JP4318620B2 - Filter and filter surface processing method - Google Patents

Description

  The present invention relates to a filter that requires heat resistance, such as a bag filter of a dust collector, and a filter surface processing method for obtaining desired heat resistance, chemical resistance, and durability in this type of filter.

  Environmental pollution caused by harmful substances such as dioxins has become a serious global environmental problem, and regulations have been strengthened globally. In industrial combustion furnaces such as boilers and incinerators, it is mandatory to remove dust.

  Dioxins are said to generate hydrocarbons and chlorine by the catalytic action of metal compounds during incomplete combustion at a relatively low combustion temperature. Even if complete combustion is performed under strict control in an incineration chamber, In the process, it is synthesized from a very small amount of precursor using metals in fly ash as a catalyst. Therefore, the high-temperature combustion chamber exhaust gas is rapidly cooled to shorten the time in the dioxin generation temperature range so that the temperature is 250 ° C. or lower when dust is collected by the bag filter. The use of organic fibers as a filter medium has become possible because the exhaust gas temperature in the bag filter has decreased, but on the other hand, since the exhaust gas temperature has been lowered, acidic substances such as sulfuric acid mist and hydrochloric acid mist in the exhaust gas dissolve in moisture. As a result, it has condensed, and the problem of damaging the filter medium by acid has arisen. Therefore, the chemical resistance (acid resistance and alkali resistance) of the organic fiber used for the filter medium has been strongly demanded.

  In order to improve the chemical resistance of the bag filter, the surface of the filter medium is coated with a melamine resin or urea resin (for example, see Patent Document 1), and the wholly aromatic polyamide fiber and fabric are treated with a fluorine resin emulsion ( For example, see Patent Document 2), a method of treating with a processing agent in which a fluororesin, a blocked polyisocyanate compound and a phenol novolak compound are arranged (see Patent Document 3, for example), and the surface of the filter medium is covered with an acid-resistant compound. The method is central.

  Also, there is a filter medium that uses a heat-resistant resin porous membrane material (membrane) such as polytetrafluoroethylene (PTFE) instead of fibers (see, for example, Patent Document 4).

JP 48-36770 A JP 56-107073 A JP-A-9-122415 Japanese National Patent Publication No. 11-506987

  In order to improve the chemical resistance of organic fibers constituting the woven fabric and non-woven fabric as the filter medium, the conventional technique of coating the filter medium surface with a processing agent easily drops off when the processing agent component only adheres to the filter material surface. Moreover, when a film was formed on the surface of the filter material, the filter was clogged, and there was a conflict between durability and filtration performance.

  In the case of PTFE membrane, it has excellent heat resistance, but in addition to the problem of high cost, there has been a problem that the performance of the membrane film is likely to deteriorate due to peeling or tearing of the membrane film.

  The present invention has been made in view of the above problems, and is intended to improve heat resistance, chemical resistance, water repellency, low friction resistance, and dust peelability without impairing filtration performance. Objective.

  ADVANTAGE OF THE INVENTION According to this invention, the filter formed by welding a heat resistant short fiber to a filter medium surface with a heat resistant resin is provided.

  Preferably, the filter is fixedly formed on the filter medium, the first layer made of the first resin having a low melting point welded to the surface of the filter medium, and the first resin layer having a higher melting point than the first resin. 2 and a second layer made of a mixture of heat-resistant short fibers.

  The filter is impregnated with heat-resistant short fibers, a dispersion of a first resin having a melting point substantially lower than the drying temperature and a second resin having a melting point higher than that of the first resin, and then dried and solidified. It can also comprise from the coating layer formed.

  The first resin can be a granular fluororesin and the second resin can be a granular polyimide resin.

More preferably, the filter is a filter medium composed of a fiber aggregate having a single yarn fineness of 0.3 to 20 DTEX and a basis weight of 80 to 900 g / m ² , a polyimide resin layer melt-formed on the surface of the filter medium, and a polyimide resin layer The heat-resistant short fibers are made of long fibers having a single yarn fineness of 0.2 to 10 DTEX in the range of 0.4 mm to 5 mm. Cut to length.

