JPH0212612B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention uses cellulose triacetate (hereinafter abbreviated as CTA) having a degree of acetylation in the range of 59.6 to 62.5% as a membrane material.
The present invention relates to a method for producing an ultrafiltration membrane by using. More specifically, by using CTA, cellulose diacetate (hereinafter referred to as CDA)
The present invention relates to a method for producing an ultrafiltration membrane using a wet method, which has improved heat resistance and hydrolysis resistance compared to the above method. In recent years, ultrafiltration membranes have been used in a variety of fields, including food, pulp and paper, fermentation, and medical fields, for resource recovery, valuable substance concentration, wastewater treatment, pure water/washing water production,
Widely used for purposes such as artificial kidneys. In addition, ultrafiltration membranes are made of a wide variety of materials, from natural polymers to synthetic polymers, and from hydrophilic polymers to hydrophobic polymers, depending on the purpose.
It is manufactured in shapes such as spiral membranes and pleated membranes. Among these many ultrafiltration membranes,
Recently, synthetic polymers, especially hydrophobic polymers, have been widely used for applications requiring chemical resistance and solvent resistance. However, while these hydrophobic polymers have the above-mentioned advantages, they also have the disadvantage that the solvents that can be used during film formation are limited and the degree of freedom in setting manufacturing conditions is low. Furthermore, in the case of membranes using hydrophobic polymers as membrane materials, the water permeation rate of pure water is said to decrease significantly over time compared to membranes made of hydrophilic materials. There are problems in using it in fields where water is required as a liquid. On the other hand, when cellulose acetate, which has moderate hydrophilicity, is used as a membrane material, there are many solvents that can be used during membrane formation compared to hydrophobic materials, and it is possible to select various membrane formation conditions. Conditions are easy to control. Furthermore, compared to hydrophobic materials,
It has the advantage that the water permeation rate in pure water decreases little over time. For these reasons, cellulose acetate has traditionally been used as a membrane material, and using a wet method,
Various selectively permeable membranes have been manufactured using phase separation phenomena. Most of the known examples relate to reverse osmosis membranes, and there are only a few examples of ultrafiltration membranes made from cellulose acetate. For example, Tokukai Akira
In Publication No. 55-3890, CTA or a mixture of CTA and CDA is used as a membrane material, dissolved in a mixed solvent of dioxane, acetone, and formamide, or a mixed solvent of dioxane, acetone, and acetamide, and further By adding hydrophobized silicic acid there, after film formation by wet method,
Immersion of the obtained membrane in a high boiling point solvent such as glycerin,
A method for preventing performance deterioration during transition to a solvent-impregnated membrane by subsequent drying treatment is shown. Furthermore, JP-A No. 55-1834 discloses that cellulose ester is used as a solvent for the ester and has a boiling point of 120
3 consisting of either a polar organic solvent at a temperature of ℃ or higher and water, or a rodan salt or a di- or trivalent cationic metal salt that has a large heat of hydration when dissolved in water.
A method for obtaining a semipermeable membrane by a wet method by dissolving it in a component-based mixed solvent is shown. Furthermore, JP-A-55-3859
The publication discloses a method of obtaining an ultrafiltration membrane by a wet method by dissolving a blend of CDA and CTA in a polar organic solvent. In general, when a membrane with selective permselectivity obtained by a wet method is left in the air, water evaporates from the dense layer on the membrane surface, and the membrane structure changes due to the rapid change in interfacial tension on the membrane surface at that time. It is known to cause performance deterioration, and has poor processability and moldability. Therefore, once the membrane obtained by the wet method was
After being immersed in a water-soluble solvent with a high boiling point such as glycerin, it is dried to form a membrane impregnated with the above-mentioned water-soluble solvent, thereby maintaining membrane performance and improving processability and formability. There is. Therefore, in the method disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 55-3890, the membrane material is mainly
In the case of ultrafiltration membranes using CTA, the method of immersing them in a high-boiling water-soluble solvent such as glycerin as described above and then drying them reduces the water permeability of the membrane, but [In this case, CTA
It has been shown that membranes obtained by adding hydrophobized silicic acid to a solution in which a mixture of CTA and CDA is dissolved in a solvent do not change their membrane performance even when subjected to dry membrane formation using the above method. ing. However, since the membrane obtained by this method contains hydrophobized silicic acid, it cannot be used in medical fields such as blood treatment, or in applications where liquid purity and eluates in the liquid are a problem. I have a problem. In addition, in the above-mentioned Japanese Patent Application Laid-Open No. 1834/1983, 2
When a semipermeable membrane is formed using a solution consisting only of the components, the membrane has a low water permeation rate and is not a useful membrane. However, adding water and metal salts to a solution of cellulose ester dissolved in a polar organic solvent It has been shown that useful membranes can be obtained by the following methods. In addition, the cellulose ester used in this case is CDA.
