Abstrict
Provided are a dust-collecting filter cloth that comprises a base
fabric and web, wherein at least the web includes modified cross-section
fibers of polyphenylene sulfide; and a bag filter made of the filter
cloth. When fitted to an exhaust gas dust collector, the bag filter
involves little pressure loss and ensures increased dust-collecting
efficiency. As being resistant to heat and ensuring good dust-collecting
efficiency, the filter cloth is useful for dust collection.
Claims
What is claimed is:
1. A dust-collecting filter cloth comprising a base fabric and
a web, wherein said web comprises modified cross-section fibers
of polyphenylene sulfide, said modified cross-section fibers having
cross sections being other than circular or oval and selected from
the group consisting of Y, V, U, L, triangle and cross shaped sections,
wherein said web is disposed on both sides of the base fabric in
the form of a dust-collecting side web containing said modified
cross-section fibers of polyphenylene sulfide and an opposite side
web comprising round cross-section fibers of polyphenylene sulfide.
2. The dust-collecting filter cloth as claimed in claim 1, wherein
the web is a fibrous laminate and a surface layer of the dust-collecting
side web comprises modified cross-section fibers of polyphenylene
sulfide.
3. The dust-collecting filter cloth as claimed in claim 1, wherein
the dust-collecting side web comprises said modified cross-section
fibers of polyphenylene sulfide.
4. The dust-collecting filter cloth as claimed in claim 1, wherein
said dust-collecting side web comprises at least 25% by weight of
said modified cross-section fibers of polyphenylene sulfide blended
or combined with other fibers.
5. The dust-collecting filter cloth as claimed in claim 1, wherein
said dust-collecting side web further contains round cross-section
fibers of polyphenylene sulfide, but comprises at least 25% by weight
of said modified cross-section fibers of polyphenylene sulfide blended
or combined with said round cross-section fibers.
6. The dust-collecting filter cloth as claimed in claim 1, wherein
said dust-collecting side web comprises at least 50% by weight of
said modified cross-section fibers of polyphenylene sulfide blended
or combined with other fibers.
7. The dust-collecting filter cloth as claimed in claim 1, wherein
said modified cross-section fibers of polyphenylene sulfide have
a Y-shaped cross-section profile.
8. The dust-collecting filter cloth as claimed in claim 1, wherein
said modified cross-section fibers of polyphenylene sulfide have
a fineness of at most 5 d.
9. The dust-collecting filter cloth as claimed in claim 1, wherein
said modified cross-section fibers of polyphenylene sulfide have
a fineness of at most 2 d.
10. The dust-collecting filter cloth as claimed in claim 1, wherein
at least a surface layer of said dust-collecting side web is of
a fibrous laminate having a fineness gradation that decreases in
the direction of the thickness of the dust-collecting side web,
with the smaller at an upper layer of the laminate.
11. The dust-collecting filter cloth as claimed in claim 1, wherein
at least the surface of the dust-collecting side web has a fibrous
laminated structure of which the fineness gradation decreases in
the direction of the thickness of the dust-collecting side web,
to be smaller in the upper layer of the laminate structure.
12. The dust-collecting filter cloth as claimed in claim 1, wherein
the surface of said dust-collecting side web is subjected to at
least one treatment of singeing and rolling.
13. The dust-collecting filter cloth as claimed in claim 1, wherein
said dust-collecting side web is bonded to said base fabric by entangling
the fibers constituting the two.
14. A bag filter made of the dust-collecting filter cloth of claim
1.
15. The bag filter as claimed in claim 14, which is sewed with
sewing thread, and the surface of said dust-collecting filter cloth
is arranged as the dust-collecting surface of said bag filter.
16. The bag filter as claimed in claim 14, which is sewed with
sewing thread of polyphenylene sulfide fibers.
Description TECHNICAL FIELD
The present invention relates to a dust-collecting filter cloth
and a bag filter.
More precisely, the invention relates to a dust-collecting filter
cloth and a bag filter having good heat resistance and good dust-collecting
efficiency.
