JPH05253416A - Production of electret filter - Google Patents

Abstract

PURPOSE:To obtain a filter excellent in collecting efficiency by applying direct voltage to a polymer fiber bundled body on one side of the surface of which a polymer film is superposed and applying voltage having inverse polarity against the charged voltage to the polymer film. CONSTITUTION:The method for producing the electret filter has a process to form the electret filter from the polymer fiber bundled body 1 which is charge treated by applying charged voltage to the polymer fiber bundled body at least on one side of the upper face or rear face of which the polymer film (B) 8 is superposed and applying voltage having inverse polarity against the charged voltage to the polymer film (B) 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an electret filter, and more particularly to a method capable of producing an electret filter having excellent collection efficiency in high yield.

[0002]

2. Description of the Related Art After molding a raw material resin into a fibrous form, the fibers are subjected to a charging treatment using an electrode in the shape of a needle, a wire or a plate, and the obtained electretized fibrous form is collected to obtain a desired electret form. A method of producing an electret filter by a step of forming into a filter shape, or a method of drawing a melt-spun fiber and subjecting the obtained drawn yarn to a corona discharge in a tense state (JP-A-60-199970). A method in which at least one surface of a web made of a conductive material is covered with a dielectric film and a corona discharge is applied (Japanese Patent Laid-Open No. 6-58242).
0-500658), a method of disposing a high-dielectric-constant insulating film between a non-woven fabric and a ground electrode, and performing corona discharge (Japanese Patent Publication No. 59-15167). Also, after the film is charged, it is made into a fibrous shape,
A method of producing an electret filter by a step of collecting the obtained electretized fibrous material and molding it into a desired filter shape is also known.

[0003]

However, in the above-mentioned conventional method, a large amount of current flows in the space between the fibers, so that the voltage does not rise and the fibers to be charged are not effectively charged. When the value is raised, electric discharge occurs and it is difficult to obtain sufficient filter performance. Further, in the case of a web having a large thickness, the surface thereof is efficiently charged, but the inside is less likely to be charged as compared with the surface, and the performance as a filter was not sufficiently exhibited. In addition, JP-A-60-500658 and Japanese Patent Publication No. 59-1516.
As described in Japanese Patent Publication No. 7, etc., the method of covering and charging with a polymer film improves the charge level, but with the passage of time, the charge amount of the film increases and discharge becomes easier,
There is a problem that the charging efficiency is reduced and the dispersion of the collection performance is increased. In the method in which the film is charged and then made into a fibrous shape, the adhesion of the film to the electrode is increased when the film is charged, which causes breakage of the film. When this film breakage occurs, the film is charged, so that the film is easily wound around a roll or the like, which causes a trouble in manufacturing.

Therefore, an object of the present invention is to manufacture an electret filter which can be efficiently charged on each fiber for forming an electret filter and is excellent in various performances such as collection efficiency. It is an object of the present invention to provide a method which is stable and can be rapidly obtained in a high yield without trouble.

[0005]

In order to solve the above-mentioned problems, the present invention provides a polymer fiber assembly by superposing a polymer film (B) on at least one of the upper surface and the lower surface of the polymer fiber assembly. A direct current voltage is applied to the body, and a voltage having a polarity opposite to the charging voltage is applied to the polymer film (B) to charge the polymer fiber assembly, and then the polymer fiber assembly is The present invention provides a method for manufacturing an electret filter, which has a step of forming an electret filter.

[0006] It is preferable that the polymer fiber aggregate is a flat fibrillated fiber aggregate formed by defibrating a polymer film.

A voltage having a polarity opposite to the charging voltage is applied to the polymer film (B) at a portion other than the portion where the polymer film (B) is superposed on the polymer fiber assembly. It is valid.

The method for producing the electret filter of the present invention (hereinafter referred to as "the method of the present invention") will be described in detail below.

In the method of the present invention, the polymer compound forming the polymer fiber aggregate may be either a polar polymer compound or a non-polar polymer compound, a crystalline polymer compound or an amorphous polymer compound. Any of molecular compounds may be used. Further, one kind of polymer compound may be used alone, or two or more kinds of polymer compounds may be mixed and used.

Examples of non-polar polymer compounds include polyolefins such as polyethylene and polypropylene, polystyrene, polytetrafluoroethylene, and tetrafluoroethylene.
Examples thereof include propylene hexafluoride copolymer.

