JP3055713B2 - Electret fiber filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter for a clean room, a filter for a building air conditioner, a filter for a vacuum cleaner,
Air purifier filter, air conditioner filter, OA
The present invention relates to an electret fiber filter which can be used as a filter for equipment and has excellent charge retention.

[0002]

2. Description of the Related Art Polyolefin (polypropylene) electrets having a high surface charge density are disclosed in
JP-A-151326 and JP-A-1-287914 propose a method of adding a stabilizer to polypropylene having a small molecular weight distribution. These are all electret materials characterized by stably retaining charge for a long time, but when used as an electret filter, the initial particle removal efficiency is low or the heat resistance is insufficient. It was not always satisfactory in that respect.

[0003]

The charge retention of the electret is considered to be related to the molecular mobility of the polymer, and as a result of intensive studies, the magnitude of the molecular mobility of the polypropylene was determined by the solid-state high-resolution pulse method ¹³ C-NMR. When defined by the spin-lattice relaxation time (T ₁ ) of the CH ₂ -based carbon nucleus in Example ₁ , an extremely small relaxation time is observed in the conventional product, which has a phase structure with a large molecular mobility, and thus has a temperature higher than room temperature. As a result, it was found that the charge retention of the electret was poor, and the particle removal efficiency was low over the initial and long term. The present invention has been made to solve the above problem, that is, to provide an electret fiber filter composed of electret polypropylene fibers having a phase structure in which the molecular mobility of polypropylene is suppressed and having excellent charge retention properties.

[0004]

SUMMARY OF THE INVENTION The present invention relates to a method for producing a spin nucleus of a CH ₂ -based carbon nucleus by a solid state high resolution pulse method ¹³ C-NMR.
Electretized polypropylene fiber obtained by electretizing a polypropylene fiber having a phase structure in which at least 20% of a component phase having a lattice relaxation time (T ₁ ) of 1 second to 10 seconds is contained in all the component phases. The present invention relates to an electret fiber filter. CH ₂ in solid state high resolution pulse method ¹³ C-NMR in the present invention
The measurement of the spin-lattice relaxation time (T ₁ ) of the base carbon nucleus refers to the magnetization of the polymer solid when it returns to the Boltzmann equilibrium state after the electromagnetic wave is applied in a constant magnetic field and then removed. This is a phase structure analysis means for examining the molecular mobility of the polymer in the fine structure from the relaxation phenomenon of the components. According to this analytical means, the spin of carbon nucleus-
As lattice relaxation time (T ₁₎ is large, the molecular mobility of the polymer is small, contrary to the spin - as lattice relaxation time (T ₁₎ is small, the molecular mobility of the polymer is greater.

The present inventors have conducted a phase structure analysis of various polypropylene materials by a solid high-resolution pulse method ¹³ C-NMR. As a result, the distribution of the spin-lattice relaxation time (T ₁ ) was determined. , A component phase having a spin-lattice relaxation time (T ₁ ) of less than 0.5 seconds;
Component phase having lattice relaxation time (T _1), and more than 10 seconds Spin - - 5-10 seconds of the spin was found that is divided into three components phase component phases having a lattice relaxation time (T _1). The spin of less than 0.5 seconds - a amorphous phase component phase having lattice relaxation time (T ₁₎ takes a random conformation, more than 10 seconds Spin - component having lattice relaxation time (T ₁₎ It is already known that the phase is a crystalline phase having a regular conformation, but the component phase having a spin-lattice relaxation time (T ₁ ) of 0.5 to 10 seconds is different from the amorphous phase and the crystalline phase As the spin-lattice relaxation time (T ₁ ) of the component phase increases and the amount of the component phase increases,
It has been found that the charge retention of the polypropylene electret is excellent.

