Dimension-stable expanded polytetrafluoroethylene fiber membrane and preparation method thereof

Abstract

The invention discloses a size-stable expanded polytetrafluoroethylene fiber membrane and a preparation method thereof.When the expanded polytetrafluoroethylene fiber membrane is prepared, polytetrafluoroethylene dispersion resin and lubricating oil are evenly mixed and then subjected to curing, blank pressing, extrusion, calendaring and degreasing treatment in sequence, a polytetrafluoroethylene base band is obtained, then a novel two-way stretching technology is adopted, and the expanded polytetrafluoroethylene fiber membrane is obtained. A polytetrafluoroethylene base band is sequentially subjected to primary longitudinal stretching, primary high-temperature setting treatment, secondary longitudinal stretching, transverse stretching, retraction in the longitudinal direction and secondary heat setting treatment, and then the expanded polytetrafluoroethylene fiber membrane with the stable size is obtained. According to the novel two-way stretching technology, the microstructure of the polytetrafluoroethylene fiber membrane can be adjusted, fiber membrane nodes are in a thin strip shape and are arranged in the transverse direction, the transverse shrinkage problem of the fiber membrane can be effectively solved on the basis that the membrane performance is not affected, and the stability of the membrane size is guaranteed.

Description

Technical Field

[0001] The invention relates to the field of membrane preparation, and in particular to a dimensionally stable expanded polytetrafluoroethylene fiber membrane and a preparation method thereof. Background Art

[0002] Expanded polytetrafluoroethylene (Expanded PTFE) is a microporous material made by stretching dispersed polytetrafluoroethylene resin. It is non-toxic, non-carcinogenic, and non-allergenic. As a new type of polymer material, expanded polytetrafluoroethylene membrane is widely used in medical treatment, separation and filtration, sealing, electrical insulation, outdoor supplies, etc. Expanded polytetrafluoroethylene membrane has a three-dimensional network structure, which is formed by many microfibers connected together, and the connection points of the fiber bundles are nodes.

[0003] The existing preparation process of expanded polytetrafluoroethylene fiber membrane is as follows: aging - compacting - extrusion - calendering - degreasing - longitudinal stretching - transverse stretching - heat setting. For example, the invention patent with application publication number CN 116834346 A discloses an expanded polytetrafluoroethylene membrane, and its preparation method includes: premixing, molding, extrusion, double-roll calendering, biaxial stretching and hot pressing. However, the structure of the membrane prepared by this process is a mesh structure formed by alternating fibers and nodes, and the nodes are mostly circular or elliptical. Since polytetrafluoroethylene polymer materials have a high cohesive force, the membrane is easy to shrink in the transverse direction after stretching, especially after transverse stretching, and the membrane pore size is difficult to maintain. To solve this problem, it is usually necessary to increase the heat setting temperature or perform hot pressing on the prepared membrane during preparation, but these methods will make it difficult to effectively control the membrane pore size and reduce the membrane permeability, which has a negative impact on the performance of the expanded polytetrafluoroethylene fiber membrane. Summary of the invention

[0004] In order to solve the above problems, in a first aspect, the present invention provides a method for preparing a dimensionally stable expanded polytetrafluoroethylene fiber membrane, which can effectively solve the problem of lateral shrinkage of the fiber membrane and ensure the stability of the membrane size.

[0005] The technical solution of the present invention to solve the above problems is as follows: A method for preparing a dimensionally stable expanded polytetrafluoroethylene fiber membrane comprises the following steps: S1, after uniformly mixing polytetrafluoroethylene dispersion resin and lubricating oil in proportion and ripening, sequentially subjecting the mixture to compacting, extrusion, calendering and degreasing treatment to obtain polytetrafluoroethylene tape; S2, longitudinally stretching the polytetrafluoroethylene tape for the first time to obtain a first stretched polytetrafluoroethylene tape; S3, subjecting the first polytetrafluoroethylene stretched tape to a first high-temperature shaping treatment; S4, performing a secondary longitudinal stretching on the first stretched polytetrafluoroethylene tape that has undergone the initial high-temperature shaping treatment to obtain a second stretched polytetrafluoroethylene tape; S5, transversely stretching the second polytetrafluoroethylene stretching tape to obtain a polytetrafluoroethylene fiber membrane; S6. The polytetrafluoroethylene fiber membrane is subjected to longitudinal heat treatment to shrink it by 0.05 to 0.2 times, and is subjected to secondary heat setting to obtain a dimensionally stable expanded polytetrafluoroethylene fiber membrane.

[0006] The heating treatment of the polytetrafluoroethylene fiber membrane along the longitudinal direction to shrink it by 0.05 to 0.2 times described in the present application refers to shrinking the polytetrafluoroethylene fiber membrane along the longitudinal direction to 80 to 95% of the polytetrafluoroethylene fiber membrane in S5.

