JPH0436724B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electret filter element that uses electrical and mechanical action to collect dust in a fluid.

[Conventional technology]

Conventionally, an electret filter element in which a large number of electret sheet-like materials are laminated in the direction of the air flow path is disclosed in Japanese Patent Application Laid-Open No. 10313/1983, D56-
Publication No. 10314 is known. However, in the filter elements disclosed in both publications, when the excessive wind speed exceeds 5 cm/sec, dust in the fluid leaks and passes through, and the collection performance is extremely reduced. In addition, in order to create a structure that does not impair collection performance under conditions where the wind velocity exceeds 5 cm/sec, there are manufacturing problems such as having to provide a long flow path or narrowing the pitch between the electric sheets. arise. Furthermore, this filter element collection method uses coulombs on the surface of the electret film to adsorb dust in the fluid. These JP-A-10313
There were limits to the improvements made in JP-A No. 56-10314.

[Problem that the invention seeks to solve]

The inventors of the present invention have conducted intensive studies on electret filter elements that do not have the above-mentioned drawbacks, and have found that:
We have arrived at the present invention. In particular, it is an object of the present invention to provide an electret filter element with improved leakage of dust in the fluid.

[Means for solving problems]

The present invention has the following configuration.

``That is, in the filter element of the present invention, the electret film and the electret fibrous sheet have a pitch between the electret films of 2 to 8 mm, and the film surface direction and the sheet surface direction are such that the fluid passes through the element. This is an electret filter element formed by laminating a large number of layers alternately so as to be substantially parallel to the direction in which the electret filter element moves.''Hereinafter, the electret filter element according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a perspective view of an electret filter element according to the present invention. In FIG. 1, 1 is an electret filter element, 2 is an electret film, 3 is an electret fibrous sheet, and 4 is an electret fibrous sheet 3.
5 indicates a frame.
The fluid to be filtered is introduced into the element 1 from the A side on the front side, passes through the electret fibrous sheet 3 which is the flow path 4, and then exits to the B side on the back side. At this time, the object to be collected such as dust contained in the fluid is mechanically collected by the electret fibrous sheet 3, and at the same time, an electric adsorption force different from this mechanical collection effect, That is, it is attracted and collected by electrostatic force. Therefore, the collection efficiency is extremely high compared to conventional filters, and once collected objects such as dust are collected mechanically and electrically, they do not fall off or scatter again. It has difficult characteristics. Moreover, by alternately laminating a large number of electret films and electret fibrous sheets, the shape of the element is stabilized, and its shape and electret performance can be maintained over a long period of time, and its performance can be stabilized.

FIG. 2 is a schematic cross-sectional view showing the charge state of the electret film 2 constituting the filter element according to the present invention.

FIG. 3 is a schematic cross-sectional view showing the charged state of the fibers forming the electret fibrous sheet 3 serving as the flow path. As shown in the figure, the charges on the electrified fibers are oriented and polarized in a certain direction.

FIG. 4 is a schematic cross-sectional view showing the charged state inside the electret fibrous sheet of FIG. 3 using charge vectors. As shown in the figure, the internal charges of the electret fibrous sheet are oriented in one direction.

FIG. 5 is a schematic diagram showing an example of a manufacturing apparatus for electrifying the film and fibrous sheet used in the electret filter element according to the present invention. In the figure, 6 indicates a sample to be electrified, 7 indicates a needle-like electrode, and 8 indicates a ground electrode. In this device, a sample 6 to be electrified is electrified by applying a high voltage direct current from a needle electrode 7 located at the upper center of the sample 6 to be electrified.

Next, the materials used for the film and fibrous sheet used in the present invention will be explained.

As raw materials for the electret film and electret fibrous sheet, there are used various polymers that can be converted into electrets, preferably synthetic polymers having electrical insulation properties with an electrical resistivity of 10 ¹³ Ω·cm or more. Examples include polyolefins, polyesters, polycarbonates, polyamides, polyfluorinated resins, acrylic resins, and vinyl chloride resins, among which polyolefins are preferred, and polypropylene is particularly preferred.

Here, the characteristics of the electret film constituting the electret filter element according to the present invention will be explained.

Electret film has a thickness of 50μ to 300μ
is preferred. If the thickness exceeds 300μ, the level of electrification will decrease;
If it is less than 50μ, vibration or flapping will occur due to the wind pressure of the passing air, making the overload state unstable. Most preferably it is 50μ to 100μ. Also,
The charge state of the electret film is that the front and back surfaces exhibit different polarities, and the charge density is +7.0 × 10 ^-10 coulombs/cm ² or more, -7.0 × 10 ^-10 coulombs / cm ² or less,
Preferably +1.0×10 ^-9 coulombs/cm ² or more, −1.0×
A value of 10 ^-9 coulombs/cm ² or less is desirable.

Next, the characteristics of the electret fibrous sheet will be explained.

