JP2002011313A - Air filter medium and air filter unit using the same - Google Patents

Abstract

(57) [Problem] To provide a filter medium for an air filter capable of simultaneously removing gas components (particularly gaseous organic substances) and dust suspended in an atmosphere. SOLUTION: Two or more polytetrafluoroethylene (PTFE) porous membranes 1 and 2 joined by an adhesive 5
A composite material having an adsorbent 6 interposed therebetween is used. Adhesive 5
Are preferably arranged at a rate of 5 g / m ² or more and 20 g / m ² or less between the PTFE porous membranes in a scattered manner. As the adhesive 5, hot melt powder is suitable. Activated carbon or the like may be used as the adsorbent 6. Furthermore, it may be reinforced by the air-permeable supporting members 3 and 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter medium for an air filter, and more particularly to a filter medium for an air filter used in a clean room for manufacturing semiconductors, electric and electronic devices such as liquid crystal devices, and food and medical care. Things. Further, the present invention relates to an air filter unit using the filter medium.

[0002]

2. Description of the Related Art Conventionally, in a clean room used in semiconductor manufacturing or the like, particulate matter such as dust has been regarded as an object to be contaminated. However, with the improvement in the degree of integration of semiconductors, contamination by gaseous organic substances present in a clean room has become a problem. In order to solve this problem, a chemical filter using a gas adsorbent such as activated carbon is generally used. However, the chemical filter itself has no particle collection performance. For this reason, an ULPA filter or a HEPA filter is used in combination in order to keep the degree of cleanliness against dust.

In recent years, as a filter medium for such a filter,
A polytetrafluoroethylene (hereinafter referred to as “PTFE”) stretched porous membrane which is clean and excellent in chemical resistance has attracted attention. Japanese Patent Application Laid-Open No. Hei 10-286437 discloses that
It has been proposed to use a web obtained by forming a PTFE powder containing a photocatalyst into a sheet and further defibrating. It has also been proposed to use a gas adsorbent with a photocatalyst. However, here, an air filter unit is used on the downstream side of the web in order to prevent the catalyst and the like from being detached from the web and mixed into the clean air. For this reason, as a whole, the apparatus is large.

[0004]

As described above, conventionally,
There is no known filter medium capable of simultaneously removing organic gas and dust in the atmosphere. Therefore, an object of the present invention is to provide a filter medium for an air filter capable of simultaneously removing gas components (particularly, gaseous organic substances) and dust suspended in an atmosphere, and an air filter unit using the same.

[0005]

In order to achieve the above object, a filter medium for an air filter of the present invention comprises a composite material having an adsorbent sandwiched between two or more porous PTFE membranes bonded by an adhesive. It is characterized by including.

In the air filter medium of the present invention, the porous PTFE membranes disposed on both sides of the adsorbent remove dust and prevent the adsorbent from falling off. In the filter medium for an air filter of the present invention, since the filter medium is sandwiched by the PTFE porous membrane, the adsorbent is less likely to fall off than when the filter medium is simply carried on defibrated PTFE fibers. Also,
Since the PTFE porous membrane is used, there is no danger of dust generation due to fine fibers unlike a filter medium made by adding a binder to glass fibers and making paper. As described above, according to the air filter medium of the present invention, organic gas and dust can be removed at the same time.

[0007] In the filter medium for an air filter of the present invention, PTF
It is preferable that the adhesive is disposed in a scattered manner between the E porous films, and it is particularly preferable that the adhesive is present in an island shape at a ratio of 5 g / m ² or more and 20 g / m ² or less.

The air filter medium of the present invention may use the above-mentioned composite material as it is, but may use a laminated air-permeable support material in order to improve the folding workability and strength.

