Electret melt-blown nonwoven fabric and manufacturing method thereof

Abstract

To provide an electret melt-blown nonwoven fabric that achieves both properties of high collecting efficiency and low pressure loss, which are incompatible with each other, and is excellent in those properties.SOLUTION: An electret melt-blown nonwoven fabric is constituted of non-conductive polymer fibers. The electret melt-blown nonwoven fabric has apparent density of 0.05 g / cm3 or more and 0.14 g / cm3 or less and satisfies following formulas 1, 2: 0.025×a*rp+0.475×a*bn≤Δa*≤0.56×a*rp+0.24×a*bn...(formula 1); 0.08×b*rp+0.72×b*bn≤Δb*≤0.40×b*rp+0.10×b*bn...(formula 2), where a*rp, b*rp are a* value and b* value when positive charge type red toner is measured by spectral colorimeter, and a*bn, b*bn are a* value and b* value when negative charge type blue toner is measured by spectral colorimeter.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an electretized meltblown nonwoven fabric. [Background technology]

[0002] Air filters have traditionally been used to remove pollen, dust, and other particles from air, and nonwoven fabrics are often used as the filter media for these air filters. Among these, the melt-blowing method, which is one of the methods for manufacturing nonwoven fabrics, is widely used to manufacture filter media for air filters, battery separators, and other products.

[0003] As a method for further improving the collection performance of the melt-blown nonwoven fabric obtained by this melt-blowing method, the melt-blown nonwoven fabric has been made into an electret (charged), and various nonwoven fabrics have been proposed so far.

[0004] For example, Patent Document 1 proposes an electret nonwoven fabric composed of single fibers made of a specific polymer composition, with the single fibers having a specific average single fiber diameter, basis weight, bulk density, and average surface charge density. It also describes that this nonwoven fabric not only has a high initial charge density, but also exhibits little charge release, especially under high temperature and high humidity conditions.

[0005] Furthermore, Patent Document 2 proposes a method for producing an electret fibrous sheet in which a fibrous sheet is placed in contact with an earth electrode, and a high voltage is applied by a non-contact type electrode while the earth electrode and the fibrous sheet are moved together to continuously electretize the sheet. It also describes that the electret fibrous sheet obtained by this method can maintain stable electret properties for a long period of time. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 6-128858 [Patent Document 2] Japanese Patent Application Publication No. 61-289177 Summary of the Invention [Problem to be solved by the invention]

[0007] The electretization methods described in Patent Documents 1 and 2 are corona discharge methods in which high voltage is applied to cause electron injection, ion migration, and dipole orientation within the nonwoven fabric, thereby imparting an electric charge to the nonwoven fabric. However, due to the manufacturing process, this corona discharge method mainly charges only the surface of the fiber sheet, making it difficult to charge the interior of the fiber sheet.

[0008] Therefore, an object of the present invention is to provide an electret melt-blown nonwoven fabric that combines the contradictory properties of high collection efficiency and low pressure loss and excels in these properties. [Means for solving the problem]

[0009] As a result of intensive research to achieve the above object, the inventors of the present invention have discovered that by spraying water onto the yarn during spinning in the melt-blowing method, it is possible to charge the interior of the resulting electret melt-blown nonwoven fabric, even if the melt-blown nonwoven fabric has a very low apparent density. It has also been found that this makes it possible to achieve both the contradictory properties of high collection efficiency and low pressure loss.

[0010] The present invention has been completed based on these findings, and provides the following inventions.

[0011] [1] An electret meltblown nonwoven fabric made of non-conductive polymer fibers and having an apparent density of 0.05 g / cm 3 More than 0.14g / cm 3 An electret melt-blown nonwoven fabric that satisfies the following formulas 1 and 2: 0.025×a *rp +0.475×a * bn ≦Δa * ≦0.56×a * rp +0.24×a * bn ...(Formula 1) 0.08×b * rp +0.72×b * bn ≦Δb * ≦0.40×b * rp +0.10×b * bn ...(Formula 2) where: a * rp is the value measured by a spectrophotometer for red positively charged toner. * is the value, b * rp is the value of red positively charged toner measured by a spectrophotometer. * is the value, a * bn is the value when measuring blue negatively charged toner using a spectrophotometer. * is the value, b * bn is the value of b when measuring blue negatively charged toner using a spectrophotometer. * is a value Δa * , Δb * are the values ​​expressed by the following equations 3 and 4, respectively. Δa * =a * ave -a * s ...(Formula 3) Δb * =b * ave -b * s ...(Formula 4) And, in equations 3 and 4, a * aveis the charge amount when the red positively charged toner and the blue negatively charged toner are attached to the electret meltblown nonwoven fabric. * is the average value of b * ave is the charge amount when the red positively charged toner and the blue negatively charged toner are attached to the electret meltblown nonwoven fabric. * is the average value of a * s is the thickness of the electret meltblown nonwoven fabric before the red positively charged toner and the blue negatively charged toner are attached. * is the value, b * s is the surface roughness of the electret meltblown nonwoven fabric before the red positively charged toner and the blue negatively charged toner are attached. * value.

[0012] [2] The electret melt-blown nonwoven fabric according to [1], wherein the average single fiber diameter is 0.5 μm or more and 3.0 μm or less.

[0013] [3] The electret melt-blown nonwoven fabric according to [1] or [2], wherein the non-conductive polymer of the non-conductive polymer fiber is a resin mainly composed of polypropylene.

