JP2001170424A - Air filter medium and air filter unit using the same - Google Patents

Abstract

(57) [Problem] To provide a filter medium for an air filter in which the initial pressure loss is low and the rise in pressure loss during use is suppressed. SOLUTION: A first polytetrafluoroethylene (P)
(TFE) A porous membrane 5 and a second porous PTFE membrane 4 having a larger average pore diameter and a smaller pressure loss than this membrane are laminated, and further sandwiched by air-permeable supporting members 3 and 3 such as a nonwoven fabric. The second porous PTFE membrane 4 on the upstream side of the air flow functions as a prefilter, and has an average pore diameter of 3 to 10 μm. The pressure loss of the entire filter medium 1 is suppressed to not more than twice the pressure loss of the first porous PTFE membrane 5 (average pore diameter 1 to 3 μm).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a filter medium for an air filter using a porous polytetrafluoroethylene (hereinafter referred to as "PTFE") membrane and an air filter unit using the same.

[0002]

2. Description of the Related Art Conventionally, as a filter medium for an air filter, a paper made by adding a binder to glass fiber has been frequently used. However, this filter medium has problems such as dust generation due to fine fibers in the filter medium and dust generation due to deterioration by chemicals such as hydrofluoric acid. Therefore, in recent years, a porous PTFE membrane that is clean and has excellent chemical resistance has been used as a filter medium for an air filter in the field of semiconductor manufacturing and the like. PT
The FE porous membrane can be manufactured by stretching a sheet-shaped PTFE fine powder to make it porous.
(Japanese Unexamined Patent Publication No. 7-196831, Japanese Patent Application Laid-Open No. 6-8168)
02 publication). Also, a method for producing a laminate of a porous PTFE membrane has been proposed (Japanese Patent Laid-Open No. 57-131236).
JP, JP-A-3-17938). An air filter medium using such a laminate has also been proposed (Japanese Patent Publication No. 9-504737).

[0003]

In a filter medium having a PTFE porous membrane laminated thereon, the pressure loss increases as the filter is used, so that it may not function sufficiently as an air filter. This phenomenon can be said to be fatal in the performance of a high-performance air filter, but this tendency is remarkable in an air filter using a PTFE porous membrane. This is the PTF
It is considered that the characteristics such as the small average pore diameter and the homogeneity of the E porous membrane accelerated the performance deterioration. That is, by blocking the fine particles in the air from closing the pores of the PTFE porous membrane, the area through which air can pass is reduced,
As a result, the pressure loss increases. In addition, the air filter is required to have a high pressure loss in the initial stage.

Accordingly, an object of the present invention is to provide a filter medium for an air filter in which a rise in pressure loss during use is suppressed while using a porous PTFE membrane. Another object of the present invention is to provide a filter medium for an air filter in which the initial pressure loss is low and the rise in pressure loss during use is suppressed. Still another object of the present invention is to provide an air filter unit using the air filter medium.

[0005]

To achieve the above object, the air filter medium of the present invention comprises at least two layers of P
A laminate of a TFE porous membrane is provided. The laminated body includes a first porous PTFE membrane and a second porous PTFE membrane having a larger average pore diameter and a smaller pressure loss than the first porous PTFE membrane.
And a TFE porous membrane. And when gas passes from one side of the filter medium to the other side,
After this gas has passed through the second porous PTFE membrane,
First PTFE so as to pass through the first PTFE porous membrane.
A porous membrane and a second PTFE porous membrane are arranged.

[0006] The second porous PTFE membrane is composed of the first PTFE.
Since the average pore diameter is larger than that of the E porous membrane, it functions as a prefilter that preferentially collects particles having a larger diameter among the fine particles in the atmosphere. As a result, an increase in pressure loss during use is suppressed. In addition, the pressure loss of the second porous PTFE membrane is smaller than that of the first porous PTFE membrane, and does not excessively increase the initial pressure loss even when the second porous PTFE membrane is laminated with the first porous PTFE membrane. .

[0007] It is preferable that the filter medium for an air filter of the present invention further includes a gas-permeable supporting material laminated on both outermost layers of the laminate. This is because handling is convenient and stable pleating can be performed.

In the filter medium for an air filter of the present invention, it is preferable that the initial pressure loss is suppressed to twice or less the pressure loss of the first porous PTFE membrane alone. Further, the average pore size of the second porous PTFE membrane is 3 μm or more and 10 μm or more.
m or less.

