Spray gun

Abstract

A spray gun 100 comprises a body 4 with a fluid passageway 32 for delivering a coating material to be sprayed to a spray tip 3. There is an adjuster nut 13 extending around the body for adjusting flow

Description

TECHNICAL FIELD 5 The present disclosure relates to a spray gun and in particular, but not exclusively, to an automatic spray gun for applying micron films of various coatings to a range of substrates. Aspects of the invention relate to a spray gun and to a method of applying a coating to a substrate, for example applying a food safe coating to a tray or applying graphene to a substrate. 10 BACKGROUND There is an ever-increasing drive to use renewable and scientifically developed materials in the coating industry as businesses look to become more environmentally 15 friendly. One such example of this change may be found in the food packaging industry. Typically, food is packaged in plastic containers or trays which contain the food and then LD enclosed within a clear plastics wrapper. The plastic container works well as it is robust C\j thereby ensuring the food contained within the container does not get damaged. Furthermore, the plastics tray is impermeable meaning that the food contained within 20 the container is kept fresh and does not leak from the container. Over recent years the food packaging industry has started to transition away from plastics containers due to the environmental ramifications associated with single use plastics, the like of which have historically been used to package food. Instead of plastic 25 containers the food packaging industry is transitioning towards environmentally friendly food containers. Environmentally friendly food containers are often made from fibrous materials such as compressed vegetable materials such as sugar cane and bamboo roots or stalks as well as paper and cardboard. However, the problem with containers made from fibrous materials is that the resultant container is permeable meaning food 30 substances may leak from the container. This is particularly problematic for liquid foods or foods having sauces. To prevent this problem containers made from fibrous materials are coated with a food safe coating that seals the walls and base of the container thereby creating a container 35 that is impermeable. This is beneficial as the food safe coating allows fibrous materials sourced sustainably to be used to create food containers. However, applying the food 1 safe coating in a consistent and reliable manner is challenging and requires a spray gun or the like to apply the coating to the fibrous material. Applying the coating in a reliable and predictable manner is important for ensuring the 5 quality of the coating on the container. As such, there is a need for a spray gun capable of applying a food safe coating to the surface of containers made from a fibrous material. Food safe coatings may comprise multiple layers such as a primer layer, a top coat and colour coded coatings that all require repeatability of film tolerance where meeting the weight and thickness tolerance of each of the coating materials and layers is critical to 10 the performance of the coating. Current spray guns are unable to provide repeatability and accuracy when applying nano type coatings having a thickness of around 10 microns or less. Furthermore, conventional spray guns often cause a mist when spraying which may contaminate the 15 surface coating which can adversely affect the performance of the coating. As such, there is a requirement for a spray gun that can apply a range of nano coating with repeatability and accurately to food containers made from a fibrous material in order to meet the external oxygen barrier, internal fibre seal, consistent weight and a quality of finish. 20 SUMMARY OF THE INVENTION According to an aspect of the present invention there is provided a spray gun for applying various coatings to a range of substrates, the spray gun comprising: a body comprising 25 a fluid passage extending longitudinally through the body from a spray tip located at a distal end of the body; a fluid adjuster nut rotatably coupled to the body such that rotating the adjuster nut varies the longitudinal position of the fluid adjuster nut relative to the body; a cartridge module located within a cavity of the fluid adjuster nut comprising a bore wherein the bore is longitudinally aligned with the fluid passage; and a solenoid 30 coupled to the cartridge module and operable to move the cartridge module between a distal position in which the cartridge module abuts a first abutment surface of the body and a proximal position in which the cartridge module abuts a second abutment surface on the adjuster nut; wherein the second abutment surface is a back stop ring secured to a proximal end of the adjuster nut; and wherein moving the cartridge module from the 35 distal position to the proximal position lifts a needle located within the fluid passage from a seated position in which the needle forms a seal between a spray tip on the body and a distal tip of the needle, and an open position in which the distal tip of the needle is lifted off the spray tip to define a measured opening between the tip of the needle and the spray tip. 5 The solenoid and cartridge module beneficially provide rapid and accurate actuation of the spray gun between the seated position and the open position. The solenoid allows the cartridge module to be rapidly moved between the proximal position and distal position and the adjuster nut ensures that the proximal position may be accurately 10 controlled. Controlling the proximal position of the cartridge module has the effect of allowing the flow rate of coating material from the spray tip to also be accurately controlled. The spray gun may be for applying a food safe coating to a food tray or container. 