Nonwoven fabric sheets, electrets, and electret filters

Abstract

The present invention provides a nonwoven fabric sheet containing plant-derived raw materials, possessing high elongation and excellent pleating properties. [Solution] The nonwoven fabric sheet of the present invention has constituent fibers comprising a plant-derived polyethylene resin, a polypropylene resin, and a thermoplastic resin different from the plant-derived polyethylene resin and the polypropylene resin, the average fiber diameter of the constituent fibers being 2 to 10 μm, and the elongation of the nonwoven fabric sheet in the MD direction according to JIS L 1913 being 50% or more.

Description

Technical Field

[0001] The present invention relates to a nonwoven sheet, an electret, and a filter using these.

Background Art

[0002] Conventionally, polymers such as polytetrafluoroethylene, polypropylene, and polyvinylidene fluoride are known as electret materials. An electret is a material that can maintain and utilize electrostatic force without continuously applying external energy by variously operating various dielectric materials. Electrets are used in microphones, sensors, generators, various protection, and separation applications by utilizing the electrostatic force against the outside.

[0003] For example, filters using fibrous materials are widely used because they have a high porosity, long life, and low air permeability resistance. Filters made of these fibrous materials capture particles on the fibers by mechanical collection mechanisms such as sieving, diffusion, and inertial collision. However, it is known that when the aerodynamic equivalent diameter of the particles to be captured is about 0.1 to 1.0 μm in a practical use environment, the filter has a minimum collection efficiency. Therefore, an electret filter that utilizes the electrostatic attraction of an electret to compensate for this weakness is used.

[0004] Most of the raw materials for electret filters use polypropylene resin derived from fossil resources, and the carbon dioxide generated during incineration is causing global warming. In addition, there is also concern about the depletion of fossil resources. Therefore, it is required to replace it with plant-derived raw materials or reduce its usage amount. However, plant-derived raw materials for polypropylene resin are not commercially produced, and it is difficult to replace them with plant-derived raw materials.

[0005] Therefore, attempts have been made to use commercially produced plant-derived polyethylene resin, and a melt-blown nonwoven fabric and an electret material using a part of plant-derived polyethylene resin have been proposed (Patent Document 1). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Public Publication WO2024 / 048433 [Patent Document 2] Special Publication No. 2011-506628 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, the meltblown nonwoven fabric described in Patent Document 1 faces the challenge of being difficult to apply to pleated filters because it breaks easily when any external force, such as pleating, is applied.

[0008] Therefore, the present invention has been made in view of the above problems, and its object is to provide a nonwoven fabric sheet, an electret sheet, and an electret filter that have excellent pleating properties even when they contain plant-derived polyethylene resin. [Means for solving the problem]

[0009] The inventors of this invention have diligently studied and conducted research to solve the above problems, and have arrived at the present invention. The present invention is as follows.

[0010] 1. A nonwoven fabric sheet having constituent fibers comprising a plant-derived polyethylene resin, a polypropylene resin, and a thermoplastic resin different from the plant-derived polyethylene resin and the polypropylene resin, wherein the average fiber diameter of the constituent fibers is 2 to 10 μm, and the nonwoven fabric sheet has an elongation in the MD direction of 50% or more in accordance with JIS L 1913. 2. The nonwoven fabric sheet according to item 1 above, wherein the constituent fibers further contain a nitrogen-containing compound and a fatty acid metal salt. 3. An electret sheet made by electretizing the nonwoven fabric sheet described in 1 or 2 above, wherein the filter media quality factor (QF) value is 1.3 or higher. 4. An electret filter having the electret sheet described in item 3 above. 5. A method for producing a nonwoven fabric sheet, comprising the steps of: melting and mixing a plant-derived polyethylene resin, a polypropylene resin, and a thermoplastic resin different from the plant-derived polyethylene resin and the polypropylene resin at 200°C or below to form pellets; and spinning the pellets at an extrusion temperature of 250°C or below to obtain a nonwoven fabric sheet. 6. A method for producing an electret sheet, comprising the steps of: melting and mixing a plant-derived polyethylene resin, a polypropylene resin, and a thermoplastic resin different from the plant-derived polyethylene resin and the polypropylene resin at 200°C or below and forming pellets; spinning the pellets at an extrusion temperature of 250°C or below to obtain a nonwoven fabric sheet; and electretizing the nonwoven fabric sheet. [Effects of the Invention]