has been shown to provide the most water permeable membranes. However, the membrane obtained in this way contains metal salts, and it is difficult to completely remove them from the membrane.
Similar to the method in the above issue, it is not suitable for use in the medical field such as blood processing, in the pure water field, or as a separation membrane for food applications. In addition, CDA is said to be the best cellulose ester to obtain a membrane with the best performance, but CDA is generally said to have poorer hydrolysis resistance than CTA. It has the disadvantage of not being heat resistant. Furthermore, in the above-mentioned Japanese Patent Application Laid-open No. 55-3859,
In the case of reverse osmosis membranes, which use a mixture of CDA and CTA as the membrane material, a non-polar organic solvent with a low boiling point such as acetone or dioxane is used because a dense layer on the membrane surface is required. It has been shown that in the case of the ultrafiltration membrane described in 2006, the dense surface layer of a reverse osmosis membrane is not necessary, and that a polar organic solvent with a relatively high boiling point may be used for this purpose.
Furthermore, it has been shown that the pore size of the resulting ultrafiltration membrane changes depending on the mixing ratio of CDA and CTA used as membrane materials. However, this Japanese Patent Application Publication No. 55-3859
For example, the above-mentioned JP-A-55-3890, JP-A-55-3890,
Although there is no problem of residual additives in the membrane as seen in the example of No. 1834,
Since a mixture of CDA and CTA is used, there are problems caused by CDA. First, it is generally said to have inferior hydrolysis resistance compared to CTA, so membrane performance tends to deteriorate due to deterioration of the membrane material over time during use, and heat resistance is not very good. Therefore, it cannot be used for processing high-temperature stock solutions, nor can it be sterilized with hot water. Taking the above circumstances into consideration, the present inventors used cellulose triacetate as the membrane material, used a mixed solvent of dioxane and a polar organic solvent with a boiling point of 120°C or higher as the main solvent, and created a polymer that could be obtained by using cellulose triacetate as the membrane material. We have discovered a method of producing an ultrafiltration membrane from a solution that has improved hydrolysis resistance and heat resistance compared to CDA, and is free from problems such as residual metal salts, and has completed the present invention. That is, the present invention uses cellulose triacetate with an acetylation degree in the range of 59.6 to 62.5%, dioxane and a boiling point of
A cellulose triacetate solution, which has a temperature of 120°C or higher and has infinite solubility in water, and is composed of a mixed solvent whose main component is a solvent for cellulose triacetate, is cast and coagulated in water. This is a method for producing an ultrafiltration membrane made of cellulose triacetate, which is characterized by producing a semipermeable membrane. Conventionally, a polymer material was dissolved in a solvent, cast onto a support such as a glass plate or woven cloth, and left to stand in an atmosphere for a certain period of time. After evaporating from the surface of the molecular solution,
The wet casting method, which produces a membrane with an asymmetric structure by immersing the used polymer in a non-solvent to solidify the polymer, is widely used as a manufacturing method for reverse osmosis membranes and ultrafiltration membranes. ing. Cellulose acetate has been widely used as a membrane material because it can be used in many solvents, is easy to handle, and has excellent stability in membrane formation. Especially CDA
It is widely used because it can be used with many solvents, and also because it allows the use of easy-to-handle solvents such as acetone as a water-soluble low-boiling solvent that is usually added to polymer solutions in wet casting methods. It has been studied and used. On the other hand, in the case of CTA, the solvents that can be used are limited compared to CDA, but it has superior heat resistance and hydrolysis resistance as a membrane material. Therefore, the present inventors selected CTA as the membrane material and proceeded with studies on film formation using a wet casting method. Examples of volatile low-boiling solvents added to the casting polymer solution include dioxane and methylene chloride. First, when a CTA solution is made and cast using only dioxane as a CTA solvent, the effect of evaporation of dioxane when left standing in an atmosphere is too large, so it is immersed in a non-solvent to solidify the polymer substance. The resulting membrane has a very dense surface layer and has almost no water permeability. Furthermore, when only methylene chloride was used as the solvent for CTA, the membrane obtained by casting had a denser surface layer and no water permeability than when only dioxane was used as the solvent. This is due to the effect of evaporation of methylene chloride when it is left standing in the atmosphere, as well as the fact that methylene chloride is poorly soluble in water. This is because the effect of suppressing speed worked. Conversely, if a membrane is formed by a wet method using only a water-soluble high-boiling solvent as the solvent for CTA, the resulting membrane has water permeability, but when evaluated using albumin as a solute, the solute rejection rate was low. As an ultrafiltration membrane, this results in a membrane with extremely large leakage and poor performance. This is because the water-soluble high-boiling solvent used hardly evaporates when left standing in the atmosphere after casting, resulting in an increase in the CTA concentration near the membrane surface and a decrease in CTA dissolving power due to a decrease in the amount of solvent. This is because the evaporation effect did not work and a dense layer was not sufficiently formed on the film surface. In addition, the solute exclusion rate here is defined by the following formula. Solute exclusion rate (%) = solute concentration in the liquid / solute concentration in the stock solution used for evaluation x 100 Therefore, when a low boiling point solvent and a water-soluble high boiling point solvent are each used alone as a solvent for CTA,
Based on the above results, we proceeded with the study thinking that by combining the two and adjusting the mixing ratio, an ultrafiltration membrane with high water permeability and high solute exclusion rate could be obtained. However, when methylene chloride is used as a low-boiling point solvent, although it is compatible with water-soluble high-boiling point solvents, a mixed solvent of the two is less effective than when each is used alone.
A significant decrease in the dissolving power for CTA has occurred,
There is a problem that a homogeneous solution of CTA required for casting cannot be obtained. On the other hand, when dioxane is used as a low boiling point solvent, it is compatible with water-soluble high boiling point solvents, and there is also the problem of reduced CTA dissolving power as a mixed solvent, as seen in the case of methylene chloride. A homogeneous solution of CTA was obtained, and the membrane obtained from this CTA solution by wet membrane formation was an ultrafiltration membrane with high water permeability and high solute exclusion rate. The major feature of the present invention is that CTA, which is a material that can be sterilized with hot water, is selected as the membrane material, and a mixture of dioxane and a water-soluble high-boiling solvent is used as the solvent, and the mixing ratio is adjusted. The object of the present invention is to obtain an ultrafiltration membrane that has high water permeability and high solute exclusion rate such as protein by adjusting the membrane pore size. The present invention will be explained in detail below. In the present invention, the CTA concentration in the CTA solution is not particularly limited, but a range of 6 wt% to 15 wt% is appropriate, preferably a concentration range of 8 wt% to 12 wt%. If the CTA concentration is less than 6wt%, the strength of the obtained film will be weak and it will not be practical. On the other hand, if it exceeds 15wt%, the viscosity of the CTA solution will become extremely large and difficult to handle. Furthermore, depending on the solvent used, CTA may not be completely dissolved. In the present invention, the high boiling point solvent used together with dioxane as a solvent for CTA is CTA which has infinite solubility in water and has a boiling point of 120°C or higher.