[0007] In the above preparation method, the polytetrafluoroethylene tape is subjected to the first high-temperature shaping treatment after the first longitudinal stretching, so that the nodes formed by the fibers are softened and stick together, and the nodes are regularly split during the second longitudinal stretching, so that the pore size distribution of the fiber membrane is uniform. The polytetrafluoroethylene fiber membrane is heated in the longitudinal direction to shrink it by 0.05 to 0.2 times, which can further shrink the fibers and nodes in the membrane and make the nodes as neatly arranged as possible. Therefore, the preparation method of the present invention can effectively solve the problem of lateral shrinkage of the fiber membrane without affecting the membrane performance, thereby ensuring the stability of the membrane size.

[0008] Preferably, in step S1, the mass ratio of polytetrafluoroethylene dispersion resin to lubricating oil is (8-12):(20-30).

[0009] Preferably, in step S1, the aging temperature is 30-80° C., and the aging time is 10-24 hours.

[0010] Preferably, in step S2, the first longitudinal stretching temperature is 200-260° C., and the first longitudinal stretching multiple is 2-5 times.

[0011] Preferably, in step S3, the temperature of the first high-temperature shaping treatment is 300-340° C., and the treatment time is 1-3 min.

[0012] Preferably, in step S4, the secondary longitudinal stretching temperature is 200-260° C., and the secondary longitudinal stretching multiple is 2-5 times.

[0013] Preferably, in step S5, the transverse stretching temperature is 250-300° C., and the transverse stretching ratio is 4-8 times.

[0014] Preferably, in step S6, the longitudinal heating shrinkage temperature is 240-280°C.

[0015] Preferably, in step S6, the secondary heat setting temperature is 330-360° C., and the secondary heat setting time is 1-3 min.

[0016] In a second aspect, the present invention provides a dimensionally stable expanded polytetrafluoroethylene fiber membrane, the fiber membrane nodes are in the form of thin strips, are arranged in the transverse direction, and have good dimensional stability; the dimensionally stable expanded polytetrafluoroethylene fiber membrane is obtained by the above-mentioned preparation method.

[0017] The present invention has the following beneficial effects: When preparing an expanded polytetrafluoroethylene fiber membrane, the present invention uniformly mixes a polytetrafluoroethylene dispersion resin and a lubricating oil, and then sequentially performs aging, embryo pressing, extrusion, calendering, and degreasing treatments to obtain a polytetrafluoroethylene-based tape, and then adopts a novel biaxial stretching process to sequentially perform an initial longitudinal stretching, an initial high-temperature shaping treatment, a secondary longitudinal stretching, a transverse stretching, a longitudinal shrinkage, and a secondary heat shaping treatment on the polytetrafluoroethylene-based tape to obtain a dimensionally stable expanded polytetrafluoroethylene fiber membrane; the novel biaxial stretching process can adjust the microstructure of the polytetrafluoroethylene fiber membrane, so that the fiber membrane nodes are in the shape of thin strips and are arranged in the transverse direction, and can effectively solve the transverse shrinkage problem of the fiber membrane without affecting the membrane performance, thereby ensuring the stability of the membrane size. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a scanning electron microscope image of the expanded polytetrafluoroethylene fiber membrane of Example 3; Figure 2 This is a scanning electron microscope image of the expanded polytetrafluoroethylene fiber membrane of Comparative Example 1. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical scheme and advantages of the present invention more clear, the present invention is further described in detail in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0020] Example 1 S1. After uniformly mixing polytetrafluoroethylene dispersion resin (Dongyue 204) and lubricating oil (aviation kerosene) in a mass ratio of 10:20, the mixture was aged at 80°C for 10 hours to obtain an aged material; the aged material was sequentially subjected to a pelletizing machine, an extruder, a calender and degreasing treatment to obtain a polytetrafluoroethylene tape; S2, longitudinally stretching the polytetrafluoroethylene tape for the first time by 2 times at 200° C. to obtain a first stretched polytetrafluoroethylene tape; S3, heating the first stretched polytetrafluoroethylene tape at 340° C. for 1 min to perform the first high-temperature shaping treatment; S4, longitudinally stretching the polytetrafluoroethylene first stretched tape that has undergone the initial high-temperature shaping treatment for a second time at 260° C. by 5 times to obtain a polytetrafluoroethylene second stretched tape; S5, stretching the second polytetrafluoroethylene stretching tape transversely by 4 times at 250° C. to obtain a polytetrafluoroethylene fiber membrane; S6. The polytetrafluoroethylene fiber membrane was heated and shrunk by 0.05 times in the longitudinal direction at 240°C, and finally subjected to secondary heat setting at 360°C for 1 minute to obtain an expanded polytetrafluoroethylene fiber membrane, which was named M1.

