# US 9,751,050 B2 · Method of forming an asymmetric membrane

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- Number: US 9,751,050 B2
- Document ID: US9751050B2
- Status: Granted
- Kind: B2
- Application number: 12/997,658
- Filed: 2009-05-13
- Published: 2011-04-21
- Granted: 2017-09-05
- Earliest claimed: 2008-06-30
- Assignees: 3M Innovative Properties Company
- Applicants: Jinsheng Zhou; Jonathan F. Hester; Derek J. Dehn; Daniel P. Meehan; Robin E. Wright
- Inventors: Jinsheng Zhou; Jonathan F. Hester; Derek J. Dehn; Daniel P. Meehan; Robin E. Wright
- Web page: https://patentgrep.com/patent/US9751050B2

## CPC

- B01D 69/02: characterised by their properties
- B01D 67/0006: {by chemical reactions (in-situ polymerisation, polycondensation, cross-linking or reaction for manufacturing composite membranes B01D69/125)}
- B01D 69/1071: {Woven, non-woven or net mesh}
- B01D 69/1218: {Layers having the same chemical composition, but different properties, e.g. pore size, molecular weight or porosity}
- B01D 69/125: {In situ manufacturing by polymerisation, polycondensation, cross-linking or chemical reaction}
- B01D 71/261: {Polyethylene}
- B01D 71/262: {Polypropylene}
- B01D 71/401: {Polymers based on the polymerisation of acrylic acid, e.g. polyacrylate}
- B01D 2323/30: Cross-linking
- B01D 2323/345: UV-treatment
- B01D 2325/0233: with clearly distinguishable layers
- B01D 2325/14: Membrane materials having negatively charged functional groups
- B01D 2325/16: Membrane materials having positively charged functional groups
- B01D 2325/36: Hydrophilic membranes
- B01D 2325/38: Hydrophobic membranes
- Y10T 428/24942: including components having same physical characteristic in differing degree
- B01D: SEPARATION (separating solids from solids by wet methods B03B, B03D; by pneumatic jigs or tables B03B; by other dry methods B07; magnetic or electrostatic separation of solid materials from solid materials or fluids, separation by high-voltage electric fields B03C; centrifuges, vortex apparatus B04; presses per se for squeezing-out liquid from liquid-containing material B30B9/02; treatment of water C02F, e.g. softening by ion-exchange C02F1/42; {arrangements of air intake cleaners in gas turbine plants F02C7/05} ; arrangements or mounting of filters in air-conditioning, air-humidification or ventilation F24F13/28)
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

The present disclosure provides methods for forming asymmetric membranes. More specifically, methods are provided for applying a polymerizable species to a porous substrate for forming a coated porous substrate. The coated porous substrate is exposed to an ultraviolet radiation source having a peak emission wavelength less than 340 nm to polymerize the polymerizable species forming a polymerized material retained within the porous substrate so that the concentration of polymerized material is greater at the first major surface than at the second major surface.

## Claims

### Claim 1

A method of forming an asymmetric membrane comprising:
providing a porous substrate having a first major surface and a second major surface;
applying a polymerizable composition to the porous substrate providing a coated porous substrate, the polymerizable composition comprising
i) at least one polymerizable species; and
ii) at least one photoinitiator; and
exposing the coated porous substrate to an ultraviolet radiation source having a peak emission wavelength less than 340 nm to polymerize the polymerizable species, wherein the photoinitiator residing at the first major surface is exposed to a greater peak irradiance of ultraviolet radiation than the photoinitiator residing further into the thickness of the porous substrate thus reducing the amount of polymerization within the pores of the substrate through the thickness of the substrate, thereby providing an asymmetric membrane, the asymmetric membrane having a polymerized material retained within the porous substrate, the polymerized material having a concentration greater at the first major surface than at the second major surface.

### Claim 2 (depends on 1)

The method of claim 1, further comprising washing the asymmetric membrane after exposing to an ultraviolet radiation source having a peak emission wavelength less than 340 nm.

### Claim 3 (depends on 1)

The method of claim 1, wherein the porous substrate is microporous.

### Claim 4 (depends on 1)

The method of claim 1, wherein the porous substrate comprises a microporous, thermally-induced phase separation membrane.

### Claim 5 (depends on 1)

The method of claim 1, wherein the porous substrate is hydrophilic.

### Claim 6 (depends on 1)

The method of claim 1, wherein the porous substrate is hydrophobic.

### Claim 7 (depends on 1)

The method of claim 1, wherein the porous substrate comprises a film, a nonwoven web, a woven web, a fiber, or combinations thereof.

### Claim 8 (depends on 7)

The method of claim 7, wherein the porous substrate further comprises a particulate.

### Claim 9 (depends on 7)

The method of claim 7, wherein the fiber is a hollow fiber.

