JPS6327540A - Hydrophilization of hydrophobic porous membrane - Google Patents

Abstract

PURPOSE:To impart a hydrophobic porous membrane with hydrophilic property having excellent durability, by keeping a crosslinkable copolymer composed of a hydrophilic vinyl monomer and a crosslinkable vinyl monomer on the surface of pores of said membrane and crosslinking the copolymer. CONSTITUTION:(A) A hydrophilic vinyl monomer such as (meth)acrylic acid, hydroxymethyl methacrylate etc., is made to react with (B) a crosslinkable vinyl monomer (preferably diacetone acrylamide) at a weight ratio (A/B) of preferably 99.5/0.5-50/50 under a mild condition to prevent the reaction of the crosslinkable functional group of the component B. The obtained copolymer having a molecular weight of preferably 10,000-500,000 is dissolved in e.g. acetone and is held on the surface of at least a part of pores of a hydrophobic porous membrane e.g. by immersing the membrane in the solution. The copolymer is heated and crosslinked keeping the above state to effect the hydrophilization of said porous membrane.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for hydrophilizing a hydrophobic porous membrane used in fields such as water treatment and blood purification.

[Conventional technology]

Hydrophobic porous membranes such as polyolefins have excellent mechanical properties and chemical resistance, so the fields of their application are rapidly expanding. However, it is difficult for hydrophobic porous membranes to allow water to pass through them as they are, and hydrophilic treatment is required to allow water and other hydrophilic liquids to pass through them. Various methods have been studied to make hydrophilic substances such as polyolefins hydrophilic by surface modification. It is not possible to simply apply the conversion method.

A method for making a hydrophobic porous membrane hydrophilic is to wet the entire surface of the porous membrane, including the micropores, with an organic solvent such as alcohol or ketone that has good compatibility with water, and then remove the organic solvent. Organic solvent wetting/water displacement method for temporary substitution, physical adsorption method for adsorbing hydrophilic substances such as polyethylene glycol or surfactants onto the surface of the porous membrane to impart hydrophilicity to the porous membrane (Unexamined Japanese Patent Publication No. No. 54-153872, JP-A-59
-24732), or a method in which radiation is irradiated while the hydrophilic monomer is held on the surface of the porous film (No.
Chemical surface modification methods such as JP-A No. 56-38333) and plasma treatment of a hydrophobic resin porous structure impregnated with a water-soluble polymer or surfactant (JP-A No. 56-157457) The law is known.

[Problem that the invention seeks to solve]

However, in the organic solvent wetting/water displacement method, once the water in the pores escapes during storage or use, the area returns to hydrophobicity and becomes unable to pass through, so the area around the porous membrane must be constantly filled with water. It is necessary to store it, and handling is complicated. Although the physical adsorption method is easy to operate, it cannot necessarily be said to be a sufficient hydrophilic method because the hydrophilic substance is desorbed during long-term use. In addition, in conventional chemical surface modification methods, when irradiating with radiation, the mechanical strength of the porous membrane base material inevitably decreases, and when plasma treatment is used, the thickness of the hydrophilic coating is too thin and fine. Problems include the fact that it is difficult to impart hydrophilicity to the entire pore surface, and it is not possible to achieve sufficient hydrophilicity within the pores of the porous membrane.

The purpose of the present invention is to solve the problems of the prior art and to provide a hydrophobic membrane that makes it possible to impart highly durable hydrophilicity to the pore surface of a hydrophobic porous membrane without damaging the substrate of the porous membrane. An object of the present invention is to provide a method for making a porous membrane hydrophilic.

[Failure to solve the problem]

The gist of the present invention is to apply a crosslinkable copolymer consisting of a vinyl-type hydrophilic monomer and a vinyl-type crosslinkable polymer (A) to at least part of the pore surface of a hydrophobic porous membrane. A method for making a hydrophobic porous membrane hydrophilic, characterized by crosslinking the membrane in a state in which the membrane is maintained in a hydrophobic state.

Materials for the hydrophobic porous membrane used in the present invention include polyethylene, polypropylene, poly-4-meth
Examples include polyolefins such as pentene and poly-3-methyl-1-butene, fluorine-based polymers such as polyvinylidene fluoride and polytetrafluoroethylene, and copolymers thereof.

