JPH06254319A - Electret filter - Google Patents

Abstract

PURPOSE:To provide the electretted polyolefin slit fiber filter having high initial and long-term particle capturing efficiency. CONSTITUTION:This electret filter is constituted of the electretted polyolefin slit fibers contg. an org. acid metal salt consisting of >=10C org. acid and ions of metal having >=4eV work function. The attenuation of the electrification quantity of the polyolefin electret is lessened by incorporating the salt consisting of the org. acid of the long carbons and the ions of the metal having the large work function into this filter. The electret filter consisting of the electretted polyolefin slit fibers having the high initial particle capturing efficiency and high electrification level over a long period of time is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electret filter which can be used for a building air conditioner filter, a vacuum cleaner filter, an air purifier filter, an air conditioner filter, an office automation equipment filter, etc. and has a high charge level for a long period of time. Regarding

[0002]

2. Description of the Related Art An electret filter using a polyolefin split fiber is disclosed in Japanese Examined Patent Publication No. 56-472.
99 gazette, Japanese Patent Publication No. 57-14467, Japanese Patent Laid-Open No. 62-
102809, Japanese Patent Laid-Open No. 1-224020, and the like. These are all electret filters having a high surface charge density, but using a filter for a long period of time reduces the particle collection efficiency due to the decay of the charge amount, and there is a problem that the collection efficiency does not recover. there were.

[0003]

SUMMARY OF THE INVENTION The present invention has solved the above problems, that is, it does not provide an electret filter having a high charge level for a long period of time by having a high initial particle collection efficiency and reducing the attenuation of the charge amount. It is what

[0004]

The present invention has arrived at the present invention as a result of extensive studies in view of such problems. The present invention relates to an electret filter composed of a polyolefin-based split fiber containing an organic acid metal salt composed of an organic acid having 10 or more carbon atoms and an ion of a metal having a work function of 4 eV or more. Organic acids include carboxylic acids, organic phosphoric acids, organic sulfonic acids and the like, and in any case, they readily form a salt with a metal ion. 10 carbon atoms
The above organic acids are specifically lauric acid, linolenic acid,
Examples thereof include t-butylbenzoic acid and di (t-butylphenyl) phosphoric acid, with lauric acid, stearic acid and t-butylbenzoic acid being preferred. When a metal salt of an organic acid having 10 or less carbon atoms is used, the hydrophilicity of the salt increases, so that charge attenuation becomes large, and it is impossible to reach a level at which this problem can be solved. In addition, metal salts of organic acids with a small number of carbon atoms may cause thermal decomposition during compounding with polyolefin resins and during film formation of polyolefin resins containing these metal salts, which is unfriendly from the viewpoint of productivity. It is right. In addition, there are many metals that form organic acids and salts, of which metals having a work function of 4 eV or more are, for example, Al,
Fe, Ni, Co, Sn, Cu, Pb, Cd, etc. are mentioned. Of these, Al is most preferable in consideration of safety, film forming property, manufacturing cost, and the like. Therefore, particularly preferable examples of the organic acid metal salt are aluminum laurate, aluminum stearate and aluminum t-butyl benzoate. In such an electret filter made from a polyolefin-based split fiber containing a salt composed of an organic acid having 10 or more carbon atoms and a metal ion having a work function of 4 eV or more, an electret amount is obtained even under high temperature and high humidity. Has a very small attenuation, the charge level is high for a long period of time, and the drop in particle collection efficiency is very small. Conversely, when an organic acid having 10 or less carbon atoms or an organic acid metal salt composed of metal ions having a work function of less than 4 eV is contained, the effect is small. In the case of a salt consisting of small alkali metal ions, the amount of charge is greatly attenuated, which is unfriendly.

