ELECTRET AND FILTER USING THE SAME

Abstract

It is provided that an electret having excellent filtering performance and a filter using the electret even in a case where polyolefin resin and magnesium element are contained. An electret comprising a polyolefin resin and a nitrogen-containing compound, wherein 0.1 to 5 parts by mass of the nitrogen-containing compound is contained to 100 parts by mass of the polyolefin resin, a proportion of a magnesium element contained in the electret is 5 to 100 ppm, and a QF value represented by the following formula is not less than 1.00 mmAq.sup.−1 when particles having particle diameters of 0.3 to 0.5 μm are to be collected.

QF [mmAq.sup.−1]=— [1n (particle penetration (%)/100)]/[ventilation resistance (mmAq)]

Claims

1. An electret comprising a polyolefin resin and a nitrogen-containing compound, wherein 0.1 to 5 parts by mass of the nitrogen-containing compound is contained to 100 parts by mass of the polyolefin resin, a proportion of a magnesium element contained in the electret is 5 to 100 ppm, and a QF value represented by the following formula is not less than 1.00 mmAq.sup.−1 when particles having particle diameters of 0.3 to 0.5 μm are to be collected.
QF [mmAq.sup.−1]=—[1n (particle penetration (%)/100)]/[ventilation resistance (mmAq)]

2. The electret according to claim 1, comprising fatty acid magnesium salt.

3. The electret according to claim 1, wherein the nitrogen-containing compound contains a hindered-amine-based compound.

4. The electret according to claim 1, wherein the electret is a fiber aggregate.

5. The electret according to claim 1, wherein the electret is produced by a meltblown method.

6. A filter comprising the electret according to claim 1.

Description

EXAMPLES

[0056] Hereinafter, embodiments of the present invention will be described. The test method is shown below.

[0057] (1) Concentration of magnesium in sample

[0058] 0.5 g of a sample was weighed into a platinum crucible, and preliminarily carbonized to 400° C. on a hot plate. Thereafter, a type FO610 electric furnace manufactured by Yamato Scientific Co., Ltd. was used to perform incineration at 550° C. for eight hours. After the incineration, 3 mL of 6.0 N hydrochloric acid was added, acid-decomposition was performed on the hot plate at 100° C., and heating was performed until the hydrochloric acid was completely volatilized. After the acid-decomposition ended, 20 mL of 1.2 N hydrochloric acid was added, and the obtained product was used as a test liquid to be measured. An amount of magnesium in the test liquid was quantified by using a SPECTROBLUE-type ICP emission spectrometer manufactured by Hitachi High-Tech Science Corporation according to a calibration curve generated with standard solution of a target element, and the concentration of magnesium in the sample was obtained according to the following equation.

[0059] Concentration of magnesium in sample: A (ppm (=mg/kg))

[0060] Concentration of magnesium in the test liquid: B (mg/L)

[0061] Magnesium concentration measured in the same method as described above except that a sample was not used (sample was not weighed into a platinum crucible): C (mg/L)

A=(B-C)×(20÷1000) (L)/(0.5÷1000) (kg)

[0062] (2) Ventilation resistance

[0063] Each sample punched into 72 mm φ was attached to an adapter having an effective ventilation diameter of 50 mm φ, piping having an inner diameter of 50 mm where a microdifferential pressure gauge was connected was coupled vertically, ventilation was carried out at 10 cm/s, and ventilation resistance (pressure loss) was measured without throttling.

[0064] (3) Particle penetration

[0065] Each sample punched into 72 mm φ was attached to an adapter having an effective ventilation diameter of 50 mm φ, and particle penetration was carried out with a filter by the following method using a light scattering type particle counter KC-01E manufactured by Rion Co., Ltd.

[0066] Evaluation particles: Airborne dust

[0067] Air velocity: 10 cm/s

[0068] Calculation of efficiency: The number of particles having particle diameters of 0.3 to 0.5 μm was measured by a light scattering calculation.

[0069] Particle penetration (%) =(the number of particles having particle diameters of 0.3 to 0.5 μm through the electret/ the number of particles having particle diameters of 0.3 to 0.5 μm before through the electret)

[0070] (4) Filter material Quality Factor (QF)

[0071] The initial QF value was calculated by the following equation using values of the ventilation resistance measured in the above (2) and the particle permeability measured in the above (3).

