Abstrict
A filter cloth comprising at least a base layer and a filtering
layer, characterized in that the ratio T/L of the thickness (T)
of the filtering layer to the length (L) of fibers of fiber bundles
constituting the filtering layer is 0.02 to 0.7 and the sum of a
projected area of the fibers onto the base layer surface is 8 to
350 times the area of the base layer surface and, a filter cloth
characterized in being constituted with at least a base layer and
a filtering layer mainly composed of fiber bundles of crimped fiber
ratio over 5%. Again, a belt type solid-liquid separating machine
characterized in being constituted with at least a mechanism in
which the filter cloth of this invention is provided on a plurality
of rollers and is moved therearound, a mechanism for supplying unfiltered
water onto an inclined belt, a mechanism for sucking supplied unfiltered
water from the rear surface of the belt, a mechanism for dewatering
a cake formed on the belt by pressurizing the same, a mechanism
for peeling off the dewatered cake and a mechanism for washing the
belt. In addition, a filtering machine characterized in being constituted
with at least a mechanism for partitioning inside and outside portions
by providing the filter cloth of this invention around a drum or
a disc-like structural member, a mechanism for passing water through
the filter cloth by supplying unfiltered water to the partitioned
outside or inside portion, a mechanism for washing the filter cloth
from the unfiltered water supply side and/or the other side and
a mechanism for discharging concentrated water produced by the washing.
Claims
What is claimed is:
1. A filter cloth for solid-liquid separation comprising at least
a base layer and a filtering layer comprising fiber bundles of crimped
fiber, said crimped fiber being present in a ratio between about
5% and about 95%, wherein said fiber has a denier of 0.001 to 1,
and wherein said filtering layer has a ratio T/L of the thickness
(T) of the filtering layer to the length (L) of fibers of fiber
bundles constituting the filtering layer, of 0.02 to 0.7, and wherein
the sum of a projected area of said fibers onto said base layer
surface is 8 to 350 times the area of the base layer surface.
2. A filter cloth for solid-liquid separation according to claim
1 characterized in that the ratio T/L of the thickness (T) of the
filtering layer to the length (L) of fibers of the fiber bundles
constituting the filtering layer is 0.02 to 0.7.
3. A filter cloth for solid-liquid separation according to claim
1 characterized in that the sum of the projected area onto the base
layer surface of the fibers of the fiber bundles constituting the
filter layer is 8 to 350 times the area of the base layer surface.
4. A filter cloth for solid-liquid separation according to claim
1 characterized in that elongations in the lengthwise direction
and the widthwise direction are 10% or less.
5. A filter cloth for solid-liquid separation according to claim
1 characterized in that an end and/or a middle portion of the fiber
bundle is integrated with the base layer.
6. A filter cloth for solid-liquid separation according to claim
5 characterized in that at least one end of the fiber bundle is
a free end.
7. A filter cloth for solid-liquid separation according to claim
1 characterized in that the fibers of the fiber bundle are opened
and bent in a specific direction.
8. A filter cloth for solid-liquid separation according to claim
1 characterized in that the apparent density of the filter cloth
for solid-liquid separation is 0.15 to 0.6 gf/cm.sup.3.
9. A filter cloth for solid-liquid separation according to claim
1 characterized in that the density of fiber bundles at the base
layer surface is 40 to 900 stumps/cm.sup.2.
10. A filter cloth for solid-liquid separation according to claim
1 characterized in that the length of the fibers of the filtering
layer is 2 mm to 20 mm.
11. A filter cloth for solid-liquid separation according to claim
1 characterized in that the structure of the base layer is a woven
fabric.
12. A filter cloth for solid liquid separation according to claim
11 characterized in that the fiber bundles constituting the filtering
layer are intertwined at root portions thereof with a weft and/or
a warp of the base layer in at least three places.
13. A belt type solid-liquid separating machine characterized in
that separation of suspended solid in unfiltered water is carried
out by transporting a belt in which a filter cloth for solid-liquid
separation according to claim 1 is used.
