JPH07136433A - Chemical-resistant filter medium and production thereof - Google Patents

Abstract

PURPOSE:To obtain a filter medium excellent in heat resistance, fire retardancy and chemical resistance, hardly causing clogging and having a long life by coating a nonwoven fabric or felt composed of fibers of a polyimide resin having a repeated unit represented by the specific general formula with a meltable fluoroplastic, etc. CONSTITUTION:A highly heat-resistant filter medium used in an incinerator of industrial or municipal solid waste is formed by coating a nonwoven fabric or felt composed of fibers of a polyimide having a repeated unit represented by the general formula (wherein n is an integer of 1 or more, x is a tetravalent aromatic group and R is at least one kind of a divalent aromatic group) with a meltable fluoroplastic or a solvent soluble room temp. curable fluoroplastic or a fluoroelastomer. This filter medium is produced, for example, by applying a dispersion prepared by dispersing a fine powder of the meltable fluoroplastic in water or an org. solvent to the nonwoven fabric or felt composed of the polyimide fibers and heating the coated nonwoven fabric or felt to 200-400 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter material having heat resistance, flame retardancy, less clogging, long life, and excellent chemical resistance, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, there has been a breathable molded product using glass fiber as a highly heat-resistant filter material, but the molded product is very bulky, and it is difficult to mold it into a thin and compact molded product. there were. As a breathable material made of glass, many breathable materials made of sintered glass are commercially available,
A fragile, thin and large breathable molding cannot be obtained. Further, glass filters generally have a drawback that they are easily clogged.

An aromatic polyimide is mentioned as a polymer material that can be used for molding a highly heat-resistant molded body. Conventionally, it is difficult to make a woven fabric of aromatic polyimide even if it is made into a filter cloth by making a breathable filter using this polymer material, and much less a molded body that can be used as a filter has not been obtained. . As a result of intensive research to obtain air-permeable molded products having high heat resistance and various porosities, the present inventors have used aromatic polyimide fibers and preformed the aromatic polyimide fibers into a nonwoven fabric or felt. , Succeeded in obtaining a filtering material by heating the aromatic polyimide fiber nonwoven fabric or felt at a temperature exceeding the glass transition point of polyimide for an appropriate time, and filed a patent application. (Japanese Patent Application No. 5-62
(No. 534)

However, since the polyimide fiber has poor hydrochloric acid resistance, when hydrogen chloride is contained in the filter gas of incinerators for industrial and municipal wastes, the performance as a filter material deteriorates in a short period of time. Further, since the alkali resistance is also poor, if the powder is alkaline in the steps of recovering the powder raw material and collecting the powder product in the chemical industry, the performance similarly deteriorates in a short period of time. For the purpose of improving chemical resistance, a method has been adopted in which it is immersed in a dispersion liquid of polytetrafluoroethylene, which has extremely excellent chemical resistance, and the surface is coated through a drying and heating process. Since the melt viscosity of is high at 10 sec ^-1 at a shear rate of 10 ¹¹ to 10 ¹³ poise even at a temperature of 340 to 380 ° C., it is difficult to cover the surface of the polyimide fiber with no gaps, and a large number of pinholes are generated, The effect of improving the chemical resistance of fibers is low.

[0005]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a filter material made of polyimide fiber, which is obtained by processing a nonwoven fabric or felt made of polyimide fiber and which is excellent in chemical resistance, particularly acid resistance and alkali resistance, and a method for producing the same. To do.

[0006]

The above object can be achieved by improving the chemical resistance by the chemical resistant filter material and the method for producing the same according to the present invention. That is, 1) a non-woven fabric or felt made of polyimide fibers having a repeating unit represented by the following general formula (1), a meltable fluororesin,
By a filtering material characterized by coating a solvent-soluble room temperature-curable fluororesin or a fluoroelastomer,

[0007]

[Chemical 5]

And 2) A fine powder dispersion or a synthetic resin of a meltable fluororesin dispersed in water or an organic solvent in a nonwoven fabric or felt made of polyimide fibers having a repeating unit represented by the following general formula (1). A fine powder dispersion liquid of a meltable fluororesin dispersed together with is applied, and 260
To 400 ° C., coating a solution of a solvent-soluble room temperature-curable fluororesin and leaving at room temperature or heating, or coating a solution or latex of a fluoroelastomer and heating the filter material. Achieved by the method.

