JPH0268371A - Production of laminate of nonwoven fabric made into electret - Google Patents

Abstract

PURPOSE:To obtain a laminate made into an electret having high surface charge density by collecting fibers transported by a fluid as a structural layer of nonwoven fabric on a sheet of substrate layer in an electric field between an impressed electrode and an earthed electrode. CONSTITUTION:Fibers 5 subjected to melt blowing by a melt blow spinneret 4 are transported by a fluid such as air flow to an electric field 9 5 having >=1KV/cm intensity of electric field formed between an impressed electrode 3 and an earthed electrode 1. On the other hand, a sheet 7 of substrate layer is moved in a state of the sheet in contact with the surface of the continuously rotatable earthed electrode 1, the fibers made into electret are collected on the surface of the sheet of substrate sheet as a structural layer of nonwoven fabric in the electric field 9 to give a laminate 8 of nonwoven fabric made into electret having high surface charge density having excellent electret performance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing a nonwoven fabric laminate that is formed by laminating a nonwoven fabric layer and a base layer, has a high surface charge density, and is well electretized.

``Prior art'' The conventional method for manufacturing electret nonwoven fabric laminates is to laminate, for example, an electret meltblown nonwoven fabric and an electretized spunbond nonwoven fabric, woven fabric, knitted fabric, or meltblown nonwoven fabric of different fineness in separate steps. This was the commonly used method.

However, such a method has drawbacks such as increasing the number of processing steps, making it uneconomical, and increasing process loss.

Further, U.S. Pat. No. 4,436,780 describes a method for obtaining a nonwoven fabric laminate by collecting a melt-blown nonwoven fabric on a base sheet, and the nonwoven fabric laminate thus obtained is subjected to an electret treatment. However, in the electretized nonwoven fabric laminate obtained in this way, the electretization tends to be more pronounced as the basis weight increases, but the inside of the nonwoven fabric is not sufficiently converted to electret. had the disadvantage that a sufficiently high aerosol collection efficiency could not be obtained.

Furthermore, Japanese Patent Application Laid-Open No. 62-263361 describes a method for converting fibers transported by a fluid into electrets. This method is fundamentally different from the method of the present invention, which will be described in detail later. In other words, in the method of directly converting into electret 1 on the collection device, the potential on the surface of the collection device does not rise because the surface of the collection device is grounded. But you don't necessarily get as high as you want.

It was not possible.

[Problems to be Solved by the Invention] In view of the above-mentioned points, an object of the present invention is to make it possible to obtain a nonwoven fabric laminate having a high surface charge density and good electret performance, and to solve the drawbacks of the prior art. It is an object of the present invention to provide a method for manufacturing a nonwoven fabric laminate that improves the uneconomical effects caused by increased costs and process losses due to an increase in the number of processing steps.

"Means for Solving the Problems" The method for producing an electret nonwoven fabric laminate of the present invention, which achieves the above-mentioned objects, has the following configuration.

That is, the fibers carried by the fluid are collected as a nonwoven structural layer on the sheet surface of the base layer sheet in an electric field formed by an applied electrode and a ground electrode, and the electret nonwoven fabric structural layer and the base are collected. This is a method for producing an electret nonwoven fabric laminate, which is characterized by obtaining a laminate consisting of at least layer sheets.

[Function] Hereinafter, the method for manufacturing the electret nonwoven fabric laminate of the present invention will be briefly described in detail.

FIG. 1 is a schematic side view schematically illustrating one embodiment of the method for producing an electret nonwoven fabric laminate of the present invention. The figure shows an example of a case carried out by

In Figure 1, 1 is a ground electrode capable of continuous rotation, 2 and 2' are DC high voltage power supplies, 3 and 3' are application electrodes, 4 is a null 1 to blown metal, and 5 is a null 1 to blown metal. 6 and 6' are turn rolls, 7 is a base layer sheet, 8 is an electret nonwoven fabric laminate, 9 is an electric field, and 10 is the direction of rotation of the earth electrode. The fibers 5 are transported by the air flow into an electric field 9 formed between the application electrode 3 and the earth electrode 1.

On the other hand, the base layer sheet 7 is guided in the direction of the arrow 10 while being in contact with the surface of the continuously rotatable ass electrode 1 and the electrode 9
leading to. The melt-blown fibers 5 and the base layer sheet 7 that have been exposed to the electric field 9 are converted into electrets, and an electret nonwoven fabric laminate 8 can be obtained.

In the present invention, the fibers conveyed by the fluid are materials that can be made into electrets and have a volume resistivity of 1014 Ω·cm or more, such as polyethylene, polypropylene, etc.
Polyamide, polyester, polycarbonate,
Long fibers or short fibers made of polymers or copolymers such as polyurethane, difuscaethylene, trifuscaethylene, etc. are suitable. Among these, polymers and copolymers such as polypropylene, polyethylene, polycarbonate, difuscaethylene, and trifuscaethylene are suitable because they have excellent electret properties.

Furthermore, it is also possible to perform electretization by mixing natural fibers such as cotton and wool, which cannot generally be converted into electrets, with the above-mentioned materials that can be converted into electrets.

In the case of materials that can be melt-spun, the method for transporting the fibers into the electric field must be easy to carry out, such as by spunbonding, melt-blowing, or opening with a multifilament ejector. Ru.

In particular, the melt-blowing method is very preferable because ultrafine fibers can be produced relatively easily and nonwoven fabric materials suitable for use in high-performance filters and wipers can be produced. Further, in the case of the spunbond method, since the fineness is relatively large, it is possible to relatively easily produce a nonwoven fabric material suitable for a low pressure loss filter material, which is preferable.

Furthermore, in the case of short fibers that have already been made into fibers, the fibers can be transported into the electric field by being dispersed in an air stream using various methods such as the air raid method.

Next, as the material for the base layer sheet, not only synthetic fiber woven fabrics, knitted fabrics, nonwoven fabrics, and porous films made of organic polymers, but also woven fabrics, knitted fabrics, and nonwoven fabrics made of cotton, silk, and wool can be used. Of course, the sheet may be a blended fiber or blended product of a plurality of materials.

In addition, polymers that can be converted into electrets, such as polypropylene, polyester, polycarnate, etc.
The base layer sheet is a woven fabric, knitted fabric, or nonwoven fabric made of fibers made of a polymer selected from polymers such as 2-futsuka ethylene and 3-futsuka ethylene and copolymerized polymers and has a volume resistivity of 1014 Ω·cm or more. When used as a raw material, it is possible to obtain a nonwoven fabric laminate in which both the fibers transported by the fluid and the base layer sheet are made of electret.

Further, when a fabric having an antistatic effect with a volume resistivity of 1012 Ω·cm or less is used as the base layer sheet, it is possible to simultaneously obtain a laminate of the antistatic fabric and the electret nonwoven fabric. This has a volume resistance value of 1012Ω・cm
This is because the following antistatic fabric loses its charge in a short period of time even if it is subjected to the Electret 1 to Reno 1 treatment and generally does not become an electret sheet. The electret nonwoven fabric dark body obtained in this manner is convenient and preferable when used in applications that require antistatic properties and aerosol collection or adsorption properties at the same time. Incidentally, a more preferable volume resistivity value of the base layer sheet in which the base layer sheet is not converted into an electret is generally 10 10 Ω·cm or less.

The degree of air permeability of the base layer sheet used in the present invention preferably has an air permeability of 1 cc/ca/sec or more when measured according to the measuring method of J15-L-1096, A particularly preferable range is 4
It is 0cc/cnf/sec or more.

This is because in order to separate and collect fibers from the fluid on the surface of the base layer sheet, it is necessary to allow the fluid to escape through the interior of the base layer sheet, and it is preferable to have a large amount of ventilation. Therefore, the most suitable material for the base layer sheet is generally a nonwoven fabric.

In the case of the embodiment shown in FIG. 1, it is more desirable that the surface of the ground electrode 1 is also made of porous material.

Also, the volume resistivity value of the base layer sheet is 1o14Ω・c.
When using a material of less than It becomes possible to obtain a nonwoven fabric laminate made into electret 1. For this purpose, it is necessary in a preferred manner to feed the base layer sheet into the electric field in contact with the earth electrode.

To explain this point in more detail, in electret formation using the corona discharge method, the overall basis weight during electret formation is important.

When a base layer sheet having a high volume resistivity value and a large basis weight is used, if the basis weight of the fibers collected thereon is large, a phenomenon occurs in which the fibers in the innermost layer are not sufficiently converted into electret. This is presumed to be because a sufficient compensation charge cannot be obtained from the base layer sheet.

Therefore, by using a material with a low volume resistivity value as the base layer sheet, a compensating charge is easily applied to the fibers carried by the fluid, making it possible to obtain an electret nonwoven fabric laminate with excellent electret properties. It is.

Further, according to the findings of the present inventors, the suitable basis weight of the base layer sheet is, for example - in the case of a spunbond nonwoven fabric composed of fibers with a fineness of 8 denyl or less in the membrane, 300 L;
J/m2 or less.

Next, the feature of the present invention is to obtain an electret nonwoven fabric laminate while depositing and collecting fibers transported by a fluid in an electric field on the surface of a base layer sheet.
In order to obtain a nonwoven fabric laminate with excellent electret properties, the electric field intensity level in such an electric field is important, and according to the findings of the present inventors, the electric field intensity is 1 kV/C.
It is important to perform electretization while depositing and collecting the fibers transported by the fluid on the surface of the base layer sheet in an electric field of m or more in order to obtain a strong electret effect.

This is because if the electric field strength is less than 1 kV/Cm, it will be difficult to generate sufficiently effective corona discharge, and the resulting electret properties, such as surface charge density, will be low, which is undesirable. In this case, the filter performance obtained will be poor. Therefore, although it depends on the actual use of the electret nonwoven fabric laminate, the preferred electric field strength within the membrane is 1.
kv/cm or more, and a more preferable range is 3 kV/cm.
It can be said that it is more than Cm.

Regarding electretization in an electric field as described above, according to the findings of the present inventors, electretization actually progresses when the fibers carried by the fluid are collected and deposited on the surface of the base layer sheet. It seems like from the moment. This is because the speed at which the fibers (nonwoven fabric) collected on the surface of the base layer sheet move through the electric field (-the speed at which the earth electrode moves) is much faster than the speed at which the fibers are transported to the surface of the base layer sheet by the fluid. This seems to be due to the fact that the fibers carried by the fluid have a much higher chance of being charged because they are slower, and that the fibers carried by the fluid are not grounded and therefore receive almost no compensating charge.

In particular, when a nonwoven fabric with a large basis weight is converted into electret without using the method of the present invention, the fibers in the inner layer of the nonwoven fabric have a relatively low degree of electretization.

In the method of the present invention, the fibers collected and deposited on the surface of the base layer sheet are charged with electric charge, and the fibers collected and deposited thereon are also charged with electric charge, which is continuously and repeatedly carried out. As the ground electrode moves, it separates from the electric field and completes the electret formation, so the entire nonwoven fabric has a high electric charge. Therefore, it is possible to obtain an electret nonwoven fabric laminate having excellent electret properties.

When carrying out the method of the present invention, a drum or an endless belt made of a metal net or a porous metal flat plate may be used as the material for the earth electrode.

Further, an auxiliary device such as an air suction device may be used inside or below the collection device (earth electrode).

Furthermore, the surface of the earth electrode has a volume resistance of 1-1012Ω・c.
By using a material coated with a material in the m range, it is possible to obtain an electret nonwoven fabric laminate with excellent roughness.

Note that in the above description, the electric field strength is a value obtained by dividing the applied voltage value by the distance between the application electrode and the earth electrode.

"Example" The present invention will be explained below with reference to Examples.

Example 1 Using the method shown in FIG. 1, an electret nonwoven fabric laminate was produced in the following manner.

That is, the collection drum (earth electrode) surface covered with a 40-mesh stainless steel net was placed at a position of 25 cm from the tip of the polymer discharge hole of the melt-blown gold at the shortest distance.

Next, an application electrode (tungsten wire) was installed at a position 8 cm above the fiber collection position on the surface of the collection drum, and a DC high voltage of -40 kV was applied to it, with an electric field strength of 5 kV.
An electric field of /cm was created between the collection tram and the application electrode.

The i-fibers and the base layer sheet were fed into this electric field under the following conditions to obtain an electret nonwoven fabric laminate.

A base layer sheet (fineness 2 denier, basis weight 30q/Tn2, air flow rate 25Occ/a) was placed in contact with the collection drum surface.
t/sec of polypropylene spunbond nonwoven fabric) was supplied at 5 m/min, and the polypropylene polymer was blow-spun from null 1 to 0.0 on the surface of the base layer sheet.
Null 1 to blown nonwoven fabrics with a fabric weight of 4 denier and a basis weight of 50 CI/Tn'' were collected.

As a result, it was possible to produce nonwoven fabric laminates from Null 1 to blown nonwoven fabric and spunbond nonwoven fabric I [both of which were made into electrets.

The electret property of this electret nonwoven fabric laminate was evaluated using an evaluation method based on surface charge density. The surface charge density was evaluated using the evaluation apparatus shown in FIG. In the figure, 11 is a metal plate electrode, 12 is a metal box, 13 is an electret sample, 14 is a capacitor, and 15 is a microammeter 15. That is, from the potential determined by the microammeter 15, the surface charge density is determined according to the following equation.

Q=CV/S Q-Surface charge density (coulombs/ca+) C=-1 Densor capacity S-Electret sample area First, when the front and back sides of the electret nonwoven fabric laminate were measured, the front surface was 6.0 x 10" coulombs/cnf, and the back side was 5°5×1010 coulombs/−.

Next, when the electret nonwoven fabric laminate was separated into a meltblown nonwoven fabric and a polypropylene spunbond nonwoven fabric and the surface charge density was measured, the surface charge density of the meltblown nonwoven fabric was −5.4×10 coulombs/cm z
The back surface was 4.8×10 −1° Cron/CXK.

In addition, polypropylene spunbond nonwoven fabric has a −
4-, 8X10-10 coulombs/aK, back side is 5.6X
It was 1010 coulombs/C♂.

Thus, it can be seen that both the melt-blown nonwoven fabric and the polypropylene spunbond nonwoven fabric are sufficiently electretized.

Example 2 Using the method shown in FIG. 1, an electret nonwoven fabric laminate was obtained in the following manner.

Only the base layer sheet used in Example 1 was changed to the following base layer sheet, and electret formation was performed under the same conditions except for the base layer sheet used in Example 1.

In other words, volume resistance value 107Ω・cm, fineness 2 denier, basis weight 1.00 CI/m2, air flow rate 100CC/
A polyamide antistatic woven fabric made of -/SeC was supplied as a base layer sheet in contact with a ground electrode, and the melt-blown nonwoven fabric was collected on the surface of the polyamide antistatic woven fabric to form an electret.

When we measured the surface charge density of this sheet, we found that the surface
-7.5X10” Coulomb/IJf, back side is 0.3X1
010 coulombs/CIIf, and the surface charge density is high, but the back surface has a low surface charge density, so the front and back surfaces are divided into electret properties and antistatic properties.
It can be seen that it is made of a special nonwoven fabric laminate with two characteristics.

Comparative Example 1 Using the method shown in FIG. 1, 1 q of nonwoven fabric laminate was made into an electret in the following manner. That is, it was installed at a position 25 cm from the surface of the collection drum (earth electrode) covered with 40 mesh stainless steel net 1 or the shortest distance from the tip of the polymer discharge hole of the melt blow nozzle.

Next, an application electrode (tungsten wire) was installed at a position Bcm above the fiber collection position on the surface of the collection drum, and a DC high voltage of -5 kV was applied to it, with an electric field strength of 0.63.
An electric field of kv/cm was created between the collection drum and the application electrode. Fibers and a base layer sheet were fed into this electric field under the following conditions to produce an electret nonwoven fabric laminate.

That is, a base layer sheet (fineness 2 denier, basis weight 30 g/Tr12, air flow rate 25
A polypropylene spunbond nonwoven fabric (0 cc/cJ/sec) was supplied at 5 m/min, and a polypropylene polymer was melt-blown spun on the surface of the base layer sheet to collect a melt-blown nonwoven fabric with a fineness of 0.04 denier and a basis weight of 500/Tr12. .

The electret property of this electret-formed nonwoven fabric laminate was evaluated by measuring the surface charge density, and it was found that the surface charge density of the nonwoven fabric laminate was 0.8×10′ coulomb/cITV, and the back surface was 1.1×10′°coulomb/crK. Because of its low strength, it was not sufficiently electretized.

[Effects of the Invention] According to the present invention as described above, the fibers transported by the fluid forming the nonwoven structure layer are electretized to the inside, and a nonwoven fabric laminate with high surface charge density can be obtained. .

In addition, by appropriately selecting the material and volume resistivity of the base layer sheet, it is possible to obtain an electret nonwoven fabric laminate for the base layer sheet, or a nonwoven structure layer consisting of fibers carried by a fluid. It is also possible to select and obtain a nonwoven fabric laminate mainly made of electret.

Further, since the electret formation is performed while the nonwoven fabric structural layer and the base layer sheet are being laminated, the process is simplified, and production can be performed with a simple process and at an advantageous cost.

[Brief explanation of the drawing]

FIG. 1 is a schematic side view schematically explaining one embodiment of the method for producing an electret nonwoven fabric laminate of the present invention. FIG. 2 is a schematic diagram illustrating a method for evaluating surface charge density. 1: Earth electrodes 2 and 2': DC high-voltage power supplies 3 and 3': Application electrode 4: Melt-blown spinning 5: Melt-blown fibers 6 and 6': Turn roll 7: Base layer sheet 8: Electret nonwoven fabric laminate 9: Electric field 10: Rotation direction of earth electrode 11: Metallic flat electrode 12 Bimetallic box 13: Electret sample 14: Capacitor 15: Microcurrent meter diagram Patent application Daito Shi Co., Ltd. Figure 2

Claims (6)

[Claims] (1) The fibers carried by the fluid are collected as a nonwoven structure layer on the sheet surface of the base layer sheet within the electric field formed between the applied electrode and the earth electrode, and the nonwoven fabric structure is made into an electret. A method for producing an electret nonwoven fabric laminate, the method comprising obtaining a laminate comprising at least a layer and a base layer sheet. (2) Electric field strength of 1kv is applied to fibers transported by fluid.
Electretization characterized by collecting as a nonwoven structural layer on the sheet surface of a base layer sheet in an electric field of /cm or more to obtain a laminate consisting of at least an electret nonwoven fabric structural layer and a base layer sheet. A method for producing a nonwoven fabric laminate. (3) The fibers transported by the fluid are applied as a non-woven structural layer on the sheet surface of the base layer sheet in contact with the earth electrode in an electric field formed between the application electrode and the earth electrode. A method for producing an electret nonwoven fabric laminate, which comprises collecting and collecting an electret nonwoven fabric layer to obtain a laminate consisting of at least an electret nonwoven fabric structure layer and a base layer sheet. (4) The fibers carried by the fluid are applied to the nonwoven structure layer on the sheet surface of the base layer sheet that is in contact with the earth electrode and is moving within the electric field formed between the application electrode and the earth electrode. A method for producing an electret nonwoven fabric laminate, which comprises obtaining a laminate comprising at least an electret nonwoven structural layer and a base layer sheet. (5) The base layer sheet has a volume resistivity of 10^1^4Ω
・Claims (1), (2), (3), or (4), characterized in that the size is less than cm.
A method for producing an electret nonwoven fabric laminate as described in Section 1. (6) The nonwoven structure layer is a nonwoven fabric layer formed by a melt blowing method.
The method for producing an electret nonwoven fabric laminate according to item 1), item (2), item (3), item (4), or item (5).