JPS6229524B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dialysis-type cellulose derivative hollow fiber and a method for producing the same. More specifically, the present invention relates to a cellulose derivative hollow fiber having a high water permeation rate, excellent permselectivity, a substantially homogeneous structure, and a cellulose derivative hollow fiber suitable for hemodialysis, and a method for producing the same.

Polymer membranes have traditionally been used for substance separation, but in recent years, their use in various fields has rapidly expanded, particularly from the standpoint of energy saving and miniaturization of devices.

Among polymer membranes, hollow fibrous membranes have a large membrane area per unit volume and have higher strength than flat membranes.
Hollow fibers have the advantage of not requiring a support as a reinforcing material, and development of hollow fibers as separation membranes is rapidly progressing.

Similar to flat membranes, hollow fibrous membranes are divided into homogeneous membranes and asymmetric membranes, and the former refers to membranes with similar structures on the membrane surface and inside, with the average diameter of the pores being substantially the same. The latter has a thin dense layer on the membrane surface,
The inside is porous, so-called a membrane that acts as a support.

In particular, this asymmetric membrane is the main component of cellulose derivative hollow fibers used for reverse osmosis, ultrafiltration, and dialysis. However, as mentioned above, asymmetric membranes have a two-layer structure, and the phenomena of substance separation and permeation occur essentially in the dense layer on the membrane surface, but the thickness of the dense layer has little effect on substance separation. Since the permeation rate of non-containing substances depends on this thickness, making this dense layer as thin as possible was the key to improving the permeation rate of low-molecular substances, so-called membrane performance. However, if the dense layer becomes thin, the dense layer may be damaged by slight flaws on the membrane surface, scratches during the hollow fiber manufacturing process, or when the membrane is installed in equipment, and the expected separation of substances may not be possible. . In other words, this is due to the high probability that pinholes will occur.

On the other hand, if cellulose derivative hollow fibers are made into a homogeneous membrane structure without the presence of a dense layer, they have excellent permselectivity and can extremely reduce the occurrence of pinholes. Ta. Moreover, in order to increase the permeation rate, it is necessary to reduce the membrane thickness, but in order to ensure a practically usable permeation rate, the membrane thickness must be on the order of several microns, which is difficult in terms of manufacturing and strength of hollow fibers. There was a big problem.

This is due to the method of producing cellulose derivative hollow fibers. In other words, the main conventional manufacturing methods are melt spinning, dry spinning, semi-wet spinning, and wet spinning that mainly use acetone as a solvent, and the hollow fibers obtained by the former two methods are The result is a homogeneous membrane, but an extremely dense structure. In semi-wet spinning, the solvent acetone is released before entering the coagulation bath, forming a dense layer, and even in completely wet spinning, the coagulation rate of acetone is extremely fast, resulting in the formation of a dense layer on the fiber surface. After all, it tends to form a dense layer and become an asymmetric film. In either case, the pores of the layer capable of separating substances have extremely small pores, which limits the permeation rate of low molecular weight substances. Therefore, an asymmetric membrane was indispensable in order to give conventional cellulose derivative hollow fibers practical performance.

However, in recent years, a method has been developed to create homogeneous pores in the wall membrane by spinning a spinning dope containing a large amount of salts, non-solvents, etc. to cellulose derivatives, and post-processing the resulting yarn. For example, it is used in the field of solid-liquid separation in which proteins with a molecular weight of 10,000 or more are passed through and suspended substances are removed. However, a so-called dialysis membrane at the molecular level, which does not allow only useful proteins with a molecular weight of 10,000 or more to permeate, but only other low-molecular weight substances, has not yet been obtained.

Therefore, the present inventors have developed a homogeneous hollow fiber membrane made of cellulose derivative hollow fibers, which has a high permeation rate and can almost completely block useful proteins with a molecular weight of 10,000 or more, while allowing only low molecular weight substances to pass through. As a result of studies aimed at this purpose, the present invention was completed.

In other words, the present invention provides a porous network structure in which the fibers have a continuous hollow part in the length direction, the fiber wall membrane has a thickness of 10 to 70μ, and is formed by a large number of pores, which are connected to each other. Moreover, the pores do not substantially contain cavities with a diameter of 0.5μ or more, and the substantial average value of the pore diameters is 10 to 500.
The cellulose derivative is added to a mixed solvent consisting of 0.2 to 20% by weight of a non-solvent for the cellulose derivative and 0.2 to 20% by weight of a non-solvent for the cellulose derivative and 99.8 to 80% by weight of a nonvolatile organic solvent. The stock solution dissolved so that the solid content C is in the range of 20 to 35% by weight is spun from the sheath of a sheath-core type spinning nozzle while maintaining the temperature t below, and at the same time, liquid is injected from the core and further solidified. The object of the present invention is to produce cellulose derivative hollow fibers as described above by coagulating them in a bath.

10 ^{( 0.0104C+ 1.23)} ≦t≦10 ^{( 0.0232C+ 1.28)} The diameter of the hollow portion of the hollow fiber in the present invention is 100μ~
1000μ is preferred, particularly 200 to 500μ.
Further, the hollow fiber wall membrane refers to the fiber portion existing outside the hollow portion of the hollow fiber.

Furthermore, the diameter of the pores in the present invention can be measured using an electron microscope or a mercury porosimeter. Further, the degree of swelling P in the present invention is a value calculated by the following formula.

P=(ρa/ρ-1) ρ: Apparent specific gravity of hollow fiber ρa: Specific gravity of fiber without pores Furthermore, the thickness of the hollow fiber membrane wall in the present invention is 10
If the thickness is less than 10μ, the mechanical strength of the hollow fiber will not be sufficient and the hollow portion will easily collapse during use, so it is not preferable. If it becomes thicker than this, the ability to separate low molecular weight substances during the separation process will decrease, making it difficult to use it as a dialysis type hollow fiber.

In addition, the hollow fiber wall membrane of the present invention has a diameter of 0.5
It is necessary to not include cavities larger than μ, and 0.5μ
The presence of cavities of the upper diameter causes pinholes. The average diameter of the pores in a hollow fiber wall membrane is measured using a mercury poromimeter, which is 10 to
It is necessary that the thickness be 500 Å, particularly in the range of 30 to 300 Å. If the average diameter of these pores is smaller than 10 Å, the separation effect of the separation membrane will decrease.
On the other hand, if the average value of the diameter becomes larger than 500 Å, useful proteins will also pass through the membrane in the separation process, which is undesirable since the separation ability of the membrane will be degraded.

Furthermore, the degree of swelling of the hollow fiber membrane wall needs to be 0.5 or more; if this value is less than 0.5, it becomes difficult to form a network structure, and the permeation rate of low molecular weight substances through the hollow fibers decreases significantly. do.

Cellulose derivatives used in the practice of the present invention include cellulose esters and cellulose ethers such as cellulose acetate, cellulose propionate, and ethyl cellulose, with cellulose acetate being particularly preferred. Solvents used to dissolve cellulose derivatives include dimethylformamide, dimethylacetamide, dimethyl sulfoxide, dioxane, acetic acid, etc.
The non-solvent used in carrying out the present invention includes water, methanol, glycerin, benzole, xylene and the like, with water being particularly preferred. The amount of these non-solvents added to the solvent is preferably in the range of 0.2 to 20% by weight; if this amount is less than 0.2% by weight, the viscosity of the cellulose derivative-containing spinning solution increases significantly, making it difficult to produce hollow fibers. On the other hand, a solvent containing 20% by weight or more of a non-solvent will not be able to sufficiently dissolve the cellulose derivative.

The solid content of cellulose derivatives in the spinning stock solution
It is necessary to dissolve the solution at a concentration of 20 to 35% by weight, but if this concentration is lower than 20% by weight, the strength of the resulting hollow fibers may be insufficient, so it is not preferable. If the amount exceeds 35% by weight, undissolved substances tend to occur in the spinning dope and the spinning operation tends to fail, which is not preferable.

When making hollow fibers using the above-mentioned spinning dope, the coagulation bath is preferably an aqueous solution of a cellulose derivative solvent, and particularly when making hollow fibers with a specific structure of the present invention, the temperature is set to 10 ⁽⁰ . ^0104C+1 . ²³⁾ ≦t≦10 ⁽⁰ . ^0232C+1 . ²⁸⁾ (In the formula, C represents the solid weight percent of the polymer in the spinning solution.) It is necessary to satisfy the following condition. be. If this temperature is lower than 10 ^{( 0.0104C+1.23 )} , the spinnability will drop significantly, which is undesirable, while if this temperature is higher than 10 ^{( 0.0232C+1.28 )} , This is not preferable because the formation of the hollow portion becomes insufficient and defects such as adhesive threads and thread spots occur frequently, and this range is illustrated in FIG.

