JP2019093367A - Electret fiber sheet and production method thereof - Google Patents

Abstract

To provide an electret fiber sheet excellent in air permeability, while having high dust collection characteristic.SOLUTION: A heat-resistant electret fiber sheet is an electret fiber sheet containing non-conductive fibers as much as 90 mass% or more. In the electret fiber sheet, fibers constituting the electret fiber sheet contain a crystal nucleus agent as much as 0.005-1.0 mass%, and a difference (Tm-Tc) between a melting point (Tm) measured by a differential scanning calorimeter (DSC) and a crystallization temperature (Tc) is 5-45°C.SELECTED DRAWING: None

Description

  The present invention relates to an electret fiber sheet excellent in air permeability while having high dust collection properties, which is suitably used as an air filter medium, and a method for producing the electret fiber sheet.

  BACKGROUND ART Conventionally, an air filter has been used to remove pollen, dust and the like in gas, and a non-woven fabric is often used as a filter material of the air filter. Among them, the melt-blowing method, which is one of the methods for producing the non-woven fabric, is widely used in the production of filter media for air filter products, battery separators and the like. The melt-blowing method is generally a method of thinning a thermoplastic polymer extruded from a spinneret into fibers by hot air injection, and forming a non-woven fabric as a fiber web by utilizing the self-bonding property of the obtained fibers. is there.

  This melt-blowing method does not require a complicated process as compared with other non-woven fabric manufacturing methods such as the spun bonding method, and has an advantage that thin fibers with a single fiber diameter of several tens μm to several μm or less can be easily obtained. Manufacturing method.

  Here, the performance required of the air filter is a high collection efficiency capable of collecting a large amount of micro dust and a low pressure loss with little resistance when the gas passes through the inside of the air filter. In order to obtain a filter medium having the above-mentioned high collection efficiency, it is suitable that the single fibers constituting the non-woven fabric have a fineness, but on the other hand, the non-woven fabric consisting of the single fibers when the single fibers are made fine There is a problem that pressure loss becomes high as the fiber density of the non-woven fabric is increased.

  Moreover, in order to obtain a filter medium with low pressure loss, it is suitable that the single fiber constituting the non-woven fabric has a large fineness, but on the other hand, if the single fiber is made large-sized, the fiber surface area in the non-woven fabric decreases. There is a problem that the collection efficiency is reduced. Thus, in the performance required for the air filter in the prior art, having a high collection efficiency and having a low pressure loss are in a contradictory relationship.

  As a method for solving the above-mentioned problems, attempts have been made to simultaneously satisfy high collection efficiency and low pressure loss by electretizing the non-woven fabric and utilizing the electrostatic action in addition to the physical action.

  For example, a method of manufacturing an electret fiber sheet is proposed in which a high voltage is applied by a non-contact type application electrode while moving the ground electrode and the non-woven fabric together while the non-woven fabric is in contact with the ground electrode. (See Patent Document 1). In addition, as a method of charging water by bringing it into contact with fibers, a jet of water or a water droplet stream is sprayed onto the fiber sheet under pressure sufficient to allow water to penetrate into the inside of the non-woven fabric to form an electret. (See Patent Document 2) or a method of causing the fiber sheet to pass over the slit-like nozzle and suctioning the water by the nozzle to make the fiber sheet permeate the water, and the positive polarity A so-called hydrocharging method has been proposed, such as a method of uniformly mixing negative charges (see Patent Document 3).

In addition, a method of obtaining a non-woven fabric having high collection efficiency and low pressure loss characteristics has been proposed by adding an additive to the fiber to the fibers constituting the non-woven fabric, specifically, 100 ° C. and made of a material obtained by blending at least one stabilizer selected from a hindered amine type, nitrogen-containing hindered phenol type, metal salt hindered phenol type or phenol type stabilizer with a high molecular weight polymer A heat-resistant electret material has been proposed in which the amount of trapped charge from the thermally stimulated depolarization current at the above temperature is 2.0 × 10 ⁻¹⁰ coulomb / cm ² or more (see Patent Document 4).

  Furthermore, there is proposed a method of suppressing clogging of particles by forming a non-woven fabric in which fine fibers and large fibers are mixed, and suppressing an increase in pressure loss by increasing gaps between the fibers (patent document 5 and Patent Document 6).