Further, the present invention also provides an air filter unit using the air filter medium. This air filter unit includes, for example, a continuous W-shaped pleated filter medium for air filter and a member for supporting the filter medium, similar to a normal unit.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing one embodiment of the air filter medium of the present invention. In this filter material for an air filter, a granular adsorbent 6 is sandwiched between a laminate (a porous PTFE porous membrane composite) composed of two layers of PTFE porous membranes 1 and 2. The two layers of porous PTFE membranes 1 and 2 are joined by an adhesive 5 interspersed. On both sides of the PTFE porous membrane composite, a gas permeable support material 3,
4 are stacked.

[0011] The porous PTFE membranes can also be joined to each other by direct thermocompression bonding without using an adhesive.
However, as shown in the figure, if the PTFE porous membrane is not joined over the entire surface but is joined in a dotted manner,
Since the adhesion area of the E porous membranes 1 and 2 can be reduced, an advantage that a filter medium having a low pressure loss is obtained is obtained. In particular, when the adsorbent is arranged between the layers, it is preferable to bond the PTFE porous membrane in a scattered manner using an adhesive arranged in an island shape. This is because the probability that the surface of the adsorbent is covered with the adhesive and the adsorption performance is reduced can be reduced.

The adhesive is not particularly limited as long as it can bond the porous PTFE membrane, but an adhesive having a low gas generating property is preferable, and specifically, a fusing agent such as hot melt powder is suitable. . Hot melt powder
It is preferable to use a material having a melting point lower than the melting point of PTFE. As a material of hot melt powder,
Polyethylene (PE), polypropylene (PP), low melting polyester, ethylene-vinyl acetate copolymer (EV
A) and the like.

The size of the hot melt powder is as follows:
A 10-200 mesh pass is preferred. The preferred amount to be adhered to the porous PTFE membrane is 5 to 20 g / m ^2. If the amount of the adhesive is too large, the air permeability of the air filter may be impaired. If the amount is too small, sufficient adhesive strength may not be obtained. The amount of the adhesive is more preferably 8 g / m ² or more, and further preferably 15 g / m ^2.
m ² or less.

The type of the adsorbent is not particularly limited as long as the object of the present invention is achieved.
For example, activated carbon, activated carbon fiber, zeolite and the like are suitable. The size of the adsorbent is not particularly limited as long as it can be sandwiched between the PTFE porous membranes.

[0015] The porous PTFE membrane is formed by extruding and / or rolling a mixture of PTFE fine powder and a liquid lubricant into a sheet, removing the liquid lubricant from the unsintered sheet, and then stretching the porous sheet to form a porous sheet. Can be obtained. In addition, if it heats to the temperature more than the melting point of PTFE after extending | stretching and bake, strength will improve. PTF
The microporous structure of the E porous membrane is preferably in a range suitable for a gas-permeable filter that does not drop off the adsorbent and that collects dust in consideration of the particle size of the adsorbent. From such a viewpoint, the average pore diameter of the PTFE porous membrane is generally 0.5
μm to 5 μm are preferred. The pressure loss of the porous PTFE membrane is preferably from 50 to 200 Pa. In addition, in this specification, as a value of the pressure loss, specifically, a value when air is transmitted at a flow rate of 5.3 cm / sec as described later is adopted. Further, the trapping efficiency is preferably 90% or more based on a measuring method described later.

The air-permeable supporting material preferably has a higher air-permeability than the PTFE porous membrane used as the trapping layer, and non-woven fabrics, woven fabrics, meshes and other porous materials can be used. The material, structure, and form are not particularly limited, but a nonwoven fabric is preferable from the viewpoint of strength, flexibility, and workability. Polyolefin (P
E, PP, etc.), nylon, polyester (polyethylene terephthalate (PET), etc.), aramid, or a composite thereof (for example, a nonwoven fabric made of fibers having a core / sheath structure, two layers of a low melting material and a high melting material) Non-woven fabric)
Fluorine-based porous membranes (for example, porous membranes such as PFA (tetrafluoroethylene / perfluoroalkylvinyl ether copolymer), FEP (tetrafluoroethylene / hexafluoropropylene copolymer), and PTFE).

