JPS59102407A - Production of ultrafiltration membrane made of cellulose triacetate - Google Patents

Abstract

PURPOSE:To produce an ultrafiltration membrane which is highly resistant to hydrolysis and heat by forming said membrane from a high polymer soln. obtd. by using cellulose triacetate as a blank material for film and a solvent mixlture composed of dioxane and a polar org. solvent as an essential solvent. CONSTITUTION:Cellulose triacetate (CTA) having 59.6-62.5% degree of acetylation is dissolved in a solvent prepd. by mixing dioxane and a solvent for CTA, such as N-methyl-2-pyrolidone, morpholine, N, N-dimethylacetamide or N, N- dimethylformamide, having >=120 deg.C b.p. and infinite solubility with water at 0.25-1.80 ratio basing on 1 dioxane, so that CTA is incorporated at 6-15% concn. The cellulose triacetate soln. prepd. by adding further <=20% a swelling agent for CTA and <=5% non-solvent such as water to the above-mentioned soln. is cast and is solidified in water to form a semipermeable membrane in water, whereby the ultrafiltration membrane having high resistance to heat and hydrolysis is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an ultrafiltration membrane using cellulose triacetate (hereinafter abbreviated as OTA) with an acetylation degree ranging from 59.6 to 62.5 as a membrane material. This relates to a manufacturing method. More specifically, 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 cellulose diacetate (hereinafter abbreviated as ODA) by using OTA'i. .

In recent years, ultrafiltration membranes have been used for food, two-paper pulp, and fermentation.

Resource recovery,
It is widely used for purposes such as concentration of valuables, wastewater treatment, pure water/wash water production, and 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 the shape of a membrane or the like. Among these many ultrafiltration membranes, synthetic polymers, especially hydrophobic polymers, have recently been widely used for applications that require chemical and solvent resistance. Although the chemical molecules have the above-mentioned advantages, they have the disadvantage that the solvents that can be used during film formation are limited and the degree of freedom in setting the manufacturing process is small. Furthermore, in the case of membranes used as hydrophobic bacterial molecule-free materials, it is said that the water permeation rate of pure water decreases over time compared to membranes made of hydrophilic materials. There are problems with its use in fields where water is required as an r-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. Membrane conditions can be easily controlled. Furthermore, compared to hydrophobic materials, it has the advantage that the water permeation rate of pure water decreases less over time. For this reason,
Conventionally, cellulose acetate was used as the membrane material, and the wet method was used.
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, in JP-A-55-3890, OTA or a mixture of OTA and CDA is used as a membrane material, and either a mixed solvent of dioxane, acetone, and formamide, or a mixed solvent of dioxane, acetone, and acetamide is used. By dissolving and adding hydrophobized silicic acid thereto, after film formation by a wet method, the resulting film is immersed in a high boiling point solvent such as glycerin, and then transferred to a solvent-impregnated film by drying. A method is shown to prevent performance degradation at times. Still JP-A-55-1
Publication No. 854 describes cellulose ester k, the ia of the ester, and s, which is a polar organic solvent with a boiling point of 120C or more and water, and a rhodan salt or di- to trivalent salt that has a large water utilization heat when dissolved in water. A method is disclosed in which a semipermeable membrane is obtained by a wet method by dissolving one of the cationic metal salts in a three-component mixed solvent.
No. 9 discloses a method of obtaining an ultrafiltration membrane by a wet method by dissolving a blend of ODA and OTA in a polar organic solvent.

Generally, 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 sudden change in interfacial tension on the membrane surface. However, it is known to cause a decline in performance and has poor processing and moldability. Therefore, the membrane obtained by the wet method is first immersed in a water-soluble solvent with a high boiling point such as glycerin, and then dried to form a membrane impregnated with the above-mentioned water-soluble bath agent. The aim is to maintain the same properties and improve processability and formability.

Therefore, in the method disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 55-3890, in the case of an ultrafiltration membrane mainly using CTA as the membrane material, a high boiling point water-soluble solvent such as glycerin as mentioned above is used. If the membrane is soaked in water and then dried, the water permeability of the membrane will decrease;
In this case, a film obtained by adding hydrophobized gold silicate to OTA or a solution of a mixture of C, TA, and ODA in a solvent will not be able to produce a film even if it is subjected to the dry film forming process using the above method. It has been shown that membrane performance does not change. 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 the purity of the P solution and eluates in the F solution are problematic. has a problem.

