JP2008296222A - Air filter filtering medium and air filter unit using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an air filter filtering medium capable of preventing clogging caused by collected dust and suppressing an increase in pressure loss. <P>SOLUTION: The air filter filtering medium comprises a polytetrafluoroethylene porous film 1 and a fibrous perforated material 2, wherein the material 2 with a range of a fiber diameter of 1 to 15 μm, a porosity of 70% or more, and a basis amount of 60 g/m<SP>2</SP>is disposed upstream the film 1. A nonwoven fabric is preferable as the material 2, and polyethylene, polypropylene, polyethylene terephtalate, and the like can be used as the material. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an air filter medium using a polytetrafluoroethylene (hereinafter referred to as “PTFE”) porous membrane, and more specifically, for example, in air or gas used in clean rooms such as the semiconductor industry and the pharmaceutical industry. Filter media used to capture airborne particles, filter media used to capture dust entering the hard disk and dust generated inside the hard disk (for example, vent filter media), or filter media used to capture dust sucked by a vacuum cleaner The present invention relates to an air filter medium that can be preferably used and an air filter unit using the same.

  2. Description of the Related Art Conventionally, an air filter unit used in a clean room or the like has often used an air filter medium obtained by making paper by adding a binder to glass fiber. However, such filter media have problems such as the presence of adhering fibrils in the filter media and self-dusting when bent by processing. Further, if the amount of the binder is increased to prevent the self-dusting, the pressure loss may increase (Japanese Patent Laid-Open No. 63-16019). Furthermore, when such a filter medium comes into contact with a certain chemical such as hydrofluoric acid, there is a problem that the glass and the binder deteriorate and generate dust.

  On the other hand, PTFE is a clean material and has excellent chemical resistance. Therefore, in recent years, the PTFE porous membrane has been used in various fields as an air filter medium, and is particularly useful as an air filter medium in fields such as semiconductor manufacturing where a strict clean environment is required.

  The PTFE porous membrane can be produced, for example, by preparing a sheet-like PTFE molded body and biaxially stretching it to make it porous. The PTFE porous membrane produced in this way has a very low pressure loss and a very high collection efficiency, and therefore has excellent dust collection performance. However, the PTFE porous membrane is weak in strength because its thickness is reduced by stretching, and it is difficult to use it alone as an air filter medium. For this reason, a composite material or a laminate of a breathable porous material as a reinforcing material on the PTFE porous membrane is used as an air filter medium (International Publication No. WO94 / 16802, Patent Document 1).

The reinforcing material is generally composed of synthetic fibers made of polyethylene (PE), since it does not shrink when laminated with a PTFE porous membrane, and moderate rigidity can be obtained even for pleating. A spunbond type nonwoven fabric having a core-sheath structure is used. For example, in an air filter unit using a filter medium in which a reinforcing material such as the nonwoven fabric is laminated on the PTFE porous membrane, the collection efficiency for particles having a particle diameter of 0.1 μm is extremely high, 99.999999% or more. It is possible to further improve the clean environment such as a clean room. However, since the reinforcing material allows the dust to permeate without being trapped, the PTFE porous membrane is likely to be clogged by the trapped dust, and the pressure loss greatly increases during use. There's a problem.
International Publication No. WO94 / 16802 Pamphlet

  Therefore, an object of the present invention is to provide an air filter medium in which an increase in pressure loss is suppressed and an air filter unit using the same.

In order to achieve the above object, an air filter medium of the present invention is an air filter medium including a PTFE porous membrane and a fiber breathable porous material, and the upstream side of the gas flow of the porous membrane A fiber-permeable porous material is disposed, and the fiber-permeable porous material has a fiber diameter in the range of 1 to 15 μm, a porosity of 70% or more, and a basis weight of 60 g / m ² or more. Features.

