GB2189404A - Fluid filter element - Google Patents

Abstract

A filter element, designed for corrosive media such as etching fluids, comprises a stack of annular filter membranes 9 bonded together alternately at inner and outer peripheries 17, 17' to form a bellows-like body with a central channel 16, support layers 10 being bonded to one or both sides of at least some membranes to space the filtering surfaces apart. Impervious end members 18, 19 may be thick as shown, or thin- walled end members may be supported in use by the walls of an enclosing housing. Membranes 9 and layers 10 are preferably of plastics (exemplified). The housing may be demountable or disposable with the filter element and also made of plastics. <IMAGE>

Description

SPECIFICATION Fluid filter element The present invention relates to a filterelementfor fluids, i.e. liquids and/or gases.

In DE-OS 3441249 there is disclosed a stack-shaped filter element of flat blanks in which the inner and outer sealing of the differentflow paths takes place through silicone-based sealing materials and pressure-distributing masks in conjunction with diverse membrane and support materials. Although the different materials which are matched one to the other in respect of the requirement forfluid tightness, do indeed provide effective sealing, they restrict the use of filter elements of that kind with aggressive media, since not all the materials present in the filter element have equal properties in relation to aggressive media.

Aggressive media are currently used in, in particular, the production of micro-electronic parts, such as wafers, the media concerned being particle-free filtered etching chemicals. The yield in usable chips depends on the purity ofthevery aggressive etching media usedforthis. The production of such elements under clean room conditions requires the smallest possible dimensions forfilters, which are employed directly before use of the chemicals, since space under laminarflow conditions is very costly.

The following, by no means exhaustive list, shows the etching media, organic solvents and gases to be filtered by such filter elements: Liquids: concentrated sulphuric acid, maximally concentrated chromic acid, Caro's acid (sulphuric acid and hydrogen peroxide), "piranha etch" (TRADE MARK), nitric acid, hydroch loric acid, hydrofluoric acid, phosphoric acid, trichloroacetic acid, acetic acid, hexafluosilicic acid, ammonium hydroxide, perchloroethylene, tricholorethane, trichloroethylene, methylene chloride, monochlor obenzene,xylene, butyl acetate, "Cellosolve" (TRADE MARK), acetone, cyclohexanone, dioxane and tetrahydrofurane.

Gases: silane, dichlorosilane, silicon tetrafluoride, boron trifluoride, carbon tetrafluoride, diborane, boron trichloride, boron, trifluoride, ammonia and arsenic hydride.

The choice of filter element materials is very restricted due to the highly aggressive chemicals which are, in part, used attemperatures of up to 80 to 140"C. Glass or metals cannot be used dueto solubility of ions. The usual plastics materials are subjectto oxidisation under the harsh conditions and pollute the chemicals with their decomposition products. Even partiallyfluorided polymers, such as PVF (polyviny Ifluoride) or PVDF (polyvinyidifluoride) are not usable for some of the mentioned applications, as they are either partially dissolved or decomposed with longer use. Forthat reason, only a small group of inert, highly substituted fluoropolymers represent usable polymer materials, namely: PTFE (polytetrafluoroethylene) for example "Teflon", "Hostaflon" (TRADEMARKS):-.

FEP (perfluoroethylene#ropylen.e-copolymerisate): for example "Teflon FEZ , "Neoflon", "Teflex" (TRADE MARKS).

ETFE (copolymer of ethylene and tetraf luornethylene), partially refluoridated: for example "Tefiel"". "ilostafion ET", "Aflonn (TRADE MARKS} PFA/T--FA (pe-#uoroethyl enevi nyether#cop-o lyrner): for exampie- "Teflon PFA", "HostaflonTFA" (TRADE MARKS).

(E)CTFE (poly-chlorotrifluoroethylene and copolym erisatewith ethylene : for example "Aclar", "Halar" (TRADE MARKS).

All these materials can be processed only with difficulty. PTFE is not processablethermoplasticaily and the remaining materials only atvery high temperatures.

According to DE-OS 21 23316, membranes can be produced of PTFE. These membranes can be processed into filters, for example into filtering candles by known techniques.

Forthe production of filters with higher performance density or packing density and higher chemical stability, the very thin areal membranes, which consist up to about 80% of air, require special precautions and techniques during further processing as well as in use.

the known seals with resilient sealing elements and contact pressure are unsuitable for use in such cases.

There is thus a need for a filter element wherein by simple means a pressure seal and specific sealing elements within the element can be dispensed with.

