Electret melt-blown nonwoven fabric and air filter medium using the same

Abstract

Provided is an electret melt-blown nonwoven fabric, and an air filter medium using the same. The electret melt-blown nonwoven fabric includes polyolefin-based resin fibers, and is made soft and has a high elongation even without special post-processing or the use of special additives, wherein the crystallization temperature at the 1st temperature rise in a cyclic DSC is 80°C or higher and 130°C or lower, and the heat ΔHm is 3.0 J / g or higher and 20.0 J / g or lower.

Description

TECHNICAL FIELD

[0001] The present application relates to an electret melt-blown nonwoven fabric having high elongation, and an air filter medium using the same. BACKGROUND

[0002] In recent years, various nonwoven fabric materials are used in sanitary materials such as disposable diapers or sanitary napkins, and medical materials such as masks, and since the use form is mostly direct contact with the human body, the nonwoven fabric is required to have excellent softness or stretch properties.

[0003] As a method of imparting softness to a nonwoven fabric, there are a method of using post-processing, or a method of modifying the raw material itself constituting the nonwoven fabric without relying on post-processing, and the like. In particular, as a method of imparting softness in post-processing, for example, a method of performing rubbing processing on a nonwoven fabric using a dyeing machine, or a method of performing a stretching operation on a nonwoven fabric by passing through a nip between pinch rollers having a speed difference or a tenter, or the like, to mechanically relax the adhesion between fibers, and the like, are exemplified. As a modification method of the nonwoven fabric itself, for example, in Patent Document 2, a softened nonwoven fabric is obtained by mixing polystyrene in polypropylene (hereinafter sometimes abbreviated as PP) as a raw material. Or, as disclosed in Patent Document 3, a method of adding a smoothing agent to a polymer, performing embossing processing after spinning while blowing cooling air, is also advocated.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT DOCUMENTS

[0006] Patent Document 1: Japanese Patent Laid-Open No. 63-132625

[0007] Patent Document 2: Japanese Patent Laid-Open No. 6-93547

[0008] Patent Document 3: Japanese Patent Laid-Open No. 2000-8259 SUMMARY

[0009] PROBLEMS TO BE SOLVED BY THE INVENTION

[0010] Generally, in a nonwoven fabric, the strength of a melt-blown nonwoven fabric (hereinafter sometimes abbreviated as MB nonwoven fabric) is low, and therefore in the existing methods disclosed in Patent Document 1 or Patent Document 2, in the case where a mechanical external force is applied, there is a tendency that the nonwoven fabric itself is broken, or even if it is not broken, the surface is roughened, and there is a problem that the value of the product is impaired. The same is true in the method using a softening agent, and there is also a problem of cost increase due to post-processing.

[0011] On the other hand, in the method as disclosed in Patent Literature 3, not only the number of steps is increased, but also a smoothing agent needs to be added to the raw material, and thus there are problems in terms of sheet strength reduction or economy.

[0012] Therefore, the present application was made in view of the circumstances, and an object thereof is to provide an electret melt-blown nonwoven fabric which is soft and has a high elongation even without special post-processing or the use of a special additive.

[0013] Technical means for solving the problem

[0014] As a result of repeated and diligent research by the present inventors and others, it was found that an electret melt-blown nonwoven fabric in which the crystallization temperature at the 1st temperature rise in a cyclic differential scanning calorimetry (DSC) is 80°C or higher and 130°C or lower and the heat ΔHm is 3.0 J / g or higher and 20.0 J / g or lower can be obtained by spraying water in a mist form at a downstream position from a die through which a polyolefin-based resin serving as a raw material is extruded, and thus an electret melt-blown nonwoven fabric which is soft and has a high elongation even without special post-processing or the use of a special additive can be provided.

[0015] The present application was made based on these insights, and according to the present application, the following invention is provided.

[0016] [1] An electret melt-blown nonwoven fabric comprising polyolefin-based resin fibers, wherein the crystallization temperature at the 1st temperature rise in a cyclic differential scanning calorimetry (DSC) is 80°C or higher and 130°C or lower and the heat ΔHm is 3.0 J / g or higher and 20.0 J / g or lower.

[0017] [2] The electret melt-blown nonwoven fabric according to [1], wherein the average fiber curvature of the polyolefin-based resin fibers is 1.10 or higher and 1.50 or lower.

[0018] [3] The electret melt-blown nonwoven fabric according to [1] or [2], wherein the average single fiber diameter of the polyolefin-based resin fibers is 0.1 μm or higher and 8.0 μm or lower.

[0019] [4] An air filter medium which is made using the electret melt-blown nonwoven fabric according to any one of [1] to [3].

