JPS62110974A - Production of electret fiber sheet - 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] [Industrial application field] The present invention relates to an electret fiber sheet.

More specifically, the present invention relates to an Electref 1 fiber sheet with a high surface charge density that can be used for filters, masks, adsorbents, etc.

[Prior art] As a method for converting fiber seams 1- into electret, Japanese Patent Application Laid-Open No. 1983
As described in Japanese Patent No. 7-101073, there is a method in which a fibrous sheet is sandwiched between a pair of dielectric layers and turned into an electret using a DC high-voltage electric field.

In this method, since both sides of the fiber sheet are sandwiched between dielectric layers, charge injection from the application side electrode is inhibited by the dielectric layer, and sufficient charge is not injected into the fiber sheet, resulting in a high surface charge density. There was a drawback that an Electref 1~ fiber sheet having the following characteristics could not be obtained.

[Problems to be Solved by the Invention] The present invention uses a dielectric material between the fiber sheet and the earth electrode, without installing a dielectric material on the application electrode side, to prevent the charge from flowing into the fiber sheet 1. The present invention provides a method for manufacturing an electresheet m-fiber sheet that facilitates injection and has a high surface charge density.

[Means for solving problems] The present invention has the following configuration.

The present invention relates to a method for producing an electret fiber sheet, which comprises bringing the fiber sheet into electret contact with opposing electrodes, and adding a dielectric material between the earth electrode and the fiber sheet to form an electret.

The manufacturing method of the present invention will be explained with reference to the drawings.

FIG. 1 is a schematic diagram showing an embodiment of the present invention.

A fiber sheet 3 is brought into contact with the applied N pole 1, and a dielectric material 4 is attached between the fiber sheet 3 and the earth electrode 2,
The DC voltage generated by the high voltage generator 5 is applied from the application tube (1) to form an electret.The current port is measured using 6.

The volume resistivity of the application electrode and ground electrode is 10-1Ω・cm
The following conductive materials are used, for example, metal materials such as iron, stainless steel, and copper.

In order to obtain a high surface charge density, the dielectric material preferably has a volume resistivity of 10 to 1017 Ω. Volume resistance is 10
If it is less than 7Ω, the applied voltage cannot be increased and spark discharge occurs, making it impossible to inject sufficient charge into the fiber sheet.

Further, the upper limit of the volume resistivity is preferably 1017Ω or less.

This is thought to prevent charge injection into the fiber sheet since no leakage current occurs if the volume resistance of the dielectric material is too large. Since the volume resistivity is related to the volume resistivity and thickness of the dielectric material, it is determined by Mugi's method.

The fiber sheet is preferably made of a material having a volume resistivity of 1012 Ω·cm or more.

This is necessary because it exists stably after charge injection. For example, polyolefins, polyesters, fluororesins, acrylonitriles, etc. are used, and nonpolar polyolefins are particularly preferred from the viewpoint of stability of the injected charge.

Further, the cover factor of the fiber sheet is preferably 60% or more.

If there are many voids, leakage current will flow from the voids, which will prevent charge injection into the fibers.

Further, the basis weight of the fiber sheet is preferably 200 g/Tr12 or less, more preferably 100 g/Tr12 or less.

This is because if the basis weight is large, the charge injection will not reach the inner fibers, so it will end up only at the surface portion.

For this reason, it is preferable that the basis weight is small.

The fiber sheet may be made of nonwoven fabric, woven fabric, knitted fabric, paper, or the like.

The average fineness of the fibers constituting the fiber sheet is 5 d or less, preferably 1 d or less, and preferably 0.

5d or less is good. This is preferable from the standpoint of increasing the cover factor and increasing the surface charge density.

The electric field strength between the electrodes is preferably 50 to 30Q KV/cm. 50 t (V/cm or less, sufficient electret formation cannot be achieved. Also, 3000 KV/cm
Above this, spark discharge occurs.

Further, the leakage current is preferably 10-6 to 10-2 mA/- from the viewpoint of electret properties.

It is preferable that the treatment is performed between instantaneous and 180 seconds.

If it is too short, sufficient charge cannot be injected, and if it is too long,
Rediscrement of the wrapped charge occurs.

The applied temperature is preferably around or above the glass transition point of the fiber sheet or material.

Although it depends on the number of times of application, if the application is applied two or more times to the front and back sides of the fiber sheet, an even higher surface charge density can be obtained. In particular, it is preferable to apply the charge to the front surface with either positive or negative polarity, then turn the fiber sheet over and apply the charge to the back surface with the opposite polarity to the previous one, since this method can obtain a high surface charge density.

The fiber sheet electretized by the above method has a surface charge density of 2X10-10 at, more preferably 5
X 1 0” C/cat or more.

Therefore, it can be used in a wide range of applications such as filters, adsorbents, and masks.

[Examples] The present invention will be explained below using Examples, but is not limited thereto.

Here, methods for measuring volume resistivity, volume resistivity, surface charge density, leakage current, and cover factor will be described.

Volume resistivity and volume resistivity were measured according to JIS-C-2318.