The diameter of the fibers constituting the electret fibrous sheet is preferably about 10μ to 100μ, preferably 15μ to 40μ. Further, this fiber preferably has crimp properties. The crimp rate is preferably 3% to 20%, particularly preferably 5% to 15%. The fiber length is
It is sufficient as long as it is 20 mm or more, and long fibers are also acceptable. Preferably about 30 mm to 100 mm. As a fibrous sheet, the basis weight is preferably 10g/m ² to 100g/m ² .
Preferably 20g/ ^m2 to 40g/ ^m2 . The apparent density is preferably about 4.0×10 ⁻³ g/cm ³ to 8.0×10 ⁻³ g/cm ³ . When the apparent density exceeds 8.0×10 ^-3 g/cm ³ , pressure loss increases when used as a filter element. Moreover, if it is less than 4.0×10 ⁻³ g/cm ³ , the stability of the shape is poor. Particularly preferably 5.5×10 ^-3 g/
cm ³ to 6.5×10 ⁻³ g/cm ³ . In order to further stabilize the form of this fibrous sheet, it is preferable that the contact portions of the fibers are fused together by heat treatment or the like. This has the effect of preventing deterioration of the shape due to the wind pressure of the passing air.

Note that when an electrified fibrous sheet is heat-treated, the charges trapped inside the sheet may be released to the outside or be annihilated by mutual charges. good.

Since such a fibrous sheet is used as a flow path of a filter element, it needs to have excellent air permeability. If the thickness of the fibrous sheet in the direction of air passage is 3 cm,
-1079 test method, it is sufficient if it is 250 cc/cm ² /sec or more. If it is less than 250cc/cm ² /sec, the pressure loss will increase when the filter element is applied. Particularly preferably, it is 300 cc/cm ² /sec or more.

Furthermore, in the present invention, since the fibrous sheet is made of electret, the collection performance is improved. In particular, since the charges are polarized in a certain direction as shown in FIG. 3, electrification can be stabilized over a long period of time. The charge density on the front and back surfaces of this electret fibrous sheet is preferably +2.0×10 ^-11 coulombs/cm ² or more -2.0×10 ^-11 coulombs/cm ² or less, preferably +5.0×10 ^-11 coulombs/cm 2 or more. cm ² or more - 5.0×10 ^-11 coulombs/cm ² or less is desirable.

Next, a method of laminating an electret film and an electret fibrous sheet will be explained.

In order to maintain the electret performance of the electret film and electret fibrous sheet over a long period of time, these laminated layers alternately stack the electret film and electret fibrous sheet so that the charge polarities on their opposing surfaces are different. It is preferable to laminate them so that At this time, it is preferable to stack the electret fibrous sheets so that the fiber filling rate is 0.9 to 1.5%. If the fiber filling rate of the electret fibrous sheet exceeds 1.5%, the pressure loss will increase when it is used as a filter element, and if it is less than 0.9%, the morphological stability will be poor. Particularly preferred is 1.0 to 1.3%. Furthermore, when laminated alternately, it is important that the thickness of the electret fibrous sheets, that is, the pitch between the electret films, be 2 to 8 mm. If the pitch between the films exceeds 8 mm, the stability of the shape will be poor due to the wind pressure of flowing air when used as a filter element. Moreover, if it is less than 2 mm, the pressure loss will increase. Particularly preferred is 3 to 5 mm. This makes it possible to maintain electrification for a longer period of time.

The fiber filling rate is determined as follows.

N=V1/V2×100 V1=W/ρ N: Fiber filling rate (%) V1: Volume occupied by fibers in unit volume (cm ³ ) V2: Unit volume (cm ³ ) W: Volume occupied by fibers in unit volume Weight occupied (g) ρ: Specific gravity of fiber (g/cm ³ ) Hereinafter, the effects of the present invention will be explained in more detail with reference to Examples and Comparative Examples.

〔Example〕

Example 1 A polypropylene film with a thickness of 65 μm was
Electrification was carried out using the electret sheet manufacturing apparatus shown in the figure, and a large number of electret films were produced. The conditions for electrification were that the temperature of the ground electrode and the film to be electrified was 25°C, the distance between the tip of the needle-shaped electrode and the ground electrode was 3 cm, the applied voltage was -30 KV, and the application time was 20 seconds. The charge densities on the front and back surfaces of the electret film obtained at this time are as follows:
-1.0×10 ^-8 coulombs/cm ² , +9.6×10 ^-9 coulombs/
It was warm in ^cm2 .

On the other hand, a fibrous sheet composed of polypropylene filament yarn has an average fiber diameter of 23μ,
The crimp rate of the filament yarn is 7% to 13%, the average fiber length is 64mm, the basis weight is 30g/ ^m2 , the apparent density is ^6.0x10-3g / ^cm3 , and the air permeability is the thickness in the air passing direction. 270cc/ ^cm2 /sec (JIS-
1079) was electrified using the same electrifying apparatus, and a large number of electret fibrous sheets were produced. The conditions for electrification are that the temperature of the earth electrode and the fibrous sheet to be electrified is 25°C, the distance between the tip of the needle electrode and the earth electrode is 3 cm, and the applied voltage is -
The voltage was 25KV and the application time was 10 seconds. The charge densities on the front and back surfaces of the electret fibrous sheet obtained at this time were -6.0×10 ^-10 coulombs/cm ² , respectively.
It was +3.3×10 ^-11 coulombs/cm ² .