Furthermore, in the above-mentioned Japanese Patent Application Laid-Open No. 55-1854, when a semipermeable membrane is formed using a two-component solution in which cellulose ester is dissolved in a polar organic solvent, the water permeation rate of the membrane is low; Although this does not result in a useful membrane, it has been shown that a useful membrane can be obtained by adding water and a metal salt to a solution of a cellulose ester in a polar organic solvent. Furthermore, it has been shown that among the cellulose esters used in this case, CDA provides a membrane with the highest water permeability. However, the membrane obtained in this way contains metal salts, which are difficult to completely remove from the membrane. It is not suitable for use in the medical field such as treatment, or as a separation membrane for food applications in the pure water field.
DA is said to be better, but in the case of ODA, generally O
It is said that it has inferior hydrolysis resistance compared to TA, and has the disadvantage of not having heat resistance.Furthermore, in the above-mentioned Japanese Patent Application Laid-open No. 55-5859, O
In the case of a reverse osmosis membrane, in which a mixture of DA and OTA is used as the membrane material, a dense layer on the membrane surface is required, so a non-polar organic solvent with a low boiling point such as acetone or dioxane is used. In the case of the ultrafurnace membrane described in .

It has been shown that the surface dense 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 ODA and OTA used as membrane materials. However, in the example of JP-A-55-3859, the above-mentioned JP-A-55-3890, JP-A-55-1
Although there is no problem of residual additives in the membrane as seen in the example of No. 834, ODA and OT are used as membrane materials.
Since a mixture of A is used, there are problems caused by ODA among them. First of all, it is generally said to have inferior hydrolysis resistance compared to CTA, so it is easy to cause a decline in membrane performance due to deterioration of the membrane material over time during use, and it also has poor heat resistance. Considering the above situation, the present inventors used cellulose triacetate as the membrane material and used dioxane as the membrane material. By using a mixed solvent of polar organic solvents with a boiling point of 120C or more as the main solvent and forming a film from the resulting polymer solution, it has improved hydrolysis resistance and heat resistance compared to paDh. The present invention was completed by discovering a method for obtaining an ultrafiltration membrane without problems such as residue, etc. In other words, the present invention uses triacetyl cellulose with an acetylation degree ranging from 59.6 to 62.5, dioxane, and a boiling point is 1,000 or more, and has infinite solubility in water, and a cellulose triacetate solution consisting of a mixed solvent whose main component is a solvent for cellulose triacetate is cast and coagulated in water. This is a method for manufacturing an ultrafiltration membrane made of cellulose triacetate, which is characterized in that the entire semipermeable membrane is manufactured using the following method.

Conventionally, a polymer material is dissolved in a solvent, the entire solution is cast onto a support such as a glass plate or woven cloth, and the material is allowed to stand in a t-atmosphere for a certain period of time, and a portion of the solvent used is poured off. evaporates from the surface of the polymer solution.

The wet casting method, which produces a membrane with an asymmetric structure by immersing it in the non-solvent of the used polymer material and coagulating the polymer material, is a method used for reverse osmosis membranes and ultrafiltration membranes. It is widely used as a manufacturing method. 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. Among them, ODA in particular can be used in many solvents, and is a water-soluble low-boiling solvent that is usually added to polymer solutions in wet casting methods, so it is difficult to handle ODA as exemplified by A7T. It has been widely studied and used because it can use easy solvents. On the other hand, OTA has better heat resistance and hydrolysis resistance as a membrane material than ODA, although the solvents that can be used are limited.

