RELATED APPLICATIONS

[0001] This patent claims priority to Great Britain Patent Application Serial No.

GB1816956.5, filed October 18, 2018, entitled“Low Static Contact Cleaning System.” The entirety of U.S. Great Britain Patent Application Serial No.

GB1816956.5 is incorporated herein by reference.

TECHNICAL FIELD

[0002] This invention relates to a contact cleaning system, particularly though not exclusively to a contact cleaning system configured to generate a low electrical field strength and to transport static electricity to ground during operation.

BACKGROUND

[0003] Contact cleaning is used to clean substrate surfaces. Once cleaned, the substrate surfaces may be used in a variety of sophisticated processes such as in the manufacturing of electronics, photovoltaics and flat panel displays. Usually, a rubber or elastomeric cleaning roller is used to remove contaminating particles from a substrate surface and an adhesive roller can then be used to remove the contaminating particles from the cleaning roller.

[0004] In operation, a contact cleaning roller contacts at least the upper surface of the substrate, removing the debris by means of adhesion removal mechanisms (e.g. Van der Waals forces and adhesion forces), where the inherent properties of the material used to form the contact cleaning roller attracts the debris and causes it to stick to the surface of the contact cleaning roller. It is thought that the contact cleaning roller pulls the contaminating particles away from the substrate surface in this manner due the attractive van der Waals forces between the particles and the roller. Consequently, existing contact cleaning rollers may ensure effectiveness in removing contaminating particles by maximising contact with the substrate surface.

[0005] Aside from the weak van der Waals forces inherent in the material of the contact cleaning roller, other charges may arise. The contact cleaning process, which relies on contact between different surfaces, has the potential to be a source of electric charge from triboelectric effects and the accumulation of electrostatic charges. As such, any equipment used in an electronics assembly factory within close proximity (for example within 100mm) of a substrate must be non-insulating and have sufficiently low surface resistance that it will prevent damage of a substrate from electrostatic discharges.

[0006] According to a well-known method of measuring surface resistance provided in American National Standard Institute (ANSI) ESD STM1 1 .1 1 -2015, any equipment for an electronics assembly factory used within 100mm of a substrate must have surface resistance of less than 1 x10 ⁹ W.

[0007] Surface resistance, Rs, is defined by the ratio of a voltage to the current along the surface of a material. It is a property of the material measured in Ohms (W) is defined as: where U is DC voltage, and surface current is Is.

[0008] Therefore, it is a condition of certain cleaning applications that the surface resistance of the cleaning surface is less than 1 x10 ⁹ W. Not only does this place a requirement on a contact cleaning roller to have a surface resistance less than 1x10 ⁹ W but, necessarily, the roller must be capable of allowing electrostatic charges to be conducted away from the cleaning surface to ground. It must also do this while it is in continuous operation, that is, the roller must allow charges to be conducted all the time it is rotating.

[0009] Bulk conductivity is normally found by measuring Volume Resistance. A well-known method of measuring volume resistance is provided in American National Standard Institute (ANSI) ESD STM1 1.12-2015.

[0010] When the contact cleaning roller has sufficient surface adhesion to clean a substrate (i.e. a part to be cleaned), electrostatic charges are likely to be generated during the contact cleaning process. Electrostatic charges of up to 6000 volts are typically generated in a contact cleaning system as a result of friction between the contact cleaning roller and the substrate to be cleaned, between the contact cleaning roller and the adhesive roll and also between the support belts carrying the substrate to be cleaned and the substrate itself.

[0011] Static bars, also known as, static eliminators or anti-static bars provide one way to eliminate static eiectricity generated on a part passing through such a contact cleaning system during operation in contact cleaning apparatus, a static bar can be located at the outlet of the cleaning roller to provide a stream of ionised air to neutralise static on the cleaned substrate surface in certain systems, a second static bar can be located at the inlet of the cleaning roller to remove static from the substrate to be cleaned. However, static bars can be expensive and, if incorrectly positioned, can introduce undesirable electrostatic charge to surfaces in the contact cleaning process. A static bar may induce electric overstress, that is, the electrical signals applied to the device exceed the tolerance parameters of the device, in a substrate to be cleaned. As electronic devices are getting smaller, the voltages required to drive the device are getting smaller (for example 5QmV to 500m V). A static bar, more specifically the ions emanating from the static bar, will induce a current in the conductors in the device causing a partial breakdown and/or blowing of the circuit. In this way, the static bar may induce latent defects

(weaknesses or electronic failures) into the circuitry of the device by creating an electric field and, therefore, electric currents, in the circuitry above the voltage tolerance for the device.

[0012] In a contact cleaning system, there are at least two places where electric overstress can occur. The first is inside the machine due to the electrical field generated during operation of the system in which the contact cleaning roller and the adhesive roller contact one another and where the contact cleaning rolier contacts the substrate to be cleaned. The second is outside the machine, by way of the static bar inducing an electric field which may cause overstress in the substrate to be cleaned.

[0013] It is an object of the invention to alleviate or mitigate at least one or more of the aforementioned problems.

[0014] An object of the invention is to alleviate or mitigate the problem of electrostatic charge build up and, therefore, electric field strength build up, derived from operation of a contact cleaning system.

[0015] A further object of the invention is to alleviate or mitigate electrostatic charge build up when using a contact cleaning roller used in a suitable contact cleaning apparatus.

[0016] A yet further object is to provide a contact cleaning system having a high reliability and reduced propensity to induce latent defects in a substrate to be cleaned. [0017] The present invention provides at least an alternative to contact cleaning systems of the prior art.

BRIEF SUMMARY OF THE DISCLOSURE

[0018] Aspects and embodiments of the invention provide contact cleaning system as claimed in the appended claims.

[0019] Where referred to herein, the term“substrate to be cleaned” shall be taken to include printed circuit boards (PCB), an electronic product, component, film or device.

[0020] According to an aspect, the present invention provides a contact cleaning system comprising a contact cleaning roller located and operable to remove debris from a substrate to be cleaned, an adhesive roll located and operable to remove debris from the surface of the contact cleaning roller, wherein the maximum electrical field strength generated within the system during operation is 300 volts.

[0021] In certain embodiments, the contact cleaning system comprises at least one sensor operable and located to measure the static electrical field strength generated within the system in operation.

[0022] In certain embodiments, the material of the contact cleaning roller and the material of the adhesive roll are selected to minimise the triboelectric effect between them. During operation of the contact cleaning system, the frictional engagement of the contact cleaning roller and the adhesive roll are the principle electrical field generators in the system. By reducing the triboelectric effect between the contact cleaning roller and the adhesive roll, the electrical field strength generated within the system during operation can be significantly reduced.

[0023] In certain embodiments, the contact cleaning roller is an elastomeric roller having a bulk conductivity. In certain embodiments the elastomeric roller comprises an elastomeric layer having a conductive surface with a surface resistance of less than 1 x 10 ⁹ W. In this way, the maximum electrical field strength generated within the system during operation can be reduced by providing an electrically conductive charge transport pathway away from the surface of the contact cleaning roller to electrical ground.

[0024] In certain embodiments, the contact cleaning roller comprises an elastomeric layer comprising an electrically conductive modifier. [0025] In certain embodiments the electrically conductive modifier comprises conductive elements.

[0026] In certain embodiments the electrically conductive modifier comprises an interconnected network of conductive elements.

[0027] In certain embodiments the conductive elements are elongate. In this way, the surface area of the conductive elements in contact with the elastomer of the elastomeric layer is increased and the retention of the elements in the elastomeric layer is enhanced.

[0028] In certain embodiments the elongate conductive elements are hollow.

[0029] In certain embodiments the conductive elements are carbon.

[0030] In certain embodiments the conductive elements are nanotubes.

[0031] In certain embodiments conductive elements are carbon nanotubes.

[0032] In certain embodiments nanotubes are single walled carbon nanotubes. In this way, a balance is maintained between the cleaning properties of the elastomeric layer and the bulk conductivity thereof. The high surface area of the nanotubes provides improvements in bonding the carbon into the elastomer when compared to particulate carbon or carbon fibres.

[0033] More specifically, the carbon nanotubes are a single carbon atom wall thickness.

[0034] In certain embodiments the elongate conductive elements are dispersed uniformly throughout the elastomer material.

[0035] In certain embodiments conductive elements are dispersed such that they are embedded and retained in the elastomeric material.

[0036] In certain embodiments the conductive elements are orientated randomly in the elastomeric material.

[0037] In certain embodiments the conductive elements have length within the range about 5 pm to about 30pm.

[0038] In certain embodiments the conductive elements have diameter within the range about 1 nm to about 200nm.

