JP4614669B2 - Filter material and filter - Google Patents
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- JP4614669B2 JP4614669B2 JP2004027109A JP2004027109A JP4614669B2 JP 4614669 B2 JP4614669 B2 JP 4614669B2 JP 2004027109 A JP2004027109 A JP 2004027109A JP 2004027109 A JP2004027109 A JP 2004027109A JP 4614669 B2 JP4614669 B2 JP 4614669B2
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本発明は濾過材及びフィルタに関する。 The present invention relates to a filter medium and a filter.
従来から、気体中や液体中における粒子を除去するために、各種フィルタが使用されてきた。例えば、フィルタを構成する濾過材として、「平均繊維径が０．５μｍ以上４μｍ以下の極細繊維が厚さ方向に１０〜４０本重ねられた繊維集合体からなり、該繊維集合体の最大孔径が２５μｍ以下でありかつ、該最大孔径と平均流量孔径の比が１．０〜１．８の範囲にあり、繊維の充填率が０．０５〜０．３５の範囲にあることを特徴とする微小粒子の濾過材。」が提案されている（特許文献１）。しかしながら、この濾過材は深さ方向における極細繊維の本数が少なく、濾過材の厚さが十分ではないため、粒子がもれやすく、十分な濾過精度及び濾過寿命が得られないものであった。 Conventionally, various filters have been used to remove particles in gas or liquid. For example, as a filter material constituting a filter, “the fiber aggregate is composed of a fiber aggregate in which 10 to 40 ultrafine fibers having an average fiber diameter of 0.5 μm to 4 μm are stacked in the thickness direction, and the maximum pore diameter of the fiber aggregate is It is 25 μm or less, the ratio of the maximum pore diameter to the average flow pore diameter is in the range of 1.0 to 1.8, and the fiber filling ratio is in the range of 0.05 to 0.35. A filter material for particles "has been proposed (Patent Document 1). However, this filter medium has a small number of ultrafine fibers in the depth direction, and the thickness of the filter medium is not sufficient. Therefore, particles are liable to leak, and sufficient filtration accuracy and filter life cannot be obtained.
別の濾過材として、「平均繊維径が１．５μｍ以上５μｍ以下の極細繊維が厚さ方向に１０〜４０本重ねられた繊維集合体からなり、該繊維集合体の最大孔径が２８μｍ〜４０μｍの範囲にありかつ、該最大孔径と平均流量孔径の比が１．５〜２．５の範囲にあり、繊維の充填率が０．０５〜０．３５の範囲にあることを特徴とする微小粒子の濾過材。」が提案されている（特許文献２）。しかしながら、この濾過材は孔径が大きく、また、粒子がもれやすいため、十分な濾過精度が得られないものであった。 As another filtering material, “consisting of a fiber assembly in which 10 to 40 ultrafine fibers having an average fiber diameter of 1.5 μm to 5 μm are stacked in the thickness direction, and the maximum pore diameter of the fiber assembly is 28 μm to 40 μm. A fine particle having a ratio between the maximum pore diameter and the average flow pore diameter in the range of 1.5 to 2.5, and a fiber filling ratio in the range of 0.05 to 0.35. Of the filter material "has been proposed (Patent Document 2). However, since this filter medium has a large pore diameter and particles are liable to leak, sufficient filtration accuracy cannot be obtained.
また、フィルタに使用できる不織布として、「平均繊維径が０．１μｍから１０μｍまでの間にある極細繊維よりなる不織布であって、目付３０ｇ／ｍ２あたりの初期引張抵抗度が１０ｋｇ／５ｃｍ幅〜３０ｋｇ／５ｃｍ幅の範囲にあることを特徴とする極細繊維不織布。」が提案されている（特許文献３）。しかしながら、この不織布は初期引張抵抗度が低いため、各種フィルタとして使用するための加工性の悪いものであった。 Further, as a nonwoven fabric that can be used for a filter, “a nonwoven fabric made of ultrafine fibers having an average fiber diameter of 0.1 μm to 10 μm, and an initial tensile resistance per 30 g / m 2 of basis weight is 10 kg / 5 cm width to An ultrafine fiber nonwoven fabric characterized by being in the range of 30 kg / 5 cm width has been proposed (Patent Document 3). However, since this nonwoven fabric has low initial tensile resistance, it has poor workability for use as various filters.
更に、多層ミクロ分離媒体として、「自己支持性多孔サブストレイト層、この自己支持性多孔サブストレイト層上に集積し接合した細繊維濾過層、この細繊維濾過層上に集積し、完全に自己接合した、１本又は２本の繊維厚さの多孔ノンハンドラブル繊維カバー層、とを備えた多層ミクロ分離媒体」が提案されている（特許文献４）。この多層ミクロ分離媒体は孔径が大きいため、十分な濾過精度が得られないものであった。 Furthermore, as a multi-layer micro separation medium, “a self-supporting porous substrate layer, a fine fiber filtration layer integrated and bonded on this self-supporting porous substrate layer, integrated on this fine fiber filtration layer and completely self-bonding” A multi-layer micro separation medium having a porous non-handleable fiber cover layer having a thickness of one or two fibers has been proposed (Patent Document 4). Since this multilayer micro separation medium has a large pore size, sufficient filtration accuracy cannot be obtained.
本発明は上述のような問題点を解決するためになされたもので、十分な濾過精度及び濾過寿命を有するとともに、各種フィルタへの加工性の優れる濾過材を提供すること、及びこの濾過材を用いたフィルタを提供することを目的とする。 The present invention has been made to solve the above-described problems, and provides a filter medium having sufficient filtration accuracy and filter life and excellent workability to various filters, and the filter medium. It aims at providing the used filter.