In the present invention, at least a component phase having a spin-lattice relaxation time (T ₁ ) of 1 second to 10 seconds is contained in all component phases (the total component phase having a relaxation time of 0.1 second or more). It is important to include 20%, this amount is 2
If it is less than 0%, the initial electretization efficiency is low and the charge retention after electretization is not preferable. In addition, the component phases of spin - lattice relaxation time (T ₁₎ is is of an excellent charge retention electret closer to the 10 seconds. The present inventors describe a component phase having a spin-lattice relaxation time (T ₁ ) of 0.5 to 10 seconds as an intermediate phase because it is a phase existing between an amorphous phase and a crystalline phase. In the present invention, the mechanism by which this intermediate phase participates in the charge retention of the electret has not been clearly understood so far. In addition, the value of the surface charge density of the electret is 1 nanometer / cm ^2.
Since it is of the order of lon, it is not easy to elucidate the structure of the trap site with high accuracy at the density of such charge trap sites. In order to obtain an electret having such a phase structure, it is effective to form a fiber by a melt blow method and then aging for a long time in a heated state or to add an additive which promotes the formation of a phase having a different aggregation state in polypropylene. In the process of transition from the molten state of polypropylene to a thermodynamically stable equilibrium state, an intermediate phase is formed, and in the case of an additive, the additive may be the nucleus of the primary crystal nucleus, but it cannot be the nucleus Even additives can be effective in forming the mesophase of the present invention.

[0007]

In the present invention, the additive to be added to the polypropylene has a melting point of 100 ° C. or more, more preferably 1 ° C.
It is important that the temperature is 20 ° C. or higher. It is not clear why the melting point of the additive contributes to the formation of the polypropylene mesophase. However, considering the crystallization process from the molten state of polypropylene, for example, the crystallization onset temperature measured by a differential thermal analyzer is about 120 ° C. Will also increase, and the crystallization onset temperature will be even lower than 120 ° C. The fact that only the additive having a melting point of 100 ° C. or more acts on the formation of the mesophase of polypropylene is considered to be important that the molecular motion of the additive is fixed before the crystallization of polypropylene starts. .

Additives that can be used in the present invention include sodium bis (4-t-butylphenyl) phosphate and sodium 2,2'-ethylidenebis (4,6-di-t-butylphenyl) phosphate. Resin modifier, tris (3,5-di-t-butyl-4-hydroxybenzyl) isocyanurate, 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane , 1,1 bis (2'-methyl-4'-hydroxy-
5'-t-butylphenyl) butane, 2,2-thio-diethylenebis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], 3,9-bis [2- {3 -(3-t-butyl-4-hydroxy-5-
Methylphenyl) propionyloxy {-1,1-dimethylethyl] -2,8,10-tetraoxaspiro [5,5] undecane, bis (2,4-di-t-butylphenyl) pentaerythritol diphosphite, Bis (2,6-di-t-butyl-4-methylphenyl) pentaerythritol diphosphite, ethylidene bis (4,6-di-t-butylphenyl) octyl phosphite, tris- (2,4-di- an antioxidant such as t-butylphenyl) phosphite, a heavy metal deactivator such as 3- (N-salicyloyl) amino-1,2,4-triazole, disalicyloyl hydrazide decanedicarboxylate, and 2- ( 2'-hydroxy-5'-methylphenyl) benzotriazole, 2- (2'-hydroxy-
3'-t-butyl-5'-methylphenyl) -5-chlorobenzotriazole, 2,2'-methylenebis [4-
(1,1,3,3-tetramethylbutyl) -6- (2N
-Benzotriazol-2-yl) phenol], bis (5-benzoyl-4-hydroxy-2-methoxyphenyl) methane, tetrakis (2,2,6,6-tetramethyl-4-piperidyl) -1,2,2 3,4-butanetetracarboxylate, 1,2,2,6,6-pentamethyl-4-piperidyl / β, β, β ′, β′-tetramethyl-3,9- [2,4,8,10 -Tetraoxaspiro (5,5) undecane] diethyl (mixed) -1,2,2
Light stabilizers such as 3,4-butanetetracarboxylate are mentioned. Among these additives, more preferred additives are sodium bis (4-t-butylphenyl) phosphate and sodium 2,2′-ethylidenebis (4,6
-Di-t-butylphenyl) phosphate, tris (3,5-di-t-butyl-4-hydroxybenzyl)
Isocyanurate, 1,1,3-tris (2-methyl-
4-hydroxy-5-tert-butylphenyl) butane, tris- (2,4-di-tert-butylphenyl) phosphite, 2- (2′-hydroxy-3′-tert-butyl-5 ′)
-Methylphenyl) -5-chlorobenzotriazole,
1,2,2,6,6-pentamethyl-4-piperidyl /
β, β, β ′, β′-tetramethyl-3,9- [2,
4,8,10-tetraoxaspiro (5,5) undecane] diethyl (mixed) -1,2,3,4-butanetetracarboxylate.

