JPS60206416A - Preparation of polysulfone membrane - Google Patents

Abstract

PURPOSE:To obtain a polysulfone membrane having a pore size of 0.03-0.2mum and high in water permeability, by setting a coagulation bath to a high temp. in a wet membrane forming process. CONSTITUTION:A polysulfone resin represented by formula is dissolved in a solvent capable of dissolving said polysulfone resin and substantially miscible with water at an ambient temp. As a concrete example, when a solvent mixture consisting of N-methyl-2-pyrrolidone and ethylene glycol monoethyl ether, of which the volumetric ratio is changed in a range of 100:0-43:47, is used, the pore size and water permeability of a membrane can be controlled to a certain degree without changing the other condition. The concn. of the polysulfone resin is pref. in a range of 16-22g/dl. By changing the temp. of a coagulation bath within a range of 35-95 deg.C, the membrane, of which the pore size is in a range of 0.03-0.2mum and the water permeability is 1.5m<3>/m<2>hrkg/cm<2> or more, is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a Borisl 7-on membrane that has a high water permeability and a large pore size.

Conventionally, separation membranes that use pressure as the driving force have been classified into the Miku-P filter (0.1 μm or more), the ultra-F
They are classified into diaphragm membranes (several tens to hundreds of membranes) and reverse osmosis membranes (sized to block inorganic ions). Microfilters are generally produced by a dry process characterized by dissolving a membrane material polymer in a mixed solvent of a good solvent and a non-solvent for the polymer, casting the solution on a flat plate, and evaporating the solvent. be done. In this method, the microstructure of the membrane is uniform in the cross-sectional direction and a symmetrical membrane is obtained. The minimum pore diameter grade of this microfilter is approximately 0.2 μm. In rare cases, there are particles less than 11.1 μm, but these have a water permeability of 1.
-/pa・hr・(k9〆go) or less, which is extremely low and is currently impractical.

In contrast to microfilters, ultrafiltration membranes are manufactured by a wet process. A membrane is obtained by dissolving a polymer serving as a membrane material in a solvent, casting it into a desired form, and then immersing the polymer in a coagulation bath made of a non-solvent and coagulating it. In this method, the fine structure of the film is the most dense on the film surface,
An asymmetric membrane with many spongy cavities inside the membrane is obtained.

Therefore, the water permeability of the membrane is mainly controlled by the dense layer on the surface of the membrane, and despite having fine pores, it exhibits relatively high water permeability.

According to the wet method, a dense layer appears on the membrane surface;
A membrane with a relatively small pore size is obtained.

For example, among the currently commercially available asymmetric ultrafurnace membranes,
Although the highest molecular weight cutoff is 3'X10', this membrane blocks more than 98% of blue dextran with a molecular weight of 2X10'. On the other hand, commercially available Q.
A microfilter with a pore size of 22 μm does not block blue dextran at all. For this reason, it is desired to develop a membrane with a pore size that is between the lower limit of the pore size of the microfilter 2 produced by the dry method and the upper limit of the pore diameter of the ultrafilter membrane produced by the wet method.

The present inventors have completed the present invention as a result of extensive research into producing an asymmetric membrane with a pore size of approximately α03 to [1L2 μm] using a wet film forming method.

The present invention relates to a wet membrane forming method for obtaining a Borisl 7-on membrane with high water permeability and a pore size of 0.05 to [L2 μm. The wet film forming method referred to here is a general method that is usually used. For example, a film forming stock solution in which a polymer, which is a membrane raw material, is dissolved in a solvent is coated on a glass plate, nonwoven fabric, paper, etc. to a thickness of several tens to hundreds of sheets. To coagulate the coated membrane raw material polymer by coating it on microns and immersing it in a coagulation bath consisting of a precipitation solvent for the membrane raw material polymer and a liquid that is easily miscible with the solvent used in the membrane forming stock solution. This is a method to obtain a separation membrane. In this case, the solvent for dissolving the membrane material polymer is generally a single solvent or a good solvent for the membrane material polymer, with the addition of various non-solvents or inorganic salts, and the solvent is often water-soluble. be done.

The coagulation bath usually uses water or a mixed liquid containing water as a main component. The temperature of the coagulation bath is usually from 0°C to 20°C.

