Filter medium

• US 20050235619A1
• Filed: 05/28/2003
• Published: 10/27/2005
• Est. Priority Date: 05/28/2002
• Status: Abandoned Application

• Current Assignee: Hollingsworth & Vose GmbH (Hollingsworth & Vose Company)
• Original Assignee: Hollingsworth & Vose GmbH (Hollingsworth & Vose Company)
• Inventors: Heinz, Beate, Schnieders, Immo
• Application Number:
  US10/515,423
• Publication Number:
  US 20050235619A1
• Time in Patent Office: Days
• US Class Current: 55/486
• CPC Class Codes: B01D 39/163 sintered or bonded

Abstract

A filter medium (10) is fashioned in a way, to effectively catch not only microparticles but also particles having nanometer dimensions. According to the invention, it comprises at least one supporting layer (20) and at least one fine fiber layer (30), the former preferably being composed of crosslinked cellulose fibers and microglass fibers, or alternatively of polymeric fibers. The diameters of the fibers in the supporting layer (20) are in the micron range and the pores of this layer mostly have cross-sections in the square micron range. The very light fine fiber layer (30) having a weight per unit area of less than 1 g/m² possesses pores ranging down to nanometer dimensions and is thermally stable at temperatures above 180° C. It comprises fibers (40) obtained from polymers by electrostatic spinning and having diameters in the nanometer range. In order to crosslink individual fibers (40) with each other or with the supporting layer (20) and thus to render them insoluble in water and chemically and thermally stable, various resins, for example, melamine resins are used. For protection and stability purposes, the filter medium (10) can be supplemented with backing or cover layers.

Claims

1. A filter medium for use in thru-flow contrivances, containing at least one supporting layer (20) and at least one fine fiber layer (30) permanently adhering to said supporting layer (20), said fine fiber layer (30) comprising electrostatically spun polymer fibers (40) having an average fiber diameter of less than and/or equal to 1 μ

m, wherein, due to the action of a catalyst, the polymer fibers are crosslinked with each other directly or indirectly via a crosslinking agent (crosslinker), which crosslinker and/or the crosslinked polymer fibers (40) are resistant to a temperature of up to 200°

C.

2. A filter medium as defined in claim 1, wherein the uncrosslinked polymer fibers (40) are resistant to temperature of up to 200°

C.

3. A filter medium as defined in claim 1, wherein the polymer fibers (40) are permanently fixed by self-adherence to at least one of the supporting layers (20).

4. A filter medium as defined in claim 1, wherein the polymer fibers (40) comprise polymers soluble in polar solvents, particularly polyvinyl alcohol, polycarboxylic acids, polyacrylamide, polyamide, polyvinyl amine, polyvinyl formamide, or copolymers formed therefrom.

5. A filter medium as defined in claim 1, wherein the polymer fibers (40) in the fine fiber layer (30) have different diameters.

6. A filter medium as defined in claim 1, wherein the fine fiber layer (30) has a preferential direction, in which the polymer fibers (40) are disposed in a well-ordered manner according to their diameter size.

7. A filter medium as defined in claim 1, wherein the crosslinking agent used to join the polymer fibers (40) to each other and/or to at least one supporting layer (20) is an at least bifunctional chemical compound, preferably a phenolic resin, a melamine-formaldehyde resin, a urea-formaldehyde resin, an epoxy resin, an acrylic resin, a wet-strength agent, or a mixture of said substances.

8. A filter medium as defined in claim 1, wherein the catalyst is a Lewis acid or Broensted acid, a Lewis base or Broensted base, or a compound having oxidizing or radical-initiating properties.

9. A filter medium as defined in claim 1, wherein the catalyst comprises heat, supersonic waves, electromagnetic radiation, preferably IR or UV radiation, or an electron beam.

10. A filter medium as defined in claim 1, wherein at least one further supporting layer (20) is provided which is or forms a cover layer, a backing layer, or another layer of filtering material, the fine fiber layer (30) being adjacent to at least one of these layers on the inflow and/or outflow side.

11. A filter medium as defined in claim 1, wherein the macroscopically measurable volume of the supporting layer (20) is unchanged following the application of the polymer fibers (40) of the fine fiber layer (30).

12. A filter medium as defined in claim 1, wherein at least one supporting layer (20) comprises organic and/or inorganic fibers, or a composite mixture thereof, particularly cellulose, synthetic fibers, or microglass fibers.

13. A filter medium as defined in claim 1, wherein at least one supporting layer (20) is impregnated with and stiffened by, or is capable of being stiffened by, a phenolic resin for example.

14. A filter medium as defined in claim 1, wherein at least one supporting layer (20) is a large-pored base medium (25) having a low filtering effect or an open-pore joining layer (60) having no filtering properties.

15. A filter medium as defined in claim 1, wherein at least one supporting layer (20) is an electret medium.

16. A filter medium as defined in claim 1, wherein at least one supporting layer (20) is surface-hydrophobic, for example due to alkylation or silylation (silanization).

17. A filter medium as defined in claim 1, wherein at least one supporting layer (20) contains one or more flameproofing agents and/or fluorescent dyes.

18. A filter medium as defined in claim 1, wherein at least one supporting layer (20) is provided with affinity ligands.

19. A particle filter or molecular filter comprising at least one filter medium (10) as defined in claim 1.

20. A process for the production of a filter medium (10) for use in thru-flow contrivances, in which at least one polymer, in the molten state or dissolved in a polar or non-polar solvent, is spun by means of a nozzle in an electric field to form polymer fibers (40), which are placed on a supporting layer (20) in the form of a fine fiber layer (30), which polymer fibers (40) have an average fiber diameter smaller than and/or equal to 1 μ

m, intermediate spaces being formed between said polymer fibers (40), wherein

a) a crosslinking agent is added to the polymer melt or the polymer solution and

b) the polymer fibers (40) placed on the supporting layer (20) crosslink and/or are crosslinked with each other and/or with the crosslinking agent with the aid of a catalyst.

21. A process as defined in claim 20, wherein the polymer fibers (40) in the fine fiber layer (30) are produced by electrospinning of a polar, preferably aqueous, solution.

22. A process as defined in claim 20, wherein a stack of layers comprising at least one supporting layer (20) and at least one fine fiber layer (30) is brought into contact with basic or acid catalysts or with electromagnetic or electron beams.

23. A process as defined in claim 20, wherein

a) the polymer fibers (40) are placed on an unimpregnated supporting layer (20), v

b) the resulting unimpregnated filter medium (10) is treated as a whole with an impregnating agent,

c) and is then cured as a whole.