JP2004000990A - Air filter pack and air filter unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-performance filter pack and a filter unit having low pressure loss and high trapping efficiency. <P>SOLUTION: The air filter pack is produced by pleating an air filter material comprising a polytetrafluoroethylene porous film and an air permeable supporting material laminated thereon. The PF<SB>1</SB>value of the air filter material exceeds 22, and the PF<SB>2</SB>value of the air filter pack exceeds 90.6. The air filter unit is obtained by housing the air filter pack in a frame and its PF<SB>3</SB>value exceeds 90.6. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to an air filter pack and an air filter unit, and more specifically, air using an air filter medium comprising a polytetrafluoroethylene (PTFE) porous membrane with low pressure loss and high particle collection efficiency. The present invention relates to a filter pack and an air filter unit.

As the degree of integration of semiconductors and the performance of liquid crystals increase, the cleanliness of the clean room is recently required to be higher and air filter units with higher particle collection efficiency are required.
Until now, high-performance air filters used in such air filter units, in particular HEPA and ULPA, have been made by folding filter media obtained by wet papermaking of glass fibers.
However, it is desired to reduce the pressure loss of the air filter unit to further reduce the blast power cost and to improve the collection efficiency to realize a higher clean space. It is very difficult to achieve pressure collection with higher pressure loss and lower pressure loss with the same collection efficiency.

Therefore, in order to manufacture a higher performance air filter unit, an air filter unit using a PTFE porous membrane having higher performance than a glass fiber filter medium has been proposed. If a PTFE porous membrane is used, a glass fiber filter medium is used. It has been reported that the pressure loss is 2/3 with the same collection efficiency as compared to the ULPA used (JP-A-5-202217, WO94 / 16802, WO98 / 26860).

Moreover, the performance of an air filter unit using a PTFE porous membrane can be further improved by a manufacturing method or a processing method, and a higher-performance PTFE porous membrane has been proposed. A single PTFE porous membrane having a high performance as a simple substance (not laminated with a breathable support material for use as a filter medium) is disclosed in JP-T-9-504737, JP-A-10-30031, JP-A-10- No. 287759 and WO 98/26860, which disclose a PTFE porous membrane having a high PF (Performance Factor) value that is an index of the performance of an air filter medium.

However, in order to use the PTFE porous membrane as an air filter medium, it is substantially necessary to laminate a breathable support material. This is because it is necessary to improve the strength of the PTFE porous membrane alone from the viewpoint of handleability and to prevent damage caused when the filter medium is processed into a desired shape.
However, as described above, a single PTFE porous membrane having a high PF value is known (for example, JP 10-30031 discloses a PTFE porous membrane having a PF value of 30). However, air filter media in which a PTFE porous membrane and a breathable support material are laminated include those having a PF value of 19.8 in JP-A-10-30031 and those having a PF value of 21.8 in WO 98/26860. Although known, those having a PF value exceeding 22 were not known.

In addition, for an air filter unit having an air filter medium obtained by laminating a breathable support material on a PTFE porous membrane bent into a pleat shape, WO98 / 26860 (however, it is not clear how it was manufactured) Although those with a PF value of 90.6 are described, those having a PF value exceeding 90.6 and the detailed production method thereof have not been known.
Japanese Patent Laid-Open No. 5-202217 WO94 / 16802 WO98 / 26860 JP 9-504737 A JP-A-10-30031, Japanese Patent Laid-Open No. 10-287759

A first object of the present invention is a pressure obtained by pleating a high-performance air filter medium obtained by laminating a breathable support material on at least one surface of a PTFE porous membrane with a small pressure loss and a high collection efficiency. An object of the present invention is to provide an air filter pack with low loss and high collection efficiency.
The second object of the present invention is an air filter pack having an air filter pack formed by pleating an air filter medium obtained by laminating a breathable support material on a PTFE porous membrane, and having a small pressure loss and a high collection efficiency. It is to provide a filter unit.
A third object of the present invention is to store an air filter pack formed by pleating an air filter medium obtained by laminating a breathable support material on a PTFE porous membrane in a frame body, maintaining high performance and compact (air An object of the present invention is to provide an air filter unit having a low folding height in an air filter pack in which a filter medium is folded into a pleat shape.

（ここで、透過率（％）＝１００−捕集効率（％）である。）
に従って計算される該濾材のＰＦ₁値が２２を越え、
　該エアフィルターパックに１．４ｃｍ／秒の濾材透過風速で空気を透過させたときの圧力損失（単位：mmＨ₂Ｏ）および粒子径０．１０〜０．１２μｍのジオクチルフタレートを用いて測定した捕集効率（単位：％）から下記式：

（ここで、透過率（％）＝１００−捕集効率（％）である。）
に従って計算される該パックのＰＦ₂値が９０．６を越えることを特徴とするエアフィルターパック、並びに
　（２）枠体、および該枠体内に収納されたプリーツ状に折り曲げたエアフィルター濾材からなるエアフィルターパックを有してなるエアフィルターユニットであって、該エアフィルター濾材は、ポリテトラフルオロエチレン多孔膜およびその少なくとも片面にラミネートされた通気性支持材料を有してなり、
　該エアフィルター濾材に５．３ｃｍ／秒の流速で空気を透過させたときの圧力損失（単位：mmＨ₂Ｏ）および粒子径０．１０〜０．１２μｍのジオクチルフタレートを用いて測定した捕集効率（単位：％）から下記式：

（ここで、透過率（％）＝１００−捕集効率（％）である。）
に従って計算される該濾材のＰＦ₁値が２２を越え、
　該エアフィルターユニットに１．４ｃｍ／秒の濾材透過風速で空気を透過させたときの圧力損失（単位：mmＨ₂Ｏ）および粒子径０．１０〜０．１２μｍのジオクチルフタレートを用いて測定した捕集効率（単位：％）から下記式：

（ここで、透過率（％）＝１００−捕集効率（％）である。）
に従って計算される該ユニットのＰＦ₃値が９０．６を越えることを特徴とするエアフィルターユニット
により達成される。 According to the invention, the object is
(1) An air filter pack formed by pleating an air filter medium having a polytetrafluoroethylene porous membrane and an air-permeable support material laminated on at least one surface thereof,
Pressure loss (unit: mmH ₂ O) when air is permeated through the air filter medium at a flow rate of 5.3 cm / sec and collection efficiency measured using dioctyl phthalate having a particle size of 0.10 to 0.12 μm (Unit:%) to the following formula:

(Here, transmittance (%) = 100−capturing efficiency (%).)
The PF ₁ value of the filter medium calculated according to
Pressure loss (unit: mmH ₂ O) when air was passed through the air filter pack at a filtration medium permeation speed of 1.4 cm / sec and trapping measured using dioctyl phthalate having a particle size of 0.10 to 0.12 μm. From the collection efficiency (unit:%), the following formula:

(Here, transmittance (%) = 100−capturing efficiency (%).)
An air filter pack characterized in that the PF ₂ value of the pack calculated in accordance with (1) exceeds 90.6, and (2) a frame, and an air filter medium folded into a pleat shape housed in the frame An air filter unit comprising an air filter pack, the air filter medium comprising a polytetrafluoroethylene porous membrane and a breathable support material laminated on at least one side thereof,
Pressure loss (unit: mmH ₂ O) when air is permeated through the air filter medium at a flow rate of 5.3 cm / sec and collection efficiency measured using dioctyl phthalate having a particle size of 0.10 to 0.12 μm (Unit:%) to the following formula:

(Here, transmittance (%) = 100−capturing efficiency (%).)
The PF ₁ value of the filter medium calculated according to
Pressure loss (unit: mmH ₂ O) when air was passed through the air filter unit at a filter medium permeation wind speed of 1.4 cm / sec and trapping measured using dioctyl phthalate having a particle size of 0.10 to 0.12 μm. From the collection efficiency (unit:%), the following formula:

(Here, transmittance (%) = 100−capturing efficiency (%).)
This is achieved by an air filter unit characterized in that the PF ₃ value of the unit calculated according to

"Air filter media"
First, an air filter medium used in the air filter pack and the air filter unit of the present invention will be described. This air filter medium is an air filter medium comprising a PTFE porous membrane and a breathable support material laminated on at least one surface thereof, and the PF ₁ value defined above exceeds 22.

