JP3082764B2 - Air filter material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter element, and more particularly to a filter element for an air filter device.
r), a filter element used in a filter device used as a ULPA (Ultra Low Penetration Air) or ultra ULPA filter and a filter medium for producing the same.

[0002]

2. Description of the Related Art Along with recent advances in science and technology and changes in lifestyles, there is an increasing need for clean spaces and clear air. Naturally, clear air is desirable in hospitals and homes, and various air purifiers are used. The same applies to the precision machinery industry and the food industry. Furthermore, in the manufacture of integrated circuits and semiconductors, in the manufacture of medicines, and in the manufacture of medical-related products such as artificial organs, much less dust is allowed than in ordinary clean spaces, and generally HEPA filters, preferably There is a need for a filter device of the ULPA filter, more preferably the ultra ULPA filter grade.

[0003] In the filter device for air cleaning as described above, a filter having a filter element made of a filter material for removing dust by passing air to be cleaned is mounted on the filter device.

FIG. 3 schematically shows an example of this filter element in a perspective view. Filter element 1 is
It consists of a filter medium 3, for example a glass fiber filter cloth, bent to form a plurality of ridges 2. Furthermore, in general, a spacer 4 is disposed between the ridges to evenly arrange the filter media (only two are illustrated by way of example). The periphery of such a filter element 1 is hermetically connected in a rectangular frame (not shown) to form a filter. As shown by the arrows, the air passing through the filter flows from the rear right of FIG. 3 through the filter medium to the front left. Such a filter element is developed, for example, by developing a high-performance filter (Osaka Chemical Research Series VOL.5 N
O.9 Published by Osaka Chemical Marketing Center)
On pages 40-41.

[0005] In the case of manufacturing a filter element as shown in the figure, the filter medium is bent in a wave form, and the bent state is fixed by, for example, a hot melt adhesive. In this case, if the separator is inserted between the filter media having a corrugated shape, the pitch of the waves will inevitably increase, and the filtration area will decrease. Furthermore, since the fixing of the filter medium with the adhesive is performed after the bending, the pitch (corresponding to p in FIG. 3) is often non-uniform. In particular, when the pitch is small, even if the pitch is slightly nonuniform, the gas flow becomes nonuniform, and the pressure loss as a whole increases and the gas drifts, which is not preferable.

[0006]

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a filter element having a uniform folding pitch of a filter medium and a filter material therefor, by overcoming the above-mentioned problems of the conventional filter element. Is the problem to be solved.

[0007]

SUMMARY OF THE INVENTION The above-mentioned object is achieved by a sheet-like filter material comprising a sheet-like filter medium having on both sides at least two elongate strips arranged longitudinally parallel to one another. Was found.

In the filter material of the present invention, the long strip material is preferably heat-fusible, and the strip material is on both sides of the filter material. this is,
This is because when the filter medium is folded, the strip materials overlap with each other to ensure a uniform folding pitch of the filter material. This strip material is present parallel to the longitudinal direction of the filter media used and over the entire length of the filter media. The number of strip materials can be appropriately selected according to the properties of the filter medium to be used, for example, flexibility and strength, but at least two on each side of the filter medium are required for the purpose of ensuring a uniform pitch. . The strip material may be arranged at any position, but is most preferably arranged at both edges of the filter medium from the viewpoint of effective use of the filter medium. In addition, when the pitch near the center is not accurately secured by only the both edges, it is preferable to arrange the strip material also in the center portion of the filter medium. Further, the strip material may or may not be on opposite sides of the same location of the filter media.

The strip material may be any material as long as it is a heat-fusible material. In this specification,
The term "thermally fusible" refers to the property of being able to melt by heating and bond together. Considering the chemical resistance and the like, polyethylene and polypropylene can be exemplified as particularly preferable heat-fusible materials. Other preferred strip materials include, for example, polyesters and fluoroplastics. Instead of a heat-sealable material, a strip material that can be bonded by interposing an adhesive may be used. In this case, it is necessary to precisely control the thickness of the adhesive applied within an acceptable range. In this regard, it is more preferable to use a heat-fusible material.

