Technical Field

This invention concerns filter walls made of non-woven fabric in turn made of polymer fibres.

More in detail, the invention concerns filter walls used to filter engine fluids such as for example fuel (diesel, petrol, LPG, methane), lubrication oils or comburent air.

Background Art

In the sector of engine fluid filtering, filter walls are used made of non-woven fabric made of polymer fibres. These filter walls are often made with a toroidal, or to be more precise, a tubular shape, using production processes such as for example the melt-blown, the spunbond or the electrospinning processes.

The opposite ends of these tubular-shaped filter walls are then fixed to respective support plates, which retain the filter wall in such a way that together they form a replaceable cartridge which can be fitted inside a filter housing.

To ensure that the filter wall possesses greater rigidity and mechanical resistance, the cartridge sometimes also comprises a perforated support tube, usually referred to as a core, which is inserted outside or inside the tubular filter wall, depending on whether the fluid flows through the wall from the inside towards the outside, or from the outside towards the inside, respectively.

In this way, the support core prevents the filter wall being deformed by fluid pressure peaks, vibrations, shocks and other stresses and strains.

To avoid the need for a support core, self-supporting tubular filter walls have been proposed.

A filter wall of this type generally comprises various concentric layers of non- woven fabric of polymer fibres, which can be made from different types of polymer and/or different fibre diameters and/or with different porosities, in such a way that at least one of the layers exhibits sufficiently high mechanical resistance properties to be able to support the other layers of the filter wall. In particular, these layers can be obtained with a melt-blown process using an apparatus comprising a plurality of devices which emit polymer filaments towards a single rotating collector shaft, the devices being arranged in line along a direction which is parallel to the axis of the collector shaft.

In this way, the first device produces a first cylindrical layer of non-woven fabric of polymer fibres around the collector shaft, which layer is then made to advance axially along the collector shaft, such that the subsequent devices can create further respective concentric layers of non-woven fabric of polymer fibres around the first layer.

By establishing the operating parameters and the polymer used in each of the devices independently, it is possible to obtain a filter wall consisting of concentric layers exhibiting different characteristics.

In an improved form of this process, a roller is used to calender the polymer fibres of the first tubular layer which is deposited on the collector shaft.

The result of this solution is a filter wall an inner layer of compressed fibres of which is significantly more rigid than the other layers, thus supporting the entire filter wall.

However, both the above-mentioned solutions have the drawback that the rigidity and the mechanical resistance of these multilayer walls do not compare with those of filter walls with a support core.

Disclosure of Invention

An aim of an embodiment of this invention is to improve known multilayer walls, in such a way as to obtain rigidity and mechanical resistance properties which are more similar to those obtainable using a support core. A further aim is to achieve this aim within a simple, rational and relatively inexpensive solution.

These aims are achieved by the characteristics of the embodiments of the invention disclosed in the independent claims. The dependent claims delineate preferred and/or particularly advantageous aspects of other embodiments of the invention. An embodiment of the invention provides a filter wall comprising at least two layers of non-woven fabric of polymer fibres. One of the two layers of non- woven fabric of polymer fibres contains nanoparticles, while one layer of non- woven fabric of polymer fibres is without nanoparticles, wherein the later of non-woven tissue of polymer fibres lacking in nanoparticles is at least partially covered with the layer of non-woven fabric of polymer fibres containing nanoparticies, and wherein the layer of non-woven fabric of polymer fibres containing nanoparticles has a greater porosity and a smaller thickness than that of the layer of non-woven fabric of polymer fibres without nanoparticles.

The expression "layer of non-woven fabric of polymer fibres containing nanoparticles" is generally taken as meaning a layer of non-woven fabric, the fibres of which comprise a polymer matrix containing nanoparticles.

These fibres can be obtained for example by means of an extrusion process: they can for example be melt-blown, spunbond or electrospun, starting from a polymer compound or mixture to which nanoparticles have been added beforehand.

The term "nanoparticles" generally indicates solid particles the size of which is measured in the order of magnitude of nanometres. Nanoparticles can have various regular or irregular shapes, including for example spheroidal, fibrous, polyhedral or flattened etc.

In an aspect of the invention, the nanoparticles comprise clay nanoparticles, also known as nanoclays.

Nanoclays can either be of natural origin, such as for example nanoparticles of kaolin talc, bentonite, montmorillonite, or of synthetic origin, such as for example those marketed by Southern Clay Products, Inc. of Gonzales Texas under the trade mark Laponite®.

In a further aspect of the invention the nanoparticles can comprise nanoparticles based on metallic elements.

Nanoparticles based on metallic elements can be made of pure metals, such as for example aluminium nanoparticles, of metal oxides, such as alumina nanoparticles, or of metallic salts, such as for example calcium carbonate nanoparticles.