The air filter medium used in the present invention only needs to have a breathable support material laminated on at least one surface of a PTFE porous membrane, and has a two-layer structure consisting of a breathable support material / PTFE porous membrane, a breathable support material / PTFE porous material. A three-layer structure composed of a membrane / breathable support material or a five-layer structure composed of breathable support material / PTFE porous membrane / breathable support material / PTFE porous membrane / breathable support material may be used. Preferably, a breathable support material is laminated on both sides of the PTFE porous membrane. In this case, handling of the PTFE porous membrane is facilitated, and damage to the PTFE porous membrane during handling can be suppressed as much as possible.

The PTFE porous membrane may be a single layer or may be composed of multiple layers as necessary. By adopting a multilayer structure, even if damage such as pinholes occurs in each single layer, it can be compensated for each other and can be easily designed according to the required filter medium performance. For example, if two layers of the PTFE porous membrane having the same performance are used, the pressure loss is doubled in calculation, but the collection efficiency can be improved.

The air filter medium used in the present invention preferably has a pressure loss of 4 mmH ₂ O or more when air is permeated at a flow rate of 5.3 cm / sec, more preferably 5 to 100 mmH ₂ O. more preferably 10~50mmH ₂ O. When the pressure loss is less than 4 mmH ₂ O, it may be difficult to increase the collection efficiency of the produced air filter unit to 99% or more. When the pressure loss exceeds 100 mmH ₂ O, the pressure of the produced air filter unit The loss value becomes very large and the use as an air filter may be restricted.

In the air filter medium used in the present invention, the PF ₁ value defined above exceeds 22, but preferably the PF ₁ value is at least 23, more preferably at least 24, and more preferably at least 25. .
If the air filter medium has a higher PF ₁ value, for example, at least 23, at least 24, or at least 25, an air filter pack and an air filter unit with higher performance (high PF ₂ value, PF ₃ value) can be obtained. As described above, the air filter unit can be made more compact (an extremely thin air filter unit) while maintaining the high performance of the air filter unit.

In the PF ₁ value in the air filter medium used in the present invention, even if the difference in the absolute value of the PF ₁ value itself is 1, the difference in the absolute value of the PF ₃ value is 4 or more. This is a calculation of the PF value. When the wind speed is changed from 5.3 cm / sec to 1.4 cm / sec, the pressure loss becomes 1.4 / 5.3, so even if the collection efficiency does not change, the PF value Is calculated to be 5.3 / 1.4 = 3.79 times. Further, since the collection efficiency is improved when the wind speed is reduced, the PF value is further improved, and the absolute value is 4 or more.

Specifically, by increasing the PF ₁ value of the air filter medium by ₁ , the PF ₃ value in the air filter unit is improved by 4 or more, and if the pressure loss of the air filter unit is the same, the collection efficiency is improved. If the collection efficiency of the air filter unit is the same, the pressure loss is reduced. For example, when the PF ₃ value of the air filter unit is increased from 92 to 96, the collection efficiency is improved from 99.9989% to 99.99935% when the pressure loss value of the air filter unit is the same as 5.4 mmH ₂ O. The effect is obtained and it can be said that it is very significant.

The trapping efficiency of the air filter medium used in the present invention is preferably 99.9% or more, and more preferably 99.99% or more. An air filter unit having a collection efficiency of HEPA level can be obtained from an air filter medium having a collection efficiency of 99.9% or more, and an ULPA can be obtained from an air filter medium having a collection efficiency of 99.99% or more. An air filter unit having a level of collection efficiency can be obtained.

Here, the PTFE porous membrane and the air-permeable support material constituting the air filter medium used in the present invention will be described.
The PTFE porous membrane that can be used in the present invention is only required to have a PF value exceeding 22, and a known PTFE porous membrane can be used. Such PTFE porous membranes are described in JP-A-10-30031, JP-A-10-287759 and JP-A-9-504737.
The PTFE porous membrane preferably used has a PF value of at least 27, more preferably at least 28.

The thickness of the PTFE porous membrane is preferably 5 μm or more, more preferably 8 μm or more. When the PTFE porous membrane having the same PF value is thick, the amount of trapped fine particles can be increased, that is, a long-life air filter medium can be obtained. Also, if the thickness of the PTFE porous membrane is large, the occurrence of pinholes is reduced during the production of the PTFE porous membrane, during the lamination of the PTFE porous membrane and the air-permeable support material, and / or when the air filter medium is pleated. be able to.

The average fiber diameter of the preferred PTFE porous membrane is 0.14 μm or less, more preferably 0.05 to 0.1 μm. According to the single fiber collection theory, when the fiber diameter of the filter medium increases, the adsorption performance of the particles to the fiber itself decreases, and when the average fiber diameter becomes 0.14 μm or more, a porous membrane having a high PF value is formed. It becomes difficult to obtain. In addition, when the average fiber diameter is 0.05 μm or less, a porous membrane having a high PF value can be achieved, but the strength of the porous membrane structure becomes weak, and as will be described later, the decrease in the PF value due to lamination becomes remarkable, and it is high as an air filter medium It becomes difficult to obtain a product having a PF value.

The filling rate of the PTFE porous membrane is 12% or less, preferably 10% or less, more preferably 8% or less. The filling rate represents the clogging of the fibers with respect to the space. The lower the filling rate, the larger the space of the porous membrane and the greater the distance between the fibers, so that the particles are more easily adsorbed to the porous membrane fiber, and the PF value is higher. This is preferable because the amount of dust retention is increased.

The PTFE porous membrane that can be preferably used in the present invention can be produced, for example, by the following method.
<Preferred PTFE porous membrane production method>
The PTFE porous membrane is preferably a stretched porous membrane.
In order to produce a PTFE stretched porous membrane, first, a liquid lubricant such as solvent naphtha and white oil is added to fine powder obtained by coagulating an aqueous PTFE emulsion polymerization dispersion, and paste extrusion is performed in a rod shape. Thereafter, the rod-like paste extrudate is rolled to obtain a PTFE green body. The thickness of the green tape at this time is usually 100 to 500 μm.

Next, the green tape is stretched in the longitudinal direction (MD direction) at a magnification of less than 2 to 10 times, and then the longitudinal stretched tape is stretched in the width direction (TD direction). At this time, it is preferable to stretch at a stretching rate in the width direction of at least 200% / second. The higher the stretching speed in the width direction, the smaller the fiber diameter of the PTFE porous membrane, making it possible to obtain a PTFE porous membrane having a higher PF value. The stretching ratio in the width direction is preferably set so that the total area ratio is 100 to 300 times.
Stretching in the longitudinal direction is performed at a temperature below the melting point of the PTFE fired body. The stretching in the width direction is performed at a temperature of 200 to 420 ° C.

The unbaked tape may be stretched in a state where two or more tapes are stacked as necessary.
The PTFE porous membrane stretched in the width direction may be heat-treated as necessary to prevent shrinkage.
In addition, in order to increase the thickness of the PTFE porous membrane and further reduce the filling rate, 10-50 parts by weight of non-fibrinated material (for example, low molecular weight PTFE) is added to 100% by weight of PTFE fine powder to the green tape to be produced. May be stretched.

The PTFE porous membrane thus obtained has a PF value exceeding 22, and a PTFE porous membrane having a PF value of at least 27 can be easily obtained. Since the total draw ratio in the longitudinal direction and the width direction is not so high, a relatively thick (5 μm or more) PTFE porous membrane is obtained, and the filling rate is low, for example, 12% or less, preferably 10% or less, more preferably And having a filling rate of 8% or less.

