KR102610908B1 - Fluorine resin membrane - Google Patents

Abstract

The fluorine resin membrane according to the present invention,
A first porous film containing a fluorine-based resin having a number average molecular weight of M ₁ ; and
It is provided on the first porous membrane, and includes a fluorine-based resin having a number average molecular weight of M ₂ , and a second porous membrane having an average pore size smaller than the average pore size of the first porous membrane,
The relationship between the number average molecular weights M ₁ and M ₂ satisfies 1.2 ≤ M ₂ /M ₁ ≤ 2.5, and at least one of the surfaces where the first porous membrane and the second porous membrane are joined is treated with atmospheric pressure plasma to obtain a peel strength. It is characterized by being 3 MPa or more.

Description

Fluorine resin membrane {Fluorine resin membrane}

The present invention relates to a fluorine-based resin membrane, and more specifically, to a multi-layered fluorine-based membrane with improved interlayer adhesion and semi-hydrophilic properties through plasma surface modification treatment.

Fluorine resin is a heat-resistant and durable resin that is resistant to chemicals and has little deformation even at a high temperature of 260 degrees, so it is used as a membrane material for gas and liquid filters and semiconductor process filters.

Additionally, since the fluoropolymer resin has low surface energy and is hydrophobic, it is difficult for the fluoropolymer membrane to be wetted by an aqueous liquid or other liquid whose surface tension is significantly greater than the surface energy of the membrane.

Therefore, during filtration of the degassed liquid with a hydrophobic porous membrane, the porous membrane can provide nucleation sites for dissolved gases coming out of solution under the driving force of the pressure gradient during the filtration process. Gases coming out of solution at these nucleation sites on hydrophobic membrane surfaces, including internal pore surfaces and external or geometric surfaces, can form gas pockets that adhere to the membrane, and as the size of these gas pockets increases due to successive degassing. , displacement of the membrane's pores by liquid may begin, which can reduce the effective filtration area of the membrane. This phenomenon usually appears as dewetting of the porous membrane.

However, when the membrane is in a non-wet state, it becomes difficult to purify or filter the same volume of process liquid per unit time as when the filter is newly installed and completely wet.

Accordingly, research was conducted to modify the surface of the PTFE membrane to make it hydrophilic in order to make the fluoropolymer membrane hydrophilic. For example, US 6,074,534 discloses an apparatus for implementing a method of increasing the wettability of a porous body in a microwave generated plasma under vacuum conditions. US Patent No. 6,709,718 also discloses RF atmospheric plasma treatment of porous membranes containing cavitating agents.

Meanwhile, the conventional membrane unit membrane made of fluorine resin has a pore size of 0.1 to 10 ㎛, and in order to improve the filtration efficiency of the membrane, it is necessary to manufacture a membrane with a pore size of less than 0.1 ㎛.

Accordingly, in order to refine the pores, a method of reducing the pore size by stacking a plurality of membranes with different pore sizes has been researched. However, due to weak interlayer adhesion, the produced fluorine resin membrane peels off and does not have sufficient strength and filtration performance. did.

US Patent No. 5,130,024

The purpose of the fluorine-based resin membrane according to one aspect of the present invention is to provide a fluorine-based membrane with high hydrophilicity.

Additionally, the purpose of the fluorine-based membrane according to the present invention is to provide a fluorine-based resin membrane that can prevent interlayer delamination.

A first porous membrane containing a fluorine-based resin having a number average molecular weight of M ₁ and a fluorine-based resin having a number average molecular weight of M ₂ provided on the first porous membrane, the average pore size of which is smaller than the average pore size of the first porous membrane. It includes a second porous membrane having an average pore size, the relationship between the number average molecular weights M ₁ and M ₂ satisfies 1.2 ≤ M ₂ /M ₁ ≤ 2.5, and the first porous membrane and the second porous membrane are joined. At least one of the surfaces is a multi-layered fluorine-based resin that has been treated with atmospheric pressure plasma and has a peel strength of 3 MPa to 7 MPa.
At this time, the fluorine resin membrane preferably has a surface contact angle of 80 to 110°.

delete

delete

delete

In addition, the water permeability of the fluorine resin membrane is preferably 200 to 1200 L/m ² *hr at a pressure of 1 bar.

In addition, the thickness T1 _of the first porous membrane and the thickness _T2 of the second porous membrane are preferably fluorine _- based resins that satisfy the relationship _{T1≤T2≤2T1} .
Additionally, the second porous membrane may be a fluorine-based resin having a number average molecular weight M ₂ of 13 x 10 ⁷ to 20 x 10 ⁷ g/mol.

delete

In addition, the relationship between the average pore size S ₁ of the first porous membrane and the average pore size S ₂ of the second porous membrane is preferably a fluorine-based resin that satisfies 1.8 ≤ S ₁ /S ₂ ≤ 2.5.

In addition, the average pore size (S ₂ ) of the second porous membrane is 0.02 to 0.5 ㎛, and is preferably smaller than or equal to the average pore size of the first porous membrane.

The fluorine-based resin membrane further includes a third porous membrane having an average pore size of 0.05 to 1.0 ㎛, and has a structure in which the second porous membrane is included between the first porous membrane and the third porous membrane, and the third porous membrane It is preferable that at least one of the surfaces to which the membrane and the second porous membrane are bonded is treated with atmospheric pressure plasma.