In a further aspect of the invention, the nanoparticles can comprise carbon- based nanoparticles.

Carbon-based nanoparticles can be formed from pure carbon, in one or more of its many allotropic forms, such as for example graphite, carbon oxides or other compounds.

The presence of a certain quantity of these nanoparticles in the polymer fibres of a layer of non-woven fabric advantageously enables the layer of non-woven fabric's mechanical resistance, resistance to abrasion, resistance to fire and elongation capacity to be improved.

However adding nanoparticles entails a significantly higher production cost than using exclusively polymer fibres.

Therefore the solution of the invention, whereby a filter wall is obtained comprising a layer of non-woven fabric of polymer fibres containing nanoparticles and a layer of non-woven fabric of polymer fibres without nanoparticles, advantageously makes it possible to obtain an overall more rigid and sturdy filter wall than the usual multilayer filter walls with no support core, yet without excessively affecting production costs.

In particular, since the layer containing nanoparticles possesses a greater porosity than the layer without nanoparticles, the nanoparticles are not able to obtain any further effect on the fluid which is filtered (for example antimicrobial, anti-bacterial or other), but have only the function of strengthening the relative layer of polymer fibres such that it can mechanically support the whole filter wall.

For this reason the layer with nanoparticles can be effectively realised with a smaller thickness with respect to the layer without nanoparticles, which provides the advantage of maintaining production costs at rather low levels. In other words, this solution enables the ultrafiltration function, performed mainly by the non-woven fabric lacking in nanoparticles, to be completely separated from the bearing function, mainly performed by the layer of non- woven fabric with nanoparticles, thus obtaining an effective saving in terms of costs.

In an aspect of the invention, the nanoparticles in the polymer fibres containing nanoparticles account for between 0.1 % and 5% of the weight of the fibres.

Thanks to this solution, the fibres exhibit particularly good mechanical properties.

This solution achieves an important advantage also from a production viewpoint, since the use of a larger quantity of nanoparticles would reduce the viscosity of the polymer compound so much as to prevent it from being spun using the previously-mentioned extrusion methods.

In another aspect of the invention, the polymer fibres of each layer of non- woven fabric can be made of a polymer chosen from among polyamide (for example nylon), polypropylene, and polyester.

These polymers have the advantages of being obtainable by means of a usual extrusion process, providing good filtering results, and being both easy to obtain and fairly inexpensive.

In a further aspect of the invention, the polymer fibres of the layer of non- woven fabric containing nanoparticles can be made of a polymer which is different from the polymer which constitutes the polymer fibres of the layer of non-woven polymer fibres without nanoparticles.

Thanks to this solution it is possible to use various polymer materials, thus exploiting the particular characteristics of each.

In an embodiment of the invention, the filter wall comprises a preferential direction of flow for the fluid to be filtered. With respect to this direction, the layer of non-woven fabric of polymer fibres containing nanoparticles is positioned upstream of the layer of non-woven fabric of polymer fibres without nanoparticles.

Although the invention does not exclude the possibility of an opposite arrangement, this embodiment has the advantage that the layer of non- woven fabric of polymer fibres containing nanoparticles can perform its support function effectively, since this layer consists of fibres which are in any case partially intertwined with the fibres of the layer which is situated downstream, and can further act as a prefilter, should it exhibit a porosity which, though greater with respect to that of the downstream layer, is sufficient to retain a determined quantity of relatively large particles.

In a further embodiment of the invention, the layer of non-woven fabric of polymer fibres without nanoparticles is interposed between two layers of non- woven fabric of polymer fibres containing nanoparticles.

Thanks to this solution, the filter wall is suitable for the fluid to flow through it in both directions, yet maintains good rigidity and mechanical resistance to fluid pressure peaks.

In a further embodiment of the invention, the layers of non-woven fabric have a tubular shape and are inserted one inside the other.

In this way, a filter wall is advantageously obtained, which overall exhibits the classic tubular form.

In an embodiment of the invention the filter wall is used to filter an engine fluid, such as for example fuel (diesel, petrol, LPG, methane), lubrication oil or comburent air.

The invention further makes available a filter comprising an outer casing provided with an inlet for a fluid to be filtered and an outlet for the filtered fluid, and a filter wall having the previously-delineated characteristics, which is arranged in such a way as to subdivide the inner volume of the outer casing into at least two chambers, of which one chamber communicates with the inlet of the fluid to be filtered, and the other chamber communicates with the filtered fluid outlet.

Further characteristics and advantages of the invention will emerge from the following description, with the aid of the appended figures of the drawings provided by way of a non-limiting example.

Brief description of the Drawings

Figure 1 schematically shows a section view of a filter for fluids of an embodiment of the invention, taken along the line l-l shown in figure 2.

