A preparation process for improving the uniformity of warp and weft strength of polytetrafluoroethylene microporous membranes

Abstract

This invention relates to a preparation process for improving the uniformity of warp and weft strength of polytetrafluoroethylene (PTFE) microporous membranes, comprising the following steps: 1) freezing PTFE raw material below zero degrees Celsius; 2) uniformly dispersing the inherent agglomerates of the frozen PTFE raw material through multi-frequency vibration to form frozen granular powder; 3) uniformly mixing the unfrozen PTFE raw material with solvent oil to form oil-coated granular pretreatment material; 4) spreading the oil-coated granular pretreatment material and the frozen granular powder layer by layer in a preforming cylinder according to a certain ratio; 5) subjecting the mixture to preforming, extrusion, calendering, and biaxial stretching to form a PTFE microporous membrane with uniform warp and weft strength. The PTFE microporous membrane produced by this preparation process exhibits uniform warp and weft strength and has minimal impact on the membrane's filtration efficiency and resistance.

Description

Technical Field

[0001] This invention relates to the field of polymer membrane preparation, specifically to a preparation process for improving the uniformity of warp and weft strength of polytetrafluoroethylene microporous membranes. Background Technology

[0002] The PTFE mesh microporous membrane formed by biaxial stretching mainly controls the pore size and porosity of the membrane through production processes such as directional calendering, longitudinal stretching, and transverse stretching. However, the membrane produced by this process has a large difference in strength between the warp and weft directions. In actual use, the direction with lower strength is prone to delamination or cracking, which greatly shortens the service life of the product and increases the cost of use. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a preparation process for improving the uniformity of warp and weft strength of polytetrafluoroethylene microporous membranes. The polytetrafluoroethylene microporous membranes produced by this preparation process have uniform warp and weft strength and do not significantly affect the filtration efficiency and resistance of the membrane.

[0004] The specific technical solution of the present invention is as follows:

[0005] A preparation process for improving the warp and weft strength uniformity of polytetrafluoroethylene microporous membranes includes the following steps:

[0006] (1) The polytetrafluoroethylene raw material is frozen at 0°C or below. After freezing, the polytetrafluoroethylene raw material is evenly dispersed by multi-frequency vibration to form frozen granular powder.

[0007] (2) Mix the unfrozen polytetrafluoroethylene raw material with solvent oil to form oil-coated granular pretreated material;

[0008] (3) According to a certain ratio, the oil-coated granular pretreatment material and the frozen granular powder are spread layer by layer in the molding cylinder, and multiple layers are spread.

[0009] (4) The mixture is preformed, extruded, calendered, and biaxially stretched to form a polytetrafluoroethylene microporous membrane with uniform strength in both warp and weft directions.

[0010] In step (1), the freezing treatment time below 0℃ is greater than 8 hours, and the multi-frequency oscillation treatment time is 0.5~6 hours. The multi-frequency oscillation is required to be carried out at an ambient temperature below 15℃.

[0011] In step (3), the mass ratio of frozen granular powder to oil-coated pretreatment material is 2-50%. The number of layers in the multi-layer paving is more than 5, and the frozen granular powder and the oil-coated pretreatment material are placed alternately. The outermost layer must be oil-coated pretreatment material.

[0012] The solvent oil mentioned in step (2) is one of kerosene or isoparaffin solvent oil.

[0013] Beneficial Effects: This invention treats the distribution of polytetrafluoroethylene (PTFE) powder according to a specific ratio before stretching, and adjusts the warp and weft strength through the arrangement of frozen particles. Through a pre-forming process, adhesive forces are generated between the oil-in-oil pre-treated particles. The stretching process then draws these particles into fibers, forming a network of micropores. The frozen particles, after pre-forming, do not exhibit adhesive forces and therefore do not participate in fiber formation; they simply adhere to the fibers. After freezing and multi-frequency oscillation treatment, the PTFE particles decompose from their original agglomerated state into nanoscale initial particles. After adhering to the fibers, they do not significantly clog the micropores. Therefore, the performance shows an increase in strength in the predetermined direction without significantly reducing the gas or liquid flux of the membrane. Attached Figure Description

[0014] Figure 1 This is a scanning electron microscope image of the polytetrafluoroethylene microporous membrane prepared in Example 1.