Japanese Patent Application Laid-Open No. 61-289177 U.S. Pat. No. 6,119,691 Unexamined-Japanese-Patent No. 2003-3367 Japanese Patent Application Laid-Open No. 63-280408 Japanese Patent Application Laid-Open No. 10-46460 Unexamined-Japanese-Patent No. 2006-37295

  However, although the collection performance is improved by electretizing the non-woven fabric as in the above-mentioned conventional proposal, for example, when used as an air filter, dust collection is carried out in terms of noise of the device main body and high air flow rate. There is a need to further reduce pressure loss while maintaining the characteristics.

  Then, in view of the problem of the conventional nonwoven fabric, the objective of this invention is providing the electret fiber sheet excellent in air permeability, having a high dust collection characteristic.

  The present invention solves the above-mentioned problems, and the electret fiber sheet of the present invention is an electret fiber sheet mainly comprising non-conductive fibers in an amount of 90% by mass or more, and the electret fiber sheet The crystal nucleating agent is contained in the fiber which composes 0.005 to 1.0% by mass, and the difference between the melting point (Tm) and the crystallization temperature (Tc) measured by differential scanning calorimeter (DSC) It is an electret fiber sheet characterized by Tm-Tc) being 5-45 ° C.

  According to a preferred embodiment of the electret fiber sheet of the present invention, the electret fiber sheet is composed of fibers made of a thermoplastic resin mainly composed of a polyolefin resin.

  According to a preferred embodiment of the electret fiber sheet of the present invention, the electret fiber sheet is made of a meltblown nonwoven fabric.

  According to a preferred embodiment of the electret fiber sheet of the present invention, an air filter medium comprising the electret fiber sheet is obtained.

  The method for producing an electret fiber sheet of the present invention is a method for producing an electret fiber sheet containing 90% by mass or more of nonconductive fibers by a melt-blowing method, and the electret as measured by differential scanning calorimeter (DSC) An electret fiber sheet characterized in that a difference (Tx-Tc) between a crystallization temperature (Tc) of the fiber sheet and a spinning temperature (Tx) when the electret fiber sheet is spun by a melt-blowing method is 10 to 130 ° C. Manufacturing method.

  According to the present invention, an electret fiber sheet excellent in air permeability can be obtained while having high dust collection characteristics. By using the electret fiber sheet of the present invention, an air filter medium having low pressure loss can be obtained while maintaining high collection efficiency.

FIG. 1 is a schematic side view showing an apparatus for measuring collection efficiency and pressure loss.

  The electret fiber sheet of the present invention is an electret fiber sheet mainly containing 90% by mass or more of non-conductive fibers, and the crystal nucleating agent is contained in the fibers constituting the electret fiber sheet in a range of 0.005 to 1.0. It is an electret fiber sheet which is contained by mass% and which has a difference (Tm-Tc) between a melting point (Tm) and a crystallization temperature (Tc) measured by a differential scanning calorimeter (DSC) of 5 to 45 ° C. or less.

  The electret fiber sheet of the present invention is an electret fiber sheet mainly comprising 90% by mass or more of non-conductive fibers. Examples of the fiber sheet include synthetic fiber woven fabrics, knitted fabrics and non-woven fabrics. In particular, in the case of an air filter, non-woven fabrics made of synthetic fibers are preferably used.

  It is a preferable aspect that the electret fiber sheet of this invention consists of a melt-blown nonwoven fabric. By using a melt-blown nonwoven fabric, fine fibers of several μm can be easily obtained without the need for complicated processes, and high dust collection characteristics can be easily achieved.

In the present invention, the non-conductivity in the non-conductive fiber means that the volume resistivity is 10 ¹² · Ω · cm or more, and the preferable embodiment is 10 ¹⁴ · Ω · cm or more. When the volume resistivity is 10 ¹² · Ω · cm or more, a large amount of charge can be maintained when electretized, and as a result, the collection performance is excellent and the pressure loss can be reduced.

