JP2003320230A - Polysulfone-based microfiltration membrane and microfilter cartridge having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polysulfone-based microfiltration membrane which reduces the elution of a hydrophilizing agent to a low level while maintaining a hydrophilicity, and a cartridge filter having the microfiltration membrane. <P>SOLUTION: The polysulfone-based microfiltration membrane containing polyvinylpyrrolidone has an abundance ratio of a nitrogen atom to a carbon atom (N/C) of 0.056 or higher measured by the ESCA (electron spectroscopy for chemical analysis) method in the surface. In the microfiltration membrane cartridge, its polysulfone-based microfiltration membrane sheet is composed of the polysulfone-based microfiltration membrane where a wetting agent is applied to both ends and the wetting agent excessively applied outside of a part to which an end plate is welded is substantially removed after assembling the cartridge. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a microfiltration filter used for microfiltration of liquids. For more details,
The present invention particularly relates to a cartridge type polysulfone microfiltration filter having high hydrophilicity, excellent water permeability, and less elution of a hydrophilizing agent.

[0002]

2. Description of the Related Art Microporous filtration membranes have been known for a long time,
(For example, R. Kesting's Synthetic Poly.
mericMembranes Published by McGraw Hill Co.) Widely used for filtration filters. Microporous filtration membranes made from cellulose esters as raw materials, those made from aliphatic polyamides as raw materials, those made from polytetrafluoroethylene as raw materials, those made from polyvinylidene fluoride as raw materials , Polysulfone-based polymer as a raw material, polyethylene as a raw material, and the like. These microporous membranes are used for filtering and sterilizing electronic industrial washing water, semiconductor manufacturing chemicals, medicinal water, pharmaceutical manufacturing process water, food water, etc., and their use and usage amount have expanded in recent years, especially particle capture. From this point of view, highly reliable microporous filtration membranes are attracting attention and are frequently used. The pore structure of a general microfiltration membrane has a structure in which every portion in the thickness direction has a similar pore size distribution. On the other hand, a film having a structure having a minimum pore size layer inside the film and a film having a structure having a minimum pore size layer on the film surface are also known.

Various filtration modules and filtration elements are manufactured and sold in order to increase the filtration flow rate and facilitate handling at the time of filtration with a microfiltration membrane. One of the typical filtration elements is a cartridge type filter element in which a filtration membrane is pleated, so-called pleated, and housed in a cartridge having a constant volume (for example, Patent Document 1). The polymers used in the above microfiltration membranes are essentially hydrophobic polymers except polyamide. Therefore, as it is, water is easily repelled during filtration, and only a low permeation flow rate can be obtained. Therefore, the hydrophilic treatment of the membrane is performed by various methods. In forming a polysulfone-based microfiltration membrane, polyvinylpyrrolidone (hereinafter referred to as PVP) is often used as a pore-forming agent in the membrane-forming stock solution (for example, Patent Document 2). Most of PVP in the stock solution for film formation is dissolved and removed in coagulation water during the film formation process, but a part remains on the surface of the film to make the film hydrophilic. Also,
Disclosed is a polysulfone microfiltration membrane cartridge filter which allows the filter to be easily wetted with water so that the integrity of the filter can be measured easily and with high precision, and thus more reliable filtration. For example, Patent Document 3).

[0004]

[Patent Document 1] JP-A-64-34403 (No. 1-
(Page 2)

[Patent Document 2] Japanese Patent Application Laid-Open No. 4-338224 (No. 2-
(P. 3)

[Patent Document 3] Japanese Unexamined Patent Publication No. 2002-224539 (page 1-2)

[0005]