There is no particular limitation as long as the solvent is
N-methyl-2-pyrrolidone, morpholine, N,
Preference is given to using solvents such as N-dimethylacetamide and N,N-dimethylformamide. Further, these solvents may be used alone or in combination. If the high boiling point solvent used is partially soluble in water or poorly soluble, the membrane obtained by membrane formation will have a very dense surface layer, resulting in a membrane with low or no water permeability. I end up. This is because when immersed in water after casting, the solvent used is difficult to mix with water, so the solution flows in the opposite direction: water enters the membrane and the solvent elutes from the membrane into the water. Among them, the elution of the solvent from the membrane occurs preferentially because the intrusion of water into the membrane is prevented. Therefore, the phase separation phenomenon due to the intrusion of water progresses slowly, resulting in the formation of a very dense surface layer, resulting in a membrane with no water permeability. Furthermore, the thickness of the obtained film is also very thin. From these results, it is necessary that the high boiling point solvent used together with dioxane as a solvent for CTA has infinite solubility in water. The proportion of the mixed solvent of dioxane and water-soluble high boiling point solvent used as a CTA solvent in the CTA solution is preferably in the range of 70 to 94 wt%, and
Regarding the mixing ratio of dioxane and water-soluble high-boiling solvent used as a solvent for CTA, the content ratio of water-soluble high-boiling solvent to dioxane in the mixed solvent must be in the range of 0.25 to 1.80. It is. When the content ratio is less than 0.25, water permeability is lost due to the formation of a very dense surface layer, and when the content ratio exceeds 1.80, the rejection rate of solutes such as proteins is greatly reduced. This is because it will be put away. As described above, the present invention uses the following as a solvent for CTA:
Although a mixed solvent containing dioxane and a solvent with a boiling point of 120°C or higher and infinite solubility in water, which is the solvent for CTA, is used as the main component, CTA does not swell in this mixed solvent. By adding a mixed solvent of a solvent and a non-solvent as an additive, the stability of film formation can be improved. Swelling agents include acetone and ethyl lactate.
It is preferable to use water as one of the solvents and as the non-solvent. The appropriate proportion of both in the CTA solution is 20 wt% or less in the case of a swelling agent, and 5 wt% or less in the case of a non-solvent. Further, the total content ratio of both needs to be 20wt% or less. If the content ratio of each exceeds the above range, the mixed solvent of dioxane and water-soluble high boiling point solvent will lack the ability to dissolve CTA.
This is because a uniform CTA solution cannot be obtained and film formation becomes impossible. By selecting CTA as a membrane material, the present invention has advantages over hydrophobic polymers in two aspects: (i) stability of membrane formation, and (ii) less deterioration of pure water permeability over time. and for CDA (i)
By improving heat resistance and (ii) hydrolysis resistance, we also solved the problem of residual metal salts in films obtained by using a mixed solvent mainly composed of dioxane and a water-soluble high-boiling solvent as a solvent. It has an advantage over existing ultrafiltration membranes in that there is no ultrafiltration. The CTA ultrafiltration membrane obtained by the method of the present invention can be used in all fields where ultrafiltration membranes are currently used, but there is particularly little decline in pure water permeability over time. In addition, it does not use any metal salt additives, uses a solvent system that is soluble in water and can be completely washed and removed, and can be sterilized with hot water at 90°C. Taking advantage of its characteristics, it is ideal for use in fields that use pure water, which is sterile and pyrogen-free water, such as medical, pharmaceutical, and pharmaceutical fields. Furthermore, since it can be sterilized with hot water, it is suitable for use in fields such as food and fermentation, and since it does not contain additives such as metal salts, it is also suitable for use as hypermorphic artificial kidneys. Hereinafter, the present invention will be explained in detail with reference to Examples. Example 1 Cellulose triacetate 8 with a degree of acetylation of 60.9 and a degree of polymerization of 350
g was dissolved in a mixed solvent of 46 g of dioxane and 46 g of N-methyl-2-pyrrolidone to prepare a casting solution.
Using a doctor blade with a slit interval of 250μ on a refined Tetron cloth (Taffeta #230 made by Toray), place it in an atmosphere of 27℃ and 60%RH for 1 hour.
Casting was carried out at a speed of m/min. An ultrafiltration membrane was obtained by introducing the membrane into water maintained at 30°C at a speed equal to the casting speed so that the residence time in the air of each part of the membrane during casting was 3 minutes. . Next, this membrane was attached to a circulating ultrafiltration membrane measuring device (membrane area 25 cm ² ), and ovalbumin (molecular weight 45,000) was added.
An aqueous solution containing 2000ppm was heated at 25℃ and a pressure of 0.5Kg/cm ² G.
The liquid was filtered under the conditions of a liquid channel height of 270μ and a circulating liquid volume of 130ml/min, and the resulting liquid was analyzed using a gel permeation chromatograph (Shodex Ionpak S manufactured by Showa Denko).
-803) to determine the albumin exclusion rate. As a result, the water permeability rate was 1.3 m ³ /m ² ·day, and the albumin rejection rate was 98.0%. In addition, when the same type of membrane was attached to the above-mentioned apparatus and the water permeability coefficient was measured using distilled water for injection at a liquid temperature of 25°C and a pressure of 3.0 Kg/cm ² G, the result was 23.0 m ³ /m ²・Day (Kg/ ^cm2
G), and it was confirmed that the membrane was excellent as an ultrafiltration membrane. The hydraulic conductivity here is 1.0Kg/
It is the amount of water permeated in 24 hours per m ² of membrane area under cm ² G pressure, expressed in m ³ , and is defined by the following formula. Hydraulic conductivity [m ³ /m ²・day (Kg/cm ² G)]=
Water permeation rate [ ^m3 / ^m2・day]/intermembrane pressure [Kg/ ^cm2G ] Example 2 N,N instead of N-methyl-2-pyrrolidone
- Example 1 except that dimethylacetamide was used
When a membrane was formed in the same manner as above and the membrane performance was measured, the water permeation rate was 1.3 as measured using an ovalbumin aqueous solution.
m ³ /m ² ·day, and the albumin exclusion rate was 96.9%.
Similarly, in the evaluation using distilled water for injection, the hydraulic conductivity
It was 31.4m ³ /m ² ·day (Kg/cm ² G). Example 3 In the same manner as in Example 1, 8 g of cellulose triacetate was mixed with 52 g of dioxane and 40 g of N,N-dimethylformamide.
g was dissolved in a mixed solvent to obtain a casting solution, and this was used to obtain an ultrafiltration membrane. The performance of the obtained membrane was evaluated in the same manner as in Example 1. As a result, the measurement results using the ovalbumin aqueous solution showed a water permeation rate of 1.3 m ³ /m ² .
On day one, the albumin exclusion rate was 96.8%. In addition, in an evaluation using distilled water for injection, the hydraulic conductivity was 20.6m ³ /m ² .
day (Kg/cm ² G). Example 4 8 g of cellulose triacetate was dissolved in a mixed solvent of 50 g of dioxane, 24 g of morpholine, 15 g of acetone, and 3 g of water, and a film was formed in the same manner as in Example 1, and the film performance was measured. As a result, in the evaluation using an aqueous ovalbumin solution, the water permeation rate was 1.3 m ³ /m ² ·day, and the albumin rejection rate was 97.6%. In addition, in an evaluation using distilled water for injection, the hydraulic conductivity was 14.4m ³ /m ² ·day (Kg/cm ² G)
It was hot. Comparative Example 1 In place of N-methyl-2-pyrrolidone in Example 1, a solvent for cellulose triacetate with a boiling point of 156
A film was formed in the same manner as in Example 1, except that cyclohexanone having a solubility in water of 15% (30°C) was used, and the film performance was evaluated. As a result, no liquid was obtained in any of the measurements using an aqueous ovalbumin solution and distilled water for injection. Comparative Example 2 In place of N-methyl-2-pyrrolidone in Example 1, a solvent for cellulose triacetate with a boiling point of 162
℃, but using furfural whose solubility in water is 8.3% (20℃), 8 g of cellulose triacetate
was dissolved in a mixed solvent of 60 g of dioxane and 32 g of furfural, and after forming a membrane in the same manner as in Example 1, the membrane performance was evaluated. As a result, as in Comparative Example 1, no liquid was obtained in either the ovalbumin aqueous solution or distilled water for injection. Comparative Example 3 In place of N-methyl-2-pyrrolidone in Example 1, a swelling agent for cellulose triacetate with a boiling point of
