JPH1066838A - Precise filter membrane cartridge filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily measure the perfectness of a filter with high accuracy by arranging a hydrophilic precise filter membrane composed of polysulfone between two honwoven fabrics one of which is characterized by that a hydrophilic polymer is applied to the surface thereof and a resin is applied to the formed hydrophilic polymer layer and subjecting the whole to pleating processing. SOLUTION: A hydrophilic precise filter membrane 3 composed of polysulfone is sandwiched between two nonwoven fabrics 2, 4 one of which is characterized by that a hydrophilic polymer is applied to the surface thereof and a resin is applied to the formed hydrophilic polymer layer and the whole is subjected to pleating processing and this pleated structure is wound around a core 5 having a large number of liquid collecting ports. An outer peripheral guard 1 is applied to the outside of the core 5 to protect the hydrophilic precise filter membrane 3. Further, end plates 6a, 6b are provided to both ends of the formed cylinder to seal the hydrophilic precise filter membrane 3. By this constitution, the perfectness of a filter can be easily measured with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a microfiltration filter used for microfiltration of a liquid. More particularly, the present invention relates to a method of manufacturing a highly reliable cartridge-type polysulfone microfiltration filter.

[0002]

2. Description of the Related Art A polysulfone membrane is disclosed in Japanese Patent Publication No. 4-68966.
And Japanese Patent Publication No. 5-85576, Japanese Patent Publication No. 6-862, Japanese Patent Publication No. 6-76510 and the like, a membrane having a structure having a minimum pore diameter layer inside the membrane is known. JP 6
Japanese Patent No. 277466 discloses a method in which polyvinyl alcohol is adhered and applied only to the seal portion of a pleated cartridge filter membrane. Tokushu Sho 59-501251
Japanese Patent Application Laid-Open No. H11-163873 proposes a method of eliminating a membrane hole only in a seal portion with an end plate. Several methods for eliminating holes have been proposed. JP-T-59-501251 further proposes a method of forming an integrated sheet having only non-porous ends and a micro-porous central portion.

[0003] Various types of filtration modules and filtration elements have been manufactured and sold in order to increase the filtration flow rate and facilitate handling at the time of filtration using a microfiltration membrane. One of the typical filtration elements is a cartridge type filter in which a filter membrane is folded and so-called pleated and housed in a cartridge of a fixed capacity.
No. 3 discloses this.

[0004]

With such a microfiltration cartridge filter, an "integrity test" is performed to increase the reliability of the filtration, and it is confirmed that the filter has no defects such as pinholes or breaks. One of the conventional methods for testing the integrity of a microfiltration membrane filter cartridge is the "bubble point method". When a gas pressure is applied to a microfiltration membrane wet with water, the pressure gradually increases from a low pressure to a high pressure. At a certain pressure, the gas suddenly starts to pass through the membrane pore, and the pressure at that time is called a bubble point. The maximum pore size of the microfiltration membrane is inversely related to the bubble point pressure, and if an abnormally large hole such as a pinhole is present in the membrane, a bubble point with a much lower pressure than expected is observed, and therefore, Incompleteness "can be found.

[0005] The "diffusion flow method" is used for integrity testing of a cartridge type microfiltration membrane having a large filtration area.
An inspection method called “pressure holding method” is generally used. In either method, a gas pressure lower than the bubble point of the membrane is applied to the microfiltration membrane that is well wetted with water, and the gas leakage to the secondary side of the membrane is measured. If a defect such as a pinhole is present in the film, a gas flow is generated or the pressure on the primary side fluctuates, so that the integrity of the film can be evaluated.