[0039] In certain embodiments the concentration of conductive elements in the elastomer is about 0.015% by weight of elastomer.

[0040] In certain embodiments the elastomeric layer comprises any suitable elastomeric material. More specifically, the elastomeric layer comprises one of silicone rubber or polyurethane. [0041] In certain embodiments the elastomer comprises silicone. In this way, a conductive silicone layer can be formed when carbon nanotubes are dispersed within the silicone material. The nanotubes are retained within the silicone polymer matrix through covalent bonding. Other additives, such as particulate materials are prone to migrate out of the silicone matrix due to the mobility of the silicone matrix. Thus, carbon nanotubes provide a retained modifying agent retained within the silicone matrix.

[0042] In certain embodiments the elastomeric layer is formed of a two-part, room- temperature curing silicone rubber.

[0043] In certain embodiments the elastomeric layer has bulk conductivity (e.g. electrical conductivity). More specifically the elastomeric layer has a conductive surface for contact with a part to be cleaned and a further conductive surface in electrical contact with a conductive pathway for charge extraction from the conductive layer to an electrically conductive core to a charge transport element in electrically connection with the electrically conductive core.

[0044] In certain embodiments the surface resistance of the, or each conductive surface is less than 1 x 10 ⁹ W. More specifically, the surface resistance of both the conductive surface and the further conductive surface of the elastomeric layer is less than 1 x 10 ⁹ W. Yet more specifically, the surface resistance of both the conductive surface and the further conductive surface of the elastomeric layer are substantially equal.

[0045] In certain embodiments the surface resistance the, or each conductive surface is in the range of about 1 x 10 ⁶ W to about 1 x 10 ⁹ W. More specifically, the surface resistance of both the conductive surface and the further conductive surface of the elastomeric layer is in the range of about 1 x 10 ⁶ W to about 1 x 10 ⁹ W. Yet more specifically, the surface resistance of both the conductive surface and the further conductive surface of the elastomeric layer are substantially equal.

[0046] In certain embodiments the elastomeric layer is in electrical contact with the conductive pathway. In this way, the contact cleaning roller is permanently electrically grounded and static will be transported away from the contact cleaning roller without the need to provide further means to neutralise the charge, such as an ionising bar.

[0047] In certain embodiments the elastomeric layer is in intimate mechanical contact with the conductive pathway. In this way, as well as the contact cleaning roller being permanently electrically grounded, any static build up on the critical cleaning surface is removed along the conductive pathway without the need for a physical contact to it that would otherwise risk wear or damage that would impair cleaning performance.

[0048] In certain embodiments the conductive pathway provides charge extraction from the elastomeric layer to ground (i.e. an electrical earth).

[0049] In certain embodiments the elastomeric layer is attached to the electrically conductive core.

[0050] In certain embodiments the elastomeric layer is in intimate contact with the electrically conductive core. More specifically, the elastomeric layer is in intimate contact with the electrically conductive core across the entire further conductive surface of the elastomeric layer. In this way, charge extraction from the

elastomeric layer to the electrically conductive core occurs across the entire further conductive surface of the elastomeric layer.

[0051] In certain embodiments the electrically conductive core is formed of a metallic conductor material. More specifically, the metallic conductor core is stainless steel.

[0052] In certain embodiments the electrically conductive core is formed of a non- metallic conductor material. More specifically, the non-metallic conductor core is carbon fibre.

[0053] In certain embodiments the electrically conductive core comprises a shaft.

[0054] In certain embodiments, the adhesive roll comprises a base layer and an adhesive layer.

[0055] In certain embodiments, the adhesive layer comprises an adhesive having electrical conductivity. In this way, the maximum electrical field strength generated within the system in operation can be reduced by providing an electrically conductive charge transport pathway away from the surface of the adhesive roll to electrical ground.

[0056] In certain embodiments the adhesive has an electrical conductivity of between 1 x1 O ⁶ and 1 x1 O ⁹ Snr ¹ .

[0057] In certain embodiments the adhesive is a silicon-free adhesive.

[0058] In certain embodiments, the base layer is a paper substrate. In this way, the static electricity, and therefore the maximum electrical field strength, generated within the system during operation is reduced because the paper base layer of the adhesive roll and the elastomer of the contact cleaning roller are much closer to one another in the triboelectric series than are the elastomer of the contact cleaning roller and a silicon adhesive and/or polymeric film base layers for other adhesive rolls for example.

[0059] In certain embodiments, the system comprises an adhesive roll having a paper base layer and an adhesive with electrical conductivity and an elastomeric roller having a bulk conductivity. In this way, the maximum electric field strength generated within the system during operation is limited due to the small

triboelectric effect between the materials of the contact cleaning roller and the adhesive roll and also because the electrical charge generated during operation of the system can be transported away from the contact cleaning roller and the adhesive roll.

[0060] In certain embodiments, the system comprises means for providing electrical charge transport configured to remove the electrical charge generated in the system during operation to electrical ground. In this way, the system reduces latent defects in a substrate to be cleaned without neutralising the electrical charge generated and/or providing ions into the system and/or onto the substrate.

[0061] In certain embodiments, the means for providing electrical charge transport comprises a charge transport element arranged to provide a charge transport pathway away from the contact cleaning roller and/or the adhesive roll to an electrical ground.

[0062] In certain embodiments, wherein the contact cleaning roller comprises an elastomeric layer with bulk conductivity (e.g. electrical conductivity) and an electrically conductive core configured to support the elastomeric layer and to provide a conductive pathway for charge transport from the contact cleaning roller to an electrical ground, the charge transport element is mechanically and electrically coupled to the electrically conductive core.

[0063] In certain embodiments the charge transport element is arranged to be coaxial with the electrically conductive core of the contact cleaning roller.

[0064] In certain embodiments, the charge transport element is mechanically and electrically coupled to the electrically conductive core by a housing retaining the charge transport element.

[0065] In certain embodiments, the housing comprises a spigot. [0066] In certain embodiments, the charge transport element is formed of electrically conductive material.

[0067] In certain embodiments, the charge transport element is metallic.

[0068] In certain embodiments the charge transport element is formed from stainless steel.

[0069] In certain embodiments the charge transport element is formed from gold plated steel.

[0070] In certain embodiments the charge transport element comprises a pin.

[0071] In certain embodiments the charge transport element comprises a pin and a resilient biasing means configured to bias the pin outwardly of the contact cleaning roller. In this way, the pin is held in an extended position, so that at least one end of the pin is protruding outwardly of the core, when the roller is rotating. Further, the length of the pin and the extension of the resilient biasing means can be modified to ensure the protruding end of the pin is suitably arranged to maintain contact with a suitable electrical grounding element.

[0072] In certain embodiments the resilient biasing means is a spring mechanism.

[0073] In certain embodiments, the electrical field in the system is removed (transferred, extracted) from the system solely through the charge transport element.

[0074] In certain embodiments, no ionisation energy is input into the system and/or the substrate during operation of the system.

[0075] In certain embodiments, the contact cleaning system comprises an electrical grounding element.

[0076] In certain embodiments, the electrical grounding element is planar.

[0077] In certain embodiments the electrical grounding element is located at an end of the contact cleaning roller. More specifically, the electrical grounding element is located in a plane perpendicular to a plane including the longitudinal axis of the contact cleaning roller.

[0078] In certain embodiments, the electrical grounding element is formed of an electrically conductive material. More specifically, the electrical grounding element is metallic. Yet more specifically, the electrical grounding element is formed of stainless steel. In this way, the grounding element provides an electrical path to ground. [0079] In certain embodiments, a charge transport pathway from the system comprises the charge transport element and the electrical grounding element.

[0080] In certain embodiments, the charge transport element is urged into contact with the electrical grounding element.

[0081] In certain embodiments a resilient biasing means is configured and located to urge the charge extraction element into contact with the electrical grounding element.

[0082] In certain embodiments, the contact cleaning system comprises a housing. More specifically, the housing encases (contains, surrounds, encloses) at least the contact cleaning roller and the adhesive roll. That is to say, at least the contact cleaning roller and the adhesive roll are disposed within the housing.

[0083] In certain embodiments, the means for providing electrical charge transport is disposed within the space defined by the housing.

[0084] In certain embodiments, the charge transport element is within the space defined by the housing.

[0085] In certain embodiments, the electrical grounding element and at least one contact cleaning roller according to an aspect of the invention are mounted within the housing. More specifically, the electrical grounding element is mounted within the housing and the at least one contact cleaning roller is mounted to the housing such that the charge extraction element is in contact with (forms a charge extraction pathway with) the electrical grounding element.

[0086] In certain embodiments, wherein at least one sensor, operable and located to measure the static electrical field generated within the system in operation, is disposed within the space defined by the housing.

