SEALING MATERIAL

Abstract

A water resistant sealing material suitable as a gasket or valve seal is described. The sealing material comprises modified chemically exfoliated vermiculite (CEV) in a proportion of 30-70% w/w sealing material and a filler in a proportion of 70-30% w/w sealing material, and optionally other additives in a proportion of 0-10% w/w sealing material. The modified CEV comprises water resistance enhancing monovalent cations. The sealing material is particularly useful to provide improved water resistance in gaskets and valve seals.

Claims

1. A water resistant sealing material comprising modified chemically exfoliated vermiculite (CEV) in a proportion of 30-70% w/w sealing material and a filler in a proportion of 30-70% w/w sealing material, and optionally other additives in a proportion of 0-10% w/w sealing material, wherein the modified CEV comprises water resistance enhancing monovalent cations.

2. A water resistant sealing material according to claim 1, wherein the water resistance enhancing monovalent cations are exchangeable cations.

3. A water resistant sealing material according to claim 1 or 2, wherein the sealing material is in the form of a sheet.

4. A water resistant sealing material according to claim 1, 2 or 3, wherein the water resistance enhancing monovalent cations in the CEV are present at cation exchange sites in the CEV.

5. A water resistant sealing material according to any of claims 1 to 4 for a dynamic or static seal.

6. A water resistant gasket or valve seal, the gasket comprising a sealing layer and optionally a core and/or support for the sealing layer, the valve seal comprising sealing material, wherein the sealing layer/sealing material comprises modified chemically exfoliated vermiculite (CEV) in a proportion of 30-70% w/w sealing layer/sealing material, and filler in a proportion of 30-70% w/w sealing layer/sealing material, and optionally other additives in a proportion of 0-10% w/w sealing layer/sealing material, wherein the modified CEV comprises water resistance enhancing monovalent cations.

7. A water resistant gasket or valve seal according to claim 6, wherein the water resistance enhancing monovalent cations are exchangeable cations.

8. A water resistant sealing material or gasket or valve seal according to any preceding claim, wherein the water resistance enhancing monovalent cation is other than lithium, n-propyl ammonium or n-butyl ammonium.

9. A water resistant sealing material or gasket or valve seal according to any preceding claim wherein the water resistance enhancing monovalent cation is selected from at least one of an alkali metal, ammonium or a quaternary ammonium compound, optionally the water resistance enhancing monovalent cation is selected from one or more of sodium, potassium, rubidium, caesium, francium, ammonium, or a quaternary ammonium compound of formula R.sub.4N.sup.+ wherein R is selected from methyl, ethyl or a combination thereof, preferably the water resistance enhancing monovalent cation is selected from one or more of potassium, ammonium and sodium, more suitably, potassium and ammonium, most suitably, potassium.

10. A water resistant sealing material or gasket or valve seal according to any preceding claim, wherein the modified CEV and filler are intimately mixed and preferably, each evenly distributed throughout the sealing material/layer/sheet, so that they form a generally homogenous mixture.

11. A water resistant sealing material or gasket or valve seal according to any preceding claim, wherein levels of modified CEV in the sealing material/layer/sheet are in the range 30-68% w/w, more typically, 35-65% w/w, most typically, 40-60% w/w sealing material/layer.

12. A water resistant sealing material or gasket or valve seal according to any preceding claim, wherein levels of filler in the sealing material/layer/sheet are in the range 32-70% w/w, more typically, 35-65% w/w, most typically, 40-60% w/w sealing material/layer.

13. A water resistant sealing material or gasket or valve seal according to any preceding claim, wherein at least 1%, more preferably, at least 5%, most preferably, at least 10% of the exchangeable cations in the gasket/valve seal/sealing layer/sealing material or sheet are waterproof enhancing monovalent cations, especially, at least 25%, more especially at least 50%, for example 70 or 80 or 90 or about 100%.

14. A water resistant sealing material or gasket or valve seal according to any preceding claim, wherein the modified CEV is at least 1%, more preferably, at least 5%, most preferably, at least 10%, for example, 25 or 50 or 70% cation exchanged with water resistance enhancing monovalent cation, more typically, at least 80% cation exchanged, most typically, at least 90% cation exchanged.

