Modified polytetrafluoroethylene for wear-resistant sealing ring and preparation method thereof

Abstract

The invention belongs to the technical field of polymer composite materials, and particularly relates to modified polytetrafluoroethylene for a wear-resistant sealing ring and a preparation method of the modified polytetrafluoroethylene. After standing, uniformly mixing polytetrafluoroethylene with the inorganic filler and polyimide to obtain a mixture, and standing the mixture at room temperature; and 2, performing cold pressing on the mixed material after standing to form a preform, sintering the preform at high temperature to form a blank material, and processing the blank material into the sealing ring. The inorganic filler and the organic filler are mixed and added, and the sintering temperature and the cooling rate are controlled in the preparation process, so that the modified polytetrafluoroethylene has good wear resistance at a lower friction coefficient on the premise of ensuring the mechanical property of the polytetrafluoroethylene, and the modified polytetrafluoroethylene can be used in a specific working environment.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer composite materials, and in particular relates to a modified polytetrafluoroethylene for a wear-resistant sealing ring and a preparation method thereof. Background Art

[0002] Polytetrafluoroethylene is a kind of engineering plastics, known as the "king of plastics". It has stable chemical properties and excellent insulation and lubrication properties, so it is widely used in various fields. At the same time, because polytetrafluoroethylene has excellent comprehensive mechanical properties and can be used in high temperature and high corrosion environments, it is one of the main materials for making sealing parts. In industry, polytetrafluoroethylene can be used to make sealing rings or other sealing parts of various components such as valve seats, valves, and bearings.

[0003] Although pure polytetrafluoroethylene has good mechanical properties, its wear resistance is extremely poor. Currently, the wear resistance of polytetrafluoroethylene is mainly increased by modifying polytetrafluoroethylene, such as direct surface modification and filling modification. Among them, filling modification generally increases the wear resistance of polytetrafluoroethylene by adding various fillers. At present, certain achievements have been made in filling modification at home and abroad. For example, the Chinese patent with publication number CN107177145A provides a filled modified polytetrafluoroethylene material and its application and preparation method. By filling stainless steel powder and molybdenum disulfide powder in polytetrafluoroethylene, the material can obtain good wear resistance, self-lubricating property and good corrosion resistance.

[0004] However, in some specific working environments, such as high-pressure sealing or high-speed shaft sealing, polytetrafluoroethylene materials are required to have better wear resistance while having a low friction coefficient. Summary of the invention

[0005] The main purpose of the present invention is to provide a modified polytetrafluoroethylene for wear-resistant sealing rings and a preparation method thereof. By mixing and adding inorganic fillers and organic fillers, and controlling the sintering temperature and the cooling rate during the preparation process, the modified polytetrafluoroethylene has good wear resistance at a lower friction coefficient while ensuring the mechanical properties of the polytetrafluoroethylene, so as to meet its use in a specific working environment.

[0006] The purpose of the present invention and the technical problem to be solved are achieved by adopting the following technical solutions:

[0007] Firstly, the present invention provides a modified polytetrafluoroethylene for a wear-resistant sealing ring. The modified polytetrafluoroethylene comprises the following components in parts by weight: 5 to 10 parts of inorganic filler, 10 to 15 parts of polyimide and 75 to 85 parts of polytetrafluoroethylene.

[0008] Furthermore, the inorganic filler includes boron nitride, graphene and graphite fluoride, the particle size of the inorganic filler is 5 to 8 μm, and the particle size of the organic filler is 25 to 30 μm.

[0009] Furthermore, the molecular weight of the polytetrafluoroethylene is 8 to 10 million, and the particle size of the polytetrafluoroethylene is 25 to 30 μm.

[0010] The present invention also provides a method for preparing modified polytetrafluoroethylene for wear-resistant sealing rings, comprising the following steps:

[0011] Step 1: Allow polytetrafluoroethylene to stand at low temperature, then mix polytetrafluoroethylene with inorganic filler and polyimide to obtain a mixture, and allow the mixture to stand at room temperature;

[0012] Step 2: cold-press the static mixture into a preform, sinter the preform at high temperature into a blank, and then process the blank into a sealing ring.