BACKGROUND ART
The filter for air purification includes one for internal filtration
and another for surface filtration. The filter for surface filtration
is used in duct collectors. For surface filtration, the filter first
catches dust on its surface to form a dust layer thereon, and the
dust layer then continues to catch dust thereon to increase its
thickness. After its thickness has increased to a certain degree,
the dust layer is removed from the surface of the filter. With that,
the filter again begins to catch dust to form a dust layer on its
surface, and this is repeated.
For the filter for surface filtration, heretofore used is non-woven
fabric. For this, there are known a needle-punched felt of which
the surface is smoothed by calendering; and a needle-punched felt
coated with a silicone resin or a fluororesin to have increased
lubricity for dust removal from it.
Regarding bag filters made of polyphenylene sulfide fibers of the
type, a filter cloth for bag filters was proposed in Japanese Patent
Laid-Open No. 57026/1997, which comprises a textile base fabric
of polyphenylene sulfide fibers and a web of polyphenylene sulfide
fibers. In Japanese Patent No. 2,576,599, proposed was a filter
cloth for bag filters, which comprises a textile base fabric of
long polyphenylene sulfide fibers and a web of polyphenylene sulfide
fibers, with its surface being laminated with a porous, polyphenylene
sulfide film. In Japanese Patent Laid-Open No. 165729/1998, proposed
was a filter cloth for bag filters, in which the fineness of the
polyphenylene sulfide fibers for the web is controlled to be at
most 1.8 d.
However, the conventional filter cloths are problematic in that
the amount of dust capable of being caught by them is small. This
is because the cross-section profile of the single fibers used in
them is circular, and the contact area thereof with dust is small.
The filter cloth prepared by laminating a resin layer on a needle-punched
felt has a high dust-collecting efficiency and it is easy to remove
dust from it. However, this is still defective in that it the pressure
loss in using it is large.
DISCLOSURE OF THE INVENTION
The object of the present invention is to provide a high-efficiency
dust-collecting filter cloth for bag filter units for exhaust gas
dust collection, and to provide a bag filter comprising the filter
cloth.
The dust-collecting filter cloth of the invention that attains
the object is essentially constituted by any of the following:
A dust-collecting filter cloth comprising a base fabric and a web,
wherein at least the web comprises modified cross-section fibers
of polyphenylene sulfide; or
A dust-collecting filter cloth comprising a base fabric and a web
with the web being disposed on the both surfaces of the base fabric,
wherein at least the web comprises modified cross-section fibers
of polyphenylene sulfide.
The bag filter of the invention is essentially constituted by the
following:
A bag filter comprising the above-mentioned dust-collecting filter
cloth.
BEST MODES OF CARRYING OUT THE INVENTION
The dust-collecting filter cloth and the bag filter of the invention
are described in detail hereinunder.
To attain the object as above, or that is, to obtain a high-efficiency
dust-collecting filter cloth and a bag filter comprising it, we,
the present inventors have assiduously studied. Incidentally, we
tried a web comprising modified cross-section fibers of polyphenylene
sulfide for dust-collecting filter cloths, and, as a result, have
succeeded in solving all the problems with conventional filter cloths.
The polyphenylene sulfide fibers for use in the invention have
been known to have good heat resistance, chemical resistance and
hydrolysis resistance, and at least 90% of the constituent units
of the fibers are of a polymer having phenylene sulfide structural
units of --(C.sub.6 H.sub.4 --S)--. Accordingly, the fibers could
form dust-collecting filter cloths having good heat resistance,
chemical resistance and hydrolysis resistance, but it is still impossible
to directly improve the filter cloths comprising them. Accordingly,
in the present invention, modified cross-section fibers of polyphenylene
sulfide are used for forming the web for dust-collecting filter
cloths. Not involving the problem of pressure loss, the dust-collecting
efficiency of the filter cloth of the invention is thereby significantly
increased.
