JP2553080B2 - Method for producing electret fiber sheet - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electret fiber sheet material that exerts a strong electric action on the outside and a method for producing the same.

<Prior Art> Conventionally, as an electret fiber sheet material, Japanese Patent Publication No. 56-47299, Japanese Patent Publication No. 59-124, and Japanese Patent Laid-Open No. 61-61.
The one proposed in Japanese Laid-Open Patent Application No. 102476 is known.

The first is to cut the electret film into a fibrous form and web-form it, and the second is to electretize the fibers during spinning and collect them on the conveyor surface to form an electret fiber sheet form. You get what you get. In these electret fiber sheet materials, since the electret fibers, which are the constituents thereof, are randomly dispersed to form a web, the directions of the polarization charges are random at the time of sheet formation, and as a result, the polarization charges are offset. Inconvenience occurs. Therefore, in these electret fiber sheet materials, an electric field is generated only inside the sheet, in the immediate vicinity of the fibers constituting the sheet, and an electric field is hardly formed outside the sheet material.

The third party is to first form a web and subject the web to a polarization treatment to produce highly oriented polarization in the web, forming an electric field to the outside world. However, even in this case, since polarization is generated by providing the web with an equal amount of positive and negative charges, even if the positive and negative charges can be separated on the front and back surfaces, the web is electrically charged. The strength of the electric field that the web exerts on the outside world to form the overlay is
It is inversely proportional to the cube of the distance from the web, and sharply decreases as the distance increases. Moreover, since the web is generally thin, the strength of the electric double layer (σ × t, σ: surface charge density, t: pressure) is also small.

In addition, a general sheet-like material made of many polymers is charged by contact with other substances or substances having the same composition as itself, friction, peeling, etc., and has a charge on its surface.
These charges are temporally and thermally unstable and cannot maintain a strong electric field with respect to the external environment for a long period of time. That is, there has been a limit in obtaining an electret fiber sheet-like material that continuously exerts a strong electric action to the outside world by the conventional technique.

<Problems to be Solved by the Invention> The present inventors have arrived at the present invention as a result of earnestly studying an electret fiber sheet-like material that does not have the above-mentioned drawbacks.
The present invention particularly aims to provide a method for producing an electret fiber sheet material having a strong electric action even at a point away from the sheet, and particularly good separation of positive and negative charges generated on the front and back of the sheet electret. It is intended to provide the method for producing the obtained electret fiber sheet material.

<Means for Solving Problems> The present invention has the following configuration.

(1) A sheet made of an insulating material having a porous structure on an earth electrode, and an electretized fiber sheet-like material are laminated so that they are located in this order, and a high voltage is applied to cause corona discharge, and the laminated material. An electret fiber sheet material having a positive and negative charge difference of 2 × 10 ⁻¹⁰ clones / cm ² or more stored in the fiber sheet material by passing a constant current through the electret. A method for producing a fibrous sheet.

(2) An electretized fiber sheet-like material and a sheet made of an insulating material having a porous structure are laminated on the ground electrode so that they are located in this order, and a high voltage is applied to cause corona discharge, and the laminate is obtained. An electret fiber sheet material having a positive and negative charge difference of 2 × 10 ⁻¹⁰ clones / cm ² or more stored in the fiber sheet material by passing a constant current through the electret. A method for producing a fibrous sheet.

It is an important feature that the electret fiber sheet obtained by the present invention has a stable positive or negative excess charge of 2 × 10 ⁻¹⁰ clones / cm ² or more in addition to positively and negatively polarized charges. . That is, not only the polarization due to the same amount of positive and negative charges, but also the electret fiber sheet-like material can have a positive or negative excess charge to form a strong electric field against the external world.

The material constituting the electret fiber sheet material in the present invention is preferably a material having an electric resistivity of 10 ¹³ Ωcm or more, preferably 10 ¹⁵ Ωcm or more, for example, polyolefin, polyester, polycarbonate, fluorine resin, vinyl resin. A fibrous material formed of synthetic resin such as resin or glass or other inorganic compounds may be used. With a material having an electrical resistivity of less than 10 ¹³ Ωcm, it is difficult to obtain stable charges for a long period of time due to internal charge transfer.

The form of the electret fiber sheet material is not particularly limited, but a cloth material is preferably selected from the viewpoint of flexibility and ease of designing for various applications.
Examples of such a cloth-like material include a non-woven fabric, a woven fabric, a knitted material, a paper-like material, and a part of them may be formed into a film. Further, in order to increase the amount of charge held per unit weight of the sheet-shaped material, the basis weight of the sheet-shaped material is preferably 100 g / m ² or less.

