JP2003117319A - Filter cloth - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a filter cloth having excellent physical characteristics such as rigidity and wear resistance at a high temperature to be suitably used as a filter cloth particularly for a bag filter and a pleated filter. SOLUTION: The filter cloth comprises polyphenylene sulfide fibers and contains polyphenylene sulfide fibers having the deniers of single fibers ranging from 2.5 dtex to 17 dtex.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter cloth, a bag filter, and a pleated filter which are made of polyphenylene sulfide fiber (hereinafter referred to as PPS fiber) and have excellent physical properties such as rigidity at high temperature and abrasion resistance. It is about.

The filter cloth of the present invention is, for example, a garbage incinerator,
It is preferably used as a filter cloth for filtering high temperature exhaust gas discharged from a coal boiler, a metal blast furnace, or the like.

[0003]

2. Description of the Related Art A filter cloth used for an exhaust gas bag filter attached to a refuse incinerator, a coal boiler, a metal smelting furnace, etc. has a high exhaust gas temperature, and the exhaust gas is represented by SOx, NOx, etc. Various chemicals and H ₂
Since it contains water such as O, heat resistance, chemical resistance and hydrolysis resistance are required.

Further, in recent years, in order to secure a larger filtration area in a limited space, a heat-resistant pleated filter in which a heat-resistant filter cloth is pleated is proposed.

Conventionally, there are PPS fibers, meta-aramid fibers, polytetrafluoroethylene fibers, polyimide fibers and the like as fibers excellent in heat resistance and chemical resistance. Using these materials, the base cloth and the web are combined. However, a filter cloth made of a non-woven fabric obtained by entangling fibers with a needle punch or a jet of water has been used.

Particularly, PPS fibers are excellent in well-balanced properties such as heat resistance, chemical resistance, hydrolysis resistance and strength.
It is suitable as a fiber constituting a filter cloth used for a bag filter. Compared with PPS fibers, for example, meta-aramid fibers and polyimide fibers are inferior in hydrolysis resistance, and polytetrafluoroethylene fibers are inferior in strength.

In general, these heat-resistant filters are chemically deteriorated by high temperature exhaust gas and chemicals contained in the exhaust gas when used in a refuse incinerator and the like, and in addition to this, pressure loss during exhaust gas filtration and during backwashing. At the same time, physical deterioration due to wear and bending due to the pulse jet of (1) progresses at the same time.

Therefore, the filter cloth used for the bag filter and the pleat type filter is required to have physical properties such as abrasion resistance in addition to the above-mentioned heat resistance, chemical resistance and hydrolysis resistance. Particularly in a pleat type filter, since it is necessary to maintain the shape of the pleat at high temperature, a filter cloth having high rigidity at high temperature is required.

In recent years, as a filter cloth having good dust peeling performance and dust collecting performance, PPS fibers having a single fiber fineness of 1.8 d (2.0 dtex) or less are arranged in a surface layer in JP-A-10-165729. Filter cloths have been proposed. However, although they have good dust peeling performance and dust collecting performance, they have low rigidity at high temperatures and insufficient wear resistance, so in actual use, pressure loss during exhaust gas filtration and backwashing There was a problem that abrasion and bending fatigue occurred due to the pulse jet, and the physical deterioration of the filter cloth progressed in addition to the chemical deterioration, resulting in damage. In addition, since it has low rigidity at high temperature, it was difficult to use it as a pleated filter.

[0010]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned problems of the prior art and to provide a filter filter made of PPS fiber having excellent physical properties such as rigidity and abrasion resistance at high temperature. Providing cloth and bag filters and pleated filters.

[0011]

Means for Solving the Problems The present invention for achieving the above object comprises a filter cloth made of PPS fibers and containing PPS fibers having a single fiber fineness within a range of 2.5 dtex to 17 dtex. It is characterized by.

The bag filter and the pleated filter of the present invention are characterized by being constituted by such a filter cloth.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The PPS fiber used in the present invention is known to have excellent heat resistance, chemical resistance and hydrolysis resistance.

It is important that the filter cloth of the present invention contains PPS fibers having a single fiber fineness within the range of 2.5 dtex to 17 dtex. 3.0 dtex to 10 dt
It is further preferred to include PPS fibers that are in the ex range. Since the PPS fibers having such a large fineness have high rigidity, the rigidity of the filter filter cloth formed of these fibers is also significantly improved. Furthermore, the above fineness makes PP less susceptible to physical deterioration due to abrasion and bending.
Since S fibers can be obtained, it is possible to obtain excellent rigidity and wear resistance even in a filter cloth made of these fibers.

