KR20140074754A - Multi-layer PTFE membrane having asymmetric porous and preparation method thereof - Google Patents

Abstract

The present invention relates to an asymmetric multi-layered PTFE membrane and a manufacturing method thereof. The asymmetric multi-layered PTFE membrane and the manufacturing method thereof according to one embodiment of the present invention improve the porosity and lifetime of the asymmetric multi-layered PTFE membrane without shrinkage, the decrease of pores, and the degradation of porosity. The method for manufacturing an asymmetric multi-layered PTFE membrane according to the present invention includes: a step of preparing first paste and second paste; a step of compressing the first paste and the second paste; a step of calendering; a step of stretching a sheet; and a step of calcining the sheet.

Description

TECHNICAL FIELD [0001] The present invention relates to asymmetric multi-layer PTFE membranes,

The present invention relates to a method of manufacturing an asymmetric multi-layered PTFE membrane, and more particularly, to a method of manufacturing an asymmetric multi-layer PTFE membrane, which does not cause a problem of shrinkage of membrane, decrease of porosity and lowering of porosity, , An asymmetric multilayer PTFE separator capable of remarkably improving the flow rate and service life, and a method of manufacturing the same.

Conventionally, a porous body made of polytetrafluoroethylene (hereinafter referred to as "PTFE ") not only has excellent chemical resistance, heat resistance, weather resistance, and nonflammability but also has properties such as non-stickiness and low friction coefficient. Moreover, since it is a porous structure, it is also excellent in transparency, flexibility, flexibility, trapping and filtering of fine particles, and the like. Therefore, the material made of PTFE is used in a wide range of fields such as filtration of fine chemicals and filters for wastewater treatment.

Among them, the PTFE filter medium mainly consists of a paste composed of a mixture of PTFE fine powder and a lubricant, which is rolled through a rolling process between the two rollers, formed into a sheet state, and after the lubricant is removed, Technology, that is, a method for producing a PTFE flat membrane, is well known.

Typically, the PTFE flat membrane has a symmetric membrane whose surface and backside pore sizes are almost the same, but the symmetric membrane has a problem that the flow rate is small at the same application pressure and clogging due to the particles occurs relatively quickly and the service life is short. By adjusting the degree of stretching by varying the temperature at the upper and lower portions of the PTFE flat film at the time of stretching, the pore structure on the cross section can be approached asymmetric. However, the uneven temperature difference between the upper and lower portions has a problem that the sheet shrinks considerably due to the surface receiving less heat. Thus, a method of producing an asymmetric separator by thermally fusing two PTFE flat membranes having different porosity and average pore size has been disclosed. However, there is a problem in that pores are damaged and porosity is decreased in the lining step, thereby reducing the flow rate.

It is an object of the present invention to provide an asymmetric multi-layered PTFE membrane capable of remarkably improving the porosity, flow rate and lifetime of the PTFE separation membrane while suppressing an increase in the cost of the membrane, And a manufacturing method thereof.

(1) a first PTFE powder, a first paste containing a liquid lubricant, and a second PTFE powder having an average molecular weight different from that of the first PTFE and a liquid lubricant, wherein the asymmetric multilayer PTFE separator comprises To form a second paste; (2) compressing the first paste and the second paste into a single preform, each of the first paste and the second paste being injected into individual input portions of a compressor including a plurality of input portions partitioned by the partition walls and being compressed by one preform; (3) calendering the preform in sheet form; (4) stretching the sheet; And (5) firing the stretched sheet; .

According to a preferred embodiment of the present invention, the difference between the average molecular weight (Mn) of the first PTFE powder and the second PTFE powder may be 3.2 × 10 ⁷ to 8.2 × 10 ⁸ .

According to another preferred embodiment of the present invention, in the step (1), the first paste contains 10 to 50 parts by weight of a liquid lubricant in 100 parts by weight of the PTFE powder, and the second paste comprises 10 to 50 parts by weight of the liquid lubricant in 100 parts by weight of the PTFE powder. 50 parts by weight.