Further, as the porous membrane, any form such as a hollow fiber membrane, flat membrane, or tubular membrane can be used, and membranes with various pore diameters can be used depending on the purpose. As a preferable example, the film thickness is about 20 to 200 μm and the porosity is 2.
Examples include those with a pore size of about 0 to 90% and a pore diameter of about (LO1 to 5 μm).

In the present invention, the vinyl-type hydrophilic polymer refers to a water-soluble polymer having a polymerizable vinyl-type double bond in the molecule, examples of which include acrylic/I/acid, methacrylic acid,
Examples include hydroxymethyl methacrylic acid, sulfur methacrylic acid, styrene sulfonic acid, and alkali metal salts thereof.

In addition, the vinyl type crosslinkable monomer (B) has a polymerizable vinyl μ type double bond in the molecule, and has an acetyl)v group, a hydroxyalkyl μ group as a functional group that can be crosslinked by a condensation reaction.
It refers to a monomer having a group, etc., and examples thereof include diacetone acrylamide, hydroxymethyl acrylamide, and the like. These crosslinking monomers (B) are known to undergo condensation reactions such as dehydration and deformed apdehyde reactions, but it is necessary to copolymerize them with hydrophilic polymers under conditions that do not allow such condensation reactions to occur. Therefore, it is possible to obtain an uncrosslinked copolymer containing a functional group involved in the crosslinking reaction in the molecule. On the other hand, instead of the crosslinking monomer (A) used in the present application, a crosslinking monomer containing two or more double bonds, which is known as a general crosslinking agent, is used to copolymerize with the hydrophilic monomer (A). In the case of producing a copolymer, a crosslinked copolymer is obtained, which is not preferable.

In the present invention, a copolymer that crosslinks through a condensation reaction is used, and this is because the copolymer performs a crosslinking reaction even without the addition of a crosslinking agent. On the other hand, when a crosslinking agent is added to cause a crosslinking reaction, the crosslinking agent remains as a contaminant in the pores of the porous membrane, which is not preferable.

In addition, in consideration of membrane contamination, it is more preferable to use diacetone acrylamide as the crosslinkable hexamer (B) since the only substance produced during the condensation crosslinking reaction of the copolymer on the pore surface of the porous membrane is water. .

The copolymer used in the present invention preferably has a hydrophilic monomer/crosslinkable monomer (B) weight composition ratio of approximately 99.5/CL5 to 50,150, and a molecular weight of approximately 1 to 500,000 to 500,000. Something makes me feel bad.

If the amount of the crosslinking monomer () is less than the above range, the crosslinking of the copolymer will be insufficient and it will not be possible to impart hydrophilicity with excellent durability to the porous membrane, which is not preferred.

Moreover, if this amount is larger than the above range, sufficient hydrophilicity cannot be imparted to the porous membrane, which is not preferable.

The ratio of hydrophilic monomer (cA)/crosslinking monomer (B) is L
L7! =~7 o/s ofhht and h=z is preferable.

If the molecular weight of the copolymer is smaller than the above range, as will be described later, for example, when the copolymer is retained on the pore surface of the porous membrane with a copolymer solution and the solvent is removed, the copolymer will be removed from the outer surface. Since the crosslinked copolymer tends to migrate to the layer, it is difficult to maintain the crosslinked copolymer uniformly on the pore surface of the porous membrane, which is not preferable. Furthermore, if the molecular weight exceeds the above range, the viscosity of the copolymer solution is too high, making it difficult to infiltrate the copolymer into the pores of the porous membrane, and making it difficult to impart sufficient hydrophilicity. So I don't like it. The molecular weight of the copolymer is 5~
More preferably, it is about 300,000.

The copolymer of the present invention can be produced by copolymerizing the hydrophilic monomer (B) and the crosslinking polymer under mild conditions in which the functional groups involved in crosslinking of the crosslinking monomer (B) do not undergo a crosslinking reaction. .