[0021] Example 2 S1. Mix polytetrafluoroethylene dispersion resin (Dongyue 216) and lubricating oil (aviation kerosene) in a mass ratio of 10:30, and mature at 30°C for 24 hours to obtain a matured material; the matured material is sequentially subjected to a compacting machine, an extruder, a calender, and degreasing treatment to obtain a polytetrafluoroethylene tape; S2, longitudinally stretching the polytetrafluoroethylene tape for the first time at 260° C. by 5 times to obtain a first stretched polytetrafluoroethylene tape; S3, heating the first stretched polytetrafluoroethylene tape at 300° C. for 3 minutes to perform the first high-temperature shaping treatment; S4, longitudinally stretching the polytetrafluoroethylene first stretched tape that has undergone the initial high-temperature shaping treatment for a second time at 200° C. by 2 times to obtain a polytetrafluoroethylene second stretched tape; S5, stretching the second polytetrafluoroethylene stretching tape transversely by 8 times at 300° C. to obtain a polytetrafluoroethylene fiber membrane; S6. The polytetrafluoroethylene fiber membrane was heated and shrunk by 0.2 times in the longitudinal direction at 280°C, and finally subjected to secondary heat setting at 330°C for 3 minutes to obtain an expanded polytetrafluoroethylene fiber membrane, which was named M2.

[0022] Example 3 S1. Mix polytetrafluoroethylene dispersion resin (Dongyue 216) and lubricating oil (aviation kerosene) in a mass ratio of 10:25, and mature at 50°C for 18 hours to obtain a matured material; the matured material is sequentially subjected to a compacting machine, an extruder, a calender, and degreasing treatment to obtain a polytetrafluoroethylene tape; S2, longitudinally stretching the polytetrafluoroethylene tape for the first time by 3 times at 240° C. to obtain a first stretched polytetrafluoroethylene tape; S3, heating the first stretched polytetrafluoroethylene tape at 320° C. for 2 minutes to perform the first high-temperature shaping treatment; S4, longitudinally stretching the polytetrafluoroethylene first stretched tape that has undergone the initial high-temperature shaping treatment for a second time at 240° C. by 3 times to obtain a polytetrafluoroethylene second stretched tape; S5, stretching the second polytetrafluoroethylene stretching tape transversely by 6 times at 290° C. to obtain a polytetrafluoroethylene fiber membrane; S6. The polytetrafluoroethylene fiber membrane was heated and shrunk by 0.1 times in the longitudinal direction at 260°C, and finally subjected to secondary heat setting at 340°C for 1.5 min to obtain an expanded polytetrafluoroethylene fiber membrane, which was named M3.

[0023] Example 4 S1. Mix polytetrafluoroethylene dispersion resin (DuPont 601) and lubricating oil (aviation kerosene) in a mass ratio of 10:22, and mature at 60°C for 15 hours to obtain a matured material; the matured material is sequentially subjected to a compacting machine, an extruder, a calender, and degreasing treatment to obtain a polytetrafluoroethylene tape; S2, longitudinally stretching the polytetrafluoroethylene tape for the first time by 2 times at 200° C. to obtain a first stretched polytetrafluoroethylene tape; S3, heating the first stretched polytetrafluoroethylene tape at 330° C. for 1.5 min to perform the first high-temperature shaping treatment; S4, longitudinally stretching the polytetrafluoroethylene first stretched tape that has undergone the initial high-temperature shaping treatment for a second time at 250° C. by 4 times to obtain a polytetrafluoroethylene second stretched tape; S5, stretching the second polytetrafluoroethylene stretching tape transversely by 4 times at 250° C. to obtain a polytetrafluoroethylene fiber membrane; S6. The polytetrafluoroethylene fiber membrane was heated and shrunk by 0.15 times in the longitudinal direction at 240°C, and finally subjected to secondary heat setting at 350°C for 1 minute to obtain an expanded polytetrafluoroethylene fiber membrane, which was named M4.

[0024] Comparative Example 1 S1. Mix polytetrafluoroethylene dispersion resin (Dongyue 216) and lubricating oil (aviation kerosene) in a mass ratio of 10:25, and mature at 50°C for 18 hours to obtain a matured material; the matured material is sequentially subjected to a compacting machine, an extruder, a calender, and degreasing treatment to obtain a polytetrafluoroethylene tape; S2, longitudinally stretching the polytetrafluoroethylene tape by 9 times at 240° C. to obtain a first stretched polytetrafluoroethylene tape; S3, stretching the first polytetrafluoroethylene stretching tape transversely by 6 times at 290° C. to obtain a polytetrafluoroethylene fiber membrane; S4. The polytetrafluoroethylene fiber membrane was heat-set at 340° C. for 1.5 min to obtain an expanded polytetrafluoroethylene fiber membrane, which was named M0.