A slight amount of PVP is eluted from the polysulfone microfiltration membrane containing the hydrophilizing agent PVP into the filtrate. If the amount of PVP added to the stock solution for film formation is reduced in order to reduce the elution of PVP, it becomes difficult to form pores and the hydrophilicity of the formed film is impaired. Tokufair 5-
In 61970, the polysulfone membrane after pore formation is washed with a polyhydric alcohol to reduce the amount of PVP remaining in the membrane to 1 to 5% of the weight of the membrane, thereby maintaining the hydrophilicity of the membrane while allowing water permeability. A method of improving sex is disclosed. However, the elution of PVP cannot be ignored in this film, and especially when used for semiconductor manufacturing, the initial TOC (Total Organ)
ic Carbon) Elution amount becomes a problem. In order to reduce the amount of elution, the residual PVP amount in the filtration membrane was reduced to 2.5% by the washing method described in Japanese Examined Patent Publication No. 5-61970, etc., and then water was removed by drying with hot air to make the membrane hydrophilic. It caused a problem that it loses its sex and interferes with its subsequent use. Microfiltration membrane cartridge filters are usually integrity tested prior to the start of filtration to confirm the presence of defects such as pinholes and poor seals. In the integrity test, water is passed through a filter attached to the filter to fill the pores of the filtration membrane with water. After that, apply air or nitrogen pressure of 50 kPa to 250 kPa and observe gas leakage to the secondary side. If there is a place where the filtration membrane becomes hydrophobic and does not get wet with water, the pores of the filtration membrane will not be blocked by water, so if pressurized gas is loaded, the gas will leak even if there are no pinholes, and the integrity will be improved. Can not be judged. Particularly difficult to get wet is where the membrane is liquid-tightly sealed with another member. In the pleated filter cartridge, the pleated membrane is rolled into a cylindrical shape and the joint is sealed, and both ends of the cylinder are sealed with a plate called an end plate. It is difficult to completely wet the edge of the welded portion between the membrane and the end plate. An object of the present invention is to provide a polysulfone membrane that maintains hydrophilicity and has little PVP elution, and a pleated cartridge filter using the polysulfone membrane.

[0006]

The above objects of the present invention have been achieved by the following aspects. (1) Polysulfone having an abundance ratio N / C of nitrogen atoms and carbon atoms of 0.056 or more on the surface of a polysulfone-based microfiltration membrane containing polyvinylpyrrolidone measured by X-ray photoelectron spectroscopy (ESCA) System microfiltration membrane. (2) The polysulfone microfiltration membrane according to item 1, wherein the amount of polyvinylpyrrolidone eluted from the polysulfone microfiltration membrane into pure water is 40 μg or less per 1 g of the polysulfone microfiltration membrane. (3) The polysulfone-based microfiltration membrane has a mass of 2.2.
Item 3. The polysulfone-based microfiltration membrane according to Item 1 or 2, which contains polyvinylpyrrolidone in an amount of 0 to 2.45% by mass. (4) A polysulfone-based microfiltration membrane sheet is sandwiched between a plurality of support materials, fold-folded, and the seams of the rolled sheets are sealed in a liquid-tight manner, and both ends of the cylinder are also end plates. In a pleated cartridge filter formed by liquid-tightly sealing with a liquid, the polysulfone microfiltration membrane sheet comprises the polysulfone microfiltration membrane described in (1) to (3) above, and (a) polysulfone microfiltration membrane. Apply a wetting agent only to both ends of the
A microfiltration membrane cartridge filter, characterized in that, after being assembled into a cartridge, the excess wetting agent other than the welded portion of the end plate is substantially removed. (5) The wetting agent applied to both ends of the microfiltration membrane is selected from polyvinylpyrrolidone, ethyl cellulose, hydroxyethyl cellulose, methyl cellulose, hydroxymethyl cellulose, and derivatives thereof, The microfiltration membrane cartridge filter according to 4). The structure of the microfiltration membrane cartridge filter of the present invention and its manufacturing method will be described in detail below.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a development view showing the entire structure of a general pleat type microfiltration membrane cartridge filter. The microfiltration membrane 3 is folded in a sandwiched state by two membrane supports 2 and 4 and wound around a core 5 having a large number of liquid collection ports. An outer peripheral cover 1 is provided on the outer side thereof to protect the microfiltration membrane.
Microfiltration membranes are sealed at both ends of the cylinder by end plates 6a and 6b. The end plate contacts the seal portion of the filter housing (not shown) via the gasket 7. The filtered liquid is collected from the liquid collecting port of the core and discharged from the fluid outlet 8.