15 Alternatively, the spray gun may be for applying graphene to a substrate. The spray gun may be configured to spray liquid graphene on to a substrate made from a plastics material such as polyethylene. The liquid graphene may be a unique nano liquid graphene mixture used to remove the static charge common with substrates such as polyethylene. 20 The spray gun may be part of an automated production line which is programmed to control relay laser signals to activate operations such as, conveyor stop start movement, the spray application operation of the automatic spray gun, the various electric motors that guides the axis movement of the spray gun, the electronic fluid and air regulators 25 that control the fluid delivery system and air pressures. In one embodiment the needle may comprise a collar positioned within the bore of the cartridge module and wherein moving the cartridge module from the distal position to the proximal position causes the cartridge module to engage the collar to lift the tip of 30 the needle off the spray tip. In another embodiment rotating the fluid adjuster nut may vary the position of the second abutment surface such that the gap between the tip of the needle and the spray tip when the needle is in the open position may be controlled. This is beneficial as rotating the fluid adjuster nut allows the flow rate of coating material being sprayed by the spray gun to be accurately controlled. In an embodiment the cartridge module may comprise a needle spring extending 5 longitudinally through the bore for urging the needle towards the seated position. This is beneficial as the needle spring may maintain the tip of the needle in the seated position when the solenoid and cartridge module are in the closed position. In one embodiment the back stop ring may be removable from the fluid adjuster nut to 10 access the cavity of the fluid adjuster nut. The back stop ring may be connected to the adjuster nut by a thread such that the back stop ring may be removed from the adjuster nut by unscrewing the back stop ring from the fluid adjuster nut. In a further embodiment the cartridge module may comprise a needle spring extending 15 longitudinally through the bore for urging the needle towards the seated position. The needle spring may abut the collar of the needle to urge the needle towards the seated position. A proximal end of the needle may be at least partially received within the needle spring. 20 The spray gun may further comprise a main spring extending between the second abutment surface and a radially extending flange on the cartridge module. The main spring may beneficially urge the cartridge towards the closed or distal position thereby allowing the cartridge module to be moved rapidly to the distal position when the solenoid is turned OFF. When the cartridge module is in the distal position the needle 25 spring may urge the needle towards the seated position and maintain the needle in the seated position. At least a portion of the cartridge module may be received within the main spring such that the main spring extends around an external surface of the cartridge module. 30 In an embodiment the main spring may be stiffer or stronger than the needle spring. This is beneficial as it ensures that the cartridge module remains seated, in the proximal position when the solenoid is deactivated. This prevents the cartridge module from moving undesirably when the solenoid is deactivated. In one embodiment the cartridge module may comprise a housing and the housing may comprise the bore. The cartridge module may further comprise a piston ring connected to a distal end of the housing and the piston ring may comprise a needle aperture through which the needle extends. The piston ring may comprise a female thread 5 located on a proximal side of the piston ring and a distal end of the housing may comprise a male thread for securing the housing to the piston ring. The radially extending flange may extend radially from the housing and a distal side of the radial flange may abut or contact the piston ring when the housing is connected to 10 the piston ring. This is beneficial as the flange of the housing may be tightened onto the piston ring thereby preventing the male thread on the housing bottoming out on the piston ring and being overtightened. In another embodiment the cartridge module may further comprise a spring guide 15 connected to a proximal end of the housing. The spring guide may be bonded to the housing. The spring guide may further comprise a shoulder for abutting the second abutment surface when the cartridge module is moved to the proximal position. The spring guide may be coupled to a solenoid shaft such that actuation of the solenoid causes the solenoid shaft and cartridge module to move between the proximal and distal 20 positions. The spray gun may comprise an air cap connected to a distal end of the spray gun and the spray gun may comprise an aperture aligned with the spray tip. The air cap may comprise a planar surface extending around the aperture and a distal end of the spray 25 tip may be longitudinally aligned with the planar surface. The air cap may be clamped to a distal end of the body by a ring. According to another aspect of the present invention there is provided a method of applying a coating material to a substrate using a spray gun, the 30 method comprising: selecting a desired flow rate of coating material from the spray gun by varying a longitudinal position of an abutment surface; and operating a solenoid coupled to move a cartridge module between a distal position in which the cartridge module abuts a first