Abstract
The invention provides a method and apparatus for treating at least part of an edge of an acoustic panel, and acoustic panels with such an edge treatment.
Claims
1. A method of coating a minor face of an acoustic panel, the acoustic panel comprising two opposed major faces and one or more minor faces that extend between the major faces, the method comprising the steps of applying a powder to at least a part of a minor face, applying a binder to the same part of the minor face, thereby forming a layer of powder and binder on the minor face, and then treating the layer to form a film.
2. The method according to claim 1, wherein the binder is particulate and is a component of the powder.
3. The method according to claim 1, wherein the binder is a liquid and is applied separately after application of the powder to at least part of the minor face.
4. The method according to claim 1, wherein the minor face is milled before application of the powder.
5. The method according to claim 1, wherein prior to application of the powder to the at least a part of a minor face, the powder is processed in a fluidised bed, and wherein the powder flows from the fluidised bed onto the at least a part of the minor face.
6. The method according to claim 5, wherein a valve system is positioned ahead of the minor face in the path of the fluidised powder, thereby controlling the flow of the powder.
7. The method according to claim 6, wherein the valve system comprises a shutter wheel, the shutter wheel rotating in cooperation with a conveyor system on which the acoustic panel is transported, wherein the shutter wheel comprises a rim wall and a rim opening to effect closed and open positions, respectively, of the valve system.
8. The method according to claim 1, wherein the powder is applied to a minor face by vacuum suction, wherein the vacuum suction is applied through the panel material.
9. The method according to claim 8, wherein at least part of the minor face to be coated is supported in a frame, the frame is provided with an inlet for the powder and the surfaces of the panel not to be coated are covered during vacuum suction, and wherein vacuum suction is applied to the panel, thereby drawing powder through the inlet and onto and into the surface to be coated.
10. The method according to claim 1, wherein the powder is packed or sprayed onto at least part of the minor face and levelled to make a smooth surface.
11. The method according to claim 1, wherein the step of treating the layer of powder and binder on the minor face to form a film comprises heating.
12. The method according to claim 1, wherein the powder comprises (a) an inorganic filler, (b) a pigment or dye component; or both (a) and (b).
13. The method according to claim 1, wherein the acoustic panel is a man-made vitreous fibre panel.
14. An acoustic panel comprising two major faces and one or more minor faces therebetween, characterised in that at least a portion of a minor face comprises a film formed according to claim 1.
15. The acoustic panel according to claim 14, wherein the film comprises (a) a binder; and (b) an inorganic filler and/or a pigment or dye.
16. The acoustic panel according to claim 14, wherein the film has a thickness of from 50 to 1000 μm.
17. A suspended ceiling or an acoustic wall comprising a support grid and a plurality of acoustic panels according to claim 14.
18. An acoustic ceiling comprising a plurality of suspended vertical baffles, wherein the vertical baffles are acoustic panels according to claim 14.
19. An acoustic ceiling comprising a free-hanging island, wherein the free-hanging island comprises an acoustic panel according to claim 14.
20. The acoustic panel according to claim 16, wherein the film has a thickness of from 50 to 500 μm.
Description
BRIEF DESCRIPTION OF DRAWINGS
[0097] FIG. 1 shows a portion of apparatus for use in the method of the invention
[0098] FIG. 2 shows a supplementary part of the apparatus of FIG. 1
[0099] FIG. 3 shows a heating element in combination with a portion of a powder application apparatus for use in the invention
[0100] FIG. 4 shows how density of the acoustic panel affects powder loading
[0101] FIG. 5 shows how a prior art paint layer without powder coating retains surface defects even after painting
[0102] FIG. 6 shows how a smooth surface is achieved with powder coating at the same time as different powder loading along the panel edge.
[0103] FIG. 7 shows how the minor face of a panel can have several distinct surfaces, which may not all require coating.
[0104] FIG. 8 shows how defects can still be visible for surfaces of the minor face which are not themselves exposed.
[0105] FIG. 9 shows a panel top view during powder application.
[0106] FIG. 10 shows a panel perspective view during powder application.