14. A belt type solid-liquid separating machine characterized in
being constituted with at least a mechanism in which a belt comprising
a filter cloth for solid-liquid separation according to claim 1
is provided on a plurality of rollers and moved therearound, a mechanism
for supplying unfiltered water onto the inclined belt, a mechanism
for sucking supplied unfiltered water from the rear surface of the
belt, a mechanism for dewatering a cake formed on the belt by pressurizing
the same, a mechanism for peeling off the dewatered cake and a mechanism
for washing the belt.
15. A belt type solid-liquid separating machine according to claim
13 comprising a mechanism for detecting the position of a side of
the belt and correcting meandering of the belt.
16. A belt type solid-liquid separating machine according to claim
14 characterized in comprising a mechanism for detecting a pressure
drop due to sucking from the rear surface of the belt, a mechanism
for starting or intensifying washing of a filter cloth for solid-liquid
separation when the pressure drop exceeds a set value and a mechanism
for stopping washing of the filter cloth for solid-liquid separation
or returning to a normal condition after a fixed time has elapsed
since washing of the filter cloth for solid-liquid separation was
started or intensified.
17. A filter cloth for solid-liquid separation defined in claim
1 characterized in being constituted with at least a base layer
and a filtering layer, characterized in that the ratio T/L of a
thickness (T) of the filtering layer to the length (L) of fibers
of fiber bundles constituting the filtering layer is 0.02 to 0.7
and the sum of a projected area of the fibers onto the base layer
surface is 10 to 250 times the area of the base layer surface.
18. A filtering filtering machine characterized in that a filter
cloth for solid-liquid separation according to claim 1 is provided
around a rotating drum or a flat plate and separation of suspended
solid in unfiltered water is carried out.
19. A filtering machine according to claim 18 characterized in
being constituted with at least a mechanism partitioning an inside
and an outside portion by providing a filter cloth for solid-liquid
separation around a drum or a disc-like structural member, a mechanism
for passing the unfiltered water through the filter cloth for solid-liquid
separation by supplying unfiltered water to the partitioned outside
or inside portion, a mechanism for washing the filter cloth for
solid-liquid separation from the unfiltered water supply side and/or
the other side of the filter cloth for solid-liquid separation and
a mechanism for discharging concentrated water produced by the washing.
20. A filter cloth according to claim 4 for solid-liquid separation
according to claim 1 characterized in being constituted with at
least a base layer and a filtering layer mainly composed of fiber
bundles of crimped fiber ratio over 10%.
21. A filtering machine according to claim 19 characterized in
that the drum or disc-like structural member is rotatable.
22. A filtering machine according to claim 19 characterized in
that the washing is a washing using a spray.
23. A filtering machine according to claim 19 characterized in
that the washing of the filter cloth for solid-liquid separation
is effected by causing a pressurized liquid to flow in the opposite
direction to the flow of the unfiltered water.
24. A filtering machine according to claim 19 characterized in
that the unfiltered water supply side is sealed except for an unfiltered
water supply opening and there is provided a mechanism which can
pressurize the unfiltered water to a pressure greater than the passing
resistance of the unfiltered water with respect to the filter cloth
for solid-liquid separation.
25. A filtering machine according to claim 19 characterizing in
comprising a mechanism for detecting the passing resistance of the
unfiltered water with respect to the filter cloth for solid-liquid
separation, a mechanism for starting or intensifying washing of
the filter cloth for solid-liquid separation when passing resistance
exceeds a set value; and a mechanism for stopping the washing of
the filter cloth for solid-liquid separation or returning to a normal
condition after a fixed time has elapsed since washing or intensifying
of washing of the filter cloth for solid-liquid separation was started.
26. A filtering machine according to claim 24 characterized in
that in the unfiltered water supply side there is provided a concentrated
water discharge opening in addition to the unfiltered water supply
opening.
27. A filtering machine according to claim 19 characterized in
comprising a mechanism for detecting the passing resistance of the
unfiltered water with respect to the filter cloth for solid-liquid
separation, a mechanism for starting or intensifying washing of
the filter cloth for solid-liquid separation when the passing resistance
exceeds an upper set value; and a mechanism for stopping the washing
of filter cloth for solid-liquid separation or returning to a normal
condition when the passing resistance falls below a lower set value.
