JP2553054C - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention relates to an electretized fiber for a dustproof filter used in semiconductor manufacturing, clean rooms for hospitals and the like, dustproof masks, domestic indoor air purifiers, and the like, and its use. More particularly, the present invention relates to an electretized fiber used for a dustproof filter capable of removing dust particles of 1 μm or less with high efficiency, and a method for producing the same. (Prior art) Conventionally, a dust filter that removes dust particles of 1 μm or less with high efficiency has been widely used, in which extremely thin glass fibers with a fiber diameter of submicron units are formed into a sheet by, for example, a wet papermaking method. Have been. Since the diameter of the glass fiber is in the submicron order, such a dustproof filter can remove dust in the submicron order and has a high dust removal efficiency, but has a high airflow resistance and a sheet shape. Therefore, it has the disadvantage that the strength is weak and brittle. Furthermore, filters using 100% glass fiber have the disadvantage that it is difficult to reduce the volume when disposing after use. Instead of a dust-proof filter using glass fiber having such a defect, ultra-fine fibers using a polymer substance are used to maintain a high polarization efficiency while maintaining high dust removal efficiency and low airflow resistance. It has been proposed to form an electret as shown and use it for a dustproof filter. For example, Japanese Patent Publication No. 56-47299 discloses that a nonpolar polymer substance is stretched into a film, then electretized by a corona charging device, and the electretized film is finely split by a split method to obtain a fibrous material. Is disclosed. The dustproof filter using the electretized fiber obtained by such a method has the advantages that dust can be removed with high efficiency by electrostatic force and the airflow resistance is low. However, since the fibers are formed by the split method, there is a limit in reducing the fiber diameter, and the diameter of the obtained fiber becomes large. A filter using such a fiber cannot remove dust in submicron units if the thickness of the filter is small, and also reduces the amount of retained dust. To increase the dust removal efficiency, the filter must be thick. Furthermore, since the film is electretized and then fiberized by the split method, the number of steps is large and the economic efficiency is impaired. Japanese Patent Publication No. 59-124 discloses that an electret in a molten or semi-molten state is obtained by melt-blowing a fiber obtained by a melt-blowing method in which a polymer substance is made into fine fibers by a composite flow of a molten polymer substance and a high-speed gas. Discloses a method of converting electretized fibers into nonwoven fabric. In this method, an electret ultrafine fiber can be obtained. However, in the molten or semi-molten state, the electret is formed by corona charging. It is difficult to maintain the charge level. (Problems to be Solved by the Invention) The present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to provide an electretized fiber which is electretized to a stable high charge level and is suitable for use in a dustproof filter. To provide. Another object of the present invention is to provide a method capable of producing a stable electretized fiber having a high charge level in a short time. (Means for Solving the Problems) The electretized fiber of the present invention is an electretized fiber used for a dustproof filter, and is obtained by cooling and solidifying an ultrafine meltblown fibrous material in which a fatty acid metal salt is blended with polypropylene . The state is electretized, thereby achieving the above object. Further, the method for producing electretized fiber of the present invention is a method for producing electretized fiber used for a dust-proof filter, in which a fatty acid metal salt is blended with polypropylene , and this is formed into an extremely fine fibrous material by a melt blow method. And a step of cooling and solidifying the ultrafine fibrous material to form an electret, thereby achieving the above object. As the electrically insulating polymer material, a thermoplastic resin is used in order to form an extremely fine fiber by a melt blow method. Further, the degree of electric insulation of the polymer material is preferably 10 ¹² Ω · cm or more in volume resistivity. As such a polymer material, polypropylene, polyethylene, polyethylene terephthalate, nylon, polymethyl methacrylate and the like are preferable. It is considered that the fatty acid metal salt blended in the polymer material effectively traps the electric