JPH06104953B2 - Method for manufacturing electretized nonwoven fabric laminate - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a non-woven fabric laminate in which a non-woven fabric layer and a base layer are laminated and which has a high surface charge density and is favorably electretized.

[Prior Art] A method for manufacturing an electretized non-woven fabric laminate that has been performed so far is, for example, laminating an electretized melt-blown non-woven fabric and an electretized spun-bonded non-woven fabric, a woven fabric, a knitted fabric or a melt-blown non-woven fabric having different fineness in different steps. The method has been generally used.

However, such a method has drawbacks such as an increase in the number of processing steps, which is uneconomical, and an increase in process loss.

Further, U.S. Pat.No. 4,436,780 describes a method of collecting a meltblown nonwoven fabric on a base sheet to obtain a nonwoven fabric laminate, and the nonwoven fabric laminate thus obtained is subjected to electretization treatment. Although it is also possible to provide, in the resulting electretized non-woven fabric laminate, since it is not so electret up to the inside of the non-woven fabric, there is a remarkable tendency as the high basis weight.
When this is used for a filter, there is a drawback that a sufficiently high aerosol collection efficiency cannot be obtained.

Further, JP-A-62-263361 discloses a method of electretizing fibers conveyed by a fluid, but the method described in the same gazette directly electretizes on a collector. However, it differs from the method of the present invention, which will be described in detail later, in terms of the substrate. That is, in the method of directly electretizing on the collecting device, the potential of the collecting device surface does not rise because the collecting device surface is grounded, and therefore the electretizing property of the low basis weight sheet is not always required in this method. It was not as high as desired.

[Problems to be Solved by the Invention] In view of the above points, an object of the present invention is to make it possible to obtain a nonwoven fabric laminate having a high electret performance with a high surface charge density, and the drawbacks of the prior art. Met. An object of the present invention is to provide a method for producing a non-woven fabric laminate, which improves uneconomicality due to cost increase due to an increase in the number of processing steps and process loss.

[Means for Solving the Problems] The method for producing an electretized nonwoven fabric laminate of the present invention that achieves the above-mentioned object has the following constitution.

That is, the fibers conveyed by the fluid, in the electric field formed between the application electrode and the ground electrode with an electric field strength of 1 kv / cm or more, the ventilation amount measured based on JIS-L-1096 is 1 cc /
Electretized non-woven fabric characterized by collecting as a non-woven structure layer on the sheet surface of the base layer sheet having a cm ² or more to obtain a laminate comprising at least an electretized non-woven fabric structure layer and a base layer sheet. It is a manufacturing method of a layered product.

[Operation] Hereinafter, the method for producing the electretized nonwoven fabric laminate of the present invention will be described in more detail.

FIG. 1 is a schematic side view schematically explaining one embodiment example of the method for producing an electretized nonwoven fabric laminate of the present invention. In particular, the formation of the non-woven structure layer is performed by a melt blown nonwoven fabric formation method. This is illustrated by taking the case of performing the above as an example.

In FIG. 1, 1 is a ground electrode capable of continuous rotation, 2 and 2'is a DC high-voltage power source, 3 and 3'is an application electrode, 4 is a melt-blowing cap, 5 is a melt-blown fiber, and 6 and 6 are shown. ′ Is a turn roll, 7 is a base layer sheet,
8 is an electretized nonwoven fabric laminate, 9 is an electric field,
10 indicates the rotation direction of the ground electrode, and the fiber 5 melt-blown from the melt-blowing mouthpiece 4 is the applying electrode 3
It is carried by an air flow into an electric field 9 formed between the and the ground electrode 1.

On the other hand, the base layer sheet 7 is a continuously rotatable earth electrode 1
While being in contact with the surface of the
Leading to. The melt-blown fibers 5 and the base layer sheet 7 that have reached the electric field 9 are electretized, and an electretized nonwoven fabric laminate 8 can be obtained.

In the present invention, the fiber conveyed by the fluid is a material having a volume resistance value of 10 ¹⁴ Ω · cm or more that can be electretized, for example, polyethylene-based, polypropylene-based, polyamide-based, polyester-based, polycarbonate-based, polyurethane-based, 2 Long fibers or short fibers made of polymers such as Hooker ethylene, 3 Hooker ethylene and copolymers are preferred. Among them, polymers such as polypropylene, polyethylene, polycarbonate, 2 fluccoethylene, 3 fluccoethylene and copolymers are preferable because they have excellent electret properties. It is also possible to mix natural fibers such as cotton and wool, which are generally not electretized, with the above-mentioned materials that can be electretized to perform electretization.

In the case of a material that can be melt-spun, the fiber can be easily conveyed into the electric field by a spunbonding method, a meltblowing method, a multifilament ejector opening method, or the like.

In particular, in the case of the melt blow method, since ultrafine fibers can be produced relatively easily, it is very preferable in that a nonwoven fabric material 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, a non-woven fabric material suitable for a low pressure loss filter material can be produced relatively easily, which is preferable.

In the case of already fiberized short fibers and the like, the fibers can be transported into the electric field by being dispersed in the air flow by various methods such as the air layer method.

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

Further, polymers capable of being electretized, for example, polypropylene-based, polyester-based, polycarbonate-based,
A woven fabric, a knitted fabric or a non-woven fabric made of a fiber made of a polymer selected from polymers such as 2 flucca ethylene and 3 flucca ethylene and a copolymerized polymer and having a volume resistivity value of 10 ¹⁴ Ω · cm or more is used as the above-mentioned substrate. When used as a material for a layered sheet, a nonwoven fabric laminate can be obtained in which the materials for both the fibers carried by the fluid and the substrate layered sheet are electretized.

Further, when a cloth having a volume resistance value of 10 ¹² Ω · cm or less and having an antistatic effect is used for the base layer sheet, a laminated product of the antistatic cloth and the electretized non-woven fabric can be obtained at the same time. . This is because the antistatic fabric having a volume resistance value of 10 ¹² Ω · cm or less generally loses its electric charge in a short period of time even if it is electret-treated, and does not generally become an electret sheet. The electretized non-woven fabric laminate obtained in this manner is convenient and preferable when it is used in applications where antistatic property and aerosol collecting property or adsorbing property are required at the same time. Incidentally, the more preferable volume resistivity value of the base layer sheet, in particular, in which the base layer sheet is not electretized, is generally 10 ¹⁰ Ω · cm or less.

The substrate layer sheet used in the present invention has an air permeability of 1 cc / cm ² / sec or more when measured according to the measuring method of JIS-L-1096 as the degree of air permeability. The particularly preferable range is 40 cc / cm ² / sec or more.

This is because the fibers are separated and collected from the fluid on the surface of the base layer sheet, so that the fluid needs to escape through the interior of the base layer sheet, and it is desirable that the ventilation amount is large. Therefore, a nonwoven fabric is generally the most suitable material for the base layer sheet.

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

When a material having a volume resistivity of 10 ¹⁴ Ω · cm or less is used for the base layer sheet, the fibers conveyed by the fluid and collected and deposited on the surface of the base layer sheet are intercalated through the base layer sheet. Since it becomes easy to obtain the compensation charge from the ground electrode side, it becomes possible to obtain an excellent electretized nonwoven fabric laminate. For this reason, it is a preferable method to supply the base layer sheet in the electric field while being in contact with the ground electrode.

To describe this point in a little more detail, in making an electret by the corona discharge method, the whole basis weight at the time of making an electret is important.

When a base layer sheet having a high volume resistance and a large basis weight is used, the fibers in the innermost layer may not be sufficiently electretized if the basis weight of the fibers collected thereon is large. It is presumed that this is because the compensation charge cannot be sufficiently obtained from the base layer sheet.

Therefore, by using a material having a low volume resistance value as the base layer sheet, it becomes possible to easily obtain a compensating charge in the fibers conveyed by the fluid, and to obtain an electretized non-woven fabric laminate having excellent electret properties. Of.

Further, according to the knowledge of the present inventors, a suitable basis weight of the base layer sheet is, for example, about 300 g / m ² or less in the case of a spunbonded nonwoven fabric generally composed of fibers having a fineness of 8 denier or less.

Next, the feature of the present invention is to deposit the fibers conveyed by the fluid in the electric field on the surface of the base layer sheet and collect them, while obtaining an electretized nonwoven fabric laminate,
In order to obtain a non-woven fabric laminate having excellent electret properties, the electric field strength level in such an electric field is important, and according to the knowledge of the present inventors, the electric field strength is 1 kv / cm or more and is transported by a fluid in an electric field. It is important to obtain a large electret effect by performing electretization while accumulating and collecting the fibers on the surface of the substrate layer sheet.