[0010]

FIG. 1 is a perspective view of a filter material 11 according to the present invention. In the embodiment shown, the filter media 13 has three heat-sealable strip materials 15 on each side thereof. Each strip material is present over the entire length of the filter material and is parallel to each other.

The present invention further provides a filter material wherein the filter medium is a polytetrafluoroethylene porous membrane laminated on at least one side with a woven or nonwoven fabric.

FIG. 2 is a schematic perspective view of the filter element of the present invention. The filter material 11 of the present invention is folded so that the heat-sealable strip materials on the same side of the filter media are adjacent to each other, and the adjacent strip materials are heat-sealed by any suitable method, for example, by ultrasonic heating. Alternatively, they may be joined by interposing an adhesive. In this case, the strip material 17 on both edges of the filter material must be completely bonded, while the central strip material 19 may or may not be bonded. Therefore, in the filter element of the present invention,
The length corresponding to twice the thickness of the strip material will correspond to the pitch.

The filter medium used in the filter element of the present invention may be any filter medium generally used in an air filter device as long as it has a certain degree of flexibility so that the above-described folding process can be performed. It may be. For example, glass cloth or synthetic fiber filter cloth can be used. In consideration of reducing the pitch (that is, reducing the degree of opening of the ridges), a filter medium of a polymer substance, for example, a porous membrane of polytetrafluoroethylene (PTFE) is preferable, and furthermore, collection of fine particles. In consideration of increasing the efficiency, reducing the pressure loss, etc., a PTF having a small pore diameter and a thin film thickness is used.
It is particularly preferred to use a filter medium such as a porous E membrane.

Above all, a filter medium such as a PTFE porous membrane laminated with a woven or non-woven fabric of polymer fibers such as polyethylene and polypropylene is used.
The bending as shown in FIG. 2 is preferable because it does not bend like a glass fiber filter medium and hence does not generate any new dust.

In the filter element of the present invention,
In consideration of pressure loss, dust collection efficiency, flexibility of the filter medium, and the like, it is preferable to use a filter medium made of polytetrafluoroethylene, and also from the viewpoint of having chemical resistance unique to a fluororesin. It is advantageous. In addition, polyester, polyethylene terephthalate as a core around the polyolefin, for example, polyethylene, polypropylene, a woven or non-woven fabric of a composite fiber coated with a heat-fusible resin such as low-melting polyester and a filter medium in a laminated structure, It is even more advantageous that the adhesive can be hermetically sealed to the strip material without using an adhesive.

In other words, the present invention provides a laminated structure obtained by laminating a woven or nonwoven fabric made of a composite fiber having a core / sheath structure on at least one surface of a polytetrafluoroethylene porous membrane. The laminate structure of the present invention can be heat-sealed to the strip material in an airtight manner by using a heat-sealing resin as the sheath component.

Further, in the laminated structure of the present invention, the woven or nonwoven fabric is made of a composite fiber having a core made of polyester or polyethylene terephthalate and coated with a heat-fusible resin made of polyethylene, polypropylene or low-melting polyester around the core. Can be used. In the laminated structure of the present invention, polyethylene, polypropylene or low melting point polyester as a sheath (coating) component in combination with polyester or polyethylene terephthalate as a core component is used to thermally fuse the filter medium to the strip material. It has the function of

