JPH09108551A - Water purifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an excellent impurity-cutting performance and improve durability by using polyolefin composite porous hollow fiber membranes having at least two porous layers with different pore diameters as hollow fiber membranes in a water purifier equipped with a hollow fiber membrane module in a filtration part. SOLUTION: Composite porous hollow fiber membranes in which at least two polyolefin porous layers having pares with different pore diameters are laminated are used as hollow fiber membranes 7 for a hollow fiber membrane module 5. This is composed of a laminate having elliptic pores consisting of microfibril bundles in which a porous layer having a reinforcing function is laminated at least on one side of a porous layer having a separation function, and each layer is oriented in the fiber axis direction and knot parts of stacked lamellas which bond both ends of the bundles. The microfibril bundles and the knot parts of stacked lamellas which constitute the pores are coated with hydrophilic copolymer of 3-30wt.% based on 100wt.% of a composite porous hollow fiber membrane precursor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water purifier provided with a hollow fiber membrane module in a filter section, and more particularly to a water purifier suitable for purifying water such as tap water to obtain delicious water that is safe for daily life. .

[0002]

2. Description of the Related Art In recent years, a water purifier equipped with a filter using a filtration membrane having fine pores such as a hollow fiber membrane and a filtration section connecting an activated carbon layer has been drawing attention and widely used for purification of tap water. Has been.

As this filter, a silicone type,
A hollow fiber membrane made of a polymer material such as polyolefin, polyester, polyamide, polysulfone, cellulose, polyurethane, etc. is focused, and the focusing end is made of polyurethane or the like so that the open end of the hollow fiber membrane is not blocked. It is often used that the hollow fiber membrane is partitioned by airtightly and the potting portion is fixed to a cylindrical case body to form a module.

In this water purifier, residual chlorine, other odorous components and organic substances contained in the raw water are removed by the activated carbon layer, and iron rust colloidal components and bacteria which are difficult to remove by chlorine sterilization are removed by the filter. This produces safe and tasty drinking water.

Various membranes have been developed as hollow fiber membranes for filters of water purifiers. As a typical example, Japanese Patent Laid-Open No. 57-66114 discloses a knotted portion of microfibrils oriented in the long axis direction of a hollow fiber membrane and a stacked lamella oriented in the thickness direction of the hollow fiber membrane. The slit-shaped micropores formed from and are laminated in the membrane wall of the hollow fiber membrane, and penetrate from one surface of the membrane to the other surface to form a uniform microporous structure in the thickness direction. , A microporous hollow fiber membrane made of polyethylene is disclosed.

This membrane is produced by melt-forming polyethylene and further stretching the shaped product. That is, after polyethylene is shaped under a specific spinning condition, an annealing treatment is performed to form lamella laminated crystals (stacked lamella) in the film wall of the shaped body, and then this shaped body is stretched to form a stack. By separating the lamellas and growing the fibrils connecting the lamella laminated crystals, the microporous film having the above specific structure is formed. Since this membrane has the above-mentioned specific microporous structure, it has excellent mechanical strength, and since it does not use a solvent in the manufacturing process, it has excellent safety characteristics.

[0007]

Recently, a water purifier has a higher water permeation performance while maintaining the fractionation performance of filtering and removing suspended solids and bacteria, further downsizing, long life,
High durability is strongly demanded. To that end, improve the water permeability of the membrane and reduce the amount of membrane stored in the cartridge, have a long-lived membrane structure that does not easily clog even when passing tap water, and the practical pressure of tap water. There is a demand for a film material having properties such as pressure resistance in the range.

However, in the case of hollow fiber membranes used in these water purifiers, if the pore diameter is too large, the fractionation performance becomes insufficient and safe drinking water cannot be provided. On the other hand, when the one having a small pore diameter and a high fractionation performance was used, the pressure loss was large, and the water permeation amount was likely to be small at about the discharge pressure of tap water at the faucet. In order to increase the amount of water permeation, the film thickness of the porous film may be made smaller, but in that case, the mechanical strength of the microporous film tends to be insufficient. Further, although the amount of water permeation can be increased even if the amount of hollow fiber membranes used is increased, it has not been possible to meet the demand for providing a water purifier that is small and easy to use.

The present inventors have been keen to develop a porous hollow fiber membrane suitable for use in a water purifier having a high fraction, a high flux, a good mechanical strength and a long life which is unlikely to be clogged. As a result of examination, the structure of a composite microporous hollow fiber membrane in which a microporous membrane having micropores capable of separating particles of a predetermined particle size is joined to a microporous membrane having micropores larger by a predetermined ratio than that By doing so, it is possible to produce a composite porous hollow fiber membrane with a small decrease in the water permeation rate of the membrane regardless of the increase in the membrane thickness, and moreover, the dense layer (a layer) that plays the role of separation in the composite porous hollow fiber membrane. The inventors have found that by selecting the filtration direction of the water to be treated in consideration of the position, a water purifier with an increased water permeation amount and less clogging can be manufactured, and the present invention has been completed.