This is because when the electric field strength is less than 1 kv / cm, the electret property that is difficult to generate corona discharge having a sufficiently high effect is obtained, for example, the surface charge density is low, which is not preferable, and when this is used for a filter application, etc. However, the obtained filter performance will be low. Therefore,
Although depending on the actual use of the electret nonwoven fabric laminate, it is important that the electric field strength is 1 kv / cm or more, and the preferable range is 3 kv / cm or more.

Regarding the electretization in the electric field as described above, according to the findings of the present inventors, the fact that the electretization actually progresses is that the fibers transported by the fluid are collected and deposited on the surface of the base layer sheet. It seems from the moment. The moving speed at which the fibers (nonwoven fabric) collected on the surface of the base layer sheet move in the electric field (= the moving speed of the ground electrode) is much faster than the moving speed of the fibers transported by the fluid to the surface of the base layer sheet. It is believed that this is due to the much higher chance of being charged due to the slowness, and that the fibers carried by the fluid are hardly grounded and therefore receive little compensation charge.

In particular, when a non-woven fabric having a large basis weight is electretized without the method of the present invention, the fibers in the inner layer of the non-woven fabric are relatively electretized.

In the method of the present invention, the fibers collected and deposited on the surface of the substrate layer sheet are charged with electric charges, and the fibers collected and deposited on the fibers are also charged with electric charge continuously and repeatedly. In this method, the non-woven fabric as a whole has a high electric charge because it is separated from the electric field along with the movement of the ground electrode and the electretization is completed. Therefore, it is possible to obtain an electretized nonwoven fabric laminate having excellent electret properties.

In carrying out the method of the present invention, the material of the ground electrode may be a drum made of a metallic net or a porous metal flat plate, or an endless belt.

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

Furthermore, by using the material of the ground electrode surface coated with a material having a volume resistance value in the range of 1-10 ¹² Ω · cm,
Further, it is possible to obtain an excellent electretized nonwoven fabric laminate.

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 ground electrode.

[Examples] Hereinafter, the present invention will be described with reference to Examples.

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

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

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 high DC voltage of -40 kv was applied to this to collect an electric field with an electric field strength of 5 kv / cm. It was formed between the collecting drum and the application electrode.

Fibers and a base layer sheet were fed into this electric field under the following conditions to obtain an electretized nonwoven fabric laminate.

A basic layer sheet (polypropylene spun band nonwoven fabric with a fineness of 2 denier, a basis weight of 30 g / m ² , and an air flow rate of 250 cc / cm ² / sec) was supplied at 5 m / min so as to contact the surface of the base layer sheet. The polypropylene polymer was melt blown to collect a melt blown nonwoven fabric having a fineness of 0.04 denier and a basis weight of 50 g / m ² .

As a result, it was possible to produce a non-woven fabric laminate in which both the melt-blown non-woven fabric and the spunbonded non-woven fabric were electretized.

The electret property of this electretized non-woven fabric laminate was evaluated by the evaluation method based on the surface charge density. The evaluation method of the surface charge density was performed using the evaluation device 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 micro ammeter 15. That is, the surface electrode density is obtained from the potential obtained by the minute ammeter 15 according to the following equation.

Q = CV / S Q = Surface charge density (Coulomb / cm ² ) C = Capacitor capacity S = Electret sample area First, the surface and the back surface of the electretized non-woven fabric laminate were measured, and the surface was −6.0 × 10 ^{−. It was 10} coulomb / cm ² and the back side was 5.5 × 10 ⁻¹⁰ coulomb / cm ² .

Next, the electretized non-woven fabric laminate was separated into a melt-blown non-woven fabric and a polypropylene spun-bonded non-woven fabric, and the surface charge density was measured. The melt-blown non-woven fabric had a surface of −5.4 × 10 ⁻¹⁰ coulomb / cm ² , and a back surface of 4.8 × 10 ⁻¹⁰ coulomb / cm ² . ×
It was 10 ⁻¹⁰ coulomb / cm ² .

The surface of polypropylene spunbonded nonwoven fabric is
It was 4.8 × 10 ^-10 coulomb / cm ² and the back surface was 5.6 × 10 ^-10 coulomb / cm ² .

Thus, it is understood that both the meltblown nonwoven fabric and the polypropylene spunbonded nonwoven fabric are sufficiently electretized.

Example 2 Using the method of FIG. 1, an electretized 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 the electretization was performed under the same conditions.
That is, a polyamide antistatic woven fabric having a volume resistance value of 10 ⁷ Ω · cm, a fineness of 2 denier, a basis weight of 100 g / m ² and an air flow rate of 100 cc / cm ² / sec was used as a base layer sheet in a state of being in contact with the ground electrode. The melt-blown nonwoven fabric was supplied and collected on the surface of the polyamide antistatic woven fabric to be electretized.