Such a porous filter medium made of polytetrafluoroethylene is obtained, for example, by stretching a semi-baked polytetrafluoroethylene and then heat setting it at a temperature equal to or higher than the melting point of the fired polytetrafluoroethylene. A polytetrafluoroethylene porous membrane, wherein the area ratio of fibrils and nodules by image processing of a scanning electron micrograph is 99: 1 to 75:25, the average fibril diameter is 0.05 μm to 0.2 μm, The maximum area of the nodule is 2 μm ² or less, and the average pore size is 0.2 μm or more.
A polytetrafluoroethylene porous membrane having a thickness of 0.5 μm, an average pore size of 0.2 μm to 0.5 μm, and a pressure loss of 10 mmH ₂ O when air is permeated at a flow rate of 5.3 cm / sec.
A polytetrafluoroethylene porous film having a thickness of １００100 mmH ₂ O, a polytetrafluoroethylene semi-fired body was stretched in a biaxial direction at an extension area magnification of at least 50 times, and heat-set at a temperature equal to or higher than the melting point of the polytetrafluoroethylene fired body. It is like a polytetrafluoroethylene porous membrane.

In such a porous membrane, it is necessary to prevent the particles adhering to the fibers of the filter from detaching again and to shield the penetrating particles in order to reliably collect the particles. For that purpose, a filter material having a pore size smaller than the size of the particles to be surely collected should be used. Therefore, a porous PTFE membrane having a small average pore diameter is preferred. If the pore size and the porosity of the filter material are the same, the pressure loss is proportional to the film thickness.

Even if the filter material has the same pressure loss, pore size, porosity, and film thickness, the particle collecting performance is different. In theory, fine fibers of 0.5 μm or less can be used and a binder can be used. It is said that it is preferable to keep the amount as small as possible, that is, to reduce the portion other than the fiber (see the Abstracts of the 52nd Annual Meeting of the Society of Chemical Engineers, Emi). The above PT
The FE porous membrane satisfies such conditions.

These PTFE porous membranes will be described in more detail including the production method. The material of the porous PTFE membrane before stretching is PTF defined in JP-A-59-152825.
This is based on the semi-fired E. The structure of the stretched porous body obtained by stretching and firing the semi-baked PTFE in the biaxial direction at a stretch area ratio of at least 50 times, preferably at least 100 times, and more preferably at least 250 times, is made of fine fibers having almost no knots. It has a unique film structure.

In addition, the PTFE thus manufactured
The average pore size of the porous membrane is extremely small, usually from 0.5 μm
0.2 μm, and the thickness of the film is 1/20 of that before stretching.
From about 1/100. These requirements are suitable for an air filter material for maintaining a high clean space for processing a fine pattern of a semiconductor.

One requirement for producing a filter having a low pressure loss is that a thin PTFE porous membrane is sufficient. However, in the conventional method (Japanese Patent Publication No. 56-17216), even if the stretching ratio is increased, the thickness is slightly reduced. Only decrease. However, when the stretching ratio is extremely increased and the thickness is reduced, the pore size increases, so that the film thickness before stretching must be reduced. However, the thickness of an industrially usable film before stretching is at most 30 μm to 50 μm. In consideration of quality and yield, a film before stretching having a thickness of about 100 μm is usually used.

In the above-mentioned production method in which the semi-sintered PTFE is stretched in the biaxial direction by at least 50 times the stretching area ratio and fired, the purpose is achieved by using a film before stretching having a thickness of about 100 μm which does not hinder industrial productivity. can do.

A general range and a preferable range of each parameter in the PTFE porous membrane are shown together. General range Preferred range Firing degree: 0.30 to 0.80 0.35 to 0.70 Stretching ratio: longitudinal direction 4 to 30 longitudinal direction 5 to 25 width direction 10 to 100 width direction 15 to 70 Total 50 to 1000 75 to 850 in total (when the total draw ratio is 250 or more, the degree of baking is particularly preferably 0.35 to 0.48.) General range Preferred range Average pore size: 0.2 to 0.5 μm 0.2 to 0.4 μm Film thickness: 0.5 to 15 μm 0.5 to 10 μm Fibril / knot area ratio: 99/1 to 75/25 99/1 to 85/15 Average fibril diameter: 0.05 to 0.5 2 μm 0.05 to 0.2 μm Maximum area of nodule: 2 μm ² or less 0.05 to 1 μm ² Pressure loss: 10 to 100 mmH ₂ O 10 to 70 mmH ₂ O

The above characteristics are obtained by the following measuring methods. Mean flow pore size measured according to the description of the average pore size of ASTM F-316-86 with (MFP) and average pore diameter. The actual measurement was made using a Coulter Porometer.
ometer) [Coulter Ele
ctronics) (UK)].

