JPH04346806A - Electret filter - Google Patents

Abstract

PURPOSE:To obtain a filter medium showing low pressure loss and high efficiency of removing particles without causing dropout of fiber which constitutes the filter medium when the filter medium is subjected to secondary working such as punching, welding, pleating, or without causing scatter of fiber during use. CONSTITUTION:The electret filter consists of nonwoven fabric having crimps which is converted into an electret. This nonwoven fabric has 0.01-0.05cc/cc fiber density.

Description

[Detailed description of the invention]

0001

TECHNICAL FIELD OF THE INVENTION The present invention relates to an electret filter having low pressure loss and high particle removal efficiency.

0002

[Industrial Application Field] The present invention is applicable to vacuum cleaners, air purifiers,
The present invention relates to a filter medium that can be used in M equipment, air conditioning equipment, etc.

0003

2. Description of the Related Art Electret filters that remove dust from the air by utilizing the static electricity of electret are disclosed in Japanese Patent Publication No. 47299/1982 and Japanese Patent Publication No. 14467/1983. The former is an electret filter made of a nonwoven fabric in which an electret nonpolar polymer film is split into fibrils, and each of the fibrils is homo-charged. The latter is an electret filter consisting of a laminate of at least two types of nonpolar polymers in which the electret film exhibits different shrinkage rates, and a nonwoven fabric obtained by splitting this film into fibrils and crimping.

0004

[Problems to be Solved by the Invention] The electret filter according to the above disclosed technology is a nonwoven fabric obtained by splitting a film into small fibers, and each fiber is not a continuous filament but a small fiber of finite length, for example, 30 to 90 mm. Therefore, there has been a problem that small fibers split during secondary processing of the filter such as punching, welding, and pleating may fall off from the nonwoven fabric layer or scatter when the filter is used.

[0005]

[Means for Solving the Problems] The present invention has been arrived at as a result of intensive studies to solve the above problems, and is a nonwoven fabric made of crimped electret filaments. Fiber packing density is 0
．． The present invention relates to an electret filter characterized in that the electret filter is 01 to 0.05 cc/cc. The filament in the present invention has a circular cross section,
It has a triangular, star-shaped, rectangular shape, etc., and is composed of one component polymer or two or more polymer components such as side-by-side type, sheath core type, eccentric sheath core type, etc., and is crimped mechanically or thermally. In addition, the filament length may be an infinite length fiber or a finite length fiber having at least 100 mm. Such filaments are made by a spinning technique such as a melt spinning method, a melt blowing method, an electrostatic field spinning method, a jet spinning method, or a flash spinning method, and are shaken off into a sheet shape onto a conveyor to form a nonwoven fabric.

[0006] The nonwoven fabric made of filaments in the present invention is subjected to electret processing by applying heat fusion processing, needle punching processing, or crimping processing between the filaments in order to increase the mechanical strength and rigidity of the nonwoven fabric, if necessary. . Further, in this case, the order of crimping and electret processing may be either first or last. The means for electret processing is not particularly limited, but examples include methods such as corona charging, electric field charging, and electron beam irradiation. In the present invention, the shape of the crimp of the filament may be regular such as a coil shape, loop shape, zigzag shape, etc., or irregular shape of two or more types thereof, and the number of crimp is 200 to 200 per meter of filament. The number is preferably 5,000, more preferably 300 to 1,000. Methods for applying crimp to the filament include air jet method, rubbing method,
There are a shaping method using gears, a latent structural crimping method, and a composite fiber crimping method, and among these methods, the latent structural crimping method and the composite fiber crimping method are preferred.

[0007] In the present invention, the filament component is an electret polymer. In a filament made of two or more types of polymers, at least one component is an electret polymer, and the other components may be either electret polymers or non-electret polymers. These electret polymers are made of non-polar polymers such as polyethylene, polypropylene, poly-4-
Examples include methyl-1-pentene, poly-3-methyl-1-butene, polytetrafluoroethylene, and mixtures of these polymers. In addition to the above-mentioned nonpolar polymer, other components include polar polymers such as polyethylene terephthalate, polyamide, polycarbonate, polysulfone, polyphenylene sulfide, polyvinylidene chloride, and mixtures thereof.

In the present invention, in the case of a two-component filament made of one type of polymer, the molecular weight of the polymer,
It is also possible to make all the components into electrets by creating physical property differences through molecular weight distribution and the inclusion of organic and inorganic additives. Examples of additives in this case include flame retardants, antibacterial agents, antifungal agents, aromatic crystal nucleating agents, polymer stabilizers, and the like. The fibers of the filaments in the present invention are 8 denier or less, preferably 1 denier or less, more preferably 0.1 denier or less, and even if all the filaments have the same fineness or a mixture of multiple finenesses. good.

[0009] It is important that the fiber packing density of the electret filter in the present invention is 0.01 to 0.05 cc/cc. When the fiber packing density exceeds this range, the pressure loss as a filter becomes too high, and when it falls below this range, problems arise in the secondary processability and handling of the filter, which is not preferable. In the present invention, in order to lower the fiber packing density, it is preferable to mix two or more types of filament fineness, and the preferred condition is that the ratio of the mixed weight of thick fineness to fine fineness is 0.5.
~5 times.

