Triboelectrified nonwoven fabric and filter medium having triboelectrified nonwoven fabric

Abstract

To provide a triboelectrified nonwoven fabric excellent in filtering performance.SOLUTION: The applicant found that a triboelectrified nonwoven fabric excellent in filtering performance can be provided by adjusting strength per fineness (unit: cN / dtex) of one type of triboelectrified fiber so as to be optimal, when it is assumed that the triboelectrified fiber constituting the triboelectrified nonwoven fabric is one type, as a result of further examination. Specifically, calculated value y of computation formula according to the invention expresses the strength per fineness (unit: cN / dtex) of the one type of triboelectrified fiber. It was found that the triboelectified nonwoven fabric in which the calculated value y is adjusted so as to be larger than 3.70 cN / dtex and less than 5.66 cN / dtex is the triboelectified nonwoven fabric excellent in filtering performance.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a triboelectric nonwoven fabric that can be used as a filter medium, and a filter medium provided with the triboelectric nonwoven fabric.

Background Art

[0002] Conventionally, air filters and masks have been required to have performance such as low pressure loss, excellent air permeability, and excellent collection efficiency for dust such as atmospheric dust and PM2.5 and pollen. In order to realize an air filter or a mask that satisfies both of these conflicting performances and has excellent filtration performance, it has been considered to provide an air filter or a mask using a filter medium provided with a charged triboelectric nonwoven fabric (hereinafter sometimes abbreviated as triboelectric nonwoven fabric).

[0003] As an example, International Publication No. 2021 / 241367 (Patent Document 1) discloses a triboelectric nonwoven fabric in which first fibers and second fibers made of different constituent resins and capable of being charged by rubbing against each other are mixed, and the first fibers and the second fibers are charged. As a specific example, in the examples of Patent Document 1, polypropylene fibers are used as the first fibers and acrylic fibers are used as the second fibers, and these fibers are mixed and rubbed against each other by feeding them to devices such as a carding machine and a needle punching machine to prepare a triboelectric nonwoven fabric in which the first fibers and the second fibers are triboelectrically charged.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In order to provide a frictionally charged nonwoven fabric with improved filtration performance, the applicant of the present application studied the prior art as disclosed in Patent Document 1 described above. However, the frictionally charged nonwoven fabric prepared based on the findings disclosed by the prior art was not necessarily excellent in its filtration performance. Specifically, it was not possible to provide a frictionally charged nonwoven fabric having excellent filtration performance, which has a high dust collection efficiency due to a high charge amount, and which can suppress a decrease in the dust collection efficiency even when the charge amount decreases as dust collection progresses because of its excellent mechanical collection ability.

[0006] Therefore, there has been a demand for providing a frictionally charged nonwoven fabric having excellent filtration performance.

Means for Solving the Problems

[0007] The first aspect of the present invention is "A frictionally charged nonwoven fabric in which first fibers and second fibers, which are made of different constituent resins and can be charged by rubbing against each other, are mixed, and the first fibers and the second fibers are charged, and The frictionally charged nonwoven fabric has a calculated value y of the following calculation formula greater than 3.70 cN / dtex and less than 5.66 cN / dtex. Record y = (a1 × a2 + b1 × b2) / 100 a1: Strength per fineness of the first fiber (unit: cN / dtex) b1: Strength per fineness of the second fiber (unit: cN / dtex) a2: Mass percentage of the first fiber in the sum of the masses of the first fiber and the second fiber b2: Mass percentage of the second fiber in the sum of the masses of the first fiber and the second fiber." is. Further, the second aspect of the present invention is "The frictionally charged nonwoven fabric according to claim 1, wherein the first fiber is a polyolefin-based resin fiber having a strength per fineness higher than 4.40 cN / dtex." is. And the third aspect of the present invention is "A filter medium comprising the triboelectric nonwoven fabric according to any one of claims 1 or 2." It is.

Advantages of the Invention

[0008] As a result of continuous study, the applicant of the present application obtained the following findings.

[0009] In order to prepare a triboelectric nonwoven fabric, it is necessary to blend the first fiber and the second fiber (hereinafter, the first fiber and the second fiber may be collectively referred to as "triboelectric fibers") and supply them to a device such as a carding machine or a needle punching machine, so as to open the fibers and rub the triboelectric fibers against each other.

[0010] At this time, if it is assumed that one type of highly rigid triboelectric fiber is supplied to a device such as a carding machine or a needle punching machine, since the highly rigid triboelectric fiber has a rigid and difficult-to-entangle property, it is difficult for the triboelectric fibers to aggregate with each other, and it is easy to prepare a triboelectric nonwoven fabric in which the constituent fibers are uniformly dispersed. As a result, it is possible to provide a triboelectric nonwoven fabric in which the constituent fibers are uniformly distributed throughout the triboelectric nonwoven fabric, and the physical properties such as strength and pore size are uniform and the mechanical collection ability is excellent. However, since the highly rigid triboelectric fiber has a rigid and difficult-to-entangle property, it is difficult for the triboelectric fibers to rub against each other, and it is difficult to provide a triboelectric nonwoven fabric rich in charge amount.