  In addition to having a function as a reinforcing material, the fiber breathable porous material having the physical properties itself has a dust collecting function and acts as a prefilter. For this reason, the air filter medium of the present invention prevents clogging in the PTFE porous membrane, can suppress an increase in pressure loss due to this, and has a longer service life. The present inventors speculate that the reason why the conventional air-permeable porous material hardly captures dust is that the fiber diameter is as thick as about 20 μm or more.

In the fiber breathable porous material, the fiber diameter is preferably in the range of 1 to 5 μm, the porosity is in the range of 70 to 90%, and the basis weight is preferably in the range of 60 to 200 g / m ^2. .

  The air filter unit of the present invention uses the air filter medium of the present invention. The air filter unit using the air filter medium of the present invention is less likely to be clogged with trapped dust and has a longer service life, so that the cost can be reduced. In particular, it is useful as an air filter unit used in semiconductor manufacturing or the like that requires a harsh clean environment.

The air filter medium of the present invention is formed by laminating a fiber permeable porous material having a fiber diameter of 1 to 15 μm, a porosity of 70% or more, and a basis weight of 60 g / m ² or more on the upstream side of the PTFE porous membrane. Clogging due to trapped dust hardly occurs and increase in pressure loss can be suppressed, so that the service life can be extended. If such an air filter medium is used, for example, in an air filter unit in a clean room in semiconductor manufacturing, clogging of the filter hardly occurs and the lifetime thereof is long, so that the cost can be reduced.

  The air filter medium of the present invention includes a PTFE porous membrane and the fiber breathable porous material having physical properties as described above, and the fiber breathable porous material is disposed upstream of the porous membrane. .

  The PTFE porous membrane is not particularly limited as long as the performance according to the intended use is exhibited. However, for example, when used as an air filter medium in a clean room for semiconductor production, etc., it has a dust collection performance. The represented Performance filter (PF) value is preferably greater than 15, and more preferably in the range of 20-40. In addition, the said PF value can be calculated | required from a following formula (Formula 1), and the collection efficiency and pressure loss in a following formula (Formula 1) can be calculated | required by the method mentioned later.

(Equation 1)
PF value =-[Log (1-collection efficiency)] × 100 / pressure loss Unit of collection efficiency:% Unit of pressure loss: mmH ₂ O
In the PTFE porous membrane, the thickness is appropriately determined depending on the size of the air filter medium to be prepared, etc. It is.

  The method for producing the PTFE porous membrane is not particularly limited, and examples thereof include those described in JP-A-10-030031, International Publication No. WO94 / 16802, and the like.

  An example of a method for producing the PTFE porous membrane is shown below. First, a liquid lubricant is added to and mixed with the unfired PTFE fine powder. The PTFE fine powder is not particularly limited, and a commercially available product can be used. The liquid lubricant is not particularly limited as long as it can wet the surface of the PTFE fine powder and can be removed later, hydrocarbon oil such as naphtha, white oil, liquid paraffin, toluene, xylene, Solvents of alcohols, ketones and esters can be used. These may be used in combination of two or more.

  The addition ratio of the liquid lubricant to the PTFE fine powder is appropriately determined depending on the type of the PTFE fine powder, the type of the liquid lubricating oil, the sheet molding conditions described later, and the like. The liquid lubricant is in the range of 15 to 35 parts by weight.

  Next, the mixture is formed into a sheet in an unfired state. Examples of the forming method include a rolling method in which the mixture is extruded into a rod shape and then rolled with a pair of rolls, and an extrusion method in which the mixture is extruded into a plate shape to form a sheet. Moreover, you may combine the said both methods. Although the thickness of this sheet-like molded object is suitably determined by the conditions of the extending | stretching performed later, etc., it is the range of 0.1-0.5 mm, for example.

  In addition, it is preferable to remove the liquid lubricant contained in the obtained sheet-like molded body by a heating method, an extraction method, or the like before the subsequent stretching step. The solvent used in the extraction method is not particularly limited, and examples thereof include normal decane, dodecane, naphtha, kerosene, and sumoyl.

  Next, it extends | stretches with respect to the said sheet-like molded object. This stretching is preferably biaxial stretching. For example, in the longitudinal direction of the sheet-like molded product, it is stretched at a temperature of 150 to 390 ° C. so that its length is in the range of 2 to 60 times, and subsequently in the width direction of the sheet-like molded product, The film is stretched at a temperature of 40 to 150 ° C. so that the length is in the range of 10 to 60 times. Thus, a PTFE porous membrane can be produced.

  In addition, the manufacturing method in particular of a PTFE porous membrane is not restrict | limited, What is necessary is just to be able to manufacture the PTFE porous membrane which exhibits the performance according to a use as mentioned above.

  Next, the fiber breathable porous material is not particularly limited as long as it has the fiber diameter, porosity and basis weight as described above, but it is a material with excellent breathability. Certain non-woven fabrics, woven fabrics, meshes (mesh-like sheets) and the like can be used. Among these, non-woven fabrics are more preferable because they are excellent in strength, flexibility, and workability. The fibers include single fibers and filaments. Preferably, the fibers are composed of the filaments because the fibers can be prevented from falling off from the air filter during use.

  The material of the fiber is not particularly limited, and examples thereof include PE, polypropylene (PP), polyethylene terephthalate (PET), and composite materials thereof. Moreover, the said fiber is a composite fiber of a core-sheath structure, It is preferable that a core part is a synthetic fiber whose melting | fusing point is relatively higher than a sheath part. If a fiber-permeable breathable porous material made of such a core-sheath structure fiber is used, shrinkage can be prevented even when laminated with a PTFE porous membrane by heating. Examples of the fiber having the core-sheath structure include those in which the core part is made of PET and the sheath part is made of PE, and those in which the core part is made of PP and the sheath part is made of PE.

  Next, the air filter medium of the present invention can be produced, for example, by laminating the fiber breathable porous material on the upstream side of the gas flow of the PTFE porous membrane. The laminating method is not particularly limited, and examples thereof include a method of bonding by heat treatment and a method of bonding using an adhesive material.

  When laminating by the heat treatment, for example, the PTFE porous membrane and the fiber breathable porous material are overlapped and brought into contact with a heating member to melt a part of the fiber breathable porous material. Can be performed by bonding them together. In particular, the method of superimposing the two and passing them between heated rolls is preferable because the heating operation can be carried out continuously. The conditions for the heat treatment are appropriately determined depending on the material of the fiber breathable porous material and the like. For example, the treatment temperature is preferably equal to or higher than the melting point of the fiber breathable porous material.

  Moreover, when laminating | stacking with the said adhesive material, what is necessary is just to interpose an adhesive material between the said PTFE porous membrane and the said fiber breathable porous material, for example. As the adhesive material, for example, PE powder having a low melting point can be used.

  As described above, the structure of the air filter medium of the present invention is not particularly limited as long as the fiber-permeable porous material is disposed on the upstream side of the gas flow of the porous membrane. For example, the porous PTFE membrane may be one layer or two or more layers. When it has the laminated body of the said PTFE porous membrane, the number of lamination | stacking is the range of 2-10 layers, for example. The PTFE porous membrane may be the same PTFE porous membrane or a different PTFE porous membrane. Examples of the method of laminating the PTFE porous membranes include a method of pressure laminating at the time of forming the PTFE porous membrane and a method of heat-sealing.

  Moreover, the said fiber-permeable porous material may be arrange | positioned like the upstream on the downstream side of a PTFE porous membrane, and a different air-permeable porous material may be arrange | positioned.

  Thus, the configuration of the air filter medium of the present invention is not particularly limited. For example, as shown in FIG. 1, the air permeability of the fiber is only formed on the upstream surface of the gas flow (arrow) of the PTFE porous membrane 1. The porous material 2 may be disposed, and as shown in FIG. 2, the fiber breathable porous material 2 may be disposed on both surfaces of the PTFE porous membrane 1. In addition, as shown in FIG. 3, a fiber-permeable porous material 2 may be disposed on the upstream surface of the gas flow (arrow) of the PTFE porous membrane 1 via an adhesive layer 3.

  The entire thickness of the air filter medium of the present invention is, for example, in the range of 0.2 to 2.0 mm, and preferably in the range of 0.25 to 1.0 mm.

  Next, the air filter unit of the present invention can be manufactured by a conventional method except that the air filter medium of the present invention is used. For example, the air filter medium of the present invention is folded into a continuous W shape (pleated) ) And can be manufactured if it is framed.

[Example]
Next, examples of the present invention will be described together with comparative examples. In addition, the measuring method of each characteristic of the fiber breathable porous material and the air filter medium in Examples and Comparative Examples is as follows.

  (1) Fiber diameter The surface of the fiber-made breathable porous material was taken with a scanning microscope (SEM) photograph, and the fiber diameter was measured.

(2) Weight per unit area A breathable porous material made of fiber was sampled at 100 cm ² , and its weight was measured with an electronic balance to determine mass (g) per 1 m ² .

  (3) The thickness of the porous porous material made of porosity fiber was measured at five points using a dial thickness gauge (measuring element diameter: 10φ, minimum scale: 10 μm), and the average value was obtained. The porosity was calculated by substituting the average value of the thickness and the weight per unit area of the fiber-permeable breathable porous material into the following formula (Equation 2).

(Equation 2)
Porosity (%) = [A− (B / C)] / A
A: True specific gravity (g / m ² ) of the material used for the fiber breathable porous material
B: Weight per unit area (g / m ² )
C: Average thickness (μm)
(4) A pressure loss sample (PTFE porous membrane or air filter medium, hereinafter the same) is set in a circular holder with an effective area of 100 cm ² , and atmospheric pressure is supplied from the inlet side while pressure difference between the inlet side and the outlet side. Then, the permeation flow rate of the sample was adjusted to 5.3 cm / second to allow the atmospheric dust to permeate, and the pressure loss (unit: mmH ₂ O) per fixed time was measured with a pressure gauge (manometer). In the case of an air filter medium, the sample was set so that the upstream side (fiber breathable porous material side) of the air filter medium was positioned on the inlet side for supplying atmospheric dust. The atmospheric dust refers to dust floating in the atmosphere.

(5) Dust Holding Capacity (DHC)
In the same manner as the pressure loss measurement method, atmospheric dust was allowed to pass through the sample, and the weight change of the sample was measured with an electronic balance at regular intervals.

(6) Collection efficiency A sample was set in the same manner as the pressure loss measurement method. Then, the permeation rate of the sample is set to 5.3 cm / sec, and polydisperse dioctyl phthalate (hereinafter referred to as “DOP”) particles having a particle size of 0.5 μm or more are provided at about 10 ⁷ particles / liter upstream of the sample. The upstream DOP particle concentration and the downstream DOP particle concentration permeating the sample were measured with a particle counter, and the collection efficiency was determined by the following equation (Equation 3). However, the target particles had a particle size in the range of 0.5 μm or more.

(Equation 3)
Collection efficiency (%) = [1− (downstream concentration / upstream concentration)] × 100
Downstream concentration unit: particle number / liter Upstream concentration unit: particle number / liter

30 parts by weight of a liquid lubricant (liquid paraffin) is uniformly mixed with 100 parts by weight of PTFE fine powder (Fullon CD-123, manufactured by Asahi ICI Fluoropolymers), and this mixture is preformed at a pressure of 20 kg / cm ^2. did. Next, the preform was extruded into a rod shape, and the rod-shaped product was passed between a pair of metal rolling rolls to obtain a long sheet-like PTFE molded body having a thickness of 0.2 mm. Next, after removing the liquid lubricant from the sheet-like PTFE molded body by an extraction method using normal decane, the liquid lubricant was wound around a tubular core body in a roll shape.

  The wound sheet-like PTFE molded body was stretched at 370 ° C. by a roll stretching method so that the length thereof was 20 times in the longitudinal direction. Subsequently, this sheet-like PTFE molded body was stretched at 100 ° C. using a tenter so that the length thereof was 10 times in the width direction to obtain a fired PTFE porous membrane.