[0010] In the present invention, the fiber packing density refers to a load applied to a sample using a compressive elasticity tester (Toyo Seiki) of 1.25.
If T is the thickness of the sample in g/cm2, the value is obtained from the following equation. Fiber packing density (cc/cc) = W ÷ (ρ x T x 104
) W = Fabric weight of the sample (g/m2) ρ = Density of the fiber material constituting the sample (g/cc) T = Thickness of the sample (cm) In general, when the fiber packing density is reduced, both pressure loss and particle removal efficiency are reduced. Although it is well known that the fiber packing density decreases in the range of the fiber packing density in the present invention, the phenomenon has been discovered that although the pressure loss is significantly reduced, the removal efficiency is not significantly reduced. In other words, it is surprising that even if the distance between the fibers constituting the electret filter becomes large, the electrostatic force of the electret acts on the particles passing through it. The present invention will now be explained in detail with reference to Examples.

(Example 1) A side-by-side type filament (components: isotactic polypropylene and polycarbonate) with a fineness of 0.5 denier was spun from a nozzle and drawn into a sheet by an air jet, and dotted emboss welding was performed. A nonwoven fabric with a basis weight of 100 g/m2 was obtained. Next, the nonwoven fabric was heated in a hot air oven at 140° C. to develop crimp, and then subjected to charging treatment by corona discharge to obtain an electret filter, Example 1. The fiber packing density of the nonwoven fabric after embossing welding is 0.1
0cc/cc, and after crimp development it is 0.05cc
/cc. Next, particle removal efficiency and pressure loss due to atmospheric dust particles of 0.3 μm were measured using a particle counter (KC-14 manufactured by Rion Co., Ltd.) and a Manostar gauge at a linear velocity of 10 cm/sec through the filter medium. Regarding the ability of fibers to fall off from the filter medium, a square filter medium cut with scissors to a side of 10 cm was placed on a black mount, and after vibration was applied for 5 minutes, the number of fibers falling off from the filter medium was measured.

[Table 1] These results are shown in Table 1.

(Comparative Example 1) An unstretched film of isotactic polypropylene with a thickness of 50 μm was stretched 8 times on a heated roll at 140° C. and charged at the same time by corona discharge. Then, the average fiber width was adjusted to 40 μm using a needle roll. An electret fiber filter medium, Comparative Example 1, was obtained by splitting. Regarding Comparative Example 1, the removal efficiency, pressure loss, fiber packing density, and fiber shedding property were measured in the same manner as in Example 1, and the results are shown in Table 2.

[Table 2] Comparing Example 1 and Comparative Example 1, while in Example 1 no fibers fell off, in Comparative Example 1 it was observed that some fibers fell off due to vibration. Regarding the filter medium properties, Example 1 using crimped filaments had high removal efficiency and low pressure loss despite having the same fiber packing density.

(Example 2) A side-by-side type filament with a fineness of 0.1 denier (components are isotactic polypropylene with a melt flow index of 500 and isotactic polypropylene with a melt flow index of 300) was spun by a melt blowing method, A nonwoven fabric with a receiving area of 30 g/m2 was prepared on a wire mesh. Next, the nonwoven fabric was charged with an electric field strength of 15 KV/cm to form an electret by corona discharge, and then the nonwoven fabric was heat-treated to develop crimp, thereby obtaining the filter medium of Example 2. The filter medium of Example 2 was measured for removal efficiency, pressure loss, fiber packing density, and number of fallen fibers in the same manner as in Example 1. The results are shown in Table 3.

[Table 3] Also in Example 2, compared to Comparative Example 1, fiber shedding property,
All of the filter media properties were excellent.

(Example 3) Isotactic polypropylene with a fineness of 1 denier was melt-spun, and after being lightly embossed while taking it off with an air jet, the fabric weight was 150 g/m2.
A spunbond nonwoven fabric was obtained. Next, the nonwoven fabric was charged with an electric field strength of 20 KV/cm by corona discharge to form an electret, and then the nonwoven fabric was stretched by 200% in the longitudinal direction to make it bulky and crimped to obtain the filter medium of Example 3. Example 3
The removal efficiency, pressure loss, fiber packing density, and number of fallen fibers were measured in the same manner as in Example 1. Table 4 shows the results.
It was shown to.

[Table 4] Compared with Comparative Example 1, Example 3 was superior in both fiber shedding properties and filtration properties.

[0015]

[Effects of the Invention] According to the present invention, since the fiber material is a crimped filament, a low pressure drop filter is provided in which the fibers constituting the filter medium do not fall off during secondary processing and do not scatter during use. do.

Claims (1)

[Claims] 1. An electret filter characterized in that it is a nonwoven fabric made of electret filaments having crimp, and the nonwoven fabric has a fiber packing density of 0.01 to 0.05 cc/cc.