Note: Descriptions are shown in the official language in which they were submitted.
CA 02228126 1998-01-28
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DESCRIPTION
FILTER CLOTH AND FILTERING MACHINE
Technical field
This invention relates to a filter cloth having a base layer constituting a basecloth 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.
Background Art
As filters for filtering fine particles included in gases such as air or liquidssuch 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 disdosed. 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
3 0 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
CA 02228126 1998-01-28
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
5 using fibers pass unfiltered water through gaps in a lattice structure of fibers and catch
particles contained in the unfiltered ~vater 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
10 cloth becomes small and the permeated water that can be filtered falls severely, and also
fouling SOOII 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
15 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
2 0 easily and as a result the gaps change greatly the particle diameter of fine particles which
can be rejecr.ed varies and it is difficult to obtain stable filtering performance. With filter
cloths of nanwoven 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
25 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
30 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
CA 02228126 1998-01-28
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
5 number of naps this has not been an effective means for increasing fine particle rejecting
performance. Reversely, because together with increases in the number of raisingoperations cutting of the fibers constituting the weft occurs everywhere, the strength of
the weft fal]s, 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
15 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 fo;r 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
20 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 parl:icle 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 disdosed in Japanese Unexamined Utility Model Publication No. H4-14112,
2 5 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
3 0 because particles having entered between standing fiber are not caught in the mesh of the
knit base eit~her and pass through the loops the fine particle rejecting performance is low.
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In addition, when during filtering the standing fibers lie down, because the directions of
the lying do~Tn 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 arefabrics for c lothing 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, but since these are
raised woven fabrics wherein individual naps are independent they are completelydifferent from the filter cloth of the present invention and also these raised woven fabrics
are chiefly i-or use in clothing and have not been applicable to filter cloths.
Disclosure of Invention
An object of this invention is to solve the above-mentioned problems
associated with conventional filter cloths and provide a new filter cloth having excellent
fine particle collecting performance, washing recovery performance and durability, and
another object is to provide a new filter cloth whose fine particle rejection in filtering
liquids is high and having high water permeability and anti-fouling durability, superior
dimension stability and long life which can be preferably used for suspended solid
separation. A further object of the invention is to provide a belt type solid-liquid
separating machine and a filtering machine fitted with this filter cloth having excellent
fine particle rejecting performance, washing recovery performance, durability, filter cloth
belt transport stability and filtering process stability and having the feature that the
conflicting characteristics of fine particle rejection and water permeability are both
obtained at a high level.
The objects of the invention are basically achieved by the following
constructions:
'A filter cloth comprising at least a base layer and a filtering layer, wherein
the ratio T/L, of the thickness (T) of the filtering layer to the length (L) of fibers of fiber
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bundles constituting the filtering laLyer is 0.()2 to 0.7 and the total projected area onto the
base layer surface of the fibers is 8 to 350 times the area of the base layer surface.'; 'A
filter cloth comprising at least a base layer and a filtering layer mainly composed of fiber
bundles of c rimped fiber ratio over 5%.'; 'A belt type solid-liquid separating machine
5 comprising 3Lt least a mechanism having fitted on a plurality of rollers and transporting
a belt in which is used a filter cloth mentioned above, a mechanism for supplying
unfiltered ~,vater onto an inclined part of the belt, a mechanism for sucking supplied
unfiltered water from the rear side of the belt, a mechanism for pressurizing and
dewatering a cake formed on the belt, a mechanism for peeling off the dewatered cake
10 and a mechanism for washing the belt.'; and 'A filtering machine comprising at least a
mechanism having a filter cloth mentioned above fitted to a drum or a disc-like structural
member and partitioning an inside part and an outside part, a mechanism for supplying
unfiltered water to the partitioned outside part or inside part and causing the unfiltered
water to pas, through the filter cloth, a mechanism for washing the filter cloth from the
15 unfiltered water supply side and/or the other side of the filter cloth, and a mechanism for
discharging concentrated water produced by the washing.'
Brief Description of Drawings
I~ig. 1 is a side view of an apparatus for measuring the water permeability
coefficient of a filter cloth.
11ig. 2 is a side view showing a filtering mechanism of a belt type solid-liquidseparating machine.
1 ig. 3 is a side view showing a mechanism of a rotary drum type continuous
2 5 filtering machine.
l~ig. 4 is a view illustrating how a crimped fiber ratio is obtained.