The filter cloth of the present invention is preferably composed of a non-woven fabric including a woven fabric and a web. In general, a web is called a non-woven fabric in which fibers are entangled with each other by needle punching or jet water flow, and this non-woven fabric has void portions uniformly dispersed, which is superior to a woven fabric in filtration characteristics. Therefore, it is preferably used as a filter cloth. However, only a nonwoven fabric composed of a web is not preferable because the tensile strength and the dimensional stability are low and the physical properties are not sufficient. Therefore, it is preferable that the web and the woven fabric are entangled and integrated by needle punching or jet water flow, whereby a filter filter cloth having excellent filtration characteristics and physical characteristics such as abrasion resistance and bending fatigue resistance. Can be obtained. The woven fabric includes a woven fabric made of spun yarn of PPS fiber, a woven fabric made of PPS multifilament, a fluorinated multifilament, spun yarn or a fabric made of slit yarn, and a spun yarn of para aramid fiber or multifilament. It is possible to use a woven fabric made of a highly functional organic fiber such as a spun yarn of polyimide fiber or a multifilament, or a woven fabric made of an inorganic fiber such as a glass fiber or a carbon fiber. It is preferable to use a spun yarn of PPS fibers or a woven fabric composed of multifilaments from the viewpoint of hydrolyzability and the like. P of 2.5 dtex or more is used.
It is more preferable to use a woven fabric made of spun yarn of PS fiber or multifilament.

PPS constituting the filter cloth of the present invention
The fiber preferably has a bending resistance of 0.022 μN / dtex or more based on the Gurley method specified in JIS L-1096. The bending resistance referred to here is an index for indicating the rigidity of an object, and the higher this value, the higher the rigidity. The bending resistance of PPS fiber is 0.022μN / dt
When it is less than ex, the rigidity of the filter cloth becomes low, and when used at high temperature, the filter cloth is deformed due to pressure loss during filtration and pressure loss during backwashing, which causes bending fatigue of the filter cloth. Since the filter cloth may be damaged, it is not preferable. Especially in pleated filters, it is necessary to maintain the shape of pleats at high temperatures,
If the bending resistance is less than 0.022 μN / dtex, the pleats may be deformed, the filtration area may be reduced, and the pressure loss may increase rapidly, which is not preferable.

The filter cloth of the present invention is obtained by containing the PPS fiber having high bending resistance as described above, and the bending resistance of the filter cloth is 65 mN-1500.
It is preferably within the range of mN. If the bending resistance of the filter cloth is less than 65 mN, the rigidity of the filter cloth becomes low, and bending fatigue of the filter cloth may be induced when used at high temperature, and the filter cloth may be damaged, which is not preferable. . Further, if the bending resistance exceeds 1500 mN, it is not preferable because the filter filter cloth is inferior in handleability when the filter cloth is installed in a dust collector or is transported. In particular, in the pleated filter, the shape retention of the pleats at high temperature is required, so that the filter filter cloth preferably has a bending resistance of 400 mN to 1500 mN. If the bending resistance of the filter cloth is less than 400 mN, the pleats may be deformed, the filtration area may be reduced, and the pressure loss may increase rapidly, which is not preferable.
If the bending resistance exceeds 1500 mN, pleating becomes difficult, which is not preferable.

The hanging length of the filter cloth of the present invention at 170 ° C. is preferably 30 mm or less.
The length of the filter cloth hanging down at 170 ℃ is 30m
If it is longer than m, the rigidity of the filter cloth at high temperature is low, and the filter cloth is deformed due to pressure loss during filtration and pressure during backwashing, causing bending fatigue of the filter cloth and damaging the filter cloth. There is a risk of this being undesirable. In particular, when used as a pleated filter, the hanging length of the filter cloth is preferably 10 mm or less. If the hanging length exceeds 10 mm, the pleated shape may be deformed and the pressure loss may increase rapidly, which is not preferable. The method for measuring the hanging length of the filter cloth of the present invention is as follows.

