JPH0144101B2 - - Google Patents

Description

[Detailed description of the invention] [Purpose of the invention]

[Industrial Application Field] The present invention relates to an air filter device for adsorbing and collecting dust particles in the air, and particularly to an air filter device using an electric filter medium. [Prior Art] There have been various types of filters for air purification, and typical examples include mechanical filters, electrostatic precipitators, and dielectric filters. However, these filters have advantages and disadvantages, especially in fields such as large-scale integrated circuit (LSI) manufacturing equipment that require a highly clean environment where particles with a particle size of 0.3 μm or less are a problem. The above-mentioned conventional filters are often impractical from the viewpoint of pressure loss, equipment and operating costs. [Problem to be Solved by the Invention] The problem to be solved by the present invention is to further develop the invention related to an electrified filter (Japanese Patent Application Laid-Open No. 56-24013), which was previously filed by the applicant of the present application, to further improve dust removal. An object of the present invention is to provide a filter device with excellent efficiency.

[Structure of the invention]

[Means for Solving the Problems] (1) Concept In the process of conducting intensive studies on means for solving the above problems, the present inventor discovered that some of the dust particles in the air that should be removed We focused on the fact that it is in an electrically neutral state with no charge. When some of these uncharged particles pass between the electret fibers that serve as the filter medium, they are polarized by the spatial electric field between the fibers and are supposed to become positively or negatively charged, but what happens to the electret fibers themselves? Since no energy is supplied, the Coulomb force acting on the uncharged particles cannot be said to be large even considering the narrow space between the fibers. Therefore, the inventor came up with the idea that if the dust particles in the air to be filtered were positively charged in some way, the performance of the electret fibers could be demonstrated to a higher degree, and as a result of experiments, The accuracy of this idea was confirmed. (2) Overview Based on the above findings, the gist of the present invention is an air filter device characterized by comprising an electric filter medium and a dust particle charging device provided upstream thereof. (3) Electret filter The electric filter referred to in the present invention is known per se, and is made of a synthetic resin that itself has a high volume resistivity and low dielectric loss, such as polyethylene, polypropylene, or polystyrene. The fibers are intertwined into a nonwoven fabric, which is then electrically charged using an appropriate method. Due to the charging, the surface of the fiber is polarized in positive and negative directions, and this state is maintained semi-permanently. (4) Dust particle charging device Devices for charging dust particles include:
Known means for ionizing the air itself introduced into the above electret filter are used, for example a combination of a corona discharge electrode and a high-voltage power supply, in which case the electrode may be a mesh electrode, a wire electrode or a needle. A shaped electrode is preferred. As for the voltage, a high voltage of 10KV or more is usually used. The polarity of the electrode may be either positive or negative, but if it is a negative electrode, the amount of ozone generated will increase, so deozonation treatment will be required. [Operation] Referring to FIG. 1, the fibers 3, 3 constituting the electric filter medium 5 are themselves positively and negatively charged, forming a strong electric field in the space between each fiber. Therefore, the fine charged particles 2, 2 in the air are caused by the attraction force between point charges (Coulomb force) of the fibers,
Each is attracted to the oppositely charged side of the fiber (the strength of the attraction force is hereinafter figuratively expressed by the length of the arrow). On the other hand, the uncharged particles 4, 4 are also polarized by the electric field between the fibers 3, 3, and are also adsorbed to the fibers 3.
Its attraction force is generally weaker than the former. Therefore,
It is important to charge the dust particles on the upstream side of the filter medium 5 in order to improve the collection efficiency.
Even ultrafine particles of about 0.1 μm can be completely captured. [Example] FIG. 2 is a schematic side sectional view of the device of the present invention. A filter medium 5 made of electret fibers 3 is arranged at the rear of the air intake pipe 6, and high voltage electrodes 7, 7, . . . are arranged at the front. Table 1 below shows the results obtained when the above-mentioned apparatus was used to ionize the intake air 8 at an applied voltage of 12 KV while passing it through various filter media.

[Table] As is clear from the above table, in both positive corona discharge and negative corona discharge, when the thickness is 20 mm or more, even with a slight pressure loss, the electret filter medium completely prevents the permeation of fine particles of 0.1 μm or more. It is clear that this is being prevented. On the other hand, with a filter medium using ordinary polypropylene nonwoven fabric, nylon nonwoven fabric, or glass fiber nonwoven fabric, even if a dust particle charging means is similarly added to the upstream side of the filter medium, the ordinary polypropylene nonwoven fabric with a thickness of 20 mm is in a negative corona discharge state. The best result was a transmittance of 7.73% when used in , so the cooperative effect of the particle charging device and the electret filter medium is obvious.

【Effect of the invention】

As explained above, the present invention has developed a reliable air filtration means that can capture 100% of ultrafine particles with a particle size of 0.1 μm, and has achieved the need for ultra-clean air for the production of high-density integrated circuits and other purposes. It provides great benefits to facilities that are

[Brief explanation of drawings]

FIG. 1 is a diagram illustrating the dust particle collection action by the electret filter medium, and FIG. 2 is a schematic side sectional view of the air filter device of the present invention. The meanings of the symbols in the diagram are as follows: 1: Overall of the invention filter device; ...5:1 electret filter medium, ...3:5 constituent fibers, ...6:1 air intake tube, 7:1 electrode; 2: charged dust particles, 4: uncharged dust particles; 8: intake air flow.

Claims (1)

[Scope of Claims] 1. An air filter device comprising an electric filter medium and a dust particle charging device provided upstream thereof. 2. The air filter device according to claim 1, wherein the electrode of the dust particle charging device is a mesh electrode, a wire electrode, or a needle electrode.