【発明の詳細な説明】[Detailed description of the invention]
（産業上の利用分野）
本発明は濾過性能ならびに機械的性質ともに優
れたポリサルホン系樹脂製精密濾過膜の製造方法
に関するものである。
膜分離技術は、その省エネルギー性、コンパク
ト性といつた面で注目され、めざましく進展して
きた。このようなシステムに用いられる選択透過
性分離膜の膜素材としては多種類のポリマーが研
究開発され、セルロース系、ポリアミド系、ポリ
アクリロニトリル系、ポリサルホン系ポリマーな
どが使用されている。なかでもポリサルホン系ポ
リマーは、元来エンジニアリングプラスチツクと
して使用されているものであるが、その耐熱性、
耐酸性、耐アルカリ性などの耐薬品性が良好であ
ることから分離膜の素材としても使用されるよう
になつてきている。このポリサルホン系の膜は特
に蒸気減菌処理が可能であり、食品処理用、医療
用、製薬用に注目され始めている。
しかし、ポリサルホン系樹脂はセルロースアセ
テート等に比較し、分子間凝集力が強すぎ、孔径
を制御するのが困難である。特に本発明で目的と
している様なスキン層で被覆されていない精密濾
過膜、即ち表面および裏面とも電子顕微鏡で観察
し得る程度の多孔構造を有している膜について
は、従来より知られている製造方法はいくつかの
問題点を有している。
なお、本発明で言う電子顕微鏡で観察し得る程
度の多孔構造を有している膜というのは一般的に
は100Å以上の孔径の孔を有しているマイクロフ
イルターまたは精密濾過膜のことであり、実用的
なものでは1000Å（0.1μｍ）以上の孔径のものが
多数上市されていることから、膜孔径としては
0.1μｍ以上あればよい。
（従来技術）
例えば、特開昭57−35906では膜形成液（以下
ドープと記す）に多量のポリエチレングリコール
（以下PEGと記す）を添加し、製膜後にPEGを抽
出して多孔質化する方法が開示されている。
（発明が解決しようとする問題点）
しかしながら、この方法ではPEGの抽出を完
全に行うには多大の労力と時間を要し、また多量
のPEGを添加した場合には過度の多孔質化が起
こり、膜の機械的性質が著しく損われることにな
る。
さらに、非溶剤が多量に添加された不安定なド
ープを用いて製膜する方法が、例えば特開昭56−
154051や特開昭59−58041に開示されている。し
かし工業化を考えた場合、ドープの性状を一定に
維持することが不安定なドープの場合には著しく
困難で、従つてこのようなドープを用いて製造さ
れた膜の品質を常に一定に保持することは非常に
困難である。
そこで本発明者らは鋭意検討した結果、上記の
ような問題を解消して、濾過性能ならびに機械的
性質の優れたポリサルホン系樹脂製精密濾過膜の
製造方法を見出し、本発明に到達した。
（発明の構成）
即ち、本発明は、「(a)ポリサルホン系樹脂５〜
14重量％、(b)ポリサルホン系樹脂の良溶剤に溶解
する水溶性のカルボン酸２〜15重量％、(c)ポリサ
ルホン系樹脂の良溶剤61〜93重量％および必要に
応じて(d)増粘剤および／または膨潤剤１〜10重量
％からなる膜形成液を用いて湿式製膜することを
特徴とするバブルポイントから求められる最大孔
径が0.1μｍ以上である精密濾過膜の製造法」であ
る。
ここで、本発明におけるバブルポイントから求
められる最大孔径が0.1μｍ以上であるものとは、
後述する純水を用いて測定したバブルポイント
（Kg／cm2）から求められる推定最大孔径が0.1μｍ
以上であるものをいう。
本発明でいうポリサルホン系樹脂としては、下
記式(1)〜(3)の構造を有する芳香族ポリサルホン系
樹脂が代表的なものである。
(Field of Industrial Application) The present invention relates to a method for manufacturing a polysulfone resin precision filtration membrane having excellent filtration performance and mechanical properties. Membrane separation technology has attracted attention for its energy saving and compactness, and has made remarkable progress. Many types of polymers have been researched and developed as membrane materials for permselective separation membranes used in such systems, and cellulose-based, polyamide-based, polyacrylonitrile-based, polysulfone-based polymers, etc. have been used. Among them, polysulfone polymers are originally used as engineering plastics, but their heat resistance and
Due to its good chemical resistance such as acid resistance and alkali resistance, it is also being used as a material for separation membranes. This polysulfone-based membrane is particularly suitable for steam sterilization, and is beginning to attract attention for use in food processing, medical care, and pharmaceuticals. However, polysulfone resins have a much stronger intermolecular cohesive force than cellulose acetate and the like, making it difficult to control the pore size. In particular, precision filtration membranes that are not covered with a skin layer as the object of the present invention, that is, membranes that have a porous structure on both the front and back surfaces that can be observed with an electron microscope, have been known for a long time. The manufacturing method has several problems. In addition, in the present invention, a membrane having a porous structure that can be observed with an electron microscope generally refers to a microfilter or precision filtration membrane having pores with a pore diameter of 100 Å or more. Many practical membrane pore diameters are on the market, with a pore size of 1000 Å (0.1 μm) or more.
