JP3432264B2 - Microporous membrane - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microporous membrane, and more particularly to a microporous membrane made of polyolefin containing activated carbon having a specific particle size. In recent years, a separation method using a microporous membrane has been rapidly used on a practical scale from the viewpoint of resource saving, energy saving, separation and purification, and the like. Numerous microporous membranes used in such a membrane separation method have been studied.For example, a filler such as calcium carbonate is dispersed in a polyolefin, and the boundary between the polyolefin and the filler is separated at the interface to form a microporous membrane. What has been proposed is proposed as having excellent water permeability such as initial water permeability and water permeability during long-term use. [0003] One of the uses of such a microporous membrane is to use the membrane formed into a hollow fiber or the like as a separation membrane of a water purifier. Water purifiers incorporating a hollow fiber membrane in the faucet of each household's water supply have become popular because of their simplicity. In this water purifier, the incorporated hollow fiber membrane causes the dead water of coliform bacteria, general bacteria, algae, mold, plankton, iron rust, and Al ₂ S contained in tap water.
Contaminant particles such as O ₄ , silica, sulfur, and Mg are removed. [0004] In addition to the above-mentioned contaminating particles, various odorous substances, for example, Cl ^- ions and gabium, which cause chalky odor, are included in the water to be washed such as the tap water. 2-Methylisoborneol (MIB), diosmin, etc., which are algae effluents that cause odor, are dissolved. However, in the purification by the hollow fiber membrane, such contaminants as dissolved in water can hardly be removed. Therefore, the water purifier is usually provided with an activated carbon layer in addition to the hollow fiber membrane. As the water passes through the activated carbon layer, the contaminants are adsorbed and removed. However, in this case, the activated carbon layer provided along with the hollow fiber membrane must be filled with a large amount of the activated carbon in order to sufficiently remove the contaminants. Was connected to. For example, 2 ppm
In order to make the tap water free of odor, it is necessary to keep the residual Cl ^- ion at 0.4 ppm or less. In this case, the activated carbon layer converts the activated carbon into a membrane area of the hollow fiber membrane of about 200 g / m ^2. It becomes necessary to fill. [0006] On the other hand, in recent years, there has been an increasing demand for smaller and lighter water purifiers, especially for household use. In the purification process using the hollow fiber membrane, even a small amount of pollutants such as odorous substances can be removed. It has been desired to remove the activated carbon layer to make the volume as small as possible. The present invention Against this background, the initial water permeation amount and is excellent in water permeability of the water permeation rate or the like during long-term use, further, Cl ^- microporous also have good capability of removing contaminants that cause odor of water such as ion It is intended to provide a conductive film. The present inventors have SUMMARY OF THE INVENTION In view of the above problems, have continued extensive studies. As a result, they have found that the above problems can be solved by using activated carbon having a specific particle size as a filler dispersed in polyolefin, and have completed the present invention. That is, the present invention relates to polyolefins 30 to 8
0% by weight and 70 to 20% by weight of activated carbon having an average particle diameter of 0.1 to 5 μm dispersed in the polyolefin . The film is molecularly oriented by stretching.