As described above, in any method of measuring the integrity of a filter cartridge, the pores of a microfiltration membrane are filled with a liquid such as water, a gas pressure is applied, and the amount of gas permeation and the pressure at which permeation starts are measured. . Therefore, if there is a part of the pores of the membrane that is not filled with the liquid, a large amount of gas permeates therefrom at a low pressure, and correct measurement cannot be performed. In filter cartridges, many membranes are folded or stacked in a certain volume, so even if the microfiltration membrane itself is very hydrophilic and easy to absorb water, bubbles in the pleated bundle will interfere when wetting the membrane. May create a location that is not wet by liquids. In particular, water, which is often used as a liquid, has a large surface tension, so that bubbles are hardly removed. For this reason, JIS K 3832 “Method for testing bubble point of microfiltration membrane element and module”
A method is proposed in which a liquid is filtered and wet while applying a filtration pressure difference of about 30 to 100 kPa while discharging air on the primary side of the housing. However, filtration of the liquid under these conditions does not always ensure perfect wetting. The location that is hard to get wet with liquid is not specified,
In particular, the place where it is difficult to get wet is where the film is sealed in a liquid-tight manner with another member. In a pleated filter cartridge, the pleated membrane is rolled into a cylindrical shape, the fit is sealed, and both ends of the cylinder are sealed to a plate called an end plate. It is difficult to completely wet the vicinity of such a membrane when sealing. Therefore, the diffusion flow rate becomes larger than the original value, and the bubble point value becomes smaller than the original value, so that the fluctuation is large. For this reason, it is not possible to distinguish between poor wetting and defects such as pinholes or tears in the filter, and it is easy to regard a non-defective product as a defect or mistake a defective product for a non-defective product. In the case of a cartridge filter using a polysulfone microfiltration membrane having a minimum pore size layer inside, the seal between the membrane and the end plate is particularly difficult to wet. On the other hand, in order to apply a filtration pressure difference of 30 to 100 kPa between the primary side and the secondary side of the membrane, a large amount of water must be permeated. For this reason, there is a problem that a large-capacity pump is prepared, and in the pharmaceutical industry, a large amount of expensive distilled water is consumed and the cost is increased.

According to the present invention, a microfiltration membrane sheet having an average pore diameter of 0.05 to 10 μm is pleated and rounded into a cylindrical shape, and the seam of the sheet is sealed in a liquid-tight manner. In a pleated cartridge filter sealed in a liquid-tight manner, at least two hydrophilic microfiltration membranes made of polysulfone are formed by applying a hydrophilic polymer to at least one surface and coating the surface with a resin. This was achieved by a microfiltration membrane cartridge filter characterized by being crimped between nonwoven fabrics.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an example of a development view showing the entire structure of a general pleated microfiltration membrane cartridge filter. The microfiltration membrane 3 is folded in a state sandwiched by two nonwoven fabrics 2 and 4 and wound around a core 5 having many liquid collecting ports. An outer guard 1 protects the microfiltration membrane on the outside. At both ends of the cylinder, end plates 6a and 6b
The microfiltration membrane is sealed. The end plate is in contact with a seal portion of a filter housing (not shown) via a gasket 7. The filtered liquid is collected from the liquid collecting port of the core and discharged from the outlet 8. FIG. 2 is a diagram schematically showing a state in which the membrane is sealed to the end plate. In the figures, 12 and 14 are cross sections of the nonwoven fabric, 13 is a cross section of the microfiltration membrane, and 17 is a cross section of the end plate. When the film and the end plate are sealed by heat, a part of the nonwoven fabric is melted by heat and integrated with the end plate. The liquid cannot easily enter the portion of the membrane inserted into the end plate because there is no escape space for air.

The microfiltration membrane that can be used in the present invention is preferably one using a polysulfone represented by Chemical Formula 1 or Chemical Formula 2 as a raw material. This shows a general manufacturing method for forming a microfiltration membrane using polysulfone. The polysulfone pellet is mixed with formamide, dimethylformamide, dimethylacetamide, dimethylsulfoxide,
-It is dissolved in a polar organic solvent such as pyrrolidone, N-methyl-2-pyrrolidone, sulfolane and the like. The solvent may be a single solvent or a mixture of plural types of solvents. In order to adjust the dissolving power of the solvent, a small amount of a solvent such as alcohol, such as methanol, ethanol, propanol or butanol, or water, which is called a non-solvent or a poor solvent, is often added. The amount of addition depends on the type of the solvent, but in the case of frequently used water, the amount is from 0.05% by weight to
%.