According to another preferred embodiment of the present invention, the step (2) may be carried out at a pressure of 18 to 25 ° C and a pressure of 1 to 3 MPa.

According to another preferred embodiment of the present invention, the stretching temperature in the step (4) is 200 to 320 ° C, and the firing temperature in the step (5) is 300 to 400 ° C.

According to another preferred embodiment of the present invention, the liquid lubricant may be at least one selected from the group consisting of liquid paraffin, naphtha, white oil, toluene, xylene, alcohol, ketone and ester.

According to another preferred embodiment of the present invention, the thickness of the sheet in the step (4) may be 500 to 1000 mu m.

According to another preferred embodiment of the present invention, the partition is arranged to be parallel to an imaginary plane bisecting an inner space along the longitudinal direction of the compressor, and the inner diameter of the compressor is divided into 1:20 to 1: 5 Point to pass through.

According to another preferred embodiment of the present invention, it is possible to further include the step of extruding the preform between the steps (2) and (3).

According to another preferred embodiment of the present invention, the step (3) may further include heating the sheet to remove the liquid lubricant between the step (3) and the step (4).

According to another preferred embodiment of the present invention, a first PTFE separation layer; And a second PTFE separation layer formed on at least one side of the first PTFE separation layer and having a molecular weight different from the average molecular weight of the first PTFE separation layer, wherein the first PTFE separation layer and the second PTFE separation layer are integrally formed And having different average pore sizes and porosities.

According to another preferred embodiment of the present invention, the first PTFE separating layer and the second PTFE separating layer may have the same stretching ratio.

According to another preferred embodiment of the present invention, the difference in the average molecular weight of the first PTFE separation layer and the second PTFE separation layer may be 3.2 × 10 ⁷ to 8.2 × 10 ⁸ .

According to another preferred embodiment of the present invention, the thickness of the first PTFE separation layer may be 1:20 to 1: 5 of the entire asymmetric multi-layered PTFE membrane.

According to another preferred embodiment of the present invention, when the average molecular weight of the first PTFE separation layer is larger than the average molecular weight of the second PTFE separation layer, the average pore size of the first PTFE separation layer is 0.05 to 1.0 탆, The average pore size of the two PTFE separating layers may be between 0.5 and 30 mu m.

The asymmetric multi-layered PTFE membrane of the present invention and its production method can significantly improve the porosity, flow rate and lifetime of asymmetric multi-layered PTFE membranes without causing problems of shrinkage, reduction of porosity and lowering of porosity, .

Fig. 1 is a schematic view of a preferred compressor which may be used in the present invention, and Fig. 2 is a perspective view of a preform produced therewith.
Fig. 3 is a schematic diagram of a preferred compressor that may be used in the present invention, and Fig. 4 is a perspective view of a preform produced therewith.
5 is a schematic diagram of an extruder that can be used in the present invention.
6 is a schematic diagram of a calender roll that can be used in the present invention.
7 is a schematic diagram of MDO (machine direction stretching) according to a preferred embodiment of the present invention.
8 is a schematic diagram of TDO (vertical stretching) according to a preferred embodiment of the present invention.
FIG. 9 is a cross-sectional view of an asymmetric two-layer PTFE separator according to a preferred embodiment of the present invention.
10 is a cross-sectional view of an asymmetric three-layer PTFE separator according to another preferred embodiment of the present invention.
11 is a cross-sectional view of an asymmetric two-layer PTFE separator according to another preferred embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in more detail with reference to the accompanying drawings.

As described above, the conventional asymmetric PTFE separation membrane can approach the pore structure on the cross section in an asymmetric form by controlling the degree of stretching by varying the temperature at the upper and lower portions of the PTFE flat membrane at the time of stretching. However, the uneven temperature difference between the upper and lower portions has a problem in that the sheet shrinks due to the surface receiving less heat. Thus, a method of producing an asymmetric separator by thermally fusing two PTFE flat membranes having different porosity and average pore size has been disclosed. However, there is a problem in that pores are damaged and porosity is decreased in the lining step, thereby reducing the flow rate.