The features of the present invention are as follows in the already-mentioned known wet film forming method:
By setting a high coagulation bath temperature, it is possible to easily obtain a polysulfone membrane with a high water permeability and a pore size α of 3 to 0.2 μm. As described in the Examples, according to the studies of the present inventors, when forming a polysulfone membrane by a normal wet membrane forming method, if the coagulation bath temperature is lower than 65°C, the water permeability and pore size will be significantly affected. It was found that while no coagulation bath temperature dependence was observed, a significant temperature dependence was observed when the coagulation bath temperature was 35° C. or higher, the pore size of the membrane became larger, and the water permeability was greatly improved. Moreover, if the temperature exceeds 95°C, operational problems such as the solvent starting to boil occur. below,
The present invention will be explained in more detail.

The polysulfone resin used in the present invention has a structure represented by the following general formula (I).

The solvent for dissolving the polysul 7-one resin may be a single solvent or a mixed solvent, as long as it can dissolve the polysul 7-one resin and is substantially miscible with water at room temperature. Of course, inorganic salts, organic substances, and other substances that are solid at room temperature may be dissolved in the solvent. Such solvents include, for example, N-methyl-2-pyrrolidone, N-methyl-2-pyrrolidone,
, N'-dimethylformamide, dimethylacetamide, etc. are generally used as main components, and these solvents include dimethylsulf7oxide, ethylene glycol monoethyl ether, which is a substantially non-solvent for borisulfon resin. ethylene glycol monomethyl ether,
These include organic substances such as acetamide, or those containing ethylene glycol, diethylene glycol, etc.

Among these solvents, a mixed solvent of N-methyl-2-pyrrolidone and ethylene glycol monoethyl ether is particularly effective. Volume ratio of N-methyl-2-pyrrolidone to ethylene glycol monoethyl ether: 1
By changing the ratio between 00:0 and 43:57, the pore size and water permeability of the membrane can be controlled to some extent without changing other conditions. Similarly, a mixed system of N,N'-dimethylformamide and ethylene glycol monoethyl ether is also effective. In this case, the mixing ratio is 100:
A range of 0 to 84:16 is desirable.

The composition of the membrane forming stock solution greatly influences the water permeability and pore size of the membrane. Among these, the concentration of polysulfone resin is 169
It is desirable that the range is from /d/ to 22k/'a1. If the resin concentration is less than 169/At, the strength of the obtained film is extremely low, making it uneasy to use, and
If it exceeds 297 dl, no significant improvement can be expected in both water permeability and pore size.Next, the coagulation bath will be explained. By changing the temperature of the coagulation bath from 35°C to 95°C, the pore size of the membrane can be adjusted to α0.
In the range of 3 to α2μm and 1.51/1・re・(k9
/cdt) or higher, but the effect varies somewhat depending on the resin concentration and the type of solvent in the membrane forming stock solution. Water is usually sufficient as the coagulating liquid, but water-soluble additives such as glycols such as ethylene glycol, diethylene glycol, propylene glycol, and glycerin may be added to the water. For polysul 7-one resin,
A good solvent may be added. However, when adding these additives to water, the volume fraction of the additives is preferably less than 70%. Even if the volume fraction exceeds 70%, a large-pore membrane with excellent water permeability can be obtained, but this is not desirable because of problems such as the slow coagulation rate of the membrane in the coagulation bath and the economical efficiency of the coagulation bath.

The Borisl 7on membrane obtained by the present invention has a pore size region that fills the gap between conventional microfilters and ultrafiltration membranes.
That is, the membrane having a pore diameter of 1.03 to 11.2 μm can be applied in many fields.

EXAMPLES The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples.

Examples 1 to 6, Comparative Examples 1' to 4' Polysulfone resin ([Udel Polysulfone P-55
00J product name, U. O. (manufactured by Company O) 1809 in 1 liter of a mixed solvent of N-methyl-2-pyrrolidone and ethylene glycol monoethyl ether at a volume ratio of 1:1! to make a homogeneous solution. This solution was cast onto a polyethylene nonwoven fabric to a thickness of 150 μm and immersed in a coagulation bath. The coagulation bath is water and its temperature is 2℃, 10℃, 20℃, 50℃, 40℃.
℃, 500G, 60℃, 70℃, 80℃, and 90℃.

After removing the solvent from the obtained membrane with distilled water for 3 days, a water permeability test was conducted. The water used for the water permeability test was distilled water at 13°C. In addition, the rejection rate of blue dextran (molecular weight 2 x 10') of these membranes was investigated. The device used was a stirring type ultrap filter device (trade name ``up-50'', manufactured by Toyo F Paper Company), and 40 d of [L1% blue dextran was put into the device and passed through the door at a pressure of LL3k9/m. When 20 d of furnace liquid was obtained, the rejection rate R was calculated from the concentration of the liquid remaining in the apparatus and the membrane permeate liquid using the following formula.

The average pore size of the membrane was determined by scanning electron micrograph.

These results are shown in Table 1.

Examples 7 to 10, Comparative Examples 5' to 7' The same borisulfon resin as in Examples 1 to 6 was mixed with N,
It was dissolved in 1 liter of N'-dimethylformamide to prepare a membrane forming stock solution. Is this solution not made of polypropylene? It was coated onto a woven fabric to a thickness of 160 μm using a doctor knife, and immediately thereafter immersed in a coagulation bath to obtain a polysulfon film. As the coagulating liquid, a mixed liquid of water/ethylene glycol=7/3 (volume) was used.

Coagulation liquid temperature: 32℃, 15℃, 30℃, 40℃, 55℃
, 80° C., and 95° C., and the performance of the obtained membranes was examined in the same manner as in Examples 1 to 6. The performance of the obtained membrane is shown in Table 2.10 Examples 11 to 13 180 g of the same bipolysul 7-one resin as in Examples 1 to 6 was mixed with N,
1 liter of solvent with a volume ratio of 11'-dimethylformamide and ethylene glycol monoethyl ether of 95:5! The mixture was dissolved in a homogeneous solution and used as a film-forming stock solution.

Spread this stock solution on a polyethylene nonwoven fabric to a thickness of approximately 200 μm.
A borisulfon film was obtained by applying the solution to a coagulating solution and immersing it in a coagulating solution. The coagulating liquid was water, and the temperature was 40°C, 60°C, and 80°C. The properties of the obtained polysulfon membrane were investigated in the same manner as in Examples 1 to 6, and the results are shown in Table 5.

Comparative Example 8/ Exactly the same as Examples 11 to 13, only the amount of Polysul 7-on resin was 150,976 liters! As a result, a polysulfon membrane was obtained. The obtained membranes have a water permeability of 2-/1●
hr (1vH or higher), but it peeled off from the polyethylene nonwoven fabric of the support.

Claims (1)

[Claims] 1. A method for obtaining a separation membrane using a wet membrane forming method using borisulfone resin having a repeating unit represented by general formula (1), wherein the coagulation bath temperature range is 35°C to 95°C, and water is used as a bath agent. A method for producing a highly water permeable polysulfonate membrane, characterized in that the main component is 2. The method according to claim 1, wherein the coagulation bath temperature is from 50°C to 95°C. 5. The coagulation bath according to claim 1 or 2, wherein 30% by volume or more of the coagulation bath is water, and other components are ethylene glyfur, diethylene glycol, propylene glycol, glycerin, or a mixed solution of two or more thereof. Method. 4. The water-soluble solvent that dissolves the borisulfone resin is N-
The method according to any one of claims 1 to 3, wherein methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, or a mixture thereof is used. 5. A patent claim characterized in that the solvent for dissolving the polysulfone resin is a mixed solvent of N,N-dimethylformamide and ethylene glycol monoethyl ether in a volume ratio ranging from 100:0 to 84:16. Range 1
The method described in any one of Items 1 to 5. & The solvent that dissolves the polysul 7-one resin is N-methyl 2
Claims 1 to 3 are characterized in that the solvent is a mixed solvent of pyrrolidone and ethylene glycol monoethyl ether with a volume WI ratio in the range of 100:0 to 45:57.
The method described in any of the sections. The concentration of polysulfone resin in the Z polysulfone resin solution ranges from 169/+i/ to 22 g/dl! A method according to any one of claims 1 to 6, characterized in that: