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WO2025182823A1 - Électret et filtre à électret - Google Patents

Électret et filtre à électret

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Publication number
WO2025182823A1
WO2025182823A1 PCT/JP2025/006095 JP2025006095W WO2025182823A1 WO 2025182823 A1 WO2025182823 A1 WO 2025182823A1 JP 2025006095 W JP2025006095 W JP 2025006095W WO 2025182823 A1 WO2025182823 A1 WO 2025182823A1
Authority
WO
WIPO (PCT)
Prior art keywords
electret
mass
parts
present
filter
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
PCT/JP2025/006095
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English (en)
Japanese (ja)
Inventor
義幸 北川
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Toyobo MC Corp
Original Assignee
Toyobo MC Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Toyobo MC Corp filed Critical Toyobo MC Corp
Publication of WO2025182823A1 publication Critical patent/WO2025182823A1/fr
Pending legal-status Critical Current
Anticipated expiration legal-status Critical

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D39/00—Filtering material for liquid or gaseous fluids
    • B01D39/14—Other self-supporting filtering material ; Other filtering material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D39/00—Filtering material for liquid or gaseous fluids
    • B01D39/14—Other self-supporting filtering material ; Other filtering material
    • B01D39/16—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C—MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03C3/00—Separating dispersed particles from gases or vapour, e.g. air, by electrostatic effect
    • B03C3/28—Plant or installations without electricity supply, e.g. using electrets
    • D—TEXTILES; PAPER
    • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
    • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
    • D04H3/00—Non-woven fabrics formed wholly or mainly of yarns or like filamentary material of substantial length
    • D04H3/005—Synthetic yarns or filaments
    • D04H3/007—Addition polymers

Definitions

  • the present invention relates to electrets and electret filters.
  • porous filters have been used in dust masks, various air conditioning elements, air purifiers, cabin filters, and various devices for the purposes of dust collection, protection, ventilation, etc.
  • porous filters filters made of fibrous materials are widely used due to their high porosity, long life, and low airflow resistance. These fibrous filters capture particles on the fibers through mechanical collection mechanisms such as interception, diffusion, and inertial impaction. It is known that in practical usage environments, filter collection efficiency reaches a minimum when the aerodynamic equivalent diameter of the particles being captured is around 0.1 to 1.0 ⁇ m.
  • methods that also incorporate electrical attraction are known. For example, methods that involve applying an electric charge to the particles to be collected, applying an electric charge to the filter, placing the filter in an electric field, or a combination of these are used.
  • Known methods of applying an electric charge to the filter include placing the filter between electrodes and causing dielectric polarization when ventilation is performed, and applying a long-lasting electrostatic charge to an insulating material. The latter method in particular does not require energy from an external power source, and is therefore widely used as an electret filter.
  • Electrets and electret filters are required to be protected from deterioration over time during transportation, storage, and use, as well as from deterioration during pleating, injection molding, lamination, and drying.
  • Patent Document 1 Patent Document 2
  • the present invention makes it possible to obtain electrets and electret filters with excellent charge stability.
  • the electrets of the present invention comprise polyolefins, which include polypropylene and poly-4-methyl-1-pentene.
  • polypropylene may be a propylene homopolymer or a copolymer primarily composed of propylene-derived units.
  • the molar fraction of propylene-derived units contained in the polymer is preferably 80 mol% or more, more preferably 85 mol% or more, even more preferably 90 mol% or more, and most preferably 95 mol% or more.
  • the copolymer may contain various olefins as copolymerization components other than propylene. Examples include ethylene and ⁇ -olefins having 4 to 20 carbon atoms. More specific examples include propylene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, and 1-eicosene.
  • the copolymer may contain only one of these, or two or more. Halogenated olefins and alicyclic olefins are also preferably used to improve the flame retardancy and rigidity of the electret.
  • the polypropylene used in the present invention preferably has a degree of stereoregularity of 85% or more, more preferably 90% or more, and even more preferably 95% or more.
  • isotactic or syndiotactic polypropylene can be preferably used.
