Liquid purification or separation – Flow – fluid pressure or material level – responsive – Filter cleaning
Reexamination Certificate
1998-02-18
2001-06-05
Savage, Matthew O. (Department: 1723)
Liquid purification or separation
Flow, fluid pressure or material level, responsive
Filter cleaning
C210S108000, C210S138000, C210S386000, C210S391000, C210S392000, C210S393000, C210S394000, C210S396000, C210S397000, C210S400000, C210S401000, C210S402000, C210S403000, C210S496000, C210S499000, C442S199000, C442S200000, C442S201000, C442S239000
Reexamination Certificate
active
06241879
ABSTRACT:
DESCRIPTION
1. Technical Field
This invention relates to a filter cloth having a base layer constituting a base cloth and a filtering layer consisting of fiber bundles having root portions in the base layer. The invention also relates to a filter cloth wherein the filtering layer is mainly composed of fiber bundles having a specified crimped fiber ratio. More particularly, the invention relates to a new filter cloth having excellent fine particle collecting performance, washing recovery performance, dimension stability, excellent in durability and excellent in water permeability, which can be preferably used for suspended material separation. The invention also relates to a belt type solid-liquid separating machine and a filtering machine in which this filter cloth is used.
2. Background Art
As filters for filtering fine particles included in gases such as air or liquids such as water or solvents, filter cloths made of woven and nonwoven fabrics in which fibers are used have been widely employed. In particular, for filtering suspended solid in water, woven fabrics of lattice structure based on the so-called 3 motive design, plain, twill and satin, have been used. In addition, for example in Japanese Patent Publication No. S62-13046 and Japanese Patent Publication No. H2-47244, filter cloths made by raising a woven fabric wherein an ultra fine fiber is used for the weft and thereby forming naps of ultra fine fiber on the surface are disclosed. In addition, as filters having fiber bundles on a surface, filters and filter cloths disclosed in Japanese Utility Model Publication No. H2-36568, Japanese Utility Model Publication No. H5-34730 and Japanese Unexamined Utility Model Publication No. H4-14112 are known. In Japanese Utility Model Publication No. H6-27672 and Japanese Utility Model Publication No. H6-30874, pile woven and knit fabrics having piles wherein crimped threads and uncrimped multifilaments are woven together are disclosed. In Japanese Patent Publication No. H1-40136 and Japanese Unexamined Patent Publication No. S58-120834, textiles made by raising woven fabrics wherein false twisted thread is used for the weft are disclosed.
However, because conventional filter cloths made of woven or knit fabrics using fibers pass unfiltered water through gaps in a lattice structure of fibers and catch particles contained in the unfiltered water in the lattice, particles smaller than the size of the gaps in the lattice are hardly caught and pass through. There have been filter cloths wherein to catch particles of small particle diameter the weaving density is increased and the size of the lattice is thereby made small, but with these the ratio of gaps in the filter cloth becomes small and the permeated water that can be filtered falls severely, and also fouling soon occurs and filtering becomes impossible. There have also been filter cloths wherein the threads or fibers constituting the woven fabric are made thin with the aim of increasing the small particle collecting performance, but with these there has been the problem that particles once lodged in the gaps between the fibers are not easy to wash off even by carrying out backwashing or the like and fouling has soon occurred. In addition, because the threads or fibers are thin, the strength of the cloth has been low and its durability has been low. With filter cloths of knit structures, on the other hand, the elongation of the knit fabric has been great and the dimensional stability has been inferior. In addition, there has been the problem that because the filter cloth deforms easily and as a result the gaps change greatly the particle diameter of fine particles which can be rejected varies and it is difficult to obtain stable filtering performance. With filter cloths of nonwoven structures, because they are three-dimensional structures of fibers and are relatively thick and dense, the particle collecting performance is good but pressure loss is high and also, because it is difficult to remove particles once caught in the three-dimensional lattice, recovery of the filtering cloths is problematical and they are inferior in reusability. In addition, because they deform easily when a tension acts on them, they are inferior in dimensional stability. In the filter cloths disclosed in Japanese Patent Publication No. S62-13046 and Japanese Patent Publication No. H2-47244, because the length of the naps is short and the quantity of the naps is also small there has been a limit on the fine particle rejecting performance. In addition, because surface layer parts of ultra fine fiber bundles constituting the weft have fibers pulled out into a loop form, fine particles are trapped by these parts and fouling tends to occur, and because once fine particles have become lodged it is difficult to remove them the performance recovery obtained by washing and the like has been inferior. Even when the number of raising operations is increased, because there is a limit on the increase in number of naps this has not been an effective means for increasing fine particle rejecting performance. Conversely, because together with increases in the number of raising operations cutting of the fibers constituting the weft occurs everywhere, the strength of the weft falls, tears occur in the warp direction of the filter cloth after a short period of use and it has only been possible to obtain filter cloths having low durability. In the filter cloths disclosed in Japanese Utility Model Publication No. H2-36568, when a base cloth and a pile are bound by setting with resin, the resin has tended to seep to the upper part of the pile and form adhered unevenness, and it has been difficult to control the application of the resin uniformly. As a result, areas of fiber bundles bound and set by resin having seeped to their upper parts become holes and because fine particle collecting cannot be performed in these areas and as filter cloths they have inevitably only been applicable to collecting particles of large particle diameter. In addition, because they are for filters for air cleaners, it has not been possible to use them for filtering liquids at all. The filter cloth disclosed in Japanese Utility Model Publication No. H5-34730 is a filter cloth wherein pile ends are bent and parted, but because to prevent pile laying down the use of a considerably thickly woven fiber of several tens of denier is necessary and because there are many gaps between the piles, the dust-collecting efficiency of particles of small particle diameter has been low. In addition, because it is a dust-collecting filter cloth for air cleaning, it has not been possible to use it for filtering liquids at all. In the filter cloth disclosed in Japanese Unexamined Utility Model Publication No. H4-14112, because standing fiber stand substantially vertically with respect to a knit base, the rate at which passing through of particles can be rejected by the fibers themselves is low and due to particles entering between the fibers standing vertically together fouling has tended to occur at an early stage of filtering. When the particle diameter is small as compared with the size of the loops of the knit base there has been the problem that because particles having entered between standing fiber are not caught in the mesh of the knit base either and pass through the loops the fine particle rejecting performance is low. In addition, when during filtering the standing fibers lie down, because the directions of the lying down are diverse and the knit base is exposed in various places, there has been a limit to an increase in rejecting performance.
The pile woven and knit fabrics disclosed in Japanese Utility Model Publication No. H6-27672 and Japanese Utility Model Publication No. H6-30874 are fabrics for clothing and for seat coverings superior in quality and luster of which the piles stand close vertically and do not perform as filter cloths at all. In Japanese Patent Publication No. H1-40136 and Japanese Unexamined Patent Publication No. S58-120834, weaving methods using false twisted wefts are disclosed,
Kato Hiroyasu
Terao Manabu
Tomida Yoshihiro
Fleming Michael A.
Miller Austin R.
Savage Matthew O.
Toray Industries Inc.
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