JP2000140531A - Filter cloth for bag filter excellent in dimensional stability and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare filter cloth for a bag filter having a fluoroplastic fiber support and excellent in long-term dimensional stability under high temp. and load. SOLUTION: In filter cloth for a bag filter excellent in dimensional stability constituted by laminating a filter layer on at least the single surface of a support, the support is formed from a knitted fabric comprising a fluoroplastic fiber and the filter layer contains staple fibers with Tg of 200 deg.C or higher. The filter cloth for the bag filter has excellent dimensional stability such that a longitudinal stretching ratio is 2% or less under load of 230 deg.C×720 hr/1 (kgf/5 cm) and is produced by laminating and integrating the support comprising the fluoroplastic fiber and the filter layer containing staple fibers with Tg of 200 deg.C or higher and subjecting them to hot air treatment of 200-350 deg.C or heating steam treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter cloth for a bag filter in which a scrim is made of polytetrafluoroethylene fiber. More specifically, the present invention relates to a filter cloth for a bag filter having excellent dimensional stability over a long period of time under a load which is assumed to be applied at a high temperature in actual use, and a method for producing the same.

[0002]

2. Description of the Related Art Exhaust gas emitted from coal-fired boilers, municipal waste incinerators, industrial waste incinerators, etc. contains not only dust but also harmful substances such as dioxin. Dust collection is very important.
A dust collector is used for separating and collecting dust from the exhaust gas, and suppression of resynthesis of dioxin in the dust collector,
The use of bag filters is also promising in terms of collection efficiency. As the filter cloth used for the bag filter, a woven cloth or a felt is generally used, and the use of a felt filter cloth is desirable from the viewpoint of high collection efficiency and filtration speed.

[0003] In exhaust gas collection of various incineration facilities, use conditions of a bag filter are various. For example, in general city waste incinerators, there are a full-scale station that operates for 24 hours, a semi-series station that performs intermittent operation, a mechanical batch type, and the like. In addition, the type and concentration of harmful gases in exhaust gas and the use of slaked lime or a reducing agent using a catalyst for removing these harmful gases require not only heat resistance but also high chemical resistance. In the cascade or mechanical batch method, durability that can withstand the effects of dew condensation due to repeated shutdowns is required. In addition, there are differences between the pulse jet method and the backwash method in dust separation and collection, and the conditions are variously different depending on the filtration speed and the concentration and particle size of the dust.

[0004] As described above, since the conditions for using the bag filter vary widely, filter cloths suitable for various conditions are selected and used for the bag filter. Among them, a felt filter cloth having a higher dust collection efficiency than a woven fabric is suitable, and as its material, polyimide, polyphenylene sulfide, polyamide, polyamide imide, polytetrafluoroethylene, or the like is used. These filter cloths are made of a woven fabric consisting of filament yarn or spun yarn as a scrim, and a web made of various short fibers is laminated and entangled on the top and bottom to form a felt, which is used for bag filters that are excellent not only in filtration characteristics but also in physical strength. I have a filter cloth.

[0005] These filter cloths are appropriately selected depending on the use conditions and the various durability of the filter cloth. Polyimide fibers, which can be used continuously at 200 ° C or higher and have an operation peak value of 200 ° C or higher, include polyimide fibers, Examples thereof include polytetrafluoroethylene fiber (PTFE) and glass fiber, which are used as general-purpose materials. Among them, polytetrafluoroethylene fiber has excellent chemical resistance, so it is used in the most severe conditions such as generation of harmful gas. Polytetrafluoroethylene fiber is 100% polytetrafluoroethylene fiber filter cloth and scrim polytetrafluoroethylene. There is known a filter cloth for a bag filter using ethylene fibers and using short fibers of a filtration layer made of a mixture of polytetrafluoroethylene fibers and glass fibers.