As long as the air-permeable support material used in the air filter medium used in the present invention does not affect the pressure loss of the air filter medium (with a pressure loss significantly lower than the pressure loss of the PTFE porous membrane), A well-known thing used for the purpose of reinforcement of a PTFE porous membrane can be used.
Preferably, a non-woven fabric having a heat-sealing property can be used at least on the surface, and more preferably a core-sheath structure fiber (for example, a fiber having a polyester core and a sheath polyethylene, a core high-melting polyester and a sheath low-melting polyester ). Since the nonwoven fabric composed of the core-sheath structure fiber can be laminated at a temperature slightly lower than the melting point of the sheath, which is lower than the core, the heat at the time of laminating the PTFE porous membrane and the breathable support material Since the history can be reduced, a decrease in the PF value can be further suppressed in a laminate of a PTFE porous membrane and a breathable support material described later.

"Lamination method of PTFE porous membrane and breathable support material"
The air filter medium used in the present invention is preferably obtained by laminating a PTFE porous membrane and a breathable support material by the following method.
Applicant: Daikin Industries, Ltd. has already manufactured and sold an air filter medium in which a PTFE porous membrane and a breathable support material are laminated, and an air filter pack and an air filter unit using the air filter medium. In general, it has been known that when a breathable support material is laminated on a PTFE porous membrane, the pressure loss generally increases. However, in addition to the increase in pressure loss, the trapping efficiency also decreases, and as a result, PF I found that the problem of a drop in value occurred. And it turned out that in order to obtain the air filter medium of higher PF value, it is very important to find the better lamination conditions which were not known conventionally.

Actually, in JP-A-10-30031, a special laminating method (conditions) is not described, so that it can be inferred that laminating is performed by a conventional method. However, in a PTFE porous membrane having a PF value of 26.6, When the air-permeable support material is laminated, the PF value of the air filter medium is lowered to 19.8. In addition, in the above prior art documents, an air filter medium having a PF value exceeding 22 is not obtained by laminating a breathable support material on a PTFE porous membrane.

By the way, regarding the method of laminating a breathable support material on the PTFE porous membrane, for example, by performing the lamination without applying pressure directly in the thickness direction of the PTFE porous membrane by the applicant, the pressure loss of the PTFE porous membrane can be reduced as much as possible. A method that can be maintained has already been proposed (Japanese Patent Laid-Open No. 6-218899). However, when laminating PTFE porous membranes having various PF values with a breathable support material by the laminating method disclosed here, PTFE porous membranes having a PF value of 22 or less showed a decrease in PF values after lamination. Although it can be prevented to some extent, the PTFE porous film having a higher PF value (for example, the PF value described in JP-A-10-30031 is 30) has a reduced PF value, that is, the PF value after lamination is 22 It turned out that only the following were obtained.

The reason why such a tendency is caused by the laminating method (conditions) disclosed in JP-A-6-218899 can be estimated as follows.
When the PF value of the PTFE porous membrane alone exceeds 22 and becomes higher, the average fiber diameter of the PTFE porous membrane becomes smaller and the filling rate becomes smaller. In general, a PTFE porous membrane having a thickness of 5 μm or more is preferably used in order to increase the amount of suspended particles that can be captured, aiming at a long life.

Such a PTFE porous membrane having a high PF value is prone to thermal aggregation of PTFE porous membrane fibers due to unwinding during lamination, compression in the thickness direction due to winding tension, and contraction due to heat. Further inferring this point, compression reduces the inter-fiber distance of the PTFE porous membrane, particularly the inter-fiber distance in the thickness direction, and the effect of collecting particles by each fiber is reduced. It is considered that the decrease in the collection effect inside the membrane causes a decrease in the overall collection efficiency. In addition, it is considered that the collection efficiency is reduced when the number of PTFE porous membrane fibers decreases due to thermal aggregation and the fiber diameter of each fiber increases. Therefore, the above phenomenon occurs even under relatively mild conditions disclosed in JP-A-6-218899, and as a result, the collection efficiency is considered to be lowered.

JP-A-6-218899 also discloses a method of laminating a PTFE porous membrane and a breathable support material by stacking only with its own weight without applying pressure. Therefore, it is considered that the PTFE porous membrane is thermally contracted to cause a decrease in the PF value. Also, with this method, it is difficult to laminate over a length (20 m or more) necessary for actually producing a filter unit.

Therefore, when the earnest laminating method (conditions) was examined based on the above considerations, it was found that the desired air filter medium of the present invention can be obtained under the following conditions.
(1) To make the thermal history during lamination extremely small,
(2) Reducing the winding and unwinding tension extremely
(3) Preferably, cooling is forcibly applied by applying cold air immediately after lamination.

Specifically, it is preferable to perform lamination as follows.
In a preferred embodiment of the present invention, the laminate of the PTFE porous membrane and the breathable support material is a breathable support material 22, 23, preferably a thermoplastic non-woven fabric, for example, the core is polyester as shown in the right half of FIG. And a non-woven fabric made of a core-sheath structure fiber whose sheath is made of polyethylene is laminated on both sides of a biaxially stretched PTFE porous membrane sent from a tenter shown in the left half of FIG. it can.

Here, the heating temperature of the heat roll 19 is preferably 130 to 220 ° C, more preferably 140 to 170 ° C. When the laminated breathable support material and the PTFE porous membrane are brought into contact with the heat roll 19, the compressive force on the roll 19 can be adjusted by the unwinding tension of the breathable support material 22, and preferably 10 to 90 g / cm in the present invention. More preferably, it is 30-70 g / cm.
More preferably, (a) when the heating temperature is 130 ° C. or higher and lower than 140 ° C., the unwinding tension is 70 to 90 g / cm and the line speed is 5 m / min or higher. (B) the heating temperature is 140 ° C. or higher and lower than 170 ° C. In this case, the unwinding tension is 30 to 70 g / cm and the line speed is 10 m / min or more. (C) When the heating temperature is 170 ° C. or more and less than 220 ° C., the unwinding tension is 10 to 30 g / cm and the line speed is 15 m. / Min or more.

The winding tension is usually set to 380 g / cm or less, preferably 300 g / cm or less. When wound around the roll 21 with high tension, the PTFE porous membrane may be compressed in the thickness direction, and the PF value may decrease.
The laminated PTFE porous membrane and the air-permeable support material are preferably cooled immediately after lamination. Cooling is performed by installing the blower nozzle 24 immediately after the heat roll 19 and forcibly introducing indoor air (preferably 50 ° C. or less, more preferably 40 ° C. or less) into the nozzle by a blower or by forced cooling. This can be done by introducing air into the nozzle and forcing the air through the nozzle onto the entire laminated air filter media.

"Air filter pack and air filter unit of the present invention"
In general, the air filter unit can be manufactured by processing an air filter medium into a pleated shape to obtain an air filter pack and incorporating the air filter pack into a frame. Specifically, the air filter unit is as follows.

Air filter units include mini-pleat type and separate type units.
Mini-pleat type unit In the production process of the mini-pleat type, the process of pleating the air filter medium, the process of opening the air filter medium that has been pleated into a pleat and applying a string-like spacer to the air filter medium, for example , The process of pleating the air filter medium coated with the spacer again, the process of cutting the pleated air filter medium into the specified size (completion of the air filter pack according to the present invention), the four sides of the air filter pack Is surrounded by a frame and the air filter pack and the frame are sealed.

As shown in FIG. 4, a method of pleating the air filter medium into a pleat is generally a method of folding with a reciprocating comb blade.
In addition, the method of pleating the air filter medium coated with the spacers again can be pleated, as shown in FIG. 6, by feeding the air filter medium with two rolls and placing a weight at the outlet to start up the roll. There is a method of starting up with a reciprocating comb blade.

