METHOD AND INSTALLATION FOR CLEANING A FILTER MATERIAL

Abstract

A method for cleaning at least one filter material, in particular a filter material used in the production of a respiratory protection mask (M), comprising the step of subjecting this filter material to a supercritical fluid, preferably supercritical CO.sub.2, with a density of less than 0.3 g/ml.

Claims

1.-18. (canceled)

19. A method of cleaning at least one filter material comprising subjecting the filter material to a supercritical fluid of a mass per unit volume less than 0.3 g/mL.

20. The method as claimed in claim 19, wherein the supercritical fluid is supercritical CO.sub.2.

21. The method as claimed in claim 19, wherein the supercritical fluid has a mass per unit volume less than or equal to 0.2.

22. The method of claim 21, wherein the supercritical fluid has a mass per unit volume less than or equal to 0.16 g/mL.

23. The method as claimed in claim 19, wherein the temperature of the supercritical fluid is less than or equal to 130° C.

24. The method of claim 23, wherein the temperature of the supercritical fluid is between 50° C. and 130° C. inclusive.

25. The method of claim 23, wherein the temperature of the supercritical fluid is between 70° C. and 100° C. inclusive.

26. The method as claimed in claim 19, wherein the pressure of the supercritical fluid is between 75 and 100 bar inclusive.

27. The method as claimed in claim 19, wherein the filter material is exposed to a mixture of the supercritical fluid and at least one additional biocidal compound.

28. The method as claimed in claim 27, wherein the total content of the additional biocidal compounds is less than or equal to 2 mole % relative to the total number of moles in the mixture.

29. The method as claimed in claim 27, wherein the additional biocidal compounds are chosen from oxidants and acids and mixtures thereof.

30. The method as claimed in claim 27, wherein the mixture includes water and at least one organic co-solvent chosen from carbon chain alcohols with three carbon atoms or fewer, carboxylic acids with three carbon atoms of or fewer, solutions of polyethylene glycol (PEG) having a molecular mass less than 200 g.Math.mol.sup.−1, acetone, dimethylsulfoxide (DMSO), and mixtures thereof.

31. The method as claim in claim 30, wherein the total content of co-solvent(s) is less than or equal to 1.5 mole % relative to the total number of moles in the mixture.

32. The method as claimed in claim 19, wherein the filter material is exposed to the supercritical fluid without mechanical agitation produced by stirring, by ultrasound or by imparting movement to the filter material.

33. The method as claimed in claim 19, wherein the filter material is exposed to expansion of the supercritical fluid at an expansion rate between 60 bar/min et 80 bar/min inclusive.

34. The method of claim 33, wherein the filter material is exposed to expansion of the supercritical fluid with at least one decompression stage.

35. The method as claimed in claim 19, including a step of counting the number of cleaning cycles to which the filter material has been subjected.

36. The method as claimed in claim 19, wherein the filter material or the mask which is made of it carrying a visual indicator the color of which pales as the cleaning cycles proceed, the method including a step of verifying that the indicator is colored to more than a certain degree before allowing reuse of the filter material.

37. The method as claimed in claim 19, applied to the cleaning of masks of FFP2 or FFP3 type.

38. The method as claimed in claim 19, applied to cleaning polypropylene fiber-based meltblown type non-woven fabric.

39. An installation for the execution of the method as defined in claim 1, including an enclosure in which the filter material or the mask or masks to be cleaned is or are placed and means for injecting into the enclosure the supercritical fluid and any other compound(s) in order to expose the filter material or the masks to a supercritical fluid having a mass per unit volume less than 0.3 g/mL.

40. A respiratory protection mask reusable after cleaning, including a non-woven fabric, including a colored indicator adapted to become progressively discolored in each cleaning cycle using the supercritical fluid, in particular the supercritical CO.sub.2, during use of the method as defined in claim 1, and to reach a predefined degree of discoloration when the mask is no longer conform.