In the present invention, the amount of the above-mentioned additive varies depending on the type of the additive, but is 0.05% to 5%.
% Is effective in forming a mesophase.

In the present invention, the phase formation of the mesophase is more effectively manifested as the thickness of the film, fiber or the like is smaller. In the molding of the fiber, melt blow spinning, flash spinning, electrostatic field spinning, and the like can be mentioned. However, melt blow spinning is the most preferred example, but is not limited thereto. In the present invention, when the polypropylene fiber of the electret fiber filter is made of a melt-blown nonwoven fabric, the range of the melt-blow spinning conditions is such that the nozzle hole diameter is 0.1 to 0.5 mm and the nozzle temperature is 200 to 300.
° C, polymer discharge rate is 0.02 per nozzle hole
5 to 2.0 g / min, traction air temperature of 230 to 400 ° C,
The traction air pressure is preferably 0.2 to 5 kg / cm ² , and the melt flow index of polypropylene is preferably 300 to 1000. The molecular weight distribution of polypropylene is not particularly limited. In the range of the spinning conditions, one having an arithmetic average fiber diameter of 1 to 3 μm by a scanning electron micrograph is obtained.

In the present invention, when the electret fiber filter is made of a melt blown nonwoven fabric,
The effective method for forming the mesophase is not limited to the addition of the additives described above. One of the methods other than the additive is heat treatment after the production of the melt-blown nonwoven fabric or 4
It is effective to perform aging for about two months in an atmosphere of 0 ° C to 90 ° C. In the melt-blown non-woven fabric to which the above-mentioned additives are not added, the phase structure other than the crystals immediately after spinning is very unstable. However, such a treatment stabilizes the phase structure thermally or with time, that is, the intermediate structure. It was found that the phase formation of the phase progressed. Another method for mesophase formation is to control by melt blow spinning conditions. Specifically, of the spinning conditions described above, the spinning draft (the ratio of the nozzle hole diameter to the fiber diameter) is 150.
The above proved to be effective. When the spinning draft is large, the degree of orientation of the fiber is increased, and the molecular chains are tensioned in the region other than the polypropylene crystal due to the orientation. The intermediate phase thus formed has a spin-lattice relaxation time (T ₁ ) of the CH ₂ -based carbon nucleus (T ₁ ) in the range of 1 to 10 seconds by solid-state high-resolution pulse method ¹³ C-NMR.
In the present invention, the method of electretizing the polypropylene fiber may be either before or after the molding of the polypropylene fiber, and specific electretization methods include charging by corona discharge, charging by electron beam irradiation, and under a high electric field. And the like. An example will be described in detail below.

[0013]

[Various measurement methods] The particle removal efficiency of the electret fiber filter was determined by using 0.3 μm NaCl particles at a wind speed of 5.3 cm / sec passing through the filter.
The downstream particle concentration is measured by a laser particle counter (manufactured by Rion, KC-14), and expressed as a percentage of the value obtained by subtracting the downstream particle concentration from the upstream particle concentration by the upstream particle concentration. Was. FIG. 1 shows an apparatus for measuring particle removal efficiency. The surface charge density of the electret fiber filter can be estimated from the value of the particle removal efficiency according to the following principle. In the case of electret fiber filters, the dominant trapping mechanism for particles is electrostatic force, so the particle removal efficiency of the filter is approximated by:

[0014]

(Equation 1) In Equation 1 E _t: particle removal efficiency of the filter E _e: particulate removal efficiency number 1 by electrostatic force than logarithmic transmission rule, is given by the following equation.

[0015]

(Equation 2)

[0016]

(Equation 3) In Equations 2 and 3, η _e : Single fiber collection efficiency due to electrostatic force α: Filling ratio L: Thickness _df : Fiber diameter By the way, single fiber collection efficiency due to electrostatic force depends on Coulomb force and induced force. Divided by the following equation.

[0017]

(Equation 4) In Equation 4, η _c : single fiber collection efficiency due to Coulomb force η _in : single fiber collection efficiency due to induced force Further, η _c and η _in are given by the following equations.

