CN110691641B - Hollow fiber membrane and method for producing hollow fiber membrane - Google Patents

Abstract

The hollow fiber membrane according to an embodiment of the present invention has: a hollow porous support formed of one or more wires; a porous joining layer laminated on an outer surface of the support, at least a portion of the porous joining layer being welded to the support; and a porous filter sheet laminated on the opposite side of the joining layer from the support, and at least a part of the porous filter sheet is welded to the joining layer.

Description

Hollow fiber membrane and method for producing hollow fiber membrane

Technical Field

The present invention relates to a hollow fiber membrane and a method for producing a hollow fiber membrane. This application is based on and claims priority from japanese patent application No.2017-135366, filed on 11/7/2017, the entire content of which is incorporated herein by reference.

Background

Conventionally, a hollow fiber membrane is known as a filtration membrane for water treatment. The hollow fiber membrane is an elongated tubular filtration membrane closed at one end, and filters water to be treated in contact with the outside, thereby obtaining filtered water on the inside.

Hollow fiber membranes have been proposed which comprise: a hollow fiber membrane having a porous stretched tube made of polytetrafluoroethylene as a support and a filtration layer on an outer surface of the support (patent document 1); and a hollow fiber membrane having a hollow woven fabric formed of fibers made of a plurality of resin filaments as a support and having a porous layer on an outer surface of the support (patent document 2).

The hollow fiber membrane of patent document 1 includes a band-shaped porous resin sheet (filtration layer) spirally wound around the outer surface of a polytetrafluoroethylene porous stretched tube (support), and the support and the filtration layer are fused and integrated at a temperature (350 ℃) equal to or higher than the melting point of the support and the filtration layer, thereby improving mechanical durability and chemical resistance.

On the other hand, the hollow fiber membrane of patent document 2 includes a dope for forming a porous layer coated on the surface of a hollow woven fabric (support) formed of fibers made of a plurality of resin filaments, and the dope for forming a porous layer is solidified in a state where the dope for forming a porous layer enters the inside of the support to form a porous layer, thereby improving the bonding strength between the support and the porous layer.

Documents of the prior art

Patent literature

Patent document 1: japanese unexamined patent publication No.2004-141753

Patent document 2: japanese patent No.5341760

Disclosure of Invention

[ means for solving the problems ]

A hollow fiber membrane according to an embodiment of the present invention includes: a hollow porous support formed of one or more linear bodies; a porous joining layer laminated on an outer surface of the support, and at least a portion of the porous joining layer is welded to the support; and a porous filter sheet laminated on the opposite side of the joining layer from the support, and at least a part of the joining layer is welded to the porous filter sheet.

A method of manufacturing a hollow fiber membrane according to an embodiment of the present invention includes: a step of heat laminating the porous bonding layer and the porous filter sheet; and a step of bringing the outer surface of the hollow porous support formed of one or more threads into contact with the bonding layer side of the sheet after the thermal lamination step, and thermally laminating the support and the sheet after the thermal lamination step.

Drawings

Fig. 1 is a schematic sectional view showing a part of a section cut in a longitudinal direction of a hollow fiber membrane according to an embodiment of the present invention.

Fig. 2 is a schematic perspective cross-sectional view illustrating a hollow fiber membrane according to an embodiment of the present invention.

Detailed Description

[ problems to be solved by the invention ]

Hollow fiber membranes used for water treatment are required to have certain water permeability as well as mechanical durability and chemical resistance. The hollow fiber membrane of patent document 1 uses a stretched porous body having no high tensile strength as a support and has a structure in which a filtration layer is directly bonded to the support, and therefore, in order to improve the mechanical durability when the hollow fiber membrane is subjected to bending deformation, further intensive consideration needs to be given. Further, the hollow fiber membrane of patent document 2 requires selection of a curable dope as a material for the porous layer, and therefore, a material having high chemical resistance such as polytetrafluoroethylene cannot be used for the porous layer, and thus the material suitable for the porous layer is limited.

The present invention was conceived based on the above circumstances, and an object is to provide a hollow fiber membrane capable of achieving both chemical resistance and mechanical durability, and to provide a method for producing the hollow fiber membrane.

[ Effect of the invention ]

According to the present invention, a hollow fiber membrane capable of achieving both chemical resistance and mechanical durability can be provided.

