JP2004089853A

JP2004089853A - Filter medium for filtering liquid

Info

Publication number: JP2004089853A
Application number: JP2002254459A
Authority: JP
Inventors: Mitsuo Yoshida; 吉田　光男; Masanobu Matsuoka; 松岡　昌伸
Original assignee: Mitsubishi Paper Mills Ltd
Current assignee: Mitsubishi Paper Mills Ltd
Priority date: 2002-08-30
Filing date: 2002-08-30
Publication date: 2004-03-25
Anticipated expiration: 2022-08-30
Also published as: JP3784354B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a filter medium for filtering liquid with a prolonged life which filters a machining liquid containing chips with a relatively coarse particle diameter produced from a work to be cut. <P>SOLUTION: The filter medium is formed by integration of the filter medium layer and a support layer. The filter medium layer contains fibrillated organic fibers of <0.5-5mass% with a fiber diameter of ≤1μm and organic fibers with a fiber diameter of ≥1μm, and a part or the whole of the organic fibers with a fiber diameter of ≥1μm is treated with fibrous organic binder. This medium layer has an average void diameter of 10-50μm and a basis weight of 5-50g/m<SP>2</SP>. The support layer is composed of organic fibers with a fiber diameter of ≥8μm containing at least one kind of synthetic fibers of polyolefin, polyamide, polyester, acryl, vinylon and vinyl chloride vinyl acetate. A part of the synthetic fiber contains at least one kind of fibrous organic binders of polyester, polyolefin, and vinyl chloride vinyl acetate. This support layer has a basis weight of 20-150g/m<SP>2</SP>. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、液体中に含有される粒子を効率良く除去し、清浄な液体を得るための液体濾過用フィルター濾材に関するものである。更に詳しくは、金属の型彫、切断加工等に使用されている放電加工機の加工液中に含まれる加工クズやＩＣ生産における基板のウエハの切断、研磨、エッチング等の工程で使用される超純水中に含まれる加工クズを効率良く除去し清浄な液体を得るための濾材、及び自動車用エンジンオイル、燃料等各種液体濾過用のフィルター濾材に関するものである。特に、多様化する放電加工機に対応して、主に下記の▲１▼、▲２▼の用途に適したものである。
▲１▼濾材の厚みが薄くフィルターユニットに入れる濾材面積が多く取れる。
▲２▼被切削物から発生する削り屑の粒径が比較的粗い加工液に適用する。
【０００２】
【従来の技術】
従来、放電加工機やＩＣ生産工程で使用されている液体濾過用フィルターや自動車用エンジンオイル、燃料等各種液体濾過用のフィルターには、天然パルプと有機繊維の混抄シートにフェノール樹脂等を含浸処理したシート、ポリエステル不織布（スパンボンド）等が使用されているが、濾過効率が低く、ライフが短い等の問題がある。
【０００３】
即ち、従来の濾材は濾材内部で粒子を捕捉する機能であり、ライフを延ばすために比較的粗い濾材を使用しており、濾材内部に粒子が入り濾材の空隙をある程度埋める迄は目標の濾過効率は得られない。濾材の空隙が埋まると圧損が上昇し液の透過性が悪くなりライフが短くなるか、濾材内部の粒子が濾材内部から流出し効率が悪くなる等の問題がある。
【０００４】
又、高性能のフィルターとしてフッ素樹脂等の多孔質シートがあるが高価なため特殊用途に限定され、放電加工機やＩＣ生産工程のように多量の液体を処理する濾材としては不適である。
【０００５】
これらの問題を解決する方法として、フィブリル化された有機繊維を用いた濾材が開発されている（特開昭５９−９２０１１号公報）。しかしながら、このような繊維を単独で用いて通常の湿式抄紙法により製造しようとした場合には、ワイヤーから流失が大きく、ワイヤーの目づまりを生じる等の製造上の問題が避けられない。たとえ濾材が得られたとしても、繊維が微細であるために得られる濾材は非常に緻密となり、その結果高い濾過効率は得られるものの濾過抵抗が高く実用に適さない。濾過抵抗を下げようとして比較的径の太いモノフィラメントの繊維を含有した場合には、抄造工程での微細繊維の流失がより多くなり、濾過効率の低下が著しく、十分な性能が得られない。
【０００６】
