Porous filter structure and process for the manufacture thereof

• US 5,928,588 A
• Filed: 11/13/1997
• Issued: 07/27/1999
• Est. Priority Date: 09/10/1996
• Status: Expired due to Term

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: Cuno Incorporated (3M Company)
• Inventors: Chen, Wei-Chih, Slovak, Jack, Repetti, Ronald V.
• Primary Examiner(s): THEISEN, MARY LYNN F
• Application Number:
  US08/969,919
• Time in Patent Office: 621 Days
• Field of Search: 264/113, 264/118, 264/122, 264/126, 264/DIG. 48, 264/913
• US Class Current: 264/113
• 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 2239/0414 Surface modifiers, e.g. comprising ion exchange groups
• 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 2239/086 Binders between particles or fibres
• CPC Class Codes: B01D 2239/10 Filtering material manufacturing
• CPC Class Codes: B01D 39/1615 of natural origin
• CPC Class Codes: B01D 39/163 sintered or bonded
• CPC Class Codes: B01D 39/2024 otherwise bonded, e.g. by resins
• CPC Class Codes: B01D 39/2044 sintered or bonded by inorganic agents
• CPC Class Codes: B01D 39/2055 Carbonaceous material solid sorbent compositions comprising free carbon B01J20/20
• CPC Class Codes: B01D 39/2062 Bonded, e.g. activated carbon blocks
• CPC Class Codes: B01D 39/2065 the material being fibrous
• CPC Class Codes: B01D 39/2079 otherwise bonded, e.g. by resins
• CPC Class Codes: B01J 20/28023 Fibres or filaments fibres or filaments in the form of membranes B01J20/28038; B01J20/28007 takes precedence
• CPC Class Codes: B01J 20/28028 Particles immobilised within fibres or filaments
• CPC Class Codes: B01J 20/2803 Sorbents comprising a binder, e.g. for forming aggregated, agglomerated or granulated products
• CPC Class Codes: B01J 20/28033 Membrane, sheet, cloth, pad, lamellar or mat
• CPC Class Codes: B01J 20/28042 Shaped bodies; Monolithic structures
• CPC Class Codes: B01J 20/28054 : characterised by their surface properties or porosity
• CPC Class Codes: B01J 20/3007 : Moulding, shaping or extruding
• CPC Class Codes: B01J 20/3042 : Use of binding agents; addition of materials ameliorating the mechanical properties of the produced sorbent
• CPC Class Codes: B29C 67/20 : for porous or cellular articles, e.g. of foam plastics, coarse-pored chemical aspects of working up macro-molecular substances to porous or cellular articles C08J9/00
• CPC Class Codes: Y10S 264/913 : From fiber or filament, or fiber or filament containing article or product, e.g. textile, cloth fabric, carpet, fiberboard

Abstract

A process for the manufacture of porous structures comprises forming a dry mixture comprising a component providing primary separation capability, a component providing green strength reinforcement capability and, a component providing binding capability and selected from the group consisting of thermoplastic and thermosetting polymers; delivering the mixture to a suitable surface and building a desired thickness thereof; densifying the mixture into tile form desired for the porous structure; removing the densified porous structure from the surface; binding the component providing the primary separation capability by melting the mixture to a temperature of up to about 20° C. higher than the melting point of any thermoplastic component providing binding capability. Porous structures (100, 110, 120, 125, 140, 175) according to the present invention comprise from about 70 to about 90 parts by weight of a component providing primary separation capability (61, 62); from about one to about 15 parts by weight of a component providing green strength reinforcement capability (64, 65); and, from about eight to about 20 parts by weight of a component providing binding capability (67, 68) and selected from the group consisting of thermoplastic and thermosetting polymers.