15. A water resistant sealing material or gasket or valve seal according to any preceding claim, wherein the fillers are inert fillers, typically plate-like or particulate fillers, suitably plate-like fillers selected from talc, other forms of vermiculite and mica, or suitably particle fillers selected from amorphous silica, quartz silica and calcium carbonate.

16. A water resistant sealing material or gasket or valve seal according to any preceding claim, wherein the d.sub.50 average particle size of the filler is in the range 10 nm to 50 m, more preferably, 50 nm to 30 m, most preferably 500 nm to 25 m.

17. A water resistant sealing material or gasket or valve seal according to any preceding claim, wherein the surface area of the filler is less than 200 m.sup.2/g, more preferably 10 m.sup.2/g, most preferably 5 m.sup.2/g.

18. A water resistant sealing material or gasket or valve seal according to any preceding claim, wherein the CEV d-spacing (clay-clay layer spacing) at ambient temperature, lies within the range 10-12 .

19. A water resistant sealing material or gasket or valve seal according to any preceding claim, wherein the water resistance enhancing monovalent cations are present in the CEV of the water resistant sealing material/sheet/layer at at least a two-fold level of increase compared to unmodified CEV, more suitably, at a level of increase of at least 10, most suitably by a level of increase 10.sup.2, especially by a level of increase of at least 10.sup.3.

20. A water resistant sealing material according to any of claims 1 to 19 which is a gasket or valve seal sealing material.

21. A valve seal according to any of claims 6 to 19 wherein the sealing material is in the form of a packing ring.

22. A valve seal according to claim 21 comprising two or more packing rings, preferably at least a first packing ring comprising sealing material according to any of claims 1 to 19 and a second packing ring comprising graphite sealing material.

23. A valve seal according to claim 21 or 22, wherein a packing ring according to any of claims 6 to 19 forms the header and/or footer of the valve seal.

24. A valve seal according to any of claims 6 to 23, wherein the seal is a valve stem seal or a ball valve seal.

25. A process of production of a sealing material comprising the steps of: a) mixing chemically exfoliated vermiculite (CEV) with a filler to form an intimate mixture thereof; b) optionally, forming a sheet from the mixture; c) optionally, drying the said sheet formed from the mixture; and d) monovalent cation exchange of the mixture/sheet/dried sheet by contact thereof with a solution of a water resistance enhancing monovalent cation.

26. A process according to claim 25, wherein after mixing of the CEV, typically wet CEV in slurry form (although dry powder CEV may be added to increase the CEV content), and the filler, the intimate mixture is formed into a sheet and at least partially dried and optionally incorporated into a gasket or valve seal prior to water resistance enhancing monovalent cation exchange.

27. A process according to claim 25 or 26, wherein the concentration of the water resistance enhancing monovalent cation solution is in the range 0.1-10 mol.dm.sup.3, more preferably, in the range 0.5-5 mol.dm.sup.3, most preferably, in the range 1-3 mol.dm.sup.3.

28. A process according to any one of claims 25 to 27, wherein the gasket/valve seal ring/sheet/sealing layer/sealing material is immersed in the monovalent cation solution of 0.2-3.0 mol.dm.sup.3 for a period of between 5-180 minutes, more preferably a solution of 0.3-1.0 mol.dm.sup.3 for a period of between 15-60 minutes.

29. A process according to any one of claims 25 to 28, wherein the mixture/sheet/dried sheet is contacted with a solution of a citrate or chloride salt of the waterproof enhancing monovalent cation, most preferably a citrate salt.

30. A process according to any one of claims 25 to 29, wherein the water resistance enhancing monovalent cation is as claimed in any of claims 1 to 19.

31. A process according to any one of claims 25 to 30, wherein the process is a process for the production of gasket sealing material or valve seal sealing material.

Description

[0083] For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example only, to the following examples and figures in which:

[0084] FIG. 1 is a beam test apparatus.

EXAMPLES

Method

[0085] Example foils were prepared from the dough composition formulations described in Table 1 by mixing of the components to form a wet dough and then by drawing a doctor blade in a casting direction across wet dough to spread an even coating over a support layer (140 gsm paper, Cresta D). The coating was dried and the support layer removed by peeling back from the dried coating. The dried coating was cut with the longer dimension parallel to the casting direction (with grain) into 5 cm2 cm foil coupons. Samples for gas Leakage testing (DIN) at 90 mm OD50 mm ID were also cut.