  • poly-4-methyl-1-pentene may be a 4-methyl-1-pentene homopolymer or a copolymer primarily composed of units derived from poly-4-methyl-1-pentene. While there are no particular limitations as long as the required properties are obtained, the molar fraction of 4-methyl-1-pentene-derived units contained in poly-4-methyl-1-pentene is preferably 80 mol% or more. It is more preferably 85 mol% or more, even more preferably 90 mol% or more, and most preferably 95 mol% or more. This is to effectively develop the properties of poly-4-methyl-1-pentene.
  • TPX registered trademark
  • DX820 manufactured by Mitsui Chemicals, Inc., which contains 97 mol% of structural units derived from 4-methyl-1-pentene and 3 mol% of structural units derived from decene-1.
  • the copolymer may contain various olefins as copolymerization components other than 4-methyl-1-pentene, such as ethylene, propylene, and ⁇ -olefins having 4 to 20 carbon atoms. More specific examples include propylene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, and 1-eicosene. It is also preferable for one or more of these to be contained in the copolymer.
  • the number of carbon atoms of the olefin contained as a copolymerization component is preferably 6 to 19, and more preferably 10 to 18. Halogenated olefins and alicyclic olefins are also preferably used to improve the flame retardancy and rigidity of the electret.
  • the poly-4-methyl-1-pentene used in the present invention preferably has a melt flow rate (MFR) of 20 to 1,000 g/10 min, more preferably 50 to 500 g/10 min, even more preferably 70 to 300 g/10 min, and particularly preferably 100 to 200 g/10 min.
  • MFR melt flow rate
  • the MFR is measured in accordance with JIS K 7210 (1999) at a test temperature and load of 260°C and 5 kg, but when using a commercially available product, the value listed in the catalog may be used.
  • the polyolefin content per 100 parts by mass of the electret is preferably 80 parts by mass or more, more preferably 85 parts by mass or more, even more preferably 90 parts by mass or more, particularly preferably 95 parts by mass or more, and most preferably 97 parts by mass or more.
  • the polyolefin content is, for example, 99.5 parts by mass or less, preferably 99 parts by mass or less.
  • sheath-core fibers or side-by-side fibers where the resins contained in the fibers are different between the left and right sides or the core and sheath, only the part containing the polyolefin is considered to be the electret of the present invention.
  • the electret of the present invention comprises a resin blend of poly-4-methyl-1-pentene and polypropylene, containing 80 to 99 parts by weight of polypropylene and 1 to 20 parts by weight of poly-4-methyl-1-pentene per 100 parts by weight of the resin contained in the electret. It has been discovered in the present invention that blending the two in predetermined amounts improves the charge stability of polypropylene. If the amount of poly-4-methyl-1-pentene is greater than the above range, processing becomes difficult, and if the amount is less, the effect of improving charge stability is difficult to achieve. For 100 parts by weight of the resin contained in the electret of the present invention, the amount of polypropylene is preferably 85 to 97 parts by weight, more preferably 90 to 95 parts by weight.
  • the amount of poly-4-methyl-1-pentene is preferably 3 to 15 parts by weight, more preferably 5 to 10 parts by weight. Furthermore, for every 100 parts by mass of the resin contained in the electret of the present invention, the total content of polypropylene and poly-4-methyl-1-pentene is preferably 90 parts by mass or more, more preferably 95 parts by mass or more, even more preferably 98 parts by mass or more, and particularly preferably 100 parts by mass.
  • the polypropylene content is preferably 80 to 99 parts by mass, and more preferably 85 to 97 parts by mass.
  • the poly-4-methyl-1-pentene content is preferably 1 to 20 parts by mass, and more preferably 3 to 15 parts by mass.
  • the electret of the present invention contains a nitrogen-containing compound in addition to polypropylene and poly-4-methyl-1-pentene. It is also preferable that the electret of the present invention further contains a fatty acid metal salt.
  • the nitrogen-containing compound and fatty acid metal salt are described below.