[ description of embodiments of the invention ]

First, embodiments of the present invention will be enumerated and explained.

A hollow fiber membrane according to an embodiment of the present invention includes: a hollow porous support formed of one or more linear bodies; a porous joining layer laminated on an outer surface of the support, at least a portion of the porous joining layer being welded to the support; and a porous filter sheet laminated on the opposite side of the joining layer from the support, and at least a part of the joining layer is welded to the porous filter sheet.

The hollow fiber membrane includes a joining layer between the support and the filter sheet, which is welded to the support and the filter sheet and joins these portions to each other, thereby firmly joining the support and the filter sheet together, and the materials of the support and the filter sheet can be relatively freely selected. Further, since the support of the hollow fiber membrane is formed of one or more strands, the support has high tensile strength and appropriate flexibility. For this reason, since the hollow fiber membrane uses a support having a high tensile strength as a base body, and the filter sheet is joined to the support through the joining layer, the filter sheet is not easily peeled from the support even when bending deformation occurs, and the pressure resistance at the time of filtration and backwashing is high. In other words, since materials having high chemical resistance can be selected for the support and the filter sheet of the hollow fiber membrane, and mechanical durability in terms of the structure of the hollow fiber membrane can be improved, chemical resistance and mechanical durability can be simultaneously achieved.

Preferably, the support is formed in a tubular shape, the filter is formed in a band shape, and the filter is wound on the outer surface of the support in a spiral or stripe shape through the joining layer. In this case, the support and the filter sheet can be easily and surely joined to each other by the joining layer.

The linear body is preferably formed of 8 to 32 resin filaments. By forming a linear body (the linear body forms a support) using 8 to 32 resin filaments, the mechanical strength of the support can be further improved.

The junction layer is preferably a nonwoven fabric or a porous resin. In this case, when the hollow fiber membrane undergoes bending deformation, the joining layer moderately deforms and disperses the tensile stress, thus making it even more difficult for the filter sheet to easily peel off from the support.

The main component of the filter sheet is preferably polytetrafluoroethylene. The chemical resistance of the hollow fiber membrane can be improved by using polytetrafluoroethylene having high chemical resistance for the filter sheet disposed on the outer surface. The main component means a component having the highest content, and for example, may mean a component having a content of 50% by mass or more.

Preferably, the average thickness of the filter sheet is 12 μm to 100 μm, the average pore diameter of the filter sheet is 0.01 μm to 0.45 μm, and the bubble point of the hollow fiber membrane is 80kPa to 200 kPa. In this case, the water permeability and the impurity removal performance of the hollow fiber membrane can be adjusted to be moderately balanced. The average pore diameter refers to a value obtained by observing 10 or more pores through a microscope and calculating the maximum diameter of the pores and the average value of the diameters in the direction perpendicular to the maximum diameter for all samples. The bubble point is a value measured in accordance with JIS-K3832 (1990) using isopropyl alcohol.

A method for manufacturing a hollow fiber membrane according to another embodiment of the present invention is a method for manufacturing a hollow fiber membrane, including: hot laminating the porous jointing layer and the porous filter sheet; and a step of bringing the outer surface of the hollow porous support formed of one or more threads into contact with the bonding layer side of the sheet after the thermal lamination step, and thermally laminating the support and the sheet after the thermal lamination step.

Since the method for producing a hollow fiber membrane welds the joining layer to the filter sheet and the joining layer of the resulting sheet to the support, the support and the filter sheet can be joined relatively easily via the joining layer. In other words, the method for producing a hollow fiber membrane can relatively easily produce a hollow fiber membrane capable of simultaneously achieving chemical resistance and mechanical durability.

[ detailed description of embodiments of the invention ]

Hereinafter, a hollow fiber membrane and a method of manufacturing the hollow fiber membrane according to an embodiment of the present invention will be described with reference to the accompanying drawings as appropriate.

[ hollow fiber membranes ]

The hollow fiber membrane 1 of fig. 1 and 2 includes: a hollow porous support 2 formed of one or more linear bodies; a porous joining layer 3 laminated on an outer surface of the support 2, and at least a part of the porous joining layer 3 is welded to the support 2; and a filter sheet 4 laminated on the opposite side of the joining layer 3 from the support 2, and at least a part of the joining layer 3 is welded to the filter sheet 4.