In addition, the liquid to serve as the core material injected from the inside of the spinneret is preferably a liquid with a coagulation value of 20 or more with respect to the cellulose derivative polymer solution, and when a liquid with this value smaller than 20 is used as the core material. , the development of a skin layer in the hollow fiber membrane wall becomes noticeable, making it difficult to create a hollow membrane with good water permeability.In addition, voids are observed in the membrane wall, making it difficult to create a hollow membrane that is prone to pinholes. This is not preferable because it forms a film. Examples of liquids with a coagulation value of 20 or higher include ethanol, methanol, butanol, glycerin, non-volatile organic solvents containing 10% or more of water, etc., and this coagulation value is 50 c.c. of a 1% solution of a cellulose derivative. While stirring, drop the liquid to be used as a core material, and add the liquid until the solution becomes cloudy.
This is the value expressed in cc number.

The coagulation bath used in producing the hollow fibers of the present invention is not particularly limited, but it is preferable to use a mixture of a non-volatile organic solvent of a cellulose derivative and a non-solvent, and in particular water is used as the non-solvent. Preferably. In particular, it is preferable to use a composition having an organic solvent/non-solvent ratio of 10/90 to 50/50 and maintained at a temperature of 20 to 40°C.

In the present invention, prior to drying the hollow fibers obtained as described above, it is preferable to treat the hollow fibers with an aqueous solution of polyhydric alcohol to contain the polyhydric alcohol, and then dry the fibers. Specific examples of polyhydric alcohols that can be used include ethylene glycol, propylene glycol, glycerin, trimethylolpropane, etc., but glycerin is preferred from the viewpoint of ease of handling. Further, the amount of polyhydric alcohol attached to the hollow fibers is preferably 20% by weight or less, more preferably 1 to 10% by weight. It is observed that as the amount of polyhydric alcohol attached increases, the equilibrium moisture content increases and the strength of the dried hollow fiber tends to decrease. On the other hand, if the amount of polyhydric alcohol attached is too small, shrinkage of the hollow fibers will occur, and the porous structure in the wall membrane will change significantly, making it difficult to obtain hollow fibers with the desired dialysis performance.

Compared to cellulose-based hollow fibers obtained by conventional methods, the hollow fibers of the present invention have more uniform diameters of the micropores in the membrane wall, and according to the production method of the present invention, the diameters of the micropores of the desired diameter are slightly more uniform. can be easily created by changing the conditions.

The present invention will be explained in more detail below with reference to specific examples, but the present invention is not limited to this scope.

Example 1 25 parts of cellulose acetate with a degree of acetylation of 55% was added to water.
Dissolved in a mixed solvent of 7.5 parts of dimethylacetamide and 67.5 parts of dimethylacetamide by stirring at 80℃ for 2 hours, and after degassing and filtering, 50℃.
He said.

The spinning stock solution is applied to the sheath part of the sheath-core type spinning nozzle at 3.0%
cc/min, while glycerin (coagulation value 25) was quantitatively fed into the core at a rate of 2.5 cc/min. Spinning solution passed through the nozzle
Glycerin (molded product) is dropped 5 cm into the air.
It was introduced into a 40% dimethylacetamide aqueous solution kept at 15°C, solidified, and rolled up at a speed of 40 m/min.
Heat treated at ℃. In order to maintain the membrane structure in a wet state, it was treated with a 30% glycerin aqueous solution and dried at 40°C.

The obtained hollow fiber has an inner diameter of 345μ and an outer diameter of 400μ. Figures 2 and 3 show 200x and 1000x enlarged photographs of the cross section of the hollow fiber, showing the outer and inner parts of the hollow fiber.
10,000 times enlarged photographs are shown in Figures 4 and 5.

As can be seen from these photographs, there are no cavities larger than 0.5μ, and the hollow fiber is a homogeneous membrane. The average diameter of the pores was 70 Å as measured by a mercury porosimeter. Further, the degree of swelling of the hollow fiber wall membrane was calculated to be 1.3 by assuming the specific gravity of cellulose acetate, lc = 1.3, and calculating the density of the fiber by measuring the fiber cross-sectional area and denier.

