WO2005102493A1 - Laminate type membrane filter element and filter cartridge using the same - Google Patents

Laminate type membrane filter element and filter cartridge using the same Download PDF

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Publication number
WO2005102493A1
WO2005102493A1 PCT/US2005/008072 US2005008072W WO2005102493A1 WO 2005102493 A1 WO2005102493 A1 WO 2005102493A1 US 2005008072 W US2005008072 W US 2005008072W WO 2005102493 A1 WO2005102493 A1 WO 2005102493A1
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WO
WIPO (PCT)
Prior art keywords
membrane filter
filter element
pleated
membrane
laminate
Prior art date
Application number
PCT/US2005/008072
Other languages
French (fr)
Inventor
Yoshiki Nomura
Kazunori Sudo
Original Assignee
Mykrolis Corporation
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Mykrolis Corporation filed Critical Mykrolis Corporation
Publication of WO2005102493A1 publication Critical patent/WO2005102493A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/10—Supported membranes; Membrane supports
    • B01D69/107—Organic support material
    • B01D69/1071—Woven, non-woven or net mesh
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/10—Supported membranes; Membrane supports
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D29/00—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor
    • B01D29/11—Filters with filtering elements stationary during filtration, e.g. pressure or suction filters, not covered by groups B01D24/00 - B01D27/00; Filtering elements therefor with bag, cage, hose, tube, sleeve or like filtering elements
    • B01D29/13—Supported filter elements
    • B01D29/15—Supported filter elements arranged for inward flow filtration
    • B01D29/21—Supported filter elements arranged for inward flow filtration with corrugated, folded or wound sheets
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D63/00—Apparatus in general for separation processes using semi-permeable membranes
    • B01D63/06—Tubular membrane modules
    • B01D63/067—Tubular membrane modules with pleated membranes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/12—Composite membranes; Ultra-thin membranes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/12—Composite membranes; Ultra-thin membranes
    • B01D69/1216—Three or more layers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/26—Polyalkenes
    • B01D71/261—Polyethylene
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/26—Polyalkenes
    • B01D71/262—Polypropylene
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2201/00—Details relating to filtering apparatus
    • B01D2201/04—Supports for the filtering elements
    • B01D2201/0407—Perforated supports on both sides of the filtering element
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2319/00—Membrane assemblies within one housing
    • B01D2319/06—Use of membranes of different materials or properties within one module
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/26—Polyalkenes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/30—Polyalkenyl halides
    • B01D71/32—Polyalkenyl halides containing fluorine atoms
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/30—Polyalkenyl halides
    • B01D71/32—Polyalkenyl halides containing fluorine atoms
    • B01D71/36—Polytetrafluoroethene

Definitions

  • the present invention relates to a membrane filter element which is advantageously used for filtration of a liquid and a filter device utilizing the filter element. More particularly, the present invention relates to a membrane filter element used for treating a liquid containing debris or foreign matters.
  • Japanese Patent 2000-508572 A discloses a post treatment of photoresist treatment liquid for printed circuits, using a combination of fluorocarbon membrane filter such as polytetrafluoroethylene (PTFE) or polyvinylidene difluoride (PNDF) or the like and polyolefin membrane filters (polypropylene, polyethylene, or the like).
  • fluorocarbon membrane filter such as polytetrafluoroethylene (PTFE) or polyvinylidene difluoride (PNDF) or the like
  • PNDF polyvinylidene difluoride
  • Japanese Patent 2001-340732 discloses a separation method using a laminate of two membrane filters for separating photoresist treatment liquid containing solid particles and gel particles.
  • This patent describes that, although a membrane filter made from a porous PTFE is effective for filtering solid debris, removal of gel particles requires a very fine pore size as well as a large driving pressure during a filtration operation. These operating conditions lead to a low filtration efficiency.
  • Japanese Patent 2001-340732 proposes to use laminated two membrane filters from these respective materials having the same or different average pore diameters to remove both the solid particles and the gel particles.
  • This patent further proposes to provide a membrane filter element of two or more laminated PTFE membranes with different average pore diameters.
