The present invention relates to a filter, and in particular to a mechanical particulate filter which can be used as a pre-filter to remove sediment from water prior to a carbon filter.

Carbon filters and similar filters are commonly used to filter water and other fluids, and remove impurities and undesirable components by chemical adsorption. They can for example be used to purify water so that it is safe to drink. Aside from carbon filters, other filters may alternatively or additionally be used, said filters functioning by chemical, physical or biological means.

Filter media may be contained within filter cartridges, and water may pass along a filter cartridge in an axial direction. Alternatively flow may be radial, for example radially inwards, in which case the water may flow into a central longitudinal channel and exit out of an open end of the cartridge.

Sometimes the carbon filter or other filter media may become blocked. To prevent or postpone this from happening, a pre-filter may be used prior to the carbon filter, to screen out particulate matter before said particulate matter can enter into, and block, the carbon filter.

In many circumstances a conventional pre-filter, for example a porous material, is effective. However, the present inventors have found that some environments require a different approach in order to maintain efficacy of the activated carbon or other filter media.

From a first aspect the present invention provides a membrane filter comprising a plurality of porous layers having successively decreasing mean pore sizes. Thus, a first layer has a particular mean pore diameter, a second layer beneath the first layer has a smaller mean pore diameter, and so on (e.g. a third layer beneath the second layer has a yet smaller mean diameter). This provides a pore size gradient such that, as water (or other fluid) passes through the layers, the largest particles are filtered out first, followed by smaller particles, followed by yet smaller particles etc. The particulate matter is thus removed by mechanical or physical means.

The filter of the present invention is particularly effective when used as a pre-filter in combination with a further filter, for example a carbon filter. The filter of the present invention may be wrapped around a carbon block such that, before water flows into the block, particulate matter is captured by the filter of the present invention. The present invention arose due to a need to address a problem associated with water filtration in areas where a large amount of colloidal clay is present in the water. It was observed that, it certain geographical locations, water filtration devices failed after only limited use. On further investigation the present inventors formed the theory that the problem was due to the presence of colloidal clay, and that the colloidal clay coagulated or clumped together to block the flow into and through a carbon filter, and blocked a conventional pre-filter.

Several attempts were made to address this problem, using a variety of different approaches. Several types of pre-filter, wrapped around a cylindrical carbon block filter, were tested. In one example, a string material was wound around the carbon block filter several times: it was thought that this might provide a physical filtration effect to remove the colloidal clay without blocking, but it was not effective:

blocking occurred after limited use, and the wrapping process was not

straightforward. In other examples, various porous non-woven and porous polymeric mats, of various thicknesses and porosities, were tested, but were also ineffective: they also became blocked quite quickly. After further experimentation, it was found that the problem could be addressed by having a graded filtration structure. Whereas some type of particulate matter (e.g. sand) can be filtered by having a pre-filter of uniform pore size, for colloidal clay it seems that it is important for the water to flow through a structure having large pores first followed by smaller pores later. This can be done by using two or more layers having successively smaller pore sizes. This enables the particulate matter to be captured without severely restricting the flow. The number of layers may be two or more, three or more, four or more, five or more, six or more, or seven or more; for example between 2 and 10.

The graded filtration effect may be achieved by wrapping a porous sheet, membrane or film, around a block several times. The pore size may be varied by process parameters, for example by the torque applied, to achieve the required variation in pore size in the flow direction. This aspect has the advantage that only a single type of substrate need be used. It should be noted that the variation in pore size as the sheet is wrapped around the block may be continuous rather than discrete. Regardless of this, however, the pore size in the flow direction (which may be in a radial direction) will decrease.

Alternatively the graded filtration effect may be achieved by using layers of material which are inherently different. The intrinsic differences could be in terms of pore size alone and/or in terms of the nature of the material (e.g. the chemical, physical or biological composition). In this case the torque does not need to be varied as the material is wrapped around the internal filter. This aspect is therefore suitable for use in pre-filters of various different types, without needing to be limited according to shape or location in relation to the downstream filter(s). Thus, the pre-filter may for example be flat or stacked. It should be noted that, whilst the above description has focused predominantly on water filtration and colloidal clay, the graded filtration concept of the present invention also applies to other fluids and particulate matter. This includes for example biological fluids for the purpose of testing and diagnosis, paints and solvents.

