JP2004261737A - Air filter medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an air filter medium the upstream side and the down stream side of which can be easily discriminated from each other and which is free from a sense of bad hygiene due to collected dust. <P>SOLUTION: The air filter medium comprises at least one porous membrane layer of polytetrafluoroethylene and at least one gas-permeable fiber material layer 2a, 2b and 3, and at least one of the two layers disposed as the outermost layer is colored. A face of the filtering material to be disposed to the upstream side (downstream side) can be easily discriminated even if the structure in the cross-sectional direction is asymmetric. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an air filter medium and a filter unit using the same.
[0002]
[Prior art]
On the intake side of the turbine, a filter medium made by adding a binder to glass fiber and making paper is often used. However, fine fibrils are attached to this filter medium, and generate self-dust when folded. For this reason, the fine fibers from which the filter medium has fallen adhere to the turbine. On the other hand, polytetrafluoroethylene (hereinafter abbreviated to “PTFE”) is a clean material and has excellent chemical resistance. An air filter medium, which is a laminate of a porous PTFE membrane and a permeable supporting material for reinforcing the PTFE porous membrane, is used, for example, in a clean room in the semiconductor industry. The air-permeable supporting material is arranged so as to sandwich the PTFE porous membrane. The air filter medium described in Patent Document 1 is one example.
[0003]
Applications of the filter medium including the porous PTFE membrane are expanding to consumer devices such as a vacuum cleaner final filter.
[0004]
[Patent Document 1] Japanese Patent Application Laid-Open No. 2000-61280
[Problems to be solved by the invention]
A filter medium containing a PTFE porous membrane has a higher collection efficiency than a filter medium made of glass fiber as long as the filter medium is compared with the same pressure loss. Therefore, when used on the intake side of a turbine or the like, there is a problem that the pressure loss during operation increases. One method of solving this problem is to increase the collection efficiency of the air-permeable supporting member disposed on the upstream side to a certain extent so as to function as a pre-filter. When the gas-permeable supporting material is a gas-permeable fiber material such as a nonwoven fabric, generally, the thinner the fibers, the higher the collection efficiency. In this case, the air-permeable supporting material disposed on the downstream side is made of a gas-permeable fiber material having a larger fiber diameter than the upstream side so as to sufficiently serve as a reinforcing material.
[0006]
Air filter media that have an asymmetric structure in the cross-section direction, such as when fiber materials with different diameters are used as the air-permeable support material on the upstream and downstream sides, need to be appropriately arranged along the upstream and downstream sides of the airflow. There is. However, in the case of an air filter medium, it is sometimes difficult to distinguish between the front and back surfaces, or it is easy to make a mistake. Further, in a consumer air filter medium such as a final filter of a vacuum cleaner, collected dust may appear unsanitary to human eyes.
[0007]
[Means for Solving the Problems]
Therefore, the present invention includes at least one layer of a porous PTFE membrane and at least one layer of a breathable fiber material, wherein at least one of the two layers disposed on the outermost layer is colored, and the colors of the outermost layers are mutually different. A different air filter media is provided.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
The air filter medium of the present invention includes, as at least one layer of the breathable fiber material, two layers of colored breathable fiber materials, and the two layers of breathable fiber materials are respectively arranged in the outermost layers. Good. When the outermost layer both of which are colored is used, the unsanitary feeling due to dust can be reduced.
[0009]
The structure of the air filter medium of the present invention is asymmetric in the cross-sectional direction, and the colors of the two outermost layers may be different from each other. The surface to be arranged on the upstream side or the downstream side can be easily determined by the outermost layer having a different color.
[0010]
In this case, the air filter medium includes, as at least one layer of the air-permeable fiber material, two or more air-permeable fiber materials having different fiber diameters from each other. May be asymmetric. Thereby, even if the air-permeable fiber material to be used as the pre-filter is included, it is easy to arrange the air-permeable fiber material on the upstream side.