Therefore, the present inventors selected OTA as the membrane material and proceeded with studies on membrane formation using a wet casting method. Examples of volatile low-boiling solvents added to the casting polymer solution include dioxane and methylene chloride. First, OTA
When using only dioxane as a solvent and casting with an OTA solution, the effect of evaporation of dioxane when standing still in the atmosphere is too large, so the polymer material is immersed in a non-solvent to solidify the polymer material. The resulting membrane has a very dense surface layer and has almost no water permeability.
:9o Also, methylene chloride only'QC! When used as a solvent for TA, the membrane obtained by casting had a denser surface layer and no water permeability than when only dioxane was used as a solvent. This is due to the effect of evaporation of methylene chloride when it is left standing in the atmosphere, and also because methylene chloride has a short bathing property in water. This is due to the effect of suppressing the exchange speed. On the contrary, C
If a membrane is formed by the same wet method using only a water-bathable high-boiling solvent as the TA solvent, the resulting membrane has water permeability, but when evaluated using albumin as a solute, the solute rejection rate was low. As an ultrafiltration membrane, the membrane has very large leakage and poor performance. This means that the water-soluble boiling point solvent used is
Because it hardly evaporates when left standing in the atmosphere after casting,
This is because the evaporation effect such as an increase in CTA concentration near the membrane surface and a decrease in OTA## force due to a decrease in the amount of solvent did not work, and a dense layer was not sufficiently formed on the membrane surface. In addition, the solute exclusion rate here is defined by the following formula.

Therefore, if a low-boiling point solvent and a water-soluble high-boiling point solvent are used alone as OTA solvents, the results shown above will be obtained. Therefore, by combining the two and adjusting the mixing ratio, We proceeded with the study thinking that we could obtain an ultrafiltration membrane with high water permeability and high solute exclusion rate. 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 both has a lower OTA than when each is used alone.
There is a problem in that the dissolving power of OTA is significantly reduced, and a homogeneous solution of OTA necessary for casting cannot be obtained.

On the other hand, when dioxane is used as a low boiling point solvent,
O
A homogeneous solution of OTA can be obtained without the problem of a decrease in TA dissolving power, and the membrane obtained from this CTA solution by wet membrane formation has high water permeability and is an ultrafiltration membrane with a high solute rejection rate. there were.

The major feature of the present invention is that 0TAi, which is a material that can be sterilized with hot water, is selected as the membrane material, and dioxane is used as the solvent.
The purpose is to obtain an ultrafiltration membrane with high water permeability and a high rate of exclusion of solutes such as proteins by using a mixture of water-soluble high boiling point solvents and adjusting the mixing ratio to adjust the membrane pore size. .

In the present invention, the degree of CTAa in the OTA solution is not particularly limited, but a concentration of 6 wt% to 15 wt% is appropriate, and preferably a concentration of 8 wt% to 12 wt%. A range is preferred. (IOT
If the A concentration is less than 6 wt%, the strength of the obtained film will be weak and cannot be put to practical use.On the other hand, if it exceeds 15 wt%, the viscosity of the TA solution will be extremely Due to their large size, they are difficult to handle, and depending on the solvent used, OTA may not be completely dissolved.

In the present invention, the high boiling point solvent used together with dioxane as a solvent for OTA is not particularly limited as long as it has an infinite solubility in water and is a CTA solvent with a boiling point of 1000 or more. N-methyl-2-pyrrolidone, morpholine, N,N-dimethylacetamide,
Preference is given to using solvents such as N,N-dimethylformamide. Further, these solvents may be used alone or in combination. If the high boiling point solvent used is partially soluble or poorly soluble in water, the resulting membrane will have a very dense surface layer, resulting in a membrane with low or no water permeability. It becomes. This is due to the fact that the solvent used is difficult to mix with water when immersed in water after casting, and the solution flows in the opposite direction: water enters the membrane and the solvent elutes from the membrane into the water. Of the flow, the elution of the solvent from the membrane occurs preferentially because the entry 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
It will be very thin. From these results, C! T.A.
The high boiling point B medium used together with dioxane as a solvent must have infinite solubility in water.

The mixed solvent of dioxane and water-soluble high boiling point solvent used as a solvent for CTA is C! The proportion in the TA solution is 70~
A range of 94 wt% is preferable, and further, regarding the mixing ratio of dioxane and water-soluble high boiling point solvent to each other in the mixed solvent used as a solvent for CT, the content ratio of the water-soluble high boiling point solvent to dioxane in the mixed solvent is 0. .25
If the Q content ratio is less than 0.25, water permeability will be lost due to the formation of a very dense surface layer; This is because if it exceeds 80, the exclusion rate of solutes such as proteins will be significantly reduced.