特開平３−１２２０８号公報では、繊維径が１μｍ以下にフィブリル化された有機繊維、繊維径１〜５μｍの極細有機繊維、及び繊維径５μｍ以上の有機繊維を配合することによって、フィブリル化された有機繊維の凝集を抑え、均質なネットワークを形成し、さらに、カレンダー処理を施して、濾材表面の平滑性を向上させ、表面濾過機構を有している濾材が提案されている。この濾材は表面濾過機構であるために、濾過性能、ライフは非常に良好である。しかし、濾材の厚みは非常に薄く、腰（硬さ）がないために、ひだ折加工ができない。さらに湿潤強度が非常に弱いために、放電加工機用フィルター、自動車エンジンオイル用フィルター、自動車燃料用フィルターに使用した場合、液体の圧力で破れてしまう。
【０００７】
又、特開昭６１−２６８３２１号公報、同６１−２６８３２５号公報、同６１−２７５４９５号公報等に密度勾配をつけた２層構成の濾材が例示されているが、これらの濾材は、２層の濾材を組合せることにより濾過効率とライフのバランスをとっており、本発明の濾材表面（濾材層のみ）で濾過性能を得る方法とは基本的に異なったものである。
【０００８】
これらの問題を解決するために、本発明者が出願した特開平０６−１２６１１２号公報の液体濾過用フィルター濾材は濾過効率が高く、且つひだ折加工性が優れ、湿潤強度も強く、現在、有用に活用されているが、放電加工機の多様化や高速化に伴い、使用するワイヤーの直径や加工速度も多様化し、かつライフ重視に対応するために新たな濾材の開発が必要とされてきた。即ち、粗削り加工時に発生する削り屑の粒子径は大きいことから、大きい粒子に対してもライフの長い濾材が求められている。
【０００９】
【発明が解決しようとする課題】
本発明は上記の欠点や問題点を解決し、被切削物から発生する削り屑の粒径が比較的粗い加工液に対してライフの長い液体濾過用濾材を提供することを目的としている。
【００１０】
【課題を解決するための手段】
これらの問題点を解決する方法として、種々の繊維の濾材への応用を検討した結果、今までに無い良好なフィルター特性が得られることを見出し、本発明を完成させた。
【００１１】
即ち、本発明の液体濾過用濾材は、該濾材が、濾材層と支持体層とを一体化してなるものであり、該濾材層が、繊維径が１μｍ以下にフィブリル化された有機繊維０．５以上５質量％未満と繊維径が１μｍ以上の有機繊維を含み、繊維径１μｍ以上の有機繊維の一部又は全部に繊維状有機バインダーを用い、且つ１０〜５０μｍの平均空隙径を有し、５〜５０ｇ／ｍ^２の坪量からなるものであり、該支持体層が、繊維径８μｍ以上の有機繊維で、ポリオレフィン系、ポリアミド系、ポリエステル系、アクリル系、ビニロン系、塩ビ酢酸ビニル系の合成繊維の少なくとも１種類を含み、その一部がポリエステル系、ポリオレフィン系、塩ビ酢酸ビニル系の繊維状有機バインダーの少なくとも１種類を含有し、且つ２０〜１５０ｇ／ｍ^２の坪量からなる液体濾過用濾材である。
さらに、濾材層の坪量と支持体層の坪量との比が１：０．５〜１：１０の範囲であり、濾材層を上流側として使用する液体濾過用濾材である。
また、濾材層と支持体層とが湿式抄紙法により抄き合わせ一体化されている液体濾過用濾材である。
また、繊維径が１μｍ以下にフィブリル化された有機繊維が、芳香族ポリアミド繊維、レーヨン繊維、溶剤紡糸法で製造されたリヨセル繊維、パルプ繊維のいずれか１種以上である液体濾過用濾材である。
【００１２】
【発明の実施の形態】
本発明の液体濾過用濾材は、薄くて表面濾過性能を有する濾材層と、液体の透過性が良く高強度でひだ折り加工性の良い支持体層とを抄合わせ一体化することにより得られる液体濾過用フィルター濾材である。
本発明の濾材に用いられる繊維径が１μｍ以下にフィブリル化された有機繊維としては、例えば、以下に示す方法で加工されたものが挙げられる。
１）合成高分子溶液を該高分子の貧溶媒中にせん断力をかけながら流下させ、繊維状フィブリルを沈澱させる方法（フィブリッド法、特公昭３５−１１８５１号公報）。
２）合成モノマーを重合させながらせん断をかけフィブリルを析出させる方法（重合せん断法、特公昭４７−２１８９８号公報）。
３）二種以上の非相溶性高分子を混合し、溶融押し出し、又は紡糸し、切断後機械的な手段で繊維状にフィブリル化する方法（スプリット法、特公昭３５−９６５１号公報）。
４）二種以上の非相溶性高分子を混合し、溶融押し出し、又は紡糸し、切断後溶剤に侵漬して一方の高分子を溶解し、繊維状にフィブリル化する方法（ポリマーブレンド溶解法、米国特許３、３８２、３０５号）。
５）合成高分子をその溶媒の沸点以上で、且高圧側から低圧側へ爆発的に噴出させた後、繊維状にフィブリル化する方法（フィラシュ紡糸法、特公昭３６−１６４６０号公報）。
６）ポリエステル系高分子に該ポリエステルに非相溶のアルカリ可溶成分をブレンドし、成形後アルカリにより減量後叩解し、繊維状にフィブリル化する方法（アルカリ減量叩解法、特開昭５６−３１５号公報）。
７）ケブラー繊維等の高結晶性、高配向性繊維を適当な繊維長に切断後、水中に分散させ、ホモジナイザー、叩解機等を用いてフィブリル化する方法（特開昭５６−１００８０１号公報、特開昭５９−９２０１１号公報）等の方法によって得られる繊維であり、具体的な例としては、ケブラー繊維を均質化装置でフィブリル化したティアラー４００Ｓ（ダイセル社製）、アルカリ減量叩解法によって得られたポリエステルパルプ、木材パルプを均質化装置でフィブリル化したセリッシュ１００Ｓ（ダイセル社製）、溶剤紡糸法で作製したリヨセル繊維、木材パルプ、その他にナイロン、ポリエチレン、ポリプロピレン等の合成繊維をビーター、ＰＦＩミル、ボールミル、ダイノミル等で叩解した繊維等が挙げられる。
【００１３】
これらフィブリル化された有機繊維の配合量は０．５以上５質量％未満が適当であり、好ましくは１〜４．５質量％である。０．５質量％未満では濾材の平均空隙径が大きくなり十分な捕集効率が得られず、また５質量％を越えると特開平０６−１２６１１２号公報の液体濾過用フィルター濾材に示すように高性能濾過領域となる。
【００１４】
本発明の濾材層に用いられる繊維径が１μｍ以上の有機繊維とは、例えば１〜５μｍのポリエステル繊維、ＰＶＡ繊維、アクリル繊維等の極細繊維が挙げられる。これらの繊維の配合量は５〜７０質量％が適当であり、好ましくは１０〜６０質量％である。５質量％未満では１μｍ以下の微細繊維のワイヤーからの流失が多く十分な濾過効率が得られず、又、湿紙のワイヤーからの剥がれが悪い等の製造上の問題を生じ、又、７０質量％を超えると濾過抵抗が大きくなり実用に適さない。
【００１５】