28. A belt type solid-liquid separating machine characterized in
being constituted with at least a mechanism in which a belt comprising
a filter cloth for solid-liquid separation is provided around a
plurality of rollers and is moved therearound, wherein said belt
comprises a filter cloth for solid-liquid separation comprising
at least a base layer and a filtering layer comprising fiber bundles
of crimped fiber, said crimped fiber being present in a ratio between
about 5% and about 95%, wherein said fiber has a denier of 0.001
to 1, and wherein said filtering layer has a ratio T/L of the thickness
(T) of the filtering layer to the length (L) of fibers of fiber
bundles constituting the filtering layer, of 0.02 to 0.7, and wherein
the sum of a projected area of said fibers onto said base layer
surface is 8 to 350 times the area of the base layer surface, a
mechanism for detecting the position of a side of the belt and correcting
meandering of the belt, a mechanism for supplying unfiltered water
onto the inclined belt, a mechanism for sucking supplied unfiltered
water from a rear surface of the belt, a mechanism for dewatering
a cake formed on the belt by pressurizing the same, a mechanism
for peeling off the dewatered cake; and a mechanism for washing
the belt, a mechanism for detecting a pressure drop due to sucking
from the rear surface of the belt, a mechanism for starting or intensifying
washing of the belt when the pressure drop exceeds a set value;
and, a mechanism for stopping washing of the belt or returning to
normal condition after a fixed time has elapsed since washing of
the belt was started or strengthened.
29. A filtering machine according to claim 28 characterized in
comprising a mechanism for detecting a pressure drop due to sucking
from the rear surface of the belt, a mechanism for starting or intensifying
washing of the belt when the pressure drop exceeds an upper set
value and, a mechanism for stopping washing of the belt or returning
to normal condition when the pressure drop falls below a lower set
value.
30. A filtering machine according to claim 28 characterized in
that the washing is washing the belt from the unfiltered water supply
side using a spray.
31. A filtering machine according to claim 19 characterized in
further comprising a mechanism for detecting the passing resistance
of the unfiltered water with respect to the filter cloth, a mechanism
for starting or intensifying washing of the filter cloth when the
passing resistance exceeds a set value and a mechanism for stopping
the washing of the filter cloth or returning to a normal condition
after a fixed time has elapsed since washing or the intensifying
of washing of the filter cloth was started.
32. A filtering machine according to claim 19 characterized in
further comprising a mechanism for detecting the passing resistance
of the unfiltered water with respect to the filter cloth, a mechanism
for starting or intensifying washing of the filter cloth when the
passing resistance exceeds an upper set value and a mechanism for
stopping the washing of the filter cloth or returning to a normal
condition when the passing resistance falls below a lower set value.
33. A belt type solid-liquid separating machine according to claim
28 characterized in that, the intensification of washing is increasing
the pressure of spray washing.
34. A filtering machine according to claim 34 characterized in
that, the normal condition washing is washing the belt using a spray
from the unfiltered water supply side of the belt and the intensifying
of washing is washing the belt using a spray from the permeate side
of the belt.
35. A belt type solid-liquid separating filtering machine according
to claim 28 characterized in that the normal condition washing is
washing the filter cloth for solid-liquid separation from the permeate
side using a spray and the intensifying of washing is washing the
filter cloth for solid-liquid separation from the unfiltered water
supply side of the filter cloth for solid-liquid separation using
a spray.
36. A filter cloth for solid-liquid separation according to claim
1, wherein said fiber bundles are provided in at least two types,
between which there is a difference in crimped fiber ratio of at
least 10%.
37. A filter cloth for solid-liquid separation according to claim
1, wherein at least one of said fiber bundles flares from a root
portion toward an end portion.
38. A filter cloth for solid-liquid separation according to claim
1, wherein a denier of at least one fiber in said fiber bundles
is about 0.001 to about 2.
39. A filter cloth for solid-liquid separation according to claim
1, wherein a denier of at least one fiber bundle is about 50 to
about 1,500.
40. A filter cloth for solid-liquid separation according to claim
10, wherein at least one stump includes about 50 to about 15,000
fibers.
41. A filter cloth for solid-liquid separation according to claim
1, wherein said base layer comprises a fiber having an initial tensile
modulus greater than about 250 kgf/mm.sup.2.
42. A filter cloth for solid-liquid separation according to claim
1, further comprising a water permeability coefficient greater than
about 1 ml/cm.sup.2 sec.