In terms of water filtration, certain areas in the north eastern USA region have a particularly high content of colloidal clay particulate in the mains line water, which cause conventional filters to block very quickly after reducing flow rates in a short period of time. The reduction in filter life can be around 80%. Customers can thereby experience no flow from drinking appliances very quickly. The present invention addresses this problem effectively, and is particularly beneficial with point of use devices. From a further aspect the present invention provides a method of manufacturing a membrane filter of the present invention comprising wrapping a porous membrane or film in an overlapping cylindrical fashion and controlling the pore size by controlling the torque during the wrapping. From a further aspect the present invention provides apparatus for manufacturing a filtration device in accordance with the present invention, comprising means for locating and rotating a cylindrical carbon block filter, means for feeding a membrane to said carbon block filter to result in more than one layer of membrane wrapped around said carbon block filter, and means for stretching an outer layer of said membrane greater than an inner layer.

The layers may be made from any porous material which can thereby work as a membrane filter. Suitable materials include polymer film materials, for example olefin film compositions, for example polypropylene materials. The film may be hot melt blown and may have perforations. One preferred type of membrane is a hot melt blown polypropylene (PP). For example, such a material having a rating of approximately 5 - 10 microns can be torque-wrapped to achieve a suitable range of porosities in different layers. The membrane may have a mean pore size, before the application of pressure, of 2 - 20 microns e.g. 5 - 10 microns for example.

The hot melt PP may be blown onto a carrier film, for example a polyester carrier film. To prepare a composite product, the membrane may be wrapped radially around the inner filter media, e.g. a carbon block filter. The multiple overlapping layers of the membrane provide a radially decreasing micron rating and therefore each layer removes a percentage of the silt particulate. The radially decreasing micron rating is achieved by controlling the membrane wrapping torque. Tension rollers may be used to control the torque and pressure. The membrane may be cut to a specific length, e.g. about 0.5 to 2m has been found to be suitable for some water filters, e.g. about lm.

The membrane may be fed by a continuous roll. Glue may be automatically applied to top and bottom edges down its total length: this allows the top and bottom surface to be sealed to adjacent layers of membrane and to the carbon block or other inner filter media. The length may be cut, and glue may be automatically applied to the cut end to seal the outer wrap of the torque wrapped product to the carbon block / inner media.

A number of different membrane or layer materials may be applied simultaneously, and the radial torque may optionally be varied for different membranes within this aspect; this allows control and flexibility in terms of bespoke application filtration. Optionally each of the plurality of layers may be less than 2mm, or less than 1mm, thick, for example between 0.3mm and 2mm thick, e.g. between 0.5 mm and 2mm thick, e.g. between 0.5mm and 1mm thick. This contrasts with some prior art pre-filters which use a single, thicker, layer.

The mean pore diameter in the outer layer may be for example within the range 8 to 20 microns. The mean pore size in the inner layer may for example be with the range 2 to 5 microns.

In one example, adjacent layers may have mean pore sizes of 10-12, 6-8, 5-6 and 3- 4 microns.

The membrane wrap of the present invention allows particulate matter to be trapped in different layers. Radial tightening torque loading is one method which allows a pre-filter to be produced which can increase the efficiency of sediment reduction and increase the efficiency and life of a filter.

The present invention will now be described in further, non-limiting detail, with reference to Figures 1 to 3 which show flow rates and capacities in respect of products tested, and Figures 4 to 10 which are photographs of a product being manufactured in accordance with the present invention.

Experimental results showing efficacy of the present invention

Summary

A trial was carried out to test the performance of an eco3 water filter (Icon Technology Systems Limited, Cheshire, UK) in the Boston area. As will be described in more detail below, results showed that an unprotected block, without any pre- filtration, resulted in a very limited life in the field. This was shown as being under 100 gallons in the Boston area. A new "eco3 filter with membrane" product, i.e. a product containing a membrane filter in accordance with the present invention wrapped around conventional filter media, extended the life of this filter to an average of 739 gallons. To improve this performance still further, for high usage clients, an eco3 parallel manifold system was also tested with 2 X eco3 filters with membrane - the throughput of this unit increased still further to deliver a volume in excess of 1500 gallons.

In comparison, a known filtration device - an Everpure OCS2 product - delivered an average throughput of 493 gallons in the trial.

Standard pre-filtration followed by an eco3 membrane filter in sequence was also tested. This delivered 672 gallons which was inferior to the new eco3 with membrane filter.

The trial described below was relatively aggressive and results in the field should be better than the results achieved in the trial by an estimated 10-15%.

A) Test Set-up and methodology

All jigs were fitted with a 60psi pressure relief valve to best replicate real life conditions. Out-feed pipes from each filter were fitted with standard gallon water meters to measure throughput. Flow rate readings were taken at differing hourly intervals.