An object of the present invention is to provide a water purifier having a long life which can secure a sufficient amount of water permeation even in a small size, has a high impurity cutting performance, and is excellent in durability.

[0011]

That is, the present invention provides a water purifier having a hollow fiber membrane module including a hollow fiber membrane in a filtration section, wherein at least a microporous layer having different pore diameters is used as the hollow fiber membrane. A water purifier characterized by using a polyolefin composite microporous hollow fiber membrane having two layers.

Further, according to the present invention, in a water purifier having a hollow fiber membrane module including a hollow fiber membrane in a filtration section, the hollow fiber membrane has a reinforcing function on at least one surface of a microporous layer a layer which has a separating function. Is a composite microporous hollow fiber membrane made of polyolefin in which microporous b-layers are laminated, and each layer of a-layer and b-layer is bonded to a plurality of microfibril bundles oriented in the fiber axis direction and both ends of the microfibril bundle. It is composed of a laminated body of elliptical micropores composed of a knotted part of a stacked lamella, the micropores communicating from the outer surface of the hollow fiber membrane toward the hollow part, The microfibril bundles forming the micropores and the knots of the stacked lamellae are covered with 3 to 30% by weight of a hydrophilic copolymer with respect to 100% by weight of the composite microporous hollow fiber membrane precursor, layer a Average between microporous microfibrils bundle present in the distance Da and the ratio is 1.3 ≦ a mean distance Db between microfibril bundles of fine pores present b layer Db /
A water purifier characterized by using a composite microporous hollow fiber membrane in a range of Da ≦ 4.0.

Further, the present invention is the above-mentioned water purifier, wherein the water to be treated is configured to flow from a layer having a large pore diameter of the composite microporous hollow fiber membrane to a layer having a small pore diameter.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION In the water purifier of the present invention, as shown in the schematic view of FIG. 1, a filter section 4 is arranged in a water purifier body 3 having a raw water inlet 1 and a water outlet 2. The hollow fiber membrane module 5 is attached to the filtration section. In this example, the hollow fiber membrane module 5 has an activated carbon layer 6 for removing residual chlorine, trihalomethane, musty odor substances, etc. contained in raw water connected to the hollow fiber membrane 7 and incorporated therein. The layer may or may not be present, and may further include a mineral component layer for elution of minerals, an ion exchange resin for removing heavy metal ions and anions such as nitrate nitrogen and nitrite nitrogen, and the like.

The hollow fiber membrane module is generally constructed such that the hollow fiber membrane is bundled and fixed in a cylindrical case with a potting agent so that it can be attached to and detached from the filter section of the water purifier body. It may be integrated with the container body. In the water purifier of the present invention, this hollow fiber membrane module comprises a composite microporous hollow fiber membrane described below.

The composite microporous hollow fiber membrane used in the water purifier of the present invention has a composite structure in which two or more polyolefin microporous layers having micropores having different pore diameters are laminated, that is, reinforced. The microporous layer b layer having a large pore size which is responsible for the function is laminated on at least one surface of the microporous layer a layer having a small pore size which is responsible for the separating function.
Therefore, the structure of the hollow fiber membrane is, for example, b on one side of layer a.
It may have a two-layer structure in which layers are laminated, or may have a three-layer structure in which b layers are laminated on both sides of an a layer. The composite microporous hollow fiber membrane preferably has an inner diameter in the range of 50 to 5000 μm. If the inner diameter is less than 50 μm, the pressure loss inside the hollow fiber membrane increases, which is not preferable in practice. Also, 5
When it is larger than 000 μm, the degree of integration of the hollow fiber membrane is lowered, so that the water permeability per unit volume is remarkably lowered.
The total film thickness is preferably 5 to 500 μm, more preferably 30 to 200 μm. Total film thickness is 5μ
When it is less than m, the mechanical strength is weak and the hollow fiber is deformed to be flat. If it is larger than 200 μm, it becomes difficult to obtain high water permeability.

The separation functional layer (layer a) may be located on either side of the reinforcing functional layer (layer b) depending on the purpose of use. It is preferable to flow from a layer having a large pore size to a layer having a small pore size. Therefore, it is possible to freely select and use whether to flow from the inside to the outside of the hollow fiber membrane or to flow in the opposite direction.

The layers a and b have micropores arranged in the fiber axis direction, and the micropores are in the layer a and b.
The micropores that communicate with each other in the layers and between the ab layers form a layered communication from one surface of the hollow fiber membrane to the other surface.

The micropores formed in the layer a are formed from microfibril bundles arranged in the fiber axis direction and knots of the stacked lamellae arranged in the direction perpendicular to the fiber axis.
The gap between the microfibril bundle and the nodule is an elliptical micropore.

The size of the micropores in the layer a is preferably 0.2 to 0.5 μm, more preferably 0.3 to 0.4 μm in terms of the average distance Da between the microfibril bundles. preferable. A hollow fiber membrane having an average distance Da between the microfibril bundles of 0.2 μm or more has a particularly large water permeability, and a hollow fiber membrane having a Da of 0.5 μm or less has good fine particle blocking ability, that is, high fractionation. It is a film.

