JP4147766B2 - Filter media spacer - Google Patents

Description

表１に示すように、実施例１及び２の黄変度は、比較例１及び２の黄変度より小さくなっている。したがって、水素添加したポリアミドスペーサは、水素添加していないポリアミドスペーサに比べ黄変度が抑えられていることが分かる。
【００４２】
＜ＴＯＣ含有量の測定＞
ＴＯＣ含有量の測定は、ガスクロマトグラフィーを用いたパージアンドトラップ方式により行った。ペレット状にした試料０．５ｇをサンプル管に入れ、高純度ヘリウムガスを、８０℃で流速５０ｍｌ／分で１５分間通気して試料から発生する揮発成分、ガス成分をサンプル管から追い出し（パージ）、トラップ管に導入した。このトラップ管において、−４０℃に冷却された吸着剤（石英ウール）に揮発成分を蓄積濃縮させた。その後、吸収剤を３５８℃に瞬間加熱し、２０秒間吸収剤に吸着した吸着物をガスとして放出した。そして、放出ガスをガスクロマトグラフィーに導入し、その量を測定し、沸点１７０℃以上の成分について、カーボン数１５の炭化水素換算で量を算出した。測定条件は以下の通りである。
ガスクロマトグラフィー：島津製作所社製「ＧＣ１７Ａ」
カラム：ＦＲＯＮＴＩＥＲ ＬＡＢ Ｕｌｔｒａ ＡＬＬＯＹ Ｃａｐｉｌｌａｒｙ Ｃｏｌｕｍｎ，ＵＡ−５
カラム温度：５０℃（５分間保持）、２８０℃（１０分間保持）、昇温速度１０℃／分
スプリット比：１：２０（カラム流量１．１ｍｌ／分）
【００４３】
表２に、水素添加されたポリアミドでの測定結果（実施例３及び実施例４）を、従来のポリアミドでの測定結果（比較例３及び比較例４）と併せて表２に示す。
【００４４】
【表２】

表２に示すように、実施例１及び２のＴＯＣ発生量は、比較例１及び２のＴＯＣ発生量とほぼ同様である。したがって、水素添加ポリアミドからなるスペーサは、従来の水素添加されていないポリアミドスペーサとほぼ同様のＴＯＣ発生量に抑えられていることが分かる。
【００４５】
＜紫外線照射による黄変度変化の測定＞
従来のポリアミド及び水素添加ポリアミドを１７０℃程度に加熱して溶融させ、離型剤を塗布した平滑なアルミ板に流し込んだ後冷却し、硬化後アルミ板から剥離し、厚さ約０．５ｍｍのポリアミドシートを得た。このシートに紫外線を照射し、照射前後の黄変度を測定した。
【００４６】
紫外線の照射条件は以下の通りである。
ＵＶ強度：７００μＷ／ｃｍ²
ＵＶ波長：３２０〜４００ｎｍ
照射時間：４日間（９６ｈｒ）
を４日間紫外線照射し、照射前後の黄変度を測定した。
【００４７】
表３に、水素添加されたポリアミドでの測定結果（実施例５）を、従来のポリアミドでの測定結果（比較例５）と併せて示す。
【００４８】
【表３】

表３に示すように、従来のポリアミド及び水素添加されたポリアミドとも黄変度は増大しているが、従来のポリアミドの黄変度の増大は非常に大きく、目視においても褐色を通り過ぎ、黒色に近い状態になった。一方、水素添加されたポリアミドは目視においては従来のポリアミドの照射前の褐色状態に留まっていた。
【００４９】
＜紫外線照射によるＴＯＣ発生量の変化の測定＞
従来のポリアミド及び水素添加ポリアミドを１７０℃程度に加熱して溶融させ、離型剤を塗布した平滑なアルミ板に流し込んだ後冷却し、硬化後アルミ板から剥離し、厚さ約０．５ｍｍのポリアミドシートを得た。このシートに紫外線を照射し、照射前後のＴＯＣ含有量の変化を測定した。
【００５０】
紫外線の照射条件は以下の通りである。
ＵＶ強度：７００μＷ／ｃｍ²
ＵＶ波長：３２０〜４００ｎｍ
照射時間：２４ｈｒ
【００５１】
また、ＴＯＣの測定は、パージアンドトラップ方式により、上述のＴＯＣ含有量の測定と同様の条件で行った。ここでは、水素添加されたポリアミド及び従来のポリアミドについてそれぞれ、紫外線照射の前後において５回ずつ行い、その平均値により比較検討した。
【００５２】
表４に、水素添加されたポリアミドでの測定結果（実施例６）を、従来のポリアミドでの測定結果（比較例６）と併せて示す。
【００５３】
【表４】