The web of 100% modified cross-section fibers of polyphenylene
sulfide is preferred for increasing the dust-collecting efficiency
of filter cloths, but from the economical viewpoint, the web of
the filter cloth of the invention may be made of modified cross-section
polyphenylene sulfide fibers blended or combined with round cross-section
polyphenylene sulfide fibers. In that case, the proportion of the
modified cross-section polyphenylene sulfide fibers is preferably
at least 25% by weight, more preferably at least 50% by weight in
view of the dust-collecting efficiency of the filter cloth.
The modified cross-section referred to herein for the profile of
the polyphenylene sulfide fibers includes Y-shaped, V-shaped, U-shaped,
L-shaped, triangular or cross-shaped section profiles, excluding
circular or oval section profiles. Of those, preferred are Y-shaped
cross-section fibers, as they are easy to card.
The fibers to constitute the web of the dust-collecting filter
cloth of the invention preferably have a fineness of at most 5 d,
more preferably at most 2 d, as they achieve good dust-collecting
efficiency. Also preferably, at least the surface layer of the web
or the surface of the web that contains the surface layer is composed
of the fibers of which the fineness falls within the defined range.
The fibers having a fineness of at most 5 d can form a tight felt
structure, and the dust-collecting capability of the filter cloth
comprising them is therefore enhanced. More preferably, the fineness
of the fibers constituting the web is graded in the direction of
the thickness of the web. Concretely, it is desirable that the fibers
are integrated to form a laminate-structured web in such a manner
that their fineness reduces by gradation in the direction of the
thickness of the web to be smaller in the upper layer of the laminate
structure. Needless-to-say, the fineness gradation referred to herein
may be for the mean fineness of the blended or combined fibers that
constitute the web. For better results, however, it is more desirable
that each of the laminated fiber layers of the web have the same
fineness and the fineness of the fiber layers is graded in the manner
defined herein.
Any fibers will do for the core, base fabric of the filter cloth
of the invention. In view of their heat resistance, however, preferred
are fluorine-containing fibers, PPS fibers, polyimide fibers, glass
fibers and the like. In view of their capability to be readily entangled
with the web, more preferred are PPS fibers. The base fabric is
a rough textile. Its warp density preferably falls between 15 and
40/inch, more preferably between 20 and 30/inch; and its weft density
preferably falls between 10 and 30/inch, more preferably between
15 and 25/inch.
In the filter cloth of the invention, the web is bonded to the
base fabric by entangling the fibers constituting the two. For entangling
them, employed is at least one treatment of needle punching and
water-jet punching. In view of the strength in entangling them,
the former needle punching is preferred. However, depending on the
pressure loss through the filter cloth and on the dust-collecting
ability of the filter cloth, the latter water-jet punching will
be preferred. As the case may be, combining the two treatments,
needle punching and water-jet punching will be preferred, as producing
well-balanced filter cloths. It is therefore desirable that the
treatment for fiber entanglement is appropriately selected and employed
herein.
Preferably, the surface of the dust-collecting filter cloth of
the invention is subjected to at least one treatment of singeing
and rolling. In case where the filter cloth is specifically desired
to have an increased dust-collecting efficiency, it is preferably
subjected to the two treatments, singeing and rolling. Concretely,
the surface of the filter cloth is singed with a burner or an IR
heater, and then pressed against a hot roll. Having been thus treated,
at least a part of the fibers constituting the surface of the filter
cloth are fused or packed tightly, or as the case may be, calendered
through the combined two treatments, whereby the dust-collecting
efficiency of the thus-treated filter cloth can be improved to a
great extent.
The bag filter of the invention can be produced by sewing the dust-collecting
filter cloth in such a manner that the surface of the filter cloth
forms the dust-collecting surface of the sewed bag. The sewing thread
for it is preferably made of the same fibers as those of the base
fabric, chemical-resistant and heat-resistant polyphenylene sulfide
fibers.
EXAMPLES
The invention is described concretely with reference to the following
Examples.
Example 1
Round cross-section short fibers of polyphenylene sulfide having
a fineness of 2.0 d, a fiber length of 51 mm, and a number of crimps,
14/inch were spun into double yarn having a single yarn count of
20 s, and a number of strands, 2. This was woven into plain fabric
of polyphenylene sulfide. Next, while being overfed at 220.degree.
