JPH0413845B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing an electret fiber sheet having a high surface charge density.

[Conventional technology]

As a continuous manufacturing method for electret fiber sheets,
As described in JP-A-57-101073, there is a continuous manufacturing method in which a fibrous sheet is electrified by line contact between two rolls having a dielectric layer.

However, this method has the drawback that, because it involves line contact, sufficient contact time is not obtained, charge injection is insufficient, and electret fiber sheets having a high surface charge density cannot be obtained continuously.

[Problem that the invention seeks to solve]

The present invention provides a method for continuously producing an electret fiber sheet having a high surface charge density by using electrodes capable of surface contact.

[Means for solving problems]

In the present invention, when a fiber sheet is brought into contact between an application electrode and a ground electrode to continuously electret, at least the surface of the ground electrode in contact with the fiber sheet is coated with a dielectric material, and the fiber sheet is The present invention relates to a method for manufacturing an electret fiber sheet, which is characterized by continuously applying high pressure to both electrodes while in surface contact with each other.

FIG. 1 is an example of an embodiment of the present invention.

In FIG. 1, a drum 1 rotating in the direction of arrow A is covered with a dielectric material 2 and is adapted to act as a ground electrode by means of a ground 3.

On the other hand, the rotating belt 4 is moved in the direction of arrow B via insulating rolls 5, 6, 7, 8, and 9 while being in pressure contact with the dielectric material 2 covering the rotating drum 1.

The rotating belt 4 is connected to a high pressure generator 10,
It is adapted to act as an application electrode. The rotating belt 4 is surrounded by a cover 11 to prevent discharge from the applied electrodes to the outside world.

The fiber sheet 12 is inserted from the direction of arrow C, and moves in the direction of arrow D while being in surface contact with the dielectric material 2 and rotating belt 4 while being subjected to surface pressure as shown in FIG. At this time, when direct current is applied by the high pressure generator 10, the fiber sheet 12 is continuously electrified, and the electret fiber sheet 13 is
is obtained.

In addition, in FIG. 1, the rotating drum 2 is connected to a ground electrode,
Although an example has been described in which the rotating belt 4 is used as the application electrode, the present invention is not limited to this example, and conversely, the rotating drum side may be used as the application electrode and the rotating belt side may be used as the ground electrode.

In short, the surface of the earth electrode is covered with a dielectric material, and the fiber sheet is in surface contact with both electrodes.
Any form may be used as long as high pressure can be continuously applied.

The rotating drum and rotating belt used as the application electrode and the ground electrode are preferably made of a conductive material, and preferably have a volume resistivity of 10 ^-1 Ω·cm or less. For example, metal materials such as iron, stainless steel, and copper can be used.

As the dielectric material, a material having a volume resistance of 10 ⁷ to 10 ¹⁸ Ω is preferable, and for example, nylon, polyester, vinyl chloride, polyolefin, polycarbonate, fluorine resin, acrylic resin, etc. can be used. Its forms include film, sheet,
The ground electrode can be coated with paint or the like.

The dielectric material may be applied not only to the ground electrode but also to the application electrode without hindering the present invention, but in order to promote charge injection into the fiber sheet, it is preferable that the application electrode is not covered.

The rotating drum 1 can also heat the fiber sheet 12, and it is preferable to heat the fiber sheet 12 at a temperature higher than the glass transition point of the material.

Further, the tension of the rotating belt 4 can be changed by appropriately moving the roll 7 that rotates the belt.
This allows the surface pressure on the fiber sheet to be changed.

The surface pressure is preferably 20 g/cm ² or more from the viewpoint of electrivity.

When the surface pressure is large, sufficient charge is injected into the interior, which is preferable.

The contact time of the fiber sheet to both electrodes is from several seconds to
300 seconds is sufficient for electrification. The insulating rolls 5, 6, 7, 8, and 9 are rolls coated with an insulating material or rolls using an insulating material. Furthermore, as a method of insulating the rotating application belt, it is also possible to insulate the inside of the belt.

The electric field strength applied between both electrodes is preferably 100 KV/cm or more; if it is less than 100 KV/cm, stable electrification cannot be obtained. Furthermore, if the applied electric field strength is too high, spark discharge will occur and electrification will be difficult, so the upper limit is preferably 5000 KV/cm or less.

In addition, the volume resistivity of the fiber sheet material is 10 ¹³ Ω・
cm or more is preferable for the stability of the electret.

For example, polyolefins (polyethylene, polypropylene, polystyrene, etc.), polyester,
Fluorine resin, polycarbonate, ionic resin,
Inorganic materials such as glass can be used.

The electret fiber sheet continuously electrified by the above method has a surface charge density of at least 2×10 ^-10 c/cm ² or even 5×
10 ^-10 c/cm ² .

A fiber sheet cover factor of 60% or more is preferable because it can increase the applied electric field strength and can sufficiently perform electrification.

The electret fiber sheet obtained by the present invention can be used in a wide range of applications including filters, adsorbents, masks, and the like.

Here, how to obtain volume resistivity, volume resistivity, cover factor, surface pressure, and surface charge density will be explained.

Volume resistivity is measured according to JIS-C-2318.

