JP2016087498A - Electret filter medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electret filter medium using a porous dielectric sheet made from a polyolefin resin that has been sufficiently and highly converted into an electret, including the inside.SOLUTION: In an electret filter medium, a value of O/C which is a molar ratio of an oxygen atom (O) and a carbon atom (C) on the surface of a porous dielectric sheet made from a polyolefin resin is 0.003-0.03.SELECTED DRAWING: None

Description

  The present invention relates to an improved electret filter medium used for capturing fine particles in a gas.

  A conventional technique for electretizing a porous dielectric sheet includes a water spray charging method.

  For example, Patent Document 1 discloses a method of electretizing a water jet or water droplet by colliding with a porous dielectric sheet. There is a description that it is preferable to use higher-purity water such as distilled water or ion-exchanged water as the water to collide with the porous dielectric sheet. However, such high-purity water has a low charging effect due to the contact between the porous dielectric sheet and water, and the porous dielectric sheet cannot be highly electretized.

  For example, Patent Document 2 discloses a method for manufacturing an electret processed product in which a mixed solution of water and a water-soluble organic solvent is applied to a non-conductive sheet, and then the non-conductive sheet is dried. In a mixed solution of water and a water-soluble organic solvent, there is a description that it is preferable to use higher-purity water such as distilled water or ion-exchanged water, but in such water, non-conductive The charging effect due to the contact between the sheet and the mixed solution is low. Moreover, since a water-soluble organic solvent is mixed for the purpose of increasing the permeability to the non-conductive sheet, the contact angle between the non-conductive sheet and the mixed solution is reduced, and the accumulated charge on the sheet is contained in the mixed solution It becomes easy to leak. As a result, there is a drawback that the non-conductive sheet cannot be highly electretized.

  For example, Patent Document 3 discloses a method for producing an electret filter material in which an aqueous solution exceeding pH 7 is sprayed onto a non-conductive porous dielectric sheet subjected to corona charging treatment, and then dried. There is a description that it is preferable to perform corona charging treatment before water is jetted to accumulate charges on the surface. However, there is a drawback that charges given by corona charging treatment are lost by jetting an aqueous solution.

  As described above, in the electret filtering material using the porous dielectric sheet, there is no electret filtering material that is sufficiently electretized to the inside of the electret filtering material.

Japanese National Patent Publication No. 9-501604 JP 2002-115177 A JP 2004-66027 A

  In view of the above-mentioned conventional problems, the present invention provides an electret filtration material that is sufficiently electretized to a high degree in an electret filtration material using a porous dielectric sheet made of polyolefin resin. Is an issue.

As a result of intensive studies to solve the above problems, the present inventors have finally completed the present invention. That is, the present invention is as follows.
1. An electret filter material in which the value of O / C, which is the molar ratio of oxygen atoms (O) to carbon atoms (C) on the surface of a porous dielectric sheet made of a polyolefin-based resin, is 0.003 to 0.03.
2. The porous dielectric sheet contains at least one additive selected from a hindered phenol stabilizer, a sulfur stabilizer, a phosphorus stabilizer, a fatty acid metal salt, and a crystal nucleating agent, and the content thereof is the porous 2. The electret filter material according to 1 above, which is 0.01 to 5 parts by weight with respect to 100 parts by weight of the conductive dielectric sheet.
3. The porous dielectric sheet made of polyolefin resin is subjected to at least one treatment selected from ozone oxidation treatment, liquid phase oxidation treatment, and plasma oxidation treatment, and then sprayed with an aqueous solution having a pH exceeding 7, and dried. Or the manufacturing method of the electret filter material of 2.

  The electret filter material using the porous dielectric sheet made of polyolefin resin according to the present invention is highly electretized by introducing oxygen atoms into the sheet surface, and provides excellent filtration performance. It has the advantage of being able to.

  Hereinafter, the present invention will be described in detail. Examples of the porous dielectric sheet made of a polyolefin resin used in the present invention include a fiber sheet (for example, a woven fabric, a knitted fabric, a nonwoven fabric, or a composite thereof), a porous film (for example, a perforated film), a foam, These complexes are included. Among them, an ultrafine fiber nonwoven fabric produced by a melt blow method is preferable. Since the ultrafine fiber nonwoven fabric has a large fiber surface area, the particle collection efficiency of the filter medium is improved.

  The porous dielectric sheet made of a polyolefin-based resin may have a configuration in which one sheet or a plurality of sheets are laminated. Further, in order to increase the sheet strength, a reinforcing material such as a spunbond nonwoven fabric may be laminated and used.