本発明の請求項１にかかる発明は、「静電紡糸法により製造された、平均繊維径が０．０１μｍ以上、０．５μｍ未満の極細繊維集合体層と、静電紡糸法により製造された平均繊維径が０．５μｍ以上、５μｍ以下の細繊維からなる細繊維集合体層とを備えていることを特徴とする、液中の微粒子用濾過材」である。このような極細繊維集合体層は効率的に粒子を精度良く濾過することができ、また、細繊維集合体層を備えていることによって、濾過寿命の長い濾過材である。また、静電紡糸法により製造された極細繊維集合体層は十分な強度を有するため、フィルタへの加工性の優れる濾過材である。
このように、細繊維集合体層が静電紡糸法により製造されているため、更に十分な強度を有するため、フィルタへの加工性の優れる濾過材である。また、極細繊維集合体層と細繊維集合体層とが同一の方法で作製されるため、極細繊維集合体層と細繊維集合体層との親和性が高く、層剥離が生じにくい。更に、極細繊維集合体層上に、静電紡糸法により形成した細繊維を集積させて細繊維集合体層を形成するか、静電紡糸法により細繊維集合体層を形成した後に、静電紡糸法により形成した極細繊維を集積させて極細繊維集合体層を形成することにより、連続して本発明の濾過材を製造できるため、製造工数を削減できるという効果も奏する。
The invention according to claim 1 of the present invention is “produced by an electrospinning method, an ultrafine fiber assembly layer having an average fiber diameter of 0.01 μm or more and less than 0.5 μm, and an electrospinning method” A filter medium for fine particles in liquid, comprising a fine fiber aggregate layer composed of fine fibers having an average fiber diameter of 0.5 μm or more and 5 μm or less. Such an ultrafine fiber aggregate layer can efficiently filter particles with high accuracy, and is a filter medium having a long filtration life by being provided with the fine fiber aggregate layer. Moreover, since the ultrafine fibrous aggregate layer prepared by an electrostatic spinning process with a sufficient strength, a filtering material having excellent processability into filter.
Thus, since the fine fiber aggregate layer is manufactured by the electrospinning method, it has a further sufficient strength, and thus is a filter material with excellent processability to a filter. Moreover, since the ultrafine fiber assembly layer and the fine fiber assembly layer are produced by the same method, the affinity between the ultrafine fiber assembly layer and the fine fiber assembly layer is high, and delamination hardly occurs. Furthermore, the fine fibers formed by the electrostatic spinning method are accumulated on the ultrafine fiber assembly layer to form the fine fiber assembly layer, or after forming the fine fiber assembly layer by the electrostatic spinning method, By collecting the ultrafine fibers formed by the spinning method to form the ultrafine fiber assembly layer, the filter medium of the present invention can be continuously produced, so that the production man-hour can be reduced.
本発明の請求項2にかかる発明は、「請求項１に記載の濾過材を備えていることを特徴とする、液中の微粒子用フィルタ」である。このように本発明のフィルタは前記濾過材を備えているため、十分な濾過精度を有するものである。また、加工性良く製造できるものである。例えば、濾過材をコマ型フィルタやカートリッジフィルタへ加工する場合、ディスク状に打ち抜いたり、プリーツ状に折ったりする必要があるが、従来の濾過材では十分な強度がないため、このような加工を行うことが困難であったが、本発明の前記濾過材は静電紡糸法で製造された極細繊維集合体層を備えた十分な強度のあるものであるため、加工性良く製造できるフィルタである。
The invention according to claim 2 of the present invention is “a filter for fine particles in a liquid , characterized in that it comprises the filter medium according to claim 1 ”. Thus, since the filter of this invention is equipped with the said filter material, it has sufficient filtration accuracy. Moreover, it can be manufactured with good workability. For example, when processing a filter medium into a coma filter or cartridge filter, it is necessary to punch it into a disk shape or fold it into a pleat. However, the conventional filter medium does not have sufficient strength. Although it was difficult to carry out, the filter medium of the present invention is a filter that can be manufactured with good workability because it has sufficient strength with an ultrafine fiber assembly layer manufactured by an electrospinning method. .
本発明の濾過材は十分な濾過精度を有するとともに、各種フィルタへの加工性の優れるものである。また、本発明のフィルタは十分な濾過精度を有するとともに、加工性良く製造できるものである。 The filter medium of the present invention has sufficient filtration accuracy and is excellent in processability to various filters. The filter of the present invention has sufficient filtration accuracy and can be manufactured with good workability.
本発明の濾過材は主濾過層として作用する平均繊維径が０．０１μｍ以上、０．５μｍ未満の極細繊維集合体層を備えている。この主濾過層である極細繊維集合体層はサブミクロンの粒子や微生物をも濾過することができる。極細繊維集合体層の平均繊維径が０．５μｍ未満であるのは、濾過材の濾過精度が優れているようにするためで、平均繊維径が小さければ小さい程、濾過精度が優れているため、０．３μｍ以下であるのが好ましい。一方で、濾過時の圧力損失が小さく、効率良く濾過することができるように、極細繊維集合体層の平均繊維径は０．０１μｍ以上であり、より効率良く濾過できるように、０．０５μｍ以上であるのがより好ましい。なお、本発明における「平均繊維径」は５０本以上の繊維の繊維径の算術平均値をいう。なお、繊維の横断面形状が非円形である場合には、横断面積と同じ面積をもつ円の直径を繊維径とみなす。 The filter medium of the present invention includes an ultrafine fiber aggregate layer having an average fiber diameter of 0.01 μm or more and less than 0.5 μm that acts as a main filtration layer. This main filtration layer, the ultrafine fiber aggregate layer, can also filter submicron particles and microorganisms. The average fiber diameter of the ultrafine fiber aggregate layer is less than 0.5 μm so that the filtration accuracy of the filter medium is excellent. The smaller the average fiber diameter, the better the filtration accuracy. , 0.3 μm or less is preferable. On the other hand, the average fiber diameter of the ultrafine fiber assembly layer is 0.01 μm or more so that the pressure loss during filtration is small and the filtration can be performed efficiently, and 0.05 μm or more so that the filtration can be performed more efficiently. It is more preferable that The “average fiber diameter” in the present invention means an arithmetic average value of fiber diameters of 50 or more fibers. When the cross-sectional shape of the fiber is non-circular, the diameter of a circle having the same area as the cross-sectional area is regarded as the fiber diameter.
なお、本発明の極細繊維集合体層を構成する極細繊維の繊維長は、特に限定するものではないが、極細繊維の脱落が発生しにくいように、０．１ｍｍ以上であるのが好ましく、特に、極細繊維が連続繊維であるのが好ましい。 The fiber length of the ultrafine fibers constituting the ultrafine fiber assembly layer of the present invention is not particularly limited, but is preferably 0.1 mm or more so that the ultrafine fibers are not easily dropped. The ultrafine fibers are preferably continuous fibers.
また、極細繊維を構成する材料は特に限定されるものではないが、例えば、ポリエチレングリコール、部分けん化ポリビニルアルコール、完全けん化ポリビニルアルコール、ポリビニルピロリドン、ポリ乳酸、ポリグリコール酸、ポリアクリロニトリル、ポリスチレン、ポリアミド、ポリイミド、ポリエチレンやポリプロピレンなどのポリオレフィンなどの有機材料、あるいは石英ガラスなどの無機材料を挙げることができる。なお、極細繊維は単一材料から構成されている必要はなく、二種類以上の材料から構成されていても良い。 The material constituting the ultrafine fiber is not particularly limited, but for example, polyethylene glycol, partially saponified polyvinyl alcohol, fully saponified polyvinyl alcohol, polyvinyl pyrrolidone, polylactic acid, polyglycolic acid, polyacrylonitrile, polystyrene, polyamide, Mention may be made of organic materials such as polyimide, polyolefins such as polyethylene and polypropylene, and inorganic materials such as quartz glass. In addition, the ultrafine fiber does not need to be comprised from the single material, and may be comprised from two or more types of materials.