A measuring piece having a length of 100 mm and a width of 20 mm is taken out from the filter cloth to measure the hanging length. As shown in FIG. 1, the taken-out measuring piece 1 has a portion of 50 mm from one end 2 of the measuring piece 1 on the upper surface of the rectangular parallelepiped measuring piece mounting block 3 by a mechanical means, or
Fix with adhesive. At this time, the other end 4 of the measuring piece 1
Is protruding from the block 3. The block 3 on which the measurement piece 1 is set is left in an atmosphere at 170 ° C. for 1 hour. During this time, the portion 5 of the measurement piece 1 protruding from the block 3 softens and hangs down. At this time, the length L in the vertical direction between the position of the end 4 of the measurement piece 1 and the plane 6 including the upper surface of the block 3 (drawn by a dotted line in FIG. 1) is measured, and this length L is It should be the hanging length. The rigidity of the filter cloth at high temperature can be evaluated by the size of the hanging length.

JIS L10 of the filter cloth of the present invention
The retention of tensile strength after the filter is abraded by the 96 Taber method is preferably 70% or more. If the retention of tensile strength after abrasion is less than 70%, when used as a bag filter, the filter cloth becomes a retainer that forms the skeleton of the bag filter due to pressure loss during filtration and pressure during backwashing. It is not preferable because it may come into contact with a so-called metal rod and the tensile strength may be reduced due to abrasion and the filter cloth may be damaged. The method of measuring the strength retention after abrasion of the filter cloth of the present invention is as follows.

The filter cloth is stipulated in JIS L-1096.
In accordance with the Taber type method wear strength, No. CS
Using -10, load the back side of the filter cloth at a load of 1,500 g for 5,0
It has been worn for 00 times, and the length of this filter cloth is 60 mm,
A test piece having a width of 30 mm is cut out, set in a tensilon measuring machine so as to sandwich a worn portion so as to have a grip interval of 25 mm, and the maximum strength when pulled at a pulling speed of 100 mm / min is measured. Next, the filter cloth before being worn is pulled under the same conditions as above, the maximum strength is measured, and the strength retention rate after wear is calculated by the following formula. The back surface referred to here means the surface on the side opposite to the surface on which dust accumulates when used as a filter. (Strength retention after wear [%]) = (Maximum strength after wear
[N]) / (maximum strength before abrasion [N]) × 100 Furthermore, the filter cloth of the present invention can sufficiently maintain its performance even in a high temperature environment. That is, the filter cloth of the present invention is
Heat-treated for 160 hours, and then the above JIS L1096
It is preferable that the retention rate of the tensile strength after the filter is abraded by the method according to the Taber method to 20% or more with respect to the tensile strength of the filter filter cloth before being treated in air at 180 ° C. . Further, it is more preferably 40% or more. The retention of tensile strength after abrasion is 2
If it is less than 0%, the filter cloth may be damaged by abrasion with the retainer when used as a bag filter, which is not preferable. The method for measuring the strength retention of the filter cloth after heat treatment and abrasion of the present invention is as follows.

The filter cloth is placed in an oven at 180 ° C.
After the heat treatment in the air for 2,160 hours, the abrasion treatment and the maximum value of tensile strength are measured by the same method as the method for measuring the strength retention after abrasion. Next, the strength retention of the filter cloth after heat treatment and abrasion is calculated by the following formula.

(Temperature retention of filter cloth after heat treatment and abrasion [%]) = (Maximum tenacity after heat treatment and abrasion
[N]) / (maximum strength before heat treatment [N]) × 100 The non-woven fabric constituting the heat-resistant filter filter fabric of the present invention is a known process for producing non-woven fabric, for example, needle punched non-woven fabric, wet non-woven fabric, spun lace non-woven fabric. , A spun bond nonwoven fabric, a melt blown nonwoven fabric, a resin bond nonwoven fabric, a chemical bond nonwoven fabric, a thermal bond nonwoven fabric, a tow opening type nonwoven fabric and an air-laid nonwoven fabric. Among these, when used as a filter filter cloth, it is preferable that the filter cloth is manufactured by a method of manufacturing a needle punched nonwoven fabric or a spunlace nonwoven fabric from the viewpoint of tensile strength of the filter filter cloth.

Furthermore, it is preferable that the filter cloth of the present invention has a fluororesin attached to at least one surface thereof. It is particularly preferred that the fluororesin is attached by coating. This makes it possible to further improve the physical durability of the filter cloth of the present invention.
Generally, a fluorine-based resin is known as a resin having excellent heat resistance, chemical resistance, and hydrolysis resistance, but in addition to these characteristics, it is also known as a resin having a very low friction coefficient, In recent years, sliding materials and bearings made of fluorocarbon resin have been manufactured. Also in the filter filter cloth of the present invention, by coating the surface of the filter cloth with a fluororesin, it becomes possible to reduce the friction coefficient of the filter cloth surface, thereby reducing wear due to friction with a retainer or the like. It becomes possible. Further, by coating the fluororesin, the fibers of the surface layer of the filter cloth are bound to each other, and the entanglement and peeling of the fibers due to physical friction are reduced, so that the wear durability is significantly improved. As the surface of the filter cloth coated with the fluororesin, it is preferable to coat the back surface of the filter cloth, that is, the surface opposite to the surface on which dust is accumulated, in order to significantly improve the physical deterioration.

The filter cloth of the present invention can improve the dust peeling performance by fusing a part of the fibers on the surface on which dust is accumulated. As a method for fusing the fibers on the surface of the filter cloth, a method such as quilling treatment or mirror processing can be used.

However, in some coal boilers or the like, the dust concentration may be high or the particle size of the dust may be very small. As described above, the surface of the filter cloth may be subjected to treatment such as burning treatment. Even if it is applied, the dust may not be removed and the pressure loss may increase. In such a case, a fine porous film or the like is provided on the surface of the filter filter cloth on which dust is accumulated to prevent the dust from entering the inside of the filter filter cloth, thereby improving the dust releasability. It is possible. As the microporous membrane, for example,
A fluorinated microporous film having good heat resistance and chemical resistance can be used.

The filter cloth thus obtained is sewn into a bag shape and is suitably used as a bag filter for collecting exhaust gas from a refuse incinerator, a coal boiler, a metal smelting furnace or the like which requires heat resistance. To be done.

When the dust collector is installed in a limited space, or when there is a demand for increasing the amount of filtered air, the filter cloth is pleated and further sewn or glued. It is also possible to form a bag and use it as a pleated filter. When using it as a pleated filter, in order to further improve the rigidity of the filter cloth, phenol resin,
It is also possible to impregnate a binder resin typified by an epoxy resin, an acrylic resin, or the like to constrain the fibers constituting the filter cloth. The processing method for impregnating the binder resin is not particularly limited, but a known method such as dipping, coating, or spraying can be used.

[0029]

The present invention will be described in more detail with reference to the following examples. The bending resistance of the PPS fiber and the bending resistance of the filter filter cloth are determined by the following methods. The sagging length, the tensile strength retention rate after abrasion and the heat retention coefficient of the filter filter cloth after heat treatment and abrasion are determined by the above method. It was measured. A. Flexibility of PPS fiber: length of PPS fiber is 50 mm,
Take out so as to have a total fineness of 2000 dtex and JIS
The bending resistance was measured by the Gurley method specified in -L1096, and a measurement value A was obtained. Next, the bending resistance per 1 dtex was calculated by the following formula. (PPS fiber bending resistance [μN / dtex]) = (measured value A [μ
N]) / 2000 [dtex] B. Bending Resistance of Filter Filter Cloth: A measurement piece having a length of 50.8 mm and a width of 25.4 mm was cut out from the filter filter cloth, and the measurement piece was measured by the Gurley method specified in JIS-L1096.

Example 1 PPS short fibers having an average single fiber fineness of 3.0 dtex, a cut length of 51 mm, and a crimp number of 14 / 2.54 cm (Toray Industries, Inc.)
Manufactured by "Torcon (R)" was used to obtain a spun yarn having a single yarn count of 20 s and a combined yarn number of 2. This is a plain weave and the warp density is 2
A PPS spun yarn woven fabric having 6 yarns / 2.54 cm and a weft yarn density of 18 yarns / 2.54 cm was obtained. Both sides of this woven fabric have an average single fiber fineness of 3.0 dtex, a cut length of 51 mm, and a crimp number of 14
A web using PPS short fibers of 2.54 cm / piece (“Torucon (R)” manufactured by Toray Industries, Inc.) is laminated, and the fabric and the web are entangled by needle punching, and the basis weight is 550.
A filter cloth having a g / m ² and a needle density of 300 needles / cm ² was obtained. The performance of the filter cloth thus obtained is shown in Table 1.