As the air-permeable supporting material, a nonwoven fabric composed of a composite fiber having a core / sheath structure in which the core component has a higher melting point than the sheath component, and a two-layer nonwoven fabric of a low-melting material and a high-melting material are more preferable. This is because the film obtained by the bonding is not easily shrunk at the time of bonding, and is easily processed as a HEPA filter or an ULPA filter, and the folding pitch can be increased when the film is processed into a filter element. The air-permeable supporting material may be disposed on only one surface of the PTFE porous membrane composite, or the PTFE composite may be used as a filter as it is.

Hereinafter, an example of a method for producing a filter medium for an air filter of the present invention will be described. The PTFE porous membrane composite material used for the filter medium for an air filter of the present invention is obtained by spraying an adsorbent and an adhesive having a melting point lower than the melting point of PTFE on a bonding surface of the PTFE porous membrane, and passing through the bonding surface. It is preferable that two or more laminated porous PTFE membranes are heated to a temperature higher than the melting point of the adhesive and lower than the melting point of the PTFE, and joined together.

Particularly, the joining of the porous PTFE membranes is preferably carried out along a roll (preferably a heatable roll provided with a heater; a hot roll), and the joining is performed while rotating the roll. This is because the PTFE porous film can be efficiently joined while suppressing the shrinkage in the width direction. By repeating this method, a multilayer PTFE composite can be easily produced.

When the PTFE porous membrane composite thus obtained is used as a laminate with a gas-permeable support, the gas-permeable support may be simply superposed on the porous PTFE-membrane composite. May be used. The bonding of the air-permeable supporting material may be performed by using an adhesive member such as an adhesive.
It may be fused to a TFE porous membrane.

The pressure loss of the entire filter medium for an air filter is preferably 50 to 200 Pa. In addition, the collection efficiency of fine particles for the entire filter medium is preferably 90% or more based on a measurement method described later.

[0022]

EXAMPLES 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 the pressure loss, the collection efficiency, and the gas removal rate in this example was performed by the following methods.

(Pressure loss) The sample is placed in an effective area of 100c.
The sample was set in a circular holder of m ² , a pressure difference was applied between the inlet side and the outlet side, and the pressure loss when the flow rate of air passing through the sample was adjusted to 5.3 cm / sec with a flow meter was measured with a pressure gauge (manometer). ). The measurement was performed at 50 points per sample, and the average of the measured values was defined as the pressure loss of the sample.

(Collection efficiency) Using the same apparatus as in the pressure loss measurement, the flow rate of air passing through the sample was adjusted to 5.3 cm / sec, and polydisperse dioctyl phthalate (DO) was provided on the upstream side.
P) is supplied so that 5 to 10 ⁶ particles / liter of 0.3 to 0.4 μm particles are measured, and the particle concentration on the upstream side and the particle concentration on the downstream side that have passed through the sample are measured by a particle counter. The collection efficiency was determined by the following equation.

Collection efficiency (%) = (1−downstream particle concentration /
Upstream particle concentration) × 100 (However, the target particles are in the range of 0.3 to 0.4 μm.)

(Gas Removal Performance) A sample (sample punched out into a circle having a diameter of 25 cm) was placed in a vacuum desiccator (internal volume: 8 liters) 11 shown in FIG. 2 and then connected to a vacuum pump (not shown). Then, the pressure inside the desiccator is reduced, and then acetaldehyde standard gas (100 ppm) diluted with nitrogen gas is supplied from the pipe 13 to the desiccator. After closing the valve to stop the supply of acetaldehyde, a pipe communicating with the photoacoustic gas monitor 12 was opened, and the concentration of acetaldehyde one day later was measured.

(Example) 30 parts by weight of a liquid lubricant (liquid paraffin) was uniformly mixed with 100 parts by weight of PTFE fine powder ("Fluon CD-123" manufactured by Asahi Glass Co., Ltd.), and the mixture was mixed at 20 kg / cm ^2. Preformed under the following conditions, then extruded into a rod shape, and further passed the rod-shaped formed body between a pair of metal rolling rolls,
A long sheet-like molded body having a thickness of 0.2 mm was obtained. After removing the liquid lubricant by an extraction method using n-decane, this sheet-like molded body was wound around a tubular core in a roll shape.