(1) A first PTFE powder, a first paste containing a liquid lubricant, a second PTFE powder having an average molecular weight different from the first PTFE and a second PTFE powder containing a liquid lubricant, ; (2) compressing the first paste and the second paste into a single preform, each of the first paste and the second paste being injected into individual input portions of a compressor including a plurality of input portions partitioned by the partition walls and being compressed by one preform; (3) calendering the preform in sheet form; (4) stretching the sheet; And (5) firing the stretched sheet to solve the above-mentioned problem. The asymmetric multi-layered PTFE membrane produced through this method can significantly improve the porosity, flow rate, and service life of the asymmetric multi-layered PTFE membrane without causing any problems of shrinkage, reduction in porosity and lowering of porosity, .

First, a first paste containing a first PTFE powder, a liquid lubricant, and a second PTFE powder having a different average molecular weight from the first PTFE and a liquid lubricant is prepared as step (1). Specifically, the first paste and the second paste of the present invention differ in the average molecular weight of the PTFE powder contained. Accordingly, the average pore size and the average porosity become different even if the multi-layered PTFE membrane is produced through the same stretching ratio at a later step. Preferably, the difference in the average molecular weight of the first PTFE powder contained in the first paste and the PTFE powder contained in the second paste may be 3.2 X 10 ⁷ to 8.2 X 10 ⁸ . If the difference in average molecular weight is less than 3.2 X 10 ⁷ , it is difficult to achieve desired physical properties as an asymmetric membrane because the difference in the average pore sizes achievable is insignificant. If the average molecular weight is larger than 8.2 X 10 ⁸ , the same drawing conditions are applied, Problems that can not be efficiently given can arise.

Preferably, the average particle size of the PTFE powder may be 300 to 500 占 퐉, but is not limited thereto.

The liquid lubricant included in the first paste and the second paste of the present invention is for performing smooth extrusion, calendering and preform formation while wetting the surface of the PTFE fine powder, and is formed by means of evaporation extraction It is not particularly limited as long as it is a substance which can be removed by the above-mentioned method. For example, as the liquid lubricant, various alcohols, ketones, esters, and the like may be used in addition to hydrocarbon oils such as liquid paraffin, naphtha, white oil, toluene, and xylene. On the other hand, the liquid lubricant of the first paste and the second paste may be the same or different from each other.

According to a preferred embodiment of the present invention, the first paste may include 10 to 50 parts by weight of a liquid lubricant based on 100 parts by weight of polytetrafluoroethylene (PTFE) powder. The second paste also has the same range of conditions as the first paste, but the first paste and the second paste may have the same or different types and / or contents of the added liquid lubricant.

Next, (2) the first paste and the second paste are put into respective input portions of the compressor including a plurality of input portions partitioned by the partition and compressed by one preform, and are compressed into one preform. Figure 1 is a schematic diagram of a preferred compressor that may be used in the present invention. 1, the cylindrical compressor 10 includes a partition 11 and is partitioned into a first inlet 12 and a second inlet 13 by the partition 11. The partition walls 11 do not extend to the discharge port so that the pastes injected into the first inlet 12 and the second inlet 13 form a single preform and can be compressed. When the first paste is injected into the first inlet 12 and the second paste is injected into the second inlet 14 through the first inlet 12 and the second inlet 14, One preform is formed and the preform is discharged to the discharge port of the compressor. FIG. 2 is a preform formed through the compressor of FIG. 1, which is divided into a first paste portion 20 and a second paste portion 21 and is hardly mixed with each other. This is because they are compressed to a certain extent in the compression stage and then combined into a solid state.

1, the partition 11 is disposed so as to be parallel to a virtual plane bisecting the internal space along the longitudinal direction of the compressor, And passes through a point where the inner diameter of the compressor is divided into 1:20 to 1: 5. In other words, the partition 11 is arranged so as to partition the inner diameter (dotted line) of the cylinder into a: b. FIG. 4 is a preform produced through the compressor of FIG. 2, in which the first paste portion 25 and the second paste portion 26 are formed asymmetrically, and the asymmetric PTFE membrane produced therefrom has a cross- It is possible to provide asymmetry and to form a stable type layer structure without the risk of structurally separating from the rolling and drawing of a single rod.