Examples of the polar polymer compound include, for example, a carboxyl group, an ester group, an amide group, a hydroxyl group, an ether group, a nitrile group, a carbonyl group,
Alternatively, it has a polar group such as a halogen atom such as a chlorine atom. Specific examples of the polar polymer compound include polyesters such as polyethylene terephthalate and polytetramethylene terephthalate; polyamides such as nylon 6, nylon 66 and nylon 12; acrylic resins such as polycarbonate, polymethylmethacrylate and polyethylacrylate. Acrylic-styrene copolymer resin (AS resin), acrylic-butadiene-styrene copolymer resin (ABS resin), polyvinyl chloride, polyvinylidene chloride, polychlorotrifluoroethylene, polyacetal, polyacrylonitrile, etc. Be done.

Further, a modified nonpolar polymer compound obtained by graft-copolymerizing a monomer having a polar group to the nonpolar polymer compound can also be used as the polar polymer compound. Such a modified nonpolar polymer compound is obtained by adding at least one selected from unsaturated carboxylic acids and their derivatives to the nonpolar polymer compound in the presence of a radical polymerization initiator such as an organic peroxide. , Graft-copolymerized and the like.

The unsaturated carboxylic acid and its derivative used for the graft modification include, for example, unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid and α-ethylacrylic acid; maleic acid, fumaric acid, itaconic acid and citraconic acid. , Tetrahydrophthalic acid, methyltetrahydrophthalic acid, endocis-bicyclo [2,2,1] hept-
5-ene-2,3-dicarboxylic acid (nadic acid), methyl-endocis-bicyclo [2,2,1] hept-5-
Unsaturated dicarboxylic acids such as ene-2,3-dicarboxylic acid (methyl nadic acid); derivatives of unsaturated carboxylic acids such as acid halides, amides, imides, acid anhydrides and esters of these unsaturated carboxylic acids. Be done. Specific examples of the derivative of this unsaturated dicarboxylic acid include maleenyl chloride,
Maleimide, maleic anhydride, citraconic anhydride, monomethyl maleate, dimethyl maleate, etc. are mentioned. These unsaturated carboxylic acids and their derivatives are
They may be used alone or in combination of two or more. In the present invention, of these, unsaturated dicarboxylic acids and acid anhydrides thereof are preferable, and maleic acid, nadic acid and acid anhydrides thereof are particularly preferable.

In the modified non-polar polymer compound, the content of these unsaturated carboxylic acid and its derivative, that is, the graft modification amount of the modified non-polar polymer compound is usually about 0.05 to 15% by weight, preferably Is 0.5-5
It is about% by weight.

In the method of the present invention, the polymer compounds may be used alone or as a mixture of two or more kinds. When two or more kinds of the above-mentioned polymer compounds are mixed and used, the polar polymer compounds may be mixed with each other, the nonpolar polymer compounds may be mixed with each other, or the polar polymer compound and the nonpolar polymer compound may be mixed. Further, a modified non-polar polymer compound may be used as a part of the polar polymer compound.

When the nonpolar polymer compound and the polar polymer compound are mixed and used, the mixing ratio of the nonpolar polymer compound / polar polymer compound is 60 to 99 / 0.5 by weight.
˜39.5, preferably 80-95 / 1-10.
When the modified nonpolar polymer compound is used as a part of the polar polymer compound, the content ratio thereof is usually about 0.5 to 20% by weight, preferably 4 to 10% by weight based on the total amount of the composition. %.

In addition to the polymer compound, if necessary, for example, heat resistance stabilizers, weather resistance stabilizers, antistatic agents, slip agents, antiblocking agents, lubricants, inorganic or organic fillers, dyes, pigments, etc. May be used.

The method of the present invention uses a polymer fiber aggregate composed of these polymer compounds as a raw material.
This polymer fiber assembly may be one obtained by defibrating a polymer film made of the polymer compound (hereinafter, referred to as “polymer film (A)”).
It may be directly fiberized by a method such as melt spinning or wet spinning. When the polymer fiber assembly is a flat fiber-like defibrated yarn assembly obtained by defibrating the polymer film (A), its cross-sectional shape is rectangular, and charging efficiency is higher than that of defibrated yarn with a circular cross section. Is preferable because it is excellent. The method for producing the polymer film (A) is not particularly limited, and any method usually used as a method for forming a film from a resin of this type can be applied. Examples thereof include an inflation film molding method, an extrusion molding method using a T-die, and a method using roll rolling. The thickness of the polymer film (A) thus obtained is the basis weight of the electret filter, which is a product,
It can be appropriately selected in advance so that the pressure loss or the like has a desired value. Usually, the thickness is about 10 to 100 μm,
In order to make the draw ratio 6 to 10 times, 20 to 50 μm
The thickness is preferably about the same.