[0015] Figure 2 This is a scanning electron microscope image of the polytetrafluoroethylene microporous membrane prepared in Example 2.

[0016] Figure 3 This is a scanning electron microscope image of the polytetrafluoroethylene microporous membrane prepared in Comparative Example 3. Detailed Implementation Example 1

[0017] 500g of polytetrafluoroethylene (PTFE) raw material was frozen at below 0°C. The frozen PTFE raw material was then uniformly dispersed by multi-frequency vibration to form frozen granular powder. 4500g of unfrozen PTFE raw material was uniformly mixed with 900g of kerosene solvent oil to form oil-coated granular pretreatment material. The 500g frozen PTFE granular powder was divided into 10 portions, and the 4500g oil-coated granular pretreatment material was evenly divided into 11 portions. The oil-coated granular pretreatment material was layered with the frozen granular powder in a preforming cylinder, alternating layers. The mixture was then preformed, extruded, calendered, and biaxially stretched to form a PTFE microporous membrane with uniform strength in both warp and weft directions. Example 2

[0018] 300g of polytetrafluoroethylene (PTFE) raw material was frozen at below 0°C. The frozen PTFE raw material was then uniformly dispersed through multi-frequency vibration to form frozen granular powder. 4700g of unfrozen PTFE raw material was uniformly mixed with 900g of isoalkane solvent oil to form an oil-coated granular pretreatment material. The 300g frozen PTFE granular powder was divided into 10 portions, and the 4700g oil-coated granular pretreatment material was evenly divided into 11 portions. The oil-coated granular pretreatment material was layered with the frozen granular powder in a preforming cylinder, alternating layers. The mixture was then preformed, extruded, calendered, and biaxially stretched to form a PTFE microporous membrane with uniform strength in both warp and weft directions.

[0019] Comparative Example 1

[0020] 5000g of unfrozen polytetrafluoroethylene (PTFE) raw material is uniformly mixed with 900g of kerosene or isoalkane solvent oil to form an oil-coated granular pretreated material. The powder is then layered and alternately spread in a preforming cylinder. The mixture is then preformed, extruded, calendered, and biaxially stretched to form a PTFE microporous membrane with uniform strength in both warp and weft directions.

[0021] Table 1 Performance data of each example membrane

[0022]

Claims

1. A process for improving the uniformity of the strength of polytetrafluoroethylene microporous membranes in the warp and weft directions, characterized by It comprises the following steps: (1) Freeze the polytetrafluoroethylene raw material below 0℃, uniformly disperse the inherent agglomerates of the raw material by multi-frequency oscillation after the freeze treatment, and form a frozen granular powder; (2) Uniformly mix the polytetrafluoroethylene raw material without freeze treatment with solvent oil to form an oil-coated granular pretreatment material; the solvent oil is one of kerosene and isomeric alkane solvent oil; (3) According to a certain ratio, layer by layer, the oil-coated granular pretreatment material and the frozen granular powder are alternately laid in the punch cylinder body to perform multi-layer laying; the number of layers of multi-layer laying is greater than 5, and one layer of frozen granular powder and one layer of oil-coated pretreatment material are alternately placed, and the outermost layer must be the oil-coated pretreatment material; (4) The mixed material is punched, pushed, calendared, and bidirectionally stretched to form a polytetrafluoroethylene microporous membrane with uniform strength in the warp and weft directions.

2. The process for improving the uniformity of the strength of polytetrafluoroethylene microporous membrane in the warp and weft directions according to claim 1, characterized by In step (1), the freeze treatment time below 0℃ is greater than 8h, the multi-frequency oscillation treatment time is 0.5~6h, and the multi-frequency oscillation requires to be performed below the ambient temperature of 15℃.

3. The process for improving the uniformity of the strength of polytetrafluoroethylene microporous membrane according to claim 1, characterized in that In step (3), the mass ratio of the frozen granular powder to the oil-coated pretreatment material is 2~50%.

Images