JPH0660462B2 - Method for manufacturing electret cloth - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing an electret cloth. More specifically, the present invention relates to a method for producing an electret cloth, which has a perfect ground contact with the cloth and is excellent in thermal stability and surface charge density.

[Conventional technology]

As a method of making the cloth electret, Japanese Patent Publication No. 49-44
No. 33 public information is known. This method is a method in which a cloth sandwiched by a dielectric sheet is directly laminated between metal flat plate electrodes to form an electret. The disadvantage of this method is that the grounding property between the dielectric sheet and the cloth is essentially insufficient, so that the injection of the compensation charge from the ground electrode cannot be sufficiently obtained. Thermally stimulated depolarization current (TSD) of this processed product
Evaluation of C) shows that the depolarization current value is small. This result suggests that electret lacks stability. Actual processed product is 40 ° C x 9
When the aerosol collection performance is evaluated after being left for 2 months in an atmosphere of 5% RH, it can be seen from the fact that the performance is degraded.

[Problems to be solved by the invention]

The present inventor has earnestly studied a method for making a fabric into an electret that can solve the above-mentioned drawbacks, and arrived at the present invention.

An object of the present invention is to provide a method for producing an electret cloth having excellent thermal stability by improving the ground contact property even in a non-woven fabric, a woven fabric, a knitted fabric or the like.

[Means for solving problems]

 The present invention has the following configurations.

When a cloth is interposed between an earth electrode and a voltage-applying electrode whose surface is coated with a liquid-containing material to form an electret, one side of the cloth is brought into contact with the liquid-containing material moistened with a semiconductor liquid and a high pressure is applied. It is a method for manufacturing an electret cloth, which is characterized by applying the electric field. Hereinafter, the present invention will be described in detail.

An example of the method for manufacturing the electret cloth of the present invention is shown in FIG. In FIG. 1, on the surface of the grounded rotating body 1 which rotates in the direction of arrow A, the semiconductor liquid 2 is fed with the semiconductor liquid supply roll 3
It is covered with the liquid-containing material 4 which is constantly wetted with. 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. Then, a small amount of the semiconductor liquid attached to the cloth is removed from 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 has a volume resistivity value of 10 ⁻¹ to 10 ⁶ Ω · m, and specifically, water is suitable, but an electric field such as a surfactant or salt is used. You may use the liquid which melt | dissolved the quality. Further, acetone or alcohol may be dissolved in water. When the volume resistance value is less than 10 ⁻¹ Ω · m, the electric charge is easily transferred from the fiber surface to the liquid,
Surface charge density is not sufficiently improved. Further, when the charge exceeds 10 ⁶ Ω · m, the charge carriers reaching the fiber surface are attached and the surface charge density immediately increases, but on the contrary, repulsion of the same charge occurs, and further improvement of the surface charge density cannot be expected. . Therefore 1
The range of 0 ⁻¹ to 10 ⁶ Ω · m is preferable, and 10 ² to 10 is particularly preferable.
Around ⁵ Ω · m is preferable for improving the surface charge density and permeating the charge carrier into the fiber. The method for measuring the volume resistivity of the liquid was based on JIS-C2110.

Next, the earth electrode is a rotating body such as a roll, a drum, or a belt conveyor, the surface of which is wet with the semiconductor liquid. Specifically, the contact angle with the semiconductor liquid is 6
It is wetted through the liquid-containing material of 0 ° or less. Examples of the liquid-containing material include knitted and woven fabrics made of natural fibers such as cotton, wool, and pulp, nonwoven fabrics, cloths such as filter papers,
Further, hydrophilic polymer fibers having a high water content may be mixed or used alone. A cloth made of these liquid-containing materials is wrapped 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 is appropriately selected depending on the conditions of the cloth to be processed symmetrically. The surface charge density can be improved by pressing the processed cloth strongly in the state where the liquid-containing material is wet with 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 liquid film may be unevenly attached, which is not preferable. A more preferable contact angle is 30 ° or less.

To determine the contact angle, place the material horizontally on a horizontal table, drop a droplet from it onto the tip of the injection needle, and observe from a horizontal horizontal position with a microscope that can measure the angle. The angle formed by the droplet is determined by the value 5 minutes after the dropping.

Examples of the processed fabric that can be electret-processed in the present invention include a non-woven fabric and a knitted fabric made of fibers such as polyolefin-based, polyester-based, fluorine-containing, vinyl chloride-based, polyamide-based, and polyacrylic-based fibers. Further, it may be in the form of a film or paper. If the volume resistivity of these is 10 ¹¹ Ω · cm or more, preferably 10 ¹³ Ω · cm or more, it is suitable as a material for electret cloth. The method for measuring the volume resistivity of the processed cloth is based on JIS-C2103.

[Action]

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 fabric is effective, but it is often not possible depending on the application.

In the present invention, a 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 measurement method is as follows. A sample 16 is sandwiched between a grounded metal foil 14 and a metal plate electrode (area 100 cm ² , true cast material) 15.
The electric potential generated by the electrostatic induction is measured by the electrometer 18 through the capacitor 17.
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 (Takeda RIKEN TR8562) S: Area of sample (cm ² ) 3 shows a block diagram for determining stimulated depolarization current. This device is an electret thermal analyzer manufactured by Toyo Seiki Seisaku-sho, Ltd., and evaluated by the following method.

The sample 19 is sandwiched between the electrodes 20 and 21 and set in the heating furnace 22. Next, the temperature controller 23 and the thermocouple 24
The temperature is raised at a constant heating rate (5 ° C./minute). The current value detected by the picoampere meter 25 is input to the data processing device 26. Meanwhile, 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.

〔Example〕

 The present invention will be described in more detail by the following 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 of 10 ³ Ω · m and a water content of 250 g.
/ M ² was set.

An average fiber diameter of 3.5 μm, a thickness of 0.14 mm, a basis weight of 20 g / m ² , and an air flow rate of 7 cc / cm ² · sec on the ground electrode surface.
Was continuously supplied at 0.3 m / min so that one surface of the melt-blown nonwoven fabric made of pre-propylene was in contact. On the other hand, a needle-shaped electrode was installed in a space 3 cm away from the earth electrode and continuously processed at a negative 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 were as shown in Table 1.3 × 10 ⁻⁹ coulomb / cm ² and the back 9.0 × 10 ⁻¹⁰ coulomb / cm ² . Furthermore, as a result of evaluating the TSDC of this processed product by the method shown in FIG. 3, there are two peaks of the electrode at 92 ° C. and 165 ° C., and the depolarization charge amount of 130 ° C. or higher is 3.5 × 10 ⁻¹⁰ coulomb. It was / cm ² .

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

Five sheets of this product were laminated and left in an atmosphere of 50 ° C. and 95% RH for one year to evaluate the aerosol collection performance, but no deterioration was observed. Further, the aerosol collecting performance was evaluated by leaving it in a dryer at 100 ° C. for 1 week, but no deterioration was observed.

It can be seen that the electret has excellent thermal stability and durability.

To determine the aerosol collection efficiency, 0.33 μm polystin spheres (monodisperse latex from Dow Chemical Co., Ltd.) are adjusted to an aerosol concentration of 500,000 / ft ³ using an atomizer (manufactured by Kanomax Japan).

When this was supplied to the filter at a surface wind speed of 1.5 m / min, collection efficiency (%) = 100− (C ₀ / C _i × 100) C ₀ = aerosol concentration after passing through the filter (pieces / ft ³ ) C _i = Aerosol concentration before passing through the filter (units / ft ³ )

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

Example 2 50 on the surface of a metal drum roll having a diameter of 40 cm and grounded
A plain woven fabric consisting of # # cotton yarn and having a woven density of vertical × horizontal = 150 × 150 yarns / inch was wound, and this was impregnated with 0.2% saline in an amount of 400 g / m ² . In addition to this, a plain woven fabric made of polypropylene split yarn (thickness 10μ x width 2mm) (length x width =
10 × 10 / inch) was supplied 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 dried filter paper, air-dried and wound. When the surface charge density of this processed product was measured for 24 hours, Table 1.8 ×
10 ^-9 coulomb / cm ² , back 9.0 x 10 ^-10 coulomb / cm
^{Was 2} . Further, the amount of depolarized charge at 130 ° C. or higher was determined from TSDC, and the result was 3.0 × 10 ⁻¹⁰ coulomb / cm ² .

This product is left in a dryer at 60 ° C for 2 weeks, then at 130 ° C
As a result of obtaining the above depolarized charge amount, there was almost no decrease. It can be seen that the electret has excellent thermal stability and durability.

〔The invention's effect〕

In the present invention, a significant grounding improvement effect can be obtained by grounding a cloth having a poor grounding property on the semiconductor liquid film. That is, a deep trap of charge carriers inside the fiber is obtained, and the thermal stability and surface charge density of the electret are improved.

Therefore, 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.

[Brief description of drawings]

FIG. 1 shows 1 of the manufacturing method of the electret cloth of the present invention.
FIG. 2 is a schematic diagram showing an example, FIG. 2 is a schematic diagram showing an apparatus for measuring surface charge density, and FIG. 3 is a block diagram for obtaining a thermally stimulated depolarization current. 1: Rotating body, 2: Semiconductor liquid 4: Liquid-containing material, 6: Fabric 9, High voltage generator, 10: Needle-shaped electrode 13: Electret fabric

Claims (4)

[Claims] 1. A liquid-containing material in which one side of the cloth is wetted with a semiconductor liquid when a cloth is interposed between an earth electrode and a voltage-applying electrode, the surface of which is covered with the liquid-containing material, to form an electret. A method for manufacturing an electret cloth, which comprises applying a high voltage to a cloth. 2. The method for producing an electret cloth according to claim 1, wherein the liquid-containing material is a cloth or a porous sheet having a contact angle with the semiconductor liquid of 60 ° or less. 3. The method for manufacturing an electret cloth according to claim 1, wherein the ground electrode is a rotating body. 4. The volume resistivity of the semiconductor liquid is 10 ^-1 to 10 ⁶
The method for producing an electret cloth according to claim (1), wherein the electret cloth has a resistance of Ω · m.