  According to the present invention, the heat-resistant fiber is cut into a predetermined length, the cut heat-resistant fiber is mixed with a dispersion liquid containing fluorine-based resin fine particles and polyimide resin fine particles, the mixed liquid is impregnated with a filter medium, and mixed. A filter surface processing method is provided in which the filter medium after liquid impregnation is heat-treated to fix the resin.

  In the present invention, the heat-resistant fiber has a cut length in the range of 0.4 mm to 5 mm. It is in the range of ~ 330 ° C.

  The filter of the present invention is constructed by welding heat-resistant short fibers to a filter medium surface with a heat-resistant resin. The filter medium is preferably a fiber assembly such as a woven fabric or a non-woven fabric. The resin layer covering the filter medium is preferably an inner and outer two layers, and heat-resistant short fibers are located in the outer layer.

  As fibers constituting the filter medium, polytetrafluoroethylene (PTFE), polyimide fiber, P84 (Inspec Fiber), polyimide amide, aramid, m-aramid (Teijin / DuPont), polyphenylene sulfide, polyester, polyacrylonitrile, etc. Organic fibers, and inorganic fibers such as metal fibers, glass fibers, silica fibers (Nichias, 3M, belCoTex manufactured by belChem), carbon fibers, and basalt fibers, but are not limited thereto.

When the filter medium is composed of a woven fabric, the fineness of a single fiber (monofilament) is 0.3 to 2.0 DTEX, and the basis weight is 80 to 900 g / m ² , preferably 300 to 900 g / m ^2. A double flat (tubular weave) or the like is suitable. Moreover, a filter cloth can also be comprised with nonwoven fabrics, such as a needle punch, instead of a woven fabric. In this case, the fineness of the single fiber (monofilament) which comprises a nonwoven fabric is 1.0-6.0DTEX, and is 80 as a fabric weight. ˜900 g / m ² , preferably 300 to 850 g / m ² .

  In the present invention, the heat-resistant fiber to be welded to the filter medium surface is one or more selected from fluorine-based fiber, glass-based fiber, silica-based fiber, heat-resistant imide-based fiber, and amide-based fiber. Fluorine fiber, glass fiber, silica fiber, heat-resistant imide fiber, and amide fiber are usually supplied as rovings (strands) with an infinite fiber length. Is cut into short fibers having a length in the range of 0.4 mm to 5 mm. The fineness of the heat-resistant fiber (fineness of the single fiber) is 0.2 to 10 DTEX, preferably 0.2 to 4.5 DTEX, which is considerably thinner than the fineness of the single fiber constituting the filter medium. Since the short fibers constituting the filter medium can be thickened, the cost of the filter medium is reduced, but the gaps between the fibers can be blocked with thin short fibers, and higher filter performance can be ensured without any loss.

  According to the present invention, the heat-resistant short fiber has a structure that is welded to the surface of the filter medium by the heat-resistant resin. The heat-resistant resin can be composed of only a binder resin (one type of resin), but a binder layer such as a polyimide resin (first resin of the present invention) and a fluorine-based resin (second resin of the present invention). And a surface treatment layer such as a resin. Here, the first resin has a melting point considerably lower than the drying and solidification temperature after impregnation, and is completely melted and welded to the surface of the filter medium in the drying step, and the second resin has a melting point substantially higher than that of the first resin and is dried. Even at a high temperature in the process, the resin is not completely melted immediately and the granular state of the resin can be maintained. That is, FIG. 1 schematically shows a preferable filter structure of the present invention when the filter medium (base cloth) is a woven cloth. The filter medium 1 formed by entanglement of fibers (filaments) is a polyimide resin or the like. The fluorine resin layer 3 (second layer of the present invention) is formed so as to be covered with the completely dissolved binder layer 2 (first layer of the present invention) and leave a considerable granular state on the binder layer 2. The heat-resistant short fibers 4 are embedded in the fluorine-based resin layer 3, and as a result, the short fibers 4 are welded to the filter medium (base fabric) 1 through the resin layers 2 and 3. In order to obtain high filtration performance, it is desirable that the inter-fiber gap in the filter medium 1 is small. However, since the fineness of the single fibers constituting the filter medium 1 cannot be reduced so much, the size of the inter-fiber gap in the filter medium 1 itself. However, in the present invention, the filter medium 1 is covered with short fibers 4 having a fineness (thin) smaller than the single fibers constituting the filter medium 1, and the size of the inter-fiber gap of the filter medium 1 is short. Compensated by the presence of the fibers 4, a filter with a smaller void structure can be obtained.