  • the electret of the present invention contains a nitrogen-containing compound that promotes charging of polyolefins by liquid contact. If the compound is not compatible with polyolefins, it is sufficient that the compound is contained in at least one of poly-4-methyl-1-pentene and polypropylene.
  • the nitrogen-containing compound content per 100 parts by mass of polyolefin is preferably 0.1 to 5 parts by mass, more preferably 0.5 to 3 parts by mass, and even more preferably 0.75 to 1.5 parts by mass.
  • an electret contains two or more types of fibers or when a single fiber contains two or more types of resins, this refers to the proportion of nitrogen-containing compounds contained in the polyolefin.
  • resins other than polyolefin these can be distinguished because they dissolve in solvents and acids and bases and have different dyeing properties.
  • Polyolefins can also be distinguished using quantitative methods such as DSC and NMR. If the nitrogen-containing compound content is less than 0.1 parts by mass, the charge amount will be low, resulting in reduced filtration properties. If it is more than 5 parts by mass, the increased hydrophilicity will result in a loss of stability as an electret.
  • the content of the nitrogen-containing compound per 100 parts by mass of the electret of the present invention is preferably 0.1 to 5 parts by mass, more preferably 0.5 to 3 parts by mass, and even more preferably 0.75 to 1.5 parts by mass. By keeping it within the above range, it is possible to improve the filtration characteristics and increase the stability as an electret.
  • the nitrogen-containing compound is preferably a hindered amine compound containing at least one of a 2,2,6,6-tetramethylpiperidyl structure and a triazine structure, and more preferably one containing a 2,2,6,6-tetramethylpiperidine structure and a triazine structure.
  • Hindered amine compounds are not particularly limited, but examples include poly[ ⁇ 6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazine-2,4-diyl ⁇ (2,2,6,6-tetramethyl-4-piperidyl)imino ⁇ hexamethylene ⁇ 2,2,6,6-tetramethyl-4-piperidyl)imino ⁇ ] (Chimasorb® 944LD, manufactured by BASF Japan Ltd.), dimethyl succinate, -1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethyl-4-piperidine polycondensate (Tinuvin (registered trademark) 622LD, manufactured by BASF Japan Ltd.), bis[1,2,2,6,6-pentamethyl-4-piperidinyl] 2-[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]-2-butylpropanedioate (Tinuvin (registered trademark) 144
  • Chimassorb (registered trademark) 944LD or Chimassorb (registered trademark) 2020FD which contain a 2,2,6,6-tetramethylpiperidine structure and a triazine structure, are preferred.
  • One type of hindered amine compound may be used alone, or two or more types may be used in combination.
  • the nitrogen-containing compound used in the present invention that promotes charging only needs to be present on at least the electret surface, and can be introduced by applying a solution to the electret surface, attaching a powder, mixing a solution into polyolefin, mixing during polymerization, melt mixing, etc.
  • the melt mixing method is superior in terms of homogeneity and processability. It can be mixed directly with the resin during melt molding. It can also be used as is, or diluted, as a pre-prepared resin compound containing a charge enhancer.
  • the addition of one or more fatty acid metal salts can further enhance charge stability.
  • a preferred amount is 0.01 to 1 part by mass per 100 parts by mass of polyolefin.
  • the fatty acid metal salt is preferably at least one selected from the group consisting of fatty acid aluminum salts and fatty acid magnesium salts, and more preferably fatty acid magnesium salts.
  • the fatty acid in the fatty acid metal salt preferably contains at least one selected from the group consisting of monocarboxylic acids and dicarboxylic acids, but may also contain hydrocarbons other than carboxylic acids.
  • fatty acid metal salt those having a fatty acid group with 10 to 50 carbon atoms are preferred, those having a fatty acid group with 12 to 30 carbon atoms are more preferred, and those having a fatty acid group with 16 to 22 carbon atoms are even more preferred. Furthermore, fatty acid metal salts having a linear fatty acid group are preferred.
  • Fatty acid aluminum salts preferably have a linear fatty acid group, and the number of fatty acid chains bonded to the aluminum may be one, two, or three, although three is preferred.
