JPH0633571B2 - Method for manufacturing electret nonwoven fabric - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention has excellent electret properties, and in particular, when used as a filter material, an electret nonwoven fabric capable of exhibiting good performance of high collection efficiency with low pressure loss. Manufacturing method.

[Prior Art] Conventionally, as a method for producing an electret filter, which is particularly aimed at lowering the pressure loss as described above, Japanese Patent Publication No.
As can be seen from Japanese Patent No. 47299, a method is known in which a material obtained by splitting an electretized film into fibers is made into a non-woven fabric.

However, in this method, since the electretized film is split into fibers to form a non-woven fabric, there is a limit in using it as an ultrafine fiber.Therefore, the aerosol collection efficiency per unit weight is not necessarily high. Met.

On the other hand, in the case of the electretized meltblown fiber nonwoven fabric, it is composed of ultrafine fibers and is relatively dense, so the aerosol collection efficiency per unit weight is high,
The pressure loss was also rather high.

Further, Japanese Patent Publication No. Sho 61-30065 discloses a method of blowing short fibers into meltblown fibers that are meltblown spun and conveyed by a fluid, but this manufacturing method is limited to a method for manufacturing a bulky nonwoven fabric. And was in a technical field different from the manufacture of electretized nonwoven fabric.

[Problems to be Solved by the Invention] The present invention is uneconomical due to an increase in the number of processing steps found when splitting an electretized film, which is a drawback of the prior art, into a nonwoven fabric, and as a filter performance, Defects such as low aerosol collection efficiency per unit weight,
Another object of the present invention is to provide a method for producing an electret nonwoven fabric capable of solving various problems such as defects such as high pressure loss found in the case of an electret meltblown nonwoven fabric filter.

[Means for Solving the Problems] The present invention has the following configurations.

That is, meltblown fibers that are meltblown spun and transported by a fluid, and short fibers or / and long fibers that are supplied in a defibrated state by air are combined and mixed,
A method for producing an electret nonwoven fabric, characterized in that the merged mixed fiber is collected on a surface of a collector in a DC electric field having an electric field strength of 1 kv / cm or more to obtain an electret nonwoven structure.

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

FIG. 1 and FIG. 2 are schematic side views for explaining one embodiment example of the method for manufacturing an electret nonwoven fabric of the present invention.

In the figure, a collection device 1, a DC high-voltage power supply 2 and 2 ', a voltage application electrode 3 and 3', a melt blow base 4, a melt blow fiber 5, a short fiber or long fiber supply device 6 and 6 ', which can be continuously rotated, are short. Fibers or long fibers (hereinafter referred to as mixed fibers) 7 and 7 ', an electret nonwoven fabric 8, an electric field 9, and a rotation direction 10 of the collector are shown, respectively.

Meltblown fiber 5 spun from meltblown spinneret 4
Is an electric field 9 formed between the application electrode 3 and the collector 1.
It is carried in by an air flow.

The mixed fiber 7 is conveyed by an air flow by the fiber supply devices 6 and 6 ', and is mixed and mixed into the meltblown fiber stream in the electric field 9, and both the meltblown fiber and the mixed fiber are collected on the surface of the collecting device. Gathered.

The electric field strength of this electric field is set to 1 kv / cm or more, and at least the meltblown fibers are electretized to become the electret nonwoven fabric 8.

Next, the melt-blown fiber will be described. The melt-blown fiber is a material capable of being electret having a volume resistivity value of 10 ¹⁴ Ω · cm or more, for example, polyethylene-based, polypropylene-based, polyamide-based, polyester-based, polycarbonate-based, polyurethane-based materials. 2 hooker ethylene,
Polymers composed of polar polymers or non-polar polymers such as 3Fucca ethylene and those composed of 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. From these, a suitable polymer selected according to the purpose of use is used and melt spinning is carried out by adjusting the spinning temperature and hot air temperature so that the desired fineness can be obtained.

Next, the mixed fiber will be described. As for the constituent material, if the mixed fiber is also desired to be electretized, the mixed fiber is prepared by using the above-described material capable of being electret having a volume resistivity value of 10 ¹⁴ cm or more. Can be configured. However, when the surface of the fiber is surface-treated with an oil agent, a surfactant or the like, electretization of the mixed fiber may not be achieved in some cases, and therefore it is preferable to remove these agents before use.

If it is not necessary to electret the mixed fibers,
Inorganic fibers such as various natural fibers and synthetic fibers having a fibrous form can be used as the target.