At this time, the thickness T ₃ of the third porous membrane and the thickness T ₁ of the first porous membrane satisfy 0.8 ≤ T ₁ /T ₃ ≤ 1.2, and the number average molecular weight M ₃ of the third porous membrane and the M ₁ satisfy 0.9 ≤ M ₁ /M ₃ ≤ 1.1 is satisfied, and the fluorine-based resin is polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), and tetrafluoroethylene-hexafluoropropylene copolymer. (FEP), from the group consisting of ethylene-tetrafluoroethylene copolymer resin (ETFE), tetrafluoroethylene-chlorotrifluoroethylene copolymer (TFE/CTFE) and ethylene-chlorotrifluoroethylene resin (ECTFE). It is preferable that it is one or more selected types of fluorine-based resin.

delete

delete

A raw material mixing step of manufacturing a first porous membrane raw material containing a fluorine-based resin with a number average molecular weight M ₁ and a second porous membrane raw material containing a fluorine-based resin with a number average molecular weight M ₂ and the raw materials of the first porous membrane and the first porous membrane raw material. 2. An extrusion step of extruding each of the porous membrane raw materials into a sheet form to form a preform, and processing each preform after the extrusion step to a desired thickness to form a first sheet for forming the first porous membrane and a second porous membrane. A rolling step of manufacturing a second sheet, a plasma treatment step of irradiating atmospheric pressure plasma on at least one surface of the first sheet and the second sheet after the rolling step, and immersing the first sheet in hydrogen peroxide. And a lamination step of stacking the second sheets and a stretching step of stretching the laminated sheets after the lamination step to form a fluorine-based membrane with a multilayer structure including a first porous membrane and a second porous membrane.

delete

delete

delete

delete

delete

At this time, the relationship between the number average molecular weight M ₁ and the M ₂ satisfies 1.2 ≤ M ₂ /M ₁ ≤ 2.5, and in the plasma treatment step, the surface of the sheet is treated at a processing speed of 1 to 5 m/min and current intensity. It is preferable to include repeating the treatment 1 to 3 times under conditions of 1 to 1.5 kW.

In addition, the processing time in the plasma treatment step is 1 to 5 seconds, and the stretching step is performed by stretching the laminated sheet 2 to 15 times in the longitudinal direction and 5 to 30 times in the transverse direction at a temperature of 200 to 400 ° C. Biaxial stretching is included, and the extrusion and rolling steps are preferably performed at a temperature of 30 to 80°C.

delete

delete

In another aspect of the present invention, a multi-layered fluorine-based membrane with improved interlayer adhesion and semi-hydrophilic properties through plasma surface modification treatment, which can prevent the above-described interlayer delamination phenomenon, is disclosed.

The fluorine resin membrane according to the present invention uses a multi-layered fluorine resin membrane treated with plasma surface, thereby preventing dewetting compared to a resin that has not been plasma surface treated during filtration of aqueous solutions, and has a relatively high water permeability (flow rate).

In addition, the fluorine resin membrane according to the present invention has the effect of effectively preventing delamination between layers and increasing the filtration performance and lifespan of the filter.

1 is a conceptual diagram of a fluorine resin membrane according to one aspect of the present invention.

Before describing the present invention in detail below, it is understood that the terms used in this specification are only for describing specific embodiments and are not intended to limit the scope of the present invention, which is limited only by the scope of the appended claims. shall. All technical and scientific terms used in this specification have the same meaning as generally understood by those skilled in the art, unless otherwise specified.

Throughout this specification and claims, unless otherwise stated, the terms comprise, comprises, and comprise mean to include the mentioned article, step, or group of articles, and steps, and any other article. , it is not used in the sense of excluding a step, a group of objects, or a group of steps.

Meanwhile, various embodiments of the present invention may be combined with any other embodiments unless clearly indicated to the contrary. Any feature indicated as being particularly preferred or advantageous may be combined with any other feature or feature indicated as being preferred or advantageous.

In the drawings, the width, length, thickness, etc. of components may be exaggerated for convenience. When explaining the drawing as a whole, it is explained from the observer's point of view, and when one component is said to be "above/below" or "above/below" another component, this is not only the case where it is "directly above/immediately below" the other component. , also includes cases where there is another component in between.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 1 is a conceptual diagram of a fluorine resin membrane according to one aspect of the present invention. According to this, the fluorine-based membrane has a multilayer structure of two or more layers including a first porous membrane and a second porous membrane.

The first porous membrane contains a fluorine-based resin, and specific examples are not limited, but include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl ether copolymer (PFA), and tetrafluoroethylene-hexafluoropropylene. Consisting of copolymer (FEP), ethylene-tetrafluoroethylene copolymer resin (ETFE), tetrafluoroethylene-chlorotrifluoroethylene copolymer (TFE/CTFE), and ethylene-chlorotrifluoroethylene resin (ECTFE). It is preferable to use at least one fluorine-based compound selected from the group, and it is more preferable to use polytetrafluoroethylene (PTFE).