また、本発明の濾材層に用いられる繊維径１μｍ以上の有機繊維には、上記繊維径１〜５μｍの繊維の他に、繊維径８μｍ以上の有機繊維としてポリオレフィン、ポリアミド、ポリエステル、ポリアクリルアミド、ビニロン等の合成繊維のほか、パルプ、リンター、リント、又はその誘導体等が挙げられ、繊維径１μｍ以上の有機繊維と併用することが望ましい。
【００１６】
本発明に用いられる繊維状有機バインダーは、芯鞘タイプ（コアシェルタイプ）、並列タイプ（サイドバイサイドタイプ）などの複合繊維が挙げられる。例えば、ポリプロピレン（芯）とポリエチレン（鞘）の組み合わせ（商品名：ダイワボウＮＢＦ−Ｈ：大和紡績社製）、ポリプロピレン（芯）とエチレンビニルアルコール（鞘）の組み合わせ（商品名：ダイワボウＮＢＦ−Ｅ：大和紡績社製）、ポリプロピレン（芯）とポリエチレン（鞘）の組み合わせ（商品名：チッソＥＳＣ：チッソ社製）、高融点ポリエステル（芯）と低融点ポリエステル（鞘）の組み合わせ（商品名：メルテイ４０８０：ユニチカ社製）が挙げられる。また、低融点のみで構成される繊維状バインダー（全融タイプ）や、ポリビニルアルコール系のような熱水性バインダーは、濾材の乾燥工程で皮膜を形成し易く、濾過抵抗が大きくなり好ましくないが、特性を阻害しない範囲で使用することはできる。　　繊維状有機バインダーの繊維径は特に限定されないが、３〜５０μｍの範囲であることが好ましく、より好ましくは７〜２０μｍである。
【００１７】
繊維径８μｍ以上の有機繊維の配合量は特に限定しないが、１０〜９５質量％であるが、これらのうち繊維状有機バインダーの配合量は全繊維量の２０〜６０質量％が適当であり、好ましくは３０〜５０質量％である。２０質量％未満では濾材の表面強度が弱く、フィルターユニットの加工性の点で問題があり、６０質量％を超えると濾過抵抗が大きくなり実用上問題がある。又、繊維径５μｍ以上の有機繊維が７０質量％を超えるとシートの平均空隙径が大きくなり、濾過性能が悪くなる。
【００１８】
本発明の濾材層の坪量は５〜５０ｇ／ｍ^２が適当であり、好ましくは１０〜４０ｇ／ｍ^２である。５ｇ／ｍ^２未満ではピンホール等により信頼性の点で問題がある。５０ｇ／ｍ^２を越えると濾過抵抗が上昇し抄紙性が悪くなり、又、表面濾過の点から坪量を増やしても効果は期待できず、コスト面でも問題がある。
【００１９】
本発明の濾材層の平均空隙径は表面濾過の点で１０〜５０μｍが適当であり、好ましくは１２〜４０μｍである。液体中の比較的粗い粒子（平均粒子径：２〜１０ミクロン、粒子径測定器：マイクロトラックにて測定）を対象とすることから平均ポア径が１０μｍ未満では過剰なスペックとなり、平均空隙径が５０μｍを超えると粒子が濾材にトラップされることなく流出してしまう。また、濾材層と支持体層合わせた濾材全体の平均空隙径は、濾材層のみの空隙径より若干小さく７〜４５μｍである。
最大空隙径については特に限定しないが、濾材の均質性の点で最大空隙径は平均空隙径の３倍以下が好ましい。
【００２０】
本発明の支持体に用いられる繊維径が８μｍ以上の有機繊維とは、ポリオレフィン、ポリアミド、ポリエステル、ポリアクリルアミド、ビニロン等の合成繊維が挙げられ、少なくとも１種類を含有する支持体である。これらの有機繊維の特徴としては、シートに腰を持たせる点で繊維強度が強く、剛直な繊維が好ましい。又、濾材を通過した微細粒子の付着によるライフの低下を抑える点で、皮膜を形成しない棒状（断面の形状が円形、楕円形、繭形等）の形態をした繊維が好ましい。他の使用できる繊維としては、皮膜の少ない未叩解の天然パルプ、麻パルプ、コットンリンター、リント、また、再生繊維としては、レーヨン、キュプラ、リヨセル繊維が、半合成繊維としては、アセテート、トリアセテート、プロミックスが、合成繊維としては、ナイロン、アクリル、ビニロン、ビニリデン、ポリ塩化ビニル、ポリエステル、ポリエチレン、ポリプロピレン、ベンゾエート、ポリクラール、フェノール系などの繊維が挙げられる。上記の繊維の他に、植物繊維として、針葉樹パルプ、広葉樹パルプなどの木材パルプや藁パルプ、竹パルプ、ケナフパルプなどの木本類、草本類を含むものとする。さらに、古紙、損紙などから得られるパルプ繊維も含まれる。
【００２１】
支持体層の繊維状有機バインダーの配合量は１０〜７０質量％の範囲が適当であり、１０質量％未満では抄紙後樹脂バインダーを含浸する工程で必要な耐水強度が得られない。又、７０質量％を超えると低融点のバインダーの皮膜が多くなり、フィルター濾材全体の圧力損失が高くなり、ライフが短くなる。
【００２２】
支持体に用いる繊維の繊維径は８μｍ以上が適当であり、繊維径が８μｍ未満では支持体の濾過抵抗が大きくなり、液体の透過性が悪くなる。しかし、抄造安定性を高めるために８μｍ以下の繊維を混合する事はできる。繊維径の上限は特に限定しないが、抄紙性等を考慮すると繊維径は５０μｍ以下が好ましい。
【００２３】
本発明の支持体の坪量は２０〜１５０ｇ／ｍ^２が適当であり、好ましくは３０〜１００ｇ／ｍ^２である。２０ｇ／ｍ^２未満ではひだ折り加工性が悪く、１５０ｇ／ｍ^２を超えると厚みが増し、ユニットに納まる濾材面積が小さくなり、又濾過抵抗が大きくなり実用上問題があると共にコスト面からも好ましくない。
【００２４】
本発明の支持体に使用する繊維は、水、及び油等による膨潤の少ない合成繊維を主体としているために、湿潤引張強度が強く、液体の圧力による濾材の破れが無い。
【００２５】
本発明のフィルター濾材は、一般紙や湿式不織布を製造するための抄紙機、例えば長網抄紙機、円網抄紙機、傾斜ワイヤー式抄紙機等を２機組合せたコンビネーションマシンによる抄合わせ等により製造される。組合せは同一タイプの抄紙機の組合せ、異種の抄紙機の組合せどちらでも可能である。
【００２６】
本発明の濾材の強度、腰（硬さ）を上げる目的で各種バインダーを含浸、コーティング、スプレー方法等で付与することが可能である。用いられるバインダーは、アクリル系、酢酸ビニル系、エポキシ系、ウレタン系、合成ゴム系、塩化ビニリデン系等のラテックス、ＰＶＡ、澱粉、フェノール樹脂等を単独、又は２種類以上を併用できる。
【００２７】
本発明の液体濾過用濾材に付与されるバインダーの量は、該フィルター濾材に対して３０質量％以下が適当であり、好ましくは２０質量％以下である。３０質量％を超えるとフィルター濾材の濾過抵抗が大きくなり、実用上問題がある。該フィルター濾材にバインダーを付与する方法としては、特に限定はしないが、サイズプレス、タブサイズ、スプレー含浸、内添等が挙げられる。