[0020] Effects of the invention

[0021] According to the present application, an electret melt-blown nonwoven fabric which is soft and has a high elongation even without special post-processing or the use of a special additive is provided. DETAILED DESCRIPTION

[0022] The electret melt-blown nonwoven fabric of the present application is an electret melt-blown nonwoven fabric containing polyolefin-based resin fibers, the crystallization temperature at the 1st temperature rise in a cyclic DSC is 80°C or higher and 130°C or lower, and the heat ΔHm is 3.0 J / g or higher and 20.0 J / g or lower. Hereinafter, the constituent elements thereof are described in detail, but the present application is not limited by the ranges described below as long as the gist thereof is not exceeded.

[0023] (Polyolefin-based resin fibers)

[0024] First, the electret melt-blown nonwoven fabric of the present application contains polyolefin-based resin fibers. By using fibers containing a polyolefin-based resin composition having a high volume resistivity and a low water absorption, i.e., polyolefin-based resin fibers, as the fibers constituting the electret melt-blown nonwoven fabric, the electrification and charge retention of the electret melt-blown nonwoven fabric can be enhanced, and high collection efficiency can be achieved by these effects.

[0025] In the present application, as the polyolefin-based resin composition, homopolymers such as polyethylene, polypropylene, polybutene, and polymethylpentene, and the like can be exemplified. In addition, copolymers obtained by copolymerizing different components in these homopolymers, or resin such as a blend of two or more different polymers, and the like can also be used. Among these, from the viewpoint of charge retention, polypropylene-based resins and polymethylpentene-based resins can be preferably used. In particular, from the viewpoint of being able to be used inexpensively and being easy to make the fiber diameter thin, polypropylene-based resins can be preferably used.

[0026] Further, in the present application, the resin composition referred to as "polyolefin-based resin composition" means a resin composition containing 80% by mass or more of polypropylene homopolymer (or polyethylene homopolymer, or the like) and propylene units (or ethylene units, or the like) among resins such as homopolymers of polypropylene (or polyethylene, or the like), copolymers (copolymers) with other components, and polymer blends with different resins. The same applies to other polyolefin-based resin compositions.

[0027] The melt flow rate (MFR) of the polyolefin-based resin composition in the present application is preferably 50 g / 10 minutes or more and 2500 g / 10 minutes or less, as measured according to the "8A method: mass measurement method" of Japanese Industrial Standards (JIS) K7210-1:2014 "Plastics - Determination of the melt mass-flow rate (MFR) and melt volume-flow rate (MVR) of thermoplastics - Part 1: Standard testing methods" at a temperature of 230°C, a load of 2.16 kg, and a measurement time of 10 minutes. By setting the melt flow rate of the polyolefin-based resin composition to be 50 g / 10 minutes or more, and more preferably 150 g / 10 minutes or more, the fiber forming the electret melt-blown nonwoven fabric becomes easier to be thin. On the other hand, by setting the melt flow rate of the polyolefin-based resin composition to be 2500 g / 10 minutes or less, and more preferably 2000 g / 10 minutes or less, the strength of the fiber sheet can be improved.

[0028] The polyolefin-based resin composition of the present application can contain a crystallization nucleating agent. By containing the crystallization nucleating agent, the temperature lowering crystallization temperature of the polyolefin-based resin composition increases, the solidification of the fiber spun rapidly proceeds, and thus the fusion of the fibers to each other is reduced, and the air permeability of the electret melt-blown nonwoven fabric is improved.

[0029] As the crystallization nucleating agent, for example, sorbitol-based nucleating agents, nonitol-based nucleating agents, xylitol-based nucleating agents, phosphoric acid-based nucleating agents, trisaminobenzene derivative nucleating agents, and carboxylic acid metal salt nucleating agents, etc. can be exemplified.

[0030] From the viewpoint of making the electret performance of the electret melt-blown nonwoven fabric better, the polyolefin-based resin composition of the present application can contain at least one hindered amine-based additive or / and triazine-based additive, in addition to the crystallization nucleating agent.

[0031] As the hindered amine-based compound, for example, poly[(6-(1,1,3,3-tetramethylbutyl)imino-1,3,5-triazine-2,4-diyl)((2,2,6,6-tetramethyl-4-piperidyl)imino]hexamethylene((2,2,6,6-tetramethyl-4-piperidyl)imino)] (manufactured by BASF JAPAN Ltd., "Chimassorb" (registered trademark) 944LD), succinic acid dimethyl-1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethylpiperidine polycondensate (manufactured by BASF JAPAN Ltd., "Tinuvin" (registered trademark) 622LD), and 2-(3,5-di-tert-butyl-4-hydroxybenzyl)-2-n-butylmalonic acid bis(1,2,2,6,6-pentamethyl-4-piperidyl) (manufactured by BASF JAPAN Ltd., "Tinuvin" (registered trademark) 144), and the like can be exemplified.