The first porous membrane preferably has an average pore size of 0.05 to 1.0 ㎛, preferably 0.1 to 0.3 ㎛, and a thickness of 5 to 50 ㎛, preferably 10 to 25 ㎛. If the average pore size is less than the above range, filtration performance may be excellent, but the transmittance may be reduced. If the average pore size exceeds the above range, the permeability may be improved, but filtration performance may be poor.

It is preferable that the longitudinal tensile strength of the first porous membrane after the stretching process is 10 MPa or more. If the tensile strength is less than 10 MPa, there is a problem that damage or deformation of the membrane surface may occur during the process of joining the multilayer membrane.

The first porous membrane has a number average molecular weight of 8 x 10 ⁷ to 11 x 10 ⁷ g/mol and a melting point of 320. It is preferable that it is from 345°C. If the number average molecular weight is below the above range, the pore size may become too large and filtration performance may deteriorate, and if the number average molecular weight is above the above range, it may be difficult to control the pore size to an appropriate level.

At this time, the number average molecular weight of the porous membrane can be calculated according to the following calculation formula 1 using the standard specific gravity measured by the method specified in ASTM D4894, ISO 12086-2 (or JIS K6935-2).

[Calculation Formula 1]

log[number average molecular weight] = (standard specific gravity -2.6113)/(-0.0579)

The second porous membrane contains a fluorine-based resin, and specific examples are not limited, but include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl ether copolymer (PFA), and tetrafluoroethylene-hexafluoropropylene. Consisting of copolymer (FEP), ethylene-tetrafluoroethylene copolymer resin (ETFE), tetrafluoroethylene-chlorotrifluoroethylene copolymer (TFE/CTFE), and ethylene-chlorotrifluoroethylene resin (ECTFE). It is preferable to use at least one fluorine-based compound selected from the group, and it is more preferable to use polytetrafluoroethylene (PTFE).

The average pore size of the second porous membrane is 0.02 to 0.5 ㎛, preferably 0.05 to 0.2 ㎛. If the average pore size of the second porous membrane is less than the above range, filtration performance may be excellent, but transmittance may be low. If the average pore size exceeds the above range, permeability may be improved, but filtration performance may be poor.

Additionally, the average pore size of the second porous membrane is preferably equal to or smaller than the average pore size of the first porous membrane, and is more preferably smaller.

At this time, the relationship between the average pore size S ₁ of the first porous membrane and the average pore size S ₂ of the second porous membrane preferably satisfies 1.2 ≤ S ₁ /S ₂ ≤ 2.5, and 1.8 ≤ S ₁ /S ₂ ≤ 2.2. It is more desirable to be satisfied. By ensuring that the average pore size ratio satisfies the above range, deformation or damage that may occur on the surface between the interface between the first porous membrane and the second porous membrane can be minimized, and the bonding force between the multilayer porous membranes can be optimized. there is.

The thickness of the second porous membrane is 5 to 50 ㎛, preferably 15 to 30 ㎛. It is preferable that the thickness T ₂ of the second porous membrane and the thickness T ₁ of the first porous membrane satisfy the relationship T ₁ ≤ T ₂ ≤ 2T ₁ . Since the relatively hard second porous membrane is mainly responsible for filtration performance, if the soft first porous membrane is much thicker than the second porous membrane by more than two times, there may be a problem of overall decrease in transmittance and filtration performance.

The longitudinal tensile strength of the second porous membrane after the stretching process is 20 MPa or more, and is preferably greater than the tensile strength of the first porous membrane. If the tensile strength is less than 20 MPa, there is a problem that damage or deformation of the membrane surface may occur during the process of joining multilayer membranes.

The number average molecular weight of the second porous membrane is 13 x 10 ⁷ to 20 x 10 ⁷ g/mol, and the melting point is 325. It is preferable that it is from 340°C. If the number average molecular weight is below the above range, the pore size may increase and filtration performance may be reduced, and if the number average molecular weight is above the above range, there is a problem in that it is difficult to form pores by stretching.

At this time, the fluorine-based resin included in the second porous membrane has a larger number average molecular weight than the first porous membrane, so that the second porous membrane has relatively hard characteristics and the first porous membrane has soft characteristics.

For this purpose, when the number average molecular weight of the fluorine-based resin contained in the first porous membrane is M ₁ and the number average molecular weight of the fluorine-based resin contained in the second porous membrane is M ₂ , the relationship between each number average molecular weight is 1.2 ≤ M ₂ / It is preferable to satisfy M ₁ ≤ 2.5, and it is more preferable to satisfy 1.5 ≤ M ₂ /M ₁ ≤ 2.0.

At least one of the surfaces where the first porous membrane and the second porous membrane are joined has a surface and chemical structure modified by plasma treatment. The plasma modified membrane can continuously maintain the NON DEWETTING effect.

Plasma treatment is preferably performed 1 to 3 times on the material surface at a processing speed of 1 to 10 m/min and a current intensity of 1 kW to 2 kW, and is preferably exposed for 1 to 5 seconds.