The thread-like body forming the support 2 is formed of 8 or more and 32 or less resin filaments, and the support 2 is formed in a tubular shape. The junction layer 3 is a nonwoven fabric or a porous resin. The filter sheet 4 is formed in a band shape. The filter sheet 4 contains polytetrafluoroethylene as a main component, the filter sheet 4 has an average thickness of 12 μm to 100 μm, and the filter sheet 4 has an average pore diameter of 0.01 μm to 0.45 μm. The filter sheet 4 is wound around the outer surface of the support 2 in a spiral or stripe shape via the joining layer 3. The hollow fiber membrane 1 has a bubble point of 80kPa to 200 kPa.

The hollow fiber membrane 1 is a hollow fiber membrane for water treatment, and as shown in fig. 1, it includes a junction layer 3 and a filter sheet 4 laminated in this order on the outer surface of a support 2. The hollow fiber membrane 1 filters the water to be treated which comes into contact from the filter sheet 4 side, and the hollow fiber membrane 1 is tubular as shown in fig. 2, so that filtered water is obtained at the hollow portion 5 located at the inner side of the support 2.

The lower limit of the bubble point of the hollow fiber membrane 1 is preferably 80kPa, more preferably 100kPa, and even more preferably 120kPa. On the other hand, the upper limit of the bubble point of the hollow fiber membrane 1 is preferably 200kPa, more preferably 180kPa, and even more preferably 160kPa. When the bubble point of the hollow fiber membrane 1 is less than the above lower limit, the water to be treated may not be sufficiently filtered. On the other hand, when the bubble point of the hollow fiber membrane 1 exceeds the above upper limit, the water flow resistance may increase and the filtration efficiency may decrease.

< support >

The support 2 is a member that becomes a matrix of the hollow fiber membrane 1, and is formed in a tubular shape. The support 2 is formed of one or more linear bodies, and the support 2 is porous to such an extent that filtered water can permeate through gaps in the linear bodies. Further, a hollow portion 5 is formed inside the support body 2.

The lower limit of the average thickness (average wall thickness) of the support 2 is preferably 0.1mm, more preferably 0.3mm, and even more preferably 0.5mm. On the other hand, the upper limit of the average thickness of the support 2 is preferably 2mm, more preferably 1.7mm, and even more preferably 1.5mm. When the average thickness of the support 2 is less than the above lower limit, the mechanical strength of the support 2 may be insufficient. On the other hand, when the average thickness of the support 2 exceeds the above upper limit, the hollow fiber membranes 1 may be excessively thick, and when a plurality of hollow fiber membranes 1 are used, the number density of the hollow fiber membranes 1 may decrease, thereby decreasing the filtration efficiency.

(Linear body)

The linear body forming the support body 2 is formed of a plurality of resin filaments to improve mechanical strength. The material for the resin filament is not particularly limited, and it may include a resin containing, for example, polyester such as polyethylene terephthalate, polyethylene, or polypropylene as a main component.

The lower limit of the number of resin filaments forming the linear body is preferably 8, more preferably 10, and even more preferably 12. On the other hand, the upper limit of the number of resin filaments forming the linear body is preferably 32, more preferably 28, and even more preferably 24. When the number of resin filaments forming the linear body is less than the above lower limit, the mechanical strength of the linear body may become insufficient. On the other hand, when the number of resin filaments exceeds the above upper limit, the manufacturing cost of the filament body may increase.

< bonding layer >

The surface of the joining layer 3 in contact with the support 2 is welded to the support 2, and the surface of the joining layer 3 in contact with the filter sheet 4 is welded to the filter sheet 4. The joining layer 3 is an intermediate layer joining the support 2 and the filter sheet 4, and the joining layer 3 is laminated between the outer surface of the tubular support 2 and the inner surface of the filter sheet 4. The joining layer 3 is melted by an amount corresponding to a predetermined thickness from the contact face with the support 2, and joined to the support 2 in the region of the melted thickness. The joining layer 3 is melted by an amount corresponding to a predetermined thickness from the contact surface with the filter sheet 4, and joined to the filter sheet 4 in the region of the melted thickness. A porous resin obtained by heat-treating resin powder, or a nonwoven fabric may be used for the joining layer 3. The material for the porous resin or the nonwoven fabric is not particularly limited, and it may include a porous resin containing, for example, polyester such as polyethylene terephthalate, polyethylene, or polypropylene as a main component. From the viewpoint of obtaining satisfactory affinity between the joining layer 3 and the support 2, the joining layer 3 is preferably made of the same material as the support 2.