表４に示すように、比較例６の紫外線照射後のＴＯＣ発生量は照射前の４倍以上であるのに対し、実施例６の紫外線照射後のＴＯＣ発生量は照射前の２倍以下になっている。したがって、水素添加したポリアミドスペーサは、水素添加していないポリアミドスペーサに比べ紫外線劣化によるＴＯＣ発生量の増加の程度が抑えられていることが分かる。
【００５４】
［他の実施形態］
（ａ）フィルタ濾材３は、ＰＴＦＥ多孔膜を利用したものに限定されない。
【００５５】
（ｂ）ＰＴＦＥ多孔膜の繊維径、通気性支持材の目付等、フィルタ濾材の構成部材の各種特性は上述のものに限定されない。
【００５６】
【発明の効果】
本発明によれば、スペーサとして例えば水素添加されたポリアミドが用いられているため、スペーサの黄変度を小さくすることができるのに加え、紫外線劣化によるＴＯＣ発生量の増加の程度を抑えることができる。これにより、エアフィルタユニットのフィルタ濾材が黄変して褐色がかって汚れたように見えるのが抑えられる。
【図面の簡単な説明】
【図１】 本発明の一実施形態によるスペーサが設けられたフィルタ濾材を備えたエアフィルタユニットを示す斜視図。
【図２】 フィルタ濾材の一部斜視図。
【図３】 フィルタ濾材にスペーサを塗布する工程の説明図。
【符号の説明】
１ エアフィルタユニット
３ フィルタ濾材
７ スペーサ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a spacer, and more particularly to a spacer provided in a direction across a crease between adjacent pleats of a filter medium having a large number of pleats that are folded along a predetermined crease.
[0002]
[Prior art]
As an air filter unit used for air cleaning in semiconductor manufacturing equipment, clean rooms, etc., equipped with a filter material made of glass fiber made of glass fiber and a porous filter film made of polytetrafluoroethylene (hereinafter referred to as PTFE) There is something. The filter medium including the PTFE porous membrane is composed of a PTFE porous membrane and a breathable support material that is heat-laminated so as to sandwich both sides of the PTFE porous membrane. When used as an air filter unit, the filter medium is normally folded back alternately along a predetermined crease and formed into a corrugated shape having a large number of pleats (the filter medium in this state is referred to as a filter pack). It is held inside the frame.
[0003]
In general, a spacer is provided on the surface of such a filter medium so that a predetermined gap is maintained between adjacent folded portions (pleats). The spacer is made of synthetic resin hot melt such as ethylene-vinyl acetate copolymer system, polyolefin system, rubber system, polyamide system, etc., and is usually heated and melted from a plurality of nozzles arranged in parallel to the surface of the filter medium. It is formed by being discharged continuously or intermittently.
[0004]
By the way, since the spacer is made of synthetic resin, gaseous organic substances (hereinafter referred to as total organic carbon: TOC) such as dodecane, tridecane, dioctyl phthalate, and siloxane are generated from the spacer itself. On the other hand, in a clean room or a semiconductor manufacturing apparatus, a lower TOC detection amount is preferable from the viewpoint of improving product quality.
[0005]
Therefore, among the above-mentioned spacer materials, polyamide that generates less TOC than other resin spacers is most suitable for use in an air filter unit installed in a clean room or a semiconductor manufacturing apparatus.
[0006]
[Problems to be solved by the invention]
The polyamide spacer usually has a brownish hue, and further, the brownish hue is strengthened by irradiating the fluorescent lamp in the room for a long time, or the oxidation proceeds with the passage of time. For this reason, when the air filter unit is viewed from a distance, the filter medium provided with the spacers may appear yellowish, and an impression may be given as if the filter medium is dirty.
[0007]
In particular, when installed in a clean room of the semiconductor manufacturing industry, a whiter appearance is preferred for the air filter unit in order to obtain an impression that the work is performed in a room with a very high degree of cleanliness.
[0008]
In addition, the polyamide spacer has a smaller amount of TOC generation than spacers made of other materials. However, when irradiated with ultraviolet rays or the like, the polyamide spacer deteriorates and the amount of TOC generation increases.
[0009]
An object of the present invention is to suppress yellowing of a spacer. Another object of the present invention is to suppress an increase in the amount of TOC generated from the spacer.
[0010]
[Means for Solving the Problems]
The spacer according to claim 1 is provided in a direction crossing the crease between adjacent pleats of the filter medium having a large number of pleats that are fold-folded along a predetermined crease. This spacer is made of polyamide, and the amount of TOC generated after UV irradiation is not more than 3 times, preferably 2.5 times or less that before UV irradiation.
[0011]
Polyamide spacers have the property of deteriorating when irradiated with ultraviolet rays and increasing the amount of TOC generated. As a result of studies conducted by the present inventors in view of such a point, it has been found that, for example, in a hydrogenated polyamide spacer, the degree of increase in the amount of TOC generation can be suppressed with less UV degradation.
[0012]
Therefore, in this spacer, the ratio of the TOC generation amount after the ultraviolet irradiation to the TOC generation amount before the ultraviolet irradiation is targeted, and in addition to suppressing the yellowing degree, the increase in the TOC generation amount due to the ultraviolet deterioration. I try to suppress the degree.
[0013]
The filter pack according to claim 2 includes a filter medium and a spacer. The filter medium has a large number of pleats that are creased along a predetermined crease. The spacer is as defined in claim 1 .
[0014]
The filter medium is a component of the air filter unit, and is usually formed into a corrugated shape that is alternately folded at predetermined intervals, and processed into a filter pack. The case where the restrained spacer is used for such a filter pack is intended.
[0015]
A filter pack according to a third aspect includes the filter pack according to the second aspect and an outer frame body in which the filter pack is accommodated. In addition, when the filtration medium permeation wind speed is 1.4 cm / sec, the pressure loss when the collection efficiency of the particles having a particle diameter of 0.3 μm or more is 99.97% or more and the filtration medium permeation wind speed is 1.4 cm / sec. Is 50 Pa or more and 500 Pa or less.
[0016]
In a clean room for semiconductor manufacturing or the like, a high cleanliness is required, and therefore a filter medium having a high collection efficiency is used. As such a filter medium, there is a HEPA (High Efficient Particulate Air) filter. The HEPA filter has a filtration efficiency of 99.97% or more when the particle diameter is 0.3 μm or more when the filter medium permeation wind speed is 1.4 cm / sec and the filter medium permeation wind speed is 1.4 cm / sec. The pressure loss is 50 Pa or more and 500 Pa or less.
[0017]
Since such a high collection type air filter unit is used to provide a clean environment, a brownish spacer causes the filter medium to appear dirty, creating a sense of discomfort for the user. There are things to do.
[0018]
Therefore, in this air filter unit, in particular, in an air filter unit that can be used as a HEPA filter, the yellowing degree of the spacer is suppressed.
[0019]