[0107] FIG. 11 shows a gate system in the open position, for controlling the flow of powder onto the panel edge.
[0108] FIG. 12 shows the rotating component of the gate system of FIG. 11, in the closed position.
[0109] FIG. 13A shows a cross-sectional view of the gate system from above, in the open position.
[0110] FIG. 13B shows the system of FIG. 13A in the closed position.
[0111] FIG. 14A shows the view A-A from FIG. 13A.
[0112] FIG. 14B shows the view B-B from FIG. 13B.
DETAILED DESCRIPTION
[0113] FIG. 1 illustrates how a minor face 2 of an acoustic panel 1 can be coated with powder to form a layer, which is then cured further down the production line to form a film. The acoustic panel 1 comprises opposing major faces 3 with four minor faces 2 extending between the major faces 3. In the production line, the acoustic panel 1 moves through a frame 4. The frame may enclose a single minor face 2, but preferably opposite minor faces 2 are subjected to a powder coating process simultaneously, with a frame 4 enclosing opposite minor faces 2 of the acoustic panel 1 (second frame not shown).
[0114] The frame 4 comprises a vacuum suction inlet 5 through which powder is drawn and sticks to the minor face 2. In this example the acoustic panel 1 is a bonded MMVF panel, which acts as a filter, thereby trapping the powder against the minor face 2 when air flows from the vacuum suction inlet 5 to the vacuum suction outlet 6.
[0115] In a production line, the powder is applied in a continuous process, such that the panel 1 moves continuously along the frame 4 and continuously against the vacuum suction outlet 6. Once the vacuum suction is removed, the powder remains adhered to the minor face 2 and the panel 1 is transported to a film formation zone (not shown). Heat is applied to cure the binder component or to otherwise form a film by another physical or chemical process. Preferably infrared heating is used because this achieves fast curing and thereby takes up least space on the production line, but other types of heating such as convection heating could be used in cases where sufficient space is available.
[0116] Although the vacuum suction outlet 6 and thus the vacuum suction head is illustrated as being applied to the major face 3 on the upper side of the panel on a conveyor, it may equally be placed on the major face 3 on the underside of the panel, or on the minor face 2 of the panel immediately downstream of the powder inlet 5 and frame 4. These alternative arrangements are not shown in the figures.
[0117] In other embodiments, the powder is applied to the panel edge 2 by means of controlled flow of fluidised powder from an application chamber 70 comprising a fluidised bed. Aspects of this are shown in FIGS. 11-14. The vacuum suction inlet 5 and outlet 6 are not essential when the fluidised bed is used, because the positive pressure from the fluidised bed generates a pressure differential causing airflow and fluidised powder flow in the direction of the panel edge 2. Nevertheless, vacuum suction may optionally be used in order to hold the powder in place on the panel edge 2 prior to the film forming zone. This also applies if the powder is applied to the panel edge 2 by means of mechanical packing (not shown).
[0118] In FIG. 2, powder handling apparatus 7 is shown supplementary to the details described for FIG. 1. The powder handling apparatus 7 may also be referred to as an “application chamber” or a “powder application chamber”. The apparatus 7 comprises a powder inlet 8 and a powder outlet 9 and is configured to supply powder to the vacuum suction inlet 5. Vacuum suction inlet 5 is also the exit route for powder travelling towards panel edge 2. A silo (not shown) which acts as a powder reservoir may be fitted to the powder inlet 8. Powder from the powder outlet 9 may be cleaned and recirculated to the powder inlet 8. When using a MMVF panel, escaped fibres are also removed by the powder outlet 9. Fibres and powder are separate prior to recirculation to the powder inlet 8, so that the powder is not wasted and the powder layer is not contaminated by loose fibres. This recycling process is especially useful on a continuous production line, because it prevents build-up of excess powder and loose fibres in the apparatus 7.
[0119] In FIG. 3, a heater 19 is illustrated downstream of the powder application apparatus. These stages are illustrated as being rather close in location, but in reality may be spaced at any suitable distance to meet the needs of a production line. The heater 19 may be any kind of heating apparatus. Preferably infrared heating is used for the heater 19 because this is much quicker than e.g. convection heating; rapid film formation is important in a continuous manufacturing process.