  As will be described later, in order to form the resin layers 2 and 3, the fluororesin and the polyimide resin are applied to the filter medium 1 in a state in which fine particles are dispersed in liquid, and are heated and solidified to form the resin layers 2 and 3. The resin completely melts and functions as a binder to weld the fluororesin + short fibers to the filter medium 1, while the fluororesin imparts a predetermined surface wear resistance to the filter and the filter material is stretched by deposits on the filter surface at high temperatures. It can be made to function so as to prevent the form from being damaged. In addition to the above-mentioned action of fixing the fluororesin fine particles to the filter surface, the polyimide resin also has a function of improving surface wear resistance and suppressing the shape of the filter material from being stretched by deposits on the filter surface at high temperatures. Demonstrate.

  In the present invention, as the polyimide resin, poly (N, N′-p-phenylene-pyromellitic imide), poly (N, N′-p-phenylene-benzophenone tetracarboxylic imide), poly (N, N ′ -P-phenylene-trimellitic acid amide imide), and their chemical structure is

の通りであり、これらのものは東レ・デュポン株式会社、東洋紡績株式会社などにより市販されている。上記のものの他、ポリイミド樹脂として、ポリ（Ｎ，Ｎ’− ｐ−フェニレン−ビフェニルテトラカルボン酸イミド）、ポリ（Ｎ，Ｎ’− ｍ−フェニレン−ピロメリット酸イミド）なども使用できるが、前記のものより耐熱性としては劣っている。

These are commercially available from Toray DuPont Co., Ltd. and Toyobo Co., Ltd. In addition to the above, poly (N, N′-p-phenylene-biphenyltetracarboxylic imide), poly (N, N′-m-phenylene-pyromellitic imide) and the like can be used as the polyimide resin. It is inferior in heat resistance than the ones.

  The fluororesin is preferably at least one selected from polytetrafluoroethylene and polychlorotrifluoroethylene. In addition to polytetrafluoroethylene and polychlorotrifluoroethylene, copolymers of tetrafluoroethylene and other vinyl monomers such as chlorotrifluoroethylene and ethylene are also possible. However, when the mixing ratio of hydrogen-containing monomers increases, Since the characteristic of resin is impaired, it is not preferable. Fluorine-based resin fine particles are commercially available from Asahi Glass Co., Ltd. and Shamrock Technology (USA), and these can be used.

  According to the filter surface processing method of the present invention, the heat-resistant fiber is cut into short fibers having a length in the range of 0.4 mm to 5 mm, and the cut short fiber is a dispersion containing fluorine resin fine particles and polyimide resin fine particles. The resin is fixed and dried by impregnating the mixture with the filter medium and heating the filter medium after impregnating the mixture to a high temperature such as 150 ° C. to 330 ° C. The melting point of the polyimide resin is as low as about 180 ° C., while the melting point of fluorine is about 320 ° C., which is considerably higher than the melting point of the polyimide resin. The polyimide resin is substantially completely melted by impregnating the dispersion containing the fluorine resin fine particles containing short fibers and the polyimide resin fine particles into the filter medium and heating at a temperature of 150 ° C. to 330 ° C. The resin will only soften. Therefore, after the heat treatment, the first layer 2 made of polyimide resin is uniformly coated on the surface of the fibers constituting the filter medium 1, and the granular fluororesin and short fibers are fixed to the first layer 2 as the second layer 3. The resulting structure of FIG. 1 is obtained.