In general, as shown in FIG. 4, the air filter medium 41 is fed out by using a nip roll (the air filter medium is fed between two drive rolls by driving the roll), and pleated with a reciprocating comb blade. Pleated into a shape, developed as shown in FIG. 5, applied with a spacer, and pleated again into a pleated shape using the roll of FIG.

The spacer used for the mini-pleat type is used for securing a pleated shape and a gas flow path, and the material of the spacer is not particularly limited, and a conventionally known polyethylene copolymer Polypropylene copolymer, EVA (ethylene vinyl acetate copolymer), hot melt resin such as polyamide, glass yarn, and the like can be used.

However, when a polyamide hot melt resin is used as a spacer in the air filter pack and the air filter unit of the present invention, a desired high PF value can be achieved, and an organic substance expressed as TOC (Total Organic Carbon). Thus, an air filter pack and an air filter unit having the added value that the generation amount of air is extremely small can be obtained.

The mini-pleat type unit is preferably used in a semiconductor manufacturing apparatus or the like. However, when an organic substance represented by the TOC is generated in semiconductor manufacturing, the organic substance adheres to the surface of the silicon wafer, and the organic substance is carbonized in a process where heat is applied. In addition, the electrical characteristics are deteriorated. The above-described air filter pack and air filter unit using a polyamide hot melt resin as a spacer can contribute to an improvement in semiconductor manufacturing yield as well as an improvement in energy efficiency due to a high PF value.

Separator type unit Separator type unit manufacturing process includes pleating the air filter media, inserting the corrugated separator between the pleated air filter media, pleated air The process includes a step of cutting the filter medium into a specified size (completion of the air filter pack referred to in the present invention), a step of surrounding the air filter pack with a frame and sealing the air filter pack and the frame.
In order to more efficiently reflect the PF value of the air filter medium having the PTFE porous membrane and the air-permeable support material of the present invention in the air filter pack and the air filter unit, the following production method is preferable.

That is, it is preferable to manufacture an air filter unit by performing at least one of the following.
(1) In the process of pleating the air filter filter medium, when feeding the air filter medium, do not apply force in the thickness direction of the air filter medium by forcing the motor to the shaft without using a nip roll. .
(2) In the step of pleating the air filter medium, after the pleating, for example, heating (usually 60 to 110 ° C.) is performed by the heating means 42, 42 ′ shown in FIG. Please attach.
(3) When the air filter medium processed into a pleat shape is spread and a string-like spacer is applied and then processed into a pleat shape again, it is forced to clean with a comb blade like a reciprocating type to clean the fold.
(4) When transporting the air filter medium in the entire process, do not use the nip roll so that the air filter medium is not compressed.

The PF ₂ value or PF ₃ value of the air filter pack or air filter unit of the present invention exceeds 90.6, preferably 92 or more, more preferably 95 or more.
In general, the higher the PF value, the lower the pressure loss value of the unit for achieving the same collection efficiency. Further, if the units have the same pressure loss, the higher the PF value, the higher the collection efficiency. When the PF ₂ value or PF ₃ value exceeds 90.6 according to the present invention, it is possible to obtain ULPA and HEPA with a pressure loss as low as previously considered impossible to achieve.

The collection efficiency of the air filter pack and the air filter unit of the present invention is preferably 99.9% or more, more preferably 99.999% or more when the filter medium permeating wind speed is 1.4 cm / sec.
The pressure loss value of the air filter pack and the air filter unit of the present invention is usually as low as possible. When the filter medium permeation speed is 1.4 cm / sec, it is preferably 1 to 25.4 mmH ₂ O, more preferably 1 to 15 mmH. ₂ O.

Here, the performance evaluation method of the air filter unit of the present invention will be described.
The shape of the air filter unit varies depending on the intended use. For example, an air filter medium is formed in a bag-like form, a pleated air filter medium, and a pleated corrugated spacer is inserted between the air filter medium to keep the air flow path For example, the filter medium is pleated into a pleat shape and a hot melt string spacer is applied in the longitudinal direction of the air filter medium in order to maintain the air flow path. Also, the height (the length of the air filter medium from one fold to the next fold) when pleating into pleats is various.

Generally, the wind speed when measuring the performance of an air filter unit is 0.5 m / sec as the surface speed of the air filter unit. However, the form of the air filter unit is different in the folding height and folding pitch as described above, so even if the opening area of the air filter unit is the same, the area of the air filter medium folded therein is different. . For this reason, even if the same air filter medium is used, the pressure loss value and the collection efficiency value are different.

This is because the performance of the air filter unit is determined by the wind speed permeating the folded air filter medium, so the air speed permeating the air filter medium differs if the amount of folding for the same unit opening area is different. This is because the collection efficiency shows different values.
That is, if the amount of folding is large, the filter medium permeating wind speed becomes small, so that the pressure loss value is small and the collection efficiency is increased. On the other hand, when the amount of folding is small, the filter medium permeating wind speed increases, and therefore the pressure loss value is large and the collection efficiency is lowered.
Therefore, when comparing the performance of individual air filter units relative to each other, it is necessary to make the air velocity permeating the air filter medium folded in the air filter unit constant rather than making the air velocity of the surface of the air filter unit constant. . In the present invention, for such reasons, relative evaluation is performed with the wind speed permeating through the air filter medium folded into the air filter unit being 1.4 cm / second.

Specifically, the method of setting the air filter unit surface speed (blowing wind speed) when the filter medium permeating wind speed is 1.4 cm / sec is as follows.
When the air filter unit opening area is Sm ² and the air filter medium folding area is sm ² (obtained from the folding height and the number of pleats), the air filter unit surface velocity V is
V = 1.4 × s / S (cm / sec) = (1.4 / 100) × s / S (m / sec)
It becomes.

According to the present invention, there is provided an air filter medium comprising a PTFE porous membrane and a breathable support material laminated on at least one surface thereof, wherein the PF ₁ value defined above exceeds 22. By using the filter medium, a compact air filter unit can be obtained while maintaining the performance as ULPA.
The performance as ULPA generally means the surface wind speed of the air filter unit used by the user, the collection efficiency is 99.9995% or more, preferably 99.9999% or more, and the pressure loss is 15 mmH ₂ O or less.

If the air filter medium used in the present invention as described above is used, an air filter unit having an air filter pack with a folding height of 30 mm or less, preferably 27 mm or less, more preferably 20 mm or less is obtained.
For example, in the case of an air filter unit having an air filter pack with a folding height of 30 mm, the trapping efficiency is 99.9999% when used at a surface wind speed of 0.5 m / sec, which is the normal air filter unit used by the user. In the case of an air filter unit having an air filter pack with a folding height of 20 mm, the pressure loss is 15 mmH ₂ O or less, and when the surface wind speed of the air filter unit is used at 0.35 m / sec (particularly thin) In the case of an air filter unit, it is usually used at a surface wind speed of 0.35 m / sec.) If the collection efficiency is set to 99.9999%, the pressure loss will be 15 mmH ₂ O or less. Thus, a thin air filter unit with a folding height of 30 mm or less can be obtained while maintaining the high performance as ULPA.

This is because, according to the air filter medium used in the present invention, the PF ₁ value, which is a performance index of pressure loss and collection efficiency, exceeds 22, preferably at least 23, more preferably at least 24, more preferably or at least 25. This is possible because That is, if the conventional PF ₁ value is 22 or less, in the case of an air filter unit with a folding height of 30 mm, when the air filter unit is used at a surface wind speed of 0.5 m / sec, the collection efficiency is 99. If it is set to 9999%, the pressure loss becomes 15 mmH ₂ O or more. If the pressure loss is set to 15 mmH ₂ O or less, the collection efficiency will be less than 99.9999%. In the case of an air filter unit with a folding height of 20 mm, when the air filter unit is used at a surface wind speed of 0.35 m / sec and the collection efficiency is set to 99.9999%, the pressure loss is still 15 mmH ₂ O or more. End up. If the pressure loss is set to 15 mmH ₂ O or less, the collection efficiency will be less than 99.9999%.