[0086] Due to the varying viscosities of the mixes, deionised water had to be added to the initial dough formulations to obtain a consistency that was castable into foils. These water additions are shown in table 1. After mixing and casting into foils, the foils were consolidated, unless indicated otherwise, to approximately 0.6 mm thickness when dry, before cutting coupons as described above. The specific thicknesses and densities are recorded in Table 1.

TABLE-US-00001 TABLE 1 Composition of Trial Foils Prior to Exchange Dry Film Dough Composition Gas Leakage CEV PCEV Dough CEV Dry Film Dry Film (prior to slurry - added - Filler - Solids Additional (% Filler Thickness Density exchange) Formulation kg Wet kg kg (%) Water (L) Dry) (% Dry) (mm) (g/cm.sup.3) (ml/min) Comments Preparative 5.00 0.94 29 (45) Talc D200 0.71 1.90 0.37 Example 1 (55) Preparative 5.00 0.94 29 (45) Talc D200 0.61 1.30 0.93 Unconsolidated Example 2 (55) Comparative 5.00 0.32 21 (100) 0.61 1.28 0.01 Preparative Example 1 Preparative 5.00 0.34 0.60 29 (65) Talc D200 0.55 1.21 0.10 Example 3 (35) Comparative 3.00 1.88 29 3.20 (20) Talc D2500 Too brittle to Preparative (80) cut - not tested Example 2 Preparative 5.00 0.76.sup.a 27 0.50 (45) Talc D200:VN3 0.73 1.56 1.32 Example 4 0.19.sup.b 4:1 (55)* Preparative 5.00 0.42 21 0.33 (65) VN3 0.67 1.31 0.09 Example 5 (35) Preparative 5.00 0.94 27 0.50 (45) MKT Mica 0.64 1.89 6.45 Example 6 (55) Preparative 5.00 0.47.sup.a 27 0.5 (45) Talc 0.65 1.62 6.10 Example 7 0.47.sup.c D200:HPF2 1:1 (55)* Preparative 5.00 0.94 29 (45) HPF2 0.71 1.78 >50 Example 8 (55) Preparative 2.00 1.20 0.38 25 4.0 (80) Talc D200 0.68 1.45 0.02 Example 9 (20) Preparative 5.00 1.83 27 2.8 (30) Talc D2500 0.64 1.42 6.60 Example 10 (70) *Total .sup.aTalc Magsil D200 .sup.bUltrasil VN3 .sup.cHPF2 Silica
Summary data for the fillers used is given in Table 2.

TABLE-US-00002 TABLE 2 Filler Data Specific Surface Oil Adsorption Median Particle Name Type Area (m.sup.2/g) (g/100 g) Size (d.sub.50) HPF 2 Silica (Quartz) 0.6 24 15 m VN3 Silica 180 14 nm (Amorphous) MKT Muskovite 7.2 64 4.5 m Mica D200 Talc 3-5 38 21 m D2500 Talc 3-5 67 5 m

[0087] Cut coupon films of the above formulations were then cation exchanged by immersion in the salt solutions 1-4 or spiral wound gaskets were immersed in salt solutions 5 and 6. [0088] 1. Control (untreated samples) [0089] 2. Samples first immersed in 0.33 M Potassium Citrate (1 N K.sup.+) before rinsing twice in deionised water and drying at 40 C. for 3 hours. [0090] 3. As 2) with 1 M Potassium Chloride (1 N K.sup.+) [0091] 4. As 3) with 1 M Sodium Chloride (1 N Na.sup.+) [0092] 5. 0.33M Caesium Citrate, procedure detailed below [0093] 6. 1.0M Ammonium Citrate, procedure detailed below

[0094] Immersion (Beam) tests were performed on coupons treated according to conditions 1 to 4 above using the apparatus illustrated in FIG. 1.