abutment surface of the body and a proximal position in which the 35 cartridge module abuts a second abutment surface on the fluid adjuster nut, wherein the second abutment surface is a back stop ring secured to a proximal end of the adjuster nut; and wherein moving the cartridge module comprises lifting a needle off a needle seat to create a gap or opening between the needle seat and a distal tip of the needle to allow 5 coating material to be sprayed from the spray gun; and wherein an atomising air supply is activated prior to moving the cartridge module and lifting the needle off the needle seat. The method of applying a nano-coating between about 1 micron and 20 micron 10 thickness may be used, for example, to apply one or more food safe coatings to a fibrous food tray. Furthermore, the method may be used to apply a nano-coating of graphene to a substrate. For example, the method may be used to apply a nano-coating of graphene to polyethylene. The method beneficially allows the coating to be applied accurately and repeatability. Furthermore, the method allows the coating to be applied 15 without any mist which is particularly advantageous when spraying liquid graphene due to the high cost of liquid graphene and also the cancerogenic nature of the material. The method may be used to apply a nano coating, for example, where a micron film needs to be applied within a 5 -10 micron tolerance with a quality of finish and with 20 repeatability with a mist free atmosphere, using a spray gun application. In an embodiment varying the longitudinal position of the abutment surface may comprise rotating an adjuster nut. Rotating the adjuster nut beneficially allows the position of the abutment surface, and thus the magnitude of the gap or opening between 25 the needle and the seat, to be accurately controlled. In another embodiment moving the cartridge module may comprise actuating a solenoid to move the cartridge module from a distal position to a proximal position. Moving the cartridge module from the distal position to the proximal position may comprise engaging 30 a collar on the needle to move or lift the needle in a proximal direction off the needle seat. The method may also comprise activating an air horn or fan pattern air prior to moving the cartridge and / or needle. The method may also comprise returning the needle to a 35 seated position in which the distal tip of the needle is seated on the needle seat. Returning the needle to the seated position may comprise using a spring to urge the needle towards the seated position. The method may comprise de-activating the atomising air supply after the distal tip of the needle is seated on the needle seat. 5 Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. 10 BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 15 Figure 1 is a schematic top view of the spray gun in accordance with embodiments of the invention; m CM Figure 2 is a cross-sectional side view of the spray gun of Figure 1 in a closed configuration; 20 I- Figure 3 is an enlarged cross-sectional side view of a cartridge module and adjuster nut of the spray gun of Figure 2; Figure 4 is a cross-sectional side view of the spray gun of Figure 2 with the 25 solenoid in an ON configuration and the fluid adjuster nut in a closed configuration; Figure 5 is a cross-sectional side view of the spray gun of Figure 2 with the solenoid in an ON configuration and the fluid adjuster nut in a further closed 30 configuration; Figure 6 is a cross-sectional side view of the spray gun of Figure 2 with the solenoid in an ON configuration and the fluid adjuster nut in an open configuration; and Figure 7 is a flowchart showing a method of applying a coating material to a surface using the spray gun of Figure 1. 5 DETAILED DESCRIPTION In general terms embodiments of the invention relate to a spray gun for applying a food safe nano coating to a fibrous food container or liquid graphene to a substrate, such as polyethylene, to remove an anti-static charge. The spray gun comprises a body with a 10 fluid passageway for delivering the coating material to be sprayed to the spray tip and an adjuster nut extending around the body for adjusting the flowrate of fluid from the spray tip. The spray gun further comprises a cartridge module housed within the adjuster nut for varying the position of the needle tip within the body. Furthermore, the cartridge module is coupled to a solenoid for actuating the needle tip between a closed 15 configuration in which the needle tip is seated and an open configuration is lifted off the needles seat such that fluid may be sprayed from the spray tip. LO C\j The spray gun may be actuated rapidly between the open and closed configurations by the solenoid thereby allowing the spray gun to be used on high volume production lines. 20 Furthermore, the adjuster nut and cartridge module allow the flow rate to be accurately controlled by a user of the spray gun and also ensures repeatability of the flow rate once a target flow rate has been selected by the user. To place embodiments of the invention in a suitable context reference will firstly be made 25 to Figure 1 which shows a schematic top view of the spray gun 100 for spraying a food safe coating on a food container (not shown) made from a fibrous material or a liquid graphene coating to polyethylene (not shown). The spray gun 100 is mounted on a mounting bracket 19 which may be moveable to vary the direction of material being sprayed from the spray gun 100 to ensure the entire surface of the food container is 30 coated by the food safe coating or similar where the graphene coating is applied to polyethylene products. The spray gun 100 may be mounted on the mounting bracket 19 and used within a factory multi spray gun production line for applying a food safe coatings to the surfaces of the food containers or to apply graphene to a substrate. 