JPH02293031A - Hydrophilic porous hollow fiber membrane - Google Patents

Abstract

PURPOSE:To obtain a hydrophilic porous hollow fiber membrane which is safely and hygienically used in the production of drinking water by forming protein films on the surfaces of the pores in a porous membrane and fixing silver on the surfaces of the pores. CONSTITUTION:Films of protein supplied as food are formed on the surfaces of the pores in a porous membrane and silver is bonded to the surfaces of the pores as required. A hydrophilic porous hollow fiber membrane which is safe and hygienic even when utilized to produce drinking water is obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a porous hollow fiber M suitable for use with water. The present invention relates to a porous hollow fiber membrane which continuously and stably has good hydrophilicity due to the presence of water, and which is also suitable as a filtration membrane for a filtration module for producing drinking water.

[Prior Art] Conventionally, when porous hollow fibers are used as water filtration membranes, for example, in hydrophobic porous hollow fibers made of polyethylene, polypropylene, borisulfone, polycarbonate, polyvinylidene fluoride, polytetrafluoroethylene, etc. must be made hydrophilic with a hydrophilic agent such as alcohol before use.

However, the wood-philicity of porous hollow fibers treated with this method is unstable; for example, if water is not used for a long period of time! 2! ! If the water is removed from the filter during the washing process after passing through the filter and left temporarily to dry the porous hollow fibers, the disadvantage is that the hydrophilicity will be greatly reduced and good water permeability will not be obtained. be.

Therefore, there has been a strong demand for the development of porous hollow fibers that do not have such drawbacks and have continuous and stable hydrophilicity.

In order to meet this demand, the present inventors created a hollow fiber that gave permanent hydrophilicity to a hydrophobic porous hollow fiber. Permanent hydrophilic porous hollow fiber membrane formed of a thin layer consisting of
No. 0 (Japanese Unexamined Patent Publication No. 61-810: J''+)], a permanent hydrophilic porous hollow fiber in which a thin film of cellulose acetate is formed on the pore surface of a hydrophobic porous hollow fiber [Patent Application No. 59-81- 16
No. 4063 (Japanese Unexamined Patent Publication No. 61-42304)], a permanent hydrophilic porous hollow fiber in which a thin film of cellulose is formed on the pore surface of a hydrophobic hollow fiber [Patent Application No. 15954-1982]
No. 3 (Japanese Unexamined Patent Publication No. 61-35804)], a permanent hydrophilic porous hollow fiber in which a thin film made of ethylene/vinyl alcohol resin is formed on the pore surface of a hydrophobic porous hollow fiber [
Patent Application No. 59-245606 (Japanese Patent Application No. 12540-1983
No. 8)]) was disclosed.

On the other hand, it has been known that silver exhibits excellent bactericidal properties and that microorganisms such as bacteria cannot grow on the silver surface.

Utilizing this characteristic of silver, it is possible to impart antibacterial properties to porous hollow fibers.

As a method for this purpose, for example, the method disclosed in Japanese Patent Application Laid-Open No. 60-261502 (Japanese Patent Application No. 59-116572) by the present inventors
No.) describes hollow fiber filtration using porous hollow fibers, which have antibacterial properties by forming a thin silver film on the surface of the pores on the outer wall side of porous polyolefin hollow fibers, as a membrane for water filtration. A module is disclosed by the inventors.

Furthermore, Japanese Patent Application Laid-Open No. 1983-298406 (Japanese Patent Application No. 1983-
No. 142301) discloses a method of forming a thin silver film on the surface of pores in the surface layer on the outer wall side of a hollow fiber by sputtering.

In addition, as a method for imparting antibacterial properties by adsorbing silver to porous hollow fibers, electroless plating is used to coat silver throughout the entire porous structure from the surface layer on the outer wall side of the hollow fiber wall to the sphere layer on the side of the hollow fiber. A method of fixing is also known.

[Problems to be Solved by the Invention] As mentioned above, in order to eliminate the drawbacks of porous hollow fibers treated with hydrophilic agents such as alcohol, various methods have been developed to impart permanent hydrophilicity to hydrophobic porous hollow fibers. method is known.

However, the safety of porous hollow fibers imparted with permanent hydrophilicity by conventional methods as filtration membranes for producing drinking water has not yet been confirmed.

For example, the permanent hydrophilic hollow fibers provided by the present inventors mentioned above all have excellent permanent hydrophilicity,
Although they are useful for filtering water for industrial use, especially for precision equipment, it has not yet been confirmed whether water filtered using these hollow fibers is safe for drinking water.