[0095] A framework 2 for the immersion beam test was constructed from 16 mm square section PVC conduit. A pair of spaced opposed conduits 4, 6 were arranged in a parallel manner with a second identical pair 8, 10 superposed on the first pair so as to leave a gap 22 there between to accommodate and clamp a test coupon 14 extending perpendicularly between the sets of superposed conduits so that the ends thereof are clamped between first 4, 8 and second 6, 10 superposed conduits. The test coupon 14 thus bridges the gap 12 between the set of superposed conduits. A glass plate weight (360 g) 24 is rested on the respective second conduits 8, 10 to thereby prevent the coupon moving during the test. The test coupon 14 and framework 2 is designed to support 1 cm at each end of the test coupon, leaving 3 cm unsupported bridging the space 12 between the conduits. A 1 coin (weight 9.5 g, diameter 22.5 mm; thickness 3.15 mm) 16 was rested on the centre of each coupon. For testing, the framework 2 was placed in a clear polypropylene container 18. The coupons were all mounted such that the surface exposed to air during casting was facing down.

[0096] The container was filled with 1 L of de-ionised water 20 so as to submerge the coupons and the coupons observed continuously for 1 to 2 hours and at intervals thereafter for 24 hours.

[0097] At 8 and 24 hours, the deterioration of the coupons which had not collapsed was assessed by measuring the downwards deflection of the coupons in mm from the horizontal, by eye, using a set square with mm graduations. The time taken for each coupon to collapse was recorded where appropriate.

Results

[0098] 1. Control:

[0099] In table 3 below, the comparative example numbers match the respective preparative example numbers in table 1 except comparative preparative example 1 is designated comparative example 11 while times to collapse in the beam test are given in minutes:secs

TABLE-US-00003 TABLE 3 Control Test results Formulation reference Time to collapse (minutes:secs) Comparative Example 1 9:44 Comparative Example 2 2:17 Comparative Example 3 2:31 Comparative Example 4 4:08 Comparative Example 5 9:30 Comparative Example 6 8:18 Comparative Example 7 3:59 Comparative Example 8 7:15 Comparative Example 9 23:04 Comparative Example 10 0:38 Comparative Example 11 37:35

[0100] Samples of 100% CEV, Comparative Example 11, lasted considerably longer than the samples containing a filler (Comparative Examples 1-10). The consolidated sample Comparative Example 1 lasted longer than unconsolidated sample Comparative Example 2.

[0101] 2. 0.33 M (1 N) Potassium Citrate

[0102] In table 4 below, the examples produced by immersion in salt solution 2 above are shown as examples 1-10 and comparative example 12. The numbers of examples 1-10 match the respective preparative numbers of table 1, except comparative preparative example 1 is designated comparative example 12.

[0103] In table 4 times to collapse in the beam test are given in minutes. However, all of the samples except the 100% CEV comparative example 12 remained unbroken after 48 hours; the vertical deflection (in mm) of the beams is recorded after 8 hours, after 24 hours, and after 48 hours.

TABLE-US-00004 TABLE 4 Potassium Citrate Test Results Vertical Time to deflection Vertical Vertical collapse after 8 deflection after deflection after Example (minutes) hours (mm) 24 hours (mm) 48 hours (mm) Example 1 0 0 0 Example 2 0 0 0 Example 3 0 0 0 Example 4 0 0 0 Example 5 2 2 2 Example 6 0 0 0 Example 7 0 0 0 Example 8 1 1 1 Example 9 2 2 2 Example 10 1 1 1 Comparative 230 Example 12

[0104] 3. 1 M (1 N) Potassium Chloride

[0105] In table 5 below, the examples produced by immersion in salt solution 3 above are shown as examples 11-20 and comparative example 13. Examples 11-20 use the preparative examples 1 to 10 respectively. Comparative example 13 uses comparative preparative example 1.

TABLE-US-00005 TABLE 5 Potassium Chloride Test Results Vertical Vertical deflection Vertical deflection deflection after Example after 8 hours (mm) after 24 hours (mm) 48 hours (mm) Example 11 0 0 0 Example 12 0 0 0 Example 13 0 0 0 Example 14 0 0 0 Example 15 1 1 1 Example 16 0 0 0 Example 17 0 0 0 Example 18 0 0 0 Example 19 1 1 1 Example 20 1 1 1 Comparative 2 Example 13
The comparative example 13, containing comparative preparative example 1 was again the only sample to break and did so between 8 and 24 hours.