The method for defibrating the polymer film (A) to produce a polymer fiber aggregate is not particularly limited, and the film may be stretched or not stretched, for example, needle rolls or the like. It can be defibrated using a defibrating machine.

In the defibration of the polymer film (A), when the film is stretched, the stretching is usually carried out at a temperature not lower than the softening point and not higher than the melting point of the polymer compound constituting the polymer film (A),
For example, it is heated to about 110 to 150 ° C., and is performed in the machine direction of the film using a roll, a hot plate, an oven, or the like. At this time, the draw ratio is usually about 5 to 10 times, preferably about 6 to 8 times in terms of good molding stability and easy defibration thereafter.

The polymer fiber aggregate obtained by defibrating the polymer film (A) may be wound on a paper tube, a drum or the like and then transferred to the next step, or continuously continuously as it is. It may be supplied to the process.

Here, the polymer fiber aggregate referred to in the method of the present invention means that the fibers are densely accumulated into a sheet form from a state in which the fibers are dispersed in a flat state in a sparse state by the manufacturing method. It includes any aggregate state up to the formed state.

Further, in the method of the present invention, when the fibers constituting the polymer fiber aggregate are fibers having a substantially rectangular cross-sectional shape, for example, the defibrated yarn is efficiently charged in the subsequent charging process. Therefore, it is preferable.

According to the method of the present invention, when the polymer fiber aggregate comprising the above polymer compound is subjected to the charging treatment, the polymer film (B) is provided on at least one of the upper surface and the lower surface of the polymer fiber aggregate. This is a method of stacking and applying a charging voltage to the polymer fiber assembly and applying a voltage having a polarity opposite to the charging voltage to the polymer film (B).

The material of the polymer film (B) laminated on the polymer fiber assembly may be any of the above-mentioned polar polymer compound and nonpolar polymer compound,
Further, it may be amorphous or crystalline. In particular,
The polymer film (B) is preferably a fluororesin film in terms of slipperiness and high insulation.

The thickness of the polymer film (B) is in the range of 1 to 1000 μm, preferably 5 to 50 μm in view of good charging efficiency.

Further, in the method of the present invention, the method and the apparatus for carrying out the charging treatment in a state where the polymer fiber aggregate and the polymer film (B) are superposed on each other are a method and a device capable of being made into a predetermined electret. If there is no particular limitation.

In the above charging device, the charging electrode is needle-shaped,
A wire-shaped electrode or the like is used, and as a charging method, a method of continuously or intermittently applying corona charge to a polymer fiber assembly is used. Also, as the ground electrode,
An electrode having a needle shape, a wire shape, a plate shape, a roll shape, or the like is used.

In the method of the present invention, the polymer film (B) laminated on the polymer fiber assembly to be charged is
The method of applying a voltage having the opposite polarity to the charging voltage applied to the polymer fiber assembly is not particularly limited, and for example, a method such as corona discharge can be used. Further, the location of applying a voltage having a polarity opposite to the charging voltage to the polymer film (B) is not particularly limited, but a location other than a portion where the polymer film (B) and the polymer fiber assembly are superposed on each other. Then, when a voltage having a polarity opposite to the charging voltage is applied to the polymer film (B), a decrease in charging efficiency with time is prevented, and the number of discharges at the time of charging is suppressed. It is preferable in that the productivity is improved.

In the method of the present invention, the polymer film (B) is superposed on at least one of the upper surface and the lower surface of the polymer fiber assembly, a direct current voltage is applied to the polymer fiber assembly, and the polymer film ( As a preferred embodiment of the method and apparatus for applying a DC voltage having a polarity opposite to that of the DC voltage to B) to perform the charging treatment, for example, the apparatus shown in FIGS. 1A and 1B and FIG. Is mentioned. Less than,
The apparatus shown in FIGS. 1A and 1B and FIG. 2 will be described. 1 (a) and 1 (b) and FIG. 2, the same members or places are designated by the same reference numerals.

