JPH06269621A - Filter medium - Google Patents

Abstract

PURPOSE:To provide a long-lived filter medium which is highly resistant against heat and chemicals and has high filtration performance and mechanical strength. CONSTITUTION:A coating material containing fine fluororesin powder 7 is applied to a base material sheet of sintered fluororesin particle 6 which has a ventilation resistance with a pressure loss of 9.8 to 490 Pa at a filtration air velocity of 0.5 to 2m/min. Next, the coat is thermally cured to form a coated layer consisting of fine fluororesin powder.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter material for separating solid particles from a gas containing solid particles, and in particular, it collects and removes dust and other particles contained in high temperature exhaust gas generated from an incinerator or the like. However, the present invention relates to a filter material suitable for taking out only purified air to the outside.

[0002]

2. Description of the Related Art Gas discharged from factory production lines, various devices, dryers, or high-temperature furnaces such as incinerators and melting furnaces contains soot and other solid particles, which causes environmental problems. It cannot be disposed outside as it is,
Only the air that has been cleaned by removing and collecting the particles by using a dust collector is taken out to the outside.

As the dust collector, an electric dust collector, a scrubber, a cyclone, a bag filter and the like are generally used. Among them, the bag filter has a simple structure and a dust collecting efficiency of 99.9% or more, It is used more widely than other dust collectors because it has an extremely high filtration capacity of 1 to 5 mg / m ³ N in the clean gas after filtration.

This bag filter was cleaned by introducing exhaust gas into a housing containing a large number of cylindrical or envelope-shaped filter media and collecting solid particles in the exhaust gas by the inner or outer surface of the filter media. The air is taken out. Filtration materials include natural fibers such as cotton and wool, polypropylene, polyester, polyacrylonitrile, polyphenylene sulfide, polyamide, polyimide, polyvinyl acetate, polytetrafluoroethylene (PTFE)
Various fibers such as synthetic fibers made of, for example, or inorganic fibers such as glass fibers are processed individually or in a mixture into a felt shape or a woven cloth shape.

In the initial stage of use, these cloth-like filter materials first form a primary adhesion layer consisting of solid particles such as dust collected near the surface thereof. This primary adhesion layer is shown in FIG.
As shown in FIG. 3, the solid particles 4 in the dust-containing gas 3 flowing in from the left side in the drawing enter the gaps between the fibers 2 near the surface of the filter medium 1 to form a layer of the solid particles 4 apparently. It is a thing. Therefore, the substantial mesh size of the filter medium 1 becomes smaller than the space between the fibers, and it becomes possible to collect finer particles. Therefore, the solid particles 4 in the dust-containing gas 3 flowing in thereafter are substantially collected by this primary adhesion layer, and the purified gas 5 is taken out from the right side of the filter medium 1 in the figure.

[0006] However, during purification of exhaust gas, solid particles are deposited on the surface of the filter material or enter into the interstices of the fibers inside the primary adhesion layer to cause a clogging phenomenon, thereby lowering the filtration efficiency. There is a drawback that. For this reason, in the bag filter, the deposited particles are regularly separated from the surface of the filter medium during operation by a shaking mechanism such as a shaking method, a backwind method, and a pulse jet method. In order to facilitate this peeling, it is chemically inert and has a low affinity for solid particles, and is a filter material braided with a fluororesin fiber, or the fiber is subjected to a surface treatment such as fluorine treatment and braided into a cloth shape. Filter media have also been put to practical use.

For the same purpose, a filter material having a structure without a primary adhesion layer has been developed. For example, JP-A-3-68
No. 409 discloses a PTFE felt with porous expanded PT.
A filter material in which FE membranes are laminated is disclosed. Similarly, as a filter medium having no primary adhesion layer, Japanese Patent Publication No.
The publication discloses a filter medium in which PTFE fine particles are filled on the surface of a filter medium matrix made of sintered polyethylene particles having a large particle size.

[0008] These filter materials can be used in a wider range because they are excellent in heat resistance and chemical resistance in addition to easy separation of solid particles.