Thus, the maximum pore diameter is network is formed consisting of the following communication hole 5 [mu] m, and a porosity of microporous membranes Ru 20% to 90% der. The polyolefin used in the present invention includes a homopolymer of an α-olefin such as polyethylene, polypropylene, polybutene-1 or polymethylpentene, and a copolymer of an α-olefin with another copolymerizable monomer. And mixtures thereof. Among them, homopolymers of propylene, copolymers of propylene with other copolymerizable monomers, and mixtures thereof are preferable in consideration of the heat resistance and moldability of the obtained microporous membrane. The above-mentioned copolymer of an α-olefin and another copolymerizable monomer generally contains at least 90% by weight of an α-olefin, particularly propylene, and at most 10% by weight of another copolymerizable monomer. Copolymers are preferred. In addition, the copolymerizable monomer is not particularly limited, and known monomers can be used. Generally, α-olefins having 2 to 8 carbon atoms, particularly, ethylene and butene are preferable. It is preferable that the activated carbon used in the present invention does not cause aggregation when mixed with a polyolefin and is uniformly dispersed. Activated carbon not only serves to form a fine communication hole by causing separation at the interface between the polyolefin and the dispersed activated carbon in the stretching step, but also has a bad smell such as a smell of chlorine when water passes through the communication hole. Used to adsorb and remove contaminants that cause it. As the activated carbon used in the present invention, a known activated carbon can be used without any limitation as long as it exhibits the above-mentioned functions. Specific examples of activated carbon that can be suitably used in the present invention include, for example, wood, sawdust,
Made from palm nut shell, lignin, cow bones, blood, lignite, cuckoo, peat, coal, etc. as raw materials, chemicals such as steam, zinc chloride, phosphoric acid, sulfuric acid, alkali, air, carbon dioxide,
Powdered activated carbon activated by heating in chlorine gas or the like is preferred. In the present invention, such activated carbon has an average particle diameter of 0.1 to 5 μm because it has good interfacial peeling properties with polyolefin and can be easily made porous by stretching. is necessary. If the average particle size of the activated carbon deviates from the above range, it becomes difficult to disperse the activated carbon in the polyolefin, and, furthermore, various bacteria contained in the water such that the maximum pore size is too large,
For example, E. coli cannot be filtered off. In order to obtain a suitably employed microporous membrane, the activated carbon preferably has an average particle size of 0.1 to 3 μm. The narrower the particle size distribution of the above activated carbon is, the more uniform pores can be obtained, and the more preferable the shape of the activated carbon is. A small shape is preferable because pores having a uniform diameter can be obtained. The blending ratio of the above-mentioned polyolefin and activated carbon having an average particle diameter of 0.1 to 5 μm is such that the polyolefin is 30 to 80% by weight, preferably 40 to 70% by weight, the activated carbon is 70 to 20% by weight, Preferably 60-3
0% by weight. The mixing ratio of the polyolefin and the activated carbon is important for maintaining the properties of the microporous membrane in a specific range and industrially advantageously producing the microporous membrane. When the ratio of the activated carbon is less than the lower limit, the pore formation of the obtained microporous membrane is not sufficient, and when the addition ratio of the activated carbon is greater than the upper limit, the moldability of the membrane deteriorates, It is not preferable because stretching tends to be insufficient. In the present invention, a film formed of a mixture of the above polyolefin and activated carbon dispersed in the polyolefin is molecularly oriented by stretching. As a result, in the microporous membrane of the present invention, the interface between the polyolefin and the activated carbon is peeled off, and communication pores having a maximum pore diameter of 5 μm or less are formed in the membrane in a network. When the maximum pore diameter of the communicating pores formed in the microporous layer exceeds 5 μm, although the water permeability of the resulting microporous membrane such as water from the surface is good, liquid / solid, liquid / gas , Liquid / liquid,
In addition, it is not preferable because the gas / solid separation performance is reduced. In the present invention, taking into account the suitability of the amount of water permeation such as tap water, the maximum pore diameter is 0.01 to 3 μm.
m is preferred. Further, in consideration of the filtration performance of Escherichia coli and the like, the maximum pore diameter is preferably 1.5 μm or less. The communicating holes formed in the microporous membrane usually have an average pore diameter of 0.005 to 3 μm. The microporous membrane of the present invention has a porosity of 2
It is 0-90%, preferably 35-80%. At this porosity, water permeability and separation performance are the most excellent. In the present invention, the thickness of the microporous membrane described above is not particularly limited, but is generally 10
It is preferably in the range of μm to 0.5 mm. In addition, the shape is not particularly limited, and can be used, for example, in the form of a film or the like according to the use mode. However, in order to function effectively as a separation membrane, it is preferable to use a hollow fiber membrane. In this case, the outer diameter of the hollow fiber membrane is 50 μm.
It is preferable to set the range to 5 mm. In the present invention, the microporous membrane described above may be manufactured by any method. Usually, the polyolefin is 30 to 80% by weight and the average particle size is 0.1 to 5%.