An air filter unit according to a fourth aspect includes the filter pack according to the second aspect and an outer frame body in which the filter pack is accommodated. Further, when the filtration medium permeation wind speed is 1.4 cm / sec, the pressure loss when the collection efficiency of the particles having a particle diameter of 0.1 μm or more is 99.9999% or more and the filtration medium permeation wind speed is 1.4 cm / sec. Is 50 Pa or more and 500 Pa or less.
[0020]
As a filter having higher collection efficiency than the above-mentioned HEPA filter, there is an ULPA (Ultra Low Penetration Air) filter. The ULPA filter has a pressure loss of 50 Pa or more and 500 Pa or less when the collection efficiency of particles having a particle diameter of 0.1 μm or more is 99.9999% or more and the filter medium permeation wind speed is 1.4 cm / sec.
[0021]
In such a ULPA filter, it is used to provide a very clean environment in addition to the above-mentioned HEPA filter. Therefore, when the filter medium looks dirty due to the brownish spacer, The feeling of discomfort given to is even greater.
[0022]
Therefore, in this air filter unit, in particular, in the air filter unit that can be used as a ULPA filter, the yellowing degree of the spacer can be suppressed.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an air filter unit 1 in which an embodiment of the present invention is adopted.
[0024]
The filter unit 1 includes a filter medium 3 and an outer frame 5 in which the filter medium 3 is accommodated.
[0025]
As shown in FIG. 2, the filter medium 3 was provided on the surface of a PTFE porous membrane, two breathable support members that were heat-laminated so as to sandwich the PTFE porous membrane from both sides, and the breathable support member. And a spacer 7.
[0026]
The PTFE porous membrane is for collecting suspended fine particles in the air. For example, the PTFE porous membrane is obtained by stretching a PTFE green body in the biaxial direction, and has a thickness of about 1 to 60 μm and a fiber diameter of 0.1. It has a fine fiber structure of about 05 to 0.2 μm.
[0027]
The breathable support material is for stabilizing the form of the PTFE porous membrane and allowing air to pass through the PTFE porous membrane, and a nonwoven fabric having a basis weight of about 15 to 100 g / m ² is used.
[0028]
After the PTFE porous membrane and the air-permeable support material are heat-laminated, the filter medium 3 is alternately folded along creases formed with a width of about 15 to 150 mm for use in an air filter unit ( It is processed into a corrugated filter pack 9 by pleating. As a result, a large number of pleats (folded portions) 4 are formed in the filter medium 3 as shown in FIG.
[0029]
The spacer 7 is for maintaining a gap between adjacent pleats 4 of the filter pack 9. The spacers 7 are provided at a plurality of positions at equal intervals in the width direction of the filter medium 3 and extending in the direction crossing the crease on both sides of the filter medium 3 by an apparatus as shown in FIG. Thereby, as for the filter pack 9, the space | interval of the adjacent pleats 4 is maintained at about 2-15 mm. In FIG. 3, reference numeral 21 denotes a heating part, 22 denotes a developing part, 23 denotes a spacer application part, and 24 denotes a rising part.
[0030]
The spacer 7 is made of polyamide and has a TOC generation amount of 500 ng / g or less. TOC refers to the total amount of various gaseous organic substances such as dodecane, tridecane, dioctyl phthalate, and siloxane. The spacer 7 is made of a hydrogenated polyamide obtained by hydrogenating a polyamide used as a conventional spacer. As a result, the spacer 7 has a yellowing degree of 15 or less. . The degree of yellowing is preferably 10 or less, more preferably 5 or less.
[0031]
The yellowing degree is calculated by the following equation from the yellowness and the yellowness of the base material as a base in the measurement method (JIS-K-7103) according to JIS standards.
[Equation 1]
Yellowing degree = YI−YI ₀
(Where YI: yellowness of test sample, YI ₀ = yellowness of base substrate, yellowness (YI) = 100 (1.28X−1.06Z) / Y, and X, Y, Z are (This is the tristimulus value of the test sample in standard light)
[0032]
The outer frame body 5 is formed by assembling four aluminum frame members, and the filter pack is accommodated in the inner space. The frame 5 and the filter medium 3 are sealed with an adhesive or the like so as to maintain airtightness, thereby forming the air filter unit 1.
[0033]
The air filter unit 1 configured in this manner preferably has a trapping efficiency of 99.97% or more for particles having a particle diameter of 0.3 μm or more when the filter medium permeation wind speed is 1.4 cm / sec. When the permeating wind speed is 1.4 cm / sec, it is more preferable that the collection efficiency of particles having a particle diameter of 0.1 μm or more is 99.9999% or more.
[0034]
【Example】
<Measurement of yellowing degree>
The polyamide used as the spacer 7 is heated to about 170 ° C., melted, poured into a smooth aluminum plate coated with a release agent, cooled, cured, peeled off the aluminum plate, and about 0.5 mm thick A polyamide sheet was obtained. And the measurement of the yellowing degree of this polyamide sheet was performed on the following conditions and procedures.
[0035]
A color difference meter “MINORUTA CR-300” manufactured by Minolta Co., Ltd. was used as an instrument for measuring the degree of yellowing. The light source was a standard light D ₆₅ with a difference in yellowing degree, and a 10-degree field of view.
[0036]
First, the numerical value of the white copy paper as the base substrate, using a color difference meter L ^* a ^* b ^* color system L ^*, a ^*, b ^* values and, XYZ colorimetric system of X, Y, The value of Z was calculated. The relationship between the values of L ^* , a ^* , b ^{* and} the values of X, Y, Z in the XYZ color system is as follows:
[Equation 2]
L ^* = 116 (Y / 100.0) ^1/3 -16
[Equation 3]
a ^* = 500 [(X / 94.83) ¹ /3-(Y / 100.0) ^1/3 ]
[Equation 4]
b ^* = 200 [(Y / 100.0) ¹ /3-(Z / 107.38) ^1/3 ]
Is calculated from
[0037]
Next, the yellowing degree (YI) is calculated from the value of the XYZ color system by the following formula:
[Equation 1]
Yellowness (YI) = 100 (1.28X−1.06Z) / Y
I asked for it.
[0038]
Next, normal polyamide and hydrogenated polyamide were formed into a sheet, placed on a base substrate, and yellowness was measured with a color difference meter in the same procedure as described above.
[0039]
Next, YI ₀ yellowness of the base material, the yellow index of the polyamide sheet was placed on the base substrate and YI, calculated as yellowness _{(ΔYI) = YI-YI 0} .
[0040]
Table 1 shows the calculation results of yellowness YI and yellowing degree ΔYI of the base substrate, the conventional polyamide (Comparative Example 1 and Comparative Example 2), and the hydrogenated polyamide (Example 1 and Example 2). It shows together with the measurement results of thickness, L ^* , a ^* , b ^* , X, Y, and Z. The measurement was performed three times, and Table 1 shows the average value.
[0041]
[Table 1]