As mentioned above, the present invention uses dioxane as a solvent for OTA, which has a boiling point of 1000 or more, has infinite solubility in water, and has C! Although this method uses a mixed solvent whose main component is a solvent for TA, the stability of film formation can be improved by adding a mixed solution of an OTA swelling agent and a non-solvent to this mixed solvent as an additive. It is possible to improve sexual performance. It is preferable to use either acetone or ethyl lactate as the swelling agent, and water as the nonsolvent. The proportion of both in the CTA solution is 20wt or less in the case of a swelling agent, and S in the case of a non-solvent.
wt- or less is appropriate. Also, the total content ratio of both is 2
It is necessary that it is less than 0wt. If each content ratio exceeds the above range, the dissolving power of the mixed solvent of dioxane and water-soluble high boiling point solvent for OTA will be insufficient, making it impossible to obtain a uniform OTA solution and making film formation impossible. This is because (0) the present invention is achieved by selecting OTA as the membrane material.
1) It has advantages over hydrophobic polymers in two points: stability of membrane formation and less deterioration of pure water permeability over time, and /fi(+) against ODA. It is possible to solve the problem of residual metal salts in films obtained by improving thermal properties and hydrolysis resistance, and 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.

Although the OTA outer door △ filtration membrane obtained by the method of the present invention can be used in all fields where ultrafiltration membranes are currently used, there is particularly little decline in pure water permeability over time. Moreover, it does not use any metal salt additives and uses a solvent system that is soluble in water and can be completely washed and removed.

Taking advantage of its characteristics such as the fact that it can be sterilized using qo'c hot water, it can be used in fields that use pure water, which is sterile and pyrogen-free water, such as medical care, medicine, and pharmaceuticals. Optimal.

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 a filtration type artificial kidney.

The present invention will be described in detail with reference to one example below. This was used as a casting solution.

This solution was refined using a Tetron cloth (Takuna 2 made by Toshi).
30) Using a doctor blade with a slit interval of 250 μm, casting was carried out at the speed of Example No. 1 in an atmosphere of 27C and 60% RH. An ultrafiltration membrane was obtained by introducing the membrane into water maintained at 50C at a speed equal to the casting speed so that the residence time in air of each part of the membrane during casting was 3 minutes. Next, this membrane was passed through a circulating ultrap membrane measuring device (
membrane area: 25 d), and ovalbumin (molecular weight: 45 d).
000) Aqueous solution containing 2000 ppm 'i2c? r,
Pressure 0.5 Gin 9G, liquid flow path height 270μ, circulating liquid volume 15
The flow liquid was filtered under the conditions of 0 minutes, and the obtained solution F was analyzed using a gel permeation chromatograph (Showa Denko 5h Odex onpak S-805) to determine the albumin exclusion rate. Water permeability rate 1.3m7rrf
・The albumin exclusion rate was 98.0%.

In addition, the same type of membrane was attached to the above-mentioned apparatus, and the hydraulic conductivity was measured using the sound of distilled water for injection under the conditions of liquid temperature of 25C2 pressure of 6°Okg/IG, and the result was 25.0 m'.
/nj'・日・Cky/alG) It was completely confirmed that the membrane was excellent as an ultrafiltration membrane. The permeability coefficient referred to here is expressed as permeability M for 24 hours under 1.0 kg/JCk side pressure and membrane surface pressure, and is defined by the following formula. .

Example 2 A membrane was formed in the same manner as in Example 1 except that N,N-dimethylacetamide was used in place of N-methyl-2-pyrrolidone, and the membrane performance was measured. Water permeation rate 1, 3 rrVrflt-a,
The albumin exclusion rate was 96.9%. Similarly, in the evaluation using distilled water for injection, the water permeability coefficient was 31.4 lr〆dyama・(Nawate G).

Example 3 Similarly to Example 1, cellulose triacetate 82 was mixed with dioxa 7
52F, N, N-dimethylformamide 401 was dissolved in a mixed solvent to obtain a casting solution, and this was used to ultrafiltrate Hf.
I got fi. 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 1.5 n1/m'B and an albumin exclusion rate of 9.
It was 6.8%. In addition, in an evaluation using distilled water for injection, the permeability coefficient was 20.6 mym''.

