Liquid purification or separation – Filter – Supported – shaped or superimposed formed mediums
Reexamination Certificate
1996-04-03
2001-05-15
Theisen, Mary Lynn (Department: 1732)
Liquid purification or separation
Filter
Supported, shaped or superimposed formed mediums
C210S497010, C210S505000, C428S903000, C156S167000, C264S006000, C264S115000, C264S122000, C264S211120
Reexamination Certificate
active
06230901
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to microfine mixed fibers spun according to melt-blown process, a fiber product consisting of the microfine mixed fibers and a process for producing the fibers and the fiber product. More particularly, it relates to fiber products consisting of microfine mixed fibers consisting of high melting point microfine fibers and low melting point microfine fibers, the melting point difference between both the fibers being 10° C. or more, and the content of the low melting point microfine fibers in the mixed fibers being 10 to 90% by weight, and a process for producing the fiber products.
Concretely, it relates to a cylindrical filter having a good pressure resistance strength and filtration accuracy and a long filtration life.
2. Description of the Related Art
Microfine fibers have been processed into non-woven fabrics or molded products and have been broadly used as the surface material for disposable diaper, dust-proof clothes, mask, wiping cloth, filter for microfiltration, etc. As the filter for microfiltration, an air filter, a filter for washing liquid during the steps of producing electronic equipments, a prefilter for water for pharmaceutical preparations, a filter for removing microorganisms from foods or potable water, etc. are known.
Japanese patent application laid-open No. Sho 54-134177 discloses a process for producing a non-woven fabric of microfine fibers wherein a thermoplastic resin is degraded to have a low viscosity in a spinning device, followed by spinning according to melt-blown process. Further, Japanese patent application laid-open No. Sho 60-99057 discloses a process for producing a non-woven fabric of microfine conjugate fibers wherein two kinds of thermoplastic resins are conjugated into side by side type, followed by spinning according to melt-blown process.
As the filter, Japanese patent application laid-open No. Sho 60-216818 discloses a filter for microfiltration obtained by stacking microfine fibers on a shaft and supporting the structure only by way of mechanical entanglement of the fibers to one another, and having a constant void ratio. Japanese patent application laid-open No. Hei 1-297113 discloses a cylindrical filter obtained by winding up non-woven fabrics, wherein the closer to the outer surface of the filter, the larger the fiber diameter and the pore diameter. Japanese patent application laid-open No. Hei 4-126508 discloses a cartridge filter consisting of microfine conjugate fibers, prepared according to melt-blown process. Japanese patent application laid-open No. Hei 5-96110 discloses a cartridge filter consisting of microfine fibers obtained according to melt-blown process, wherein the fiber diameter is successively varied.
In the case of conventional non-woven fabrics consisting of microfine fibers of a single component, as the structure have been supported mainly by entanglement of fibers with one another, drawbacks have been raised that the non-woven fabrics have a low strength and many fluffs, and are unsuitable to apply for the surface material for disposable diaper. When the fabrics are heat-treated by means of heating rolls or the like, in order to enhance the strength of the fabrics, then the fibers are liable to melt and the resulting non-woven fabrics become film-like and has an inferior feeling.
Further, in the case of conventional filters using microfine fibers of a single component, adhesion between fibers is few. Thus, drawbacks have been raised that the filtration accuracy varies due to heat-sterilizing treatment, high temperature filtration, vibration or the like, the hardness is low and the withstanding pressure is insufficient.
Further, the conjugate melt-blown process has drawbacks that the spinneret is complicated and expensive, and it is difficult to control the melt viscosity for uniformly feeding different kinds of polymers into the respective extrusion holes.
SUMMARY OF THE INVENTION
The present inventors have made extensive research in order to solve the above problems, and as a result have found that when a high melting point resin and a low melting point resin, having a melting point difference of 10° C. or more, are extruded from the respective extruders therefor, while controlling the quantity of the low melting point resin extruded so as to give 10 to 90% by weight based upon the total weight of the resins extruded, and so as to give high melting point microfine fibers and low melting point microfine fibers, followed by spinning according to melt-blown process, and subjecting the resulting microfine mixed fibers consisting of high melting point microfine fibers and low melting point microfine fibers, to suitable molding processing and heat-treatment, to obtain the resulting web, which is then processed into a non-woven fabric or a cylindrical filter, each having superior properties; and have completed the present invention.
The present invention has the following aspects.
(1) A web composed of microfine mixed fibers spun according to melt-blown process and consisting of high melting point .microfine fibers and low melting point microfine fibers having a melting point difference of 10° C. or more, the low melting point microfine fibers being contained in a proportion of 10 to 90% by weight in the microfine mixed fibers.
(2) A non-woven fabric composed of microfine mixed fibers, spun according to melt-blown process and consisting of high melting point microfine fibers and low melting point microfine fibers having a melting point difference of 10° C. or more, the high melting point microfine fibers having been fixed by melt adhesion of the low melting point microfine fibers contained in the microfine fiber mixture in a proportion of 10 to 90% by weight.
(3) A molded product having a three dimensional structure composed of microfine mixed fibers, spun according to melt-blown process and consisting of high melting point microfine fibers and low melting point microfine fibers having a melting point difference of 10° C. or more, the high melting point microfine fibers having been fixed by melt adhesion of the low melting point microfine fibers contained in the microfine fiber mixture in a proportion of 10 to 90% by weight.
(4) A cylindrical filter composed of microfine mixed fibers, spun according to melt-blown process and consisting of high melting point microfine fibers and low melting point microfine fibers having a melting point difference of 10° C. or more, the high melting point microfine fibers having been fixed by melt adhesion of the low melting point microfine fibers contained in the microfine fiber mixture in a proportion of 10 to 90% by weight.
(5) A fiber product according to any one of items (1) to (4), wherein either one of the high melting point microfine fibers or the low melting point microfine fibers are conjugate fibers.
(6) A fiber product according to any one of items (1) to (5), wherein the fiber diameter of the high melting point microfine fibers and/or the low melting point microfine fibers is 20 &mgr;m or less.
(7) A fiber product according to any one of items (1) to (5), wherein the fiber diameter of the high melting point microfine fibers and/or the low melting point microfine fibers is 0.1 to 10 &mgr;m.
(8) A cylindrical filter according to item (4), wherein the fiber diameter of the high melting point microfine fibers and/or the low melting point microfine fibers is successively reduced along the filtration direction of the filter and the ratio of the maximum fiber diameter to the minimum one is twice or more.
(9) A cylindrical filter according to item (4), wherein the pore diameter of a filtration layer of the filter is successively reduced along the filtration direction of the filter and the ratio of the maximum pore diameter to the minimum one is twice or more.
(10) A cylindrical filter according to item (4), wherein the pore diameter of a filtration layer of the filter is varied in the order of large, small and large along the filtration direction, and the ratio of the maximum pore diameter to the minimum
Nagae Kazuyuki
Ogata Satoshi
Yamamoto Kazue
Chisso Corporation
Fay Sharpe Fagan Minnich & McKee LLP
Theisen Mary Lynn
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