  • This patent also proposes a membrane filter element of two or more laminated polyolefin membranes with different average pore diameters for the same purpose.
  • the proposed laminate type membrane filter elements have a disadvantage in that the filtration flow rate through them is lower than through a single membrane filter element.
  • a composite membrane filter formed from membrane filters each having asymmetric pore diameter distribution (pore diameter having a gradient from the upstream side to the downstream side of the membrane filter) is used with the pore diameter being larger on the upstream side to enhance the filtration performance. Accordingly this type filter may be used in the present invention.
  • the orientation of the membrane filters must be confirmed during the manufacturing process, resulting in lower production efficiency. Thus, if a wrong orientation of the membrane filters is selected, the filtration performance of the product is lowered.
  • filtration performance is improved to a great extent by interposing a non-woven fabric, woven fabric or a net having openings larger than the pores of the membrane filter elements between an upstream side membrane filter element and downstream side membrane filter element.
  • the present invention provides a membrane filter element comprising a laminate comprising at least one upstream side membrane filter, at least one downstream side membrane filter having an average pore diameter smaller than that of the upstream side membrane filter, and a separator layer interposed between the upstream and downstream side membrane filters and having pores that do not hindering flow of liquid through the membrane filter element.
  • the membrane filter element of the invention is formed such that one of the upstream and downstream side membrane filters is made of a polyfluorocarbon, and the other is made of a polyolefin resin.
  • the membrane filter element of the invention is formed such that the separator layer is a sheet material selected from non-woven fabric, net and woven fabric.
  • the membrane filter element of the invention is formed such that at least one of the upstream and downstream side membrane filters has asymmetric distribution of the pore diameters and is oriented in the filtration direction or reverse direction.
  • the membrane filter element of the invention is formed by the steps of (a) superposing a pair of perforate support sheets on both surfaces of the membrane filter element, (b) folding the resulting laminate into a pleated body, (c) forming the pleated body into an endless form, (d) bonding lateral edges of the laminate, and (e) encasing the pleated endless bonded body in a space formed between a rigid inner perforate cylinder and a rigid outer perforate cylinder.
  • the present invention provides a filter unit formed by superposing a pair of perforate support sheets on both surfaces of any of the membrane filter elements described above, by the following steps; (a) folding the resulting laminate into a pleated body, (b) forming the pleated body into an endless form, (c) bonding lateral edges of the laminate, and (d) encasing the pleated endless bonded body in a space formed between a rigid inner perforate cylinder and a rigid outer perforate cylinder.
  • Fig. 1 is a perspective view of a filter element of this invention.
  • Fig. 2 is a diagram of a PRIOR ART filter unit in which the present invention can be used.
  • a membrane filter laminate comprising at least one upstream side membrane filter, at least one downstream side membrane filter having an average pore diameter smaller than that of the upstream side membrane filter, and a separator layer interposed between the upstream side and downstream side membrane filters and having perforations sufficiently large that they do not hinder flow of liquid.
  • the upstream side membrane filter has a larger average pore diameter than the downstream side membrane but for filtration of solid particles and gel particles, for example, membrane filters having the same average pore diameter may be used. It is preferred that one of the upstream and downstream side membrane filters is made of a fluorocarbon resin, and the other membrane filter is made of a polyolefin resin.
  • the separator layer used herein is a sheet material selected from non-woven fabric, net and woven fabric or other porous sheet materials having pores or perforations sufficiently large to allow free flow of filtrate having reduced concentration of particles having larger average particle size.
  • the pores or opening in the separation layer are larger than the pore diameter of the upstream side membrane filter and the downstream side membrane.
  • At least one of the upstream and downstream side membrane filters has an asymmetric distribution of pores and is oriented in either the filtration direction or the reverse direction. It is surprising that the orientation of the asymmetric membrane filters with respect to the filtration direction has little bearing on the result when the construction of the present invention is adopted. Accordingly, the process for manufacturing a membrane filter element and a filter device using the composite membrane filter according to the present invention is facilitated since the asymmetric membrane filter can be oriented in either direction.