[0009]

[Chemical 6]

The essence of the present invention is to protect the surface of the filter material with a chemical resistant film without impairing air permeability, in order to impart chemical resistance to the filter material composed of polyimide fibers.

In order to impart chemical resistance to the filter material composed of the polyimide fibers, as a fine powder dispersion liquid dispersed alone or together with a synthetic resin in water or an organic solvent on the surface of a nonwoven fabric or felt composed of the polyimide fibers. Examples of the meltable fluororesin to be applied are tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene / hexafluoropropylene copolymer, ethylene / tetrafluoroethylene copolymer, and ethylene / chlorotrifluoroethylene. Examples thereof include copolymers.

The meltable fluororesin used in the present invention has a temperature range in which the polyimide fibers are not deteriorated by heat.
It must have an appropriate melt viscosity so that it can be melted and flowed to cover the fiber surface without gaps. Therefore, in FIG. 1 showing the relationship between the temperature and the melt viscosity of the resin, A
It is desirable that the melt viscosity be in a range not exceeding the line segment AB connecting the points B and B. That is, the shear rate is 1
At 0 sec ^-1 , the melt viscosity is 10 at a temperature of 260 ° C.
It is preferable that the temperature is ⁶ poises and 10 ⁵ poises or less at a temperature of 400 ° C. A meltable fluororesin having a large melt viscosity exceeding this range has low fluidity, cannot cover the fiber surface without gaps, and causes pinholes, so that the obtained filter medium has poor chemical resistance. Become.

The meltable fluororesin which meets the object of the present invention is a tetrafluoroethylene / perpropylalkyl vinyl ether copolymer (shear rate 1
Melt viscosity of 10 ⁴ to 10 ⁵ at ⁰ sec ⁻¹ and temperature of 380 ° C.
Poise), tetrafluoroethylene / hexafluoropropylene copolymer represented by the chemical formula (shear rate 10 sec
^-1 , melt viscosity of 4 × 10 ⁴ to 4 × 10 ⁵ at a temperature of 380 ° C.
Poise), ethylene-tetrafluoroethylene copolymer represented by the chemical formula (shear rate 10 sec ^-1 , 300 to 33)
The melt viscosity is 10 ⁴ to 10 ⁵ poise at a temperature of 0 ° C., and the ethylene / chlorotrifluoroethylene copolymer shown in the chemical formula (shear rate 10 sec ⁻¹ , the melt viscosity at a temperature of 260 to 315 ° C. is 2 × 10 ^3). ~ 2 x 10 ⁵ poise).

[0014]

[Chemical 7]

A polyimide fiber molded body is dipped in a dispersion liquid having a concentration of 10% to 60% in which the above-mentioned meltable fluororesin fine particles are dispersed in a dispersion medium. Deposited, then 260-400
It is possible to heat and melt at 0 ° C. to flow the particles, to fuse the fine particles to each other, and to cover the surface of the fiber without any gap. In this case, if the concentration of the fusible fluororesin fine particles is within an appropriate range, the performance as a filtering material can be exhibited without impairing the air permeability of the polyimide fiber nonwoven fabric or the felt. Dispersion of the meltable fluororesin fine particles, in addition to the dispersion of the meltable fluororesin fine particles alone in water or an organic solvent, water, an epoxy resin, a phenolic resin, a urethane resin in the organic solvent, or A dispersion liquid in which a synthetic resin such as a silicone resin is mixed with the fusible fluororesin fine particles and dispersed is also applicable. Moreover, it is preferable that these synthetic resins are resins of initial condensation.

Further, as an example of a solvent-soluble room temperature-curable fluororesin which is applied as a solution to the surface of a nonwoven fabric or felt made of polyimide fiber in order to impart chemical resistance to the filter material made of the polyimide fiber, fluorinated one is Examples thereof include vinylidene-based copolymers, fluoroolefin / hydrocarbon-based vinyl ether copolymers, and fluoroepoxy resins. The solvent-soluble cold-setting fluororesin is
It is desirable that it can be cured by being dissolved in an organic solvent and left at room temperature or heated at a temperature that does not affect the polyimide fiber. Solvent-soluble room-temperature-curable fluororesins that meet this purpose include fluoroolefin / hydrocarbon-based vinyl ether copolymers represented by the chemical formula.