本発明の極細繊維集合体層は上述のような極細繊維から構成されているが、極細繊維は束状になく、極細繊維が分散した状態にあるのが好ましい。これは、極細繊維が束状に集合した状態にあると、平均繊維径が小さいにもかかわらず、太い繊維と大差がなく、濾過性能が劣る傾向があるためである。 The ultrafine fiber assembly layer of the present invention is composed of the ultrafine fibers as described above, but the ultrafine fibers are preferably not in a bundle shape and are in a state where the ultrafine fibers are dispersed. This is because, when the ultrafine fibers are in a bundled state, the average fiber diameter is small, but there is no great difference from thick fibers, and the filtration performance tends to be inferior.
このような極細繊維集合体層は静電紡糸法により製造されたものである。このように静電紡糸法により製造された極細繊維集合体層は十分な強度を有するため、各種フィルタへの加工性に優れている。この静電紡糸法とは従来公知の方法であり、ノズル等から供給した紡糸溶液に対して電界を作用させることにより延伸して繊維化する方法である。 Such an ultrafine fiber assembly layer is manufactured by an electrospinning method. Since the ultrafine fiber aggregate layer produced by the electrostatic spinning method has sufficient strength, it is excellent in processability to various filters. This electrostatic spinning method is a conventionally known method, and is a method of drawing and fiberizing by applying an electric field to a spinning solution supplied from a nozzle or the like.
より具体的には、まず、紡糸溶液を用意する。この紡糸溶液は極細繊維構成材料を溶解させた溶液である。例えば、ポリエチレングリコール、部分けん化ポリビニルアルコール、完全けん化ポリビニルアルコール、ポリビニルピロリドン、ポリ乳酸、ポリグリコール酸、ポリアクリロニトリル、ポリスチレン、ポリアミド、ポリエチレンやポリプロピレンなどのポリオレフィンなどの有機高分子を溶解させた溶液、或いは金属アルコキシドを加水分解した曳糸性のゾル溶液を使用することができる。これら例示以外の材料を溶解させた紡糸溶液も使用可能であり、例示以外の材料も含めて、二種類以上の材料を溶解させた紡糸溶液も用いることができる。 More specifically, first, a spinning solution is prepared. This spinning solution is a solution in which an ultrafine fiber constituent material is dissolved. For example, polyethylene glycol, partially saponified polyvinyl alcohol, fully saponified polyvinyl alcohol, polyvinyl pyrrolidone, polylactic acid, polyglycolic acid, polyacrylonitrile, polystyrene, polyamide, a solution in which an organic polymer such as polyolefin such as polyethylene or polypropylene is dissolved, or A spinnable sol solution obtained by hydrolyzing a metal alkoxide can be used. Spinning solutions in which materials other than those exemplified above are dissolved can also be used, and spinning solutions in which two or more kinds of materials including those other than those exemplified are dissolved can also be used.
紡糸溶液の溶媒は極細繊維構成材料によって異なり、特に限定するものではないが、例えば、水、アセトン、メタノール、エタノール、エタノール、プロパノール、イソプロパノール、トルエン、ベンゼン、シクロヘキサン、シクロヘキサノン、テトラヒドロフラン、ジメチルスルホキシド、１，４−ジオキサン、四塩化炭素、塩化メチレン、クロロホルム、ピリジン、トリクロロエタン、Ｎ，Ｎ−ジメチルホルムアミド、Ｎ，Ｎ−ジメチルアセトアミド、Ｎ−メチル−２−ピロリドン、エチレンカーボネート、ジエチルカーボネート、プロピレンカーボネート、アセトニトリルなどを挙げることができる。これらの例示以外の溶媒も使用可能であり、例示以外の溶媒も含めて、２種以上の溶媒を用いた混合溶液も使用することができる。 The solvent of the spinning solution varies depending on the ultrafine fiber constituent material and is not particularly limited. For example, water, acetone, methanol, ethanol, ethanol, propanol, isopropanol, toluene, benzene, cyclohexane, cyclohexanone, tetrahydrofuran, dimethyl sulfoxide, 1 , 4-dioxane, carbon tetrachloride, methylene chloride, chloroform, pyridine, trichloroethane, N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, ethylene carbonate, diethyl carbonate, propylene carbonate, acetonitrile And so on. Solvents other than those exemplified above can also be used, and mixed solutions using two or more solvents including solvents other than those exemplified can also be used.
このような紡糸溶液をノズルへ供給し、ノズルから押し出すとともに、押し出した紡糸溶液に電界を作用させて極細繊維化する。この紡糸溶液の押し出し方向は特に限定するものではないが、紡糸溶液の滴下が生じにくいように、ノズルからの押し出し方向と重力の作用方向とが一致しないのが好ましい。特には、重力の作用方向と反対方向又は重力の作用方向と直角方向に紡糸溶液を押し出すのが好ましい。 Such a spinning solution is supplied to a nozzle and extruded from the nozzle, and an electric field is applied to the extruded spinning solution to form an ultrafine fiber. The direction of extrusion of the spinning solution is not particularly limited, but it is preferable that the direction of extrusion from the nozzle does not coincide with the direction of gravity so that the spinning solution does not easily drop. In particular, it is preferable to extrude the spinning solution in a direction opposite to the direction of gravity or in a direction perpendicular to the direction of gravity.
この紡糸溶液を押し出すノズルの直径は、極細繊維の平均繊維径によって変化するが、極細繊維の平均繊維径を０．５μｍ未満とすることができるように、ノズルの直径（内径）は０．１〜２．０ｍｍ程度であるのが好ましい。 The diameter of the nozzle for extruding this spinning solution varies depending on the average fiber diameter of the ultrafine fibers, but the nozzle diameter (inner diameter) is 0.1 so that the average fiber diameter of the ultrafine fibers can be less than 0.5 μm. It is preferable that it is about -2.0 mm.
また、ノズルは金属製であっても、非金属製であっても良い。ノズルが金属製であればノズルを一方の電極として使用することができ、ノズルが非金属製である場合には、ノズルの内部に電極を設置することにより、押し出した紡糸溶液に電界を作用させることができる。 The nozzle may be made of metal or non-metal. If the nozzle is made of metal, the nozzle can be used as one electrode. If the nozzle is made of non-metal, an electric field is applied to the extruded spinning solution by installing an electrode inside the nozzle. be able to.
このようなノズルから紡糸溶液を押し出した後、押し出した紡糸溶液に電界を作用させることにより延伸して極細繊維化する。この電界は、極細繊維の平均繊維径、ノズルと極細繊維を集積する捕集体との距離、紡糸溶液の溶媒、紡糸溶液の粘度などによって変化するため、特に限定するものではないが、極細繊維の平均繊維径を０．５μｍ未満とするには、０．２〜５ｋＶ／ｃｍであるのが好ましい。印加する電界が大きければ、その電界値の増加に応じて極細繊維の平均繊維径が小さくなる傾向があるが、５ｋＶ／ｃｍを超えると、空気の絶縁破壊が生じやすいので好ましくない。また、０．２ｋＶ／ｃｍ未満になると、繊維形状となりにくい。 After extruding the spinning solution from such a nozzle, the extruded spinning solution is stretched by applying an electric field to form ultrafine fibers. This electric field varies depending on the average fiber diameter of the ultrafine fibers, the distance between the nozzle and the collector for collecting the ultrafine fibers, the solvent of the spinning solution, the viscosity of the spinning solution, and the like. In order to make the average fiber diameter less than 0.5 μm, it is preferably 0.2 to 5 kV / cm. If the electric field to be applied is large, the average fiber diameter of the ultrafine fibers tends to decrease as the electric field value increases, but if it exceeds 5 kV / cm, air breakdown tends to occur, which is not preferable. Moreover, if it is less than 0.2 kV / cm, it is difficult to form a fiber shape.
前述のように押し出した紡糸溶液に電界を作用させることにより、紡糸溶液に静電荷が蓄積され、捕集体側の電極（後述）によって電気的に引張られ、引き伸ばされて極細繊維化する。電気的に引き伸ばしているため、繊維が捕集体に近づくにしたがって、電界により繊維の速度が加速され、平均繊維径のより小さい極細繊維となる。また、溶媒の蒸発によって細くなり、静電気密度が高まり、その電気的反発力によって分裂し、更に平均繊維径の小さい極細繊維になると考えている。 By applying an electric field to the extruded spinning solution as described above, an electrostatic charge is accumulated in the spinning solution, and is electrically pulled and stretched by an electrode (described later) on the collector side to form an ultrafine fiber. Since the fibers are electrically stretched, the speed of the fibers is accelerated by the electric field as the fibers approach the collector, resulting in ultrafine fibers having a smaller average fiber diameter. In addition, it is thought that it becomes thin by evaporation of the solvent, the electrostatic density is increased, it is split by the electric repulsive force, and it becomes an ultrafine fiber having a smaller average fiber diameter.
このような電界は、例えば、ノズル（金属製ノズルの場合にはノズル自体、ガラスや樹脂などの非金属製ノズルの場合にはノズルの内部の電極）と捕集体との間に電位差を設けることによって、作用させることができる。例えば、ノズルに電圧を印加するとともに捕集体をアースすることによって電位差を設けることができるし、逆に、捕集体に電圧を印加するとともにノズルをアースすることによって電位差を設けることもできる。なお、電圧を印加する装置は特に限定されるものではないが、直流高電圧発生装置を使用できるほか、ヴァン・デ・グラフ起電機を用いることもできる。また、印加電圧は前述のような電界強度とすることができるのであれば良く、特に限定するものではないが、５〜５０ＫＶ程度であるのが好ましい。 For example, such an electric field provides a potential difference between a nozzle (in the case of a metal nozzle, the nozzle itself, in the case of a non-metallic nozzle such as glass or resin, an electrode inside the nozzle) and the collector. Can act. For example, a potential difference can be provided by applying a voltage to the nozzle and grounding the collector, and conversely, a potential difference can be provided by applying a voltage to the collector and grounding the nozzle. The apparatus for applying the voltage is not particularly limited, but a DC high voltage generator can be used, and a Van de Graf electromotive machine can also be used. The applied voltage is not particularly limited as long as the electric field intensity can be set as described above, but is preferably about 5 to 50 KV.
なお、印加する電圧の極性はプラスとマイナスのいずれであっても良い。しかしながら、極細繊維の拡がりを抑制し、孔径が小さく、しかも孔径分布の狭い極細繊維集合体層を形成できるように、ノズル側をプラス電位となるようにするのが好ましい。特に、電圧印加時のコロナ放電を抑制しやすいように、捕集体側の対向電極を接地し、ノズル側をプラスに印加して、ノズル側をプラス電位となるようにするのが好ましい。 Note that the polarity of the applied voltage may be either positive or negative. However, it is preferable to make the nozzle side have a positive potential so that the expansion of the ultrafine fibers can be suppressed, an ultrafine fiber assembly layer having a small pore diameter and a narrow pore diameter distribution can be formed. In particular, it is preferable that the counter electrode on the collector side is grounded, the nozzle side is applied positively, and the nozzle side has a positive potential so that corona discharge during voltage application can be easily suppressed.
次いで、前記繊維化した極細繊維を捕集体上に集積させて極細繊維集合体層を形成できる。この捕集体は極細繊維を捕集できるものであれば良く、特に限定されるものではないが、例えば、金属製や炭素などの導電性材料、又は有機高分子などの非導電性材料からなる、不織布、織物、編物、ネット、平板、ドラム、或いはベルトを使用できる。また、場合によっては水や有機溶媒などの液体を捕集体として使用できる。 Subsequently, the ultrafine fibers that have been made into fibers can be accumulated on the collecting body to form an ultrafine fiber assembly layer. The collector is not particularly limited as long as it can collect ultrafine fibers, and is made of, for example, a conductive material such as metal or carbon, or a non-conductive material such as an organic polymer. Nonwoven fabric, woven fabric, knitted fabric, net, flat plate, drum, or belt can be used. In some cases, a liquid such as water or an organic solvent can be used as a collector.
前述のように捕集体を他方の電極として使用する場合には、捕集体は体積抵抗が１０９Ω以下の導電性材料（例えば、金属製）からなるのが好ましい。一方、ノズル側から見て、捕集体よりも後方に対向電極として導電性材料を配置する場合には、捕集体は必ずしも導電性材料である必要はない。後者のように、捕集体よりも後方に対向電極を配置する場合、捕集体と対向電極とは接触していても良いし、離間していても良い。 As described above, when the collector is used as the other electrode, the collector is preferably made of a conductive material (for example, made of metal) having a volume resistance of 10 9 Ω or less. On the other hand, when the conductive material is disposed as the counter electrode behind the collector as viewed from the nozzle side, the collector does not necessarily need to be a conductive material. As in the latter case, when the counter electrode is disposed behind the collector, the collector and the counter electrode may be in contact with each other or may be separated from each other.