[0032] In addition, as the triazine-based additive, for example, poly[(6-(1,1,3,3-tetramethylbutyl)imino-1,3,5-triazine-2,4-diyl)((2,2,6,6-tetramethyl-4-piperidyl)imino]hexamethylene((2,2,6,6-tetramethyl-4-piperidyl)imino)] (manufactured by BASF JAPAN Ltd., "Chimassorb" (registered trademark) 944LD), and 2-(4,6-diphenyl-1,3,5-triazine-2-yl)-5-((hexyl)oxy)-phenol (manufactured by BASF JAPAN Ltd., "Tinuvin" (registered trademark) 1577FF), and the like can be exemplified.

[0033] The addition amount of the hindered amine-based additive and / or the triazine-based additive is preferably 0.5% by mass or more and 5% by mass or less, and more preferably 0.7% by mass or more and 3% by mass or less, with respect to the total mass of the polyolefin-based resin composition. By setting the addition amount to the range, it is easy to obtain an electret melt-blown nonwoven fabric excellent in dust capturing properties.

[0034] The content of hindered amine additives and / or triazine additives can be determined, for example, by Soxhlet extraction of the electret meltblown nonwoven fabric using a methanol / chloroform mixed solution, repeatedly subjecting the extract to high performance liquid chromatography (HPLC) preparation, and subjecting each preparation to infrared spectroscopy (IR), gas chromatography (GC), gas chromatography-mass spectrometry (GC / MS), matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS), and hydrogen nuclear magnetic resonance spectroscopy (HNMR). 1 H-NMR) determination and Carbon-13 Nuclear Magnetic Resonance Spectrometry, 13 The structure was confirmed by C-NMR measurement. The weight of the preparations contained in the additives was totaled to determine the ratio relative to the total electret meltblown nonwoven fabric, which was defined as the content of the hindered amine additive and / or triazine additive.

[0035] The polyolefin resin composition used in the present invention may contain additives such as a heat stabilizer, a weathering agent, and a polymerization inhibitor, as long as the effects of the present invention are not impaired.

[0036] The polyolefin resin fiber used in the electret meltblown nonwoven fabric of the present invention may be a composite fiber comprising the polyolefin resin composition, and may be in the form of, for example, core-sheath type, eccentric core-sheath type, side-by-side type, split type, island-in-the-sea type, or alloy type composite fibers.

[0037] The polyolefin resin fibers comprise the polyolefin resin composition and preferably have an average single fiber diameter of 0.1 μm to 8.0 μm. By setting the average single fiber diameter to preferably 0.1 μm or greater, more preferably 0.3 μm or greater, and even more preferably 0.5 μm or greater, the strength of the fiber sheet can be improved. On the other hand, by setting the average single fiber diameter to 8.0 μm or less, more preferably 7.0 μm or less, and even more preferably 5.0 μm or less, the collection efficiency of the electret meltblown nonwoven fabric can be improved.

[0038] Furthermore, to calculate the average single fiber diameter of the polyolefin resin fibers used in electret meltblown nonwoven fabrics, 15 3 mm x 3 mm measurement samples were collected from three points in the width direction of the fiber sheet (two at the side ends and one at the center) and five points at 5 cm intervals along the length of the sheet, for a total of 15 points. Using a scanning electron microscope (e.g., the "VHX-D500" manufactured by Keyence Corporation) at a magnification of 3000x, one fiber surface photograph was taken from each of the collected measurement samples, for a total of 15 photographs. The single fiber diameter was then measured for all fibers whose fiber diameter (single fiber diameter) was clearly visible in the photographs, and the arithmetic mean of these values, rounded to the second decimal place, was used as the average single fiber diameter.

[0039] In the electret meltblown nonwoven fabric of the present invention, the polyolefin resin fibers preferably have an average fiber curvature of 1.10 or greater and 1.50 or less. By setting the average fiber curvature to preferably 1.10 or greater, more preferably 1.30 or greater, the inter-fiber spaces are widened, resulting in a high volume, low pressure drop, and high elongation when stretched. On the other hand, by setting the average fiber curvature to 1.50 or less, more preferably 1.40 or less, the fiber rigidity is increased, resulting in an electret meltblown nonwoven fabric with high morphological stability.

[0040] In the present invention, the average fiber curvature of the polyolefin resin fibers in the electret meltblown nonwoven fabric can be controlled by performing an appropriate quenching treatment from one direction immediately after spinning the polyolefin resin fibers. Specifically, this can be achieved by blowing cold air from one direction immediately after spinning (in the area directly below the die), or by spraying water in a mist from one direction during spinning (in the area from directly below the die to the collecting portion). The spraying of water in a mist is most preferred because it can be combined with the electret treatment.

[0041] In the above, there is no particular limitation on the amount of water sprayed as long as the water contacts the spun filaments, and the spray amount can be appropriately adjusted to achieve the target fiber curvature. However, since a drying process is not required during electret processing, it is ideal that the water / polymer percentage [%] described later is greater than 300% and less than 500%.

