JP7052258B2 - Electret fiber sheet and air filter filter media - Google Patents

Description

The present invention relates to an electret fiber sheet, which is an electretized fiber sheet. More specifically, the present invention relates to an electret fiber sheet having excellent electret stability at high temperatures and high dust collection characteristics. The present invention also relates to an air filter filter medium made of such an electret fiber sheet.

Conventionally, an air filter has been used to remove pollen, dust, etc. in a gas, and a non-woven fabric is often used as a filter medium for the air filter. The melt blow method, which is one of the methods for manufacturing non-woven fabrics, is widely used in the manufacture of filter media, battery separators, etc. for air filter products. The melt blow method is generally a method in which a thermoplastic polymer extruded from a spinneret is atomized into fibers by injecting hot air and formed as a fiber web by utilizing the self-fusion characteristics of the obtained fibers. This melt blow method has an advantage that it does not require a complicated process and can easily obtain fine fibers of several tens of μm to several μm or less, as compared with other non-woven fabric manufacturing methods such as the spunbond method. ..

The performance required for an air filter is high collection efficiency that can collect a large amount of microscopic dust, and low pressure loss with low resistance when gas passes through the inside of the air filter. In order to obtain the above-mentioned filter medium having high collection efficiency, it is suitable that the single fibers constituting the non-woven fabric have a fine fineness, but on the other hand, when the single fibers are made fine, the non-woven fabric is easily crushed. There is a problem that the pressure loss increases due to the increase in fiber density.

Further, in order to obtain a filter medium having a low pressure loss, it is suitable that the single fibers constituting the non-woven fabric have a high fineness, but on the other hand, when the single fibers are made thick, the surface area of the fibers in the non-woven fabric decreases. Therefore, there is a problem that the collection efficiency is lowered. As described above, having a high collection efficiency and having a low pressure loss are in a contradictory relationship.

As a method for solving the above-mentioned problems, attempts have been made to simultaneously satisfy high collection efficiency and low pressure loss by converting a non-woven fabric into an electret and utilizing an electrostatic action in addition to a physical action.

For example, there is a method for manufacturing an electret fiber sheet in which a non-woven fabric is in contact with a ground electrode, and the ground electrode and the non-woven fabric are moved together while high voltage is applied by a non-contact type application electrode to continuously electret. It has been proposed (Patent Document 1). Another method of bringing water into contact with the fibers to charge them is to spray the fiber sheet with a jet of water or a water droplet flow at a pressure sufficient to allow the water to penetrate into the inside of the non-woven fabric to form an electret, which has positive and negative properties. (Patent Document 2), a method of uniformly mixing the electric charges of the above, or a method of passing water through a slit-shaped nozzle and sucking water with the nozzle to allow water to permeate the fiber sheet, resulting in positive and negative properties. A so-called hydrocharge method, such as a method of uniformly mixing charges (Patent Document 3), has been proposed.

Japanese Unexamined Patent Publication No. 61-289177 U.S. Pat. No. 6119691 Japanese Patent Application Laid-Open No. 2003-3637

Although the collection performance was improved by converting the fiber sheet into an electret as in the methods described in Patent Documents 1 to 3, the heat stability of the electret during molding and storage of the fiber sheet, for example, when used as a filter. The level of sex was not yet sufficient.

An object of the present invention is to provide an electret fiber sheet having excellent electret stability at high temperatures and high dust collection characteristics in view of the problems of conventional electret technology.

The present invention is intended to solve the above problems, and the electret fiber sheet of the present invention is an electret fiber sheet mainly containing non-conductive fibers and is represented by the following general formula (a). An electret fiber sheet containing 0.05 to 1.0% by mass of the compound.

In the general formula (a), M represents an alkali metal, an alkaline earth metal, aluminum, zinc, copper, or a salt structure of these metals. n is 1 or 2. R ¹ , R ² , R ³ and R ⁴ independently represent hydrogen or an alkyl group having 1 to 6 carbon atoms, respectively.