The plasma used is an atmospheric pressure plasma suitable for the roll-to-roll process, and after creating chemical reaction active sites on the surface of the fluorine-based porous film with the atmospheric pressure plasma, they are immediately exposed to hydrogen peroxide to form a large amount of hydroxyl groups on the surface of the fluorine-based porous film. do. The fluorine resin porous membrane formed in this way has hydroxyl groups detected on the surface by IR analysis, and the surface contact angle is 80 to 110°, resulting in a semi-hydrophilic or non-dewetting effect, and thus the water permeability (or water permeability) is 200. to 1,200 L/m ² *hr @1bar, preferably 300 to 600 L/m ² *hr @1bar.

To evaluate water permeability, install a PTFE membrane wetted with alcohol, stabilize it by flowing DI water for 30 minutes at a pressure of 1 bar (=1 kg/㎠), and then check the weight of the DI water that passed through after 30 minutes and convert it into units. Evaluate based on value.

In addition, the porous membrane with the modified surface has a strong adhesive and peeling strength with other porous membranes due to the surface roughened through plasma treatment and the activated hydroxyl group (-OH). On the other hand, the multilayer membrane containing the surface-modified porous membrane can measure the peel strength between the first porous membrane and the second porous membrane using an ultimate test machine according to ASTM D3330, and the fluorine resin membrane of the present invention The silver peel strength is 3 MPa to 7 MPa, preferably 4.5 MPa to 7 MPa, and preferably 6 MPa to 7 MPa.

At this time, the peel strength can be measured by peeling the first or second porous membrane from the multi-layer structured membrane of the present invention, and if the peel strength does not satisfy the above range, the gap between the porous films constituting the multi-layer structured membrane There may be problems with poor durability as surface peeling occurs easily.

According to a preferred embodiment of the present invention, the fluorine-based resin membrane has a multi-layer structure of three or more layers, including a third porous film in addition to the above-mentioned first and second porous films.

At this time, the fluorine-based resin membrane has a structure including a second porous membrane between the first porous membrane and the third porous membrane, and at least one surface to which each porous membrane is joined has a surface and chemical structure modified by plasma treatment. , the plasma-modified membrane can continuously maintain the NON DEWETTING effect.

The third porous membrane contains a fluorine-based resin, and specific examples are not limited, but include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl ether copolymer (PFA), and tetrafluoroethylene-hexafluoropropylene. Consisting of copolymer (FEP), ethylene-tetrafluoroethylene copolymer resin (ETFE), tetrafluoroethylene-chlorotrifluoroethylene copolymer (TFE/CTFE), and ethylene-chlorotrifluoroethylene resin (ECTFE). It is preferable to use at least one fluorine-based compound selected from the group, and it is more preferable to use polytetrafluoroethylene (PTFE).

The third porous membrane has an average pore size after the stretching process of 0.05 to 1.0 ㎛, more preferably 0.2 to 0.3 ㎛. If the average pore size is less than the above range, filtration performance may be excellent, but the transmittance may be reduced. If the average pore size exceeds the above range, the permeability may be improved, but filtration performance may be reduced.

Additionally, the average pore size of the third porous membrane is preferably equal to or larger than the average pore size of the second porous membrane, and is more preferably larger. At this time, the relationship between the average pore size S ₃ of the third porous membrane and the average pore size S ₂ of the second porous membrane preferably satisfies 1.2 ≤ S ₃ /S ₂ ≤ 2.5, and 1.8 ≤ S ₃ /S ₂ ≤ 2.2. It is more desirable to be satisfied. By ensuring that the ratio of average pore size values satisfies the above range, deformation or damage that may occur on the surface between the interface between the third porous membrane and the second porous membrane can be minimized, and the bonding force between the multilayer porous membranes can be optimized. there is.

The third porous membrane preferably has a thickness of 5 to 50 ㎛. At this time, it is preferable that the relationship between the thickness T ₁ of the first porous membrane and the thickness T ₃ of the third porous membrane satisfies the relationship of 0.8 ≤ T ₁ /T ₃ ≤ 1.2, and the value of T ₁ /T ₃ satisfies 1. It is most desirable. By satisfying the above range, when the second porous membrane is included between the first porous membrane and the third porous membrane, twisting or deformation due to external stimulation or pressure can be minimized and the joint strength can be prevented from deteriorating. there is.

The tensile strength of the third porous membrane is preferably 10 MPa or more. If the tensile strength is less than 10 MPa, there is a problem that damage or deformation of the membrane surface may occur during the process of joining the multilayer membrane.

The third porous membrane has a number average molecular weight of 8 x 10 ⁷ to 11 x 10 ⁷ g/mol and a melting point of 320. It is preferable that it is from 345°C. If the number average molecular weight is below the above range, the pore size may become too large and filtration performance may deteriorate, and if the number average molecular weight is above the above range, it may be difficult to control the pore size to an appropriate level.

In addition, it is preferable that the number average molecular weight M ₃ of the third porous membrane satisfies the relationship with the number average molecular weight M ₁ of the first porous membrane 0.9 ≤ M ₁ /M ₃ ≤ 1.1, and the value of M ₁ /M ₃ is 1. It is most desirable to satisfy . By satisfying the above range, if a second porous membrane is included between the first porous membrane and the third porous membrane, twisting or deformation due to external stimulation or pressure can be minimized and the joint strength can be prevented from deteriorating. there is.

Hereinafter, the manufacturing method of the above-described fluorine-based resin membrane will be described.

