JP2710711B2 - Cellulose diacetate hollow fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a selectively permeable hollow fiber comprising a specific polymer. More specifically, the present invention provides a permselective cellulose-based hollow fiber mainly composed of a cellulose diacetate polymer having a high average polymerization degree different from that of the prior art.

[0002]

2. Description of the Related Art Selectively permeable hollow fibers have been practically used in reverse osmosis and hemodialysis. In particular, hollow fiber hemodialyzers are often used at present for purifying blood of patients with renal failure. In this method, a large number of dialysis membranes, for example, hollow fiber membranes, are housed in a housing, a patient's blood is allowed to flow inside the hollow, and a dialysate is allowed to flow between the outsides, that is, between the hollow fibers. Through the dialysis, waste substances in the blood are removed to correct the electrolyte concentration, and a pressure difference is applied between the inside and outside of the hollow fiber to remove excess water in the blood by ultrafiltration. Furthermore, hollow fibers are used to separate plasma alone from blood or to remove specific components from the plasma to treat autoimmune diseases and the like. As described above, the hollow fiber for blood treatment must selectively allow a specific substance to permeate according to the purpose. The performance is determined by the material of the hollow fiber, the porosity (the size and number of pores, etc.), the film thickness and the like.

[0003] As a material of a hollow fiber for a hemodialyzer, cellulose or cellulose acetate is generally often used. In particular, cellulose acetate can be produced relatively easily by commonly used spinning methods such as plasticizing melt spinning and wet spinning, and when the obtained hollow fiber is used for hemodialysis treatment, for example, compared to the case of a cellulose hollow fiber. Thus, there is an advantage that complement activity can be suppressed to some extent.

However, in the conventional cellulose diacetate hollow fiber, the degree of polymerization of the cellulose itself tends to decrease at the stage of acetylating the cellulose, and a high degree of polymerization of only about 170 to 200 was obtained at most.

[0005]

SUMMARY OF THE INVENTION The present inventor has found that using conventional cellulose diacetate having a degree of polymerization of at most 200, if the concentration of the polymer is lowered to increase the material permeability, the viscosity of the spinning dope will be insufficient. In such a case, it is difficult to reduce the film thickness, and in particular, the shape of the fin extending in the axial direction is difficult to be sharp, and as a result, a desired selectively permeable hollow fiber is obtained. We worked diligently to improve the difficulties. Conversely, with the same fin shape, the polymer concentration can be increased and the porosity in the membrane can be increased to increase the permeability of the substance.

[0006]

The present inventors have obtained cellulose diacetate having a higher polymerization degree than that of the conventional cellulose diacetate hollow fiber, and have used the cellulose diacetate having a high polymerization degree. The present inventors have found that a selectively permeable hollow fiber having more excellent properties can be obtained, and have reached the present invention.

That is, the present invention relates to a hollow fiber having a permselective wall membrane consisting essentially of cellulose diacetate, wherein the average degree of polymerization of the cellulose diacetate is substantially in the range of 230 to 400. At least one fin extending in the axial direction is provided on the outer surface side of the wall membrane, the thickness of the fin-free portion of the wall membrane is 20 μm or less, and the average cutting strength of the hollow fiber is 0. It is a cellulose diacetate hollow fiber characterized by being at least 4 g / de. The selectively permeable wall membrane of the hollow fiber of the present invention is suitable for a substance selectively permeable membrane for treating body fluids.

Hereinafter, the present invention will be described in more detail. First, the selectively permeable cellulose diacetate hollow fiber of the present invention contains a substantial component of a substantially cellulose diacetate polymer. As such a substantial cellulose diacetate polymer, those which are usually within the range handled as cellulose diacetate, specifically, those having an average acetylation degree within the range of 50 to 57% can be mentioned.

[0009] The cellulose diacetate polymer of the present invention is characterized by having an average degree of polymerization of 230 to 400. Here, the average degree of polymerization means a value obtained by dividing the weight average molecular weight by the molecular weight of the repeating unit of the polymer. As a method for measuring the weight average molecular weight, for example, gel filtration chromatography, measurement of viscosity, measurement of sedimentation equilibrium,
Light scattering method may be used.

When the average degree of polymerization of the cellulose diacetate polymer is less than 230, it is difficult to obtain a cellulose diacetate hollow fiber having high fins and high permselectivity. Further, it is difficult to obtain a hollow fiber having a low rewetting elongation rate. In addition, when the polymer concentration during spinning is reduced in order to increase the permeability of the substance by the hollow fiber, the polymer viscosity is too low, and the spinnability becomes very poor. The average degree of polymerization is more preferably from 240 to 350, and particularly preferably from 250 to 30.
0 is preferred.