[0013] Furthermore, in the step 1, the standing temperature of the polytetrafluoroethylene is 0-4°C, the standing time is 6-12 hours, the mixing time is 4-5 minutes, and the mixing times are 2-3 times; and the standing time of the mixture is 24 hours.

[0014] Furthermore, in the step 2, the cold pressing pressure is 40-50 MPa, and the cold pressing time is 30-35 min.

[0015] Furthermore, in the step 2, the sintering temperature is 360-365° C., and the sintering time is 4-5 hours.

[0016] Furthermore, in the sintering process in step 2, the heating rate at 315°C and below is 50-60°C / h, and the heating rate above 315°C is 25-35°C / h; the cooling rate at 300°C and above is 25-35°C / h, and the cooling rate below 300°C is 50-70°C / h.

[0017] Beneficial effects of the present invention:

[0018] 1) The present invention adds inorganic fillers to polytetrafluoroethylene, which can significantly improve the wear resistance of the modified polytetrafluoroethylene and reduce its friction coefficient by taking advantage of the excellent lubricity and wear resistance of the inorganic fillers. At the same time, polyimide is added to the modified polytetrafluoroethylene to effectively solve the problem of large local defects and significant stress concentration caused by the addition of inorganic fillers, which leads to a significant decrease in the tensile strength and elongation at break of the material, and further enhances its wear resistance. The modified polytetrafluoroethylene material obtained by the composite modification not only has strong wear resistance, but also has a low friction coefficient and good mechanical properties.

[0019] 2) The present invention adopts a cold pressing sintering process in the preparation method. By controlling the cold pressing molding pressure in the cold pressing stage, it is ensured that the good mechanical properties of the polytetrafluoroethylene material can be fully released. At the same time, adjusting the sintering temperature can ensure that the macromolecular chains in the polytetrafluoroethylene can be fully active, improve the structural density of the material, and then improve its mechanical properties. In the cooling stage, the cooling rate is increased to reduce the crystallinity of the material, thereby improving the tensile strength and elongation at break of the material. DETAILED DESCRIPTION

[0020] Example 1

[0021] This embodiment provides a modified polytetrafluoroethylene for a wear-resistant sealing ring, comprising the following components by weight: 5 parts of inorganic filler, 15 parts of polyimide and 75 parts of polytetrafluoroethylene, wherein the inorganic filler is boron nitride. In this embodiment, polytetrafluoroethylene of M-18F grade produced by Daikin Industries, Ltd. of Japan is selected, and the average particle size is 25 μm. Boron nitride and polyimide are purchased from the market, and the average particle sizes are 5 μm and 30 μm, respectively.

[0022] This embodiment also provides a method for preparing modified polytetrafluoroethylene for wear-resistant sealing rings, which is used to prepare modified polytetrafluoroethylene, and specifically includes the following steps:

[0023] Step 1: Allow polytetrafluoroethylene to stand at low temperature, then mix polytetrafluoroethylene with inorganic filler and polyimide to obtain a mixture, and allow the mixture to stand at room temperature;

[0024] Specifically, the purchased polytetrafluoroethylene suspension resin powder was placed in an environment of 5°C and allowed to stand for 6 hours. Then the resin powder and the above-mentioned boron nitride and polyimide were weighed according to the ratio and added to a high-speed mixer for 4 minutes, and then allowed to stand for 10 minutes and then mixed for another 4 minutes to ensure that the raw materials were fully mixed. The mixed mixture was allowed to stand at room temperature for 24 hours to ensure that the raw materials were fully reacted.

[0025] Step 2: cold-press the static mixture into a preform, sinter the preform at high temperature into a blank, and then process the blank into a sealing ring.

