JPH0369663A - Production of cellular sheet converted into electret - Google Patents

Abstract

PURPOSE:To obtain the subject sheet, having a large amount of held electric charges and uniform electrified state and useful as acoustic apparatuses, etc., by superposing a cellular dielectric sheet on the surface of a solid dielectric sheet, carrying out discharge and injecting electric charges thereinto. CONSTITUTION:The objective sheet obtained by superposing a cellular dielectric sheet 12 on the surface of a solid dielectric sheet 5 having at least 4kV surface potential and injecting electric charges thereinto by discharge of the above- mentioned dielectric sheet. Furthermore, in charging, a self-discharging type electrode 9 is preferably provided in an opposite direction of the surface of the aforementioned sheet 5 to carry out charging. For example, polypropylene, etc., are preferably used as the sheet 12 and polyvinyl chloride, etc., are preferably used as the sheet 5.

Description

[Detailed Description of the Invention] (Industrial Application Fields) Electrets are used in audio equipment, various sensors, electret motors, electret switches, air filters, bone fracture treatment materials, etc. by utilizing their semi-permanent charge trapping properties. ing.

(Prior art) Porous dielectric sheets, unlike solid conductor sheets such as films, have spaces within the material, so high voltage cannot be applied when converting them into electrets, and there is a risk of contact with the earth. Due to the problem that it was not possible to inject a highly effective burden, such as poor performance, it was not possible to convert the high power to an electret. As a method to solve this problem, for example, the method described in Japanese Patent Publication No. 59-151671 involves corona charging a nonwoven fabric on an insulating film. This is an attempt to improve the performance of nonwoven electret. However, even if this method is used, most of the charges pass through the space of the nonwoven fabric, and there is a limit to the amount of charge retention t8 of the nonwoven fabric.

Furthermore, a method of corona charging a fiber sheet using a liquid electrode as a ground electrode described in JP-A No. 61-102478 improves the contact between the fiber and the ground electrode and improves charge injection properties. However, the dielectric breakdown voltage of the liquid electrode was low, and effective charge injection did not occur, so there was still a limit to the amount of charge that the fiber sheet could retain. Against this background, there has been a strong desire for a method of retaining charges in a porous dielectric sheet at a higher density.

(Problems to be Solved by the Invention) The present invention solves the uneven charging state or low charging state of the porous electret sheet using a novel electret-forming method.

(Means for solving the problem) In order to solve the problems of the conventional method of converting porous dielectric sheets into electrets, various charging methods have been intensively investigated. When porous dielectric sheets are stacked together, and at that time, a self-discharge type electrode is installed on the solid electrolyte sheet and charge is injected by discharge, an electret porous sheet with a high charge amount is formed. I found out what I can get.

That is, the present invention provides a porous dielectric sheet with at least 4 porous dielectric sheets.
The present invention relates to a method for producing an electret porous sheet, which is characterized in that it is superimposed on the surface of a solid conductor sheet having a surface potential of kv, and charge is injected by discharge of the dielectric sheet.

The manner in which a porous dielectric sheet with a high (; F charge) can be obtained by the method of the present invention will be explained using figures. The electric charge 3 ejected from the electrode 2 travels toward the ground 6, and many electric charges reach the solid dielectric sheet 5.
accumulated on top.

Next, as shown in FIG. 2, a porous dielectric sheet 7 is superimposed on the solid electrolyte sheet immediately after being charged by corona charging, and at the same time a self-discharge type electrode 9 is provided on top of the porous dielectric sheet 7.
The charge 4 is discharged toward the self-discharge type electrode 9, that is, a discharge occurs. At this time, charges are uniformly and permanently trapped in the porous dielectric sheet 7 in the plane direction. The reason why the electretization method according to the present invention can produce electrets with a higher charge amount than the conventional electretization method is because in the conventional method, for example, when using corona charging, the concentration of charge immediately below the tip of the needle that generates corona is electretization with a high charge amount, but only a low charge amount is obtained in areas other than the tip of the needle, resulting in spots of .;1f charge amount on the porous dielectric sheet.

In the porous electret sheet produced by the method of the present invention, the charges uniformly accumulated on the surface of the solid electrolyte sheet are superimposed and at the same time discharge is caused to the porous dielectric sheet with a low surface potential, resulting in extremely uniform charge injection. As a result, an electret porous sheet with a uniformly charged state and a high charge amount not found in conventional methods can be obtained.