  In the present invention, to comprise non-conductive fibers means to include 90% by mass or more of non-conductive fibers in the electret fiber sheet. The proportion of non-conductive fibers contained in the electret fiber sheet is preferably 95% by mass or more, and more preferably 97% by mass or more. When the amount of nonconductive fibers in the electret fiber sheet is less than 90% by mass, sufficient electret performance can not be obtained.

  In addition to the non-conductivity, a matting agent, a pigment, an antifungal agent, an antibacterial agent, a flame retardant and the like can be added as long as the effects of the present invention are not impaired.

  Examples of resin materials of non-conductive fibers used in the present invention include polyolefin resins such as polyethylene and polypropylene, polyester resins such as polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate and polylactic acid, polycarbonate resins, Examples thereof include elastomers such as polystyrene resins, polyphenylene sulfide resins, fluorine resins, polystyrene elastomers, polyolefin elastomers, polyester elastomers, polyamide elastomers and polyurethane elastomers, and copolymers or mixtures thereof.

  Among these, polyolefin resins are preferably used. Polyolefin resins have high volume resistivity and low water absorption, so they have high chargeability and charge retention when fiberized. Therefore, high collection efficiency can be achieved.

  Examples of the polyolefin resin include homopolymers such as polyethylene, polypropylene, polybutene and polymethylpentene. Also, copolymers obtained by copolymerizing different components to these homopolymers, or two or more different polymer blends may be used. Among these, polypropylene and polymethylpentene are preferably used from the viewpoint of charge retention. In addition, polypropylene is more preferably used from the viewpoint of low cost.

  The electret fiber sheet of the present invention contains 0.005 to 1.0% by mass, preferably 0.007 to 0.5% by mass of a crystal nucleating agent in (long) fibers constituting the electret fiber sheet. . By containing the crystal nucleating agent, the crystallization temperature of the non-conductive fiber is increased, solidification of the fiber at the time of spinning progresses rapidly, fusion between the fibers is reduced, and air permeability is improved.

The content of the crystal nucleating agent as referred to herein can be determined, for example, as follows. The nonwoven fabric is subjected to Soxhlet extraction with a methanol / chloroform mixed solution, and then the HPLC fraction is repeated for the extract, and the IR measurement, GC measurement, GC / MS measurement, MALDI-MS measurement, ¹ H-NMR measurement, for each fraction. And the structure is confirmed by ¹³ C-NMR measurement. Next, the mass of the separated material containing the crystal nucleating agent is totaled to determine the ratio to the whole nonwoven fabric, and this is taken as the content of the crystal nucleating agent.

  When the content of the crystal nucleating agent is less than 0.005% by mass, the rate of increase in air flow rate during heat treatment is small. On the other hand, when the content of the crystal nucleating agent exceeds 1.0% by mass, the spinnability deteriorates and the cost also becomes disadvantageous.

  The crystal nucleating agent is limited to sorbitol-based nucleating agent, nonitol-based nucleating agent, chrysitol-based nucleating agent, phosphoric acid-based nucleating agent, triaminobenzene derivative nucleating agent, and metal carboxylate salt nucleating agent.

  Sorbitol-type nucleating agents include, for example, dibenzylidene sorbitol (DBS), monomethyl dibenzylidene sorbitol (eg, 1,3: 2,4-bis (p-methylbenzylidene) sorbitol (p-MDBS)), dimethyl dibenzylidene sorbitol (Eg, 1,3: 2,4-bis (3,4-dimethylbenzylidene) sorbitol (3,4-DMDBS)) and the like, and “Millad” (registered trademark) 3988 (manufactured by Milliken Japan Co., Ltd.) And “Gelol” E-200 (manufactured by Shin Nippon Rika Co., Ltd.) and the like.

  Nonitol based nucleating agents include, for example, 1,2,3-trideoxy-4,6: 5,7-bis-[(4-propylphenyl) methylene] -nonitol, etc., and “Millad” (registered trademark) Examples include NX 8000 (manufactured by Milliken Japan Ltd.).

  Examples of the xylitol nucleating agent include bis-1,3: 2,4- (5 ', 6', 7 ', 8'-tetrahydro-2-naphthaldehyde benzylidene) 1-allyl xylitol and the like.