QF [mmAq.sup.−1]=—[1n (particle penetration (%)/100)]/[ventilation resistance (mmAq)]

Example 1

[0072] A product obtained by adding 0.00025 parts by mass of magnesium stearate (melting point: 88° C.) and 1 part by mass of Chimassorb (registered trademark) 944 manufactured by BASF as a hindered-amine-based compound to 100 parts by mass of polypropylene homopolymer having a magnesium concentration of not larger than 0.1 ppm and a melt flow rate (MFR) of 1200 g/10 minutes, was spun by using a meltblowing device at a resin temperature of 260° C. and an air temperature of 260° C., to obtain a fiber sheet having a weight per unit area of 20 g/m.sup.2. Water having an electric conductivity of 0.7 μS/cm and a pH of 6.8 was caused to collide with the obtained fiber sheet to perform charging, and the obtained product was then left as it was at 100° C. for 30 minutes and thus dried, thereby obtaining an electret filter. The ventilation resistance was 3.60 mmAq, a QF value was 1.13 mmAq.sup.−1, and a magnesium concentration was 7.8 ppm.

Examples 2 to 8 and Comparative examples 1 to 4

[0073] Electret filters were each produced in the same manner as in example 1 except that an amount of magnesium stearate to be added was as indicated in Table 1.

Comparative example 5

[0074] An electret filter was produced in the same manner as in example 5 except that a hindered-amine-based compound was not added.

Comparative example 6

[0075] An electret filter was produced in the same manner as in example 5 except that the obtained fiber sheet was charged by corona discharge.

[0076] Results of the examples and the comparative examples are systematically indicated below in Table 1.

TABLE-US-00001 TABLE 1 Polypropylene Magnesium homopolymer stearate (parts by (parts by Hindered-amine mass) mass) (parts by mass) Charging method Comparative 100 0 1 Water was caused to collide Example 1 to perform charging Comparative 100 0.00005 1 Water was caused to collide Example 2 to perform charging Example 1 100 0.00025 1 Water was caused to collide to perform charging Example 2 100 0.0005 1 Water was caused to collide to perform charging Example 3 100 0.00075 1 Water was caused to collide to perform charging Example 4 100 0.00085 1 Water was caused to collide to perform charging Example 5 100 0.001 1 Water was caused to collide to perform charging Example 6 100 0.0015 1 Water was caused to collide to perform charging Example 7 100 0.002 1 Water was caused to collide to perform charging Example 8 100 0.0025 1 Water was caused to collide to perform charging Comparative 100 0.005 1 Water was caused to collide Example 3 to perform charging Comparative 100 0.0075 1 Water was caused to collide Example 4 to perform charging Comparative 100 0.001 0 Water was caused to collide Example 5 to perform charging Comparative 100 0.001 1 Corona discharge method Example 6 Magnesium Ventilation Particle concentration resistance penetration QF value (ppm) (mmAq) (%) (mmAq.sup.−1) Comparative 0.1 or less 3.55 7.0 0.75 Example 1 Comparative 1.5 3.47 4.7 0.88 Example 2 Example 1 7.8 3.60 1.7 1.13 Example 2 16.3 3.70 0.4 1.52 Example 3 26.2 3.68 0.3 1.58 Example 4 30.4 3.65 0.3 1.61 Example 5 38.6 3.71 0.4 1.48 Example 6 56.1 3.62 1.0 1.28 Example 7 76.5 3.63 1.5 1.15 Example 8 98.7 3.64 2.2 1.05 Comparative 199 3.58 10.5 0.63 Example 3 Comparative 302 3.45 17.2 0.51 Example 4 Comparative 38.6 3.42 21.5 0.45 Example 5 Comparative 38.6 3.51 14.5 0.55 Example 6

[0077] According to examples 1 to 8, the electret filter that had proportions of the contained magnesium element and nitrogen-containing compound within the predetermined ranges and that was charged by collision of water, had a high QF value and enhanced filtering properties. For the electrets according to examples 1 to 8, a fineness was calculated as a geometric mean by measuring fiber diameters of 50 fibers which did not overlap each other in one visual field with a scanning electron microscope. The fineness of each of the electrets was in a range of 2 to 2.5 μm.

[0078] Meanwhile, in comparative examples 1 to 4, a proportion of the contained magnesium element was outside the predetermined range, and, thus, the QF value was low and the filtering properties were insufficient. In both of comparative example 5 in which a hindered-amine-based compound was not added, and comparative example 6 in which charging was performed by corona discharge, each of the QF value was low and each of the filtering properties were insufficient.

INDUSTRIAL APPLICABILITY

[0079] The electret of the present invention exhibits excellent filtering performance, and can thus be used as a filter in various applications such as dust protective masks and air cleaners.