[0026] Specifically, the uniformly mixed mixture is allowed to stand in an environment of 25°C for 24 hours, and then the mixture is evenly laid in a mold, and a preform is formed by a hydraulic forming machine at a pressure of 50MPa for 30 minutes. The preform is transferred to room temperature and allowed to stand for 24 hours before being sintered into a blank in a high-temperature atmosphere furnace, and the blank is subsequently machined into a sealing ring. In this embodiment, the sintering temperature is 360°C and the sintering time is 4.5 hours. During the sintering process, the heating rate at 315°C and below is 60°C / h, and the heating rate above 315°C is 30°C / h. When cooling, the cooling rate at 300°C and above is 30°C / h, and the cooling rate below 300°C is 50°C / h.

[0027] Example 2

[0028] The difference between this embodiment and embodiment 1 is that the raw material ratio in the modified polytetrafluoroethylene is different, specifically: 10 parts of inorganic filler, 10 parts of polyimide and 85 parts of polytetrafluoroethylene, wherein the inorganic filler is boron nitride. The raw material source and preparation method are the same as those in embodiment 1.

[0029] Example 3

[0030] The difference between this embodiment and embodiment 1 is that the inorganic filler is graphene. The source of raw materials and the preparation method are the same as those in embodiment 1.

[0031] Example 4

[0032] The difference between this embodiment and embodiment 1 is that the cold pressing pressure in step 1 is 40 MPa. The source of raw materials and other preparation steps and parameters are consistent with those in embodiment 1.

[0033] Comparative Example 1

[0034] The difference between this comparative example and Example 1 is that the raw material ratio in the modified polytetrafluoroethylene is different, specifically: 15 parts of inorganic filler, 10 parts of polyimide and 75 parts of polytetrafluoroethylene, wherein the inorganic filler is boron nitride. The raw material source and preparation method are the same as those in Example 1.

[0035] Comparative Example 2

[0036] The difference between this comparative example and Example 1 is that the raw material ratio in the modified polytetrafluoroethylene is different, specifically: 5 parts of inorganic filler, 15 parts of polyimide and 80 parts of polytetrafluoroethylene, wherein the inorganic filler is boron nitride. The raw material source and preparation method are the same as those in Example 1.

[0037] Comparative Example 3

[0038] The difference between this comparative example and Example 1 is that the cold pressing pressure in step 1 is 30 MPa. The source of raw materials and other preparation steps and parameters are consistent with those in Example 1.

[0039] Comparative Example 4

[0040] The difference between this comparative example and Example 1 is that the cold pressing pressure in step 1 is 60 MPa. The source of raw materials and other preparation steps and parameters are consistent with those in Example 1.

[0041] Comparative Example 5

[0042] The difference between this comparative example and Example 1 is that the sintering temperature in step 2 is 370° C. The source of raw materials and other preparation steps and parameters are consistent with those in Example 1.

[0043] Comparative Example 6

[0044] The difference between this comparative example and Example 1 is that the cooling rate is different. Specifically, during the sintering process, the heating rate at 315°C and below is 50°C / h, and the heating rate above 315°C is 30°C / h. During cooling, the cooling rate at 300°C and above is 30°C / h, and the cooling rate below 300°C is 20°C / h.

[0045] Comparative Example 7

[0046] The difference between this comparative example and Example 1 is that no polyimide is added. The raw material ratio in the modified polytetrafluoroethylene is 5 parts of boron nitride and 95 parts of polytetrafluoroethylene. The raw material source and other preparation methods are consistent with Example 1.

[0047] Comparative Example 8

[0048] The raw material ratio in the modified polytetrafluoroethylene is different, specifically: 3 parts of inorganic filler, 5 parts of polyimide and 92 parts of polytetrafluoroethylene, wherein the inorganic filler is boron nitride. The raw material source and preparation method are consistent with Example 1.

[0049] The comprehensive properties of the blanks prepared in the above embodiments and comparative examples were tested, and the experimental results are shown in Table 1.