In the present invention, it is still unclear as to why the salt composed of the above organic acid and a metal ion having a work function of 4 eV or more reduces the charge amount attenuation of the polyolefin. When polyolefin is charged by an appropriate method, it is charged in the polyolefin (electrons and holes)
Is injected into the electret body. Structural defects of the polymer and impurities themselves in the polymer are considered as the top charge sites in the polyolefin electret. It is also reported that the dipole in the impurity stabilizes the charges trapped in the structural defects. The work function is defined as "the minimum energy required to extract one electron in a solid from the Fermi level to the vacuum level". That is, it means that a metal having a higher work function has more stable electrons and is less likely to be ionized. When a metal having a large work function is contained in the polyolefin, electrons in the injected charge are trapped and stabilized in the metal itself or in the vicinity thereof, so that the escape of electrons and the neutralization due to the bonding with holes are less likely to occur. It is estimated that the attenuation of the charge amount is smaller than that in the case where no such metal is contained. Incidentally, it is considered that these organic acid metal salts exist in the amorphous phase or the crystalline amorphous interface phase in the polyolefin.

In the present invention, the amount of the above-mentioned organic acid metal salt compounded is 0.1 to 5.0% by weight of the polyolefin.
It is preferably 0.5 to 3.0% by weight. If the compounding amount is less than this, the effect is not sufficient, and if the compounding amount is more than this, the effect does not change.

The organic acid metal salt in the present invention may be blended with the polyolefin either before or after the polymerization. In the case of blending after polymerization, there is a method in which the above-mentioned blending amount of the organic acid metal salt is mixed with the powder or resin of the polyolefin resin and uniformly dispersed, and then melt-kneaded with an extruder, a kneader or the like.

In general, an antioxidant is added to an ori-olefin in order to prevent thermal deterioration and oxidative deterioration. In the present invention, it is indispensable to add an antioxidant in addition to the above-mentioned organic metal salt, but these antioxidants do not inhibit the above-mentioned organic acid metal salt withdrawal effect.

In the present invention, the work function of a metal is measured by (1) a thermoelectron emission method for measuring one electron emitted by heating in a high vacuum, and (2) in a high vacuum. Photoelectron emission method for measuring one electron emitted by irradiating light, (3)
There are an electric field electron emission method that measures one electron emitted by applying a strong electric field, and (4) there is a blood color potential difference method that calculates the work function by measuring the contact potential difference between two substances. These four measurement methods Any of the above may be used. In the methods of (1) to (3), the work function is calculated from the current value of the emitted electrons by the relational expression of the altitude. Further, in the method of (4), the work function is calculated from the contact potential difference by the relational expression of high altitude.

Polyolefin in the present invention includes polypropylene, polyethylene, polystyrene, poly-4-methyl-1-pentene, poly-3-methyl-1-butene, etc., among which polypropylene is preferred.

In the present invention, split fibers are fibers obtained by finely splitting a uniaxially heat-stretched film in the stretching direction, and may be continuous fibers or discontinuous fibers. The width of the split fiber is several μm to several 100 μm,
The distribution is not particularly limited, but a preferable range is, for example, 20% or more of fibers having a size of less than 20 μm, 20 to 20.
30% or less of fibers of less than 40 μm and 30% or less of fibers of 40 μm or more. Here, the content of thin fibers of less than 20 μm and thick fibers of 40 μm or more is particularly important. In the present invention, as a method for producing split fibers, a method in which a file, a needle, or a roll in which a blade is implanted is rotated at a high speed to damage the uniaxially heat-stretched film or to make fine cuts is mentioned.

In the present invention, the method of electretizing the fibers may be before or after splitting. Specific electret methods include charging by corona discharge, charging by electron beam irradiation, charging under a high electric field and the like. Can be mentioned.

The electretized polyolefin-based split fiber obtained in the present invention is formed into a non-woven sheet by carding, and then needle punched, hot embossing calendering or ultrasonic welding is performed to obtain an electret filter.

The electret filter of the present invention can be used as a single material, but if necessary, it can be used by laminating it with a net, a non-woven fabric, a woven fabric, etc. by needle punching, ultrasonic welding or hot embossing calendering. it can. If necessary, it can also be used by laminating with a net, a non-woven fabric, a woven fabric, etc. by needle punching, ultrasonic welding or hot embossing calendering.