charge reaching the fiber from the ion stream emitted from the corona electrode, for example, when it is electretized. Examples of such fatty acid metal salts include compounds of fatty acids such as lauric acid, palmitic acid, stearic acid, and oleic acid, and metals such as aluminum, magnesium, calcium, and zinc. Such a fatty acid metal salt may be blended in a range of 100 ppm or more, preferably 300 ppm or more and 2000 ppm or less on a metal basis. The polymer material containing the fatty acid metal salt is formed into an ultrafine fiber by a melt blow method, cooled, solidified, and then electretized. There are flash spinning, electrostatic spinning, centrifugal spinning, etc. as a method for making polymer materials into ultrafine fibrous materials. However, in order to make polymer materials into ultrafine fibrous materials and to electretize them to a high charge level, , Melt blow method is most suitable. As shown in Fig. 1, the melt blow method
Heated air is spouted from the air supply pipe 13 at high speed around the tip of the nozzle 11 heated by the nozzle 12, and the molten polymer material 14 is discharged from the tip of the nozzle 11 into the heated air. A composite flow of the polymer and the heated air is formed, and the discharged molten polymer material 14 is formed into a fine fiber. The molten polymer material 14 formed into a fibrous form by the melt blow method is cooled and solidified, and then electretized by, for example, charging using a corona electrode 15 as shown in FIG. 2 to obtain electretized fibers. According to the melt blow method,
Since the polymer material is discharged from the nozzle at high speed in an uncured state, such as in a molten or semi-molten state, if such a polymer material is corona-charged, the charge is captured and the charge neutralizing action is performed in parallel. Occurs, and the charging level is at a certain level, but the charging level is not sufficient. However, since the fatty acid metal salt is blended in the fibrous polymer material, the fatty acid metal salt is effective for the fibrous polymer material flowing at high speed even if the corona charging time is as short as several milliseconds. Since the electric charge can be trapped in a specific manner, the charge level is set to a high level. In addition, after the polymer material is completely solidified, the fatty acid metal salt effectively captures the charge that has reached the surface of the polymer material, so that a high charge level is ensured. The electretized fiber thus obtained is, for example, a nonwoven fabric,
Used as a dustproof filter. Electretization can be evaluated relatively easily by directly measuring the surface charge of an electretized material, for example, in the form of a film using a vibrating capacitance electrometer, and tracking the change over time. However, when the electretized fiber is made into a nonwoven fabric, an electric field is hardly formed on the surface layer of the nonwoven fabric, and the surface charge cannot be measured. Because the electretized fibers are randomly arranged in the nonwoven fabric, the electric field formed by each fiber is
This is because they are offset in the nonwoven fabric. For this reason, the evaluation of the electretization of the nonwoven fabric is performed by an indirect method by using the nonwoven fabric as a dustproof filter and evaluating the dust removal efficiency. That is, if the nonwoven fabric is electretized to a high charge level, the dust removal efficiency is improved and the nonwoven fabric is used as a dustproof filter for a long time. (Example) An example of the present invention will be described below. Example 1 Polypropylene was used as an insulating polymer material, and magnesium stearate [(C ₁₇ H ₃₅ COO) ₂ Mg] was used as a fatty acid metal salt, and 500 ppm based on magnesium.
They were compounded and extruded from 0.2 mm diameter nozzles arranged in series using a 200 mm diameter horizontal extruder. Hot air at 300 ° C was blown out from slits provided on both sides of each nozzle, and ultrafine fibers were formed by melt blow method. A corona electrode is placed 250 mm downstream from the nozzle surface, a voltage of -30 KV is applied to the corona electrode, and the fibrous material discharged from the nozzle and solidified by cooling until reaching the corona electrode is discharged. Electretized. A suction box is provided downstream of the corona electrode, and the electretized fibers are sandwiched between air-permeable sheets on the suction box to form an electret having a basis weight of 40 g / m ² and an average fiber diameter of 5 μm. A web of fibers was obtained. Air containing submicron units of salt particles is passed through this web at a ventilation speed of 10 cm / sec.