[0014] [4] A method for producing an electret melt-blown nonwoven fabric according to any one of [1] to [3], wherein a non-conductive polymer is melt-spun from a spinneret having a plurality of spinning holes in the width direction, and the spun yarn is collected in a collecting device below to form a melt-blown nonwoven fabric, and water is sprayed onto the spun yarn between the spinneret and the collecting device to make the melt-blown nonwoven fabric into an electret. [Effects of the Invention]

[0015] According to the present invention, even a nonwoven fabric having a very low apparent density can be electretized to its interior, thereby providing a melt-blown nonwoven fabric that achieves both the contradictory properties of high collection efficiency and low pressure loss. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic side view showing a measuring device for collection efficiency and pressure loss. DETAILED DESCRIPTION OF THE INVENTION

[0017] The electret meltblown nonwoven fabric of the present invention is an electret meltblown nonwoven fabric made of non-conductive polymer fibers and has an apparent density of 0.05 g / cm 3 More than 0.14g / cm 3 and satisfies the following formulas 1 and 2. 0.025×a * rp +0.475×a * bn ≦Δa * ≦0.56×a * rp +0.24×a * bn ...(Formula 1) 0.08×b * rp +0.72×b * bn ≦Δb * ≦0.40×b * rp +0.10×b * bn ...(Formula 2) where: a * rp is the value measured by a spectrophotometer for red positively charged toner. * is the value, b * rp is the value of red positively charged toner measured by a spectrophotometer. * is the value, a * bn is the value when measuring blue negatively charged toner using a spectrophotometer. * is the value, b * bnis the value of b when measuring blue negatively charged toner using a spectrophotometer. * is a value Δa * , Δb * are the values ​​expressed by the following equations 3 and 4, respectively. Δa * =a * ave -a * s ...(Formula 3) Δb * =b * ave -b * s ...(Formula 4) And, in equations 3 and 4, a * ave is the charge amount when the red positively charged toner and the blue negatively charged toner are attached to the electret meltblown nonwoven fabric. * is the average value of b * ave is the charge amount when the red positively charged toner and the blue negatively charged toner are attached to the electret meltblown nonwoven fabric. * is the average value of a * s is the thickness of the electret meltblown nonwoven fabric before the red positively charged toner and the blue negatively charged toner are attached. * is the value, b * s is the surface roughness of the electret meltblown nonwoven fabric before the red positively charged toner and the blue negatively charged toner are attached. * value.

[0018] The components will be described in detail below, but the present invention is not limited to the scope of the following description as long as it does not deviate from the gist of the present invention.

[0019] Here, a in the present invention * value and b * The value is the "L" standardized by the International Commission on Illumination (CIE). * a* b * Color Space "a * value and b * Points to a value.

[0020] Furthermore, in the present invention, when the expression "thermoplastic resin mainly composed of..." is used, it refers to a thermoplastic resin in which "..." accounts for 50% by mass or more of the total constituent components.

[0021] (non-conductive polymer fibers) First, the electret meltblown nonwoven fabric of the present invention is composed of non-conductive polymer fibers. The non-conductive polymer fibers are fibers made of a non-conductive polymer, and the non-conductive polymer refers to a thermoplastic resin that is not substantially conductive, and is not particularly limited as long as it is a thermoplastic resin that has non-conductive properties. The thermoplastic resin that has non-conductive properties preferably has a volume resistivity of 10 12 Resin with a minimum of 10 Ω cm, more preferably 10 14 Thermoplastic resins that are mainly composed of resins with a hardness of Ω·cm or more are preferable.

[0022] Examples of non-conductive polymers include thermoplastic resins based on polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polylactic acid, polycarbonate, polystyrene, polyphenylene sulfite, fluorine-based resins, and mixtures and copolymers thereof. Among these, thermoplastic resins based on polyolefins or polylactic acid are preferred from the viewpoint of electret performance. Furthermore, thermoplastic resins based on polypropylene, particularly polypropylene homopolymers, copolymers with other components, and polymer blends with different resins, are even more preferred, including polypropylene homopolymers and resins containing 80% or more by mass of propylene units. Among polyethylene homopolymers, copolymers with other components, and polymer blends with different resins, polyethylene homopolymers and resins containing 80% or more by mass of ethylene units are also preferred. The same applies to other polyolefin-based resin compositions.

[0023] The non-conductive polymer in the present invention preferably has a melt flow rate (MFR) of 50 g / 10 min or more and 2500 g / 10 min or less, measured at 230°C under a load of 2.16 kg for 10 minutes, according to "8A Method: Mass Measurement" in JIS K7210-1:2014 "Plastics - Determination of Melt Mass Flow Rate (MFR) and Melt Volume Flow Rate (MVR) of Thermoplastics - Part 1: Standard Test Methods." By setting the melt flow rate of the non-conductive polymer to preferably 50 g / 10 min or more, more preferably 150 g / 10 min or more, it becomes easier to reduce the diameter of the fibers constituting the electret melt-blown nonwoven fabric. On the other hand, by setting the melt flow rate of the non-conductive polymer to preferably 2500 g / 10 min or less, more preferably 2000 g / 10 min or less, the strength of the electret melt-blown nonwoven fabric can be improved.

[0024] The non-conductive polymer of the present invention may contain a nucleating agent. By containing 0.005% by mass to 1.0% by mass, and preferably 0.007% by mass to 0.5% by mass of the nucleating agent, the crystallization temperature of the non-conductive fiber increases, the solidification of the fiber during spinning progresses quickly, and the fusion of the fibers is reduced, thereby reducing the apparent density and improving the breathability.