Example 2 PPS staple fibers having an average single fiber fineness of 7.7 dtex, a cut length of 51 mm, and a crimp number of 14 / 2.54 cm (Toray Industries, Inc.)
Manufactured by "Torcon (R)" was used to obtain a spun yarn having a single yarn count of 20 s and a combined yarn number of 2. This is a plain weave and the warp density is 2
A PPS spun yarn woven fabric having 6 yarns / 2.54 cm and a weft yarn density of 18 yarns / 2.54 cm was obtained. Both sides of this woven fabric have an average single fiber fineness of 7.7 dtex, a cut length of 51 mm, and a crimp number of 14
A web using PPS short fibers of 2.54 cm / piece (“Torucon (R)” manufactured by Toray Industries, Inc.) is laminated, and the fabric and the web are entangled by needle punching, and the basis weight is 556.
A filter cloth having a g / m ² and a needle density of 300 needles / cm ² was obtained. The performance of the filter cloth thus obtained is shown in Table 1.

Example 3 PPS staple fibers having an average single fiber fineness of 3.0 dtex, a cut length of 51 mm, and a crimp number of 14 / 2.54 cm (Toray Industries, Inc.)
Manufactured by "Torcon (R)" was used to obtain a spun yarn having a single yarn count of 20 s and a combined yarn number of 2. This is a plain weave and the warp density is 2
A PPS spun yarn woven fabric having 6 yarns / 2.54 cm and a weft yarn density of 18 yarns / 2.54 cm was obtained. The surface layer of this woven fabric has an average single fiber fineness of 3.0 dtex, a cut length of 51 mm, and a crimp number of 14
A web using PPS short fibers of 2.54 cm / piece (“Torcon (R)” manufactured by Toray Industries, Inc.) was laminated, and then an average single fiber fineness of 7.7 dtex and a cut length of 51 mm were applied to the back surface layer of this woven fabric. A web using PPS short fibers having 14 crimps / 2.54 cm (“Torucon (R)” manufactured by Toray Industries, Inc.) is laminated, and the fabric and the web are entangled by needle punching, and the basis weight is 544 g / m. ² , needle density 300 / cm
A filter cloth of ² was obtained. The performance of the filter cloth thus obtained is shown in Table 1. The front surface layer here means a layer on the side where dust accumulates when used as a filter, and the back surface layer means a layer on the opposite side.

Comparative Example 1 Average single fiber fineness 2.2 dtex, cut length 51 mm, winding
14 PPS / 2.54 cm PPS staple fibers (Toray Industries, Inc.)
"Torcon (R)" manufactured by using, single yarn count 20s, compound yarn
Two spun yarns were obtained. This is a plain weave and the warp density is 2
6 threads / 2.54 cm, weft density 18 threads / 2.54 cm
A PPS spun yarn fabric was obtained. Average monofilaments on both sides of this fabric
Fineness 2.2 dtex, cut length 51 mm, crimp number 14 pieces
/2.54 cm PPS short fiber (Toray Industries, Inc., “Turkey
(R (R) ”) is used to stack webs and needle punch
Fabric and web are entangled by processing, and areal weight 551g /
m ², Needle density 300 / cm²Get the filter cloth of
It was The performance of the filter cloth thus obtained is shown in Table 1.

From Table 1, the filter cloths of Examples 1 to 3 were superior to the filter cloths of Comparative Example 1 in rigidity at room temperature, rigidity at high temperature, and abrasion resistance.

[0035]

[Table 1]

[0036]

According to the present invention, polyphenylene sulfide fibers are used and the single fiber fineness is 2.5 dte.
By containing the polyphenylene sulfide fiber having a single fiber fineness within the range of x to 17 dtex, the filter cloth having high rigidity at room temperature and high temperature and having excellent abrasion resistance can also be obtained. When the filter cloth is made of a non-woven fabric including a woven fabric and a web, the filter cloth can have excellent tensile strength and dimensional stability.

Further, the polyphenylene sulfide fiber used in the filter cloth of the present invention is JIS L-109.
Stiffness based on the Gurley method specified in 6 is 0.022 μN
/ Dtex or more, a filter cloth with high rigidity can be obtained, and when used at high temperature, deformation of the filter cloth caused by pressure loss during filtration and pressure during backwash can be suppressed, It is possible to prevent bending fatigue and breakage of the cloth.