Such conditions include, for example, using a good solvent such as acetone or methyl ethyl ketone, with a monomer concentration of about 1 to 10% by weight, and adding a radical initiator to 7 units (1
A solution polymerization method in which about 0.01 to 1 fold is added and the temperature is about 30 to 60°C can be mentioned. Alternatively, a bulk polymerization method may be employed in which no solvent is used and the other conditions are substantially the same as those described above, or photopolymerization may be carried out using a photopolymerization initiator.

In the present invention, the copolymer is held on at least some pore surfaces of a hydrophobic porous membrane, and at least some pore surfaces refers to a part or all of the pore surfaces, and The copolymer may or may not be retained on the outer surface of the membrane.

Various methods can be used to retain the copolymer on the pore surface of the porous membrane, but it is possible to prepare a solution in which the copolymer is dissolved in an appropriate solvent such as an organic solvent or water. However, it is possible to adopt a method in which the porous membrane is immersed in the solution, or a method in which a module is manufactured using the porous membrane and then the solution is press-fitted into the porous membrane.

Used here! Although 8vX is required to be able to dissolve the copolymer, it is preferable to use a low boiling point solvent that can be removed under conditions that do not cause a crosslinking reaction of the copolymer. Solvents that meet these conditions include water, acetone, methyl ethyl ketone, methanol-μ, ethanol,
Among these solvents, acetone having a Torr point of 60° C. or lower is particularly preferred.

The content of the copolymer in the solution and the solution viscosity depend on the molecular weight of the copolymer, the interfacial tension of the solution, etc., and cannot be limited to a certain part, but the content of the copolymer in the solution! The amount is preferably about 4F to 50m [%], and the solution viscosity is preferably about 10 to 100 centivoice.

In this way, the solution is introduced into the pores of the hydrophobic porous membrane, and then the solvent is removed by a drying method, a reduced pressure method, etc. to remove the uncrosslinked copolymer from at least part of the hydrophobic porous membrane. can be retained on the pore surface of the part. By crosslinking the uncrosslinked copolymer in this state, the crosslinked copolymer can be retained on the pore surface of the hydrophobic porous lion.

A heating method is suitable as the crosslinking condition, and the temperature is 60 to 80℃.
Conditions of about 5 minutes to 2 hours at about 0.degree. C. can be adopted.

After the crosslinking reaction is completed, the uncrosslinked copolymer may be washed with a suitable solvent if necessary.

Although the hydrophilization of the present invention can be carried out in this manner, it is preferable that the amount of the copolymer retained on the pore surface of the porous membrane by the hydrophilization is approximately 0.5 to 3-0% by weight. , about 1 to 20% by weight is particularly preferable.

〔Example〕

The present invention will be specifically explained below using Examples.

In the Examples, the water permeability and the water permeability by the alcohol hydrophilization method were each measured by the following method using a test membrane module with an effective membrane area of 165 cm.

(1) Hydraulic pressure: α1kg every minute from one side of the test membrane module (in the case of hollow fiber membranes, from the inside of the hollow fibers (!jj+)
Water at 25° C. is supplied while increasing the water pressure at a rate of /-, and the water pressure is measured when the amount of permeated water reaches 50 g and 50 m/.

Next, plot the water pressure on the horizontal axis and the amount of permeated water on the vertical axis.
Find the pressure value at the point where the straight line connecting the two plotted points intersects with the horizontal axis, and use that value as the permeability pressure.

(2) Water permeability in the alco-p hydrophilization method; ethanol-μ was flowed at a flow rate of 25 g/min from one side of the test membrane module that had not been hydrophilized (inside the hollow fiber membrane in the case of hollow fiber membranes). After applying pressure for 15 minutes to sufficiently wet the inside of the pores of the porous membrane with ethanol, water was flowed at a flow rate of 100 g/min for 15 minutes to replace the ethanol present inside the pores with water. Next, water at 25°C was poured from one side of the test membrane module (inside the hollow fiber in the case of hollow fibers), the amount of permeated water at a transmembrane pressure difference of 50 tm Hg was measured, and the water permeability (1/ -・hr−mHg).

Example 1 A solution consisting of 80 parts of hydroxymethyl methacrylic acid, 20 parts of diamineptone acrylamide, 5 parts of pencil peroxide (LQ), and 530 parts of acetone was heated at 55° C. for 5 hours in a nitrogen atmosphere to obtain a copolymer. .