In other words, these hollow fibers have a structure in which a thin film of the above-mentioned hydrophilic resin is formed on the surface of the porous pores of the hydrophobic hollow fiber, but these hydrophilic resins are removed from the surface of the porous structure during the water filtration process. It has not been confirmed whether the filtered water is safe for drinking if it were to peel off and fall off, or if it were mixed into the filtered water.

Therefore, there is a strong demand for the development of porous hollow fibers with permanent hydrophilicity that can provide water that is safe for drinking.

On the other hand, as mentioned above, various methods have been studied for imparting antibacterial properties to porous hollow fibers using silver, and conventional methods still have problems that need to be improved. .

For example, as mentioned above, hydrophobic porous hollow fibers are mainly used, and metallic silver itself is also hydrophobic, so
The porous hollow fibers to which silver is fixed exhibit hydrophobicity, and when used for water filtration, pretreatment with a hydrophilic agent such as alcohol is required.

Furthermore, the wood-philicity imparted by a hydrophilizing agent such as alcohol lacks stability as described above.

Furthermore, in the method of fixing silver to the surface layer on the outer wall side of the porous hollow fiber using the vacuum evaporation method described in JP-A-60-261502, it is difficult to fix silver uniformly over the entire surface layer. In many cases, the occurrence of areas where a thin silver film is not formed is unavoidable.

On the other hand, even in the method of fixing silver by sputtering described in JP-A-62-298406, it is difficult to fix silver uniformly over the entire surface layer on the outer wall side of the porous hollow fibers, and the cost is $11. It cannot be said that it is completely bacteriostatic.

Furthermore, in the method of fixing silver over the entire hollow fiber wall by electroless plating, silver is reduced and precipitated within the pores, but the amount of silver deposited within each pore is adjusted over the entire hollow fiber wall. This is difficult, and a significant decrease in water permeability due to the clogging of pores by precipitated silver is unavoidable.

The purpose of the present invention is to solve the above-mentioned problems with the conventional porous hollow fibers used for water filtration, to have continuously stable hydrophilicity, and to have safety problems for producing drinking water. The object of the present invention is to provide a porous hollow system membrane without any porosity.

Another object of the present invention is to provide a hydrophilic porous hollow fiber membrane suitable for water filtration and having a structure suitable for imparting bactericidal properties with silver.

Another object of the present invention is to provide a porous hollow fiber membrane suitable for water filtration that has continuously stable hydrophilicity and safety for producing drinking water, and has excellent dryness control properties. There is a particular thing.

[Means for Solving the Problems] The hydrophilic porous hollow fiber membrane of the present invention has a protein thin film formed on at least a portion of the surface of the porous fiber membrane.

A hydrophilic porous hollow fiber membrane with excellent bacteriostatic properties can be obtained by bonding silver to the protein thin film held in the hydrophilic porous hollow fiber membrane of the present invention, if necessary.

The pore surface of the porous membrane in the present invention includes the pore inner surface and the pore outer surface of the porous structure portion of the hollow fiber wall. Specifically, the outer surface of the pore is a surface located on the outer wall surface of the hollow fiber wall and the inner wall surface on the hollow side.

Moreover, at least a part of the pore surface refers to all or part of the inner surface and outer surface of the pore.

Porous hollow fiber membranes that can be used to form the hydrophilic porous hollow fiber membrane of the present invention include, for example, polyethylene, polypropylene, polysulfone, polyethersulfone, polycarbonate, polyvinylidene fluoride, polytetrafluoroethylene, polyamide, polyimide, PVC,
Preferred examples include hydrophobic porous hollow fiber membranes in which micropores made of polymethyl methacrylate, cellulose acetate, etc. are interconnected from the inner wall surface to the outer wall surface of the hollow fiber wall.

In order to form a uniform protein thin film on a hydrophobic porous hollow fiber membrane, a method is preferably used in which a temporary hydrophilic treatment is performed prior to the protein thin film formation treatment.

Examples of proteins constituting the protein thin film formed on the pore surface of the porous hollow fiber membrane include large q casein, milk casein, gelatin, yeast protein, corn protein, and proteins derived from petroleum-utilizing organisms. Insoluble proteins can be used, and soybean casein and milk casein are particularly suitable when considering industrial productivity. However, it is not limited to these as long as it can form the protein thin film aimed at in the present invention.