35 As shown in Figure 1, the spray gun 100 comprises a body 4 and a solenoid 16 coupled to the body 4 by the solenoid shaft 15. The solenoid 16 is configured to actuate the spray 8 gun 100 between a closed configuration in which the spray tip (not shown in Figure 1) is sealed thereby preventing coating material from being sprayed from the spray tip and an open configuration in which the spray tip is open such that coating material may be sprayed from the spray gun 100. The body 4 and solenoid 16 are mounted to the 5 mounting bracket 19 by a pair of bolts for securing the body 4 and solenoid 16 to the mounting bracket 19 respectively. The spray gun 100 further comprises a fluid adjuster nut 13 extending around a proximal end of the body 4. The fluid adjustor nut 13 is rotatably coupled to the body 4 by a thread 10 such that the longitudinal position of the fluid adjuster nut 13 relative to the body 4 may be adjusted by rotating the fluid adjuster nut 13 on the thread on the external surface of the body 4. The fluid adjuster nut 13 may comprises a visual scale such that a user of the spray gun 100 may select a desired flow rate of coating material from the spray gun 100 by rotating the fluid adjuster nut 13 to a position that corresponds with the target 15 flow rate. The atomising air inlet 18 and fan pattern air inlet 17 are also shown in Figure 1, these are connected by flexible airlines to separate electronically controlled air regulators, which control the opening and closing operation sequences and the air pressure requirements for the various micron film tolerance and fan pattern width requirements. 20 Turning now to Figure 2 there is shown a cross-sectional side view of the spray gun 100. The body 4 of the spray gun 100 comprises a central bore that defines a fluid flow passageway 32 for receiving the coating to be applied by the spray gun 100. A needle 5 extends along the fluid flow passageway 32 and, when in the closed configuration (as 25 shown in Figure 2), forms a seal with the needle seat or spray tip 3 at the distal end of the body 4. The body 4 further comprises a fluid inlet 34 for delivering the coating material to the fluid flow passageway 32. Typically, the coating material is supplied to the spray gun 100 via the fluid inlet 34 from a low pressure feed system, using a circulation with a back pressure valve to maintain sufficient coating pressure to the spray 30 gun 100. Circulating the coating material is beneficial as it helps to maintain a consistent viscosity and filtration thereby improving the accuracy and repeatability of the flow rate of coating material from the spray gun 100. The proximal surface 50 or first abutment surface of the body 4 comprises an annular 35 opening 36 which extends around the fluid flow passageway 32 and needle 5 such that the needle 5 extends through an aperture 38 in the base of the annular opening 36. A seal nut 7 is located within the annular opening 36 and a seal 6, typically an O-ring, encircles the needle 5 at the aperture 38. The seal nut 7 accommodates the seal 6 within an annular recess located on the distal end surface of the seal nut 7 such that the 5 pressure applied to the seal 6 by the seal nut 7 may be varied by rotating the seal nut 7 within the thread between the seal nut 7 and the body 4. The seal 6 beneficially prevents any coating material from leaking from the fluid flow passageway 32. The body 4 further comprises an air cap 2 positioned on a distal surface of the body 4 10 for creating the fan pattern of the coating expelled from the spraytip 3. The air cap 2 is clamped to the distal end of the body 4 by a ring 1. The ring 1 is fitted to the distal end of the body 4 by a thread which presses the air cap 2 against the end face of the distal end of the body 4. As shown in Figure 1, the air cap 2 comprises two air horns 17, 18 for respectively controlling the fan pattern focal point and fluid atomisation of coating 15 material being sprayed by the spray gun 100. The spraytip 3 is longitudinally aligned with an outer planar surface of the air cap 2. This is beneficial as aligning the spraytip 3 LO the outer surface of the air cap 2 reduces turbulence of the sprayed material from the CM spray gun 100 and further allows the focal point of the fan to be controlled accurately by the air from the two air horns 17, 18 shown in Figure 1. 20 The body 4 comprises an atomising air inlet 18 (best viewed in Figure 1)for delivering the atomising air to the spraytip 3. The atomising air inlet 18is configured to deliver atomising air to the spraytip 3 before the needle 5 is lifted off the seat within the spraytip 3. Similarly, when moving the needle 5 from the open position to the closed position the 25 needle 5 is first seated and then the atomising air is turned off after the needle 5 is seated. This is beneficial as it reduces spatter or spray of the coating material from the spray gun 100 thereby ensuring a high quality finish is applied by the spray gun 100. The fan pattern controlled by the air horns 2 may be controlled separately from the atomising air such that the fan pattern may be controlled independently from the 30 atomising air pressure. The fan pattern air inlet 17 is closed simultaneously and independently with the closing of the atomising air inlet 18. The proximal end of the needle 5 is located within a cartridge module 30 housed within the fluid adjuster nut 13. The cartridge module 30 is coupled to the solenoid shaft 15 35 such that activating the solenoid 16 causes movement of the cartridge module 30 which in turn causes the tip of the needle