  • the present invention also provides a filter unit which is prepared by superposing a pair of perforate support sheets on both surfaces of the membrane filter elements of the present invention, folding the resulting laminate into a pleated body, forming the pleated body into an endless form, bonding lateral edges of the laminate, and encasing the pleated endless bonded body in a space formed between a rigid inner perforate cylinder and a rigid outer perforate cylinder.
  • any conventional membrane filters can be used in the present invention depending on the applications.
  • Resins used for such membranes include polytetrafluoroethylene, polydifluorovinylidene (PNDF), tetrafluoroethylene- perfluoroalkylvinylether copolymer or the like.
  • Other polymers which can be used include polypropylene, polyethylene, polystyrene, polyamide, polycarbonate, polyethersulfone, polyetherketone, copolymer of these polymers, and polymer alloys.
  • Polytetrafluoroethylene resin is particularly useful in applications which require high heat resistance and/or corrosion resistance.
  • the resins other than polyfluorocarbons are low in cost than the latter for composing membrane filter.
  • membranes may be used in appropriate combination depending on the applications.
  • a polyfluorocarbon adapted to filter solid particles and a polyolefin resin adapted to filter gel particles may be used in combination.
  • Membrane filters of the same or similar composition may be used with different average pore diameters.
  • the upstream side membrane filter has a larger average pore diameter than the downstream side membrane filter but for filtering solid particles and gel particles, those having the same average pore diameter may be used.
  • those having asymmetric pore size distribution may be used for higher filtration performance.
  • a laminate filter element comprises (a) a single PTFE membrane filter on the upstream side and a single polyethylene membrane filter on the downstream side or (b) three or more membrane filters containing two layers of PTFE membrane filter on the upstream side and/or two layers of polyethylene membrane filter on the downstream side; and a separator layer interposed at least between the upstream side membrane filter(s) and the downstream side membrane filter(s).
  • the upstream side membrane filter(s) can have an average pore diameter of 0.05-10 ⁇ m and the downstream side membrane filter(s) has an average pore diameter of 0.02-1.0 ⁇ m, and preferably the average pore diameter of the downstream side membrane filter is the same as or smaller average diameter than the upstream side membrane filter.
  • the separator layer to be interposed between the upstream and downstream membrane filters may be selected from non-woven fabric, net, woven fabric or other sheet materials which do not hinder free flow of filtrate permeated through the upstream side membrane filter to the downstream side membrane filter.
  • Materials used for the non-woven fabric, net and woven fabric interposed between the membrane filters include polydifluorovinylidene, tetrafluoroethylene- prefluoroalkylvinylether copolymer, and trichlorofluoro- ethylene-ethylene copolymer.
  • Other usable resins include polypropylene, polyethylene, polystyrene, polysulfone, polyamide, polycarbonate, polyethersulfone, polyetherketone, their copolymers, or polymer alloys. These materials are selected taking into consideration the necessary heat and corrosion resistances to the solution to be treated.
  • the thickness of the separator layer interposed between the membrane filters should be as thin as possible so long as the flow of the liquid to be filtered is not hindered. If the thickness is too large, the volume occupied by the separator layer in the membrane filter element becomes large and the filtering surface area is decreased per unit volume of the filter element. Accordingly, the design point should have such a balance such that the flow rate is maximized although the surface area is reduced.
  • the thickness of the separator layer may be selected within the range of 10-300 ⁇ m.
  • the upstream side or downstream side membrane filters are constituted from two or more membranes it is preferred to insert a separator layer between the upstream side or downstream side of the membranes.
  • the laminate filter element of this invention is utilized to form a filter unit constructed in a manner such as is described in Japanese Patent, 5-111622 A which is incorporated herein by reference.
  • the purpose of the invention was described as being to obtain a filter film whose upper and lower end edges are surely sealed liquid-tightly by making an edge films be along the upper and lower end edges of a filter film to weld them then making perforated support bodies along both faces to form a accordion plate-shaped body and immersing the edge film in the substance whose end plates are fused.
  • Figure 2 of this disclosure is taken from the published Abstract of JP 5- 111622. In the published Abstract, the following information is provided regarding Figure 2:
  • a pair of perforate support sheets (such as non- woven fabric) is superposed on both surfaces of the laminate type membrane filter element of the present invention.
  • the resulting construction then is folded into an accordion-pleated body, which is then formed into an endless form.
  • the lateral edges of the laminate are bonded and the upper and lower edges of the pleated filter element are immersed in molten surfaces of upper and lower end caps (adhesive auxiliary edge film strips may be bonded on the upper and lower edges of the filter element if the adhesion is not sufficient).
  • the caps are cooled to completely seal the membrane filters with the end caps.
  • the capped filter element is then supported from inside and outside by a rigid inner perforate cylinder and a rigid outer perforate cylinder.
  • a membrane filter element of the present invention supported by perforate support members is shown.
  • the membrane filter element includes, from the upstream side, a perforate or porous support member 1, an upstream side membrane filter 2, a separator layer 3, a downstream side membrane filter 4, and a downstream side porous or perforate support member 5.
  • the upstream side membrane filter 2, the separator layer 3 and the downstream side membrane filter 4 constitute the laminate membrane filter element of this invention.
  • support members 1 and 5 are superposed on the entire opposite surfaces of the filter member element and folded into pleated form, which is then formed into an endless shape.
  • the overlapping lateral edges are bonded by welding, and the endless pleated body is inserted between an inner and outer perforate support cylinders of a synthetic resin (not shown) and the upper and lower edges (only the upper edge is seen in the drawing) and bonded by welding to upper and lower end caps (not shown) together with the inner and outer support cylinders to complete the filter unit.
  • the resulting filter unit is inserted in a hermetic cartridge housing to form a filter cartridge.
  • Various filter units were prepared from composite membrane filters prepared by laminating PTFE membrane filters and UPE (ultrahigh molecular weight polyethylene) membrane filters having filters with the average pore sizes listed in Table 1.
  • the upstream side membrane filters had nominal average pore diameters larger than the downstream side membrane filters.
  • the UPE membrane filters are of asymmetric type and in Table 1 the indication "top” means that the smaller pore side was on the downstream side and “bottom” means that the larger pore side was on the downstream side.
  • a polypropylene separator layer non- woven fabric having a thickness of 200 ⁇ m
  • membrane filters were directly laminated with no interposing separator layer.
  • a composite membrane filter unit may be constituted without care to the orientation of asymmetric membrane filter.
  • the present invention can enhance the filtration rate of membrane filter element or filter unit in which a plurality of different membrane filters laminated by interposing a separator layer between the membrane filters and accordingly the period of time required for performing filtration operation is reduced and the cost of the filtration operation is reduced.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Separation Using Semi-Permeable Membranes (AREA)

Abstract

A membrane filter element is provided comprising a laminate of an upstream filter and a downstream filter having a separator layer interposed therebetween.

Description

LAMINATE TYPE MEMBRANE FILTER ELEMENT AND FILTER CARTRIDGE USING THE SAME
PRIORITY CLAIM
This application claims priority from U.S. Provisional Patent Application Serial No. 60/555,485, filed 23 March 2004.
BACKGROUND OF THE INVENTION
The present invention relates to a membrane filter element which is advantageously used for filtration of a liquid and a filter device utilizing the filter element. More particularly, the present invention relates to a membrane filter element used for treating a liquid containing debris or foreign matters.
Japanese Patent 2000-508572 A (WO97/25127) discloses a post treatment of photoresist treatment liquid for printed circuits, using a combination of fluorocarbon membrane filter such as polytetrafluoroethylene (PTFE) or polyvinylidene difluoride (PNDF) or the like and polyolefin membrane filters (polypropylene, polyethylene, or the like). However, the purpose of such combination is not disclosed.
On the other hand, Japanese Patent 2001-340732 discloses a separation method using a laminate of two membrane filters for separating photoresist treatment liquid containing solid particles and gel particles. This patent describes that, although a membrane filter made from a porous PTFE is effective for filtering solid debris, removal of gel particles requires a very fine pore size as well as a large driving pressure during a filtration operation. These operating conditions lead to a low filtration efficiency.