本発明の濾過材は上述のような極細繊維集合体層に加えて、平均繊維径が０．５μｍ以上、５μｍ以下の細繊維集合体層を備えていることによって、濾過寿命の長い濾過材であることができる。これは、細繊維集合体層で、ある程度の粒子を濾過した後に、極細繊維集合体層で残りの粒子を濾過させることができ、極細繊維集合体層にかかる負荷を低減できるためである。つまり、細繊維集合体層は、濾過時におけるプレフィルタとして機能させることができる。 In addition to the ultrafine fiber aggregate layer as described above, the filter medium of the present invention is provided with a fine fiber aggregate layer having an average fiber diameter of 0.5 μm or more and 5 μm or less. Can be. This is because after a certain amount of particles are filtered by the fine fiber assembly layer, the remaining particles can be filtered by the ultrafine fiber assembly layer, and the load on the ultrafine fiber assembly layer can be reduced. That is, the fine fiber assembly layer can function as a prefilter during filtration.
この細繊維集合体層の平均繊維径は、濾過時の圧力損失が小さいように、０．５μｍ以上であり、より好ましくは０．６μｍ以上である。他方、比較的大きな粒子や微生物を濾過でき、極細繊維集合体層への負荷が大きくなって濾過寿命が短くならないように、５μｍ以下であり、３μｍ以下であるのがより好ましい。 The average fiber diameter of the fine fiber aggregate layer is 0.5 μm or more, and more preferably 0.6 μm or more so that the pressure loss during filtration is small. On the other hand, it is 5 μm or less and more preferably 3 μm or less so that relatively large particles and microorganisms can be filtered and the load on the ultrafine fiber assembly layer is increased and the filtration life is not shortened.
細繊維集合体層を構成する細繊維の繊維長は特に限定するものではないが、細繊維の脱落が発生しにくいように、０．１ｍｍ以上であるのが好ましく、特に、細繊維が連続繊維であるのが好ましい。 The fiber length of the fine fibers constituting the fine fiber assembly layer is not particularly limited, but is preferably 0.1 mm or more so that the fine fibers are not easily dropped off. In particular, the fine fibers are continuous fibers. Is preferred.
また、細繊維を構成する材料は特に限定されるものではないが、極細繊維と全く同様の材料から構成することができる。細繊維集合体層も極細繊維集合体層と同様の理由で、細繊維は束状になく、細繊維が分散した状態にあるのが好ましい。 Moreover, the material which comprises a fine fiber is not specifically limited, However, It can comprise from the completely same material as an ultrafine fiber. For the same reason as the ultrafine fiber aggregate layer, the fine fiber aggregate layer is preferably not in the form of a bundle but in a state in which the fine fibers are dispersed.
このような細繊維集合体層は平均繊維径が０．５μｍ以上、５μｍ以下の細繊維からなる限り、特に限定するものではないが、例えば、湿式法、メルトブロー法、静電紡糸法により形成することができる。特に、細繊維集合体層も静電紡糸法により形成すると、濾過材が更に十分な強度を有し、各種フィルタへの加工性に優れているため好適である。また、極細繊維集合体層と細繊維集合体層とが同一の方法で作製されるため、極細繊維集合体層と細繊維集合体層との親和性が高く、層剥離が生じにくい。更に、極細繊維集合体層上に、静電紡糸法により形成した細繊維を集積させて細繊維集合体層を形成するか、静電紡糸法により細繊維集合体層を形成した後に、静電紡糸法により形成した極細繊維を集積させて極細繊維集合体層を形成することにより、連続して本発明の濾過材を製造できるため、製造工数を削減することができる。 Such a fine fiber aggregate layer is not particularly limited as long as it consists of fine fibers having an average fiber diameter of 0.5 μm or more and 5 μm or less. For example, it is formed by a wet method, a melt blow method, or an electrostatic spinning method. be able to. In particular, when the fine fiber aggregate layer is also formed by an electrospinning method, the filter medium has a further sufficient strength and is excellent in processability to various filters. Moreover, since the ultrafine fiber assembly layer and the fine fiber assembly layer are produced by the same method, the affinity between the ultrafine fiber assembly layer and the fine fiber assembly layer is high, and delamination hardly occurs. Furthermore, the fine fibers formed by the electrostatic spinning method are accumulated on the ultrafine fiber assembly layer to form the fine fiber assembly layer, or after forming the fine fiber assembly layer by the electrostatic spinning method, By collecting the ultrafine fibers formed by the spinning method to form the ultrafine fiber assembly layer, the filter medium of the present invention can be continuously produced, so that the number of production steps can be reduced.
なお、静電紡糸法により細繊維集合体層を形成する場合には、例えば、ノズル直径を太くする、電界強度を弱くする、紡糸溶液の濃度を濃くする、及び／又は静電紡糸を行う紡糸空間における相対湿度を、極細繊維集合体層を製造する際の紡糸空間における相対湿度よりも高く設定する、などのように条件を変更して０．５μｍ以上、５μｍ以下の細繊維を紡糸すること以外は、極細繊維集合体層と全く同様にして形成することができる。 In the case where the fine fiber assembly layer is formed by the electrospinning method, for example, the spinning is performed by increasing the nozzle diameter, decreasing the electric field strength, increasing the concentration of the spinning solution, and / or performing the electrospinning. Spinning fine fibers of 0.5 μm or more and 5 μm or less by changing the conditions such as setting the relative humidity in the space to be higher than the relative humidity in the spinning space when manufacturing the ultrafine fiber assembly layer Except for the above, it can be formed in the same manner as the ultrafine fiber assembly layer.
本発明の濾過材は上述のような極細繊維集合体層と細繊維集合体層とを備えているが、これら層以外に、湿式不織布層、乾式不織布層、スパンボンド不織布層、織物層、或いは編物層を備えることによって、濾過材の強度を更に高めても良い。 The filter medium of the present invention includes the ultrafine fiber assembly layer and the fine fiber assembly layer as described above, but in addition to these layers, a wet nonwoven fabric layer, a dry nonwoven fabric layer, a spunbond nonwoven fabric layer, a fabric layer, or By providing a knitted layer, the strength of the filter medium may be further increased.