[0010]

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To the polysulfone solution, at least one kind of an inorganic electrolyte, an organic electrolyte, a polymer, or the like, which is usually called a swelling agent or a foaming agent, is added to control the porous structure. Examples of the swelling agent that can be used in the present invention include hydrophilic polymers such as polyethylene glycol and polyvinylpyrrolidone, metal salts of inorganic acids such as salt, sodium nitrate, potassium nitrate, sodium sulfate, zinc chloride and magnesium bromide, sodium acetate, formic acid Organic acid salts such as sodium and potassium butyrate, polymer electrolytes such as sodium polystyrenesulfonate and polyvinylbenzyltrimethylammonium chloride, and ionic surfactants such as sodium dioctylsulfosuccinate and sodium alkylmethyltaurate are used. Some of these swelling agents alone show some effects even when added to the polymer solution, but when these swelling agents are added as an aqueous solution, they may show particularly remarkable effects. The addition amount of the swelling agent is not particularly limited as long as the uniformity of the solution is not lost by the addition, but it is usually 0.5% by weight to 35% by weight of the stock solution for film formation. The concentration of polysulfone as a film forming stock solution is 5 to 35% by weight, preferably 10 to 30% by weight.
When it exceeds 35% by weight, the water permeability of the obtained microporous membrane becomes so small that it has no practical meaning, and when it is less than 5% by weight, a microfiltration membrane having a sufficient separation ability cannot be obtained. .

The membrane-forming stock solution prepared as described above is cast on a support, and the polymer solution membrane together with the support is immersed in the coagulation solution immediately after casting or after a certain period of time. Water is most commonly used as the coagulation liquid, but an organic solvent that does not dissolve the polymer may be used, or two or more of these non-solvents may be used in combination. As the support, a metal plate such as a copper plate or a stainless steel plate, a plastic sheet such as polyester or polyethylene, and a glass plate can be used. The casting membrane in which the polymer was precipitated in the coagulation liquid to form pores was peeled off the membrane from the support as necessary, followed by washing with water,
Perform hot water washing, solvent washing, etc., and dry. When a non-woven fabric, a woven fabric or paper is used as the support, the membrane is washed and dried as it is without peeling off the support.

A brief description will be given of a method for forming a polysulfone membrane having an inner minimum pore diameter, which is characterized in that it is hardly clogged, has a long-term filtration performance, and has a feature that the filtration layer is hidden inside the membrane and is not easily damaged. A temperature of 15-60 ° C. and a relative humidity of 10-80 ° C. are applied to the surface of a liquid film obtained by casting a film forming stock solution on a support.
%, The air speed adjusted in the range of 0.2 to 4 m / sec.
There is an important technique for appropriately adjusting the amount of evaporation of the solvent vapor and the amount of absorption of the non-solvent vapor from the atmosphere (absorption of moisture) by exposure for 40 seconds. For such a preparation, for example, a film forming stock solution is cast on a casting support, and is subjected to 25 ° C. and an absolute humidity of 2 ° C.
The coacervation phase is brought to a depth of 1 μm or more, preferably 1 to 30 μm from the outermost surface layer of the liquid film by applying air of gH ₂ O / kg Air or more to the casting surface at a wind speed of 0.2 m / sec or more. Can be formed. Immediately thereafter, it is immersed in a coagulation liquid to form a porous film. In the film obtained in this manner, the deepest part of the part where coacervation has occurred becomes the minimum pore diameter layer. The pore size on the back surface is 10 to 100 with respect to the pore size on the front surface of such an inner minimum pore size layer film.
About 0 times, and its specific surface area measured by BET method is 8 ~
80 m ² / g are obtained. A preferable specific surface area having both the mechanical strength and the filtration capacity of the membrane is 20 to 60 m ^2.
/ G. When the porosity of the membrane is increased, the permeability of water (liquid) is improved. However, when the porosity is too large, the membrane becomes brittle and cannot be used. Therefore, the preferred porosity is 55 to 87%, and particularly preferably 70 to 87%.
84%. The porosity of the membrane is greatly affected by the polysulfone concentration and the swelling agent concentration in the membrane-forming stock solution. When the polysulfone concentration is low and the swelling agent concentration is high, the porosity increases. It is slightly affected by the amount of water absorbed from the air immediately after film formation and the temperature of the coagulating liquid.