On the other hand, it is known that a filter element made from a porous polyolefin is effective for filtration of gel particles. Accordingly, Japanese Patent 2001-340732 proposes to use laminated two membrane filters from these respective materials having the same or different average pore diameters to remove both the solid particles and the gel particles. This patent further proposes to provide a membrane filter element of two or more laminated PTFE membranes with different average pore diameters. This patent also proposes a membrane filter element of two or more laminated polyolefin membranes with different average pore diameters for the same purpose. However, the proposed laminate type membrane filter elements have a disadvantage in that the filtration flow rate through them is lower than through a single membrane filter element.
Also, it is known that a composite membrane filter formed from membrane filters each having asymmetric pore diameter distribution (pore diameter having a gradient from the upstream side to the downstream side of the membrane filter) is used with the pore diameter being larger on the upstream side to enhance the filtration performance. Accordingly this type filter may be used in the present invention. However, the orientation of the membrane filters must be confirmed during the manufacturing process, resulting in lower production efficiency. Thus, if a wrong orientation of the membrane filters is selected, the filtration performance of the product is lowered.
SUMMARY OF THE INVENTION
In accordance with this invention, it has been found that when filtering a liquid with laminated membrane filters, liquid flow is obstructed at the interface of the laminated membrane filter elements due to the fact that the respective membrane filter elements constituting the laminate are in intimate contact with each other, resulting in insufficient filtration performance of the downstream side membrane.
In accordance with the present invention, it has been found that filtration performance is improved to a great extent by interposing a non-woven fabric, woven fabric or a net having openings larger than the pores of the membrane filter elements between an upstream side membrane filter element and downstream side membrane filter element.
Thus, in one embodiment, the present invention provides a membrane filter element comprising a laminate comprising at least one upstream side membrane filter, at least one downstream side membrane filter having an average pore diameter smaller than that of the upstream side membrane filter, and a separator layer interposed between the upstream and downstream side membrane filters and having pores that do not hindering flow of liquid through the membrane filter element.
Preferably the membrane filter element of the invention is formed such that one of the upstream and downstream side membrane filters is made of a polyfluorocarbon, and the other is made of a polyolefin resin.
Preferably the membrane filter element of the invention is formed such that the separator layer is a sheet material selected from non-woven fabric, net and woven fabric.
Preferably the membrane filter element of the invention is formed such that at least one of the upstream and downstream side membrane filters has asymmetric distribution of the pore diameters and is oriented in the filtration direction or reverse direction.
Preferably the membrane filter element of the invention is formed by the steps of (a) superposing a pair of perforate support sheets on both surfaces of the membrane filter element, (b) folding the resulting laminate into a pleated body, (c) forming the pleated body into an endless form, (d) bonding lateral edges of the laminate, and (e) encasing the pleated endless bonded body in a space formed between a rigid inner perforate cylinder and a rigid outer perforate cylinder. hi another embodiment, the present invention provides a filter unit formed by superposing a pair of perforate support sheets on both surfaces of any of the membrane filter elements described above, by the following steps; (a) folding the resulting laminate into a pleated body, (b) forming the pleated body into an endless form, (c) bonding lateral edges of the laminate, and (d) encasing the pleated endless bonded body in a space formed between a rigid inner perforate cylinder and a rigid outer perforate cylinder.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a perspective view of a filter element of this invention.
Fig. 2 is a diagram of a PRIOR ART filter unit in which the present invention can be used.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
In accordance with this invention, it has been found that filtration performance is enhanced to a great extent by a membrane filter laminate comprising at least one upstream side membrane filter, at least one downstream side membrane filter having an average pore diameter smaller than that of the upstream side membrane filter, and a separator layer interposed between the upstream side and downstream side membrane filters and having perforations sufficiently large that they do not hinder flow of liquid.
The upstream side membrane filter has a larger average pore diameter than the downstream side membrane but for filtration of solid particles and gel particles, for example, membrane filters having the same average pore diameter may be used. It is preferred that one of the upstream and downstream side membrane filters is made of a fluorocarbon resin, and the other membrane filter is made of a polyolefin resin.
The separator layer used herein is a sheet material selected from non-woven fabric, net and woven fabric or other porous sheet materials having pores or perforations sufficiently large to allow free flow of filtrate having reduced concentration of particles having larger average particle size. The pores or opening in the separation layer are larger than the pore diameter of the upstream side membrane filter and the downstream side membrane.
At least one of the upstream and downstream side membrane filters has an asymmetric distribution of pores and is oriented in either the filtration direction or the reverse direction. It is surprising that the orientation of the asymmetric membrane filters with respect to the filtration direction has little bearing on the result when the construction of the present invention is adopted. Accordingly, the process for manufacturing a membrane filter element and a filter device using the composite membrane filter according to the present invention is facilitated since the asymmetric membrane filter can be oriented in either direction.
The present invention also provides a filter unit which is prepared by superposing a pair of perforate support sheets on both surfaces of the membrane filter elements of the present invention, folding the resulting laminate into a pleated body, forming the pleated body into an endless form, bonding lateral edges of the laminate, and encasing the pleated endless bonded body in a space formed between a rigid inner perforate cylinder and a rigid outer perforate cylinder.
Any conventional membrane filters can be used in the present invention depending on the applications. Resins used for such membranes include polytetrafluoroethylene, polydifluorovinylidene (PNDF), tetrafluoroethylene- perfluoroalkylvinylether copolymer or the like. Other polymers which can be used include polypropylene, polyethylene, polystyrene, polyamide, polycarbonate, polyethersulfone, polyetherketone, copolymer of these polymers, and polymer alloys. Polytetrafluoroethylene resin is particularly useful in applications which require high heat resistance and/or corrosion resistance. The resins other than polyfluorocarbons are low in cost than the latter for composing membrane filter.
These membranes may be used in appropriate combination depending on the applications. For example, for filtering a photoresist treatment liquid, a polyfluorocarbon adapted to filter solid particles and a polyolefin resin adapted to filter gel particles may be used in combination. Membrane filters of the same or similar composition may be used with different average pore diameters.
In general, the upstream side membrane filter has a larger average pore diameter than the downstream side membrane filter but for filtering solid particles and gel particles, those having the same average pore diameter may be used. For these membrane filters, those having asymmetric pore size distribution may be used for higher filtration performance.
As a specific example, a laminate filter element comprises (a) a single PTFE membrane filter on the upstream side and a single polyethylene membrane filter on the downstream side or (b) three or more membrane filters containing two layers of PTFE membrane filter on the upstream side and/or two layers of polyethylene membrane filter on the downstream side; and a separator layer interposed at least between the upstream side membrane filter(s) and the downstream side membrane filter(s). Specifically, the upstream side membrane filter(s) can have an average pore diameter of 0.05-10 μm and the downstream side membrane filter(s) has an average pore diameter of 0.02-1.0 μm, and preferably the average pore diameter of the downstream side membrane filter is the same as or smaller average diameter than the upstream side membrane filter. The separator layer to be interposed between the upstream and downstream membrane filters may be selected from non-woven fabric, net, woven fabric or other sheet materials which do not hinder free flow of filtrate permeated through the upstream side membrane filter to the downstream side membrane filter. Through the use of the separator layer, the flow of the liquid is not obstructed at the interface between the upstream side and downstream side membrane filters, and the filtration rate is increased remarkably over the conventional laminate membrane filter element.
Materials used for the non-woven fabric, net and woven fabric interposed between the membrane filters include polydifluorovinylidene, tetrafluoroethylene- prefluoroalkylvinylether copolymer, and trichlorofluoro- ethylene-ethylene copolymer. Other usable resins include polypropylene, polyethylene, polystyrene, polysulfone, polyamide, polycarbonate, polyethersulfone, polyetherketone, their copolymers, or polymer alloys. These materials are selected taking into consideration the necessary heat and corrosion resistances to the solution to be treated.
The thickness of the separator layer interposed between the membrane filters should be as thin as possible so long as the flow of the liquid to be filtered is not hindered. If the thickness is too large, the volume occupied by the separator layer in the membrane filter element becomes large and the filtering surface area is decreased per unit volume of the filter element. Accordingly, the design point should have such a balance such that the flow rate is maximized although the surface area is reduced. For example, the thickness of the separator layer may be selected within the range of 10-300 μm.
When the upstream side or downstream side membrane filters are constituted from two or more membranes it is preferred to insert a separator layer between the upstream side or downstream side of the membranes.
In use, the laminate filter element of this invention is utilized to form a filter unit constructed in a manner such as is described in Japanese Patent, 5-111622 A which is incorporated herein by reference. In the published Abstract of that patent the purpose of the invention was described as being to obtain a filter film whose upper and lower end edges are surely sealed liquid-tightly by making an edge films be along the upper and lower end edges of a filter film to weld them then making perforated support bodies along both faces to form a accordion plate-shaped body and immersing the edge film in the substance whose end plates are fused.
Figure 2 of this disclosure is taken from the published Abstract of JP 5- 111622. In the published Abstract, the following information is provided regarding Figure 2:
After a filter membrane 31 of tetrafluoroethylene resin, etc., and non- perforated edge films 23 made of thermoplastic resin are continuously fed and the edge films are superimposed on the filter membrane 31 at both edge parts, the superimposed substances are passed through hot rolls heated above the melting point of the edge film 23 to weld them. Next, perforated support bodies, such as nets made of thermoplastic resin are put on the both faces of the welded body to laminate them and the laminated body is folded in the form of accordion pleats. Further, the pleat-shaped laminated body is made in the endless shape and the perforated support bodies are superimposed and welded at both side edges to form a welded body which is immersed in thin holes of the membrane 31 and sealed to form a cylindrical body 24. Thus the filter membrane whose upper and lower end edges are surely sealed liquid- tightly is obtained.
A pair of perforate support sheets (such as non- woven fabric) is superposed on both surfaces of the laminate type membrane filter element of the present invention. The resulting construction then is folded into an accordion-pleated body, which is then formed into an endless form. The lateral edges of the laminate are bonded and the upper and lower edges of the pleated filter element are immersed in molten surfaces of upper and lower end caps (adhesive auxiliary edge film strips may be bonded on the upper and lower edges of the filter element if the adhesion is not sufficient). The caps are cooled to completely seal the membrane filters with the end caps. The capped filter element is then supported from inside and outside by a rigid inner perforate cylinder and a rigid outer perforate cylinder.
Referring to Fig. 1, a membrane filter element of the present invention supported by perforate support members is shown. The membrane filter element includes, from the upstream side, a perforate or porous support member 1, an upstream side membrane filter 2, a separator layer 3, a downstream side membrane filter 4, and a downstream side porous or perforate support member 5. Among them, the upstream side membrane filter 2, the separator layer 3 and the downstream side membrane filter 4 constitute the laminate membrane filter element of this invention. To construct a filter unit, support members 1 and 5 are superposed on the entire opposite surfaces of the filter member element and folded into pleated form, which is then formed into an endless shape. The overlapping lateral edges are bonded by welding, and the endless pleated body is inserted between an inner and outer perforate support cylinders of a synthetic resin (not shown) and the upper and lower edges (only the upper edge is seen in the drawing) and bonded by welding to upper and lower end caps (not shown) together with the inner and outer support cylinders to complete the filter unit. The resulting filter unit is inserted in a hermetic cartridge housing to form a filter cartridge.
The following example illustrates the present invention and is not intended to limit the same.
Example 1
Various filter units were prepared from composite membrane filters prepared by laminating PTFE membrane filters and UPE (ultrahigh molecular weight polyethylene) membrane filters having filters with the average pore sizes listed in Table 1. The upstream side membrane filters had nominal average pore diameters larger than the downstream side membrane filters. Among them, the UPE membrane filters are of asymmetric type and in Table 1 the indication "top" means that the smaller pore side was on the downstream side and "bottom" means that the larger pore side was on the downstream side. In the Examples, a polypropylene separator layer (non- woven fabric having a thickness of 200 μm) was inserted between the membrane filters and in the Comparative Examples, membrane filters were directly laminated with no interposing separator layer. These laminates were punched into circular discs having a diameter of 47 mm and set on a holder, a differential pressure of O.lMPa was applied, and the lapse of time required for passage of 100 ml of 100% -PA (isopropyl alcohol) was measured. The result is shown in Table 1.
