IMPROVEMENTS IN OR RELATING TO FILTERS

Abstract

A removable filter is provided. The filter comprises a porous substrate; and an anti-pathogenic coating provided on at least part of the porous substrate. The concentration of the coating varies across the substrate to provide a coating pattern.

Claims

1. A removable filter comprising: a porous substrate; and an anti-pathogenic coating provided on at least part of the porous substrate wherein the concentration of the coating varies across the substrate to provide a coating pattern.

2. The filter according to claim 1, wherein the coating is an anti-viral coating.

3. The filter according to claim 1 or claim 2, wherein the coating is an antibacterial coating.

4. The filter according to any one of the preceding claims, wherein the coating pattern is a 2-dimensional coating pattern.

5. The filter according to any one of the preceding claims, wherein the concentration of the coating is higher in the centre of the substrate than at the edges.

6. The filter according to any one of the preceding claims, wherein the coating is provided on less than 90% of the substrate.

7. The filter according to any one of the preceding claims, wherein the porosity of the substrate with the coating is substantially the same as the porosity of the substrate without the coating.

8. The filter according to any one of the preceding claims, wherein the quantity of coating applied to the substrate is equal to or below the saturated absorbance capacity of the substrate.

9. The filter according to any one of the preceding claims, wherein the substrate is made up of more than one layer and the coating penetrates only one layer.

10. The filter according to any one of the preceding claims, wherein the substrate has a predetermined thickness and the coating penetrates less than 50% of the thickness of the substrate.

11. The filter according to any one of the preceding claims, wherein the substrate has a predetermined thickness and the coating penetrates less than 5% of the thickness of the substrate.

12. The filter according to any one of the preceding claims, wherein the porous substrate has a front face and a reverse face and wherein the coating is provided to both the front face and the reverse face.

13. The filter according to claim 12, wherein the coating pattern is different on the front face from the reverse face.

14. The filter according to any one of the preceding claims, wherein the coating further comprises a dye.

15. The filter according to any one of the preceding claims, wherein the filter further comprises an indicator mark.

16. The filter according to claim 15, wherein the indicator mark is provided using a security ink.

17. The filter according to claim 15 or claim 16, wherein the indicator mark confirms the integrity of the filter.

18. A face mask comprising at least one layer including a pocket for a filter according to any one of claims 1 to 17.

19. The face mask according to claim 18, wherein the mask comprises multiple layers, one of which includes the pocket for the filter.

20. The face mask according to claim 18 or claim 19, further comprising fixings to attach the mask to the user.

21. The face mask according to claim 20, wherein the fixings are configured to attach to the user's ears.

22. The face mask according to claim 20, wherein the fixings are configured to attach around the user's head.

23. The face mask according to any one of claims 18 to 22, further comprising a nose clip.

24. An air purification device comprising at least one filter according to any one of claims 1 to 17.

25. A method of manufacturing a filter according to any one of claims 1 to 17, the method comprising the steps of: providing a roll of substrate material on a vacuum conveyor belt, providing a coating to at least part of the substrate using an array of digitally controlled nozzle dispensers, cutting the roll of substrate into individual filters according to any one of claims 1 to 17.

26. The method according to claim 25, wherein the step of providing a coating comprises the sub-steps of: atomising the coating fluid using an 2D array of nozzles to generate a pattern, directing the flow of atomised droplets into the substrate with an applied airflow to control the 3D distribution, drying or fixing the chemistry to provide a homogeneous coating that minimally affects the pore structure of the filter material.

27. The method according to claim 25 or claim 26, wherein the step of cutting the roll of substrate precedes the step of applying the coating.

28. The method according to claim 25 or claim 26, wherein the step of cutting the roll of substrate follows the step of applying the coating.

29. The method according to any one of claims 25 to 28, further comprising the step of providing an indicator mark using a further array of digitally controlled nozzle dispensers.

Description

[0056] The present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

[0057] FIG. 1 shows a filter according to the present invention;

[0058] FIG. 2 shows a mask comprising the filter of FIG. 1;

[0059] FIG. 3 is a schematic of the 3D coating of the filter of FIG. 1;

[0060] FIG. 4 is a side view of an apparatus for manufacturing filters of FIG. 1; and

[0061] FIG. 5 is a part perspective view of an alternative apparatus for manufacturing filters of FIG. 1.

[0062] FIG. 1 shows a filter 10 which includes a porous substrate 12 and an anti-pathogenic coating 14 applied over at least part of the surface. In the illustrated example the coating 14 is applied over the majority of the filter 10, the only exception being the edges of the filter. There is an area 16 that is central between the left and right sides and extends substantially across the full height of the coated area that has a higher concentration of coating material. This area is selected as it is the part of the filter 10 that will experience the highest air flow, in use. It is therefore the area where pathogens are most likely to contact and therefore the area where the anti-pathogenic coating is most needed.