The thickness of the layer a is preferably 0.5 to 20 μm, more preferably 3 to 12 μm. When the thickness of the a layer is less than 0.5 μm, pinhole defects tend to occur in the a layer, while when the thickness of the a layer exceeds 20 μm, the water permeability of the hollow fiber membrane decreases. Tend to do. Further, the film thickness of the layer a is preferably 1/3 or less of the total film thickness, and it becomes difficult to effectively obtain high water permeability with a hollow fiber membrane thicker than this.

The microporous layer b layer has a reinforcing function of supporting the microporous layer a layer which has a separating function in the composite hollow fiber membrane. Like the layer a, the layer b also has a laminated structure of micropores oriented in the fiber axis direction, and the micropores are formed by microfibril bundles and knots of the stacked lamellae. The size of the micropores in the b layer is preferably 0.2 to 1 μm, and more preferably 0.4 to 0.5 μm in terms of the average distance Db between the microfibril bundles. A hollow fiber membrane having a b-layer with micropores having a Db of less than 0.2 μm tends to have a reduced water permeation rate, while when Db exceeds 1 μm, a hollow-fiber membrane having a b-layer having the micropores. Mechanical strength tends to decrease.

The average distance Lb between the nodules of the stacked lamella in the layer b is preferably 0.4 to 4.0 μm, more preferably 0.7 to 2.0 μm. The water permeation rate tends to decrease in a hollow fiber membrane having a b-layer composed of micropores having Lb of less than 0.4 μm.
When it exceeds 4.0 μm, the mechanical strength of the hollow fiber membrane tends to decrease.

In the hollow fiber membrane used in the present invention, Db and Da
The ratio is preferably 1.3 ≦ Db / Da ≦ 4.0. With a hollow fiber membrane having a Db / Da of less than 1.3, the water purifier of the present invention is unlikely to be a water purifier with a high fractionation and a large water permeation rate, and the clogging resistance of the present invention is also reduced. Is not preferred. On the other hand, when Db / Da exceeds 4.0, the difference in the physical properties of the polyolefins adjacent to each other increases, and spinning or drawing stability tends to decrease.

In the composite microporous hollow fiber membrane used in the water purifier of the present invention, it is preferable that the maximum pore size of the membrane determined by the bubble point method is in the range of 0.05 to 1.0 μm. A hollow fiber membrane having a maximum pore size of less than 0.05 μm tends to decrease the water permeation rate, and when it exceeds 1.0 μm,
The mechanical strength decreases.

The polyolefins used as the material for forming the composite hollow fiber membrane are, for example, polyethylene, polypropylene, poly-3-methylbutene-1, poly-4-methylpentene-1, polyvinylidene fluoride alone or a mixture of these polymers. Can be used. The MI value (melt index value) of polyolefins measured by ASTM D-1238 is preferably in the range of 0.1 to 50, more preferably in the range of 0.3 to 15. Since the melt viscosity of a polyolefin having an MI value of 0.1 or higher is too high, it is difficult to shape it and it is difficult to form a desired microporous membrane. On the other hand, a polyolefin having an MI value of more than 50 has a too low melt viscosity, which makes it difficult to perform stable shaping. The preferred density of the polyolefin varies depending on the material used, but for example, in the case of polyethylene, it is preferably 0.95 g / cm ³ or more, and in the case of polypropylene, it is preferably 0.91 g / cm ³ or more.

In making this composite microporous hollow fiber membrane,
When the MI value MIa of the polyolefin for forming the a layer and the MI value MIb of the polyolefin for forming the b layer are selected such that MIa <MIb, the density ρa of the polyolefin for forming the a layer and the polyolefin ρb for forming the b layer are almost equal to each other. They can be manufactured evenly. Conversely, if each polyolefin is selected so that ρa <ρb, MIa,
This composite microporous hollow fiber membrane can be obtained even if the MIb is almost the same. It is preferable to select the respective polyolefins so as to satisfy both the relations of MIa <MIb and ρa <ρb, because this composite microporous hollow fiber membrane can be efficiently produced.

The average distance between the microfibril bundles of micropores referred to in the present invention is measured as follows. That is, a 6 cm square portion of a 6500-times transmission electron micrograph of a sample obtained by cutting an ultrathin section from the hollow fiber membrane in the fiber axis direction is taken into the CRT screen of the image processing apparatus (Fig. 2 is a schematic diagram of this image). Indicates). From the top side of the captured image to the direction perpendicular to the fiber axis direction, to the bottom side,
Sequentially draw the first to nth scanning lines at a pitch of 0.052 μm. Excluding the portion where the average distance between the microfibril bundles indicated by α cannot be measured, each distance of the line segments passing through the hole portion in the first scanning line, for example, the sum of a ₁ to a ₅ Then, the sum of b ₁ to b ₆ is similarly calculated for the second scanning line, and the sum of n ₁ to n ₆ of the nth scanning line is sequentially calculated to obtain the sum (distance sum). Next, the number of fine holes (1
(5 for the second scan line, 6 for the second scan line, 6 for the nth scan line)
Then, the sum of distances / the sum of numbers is determined as the average intervals Da and Db.