Next, the form of the mixed fiber will be described. In order to express the bulkiness of the electret nonwoven fabric, the crimped fiber is more suitable than the linear fiber. This is because fibers having a crimp have a larger bulk density, and in this case, the number of crimps is suitably 2 / inch or more. Further, the fineness is suitably 0.1 denier or more and 10 denier or less. 0.
When it is less than 1 denier, the shape retention is low, which is not preferable. When it is 10 denier or more, in order to obtain uniform bulkiness over the entire surface of the nonwoven fabric, it is necessary to blow and mix a large amount, which makes it difficult to obtain high collection efficiency, which is not preferable, and short fibers are used as the mixed fiber. In this case, a large number of short fiber tips project from the surface of the meltblown non-woven fabric to deteriorate the appearance of the product and further induce spark discharge during electretization, which is not preferable. From such a point, the preferable range is 1 denier or more and less than 7 denier.

The fiber length can be used for both short fibers and long fibers, and is not particularly limited. However, since long fibers are easily entangled with each other, it is necessary to defibrate the fibers sufficiently. As this method, charging by a rubbing method or positive corona discharge is preferable because the amount of charge can be increased and the defibration property can be improved.

Next, the melting point of the mixed fiber will be described. It is preferable to use a fiber having a melting point lower than that of the meltblown fiber because the following advantages can be obtained.

That is, by performing heat treatment at the melting point of the mixed fiber or higher, at least a part of the mixed fiber is melted and fused with the meltblown fiber, the integrity of the mixed fiber and the meltblown fiber is obtained, and the morphological stability of the entire nonwoven fabric is stabilized. This is preferable because it increases the property.

However, it is not always necessary to configure the mixed fiber with a fiber component having a melting point lower than that of the meltblown fiber, and if the mixed fiber includes at least a fiber component having a lower melting point than the meltblown fiber. It is sufficient, and specifically, it is preferable to use, for example, a composite fiber having a high-melting point fiber component as a core and a low-melting point fiber component as a sheath in order to further strengthen the integrity.

For example, using polypropylene for the high melting point fiber component of the core,
Further, the mixed fiber of the composite fiber using polyethylene as the low melting point fiber component of the sheath has a large melting point difference even when polypropylene is used as the melt blown fiber, so that the electret property is not impaired even if heat treatment is applied, and the electret nonwoven fabric It is the most suitable material because it requires less shrinkage.

Next, a method for merging and mixing the mixed fibers into the meltblown fibers will be described.

The first mixing method is to disintegrate and disintegrate the short fibers in advance with a card or the like, between the melt blow nozzle and the collecting device,
This is a method of dropping and mixing in a state close to a natural drop, that is, a method as shown in FIG.

The feature of the electret nonwoven fabric obtained by this method is that a large amount of mixed fibers is mixed on one side (upper side in the drawing) of the cross section.

That is, in this method, it is possible to produce an electret nonwoven fabric having different bulk densities in the cross-sectional direction, and a filter structure using this nonwoven fabric has a dust adhesion amount when the bulk density side is used in the filter as the air upstream side. It is preferable because the filter has a longer life and has a longer life.

The mixing position of the mixed fibers is carried out between the melt-blowing mouthpiece 4 and the application electrode 3, but it is preferable to mix the fibers after the turbulent flow region where the flow of air discharged together with the melt-blowing changes from the rectification region to the turbulent flow region.

This is because mixing in the rectifying region disturbs the flow of meltblown fibers and impairs the uniformity of the nonwoven fabric. The turbulent region is
Since the entanglement of the fibers begins to occur in the region where the air flow is stalled, the meltblown fibers are relatively entangled with the mixed fibers, but the degree of impairing the uniformity of the nonwoven fabric is small, which is preferable.

The second mixing method is a method in which short fibers and the like that have been defibrated and dispersed in the air are blown into the electric field by an apparatus as shown in FIG.

The characteristic of this method of blowing into the electric field is that the mixed fibers are well mixed throughout the electret nonwoven fabric because the mixed fibers reach the inner depth of the melt-blown fiber group being conveyed by air, and have a relatively uniform bulk density. That is, an electret nonwoven fabric is obtained. Further, since the particles are blown into the electric field, the uniformity of the meltblown fibers is relatively low. This is considered to be because the direction of the electric field of the electric field can be made to be the same as the direction of the air flow, so that the blown fibers do not disturb the flow of the meltblown fibers because the fiber axis directions are quickly aligned with the direction of the electric field.

The blowing direction of the mixed fibers is preferably within 145 ° when the flow direction of the meltblown fibers is 0 °.