In general, a film is formed by forming a mixture of 70 to 20% by weight of activated carbon having a thickness of μm, and then stretching the film. At that time, it may be difficult to mix the polyolefin component and the activated carbon component in a large amount and uniformly, and in such a case, it is preferable to mix a specific amount of a dispersant in such mixing. That is, it is preferable to add 0.1 to 20 parts by weight of a dispersant to 100 parts by weight of the total amount of the polyolefin component and the activated carbon component in order to obtain a microporous hollow fiber membrane having a uniform pore diameter. As the dispersant, a known compound added as a plasticizer to various synthetic resins can be used without particular limitation. The dispersants generally preferably used are polyester-based plasticizers and epoxy-based plasticizers, and terminally OH-terminated polybutadiene is also preferably used. These are exemplified as follows. The polyester plasticizer is generally used in an esterification reaction of a dibasic acid or a tribasic acid having a linear or aromatic ring having 4 to 8 carbon atoms with a linear dihydric alcohol having 2 to 5 carbon atoms. Those that have been made are preferred. Specific examples of those particularly preferably used include dibasic acids or tribasic acids such as sebacic acid, adipic acid, phthalic acid, azelaic acid and trimellitic acid, and ethylene glycol,
Polyester compounds such as propylene glycol, butylene glycol, neopentyl glycol, and long-chain alkylene glycol, especially polyester compounds comprising adipic acid or sebacic acid and propylene glycol, butylene glycol or long-chain alkylene glycol. Is preferably used. The epoxy plasticizer has 8 carbon atoms.
Epoxidized double bonds of monobasic linear unsaturated acids of from 24 to 24 are preferred. Particularly preferred examples include epoxidized soybean oil and epoxidized linseed oil, which can be used alone or in combination. Further, a plasticizer having a polybutadiene having a degree of polymerization of 500 to 3,000, preferably 500 to 1,000 at both ends of OH is preferably used as a dispersant. In mixing the above components, a coloring agent, a lubricant,
It is often a good practice to add known additives such as antioxidants, antioxidants, hydrophilizing agents, hydrophobizing agents and the like. The above mixture can be melt-formed into a hollow fiber or the like under specific conditions and then stretched to obtain the microporous membrane of the present invention. Here, in the case of forming a film of the above mixture on a hollow fiber, the method is not particularly limited, but is generally formed into a hollow fiber using a known extruder for manufacturing a hollow fiber equipped with a double cylindrical die. Is preferred. The method of stretching the unstretched film-like material is not particularly limited, but generally, it is uniaxially stretched by a difference in the rotation speed ratio between two pairs of Nelson rolls or the like. A method of sequentially stretching in the horizontal direction by a known widening stretching machine or the like, or a method of simultaneously stretching in the vertical and horizontal directions is employed. In this case, the stretching magnification is preferably preferably in the range of 1.5 to 10 times the area stretching magnification.