According to the present invention there is provided a filter element for fluid filtration in a housing, the filter element comprising a plurality offluid permeable filter sheets fluidtightly interconnected attheir circumference and at inner annular regions thereof to form a concertina-shaped filter body for filtration of fluid passing between the interior and the exterior of the body by way of outer annular regions of the filter sheets and a plurality of support sheets disposed between and in contact with the filter sheets at said outer annular regions, each of the filter sheets having an opening in the area surrounded by said inner annular region thereof and the openings in the filter sheets providing an internal passageforfluidflow substantially perpendicularly to the planes of said outer annular regions.

Each ofthe filter sheets may be, for example, circular or polygonal. Preferably, the opening in each filter sheet is disposed in a central region thereof. Each ofthefilter sheets may comprise weldable synthetic material, as may each ofthe support sheets. The supportsheets can be laminated on the filter sheets at either or both sides thereof. Expediently, each of the filter sheets comprises a material with a base of polymers substituted by fluorine, while each of the support sheets may be a fleece, a tissue, a stamped or perforated film or a grating. For preference, each of the support sheets comprises a material with a base of polymers substituted by fluorine. The support sheets can, moreover, comprise perforated and stamped drainage films coated on the sides ofthe filter sheets.

In a preferred embodiment, the filter element comprises a respective end memberfluidtightly connected to said inner annular region ofthefilter sheetateach endofthe filter body, one of the end members being arranged to close said passage at the associated end ofthe body and the other end member being provided with an opening communicating with the passage. Each ofthe end members can comprise a film of dense material, and a coupling adapter can be fixed to said other end member. In addition,respective pressure plates can be disposed against and outward lyofthe end members,the plates being intercon nected bytensioning elements engaged in openended slots in the plates.

Through the particular construction of such a filter element embodying the invention and the consequently available range of choice ofthefilter materials to be employed and the auxiliary means supporting the filtration and guidance offluid, a large filter area can be achieved for a small volume. The number of components and materials (in chemical respect) can be reduced to a minimum. Avariability ofthe area with uniform constructional elements can be possible for a small numberof basic units.

An embodimentofthe present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which: Fig. 1 is a schematic axial sectional view of a first filter element embodying the invention; Fig. 2 is a sectional view of two filter sheets, with support sheets, in the element of Fig. 1; Fig. 3 is a detail, to an enlarged scale, of the element of Fig. 1, in the region of an upper connecting member of the element; Fig. 4 is a schematic axial sectional view of parts a second filter element embodying the invention; Fig. 5 is a schematic axial sectional view of part of a third filter element embodying the invention; Fig. 6 is a schematic axial sectional view of part of a fourth filter element embodying the invention;; Fig. 7 is a detail, in section, of part of a fifth filter element embodying the invention; Fig. 8 is a front elevation ofa housing of a filter unit incorporating afilterelementembodyingtheinven- tion; Fig. 9 is a cross-section of the housing, with filter element, along the line 9-9 in fig. 8; Fig. 10 us a perspective view of the filter element of Figs. 1,8 and 9; Fig. 11 is a perspective view of a cylindrical filter element embodying the invention; Fig. 12 is a schematic axial sectional view of yet anotherfilter element embodying the invention; Fig. 13 is a viewfrom below ofthe filter element of Fig. 12; and Fig. 14 is a schematic sectional perspective view of partofthefilter element of Fig. 12.

Referring now to the drawings, there are shown differentembodiments of a filterelement8which employs filter orblanks 9 in theform of membranes, which are most difficultto connect, of fluoropolymers. PTFE presents particular difficulties to gluing or welding; in particular, membranes of PTFE are difficultto glue and to weld together in view oftheirstructure. PTFE membranes, as disclosed in DE-OS 2123316, consist of a vibrille-and-knot struc ture with a plurality of air inclusions, which have thermal insulating properties and thus resistwelding.

If welding is carried out under conditions of high temperature and pressure, there is a risk of damage to the sensitive membranes.

In filter elements embodying the present invention, the PTFE membranes are preferablyalreadycoated with oneortwothin supportlayerorlayersforthe formation of a laminate. Such layers can be tissues 10 or fleeces 13 of chemically inert, thermoplastic fluoropolymerswith lowest possible softening point.

Similarly, tissues 11 on a base offluoropolymers of somewhat larger size, can be used as draining support layers. In the same sense, stamped and possibly perforated films 12 can be employed in the alternative.

As shown in Fig. 2, two filter blanks 9 with integrated welded tissues 10 are initially laid one on the other and connected in leak-proof manner by an annularwelding seam 17 in the central region and provided in the inner annular region with a passage 16, which isto serve for conducting away filtrate.

In the present embodiment, the filter blanks 9 with integrated welded tissues 10 are formed to be square.

These are stacked one on the other in pairs as shown in Fig. 1. Thereafter, the individual welding together 17' atthe peripherytakes placefortheformation of a concertina-like layer and compound geometry.

In orderto be able to manipulate the filter element 8 as disposable device during assembly and disassembly, the element is provided at one side with a terminating part 18, which covers the central passage 16 and is connected at its periphery in leakproof mannerwith thefilter blank 9with supporting layer 10 lying thereunder. Similarly, the othersideofthefilter element8 is equipped with a further terminating part 19with central connecting stub pipe 19' and con nectedwiththeelement8attheperipheryor, as illustrated, in the central region at the seam 17. All passages 16 ofthefilter element 8 open into the stub pipe 19' ofthe part 19.As is evidentfrom Figs. 8 and 9, the housing 1 consists of two housing parts 2 and 3, which are also made from material resistant to highly aggressive media, for exam ple from PTFE. Apartfrom stub pipes 4 and 5for inlet and outlet, an outlet opening 6 and ventilation opening 7 are provided.

In ordertofacilitate manipulation ofthe filter element 8, the relatively stiff terminating parts 18 and 19 are connected together by several bands 20, which stabilise the filter element 8 in axial and radial direction. In that case, the individual filter blanks 9 lie closely on the draining support layers 10,11,12 and 13 in order to optimise packing density and obtain defined flow paths, thus departing from the simplified illustrations according to Figs. 1 to 7.

In the embodiment according to Fig. 4, a filter blank 9 is supported at both sides by a welded tissue 10 and built up as laminate,whilstthe neighbouring filter blank9 is constructed without an integrated support.

In the concertina-like structure and compound geometry, however, the two filter blanks are supported at both sides by the tissue 10.

In the embodiment according to Fig. 5, the welded tissues 11 extend between the blanks 9 and are connected merely atthe welded rims 17 and 17' with the blanks 9 orterminating parts 18 and 19.

In the embodiment of Fig. 6, a sinously stamped film with passages, which in respect oftheir longitudinal grooves are arranged crosswise, is used as supporting layer.

Inthe embodiment of Fig. 7,thefilter blank9 and fleece 13 are in the form of a laminate, which are additionally supported by welded tissues 11. Fig. 7 is comparable with Fig. 2.

Waste-free polygonal shapes are preferred, for example the square shape illustrated in Figs. 8 to 10, particularly when expensive filter materials are concerned. Generally, however, a variety of outline shapes is possible, for example a circularly round or cylindrical form as shown in Fig. 11.Here, too, the filter element 8' is connected by two bands 20 linking the terminating parts 18 and 19 for easier manipulation andforstabilisation. Thefilterelements of Fig. 10 can in simple manner be connected with the connecting stub pipe 4 after removal ofthe housing part 2, so that the housing is divided up into two chambers 14 (retentate chamber) and 15 (permeate chamber).

Figs. 12to 14 show an embodiment in which, to minimisewasteoftheveryexpensive materials of the filterelement, the upper and lowerterminating parts 18 and Igare constructed as thin films or as terminating filter membranes 9 with perforated film 12. The latter has only protective function forthe membrane9.A connecting adapter 19", serving as an outlet stub pipe, is welded or glued directly onto the lower terminating part 19.

The filter element 8 is formed, according to Fig. 14, from a membrane 9 covered at both sides by a perforated film 12, wherein individual modules M (as indicated atthe left in Fig. 14) can be prefabricated and tested individually.

Inorderto be ableto stabilise the filterelements in the housing and achieve a favourable packing density, the filter element is covered atthetop and bottom with re-usable pressure plates 21 and 22, which are held at a spacing by re-usable tensioning bolts 24. The tensioning bolts 24 are of fixed length and simply insertable into open-ended bearing grooves or slots 23 ofthetwo pressure plates 21 and 22. The lower plate 22 has a passage 22' forthe adapter 19". Thus, onlythe filter element 8 with adapter 19"forms a consumable item. The filter element 8 shown in Figs.

12to 14 can be inserted into a housing ofthe kind shown in Figs. 8 and 9. The individual elements according to Figs. 1 to 7 and 14 lie one closely against the other in the operational state and are shown at large spacing onlyfor reasons of clarity.

For certain fields of use, it is the practice to perform, instead of static filtration, dynamic filtration in which the retentate is conducted constantly in circulation into the retentate chamber 14. Forthis purpose, an additional outlet stub pipe 5' can be provided in the retentate chamber 14 according to Figs. 8 and 9. In that casethefilter layers are flowed over laminarly around the closed core 17. For this purpose, it can be advantageous to arrange the closed core 17 and correspondingly the outlet stub pipe 4, 19' or 19" eccentrically, i.e. in the proximity of the periphery of the filter element 8.

The filter element 8 can also be enclosed in a capsulated disposable housing in place of a re-usable housing 1.

The O-ring seals 25 which are arranged in the housing 1 or in the connecting adapter 19" ofthefilter element 8, can form resilientsealing elements sheathed by PTFE, so that the entire filter unit can be formed of PTFEforthefiltration of highly aggressive media.

The filter blanks can be made of other, ndt directly weldable materials when appropriate welding aids are employed. These can consistofannularweldingfilms which are positioned inthe region oftheannular zonesto be connected and bring aboutthe anchoring of not directlyweldable materials.

It is to be understood thatthe concertina-like joining hereinbefore described can be realised in simpler manner with the aid of inherently weldable material, for example on a base of polyamide, polysulfone, polypropylene, polyvinylidenedifluoride, polyester or polyurethane.

Claims (25)

1. Afilter elementforfluid filtration in a housing, the filter element comprising a plurality of fluid permeablefiltersheetsfluidtightly interconnected at their circumference and at inner annular regions thereof to form a concertina-shaped filter body for filtration offluid passing between the interior and the exterior of the body byway of outer annular regions of the filter sheets and a plurality ofsupportsheets disposed between and in contactwith the filter sheets at said outer annular regions, each of the filter sheets having an opening in the area surrounded by said inner annular region thereof and the openings in the filter sheets providing an internal passageforfluid flow substantiallyperpendicularly to the planes of said outer annular regions.

2. Afilter element as claimed in claim 1, wherein each ofthefiltersheets is circular.

3. Afilter element as claimed in claim 1, wherein each of the filter sheets is polygonal.

4. Afilter element as claimed in any one ofthe preceding claims, wherein the opening in each filter sheet is disposed in a central region thereof.

5. Afilterelementas claimed in any one ofthe preceding claims, wherein each of the filter sheets comprises weldable synthetic material.

6. Afilter element as claimed in any one ofthe preceding claims, wherein each of the support sheets comprises weldable synthetic material.

7. Afilter element as claimed in claim 6, wherein the support sheets are laminated on the filter sheets at either or both sides thereof.

8. Afilter element as claimed in any one ofthe preceding claims, wherein each of the filter sheets comprises a material with a base of polymers substituted by fluorine.

9. Afilter element as claimed in any one ofthe preceding claims, wherein each of the support sheets is a fleece, a tissue, a stamped or perforated film or a grating.

10. Afilter element as claimed in any one ofthe preceding claims, wherein each ofthe support sheets comprises a material with a base of polymers substituted by fluorine.

11. Afilter element as claimed in any one of the preceding claims, comprising a respective end mem berfluidtightlyconnectedtosaid innerannularregion of the filter sheet at each end ofthefilter body, one of the end members being arranged to close said passage atthe associated end ofthe body and the other end member being provided with an opening communicating with the passage.

12. Afilter element as claimed in claim 1,wherein the support sheets comprise perforated and stamped drainagefilms coated on the sides ofthe filter sheets.

13. Afilter element as claimed in claim 11,wherein each of the end members comprises a film of dense material.

14. Afilterelementasclaimed in claim 13, comprising a coupling adapterfixed to said other end member.

15. Afilter element as claimed in anyone of claims 11,13 and 14, comprising respective pressure plates disposed against and outwardly of the end members, the plates being interconnected bytensioning elements engaged in open-ended slots in the plates.

16. A filter element substantially as hereinbefore described with reference to Figs. 1 to 3 of the accompanying drawings.

17. Afilter element substantially as hereinbefore described with reference to Fig. 4 of the accompanying drawings.

18. A filter element substantially as hereinbefore described with reference to Fig. 5 ofthe accompanying drawings.

19. Afilter element substantially as hereinbefore described with reference to Fig. 6 of the accompanying drawings.

20. A filter element substantially as hereinibe#re described with reference to Fig. 7 ofthe accompanying drawings.

21. Afilterelementsubstantiallyas hereinbefore described with reference to Figs. 8 to 10 ofthe accompanying drawings.

22. Afilter element substantially as herein before describedwith referenceto Fig. 11 oftheaccompany- ing drawings.

23. Afilter element substantially as hereinbefore described with referenceto Figs. 12to l4ofthe accompanying drawings.

24. Afilterunitcomprising a housing and a filter element as claimed in any one ofthe preceding claims arranged in the housing,the housing having afirst part communicating with a space around the filter body and a second part communicating with the passage.

25. Afilterunit substantially as hereinbefore described with reference to Figs.8to 10 ofthe accompanying drawings.