Example 4 Cellulose triacetate 81 was dissolved in a mixed solvent of dioxane, 5o2°, morpholine, 24f, acetone, 15F, and water, 3SF, 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 the ovalbumin aqueous solution, the water permeation rate was 1.5 +fn? Field.

The albumin exclusion rate was 97.6%. In addition, in the evaluation using distilled water for injection, the permeability coefficient was 14.4 m > 2 peaks (kg
/cyl G).

Comparative Example 1 Example 10KJ-Methyl-2-pyrrolidone was replaced with cyclohexanone, which is a solvent for cellulose triacetate and has a boiling point of 1560 but a solubility in water of 15C (30C). A film was formed in the same manner as in Example 1, and the film performance was evaluated. As a result, no solution F was obtained in any of the measurements using an aqueous ovalbumin solution and distilled water for injection.

Comparative Example 2 In place of 19-methyl-2-pyrrolidone in Example 1, a solvent for cellulose triacetate having a boiling point was used.

162C, but the solubility in water is 8.3% (20C)
Using furfural, cellulose triacetate 82,
It was dissolved in a mixed solvent of dioxane 60F and furfural 522, and after film formation in the same manner as in Example 1, the film performance was evaluated. As a result, as in Comparative Example 1, no r liquid was obtained in either the measurement of the ovalbumin aqueous solution or the 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 211C,
Using formamide, which has infinite solubility in water, cellulose triacetate 82 was mixed with dioxane 601. After dissolving in a mixed solvent of formamide 521 and forming a film in the same manner as in Example 1, the film performance was evaluated. As a result, in the case of an aqueous ovalbumin solution, the water permeation rate was 1.2 + rVm.

The albumin exclusion rate was 88g. Therefore, it was confirmed that the addition of a swelling agent instead of a solvent for cellulose triacetate significantly reduced the albumin exclusion rate.Also, in the evaluation using distilled water for injection, the hydraulic conductivity was 19. 8 Jrl-E3・
(kg/ca G).

Example 5 8f of cellulose triacetate, 30g of dioxane.

After film formation, the film performance was evaluated. As a result, in the case of an aqueous ovalbumin solution, the water permeation rate was 1.3ψν.

The albumin exclusion rate was 97.5%. Furthermore, in the evaluation using distilled water for injection, the hydraulic conductivity was 20.3rQ/rt1
'It was Yama (Yunei 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. It is possible to improve the stability of film formation as indicated by improved reproducibility, reduced variation in film performance, and the like.

Example 6 An OTA ultrafiltration membrane was produced in the same manner as in Example 1, and a polysulfone ultrafiltration membrane was selected as an example of a membrane using the obtained membrane and a hydrophobic polymer as the membrane material. A comparison of the performance was made under the same conditions. In the evaluation, distilled water for injection was used as the stock solution, and the transmembrane pressure difference was 3.0 kg/(d
This was done by comparing the change in hydraulic conductivity over time in G. By the way, the commercially available polysulfone ultrafiltration membrane used for the evaluation here is (IJ Amicon UltraF Filter).
uPM 30 [minute 1i molecule Jt 30,000t! 'B Water filtration speed 2-5 m/J・min (pressure 3.81G
+5 minutes after the start)].

Toyo p paper ultra filtration membrane UK-50 [molecular weight cut off 50,000 Pure water filtration rate 1-3 ml/ai・min (pressure 4.01
There are two types: v/dG)). It should be noted that data on the molecular weight cut off and pure water p overrate are both catalog values. The results are shown in Table 1.

From the above results, when polysulfone, which is a hydrophobic polymer, is used as a membrane material, the pure water permeability coefficient is high at the very beginning, but after that, a rapid decrease is observed in a short period of time. It can be seen that the decrease in the coefficient over time is very large.On the other hand, the OTA obtained by the present invention
In the case of manufactured ultrafiltration membranes, the change over time in the pure water permeability coefficient is very small, and it is possible to secure a stable amount of pure water permeation over time, demonstrating the superiority of the CTa membrane.