  • Specific examples of fatty acid aluminum salts include aluminum salts of linear saturated fatty acids such as aluminum laurate, aluminum myristate, aluminum palmitate, aluminum stearate, and aluminum behenate; and aluminum salts of linear unsaturated fatty acids such as aluminum oleate.
  • aluminum salts of linear saturated fatty acids are preferred, and aluminum stearate is more preferred.
  • the fatty acid magnesium salt has a straight-chain fatty acid group, and the fatty acid chain bonded to the magnesium may be one or two, although two is preferred.
  • Specific examples of fatty acid magnesium salts include magnesium salts of straight-chain saturated fatty acids such as magnesium laurate, magnesium myristate, magnesium palmitate, magnesium stearate, and magnesium behenate; and magnesium salts of straight-chain unsaturated fatty acids such as magnesium oleate.
  • magnesium salts of straight-chain saturated fatty acids are preferred, and magnesium stearate is more preferred.
  • the electret of the present invention preferably has a total content of polypropylene, poly-4-methyl-1-pentene, nitrogen-containing compound, and fatty acid metal salt of 95% by mass or more, more preferably 98% by mass or more, even more preferably 99% by mass or more, particularly preferably 99.5% by mass or more, and most preferably 100% by mass.
  • the electret of the present invention can be used in any desired shape, but the electret function can be utilized, for example, as a fibrous material, film, extrusion molding material, porous membrane, powder, or surface coating layer on other materials. Of these, fibrous materials (fiber sheets) are particularly preferred when the electret is used for filtering purposes.
  • the above-mentioned fibrous material is preferably a fiber assembly, and examples of the fiber assembly include nonwoven fabrics, woven and knitted fabrics, cotton-like materials, and other fibrous materials made from long or short fibers, as well as fibrous materials obtained from stretched films.
  • a fiber assembly is one that is recognized to have a fibrous form when the surface of the electret is observed using a scanning electron microscope, optical microscope, or other device, and in which at least some of the fibers that make up the fiber assembly are integrated together by melting or entangling with each other.
  • Nonwoven fabrics can be obtained by any conventional method, including sheeting short fibers such as single-component fibers, composite fibers such as core-sheath fibers or side-by-side fibers, or split fibers using carding, airlaid, or wet papermaking methods, or sheeting continuous fibers using the spunbond, meltblown, electrospinning, or force spinning methods.
  • Nonwoven fabrics obtained by the spunbond, meltblown, melt electrospinning, or melt force spinning methods are more preferred, as they do not require treatment of residual solvents or spinning oils adhering to the surface, and nonwoven fabrics obtained by the spunbond or meltblown methods are particularly preferred.
  • melt extrusion in the range of 150°C to 350°C, more preferably in the range of 170°C to 330°C, even more preferably in the range of 200°C to 310°C, and most preferably in the range of 230°C to 300°C.
  • melt extrusion in the range of 150°C to 350°C, more preferably in the range of 170°C to 330°C, even more preferably in the range of 200°C to 310°C, and most preferably in the range of 230°C to 300°C.
  • the average diameter of the fibers making up the fiber assembly is preferably 0.001 to 100 ⁇ m, more preferably 0.05 to 50 ⁇ m, even more preferably 0.1 to 30 ⁇ m, particularly preferably 0.3 to 25 ⁇ m, and most preferably 0.5 to 20 ⁇ m. If the average fiber diameter is thicker than 100 ⁇ m, it is difficult to achieve practical collection efficiency, and the efficiency drops significantly when the charge decays. If the average fiber diameter is thinner than 0.001 ⁇ m, it may be difficult to obtain a charged electret.
  • the average fiber diameter can be calculated, for example, by using a scanning electron microscope to measure the diameters of 50 fibers in the same field of view, ensuring no fibers overlap, and then taking the geometric mean.
  • a fiber aggregate may be composed of a single fiber made from a single manufacturing method or material, or it may be composed of two or more types of fibers that differ in manufacturing method, material, or average diameter.