Explanation of the Reference Numerals
]: upper filtering pipe 2: filter cloth
,: metal gauze 4: measuring cylinder
S: pump 6: distilled water
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l: clamp 8: cock
'3: lower filtering pipe 10: filter cloth
].1: unfiltered water 12: unfiltered water tank
].2a: frame 13: mirror finished transfer roller
] 3a: press roller 13b: rotating roller
] 4: cake 15: surface washing spray
] 6: washing discharge hole 17: backwashing spray
18: pressure-reducing blower 19: scraper
20: filtered water 21: filter cloth
22: unfiltered water 23: filtered water
24: concentrated water 24a: concentrated water tray
25: washing water pump 26: backwashing spray
27: surface washing spray 28: rotary drum
29: loss water head 30: fiber
31: straight line ab 32: straight line cd
33: crossing point
Best Modes for Carrying Out the Invention
2 0 Iiibers which can be used in fiber bundles constituting a filtering layer of the
invention are made of polymer substances having fiber formability, and examples thereof
include polvamides and aromatic polyamides such as nylon 6, nylon 66, nylon 12 and
copolymers of polyamides, polyesters such as polyethylene terephthalate, copolymers
of polyethylene terephthalate, polybutylene terephthalate and copolymers polybutylene
2 5 terephthalate, polyolefins such as all-aromatic polyesters, polyethylene and
polypropylene, and polyurethane, polyacrylonitrile, polyvinyl chloride, polyvinyl
alcohol, vinyl polymers, polyvinylidene chloride, polyhydrosulfite, polyethylenefluoride, copolymers of polyethylene fluoride and polyoxymethylene. Composite fibers
and combinations of different types of fiber of core and sheath structure, multiple core
3 0 and sheath structure, islands in the sea structure or bimetal structure or the like made by
combining a plurality of these polymer substances are used according to the application.
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As the thickness of the fiber, a relatively thin two denier or less is preferable,
but to increa.se fine particle collecting performance 0.001 to 1 denier is more preferable
and to increase fine particle collecting performance while keeping the durability of the
fiber high 0.03 to 0.5 denier is still more preferable.
A fiber bundle of this invention is made by arranging multiple fibers of
different kinds or of the same kind arranged together in the form of a bundle. Preferably,
at least one end of each fiber bundle constituting a filtering layer is a free end, and the
other end or a middle portion of the fiber bundle is integrated with the base layer. Free
end refers lo a state wherein the end of the fiber is released and can move freely.
Preferably, the fiber bundle flares from its root portion toward its end and is bent and
inclined in a predetermined direction such as the length direction or the width direction
of the filter cloth.
An end portion of the fiber bundle or a middle portion of the fiber bundle and
the base layer are integrated by intertwining with threads of the base layer, adhesion with
an adhesive, thermal fusion, ultrasonic adhesion or a combination of these. A filter cloth
of a structure wherein the structure of the base layer is woven and root portions of the
fiber bundles of the filtering layer are mutually intertwined with the weft and/or the warp
of the base layer in at least three places is preferable because the fiber bundles do not
readily come off during use. The integrated portions are preferably arranged on the base
2 0 layer surface regularly, but even when they are not arranged regularly, preferably there
are no areas where the fiber bundles are sparse or areas where there are no fiber bundles,
which areas have an affect on the filtering performance, and the integrated portions are
disposed so as to be positioned uniformly over the base layer surface.
1'o achieve the objects of the invention it is necessary that when the average
length fron-l where the fiber bundles are fixed integrally with the base layer, i.e. the
highest surface position of the base layer, of the fiber bundle fibers thereon is written L
(mm) and the thickness of the filtering layer is written T(mm), T/L is 0.02 to 0.7. When
T/L is less than 0.02 the fine particle collecting performance is low and it is not possible
to hold many fine particles in the filtering layer, or the filtering layer is too dense and
soon clogs easily, and therefore this is not preferable. When it is greater than 0.7,
because fine particles are hardly filtered in the surface part of the filtering layer and
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readily enter the inside of the filtering layer and pass straight through without being
blocked it is not possible to obtain a high rejection and therefore this is not preferable.
In addition, when it is greater than 0.7 and the base layer has a dense structure, fine
particles having entered the inside accumulate and cause fouling, and even when
5 washing is c arried out fine particles having entered the inside are difficult to wash off
and the washing recovery performance is poor and therefore this is not preferable.
Preferable as a value of T/L is 0.02 to 0.6, and more preferable is 0.02 to 0.5. When the
fiber of the filtering layer is 0.5 denier or less, 0.02 to 0.25 is particularly preferable.
]:t is necessary that when all the fibers of a filtering layer in the invention are
10 lined up on a plane, the sum of the projected areas of the individual fibers on the plane
is 8 to 350 times the corresponding area of the filter cloth.
When it is smaller than 8 times this, because covering of the base layer
surface by the fibers is insufficient and collecting of particles is not carried out
satisfactorily, the rejection is low, and, because the quantity of particles held in the
15 filtering layer is small, there has been the problem that once fouling starts to occur a rise
in filtering pressure rapidly occurs. In addition, when on the other hand it is greater than
350 times, the quantity of fibers in the filtering layer is too great, the water permeability
falls severely, the amount which can be processed decreases and efficient processing is
not possible. From 10 to 250 times, more favorable results can be obtained through
2 0 balancing of a high rejection and a high water permeability.
]n addition, in the invention, to catch particularly small particles, it is
necessary that the filtering layer be mainly made of fiber bundles whose crimped fiber
ratio is 5% or more. When the crimped fiber ratio is lower than 5%, fibers constituting
the fiber bundles easily converge with each other, the surface of the filter cloth is not
2 5 sufficiently covered by fibers, gaps form between fiber bundles and particle collecting
is not satisfa~ctory. When on the other hand the crimped fiber ratio is excessively high,
entangling of fibers with each other becomes too strong, the fiber bundles become
bundle-like aggregates, covering of the surface of the filter cloth by fibers again becomes
insufficient and, depending on the conditions, cases of the particle collecting
30 performance falling may occur. To reduce poor fiber bundle flaring caused by
converging and entangling of fibers and to form suitable spaces between fibers and
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thereby raise particle collecting performance a crimped fiber ratio of 10 to 95% is
preferable, and more preferable results can be obtained with a crimped fiber ratio of 15
to 90%.
In addition, the filtering layer is preferably mainly made of fiber bundles of
5 at least two types between which there is a difference in crimped fiber ratio of 10% or
more. As forms wherein there is a difference in crimped fiber ratio there are: [1] cases
wherein one bundle is made of two types of fiber and a difference is provided in the
crimped fiber ratios of these two types of fiber, [2] cases wherein a difference in crimped
fiber ratio is provided between fiber bundles and [3] cases of both of these, and an
10 optimum form is selected according to the application and the required performance.
When fine particles are to be caught, form [1] is suitable. When relatively large particles
whose average particle diameter exceeds 25,um are to be caught, forms [2] and [3] are
preferable. When the crimped fiber ratio difference is smaller than 10%, the effect of
providing the difference in crimped fiber ratio does not readily appear. As at least two
15 types of fiber bundle between which there is a difference in crimped fiber ratio of 10%
or more, a case wherein the crimped fiber ratios of at least two types of fiber bundles are
over 5% is preferable, but a combination wherein the crimped fiber ratio of at least one
type of fiber bundle is less than 5% can also be employed in a limited range.
To impart this crimped fiber ratio, it can be achieved easily by means of a
2 0 false thread-twisting process. There is no particular limitation on the process, but for
example, as a false thread-twisting process, using an intersecting belt type twister, with
conditions of thread speed 300m/min, heating plate temperature stage one 210~C, stage
two 190~C, twister intersecting angle 110~ and belt/thread speed ratio 1.39, for example
when the fa.lse twisting draw ratio is adjusted to 1.005 and the reset overfeed rate is
2 5 adjusted to 5%, a false twisted thread of crimped fiber ratio 55.7% can be obtained.
Alternatively, to achieve the objects of the invention, the filtering layer is
preferably mainly made of fiber bundles whose percentage crimp is 2 to 45%, a
percentage crimp of 2 to 35% is more preferable and a percentage crimp of 2 to 25% is
still more preferable. For example, when the percentage crimp is 3.2~o, a crimped fiber
3 0 ratio of 55. 7% can be obtained. Percentage crimp is defined below under the heading
'Definitions of the Parameters'.
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The number of fiber bundless in the base layer surface should be made such
that the particle collecting performance does not deteriorate because the number of
stumps is too low and the gaps between the stumps are too large and the parts of the base
layer where these gaps occur cannot be fully covered. In addition, conversely, when the
5 number of stumps is too great the gaps between the stumps are too narrow, the gas and
liquid passing resistance increases and pressure losses become high and the amount
which can be processed also decreases. In addition, particles having entered between
fiber bundles and inside fiber bundles become difficult to remove and the recovery
performance of the filter cloth falls. Therefore, the frequency of appearance of fiber
bundles at the base layer surface is preferably 40 to 900 stumps/cm2. More preferable
results can be obtained when it is 50 to S00 stumps/cm2.
The total denier of fiber bundles per one stump of the filtering layer, like thedensity of fiber bundless, should also be made such that gap parts of the base layer can
be covered, and on the other hand attention should be paid to ensuring that the passing
resistance does not increase and pressure losses do not become high because the fiber
bundles are too thick and the gaps between stumps are too narrow. The total denier of
fiber bund] es per filtering layer stump can be changed according to the target
performance and purpose of use of the filter cloth and the thickness of the fibers used in
the fiber bundles, but 50 to 1500 denier is preferable. When the fiber used for the fiber
2 0 bundles is thicker than 2 denier S0 to 750 is more preferable, and when the fiber used for
the fiber bundles is less than 1 denier 100 to 1500 denier is more preferable. Preferably
also, a composite fiber is used for the fiber bundles of the filtering layer and made into
an ultra fine fiber by some components being removed by being dissolved or beingseparated in the manufacturing process. In this case, because the size of an ordinary
composite :Eber is thicker than 2 denier, the fiber bundle is preferably less than 750
denier so that work in the manufacturing process is easy. In addition, the number of
fibers per stump is a value determined by the total denier of the fiber bundles and the
thickness of the fibers used in the fiber bundles, but S0 to 15000 fibers/stump is
preferable a.nd 150 to 15000 fibers/stump is more preferable. With ultra fine fibers under
3 0 O.S denier 300 to 15000 fibers/stump and with ultra fine fibers under 0.2 denier S00 to
15000 fibers/stump is particularly preferable.
CA 02228l26 l998-0l-28
'~hen the length of the ~lbers of the filtering layer becomes too short, becausethe quantity of fibers which can contribute to filtering becomes small, the particle
collecting perfor~mance falls. In addition, because the fibers become difficult to bend and
the end portions of the fibers tend to stand vertically together on the surface of the
filtering layer, particles accumulate between the fibers standing vertically together and
tend to cause fouling, and the washing recovery performance also falls. When on the
other hand the length of the fibers of the filtering layer becomes too long, the particle
collecting performance is good but the gas and liquid passing resistance becomes high
and the amount which can be processed also decreases. In addition, during filtering,
fibers entangle with each other and tend to form nep-shaped lumps. For these reasons,
the length of the fibers of the filtering layer is preferably 2mm to 20mm. When it is
2mm to 15rmm, more preferable results can be obtained. The fiber length referred to here
is the average length of the fiber bundle fibers from where the fiber bundles are fixed
integrally with the base layer, i.e. the highest surface position of the base layer, to the
free ends.
