Filter for water treatment filtering and method for producing the same
The problem to be solved by the present invention is to provide a filter medium for a water treatment filter having contradictory characteristics, that is, hydrophilicity and chemical resistance, and a long life, and to provide the production method thereof. A filter medium for a water treatment filter according to the present invention is characterized in comprising a porous base material having a hydrophilic coating layer; wherein the hydrophilic coating layer has a cross-linked hydrophilic polymer and a high electron density part; a hydrophilic polymer in the cross-linked hydrophilic polymer is cross-linked with an aliphatic saturated hydrocarbon group which may contain one or more functional groups selected from a group consisting of an ether group, a hydroxy group and an amino group; the high electron density part has π electrons; and the high electron density part is covalently bonded to the cross-linked hydrophilic polymer.
1. A filter medium for a water treatment filter, comprising
a) porous base material, wherein the porous base material has no π electrons; and
b) a hydrophilic coating layer, wherein the porous base material is coated with the hydrophilic coating layer; and wherein the hydrophilic coating layer comprises
1) a cross-linked hydrophilic polymer comprising:
i) hydrophilic polymer having a main chain, wherein the main chain of the hydrophilic polymer has no π electrons; and
ii) a cross-linked chain formed by cross-linking the hydrophilic polymer with an aliphatic saturated hydrocarbon group containing one or more functional groups selected from a group consisting of an ether group, a hydroxy group and an amino group, and wherein the cross-linked chain has no π electrons; and
2) a high electron density part having π electrons; and the high electron density part is covalently bonded to the cross-linked hydrophilic polymer.
2. The filter medium for a water treatment filter according to claim 1 , wherein the high electron density part has one or more selected from a group consisting of an aliphatic unsaturated hydrocarbon group, an aromatic hydrocarbon group, a heteroaromatic hydrocarbon group, a carbonyl group, a nitrile group, a sulfoxide bond, a sulfonyl bond and a sulfonic group.
3. The filter medium for a water treatment filter according to claim 1 , wherein the high electron density part has an amide bond.
4. The filter medium for a water treatment filter according to claim 1 , wherein the high electron density part has an aromatic hydrocarbon group.
5. The filter medium for a water treatment filter according to claim 1 , wherein the high electron density part further has a hydrophilic group.
6. The filter medium for a water treatment filter according to claim 5 , wherein the hydrophilic group is one or more selected from a group consisting of a hydroxy group, a sulfonic group, a carboxy group and an amino group.
7. The filter medium for a water treatment filter according to claim 1 , wherein the porous base material is a porous fluororesin membrane.
8. The filter medium for a water treatment filter according to claim 7 , wherein the porous fluororesin membrane is a porous PTFE membrane.
9. The filter medium for a water treatment filter according to claim 1 , wherein the hydrophilic polymer is polyvinyl alcohol, ethylene-vinylalcohol copolymer, tetrafluoroethylene-vinylalcohol copolymer, polyalkylene glycol or a metal alkoxide.
10. A water treatment filter, comprising a filter medium for a water treatment filter according to claim 1 .
11. The water treatment filter according to claim 10 , wherein water permeability at 20 kPa transmembrane pressure difference is 1 mL/min/cm 2 or more.
12. The water treatment filter according to claim 11 , wherein a decreasing rate of water permeability is 70% or less after soaking in a 0.6 mass % sodium hypochlorite aqueous solution for two weeks.
13. A water treatment apparatus, comprising a water treatment filter according to claim 10 .
14. A method for producing the filter medium for a water treatment filter according to claim 1 , comprising the steps of
soaking the porous base material in a hydrophilic polymer solution and a cross-linking agent solution,
cross-linking the hydrophilic polymer with the aliphatic saturated hydrocarbon group containing one or more functional groups selected from a group consisting of an ether group, a hydroxy group and an amino group, and
reacting the cross-linked hydrophilic polymer with a precursor compound of the high electron density part having a π electron, to covalently bond the high electron density part to the cross-linked hydrophilic polymer.
15. A method for improving oxidation resistance property of a filter medium for a water treatment filter, comprising the steps of
1) providing a porous base material having a hydrophilic coating layer,
a) wherein the porous base material has no π electrons, and
b) wherein the hydrophilic coating layer comprises a cross-linked hydrophilic polymer comprising:
i) hydrophilic polymer having a main chain, wherein the main chain of the hydrophilic polymer has no π electrons; and
ii) a cross-linked chain formed by cross-linking the hydrophilic polymer with an aliphatic saturated hydrocarbon group containing one or more functional groups selected from a group consisting of an ether group, a hydroxy group and an amino group, and wherein the cross-linked chain has no π electrons; and
2) covalently bonding a high electron density part having a π electron to the hydrophilic coating layer on the porous base material, thereby improving the oxidation resistance property against an oxidizing agent used for washing the water treatment filter.