[0087] In certain embodiments, the maximum electrical field measured by the at least one sensor within the housing is below 300 volts.

[0088] In certain embodiments the maximum electrical field strength generated within the system during operation is 200 volts. More specifically, the maximum electrical field strength generated within the system during operation is 100 volts.

[0089] In certain embodiments the maximum electrical field strength generated within the system during operation is 30 volts.

[0090] In certain embodiments the contact cleaning system comprises a plurality of contact cleaning rollers. [0091] In certain embodiments the contact cleaning system comprises a plurality of adhesive rolls each located and operable to remove debris from the surface of a contact cleaning roller of the system.

[0092] According to an aspect of the invention, there is provided a contact cleaning roller comprising: a cleaning surface assembly comprising an elastomeric layer with bulk conductivity (e.g. electrical conductivity), an electrically conductive core configured to support the cleaning surface assembly and to provide a conductive pathway for charge extraction from the cleaning surface assembly; and a charge transport element arranged to provide a charge transport pathway away from the electrically conductive core.

[0093] In certain embodiments, the charge transport element is mechanically and electrically coupled to the electrically conductive core. In this way, the contact cleaning roller is permanently electrically grounded and static electricity will be transported away from the assembly without the need to provide further means to neutralise the charge, such as a static bar. Further, any static build up on the critical cleaning surface is transported away from the cleaning surface without the need for a physical contact to it that would otherwise risk wear or damage that would impair cleaning performance.

[0094] In certain embodiments the charge transport element is mechanically and electrically coupled to the electrically conductive core by a housing retaining the charge transport element. In this way, the housing is retained in the end of the electrically conductive core and, in turn, the charge transport element is retained in the housing and protrudes outwardly from the housing and the core.

[0095] In certain embodiments the housing comprises a spigot. In certain embodiments the housing comprises a spigot adapted to engage and disengage a resilient biasing means coupled to the charge transport element. In certain embodiments, the spigot may be inserted into the electrically conductive core, typically an end of the electrically conductive core. In this way, the charge transport element may be held by the spigot in the end of the electrically conductive core and protruding outwardly from the core.

[0096] In certain embodiments the housing is integral with the core.

[0097] In certain embodiments the resilient biasing means is a spring mechanism.

[0098] In certain embodiments the spring mechanism is arranged to be coaxial with the electrically conductive core. [0099] In certain embodiments the spring mechanism is received in a spring contact receptacle within the housing (e.g. spigot). In certain embodiments the spring contact receptacle has a surface coated with (electrically) conductive material. More specifically, the conductive material is gold plate.

[00100] In certain embodiments the electrically conductive core comprises a shaft. In this way, the shaft may be mounted on the housing of a contact cleaning apparatus enabling the roller to rotate relative to the housing of the apparatus.

[00101] In certain embodiments the shaft is hollow. More specifically, the hollow shaft is formed of an electrically conductive material.

[00102] In certain embodiments, the charge transport element (e.g. pin) is mounted on or in the end of the shaft. In certain embodiments, the charge extraction element (e.g. pin) is mechanically and electrically coupled, directly or indirectly, to the electrically conductive core by the shaft.

[00103] In certain embodiments the shaft receives a spigot mounted in each of the ends of a hollow core of the roller. More specifically, each spigot may comprise a mounting for coupling to the housing of the contact cleaning system. The mounting allows the roller to rotate relative to the housing when the contact cleaning roller is mounted to the housing of the system.

[00104] In certain embodiments, one or each spigot receives a charge transport element (e.g. pin).

[00105] According to another aspect, the present invention provides a contact cleaning system comprising a contact cleaning roller configured to remove debris from a substrate to be cleaned, an adhesive roll configured and located to remove debris from the surface of the contact cleaning roller, wherein the contact cleaning roller is a roller according to an aspect of the present invention and further wherein the maximum electrical field strength generated within the system during operation is 300 volts.

[00106] In certain embodiments, the contact cleaning system does not comprise a ionising bar. The system of the present invention does not require the presence of a ionising bar to remove (reduce) electrostatic charge generated during the contact cleaning process. The contact cleaning system of the invention meets the requirements of being a low static system without the need for a ionising bar at the outlet and/or at the inlet of the contact cleaning roller. BRIEF DESCRIPTION OF THE DRAWINGS

[00107] Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:

[00108] Figure 1 is a schematic side view of a contact cleaning system in accordance with embodiments of the present invention;

[00109] Figure 2 is a schematic representation of a contact cleaning system in accordance with an embodiment of the present invention comprising a contact cleaning roller according to an embodiment of the invention in contact with an electrical grounding element;

[00110] Figure 3 is a schematic cross-section of the contact cleaning system of Figure 2 taken along the line A-A; and

[00111] Figure 4 is a schematic representation of a contact cleaning system in accordance with the embodiment of the present invention comprising a contact cleaning roller according to an embodiment of the invention wherein the electrical grounding element is disconnected from the contact cleaning roller.

DETAILED DESCRIPTION

[00112] Figure 1 is a schematic side view of a contact cleaning system in accordance with embodiments of the present invention. The contact cleaning system 1 comprises a contact cleaning roller 2 and an adhesive roller 3 mounted above a conveyor 4 on which a plurality of substrates 5 for cleaning are carried.

The contact cleaning roller 2 is elongate and generally cylindrical in shape, and is mounted on a holder (not shown) having an axis perpendicular to the plane of view about which the contact cleaning roller 2 is free to rotate. The contact cleaning roller 2 comprises a silicone elastomer layer surrounding an electrically conductive shaft. The specific structure of the contact cleaning roller 2 is described in more detail below. The adhesive roller 3 is generally cylindrical in shape, and comprises a body having a surface on which adhesive having electrical conductivity is present, and is also mounted on a holder (not shown) having an axis perpendicular to the plane of view and parallel to that of the contact cleaning roller 2 about which the adhesive roller 3 is free to rotate. The adhesive roller 3 comprises a paper base and an adhesive on the base layer, the adhesive having electrical conductivity.

The contact cleaning roller 2 and adhesive roller 3 are mounted in a housing 25a, 25b in such a manner so as to be in contact with one another such that clockwise rotational movement of the contact cleaning roller 2 results in counter-clockwise rotational movement of the adhesive roller 3 and vice versa. The need for the contact cleaning roller 2 and adhesive roller 3 to be in contact will be clear from the description of use below. The contact cleaning roller 2 is also mounted so as to be able to be in contact with the surface of a substrate 5 to be cleaned as it passes on a conveyor located below the axis of the conveyor 4.

[00113] As the contact cleaning roller 2 and adhesive roll 3 rotate against one another, the materials of the contact cleaning roller 2 and adhesive roll 3 are close enough in the triboelectric series such that the maximum electric field strength generated within the system in operation is 300 volts. In the depicted embodiment, the adhesive roll is formed of a sheeted roll having a paper base and a silicon-free adhesive having electrical conductivity and the contact cleaning roller 2 has an elastomeric layer comprising an interconnected network of a conductive modifier, such as single walled carbon nanotubes, thus giving the elastomeric layer a bulk conductivity. In this way, the maximum field strength generated during operation of the contact cleaning system 1 is between 1 volt and 300 volts.

[00114] Substrates 5 to be cleaned are processed as follows. A substrate 5 is positioned on the upper surface 6 of a conveyor 4, which in Figure 1 moves from right to left as indicated by arrow A. The substrate 5 to be cleaned passes underneath the contact cleaning roller 2, which rotates in a clockwise direction as indicated by arrow B. Before coming into contact with the contact cleaning roller 2, the upper surface of the substrate 5 is covered with debris 7 requiring removal, such as dust. The contact cleaning roller 2 contacts the upper surface of the substrate 5, removing the debris 7 by means of a removal mechanism, where the inherent polarity of the material used to form the contact cleaning roller 2 attracts the debris 7 and causes it to stick to the surface of the contact cleaning roller 2.

The relative attractive force between the surface of the contact cleaning roller 2 and the debris 7 is greater than that between the debris 7 and the surface of the substrate 5, hence the debris 7 is removed. The now clean substrate 5 continues along the conveyor 4 to a removal station (not shown) and the lower surface 8 of the conveyor passes back, forming a loop, in a left-right direction in Figure 1 , as indicated by arrow D. In order to clean the contact cleaning roller 2, the adhesive roller, rotating in a counter-clockwise direction as indicated by arrow C contacts the surface of the contact cleaning roller 2. At this point the adhesive force between the debris 7 and the adhesive present on the surface of the adhesive roller 3 is greater than the adhesion force holding the debris 7 onto the surface of the contact cleaning roller 2, and the debris is removed. The contact cleaning roller 3 then rotates to present a clean surface to the next substrate 5 to be cleaned.

[00115] Figure 2 depicts a contact cleaning system 100 in accordance with an embodiment of the present invention. The contact cleaning system 100, comprises a contact cleaning roller 102, which can be used as the contact cleaning roller 2 in the contact cleaning system 1 of Figure 1.

[00116] The contact cleaning roller 102 is an elongate, generally cylindrical shape, comprising a silicone elastomeric layer 1 10 with a conductive surface, and a hollow core (see Figure 3, 1 12) having an electrically conductive surface and a bore therethrough. The outer surface of the electrically conductive surface of the core is in mechanical and electrical contact with the inner surface of the silicone

elastomeric layer 1 10 along its length. In this way, the entire surface of the core and the silicone elastomeric layer in contact with the core provides an electrical charge path.

[00117] The elastomeric layer 1 10 and core 1 12 share a common axis denoted by the line CA, about which the contact cleaning roller 102 is free to rotate. Spigots 1 18 and 1 18b are mounted in each end of the core 1 12 and provide a mounting 1 16 and 1 16b at each end. The mountings 1 16 and 1 16b can be attached to a housing (not shown) of the system 100 which allow the mountings 1 16 and 1 16b and, therefore the cleaning roller 102 to rotate about the axis CA. Each spigot 1 18, 1 18b is formed of stainless steel (or aluminium) conductive material and is in mechanical and electrical contact with and abutting the electrically conductive surface of the core 1 12. The spigot 1 18 retains a gold plated stainless steel charge extraction element, pin 120, in a recess 122 the surface of which is gold plated to assist in the electrical charge transfer from the surface of the core 1 12 to the spigot 1 18, to the surface of recess 122 and into the pin 120. The pin 120 is spring loaded (not shown) in the recess 122 so as to resiliently bias the pin 120 outwardly of the spigot 1 18 towards a grounding element 124, configured as a stainless steel plate. In other words, the pin 120 is part enclosed within the recess 122 so that one end of the pin is arranged to protrude beyond the recess 122 and contact the grounding element 124. The grounding element 124 is in electrical contact with an electrical ground 126. In the depicted embodiment the grounding element 124 is positioned with a plane that is substantially perpendicular to the common axis CA.

[00118] The pin 120 is inserted into the spigot 1 18 through mounting 1 16 and is displaceable along the common axis CA by a spring (not shown) towards and away from the grounding element 124. In this way, the contact cleaning roller 102 is easily installed into the contact cleaning system 100 and connected to the electrical ground 126.

[00119] The spring (not shown) within recess 122 is configured to bias the pin 120 outwardly of the contact cleaning roller 102 so that the pin 120 is held in an extended position protruding outwardly of the core 1 12 so that the pin 120 is urged into mechanical and electrical contact with the grounding element 124 whilst the contact cleaning roller 102 is rotating. In this way, once the contact cleaning roller is installed, an electrical charge extraction path exists permanently from the surface of the elastomeric layer 1 10, into the electrically conductive core 1 12, into the metallic spigot 1 18 and the gold-plated surface of recess 122, into metallic pin 120 and on into stainless steel grounding element 124 and to ground 126. In this way, electrostatic charges created during the contact cleaning process by the rotation of the contact cleaning roller 102 and its contact with a substrate to be cleaned (not shown), are dissipated to ground 126 through the contact cleaning system 100.

[00120] It will also be appreciated that, once installed, in this arrangement any static charge will dissipate automatically from the elastomeric layer 1 10 due to the permanent mechanical and electrical contacts to ground 126. The electrical charge extractive path from the contact cleaning system 100 to the ground 126 is also tolerant of slight relative movement between the contact cleaning roller 102 and the grounding element 124 and static dissipation is not reliant on precise positioning of the component features so long as mechanical and electrical contacts are maintained.

[00121] Furthermore, should any parts become slightly worn or misaligned during use the resilient biasing of the pin ensures electrical and mechanical contact will be maintained without disrupting the electrical charge extractive path.

[00122] Providing a network of single walled carbon nanotubes (not shown) in the elastomeric layer 1 10, ensures the layer 1 10 has a bulk electrical conductivity which in turn ensures a charge extraction pathway to ground 126 is provided by the roller 102.