In addition, the filter cloth JIS L-10
The bending resistance based on the Gurley method specified in 96 is 65 mN to 1
Within the range of 500 mN, the rigidity is high, and bending fatigue does not easily occur even when used at high temperature, and it is possible to prevent damage. Furthermore, the bending resistance is 400 m
When it is in the range of N to 1500 mN, the pleats are less likely to be deformed even when used in a pleated filter,
It is effective in preventing a rapid increase in pressure loss due to a reduction in filtration area.

The filter cloth as described above further comprises 170
If the hanging length at 30 ° C. is 30 mm or less, it is possible to obtain a filter cloth with high rigidity, and the filter cloth is generated due to the pressure loss during filtration and the pressure during backwash when used at high temperature. The deformation of the filter cloth can be suppressed and bending fatigue and damage of the filter cloth can be prevented.

The tensile strength after being abraded by the JIS L-1096 Taber method is 7 times that before the abrasion.
If it is 0% or more, when used as a filter,
Even if the filter cloth is in contact with the metal, the tensile strength is less likely to decrease due to abrasion, so that the filter cloth is less likely to be damaged.

Furthermore, when the tensile strength after heat treatment in air at 180 ° C. for 2,160 hours and abrasion by the JIS L-1096 Taber type method is 20% or more of the tensile strength before heat treatment, The above effect can be obtained even in a high temperature environment.

If the fluororesin is attached to at least one side, the wear resistance of the filter cloth can be significantly improved, and at least some of the fibers on one side are fused or at least one side is fused. When it is taken out, it is possible to improve the releasability by subjecting it to a hair-burning treatment or by having a microporous membrane on at least one side.

Since the bag filter and the pleated filter of the present invention are formed by forming the above-mentioned filter cloth into a bag shape, they are excellent in physical properties such as rigidity and abrasion resistance at high temperature, and are heat resistant. Garbage incinerator, which requires high quality,
It can be suitably used for a coal boiler or a metal blast furnace.

[Brief description of drawings]

FIG. 1 is a perspective view showing a method for measuring a hanging length of a filter cloth according to the present invention.

[Explanation of symbols]

1: Measuring piece 2: One end of the measuring piece 3: Placement block for measuring pieces 4: One end of the measurement piece 5: Measuring piece protruding from the block 6: Virtual plane including the upper surface of the block 3

Claims (15)

[Claims] 1. A polyphenylene sulfide fiber having a single fiber fineness of 2.5 dtex to 17 dtex.
A filter cloth characterized by containing polyphenylene sulfide fiber within the range. 2. The filter filter cloth according to claim 1, comprising polyphenylene sulfide fibers having a single fiber fineness within a range of 3.0 to 10 dtex. 3. The filter cloth according to claim 1, which is made of a non-woven fabric including a woven fabric and a web. 4. A polyphenylene sulfide fiber according to JI
The filter cloth according to any one of claims 1 to 3, which has a bending resistance based on the Gurley method specified by SL-1096 of 0.022 µN / dtex or more. 5. The filter cloth according to any one of claims 1 to 4, which has a bending resistance of 65 mN to 1500 mN based on the Gurley method specified in JIS L-1096. 6. The filter filter cloth according to claim 5, which has a bending resistance of 400 mN to 1500 mN based on the Gurley method specified in JIS L-1096. 7. The filter cloth according to claim 1, having a hanging length at 170 ° C. of 30 mm or less. 8. The filter filter cloth according to claim 1, wherein the tensile strength after being abraded by the JIS L-1096 Taber type method is 70% or more of the tensile strength before being abraded. 9. Tensile strength after heat treatment in air at 180 ° C. for 2,160 hours and abrasion by JIS L-1096 Taber method is 20% of that before heat treatment.
It is above, The filter cloth in any one of Claims 1-8. 10. The filter cloth according to any one of claims 1 to 9, wherein a fluororesin is attached to at least one surface. 11. The filter cloth according to any one of claims 1 to 10, wherein at least a part of the fibers on one surface is fused. 12. The filter cloth according to any one of claims 1 to 11, wherein at least one surface thereof has been subjected to a scorch treatment. 13. The filter cloth according to claim 1, which has a microporous membrane on at least one surface. 14. A bag filter comprising the filter cloth according to claim 1 formed into a bag shape. 15. A pleated filter, characterized in that the filter cloth according to any one of claims 1 to 14 is folded into a pleated shape and formed into a bag shape.