C., this was heat-set for 45 seconds to be a base fabric having
a warp density of 26/inch and a weft density of 18/inch. Y-shaped
cross-section fibers and round cross-section fibers all of polyphenylene
sulfide having a fineness of 2.0 d, a fiber length of 51 mm, and
a number of crimps, 14/inch were blended in a ratio by weight of
30/70 and formed into a web, and the web was laminated on the dust-collecting
surface of the base fabric. On the back surface of the base fabric,
laminated was a web of round cross-section fibers of polyphenylene
sulfide having a fineness of 2.0 d, a fiber length of 51 mm, and
a number of crimps, 14/inch. With that, this was needle-punched
to be a needle felt. The felt was singed with a burner, and then
pressed against a hot roll having a surface temperature of 200.degree.
C. The filter cloth thus obtained had a Metsuke (unit weight) of
552 g/m.sup.2 and a thickness of 1.72 mm.
Example 2
In the same manner and under the same condition as in Example 1,
herein obtained was a filter cloth having a Metsuke of 543 g/m.sup.2
and a thickness of 1.77 mm. In this, however, the ratio by weight
of the Y-shaped cross-section polyphenylene sulfide fibers to the
round cross-section polyphenylene sulfide fibers was 90/10.
Example 3
In the same manner and under the same condition as in Example 1,
herein obtained was a filter cloth having a Metsuke of 548 g/m.sup.2
and a thickness of 1.76 mm. In this, however, the Y-shaped cross-section
polyphenylene sulfide fibers constituting the web to be on the dust-collecting
surface of the base fabric had a fineness of 1.5 d, a fiber length
of 51 mm, and a number of crimps, 14/inch.
Example 4
In the same manner and under the same condition as in Example 2,
herein obtained was a filter cloth having a Metsuke of 548 g/m.sup.2
and a thickness of 1.76 mm. In this, however, the Y-shaped cross-section
polyphenylene sulfide fibers constituting the web to be on the dust-collecting
surface of the base fabric had a fineness of 4.0 d, a fiber length
of 51 mm, and a number of crimps, 14/inch.
Comparative Example 1
Round cross-section polyphenylene sulfide filaments having a fineness
of 4 d and a number of filaments, 100 were woven into plain fabric
of polyphenylene sulfide. Next, while being overfed at 220.degree.
C., this was heat-set for 45 seconds to be a base fabric having
a warp density of 26/inch and a weft density of 26/inch. Round cross-section
polyphenylene sulfide fibers having a fineness of 2.0 d, a fiber
length of 51 mm, and a number of crimps, 14/inch were formed into
a web, and the web was laminated on the both surfaces of the base
fabric. With that, this was needle-punched to be a needle felt.
The felt was singed with a burner, and then pressed against a hot
roll having a surface temperature of 200.degree. C. The filter cloth
thus obtained had a Metsuke of 568 g/m.sup.2 and a thickness of
1.71 mm.
Comparative Example 2
Round cross-section short fibers of polyethylene terephthalate
having a fineness of 2.0 d, a fiber length of 51 mm, and a number
of crimps, 14/inch were spun into double yarn having a single yarn
count of 20 s, and a number of strands, 2. This was woven into plain
fabric of polyethylene terephthalate. Next, while being overfed
at 220.degree. C., this was heat-set for 45 seconds to be a base
fabric having a warp density of 26/inch and a weft density of 18/inch.
Y-shaped cross-section fibers of polyethylene terephthalate having
a fineness of 1.5 d, a fiber length of 51 mm, and a number of crimps,
14/inch and round cross-section fibers of polyethylene terephthalate
having a fineness of 2.0 d, a fiber length of 51 mm, and a number
of crimps, 14/inch were blended in a ratio by weight of 90/10 and
formed into a web, and the web was laminated on the dust-collecting
surface of the base fabric. On the back surface of the base fabric,
laminated was a web of round cross-section fibers of polyethylene
terephthalate having a fineness of 2.0 d, a fiber length of 51 mm,
and a number of crimps, 14/inch. With that, this was needle-punched
to be a needle felt. The felt was singed with a burner, and then
pressed against a hot roll having a surface temperature of 200.degree.