Volume resistivity (Ω) = P・t/19.6 P: Volume resistivity (Ω・cm) t: Sample thickness (cm) The cover factor is determined by measuring the sample (2
× 2 cm) was created on a 1 mm square graph paper, and the bright area B where light passed through and the shadow area C where light was blocked by the fibers were calculated using the formula below. .

Cover factor (%)=(C/B+C)×100 The tension of the rotating belt was measured, and the surface pressure was calculated from this value using the formula below.

Surface pressure P=2T/R P: Surface pressure (g/cm ² ) T: Tension (g/cm) R: Drum radius (cm) The surface charge density was measured by the method shown in FIG.

That is, the schematic diagram of the surface charge density measuring device is shown in the third figure.
As shown in the figure, an electret fiber sheet sample 14 is placed on a grounded metal plate 15, and then another metal electrode (4 cm diameter) is approached from above and brought into contact with the sample 14 (4 cm diameter). The electric charge existing on the surface of the sample 14 is generated in the metal electrode 16 by electrostatic induction, this electric charge is stored in the capacitor 17, and the potential is measured with the electrometer 18. The surface electric charge on the surface of the sample 14 is calculated by the following formula. The density was determined.

Surface charge density (C/cm ² )=C×V/AC C: Capacitor capacity (Furad) V: Potential (volt) A: Electrode area (cm ² ) [Example] Example 1 As a fiber sheet, cover factor 99.5% A melt-blown nonwoven fabric made of polypropylene having a sheet thickness of 1.0 mm, a sheet basis weight of 150 g/m ² , an average fiber diameter of 3.5 μm, and a volume resistivity of 10 ¹⁶ Ω·cm was used.

The application method is as shown in Figure 1, using a rotating belt made of stainless steel with a volume resistivity of 10 ¹⁵ Ω cm and a width of 30 cm, and an iron material with a volume resistivity of 10 ¹⁵ Ω cm as the ground electrode. A drum was used. A surface pressure of 200 g/cm ² was applied to the fiber sheet, and an applied electric field strength of 650 KV/cm was applied at room temperature.

The length receiving surface pressure is (m/c direction)
The distance was 1.5 m, and the treatment time was 50 seconds.

The rotating drum of the earth electrode was coated with a nylon sheet having a volume resistance of 2.9×10 ⁹ Ω and a thickness of 0.5 mm as a dielectric material.

As a result, the obtained electret fiber sheet has a surface charge intensity of +8.7×
10 ^-10 c/cm ² , and -7.4×10 ^-10 c/cm ² on the back side.

This sheet was left indoors for two months, but no decrease in surface charge density was observed.

Example 2 As a fiber sheet, polypropylene filament (500D) with a volume resistivity of 10 ¹⁶ Ω・cm was used for the warp and weft yarns, and a satin fabric was used with a warp yarn density of 80 yarns/in and a weft yarn density of 57 yarns/in. .

Coverage factor was 99%.

The application method used the same device as in Example 1, but the coating material of the rotating drum earth electrode had a volume resistance of 5×
A 10 ¹² Ω polypropylene film was used.

The applied electric field strength was 700 KV/cm and the treatment was performed at 30°C for 40 seconds. The surface pressure at this time was 350 g/cm ² .

The surface charge density of the obtained electret fiber sheet was 9.1×10 ^-10 c/cm ² on the front surface and 8.5× on the back surface.
It was 10 ^-10 c/ ^cm2 . This sheet was left indoors at room temperature for 10 months, but no decrease in surface charge density was observed.

〔Effect of the invention〕

In the present invention, the surface of the ground electrode that comes into contact with the fiber sheet is coated with a dielectric material, and the voltage is applied through surface contact between the ground electrode and the application electrode, so that electrification is efficiently achieved and a high surface density can be obtained. .

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing an embodiment of the method for producing an electret fiber sheet according to the present invention, Fig. 2 is a partially enlarged schematic diagram showing the surface contact state of Fig. It is a schematic diagram showing a measuring device. 1; Rotating drum, 2; Dielectric material, 3, 3';
Earth, 4; Rotating belt, 5, 6, 7, 8, 9;
Insulation roll, 10; High pressure generator, 11; Cover,
12; fiber sheet; 13; electret fiber sheet.

Claims (1)

[Claims] 1. When a fiber sheet is brought into contact between an application electrode and a ground electrode to continuously electret, at least the surface of the ground electrode that contacts the fiber sheet is covered with a dielectric material, and the fiber sheet is brought into contact with the ground electrode. A method for manufacturing an electret fiber sheet, characterized in that the sheet is continuously subjected to high pressure application treatment while the sheet is in surface contact with both electrodes. 2 Claim 1 in which the electrode is drum-shaped
A method for producing an electret fiber sheet as described in Section 1. 3 Claim 1 in which the electrode is belt-shaped
A method for producing an electret fiber sheet as described in Section 1. 4. The method for producing an electret fiber sheet according to claim 1, wherein the dielectric material has a volume resistivity of 10 ⁷ to ^{10 18} Ω. 5. The method for producing an electret fiber sheet according to claim 1, wherein the fiber sheet contains 60% or more of kava factor. 6. The method for producing an electret fiber sheet according to claim 1, wherein the applied electric field strength is 100 KV/cm or more.