Claims

1. A process for the manufacture of porous structures comprising:

forming a dry mixture comprising a component providing primary separation capability, a component providing green strength reinforcement capability and, a component providing binding capability and selected from the group consisting of thermoplastic and thermosetting polymers;

delivering said mixture to a suitable surface and building a desired thickness thereof;

densifying said mixture into the form desired for said porous structure;

removing said densified porous structure from said surface;

binding said component providing said primary separation capability by heating said densified porous structure to a temperature of up to about 20°

C. higher than the melting point of any said thermoplastic component providing binding capability.

2. A process for the manufacture of porous structures, as set forth in claim 1, wherein said step of forming includes the step of selecting first, second and third components, each said component providing one of said three capabilities.

3. A process for the manufacture of porous structures, as set forth in claim 1, wherein said step of forming includes the step of selecting two of said three components, which together provide said three capabilities.

4. A process for the manufacture of porous structures, as set forth in claim 1, wherein said step of forming includes the step of selecting one component providing said primary separation capability, said green strength reinforcement capability and said binding capability.

5. A process for the manufacture of porous structures, as set forth in claim 1, wherein said steps of delivering and densifying are conducted via compression tooling.

6. A process for the manufacture of porous structures, as set forth in claim 1, wherein said step of delivering includes the step of filling a mold with said mixture and said step of densifying is conducted by isostatic compression of said mixture into the shape of the porous structure, having sufficient green strength to be self-supporting.

7. A process for the manufacture of porous structures, as set forth in claim 6, including the additional step of providing a mandrel in said mold prior to said step of filling.

8. A process for the manufacture of porous structures, as set forth in claim 7, wherein said shape of the porous structure is cylindrical and said porous structure is hollow.

9. A process for the manufacture of porous structures, as set forth in claim 8 wherein said shape has a L/D ratio of at least about 3:

1.

10. A process for the manufacture of porous structures, as set forth in claim 6, including the additional steps of filling said mold with at least a second dry mixture of said components around said porous structure;

and isostatically compressing said second mixture around said porous structure, thereby providing a layered porous structure having sufficient green strength to be self-supporting.

11. A process for the manufacture of porous structures, as set forth in claim 10, wherein said additional steps are conducted after said step of removing and including the further step of returning said porous structure to said mold prior to said additional steps.

12. A process for the manufacture of porous structures, as set forth in claim 6, wherein said shape of the porous structure is cylindrical and including the additional steps of

providing a mandrel within said mold and at least one cylindrical sleeve, concentric with said mandrel, said sleeve and said mandrel defining separate volumes and wherein said step of delivering includes the steps of filling the volume defined between the mold and said sleeve with a first dry mixture of components and filling the volume defined between said sleeve and said mandrel with a second dry mixture of components, different from said first;

and

removing said sleeve from said mold prior to said step of densifying.

13. A process for the manufacture of porous structures, as set forth in claim 12, including the additional steps of

providing one or more additional cylindrical sleeves, concentric with said mandrel, said sleeves additional defining separate volumes and wherein said step of delivering includes the step of filling the volume defined between adjacent sleeves with a second dry mixture of components;

and

removing said sleeves from said mold prior to said step of densifying.

14. A process for the manufacture of porous structures, as set forth in claim 6, wherein said shape of the porous structure is cylindrical and including the additional steps of

providing a mandrel within said mold;

and

filling the volume defined between the mold and said mandrel with at least first and second dry mixtures of components in concentric layers around said mandrel, prior to said step of densifying, said second dry mixture of components being different from said first.

15. A process for the manufacture of porous structures, as set forth in claim 14, including the additional steps of filling said mold with at least a third dry mixture of said components around said porous structure;

and isostatically compressing said second mixture around said porous structure, thereby providing a layered porous structure having sufficient green strength to be self-supporting.

16. A process for the manufacture of porous structures, as set forth in claim 15, wherein said additional steps are conducted after said step of removing and including the further step of returning said porous structure to said mold prior to said additional steps.

17. A process for the manufacture of porous structures, as set forth in claim 1, wherein said step of delivering includes the step of applying said mixture onto a flat support surface and said step of densifying includes the step of pressing said delivered mixture into a sheet of reduced thickness, having sufficient green strength to be self-supporting.