In the charging device shown in FIG. 1 (a), the polymer fiber aggregate 1 transferred from the defibrating step is introduced into the charging device by the rolls 2a and 2b, and taken up by the rolls 3a and 3b. .. This polymer fiber assembly 1 passes between a roll-shaped ground electrode 4 and a needle-shaped charge electrode 6 which is held at a predetermined voltage V ₁ by a DC power supply 5 with respect to the ground electrode 4 to charge the ground electrode 4. Processing is performed.
At this time, the roll-shaped ground electrode 4 and the roll 7 arranged corresponding to the ground electrode 4 rotate in conjunction with each other, and the polymer wound between the ground electrode 4 and the roll 7 The film (B) 8 is charged in a state of being superposed on the lower surface of the conveyed polymer fiber assembly 1. Also,
The roll 7 is grounded, and the polymer film (B) 8 is applied with a voltage having a polarity opposite to that of the charging electrode 6 by an electrode to which a DC voltage having a polarity opposite to that of the DC power source 5 is applied by a DC power source 9. It After the charging treatment, the polymer fiber assembly 1 is electretized by the rolls 3a and 3b.
Are transferred to the next step.

In the charging device shown in FIG. 1 (b), the polymer fiber aggregate 1 transferred from the defibrating step is introduced into the charging device by the rolls 2a and 2b and taken up by the rolls 3a and 3b. .. The polymer fiber assembly 1 passes between a roll-shaped ground electrode 4 and a wire-shaped charging electrode 6 which is held at a predetermined voltage V by a DC power supply 5 with respect to the ground electrode 4, and the charging process is performed. Is given. At this time, the roll-shaped ground electrode 4 and the roll 7 arranged corresponding to the ground electrode 4 rotate in conjunction with each other, and the polymer wound between the ground electrode 4 and the roll 7 The film (B) 8 is charged in a state of being superposed on the lower surface of the conveyed polymer fiber assembly 1. Also,
The roll 7 is grounded, and a voltage opposite to that of the charging electrode 6 is applied to the polymer film (B) 8 by an electrode to which a DC voltage having a polarity opposite to that of the DC power source 5 is applied by a DC power source 9. After the charging treatment, the electretized polymer fiber assembly 1 is transferred to the next step by the rolls 3a and 3b.

Further, in the charging device shown in FIG. 2, the polymer fiber assembly 1 transferred from the defibration process is provided with a roll-shaped ground electrode 4 and a predetermined DC power source 5 for the ground electrode 4. Wire-shaped charging electrode 6 held at voltage V
And a charging process is performed. At this time, the polymer film wound around the ground electrode 4 in a roll shape and applied with a voltage reverse to that of the charging electrode 6 by the electrode to which a direct current voltage is applied by the direct current electrode 9 in the opposite polarity to the direct current power source 5. (B) 8 is charged in a state of being superposed on the lower surface of the polymer fiber assembly 1 being transferred. The roll-shaped ground electrode 4 is grounded. This Figure 2
Since the apparatus shown in (1) does not cause wrinkles due to deviation of the polymer film or the like, high-speed molding is possible, and the polymer film is less likely to be cut by discharge, so that the production stability is improved.

In the method of the present invention, the voltage applied between the charging electrode and the ground electrode for performing the charging treatment is usually about 3 to 30 kV, preferably 5 to 15 kV.
It is a degree. Also, the gap between the charging electrode and the ground electrode is
Usually about 3 to 30 mm, preferably 5 to 15 m
It is about m. Further, the residence time of the polymer fiber aggregate between both electrodes is usually about 0.01 to 1 second.
Furthermore, the ambient atmospheric temperature at the time of the charging treatment is not particularly limited, and it is preferably around room temperature.

In the method of the present invention, the electrified fiber can be obtained by, for example, cutting the polymer fiber aggregate charged as described above to 90 mm with a cutter and applying it to a cotton opener. Further, the obtained electretized fiber can be made to have a desired thickness by previously selecting the thickness of the film used for defibration, the draw ratio, the degree of defibration, and the like. Further, the cotton opening machine used is not particularly limited and may be one normally used in this type of cotton opening process.

Next, the obtained electretized fibers can be collected and molded into a desired shape to obtain an electret filter.

Molding of electretized fibers is carried out, for example, by
The electretized fiber obtained as described above can be produced by weaving, knitting, tufting, or molding into a non-woven fabric according to a conventional method.
For example, a raw material having a desired property can be manufactured according to a method such as needle punching, thermal bonding, ultrasonic bonding or the like.

The electret filter produced by the method of the present invention is used in a form cut into a predetermined size or folded in a pleat shape. At this time, the electret filter can be used alone or by laminating a commonly-used non-woven fabric according to a conventional method.

