JPS60199971A - Electret fiber and its production - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to an electret fiber and a method for producing the same, and is used, for example, as a filter for purifying air, and in particular to a cylindrical electret fiber and a method for producing the same. , concerning its manufacturing method.

[Background of the invention]

Conventionally, various filters have been used for the purpose of collecting dust in open air. However, there was nothing that could achieve "high collection efficiency with low pressure loss."

These two characteristics are contradictory.

In this respect, electret fibers that stably hold static electricity for a long time can collect dust with their electrostatic force, and can therefore be expected to have low pressure loss and high collection efficiency.

As a method for imparting electric charge to fibers, for example, as disclosed in Japanese Patent Publication No. 56-47299,
The film-like sort is polarized in advance to form an electret, which is then cut at one point to produce fibers. According to this method, the cross section of the conventional electret fiber becomes rectangular, as shown in FIG. 1, which is a perspective view showing the cross section and polarization state of the conventional electret fiber.

For example, if a fiber aggregate (so-called non-woven fabric) is made using the needle punch method and used as a filter, charges of different polarities will coexist in the vicinity of each other, and the fibers will adhere to each other. The disadvantage is that the charge density decreases, and since the fiber cross section is rectangular, it also has the disadvantage that the pressure loss is higher than that of cylindrical fibers.

Furthermore, JP-A-54-113900 describes a method for producing cylindrical fibers as shown in FIG. 2, which is a perspective view showing the cross section and polarization state of conventional electret fibers. However, since charges of different polarity exist on the surface of the same fiber, the charge density decreases due to the above-mentioned reason, resulting in a decrease in collection performance.

[Purpose of the invention]

An object of the present invention is to provide an electret fiber used in an air purifying filter with high dust collection efficiency, and a method for producing the same. It is something.

[Summary of the invention]

The structure of the electret fiber according to the present invention is that it is formed into a hollow shape, and the center part of the fiber and the surface part of the fiber have different charge polarities.

Additionally, the surface of the fibers that make up the air purifying filter can all have the same polar charge, and the performance of the filter depends on the surface charge density of the fibers. From the table, the fiber has a high charge density and the charge density does not decrease.

Furthermore, the method for producing electret fiber according to the present invention includes:
An electrode is disposed within the extrusion nozzle, an electric field is formed between the electrode and the outside, and the product is manufactured by injection molding from the extrusion nozzle.

[Embodiments of the invention]

Examples of the electret fiber and the method for producing the same according to the present invention will be described with reference to the drawings.

First, FIGS. 3A and 3B are perspective views showing the cross section and polarization state of electret fibers according to each example of the present invention.

Therefore, the material of the electret fiber according to the present invention is
Although not limited in any way, here, including the manufacturing method described below, the thermoplastic material (for example, polyolefin, etc.), a representative example of which is polypropyv:y (
(CH2CHCH3:Ill% or less is abbreviated as PP.

).

That is, both (a) and (b) in Fig. 3 are constructed so that the charge polarity of the fiber center and the fiber surface are different, and are hollow in shape. is such that it is polarized into an outer surface related to the fiber surface portion and an inner surface related to the fiber center portion.

In the diagram (a), the charge on the external surface is positive and the charge on the internal surface is negative, and (b) is,
It is the opposite.

In this configuration, the charge on the external surface that comes into contact with the air and is purified is either positive or negative.

That is, the hollow inner surface cannot come into contact with air.

Further, since it has a hollow shape, the positive and negative charges have the effect of not coming into contact with each other.

Furthermore, it has been impossible to measure the charge density of conventional electret fibers.

In other words, the objects shown in Figures 1 and 2 that I explained earlier are polarized as shown, so it was not possible to determine the correct pupil using a Faraday gauge that measures all positive and negative charges. It is.

Furthermore, it was also difficult to measure the surface potential of a single fiber.

That is, this is because a measurement electrode that is thinner than the fiber diameter is required.

On the other hand, in the case of the above embodiment, since the surface charge polarity is single, the charge density can be measured even with a Faraday gauge.

Next, the electret fibers according to the above embodiments were aggregated by needle punching to make a non-woven filter (how to make these is detailed in the Synthetic Fiber Handbook published by Maruzen), and a conventional product. The measurement results of collection efficiency, pressure loss, and charge density for PP filters, glass filters, and electret filters are shown in Figure 4, and B for AsNOs for NO4 in the figure is, respectively.
This example relates to a filter using electret fibers manufactured according to Examples 1 and 2, which will be described later.

These measurements were carried out using a filter performance testing device whose configuration is shown schematically in FIG.

In other words, in Fig. 5, 7 is a filter, 8 is a dust monitor (Hitachi Electronics Engineering Co., Ltd.: Laser Dust Monitor TSI-400), 9 is a differential pressure gauge, and 10 is an air indicator, which indicates air inside the duct. The concentration of dust (smoke, smoke particle size is 0.3 to 0.5 μm) flowing through the
air 10 with a concentration of Co/m3) is passed through the filter 7.
(pieces/m3),
The concentration was measured with a dust monitor 8, the dust collection efficiency was calculated using ξ=1-(Co/ct), and the pressure loss of the filter was measured with a differential pressure gauge 9.