Next, an acetone solution containing 5% by weight of this copolymer was prepared, and the porosity was 70 cm, the film thickness was 42 μm, and the water permeability was 4.5.
After immersing a porous plastic membrane of polyethylene with a water permeability of 55 t/rrL2·hr-wIHg in this solution for 5 seconds, it was heated to 25°C.
The solvent was removed by air drying for 2 hours at 70°C.
and heated for 30 minutes.

When the weight of the porous membrane thus obtained was measured, a weight increase of 12% by weight was observed, and the permeability pressure was Q, 1
kg7m”.This porous 7m membrane is still JIS
When the cross section was observed after being immersed in a reagent with a surface tension of 54 dyne/cn1 described in K676B, it was found that the entire surface in both the thick and thick directions was dyed almost uniformly.

Furthermore, this porous membrane was soaked in 100-g of water at 55°C.
TOC in water after 50 hours and 200 hours of immersion in
When measured, they were 0.8 ppm and cL9, respectively.
It was confirmed that the copolymer was firmly retained in the porous membrane. Furthermore, there was no difference in tensile strength and elongation before and after the hydrophilic treatment.

Example 2 Nutilence μ Sodium phonate 75 parts, Hydroxymethyμ acrylamide 25 parts, Pencey μ Phenei μ Acetyl μ
A solution consisting of 3 parts of peroxide CLO'3 and 330 parts of acetone was heated at 50° C. for 2 hours in a nitrogen atmosphere to obtain a copolymer.

Next, an ethanol solution containing three layers of this copolymer was prepared, and the porosity was 50 cm, the membrane thickness was 22 μm, the inner diameter was 210 μm, the water permeability was 15 kg/cm”, and the water permeability by the alcohol-fi/hydrophilization method was (L 417m"・hr - This solution was applied to a porous hollow fiber membrane made of polypropylene, which was easily chilled with Hg, for 2 hours.
kg/cm'' for 3 seconds, air-dried in air at 25°C for 2 hours to remove the solvent, and then heated at 70°C for 30 minutes.

When the weight of the porous membrane thus obtained was measured, it was found that the weight increased by 10% by weight, and the permeability pressure was 0.5'.
It was 9/an2.

Further, when this porous membrane was immersed in a detangling reagent having a surface tension of 54 dyne/α as specified in JIS K6768 and its cross section was observed, it was found that the entire surface in the thickness direction was dyed almost uniformly.

Furthermore, this porous membrane 1.009 was immersed in 100 °C of water at 55°C, and the TOC in the water was measured after 50 hours and 200 hours, and it was found to be 1.0 ppm and 1.0 ppm, respectively.
It was confirmed that the amount of components eluted into water was small, and that the copolymer was firmly retained in the porous membrane. Furthermore, there was no difference in tensile strength and elongation before and after the hydrophilic treatment.

〔Effect of the invention〕

As is clear from the results of the examples, according to the method of the present invention,
It is possible to retain the copolymer over almost the entire surface of the pores of the porous membrane without reducing the mechanical strength of the porous membrane. can.

Further, in the present invention, since a copolymer capable of condensation and crosslinking is used, it is possible to reduce the amount of contaminants remaining in the pores of the porous membrane after the hydrophilic treatment.

Claims (3)

[Claims] (1) A copolymer that can be crosslinked by a condensation reaction consisting of a vinyl-type hydrophilic monomer (A) and a vinyl-type crosslinkable monomer (B) is applied to the surface of at least some pores of a hydrophobic porous membrane. A method for making a hydrophobic porous membrane hydrophilic, characterized by crosslinking it in a retained state. (2) The vinyl-type hydrophilic monomer (A) is acrylic acid,
The method according to claim 1, which is methacrylic acid, hydroxymethyl methacrylic acid, sulfoethyl methacrylic acid, styrene sulfonic acid, or an alkali metal salt thereof. (3) The method according to claim 1, wherein the vinyl crosslinking monomer (B) is diacetone acrylamide or hydroxymethyl acrylamide.