[0011] On the other hand, if it is assumed that one type of low-rigidity triboelectric fiber is supplied to a device such as a carding machine or a needle punching machine, since the low-rigidity triboelectric fiber has a flexible and easy-to-entangle property, it is easy for the triboelectric fibers to rub against each other, and it is possible to provide a triboelectric nonwoven fabric rich in charge amount. However, since the low-rigidity triboelectric fiber has a flexible and easy-to-entangle property, it is easy for the triboelectric fibers to aggregate with each other, and it is difficult to prepare a triboelectric nonwoven fabric in which the constituent fibers are uniformly dispersed. As a result, it is difficult to provide a triboelectric nonwoven fabric in which the constituent fibers are uniformly distributed throughout the triboelectric nonwoven fabric, and the physical properties such as strength and pore size are uniform and the mechanical collection ability is excellent.

[0012] That is, in order to provide a triboelectric nonwoven fabric with excellent filtration performance, which has a high dust collection efficiency due to its rich charge amount and can suppress the decrease in dust collection efficiency due to its excellent mechanical dust collection ability, it is considered necessary that the triboelectric nonwoven fabric is composed of triboelectric fibers having an optimal rigidity.

[0013] As a result of further research by the applicant of the present application, it has been found that by adjusting the strength per fineness (unit: cN / dtex) of the single type of triboelectric fiber when assuming that the triboelectric nonwoven fabric is composed of a single type of triboelectric fiber to an optimal value, a triboelectric nonwoven fabric with excellent filtration performance can be provided.

[0014] Specifically, the calculated value y of the following calculation formula represents the strength per fineness (unit: cN / dtex) of the single type of triboelectric fiber, and it has been found that a triboelectric nonwoven fabric in which the calculated value y is adjusted to be greater than 3.70 cN / dtex and less than 5.66 cN / dtex is a triboelectric nonwoven fabric with excellent filtration performance. Note y=(a1×a2 + b1×b2) / 100 a1: Strength per fineness of the first fiber (unit: cN / dtex) b1: Strength per fineness of the second fiber (unit: cN / dtex) a2: Mass percentage of the first fiber in the sum of the masses of the first fiber and the second fiber b2: Mass percentage of the second fiber in the sum of the masses of the first fiber and the second fiber. Therefore, the present invention can provide a triboelectric nonwoven fabric with excellent filtration performance.

[0015] In addition, by providing a polyolefin resin fiber having a strength per fineness higher than 4.40 cN / dtex as the first fiber, a triboelectric nonwoven fabric with excellent filtration performance can be provided.

[0016] From the above, by using the triboelectric nonwoven fabric according to the present invention, a filter medium with excellent filtration performance can be provided.

Best Mode for Carrying Out the Invention

[0017] In the present invention, various configurations can be appropriately selected, such as the following configurations. Note that various measurements described in the present invention are carried out under the condition of a temperature of 25 °C under normal pressure unless otherwise specified or defined. And, unless otherwise specified or defined, various measurement results described in the present invention are measured up to a value one digit smaller than the required value, and the required value is calculated by rounding off the obtained value. As a specific example, when the value up to the first decimal place is the required value, the value up to the second decimal place is obtained by measurement, and the value up to the first decimal place is calculated by rounding off the obtained value of the second decimal place, and this value is taken as the required value. Also, each upper limit value and each lower limit value exemplified in the present invention can be arbitrarily combined.

[0018] In the triboelectric nonwoven fabric according to the present invention, first fibers and second fibers having different constituent resins and capable of being charged by rubbing against each other are mixed. The phrase "first fibers and second fibers having different constituent resins and capable of being charged by rubbing against each other" as used herein means · Two or more types of fibers are mixed in the triboelectric nonwoven fabric, and in the two or more types of fibers, the constituent resin on the surface (excluding both ends) of the first fiber of the first type is different from the constituent resin on the surface (excluding both ends) of the second fiber of the second type, and · A combination of the first fiber and the second fiber in which the rubbed fiber surface portions are charged by rubbing the surfaces of the first fiber and the second fiber against each other, · The first fiber and the second fiber are in contact with each other and exist together, is meant.

[0019] Also, the first fiber and the second fiber are charged by rubbing the surface portions of the fibers against each other.

[0020] The types of triboelectric fibers can be appropriately selected as long as they are combinations of fibers that become charged by rubbing against each other. As combinations of the first fiber and the second fiber, for example, combinations of polyolefin fibers and acrylic fibers; combinations of fluorine-based fibers and polyamide fibers, wool, glass fibers, silk, or rayon fibers; combinations of urethane-based fibers and polyamide fibers, wool, glass fibers, silk, or rayon fibers; combinations of vinyl chloride-based fibers and polyamide fibers, wool, glass fibers, silk, or rayon fibers; combinations of polyolefin fibers and polyamide fibers, wool, glass fibers, silk, or rayon fibers; combinations of acrylic fibers and polyamide fibers, wool, glass fibers, silk, or rayon fibers; combinations of vinylon fibers and polyamide fibers, wool, glass fibers, silk, or rayon fibers; combinations of polyester fibers and polyamide fibers, wool, glass fibers, silk, or rayon fibers; combinations of acetate fibers and polyamide fibers, wool, glass fibers, silk, or rayon fibers; combinations of polyolefin fibers and polyester fibers, etc. can be mentioned.