[0009]

As described above, the bag filter has a dust collection efficiency of 99.9% or more and a dust concentration of 1 to 5 mg / m ³ N in the clean gas after filtration, which is extremely high. Although it has a filter material consisting only of fibers, the so-called "blowing phenomenon" occurs when the primary adhesion layer is not formed due to its structure.
And cannot perform an effective filtration function. Particularly, in the initial stage of use, the primary adhesion layer is not formed at all, and it takes a considerable time to form and stabilize it. For this reason, it is necessary to pre-coat the surface of the filter material with a powder of the same kind as the powder to be collected or another powder before use to form a primary adhesion layer in advance.

In addition to the problem of the primary adhesion layer at the initial stage of use, the action of the scrubbing mechanism during bag filter operation causes
In addition to the solid particles adhered to and deposited on the surface of the filter material, the solid particles forming the primary adhesion layer may be separated. As a result, the blow-through state is temporarily established until the primary adhesion layer is formed again, and filtration is not performed. In addition, even if the removal mechanism suppresses the adhesion and accumulation of solid particles on the surface of the filter medium, the solid particles may accumulate thickly on the surface of the filter medium due to long-term use, or the gaps between the fibers inside It penetrates into the fiber and accumulates between the fibers, causing a so-called "clogging phenomenon". As a result of this clogging phenomenon, the pressure loss of the filter medium increases, the amount of processing gas decreases, and the filtration efficiency decreases.

In order to suppress the progress of the clogging phenomenon, it is necessary to treat the exhaust gas at a relatively low flow rate of 0.5 to 1.5 m / min. Further, the solid particles once entering the inside of the filter medium cannot be removed by an ordinary scrubbing mechanism, and careful cleaning with a chemical solution or water is required for removing them. However, since the primary adhesion layer is also removed along with this cleaning, the same phenomenon as the blow-through occurs at the time of reuse, and it takes time to stabilize the filtration performance, and after cleaning such as drying and precoating. Post-treatment is required. Further, the life of the filter medium is shortened due to damage caused by contact between fibers during cleaning or a cleaning jig, heat deterioration of fibers during the drying process, and the like.

Further, in order to improve the releasability from the solid particles and to increase the mechanical strength and the chemical strength, in order to subject the fibers constituting the filter medium to chemical treatment or film treatment, a chemical dipping step or a drying step is required. Various processes such as a process, a dispersion process, a waste liquid treatment process are required. On the other hand, regarding the filter medium having a structure without a primary adhesion layer, the laminated filter medium as described in JP-A-3-68409 requires a heating and pressure laminating device for laminating. In addition to the problems related to the production of the product, the filtering material vibrates and the surface porous film peels off due to the removal during filtration, or the adhesive spreads like a film to form a non-air-permeable film. There are structural problems such as blocking the pores of the membrane and blocking the passage of exhaust gas through the filter material.

Further, in the filter medium described in JP-B-2-39926, in which PTFE fine particles are filled on the surface of the filter medium matrix made of polyethylene sintered particles having a large particle diameter,
Since the base material of the filter medium is polyethylene, it cannot be used at high temperatures, and its resistance to moisture and chemical substances in the exhaust gas is low, which limits its use conditions. Therefore, it is an object of the present invention to provide a filter medium which is excellent in chemical and mechanical strength in addition to filtration performance and which can treat high temperature exhaust gas.

[0014]

As a result of repeated improvements to solve the above-mentioned problems relating to the filtering material, the present inventors have found that a porous material made of a fluororesin sintered body such as PTFE having excellent chemical and mechanical strength. By filling the surface of a high quality base material sheet with a fine powder of fluororesin, it has been found that the filtration performance is excellent and it can be treated with a high temperature gas, and the present invention has been completed.