[0025] The expanded polytetrafluoroethylene fiber membranes obtained in Examples 1 to 4 and Comparative Example 1 were tested. The testing method was as follows: the prepared samples were cut into rolls with a width of 50±0.1 cm and a length of 100±0.1 m, stored at 30°C, and the sample width was tested every 10 days. The test results are shown in the following table.

[0026] Table 1: Sample lateral width test data table Sample No. Weight(g) 10d Horizontal Width (cm) 20d horizontal width (cm) 30d horizontal width (cm) M1 4~6 50±0.1 50±0.1 50±0.1 M2 4~6 50±0.1 50±0.1 50±0.1 M3 7~8 50±0.1 50±0.1 50±0.1 M4 10~12 50±0.1 50±0.1 50±0.1 M0 7~8 49±0.1 48.1±0.1 47.2±0.1 It can be seen from Table 1 that the lateral width of the expanded polytetrafluoroethylene fiber membranes prepared in Examples 1 to 4 did not change after 30 days, and there was no lateral shrinkage problem; while the lateral width of the expanded polytetrafluoroethylene fiber membrane prepared in Comparative Example 1 decreased after 10 days, 20 days, and 30 days, that is, it had a lateral shrinkage problem.

[0027] Figure 1 This is a scanning electron microscope image of the expanded polytetrafluoroethylene fiber membrane prepared in Example 3, in which the fiber membrane nodes are in the shape of thin strips and are arranged in the transverse direction; Figure 2 This is a scanning electron microscope image of the expanded polytetrafluoroethylene fiber membrane prepared in Comparative Example 1. The structure of the membrane is a mesh structure formed by alternating fibers and nodes, and most of the nodes are circular or elliptical.

[0028] In summary, the expanded polytetrafluoroethylene fiber membrane prepared by the method of the present invention can effectively solve the problem of lateral shrinkage of the fiber membrane without affecting the membrane performance, thereby ensuring the stability of the membrane size.

Claims

1. A method for preparing a dimensionally stable expanded polytetrafluoroethylene fiber membrane, characterized in that: The following steps are involved: S1, after uniformly mixing polytetrafluoroethylene dispersion resin and lubricating oil in proportion and ripening, sequentially subjecting the mixture to compacting, extrusion, calendering and degreasing treatment to obtain polytetrafluoroethylene tape; S2, longitudinally stretching the polytetrafluoroethylene tape for the first time to obtain a first stretched polytetrafluoroethylene tape; S3, subjecting the first polytetrafluoroethylene stretched tape to a first high-temperature shaping treatment; S4, performing a secondary longitudinal stretching on the first stretched polytetrafluoroethylene tape that has undergone the initial high-temperature shaping treatment to obtain a second stretched polytetrafluoroethylene tape; S5, transversely stretching the second polytetrafluoroethylene stretching tape to obtain a polytetrafluoroethylene fiber membrane; S6. The polytetrafluoroethylene fiber membrane is subjected to longitudinal heat treatment to shrink it by 0.05 to 0.2 times, and is subjected to secondary heat setting to obtain a dimensionally stable expanded polytetrafluoroethylene fiber membrane.

2. The preparation method according to claim 1, characterized in that: In the step S1, the mass ratio of the polytetrafluoroethylene dispersion resin to the lubricating oil is (8-12):(20-30).

3. The preparation method according to claim 1, characterized in that: In the step S1, the aging temperature is 30-80° C., and the aging time is 10-24 hours.

4. The preparation method according to claim 1, characterized in that: In the step S2, the first longitudinal stretching temperature is 200-260°C, and the first longitudinal stretching multiple is 2-5 times.

5. The preparation method according to claim 1, characterized in that: In step S3, the temperature of the first high-temperature setting treatment is 300-340° C., and the treatment time is 1-3 minutes.

6. The preparation method according to claim 1, characterized in that: In the step S4, the secondary longitudinal stretching temperature is 200-260° C., and the secondary longitudinal stretching multiple is 2-5 times.

7. The preparation method according to claim 1, characterized in that: In the step S5, the transverse stretching temperature is 250-300° C., and the transverse stretching ratio is 4-8 times.

8. The preparation method according to claim 1, characterized in that: In step S6, the longitudinal heating shrinkage temperature is 240-280°C.

9. The preparation method according to claim 1, characterized in that: In the step S6, the secondary heat setting temperature is 330-360° C., and the secondary heat setting time is 1-3 min.

10. A dimensionally stable expanded polytetrafluoroethylene fiber membrane prepared by the method according to any one of claims 1 to 9.

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