As shown in Table 1, the yellowing degree of Examples 1 and 2 is smaller than the yellowing degree of Comparative Examples 1 and 2. Accordingly, it can be seen that the degree of yellowing is suppressed in the hydrogenated polyamide spacer compared to the non-hydrogenated polyamide spacer.
[0042]
<Measurement of TOC content>
The TOC content was measured by a purge and trap method using gas chromatography. Place 0.5 g of the pelletized sample into the sample tube and vent high-purity helium gas at 80 ° C. at a flow rate of 50 ml / min for 15 minutes to purge the volatile and gas components generated from the sample from the sample tube (purge). , Introduced into the trap tube. In this trap tube, volatile components were accumulated and concentrated in an adsorbent (quartz wool) cooled to −40 ° C. Thereafter, the absorbent was instantaneously heated to 358 ° C., and the adsorbate adsorbed on the absorbent for 20 seconds was released as a gas. Then, the released gas was introduced into gas chromatography, the amount thereof was measured, and the amount of components having a boiling point of 170 ° C. or higher was calculated in terms of hydrocarbon having 15 carbon atoms. The measurement conditions are as follows.
Gas chromatography: “GC17A” manufactured by Shimadzu Corporation
Column: FRONTIER LAB Ultra ALLOY Capillary Column, UA-5
Column temperature: 50 ° C. (held for 5 minutes), 280 ° C. (held for 10 minutes), temperature rising rate: 10 ° C./minute Split ratio: 1:20 (column flow rate: 1.1 ml / minute)
[0043]
Table 2 shows the measurement results (Example 3 and Example 4) for the hydrogenated polyamide together with the measurement results (Comparative Example 3 and Comparative Example 4) for the conventional polyamide.
[0044]
[Table 2]

