KR101599111B1 - PTFE hollow fiber membrane and production method thereof - Google Patents

Abstract

The method for producing a PTFE hollow fiber membrane of the present invention comprises the steps of: (1) mixing a polytetrafluoroethylene (PTFE) powder and a liquid lubricant to prepare a PTFE paste; (2) compressing the PTFE paste to produce a hollow PTFE billet; (3) extruding the PTFE billet into a PTFE tube; (4) heating the PTFE tube to remove the liquid lubricant; And (5) stretching the PTFE tube 1.1 to 1.7 times and firing the PTFE hollow fiber membrane to produce the PTFE hollow fiber membrane.
Accordingly, the pressure resistance and longitudinal shrinkage in the transverse direction can be prevented without increasing the outer diameter of the PTFE hollow fiber membrane without increasing the manufacturing cost.

Description

TECHNICAL FIELD [0001] The present invention relates to a PTFE hollow fiber membrane and a production method thereof,

The present invention relates to a PTFE hollow fiber membrane, and more particularly, to a PTFE hollow fiber membrane having improved pressure resistance and a method of manufacturing the PTFE hollow fiber membrane.

BACKGROUND ART [0002] Porous materials composed of polytetrafluoroethylene (hereinafter referred to as "PTFE") are not only excellent in chemical resistance, heat resistance, weather resistance, and nonflammability, but also have properties such as non-tackiness 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. For this reason, a 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 separating membrane is mainly composed of a paste composed of a mixture of PTFE fine powder and a lubricant, is rolled through a rolling process between the two rollers, formed into a sheet, and after the lubricant is removed, The PTFE separation membrane produced by this stretching includes a porous body inside the porous body, and the porous body includes a plurality of fine fibrils (fine fibers) and the fibrils (Nodules) connected to each other by a microstructure, and this microstructure forms a continuous porous microstructure.

Meanwhile, the PTFE separation membrane may be formed of a hollow fiber membrane, and the PTFE hollow fiber membrane may be manufactured by a paste extrusion method.

The PTFE hollow fiber membrane manufactured by the paste extrusion method controls the porosity by the stretching and sintering process. Although it is easy to secure the porosity of the membrane at the time of stretching, the strength and pressure resistance in the transverse direction become insufficient, There is a problem that easily occurs.

Japanese Patent Application Laid-Open No. 2004-0036618 discloses a method of winding a PTFE tape serving as a filtration layer on the outside in a spiral direction to adhere to each other to solve problems such as pore size reduction and pressure resistance (see FIG. 1).

Specifically, the porous soft PTFE tube 30 is prepared by paste extrusion molding, and the PTFE porous soft resin sheet 31 is superimposed and spirally wound on the entire outer peripheral surface thereof. As a result, as shown in FIG. 2, a skin layer is provided outside the support layer.

However, this method has two layers of PTFE membranes, which are complicated to manufacture and costly, and the outer diameter of the hollow fiber membrane becomes very large, so that the degree of integration of the PTFE hollow fiber membrane in the filter module becomes low.

Therefore, there is a need to develop a technique for preventing pressure resistance and longitudinal shrinkage in the transverse direction without increasing the outer diameter of the PTFE hollow fiber membrane without increasing the manufacturing cost.

The present invention provides a PTFE hollow fiber membrane having a novel structure capable of improving the pressure resistance and preventing shrinkage in the longitudinal direction by controlling the ratio of the node to the fibril on the outer surface of the PTFE hollow fiber membrane.

It is another object of the present invention to provide a method for producing a PTFE hollow fiber membrane having a novel structure in which pressure resistance is improved and longitudinal shrinkage is prevented.

In order to solve the above problems, in the PTFE hollow fiber membrane according to one aspect of the present invention, the longitudinal length ratio of the node to the fibril on the outer surface of the PTFE hollow fiber membrane is 10: 1 or less.

Further, in the PTFE hollow fiber membrane according to another aspect of the present invention, the area ratio of the node on the outer surface of the PTFE hollow fiber membrane is 5 to 9 times the area ratio of the fibril.

In the PTFE hollow fiber membrane, the average pore size is preferably 0.1 to 0.4 mu m.

In the PTFE hollow fiber membrane, it is preferable that at least 70% of the total pores exist in the range of ± 0.1 μm of the average pore size.

According to another aspect of the present invention, there is provided a method of manufacturing a PTFE hollow fiber membrane, comprising the steps of: (1) preparing a PTFE paste by mixing polytetrafluoroethylene (PTFE) powder and a liquid lubricant; (2) compressing the PTFE paste to produce a hollow PTFE billet; (3) extruding the PTFE billet into a PTFE tube; (4) heating the PTFE tube to remove the liquid lubricant; And (5) stretching the PTFE tube to 1.1 to 1.7 times and firing the PTFE hollow fiber membrane to produce the PTFE hollow fiber membrane.