It is sufficient if it is 0.1 μm or more. (Prior art) For example, in JP-A-57-35906, a method is proposed in which a large amount of polyethylene glycol (hereinafter referred to as PEG) is added to a film forming solution (hereinafter referred to as dope), and the PEG is extracted after film formation to make it porous. is disclosed. (Problems to be solved by the invention) However, this method requires a lot of effort and time to completely extract PEG, and when a large amount of PEG is added, excessive porosity may occur. , the mechanical properties of the membrane will be significantly impaired. Furthermore, a method of forming a film using an unstable dope containing a large amount of non-solvent has been proposed, for example, in
154051 and Japanese Patent Application Laid-Open No. 59-58041. However, when considering industrialization, it is extremely difficult to maintain the properties of the dope constant if the dope is unstable, and therefore it is difficult to maintain the quality of the film manufactured using such a dope at all times. That is extremely difficult. As a result of intensive studies, the present inventors have found a method for producing a polysulfone-based resin precision filtration membrane that solves the above-mentioned problems and has excellent filtration performance and mechanical properties, and have arrived at the present invention. (Structure of the Invention) That is, the present invention provides “(a) polysulfone resin 5 to
14% by weight, (b) 2 to 15% by weight of a water-soluble carboxylic acid that dissolves in a good solvent for polysulfone resins, (c) 61 to 93% by weight as a good solvent for polysulfone resins, and (d) increased as necessary. A method for producing a precision filtration membrane having a maximum pore diameter of 0.1 μm or more as determined from the bubble point, which is characterized by wet membrane formation using a membrane-forming liquid containing 1 to 10% by weight of a sticky agent and/or a swelling agent. be. Here, in the present invention, the maximum pore diameter determined from the bubble point is 0.1 μm or more,
The estimated maximum pore diameter determined from the bubble point (Kg/cm 2 ) measured using pure water described below is 0.1 μm.
This refers to things that are more than that. As the polysulfone resin referred to in the present invention, aromatic polysulfone resins having structures of the following formulas (1) to (3) are representative.
【化】[ka]
【化】[ka]
〔ただし
γ：25℃の水の表面張力72dyhe／cm
θ：ポリサルホン系樹脂と水との接触角
（(1)式の樹脂では78゜）〕〔however
γ: Surface tension of water at 25℃ 72dyhe/cm
θ: Contact angle between polysulfone resin and water
(78° for the resin of formula (1))
実施例 １
(1)式のポリエーテルサルホン樹脂（商品名、
Victrex4800P、ICI社製）14重量部およびしゆう
酸９重量部を２−ピロリドン77重量部に溶解し、
11000CP（25℃）の粘度を有する均一なドープを
得た。これを室温雰囲気中で、ガラス板上に厚み
300μｍに流延し、60秒後に室温の水中に浸漬し
た後水洗して精密濾過膜を得た。この膜のLpは
12.2ml／cm2・minだり、B.P.は3.2Kg／cm2（DM0.2μ
ｍ）であつた。また膜厚は140μｍであり、破断
点における強度は210ｇ／mm2、伸度は46％を示し
た。
実施例 ２
(1)式のポリエーテルサルホン樹脂12重量部およ
びしゆう酸８重量部を２−ピロリドン80重量部に
溶解し、3800CP（25℃）の粘度を有する均一なド
ープを得た。これを室温雰囲気中でガラス板上に
厚み300μｍに流延し100秒後に35℃の80重量％２
−ピロリドン水溶液に浸漬した後、水洗して精密
濾過膜を得た。この膜のLpは24.8ml／cm2・minで
あり、B.P.は1.4Kg／cm2（DM0.4μｍ）であつた。
また膜厚は120μｍであり破断点における強度330
ｇ／mm2、伸度29％を示した。
実施例 ３
(1)式のポリエーテルサルホン樹脂12重量部およ
び酢酸10重量部をジメチルスルホキシド78重量部
に溶解し、均一なドープを得た。これを室温雰囲
気中でガラス板上に厚み350μｍに流延し放置時
間60秒後に室温の水中に浸漬した後、水洗して精
密濾過膜を得た。この膜のLpは8.3ml／cm2・
min・Kg／cm2であり、B.P.は2.3Kg／cm2（DM0.3μ
ｍ）であつた。また膜厚は170μｍであり、破断
点における強度は250ｇ／mm2、伸度29.5％を示し
た。
実施例 ４
酢酸の代わりにくえん酸を、ジメチルスルホキ
シドの代わりにＮ−メチル−２ビロリドンを用
い、放置時間を120秒とする以外は実施例３と同
様の方法で精密濾過膜を得た。この膜のLPは5.8
ml／cm2・min・Kg／cm2であり、B.P.は2.2Kg／cm2
（DM0.3μｍ）であつた。また膜厚は180μｍであり
破断点における強度は270ｇ／mm2、伸度44.5％を
示した。
実施例 ５
くえん酸の代わりに安息香酸を用い、Ｎ−メチ
ル−２ピロリドンの代わりにジメチルホルムアミ
ドを用いる以外は実施例４と同様の方法で精密濾
過膜を得た。この膜のLpは12.5ml／cm2・min・
Kg／cm2であり、B.P.は2.2Kg／cm2（DM0.3μｍ）で
あつた。また膜厚は130μｍであり、破断点にお
ける強度は440ｇ／mm2、伸度72.5％を示した。
実施例 ６
(1)式のポリエーテルサルホン樹脂10重量部およ
びしゆう酸10重量部を２ピロリドン80重量部に溶
解し、粘度1700CP（25℃）のドープを得た。これ
をガラス板上に200μｍの厚みで流延し、室温雰
囲気下で120秒放置後室温の水中に浸漬した後、
水洗して精密濾過膜を得た。この膜のLpは93.6
ml／cm2・min・Kg／cm2であり、B.P.は1.2Kg／cm2
（DM0.5μｍ）であつた。また破断点の強度は430
ｇ／mm2、伸度は47％であつた。
比較例 １
(1)式のポリエーテルサルホン10重量部を90重量
部の２ピロリドンに溶解し、均一なドープを得
た。このドープをガラス板上に厚み350μｍで流
延し、室温雰囲気中で120秒放置後室温の水中に
浸漬した後水洗して膜を得た。この膜にはピンホ
ールや凹凸が多数認められ、Lpも2.1ml／cm2・
min・Kg／cm2という低い値であつた。
比較例 ２
くえん酸20重量部を２−ピロリドン70重量部に
溶解し、これに(1)式のポリエーテルサルホン10重
量部を加え70℃で撹拌し続けたが、ポリエーテル
サルホンは溶解しなかつた。
比較例 ３
(1)式のポリエーテルサルホン２重量部としゆう
酸10重量部を２−ピロリドン88重量部に溶解し、
均一なドープを得た。このドープをガラス板上に
厚み350μｍで流延し、室温雰囲気下で120秒放置
後室温の水中に浸漬したが、膜を形成することな
く白濁するのみであつた。
Example 1 Polyethersulfone resin of formula (1) (trade name,
14 parts by weight of Victrex 4800P (manufactured by ICI) and 9 parts by weight of oxalic acid were dissolved in 77 parts by weight of 2-pyrrolidone,
A homogeneous dope with a viscosity of 11000CP (25°C) was obtained. This is then placed on a glass plate in a room temperature atmosphere.
The membrane was cast to a thickness of 300 μm, and 60 seconds later, it was immersed in water at room temperature and then washed with water to obtain a microfiltration membrane. The Lp of this membrane is
12.2ml/cm 2・min, BP is 3.2Kg/cm 2 (D M 0.2μ
It was m). The film thickness was 140 μm, the strength at the breaking point was 210 g/mm 2 , and the elongation was 46%. Example 2 12 parts by weight of polyether sulfone resin of formula (1) and 8 parts by weight of oxalic acid were dissolved in 80 parts by weight of 2-pyrrolidone to obtain a uniform dope having a viscosity of 3800CP (25°C). This was cast on a glass plate to a thickness of 300 μm in a room temperature atmosphere, and after 100 seconds it was heated to 80% by weight at 35°C.
- After immersing in a pyrrolidone aqueous solution, the membrane was washed with water to obtain a microfiltration membrane. The Lp of this membrane was 24.8 ml/cm 2 ·min, and the BP was 1.4 Kg/cm 2 ( DM 0.4 μm).
The film thickness is 120 μm and the strength at the breaking point is 330
g/mm 2 and elongation of 29%. Example 3 12 parts by weight of polyether sulfone resin of formula (1) and 10 parts by weight of acetic acid were dissolved in 78 parts by weight of dimethyl sulfoxide to obtain a uniform dope. This was cast on a glass plate to a thickness of 350 μm in a room temperature atmosphere, left for 60 seconds, immersed in water at room temperature, and washed with water to obtain a microfiltration membrane. The Lp of this membrane is 8.3ml/ cm2・
min・Kg/cm 2 and BP is 2.3Kg/cm 2 (D M 0.3μ
It was m). The film thickness was 170 μm, and the strength at the breaking point was 250 g/mm 2 and the elongation was 29.5%. Example 4 A microfiltration membrane was obtained in the same manner as in Example 3, except that citric acid was used instead of acetic acid, N-methyl-2-pyrrolidone was used instead of dimethyl sulfoxide, and the standing time was 120 seconds. The LP of this membrane is 5.8
ml/cm 2・min・Kg/cm 2 and BP is 2.2Kg/cm 2
(D M 0.3 μm). The film thickness was 180 μm, the strength at the breaking point was 270 g/mm 2 , and the elongation was 44.5%. Example 5 A microfiltration membrane was obtained in the same manner as in Example 4, except that benzoic acid was used instead of citric acid and dimethylformamide was used instead of N-methyl-2-pyrrolidone. The Lp of this membrane is 12.5ml/cm 2・min・
Kg/cm 2 and BP was 2.2 Kg/cm 2 ( DM 0.3 μm). The film thickness was 130 μm, the strength at the breaking point was 440 g/mm 2 , and the elongation was 72.5%. Example 6 10 parts by weight of the polyether sulfone resin of formula (1) and 10 parts by weight of oxalic acid were dissolved in 80 parts by weight of 2-pyrrolidone to obtain a dope with a viscosity of 1700CP (25°C). This was cast onto a glass plate to a thickness of 200 μm, left in a room temperature atmosphere for 120 seconds, and then immersed in room temperature water.
A microfiltration membrane was obtained by washing with water. The Lp of this membrane is 93.6
ml/cm 2・min・Kg/cm 2 and BP is 1.2Kg/cm 2
(D M 0.5 μm). Also, the strength at the breaking point is 430
g/mm 2 and elongation was 47%. Comparative Example 1 10 parts by weight of polyether sulfone of formula (1) was dissolved in 90 parts by weight of 2-pyrrolidone to obtain a uniform dope. This dope was cast onto a glass plate to a thickness of 350 μm, left in a room temperature atmosphere for 120 seconds, immersed in room temperature water, and washed with water to obtain a film. Many pinholes and irregularities were observed in this film, and the Lp was 2.1ml/ cm2 .
The value was as low as min・Kg/cm 2 . Comparative Example 2 20 parts by weight of citric acid was dissolved in 70 parts by weight of 2-pyrrolidone, 10 parts by weight of polyethersulfone of formula (1) was added thereto, and stirring was continued at 70°C, but the polyethersulfone was not dissolved. I didn't. Comparative Example 3 2 parts by weight of polyether sulfone of formula (1) and 10 parts by weight of oxalic acid were dissolved in 88 parts by weight of 2-pyrrolidone,
A uniform dope was obtained. This dope was cast onto a glass plate to a thickness of 350 μm, left in an atmosphere at room temperature for 120 seconds, and then immersed in water at room temperature, but it only became cloudy without forming a film.