As is clear from FIG. 4 above, the performance is greatly improved compared to conventional filters.

The reason why the collection efficiency is higher than that of the conventional electret filter (NO3) is that the polarity of charge on the fiber surface in contact with the air is single.

Next, each example of the method for manufacturing the electret fiber according to the above example will be described, and the material of the electret fiber is the same as described above.

Example 1 First, FIG. 6 is a manufacturing process diagram of an electret fiber manufacturing method according to an example of the present invention.

That is, the pellet PP is heated and melted (approximately 240 C) in a part of the extruder screw described below.
Next, it is extruded from an extrusion nozzle, injection molded, and then charged, and if necessary, this is transferred to, for example, filter production.

FIG. 7 is a sectional view of the extruder exit portion described above.

That is, 1 is a head, which is electrically grounded, and the molten PP 7 is injected from a nozzle 2 that is an extrusion nozzle.

This nozzle 2 is provided with a head 1 and an electrode 3 separated by an insulator 4, which is connected to a power source 5.

Therefore, an electric field is formed between the electrode 3 and the head 1 to solidify the PP from a molten state and turn it into an electret.

Furthermore, the fibers are made into fine fibers by drawing after this.

At this time, the crystallinity of PP grows and the electret has the advantage of being stabilized.

In this embodiment, however, PP is converted into a electret due to dipole moment polarization, and is mainly composed of hetero charges.

The shape and charge distribution of the electret fiber thus obtained are as shown in FIG. 3, which are hollow and have polarized charges on the outer surface and the inner surface. That is, there is a clear difference in polarity from the conventional electret fibers as shown in FIGS.

By changing the polarity of the power source 5, the result shown in FIG. 3 (a) or (b) can be obtained.

A specific example of the above fabrication will be described next.

First, the diameter of the nozzle 2 in FIG. 7 is 4m+φ.

The diameter of the electrode 3 is set to 2 mm. In addition, the potential of electrode 3 was set to minus IKV, and the extrusion speed of PP was set to 1 W at 240C.
In/s, the winding speed was set to 25 m/s (spreading rate 25,000) to obtain fibers with a diameter of 25 μm.

When the stain loading density of this fiber was measured using a Faraday gauge shown in the Chemical Society of Japan Cotton: New Experimental Chemistry Course (19) Polymer Chemistry (N), it was +3.5 x 10" Coulombs/g. Ta. This is 2X10-7 coulombs/
cm 2, and the conventionally known film-like electret is 0.4 to 1xio-' coulomb/Cm
It can be said that the charge density is several times higher than that of 2.

Moreover, the fact that the charge polarity of the fiber is positive proves the characteristics of the electret fiber of the present invention described above.

Example 2 The manufacturing process is shown in Figure 6 above.

FIG. 8 is a sectional view of the extruder exit portion.

In the figure, IA is the head, 2 people are the nozzles, 3A is the electrode, 5 is the power source, and 6 is the counter electrode.

That is, in the illustrated configuration, the head IA and the electrode 3
A is an example in which the counter electrode 6 is electrically connected, and the counter electrode 6 is installed outside the two nozzles, and the electric field between them turns the PP into an electret.

In the figure, the counter electrode 6 is at high voltage, but its polarity is not limited as in the previous figure 7.

In the configuration shown in FIG. 7, as mentioned above, PP
Due to dipole moment polarization, it becomes an electret, so the hetero charge becomes the main charge, but in the case shown in Fig. 8, corona discharge occurs, so ion implantation becomes noticeable, and the homo charge becomes the main charge. It is.

A specific example of the above fabrication will be described next.

The diameter of the two nozzles in Figure 8 is 4wφ.

The diameter of electrode 3A is 2mm φ, and the electrode potential of counter electrode 6 is plus IK.
V, and the other extrusion speed, winding speed, etc. were the same as in Example 1, and fibers could be obtained.

〔Effect of the invention〕

According to the present invention, it is possible to obtain electret fibers having a single charge and a high charge density, and an air cleaning filter having a high collection efficiency accordingly, and it can be said that the present invention has excellent practical effects.

[Brief explanation of the drawing]

FIGS. 1 and 2 are perspective views showing the cross section and polarization state of conventional electret fibers, and FIGS. FIG. 4 is a perspective view showing the state, and FIG.
The figure is a schematic configuration diagram of a filter performance testing device, FIG. 6 is a manufacturing process diagram of the electret fiber manufacturing method according to the embodiment of the present invention, and FIGS. 7 and 8 are used for each manufacturing method. FIG. 1, IA... Spatula)", 2, 2A... Nozzle, 3,
3A... Electrode, 4... Insulator, 5... Power supply, 6...
...the opposite. Agent: Patent attorney Kosaku Fukuda (and 1 other person) Figure 1 ``$z's v41 ¥1 'fyt, Mouth Belt Self-inflicted cancer Charged Noruta Figure 9 Figure t

Claims (1)

[Scope of Claims] 1. An electret fiber formed into a hollow shape and configured such that the center portion of the fiber and the surface portion of the fiber have different charge polarities. 2. A method for producing electret fibers, characterized in that an electrode is disposed within an extrusion nozzle, an electric field is formed between the electrode and the outside, and the electret fiber is produced by injection molding from the extrusion nozzle.