[0011] The present invention provides nonwoven fabric sheets, electret sheets, and electret filters with high elongation, even when containing plant-derived polyethylene resin. Therefore, they are less likely to break even when external forces are applied during processing steps such as pleating. Due to their excellent processability, they can be made thinner. Furthermore, they are less likely to break even when used in combination with adsorbents such as activated carbon. Thus, filters and filter units with high strength and high collection efficiency can be provided. [Modes for carrying out the invention]

[0012] The present invention will be described in detail below, but the present invention is not limited to what is described below, and it is possible to implement it with appropriate modifications within the scope that is consistent with the spirit of the preceding and following, and all such modifications are included within the technical scope of the present invention.

[0013] The nonwoven fabric sheet of the present invention has constituent fibers comprising a plant-derived polyethylene resin, a polypropylene resin, and a thermoplastic resin different from the plant-derived polyethylene resin and the polypropylene resin.

[0014] The plant-derived polyethylene resin used in the present invention may contain 1 to 100% by mass of plant-derived polyethylene resin, more preferably 20 to 100% by mass, even more preferably 50 to 100% by mass, and most preferably 80 to 100% by mass. It is also preferable that it consists solely of plant-derived polyethylene. In the present invention, "plant-derived" means that it contains carbon derived from plant raw materials. In the case of a mixture with fossil raw materials, it can be calculated from the carbon ratio contained in the total polyethylene.

[0015] The plant-derived polyethylene resin of the present invention is a homopolymer of plant-derived ethylene derived from bioethanol obtained from plant raw materials, or a copolymer of said plant-derived ethylene with a small amount of other comonomers. Methods for producing plant-derived ethylene, plant-derived α-olefin, and plant-derived polyethylene resin are described in detail in, for example, Patent Document 2. Examples of commercially available plant-derived polyethylene resins include Green PE manufactured by Braskem SA.

[0016] The proportion of plant-derived polyethylene resin to 100% by mass of the nonwoven fabric sheet of the present invention is not particularly limited, but is preferably 10 to 98% by mass, more preferably 15 to 95% by mass, and even more preferably 20 to 90% by mass.

[0017] The polypropylene resin used in the present invention may be "derived from fossil raw materials", "derived from plants", or a mixture of both, and a composition advantageous from the viewpoints of availability and LCA can be selected. "Derived from fossil raw materials" means, as in the past, that the main component is a component obtained by thermally decomposing naphtha obtained from fossil raw materials represented by petroleum, coal, natural gas, etc. "Derived from plants" is obtained from bio-propylene and bio-naphtha, similar to polyethylene. The polypropylene resin used in the present invention is any polypropylene resin suitable for the non-woven fabric sheet.

[0018] The ratio of the polypropylene resin to 100% by mass of the non-woven fabric sheet of the present invention is not particularly limited, but is preferably 2 to 90% by mass, more preferably 5 to 85% by mass, and even more preferably 10 to 80% by mass.

[0019] As the third thermoplastic resin different from the plant-derived polyethylene resin and polypropylene resin in the present invention, a thermoplastic resin capable of controlling the dispersion structure from the viewpoint of compatibility is preferable. Examples of such compounds include, for commercially available products, Dynaron (registered trademark) 6200P, Clayton (trademark) MD1648, etc. These are not particularly limited, and thermoplastic resins described in "Development, Evaluation, Recycling of Plastic Compatibilizers" (published by CMC) can also be preferably used. Furthermore, these thermoplastic resins may be used alone or in combination of two or more.