[0017]

[Chemical 8]

Furthermore, in order to impart chemical resistance to the filter material composed of the polyimide fibers, an example of the fluoroelastomer which is applied as a solution or latex to the surface of the nonwoven fabric composed of the polyimide fibers or the felt is vinylidene fluoride. Ride / hexafluoropropylene-based and tetrafluoroethylene / propylene-based copolymers may be mentioned. The fluorine-based elastomer used for this purpose is one that can be dissolved in an organic solvent,
Alternatively, those which form an emulsion with water are preferable. Further, it is desirable that the fluoroelastomer is easily vulcanized within a temperature range where the polyimide fiber is not deteriorated by heat, and that the vulcanization exhibits chemical resistance and heat resistance. Fluorine-based elastomers that meet this object include copolymers of vinylidene fluoride (CH ₂ ═CF ₂ ) and hexafluoropropylene (CF ₂ ═CF—CF ₃ ) and (CF ₂ ═)
CF ₂ ) and propylene (CH ₂ ═CH—CH ₃ ) and the like. The fluoroelastomer is a polymer or copolymer before vulcanization.

[0019]

The present invention makes it possible to impart good chemical resistance to a filter material made of a polyimide fiber nonwoven fabric or felt by coating a meltable fluororesin, a solvent-soluble cold-setting fluororesin and a fluoroelastomer. It is a thing.

[0020]

EXAMPLES An example of the above-mentioned filter material made of the highly heat-resistant polyimide molding of the present invention and a method for producing the same will be described below with reference to examples. However, the present invention is not limited to the examples below.

Example 1 30 g of a tetrafluoroethylene / perfluoropropyl vinyl ether copolymer having an average particle size of 0.4 μm was dispersed in a container containing 70 g of distilled water and 0.8 g of polyethylene glycol fatty acid ester while stirring little by little. , A dispersion was prepared. Next, benzophenone-3,3'4
Thickness preformed by a needle punch method from polyimide fibers having a draw ratio of 1: 5 and a thickness of 30 μm, which were produced from 4′-tetracarboxylic dianhydride and 4,4′-methylene-bis- (tolylene isocyanate). 2 mm, weight 47
Width 45 mm, length 120 mm from 5 g / m ² felt
The test piece was cut out. The chemical structural formula of the polyimide constituting the above-mentioned polyimide fiber is shown in the chemical formula.

[0022]

[Chemical 9]

The test piece was immersed in the above-mentioned dispersion for 5 minutes, then pulled up and kept at 70 ° C. for 5 hours to be dried,
Subsequently, the surface of the polyimide fiber was coated with a coating film of tetrafluoroethylene / perfluoropropyl vinyl ether copolymer by keeping it in an electric furnace maintained at a temperature of 380 ° C. for 3 minutes. The weight of the test piece was measured and the amount of coating film adhered was calculated. Insert this test piece into a pipe with a diameter of 20 mm and
The air flow rate was measured under a pressure of g / cm ² . Also, this test piece was placed in a 10% hydrochloric acid solution at 23 ° C. for 5 hours for 5%.
The sample was immersed in the sodium hydroxide solution for 120 hours, washed with water and dried, and then the tensile strength was measured to calculate the retention rate. The results are shown in Table 1.

[0024]

[Table 1]

Example 2 The polyimide fiber test piece used in Example 1 was immersed in a tetrafluoroethylene / hexafluoropropylene copolymer dispersion having an average particle size of 0.2 μm prepared in the same manner as in Example 1 for 5 minutes. After that, the liquid is pulled up from the liquid, kept at 70 ° C. for 5 hours to be dried, and then kept in an electric furnace kept at a temperature of 380 ° C. for 3 minutes so that the surface of the polyimide fiber is tetrafluoroethylene hexafluoro. Coated with a coating of propylene copolymer. The weight and air permeability were measured in the same manner as in Example 1, and the sample was dipped in a 10% hydrochloric acid solution at 23 ° C. for 200 hours and a 5% sodium hydroxide solution for 120 hours,
After washing with water and drying, the tensile strength was measured and the retention rate was calculated.
The results are shown in Table 1.