  Further, the phosphoric acid-based nucleating agent includes, for example, aluminum-bis (4,4 ', 6,6'-tetra-tert-butyl-2,2'-methylene diphenyl-phosphate) -hydroxide and the like, "Adekastab" (registered trademark) NA-11 (made by ADEKA), "Adekastab" (registered trademark) NA-21 (made by ADEKA), etc. are mentioned.

  Examples of triaminobenzene derivative nucleating agents include 1,3,5-tris (2,2-dimethylpropanamido) benzene and the like, and “Irgaclear” (registered trademark) XT386 ”(manufactured by BASF Japan Ltd.) Etc.

  Further, metal carboxylate nucleating agents include, for example, sodium benzoate, calcium 1,2-cyclohexanedicarboxylate and the like.

  In addition to the above-described crystal nucleating agent, additives such as a heat stabilizer, a weathering agent, and a polymerization inhibitor may be added to the fibers (materials) constituting the electret fiber sheet of the present invention. In particular, from the viewpoint of improving the electret performance when melt-blown non-woven fabric is treated with an electret, it is preferable to add at least one kind of hindered amine additive or / and triazine additive to the above-mentioned fiber (material) It is.

  As the hindered amine 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 Co., Ltd., “Kimasorb” (registered trademark) 944 LD ), 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-t-butyl-4-hydroxybenzyl) -2-n-butyl malonate bis (1,2,2,6,6-pentamethyl-4-piperidyl) (BASF) Yapan Ltd., "Tinuvin" ® 144), and the like.

  Moreover, as a triazine type 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., “Kimasorb” (registered trademark) ) 944 LD), and 2- (4,6-diphenyl-1,3,5-triazin-2-yl) -5-((hexyl) oxy) -phenol (manufactured by BASF Japan Ltd., “tinuvin” (registered trademark) Trademark) 1577FF) etc. can be mentioned.

  The amount of the above-mentioned hindered amine additive and / or triazine additive is preferably 0.5 to 5% by mass, more preferably 0.7 to 3% by mass, based on the mass of the electret fiber sheet. is there. By setting the addition amount in this range, excellent dust collection characteristics can be easily obtained when electretizing.

  Next, the manufacturing method of the electret fiber sheet of this invention is demonstrated.

  First, after the thermoplastic resin material and the additive are kneaded, this is extruded from an extruder and processed into a desired structure such as fibers, a fiber web and a non-woven fabric. As a method of kneading the above-mentioned compound and the resin material, a method of mixing and supplying them to the extruder hopper of a spinning machine, kneading the mixture in the extruder and feeding it directly to the spinner, or in advance the above compound and resin The material is kneaded by a kneading extruder, a static kneader or the like to prepare a master chip, which is melted in the extruder and supplied to a die part, and the like.

  The resulting fibers are then used to form a fibrous sheet in a conventional manner. For example, in the case where the fiber sheet is made of a woven fabric or a knitted fabric, the above-mentioned fibers can be used to form a yarn, and then the fiber sheet can be manufactured by weaving or knitting (knitting and knitting).

  When the fiber sheet is made of a non-woven fabric, the fiber web is formed by a dry method or a wet method using the above-mentioned fibers, and then the fiber web is bonded to produce a non-woven fabric. After being formed by a bonding method or a melt-blowing method, the fibrous web can be bonded to produce a non-woven fabric. In addition, a non-woven fabric mainly composed of nanofibers can be manufactured by an electrostatic spinning method or a method of eluting a sea portion of sea-island fibers.

  Next, the fiber sheet obtained in this manner is subjected to an electretization treatment to form an electret fiber sheet. The electretization treatment can be carried out on a single fiber sheet, or can be carried out on a laminated fiber sheet laminated with another fiber sheet.

  As a method of electretization used for manufacture of the electret fiber sheet of the present invention, a method of electretizing by applying water to a nonconductive fiber sheet and then drying it is preferably used. As a method of applying water to the fiber sheet, a method of spraying a jet stream or water droplet stream of water with a pressure sufficient for the water to penetrate into the fiber sheet, or one side of the fiber sheet after or while applying water Allowing the fiber sheet to penetrate into the fiber sheet by immersing the fiber sheet in a mixed solution of water and a water-soluble organic solvent such as isopropyl alcohol, ethyl alcohol and acetone. Methods etc.