In order to produce the composite microporous hollow fiber membrane used in the water purifier of the present invention, first, an intermediate composite microporous hollow fiber membrane precursor is prepared, and then a coating treatment with a hydrophilic copolymer is carried out. Good. In order to make a precursor, it is necessary to select a polyolefin that satisfies the above conditions, perform melt composite spinning using a nozzle that has two or more annular discharge ports that are concentrically arranged, and obtain a multilayer body. It is achieved by performing heat treatment and stretching accordingly.

The means for imparting a difference in pore size to the layers adjacent to each other is achieved by compounding polyolefins having different densities and MI values. In this case, the density of the polyethylene used preferably at 0.955 g / cm ³ or more in the measurement method shown in JISK6760, still more preferably 0.960 g / cm ³ or more. When the density is less than 0.955 g / cm ³ , the formation of fine pores by stretching is not uniform, which is not preferable.

The MI value is JISK6760.
It is preferably in the range of 0.05 to 20.0 g / 10 minutes, more preferably 0.1 to 5.0 g.
/ 10 minutes. When the MI value is less than 0.05 g / 10 minutes, the polymer viscosity is so high that melt spinning becomes difficult, which is not preferable. Further, if it exceeds 20.0 g / 10 minutes, the crystal orientation of the multilayer body becomes insufficient, and a uniform fine pore structure cannot be obtained. The fine pores formed by the melt spinning or drawing method can be obtained by arranging polyethylene whose density or MI value is adjusted to obtain the composite microporous hollow fiber membrane of the present invention laminated with two or more layers having different pore sizes. it can.

The density or MI value of polyethylene described above can be freely adjusted by setting polymerization conditions, blending, etc., and can be selected as necessary.

The spinning temperature is not lower than the melting point of the polyolefin (preferably 10 to 100 ° C. higher than the melting point), and the discharged product is 0.1 to 3 m in an atmosphere of 10 to 40 ° C.
The multilayered body obtained by taking up at a take-up speed of / sec was heat-treated as it was or at a temperature not higher than the melting point of the polyolefin (preferably 5 to 50 ° C. lower than the melting point) to form a stacked lamella. After that, the multi-layer body is stretched and subjected to an opening treatment. As for stretching, it is preferable to carry out hot stretching after cold stretching. Cold stretching is a process of causing structural destruction of a multilayer body at a relatively low temperature to generate microcracks between stacked lamellas, and the cold stretching is performed in a range of 0 ° C. to 50 ° C. lower than the melting point of the polymer. It is preferable to carry out. When polyethylene is used as the polyolefin, the cold stretching temperature is in the range of 0 to 80 ° C, preferably 10 to 50 ° C. The cold stretching ratio is preferably 5 to 200%. When it is 5% or less, the generation of microcracks becomes insufficient, and it becomes difficult to obtain a target pore size. Also, 200
If it exceeds%, deformation of the stack lamella occurs and the porosity of each microporous layer decreases, which is not preferable.

The subsequent hot stretching is a process of expanding the microcracks generated in the multilayer body and forming microfibrils between the stacked lamellae to form a porous film having slit-like micropores. The hot stretching temperature is preferably as high as possible within the range not exceeding the melting point of the polyolefin. The heat draw ratio may be appropriately selected depending on the target pore size, but is 50 to 2000.
%, Preferably 100 to 1000%, in terms of process stability.

Further, in order to obtain the dimensional stability of the obtained composite porous membrane precursor, heat setting is performed under a fixed length or in a state where the membrane is slightly relaxed. In order to effectively perform heat setting, the heat setting temperature is preferably the stretching temperature or higher and the melting point temperature or lower.

As described above, by melt-composite spinning and stretch porosification, a large number of microfibrils in which the a-layer and the b-layer are oriented in the stretching axis direction of each layer and the knotted portion of the stacked lamella bonded at both ends of the microfibril A hollow fiber membrane-shaped precursor is obtained which is constituted by a slit-shaped laminated body constituted by, and the micropores penetrate from one surface of the membrane to the other surface.

Next, a step of imparting permanent hydrophilicity to the obtained multilayer composite film precursor is applied. The hydrophilic copolymer used here is preferably a copolymer containing 20 mol% or more of ethylene and 10 mol% or more of a hydrophilic monomer,
These copolymers may be any type of copolymers such as random copolymers, block copolymers and graft copolymers. The ethylene content in the copolymer is 2
At 0 mol% Sueman, the copolymer has a weak affinity for the precursor, and the precursor is soaked in the hydrophilic copolymer solution to be hydrophilic at a ratio of 3 to 30% by weight relative to 100% by weight of the precursor. It is not preferable because it becomes difficult to coat the copolymer.

The hydrophilic monomer used when polymerizing this hydrophilic copolymer is, for example, vinyl alcohol,
(Meth) acrylic acid and its salts, hydroxyethyl (meth) acrylate, polyethylene glycol (meth) acrylic acid ester, vinylpyrrolidone, vinyl compounds such as acrylamide can be mentioned, and one or more of these hydrophilic monomers may be contained. However, vinyl alcohol may be mentioned as a particularly preferable monomer. Further, this hydrophilic copolymer may contain one or more third components other than ethylene and the hydrophilic monomer,
Examples of the third component include vinyl acetate, (meth) acrylic acid ester, vinyl alcohol fatty acid ester, vinyl alcohol formal compound and butyral compound.

