JP2531475B2 - Electret fabric - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to electret fabrics. More specifically, it relates to an electret cloth capable of exerting a large electric effect on the outside world.

[0002]

2. Description of the Related Art Conventionally, as an electret technology for cloth, the invention described in Japanese Patent Publication No. 49-4433 is known.

In the invention disclosed in Japanese Patent Publication No. 49-4433, since a dielectric sheet is sandwiched between metallic flat plate electrodes, the cloth is directly superposed on the cloth to form an electret. It has a drawback that it does not enter into, and the injected charge that entered is almost the same value on the front and back surfaces.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide an electret cloth capable of exerting a large electric effect on the outside by increasing the difference in charge density between the front and back surfaces.

That is, for example, such an electret nonwoven fabric is preferable in order to electrically attach dust on various devices, dust on a table, and the like. Further, since it is in a cloth state, it has a high dust retaining effect after adhesion (for example, an average substance such as a film has a low retaining effect).

[0006]

The electret cloth of the present invention which achieves the above object is an electret cloth having electric charges on the front and back surfaces, and the difference in surface charge density between the front and back surfaces is 4 × 10 ^{−10 to} 9 × 10. It is an electret cloth characterized in that it is ⁻¹⁰ coulomb / cm ² .

[0007]

The present invention will be described in more detail with reference to the drawings. The electret fabric of the present invention has charges on the front and back surfaces, and the difference in surface charge density between the front and back surfaces is 4 ×.
It has a large difference of 10 ^{−10 to} 9 × 10 ⁻¹⁰ coulomb / cm ² .

When the difference between the surface charge densities held on the front and back surfaces is large as described above, a greater electric effect can be realized and exerted on the outside world. The difference is 4 × 10 ^-10 coulomb / cm
Those smaller than ² are less effective, and 9 × 1
Those larger than 0 ^-10 coulomb / cm ² are difficult to manufacture according to the knowledge of the present inventors.

FIG. 1 shows an example of the method for manufacturing the electret cloth of the present invention. The surface of the rotating body 1 which is grounded and rotates in the direction of arrow A in FIG. 1 is covered with the liquid-containing material 4 in which the semiconductor liquid 2 is constantly wet by the semiconductor liquid supply roll 3. On the other hand, the fabric 6 supplied by the delivery roll 5 is supplied by the turn rolls 7 and 8 so that one surface thereof comes into contact with the semiconductor liquid on the surface wetted by the liquid-containing material 4, and the space 6 passes through the high voltage generator 9. Electret processing is performed by the needle-shaped electrode 10 installed at.
Next, a small amount of the semiconductor liquid attached to the cloth is dried by the hot air generator 11, and the electret cloth 13 is wound up via the winding roll 12.

The semiconductor liquid referred to in the present invention is 10 ^-1 to 1
It has a volume resistivity value of 0 ⁶ Ω · m, and specifically, water is preferable, but a liquid in which an electrolyte such as a surfactant or salt is dissolved may be used. In addition, acetone or alcohol may be dissolved in water. Volume resistance value is 10 ^-1
When it is less than Ω · m, the electric charge is likely to move from the fiber surface to the liquid, and the surface charge density is not sufficiently improved.
Further, when the value exceeds 10 ⁶ Ω · m, the charge carriers reaching the fiber surface are attached and the surface charge density is rapidly increased, but on the contrary, repulsion of the same charge occurs, and further improvement of the surface charge density cannot be expected. . Therefore, the range of 10 ⁻¹ to 10 ⁶ Ω · m is preferable. In particular, the vicinity of 10 ² to 10 ⁵ Ω · m is preferable for improving the surface charge density and permeating the charge carrier into the fiber. The volume resistivity of the liquid was measured according to JIS-C2110.

Next, the earth electrode is a rotating body such as a roll, a drum or a belt conveyor, and the surface thereof is wet with the semiconductor liquid. Specifically, it is wetted through a liquid-containing material having a contact angle with the semiconductor liquid of 60 ° or less. As the liquid-containing material, for example, cotton, wool, knitted fabric made of natural fibers such as pulp, non-woven fabric, cloth such as filter paper, or a mixture of hydrophilic high-polymer fiber having a high moisture content, It may be used alone. A cloth made of these liquid-containing materials is wound around the surface of the rotating body for use, or metal, ceramic, hydrophilic plastic, etc. are engraved or embossed or roughened or microporous to give liquid retention. The rotating body may be made of such a liquid-containing material. At the time of electretization, the liquid-containing material on the surface of the earth electrode is used while being wet with the semiconductor liquid. In this case, the degree of wetting may be appropriately selected depending on the conditions of the cloth to be processed. The surface charge density can be improved by pressing the processed cloth strongly in the state where the liquid-containing material wets the semiconductor liquid and performing the electret processing. The preferred method in the present invention is to cover the surface of the earth electrode with the surface of the liquid-containing material as a highly wettable coating with a continuous semiconductor liquid. By this method, the groundability of the processed fabric is made more uniform.

Therefore, it is necessary to make the contact angle between the semiconductor liquid and the liquid-containing material 60 ° or less. If it exceeds 60 °, the adhesion of the liquid film becomes uneven, which is not preferable. A more preferable contact angle is 30 ° or less. To find the contact angle,
Place the material horizontally on a horizontal table, drop a droplet from the top of the needle from the tip of the injection needle, and observe from a side horizontal position with a microscope that can measure the angle. Drop the angle between the material surface and the droplet 5 Calculate with the value after minutes.

In the present invention, the ground electrode surface, the surface of which is coated with the liquid-containing material, has a high surface charge density as an electret material. This is because the electric charge is sufficiently injected because the adhesion between the material to be electret and the ground electrode made of the liquid-containing material is good. Therefore, the difference between the surface charge densities of the front and back surfaces described above is 4 × 1.
Electret fabrics having a large difference of 0 ^{−10 to} 9 × 10 ⁻¹⁰ coulomb / cm ² can be manufactured.

Electret processed fabrics include polyolefins, polyesters, fluorine-containing fabrics,
Non-woven fabrics and knitted fabrics made of fibers such as vinyl chloride, polyamide, and polyacrylics. It may also be in the form of a film or paper. These volume resistivities are 1
If it is 0 ¹¹ Ω · cm or more, preferably 10 ¹³ Ω · cm or more, it is suitable for the material of the electret cloth. The method for measuring the volume resistivity of the processed cloth is based on JIS-C2103.

Since the cloth generally has a surface with large irregularities, the actual contact area of the cloth, that is, the ground contact area is extremely small even when the cloth is placed on a grounded metal flat plate. In order to improve the ground contact property, flattening the cloth is effective, but it is often impossible depending on the application.

In the present invention, the semiconductor liquid is used as a grounding material in order to improve the groundability of the cloth. The liquid can be deformed depending on the unevenness of the cloth and the fiber shape. Generally, the most suitable material for electretization is represented by polypropylene, polyethylene, and polytetrafluoroethylene, which have high water repellency and rarely contain liquid. Therefore, the liquid does not penetrate into the inside of the cloth, and the cloth is deformed so as to fill the surface irregularities of the cloth and comes into contact with the cloth. Therefore, the contact area with the ground electrode is significantly increased, and the groundability is improved. By improving the grounding property, a large amount of compensation charges can be obtained. As a result, the surface charge density of the fabric is improved and the amount of charge carriers internally trapped is increased.

The surface charge density is determined by the method shown in FIG. The measuring method is as follows. A sample 16 is sandwiched between a grounded metal box 14 and a metal plate electrode (area 100 cm ² , true cast material) 15, and an electric charge generated by electrostatic induction is passed through a capacitor 17 by an electrometer 18. Measure the potential. The surface charge density is calculated from the measured potential by the following formula.

Q = C × V / S Q: Surface charge density (Coulomb / cm ² ) C: Capacitor capacity V: High performance electrometer (Shiki RIKEN TR856
2) S: Area of sample (cm ² ) FIG. 3 shows a block diagram for obtaining the heat-stimulated depolarization current. This device is an electret thermal analyzer manufactured by Toyo Seiki Seisaku-sho, Ltd., and evaluated by the following method.

A sample 19 is sandwiched between electrodes 20 and 21 and set in a heating furnace 22. Next, the temperature controller 23
And the thermocouple 24 raises the temperature at a constant temperature rising rate (5 ° C./min). The current value detected by the picoampere meter 25 is input to the data processing device 26. On the other hand, the temperature measured by the thermocouple 24 is also input to the data processing device 26, and the recorder 27 records the relationship between the temperature and TSDC.

[0020]

According to the electret cloth of the present invention,
Since the difference in charge density between the front and back is large, the electric effect on the external environment becomes large, and the electric adsorption effect of dust, fine particles, bacteria, etc. becomes high.

Therefore, the electret cloth according to the present invention can exhibit excellent properties as a wiping material, a hair cap material, a cover material for various devices, a filter and the like.

Further, when the processed product of the electret cloth obtained by the present invention is used for, for example, a filter, it can be stably used even under environmental conditions of high temperature and humidity.
Further, even when immersed in methanol, ethanol, or the like, the decrease in surface charge density is small, and an excellent chemical resistance is obtained.

[0023]

EXAMPLES The present invention will be described in detail below with reference to examples.

Example 1 A pulp filter paper having a thickness of 300 μm and a basis weight of 125 g / m ² was wound around a grounded metal drum roll having a diameter of 40 cm, and water having a volume specific resistance value of 10 ³ Ω · m was used.
It was set to 0 g / m ² .

On the surface of this earth pole, an average fiber diameter of 3.5
μm, thickness 0.14 mm, basis weight 20 g / m ² , ventilation rate 7
The melt-blown non-woven fabric made of polypropylene having a cc / cm ² · second was continuously fed at 0.3 m / min so that one side was in contact. On the other hand, a needle-shaped electrode was placed in a space 3 cm away from the earth electrode and continuously processed at a negative voltage of 30 kV. Then, the product was dehydrated and dried with warm air of 40 ° C. and wound up. The processed product was wrapped in aluminum foil, and after 24 hours, the surface charge density was evaluated by the method shown in FIG. The results are shown in Table 1.3 x 10
^-9 coulomb / cm ² , back 9.0 × 10 ^-10 coulomb / c
m ² . Furthermore, as a result of evaluating the TSDC of this processed product by the method shown in FIG. 3, the electrode peaks were 92 ° C. and 165 ° C.
There are two peaks at ℃, and the depolarization charge amount above 130 ℃ is 3.
5 was × 10 ^{-1 0} coulombs / cm ^2.

The depolarization charge amount is obtained by dividing the area under the current curve obtained by the TSDC measurement by the area of the sample.

Five pieces of this product are laminated and 50 ° C. × 95% R
The sample was allowed to stand for one year in an H 2 atmosphere and the aerosol collection performance was evaluated, but no deterioration was observed. Also, 100 ℃
Then, the aerosol collecting performance was evaluated by leaving it in a dryer for 1 week, but no deterioration was observed. From these results,
It can be seen that the electret has excellent thermal stability and durability.

The method of obtaining the aerosol collection efficiency is 0.33.
Using a atomizer (manufactured by Japan Canomax), a μm-polystin sphere (monodisperse latex of Dow Chemical Co., Ltd.)
Adjust the aerosol concentration to 500,000 / ft ³ .

When this was supplied to the filter at a surface wind speed of 1.5 m / min, collection efficiency (%) = 100- (C _o / C _i × 100) C _o = filter ≧ aerosol concentration after passing (piece / ft ³ ) C _i = filter-determined by the aerosol concentration before passing (pieces / ft ³ ).

To determine the aerosol concentration, an aerosol monitor (AN105) manufactured by Hitachi, Ltd. was used.

The difference between the surface charge densities of the front and back surfaces of the electret cloth thus obtained is 4.0 × 10 ^-10 coulomb / cm ² . The electret cloth was excellent in dust collecting performance as a wiping material due to its charge characteristics and was extremely excellent. Example 2 5 was applied to the surface of a grounded metal drum roll having a diameter of 40 cm.
Woven density made of 0 mesh cotton yarn x width = 150 x
Wrap 150 woven / inch plain weave, 0.2%
The saline was made to contain 400 g / m ² . A plain woven fabric (vertical × horizontal = 10 × 10 yarns / inch) made of polypropylene split yarn (thickness 10 μ × width 2 mm) was supplied thereto at 0.3 m / min. On the other hand, a DC voltage of negative 30 kV was processed by a needle-shaped electrode placed in a space 3 cm away from the surface of the earth electrode. Then, it was dehydrated with a dry filter paper, air-dried, and then wound. When the surface charge density of this processed product was measured for 24 hours, it was found to be 1.8 × 10 ^-9 coulomb / c in Table.
m ² and back 9.0 × 10 ⁻¹⁰ coulomb / cm ² .
Further, the depolarization charge amount at 130 ° C. or higher was determined from TSDC, and the result was 3.0 × 10 ⁻¹⁰ coulomb / cm ² .

After this was left in a dryer at 60 ° C. for 2 weeks, the amount of depolarization charge at 130 ° C. or higher was determined, and as a result, almost no decrease was observed. It can be seen that the electret has excellent thermal stability and durability.

The difference in surface charge density between the front and back surfaces of the electret cloth thus obtained is 9.0 × 10 ^-10 coulomb / cm ² . This electret cloth was very excellent as a material for a hair cap (dustproof hat) because of its charge characteristics.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a method for manufacturing an electret cloth of the present invention.

FIG. 2 is a schematic diagram showing an apparatus for measuring surface charge density.

FIG. 3 is a block diagram for obtaining a thermally stimulated depolarizing current.

[Explanation of symbols]

 1: Rotating body 2: Semiconductor liquid 3: Semiconductor liquid supply roll 4: Liquid containing material 5: Delivery roll 6: Fabric 7, 8: Turn roll 9: High voltage generator 10: Needle-shaped electrode 11: Hot air generator 12: Winding roll 13: Electret cloth

Claims (1)

(57) [Claims] 1. An electret cloth having electric charges on the front and back surfaces has a surface charge density difference of 4 × 10 ⁻¹⁰ between the front and back surfaces.
Electret cloth characterized in that it is ~ 9 × 10 ^-10 coulomb / cm ² .