To avoid the filter cloth greatly deforming when a strong tension acts thereon,
the percentage elongation in the length direction and the width direction is preferably
below 10%. The percentage elongation referred to here is measured under standardconditions by marking a strip-shaped test piece of width 3cm with a 20cm spacing,
2 0 applying a load of 12kgf to the test piece in the length direction thereof, applying a load
of 6kgf to the test piece in the width direction thereof and measuring the length between
the marking, after 90 minutes. The percentage elongation at this time is obtained using
the following equation:
percentage elongation = (b-a) . _ x 100 (%)
2 5 lIere, _ is the length between the markings when an initial load of 100gf was
applied to the test piece and b is the length between the markings, with the loads still
applied, 90 minutes after the loads were applied. To avoid the meshes of the base layer
from expanding and the filtering performance consequently falling, a percentage
elongation i31 the warp direction of less than 8% is more preferable and less than 6% is
3 0 still more preferable. A value of percentage elongation in the width direction slightly
higher as coimpared with the length direction is tolerable, but nevertheless preferably less
_l
CA 02228126 1998-01-28
than 9% is g1ood and less than 7~o is more preferable.
To avoid the filter cloth greatly cleforming and to obtain a filter cloth havingexcellent dirnensional stability, using as the fiber of the base layer mainly a fiber whose
initial tensile modulus measured by the method of JIS L1013 is over 250kgf/mm2,
preferably over 300kgf/mm2 and more preferably over 350kgf/mm2 is recommended. In
addition, as -the form of the fiber, a fiber of a straight form which does not extend easily
is preferable to a fiber crimped and having an easily extending structure such as a false
twisted thread. Furthermore, to produce a filter cloth excelling in dimensional stability,
the structure of the base layer is preferably woven. In actual filtering, when filtering is
carried out by a filter cloth alone without a wire gauze or a porous plate being disposed
downstream of the filter cloth, with a knit or nonwoven filter cloth the filter cloth readily
deforms under weak tensions by swelling and extending out of shape. In addition, the
apparent density of the filter cloth is preferably 0.15 to 0.6gf/cm3. The apparent density
(gf/cm3) of the filter cloth is obtained by dividing the weight(gf/m2) per 1 square meter
of the filter cloth, by the thickness T1 of the filter cloth obtained by a measuring method
set forth in parameter definition (2), which will be further discussed later, and matching
the units. When the apparent density is too low the fine particle collecting performance
is not satisfactory and when it is too high the water permeability becomes inadequate.
To balance the fine particle collecting performance and the water permeability, the
2 0 apparent density of the filter cloth is preferably 0.2 to 0.6gf/cm3. An apparent density
of 0.25 to O.5gf/cm3 is more preferable.
When separating suspended solid, with respect to unfiltered water whose
suspended solid concentration is over a few hundred ppm, for example as shown in Fig.
2, a belt type solid-liquid separating machine of a structure wherein a belt made using
2 5 a filter cloth of the invention is transported to carry out separation of suspended solid in
unfiltered water has excellent performance characteristics such as that the transport
stability of the belt is high, it is possible to catch fine particles efficiently and the
durability is high.
1'his solid-liquid separating machine will now be described in further detail
3 0 on the basis of Fig. 2, but the invention is in no way limited by this.
That is, an endless belt 10 is made using a filter cloth of the invention. In this
CA 02228126 1998-01-28
belt 10, as the material thereof just a filter cloth of the invention may be used, but
alternatively a intensifying material may be disposed along the sides of the belt to
reinforce its strength, a material of low water permeability may be laid to prevent water
leakage from the sides or a belt with holes may be attached and the belt guided by
5 sprockets on the machine side to increase dimension stability.
This belt 10 is fitted to a plurality of rollers (13a, 13b) and transported in the
direction of the arrows, and unfiltered water 11 is supplied to a unfiltered water tank 12
above an inclined part of the belt. The unfiltered water tank 12 is surrounded by a frame
12a and can hold unfiltered water. The travelling belt 10 forms the bottom of the
unfiltered water tank 12. Filtered water 20 having passed through the belt 10 is obtained,
but at this tiime a mechanism for sucking supplied unfiltered water from the rear surface
of the belt, for example a pressure-reducing blower 18, is preferably used. A cake 14
formed on the belt is pressed and dewatered by a mirror finished transfer roller 13 and
press rollers 13a. The cake 14 is transferred to the surface of the mirror finished transfer
15 roller 13 and scraped off by a scraper 19 and collected. In this case, the side with the
filtering layer is made to face the surface of the mirror finished transfer roller 13. In
addition, thc fibers of the filtering layer are preferably set so that they lie in the opposite
direction to the transport direction of the belt, i.e. toward the rear.
