JPS6249912A - Production of microporous membrane - Google Patents

Abstract

PURPOSE:To obtain the titled polysulfone microporous membrane having excellent water permeability by forming the membrane from a soln. of 5-50wt% polysulfone and 0.1-60wt%, based on the polysulfone, sulfonated polysulfone in a polar org. solvent. CONSTITUTION:From 5 to 50wt% polysulfone not having a dissociable group and 0.1-60wt%, based on the polysulfone, sulfonated polysulfone are dissolved in a polar org. solvent. The sulfonation rate of the sulfonated polysulfone is preferably controlled to 0.1-4. A solvent dissolving polysulfone and soluble in water is used as the solvent. The soln. is cast on a glass sheet in 150mu liq. thickness, the sheet is immersed in water as the coagulating liq. and the polysulfone membrane is obtained.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for producing a microporous membrane, particularly polysulfone for precision filtration of aqueous and non-aqueous liquids used in the electronic industry, pharmaceutical industry, and food industry. The present invention relates to a method for producing a filter medium using as a raw material.

(Prior Art) Microporous membranes have been known for a long time (for example, R, Ke
rsynthetic Polymer M by sing
embraneJMcGraw Hi11) It is widely used in filtration filters, etc. Microporous membrane is
For example, U.S. Patent Nos. 1,421.341 and 3,133.
゜No. 132, No. 2,944.017, Special Publication No. 43-1
No. 5698, Special Publication No. 45-33313, No. 48-39
As described in U.S. Pat. No. 586, U.S. Pat.
No. 15, No. 4,340.479, No. 4,340,48
No. 0, No. 4゜450.126, German patent DE3,1
38゜525, those manufactured using aliphatic polyamides as raw materials as described in JP-A-58-37842, etc., U.S. Pat. Nos. 4,196,070 and 4,34
No. 0,482, JP-A-55-99934, JP-A-58
-Produced from polyfluorocarbon as raw material as described in No. 91732, etc., JP-A-56-1
No. 54051, JP-A-56-86941, JP-A-56
There are those using polysulfone as a raw material, such as those described in German Patent No. 0LS3003400, and those using polypropylene as a raw material, such as those described in German Patent No. 0LS3003400. These microporous membranes are used for filtering and sterilizing cleaning water for the electronic industry, water for medical purposes, water for pharmaceutical manufacturing processes, water for food use, etc., and their applications and usage have been expanding in recent years. Microporous membranes made from polysulfone are attracting attention because they are capable of filtering liquids containing acids and alkalis, as well as being used for most filtration applications, both aqueous and non-aqueous. family polysulfones are frequently used.

However, since aromatic polysulfone is a material with low hydrophilicity, it does not get wet with water, and has poor water permeability. There was a drawback that the marked areas became dead spaces, causing an air lock phenomenon in which filtration efficiency deteriorated.

Therefore, in order to improve water permeability, for example, inorganic salts such as ZnCl2 or organic substances such as alcohol are added to the membrane forming stock solution as modifiers, or polysulfone is sulfonated (Journal of Polymer Science, Vol. 20, 1885).
(1976)) has been conventionally performed.

(Problems to be Solved by the Invention) However, in the former case, there is a drawback that the modifier dissolves during use as a filtration membrane, and in the latter case,
Not only is the sulfonation step complicated, but the sulfonation deteriorates membrane-forming ability and mechanical performance, and it also cannot be used with alkali-containing liquids.

As a result of intensive studies to solve these conventional drawbacks, the present inventors found that when polysulfone is blended with a certain amount of sulfonated polysulfone, the film forming ability and the performance of the formed film are lower than that of the original polysulfone. We discovered that microporous membranes with good water permeability can be obtained by adding only a small amount of sulfonated polysulfone by selecting the coagulation liquid during membrane formation. The invention has been achieved.

Therefore, the first object of the present invention is to provide a polysulfone microporous membrane with good water permeability.

A second object of the present invention is to provide a polysulfone microporous membrane that has sufficient biological safety and has good water permeability without eluates in the filtrate. A third object of the present invention is to provide a polysulfone microporous membrane with sufficient acid and alkali resistance and good water permeability. A fourth object of the present invention is to provide a method for imparting hydrophilicity to the surface of polysulfone without degrading its properties as a microporous membrane.