[0021] Among these, when it is a combination of polyolefin fibers and acrylic fibers, it is possible to increase the charge amount by rubbing the triboelectric fibers against each other, and it is preferable because it is possible to realize a triboelectric nonwoven fabric that can provide an air filter or a mask with excellent collection efficiency.

[0022] Examples of the constituent resin of the polyolefin fiber include, for example, polypropylene resin, polyethylene resin, polystyrene resin, vinyl acetate copolymer resin with these resins, ethylene-propylene copolymer, or resins in which a part of these resins is substituted with a nitrile group, a cyano group, or a halogen. The polyolefin fiber can be composed of one type or two or more types of these constituent resins. For example, it may be a core-sheath type composite fiber in which the sheath component is made of a polyolefin resin.

[0023] In addition, the constituent resin of the polyolefin fiber (especially the resin constituting the surface of the polyolefin fiber) preferably contains a phosphorus-based additive or a sulfur-based additive. By containing a phosphorus-based additive or a sulfur-based additive, it is possible to realize a frictionally charged nonwoven fabric with a large charge amount, which is preferable. Note that if the total amount of these additives increases, the spinnability may deteriorate. Therefore, the total amount of the additives is preferably 5% by mass or less of the polyolefin fiber, more preferably 2% by mass or less, and even more preferably 1% by mass or less.

[0024] Examples of the phosphorus-based additive include phosphorus-based antioxidants such as tris(nonylphenyl) phosphite, tris(2,4-di-t-butylphenyl) phosphite, distearyl pentaerythritol diphosphite, bis(2,4-di-t-butylphenyl) pentaerythritol phosphite, bis(2,6-di-t-butyl-4-methylphenyl) pentaerythritol phosphite, 2,2-methylenebis(4,6-di-t-butylphenyl) octyl phosphite, tetrakis(2,4-di-t-butylphenyl)-4,4'-biphenylene-di-phosphonite, bis(2,4-bis(1,1-dimethylethyl)-6-methylphenyl) ethyl ester phosphite, tetrakis(2,4-di-t-butylphenyl)(1,1-biphenyl)-4,4'-diyl bisphosphonite, bis(bis(2,4-di-t-butyl-5-methylphenoxy) phosphino).

[0025] This phosphorus-based additive is preferably contained in the polyolefin fiber in an amount of 0.01% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.3% by mass or more, and even more preferably 0.6% by mass or more.

[0026] As sulfur-based additives, sulfur-based antioxidants such as dilauryl-3,3'-thiodipropionate, dimyristyl-3,3'-thiodipropionate, distearyl-3,3'-thiodipropionate, and pentaerythritol tetrakis can be preferably used. It is preferable that this sulfur-based additive is contained in the polyolefin-based fiber in an amount of 0.01% by mass or more, and more preferably 0.1% by mass or more.

[0027] As acrylic fibers, either polyacrylonitrile-based fibers having acrylonitrile as the main component (85% or more) or modacrylic fibers containing 35% or more and less than 85% of acrylonitrile can be used. In addition, there are two types of acrylic fibers: those spun using an organic solvent and those spun using an inorganic solvent, and any of them may be used. In particular, by adopting acrylic fibers spun using an organic solvent, a triboelectric nonwoven fabric with a large charge amount can be realized, which is preferable. Many of the acrylic fibers spun using an organic solvent have constricted portions on the fiber surface, and their fiber cross-sections are non-circular and have a deformed cross-section. Therefore, having such a deformed cross-section is considered to act advantageously on the charged state after triboelectrification and the like.

[0028] The triboelectric fiber can be obtained by known methods such as, for example, the melt spinning method, the dry spinning method, the wet spinning method, the direct spinning method (melt blowing method, spunbond method, electrospinning method, etc.), a method of extracting fibers with a small fiber diameter by removing one or more resin components from composite fibers, and a method of obtaining fibers by beating and splitting fibers.

[0029] The fiber length of the triboelectric fiber is not particularly limited as long as the object of the present invention can be achieved. It may be a fiber cut to a specific length such as a short fiber, or a fiber having a continuous length that has not been cut to a specific length and is manufactured by a direct spinning method (continuous fiber). However, by adopting short-fiber triboelectric fibers, it is easy to provide a triboelectric nonwoven fabric in which the triboelectric fibers are uniformly distributed. As a result, it is preferable because a triboelectric nonwoven fabric having uniform physical properties such as strength and pore size and excellent mechanical collection ability can be provided. Specifically, the fiber length of the triboelectric fiber is preferably 3 to 150 mm, preferably 10 to 100 mm, and preferably 30 to 80 mm. The "fiber length" means the average fiber length measured by the method specified in JIS L1015 (Chemical Fiber Staple Test Method): 2021, Section 8.4.1, Method B (Corrected Staple Diagram Method).

[0030] The fineness (unit: dtex) of the triboelectric fiber is appropriately adjusted so as to provide a triboelectric nonwoven fabric having excellent filtration performance. The fineness of the triboelectric fiber is preferably 0.1 to 10 dtex, preferably 0.3 to 7 dtex, preferably 0.6 to 5 dtex, and most preferably 0.8 to 3 dtex. The "fineness" means a value measured by the method specified in JIS L1015 (Chemical Fiber Staple Test Method): 2021, Section 8.5.1, Method A (Normal Method).

[0031] Also, the strength (unit: cN, centinewton) of the triboelectric fiber is appropriately adjusted so as to provide a triboelectric nonwoven fabric having excellent filtration performance. The strength of the triboelectric fiber is preferably 1 to 16 cN, preferably 1.5 to 14 cN, and preferably 2.5 to 12 cN. The "strength" is obtained by converting the load (unit: N) at the time of breakage of the sample (triboelectric fiber) measured by the method specified in JIS L1015 (Chemical Fiber Staple Test Method): 2021, Section 8.7.1.

[0032] Also, the "strength per fineness of the first fiber (unit: cN / dtex)" and the "strength per fineness of the second fiber (unit: cN / dtex)", which are calculated by dividing the fineness of the first fiber and the second fiber by their strength, are appropriately adjusted so as to provide a triboelectric nonwoven fabric with excellent filtration performance. These strengths per fineness are preferably 1.00 cN / dtex or more, preferably 1.50 cN / dtex or more, preferably 2.00 cN / dtex or more, preferably 3.00 cN / dtex or more, preferably 4.00 cN / dtex or more, preferably 5.00 cN / dtex or more, preferably 6.00 cN / dtex or more. The upper limit is also appropriately adjusted, but 10.00 cN / dtex or less is realistic, 9.00 cN / dtex or less is more realistic, 8.00 cN / dtex or less is more realistic, and 7.00 cN / dtex or less is more realistic.

[0033] In particular, it is preferable to adopt a polyolefin resin fiber having a strength per fineness higher than 4.40 cN / dtex as the first fiber, whereby a triboelectric nonwoven fabric with excellent filtration performance can be provided. Such a polyolefin resin fiber having a high strength per fineness can be prepared by stretching the spun polyolefin resin fiber at a high magnification. Alternatively, it can be prepared by spinning a polyolefin resin having high rigidity.

[0034] The mass ratio of the first fiber and the second fiber constituting the triboelectric nonwoven fabric can be appropriately adjusted. For example, the mass ratio of the first fiber and the second fiber can be 5 mass%:95 mass% to 95 mass%:5 mass%, can be 15 mass%:85 mass% to 85 mass%:15 mass%, can be 25 mass%:75 mass% to 75 mass%:25 mass%, and can be 40 mass%:60 mass% to 60 mass%:40 mass%.

[0035] Note that the triboelectric nonwoven fabric may contain fibers other than the first fiber and the second fiber. As an example of a triboelectric nonwoven fabric containing fibers other than the first fiber and the second fiber, it can be a triboelectric nonwoven fabric prepared by entangling the first fiber, the second fiber, and other fibers. Alternatively, it can be a triboelectric nonwoven fabric prepared by laminating and entangling a web composed of the first fiber and the second fiber and another fabric (such as a spunbond nonwoven fabric), where the first fiber, the second fiber, and the constituent fibers of the other fabric that make up the web are entangled to form a laminated and integrated triboelectric nonwoven fabric.

[0036] However, in order to provide a triboelectric nonwoven fabric with excellent filtration performance, it is preferable that the constituent fibers of the triboelectric nonwoven fabric are only the first fiber and the second fiber.

[0037] The fibers constituting the triboelectric nonwoven fabric may be integrated with each other by a binder or fiber adhesion. However, in order to provide a triboelectric nonwoven fabric with a large amount of charge generated by efficient rubbing between the triboelectric fibers, and in order to provide a triboelectric nonwoven fabric in which the triboelectric fibers rub against each other and charge is generated when gas passes through the triboelectric nonwoven fabric, it is preferable that the fibers constituting the triboelectric nonwoven fabric are not integrated with each other by a binder or fiber adhesion, but are only entangled with each other. In addition, it is preferable to provide a triboelectric nonwoven fabric that is less likely to cause contamination and less likely to have its texture deteriorated by a triboelectric nonwoven fabric in which the fibers are only entangled with each other.

[0038] The constituent fibers of the triboelectric nonwoven fabric may contain an oil agent on their surfaces. The type of the oil agent can be appropriately selected, and a hydrophilic oil agent or a non-hydrophilic oil agent can be adopted. For example, as a hydrophilic oil agent, there is an agent obtained by adding a wetting agent such as an anionic surfactant, a cationic surfactant, or a nonionic surfactant to a lubricant such as a mineral oil or a synthetic oil. Also, for example, as a non-hydrophilic oil agent, there is an agent obtained by adding a fluorine-based or silicone-based component to a lubricant such as a mineral oil or a synthetic oil.

[0039] The mass percentage of the sizing agent contained in the constituent fibers of the triboelectric nonwoven fabric can be adjusted as appropriate, but the mass percentage of the sizing agent in the fiber mass is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, still more preferably 0.08% by mass or more, even more preferably 0.10% by mass or more, and particularly preferably 0.11% by mass or more. The upper limit can be adjusted as appropriate, but it is practical that it is 1% by mass or less.

