although the specific embodiments of the present invention have been described in detail, those skilled in the art will understand that various modifications and variations can be made to the details based on all the teachings disclosed, and these changes are within the scope of protection of the present invention. The full scope of the present invention is given by the appended claims and any equivalents thereof.

Claims

1. A modified polyimide, wherein the modified polyimide is prepared from a composition comprising the following components: Polyimide, nanocomposite nucleating agent, wear-resistant lubricant and antioxidant, wherein the nanocomposite nucleating agent is a blend of nano-polyimide powder and nano-tungsten disulfide powder with surface organic treatment; in, In parts by weight, the polyimide is 90-94 parts, the nano-composite nucleating agent is 0.5-1.5 parts, the wear-resistant lubricant is 3-6 parts, and the antioxidant is 0.1-0.8 parts.

2. The modified polyimide of claim 1, having one or more of the following characteristics: (1) The polyimide is a thermoplastic polyimide; (2) The nanocomposite nucleating agent comprises 70 to 100 parts of nano polyimide powder and 20 to 40 parts of surface organically treated nano tungsten disulfide powder; (3) The nano polyimide powder is nano thermoplastic polyimide powder; (4) The average particle size of the nanocomposite nucleating agent is 1 to 100 nanometers.

3. The modified polyimide according to claim 1 or 2, wherein the nanocomposite nucleating agent is prepared by a method comprising the following steps: (1) Weigh 70-100 parts of nano-polyimide powder and 20-40 parts of tungsten disulfide powder with surface organic treatment for later use; (2) The two powders are placed in a ball mill and subjected to ball milling treatment.

4. The modified polyimide according to any one of claims 1 to 3, wherein the surface organic treatment refers to treatment with C8-C22 alkyl chain fatty acids (such as stearic acid) and C8-C22 alkyl chain fatty amines (such as octadecylamine); Preferably, the organic treatment comprises: An organic solvent (such as chloroform) is mixed with tungsten disulfide powder and heated, C8-C22 alkyl chain fatty acid and C8-C22 alkyl chain fatty amine are added to the solution, and then an amidation dehydrating agent (such as N'N-dicyclohexylcarbodiimide) is added dropwise. After the reaction, solid-liquid separation is performed and the solid is collected.

5. The modified polyimide according to any one of claims 1 to 4, wherein the wear-resistant lubricant is micronized tungsten disulfide powder with an organic surface treatment; Preferably, the particle size of the micron tungsten disulfide powder is 20 to 100 microns; Preferably, the micron tungsten disulfide powder is subjected to the organic treatment defined in claim 4.

6. The modified polyimide according to any one of claims 1 to 5, wherein the antioxidant is a nitrogen-containing hindered phenol antioxidant, such as Anti-1098.

7. The modified polyimide according to any one of claims 1 to 6, which is obtained by blending the composition defined in any one of claims 1 to 6.

8. A method for preparing a support ring, comprising extruding and granulating the modified polyimide according to any one of claims 1 to 7 and injection molding the modified polyimide into a support ring; Preferably, the method comprises the following steps: (1) Weighing polyimide, nanocomposite nucleating agent, wear-resistant lubricant and antioxidant according to a certain ratio for use, and putting polyimide and nanocomposite nucleating agent into an oven for drying; (2) placing the raw materials in step (1) into a high-speed mixer and mixing them uniformly at high speed; (3) placing the mixed material in step (2) into a twin-screw extruder for extrusion granulation; (4) adding the granules in step (3) into an injection molding machine and injection molding them into a support ring sample; Preferably, in step (2), the high-speed mixing speed is 1500-2000 rpm, and the time is 1-3 hours; Preferably, in step (3), the melt extrusion temperature of the twin-screw extruder is 345-385° C., and the screw speed is 60-100 rpm; Preferably, in step (4), the injection temperature of the injection molding machine is 360-400°C, and the mold temperature is 180-220°C.

9. A support ring, which is made from the modified polyimide according to any one of claims 1 to 7 or from the method according to claim 8.

10. A hydraulic cylinder or a gas cylinder comprising the support ring of claim 9.

11. A hydraulic system comprising the hydraulic cylinder of claim 10.

12. A pneumatic system comprising the cylinder of claim 10.

13. An engineering machine comprising the hydraulic system of claim 11 or the pneumatic system of claim 12.

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