(Means for Solving the Problems) The above aspects of the present invention include 5-50i[;1% of polysulfone having no dissociative group and 0.1-60% by weight of sulfonated polysulfone with respect to the polysulfone. This was achieved by a method for producing a microporous membrane, which is characterized by casting a membrane-forming stock solution dissolved in a scratchy organic solvent and coagulating the cast membrane in a hydrophilic coagulating liquid.

The polysulfone used in the present invention is generally referred to as polysulfone A, which is represented by the following. n is a positive integer. Such polysulfones include, for example, Union Carbide Corporation's Needel P-1700 and Needel P-3500 (trade name).
It is commercially available as.

The sulfonated polysulfone mentioned here is typically represented by the following general formula (■).

General Formula (II) Here, M represents a cation such as hydrogen, an alkali metal, an amine, or an alkyl-substituted amine. Further, the introduction position of the sulfone group is not particularly limited, and n is the same as the above-mentioned n and is a positive integer.

These compounds can be prepared using polysulfone in a conventional manner, e.g., Journal of Applied Polymer Science, Vol. 20.
Volume (J, App 1. Polymer Sci,
Vol. 20), pp. 1885-1903 (1976)
It can be synthesized by sulfonation according to the method described in . Further, the sulfonation rate can be controlled by the ratio of S03 to polysulfone, but in the present invention, it is preferably 0.1 to 4, particularly 0.2 to 2.

Further, M in the general formula (II) is preferably a monovalent cation, particularly preferably a hydrogen type.

The film properties of sulfonated polymers deteriorate compared to those without sulfonation, except for the fact that they become hydrophilic, and as the amount of sulfonated polysulfone increases, alkali resistance deteriorates. The amount of sulfonated polysulfone used is preferably 60% by weight or less, particularly 10% by weight or less of the polysulfone in the membrane forming stock solution, and in order to impart hydrophilicity to the surface of the microporous membrane, .1% by weight or more is preferable. 0. 1
There is no membrane with sufficient hydrophilicity at less than 1% by weight.
On the other hand, if it is 60% by weight or more, the t which polysulfone originally has
a) This is not preferable because mechanical strength is lost.

The range that satisfies sufficient hydrophilicity and mechanical strength is 1 to 10% by weight.

Since the sulfonated polysulfone and polysulfone used in the present invention have the same skeleton, they are easily compatible (particularly when the amount of sulfonated polysulfone is large enough to cover the surface of the T-degree microporous membrane, the sulfone group is By directing the polysulfone toward the outside of the membrane, it is possible to stably make only the surface hydrophilic while retaining the original physical properties of polysulfone.In this way, orienting the sulfone group to the outside of the membrane is extremely important in the present invention. However, this can be achieved by selecting the coagulation liquid.

Next, the method for manufacturing the microporous membrane of the present invention will be explained in more detail.

First, polysulfone is dissolved in a solvent that dissolves in water, such as dimethylacetamide, dimethylformamide, tetrahydrofuran, 2-pyrrolidone, N-methyl-2-pyrrolidone, etc., and further, if necessary, to control the pore size. Solvents that are poor solvents for water or polysulfone and that dissolve in water, such as alcohols such as methanol, ethanol, and isopropyl alcohol,
A polymer solution is prepared by adding glycols such as ethylene glycol and propylene glycol, water-soluble polymers such as polyethylene glycol, polypropylene glycol, polystyrene sulfonic acid, and polyvinylpyrrolidone. The sulfonated polysulfone used in the present invention is added and dissolved in an amount of 0.1 to 60% by weight, preferably 1 to 10% by weight, to the polysulfone in this stock solution to prepare a polysulfone film forming stock solution.

This stock solution is cast onto a glass plate using a doctor blade to a thickness of 150 μm, and immersed in water, which is a coagulating liquid, to obtain a polysulfone film. Even if the membrane thus obtained is in a dry state, when it is floated on water, water immediately seeps from the back surface to the surface due to the hydrophilic nature of the membrane.

(Function) This is because when polysulfone precipitates and coagulates in the coagulation liquid, the sulfonic acid groups of the sulfonated polysulfone are preferentially oriented toward the aqueous phase that is in contact with the surface of the polysulfone. This phenomenon occurs only when is water or a hydrophilic solution. That is, in the coagulation liquid, preferential orientation of the sulfone groups occurs due to the surface activity of the sulfonated polysulfone at the polymer phase/water interface, and as a result, the amount of sulfonated polysulfone added is only a few percent of the polysulfone. However, it can exhibit extremely effective hydrophilic properties. Therefore, coagulating liquids with weak hydrophilicity, such as butanol and amyl alcohol, do not easily cause interfacial orientation of sulfonated polysulfone (a film with sufficient hydrophilicity cannot be obtained, but if the coagulating liquid is hydrophilic, A microporous membrane that achieves the object of the present invention can be obtained by using them alone or in combination.As the hydrophilic coagulating liquid that can be used in the present invention, for example, water Including methanol, ethanol, isopropyl alcohol, glycerin,
Mention may be made of polyethylene glycols and mixtures thereof.

The microporous membrane obtained according to the present invention has a hydrophilic surface while retaining the mechanical properties, acid resistance and alkali resistance inherent to polysulfone, and thus has significantly improved water permeability.

Furthermore, since the amount of sulfonated polysulfone used is small, the complicated step of sulfonation can be kept to a minimum.

In addition, since the skeleton of sulfonated polysulfone is the same as that of polysulfone, the compatibility between the two is good, and the alkali resistance is also sufficient.

The present invention will be explained in more detail below with reference to Examples, but the present invention is not limited thereto.

(Example) Synthesis Example-1, Synthesis of sulfonated polysulfone 1. 18 ml of triethyl phosphate in 125 ml of 2-dichloroethane
．． A solution containing 6 g (0,102 mol) of
16.3g of sulfuric anhydride (0,2
04 mol) was added slowly, SO3/ (C2H50)
3PO created a 2/1 complex. Next, 45.1 g (0.3
4 mol, repeating unit) to 1,2-dichloroethane 30
The solution dissolved in 0 ml of 1,2-dichloroethane 33
The mixture was simultaneously added dropwise to 0 ml with strong stirring. The generated precipitate turned into a slurry when the temperature was raised to 35°C, and this was stirred for 30 minutes. Filter the slurry, 1
, 2-dichloroethane for 20 minutes and dried under reduced pressure at 60°C. In this way, 1 per repetition unit of PSF
(503M of [!i! was introduced. The yield was 60 g.

Synthesis Example-2, Synthesis of Sulfonated Polysulfone Sodium Salt 165mj of isopropanol was added to the free acid slurry synthesized in the same manner as Synthesis Example-1! was added and dissolved. Add to this an excess of 22°0g of sodium methoxide (0,408
A 28% methanol solution containing mol) was added. After neutralizing with hydrochloric acid, washing twice with isopropanol and twice with distilled water, drying under reduced pressure with e90'c to obtain 1 per repeating unit of PSF.
1,0-3O3Na/PSF with -5o3Na
51 g of white powder was obtained.

Example 1 Polysulfone (Union Carbide Corporation Needel P3500) 10%, N-methyl-2-pyrrolidone 75%, polyethylene glycol 100015%
Sulfonated polysulfone (acid type) was added to the solution at a concentration of 0%, 1%, 3%, and 5% based on the polysulfone, and dissolved with stirring.

However, all percentages are by weight. The membrane-forming stock solution was cast onto a glass plate to a thickness of 150 μm, and the plate was immersed in water (25° C.) to obtain a microporous membrane.

In order to examine the hydrophilicity of the obtained membrane, the dried membrane was floated on the water surface, and the time taken for water to penetrate the surface was measured, and the results are shown in Table 3.

Table 1 As is clear from Table 1, it was demonstrated that the present invention, in which sulfonated polysulfone was added, had extremely good hydrophilicity.

Example 2 The membrane-forming stock solution used in Example 1, in which 5% of sulfonated polysulfone was added to polysulfone, was cast onto a glass plate and immersed in the following coagulation solution to obtain a microporous membrane.

The hydrophilicity was examined in the same manner as in Example 1, and the results are as shown in Table 2.

As is clear from the results in Table ■ Table ■, when a hydrophilic coagulation liquid is used, the water permeation time of the resulting microporous membrane is shorter, resulting in a microporous membrane with good hydrophilicity. However, it has been demonstrated that it is more effective.

Claims (1)

[Claims] 5 to 50% by weight of polysulfone having no dissociable groups;
The sulfonated polysulfone is 0.1 to
1. A method for producing a microporous membrane, comprising casting a membrane forming stock solution dissolved in a polar organic solvent containing 60% by weight, and coagulating the cast membrane in a hydrophilic coagulating liquid.