to be lifted off the needle seat or spray tip 3, when prior movement of the fluid adjustment nut 13 is positioned to suit the flow rate. The cartridge module 30 is formed from a piston 8, a housing 9 and a spring guide 10 which together form the cartridge module 30. Turning now to Figure 3, an enlarged view of the cartridge module 30 of Figure 2 is shown. The piston 8 is located at a distal end of the cartridge module 30 such that a distal surface of the piston 8 abuts the first abutment surface or proximal surface 50 of the body 4 when the solenoid 16 is OFF as shown in Figure 2 and 3. The piston 8 is a 10 disc having annular recesses located on opposing distal and proximal sides of the piston 8. The annular recess located on the distal face of the piston 8 is configured to provide clearance for the seal nut 7 located on the body 4 such that the seal nut 7 may be adjusted, where the seal nut 7 may sit proud of the body 4, to vary the pressure on the seal 6 without interfering with the piston 8. A lip extending around the annular recess on 15 the distal surface of the piston 8 abuts and rests against the proximal surface 50 of the body 4. The piston 8 further comprises a piston aperture 35 extending through the centre of the piston 8. The piston aperture 35 is dimensioned to provide a clearance fit with the 20 external surface of the needle 5 (as shown in Figure 2) such that the piston 8, and thus cartridge module 30, may move freely relative to the needle 5. The annular recess located on the proximal side of the piston 8 comprises an internal thread extending along the internal side surface of the annular recess. The threaded 25 annular recess on the proximal side of the piston 8 forms a female thread configured to receive a corresponding male thread on the distal end of the housing 9. When the housing 9 is secured to the piston 8 by the threaded portion of the housing 9 and piston 8 a radially extending shoulder 39 on an external surface of the housing 9 abuts the proximal surface on the piston 8. The radially extending shoulder 39 beneficially controls 30 the depth that the male thread of the housing 9 extends into the female thread of the piston 8 thereby preventing overtightening of the housing 9 onto the piston 8. As shown in Figure 3 the housing 9 is positioned between the piston 8 and spring guide 10 of the cartridge module 30. The housing 9 comprises a central bore 42 extending 35 through the housing 9. The central bore 42 is longitudinally aligned with a longitudinal axis of the needle 5, and thus the fluid flow passageway 32, and a proximal end of the needle 5 is located within the central bore 42. The central bore 42 is dimensioned so as to accommodate a needle shoulder 44 located on a proximal end of the needle 5 as is discussed in further detail below. 5 The cartridge module 30 further comprises a spring guide 10 secured to a proximal end of the housing 9. The spring guide 10 is configured to secure the cartridge module 30 to the solenoid 16 via the solenoid shaft 15. As best viewed in Figure 3, the spring guide comprises an annular recess 46 on a distal surface of the spring guide 10 for receiving 10 a corresponding protrusion on the proximal side of the housing 9. The spring guide 10 may be bonded to the protrusion on the proximal side of the housing 9 or the housing may comprise a male thread configured to engage a corresponding female thread located on the distal surface of the spring guide 10. Bonding the spring guide 10 to the housing 9 beneficially improves the manufacturability of the spring guide 10 and housing 15 9. 20 The spring guide 10 further comprises a spring protrusion 48 extending distally from the base of the annular recess 46. The spring protrusion 48 is configured to locate and support a needle spring 11 extending between the spring guide 10 and the needle shoulder 44. The needle spring 11 is configured to urge the needle 5 in a distal direction to keep the needle 5 seated when the solenoid 16 is OFF to prevent any coating material leaking from the spray tip 3. The needle spring 11 extends through the bore 42 of the housing 9 between the spring guide 10 and the needle shoulder 44. 25 As shown in Figure 3, a proximal end of the needle 5 is received within the needle spring 11 as the distal end of the needle spring rests against the needle shoulder 44. Similarly, the proximal end of the needle spring 11 extends over the spring protrusion 48. Locating the spring needle 11 with the spring protrusion 48 and the proximal end of the needle 5 beneficially secures the needle spring 11 in position and allows the needle spring 11 to 30 maintain the needle 5 in a seated position when the spray gun 100 is in the OFF configuration. As best viewed in Figure 2 the fluid adjuster nut 13 is rotatably secured to the body 4 by a thread 54 and the cartridge module 30 is encased by the fluid adjuster nut 13. Rotating 35 the fluid adjuster nut 13 varies the longitudinal position of the fluid adjuster nut 13 relative to the body 4 which in turn varies the flow rate of coating material from the spray tip 3 of the spray gun 100 when the solenoid is in the ON configuration. The fluid adjuster nut 13 is a nut having an opening at its distal end for at least partially 5 receiving a proximal end of the housing 4. The distal opening of the fluid adjuster nut 13 comprises a female thread configured to cooperate with a corresponding male thread position on the proximal end of the body 4. The fluid adjuster nut 13 comprises a chamber that encases the cartridge module 30 such that the cartridge module is housed within the fluid adjuster nut 13. The fluid adjuster nut 13 further comprises an inwardly 10 extending shoulder 52 within the chamber of the fluid adjuster nut 13. The shoulder 52 is located at a proximal end of the fluid adjuster nut 13 and extends radially inwardly from the internal surface of the fluid adjuster nut 13. The fluid adjuster nut 13 comprises a female thread located proximally of the shoulder 15 52. A backstop 14 may be screwed into the female thread such that the backstop 14 abuts the shoulder 52 of the fluid adjuster nut 13. The backstop 14 provides a second abutment surface that beneficially inhibits movement of the cartridge module 30 when the solenoid 16 is ON and the cartridge module is in an open or proximal position. As such, adjusting the longitudinal position of the fluid adjuster nut 13 in turn varies the 20 position of the backstop 14 thereby allowing the distance the needle 5 is lifted off the spray tip 3 to be controlled accurately by controlling the longitudinal position of the cartridge module 30 when it is in the proximal position. A main spring 12 extends between the second abutment surface on the backstop 14 25 and the shoulder 39 on the housing 9. The main spring 12 beneficially urges the cartridge module 30 towards the distal position in which the piston 8 abuts the first abutment surface or proximal surface 50. As such, the main spring 12 returns the cartridge module 30 to the distal position when the solenoid 16 is OFF. Furthermore, the main spring 12 maintains pressure on the needle spring 11. The main spring 12 is stiffer or stronger 30 than the needle spring 11 such that the main spring 12 maintains the cartridge 30 seated when the needle 5 is in the closed position. Furthermore, the main spring 12 allows rapid closing of the needle when the solenoid 16 is turned off and the needle 5 is to return to the closed or seated position. This is 35 beneficial as it allows rapid control of the spray gun 100 between an ON and an OFF configuration. This is particularly important when applying a nano coating, of about 5 to 10 microns thickness, to a surface where rapid open and closing of the needle 5 is important for achieving a precise coating requirement. When applying a food safe coating to an individual food tray the total weight of the coating is 3g or 2.9ml with a 5% 5 tolerance of coating material which may be applied to the base of a moving tray or applied in a stopped position to the side walls over about 10 seconds of spraying time. Turning now to Figure 4 there is shown a side view of the spray gun 100 with the solenoid 15 in the ON configuration. In Figure 4 the fluid adjustor nut 13 is in a closed position 10 such that the backstop 14 is positioned so as to inhibit movement of the cartridge module 30 such that the needle tip remains seated on the spray tip 3 when the solenoid 16 is actuated to the ON position. As shown in Figure 4 when the cartridge module 30 is moved in a proximal direction away from the proximal end face of the body 4 to the proximal position in which the spring guide 10 abuts the second abutment surface the 15 needle collar 44 (not shown in Figure 4) does not contact the piston 8 and as such the needle tip remains seated. Whilst Figure 4 shows relative dimensions between various LO components within the spray gun 100 the skilled reader will understand that these are CM indicative dimensions and may be varied depending on the size of the spray gun 100 and the application the spray gun 100 is being used in. 20 As shown in Figure 4 when the solenoid 16 is activated to the ON configuration the “ solenoid shaft 15 moves in a proximal direction which in turn also causes the cartridge module 30 to move in a proximal direction to the proximal position, thereby lifting the piston 8 off the first abutment surface or proximal face 50 of the body 4. Moving the 25 cartridge module 30 in the proximal direction brings the spring guide 10 into contact with the back stop 14 or second abutment surface as shown in Figure 4 such that the spring guide shoulder abuts the back stop 14. When the fluid adjuster nut 13 is in the closed position such that actuating the solenoid 30 16 does not lift the tip of the needle 5 off the spray tip 3 a collar gap is maintained between the piston 8 and the needle shoulder 44. In the example shown in Figure 4 the collar gap is 1.5mm, the needle spring 11 urges the needle 5 towards the spray tip 3 such that actuating the solenoid 16 when the fluid adjuster nut 13 is in the closed position does not lift the needle tip off the spray tip 3, still retaining a seal. 35 Turning now to Figure 5, the spray gun 100 is shown with the fluid adjuster nut 13 rotated to a position in which the back stop 14 is positioned such that actuating the solenoid 16 causes the piston 8 within the cartridge module 30 to engage the needle collar 44 but without lifting the tip of the needle 5 off the spray tip 3. The position shown in Figure 4 5 may be a reference position or a zero flow rate position that is marked on the fluid adjuster nut 13 to indicate to a user of the spray gun 100 that by further turning of the fluid adjuster nut 13 to move the back stop 14 in a further proximal direction relative to the body 4 will cause coating material to be sprayed from the spray tip 3 of the spray gun 100. 