【００２８】
又、必要に応じ濾材の特性を阻害しない範囲で撥水剤、分散剤、歩留り向上剤、染料等の添加剤を配合することができる。
【００２９】
【実施例】
以下、本発明を実施例により説明するが、本発明はこれらに何等限定されるものではない。
【００３０】
実施例１
（濾材層の作製）
パルパー分散機が設置されている２ｍ^３の分散タンクに、分散水を１ｍ^３注入した後、ケブラー微細繊維（ティアラー４００Ｓ、ダイセル化学社製）、極細ポリエステル繊維（帝人社製、０．１デシテックス×３ｍｍ、直径約３μｍ）、ポリエステル繊維（帝人社製、０．６デシテックス×５ｍｍ、直径約７μｍ）、繊維状有機バインダーとして熱接着性（芯鞘タイプ）ポリエステル繊維（ユニチカ社製４０８０、２．２デシテックス×５ｍｍ、直径約１５μｍ）を１：２０：２９：５０の繊維配合比率になるように投入し、１０分間分散して水性スラリーを作製し、円網抄紙機を用いて坪量２０ｇ／ｍ^２の濾材層を形成する。
（支持体層の作製）
パルパー分散機が設置された２ｍ^３の分散タンクに、分散水を１ｍ^３注入した後、ＮＢＫＰ（三菱製紙社製）、繊維状有機バインダーとして熱接着性（芯鞘タイプ）ポリエステル繊維（ユニチカ社製４０８０、２．２×５ｍｍ、直径約１５μｍ）を４０：６０の繊維配合比率になるように投入し、３０分間分散して水性スラリーを作製し、円網抄紙機を用いて坪量４５ｇ／ｍ^２の支持体層を形成する。
上記の濾材層と支持体層とを円網抄紙機２機が直列に設置されているコンビネーションマシンで湿紙の状態で抄き合わせて一体化した後、プレス加工し、表面温度１２０℃のシリンダードライヤーで乾燥して６５ｇ／ｍ^２の濾材を作製した。該濾材に市販のアクリル系エマルジョンを固形分で５ｇ／ｍ^２含浸後、乾燥させ液体濾過用濾材を作製した。
【００３１】
実施例２
実施例１の濾材層の繊維配合比率を２．５：２０：２７．５：５０にした以外は、実施例１と同様の方法で液体濾過用濾材を作製した。
【００３２】
実施例３
実施例１の濾材層の繊維配合比率を４．５：２０：２５．５：５０にした以外は、実施例１と同様の方法で液体濾過用濾材を作製した。
【００３３】
比較例１
実施例１の濾材層の繊維配合比率を０：２０：３０：５０にした以外は、実施例１と同様の方法で液体濾過用濾材を作製した。
【００３４】
比較例２
実施例１の濾材層の繊維配合比率を６：２０：２４：５０にした以外は、実施例１と同様の方法で液体濾過用濾材を作製した。
【００３５】
実施例及び比較例における空隙径、ライフは以下の方法で測定した。
濾材の空隙径：濾材の空隙径は、ＡＳＴＭ−Ｆ−３１６記載のバブルポイント法及びミーンフロー法により最大空隙径、平均空隙径を求めた。
【００３６】
ライフ：ライフ試験は、液体濾過用濾材をプリーツ加工してフィルターを作製し、粗加工用の直径０．３２ｍｍのワイヤーを使用する放電加工機のフィルターセット部位にセットし、連続で切削加工した際にフィルター圧が２．０ｋｇ／ｃｍ^２になるまでの時間を測定した。
結果を表１に示す。
【００３７】
【表１】

【００３８】
これらの結果より、繊維径が１μｍ以下にフィブリル化された有機繊維を１〜４．５質量％配合した実施例１，２，３の液体濾過用濾材は、繊維径が１μｍ以下にフィブリル化された有機繊維を全く配合していない比較例１、並びに６質量％配合した比較例２に比較してライフが長いことが分かる。また、比較例１はライフ測定の際の初期の濁りが著しく、実際に使用することは不可能な状態であったが、実施例１〜３，並びに比較例２は使用可能な濁りの状態であった。プリーツ加工性、引張強度、湿潤引張強度に関しては、実施例１〜３、比較例１、２共に良好であり問題なかった。
【００３９】
【発明の効果】
本発明の液体濾過用濾材は、濾材層に配合する繊維径が１μｍ以下にフィブリル化された有機繊維の配合比率をコントロールする事により、放電加工機の荒削り加工の際等にライフを満足させることが出来る。そのためには、他に繊維径１μｍ以上の有機繊維として繊維径１〜５μｍの極細有機繊維、及び繊維径８μｍ以上の有機繊維を組み合わせることが重要である。これにより繊維径１μｍ以下の繊維の凝集が抑えられ、繊維径１〜５μｍの極細繊維が良く絡み合いより均一なネットワークを形成し、均質で微細な空隙径を有し、粒子を濾材表面で濾過するという表面濾過機能を有するためである。
又、この濾材に濾過抵抗の少ない繊維から成る支持体を抄合わせすることにより、濾材のみでは得られなかったひだ折り加工性、湿潤引張強度が良好で、ライフの長い液体濾過用濾材が得られた。[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to a filter medium for liquid filtration for efficiently removing particles contained in a liquid and obtaining a clean liquid. More specifically, processing scraps contained in a machining fluid of an electric discharge machine used for metal engraving, cutting, etc., and super-ultrasonic used in a process of cutting, polishing, etching, etc. of a substrate wafer in IC production. The present invention relates to a filter medium for efficiently removing processing waste contained in pure water to obtain a clean liquid, and a filter medium for filtering various liquids such as engine oil and fuel for automobiles. In particular, it is suitable mainly for the following applications (1) and (2) in response to diversifying electric discharge machines.
{Circle around (1)} The thickness of the filter medium is small, and the area of the filter medium to be put into the filter unit can be increased.
{Circle around (2)} Applied to machining fluids having relatively coarse particle diameters of shavings generated from the workpiece.
[0002]
[Prior art]
Conventionally, liquid filtration filters used in electric discharge machines and IC production processes and filters for various liquid filtration such as engine oils and fuels for automobiles are impregnated with phenol resin etc. in a mixed sheet of natural pulp and organic fiber. However, there are problems such as low filtration efficiency and short life.
[0003]
That is, the conventional filter medium has a function of trapping particles inside the filter medium, and uses a relatively coarse filter medium to extend the life, and the target filtration efficiency until particles enter the inside of the filter medium and fill the pores of the filter medium to some extent. Cannot be obtained. When the voids in the filter medium are filled, there is a problem that pressure loss increases and liquid permeability deteriorates, shortening the life, or particles inside the filter medium flow out of the filter medium to lower efficiency.
[0004]
As a high-performance filter, there is a porous sheet made of a fluororesin or the like, but it is expensive, so it is limited to special applications, and is not suitable as a filter medium for treating a large amount of liquid as in an electric discharge machine or an IC production process.
[0005]
As a method for solving these problems, a filter medium using fibrillated organic fibers has been developed (JP-A-59-92011). However, when an attempt is made to produce such a fiber alone by a usual wet papermaking method, there is an inevitable production problem such as a large loss from the wire and clogging of the wire. Even if a filter medium is obtained, the filter medium obtained is very dense due to the fine fibers, and as a result, although high filtration efficiency is obtained, the filtration resistance is high and is not suitable for practical use. In the case of containing monofilament fibers having a relatively large diameter in an attempt to reduce the filtration resistance, the loss of fine fibers in the papermaking process is increased, and the filtration efficiency is significantly reduced, and sufficient performance cannot be obtained.
[0006]
In JP-A-3-12208, fibrillation is performed by blending an organic fiber having a fiber diameter of 1 μm or less, an ultrafine organic fiber having a fiber diameter of 1 to 5 μm, and an organic fiber having a fiber diameter of 5 μm or more. There has been proposed a filter medium which suppresses agglomeration of organic fibers, forms a homogeneous network, and further performs a calendering treatment to improve the smoothness of the filter medium surface and has a surface filtration mechanism. Since this filter medium has a surface filtration mechanism, the filtration performance and life are very good. However, the thickness of the filter medium is very thin, and there is no stiffness (hardness). Further, since the wet strength is very weak, when used for a filter for an electric discharge machine, a filter for an automobile engine oil, or a filter for an automobile fuel, the filter is broken by the pressure of the liquid.
[0007]
JP-A-61-268321, JP-A-61-268325, JP-A-61-275495, and the like exemplify a two-layer filter medium having a density gradient. The filter efficiency and the life are balanced by combining the filter media of the present invention, which is basically different from the method of obtaining the filtration performance on the filter media surface (only the filter media layer) of the present invention.
[0008]
In order to solve these problems, the filter medium for liquid filtration disclosed in Japanese Patent Application Laid-Open No. 06-126112 filed by the present inventor has high filtration efficiency, excellent foldability, strong wet strength, and is currently useful. However, with the diversification and speeding up of electric discharge machines, the diameter and processing speed of the wires used have diversified, and the development of new filter media has been required to respond to the importance of life. . That is, since the particle diameter of the shavings generated at the time of rough cutting is large, a filter medium having a long life is required even for large particles.
[0009]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks and problems, and to provide a filter medium for liquid filtration which has a long life with respect to a machining fluid having a relatively coarse particle diameter of shavings generated from a workpiece.
[0010]
[Means for Solving the Problems]
As a method of solving these problems, as a result of examining the application of various fibers to a filter medium, it was found that excellent filter characteristics could be obtained, and the present invention was completed.
[0011]
That is, in the filter medium for liquid filtration of the present invention, the filter medium is obtained by integrating a filter medium layer and a support layer, and the filter medium layer has a fiber diameter of 1 μm or less. 5 to less than 5% by mass and an organic fiber having a fiber diameter of 1 μm or more, using a fibrous organic binder for part or all of the organic fiber having a fiber diameter of 1 μm or more, and having an average pore diameter of 10 to 50 μm, It is those consisting of basis weight of 5 to 50 g / m ^2, the support layer, a fiber diameter of 8μm or more organic fibers, polyolefin, polyamide, polyester, acrylic, vinylon, vinyl PVC acetate system comprising at least one synthetic fiber, a portion of polyester, polyolefin, and contains at least one fibrous organic binder vinyl PVC acetate-based, and the basis weight of 20 to 150 g / m ² That is a liquid filtration for the filter medium.