The material of the porous dielectric sheet made of polyolefin-based resin may be composed of one kind or a plurality of kinds of materials, but at least one kind of material having a volume resistivity of 10 ¹⁴ Ωcm or more from the viewpoint of charge retention. It is preferable to include the above. If the porous dielectric sheet is composed only of a material having a volume resistivity of less than 10 ¹⁴ Ωcm, it is difficult to accumulate charges, making it highly difficult to make electrets, and the charge life of the filter medium becomes extremely short. Problem arises. Among polyolefin resins, polypropylene is preferable.

Porous dielectric sheet made of polyolefin resin, if the melt blown nonwoven fabric made of polypropylene, basis weight is preferably ^{5~100g / m 2, 10~60g / m} 2 is more preferable. 1-20 micrometers is preferable and, as for the average fiber diameter of the fiber which comprises a melt blown nonwoven fabric, 1-10 micrometers is more preferable.

  The O / C ratio, which is the molar ratio of oxygen atoms (O) to carbon atoms (C) on the surface of the porous dielectric sheet made of polyolefin resin, is 0.003 to 0.03, preferably 0.003. It is -0.02, More preferably, it is 0.003-0.015. When the value of the O / C ratio is less than 0.003, electric charges cannot be trapped in the porous dielectric sheet, so that it cannot be sufficiently electretized. On the other hand, when it exceeds 0.03, the hydrophilicity of the porous dielectric sheet increases, and the charge applied to the porous dielectric sheet disappears due to long-term contact with water.

  The porous dielectric sheet made of polyolefin resin contains at least one additive selected from a hindered phenol stabilizer, a sulfur stabilizer, a phosphorus stabilizer, a fatty acid metal salt, and a crystal nucleating agent. Preferably it is. By containing these additives, the electret property of the porous dielectric sheet is dramatically improved.

  The hindered phenol-based additive is not particularly limited, but pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] (Irganox 1010, manufactured by BASF) ), Octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate (Irganox 1076, manufactured by BASF), tris- (3,5-di-t-butyl-4-hydroxybenzyl)- Isocyanurate (Irganox 3114, manufactured by BASF), 3,9-bis- {2- [3- (3-t-butyl-4-hydroxy-5-methylphenyl) -propionyloxy] -1,1-dimethylethyl } -2,4,8,10-tetraoxaspiro- [5,5] undecane (Sumilyzer GA-80 Sumitomo Chemical Co., Ltd.), and the like.

  Although it does not necessarily limit as a sulfur type stabilizer, Di-lauryl-3,3-thiodipropionic acid ester (DLTDP), di-stearyl-3,3-thiodipropionic acid ester (DSTDP), etc. Is mentioned.

  The phosphorus stabilizer is not particularly limited, but tris (2,4-di-t-butylphenyl) phosphite (Irgafos168, manufactured by BASF), di (2,6-di-t-butyl). -4-methylphenyl) -pentaerythritol diphosphite (PEP-36, manufactured by ADEKA), 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (HCA, manufactured by Sanko) Etc.

  Although it does not necessarily limit as a fatty-acid metal salt, What has a linear fatty acid group is preferable. The fatty acid group preferably has 10 to 20 carbon atoms. Specific examples include aluminum laurate, aluminum myristate, aluminum palmitate, aluminum stearate, magnesium laurate, magnesium myristate, magnesium palmitate, and magnesium stearate.

  The crystal nucleating agent is not particularly limited, but sodium bis (4-t-butylphenyl) phosphate (NA-10, manufactured by ADEKA), 2,2′-methylenebisphosphate (4,6- Di-t-butylphenyl) sodium (NA-11, manufactured by ADEKA), rosin crystal nucleating agent pine crystal KM-1500 (manufactured by Arakawa Chemical Industries), and the like.

  The content of the additive is preferably 0.01 to 5 parts by weight, more preferably 0.025 to 2.5 parts by weight with respect to 100 parts by weight of the porous dielectric sheet. More preferably, it is 0.05 to 2 parts by weight. If the content is small, the electretization effect is not sufficient. Conversely, even if the content is large, the effect is saturated and bleeds out.

  The method of introducing oxygen to the surface of the porous dielectric sheet made of polyolefin resin is not particularly limited, but exposure to an ozone atmosphere, oxidation liquid such as nitric acid or sodium hypochlorite solution, etc. Examples thereof include contact and plasma treatment.

  The aqueous solution sprayed onto the porous dielectric sheet made of polyolefin resin preferably has a pH exceeding 7. When an aqueous solution having a pH of 7 or less is used, it is difficult to highly electretize the porous dielectric sheet. The type of the aqueous solution is not particularly limited, but preferably sodium hydroxide, potassium hydroxide, hypochlorite, ammonia, ammonium salt, amines, carbonate, bicarbonate, etc. are dissolved. Aqueous solution. Surfactants and organic solvents not only increase the permeability of the aqueous solution to the porous dielectric sheet, but also form a film on the surface of the porous dielectric sheet to prevent high electrets of the porous dielectric sheet. Should not be contained in the aqueous solution.