The coating amount of the hydrophilic copolymer on the composite porous membrane precursor is 3 to 30% by weight in terms of the precursor weight.
Range. A microporous membrane having a hydrophilic copolymer coating amount of less than 3% by weight has a poor affinity for water and insufficient water permeability to the microporous membrane, while the hydrophilic copolymer coating amount is insufficient. Thirty
If the amount is more than 10% by weight, the copolymer tends to block the pores of the microporous membrane and the water permeability thereof tends to decrease.

The solvent for the hydrophilic copolymer is preferably a water-miscible organic solvent, and specific examples thereof include alcohols such as methanol, ethanol, n-propanol and isopropyl alcohol, dimethyl sulfoxide, dimethylformamide and the like. Can be raised. These solvents can be used alone, but a mixture with water is more preferable because it has a strong solubility in the hydrophilic copolymer. Also, the ease of making a vapor-containing atmosphere of the solvent used in drying the microporous membrane coated with the hydrophilic copolymer, that is,
From the viewpoint of low vapor pressure of the solvent and low toxicity to the human body, it is particularly preferable to use an alcohol having a boiling point of less than 100 ° C., for example, a mixed solvent of water with methanol, ethanol, isopropyl alcohol and the like. The mixing ratio of the water-miscible organic solvent and water may be within a range that does not impair the permeability to the precursor and does not reduce the dissolution of the copolymer,
When ethanol is used as the organic solvent, the ethanol / water ratio is preferably in the range of 90/10 to 30/70 (vol%), although it varies depending on the type of the copolymer used.

The concentration of the hydrophilic copolymer solution is 0.1 to 1
It is about 0% by weight, preferably 0.5 to 5% by weight. When the precursor is treated with a solution having a concentration of less than 0.1% by weight, it is difficult to uniformly coat the hydrophilic copolymer, and if the concentration exceeds 10% by weight, the solution viscosity becomes too large. When treated, the micropores of the multi-layer composite hollow fiber membrane are blocked with the copolymer. As a method of immersing the precursor in the hydrophilic copolymer solution, the precursor solution may be dipped twice or more in the copolymer solution having the same concentration, or may be dipped twice or more in the solutions having different concentrations.

The higher the temperature of the hydrophilic copolymer solution to be subjected to the dipping treatment, the lower the viscosity thereof, and the better the permeability of leaching to the precursor, which is preferable, but from the viewpoint of safety, it should be below the boiling point of the solution. Is preferred.

The dipping treatment time varies depending on the film thickness, fine pore diameter and porosity of the precursor used, but it is preferably in the range of several seconds to several minutes.

The precursor is soaked in a hydrophilic polymer solution and before being subjected to a drying treatment, the vapor of an organic solvent is contained in an amount of 3 vol% or more, and the temperature is raised from room temperature to a temperature not higher than the boiling point of the solvent at least. It is necessary to stay for 30 seconds or more and perform the setting process.

The purpose of this treatment step is to prevent the clogging of the micropores by forming a film of the hydrophilic copolymer on the surface of the knots between the microfibrils and the stack lamella forming the precursor. Another object is to bind the microfibrils and increase the diameter of the slit-shaped micropores to form elliptical micropores to increase the amount of water permeation and increase the affinity with the treated water.

In order to prevent the film formation of the hydrophilic copolymer on the precursor surface during the setting step, it is necessary to prevent the rapid drying on the precursor surface. For that purpose, the precursor surface of the copolymer solution is required. It is necessary to suppress the evaporation rate at the same time and to keep the precursor surface wet with the solvent. From this viewpoint, the atmosphere of the setting process should be 3 vol% or more of the water-miscible organic solvent vapor. Will be required.

The evaporation rate of the solvent from the precursor in the setting step is preferably as low as possible, and the atmosphere in the setting step is preferably close to the saturated vapor concentration of the solvent. Further, in order to slow down the evaporation of the solvent on the precursor surface in this step, it is better to lower the setting temperature, but if it is too low, the phenomenon that the solvent removal in the setting step does not proceed is not preferable. Therefore, the temperature of the atmosphere is preferably room temperature or higher and not higher than the boiling point of the water-miscible solvent.

The precursor after immersion is raised in the atmosphere from the immersion bath, and the angle of rise is preferably in the range of 45 ° to 90 °. By starting up, a part of the copolymer solution attached to the precursor is drained from the precursor by its own weight. The amount of the liquid removed depends on the speed at which the precursor rises from the bath surface, the viscosity of the immersion solution, the height at which the precursor rises from the bath surface, and the like. Wiping off of the solution on the surface of the precursor by means of guides, slits or the like may be used as an auxiliary means for enhancing the liquid removal effect in the setting step.