18. A process for the manufacture of porous structures, as set forth in claim 17, including the additional step of applying at least a second dry mixture of components onto said first delivered mixture, prior to said step of densifying.

19. A process for the manufacture of porous structures, as set forth in claim 17, including the additional steps of applying at least a second mixture, different from said delivered mixture, onto said densified sheet and pressing said second delivered mixture and said densifed sheet into a layered sheet of reduced thickness, having sufficient green strength to be self-supporting.

20. A process for the manufacture of porous structures, as set forth in claim 19, including the additional step of cutting desired shapes of porous structures from said sheet of reduced thickness.

21. A process for the manufacture of porous structures, as set forth in claim 1, wherein said component providing primary separation capability is selected from the group consisting of carbon particles, diatomaceous earth, perlite, activated alumina, silica, zeolites, natural fibers, and man-made fibers.

22. A process for the manufacture of porous structures, as set forth in claim 21, wherein said natural fibers are selected from the group consisting of cellulose, wool, jute, hemp and said man-made varieties are selected from the group consisting of fibers made of polyolefins, polyesters, carbon, graphite, glasses, acrylics, rayons, nylons, aramids, multi-component fibers and mixtures thereof.

23. A process for the manufacture of porous structures, as set forth in claim 1, wherein said component providing green strength reinforcement is selected from the group consisting of fibers selected from the group consisting of polyolefins, polyesters, nylons, aramids, rayons and mixtures thereof and liquid green strength agents and mixtures thereof.

24. A process for the manufacture of porous structures, as set forth in claim 23, wherein said liquid green strength agents are selected from the group consisting of styrene-butadiene, poly(ethylene-vinyl acetate), and acrylate latexes;

methyl-cellulose and hydroxypropyl methyl-cellulose, carboxymethyl cellulose, hydroxyethyl cellulose;

polyvinyl alcohol;

polyvinyl pyrrolidone;

polyacrylic acid;

polyethylene oxide;

polyethyleneimine;

polyacrylamide;

natural gums and copolymers thereof;

water and mixtures with one or more of the foregoing liquid green strength agents.

25. A process for the manufacture of porous structures, as set forth in claim 1, wherein said thermoplastic and thermosetting polymer component providing binding capability is selected from the group consisting of polyolefin, epoxy, phenol-formaldehyde and melamine-formaldehyde resin powders and polyolefin fibers.

26. A process for the manufacture of porous structures, as set forth in claim 1, including the additional step of adding an optional component selected from the group consisting of cationic charged resins, ion-exchange materials, perlite, diatomaceous earth, activated alumina, zeolites, resin solutions, latexes, metallic materials and fibers, cellulose, carbon particles, carbon fibers, rayon fibers, nylon fibers, polypropylene fibers, polyester fibers, glass fibers, steel fibers and graphite fibers, including mixtures thereof in an amount ranging from about 0.1 to about 90 percent by weight, with an attendant decrease in the amount of primary media.

27. A process for the manufacture of porous structures, as set forth in claim 1, including the additional step of cationically charging said optional component selected from the group consisting of perlite, diatomaceous earth, activated alumina, zeolites, cellulose, rayon fibers, nylon fibers and carbon particles.

28. A process for the manufacture of porous structures, as set forth in claim 27, wherein said step of cationically charging said optional component is conducted prior to said step of forming and including the additional step of adding said cationically charged component to said mixture.

29. A process for the manufacture of porous structures, as set forth in claim 1, wherein the desired form created by said step of densifying said mixture is a flat layer.

30. A process for the manufacture of porous structures, as set forth in claim 29, including the additional steps of forming at least a second mixture of said components;

densifying said second mixture to form a flat layer and combining said layers to form a multiple layered product.

31. A process for the manufacture of porous structures, as set forth in claim 1, including the additional step of cationically charging any of said components, providing one or more of said three capabilities which comprise particulate media.