According to the present invention, an electret fiber sheet having excellent electret stability at high temperatures and high dust collection characteristics can be obtained. By using such an electret fiber sheet, it is possible to provide an air filter filter medium having high dust collecting characteristics even at a high temperature.

FIG. 1 is a schematic side view showing a measuring device for collection efficiency and pressure loss.

The electret fiber sheet of the present invention is an electret fiber sheet mainly containing non-conductive fibers, and contains 0.05 to 1.0% by mass of the compound represented by the following general formula (a). Is.

In the general formula (a), M represents an alkali metal, an alkaline earth metal, aluminum, zinc, copper, or a salt structure of these metals. n is 1 or 2. R ¹ , R ² , R ³ and R ⁴ independently represent hydrogen or an alkyl group having 1 to 6 carbon atoms, respectively.

The electret fiber sheet of the present invention is an electret fiber sheet mainly containing non-conductive fibers. Examples of the fiber sheet include synthetic fiber woven fabrics, knitted fabrics, and non-woven fabrics. In particular, in the case of an air filter, a non-woven fabric made of synthetic fibers is preferable.

The electret fiber sheet of the present invention is preferably made of melt blown non-woven fabric. Since it is made of a melt-blown non-woven fabric, fine fibers of several μm can be easily obtained without requiring a complicated process, and it is possible to easily achieve high dust collecting characteristics.

In the present invention, the non-conductive means that the volume resistivity is 10 ¹² · Ω · cm or more, and it is preferable that the volume resistivity is 10 ¹⁴ · Ω · cm or more.

In the present invention, "mainly containing non-conductive fibers" means that 90% by mass or more of non-conductive fibers are contained in the electret fiber sheet. It is preferably 95% by mass or more, more preferably 97% by mass or more. If the amount of non-conductive fibers in the electret fiber sheet is less than 90% by mass, sufficient electret performance cannot be obtained, which is not preferable.

Examples of the non-conductive fiber resin material used in the present invention include polyolefin resins such as polyethylene and polypropylene, polyester resins such as polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate and polylactic acid, and polycarbonate resins. Examples thereof include polystyrene-based resins, polyphenylene sulfide-based resins, fluororesins, polystyrene elastomers, polyolefin elastomers, polyester elastomers, polyamide elastomers, elastomers such as polyurethane elastomers, and copolymers or mixtures thereof.

Among these, polyolefin-based resins are preferably used. Since the polyolefin resin has a high volume resistivity and a low water absorption, it has strong chargeability and charge retention when fiberized. Therefore, high collection efficiency can be achieved.

Examples of the type of polyolefin resin include homopolymers such as polyethylene, polypropylene, polybutene and polymethylpentene. Further, a copolymer obtained by copolymerizing these homopolymers with different components or a blended product of two or more different polymers can also be used. Among these, polypropylene and polymethylpentene are preferably used from the viewpoint of charge retention. Further, polypropylene is more preferably used from the viewpoint that it can be used inexpensively.

The electret fiber sheet of the present invention contains 0.05 to 1.0% by mass of the compound represented by the following general formula (a).

In the general formula (a), M represents an alkali metal, an alkaline earth metal, aluminum, zinc, copper, or a salt structure of these metals. In the present invention, the salt structure of a metal means a structure in which atoms or atomic groups forming a salt are bonded to the metal by one or more less than the valence of the metal. For example, Mg-OH, which is a structure in which one hydroxide ion is bonded to magnesium, which is a divalent metal, and Al, which is a structure in which one or two chloride ions are bonded to aluminum, which is a trivalent metal. Examples thereof include structures such as -Cl or Al-Cl ₂ .

Specific examples of the alkali metal include sodium, potassium, lithium and the like.

Specific examples of alkaline earth metals include calcium, magnesium, barium and the like.

Examples of the atom or atomic group forming the salt include a halide ion, a hydroxide ion and the like.

Of these, an aluminum salt structure is preferable in terms of electret stability at high temperatures, and a structure in which hydroxide ions are bonded to aluminum is more preferable.

In the general formula (a), n is 1 or 2. From the viewpoint of electret stability at high temperatures, n is preferably 2.