Volume resistivity (Ω)=(ρ·t)/19.6ρ: Volume resistivity (Ω·cm) t: Sample thickness (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 FIG. 2, in which an electret fiber sheet sample 7 is placed on a grounded metal plate 8, and then another metal electrode (4 cm diameter) 9 is approached from above. The electric charge existing on the sample surface is generated in the metal electrode 9 by electrostatic induction, this electric charge is stored in the capacitor 10, the potential is measured by the electrometer 11, and the electric potential of the sample surface is calculated by the following formula. The surface charge density was determined.

Surface charge density I31? (c/crK) =CXV/AC:
Condenry capacitance (Farad) V: Potential (volt) A: Electrode area (-) Leakage current was determined by measuring the current generated by the applied electrode with an electrometer using the method shown in FIG.

The leakage current was determined by dividing this value by the area of the applied fiber sheet.

The cover factor was measured using a magnifying projector to measure the sample (2Cm
A shading of 2 cm) was created on a 1 mm square graph paper, and the bright area created by the transmission of light was defined as B, and the shaded area created by the fiber blocking the light was determined by the following formula. .

Cover factor (%) = (C/ (B+C))xloo Example 1 As a fiber sheet, cover factor 99%, sheet thickness 0.2 mm, sheet weight 150 g/m', single fiber fineness 3 d, volume resistivity 1016 Ω・A woven fabric was used using a polypropylene material of cm.

This fabric was made into an electret by the method of Example 1. Iron material with a volume resistivity of 10-5 Ω cm was used for both electrodes, and the dielectric material had a thickness Q of 1 mm and a volume resistivity of 1°2×101.
No. 30 polypropylene film was used.

Applied voltage -20KV (electric field strength 666 V/cm),
Leakage current 3.5x 10-5mA/clI! , and treated for 40 seconds at room temperature.

The surface charge density of the obtained Electref 1 fabric is -
It was 5.8 C/cJ, and the back side was +5.1 C/cJ.

Although it was left at room temperature for one month, no decrease in surface charge density was observed.

Example 2 Cover factor 99.5%, sheet thickness 0°1 mm,
A melt-blown nonwoven fabric made of a polypropylene material with an average fineness of 0.2 d, a volume resistivity of 1016 Ω·cm, and a basis weight of 40 g/T112 was used for the fiber sheet.

This nonwoven fabric was made into Electref 1 by the method of Example 1.

An iron material with a volume resistivity of 10-50 cm was used for both electrodes, and a 1 mm thick nylon sheet with a volume resistivity of 2.9×10 9 Ω was used as the dielectric material.

The applied voltage was -10 KV (electric field strength: 909 V/Cm), the leakage current was 1, 1 x 10'm A10yfr.

The treatment time was 3QSeC and the temperature was 25°C.

As a result, the surface charge density of the obtained electret nonwoven fabric was +8.5 x 10'' c/cnf on the front surface and -7.1 x 10-10 c layer on the back surface.

Although it was left at room temperature for 3 months, no decrease in surface charge density was observed.

Comparative Example 1 Using the fiber sheet used in Example 1,
This was carried out in accordance with the method described in Japanese Patent No. 101073.

That is, two polypropylene films having a thickness Q of 1 mm and a volume resistance of 1.2×10 13 Ω were used as dielectric materials, and an R fiber sheet was sandwiched therebetween, and the film was treated at -20 KV for 40 seconds. As a result, the surface charge density of the obtained fabric was -4.9 x 10" c/i on the front surface and +4.2 x 10" c/i on the back surface.
- ” It showed a low value in c/cJ.

Furthermore, when this fabric was left hanging for one month, a decrease in surface charge density of about 50% was observed.

[Effects of the Invention] In the present invention, a dielectric material is attached between the fiber sheet and the earth electrode, and high voltage is directly applied by the application electrode, so that charge injection into the fiber sheet can be easily performed. Therefore, an electret fiber sheet with high surface charge density can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the present invention, and FIG. 2 is a schematic diagram showing an apparatus for measuring surface charge density. 1: Application electrode 2: Earth electrode 3: Fiber sheet 4: Dielectric material 5: High voltage generator 6: Ammeter 7: Electret fiber sheet 8: Metal electrode 9: Earth electrode 10: Capacitor 11: Electrometer

Claims (5)

[Claims] (1) When converting a fiber sheet into an electret using opposing electrodes, an application electrode is brought into contact with one side of the fiber sheet, and a dielectric material is added between the ground electrode and the fiber sheet to convert the fiber sheet into an electret. A method for producing an electret fiber sheet characterized by: (2) The method for producing an electret fiber sheet according to claim (1), wherein the fiber sheet has a cover factor of 60% or more. (3) The method for producing an electret fiber sheet according to claim (1), wherein the fiber sheet has a basis weight of 200 g/m^2 or less. (4) The method for producing an electret fiber sheet according to claim (1), wherein the fiber sheet is polyolefin-based. (5) Dielectric material has a volume resistance of 10^7 to 10^1^7Ω
A method for producing an electret fiber sheet according to claim (1).