The method of hydrophilizing the surface of polysulfone, which is originally hydrophobic, includes a method of adding a hydrophilizing agent to the film forming stock solution and a method of hydrophilizing the surface of the polysulfone skeleton by chemical treatment after forming the porous film. There is a way to do that. In the former method, polyethylene glycol, polyvinylpyrrolidone, sulfonated polysulfone (Japanese Patent Publication No. 5-705)
4) and a hydrophilic polyurethane prepolymer (U.S. Pat. No. 4,137,200, U.S. Pat. No. 130,82).
No. 6 (described on Dec. 9, 1987) or the like) in an amount of 5 to 65% by weight based on the amount of polysulfone.
Added. Some or most of the added hydrophilic polymer dissolves in the coagulation solution and is lost, or is lost in the subsequent washing process.However, in such a film forming process, the hydrophilic polymer is largely distributed on the surface of the polysulfone skeleton. , Resulting in a hydrophilic polysulfone microfiltration membrane. As disclosed in JP-A-7-51550, a chemical treatment after film formation is performed by coating a monomer comprising hydroxyalkyl acrylate or methacrylate, acrylamide or methacrylamide, polar substituted acrylate or methacrylate, etc. on a hydrophobic microfiltration membrane. For free radical polymerization.

The microfiltration membrane 13 formed in this manner is usually folded by a known method. The folds of the filter media are cut off using a cutter knife or the like to cut the irregular portions at both ends in order to align both ends, and then rounded into a cylindrical shape. Or a liquid-tight seal using an adhesive. The nonwoven fabric used in the present invention is usually a hydrophilic nonwoven fabric. In particular, it is essential that the nonwoven fabric used on the primary side of the filtration membrane is hydrophilic. The hydrophilicity of the non-woven fabric means that the non-woven fabric has a higher affinity for water than air, and when the non-woven fabric comes into contact with water, it naturally absorbs water and releases air without applying any extra force. A measure of the hydrophilicity is that, for example, when a water droplet of 0.2 ml is gently placed on a nonwoven fabric placed on a desk, the water droplet is absorbed into the sheet within 2 minutes and loses the round shape of the water droplet. It is highly preferred that the sheet has such a hydrophilic property that water droplets are absorbed by the sheet within 20 seconds. The general role of nonwovens is firstly to direct the liquid to be filtered into the interior of the membrane folds so that the entire membrane folded into the cartridge can be used effectively for filtration. The second role of the nonwoven is to protect the microfiltration membrane. Accordingly, the nonwoven fabric is required to have a large number of voids and a low resistance to liquid permeation, and an appropriate strength. Furthermore, in the present invention, as a third role, it is necessary to easily release bubbles during filtration to increase the contact area between the microfiltration membrane and the liquid.

Most of the nonwoven fabrics used in conventional pleated microfiltration membrane cartridge filters are nonwoven fabrics of hydrophobic polyester or polypropylene. However, such a hydrophobic nonwoven fabric retains and hardly releases bubbles during filtration, and thus the membrane is hardly in contact with the filtered liquid and the membrane is hardly wetted by the liquid. In particular, air bubbles are difficult to escape at the seal portion of the end plate, and the holes of the membrane inserted into the seal portion have no escape route for air, so that they are particularly hard to wet with liquid. However, when using a hydrophilic non-woven fabric that has a small contact angle with water and easily penetrates water, air bubbles are easily released from the non-woven fabric voids and the membrane comes into direct contact with the liquid (water). It becomes easy to get wet.

