Gas separation – Combined or convertible – In environmental air enclosure
Reexamination Certificate
2000-10-10
2002-05-21
Simmons, David A. (Department: 1724)
Gas separation
Combined or convertible
In environmental air enclosure
C055S521000, C055S524000, C055S528000, C454S187000
Reexamination Certificate
active
06391075
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an air filter part having a filter medium capable of cleaning air in at least a portion thereof, and a method of packaging the air filter part. The air filter part is contained in a package that suppresses the absorption of organic substances by the air filter part and a method of packaging the air filter part.
2. Background Information
In a clean room or in a semiconductor production device, electronic parts such as semiconductors, liquid display devices are produced in an environment in which the air is treated to capture floating particles. For example, an air filter unit having high collection efficiency, such as HEPA (high efficiency particulate air) filter or ULPA (ultra low penetration air) filter is used to capture floating finer particles in a clean room or in a semiconductor production device. The air filter unit of this type is typically a unit equipped with a high collection type filter medium and a frame having the filter medium incorporated therein. The filter medium is formed by, for example, laminating a porous film formed by laminating polytetrafluoroethylene (hereinafter referred to as “PTFE” for simplicity) and non-woven fabrics arranged so as to interpose the PTFE porous film from both sides thereof. The filter medium is processed in a given shape that is incorporated inside the frame.
When such an air filter unit is placed at an airway of a clean room and operation is started, air outside the clean room permeates the air filter unit and is introduced into the clean room from the airway. At that time, floating fine particles in air are captured by the filter medium by the colliding fibers of the filter medium.
The air filter unit of this type is generally packed in a bag made of a resin such as polyethylene (hereinafter referred to as “PE” for simplicity) after production, the bag is further packaged with cardboard, and the package is then delivered. Furthermore, there is the case that a filter medium and a product obtained by processing the filter medium into a given shape (hereinafter referred to as an “air filter pleat pack”) are each independently delivered in the state that it is packaged with the PE bag, the cardboard or the like.
Not only floating fine particles but also gaseous organic substances generated from paint or the like on walls of a clean room although a slight amount floats in a clean room. If those substances adhere onto semiconductor elements, wafers or the like, the electric properties of the products are impaired, and this results in decrease in the quality of products. In particular, high boiling point substances such as dioctyl phthalate (hereinafter referred to as “DOP” for simplicity), dibutyl phthalate (hereinafter referred to as “DBP” for simplicity), hydrocarbons having at least 15 carbon atoms or the like are difficult to volatilize. As a result, once those substances are adhered onto products, it is difficult to remove those substances from the products. For this reason, a chemical filter is often arranged within the clean room in order to remove those organic substances, and the amount of floating substances is suppressed to a predetermined standard or less.
However, according to the recent studies by the applicant of the present invention, it has been understood that those organic substances are generated not only from the interior walls of the clean room, but also from the air filter unit itself arranged within the clean room. In addition, it has been determined that those organic substances are generated from outside air and in particular from cardboard as a packaging material, and adsorbed on the filter medium, and the organic substances may possibly be generated from the PE bag.
In the conventional packaging form, a filter material such as a PE bag is arranged between an air filter unit and cardboard. Since organic substances generated from the cardboard permeate the PE bag, the organic substances are already in a state of adhering to the filter medium before use. Similar problems like this also occur in the case where a filter medium or the air filter pleat pack is independently packaged. In particular, a high collection type filter medium using PTFE porous film is more apt to adsorb such organic substances as compared with the conventional glass filter medium.
An air filter unit disclosed in Japanese Patent Laid-Open Application No. Hei 10-286415 is already proposed as an air filter part, in which content of organic substances is suppressed to a predetermined amount or less. In the air filter unit disclosed in this Japanese publication, measurement of the content of organic substances is conducted by a purge and trap method. In this conventional method, air having a temperature of about 40° C. is blown through an air filter unit at a predetermined flow rate. Then, the amount of organic substances detected from the air permeating through the other side of the air filter unit is measured. Thus, the amount of organic substances contained in the air filter unit is measured.
In this method, organic substances having relatively low boiling point can effectively be measured. However, regarding organic substances having high boiling point such as boiling point exceeding 270° C., since measurement conditions are mild, the organic substances cannot sufficiently be separated from the air filter unit. As a result, the content of high boiling point substances such as DBP or DOP cannot effectively be measured.
In view of the above, there exists a need for an air filter part which overcomes the above mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to suppress adhesion of organic substances from the packaging onto an air filter.
The present invention provides an air filter part having a filter medium capable of cleaning air in at least a portion thereof, in which the DBP content per 1 g of the filter medium is 1.0 &mgr;g or less prior to use of the filter medium.
The “air filter part” of the present invention as used herein includes, for example, but not limited to, a filter medium, an air filter pleat pack and an air filter unit (each being described hereinafter). The air filter unit is mainly explained below as an example of the air filter part.
As previously mentioned, although in slight amounts, gaseous organic substances such as DBP, DOP, hydrocarbons having at least 15 carbon atoms, and the like are generated from paint or the like on the interior walls of the clean room. These gaseous organic substances can degrade the products being produced in the clean room. For example, a chemical filter is typically arranged in the clean room in order to remove the organic substances. Thus, the amount of floating substances in the clean room is suppressed to a predetermined standard or less.
However, according to the recent studies by the applicant of the present invention, it has been understood that those organic substances are generated not only from the interior walls of the clean room, but also from the air filter unit itself arranged in the clean room or a semiconductor production device or the like. In addition, it has been determined from the studies by the applicant of the present invention that the air filter unit is already in a state contaminated with those organic substances prior to using the same.
Therefore, the air filter part of the present invention is prepared such that the DBP content per 1 g of a filter medium is a given predetermined amount or less prior to use, and thus, the inside of the clean room is suppressed from contamination in the case where the air filter part is arranged in the clean room.
The term “prior to use” as used herein means the time at which the package of the air filter unit is opened after at least about 50 hours in the package so as to remove the air filter part containing the filter medium. T
Hirano Seiichi
Inoue Osamu
Meiji Kazuhiro
Ohno Shinji
Daikin Industries Ltd.
Pham Minh-Chau T.
Shinjyu Global IP Counselors, LLP
Simmons David A.
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