[0040] The triboelectric nonwoven fabric according to the present invention is characterized in that the calculated value y of the following calculation formula is greater than 3.70 cN / dtex and less than 5.66 cN / dtex. Record y = (a1 × a2 + b1 × b2) / 100 a1: Strength per fineness of the first fiber (unit: cN / dtex) b1: Strength per fineness of the second fiber (unit: cN / dtex) a2: Mass percentage of the first fiber in the sum of the masses of the first fiber and the second fiber b2: Mass percentage of the second fiber in the sum of the masses of the first fiber and the second fiber.

[0041] As a result of further study by the applicant of the present application, when assuming that there is one type of triboelectric fiber constituting the triboelectric nonwoven fabric, by adjusting the strength per fineness (unit: cN / dtex) of the one type of triboelectric fiber to an optimal value, it has been found that a triboelectric nonwoven fabric excellent in filtration performance can be provided.

[0042] Specifically, the calculated value y of the following calculation formula represents the strength per fineness (unit: cN / dtex) of the one type of triboelectric fiber, and it has been found that a triboelectric nonwoven fabric in which the calculated value y is adjusted to be greater than 3.70 cN / dtex and less than 5.66 cN / dtex is a triboelectric nonwoven fabric excellent in filtration performance.

[0043] Although the value of the calculated value y can be appropriately adjusted within the above-described range, in order to provide a triboelectric nonwoven fabric having excellent filtration performance, its lower limit value is preferably 4.00 cN / dtex or more, more preferably 4.50 cN / dtex or more. And its upper limit value is preferably 5.50 cN / dtex or less, more preferably 5.30 cN / dtex or less.

[0044] The basis weight of the triboelectric nonwoven fabric can be appropriately adjusted according to the use and required physical properties, and is not particularly limited, but is preferably 15 to 600 g / m2, more preferably 25 to 400 g / m2, and still more preferably 50 to 300 g / m2. Note that the "basis weight" is the mass per 1 m2, and means the "mass per unit area" measured by the method specified in JIS L1085 (Test Method for Nonwoven Fabrics): 1998, Section 6.2.

[0045] The thickness of the triboelectric nonwoven fabric can be appropriately adjusted according to the use and required physical properties, and is not particularly limited, but can be 0.5 to 6 mm, can be 1 to 5 mm, and can be 1.5 to 4 mm. Note that the "thickness" in the present invention means the value obtained by randomly selecting 5 locations to measure the thickness in the load area where a load of 0.98 N (= 100 gf) is applied in the thickness direction per 5 cm2 of the area with respect to the main surface of the triboelectric nonwoven fabric, and calculating the arithmetic mean of those thicknesses. Such thickness measurement can be carried out, for example, by a high-precision digital length measuring instrument (manufactured by Mitutoyo Corporation, Lightmatic (registered trademark)).

[0046] Next, a manufacturing method of the triboelectric nonwoven fabric according to the present invention will be described with an example. Note that the description of the configuration described above will be omitted. (Step 1) A step of preparing a web in which the first fiber and the second fiber are mixed. (Step 2) A step of rubbing the first fiber and the second fiber against each other by applying an external force to the web. It can be a manufacturing method of a triboelectric nonwoven fabric having these.

[0047] First, (Step 1) will be described.

[0048] The method for preparing a web in which the first fiber and the second fiber are mixed can be appropriately selected. Examples include a method of blending the first fiber and the second fiber in the required mass ratio, feeding them to a carding device to prepare a web; a method of feeding the first fiber and the second fiber prepared to have the required mass ratio to an air-laying device for deposition to prepare a web; or a method of spinning the first fiber and the second fiber respectively in the required mass ratio using direct spinning such as meltblown nonwoven fabric, spunbond nonwoven fabric, or electrospun nonwoven fabric, and collecting them on the same collector. Also, a method can be adopted in which the first fiber is spun using direct spinning, and the second fiber, which is a short fiber, is supplied to and mixed with the flying first fiber during spinning, and then collected on the same collector to form a fiber web; or a method in which the first fiber is spun using direct spinning, the spun first fiber is collected by a collector, and the second fiber, which is a short fiber, is supplied to the collector and mixed with the first fiber to form a fiber web.

[0049] Various values such as the basis weight and thickness of the web are appropriately adjusted so that the triboelectric nonwoven fabric according to the present invention can be prepared. The web may contain adhesive fibers in the constituent fibers, but in order to provide a triboelectric nonwoven fabric with a large charge amount by efficient rubbing between the triboelectric fibers, it is preferable that the constituent fibers of the web are not adhered by adhesive fibers, and a web in which the constituent fibers are only the first fiber and the second fiber is preferable.

[0050] Also, the web may be adhered with an adhesive, but in order to provide a triboelectric nonwoven fabric with a large charge amount by efficient rubbing between the triboelectric fibers, it is preferable that the constituent fibers of the web are not adhered by the adhesive.

[0051] Next, (Step 2) will be described.

[0052] The method of applying an external force to the web can be appropriately selected. For example, a method of feeding the web into a needle punching machine, a method of feeding the web into a water entanglement device, a method of rubbing the web using hands, a brush, or wind to rub the first fiber and the second fiber against each other, or a method of rubbing the first fiber and the second fiber against each other by applying a tension to the web in a direction perpendicular to its thickness direction as disclosed in International Publication No. 2021 / 241367 can be adopted.

[0053] In addition, when applying these external forces, the temperature and humidity conditions can be appropriately adjusted. However, the temperature condition of the device environment is preferably 10 to 30 °C (preferably 25 °C), and the humidity condition is preferably 80% RH or less, more preferably 70% RH or less, and still more preferably 60% RH or less. The lower limit value can be appropriately adjusted, but 10% RH or more is realistic.

[0054] When feeding the web into a needle punching machine, the needle punching conditions such as the type of barbs and the needle density are appropriately adjusted. In this step, the needle punching treatment may be performed on only one main surface of the web or on both main surfaces of the web. Also, the number of needle punching treatments may be once or multiple times.

[0055] When feeding the web into a water entanglement device, the strength of the water flow, the interval and arrangement of the nozzles for emitting the water flow, etc. are appropriately adjusted. In this step, the water entanglement treatment may be performed on only one main surface of the web or on both main surfaces of the web. Also, the number of water entanglement treatments may be once or multiple times. Also, the type of water used for the water entanglement treatment can be appropriately selected, and for example, it can be industrial water, tap water, distilled water, pure water, etc. In addition, in order to dry the water entanglement web prepared in this way, it can be fed into a heating device, dried by exposing it to the atmosphere or under reduced pressure without heating, etc.

[0056] The above-described method of applying an external force to the web may be combined to rub the first fiber and the second fiber against each other. As a specific example, a method of feeding the web after being subjected to a water entanglement device and dried to a needle punching machine, a method of applying a tension to the web after being subjected to a water entanglement device and dried in a direction perpendicular to the thickness direction thereof, etc. can be adopted.

[0057] The triboelectric nonwoven fabric produced in this way can be used alone as a filter medium, but a filter medium may be constituted by laminating a cover material, a support, and / or a prefilter, a backup filter, etc. on the triboelectric nonwoven fabric. As the cover material, the support, and / or the prefilter, the backup filter, known ones can be adopted, for example, fabrics such as nonwoven fabrics, woven fabrics or knitted fabrics, porous films, breathable foams, etc. can be adopted. In addition, even a laminated filter material formed by simply overlapping the exemplified one and the triboelectric nonwoven fabric, a laminated filter material formed by interlayer adhesion with a binder, a hot melt material (powder, sheet (for example, hot melt web, hot melt film, etc.), etc.) or fiber adhesion, or a laminated filter material formed by interlayer adhesion by subjecting to an adhesion treatment such as heat sealing or ultrasonic welding may be used.

[0058] In addition, the outer shape of the triboelectric nonwoven fabric and the laminated filter material can be appropriately adjusted and is not particularly limited, but for example, it can be a two-dimensional sheet shape, a three-dimensional corrugated shape, a pleated shape, a cylindrical shape, etc. In addition, the triboelectric nonwoven fabric and the laminated filter material can have a cut-out portion, a punched portion, or a notch portion so as to be housed in the mask or filter to be provided.

Example

[0059] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0060] (Preparation of Fibers) Three types of polypropylene fibers A to C were prepared as the first fiber, and three types of acrylic fibers a to c were prepared as the second fiber. The various configurations of these fibers are summarized in Table 1.

[0061]

Table 1

[0062] (Comparative Example 1) Polypropylene fiber A was adopted as the first fiber, and acrylic fiber a was adopted as the second fiber. The adopted first fiber and second fiber were blended at a mass ratio of 50% by mass: 50% by mass, and were opened by feeding them to a carding machine to prepare a web. Next, by feeding the prepared web to a water entanglement device, the first fiber and the second fiber were washed with water and the first fiber and the second fiber were entangled with each other. Then, it was fed to a dry heat dryer and dried to prepare a water entanglement web. Thereafter, a spunbond nonwoven fabric made of a polyolefin resin (basis weight: 20 g / m2, thickness: 0.22 mm, average fiber diameter: 21 μm) prepared separately was laminated on the water entanglement web, and needle punching treatment was performed from the water entanglement web side. As a result, the first fiber and the second fiber were strongly rubbed against each other, and the first fiber and the second fiber constituting the water entanglement web and the constituent fibers of the spunbond nonwoven fabric were entangled and laminated integrally to prepare a laminated filter medium (basis weight: 120 g / m2, thickness: 1.6 mm) provided with a frictionally charged nonwoven fabric.

[0063] (Comparative Examples 2 to 4, Examples 1 to 6) As described in Tables 2 to 3, any one of three types of polypropylene fibers A to C was adopted as the first fiber, and any one of three types of acrylic fibers a to c was adopted as the second fiber. In addition, laminated filter media provided with frictionally charged nonwoven fabrics having a basis weight of 120 g / m2 were each prepared in the same manner as in Comparative Example 1, except that the adopted first fiber and second fiber were blended at the mass ratios described in Tables 2 to 3.

[0064]

Table 2

[0065] [Table 3]

[0066] The performance of the friction-charged nonwoven fabrics of the examples and comparative examples prepared as described above was summarized in Tables 4 to 5. The performance of the friction-charged nonwoven fabric was evaluated using the following method.