The polysulfone-based polymer has the general formula (I):
Polymers represented by (II) or general formula (III) are known. Further, the bubble point of the microfiltration membrane that can be used in the present invention (using ethanol as a measurement liquid,
(Measured by the method of ASTM F316) is preferably 20 kPa to 800 kPa, more preferably 40 kPa to 5
It is 00 kPa.

[0009]

[Chemical 1]

A method for producing a polysulfone type microfiltration membrane hydrophilized with PVP is described in detail in Japanese Patent Publication No. 5-61970. The present inventor has made the following assumption as a result of analyzing the existing state of PVP remaining in the polysulfone membrane thus formed. A large amount of P is still present in the film immediately after pore formation.
The VP remains only on the surface of the polysulfone fibrous material that constitutes the pores. Some PVP is simply attached to the surface of the polysulfone fibrous material (hereinafter referred to as the attached PVP). Another part is mixed with the polysulfone molecule and exists integrally (hereinafter referred to as compatibilized PVP). In the intermediate state between the adhered PVP and the compatible PVP, there is also a PVP in which a part of the molecule is compatible with the polysulfone and a part of the molecule is adhered to the surface of the polysulfone fibrous material (hereinafter referred to as the intermediate state PVP). The adhered PVP contributes significantly to the hydrophilicity, while it easily elutes and fouls the filtrate. The compatible PVP hardly elutes into the filtrate, but does not contribute to hydrophilicity. Mesomorphic PVP contributes significantly to hydrophilicity and very little elution into the filtrate. That is, if only the attached PVP is removed and the intermediate PVP is left, both hydrophilicity and elution property may be satisfied.

The method of removing the excess PVP while leaving the minimum required amount of PVP from the membrane can be achieved by immersing in hot water at 60 ° C. or higher or immersing in a solvent. As a cleaning solvent, in addition to the polyhydric alcohols described in Japanese Patent Publication No. 5-61970, methanol, ethanol, propanol, etc. 1
Polyhydric alcohols are also useful. Since the monohydric alcohol has a strong detergency, a sufficient effect can be obtained even in a mixed solution with water, and the washing temperature can be sufficiently effected at a temperature from room temperature to at most 50 ° C. 50 ° C because polyhydric alcohol has high viscosity
If it is not heated to lower the viscosity, it cannot be washed efficiently. A suitable immersion time is 10 minutes to 5 hours. After the immersion in the solvent, it can be washed with running water to prevent the PVP dissolved in the solvent from reattaching to the membrane. However, as described above, the membrane in which the amount of residual PVP in the filtration membrane is reduced to 2.5% by mass by washing or the like may retain hydrophilicity, but hot air may be used during drying after washing. It is known that the membrane may be rendered hydrophobic by drying or the like, and the hydrophilicity and hydrophobicity of the filtration membrane cannot be determined only by the residual PVP amount.
The present inventor diligently studied the conditions for maintaining the hydrophilicity of the filtration membrane, and as a result, nitrogen atoms and carbon atoms on the surface of the polysulfone-based microfiltration membrane containing polyvinylpyrrolidone measured by X-ray photoelectron spectroscopy (ESCA). When the abundance ratio N / C of 0.056 or more was 0.056 or more, it was discovered that the hydrophilicity required for the filtration membrane was retained, and the present invention was achieved. N / C
The ratio is more preferably 0.062 or more, and particularly preferably 0.067 or more. When the N / C ratio is less than 0.056, the filtration membrane becomes hydrophobic and repels water.
This may prevent the filter user from performing an integrity test before the start of filtration, or may cause a significant drop in filtrate permeation flow. Furthermore, the present inventor has found that PV depending on the degree of cleaning is used.
It was found that the remaining amount of P on the film surface, the temperature at the time of drying, the absolute humidity, the drying time, etc. have a great influence on the N / C ratio.

Surprisingly, residual P is left after washing with a solvent.
It was found that the N / C ratio of the filtration membrane having the reduced VP amount largely changed depending on the subsequent drying conditions. For example, the N / C ratio was 0.060 or more when the film in which the residual PVA amount was reduced to 2.5% by mass was naturally dried, but decreased to less than 0.056 when the film was dried with hot air. It was In hot air drying of the cartridge filter,
The water in the pleat folds evaporates, and it takes time for the water vapor generated to diffuse to the outside of the filter, and the inside of the pleat folds is exposed to a high temperature and high humidity atmosphere for a long time (10 hours to about 20 hours). During this time, the polysulfone absorbs a large amount of water and plasticizes, and the molecular chains move easily. As a result, the PVP molecules mixed with the polysulfone are directed toward the inside of the polysulfone fiber, which is more energetically stable than the air interface. It is estimated that they are changing or diving.