[0006]

However, as described above, the filter cloth for bag filter using the polytetrafluoroethylene fiber for the scrim has a problem that the bag filter itself is easily stretched, and thus the filter cloth is clogged and dust for a long time is generated. The problem that separation and collection cannot be performed has occurred in practical use. This is a phenomenon that occurs not only in the back-washing type dust removing method that places a greater load on the bag filter cloth, but also in the pulse jet removing method, and improvement is desired. This phenomenon is the same in a filter cloth in which a polytetrafluoroethylene fiber and a glass fiber are mixed in a filter layer, and it is presumed that the filtration property is caused by the fiber characteristics of the polytetrafluoroethylene fiber itself. The same polyimide fiber that can be used continuously at 200 ° C. or higher has no melting point and a glass transition temperature of 315 ° C.
Whereas, the polytetrafluoroethylene fiber is
With a melting point of 327 ° C and a glass transition temperature of 126 ° C (literature value, introduction to polymer chemistry, chemical coterie), the thermal properties are at relatively low levels. Even with the effect of entanglement of short fibers, glass fibers do not shrink at all, and therefore have the effect of mere physical entanglement. The effect of the entanglement of the short fibers of polytetrafluoroethylene is smaller at high temperatures and under an actual load because the glass transition temperature is lower than in actual use. Therefore, the filter cloth for a bag filter in which the support is made of polytetrafluoroethylene fiber and the filtration layer is made of polytetrafluoroethylene fiber or glass fiber, when using a temperature higher than the glass transition temperature, the weight of the filter cloth and It is presumed that the filter cloth is stretched even by a load such as the weight of the retainer and the weight of the dust, and as a result, the filter cloth is opened and dust enters and causes clogging.

[0007] The present invention solves the above-mentioned problems of the filter cloth for a bag filter of the prior art, and in particular, a filter cloth using polytetrafluoroethylene fibers as a support.
An object of the present invention is to propose a filter cloth for a bag filter which is free from elongation of the filter cloth and clogging of dust and has excellent dimensional stability over a long period of time in actual use at about 0 ° C.

[0008]

That is, the present invention relates to a filter cloth for a bag filter in which a filter layer is laminated on at least one surface of a support, wherein the support is a woven or knitted fabric made of a fluorine-based fiber, The layer has a dimensional stability characterized by a vertical elongation of 2% or less under a load of 1 (kgf / 5cm) at 230 ° C for 720 hours containing short fibers having a Tg of 200 ° C or higher. It is an excellent filter cloth for bag filters. Specifically, the filter cloth for a bag filter having excellent dimensional stability as described above, wherein the filter layer contains short fibers of fibers having a Tg of 200 ° C. or more at a ratio of 15 to 100% by weight, A filter cloth for a bag filter having excellent dimensional stability as described above, wherein the elongation in the vertical direction under a load of 1 (kg / 5 cm) at 230 ° C. for 3 hours is 1% or less; The filter cloth for a bag filter having excellent dimensional stability as described above, wherein the fiber is polytetrafluoroethylene.

Further, the present invention provides a method comprising laminating and integrating a support made of a fluorine-based fiber and a filtration layer containing short fibers having a Tg of 200 ° C. or more, followed by a hot air treatment at 200 to 350 ° C. or a steam treatment. This is a method for producing a filter cloth for a bag filter having excellent dimensional stability. Specifically, the lamination and integration process is a needle punch, or a method for producing a filter fabric for a bag filter having excellent dimensional stability as described above, which is characterized by using a water punch. The method for producing a filter fabric for a bag filter having excellent dimensional stability as described above, characterized by applying a melt press to the filtration surface, and performing a baking treatment on the filtration surface after the lamination and integration process. A method for producing a filter cloth for a bag filter having excellent dimensional stability as described above.

[0010] Since the polytetrafluoroethylene fiber has a low glass transition temperature of 126 ° C, it expands under a practical load of around 200 ° C. On the other hand, as an example of Tg of 200 ° C., there is polyimide fiber. The polyimide fiber has no melting point, has a high glass transition temperature of 315 ° C., and has high heat resistance, and hardly shrinks at 200 ° C. or less even under no load.
However, heat treatment near the glass transition temperature causes a large shrinkage and a maximum shrinkage stress. Utilizing this property, it is composed of a polytetrafluoroethylene fiber support, and the filter layer contains short fibers having a Tg of 200 ° C. or more, and is integrated with the support,
By performing the heat treatment, in actual use at about 200 ° C., the filter cloth does not elongate and has no dust clogging due to its own weight, retainer, and dust load, and can exhibit excellent dimensional stability over a long period of time.

Hereinafter, the present invention will be described in detail. In order to obtain a filter cloth for a bag filter in which the support is made of a fluorine-based fiber and has excellent dimensional stability over a long period of time at a high temperature, the filter layer contains at least a short fiber having a Tg of 200 ° C. or more. It is necessary to perform a heat treatment after laminating and unifying the support and the filtration layer. In the present invention, the filtration temperature is higher than the actual use temperature of the bag filter, and a polyimide fiber that contracts due to a high-temperature treatment is used for the filtration layer, and is laminated and integrated with a support made of polytetrafluoroethylene fiber and heat-treated. The entanglement of the short fibers in the layer increases, and the elongation due to the scrim can be suppressed. As a result, a filter cloth for a bag filter having excellent dimensional stability at high temperatures can be obtained.