[0020] The ratio of the nitrogen-containing compound to 100% by mass of the non-woven fabric sheet of the present invention is preferably 0.1 to 5% by mass, more preferably 0.5 to 3% by mass, and even more preferably 0.75 to 1.5% by mass. When the content ratio of the nitrogen-containing compound is 0.1% by mass or more, when electretized, the charge amount increases and the deterioration of the filtration characteristics can be suppressed, and when it is 5% by mass or less, the hygroscopicity decreases and the charge stability improves.

[0021] The nitrogen-containing compound is not particularly limited as long as it provides the desired properties described above, but it is preferably a hindered amine compound containing at least one of a 2,2,6,6-tetramethylpiperidine structure and a triazine structure, and it is more preferably a hindered amine compound containing a 2,2,6,6-tetramethylpiperidine structure and a triazine structure.

[0022] 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}] (Kimasorb® 944LD, manufactured by BASF Japan), dimethyl-1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethyl-4-piperidine polycondensate (Tinuvin® 622LD, manufactured by BASF Japan), and 2-[[3,5-bis(1,1-dimethylethyl)-4-hydroxy Examples include phenylmethyl]-2-butylpropanediate bis[1,2,2,6,6-pentamethyl-4-piperidinyl] (Tinuvin® 144, manufactured by BASF Japan), dibutylamine 1,3,5-triazine·N,N-bis(2,2,6,6-tetramethyl-4-piperidyl)-1,6-hexamethylenediamine·N-(2,2,6,6-tetramethyl-4-piperidyl)butylamine polycondensate (Chimasorb® 2020FDL, manufactured by BASF Japan), and 2-(4,6-diphenyl-1,3,5-triazine-2-yl)-5-(hexyloxy)-phenol (Tinuvin® 1577FF, manufactured by BASF Japan). In particular, it is preferable that the compound contains a 2,2,6,6-tetramethylpiperidine structure and a triazine structure, and more preferably Kimasove® 944LD or Kimasove® 2020FD. One of the above compounds may be used alone as the hindered amine compound, or two or more may be used in combination.

[0023] The content ratio of fatty acid metal salts per 100% by mass of the nonwoven fabric sheet of the present invention is preferably 0.01 to 1.0% by mass, more preferably 0.025 to 0.5% by mass, and even more preferably 0.05 to 0.1% by mass. When the content ratio of fatty acid metal salts is 0.01% by mass or more, the thermal stability of the charge is improved, and the decrease in dust collection performance due to heat during processes such as pleating can be suppressed. Furthermore, when it is 1.0% by mass or less, a decrease in the filter material quality coefficient can be prevented.

[0024] The fatty acid group is not particularly limited, but it is preferably a straight-chain saturated fatty acid group, and the fatty acid group has 10 to 50 carbon atoms. Specifically, examples include lauric acid, myristic acid, palmitic acid, and stearic acid. Zinc, aluminum, and magnesium are preferred as metal elements.

[0025] The nonwoven fabric sheet of the present invention may contain other polymers, colorants, stabilizers, nucleating agents, and other compounding agents as needed, to the extent that it does not impair the objective of the present invention. Examples of components that may be optionally added include conventionally known antioxidants, heat-resistant stabilizers, weather-resistant stabilizers and other stabilizers, slip agents, antiblocking agents, antifogging agents, lubricants, dyes, pigments, natural oils, synthetic oils, and the like.

[0026] The average fiber diameter of the constituent fibers of the nonwoven fabric sheet of the present invention is preferably 2 to 10 μm. The above average fiber diameter is measured using a scanning electron microscope, measuring the fiber diameter of 100 fibers in each layer so that there is no overlap of fibers in the same field of view. If the average fiber diameter is thicker than 10 μm, it is difficult to obtain a practically high collection efficiency. Furthermore, if the average fiber diameter is thinner than 2 μm, productivity decreases significantly, making it practically difficult to manufacture.