The method of the present invention is particularly effective when applied to a bulky nonwoven fabric having a bulk density of 88 to 98%. That is, it is difficult to obtain such a melt-blown nonwoven fabric having a bulkiness of 88 to 98% because the melt-blown method of transporting and collecting the melt-blown fibers is inevitably bulky. Therefore, according to the method of the present invention. In this case, the bulky product described above can be easily obtained.

Of course, the method of the present invention has a bulk density of 80 to 87%.
From the standpoint of bulkiness, a meltblown non-woven fabric which is ordinary can be manufactured.

In addition, once a bulky nonwoven fabric as described above is obtained, it is possible to adjust the bulk and perform desired post-finishing by finishing processing such as embossing and calendering, producing various high-value-added meltblown nonwoven fabrics. You can also do it.

The bulk density is a value obtained from the volume ratio of only the fibers in the apparent volume of the nonwoven fabric.

The range of mixing the mixed fibers with the meltblown fibers is preferably 5 to 70% (based on the weight of the meltblown fibers) in order to obtain the above-mentioned bulky effect.

Further, when it is desired to give a special functional characteristic by mixing the mixed fibers, the mixing ratio may be smaller.
-30% (based on the weight of meltblown fiber) is preferable.

Next, in the method of the present invention, the electric field strength is extremely important in order to obtain an intended electret nonwoven fabric having excellent electret properties, and the electric field strength is 1 kv /
It is important to perform electretization while depositing and collecting fibers and mixed fibers transported by a fluid in an electric field of cm or more on the surface of the collector.

When the electric field strength is 1 kv / cm or less, corona discharge does not sufficiently occur, and thus the electret property obtained, for example, the surface charge density becomes low, and when this is used for a filter application, the filter performance obtained becomes low. Will end up.

According to the knowledge of the present inventors, a preferable electric field strength is 3 kv /
It is more than cm.

The electric field strength is obtained by dividing the applied voltage value by the linear distance between the applying electrode and the collector.

Next, the collecting device will be explained. A drum and an endless belt capable of continuous rotation are most suitable, and the surface material thereof is preferably a metallic net or a porous metal flat plate. In addition, an auxiliary device such as an air suction device may be used inside or under the collection device.

Furthermore, the surface of the material is made to have a volume resistivity value of 10 ⁰ to 10 ¹² Ω.
-By using a material coated with a material in the cm range, a more excellent electret nonwoven fabric can be obtained.

[Examples] The present invention will be described in more detail with reference to Examples.

Example 1 An electret nonwoven fabric was obtained in the following manner by using the method shown in FIG.

The surface of the collector covered with a 40-mesh stainless steel net was set so that it would be located at a position of 35 cm, which is the shortest distance from the tip of the polymer discharge hole of the melt blow die.

Next, an application electrode was installed at a position 8 cm above the fiber collection position from the surface of the collection device, a high DC voltage of -48 kv was applied thereto, and an electric field with an electric field strength of 6 kv / cm was applied to the collection drum. It was formed between the electrodes.

In this electric field, polypropylene having a fineness of 0.04 denier was melt blown and mixed fibers were supplied under the following conditions to obtain an electret nonwoven fabric.

That is, fineness 3 denier, fiber length 50 mm, crimp number 14
Pieces / inch, material polypropylene was mixed at a mixing angle of 60 degrees and deposited on the surface of the collector. Collect and electret non-woven fabric (Basis weight 100g / m ² , thickness 3.0mm) 5m / mi
obtained in n.

The melt-blown fibers and the mixed fibers of the obtained electret nonwoven fabric are divided into the following basis weights: melt-blown fibers 80 g /
m ^2, with mixed fibers 20 g / m ^2, the mixing ratio was 35%. The bulk density was 96.3%.

The electret property of this electret non-woven fabric was evaluated based on the size of the aerosol collection efficiency and pressure loss when used as a filter, and the surface charge density.

The evaluation of the aerosol collection efficiency and the pressure loss was carried out by using the evaluation device shown in FIG. 3 under the condition that the sample passing wind speed was 1.5 m / min and the polystyrene particle size was 0.3 μm.

The method for obtaining the aerosol collection efficiency is to obtain the aerosol concentrations on the upstream and downstream sides of the evaluation sample with a particle counter,
Calculate by the following formula.

Co: Downstream aerosol concentration (units / Ft ³ ) Ci: Upstream aerosol concentration (units / Ft ³ ) The pressure loss was read directly from the instrument.

The numbers in the figure indicate particle counter 11 (US PM
S company's LAS-X-CRT), evaluation sample 12, pressure loss meter 13 (manostar gauge of the film industry), sampling tube 14, flow meter 15, air suction pump 16, atomizer 17 (manufactured by Japan Canomax Co., Ltd.), Pressurized air source 1
8, polystyrene solution 19, drying cylinder 20, sample holder 2
1 is shown respectively.