[0011]
FIG. 1 is a sectional view showing an example of the filter medium of the present invention. In the embodiment shown in FIG. 1, two layers of breathable fiber materials 2 are arranged so as to sandwich the porous PTFE membrane 1. At least one, and preferably both, of the breathable fiber materials 2 and 2 are colored. The mass-produced breathable fiber material is generally white, but if the outermost layer is colored, the discoloration of the filter medium due to the collected dust becomes inconspicuous. The coloring treatment of the outermost layer can reduce unsanitary feeling due to discoloration in a final filter of a vacuum cleaner or an air filter for general air conditioning. Since the coloring treatment of the filter medium (filter medium having a symmetric structure in the cross-sectional direction) is mainly for preventing discoloration, the air-permeable fiber materials 2 and 2 may be colored in the same color.
[0012]
FIG. 2 is a sectional view showing another example of the filter medium of the present invention. In the embodiment shown in FIG. 2, two layers of the breathable fiber material 2a and 3 are arranged on one surface of the porous PTFE membrane 1, and the breathable fiber material 2b is arranged on the other surface. The breathable fiber material 3 has a relatively smaller fiber diameter than the breathable fiber materials 2a and 2b, and has a higher collection efficiency. This fiber material 3 is arranged on the upstream side to serve as a pre-filter. In this filter medium, one or both of the air-permeable fiber materials 2b and 3 disposed in the outermost layer are colored, and the appearance of the fiber materials 2b and 3 is different. Since the main purpose of the coloring treatment of the filter medium is to discriminate between the front and back sides, one of the breathable fiber materials 2b and 3 may be left white without being subjected to the coloring treatment.
[0013]
The air filter medium of the present invention is not limited to the configuration illustrated in FIGS. 1 and 2, and may have various membrane configurations. The air filter medium may include, for example, a plurality of PTFE porous membranes. For example, the PTFE porous membrane may be disposed on one of the outermost layers, and the other of the outermost layers may include a colored air-permeable fiber material. It may be arranged. The air filter medium preferably has a collection efficiency of 99.97% or more measured with a particle size of 0.3 to 0.4 μm based on a method described later, and can be used as a HEPA filter. Further, based on a method described later, the collection efficiency measured at a particle size of 0.1 to 0.2 μm is preferably 99.995% or more, and can be used as an ULPA filter.
[0014]
The air-permeable fiber material only needs to have higher air permeability than the porous PTFE membrane, and there is no limitation on the structure or form of the non-woven fabric, woven fabric, mesh (mesh-like sheet), felt, or the like. However, a nonwoven fabric is preferable from the viewpoints of strength, collecting property, flexibility, workability, and the like. Examples of the fibers include semi-synthetic fibers such as cellulose and viscose, polyesters (such as polyethylene terephthalate (PET)), polyolefins (such as polyethylene (PE) and polypropylene (PP)), polyamides, acrylics, polysulfones, polyamide imides, polyimides, and the like. Synthetic fibers such as polyphenylene sulfide and polyvinylidene fluoride may be used.
[0015]
There is no particular limitation on the fiber diameter of the breathable fiber material. The fiber diameter of the breathable fiber material 3 for forming a pre-filter is preferably 0.2 μm to 15 μm.
[0016]
The PTFE porous membrane may be one obtained by a conventionally known manufacturing method. The PTFE porous membrane is produced by uniaxially or biaxially stretching a PTFE sheet. In general, a PTFE sheet is prepared by preforming a paste-like admixture obtained by adding a liquid lubricant to PTFE fine powder, extruding the preform into a paste, and rolling to form a sheet. The liquid lubricant is not particularly limited as long as it can wet the surface of the PTFE fine powder and can be removed by extraction or heating, and hydrocarbons such as liquid paraffin, naphtha, and white oil may be used. The appropriate amount of the liquid lubricant to be added is 5 to 50 parts by weight based on 100 parts by weight of the PTFE fine powder. The preforming may be performed at such a pressure that the liquid lubricant is not squeezed out. The liquid lubricant may be removed in advance from the PTFE sheet to be stretched, but may be removed after stretching.
[0017]
The PTFE porous membrane is not particularly limited, but preferably has characteristics of an average pore diameter of 0.01 to 5 μm, an average fiber diameter of 0.02 to 0.3 μm, and a pressure loss of 50 to 1000 Pa. The pressure loss is based on a value obtained by measuring air permeated at a flow rate of 5.3 cm / sec.