[0027] The basis weight of the nonwoven fabric sheet of the present invention is 1 to 80 g / m². 2 It is preferable that the concentration be 5-60 g / m2, more preferably 10-50 g / m2. 2 It is even more preferable that the amount be 15-40 g / m². 2 It is particularly preferable that this be the case.

[0028] The thickness of the nonwoven fabric sheet of the present invention is preferably 0.10 to 1.00 mm, more preferably 0.15 to 0.80 mm, and even more preferably 0.20 to 0.60 mm.

[0029] The most important aspect of this invention is that the elongation of the nonwoven fabric sheet in the MD (machine direction) direction, in accordance with JIS L 1913, is 50% or more. More preferably, it is 80% or more, and even more preferably, 100% or more. In other words, by setting the elongation in the MD direction to the above, tearing is less likely to occur when the nonwoven fabric sheet is subjected to desired processing such as pleating. Furthermore, tearing can be suppressed when a laminate with an adsorbent such as activated carbon is pleated. If the elongation in the MD direction is less than 50%, there is a possibility of tearing when processing such as pleating is performed.

[0030] The nonwoven fabric sheet of the present invention is not particularly limited as long as the desired effect can be obtained, but it is preferable to nonwoven it by the meltblown method. As a specific method for obtaining the desired nonwoven fabric sheet by the meltblown method, it is preferable to adjust the fiber orientation and degree of fusion in a conventionally known meltblown method, and this can be done by adjusting the conveying speed, conveyor angle, collection distance, discharge amount, nozzle pitch, nozzle L / D, resin temperature, hot air temperature, hot air flow rate, etc.

[0031] The nonwoven fabric sheet of the present invention is formed by melting and mixing a plant-derived polyethylene resin, a polypropylene resin, and a thermoplastic resin different from the plant-derived polyethylene resin and the polypropylene resin in a twin-screw extruder at a melting temperature of 200°C or lower, and then pelletizing them. If the melting temperature is too high, thermal decomposition may cause a decrease in molecular weight, which may reduce the elongation of the nonwoven fabric sheet. Nitrogen-containing compounds and fatty acid metal salts having 10 to 50 carbon atoms may be added during the melting and mixing process, or during the formation of the nonwoven fabric sheet.

[0032] The pellets obtained by melting and mixing are melted again at an extrusion temperature of 250°C or lower and spun into a nonwoven sheet. If the extrusion temperature is too high when forming the nonwoven sheet, thermal decomposition may cause a decrease in molecular weight, potentially reducing the elongation of the nonwoven sheet. If the extrusion temperature is too low, it will be difficult to make the fibers fine. The extrusion temperature is the set temperature of the extruder, and the temperature after the extruder can be set arbitrarily.

[0033] When electretizing a nonwoven fabric sheet, a method of electrostatic treatment involving contact or impact with a liquid (liquid contact charging method) is preferred, and an electret sheet with high filtration characteristics can be obtained using the liquid contact charging method. More specifically, a method of contacting or impacting a fibrous material with a liquid by means of suction, pressurization, or ejection is preferred.

[0034] In the liquid contact charging method, the liquid to be contacted or impacted is not particularly limited as long as the desired properties can be obtained, but water is preferred in terms of handling and performance. A liquid obtained by adding a secondary component (a component other than water) to water may 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.

[0035] In the liquid contact charging method, the liquid to be contacted or impacted preferably has a pH of 1 to 11, more preferably 3 to 9, and even more preferably 5 to 7. Furthermore, the liquid to be contacted or impacted preferably has an electrical conductivity of 100 μS / cm or less, more preferably 10 μS / cm or less, and even more preferably 3 μS / cm or less.