The fluorine resin membrane includes a raw material mixing step, an extrusion step, a rolling step, a plasma treatment step, a lamination step, and a stretching step.

The raw material mixing step includes a raw material mixing step for the first porous membrane and a raw material mixing step for the second porous membrane, and the raw materials for the porous membrane forming each layer are manufactured by mixing a fluorine-based resin and a lubricant.

The fluorine-based resin contained in the raw materials of the first porous membrane is not limited to specific examples, but includes polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl ether copolymer (PFA), and tetrafluoroethylene-hexafluoroethylene. propylene copolymer (FEP), ethylene-tetrafluoroethylene copolymer resin (ETFE), tetrafluoroethylene-chlorotrifluoroethylene copolymer (TFE/CTFE), and ethylene-chlorotrifluoroethylene resin (ECTFE). It is preferable to use at least one fluorine-based compound selected from the group consisting of, and it is more preferable to use polytetrafluoroethylene (PTFE).

In addition, it is preferable to use the fluorine resin included in the raw materials of the first porous membrane with a tensile strength of 10 MPa or more. If the tensile strength is less than 10 MPa, damage or deformation of the membrane surface may occur during the process of joining the multilayer membrane. There is a problem.

The lubricant included in the raw material of the first porous membrane may be a diester-based, polyol-ester-based, or isoparaffin-based lubricant, but isoparaffin-based lubricants are preferred because they are thermally and chemically stable and are not corrosive. At this time, an isoparaffin-based lubricant with a viscosity of 3.5 to 4.5 mm ² /s at 25°C, a flash point of 40 to 100°C, and an aromatic content of 0.01 wt% or less can be preferably used.

The amount of lubricant used varies depending on the type of lubricant, molding conditions, etc., but in order to implement a membrane with a pore size of less than 1.0 ㎛, it is preferable to mix it in the range of 20 to 30 parts by weight relative to 100 parts by weight of the fluorine resin.

The fluorine-based resin contained in the raw materials of the second porous membrane is not limited to specific examples, but includes polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl ether copolymer (PFA), and tetrafluoroethylene-hexafluoride. propylene copolymer (FEP), ethylene-tetrafluoroethylene copolymer resin (ETFE), tetrafluoroethylene-chlorotrifluoroethylene copolymer (TFE/CTFE), and ethylene-chlorotrifluoroethylene resin (ECTFE). It is preferable to use at least one fluorine-based compound selected from the group consisting of, and it is more preferable to use polytetrafluoroethylene (PTFE).

In addition, it is desirable to use the fluorine resin included in the raw materials of the second porous membrane with a tensile strength of 20 MPa or more. If the tensile strength is less than 20 MPa, damage or deformation of the membrane surface may occur during the process of joining the multilayer membrane. There is a problem.

In an embodiment of the present invention, the fluorine-based resin contained in the raw materials of the second porous membrane has a larger number average molecular weight than the fluorine-based resin contained in the raw materials of the first porous membrane, so that the formed second porous membrane has relatively hard characteristics. And, the first porous membrane has the characteristic of being relatively soft.

For this purpose, when the number average molecular weight of the fluorine-based resin contained in the first porous membrane raw material is M ₁ and the number average molecular weight of the fluorine-based resin contained in the second porous membrane raw material is M ₂ , the relationship between each number average molecular weight is 1.2 ≤ M. It is preferable to satisfy ₂ /M ₁ ≤ 2.5, and it is more preferable to satisfy 1.5 ≤ M ₂ /M ₁ ≤ 2.0.

That is, the first porous membrane with large pores is made of soft material, and the second porous membrane with small pores is made of hard material, so that as the first porous membrane is stretched, deformation or damage occurs at the interface of the second porous membrane with small pores. filtration can be minimized, and by not damaging the second porous membrane, the overall pore size formed in the second porous membrane can be made uniform and filtration performance and bonding strength can be optimized.

At this time, in order to satisfy the above-mentioned conditions, the raw material of the first porous membrane has a number average molecular weight of 8 x 10 ⁷ to 11 x 10 ⁷ g/mol and a melting point of 320. It is preferable that it contains a fluorine-based resin having a temperature ranging from 345°C. If the number average molecular weight is below the above range, the pore size may become too large and filtration performance may deteriorate, and if the number average molecular weight is above the above range, it may be difficult to control the pore size to an appropriate level.

In addition, the raw material of the second porous membrane has a number average molecular weight of 13 x 10 ⁷ to 20 x 10 ⁷ g/mol and a melting point of 325. It is manufactured by mixing a fluorine-based resin with a temperature ranging from 340°C to a lubricant.

At this time, the lubricant included in the raw material of the second porous membrane may be a diester-based, polyol ester-based, or isoparaffin-based lubricant, but isoparaffin-based lubricants are preferred because they are thermally and chemically stable and are not corrosive. At this time, the isoparaffin-based lubricant may preferably have a viscosity of 3.5 to 4.5 mm ² /s at 25°C, a flash point of 40 to 100°C, and an aromatic content of 0.01 wt% or less. The amount of lubricant used varies depending on the type of lubricant, molding conditions, etc., but in order to implement a membrane with a pore size of less than 0.5 ㎛, it is preferable to mix it in the range of 20 to 25 parts by weight relative to 100 parts by weight of the fluorine resin.