[0120] FIG. 4 shows a schematic cross-section of a panel edge 2 with areas of higher density 10 and lower density 11. Powder is drawn onto the panel edge 2 by vacuum suction in the direction of the arrows 12. More powder is transported to and penetrates further into the lower density areas 11 due to the lower resistance to airflow and preferentially settles in the lower density areas 11. This function of the powder contributes to the even, finished surface achieved in the method of the invention.
[0121] A painted panel edge 2 (prior art) is shown schematically in FIG. 5. The paint, which is usually waterborne in this context, settles evenly on the panel edge 2, regardless of edge defects 13a, forming a uniform film thickness. This means that the painted surface 14 retains the edge defects 13b.
[0122] FIG. 6 shows schematically how the powder application of the invention can both provide a smooth exterior surface to a panel edge and fill in the surface defects. This results in a uniform, strengthened edge, which compensates for differences in density, holes and any other inhomogeneity in the raw panel edge. The panel moves along a continuous production line in the direction of arrows Powder 16 has been applied to a minor face 2 of the panel and has filled out the surface defects 13a. A fixed guide element 17 smooths out the powder 16 to make a flat surface 18 ready for film forming (in the case where the powder 16 comprises a binder) or for spraying of binder and then film forming (in the case where the binder is separate from the powder 16).
[0123] In FIG. 7, two acoustic panels 1 are illustrated side-by-side. Each panel has a minor face 2 having a distinct edge profile, which is specially adapted for a suspended ceiling. The individual surfaces 2a of each panel edge 2 will be visible in the installed state and the individual surfaces 2b will match to face each other in the installed state. Surfaces 2a and 2b are treated in accordance with the invention, whereas the remaining two individual surfaces of each panel edge 2 in this example are left untreated because they will not be visible, thereby saving materials and costs. The installed state is illustrated in FIG. 8.
[0124] FIG. 8 shows schematically the benefits of the invention in a suspended ceiling comprising a plurality of adjacent acoustic tiles 1. The acoustic tiles 1 have a special edge profile to enable suspension from a grid. In the example shown in FIG. 8, the minor face 2 is thus made up of four distinct surfaces. Although only two special edge profiles are shown in cross section in FIG. 8 for illustrative purposes, in a real life application one or more of the remaining three minor faces (not shown) of each rectangular panel would normally also comprise a special edge profile and an array of many acoustic tiles would be provided to make up a whole ceiling. The major face 3 shown in FIG. 8 is visible to a person standing underneath the ceiling. One of the surfaces of the minor face 2 is visible when the suspended ceiling is in place and one of the surfaces abuts to an adjacent tile. Any defects 13a in the topography of the abutted surface will be visible when the suspended ceiling is in place, even though that surface is not itself exposed.
[0125] In this type of end-use application, the method of the invention may suitably be implemented on the exposed surface and the abutted surface, but not on the remaining parts of the minor face, which will not be visible in use. This reduces the materials needed to achieve the uniform visual appearance of the minor faces of the acoustic tiles.
[0126] FIGS. 9 and 10 show an embodiment of how a certain thickness of the powder layer can be achieved in practice. The dimensions in these figures are exaggerated to demonstrate the principle. For thinner powder layers of approximately 1 mm or thinner, the powder remains in place after the vacuum is removed and before the film-forming process, due to e.g. friction, electro static forces acting at the surface of fibres and particles, and moisture. The vacuum suction may however influence powder at greater distances away from the panel edge, for example up to approximately 2 cm thickness of powder. In these cases, the powder will not all remain adhered to the surface between removal of the vacuum suction and beginning of the film forming process.
[0127] In FIG. 9 a panel 1 is shown moving through the powder application stage of a production line. The panel 1 travels in direction 15 and a vacuum suction is achieved in the same manner as described above, with vacuum outlet 6 being shown in this case on the upper major face of the panel 1. However, in this and other embodiments including those described with respect to FIGS. 1-8, the vacuum suction outlet 6 may be located at the underside of the major face or on the minor face immediately ahead of the powder and vacuum inlet apparatus 7.