[0036] The filter media quality factor (QF) value is an index that shows the relationship between collection efficiency and airflow resistance, and is expressed by the following formula. The electret sheet of the present invention has a QF value of 1.3 or higher, preferably 1.4 or higher, and more preferably 1.5 or higher. The higher the QF value, the higher the collection efficiency and the lower the airflow resistance, resulting in a high-performance filter. Electret sheets with a QF value of less than 1.3 have problems such as excessively low collection efficiency or excessively high airflow resistance. The QF value in this specification is calculated based on the airflow resistance when air is passed through in the thickness direction at an airflow velocity of 10.4 cm / s and the number of particles counted by a laser particle counter in the particle size category of 0.3 to 0.5 μm. QF value [mmAq] -1 ]=-[ln(1-(particle collection efficiency (%) / 100))] / [airflow resistance (mmAq)]

[0037] When the electret sheet of the present invention is used as a filter, the particle collection efficiency at a wind speed of 10.4 cm / s can be adjusted in various ways depending on the required characteristics, but it is preferably 50% or more, more preferably 70% or more, even more preferably 80% or more, and particularly preferably 90% or more. The particle collection efficiency described herein is calculated based on the number of particles in the particle size category of 0.3 to 0.5 μm measured 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 10.4 cm / s.

[0038] When the electret sheet of the present invention is used as a filter, the airflow resistance at a wind speed of 10.4 cm / s is preferably in the range of 0.05 to 50 mmAq, more preferably 0.2 to 30 mmAq, and particularly preferably 0.5 to 20 mmAq. If the airflow resistance is too low, the filter performance will be insufficient, and if the airflow resistance is too high, the advantages of the electret filter will be lost.

[0039] The electret sheet of the present invention may also be a filter consisting solely of the electret sheet, or a filter made by combining the electret sheet with other materials. The shape of the filter is not particularly limited and may be a sheet-like filter with a wavy shape such as pleating or corrugation, or a filter without such processing.

[0040] When the electret sheet of the present invention is used as a filter, it can be used in combination with other components as needed. That is, the electret filter of the present invention can be used in combination with a pre-filter layer, a fiber protection layer, a reinforcing member, a functional fiber layer, an adsorbent layer, and the like.

[0041] Examples of pre-filter layers and fiber protection layers include spunbond nonwoven fabric, thermal bond nonwoven fabric, and foamed urethane, while examples of reinforcing members include thermal bond nonwoven fabric and various types of nets. Functional fiber layers include antibacterial, antiviral, and colored fiber layers for identification and design purposes, while examples of adsorbent layers include activated carbon and silica gel.

[0042] The nonwoven fabric sheets, electret sheets, and electret filters of the present invention can be used in a wide range of applications. In particular, they can be suitably used as filters for protection of various devices, such as dust masks, dustproof clothing, various air conditioning elements, air purifiers, cabin filters, and other protective equipment, for purposes such as protection, breathability, stain resistance, and waterproofing. [Examples]

[0043] The present invention will be described in more detail below with reference to examples, but the present invention is not limited by the following examples, and it is certainly possible to implement it with appropriate modifications within the scope that is consistent with the spirit of the preceding and following descriptions, and all such modifications are included within the technical scope of the present invention.

[0044] First, let's look at each test method. (1) Air resistance A sample punched out to 72mmφ is attached to a 50mmφ effective airflow adapter, and a slight differential pressure is applied. Two pipes with an inner diameter of 50 mm, each connected to a meter, were linked vertically. Air was passed through the sample in the thickness direction at a wind speed of 10.4 cm / s, and the differential pressure between the top and bottom of the sample without any constriction was measured as the airflow resistance (pressure loss).