[0042] Further, in calculating the average fiber curvature of the polyolefin-based resin fiber, 15 measurement samples of 3 mm x 3 mm were collected from 3 points in the width direction of the nonwoven fabric (2 points at the side ends and 1 point at the center), 5 points every 5 cm in the length direction, for a total of 15 points, a photograph of the fiber surface was taken at a magnification of 200x using a scanning electron microscope (for example, "VHX-D500" manufactured by Keyence Co., Ltd.), and a total of 15 photographs were taken. Then, the linear distance (L1) between the two ends of the fiber and the actual fiber length (L2) were measured for all fibers in which the fiber length was 750 μm or more that could be clearly confirmed in the photographs, and the curvature (L2 / L1) of each was calculated, and the value obtained by rounding off the third decimal place of the arithmetic mean of these to the nearest integer was set as the average fiber curvature (unitless).

[0043] (Electret melt-blown nonwoven fabric)

[0044] The electret melt-blown nonwoven fabric of the present application is composed of the polyolefin-based resin fiber. Also, the crystallization temperature at the 1st heating in the cyclic DSC of the electret melt-blown nonwoven fabric of the present application is 80°C or higher and 130°C or lower, and the heat ΔHm of crystallization is 3.0 J / g or higher and 20.0 J / g or lower.

[0045] First, by setting the crystallization temperature at the 1st heating in the cyclic DSC to 80°C or higher, preferably to 85°C or higher, and more preferably to 90°C or higher, a crystallization region of moderate strength can be formed, and an electret melt-blown nonwoven fabric of sufficient sheet strength can be produced. On the other hand, by setting the crystallization temperature at the 1st heating in the cyclic DSC to 130°C or lower, preferably to 115°C or lower, and more preferably to 110°C or lower, a region of incomplete crystallization can be formed, and an electret melt-blown nonwoven fabric having a high elongation at the time of stretching can be produced.

[0046] Also, by setting the heat ΔHm of crystallization at the 1st heating in the cyclic DSC to 3.0 J / g or higher, preferably to 4.0 J / g or higher, and more preferably to 5.0 J / g or higher, the region of incomplete crystallization is sufficient, and an electret melt-blown nonwoven fabric having a high elongation at the time of stretching can be produced. On the other hand, by setting the heat ΔHm of crystallization at the 1st heating in the cyclic DSC to 20.0 J / g or lower, preferably to 17.5 J / g or lower, and more preferably to 15.0 J / g or lower, an electret melt-blown nonwoven fabric having a small shrinkage at the time of heat processing and high form stability can be produced.

[0047] In the present application, the crystallization temperature at the 1st heating in the cyclic DSC and the heat ΔHm thereof refer to values measured and calculated by the following method. That is,

[0048] (i) Randomly collect three 5-mg test pieces from the electret melt-blown nonwoven fabric.

[0049] (ii) Using a differential scanning calorimeter (for example, "Q100" manufactured by TA Instruments, Inc., or the like), perform 1st heating (first heating) → cooling and perform measurement under the following conditions.

[0050] • Measurement environment: nitrogen flow (50 ml / min)

[0051] • Temperature range: 20°C to 200°C

[0052] • Heating rate: 20°C / min

[0053] • Cooling rate: 20°C / min

[0054] • Sample amount: 5 mg

[0055] (iii) With respect to the crystallization temperature, read the exothermic peak top temperature during the 1st heating. In addition, the heat ΔHm (J / g) at the time of crystallization is calculated from the exothermic peak above 80°C and below 130°C during heating and the endothermic curve during cooling.

[0056] (iv) Perform three measurements, and for the crystallization temperature (°C), round off the arithmetic mean to the first digit after the decimal point, and for the heat ΔHm (J / g), round off the arithmetic mean to the second digit after the decimal point.

[0057] In the present application, the crystallization temperature at the time of 1st heating in the cyclic DSC of the electret melt-blown nonwoven fabric, and the heat ΔHm at the time of crystallization can be controlled by forming an appropriate non-crystalline portion in the polyolefin-based resin fiber constituting the electret melt-blown nonwoven fabric. Specifically, it can be controlled by changing the type of polyolefin-based resin used, or adding a crystallization nucleating agent or an elastomer or the like additive, or quenching the spun polymer by misting water or the like during spinning.

[0058] The unit area weight of the electret melt-blown nonwoven fabric of the present application is preferably 3 g / m 2 or less and 100 g / m 2 or less. By setting the unit area weight of the electret melt-blown nonwoven fabric to 3 g / m 2 or more, more preferably 5 g / m 2 or more, and further preferably 10 g / m 2 or more, the collection efficiency of the electret melt-blown nonwoven fabric can be improved. On the other hand, by setting it to 100 g / m 2 or less, more preferably 70 g / m 2Below, more preferably set to 50g / m 2 As a result, it is possible to suppress the collapse of pleats when pleating the electret meltblown nonwoven fabric as an air filter unit.