That is, the problem is that the filtration wind velocity is 0.5 to 2 m.
/ Min on the surface of the base material made of porous fluororesin having a pressure loss of 9.8 to 490 Pa,
This can be solved by a filtering material having a fluororesin fine powder coating layer. The base material sheet used in the present invention is not limited to the type of fluororesin as long as it is a porous fluororesin sheet having a ventilation resistance of a pressure loss of 9.8 to 490 Pa at a filtration wind velocity of 0.5 to 2 m / min. For example, PTFE, hexafluoropropylene, polychlorotrifluoroethylene, tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer,
Tetrafluoroethylene / hexafluoropropylene copolymer, ethylene / tetrafluoroethylene copolymer, ethylene / chlorotrifluoroethylene copolymer, polyvinylidene fluoride, polyvinyl fluoride and the like can be appropriately selected.

In order for the base material sheet to satisfy the above ventilation resistance, it depends on the particle size of the fluororesin and the thickness of the sheet. For example, the resin has an average particle size of 20 to 50 μm and a thickness of 2.
In the case of a base material sheet of about mm, the bulk density is 1 to 2 g / c
If the m ³ and the porosity are 30% or more, the above ventilation resistance can be obtained. Such a base material sheet is filled with a fluororesin powder in a mold and pressure-molded so as to have a volume ratio of 40 to 60% of that at the time of filling, and a sintering temperature of the resin, for example, 340 in the case of PTFE. After sintering at ˜360 ° C. for several hours, the surface of the obtained sintered body is processed into a thin skin by skiving.

Since the base material sheet is composed of particles having a large diameter of several tens of μm, unevenness of a similar scale is formed on the surface thereof, and the unevenness has a finer fluorine content than that of the base material sheet. The resin fine powder is filled. The coating agent is a suspension prepared by mixing a fluororesin fine powder having an average particle size of 10 μm or less, preferably 5 μm or less, and a binder made of a heat resistant resin or a thermosetting resin adhesive in an alcohol solvent.

The type of fluororesin that constitutes the fluororesin fine powder is not particularly limited, and the same resin as the fluororesin that constitutes the matrix sheet can be appropriately selected and used. Any binder may be used as long as it is alcohol-soluble and has a heat resistant temperature of 200 ° C. or higher. For example, a typical thermosetting resin such as a phenol resin, a melamine resin, or a resorcinol resin can be used. Above all, solid content 50-60
A wt% phenolic resin alcohol solution adhesive is preferred.

The solvent is a monovalent lower alcohol such as methanol, ethanol, propyl alcohol, isopropyl alcohol, butyl alcohol or isobutyl alcohol, and ethyl alcohol is preferable from the viewpoint of toxicity and viscosity. The mixing ratio of the coating material according to the present invention is such that the fluororesin fine powder is 10 to 50 wt% and the binder is 1 to
A range of 5 wt% and solvent 50-200 wt% is preferred.

The method of forming the coating layer on the surface of the base material sheet is not particularly limited, and the coating material may be formed into a film thickness of several tens of μm, preferably 20 to 30 μm by using a known means such as spraying or brush. Is applied to the sheet so that the coating material and the sheet are heated to the curing temperature of the binder, and the coating material and the sheet are fixed by heat curing. As a result, a coating layer having fine communication holes having a pore diameter of several μm or less can be obtained.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A filter material according to the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the examples described below, and various modifications can be made. After filling the mold with PTFE powder with an average particle size of 50 μm and compressing it to a volume ratio of 60% of the filling, it was molded into a cylindrical mold, then taken out of the mold and allowed to stand in a heating furnace and aired. During,
Sintered at 340 ° C. for 4 hours. After sintering, let cool to room temperature,
A fluororesin porous base material sheet having a thickness of 0.5 mm was obtained by skiving. The bulk density of the obtained sheet is 1.3 g.
/ Pa ³ / cm ³ at a passing wind speed of 1 m / min, approximately 50 Pa
Showed a ventilation resistance of.

After applying the coating agent having the compounding ratio shown in Table 1 to the surface of the base material sheet, the coating material is heated in a heating furnace at 150 ° C. for 30 minutes to cure the coating material. A 30 μm-thick coating layer was formed to obtain a filter medium.