The electret film and electret fibrous sheet thus obtained were cut into strips of 4 cm x 19 cm, and the charge polarities of the opposing faces were set to be different, so that the fiber filling rate of the electret fibrous sheet was 1.1%. A large number of layers were stacked alternately so that
At this time, the pitch between the electric films is 3.
mm, and this 3 mm was the thickness of the electret fibrous sheet serving as the flow path. This laminated product is placed in a frame with an inner frame of 19 cm x 19 cm and a width of 4 cm, and the inner surface of the frame and the electret film and electret fibrous sheet are completely fixed with adhesive. A filter element as shown in Fig. 1 was created in which there is no

In this electric filter element,
Air with an average particle diameter of 0.1 μ was flowed in at a speed of 10 cm/sec, and the collection efficiency of the filter element before and after the filter element was determined using a CNC manufactured by Nippon Kanomax Co., Ltd. At the same time, the pressure loss was measured.

As a result, the initial collection efficiency for collecting dust of 0.005μ to 1μ was 87.8%, and the pressure loss was 0.4mmH ₂ O. In addition, when the performance was similarly measured after one month of continuous use, the collection efficiency was 86.2% and the pressure loss was 0.5mm.
H ₂ O, and there was almost no change in the initial performance.

Comparative Example 1 Only the same electret film as in Example 1 was used, and the charge polarity on the opposite sides of the electret film was set to be different polarities, and as much as possible without inserting an electret fibrous sheet between the electret films. A filter element was prepared in which the distance between the electret films was narrowed to 0.8 mm and the length of the flow path was four times that of Example 1, and similar performance evaluations were conducted.

As a result, the initial collection efficiency was 58.4%, the pressure loss was 0.2mmH ₂ O, and the collection efficiency after one month of continuous use was 58.4%.
The pressure loss was only 53.2%, and the pressure loss was 0.2 mmH ₂ O.

Comparative Example 2 Using the same electret film as in Example 1, and without electrifying the fibrous sheet with the same structure as in Example 1, the fiber filling rate of the electret fibrous sheet was the same as in Example 1. A filter element similar to that of Example 1 was prepared by alternately laminating a large number of electret films and fibrous sheets so that the following properties were evaluated.

As a result, the initial collection efficiency was 58.7%, the pressure loss was 0.4mmH ₂ O, and the collection efficiency after one month of continuous collection was 58.7%.
The pressure loss was only 51.2%, and the pressure loss was 0.5 mmH ₂ O.

Comparative Example 3 Only the same electret fibrous sheet as in Example 1 was used, the opposite sides of the electret fibrous sheet had charge polarities of different polarities, and the fiber filling rate of the electret fibrous sheet was the same as in Example 1. A similar filter element was created and a similar performance evaluation was conducted.

As a result, the initial collection efficiency was 64.5%, the pressure loss was 0.35mmH ₂ O, and the collection efficiency for one continuous month was 64.5%.
58.7%, and the pressure loss was 0.55 mmH ₂ O.

This increase in pressure loss is caused by the lack of a film that stabilizes the excessive state in parallel to the flow path direction, and the air introduced into the filter element is diffused inside the filter element, worsening the morphology of the fibrous sheet. This is due to an increase in pressure loss.

〔Effect of the invention〕

The electric filter element of the present invention has excellent collection performance because it mechanically and electrically collects objects to be collected, such as dust, in a fluid. Furthermore, since a large number of polarized electret films and electret fibrous sheets are alternately laminated, the shape retention of the fibrous sheets and flow channels is excellent. In addition, because it has good liquid permeability and low pressure loss, it is used in a wide range of fields, from general building air conditioning to small air purifiers.

[Brief explanation of drawings]

FIG. 1 is a perspective view of the electret filter element of the present invention, FIG. 2 is a schematic sectional view showing the charged state of the electret film used in the filter element of the present invention, and FIG. 3 is a perspective view of the electret film used in the filter element of the present invention. A schematic cross-sectional view showing the polarization charge state of the fibers constituting the electret fibrous sheet. Fig. 4 is a schematic diagram showing the orientation state of polarization charges inside the electret fibrous sheet using charge vectors. Fig. 5 shows the electret film. FIG. 2 is a schematic diagram showing an example of an apparatus for manufacturing an electret fibrous sheet. 1: Filter element, 2: Electret film, 3: Electret fibrous sheet,
4: Channel, 5: Frame, 6: Sample to be electrified, 7: Needle electrode, 8: Earth electrode.

Claims (1)

[Scope of Claims] 1. An electret film and an electret fibrous sheet, the pitch between the electret films is 2 to 8 mm, and the film surface direction and the sheet surface direction are the directions in which fluid passes through the element. An electret filter element consisting of a large number of alternating layers that are substantially parallel to each other. 2. The electret filter element according to claim 1, wherein the front and back surfaces of the electret film have different charge states. 3. The electret filter element according to claim 1, wherein the front and back surfaces of the electret fibrous sheet have different charge states.