[0027] Using the film thickness Mitutoyo Corporation Ltd. 1D-110MH type film thickness meter, the thickness of the entire measured repeatedly five porous membrane dividing the thickness at 5, one obtained value Film thickness.

The pressure loss porous membrane is cut into a circle having a diameter of 47 mm, and the effective transmission area is 1
The filter was set in a 2.6 cm ² filter holder, the inlet side of the filter was pressurized to 0.4 kg / cm ² , the flow rate of air exiting from the outlet side was adjusted with a flow meter manufactured by Kamishima Seisakusho, and the permeation rate of the porous membrane was 5.3 c.
m / sec. The pressure loss at that time is measured with a manometer.

Degree of firing First, a sample of 3.0 ± 0.1 mg was weighed and cut from the unfired PTFE, and a crystal melting curve was first determined using this sample. Similarly, a sample of 3.0 ± 0.1 mg is weighed and cut from the semi-baked PTFE, and a crystal melting curve is obtained using this sample.

The crystal melting curve was measured by a differential scanning calorimeter (hereinafter, referred to as
It is called "DSC". For example, DSC-50 manufactured by Shimadzu Corporation
(Type). First, a sample of the unfired PTFE is charged into a DSC aluminum pan, and the heat of fusion of the unfired body and the heat of fusion of the fired body are measured in the following procedure. (1) The sample is heated to 250 ° C. at a heating rate of 50 ° C./min and then from 250 ° C. to 380 at a heating rate of 10 ° C./min.
Heat to ° C. One example of the crystal melting curve recorded in this heating step is shown as curve A in FIG. The peak position of the endothermic curve appearing in this step is defined as “the melting point of the unfired PTFE” or “the melting point of the PTFE fine powder”. (2) Immediately after heating to 380 ° C, the sample is cooled to 250 ° C at a cooling rate of 10 ° C / min. (3) The sample is heated again to 380 ° C. at a heating rate of 10 ° C./min. One example of a crystal melting curve recorded in the heating step (3) is shown as a curve B in FIG. The peak position of the endothermic curve appearing in the heating step (3) is defined as "the melting point of the fired PTFE".

Subsequently, the crystal melting curve of the semi-baked PTFE is recorded according to the step (1). Curve 1 in this case
An example is shown in FIG. The heat of fusion of the unfired, fired, and semi-fired PTFE bodies is proportional to the area between the endothermic curve and the baseline, and is automatically calculated by setting the analysis temperature in DSC-50, manufactured by Shimadzu Corporation. .

Therefore, the degree of firing is calculated by the following equation. Firing degree = (ΔH ₁ −ΔH ₃ ) / (ΔH ₁ −ΔH ₂ ) where ΔH ₁ is the heat of fusion of the unfired PTFE and ΔH ₂ is P
The heat of fusion of the fired TFE, ΔH _3, is the heat of fusion of the semi-fired PTFE. Japanese Patent Application Laid-Open No.
A detailed description is given in -152825.

The area ratio between the image analysis fibrils and the nodules, the average fibril diameter, and the maximum nodule area are measured by the following methods. A photograph of the surface of the porous film is taken with a scanning electron microscope (Hitachi S-4000 type is Hitachi E
1030 type) (SEM photograph. Magnification 1000 times to 50 times)
00 times). This photograph is processed by an image processing device (main unit name: Nippon Avionics Co., Ltd., TV image processor TVIP-
4100II, name of control software: Ratok System Engineering Co., Ltd., TV image processor Image command 4198), separates into nodules and fibrils, and obtains an image consisting only of nodules and an image consisting only of fibers. The maximum nodule area is obtained by arithmetically processing the image consisting of nodules only, and the image consisting only of fibrils is arithmetically processed to obtain the average diameter of fibrils (the total area is 1 / the total circumference).
Divide by 2). The area ratio between the fibril and the nodule can be obtained from the ratio of the sum of the areas of the fibril image and the nodule image.