  PTFE fibers as heat-resistant short fibers include Profilene (Lentining), Yumiflon (YMT) and Toyoflon (Toray), but the PTFE fibers of the previous two companies have a modified cross section and improve the filter performance more. be able to. The fiber used depends on the purpose of use, but 1.5 DTEX (average value) to 4.0 DTEX (average value) is preferable. The mixing ratio with the mixed resin (short fiber-mixed resin weight ratio) is preferably 5 to 50%, and from the viewpoint of processing, a range of 10% to 30% is particularly desirable.

  The size of the fluorine resin fine particles and the polyimide resin fine particles is preferably as small as possible, but is practically 0.5 to 10 μm.

  The mixing ratio (weight ratio) of the fluororesin fine particles and the polyimide resin fine particles when impregnating the heat resistant fiber is preferably 100: 5-70, more preferably 100: 20-40. When the amount of polyimide resin fine particles exceeds 70 (parts by weight) with respect to 100 (parts by weight) of the fluorine resin fine particles, the fluorine resin fine particles are coated on the polyimide resin, and the effect of the polyimide resin fine particles is sufficiently exerted particularly in water repellency. If the amount is less than 5 (parts by weight), the polyimide resin fine particles easily fall off and the durability is inferior.

  In order to uniformly disperse the short fibers (cut fibers) to be mixed, the fluororesin fine particles and the polyimide resin fine particles are made into a dispersion containing them, preferably an aqueous dispersion using water as a dispersion medium, and this is impregnated into the filter medium. Let The higher the solid content concentration in the dispersion, the more can be deposited at a time, but the solid content is preferably about 10 to 60% by weight from the viewpoint of handling. More preferred is about 15-30% by weight. In the production of the dispersion, a dispersion stabilizer such as a surfactant may be added, but the present invention does not limit these additions.

  The filter medium can be impregnated with the dispersion by a roller coating method, a dipping method, or a spray coating method as a simple method. Fluorine-based resin particles and polyimide resin particles containing short fibers are attached to the filter medium surface by these methods, but the required amount of adhesion may not be obtained by one impregnation depending on the concentration of the dispersion and the impregnation method, In this case, the solid content is reduced as much as possible, and the impregnation and drying are repeated to satisfy a predetermined adhesion amount.

The short fibers adhering to the filter medium are fixed by the fluorine resin fine particles and the polyimide resin fine particles, but the total amount is preferably 10 to 100 g / m ² , more preferably 25 to 60 g / m ² . The range of the amount of adhesion is determined as an optimum value from the viewpoint of heat resistance, chemical resistance and durability of the filter targeted by the present invention, and is determined by the diameter of the short fiber used and solidification of the resin. To do. When the amount is more than 100 g / m ² , the effect is sufficient, but there is little further improvement in the effect due to the increase in the amount of adhesion, which may be disadvantageous from an economical point of view, and further filter characteristics such as air permeability and hardness. May be damaged. Conversely, if it is less than 10 g / m ² , the object of the present invention may not be sufficiently achieved.

  In order to fix the short fibers to the filter medium, the short fibers are uniformly dispersed and impregnated in a dispersion containing fluorine resin fine particles and polyimide resin fine particles, and then most of the water is evaporated by preliminary drying, and then 150 to 330. The resin is cured by heating at ℃, preferably 180-200 ℃, for 5-60 minutes, preferably 10-30 minutes. By this treatment, the polyimide resin fine particles on the surface of the filter medium are softened, and the short fibers are partially fixed on the surface of the filter medium. Therefore, this heating temperature should be selected in consideration of the type of polyimide resin used.

  In the case of using fluorine-based short fibers (cut fibers), the fibers are more uniformly fixed to the clothing cloth by processing at around 327 ° C. of the melting point. (High temperature calendar process etc.) The performance of the filter effect can be improved.

  In the heat treatment, the short fibers are deformed, and the surface of the fibers constituting the filter medium is thinly coated with polyimide resin, and the short fibers are fixed by the polyimide resin. Chemical resistance and acid resistance of the filter are realized by the polyimide resin coating. In this state, a filter is used to add PTFE resin to the surface structure of short fibers and the like, and the performance is improved comparable to a membrane film.