Example 3 An average particle size of 0.
4 μm ethylene / tetrafluoroethylene copolymer 3
0 g was dispersed little by little while stirring to prepare a dispersion liquid. The polyimide fiber test piece used in Example 1 was immersed in the dispersion liquid prepared by the above method for 5 minutes, then withdrawn from the liquid and kept at 70 ° C. for 5 hours to be dried, and subsequently at a temperature of 320 ° C. The surface of the polyimide fiber was coated with an ethylene / tetrafluoroethylene copolymer coating film by keeping it in an electric furnace kept at 3 minutes. The weight and the air permeability were measured in the same manner as in Example 1 to obtain 200% in a 10% hydrochloric acid solution at 23 ° C.
After being immersed in a 5% sodium hydroxide solution for 120 hours, washed with water and dried, the tensile strength was measured and the retention rate was calculated. The results are shown in Table 1.

Example 4 Ethyl alcohol 60 g, B-stage phenol resin 5
In a container containing g, 30 g of a tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer having an average particle size of 0.4 μm was dispersed little by little while stirring to prepare a dispersion liquid. This test piece was added to the above 30% concentration dispersion liquid.
After soaking for 1 minute, pull up, hold at 70 ° C for 1 hour to dry, and then place in an electric furnace kept at a temperature of 380 ° C for 3 hours.
After holding for a minute, the surface of the polyimide fiber was coated with a coating film of a tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer. The weight and the air permeability were measured in the same manner as in Example 1, and 200% in a 10% hydrochloric acid solution at 23 ° C.
After being immersed in a 5% sodium hydroxide solution for 120 hours, washed with water and dried, the tensile strength was measured and the retention rate was calculated. The results are shown in Table 1.

Example 5 A container containing 68 g of methyl ethyl ketone and 2 g of Coronate EH (isocyanate curing agent) was charged with fluoroethylene.
Ethylene ethyl ether copolymer (molecular weight 80,000) 30
g was dissolved little by little with stirring. The polyimide fiber test piece used in Example 1 was immersed in the solution prepared by the above method for 5 minutes, then pulled out of the solution and kept at 50 ° C. for 5 hours to volatilize methyl ethyl ketone, and then at room temperature for 3 days. After standing, a cured coating film of fluoroethylene / ethylene ethyl ether copolymer was formed on the surface of the polyimide fiber. The weight and the air permeability were measured in the same manner as in Example 1,
Further, the sample was dipped in a 10% hydrochloric acid solution at 23 ° C. for 200 hours and a 5% sodium hydroxide solution for 120 hours, washed with water and dried, and then the tensile strength was measured to calculate the retention rate. Second result
Shown in the table.

[0029]

[Table 2]

Example 6 30 g of vinylidene fluoride / hexafluoropropylene copolymer was dissolved in a container containing 68 g of ethyl acetate and 2 g of polyamine while stirring little by little. The polyimide fiber test piece used in Example 1 was immersed in the solution prepared by the above-mentioned method for 5 minutes, then pulled up from the solution, sufficiently drained, and kept at 50 ° C. for 24 hours to volatilize the solvent. Next, it was heated at 150 ° C. for 30 minutes to form a vulcanized film of vinylidene fluoride / hexafluoropropylene copolymer on the surface of the polyimide fiber. The weight and the air permeability were measured in the same manner as in Example 1, and at 1
The sample was immersed in a 0% hydrochloric acid solution for 200 hours and a 5% sodium hydroxide solution for 120 hours, washed with water and dried, and then the tensile strength was measured to calculate the retention rate. The results are shown in Table 2.

Example 7 To 100 g of an aqueous latex containing 50% by weight of vinylidene fluoride / hexafluoropropylene copolymer, 5 g of a polyol vulcanizing agent was added, and the polyimide fiber test piece used in Example 1 was dipped for 5 minutes. It was pulled up, drained sufficiently, and kept at 70 ° C. for 1 hour to be dried. Then 15
By heating at 0 ° C. for 30 minutes, a cured film of vinylidene fluoride / hexafluoropropylene copolymer was formed on the surface of the polyimide fiber. The weight and the air permeability were measured in the same manner as in Example 1, and 2% was added to a 10% hydrochloric acid solution at 23 ° C.
It was immersed in a 5% sodium hydroxide solution for 00 hours for 120 hours, washed with water and dried, and then the tensile strength was measured to calculate the retention rate. The results are shown in Table 3.