[0018]

(Equation 5)

[0019]

(Equation 6) Where C _m : Cunningham's correction coefficient q: particle charge ρ: surface charge density μ: air viscosity ε ₀ : vacuum permittivity ε _p : particle permittivity u: filtration speed d _p : particle diameter Taking into account the contribution of the induced force to the uncharged particles and the contribution of the Coulomb force to the charged particles, η _e is the single fiber collection efficiency due to the induced force and the single fiber collection due to the Coulomb force acting on one charged particle. It is expressed by the following equation, which is the sum from the efficiency to the single fiber collection efficiency due to the Coulomb force acting on the n charged particles.

[0020]

(Equation 7) η _ci : single fiber collection efficiency due to Coulomb force acting on i charged particles N _i : fraction of i charged particles Particle removal efficiency of filter measured and Equation 2 The surface charge density ρ of the fiber constituting the filter can be estimated by calculating the surface charge density ρ by computer processing so that the left side and the right side of the equation 7 are equal using 6. The charge retention was evaluated by electretization 1.
For particle removal efficiency of the day after (E ₀₎ from estimated surface charge density (ρ _0), the surface charge density ([rho ₁₎ was estimated from the particle removal efficiency after 24 hours heat treatment at 40 ℃ (E _1), the following equation Was calculated.

[0021]

(Equation 8) The solid-state high-resolution pulse method ¹³ C-NMR was measured using a Varian XL-300 ( ¹³ C; 75.5 MHz),
/ MAS (Cross Polarization / Magic AngleSpinning
) Method. For the measurement of the spin-lattice relaxation time (T ₁ ), a pulse sequence developed by Torchia was used. This pulse sequence is composed of two parts. In the first sequence, the ¹³ C spin obtained in the CP is tilted in the + Z direction to set an appropriate waiting time, and then the relaxation is observed. ¹³ C for the second series
The same observation will be made after tilting the spin in the −Z direction. Therefore, the obtained spectrum appears as the difference obtained between the two series. By changing the above waiting time by several steps,
A spectrum corresponding to the waiting time is obtained. FIG.
FIG. 3 shows an example of a spectrum measured by changing the waiting time in this way. CH in these spectra
Fig. 4 is a plot of the _two integrated intensities against the waiting time.
Is obtained. If the sample subjected to observation is a multi-component system composed of n phase components having various spin-lattice relaxation times (T ₁ ), the relaxation curve is represented by the following equation.

[0022]

(Equation 9) Here, <X ₀ > j: integrated intensity of j-th data (spectrum) n: number of components Ai: integrated intensity of i-th component t: waiting time T ₁ i: spin-lattice relaxation time of i-th component Therefore, in order to determine n, Ai, and T ₁ i, the plot of the waiting time and the integrated intensity is nonlinearly optimized by the simplex method. As a method, (1) a method of analyzing assuming that the spin-lattice relaxation time has a distribution and the relative proportions of many determined components are different (analysis by distribution), (2) assuming the number of several components And the spin of each component
There are two methods (analysis by histogram) using the value of the lattice relaxation time and its relative amount as variables. FIG. 4 shows an analysis result of the obtained spectrum when the above two methods are used. The results with the two methods show good agreement.

[0023]

EXAMPLES Examples 1 to 8 The melt flow index was 500 and the molecular weight distribution was Mw.
The additives shown in Table 1 were respectively added to the isotactic polypropylene having an Mn / Mn of 4 and a nozzle hole diameter of 0.2 mm and a nozzle temperature of 270 to 29.
0 ° C, polymer discharge amount 0.2g per nozzle hole
/ Min, traction air temperature 350 ° C, traction air pressure 3kg / cm
Width 10cm ² conditions, the average by melt-blown nonwoven fabric (scanning electron micrograph of the basis weight 30 g / m ² fiber diameter 2.
0 μm, a spinning draft 100) was prepared. Then, immediately after this nonwoven fabric was placed on an earth electrode on which a semiconductor sheet was spread, a direct current high voltage was applied with a corona electrode at an electric field of +17 kV / cm for 5 seconds to obtain an electret fiber filter. The results are shown in Table 1.