[0018]
Since the PTFE porous membrane is porous, it usually appears white. A common grade of breathable fiber material is also white. The coloring treatment is not particularly limited, but can be performed by, for example, kneading a pigment or dyeing with a dye.
[0019]
When kneading a pigment into a breathable fiber material, it is preferable to melt and knead a resin material as a raw material. When the pigment is kneaded into the PTFE porous membrane, the pigment may be added to the PTFE fine powder together with the liquid lubricant. A plurality of types of pigments may be kneaded to exhibit other functions such as conductivity. When a dye is used, the air-permeable fiber material or the PTFE porous film to be colored may be immersed in the dye. However, they may be immersed in a dye after being laminated to form a filter medium.
[0020]
The PTFE porous membrane and the breathable fiber material may be simply overlapped, or may be composited by a method such as heat lamination or adhesive lamination. Specifically, for example, there is a method in which a powder or a web having a melting point lower than the melting point of the raw fiber of the breathable fiber material and the melting point of PTFE is interposed between the porous PTFE membrane and the fiber material and heated. . If the melting point of the breathable fiber material is lower than the melting point of PTFE, a part of the fiber material may be melted to form a composite. A method of compounding the PTFE porous membrane and the breathable fiber material using an adhesive may be used. In this case, as the adhesive, a two-component adhesive or a self-crosslinking adhesive by heat is suitable. An epoxy resin may be used as the two-liquid mixing type, and a vinyl acetate-ethylene copolymer or an ethylene-vinyl chloride copolymer may be used as the self-crosslinking type by heat.
[0021]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited to the following Examples. The measurement of pressure loss and collection efficiency was performed by the following methods.
[0022]
(Pressure loss)
The sample was set in a circular holder having an effective area of 100 cm ² , a pressure difference was applied between the upstream side and the downstream side, and the pressure loss when the air permeation speed was adjusted to 5.3 cm / sec with a flow meter was measured using a pressure gauge ( (Manometer). The measurement was performed at 10 points per sample, and the average of the measured values was defined as the pressure loss of the sample.
[0023]
(Collection efficiency)
Using the same apparatus as that for measuring the pressure loss, the air permeation velocity was adjusted to 5.3 cm / sec, and about 10 to 10 polydisperse dioctyl phthalate (DOP) particles having a particle size of 0.3 to 0.4 μm were provided on the upstream side. The particles were supplied at ⁷ particles / liter, and the particle concentration on the upstream side and the particle concentration on the downstream side that had passed through the sample were measured with a particle counter, and the trapping efficiency was calculated based on the following equation. Incidentally, the DOP particles having a particle diameter of 0.1 to 0.2 [mu] m, determine the collection efficiency by supplying to be about 10 ⁸ cells / liter.
[0024]
Collection efficiency (%) = (1−downstream particle concentration / upstream particle concentration) × 100
[0025]
(Example 1)
20 parts by weight of a liquid lubricant (dodecane) is uniformly mixed with 100 parts by weight of PTFE fine powder (Aflon CD123 manufactured by Asahi Glass Fluoropolymers Co., Ltd.), and this mixture is preformed, and then molded into a round bar by paste extrusion. did. Further, the round bar-shaped formed body was passed between a pair of metal rolling rolls to obtain a sheet-shaped formed body having a thickness of 0.2 mm. Subsequently, the liquid lubricant was removed from the sheet-like molded body by an extraction method using normal decane.
[0026]
This sheet-like molded body is biaxially stretched to collect a PTFE porous membrane (thickness: 10 μm, average pore size: 1.0 μm, porosity: 93%, pressure loss: 160 Pa, DOP particle size: 0.3 to 0.4 μm). An efficiency of 99.999% was obtained.