[0045] (2) Particle collection efficiency and particle transmission rate A sample punched to 72 mm in diameter was mounted in an adapter with an effective airflow diameter of 50 mm in diameter. Air was passed through the sample in the thickness direction at a wind speed of 10.4 cm / s, and the particle collection efficiency was measured using a light scattering particle counter KC-01E manufactured by Rion Co., Ltd. in the following manner. Particles evaluated: atmospheric dust particles Wind speed: 10.4cm / s Particle collection efficiency [%] = (1 - (Number concentration of particles with a particle size of 0.3 to 0.5 μm after sample transmission ÷ Number concentration of particles with a particle size of 0.3 to 0.5 μm before sample transmission)) × 100 Particle transmittance = (Number concentration of particles with a particle size of 0.3 to 0.5 μm after sample transmission ÷ Number concentration of particles with a particle size of 0.3 to 0.5 μm before sample transmission)

[0046] (3) Filter media quality factor (QF) value Using the values ​​of the air permeability resistance measured in (1) above and the particle transmittance measured in (2) above, the QF value was calculated using the following formula. QF[mmAq -1 ]=-[ln(1-(particle collection efficiency (%) / 100))] / [airflow resistance (mmAq)]

[0047] (4) Inspection Six samples were punched out to a diameter of 72 mm, and the weight of each sample was measured. The obtained values ​​were converted to a unit area, and the arithmetic mean of these values ​​was rounded to two decimal places.

[0048] (5) Thickness The thickness of each sample whose basis weight was measured was measured using a thickness gauge with a 7g load, and the arithmetic mean of these measurements was rounded to the third decimal place.

[0049] (6) Average fiber diameter Five arbitrary points were selected from the sample, and the diameter of a single fiber was measured at each point using an electron microscope (n=20). The average fiber diameter was then calculated using the arithmetic mean.

[0050] (7) Elongation in the MD direction In accordance with JIS L 1913 6.3, a sample measuring 50 mm in width and 200 mm in length was prepared. The sample was placed in the testing machine in the longitudinal direction, and four tensile tests were performed in the longitudinal direction (MD direction) of the sample under the conditions of a gripping distance of 150 mm and a tensile speed of 200 mm / min. After converting the displacement at fracture to elongation, the elongation in the MD direction was obtained by rounding the arithmetic mean of these values ​​to two decimal places.

[0051] (8) Pleating properties Reinforcement material (wet-laid non-woven fabric, 30g / m 2 ) on top of activated carbon particles (average particle size 200 μm, 500 g / m²) 2 ) and polyethylene powder (average particle size 20 μm, 30 g / m²) 2 After spraying the material and then laminating fiber sheets, the material was held at 110°C under a load of 4.5 kg for 1 minute to obtain an activated carbon sheet. The obtained activated carbon sheet was pleated using a pleating machine and judged according to the following criteria. ○: There are no tears or other damage to the non-woven fabric sheet; it is in good condition. △: Some non-woven fabric sheets are torn and cannot be used as a product. ×: The non-woven fabric sheet is completely torn and cannot be pleated.

[0052] <Example 1> The raw materials used were 30% by mass of plant-derived high-density polyethylene resin (biomass content 90% or more) with a melt flow rate (MFR) of 20 g / 10 min, 64.925% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 200 g / 10 min, 3% by mass of DYNARON® 6200P, 1% by mass of Chimassorb® 944, 0.075% by mass of magnesium stearate, and 1% by mass of SumiLizer® GP. The raw materials were melted and mixed in a twin-screw extruder at a molten resin temperature of 192°C and pelletized. The obtained pellets were melt-spun using a melt-blown apparatus with an extrusion temperature of 240°C, a die temperature of 280°C, and adjusted hot air volume to obtain a nonwoven fabric sheet with an average fiber diameter of 7.1 μm. The obtained nonwoven fabric sheet was charged by passing water with an electrical conductivity of 0.7 μS / cm and a pH of 6.8 from the surface to the back, and then air-dried at 25°C to obtain an electret sheet.

[0053] <Example 2> Melt spinning was performed in the same manner as in Example 1, except that the hot air volume was adjusted, to obtain a nonwoven fabric sheet and an electret with an average fiber diameter of 4.6 μm.

[0054] <Example 3> Melt spinning was performed in the same manner as in Example 1, except that the die temperature was 290°C and the hot air volume was adjusted, to obtain a nonwoven fabric sheet and an electroret sheet with an average fiber diameter of 3.6 μm.