### Claim 10 (depends on 1)

The method of claim 1, wherein the porous substrate comprises polyolefins, polyamides, fluorinated polymers, poly(ether)sulfones, cellulosics, poly(ether)imides, polyacrylonitriles, polyvinyl chlorides, ceramics, or combinations thereof.

### Claim 11 (depends on 10)

The method of claim 10, wherein the porous substrate comprises polyolefins.

### Claim 12 (depends on 11)

The method of claim 11, wherein the polyolefins comprise polyethylene or polypropylene.

### Claim 13 (depends on 10)

The method of claim 10, wherein the porous substrate comprises polyamides.

### Claim 14 (depends on 13)

The method of claim 13, wherein the polyamides comprise nylon 6,6.

### Claim 15 (depends on 1)

The method of claim 1, wherein applying comprises die coating, roll coating, dip coating, spray coating, curtain coating, slide coating or combinations thereof.

### Claim 16 (depends on 1)

The method of claim 1, wherein applying the polymerizable composition comprises immersing or saturating the porous substrate.

### Claim 17 (depends on 1)

The method of claim 1, wherein applying the polymerizable composition comprises immersing or saturating a portion of the thickness of the porous substrate to at least one micrometer from the first major surface.

### Claim 18 (depends on 1)

The method of claim 1, wherein at least one of the polymerizable species comprises acrylates, (meth)acrylates, (meth)acrylamides, styrenics, allylics, vinyl ethers, or combinations thereof.

### Claim 19 (depends on 18)

The method of claim 18, wherein at least one of the polymerizable species comprises an ionic group.

### Claim 20 (depends on 19)

The method of claim 19, wherein the ionic group comprises a sulfonic acid or a sulfonic acid salt.

### Claim 21 (depends on 19)

The method of claim 19, wherein the ionic group comprises an amine or a quaternary ammonium salt.

### Claim 22 (depends on 19)

The method of claim 19, wherein the ionic group comprises a carboxylic acid or a carboxylic acid salt.

### Claim 23 (depends on 19)

The method of claim 19, wherein the ionic group comprises a phosphonic acid or a phosphonic acid salt.

### Claim 24 (depends on 19)

The method of claim 19, wherein the ionic group is positively charged, negatively charged, or combinations thereof.

### Claim 25 (depends on 1)

The method of claim 1, wherein the polymerizable composition further comprises a solvent.

### Claim 26 (depends on 1)

The method of claim 1, wherein exposing the coated porous substrate comprises providing an inert environment.

### Claim 27 (depends on 1)

The method of claim 1, wherein the ultraviolet radiation source having a peak emission less than 340 nm is a narrow bandwidth ultraviolet radiation source.

### Claim 28 (depends on 27)

The method of claim 27, wherein the ultraviolet radiation source comprises monochromatic radiation sources, fluorescent radiation sources or combinations thereof.

### Claim 29 (depends on 1)

The method of claim 1, wherein the ultraviolet radiation source comprises a plurality of monochromatic radiation sources.

### Claim 30 (depends on 29)

The method of claim 29, wherein the plurality of monochromatic radiation sources comprises excimer lamp sources, low pressure mercury lamp sources, light emitting diodes, laser sources, or combinations thereof.

### Claim 31 (depends on 1)

The method of claim 1, where the ultraviolet radiation source comprises a plurality of fluorescent radiation sources.

### Claim 32 (depends on 1)

The method of claim 1, wherein the ultraviolet radiation source comprises a peak emission wavelength in a range of about 140 nm to about 320 nm.

### Claim 33 (depends on 1)

The method of claim 1, wherein the ultraviolet radiation source comprises a peak emission wavelength in a range of about 200 nm to about 300 nm.

### Claim 34 (depends on 1)

The method of claim 1, wherein the first major surface of the asymmetric membrane is hydrophilic, and the second major surface of the asymmetric membrane is hydrophobic.

### Claim 35 (depends on 1)

The method of claim 1, wherein the first major surface of the asymmetric membrane is hydrophobic, and the second major surface of the asymmetric membrane is hydrophilic.

### Claim 36 (depends on 1)

The method of claim 1, further comprising positioning the coated porous substrate between a transparent first layer and a second layer to form a multilayer structure, the transparent first layer positioned adjacent to the first major surface and the second layer positioned adjacent to the second major surface, the transparent first layer nearest the ultraviolet radiation source, wherein the transparent first layer and the second layer comprise continuous sheets of materials, wherein the transparent first layer and the second layer provide protection to the membrane from exposure to oxygen, and wherein exposing the coated porous substrate to the ultraviolet radiation source having a peak emission wavelength less than 340 nm comprises exposing the multilayer structure to ultraviolet radiation.

### Claim 37 (depends on 36)

The method of claim 36, further comprising removing the transparent first layer and the second layer from the multilayer structure after treating the coated porous substrate with the ultraviolet radiation source having a peak emission wavelength less than 340 nm.

### Claim 38 (depends on 1)

A method of claim 1, wherein the polymerizable composition further comprises a crosslinker.