Regarding the electrical performance of the electret fiber sheet material of the present invention, the greater the amount of electric charge that it possesses, the better. The amount of electric charge is preferably 2 × 10 ⁻¹⁰ coulomb / cm ² or more. This charge amount is generated by the excess of either one of the positive and negative charges possessed by the electret fibrous sheet, so that the sign may be either and can be selected according to the purpose of use.

Hereinafter, the method for producing the electret fiber sheet material of the present invention will be described with reference to the drawings. 1 and 2 are schematic views showing an embodiment of an electretization apparatus used in the method for producing an electret fibrous sheet material of the present invention, in which 1 is a discharge electrode, 2 is a sheet to be electretized, 3
Is an attachment made of an insulating material, and 4 is a grounded metal plate.

When a sheet-like material composed of a fibrous composition is exposed to corona discharge by a high DC voltage and made into an electret, the sheet-like material is homogenous in the thickness direction depending on its constituent material, morphology and application conditions (the same direction as the applied voltage). Alternatively, it has a hetero polarization (direction opposite to the applied voltage). At this time, inside the sheet-like material, uniform polarization is generated by a constant current flowing inside the sheet, but on the surface directly facing the applying electrode and the surface directly facing the ground electrode, Of the positive charge and the negative charge become excessive by the injection of the electric charge of and the injection of the compensation charge from the ground electrode. With the conventional application method, the positive and negative charges generated on the front and back surfaces of the sheet could not be separated, so that the sheet as a whole could obtain only electrically neutral ones. The manufacturing method of the present invention is a sheet-like material to be electretized, which is subjected to an application treatment in a state where it is laminated with an attachment made of another insulating material, and then separated to give a positive or negative charge injection or a compensation charge injection. To obtain an electret fiber sheet material having an excessive electric charge.

In the manufacturing method, the sheet-like material made of another insulating material to be laminated with the electretized fiber sheet-like material when a high voltage is applied must be an insulating material and have a porous structure (pore structure). . That is, unless an insulator having a porous structure is used as the insulator, a constant current cannot be passed inside the sheet as described above, and an electret sheet having a uniform polarization structure can be obtained. I can't. In particular, when a film-shaped insulator is used, a steady current does not flow at all,
Electret sheets such as those obtained with the present invention cannot be manufactured.

In the method of the present invention, the non-woven fabric or woven or knitted material having a porous structure as an insulating material is capable of flowing an electric current through the porous structure portion when electretization is applied, so that the electretized fiber sheet This is a requirement for preventing the current from flowing and for allowing an appropriate compensating charge to enter the electretized fiber sheet from the ground electrode side. Since a non-woven fabric or a woven or knitted fabric having a porous structure is present as this insulator, a charge difference is generated between the front and back surfaces of the electretized fiber sheet material. When an insulating material having no porous structure is used, a current does not flow, so that it cannot be electretized and, of course, a difference in charge cannot be generated between the front and back surfaces of the electretized fibrous sheet material. The charge specific resistance of the insulator is 10 ⁷ Ωcm
Above, preferably 10 ¹⁰ Ωcm or more, and various synthetic polymers and natural polymers can be mentioned. Examples of the form of the sheet-like product include woven and knitted fabrics, non-woven fabrics, and the like, and sponge-like products containing air bubbles. Some or all of them formed into a film do not have a porous structure. It is not preferable and cannot be used in the method of the present invention. Further, the thickness of the insulating material does not have a great influence on the performance of the obtained electret fiber sheet material, but a thickness of 2 mm or less is preferable in terms of prevention of spark discharge and power consumption.

In the above-mentioned manufacturing method, one surface of the electretized fibrous sheet-like material is required to directly face the discharge electrode or the ground electrode, but the cover factor is small, and the flow of charges in the space is substantially reduced. It does not matter if it is through a sheet that does not obstruct.

As a method of applying a high voltage, it is preferable to use a discharge electrode and expose the sheet-like material under corona discharge generated by applying a DC voltage to the discharge electrode. The temperature at the time of application is preferably above the glass transition point and below the melting point of the electretized fibrous sheet material. The value of the "difference in positive and negative electric charges held as a fibrous sheet" defined in the present invention is measured as one electric charge value using a Faraday cage. Therefore, the positive and negative values are not separately measured, and the difference is not calculated by calculating from the two measured values.

<Example> Example 1 Electretized fiber sheet (weight per unit area: 20 g / m ² , average fineness: 0.04 denier, thickness: 0.12 mm polypropylene meltblown nonwoven fabric), average fineness: 0.04 denier, thickness: 0.48 mm
The polypropylene meltblown non-woven fabric of, was laminated so that the electret fiber sheet material becomes the outermost layer on the grounding surface side, exposed under negative corona discharge for 30 seconds and applied with a high voltage to obtain an electret fiber sheet material. .

