JPH04305214A - Electret filter - Google Patents

Abstract

PURPOSE:To provide the electret filter which is higher in electrostatic charge quantity than the electrostatic charge quantity of conventional air filters and can drastically suppress the degradation in capturing efficiency by the dust load of tobacco smoke, etc. CONSTITUTION:After a vapor deposited metallic layer consisting of copper, silver, etc., is formed on a film, this layer is converted to an electret and the film is split to fibers and is made into a nonwoven fabric, by which the electret filter is obtd.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electret filter, and more particularly to an electret filter that can be used in air filters such as filters for air cleaning equipment, air conditioning filters, and exhaust filters for vacuum cleaners, masks, and the like.

0002

[Prior Art] A technique for converting a film into an electret, dividing it into fibers, and converting the fiber into a non-woven fabric to form an electret filter is disclosed in Japanese Patent Publication No. 56-47299.
It is disclosed in Japanese Patent Application Laid-Open No. 62-102809. The former method involves stretching a film made of a non-polar polymer material, converting it into an electret by charging it, and then splitting it. In addition to the former technique, the latter is characterized by limiting the fiber diameter or fiber width of the fibers obtained by splitting, and at the same time allowing the non-polar polymer to contain a polar polymer at a maximum of 40 wt%.

0003

[Problem to be solved by the invention] When the electret filter obtained by these techniques is used for a long period of time, static electricity is neutralized and reduced due to the load of dust such as cigarette smoke, and the amount of charge decreases over time. However, there was a problem in that the collection efficiency decreased.

The present invention has been made in view of the above-mentioned circumstances, and has a higher charge amount than conventional electret filters, which significantly suppresses the reduction in collection efficiency due to dust loads such as cigarette smoke. The aim is to provide an electret filter that can.

[0005]

[Means for Solving the Problems] The present invention, which has solved the above-mentioned objects, is characterized in that after a metal vapor-deposited layer is formed on a film, it is made into an electret, split, and made into a non-woven fabric.

[0006]

[Function] As a result of extensive research, the present inventors have found that if the film is subjected to metal vapor deposition treatment in advance and then converted into an electret, it is possible to improve the adhesion between the metal vapor deposited layer and the earth electrode, and to reduce the amount of charge injected. It has become possible to obtain an extremely high amount of charge by increasing the amount of charge, and as a result, it has been found that an electret filter with stable performance against dust loads such as cigarette smoke can be obtained.

[0007] Although it has not been elucidated why applying metal vapor deposition to a film before electret formation leads to a high amount of charge, compared to the electret film before metal vapor deposition, the electret film after metal vapor deposition has less metal vapor deposition. Since the surface potential is uniform over the entire surface of the film, it is presumed that uniform charge injection by forming the metal vapor deposition film has a positive effect on improving the amount of charge.

[0008] As the film material according to the present invention, a non-polar polymeric material is preferable in order to stabilize the amount of charge over time, and specifically, polyethylene, polypropylene, α
-Polyolefin, polystyrene, polytetrafluoroethylene, etc. may be mentioned. The thickness of the above film is 50 μm.
The thickness is preferably 20 μm or less, more preferably 20 μm or less.

[0009] Splitting a film in the present invention means cutting the film in the width direction into fibers with a width of 1 mm or less, and the film is preferably a uniaxially oriented film, which is cut into fibers with a constant width. You can also split it with
You can also split it at random widths.

[0010] In addition, a nonwoven fabric obtained by splitting a film made of a polymeric material has an appropriate weight of 10 to 300 g/m2, and a balance between collection efficiency and pressure loss is achieved within the range of 30 to 100 g/m2. It becomes more practical. The average fiber width of the fibers constituting the nonwoven fabric is 300μ
m or less, more preferably 100 μm or less.

[0011] The metal vapor deposition treatment in the present invention may be carried out according to a conventional method of vaporizing the metal under vacuum and depositing it on the surface of the film. The thickness of the metal deposition layer is 1000 Å
A range of ~100 Å is preferred, and a range of 700 Å to 300 Å is more preferred. The metal vapor deposition layer may be formed over the entire surface of the film or may be formed partially. The metal used in the metal vapor deposition treatment is preferably tin, copper, zinc, silver, aluminum, etc. Especially, when copper or silver is used, antibacterial action can also be imparted.

[0012] As a method of charging the film having the metal vapor deposited layer, corona charging, electric field charging, and hot electric field charging are preferred, and electron irradiation and the like can also be used. When using corona charging and electric field charging, the electric field strength is 10kV.
/cm 2 or more is preferable, and 20 kV/cm or more is more preferable. In the case of electron irradiation, 0.1 to 1.0 Mra
d irradiation is desirable.

[0013] In the electret filter according to the present invention, after applying an electric charge to the film having the metal vapor deposited layer,
Since it is composed of fibers obtained by splitting, it has an extremely high electrostatic charge and not only achieves high collection efficiency, but also suppresses as much as possible the reduction in collection efficiency due to dust loads such as cigarette smoke. It has the characteristic of being able to

[0014]

[Example] A polypropylene film with a thickness of 10 μm that has been subjected to aluminum vapor deposition processing (thickness of 500 Å) is charged at 20 kV/cm for 10 seconds, split into fibers with an average width of 40 μm, and then with a fabric weight of 100 g/m2. An electret filter was manufactured as Example 1.

Further, an electret filter of Comparative Example 1 was obtained in the same manner as in the Example except that the aluminum vapor deposition process was not performed.

Next, an electret filter was produced in the same manner as in Example 1, except that after electretization and fiber splitting, aluminum vapor deposition was performed, and this was used as Comparative Example 2.

For the electret filters of Example 1 and Comparative Examples 1 and 2, the particle size was 0 at a linear velocity of 10 cm/s.
．． Atmospheric dust collection efficiency of 3 μm or more can be achieved using a light scattering particle counter (RION Particle Counter KC-OIA).
). The results are shown in Table 1.

[0018]

[Table 1]

Next, the surface potential of the above electret filter was measured using a Kawaguchi electric surface potentiometer S-211. The results are shown in Table 2.

[0020]

[Table 2]

Furthermore, up to 300 cigarettes were loaded with dust, and the corresponding dust removal efficiency was measured. The results are shown in Figure 1.

From Table 1, it can be seen that although the pressure loss of Example 1 is almost the same as that of Comparative Examples 1 and 2, the atmospheric dust collection efficiency is extremely high. Moreover, when looking at Table 2, the surface potential of Example 1 is significantly higher than that of Comparative Example 2. Moreover, in Comparative Example 2, in which aluminum vapor deposition was performed after the electret treatment, the collection efficiency and surface potential were comparable to those of Comparative Example 1, and no significant difference was observed.

Furthermore, it can be seen from FIG. 1 that in comparison with Comparative Examples 2 and 3, Example 1 can significantly suppress the reduction in dust removal efficiency due to the load of cigarette smoke.

[0024]

[Effects of the Invention] Since the present invention is constructed as described above, it is possible to obtain a higher amount of electrification compared to the conventional technology, and therefore, the reduction in collection efficiency due to the load of dust such as cigarette smoke is significantly suppressed. Now we can provide electret film.

[Brief explanation of drawings]

FIG. 1 is a graph showing changes in dust removal efficiency of an electret film according to the present invention and a comparative example.

Claims (1)

[Claims] [Claim 1] After forming a metal vapor deposition layer on the film,
An electret filter characterized by being made into an electret, split into fibers, and made into a non-woven fabric.