[0025] The content of the crystal nucleating agent here can be determined, for example, as follows: After Soxhlet extraction of an electret melt-blown nonwoven fabric with a methanol / chloroform mixed solution, the extract is repeatedly fractionated by HPLC, and each fraction is subjected to IR measurement, GC measurement, GC / MS measurement, MALDI-MS measurement, and 1 H-NMR measurement, and 13 The structure is confirmed by C-NMR measurement. Next, the masses of the fractions containing the nucleating agent are totaled, and the ratio to the total mass of the electret melt-blown nonwoven fabric is calculated, which is the content of the nucleating agent.

[0026] Examples of the crystal nucleating agent include sorbitol-based nucleating agents, nonitol-based nucleating agents, xylitol-based nucleating agents, phosphoric acid-based nucleating agents, triaminobenzene derivative nucleating agents, and metal carboxylate nucleating agents.

[0027] Sorbitol-based nucleating agents include, for example, dibenzylidene sorbitol (DBS), monomethyldibenzylidene sorbitol (e.g., 1,3:2,4-bis(p-methylbenzylidene)sorbitol (p-MDBS)), dimethyldibenzylidene sorbitol (e.g., 1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol (3,4-DMDBS)), and the like, and examples thereof include "Millad" (registered trademark) 3988 (manufactured by Milliken Japan Co., Ltd.) and "Gelall" (registered trademark) E-200 (manufactured by New Japan Chemical Co., Ltd.).

[0028] Nonitol-based nucleating agents include, for example, 1,2,3-trideoxy-4,6:5,7-bis-[(4-propylphenyl)methylene]-nonitol, and examples thereof include "Millad" (registered trademark) NX8000 (manufactured by Milliken Japan Co., Ltd.).

[0029] Xylitol-based nucleating agents include, for example, bis-1,3:2,4-(5',6',7',8'-tetrahydro-2-naphthaldehyde benzylidene) 1-allyl xylitol.

[0030] Furthermore, examples of phosphoric acid-based nucleating agents include aluminum-bis(4,4',6,6'-tetra-tert-butyl-2,2'-methylenediphenyl-phosphate)-hydroxide, and examples thereof include "ADK STAB" (registered trademark) NA-11 (manufactured by ADEKA CORPORATION) and "ADK STAB" (registered trademark) NA-21 (manufactured by ADEKA CORPORATION).

[0031] Examples of triaminobenzene derivative nucleating agents include 1,3,5-tris(2,2-dimethylpropanamido)benzene, and examples thereof include "Irgaclear" (registered trademark) XT386 (manufactured by BASF Japan Ltd.).

[0032] Further, metal carboxylate nucleating agents include, for example, sodium benzoate and calcium salt of 1,2-cyclohexanedicarboxylate.

[0033] In addition to the nucleating agent, the non-conductive polymer according to the present invention may contain at least one hindered amine additive or / and triazine additive, from the viewpoint of improving the electret performance of the electret melt-blown nonwoven fabric.

[0034] Examples of the hindered amine compound include 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), dimethyl succinate-1-(2 2-(3,5-di-t-butyl-4-hydroxybenzyl)-2-n-butylmalonate bis(1,2,2,6,6-pentamethyl-4-piperidyl) (manufactured by BASF Japan Ltd., "Tinuvin" (registered trademark) 144).

[0035] Examples of triazine additives include 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-triazin-2-yl)-5-((hexyl)oxy)-phenol (manufactured by BASF Japan Ltd., "Tinuvin" (registered trademark) 1577FF).

[0036] The amount of the hindered amine additive and / or triazine additive added is preferably 0.5% by mass or more and 5% by mass or less, more preferably 0.7% by mass or more and 3% by mass or less, based on the total mass of the non-conductive polymer. By setting the amount added within this range, an electret melt-blown nonwoven fabric with excellent dust collection properties can be easily obtained.

[0037] The content of the hindered amine additive and / or triazine additive can be determined, for example, as follows: After the electret melt-blown nonwoven fabric is subjected to Soxhlet extraction with a methanol / chloroform mixed solution, the extract is repeatedly fractionated by HPLC, and each fraction is subjected to IR measurement, GC measurement, GC / MS measurement, MALDI-MS measurement, and the like. 1 H-NMR measurement, and 13 The structure is confirmed by C-NMR measurement. The masses of the fractions containing the additives are added together to determine the percentage relative to the total electret melt-blown nonwoven fabric, which is the content of the hindered amine additive and / or triazine additive.

[0038] Additives such as heat stabilizers, weather resistance agents, polymerization inhibitors, antiviral agents, antibacterial agents and antiallergens can be added to the non-conductive polymer according to the present invention, as long as they do not impair the effects of the present invention.

[0039] The non-conductive polymer fiber according to the present invention may be a composite fiber made of the non-conductive polymer described above, and may take the form of a composite fiber such as a core-sheath type, an eccentric core-sheath type, a side-by-side type, a split type, an islands-in-the-sea type, or an alloy type.

[0040] Furthermore, the non-conductive polymer fibers according to the present invention preferably have an average single fiber diameter of 0.5 μm or more and 3.0 μm or less. By making the average single fiber diameter preferably 0.5 μm or more, more preferably 1.0 μm or more, and even more preferably 1.3 μm or more, the strength of the electret melt-blown nonwoven fabric can be improved. On the other hand, by making the average single fiber diameter 3.0 μm or less, more preferably 2.5 μm or less, and even more preferably 1.8 μm or less, the collection efficiency of the electret melt-blown nonwoven fabric can be improved.