Surprisingly, it can be seen that if the folding height of the air filter medium is reduced, the structural resistance of the air filter unit is drastically reduced, and the performance of the original air filter medium is reflected by the performance of the air filter unit. It was.
The structural resistance is the frictional resistance between the air filter medium and the air generated when the air passes through the pleat gap, and the pressure loss of the air filter unit is the pressure loss when air passes through the air filter medium. Expressed as the sum of structural resistances.

Specifically, in a mini-pleat type air filter unit with a folding height of 55 mm, when the surface wind speed of the air filter unit is 0.5 m / second, a structural resistance of about 1 mmH ₂ O occurs. When the thickness is 35 mm or less, the structural resistance decreases rapidly, and when the folding height is 30 mm or less, the structural resistance is almost eliminated, and the performance of the air filter unit becomes comparable to the performance inherent in the air filter medium.

The air filter medium used in the present invention can be used particularly for the applications of the air filter pack and the air filter unit of the present invention, but is processed into other suitable forms, for example, an air purifier filter, a vacuum cleaner filter, and an air conditioner. Filters, automobile air intake filters, deodorizer filters, nuclear exhaust filters, bio clean room filters, pharmaceutical manufacturing clean room filters, hospital operating room air intake filters, precision instrument / machine filters, pollen masks , Gas (N ₂ , Air, SiCl _4, etc.) In-line filters and water / chemical liquid filters can also be used.
The air filter unit of the present invention includes semiconductor industry, liquid crystal industry, medical, food industry, biotechnology and other clean rooms, diffusion furnaces, coater developers, wet stations, chemical vapor deposition (CVD), steppers, stockers, dry etching equipment, It can be used for applications such as plasma etching equipment, clean booths, clean chambers, wafer inspection equipment (surf scan, prober), FFU (fan filter unit), and semiconductor manufacturing equipment such as CMP. In particular, the thin air filter unit is epoch-making in that the FFU can be thinned or incorporated in semiconductor manufacturing equipment, so that the installation space can be reduced, resulting in downsizing of the equipment and light construction that can be easily implemented. Air filter unit.

Hereinafter, the present invention will be specifically described with reference examples and examples.
In Reference Examples and Examples, the thickness of PTFE porous membrane, filling rate, average fiber diameter, pressure loss, collection efficiency, PF value and presence / absence of leakage; pressure loss of air filter media, permeability, collection efficiency, PF ₁ value and presence / absence of leakage; and pressure loss, transmittance, collection efficiency, PF ₃ value, presence / absence of leakage and TOC generation amount of the air filter unit were measured as follows.
In the present invention, the collection efficiency of the filter medium and the air filter unit and the measurement of the leak inspection of the filter medium used dioctyl phthalate (DOP) as the test particles. However, from the viewpoint of reducing TOC generation, conventional TOC generation is low. It is also possible to use inspection particles proposed as (for example, silica particles, polystyrene latex particles, etc.).

PTFE porous film having a thickness of a film thickness meter (1D-110MH type, manufactured by Mitutoyo Corporation) was used, the film thickness of the entire measured repeatedly five a PTFE porous membrane, one of the numerical value obtained by dividing the value in 5 Film thickness.

The PTFE porous membrane whose thickness was measured was cut into 20 × 20 cm, the weight was measured, and the filling rate was obtained from the following formula.

Using an average fiber diameter scanning electron microscope (S-40000 type, manufactured by Hitachi, Ltd.) of the PTFE porous membrane, an enlarged photograph (7000 times) of the PTFE porous membrane is taken. Cut this photo into 4 large pieces and draw 4 straight lines of the same length (length: 24.5 cm long, 29.5 cm wide) at 5 cm intervals on the photo. The diameter of a certain PTFE fiber was measured, and the average was taken as the average fiber diameter of the PTFE fiber.

Pressure loss of PTFE porous membrane and air filter medium (mmH ₂ O)
The measurement sample of the PTFE porous membrane and the air filter medium was set in a filter holder having a diameter of 100 mm, the inlet side was pressurized with a compressor, and the flow rate of air permeated with a flow meter was adjusted to 5.3 cm / second. The pressure loss at this time was measured with a manometer.

Collection efficiency of PTFE porous membrane and air filter media (%)
The measurement sample of the PTFE porous membrane and the air filter medium was set in a filter holder having a diameter of 100 mm, the inlet side was pressurized with a compressor, and the flow rate of air permeated with a flow meter was adjusted to 5.3 cm / second. In this state, a polydisperse DOP having a particle diameter of 0.1 to 0.12 μm was flowed from the upstream side at a particle concentration of 10 ⁸ particles / 300 ml, and a particle counter (PMS LAS-X-CRT PARTICLE MEASURING SYSTEM INC. PMS), the same below), the number of permeated particles of DOP with a particle size of 0.10 to 0.12 μm was determined, the upstream particle concentration was Ci, and the downstream particle concentration was Co. Was calculated.

For air filter media with very high collection efficiency, measurement was performed with a longer suction time and a larger amount of sampling air. For example, if the suction time is 10 times, the number of counted particles on the downstream side is 10 times, that is, the measurement sensitivity is 10 times.

Permeability (%) of PTFE porous membrane and air filter media
The transmittance of the PTFE porous membrane and the air filter medium was determined by the following formula.

（ここで、透過率（％）＝１００−捕集効率（％）である。）
により求めた。
　一方、エアフィルター濾材のＰＦ₁値は先に記載した式に従って求めた。 PF value of PTFE porous membrane and air filter medium PF value of PTFE porous membrane is

(Here, transmittance (%) = 100−capturing efficiency (%).)
Determined by
On the other hand, the PF ₁ value of the air filter medium was determined according to the formula described above.

Presence or absence of leakage of PTFE porous membrane and air filter media Set the measurement sample of PTFE porous membrane and air filter media in a filter holder with a diameter of 100 mm, pressurize the inlet side with a compressor, and adjust the flow rate of air permeated with a flow meter to 5. It adjusted to 3 cm / sec. Flowing a polydisperse DOP from the upstream side in this state a particle concentration of 10 ^8/300 ml, depending on the installation the particle counter on the downstream side, determine the number of transmission particles having径別, the particle size upstream from the ratio of the number of downstream particle The collection efficiency of 0.10 to 0.12 μm and 0.25 to 0.35 μm DOP particles was determined, and the collection efficiency of DOP particles having a particle size of 0.25 to 0.35 μm was 0.10 to 0.12 μm. It was determined that there was no leak if it was 100 times higher than the DOP collection efficiency.

Pressure loss of air filter unit (mmH ₂ O)
The apparatus shown in FIG. 3 was used, and after adjusting the air filter unit so that the wind speed permeating the air filter medium was adjusted to 1.4 cm / second, the pressure loss before and after the air filter unit was measured with a manometer.
In addition, description of the code | symbol in FIG. 3 is as follows.
31: Blower, 32, 32 ': HEPA filter, 33: Test particle introduction tube, 34, 34': Rectifying plate, 35: Upstream test particle sampling tube, 36: Static pressure measurement hole, 37: Test filter Unit, 38: Particle collection tube for downstream test, 39: Laminar flow meter

Air filter unit collection efficiency (%)
Using the apparatus shown in FIG. 3, after the air filter unit is mounted, the wind speed permeating the air filter medium is adjusted to be 1.4 cm / sec. In this state, the particle diameter is 0.1 to 0.12 μm on the upstream side. Of DOP particles at a concentration of 1 × 10 ⁹ / ft ³ , the number of particles with a downstream particle diameter of 0.1 to 0.12 μm is measured with a particle counter, the upstream particle concentration is Ci, and the downstream particle concentration is Co. The collection efficiency of the measurement sample was calculated by the following formula.