[0027]
The porous PTFE membrane thus obtained is overlapped with two colored PET / PE core-sheath nonwoven fabrics (gray, basis weight 30 g / m ² ) so that the nonwoven fabric sandwiches the porous membrane, and the sheath of the nonwoven fabric is obtained. Thermal lamination was performed by passing between a pair of rolls heated to 180 ° C. higher than the melting point of the part PE. Thus, an air filter medium including the PTFE porous membrane and the air-permeable fiber material was obtained. The collection efficiency of this air filter medium was 99.999% for a DOP particle size of 0.3 to 0.4 μm.
[0028]
(Comparative Example 1)
An air filter medium comprising a PTFE porous membrane and a permeable fiber material was obtained in the same manner as in Example 1 except that a non-colored PET / PE core-sheath nonwoven fabric (white, basis weight 30 g / m ² ) was used. Was.
[0029]
(Example 2)
A porous PTFE membrane was obtained in the same manner as in Example 1. On the other hand, a PP nonwoven fabric (white, a basis weight of 30 g / m ² , a fiber diameter of about 0.5 to 3 μm) is used as a first breathable fiber material, and a PET / PE core-sheath nonwoven fabric (white, a basis weight) is used as a second breathable fiber material. the amount 30 g / ^{m 2,} a fiber diameter of about 20 [mu] m), the third breathable fibrous materials as PET / PE core-sheath nonwoven fabric coloring treatment (gray, basis weight 30 g / ^{m 2,} a fiber diameter of about 20 [mu] m), were prepared, respectively.
[0030]
The first air-permeable fiber material and the second air-permeable fiber material were superimposed on each other, and passed through a pair of rolls heated to 140 ° C. to perform heat lamination to obtain a laminate of the air-permeable fiber material. On the other hand, the PTFE porous membrane and the third permeable fiber material are overlapped, and heat lamination is performed by passing the PTFE porous membrane through a pair of rolls heated to 180 ° C. to form a laminate of the PTFE porous membrane and the permeable fiber material. Obtained. Next, the two laminates were overlapped so that the porous PTFE membrane and the second air-permeable fiber material were in contact with each other, and passed through a pair of rolls heated to 130 ° C. to perform thermal lamination. Thus, an air filter medium was obtained.
[0031]
(Comparative Example 2)
An air filter medium was prepared in the same manner as in Example 2 except that a non-colored PET / PE sheath-core nonwoven fabric (white, weight per unit area: 30 g / m ² , fiber diameter: about 20 μm) was used as the third breathable fiber material. Obtained.
[0032]
The air filter medium obtained from each of Example 1 and Comparative Example 1 was set in a circular holder having an effective area of 100 cm ² , and atmospheric dust was supplied for 10 hours while sucking so that the permeation flow rate was 5.3 cm / sec. With the air filter medium of Comparative Example 1, dirt due to atmospheric dust could be confirmed even at a distance of 10 m, but no dirt was observed with the air filter medium of Example 1. The front and back of the air filter medium obtained from Comparative Example 2 could not be distinguished visually, but the front and back of the air filter medium obtained from Example 2 could be easily distinguished visually.
[0033]
【The invention's effect】
As described above, according to the present invention, an air filter medium capable of easily distinguishing a surface to be disposed on the upper (lower) flow side and an air filter medium capable of eliminating an unnatural appearance due to collected dust are provided. it can.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing one embodiment of a filter medium of the present invention.
FIG. 2 is a cross-sectional view showing another embodiment of the filter medium of the present invention.
[Explanation of symbols]
1 PTFE porous membrane 2, 2a, 2b, 3 breathable fiber material

Claims (4)

An air filter medium comprising at least one layer of a polytetrafluoroethylene porous membrane and at least one layer of a breathable fiber material, wherein at least one of two layers disposed on the outermost layer is colored. 2. The air filter medium according to claim 1, wherein the at least one layer of the air-permeable fiber material includes two layers of a color-treated air-permeable fiber material, and the two layers of the air-permeable fiber material are respectively disposed on the outermost layers. . The air filter medium according to claim 1, wherein the structure is asymmetric in a cross-sectional direction, and the colors of the two layers are different from each other. 4. The at least one layer of breathable fiber material includes two or more breathable fiber materials having different fiber diameters, and the structure is asymmetric due to the two or more breathable fiber materials. 2. The air filter medium according to item 1.

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