[0059] In addition, regarding the basis weight of the electret meltblown nonwoven fabric in the present invention, samples of 15 cm × 15 cm in lengthwise × transverse direction were collected at random from the electret meltblown nonwoven fabric, and the values ​​obtained by measuring the mass of these samples were converted into the basis weight per 1 m 2 The value of each sample is calculated as the arithmetic mean (g / m 2 ) is rounded to the first decimal place to calculate the unit area weight of the fiber sheet (g / m 2 ).

[0060] By having an electret meltblown nonwoven fabric thickness of 0.05 mm or greater, more preferably 0.08 mm or greater, and even more preferably 0.12 mm or greater, the strength of the sheet can be further increased, thereby suppressing sheet breakage during processing into air filter units. Furthermore, by having an electret meltblown nonwoven fabric thickness of 0.40 mm or less, more preferably 0.35 mm or less, and even more preferably 0.30 mm or less, collapse of pleats during pleating of the electret meltblown nonwoven fabric into an air filter unit can be suppressed.

[0061] In addition, regarding the thickness of the electret meltblown nonwoven fabric in the present invention, a thickness meter (for example, "TECLOCK" (registered trademark) SM-114 manufactured by TECLOCK Co., Ltd.) is used to measure the thickness of the electret meltblown nonwoven fabric at equal intervals in the width direction at 10 points, and the third decimal place is rounded off from the average value to calculate the thickness (mm) of the electret meltblown nonwoven fabric.

[0062] (Manufacturing method of electret meltblown nonwoven fabric)

[0063] The electret meltblown nonwoven fabric of the present invention can be produced, for example, by the following method.

[0064] First, the polyolefin resin composition is prepared. Next, the polyolefin resin composition is extruded from a die having a predetermined aperture to form filaments. Air heated to approximately 250°C to 350°C (hereinafter sometimes simply referred to as hot air) is blown at a predetermined angle onto the extruded filaments to reduce their diameter. The filaments are then deposited in a collecting portion to form a meltblown nonwoven fabric.

[0065] Alternatively, after the hot air is injected, liquid droplets may be sprayed in a mist form until the filaments are accumulated in the collecting section to quench the spun polymer. The spraying of water in a mist form is most preferred because it can be combined with the electret treatment.

[0066] With respect to the amount of water spray, the following formula is desirable:

[0067] (Wp / Wf) x 100

[0068] (In the formula, Wp is the water ejection mass of the spray nozzle per unit width per unit time, and Wf is the ejection mass of the non-conductive polymer per unit width per unit time)

[0069] The water / polymer percentage [%] is 300% or more and less than 500%. If the water / polymer percentage is less than 500%, the moisture is sufficiently evaporated due to the heat of the spun polymer, and even in the case of a small amount of polymer ejection, a high-quality electret melt-blown nonwoven fabric can be obtained without a drying process. On the other hand, if the water / polymer percentage is 300% or more, the charging amount of the nonwoven fabric is sufficient, and thus an electret melt-blown nonwoven fabric exhibiting high collection efficiency can be obtained.

[0070] As the spray device of the liquid droplets, a single-hole type spray nozzle that sprays water droplets in a conical or fan shape and in a mist shape from a single hole, or a slit type spray nozzle that sprays water droplets in a strip shape and in a mist shape from a slit-shaped spray outlet, or the like can be used. Among them, in terms of being able to uniformly impart even a small amount of water in the width direction, it is further preferable to use a spray nozzle that includes a plurality of water spray outlets arranged in the width direction, and a pair of air spray outlets that are continuously or intermittently opened across the width direction and are disposed facing each other in a manner sandwiching the plurality of water spray outlets, and that causes air sprayed from the air spray outlets to collide with water sprayed from the plurality of water spray outlets.

[0071] In addition, the position at which the liquid droplets are sprayed or sprayed in a mist shape can be anywhere between the position from which the hot air is sprayed and the collection net, but can be preferably a position that is 7.5 cm or more away downward from the die. Desirably, it is more preferably 8 cm or more, and further preferably 9 cm. In a region that is less than 7.5 cm from the die, the temperature is high due to heat dissipation from the die, and the spun yarn itself is also high in temperature, and thus the sprayed water or misted water sometimes partially evaporates. Therefore, by setting the position at which the liquid droplets are sprayed or sprayed in a mist shape to a position that is 7.5 cm or more away downward from the die, the spun yarn is sufficiently solidified to become a yarn, and thereafter, during the period until it becomes a nonwoven fabric, the liquid droplets that are sprayed or sprayed in a mist shape can be sufficiently spread. As a result, various physical properties of the electret melt-blown nonwoven fabric can be improved.

[0072] Further, after the hot air is blown, during a period until the filaments are accumulated in the collection section, the melt-blown nonwoven fabric obtained is subjected to an electret treatment without spraying the droplets, thereby producing an electret melt-blown nonwoven fabric. The electret treatment can be performed on a single layer of the melt-blown nonwoven fabric, and can also be performed on a laminated fiber sheet obtained by laminating other fiber sheets.