The fluorine-containing fiber constituting the support of the present invention is preferably a fiber having at least 90% or more of fluorine atoms in a main chain or a side chain. The more preferred. Among them, polytetrafluoroethylene is preferred.

As the fluorine-based fiber used for the support, a woven fabric composed of a multifilament yarn, a spun yarn, a monofilament yarn or the like is used. can do.

[0014] The short fibers for forming a filtration layer used in the present invention are:
A polyimide fiber having a Tg of 200 ° C. or higher is most preferable. The ratio of the short fibers to the filtration layer fibers is 15 to 100.
% By weight. More preferably, 30
１００100% by weight. Examples of short fibers that form a filtration layer by mixing with fibers having a Tg of 200 ° C. or higher include polytetrafluoroethylene, polyphenylene sulfide, polyamide, polyamideimide, polybenzimidazole, and glass.

The fiber diameter of the polyimide and other short fibers forming the filtration layer is 0.1 to 100 from the viewpoint of filtration.
μm is preferred, and more preferably 1 to 50 μm. Furthermore, there are various fiber cross-sectional shapes such as a round shape, a triangular shape, a trilobal shape, and a random shape, but the shape is not particularly limited. From the viewpoint of capturing fine particles, those having a large specific surface area are preferable, and a polyimide fiber having a random irregular cross section is most suitable not only for suppression of elongation but also for filtration with a low exhaust gas concentration.

As the heat treatment used in the present invention, the hot air treatment temperature is 200 to 350 ° C., preferably 280 to 340.
° C. By performing the heat treatment near the glass transition temperature of the polyimide fiber, sufficient shrinkage of the polyimide fiber can be given in a short time. In addition, heat treatment using a heating steam or a heat calender can also be performed. After the heat treatment, a press with a heating roll for the purpose of improving the filtration characteristics, a baking of the filtration surface, or the like can be performed.

In the present invention, at 230 ° C. for 3 hours, 1 (kg / 5c
m) It is preferable that the elongation percentage in the filter cloth length direction under load is 1% or less. Conventionally, there is a hot stretch rate as this type of elongation rate measurement, which is evaluated under a load of 1 pound (453 g) at 230 ° C. for 3 hours. However, since a bug is generally about 5 m and the corresponding weight of the retainer and the load of the dust itself are applied, it is estimated that a load of at least 1 (kg / 5 cm) is applied per 5 (cm).
Under a load of pounds and for 3 hours, proper evaluation was not possible. It is estimated that it takes 1 (kgf / 5cm) at least for a width of 5 (cm) in the bagate direction, and a hot stretch evaluation of 1 (kgf / 5cm) was performed as a more appropriate evaluation in a short time.

In actual use, the temperature is usually about 3 to about 200 ° C.
For 5 years, a long-term evaluation under high temperature and load is necessary because a filter cloth for bag filters is used. Therefore, in the present invention, a hot stretch evaluation under a high temperature and a load of 720 hours corresponding to about one month was performed. In the present invention, 2
It is important that the elongation in the vertical direction of the filter cloth under a load of 1 (kgf / 5 cm) at 30 ° C. for 720 hours is 2% or less, preferably 1% or less.

The filter cloth for a bag filter used in the present invention comprises:
A support made of polytetrafluoroethylene fiber;
The filter cloth is composed of a filtration layer containing polyimide short fibers having a temperature of 200 ° C. or higher. Examples of a method for forming the filter cloth include a needle punching method and a water punching method.

【Example】

Hereinafter, the present invention will be described more specifically with reference to examples. Note that the present invention is not limited to only these examples. Each physical property value described in Examples and Comparative Examples was measured according to the following measurement methods.

(1) Measurement of elongation (%) in the direction of filter cloth length at 230 ° C. for 3 hours. Insert a mark of 20 (cm) in the vertical direction at the center of a filter cloth sample for a bag filter with a length of 25 (cm) and a width of 5 (cm) in the vertical direction, and load 1 pound and 1 (kgf / 5cm). 230 ° C
For 3 hours, and the elongation was measured. In addition, as the heat treatment oven, a blast constant temperature oven (manufactured by Yamato Scientific Co., Ltd.) was used.