10 Turning now to Figure 6, the spray gun 100 is shown in an open position in which the distal tip of the needle 5 is lifted off the spray tip 3 by the cartridge module 30. As shown in Figure 6, the cartridge module 30 has been actuated by the solenoid 16 such that the piston 8 of the cartridge module 30 has been lifted off the proximal face 50 of the body 15 4 by 4mm. In turn, the proximal face of the piston 8 engages the needle shoulder 44 to lift the distal tip of the needle 5 off the spray tip 3. Lifting the distal tip of the needle 5 off the spray tip 3 allows coating material to be expelled from the spray gun 100 to coat the surface of a food container made from a fibrous material. Where test weights of the coated tray would provide the knowledge to allow fine tune movements of the fluid 20 adjustment nut 13 by turning to the respective higher or lower digital number to increase or decrease the material flow rate. Beneficially, the fluid adjuster nut 13 allows the longitudinal position of the backstop 14 to be controlled accurately which in turn has the effect of varying the resultant gap 25 between the distal tip of the needle 5 and the spray tip 3 when the solenoid 16 is actuated to the ON position. As such, the flow rate of coating material expelled from the spray gun 100 may be controlled accurately. When the cartridge module 30 is in the open position, as shown in Figure 6, the needle 30 spring 11 beneficially urges the needle shoulder 44 in a distal direction towards the piston 8. This is beneficial as the needle spring 11 ensures that contact is maintained between the piston 8 and needles shoulder 44 thereby allowing accurate control and repeatability of the position of the needle 5. Furthermore, when the solenoid 16 and thus cartridge module 30 are returned to the OFF or closed position the needle spring 11 returns the distal tip of the needle 5 to the seated position in which the tip of the needle 5 forms a seal with the needle seat or spray tip 3. Similarly, when the solenoid 16 is deactivated the main spring 12 urges the 5 cartridge module 30 back to a closed or OFF position in which the piston 8 abuts the proximal surface of the body 4. The solenoid 16 beneficially allows the spray gun 100 to be actuated rapidly between an ON position and OFF position. Furthermore, the fluid adjuster nut 13 and back stop 10 14 ensure that the position of the cartridge module 30 may be accurately controlled thereby allowing the flow rate of coating material from the spray gun 100 to also be accurately controlled. Once a user selects a desired flow rate the back stop 14 does not move thereby providing repeatability of the flow rate of coating material from the spray gun 100. 15 20 Turning now to Figure 7 a flow chart outlining a method of spraying a coating on a surface, such as a surface of a food tray, using a spray gun 100 is shown. In Step 701 a user of the spray gun 100 selects a desired flow rate of coating material to be sprayed by the spray gun 100. Selecting a flow rate of coating material from the spray gun 100 may comprise rotating a fluid adjuster nut 13 to vary a longitudinal position of the back stop 14 to control the distance the needle 5 is lifted off the needle seat when in the open position. In Step 702 the atomising air and fan air are turned on. The air pressure of the atomising 25 air and fan air may be controlled independently of each other to allow a user of the spray gun 100 to control the particle size of coating material and also the fan width independently of each other. The atomising and fan pattern air are programmed within the automated system to activate electronically controlled air regulators to the on position from laser signals that detect the moving or stationary spraying positions of 30 objects such as a tray. In Step 703, once the atomising air and fan air are turned ON the needle 5 is lifted off its seat or spray tip 3. The needle 5 may be lifted off the spray tip 3 by actuating a solenoid 16 to move the needle 5 in a proximal direction. Actuating the solenoid 16 may 35 cause the cartridge 30 to move in a proximal direction and to engage a needle collar to lift the needle 5 off the spray tip 3. In Step 704, when the needle 5 is lifted off the spray tip 3 the coating material is sprayed on the spray surface of the food tray. Spraying the coating material may comprise varying the position of the gun such that the coating material is applied evenly to the entire surface that is to be coated. The fluid flow is 5 programmed within the automated system to activate an electronically controlled fluid regulator to the on position after the activation of the atomising and fan pattern air flow. In Step 705, the needle 5 is returned to the seated position. Returning the needle 5 to the seated positioned may comprise turning the solenoid OFF and urging the needle 5 10 to the seated position using a needle spring 11 and main spring 12. The main spring 12 may urge the cartridge 30 to a seated position and the needle spring 11 may urge the needle to the seated position. In Step 706 the atomising air and fan air are turned off. The fluid flow is programmed within the automated system to activate an electronically controlled fluid regulator to the off position after completing the measured spray 15 application requirement. The spray gun 100 may be connected to a processor or control module within a control system for actuating the solenoid 16 and controlling the spray gun 100. For example, the spray gun 100 may be used within a production line for applying the various coatings 20 to a range of substrates. For example, the spray gun 100 may be used in a production line for applying one or more food safe coatings to a food tray or for applying liquid graphene to a substrate such as applying graphene to polyethylene. The control system may activate the spray gun 100 in the x, y, z and also rotational movement as required to suit any geometrical shape when a tray is ready to be sprayed and deactivate the 25 spray gun 100 and movement when the coating has been applied to the tray and the gun is awaiting the next tray to be sprayed in the production line. It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application, where multi spray 30 guns may be used effectively to meet production demands.