Examples of the hydrophilic nonwoven fabric include nonwoven fabrics and paper made of hydrophilic cellulose as a raw material, and those obtained by making the surface of a glass fiber nonwoven fabric hydrophilic by chemical treatment or physical treatment. The physicochemical properties of the hydrophilic nonwoven fabric used in the pleated microfiltration cartridge filter are required to have flexibility and moderate strength against bending of the nonwoven fabric in the step of folding the polysulfone membrane. Polyester and polyolefin have flexibility and moderate strength and are inexpensive materials, but their surfaces are hydrophobic. The surface can be made hydrophilic by previously dissolving the hydrophilic polymer in an aqueous or organic solvent-based solvent and attaching it to the surface of the hydrophobic nonwoven fabric or hydrophobic fiber. Further, by coating the hydrophilic surface with a resin, the hydrophobic function can be maintained for a long time in the hydrophobic nonwoven fabric or the hydrophobic fiber.
Such a method is disclosed in JP-A-6-338309, JP-A-6-338310, and JP-A-6-333811. Compounds constituting the hydrophobic nonwoven fabric or the hydrophobic fibers used in the present invention are polyethylene, polypropylene, propylene-ethylene copolymer, polybutene,
Examples thereof include polymethylpentene-1, an ethylene-vinyl acetate polymer, and polystyrene. Of these, polyolefin is preferable, and polypropylene is more preferable. Further, as the compound constituting the hydrophilic polymer that can be used in the present invention, acrylic acid, methacrylic acid,
Styrene sulfonic acid, vinyl alcohol, vinyl sulfonic acid, maleic acid, endic acid, fumaric acid, tetrahydrophthalic acid, itaconic acid, citraconic acid, crotonic acid, isocrotonic acid and the like, and amides, imides, anhydrides and esters, etc. Derivatives and metal salts thereof. These compounds may be used alone, or may contain a plurality of compounds, or may contain a compound constituting a hydrophobic nonwoven fabric or a hydrophobic fiber such as ethylene.

The width of the pleat pleats is usually pleated so as to be 5 mm to 25 mm. In the present invention, the diameter is preferably set to 5 mm to 12 mm in order to easily release bubbles. In particular, it is preferable to set the distance from 7 mm to 10.5 mm. There are several methods for the end sealing step depending on the material of the end plate.
When using a thermosetting epoxy resin for the end plate, pour the liquid of the prepared epoxy resin adhesive into the potting mold, pre-cure it, and make the viscosity of the adhesive moderately high. One end is inserted into the epoxy adhesive. After that, it is completely cured by heating.
When the material of the end plate is a thermoplastic resin such as polypropylene or polyester, a method of inserting one end surface of a cylindrical filter medium into the resin immediately after pouring the hot-melted resin into a mold is performed. On the other hand, only the sealing surface of the already molded end plate is brought into contact with the hot plate or irradiated with an infrared heater to melt only the plate surface, and one end surface of the cylindrical filter medium is pressed against the molten surface of the plate and welded. The method is also performed. The state of air bleeding also changes depending on the structure of the outer peripheral guard 1 used. Preferably, as shown in FIG.
It is preferable to provide a small window for allowing air to escape when sealing the outer peripheral guard with the end plate.

[0019]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to the contents of the examples. Example 1 An example of the production of a microfiltration membrane made of polysulfone is shown. Polysulfone (Amoco P-3500) 15
Parts, 70 parts of N-methyl-2-pyrrolidone, 15 parts of polyvinylpyrrolidone, 2 parts of lithium chloride, and 1.3 parts of water are uniformly dissolved to prepare a stock solution for film formation. The product thickness is 18
Cast to 0 μm, temperature 25 ° C, relative humidity 50
%, Air of 1.0 m / sec was applied to the surface of the liquid film cast for 8 seconds, and immediately immersed in a coagulation bath filled with water at 25 ° C. to obtain a microporous film. The bubble point of this membrane due to water is 1
It was 50 kPa.

Example 2 Example 1 between two rayon nonwoven fabrics having a basis weight of 50 g / m ^2.
Pleated to a pleat width of 10 mm with the film made in step 1. The pleats of 125 ridges are removed and rounded into a cylinder, and the joint is sealed with an epoxy adhesive. Both ends of cylinder 5
Each mm was cut off, and the cut surface was sealed with an epoxy adhesive to complete a cartridge filter. Permeate water at a flow rate of 160 l / h for 15 minutes through the cartridge filter, and then
The air permeation amount was measured with an air pressure of 00 pPa applied. The permeation amount was 8 ml / min or less, and the water wettability of this cartridge filter was good.