[0106] 4. 1 M (1 N) Sodium Chloride

[0107] In table 6 below, the examples produced by immersion in salt solution 4 above are shown as examples 21-29 and comparative example 14. Examples 21-29 use the preparative examples 1 to 9 respectively. Comparative example 14 uses comparative preparative example 1.

TABLE-US-00006 TABLE 6 Sodium Chloride Test Results Vertical Vertical deflection Vertical deflection deflection after Example after 8 hours (mm) after 24 hours (mm) 48 hours (mm) Example 21 0 1 1 Example 22 1 1 2 Example 23 2 2 3 Example 24 1 1 2 Example 25 1 1 2 Example 26 0 1 1 Example 27 1 1 2 Example 28 1 1 2 Example 29 1 1 2 Comparative 2 Example 14

[0108] Again, comparative example 14 broke between 8 and 24 hours as for solution 3. The remaining samples deflected more than the corresponding examples for solution 3.

[0109] 5. 0.33M Caesium Citrate

[0110] Caesium citrate was prepared at 0.33M concentration by slowly dissolving 66 g of caesium carbonate in a de-ionised water solution of 42 g citric acid monohydrate (both from Sigma Aldrich). The solution was made up to 400 ml before use, and left to stand for 24 hours to allow excess carbon dioxide to dissipate from solution. In example 30 a spiral wound gasket containing a sealing layer formed from preparative example 3 was immersed in the cation solution for 1 hour, rinsed, dried and tested by immersion in water for 30 minutes.

[0111] Water resistance of a gasket sealing layer prevents the filler from softening and extruding from the gasket, which reduces the structural integrity of the gasket. In a control sample that was not subject to cation exchange, after 30 minutes immersion in water most of the filler had been extruded. However, in example 30 there was no visual extrusion of the filler.

[0112] 6. 1 M Ammonium Citrate

[0113] Ammonium citrate was formed at 1 M concentration by slowly adding 58 g ammonium carbonate (from Sigma Aldrich) to 84 g of citric acid monohydrate in de-ionised water and making up to 400 ml . A 0.33 M solution was formed by halving these quantities in a total 600 ml solution. In both cases, the solutions were left for 24 hours before use to dissipate carbon dioxide.

[0114] In example 31, a spiral wound gasket containing a sealing layer formed from preparative example 3 was immersed in the 1 M concentration solution for 1 hour, rinsed, dried and tested by immersion in water for 30 minutes.

[0115] In example 32, a spiral wound gasket containing a sealing layer formed from preparative example 3 was immersed in the 0.33 M concentration solution for 1 hour, rinsed, dried and tested by immersion in water for 30 minutes.

[0116] The gaskets of both example 31 and example 32 imparted advantageous levels of waterproofing to the gaskets as there was no visual extrusion of the filler.

Leakage Testing

[0117] Modified SHELL gas leakage tests were performed on gaskets containing a treated sheet formed according to either preparative example 1 or preparative example 3 and using various cation solutions.

[0118] All the SHELL tests were carried out on 4 Class 300 gaskets (according to ANSI B16.5) having a wire of 316 L and containing the treated sheet.

[0119] The test rig had a welding neck flange with a raised face. The test volume of the rig was approx. 2.0 litres. The following materials were used:

[0120] Flanges: ASTM A 182 Gr. F11 or F12

[0121] Pipe: ASTM A 335 P11

[0122] Stud bolts: ASTM A 193 Gr. B16

[0123] Nuts: ASTM A 194 Gr. 4H.

[0124] The roughness of the flange facing was a smooth finish (Ra 3.2-6.3 m). All sample gaskets were dried for 1 hour at 100 C. prior to testing.

[0125] To test the gaskets at ambient temperature, an initial bolt stress 290 MPa (i.e. 71 MPa on stressed area of kammprofile, 107 MPa on stressed area of spiral wound gasket with inner and outer rings) was applied and the internal pressure raised to 5.2 MPa. After a setting time of 30 minutes, the pressure was maintained for 1 hour, after which the internal pressure was recorded.