A belt type solid-liquid separating machine of this construction has excellent
2 0 washing recovery performance and filter cloth processing stability and has the feature
that the conflicting characteristics of suspended solid collecting performance and the
amount which can be processed are both obtained at a high level.
ln addition, with a belt type solid-liquid separating machine having a function
whereby the position of the belt is detected by detecting devices such as infrared or laser
25 optical sensors or contact type sensors and when the position of the belt has deviated
greatly during transport an output signal is transmitted to a mechanism for correcting
meandering of the belt and the belt is returned to its correct position, belt transport
stability of a higher level can be obtained and unmanned operation over a long period
is possible. In addition, with a belt type solid-liquid separating machine having a
3 0 mechanism for detecting a degree of pressure drop for sucking from the rear surface of
the belt and a mechanism for starting washing of the filtér cloth by spraying spray water
CA 02228126 1998-01-28
or intensifying washing by raising the spray pressure when this degree of pressure drop
exceeds a predeterrnined value and a mechanism for stopping washing of the filter cloth
or returningr it to a normal condition after a predetermined time has elapsed since
washing of the filter cloth was started or intensified it is possible, for gradually
progressing fouling of the filter cloth, to recover automatically from this and stable
operation over a longer time is possible. In addition, water for washing can be saved and
operation at a low running cost becomes possible. In this belt type solid-liquidseparating machine, better performance can be obtained by the filter cloth being fitted
so that the filtering layer is on the unfiltered water supply side. By a combination of the
mechanisms described above and a filter cloth of the invention, this superior
performance is achieved for the first time ever.
~7ith respect to unfiltered water whose suspended solid concentration is a
relatively low concentration of less than a few hundred ppm, for example as shown in
Fig. 3, a filtering machine having a structure wherein a filter cloth of the invention is
fitted to a rotating drum or a flat plate and unfiltered water is passed through the filter
cloth to carry out separation of suspended solid has superior fine particle collecting
performance and washing recovery performance and has the excellent performance
characteristic that water permeability and fine particle collecting performance are both
obtained at a high level.
2 0 1'his solid-liquid separating machine will now be described in further detail
on the basis of Fig. 3, but the invention is in no way limited by this.
1'hat is, a filter cloth 21 of the invention is fitted around a drum or disc-like
structural member such as a rotary drum 28 rotating in the direction of the arrows so as
to partition an inside and an outside thereof. The filter cloth is supported by a plurality
2 5 of intensifying ribs extending for example in the width direction along the periphery of
the rotary drum, i.e. the surface on which the filter cloth 21 is fitted, and water being
filtered passes through gaps between the ribs. In the case shown in Fig. 3, unfiltered
water 22 is supplied to the partitioned inside and then passed through the filter cloth, but
a method wherein, in reverse, it is supplied from outside and passed through to the inside
may alternatively be used. In particular, by employing a construction wherein a
backwashing spray 26 and a concentrated water tray 24a are disposed so as to face each
1~
CA 02228126 1998-01-28
other, unfiltered water and concentrated water do not mix and efficiency is good. As a
mechanism for washing the filter cloth, there may be provided either a mechanism such
as a surface washing spray 27 which washes t'rom the unfiltered water supply side or a
mechanism such as the backwashing spray 26 which washes from the filtered water
5 delivery side, or both may be provided. In this mechanism unfiltered water inside the
drum is caused to be filtered by the filter cloth by a pressure difference of a loss water
head 29 and filtered water 23 is thereby obtained, but when necessary the unfiltered
water side may be pressurized to raise the filtering speed. In Fig. 3, pipes of the
unfiltered water 22, the concentrated water 24 and the surface washing spray 27 are
10 shown crossing the periphery of the drum on which the filter cloth is disposed, but in
practice these pipes enter the inside of the dnum for example through axial centers of the
side faces oi-'the drum. With a filtering machine of this construction it is not necessary
to temporarily stop the filtering process to perform backwashing and therefore filtering
processing can be carried out continuously, and the filtering machine has a hitherto
15 unachievable superior filtering performance based on a synergistic effect of this and the
superior fine particle rejection, dimension stability, washing recovery performance and
high water permeability of the filter cloth of the invention. Higher performance is
obtained by fitting a filtering cloth of the invention so that the filtering layer is on the
unfiltered water supply side. In addition, by adopting a construction wherein a drum or
2 0 disc-like stmctural member can be rotated it is possible to continuously repeatedly carry
out filtering, washing of the filter cloth and recovery of suspended solid concentrated
liquid and this is therefore preferable. By making washing of the filter cloth blast-flow
washing usiing a spray, washing can be carried out efficiently with a small quantity of
water. Adopting a mechanism causing pressurized liquid to flow in the opposite
25 direction to the flow of the unfiltered water for washing of the filter cloth also is a
preferable method for removing suspended solid accumulated on the surface of the filter
cloth. In adclition, with a filtering machine having a mechanism for detecting the water
surface position by means of an electrode rod, an optical sensor or a float or the like or
detecting the water depth by means of a pressure gauge or a pressure sensor or the like
3 0 and thereby detecting the passing resistance (pressure loss) of when the unfiltered water
passes through the filter cloth, a mechanism for starting or intensifying washing of the
CA 02228126 1998-01-28
filter cloth when the passing resistance exceeds a preset value and a mechanism for
stopping washing of the filter cloth or returning it to a normal condition after a fixed
time has elapsed since washing of the filter cloth was started or intensified it is possible
to increase ~,vashing of the filter cloth and thereby increase the amount processed and
prevent unfi]tered water from overflowing at times when the concentration of suspended
solid in the ~mfiltered water has suddenly changed and become high or when the flowrate
of unfiltered water has suddenly increased and fouling of the filter cloth has
consequently progressed rapidly. It is also possible to conduct unmanned automatic
operation for long periods. Furthermore, a filtering machine wherein the unfiltered water
supply side is of a structure sealed except for a unfiltered water supply opening thereby
provides a rnechanism for pressurizing and supplying unfiltered water thereby having
a mechanisrn which can pressurize unfiltered water to a high pressure greater than the
passing resistance of the unfiltered water with respect to the filter cloth can be effectively
used to raise the amount of water processed. In addition, even when using a filter cloth
having a hi;gh fine particle rejection but a low water permeability coefficient, a high
amount of water processed can be obtained and collecting of more minute fine particles
can be efficiently achieved.