While the present invention has been described with respect to a circular cross section of a compressor, it is apparent to those skilled in the art that the compressor can be designed in various shapes such as a rectangular shape and an elliptical shape. In addition, the number of the barrier ribs may also be plural, and a plurality of the charging holes may be formed.

On the other hand, the temperature and the pressure inside the compressor can be set according to the condition of the compressor applied in the production of the conventional PTFE separator, and preferably the pressure can be performed at 18 to 25 ° C and 1 to 3 MPa.

The method may further include a step of extruding the preform from an extruder between steps (2) and (3). Specifically, the extruder which can be used in the present invention can be used without limitation as long as it is usually used for the production of a polymer membrane, and can be preferably a ram extruder. FIG. 5 is a schematic view of an extruder which can be used in the present invention. The preform obtained through the step (2) is introduced into the extruder 30, and the extrudate 31 is extruded do. In this case, the extrudate 31 having various cross sections may be manufactured according to the shape of the extruder 30, and preferably it may have a rod shape. The size of the extrudate can also be set according to the conditions. The extrusion conditions may be carried out under the conditions of a conventional PTFE separation membrane extrusion process, and preferably the step (3) may be carried out at a pressure of 1 to 25 MPa at 35 to 75 캜. On the other hand, if the preform compacted through step (2) has a dividing surface, the dividing surface can be removed through an extrusion step.

Next, in step (3), the extruded extrudate or the preform is calendered in a sheet form. Fig. 6 is a schematic view of a calender roll that can be used in the present invention. When the extrudate or the like passes through a calender roll 40, it is spread into a sheet shape 41. Fig. In this case, preferably, the sheet may have a thickness of 500 to 1000 mu m.

Next, the method may further include heating the calendered sheet between steps (3) and (4) to remove the liquid lubricant. Specifically, the heating temperature of the sheet may be in the range of the temperature at which the liquid lubricant is removed, preferably 120 to 200 ° C.

In the next step (4), the sheet from which the liquid lubricant is removed is stretched to form pores. Specifically, the PTFE separator forms a pore composed of a node and a fibril through a stretching process, and biaxial stretching can be performed for this purpose. In this case, transverse stretching may preferably be stretching at 1.2 to 15 times, and longitudinal stretching may be stretching at 1.2 to 15 times. More specifically, a conventional PTFE sheet is conveyed through a roller. In this case, the biaxial stretching can be performed using the speed difference between the rollers.

7 is a schematic view showing a step of longitudinally stretching the sheet 50 from which the liquid lubricant has been removed. FIG. 8 is a schematic view showing a step of transversely stretching the longitudinally stretched sheet 50, wherein the longitudinal stretching and the transverse stretching Can be performed independently of the order. The stretching temperature may also be 150 to 320 DEG C, but is not limited thereto.

As a final step (5), the stretched PTFE separation membrane is fired to prevent heat shrinkage. The firing temperature in the step (5) may be performed at 300 to 400 ° C for 10 seconds to 10 minutes.

