Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Patent
1996-06-17
1999-01-26
McCamish, Marion E.
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
21032189, 210491, 21050023, 264 41, 2642107, 2642108, 2642888, 427245, 4283159, 4283166, 4283193, 428376, 428398, 428902, 428910, B01D 6908, B01D 6912, B01D 7126, B01D 7138
Patent
active
058636455
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a composite microporous polyolefin membrane, which is effectively used in ultra-filtration and precision filtration, and to a method of producing the same. Specifically, this invention relates to a composite microporous polyolefin membrane having a high separation capability and a high film strength, and comprising a micro-porous polyolefin layer, having a function of reinforcing the film strength, being bonded to at least one surface of a microporous polyolefin layer having the function of separation and to a method of producing the same.
DESCRIPTION OF THE PRIOR ART
Microporous membranes are used in a wide variety of applications comprising industrial applications such as a treatment of industrial wastes, a treatment of processing water used in industrial applications, a production of ultrapure water and the like, and air purification applications such as air filters, bag filters and the like.
A large number of polymer materials have been studied and various membranes have been developed as materials for microporous membranes. For example, Japanese Patent Laid-Open Publication Sho.57-66114 discloses a polyethylene porous hollow fiber membrane having a uniform microporous structure in the thickness direction of the membrane, wherein slit-like micropores comprising microfibrils oriented in the fiber lengthwise direction and knotted portions of stacked lamella oriented in the thickness direction are stacked inside of membrane walls of hollow fiber membrane, and whereby one surface of the membrane is communicating with the other surface of the membrane.
The membrane is manufactured by a melt forming of polyethylene followed by a further stretching of the formed body. In another word, a microporous membrane having the above-mentioned specific structure is formed by steps comprising, subjecting polyethylene to an annealing treatment after being formed under a specific spinning condition, forming crystals composed of stacked lamella (hereinafter referred to "stacked lamella") inside of membrane walls of the formed body, then stretching the formed body thereby increasing the distance between these lamella and promoting the growth of fibrils connecting each crystal of stacked lamella. The membrane having the above specific structure is characterized by that it has an excellent mechanical strength and is also high in safety because no solvent is used in the manufacturing process.
However, the microporous polyolefin membrane thus obtained by the above-mentioned method has a structure wherein stacking structure of micropores is uniform in the thickness direction of the membrane. The data disclosed in the experiments show that the mean pore diameter of the membrane is 0.82 .mu.m (measured by a mercury porosimeter), and the water permeability is 4.2 l/m.sup.2 .multidot.hr.multidot.mmHg. Although the water permeability of the membrane is large, separation characteristic is not sufficient.
Japanese Patent Publication Hei.3-70539 also discloses a hydrophilic microporous polyethylene membrane, as shown in FIG. 4, covered by ethylene-vinyl alcohol copolymer. This membrane has a permeability of 1.1 to 20.2 l/m.sup.2 .multidot.hr.multidot.mmHg. However, this membrane has a 3 dimensionally meshed structure wherein overall micropores are uniform. Therefore, membranes having a higher separation capability does not necessarily have a sufficient permeability. For example, a membrane having a maximum pore diameter of 0.15 .mu.m obtained by the Bubble-Point method has a low permeability of 1.1 l/m.sup.2 .multidot.hr.multidot.mmHg, and in the range of high separation capability, a sufficient permeability can not necessarily be obtained.
Japanese Patent Publication Sho.62-44046, and Japanese Patent Laid-Open Publication Sho.62-269706 disclose an invention of composite hollow fiber membrane obtained by joining different layers having microporous structures. However, the air permeability of the membranes obtained by these inventions is shown to be 23,000 l/m.sup.2 .multidot.hr.multid
REFERENCES:
patent: 4384023 (1983-05-01), Okamura et al.
patent: 4401567 (1983-08-01), Shindo et al.
patent: 4530809 (1985-07-01), Shindo et al.
patent: 4808315 (1989-02-01), Manabe et al.
patent: 5084173 (1992-01-01), Nitadori et al.
Misoo Kunio
Ohbori Kohji
Shibata Noritaka
Copenheaver Blame R.
McCamish Marion E.
Mitsubishi Rayon Co. Ltd.
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