[0073] In this case, as a method of performing the electret treatment, a method of performing electret treatment by applying water to a non-conductive melt-blown nonwoven fabric and then drying the same can be preferably used. As a method of applying water to the melt-blown nonwoven fabric, a method of spraying a mist or a stream of droplets of water at a sufficient pressure so that the water penetrates into the melt-blown nonwoven fabric, a method of applying water and then sucking the water from one side of the melt-blown nonwoven fabric while applying water so that the water penetrates into the melt-blown nonwoven fabric, and a method of immersing the melt-blown nonwoven fabric in a mixed solution of a water-soluble organic solvent such as isopropyl alcohol, ethanol, acetone, and water so that the water penetrates into the fiber sheet, and the like can be exemplified.

[0074] Further, a drying method of the electret melt-blown nonwoven fabric after the water penetration can use any of the methods known in the art. For example, a hot air drying method, a vacuum drying method, a natural drying method, and the like can be applied. Among them, the hot air drying method is preferable because continuous treatment can be performed. In the case of the hot air drying method, a temperature which does not deactivate the electret to a certain extent is required as a drying temperature. It can be preferably 120°C or lower, more preferably 100°C or lower, and further preferably 80°C or lower. In addition, before the hot air drying, as a pre-drying, it is further preferable to remove the remaining water by nip rolls, water absorption rolls, suction, and the like.

[0075] In the present application, as water used when the droplets are sprayed in a mist form during a period from when the hot air is blown until the filaments are accumulated in the collection section, or water used when the melt-blown nonwoven fabric is subjected to an electret treatment, water which is as clean as possible after removing dirt by a liquid filter or the like is preferably used. In particular, ion-exchanged water, distilled water, filtered water which has passed through a reverse osmosis membrane, and the like pure water can be preferably used. In addition, as a level of the pure water, a conductivity of 10 3 μS / m or lower, and more preferably a conductivity of 10 2 μS / m or lower is preferable. In addition, a water-soluble organic solvent such as isopropyl alcohol, ethanol, acetone, and the like can be mixed in the water within a range which does not affect the collection properties.

[0076] (Air filter medium)

[0077] The air filter filter material of the present application is made using the electret melt-blown nonwoven fabric of the present application. As a method for obtaining the air filter filter material of the present application from the electret melt-blown nonwoven fabric of the present application, a publicly known method can be used. For example, the electret melt-blown nonwoven fabric of the present application can be joined with a skeleton sheet to make a laminated sheet. The skeleton sheet is for capturing larger dust, and is joined with the electret melt-blown nonwoven fabric to obtain a skeleton sheet required for rigidity as a filter material. As the skeleton sheet, for example, a nonwoven fabric, a woven fabric, etc. containing polyester fibers, polypropylene fibers, rayon fibers, glass fibers, natural pulp, etc. can be used.

[0078] The air filter filter material of the present application can be directly assembled in a frame material in a sheet-like state to be used as a filter unit. Alternatively, the air filter filter material can be repeatedly subjected to mountain folding and valley folding to perform pleat processing, and used as a pleated filter unit provided in a frame material.

[0079] The air filter filter material of the present application is suitable for all air filters, and is particularly suitable for high-performance applications of air-conditioning filters, air purifier filters, and automobile passenger compartment filters.

[0080] Examples

[0081] Next, the present application will be specifically described based on examples. However, the present application is not limited only to these examples. Further, in the measurement of each property, those not particularly described are measured based on the method described.

[0082] (1) Average single fiber diameter (μm) of polyolefin-based resin fibers:

[0083] "VHX-D500" manufactured by Keyence Co., Ltd. was used as a scanning electron microscope, and measurement and calculation were performed by the method.

[0084] (2) Average fiber curvature of polyolefin-based resin fibers:

[0085] "VHX-D500" manufactured by Keyence Co., Ltd. was used as a scanning electron microscope, and measurement and calculation were performed by the method.

[0086] (3) Crystallization temperature (°C) at the 1st temperature rise and heat of crystallization ΔHm (J / g) in the cyclic DSC of the electret melt-blown nonwoven fabric:

[0087] "Q100" manufactured by TA Instruments Co., Ltd. was used as a differential scanning calorimeter, and measurement and calculation were performed by the method. In Table 1, "crystallization temperature" and "heat of crystallization ΔHm" are abbreviated, respectively.

[0088] (4) Unit area weight (g / m2) of the electret melt-blown nonwoven fabric: 2 ) :

[0089] The unit area weight of the electret melt-blown nonwoven fabric is measured and calculated by the method.

