Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
2001-08-10
2004-06-08
Singh, Arti R. (Department: 1771)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S304400, C442S340000, C442S341000, C442S344000, C442S346000, C442S350000, C442S381000, C442S389000, C442S394000, C442S414000, C442S415000, C442S417000
Reexamination Certificate
active
06746760
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gas adsorption sheet having a deodorizing function and an air-purifying filter having a dust-removing function and a deodorizing function, and relates to a method for producing the gas adsorption sheet.
2. Description of the Related Art
Heretofore, a granular activated carbon has generally been used for purification or deodorizing of a gas or liquid because of its cheap price, good air permeability and strong adsorbability for a solute in an aerosol or solution.
As one of techniques of applying such a granular activated carbon to an air-purifying filter, there is a sheet-like adsorption material to be used by passing an air to be purified through the sheet in a direction perpendicular to the sheet surface. However, it is not easy to form into a filter by using the granular activated carbon alone in such a sheet-like adsorption material. Even if the filter could be formed by using some carrier, there arises a problem that the granular activated carbon is easily released and lost from the carrier. Under these circumstances, it has been required to develop a technique capable of effectively using the above granular activated carbon as a raw material of the air-purifying filter.
On the other hand, with the increase of a problem about dust contamination, there has been required an air-purifying filter comprising a filter having a dust-removing function and a filter having a deodorizing function in combination. However, in the configuration wherein a dust-removing filter and a deodorizing filter are separately provided, there was a problem about the space or a problem that the cost is liable to become higher.
As a technique of effectively using the granular activated carbon as a raw material of the air-purifying filter, there is known a method of carrying an activated carbon with a non-woven fabric, a net-like substrate or polyurethane foam at present.
For example, JP-A-48-72088 discloses a gas adsorption sheet obtained by applying an adhesive on a non-woven sheet and distributing an activated carbon thereon. However, in the case of such a gas adsorption sheet, when the activated carbon strongly fixed is required, the pore surface of the non-woven fabric must be coated with a large amount of the adhesive. As a result, the air permeation resistance becomes higher and there was a problem that early clogging is liable to be caused by comparatively coarse powders such as pollen, sand dust, spike dust and the like.
JP-A-9-285531 discloses a gas adsorption sheet obtained by coating a binder on a net-like substrate to reduce pressure loss and then carrying an activated carbon, while JP-B-4-35201 discloses a gas adsorption sheet obtained by coating a binder on a polyurethane foam and then carrying an activated carbon. However, in order to put such a gas adsorption sheet to practical use as a filter, it is necessary to further laminate some sheet for preventing an activated carbon from falling off at least on the downstream side. Since the sheet for preventing an activated carbon from falling off is peeled off by a wind pressure during use even if the sheet is merely laminated without fixing, it is necessary to fix it by some method. One method includes a method using an adhesive. In this method, however, the same phenomenon as that described above occurs and the air permeation resistance becomes higher. A method using no binder includes an entangling method using a needle punch. However, since a fixing force of the activated carbon is small, the falling off degree of the activated carbon becomes larger to lower the deodorizing capability. Therefore, it was a problem on practical use.
Also, the specification of U.S. Pat. No. 5,605,746 discloses a fibrous structure comprising a non-woven fiber matrix formed from composite fibers of a heat adhesive fiber and the other fiber, and a granular activated carbon or the like entrapped in and fusion bonded to the matrix. In addition, the specification of U.S. Pat. No. 5,674,339 discloses a production method of such a fibrous structure. The production method comprises steps of dry forming an open fibrous web structure comprising the heat adhesive fiber and the other fiber, distributing and entrapping the granular activated carbon having a suitable size, weight, and the like in the web structure, and heating to fix the granular activated carbon or the like to the web structure by melt bonding.
However, in such a method for fixing the granular activated carbon by heat adhesive fiber, it is difficult to fix it with reliability so as not to fall off. Therefore strongly fixing of the granular activated carbon and adsorption or air-permeation property can not easily coexist as well as the above prior arts.
As explained above, a satisfactory gas adsorption sheet or air-purifying filter which firmly carries a granular activated carbon and is superior in adsorbability to a gas with bad odor and folding processability, and which causes small pressure loss and little clogging with dust, is not still obtained at present.
On the other hand, various filters obtained by integrally laminating a dust-removing filter and a deodorizing filter have been proposed to solve the problem about insufficient dust-removing performance.
For example, JP-A-4-74505 discloses a filter obtained by bonding a dust-removing filter using an electret non-woven fabric and a deodorizing filter formed by using a suspension of a granular activated carbon in a latex as an adhesive, and integrally forming the resultant into a shape of pleats. However, the electret non-woven fabric disclosed in this publication is a so-called span-bond type electret non-woven fabric. In the case of this non-woven fabric, the dust-removing function is insufficient. Since early clogging occurs to cause rapid increase of pressure loss, a life time of the filter is over before that of the deodorizing sheet is over. Therefore, it was not satisfactory in view of the filter function and economy.
JP-A-7-265640 discloses a filter wherein dust is three-dimensionally trapped by raising an electret fiber, thereby making it hard to cause clogging. The electret fiber disclosed in this publication is also a so-called span-bond type electret filter and, therefore, the charge rate was low and satisfactory dust-removing efficiency could not be obtained.
As described above, there is still to be obtained a filter having a combined function of dust-removing and deodorizing, which exerts a sufficient dust-removing effect and has a long filter life, at present.
Under these circumstances, the present invention has been accomplished. That is, an object of the present invention is to provide a gas adsorption sheet having good air permeability and excellent retention of an activated carbon, and an air-purifying filter whose dust-removing performance can be maintained for a long period to provide a method for producing the gas adsorption sheet.
To attain the above object, the present inventors have studied intensively about a structure for retaining the granular activated carbon by using a fiber and formation thereof. As a result, they have found that a gas adsorption sheet having good fixing strength of the granular activated carbon and good air permeability can be obtained by substantially fixing the granular activated carbon using a supporting fiber, not fixing the activated carbon using an adhesive.
The present inventors have also found that the above sheet can be preferably produced by mixing the granular activated carbon with the supporting fiber and subjecting the mixture to a wet paper method. In that case, they have found that it becomes possible to make the structure for retaining the granular activated carbon using the supporting fiber more strong and stable by adding a small amount of an adhesive fiber, in addition to the above granular activated carbon and supporting fiber.
The present invention provides a gas adsorption sheet characterized in that the deodorizing sheet and electret non-woven fabric are integrally laminated and, furthermore
Imagawa Masayuki
Minemura Shinichi
Morrison & Foerster / LLP
Pratt Christopher
Singh Arti R.
Toyobo Co., LTD
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