  The filter obtained by the surface processing method for a filter of the present invention can improve heat resistance, chemical resistance, water repellency, low friction resistance, and dust releasability without impairing filtration characteristics. Furthermore, there is an advantage that the length elongation due to the adhesion of dust is small, and deterioration (filter cloth breakage) can be prevented by a more stable dimensional change. Moreover, in the filter using glass fiber, the problem of bending wear may occur, but this problem is also reduced by the surface processing treatment of the present invention.

Fluorine-based resin fine particles comprising polytetrafluoroethylene containing a filter medium having a basis weight of 580 g / m ^{2 made} of glass double weave at a weight ratio of 1.7 DTEX (average) of PTFE short fibers of 15% (ratio to the total resin weight) ( Impregnating an aqueous dispersion containing polyimide resin fine particles (particle size: about 1 μm) composed of poly (N, N′-p-phenylene-pyromellitic imide) at a weight ratio of 100: 20 with a particle size of about 1 μm), A solid content of 20 g / m ² was adhered to the surface of the filter medium. After most of the water was evaporated, the resin was cured by heating at 200 ° C. for 30 minutes. Furthermore, the surface calendar process was performed at 330 degreeC.

This was used in an incinerator as a bug filter. The untreated filter has been unusable due to clogging in about half a year, whereas it has been usable for more than one year. The air permeability of the untreated product fell to 0.31 cm ³ / cm ² / sec in the sampling inspection during half-year use, whereas the processed product of the present invention was good at about 5.0 cm ³ / cm ² / sec. Air permeability is maintained (air permeability when new is 8 cm ³ / cm ² / sec). In addition, the amount of dust adhering to the bag filter was over 1000 g / m ² for the untreated product, whereas it was about 180 g / m ² for the processed product, confirming that the dust was removed well. It was.

A filter medium having a weight per unit area of 480 g / m ^{2 made} of polyimide contains 1.7 DTEX (average) PTFE short fibers in a 15% weight ratio (ratio to the total resin weight) in the same manner as in Example 1. An aqueous dispersion containing polyimide resin fine particles at a weight ratio of 100: 20 was impregnated, and a solid content of 25 g / m ² was adhered to the surface of the filter medium. After most of the water was evaporated, it was heated at 200 ° C. for 30 minutes to cure the resin to form a bag filter, which was used in a coal coke oven with a strong acidic atmosphere. The conventional untreated product has been used for about 2 years, and the strength when cutting in the cylindrical direction of the bag filter has dropped to about 30% of the new product, whereas the fluororesin fine particle and polyimide resin fine particle processed product are 3 years old. In use, the strength at cutting was close to 60% of the new product.

3.5DTEX (average) PTFE short fiber, 2.2DTEX polyimide fiber short fiber weight ratio of 60:40 mixing ratio of 30g / m ² in polyimide resin / PTFE
The mixture was mixed with the resin mixed solution, coated onto a double woven fabric having a basis weight of 650 g / m ² glass as in Example 1, dried, and then heated and dried at 280 ° C. for 2 minutes. Dispersion and fluorine-based trees have the property of softening at high temperatures. From Example 1, performance was improved in a clogging test using a pulse test machine.

^On the surface of a filter medium having a basis weight of 700 g / m ^{2 made} of 100% PTFE, 3.5 DTEX (average) PTFE short fibers / 9 micron basalt fiber (mixing ratio 5: 5) is mixed with polytetra Fluorine-based resin fine particles (particle size: about 1 μm) made of fluoroethylene and polyimide resin fine particles (particle size: about 1 μm) made of poly (N, N′-p-phenylene-pyromellitic imide) in a weight ratio of 100: 20 The solid dispersion was impregnated in an aqueous dispersion containing 1 to allow a solid content of 20 g / m ² to adhere to the surface of the filter medium. After most of the water was evaporated, the resin was cured by heating at 200 ° C. for 30 minutes, and then heat setting was performed at 330 ° C. above the PTFE melting temperature.