The extrusion step is a step of forming a preform by extruding the porous membrane mixed raw material prepared in the above step into a sheet. It can be manufactured by extruding mixed raw materials into a sheet form by applying a typical hydraulic cylinder and a T-Die mold. Extrusion is preferably performed at a speed of 50 m/min or less at a temperature of 30 to 80 ° C. The thickness is preferably 500 to 2,000 ㎛.

The rolling step is a step of manufacturing a first sheet for forming a first porous membrane and a second sheet for forming a second porous membrane by processing each extruded sheet produced in the extrusion step to a desired thickness. In general, the extruded sheet can be produced to a uniform desired thickness by passing it through a roll press, and rolling is preferably performed to a thickness of 100 to 800 ㎛ at a temperature of 30 to 80 ° C.

Additionally, after the rolling step, the step of drying the extruded material at a temperature of 100 to 300° C. may be further included. Through this drying step, the liquid lubricant can be completely removed from the extruded and rolled laminate.

The plasma treatment step is a step of modifying at least one surface of the rolled sheet. Perform atmospheric pressure plasma treatment, immerse in previously prepared hydrogen peroxide solution immediately after atmospheric pressure plasma treatment, wash, and dry again. Atmospheric pressure plasma treatment can provide a non-dewetting effect that lasts for more than 2 months on the rolled sheet surface.

Atmospheric pressure plasma treatment is a processing method that modifies the surface of a material. Depending on the type and conditions of the inert gas, it has effects such as making the surface hydrophilic, improving roughness, and improving adhesion. It only reacts on the surface layer of the material and does not affect the strength of the material itself. It has characteristics.

For atmospheric pressure plasma treatment, the sheet is preferably placed 0.5 to 5 cm away from the electrode, more preferably 1 to 2 cm away from the electrode.

In addition, the plasma treatment step is preferably repeated 1 to 3 times under conditions of a current intensity of 1 to 2 kW while flowing each sheet at a speed of 1 to 5 m/min, and the exposure time is 1 to 5 seconds. desirable.

The plasma-treated sheet is immersed in hydrogen peroxide at a concentration of 10 to 35% of room temperature for 10 to 60 seconds, then washed with water and dried.

The stacking step is a step of sequentially stacking the first sheet and the second sheet made of rolled sheets. In the lamination step, it is preferable that the first to second porous membranes are each manufactured to a thickness of 5 to 50 ㎛. If the thickness is below the above range, filtration performance may be reduced, and if the thickness is above the range, the transmittance may be reduced, so it is preferable to configure it within the above range.

The stretching step is a step of stretching the laminated sheets to the desired pore size. Stretching is carried out as a whole through biaxial stretching. First, the speed ratio is adjusted between the rolls whose rotation speeds can be adjusted, and stretching is carried out at the desired ratio in the longitudinal direction. Thereafter, the membrane stretched in the longitudinal direction can be stretched in the transverse direction (width direction) in an oven using a tenter to produce a biaxially stretched membrane.

The stretching ratio in the stretching step can be determined depending on the purpose of the membrane being manufactured, and the stretching step in the present invention is preferably stretched 2 to 15 times in the longitudinal direction and 5 to 30 times in the transverse direction.

The temperature in the stretching step may be near or below the melting point of the extruded material, and in the present invention, stretching is preferably performed at a temperature of 200 to 400°C to improve interlayer peel strength.

In the stretching step, the laminated sheet is stretched biaxially to form a fluorine-based membrane including a first porous film and a second porous film. At this time, when the first porous membrane is rolled on a roller during stretching, it easily penetrates and is compressed into the pores of the second porous membrane due to its ductile nature, thereby increasing the bonding force.

It is preferable that the first porous membrane and the second porous membrane formed in the stretching step each have a thickness in the range of 5 to 50 ㎛. If the thickness is below the above range, filtration performance may be reduced, and if the thickness is above the range, the transmittance may be reduced, so it is preferable to configure it within the above range.

In addition, it is preferable that the thickness T ₂ of the second porous membrane and the thickness T ₁ of the first porous membrane satisfy the relationship T ₁ ≤ T ₂ ≤ 2T ₁ . Since the relatively hard second porous membrane is mainly responsible for filtration performance, if the soft first porous membrane is much thicker than the second porous membrane by more than two times, there may be a problem of overall decrease in transmittance and filtration performance.

Additionally, a step of sintering the extruded material may be additionally performed before the stretching step. Sintering of this extruded material can be carried out, for example, at temperatures between 200 and 400°C.

Each layer of the fluorine resin porous membrane that has gone through the above-mentioned steps has uniform micropores, and the hydrophilic properties are improved by atmospheric pressure plasma treatment, and the adhesion between each layer of the porous membrane is excellent.

In addition, the fluorine resin porous membrane according to the present invention can form fine pores at the interface where soft PTFE is joined between hard PTFE when extruded, and provides stable filtration efficiency by preventing delamination.

Below, we will look at embodiments of the present invention.

<Example 1: Preparation of two-layer fluorine-based resin membrane>

A mixture formed by mixing PTFE Powder (Daikin Industries, Ltd.) with a number average molecular weight of ¹¹ An extruded sheet for forming a first porous membrane with a thickness of about 1,650 ㎛ was manufactured by extruding at a speed of . Then, the extruded sheet was passed through a roll press to produce a first sheet with a thickness of approximately 200 ㎛.