The electret filter obtained by the manufacturing method of the present invention, for example, has the advantage that it can efficiently collect fine particles of 1 μm or less in size,
It is suitable for applications such as air cleaning materials, vacuum cleaner filters, air conditioner filters, and masks.

[0040]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples of the present invention.

Example 1 Polypropylene (Mitsui Petrochemical Co., Ltd., Hipol B200, MFR: 0.
5 g / 10 min) 9000 g, polycarbonate (manufactured by General Electric Co., Lexan 101) 500 g and maleic anhydride-modified polypropylene (maleic anhydride graft modification amount: 3% by weight) 500 g were mixed to prepare a resin composition.

The resin composition thus obtained was supplied to an inflation film molding machine (manufactured by Toshiba Machine Co., Ltd.) for 24 hours.
It was formed into a film having a thickness of 30 μm at 0 ° C. Next, this film was stretched with a hot plate at a stretching ratio of 6.6 times in the longitudinal direction at 135 ° C., and was hung on a needle-shaped roll to be fibrillated into a mesh, and the obtained defibrated yarn was Fluorine resin film with a thickness of 25 μm on the lower surface (FEP, manufactured by Daikin Industries, Ltd.,
Neocron NF-0025) is piled up and this is shown in FIG.
Corona discharge by applying an applied voltage of -9 kV (direct current) between the charging electrode of the charging device having the structure shown in FIG. Was charged and subjected to a charging treatment, and then wound on a paper tube.
At this time, a DC voltage of +7 kV was applied to the FEP film. Then, unwind the electretized defibrated yarn from the paper tube and cut it to 90 mm with a cutter,
It was applied to a cotton opener to obtain electretized raw cotton.

The obtained electret raw cotton is supplied to a web forming machine to form a web,
Needle punching was performed to produce an electret filter having a basis weight of 100 g / m ² and a thickness of 2 mm. The formability at this time was evaluated by the number of breaks of the defibrated yarn and the number of occurrences of discharge, and is shown in Table 1. Moreover, the collection efficiency of the obtained electret filter was measured according to the following method. The results are shown in Table 1.

Collection efficiency The collection efficiency was measured using the measuring device schematically shown in FIG. First, aerosol generator (made by Nippon Kagaku Kogyo Co., Ltd.) 21
NaCl particles (particle diameter: 0.3 μm) were supplied from the above, and clean air passed through the air filter 22 was supplied to the chamber 23. After the concentration of NaCl particles in the chamber 23 reaches a constant concentration (2 to 6 × 10 ⁶ ), the blower 24 is operated to adjust the flow rate of the gas in the chamber 23 through the flow path 25 with the flow rate adjusting valve 26. Sucked. When the flow velocity measured by the anemometer 27 reaches a constant velocity (0.5 m / sec), the NaCl particle concentration Cin in the upstream side and the downstream side of the electret filter 28, which is the measurement target, disposed in the flow passage 25. And Cout with a particle counter (KC-01B manufactured by Rion Co.) 29a and 29b,
Each was measured. The collection efficiency was calculated based on the following formula. Collection efficiency = [1- (Cout / Cin)] × 100 (%)

(Example 2) F was formed on the upper surface of the polymer fiber assembly.
An electret filter was manufactured in the same manner as in Example 1 except that EP films were overlaid and a voltage of +7.5 kV was applied to the FEP films. The moldability and the collection efficiency of the obtained electret filter were evaluated or measured.
The results are shown in Table 1.

Example 3 An electret filter was manufactured in the same manner as in Example 1 except that a polypropylene film having a thickness of 30 μm was used instead of the FEP film and a voltage of +7.5 kV was applied to the polypropylene film. The moldability and the collection efficiency of the obtained electret filter were evaluated or measured. The results are shown in Table 1.

Example 4 An electret filter was manufactured in the same manner as in Example 1 except that a Kapton film having a thickness of 50 μm was used instead of the FEP film and a voltage of +7.5 kV was applied to the Kapton film. The moldability and the collection efficiency of the obtained electret filter were evaluated or measured. The results are shown in Table 1.

(Example 5) The defibrated yarn obtained in the same manner as in Example 1 was supplied to the charging device shown in Fig. 2 to form a needle-shaped charging electrode and a fluororesin film (F) having a thickness of 25 µm.
EP), an applied voltage: −8 kV, an electrode interval: 8 mm, a residence time: 0.
After performing the charging treatment under the condition of 5 seconds, the electretized defibrated yarn was wound around a paper tube. At this time, a DC voltage of +8 kV was applied to the FEP film. Next, the electretized defibrated yarn was treated in the same manner as in Example 1 to form an electret filter, the moldability at this time was evaluated, and the collection efficiency of the obtained electret filter was measured. The results are shown in Table 1.