C. The filter cloth thus obtained had a Metsuke of 561 g/m.sup.2
and a thickness of 1.71 mm.
The dust-collecting capability of the laminates produced in Examples
1 and 2 and Comparative Example 1 was measured according to the
method mentioned below. The result is given in Table 1.
[Dust-Collecting Capability]
Dust of group 10 stipulated in JIS-Z-8901 was used. Air containing
the dust was filtered through each laminate until the pressure loss
through it increased by 20 mmAq. The dust concentration in the air
tested was 12 g/m.sup.3, and the filtration air flow rate was 1.5
m/min. From the amount of the dust in the air applied to the filter
cloth (A) and the amount of the dust having passed through the filter
cloth (B), the dust-collecting capability of the filter cloth was
obtained according to the following equation.
wherein, A indicates the amount of the dust in the air applied
to the filter cloth; B indicates the amount of the dust having passed
through the filter cloth.
TABLE 1 Example 1 Example 2 Comp. Example 1 Constitution of Filter
Dust-Collecting 2.0 d-Y 30% 2.0 d-Y 90% 2.0 d-Round 100% Cloth Surface
2.0 d-Round 70% 2.0 d-Round 10% Back Surface 2.0 d-Round 100% Dust-Collecting
Capability (%) 99.94 99.98 99.78
In the table; 2.0 d-Y means 2.0 denier Y-shaped cross-section fibers,
2.0 d-Round means 2.0 denier round cross-section fibers.
As in Table 1, the duct-collecting capability of the filter cloths
of Examples 1 and 2 is higher than that of the filter cloth of Comparative
Example 1.
The dust-collecting filter cloths of Example 1 and Comparative
Example 1 were separately sewed to form bag filters, for which the
sewing thread used was prepared by spinning the polyphenylene sulfide
short fibers of Example 1 having a fineness of 2.0 d, a fiber length
of 51 mm, and a number of crimps, 14/inch into double yarn having
a single yarn count of 20 s, and a number of strands, 2. The bag
filters had a diameter of 20 cm and a length of 4 m. Fitted to an
exhaust gas dust collector, each bag filter was tested for the following:
[Concentration of Dust Leak]
Dust of group 10 stipulated in JIS-Z-8901 was used. Air containing
the dust was filtered through the bag filter until the pressure
loss through it increased by 20 mmAq. The dust concentration in
the air tested was 12 g/m.sup.3, and the filtration air flow rate
was 1.5 m/min. From the overall amount of the dust having passed
through the bag filter (A) and the overall amount of the air having
passed through it (B), the concentration of the dust leak through
the bag filter was obtained according to the following equation.
wherein, A indicates the overall amount of the dust having passed
through the bag filter (mg); B indicates the overall amount of the
air having passed through the bag filter (m.sup.3).
The concentration of dust leak through each bag filter is as follows:
Bag filter of cloth of Example 1:1.29 mg/M.sup.3. Bag filter of
cloth of Comparative Example 1:4.62 mg/m.sup.3.
As in the above, the concentration of dust leak through the bag
filter of the dust-collecting filter cloth of Comparative Example
1 is about 3.5 times that of the filter cloth of Example 1.
Further, the dust-collecting filter cloths of Examples 1 to 4 and
Comparative Examples 1 to 3 were separately sewed to form bag filters,
for which the sewing thread used was prepared by spinning the polyphenylene
sulfide short fibers of Example 1 having a fineness of 2.0 d, a
fiber length of 51 mm, and a number of crimps, 14/inch into double
yarn having a single yarn count of 20 s, and a number of strands,
2. The bag filters had a diameter of 20 cm and a length of 4 m.
With each bag filter being fitted thereto, an exhaust gas dust collector
was continuously run for 1000 hours to test the bag filter. The
test data are given in Table 2.