In addition, the mixture formed by mixing PTFE Powder (Daikin Industries, Ltd.) with a number average molecular weight of ¹⁷ An extruded sheet for forming a second porous film with a thickness of about 750 ㎛ was manufactured by extruding at a speed of /min. Then, the extruded sheet was passed through a roll press to produce a second sheet with a thickness of approximately 250 ㎛.

Then, the manufactured sheet was heated at a temperature of about 250° C. to completely dry and remove the liquid lubricant, and both sides of the first sheet and the second sheet were treated with atmospheric pressure plasma.

Atmospheric pressure plasma was treated at a distance of 1 cm from each sheet at a power of 1.5 kW and 2 m/min.

After the drying process, the first sheet and the second sheet were stacked to form a two-layer sheet.

Then, the two-layer sheet was extended 9 times in the longitudinal direction at a roll temperature of 300 ℃ to 340 ℃, and then extended 18 times in the transverse direction using a tenter in an oven at 320 ℃ to 400 ℃ to be biaxially stretched. A fluorine-based resin membrane was prepared.

The thickness of the manufactured fluorine-based resin membrane, including the first porous film and the second porous film, was measured to be about 35 ㎛.

<Example 2: Preparation of three-layer structure fluorine-based resin membrane>

Using the sheet treated with atmospheric pressure plasma in Example 1, a second sheet was laminated between the two first sheets and stretched in the same manner as in Example 1 to prepare a three-layer fluorine-based membrane.

The manufactured fluorine resin membrane was measured to have a thickness of about 50 ㎛ including the first porous membrane, the second porous membrane, and the third porous membrane.

Reference example

<Reference Example 1: Manufacturing of a two-layer fluorine-based resin membrane>

In the method of manufacturing the fluorine-based resin membrane of Example 1, the fluorine-based resin membrane was manufactured in the same manner as Example 1, except that atmospheric pressure plasma treatment was not performed.

<Reference Example 2: Manufacture of three-layer structure fluorine-based resin membrane>

In the method of manufacturing a fluorine-based resin membrane in Example 2, a fluorine-based resin membrane was manufactured in the same manner as Example 2, except that atmospheric pressure plasma treatment was not performed.

Experiment example

<Experimental Example 1: Contact angle measurement>

The contact angle of the manufactured fluorine resin membrane with water was measured according to ASTM D5946, and the results are shown in Table 1.

Contact angle (°) Example 1 90 Example 2 89 Reference example 1 128 Reference example 2 127

<Experimental Example 2: Measurement of water permeability (or water permeability)>

To measure the water permeability of the manufactured fluorine resin membrane, a PTFE membrane soaked in IPA for 10 minutes was stabilized by flowing distilled water for 30 minutes at a pressure of 1 bar, and then the amount of water permeating the membrane for 1 hour was measured, and the area of the membrane was 1 m. The value was calculated as ² and the results are shown in Table 2.

Water permeability (L/m ² *hr) Example 1 487 Example 2 252 Reference example 1 300 Reference example 2 181

<Experimental Example 3: Peel strength measurement>

The tensile strength and peel strength of the manufactured fluorine resin membrane were measured using a universal testing machine (UTM).

Membrane specimens with a ratio of 100 mm In order to prevent deformation such as shrinkage of the specimen during peeling, it was attached to an adhesive tape with higher peel strength, and the peeling strength was measured by applying the 180° Peel Test method between the interfaces between the layers of the porous membrane and calculated as the average value of three times.

Peel strength (MPa) Example 1 6.2 Example 2 6.5 Reference example 1 4.1 Reference example 2 4.0

It was confirmed that the peel strength of the membrane of the example was improved by about 0.6 times compared to the membrane of the reference example where the surface was not plasma treated during the manufacturing process. Accordingly, when a membrane was formed by bonding a membrane treated with atmospheric pressure plasma to the surface, the bonding strength It was also found that there was improvement.

<Experimental Example 4: Measurement of thickness of multilayer membrane and porous membrane>

The thickness of the manufactured fluorine resin membrane and the shape and thickness of the porous membrane constituting each layer were confirmed using a scanning electron microscope (SEM) equipment, and the confirmation results are shown in Table 4.

First porous film thickness Second porous film thickness Third porous film thickness multilayer membrane
thickness Example 1 15㎛ 20㎛ - 35㎛ Example 2 15㎛ 20㎛ 15㎛ 50㎛ Reference example 1 15㎛ 20㎛ - 35㎛ Reference example 2 15㎛ 20㎛ 15㎛ 50㎛

<Experimental Example 5: Pore size analysis>

The pore size of each porous membrane constituting the manufactured fluorine resin membrane was measured using a capillary flow porometer (CFP).

In order to measure the pore size of each porous membrane, each layer of the laminated membrane was separated by heating in alcohol, and the membrane of the separated layer was dried and the pore size of each was measured. The measured pore size results are shown in Table 5.