This sheet-like molded product was stretched 20 times in the longitudinal direction at 370 ° C. by a roll stretching method. Next, the stretched sheet-like molded body was heated at 100 ° C. in the width direction using a tenter.
To obtain a PTFE porous membrane in a fired state.
The collection efficiency and pressure loss of this film were measured. Table 1 shows the results.

On the other hand, activated carbon (manufactured by Kanto Chemical Co., Ltd.) having an average particle size of 20 μm as an adsorbent and PE powder (low-density PE, manufactured by Tokyo Ink Co .; 30 mesh pass, melting point: 98 ° C.) as a hot melt powder are weight ratio. To obtain a mixed powder.

Two porous PTFE membranes prepared as described above were prepared, and the mixed powder was sprayed on the one side of the one side of the membrane almost uniformly so as to be 20 g / m ^2. With the PTFE porous membranes superimposed on the membrane surface,
Both PTFEs along the hot roll heated to 150 ° C
The porous membrane was bonded.

Further, as a reinforcing material, a nonwoven fabric made of a composite fiber having a core / sheath structure ("ELEVES" manufactured by Unitika Ltd.)
TO303WDO "; a basis weight of 30g / m ² of PET / P
E core sheath nonwoven fabric, melting point of sheath part PE 129 ° C, softening point 74
° C, melting point 261 ° C of the core PET) were prepared, and 175 were placed on both sides of the PTFE porous membrane laminate obtained above.
Lamination was carried out by following a roll heated to ° C.

The cross-sectional structure of the filter medium for an air filter thus obtained is the same as that shown in FIG. For this filter medium, pressure loss, collection efficiency, and gas removal performance were measured. The results are shown in Table 1.

Comparative Example The above PE was used in place of the above mixed powder.
A filter medium for an air filter was obtained in the same manner as in the above example, except that only the powder was sprayed at 10 g / m ² . This filter medium has a cross-sectional structure as shown in FIG. For this filter medium, pressure loss, collection efficiency, and gas removal performance were measured. The results are shown in Table 1.

In order to confirm the desorption of the adsorbent, the number of transmitted particles of 2 μm or more was measured by a particle counter at the time of measuring the collection efficiency. As a result, the number of transmitted particles was 0 in both the examples and comparative examples. . From this, it was confirmed that the adsorbent having an average particle diameter of 20 μm did not fall off.

(Table 1) ―――――――――――――――――――――――――――――――― Pressure loss Collection efficiency Gas removal performance ( (Concentration after one day) [Pa] [%] [ppm] ―――――――――――――――――――――――――――――――― 250 99.99 50 Comparative example 220 99.99 100 ―――――――――――――――――――――――――――――――― PTFE porous membrane Non-consolidated 80 99.5 − ――――――――――――――――――――――――――――――――――

[0036]

As described above, according to the present invention,
A filter material for a PTFE air filter capable of simultaneously removing gaseous organic substances and dust floating in an atmosphere and an air filter unit using the same can be provided.

[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 diagram showing a configuration of an apparatus used for measuring gas removal performance in Examples.

FIG. 3 is a cross-sectional view showing a filter medium manufactured for comparison.

[Explanation of symbols]

 1, PTFE porous membrane 3, 4 Air-permeable support material 5 Adhesive 6 Adsorbent

Claims (4)

[Claims] 1. A filter medium for an air filter, comprising a composite material in which an adsorbent is sandwiched between two or more polytetrafluoroethylene porous membranes bonded by an adhesive. 2. The filter medium for an air filter according to claim 1, wherein the adhesive is present at a rate of 5 g / m ² or more and 20 g / m ² or less between the porous polytetrafluoroethylene membranes. 3. The filter medium for an air filter according to claim 1, further comprising a gas-permeable supporting material laminated with the composite material. 4. An air filter unit comprising the air filter medium according to claim 1.