In the present invention, as water used for electretization, it is preferable to use a liquid filter or the like from which dirt has been removed and which is as clean as possible. In particular, pure water such as ion exchange water, distilled water and filtered water permeated with a reverse osmosis membrane is preferably used. Further, the level as pure water is preferably 10 ³ μS / m or less in conductivity, more preferably 10 ² μS / m or less. Moreover, the water can be mixed with a water-soluble organic solvent as long as the water collection property is not affected.

  It is preferable that the average single fiber diameter of the fiber which comprises the electret fiber sheet of this invention is the range of 0.1-8.0 micrometers. When the average single fiber diameter is preferably 0.1 to 8.0 μm, more preferably 0.3 to 7.0 μm, and still more preferably 0.5 to 5.0 μm, the air permeability and dust collection properties are excellent. The electret fiber sheet can be easily obtained.

Moreover, it is preferable that the fabric weight of the electret fiber sheet of this invention is the range of 3-100 g / m < ² >. By setting the fabric weight to 3 to 100 g / m ² , preferably 5 to 70 g / m ² , more preferably 10 to 50 g / m ² , an electret fiber sheet excellent in air permeability and dust collection characteristics is easily obtained. .

  Furthermore, when the electret fiber sheet of the present invention is used for a high collection performance air filter, it is calculated from the collection efficiency and pressure loss of polystyrene particles having a particle diameter of 0.3 to 0.5 μm at a filtration wind speed of 4.5 m / min. The QF value to be obtained is preferably 0.20 or more, more preferably 0.22 or more. When an electret fiber sheet having a QF value of 0.20 or more is used as an air filter medium, it is easy to obtain filter performance excellent in high collection efficiency and air permeability.

  The electret fiber sheet of the present invention has a difference (Tm-Tc) between the crystallization temperature (Tc) and the melting point (Tm) of the fiber sheet of 5 to 45 ° C., preferably 10 to 40 ° C. By setting Tm-Tc to 5 to 45 ° C., it becomes easy to obtain a meltblown nonwoven fabric excellent in air permeability and dust collection characteristics. When Tm-Tc is greater than 45 ° C., the cooling efficiency of the fibers when manufacturing the non-woven fabric is reduced, and the fusion of the fibers is increased, so that the air permeability is reduced. When Tm-Tc is lower than 5 ° C., the fusion of fibers is reduced and the strength of the non-woven fabric is reduced.

  In the electret fiber sheet of the present invention, the difference (Tx-Tc) between the spinning temperature (Tx) and the crystallization temperature (Tc) when producing the fiber sheet by a melt-blowing method is preferably 10 to 130 ° C., more preferably Is 20-125 ° C. Here, the spinning temperature refers to the nozzle temperature. By setting the Tx-Tc to 10 to 130 ° C., cooling of the fiber during spinning by the melt-blowing method proceeds and a fiber sheet with less inter-fiber fusion is easily obtained, and if Tx-Tc becomes larger than 130 ° C., fusion occurs It is easy to increase and air permeability may decrease. If Tx-Tc is smaller than 10 ° C., fusion may be reduced and the strength of the non-woven fabric may be reduced.

  The electret fiber sheet of the present invention can be suitably used as a filter medium of an air filter.

  The air filter medium of the present invention comprises the electret fiber sheet of the present invention. A known method can be used as a method of obtaining the air filter medium of the present invention from the electret fiber sheet of the present invention. For example, the method described in JP-A-2004-82109 can be used.

  The air filter medium of the present invention is suitable for high performance applications such as air filters in general, air conditioning filters, air purifier filters, and automobile cabin filters.

  Next, the electret fiber sheet of the present invention will be specifically described by way of examples.

(1) Weight of electret fiber sheet:
The weight of the electret fiber sheet of vertical × horizontal = 15 cm × 15 cm was measured for one sample. The obtained value was converted into a value per 1 m ^2, rounded off to the first decimal place, was calculated of the electret fiber sheet basis weight (g / m ^2).

