Method of charging electret filter media

• US 5,496,507 A
• Filed: 08/17/1994
• Issued: 03/05/1996
• Est. Priority Date: 08/17/1993
• Status: Expired due to Term

• Current Assignee: Minnesota Mining and Manufacturing Co (3M Company)
• Original Assignee: Minnesota Mining and Manufacturing Co (3M Company)
• Inventors: Angadjivand, Seyed A., Jones, Marvin E., Meyer, Daniel E.
• Primary Examiner(s): THURLOW, JEFFERY
• Application Number:
  US08/291,611
• Time in Patent Office: 566 Days
• Field of Search: 264/22, 264/24, 264/27, 264/12, 264/10, 264/176.1, 264/232-234, 55/527, 55/528, 55/DIG. 39, 204/168, 128/206.12
• US Class Current: 264/423
• CPC Class Codes: A62B 23/025 the filter having substantially the shape of a mask surgical face masks A41D13/11
• CPC Class Codes: B01D 2239/0225 Side-by-side
• CPC Class Codes: B01D 2239/0233 Island-in-sea
• CPC Class Codes: B01D 2239/0407 comprising particulate additives, e.g. adsorbents
• CPC Class Codes: B01D 2239/0435 Electret
• CPC Class Codes: B01D 2239/0618 Non-woven
• CPC Class Codes: B01D 2239/0622 Melt-blown
• CPC Class Codes: B01D 2239/064 The fibres being mixed
• CPC Class Codes: B01D 2239/065 More than one layer present in the filtering material
• CPC Class Codes: B01D 2239/0654 Support layers
• CPC Class Codes: B01D 2239/0663 The layers being joined by hydro-entangling
• CPC Class Codes: B01D 2239/069 Special geometry of layers
• CPC Class Codes: B01D 2239/10 Filtering material manufacturing
• CPC Class Codes: B01D 2239/1233 Fibre diameter
• CPC Class Codes: B01D 2239/1291 Other parameters
• CPC Class Codes: B01D 39/08 Filter cloth, i.e. woven, knitted or interlaced material metallic B01D39/10
• CPC Class Codes: B01D 39/1623 of synthetic origin
• CPC Class Codes: D04H 1/407 containing absorbing substances, e.g. activated carbon
• CPC Class Codes: D04H 1/4291 Olefin series
• CPC Class Codes: D04H 1/43828 sheath-core
• CPC Class Codes: D04H 1/43835 : Mixed fibres, e.g. at least two chemically different fibres or fibre blends
• CPC Class Codes: D04H 1/43838 : Ultrafine fibres, e.g. microfibres
• CPC Class Codes: D04H 1/492 : by fluid jet D04H1/49 takes precedence
• CPC Class Codes: D04H 1/56 : in association with fibre formation, e.g. immediately following extrusion of staple fibres
• CPC Class Codes: D06M 10/025 : Corona discharge or low temperature plasma
• CPC Class Codes: D06M 11/05 : with water, e.g. steam; with heavy water
• CPC Class Codes: D06M 2101/18 : Synthetic fibres consisting of macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
• CPC Class Codes: Y10S 264/48 : Processes of making filters
• CPC Class Codes: Y10S 55/05 : Methods of making filter
• CPC Class Codes: Y10S 55/35 : Respirators and register filters
• CPC Class Codes: Y10S 55/39 : Electrets separator
• CPC Class Codes: Y10T 442/626 : Microfiber is synthetic polymer

Abstract

A method of charging a nonwoven web of thermoplastic microfibers to provide electret filter media is provided. The method includes impinging on a nonwoven web of thermoplastic nonconductive microfibers capable of having a high quantity of trapped charge jets of water or a stream of water droplets at a pressure sufficient to provide the web with filtration enhancing electret charge and drying said web.

Claims

1. A method of charging a nonwoven web of thermoplastic microfibers to provide electret filter media comprising (1) impinging on a nonwoven web of thermoplastic nonconductive microfibers which have a resistivity greater than 10¹⁶ ohm cm and are capable of having a high quantity of trapped charge, jets of water or a stream of water droplets at a pressure sufficient to provide the web with filtration enhancing electret charge and (2) drying said web.

2. The method of claim 1 wherein said jets of water are provided by a hydroentangling device.

3. The method of claim 1 wherein said stream of water droplets is provided by a nebulizer.

4. The method of claim 1 wherein said jets of water or stream of water droplets is provided at a pressure in the range of about 69 to 3450 kPa.

5. The method of claim 1 wherein said web is subjected to corona discharge treatment prior to impingement of said jets of water or said stream of water droplets.

6. The method of claim 1 wherein said web further contains staple fiber.

7. The method of claim 6 wherein said staple fiber comprises up to 90 weight percent of said web.

8. The method of claim 1 wherein said web has a basis weight of about 5 to 500 g/m².

9. The method of claim 1 wherein said web has a thickness of about 0.25 to 20 mm.

10. The method of claim 1 wherein said microfibers have an effective fiber diameter of about 3 to 30 μ

m.

11. The method of claim 1 wherein said microfibers are polypropylene, poly(4-methyl-1-pentene) or blends thereof.

12. The method of claim 1 wherein said microfibers comprise polypropylene and poly(4-methyl-1-pentene).

13. The method of claim 12 wherein the polypropylene and poly(4-methyl-1-pentene) are layered in said microfibers.