[0055] <Example 4> The raw materials used were 50% by mass of plant-derived high-density polyethylene resin (biomass content 90% or more) with a melt flow rate (MFR) of 20 g / 10 min, 44.925% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 200 g / 10 min, 3% by mass of DYNARON® 6200P, 1% by mass of Chimassorb® 944, 0.075% by mass of magnesium stearate, and 1% by mass of SumiLizer® GP. Nonwoven fabric sheets and electret sheets with an average fiber diameter of 5.1 μm were obtained in the same manner as in Example 1, except for the raw materials.

[0056] <Example 5> As raw materials, 30% by mass of plant-derived high-density polyethylene resin (biomass content 90% or more) with a melt flow rate (MFR) of 20 g / 10 min, 66.425% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 200 g / 10 min, 1.5% by mass of Kraton® MD1648, 1% by mass of Chimassorb® 944, 0.075% by mass of magnesium stearate, and 1% by mass of SumiLizer® GP were used. Nonwoven fabric sheets and electret sheets with an average fiber diameter of 6.3 μm were obtained in the same manner as in Example 1, except for the raw materials.

[0057] <Example 6> Melt spinning was performed in the same manner as in Example 5, except that the hot air volume was adjusted, to obtain a nonwoven fabric sheet and an electroret sheet with an average fiber diameter of 4.4 μm.

[0058] <Example 7> Melt spinning was performed in the same manner as in Example 6, except that the die temperature was 290°C and the hot air volume was adjusted, to obtain a nonwoven fabric sheet and an electroret sheet with an average fiber diameter of 3.4 μm.

[0059] <Comparative Example 1> The raw materials used were 30% by mass of plant-derived high-density polyethylene resin (biomass content 90% or more) with a melt flow rate (MFR) of 20 g / 10 min, 64.925% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 200 g / 10 min, 3% by mass of DYNARON® 6200P, 1% by mass of Chimassorb® 944, 0.075% by mass of magnesium stearate, and 1% by mass of SumiLizer® GP. The raw materials were melted and mixed in a twin-screw extruder at a molten resin temperature of 192°C and pelletized. The obtained pellets were melt-spun using a melt-blown apparatus with an extrusion temperature of 260°C, a die temperature of 295°C, and adjusted hot air volume to obtain a nonwoven fabric sheet with an average fiber diameter of 7.1 μm. The obtained nonwoven fabric sheet was charged by passing water with an electrical conductivity of 0.7 μS / cm and a pH of 6.8 from the surface to the back, and then air-dried at 25°C to obtain an electret sheet.

[0060] <Comparative Example 2> Melt spinning was performed in the same manner as in Comparative Example 1, except that the hot air volume was adjusted, to obtain a nonwoven fabric sheet and an electroret sheet with an average fiber diameter of 4.6 μm.

[0061] <Example 3> Melt spinning was performed in the same manner as in Comparative Example 1, except that the hot air volume was adjusted, to obtain a nonwoven fabric sheet and an electroret sheet with an average fiber diameter of 3.3 μm.

[0062] <Comparative Example 4> As raw materials, 50% by mass of plant-derived high-density polyethylene resin (biomass content 90% or more) with a melt flow rate (MFR) of 20 g / 10 min, 44.925% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 200 g / 10 min, 3% by mass of DYNARON® 6200P, 1% by mass of Chimassorb® 944, 0.075% by mass of magnesium stearate, and 1% by mass of SumiLizer® GP were used. Nonwoven fabric sheets and electret sheets with an average fiber diameter of 5.8 μm were obtained in the same manner as in Comparative Example 1, except for the raw materials.

[0063] <Comparative Example 5> As raw materials, 30% by mass of plant-derived high-density polyethylene resin (biomass content 90% or more) with a melt flow rate (MFR) of 20 g / 10 min, 66.425% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 200 g / 10 min, 1.5% by mass of Kraton® MD1648, 1% by mass of Chimassorb® 944, 0.075% by mass of magnesium stearate, and 1% by mass of SumiLizer® GP were used. Nonwoven fabric sheets and electret sheets with an average fiber diameter of 3.6 μm were obtained in the same manner as in Comparative Example 1, except for the raw materials.

[0064] <Comparative Example 6> Melt spinning was performed in the same manner as in Comparative Example 5, except that the hot air volume was adjusted, to obtain a nonwoven fabric sheet and an electroret sheet with an average fiber diameter of 2.7 μm.

[0065] <Comparative Example 7> As raw materials, 30% by mass of plant-derived high-density polyethylene resin (biomass content 90% or more) with a melt flow rate (MFR) of 20 g / 10 min, 64.925% by mass of petroleum-derived polypropylene resin with a melt flow rate (MFR) of 60 g / 10 min, 3% by mass of DYNARON® 6200P, 1% by mass of Chimassorb® 944, 0.075% by mass of magnesium stearate, and 1% by mass of SumiLizer® GP were used. The raw materials were melted and mixed in a twin-screw extruder at a molten resin temperature of 168°C and pelletized. The obtained pellets were melt-spun using a melt-blown apparatus with an extrusion temperature of 280°C, a die temperature of 310°C, and adjusted hot air volume to obtain nonwoven fabric sheets and electret sheets with an average fiber diameter of 6.3 μm.

[0066] The electret sheets obtained in Examples 1-7 and Comparative Examples 1-7 were subjected to the measurements described in (1)-(8) above. The measured values ​​for Examples 1-7 are shown in Table 1, and the measured values ​​for Comparative Examples 1-7 are shown in Table 2.

[0067] [Table 1]

[0068] [Table 2]

[0069] As can be seen from Tables 1 and 2, Examples 1-7 have higher elongation of the nonwoven fabric sheets and better pleating properties compared to Comparative Examples 1-7. They also have higher QF values ​​and superior filter performance. [Industrial applicability]

[0070] The nonwoven fabric sheets, electrets, and electret filters of the present invention possess high elongation and high collection efficiency, making them suitable for use as filters in applications such as dustproof clothing, dustproof masks, and air purifiers, and thus making a significant contribution to industry. Furthermore, since they use plant-derived raw materials, they also contribute to reducing environmental impact. However, their range of applications is not limited to those described herein.

Claims

1. A nonwoven fabric sheet having constituent fibers comprising a plant-derived polyethylene resin, a polypropylene resin, and a thermoplastic resin different from the plant-derived polyethylene resin and the polypropylene resin, The average fiber diameter of the constituent fibers is 2 to 10 μm. A nonwoven fabric sheet having an elongation in the MD direction of 50% or more, in accordance with JIS L 1913.

2. The nonwoven fabric sheet according to claim 1, wherein the constituent fibers further comprise a nitrogen-containing compound and a fatty acid metal salt.

3. An electret sheet made by electretizing a nonwoven fabric sheet as described in claim 1 or 2, wherein the filter media quality factor (QF) value is 1.3 or higher.

4. An electret filter having the electret sheet described in claim 3.

5. A process of melting and mixing a plant-derived polyethylene resin, a polypropylene resin, and a thermoplastic resin different from the plant-derived polyethylene resin and the polypropylene resin at 200°C or below, and then forming them into pellets. A method for producing a nonwoven fabric sheet, comprising the step of spinning the pellets at an extrusion temperature of 250°C or lower to obtain a nonwoven fabric sheet.

6. A process of melting and mixing a plant-derived polyethylene resin, a polypropylene resin, and a thermoplastic resin different from the plant-derived polyethylene resin and the polypropylene resin at 200°C or below, and then forming them into pellets. The process of spinning the aforementioned pellets at an extrusion temperature of 250°C or lower to obtain a nonwoven fabric sheet, A method for producing an electret sheet, comprising the step of electretizing the nonwoven fabric sheet.

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