JP2003003367A - Electret fiber sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electret fiber sheet which has high performance enabling the achievement of high dust-collecting characteristics that can not be achieved by electret fiber sheets prepared by conventional corona discharge methods. SOLUTION: This electret fiber sheet is characterized by electrically charging a fiber sheet so that both positive polarity and negative polarity exist together on the front and back sides of the fiber sheet and so that the total area of the charged portions is >=50% based on the whole area of each of both the front and back sides of the fiber sheet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electret fiber sheet, and more particularly to a high-performance electret fiber sheet that exhibits high dust collection efficiency as an air filter.

[0002]

2. Description of the Related Art Electretized fiber sheets are
When used as an air filter, it is widely used because of its low pressure loss and high dust collection performance. As a conventional method for producing such an electret fiber sheet, a method in which a high voltage is applied to a fiber sheet such as a synthetic fiber nonwoven fabric to form an electret by corona discharge is generally used (JP-A-61-102476). (See gazette, etc.).

When the electret fiber sheet produced by the corona discharge method is used as an air filter, the dust collection efficiency is about 99.5%, which is a considerably high rate. However, when the area of the electret fiber sheet charged with electric charges is measured, it is about 20 to 30% of the total area of the fiber sheet. In rare cases, only one side has 50% or more of the total area of one side, but the opposite side has an unbalanced state in which the charged area is extremely low. for that reason,
The charging pattern was in a rough state as a whole, and there was a limit to improving the dust collection efficiency above the above level.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electret fiber sheet having a high performance which achieves a high dust collecting property which cannot be achieved by the conventional corona discharge electret fiber sheet. .

[0005]

The electret fiber sheet of the present invention for solving the above problems is charged so that both positive and negative charges are mixed on the front and back surfaces of the fiber sheet,
The total area of one surface of the charged portion is 50% or more with respect to the total area of each surface on both front and back surfaces.

As described above, both positive and negative charges are mixed, and the total area of one side of the charged portion is 50% or more of the total area of each side, so that the air Dust collection efficiency as a filter is 99.5% of that of the conventional corona discharge electret fiber sheet.
It can be as high as 99.999% or more from a moderate level.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The electret fiber sheet of the present invention is not particularly limited as long as it is made of a non-conductive fiber material. For example, synthetic fabrics, knits,
Nonwoven fabrics and the like can be mentioned. In particular, for an air filter, a synthetic fiber non-woven fabric is preferable, and a melt blown non-woven fabric is particularly preferable.

The material of the non-conductive sheet preferably has a volume resistivity of 10 ¹² Ω · cm or more, more preferably 1
A material of 0 ¹⁴ · Ω · cm or more is preferable. Examples thereof include polyolefins such as polyethylene and polypropylene, polyethylene terephthalate, polyesters such as polylactic acid, polycarbonate, polystyrene, polyphenylene sulphite, fluororesins, and mixtures thereof. Among these, those mainly composed of polyolefin or polylactic acid are preferable from the viewpoint of electret performance, and those mainly composed of polypropylene are more preferable.

The electret fiber sheet of the present invention is charged so that both positive and negative charges are mixed on the front and back surfaces of the non-conductive fiber sheet as described above, and the total of the charged parts per one side. The area is 50% or more, preferably 70% or more, of the total area of each surface on both the front and back sides. In this way, by setting the total area of the charged portions on both the front and back surfaces to be 50% or more of each surface, the dust collection efficiency when used in an air filter can be set to a high level of 99.999% or more.

In the present invention, at least one of the positive and negative polar charges is charged so as to be distributed as a large number of island-shaped minute charging patterns. Moreover, the area per minute charging pattern is made as small as possible, the average area is 0.01 mm ² or less, and the maximum area is 0.05 mm.
^{Be no} more than ² . Further, it is desirable that the number of minute charging patterns existing per 1 mm ^{2 of the} fiber sheet is 20 or more.

The shape of the island-shaped minute charging pattern is not particularly limited. For example, a circle, an ellipse, a branch, a star, etc. can be mentioned. As a form in which both positive and negative electric charges including such a minute charging pattern are mixed, there are the following three cases.