Examples
l'he examples shown below are for making the invention clear, and the
invention is not limited to these.
Examples 1 to 6, Comparative examples 1 to 4
A fabric was made using as a base layer thread a 150 denier, 48 filament
thread (F1) rnade of polyethylene terephthalate for the warp and the weft, and a double
fabric consisting of upper and lower sheets of fabric was made using as fiber bundles of
a filtering layer a 240 denier, 576 filament thread (F2) made of polyethylene
terephthalate. This fabric is a double fabric comprising fiber bundles of a filtering layer
3 0 extending back and forth repeatedly between upper and lower sheets of fabric separated
by a designated space. The F2 fiber bundles have points mutually intertwining with the
] 6
CA 02228126 1998-01-28
wefts of the upper and lower fabrics and integrating the two. By slicing the integrated
fabric obtained in parallel with the surfaces of the fabric at a designated position in the
thickness direction, a number of fabrics having different lengths of filtering layer fibers
were obtained. Next, the fiber bundles were flared by the fiber bundle sides of these
5 fabrics being brought into contact with the surface of a rotary brush roller having fine
irregularities whereby the fibers were made to spread out all over the surface of the
filtering layer and simultaneously aligned in the same direction. Then, the fiber bundles
were fixed in this state by the fabrics being passed between a heated smooth metal roller
and a rubber roller with the fiber bundle side in contact with the surface of the metal
10 roller. At this time, the clearance between the rollers was changed according to
standards of the fabrics and filter cloths obtained in this way having different filtering
layer thicknesses were made. The filtering performances of a number of filter cloths
having different T/L ratios and multiplying factors of the projected area of the filtering
layer fiber bundle fibers with respect to the base layer area were evaluated. The
15 evaluations were, as shown in Fig. 2, carried out using a belt type solid-liquid separating
machine having a mechanism which effects filtering by sucking unfiltered water
introduced onto a filter cloth travelling as endless belt from the back side and transferred
a cake forrr~ed on the filter cloth onto a mirror finished roller and collected. In the
evaluations, a surplus sludge of an activated sludge process containing 5320mg/liter of
20 suspended solid of average particle diameter 17.5,~m was used as the unfiltered water.
The results obtained were as shown in Table 1.
Firom this it can be seen that with the filter cloths of the invention the
rejection of suspended solid in the discharged water and the initial water permeability
coefficient are high and the time until the limit water permeability coefficient is reached
25 is also long. In Comparative example 1, on the other hand, which has a small value of
T/L, the rejection and the water permeability coefficient are both low and the time to the
limit water permeability coefficient is also short. With the filter cloth of Comparative
example 2, ~vherein TIL is too high, the water permeability coefficient is high and the
time to the limit water permeability coefficient is also long, but the rejection is
30 particularly ]ow. With Comparative example 3, because T/L and the projected area ratio
are too high, the water permeability coefficient is particularly low and the time to the
~ 7
CA 02228126 1998-01-28
limit water permeability coefficient is also particularly short. In Comparative example
4, because T/L is too low, although the rejection is high the water permeabilitycoefficient is extremely low and the time taken to reach the limit water permeability
coefficient is also extremely low.
Examples 7 to 14, Comparative examples S to 7
~ fabric was made using as a base layer thread (F3) a 250 denier, 48 filament
thread made of polyethylene terephthalate for the warp and the weft, and a double fabric
consisting of upper and lower sheets of fabric was made using as fiber bundles (F4) of
10 a filtering layer a number of false twisted threads having different percentage crimp
made by carrying out false thread-twisting on a 300 denier, 720 filament thread made of
polyethylene terephthalate.
This fabric is a double fabric comprising F4 extending back and forth
repeatedly between upper and lower sheets of fabric separated by a predetermined space.