  • the electretization method used in the present invention is not particularly limited as long as it provides the desired properties when the electret is used, but a method of contacting or impacting a liquid (liquid contact charging method) is preferred, as this method can produce electrets with excellent filtration properties. More specifically, a method of contacting or impacting a liquid with a fiber aggregate or the like prior to electretization by suction, pressure, spraying, or other methods is preferred.
  • the liquid that is brought into contact or collision is not particularly limited as long as it can achieve the desired characteristics, but water is preferable in terms of ease of handling and performance.
  • a liquid in which a secondary component (a component other than water) has been added to water may also be used instead of water, and the conductivity and pH of the liquid can be adjusted by the type and amount of the secondary component added.
  • the liquid that is brought into contact or collision in the liquid contact charging method preferably has a pH of 1 to 11, more preferably a pH of 3 to 9, and even more preferably a pH of 5 to 7. Furthermore, the liquid that is brought into contact or collision in the liquid contact charging method preferably has a conductivity of 100 ⁇ S/cm or less, more preferably 10 ⁇ S/cm or less, and even more preferably 3 ⁇ S/cm or less.
  • the QF value which is the quality factor of the filter medium
  • the QF value is, for example, 0.1 mmAq -1 or more, preferably 0.11 mmAq -1 or more , more preferably 0.12 mmAq -1 or more, even more preferably 0.13 mmAq -1 or more, particularly preferably 0.14 mmAq -1 or more, and most preferably 1.0 mmAq -1 or more.
  • the QF value exceeds the above-mentioned value for an electret filter having an average fiber diameter of 0.5 to 5 ⁇ m produced by the meltblown method.
  • the QF value in this specification is calculated based on the airflow resistance when air is passed through the filter thickness direction at a wind speed of 10 cm/s and the number count value in the particle size range of 0.3 to 0.5 ⁇ m using a laser particle counter.
  • the particle collection efficiency at a wind speed of 10 cm/s can be adjusted in various ways depending on the required characteristics, but is preferably 50% or more, more preferably 70% or more, even more preferably 90% or more, and most preferably 95% or more.
  • the particle collection efficiency is calculated based on the number of particles in the 0.3-0.5 ⁇ m particle size range counted by a laser particle counter before and after passing through the filter when air is passed through the filter in the thickness direction at a wind speed of 10 cm/s.
  • the airflow resistance at a wind speed of 10 cm/s is preferably in the range of 0.05 to 50 mmAq, more preferably 0.2 to 30 mmAq, and most preferably 0.5 to 20 mmAq. If the airflow resistance is too small, the filter performance will be insufficient, and if the airflow resistance is too large, the advantages of the filter will be lost.
  • the above filter media quality factor (QF) value is generally 0.1 or less when using a non-electret fiber aggregate, and for filter applications it is preferably 0.5 or more, more preferably 1.0 or more, even more preferably 1.1 or more, and most preferably 1.2 or more.
  • the liquid contact charging method using water involves a heat drying process, and filter applications involve a pleating process or long-term storage. Therefore, it is preferable that the above filter media quality factor (QF) be maintained not only immediately after electretization, but also after heat treatment and ultra-basic storage.
  • the charge stability of the electret is evaluated by the TSC (thermally stimulated current) method.
  • the method is as follows. (1) A sheet-like fiber assembly is charged in an electric field to form an electret. (2) Electrodes are brought into contact with both surfaces of the electret so that they face each other. (3) Connect high-impedance picoammeters to the electrodes on both surfaces. (4) After placing the test piece in a heating bath at 30°C or less and short-circuiting it, the test piece is heated from 25°C to 180°C at a rate of 5°C/min. (5) The horizontal axis represents the electrode temperature and the vertical axis represents the current value. This allows the charge transfer characteristics at each temperature to be measured.
  • the TSC method includes both contact and non-contact methods.
  • the contact method is used from the viewpoints of sensitivity and stable evaluation results obtained by performing a short-circuit operation before heating.
  • the depolarization temperature in the TSC method is related to the charge stability of the electret and its performance stability as a filter (see, for example, Bulletin of Osaka Institute of Technology, 66(1), 1-18, and Patent No. 3199947).