Using formamide, which has an infinite solubility in water at 211℃, 8g of cellulose triacetate
was dissolved in a mixed solvent of 60 g of dioxane and 32 g of formamide, and after forming a membrane in the same manner as in Example 1, the membrane performance was evaluated. As a result, in the case of ovalbumin aqueous solution, the water permeation rate was 1.2 m ³ /m ² ·day, and the albumin exclusion rate was
It became 88%. Therefore, it was confirmed that adding a swelling agent instead of a solvent for cellulose triacetate significantly lowers the albumin exclusion rate. Further, in an evaluation using distilled water for injection, the hydraulic conductivity was 19.8 m ³ /m ² ·day (Kg/cm ² G). Example 5 8 g of cellulose triacetate was mixed with 30 g of dioxane, N
-Methyl-2-pyrrolidone 51g, ethyl lactate 8g
g and 3 g of water, and after forming a film in the same manner as in Example 1, the film performance was evaluated. As a result, in the case of ovalbumin aqueous solution, the water permeation rate was 1.3 m ³ /m ² ·day;
The albumin exclusion rate was 97.5%. Furthermore, in an evaluation using distilled water for injection, the hydraulic conductivity was 20.3m ³ /m ² .
day (Kg/cm ² G). As a result, it was confirmed that the membrane performance was almost the same as in Example 1 even in the system in which ethyl lactate + water was added. However, by adding additives, it is possible to improve the stability of film formation as shown by improved reproducibility of film performance, reduced variation in film performance, and the like. Example 6 A CTA ultrafiltration membrane was prepared in the same manner as in Example 1,
An ultrafiltration membrane made of polysulfone was selected as an example of a membrane using the obtained membrane and a hydrophobic polymer as a membrane material, and the performance of the two was compared under the same conditions. The evaluation used distilled water for injection as the stock solution.
This was done by comparing the change in hydraulic conductivity over time at an intermembrane pressure difference of 3.0 kg/cm ² G. By the way,
The commercially available polysulfone ultrafiltration membranes used in this evaluation are (i) ultrafiltration membrane PM30 manufactured by Amicon [molecular weight cut off: 30,000, pure water overrate: 2 to 5 ml/cm ² min
(Pressure 3.8 Kg/cm ² G, 5 minutes after start)], Toyo Shi ultrafiltration membrane UK-50 [molecular weight cut off 50,000, pure water overrate 1-3 ml/cm ² min (pressure 4.0 Kg/ cm ² G)〕2
It is a kind. Note that data on molecular weight cutoff and pure water overrate are both catalog values.
The results are shown in Table 1.

[Table] From the above results, when polysulfone, which is a hydrophobic polymer, is used as the membrane material, the pure water permeability coefficient is high at the very beginning, but after that,
A rapid decrease was observed within a short period of time, indicating that the decrease in the pure water permeability coefficient over time was extremely large. On the other hand, in the case of the CTA ultrafiltration membrane obtained by the present invention, the change in the pure water permeability coefficient over time is very small, and it is possible to secure the amount of pure water permeation that changes over time. Superiority is shown. Example 7 Similar to Example 6, a sample was produced according to the present invention.
Ultrafiltration membrane made by CTA and our patented patent application in 1972
-Produced according to the method shown in Publication No. 134608
A comparative study was conducted regarding heat resistance with ultrafiltration membranes made from CDA. The method of JP-A-54-134608 is about dissolving cellulose diacetate in a mixed solvent consisting of N,N-dimethylformamide, acetone, water and cyclohexane, using water as a coagulating liquid, and forming a film by a wet method. This is what is shown. The evaluation was carried out in the same manner as in Example 1, using ovalbumin (molecular weight 45,000) as the solute.