[0041] The average single fiber diameter of the non-conductive polymer fiber according to the present invention is determined by randomly collecting ten 3 mm × 3 mm measurement samples from an electret melt-blown nonwoven fabric, adjusting the magnification to 4000 times using a scanning electron microscope (SEM, such as the VHX-D500 manufactured by Keyence Corporation), and taking one fiber surface photograph from each of the collected measurement samples, for a total of ten photographs. The single fiber diameter is measured for fibers in which the fiber diameter (single fiber diameter) can be clearly identified in the photographs, and the average value is rounded to one decimal place.

[0042] (electret meltblown nonwoven fabric) The electret meltblown nonwoven fabric of the present invention is composed of the non-conductive polymer fibers. The electret meltblown nonwoven fabric of the present invention has an apparent density of 0.05 g / cm. 3 More than 0.14g / cm 3 The following is the result.

[0043] Apparent density of 0.05 g / cm 3 or more, preferably 0.07 g / cm 3 More preferably, 0.09 g / cm 3 By setting the apparent density to 0.14 g / cm or more, the strength of the electret melt-blown nonwoven fabric can be improved. 3 or less, preferably 0.13 g / cm 3 or less, more preferably 0.11 g / cm 3 By setting the size below this, it is possible to suppress an increase in pressure loss even if the collection efficiency is increased by making the size finer.

[0044] In the present invention, the apparent density of the electret melt-blown nonwoven fabric refers to a value measured and calculated by the following method. (i) Three small pieces (length x width = 50 cm (longitudinal direction) x 10 cm (transverse direction)) of measurement samples were randomly taken from the electret melt-blown nonwoven fabric, and the mass of the samples was measured and the obtained value was used as 1 m 2The average value is converted to the value per unit area, and the average value is rounded off to the nearest tenth to obtain the basis weight (g / m 2 ) is calculated. (ii) Using a thickness meter (for example, "TECLOCK" (registered trademark) SM-114 manufactured by TECLOCK Corporation), the thickness of the electret melt-blown nonwoven fabric is measured at 10 points at equal intervals in the width direction, and the average value is rounded to two decimal places to calculate the thickness (mm) of the electret melt-blown nonwoven fabric. (iii) Divide the basis weight obtained in (i) by the thickness obtained in (ii), and round off the obtained value to two decimal places.

[0045] In addition, electret melt-blown nonwoven fabric has a basis weight of 10 g / m 2 More than 40g / m 2 It is preferable that:

[0046] Weight: 10g / m 2 or more, preferably 15 g / m 2 More preferably, 18 g / m 2 By setting the weight to 40 g / m or more, the strength of the electret melt-blown nonwoven fabric can be improved. 2 Less than 35 g / m 2 Less than 30 g / m, more preferably 2 By setting the following, an electret melt-blown nonwoven fabric with low pressure loss can be obtained.

[0047] In the present invention, the basis weight of the electret melt-blown nonwoven fabric refers to the value measured and calculated by the method described in (i) of the method for measuring and calculating the apparent density of the electret melt-blown nonwoven fabric described above.

[0048] The electret melt-blown nonwoven fabric preferably has a thickness of 0.02 mm or more and 2.0 mm or less.

[0049] By setting the thickness to 0.02 mm or more, preferably 0.03 mm or more, more preferably 0.05 mm or more, an electret melt-blown nonwoven fabric with low pressure loss can be obtained. On the other hand, by setting the thickness to 2.0 mm or less, preferably 1.0 mm or less, more preferably 0.7 mm or less, the strength of the electret melt-blown nonwoven fabric can be improved.

[0050] In the present invention, the thickness of the electret melt-blown nonwoven fabric refers to the value measured and calculated by the method described in (ii) of the method for measuring and calculating the apparent density of the electret melt-blown nonwoven fabric.

[0051] Next, the electret melt-blown nonwoven fabric of the present invention satisfies the following formulas 1 and 2. 0.025×a * rp +0.475×a * bn ≦Δa * ≦0.56×a * rp +0.24×a * bn ...(Formula 1) 0.08×b * rp +0.72×b * bn ≦Δb * ≦0.40×b * rp +0.10×b * bn ...(Formula 2) where: a * rp is the value measured by a spectrophotometer for red positively charged toner. * is the value, b * rp is the value of red positively charged toner measured by a spectrophotometer. * is the value, a * bn is the value when measuring blue negatively charged toner using a spectrophotometer. * is the value, b* bn is the value of b when measuring blue negatively charged toner using a spectrophotometer. * is a value Δa * , Δb * are the values ​​expressed by the following equations 3 and 4, respectively. Δa * =a * ave -a * s ...(Formula 3) Δb * =b * ave -b * s ...(Formula 4) And, in equations 3 and 4, a * ave is the charge amount when the red positively charged toner and the blue negatively charged toner are attached to the electret meltblown nonwoven fabric. * is the average value of b * ave is the charge amount when the red positively charged toner and the blue negatively charged toner are attached to the electret meltblown nonwoven fabric. * is the average value of a * s is the thickness of the electret meltblown nonwoven fabric before the red positively charged toner and the blue negatively charged toner are attached. * is the value, b * s is the surface roughness of the electret meltblown nonwoven fabric before the red positively charged toner and the blue negatively charged toner are attached. * value.

[0052] However, it is practically impossible to quantitatively and nondestructively evaluate the charge distribution of an electret meltblown nonwoven fabric. Therefore, the charge distribution in the electret meltblown nonwoven fabric of the present invention is visualized by adhering a red positively charged toner and a blue negatively charged toner to the electret meltblown nonwoven fabric, thereby identifying the state of the charge distribution. The charge distribution by the toners obtained by this method depends on the charge of the electret meltblown nonwoven fabric: if the fibers have a negative charge, red toner will adhere, and if the fibers have a positive charge, blue toner will adhere. Furthermore, the greater the charge amount, the more toner corresponding to that polarity will adhere, and the deeper the color will become.

[0053] The above-mentioned Δa obtained by this evaluation * , Δb * By satisfying formula 1 and formula 2, the electret melt-blown nonwoven fabric is charged to the inside, and the electret melt-blown nonwoven fabric exhibits a higher collection efficiency than electret melt-blown nonwoven fabrics that have been subjected to charging processing using a corona discharge method.

[0054] In particular, it is preferable that Formula 1 satisfies the following Formula 1-1, and it is more preferable that Formula 1-2 is satisfied. 0.05×a * rp +0.45×a * bn ≦Δa * ≦0.40×a * rp +0.40×a * bn ...(Formula 1-1) 0.10×a * rp +0.40×a * bn ≦Δa * ≦0.32×a * rp +0.48×a * bn ...(Formula 1-2) Regarding formula 2, it is preferable that the following formula 2-1 is satisfied, and it is more preferable that the following formula 2-2 is satisfied: 0.16×b * rp +0.64×b * bn ≦Δb * ≦0.25×b * rp +0.25×b * bn ...(Formula 2-1) 0.24×b * rp +0.56×b * bn ≦Δb * ≦0.20×b * rp +0.30×b * bn ...(Formula 2-2) The more Formula 1, Formula 1-1, and Formula 1-2 are satisfied, or the more Formula 2, Formula 2-1, and Formula 2-2 are satisfied, the higher the collection efficiency of the electret meltblown nonwoven fabric will be.

[0055] Here, in the present invention, Δa of the electret melt-blown nonwoven fabric * , Δb * (both units are omitted), and the a of red positively charged toner and blue negatively charged toner * value, b * value(a * rp , b * rp , a * bn , b * bn , both unitless) is a value measured and calculated using the following method in an environment with humidity of 50% or less. (i) Three test pieces measuring 8 cm in length and 25 cm in width are randomly taken from the electret melt-blown nonwoven fabric, excluding 30 mm from the edge of the electret melt-blown nonwoven fabric. Note that the electret melt-blown nonwoven fabrics taken should be free from any oil in order to prevent changes in their charge distribution. (ii) Red positively charged toner (for example, "IKT-821-2M" manufactured by IKK Shoji Co., Ltd.) and blue negatively charged toner (for example, "ART CYAN TONER" manufactured by Aimex Co., Ltd.) * value, b * value(a * rp , b * rp , a * bn , b * bn , all unitless) is measured using a spectrophotometer (for example, a spectrophotometer "CM3700D" manufactured by Minolta Co., Ltd.) according to the methods shown in (ii-1) and (ii-2) below. (ii-1) Place two teaspoons of red positively charged toner or blue negatively charged toner on a white standard plate (for example, EVER-WHITE (registered trademark) No. 9582 manufactured by Evers Corporation) and spread it evenly and evenly across the entire test piece so that the base material of the white standard plate is not visible. (ii-2) Using the above spectrophotometer, under the conditions of Illuminant C and a viewing angle of 2°, * value, b * The values ​​were measured three times, and the arithmetic mean value of each value was calculated as the a * value, b * value(a * rp , b * rp , a * bn , b * bn ) (iii) Red positively charged toner and blue negatively charged toner are mixed in equal amounts (mixed so that the mass ratio of red positively charged toner to blue negatively charged toner is 50:50) to prepare a purple mixed toner. (iv) Place the prepared mixed toner evenly on a 100 mesh (100 holes per 25.4 mm) plain woven wire mesh, and while vibrating the plain woven wire mesh, sprinkle the mixed toner onto the test piece until the base material is no longer visible. At this time, do not apply pressure to the mixed toner with your hands or an object (such as an iron plate) or rub it against the test piece. (v) The test piece is held at a corner and shaken up and down approximately 20 times with an amplitude of approximately 5 cm to remove any remaining excess mixed toner. (vi) Repeat steps (iv) and (v) above three times for the same test piece. (vii) Perform steps (iv) to (vi) above on three randomly selected test pieces. (viii) The test piece with the mixed toner placed thereon is set in a laminating pouch film (for example, "FCP10216303" manufactured by Fujipla Inc.), and heated using a pouch laminator (for example, "DS320P" manufactured by Japan GBC Inc.) (in the case of the "DS320P" manufactured by Japan GBC Inc., heating is performed at output dial 1), to adhere and form a laminated pouch. Similarly, a test piece without the mixed toner placed thereon is also set in a laminating pouch film, and heated using a pouch laminator to adhere and form a laminated pouch. (ix) a when the red positively charged toner and the blue negatively charged toner, which are laminated and pouched, are attached to an electret melt-blown nonwoven fabric. * value and b * The value is measured continuously at 5 mm intervals across a 20 cm width at the center of the sample. * value and b * The average value of each test piece was calculated. * The average value is a * ave , b * The average value is b * ave The spectrophotometric measurement conditions are as follows: [Spectrophotometric measurement conditions] ·Field of view: 10° ·Light source: D65 ·Measurement: Reflection ·Specular reflection light processing: SCE Measurement diameter: SAV (3mm x 5mm) ·UV condition: 100%FULL (x) As in (ix), for the laminated pouched test piece without mixed toner,* value and b * The average value of each of the values ​​was calculated to obtain the a of the electret melt-blown nonwoven fabric before the red positively charged toner and the blue negatively charged toner were attached. * Value: a * s , b * Value: b * s get. (xi) According to the above formulas 3 and 4, Δa * , Δb * respectively.

[0056] (Method for manufacturing electret meltblown nonwoven fabric) Next, a method for producing an electret melt-blown nonwoven fabric of the present invention will be described. The method for producing an electret melt-blown nonwoven fabric of the present invention is preferably as follows. That is, when a non-conductive polymer is melt-spun from a spinneret having a plurality of spinning holes in the width direction and the spun yarn is collected in a collector below to form a melt-blown nonwoven fabric, water is sprayed onto the spun yarn between the spinneret and the collector to make the melt-blown nonwoven fabric electret. A preferred embodiment thereof will be described in further detail below.

[0057] First, the non-conductive polymer is melt-spun from a spinneret having multiple spinning holes in the width direction. Immediately after the non-conductive polymer is discharged, heated air or the like (hereinafter sometimes simply referred to as hot air) is sprayed from a certain angle onto the non-conductive polymer to thin the diameter of the polymer. The spun yarn is then collected in a collector below to form a melt-blown nonwoven fabric.

[0058] When a nucleating agent is not added to the non-conductive polymer, the collection distance, which is the distance from the spinning holes of the spinneret to the collection device, is preferably 18 cm to 32 cm, more preferably 20 cm to 28 cm. A collection distance of 18 cm or more weakens the fusion of the fibers, reducing the apparent density and resulting in a sheet with low pressure loss. A collection distance of 32 cm or less can improve the strength of the electret melt-blown nonwoven fabric.

[0059] When a nucleating agent is added to the non-conductive polymer, the collection distance is preferably 15 cm to 25 cm, more preferably 17 cm to 23 cm. A collection distance of 15 cm or more weakens the fusion of the fibers, reducing the apparent density and resulting in a sheet with low pressure loss. A collection distance of 25 cm or less improves the strength of the electret melt-blown nonwoven fabric.

[0060] When the spun yarn is collected in a collecting device below to be made into a melt-blown nonwoven fabric, water is sprayed onto the spun yarn between the spinneret and the collecting device to make the melt-blown nonwoven fabric into an electret.

[0061] The water spraying device may be a single-hole spray nozzle that sprays water droplets in a conical or fan shape from a single hole, a slit-type spray nozzle that sprays water droplets in a band shape from a slit-shaped outlet, etc. Among these, in terms of being able to apply even a small amount of water uniformly in the width direction, it is more preferable to use a spray nozzle that has a plurality of water outlets arranged in the width direction and a pair of air outlets that open continuously or intermittently across the width direction and are arranged opposite each other so as to sandwich the plurality of water outlets, and that causes air discharged from the air outlet to collide with the water discharged from the plurality of water outlets.

[0062] The position where the water is sprayed may be anywhere between the hot air injection position and the collection device, but it is preferably at least 7.5 cm below the spinneret. More preferably, it is at least 8.0 cm, and even more preferably, it is at least 9.0 cm. In areas less than 7.5 cm from the spinneret, the temperature is high due to heat radiation from the spinneret, and the spun yarn itself is also at a high temperature, so some of the sprayed water may evaporate. Therefore, by spraying water at a position at least 7.5 cm below the spinneret, the sprayed water can be sufficiently distributed until the spun yarn is fully solidified and then becomes a nonwoven fabric. As a result, the collection performance of the electret melt-blown nonwoven fabric can be improved.

[0063] In the present invention, it is preferable to use water to be sprayed that has been cleaned using a liquid filter or the like and is as clean as possible. In particular, pure water such as ion-exchanged water, distilled water, and filtered water that has passed through a reverse osmosis membrane is preferably used. In addition, the level of pure water is such that the conductivity is 10 3 It is preferable that the conductivity is 10 μS / m or less. 2 It is more preferable that the electrical conductivity is μS / m or less. Furthermore, the water can be mixed with a water-soluble organic solvent such as isopropyl alcohol, ethyl alcohol, or acetone, as long as it does not affect the collection properties.

[0064] If necessary, the melt-blown nonwoven fabric after collection may be heated and dried. By heating and drying, excess water evaporates, and the melt-blown nonwoven fabric is further charged by peeling electrification when the water evaporates, thereby obtaining an electret melt-blown nonwoven fabric with high collection performance. In addition, the heat treatment causes some of the fibers to shrink and bend, increasing the thickness of the electret melt-blown nonwoven fabric, reducing the apparent density and providing an electret melt-blown nonwoven fabric with low pressure loss. [Example]

[0065] The present invention will now be described in detail with reference to examples, although the present invention is not limited to these examples.

[0066] [Measurement method] The values ​​of the various properties in the examples were determined by the following methods. Unless otherwise specified, the measurements of the various physical properties were carried out according to the methods described above.

[0067] (1) Electret meltblown nonwoven fabric a * ave , b * ave , a * s , b * s , Δa * , Δb *(All units are unitless): The above-mentioned properties of the electret melt-blown nonwoven fabric were measured and calculated by the above-mentioned methods. The toners used were "IKT-821-2M" manufactured by IKK Shoji Co., Ltd. as a red positively charged toner and "ART CYAN TONER" manufactured by IMEX Co., Ltd. as a blue negatively charged toner. The following devices and instruments were used. Spectrophotometer: Minolta Co., Ltd. Spectrophotometer "CM3700D" White standard plate: EVER-WHITE (registered trademark) No. 9582 manufactured by EVER'S Co., Ltd. Laminated pouch film: Fujipla Co., Ltd. "FCP10216303" Pouch laminator: Japan GBC Corporation "DS320P" The toner used in the measurement had the following various values ​​measured with a spectrophotometer: * rp is the L when a red positively charged toner (IKK Shoji Co., Ltd.'s "IKT-821-2M") is measured using a spectrophotometer. * is the value, L * bn is the L when a blue negatively charged toner ("ART CYAN TONER" manufactured by Aimex Co., Ltd.) is measured using a spectrophotometer. * value. L * rp (unitless): 41.52 a * rp (unitless): 68.59 ·b * rp (unitless): 12.23 L * bn (unitless): 32.91 a * bn (No units): 1.00 ·b * bn (unitless):-52.00 .

[0068] (2) Average single fiber diameter of non-conductive polymer fibers (μm): The average single fiber diameter of the non-conductive polymer fibers was measured and calculated by the above-mentioned method.

[0069] (3) Apparent density (g / cm) of electret meltblown nonwoven fabric 3 ), basis weight (g / m 2 ), Thickness (mm): The apparent density, basis weight and thickness of the electret melt-blown nonwoven fabric were measured and calculated by the above-mentioned methods.

[0070] (4) Collection performance (collection efficiency (%), pressure loss (Pa), QF value (Pa -1 )): The collection efficiency, pressure loss, and QF value of the electret melt-blown nonwoven fabric were measured and calculated using the following procedure. A. Take one measurement sample M (total of five) measuring 15cm x 15cm at each of five locations across the width of the nonwoven fabric. B. Prepare the collection efficiency measurement device shown in the schematic diagram of Figure 1. This collection efficiency measurement device has a dust storage box 2 connected upstream of a sample holder 1 in which a measurement sample M is set, and a flow meter 3, a flow control valve 4, and a blower 5 connected downstream. A particle counter 6 is also attached to the sample holder 1, and via a selector cock 7, the number of dust particles on both the upstream and downstream sides of the measurement sample M can be measured. C. A 10% aqueous solution of polystyrene particles ("OptiBind", manufactured by ThermoScientific, product number: 9100079710290) is diluted 200 times with distilled water and filled into dust storage box 2. D. Place the measurement sample M in the sample holder 1, and adjust the airflow rate with the flow control valve 4 so that the airflow rate through the filter is 4.5 m / min. The dust concentration is set to 10,000 to 40,000 particles / 2.83 x 10 -4 m 3 (0.01ft 3 ) range. E. Measure the number of dust particles D upstream and the number of dust particles d downstream of the measurement sample M three times per measurement sample using a particle counter 6 ("KC-01D" manufactured by Rion Co., Ltd.), and calculate the collection efficiency (%) of 0.3 to 0.5 μm particles using the following formula based on JIS K0901:1991 "Test method for shape, dimensions and performance of filter media for collecting dust samples in gas." Collection efficiency (%) = [1-(d / D)] × 100 (formula) (where d represents the total number of particles measured three times downstream, and D represents the total number of particles measured three times upstream.) F. At the same time, the static pressure difference between the upstream and downstream of the measurement sample M is read using a pressure gauge 8, and the pressure loss (Pa) of the measurement sample M is calculated. G. The average value of the collection efficiency (%) for measurement sample M is calculated, and the value obtained by rounding off to three decimal places is taken as the collection efficiency (%) of the electret melt-blown nonwoven fabric. H. The average value of the pressure loss (Pa) for measurement sample M is calculated, and the value obtained by rounding off to one decimal place is regarded as the pressure loss (Pa) of the electret melt-blown nonwoven fabric. I. QF value (Pa -1 ) is calculated using the following formula. The QF value indicates the relationship between collection efficiency and pressure loss, and the higher the QF value, the higher the collection efficiency and the lower the pressure loss. QF value (Pa -1 ) = -[ln(1-(collection efficiency (%)) / 100)] / (pressure loss (Pa)) ··· (equation).

[0071] [Example 1] As the non-conductive polymer, a polypropylene resin with a melt flow rate of 900 g / 10 min was used, which contained 1 mass % of the hindered amine compound "Chimasorb" (registered trademark) 944 (manufactured by BASF Japan Ltd., described as "C944" in Table 1) and 0.03 mass % of the crystal nucleating agent "Irgaclear XT386" (manufactured by BASF Japan Ltd., described as "XT386" in Table 1).

[0072] This non-conductive polymer was charged into the raw material hopper of a spinning machine, and then the molten non-conductive polymer was discharged from a die having discharge holes with a diameter of 0.4 mm (hole pitch: 1.0 mm) at a die temperature of 290°C and a single-hole discharge rate of 0.2 g / (minutes / hole) over a collection distance (the distance from the die to the collector) of 25 cm. Immediately after the yarn was discharged from the spinneret, air heated to 300°C (hot air) was sprayed at a pressure of 0.20 MPa onto the yarn. Furthermore, a spray nozzle was added, which had multiple water outlets arranged widthwise at a distance of 12 cm below the spinneret, and a pair of air outlets, which opened continuously or intermittently across the width and were arranged opposite each other on either side of the multiple water outlets. This spray nozzle collided the water discharged from the multiple water outlets with the air discharged from the air outlets. Pure water with a conductivity of 90 μS / m was sprayed toward the yarn at a flow rate of 1 L / min m per unit width (1 m) of the spinning width (the width direction of the production line, which will later become the cross direction (CD) of the electret meltblown nonwoven fabric). The yarn was then deposited on a collection net with an adjustable conveyor speed, yielding an electret meltblown nonwoven fabric. The physical properties of this electret meltblown nonwoven fabric are shown in Table 1.

[0073] [Example 2] A melt-blown nonwoven fabric was produced in the same manner as in Example 1, except that the collection distance was changed from 25 cm to 18 cm. The measurement results of the physical properties of this electret melt-blown nonwoven fabric are shown in Table 1.

[0074] [Example 3] As the non-conductive polymer, a polypropylene resin having a melt flow rate of 900 g / 10 min containing 1% by mass of the hindered amine compound "Chimasorb" (registered trademark) 944 (manufactured by BASF Japan Ltd.) and 0.03% by mass of the nucleating agent "Irgaclear XT386" (manufactured by BASF Japan Ltd.) was used, but instead a polypropylene resin having a melt flow rate of 1100 g / 10 min that did not contain a hindered amine compound or a nucleating agent was used, and the collection distance was changed from 25 cm to 28 cm. A melt-blown nonwoven fabric was produced in the same manner as in Example 1. The measurement results of the physical properties of this electret melt-blown nonwoven fabric are shown in Table 1.

[0075] [Comparative Example 1] A melt-blown nonwoven fabric was produced in the same manner as in Example 1, except that the collection distance was changed from 25 cm to 15 cm. The measurement results of the physical properties of this electret melt-blown nonwoven fabric are shown in Table 1.

[0076] Comparative Example 2 A meltblown nonwoven fabric was produced in the same manner as in Example 1, except that water spraying during spinning was not performed, whereas in Example 1, water spraying was not performed. The obtained meltblown nonwoven fabric was then subjected to an electrification treatment by a corona discharge method. The specific conditions for the corona discharge method are as follows. Power supply: DC high voltage stabilized power supply Linear distance between electrodes to which voltage is applied: 30 mm Applied voltage: -38kV ·Temperature: 25℃ Processing speed: 1m / min The measurement results of the physical properties of this electret meltblown nonwoven fabric are shown in Table 1.

[0077] [Table 1]

[0078] As is clear from Table 1, it can be confirmed that by reducing the apparent density, the QF value is higher than in Comparative Example 1, which has a high apparent density. Furthermore, it can be confirmed that Examples 1 to 3 of the present invention have a higher QF value than Comparative Example 2, which was subjected to charging processing by a corona discharge method, by spraying water during spinning to electretize the interior of the electret melt-blown nonwoven fabric. From these facts, according to the present invention, even nonwoven fabrics with very low apparent density can be electretized all the way to the interior, so a melt-blown nonwoven fabric is provided that achieves both the contradictory properties of high collection efficiency and low pressure loss. [Explanation of symbols]

[0079] 1: Sample holder 2: Dust storage box 3:Flow meter 4: Flow control valve 5: Blower 6: Particle Counter 7: Switch cock 8: Pressure gauge M: Measurement sample

Claims

1. An electret meltblown nonwoven fabric made of non-conductive polymer fibers and having an apparent density of 0.05 g / cm ３ 0.14g / cm or more ３ An electret melt-blown nonwoven fabric which satisfies the following formulas 1 and 2. 0.025×a ＊ ｒｐ +0.475×a ＊ ｂｎ ≦Δa ＊ ≦0.56×a ＊ ｒｐ +0.24×a ＊ ｂｎ ・・・(Formula 1) 0.08×b ＊ ｒｐ +0.72×b ＊ ｂｎ ≦Δb ＊ ≦0.40×b ＊ ｒｐ +0.10×b ＊ ｂｎ …………(Formula 2) where: a ＊ ｒｐ is the value measured by a spectrophotometer for red positively charged toner. ＊ is the value, b ＊ ｒｐ is the value of red positively charged toner measured by a spectrophotometer. ＊ is the value, a ＊ ｂｎ is the value when a negatively charged blue toner is measured using a spectrophotometer. ＊ is the value, b ＊ ｂｎ is the value of b when measuring blue negatively charged toner using a spectrophotometer. ＊ is a value Δa ＊ , Δb ＊ are values ​​expressed by the following equations 3 and 4, respectively. Δa ＊ = a ＊ ａｖｅ − a ＊ ｓ ··· (Equation 3) Δb ＊ =b ＊ ａｖｅ -b ＊ ｓ …………(Formula 4) And, in equations 3 and 4, a ＊ ａｖｅ is the charge amount when the red positively charged toner and the blue negatively charged toner are attached to the electret meltblown nonwoven fabric. ＊ is the average value of b ＊ ａｖｅ is the charge amount when the red positively charged toner and the blue negatively charged toner are attached to the electret meltblown nonwoven fabric. ＊ is the average value of a ＊ ｓ is the thickness of the electret meltblown nonwoven fabric before the red positively charged toner and the blue negatively charged toner are attached. ＊ is the value, b ＊ ｓ b of the electret melt-blown nonwoven fabric before the red positively charged toner and the blue negatively charged toner are attached ＊ value.

2. The electret melt-blown nonwoven fabric according to claim 1, wherein the average single fiber diameter is 0.5 μm or more and 3.0 μm or less.

3. The electret meltblown nonwoven fabric according to claim 1 or 2, wherein the nonconductive polymer of the nonconductive polymer fibers is a resin containing polypropylene as a main component.

4. 3. The method for producing an electret melt-blown nonwoven fabric according to claim 1, wherein a non-conductive polymer is melt-spun from a spinneret having a plurality of spinning holes in the width direction, and the spun yarn is collected in a collecting device below to form a melt-blown nonwoven fabric.

4. The method for producing an electret melt-blown nonwoven fabric according to claim 1, wherein water is sprayed onto the spun yarn between the spinneret and the collecting device to convert the melt-blown nonwoven fabric into an electret.

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