(2) Average single fiber diameter:
About the average single fiber diameter, 10 measurement samples of 3 mm × 3 mm are collected from any place of the electret fiber sheet, the magnification is adjusted to 1000 to 3000 times with a scanning electron microscope, and fibers are collected from the measurement samples A total of 10 photographs were taken, one for each of the front photographs. The single fiber diameter was measured about the fiber which can confirm the fiber diameter (single fiber diameter) in a photograph clearly, and the 2nd place after the decimal point of the average value was rounded off, and it was set as the average single fiber diameter.

(3) Thickness of electret fiber sheet:
Using a thickness gauge (“TECLOCK” (registered trademark) SM-114 manufactured by Techlock Co., Ltd.), the thickness of the electret fiber sheet is measured at 10 points at equal intervals in the width direction, and the third decimal place is rounded off from the average value And the thickness.

(4) Melting point (Tm), crystallization temperature (Tc):
It measured on condition of the following using the differential scanning calorimeter (Q100 made from TA Instruments), and made endothermic peak top temperature the melting point (Tm) of a measuring object. Moreover, the exothermic peak top temperature in the cooling process was made into the crystallization temperature (Tc) of a measuring object.
Measurement atmosphere: nitrogen flow (50 ml / min)
· Temperature range: -50 to 200 ° C
· Heating rate: 10 ° C / minute
Sample amount: 5 mg.

(5) Collection performance (collection efficiency and pressure loss) of electret fiber sheet:
At five places in the width direction of the electret fiber sheet, measurement samples for measurement of vertical × horizontal = 15 cm × 15 cm were collected, and for each sample, collection efficiency was measured using a collection efficiency measurement device shown in FIG. In the collection efficiency measurement apparatus shown in FIG. 1, the dust storage box 2 is connected to the upstream side of the sample holder 1 in which the measurement sample M is set, and the flow meter 3, the flow control valve 4 and the blower 5 are connected downstream. It is done. In addition, the particle counter 6 is used for the sample holder 1, and the number of dust on the upstream side of the measurement sample M and the number of dust on the downstream side can be measured via the switching cock 7. Furthermore, the sample holder 1 is equipped with a pressure gauge 8 so that the static pressure difference upstream and downstream of the measurement sample M can be read.

In measurement of collection efficiency, polystyrene 0.309 U 10% solution (Manufacturer: Nacalai Tesque, Inc.) is diluted to 200 times with distilled water and filled in the dust storage box 2. Next, the measurement sample M is set in the sample holder 1 and the air volume is adjusted by the flow control valve 4 so that the filter passing speed is 4.5 m / min, and the dust concentration is 10,000 to 40,000 pieces / 2 Stabilize in the range of 0.83 × 10 ^-4 m ³ (0.01 ft ³ ), and use the particle counter 6 (KC-01D, manufactured by Rion Co., Ltd.) as the number D of dust in the upstream of the measurement sample M and the number D of dust in the downstream. Measured 3 times per each measurement sample, and based on JIS K 0901 (1991) “shape, size and performance test method of filter material for collecting dust sample in gas”, using the following formula, 0. 0. The collection efficiency (%) of 3-0.5 μm particles was determined. The average value of three measurement samples was taken as the final collection efficiency.
Collection efficiency (%) = [1- (d / D)] × 100
(Here, d represents the total number of downstream dust measured three times, and D represents the total number of upstream dust measured three times.)

  The higher the non-woven fabric, the lower the number of downstream dusts, and the higher the collection efficiency. The pressure loss was determined by reading the static pressure difference between the upstream and downstream of the measurement sample M at the time of measurement of collection efficiency with the pressure gauge 8. The average value of five measurement samples was taken as the final pressure loss.

(6) QF value of electret fiber sheet:
The QF value which is an index of filtration performance is calculated by the following equation using the collection efficiency and the pressure loss. The lower the pressure loss and the higher the collection efficiency, the higher the QF value, indicating that the filtration performance is better.
QF value (Pa- ¹ ) =-[ln (1-collection efficiency (%) / 100)] / pressure loss (Pa).

Example 1
As a thermoplastic resin raw material, 0.03% by mass of crystal nucleating agent “Irgaclear” (registered trademark) XT386 (manufactured by BASF Japan Ltd.) and a hindered amine compound “Kimasorb” (registered trademark) 944 (manufactured by BASF Japan Ltd.) A polypropylene resin having a melt flow rate of 850 g / 10 minutes and containing 1% by mass of A) was used.