[0126] To test the gaskets at elevated temperature, an initial bolt stress 290 MPa (i.e. 71 MPa on stressed area of kammprofile, 107 MPa on stressed area of spiral-wound) was applied and the joint containing the test gasket was heated up at a rate of about 100 C./h up to 450 C. When the temperature had reached 450 C. the internal pressure was raised to around 3.4 MPa. The temperature was maintained for 1 hour, after which the internal pressure was recorded. The joint was then allowed to cool down to ambient temperature before the heating cycle was repeated.

[0127] The results of the SHELL tests are shown in table 7 below. No additional gas was applied during testing.

TABLE-US-00007 TABLE 7 Gas leakage Test Results SHELL Test Measurements (MPa) Loss Preparative Consolidated Immersion in after 12 Gasket Type example Sheet type (y/n)? Treatment Water R.T. Cycle 1 Cycle 2 Cycle 3 Loss cycles Spiral- 3 Comparative Y None n/a 5.21-5.21 3.39-3.37 3.35 3.32 0.07 0.27 wound example gaskets with 15 inner and 3 Example Y 1M Potassium n/a 5.20-5.19 3.38-3.38 3.36 3.33 0.05 0.19 outer guide 33 Citrate/15 Min rings 3 Example Y 1M Potassium 30 Min 5.20-5.20 3.38-3.37 3.35 3.33 0.05 34 Citrate/15 Min 3 Example Y 1M Sodium n/a 5.20-5.20 3.39-3.38 3.36 3.34 0.05 35 Citrate/15 Min 3 Example N 1M Potassium n/a 5.21-5.20 3.38-3.38 3.36 3.34 0.04 36 Citrate/15 Min 3 Example N 1M Ammonium n/a 5.20-5.20 3.39-3.38 3.36 3.33 0.06 37 Citrate/15 Min Kammprofile 1 Example N 1M Potassium n/a 5.17-5.17 3.39-3.38 3.37 3.36 0.03 0.05 gaskets 38 Citrate/60 Min 1 Example N 1M Potassium 30 Min 5.20-5.20 3.40-3.39 3.38 3.37 0.03 39 Citrate/15 Min

[0128] Table 7 shows that Spiral Wound Gaskets containing the treated sealing material perform better in gas leakage performance than the untreated sample whether consolidated or unconsolidated. The kammprofile gasket immersed for 15 min in potassium citrate performs as well as that immersed for 60 min. Accordingly, the waterproofing does not result in deleterious gas leakage performance.

[0129] As shown by the above examples, the use of various fillers, covering a wide range of particle sizes and specific surface areas, added to CEV in combination with a treatment of monovalent water resistance enhancing cations results in an enhancement of the water resistance of the combined filler and CEV materials.

[0130] Specifically, table 3 shows that in the untreated state, 100% CEV materials have better water resistance than filled but untreated CEV materials. In contrast, tables 4, 5, 6, and 7 show that treatment of the same materials as used in table 3 with a water resistance enhancing cation containing solution surprisingly results in the filled CEV material presenting better water resistance than the treated, and untreated, 100% CEV material.

[0131] Further, the examples show that a range of water resistance enhancing cations are suitable in the present invention.

[0132] Example 40-41 relate to TH894 rings (TH894 packing is an exfoliated vermiculite based packing available from Flexitallicthe product is reinforced with Inconel wire).

Method & Results

[0133] Segments of TH894 packing were blocked into rings of 10 mm x-section and 45 mm diameter. Example 40 is a comparative example with no waterproofing treatment, Example 40 is subjected to 8 hours immersion in deionised water, and Example 41 is a sample treated with potassium citrate, by immersing the ring for 1 hour in 0.33 M solution, subsequently rinsing in tap water and then drying 2 hours at 50 C. which is then also subjected to 8 hours immersion in deionised water.

[0134] The samples immersed in water (Examples 40 and 41) were weighed prior to and after 8 hours immersion; example 40 gained 53.8% weight, due to water adsorption, while example 41 gained only 25.1%. The treated example 41 visibly swelled less than the untreated example 40, and did not feel as soft when removed from the water.

Example 42

[0135] A sample of TH894 was treated by coating on a saturated solution of potassium citrate (3 M) rinsing and drying as detailed for example 41. Testing was again carried out by immersing in deionised water for 8 hours; the swelling was intermediate between the untreated example 40 and the immersion treated example 41 and the weight gain, after water immersion, was 45.3%.

[0136] Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0137] All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

[0138] Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0139] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.