[0063] The substrate 12 is a multilayer substrate that is made up of four layers. In other examples, there may be 2, 3, 5, 6, 7, 8 or more layers. The substrate 12 has a reverse face (shown in FIG. 1) and a front face (not shown). The front face, which faces the world, in use, is more likely to have a homogenous coating, rather than the concentration gradient shown for the reverse face in FIG. 1.

[0064] The coating 14 includes a dye so that there is a witness to the location and configuration of the coating on each side of the filter 10. The darker the dye, the higher the concentration both of dye particles and anti-pathogenic coating. This provides the user with an intuitive indication as to the correct orientation of the filter within a mask as the high concentration area needs to be adjacent to the nose and mouth of the user.

[0065] The filter 10 also includes an indicator mark 18. In the illustrated example, the indicator mark 18 is a text mark that reads “replace filter” and this mark will only become visible when the coating 14 has expired or been compromised. In other examples, not shown in FIG. 1, the indicator mark can be a trade mark or other branding logo printed in security ink to reassure the user that the filter 10 is a genuine product provided by the brand holder.

[0066] FIG. 2 shows a mask 20 having one or more layers of fabric 22; one or more fixings 24 and a pocket 26 into which the filter 10 is inserted. The filter 10 shown in FIG. 2 is shaped to conform to the mask 20 rather than being a simple rectangle as shown in FIG. 1. The filter 10 can take any suitable shape and the level of conformity to the mask 20 will depend on how customised the filter 10 is to a particular mask or, conversely, how universally applicable the filter 10 may be. The mask 20 of FIG. 2 has three layers, one of which includes the pocket 26. The fixings 24 are ear loops and are elastic so that they stretch around the user's ears. However, in other examples, not shown in the accompanying drawings, the fixings may be elastic loops to go around the head of the user. The mask 20 also includes a nose clip 28 which, in the illustrated example is a wire to aid the close conformance of the mask 20 to the user's face to ensure that air does not flow around the mask and into the user's mouth and nose, but rather the air preferentially flows through the filter 10. The nose clip 28 may not be required, depending on the selection of the material from which the mask 20 is formed and on the shaping of the layers of fabric and the type of fixing selected.

[0067] FIG. 3 shows an apparatus 30 for providing the three-dimensional control of the application of a coating 14 to a porous substrate 12. The coating fluid is provided in a header tank 31. The coating fluid 33 comprises an anti-pathogenic chemistry and a carrier. The carrier may be water, a solvent or a hot melt. Coating of the filter 10 is achieved by utilising an array 32 comprising a plurality of individually addressable spray nozzles 34 that can be turned on and off by digital data to coat a digitally-defined image or pattern. The nozzles 34 are actuated by an array of piezoelectric actuators 36 with one piezoelectric actuator being provided to each spray nozzle 34. The actuation of the piezoelectric actuators 36 results in the issuance of an atomised fluid spray 39 of the coating material onto the filter 10. As the filter 10 moves in the direction A indicated in FIG. 2, this enables 2D control of the applied pattern at up to 50 dots per inch resolution, i.e. with a resolution between 5 mm and 0.5 mm.

[0068] Beneath the filter 10 there is provided a vacuum pump 38 which controls the level of penetration of the coating material into the filter 10. The penetration of the coating into the fabric is controlled by airflow through the substrate, which is applied by an under-web vacuum, which determines the depth of penetration of the coating. By combining two-dimensional patterning with control over the coating penetration, it is possible to precisely deposit the coating to substantially eliminate any pore filling and deliver the coating dose required to coat the fibres only with 3D control over coating placement.

[0069] FIG. 4 shows a configuration where the filters 10 are cut from a roll of porous substrate before they are printed with the coating material. The vacuum pump 38 is situated within a vacuum conveyor belt 40 which holds the filters 10 firmly in place whilst they are coated. The vacuum conveyor belt 40 is configured to move the filters 10 from left to right in the illustration. The apparatus 30 includes a control system (not shown) which instructs the piezoelectric actuators 36 to turn on and off as each filter 10 is positioned for coating. This ensures that there is no wastage of the coating fluid 33 as the piezoelectric actuators are only active when a filter 10 is present and therefore the volume of coating fluid 33 used is minimised.

[0070] The coating application method utilises the capability to print two-dimensional patterns and is uniquely suitable for coating discrete substrate ports, such as filters for facemasks or elements of a filter cartridge. These discrete elements can be presented to the coating system on a transport system such as a conveyer belt 40, which presents the parts to the coating system. The coating system can be switched on and off using a stream of digital data from the line. The coatings can be applied to pre-defined areas based a digital image.