41. A respiratory protection mask reusable after cleaning, including a non-woven fabric, and an identifier enabling tracking of the cleaning thereof using the method as claimed in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The invention may be better understood upon reading the following detailed description of non-limiting embodiments thereof and examining the appended drawings, in which:

[0045] FIG. 1 is a T/P state diagram illustrating conditions of temperature and of pressure suitable for use of the method according to the invention employing a mass per unit volume of 0.15 g/mL,

[0046] FIG. 2 represents results of comparative tests using different masses per unit volume of supercritical CO.sub.2,

[0047] FIG. 3 represents in a simplified and schematic manner a treatment installation according to the invention,

[0048] FIG. 4 represents an example of a reusable mask carrying a colored indicator, and

[0049] FIG. 5 represents an example of a reusable mask carrying an identifier.

DETAILED DESCRIPTION

[0050] In accordance with the invention, cleaning by the supercritical fluid is carried out under conditions assuring a mass per unit volume thereof less than 0.3 g/mL and preferably close to 0.15 g/mL. The supercritical fluid is preferably supercritical CO.sub.2.

[0051] There has been represented in FIG. 1 a diagram showing the evolution of the T/P pair for obtaining supercritical CO.sub.2 with a mass per unit volume equal to 0.15 g/mL.

[0052] It is seen that different temperature and pressure pairs may be used to obtain this mass per unit volume of 0.15 g/mL, for example 75 bar and 70° C. or 80 bar and 95° C. Under these conditions the filtration properties of masks of FFP2 or FFP3 type are preserved, in particular those of masks including a polypropylene fiber meltblown type non-woven fabric.

[0053] There have been represented in FIG. 2 results of comparative tests showing that for masses per unit volume greater than or equal to 0.35 g/mL this is no longer the case. The curves represent the filtration efficacy as a function of the electron mobility diameter in millimeters. In these tests the masks are treated for one hour with supercritical CO.sub.2 and the rate of expansion at the end of the treatment is 70 bar/min. The masks that were the subject matter of these tests are Kolmi OpAirPro Oxyge FFP2 type masks.

[0054] It is seen in FIG. 2 that the filtration efficacy remains substantially the same as that of the original mask for the masks subjected to supercritical CO.sub.2 with a mass per unit volume equal to 0.15 g/mL, whereas this is not the case in the tests in which the masks were subjected to masses per unit volume of 0.35, 0.45 or 0.65 g/mL.

[0055] In fact, for a given temperature, the tests show that the filtration efficacy decreases the higher the pressure and thus the mass per unit volume and that the filtration properties are preserved if the pressure is chosen so as to obtain supercritical CO.sub.2 with a mass per unit volume equal to 0.15 g/mL (see tests at 70° C. and 75/140/200 bar and tests at 95° C. and 80/150 bar).

[0056] Thus the invention enables the reuse of treated masks of FFP2 or FFP3 type. In fact, the invention makes it possible to clean the masks whilst preserving their filtration properties, that is to say preserving both their mechanical barrier, i.e. the fibrous structure, and their electrostatic barrier, i.e. the presence of surface electrical charge.

[0057] To reinforce the biocidal character of the treatment, at least one biocidal compound, for example oxygenated water, is advantageously added to the supercritical CO.sub.2.

[0058] Given that water is weakly soluble in supercritical CO.sub.2 an organic co-solvent, for example ethanol, having an affinity for water and CO.sub.2 is added.

[0059] Thus in embodiments of the invention the supercritical CO.sub.2 is mixed with alcohol and with oxygenated water at 30 wt % in water in the following proportions: [0060] Supercritical CO.sub.2: 300 mL [0061] Oxygenated water 30 wt % in water: 0.25 mL [0062] Ethanol: 0.25 mL

[0063] Tests have shown that treatment using a mixture of this kind had a biocidal activity, including against highly-resistant germs such as spores of Geobacillus stearothermophilus.

[0064] Likewise, tests with blood spots of animal origin on the masks show that the method has good cleaning action for this kind of soiling.

[0065] The inventors have found that carrying out expansion at a certain rate, not too low, nor too high, leads to the best results where the removal of soiling is concerned, whilst avoiding the use of any mechanical agitation, as emerges from table 1 below.