Example 4 was evaluated for slip properties and wear resistance at normal temperature and high temperature (180 ° C.). As Comparative Example 1, fluorinated resin fine particles (particle size: about 1 μm) of a mixed product such as butyl rubber are used instead of polytetrafluoroethylene, and a solid content of 100 g / m ² is adhered to the surface of the filter medium and dried until no moisture is present. And curing at 180 ° C. for 10 minutes. The dimensional instability of the PTFE filter at high temperature was partially improved. That is, compared with half-year use of the same product with a length of 600 cm (operating temperature average 180 ° C.), the treated product had an elongation of only 3 cm, and there was a significant improvement over the untreated product with an elongation of 25 cm.

The filter of the present invention (in this case, the filter obtained in Example 2) was evaluated for slipperiness (normal temperature (25 ° C.) and high temperature (180 ° C.)) and wear resistance. The slip property was measured by measuring the coefficient of static friction by the gradient method. Further, the abrasion resistance was measured by measuring the number of rubbing of the abrasion test until the base fabric was exposed by the JIS1096.88.17.3C method (taper type method). As Comparative Example 2, the same treatment as in Example 2 was carried out except that the dispersion did not contain PTFE short fibers to obtain a filter having a surface treated with a fluororesin and a polyimide resin. Further, as Comparative Example 3, a solution containing 1 to 10% of a trifluoride resin component was applied to the surface of the filter medium at 100 to 300 g / m ² , dried until no water was left, and then 3 to 10 at 130 to 180 ° C. The filter obtained by curing the resin for minutes was prepared. The measurement results are shown in Table 1.

Table 1
Comparative Example 2 Comparative Example 3 of the present invention
Sliding property (room temperature) ◎ 0.13 ◎ 0.16 ◎ 0.18
Sliding property (at high temperature) ◎ 0.15 ◎ 0.17 ○ 0.29 ^{* 1}
Abrasion resistance ◎ 27000 times ○ 21000 times × 17000 times
* 1: Some softening of the resin was observed.

  As shown in Table 1, it was found that excellent characteristics with respect to slipping and abrasion resistance can be obtained by the present invention.

A filter performance confirmation test was performed on the filter of the present invention (filter of Example 2). The testing machine was a miniature bug filter testing machine. The test dust was 10 types of fly ash, the filtration rate was 3.0 m / min, the dust concentration was 10 g / m ³ , and the test time was 7 hours. For comparison, Gore 4427 type PTFE membrane B (Comparative Example 4), Comparative Example 2, and untreated raw filter medium (Comparative Example 5) were tested under the same conditions. The results are shown in Table 2.

Table 2
Dust passage amount Filtration performance The present invention Very small amount ◎
Comparative Example 4 Very small amount ◎
Comparative Example 2 Small amount ○
Comparative Example 5 First with dust passing △

  From the clogging test in Table 2, it was found that the filter of the present invention had a filtration performance equivalent to that of the PTFE membrane (Comparative Example 4).

  According to this invention, compared with the case where the filter medium surface is simply coated with a resin, by adding heat-resistant short fibers to the resin layer in addition to the resin coat, the required filtration performance is improved while improving the peelability. The effect to ensure is produced.

FIG. 1 is a diagram schematically showing the surface structure of the filter of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Filter medium 2 ... Binder 3 ... Fluorine-type resin layer 4 ... Heat-resistant short fiber

Claims (1)

A heat-resistant short fiber is welded to a filter medium surface with a heat-resistant resin, and the heat-resistant short fiber is at least one selected from basalt fiber as a silica-based fiber and polyimide fiber as a heat-resistant imide-based fiber. polytetrafluoroethylene fibers are constituted by added, also heat-resistant resin of the filter medium surface a first layer made of a polyimide resin, by a fluorine-based resin is fixed formed on the first resin layer Li Cheng first Ri Do from a two-layer, the heat-resistant staple fibers that are embedded filter to the second layer.

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