JPH0663175B2 - Method for manufacturing electret sheet - Google Patents

Description

The present invention relates to a method for manufacturing an electret sheet.
More specifically, the present invention relates to a method for manufacturing an electret sheet having different polarity sections that are excellent in dust collection and adsorption.

[Prior Art] Since atmospheric dust has a charge distribution according to the Boltzmann distribution, dust of positive charge, negative charge, and no charge is mixed. Further, it is said that dust generated from a human source has a distribution in which the polarities of charges are biased.

It is known that when these dusts are adsorbed or collected, it is desirable to collect them with a cloth having a polarity opposite to the electric charge of the dusts.

However, in the case of a conventional electret sheet, for example, an electret sheet obtained by splitting and assembling an electretized film, the positive and negative polarities cancel each other because the constituent fibers polarized in + and-are mixed at random. , Inferior in collection performance and adsorption. Further, in the case of a sheet whose surfaces have the same polarity, when the aerosol having mixed polarities is adsorbed or collected, the aerosol having the same polarity is repelled and the adsorption performance is deteriorated.

Heretofore, there has not been an electret sheet in which compartments having different polarities which are optimal for adsorbing or collecting an aerosol in which particles having different polarities are mixed are mixed.

[Problems to be Solved by the Invention] The present inventors have arrived at the present invention as a result of earnestly examining an electret sheet having the above-mentioned drawbacks and excellent in adsorption performance and collection performance. In particular, the present invention aims to provide an electret sheet which is excellent in collecting or collecting dust in which particles of different polarities are mixed.

[Means for Solving Problems] The present invention has the following configurations. That is, at the time of electretization between the charges of the two poles, a separator made of a material having a volume resistivity value of 10 ¹² Ω · cm or more is used to isolate a part of the application electrode and the electret sheet surface, The present invention relates to a method for manufacturing an electret sheet, characterized in that the applied voltage polarity is selected so that the isolation portions on the surface of the electret sheet have opposite polarities, and high voltage is applied only to the isolation portion.

1 and 2 are schematic views showing an example of the manufacturing method of the present invention.

In FIG. 1, a work piece 1 is closely attached to a grounded metallic flat plate electrode 2 and an application electrode 4 is connected to a high voltage generator 3.
A high voltage applying method for corona discharge treatment is shown by. First
First, the surface of the workpiece 1 is electretized to have the same polarity by the method shown in the figure.

Next, according to the method shown in FIG. 2, a part of the surface of the sheet 6 electretized by the method shown in FIG. 1 is isolated as shown in FIG. 6
The applied voltage polarity is selected so that the isolation portion B on the surface has the opposite polarity, and high voltage is applied only to the isolation portion B. As a result,
In the isolated portion B, a partition having a polarity opposite to that of the non-isolated portion A and having a different polarity is formed.

Therefore, compartments having different polarities are mixed on the surface of the electret sheet.

The separator used in the present invention is made of a material having a volume resistivity value of 10 ¹² Ω · cm or more, and is made of a polymer such as a polyolefin type, a polyester type, or a fluorine type, and has a thickness of 0.1 mm or more. Composed of planks. The shape of the separator may be a structure in which only the lower part is vacant as shown in FIG. 2, or a part or all of the upper part may be vacant. Regardless of the shape, the volume resistivity of the separator is 10
It must be ¹² Ω · cm or more. This is because it is necessary to limit the spread of the electric field and apply high voltage only to the isolation portion. For example, forming a separator with a material of less than 10 ¹² Ω · cm causes the following defects. Due to its low ability to limit the spread of the electric field, thicker materials must be used. As a result, it becomes difficult to reduce the interval between the sections having different polarities.

Also, when the separator is made of a thin material, the lines other than the separator are weakly electretized due to the lines of electric force leaking through the separator, and the electret property is deteriorated.
The difference in polarity becomes unclear. Therefore,
It is necessary that the material constituting the separator has a volume resistivity value of 10 ¹² Ω · cm or more, preferably 10 ¹⁴ Ω · cm or more.

The distance between the lower part of the peeling body and the object to be processed when a high voltage is applied is preferably about 0 to 3 mm, preferably about 0 to 1 mm. This is to minimize the decrease in electret property caused by the electric lines of force leaking out from the lower portion of the separator.

The shape of the separator is the shape, size, and size of the sections of the electret sheet in which sections with different polarities to be created are mixed.
It can be decided according to the design etc.

Further, the number of separators used in the electret processing can be freely selected.

The type of the applying electrode may be a needle type, a wire type, or even if a grid electrode is used in combination with these electrodes, the present invention can be implemented.

When a high voltage is applied using a cloth, for the purpose of improving electret characteristics, 10 ² to 10 ⁶ Ω · cm, or
When one surface of a sheet having a volume resistivity of 10 ¹⁴ Ω · cm or more is brought into close contact with a grounded metallic flat plate electrode, and then the cloth is brought into close contact with the other surface of the sheet to apply a high voltage. In addition, it is possible to obtain an excellent electret sheet cloth in which sections having different polarities are mixed.