[0071] FIG. 5 shows an alternative configuration in which the roll of porous material is provided prior to cutting into filters 10. The coating is applied in discrete shapes and the cutting follows the printing. Again, as with the configuration shown in FIG. 4, there is no wastage of coating fluid 33 because the piezoelectric actuators are controlled only to dispense in the areas where the coating is desired.

[0072] In conjunction with the examples of FIGS. 4 or 5, there may be further provided a separate array of individually addressable spray nozzles that can print an indicator mark. This can be one or more of a quality assurance mark such as a branding logo or trade mark shown in security ink to assure the user that the product is genuine. Alternatively or additionally the indicator mark can be a usage mark that indicates when the anti-pathogenic materials in the coating have expired or been compromised.

[0073] The array of flow channel dispensers disclosed herein, which are based on those configured in the printhead disclosed in WO 2017/187153, are particularly suited to the present method. The array has the features of a digitally controllable fluid flow both in the conveyance direction and cross direction, highly accurate deposition, high cross-web homogeneity, the possibility of instant image changeovers due to the digital control of the elements, and a high droplet velocity of greater than 5 ms.sup.−1 to ensure penetration into the textile and with the addition of a parallel airflow applied below or above the substrate but without further adsorption encouraging steps.

[0074] A key application for this invention is in the coating of facemask filters for reduction of human-to-human pathogen transmission. The application of anti-pathogen chemistry to filters within facemasks has the potential to reduce the transmission to the user, when handling the facemask or breathing through the facemask in the case where it has been contaminated by a pathogenic microorganism or virus. Examples of the pathogens, which may be present include: [0075] 1. Streptococcus pneumoniae, [0076] 2. Haemophilus influenzae, [0077] 3. Staphylococcus aureus, [0078] 4. Moraxella catarrhalis) and seven common respiratory viruses [0079] 5. Rhinoviruses (hRV), [0080] 6. Respiratory syncytial virus (RSV), [0081] 7. Adenoviruses (AdV), [0082] 8. Coronavirus (CoV), [0083] 9. Influenza viruses (IV), [0084] 10. Para-influenza viruses (PIV), [0085] 11. Human metapneumovirus (hMPV))

[0086] This invention is designed to enable the industrial production of anti-viral chemistry coated facemask filters based on several unique aspects to the technology: [0087] 1. Capability to 2D pattern, depositing the chemistry on a discrete substrate item [0088] 2. Capability to control penetration of the coating into the substrate using airflow [0089] 3. Capability to coat the chemistry with very low level of pore filling due to the distribution of liquid within the filter structure [0090] 4. Capability to deposit the coating onto one or two sides of the substrate.

[0091] Furthermore, it has been found that this method of coating application, wherein the coating is finely dispersed over the surface structures of the filter membrane materials results in coatings that are more effective on a mass basis. This enables less coating to be applied to deliver the same level of biological activity.

Example 1

[0092] Deposition of silver containing aqueous chemistry onto a four-layer facemask filter. The silver containing coating chemistry is applied as a water-based suspension at 10 wt % to a four-layer PM2.5 (2.5 micron) filter using the digital spray array. An airflow of ˜10 m/sec is applied to the underside of the filter using a vacuum conveyer belt and the coating is dispensed in a 2D pattern that matches the shape of the filter. The airflow is selected to localise the coating on the top layer of the four-layer filter, maximising the concentration of the coating in the layer that will be in contact with airborne pathogens entering a facemask from outside.

[0093] The coated filter was tested for antibacterial efficacy of the filter was tested according to ISO 20743:2013 and it was found that >99.9% of test bacteria (Bacterium: Staphylococcus aureus) (ATCC6538P) were inactivated by the material. The test result indicated that the biological activity of the coating applied using the method according to the invention is more effective than when the coating is applied using traditional coating techniques.

[0094] Various further aspects and embodiments of the present invention will be apparent to those skilled in the art in view of the present disclosure.

[0095] “and/or” where used herein is to be taken as specific disclosure of each of the two specified features or components with or without the other. For example “A and/or B” is to be taken as specific disclosure of each of (i) A, (ii) B and (iii) A and B, just as if each is set out individually herein.

[0096] Unless context dictates otherwise, the descriptions and definitions of the features set out above are not limited to any particular aspect or embodiment of the invention and apply equally to all aspects and embodiments which are described.

[0097] It will further be appreciated by those skilled in the art that although the invention has been described by way of example with reference to several embodiments, it is not limited to the disclosed embodiments and that alternative embodiments could be constructed without departing from the scope of the invention as defined in the appended claims.