[0067] (Evaluation method for fiber distribution) Ten square-shaped sections (10 cm on each side) were taken from the laminated filter medium equipped with the friction-charged nonwoven fabric. The ten sections thus taken were arranged on a flat plate to prepare a single sample having a main surface area of 1000 cm3. Next, ten people visually checked the main surface of the laminated filter medium in the prepared sample, which was derived from the water flow bonding web in the laminated filter medium, to determine whether there were fiber lumps on the main surface. When there were fiber lumps, the number thereof was counted. The fiber lump refers to a fiber lump having an area of 3.14 mm2 or more when viewed from the main surface, which was formed by the aggregation of the constituent fibers of the friction-charged nonwoven fabric (for example, a fiber lump having a substantially circular, substantially elliptical or irregular shape). The evaluation results were tabulated. When the average number of fiber lumps present on the main surface in the sample was two or less and eight or more people out of ten judged so, the laminated filter medium from which the sections constituting the sample were taken was evaluated that the constituent fibers were uniformly distributed throughout the friction-charged nonwoven fabric portion. An ○ mark was described in Tables 4 to 5 for the laminated filter medium for which such evaluation was made. When other judgments were made, the laminated filter medium from which the sections constituting the sample were taken was evaluated that the constituent fibers were not uniformly distributed throughout the friction-charged nonwoven fabric portion. An × mark was described in Tables 4 to 5 for the laminated filter medium for which such evaluation was made.

[0068] (Measurement method for collection efficiency) A test piece (10 cm on each side) having a square shape was taken from the laminated filter medium. Then, the test piece taken was attached to the mask performance inspection device measuring device "AP-9000" manufactured by Shibata Scientific Co., Ltd. to measure the collection efficiency of the particles exhibited by the test piece. Specifically, the test flow rate was adjusted to 30 liters per minute per 56.7 cm2 of the effective filtration area of the test piece, and a test air flow containing sodium chloride particles (median particle size distribution: 0.06 to 0.10 μm, geometric standard deviation: 1.8 or less) at a concentration of 50 mg / m3 or less (concentration variation: ±15% or less) was supplied to the upstream side of the test piece (the side of the triboelectric nonwoven fabric in the test piece). Then, after supplying the test air flow for 1 minute, the concentrations of the sodium chloride particles present on the upstream side and the downstream side of the test piece (the side of the spunbond nonwoven fabric in the test piece) were measured using a light scattering dust concentration meter, respectively. Next, the concentration of the sodium chloride particles collected by the test piece was calculated from the measured concentrations. Then, the percentage of the concentration of the sodium chloride particles collected by the test piece in the concentration of the sodium chloride particles supplied to the upstream side of the test piece was calculated, and this value was defined as the initial collection efficiency of the test piece (unit: %).

[0069] The laminated filter media evaluated to have an initial collection efficiency higher than that of the laminated filter media (collection efficiency: 92.3%) prepared in Comparative Example 4 were determined to be laminated filter media rich in charge amount and excellent in the initial collection efficiency of particles. The initial collection efficiencies of the laminated filter media prepared in Examples 2 to 3 were higher than 92.3%.

[0070] As a result of subjecting the laminated filter media provided with the triboelectric nonwoven fabrics prepared in Comparative Examples 1 to 3 to the above-described (evaluation method of fiber distribution), it was evaluated that the constituent fibers were not uniformly distributed throughout the triboelectric nonwoven fabric portion. That is, the laminated filter media provided with the triboelectric nonwoven fabrics prepared in Comparative Examples 1 to 3 were considered to have non-uniform physical properties such as strength and pore size and inferior mechanical collection ability because the constituent fibers were not uniformly distributed throughout the triboelectric nonwoven fabric portion. Therefore, when dust collection progressed and the charge amount decreased, it was considered that the collection efficiency of dust was likely to decrease because of the inferior mechanical collection ability.

[0071] On the other hand, as a result of subjecting the laminated filter media prepared in Comparative Examples 1 to 3 to the above-described (evaluation method of charging performance), they were evaluated to be excellent in the initial collection performance of particles.

[0072] From the above results, it was considered that the laminated filter media prepared in Comparative Examples 1 to 3 were excellent in the initial particle collection efficiency because the triboelectric fibers were easily rubbed against each other and had a large charge amount.

[0073] Further, as a result of subjecting the laminated filter medium provided with the triboelectric nonwoven fabric prepared in Comparative Example 4 to the above-described (evaluation method of fiber distribution), it was evaluated that the constituent fibers were uniformly distributed throughout the triboelectric nonwoven fabric portion. That is, the laminated filter medium provided with the triboelectric nonwoven fabric prepared in Comparative Example 4 was considered to have uniform physical properties such as strength and pore size and excellent mechanical collection ability because the constituent fibers were uniformly distributed throughout the triboelectric nonwoven fabric portion. And even when the collection of dust progressed and the charge amount decreased, it was considered that the decrease in the collection efficiency of dust was suppressed because of the excellent mechanical collection ability.

[0074] On the other hand, as a result of subjecting the laminated filter medium prepared in Comparative Example 4 to the above-described (evaluation method of charge performance), it was evaluated that the initial particle collection efficiency was inferior.

[0075] From the above results, it was considered that the laminated filter medium prepared in Comparative Example 4 was inferior in the initial particle collection efficiency because the triboelectric fibers were difficult to rub against each other and had a small charge amount.