The obtained electret fiber sheet-like material was stored in aluminum foil for 24 hours, and the amount of charge held by the electret fiber sheet-like material was measured using a Faraday cage. , And the charge amount was −6.8 × 10 ⁻¹⁰ coulomb / cm ² . The obtained sheet-shaped material was excellent in dust adsorption.

Example 2 The same electretized fiber sheet material as used in Example 1 and a polyethylene meltblown nonwoven fabric having a basis weight of 70 g / m ² and a thickness of 0.6 mm were used. It was laminated so as to be an outer layer, exposed to negative corona discharge for 30 seconds and applied with a high voltage to obtain an electret fiber sheet.

The obtained electret fiber sheet-like material was stored in aluminum foil for 24 hours, and the amount of charge held by the electret fiber sheet-like material was measured using a Faraday cage. , And the charge amount was −5.0 × 10 ⁻¹⁰ clone / cm ² . The obtained sheet-shaped material was excellent in dust adsorption.

Example 3 The same electret fiber sheet as used in Example 1 with a basis weight of 40 g / m ² , average fineness of 0.04 denier and thickness
0.24 mm polypropylene meltblown non-woven fabric is laminated so that the electret fiber sheet material is the outermost layer on the grounding surface side, exposed for 30 seconds under positive corona discharge and high voltage is applied, and the electret fiber sheet material is Obtained.

The obtained electret fiber sheet-like material was stored in an aluminum foil for 24 hours, and then the amount of charge held by the electret fiber sheet-like material was measured using a Faraday cage. , And the amount of charge was + 5.0 × 10 ^-10 coulomb / cm ² . The obtained sheet-shaped material was excellent in dust adsorption.

Comparative Example 1 The same electret fiber sheet material as that used in Example 1 above was placed directly on a grounded stainless steel plate and exposed to a positive corona discharge for 30 seconds without covering the upper surface to obtain an electret fiber sheet. A substance was obtained.

After storing the obtained electret fiber sheet for 24 hours in aluminum foil, the difference in the amount of positive and negative charges held by the electret fiber sheet measured using a Faraday cage is 0.7 × 10 ^-10 coulomb / cm. ^{Was 2} . The obtained sheet-like material was inferior in dust adsorption.

Comparative Example 2 The same weight as the electretized fibrous sheet material used in Example 1 above was weighted 40 g / m ² , respectively, and the average fineness
The sheet was covered with a polypropylene melt blown nonwoven fabric of 0.04 denier and a thickness of 0.24 mm, and exposed under negative corona discharge for 30 seconds to obtain an electret fiber sheet.

After storing the obtained electret fiber sheet for 24 hours in aluminum foil, the difference in the amount of positive and negative charges held by the electret fiber sheet measured using a Faraday cage is 0.5 × 10 ^-10 coulomb / cm. It was less than ² .
The obtained sheet-like material was inferior in dust adsorption.

<Effects of the Invention> Since the electret fiber sheet material obtained by the method of the present invention can form a stronger electric field to the outside as compared with the conventional electret fiber sheet material, the adsorptivity of dust, etc. It is an electret fiber sheet material which is excellent in terms of workability, adhesiveness, electrical stimulation, and the like.

The electret fiber sheet material obtained by the present invention is effective as a filter material, a wiper material, an adsorption material, a medical material, a sensor material, and the like.

[Brief description of drawings]

FIG. 1 and FIG. 2 are schematic views showing one embodiment of an electretization device used in the method for producing an electret fibrous sheet material of the present invention. 1: Discharge electrode, 2: Electretized sheet, 3: Attachment made of insulator, 4: Grounded metal plate.

Claims (2)

(57) [Claims] 1. A sheet made of an insulating material having a porous structure on an earth electrode, and an electretized fiber sheet material are laminated in this order, and a high voltage is applied to cause corona discharge. A constant current is passed through the laminate to obtain an electretized fiber sheet material having a positive and negative charge difference of 2 × 10 ⁻¹⁰ clones / cm ² or more as a fiber sheet material. A method for manufacturing an electret fiber sheet material. 2. A sheet made of an electretized fiber sheet and a sheet made of an insulating material having a porous structure are laminated on the ground electrode in this order, and a high voltage is applied to cause corona discharge, A constant current is passed through the laminate to obtain an electretized fiber sheet material having a positive and negative charge difference of 2 × 10 ⁻¹⁰ clones / cm ² or more as a fiber sheet material. A method for manufacturing an electret fiber sheet material.