The present inventor has found that the hydrophobicity of the membrane due to drying can be prevented by vacuum drying or reduced pressure drying instead of hot air drying. It is preferable that the atmospheric pressure at the time of drying is as low as possible because it is effective in maintaining hydrophilicity and the drying time is shortened. However, even under reduced pressure of about 50 kPa, for example, there is an effect of preventing hydrophobicity. The pressure is preferably reduced to 10 kPa or less and dried. The drying temperature is not particularly limited, but the vacuum drying may deprive the heat of vaporization to freeze the membrane, and if the water in the membrane freezes, it may expand and destroy the pores. Is preferably vacuum dried while being heated to 60 ° C. or higher.

In order to suppress the amount of PVP eluted in the filtrate within a permissible range when the liquid for various uses is filtered using the filtration membrane of the present invention, the PVP eluted in pure water by the method described below is used. It is desirable to specify the amount. The amount of PVP eluted in pure water is 40 μg or less, particularly preferably 25 μg or less, per 1 g of the membrane. On the other hand, the amount of PVP eluted from the polysulfone membrane before solvent cleaning is 120 μg or more. The PVP elution amount was measured as follows, but is not limited to this method. Capacity of about 28g membrane
It is packed in a 500 ml wide-mouthed bottle, filled with 450 ml of pure water, and slowly rolled on two rolls of a ball mill for 4 hours for extraction. Keep room temperature at 20 to 25 ° C. Transfer the extract to a 125 ml shaped flask and freeze-dry the water to dryness. The eluate adhering to the surface of the eggplant-shaped flask is redissolved in 2 ml of a mixed solution of water and methanol made of only deuterium, and this solution is subjected to a nuclear magnetic resonance apparatus to quantify the hydrogen signal peculiar to PVP.

The amount of PVP remaining in the washed membrane can be measured by quantifying the amount of nitrogen element in the membrane to determine a preferable amount of residual PVP. Preferable residual P
The amount of VP is 2.20 mass% to 2.4 with respect to the mass of the film.
It is 5% by mass. If it is less than 2.20 mass%, the hydrophilicity of the film cannot be maintained. If it exceeds 2.45% by mass, the eluted PV
The amount of A increases above 40 μg, impairing the quality of the filtrate. A more preferable residual PVP amount is 2.27% by mass to 2.40.
It is% by mass. The cleaning may be performed after the cartridge is processed and before the integrity test. The amount of PVP was quantified by decomposing the membrane by the Kjeldahl method to convert nitrogen contained in PVP molecules in the polysulfone membrane into ammonium ion, isolating the ammonium ion, and then quantifying the amount of ammonium ion by the ion chromato method.

As described above, it is possible to prevent the membrane from becoming hydrophobic by vacuum-drying the membrane in which the amount of eluted PVP is reduced by washing with a solvent. However, it is difficult to perfect the wettability of the weld when it is assembled into a cartridge. Therefore, when processing into a cartridge, a wetting agent is sufficiently applied only to both ends of the film which is particularly hard to get wet with water. The wetting agent used for coating both ends is preferably a material that is safe even when mixed in foods and pharmaceuticals and can be easily washed and removed with water. As such materials, polyvinylpyrrolidone and its derivatives, methyl cellulose, hydroxymethyl cellulose and their derivatives, hydrophilic polymers such as ethyl cellulose, hydroxyethyl cellulose and their derivatives are highly safe and highly wettable, Moreover, it is preferable because it can be easily washed off with water. Surfactants such as alkyl sulfonates having 6 to 24 carbon atoms and sucrose higher fatty acid ester are also preferable for the same reason. As the alkyl sulfonate, sodium salt, potassium salt and lithium salt are preferable. The preferred carbon number of the fatty acid of the sucrose fatty acid ester is 6 to 24.