3 and 4 are schematic diagrams showing such a method.

That is, FIG. 3 shows a method of applying a high voltage to the surface of the cloth 8 through the sheet 7 as in FIG. FIG. 4 shows a case where the electret cloth 9 obtained in FIG. 3 is separated from the electret cloth 9 through the sheet 7 in the same manner as in FIG. And isolate as shown in the figure, and the isolation portion B on the surface of the electret fabric 9
The polarity of the applied voltage is selected so as to have the opposite polarity to that of No. 1, and high voltage is applied only to the isolation part B. As a result, in the isolated portion B, a partition having a polarity opposite to that of the non-isolated portion A is formed.

The material of the sheet 7 used in the present invention has a volume resistivity value of
In the case of 10 ¹² Ω · cm or more, a sheet made of polyolefin-based, polyester-based, polyamide-based, or fluorine-based polymer may be used as it is. Also, in the case of a sheet having a volume resistivity value of 10 ² to 10 ⁶ Ω · cm, an antistatic agent, carbon black, carbon fiber, conductive zinc white, etc. are kneaded into a polymer such as polyolefin or polyamide. It is a sheet made by adjusting the volume resistivity.

The object to be processed used in the present invention has a volume resistivity value of 10 ¹⁴
This refers to woven and knitted fabrics, non-woven fabrics and films, and plastic sheet-like products made of organic polymer materials of Ω · cm or more. In order to be an excellent electret, it is necessary that the charge carriers trapped in the organic polymer by applying a high voltage remain inside the material. But below 10 ¹⁴ Ωcm,
Since the charge carriers move easily, the polarization due to the high voltage application cannot be maintained.

Therefore, an electret sheet in which sections having different polarities are mixed cannot be obtained.

In the production of the electret sheet of the present invention in which compartments having different polarities are mixed, the high voltage may be applied once or more. Further, the temperature at the time of applying high voltage is preferably within a temperature range higher than Tg of the target material by Tg plus 150 ° C.

The volume resistivity value was measured according to ASTM-D257.

[Operation] Regarding the polarity relationship between the front surface and the back surface of the electret sheet, if the surface has a positive polarity, the back surface exhibits a negative polarity. Also, the surface has a negative polarity and the back surface has a positive polarity, which is an inverse relationship.

This is due to the polarity of the charge carriers trapped inside the material. That is, charge carriers having a positive charge are present on the positive surface. When this surface is provided with the same amount of negative charge carriers as the amount of positive charges, it is neutralized and becomes uncharged. Further, when an excessive amount of negative charge carriers is given, the number of negative trap charge carriers increases and the negative polarity is exhibited. Similarly, even if a positive charge is applied to the negative surface, the negative polarity changes to the positive polarity.

Therefore, by applying a high voltage so that only the isolated portion has the opposite polarity, it is possible to produce an electret sheet in which sections having different polarities are mixed.

Further, the dust collecting property and the adsorbing property are excellent because electric neutralization is not small because compartments having different polarities are mixed on the same surface of the electret sheet.

FIG. 5 and FIG. 6 are schematic views showing this situation. FIG. 5 shows an electret non-woven fabric in which the directions of the lines of electric force of electretized fibers are randomly disturbed. FIG. 6 shows an electret non-woven fabric in which compartments of different polarities according to the present invention are mixed. Both are transverse cross-sectional views showing only the surface portion. Lines a and b in the figure indicate the directions of the respective lines of electric force.

In FIG. 5, the electric lines of force a are canceled out and the effect is reduced. However, in the case of the electret sheet of the present invention of FIG. 6, the electric lines of force b on the outermost surface of the electret sheet are less canceled out, so that the action is effective. A sheet with excellent dust collection and adsorption.

Example Next, an example will be described in more detail.

The evaluation method of the surface charge density shown in the examples is performed as follows. Using the evaluation device of FIG. 7, the sample is set on the bottom of the grounded metal box and sandwiched by the electrodes. The surface charge density is calculated from the observed potential by the following formula.

Q = CV / S Q: Surface charge density (Coulomb / cm ² ) C: Capacitor capacity (μF) V: Measurement potential (V) S: Sample area (cm ² ) Numbers 10 and 11 in the figure are metallic boxes , 12 is an electret sheet, 13 is a metal plate electrode, 14 is a capacitor, 15
Is a picoampere meter.

The collection efficiency is determined as follows. Air containing aerosol is passed through the sample at a rate of 2.5 cm per second, and the collection efficiency is calculated using the following formula from the aerosol concentration (number / ft ³ ) before passing the sample and the concentration change of the aerosol after passing the sample. In addition, the measurement of the aerosol concentration can be performed by using a condensation meter (CN
C) (manufactured by Japan Canomax) was used.