(1) A case in which the positive charge is sea and the positive charge is mixed in the sea so that a large number of minute charge patterns of the negative charge are densely dispersed in the sea.

(2) A case where the negative charge is sea and the negative charge is mixed in the sea so that a large number of minute charge patterns of the positive charge are densely dispersed.

(3) A case in which charges of both positive and negative polarities are closely mixed in the form of minute charging patterns.

Of the three cases described above, particularly negative charges form a minute charging pattern (1) or (3).
Is preferred. This is because a negative charge pattern is easier to form than a positive charge pattern, and the electret fiber sheet is excellent in charge retention. Generally, charging is performed by giving and receiving electrons, and in the case of insulators that do not easily emit electrons such as fibers, minute charging that occurs by receiving electrons (due to minute discharge, etc.), that is, negative minute charging, is more likely to occur. It is thought to be because.

As described above, at least one of the positive and negative polarities is mixed to form a minute charging pattern, and the area of the minute charging pattern is made as small as possible. It is possible to improve the charge retention characteristics of the fiber sheet and extend the life. In other words, since the positive and negative charges are closely mixed, the electric field is closed between the positive and negative charges, and it is difficult for the charges to be neutralized without the ions moving from the atmosphere or the static eliminator. Therefore, it becomes possible to maintain the charged state at a long time.

In the present invention, the area of the charged portion, the number of charging patterns, etc. used for specifying the invention can be measured by visualizing the charged portion by a dust figure method. The dust figure method is described in "Static Handbook", 1st edition, edited by The Institute of Static Electricity, page 373, but visualized by bringing charged colored fine particles (developer) close to a charged body and adhering and developing with electrostatic force. Is the way to do it.

The method of measuring the area and the number of charging patterns in the present invention is performed by the dust figure method as follows.

(1) As the developing material, a general powder toner used in a color copying machine is used, and when the fiber sheet is developed, the gap between the single yarns is sufficiently developed. After sprinkling a large amount on the sheet, the excess developer remaining in the sheet is shaken off regardless of the electrostatic force. As the developer, a mixture of the following red positively chargeable toner and blue negatively chargeable toner is used. Visualization shall be performed in an environment with a humidity of 50%.

Positively chargeable toner (red): Particle size; Weight average particle size 14.8 μm (6 μm or less;
0.2 wt%, 25 μm or more; 1.8 wt%) Specific charge; −1.2 μC / g Negatively-charged toner (blue): Particle size; Weight average particle size 12.5 μm (6 μm or less;
0.8 wt%, 20 μm or more; 1.6 wt%) Specific charge: −23.1 μC / g The average particle size of the toner shown here is manufactured by COULTER.
It is a value measured by MULTISIZER II using an aperture tube having a diameter of 100 μm. Regarding the specific charge, a blow-off method charge amount measuring device (TB-
It is the value measured by 500 type). Specifically, toner to be measured and iron powder carrier (TSV-200R from Powder Tech Co.)
Were mixed at a weight ratio of 1:19 and stirred by a ball mill for 5 minutes, and then 0.2 g of the powder sample was placed in the measurement cell of the charge amount measuring device, and the blow pressure was adjusted to 0.
The value measured using a stainless steel mesh of 400 mesh for the mesh screen was 5 kg / cm ² , blowing time of 60 seconds, and the measured value was the toner weight (0.2 g × 1/20 = 0.0
The value is divided by 1 g).

(2) A magnified image is obtained from a fiber sheet whose positive / negative charge distribution is visualized by using an optical microscope with a depth of field of 0.1 mm or more. A digital copy of the enlarged image or a hard copy of the enlarged image (A6
Color scanner (resolution 300 dpi or more)
As described above, RGB digital data of 256 gradations) are obtained to obtain digital data.