The asymmetric multi-layer PTFE separator of the present invention produced by the above-mentioned method comprises a first PTFE separation layer; And a second PTFE separation layer formed on at least one side of the first PTFE separation layer and having a molecular weight different from the average molecular weight of the first PTFE separation layer, wherein the first PTFE separation layer and the second PTFE separation layer are integrally formed And have different average pore sizes and porosity. The first PTFE layer and the second PTFE layer may be formed by molding the first PTFE separating layer and the second PTFE separating layer into one from the manufacturing step of the preformed article without performing heat fusion or the like or using an unequal heating method of the PTFE layer The porosity, the flow rate and the service life of the asymmetric multi-layered PTFE membrane can be remarkably improved without causing problems of shrinkage, reduction of porosity and lowering of porosity, and without increasing the cost of membrane formation. In addition, the first PTFE separation layer and the second PTFE separation layer may have the same stretching ratio because the stretching process is performed in a state where the first PTFE separation layer and the second PTFE separation layer are laminated together. 10 is a cross-sectional view of an asymmetric two-layer PTFE separator 100 according to one preferred embodiment of the present invention, in which the first PTFE layer 101 and the second PTFE layer 102 have a different pore- But it is laminated with one sheet from the manufacturing process step without heat fusion. 11 is a sectional view of an asymmetric three-layer PTFE separator 110 according to a preferred embodiment of the present invention, in which a first PTFE layer 111, a second PTFE layer 112 and a third PTFE layer having different physical properties are integrated .

Meanwhile, when the separator is manufactured through the asymmetric compressor as shown in FIG. 3, the thickness of the first PTFE separator may be 1:20 to 1: 5 of the total asymmetric multilayer PTFE separator. FIG. 11 is a cross-sectional view of an asymmetric two-layer PTFE separation membrane 120 in which the first PTFE layer 121 and the second PTFE layer 122 are layers having different porosity and the like, And the thicknesses of the respective layers are different from each other. By minimizing the thickness of the selective layer, it is possible to improve the particle removal rate to high flow rate (see Table 1).

According to another preferred embodiment of the present invention, when the average molecular weight of the first PTFE separation layer is larger than the average molecular weight of the second PTFE separation layer, the average pore size of the first PTFE separation layer is 0.05 to 1.0 탆, The average pore size of the two PTFE separating layers may be between 0.5 and 30 mu m. Thus, it is possible to remarkably improve the porosity, flow rate and life of the asymmetric multi-layered PTFE membrane without causing any problems such as shrinkage, reduction of porosity and lowering of porosity, and without increasing the cost of membrane formation.

Hereinafter, the structure and effect of the present invention will be described in more detail with reference to examples and comparative examples. However, this embodiment is only an example for explaining the present invention in more detail, and the scope of the present invention is not limited to these embodiments.

≪ Example 1 >

Average molecular weight 9.2 X 10⁷, And 20 parts by weight of liquid paraffin (Exopon Mobil product, trade name: Isopar-H) as a liquid lubricant were mixed with 100 parts by weight of PTFE fine powder having an average diameter of 500 탆 to prepare a first PTFE paste. An average molecular weight of 1.0 X 10 <⁷ And 20 parts by weight of liquid paraffin (product of Exxon Mobil, trade name: Isopar-H) as a liquid lubricant were mixed with 100 parts by weight of PTFE fine powder having an average diameter of 500 탆 to prepare a second PTFE paste. As shown in Fig. 1, the barrier ribs were placed in both inlet ports of a compressor for dividing the inner diameter by 1: 1, and compressed at a pressure of 3 MPa at 20 캜 to prepare a preform. The prepared preform was introduced into the ram extruder. The conditions inside the ram extruder were extrusion molded into a rod shape having an outer diameter of 10 mm by performing an extrusion process at a pressure of 2 MPa (20 kg / cm 2) and at 50 캜. Thereafter, the extruded rod was passed through a calender roll to form a sheet, followed by a continuous process, and then the formed PTFE sheet was heated at 190 DEG C for 5 minutes to remove liquid paraffin. The continuously formed PTFE separating membrane was stretched 10 times in the longitudinal direction and 10 times in the transverse direction at 200 DEG C by the speed difference between the rollers to form pores and then fired at 380 DEG C to form an asymmetric two- (Thickness: 60 탆).