[0050] Table 1: Comprehensive performance experimental data table of embodiments and comparative examples

[0051]

[0052]

[0053] Experimental results analysis:

[0054] From the above results, it can be seen that the modified polytetrafluoroethylene for wear-resistant sealing rings provided by the present invention has strong rated tensile strength and elongation at break, which can meet the mechanical performance requirements of most sealing rings. At the same time, the modified polytetrafluoroethylene for wear-resistant sealing rings provided by the present invention has very strong anti-friction performance. Under the test conditions of 200N, 200R, and 2H, its friction coefficient is stable at around 0.19, and the minimum volume wear rate can reach 2.9×10-6 mm 3 (N·M). Compared with pure polytetrafluoroethylene (volume wear rate is 851×10 -6 mm 3 (N·M)) was increased by about 300 times.

[0055] Compared with the example, the comparative example 1 increases the amount of inorganic filler, which further reduces the friction coefficient of the material, but its mechanical properties are significantly reduced, and the wear resistance is not improved.

[0056] Compared with the example, the amount of polyimide in comparative example 2 is increased. Excessive polyimide will cause the various properties of modified polytetrafluoroethylene to decrease. This is because the addition of excessive polyimide will make the properties of the polyimide itself more prominent during the use of the material, resulting in the failure of the adhesion between the polyimide and the inorganic filler and polytetrafluoroethylene.

[0057] Compared with the examples, the amount of inorganic filler added and polyimide in Comparative Example 8 were reduced, which resulted in a significant decrease in the comprehensive performance of the modified polytetrafluoroethylene prepared therefrom.

[0058] Comparative Examples 3 to 6 all change the parameters in the preparation, which will lead to a decrease in the mechanical properties of the modified polytetrafluoroethylene material.

[0059] It is obvious to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be regarded as exemplary and non-restrictive from any point of view. In addition, it should be understood that although this specification is described in accordance with the embodiments, it does not contain only one technical solution. This narrative of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in the embodiments can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A modified polytetrafluoroethylene for wear-resistant sealing ring, characterized in that: The modified polytetrafluoroethylene comprises the following components in parts by weight: 5 to 10 parts of inorganic filler, 10 to 15 parts of polyimide and 75 to 85 parts of polytetrafluoroethylene.

2. The modified polytetrafluoroethylene for wear-resistant sealing ring according to claim 1, characterized in that: The inorganic filler comprises boron nitride, graphene and graphite fluoride. The particle size of the inorganic filler is 5 to 8 μm, and the particle size of the organic filler is 25 to 30 μm.

3. The modified polytetrafluoroethylene for wear-resistant sealing ring according to claim 2, characterized in that: The molecular weight of the polytetrafluoroethylene is 8 to 10 million, and the particle size of the polytetrafluoroethylene is 25 to 30 μm.

4. A method for preparing a modified polytetrafluoroethylene for a wear-resistant sealing ring as claimed in any one of claims 1 to 4, characterized in that: The following steps are involved: Step 1: Allow polytetrafluoroethylene to stand at low temperature, then mix polytetrafluoroethylene with inorganic filler and polyimide to obtain a mixture, and allow the mixture to stand at room temperature; Step 2: cold-press the static mixture into a preform, sinter the preform at high temperature into a blank, and then process the blank into a sealing ring.

5. A method for preparing modified polytetrafluoroethylene for wear-resistant sealing ring according to claim 4, Features: In the step 1, the standing temperature of the polytetrafluoroethylene is 0-4°C, and the standing time is 6-12 hours; the mixing time is 4-5 minutes, and the mixing times are 2-3 times; and the standing time of the mixture is 24 hours.

6. A method for preparing a modified polytetrafluoroethylene for a wear-resistant sealing ring according to claim 5 The method is characterized by: In the step 2, the cold pressing pressure is 40-50 MPa, and the cold pressing time is 30-35 min.

7. A method for preparing a modified polytetrafluoroethylene for a wear-resistant sealing ring according to claim 6 The method is characterized by: In the step 2, the sintering temperature is 360-365° C., and the sintering time is 4-5 hours.

8. A method for preparing modified polytetrafluoroethylene for wear-resistant sealing rings according to claim 7, characterized in that: During the sintering process in step 2, the heating rate at 315°C and below is 50-60°C / h, and the heating rate above 315°C is 25-35°C / h; the cooling rate at 300°C and above is 25-35°C / h, and the cooling rate below 300°C is 50-70°C / h.

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