TABLE-US-00001 TABLE 1 Comparison of the effects of treatment with supercritical CO.sub.2 on agitation in the reactor and cleaning of soiling on masks (visual observation) as a function of the treatment rate: ±, low effectiveness; +, moderate effectiveness; +++ very effectiveness/performance Agitation in the reactor Cleaning of soiling Slow expansion + ± ~30 bar.min.sup.−1 Fast expansion +++ +++ ~70 bar.min.sup.−1

[0066] It is seen in table 1 that the expansion rate is therefore preferably between 60 and 80 bar/min inclusive. An expansion rate of this kind makes it possible to create agitation and therefore significantly to improve the removal of soiling. It is therefore possible not to use mechanical agitation, for example by rotation of the treatment enclosure, since it is the expansion that creates the agitation.

[0067] The expansion is preferably effected with at least one stage at substantially P.sub.0/2, P.sub.0 designating the pressure during treatment. The P.sub.0/2 stage may in itself be relatively short, for example of the order of a few seconds.

[0068] The method may be carried out in an installation 1 as represented schematically in FIG. 3.

[0069] The installation 1 includes a treatment enclosure 10, for example of the autoclave type, in which the mask or masks M to be treated is or are placed.

[0070] Supercritical CO.sub.2 may be injected by means of a pump 11 connected to a reservoir 12 storing CO.sub.2.

[0071] Additional compounds contained in at least one reservoir 18 may be introduced into the enclosure 10 by any appropriate means, for example by means of a pump 13.

[0072] The installation advantageously includes a programmable pressure and temperature regulator enabling a predefined temperature and pressure cycle to be tracked.

[0073] The supercritical CO.sub.2 is expanded via a separator 14 enabling recovery of the CO.sub.2 without the additional compounds, which may be contaminated, and which may be evacuated at 16 to any appropriate recovery means.

[0074] The gaseous CO.sub.2 at the outlet of the separator 14 may be fed into a filter 15, for example an activated carbon filter, before being stored in the reservoir 12 for subsequent reuse.

[0075] The enclosure 10 may have no mechanical agitator and the masks M may remain immobile inside it during the treatment.

[0076] Tracking of the number of cleaning cycles that the same mask has undergone is preferably provided.

[0077] One way of providing this tracking is to provide the mask with a colored indicator 20 as illustrated in FIG. 4, produced so as to lose only part of its color on each cleaning cycle. Thus the choice may be made to produce this mark using an ink the solubility of which in supercritical CO.sub.2 is known and enables it to resist a little on each cleaning cycle.

[0078] The mark may be produced so that its erasure substantially coincides with the maximum number of washing cycles that is authorized for the mask.

[0079] As illustrated in FIG. 5 the mask may likewise be provided with an identifier 21, for example a bar code or QR code, or an RFID chip, for supplying a database with information as to the number of cleaning cycles to which the mask has been subjected and thus to be sure that a given mask has not undergone too high a number of cleanings.

[0080] The presence of an identifier may if appropriate enable the cleaned mask to be redistributed to the same user.

[0081] If a plurality of masks are repackaged together, the repackaged masks have preferably undergone the same number of cleaning cycles.

[0082] Of course, the invention is not limited to the examples that have just been described.

[0083] For example, although the invention applies in particular to masks of FFP2 or FFP3 type, it may equally be applied to surgical type masks including a meltblown type non-woven fabric, in particular one based on polypropylene fibers, for example Spunbond-Meltblown-Spunbond (SMS) surgical masks.

[0084] The treated masks may be equipped with valves or not.

[0085] The invention applies equally to cleaning filter materials in disk form, for example, intended to be removably mounted in corresponding housings on shells of plastic material masks.

[0086] The supercritical fluid may be other than supercritical CO.sub.2, for example nitrogen protoxide N.sub.2O which has similar characteristics, or a mixture of CO.sub.2 and N.sub.2O.

[0087] If necessary, the masks or the filter material may after cleaning be subjected to any additional treatment aiming to reinforce its filter properties.

[0088] If necessary, other compounds, in particular biocides, may be added to the supercritical fluid.

[0089] The cleaned masks may be repackaged, in particular in a plastic material sachet or cardboard box.