[0090] (5) Thickness (mm) of the electret melt-blown nonwoven fabric:

[0091] The thickness of the electret melt-blown nonwoven fabric is measured and calculated by the method using "TECLOCK" (registered trademark) SM-114 manufactured by TECLOCK Co., Ltd.

[0092] (6) Tensile strength (N / cm), tensile elongation (%) of the electret melt-blown nonwoven fabric:

[0093] The tensile strength of the electret melt-blown nonwoven fabric is measured using a Tensilon universal testing machine "RTG-1250" manufactured by A&D Co., Ltd. as a tensile testing machine, and according to the A method (strip method) described in "8.14.1 JIS method" of "8.14 Tensile strength and elongation" of JIS L1096:2010 "Textile and Knit Fabric: Test Method for Fabrics". In addition, the size of the test piece at the time of cutting is set to 5 cm in width and 20 cm in length, and the number of test pieces is set to 5 pieces in the longitudinal direction (Machine Direction, MD) (the length direction of the electret melt-blown nonwoven fabric) and the transverse direction (Cross Direction, CD) (the width direction of the electret melt-blown nonwoven fabric), respectively. The measurement is performed under the conditions of a grip interval of 10 cm and a tensile speed of 10 cm / minute, the load at the time of cutting (the maximum load in the case where the load at the time of cutting is not the maximum load) of 5 test pieces is divided by the width, and the arithmetic mean value (N / cm) is rounded off to the second decimal place to obtain a value. The tensile strength (N / cm) of the electret melt-blown nonwoven fabric is calculated, and the arithmetic mean value (%) of the elongation at the time of cutting (the maximum load at the time of cutting in the case where the load at the time of cutting is not the maximum load) is rounded off to the first decimal place to obtain a value. The tensile elongation (%) of the electret melt-blown nonwoven fabric in the MD direction or the CD direction is calculated.

[0094] [Example 1]

[0095] A polypropylene resin having a melt flow rate of 850 g / 10 minutes was used. After the polypropylene resin was fed to a raw material hopper of a spinning machine, the melted polypropylene resin was extruded from a die having a discharge hole with a diameter of 0.4 mm (hole pitch: 1.0 mm) at a temperature of 270°C of the die, a single-hole discharge amount of 0.28 g / minute / hole. Air (hot air) heated to 300°C was sprayed to the filament immediately after being discharged from the die at a pressure of 0.025 MPa, and further, pure water having a conductivity of 90 μS / m was sprayed in mist form to the filament which had moved 10 cm downward from the die from a spray nozzle. The spray nozzle included a plurality of water discharge ports arranged in a width direction of the die, and a pair of air discharge ports which were continuously or intermittently opened across the width direction and were arranged facing each other in a manner of sandwiching the plurality of water discharge ports, and the spray nozzle collided the air discharged from the air discharge ports with the water discharged from the plurality of water discharge ports, thereby spraying the water in mist form to the filament. The pure water having a conductivity of 90 μS / m was sprayed in mist form by the spray nozzle toward the filament at a flow rate of 667 mL / minute / m per unit width (1 m) of a spinning width (a width direction of a production line, and a direction of a width direction (CD direction) of the electret melt-blown nonwoven fabric in a subsequent process) at an air pressure of 1.5 MPa, in a manner that a water / polymer percentage became 242%. Then, the filament was accumulated on a collection net whose conveyer speed was adjustable, thereby obtaining an electret melt-blown nonwoven fabric having a weight per unit area of 20 g / m 2 The results of measurement of the properties of the electret melt-blown nonwoven fabric are shown in Table 1.

[0096] [Example 2]

[0097] In Example 1, when the pure water was sprayed in mist form to the filament, the case where the flow rate was 667 mL / minute / m, the air pressure was 1.5 MPa, and the water / polymer percentage was 242% was changed to a case where the flow rate was 333 mL / minute / m, the air pressure was 0.7 MPa, and the water / polymer percentage was 121%, and otherwise, the melt-blown nonwoven fabric was manufactured in the same manner as in Example 1. The results of measurement of the properties of the electret melt-blown nonwoven fabric are shown in Table 1.

[0098] [Example 3]

[0099] In Example 1, the case where the single-hole ejection amount of the polypropylene resin was 0.28 g / min / hole, the pressure of the hot air was 0.025 MPa, and the water / polymer percentage when pure water was sprayed in mist form toward the filaments was 242% was changed to a single-hole ejection amount of 0.35 g / min / hole, a pressure of the hot air of 0.027 MPa, and a water / polymer percentage of 155%, and a melt-blown nonwoven fabric was produced in the same manner as in Example 1, except for the above. The results of measuring the properties of the electret melt-blown nonwoven fabric are shown in Table 1.

[0100] [Example 4]

[0101] In Example 3, the case where the water / polymer percentage when pure water was sprayed in mist form toward the filaments was 155% was changed to a water / polymer percentage of 190%, and a melt-blown nonwoven fabric was produced in the same manner as in Example 3, except for the above. The results of measuring the properties of the electret melt-blown nonwoven fabric are shown in Table 1.