The particle concentration of 0.5 to 1.0 μm was measured by the light scattering counting method for the inlet and outlet concentrations to determine the dust removal efficiency. The dust removal efficiency in this case was 95%. Example 2 Example 2 is the same as Example 1 except that the magnesium stearate used as the fatty acid metal salt was 1000 ppm based on magnesium. The dust removal efficiency in this case is
98%. Example 3 Polypropylene was used as an insulating polymer material, and aluminum palmitate [(C ₁₅ H ₃₁ COO) ₃ Al] was used as a fatty acid metal salt in an amount of 500 ppm based on aluminum.
The mixture was blended, and a web of electretized fibers having a basis weight of 40 g / m ² and an average fiber diameter of 5 μm was prepared in the same manner as in Example 1, and the dust removal efficiency was determined in the same manner as in Example 1. The dust removal efficiency was 96%. Example 4 Example 4 is the same as Example 3 except that aluminum palmitate compounded as a fatty acid metal salt was compounded at 1000 ppm based on aluminum. The dust removal efficiency was 98%. Comparative Example 1 The same as Example 1 except that the corona electrode was disposed at a position 30 mm from the nozzle surface, and corona charging was performed in a state where the fibers discharged from the nozzle were not completely solidified. The dust removal efficiency was 80%. Comparative Example 2 The same as Example 1 except that corona charging by the corona electrode was not performed. The dust removal efficiency was 44%. Comparative Example 3 Example 1 was the same as Example 1 except that magnesium stearate as a fatty acid metal salt was not used, and only polypropylene which was an insulating polymer material was used. The dust removal efficiency was 75%. Comparative Example 4 Except that the corona electrode was arranged at a position of 30 mm from the nozzle surface and the corona charging was performed in a state where the fibers (compounded only with polypropylene) discharged from the nozzle were not solidified.
This is the same as Comparative Example 3. The dust removal efficiency was 70%. Comparative Example 5 The same as Comparative Example 3 except that corona charging by the corona electrode was not performed. The dust removal efficiency was 30%. Comparative Example 6 Polypropylene was used as the insulating polymer material, and magnesium stearate was blended as a fatty acid metal salt in an amount of 500 ppm on a magnesium basis. In the process, -3
Electret fibers with an average fiber diameter of 20 μm were obtained by corona charging at 0 KV.
This was sandwiched between air-permeable sheets, and a web having a basis weight of 40 g / m ² was used to determine dust removal efficiency in the same manner as in Example 1. The dust removal efficiency was 53%. Comparative Example 7 Same as Example 3 except that corona charging by the corona electrode was not performed. The dust removal efficiency was 46%. Examples 1 to 4 and Comparative Examples 1 to 7 are summarized in Table 1. The electretized fiber obtained by the method of the present invention functions as a dustproof filter having a dust removal efficiency of 95% or more, and the dust removal efficiency hardly decreased even after 4 months. (Effect of the Invention) Since the electretized fiber of the present invention is formed by mixing a fatty acid metal salt with insulating polypropylene and cooling and solidifying a very fine melt-blown fibrous material, the electretized fiber of the present invention has the following characteristics. In order to effectively supplement the charge that the salt has reached the surface of the polypropylene , it is ensured that the charge level is high, and a very fine electretized fiber electretized to a stable high charge level is obtained, and this electretized fiber is used. And a dustproof filter with high dust removal efficiency can be easily obtained. In addition, according to the method for producing electretized fiber of the present invention, an ultrafine fiber electretized to a stable high charge level can be obtained, and thus the produced electretized fiber is suitable for use in a dustproof filter. .

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view for explaining the principle of the melt blow method, and FIG. 2 is a schematic view of electretization by corona charging. 11 ... Nozzle, 14 ... Polymer material, 15 ... Corona electrode.

Claims (1)

[Claims] 1. An electretized fiber used for a dustproof filter, which is an electretized fiber formed by cooling and solidifying an ultrafine meltblown fibrous material obtained by mixing a fatty acid metal salt with polypropylene . 2. This is a method for producing electretized fibers used for a dustproof filter. A process in which a fatty acid metal salt is blended with polypropylene to produce a fine fibrous material by a melt blow method, and the fine fibrous material is cooled and solidified. A process for producing electret fibers, which comprises: