The present invention relates to a serviceable part for an electrical appliance. Aspects of the invention relate to a serviceable part, a serviceable filter assembly and an electrical appliance. In particular, but not exclusively, the invention relates to a serviceable filter assembly for use in an electrical appliance, such as a vacuum cleaner.

A vacuum cleaning appliance or, more simply, “vacuum cleaner”, typically comprises a main body which is equipped with a suction motor, a dust separator, and a cleaner head connected to the dust separator usually by a separable coupling. The dust separator is the main mechanism by which the vacuum cleaner removes dirt and debris from the airflow through the machine, and this applies whether the dust separator relies on a cyclonic separation system or otherwise.

Although dust separators are generally very efficient at removing dirt and debris from the airflow, fine particles remain in the airflow that exits the dust separator and travels towards the suction motor. It is important that the suction motor is protected from these fine particles as they can be potentially damaging to some of its components. It is also important to make the exhaust airflow that is discharged from the vacuum cleaner as clean as possible. Thus, typically, a vacuum cleaner includes two filters: a first filter, also called a “pre-motor filter” or “pre- filter”, which is located in the airflow through the machine downstream of the dust separator but upstream of the suction motor; and a second filter, also called a “post-motor filter” or “post-filter”, that is located in the airflow downstream of the suction motor, before the airflow exhausts from the machine.

It is known to house the pre-motor filter medium in a filter assembly which can be removed easily by the user for cleaning purposes. Sometimes the pre-filter is mounted in a common unit with the post-filter. Regardless, once the filter assembly is removed from the appliance, the pre-filter can be washed, and dried, and then the filter assembly can be replaced in the appliance. It has been observed that dust and fine particulate matter which collects on the filter medium are difficult to wash off. This gives rise to a pressure drop across the filter medium which makes it harder for the air flow to be driven through the filter medium, in use, introducing inefficiency into the system. A further problem is that, when washed to remove the dust and fine particulate matter adequately, the filter medium can take a long time to dry thoroughly. This presents several problems. For example, the user is unable to use the device again until the filter medium has dried thoroughly, or, if used before the filter medium is fully dry, performance of the device may be affected and/or water ingress within the device may lead to water damage.

It is an object of the invention to address at least one of the aforementioned problems and improve the washability of the filter medium.

SUMMARY OF THE INVENTION.

According to a first aspect of the present invention there is provided a serviceable part for use in an electrical appliance, the serviceable part comprising a motor for generating an airflow through the appliance, in use, and a filter assembly for filtering dust and/or particulate matter from the airflow, wherein the filter assembly includes a membrane comprising a fibre structure of filter material which incorporates an omniphobic additive to alter an oil transfer characteristic of the membrane compared to a membrane comprising a fibre structure without the omniphobic additive.

The invention provides the advantage that the drying time of the filter assembly is noticeably reduced after washing compared to a conventional fitler assembly which does not have a fibre structure incorporating an omniphobic additive. The reduction in drying time means there is less device downtime for the user.

The fibre structure is preferably a non-woven fibre structure.

Also, the incorporation of the omniphobic additive within the fibre structure means that the washability of the filter assembly is improved. In other words, the filter assembly needs less regular washing to remove the dust from the membrane, which leads to less degradation of filter performance compared to conventional assemblies.

In one embodiment, the filter assembly is a post-filter for filtering dust and/or particulate matter from the airflow downstream of the motor.

The omniphobic additive is both hydrophobic and oleophobic.

By way of example, the omniphobic additive may be embedded within the fibre structure.

The fibre structure may be formed from a biodegradable material, providing longer term environmental benefits at the end of life of the filter assembly. Other features of the filter assembly may also be formed from a biodegradable material, such as the housing or casing.

The membrane may be formed from electrospun or force spun fibre material together with the omniphobic additive.

The membrane typically comprises a nanofibre structure comprising fibres of a fibre diameter between 50nm and 250nm, and preferably no more than 230nm.

The membrane typically comprises a nanofibre structure having a fibre density of between 1-3 grams per square metre, and typically approximately 2 grams per square metre (aerial density).

In one embodiment, the membrane is configured so that the mass of water that is retained on the membrane after a wash service is at least 40% reduced compared to an untreated membrane filter.

By way of example, the filter assembly is a cylindrical filter assembly in which the membrane forms a cylindrical structure. The filter assembly further includes a pre-fi Iter which is located upstream of the motor to filter the airflow before it passes through the motor. For example, the pre-filter and the post-filter may be located in the same serviceable unit.

The serviceable part may form part of a vacuum cleaner.

According to a second aspect of the invention, there is provided an electrical appliance comprising the serviceable part of the first aspect.

The electrical appliance may be a dust separation device forming part of a vacuum cleaner.

It will be appreciated that preferred and/or optional features of the first aspect of the invention may be incorporated alone or in appropriate combination in the second aspect of the invention also.

Brief Description of Drawings

The present invention will now be described, by way of example only, with reference to the following figures in which:

Figure 1 is a side view of a portable vacuum cleaner comprising a filter assembly of the present invention;

Figure 2 is a side view of a filter assembly for use in the vacuum cleaner in Figure 1 ;

Figure 3 is a schematic diagram of a known filter structure for use in the filter assembly in Figure 2;

Figure 4 is a schematic diagram of a filter structure of a first embodiment of the invention, for use in the filter assembly in Figure 2; Figures 5(a) and Figures 5(b) are schematic diagram to show the surface contact angle for a phobic material (e.g. hydrophobic or oleophobic) compared to a philic material (e.g. hydrophilic or oleophilic); and

Figure 6 is a graph showing the percentage increase in resistance of the post filter over a period of several months, and including an indication of the wash cycles required for a conventional filter structure shown in Figure 3 compared to a filter structure shown in Figure 4.

Detailed Description

Figure 1 shows a perspective view of a dust separation device, referred to generally as 10, with which a filter assembly 12 of an embodiment of the invention is used. The dust separation device 10 forms a part of a vacuum cleaner which includes, at one end of an elongated section (referred to as the wand), a cleaner head (not shown). The dust separation device 10 is located at the other end of the wand to the cleaner head. The dust separation device 10 connects to one end of a device housing 14 in a removable manner. The other end of the device housing 14 connects to the wand (not shown).

The dust separation device 10 includes the device housing 14 having a handle 16 for manipulation by the user. Typically, the handle 16 houses a battery pack inside one handle section 18 which may contain one or more replaceable or rechargeable batteries for powering the dust separation device 10. The device housing 14 houses various components of the dust separation device 10, as is known in the art, including a cyclone assembly and a brushless electric motor (not shown). The dust separation device 10 utilises cyclonic separation to separate dirt and debris from an airflow through the device to enable the cleaning of a surface as the cleaner head is swept over the surface. The brushless electric motor is a direct current motor which is operated on a switched reluctance principle and is controlled by means of a printed circuit board (PCB) (not visible in Figure 1) which receives power from the battery pack 18. The filter assembly 12 provides a pre-motor filter stage and a post-filter stage. The prefilter stage (referred to as the pre-filter) provides filtration of the airflow through the device prior to the airflow reaching the motor and provides a relatively course filter stage. The post-filter stage (referred to as the post-filter) provides filtration of the airflow through the device downstream of the motor and provides a relatively fine filter stage.

As shown in more detail in Figure 2, the filter assembly 12 comprises an annular filter member 22, one end of which is received in an annular support 24. At the other end (the upper end), the filter member 22 extends into a vented casing 26. The vented casing 26 has an enlarged diameter compared to the diameter of the filter member 20.

In order to clean the filter assembly 12 it is necessary to first disconnect the filter assembly 12 from the dust separation device 10. It is a known problem that during use the filter assembly tends to become blocked with dirt and debris and therefore regular cleaning is required to ensure effective operation and prolonged service life for the vacuum cleaner. When the filter assembly 12 is removed from the dust separation device 10, upturning the filter assembly 12 from the orientation shown in Figure 2 allows the filter assembly 12 to be filled with water through the open annular support 24. As water fills the upturned filter assembly 12, it can be swirled around the filter member 22 to clean it, typically running the filter member 22 under a running water tap or immersing it in water. The filter member 22 and the remaining parts of the filter assembly 12 should then be fully dried before re-connecting to the dust separation device 10.

Typically, the post-filter holds less dust particulates than the pre-filter and needs less washing. The post-filter also collects much finer particles than the pre-filter. However, regardless of dust content, in the arrangement of Figure 2, where the pre-filter and the post-filter are formed in a common assembly, the two are washed together. This common assembly is not always the case, however, and in other arrangements the parts are not linked and so the pre-filter and the post-filter can be washed separately.

Figure 3 shows a schematic diagram of a filter member of a post-filter 30 of the type described previously, illustrating a first support layer 32 and a second support layer 34 which sandwich a fibre membrane 34 between them. The arrow X indicates the direction of the airflow through the filter structure 30, as driven by the motor. The first and second support layers 32, 36 are typically formed from a layer of relatively thick fibres, typically a spunbond media of light textile or gauze. The fibre membrane 34 comprises a layer of relatively fine fibres, such as PTFE. The PTFE material is hydrophobic so that tends to repel water droplets, but is oleophilic so that it tends to attract oils. Because the PTFE is oleophilic, oils within the dust particulates tend to wick across the surface of the fibre membrane 34, clinging to the surface, because the surface attracts the oils. For the purpose of capturing oil-carrying dust particulates which are sucked through the device, this is a beneficial feature of the PTFE fibre layer. However, the oils tend to block pores within the fine structure of the fibre membrane 34 giving rise to a pressure drop when the device is used. Washing of the filter assembly, as described above, is one way to try and address this problem. Water used for washing must pass through the first support layer 32 to pick up the dust which is captured by the fibre membrane 34, but if the water does not wash off quickly, or thoroughly, dust particles can be redeposited back onto the fibre membrane 34. It is therefore difficult for the water to remove oils from the oleophilic surface of the filter membrane 34.

In order to address the aforementioned problem, Figure 4 shows the filter member 40 of a post-filter in accordance with a first embodiment of the invention. Here, the filter member 40 comprises a nanofibre membrane 44 which contains, incorporates or is otherwise integrated with an omniphobic additive material 42. The omniphobic additive is one which tends to repel both water and oil (i.e. it has hydrophobic and oleophobic character). The illustration in Figure 4 is not representative of the actual appearance of the filter member 40 as the omniphobic additive is not a coating on the surface of the nanofibre membrane 44, which would destroy the filtration function of the filter, but forms an integral part of the nanofibre structure 44. The presence of the omniphobic additive 42 within the nanofibre structure 44 has the effect of altering the oil retention characteristic of the filter member 40, compared to a nanofibre structure which does not incorporate an omniphobic additive, as will become apparent from the following description.

Figure 5(a) illustrates a layer 50 of oleophobic material, which is a material which tends to repel oil. Equally, the layer 50 could represent a hydrophobic material, which is a material which tends to repel water. An oleophobic material is defined as one in which the angle of contact A of an oil droplet 52 with a contact surface is relatively high (at least 90 degrees). In the example illustration shown the contact angle A for the water droplet 52 is around 140 degrees, and hence the layer 50 is oleophobic. In contrast, Figure 5(b) shows a material which is oleophilic, in which the contact angle B for the water droplet is very low (less than 90 degrees). The illustration applies equally to hydrophobic (water repellent) materials and oleophobic (oil repellent) materials. In the invention, it is an important characteristic of the additive material incorporated within, or otherwise integrally formed with, the nanofibre structure of the filter membrane 44 that it is both oleophobic and hydrophobic (i.e. omniphobic). In other words, the nanofibre structure incorporates an omniphobic additive which tends to repel both oil and water.

Referring again to Figure 4, the filter member 40 may be formed by means of an electrospinning process by which the omniphobic additive 42 is incorporated into the fabric of the filter membrane 44 as it is spun. Thus, the omniphobic additive 42 forms an integral part of the polymeric structure of the membrane. Importantly, the omniphobic additive 42 which is incorporated within the filter membrane 44 must not hinder the filtration performance so that, whilst dust particulates which are carried in the airflow are prevented from passing through the membrane, the resistance to airflow through the filter membrane 44 must also be unaffected by the omniphobic additive 42. It is an important feature of the filter membrane 40 that the overall filter performance is not degraded, whilst the omniphobicity is present to provide washability improvements. In some embodiments the filter member 40 may be a biodegradable filter member comprising the omniphobic additive. This has benefits at the end of life of the serviceable part when the part needs to be disposed of and replaced.

It is important to note that simply coating the filter membrane 44 with an omniphobic additive 42 is not satisfactory and renders the membrane ineffective for filtration as the gaps between fibres are so small and the coating layer so thick that the act of coating the fibres would likely cause the gaps between them to become blocked, effectively clogging the filter. Other methods may be used to form the integrated membrane/omniphobic material, including force spinning and electro spinning, but avoiding mere coating of the fibres. Typically, the fibres of the filter membrane 44 have a fibre diameter of between approximately 50nm and 250nm, and preferably between 50nm and 230nm. The median fibre diameter is typically between 90-100 nm. The fibre length is typically in excess of 20 pm. The aspect ratio of the fibres (length to diameter) is typically much greater than 1. The fibres do not have an equal spacing but are instead laid down in a randomised orientation by, for example, an electrospinning process. The area density is typically between 1-3 grams per square metre, and typically 2 grams per square metre.

Figure 6 is a bar chart to show the improvement in washability which can be achieved using the filter member 40 of the invention (as in Figure 4), including the omniphobic additive, when used in a post-filter for the vacuum cleaner in Figure 1. The bar chart shows percentage increase in post filter resistance. The left-hand bars of each bar pair illustrate the performance for a conventional post-filter 30, including the filter member 30 shown in Figure 3, whereas the right-hand bars of each bar pair illustrate the performance for a filter member 40 of the present invention.

Over time it can be seen that the resistance of the post filter increases for both filter structures 30,40. However, the wash symbols 60 within the bars illustrate how many times the filter member has had to be washed to remove dust laden on the structure. Comparing the left and right sides of the bars of each bar pair it can be seen that after 3 months the conventional filter member 30 has had to be washed three times compared to a single wash for the filter member 40 of the invention. Comparing the bars of each pair after 12 months shows that the conventional filter member 30 has had to be washed 17 times compared to the 5 times that the filter member 40 of the invention has been washed. This improvement in washability is a significant benefit in the invention as it reduces inconvenience for the user in having to perform wash cycles, which can be carried out less frequently to achieve the same performance, but also the effects of degradation on filter performance due to washing are limited due to the need to wash the filter less.

It will be appreciated that various alternative embodiments to those described previously are also envisaged without departing from the scope of the appended claims.