≪ Example 2 >

A first PTFE paste was prepared by mixing 20 parts by weight of liquid paraffin (trade name: Isopar-H available from Exxon Mobil) as a liquid lubricant with 100 parts by weight of a PTFE fine powder having an average molecular weight of 9.2 X 10 ⁷ and an average diameter of 500 μm . A second PTFE paste was prepared by mixing 20 parts by weight of liquid paraffin (Exopon Mobil, trade name: Isopar-H) as a liquid lubricant with 100 parts by weight of a PTFE fine powder having an average molecular weight of 4.2 X 10 ⁷ and an average diameter of 500 μm . A third PTFE paste was prepared by mixing 20 parts by weight of liquid paraffin (Exopon Mobil, trade name: Isopar-H) as a liquid lubricant with 100 parts by weight of a PTFE fine powder having an average molecular weight of 1.0 X 10 ⁷ and an average diameter of 500 μm . The asymmetric three-layered PTFE membrane (thickness: 60 袖 m) as shown in Fig. 10 was prepared in the same manner as in Example 1 except that each of the membranes was charged into a cylindrical compressor equipped with a partition wall having an inner diameter of 1: 1: 1.

≪ Example 3 >

As shown in Fig. 3, the same procedure as in Example 1 was carried out, except that the first paste was charged into a narrow inlet and the second paste was charged into a wide inlet to the compressor in which the partition wall had an inner diameter of 1: 9, (Thickness: 60 탆) was prepared.

<Example 4>

A PTFE fine powder having an average molecular weight of 4.0 X 10 ⁷ and an average diameter of 500 탆 was used as the first paste, and a PTFE fine powder having a second paste of 6.0 × 10 ⁷ and an average diameter of 500 탆 was used The same procedure as in Example 1 was carried out to prepare an asymmetric 2-layer PTFE separator.

&Lt; Comparative Example 1 &

20 parts by weight of liquid paraffin (product of Exxon Mobil, trade name: Isopar-H) as a liquid lubricant was mixed with 100 parts by weight of a PTFE fine powder having an average molecular weight of 9.2 X 10 ⁷ and an average diameter of 500 탆 to prepare a PTFE paste, The asymmetric PTFE separator (thickness: 60 탆) was prepared in the same manner as in Example 1 except that the upper surface of the separator was treated at 260 캜 and the lower surface thereof was treated at 180 캜.

&Lt; Comparative Example 2 &

A second PTFE separator (thickness 30 μm) was prepared by using the first paste of Example 1 and a second PTFE separator (thickness 30 μm) was prepared. The PTFE separator was thermally fused at 390 ° C. to form an asymmetric 2-layer PTFE separator .

<Experimental Example>

The properties of the PTFE separation membranes of Examples 1 to 3 and Comparative Examples 1 and 2 were evaluated as described below, and the results are shown in Table 1.

1. Measurement of permeability

IPA was filtered using a permeation cell under a constant pressure of 1 bar at 25 ° C, and the treatment flow rate was expressed as LMH.

2. Measurement of particle removal rate

The PTFF membrane was attached to the permeable cell, and the IPA was filtered and sufficiently wetted. Then, a diluted solution of pure water (ISO Fine Test Dust) was injected through the gear pump into the permeable cell. At this time, the number of particles having a size of 0.5 μm or more before and after the passage of the filter was measured, and the change in the number of particles was expressed as a percentage.

3. Shrinkage phenomenon

The shrinkage of the PTFE membrane was observed visually, and the results are shown in Table 1.

O: Not generated, X: Occurred

4. Appearance evaluation

The appearance of the degree of pore damage and the like on the multilayered joint surface of the PTFE membrane was evaluated by an electron microscope and the results are shown in Table 1.

⊚: very excellent, ∘: excellent, △: fair, X: severe damage

division IPA Transmittance (LMH)
25 ° C 1 bar Particle removal rate (%) Contraction phenomenon Appearance evaluation Example 1 22,240 89.5 ○ ◎ Example 2 21,200 93.0 ○ ◎ Example 3 23,140 88.2 ○ ○ Example 4 22,880 85.7 ○ ○ Comparative Example 1 17,570 90.4 ○ △ Comparative Example 2 16,920 91.7 × △