Pore size (average) First porous membrane (S ₁ ) Second porous membrane (S ₂ ) Third porous membrane (S ₃ ) multilayer membrane Example 1 0.21 ㎛ 0.11 ㎛ - 0.093 ㎛ Example 2 0.23 ㎛ 0.11 ㎛ 0.21 ㎛ 0.081 ㎛ Reference example 1 0.24 ㎛ 0.11 ㎛ - 0.101 ㎛ Reference example 2 0.22 ㎛ 0.11 ㎛ 0.21 ㎛ 0.088 ㎛

The features, structures, effects, etc. illustrated in each of the above-described embodiments can be combined or modified for other embodiments by those skilled in the art. Therefore, contents related to such combinations and modifications should be construed as being included in the scope of the present invention.

Claims (15)

A first porous film containing a fluorine-based resin having a number average molecular weight of M ₁ ;
a second porous membrane provided on the first porous membrane, including a fluorine-based resin having a number average molecular weight of M ₂ , and having an average pore size smaller than the average pore size of the first porous membrane; and
It includes a third porous membrane having an average pore size of 0.05 to 1.0 ㎛,
The relationship between the number average molecular weights M ₁ and M ₂ satisfies 1.2 ≤ M ₂ /M ₁ ≤ 2.5, and at least one of the surfaces where the first porous membrane and the second porous membrane are joined is treated with atmospheric pressure plasma to obtain a peel strength. 3 MPa to 7 MPa,
A fluorine-based resin membrane having a structure including the second porous membrane between the first porous membrane and the third porous membrane, and at least one of the surfaces where the third porous membrane and the second porous membrane are joined is treated with atmospheric pressure plasma. According to paragraph 1,
The fluorine-based resin membrane has a surface contact angle of 80 to 110°. According to paragraph 2,
The fluorine-based resin membrane has a water permeability of 200 to 1200 L/m ² *hr at a pressure of 1 bar. According to paragraph 3,
A fluorine resin membrane in which the thickness T ₁ of the first porous membrane and the thickness T ₂ of the second porous membrane satisfy the relationship T ₁ ≤ T ₂ ≤ 2T ₁ . According to paragraph 4,
A fluorine-based resin membrane wherein the number average molecular weight M ₂ of the second porous membrane is 13 x 10 ⁷ to 20 x 10 ⁷ g/mol. According to clause 5,
The relationship between the average pore size S ₁ of the first porous membrane and the average pore size S ₂ of the second porous membrane is a fluorine resin membrane that satisfies 1.8 ≤ S ₁ /S ₂ ≤ 2.5. According to clause 6,
The average pore size (S ₂ ) of the second porous membrane is 0.02 to 0.5 ㎛, and is smaller than or equal to the average pore size of the first porous membrane. delete In clause 7,
A fluorine-based resin membrane in which the thickness T ₃ of the third porous membrane and the thickness T ₁ of the first porous membrane satisfy 0.8 ≤ T ₁ /T ₃ ≤ 1.2. According to clause 9,
The number average molecular weight M ₃ and M ₁ of the third porous membrane are fluorine-based resin membranes satisfying 0.9 ≤ M ₁ /M ₃ ≤ 1.1. According to clause 10,
The fluorine-based resin is polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and ethylene-tetrafluoroethylene copolymer. A fluorine-based resin membrane that is at least one selected from the group consisting of polymer resin (ETFE), tetrafluoroethylene-chlorotrifluoroethylene copolymer (TFE/CTFE), and ethylene-chlorotrifluoroethylene resin (ECTFE). A raw material mixing step of producing a first porous membrane raw material containing a fluorine-based resin with a number average molecular weight M ₁ and a second porous membrane raw material containing a fluorine-based resin with a number average molecular weight M ₂ ;
An extrusion step of forming a preform by extruding the raw materials of the first porous membrane and the raw materials of the second porous membrane into a sheet form, respectively;
A rolling step of processing each preform after the extrusion step to a desired thickness to manufacture the first sheet for forming the first porous membrane and the second sheet for forming the second porous membrane;
A plasma treatment step of irradiating atmospheric pressure plasma to at least one surface of the first sheet and the second sheet after the rolling step and immersing it in hydrogen peroxide solution;
A stacking step of stacking the plasma-treated first sheet and the second sheet; and
A stretching step of stretching the laminated sheet after the lamination step to form a multi-layered fluorine-based membrane including a first porous membrane and a second porous membrane,
The relationship between the number average molecular weight M ₁ and the M ₂ satisfies 1.2 ≤ M ₂ /M ₁ ≤ 2.5, and in the plasma treatment step, the surface of the sheet is treated at a processing speed of 1 to 5 m/min and a current intensity of 1 to 1.5. A method of manufacturing a multi-layered fluorine-based resin membrane comprising repeating the treatment 1 to 3 times under kW conditions. According to clause 12,
A method of manufacturing a fluorine-based resin membrane in which the processing time in the plasma treatment step is 1 to 5 seconds. According to clause 13,
The stretching step is a fluorine resin membrane manufacturing method comprising biaxial stretching of stretching the laminated sheet 2 to 15 times in the longitudinal direction and 5 to 30 times in the transverse direction at a temperature of 200 to 400°C. According to clause 14,
A method of manufacturing a fluorine-based resin membrane in which the extrusion step and the rolling step are performed at a temperature of 30 to 80 ° C.