[Concentration of Dust Leak]
After the dust collector was run for 1000 hours, the concentration
of the dust leak through the bag filter was obtained from the overall
amount of the dust having passed through the bag filter (A) and
the overall amount of the exhaust gas having passed through it (B),
according to the following equation.
wherein, A indicates the overall amount of the dust having passed
through the bag filter (mg);
B indicates the overall amount of the exhaust gas having passed
through the bag filter (m.sup.3).
[Pressure Loss after Dust Removal]
After the dust collector was run for 1000 hours, the dust having
adhered onto the bag filter was removed by applying a pressure of
3 kg/cm.sup.2 thereto, and then the pressure loss through the bag
filter was measured. Briefly, a current of air was passed through
the bag filter at a flow speed of 1.5 m/min, and the pressure difference
between the pressure just after the bag filter and the atmospheric
pressure was measured with a manometer (from Yamamoto Electric).
This indicates the pressure loss.
[Strength Retention]
After the dust collector was run for 1000 hours, the strength retention
of the bag filter was obtained from the tensile strength at break
of the bag filter after the running test (A) and the strength at
break of the fresh bag filter before the running test (B). To measure
the tensile strength at break of the bag filter, used was a Tensilon
tensile strength tester. The cloth sample tested had a width of
50 mm; the distance between the fixtures was 100 mm; and the stress
rate was 100 mm/min.
wherein, A indicates the tensile strength at break of the sample
cloth of the bag filter after the 1000-hour running test (kgf/5
cm); B indicates the tensile strength at break of the sample cloth
of the fresh bag filter before the test (kgf/5 cm).
[Exhaust Gas Dust Collector Running Condition] Dust Concentration:
8 g/m.sup.3 Filtration Air Flow Rate: 1.1 m/min Exhaust Gas Temperature:
160.degree. C. Exhaust Gas Oxygen Concentration: 8.9 vol. % Exhaust
Gas H.sub.2 O Concentration: 39.0 vol. % Exhaust Gas SOx concentration:
72 ppm Exhaust Gas NOx concentration: 126 ppm Exhaust Gas HCl concentration:
168 ppm
TABLE 2 Example 1 Example 2 Example 3 Example 4 Comp. Ex. 1 Comp.
Ex. 2 Constitution Dust- 2.0 d-Y: 30% 2.0 d-Y: 90% 1.5 d-Y: 30%
4.0 d-Y: 90% 2.0 d-Round: 1.5 d-Y: 90% of Filter Collecting 2.0
d-Round: 70% 2.0 d-Round: 10% 2.0 d-Round: 70 % 2.0 d-Round: 10%
100% 2.0 d-Round: 10% Cloth Surface Back Surface 2.0 d-Round: 100%
Material of Polyphenylene Sulfide PET Filter Cloth Concentration
of 0.61 0.45 0.30 0.88 2.32 0.33 Dust Leak (mg/m.sup.3) Pressure
Loss 21.3 19.5 16.3 24.2 46.1 18.2 after Dust Removal (mmAq) Strength
Retention 88.9 88.4 87.2 88.5 89.6 48.2 after 1000-hour running
test (%)
In the table; 2.0 d-Y means 2.0 denier Y-shaped cross-section fibers,
2.0 d-Round means 2.0 denier round cross-section fibers, 1.5 d-Y
means 1.5 denier Y-shaped cross-section fibers, 4.0 d-Y means 4.0
denier Y-shaped cross-section fibers, PET means polyethylene terephthalate.
As in Table 2, the concentration of dust leak through the bag filters
of the cloths of Examples 1 to 4 is low, and the pressure loss through
them after dust removal is low. In addition, the strength retention
of the bag filters after the 1000-hour running test was high.
INDUSTRIAL APPLICABILITY
Not involving the problem of pressure loss through it, the dust-collecting
efficiency of the filter cloth of the invention is high. The bag
filter made of the dust-collecting filter cloth of the invention
realizes a dust collector having improved dust-collecting efficiency.
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