[0015]

[Various measurement methods] The particle collection efficiency of the electret filter is 0.3 μm of NaCl particles, and the particle concentration on the upstream side and the downstream side of the filter is respectively measured with a laser particle counter (KC manufactured by Rion Co. The value obtained by subtracting the particle concentration on the downstream side from the particle concentration on the upstream side was divided by the particle concentration on the upstream side, and expressed as a percentage. The pressure loss of the electret filter was measured with a Manostar gauge. FIG. 1 shows an apparatus for measuring particle collection efficiency. The charge retention rate was evaluated by measuring the particle transmittance (100−) obtained from the initial particle collection efficiency (E ₀ ) of the filter.
E ₀₎ for the natural logarithm 1n of (100-E _0), 6
It was calculated from the natural logarithmic value 1n (100-E ₁ ) of the particle transmittance (100-E ₁ ) obtained from the particle collection efficiency (E ₁ ) after treatment at 0 ° C. and 100 ° C. for 24 hours, using the following formula. .

[0016]

[Equation 1]

[0017]

EXAMPLES The present invention will be specifically described below with reference to examples.

Examples 1 to 6 Isotactic polypropylene having a melt flow index of 6, Mw / Mn of 5 and an organic acid metal salt shown in Table 1 in addition to an antioxidant was used to obtain a width of 300 mm. A cast film having a thickness of 50 μm was formed by a T-die, and then this cast film was stretched at a first stage by a three-stage hot roll stretching method, stretched 2.5 times at 110 ° C., a second stage,
Two-fold stretching at 120 ° C., a third stage, and 1.3-fold stretching at 135 ° C. were continuously performed. After that, a high voltage of 15 kV was applied by a needle electrode, and then the film was split with a needle roll to obtain split fibers. Next, add this split fiber to 75 mm
After being cut into pieces, they were supplied to a card, carded and needle-punched to produce the electret filters of Examples 1 to 6.

Comparative Examples 1 to 3 For comparison, the melt flow index and Mw / Mn are the same as those of the examples, and the antioxidant, the organic acid having 10 or more carbon atoms as shown in Table 1, and the work function are An electret polypropylene of Comparative Examples 1 to 3 was formed by forming a film of isotactic polypropylene mixed with a salt containing a metal ion of less than 4 eV in the same manner as in the example, and then stretching, charging, splitting, and forming a nonwoven fabric under exactly the same conditions. Was produced.

Comparative Examples 4 to 5 For comparison, the melt flow index and Mw / Mn are the same as those of the examples, and the antioxidant, the organic acid having 10 or more carbon atoms as shown in Table 1 and the work function are Electret filters of Comparative Examples 4 to 5 were formed by forming an isotactic polypropylene film containing a salt composed of metal ions of 4 eV or more in the same manner as in the example, and then stretching, charging, splitting and forming a nonwoven fabric under exactly the same conditions. Was produced.

Comparative Example 6 For comparison, an isotactic polypropylene having the same melt flow index and Mw / Mn as that of the example but containing only an antioxidant was formed in the same manner as in the example, and then under the same conditions. In, the electret filters of Comparative Examples 4 to 5 were produced by stretching, charging, splitting, and forming into a non-woven fabric.

Table 1 shows the types of organic acid metal salts blended with polypropylene, the work function of the metal and the blending amount. Table 2 shows the initial performance of each electret filter.
The measurement results of the charge retention rate after treatment at 60 ° C. and 100 ° C. for 24 hours are summarized.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

EFFECTS OF THE INVENTION The present invention contains the organic acid metal salt composed of an organic acid having 10 or more carbon atoms and an ion of a metal having a work function of 4 eV or more in the polyolefin as described above. Provided is an electret filter composed of a polyolefin-based split fiber having a high particle collection efficiency in the initial and long-term after electretization by reducing the amount of attenuation.

[Brief description of drawings]

FIG. 1 is a schematic view showing a method for measuring particle collection efficiency of an electret filter.

[Explanation of Codes] 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 neutralizer

Claims (1)

[Claims] 1. An electretized polyolefin-based split fiber filter containing an organic acid metal salt, wherein the organic acid metal salt is an organic acid having 10 or more carbon atoms and a metal ion having a work function of 4 eV or more. Electret filter characterized by being composed of.