Air filter unit transmittance (%)
The transmittance of the air filter unit was obtained from the following formula.

PF value of air filter pack and air filter unit The PF ₂ value and PF ₃ value of the air filter pack and air filter unit were determined according to the formulas described above.
By the way, since the performance of the air filter pack cannot be measured by itself, the measurement is performed as an air filter unit in which a frame is attached to each side of the air filter pack and the air filter pack and the frame are sealed in order to perform the measurement. As a result, the PF ₂ value and the PF ₃ value of the air filter pack and the air filter unit are the same value.

Presence or absence of leakage of air filter unit JACA No. The test was performed in accordance with 10C 4.5.4 (published by Japan Air Cleaners Association, 1979 “Air Cleaner Performance Test Method Standard”).
Silica particles generated from a Ruskin nozzle are mixed with clean air to prepare a test fluid containing particles having a particle size of 0.1 μm or more at a concentration of 10 ⁸ particles / ft ³ or more. Next, the inspection fluid is passed through the air filter unit from the upstream side of the air filter unit so that the wind speed on the surface of the air filter unit is 0.5 m / sec. Then, while the scanning probe is scanned at a speed of 5 cm per second at a position 25 mm downstream of the air filter unit, the downstream air is sucked in at 28.3 liters / minute, and the downstream silica particle concentration is detected by the particle counter. Measure. However, this scanning is performed over the entire surface of the filter medium of the air filter unit and the joint between the filter medium and the frame, and the strokes are slightly overlapped. If there is a leak in the air filter unit, the particle size distribution of the silica particles on the downstream side is the same as the particle size distribution on the upstream side, and therefore it can be determined.

Measurement of the amount of TOC generated from the air filter unit The measurement of the amount of TOC generated from the air filter unit is performed through the HEPA filter and the organic substance removal chemical filter, and the air subjected to the particle and organic substance treatment is passed through the air filter unit to be tested. The air downstream of the air filter unit is subjected to suction sampling using a porous polymer adsorbent (TENAX GR) to adsorb organic matter. The conditions at this time are as follows.
・ Test air filter unit permeate wind speed: 0.35 m / sec ・ Downstream air sampling amount: 2 L / min × 100 min

Next, the organic substance adsorbed on the porous polymer adsorbent in the multi-TENAX tube was analyzed using a Curie Point Purge and Trap Sampler (JHS-100A manufactured by Nihon Analytical Industrial Co., Ltd.). That is, a TENAX tube having adsorbed organic substances in the downstream air is heated to 230 ° C., high purity helium gas is allowed to flow there, the adsorbed material is purged (purged), and introduced into the trap tube. In this trap tube, it is accumulated and concentrated in an adsorbent (quartz wool) cooled to −40 ° C. Thereafter, the adsorbent is instantaneously heated to 358 ° C., and the adsorbate adsorbed on the adsorbent for 20 seconds is released as a gas. And the said discharge | released gas is introduce | transduced into a gas chromatography, and the quantity is measured as an organic substance total amount. From the total amount of organic matter and the downstream sampling air amount, the amount of generated organic matter was expressed as ng / m ³ . The measurement conditions for gas chromatography are as follows.
-Gas chromatography: GC14A (manufactured by Shimadzu Corporation)
・ Column: FRONTIER LAB ULTRA ALLOY Capillary Column UA-5
Column temperature: 50 ° C. → 280 ° C. (10 minutes hold), temperature rising rate 10 ° C./min

Reference example 1
To 100 parts by weight of PTFE fine powder with a number average molecular weight of 6.2 million (Daikin Industries Co., Ltd. Polyflon Fine Powder F-104U), 25 parts by weight of hydrocarbon oil (Isopar made by Esso Petroleum Co., Ltd.) as an extrusion aid is added. Mixed.
This mixture was formed into a round bar by paste extrusion. This round bar-shaped molded body was molded into a film by a calendar roll heated to 70 ° C. to obtain a PTFE film. This film was passed through a hot air drying oven at 250 ° C. to evaporate and remove the extrusion aid, thereby obtaining an unfired film having an average thickness of 200 μm and an average width of 150 mm.
Next, this unsintered PTFE film was stretched at a stretch ratio of 5 in the longitudinal direction using the apparatus shown in FIG. The unsintered film was set on roll 1, and the stretched film was wound on winding roll 2. The stretching temperature was 250 ° C.

The obtained longitudinally stretched film was stretched at a stretch ratio of 30 times in the width direction using a device (tenter) shown in the left half of FIG. At this time, the stretching temperature was 290 ° C., the heat setting temperature was 360 ° C., and the stretching speed was 330% / second.

Reference example 2
The longitudinally stretched film obtained in Reference Example 1 was stretched in the width direction at a stretch ratio of 40 times using the apparatus shown in the left half of FIG. At this time, the stretching temperature was 290 ° C., the heat setting temperature was 350 ° C., and the stretching speed was 440% / second.

Reference example 3
The longitudinally stretched film obtained in Reference Example 1 was stretched in the width direction at a stretch ratio of 25 using the apparatus shown in the left half of FIG. At this time, the stretching temperature was 290 ° C., the heat setting temperature was 380 ° C., and the stretching speed was 275% / second.

The physical properties of the PTFE porous membranes obtained in Reference Examples 1 to 3 are as follows.

Reference example 4
FIG. 2 shows a polyethylene / polyester heat-fusible non-woven fabric (upper surface: Elves T0703WDO (manufactured by Unitika); bottom: trade name: Elfit E0353WTO (manufactured by Unitika)) on both sides of the PTFE porous membrane prepared in Reference Example 1. An air filter medium was obtained by heat fusion using an apparatus. The heat sealing conditions at this time were as follows.

Roll 19 heating temperature 160 ℃
Line speed 15m / min unwinding tension 50g / cm (unwinding tension of nonwoven fabric 22)
Winding tension 280g / cm

Reference Example 5
FIG. 2 shows a polyethylene / polyester heat-fusible non-woven fabric (upper surface: Elves T0703WDO (manufactured by Unitika); bottom: trade name: Elfit E0353WTO (manufactured by Unitika)) on both sides of the PTFE porous membrane prepared in Reference Example 1. An air filter medium was obtained by heat fusion using an apparatus. The heat sealing conditions at this time were as follows.
Roll 19 heating temperature 180 ℃
Line speed 15m / min unwinding tension 20g / cm (unwinding tension of nonwoven fabric 22)
Winding tension 280g / cm

Reference Example 6
An air filter medium was obtained in the same manner as in Reference Example 4 except that a cold air blowing device was provided immediately after the heating roll 19 and the air filter medium discharged from the roll 19 was cooled by blowing air at 20 ° C.

Reference Example 7
An air filter medium was prepared in the same manner as in Reference Example 4 except that the PTFE porous membrane prepared in Example 2 was used.

Reference Example 8
An air filter medium was prepared in the same manner as in Example 6 except that the PTFE porous membrane prepared in Example 2 was used.

Reference Example 9
Using the PTFE porous membrane produced in Reference Example 1, the conditions of Example 7 described in JP-A-6-218899 (heating temperature 160 ° C., line speed 10 m / min, unwinding tension 90 g / cm) Using the apparatus shown in Fig. 2, heat-sealing non-woven fabric made of polyethylene / polyester (upper surface: Elves T0703WDO (product of Unitika); bottom: product name Elfit E0353WTO (product of Unitika)) is fused on both sides of the PTFE porous membrane. Thus, an air filter medium was obtained. The winding was performed with a winding tension of 280 g / cm.

Reference Example 10
An air filter medium was obtained in the same manner as in Reference Example 9 except that the PTFE porous membrane prepared in Reference Example 2 was used.

The physical properties of the air filter media manufactured in Reference Examples 4 to 10 are as follows.

Thus, according to the present invention, PTFE porous film is extremely small decrease in the PF ₁ values compared to a single, more than 22 PF ₁ value even after lamination of the air-permeable support member could be achieved.
Further, from the results of Reference Examples 6 and 8, it was found that the PF ₁ value was further improved when cooled immediately after lamination.
On the other hand, as can be understood from the reference examples 9 to 10, under the mild laminating conditions described in JP-A-6-218899, an increase in pressure loss can be suppressed, but a decrease in collection efficiency cannot be prevented. In addition, it was found that the PF1 value of the air filter medium laminated with the air-permeable support material was lowered to 22 or less even when the PTFE porous membrane alone had a high PF value.

Example 1
The air filter medium produced in Reference Example 4 was pleated to a height of 5.5 cm with a reciprocating folder, and after pleating, it was folded at a temperature of 90 ° C. After this, open the pleated air filter media, apply a polyamide hot melt resin spacer, start up again with a reciprocating starter in a pleated shape, cut it into 58cm x 58cm, and remove the air filter pack. Obtained. At this time, the pleat interval was 3.125 mm / pleat.
In the process so far, when the air filter medium is fed out, a motor is attached to the shaft to forcibly feed it so that no force is applied in the thickness direction of the air filter medium. Further, when conveying the air filter medium, a nip roll was not used so that no compression force was applied to the air filter medium.

Next, prepare an anodized aluminum frame with an outer dimension of 61 cm x 61 cm, an inner dimension of 58 cm x 58 cm, and a thickness of 6.5 cm, put an air filter pack that has been pleated into this frame, and air filter with urethane adhesive The air filter unit was prepared by sealing the periphery of the pack and the aluminum frame.

Example 2
An air filter unit was produced in the same manner as in Example 1 except that re-starting was performed using a roll starter.

Example 3
An air filter unit was produced in the same manner as in Example 1 except that the air filter medium of Reference Example 8 was used.

Reference Example 11
An air filter unit was produced in the same manner as in Example 1 except that the air filter medium was folded with a reciprocating machine and no heat was applied and the crease was not creased.

Reference Example 12
An air filter unit was produced in the same manner as in Example 1 except that a nip roll was used when the air filter medium was fed from the roll.

About the air filter unit produced in Examples 1-3 and Reference Examples 11-12, the air velocity was set so that the filter medium permeation | transmission wind speed might be set to 1.4 cm / sec, and the pressure loss and collection efficiency of the air filter unit were measured. .
In these air filter units, the surface speed of the air filter unit when the filter medium permeating wind speed is 1.4 cm / second is as follows.
Since the inner dimension of each air filter unit is 58 cm × 58 cm, the opening area of the air filter unit is 58 cm × 58 cm = 3364 cm ² = 0.3364 m ² . On the other hand, regarding the area of the folded air filter medium, first, when the number of pleats is calculated, 580 mm ÷ 3.125 mm / pleat = 185 pleats. From this, the length of the air filter medium is 5.5 cm × 185 × 2 = 22035 cm. = 20.35 m. Moreover, since the width of the air filter medium is 58 cm = 0.58 m, the area of the air filter medium is 20.35 × 0.58 = 11.803 m ² . From the opening area of the air filter unit and the area of the air filter medium, the surface speed of the air filter unit is 1.4 cm / second × 11.803 m ² ÷ 0.3364 m ² = 49. 12 cm / sec = 0.4912 m / sec. The actual pressure loss of the air filter unit was measured at this surface speed.

The performance of the air filter unit produced in Examples 1 to 3 and References 11 to 12 is as follows.

As can be understood from the results shown in Table 3, a PF ₃ value exceeding 90.6 cannot be achieved by the usual method (using nip rolls and not applying heat after folding the filter medium with a reciprocating machine). However, an air filter unit having a desired high PF3 value could be obtained by using a nip roll and folding the filter medium with a reciprocating machine and then applying heat to the crease.
In addition, when starting up again in a pleated form, it can be seen that using a reciprocating starter is preferable to obtaining a higher PF ₃ value than a roll starter.

Example 4
The air filter medium produced in Reference Example 4 was pleated at a height of 13 cm using a reciprocating fold, and was creased at a temperature of 80 ° C. after pleating. Thereafter, a separator obtained by corrugating an aluminum foil having a thickness of 35 μm to a height of 2.4 mm was inserted between the pleated air filter media, and cut into a size of 58 cm × 58 cm. At this time, the pleat interval was 5.0 mm / pleat.
In the process so far, when the air filter medium is fed out, a motor is attached to the shaft to forcibly feed it so that no force is applied in the thickness direction of the air filter medium. Further, when conveying the air filter medium, a nip roll was not used so that no compression force was applied to the air filter medium.

Next, prepare an anodized aluminum frame with an outer dimension of 61 cm x 61 cm, an inner dimension of 58 cm x 58 cm, and a thickness of 15 cm. Place the pleated air filter pack in this frame, and surround the air filter pack with urethane adhesive. The aluminum frame was sealed to produce an air filter unit.
With respect to this air filter unit, the air velocity was set so that the filter medium permeation wind speed was 1.4 cm / second, and the pressure loss and the collection efficiency of the air filter unit were measured. In this air filter unit, the surface speed of the air filter unit when the filter medium permeating wind speed is 1.4 cm / second is 0.7279 m / second as calculated in the same manner as in Examples 1 to 3 and Reference Examples 11 to 12. Become. The actual pressure loss of the air filter unit was measured at this surface speed.

The performance of the air filter unit produced in Example 4 is as follows.

It was found that even if the air filter unit has a different shape as described above, an air filter unit having almost the same performance can be obtained if the air filter unit is produced without deterioration of the air filter medium.

Example 5
An air filter unit was produced in the same manner as in Example 1 except that the air filter medium produced in Reference Example 4 was pleated to a height of 3.0 cm using a reciprocating folder.

Example 6
An air filter unit was produced in the same manner as in Example 1 except that the air filter medium produced in Reference Example 8 was pleated to a height of 3.0 cm using a reciprocating folder.

Example 7
An air filter unit was produced in the same manner as in Example 1 except that the air filter medium produced in Reference Example 4 was pleated to a height of 2.0 cm with a reciprocating folder.

Example 8
An air filter unit was produced in the same manner as in Example 1 except that the air filter medium produced in Example 8 was pleated to a height of 2.0 cm with a reciprocating folder.

Reference Example 13
An air filter unit was produced in the same manner as in Example 1 except that the air filter medium produced in Reference Example 9 was pleated to a height of 3.0 cm using a reciprocating folder.

Reference Example 14
An air filter unit was produced in the same manner as in Example 1 except that the air filter medium produced in Reference Example 10 was pleated to a height of 3.0 cm with a reciprocating folder.

Reference Example 15
An air filter unit was produced in the same manner as in Example 1 except that the air filter medium produced in Reference Example 9 was pleated to a height of 2.0 cm with a reciprocating folder.

Reference Example 16
An air filter unit was produced in the same manner as in Example 1 except that the air filter medium produced in Reference Example 10 was pleated to a height of 2.0 cm with a reciprocating folder.

For these air filter units, the pressure loss and the collection efficiency of the air filter unit were measured by setting the wind speed so that the filter medium permeating wind speed was 1.4 cm / sec. In addition, when the surface air speed of the air filter unit when the filter medium permeating wind speed is 1.4 cm / sec in these air filter units is calculated in the same manner as in Examples 1 to 3 and Reference Examples 11 to 12, the folding height is The 30 mm air filter unit is 0.2679 m / sec, and the 20 mm folding height is 0.1786 m / sec. The actual pressure loss of the air filter unit was measured at this surface speed.

The performances of the air filter units produced in Examples 5 to 8 and Reference Examples 13 to 16 are as follows.

Next, for the air filter units produced in Examples 5 to 8 and Reference Examples 13 to 16, the air filter unit having a folding height of 30 mm was measured for pressure loss and collection efficiency at a surface wind speed of 0.5 m / sec. The results are shown in Table 6. The air filter unit with a folding height of 20 mm was measured for pressure loss and collection efficiency at a surface wind speed of 0.35 m / sec. The results are shown in Table 7.

From the results shown in Table 5, it can be seen that the pressure loss value of the air filter unit substantially matches the pressure loss value calculated from the pressure loss value of the air filter medium, and there is almost no structural resistance. That is, in Examples 5 and 7, the pressure loss value of 5.3 cm / sec of the air filter medium used is 26 mmH ₂ O, and the calculated pressure loss value at 1.4 cm / sec is 26 mmH ₂ O × 1.4 / 5.3 = 6.87 mmH ₂ O, which is substantially the same as the pressure loss value of the actual air filter unit. Similarly, in Examples 6 and 8, the pressure loss value of 5.3 cm / sec of the air filter medium used is 23 mmH ₂ O, and the calculated pressure loss value at 1.4 cm / sec is 23 mmH ₂ O × 1.4 / 5.3 = 6.08 mmH ₂ O, which is substantially the same as the pressure loss value of the actual air filter unit.

Further, from the results shown in Tables 6 and 7, the air filter medium having a PF ₁ value of 22 or less has a low collection efficiency at the wind speed actually used by the user when the folding height is 30 mm or less. Although 99.999% is not realized as well as 99.9995%, which is a general performance as ULPA, when an air filter medium with a PF ₁ value exceeding 22 is used, the performance as ULPA even if the folding height is 30 mm or less It was found that can be realized.

It was found that the pressure loss of the air filter unit shown in Tables 6 and 7 also almost coincided with the pressure loss value calculated from the pressure loss value of the air filter medium, and there was almost no structural resistance. Specifically, the pressure loss of the air filter unit calculated from the pressure loss value of the air filter medium is 12.82 mmH ₂ O in Example 5 and Reference Example 13 in Table 6, and 11.34 mmH in Example 6 and Reference Example 14. ₂ O. In Example 7 and Reference Example 15 in Table 7, it was 13.46 mmH ₂ O, and in Example 8 and Reference Example 16 it was 11.91 mmH ₂ O.

Example 9
An air filter unit was produced in the same manner as in Example 1 except that EVA hot melt resin was used for the spacer. The amount of spacer applied was the same as in Example 1. Further, the same sealant was used for the air filter pack and the aluminum frame.

About the air filter unit produced in Example 1 and Example 9, the amount of TOC generated from the air filter unit was measured. The results are as follows.

From the results shown in Table 8, the air filter unit having an air filter pack made of an air filter medium used in the present invention using a polyamide hot melt resin as a spacer is compared with that using an EVA hot melt resin as a spacer. It has been found that the amount of TOC generated is drastically reduced to about 1/20.

It is a schematic diagram of the apparatus used for extending | stretching to the longitudinal direction of a PTFE film. It is a figure which shows typically the apparatus (left half) used for extending | stretching to the width direction of a PTFE film, and the apparatus (right half) which laminates a breathable support material on a PTFE film. It is a schematic diagram of the measuring device of the pressure loss of a filter unit. It is a schematic diagram of a reciprocating folder. It is a schematic diagram which shows a spacer application | coating process. It is a schematic diagram of a roll up machine.

Explanation of symbols

1: Unwinding roll, 2: Winding roll, 3, 4, 6, 7, 10: Roll,
15: Preheating oven, 16: Stretching oven, 17: Heat setting oven 31: Blower, 32, 32 ': HEPA filter, 33: Test particle introduction tube, 34, 34': Rectifying plate, 35: Upstream test particle Collection tube, 36: Static pressure measurement hole, 37: Test filter unit, 38: Particle collection tube for downstream test, 39: Laminar flow rate

Claims (14)

An air filter pack formed by pleating an air filter medium comprising a polytetrafluoroethylene porous membrane and a breathable support material laminated on at least one side thereof,
Pressure loss (unit: mmH ₂ O) when air is permeated through the air filter medium at a flow rate of 5.3 cm / sec and collection efficiency measured using dioctyl phthalate having a particle size of 0.10 to 0.12 μm (Unit:%) to the following formula:

(Here, transmittance (%) = 100−capturing efficiency (%).)
The PF ₁ value of the filter medium calculated according to
Pressure loss (unit: mmH ₂ O) when air was passed through the air filter pack at a filtration medium permeation speed of 1.4 cm / sec and trapping measured using dioctyl phthalate having a particle size of 0.10 to 0.12 μm. From the collection efficiency (unit:%), the following formula:

(Here, transmittance (%) = 100−capturing efficiency (%).)
An air filter pack characterized in that the PF ₂ value of the pack calculated according to The air filter pack according to claim 1, wherein the pressure loss of the air filter medium when air is permeated at a flow rate of 5.3 cm / sec is 4 mmH ₂ O or more. The air filter pack according to claim 1 or 2, wherein the air filter pack has a PF ₂ value of at least 92. The collection efficiency measured by using dioctyl phthalate having a particle diameter of 0.10 to 0.12 μm when air is permeated at a filter medium permeating wind speed of 1.4 cm / sec is 99.9% or more. The air filter pack according to any one of the above. The air filter pack according to claim 4, wherein the collection efficiency is 99.999% or more. The air filter pack according to any one of claims 1 to 5, wherein the air filter pack is a mini-pleat type having a spacer made of a polyamide hot melt resin. The pressure loss of the air filter pack when the folding height is 30 mm or less and air is permeated at a filter medium permeating wind speed of 1.4 cm / sec is 1 to 25.4 mmH ₂ O. The air filter pack described in 1. An air filter unit comprising a frame and an air filter pack made of an air filter medium folded in a pleat shape housed in the frame, the air filter medium comprising a polytetrafluoroethylene porous membrane and its Having a breathable support material laminated on at least one side;
Pressure loss (unit: mmH ₂ O) when air is permeated through the air filter medium at a flow rate of 5.3 cm / sec and collection efficiency measured using dioctyl phthalate having a particle size of 0.10 to 0.12 μm (Unit:%) to the following formula:

(Here, transmittance (%) = 100−capturing efficiency (%).)
The PF ₁ value of the filter medium calculated according to
Pressure loss (unit: mmH ₂ O) when air was passed through the air filter unit at a filter medium permeation wind speed of 1.4 cm / sec and trapping measured using dioctyl phthalate having a particle size of 0.10 to 0.12 μm. From the collection efficiency (unit:%), the following formula:

(Here, transmittance (%) = 100−capturing efficiency (%).)
An air filter unit characterized in that the PF ₃ value of the unit calculated according to The air filter unit according to claim 8, wherein the pressure loss of the air filter medium when air is permeated at a flow rate of 5.3 cm / sec is 4 mmH ₂ O or more. The air filter unit according to claim 8 or 9, wherein the air filter unit has a PF ₃ value of at least 92. The collection efficiency measured by using dioctyl phthalate having a particle diameter of 0.10 to 0.12 µm when air is permeated at a filter medium permeating wind speed of 1.4 cm / sec is 99.9% or more. The air filter unit according to any one of the above. The air filter unit according to claim 11, wherein the collection efficiency is 99.999% or more. The air filter unit according to any one of claims 8 to 12, wherein the air filter pack made of an air filter medium folded into a pleat shape housed in a frame is a mini-pleat type having a spacer made of polyamide hot melt resin. The folding height of the air filter pack is 30 mm or less, and the air filter unit has a pressure loss of 1 to 25.4 mmH ₂ O when air is permeated at a filter medium permeating wind speed of 1.4 cm / sec. The air filter unit according to any one of claims 8 to 13.

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