本発明の濾過材は、例えば、極細繊維集合体層と細繊維集合体層とを別々に製造した後に、例えば、カレンダー等で圧力を加えて、一体化して製造することができる。なお、濾過材の空隙が減って見掛密度が大きくなり、濾過寿命が短くならないように、圧力はできるだけ低い圧力（５０ｋＰａ以下）を加えるのが好ましい。極細繊維集合体層及び細繊維集合体層は表面積が非常に大きいため、低い圧力で加圧するだけでも一体化させることができる。また、加圧前又は加圧時に加熱しても良いし、加熱しなくても一体化できる。 The filter medium of the present invention can be manufactured by, for example, integrating an ultrafine fiber assembly layer and a fine fiber assembly layer separately, and then, for example, applying pressure with a calendar or the like. Note that it is preferable to apply a pressure as low as possible (50 kPa or less) so that the gap of the filter medium is reduced and the apparent density is increased and the filtration life is not shortened. Since the ultrafine fiber assembly layer and the fine fiber assembly layer have a very large surface area, they can be integrated by simply applying pressure at a low pressure. Moreover, it may be heated before or during pressurization, or can be integrated without heating.
本発明のフィルタは上述のような本発明の濾過材を備えているため、十分な濾過精度を有するとともに、加工性良く製造できるものである。本発明のフィルタは上述のような本発明の濾過材を備えていること以外は、従来のサーフェスフィルタやデプスフィルタと全く同様であることができる。例えば、濾過材の濾過面積を広くするために、濾過材をプリーツ状に加工したフィルタであることができるし、濾過寿命を更に長くするために、本発明の濾過材の極細繊維集合体層よりも孔径が小さいか、本発明の濾過材の細繊維集合体層よりも孔径の大きい濾過材を更に積層したフィルタであることができるし、或いはこれらを組み合わせたフィルタであることもできる。なお、一般的には、比較的濾過量の多い用途ではカートリッジ型に加工し、比較的濾過量の少ない用途ではコマ型に加工する。前者のカートリッジフィルタは、主に製薬、食品、飲料の産業用途に使用し、微生物や微粒子を濾過することができ、後者のコマ型フィルタは、主に実験室等で、無粒子水、無菌水の作製、培地、試薬、染色液など各種溶液の濾過滅菌及び清澄濾過を行うことができる。 Since the filter of the present invention includes the above-described filter medium of the present invention, it has sufficient filtration accuracy and can be manufactured with good workability. The filter of the present invention can be exactly the same as the conventional surface filter and depth filter except that the filter medium of the present invention as described above is provided. For example, in order to increase the filtration area of the filter medium, it can be a filter obtained by processing the filter medium into a pleat shape, and in order to further increase the filter life, the ultrafine fiber assembly layer of the filter medium of the present invention can be used. In addition, the filter may be a filter in which a filter medium having a small pore diameter or a pore diameter larger than that of the fine fiber aggregate layer of the filter medium of the present invention is further laminated, or a filter in which these are combined. In general, it is processed into a cartridge type for applications with a relatively large amount of filtration, and processed into a top type for applications with a relatively small amount of filtration. The former cartridge filter is mainly used for pharmaceutical, food and beverage industrial applications and can filter microorganisms and fine particles. The latter type of filter is mainly used in laboratories, etc. And sterilization and clarification filtration of various solutions such as culture media, reagents and staining solutions.
以下に、本発明の実施例を記載するが、本発明は以下の実施例に限定されるものではない。 Examples of the present invention will be described below, but the present invention is not limited to the following examples.
（実施例１）
（極細繊維集合体層の形成）
数平均分子量１５万のポリアクリロニトリルを、ジメチルホルムアミドに溶解させた、濃度１０ｍａｓｓ％の紡糸溶液を用意した。
Example 1
(Formation of ultrafine fiber assembly layer)
A spinning solution having a concentration of 10 mass% in which polyacrylonitrile having a number average molecular weight of 150,000 was dissolved in dimethylformamide was prepared.
また、シリンジにポリテトラフルオロエチレン製チューブを接続し、更に前記チューブの先端に、内径が０．６ｍｍのステンレス製ノズルを取り付けて、紡糸装置とした。次いで、前記ノズルに高電圧電源を接続した。更に、前記ノズルと対向し、１０ｃｍ離れた位置に、表面に導電フッ素加工を施したステンレス薄板を取り付けたドラム（捕集体、接地）を設置した。 Further, a polytetrafluoroethylene tube was connected to the syringe, and a stainless steel nozzle having an inner diameter of 0.6 mm was attached to the tip of the tube to obtain a spinning device. Next, a high voltage power source was connected to the nozzle. Furthermore, a drum (collector, grounding) having a stainless steel thin plate with conductive fluorine processing on the surface was installed at a position 10 cm away from the nozzle.
次いで、前記紡糸溶液を前記シリンジに入れ、マイクロフィーダーを用いて、重量の作用方向と直角の方向へ押し出す（押し出し量：２．５ｇ／時間）とともに、前記ドラムを一定速度（表面速度：０．９ｍ／分）で回転させながら、前記高電圧電源からノズルに＋１５ＫＶの電圧を印加して、押し出した紡糸溶液に電界を作用させて極細繊維化し、前記ドラムのステンレス薄板上に連続した極細繊維を集積させて極細繊維集合体層を形成した。なお、極細繊維集合体層の形成、つまり静電紡糸は紡糸空間の相対湿度を３０％とした環境下で行った。また、極細繊維集合体層を形成する際に、前記ノズルはドラムの回転方向と直角方向に一定速度（移動速度：２．５ｃｍ／分）で往復揺動させて、極細繊維の分散性を高め、極細繊維集合体層の均一性を高めた。このように、極細繊維は束の状態にはなく、個々の極細繊維が均一に分散した状態にあった。 Next, the spinning solution is put into the syringe, and the micro-feeder is used to extrude in a direction perpendicular to the direction of weight action (amount of extrusion: 2.5 g / hour), and the drum is driven at a constant speed (surface speed: 0. 0). While rotating at 9 m / min), a voltage of +15 KV is applied to the nozzle from the high-voltage power source, and an electric field is applied to the extruded spinning solution to form ultrafine fibers. Continuous ultrafine fibers are formed on the stainless steel thin plate of the drum. The ultrafine fiber assembly layer was formed by accumulating. The formation of the ultrafine fiber assembly layer, that is, electrostatic spinning was performed in an environment where the relative humidity of the spinning space was 30%. When forming the ultrafine fiber assembly layer, the nozzle is reciprocally swung at a constant speed (moving speed: 2.5 cm / min) in the direction perpendicular to the rotation direction of the drum to enhance the dispersibility of the ultrafine fibers. The uniformity of the ultrafine fiber assembly layer was improved. Thus, the ultrafine fibers were not in a bundled state, but the individual ultrafine fibers were uniformly dispersed.