Thirty of the resulting hollow fibers were glued together at both ends with an adhesive, and a mixed aqueous solution of urea, creanitine, and albumin was dialyzed. Urea and creanitine permeated sufficiently, but albumin was almost completely blocked. The water permeation rate was 2.5×10 ^-3 (cc/cm ² min atm).

Example 2 26 parts of cellulose diacetate with a degree of acetylation of 53% was dissolved in a mixed solvent of 66.6 parts of dimethylacetamide and 7.4 parts of water at 80°C, and after sufficient defoaming, the temperature was raised to 60°C and 4H spinning was performed using a gear pump. In the nozzle sheath
It was delivered at a rate of 1.8cc/min. At the same time from the core
30% dimethylacetamide aqueous solution (coagulation value 28)
Injected at a rate of 2.1 cc/min, immediately coagulated in a coagulation bath of 40% dimethylacetamide aqueous solution kept at 20°C, rolled up at a rate of 4 m/min, washed with water, and then heated to 80°C.
heat treated.

The obtained hollow fiber had the same structure as Example 1, had no cavities larger than 0.5μ, had an inner diameter of 400μ, and an outer diameter of
With a swelling degree of 1.7 at 480 μ and an average diameter of 60 Å, urea and creanikine were sufficiently permeable, but albumin was almost completely blocked. The water permeation rate is 8.8×10 ^-3 (cc/cm ²・min・
ATM)

Comparative Example 1 In Example 2, when the polymer solution temperature was set to 90°C and 25°C, respectively, the former did not form a hollow part and many defects such as adhesive threads, yarn unevenness, and pinholes occurred, and the latter did not allow stable spinning. Nakatsuta.

Example 3 Dimethylformamide to 24 parts of ethyl cellulose
Dissolved in a solvent of 70 parts and 6 parts water at 80℃ (After sufficient degassing, the temperature was set to 60℃ and 3.5
cc/min, while n-butanol (coagulation value: 70) was fed into the core at a rate of 2.7 cc/min. They were dropped 3 cm into the atmosphere, introduced into a coagulation bath of 30% dimethylformamide aqueous solution kept at 18°C, coagulated, rolled up at a speed of 45 m/min, washed with water, and heat-treated at 75°C.

The obtained fiber showed a structure similar to that of Example 1.
No cavities larger than 0.5μ, inner diameter 270μ, outer diameter 370
The degree of swelling was 2.5 μ, and the pores had an average diameter of 80 Å. Urea and creanitine permeated through this hollow fiber sufficiently quickly, but albumin was almost completely blocked.
The water permeation rate is 7.3×10 ^-3 (cc/min・cm ²・atm)
It was hot.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between the temperature of a polymer solution capable of forming the hollow fiber of the present invention and its solid content concentration, Figure 2 is a 200 times enlarged photograph of the hollow fiber of the present invention, The figure is a 1000 times enlarged photograph of the inside of the hollow fiber of the present invention, and FIGS. 4 and 5 are 10000 times enlarged photographs of the outside and inside of the hollow fiber of the present invention.

Claims (1)

[Claims] 1. A non-solvent for cellulose derivatives of 0.2 to 20
The cellulose derivative is added to a mixed solvent consisting of 99.8 to 80% by weight of a non-volatile solvent and its solid content is C.
While keeping the stock solution dissolved in a range of 20 to 35% by weight at the temperature t below, spin it from the sheath of a sheath-core spinning nozzle, and at the same time inject a liquid with a coagulation value of 20 or more with respect to the cellulose derivative solution from the core. Furthermore, the fiber is coagulated in a coagulation bath, and has a continuous hollow part in the length direction of the fiber, the thickness of the fiber wall membrane is 10 to 70μ, and it is formed by a large number of pores. It forms a porous network structure connected to each other, and the pores are substantially 0.5μ in diameter.
Does not contain any cavities and has an average pore diameter of
A method for producing a dialyzed cellulose derivative hollow fiber having a diameter of 10-500 Å and a fiber wall swelling degree of 0.5 or more. 10 ^{( 0.0104C+ 1.23)} ≦t≦10 ^{( 0.0232C+ 1.28)}