In the method of producing the PTFE hollow fiber membrane, the liquid lubricant is preferably contained in an amount of 18 to 23 parts by weight based on 100 parts by weight of the polytetrafluoroethylene (PTFE) powder.

In the above method of producing a PTFE hollow fiber membrane, it is preferable that the PTFE hollow fiber membrane is stretched such that the longitudinal length ratio between the node and the fibril is 10: 1 or less on the outer surface of the PTFE hollow fiber membrane.

In the above-mentioned method of producing a PTFE hollow fiber membrane, it is preferable that the area ratio of the node on the outer surface of the PTFE hollow fiber membrane is 5 to 9 times larger than the area ratio of the fibril.

In the above-mentioned process for producing a PTFE hollow fiber membrane, it is preferable to stretch so that the average pore size becomes 0.1 to 0.4 μm.

According to the method for producing a PTFE hollow fiber membrane of the present invention, the pressure resistance can be improved and contraction in the longitudinal direction can be prevented by controlling the ratio of the node to the fibril on the outer surface of the PTFE hollow fiber membrane. As a result, not only the water permeability can be improved but also the pressure resistance can be improved.

Also, the PTFE hollow fiber membrane manufacturing method of the present invention can improve the pressure resistance without increasing the outer diameter of the hollow fiber membrane, thereby improving the degree of integration of the PTFE hollow fiber membrane in the filter module.

1 is a schematic view of a conventional method for producing a pressure-resistant PTFE hollow fiber membrane.
2 is a SEM photograph of a conventional pressure-resistance-improving PTFE hollow fiber membrane.
3 is an SEM photograph of the outer surface of the PTFE hollow fiber membrane produced by quadrupling the elongation ratio of the PTFE unstretched hollow fiber membrane.
4 is a SEM photograph of the outer surface of the PTFE hollow fiber membrane produced by stretching the stretching ratio of the PTFE unstretched hollow fiber membrane to 1.5 times.

The PTFE hollow fiber membrane of the present invention is prepared by extruding a paste-like PTFE raw material to an outer diameter of a predetermined size to prepare an unstretched hollow fiber membrane, stretching the prepared unstretched hollow fiber membrane to generate a certain ratio of nodes and fibrils, And achieve longitudinal shrinkage prevention characteristics.

In the present invention, the area ratio of the nodes in the ratio of the node to the fibril is higher on the outer surface of the PTFE hollow fiber membrane, and the porosity on the outer surface is lowered at the cross section of the hollow fiber membrane. Since the outer surface receives a lot of stress compared with the inner surface and is radiated, the outer surface is lower than the central portion.

Accordingly, the PTFE hollow fiber membrane of the present invention has a single layer structure or a tabular skin having a low degree of porosity in a center portion having high porosity, and substantially has the same effect as a multi-layer structure. The degree of integration of the PTFE hollow fiber membrane can be kept high in the filter module.

The above-mentioned structure of the PTFE hollow fiber membrane of the present invention is constituted by shortening the longitudinal length of the fibrils so as to lower the surface porosity on the outer surface by controlling the stretching ratio.

In the present invention, the stretching ratio of the PTFE hollow fiber membrane is adjusted so that the ratio of the area of the nodules is 5 to 9 times higher than the area of the fibrils, without raising the surface porosity by lowering the stretching ratio.

As a result, the PTFE hollow fiber membrane of the present invention has a low surface porosity due to a low fibril length on the outer surface, and as a result, it is possible to achieve high pressure resistance and high shrinkage resistance in the longitudinal direction.

In the present invention, the longitudinal length ratio of the node to the fibril on the outer surface of the PTFE hollow fiber membrane is preferably controlled to be 10: 1 or less.

In the present invention, the stretching ratio of the PTFE unstretched hollow fiber membrane is preferably 1.1 to 1.7 times.

When the draw ratio is less than 1.1 times, the longitudinal length ratio between the node and the fibrils exceeds 10: 1 and the pore size on the outer surface becomes excessively small. When the draw ratio exceeds 1.7 times, the longitudinal length of the fibrils becomes The pore size of the outer surface becomes excessively large and the desired pressure resistance is not achieved.

On the other hand, FIG. 3, which is an SEM photograph of the outer surface of the PTFE hollow fiber membrane produced by stretching the PTFE unstretched hollow fiber membrane at a stretching ratio of 4 times, shows that the longitudinal length of the fibril becomes long and the pore size on the outer surface becomes excessively large Is formed.

4, which is an SEM photograph of the outer surface of the PTFE hollow fiber membrane produced by making the stretching ratio of the PTFE unstretched hollow fiber membrane 1.5 times as high as the range of the present invention, the longitudinal length of the fibrils is short, And the outer surface of the PTFE hollow fiber membrane is formed to have sufficient pressure resistance.

In addition, the PTFE hollow fiber membrane of the present invention can improve porosity and remarkably improve water permeability even when the average pore size is small.

The method of manufacturing a PTFE hollow fiber membrane of the present invention comprises the steps of: (1) preparing a PTFE paste by mixing polytetrafluoroethylene (PTFE) powder and a liquid lubricant; (2) compressing the PTFE paste to produce a hollow PTFE billet; (3) extruding the PTFE billet into a PTFE tube; (4) heating the PTFE tube to remove the liquid lubricant; And (5) stretching and firing the PTFE tube to produce a PTFE hollow fiber membrane.

Hereinafter, the present invention will be described in detail.

First, as step (1), a polytetrafluoroethylene (PTFE) powder and a liquid lubricant are mixed to prepare a paste. The PTFE powder contained in the paste of the present invention can be used without limitation as long as it is conventionally used in the PTFE separation membrane. Preferably, the average particle diameter of the PTFE powder may be 300 to 500 탆, but is not limited thereto. The molecular weight and the like are not particularly limited, and commercially available products may be used. Examples thereof include Polyflon F-104 (Daikin Industries) and Fluon CD-123 (Asahi ICI Fluoropolymers Co., Ltd.).

The liquid lubricant contained in the paste of the present invention is for performing smooth extrusion without wetting the surface of the PTFE fine powder and is not particularly limited as long as it is a material that can be removed by means such as evaporation extraction by heat after forming into a hollow fiber membrane. 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.

The paste is preferably prepared by mixing 18 to 23 parts by weight of a liquid lubricant with respect to 100 parts by weight of polytetrafluoroethylene (PTFE) powder.

Next, as step (2), a hollow PTFE billet is produced using a PTFE face. This is done by compressing the paste in a compressor and preforming it into a hollow PTFE billet.

Specifically, compressors usable in the present invention can be used without limitation as long as they are capable of producing a hollow PTFE billet. Specifically, when the paste flows into the compressor, the paste can be formed into a preform by applying pressure. In the present invention, the preform is manufactured to have a hollow section. The size of the preform may also be set according to conditions.

Next, as step (3), the PTFE billet is extruded into a PTFE tube.

Specifically, the extruder which can be used in the present invention can be used without limitation as long as it can form a PTFE tube.

Specifically, the PTFE billet is introduced into the extruder, and the PTFE billet is extruded into the PTFE tube while passing through the inside of the extruder. The size of the extrudate can also be set according to the conditions. The extrusion conditions are preferably carried out at a pressure of 10 to 25 MPa at 35 to 75 캜.

Next, in step (4), the PTFE tube is heated 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 (5), the PTFE tube from which the liquid lubricant is removed is stretched. At this time, the length of the node is made long and the longitudinal length of the fibril is shortened so as to lower the surface porosity at the outer surface of the PTFE hollow fiber membrane.

As a result, the PTFE hollow fiber membrane of the present invention has a low surface porosity due to a low fibril length on the outer surface, and as a result, it is possible to achieve high pressure resistance and high shrinkage resistance in the longitudinal direction.

In the present invention, the stretching ratio of the PTFE unstretched hollow fiber membrane is preferably 1.1 to 1.7 times.

When the draw ratio is less than 1.1 times, the longitudinal length ratio between the node and the fibrils exceeds 10: 1 and the pore size on the outer surface becomes excessively small. When the draw ratio exceeds 1.7 times, the longitudinal length of the fibrils becomes The pore size of the outer surface becomes excessively large and the desired pressure resistance is not achieved.

Accordingly, small pores can be densely formed in the dense pore size range of the average pore size due to the generated pores while reducing the average pore size. The stretching temperature may also be 150 to 320 DEG C, but is not limited thereto.

The stretched PTFE hollow fiber membrane is then fired to prevent heat shrinkage. The firing temperature can be performed at 300 to 400 DEG C for 10 seconds to 10 minutes.

The porous PTFE hollow fiber membrane of the present invention produced through the above-described method has an average pore size of 0.1 to 0.4 μm, and pores of 70% or more of the total pores are present within a range of ± 0.1 μm of a predetermined average pore size. For example, when the average pore size of the porous PTFE separation membrane is 0.2 μm, 70% of the pores are concentrated in the range of 0.1 to 0.3 μm in the range of ± 0.1 μm. Accordingly, the PTFE hollow fiber membrane of the present invention can achieve high water permeability because of high porosity even if the average pore size is small.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Hereinafter, the present invention will be described in detail with reference to preferred embodiments and accompanying drawings, which will be easily understood by those skilled in the art. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

Example 1

21 parts by weight of liquid paraffin (Exopon Mobil, trade name: Isopar-H) as a liquid lubricant was mixed with 79 parts by weight of a PTFE fine powder having an average diameter of 500 mu m (DF-130, Solvay) to form a PTFE paste.

The PTFE paste was compressed at 20 DEG C under a pressure of 3 MPa using a compressor to form a hollow PTFE billet.

The PTFE billet was introduced into the extruder, and a PTFE tube having an outer diameter of 2 mm and an inner diameter of 1 mm was formed under the conditions of an inner pressure of 50 MPa (500 kg / cm 2) and an extrusion process at 50 ° C.

The formed PTFE tube was then heated at 120 DEG C for 5 minutes to remove liquid paraffin.

Thereafter, the formed PTFE tube was stretched 1.5 times in the longitudinal direction at 320 DEG C by the speed difference between the rollers to form pores in the PTFE hollow fiber membrane to form nodes and fibrils, and then fired at 390 DEG C to obtain the desired PTFE hollow The desert was prepared.

The hollow size of the PTFE hollow fiber membrane prepared in Example 1 was 0.9 mm, the wall thickness of the PTFE hollow fiber membrane was 0.5 mm, the average pore size was 0.2 μm, and the porosity was 73%. An SEM image of the outer surface of the PTFE hollow fiber membrane produced by Example 1 is shown in FIG.

Comparative Example 1

The procedure of Example 1 was repeated except that the stretching ratio was changed to 4 times.

The average pore size of the PTFE hollow fiber membrane produced by Comparative Example 1 was 1.6 탆. An SEM image of the outer surface of the PTFE hollow fiber membrane produced by Comparative Example 1 is shown in FIG.

The longitudinal shrinkages of the PTFE hollow fiber membranes prepared in Example 1 and Comparative Example 1 were 10% and 50%, respectively.

Stretching Pore size Contraction ratio Example 1.5 0.2 탆 10% Comparative Example 4 1.6 탆 50%

As can be seen from Table 1, in Example 1 in which the stretching ratio was 1.5 times, the longitudinal shrinkage ratio was good at 10%, but in Comparative Example 1 in which the stretching ratio was 4 times, the longitudinal shrinkage ratio was 50%.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, Do.

Claims (9)

In the PTFE hollow fiber membrane,
The longitudinal length ratio of the node to the fibril on the outer surface of the PTFE hollow fiber membrane is 10: 1 or less,
The area ratio of the nodes on the outer surface of the PTFE hollow fiber membrane is 5 to 9 times larger than the area ratio of the fibrils,
The average pore size is 0.1 to 0.4 mu m,
70% or more of the total pores within the range of ± 0.1 μm of the average pore size
A PTFE hollow fiber membrane for improving the pressure resistance of PTFE hollow fiber membrane, preventing shrinkage in longitudinal direction, and improving water permeability.
delete delete delete In the process for producing a PTFE hollow fiber membrane,
(1) mixing a polytetrafluoroethylene (PTFE) powder and a liquid lubricant to prepare a PTFE paste;
(2) compressing the PTFE paste to produce a hollow PTFE billet;
(3) extruding the PTFE billet into a PTFE tube;
(4) heating the PTFE tube to remove the liquid lubricant; And
(5) stretching the PTFE tube 1.1 to 1.7 times and firing to produce a PTFE hollow fiber membrane; Lt; / RTI >
Wherein the longitudinal ratio of the node to the fibril in the outer surface of the PTFE hollow fiber membrane is 10: 1 or less, the area ratio of the node on the outer surface of the PTFE hollow fiber membrane is 5 to 9 times larger than the area ratio of the fibril, Characterized in that the PTFE hollow fiber membrane has a pore size of 0.1 to 0.4 탆 and is stretched so as to have pores of 70% or more of the total pores within a range of ± 0.1 탆 of the average pore size. The PTFE hollow fiber membrane is improved in pressure resistance, (Method for Manufacturing PTFE Hollow Fiber Membrane for Enhanced Water Transmission). 6. The method of claim 5,
Wherein the liquid lubricant is contained in an amount of 18 to 23 parts by weight based on 100 parts by weight of the polytetrafluoroethylene (PTFE) powder. delete delete delete

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