[00123] As best seen in Figure 3, the spigot 1 18 including the mounting 1 16 is coupled to the core 1 12 by inserting the spigot 1 18 into the end of the electrically conductive core 1 12. The spigot 1 18 having a recess 122 coaxial with the common axis CA and extending partially through the length of the spigot 1 18. Aptly, the spigot 1 18 is formed from a conductive material such as aluminium or stainless steel.

[00124] The pin 120 and the biasing spring (not shown) are located in the recess (e.g. receptacle) 122 and are in mechanical and electrical contact with the inner surface of mounting 1 16 and the spigot surrounding recess 122.

[00125] The contact pin 120 is inserted into the recess 122 and protrudes outwardly of the mounting 1 16 into electrical and mechanical contact with the grounding element 124. Aptly, the contact pin 120 is surrounded by a spring mechanism (not shown) within the recess 122. The contact pin 120 and the surface of the recess 122 are each gold plated.

[00126] When the contact cleaning roller 102 is in use (i.e. is in rotational movement and in contact with the substrate 5 to be cleaned), an electrostatic charge builds up on the surface of the elastomeric layer 1 10. The layer 1 10, comprising single walled carbon nanotubes and having a bulk conductivity provides a conductive pathway from the outer surface of the elastomeric layer 1 10 to the core 1 12, from the core 1 12 to the spigot 1 18 and the mounting 1 16 and recess 122. When the resilient biasing means is configured to bias the contact pin 120 outwardly of the roller 102 to be in mechanical and electrical contact with the grounding element 124, the electrostatic charge is directed in the conductive pathway from the spigot 1 18, the mounting 1 16, and the surface of the recess 122 through the contact pin 120, onto the grounding element 124 and into the electrical ground 126. In this embodiment of the invention when the roller 102 is in use, the conductive pathway from the surface of the elastomeric layer 1 10 comprises (in order of charge dissipation) the elastomeric layer 1 10, the core 1 12, the spigot 1 18, the surface of the recess 122 and the mounting 1 16, the contact pin 120, the grounding element 124, to an electrical ground 126. The overall effect of this is the dissipation of electrostatic charge directed away from the outer surface of the roller 102 towards an electrical ground 126. [00127] Figure 4 depicts the contact cleaning system 100 when the conductive pathway between the outer surface of the elastomeric layer 1 10 and the ground 126 is disconnected by moving the contact pin 120 away from the grounding element 124. In Figure 4, the contact pin 120 is not in mechanical or electrical contact with the grounding element 124. This configuration is useful when the roller 102 needs to be changed or otherwise removed from the system.

[00128] Various modifications of the contact cleaning system 1 , 100 are envisaged. For example, a further contact cleaning roller 102 and an associated adhesive roller can be provided to clean the opposite side of a substrate 5. In such an embodiment, contact cleaning rollers and associated adhesive rollers would be positioned on each side of conveyor 4 (Figure 1 ).

[00129] Additional contact cleaning roller 102 and an associated adhesive roller can be provided in spaced apart relation on one or both sides of conveyor 4. In this way, additional single-sided and/or two-sided cleaning can be provided.

[00130] The contact pin, grounding element and spigot may be formed of any suitable conductor material. A metallic conductor such as aluminium or stainless steel is preferred in a clean working environment as it is easily cleaned and does not degrade or create debris when frictional forces are generated during use of the system.

[00131] In certain embodiments the contact cleaning system may comprise a charge extraction pathway at each end of the contact cleaning roller. Such a system will have a charge extraction element (e.g. a pin) at each end of the roller, each urged into contact with an electrical grounding element which in turn is electrically connected to an electrically grounding element (electrical earth).

[00132] In certain embodiments the spigot may be replaced by integrating the housing within the core. For example, an annular wall or another suitable feature may be provided on the inside surface of the core which supports the inner end of a resilient biasing means. Any appropriate feature may be chosen so long as it provides a mechanical and electrical contact between the core and the resiliently biasing means and so long as it biases the charge extraction element, such as a pin outwards from the core.

[00133] In certain embodiments, the charge extraction element may protrude from the electrical grounding element. In this arrangement, the charge extraction element may extend to be received within the core, or within a suitable housing attached to the core or, again, to be received in any other suitable recess arranged within the core, so as to provide a suitable mechanical and electrical contact and maintain an electrical charge transport pathway.

[00134] Throughout the description and claims of this specification, the words “comprise” and“contain” and variations of them mean“including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[00135] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.