This setting time is at least 30
Seconds are required, during which the copolymer solution is concentrated as the solvent evaporates from the precursor and the membrane is homogenized by migration on the microfibrils and the surface of the stacked lamella. In particular, when the precursor is continuously treated with the hydrophilic copolymer solution, the setting time must be at least 30 seconds or longer. If the setting is less than 30 seconds, the concentration due to the evaporation of the solvent is insufficient, and drying is performed with the excess solution attached to the precursor, and the hydrophilic copolymer causes blockage of micropores. At the same time, the uniform adhesion of the copolymer within the membrane structure becomes insufficient, and it is difficult to obtain a microporous hollow fiber membrane having good water permeability and fractionation performance.

The evaporation amount of the solvent from the precursor when the setting time is 30 seconds is preferably about 15 to 30% of the hydrophilic copolymer solution used. As a method of controlling the evaporation amount of the solvent from the precursor in the setting step, there may be mentioned a setting atmosphere temperature, a method of blowing a gas such as air or an inert gas into the atmosphere.

The drying step is performed by covering and converging the microfibrils forming the innumerable slit-shaped fine pores obtained by the stretching method with the hydrophilic copolymer, and changing the structure into elliptical fine pores to enlarge the pore diameter. This is an important step for fixing. Further, since the hollow fiber membrane shrinks at the same time as the drying, the shrinkage is taken into consideration, and the yarn feeding speed before the drying step is made higher than the winding speed after the drying. By making the particles hydrophilic while sufficiently shrinking them, it is possible to increase the pore size and improve the water permeability.

If the feeding speed before drying with respect to the winding speed is faster than the shrinkage of the hollow fiber membrane, slackening of the yarn occurs before drying and the process stability decreases. On the contrary, when the feeding speed is equal to the winding speed without considering the shrinkage of the hollow fiber membrane, the yarn is pulled against the shrinkage of the yarn in the drying process and processed under high tension, so As it is, the treatment is performed without expanding the hole diameter to an elliptical shape, and sufficient water permeability cannot be obtained. Therefore, it is necessary to adjust the feeding and winding speeds before and after drying, depending on the degree of shrinkage of the hollow fiber membrane to be treated.

The precursor which has been set may be dried by a known drying method such as vacuum drying or hot air drying. The drying temperature may be a temperature at which the composite microporous hollow fiber membrane is not deformed by heat. For example, in the case of a polyethylene composite microporous hollow fiber membrane, drying at a temperature of 120 ° C or lower is preferable, and drying at a temperature of 40 to 70 ° C is particularly preferable. The drying time varies depending on the pore size of the fine pores, the film thickness, the processing speed, etc., but it may be about 1 to 10 minutes as long as the hollow fiber membrane is sufficiently dried.

The amount of the hydrophilic copolymer attached to the composite microporous hollow fiber membrane is about 3 to 3 with respect to the weight of the composite microporous hollow fiber precursor, which is the substrate, in terms of filtration characteristics.
It is 30% by weight, preferably 3 to 15% by weight.

The final adhesion rate of the ethylene copolymer to the porous membrane can be adjusted by appropriately setting the concentration of the hydrophilizing solution, the conditions of the liquid removal treatment, and the like.

By the coating treatment with the hydrophilic copolymer, the microfibrils of the microporous hollow fiber membrane precursor are converged into a microfibril bundle, and the slit-like micropores are elliptical micropores.

The fractionation characteristics of the composite microporous hollow fiber membrane used in the present invention are not particularly limited, but especially when used in household water purifiers and medical fields, it is necessary to be able to remove bacteria in water, The pore size of the membrane is preferably 0.2 μm or less.

In the case of a water purifier for aseptic water production in the medical field, etc., the above-mentioned porous hollow fiber membrane is filled in an appropriate container, one end or both ends of the hollow fiber membrane are fixed with a resin, and the end portion is fixed. A hollow fiber membrane module is created by opening and used as a water purifier.

In a water purifier used for beverages or in domestic life, activated carbon or the like is added as a constituent element of the filtration section in addition to the hollow fiber membrane in order to remove residual chlorine and the like.

The activated carbon used in the present invention is not limited as long as it has the ability to reduce residual chlorine and the ability to adsorb organic substances such as trihalomethane and pesticides. Activated carbon such as fibrous or formed carbon can be used. The raw material is not particularly limited, and natural product type activated carbon such as coconut shell activated carbon, bone charcoal and charcoal type activated carbon, pitch type petroleum coke type activated carbon and the like can be used. The activation method is also not particularly limited, and activation methods such as steam activation and chemical activation are used.

Further, since the passing speed of the water to be passed through the activated carbon is very high as compared with the usual method of using the activated carbon, it is preferable that the bulk density is large, and the pressure loss is small in relation to the tap water pressure. preferable. Most of the adsorbed substances have relatively small molecular weights, and in view of cost, steam activated granular coconut husk activated carbon is most preferable.

The activated carbon of the present invention may be one in which a heavy metal such as silver is impregnated in order to impart antibacterial properties, but one in which an excessively large amount of heavy metal is eluted is not preferred. Those having antibacterial properties are relatively preferably used.