When spraying the aqueous solution onto a porous dielectric sheet made of a polyolefin resin, the sheet is placed on a mesh-like support having an air permeability of 50 to 400 cm ³ / cm ² / second, and the aqueous solution is jetted from above to support the mesh-like support. The lower part of the body is preferably in a reduced pressure state. The air permeability is measured using a frangole type tester described in JIS L1096. The net-like support is specifically a porous structure made of a metal yarn or plastic yarn woven material, and examples thereof include plain weave, twill weave and satin weave. Examples of the metal material include stainless steel and bronze, and examples of the plastic material include polypropylene, polyester, polyurethane, nylon, and polyphenylene sulfide.

The injection of the aqueous solution is a pressure sufficient to allow the aqueous solution to pass through the sheet from a nozzle having a large number of orifices along the width direction of the sheet placed several cm above the porous dielectric sheet made of polyolefin resin. Inject with. The pressure sufficient to pass depends on the basis weight of the porous dielectric sheet. For example, when the basis weight is 5 to 20 g / m ² , 0.3 to ² MPa, 20 to 50 g / m ² is 0.6 to 3 MPa, and 50 to 100 g / m ² is 1 to 4 MPa. preferable. If the pressure is too high, pinholes will open in the porous dielectric sheet and the filtration performance will deteriorate. Further, if the aqueous solution cannot sufficiently pass through the porous dielectric sheet because the pressure is too low, the porous dielectric sheet cannot be highly electretized. The nozzle is preferably one in which orifices having a diameter of 0.05 to 0.2 mm are arranged in one or more rows with a pitch of 0.5 to 3 mm. Further, the jetting process can be continuously performed by making the mesh support movable and transporting the porous dielectric sheet in the longitudinal direction. Although the conveyance speed is not particularly limited, a preferable range is 1 to 100 m / min. Further, the optimum number of injections and the treatment surface (one side or both sides) are not particularly limited because they depend on the basis weight of the porous dielectric sheet and the average fiber diameter.

  At the same time as the injection of the aqueous solution, it is preferable that the lower portion of the mesh support is brought into a reduced pressure state using an exhaust blower or the like. The suction negative pressure is not particularly limited, but 200 to 2000 mmAq is preferable. When the pressure is reduced, the aqueous solution can sufficiently pass through the porous dielectric sheet, and the porous dielectric sheet can be highly electretized.

  A conventionally known method can be used as a drying method after the aqueous solution is sprayed onto the porous dielectric sheet. For example, a method such as a hot air drying method, a vacuum drying method, or a natural drying method is applicable. Of these, the hot air drying method is preferable because continuous processing is possible. In the case of the hot air drying method, the drying temperature needs to be a temperature that does not cause the electret to disappear. Preferably it is 120 degrees C or less, More preferably, it is 100 degrees C or less, More preferably, it is good to set it as 80 degrees C or less. Moreover, it is more preferable to remove excess moisture by nip roll, water absorbing roll, suction suction or the like as preliminary drying before hot air drying.

  Hereinafter, the effects of the present invention will be described more specifically by way of examples. In the following, a melt blown nonwoven fabric produced by a conventionally known method is used as the porous dielectric, but this is not a property that limits the method of the present invention, and any design changes may be made in accordance with the purpose described above or below. Is also included in the technical scope of the present invention.

(O / C ratio measurement method)
By dividing the spectral intensity caused by the 1s orbital of oxygen on the surface of the porous dielectric sheet by ESCA by the spectral intensity caused by the 1s orbital of carbon, the O / C ratio of the porous dielectric sheet is obtained. Calculated.

(Method for measuring pH of aqueous solution)
The pH of the aqueous solution prepared using a low conductivity water / nonaqueous solvent pH electrode (6377-10D manufactured by HORIBA) as the electrode and under the condition of a water temperature of 25 ° C. according to the pH measurement method described in JIS-Z8802. Was measured.

(Aqueous solution injection treatment)
A porous dielectric sheet is placed on a reticulated support (96 mesh) having an air permeability of 120 cm ³ / cm ² / sec, and an aqueous solution at a pressure of 2 MPa from a nozzle having a diameter of 0.1 mmφ and a pitch of 0.6 mm located 3 cm above the nonwoven fabric. An injection process was performed. The base water is high-purity water obtained by subjecting general tap water to two-stage reverse osmosis membrane treatment and then ion exchange membrane treatment, and 10 ppm of potassium carbonate (manufactured by Nacalai Tesque) dissolved in the base water. And an aqueous jet solution having a pH of 9.6 was prepared. The conveyance speed of the support was 3 m / min, and the lower part of the net-like support just below the nozzle was in a reduced pressure state of 600 mmAq. This treatment was performed 3 times on the surface of the sheet. Thereafter, the sheet was naturally dried or kept in a hot air oven at 80 ° C. for 1 minute to dry.