15 The F4 fiber bundles have points mutually intertwining with the wefts of the upper and
lower fabrics and integrating the two. By slicing the integrated double fabric obtained
in parallel with the surfaces of the fabric at a designated position in the thickness
direction, fabrics of which the surface of the filtering layer is free ends of fiber bundles
were obtained. Next, these fabrics were passed between a rotating brush roller and a back
20 roller whereby the fiber bundles were brushed and flared and the fibers were made to
spread out all over the surface of the filtering layer and simultaneously aligned in the
same direction. Then, the flared fiber bundle side was pressed with a tension applied
thereto against the surface of a heated metal roller to set the fiber bundles and a filter
cloth was thereby made. The filtering performances of filter cloths obtained in this way
25 were evaluated. The evaluations were carried out using a rotary drum type continuous
filtering machine having a filter cloth fitted onto a rotating drum with the filtering layer
on the inner side and of a mechanism which effects filtering of unfiltered water guided
into the drum to the outside as shown in Fig. 3. In the evaluations, lake water whose
concentration of suspended solid including fine particles of small particle diameter was
30 approximately 11mg/liter with an average particle diameter of 7.8~m was used as the
unfiltered water. The results obtained were as shown rn Table 2.
18
CA 02228126 1998-01-28
~ E. ~~
_ a; O O o o o c O o
C 3~ ~ ~ o ~ ~ ~ o
~_ 3 ~
,_
C~
,
o ~ ~ x a~
.
, ,_
, C~
~ o ~ ~ ~, X ~ o
~ . .
~ ~ .
E~
~ o ~ t-- ~,X ~ oo ~ ~o
~ _,
C E-
C, ~ ~ ~ _ t-- ~ ~ o ~ X
E-
_ ~
E ~ o ~ o v~ ~ x
m s E c~ ~ c~ ~i ,~.
D C
L L L L L L ~ L~_ L ~_ L ~, L
U~ O ~ O
Table 2
. , ~ Fiber BundleE~ilter Layer .~ r
~ ~IIIII~)~u rlu~l Length L (I) (2) (mm) T/L ~"Opp~n~ w~ r ~ao
Examplc 7 5.5 2.4 0.3 0.13 71 13.3
Example 8 11.3 24. 1.1 0.46 74 10.4
Example 9 16.2 5.5 0.8 0.15 91 14.3 D
Example 10 16.5 18.2 6.4 0.35 87 15.~3
Example 11 25.6 8.0 1.6 0.20 93 15.2
Example 12 55.7 5.1 1.4 0.27 90 14.0
lU Example 13 89.4 5.3 1.0 0.19 81 12.8
Example 14 94.6 5.2 1.2 0.23 72 12.1
Comparativc Example5 0.0 2.5 ().()4 0.015 58 23.7
Comparativc Example 6 1.3 2.5 1.9 0.76 39 10.5
Comparativc Examplc 7 0.0 5.5 0.09 0.016 72 25.1
CA 02228126 1998-01-28
From this it can be seen that in the filter cloths of Examples 7 to 14 of the
invention the rejection of suspended solid in the unfiltered water is high and the loss
water head is also at a low level, and a balance of rejection and water permeability
has been achieved. In Comparative examples 5 to 7, on the other hand, wherein fiber
S bundles having low crimped fiber ratios were used for the filtering layer, in those
with which the rejection was high the loss water head was also high and in those with
which the loss water head was low the rejection was also low, and in no case was a
balance between rejection and water permeability obtained.
Definitions of the Parameters
(1) Fiber Bundle Length
The average value of the length of the constituent fibers from the upper
end surface of the base layer (when the base layer is a woven fabric and the surface
has ridges, the upper ends of the ridges) to the free ends of the fiber bundles of the
filtering layer. When the fiber bundles form loops, it is defined as the average length
of the fiber bundle fibers above the upper end surface of the base layer.
(2) Filterin,g Layer Thickness
Nine approximately 3cm x 3cm test pieces are collected, and three of these
are stacked ~md placed on the pressurizing table of a compressive elasticity tester. A
2cm2 probe is placed on the test pieces with a load of 6g and the thickness after ten
seconds is measured. The average value of three measurements is obtained and
divided by t:hree to calculate the thickness Tl of one piece. Then, for samples of base
layer made by removing the fiber bundles of the filtering layer from a filter cloth, the
thickness T7 of one piece is calculated by the same method as that in which Tl was
obtained. The thickness T of the filtering layer is obtained from the equation T=Tl-
T2 (mm)
(3) Projected Area Ratio
As shown in the equation below, the projected area ratio can be defined
as the value obtained by multiplying together the average value (D) of the diameter
~1
CA 02228126 1998-01-28
(in the case of a modified cross-section fiber, the major axis) of the fibers of the
filtering layer, the length (L) obtained as described in (1) above and the number (N)
of the fiber bundle fibers of the filtering layer per unit area of the filter cloth and
dividing the product obtained by the unit area (S).
S projected area ratio = D x L x N . S
(4) Rejection
When the suspended solid concentrations of the unfiltered water and the
filtered water are respectively Cl and C2, the rejection R is obtained from the
10 equation R=(Cl-C2) . Clx100. The suspended solid concentrations are measured
based on JIS K0102.