43. A filter cloth for solid-liquid separation according to claim
1, wherein a percentage crimp of said fiber bundles is between about
2 and about 45.
44. A filter cloth for solid-liquid separation as defined in claim
1 wherein the crimped fiber ratio is 10%-95%.
45. A filter cloth for solid-liquid separation as defined in claim
1 wherein the crimped fiber ratio is 15%-90%.
Description 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, but since
these are raised woven fabrics wherein individual naps are independent
they are completely different from the filter cloth of the present
invention and also these raised woven fabrics are chiefly for 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 bundles constituting
the filtering layer is 0.02 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 crimped fiber ratio over 5%.`; `A belt type solid-liquid
separating machine comprising at 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
water 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 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
pass through the filter cloth, a mechanism for washing the filter
cloth from the 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
FIG. 1 is a side view of an apparatus for measuring the water permeability
coefficient of a filter cloth.
FIG. 2 is a side view showing a filtering mechanism of a belt type
solid-liquid separating machine.
FIG. 3 is a side view showing a mechanism of a rotary drum type
continuous filtering machine.
FIG. 4 is a view illustrating how a crimped fiber ratio is obtained.
FIG. 5 is a view illustrating fiber bundles constituting a filtering
layer intertwined at root portions thereof with a weft and/or warp
of a base layer in at least three places.
EXPLANATION OF THE REFERENCE NUMERALS
1: upper filtering pipe 2: filter cloth 3: metal gauze 4: measuring
cylinder 5: pump 6: distilled water 7: clamp 8: cock 9: lower filtering
pipe 10: filter cloth 11: unfiltered water 12: unfiltered water
tank 12a: frame 13: mirror finished transfer roller 13a: press roller
13b: rotating roller 14: cake 15: surface washing spray 16: 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
Fibers 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 polyamides 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 terephthalate, polyolefins such as all-aromatic polyesters,
polyethylene and polypropylene, and polyurethane, polyacrylonitrile,
polyvinyl chloride, polyvinyl alcohol, vinyl polymers, polyvinylidene
chloride, polyhydrosulfite, polyethylene fluoride, copolymers of
polyethylene fluoride and polyoxymethylene. Composite fibers and
combinations of different types of fiber of core and sheath structure,
multiple core 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.
As the thickness of the fiber, a relatively thin two denier or
less is preferable, but to increase 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 to 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 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 effect on the filtering performance, and the integrated
portions are disposed so as to be positioned uniformly over the
base layer surface.
To achieve the objects of the invention it is necessary that when
the average length from 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 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 washing is carried 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.
It is necessary that when all the fibers of a filtering layer in
the invention are 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 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 balancing of a high rejection and a high water
permeability.
In 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 sufficiently covered by fibers, gaps form between fiber bundles
and particle collecting is not satisfactory. 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 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 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 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 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 .mu.m 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 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 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 300 m/min, heating plate temperature stage one 210.degree.
C., stage two 190.degree. C., twister intersecting angle 110.degree.
and belt/thread speed ratio 1.39, for example when the false twisting
draw ratio is adjusted to 1.005 and the reset overfeed rate is 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%, a crimped fiber ratio
of 55.7% can be obtained. Percentage crimp is defined below under
the heading `Definitions of the Parameters`.
The number of fiber bundles 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 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/cm.sup.2. More preferable results
can be obtained when it is 50 to 500 stumps/cm.sup.2.
The total denier of fiber bundles per one stump of the filtering
layer, like the density of fiber bundles, 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 bundles 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 bundles is thicker than 2 denier 50
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 being separated in
the manufacturing process. In this case, because the size of an
ordinary composite fiber 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 50 to
15000 fibers/stump is preferable and 150 to 15000 fibers/stump is
more preferable. With ultra fine fibers under 0.5 denier 300 to
15000 fibers/stump and with ultra fine fibers under 0.2 denier 500
to 15000 fibers/stump is particularly preferable.