[0076] (Method of comprehensive evaluation) As a result of evaluating the above-described charge performance and fiber distribution, for a laminated filter medium in which the evaluation of the fiber distribution was evaluated as ○ and the initial collection efficiency was higher than 92.3%, a ◎ mark was described in Tables 4 to 5. The laminated filter medium was considered to be excellent in filtration performance in the long term. On the other hand, as a result of evaluating the above-described charge performance and fiber distribution, for a laminated filter medium in which the evaluation of the fiber distribution was evaluated as × and / or the collection efficiency was 92.3% or less, an × mark was described in Tables 4 to 5. The laminated filter medium was considered to be inferior in long-term filtration performance compared to the laminated filter medium evaluated as ◎ as described above.

[0077] [Table 4]

[0078]

Table 5

[0079] From the results of comparing Comparative Examples 1 to 3 with the Examples, it was found that the laminated filter medium provided with the triboelectric nonwoven fabric having a calculated value y greater than 3.70 cN / dtex has uniform physical properties such as strength and pore size and excellent mechanical collection ability because the constituent fibers are uniformly distributed throughout the triboelectric nonwoven fabric portion.

[0080] Also, from the results of comparing the Examples with Comparative Example 4, it was found that the laminated filter medium provided with the triboelectric nonwoven fabric having a calculated value y less than 5.66 cN / dtex is excellent in the initial particle collection efficiency because the triboelectric fibers are easily rubbed against each other and have a large charge amount.

[0081] From the above, it was found that the laminated filter medium provided with the triboelectric nonwoven fabric according to the present invention having a calculated value y greater than 3.70 cN / dtex and less than 5.66 cN / dtex is excellent in filtration performance over a long period of time.

[0082] Also, as summarized in Tables 6 to 7, from the results of comparing Comparative Example 2 with Examples 1 and 3, by adopting a polyolefin-based resin fiber having a strength per fineness higher than 4.40 cN / dtex as the first fiber, it was found that a laminated filter medium provided with a triboelectric nonwoven fabric excellent in filtration performance over a long period of time can be provided.

[0083]

Table 6

[0084]

Table 7

[0085] (Example 7) Polypropylene fiber C was adopted as the first fiber, and acrylic fiber a was adopted as the second fiber. The first fiber and the second fiber used were blended at a mass ratio of 50% by mass: 50% by mass, and opened by feeding them to a carding machine to prepare a web. Next, the prepared web was fed to a water flow entanglement device to wash the first fiber and the second fiber with water and entangle the first fiber and the second fiber with each other. Then, it was fed to a dry heat dryer and dried to prepare a water flow entangled web. Then, the water flow entangled web was wound around a roll while applying a tension in a direction perpendicular to its thickness direction. After that, a separately prepared spunbond nonwoven fabric made of a polyolefin resin (basis weight: 20 g / m2, thickness: 0.22 mm, average fiber diameter: 21 μm) and the water flow entangled web unwound from the roll were laminated and fed to a needle punching device to perform needle punching treatment from the water flow entangled web side. As a result, the first fiber and the second fiber were strongly rubbed against each other, and the first fiber and the second fiber constituting the water flow entangled web and the constituent fibers of the spunbond nonwoven fabric were entangled and laminated integrally to prepare a laminated filter medium (basis weight: 75 g / m2, thickness: 1.1 mm) provided with a triboelectric nonwoven fabric.

[0086] The results of subjecting the laminated filter medium provided with the triboelectric nonwoven fabric prepared in this way to the above-mentioned (evaluation method of fiber distribution) and (evaluation method of charging performance) were evaluated such that the constituent fibers were uniformly distributed throughout the triboelectric nonwoven fabric part, and it was also evaluated as a laminated filter medium having excellent initial particle collection efficiency (overall evaluation was ◎). Therefore, it was found that the laminated filter medium provided with the triboelectric nonwoven fabric prepared in Example 7 has excellent filtration performance in the long term.

Industrial Applicability

[0087] By using the triboelectric nonwoven fabric according to the present invention, for example, air filters for various vehicle applications such as automobiles and airplanes, air cleaners, OA equipment, medical equipment, and other consumer product applications, industrial facility applications such as food and medical product production factory applications, precision equipment manufacturing factory applications, indoor cultivation facilities for agricultural crops, general household applications, or office buildings, and masks can be prepared.

Claims

1. A triboelectric nonwoven fabric in which first fibers and second fibers, which are made of different resins and can be charged by rubbing against each other, are mixed, and the first fibers and the second fibers are charged. The triboelectric nonwoven fabric, wherein the calculated value y of the following formula is greater than 3.70 cN / dtex and less than 5.66 cN / dtex. Where y = (a1 × a2 + b1 × b2) / 100 a1: Strength per fineness of the first fiber (unit: cN / dtex) b1: Strength per fineness of the second fiber (unit: cN / dtex) a2: Mass percentage of the first fiber in the sum of the masses of the first fiber and the second fiber b2: Mass percentage of the second fiber in the sum of the masses of the first fiber and the second fiber.

2. The triboelectric nonwoven fabric according to claim 1, wherein the first fiber is a polyolefin resin fiber having a strength per fineness higher than 4.40 cN / dtex.

3. A filter medium comprising the triboelectric nonwoven fabric according to any one of claims 1 or 2.

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