As shown in Table 2, the amount of TOC generated in Examples 1 and 2 is substantially the same as the amount of TOC generated in Comparative Examples 1 and 2. Therefore, it can be seen that the spacer made of hydrogenated polyamide is suppressed to the same TOC generation amount as that of the conventional non-hydrogenated polyamide spacer.
[0045]
<Measurement of yellowing change by UV irradiation>
Conventional polyamide and hydrogenated polyamide are heated to about 170 ° C. and melted, poured into a smooth aluminum plate coated with a release agent, cooled, peeled off from the aluminum plate after curing, and have a thickness of about 0.5 mm. A polyamide sheet was obtained. This sheet was irradiated with ultraviolet rays, and the yellowing degree before and after the irradiation was measured.
[0046]
The irradiation conditions of ultraviolet rays are as follows.
UV intensity: 700 μW / cm ²
UV wavelength: 320 to 400 nm
Irradiation time: 4 days (96 hr)
Was irradiated with ultraviolet rays for 4 days, and the degree of yellowing before and after the irradiation was measured.
[0047]
Table 3 shows the measurement results (Example 5) of the hydrogenated polyamide together with the measurement results (Comparative Example 5) of the conventional polyamide.
[0048]
[Table 3]

As shown in Table 3, the yellowing degree of both the conventional polyamide and the hydrogenated polyamide is increased, but the increase in the yellowing degree of the conventional polyamide is very large. It became close. On the other hand, the hydrogenated polyamide remained visually in the brown state before irradiation of the conventional polyamide.
[0049]
<Measurement of TOC generation amount due to UV irradiation>
Conventional polyamide and hydrogenated polyamide are heated to about 170 ° C. and melted, poured into a smooth aluminum plate coated with a release agent, cooled, peeled off from the aluminum plate after curing, and have a thickness of about 0.5 mm. A polyamide sheet was obtained. This sheet was irradiated with ultraviolet rays, and the change in the TOC content before and after irradiation was measured.
[0050]
The irradiation conditions of ultraviolet rays are as follows.
UV intensity: 700 μW / cm ²
UV wavelength: 320 to 400 nm
Irradiation time: 24 hr
[0051]
Moreover, the measurement of TOC was performed by the purge and trap method under the same conditions as the above-described measurement of the TOC content. Here, the hydrogenated polyamide and the conventional polyamide were each subjected to 5 times before and after the ultraviolet irradiation, and the comparison was made based on the average value.
[0052]
Table 4 shows the measurement results (Example 6) of the hydrogenated polyamide together with the measurement results (Comparative Example 6) of the conventional polyamide.
[0053]
[Table 4]