When the length of the fibers of the filtering layer becomes too
short, because the quantity of fibers which can contribute to filtering
becomes small, the particle collecting performance 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 2 mm to 20 mm. When it is 2 mm
to 15 mm, 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 standard conditions
by marking a strip-shaped test piece of width 3 cm with a 20 cm
spacing, applying a load of 12 kgf to the test piece in the length
direction thereof, applying a load of 6 kgf to the test piece in
the width direction thereof and measuring the length between the
markings after 90 minutes. The percentage elongation at this time
is obtained using the following equation:
Here, a is the length between the markings when an initial load
of 100 gf 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 in the warp direction of less than 8% is more preferable
and less than 6% is still more preferable. A value of percentage
elongation in the width direction slightly higher as compared with
the length direction is tolerable; but nevertheless preferably less
than 9% is good and less than 7% is more preferable.
To avoid the filter cloth greatly deforming and to obtain a filter
cloth having excellent dimensional 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 250 kgf/mm.sup.2, preferably
over 300 kgf/mm.sup.2 and more preferably over 350 kgf/mm.sup.2
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 0.6 gf/cm.sup.3. The apparent
density (gf/cm.sup.3) of the filter cloth is obtained by dividing
the weight(gf/m.sup.2) 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 apparent density of the filter cloth is preferably
0.2 to 0.6 gf/cm.sup.3. An apparent density of 0.25 to 0.5 gf/cm.sup.3
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 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.
This solid-liquid separating machine will now be described in further
detail 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 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 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 time 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 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, the 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 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.
In 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 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 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 filter cloth by
spraying spray water or intensifying washing by raising the spray
pressure when this degree of pressure drop exceeds a predetermined
value and a mechanism for stopping washing of the filter cloth or
returning 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-liquid separating 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.
With 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.
This 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.
That 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
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 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 from the unfiltered water supply side
or a mechanism such as the backwashing spray 26 which washes from
the filtered water 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 shown crossing the
periphery of the drum on which the filter cloth is disposed, but
in practice these pipes enter the inside of the drum for example
through axial centers of the side faces of 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 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 disc-like
structural 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
using 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 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 addition, 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
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 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 washing of
the filter cloth and thereby increase the amount processed and prevent
unfiltered water from overflowing at times when the concentration
of suspended solid in the unfiltered 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 mechanism for pressurizing
and supplying unfiltered water thereby having a mechanism 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
high 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
The 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) 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 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 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
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 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
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 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 formed on the filter cloth onto a mirror finished
roller and collected. In the evaluations, a surplus sludge of an
activated sludge process containing 5320 mg/liter of suspended solid
of average particle diameter 17.5 .mu.m was used as the unfiltered
water. The results obtained were as shown in Table 1.
From 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 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, wherein
T/L 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 particularly low. 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
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 permeability coefficient is extremely low and
the time taken to reach the limit water permeability coefficient
is also extremely low.
Examples 7 to 14, Comparative Examples 5 to 7
A 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 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. 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 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 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 approximately
11 mg/liter with an average particle diameter of 7.8 .mu.m was used
as the unfiltered water. The results obtained were as shown in Table
2.
TABLE 1 Water Time to Limit Fiber Bundle Filter Layer Permeability
Water Perm. Length L (1) Thickness T (2) Projected Area Rejecting
(4) Coefficient (5) Coefficient (6) (mm) (mm) T/L ratio (3) (times)
(%) (ml/cm.sup.2 sec) (hours) Example 1 2.5 0.3 0.12 10 90.1 11.4
1840 Example 2 3.0 1.5 0.50 45 91.5 10.3 1920 Example 3 8.5 1.4
0.16 34 93.4 8.5 1500 Example 4 10.5 7.0 0.67 246 98.6 9.3 1600
Example 5 19.0 2.9 0.15 278 99.7 7.5 1360 Example 6 19.5 11.3 0.58
343 99.4 7.1 1220 Comparative 1.5 0.23 0.015 3 75.4 3.9 400 Example
1 Comparative 1.5 1.2 0.8 5 55.8 9.8 1520 Example 2 Comparative
10.8 8.1 0.75 410 98.5 3.1 480 Example 3 Comparative 25.0 0.4 0.016
34 99.7 1.6 40 Example 4
TABLE 2 Fiber Bundle Filter Layer Crimped Fiber Length L (1) Thickness
T Stopping (4) Loss Water Head Ratio (7) (%) (mm) (2) (mm) T/L (%)
(8) (cm) Example 7 5.5 2.4 0.3 0.13 71 13.3 Example 8 11.3 2.4 1.1
0.46 74 10.4 Example 9 16.2 5.5 0.8 0.15 91 14.3 Example 10 16.5
18.2 6.4 0.35 87 15.8 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 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 Comparative 0.0 2.5 0.04 0.015
58 23.7 Example 5 Comparative 1.3 2.5 1.9 0.76 39 10.5 Example 6
Comparative 0.0 5.5 0.09 0.016 72 25.1 Example 7
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 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) Filtering Layer Thickness
Nine approximately 3 cm.times.3 cm test pieces are collected, and
three of these are stacked and placed on the pressuring table of
a compressive elasticity tester. A 2 cm.sup.2 probe is placed on
the test pieces with a load of 6 g and the thickness after ten seconds
is measured. The average value of three measurements is obtained
and divided by three to calculate the thickness T.sub.1 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 T.sub.2
of one piece is calculated by the same method as that in which T.sub.1
was obtained. The thickness T of the filtering layer is obtained
from the equation T=T.sub.1 -T.sub.2 (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 (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).