[0128] In FIG. 9, a gap, shown between arrows 20, is provided between the minor face to which the powder is applied and the apparatus 7. This gap smooths the powder and controls its thickness. This is useful in all implementations of the invention but has particular utility when a thicker powder layer, for example up to 2 cm, is applied to the panel edge 2.
[0129] The same principle can be seen in more detail in FIG. 10. The thicker layer of powder 16 requires continuous vacuum suction to be held onto the panel edge 2 until film formation. This may be achieved by implementing a larger vacuum head, elongated in direction 15, and/or by providing a plurality of vacuum suction heads along the production line. The powder 16 is applied to a portion of the minor face 2 and its shape and thickness can be controlled by the frame 4, in particular the interior profile of the frame 4 and its distance from the panel edge 2, i.e. the size of the gap 20 as shown in FIG. 9. The frame 4 may be angled relative to the panel edge 2 so that the final powder thickness is not exactly the same as the gap 20.
[0130] A preferred embodiment of the invention utilises a fluidised bed in order to handle the powder in the same manner as if it were a liquid. Fluidised bed apparatus and methods are known to those in the art and not shown here; the application chambers 7 and 70 illustrated in the figures may incorporate a fluidised bed system instead of a simple hopper.
[0131] The use of a fluidised bed and fluidised powder enables a more even coating of the panel edges, especially at the corners. It is preferred to use a valve system in combination with the fluidised bed because, although still dry and thus not messy like prior art systems, the fluidised powder flows in similar manner as a liquid and will continue to flow from the outlet 90 even when there is no juxtaposed panel edge to coat.
[0132] A valve system has been developed for use with the invention. Although described with respect to a fluidised powder, it could also be used with a conventional hopper or other powder handling apparatus (application chamber) 7. A preferred implementation of the valve system is described below with respect to FIGS. 11-14.
[0133] The valve system illustrated in FIGS. 11-14 comprises a shutter wheel 21 housed within application chamber 70, as shown in FIG. 11. During a continuous production line process, the shutter wheel 21 is completely submerged within the fluidised powder inside the application chamber 70. Powder is introduced into the application chamber 70 from the top and falls into the fluidised bed, thereby becoming fluidised. The shutter wheel 21 may be substantially cylindrical as can be seen in FIG. 12. The side wall of the shutter wheel 21 comprises alternating shutter rim openings 22 and shutter rim walls 23. The openings 22 and walls 23 align with powder outlet 90, thereby forming a valve for the fluidised powder in the application chamber 70. As a minimum there is at least one shutter rim opening 22 and at least one shutter rim wall 23. The shutter wheel comprises an axel 26 connectable to a motor (not shown).
[0134] The rate of input of powder into the application chamber 70 may optionally be controlled by means of a floating device in the fluidised bed, which ceases to break a laser beam when the level of fluidised powder with the application chamber 70 is too low (not shown). The floating device is in communication with a valve for the powder inlet (this optional feature is not shown).
[0135] The application chamber 70 comprises a powder outlet 90 through which the fluidised powder flows from the application chamber 70 to the panel edge (not shown in FIGS. 11-14). The shutter wheel 21 rotates such that the outlet 90 is alternately juxtaposed by a shutter rim opening 22 and a shutter rim wall 23. FIG. 13A shows the shutter wheel 21 acting as an open valve such that powder may flow from the application chamber 70 an onto a panel edge (not shown in FIGS. 11-14), i.e. when a shutter rim opening 22 juxtaposes the outlet 90. Flow of fluidised powder may be effected by means of positive pressure from within a fluidised bed. FIG. 13B shows the opening 90 juxtaposed by a shutter rim wall 23, i.e. a closed valve such that fluidised powder does not flow.
[0136] Preferably the shutter wheel 21 rotates in a direction 15A in coordination with the direction 15 of the panels (not shown) moving along the production line, as indicated in FIG. 13B.
[0137] In a manner analogous to that shown in FIG. 2 with application chamber 7 and frame 4, the application chamber 70 shown in FIG. 11 may be attached to a frame 4, for example by means of rivets, bolts, screws and the like using apertures 27.
[0138] FIG. 14A corresponds to the cross-section A-A from FIG. 13A. It shows in more detail the open valve position for the shutter wheel 21, whereby a shutter rim opening 22 is aligned with the outlet 90. Plate 24 forms the base of the fluidised bed and is permeable to air. Air is directed into the fluidised bed from the base upwards via air inlet 25, through plate 24 and up through the powder, pressurising and thereby fluidising the powder. Plate 24 may be, for example, an air-permeable plastic with thickness 5-6 mm. Other suitable membrane materials for plate 24 may be implemented by those skilled in the art of fluidised bed design. This air flow generates positive pressure within the application chamber 70, which together with the action of gravity causes fluidised powder to flow from the application chamber 70 to a juxtaposed panel edge (not shown) when the valve system is in the open position as illustrated in FIG. 14A.
[0139] Similarly, FIG. 14B corresponds to the cross-section B-B from FIG. 14B. Here the closed valve position can be seen in more detail, whereby a shutter rim wall 23 aligns with the powder outlet 90 (not visible in FIG. 14B, but position indicated for reference).
[0140] The rotation speed of the shutter wheel 21 need not be constant and could run in a stepwise, stop-start manner according to the needs of the production line. The relative time periods at which the valve system is open and closed can be controlled such that powder only flows out when there is a panel edge to coat. This may be controlled by a system programme or, ideally, by a detector system in communication with the motor (not shown) for the shutter wheel. The detector system (not shown) may be set up in any appropriate manner to those known in the art, for example optical or thermal imaging on the production line to detect the presence or absence of a surface to coat.
[0141] In FIGS. 11-14, although not indicated, vacuum suction may be applied as described above with respect to FIGS. 1-10. However, vacuum suction is not essential when using a fluidised bed system to generate a flow of powder through the outlet 5, 90 to the panel edge 2. In this case, the vacuum suction may be applied to increase the air stream for the powder, to better retain the powder on the panel edge prior to film formation, other or a combination of purposes.
[0142] The valve system described with respect to FIGS. 11-14 may also be implemented with embodiments other than a fluidised bed powder handling apparatus.
[0143] The valve system illustrated in FIGS. 11-14 is a preferred implementation.
[0144] Another implementation (not shown) of the valve system is external to the fluidised bed application chamber 70. An apertured ring may be positioned around the application chamber 70, the ring acting as a shutter wheel. The ring comprises windows (shutter rim openings), interposing solid segments of the ring (shutter rim walls). The ring comprises means for engaging a motor, such as apertures functioning in the manner of a camera film.
[0145] Alternative valve systems suitable for use with the invention may involve a simple sliding gate or another suitable closable exit from the application chamber 7, 70 for the powder.
LIST OF REFERENCE NUMERALS
[0146] 1 acoustic panel [0147] 2 minor face of acoustic panel [0148] 2a exposed part of minor face [0149] 2b abutting part of minor face [0150] 3 major face of acoustic panel [0151] 4 frame [0152] 5 vacuum suction inlet (powder outlet from application chamber to panel edge) [0153] 6 vacuum suction outlet [0154] 7 apparatus (application chamber) [0155] 8 powder inlet [0156] 9 powder outlet (for cleaning and recirculating powder) [0157] 10 higher density areas of panel edge [0158] 11 lower density areas of panel edge [0159] 12 direction of air flow in vacuum suction method [0160] 13a edge defects in panel [0161] 13b edge defects in painted panel (prior art) [0162] 14 painted surface (prior art) [0163] 15 direction of travel of panel on a continuous production line [0164] 15A direction of rotation of shutter wheel [0165] 16 powder [0166] 17 guide element [0167] 18 flat surface [0168] 19 heater [0169] 20 frame gap [0170] 21 Shutter wheel [0171] 22 Shutter rim opening [0172] 23 Shutter rim wall [0173] 24 Plate (base of fluidised bed) [0174] 25 Air inlet [0175] 26 Axel [0176] 27 Apertures [0177] 70 Powder handling apparatus (application chamber) [0178] 90 Fluidised powder outlet