  • the present inventors have also found that there is a correlation between the charge stability of electrets prepared by the corona charging method for use in the TSC method and electrets obtained by the liquid contact method.
  • corona discharge is used to unevenly distribute charge (quantity and polarity) in the thickness direction so that sufficient depolarization current can be observed in the TSC method.
  • the atmosphere and sample temperature during charging are below 30°C so as not to affect the measurement results in the TSC method. Because the corona discharge method used in this invention is not intended for surface treatments such as oxidation or etching, it is essential that the equipment and conditions used are those generally used in electret manufacturing and research.
  • measurement using the TSC method should begin within 10 minutes in an environment with an ambient temperature of 30°C or less. Materials that have been transported, stored, heated, or otherwise processed after electret production must be re-electretized using the method described above and then measured.
  • the purpose of evaluation using the TSC method in this invention is to evaluate the material's essential thermal charge stability and to eliminate the effects of changes in charge quantity due to various processes and the passage of time. In other words, even for fibrous materials, laminates, etc. that have been subjected to various histories (time, temperature, etc.), it is essential to evaluate them before thermal cleaning by separating the electret portion, charging it, and then performing TSC measurement. Paradoxically, electrets and electret filters with a high QF and the a/b ratio of this invention have excellent filtration properties and charge stability.
  • a/b (/ denotes division) is preferably 0.3 or less, more preferably 0.2 or less, and most preferably 0.1 or less. It is important to use reasonable values with continuity for the maximum current values shown above. This value should exclude momentary spikes due to noise and abnormal values due to short-circuit current, and should be determined as a reasonable value in light of the preceding and following values. The smaller the a/b value, the smaller the depolarization rate at temperatures below 100°C, resulting in smaller charge decay during the pleating process, transportation, and storage, resulting in electrets and electret filters with excellent practicality.
  • the depolarization charge amount is expressed as the a/b ratio, and it goes without saying that it is preferable for the depolarization charge amount during corona charging to be larger at higher temperatures.
  • the peak temperature and rise temperature showing the maximum value are preferably high, with the peak temperature being 135°C or higher, more preferably 140°C or higher, and most preferably 145°C or higher.
  • the rise temperature is preferably 80°C or higher, more preferably 90°C or higher, even more preferably 100°C or higher, and most preferably 110°C or higher.
  • the rise temperature can be calculated as the tangent to the measured values before and after the peak.
  • a low melting point is achieved, preventing oxidation, and it is also possible to raise the peak temperature normally associated with polypropylene.
  • the peak temperature corresponds to the activation energy and relaxation time, and a high peak temperature results in excellent charge stability and charge life.
  • the filter quality factor can be used as a parameter related to charge amount.
  • the natural logarithm ratio of transmittance before and after various treatments (referred to as performance maintenance rate in the present invention) can be used.
  • As particles artificially generated particles can be balanced charged, or atmospheric dust can be used.
  • As for the detector as long as it can limit the range of particle diameter, it can obtain either concentration or number.
  • electrostatic attraction it is preferable that electrostatic attraction is dominant.
  • the passing wind speed is 10 cm/s
  • the pressure difference before and after the sample is compared using a micro-differential pressure meter
  • the particle number concentration before and after the sample in the diameter range of 0.3 to 0.5 ⁇ m is compared using a laser particle counter, thereby calculating particle transmittance, particle collection efficiency, filter quality factor, and performance maintenance rate.
  • Particle transmittance [-] (particle number concentration downstream of sample) / (particle number concentration upstream of sample)
  • Particle collection efficiency [%] (1 - particle transmittance [-]) x 100
  • Filter quality factor QF [mmAq ⁇ 1 ] ⁇ (ln(particle permeability [ ⁇ ])/(airflow resistance [mmAq]))
  • Performance retention rate [-] ln (particle transmittance after treatment [-]) / ln (particle transmittance before treatment [-])
  • the above filter media quality factor (QF) value is generally 0.1 or less when using fibrous material that has not been electretized, and for filter applications it is preferably 0.5 or more, more preferably 1.0 or more, even more preferably 1.1 or more, and most preferably 1.2 or more.