(2) Measurement of elongation in the vertical direction of the filter cloth at 230 ° C. for 720 hours. As in the three-hour evaluation in (1), mark the sample,
1 pound, 1 (kgf / 5cm) load, 720 ℃ at 230 ℃
The length after the time treatment was measured, and the elongation was measured.
As in (1), constant temperature air ventilator (Yamato Scientific Co., Ltd.)
Was evaluated using

(3) Tensile Strength According to JIS L 1096, the tensile strength of the filter cloth in the vertical direction was measured by a cut strip method.

(4) Air permeability The air permeability of the filter cloth was measured by the Frazier method according to JIS L 1096.

Example 1 A filter fabric for a bag filter was prepared by weaving a scrim as described below and integrating it with a filter layer made of short fibers by a general needle punching method.
The support is made of polytetrafluoroethylene fiber having an average fineness of 400 denier (a PTFE fiber manufactured by Lenting, PROFIL
EN) with plain weave, vertical / horizontal, 25/25 / inch
Made a job at. The basis weight was 90 (g / m ² ), and the scrim of the filter cloth for bag filter was used.

The short fibers for the filtration layer used in Example 1 were 100% polyimide fibers (P84, manufactured by Toyobo Co., Ltd.)
It was 2 denier and 60 mm. The polyimide short fiber for the filtration layer was first preliminarily opened, and then supplied to a roller card for fine opening and fiber arrangement. And the web was laminated | stacked by the cross layer, and the filtration layer was obtained through the pre knee pan and the finishing knee pan. Thereafter, the filtration layers were laminated on and under a scrim made of polytetrafluoroethylene, and subjected to a heat calender roll treatment in which a pre-kneader and a finishing kneader were similarly performed. Thereafter, a hot air treatment was performed at 320 ° C. for 30 seconds, and the filter surface was burnt with a burner. The basis weight is 521 (g / m ² ), thickness 2.1 (mm), air permeability 16
(cc / cm ² · s), and a filter cloth for a bag filter comprising a PTFE support and a filtration layer comprising polyimide fibers was obtained.

Example 2 Using a support made of the same polytetrafluoroethylene fiber as in Example 1, the short fibers forming the filtration layer were made of the same polyimide fiber and polytetrafluoroethylene short fiber as in Example 1. Fiber (Lenting P
P84 / PROFILEN = 70/3 for TFE fiber, PROFILEN)
It was used at a weight ratio of 0. PROFILEN short fibers of 2.5 denier and 53 (mm) were used. P84 forming a filtration layer
Short fibers and PTFE short fibers are subjected to pre-spreading as in Example 1, subjected to a roller card, finely spread, fiber arrangement is performed, and then a web is laminated by a cross layer, and then filtered through a pre-knee pan and a finished knee pan. Layer obtained. Example 1
The filtration layers were laminated on the upper and lower sides of the support in the same manner as described above, and pre-kneading and finishing kneading were performed. Then, in the same manner as in Example 1, hot calendering and scalding were performed. Thereafter, hot air treatment at 320 ° C. for 30 seconds is performed in the same manner as in Example 1, and P
Filtration layer consisting of TFE support, polyimide fiber and PTF
A filter cloth for bag filter made of E fiber was obtained. The basis weight is
542 (g / m ² ), thickness 2.2 (mm), air permeability 17 (cc / cm ² · s)
Met.

(Example 3) A support made of PTFE fiber similar to that of Example 1 was used, and a polyimide layer and PTFE fiber similar to those of Examples 1 and 2 were used for a filtration layer. Further, polyphenylene sulfide (PPS) was used. Three types of short fibers (PROCON, manufactured by Toyobo Co., Ltd.) of 2 denier and 60 (mm) were used. The mixing ratio of the short fibers forming the filtration layer is polyimide / PT.
FE / PPS = 40/30/30. Example 1,
Needle punching was performed in the same manner as in Example 2, heat calendering, hair sintering, and heat treatment were also performed. Weight 551 (g / m ² ), thickness 2.2 (mm), air permeability 14 (cc / cm ² ·
s) The support is made of PTFE fiber and the filtration layer is P84, P
A filter cloth for bag filter consisting of TFE and PPS was obtained.