Formation of a protein thin film on the pore surface of a porous membrane can be achieved by, for example,
This can be carried out by contacting and adhering a protein solution to the pore surface, immersing it in a solution for coagulating the protein, and coating the pore surface with a thin film of coagulated protein.

In this method, the pH and protein concentration of the protein solution, the type and concentration of the coagulant, and the conditions such as pH and temperature in the coagulation process are appropriately selected depending on the type of protein used.

For example, when forming a coagulated thin film of casein, an alkaline aqueous solution of casein is brought into contact with the pore surface of the porous membrane, and then this is immersed in a coagulant solution such as an acidic aqueous solution to coagulate casein. Subsequently, by washing with water and drying, a thin film of casein can be formed on the surface of the pores of the porous membrane.

In this case, the concentration of casein used is 0.5-3ti%
A range of is preferred.

When the concentration of casein is less than 0.5% by weight, it is impossible to form a thin layer of casein having a porous structure with a uniform surface, making it difficult to impart good hydrophilicity.

Further, when the concentration of casein exceeds 3% by weight, the amount of coagulated casein becomes too large, which is not preferable because the pores are likely to be clogged, which causes a decrease in water permeability.

In addition, even for proteins other than casein, by appropriately selecting the concentration etc., it is possible to form a uniform protein thin film on the pore surface of the porous membrane.

The porous hollow fiber membrane of the present invention having the above structure is excellent because a thin film of protein rich in hydrophilic functional groups such as amino groups, carboxyl groups, and hydroxyl groups is formed on the pore surface of the porous membrane. It has high hydrophilicity and can exhibit good water permeability.

It is preferable that the protein thin film be formed uniformly and as thinly as possible on the pore surface of the porous membrane in order to maintain good water permeability without reducing the effective capacity of the pores for filtration.

From this point of view, for example, when forming a thin film of casein, the pore surface of the porous membrane to which the above-mentioned alkaline aqueous casein solution is attached is subjected to wet coagulation treatment in an acidic aqueous solution, followed by washing with water and drying. Death is preferred.

By using this method, it becomes possible to form a uniform thin film with a small amount of protein on the pore surface of the porous membrane, and good water repellency can be maintained.

In the porous hollow fiber membrane of the present invention, the protein thin film has good adhesion to the pore surface of the porous membrane, and does not easily peel off when incorporated into a filtration module and used for water filtration. .

In addition, even if the porous hollow fiber retaining the protein thin film of the present invention is once dried during the cleaning process of the filtration module, it continues to have good hydrophilicity, and hydrophilic treatment with alcohol etc. Not necessary.

Furthermore, since the protein thin film in the present invention is made of materials that are supplied as food, for example, in the production of drinking water, in the unlikely event that the protein film peels off and falls off, it may not be supplied as a drink. Even if it is mixed into filtered water, there is no problem with the safety of the filtered water as drinking water.

On the other hand, the hydrophilic porous hollow fiber membrane of the present invention has a structure suitable for obtaining bacteriostatic properties by fixing silver to the pore surfaces of the porous membrane.

That is, protein easily binds to silver ions, and when the protein is immersed in an aqueous silver nitrate solution, the silver ions form a chelate bond with the protein and have the property of coagulating the protein.

Therefore, by contacting the protein thin film formed on the pore surface of the porous hollow fiber membrane with silver ions, silver can be unevenly bonded to the protein thin film, and the porous hollow fiber membrane has excellent bactericidal properties. Thread membranes can be easily obtained.

Moreover, since the hydrophilicity of the porous hollow fiber membrane is not impaired by the binding of silver to the protein thin film, it is possible to obtain a porous hollow fiber membrane having excellent hydrophilicity, water permeability, and bacteriostatic properties.

For bonding silver to the protein thin film, for example, a method in which the protein thin film formed on the pore surface of the porous 1li is brought into contact with an aqueous solution of a silver salt can be suitably used.

As this silver salt, silver nitrate can be suitably used.

For example, a porous hollow fiber 11Q with a protein thin film formed in an aqueous solution at 25°C containing 0.02% by weight of silver nitrate is used.
After immersing for about 0 minutes, washing with water and drying, silver can be bonded unevenly to the protein thin film.

[Examples] The present invention will be explained in more detail below using Examples and Comparative Examples.

In addition, the bacteriostatic property and water permeability in the following Examples and Comparative Examples were measured by the following methods.

(1) Measurement of bacteriostatic property: A 1cm sample of porous hollow fiber membranes was placed side by side on an agar medium inoculated with Staphylococcus aureus (S. aureus), and incubated at 37°C for 24 hours. After culturing for a period of time, the presence or absence of bacterial growth on the surface of the test sample was observed to determine the bacteriostatic effect.

(Judgment) ○: No bacterial growth was observed on the sample surface.

×: Bacterial growth was observed on the sample surface. Rena.

(2) Measurement with water permeability: 400 sample porous hollow fiber membranes were bundled in a U-shape, the opening of each hollow fiber membrane was solidified with resin, and fixed at a predetermined position in a container with the structure shown in Figure 1. A filtration module was manufactured.

The effective length of the porous hollow fiber membrane tested was 16 cm, and the resin 3
The length of the buried part within was 1 cm.

Water is supplied to this filtration module 1 from the water inlet 4 and directed from the outer wall surface of each hollow fiber membrane 2 to the hollow part at a water pressure of 1 kg/
cm" for 1 minute, measure the amount of water discharged from the water inlet 5, calculate the amount of water permeated per unit surface area of the hollow fiber membrane from the results, and calculate the water permeability (mjl/min).
．． -cm2).

In addition, in the measurement of water permeability of a hydrophobic porous hollow fiber membrane in the following comparative example, prior to water permeation, the hydrophobic porous hollow fiber membrane was immersed in ethyl alcohol at 25 ° C. for 30 minutes to make it hydrophilic. Washed with water.

Example 1 Hydrophobic porous polyethylene hollow fiber membrane (trade name EHF27
0T, outer diameter 380μ, inner diameter 270 scales, manufactured by Mitsubishi Rayon Co., Ltd.) was immersed in ethyl alcohol at 25°C for 5 minutes, then immersed in running water at 25°C for 30 minutes and pulled out.
Then 1% by weight of soybean casein and 0% sodium hydroxide.
2 in an alkaline aqueous solution of casein containing 3% by weight.
The sample was immersed at 5° C. for 8 hours to adhere an alkaline aqueous solution of casein to the surface of the porous structure, and then pulled out.

Next, the porous hollow fiber membrane holding this alkaline aqueous solution of casein was immersed for 1 minute in an acidic aqueous solution at 25°C containing 1% by weight of acetic acid to coagulate the casein, and then thoroughly washed with water. The membrane was dried to obtain a hydrophilic porous polyethylene hollow fiber membrane.

When the outer surface of the obtained hydrophilic porous hollow fiber membrane was observed using an electron microscope, it was observed that a thin film of casein was evenly formed on the surface of the porous structure of the hollow fiber wall.

Table 1 shows the results of measuring the water permeability of this hydrophilic porous hollow fiber membrane.

As is clear from the results in Table 1, the hydrophilic porous hollow fiber membrane obtained in this example has good water permeability, and the 'tLA module incorporating the hydrophilic porous hollow fiber membrane was No hydrophilic treatment with alcohol or the like was required, and the product could be used as it was for water filtration.

Furthermore, after being used for filtration treatment, the filtration module was washed, dried, and reused for water filtration, and its water permeability was measured, and it was found that good water permeability was maintained.

Example 2 Hydrophobic porous boris sulfone hollow fiber membrane (outer diameter 440 μs,
A thin casein film was formed on the surface of the porous structure in the same manner as in Example 1, except that the inner diameter was 330 μm.
A hydrophilized porous borisulfone hollow fiber +i was obtained.

Table 1 shows the results of measuring the water permeability of the obtained hydrophilic porous hollow fiber membrane.

As is clear from the results in Table 1, the hydrophilic porous hollow fiber membrane obtained in this example also has good water permeability, and the filtration module incorporating this hollow fiber membrane also No hydrophilic treatment was required, and the water could be directly filtered.

Furthermore, after being used for filtration, the filtration module was washed, dried, and reused for water filtration, and its water permeability was measured, and it was found that good water permeability was maintained.

Example 3 The hydrophilic porous polyethylene hollow fiber membrane having the casein thin film obtained in Example 1 was treated with 0.02% by weight of silver nitrate at 25°C.
After immersing in an aqueous solution for 5 minutes to bond silver to the casein thin film, washing with water at 25 ° C. for 10 minutes using an ultrasonic cleaner, then vacuum drying at 40 ° C. for 24 hours using a vacuum dryer, Silver was bonded to the surface layer of the casein thin film to obtain a hydrophilic porous polyethylene hollow fiber membrane colored gray.

Table 1 shows the results of the water permeability and bacteriostatic properties of the obtained hydrophilic porous hollow fiber membrane.

As is clear from the results in Table 1, the hydrophilic porous hollow fiber membrane obtained in this example also has good water permeability, and the filtration module incorporating this hollow fiber membrane also No hydrophilic treatment was required, and it could be used as it was for water filtration treatment.

Furthermore, after being used for filtration, the filtration module was washed, dried, and reused for water filtration, and its water permeability and bacteriostatic properties were measured, and it was found that good water permeability and bacteriostatic properties were maintained. .

Example 4 A hydrophilic porous pososulfone hollow fiber with silver bonded to the surface layer of the casein thin film was prepared in the same manner as in Example 3 except that the hydrophilic porous polysulfone hollow fiber membrane having the casein thin film obtained in Example 2 was used. A membrane was obtained.

Table 1 shows the results of the water permeability and bacteriostatic properties of the obtained hydrophilic porous hollow fiber membrane.

As is clear from the results in Table 1, the hydrophilic porous hollow fiber membrane obtained in this example also has good water permeability, and the filtration module incorporating this hollow fiber membrane also No hydrophilic treatment was required, and it could be used as it was for water filtration treatment.

Furthermore, after using it for filtration treatment, the filtration module was washed, dried, and reused for water filtration, and its water permeability and bacteriostatic properties were measured, and it was found that good water permeability and bacteriostatic properties were maintained. .

Comparative Example 1 The water permeability and antibacterial properties of the hydrophobic porous polyethylene hollow fiber membrane used in Example 1 were measured, and the results shown in Table 1 were obtained.

Next, the filtration module incorporating this hydrophobic porous hollow fiber membrane is subjected to hydrophilization treatment with ethyl alcohol and used for filtration treatment, and then the filtration module is washed,
After drying, it was reused for water filtration and its water permeability was measured, and it was found that the water permeability had decreased.

Comparative Example 2 The water permeability and bacteriostatic properties of the hydrophobic porous polysulfone hollow fiber membrane used in Example 2 were measured, and the results shown in Table 1 were obtained.

Next, the filtration module incorporating this hydrophobic porous hollow fiber membrane is subjected to hydrophilic treatment with ethyl alcohol and used for filtration treatment, and then the filtration module is washed,
After drying, it was reused for water filtration and its water permeability was measured, and it was found that the water permeability had decreased.

Table 1 [Effects of the Invention] The hydrophilic porous hollow fiber membrane of the present invention has excellent hydrophilicity continuously and stably because the protein thin film is formed on the surface of the porous structure. The filtration module made using this does not require treatment with a hydrophilic agent such as alcohol, can be used directly for water filtration, and can be directly reused even after being dried.

The protein thin film in the hydrophilic porous hollow fiber membrane of the present invention is
Since it is composed of proteins that pose no safety problems, even when a filtration module made using this is used for producing drinking water, it is possible to provide safe and sanitary filtered water for drinking t1.

Furthermore, the protein thin film of the hydrophilic porous hollow fiber membrane of the present invention has an excellent silver binding ability and has a structure suitable for obtaining bacteriostatic properties by binding silver as necessary. Therefore, by using this hydrophilic porous hollow fiber membrane, a hydrophilic porous hollow fiber membrane imparted with excellent jttlJ bactericidal properties due to silver binding can be formed very easily. Moreover, the hydrophilic porous hollow fiber membrane of the present invention has the advantage that the above-mentioned properties are not impaired even when silver is bonded to the protein thin film.

In filtration by a filtration module using a hydrophilic porous hollow fiber membrane having a thin layer of silver-bonded protein as a filtration membrane, the growth of microorganisms such as bacteria captured on the hollow fiber wall is suppressed, and the bacteria It effectively prevents the deterioration of water, the generation of odor, and the clogging of the hollow fiber pores due to the proliferation of microorganisms such as microorganisms, enabling highly reliable filtration that maintains safe and sanitary conditions at all times. becomes.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing the configuration of a filtration module manufactured when measuring water permeability. 1: Filtration module 2: Porous hollow fiber membrane 3: Resin 4, 5: Water port Patent applicant Mitsubishi Rayon Co., Ltd.

Claims (1)

[Scope of Claims] 1) A hydrophilic porous hollow fiber membrane having a protein thin film formed on at least a portion of the surface of the porous membrane. 2) The hydrophilic porous hollow fiber membrane according to claim 1, wherein silver is bonded to a protein thin membrane.