（細繊維集合体層の形成）
数平均分子量５０万のポリアクリロニトリルを、ジメチルホルムアミドに溶解させた、濃度１２ｍａｓｓ％紡糸溶液を用意したこと以外は（極細繊維集合体層の形成）と全く同様にして細繊維集合体層を形成した。この細繊維は連続繊維であり、また、細繊維は束の状態にはなく、個々の細繊維が均一に分散した状態にあった。
(Formation of fine fiber assembly layer)
A fine fiber aggregate layer was formed in exactly the same manner as in (Formation of ultrafine fiber aggregate layer) except that a 12 mass% spinning solution having polyacrylonitrile with a number average molecular weight of 500,000 dissolved in dimethylformamide was prepared. . The fine fibers were continuous fibers, and the fine fibers were not in a bundle state, but the individual fine fibers were uniformly dispersed.
（濾過材の製造）
前記極細繊維集合体層を４枚積層し、更に極細繊維集合体層上に、前記細繊維集合体層を２枚積層した後、ローラプレス機（旭繊維機械工業（株）製、ＪＲ−１０００ＬＴＳ）を用い、温度１３０℃、ゲージ圧４．９ｋＰａ、時間６０秒の条件で加熱加圧して濾過材を製造した。この濾過材の物性は表１に示す通りであった。なお、この濾過材を用いてコマ型フィルタを製造することができ、加工性の優れるものであった。
(Manufacture of filter media)
After laminating 4 sheets of the ultrafine fiber assembly layer and further laminating 2 sheets of the fine fiber assembly layer on the ultrafine fiber assembly layer, a roller press machine (Asahi Textile Machinery Co., Ltd., JR-1000LTS). ) And heated and pressurized under the conditions of a temperature of 130 ° C., a gauge pressure of 4.9 kPa, and a time of 60 seconds to produce a filter medium. The physical properties of this filter medium are as shown in Table 1. A coma filter could be manufactured using this filter material, and the processability was excellent.
（参考例1）
（細繊維集合体層の形成）
ポリプロピレン単繊維（繊維径：２μｍ、繊維長：２ｍｍ）８０ｍａｓｓ％と、ポリプロピレン（芯）／ポリエチレン（鞘）からなる芯鞘繊維（繊度：０．８ｄｔｅｘ、繊維長：５ｍｍ）２０ｍａｓｓ％とからなるスラリーを抄紙し、乾燥した後、温度１４０℃で加熱することにより、前記芯鞘繊維の鞘成分を融着させた湿式不織布を製造し、この湿式不織布を細繊維集合体層とした。
( Reference Example 1 )
(Formation of fine fiber assembly layer)
Slurry composed of 80% by mass of single polypropylene fiber (fiber diameter: 2 μm, fiber length: 2 mm) and 20% by mass of core-sheath fiber (fineness: 0.8 dtex, fiber length: 5 mm) made of polypropylene (core) / polyethylene (sheath). After the paper was made and dried, a wet nonwoven fabric in which the sheath component of the core-sheath fiber was fused was manufactured by heating at 140 ° C., and this wet nonwoven fabric was used as a fine fiber assembly layer.
（濾過材の製造）
実施例１と同じ極細繊維集合体層を４枚積層し、更に極細繊維集合体層上に、前記細繊維集合体層を１枚積層した後、実施例１と同様の条件で濾過材を製造した。この濾過材の物性は表１に示す通りであった。なお、この濾過材を用いてコマ型フィルタを製造することができ、加工性の優れるものであった。
(Manufacture of filter media)
Four ultrafine fiber aggregate layers same as those in Example 1 were laminated, and one fine fiber aggregate layer was laminated on the ultrafine fiber aggregate layer, and then a filter medium was produced under the same conditions as in Example 1. did. The physical properties of this filter medium are as shown in Table 1. A coma filter could be manufactured using this filter material, and the processability was excellent.
（参考例2）
（細繊維集合体層の形成）
ポリプロピレン製ペレット（ＭＩ：５００ｇ／１０ｍｉｎ．）を、ダイ温度３２０℃、エアー量１ｍ当り５Ｎｍ３／ｍｉｎ．で紡糸してメルトブロー不織布を製造し、このメルトブロー不織布を細繊維集合体層とした。
( Reference Example 2 )
(Formation of fine fiber assembly layer)
Polypropylene pellets (MI: 500 g / 10 min.) Were applied at a die temperature of 320 ° C. and an air amount of 5 Nm 3 / min. The melt-blown nonwoven fabric was produced by spinning with, and this melt-blown nonwoven fabric was used as a fine fiber assembly layer.
（濾過材の製造）
実施例１と同じ極細繊維集合体層を４枚積層し、更に極細繊維集合体層上に、前記細繊維集合体層を１枚積層した後、実施例１と同様の条件で濾過材を製造した。この濾過材の物性は表１に示す通りであった。なお、この濾過材を用いてコマ型フィルタを製造することができ、加工性の優れるものであった。
(Manufacture of filter media)
Four ultrafine fiber aggregate layers same as those in Example 1 were laminated, and one fine fiber aggregate layer was laminated on the ultrafine fiber aggregate layer, and then a filter medium was produced under the same conditions as in Example 1. did. The physical properties of this filter medium are as shown in Table 1. A coma filter could be manufactured using this filter material, and the processability was excellent.
（比較例１）
（第１細繊維集合体層の形成）
数平均分子量１５万のポリアクリロニトリルを、ジメチルホルムアミドに溶解させた、濃度１５ｍａｓｓ％紡糸溶液を用意したこと以外は実施例１と全く同様にして第１細繊維集合体層を形成した。この第１細繊維集合体層を構成する繊維は連続繊維であり、また、細繊維は束の状態にはなく、個々の細繊維が均一に分散した状態にあった。
(Comparative Example 1)
(Formation of first fine fiber assembly layer)
A first fine fiber aggregate layer was formed in the same manner as in Example 1 except that a 15 mass% spinning solution having a number average molecular weight of 150,000 dissolved in dimethylformamide was prepared. The fibers constituting the first fine fiber assembly layer were continuous fibers, and the fine fibers were not in a bundle state, but the individual fine fibers were uniformly dispersed.