In the present invention, the porous dielectric sheet is preferably made of highly insulating materials such as olefinic polymers such as polyethylene, polypropylene and α-polyolefin, polyester, polystyrene, polyvinylidene fluoride, Teflon, etc.
Examples include synthetic resins such as polycarbonate, polysulfone, polyacrylonitrile, polyvinyl chloride, and polyvinylidene chloride, copolymers and blend compositions of two or more thereof, and nonpolar glass.

The forms of the porous dielectric sheet used in the present invention include a sponge-like sheet, woven fabric, non-woven fabric, and particles.

Examples include child sintered sheets and composite sheets thereof, and those having a thickness of 0.05 to 10 mm are suitable.

In addition, the packing density is preferably 0.01 to 0.9
cc/ CC, more preferably 0.03 to 0.3 cc/
cc1 can be more preferably 0.05 to 0.2 cc/cc.

The solid electrolyte sheet used in the present invention is preferably made of a material that has a large charge accumulation capacity and that causes rapid discharge, such as olefinic polymers such as polyethylene, polypropylene, and α-polyolefin, polyester, polystyrene, and polyfluoride. Synthetic resins such as vinylidene, Teflon, polycarbonate, polysulfone, polyacrylonitrile, polyvinyl chloride, polyvinylidene chloride, copolymers and blend compositions of two or more of these, 111 substances such as silicone, non-polar glass, etc. Can be mentioned.

In the present invention, the surface potential of the solid conductor sheet is preferably at least 4 kV, more preferably 8 kV.
v or more -L1, more preferably 9 kv or more. This surface potential is an electrostatic charging voltage at a position 1 cm above the solid conductor sheet, and is a value measured using a current collecting potential measuring device.

In the present invention, a needle, wire, flat plate, knife, bar, etc. is used as the self-discharge type electrode, and the polarity of the electrode can be OV, that is, earth, or the polarity can be reversed to the polarity applied in the charging process. preferable.

In the present invention, methods for charging the solid dielectric sheet include corona charging, electric field charging, electron beam irradiation, and the like.

In the present invention, when a solid dielectric sheet having a surface potential is laminated with a porous dielectric sheet, it is preferred that the solid dielectric sheet is laminated with the porous dielectric sheet immediately after the charging step. In order to rapidly form this delicate strip f[, there is a method in which a solid dielectric sheet and a porous dielectric sheet are overlapped in advance, and the charging process and the discharging process of the solid dielectric sheet are made continuous. Figures 3 and 4
The figure shows an outline of a method for continuously performing the L-kigyoku process. FIG. 3 shows an apparatus comprising a roller 11 lined with a layered solid dielectric sheet and a charging device 10. A solid dielectric layer is placed so as to be continuously superimposed on the porous dielectric sheet 12 immediately after the charging process. FIG. 4 shows the device shown in FIG. 3 with a self-discharge type electrode 13 added, and a porous dielectric sheet 12a.
Alternatively, it is unwound from the position 12b and superimposed on the roller 11. Although an embodiment of a method for continuously assembling solid dielectric sheets has been shown here, any configuration and shape may be used as long as the apparatus can basically perform the same process.

(Function) In the present invention, the porous dielectric sheet is electretized uniformly and with a high charge amount by the uniform discharge action in the plane direction from the solid lightning dielectric sheet having a surface potential of at least 4 kV, Ru. This method of producing an electret porous sheet is a novel method never seen before.

(Examples) Example 1 A nonwoven fabric made of ultrafine polypropylene fibers (average fibers: 41.9 u) with a basis weight of 25 g/rl and a thickness of 0.3 mm was made into an electret using the apparatus shown in FIG.

The solid dielectric sheet was charged by corona charging using a needle electrode, and the applied voltage was 20 kv1 and the application time was 10 seconds. The surface potential of the dielectric sheet is 1
It was 2kv. A polyvinyl chloride sheet with a thickness of 60 pm was used as the dielectric sheet.

The nonwoven fabric was used as an air filter, and its removal efficiency was evaluated based on salt particles (average particle size: 0.3 μm, geometric standard deviation: 1.2
), and the measurement was carried out using the filter removal efficiency measuring term shown in FIG. The electret nonwoven fabric 17 is installed in the duct +-te, and the flow meter 18 is set at a ventilation speed of 5,
Controlled to 3 cm/sec, non-woven;
/i] The number of salt particles upstream and downstream was counted using a laser particle counter (KC-14 manufactured by RION). The removal efficiency was 99.8%.

The removal efficiency was calculated using the following formula.