(4) Rejection
When the suspended solid concentrations of the unfiltered water
and the filtered water are respectively C.sub.1 and C.sub.2, the
rejection R is obtained from the equation R=(C.sub.1 -C.sub.2).div.C.sub.1.times.100.
The suspended solid concentrations are measured based on JIS K0102.
(5) Water Permeability Coefficient
The apparatus shown in FIG. 1 is used. A new sample is wetted by
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 500 mm is maintained a cock
is opened and 1 to 1.5 liters of filtered water are collected. The
time for which the cock is fully open is simultaneously measured,
and the water permeability coefficient K is obtained by the following
equation:
where W is the 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 (cm.sup.2). The initial water permeability
coefficients shown in Table 1 are water permeability coefficient
values of new samples tested before unfiltered water was passed
through them.
(6) A water permeability coefficient of 1 ml/cm.sup.2.sec is selected
as a limit water permeability coefficient. Carrying out filtering
of unfiltered water causes the 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 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.
(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.degree. C. in such a way that fibers do not become
entangled with each other.
B. The liquid with fibers dispersed therein is dripped onto a slide
glass 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 magnification is made 30 to 150 times, whereby the work
described below under D. 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 diameter is defined as R and a point on the fiber centerline
corresponding to a straight line distance of 200 times R from the
center point a of one end of the fiber is defined as b. Point a
and point b are connected by a straight line. When the straight
line ab and the centerline of the fiber cross or touch at a point
other than point a and point b, the fiber is counted as a crimped
fiber. When the straight line ab and the fiber do not cross or touch
at any point other than point a 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 straight line distance of 200
times R from c is defined as d. When the straight 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 ab or the straight line cd and the centerline of the fiber
are mutually superposed and touch at all points, but in this case
the fiber is not counted as a crimped fiber. Only cases wherein
the centerline of the fiber once leaves the straight line ab or
the straight line cd and then crosses or touches it again is the
fiber counted as a crimped fiber.
E. The determination described above in D is carried out for 100
fibers and the crimped fiber ratio is obtained using the following
equation:
(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
40 cm, number of turns 10 is made out of the thread being measured
using a hank winder.
B. The hank is hung on a hook and put into a transparent container
containing water at 20.degree. C.
C. For each of twenty doubled threads, an initial load of 0.002
gf per 1 denier is applied to the hank and after two minutes the
length L.sub.0 of the doubled hank is measured in the water.
D. Next, in addition to the initial load, a fixed load of 0.1 gf
is applied to the hank and the length L.sub.1 of the doubled hank
after two minutes is measured.
E. The percentage crimp is obtained using the following equation:
Industrial Applicability
With 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 superior dimension stability. In
addition, according to another construction of the invention, it
is possible to obtain a new filter cloth having excellent fine particle
collecting performance, resistance to fouling and durability and
also having superior water permeability which can be preferably
used for separating out suspended solid. In particular, even fine
particles of particle diameter below 20 to 30 .mu.m, 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 less than a few .mu.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 drinking
water, separation of coagulated matter in waste water treatment
and plankton separation of reservoirs and lakes and marshes. |