Further, in order to remove heavy metal ions and anions such as nitrate nitrogen and nitrite nitrogen in tap water, an ion exchange resin can be used in addition to the hollow fiber membrane and activated carbon.

In the water purifier of the present invention, it is desirable that the composite microporous hollow fiber membrane is present in the final stage of filtration near the purified water outlet of the water purifier.

[0065]

EXAMPLES The composite microporous hollow fiber membranes used in the water purifier of the present invention will be described in more detail below with reference to production examples. In addition,
Various measurements and evaluations in the production examples were carried out by the following methods. 1. The ethanol concentration in the atmosphere was measured using a gas detector tube (Gastec detector tube, trade name, manufactured by Gastec Co., Ltd.). 2. The coating amount of the hydrophilic copolymer was calculated according to the following formula.

[0066]

(Equation 1) 3. The fractional particle size is 0.1 wt% of a surfactant (polyethylene glycol-p-isooctylphenyl ether) in a hollow fiber membrane module having a membrane area of about 50 cm ² and a polystyrene latex of a single dispersed particle size of a predetermined particle size. The particles were filtered, and the concentration of latex particles in the filtrate was measured with a Hitachi spectrophotometer (U-3400) at a wavelength of 320 nm to determine the particle diameter at a capture rate of 90%.

Production Example 1 High density polyethylene (HB530, high density polyethylene (HB4) having a density of 0.967 g / cm ³ and an MI value of 0.3.
30 and 33% by weight of Mitsubishi Chemical Co., Ltd. are melt-kneaded,
A blend polymer having a density of 0.965 g / cm ³ and an MI value of 0.3 was obtained.

Next, using a hollow fiber manufacturing nozzle having two concentric circular tubular discharge ports, the blended polymer was discharged from the inner discharge port and the density was 0.967 g / m from the outer discharge port. High density polyethylene having a cm ³ and an MI value of 0.3 was discharged and melt-spun. At this time, the discharge temperature is 170 ° C., the inner layer side discharge amount is 0.56 g / min, the outer layer side discharge amount is 2.24 g / min, the inner layer / outer layer discharge amount ratio is 1/4, the discharge linear velocity is 47 cm / min, and the degree is 21 ° C. Winding was performed at a winding speed of 35 m / min while uniformly applying a cooling wind of 1 m / sec to the periphery of the yarn to obtain an unstretched composite hollow fiber.

The unstretched hollow fiber obtained was heat-treated for 16 hours in the air heated to 125 ° C. with a constant length. Furthermore, this heat treated yarn is put between rollers kept at 30 ° C for 25
% Cold stretching, followed by hot stretching in a heating furnace at 119 ° C. so that the total stretching amount becomes 500%, and further 120
Heat setting was performed in a heating furnace at ℃ while keeping the length constant to obtain a composite microporous hollow fiber membrane precursor composed of two layers.

Next, an ethylene-vinyl alcohol copolymer (Soarnol DC320) having an ethylene content of 32 mol% was used.
3. Nippon Synthetic Chemical Industry Co., Ltd.) was dissolved in an ethanol / water = 60/40 vol% mixed solution at 70 ° C. in an amount of 1.0% by weight to prepare a hydrophilic copolymer agent solution. 10 parts of the above composite porous hollow fiber membrane precursor was added to this hydrophilic copolymer solution.
After soaking for 0 second, the precursor was pulled up, and a part of the hydrophilizing agent solution excessively attached to the surface was squeezed out by a guide. Continuing, ethanol vapor concentration 40 vol%, 6
After standing up in a 0 ° C. atmosphere at a rising angle of 90 ° and staying for 100 seconds to evenly attach the hydrophilic agent to the inner surfaces of the precursor micropores, 10% overfeed with hot air at 70 ° C. The solvent was dried. The ethylene-vinyl alcohol copolymer adhesion rate of the obtained hydrophilicized composite hollow fiber membrane was 10.5% by weight.

The obtained composite microporous hollow fiber membrane was observed with a scanning electron microscope. As a result, the inner and outer surfaces and the inner surface of the micropores of the composite microporous hollow fiber membrane were thin films of ethylene-vinyl alcohol copolymer. The average distance (Da) between the microfibril bundles of the micropores in the inner layer (a layer) is 0.35.
The average distance (Db) between the microfibril bundles of the micropores of the outer layer (layer b) was 0.47 μm. At this time, D
b / Da = 1.34, the thickness of the inner layer that is the separation functional layer is 1
It was 2 μm. The characteristics of the obtained hollow fiber membrane are shown in Table 1.

Production Example 2 The polymer used for the inner layer and the polymer used for the outer layer in Production Example 1 were reversed, and the blended polymer was discharged from the outer outlet.
Except that the high-density polyethylene having a density of 0.967 and an MI value of 0.3 was discharged from the inner discharge port at an outer layer side discharge rate of 0.56 g / min and an outer layer side discharge rate of 2.24 g / min, and was melt-spun. A composite microporous hollow fiber membrane was produced under the same conditions as in Production Example 1. The obtained composite microporous hollow fiber membrane has an outer layer (a layer).
The average distance (Da) between the microfibril bundles of the micropores in the inside is 0.34 μm, the average distance between the microfibril bundles of the micropores in the inner layer (layer b) is 0.48 μm, and Db / Da =
1. The characteristics are shown in Table 1.