(S) Water Permeability Coefficient
The apparatus shown in Fig. 1 is used. A new sample is wetted by
15 immersion in distilled water for twenty-four hours before the measurement. The
filter cloth is placed on a wire gauze mesh on the top of a lower filtering pipe and this
is fixed to an upper filtering pipe with a clamp. Distilled water is filled into the upper
filtering pipe and while a water head height of SOOmm is m~int~ined a cock is opened
and 1 to 1.5 liters of filtered water are collected. The time for which the cock is fully
20 open is simultaneously measured, and the water permeability coefficient K is
obtained by the following equation:
K=W . (9.6xS) (ml/cm2.sec),
where W is l:he filtered water collected (ml), S is the time for which the cock is fully
open (seconds) and 9.6 is the filtering area of the filter cloth (cm2). The initial water
25 permeability coefficients shown in Table 1 are water permeability coefficient values
of new samples tested before unfiltered water was passed through them.
(6) A watcr permeability coefficient of 1ml/cm2.sec is selected as a limit waterpermeability coefficient. Carrying out filtering of unfiltered water causes the
30 permeability performance to gradually fall, and the water permeability coefficient of
the filter cloth soon falls to this limit water permeability coefficient; the longer the
CA 02228126 1998-01-28
time over which filtering is carried out until the water permeability coefficient
reaches this limit water permeability coefficient (the time to limit water permeability
coefficient) is, the better the filter cloth is.
5 (7) Crimped Fiber Ratio
Measuring is carried out by the following procedure:
A. Fiber bundle fibers of the filtering layer are cut off and dispersed in
water at 20''C in such a way that fibers do not become entangled with each other.
13. The liquid with fibers dispersed therein is dripped onto a slide glass
10 and pressed from above with a cover glass to sandwich the fibers and disperse them
in a flat plane.
C. A photograph of this is taken with a microscope from directly above.
The m~nification is made 30 to 150 times, whereby the work described below underD. is easy to perform, and changed according to the thickness of the fibers.
D. A model view of a microscope photograph is shown in Fig. 4. The
fiber diamel:er is defined as R and a point on the fiber centerline corresponding to a
straight linc distance of 200 times R from the center point a of one end of the fiber
is defined <lS b. Point a and point b are connected by a straight line. When thestraight line ab and the centerline of the fiber cross or touch at a point other than point
20 a and point Ib, the fiber is counted as a crimped fiber. When the straight line _b and
the fiber do not cross or touch at any point other than point 3 and point b, the fiber is
not counted as a crimped fiber. The same procedure is carried out with respect to the
center point c of the other end of the same fiber, and the point on the fiber centerline
at a straighl: line distance of 200 times R from c is defined as d. When the straight
25 line cd and the centerline of the fiber cross or touch at a point other than point c or
point d, the fiber is counted as a crimped fiber again. When the straight line cd and
the fiber do not cross or touch at any point other than point c or point d, the fiber is
not counted as a crimped fiber again. When the fiber is completely straight over the
range of the straight line distance of 200 times R, the straight line _b or the straight
30 line cd and the centerline of the fiber are mutually superposed and touch at all points,
but in this c ase the fiber is not counted as a crimped fiber. Only cases wherein the
CA 02228126 1998-01-28
centerline of the fiber once leaves the straight line _b or the straight line cd and then
crosses or touches it again is the fiber counted as a crimped fiber.
l . The determination described above in D is carried out for 100 fibers
and the crimped fiber ratio is obtained using the following equation:
S crimped fiber ratio = crimped fiber count . 200 x 100 (~o)
(8) Loss Water Head
The difference between the water level of the unfiltered water inside the
rotary drum and the water level of the filtered water is taken as the loss water head.
(9) Percentage Crimp
This is measured by the following procedure:
A. Under standard conditions, a hank of circumferential length 40cm,
number of turns 10 is made out of the thread being measured using a hank winder.13. The hank is hung on a hook and put into a transparent container
containing water at 20~C.
('. For each of twenty doubled threads, an initial load of 0.002gf per 1
denier is applied to the hank and after two minutes the length Lo of the doubled hank
is measured in the water.
I). Next, in addition to the initial load, a fixed load of 0.1gf is applied to
the hank and the length Ll of the doubled hank after two minutes is measured.
1 . The percentage crimp is obtained using the following equation:
percentage crimp = (Ll-Lo) . Ll x 100 (~o)
Industrial Applicability
~ ith this invention, by adopting the kind of construction described above,
it is possible to obtain a filter cloth having excellent fine particle collecting
performance and washing recovery performance and having high durability and
30 superior dirnension stability. In addition, according to another construction of the
invention, it is possible to obtain a new fïlter cloth having excellent fine particle
collecting performance, resistance to fouling and durability and also having superior
~4
CA 02228126 1998-01-28
water permeability which can be preferably used for separating out suspended solid.
In particular, even fine particles of particle diameter below 20 to 30,um, which with
conventional filter cloths it has been difficult to deal with, processing with a filter
cloth of the invention is possible, and even minute particles of from submicrons to
5 less than a iew ,~m can be coped with satisfactorily. The types of fine particles are
not limited in any way, but because the invention is particularly suitable for
separating fine particles having irregularities in their surfaces like plankton, it can be
preferably used in applications such as removal of microorganisms from elevated
water tanks and cooling towers, purification or pre-treatment of industrial water or
10 drinking water, separation of coagulated matter in waste water treatment and plankton
separation of reservoirs and lakes and marshes.
~5