When stretching only in the uniaxial direction (the longitudinal direction of the hollow fiber),
In general, it is preferable to stretch 1.5 to 8 times, preferably 3 to 7 times. When stretching in the biaxial direction, 1
1.2 times or more, preferably 1.5 times or more in the axial direction (longitudinal direction of the hollow fibers), and 1.2 times or more, preferably 1.5 times or more in the biaxial direction (the circumferential direction of the hollow fibers). The stretching is preferably 2 to 5 times in the uniaxial direction and 2 to 5 times in the biaxial direction. The stretching temperature is generally from room temperature to the melting point of the polyolefin, and preferably from 10 to 100 ° C. below the melting point. The microporous membrane obtained by stretching is further subjected to a heat treatment under tension, for example, a heat-setting treatment at a temperature not lower than the stretching temperature and not higher than the melting point, and then cooled to room temperature to obtain the desired product. Is preferred. In addition, it is a preferable embodiment to perform a surface treatment such as a corona discharge treatment, a hydrophilic treatment, or a hydrophobic treatment for the purpose of improving the adhesiveness. In the microporous membrane produced by the above method, the polyolefin is molecularly oriented by stretching,
Alternatively, by further heat fixing, the heat resistance of the film itself is significantly improved, and the mechanical strength is also improved. In particular, in the case of heat setting, the dimensional stability at normal temperature and high temperature is also remarkably improved. The microporous membrane obtained by the present invention is composed of a polyolefin homopolymer or an olefin and another copolymerizable monomer, and is excellent in heat resistance because it is rich in olefin. It also has excellent physical properties such as strength, chemical resistance and biocompatibility. Furthermore, since the activated carbon contained in the microporous membrane obtained in the present invention is a heat-resistant, insoluble, infusible filler rich in chemical resistance, the obtained microporous membrane has high reliability in use. For example, there is no trouble that the activated carbon is eluted when a specific substance is separated. In addition, the moldability, the dispersibility of activated carbon, the stretchability, and the like at the time of production are excellent, and uneven thickness, surface irregularities, fish eyes, and the like are suppressed, and stable production can be achieved. In addition, it has a good ability to remove dissolved substances such as Cl ^- ions which cause odor in tap water. For example, a film formed on a hollow fiber membrane has a Cl ^- ion concentration of about 20%.
%. Therefore, when the microporous membrane of the present invention is incorporated into a water purifier as a hollow fiber membrane, the capacity of the activated carbon layer incorporated and incorporated can be reduced by about 20%, and the water purifier can be made compact. It becomes possible. Further, the microporous membrane of the present invention has excellent water permeability. For example, the membrane formed on the hollow fiber membrane has a large initial water permeability of 100 l / m ² · hr · atm or more, and more preferably 200 to 2000 l. / M ² · hr · atm, and the decrease in water permeability due to clogging is small.
For example, even after filtering 2 tons of clean water, 100
It has a water permeability of 1 / m ² · hr · atm or more. Therefore, the microporous membrane obtained by the present invention can be used as a filtration membrane for a long time, and has a Cl ^- ion adsorption capacity,
Enables downsizing of water purifiers. From the above properties, the microporous membrane of the present invention is:
Can be used as a filtration membrane for household water purifiers, as well as air filters for dust removal, sterilization and deodorization; gas separation membranes; wastewater treatment; clean water production in the food, electronics and pharmaceutical industries; blood purification in the medical field It is suitable for use as a support for microfiltration, ultrafiltration, reverse osmosis membrane, pervaporation, etc. EXAMPLES The present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples. The physical properties and judgments of the hollow fiber membranes shown in Examples and Comparative Examples indicate values measured or judged by the following methods. Maximum pore diameter (μ): Measured by a methanol bubble point method. The porosity was measured by a mercury intrusion porosimeter. Nitrogen gas permeation amount: Ten microporous hollow fiber membranes were bundled and the hollow fiber membrane opening was hardened with epoxy resin to produce a module. The effective length of the hollow fiber excluding the resin embedded part is 1
It was 5 cm. The pressure of 0.5atm with N ₂ gas to the module hollow fiber membranes went 25 ° C., determine the amount of N ₂ gas through the wall of the hollow fiber membrane. The membrane area was (outer diameter + inner diameter) / 2 base. Water permeation amount: Ten microporous hollow fiber membranes were bundled, and the opening of the hollow fiber membrane was solidified with epoxy resin to produce a module. The effective length of the hollow fiber excluding the resin embedded part is 15
cm. In the measurement of water permeability, the module was immersed in a 2% ethanol solution of a nonionic surfactant having an HLB of 21 and then water of 1 atm was applied to determine the amount of water passing through the wall surface of the hollow fiber membrane. . The membrane area was (outer diameter + inner diameter) / 2 base. The value obtained when the water permeability test was first performed for 3 minutes was defined as the initial water permeability, and the value after passing 2 tons of clean water was defined as the 2 ton water permeability. The tap water used for the water permeability test was tap water from Tokuyama City, Yamaguchi Prefecture containing 6.5 ppm of Cl ^- ions. Cl ^- ion concentration: Measured using an ion chromatograph based on the method specified in Ministry of Health and Welfare Ordinance No. 69 “Ministerial Ordinance on Water Quality Standards” Moldability: The unstretched hollow fiber membrane was visually observed and touched by hand, and evaluated according to the following criteria. Good: Uneven thickness and no irregularities on the surface. Slightly good; one of uneven thickness and unevenness on the surface is minute. Slightly poor: Both thickness unevenness and surface irregularities are very small. Defective: A state in which both uneven thickness and surface irregularities are severe. Dispersibility: The hollow fiber membrane obtained by stretching was visually observed and judged whether or not there was a fish eye. Good; no fish eyes. Slightly good; state with very small fish eyes Slightly poor; state with very small fish eyes Poor; state where fish eyes are severely observed Stretchability: The stretchability was determined by stretching the unstretched hollow fiber membrane in the longitudinal direction of the hollow fiber. Good: A state in which stretching is performed uniformly without cutting or tearing. Slightly good: Stretching is performed almost uniformly, and a very small unstretched portion exists. Slightly poor: Even if stretching is performed, a part of the unstretched portion exists. Stretching was not possible; cutting and tearing occurred and stretching was not possible. Examples 1 to 6 and Comparative Examples 1 to 4 A composition comprising a resin, activated carbon and a dispersant as shown in Table 1 was mixed for 5 minutes by a supermixer, and then the mixture was extruded at 230 ° C. by a twin screw extruder. And cut into pellets. The obtained pellet is screwed with a diameter of 20 mm.
The extruder is extruded at 230 ° C from a hollow fiber manufacturing nozzle having a double-tube structure of 0.7 mm in diameter attached to an extruder with φ, L / D = 22, put into a water tank in which water at about 20 ° C circulates, and cooled. At a rate of 10 to 50 m / min to obtain an undrawn hollow fiber. The undrawn hollow fiber was uniaxially stretched at a stretching ratio of 4 at 120 ° C. between two pairs of Nelson rolls having different rotation speeds. A porous hollow fiber membrane was obtained. Table 2 shows the physical properties of the obtained microporous hollow fiber membrane. The following products were used for the resin, activated carbon and dispersant used. Polypropylene; PN-1 manufactured by Tokuyama Soda Co., Ltd.
20 (trade name) Density 0.91 g / cm ³ , intrinsic viscosity measured with tetralin at 135 ° C 2.38 dl / g, melting point 166 ° C propylene-ethylene copolymer; MS manufactured by Tokuyama Soda Co., Ltd.
-624 (trade name) density 0.90 g / cm ³ , intrinsic viscosity 2.28 dl / g measured at 135 ° C tetralin, melting point 163 ° C, ethylene content 4.7% by weight. Polyethylene: Mitsui Petrochemical Industry Co., Ltd.
High density polyethylene, HIZEX 1300J (trade name), melt index 1.3g / 10min. Activated carbon; powdered activated carbon; (A) Charco, manufactured by Wako Pure Chemical Industries, Ltd.
al, Bone (trade name), bone char having an average particle diameter of 0.2 μm. (B) Steam activated carbon manufactured by Takeda Pharmaceutical Co., Ltd. Average particle size 2 μm. (C) Charco, manufactured by Wako Pure Chemical Industries, Ltd.
al, Activated, Powder (trade name),
Activated carbon having an average particle size of 10 μm. Granular activated carbon; manufactured by Kuraray Chemical Co., Ltd.
Palm shell crushed charcoal. The average particle size is 200 μm. Dispersant: Nippon Soda Co., Ltd., OH-terminated polybutadiene, GI-1000 (trade name). [Table 1] [Table 2]

Claims (1)

(57) [Claims 1] 30 to 80% by weight of a polyolefin and an average particle size dispersed in the polyolefin of 0.1 to 5%.
μm of activated carbon of 70 to 20% by weight .
A film having a maximum pore diameter of 5 μm or less is formed by the stretching.
Is, and, microporous membrane porosity Ru 20% to 90% der.