When the average degree of polymerization of the cellulose diacetate polymer is 400 or more, it is difficult to produce the polymer itself, and when the hollow fiber is melt-spun, the temperature becomes extremely high, and the decomposition of the cellulose diacetate is difficult. Easier to do.

The cellulose diacetate hollow fiber of the present invention contains such a cellulose diacetate polymer as a main component, and its specific content is preferably 50% or more, more preferably 70% or more. In addition, the components contained other than that are not particularly limited, for example, polymethyl methacrylate, polyethylene, polypropylene,
Organic polymers such as polyacrylonitrile, polyvinyl alcohol, and nitrocellulose are exemplified.

Further, the outer diameter (d) of the hollow fiber of the present invention is, for example, 100% in the case of body fluid treatment such as hemodialysis.
~ 400μ, more preferably 200 ~ 300μ. The film thickness (h) is not more than 20 μm, and more preferably 5 to 20
μ, particularly preferably 10 to 15 μ.

The cellulosic hollow fiber of the present invention has a fin extending in the longitudinal direction at the outer periphery, and the ratio H / W of the height H to the width W of the fin is 0.5 or more. It is characterized by being. If the ratio H / W is less than 0.5, it is not preferable because the effect of preventing the hollow fibers from sticking together when housed in the fluid separator cannot be obtained. H / W is more preferably 0.8 or more. Note that the fin width W means a width at a position １ ／ of the fin height H.

Further, in the present invention, the number x of the fins of the hollow fiber is at least 1. However, when it is 11 or more, the effective membrane area is significantly reduced by the root of the fin. The transmission performance is remarkably reduced, which is not practical. That is, such x is generally 1 to 10, more preferably 2 to 8, and the particularly effective range is 3 to 10.
~ 7.

In this case, the height (H) of the fin is 5
-100 μm, more preferably 9-60 μm. The ratio H / h between the fin height and the film thickness is preferably 0.5-3, more preferably 1-2. Furthermore, the ratio H / d of the average height H (μ) of the fins and the average outer diameter d (μ) of the hollow fibers excluding the fins.
Is preferably in the range of 0.01 to 1, more preferably in the range of 0.02 to 0.5, and particularly preferably in the range of 0.03 to 0.2. The width of the root of the fin is desirably narrower than that of the upper part of the fin. However, usually, after the spinning dope is discharged from the spinneret, the root tends to be wider due to the surface tension of the stock solution. The width of the root is suitably 15 to 50 μm, preferably 20 to 40 μm. A hollow fiber in such a range is preferable because it has good circularity and hardly causes blood coagulation or residual blood in the hollow fiber.

Further, among the hollow fibers of the present invention, those having an average breaking strength of at least 0.4 g / de are preferred, and those having an average breaking strength of at least 0.6 g / de are more preferred. 0.4g strength
When the ratio is less than / de, the shape retention is poor, and it is easily broken during the hollow fiber manufacturing process and the fluid separator manufacturing process. In particular, when the outer diameter d is 100 to 300 µm and the film thickness is 5 to 20 µm. In the case of a hollow fiber, the tendency is large. The upper limit of the strength is not particularly limited. For example, 0.9 g /
De or less is common.

Further, the hollow fiber of the present invention is characterized in that its rewetting elongation is 3% or less. Rewetting elongation rate is 3
%, The elongation of the hollow fibers when filled with water or an aqueous solution after being stored in a fluid separator substantially in a dry state and brought into a rewet state is too large, and the local adhesion between the hollow fibers is large. And the hollow fiber is liable to be bent, which is not preferable. The rewetting elongation rate is 2.5%
The following are more preferred. The lower limit of the rewetting elongation rate is not particularly limited, but if it is 0.5% or more, more preferably 1% or more, the hollow fiber exhibits an appropriate elongation at the time of rewetting in the fluid separator. Also, the effect of spreading the hollow fiber bundle throughout the fluid separator can be obtained. The rewetting elongation α is about 0.1 g when the hollow fiber in a substantially dry state is measured with a load L of about 0.1 g / de and the hollow fiber is wetted with water.
The length L ₁ when measured under a load of / de is measured, and α
= {(L ₁ −L) / L} × 100. Here, the “substantially dry state” means that the glycerin content obtained by immersing the hollow fiber in an aqueous glycerin solution and then drying is 30 to 60%, and the water content is 0.5.
状態 9%.

