JPS5932562B2 - Hollow fibrous membrane and its manufacturing method - Google Patents

Description

Detailed Description of the Invention The present invention relates to a hollow fibrous membrane having excellent water permeability and substance separation ability, particularly an acrylonitrile-based hollow fibrous membrane having a dense layer inside the hollow space, and a novel method for producing the same. .

The technology of separating various substances using ultrafiltration membranes has been widely used for a long time, but in recent years cellulose acetate membranes and collagen membranes have been newly developed. It has come to be applied to a wide range of applications such as the food industry, medical field, electronic industry, and pollution prevention.

In particular, hollow fibrous membranes made by molding ultrafiltration membranes into hollow shapes have been attracting attention because they have a large pore area and can be made into compact devices, and research and development are being actively conducted on them. There is.

In general, the three basic performance requirements for ultrafiltration membranes are: ■ High water permeability, ■ High material axiom ability, and ■ Excellent chemical resistance and long membrane life. .

For this purpose, two things are particularly required: selection of an appropriate material and control of the membrane structure, such as having a dense layer on the surface and a porous layer inside.

Therefore, many techniques for controlling membrane structure have been published, and hollow fibrous membranes are no exception.

However, in the case of hollow fibrous membranes, although those having a dense layer on the outside are well known, there are very few examples of fibers having a dense layer on the inside.

When applying hollow fibers to the medical field, an internal pressure method is often adopted in which a processing liquid is passed inside the fibers, but in this case, hollow fibers having a dense layer on the inner surface are naturally required.

However, it is much more difficult to manufacture hollow fibers having a dense layer on the inner surface by a wet spinning method than those having a dense layer on the outer surface.

The reason for this is that when attempting to produce hollow fibers using the wet spinning method, it is generally produced by passing a coagulant through the interior (core), but the composition of the internal coagulant or the introduction conditions may vary depending on the nozzle structure used, etc. This is because it is difficult to form an internal dense layer due to the limitations.

In view of the current situation, the present inventors have conducted intensive research on a method for easily producing hollow fibers having a dense layer inside by a wet spinning method, and as a result, they have arrived at the present invention.

That is, the present invention uses a known sheath-core type nozzle, feeds the spinning dope from the sheath part, and feeds air or inert gas from the core part, thereby creating a state containing air or inert gas inside. The present invention relates to an acrylonitrile-based hollow fibrous membrane having a dense layer on its inner surface, which is characterized by being spun into a coagulation bath, and a wet spinning method thereof.

The most important factor determining the membrane performance of hollow fibrous membranes is the selection of the membrane material.

The selection of the membrane material must be made by taking into consideration the properties of the material itself, such as its hydrophilicity, as well as the ease of molding from the perspective of controlling the membrane structure.

Among the many synthetic polymers, we have searched and examined various polymers that satisfy these two conditions, and as a result, acrylonitrile polymers are the most suitable.

Acrylonitrile polymers have a very high affinity for water, and voids are easily generated by wet spinning.
Moreover, by selecting molding conditions, its size, shape, etc. can be controlled.

The acrylonitrile polymer used in the present invention is a polymer comprising 50% by weight or more of acrylonitrile and 0 to 50% by weight of one or more known monomers copolymerizable with acrylonitrile.

In addition, the solvents used to dissolve acrylonitrile during the production of hollow fibers include organic solvents such as dimethylformamide, dimethylacetamide, and dimethylsulfoxide;
Known acrylonitrile solvents such as ordinary salts of chloride, rhodan salts, inorganic concentrated aqueous solutions of nitric acid and the like can be used.

The polymer concentration of the spinning dope used varies greatly depending on the polymerization degree of the polymer, the type of composition solvent, etc., but is generally 5 to 3.
5% by weight is suitable.

In addition, the viscosity of the spinning dope is particularly important because it is necessary to introduce air or inert gas from the core in relation to the concentration of the dope. If the viscosity is too low, the air pressure introduced from the core will cause the spinning dope to become hollow. It becomes impossible to maintain

Generally, the suitable viscosity of the spinning dope is 200 poise or more, preferably 500 poise or more.

Air or an inert gas such as nitrogen or argon is suitably introduced from the core.

The introduction pressure varies greatly depending on the viscosity of the spinning dope, the shape of the sheath-core nozzle, etc., but is generally 0.3cr11.
．． Extremely low pressure on the order of ~50 CrrL water column pressure is used.

Of course, depending on the nozzle shape, it may be possible to use a higher introduction pressure.

A technique for introducing air or an inert gas into the core during the production of hollow fibers is not yet known in the production of hollow fibers by wet spinning.

This is presumed to be because it is difficult to make hollow fibers with the desired shape and structure using C gas as the core material due to the properties of the stock solution and the coagulation behavior of the polymer solution. It has become clear that hollowing can be achieved by adjusting the viscosity, air introduction pressure, etc.