Definition of a nodule A nodule satisfies one of the following. (1) A plurality of fibrils are connected to each other (FIG. 6: a portion filled with dots). (2) A connected group is larger than the fibril diameter (FIGS. 9 and 10: hatched portion). (3) Primary particles And the primary particles are gathered, and the fibrils are extended radially therefrom (FIGS. 7, 8, and 11: hatched portions). FIG. 12 is an example not regarded as a nodule. That is, if the fibrils are branched, but the fibrils and the bifurcation have the same diameter, the bifurcation is not considered a nodule.

Specifically, an unfired film (thickness: 100 μm) obtained by paste extrusion of PTFE fine powder (“Polyflon Fine Powder F-104” manufactured by Daikin Industries, Ltd.) was placed in an oven at 339 ° C. A heat treatment was performed for 50 seconds to obtain a semi-baked film having a baking degree of 0.50. It is obtained by performing double stretching (total of 200 times the film area before stretching) and performing heat setting at 350 ° C. for 3 minutes so that the stretched film does not shrink. The porous PTFE membrane thus obtained has a thickness of 1.0 μm, an average pore diameter of 0.28 μm, an area ratio between fibrils and nodes of 95: 5, and an average fibril diameter of 0.14.
μm, the maximum nodal area is 0.38 μm ² , and the pressure loss when passing air at a flow rate of 5.3 cm / sec is 45 mmH ₂ O.

As the woven or nonwoven fabric to be laminated with the filter medium as described above, for example, Elves (registered trademark) commercially available from Unitika Ltd. can be used.

[0037]

By using the filter material of the present invention, a filter element having a constant fold pitch can be easily manufactured. Therefore, when gas is filtered using the filter element of the present invention in a filter device, the filter medium is uniformly used without causing gas drift.

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing a filter material of the present invention.

FIG. 2 is a perspective view schematically showing a filter element of the present invention.

FIG. 3 is a perspective view schematically showing a conventional filter element.

FIG. 4 is a diagram showing an example of a crystal melting curve of unfired PTFE and fired PTFE measured by DSC when measuring the degree of firing.

FIG. 5 is a view showing an example of a crystal melting curve of semi-baked PTFE measured by DSC when measuring a degree of firing.

FIG. 6 is a schematic view of an example of a fibril one-node structure.

FIG. 7 is a schematic diagram of an example of a fibril one-node structure.

FIG. 8 is a schematic diagram of an example of a fibril one-node structure.

FIG. 9 is a schematic view of an example of a fibril one-node structure.

FIG. 10 is a schematic view of an example of a fibril one-node structure.

FIG. 11 is a schematic view of an example of a fibril one-node structure.

FIG. 12 is a schematic view of an example of a fibril one-node structure.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Filter element, 2 ... Ridge part, 3 ... Filter medium, 4 ... Spacer, 11 ... Filter material, 13
... filter media, 15 ... strip material, 17 ... strip material on both sides, 19 ... center strip material.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-146107 (JP, A) JP-A-62-83017 (JP, A) JP-A-52-80579 (JP, A) 125320 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) B01D 39 / 14,46 / 54 B01D 69 / 12,71 / 36

Claims (2)

(57) [Claims] 1. A high performance air filter device comprising a nonwoven fabric made of a composite fiber having a core / sheath structure and using a heat-fusible resin as a sheath component on at least one surface of a polytetrafluoroethylene porous membrane. Air filter material. 2. The non-woven fabric according to claim 1, wherein the non-woven fabric is made of a composite fiber having a polyester or polyethylene terephthalate core and a heat-fusible resin made of polyethylene, polypropylene or low-melting polyester coated around the core. Air filter material.