A polypropylene resin raw material is charged into a raw material hopper of a spinning machine, and a single hole discharge amount is 0.29 g / min by a melt blow method using a die (hole pitch: 1.0 mm) having a discharge hole with a diameter of 0.4 mm. A fiber sheet with a fabric weight of 23 g / m ² was obtained by spraying under the conditions of: hole, nozzle temperature: 250 ° C., air temperature: 260 ° C., air pressure: 0.09 MPa and adjusting the collection conveyor speed.

  Next, while running the obtained fiber sheet along the water surface of a water tank to which pure water is supplied, the slit-like suction nozzle is brought into contact with the surface to suck the water, whereby the entire surface of the fiber sheet is watered. And then dried with hot air at a temperature of 100 ° C. after draining to obtain an electret fiber sheet. The measured values and the calculated values of the obtained electret fiber sheet are shown in Table 1.

Example 2
As a thermoplastic resin raw material, 0.30% by mass of a crystal nucleating agent "ADEKA STAB" (registered trademark) NA-21 (manufactured by ADEKA Co., Ltd.) and a hindered amine compound "KIMASORB" (registered trademark) 944 (BASF Japan (traded) Electret fiber sheet was obtained by the same method as in Example 1 except that it contained 1% by mass), the nozzle temperature was 260 ° C., and the air temperature was 265 ° C. The obtained results are shown in Table 1.

Comparative Example 1
Electret fiber in the same manner as in Example 1 except that the crystal nucleating agent “Irgaclear” (registered trademark) XT386 (manufactured by BASF Japan Ltd.) is not added to the polypropylene used in Example 1 as a thermoplastic resin raw material. I got a sheet.

  Each characteristic value was measured by the method similar to Example 1 about the obtained electret fiber sheet. The obtained results are shown in Table 1.

  As is clear from Table 1, Example 1 and Example 2 of the present invention contain a crystal nucleating agent in the thermoplastic resin raw material, and the difference (Tm-Tc) between the melting point (Tm) and the crystallization temperature (Tc) is As it is in the range of 5 to 45 ° C., it showed high collection efficiency and low pressure loss, and the QF value showed a collection performance characteristic of 0.20 or more.

  On the other hand, Comparative Example 1 in which the thermoplastic resin raw material does not contain the crystal nucleating agent and Tm-Tc is larger than 45 ° C. does not have both high collection efficiency and low pressure loss, and the QF value is less than 0.20. Performance characteristics of

  As described above, the electret fiber sheet of the present invention containing 0.005 to 1.0% by mass of a crystal nucleating agent as a thermoplastic resin raw material and having a Tm-Tc of 5 to 45 ° C. has high dust collection characteristics. While having, it was excellent in breathability.

1: Sample holder 2: Dust storage box 3: Flow meter 4: Flow control valve 5: Blower 6: Particle counter 7: Switching cock 8: Pressure gauge M: Measurement sample

Claims (5)

  An electret fiber sheet comprising 90% by mass or more of non-conductive fibers, wherein a crystal nucleating agent is contained in 0.005 to 1.0% by mass in fibers constituting the electret fiber sheet, and a differential scanning An electret fiber sheet, wherein a difference (Tm-Tc) between a melting point (Tm) and a crystallization temperature (Tc) measured by a calorimeter (DSC) is 5 to 45 ° C.   The electret fiber sheet according to claim 1, wherein the electret fiber sheet is composed of fibers made of a thermoplastic resin mainly composed of a polyolefin resin.   The electret fiber sheet according to claim 1 or 2, which is made of a melt-blown non-woven fabric.   An air filter medium comprising the electret fiber sheet according to any one of claims 1 to 3.   A method for producing an electret fiber sheet comprising 90% by mass or more of nonconductive fibers by a melt blow method, wherein the crystallization temperature (Tc) of the electret fiber sheet measured by differential scanning calorimeter (DSC) and the above A method for producing an electret fiber sheet, wherein the difference (Tx-Tc) in the spinning temperature (Tx) when spinning the electret fiber sheet by a melt-blowing method is 10 to 130 ° C.

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