Example 6 An electret filter was formed in the same manner as in Example 1 except that a polypropylene film having a thickness of 30 μm (F301 manufactured by Mitsui Petrochemical Industry Co., Ltd.) was used as the polymer film. The moldability was evaluated, and the collection efficiency of the obtained electret filter was measured. The results are shown in Table 1.

Example 7 A Kapton film having a thickness of 50 μm was used as a polymer film, and a charging DC voltage: −
An electret filter was molded in the same manner as in Example 1 except that a DC voltage of 9 kV and +8.5 kV was applied to the Kapton film, the moldability was evaluated, and the collection efficiency of the obtained electret filter was measured. The results are shown in Table 1.

Example 8 As the polymer film, a porous polypropylene film (PF2000, Ube Industries, Ltd., PF2000, porosity: 20%) having a thickness of 30 μm was used, and the charging DC voltage was −8.2 kV and the porous polypropylene film was used. An electret filter was molded in the same manner as in Example 1 except that a DC voltage of +7.2 kV was applied to the sample, the moldability was evaluated, and the collection efficiency of the obtained electret filter was measured. The results are shown in Table 1.

(Example 9) As a polymer film, a porous polypropylene film having a thickness of 30 μm (PF5010, Ube Industries, PF5010, porosity: 50%) was used, and a charging DC voltage was -8.2 kV and a porous polypropylene film. An electret filter was molded in the same manner as in Example 1 except that a DC voltage of +7.2 kV was applied to the sample, the moldability was evaluated, and the collection efficiency of the obtained electret filter was measured. The results are shown in Table 1.

(Comparative Example 1) An electret filter was produced in the same manner as in Example 1 except that the stretched film produced in Example 1 was defibrated and then directly supplied to the electrodes for charging treatment. .. The moldability and collection efficiency of the obtained electret filter were evaluated or measured. The results are shown in Table 1.

(Comparative Example 2) An electret filter was prepared in the same manner as in Example 1 except that a FEP film was used as the polymer film (B) and was superposed on the lower surface of the defibrated yarn, and no positive voltage was applied to the FEP film. Was manufactured. The moldability and collection efficiency of the obtained electret filter were evaluated or measured. The results are shown in Table 1.

[0055]

[0056]

[0057]

EFFECTS OF THE INVENTION According to the method of the present invention, an electret filter excellent in various performances such as a collection efficiency which cannot be achieved by the conventional method can be obtained without causing manufacturing trouble as in the conventional method. It can be stably and efficiently manufactured quickly.

[Brief description of drawings]

1A and 1B are schematic views showing a configuration of an apparatus used for charging processing, respectively.

FIG. 2 is a schematic diagram showing another configuration of an apparatus used for charging processing.

FIG. 3 is a schematic diagram showing a configuration of an apparatus used for measuring collection efficiency.

[Explanation of symbols]

 1 Polymer Fiber Aggregate 2a, 2b Roll 3a, 3b Roll 4 Ground Electrode 5 DC Power Supply 6 Charging Electrode 7 Roll 8 Polymer Film (B) 9 DC Power Supply 21 Aerosol Generator 22 Air Filter 23 Chamber 24 Blower 25 Distribution Channel 26 Flow rate adjusting valve 27 Velocity meter 28 Electret filter 29a, 29b Particle counter

Claims (4)

[Claims] 1. A polymer film (B) is superposed on at least one of the upper surface and the lower surface of a polymer fiber assembly, and a direct current voltage is applied to the polymer fiber assembly, and the polymer film (B) is applied to the polymer film (B). A method for producing an electret filter, comprising a step of applying a voltage having a polarity opposite to that of the charging voltage to subject the polymer fiber assembly to a charging treatment and then molding the polymer fiber assembly into an electret filter. 2. The method for producing an electret filter according to claim 1, wherein the polymer fiber aggregate is a flat fiber-disentangled yarn aggregate formed by defibrating a polymer film. 3. The polymer film (B) is applied with a voltage having a polarity opposite to the charging voltage to the polymer film (B) at a portion other than the portion where the polymer film (B) is superposed. Item 3. A method for manufacturing an electret filter according to Item 1 or 2. 4. The polymer film (B) has a porosity of 50.
% Or less film, The manufacturing method of the electret filter in any one of Claims 1-3.