Comparative Production Example 1 The blend polymer used for the inner layer side in Production Example 1 was discharged at a discharge rate of 2.8 g / min and melt-spun, using a hollow fiber manufacturing nozzle having a single tubular discharge port. The discharge temperature at that time was 170 ° C., and the film was wound at a winding speed of 35 m / min. The obtained unstretched hollow fibers were heat-treated, stretched and hydrophilized under the same conditions as in Production Example 1, and the membrane properties of the porous hollow fiber membranes are shown in Table 1.

[0074]

[Table 1] Examples 1 and 2 and Comparative Examples Using various composite microporous hollow fiber membranes and uniform microporous hollow fiber membranes prepared in Production Examples and Comparative Production Examples, they were housed in a U shape, and the ends thereof were stored. Fixing with a potting resin and cutting to keep one end of the hollow fiber membrane open, create a hollow fiber membrane module with an effective membrane area of 0.16 m ² similar to that shown in Fig. 1 and attach it to the water purifier. did. Tap water was supplied to these water purifiers at a differential pressure of 1 kg / cm ² , and the discharge amount of water at that time was measured. The results are shown in Table 2.

When the water purifier using the separation layer inner layered composite membrane shown in Example 1 is water-filtered from the outer surface to the inner surface of the hollow fiber membrane in Nagoya city water, it has the same fractionation. The flow rate was higher and the clogging resistance was superior to that of the uniform membrane, and the filtration life could be extended. The resistance to clogging was indicated by the cumulative flow rate at the time when the initial permeation rate was reduced to 50%.

[0076]

[Table 2]

[0077]

EFFECT OF THE INVENTION The water purifier of the present invention comprises a polyolefin microporous hollow fiber membrane having at least two microporous layers having different pore sizes in the filtration section, and a reinforcing function layer of this composite membrane. By increasing the pore size, compared to the case of using a conventional hollow fiber with the same fractionation performance, it is possible to obtain a high filtration flow rate while maintaining the fractionation performance capable of cutting bacteria, and the membrane area used By reducing it, the water purifier cartridge can be made compact.

By flowing the filtration direction of this composite microporous hollow fiber membrane from the layer having a large pore size to the layer having a small pore size, the anti-clogging property is excellent and the life of the water purifier can be extended. Became. Furthermore, since the membrane has excellent durability and there is almost no eluate from the membrane, clean and highly safe purified water can be supplied.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a water purifier of the present invention.

FIG. 2 is a schematic diagram for explaining a method of measuring an average distance between microfibril bundles of micropores.

[Explanation of symbols]

 1 Raw Water Inlet 2 Water Discharge Port 3 Water Purifier Main Body 4 Filtration Section 5 Hollow Fiber Membrane Module 6 Activated Carbon Layer 7 Hollow Fiber Membrane

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kazuhiko Matsubayashi 2-3-19 Kyobashi, Chuo-ku, Tokyo Mitsubishi Rayon Co., Ltd. (72) Inventor Manabu Yano 2-3-19 Kyobashi, Chuo-ku, Tokyo Within Mitsubishi Rayon Co., Ltd.

Claims (4)

[Claims] 1. In a water purifier having a hollow fiber membrane module including a hollow fiber membrane in a filter section, a composite polyolefin microporous hollow having at least two microporous layers having different pore diameters as the hollow fiber membrane. A water purifier characterized by using a thread film. 2. A water purifier equipped with a hollow fiber membrane module including a hollow fiber membrane in a filtration section, wherein the hollow fiber membrane has a microporous layer a having a separating function and at least one surface of the microporous layer a having a reinforcing function of reinforcing a microporous layer. It is a composite microporous hollow fiber membrane made of polyolefin in which a layer b of a polymer is laminated, wherein a layer a and a layer b are a plurality of microfibril bundles oriented in the fiber axis direction It is composed of a laminated body of elliptical micropores composed of a knotted portion, the micropores communicating from the outer surface of the hollow fiber membrane toward the hollow portion, and forming the micropores of the hollow fiber membrane. The microfibril bundles and the knots of the stacked lamellae are 3 to 30 with respect to 100% by weight of the composite microporous hollow fiber membrane precursor.
It is covered with a hydrophilic copolymer of weight% and
The ratio of the average distance Da between the microfibril bundles of the micropores present in the layer and the average distance Db between the microfibril bundles of the micropores present in layer b is 1.3 ≦ Db / Da ≦ 4.0. A water purifier characterized by using a composite microporous hollow fiber membrane in the range of: 3. The composite microporous hollow fiber membrane made of polyolefin having at least two microporous layers having different pore diameters, and the activated carbon constituting the filtration section.
Water purifier as described. 4. The water purifier according to claim 1, wherein the water to be treated is configured to flow from a layer having a large pore diameter of the composite microporous hollow fiber membrane toward a layer having a small pore diameter.