The lower limit of the average thickness of the bonding layer 3 is preferably 10 μm, more preferably 20 μm, and even more preferably 30 μm. On the other hand, the upper limit of the average thickness of the bonding layer 3 is preferably 200 μm, more preferably 150 μm, and even more preferably 100 μm. When the average thickness of the joining layer 3 is less than the above lower limit, the fusion of the joining layer 3 to the support 2 and the filter sheet 4 may be insufficient, and the joining strength of the joining layer 3 may be insufficient. On the other hand, when the average thickness of the joining layer 3 exceeds the above upper limit, the hollow fiber membrane 1 may become excessively thick, and when a plurality of hollow fiber membranes 1 are used, the number density of the hollow fiber membranes 1 may decrease, resulting in a decrease in filtration efficiency.

Since the support 2 and the filter sheet 4 are welded when the hollow fiber membrane 1 is manufactured, the melting point of the joining layer 3 is preferably equal to or less than the melting point of the support 2 and equal to or less than the melting point of the filter sheet 4. For example, in the case of using polytetrafluoroethylene (melting point of about 327 ℃) for the filter sheet 4 and polyethylene terephthalate, polyethylene, or polypropylene (melting point of about 110 ℃ to about 260 ℃) for the support 2, the junction layer 3 is preferably made of the same material as the support 2 or a material having a melting point less than or equal to that of the support 2.

< Filter sheet >

The filter sheet 4 is a belt-like porous sheet disposed on the outer surface of the junction layer 3, and has a function of filtering water to be treated. A porous resin having chemical resistance is preferably used for the filter sheet 4, and the porous resin may contain polytetrafluoroethylene as a main component. The filter sheet 4 is wound on the outer surface of the tubular support 2 in a spiral or stripe shape, and is arranged to cover the outer surface of the hollow fiber membrane 1. Further, the filter sheet 4 is wound in a gapless manner with respect to the outer surface of the support body 2 such that the side edge portions of the filter sheet 4 overlap each other. In other words, the hollow fiber membrane 1 includes the overlapping portion 6 where the filter sheet 4 is wound and overlapped in a spiral or stripe shape. In the overlapping portion 6, the support 2, the joining layer 3, the filter sheet 4, the joining layer 3, and the filter sheet 4 are joined in this order.

The lower limit of the average thickness of the filter sheet 4 is preferably 12 μm, more preferably 15 μm, even more preferably 18 μm. On the other hand, the upper limit of the average thickness of the filter sheet 4 is preferably 100 μm, more preferably 80 μm, and even more preferably 60 μm. When the average thickness of the filter sheet 4 is less than the above lower limit, the water to be treated may not be sufficiently filtered. On the other hand, when the average thickness of the filter sheet 4 exceeds the above upper limit, the water flow resistance may increase and the filtration efficiency may decrease.

The lower limit of the average pore diameter of the filter sheet 4 is preferably 0.01. Mu.m, more preferably 0.05. Mu.m, even more preferably 0.10. Mu.m. On the other hand, the upper limit of the average pore diameter of the filter sheet 4 is preferably 0.45. Mu.m, more preferably 0.40. Mu.m, and even more preferably 0.35. Mu.m. When the average pore diameter of the filter sheet 4 is less than the above lower limit, the water flow resistance may increase and the filtration efficiency may decrease. On the other hand, when the average pore diameter of the filter sheet 4 exceeds the above upper limit, the water to be treated may not be sufficiently filtered.

[ method for producing hollow fiber Membrane ]

The method for manufacturing a hollow fiber membrane is a method for manufacturing a hollow fiber membrane, which includes: a first lamination step of thermally laminating the porous bonding layer 3 and the porous filter sheet 4; and a second lamination step of bringing the outer surface of the hollow porous support 2 formed of one or more threads into contact with the joining layer 3 side of the sheet after the first thermal lamination step, and thermally laminating the support 2 and the sheet after the first thermal lamination.