Example 3 A nonwoven fabric sheet having a basis weight of 50 g / m ² was produced using polypropylene having a fineness of 1.5 d. Also, a styrene-2-ethylhexyl acrylate copolymer emulsion was prepared so as to contain 40% by weight of 2-ethylhexyl acrylate, and the above-mentioned nonwoven fabric sheet was coated and dried to 9% of DPU to obtain a hydrophilic nonwoven fabric. Obtained. The film of Example 1 was sandwiched between the two nonwoven fabrics, and pleated to a pleat width of 10 mm.
The 125 mountain folds are removed and rounded into a cylinder, and the joint is sealed with an epoxy adhesive. The cylinder was cut off at both ends by 5 mm, and the cut surface was sealed with an epoxy adhesive to complete a cartridge filter. Water is allowed to permeate through the cartridge filter at a flow rate of 160 liter / h for 15 minutes.
When the amount of permeation of air was measured while applying an air pressure of 0 kPa, the permeation amount was 8 ml / min or less, and the water wettability of this cartridge filter was good.

Comparative Example 1 A nonwoven fabric sheet having a basis weight of 50 g / m ² was produced using polypropylene having a fineness of 1.5 d. Example 1 between two nonwoven fabrics
Pleated with a pleat width of 10 mm across the
The ridges of the mountain are removed and rounded into a cylinder, and the joint is sealed with an epoxy adhesive. The cylinder was cut off at both ends by 5 mm, and the cut surface was sealed with an epoxy adhesive to complete a cartridge filter. Water is allowed to permeate through the cartridge filter at a flow rate of 160 liter / h for 15 minutes.
When the air permeation amount was measured with the air pressure applied, the permeation amount was 100 ml / min or more, and the water wettability of this cartridge filter was poor.

[0023]

According to the present invention, the polysulfone microfiltration membrane cartridge filter can be very easily wetted with water. As a result, the integrity of the filter can be measured easily and with high accuracy, and thus more reliable filtration can be performed. In particular, the effect is remarkable in anisotropically structured membrane cartridge filters in which the pore diameters on both surfaces of the membrane are at least twice the pore diameter of the smallest pore size layer inside the membrane.

[Brief description of the drawings]

FIG. 1 is a view illustrating a structure of a general pleated cartridge filter.

FIG. 2 is a diagram illustrating a structure near an end seal portion according to the embodiment of the present invention.

FIG. 3 is a diagram in which a small air vent window is installed on an outer guard.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Perimeter guard 2 Liquid permeable sheet 3 Filtration membrane 4 Liquid permeable sheet 5 Core 6a End plate 6b End plate 7 Gasket 8 Outlet 9a Air vent small window 9b Air vent small window 9c Air vent small window 12 Liquid permeable sheet 13 Filtration membrane 14 Pass Liquid sheet 17 End plate

Claims (7)

[Claims] 1. A microfiltration membrane sheet having an average pore diameter of 0.05 to 10 μm is pleated and rolled into a cylindrical shape, and the seams of the sheet are sealed in a liquid-tight manner. In a tightly sealed pleated cartridge filter, a hydrophilic microfiltration membrane made of polysulfone is provided on at least one sheet of a hydrophilic polymer on at least one sheet, and the surface is coated with a resin. A microfiltration membrane cartridge filter characterized by being crimped and sandwiched between. 2. The microfiltration cartridge filter according to claim 1, wherein the surface of the hydrophilic polymer and the material to be coated with the resin are in the form of a non-woven fabric. 3. The microfiltration cartridge filter according to claim 1, wherein the surface of the hydrophilic polymer and the material to be coated with the resin are in the form of fibers. 4. The microfiltration membrane cartridge filter according to claim 1, wherein said hydrophilic microfiltration membrane has an anisotropic structure having a minimum pore size layer in the thickness direction. 5. The microfiltration membrane cartridge filter according to claim 1, wherein the width of the pleat fold is 5 mm or more and 12 mm or less. 6. The microfiltration membrane cartridge filter according to claim 2, wherein the porosity is 55 to 87%. 7. The microfiltration membrane cartridge filter according to claim 2, wherein the specific surface area is 8 to 80 m ² / g.