Furthermore, compared to the conventional technique of introducing a coagulant into the interior, in the case of the present invention, the dense layer formed on the inner surface is very thin, less than 1/3 of the total film thickness, and substantially more than 100 Å. In contrast, with conventional technology that introduces a coagulant inside, the dense layer is thick and uneven, and in extreme cases, voids may exist locally in the dense layer. It is nearly impossible to eliminate this completely due to manufacturing technology.

In particular, in the case of wet spinning using organic solvents, it is necessary to keep the spinning solution above a certain temperature in order to maintain the stability of the stock solution, but considering the nozzle shape, it is not possible to keep only the internal coagulant at a low temperature. This is difficult and therefore tends to make it difficult to obtain a dense structure.

This has a very large effect on the ultrafiltration performance of the hollow fibers obtained.

In other words, as has been repeatedly stated, the performance of the ultrafiltration membrane is that it has high water permeability and good ultrafiltration accuracy (
The two basic requirements are that the hollow fiber of the present invention has a thickness of 1/3 or less of the total membrane thickness, especially 5 μ or less, and has pores of 100 Å or more. A fiber having a dense layer that is uniform and free from unevenness satisfies both of these two conditions and is far superior to fibers using conventional internal coagulants.

As explained above, the hollow fibrous membrane of the present invention is
It has a dense layer inside and has excellent ultrafiltration performance, and its manufacturing method involves an innovative technology that involves introducing air or inert gas into the core using a wet spinning method. The industrial value is extremely large.

The present invention will be explained in more detail with reference to Examples below.

Note that all percentages in the examples are based on weight.

Example 1 Consisting of 94% acrylonitrile and 6% methyl acrylate, specific viscosity 0.16. A 26% spinning stock solution was prepared by dissolving the copolymer (measured at 1 g/100 rnl in dimethylformamide at 25°C) in dimethylacetamide.

The viscosity of the spinning dope was 280 poise at 80°C.

Using the sheath-core type nozzle shown in FIG. 1, this spinning dope was fed through the sheath, and air was introduced through the core at a micropressure of 10 m71 L water column pressure.

With this core containing air, the spinneret is heated to 6
It was spun into a 0% dimethylacetamide aqueous solution and coagulated, and the coagulated thread was washed in hot water at 98°C.

The obtained hollow fiber had an outer diameter of 400 μm and an inner diameter of 310 μm, and had a dense layer inside and a porous layer outside.

The average thickness of the dense layer was 066μ.

In addition, the water permeability was measured by the internal pressure method (1 atm) at 23 gfd (gallon/feet2. day).
) showed a high water permeability.

Next, the ultrafiltration performance was tested using an aqueous dextrin solution, and an excellent result was obtained in which 97% of dextrin with a molecular weight of 3.800 was removed.

Example 2 A copolymer containing 90% acrylonitrile, 7% vinyl acetate, 3% acrylamide and a specific viscosity of 0.18 was dissolved in dimethylformamide to prepare a 28% spinning stock solution.

The viscosity of the spinning dope was 600 poise at 95°C.

This stock solution was discharged from the sheath of the sheath-core type nozzle shown in FIG. 1, and slightly pressurized air at a water column pressure of 15 mm was introduced from the core.

The filamentous material discharged with air in its core is suspended in the air (
After passing through (room temperature), it was introduced into a coagulation bath consisting of a 70% dimethylformamide aqueous solution at 40°C to complete external coagulation.

Subsequently, the film was washed in boiling water and stretched 1.3 times at the same time.

The obtained hollow fiber has a dense layer that does not have pores of 100 Å or more inside (thickness of dense layer/total film thickness - 1/155)
exists.

This water permeability is 25 gfd (1 atm) and the molecular weight is 400.
00 dextran was removed and separated by 99.5%.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of a sheath-core type nozzle used for manufacturing the hollow fibrous membrane of the present invention. 1 is a stock solution supply port, 2 is a core air or inert gas supply port, 3 is a molding nozzle, 4 is an air or inert gas introduction pipe, 5 is an air or inert gas introduction path, and 6 is a stock solution discharge Show the path.

Claims (1)

[Scope of Claims] 1. It is characterized by comprising 50% by weight or more of acrylonitrile, having a dense layer on the inner surface that does not substantially contain pores of 100 Å or more, and furthermore, the thickness of this dense layer is 5 μ or less. Hollow fibrous membrane. 2 Using a sheath-core type nozzle, a spinning stock solution consisting of a polymer of 50% or more acrylonitrile with a viscosity of 200 poise or more is introduced from the sheath part, and air or inert gas at a slight pressure is introduced from the core part to perform a wet process. A method for producing a hollow fibrous membrane having a dense layer substantially free of pores of 100 Å or more on its inner surface, the method comprising spinning the membrane.