Figure 2 is a section view along the line ll-ll shown in figure 1 . Figure 3 schematically shows a section view of a filter for fluids of a further embodiment of the invention, taken along the line Ill-Ill shown in figure 4. Figure 4 is a section view taken along the line IV-IV of figure 3.

Figure 5 schematically shows a section view of a filter for fluids in a further embodiment of the invention, taken along the line V-V shown in figure 6. Figure 6 is a section view along VI-VI of figure 5.

Figure 7 schematically shows an apparatus for obtaining a filter wall of the type which is mounted in the filter of figure 1 .

Figures 1 to 6 schematically illustrate a filter 10 for engine fluids, for example fuel (diesel, petrol, LPG, methane), lubrication oil or comburent air.

Best Mode for Carrying Out the Invention

The filter 10 is provided with an outer casing 1 1 , comprising a cup-shaped body 12 and a cover 13 which closes the mouth of the cup-shaped body 12. Two access conduits, 14 and 15 are afforded in the cover 13, for entry and exit of the fluid to be filtered.

A filter cartridge 16, comprising a filter wall 30 of toroidal, or more precisely cylindrical form, is mounted inside the outer casing 1 1 , the bases of which cylinder are fixed and closed by an upper support plate 17 and by a lower support plate 18 respectively.

While the lower plate 18 is completely closed, the upper plate 17 affords a central through hole 19 which communicates with the inner cavity of the cylindrical filter wall 30.

The through hole 19 is sealedly inserted onto a tang 20 of the cover 13, which tang 20 delimits a tract of the access conduit 14 and projects inside the casing 1 1.

In this way, the filter wall 30 subdivides the inner volume of the outer casing 1 1 into two distinct chambers, an inner chamber 21 which communicates with the access conduit 14, and an outer chamber 22 which communicates with the access conduit 15.

Consequently the fluid to be filtered is forced to flow through the wall 30 radially, i.e. in the direction of the thickness of its cylindrical wall. As regards the thickness of the cylindrical wall, the filter wall 30 comprises two filter layers with different characteristics, one being a layer 31 of non- woven fabric of polymer fibres containing nanoparticles, and the other being a layer 32 of non-woven fabric of polymer fibres without nanoparticles.

Thus both layers 31 and 32 are cylindrical in shape and arranged coaxially, one inside the other.

In this way, one of the cylindrical surfaces which delimit the thickness of the layer 32 is completely covered by the layer 31 and vice versa.

In detail, the polymer fibres of the layer 31 can be made with a polymer chosen from among polyamide (e.g. nylon), polypropylene and polyester. These polymer fibres contain a quantity of nanoparticles which preferably constitutes between 0.1 % and 5% of the total weight of the fibres.

Nanoparticles are generally defined as being solid particles the size of which is of the order of magnitude of nanometres. Nanoparticles can be of various shapes, both regular and irregular, including spheroidal, fibrous, polyhedral, flat and so on.

The nanoparticles of the layer 31 can comprise clay nanoparticles, also known as nanoclays. Nanoclays can be of natural origin, such as for example nanoparticles of kaolin talc, bentonite, montmorillonite, or of synthetic origin, such as for example those known under the trade mark Laponite® marketed by Southern Clay Products, Inc. of Gonzales, Texas.

The nanoparticles of the layer 31 can further comprise nanoparticles based on metallic elements, among which nanoparticles which are made from pure metals, such as for example aluminium nanoparticles, from metallic oxides, such as for example alumina nanoparticles, or from metallic salts, such as calcium carbonate nanoparticles.

The nanoparticles of the layer 31 can further comprise carbon-based nanoparticles, including nanoparticles made from pure carbon, in one or more of its various allotropes, such as for example graphite, carbon oxides or other compounds.

The presence of these nanoparticles in the polymer fibres endows the layer 31 with better chemical-physical characteristics than those in layer 32, in particular as regards mechanical resistance, resistance to abrasion, flame resistance and elongation capacity.

Thanks to these characteristics of the layer 31 , the filter wall 30 is overall sufficiently rigid and sturdy to be used in the filter 10, without the support of a conventional supporting core.

The layer 32 is significantly thicker than the layer 31 .

In this way, the filter wall 30 exhibits high overall filtering efficiency, while keeping production costs rather low, given that only the thinner layer 31 contains nanoparticles.

The polymer fibres of the layer 32 can be made with a polymer chosen from among polyamide (for example nylon), polypropylene and polyester.

These polymer fibres can be made of the same polymer with which the polymer fibres of the layer 31 are made, or can be made of a different polymer.

For example, layers 31 and 32 can both be made of nylon polymer fibres, with the fibres of the layer 31 also containing nanoparticles.

Alternatively, the layer 31 could be made of nylon fibres and nanoparticles, while the layer 32 could be made of fibres which are entirely of polyester. In the last above case, since polyester possesses hydrophobic properties, the layer 32 can act both as a filter for, and as a barrier against water.

The layer 32 could also be divided into a plurality of thinner layers of non- woven fabric of polymer fibres without nanoparticles, in which the fibres of each of the layers can be made of the same basic polymer or of different polymers.

In the embodiment shown in figures 1 and 2, the access conduit 14 acts as an inlet for the fluid to be filtered, while the access. conduit. 15 acts as an outlet for the filtered fluid, such that the direction of flow through the filter wall 30 is from the inner chamber 21 towards the outer chamber 22, as indicated by the arrows.

in this case, the layer 31 is preferably arranged inside the layer 32. In effect, the layer 31 is exposed to the inner chamber 21 while the layer 32 is exposed to the outer chamber 22, thus the layer 31 is arranged upstream of the layer 32 with respect to the flow direction through the filter.

In the embodiment shown in figures 3 and 4 however, the access conduit 14 acts as an outlet for the filtered fluid, while the access conduit 15 acts as an inlet for the fluid to be filtered, thus the flow direction through the filter wall 30 is from the outer chamber 22 towards the inner chamber 21 , as shown by the arrows.

In this case, the layer 31 is preferably arranged outside the layer 32.

In effect, the layer 31 is exposed to the outer chamber 22 while the layer 32 is exposed to the inner chamber 21 , thus the layer 31 is always arranged upstream of the layer 32 with respect to the direction of flow of the fluid.

The fact of arranging the layer 31 upstream from the layer 32 provides certain advantages.

In particular, the layer 31 can support the layer 32 effectively during fluid pressure peaks, or following vibrations, shocks or other similar stresses, since it consists of fibres that are in any case partially intertwined with those of the downstream layer 32.

Further, the layer 31 can act as a pre-filter, if its porosity, while higher than that of the layer 32, is sufficient to retain a predetermined quantity of relatively large particles.

In the embodiment shown in figures 5 and 6, the access conduits 14 and 15 can optionally act as either an inlet or an outlet for the fluid, thus the flow direction through the filter wall 30 can alternatively be from the outer chamber 22 towards the inner chamber 21 , or the opposite, from the inner chamber 21 towards the outer chamber 22.

In this case, the layer 32 of the filter wall 30 is preferably comprised between two layers 31 of non-woven fabric of polymer fibres containing nanoparticles. Thanks to this solution, the filter wall 30 is self-supporting both when the fluid flows in one direction and when it flows in an opposite direction. The previously-described filter walls 30 can be made using a continuous melt-blown process, which is obtained with an apparatus 40 of the type shown schematically in figure 7.

The apparatus 40 comprises a collector shaft 41 , which is activated to rotate about its longitudinal axis X by a suitable motor.

The apparatus 40 further comprises three filament-producing devices which are respectively indicated by reference numerals 43, 44, and 45, and arranged in line along a parallel direction to the longitudinal axis X of the collector shaft 41 .

Each filament-producing device 43-45 schematically comprises a tank for a polymer compound or paste in a fluid or semi-fluid state, and an extruder comprising one or more nozzles destined to act upon the polymer compound or paste in such a way as to subdivide the compound or paste into a plurality of thin filaments. Jets of hot air or hot gas are used to reduce the diameter of the fibres to micrometric dimensions, in such a way that the fibres can be deposited on the collector shaft 41 as the shaft 41 rotates.

In this way, the first device 43 realises a first cylindrical layer of non-woven fabric of polymer fibres around the collector shaft 41 , the layer then being made to advance axially along the collector shaft 4 , by means of suitable motorised advancement rollers 46, in order to enable the subsequent devices 44 and 45 to realise further respective concentric layers of non-woven fabric of polymer fibres around the first layer.

Consequently the layers obtained from devices 43-45 are not physically separated from each other, the fibres of each layer always being partially intertwined at the interface zone with those of the adjacent layer.

This process produces a single continuous cylindrical sleeve of multilayer non-woven fabric, which is then cut crossways into sections, each of which gives rise to a filter wall.

In the example shown in figure 7, the apparatus 40 is predisposed to make filter walls of the type illustrated in figures 1 and 2.

The first device 43 is therefore loaded with a polymer compound or paste, to which the desired quantity of nanoparticles is added, such as to obtain the layer 31 , while the subsequent devices 44 and 45 are loaded with a compound or polymer mixture lacking in nanoparticles, in such a way as to obtain overall the layer 32.

Obviously a person skilled in the art could introduce numerous technical- applicational modifications to the filter walls 30 described herein above, without thereby forsaking the ambit of the invention as claimed herein below.