[0024]

[Table 1] Additive type A: sodium 2,2'-ethylidenebis (4,6-di-t-butylphenyl) phosphate B: sodium bis (4-t-butylphenyl) phosphate C: tris (3,5-di- t-butyl-4-hydroxybenzyl) isocyanurate D: 1,1,3-tris (2-methyl-4′-hydroxy-5′-t-butylphenyl) butane E: 1,1 bis (2′-methyl) -4'-hydroxy-
5'-t-butylphenyl) butane F: tris- (2,4-di-t-butylphenyl) phosphite G: 2- (2'-hydroxy-3'-t-butyl-5 '
-Methylphenyl) -5-chlorobenzotriazole H: 1,2,2,6,6-pentamethyl-4-piperidyl / β, β, β ′, β′-tetramethyl-3,9-
[2,4,8,10-tetraoxaspiro (5,5) undecane] diethyl (mixed) -1,2,3,4-butanetetracarboxylate

Comparative Examples 1 to 5 The same conditions as in Examples 1 to 8 were used when the same isotactic polypropylene as in Examples 1 to 8 was used and an additive having a melting point of 100 ° C. or less was added, and when no additive was added. To prepare a melt blown nonwoven fabric, and charged to obtain an electret fiber filter. Table 2 shows the results.

[0026]

[Table 2] I: octadecyl-3- (3,5-di-t-butyl-4)
-Hydroxyphenyl) propionate J: distearyl-3,3′-thiodipropionate K: pentaerythritol tetra (β-lauryl-thiopropionate) ester L: bis (2,2,6,6-tetramethyl) -4-piperidinyl) sebacate

Examples 9-10 Octadecyl-3- (3,3, an additive having a melting point of 50 ° C.
Using isotactic polypropylene having a melt flow index of 300 and a molecular weight distribution of 3 in Mw / Mn, containing 0.03% of (5-di-butyl-4-hydroxyphenyl) propionate, Examples 1 to
A melt-blown nonwoven fabric was prepared under the same conditions as in Example 8, immediately after heat-treated at 140 ° C for 24 hours, charged under the same conditions as Examples 1 to 8 (Example 9), and charged about 2 months after spinning. (Example 10) An electret fiber filter was obtained. Table 3 shows the results.

Example 11 A nozzle hole diameter of 0.3 mm and a nozzle temperature of 270 to 270 were obtained from the same isotactic polypropylene as in Examples 9 to 10.
290 ° C., polymer discharge amount 0.1% per nozzle hole.
3g / min, traction air temperature 350 ° C, traction air pressure 3kg /
cm ² (average fiber diameter 2.0 μm) (spinning draft 1
50), a melt-blown nonwoven fabric having a basis weight of 30 g / m ² was produced, and immediately thereafter, charged under the same conditions as in Examples 1 to 8, to obtain an electret fiber filter. The results are shown in Table 3.

[0029]

[Table 3] Examples 12-13 Melt flow index was 300 and molecular weight distribution was Mw /
In isotactic polypropylene having Mn of 2.8 and 6, respectively, 1,1,3-tris (2-methyl-4-hydroxy-5) as an additive having a melting point of 186 ° C.
(T-butylphenyl) butane was added in an amount of 0.3% to prepare a melt-blown nonwoven fabric (spinning draft 100) under the same conditions as in Examples 1 to 8, and then immediately charged under the same conditions as in Examples 1 to 8. Thus, an electret fiber filter was obtained. Table 4 shows the results.

[0030]

[Table 4]

Comparative Examples 6 and 7 The melt flow index was 500 and the molecular weight distribution was M
An isotactic polypropylene having a w / Mn of 3,7 respectively was added with 0.3% of octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate as an additive having a melting point of 50 ° C. %, And a melt-blown nonwoven fabric (spinning draft 100) was prepared under the same conditions as in Examples 1 to 8, and then immediately charged under the same conditions as in Examples 1 to 8, to obtain an electret fiber filter. Table 5 shows the results.

[0032]

[Table 5]