As can be seen from Table 1, the membranes of Examples 1 to 4 of the present invention were superior in permeability and particle removal rate as compared with the membranes of Comparative Examples 1 and 2, and had almost no pore damage and shrinkage. On the other hand, the PTFE sheet of the three-layer structure of Example 2 had slightly lower IPA permeability as compared with Example 1, but the porosity of the front surface and the back surface was the same, but the asymmetry of the sheet with the same thickness was improved, Efficiency is greatly improved. Example 3 shows that the content ratio of the high molecular weight polymer constituting the upper layer of Example 1 is reduced to 10%, and the thickness of the selective layer is minimized, thereby exhibiting excellent particle removal rate with respect to the high flow rate. On the other hand, in Example 4 in which the difference in average molecular weight was small, the effect of the physical properties and the particle removal rate was lower than that in Example 1.

The PTFE separator prepared by the method of the present invention can be widely used in the fields of fibers and filtration membranes.

Claims (15)

(1) preparing a second paste comprising a first PTFE powder, a first paste containing a liquid lubricant, and a second PTFE powder having a different average molecular weight from the first PTFE and a liquid lubricant;
(2) compressing the first paste and the second paste into a single preform, each of the first paste and the second paste being injected into individual input portions of a compressor including a plurality of input portions partitioned by the partition walls and being compressed by one preform;
(3) calendering the preform in sheet form;
(4) stretching the sheet; And
(5) firing the stretched sheet; Lt; RTI ID = 0.0 &gt; PTFE &lt; / RTI &gt; The method according to claim 1,
Wherein the difference between the average molecular weights of the first PTFE powder and the second PTFE powder is 3.2 X 10 ⁷ to 8.2 X 10 ⁸ . The method according to claim 1,
Wherein the first paste comprises 10 to 50 parts by weight of the liquid lubricant in 100 parts by weight of the PTFE powder and the second paste comprises 10 to 50 parts by weight of the liquid lubricant in 100 parts by weight of the PTFE powder. A method of producing a PTFE membrane. The method according to claim 1,
Wherein the step (2) is carried out at a pressure of 18 to 25 캜 and a pressure of 1 to 3 MPa. The method according to claim 1, wherein the stretching temperature in step (4) is 200 to 320 ° C, and the firing temperature in step (5) is 300 to 400 ° C. The method as claimed in claim 1, wherein the liquid lubricant is at least one selected from the group consisting of liquid paraffin, naphtha, white oil, toluene, xylene, alcohol, ketone and ester. The method as claimed in claim 1, wherein the thickness of the sheet in the step (3) is 500 to 1000 占 퐉. The method according to claim 1,
Characterized in that the partition is disposed so as to be parallel to an imaginary plane bisecting the internal space along the longitudinal direction of the compressor and passes through a point dividing the inner diameter of the compressor by 1: 2 to 1:20, A method of producing a PTFE membrane. The method according to claim 1,
Further comprising the step of extruding the preform between the step (2) and the step (3). The method according to claim 1,
Further comprising the step of heating the sheet between steps (3) and (4) to remove the liquid lubricant. A first PTFE separation layer;
And a second PTFE separation layer formed on at least one side of the first PTFE separation layer and having a molecular weight different from the average molecular weight of the first PTFE separation layer, wherein the first PTFE separation layer and the second PTFE separation layer are integrally formed And having different average pore sizes and porosities. 12. The method of claim 11,
Wherein the first PTFE separating layer and the second PTFE separating layer have the same stretching ratio. 12. The method of claim 11,
Wherein the difference between the average molecular weights of the first PTFE separation layer and the second PTFE separation layer is 3.2 X 10 ⁷ to 8.2 X 10 ⁸ . 12. The method of claim 11,
Wherein the thickness of the first PTFE separating layer is 1: 2 to 1:20 of the total asymmetric multilayer PTFE separating membrane. 12. The method of claim 11,
When the average molecular weight of the first PTFE separation layer is larger than the average molecular weight of the second PTFE separation layer, the average pore size of the first PTFE separation layer is 0.05 to 1.0 탆, and the average pore size of the second PTFE separation layer is 0.5 to 30 Lt; RTI ID = 0.0 &gt; m. &Lt; / RTI &gt;

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