(Evaluation of filtration characteristics)
The pressure loss (PD) was obtained by installing an electret filter medium sample in a duct and controlling the linear passage speed of the filter medium to 10 cm / second, and reading the static pressure difference upstream and downstream of the electret filter medium with a pressure gauge. The particle collection efficiency E (%) was evaluated at 10 cm / second using atmospheric dust particles having a particle diameter of 0.3 μm. Using the pressure loss PD (mmAq) and the particle collection efficiency E (%), the filter medium quality factor QF was calculated from the following formula.
QF = -LN ((100-E) / 100) / PD

(Evaluation of average fiber diameter)
The fiber diameter was measured for 100 fibers enlarged by SEM photographs, and the average value Dfs [μm] was determined.

<Example 1>
0.05 part by weight of Irganox 1010 is blended with 100 parts by weight of polypropylene resin (manufactured by Prime Polymer Co., Ltd.) having a melt flow index 700, and a melt blown nonwoven fabric having a basis weight of 20 g / m ² and an average fiber diameter (Dfs) of 1.1 μm is produced. did. Air containing 6.8 ppm of ozone generated by silent discharge was passed through the melt blown nonwoven fabric at 20 cm / sec for 30 minutes. Then, the aqueous solution injection process was performed and the electret filter material was obtained. The evaluation results of the obtained electret filter material are shown in Table 1.

<Example 2>
The meltblown nonwoven fabric used in Example 1 is impregnated with ethanol (manufactured by Nacalai Tesque, Inc .; purity 99.5%), and then immersed in an aqueous solution (made by Wako Pure Chemical Industries, Ltd.) containing 5% sodium hypochlorite. Thus, the aqueous solution was impregnated to the inside, and oxidation treatment was performed at 80 ° C. for 30 minutes. Then, the aqueous solution injection process was performed and the electret filter material was obtained. The evaluation results of the obtained electret filter material are shown in Table 1.

<Example 3>
3 parts by weight of Irganox 1010 was blended with the resin used in Example 1 to prepare a melt blown nonwoven fabric having a basis weight of 20 g / m ² and an average fiber diameter (Dfs) of 1.1 μm. Air containing 6.8 ppm of ozone generated by silent discharge was passed through the melt blown nonwoven fabric at 20 cm / sec for 30 minutes. Then, the aqueous solution injection process was performed and the electret filter material was obtained. The evaluation results of the obtained electret filter material are shown in Table 1.

<Example 4>
Nothing was blended with the resin used in Example 1, and a melt blown nonwoven fabric having a basis weight of 20 g / m ² and an average fiber diameter (Dfs) of 1.1 μm was produced. A direct current corona charge was applied for 15 seconds under the condition of −20 kV / cm, and an aqueous solution injection treatment was performed to obtain an electret filter material. The evaluation results of the obtained electret filter material are shown in Table 1.

<Comparative Example 1>
The melt-blown nonwoven fabric used in Example 1 was not subjected to any treatment, and an aqueous solution injection treatment was performed to obtain an electret filter material. The evaluation results of the obtained electret filter material are shown in Table 1.

<Comparative Example 2>
A direct current corona charge was applied to the meltblown nonwoven fabric used in Example 1 for 15 seconds under the condition of −10 kV / cm, and an aqueous solution injection treatment was performed to obtain an electret filter material. The evaluation results of the obtained electret filter material are shown in Table 1.

  As is clear from Table 1, Examples 1-4 showed high particle collection efficiency. In contrast, Comparative Examples 1 and 2 having a low O / C ratio remained low in particle collection efficiency and QF as compared with Examples 1 to 4, and it was confirmed that they could not be highly electretized.

  The electret filter material using the porous dielectric sheet made of polyolefin resin according to the present invention is highly electretized by introducing oxygen atoms into the sheet surface, and provides excellent filtration performance. It can make a great contribution to the industry.

Claims (3)

  An electret filter material in which the value of O / C, which is the molar ratio of oxygen atoms (O) to carbon atoms (C) on the surface of a porous dielectric sheet made of a polyolefin-based resin, is 0.003 to 0.03.   The porous dielectric sheet contains at least one additive selected from a hindered phenol stabilizer, a sulfur stabilizer, a phosphorus stabilizer, a fatty acid metal salt, and a crystal nucleating agent, and the content thereof is the porous The electret filter material according to claim 1, wherein the content is 0.01 to 5 parts by weight with respect to 100 parts by weight of the conductive dielectric sheet.   A porous dielectric sheet made of a polyolefin resin is subjected to at least one treatment selected from ozone oxidation treatment, liquid phase oxidation treatment, and plasma oxidation treatment, and then an aqueous solution having a pH of more than 7 is sprayed and dried. The manufacturing method of the electret filter material of 1 or 2.