η = 100 − {(C _o / C _i ) × 100} η = collection efficiency (%) C _i = aerosol concentration before sample passage (number / ft ³ ) C _o = aerosol concentration after sample passage (number / number) ft ³ ) Atmospheric dust was used as the aerosol.

[Example] Example 1 A polypropylene film (thickness: 10 µm) was adhered to a grounded metallic flat plate electrode as shown in Fig. 1, and a voltage of -20 KV at a distance of 3 cm between the needle electrode and the metallic flat plate electrode. High voltage was applied for 10 seconds. The polarity of this film was investigated by the method of measuring the surface charge density. Surface is -8 × 10 ^-9 coulomb / cm
^It was negatively electretized at ² . Next, as shown in Fig. 2, with the film surface facing upward, it was re-adhered to the grounded metallic flat plate electrode again, and the side wall was made of Teflon separator with a thickness of 2 mm (length x width x height). Size = 2cm × 2cm × 3.5c
(2) Place two separators with 5 mm long needle-shaped electrodes set in the innermost part of m) directly on the film at 20 mm intervals, and at a positive 20 KV
High voltage was applied for 60 seconds. When the surface charge density of the isolated portion B was measured, it was positively charged at + 9 × 10 ⁻⁹ coulomb / cm ² . On the other hand, the non-isolated area A was not affected at -8 × 10 ^-9 coulomb / cm ² . An electret film in which compartments having different polarities were mixed was obtained.

Example 2 A polypropylene film (thickness of 5.0 μm) was adhered onto a metallic flat plate electrode as shown in FIG. 3, and a polypropylene meltblown nonwoven fabric (average fiber diameter 2.5 μm, fiber filling rate) was attached to the other surface of the polypropylene film. 15%, basis weight 20g /
m ² ) was in close contact.

Set in a space 3 cm away from the metallic flat plate electrode, + 20K
It was treated with a positive DC voltage of V for 10 seconds. The surface of this non-woven fabric was exactly electretized. Next, as shown in Fig. 4, the separators (vertical x horizontal x height = 1 cm x 1 cm x 3.5 cm) with needle-shaped electrodes set were placed at 1 cm intervals on the positively electretized surface. A total of 25 pieces, 5 pieces in the vertical direction and 5 pieces in the horizontal direction, were arranged and subjected to corona discharge treatment at negative -20 KV for 60 seconds. The surface charge density of the isolated portion B was −7 × 10 ⁻¹⁰ coulomb / cm ^{2 and} was negatively charged. On the other hand, the non-isolated portion A was positively charged at + 8 × 10 ⁻¹⁰ coulomb / cm ² .
An electret non-woven fabric in which compartments having different polarities were mixed was obtained.

When 3 sheets of this sheet were piled up and the collection performance was evaluated, it was 99.9.
It was 994%.

When three electret non-woven fabrics before being made to have different polarities were stacked and the collection performance was evaluated in the same manner, it was 99.9990%. It can be seen that the electret in which the sections with different polarities are mixed is slightly better.

[Effects of the Invention] The electret sheet of the present invention has compartments of different polarities mixed on the same surface. Since the partition is made large in an area that is not electrically neutralized,
When the negatively charged dust floats in the vicinity of the electret sheet, it is attracted by the electrostatic force of the different polarity section and is collected and adsorbed. Therefore, by using the electret sheet in which the sections having different polarities are mixed, it is possible to produce an excellent trapping material and adsorbent.

As a use, it is also possible to perform dyeing or chemical treatment of a specific portion by selectively adsorbing a mask, a filter, a dust adsorbent, or a charged dye or chemical to an electret sheet.

[Brief description of drawings]

1 to 4 are schematic views showing an example of an embodiment of the present invention, FIG. 5 is a schematic view of a cross section of an electret nonwoven fabric composed of electretized fibers, and FIG. 6 is a production method of the present invention. FIG. 7 is a schematic diagram of a cross section of an electret nonwoven fabric in which compartments having different polarities made in (4) are mixed, and FIG. 7 is a schematic diagram of a surface charge density measuring device. 1: Object to be processed, 2: Metallic flat plate electrode grounded 3: High voltage generator 4: Applied electrode, 5: Isolator 6: Electretized sheet 7: Sheet, 8: Fabric 9: Electretized fabric 10,11 : Grounded metal box 12: Electret sheet 13: Metal plate electrode 14: Capacitor 15: Picoampere meter A: Non-isolated area B: Isolated area a, b: Electric flux lines

Claims (1)

[Claims] 1. When an electret is formed between two electric charges, a separator made of a material having a volume resistivity of 10 ¹² Ω · cm or more is used to remove a part of the surface of the electret electrode sheet from the application electrode. A method for manufacturing an electret sheet, characterized in that the electret sheet is isolated, and the applied voltage polarity is selected so that the polarities of the isolating portion on the surface of the electret sheet are opposite.