The evaluation method of the surface charge density was performed using the evaluation device shown in FIG.

In the figure, a metallic plate electrode 22, a metal box 24, an electret sample 24, a capacitor 25, and a micro ammeter 12 are shown.

The surface charge density is obtained from the potential obtained by the micro ammeter according to the following equation.

Q = CV / S Q = Surface charge density (Coulomb / cm ² ) C = Capacitor capacity S = Electret sample area First, when the surface charge density was evaluated, the surface was -8.0.
^{X10 -10} coulombs / cm ² and back surface 7.5 × 10 ^-10 coulombs / cm ² , showing that they are sufficiently electretized.

Next, the aerosol collection efficiency and pressure loss were evaluated. As a result, the collection efficiency is 99% or more and the pressure loss is 1.3 mm.
It was Aq. It can be seen that the collection efficiency is high despite the extremely low pressure loss.

When the cross section was observed, it was possible to observe that the mixed fibers were mixed relatively uniformly as a whole.

Example 2 An electret nonwoven fabric was obtained in the following manner using the method shown in FIG.

The surface of the collector covered with a 40-mesh stainless steel net was set at a position of 35 cm which is connected at the shortest distance from the tip of the polymer discharge hole of the melt blow die.

Next, an application electrode was installed at a position 8 cm above the fiber collection position from the surface of the collection device, a high DC voltage of -48 kv was applied thereto, and an electric field with an electric field strength of 6 kv / cm was applied to the collection drum. It was formed between the electrodes.

In this electric field, polypropylene having a fineness of 0.04 denier was melt blown and mixed fibers were supplied under the following conditions to obtain an electret nonwoven fabric.

Fineness 2 denier, fiber length 55 mm, crimp number 15 / inch, material polypropylene mixed in almost naturally
The electret non-woven fabric (weight per unit area: 100 g / m ² , thickness: 2.2 mm, mixing ratio: 25%, bulk density: 95%) was obtained at 5 m / min by depositing and collecting on the surface of the collector. The electret property of this electret non-woven fabric was evaluated based on the size of the aerosol collection efficiency and pressure loss when used as a filter, and the surface charge density.

The surface charge density is -5.2 × 10 ^-10 coulomb / c on the surface.
It is m ² and the back surface is 7.4 × 10 ⁻¹⁰ coulomb / cm ^2, which means that the electretization is excellent.

Next, when the collection efficiency and the pressure loss were evaluated, the collection efficiency was 99.9% or more, and the pressure loss was 2.5 mm.
It was Aq.

When the cross section was observed, it was found that the back surface had a low bulk density and the surface had a high bulk density because there were relatively many mixed fibers on the front surface side.

It was found that this structure is a factor that realizes low pressure loss and high collection efficiency.

Example 3 An electret nonwoven fabric was obtained in the following manner using the method shown in FIG.

The surface of the collector covered with a 40-mesh stainless steel net was set at a position of 35 cm which is connected at the shortest distance from the tip of the polymer discharge hole of the melt blow die.

Next, an application electrode was installed at a position 8 cm above the fiber collection position from the surface of the collection device, a high DC voltage of -48 kv was applied thereto, and an electric field with an electric field strength of 6 kv / cm was applied to the collection drum. It was formed between the electrodes.

In this electric field, polypropylene having a fineness of 0.01 denier was melt blown and mixed fibers were supplied under the following conditions to obtain an electret nonwoven fabric.

Fineness 6 denier, fiber length 50 mm, crimp number 12 / inch, material, composite fiber with polypropylene as core and polyethylene as sheath (spinning oil adhering) was mixed at a mixing angle of 60 degrees and deposited on the surface of the collection device. It was collected to obtain an electret nonwoven fabric (area weight: 100 g / m ² , thickness: 2.7 mm) at 5 m / min.

The resulting weight of the meltblown fibers and mixed fibers of the electret nonwoven fabric, meltblown fibers 70 g / m ^2, mixing ratio 43% mixed fibers 30 g / m ^2, a bulk density is 95.
It was 9%.

The electret non-woven fabric obtained is heated at 120 ° C. in a heat treatment machine.
As a result of performing the treatment for 2 minutes, it was confirmed that the polyethylene sheath was melted and the melt-blown fibers were adhered, so that the morphological stability was remarkably improved.

Further, this nonwoven fabric had a good electret property.

Comparative Example 1 The surface of the collector covered with a 40-mesh stainless steel net was placed at a position of 35 cm which is the shortest distance from the tip of the polymer discharge hole of the melt blow die.

Next, an application electrode was installed at a position 8 cm above the fiber collection position from the surface of the collection device, a high DC voltage of -48 kv was applied thereto, and an electric field with an electric field strength of 6 kv / cm was applied to the collection drum. It was formed between the electrodes.

In this electric field, polypropylene having a fineness of 0.04 denier was melt-blown to obtain an electret nonwoven fabric having a basis weight of 100 g and a thickness of 0.5 mm at a processing speed of 5 m / min.

The electret property of this electret non-woven fabric was evaluated based on the size of the aerosol collection efficiency and pressure loss when used as a filter, and the surface charge density.

The surface charge density is -9.2 × 10 ^-10 coulomb / c on the surface.
It is m ² and the back surface is 8.4 × 10 ^-10 coulomb / cm ² , and it can be seen that it is well electretized.

Next, when the collection efficiency and the pressure loss were evaluated, the collection efficiency was 99.99% or more, and the pressure loss was 5.5 m.
It was mAq.

It was found that the collection efficiency was extremely high, but it was somewhat unsuitable for air purifier applications in general rooms that require high pressure loss and low pressure loss.

[Effects of the Invention] The effects of the present invention are as follows: In a state where short fibers and long fibers are mixed in a melt blown fiber group conveyed by a fluid, an electric field strength of 1 kv / cm or more is applied to the collector surface. Since it is electretized while collecting it as a non-woven structure layer, both meltblown fibers and mixed fibers carried by the fluid are sufficiently electreted inside the nonwoven fabric, and it is possible to obtain an electret nonwoven fabric with high surface charge density. Is.

Further, since the meltblown fibers are collected together with the mixed fibers, the collection of the meltblown fibers becomes three-dimensional, resulting in a space inside the nonwoven fabric, and the obtained electret nonwoven fabric becomes bulky and has a low pressure loss. It becomes possible to obtain an electret nonwoven fabric.

Furthermore, by appropriately changing the mixing method as in the method shown in FIGS. 1 and 2, it is possible to control in which position of the electret nonwoven fabric the mixed fiber is mixed, and select the pressure loss and the collection efficiency. It is possible to

In other words, the method of mixing in a state similar to natural fall allows the processing of electret non-woven fabric with a density gradient, and since this structure has a structure in which the amount of added dust is large, it maintains the initial collection efficiency while maintaining the filter efficiency. It has a long life.

Further, in the method of blowing the mixed fibers into the electric field, it is possible to minimize the occurrence of unevenness of the meltblown fibers by blowing the mixed fibers by the action of the electric field.

Furthermore, mixed fibers are mixed into the entire layer of meltblown nonwoven fabric,
Since it can be distributed, it is possible to process a good electret nonwoven fabric with a particularly low pressure loss.

[Brief description of drawings]

FIG. 1 and FIG. 2 are schematic side views for explaining one embodiment example of the method for manufacturing an electret nonwoven fabric of the present invention. FIG. 3 is a schematic side view of an apparatus for evaluating aerosol collection efficiency and pressure loss. FIG. 4 is a schematic side view of an apparatus for evaluating surface charge density. 1: Collection device 2 and 2 ': DC high voltage power supply 3 and 3': Application electrode, 4: Melt blown cap 5: Melt blown fiber 6 and 6 ': Short fiber or long fiber supply device 7 and 7': Short fiber Or long fiber (mixed fiber) 8: Electret nonwoven fabric 9: Electric field, 10: Direction of rotation 11: Particle counter 12: Evaluation sample, 13: Pressure loss meter 14: Sampling tube, 15: Flow meter 16: Air suction device, 17: Atomizer 18: Pressurized air source, 19: Polystyrene liquid 20: Drying cylinder, 21: Sample holder 22: Amnesium 241 (radioactive isotope) 23: Metal plate electrode, 24: Metal box 25: Capacitor, 26: Micro Ammeter

Claims (3)

[Claims] 1. Meltblown fibers that are meltblown spun and transported by a fluid, and short fibers and / or long fibers that are supplied in a defibrated state by air are merged and mixed, and the merged mixed fibers have an electric field strength of 1 kv / cm or more. A method for producing an electret non-woven fabric, comprising collecting the electret non-woven structure on the surface of a collector in the DC electric field. 2. The electret nonwoven fabric according to claim 1, wherein the short fiber or the long fiber is configured to include at least a fiber component having a melting point lower than the melting point of the meltblown fiber. Manufacturing method. 3. The short fiber or the long fiber is a fiber having a volume resistivity value of 10 ¹⁴ Ω · cm or more, according to claim (1) or (2). Method for manufacturing electret nonwoven fabric.