[0102] [Example 5]

[0103] In Example 3, the case where the water / polymer percentage when pure water was sprayed in mist form toward the filaments was 155% was changed to a water / polymer percentage of 381%, and a melt-blown nonwoven fabric was produced in the same manner as in Example 3, except for the above. The results of measuring the properties of the electret melt-blown nonwoven fabric are shown in Table 1.

[0104] [Example 6]

[0105] In Example 3, the case where the water / polymer percentage when pure water was sprayed in mist form toward the filaments was 155% was changed to a water / polymer percentage of 476%, and a melt-blown nonwoven fabric was produced in the same manner as in Example 3, except for the above. The results of measuring the properties of the electret melt-blown nonwoven fabric are shown in Table 1.

[0106] [Comparative Example 1]

[0107] In Example 1, the case where pure water was sprayed in mist form toward the filaments using a spray nozzle was changed to stopping the supply of pure water to the spray nozzle and blowing only air that was sprayed from the air ejection port of the spray nozzle, and a melt-blown nonwoven fabric was produced in the same manner as in Example 1, except for the above. The results of measuring the properties of the electret melt-blown nonwoven fabric are shown in Table 1.

[0108] [Comparative Example 2]

[0109] In Example 3, the case where pure water was sprayed in mist form toward the filaments using a spray nozzle was changed to stopping the supply of pure water to the spray nozzle and blowing only air that was sprayed from the air ejection port of the spray nozzle, and a melt-blown nonwoven fabric was produced in the same manner as in Example 3, except for the above. The results of measuring the properties of the electret melt-blown nonwoven fabric are shown in Table 1.

[0110] [Comparative Example 3]

[0111] In Example 3, the case where the water / polymer percentage at the time of misty spraying of pure water to the yarns was 155% was set to a water / polymer percentage of 95%, and otherwise, a melt-blown nonwoven fabric was produced in the same manner as in Example 3. The results of measurement of the properties of the electret melt-blown nonwoven fabric are shown in Table 1.

[0112] [Table 1]

[0113]

Table 1

[0114]

[0115] As is clear from Table 1, in Examples 1 to 6 of the present application, the crystallization heat at around 100°C was generated by misty spraying of water in the spinning, and it is considered that amorphous portions exist in the fibers, and the stress is dispersed at the time of stretching. In addition, since the average fiber curvature is also high, the voids between the fibers are sufficient, and the fibers easily elongate at the time of stretching of the sheet. Accordingly, in Examples 1 to 6, the elongation in the CD direction was high at 100% or more.

[0116] On the other hand, in Comparative Examples 1 and 2 in which water was not misty sprayed and only air was used for quenching, the crystallization heat at the time of temperature increase was not confirmed, and it is considered that the fibers were uniformly crystallized, and the stress was not dispersed at the time of stretching. In addition, since the average fiber curvature was also low to 1.07 or less, the voids between the fibers were small. Accordingly, in Comparative Examples 1 and 2, even in the CD direction in which the elongation was high, the elongation was low to 76% or less, and a sufficient effect was not confirmed.

[0117] In addition, in Comparative Example 3 in which the water / polymer percentage was as low as 95%, the average fiber curvature was 1.12, and although there were voids between the fibers, the crystallization heat at around 100°C was low to 1.8 J / g due to insufficient cooling of the fibers, and the stress could not be sufficiently dispersed at the time of stretching of the sheet. Accordingly, the elongation in the CD direction was low to 92%, and a sufficient effect could not be confirmed.

[0118] As described above, by the production method of the present application, it is possible to provide an electret melt-blown nonwoven fabric that is soft without performing a post-processing treatment or adding an elastomer resin and a smoothing agent or the like, and further has a high elongation of 100% to 120% or so in one direction, which cannot be exhibited by the conventional melt-blown nonwoven fabric containing a polyolefin-based resin fiber.

Claims

1. An electret melt-blown nonwoven fabric comprising polyolefin-based resin fibers, wherein the electret melt-blown nonwoven fabric has a crystallization temperature of 80°C or higher and 130°C or lower at the first temperature increase in a cyclic differential scanning calorimetry, and a heat quantity ΔHm of 3.0 J / g or higher and 20.0 J / g or lower, and the polyolefin-based resin fibers are polypropylene resin fibers comprising a hindered amine compound.

2. The electret melt-blown nonwoven fabric according to claim 1, wherein The average fiber curvature of the polyolefin-based resin fibers is 1.10 or higher and 1.50 or lower.

3. The electret melt-blown nonwoven fabric according to claim 1 or 2, wherein The average single fiber diameter of the polyolefin-based resin fibers is 0.1 μm or higher and 8.0 μm or lower.

4. An air filter medium made using the electret melt-blown nonwoven fabric according to claim 1 or 2.

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