The application amount of the wetting agent is preferably as small as possible within the range where the wettability of the cartridge filter with water is achieved. A preferable coating amount of polyvinylpyrrolidone and its derivative is 1 to 6 g / m ² , and a particularly preferable coating amount is 2 to 4 g / m ² . The preferred coating amount of methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, hydroxyethyl cellulose and their derivatives is 0.
1 to 1 g / m ² , particularly preferred coating amount is 0.2 to 0.6 g
/ m ² . The preferred coating amount of surfactant is 0.05 to 1g
/ m ² , and a particularly preferable coating amount is 0.1 to 0.3 g / m ² . The location of application only needs to be a few millimeters from each end of the membrane. 0.1 mm from the end plate or the part that is embedded in the adhesive due to welding
Theoretically, it is sufficient if it is applied over a wide range. Considering the risk of variation in the coating width, it is preferable to apply a wide area from the end plate or the part that is embedded in the adhesive plus 2 to 5 mm. Even if it is applied by 5 mm or more, the disadvantage that the amount of elution from the finished cartridge filter will increase will increase. The coating method is not particularly limited. A solution obtained by impregnating a sponge or cloth with an aqueous solution of a wetting agent may be brought into contact with the application portion of the microfiltration membrane, or may be applied by a known method such as bead coating, gravure coating or wire bar coating.

The microfiltration membrane is usually sandwiched between two membrane supports and crimped by a known method. Nonwoven fabric, woven fabric, net or the like is used as the membrane support.
The role of the membrane support is not only to reinforce the filtration membrane against fluctuations in filtration pressure but also to introduce the liquid into the back of the fold. Therefore, it is necessary to have an appropriate liquid permeability and a physical strength sufficiently higher than that of the filtration membrane. Any sheet material having such a function can be used.

Pleats are usually pleated so that the width of the pleat is from 5 mm to 25 mm. There are several methods for the end sealing process depending on the material of the end plate, but all of them are carried out by the conventionally known publicly known technique. When using thermosetting epoxy resin for the end plate, pour the liquid epoxy resin adhesive prepared in the potting mold,
After pre-curing to increase the viscosity of the adhesive moderately,
One end of the cylindrical filter medium is inserted into this epoxy adhesive. Then, it is heated and completely cured. When the material of the end plate is a thermoplastic resin such as polypropylene or polyester, a method of inserting one end surface of the cylindrical filter medium into the resin immediately after the molten resin is poured into the mold is used. On the other hand, only the sealing surface of the already molded end plate is brought into contact with the heating 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 melting surface of the plate to weld it. The method is also done.

In order to test the integrity of the seal, the assembled cartridge filter is sufficiently immersed in hot water or a solvent as described above, and then washed with pure water.
Apply an air pressure of 50 kPa to 250 kPa, measure the leakage of air to the secondary side, and then dry and make a pass / fail judgment. The hydrophilizing agent applied to both ends of the film is easily dissolved in hot water or a solvent except the part embedded in the end plate and removed, so that there is no problem. Conventionally, the cartridge filter is dried by placing the filter in an oven in which hot air is circulated, and in the present invention, it is preferable to use a vacuum drying method or a reduced pressure drying method.

[0021]

EXAMPLES The present invention is described in detail below with reference to examples, but the present invention is not limited to the contents of these examples. Example 1 Production of microfiltration membrane Polysulfone (P-3500 manufactured by Amoco) 15 parts, N
-Methyl-2-pyrrolidone (70 parts), polyvinylpyrrolidone (15 parts), lithium chloride (2 parts) and water (1.3 parts) are uniformly dissolved to prepare a stock solution for film formation. The product thickness is 180 μm
It is cast on a polyester film at a temperature of 2
Air at 5 ° C., relative humidity 50% and wind speed 1.0 m / sec was applied to the surface of the liquid film that had been cast for 8 seconds, and immediately immersed in a coagulation bath filled with water at 25 ° C. to obtain a microporous film (average pore size 0 0.7 μm, porosity 78.2%) was obtained. The bubble point due to ethanol of this film peeled off from the polyester film was 65 kPa. When the cross section of this membrane was observed with a scanning electron microscope, an anisotropic pore structure having a minimum pore size layer inside the membrane was observed.