[0023]

[Table 1]

The obtained filter medium has a passing wind velocity of 1 m / min.
Showed a ventilation resistance of about 400 Pa. An enlarged cross-sectional view of the obtained filtering material is shown in FIG. As shown in the figure, the filter medium 1 according to the present invention has a structure in which the PTFE fine particles 7 are filled in the irregularities on the surface of the base material sheet made of the PTFE sintered particles 6, and the dust-containing gas flowing from the left side in the figure. The solid particles 4 in 3 are collected by the PTFE fine particles 7, and only the purified air 5 is taken out from the right side of the filter medium 1 in the figure. At this time, the solid particles 4 are PT
Since it cannot penetrate into the base material sheet made of FE sintered particles 6,
It is collected on the surface of the filter medium.

As shown in FIG. 2, the filter medium 1 is attached to a support 8 and is attached to a filter element 9 having a diameter of 117 mm and a height of 1000 mm, and a particle diameter of 0.5 to 10 is obtained.
2 μm, containing solid particles of concentration 500 mg / m ³ N 2
The hot dust-containing gas 3 at 50 ° C. was continuously filtered under the condition that the filtration wind speed was 2 m / min. The concentration of solid particles contained in the purified gas 5 after filtration was 1 mg / m ³ N or less.

During the filtration, the pressure loss of the filter medium was measured every predetermined time. The measurement result is shown in FIG. It can be seen that the filter material of the present invention shows little change in pressure loss (ΔP) with time and always exhibits stable filtration performance.

[0027]

As described above, in the filter material of the present invention, the surface of the base material sheet is covered with the coating layer made of the fluororesin fine powder, so that the solid particles and the moisture in the exhaust gas are contained inside the base material sheet. Hard to enter, clogging and condensation,
Generation of dissolution and precipitation is suppressed, and stable filtration performance is maintained for a long period of time. Further, since the clogging phenomenon does not occur, the filtration flow rate can be increased, the processing time is shortened, and the filtration efficiency is remarkably improved.

Since both the base material sheet and the coating layer are made of fluororesin, they have excellent heat resistance and chemical resistance, and can treat exhaust gas containing various chemical substances such as high temperature exhaust gas and household waste. Further, since the solid particles contained in the exhaust gas, water, and oil have a low affinity, deposition of solid particles on the surface of the filter medium is suppressed, and cleaning is easy and surface deposits can be removed by simply sprinkling water. It can be completely removed by washing, and can be used immediately after washing without a drying step.

Further, since the base material sheet is a sintered body of fluororesin, the base material sheet is superior in mechanical strength as compared with the fibrous base material sheet, and the fluororesin fine particles constituting the coating layer also have an anchor effect due to the anchor effect. Since it is fixed on the surface, it has a large resistance to shaking and shock during operation,
There is no risk of damage. Further, since the structure does not have a primary adhesion layer, there is no problem of blow-through or pre-coating at the beginning of operation or at the time of reuse after cleaning.

Regarding the manufacturing method, in the present invention, since it is sufficient to apply the coating agent containing the fluororesin fine powder to the base material sheet and heat-cure it, when the fiber is subjected to a chemical treatment or a film treatment, or when it is porous. Compared to the conventional case of stacking fluororesin films, the number of steps is smaller and special equipment
It can be manufactured at low cost without requiring equipment.

[Brief description of drawings]

FIG. 1 is an enlarged cross-sectional view of a filter medium according to the present invention.

FIG. 2 is a view showing a state in which the filter medium according to the present invention is attached to a filter element.

FIG. 3 is a diagram showing changes over time in pressure loss of the filter medium according to the present invention.

FIG. 4 is an enlarged cross-sectional view of a conventional filter medium.

[Explanation of symbols]

 1 Filtration Material 2 Fiber 3 Dust-Containing Gas 4 Solid Particle 5 Purification Gas 6 Fluororesin Sintered Particle (Base Material Sheet) 7 Fluororesin Fine Particle (Coating Layer) 8 Support 9 Filter Element

Claims (1)

[Claims] 1. A fluororesin fine powder coating layer is provided on the surface of a base material made of a porous fluororesin having a ventilation resistance with a pressure loss of 9.8 to 490 Pa at a filtration wind velocity of 0.5 to 2 m / min. Characteristic filter material.