JPH04326910A - Production of electret filter - Google Patents

Abstract

PURPOSE:To obtain an electret filter enhanced in charge quantity, excellent in collection efficiency and reduced in the lowering of collection efficiency even at the time of the large loading with dust. CONSTITUTION:A metallized layer is applied to the surface of a film made of a non-polar polymer material to form an electret film and this film is fibrilated to obtain divided fibers which are, in turn, formed into a nonwoven fabric to be used as a filter.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to air filters, and more particularly to a method for producing an electret air filter that can be used for air cleaner filters, air conditioning filters, vacuum cleaner exhaust filters, masks, and the like.

0002

[Prior Art] A technique for converting a film into an electret, splitting it into fibers, and converting this into a non-woven fabric into an electret filter was disclosed in the Japanese Patent Publication No. 56-47.
No. 299, JP-A-62-102809 is disclosed. The former method involves stretching a film made of a non-polar polymer material, electrically charging it, turning it into an electret, and splitting it. In addition to the former technique, the latter technique is characterized by limiting the fiber diameter or fiber width of the fiber 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

[Problems 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, and the amount of charge is reduced over time. There was a problem that collection efficiency decreased. The inventors of the present invention have conducted intensive studies to solve the above problems, and as a result, they have arrived at the present invention.

0004

[Means for Solving the Problems] The present invention is an electret filter in which an electret film having a metal vapor deposited layer is split and made into a nonwoven fabric, and is characterized in that the metal vapor deposit layer is applied at the stage of a non-electret film, and then the electret film is formed. The present invention relates to a method for manufacturing an electret filter. The present invention improves the adhesion between the metal vapor deposition layer and the earth electrode by performing metal vapor deposition treatment on the electret film and then converting it into an electret film, thereby increasing the amount of injected charge to obtain an extremely high charge amount. The present invention is characterized by obtaining an electret filter whose performance is stable against dust loads such as cigarette smoke. It is not clear why metal vapor deposition treatment before electret formation on the film leads to a high amount of charge, but compared to an undeposited electret film, the surface potential becomes very uniform throughout the electret film, so metal vapor deposition It is presumed that the uniformity of charge injection by the film is related to the improvement in the amount of charge. The electret film in the present invention is preferably a non-polar polymer material in order to stabilize the amount of charge over time, and specific examples include polyethylene, polypropylene, α-polyolefin, polystyrene, polytetrafluoroethylene, etc. . The thickness of the film is 50 μm or less, more preferably 20 μm or less. Furthermore, in the present invention, splitting a film means cutting the film into fibers by cutting the film in a width of 1 mm or less in the width direction, and there are methods such as slitting the film at a constant width or splitting at random widths. . In addition, in the present invention, the nonwoven fabric obtained by splitting a film made of a polymeric material has a fabric weight of 10 to 30.
0 g/m2 is appropriate, and within the range of 30 to 100 g/m2, the balance between collection efficiency and pressure loss becomes more practical. The average fiber width of the fibers constituting the nonwoven fabric is 300 μm or less, more preferably 100 μm or less.
It is less than μm. In the present invention, the metal vapor deposition process is usually performed by attaching a metal in a vapor state to the surface of the film under vacuum. The thickness of the metal vapor deposition layer is 1000
The range is from Å to 100 Å, more preferably from 700 Å to 3
It is in the range of 00 Å. There is no problem whether the metal vapor deposition layer is applied over the entire surface of the film or only partially. The metals used for metal vapor deposition include tin, copper, zinc, silver,
Aluminum and the like are preferred, and copper and silver can also impart antibacterial effects. In the present invention, as a method for charging the film having a metal vapor deposited layer, corona charging, electric field charging, and hot electric field are preferable, but electron irradiation and the like can also be used. In the case of corona charging and electric field charging, 10 kV/c
Irradiation is preferably at least 20 kV/cm, more preferably at least 20 kV/cm, and in the case of electron irradiation, at 0.1 to 1.0 Mrad.

[0005]

[Function] The electret filter manufactured by the above method is composed of fibers obtained by applying an electric charge to a film having a metal vapor-deposited layer and then splitting the film, so the amount of charge is extremely high and the collection efficiency is high. Not only is it possible to obtain this, but the collection efficiency is also less likely to decrease due to dust loads such as cigarette smoke.

[0006]

[Examples] Examples of air filters according to the present invention will be shown below. 20 for a 10 μm thick polypropylene film treated with aluminum vapor deposition (500 Å thick)
After charging at kV/cm for 10 seconds and splitting the fibers to an average width of 40 μm, an air filter with a basis weight of 100 g/m 2 was manufactured as Example 1. In addition, as a comparative example, the same film as in Example 1 was made into electret under the same charging conditions without vapor deposition, and split under the same splitting conditions to obtain a fabric weight of 100 g/m.
Comparative example 1 was made by manufacturing an electret filter with
And so. Next, the same polypropylene film was made into electret under the same charging conditions, split under the same splitting conditions, and then subjected to aluminum evaporation processing (thickness: 500 Å) to produce an air filter with a basis weight of 100 g/m2. Comparative Example 2
And so. For these three particles, the particle size is 0.
A light scattering particle counter (R
It was measured using an ION particle counter KC-01A). The results are shown in Table 1. The surface potentials of these three materials were measured using a Kawaguchi electric surface potential meter S-211. The results are shown in Table 2. Furthermore, in order to examine the dust load characteristics, 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, from Table 2, the surface potential of Example 1 is significantly higher than that of Comparative Example 2. Comparative Example 2, in which aluminum vapor deposition was performed after electret, had the same collection efficiency and surface potential as Comparative Example 1, and there was no significant difference. Further, in FIG. 1, Example 1 showed a significantly smaller decrease in dust removal efficiency due to the load of tobacco smoke than Comparative Examples 2 and 3.

[0007]

[Effects of the Invention] Compared to the conventional technology of splitting an electret film to make an air filter, the present invention performs metal vapor deposition on the film before making it into an electret, so it is possible to obtain a higher amount of charge. This makes it possible to significantly suppress the reduction in collection efficiency due to dust loads such as cigarette smoke.

[0008]

[Brief explanation of drawings]

Figure 1 is a diagram showing the filter's removal efficiency for cigarette smoke, and the dust load characteristics are evaluated by varying the number of cigarettes.

[Table 1]

[Table 2]

Claims (1)

[Claims] 1. An electret filter characterized in that a metal vapor-deposited layer is applied to the surface of a film made from a non-polar polymeric material, the film is treated to become an electret, the fibers are split, and the resulting split fibers are made into a non-woven fabric. manufacturing method.