The test jigs were set up on 3 mains feed lines as follows:

(In the following, "eco3 G1500_05e" denotes a carbon block filter commercially available from Icon Technology Systems Limited, Cheshire, UK, with a nominal carbon filter pore size of 0.5 microns, "new eco3 G1500_05e with membrane" denotes the same carbon filter with a membrane filter in accordance with the present invention wrapped around it as a pre-filter.)

• Line 1 - 3 new eco3 G1500_05e with membrane

1 Everpure OCS2

• Line 2* -

3 new eco3 G1500_05e with membrane

1 Everpure OCS2

Timed on a regime of 2hrs On - 30 min Off using solenoid valves after the first day to simulate point of use (POU) cooler use under accelerated conditions

• Line 3 - 1 eco3 Series manifold - sedi pp hot melt blown ("sedi" denotes a sediment filter, and "pp" denotes polypropylene) + new G1500_05e with membrane, running in sequential operation

1 eco3 Parallel manifold - 2 new G1500_05e with membrane, running in parallel operation

All filters were flow tested using the same protocol. They were either timed to record a) the number of seconds to run 2 litres of water or b) the volume of water in fluid ounces dispensed in 1 minute. The flow rates and water throughput in gallons were recorded at hourly intervals throughout the trial.

All test jigs ran constantly for 24 hour periods on flow, for up to 5 days, or until the filter flow rates dropped below 0.51pm - 0.13gpm. All filters were closed off when the flow measurements were taken. It was considered that the constant flow testing operation, with stop start on flow reading appeared to be a more aggressive testing regime than a POU cooler in a field application. As a result, we would expect to see a percentage increase of approximately 10-15% in the measured volume output under actual POL ⁾ cooler use in the field. B) Nature of the problem faced - Offending Boston area particulate

The particulate water quality issue in the Boston area water constitutes a brown clay/silt like media. This readily coagulates onto the surface of water filters. Its size range is small, at an average of between 2 and 10 microns. Particles are only visible to the naked eye if larger than 40 microns in size, so this contaminant is not seen in the water supply.

The manifestation of this contaminant is that it quickly adheres to the surface of water filters, and rapidly reduces the flow rate, overall volume capacity and life of the filter.

The membrane system of the present invention may be added to the eco3 filter. This provides a depth type filtration through having a number of layers, which increase its surface area and dirt holding capacity. After some use, the outer layers of the membrane are seen as a darker brown through heavier contaminant exposure whilst the inner ones are almost white showing more limited penetration. Essentially, the new filter of the present invention pre-filters the incoming water to protect the carbon block and the filter system from blocking and also removes all of the offending contaminants specified.

We have found in previous field trials that any carbon block installed in this area of the USA without any pre-filtration protection will have an expected volume capacity of less than 100 gallons only. C) Summary of results after 5 days' testing Using a common test reference point for filter sample comparison, with a minimum flow rate of 0.5lpm/0.13gpm (deemed minimal acceptable flow rate for normal field conditions), the filters achieved the following gallons of throughput under constant flow/accelerated test conditions -

• Unprotected 0.5 micron carbon block - no pre-filtration = less than 100 gallons

• Everpure OCS2 = 493 gallons

• eco3 Gold VH1 G1500_05e with membrane in accordance with the present invention = 739 gallons

• eco3 Series manifold - pre filter PP hot melt followed by 2 eco3 Gold VH1 G1500_05e with membrane = 672 gallons

• eco3 Parallel manifold - 2 eco3 Gold VH1 G1500_05e with membrane =

1645 gallons

Figure 1 is a graph showing flow rate on the horizontal axis and total gallons of throughput on the vertical axis.

The graph shows the improvement compared with a standard non pre-filtered eco3 VH1 G1500_05e, which is as follows:

• eco3 Parallel Manifold fitted with 2 VH1 G1500_05e with membrane shows a 1554 gallon and 22 fold improvement

• eco3 VH1 G1500_05e with membrane shows a 669 gallon and almost a 10 fold improvement

• eco3 Series Manifold with a separate pre-filter and VH1 G1500_05e with membrane offers a 572 gallon and an 8 fold improvement

Thus, the new eco3 plus membrane shows an extended performance up to 739 gallons. The new eco3 Parallel Manifold shows significant further extended performance. The OCS2 shows a flat line and output performance in the second half of life

Figure 2 is a bar chart showing the gallons capacity. It shows the volumes in gallons of water recorded for each filter variant tested. The standard eco3 product without any pre-filtration produced a very low output figure of less than 100 gallons. The Everpure OCS2 product produced an output of 439 gallons. The eco3 sequential manifold system produced an output of 672 gallons. The new eco3 filter with membrane produced an output of 739 gallons. The eco3 parallel manifold system produced an output of 1650 gallons.