  • the material may be subjected to a heat drying process, and in filter applications it may be subjected to a pleating process or long-term storage. Therefore, it is preferable that the above filter media quality factor (QF) be maintained not only immediately after electretization but also after heat treatment.
  • the electret of the present invention may be used in combination with other components as needed.
  • the electret of the present invention is used for filtering, it is preferable to use it in combination with, for example, a prefilter layer, a fiber protection layer, a reinforcing member, or a functional fiber layer.
  • Electret filters using the electret of the present invention are also included in the scope of the present invention.
  • pre-filter layers and fiber protection layers include spunbond nonwoven fabrics, thermal-bond nonwoven fabrics, and urethane foam.
  • reinforcing members include thermal-bond nonwoven fabrics and various nets.
  • functional fiber layers include antibacterial, antiviral, and colored fiber layers for identification and design purposes.
  • the electret of the present invention can be used in a wide range of applications.
  • it can be used effectively as a filter for protecting various devices, such as dust masks, dust clothing, various air conditioning elements, air purifiers, cabin filters, and other devices, for purposes such as protection, ventilation, stain resistance, and waterproofing.
  • Depolarization current measurement by TSC method Measurement was carried out using a thermally stimulated current measuring device under the following conditions: The measurement end point was set to 180°C in order to exclude the polymethylpentene peak present at 200°C or higher and to determine the peak temperature derived from polypropylene.
  • Corona charging Flat needle electrodes were arranged in a staggered pattern at 10 mm intervals, with a 0.5 mm thick silicone rubber sheet placed on the ground surface. The sample (fiber sheet) was charged and converted into an electret at a gap of 10 mm, an applied voltage of 20 kV, and a charging time of 30 seconds.
  • TSC electrodes A pair of circular electrodes (20 mm in diameter) were placed opposite each other with an electret sample (25 mm in diameter) sandwiched between them. The surfaces of both electrodes were in contact with the sample surface. Temperature conditions: 25°C to 180°C, increasing at 5°C/min. Other: After placing the sample between the electrodes, the electrodes were short-circuited to set the current value at zero.
  • the obtained data was plotted with the horizontal axis representing temperature (°C) and the vertical axis representing current value (-), and the maximum value (peak height) of the depolarized current between 50°C and 100°C was defined as a, and the maximum value (peak height) of the depolarized current between 100°C and 180°C was defined as b, to calculate the a/b value.
  • Example 1 90 parts by mass of polypropylene homopolymer, 10 parts by mass of poly-4-methyl-1-pentene resin (DX820, 4-methyl-1-pentene-decene-1 copolymer, manufactured by Mitsui Chemicals, Inc., MFR: 180 g/10 min (260 °C, 5 kg)), and 1 part by mass of nitrogen-containing compound (Chimassorb (registered trademark) 944LD, manufactured by BASF) were prepared and mixed in a blender. This mixture was spun using a meltblown machine to obtain a fiber sheet (both a fiber assembly and a nonwoven fabric) with a basis weight of 30 g/ m2 . The depolarization current of the obtained fiber sheet was measured using the TSC method described above. The TSC peak temperature was 153 °C, and the a/b value was 0.28.
  • DX820 4-methyl-1-pentene-decene-1 copolymer, manufactured by Mitsui Chemicals, Inc., MFR: 180 g/10
  • Example 2 95 parts by mass of polypropylene homopolymer, 5 parts by mass of poly-4-methyl-1-pentene resin (DX310, 4-methyl-1-pentene-hexadecene-octadecene copolymer, manufactured by Mitsui Chemicals, Inc., MFR: 100 g/10 min (260°C, 5 kg)), and 1 part by mass of nitrogen-containing compound (Chimassorb (registered trademark) 944LD, manufactured by BASF) were prepared and mixed in a blender. This mixture was spun using a meltblown machine to obtain a fiber sheet with a basis weight of 30 g/ m2 . The depolarization current of the obtained fiber sheet was measured using the TSC method described above. The TSC peak temperature was 148°C, and the a/b value was 0.38.