< first laminating step >

In the first lamination process, the joining layer 3 and the filter sheet 4 are thermally laminated in a state where the joining layer 3 and one surface of the filter sheet 4 are overlapped in a plan view, and the joining layer 3 is welded to the filter sheet 4. The melting point of the material used for the bonding layer 3 may be lower than the melting point of the filter sheet 4.

The thermal lamination method is not limited to a specific method. For example, the method may melt one side surface of joining layer 3 in an amount corresponding to a predetermined thickness, followed by cooling in a state where filter sheet 4 is in contact with the melted surface, thereby welding joining layer 3 to filter sheet 4. Alternatively, the method may heat the filter sheet 4 side in a state where the joining layer 3 and the filter sheet 4 are laminated together to melt the joining layer 3 near the filter sheet 4 by an amount corresponding to a predetermined thickness, followed by cooling, thereby welding the joining layer 3 to the filter sheet 4. It is preferable that the joining layer 3 is melted at a temperature of about 10 to about 50 ℃ higher than the melting point of the joining layer 3 in an amount corresponding to a predetermined thickness.

The laminated sheet after the first laminating step is formed into a belt shape by using, for example, a method such as cutting before the second laminating step. Since the laminated sheet after the first laminating step only needs to be in a band shape, instead of forming the laminated sheet after the first laminating step into a band shape, for example, a method of obtaining a band-shaped laminated sheet by performing the first laminating step using the band-shaped filter sheet 4 may be employed.

< second lamination step >

The second laminating step is to thermally laminate the laminated sheet and the support 2 in a state where the joining layer 3 side of the laminated sheet after the first laminating step is in contact with the outer surface of the tubular support 2. Thus, the joining layer 3 is welded to the support 2. The support 2 may be made of the same material as the junction layer 3, or may be made of a material having a melting point higher than or equal to that of the junction layer 3.

When laminating the tape-shaped laminate sheet and the support 2, the tape-shaped laminate sheet is wound on the outer surface of the tubular support 2 in a spiral or stripe shape so that the joining layer 3 and the filter sheet 4 are laminated in this order on the outer surface of the support 2. Since the outer surface of the produced hollow fiber membrane 1 needs to be covered with the filter sheet 4 without a gap, the band-shaped laminate sheet is wound on the support 2 in a spiral or stripe shape so that the side edge portions of the laminate sheet overlap each other.

The thermal lamination method is not limited to a specific method. For example, the method may melt the joining layer 3 side of the belt-shaped laminated sheet in an amount corresponding to a predetermined thickness, and then wind the belt-shaped laminated sheet on the support 2 in a spiral or stripe shape while bringing the outer surface of the support 2 and the upper surface of the side edge portion of the laminated sheet into contact with the molten surfaces, respectively, to weld the joining layer 3 to the support 2. It is preferable that the joining layer 3 is melted at a temperature of about 10 to about 50 ℃ higher than the melting point of the joining layer 3 in an amount corresponding to a predetermined thickness.

(advantages)

Since the hollow fiber membrane 1 includes the joining layer 3 between the support 2 and the filter sheet 4, and the joining layer 3 is welded to the support 2 and the filter sheet 4 and joins these portions to each other, the support 2 and the filter sheet 4 are firmly joined together. Further, since the support 2 of the hollow fiber membrane 1 is formed of a linear body formed by 8 or more and 32 or less resin filaments, the support 2 has high tensile strength and appropriate flexibility. Further, since the joining layer 3 of the hollow fiber membrane 1 is a nonwoven fabric or a porous resin, when the hollow fiber membrane 1 is deformed by bending, the joining layer 3 is appropriately deformed and the tensile stress is dispersed. For this reason, since hollow fiber membrane 1 uses support 2 having high tensile strength as a base, and filter sheet 4 is joined to this support 2 by joining layer 3, even when bending deformation occurs, filter sheet 4 and joining layer 3 are not easily peeled from support 2, and pressure resistance at the time of filtration or backwashing is high. Further, since polytetrafluoroethylene having high chemical resistance is used for the filter sheet 4 of the hollow fiber membrane 1, the hollow fiber membrane 1 can achieve both chemical resistance and mechanical durability. Further, since the bubble point of the hollow fiber membrane 1 is 80kPa to 200kPa, the water permeability and the impurity removal performance of the hollow fiber membrane 1 can be adjusted to be appropriately balanced.