Figure 3 is similar to Figure 1 except that it shows less data, to highlight the improvement provided to an eco 3 filter by using a membrane pre-filter of the present invention around said eco 3 filter. The standard eco3 product without any pre-filtration produces a very low output figure of less than 100 gallons. The new eco3 filter with membrane produces an output of 739 gallons. The eco3 parallel manifold system produces an output of 1650 gallons.

Example - manufacture of radial torque membrane filter

Apparatus may apply the membrane from a roll, for example a 500m roll, enabling continuous feed. Alternatively membrane can be fed into a slightly different designed machine as pre-cut sections. Multiple membranes could also be fed on similar designed machine. Membrane may be cut at a set length.

The apparatus allows automatic gluing of both outer edges and the last edge of wrap.

The required pressure (torque) at the point of wrapping to the inner media (e.g. carbon block) may be set via sprung loaded rollers. By the nature of the process and the thickness of the membrane each full rotation applies additional pressure (torque) to the membrane. This could also be applied via small stepper motors where varying torque is required.

As more pressure is applied, the film is stretched and the pore size increases.

The media (e.g. carbon block) may be automatically fed into a top holding roller and located on the central axis, and a compressive pad may be used to drive the media (carbon block) which will always override the torque pressure on the membrane rollers.

Once the membrane is completely wrapped and glued to seal the top and bottom radial surface and the final edge on the membrane it is ejected from the machine The machine controls not only the pressure and torque to the membrane but also its position on the media (carbon block).

The design of the machine utilizes bespoke control software to allow full flexibility in terms of setting the length of the membrane, glue application, cutting, feeding and rolling. The media (carbon block) diameter can also be varied along with the width of the membrane itself.

Some specific details of possible materials, methods and apparatus are as follows, though it will be understood that these may be varied.

The membrane component is an FDA hot melt blown polypropylene material adhered to a perforated polystyrene carrier. The percentage flow through the membrane is dependent upon the density of the polypropylene and the perforation area of the polystyrene carrier. Similar type of materials are used in air filtration. The density may be specified and measured as a high specification air filtration membrane, having a particular flow through the unit at a specific rate when feeding air at a specific surface area. The media / carbon block is about 38mm in diameter, although other diameters are suitable, e.g. about 80mm diameter locks in larger capacity applications.

The membrane is about 1000mm in length and about 140mm wide, the thickness is 0.5- 0.6mm and the density is 100g/ m ² .

Other details of the membrane:

Specific air flow details: 32 Lpm in

Pressure drop on 5.33cm ² : >90%

Resistance mm H ₂ 0: 3.8-4.2.

On a larger capacity carbon block the membrane could be increased depending on the specific filtration requirement.

The apparatus locates a roll of membrane and auto-feeds to a positioning conveyor, this allows the membrane to be cut and the adhesive applied in tolerance, controlled via software.

The membrane is attached to the carbon block and tightly wound around its circumference. The machine design gradually reduces the tightness (radial torque) on each circumference wrapped. In this example the total number of layers of membrane is about 7-8. To prevent any water ^' bleed ¹ through the top & bottom cylindrical surface (ie the 7-8 edges of the membrane radially) a hot melt adhesive (FDA grade) is automatically applied to both linear edges. The adhesive volume, position & temperature are all automatically controlled. The final application of hot melt adhesive is again automatically applied and controlled by the machine - this is on the final open radial end of the membrane. The rotation and torque of the machine again controls the adhesive performance.

The carbon block is manually loaded to a feeder where the machine will accept and position one block per cycle onto the centre location spindle, whilst the drive is applied via a compressive pad to the end face of the block. The membrane with the applied adhesive is then automatically fed to the rollers rotating under torque pressure onto the block. An alternative design on this station would use stepper motors to lift / lower the bottom roller on ever circumferential rotation.

Once the full 1000mm membrane is applied the complete unit is ejected automatically into a packaging tray.

The media and membrane are then fed into a filter assembly line to produce the finished filter cartridge.

Batch sample testing from production defines the required flow rate through the finished membrane and block assembly. Further particulate testing on a test jig defines the sediment loading capacity. The flow rate in the finished product may be approximately 0.55 gph at 45 psi incoming water pressure.