Table 1
Note: All membranes are asymmetric type. Top: Upstream side has larger pore size. Bottom: Downstream side has larger pore size. Time is in seconds
As seen from Table 1, Examples which used non- woven fabrics (separators) exhibit shorter filtration times than Comparative Examples which did not use the separators and the difference between them is large. Accordingly the use of separators enhances the filtration performance to a great extent.
On the other hand, there is little difference between the top and bottom orientations of the membrane filters in the Examples of the present invention while the difference is large in the Comparative Examples. Accordingly, by using a separator, a composite membrane filter unit may be constituted without care to the orientation of asymmetric membrane filter.
From the foregoing, it is shown that the present invention can enhance the filtration rate of membrane filter element or filter unit in which a plurality of different membrane filters laminated by interposing a separator layer between the membrane filters and accordingly the period of time required for performing filtration operation is reduced and the cost of the filtration operation is reduced.
In addition, according to the present invention, it is not necessary to pay attention to the flow orientation even if membrane filters have asymmetric pore diameter distribution, and accordingly the production cost can be reduced.

Claims

1. A membrane filter element comprising a laminate comprising at least one upstream side membrane filter, at least one downstream side membrane filter having an average pore diameter smaller than that of the upstream side membrane filter, and a separator layer interposed between the upstream and downstream side membrane filters and having pores that do not hindering flow of liquid through the membrane filter element.
2. A membrane filter element according to Claim 1 wherein one of the upstream and downstream side membrane filters is made of a polyfluorocarbon, and the other is made of a polyolefin resin.
3. A membrane filter element according to Claims 1 or 2, wherein the separator layer is a sheet material selected from non-woven fabric, net and woven fabric.
4. A membrane filter element according to any one of Claims 1 or 2, wherein at least one of the upstream and downstream side membrane filters has asymmetric distribution of the pore diameters and is oriented in the filtration direction or reverse direction.
5. A filter unit formed by superposing a pair of perforate support sheets on both surfaces of the membrane filter element according to one of Claims 1 or 2, folding the resulting laminate into a pleated body, forming the pleated body into an endless form, bonding lateral edges of the laminate, and encasing the pleated endless bonded body in a space formed between a rigid inner perforate cylinder and a rigid outer perforate cylinder.
6. A filter unit formed by superposing a pair of perforate support sheets on both surfaces of the membrane filter element according to Claim 3, folding the resulting laminate into a pleated body, forming the pleated body into an endless form, bonding lateral edges of the laminate, and encasing the pleated endless bonded body in a space formed between a rigid inner perforate cylinder and a rigid outer perforate cylinder.
7. A filter unit formed by superposing a pair of perforate support sheets on both surfaces of the membrane filter element according to Claim 4, folding the resulting laminate into a pleated body, forming the pleated body into an endless form, bonding lateral edges of the laminate, and encasing the pleated endless bonded body in a space formed between a rigid inner perforate cylinder and a rigid outer perforate cylinder.
PCT/US2005/008072 2004-03-23 2005-03-09 Laminate type membrane filter element and filter cartridge using the same WO2005102493A1 (en)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4206050A (en) * 1977-05-16 1980-06-03 Hoechst Aktiengesellschaft Membrane unit and apparatus for removing metabolite contaminants from blood
US6264044B1 (en) * 1997-04-11 2001-07-24 Cuno, Inc. Reinforced, three zone microporous membrane
JP2001340732A (en) * 2000-05-31 2001-12-11 Pall Corp Laminated filter element

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4206050A (en) * 1977-05-16 1980-06-03 Hoechst Aktiengesellschaft Membrane unit and apparatus for removing metabolite contaminants from blood
US6264044B1 (en) * 1997-04-11 2001-07-24 Cuno, Inc. Reinforced, three zone microporous membrane
JP2001340732A (en) * 2000-05-31 2001-12-11 Pall Corp Laminated filter element

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