(Comparative Example 1) A support made of the same PTFE fiber as in Example 1 was used, and the filtration layer was made of PTFE fiber 100
%. Needle punching, heat calendering, and heat treatment were performed in the same manner as in Example 1, and PTFE fiber 1
A filter cloth for bag filters consisting of 00% was obtained. The basis weight is 6
71 (g / m ² ), thickness 1.6 (mm), air permeability 13 (cc / cm ² · s)
A filter cloth for a bag filter was obtained.

(Comparative Example 2) The same support made of PTFE fiber as in Example 1 was used, and the filtration layer was made of 85% PTFE fiber.
Needle punching, heat calendering, and heat treatment were performed in the same manner as in Example 2 with the glass fiber and 15% of glass fiber to obtain a filter cloth for a bag filter. The basis weight is 660 (g / m ² ) and the thickness is 1.5 (m
m) and the air permeability was 12 (cc / cm ² · s).

Examples 1 to 3 and Comparative Examples 1 and 2
Table 1 shows the elongation percentage at 230 ° C. for 3 hours and 230 ° C. for 720 hours, and other physical properties of the sample.

As described above, from the results of the measurement, it can be seen that the filter cloth tends to stretch as if a problem occurred in an actual machine when a load was applied. Under a load of 1 pound under 230 ° C. × 3 hours called hot stretch, all of the filter cloths have good elongation within 1%, but are expected to be used even in a short time in actual use (1 kgf / kg). When a load of 5 cm) is applied, the elongation percentages of Comparative Examples 1 and 2, which do not contain polyimide fiber, exceed 1%, which may not only cause a problem of elongation in actual use, but also give an appropriate evaluation. I understand that there is no. Furthermore, in the long-term evaluation of 720 hours, the elongation rate of Comparative Examples 1 and 2 was further increased, and 1 (kgf / 5c
Under the load of m), it shows an elongation of 2% or more, which is presumed to be the cause of dust clogging.

On the other hand, Examples 1 to 3 in which the filtration layer contains polyimide fiber showed a very small elongation even at 1 (kgf / 5 cm) as well as 1 pound at 230 ° C. for 3 hours.
In the long-term evaluation of 720 hours, the elongation rate was 1% or less for both 1pound and 1 (kgf / 5cm). It was found that the elongation was very small compared to the comparative example, and high dimensional stability under high temperature and load. Shows sex.

[0034]

According to the present invention, in a filter fabric for a bag filter comprising a polytetrafluoroethylene fiber support, a polyimide fiber having a higher glass transition temperature than that actually used is contained in a filtration layer, and heat treatment is performed. It has made it possible to provide a filter fabric for a bag filter that exhibits excellent dimensional stability over a long period of time under high temperature and load.

Claims (8)

[Claims] 1. A bag filter fabric in which a filter layer is laminated on at least one side of a support, wherein the support is a woven or knitted fabric made of fluorine-based fibers, and the filter layer has a Tg of 2 or more.
230 ° C x 720 hours containing short fibers of 00 ° C or more,
The elongation percentage in the vertical direction under a load of 1 (kgf / 5cm) is 2
% Or less, the filter cloth for a bag filter having excellent dimensional stability. 2. The filtration layer contains 15 to 100% by weight of Tg.
2. The filter cloth for a bag filter having excellent dimensional stability according to claim 1, wherein the filter cloth contains short fibers of fibers having a temperature of 200 ° C. or higher. 3. The bag filter having excellent dimensional stability according to claim 1, wherein the elongation in the vertical direction under a load of 1 (kg / 5 cm) at 230 ° C. for 3 hours is 1% or less. Filter cloth. 4. The filter cloth for a bag filter having excellent dimensional stability according to claim 1, wherein the fluorine-based fiber is polytetrafluoroethylene. 5. A support comprising a fluorine-based fiber and having a Tg of 20
After laminating and integrating a filtration layer containing short fibers of 0 ° C. or higher, 2
A method for producing a filter fabric for a bag filter having excellent dimensional stability, characterized by performing a hot air treatment at 00 to 350 ° C. or a steam treatment. 6. The method for producing a filter cloth for a bag filter having excellent dimensional stability according to claim 5, wherein the lamination and integration treatment is performed by a needle punch or a water punch. 7. The method for producing a filter cloth for a bag filter having excellent dimensional stability according to claim 5, wherein after the lamination and integration treatment, the filtration surface is subjected to a melt press by a heating roll. 8. The method for producing a filter cloth for a bag filter having excellent dimensional stability according to claim 5, further comprising subjecting the filtration surface to a hair burning treatment after the lamination and integration processing.