Further, the present invention also provides an air fill unit using the air filter medium. This air filter unit includes, for example, a continuous W-shaped pleated filter medium and a member that supports 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 the filter medium 1 for an air filter, a laminate 2 composed of two layers of a porous PTFE membrane is used as a trapping layer, and air-permeable supporting members 3 and 3 are joined to both outermost layers of the trapping layer. Needless to say, the air-permeable supporting member 3 may be arranged only on one of the surfaces.
The laminate 2 of the TFE porous membrane may be used as it is as a filter medium. In the laminate 2, the second porous PTFE membrane 4 is disposed on the upstream side of the airflow passing through the laminate, and the first porous PTFE membrane 5 is disposed on the downstream side. The second porous PTFE membrane 4 functions as a pre-filter of the first porous PTFE membrane 5 and functions as a main filter. The second PTFE porous membrane 4 has a larger average pore diameter and a smaller pressure than the first PTFE porous membrane 5. With losses.

[0011] 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 it to form a porous sheet. Can be obtained. Further, if the film is heated to a temperature equal to or higher than the melting point of PTFE and fired after stretching, the strength is improved. The laminated body 2 of the porous PTFE membrane can be prepared by any of the known methods for manufacturing a porous PTFE membrane.
It can be manufactured by a method including a step of laminating a TFE porous film. PT including such a lamination process
The method for producing the FE porous membrane will be exemplified below.

1) A preform is prepared in which a plurality of layers including PTFE fine powder and a liquid lubricant are laminated. The preformed body is sequentially extruded, rolled, stretched, and the like to obtain a laminate of a porous PTFE membrane. 2) Laminate a plurality of unfired PTFE sheets containing a liquid lubricant. This laminate is sequentially subjected to rolling, stretching, and the like in the same manner as in the conventional production method, to obtain a laminate of a PTFE porous membrane. 3) A plurality of unfired PTFE porous membranes are pressed and laminated. 4) PTFE manufactured individually as in the examples described later
The porous film is laminated after firing.

What affects the porous structure of the porous PTFE membrane is the raw materials used and various conditions in the rolling and stretching steps. In the laminate of the PTFE porous film, the raw materials and various conditions in the process are adjusted for each layer. Although such adjustment is not particularly limited, for example, the adjustment is performed based on the molecular weight of the PTFE fine powder, the rolling conditions for forming the unfired PTFE sheet, the stretching conditions for forming the unfired PTFE porous film, and the like.

The average pore size of the second porous PTFE membrane serving as the prefilter is preferably in the above range, but is particularly preferably 5 μm or more, and more preferably 10 μm or less. Second PTF
If the average pore size of the E porous membrane is too large, it may not function sufficiently as a prefilter, and if it is too small, the pressure loss may increase early. The average pore size of the first porous PTFE membrane serving as a main filter is preferably 1 μm or more and less than 3 μm. If the average pore size of the first PTFE porous membrane is too large, it may not be possible to secure a sufficient collection efficiency, and if it is too small, the pressure loss may be excessive.

The pressure loss of the _second porous PTFE membrane is preferably ₂ mmH ₂ O or more and less than 15 mmH ₂ O. Second
If the pressure loss of the PTFE porous membrane is too large, the pressure loss of the entire filter medium may be excessively increased, and if too small, the filter may not function sufficiently as a prefilter.
Further, the pressure loss of the first porous PTFE membrane serving as a main filter is preferably 15 mmH ₂ O or more and 30 mmH ₂ O or less. If the pressure loss of the first PTFE porous membrane is too large, the pressure loss of the entire filter medium may be excessively increased,
If it is too small, it may not be possible to secure sufficient collection efficiency. 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.

Hereinafter, a method for measuring the average pore diameter and the pressure loss of the porous PTFE membrane will be described. As a method for measuring the pore size distribution of a porous membrane, a method described in ASTM F316-86 is widely used, and an automated measuring device is also commercially available. In this method, with a porous membrane immersed in a liquid having a known surface tension fixed to a holder, the liquid is expelled from the membrane by pressurization from one side, and the pore size is determined from the pressure. This method is not only simple and has high reproducibility, but also makes it possible to simultaneously measure the average pore size, the maximum pore size, and the pore size distribution by using an automated measuring device. Also in the present specification, the average pore size is specifically defined by Porous Mater according to ASTM F316-86.
The value measured using "Perm-Porometer" manufactured by ial Inc. is adopted.

The measurement of pressure loss is also generally performed as one of the performance evaluations of a porous PTFE membrane. In this specification,
With the PTFE porous membrane set in a circular holder having an effective area of 100 cm ² , the pressure loss when air was transmitted at a wind speed of 5.3 cm / sec was measured with a manometer.