As the fiber breathable porous material disposed on the upstream side of the PTFE porous membrane, a commercially available PP non-woven fabric having a fiber diameter of about 10 μm and a basis weight of 60 g / m ² was used. Then, the fiber breathable porous material is stacked on the upstream side of the PTFE porous membrane, and a PE / PET core sheath nonwoven fabric having a fiber diameter of 20 μm and a basis weight of 30 g / m ² is provided on the downstream side of the PTFE porous membrane. After stacking, this was passed by passing between a pair of rolls heated to 145 ° C. to produce an air filter medium.

Except that a commercially available PP nonwoven fabric with a fiber diameter of about 10 μm and a basis weight of 80 g / m ² was used as the fiber breathable porous material laminated on the upstream side of the PTFE porous membrane, the same as in Example 1 above. Thus, a porous PTFE membrane and an air filter medium were prepared.

The same as in Example 1 except that a commercially available PP nonwoven fabric having a fiber diameter of about 10 μm and a basis weight of 100 g / m ² was used as the fiber breathable porous material laminated on the upstream side of the PTFE porous membrane. Thus, a porous PTFE membrane and an air filter medium were prepared.

As in Example 1 except that a commercially available PP nonwoven fabric with a fiber diameter of about 3 μm and a basis weight of 100 g / m ² was used as the fiber breathable porous material laminated on the upstream side of the PTFE porous membrane. Thus, a porous PTFE membrane and an air filter medium were prepared.

(Comparative Example 1)
As in Example 1 except that a commercially available PP nonwoven fabric having a fiber diameter of about 20 μm and a basis weight of 70 g / m ² was used as the fiber breathable porous material laminated on the upstream side of the PTFE porous membrane. Thus, a porous PTFE membrane and an air filter medium were prepared.

  In the examples and comparative examples, the fiber diameter, basis weight, porosity, and collection efficiency were measured for the fiber breathable porous material laminated on the upstream side of the PTFE porous membrane before producing the air filter medium. It is shown in Table 1 below. Moreover, the result of having measured the pressure loss and DHC about the air filter medium produced in the Example and the comparative example is shown in FIG.

  As shown in Table 1, the air-permeable porous material used in each example has a smaller fiber diameter than that of the fiber-permeable air-permeable material of Comparative Example 1, and dust particles having a particle diameter of 0.5 μm or more. The collection efficiency was high. As shown in FIG. 4, the air filter medium of each example using such a fiber-permeable porous material having a high collection efficiency has a pressure loss at the same DHC value as compared with the air filter medium of the comparative example. The rise was low. As can be seen from Examples 1, 2, and 3, the larger the basis weight of the fiber-permeable porous material used, the lower the pressure loss of the air filter medium at the same DHC value. As can be seen, the smaller the fiber diameter of the fiber breathable porous material used, the lower the pressure loss of the air filter media at the same DHC value.

It is sectional drawing which shows the structure outline of an example of the air filter medium of this invention. It is sectional drawing which shows the structure outline of the other example of the air filter medium of this invention. It is sectional drawing which shows the structure outline of the further another example of the air filter medium of this invention. It is a graph which shows the relationship between DHC and pressure loss of the air filter medium in one Example of this invention.

Explanation of symbols

1: PTFE porous membrane 2: Fiber-permeable porous material 3: Adhesive layer

Claims (3)

An air filter medium comprising a polytetrafluoroethylene porous membrane and a fiber breathable porous material, wherein the fiber breathable porous material is disposed upstream of the gas flow of the porous membrane, The air filter medium is characterized in that the air-permeable porous material has a fiber diameter in the range of 1 to 15 μm, a porosity of 70% or more, and a basis weight of 60 g / m ² or more.   The air filter medium according to claim 1, wherein the fiber-permeable porous material is a nonwoven fabric.   An air filter unit using the air filter medium according to claim 1.

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