JP2002001023A - Factory air-conditioning filter system and factory air- conditioning method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an advanced air-cleaning filter system by reducing loads on an HEPA filter and a ULPA filter without lowering the life of a high efficiency filter. SOLUTION: A filter using an electret nonwoven fabric obtained by the melt-blowing method is connected to the HEPA filter and/or the ULPA filter in series. By using this filter system as a moderate/high efficiency filter, high collection effect is realized and the lives of the HEPA filter and the ULPA filter are prolonged, so that a filter system suitable for a clean room can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air filter used for removing dust existing in the air, and more particularly, to an electret filter having a low pressure loss and a high collection efficiency, and an electret filter having the same. The present invention relates to a factory air conditioning filter system and a factory air conditioning method in which an electret filter and a HEPA filter or a ULPA filter having a higher collection efficiency are used in combination.

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air filter for removing dust existing in the outside air or circulating air, which is installed in an air conditioner for air conditioning in a factory for manufacturing semiconductor-related products, food products or chemicals. It is about. In particular, it is used for air-conditioning for factories for manufacturing semiconductors and other clean rooms. Efficient operation of the overall filter system by reducing the load on HEPA filters and / or ULPA filters and other final filters used in combination with HEPA filters and ULPA filters used when high cleanliness is required And an air conditioning method for achieving the above.

[0003]

2. Description of the Related Art Conventionally, air conditioners have been used for air conditioning in various factories. The air conditioner is provided with various air filters for the purpose of removing dust from outside air or circulating air and maintaining or improving indoor cleanliness. Usually, a prefilter for removing dust using a nonwoven fabric made of glass fiber mat or synthetic polymer fiber is used near the outside air intake, and then the glass fiber filter paper is folded in a zigzag and arranged in a predetermined frame. A medium-performance filter is installed in the filter chamber.

Further, an ultra-high-performance filter such as a HEPA filter or an ULPA filter is installed as a final filter downstream of the medium-performance filter. H
The EPA filter has a particle removal efficiency of 0.3 μm
This filter is used in a high-performance air purification device that is guaranteed to be 99.97% or more of DOP particles, and is widely used. 0.1 μm ULPA filter
Is an ultra-high-efficiency filter having an efficiency of 99.999% or more for particles. In all cases, in fields where extremely high cleanliness is required, such as in semiconductor-related factories, a HEPA filter is placed downstream of the medium-performance filter.
Furthermore, HEPA is installed on the ceiling in the clean room on the downstream side.
In some cases, filters and ULPA filters are installed. Such a filter installation method increases the collection efficiency of the filter as it goes downstream,
It is intended to reduce the load on the final filter, balance the life of each filter, and operate efficiently as an overall filter system. In some cases, an air washer or the like is installed between the pre-filter and the high-performance filter. In particular, HEPA filters and ULPA filters are expensive and replacement costs are high. When installed in a clean room, they are usually operated so as not to be replaced, and attempts have been made to reduce the load on the filters and extend their life. I have.

[0005] A method of reducing the load on the HEPA filter / ULPA filter can be easily achieved by increasing the collection efficiency of a medium-performance filter installed upstream of the filter. A conventionally used medium-performance filter is a type in which glass fiber filter paper is zigzag folded. As for the collection efficiency, a type with a collection efficiency of 90% in JIS B 9908 type 2 is mainly used, and the collection efficiency for particles having a particle diameter of 0.3 μm targeted at actual use in a factory is 50%. Such an improvement in the collection efficiency of a filter using glass fiber filter paper is achieved by reducing the fiber diameter of the glass fiber, but at the same time, causes an increase in pressure loss, which is a factor in shortening the life of the medium-high performance filter itself. Becomes

[0006] In addition, a medium-performance filter (=
Glass fiber) is replaced and disposed of, but because it uses glass fiber, it cannot be incinerated and must be landfilled as industrial waste.
At present, it is difficult to use it from the viewpoint of consideration for the environment.

[0007]

The object of the present invention is to reduce the load on the HEPA filter / ULPA filter disposed downstream of the medium-performance filter without reducing the service life of the medium-performance filter itself. Accordingly, it is an object of the present invention to provide a filter system for factory air-conditioning, which extends the service life and enables the medium-high performance filter to be incinerated after use.

[0008]

The present invention has been made as a result of intensive studies in view of the above problems. As described above, in the glass fiber filter paper, when the collection efficiency is increased, the pressure loss increases accordingly. This is because the particle collection mechanism of the glass fiber filter paper is "blocking""browndiffusion"
This is because they rely only on mechanical collection mechanisms such as "gravitational sedimentation" and "inertial collision".

According to the present invention, an electrostatic mechanism by electretization is added to the mechanical collecting mechanism to achieve a dramatic improvement in the collecting efficiency while suppressing an increase in pressure loss. In other words, by using a material whose collection efficiency by the mechanical collection mechanism is equivalent to that of glass fiber filter paper and using it as an electret, the effect of adding the electrostatic collection mechanism to the mechanical collection mechanism does not increase the pressure loss. Improved collection efficiency can be obtained. FIG. 1 shows the collection efficiency of the glass fiber filter paper with respect to the particle diameter under a wind speed of 5 cm / s. Furthermore, the pressure loss and the collection efficiency with respect to the particle diameter of a polypropylene melt blown nonwoven fabric having the same collection efficiency as that of the glass fiber filter paper in the non-electret state, and the collection efficiency with respect to the particle diameter of the product obtained by electretization are shown. In glass fiber filter paper and non-electret polypropylene meltblown nonwoven fabric, particles are collected only by a mechanical collection mechanism, whereas in electretized polypropylene meltblown nonwoven fabric, an electrostatic collection mechanism is added in addition to a mechanical collection mechanism. Acts to improve the collection efficiency. In particular, in the former two, since the dramatic improvement is achieved in a region of relatively low collection efficiency and a small particle diameter, the load on a final filter such as a HEPA filter or an ULPA filter disposed downstream is reduced. Will be.

The filter medium containing the nonwoven fabric used in the present invention has a collection efficiency of 50% or more for particles having a particle diameter of 0.3 μm by a mechanical collection mechanism, and is used in an electret state. Therefore, the collection efficiency can be improved without increasing the pressure loss. Medium-performance filter using this filter medium and HEP downstream
By using a filter system that uses a combination of the A filter and the ULPA filter, the service life of both the medium-performance filter and the HEPA filter and the ULPA filter can be extended, and the entire filter system can be operated more efficiently.

As a characteristic of the electret filter,
As the dust is collected, the effect of shielding the electric flux lines of the collected dust and the loss of electric charge when collecting dust and mist to which an organic solvent or the like has adhered may occur. However, in the present invention, the particle diameter is 0.3 μm only by the mechanical trapping mechanism.
It is possible to maintain the collection efficiency for particles of 50% or more. Further, similarly to the glass fiber filter paper, clogging due to dust accumulation has an effect of increasing the collection efficiency, so that the attenuation of the electrostatic effect is compensated. That is, the collection efficiency is improved while suppressing an increase in pressure loss, and the load on the HEPA filter / ULPA filter arranged on the downstream side is reduced.

The fibers used for the non-woven fabric constituting the filter medium in the present invention include polypropylene, polyethylene, poly-3-methyl-1-butene, poly-4-methyl-1-pentene and polyvinylidene fluoride. ,
There are insulating organic fibers such as polytetrafluoroethylene, polycarbonate, polystyrene, polyvinylidene chloride, polyethylene terephthalate, polyamide, polyacrylonitrile, polysulfone, and polyphenylene oxide, and insulating inorganic fibers such as borosilicate glass and quartz glass. Examples thereof include polypropylene, poly-3-methyl-1-butene, poly-4-methyl-1-pentene, polyvinylidene fluoride, and polycarbonate.
In particular, polypropylene is advantageous in terms of manufacturing method and price,
Further, when incinerated, it mainly becomes carbon dioxide and water, which is very suitable.

The average fiber diameter of the fibers used in the nonwoven fabric having a collection efficiency of 50% or more for 0.3 μm particles by the mechanical collection mechanism constituting the filter medium of the present invention is 0.1 μm or more and 3 μm or less; Preferably it is 0.5 μm or more and 2.5 μm or less. When the thickness is 0.1 μm or less, the collection efficiency increases, but the pressure loss increases, and
If it is not less than μm, the collection efficiency is insufficient, and the effect of reducing the load on the final filter such as the HEPA filter or ULPA filter disposed downstream cannot be obtained. And the basis weight of the nonwoven fabric is 10 g / m ² or more and 100 g / m ^2.
m ² or less, preferably 10 g / m ² or more and 50 g / m ^2
2 or less. If it is 10 g / m ² or less, the collection efficiency is insufficient, and the HEPA filter UL
The effect of reducing the load on the final filter such as the PA filter cannot be obtained. Conversely, if it is 100 g / m ² or more, the trapping efficiency will increase, but the pressure loss will increase. As a production method, a melt blown method is suitably used.
The nonwoven fabric can be used alone as a filter medium, but can be used by laminating with various nonwoven fabrics, sheets, nets, etc. in order to supplement the mechanical strength required for processing or practical use.

[0014]

DETAILED DESCRIPTION OF THE INVENTION The present invention has an average fiber diameter of 2.3 .mu.m.
m, and a polypropylene fiber is spun by a melt blow method so as to have a basis weight of 30 g / m ² to form a nonwoven fabric.
Electret was formed by corona discharge to obtain a medium-performance filter. Examples of a method of forming the nonwoven fabric into an electret include corona charging, electric field charging, hot electric field charging, electron beam irradiation, and the like, but are not particularly limited thereto.
Any charging method can be used as long as the charge is stably held at a high charge amount. 10 kv / cm or more, preferably 15 kv / cm or more in the case of corona charging method or electric field charging method
An electric field strength of kv / cm or more is suitable, and in the case of electron beam irradiation, irradiation of 0.1 Mrad or more and 1 Mrad or less is desirable.

A HEPA filter or an ULPA filter was installed downstream of the medium-performance filter with respect to the flow of air, and a comparison with a filter made of glass fiber was performed. HEPA filter is made by Toyobo HE
PA filter: TG-50C-PT-C was used.

The initial pressure loss and the initial collection efficiency of 0.3 μm particles are determined by installing filters in independent ducts, respectively.
A pre-filter with a collection efficiency of 80% in JIS B 9908 format 3 was placed on each upstream side,
An outside air ventilation test was carried out under the same environment at a flow rate of min. Example 1 and Comparative Examples 1 to 3 are provided with a pressure loss measurement port and an air sampling port upstream and downstream of the medium-high performance filter installation section, and a pressure loss measurement port upstream and downstream of the HEPA filter installation section. And the transition of the collection efficiency for 0.3 μm particles,
Further, with respect to the HEPA filter, the transition of the pressure loss was measured. This test was performed until the pressure loss of the medium-performance filters of Example 1 and Comparative Examples 1 to 3 reached 300 Pa, respectively.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the following examples do not limit the present invention, and all modifications and alterations without departing from the spirit of the present invention fall within the technical scope of the present invention. Included.

[0018]

EXAMPLES (Example 1) Average fiber diameter 2.3 μm, basis weight 3
Laminating a 0 g / m ² polypropylene meltblown nonwoven fabric made of polyolefin heat fusion fibers having an average fiber diameter of 35μm to basis weight 60 g / m ² of dry non-woven fabric that has been subjected to electret processing a filter medium, folds the present filter material After folding, insert the corrugated aluminum separator between the folds and fold it into the outer frame made of plywood to obtain the rated size (610 mm width, 610 mm height,
(290 mm deep). The folded area of the filter medium was 16 m ² . A HEPA filter (Toyobo HEPA) is installed downstream of this medium-performance filter.
A filter in which filters TG-50C-PT-C) were arranged and combined was referred to as Example 1. (Comparative Example 1) A medium-high-performance filter using a glass fiber filter paper as a filter medium and having a collection efficiency of 90% in JIS B 9908 type 2 (Shinwa Tec 9-2424-1)
2AW) and a HEPA filter (Toyobo H) as in Example 1.
An EPA filter (TG-50C-PT-C) was arranged and combined to obtain Comparative Example 1. (Comparative Example 2) A glass fiber filter made of glass fiber having an average fiber diameter of 3.5 µm and an organic binder and having a basis weight of 75 g / m ² manufactured by wet papermaking was used as a filter medium, and the same method as in Example 1 was used. A medium-performance filter of the same size was manufactured. The folded area of the filter medium was 16 m ² . The HEPA filter (Toyobo H
An EPA filter (TG-50C-PT-C) was arranged and combined to obtain Comparative Example 2. (Comparative Example 3) Average fiber diameter 3.5 μm, basis weight 22 g / m ²
Average fiber diameter of 3 for polypropylene melt blown nonwoven fabric
A basis weight 60 made of a 5 μm polyolefin heat-fusible fiber
A filter medium was formed by laminating g / m ² dry nonwoven fabric and subjected to an electretization process, and a medium-performance filter of the same size was manufactured in the same manner as in Example 1. The folded area of the filter medium was 16 m ² . To this, as in Example 1, H
EPA filter (Toyobo HEPA filter TG-
50C-PT-C) was placed and combined as Comparative Example 3.

FIG. 2 shows the transition of the pressure loss of the high-performance filters of Example 1 and Comparative Examples 1 to 3, FIG. 3 shows the transition of the collection efficiency for 0.3 μm particles, and FIG. 4 shows the transition of the pressure loss of the HEPA filter. Shown in Example 1 and Comparative Example 1
For each of the medium-to-high-performance filters and HEPA filters of Nos. 3 to 3, a pressure drop of 300 P is used as an index of service life.
Table 1 shows the time required to reach a.

[0020]

[Table 1]

As shown in FIG. 2 and FIG.
The increase in the pressure loss of the medium-high performance filter shows the same transition as in Comparative Examples 1 and 2, and the trapping efficiency always changes at a higher level than Comparative Examples 1 and 2. FIG. 4 shows the HEPA of the first embodiment.
The increase in the pressure loss of the filter is extremely slow as compared with Comparative Examples 1 and 2. That is, the load on the HEPA filter is reduced. Further, as shown in Table 1, Example 1
The time required for the pressure loss of the HEPA filter to reach 300 Pa is about twice that of Comparative Examples 1 to 3,
It can be seen that the service life has been dramatically improved. On the other hand, the pressure loss of the medium-performance filter of Example 1 was 300
The time required to reach Pa is slightly inferior to Comparative Example 3, but equivalent to Comparative Examples 1 and 2, and can be said to have a sufficient service life. Note that in Example 1 and Comparative Example 3, the trapping efficiency of the medium-high-performance filter showed a tendency to temporarily decrease and then recover, but this was due to the decrease in the trapping efficiency due to the attenuation of the electrostatic effect and the subsequent decrease. Recovery due to clogging has occurred. In Comparative Example 3, the collection efficiency of the medium-to-high-performance filter is significantly reduced, and the initial collection efficiency is at a higher level than those of Comparative Examples 1 and 2, but lowers to a level lower than these. For this reason, in Comparative Example 3, the load on the HEPA filter was increased, and as shown in FIG. 4, the gradient of the increase in the pressure loss of the HEPA filter was increased. That is, H
The load on the EPA filter has increased. On the other hand, in Example 1, the degree of lowering of the collection efficiency of the medium-high performance filter is small, and the medium-high performance filter of Example 1 using the same material that has not been electretized as the filter medium,
The trapping efficiency of the medium-performance filter of Comparative Example 2 having the same initial trapping efficiency does not fall below the trapping efficiency. This is because the filter medium used in the medium-performance filter of Example 1 was Comparative Example 1,
This is because, in addition to having a mechanical collection mechanism equivalent to that of the filter medium used in the medium-performance filter of Comparative Example 2, an electrostatic collection mechanism was provided by electret processing. Therefore, the medium-performance filter according to the first embodiment can extend the service life of the HEPA filter without shortening the service life of the filter itself, thereby making the operation of the entire filter system efficient.

[0022]

According to the present invention, final filters such as HEPA filters and ULPA filters installed in air-conditioning equipment for air-conditioning in factories that manufacture semiconductor-related products, foods, chemicals, and the like that require high cleanliness space. Load is reduced, and the replacement life can be extended. In addition, the medium and high performance filters also have a sufficient life and can be efficiently operated as a whole filter system, thereby contributing to a reduction in running cost.

[Brief description of the drawings]

Fig. 1 Glass fiber filter paper and collection efficiency

Fig. 2 Pressure drop and operation time of a medium-performance filter

Fig. 3 Medium-high-performance filter collection efficiency and operation time

FIG. 4 HEPA filter pressure loss and operating time

Claims (3)

[Claims] 1. A combination of at least (1) a filter using a filter medium containing electretized nonwoven fabric and (2) a HEPA filter and / or (3) a filter having a higher collection efficiency. The factory air conditioning filter system. 2. An average fiber diameter of 0.5 μm or more and 3 μm or less,
The filter system for factory air conditioning according to claim 1, further comprising a melt blown nonwoven fabric having a basis weight of 10 g / m2 or more and 100 g / m2 or less. 3. A factory air conditioning method for a clean room using the filter system according to claim 1.