In the general formula (a), R ¹ , R ² , R ³ and R ⁴ independently represent hydrogen or an alkyl group having 1 to 6 carbon atoms, respectively.

The content of the compound represented by the general formula (a) is 0.05 to 1.0% by mass, preferably 0.1 to 0.5% by mass, based on the mass of the electret fiber sheet. By setting the addition amount in this range, the electret stability is improved under high temperature, and excellent dust collection characteristics can be obtained. If the content of the compound represented by the general formula (a) is less than 0.05% by mass, the collection efficiency at high temperature decreases. On the other hand, if the content of the compound exceeds 1.0% by mass, the spinnability is deteriorated and the cost is disadvantageous.

The electret fiber sheet of the present invention may contain a crystal nucleating agent in addition to the compound represented by the above general formula (a). Specific examples of the crystal nucleating agent include dibenzylidene sorbitol-type compounds, phosphoric acid-based nucleating agents, sodium benzoate and the like. Examples of the divenzylidene sorbitol type compound include dibenzylidene sorbitol (DBS), monomethyldibenzidene sorbitol (for example, 1,3: 2,4-bis (p-methylbenzidene) sorbitol (p-MDBS)), and dimethyldibenzidene sorbitol (p-MDBS). For example, 1,3: 2,4-bis (3,4-dimethylbenzylidene) sorbitol (3,4-DMDBS)) and the like are included.

In addition to the above-mentioned crystal nucleating agent, additives generally used for electret fiber sheets such as heat stabilizers, weather resistant agents and polymerization inhibitors can be added to the electret fiber sheet of the present invention.

From the viewpoint of improving the weather resistance and improving the electret performance, the electret fiber sheet of the present invention may contain at least one hindered amine-based additive and / or a triazine-based additive in the resin material. preferable.

Of the above two types of additives, examples of the hindered amine compound include 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)] (BASF Japan Co., Ltd. , "Kimasorb" (registered trademark) 944LD), Dimethyl-1- (2-hydroxyethyl) succinate-2,2,6,6-tetramethylpiperidine polycondensate (manufactured by BASF Japan Co., Ltd.) , "Tinubin"® 622LD), and 2- (3,5-di-t-butyl-4-hydroxybenzyl) -2-n-butylmalonate bis (1,2,2,6,6- Pentamethyl-4-piperidyl) (manufactured by BASF Japan Co., Ltd., "Tinubin" (registered trademark) 144) and the like can be mentioned.

Examples of the triazine-based additive include 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)] (BASF Japan Co., Ltd., "Kimasorb" (registered trademark) ) 944LD), and 2- (4,6-diphenyl-1,3,5-triazine-2-yl) -5-((hexyl) oxy) -phenol (manufactured by BASF Japan Co., Ltd., "Chinubin" (registered) Trademark) 1577FF) and the like can be mentioned.

Among these, it is preferable to use a hindered amine-based additive from the viewpoint of further improving the electlet performance, and in particular, poly [(6- (1,1,3,3-tetramethylbutyl) imino-1,3) is preferable. , 5-Triazine-2,4-diyl) ((2,2,6,6-tetramethyl-4-piperidyl) imino) Hexamethylene ((2,2,6,6-tetramethyl-4-piperidyl) imino) )] (BASF Japan Co., Ltd., "Kimasorb" (registered trademark) 944LD) is preferably used.

The total amount of the above-mentioned hindered amine-based additive and triazine-based additive added is preferably 0.5 to 5% by mass, more preferably 0.7 to 3% by mass, based on the mass of the electret fiber sheet. be. By setting the addition amount in this range, it becomes easy to obtain excellent dust collecting characteristics when electretized.

The method for producing the electret fiber sheet of the present invention is not particularly limited, but it can be produced, for example, by the following method.

First, the compound and resin material represented by the general formula (a) as described above are prepared. Then, after the compound and the resin material are kneaded, they are extruded from an extruder and processed into a desired structure such as a fiber, a fiber web, or a non-woven fabric. As a method of kneading the compound and the resin material, a method of mixing and supplying them to the extruder hopper of the spinning machine, kneading them in the extruder and supplying them directly to the mouthpiece, or kneading the compound and the resin material in advance. There is a method of kneading with an extruder, a static kneader, or the like to produce a master chip, melting the master chip in the extruder, and supplying the master chip to the mouthpiece.