It is preferable that the first porous PTFE membrane has a PF (Performance of Filter) value indicating a trapping performance of more than 15. Here, the PF value is a numerical value obtained by the following equation (1).

PF value = {− log (1-E / 100) / L} × 100 (1)

In the equation (1), L represents a pressure loss,
Specifically, numerical values [mmH ₂ measured in the same manner as above]
O]. E represents the collection efficiency, and specifically,
While setting the sample in the same device as the pressure loss measurement and allowing air at the same flow rate to pass, the particle diameter is 0.1 to 0.2 μm.
Of polydispersed dioctyl phthalate (DOP) is supplied as an aerosol at about 10 ⁸ particles / liter, and the particle concentration on the upstream and downstream sides of the sample is measured by a particle counter (LPC). 2)
Is the ratio determined by

Collection efficiency (E) = (1−downstream particle concentration / upstream particle concentration) × 100 (2)

The air-permeable supporting material only needs to have better air permeability than the porous PTFE membrane, and non-woven fabric, woven fabric, mesh, 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. Further, for reasons such as easy adhesion, a nonwoven fabric made of a composite fiber having a core / sheath structure in which the core component has a higher melting point than the sheath component is more preferable.

The bonding between the air-permeable supporting material and the PTFE porous membrane laminate can be performed by using an adhesive member such as an adhesive, and fusion is performed by heating and melting a part of the air-permeable supporting material. It can also be done in a way that does. As mentioned above,
Porous support material and PTFE porous membrane laminate, and PTF
It is preferable that the E porous membranes are joined to each other and integrated as a filter medium.

In order to prevent the pressure loss in the initial state from excessively increasing as compared with the pressure loss of the first PTFE porous membrane, the second PTFE porous membrane serving as a pre-filter should be made of the first PTFE porous membrane. Only on the upstream side of the membrane (in other words, the first
Only on one side of the PTFE porous membrane), the second PT
It is preferable that an FE porous membrane is disposed. Considering a normal use form, one of the particularly preferable forms of the present invention is, as shown in FIG.
, A second porous PTFE membrane 4, a first PTFE porous membrane 5, and a second permeable support material 3 are laminated in this order.

[0025]

The present invention will be described more specifically with reference to the following examples. The average pore size and pressure loss in the following examples were measured by the methods described above.

(Example 1) PTFE fine powder (Asahi
"Aflon CD-123" manufactured by Glass Fluoropolymers;
(Hereinafter referred to as "PTFE Fine Powder A")
17% by weight of liquid lubricant (naphtha) to parts by weight
Was blended. 20 kg / cm ^TwoReserved under the conditions
Molded and then extruded into a rod shape.
Further, the rod-shaped compact is placed between a pair of metal rolling rolls.
Then, a long sheet having a thickness of 250 μm was obtained. This sea
Stretched 15 times in the longitudinal direction of the sheet at a stretching temperature of 290 ° C
Then, the sheet is drawn at a stretching temperature of 80 ° C. by a tenter method.
Stretched 30 times in the width direction to obtain an unfired PTFE porous membrane
Was. This unfired PTFE porous membrane is fixed in size.
And heat-treated at 400 ° C for 10 seconds.
The formed PTFE porous membrane (hereinafter referred to as “PTFE porous membrane”
A ").

On the other hand, PTFE fine powder A100
19 parts by weight of a liquid lubricant (naphtha) was uniformly blended with respect to parts by weight, and preformed, extruded, and rolled under the same conditions as above.
A long sheet having a thickness of 250 μm was obtained. This sheet is 29
The sheet was stretched 20 times in the longitudinal direction of the sheet at a stretching temperature of 0 ° C., and further stretched 30 times in the sheet width direction at a stretching temperature of 80 ° C. by a tenter method to obtain an unfired PTFE porous membrane. This unfired PTFE porous membrane is fixed to a size of 400
Baked P with a thickness of 10 μm
TFE porous membrane (hereinafter referred to as "PTFE porous membrane B")
I got

Table 1 shows the average pore size and pressure loss of the porous PTFE membranes A and B measured as described above.

(Table 1) ―――――――――――――――――――――――――――― Average pore diameter (μm) Pressure loss (mmH ₂₀ ) ― ――――――――――――――――――――――――――――― Porous PTFE membrane A 3 20 Porous PTFE membrane B 5 10 ――――――― ―――――――――――――――――――――――

Each one of the porous PTFE membranes A and PTF
The E porous membrane B was laminated to prepare a filter medium made of a PTFE porous membrane laminate. 150μ thickness on both sides of this filter medium
m, polyethylene terephthalate (PET) / polyester (PE) core-sheath nonwoven fabric with a basis weight of 30 g / m ² (“Elves T0303WDO” manufactured by Unitika, melting point of sheath part PE: 129)
C) is laminated by a heat lamination method (roll temperature 140 ° C.) using a pair of rolls, and a PTFE porous membrane laminate is sandwiched and integrated by a nonwoven fabric from both sides and integrated (FIG. 1). 1 ").

Comparative Example 1 A nonwoven fabric was laminated in the same manner as in Example 1 except that only one layer of the PTFE porous membrane A was used instead of the above-mentioned PTFE porous membrane laminate.
(“Filter medium 2”) was obtained.

Comparative Example 2 A nonwoven fabric was laminated in the same manner as in Example 1 except that a laminate composed of two layers of the PTFE porous membrane A was used instead of the porous PTFE membrane laminate. Then, a filter medium ("filter medium 3") was obtained.

Table 2 shows the pressure losses of the filter media 1, 2, and 3 measured as described above. The pressure loss of the filter medium 1 is PT
The measurement was performed with the FE porous membrane B as the upstream side of the air flow.

(Table 2) ―――――――――――――――――――――――― Pressure loss (mmH ₂₀ ) ―――――――――――― ―――――――――――― Filter media 1 35 Filter media 2 25 Filter media 3 45 ――――――――――――――――――――――――

The above filter villages 1, 2, and 3 have an effective area of 100 cm.
² was set in the circular holder, and air containing fine particles was ventilated at a wind speed of 5.3 cm / sec.
The TFE porous membrane B was on the upstream side). As fine particles,
A polydispersed dioctyl phthalate (DOP) having a particle diameter of 0.1 to 0.2 μm was supplied as an aerosol at about 10 ⁶ particles / liter. Table 3 shows the pressure loss after the lapse of a predetermined time.

(Table 3) ―――――――――――――――――――――――――――――――― Pressure loss (mmH ₂₀ ) Initial ( (0 hour) After 1 hour After 10 hours After 20 hours After 100 hours ―――――――――――――――――――――――――――――――――― Filter media 1 35 38 42 45 48 Filter village 2 25 30 38 48 56 Filter village 3 45 50 60 70 80 ――――――――――――――――――――――――――― ―――――――

Table 3 shows that the increase in pressure loss of the filter medium 1 is suppressed to be lower than that of the filter medium 2 and the filter medium 3.

[0038]

As described above, according to the present invention,
It is possible to provide an air filter medium and an air filter in which an increase in pressure loss during use is suppressed. In particular, it is possible to suppress an increase in pressure loss while keeping the initial pressure loss low.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of one embodiment of a filter medium for an air filter of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Air filter medium 2 PTFE porous membrane laminated body 3 Air permeable support material 4 2nd PTFE porous membrane 5 1st PTFE porous membrane

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 4D006 GA44 HA41 JA02A JA02C KA16 MA03 MA09 MA21 MA22 MB03 MC30 MC30X NA34 NA39 NA47 NA62 NA69 PA05 PB17 PC01 4D019 AA01 BA13 BB08 BD01 BD02 CA02 CB02 CB06 CB10 4F074 AA39 DA04 DA20 DA24 DA43

Claims (5)

[Claims] 1. A filter medium for an air filter, comprising a laminate of at least two layers of a polytetrafluoroethylene porous membrane, comprising: a first polytetrafluoroethylene porous membrane; and a first polytetrafluoroethylene porous membrane. A second polytetrafluoroethylene porous membrane having a larger average pore diameter and a smaller pressure loss than the membrane, wherein the gas passing from one surface to the other surface of the filter medium is the second polytetrafluoroethylene. The first polytetrafluoroethylene porous membrane and the second polytetrafluoroethylene porous membrane so that they pass through the first polytetrafluoroethylene porous membrane after passing through the ethylene porous membrane. A filter medium for an air filter, wherein is disposed. 2. The filter medium for an air filter according to claim 1, further comprising a permeable support material laminated on both outermost layers of the laminate. 3. The filter medium for an air filter according to claim 1, wherein the filter medium has a pressure loss of twice or less the pressure loss of the first porous polytetrafluoroethylene membrane. 4. The filter medium for an air filter according to claim 1, wherein the average pore diameter of the second porous polytetrafluoroethylene membrane is 3 μm or more and 10 μm or less. 5. An air filter unit using the air filter medium according to claim 1. Description: