JP5531667B2 - Manufacturing method of polyvinylidene fluoride porous membrane - Google Patents
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本発明は、ポリフッ化ビニリデン多孔質膜の製造法に関する。さらに詳しくは、熱誘起相分離法によるポリフッ化ビニリデン多孔質膜の製造法に関する。 The present invention relates to a method for producing a polyvinylidene fluoride porous membrane. More specifically, the present invention relates to a method for producing a polyvinylidene fluoride porous membrane by a thermally induced phase separation method.
膜ロ過による浄水処理や下廃水処理は、これ迄の凝集沈殿のロ過方式と比較し、運転の維持や管理が容易であり、処理水質も良好であることから、近年水処理分野で幅広く用いられている。特に、これらの処理方式は、従来法では除去が不十分であったクリプトスポリジウム等の病原性微生物を完全に除去できることが大きな特徴として挙げられる。 Compared with conventional filtration methods for coagulation and sedimentation, purification water treatment and membrane wastewater treatment by membrane filtration are easier to maintain and manage, and the quality of the treated water is good. It is used. In particular, these treatment methods are characterized by the ability to completely remove pathogenic microorganisms such as Cryptosporidium, which was insufficiently removed by conventional methods.
これらの膜ロ過に用いられる素材としては、微粒子や有機物等のファウリング物質に対する耐汚染性にすぐれているポリフッ化ビニリデン系樹脂が注目されている。就中、熱誘起相分離法を製膜基本原理として得られるポリフッ化ビニリデン多孔質膜は、従来の非溶媒誘起相分離法(液・液分離法)で得られる膜の課題であった機械的強度やマクロボイドの生成という問題が解決され、さらに化学的耐久性にもすぐれていることから、近年盛んに開発が行われている。 As a material used for these membrane filtrations, a polyvinylidene fluoride resin that is excellent in contamination resistance against fouling substances such as fine particles and organic substances has attracted attention. In particular, the polyvinylidene fluoride porous membrane obtained using the thermally induced phase separation method as the basic principle of membrane formation is a mechanical problem that has been a problem of membranes obtained by the conventional non-solvent induced phase separation method (liquid / liquid separation method). In recent years, it has been actively developed because it solves the problems of strength and generation of macrovoids, and also has excellent chemical durability.
熱誘起相分離法によりポリフッ化ビニリデン系多孔質膜の製造法として、ジブチルフタレート、ジオクチルジフタレート等のフタル酸エステルを溶媒として使用する方法が提案されている(特許文献１参照)。 As a method for producing a polyvinylidene fluoride porous membrane by a thermally induced phase separation method, a method using a phthalic acid ester such as dibutyl phthalate or dioctyl diphthalate as a solvent has been proposed (see Patent Document 1).
しかしながら、フタル酸エステルは内分泌攪乱物質の一種ではないかと世界的に問題視されており、国内においても食品の器具、容器包装、合成樹脂製玩具等において、ジオクチルフタレート(DOP)の使用禁止がそれぞれとりまとめられている。このため、フタル酸エステルを溶媒に使用する場合には、製膜後の工程において、溶媒を極く微量まで抽出することが求められる。 However, phthalate esters are regarded as a problem worldwide as a kind of endocrine disruptor, and in Japan, the use of dioctyl phthalate (DOP) is prohibited in food utensils, containers and packaging, synthetic resin toys, etc. It is compiled. For this reason, when using a phthalate ester as a solvent, it is required to extract a very small amount of the solvent in the step after film formation.
しかるに、フタル酸エステルは、ポリ塩化ビニルを始めとした合成樹脂の可塑剤として、好適・広範囲に用いられていることもあり、その性質から抽出し難い物質である。このため、抽出溶剤には、各種有機化合物の溶解性にすぐれている塩化メチレンが一般に用いられている。この塩化メチレンは、それの化学的安全性のため、一旦環境中に放出されると分解し難いため、PRTR法規制物質としてそれの利用と廃棄とが監視され、大気中の放出量も削除することが求められている。さらに、人体への毒性も懸念される物質でもある。 However, phthalate esters are suitable and widely used as plasticizers for synthetic resins such as polyvinyl chloride, and are difficult to extract due to their properties. For this reason, methylene chloride, which is excellent in solubility of various organic compounds, is generally used as the extraction solvent. Because this methylene chloride is difficult to decompose once released into the environment due to its chemical safety, its use and disposal is monitored as a PRTR regulated substance, and the amount released into the atmosphere is also deleted It is demanded. In addition, it is a substance that is also of concern for human toxicity.
また、フタル酸エステルに代り、アジピン酸エステルを溶媒として使用する方法も開示されているが(特許文献２参照)、抽出溶媒に塩化メチレンを使用する点ではフタル酸エステルの場合と同様である。 In addition, a method of using adipic acid ester as a solvent instead of phthalic acid ester is also disclosed (see Patent Document 2), but the same point as in the case of phthalic acid ester is that methylene chloride is used as the extraction solvent.
一方、γ-ブチロラクトンやジメチルスルホキシド等の水溶性有機溶媒を用いた熱誘起相分離法によるポリフッ化ビニリデン系多孔質膜の製造法も開示されており(特許文献３〜４参照)、これらの溶媒の抽出は水で可能であるものの、得られる膜の構造は粗大な球晶が連なる構造であるため、機械的強度の低下は避けられない。 On the other hand, a method for producing a polyvinylidene fluoride porous membrane by a thermally induced phase separation method using a water-soluble organic solvent such as γ-butyrolactone or dimethyl sulfoxide is also disclosed (see Patent Documents 3 to 4), and these solvents are also disclosed. However, since the structure of the obtained film is a structure in which coarse spherulites are connected, a decrease in mechanical strength is inevitable.
さらに、このような球晶の生成を抑制する方法として、無機粒子を製膜原液に添加する方法が知られてはいるが(特許文献５参照)、無機粒子の抽出に水酸化ナトリウム水溶液等の強アルカリが使用されるためコスト高になるばかりではなく、無機粒子の分散性が悪い場合にはピンホールを生ずるおそれがみられる。 Furthermore, as a method for suppressing the formation of such spherulites, a method of adding inorganic particles to a film-forming stock solution is known (see Patent Document 5). For extraction of inorganic particles, a sodium hydroxide aqueous solution or the like is used. Since strong alkali is used, not only is the cost high, but there is a possibility that pinholes may occur when the dispersibility of the inorganic particles is poor.
以上の事実をふまえ、本発明者は熱誘起相分離法によるポリフッ化ビニリデン系多孔質膜を製造するに際し、製膜溶媒としてクエン酸エステルを用いることに注目した。クエン酸エステルは、米国食品医薬品局(FDA)や英国プラスチック連盟(BPF)においても広く安全性が認められた化合物であり、欧州委員会の科学詰問委員会(CSTEE)においても、安全であることが意見表明されている(非特許文献１参照)。このため、食品に直接触れる可能性があるプラスチック製品やプラスチック製品の可塑剤として好適に使用されている。 Based on the above facts, the present inventor has paid attention to the use of citrate ester as a film-forming solvent when manufacturing a polyvinylidene fluoride-based porous film by a heat-induced phase separation method. Citrate esters are widely recognized as safe by the US Food and Drug Administration (FDA) and the British Plastics Federation (BPF), and are also safe by the European Commission's Scientific Check Committee (CSTEE). Has been expressed (see Non-Patent Document 1). For this reason, it is suitably used as a plastic product that may be in direct contact with food or as a plasticizer for plastic products.
しかるに、クエン酸エステルを製膜溶媒として用いた場合、得られるポリフッ化ビニリデン系多孔質膜の膜断面構造は、微小な球晶が連なる構造であって、それの最大孔径はロ過膜としては不適な大きな値を示していた。 However, when citrate is used as a film-forming solvent, the resulting polyvinylidene fluoride porous membrane has a cross-sectional structure of minute spherulites whose maximum pore size is It showed an inappropriate large value.
本発明の目的は、熱誘起相分離法によるポリフッ化ビニリデン多孔質膜の製造法であって、明瞭な球晶がなく、しかも所望の膜性能を有するものを製造する方法を提供することにある。 An object of the present invention is to provide a method for producing a polyvinylidene fluoride porous membrane by a thermally induced phase separation method, which has no clear spherulites and has a desired membrane performance. .
かかる本発明の目的は、重量平均分子量Mwが100,000〜300,000のポリフッ化ビニリデン樹脂25〜35重量％と一般式
(ここでR1、R2、R3はいずれもブチル基であり、R4はアシル基である)で表わされるクエン酸エステル化合物75〜65重量％との混合物を溶融成形した後、クエン酸エステル化合物抽出溶媒でクエン酸エステル化合物を除去し、成形体を多孔質化して、バブルポイント法(ASTM F316-86準拠)で求められた最大孔径が1μm以下で、膜断面構造に明確な球晶が確認されないポリフッ化ビニリデン多孔質膜を製造する方法によって達成される。
The object of the present invention is to provide 25 to 35% by weight of a polyvinylidene fluoride resin having a weight average molecular weight Mw of 100,000 to 300,000 and a general formula
(Wherein R 1 , R 2 and R 3 are all butyl groups and R 4 is an acyl group) The citrate compound is removed with an ester compound extraction solvent, the molded body is made porous , and the maximum pore size determined by the bubble point method (according to ASTM F316-86) is 1 μm or less, and the spherulite is clear in the membrane cross-sectional structure. This is achieved by a method of manufacturing a polyvinylidene fluoride porous membrane in which no is confirmed .
本発明方法により、前記の如き問題点を有するフタル酸エステル、塩化メチレン、添加剤として無機粒子等を使用することなく、人体に対する安全性が高くかつ環境負荷の小さい製膜溶媒を用い、かつ明瞭な球晶のない、所望の膜性能(最大孔径、空孔率、透水量など)を有するポリフッ化ビニリデン多孔質膜が得られる。 According to the method of the present invention, a phthalate ester having the above-mentioned problems, methylene chloride, a film-forming solvent that is highly safe for the human body and has a low environmental impact is used, without using inorganic particles as an additive, and clearly. Thus, a polyvinylidene fluoride porous film having desired film performance (maximum pore diameter, porosity, water permeability, etc.) free of spherulites can be obtained.
本発明方法においては、熱誘起相分離法によってポリフッ化ビニリデン多孔質膜が製造される。 In the method of the present invention, a polyvinylidene fluoride porous membrane is produced by a thermally induced phase separation method.
従来用いられている非溶媒誘起相分離法では、膜形成性樹脂をその良溶媒中に均質に溶解させたドープ液(製膜原液)を調製し、これを中空糸状に吐出しまたは平膜状にキャストした後、貧溶媒中に浸漬することにより、ドープ液中に貧溶媒が拡散してポリマー層と溶液層(良溶媒＋貧溶媒)とに相分離(凝固)させ、多孔質体を得る方法であるのに対し、熱誘起相分離法では、熱可塑性樹脂を加熱溶融させた状態で溶媒や添加剤(無機粒子等の造孔剤)とを均質混合し、これを加熱溶融状態で中空糸状または平膜状に成形した後、成形体を成形体成分の非溶解性液体(水など)への浸漬または空気中で冷却することでポリマー層と溶媒層とを相分離させ、これを溶液浸漬して膜中の溶媒や充填剤等を抽出し、多孔質を得るという方法がとられている。 In the conventional non-solvent induced phase separation method, a dope solution (film forming stock solution) in which a film-forming resin is homogeneously dissolved in a good solvent is prepared and discharged into a hollow fiber shape or a flat membrane shape. After being cast into a poor solvent, the poor solvent diffuses into the dope solution and phase separates (solidifies) into a polymer layer and a solution layer (good solvent + poor solvent) to obtain a porous body. In contrast, in the thermally induced phase separation method, a thermoplastic resin is heated and melted and homogeneously mixed with a solvent and an additive (pore forming agent such as inorganic particles), and this is heated and melted in a hollow state. After forming into a filament or flat film, the molded body is immersed in a non-soluble liquid (such as water) of the molded body component or cooled in air to cause phase separation between the polymer layer and the solvent layer. A method of obtaining a porous material by immersing and extracting a solvent, a filler and the like in the film is used.
かかる熱誘起相分離法が適用されるポリフッ化ビニリデン樹脂であるフッ化ビニリデン単独重合体の重量平均分子量Mw(GPS法によるポリスチレン換算分子量として測定)は、100,000〜300,000程度であることが好ましい。Mwがこれよりも大きくなると、球晶構造の生成が顕著となり、一方Mwがこれよりも小さくなると、機械的強度が低下するようになる。 The weight average molecular weight Mw (measured as a polystyrene-equivalent molecular weight by the GPS method) of the vinylidene fluoride homopolymer, which is a polyvinylidene fluoride resin to which such thermally induced phase separation method is applied, is preferably about 100,000 to 300,000. When Mw is larger than this, the formation of spherulite structure becomes remarkable, while when Mw is smaller than this, the mechanical strength is lowered.
熱誘起相分離法では、一般に熱可塑性樹脂と溶媒との混合物である製膜原液中の樹脂濃度が増大すると、球晶の生成が抑制される方向に働くが、本発明の製膜原液にあっては樹脂濃度が増大するとかえって球晶が生成し、また樹脂濃度が小さくなると微細な球晶構造の生成がみられるので、ポリフッ化ビニリデン樹脂は溶媒であるクエン酸エステル化合物との合計量中25〜35重量％の割合で用いられなければならない。 In the thermally induced phase separation method, when the resin concentration in the film-forming stock solution, which is generally a mixture of a thermoplastic resin and a solvent, increases, the formation of spherulites is suppressed. In contrast, when the resin concentration is increased, spherulites are formed, and when the resin concentration is decreased, formation of fine spherulite structures is observed. Therefore, the polyvinylidene fluoride resin is 25% of the total amount of the citrate compound as a solvent. Must be used in a proportion of ~ 35% by weight.
前記一般記で表わされるクエン酸エステル化合物において、基R1、R2、R3はいずれもブチル基であり、基R4はアセチル基、ベンゾイル基等のアシル基であり、好ましくはアセチルクエン酸トリブチルが用いられる。 In the citrate compound represented by the above general formula, the groups R 1 , R 2 and R 3 are all butyl groups , and the group R 4 is an acyl group such as an acetyl group and a benzoyl group, preferably acetyl citrate Tributyl is used.
基R1、R2、R3において、C 3 以下の炭素数を有するクエン酸アルキルエステルでは、得られるポリフッ化ビニリデン多孔質膜の断面構造中に顕著な球晶の生成が認められ、基R4が水素原子である場合にも同様である。一方、基R1、R2、R3において、アルキル基がC7以上の炭素数を有するクエン酸アルキルエステルでは、ポリフッ化ビニリデン樹脂との相溶性が悪化したり、得られた成形体からのクエン酸アルキルエステルの抽出が困難となる。 In the groups R 1 , R 2 and R 3 , in the alkyl citrate having a carbon number of C 3 or less , remarkable spherulite formation was observed in the cross-sectional structure of the obtained polyvinylidene fluoride porous film, and the group R The same applies when 4 is a hydrogen atom. On the other hand, in the groups R 1 , R 2 , and R 3 , in the alkyl citrate ester in which the alkyl group has a carbon number of C 7 or more, the compatibility with the polyvinylidene fluoride resin is deteriorated, or from the obtained molded body Extraction of alkyl citrate becomes difficult.
本発明方法においては、クエン酸エステル化合物はポリフッ化ビニリデン樹脂との合計量中75〜65重量％の割合で用いられる。 In the method of the present invention, the citrate ester compound is used in a proportion of 75 to 65% by weight in the total amount with the polyvinylidene fluoride resin.
ポリフッ化ビニリデン樹脂とクエン酸エステル化合物との所定割合の混合物は、それを溶融成形した後、クエン酸エステル化合物抽出溶媒でクエン酸化合物を除去し、成形体を多孔質化させるという熱誘起相分離法が適用される。 Heat-induced phase separation in which a mixture of polyvinylidene fluoride resin and citrate compound is melt-molded, and then the citric acid compound is removed with a citrate ester extraction solvent to make the molded body porous. The law applies.
その溶融混合温度や溶融成形温度は、ポリフッ化ビニリデン樹脂が溶融し、一相に混じり合う温度以上で、かつクエン酸エステル化合物の沸点以下の温度であり、一般には約150〜200℃、好ましくは約160〜180℃である。成形される多孔質体の形状は、平膜状でも中空糸膜状でもよい。 The melt mixing temperature or melt molding temperature is a temperature not lower than the temperature at which the polyvinylidene fluoride resin is melted and mixed in one phase and not higher than the boiling point of the citrate ester compound, generally about 150 to 200 ° C., preferably It is about 160-180 degreeC. The shape of the molded porous body may be a flat membrane or a hollow fiber membrane.
平膜状の場合には、溶融混合物をTダイ等のダイスからシート状に押し出し、キャストロールを経て冷却固化させる方法、あるいは溶融混合物を予め冷却固化し、その固化物を熱プレスにより再度溶融させて成形し、冷却固化させる方法などが適用される。その膜厚は、一般に0.1〜1.0mm、好ましくは0.2〜0.5mmに設定される。 In the case of a flat film, the molten mixture is extruded from a die such as a T-die into a sheet and cooled and solidified via a cast roll, or the molten mixture is cooled and solidified in advance, and the solidified product is melted again by hot pressing. A method of forming and cooling and solidifying is applied. The film thickness is generally set to 0.1 to 1.0 mm, preferably 0.2 to 0.5 mm.
中空糸膜状の場合には、二重環状ノズルから中空糸膜状に溶融押出し、所定の空走区間を経た後、冷却浴中に浸漬して固化させる方法が一般にとられる。冷却浴としては、廉価でかつ熱容量も大きいことから水が好んで用いられるが、成形体成分が溶解しない他の溶剤あるいは空冷であってもよい。また、中空糸膜の中空部形成用の流体には、押出温度以上の沸点を有する非溶解性の液体や空気、窒素等の気体を使用することができる。その膜厚は、一般に0.05〜3.0mm、好ましくは0.2〜2.0mmであり、外径は一般に0.1〜5.0mm、好ましくは0.3〜3.0mmに設定される。 In the case of a hollow fiber membrane, a method is generally employed in which it is melt-extruded from a double annular nozzle into a hollow fiber membrane, passed through a predetermined idle running section, and then immersed in a cooling bath to solidify. As the cooling bath, water is preferably used because it is inexpensive and has a large heat capacity. However, other solvents that do not dissolve the molded body components or air cooling may be used. The fluid for forming the hollow portion of the hollow fiber membrane may be an insoluble liquid having a boiling point equal to or higher than the extrusion temperature, or a gas such as air or nitrogen. The film thickness is generally 0.05 to 3.0 mm, preferably 0.2 to 2.0 mm, and the outer diameter is generally set to 0.1 to 5.0 mm, preferably 0.3 to 3.0 mm.
成形体を多孔質化するために用いられる製膜溶液(クエン酸エステル化合物)抽出溶媒としては、例えばメタノール、エタノール、イソプロパノール等のアルコール系溶媒、メチルエチルケトン、メチルイソブチルケトン等のケトン系溶媒、n-ヘキサン、シクロヘキサン等の炭化水素系溶媒が挙げられる。 Examples of the film forming solution (citrate ester compound) extraction solvent used to make the molded body porous include alcohol solvents such as methanol, ethanol and isopropanol, ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone, and n- Examples thereof include hydrocarbon solvents such as hexane and cyclohexane.
このようにして多孔質化されたポリフッ化ビニリデン多孔質膜の内部構造は、明瞭な球晶構造が確認されず、10μm以上のマクロボイドがみられないことが望ましい。また、その孔径は、3〜5μmのクリプトスポリジウムを阻止するという観点からは、バブルポイント法で求められる最大孔径が1μm以下、好ましくは0.7μm以下でなければならないが、本発明に係るポリフッ化ビニリデン多孔質膜はこうした要求を十分に満足させる。 As for the internal structure of the porous polyvinylidene fluoride membrane thus made porous, it is desirable that a clear spherulite structure is not confirmed and macrovoids of 10 μm or more are not observed. Further, from the viewpoint of blocking 3 to 5 μm of Cryptosporidium, the maximum pore size required by the bubble point method should be 1 μm or less, preferably 0.7 μm or less, but the polyvinylidene fluoride according to the present invention. The porous membrane sufficiently satisfies these requirements.
次に、実施例について本発明を説明する。 Next, the present invention will be described with reference to examples.
実施例
ポリフッ化ビニリデン樹脂(シグマアルドリッチ社製品；Mw275,000)30重量％とアセチルクエン酸トリブチル70重量％とを、ニーダを用いて170℃の温度で溶融混合した後、冷却した。冷却固化した混合物を、170℃に加熱したSUS鋼板を用いて、スペース厚みが0.5mmとなるように熱プレスした後、20℃の水冷却浴中で固化させることにより、フィルム状成形体を得た。得られた成形体をエタノール中に浸漬させ、アセチルクエン酸トリブチルを抽出、除去した後乾燥することにより、平膜状ポリフッ化ビニリデン多孔質膜を得た。
Example 30% by weight of polyvinylidene fluoride resin (manufactured by Sigma-Aldrich; Mw275,000) and 70% by weight of tributyl acetylcitrate were melt mixed at a temperature of 170 ° C. using a kneader, and then cooled. The chilled and solidified mixture is hot-pressed using a SUS steel plate heated to 170 ° C so that the space thickness is 0.5 mm, and then solidified in a 20 ° C water cooling bath to obtain a film-like molded product. It was. The obtained molded body was immersed in ethanol to extract and remove tributyl acetylcitrate and then dried to obtain a flat membrane-like polyvinylidene fluoride porous membrane.
得られた多孔質平膜の断面構造を走査型電子顕微鏡で観察したところ、図１に示される如く明瞭な球晶構造は生じておらず、また10μm以上のマクロボイドは存在しなかった。なお、図２は、膜表面の走査型電子顕微鏡写真である。 When the cross-sectional structure of the obtained porous flat membrane was observed with a scanning electron microscope, a clear spherulite structure did not occur as shown in FIG. 1, and no macrovoids of 10 μm or more were present. FIG. 2 is a scanning electron micrograph of the film surface.
さらに、この多孔質平膜について、次の各項目の測定を行った。
最大孔径：ASTM F316-86に基づき、バブルポイント法により測定
液体としてエタノールを使用し、25℃におけるバブルポイントを、次式
から算出した
最大孔径(μm)＝(2860×T)／P
T：表面張力(単位：mN/m)
P：最初に気泡が検知される空気圧力(単位：Pa)
空孔率：平膜の面積および厚みを測定し、ポリフッ化ビニリデンの比重1.78を用い
て、次式から算出した
空孔率(％)＝(1−W／V／1.78)×100
W：平膜の重量(単位：g)
V：見掛け体積(単位：cm3)
透水量：平膜を直径25mmの円形状に打ち抜き、これをロ過ホルダー(アドバンテッ
ク社製攪拌型ウルトラホルダーUHP-25K；有効ロ過面積3.5cm2)にセットし
、25℃、0.1MPaの引加圧条件下で透水試験を行った
Further, for the porous flat membrane, the following items were measured.
Maximum pore size: measured by the bubble point method based on ASTM F316-86
Using ethanol as the liquid, the bubble point at 25 ° C
Calculated from
Maximum pore size (μm) = (2860 × T) / P
T: Surface tension (Unit: mN / m)
P: Air pressure at which bubbles are first detected (unit: Pa)
Porosity: Measure the area and thickness of the flat membrane and use a specific gravity of 1.78 polyvinylidene fluoride
Calculated from the following equation:
Porosity (%) = (1−W / V / 1.78) × 100
W: Weight of flat membrane (unit: g)
V: Apparent volume (unit: cm 3 )
Permeability: punched flat membrane into a circular shape with a diameter of 25mm,
Click manufactured agitation type ultra holder UHP-25K; Set Enable B to the over area 3.5 cm 2)
, 25 ° C, 0.1 MPa under water pressure test
比較例１
実施例において、アセチルクエン酸トリブチルの代りに同量のアセチルクエン酸トリエチルを用いると、得られた平膜状ポリフッ化ビニリデン多孔質膜の断面には、顕著な球晶の生成が確認された(図３参照)。
Comparative Example 1
In the examples, when the same amount of triethyl acetyl citrate was used instead of tributyl acetyl citrate, formation of remarkable spherulites was confirmed in the cross section of the obtained flat membrane-like polyvinylidene fluoride porous membrane ( (See FIG. 3).
比較例２
実施例において、アセチルクエン酸トリブチルの代りに同量のアセチルクエン酸トリメチルを用いると、得られた平膜状ポリフッ化ビニリデン多孔質膜の断面には、顕著な球晶の生成が確認された(図４参照)。
Comparative Example 2
In the examples, when the same amount of trimethyl acetylcitrate was used instead of tributyl acetylcitrate, the formation of significant spherulites was confirmed in the cross section of the obtained flat membrane-like polyvinylidene fluoride porous membrane ( (See FIG. 4).
比較例３
実施例において、アセチルクエン酸トリブチルの代りに同量のクエン酸トリエチルを用いると、得られた平膜状ポリフッ化ビニリデン多孔質膜の断面には、直径10μm以上の顕著な球晶の生成が確認された(図５参照)。
Comparative Example 3
In the examples, when the same amount of triethyl citrate was used instead of tributyl acetyl citrate, the formation of remarkable spherulites with a diameter of 10 μm or more was confirmed in the cross section of the obtained flat membrane-like polyvinylidene fluoride porous membrane. (See FIG. 5).
比較例４
実施例において、アセチルクエン酸トリブチルの代りに同量のクエン酸トリブチルを用いると、得られた平膜状ポリフッ化ビニリデン多孔質膜の断面には、直径10μm以上の顕著な球晶の生成が確認された(図６参照)。
Comparative Example 4
In the Examples, when the same amount of tributyl citrate was used instead of acetyl tributyl citrate, it was confirmed that significant spherulites with a diameter of 10 μm or more were formed in the cross section of the obtained flat membrane-like polyvinylidene fluoride porous membrane. (See FIG. 6).
比較例５
実施例において、ポリフッ化ビニリデン樹脂としてMw534,000(シグマアルドリッチ社製品)を同量用いると、得られた平膜状ポリフッ化ビニリデン多孔質膜の断面には、直径10μm以上の顕著な球晶の生成が確認された(図７参照)。
Comparative Example 5
In the examples, when the same amount of Mw 534,000 (Sigma-Aldrich product) is used as the polyvinylidene fluoride resin, the cross section of the obtained flat film-like polyvinylidene fluoride porous film has a remarkable spherulite diameter of 10 μm or more. Generation was confirmed (see FIG. 7).
比較例６
実施例において、ポリフッ化ビニリデン樹脂(Mw275,000)の割合を40重量％に、またアセチルクエン酸トリブチルの割合を60重量％にそれぞれ変更して用いると、得られた平膜状ポリフッ化ビニリデン多孔質膜の断面には、顕著な球晶の生成が確認された(図８参照)。
Comparative Example 6
In the examples, when the proportion of polyvinylidene fluoride resin (Mw275,000) was changed to 40% by weight and the proportion of tributyl acetylcitrate was changed to 60% by weight, the obtained flat membrane-like polyvinylidene fluoride porous material was used. Prominent spherulite formation was confirmed in the cross section of the membrane (see FIG. 8).
比較例７
実施例において、ポリフッ化ビニリデン樹脂(Mw275,000)の割合を20重量％に、またアセチルクエン酸トリブチルの割合を80重量％にそれぞれ変更して用いると、得られた平膜状ポリフッ化ビニリデン多孔質膜の断面には、微細な球晶の生成が確認された(図９参照)。
Comparative Example 7
In the examples, when the ratio of polyvinylidene fluoride resin (Mw275,000) was changed to 20% by weight and the ratio of tributyl acetylcitrate was changed to 80% by weight, the obtained flat film-like polyvinylidene fluoride porous film was used. Formation of fine spherulites was confirmed in the cross section of the membrane (see FIG. 9).
以上の実施例および各比較例で得られた結果は、次の表に示される。
表
例 最大孔径(μm) 空孔率(％) 透水量(L/m 2 /hr)
実施例 0.7 71 2500
比較例１ ＞2 72 3700
〃 ２ ＞2 71 3400
〃 ３ ＞2 74 4400
〃 ４ ＞2 72 5000
〃 ５ ＞2 70 4200
〃 ６ 1.6 69 700
〃 ７ 1.4 79 5400
The results obtained in the above examples and comparative examples are shown in the following table.
table
Example Maximum pore size (μm) Porosity (%) Water permeability (L / m 2 / hr)
Example 0.7 71 2500
Comparative Example 1> 2 72 3700
〃 2> 2 71 3400
３ 3> 2 74 4400
４ 4> 2 72 5000
５ 5> 2 70 4200
1.6 6 1.6 69 700
７ 7 1.4 79 5400
Claims (3)
(ここでR1、R2、R3はいずれもブチル基であり、R4はアシル基である)で表わされるクエン酸エステル化合物75〜65重量％との混合物を溶融成形した後、クエン酸エステル化合物抽出溶媒でクエン酸エステル化合物を除去し、成形体を多孔質化させることを特徴とする、バブルポイント法(ASTM F316-86準拠)で求められた最大孔径が1μm以下で、膜断面構造に明確な球晶が確認されないポリフッ化ビニリデン多孔質膜の製造法。 Polyvinylidene fluoride resin having a weight average molecular weight Mw of 100,000 to 300,000, 25 to 35% by weight, and a general formula
(Wherein R 1 , R 2 and R 3 are all butyl groups and R 4 is an acyl group) The maximum pore size determined by the bubble point method (according to ASTM F316-86) is 1 μm or less, and the cross-sectional structure of the membrane is characterized by removing the citrate ester compound with an ester compound extraction solvent and making the molded body porous A method for producing a polyvinylidene fluoride porous film in which no clear spherulites are observed .
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