When the surface charge density of this sheet was measured, the surface was
-7.5 × 10 ^-10 coulombs / cm ² , which has a high charge density on the front surface, but a low charge density on the back surface, so two characteristics are given: electret property and antistatic property are distinguished on the front and back. It can be seen that it is a special non-woven fabric laminate having.

Comparative Example 1 Using the method shown in FIG. 1, an electretized nonwoven fabric laminate was obtained in the following manner. That is, the surface of the collecting drum (ground electrode) covered with a 40-mesh stainless steel net was placed at a position of 25 cm which is the shortest distance from the tip of the polymer discharge hole of the melt blow die.

Next, an application electrode (tungsten wire) was installed 8 cm above the fiber collection position on the surface of the collection drum, and a high DC voltage of -5 kv was applied to this, and an electric field of electric field strength of 0.63 kv / cm was applied. It was formed between the collecting drum and the application electrode. Into this electric field, the fibers and the base layer sheet were supplied under the following conditions to produce an electretized nonwoven fabric laminate.

That is, the base layer sheet (fineness 2 denier, basis weight 30 g / m ² , ventilation rate 250 cc / cm ² / sec so as to contact the surface of the collection drum.
Polypropylene spunbonded non-woven fabric) was supplied at a rate of 5 m / min, and polypropylene polymer was melt-blown on the surface of the base layer sheet to collect a melt-blown non-woven fabric having 0.04 denier fiber and a basis weight of 50 g / m ² .

The electret property of this electretized non-woven fabric laminate was evaluated by measuring the surface charge density, and it was found that the surface of the non-woven fabric laminate was 0.8 × 10 ^-10 coulomb / cm ² and the back face was 1.1 ×.
It was 10 ⁻¹⁰ coulomb / cm ² , and it was not sufficiently electretized because of the low electric field strength.

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

Further, by appropriately selecting the material of the base layer sheet and the volume resistance value, a non-woven fabric laminate in which the base layer sheet is also electretized can be obtained, or only a non-woven structure layer made of fibers conveyed by fluid is used. It is also possible to select and obtain a non-woven fabric laminate that is mainly electretized.

In addition, since the electretization is performed while the nonwoven fabric structure layer and the base layer sheet are being laminated, the process is simplified, and the simple process enables cost-effective production.

[Brief description of drawings]

FIG. 1 is a schematic side view schematically explaining one embodiment example of the method for producing an electretized nonwoven fabric laminate of the present invention. FIG. 2 is a schematic diagram illustrating a method of evaluating the surface charge density. 1: Ground electrode 2 and 2 ': DC high voltage power source 3 and 3': Applied electrode 4: Melt blown cap 5: Melt blown fiber 6 and 6 ': Turn roll 7: Base layer sheet 8: Electretized nonwoven fabric laminate 9: Electric field 10: Rotation direction of ground electrode 11: Metal plate electrode 12: Metal box 13: Electret sample 14: Capacitor 15: Micro ammeter

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location D04H 1/72 B 7199-3B C 7199-3B // B01D 39/14 E D06M 101: 18

Claims (5)

[Claims] 1. A ventilation amount of a fiber conveyed by a fluid measured in accordance with JIS-L-1096 in an electric field formed between an applying electrode and an earth electrode and having an electric field strength of 1 kv / cm or more. 1c
Collected as a non-woven structure layer on the sheet surface of the base layer sheet having a c / cm ² or more, to obtain a laminate comprising at least a non-woven structure layer and a base layer sheet which are electretized, and are electretized. For producing a laminated nonwoven fabric. 2. The method for producing an electretized non-woven fabric laminate according to claim 1, wherein the base layer sheet is in contact with the ground electrode. 3. The method for producing an electretized nonwoven fabric laminate according to claim 1, wherein the base layer sheet is in contact with the ground electrode and is moving. 4. The base layer sheet has a volume resistance value of 10 ¹⁴ Ω.
The method for producing an electretized non-woven fabric laminate according to claim (1), (2) or (3), characterized in that the nonwoven fabric has a size of not more than cm. 5. The non-woven structure layer is a non-woven fabric layer formed by a melt-blowing method, in claim (1), (2), (3) or (). 4)
Item 7. A method for producing an electretized non-woven fabric laminate.