  • DX310 4-methyl-1-pentene-hexadecene-octadecene copolymer, manufactured by Mitsui Chemicals, Inc., MFR
  • Example 3 90 parts by mass of polypropylene homopolymer, 10 parts by mass of poly-4-methyl-1-pentene resin (DX820, manufactured by Mitsui Chemicals, Inc.), 1 part by mass of nitrogen-containing compound (Chimassorb (registered trademark) 944LD, manufactured by BASF), and 0.1 part by mass of magnesium stearate were prepared and mixed in a blender. This mixture was spun using a meltblown machine to obtain a fiber sheet with a basis weight of 30 g/ m2 . The depolarization current of the obtained fiber sheet was measured using the TSC method described above. The TSC peak temperature was 154°C, and the a/b value was 0.05.
  • Example 4 95 parts by mass of polypropylene homopolymer, 5 parts by mass of poly-4-methyl-1-pentene resin (DX310, manufactured by Mitsui Chemicals, Inc.), 1 part by mass of a nitrogen-containing compound (Chimassorb (registered trademark) 944LD, manufactured by BASF), and 0.1 parts by mass of magnesium stearate were prepared and mixed in a blender. This mixture was spun using a meltblown machine to obtain a fiber sheet with a basis weight of 30 g/ m2 . The depolarization current of the obtained fiber sheet was measured using the TSC method described above. The TSC peak temperature was 148°C, and the a/b value was 0.07.
  • Examples 1 and 3 and Examples 2 and 4 show that by adding magnesium stearate, it is possible to reduce depolarization below 100°C while maintaining a high TSC peak temperature, thereby further improving charge stability.
  • an electret and a filter having excellent charge stability can be obtained, which can greatly contribute to industry.
  • the electret of the present invention has excellent charge amount and charge density, and can be suitably used in particular for filters in dustproof clothing, dustproof masks, air purifiers, etc.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Textile Engineering (AREA)
  • Filtering Materials (AREA)

Abstract

L'invention concerne un électret ayant une stabilité de charge améliorée. Un électret selon la présente invention a une température de pic de 140 °C ou plus selon un procédé TSC après avoir été chargé dans un champ électrique. L'électret contient un composé contenant de l'azote, et dans 100 parties en masse de résine contenue dans l'électret, 80 à 99 parties en masse sont du polypropylène, et 1 à 20 parties en masse sont du poly-4-méthyl-1-pentène.
PCT/JP2025/006095 2024-02-28 2025-02-21 Électret et filtre à électret Pending WO2025182823A1 (fr)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2553054B2 (ja) * 1986-11-12 1996-11-13 東洋紡績株式会社 エレクトレツト化繊維およびその製造方法
JP2007092242A (ja) * 2005-09-29 2007-04-12 Japan Vilene Co Ltd エレクトレットシートの製造方法
JP2022098993A (ja) * 2020-12-22 2022-07-04 東洋紡株式会社 メルトブロー不織布及びエアフィルター
WO2023176922A1 (fr) * 2022-03-18 2023-09-21 ダイキン工業株式会社 Matériau électret, filtre et mélange maître
WO2023210759A1 (fr) * 2022-04-28 2023-11-02 東洋紡エムシー株式会社 Électret, et filtre à électrets

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2553054B2 (ja) * 1986-11-12 1996-11-13 東洋紡績株式会社 エレクトレツト化繊維およびその製造方法
JP2007092242A (ja) * 2005-09-29 2007-04-12 Japan Vilene Co Ltd エレクトレットシートの製造方法
JP2022098993A (ja) * 2020-12-22 2022-07-04 東洋紡株式会社 メルトブロー不織布及びエアフィルター
WO2023176922A1 (fr) * 2022-03-18 2023-09-21 ダイキン工業株式会社 Matériau électret, filtre et mélange maître
WO2023210759A1 (fr) * 2022-04-28 2023-11-02 東洋紡エムシー株式会社 Électret, et filtre à électrets

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