Removal efficiency (%) = (1-(number of particles on the downstream side)/(number of particles on the second stream side)) The dielectric sheet was charged by corona charging using a needle electrode, and the applied voltage was 10 kV and the application time was 10 seconds.The surface potential of the dielectric sheet was 5 kV.The electric sheet A polyvinyl chloride sheet with a thickness of 60 mm was used.

The removal efficiency of the nonwoven fabric was 91.5%.

Comparative Example 1 The same polypropylene nonwoven fabric as in Example 1 was made into an electret using the apparatus shown in FIG. of a solid dielectric sheet,
l) Electric treatment is performed by corona charging using a side electrode,
The applied voltage at that time was (3 kV, and the application time was 10 seconds. The surface potential of the dielectric sheet was 3 kV. As the dielectric sheet, a polyvinyl chloride sheet of 80/-1111', ': was used. The removal efficiency of the nonwoven fabric was 49%.

Comparative Example 2 The same polypropylene nonwoven material 11 as in Example 1 was not made into an electret at all. The removal efficiency of the nonwoven fabric is 4
It was 5%.

In an electret filter, the higher the removal efficiency, the greater the amount of charge retention, and the effect of the present invention was clear.

Example 3 Fabric weight 20 made of polystyrene microparticles (particle size 2)
A particle-filled porous sheet of g/+/1 thickness of 0.15 m+s was made into an electret using the apparatus shown in FIG. The solid dielectric sheet was charged with a corona <11 using a tungsten wire with an opening diameter of 0.1, and the applied voltage was 301 (v1 application time was 10 seconds. The surface potential of the dielectric sheet was was LOkv. A deck stainless steel plate was used as a self-discharge type electrode, and corona charging and inversion were performed at 3 kV for 5 seconds. As a medium electrolyte sheet, a Teflon sheet with a thickness of 0.3 was used. The surface potential distribution of the porous sheet was measured using a surface potentiometer.
-1 When measured using Denkisha Model S-211) 1
It had a very uniform surface potential distribution of 800±100V in the direction of the shell.

Comparative Example 3 The same porous sheet filled with polystyrene microparticles as in Example 2 was corona charged under the same conditions as in Example 2, and separated from the Teflon sheet after the charging treatment. The surface potential of the porous sheet was 600±500V.

Comparative Example 4 The same porous sheet filled with polystyrene microparticles as in Example 2 was made into an electret using the apparatus shown in FIG. The dielectric treatment of the solid dielectric sheet was performed by corona charging using a 0.1 m-φ tungsten wire, and the applied voltage was 10 kV and the application time was 10 seconds.The surface potential of the dielectric sheet The voltage was 4kV.A flat stainless steel plate was used as the self-discharge type electrode, and the charging was carried out at 3kV for 5 seconds with the opposite polarity to corona charging.As the solid electrolyte sheet, a Teflon sheet with a thickness of 0.31fi11 was used. The surface potential distribution of the porous sheet was 1100±
It was 150V.

In the case of electret sheets, the higher the surface potential,
This means that the amount of charge retained is large, and the smaller the variation in the surface potential distribution, the more uniform the charged state is, and the effect of the present invention was clear.

It can be seen from the above examples and comparative examples that the method for producing an electret porous sheet according to the present invention is excellent.

(Effects of the Invention) The method of forming an electret from a porous dielectric sheet according to the present invention has a high charge retention capacity that could not be obtained by conventional charging methods, and an electret having a uniform electrical state. It is possible to obtain a porous sheet.

[Brief explanation of drawings]

Figure 1 shows the charge accumulation state of the solid electrolyte sheet during corona charging, and Figure 2 shows the overlapping of the solid electrolyte sheet and the porous dielectric sheet immediately after corona charging is completed. FIGS. 3 and 4 are schematic diagrams of the electretization device for porous dielectric sheets according to the present invention, and FIG.
The figure is a schematic diagram of a filter removal efficiency measuring device.

Claims (2)

[Claims] (1) A method for producing an electret porous sheet, which comprises superimposing a porous dielectric sheet on the surface of a solid dielectric sheet having a surface potential of at least 4 kV, and injecting charge by discharging the dielectric sheet. (2) When a porous dielectric sheet is superimposed on the surface of a solid dielectric sheet having a surface potential of at least 4 kV and the dielectric sheet is charged by discharge, self-discharge occurs in the opposite direction of the surface of the solid dielectric sheet. A method for producing an electret porous sheet, characterized by installing a type electrode and charging it.