[0032]

[Table 3]

Comparative Example 1 The same polyimide fiber test piece as used in Example 1, which was not coated with the fusible fluororesin fine particles, was measured for weight and air permeability, and was 10% at 23 ° C. 200% hydrochloric acid solution for 200 hours, 5% sodium hydroxide solution for 12 hours
After soaking for 0 hour, washing with water and drying, the tensile strength was measured and the retention rate was calculated. The results are shown in Table 3.

Comparative Example 2 The polyimide fiber test piece used in Example 1 was immersed in a polytetrafluoroethylene dispersion liquid having an average particle size of 0.4 μm prepared in the same manner as in Example 1 for 5 minutes and then pulled up. It was kept at 70 ° C. for 24 hours to be dried, and then kept at 380 ° C. for 3 minutes in an electric furnace to coat the surface of the polyimide fiber with polytetrafluoroethylene. Example 1
In the same manner as above, measure the weight and air permeability, and at 23 ° C, soak in a 10% hydrochloric acid solution for 200 hours, a 5% sodium hydroxide solution for 120 hours, wash with water and dry, and then measure the tensile strength. Then, the retention rate was calculated. The results are shown in Table 3. The same weight and air permeability as those not coated with the fusible fluororesin fine particles were measured, and the value was 1 at 23 ° C.
The sample was dipped in a 0% hydrochloric acid solution for 200 hours and a 5% sodium hydroxide solution for 120 hours, washed with water and dried, and then the tensile strength was measured to calculate the retention rate. The results are shown in Table 3.

[0035]

EFFECT OF THE INVENTION A non-woven fabric or felt made of polyimide fibers is coated with a meltable fluororesin, a solvent-soluble room temperature curable fluororesin and a fluoroelastomer to develop a polyimide fiber filter material having improved chemical resistance. As a result, the field of application as a filter medium has been significantly expanded. By the filtration material manufacturing method of the present invention, the non-woven fabric or felt made of polyimide fibers is coated with a meltable fluororesin, a solvent-soluble room temperature-curable fluororesin and a fluoroelastomer to improve chemical resistance which is a weak point of polyimide. However, it has become possible to develop a filter material made of polyimide fiber with improved chemical resistance.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between melt viscosity of meltable fluororesin and temperature.

[Explanation of Codes] This is the range of melt viscosity exhibited by the tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer. This is the range of melt viscosity exhibited by the tetrafluoroethylene / hexafluoropropylene copolymer. It is within the range of the melt viscosity exhibited by the ethylene / tetrafluoroethylene copolymer. This is the range of melt viscosity exhibited by the ethylene / chlorotrifluoroethylene copolymer. This is the range of the melt viscosity of polytetrafluoroethylene.

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Claims (4)

[Claims] 1. A non-woven fabric or felt made of a polyimide fiber having a repeating unit represented by the following general formula (1) is coated with a meltable fluororesin, a solvent-soluble room temperature curable fluororesin or a fluoroelastomer. Filter material to be. [Chemical 1] 2. A non-woven fabric or felt made of polyimide fibers having a repeating unit represented by the following general formula (1), together with a fine powder dispersion of a meltable fluororesin dispersed in water or an organic solvent, or a synthetic resin. A fine powder dispersion liquid of the melted fluororesin that has been dispersed is applied to the coating solution,
A method for producing a filter medium, which comprises heating to ° C. [Chemical 2] 3. A non-woven fabric or felt made of polyimide fibers having a repeating unit represented by the following general formula (1) is coated with a solution of a solvent-soluble room temperature-curable fluororesin, and left standing at room temperature or heated. A method for producing a filter material. [Chemical 3] 4. A method for producing a filtering material, which comprises applying a solution or latex of a fluorine-based elastomer to a nonwoven fabric or felt made of polyimide fibers having a repeating unit represented by the following general formula (1) and heating the nonwoven fabric or felt. Method. [Chemical 4]