Coating of Wetting Agent on Membrane Edge Part A 3.5% aqueous solution of polyvinylpyrrolidone K-25 was applied on each widthwise 10 mm width of the formed microfiltration membrane. For the application, a slender felt was inserted into the tip of the vinyl tube, and the tip of the felt was exposed about 1 cm from the tube. The part of the felt that exposed the face was lightly contacted with the filtration membrane, and the liquid was sent to the felt at a flow rate of 2.5 ml per minute with a non-pulsating pump. After the main membrane was dried, both ends of the filtration membrane were cut at approximately the central position of the coating position and wound up with a membrane width of 240 mm. Cartridge and washing treatment The above membrane is sandwiched between two polypropylene non-woven fabrics, pleated to a pleat width of 10 mm, pleats of 138 ridges are taken and rounded into a cylindrical shape, and the joints are welded with an impulse sealer. Both ends of the cylinder were cut off by 5 mm, and the cut surface was heat-welded to a polypropylene end plate to complete a filter cartridge. This filter cartridge was immersed in an ethanol aqueous solution for 1 hour while changing the concentration and temperature of the ethanol aqueous solution, and then washed with water for 4 minutes while filtering pure water at 25 ° C. P remaining on the membrane after washing
The VP amount and the PVP elution amount were measured and shown in Table 1.

Drying Treatment The washed cartridge filters were vacuum dried at 70 ° C. (atmospheric pressure less than 1 kPa) and dried at 70 ° C. hot air for comparison. ESCA measurement was performed on the surface of the filtration membrane (the side of the polyester film was measured) taken out from the vacuum dried filter, and the abundance ratio N / C values of nitrogen and carbon were calculated and shown in Table 1. At the same time, the filtration membrane was floated on the water surface to observe how water permeated into the membrane pores, and the hydrophilicity / hydrophobicity of the membrane was evaluated.

[0024]

[Table 1]

[0025]

By carrying out the present invention, it is possible to provide a polysulfone microfiltration membrane cartridge filter in which the hydrophilicity of the membrane is maintained and the hydrophilizing agent PVP is less eluted.

[Brief description of drawings]

FIG. 1 shows a structure of a general pleated cartridge filter.

[Explanation of symbols]

1. Perimeter cover 2. Membrane support 3. Microfiltration membrane 4. Membrane support 5. Core 6a, 6b. end plate 7. gasket 8. Liquid outlet

Claims (5)

[Claims] 1. The abundance ratio N / C of nitrogen atoms and carbon atoms on the surface of a polysulfone-based microfiltration membrane containing polyvinylpyrrolidone measured by X-ray photoelectron spectroscopy (ESCA) is 0.0.
A polysulfone-based microfiltration membrane characterized by having 56 or more. 2. The amount of polyvinylpyrrolidone eluted from pure water of the polysulfone microfiltration membrane into the polysulfone microfiltration membrane 1
4. It is 40 μg or less per g.
The polysulfone-based microfiltration membrane described in. 3. The polysulfone microfiltration membrane according to claim 1 or 2, wherein the polysulfone microfiltration membrane contains polyvinylpyrrolidone in an amount of 2.20 to 2.45% by mass of the membrane mass. film. 4. A polysulfone-based microfiltration membrane sheet is sandwiched between a plurality of support materials, fold-folded, and the seams of the cylindrical sheets are liquid-tightly sealed, and both ends of the cylinder are also sealed. In a pleated cartridge filter formed by liquid-tightly sealing with an end plate, the polysulfone-based microfiltration membrane sheet comprises the polysulfone-based microfiltration membrane described in claims 1 to 3, and (a) polysulfone-based microfiltration membrane A microfiltration membrane cartridge characterized in that the wetting agent is applied only to both ends of the membrane, and after assembly into a cartridge (b), the excess wetting agent other than the end plate welding portion is substantially removed. filter. 5. The wetting agent applied to both ends of the microfiltration membrane is selected from polyvinylpyrrolidone, ethyl cellulose, hydroxyethyl cellulose, methyl cellulose, hydroxymethyl cellulose, and derivatives thereof. The microfiltration membrane cartridge filter according to claim 4.