Claims

1. A spray gun for applying a coating to a substrate, the spray gun comprising: 5a body comprising a fluid passage extending longitudinally through the body from a spray tip located at a distal end of the body;a fluid adjuster nut rotatably coupled to the body such that rotating the10 fluid adjuster nut varies the longitudinal position of the fluid adjuster nutrelative to the body;a cartridge module located within a cavity of the fluid adjuster nut comprising a bore wherein the bore is longitudinally aligned with the fluid15 passage; anda solenoid coupled to the cartridge module and operable to move the cartridge module between a distal position in which the cartridge module abuts a first abutment surface of the body and a proximal position in20 which the cartridge module abuts a second abutment surface on the fluidadjuster nut wherein the second abutment surface is a back stop ring secured to a proximal end of the adjuster nut; andwherein moving the cartridge module from the distal position to the25 proximal position lifts a needle located within the fluid passage from aseated position in which the needle forms a seal between a spray tip on the body and a distal tip of the needle, and an open position in which the distal tip of the needle is lifted off the spray tip to define a gap between the tip of the needle and the spray tip.

302. A spray gun as claimed in Claim 1, wherein the needle comprises a collar positioned within the bore of the cartridge module and wherein moving the cartridge module from the distal position to the proximal position causes the cartridge module to engage the collar to lift the tip of the needle off the spray35 tip.

3. A spray gun as claimed in Claim 1 or Claim 2, wherein rotating the adjuster nut varies the position of the second abutment surface such that the gap between the tip of the needle and the spray tip when the needle is in the open position 5 may be controlled.

4. A spray gun as claimed in any preceding claim, wherein the back stop ring is removable from the adjuster nut to access the cavity of the adjuster nut.10 5. A spray gun as claimed in any preceding claim, wherein the cartridge modulecomprises a needle spring extending longitudinally through the bore for urging the needle towards the seated position.

6. A spray gun as claimed in Claim 5, when dependent on Claim 2, wherein the15 needle spring abuts the collar to urge the needle towards the seated position.

7. A spray gun as claimed in Claim 5 or Claim 6, wherein the spray gun comprisesa main spring extending between the second abutment surface and a radially extending flange on the cartridge module.

8. A spray gun as claimed in Claim 7, wherein at least a portion of the cartridge module is received within the main spring.

9. A spray gun as claimed in Claim 8, wherein the main spring is stronger than the25 needle spring.

10. A spray gun as claimed in any preceding claim, wherein the cartridge module comprises a housing and wherein the housing comprises the bore.30 11. A spray gun as claimed in Claim 10, wherein the cartridge module furthercomprises a piston ring connected to a distal end of the housing and wherein the piston ring comprises a needle aperture through which the needle extends.

12. A spray gun as claimed in Claim 11, wherein the piston ring comprises a female thread located on a proximal side of the piston ring and wherein a distal end of the housing comprises a male thread for securing the housing to the piston ring.5 13. A spray gun as claimed in Claim 11 or 12 when dependent on Claim 7, whereinthe radially extending flange extends radially from the housing and wherein a distal side of the radial flange abuts the piston ring when the housing is connected to the piston ring.10 14. A spray gun as claimed in any one of Claims 10 to 13, wherein the cartridgemodule further comprises a spring guide connected to a proximal end of the housing.

15. A spray gun as claimed in Claim 14, wherein the spring guide is bonded to the15 housing.LDC\j 16. A spray gun as claimed in Claim 14 or 15, wherein the spring guide comprises ashoulder for abutting the second abutment surface when the cartridge module is moved to the proximal position.I^.    2017. A spray gun as claimed in any one of Claims 14 to 16, wherein the spring guide is coupled to a solenoid shaft such that actuation of the solenoid causes the solenoid shaft and cartridge module to move between the proximal and distal positions.2518. A method of applying a coating material to a substrate using a spray gun, themethod comprising:selecting a desired flow rate of coating material from the spray gun by30varying a longitudinal position of an abutment surface; andoperating a solenoid coupled to move a cartridge module between a distal position in which the cartridge module abuts a first abutment surface of the body and a proximal position in which the cartridge module35 abuts a second abutment surface on the fluid adjuster nut, wherein thesecond abutment surface is a back stop ring secured to a proximal end of the adjuster nut; andwherein moving the cartridge module comprises lifting a needle off a 5 needle seat to create a gap between the needle seat and a distal tip ofthe needle to allow coating material to be sprayed from the spray gun; and wherein an atomising air supply is activated prior to moving the cartridge module and lifting the needle off the needle seat.10 19. A method as claimed in Claim 18, wherein varying the longitudinal position of theabutment surface comprises rotating a fluid adjuster nut.20.15LO CM 21A method as claimed in Claim 18 or Claim 19, wherein moving the cartridge module comprises actuating a solenoid to move the cartridge module from a distal position to a proximal position.A method as claimed in Claim 20, wherein moving the cartridge from the distal position to the proximal position comprises engaging a collar on the needle to move the needle in a proximal direction.A method as claimed in any one of Claims 19 to 21, comprising returning the needle to a seated position in which the distal tip of the needle is seated on the needle seat.25 23. A method as claimed in Claim 22, when dependent on Claim 19, comprising deactivating the atomising air supply after the distal tip of the needle is seated on the needle seat.

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