0.5Kg/cm ² using 2000ppm aqueous solution as stock solution for evaluation
The water permeation rate and ovalbumin exclusion rate under G pressure were compared before and after heat treatment. The results are shown in Table 2.

[Table] From the results in Table 2, the membrane performance of CTA membrane hardly changes even if it is subjected to hot water treatment at 90℃ for 10 hours, whereas in the case of CDA membrane, it is treated for a short time of 15 minutes at 85℃. Despite the heat treatment, there was a tendency for the water permeation rate to decrease and the ovalbumin exclusion rate to decrease. From this result, it is clear that the CTA film is superior to the CDA film in terms of heat resistance. Example 8 Similar to Example 7, a sample was produced according to the present invention.
Ultrafiltration membrane made by CTA and ultrafiltration artificial kidney module “Hemofresh” made by Daicel Chemical Industries, Ltd.
The CDA ultrafiltration membrane used in this study was evaluated using fresh bovine blood, and the performance was compared. For the evaluation, fresh bovine blood (hematocrit value 28%, total protein concentration 3.7%) diluted with physiological saline was used, and the evaluation membrane was attached to a circulating ultrafiltration membrane measuring device in the same manner as in Example 1, and the membrane was heated at 25°C and under pressure. 0.5Kg/cm ² G, liquid flow path height
270μ, circulating liquid volume 40ml/min,
The protein concentration of the obtained solution and stock solution for evaluation was
It was analyzed by GPC and protein permeability was calculated.
The results are shown in Table 3.

[Table] From the results in Table 3, the results obtained by the present invention
It has been confirmed that the ultrafiltration membrane made by CTA has the same performance as the ultrafiltration membrane made by CDA currently used in the hyperdiaphragm artificial kidney module, and is suitable as an ultrafiltration membrane for the hyperdiaphragm artificial kidney module. It became clear that there was.

Claims (1)

[Claims] 1. Cellulose triacetate with an acetylation degree in the range of 59.6 to 62.5%, dioxane and a boiling point of 120°C or higher,
In addition, a semipermeable membrane is produced by casting a cellulose triacetate solution consisting of a mixed solvent whose main component is a solvent that has infinite solubility in water and is the solvent for cellulose triacetate, and coagulates it in water. A method for producing an ultrafiltration membrane made of cellulose triacetate, characterized by: 2 The concentration of cellulose triacetate in the cellulose triacetate solution used for casting is 6 to 15 wt%, preferably 8
The manufacturing method according to claim 1, wherein the content is 12 wt%. 3 The solvent that has a boiling point of 120°C or higher and has infinite solubility in water and is a solvent for cellulose triacetate is N-methyl-2-pyrrolidone, morpholine, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone, morpholine, N,N-dimethylacetamide, and ，
The manufacturing method according to claim 1, wherein one or more types are selected from the group consisting of N-dimethylformamide. 4 The boiling point of dioxane is 120℃ or higher, and
The solubility in water is infinite, and the proportion of the mixed solvent with the solvent that is the solvent for cellulose triacetate in the cellulose triacetate solution is 70 to 94 wt%,
The manufacturing method according to claim 1 or 3, wherein the content ratio of the solvent other than dioxane to dioxane in the mixed solvent is within the range of 0.25 to 1.80. 5. A swelling agent for cellulose triacetate as an additive in a mixed solvent whose main components are dioxane and a solvent that has a boiling point of 120°C or higher and has infinite solubility in water and is a solvent for cellulose triacetate. The manufacturing method according to claim 1, wherein a mixed solvent of and a non-solvent is added. 6. The manufacturing method according to claim 5, wherein the swelling agent is either acetone or ethyl lactate, and the nonsolvent is water. 7 The proportion of the swelling agent and non-solvent in the cellulose triacetate solution is 20 wt% or less,
The latter is 5wt% or less, and its total content is
Claim 5 or 6 which is 20wt% or less
Manufacturing method described in section.