As shown in Table 4, the amount of TOC generated after UV irradiation in Comparative Example 6 was 4 times or more before irradiation, whereas the amount of TOC generated after UV irradiation in Example 6 was 2 times or less before irradiation. It has become. Therefore, it can be seen that the hydrogenated polyamide spacer suppresses the degree of increase in the amount of TOC generated due to UV degradation compared to the non-hydrogenated polyamide spacer.
[0054]
[Other Embodiments]
(A) The filter medium 3 is not limited to one using a PTFE porous membrane.
[0055]
(B) Various characteristics of the constituent members of the filter medium, such as the fiber diameter of the PTFE porous membrane and the basis weight of the air-permeable support material, are not limited to those described above.
[0056]
【The invention's effect】
According to the present invention, since, for example, a hydrogenated polyamide is used as the spacer, it is possible to reduce the degree of yellowing of the spacer and to suppress the degree of increase in the TOC generation amount due to ultraviolet deterioration. I can . As a result, the filter medium of the air filter unit can be prevented from yellowing and appearing brownish and dirty.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an air filter unit including a filter medium provided with a spacer according to an embodiment of the present invention.
FIG. 2 is a partial perspective view of a filter medium.
FIG. 3 is an explanatory diagram of a process of applying a spacer to a filter medium.
[Explanation of symbols]
1 Air filter unit 3 Filter media 7 Spacer

Claims (4)

A spacer provided in a direction across the fold between adjacent pleats of filter media having a plurality of pleats formed by folds along a predetermined fold,
It is made of polyamide, and the total organic carbon generation amount after ultraviolet irradiation is not more than three times the generation amount before ultraviolet irradiation.
Filter media spacer. A filter medium having a large number of pleats that are creased along a predetermined crease;
A spacer according to claim 1 ;
Filter pack with A filter pack according to claim 2 ;
An outer frame body in which the filter pack is stored,
When the filtration medium permeation wind speed is 1.4 cm / sec, the pressure loss is 50 Pa when the collection efficiency of the particles having a particle diameter of 0.3 μm or more is 99.97% or more and the filtration medium permeation wind speed is 1.4 cm / sec. Or more and 500 Pa or less,
Air filter unit. A filter pack according to claim 2 ;
An outer frame body in which the filter pack is stored,
When the filtration medium permeation wind speed is 1.4 cm / sec, the pressure loss is 50 Pa when the collection efficiency of particles having a particle diameter of 0.1 μm or more is 99.9999% or more and the filtration medium permeation wind speed is 1.4 cm / sec. Or more and 500 Pa or less,
Air filter unit.

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