Further, among the thin hollow fibers of the present invention,
Preferably, the material has a bending stiffness substantially in the range of 200 mg / 200 or more, and preferably has a burst pressure of 4 kg / cm ² or more as a pressure resistance when pressed into the hollow fiber when wet. In the range, the handling of the hollow fiber is easy at the time of manufacturing the fluid separator, etc., the length of each hollow fiber within the fluid separator tends to be uniform, and the pressure during the use of the separator is increased. An advantage is obtained that the hollow fiber is less likely to be damaged by the operation.

Further, the cellulose diacetate hollow fiber of the thin film of the present invention has a selective permeability of a fluid. More specifically, for example, in the case of a hollow fiber for hemodialysis, the portion excluding the fin portion is used. Of the water permeation performance UFR of 3.0 to 3.0
Those having a range of 40.0 ml / (m ² · hr · mmHg) are preferable, and especially 5.0 to 30.0 ml / (m ² · hr · mmHg).
Is good.

The cellulosic hollow fiber having selective permeability according to the present invention exhibits excellent separation performance in fluid separation. The fluid separation is not particularly limited, and examples thereof include liquid separation such as dialysis, ultrafiltration, and reverse osmosis, and gas separation such as for artificial lungs. In particular, the hollow fiber of the present invention is suitable for separation due to a difference in diffusion speed, such as dialysis, which requires that the fluid flow state outside the hollow fiber is good, and for blood treatment that requires smooth flow inside the hollow fiber. Are suitable.

The method for producing the hollow fiber of the present invention may be any of melt spinning, wet spinning, semi-dry semi-wet spinning and the like. That is, in the case of the melt spinning method, the spinning stock solution is a heated melt, and the melt is discharged from the spinneret, cooled and solidified to form hollow fibers with fins, and then the cellulose diester polymer is dissolved. A finned cellulose diacetate hollow fiber having selective permeability is obtained by extracting and removing at least a part of the additive in the finned hollow fiber with a solvent capable of dissolving the additive without using the solvent.

Hereinafter, the present invention will be described in more detail with reference to Examples.
The present invention is not limited by these examples.

[0024]

EXAMPLES AND COMPARATIVE EXAMPLES To 100 parts of cellulose diacetate having an average degree of polymerization of 260 and 170, 170 parts of a mixture of polyethylene glycol (molecular weight: 400) and diglycerin at a ratio of 4 to 1 was added and mixed. 18
The mixture was melted at 0 ° C. to 190 ° C. and spun using a die having a double annular slit for a finned hollow fiber. Next, polyethylene glycol and diglycerin were extracted with hot water and wound up, and then a hollow fiber bundle was assembled into a hemodialyzer having an effective membrane area of about 1 m ² . Table 1 below shows the properties of the obtained hollow fiber and hemodialyzer.

The urea dialysance was measured at 37 ° C. using a urea aqueous solution having an average blood side velocity of about 1.2 cm / sec in the hollow fiber and water having an average flow rate of about 1.8 cm / sec on the dialysate side. did. In addition, yarn spots indicate the maximum value-minimum value of the inner diameter of the hollow fiber in 30 holes.

[0026]

[Table 1]

[0027]

The hollow fiber of the present invention has an average degree of polymerization higher than that of a normal one, and the viscosity of the spinning solution at a certain polymer concentration is high, so that the spinnability is very good. That is, yarn breakage during spinning is small, and yarn spots are reduced. On the other hand, since the viscosity of the spun polymer is high, in the case of the hollow fiber with fin, the shape of the fin is sharp and the dialysis efficiency when assembled as a hemodialyzer, that is, the urea dialysance shows a very high level.

Claims (2)

(57) [Claims] 1. A hollow fiber having a permselective wall membrane consisting essentially of cellulose diacetate, wherein the average degree of polymerization of the substantial cellulose diacetate is in the range of 230-400. At least one fin extending in the axial direction on the outer surface side, the thickness of the fin-free portion of the wall film is 20 μm or less, and the average cutting strength of the hollow fiber is 0.4 g / de. A cellulose diacetate hollow fiber characterized by the above. 2. The cellulose diacetate hollow fiber according to claim 1, wherein the permselectivity of the wall membrane is a substance permselectivity for treating a body fluid.