The fibers are then used to form fiber sheets by conventional methods. For example, when the fiber sheet is made of a woven fabric or a knitted fabric, it can be manufactured by forming a yarn using the fiber and then weaving or knitting. When the fiber sheet is made of a non-woven fabric, the fiber web is formed by a dry method or a wet method using the fiber, and then the fiber web is bonded to produce a non-woven fabric, or the fiber web is spun-bonded. After forming by the or melt blow method, the fiber web can be bonded to produce a non-woven fabric. Further, a non-woven fabric mainly composed of nanofibers can be produced by an electrostatic spinning method or a method of eluting the sea portion of sea island fibers.

Next, the fiber sheet is subjected to an electret-forming treatment to obtain an electret fiber sheet. The electret formation treatment may be carried out on a single layer of the fiber sheet or on a laminated fiber sheet laminated with another sheet.

As a method for electretizing used in the production of the electret fiber sheet of the present invention, a method for electretizing by adding water to the non-conductive fiber sheet and then drying it is preferably used. As a method of applying water to the fiber sheet, a method of spraying a water jet or a water droplet flow at a pressure sufficient to allow water to permeate into the inside of the fiber sheet, or a method of applying water after or while applying water to the fiber sheet. A method of sucking from one side to allow water to penetrate into the fiber sheet, and a method of immersing the fiber sheet in a mixed solution of water and a water-soluble organic solvent such as isopropyl alcohol, ethyl alcohol and acetone to allow water to penetrate into the fiber sheet. The method and the like can be mentioned.

In the present invention, as the water used for electretization, it is preferable to use water from which stains have been removed by a liquid filter or the like and which is as clean as possible. In particular, pure water such as ion-exchanged water, distilled water, and filtered water permeated by a reverse osmosis membrane is preferably used. The level of pure water is preferably 103 μS / m or less in terms of conductivity ^, and ^more preferably 102 μS / m or less. In addition, a water-soluble organic solvent can be mixed with the above water as long as the collection characteristics are not affected.

The average single fiber diameter of the fibers constituting the electret fiber sheet of the present invention is preferably in the range of 0.1 to 8.0 μm. By setting the average single fiber diameter to preferably 0.1 to 8.0 μm, more preferably 0.3 to 7.0 μm, and further preferably 0.5 to 5.0 μm, excellent air permeability and dust collection characteristics are obtained. Electret fiber sheet can be easily obtained.

The basis weight of the electret fiber sheet of the present invention is preferably in the range of 3 to 100 g / m ² . By setting the basis weight to 3 to 100 g / m ² , preferably 5 to 70 g / m ² , and more preferably 10 to 50 g / m ² , it becomes easy to obtain an electret fiber sheet having excellent air permeability and dust collection characteristics. ..

The electret fiber sheet of the present invention preferably has a collection efficiency maintenance rate of 98.5% or more, more preferably 99.0% or more, before and after heat treatment at 140 ° C. for 5 minutes. By setting the collection efficiency maintenance rate before and after heat treatment at 140 ° C. for 5 minutes within this range, it is possible to easily obtain an air filter filter medium having high dust collection characteristics even at high temperatures.

The electret fiber sheet of the present invention can be suitably used as a filter medium for an air filter.

The air filter filter medium of the present invention comprises the electret fiber sheet of the present invention. As a method for obtaining the air filter filter medium of the present invention from the electret fiber sheet of the present invention, a known method can be used. For example, the method described in JP-A-2004-82109 can be used.

The air filter filter medium of the present invention is suitable for high-performance applications such as air filters in general, air filters for air purifiers, filters for air purifiers, and automobile cabin filters, but its application range is not limited to these.

(1) The mass of the electret fiber sheet having a basis weight of vertical × horizontal = 15 cm × 15 cm was measured for one sample. The obtained value was converted into a value per 1 m ² , and the first decimal place was rounded off to calculate the basis weight (g / m ² ) of the electret fiber sheet.

(2) Average single fiber diameter:
For the average single fiber diameter, 10 measurement samples of 3 mm × 3 mm were collected from any location on the electret fiber sheet, the magnification was adjusted to 1000 to 3000 times with a scanning electron microscope, and the fibers were collected from the measured samples. A total of 10 surface photographs were taken, one for each. The single fiber diameter was measured for the fiber whose fiber diameter (single fiber diameter) can be clearly confirmed in the photograph, and the second decimal place of the average value was rounded off to obtain the average single fiber diameter.

(3) Using a thickness thickness gauge ("TECLOCK" (registered trademark) SM-114 manufactured by Teklock Co., Ltd.), measure the thickness of the electret fiber sheet at 10 points at equal intervals in the width direction, and measure the thickness at 10 points from the average value to the third decimal place. The decimal point was rounded to the thickness.

(4) Collection performance (collection efficiency)
Measurement samples of vertical × horizontal = 15 cm × 15 cm were collected at five locations in the width direction of the electret fiber sheet, and the collection efficiency of each sample was measured using the collection efficiency measuring device shown in FIG. In the collection efficiency measuring device of FIG. 1, the dust storage box 2 is connected to the upstream side of the sample holder 1 in which the measurement sample M is set, and the flow meter 3, the flow rate adjusting valve 4 and the blower 5 are connected to the downstream side. ing. Further, a particle counter 6 is used for the sample holder 1, and the number of dusts on the upstream side and the number of dusts on the downstream side of the measurement sample M can be measured via the switching cock 7, respectively. Further, the sample holder 1 is provided with a pressure gauge 8, and can read the static pressure difference between the upstream and the downstream of the measurement sample M.

In measuring the collection efficiency, a polystyrene 0.309U 10% solution (manufacturer: Nacalai Tesque Co., Ltd.) is diluted up to 200 times with distilled water and filled in the dust storage box 2. Next, the measurement sample M is set in the sample holder 1, the air volume is adjusted by the flow rate adjusting valve 4 so that the filter passing speed is 4.5 m / min, and the dust concentration is 10,000 to 40,000 / 2. Stabilize in the range of .83 × 10 ^-4 m ³ (0.01ft ³ ), and set the number of dust D upstream and the number d downstream of the measurement sample M with a particle counter 6 (KC-01D manufactured by Rion). Measured three times per measurement sample, and based on JIS K 0901 (1991) "Shape, dimensions and performance test method of filter material for collecting dust samples in gas", using the following formula, 0. The collection efficiency (%) of 3 to 0.5 μm particles was determined. The average value of the three measurement samples was taken as the final collection efficiency.
-Collecting efficiency (%) = [1- (d / D)] x 100
(However, d represents the total number of three-time measurements of downstream dust, and D represents the total number of three-time measurements of upstream dust.)
(5) Collection efficiency maintenance rate (%)
The electret fiber sheet was cut into vertical x horizontal = 15 cm x 15 cm, and each sample was hung in a hot air dryer (TABAI PHH-100) set at 110 ° C, 120 ° C, and 140 ° C. The state was heat-treated for 5 minutes. The collection efficiency of the heat-treated sample is measured by the method (3) above, the collection efficiency maintenance rate before and after the heat treatment is calculated using the following formula, and the average value of the three measurement samples is the final value. The collection efficiency maintenance rate before and after the heat treatment was used.
・ Collection efficiency maintenance rate (%) = (collection efficiency after heat treatment / collection efficiency before heat treatment) × 100
[Example 1]
As raw materials, 0.3% by mass of "ADEKA STAB" (registered trademark) NA-21 (manufactured by ADEKA Corporation) represented by the following formula (b) and hindered amine compound "Kimasorb" (registered trademark) 944 (BASF) Polypropylene containing 1% by mass (manufactured by Japan Co., Ltd.) and having a melt flow rate of 850 g / 10 minutes was used.

The raw material is charged into the raw material hopper of the spinning machine, and the melt blow method is used by using a mouthpiece (hole pitch: 1 mm, number of holes: 151 holes, width: 150 mm) in which discharge holes having a diameter of 0.4 mm are arranged in a straight line. A non-woven fabric sheet having a grain size of 25 g / m ² was obtained by spraying under the conditions of a polymer discharge rate of 27 g / min, a nozzle temperature of 260 ° C., and an air pressure of 0.10 MPa, and adjusting the collection conveyor speed. Subsequently, while running along the water surface of the water tank to which pure water is supplied, a slit-shaped suction nozzle is brought into contact with the surface of the water tank to suck water, so that the water permeates the entire surface of the fiber sheet, and after draining. By air-drying, an electretized melt-blown non-woven fabric was obtained.

The obtained electret fiber sheet is heat-treated for 5 minutes in a hot air dryer set at 110 ° C, 120 ° C, and 140 ° C, respectively, and the collection efficiency before and after the heat treatment is measured to maintain the collection efficiency at each temperature. The rate was calculated. Table 1 shows the measured values and calculated values of the electret fiber sheet.

[Example 2] As raw materials, 0.1% by mass of "ADEKA STAB" (registered trademark) NA-21 (manufactured by ADEKA Corporation) and hindered amine compound "Kimasorb" (registered trademark) 944 (BASF Japan Ltd.) A melt-blown nonwoven fabric was obtained as an electret under the same conditions as in Example 1 except that it contained 1% by mass.

Each characteristic value of the obtained electret fiber sheet was measured by the same method as in Example 1. The results obtained are shown in Table 1.

[Comparative Example 1]
An electret fiber sheet was obtained by the same method as in Example 1 except that NA-21 was not added to the polypropylene used in Example 1 as a raw material.

Each characteristic value of the obtained electret fiber sheet was measured by the same method as in Example 1. The results obtained are shown in Table 1.

[Comparative Example 2]
As raw materials, 0.03% by mass of "ADEKA STAB" (registered trademark) NA-21 (manufactured by ADEKA Corporation) and 1 mass of hindered amine compound "Kimasorb" (registered trademark) 944 (manufactured by BASF Japan Ltd.) An electretized melt-blown nonwoven fabric was obtained under the same conditions as in Example 1 except that it contained%.

Each characteristic value of the obtained electret fiber sheet was measured by the same method as in Example 1. The results obtained are shown in Table 1.

As is clear from Table 1, Examples 1 and 2 of the present invention contain a compound represented by the formula (b), which is one of the compounds represented by the general formula (a), and therefore, therefore, at a high temperature. The electret stability was excellent, and the collection efficiency maintenance rate of the electret fiber sheet heat-treated at 140 ° C. was as high as 98.5% or more.

On the other hand, in Comparative Example 1 containing no compound represented by the general formula (a) and Comparative Example 2 containing only 0.03% by mass of the compound represented by the general formula (a), the heat treatment was carried out. Compared to Examples 1 and 2, the collection efficiency before the heat treatment showed the same level of performance, but the result was that the collection efficiency was significantly reduced after the heat treatment.

As described above, the electret fiber sheet containing the compound represented by the general formula (a) has excellent electret stability at high temperatures and exhibits high collection efficiency.

1: Sample holder 2: Dust storage box 3: Flow meter 4: Flow rate adjustment valve 5: Blower 6: Particle counter 7: Switching cock 8: Pressure gauge M: Measurement sample

Claims (3)

An electret fiber sheet mainly containing non-conductive fibers, which contains 0.05 to 1.0% by mass of a compound represented by the following general formula (a) and is trapped before and after heat treatment at 140 ° C. for 5 minutes. An electret fiber sheet having a collection efficiency maintenance rate of 98.5% or more .

(In the general formula (a), M represents an alkali metal, an alkaline earth metal, aluminum, zinc, copper, or a salt structure of these metals. N is 1 or 2. R ¹ , R ² , R ³ And ^R4 independently represent hydrogen or an alkyl group having 1 to 6 carbon atoms.) The electret fiber sheet according to claim 1, which is made of a melt blown nonwoven fabric. An air filter filter medium made of the electret fiber sheet according to claim 1 or 2 .

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