The spin-lattice relaxation times (T ₁ ) of the intermediate phase in the melt-blown nonwoven fabrics of Examples 1 to 8 were all 1.
Comparative examples 1 to 5 produced under the same conditions, although values of 5 seconds or more were shown, and Examples 1 to 3 showed high values of 3 seconds or more.
All melt blown nonwoven fabrics were 1 second or less. The component amount of the intermediate phase also shows the same tendency as the spin-lattice relaxation time (T ₁ ).
The above is shown. In Examples 1 to 8 in which these melt blown nonwoven fabrics were electretized, the initial particle removal efficiency was 9%.
Comparative Example 1 shows a high value of 9.5% or more.
-5 was as low as 97-98%. Also, as for the charge retention, Examples 1 to 8 showed a high retention of 90% or more, and among them, Example 1 showed no decrease.
On the other hand, Comparative Examples 1 to 5 had a charge retention of 70 to 80%. The spin-lattice relaxation time (T ₁ ) of the intermediate phase in the melt-blown nonwoven fabrics of Examples 9 to 11 is 1 second or more;
In addition, the initial particle removal efficiency and the charge retention rate are higher than those in Comparative Example 1. Examples 12-1
3 and Comparative Examples 6 and 7, it was confirmed that the molecular weight distribution of the polypropylene had no correlation with the spin-lattice relaxation time (T ₁ ) of the mesophase, the initial particle removal efficiency, and the charge retention. In Examples 12 and 13, almost the same results as in Example 4 were obtained, and in Comparative Examples 6 and 7, almost the same results as in Comparative Example 1 were obtained.

[0034]

As described above, the present invention comprises an electretized polypropylene fiber having a high initial and long term particle removal efficiency after electretization and having an excellent charge retention property by having an intermediate phase having a small molecular mobility as described above. Provided is an electret fiber filter.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a method for measuring the particle removal efficiency of an electret fiber filter. 1: Duct 2: Upstream sampling pipe 3: Downstream sampling pipe 4: Differential pressure gauge 5: Laser particle counter 6: Flow meter 7: Valve 8: Blower 9: Electret fiber filter 10: NaCl particle generator 11: Americium neutralization vessel

FIG. 2 is a solid high-resolution ¹³ C-NM of a polypropylene meltblown fiber measured by changing the waiting time.
It is an example of an R spectrum. In the figure, the vertical axis indicates the peak intensity, and the horizontal axis indicates the chemical shift. A: CH ₂ B: CH C: CH ₃ 1: waiting time 0.04 seconds 2: waiting time 0.1 seconds 3: waiting time 0.2 seconds 4: waiting time 0.4 seconds 5: waiting time 0.8 Second 6: Waiting time 1.6 seconds 7: Waiting time 3.2 seconds A: Integral curve B: Integral intensity obtained from the integral curve
The value on the left indicates the integrated intensity of peak A, and the value on the right indicates the integrated intensity of peak B plus peak C.

FIG. 3 is a solid high-resolution ¹³ C-NM of a polypropylene melt-blown fiber measured by changing the waiting time.
It is an example of an R spectrum. In the figure, the vertical axis indicates the peak intensity, and the horizontal axis indicates the chemical shift. A: CH ₂ B: CH C: CH ₃ 8: waiting time 6.4 seconds 9: waiting time 12.8 seconds 10: waiting time 25.6 seconds 11: waiting time 36.0 seconds 12: waiting time 51.2 Second 13: Waiting time 72.0 seconds 14: Waiting time 102.0 seconds

FIG. 4 is a relaxation curve obtained from the spectrum of FIG. The vertical axis indicates the integrated intensity of the CH ₂ group, and the horizontal axis indicates the waiting time (second). 1: Measurement data 2: Analysis result by optimization (analysis by distribution) 3: Difference between 2 and 3

FIG. 5 shows a result of an analysis of a phase structure obtained by analyzing the spectra of FIGS. 2 and 3 by a distribution analysis method.
(The sum of the integrated values from the baseline to the baseline of each component is 1), and the horizontal axis shows the spin-lattice relaxation time (unit: seconds).

FIG. 6 shows an analysis result of a phase structure obtained by analyzing the spectra of FIGS. 2 and 3 by histogram analysis. The vertical axis indicates the relative amount of each component phase (totaling 1), and the horizontal axis indicates Indicates a spin-lattice relaxation time (second). 8: Waiting time 6.4 seconds 9: Waiting time 12.8 seconds 10: Waiting time 25.6 seconds 11: Waiting time 36.0 seconds 12: Waiting time 51.2 seconds 13: Waiting time 72.0 seconds 14: Wait time 102.0 seconds

Claims (1)

(57) [Claims] 1. An electret fiber filter comprising electretized polypropylene fiber, wherein said polypropylene fiber has a solid high-resolution pulse method ¹³ C-NM.
Spin-lattice relaxation time (T ₁ ) of CH ₂ -based carbon nucleus by R
An electret fiber filter comprising an electretized polypropylene fiber, wherein the component phase has a phase structure in which at least 20% is contained in all the component phases for 1 to 10 seconds.