The method for producing a hollow fiber membrane welds the joining layer 3 to the filter sheet 4 and welds the joining layer 3 of the resulting sheet to the support 2, and therefore the support 2 and the filter sheet 4 can be joined relatively easily via the joining layer 3. Further, since the production method of the hollow fiber membrane winds the band-shaped filter sheet 4 on the outer surface of the tubular support 2 in a spiral or stripe shape so that the side edge portions of the filter sheet 4 overlap each other, the hollow fiber membrane 1 can be produced in which the outer surface is covered with the filter sheet 4 without a gap, and the support 2 and the filter sheet 4 can be easily and surely joined to each other by the joining layer 3.

[ other embodiments ]

The present invention is not limited to the examples of the above-described embodiments. The scope of the present invention is not limited to the constitution of the above-described embodiments, and is intended to include all modifications within the meaning and scope of the claims and their equivalents.

In the above embodiment, the support 2 is formed in a tubular shape, however, the support 2 is not limited to a tubular shape as long as the support 2 includes the hollow portion 5 formed inside thereof.

In the above embodiment, the band-shaped filter sheet 4 is wound in a spiral or stripe shape on the outer surface of the tubular support 2, however, the support 2, the joining layer 3, and the filter sheet 4 may be joined according to other procedures as long as the laminated structure includes the filter sheet 4 joined to the outer surface of the support 2 through the joining layer 3.

Industrial applicability

The hollow fiber membrane according to the present invention and the hollow fiber membrane manufactured by the manufacturing method of the hollow fiber membrane according to the present invention can achieve both chemical resistance and mechanical durability.

Description of the reference numerals

1. Hollow fiber membrane

2. Support body

3. Bonding layer

4. Filter disc

5. Hollow part

6. Overlapping part

Claims (4)

1. A hollow fiber membrane comprising:

a hollow porous support formed of one or more thread-like bodies formed of 8 or more and 32 or less resin filaments, a material of the resin filaments including a resin containing polyethylene terephthalate, polyethylene, or polypropylene as a main component;

a porous joining layer laminated on an outer surface of the support, and at least a portion of the porous joining layer is welded to the support; and

a porous filter sheet laminated on the opposite side of the joining layer from the support body, and at least a part of the joining layer is welded to the porous filter sheet, wherein

The junction layer is made of a nonwoven fabric or a porous resin, has a melting point smaller than that of the support, and has an average thickness in a range of 10 μm to 200 μm,

the main component of the filter sheet is polytetrafluoroethylene,

the hollow fiber membrane has a bubble point of 80kPa to 200kPa,

the support is formed in a tubular shape, the filter sheet is formed in a band shape, and the filter sheet is wound on an outer surface of the support in a spiral or stripe shape by the joining layer.

2. The hollow fiber membrane according to claim 1, wherein the joining layer is made of a material that is the same kind as the support and has a melting point smaller than that of the support.

3. The hollow fiber membrane of claim 1 or 2, wherein

The average thickness of the filter sheet is more than 12 mu m and less than 100 mu m,

the average pore diameter of the filter sheet is 0.01-0.45 [ mu ] m.

4. A method of making a hollow fiber membrane comprising:

a step of heat laminating the porous bonding layer and the porous filter sheet; and

a step of bringing the outer surface of a hollow porous support formed of one or more wires into contact with the bonding layer side of the sheet after the thermal lamination step, and thermally laminating the support and the sheet after the thermal lamination step, wherein

The junction layer is made of a nonwoven fabric or a porous resin, has a melting point smaller than that of the support, and has an average thickness in a range of 10 μm to 200 μm,

the filament body is formed by more than 8 and less than 32 resin filaments, the material of the resin filaments comprises resin containing polyethylene terephthalate, polyethylene or polypropylene as main component,

the main component of the filter sheet is polytetrafluoroethylene,

the hollow fiber membrane has a bubble point of 80kPa to 200kPa,

the support is formed in a tubular shape, the filter sheet is formed in a band shape, and the filter sheet is wound on an outer surface of the support in a spiral or stripe shape by the joining layer.

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