（濾過材の製造）
前記第１細繊維集合体層を４枚積層し、更に第１細繊維集合体層上に、実施例１と同じ細繊維集合体層（第２細繊維集合体層）を２枚積層した後、実施例１と同様の条件で濾過材を製造した。この濾過材の物性は表１に示す通りであった。
(Manufacture of filter media)
After laminating four sheets of the first fine fiber aggregate layer and further laminating two fine fiber aggregate layers (second fine fiber aggregate layer) same as Example 1 on the first fine fiber aggregate layer A filter medium was produced under the same conditions as in Example 1. The physical properties of this filter medium are as shown in Table 1.
（比較例２）
実施例１と同じ極細繊維集合体層を６枚積層した後、実施例１と同様の条件で濾過材を製造した。この濾過材の物性は表１に示す通りであった。
(Comparative Example 2)
After six ultrafine fiber aggregate layers as in Example 1 were laminated, a filter medium was produced under the same conditions as in Example 1. The physical properties of this filter medium are as shown in Table 1.
（比較例３）
（太繊維集合体層の形成）
ポリプロピレン製ペレット（ＭＩ：５００ｇ／１０ｍｉｎ．）を、ダイ温度２７０℃、エアー量１ｍ当り４Ｎｍ３／ｍｉｎ．で紡糸してメルトブロー不織布を製造し、このメルトブロー不織布を太繊維集合体層とした。
(Comparative Example 3)
(Formation of thick fiber aggregate layer)
Polypropylene pellets (MI: 500 g / 10 min.) Were added at a die temperature of 270 ° C. and 4 Nm 3 / min. The melt-blown nonwoven fabric was produced by spinning with a thick fiber aggregate layer.
（濾過材の製造）
実施例１と同じ極細繊維集合体層を４枚積層し、更に極細繊維集合体層上に、前記太繊維集合体層を２枚積層した後、実施例１と同様の条件で濾過材を製造した。この濾過材の物性は表１に示す通りであった。
(Manufacture of filter media)
Four ultrafine fiber aggregate layers as in Example 1 were laminated, and two thick fiber aggregate layers were further laminated on the ultrafine fiber aggregate layer, and then a filter medium was produced under the same conditions as in Example 1. did. The physical properties of this filter medium are as shown in Table 1.
（濾過精度及び濾過寿命の測定）
アルミナ球形微粒子（株式会社マイクロン製、平均粒子径：１μｍ）を純水に分散させ、均一に攪拌して試験液とした。そして、この試験液に含まれる粒子数をパーティクルセンサー（ＬｉＱｕｉｌａｚ ＳＯ３：ＰＭＳ社製）を用いて、０．４〜１．０μｍの粒子数を測定した（Ａ）。
(Measurement of filtration accuracy and filtration life)
Alumina spherical fine particles (manufactured by Micron Co., Ltd., average particle size: 1 μm) were dispersed in pure water and stirred uniformly to obtain a test solution. Then, the number of particles contained in this test solution was measured using a particle sensor (LiQuilaz SO3: PMS) (A).
実施例１と参考例1〜2及び比較例１〜３の各濾過材を直径２５ｍｍに打ち抜き、細繊維集合体層側（比較例１の場合には第２細繊維集合体層側、比較例３の場合には太繊維集合体層側）がインレット側となるようにサンプルホルダーにセットした後、前記試験液を攪拌しながら、流量１００ｍＬ／分で通水させた。
The filter media of Example 1 , Reference Examples 1 to 2 and Comparative Examples 1 to 3 were punched out to a diameter of 25 mm, and the fine fiber assembly layer side (in the case of Comparative Example 1, the second fine fiber assembly layer side, comparative example) In the case of 3, the thick fiber aggregate layer side) was set on the sample holder so as to be on the inlet side, and then the test solution was allowed to flow at a flow rate of 100 mL / min while stirring.
そして、サンプルホルダーの前に圧力計を設置し、濾過開始直後、及び圧力が４００ＫＰａに達したときの濾液を採取し、この濾液に含まれる粒子数をパーティクルセンサー（ＬｉＱｕｉｌａｚ ＳＯ３）を用いて、０．４〜１．０μｍの粒子数を測定した（Ｂ）。 Then, a pressure gauge is installed in front of the sample holder, and the filtrate is collected immediately after the start of filtration and when the pressure reaches 400 KPa, and the number of particles contained in the filtrate is measured using a particle sensor (LiQuilaz SO3). The number of particles of 4-1.0 μm was measured (B).
その後、粒子捕捉性能（Ｅ）を次式により算出した。また、圧力が４００ＫＰａに達するまでの試験液の濾過量を測定し、各濾過材の濾過寿命とした。粒子捕捉性能（Ｅ）の値が大きい程、濾過精度に優れ、濾過量が多い程、濾過寿命が長いことを意味している。これらの結果は表１に示す通りであった。
Ｅ＝ｌｏｇ１０（Ａ／Ｂ）
ここで、Ｅは粒子捕捉性能、Ａは濾過前の粒子数（単位：個／ｍＬ）、Ｂは濾過後の粒子数（単位：個／ｍＬ）をそれぞれ意味する。
Thereafter, the particle trapping performance (E) was calculated by the following formula. Moreover, the filtration amount of the test liquid until a pressure reaches to 400 KPa was measured, and it was set as the filtration life of each filter medium. The larger the value of the particle trapping performance (E), the better the filtration accuracy, and the greater the amount of filtration, the longer the filtration life. These results were as shown in Table 1.
E = log 10 (A / B)
Here, E means the particle capturing performance, A means the number of particles before filtration (unit: pieces / mL), and B means the number of particles after filtration (unit: pieces / mL).
表１から明らかなように、本発明の濾過材は濾過精度、濾過寿命ともに優れている。これに対して、比較例１は濾過寿命は長いものの、濾過精度の悪いものであった。これは本発明の極細繊維集合体層に相当する層を備えていないためであると考えられた。また、比較例２及び比較例３は濾過精度は優れているものの、濾過寿命は本発明の濾過材の半分程度であった。これは本発明の細繊維集合体層に相当する層を備えておらず、粒子を保持できなかったか（比較例２）、粒子が素通りして極細繊維集合体層への負荷が大きかったため（比較例３）と考えられた。
As is clear from Table 1, the filtration medium of the present invention is excellent in both filtration accuracy and filtration life. In contrast, Comparative Example 1 had a long filtration life but poor filtration accuracy. This was considered to be because the layer corresponding to the ultrafine fiber assembly layer of the present invention was not provided. Moreover, although the comparative example 2 and the comparative example 3 were excellent in the filtration precision, the filtration lifetime was about half of the filter material of this invention. This is because a layer corresponding to the fine fiber assembly layer of the present invention was not provided and the particles could not be retained (Comparative Example 2), or the particles passed through and the load on the ultrafine fiber assembly layer was large (Comparison) Example 3).
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