JP2000157810A - Air filter for removing chemical substance and clean unit having the same incorporated therein - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a used filter material detachable and regenerable and to enable the disuse thereof in a harmless state. SOLUTION: An air filter consists of a filter case frame 3 having an air inlet opening part 1 and an air discharge opening part, the air permeable partition having a wavy or pleated shape arranged in the filter case frame 3 so as to traverse the air flow passage from the air inlet opening part 1 to the air discharge opening part and filter cloths 5-7 having chemical substance removing capacity laid on the air inlet side of the air permeable partition 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air filter suitable for removing chemical pollutants in air to a very low concentration level required in a semiconductor process, and an air circulation type clean unit incorporating the filter. About.

[0002]

[Prior Art] With the advancement of semiconductor devices,
The clean environment required for the device manufacturing process is not only dust-free, but also acid gases such as HCl and HF in air, N
It has become necessary to remove alkaline gases such as H ₃ and amines and organic substances. An air filter for removing chemical substances, usually called a chemical filter, used for this purpose may have a two-dimensional spread, i.e., a sheet or cloth, as a filter for removing these substances from the air. Many. These filters have a pleated structure similar to a HEPA filter for dust removal, and three types are commercially available for an acidic gas, an alkaline gas, and an organic material, respectively, corresponding to the above-mentioned contaminants.

[0003] The pleated filter body is adhered to the plastic frame of the filter with an adhesive so that there is no leakage at the edge. Since the chemical substance removing action of the chemical filter is due to a chemical reaction, the time required for the reaction runs short if the air flows quickly through the filter body. Therefore, the filter body is folded in a pleated shape to expand the filtration area, and the flow rate per unit area of the filter body is reduced, so that the air residence time (residence time) is lengthened. Such an increase in the area of the filter has the advantages of increasing the removal capacity and reducing the pressure loss. Since these chemical filters are imperfect in terms of dust removal, they are usually installed on the windward side of HEPA or ULPA filters for dust removal.

[0004]

In order to remove such chemical contaminants and obtain a cleanliness that does not substantially affect the process of ultra-high-performance semiconductors, the filter medium has a high removal performance. And sheet-like or cloth-like ones are quite expensive. Therefore, an environment in which all acidic gases, alkaline gases, organic substances, and other harmful gases have been removed to a low concentration level necessary for the semiconductor process (hereinafter referred to as an “ultra-clean environment”) is provided by manufacturing equipment and evaluation equipment. It is reasonable to use only the environment inside the clean booth or clean bench. However, for this ultra-clean environment, the three filters must be arranged in series on the windward side of a dust filter such as ULPA. The pleated structure filter essentially needs a thickness, and the usual commercial product is 15 to 30 cm.
There is about thickness. In a clean room for semiconductors, the height of the ceiling is limited, and if four filters are arranged one on top of the other, the ultra-clean environment in the booth or bench becomes narrow and lacks practicality. Moving the filter to a different location requires more space for booths and benches. Either way, the space factor gets worse.

In order to suppress the increase in volume due to the addition of three chemical filters, it is necessary to remove a chemical substance in which the edge of a conventional pleated filter element is adhered to a frame as shown in Japanese Patent Application Laid-Open No. 7-204439. In the air filter for use, it is effective to lay two filter cloths having different removal functions in the grooves of the filter body, and only one chemical filter is required. In this case, the use of an ion-exchange filter cloth as the filter cloth to be laid has an advantage that when these are deteriorated, they can be regenerated by treatment with a chemical solution. However, the pleated filter body that is laid is difficult to regenerate after the end of its life because the edges of the filter body are adhered, and the filter itself must be discarded.
Therefore, in order to extend the life, the area of the pleated filter body must be increased as much as possible, which is inconsistent in terms of space factor.

Conventional chemical filters having a pleated structure must be treated as industrial waste when their filter materials, including those on which filter cloths are laid, have deteriorated removal ability and their life has expired. Filters are a problem because of their large volume. If a filter can be constructed simply by laying several layers of filter cloths that do not adhere to the edges, the filter case can be used repeatedly and the ion-exchange filter cloths can be regenerated repeatedly, thereby significantly reducing the generation of industrial waste.

In order to lay several filter cloths in the pleated grooves, the pitch of the pleats must be increased, especially in the case of a filter cloth having a thickness of about 5 mm. As a result, the area of the filter cloth is reduced, the removal capacity is reduced, and the deterioration is accelerated. To fully demonstrate the characteristics of the method of laying filter cloth,
It is important to be able to determine the optimal replacement time.

It is an object of the present invention to provide an air filter for removing a chemical substance from which a filter medium to be used can be detached, renewable or harmless and discarded, and a clean unit using the air filter.

[0009]

According to the present invention, there is provided a filter case frame having an air introduction side opening and an air discharge side opening, and the filter case frame is provided inside the filter case frame from the air introduction side opening. A permeable partition having a corrugated or pleated shape disposed transversely to the air flow path to the air discharge opening; and at least one chemical removal capability laid over the permeable partition. An air filter for removing chemical substances comprising a filter cloth is provided.

[0010] In a particularly preferred embodiment of the air filter of the present invention, the air-permeable partition is a net or woven cloth made of aluminum or stainless steel wire, and the filter cloth capable of removing chemical substances. A filter cloth for absorbing at least one acidic ion, said air filter being disposed on the windward side of said air-permeable partition.

According to the present invention, an isolated clean space having an air inlet, an air outlet and an openable and closable door, and the air discharged from the air outlet are placed in a container whose inside is isolated from the external environment. An air circulation type clean unit including at least one air filter including an air passage for recirculating to the air inlet and being arranged so as to traverse the air flow path; A clean unit is provided, one of which is the chemical substance removing filter according to the present invention.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to specific examples shown in the accompanying drawings. <Chemical substance removal air filter> The chemical substance removal air filter of the present invention comprises a filter case and a filter cloth for chemical substance removal laid therein. FIG. 1 is a perspective view showing a filter case used in the present invention. The filter case frame 3 has an air introduction (windward) opening 1 and an air discharge side (leeward) opening 2, and a corrugated or pleated partition 4 disposed inside the filter case frame 3. ing. Preferably, the shape of the partition 4 is substantially constant. The filter case frame 3 includes a front wall 3a, a rear wall 3b, and two side walls 3c and 3d, and the front wall 3a is partially cut away for convenience of explanation. Partition 4
Has a substantially corrugated or pleated shape and an outer shape as viewed from above, and the size of the outer shape is substantially the same as the inner diameter of the case frame 3, and the surrounding walls 3a, 3b, 3c,
The periphery bordering 3d is fixed to these walls. For example, they are fitted into grooves provided in these walls, and are screwed to the walls at a plurality of locations.

The material of the filter case 3 is preferably a plastic with a small outgas such as polycarbonate or a light metal such as aluminum. In particular, when used in an environment containing a strongly acidic gas, it is desirable to paint with a paint that is acid resistant and has low outgassing.

Since the corrugated or pleated partition 4 mainly functions as a support for the filter cloth, a material having a certain rigidity is preferable so as to maintain a certain shape. In addition, the partition 4 needs to have a sufficiently high porosity so as not to cause a pressure loss with respect to the flow of air. From such a demand, a preferable material is, for example, a hard plastic (a soft material is not only difficult to maintain its shape but also generates an organic substance such as a plasticizer as outgas).
And a metal net formed of a wire such as a metal such as aluminum or stainless steel, or a molded product of a woven fabric.

For dust having a size of 0.1 μm, neither the filter cloth for removing chemical substances nor the partition 4 having a large porosity has a removing effect.
A HEPA filter or the like is required. In the case of a clean space where precise dust removal is not required, that is, dust having a size of 1 μm needs to be removed, a woven cloth of stainless steel wire (for example, Bekinit (trade name)) having such a dust removing ability is formed into a corrugated partition 4. This eliminates the need for a post-dust filter.

FIG. 2 is a perspective view showing an embodiment of the air filter for removing chemical substances according to the present invention. Members corresponding to those shown in FIG. 1 are denoted by the same reference numerals. FIG.
Indicates that three types of filter cloths 5, 6, 7 for removing chemical substances are laid in this order from the bottom on the corrugated or pleated partition net 4 of the filter case of FIG.

In general, the filter cloth used in the present invention desirably has a basis weight of a reactant that causes an absorption reaction with respect to a chemical substance to be removed at least 100 g / m ² or more.
A basis weight of 300 g / m ² is sufficient, and in the case of a filter cloth for removing organic substances, even if the basis weight of activated carbon fiber is about 200 g / m ² , the purpose can be achieved for the time being. If the basis weight is large, the filter cloth becomes thick, but the degree is affected by the properties of the filter cloth itself. When a plurality of filter cloths are stacked in the present invention, if the total thickness of the stacked layers is large, the pitch of the groove of the partition 4 becomes large and the area of the filter cloth becomes small. Therefore, the total thickness is preferably about 15 mm or less.

If a soft cloth having a thickness of about 5 mm is used as the filter cloth, it can be laid so that air can pass uniformly over the entire surface of the filter cloth even when three sheets are formed with a groove pitch of 5 to 6 cm. The air flow rate for maintaining the clean space of the clean bench or the clean booth is preferably about 0.5 m / sec from the viewpoint of economy. At this flow rate, the thickness of the filter cloth is about 5m
m and the groove pitch is 5-6 cm, the residence time of the filter cloth is 0.06-0.10 seconds. Therefore, any filter cloth having a residence time of 0.06 seconds and sufficient chemical removal ability can be used in the present invention. The filter cloth is usually laid on the entire surface of the pleat net or the windward groove of the woven cloth so as to contact the inner surface of the filter case without any gap. The filter cloth 5,
Since the pitch is relatively large when any one of 6 and 7 is deteriorated, if it is necessary to remove only the deteriorated portion, the entirety can be taken out once and replaced easily. According to the present invention, when effective cleaning against rising air is possible by laying a specific filter cloth, the filter cloth is laid downwind of the surface of the partition 4 so that the laid filter cloth does not fall. I can do it.

As the filter cloths 5, 6, and 7 having a sufficient chemical contamination removing ability with a residence time of 0.06 seconds, there is a commercially available non-woven fabric of activated carbon fiber for removing organic substances. For example, a product having a basis weight of 200 g / m ² and a basis weight of 300 g / m ² can be used. Activated carbon has different organic substances that can be effectively removed depending on its manufacturing method.
The type is selected according to the object to be removed, and if necessary, two types, that is, two sheets having different removal performances are used. If the activated carbon fiber filter cloth deteriorates, it is difficult to regenerate it.

For acidic ions, such activated carbon fiber
KOH or KMnO for fiber non-woven fabric _FourIs attached to
Available. In addition, Kuraray's products use anion exchange fibers.
Weight of fiber 300g / m^TwoNon-woven filter cloth can be used.
In the latter case, if the battery deteriorates, it can be re-produced repeatedly.
Are better. As described above, the filter case
Aluminum or stainless steel used as material
If this is the case, remove at least a portion of the filter cloth
It is preferable that at least one of them is this filter cloth for removing acidic ions.
No. As described later, these materials contain trace amounts of HC in air.
l reacts with aluminum or stainless steel
Chloride, which pollutes downwind air.
You.

For alkaline ions, activated carbon fiber nonwoven fabrics to which phosphoric acids are added can be used. In addition, the product of Kuraray Co., Ltd., the basis weight of cation exchange fiber is 30
A non-woven filter cloth of 0 g / m ² can be used. In the latter case, when the battery is deteriorated, it can be repeatedly reproduced, so that it is economical.

Each of the above-mentioned activated carbon fiber filter cloth and ion exchange filter cloth has a specific gravity of about 0.1 and a high porosity, and the pressure loss of the filter cloth itself is extremely small. Since the partition 4 is the pressure loss can or very small negligible, the pressure loss as a whole a filter is very small, it is usually 10 mm H ₂ O or less. Moreover, the residence time of each filter cloth is 0.
When sufficient removal performance can be obtained in about 06 seconds, the resistance of the filter cloth itself to the passing air is small as described above, so even if there is some gap around the filter cloth, the filter cloth area is small. In other words, it has been confirmed from the examples that the chemical substance removing effect is sufficiently obtained even when the ratio to the peripheral length is about 1 cm. Therefore, when laying the filter cloth, a sufficient effect of removing chemical substances can be obtained by laying the filter cloth so that there is as little space as possible in the periphery. In the air filter of the present invention, when a plurality of filter cloths are laid one upon another, it may be necessary to relatively widen the wave of the partition or the groove pitch of the pleats.

In this case, the area of each filter cloth is reduced. Therefore, the service life is shortened, and it is necessary to replace the battery at an optimal time from the viewpoint of economy. Therefore, the life of the filter cloth must be easily determined. If trace amounts of organic substances, acidic ions, ammonia and the like in the purified air downstream of the air filter can be easily evaluated, the change of the filter cloth can be determined based on the change in this value. For this purpose, the organic matter is the contact angle of water droplets on the surface of a clean silicon wafer as it is left, and the ammonia is a highly sensitive detector tube (U.S. Patent No. 30293).
No. 6) is effective.

However, regarding the deterioration of the filter cloth for acidic ions, there has not been known a method for simply quantifying the concentration of acid ions in clean air. In contrast, the present inventor was able to easily determine the acid ion concentration in the clean air by the following method.

In the present invention, when aluminum or stainless steel is used as the material of the partition which is the support on which the filter cloth is laid, the deterioration of the acid gas filter can be easily evaluated. If there is an HCl component in the air, it reacts with aluminum, albeit in a very small amount, to generate AlCl ₃ , and also reacts with stainless steel to generate FeCl ₃ . Among the metal chlorides, AlCl ₃ and FeCl ₃ exhibit special properties, and have a slight vapor pressure even at room temperature. Extrapolating from existing data, the saturated vapor pressure at 25 ° C is AlCl
₃ at about 10 ^-3 atm, FeCl ₃ is estimated to be about 5 × 10 ^-5 atm. It is considered that they are scattered in the form of Al ₂ Cl ₆ or Fe ₂ Cl ₆ , respectively.
Up to the latter, which can be in the air up to 60 ppb. For a filter cloth for removing an acidic gas, for example, an anion-exchange filter cloth, the smaller the ionic value, the sooner the removal efficiency decreases. That is, even if the mist such as sulfuric acid or phosphoric acid still has sufficient removal ability, the removal ability of hydrochloric acid is reduced first. Therefore, in this filter cloth, it is difficult to remove hydrochloric acid at an early stage of deterioration, and Al ₂ Cl ₆ and Fe ₂ Cl ₆ are contained in the air downstream of the filter, although they are in very small amounts. Such Al and Fe contaminate the clean silicon surface left in the air. On the other hand, when an ultra-clean environment is required for semiconductors, a clean silicon wafer is left in this environment for a long time, and the degree of metal contamination on the surface is routinely managed by analysis. For example, in the analysis combining the gas phase decomposition method and the flameless atomic absorption, the contamination state of Al and Fe can be grasped. When the Cl concentration in the air downstream of the air filter reaches 0.2 ppb, Al and Fe on the silicon wafer left at that location for one month contain 5 × 10 ¹⁰ atoms.
It is empirically known to be about s / cm ² . Therefore, the life of the filter cloth for removing acidic ions spread on the air filter case of the present invention can be easily determined by using the result of the environmental analysis of the silicon surface metal.

Chemical contaminants to be removed by the air filter of the present invention, that is, chemical contaminants in the air which are harmful to the semiconductor process, include acid gases such as HF, HCl and H ₂ SO ₄ , NH ₃ and amines. Alkaline gas, dioctyl phthalate (DOP) which is easily adsorbed on the surface of silicon or silicon oxide film, butylhydroxytoluene (BH)
T), hexamethyldisilazane, siloxanes, phosphates, and other organic substances. To remove all of these, three types of filter cloths are required as described above.

<Air Circulation Clean Unit> FIG. 3 is a front sectional view of one embodiment of the air circulation clean unit of the present invention, and FIG. 4 is a side sectional view. 3 and 4, this clean unit is provided with a partition wall 9 in a container 8.
Is vertically provided, and the partition wall 9 is provided on the upper surface wall 1 in the container 8.
0 and the bottom wall 11, but the two side walls 1
It is fixed to 2 and 13 without gap. The partition wall 9, the front wall 14 of the container 8, and the two side walls 12 and 13 surround the isolated clean space 15. Part of the front wall 14 is a door 16 that can be opened and closed. A permeable partition (air inlet) 17 is provided between the upper end of the partition wall 9 and the front wall 14, and a permeable partition, for example, a grid 18 is also provided at the lower part (air outlet) of the clean required space 15. As a result, a process device and an evaluation device can be installed. An air circulation path (duct) 20 is formed by the partition wall 9, the rear wall 19, and the two side walls 12 and 13. Breathable partition 1
8, an air filter 21 for removing a chemical substance of the present invention similar to that shown in FIG. 2 is mounted so as to be able to enter and exit the drawer frame 22, and between the lower surface and the bottom 11. The space 20 a and the space 20 b between the air-permeable partition 17 and the top wall 10 form a part of the air circulation path 20.
In the lower part of the circulation path behind the partition wall 9, a filter cloth capable of removing harmful gas which is likely to be generated at the time of an accident or adjustment in the space 15 is provided on a vertical pleat made of stainless steel wire netting. The air filter 23 for removing chemical substances of the present invention, which is laid on the side (above the pleat groove), is mounted and prepared for an abnormal situation. The filter also has a structure that can be detachably inserted into and removed from the rear wall 19 of the container with the handle 24. Further, a temperature control mechanism 25 for circulating air is incorporated and placed in the air circulation path on this. Below the air-permeable partition 17, there is a fan 26 for blowing air, and further below this, a pleated precision dust filter 27 (ULPA or HE).
PA), and a space surrounded by the lower surface thereof, the air-permeable partition plate 18 and the walls 9, 12, 13, and 14 is the clean-required space 15. The air sent by the fan was 27, 15,
The components and spaces of 21, 20a, 23, 25, 20b, 17, and 26 are sequentially circulated to clean the air.
In addition, when there is no possibility that a device or a component placed in the space 15 generates abnormal harmful gas in particular, the air filter 23 for measures against abnormalities can be omitted, and no heat is generated in the space 15. In this case, the temperature control mechanism 25 can be omitted.

The above air filter is to be removed.
70% of its own removal performance against chemical pollutants
Even if the air circulation
As long as the air filter of the present invention is used in the knit,
The super clean ring in the space 15 is effective because of the power reduction effect of pollution.
Very low levels of chemical pollutants required by the environment
Is done. That is, HCl, H_TwoSO_Four, HNO_Three, H_ThreePO
_Four, NH_ThreeAnd so on, and release for 48 hours
Carbon concentration on the clean silicon surface ¹³atoms
/cm^TwoIt can be as follows.

[0029]

EXAMPLE 1 In the filter of FIG. 2, the case frame 3 was made of aluminum, the partition 4 was made of aluminum mesh, and the laid filter cloth 5 was an activated carbon fiber filter cloth, a product of Osaka Gas Chemical Co., Ltd. Adol "200g /
m ² , the laid filter cloth 6 was Kuraray Co., Ltd. anion exchange fiber filter cloth with a basis weight of 300 g / m ² , and the laid filter cloth 7 was
The basis weight of the cation exchange fiber filter cloth made by Kuraray was 300 g / m ^2, and this was used as the clean bench type container 8 shown in FIGS.
21. However, the temperature control mechanism 25 is omitted. Most of the container is made of stainless steel plate, and similar to this filter, two cation-exchange fiber filter cloths are laid above the partition surface in an aluminum partition with only a few grooves and deep, and mounted as a filter 23. did. For the transparent part of the door, a polycarbonate plate that does not easily generate organic outgas was used.

This container is provided with a transfer wheel, which is transported and lent to a manufacturer of the resist coating apparatus, and the development mechanism is housed in the space requiring cleansing 14 and immediately below the ULPA filter when operating with 10% of outside air taken in. Was evaluated for cleanliness. That is,
The air at this measurement point was absorbed into ultrapure water with an impinger, sampled, and anions and cations were analyzed by ion chromatography. In addition, a Si chip cleaned by high-temperature oxidation was left in this part during the operation time, and the surface of this chip was subjected to charged particle activation analysis by deuteron irradiation to examine the increase in surface carbon concentration due to organic contamination. Further, when the development mechanism failed and ammonia caused by hexamethyldisilazane was generated for several hours to the extent that it smelled, a simple analysis was performed at a location 20a using a high-sensitivity detection tube for ammonia.

As a result, at least 1 pp
b about the presence was supposed to HCl and H ₂ S0 ₄ acid gases, such as is without any problems at lower than 0.1 ppb, since NH ₃ is beyond the 1ppb at some point in the measurement of the detector tube when the mechanism fails, The filter was immediately pulled out using the draw-out mechanism 22, the cation exchange fiber filter cloth was replaced, and the deteriorated filter cloth was regenerated and prepared for the next use. However, as a result of the ion chromatography immediately below ULPA, the filter 23 was working effectively, and NH ₃ did not exceed 0.3 ppb. In addition, the Si surface of the neglected chip also has a carbon concentration of 5 ×
It did not exceed 10 ¹³ atoms / cm ² , indicating that the ultra-clean environment was maintained in the space 15.

Example 2 As a stocker for storing a wafer for a long time in a carrier without a lid, having the same structure as that of Example 1 and using only one filter 21, the corrugated partition is made of stainless steel mesh. A small container was used. Note that the filter 23 is not mounted. This stocker is placed adjacent to the RCA cleaning device to study the timing of deterioration and replacement of the anion exchange filter cloth for acidic gas.
A place where the HCl concentration in the ambient air was close to 1 ppb was selected. During the study period, store only the wafer carrier with the lid, and place the surface-cleaned wafer for environmental cleanliness evaluation in the clean space 1.
And allowed to stand for one month at a corner in the 5, to analyze Fe standing wafer surface by the total reflection fluorescent X-ray apparatus, Fe is 10 ¹⁰ atoms /
After confirming that it was not more than cm ² , the wafer for evaluation was again left for one month. Simultaneously with the surface analysis, it was confirmed by the same impinger sampling as in Example 1 that the concentration of HCl in the air in the container was 0.1 ppb or less. When the wafer reached 5 × 10 ¹⁰ atoms / cm ² after being left for one month, the HCl concentration in the air in the container was 0.3 ppb. Therefore 1
It was found that the anion exchange filter cloth should be replaced when Fe of 0 ¹⁰ atoms / cm ² or more was detected.

Example 3 In the filter of FIG.
The case frame 3 is made of aluminum, and the partition 4 has 14 grooves.
The filter has a filtration area of about 2m ² (0.6m x 3.3m), and the filter cloth to be laid has a thickness of about 2.5mm from the windward side. Replacement fiber filter cloth (weight per unit area: 200 g / m ² ), about 2 mm thick KO
Activated carbon fiber filter cloth impregnated with H at a basis weight of 200 g / m ² ,
Kuraray Co., Ltd. cation exchange fiber filter cloth (basis weight 300 g / m ² ) with a thickness of about 4 mm, and a basis weight of 300 g with a thickness of about 8 mm
/ M ² for removing organic substances. A clean booth type container 8 having six filters and having a structure similar to that of the clean unit shown in FIGS. 3 and 4 and having a height of the ultra-clean required area 15 enough to allow an operator to enter was prepared. Note that the filter 23 is not mounted. Most of the constituent materials of the container were stainless steel plates, and a door with an air shower for carrying in the storage device and for entering and leaving the workers was provided instead of the door 16. The storage device is an ion chromatography device that requires as little as possible anions and cations in the environment at the time of measurement.This clean booth uses heated hydrochloric acid, heated sulfuric acid, and relatively large amounts of heated ammonia. It was placed in the analysis room. After 10% of the outside air was introduced into the clean required area 15 in the chemical analysis chamber and the air flow rate was 0.4 m / sec and moved for 6 months, the cleanliness immediately below the ULPA filter was evaluated by the impinger method as in Example 1. . In this case, the residence time of the anion exchange fiber filter cloth was as short as 0.03 seconds, and the sulfuric acid could still be sufficiently removed, but the effect of removing hydrochloric acid was significantly reduced. However, the activated carbon fiber filter cloth impregnated with KOH can still sufficiently remove the hydrochloric acid even at this residence time, and both of them complement the drawbacks in life due to the use of the small area filter cloth. There is no need to worry about the possibility that potassium ions (K ⁺ ) may be released from the activated carbon fibers of the impregnated KOH, even if they are slightly released, because they are adsorbed by the subsequent cation exchange fiber filter cloth. Cleanliness evaluation result is HC
1, H ₂ SO ₄ and NH ₃ were both 0.1 ppb or less, and there was no problem in ion chromatography measurement. The measurement error is small, and for example, for 3 ppb Cl, the result of the measurement at the same time for 5 days shows that the average value is 2.983, the standard deviation is 0.04, and the result is small.

Example 4 In order to evaluate the effect of the chemical substance removal air filter of the present invention by simulation, a radioactive tracer method was carried out using an instrument as schematically shown in FIG. The pollutant chemicals evaluated were HCl as an acid gas and methylamine CH ₃ as an alkaline gas.
The NH _2, chose the BHT as organic matter. HCl was labeled with the radioisotope ³⁵ Cl, and methylamine and BHT were labeled with the radioisotope ¹⁴ C. As a filter cloth for testing the ability to capture these contaminants, Kuraray's anion exchange filter cloth (basis weight: 300 g / m ² ) is used for acid gas, and Kuraray's cation is used for alkaline gas. An exchange filter cloth (basis weight 300 g / m ² ) was used. For organic substances, an activated carbon fiber filter cloth (trade name: Adol) was used at a basis weight of 200 g / m ² . Each thickness is about 5 mm. These have a diameter of 30
It was cut into a circular disk of mm to obtain an evaluation sample. An evaluation holder 29 composed of three plastic cylinders 29a, 29b, and 29c having an inner diameter of 30 mm has 29a in 29b and 29b in 29c.
It is designed to fit airtightly. 29b and 29c
Are provided with aluminum net partitions 30, 31 in the cylinder, respectively. In 29a, air introduced from the air inlet 32 is uniformly flown into the filter cloth surface in the cylinder of 29b.
An aluminum mesh partition 33 is also provided here. Numeral 34 denotes an evaporator which makes the radioisotope-labeled contaminant 35 gasify. The contaminant can be adjusted to 1 ppm when air is sent from an air inlet 36.

In the evaluation, the filter cloth for alkali 37, the filter cloth for acid 38, and the filter cloth for organic substance 39 were always stacked in this order, and fitted into the cylinder 29b so that the organic substance was placed on the partition 30.
Moreover, the filter cloth for acid gas above the partition 31 when the evaluation of the ³⁵ Cl label chlorine, filter cloth for alkaline gas when the evaluation of the ¹⁴ C-labeled methyl amine, organic materials when the ¹⁴ C-labeled BHT The filter cloth was fitted as in 40.

The air introduction speed was controlled so that the residence time of the filter cloth was 0.06 seconds. Calculate the saturated molar amount of the air containing each radioisotope-labeled contaminant at a predetermined concentration from the collection capacity of the filter cloth provided by the manufacturer, and 80% of the contaminants pass through the filter cloth. The amount of time it took to flow into this holder. Every time the evaluation process was completed, the radioactivity of all filter cloth samples was measured and discarded. Each time the contaminants in the evaporator 34 change, the holder 2
9 was replaced and used.

As a result, when evaluated with air containing hydrochloric acid, radioactivity was detected only on the filter cloth 38 on the partition 30,
The radioactivity of the filter cloth 40 is about 1% of that of the filter cloth 38, and the radioactivity is strongly detected in the filter cloth 37 in the evaluation of methylamine.
Almost 2% of 37 filter cloths were detected in 39 filter cloths, and almost no detection was detected in 40 filter cloths. In the case of BHT, radiation is detected only at 39 on the partition 30, and 40 filter cloths are 39
About 5% of the filter cloth. In this filter cloth sample, the ratio of the area to the peripheral length (filter cloth area (cm ² ) / perimeter length (c)
Even if m)) was only 0.8 cm, a sufficient effect of removing chemical substances was obtained only by fitting the filter cloth.

[0038]

In the air filter for removing chemical substances according to the present invention, since all of the filter cloth for removing chemical substances to be used is laid free on the partition provided in the filter case, the filter cloth deteriorates. Can be replaced and the filter case can be used repeatedly. In addition, when an ion exchange filter cloth is used, the filter medium can be regenerated for an acidic gas or an alkaline gas, and can be used repeatedly 10 times or more. The filter material for organic matter is activated carbon fiber filter cloth, which is made of carbon itself and has no problem in incineration. Further, since the preferable material of the filter case is aluminum and stainless steel which can be separated and recovered, it is easy to recycle even if it is finally disposed after repeated use. Therefore, the air filter of the present invention is ideal in terms of industrial waste treatment.

When laying several thick filter cloths, the air does not pass uniformly through the filter cloth unless a certain filter cloth is degraded unless the waveform of the partition and the pitch of the pleated shape are expanded to some extent. Can be difficult to replace. When the pitch is widened, the effect of removing the chemical substance is reduced because the area of the filter cloth is reduced. However, the filter cloth of the present invention can easily determine and grasp the optimal replacement time.

As described above, the filter cloth used in the present invention can easily know the optimum time for replacement due to deterioration, and can be easily replaced. The following effects can be obtained by using. In other words, when an ultra-clean environment is required for a short period of time, or when a mobile ultra-clean environment requiring a large number of opportunities to replace the filter cloth is required, an air filter with a small filter cloth area is desired. Air filters are highly preferred and can significantly reduce the initial investment as a filter. Since the air filter of the present invention is suitable for such short-term or mobile use, and the volume required for chemical pollution removal is considerably small, the clean unit of the present invention is installed in a clean room as a clean bench or a clean booth. Even so, it is possible to make the required clean space in the container relatively large.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a filter case used in the present invention.

FIG. 2 is a perspective view showing an embodiment of an air filter for removing chemical substances according to the present invention.

FIG. 3 is a front sectional view of one embodiment of the air circulation type clean unit of the present invention.

FIG. 4 is a side sectional view of an embodiment of the air circulation type clean unit of the present invention.

FIG. 5 is a longitudinal sectional view of a device used in Example 4 for evaluating the effect of the air filter of the present invention by simulation.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 air introduction side opening 2 air discharge side opening 3 filter case frame 4 partition 5 filter cloth for chemical substance removal 6 filter cloth for chemical substance removal 7 filter cloth for chemical substance removal 8 container 15 isolated clean required space 21 air for chemical substance removal Filter 23 Chemical substance removal air filter 26 Fan 27 Precision dust filter 29 Holder 30 Partition 31 Partition 35 Radioisotope-labeled contaminants

Continued on the front page F term (reference) 4D019 AA01 AA10 BA03 BA13 BB02 BB10 BC04 BC05 CA02 CB01 CB03 4D058 JA13 JB04 JB14 JB24 JB39 JB41 KA01 KA08 KA16 KA23 KB11 QA11 QA21 QA25 SA04

Claims (7)

[Claims] A filter case frame having an air introduction side opening and an air discharge side opening; and an air flow path from the air introduction side opening to the air discharge opening inside the filter case frame. For removing chemical substances, comprising: a gas-permeable partition having a corrugated or pleated shape arranged in a transverse manner; and at least one filter cloth capable of removing the chemical substances laid on the gas-permeable partition. air filter. 2. The air filter according to claim 1, wherein the air-permeable partition is a net or woven cloth made of aluminum or stainless steel wire. 3. The air according to claim 2, wherein the filter cloth capable of removing chemical substances is a filter cloth that absorbs at least one sheet of acidic ions and is laid on the windward side of the air-permeable partition. filter. 4. The air filter according to claim 3, wherein a filter cloth for absorbing at least one organic substance is further laid on the filter cloth. 5. The air filter according to claim 3, wherein at least one sheet of filter cloth that absorbs alkaline ions is laid on the filter cloth. 6. The filter cloth according to claim 1, wherein an anion exchange fiber filter cloth, an activated carbon fiber filter cloth impregnated with an alkaline substance, a cation exchange fiber filter cloth, and an activated carbon fiber filter cloth for removing organic substances are arranged in this order from the windward side. Air filter. 7. An isolated clean space having an air inlet, an air outlet, and a door that can be opened and closed, and recirculated air discharged from the air outlet to the air inlet in a container whose inside is isolated from the external environment. 8. An air circulating clean unit comprising at least one air filter including an air passage to be circulated and disposed transversely to said air flow path, wherein at least one of said air filters is provided.
A clean unit, characterized by being the filter for removing a chemical substance according to (1).