Further, the ratio of the basis weight of the filter medium layer to the basis weight of the support layer is in the range of 1: 0.5 to 1:10, and the filter medium for liquid filtration uses the filter medium layer as the upstream side.
Further, it is a filter medium for liquid filtration in which a filter medium layer and a support layer are formed by a wet papermaking method and integrated.
Further, the organic fiber fibrillated to a fiber diameter of 1 μm or less is a filter medium for liquid filtration, which is one or more of aromatic polyamide fiber, rayon fiber, lyocell fiber produced by a solvent spinning method, and pulp fiber. .
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
The filter medium for liquid filtration of the present invention is a liquid obtained by combining and integrating a thin filter medium layer having surface filtration performance and a support layer having high liquid permeability and high strength and good foldability. It is a filter medium for filtration.
Examples of the organic fibers fibrillated to a fiber diameter of 1 μm or less for use in the filter medium of the present invention include those processed by the following method.
1) A method in which a synthetic polymer solution is allowed to flow down into a poor solvent for the polymer while applying a shear force to precipitate fibrous fibrils (Fibrid method, Japanese Patent Publication No. 35-11851).
2) A method of precipitating fibrils by shearing while polymerizing a synthetic monomer (polymerization shearing method, Japanese Patent Publication No. 47-21898).
3) A method in which two or more incompatible polymers are mixed, melt-extruded or spun, cut, and fibrillated into fibrils by mechanical means (split method, Japanese Patent Publication No. 35-9651).
4) A method in which two or more incompatible polymers are mixed, melt-extruded or spun, cut, then immersed in a solvent, one of the polymers is dissolved, and fibrillated into a fibrous form (polymer blend dissolution method). U.S. Pat. No. 3,382,305).
5) A method in which the synthetic polymer is explosively ejected from the high pressure side to the low pressure side at a temperature higher than the boiling point of the solvent and fibrillated into a fibrous form (Philash spinning method, JP-B-36-16460).
6) A method of blending a polyester-based polymer with an alkali-soluble component incompatible with the polyester, reducing the weight with an alkali after molding, beaten, and fibrillating into a fibrous form (alkali weight-reducing beating method, JP-A-56-315). Publication).
7) A method of cutting highly crystalline and highly oriented fibers such as Kevlar fibers into an appropriate fiber length, dispersing the fibers in water, and fibrillating them using a homogenizer, a beater or the like (JP-A-56-100801, JP-A-59-92011), and specific examples thereof include a tearer 400S (manufactured by Daicel Corporation) in which Kevlar fiber is fibrillated with a homogenizer, and an alkali weight reduction beating method. Polyester pulp, Selish 100S (manufactured by Daicel Corporation) obtained by fibrillating wood pulp with a homogenizer, lyocell fiber produced by solvent spinning, wood pulp, and other synthetic fibers such as nylon, polyethylene, and polypropylene as beaters and PFI. Fibers beaten by a mill, a ball mill, a dyno mill, and the like are included.
[0013]
The amount of the fibrillated organic fibers is suitably 0.5 or more and less than 5% by mass, and preferably 1 to 4.5% by mass. If the amount is less than 0.5% by mass, the average pore size of the filter medium becomes too large to obtain a sufficient collection efficiency. If the amount exceeds 5% by mass, the filter medium for liquid filtration as disclosed in JP-A-06-126112 is high. It becomes the performance filtration area.
[0014]
Examples of the organic fiber having a fiber diameter of 1 μm or more used in the filter medium layer of the present invention include ultrafine fibers such as 1 to 5 μm polyester fiber, PVA fiber, and acrylic fiber. The blending amount of these fibers is suitably from 5 to 70% by mass, and preferably from 10 to 60% by mass. If the amount is less than 5% by mass, fine fibers having a size of 1 μm or less flow out of the wire, failing to obtain a sufficient filtration efficiency, and causing problems in production such as poor peeling of the wet paper web from the wire. %, The filtration resistance becomes large and is not suitable for practical use.
[0015]
The organic fibers having a fiber diameter of 1 μm or more used in the filter medium layer of the present invention include, in addition to the fibers having a fiber diameter of 1 to 5 μm, organic fibers having a fiber diameter of 8 μm or more, such as polyolefin, polyamide, polyester, polyacrylamide, and vinylon. In addition to synthetic fibers such as pulp, linter, lint, and derivatives thereof, it is preferable to use together with organic fibers having a fiber diameter of 1 μm or more.
[0016]
Examples of the fibrous organic binder used in the present invention include composite fibers such as a core-sheath type (core-shell type) and a side-by-side type (side-by-side type). For example, a combination of polypropylene (core) and polyethylene (sheath) (trade name: Daiwabo NBF-H: manufactured by Daiwa Spinning Co., Ltd.), a combination of polypropylene (core) and ethylene vinyl alcohol (sheath) (trade name: Daiwabo NBF-E: Combination of polypropylene (core) and polyethylene (sheath) (trade name: Chisso ESC: made by Chisso), combination of high melting polyester (core) and low melting polyester (sheath) (trade name: Melty 4080) : Unitika Ltd.). In addition, a fibrous binder composed of only a low melting point (total fusion type) or a hot water binder such as a polyvinyl alcohol type is not preferred because a film is easily formed in a drying step of a filter medium and filtration resistance is increased. It can be used as long as the properties are not impaired. The fiber diameter of the fibrous organic binder is not particularly limited, but is preferably in the range of 3 to 50 μm, more preferably 7 to 20 μm.
[0017]
The compounding amount of the organic fiber having a fiber diameter of 8 μm or more is not particularly limited, but is 10 to 95% by mass. Among these, the compounding amount of the fibrous organic binder is suitably 20 to 60% by mass of the total fiber amount. Preferably it is 30 to 50% by mass. If the amount is less than 20% by mass, the surface strength of the filter medium is low, and there is a problem in the workability of the filter unit. If the amount exceeds 60% by mass, the filtration resistance increases and there is a practical problem. On the other hand, when the organic fibers having a fiber diameter of 5 μm or more exceed 70% by mass, the average void diameter of the sheet increases, and the filtration performance deteriorates.
[0018]
The basis weight of the filter medium layer of the present invention is suitably from 5 to 50 g / m ² , and preferably from 10 to 40 g / m ² . If it is less than 5 g / m ² , there is a problem in reliability due to pinholes and the like. If it exceeds 50 g / m ² , the filtration resistance increases and the papermaking properties deteriorate, and the effect cannot be expected even if the basis weight is increased from the point of surface filtration, and there is a problem in cost.
[0019]
The average pore diameter of the filter medium layer of the present invention is suitably from 10 to 50 μm, and preferably from 12 to 40 μm, from the viewpoint of surface filtration. Since the method is intended for relatively coarse particles (average particle diameter: 2 to 10 microns, particle diameter measuring device: measured with a microtrack) in a liquid, if the average pore diameter is less than 10 μm, the specification becomes excessive. If it exceeds 50 μm, the particles flow out without being trapped by the filter medium. The average pore diameter of the entire filter medium including the filter medium layer and the support layer is 7 to 45 μm, which is slightly smaller than the pore diameter of the filter medium layer alone.
Although there is no particular limitation on the maximum pore diameter, the maximum pore diameter is preferably three times or less the average pore diameter in terms of the homogeneity of the filter medium.
[0020]
The organic fiber having a fiber diameter of 8 μm or more used for the support of the present invention includes synthetic fibers such as polyolefin, polyamide, polyester, polyacrylamide, and vinylon, and is a support containing at least one kind. As a characteristic of these organic fibers, rigid fibers are preferred in terms of giving the sheet a stiffness and having high fiber strength. Further, from the viewpoint of suppressing a decrease in life due to the attachment of fine particles that have passed through the filter medium, a fiber in the form of a rod (cross section is circular, elliptical, cocoon, or the like) that does not form a film is preferable. Other usable fibers include unbeaten natural pulp, hemp pulp, cotton linter, and lint with less film, and regenerated fibers such as rayon, cupra, and lyocell fibers, and semi-synthetic fibers such as acetate and triacetate. As the promix, synthetic fibers include fibers of nylon, acrylic, vinylon, vinylidene, polyvinyl chloride, polyester, polyethylene, polypropylene, benzoate, polyclar, phenol type and the like. In addition to the above fibers, the plant fibers include woody pulp such as softwood pulp and hardwood pulp, and woody plants and herbs such as straw pulp, bamboo pulp, and kenaf pulp. Further, pulp fibers obtained from waste paper, broke, and the like are also included.
[0021]
The compounding amount of the fibrous organic binder in the support layer is suitably in the range of 10 to 70% by mass. If the amount is less than 10% by mass, the necessary water resistance cannot be obtained in the step of impregnating the resin binder after papermaking. On the other hand, when the content exceeds 70% by mass, the coating film of the binder having a low melting point increases, the pressure loss of the entire filter medium increases, and the life becomes short.
[0022]
The fiber diameter of the fiber used for the support is suitably 8 μm or more. If the fiber diameter is less than 8 μm, the filtration resistance of the support increases and the liquid permeability deteriorates. However, fibers having a size of 8 μm or less can be mixed to enhance papermaking stability. Although the upper limit of the fiber diameter is not particularly limited, the fiber diameter is preferably 50 μm or less in consideration of papermaking properties and the like.
[0023]
The basis weight of the support of the present invention is suitably from ²⁰ to 150 g / m ² , and preferably from 30 to 100 g / m ² . When it is less than 20 g / m ² , the foldability is poor, and when it exceeds 150 g / m ² , the thickness increases, the area of the filter medium to be accommodated in the unit becomes small, and the filtration resistance increases, which is problematic in practical use and is preferable from the viewpoint of cost. Absent.
[0024]
The fibers used for the support of the present invention are mainly made of synthetic fibers that are less swelled by water and oil, so that they have high wet tensile strength and do not break the filter medium due to liquid pressure.
[0025]
The filter medium of the present invention is manufactured by combining a paper machine for producing general paper and wet nonwoven fabric, for example, a combination machine combining two machines of fourdrinier paper machine, circular net paper machine, inclined wire paper machine and the like. Is done. The combination can be a combination of the same type of paper machine or a combination of different types of paper machine.
[0026]
For the purpose of increasing the strength and stiffness (hardness) of the filter medium of the present invention, various binders can be applied by impregnation, coating, spraying, or the like. As the binder to be used, latexes such as acrylic, vinyl acetate, epoxy, urethane, synthetic rubber, and vinylidene chloride, PVA, starch, and phenol resin can be used alone or in combination of two or more.
[0027]
The amount of the binder provided to the filter medium for liquid filtration of the present invention is suitably 30% by mass or less, and preferably 20% by mass or less, based on the filter medium. If it exceeds 30% by mass, the filtration resistance of the filter medium becomes large, and there is a practical problem. The method for applying the binder to the filter medium is not particularly limited, and examples thereof include size press, tab size, spray impregnation, and internal addition.
[0028]
If necessary, additives such as a water repellent, a dispersant, a retention aid, and a dye can be added as long as the properties of the filter medium are not impaired.
[0029]
【Example】
Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto.
[0030]
Example 1
(Preparation of filter medium layer)
After injecting 1 m ^{3 of} dispersion water into a 2 m ³ dispersion tank in which a pulper disperser is installed, Kevlar fine fibers (Tearer 400S, manufactured by Daicel Chemical Industries, Ltd.) and ultrafine polyester fibers (manufactured by Teijin Limited, 0.1 decitex × 3 mm, diameter of about 3 μm), polyester fiber (manufactured by Teijin Limited, 0.6 decitex × 5 mm, diameter of about 7 μm), heat-adhesive (core-sheath type) polyester fiber as a fibrous organic binder (4080, 2.2 manufactured by Unitika) (Decitex × 5 mm, diameter of about 15 μm) was added so as to have a fiber mixing ratio of 1: 20: 29: 50, and dispersed for 10 minutes to produce an aqueous slurry. The basis weight was 20 g / m 2 using a circular paper machine. ² is formed.
(Preparation of support layer)
After injecting 1 m ^{3 of} dispersing water into a 2 m ³ dispersing tank in which a pulper dispersing machine is installed, NBKP (manufactured by Mitsubishi Paper Mills), a heat-adhesive (core-sheath type) polyester fiber (produced by Unitika) as a fibrous organic binder 4080, 2.2 × 5 mm, diameter of about 15 μm) was added so as to have a fiber mixing ratio of 40:60, and dispersed for 30 minutes to produce an aqueous slurry. The basis weight was 45 g / m 2 using a round paper machine. ^{A second} support layer is formed.
The filter medium layer and the support layer were combined in a wet paper state using a combination machine in which two circular web paper machines were installed in series, integrated, and then pressed to form a cylinder having a surface temperature of 120 ° C. The resultant was dried with a drier to prepare a filter medium of 65 g / m ² . The filter medium was impregnated with a commercially available acrylic emulsion at a solid content of 5 g / m ² and then dried to prepare a filter medium for liquid filtration.
[0031]
Example 2
A filter medium for liquid filtration was produced in the same manner as in Example 1, except that the fiber mixing ratio of the filter medium layer in Example 1 was changed to 2.5: 20: 27.5: 50.
[0032]
Example 3
A filter medium for liquid filtration was produced in the same manner as in Example 1, except that the fiber mixing ratio of the filter medium layer in Example 1 was 4.5: 20: 25.5: 50.
[0033]
Comparative Example 1
A filter medium for liquid filtration was produced in the same manner as in Example 1 except that the fiber mixing ratio of the filter medium layer in Example 1 was set to 0: 20: 30: 50.
[0034]
Comparative Example 2
A filter medium for liquid filtration was produced in the same manner as in Example 1 except that the fiber mixing ratio of the filter medium layer in Example 1 was 6: 20: 24: 50.
[0035]
The void diameter and life in the examples and comparative examples were measured by the following methods.
Void diameter of filter medium: The maximum pore diameter and average pore diameter were determined by the bubble point method and mean flow method described in ASTM-F-316.
[0036]
Life: The life test is performed by pleating a filter medium for liquid filtration to produce a filter, setting it in the filter set part of an electric discharge machine using a 0.32 mm diameter wire for rough processing, and performing continuous cutting. The time until the filter pressure reached 2.0 kg / cm ² was measured.
Table 1 shows the results.
[0037]
[Table 1]

[0038]
From these results, the filter media for liquid filtration of Examples 1, 2, and 3 in which 1 to 4.5% by mass of the organic fibers fibrillated to a fiber diameter of 1 μm or less were fibrillated to a fiber diameter of 1 μm or less. It can be seen that the life is longer as compared to Comparative Example 1 in which no organic fiber was blended and Comparative Example 2 in which 6% by mass was blended. In Comparative Example 1, the initial turbidity at the time of measuring the life was remarkable, and it was impossible to actually use it. there were. Regarding pleating workability, tensile strength, and wet tensile strength, Examples 1 to 3 and Comparative Examples 1 and 2 were all good and had no problems.
[0039]
【The invention's effect】
The filter medium for liquid filtration according to the present invention satisfies the life at the time of rough machining of an electric discharge machine by controlling the blending ratio of the organic fibers fibrillated to a fiber diameter of 1 μm or less to be blended in the filter medium layer. Can be done. For that purpose, it is important to combine an ultrafine organic fiber having a fiber diameter of 1 to 5 μm and an organic fiber having a fiber diameter of 8 μm or more as an organic fiber having a fiber diameter of 1 μm or more. This suppresses agglomeration of fibers having a fiber diameter of 1 μm or less, and fine fibers having a fiber diameter of 1 to 5 μm are well entangled to form a more uniform network, have a uniform and fine pore diameter, and filter particles on the surface of the filter medium. This is because it has a surface filtration function.
In addition, by assembling a support made of a fiber with low filtration resistance into the filter medium, a filter medium for liquid filtration having a long life, which has good foldability and wet tensile strength, which cannot be obtained by the filter medium alone, can be obtained. Was.

Claims

In a filter medium for liquid filtration, the filter medium is obtained by integrating a filter medium layer and a support layer, and the filter medium layer is 0.5 to 5% by mass of an organic fiber fibrillated to a fiber diameter of 1 μm or less. Less than or equal to 1 μm or more, including a part or all of the organic fibers having a fiber diameter of 1 μm or more, using a fibrous organic binder, having an average pore diameter of 10 to 50 μm, and 5 to 50 g / m 2. are those composed of ^two of the basis weight, the support layer, a fiber diameter of 8μm or more organic fibers, polyolefin, polyamide, polyester, acrylic, vinylon, synthetic fibers PVC vinyl acetate least 1 It includes a type, a portion of polyester, polyolefin, and contains at least one fibrous organic binder vinyl PVC acetate-based, and it consists of a basis weight of 20 to 150 g / m ² Liquid filtration medium, wherein.

The liquid according to claim 1, wherein the ratio of the basis weight of the filter medium layer to the basis weight of the support layer is in the range of 1: 0.5 to 1:10, and the filter medium layer is used as an upstream side. Filter media for filtration.

The filter medium for liquid filtration according to claim 1 or 2, wherein the filter medium layer and the support layer are combined by a wet papermaking method.

2. The organic fiber fibrillated to a fiber diameter of 1 μm or less is one or more of aromatic polyamide fiber, rayon fiber, lyocell fiber produced by a solvent spinning method, and pulp fiber. The filter medium for liquid filtration according to any one of claims 1 to 3.