(3) From the image converted into digital data in (2), the positive charging portion (blue) by photo retouching software,
Divide into three areas, a negatively charged portion (red) and an uncharged portion (colorless). The center value of the color to be cut is determined by extracting the color information of the portion where the toner is attached and the portion where the toner is not attached in the digital image in RGB or CMYK mode. It is preferable to determine the average value of 10 points or more.

(4) The negatively charged area of the image divided in (3) is made the same color as the uncharged area, and gray scale conversion and binarization conversion are performed to blacken only the positively charged area (others). Create a white image. By the same process for the negatively charged area and the uncharged area,
Create an image in which only that area is blackened.

(5) The surrounding 8 pixels are examined with an arbitrary black pixel (charged portion) as the central pixel, and if there are black pixels, they are regarded as belonging to the same block. This operation is performed for all pixels.

(6) For a square image of 1 mm square,
The number of black pixel clusters detected in (5) is counted, and the number of pixels in each cluster is calculated. However, a portion where a plurality of toner particles are continuously adhered is regarded as a charging portion. Therefore, the black pixel portion having an area of 0.0002 mm ² (the same size as the projected area of two circular particles having a diameter of 12 μm) or less is deleted from the data.

(7) From the data obtained as described above, 1 mm
Calculate the number of patterns, the average area, and the maximum area of the positive (and negative) charged areas in the square pixel of the corner.

(8) In the case of manufacturing a wide sheet of 50 cm or more, 5 or more points in the width direction are sampled in the charging section, and the number of patterns in the charging area is determined by the operations (1) to (7) in each sample. Calculate the average area and maximum area. The number of patterns of all samples, the average area and the average value of the maximum area are calculated, and the average value is evaluated.

The electret fiber sheet having high performance as described above is difficult to obtain by the conventional corona discharge method. As a particularly preferred method, while running the non-conductive fiber sheet, a slit-shaped suction nozzle is brought into contact with one surface of the sheet so as to cross the sheet width direction, and the sheet surface on the opposite side of the contact portion is brought into contact with the water surface or It is preferable to immerse the product in such a state that water is drawn from the suction nozzle so that it penetrates in the thickness direction of the sheet, the water is evenly permeated into the non-conductive fiber sheet, and this is dried to form an electret. .

By thus completely permeating water in the plane direction and the thickness direction of the non-conductive fiber sheet, the non-conductive fiber sheet after the drying treatment can be made into a high-performance electret sheet. . As a drying method, any conventionally known method can be applied. For example, methods such as a hot air drying method, a vacuum drying method and a natural drying method can be applied. Of these, the hot air drying method is preferable because continuous treatment is possible.

Further, the non-conductive sheet used for producing the electret fiber sheet of the present invention may be blended with at least one of a hindered amine type additive and a triazine type additive. By including such an additive in the non-conductive sheet, it is possible to maintain particularly high electret performance for the non-conductive sheet.

Among the above two kinds of additives, as a hindered amine-based additive, poly [((6- (1,1,3,
3, -Tetramethylbutyl) imino-1,3,5-triazine-2,4-diyl) ((2,2,6,6, -tetramethyl-4-piperidyl) imino) hexamethylene ((2,2 , 6,6, -Tetramethyl-4-piperidyl) imino)] (manufactured by Ciba Geigy, Chimasoap 944L
D), dimethyl-1- (2-hydroxyethyl) -4-hydroxy-2,2,6,6-tetramethylpiperidine polycondensation product (manufactured by Ciba Geigy, Tinupine 622)
LD), 2- (3,5-di-t-butyl-4-hydroxybenzyl) -2-n-butylmalonate bis (1,2,
2,6,6-pentamethyl-4-piperidyl) (manufactured by Ciba Geigy, tinupin 144) and the like.

As the triazine-based additive, the above-mentioned poly [((6- (1,1,3,3, -tetramethylbutyl) imino-1,3,5-triazine-2,4-diyl) is used. ((2,2,6,6-tetramethyl-4-piperidyl) imino) hexamethylene ((2,2,6,6-
Tetramethyl-4-piperidyl) imino)] (Ciba Geigy, Chimasorp 944LD), 2- (4,6-diphenyl-1,3,5-triazin-2-yl) -5-
((Hexyl) oxy) -phenol (manufactured by Ciba Geigy, Tinupine 1577FF) and the like can be mentioned. Among these, hindered amine-based additives are particularly preferable.

The amount of the hindered amine-based additive or triazine-based additive added to the non-conductive sheet is not particularly limited, but is preferably in the range of 0.5 to 5% by weight, more preferably 0.7. The range of 3 wt% is preferable. If the amount added is less than 0.5% by weight, it becomes difficult to obtain the desired high-level electret performance. Further, if the amount is too large to exceed 5% by weight, the spinnability and the film-forming property are deteriorated and the cost becomes disadvantageous, which is not preferable.

In the non-conductive sheet, in addition to the above-mentioned additives, known additives such as heat stabilizers, weather resistance agents, and polymerization inhibitors which are generally used in non-conductive sheets of electret processed products. You may add.

In the production of the electret fiber sheet of the present invention, the water to be permeated into the non-conductive sheet may be water which has been cleaned as much as possible by removing stains with a liquid filter or the like. Particularly, pure water such as ion-exchanged water, distilled water, and reverse osmosis membrane filtered water is preferable. The purity of pure water is preferably 10 ³ μS / m or less in terms of conductivity, and more preferably 10 ² μS / m or less.

It is preferable to use water containing a water-soluble organic solvent. By adding the water-soluble organic solvent, it is possible to further improve the permeability of water to the non-conductive sheet. The water-soluble organic solvent preferably has a boiling point lower than that of water. That is, since the water-soluble organic solvent is added to improve the water permeability of the non-conductive sheet, it is preferable to vaporize and dry the sheet as soon as possible after the water has permeated the sheet. More preferably, a water-soluble organic solvent having a boiling point difference from water of 10 ° C. or more is preferable.

The type of water-soluble organic solvent is not particularly limited as long as it improves the permeability of water to the non-conductive sheet. For example, alcohols such as methyl alcohol, ethyl alcohol and isopropyl alcohol, acetone, ketones such as methyl ethyl ketones, propyl acetate,
Examples thereof include esters such as butyl acetate, aldehydes, carboxylic acids and the like. In particular, alcohols or ketones are preferable, and it is particularly preferable to use at least one kind of acetone, isopropyl alcohol, and ethanol. It is more preferable to use isopropyl alcohol as a main component.

The concentration of the water-soluble organic solvent in water is not particularly limited as long as it has the effect of improving the permeability, but it is preferably 3 to 15% by weight. Particularly, in the case of isopropyl alcohol, the range of 3 to 10% by weight is preferable.

1 (A) and 1 (B) exemplify an apparatus for carrying out the above-described method for producing an electret fiber sheet of the present invention.

In FIGS. 1A and 1B, the cloth making apparatus 1
Then, the molten polymer is spun out from the melt blow spinning machine 18 together with the jet stream of the compressed heated air as ultrafine short fibers, which are collected on the lower net conveyor 19 to form a sheet-shaped non-conductive fiber sheet S. , To the downstream infiltration device 2. When traveling so as to contact the water surface of the aquarium 21,
By sucking water from the slit-shaped suction nozzle 22 that is in contact with the surface, the water in the middle of the suction is permeated into the sheet.

In the permeation apparatus 2, water is supplied to the water tank 21 from the supply pipe 23, is temporarily stored, then overflows from the upper edge to the overflow tank 24 and is drained from the drain pipe 25. The non-conductive fiber sheet S runs while one surface (lower surface) of the non-conductive fiber sheet S is in contact with the water surface of the water tank 21 by the guide rollers 26, 26, and a slit-shaped suction nozzle is provided on the upper surface side of the non-conductive fiber sheet S in contact with the water surface. 22 abuts so as to cross the width direction.

The suction nozzle 22 sucks water in contact with the lower surface side of the non-conductive fiber sheet S by a suction action, moves the water so as to penetrate through the non-conductive fiber sheet S in the thickness direction, and moves the water in the entire thickness direction. Immerse the water evenly. Since the slit-shaped suction nozzle 22 crosses the sheet width direction,
This permeation action in the sheet thickness direction is carried out in every corner of the sheet surface.

Non-conductive fiber sheet S in which water is permeated
The excess water is squeezed out in advance by the suction action of the suction nozzle 3, and then transferred to the drying device 4. A plurality of guide rollers 41 are provided in the drying device 4 in a zigzag shape, and heated air is supplied from a supply port 42 and discharged from an exhaust port 43, so that the inside is in a heated state.
The non-conductive fiber sheet S is dried while moving the guide roller 41 in a zigzag shape, becomes an electretized sheet, is carried out, and becomes the electretized sheet 5 wound in a roll shape.

The electretized sheet thus obtained is charged so that both positive and negative charges are mixed on the front and back surfaces, and the total area per charged surface of the charged portion is the same for both front and back surfaces. It is a high-performance electret sheet with a total area of 50% or more.

[0045]

EXAMPLES The method of measuring the charging portion and the method of measuring the characteristic values used in the examples described below were performed as follows.

[Measuring Method of Charged Part] (1) Visualization of charge distribution of the fiber sheet with the toner having the above-mentioned charging characteristics.

(2) Magnification observation with an optical microscope. The optical microscope used was a Micro High Scope system manufactured by Hi-Rox Corporation, and the zoom lens used was 250 times. A hard copy of a magnified image in color was obtained with a video printer. The magnified image obtained was read by a color scanner and converted into digital data. The resolution is 300 dpi, 256 gradations for each RGB, and the scanner used is Linotype Hell (Germany).
It was a sapphire of elberg Prepress).

(3) This image data was divided into three areas of a positively charged portion (blue), a negatively charged portion (red) and a non-charged portion (colorless) using photo retouching software (Photoshop ver.5.5J). The index color mode conversion command was used for division. At this time, the center color of the color to be replaced was set as follows based on the color information of the blue / red toner attached portion and the non-attached portion.

Positively charged portion: RGB = 50, 90, 140 Negatively charged portion: RGB = 140, 60, 70 Uncharged portion: RGB = 140, 160, 180 (4) Color the negatively charged portion area of this cut image. The area is selected by a command to specify the area, and the selected area is erased to make it the same color as the non-charged area. By performing the grayscale mode conversion and the 2-gradation, a monochrome 2-gradation image in which only the positively charged portion area is blackened (the other portions are white) can be obtained. With respect to the negatively charged area and the non-charged area, the same processing is performed to create an image in which the area is blackened.

(5) For the subsequent work, the image processing software HALXON ver. 5 manufactured by MVTec of Germany was used. With a certain black pixel (charged part) as the central pixel, check the surrounding 8 pixels,
If there are black pixels, they are considered to belong to the same block. Do this for all screens. In addition, the measurement was performed including the charging pattern in contact with the edge portion of the image.

[Collection Performance] The collection performance was measured by the collection performance measuring device shown in FIG. This collection performance measuring device is used for measuring sample M
The dust storage box 12 is connected to the upstream side of the sample holder 11 in which is set, and the flow meter 13, the flow rate adjusting valve 14, and the blower 15 are connected to the downstream side. In addition, the sample counter 11 is provided with a particle counter 16, and this particle counter 16 is used to change the cock 17.
The number of dusts on the upstream side and the number of dusts on the downstream side of the measurement sample M can be respectively measured via.

When measuring the collection performance, the diameter was 0.3 μm.
m polystyrene standard latex powder is filled in the dust storage box 12, the sample M is set in the holder 11, and the air volume is adjusted by the flow rate adjusting valve 14 so that the filter passing speed becomes 6.5 m / min. 10,000 ~
Stabilize in the range of 40,000 pieces / 2.83 × 10 ⁻⁴ m ³ (0.01 ft ³ ), and count the number of dust particles D upstream of the sample M and the number of dust particles downstream d by the particle counter 16 (manufactured by Rion Co.
KC-01B) was measured 10 times, JIS K-0901
Based on the above, the collection performance (%) was determined by the following calculation formula.

Collection performance (%) = [1- (d / D)] × 100, where d is the number of dust particles in the downstream D: the number of dust particles in the upstream [average fiber diameter] About 100 fibers enlarged by the SEM photograph The diameter was measured and the average value was calculated.

Example 1 As a raw material, a melt index MI was 700 and a triazine-based additive (Ciba Geigy, Kimasorb 944)
1% polypropylene was used, and the apparatus shown in FIG. 1 was used as a manufacturing apparatus. First, a melt blown nonwoven fabric having a basis weight of 40 g / m ² and an average fiber diameter of 2.0 μm was manufactured, followed by reverse osmosis membrane. While running along the water surface of the water tank to which the filtered water is supplied, a slit-shaped suction nozzle is brought into contact with the surface of the water tank to suck water to perform the permeation treatment, and after the water is drained, hot air drying is performed at 80 ° C. for 20 minutes. As a result, an electretized meltblown nonwoven fabric was obtained.

The electretized meltblown nonwoven fabric obtained as described above had positive and negative polar charges as shown in Table 1 below on both front and back surfaces. When this was used as an air filter and the collection performance was measured, it was 99.9997%.
Met.

[0056]

[Table 1]

Comparative Example 1 The same meltblown non-woven fabric as in Example 1 was used as a raw material, and was applied with a high voltage (+25 kV) by a high voltage application device.

The meltblown nonwoven fabrics obtained are listed in Table 2 below.
It was charged like. When the collection performance was measured using this as an air filter, it was 99.5%.
It was a low level compared to.

[0059]

[Table 2]

[0060]

As described above, according to the electret fiber sheet of the present invention, both the front and back surfaces of the fiber sheet are charged so that both positive and negative charges are mixed, and the total area of one side of the charged portion is charged. Is set to 50% or more with respect to the total area of each surface on both front and back sides, so that the dust collection efficiency as an air filter is about 99.5% of that of a conventional corona discharge electret fiber sheet. It can be as high as 99.999% or more.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of an apparatus for carrying out the method for producing an electret fiber sheet of the present invention.

FIG. 2 is a schematic view showing a device for measuring collection performance.

[Explanation of symbols]

1 Fabrication device 2 Penetration device 21 aquarium 22 Suction nozzle 4 drying equipment S Non-conductive fiber sheet

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) D04H 1/42 D06M 101: 20 // D06M 101: 20 7/02 A (72) Inventor Yasugi Horiguchi Shiga 1-1 1-1 Sonoyama, Otsu, Tochi, Japan Toray Co., Ltd. Shiga Plant F Term (reference) 4D019 AA01 BA13 BB03 BC01 CB06 4D054 AA11 BC02 BC16 4L031 AA14 AB34 BA08 BA36 CB10 4L047 AA14 AB03 BA23 BB02 CB10 CC12 DA00 EA

Claims (7)

[Claims] 1. A surface of a fiber sheet is charged so that both positive and negative charges are mixed, and the total area of one side of the charged portion is 50 relative to the total area of each side.
% Electret fiber sheet. 2. At least one of the positive and negative charges has an island-shaped distribution of minute charging patterns, and the average area of each minute charging pattern is 0.01 mm ^2.
The electret fiber sheet according to claim 1, which has a maximum area of 0.05 mm ² or less. 3. The fiber sheet 1m having the minute charging pattern
The electret fiber sheet according to claim 2, wherein the number per m ² is 20 or more. 4. The electret fiber sheet according to claim 2, wherein the negative charges form a fine charging pattern. 5. The electret fiber sheet according to claim 1, wherein the fiber sheet is made of a synthetic fiber nonwoven fabric. 6. The electret fiber sheet according to claim 5, wherein the synthetic fiber non-woven fabric is composed mainly of polypropylene fibers. 7. The fiber sheet contains 0.5 or more of at least one of a hindered amine-based additive and a triazine-based additive.
The electret fiber sheet according to any one of claims 1 to 6, which comprises -5% by weight.