Example 7 Similar to Example 6, misfire F! The CTA ultrafiltration membrane made from AK and the
A comparative study was conducted regarding heat resistance with an ODA ultrafiltration membrane produced according to the method shown in Publication No. B. The method of JP-A-54608 is based on cellulose diacetate "e".
This shows a method of forming a P film by a wet method by dissolving it in a mixed solvent consisting of NsN-dimethylformamide, acetone, water and cyclohexane, and using water as a coagulating liquid. The evaluation was carried out in the same manner as in Example 1, using ovalbumin (molecule i 45000) as the solute! A 2000'ppm aqueous solution of ovalbumin was used as the stock solution for evaluation.
．． This was done by comparing the water permeation rate and ovalbumin exclusion rate under 9/4G pressure before and after heat treatment.

The results are shown in Table 2.

Table 2: Ratio of effects of heat treatment on OTA and ODA membranes From the results in Table 2, it is clear that the membrane performance of OTA membranes hardly changes even when subjected to hot water treatment at 90C for 10 hours; In the case of the membrane, despite the short heat treatment at 85C for 115 minutes, there is a tendency for the water permeation rate to decrease and the ovalbumin exclusion rate to decrease. From this result, it is clear that the OTA film is superior to the ODA film in terms of heat resistance.

Example 8 The CT Afi ultrafiltration membrane and the ODA ultrap filtration membrane used in the E-filtration type artificial kidney module Hem0fresh manufactured by Daicel Chemical Industries, Ltd. were evaluated using fresh bovine blood, and their performance was compared. I did this.

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 the circulating room ultrapolar membrane measuring device in the same manner as in Example 1. , 25C2 pressure 0-5'v'cA Gr liquid flow path height 2
The flowing liquid was filtered under the conditions of 70μ and circulating liquid volume dQmp, and the obtained n k F solution and the protein concentration V of the stock solution for evaluation were collected as G P
The protein permeability was calculated by oxygen analysis. The results
It is shown in Table 3.

Table 3 OTA, C! From the results of Table 3, which compares the performance of both DA and ultrafiltration traces with fresh bovine blood, it is clear that
It has been confirmed that the TA ultrafiltration membrane has the same performance as the ODA ultrafiltration membrane currently used in the filtration type artificial kidney module, and is suitable as an ultrafiltration membrane for the filtration type artificial kidney module. It became clear that

Applicant's agent Shuu Furutani

Claims (1)

[Scope of Claims] 1 Cellulose triacetate with an acetylation degree in the range of 59.6 to 62.5%, dioxane, and a boiling point of 1000 or more and infinite solubility in water, An ultrafiltration membrane made of cellulose triacetate, characterized in that a semipermeable membrane is produced by casting a cellulose triacetate solution consisting of a mixed solvent whose main component is a solvent for cellulose acetate and coagulating it in water. manufacturing method. 52 Cellulose triacetate concentration in cellulose triacetate solution used for casting is 6 to 1
5 wt%, preferably 8 to 12 wtq6. 5 The solvent, which has a boiling point of 1000 or more, has infinite solubility in water, and is a solvent for cellulose triacetate, is N-methyl-2-pyro 1 selected from the group 6.
The manufacturing method according to claim 1, which is one or more types. Dioxane has a boiling point of 1000 or more, has infinite solubility in water, and has a proportion of 70 to 94 wtq6 in the cellulose triacetate solution of a mixed solvent with a solvent that is a solvent for cellulose triacetate. Claim 1, 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.
The manufacturing method described in item 1 or 5. A swelling agent for cellulose triacetate as an additive in a mixed solution containing dioxane and a solvent having a boiling point of 1000 or more and infinite solubility in water and which is a solvent for cellulose triacetate. The manufacturing method according to claim 1, characterized in that a mixed solvent of a non-solvent is used. Whether the swelling agent is acetone or ethyl lactate7 The proportion of the swelling agent and nonsolvent in the cellulose triacetate solution is
7. The manufacturing method according to claim 5 or 6, wherein the former is 20 wt% or less, the latter is 5 wt% or less, and the total content thereof is 20 wt% or less.