Acoustic absorbing panel provided with a decorative design pattern and a method and apparatus for manufacturing the panel

The invention concerns an acoustic absorbing panel with a decorative design pattern comprising a board comprising mineral fibres, said board having two major surfaces and four minor side surfaces. Said panel further comprising a fleece layer attached to at least one major surface of the mineral fibre board, and a layer of paint applied to said fleece layer on at least a major surface. The invention also concerns a method and an apparatus for manufacturing the acoustical absorbing panel.

This type of acoustical absorbing panel is known from ceiling panels provided with a painted fleece layer and a decorative design pattern. The decorative design pattern has been provided by applying the paint layer by use of a ro- tating drum having the pattern on its outside surface, whereby this pattern is printed in the paint layer.

This technique is relatively difficult to control and results in a paint layer which is not as homogenous as preferred. The technique is also relatively expensive due to waste of paint.

For instance, only minor spots, such as a few square millimetres each, may be left without paint, which leaves a pattern on the surface. However, the quality of this pattern may be less than perfect, as some of the minor spots may be filled with paint anyway and hence not visible.

US 6, 675,551 B1 discloses a plate-shaped constructional element comprising a plate made of a solid material and perforated by relatively large holes, whereby a micro-perforated sheet or thin plate is disposed on one of the plate surfaces of said plate-shaped constructional element in order to attenuate vibrations of the air in the micro-perforations. Although the micro-

perforations may form a pattern on the plate-shaped constructional element, this may be an expensive solution. Furthermore, painting of the micro- perforated sheet or thin plate may result in an irregular pattern, as some of the micro-perforations may clog up and consequently not be visible.

EP 1 840 287 A2 discloses a sound-absorbing panel comprising a relatively thick layer of porous sound-absorbing base material and a relatively thin porous veneer having pierced apertures formed by laser machining. However, this panel has the same disadvantages as mentioned above regarding pro- duction costs and possible clogging-up when painted.

It is an object of the present invention to provide an acoustic absorbing panel with a decorative design pattern, whereby the panel is simpler to manufacture and has a more accurately defined decorative design pattern.

These problems have been solved by an acoustic absorbing panel according to the invention where the fleece layer comprise lasting changes made by a laser beam, wherein the lasting changes have the form of changed colour or tint of the fleece material due to the heating effect by the laser, wherein said lasting changes are in the form of a decorative design pattern, and wherein the layer of paint has a composition and/or a thickness such that said decorative design pattern is visible through said layer of paint.

With this solution it will be possible to apply a homogenous layer of paint by a more efficient technique and at the same time obtain a decorative design pattern of a more regular quality.

Compared with prior art printing technologies, the laser will not add any additional material, such as ink, to the fleece, and hence the ceiling tiles will not be affected with regard to fire properties, environmental impact, (e.g. to the indoor climate), or acoustics (no ink closes off the surface, which otherwise

could reduce air permeability of the fleece). Further any printing technology adding ink is very expensive compared to laser marking, which also requires less maintenance. A further advantage of laser marking according to the invention is that it can easily be implemented in the production line.

In a preferred embodiment of the invention the lasting changes which are forming said pattern in the fleece layer have the form of dark spots, before the layer of paint is applied to said fleece layer. Thereby, the decorative design pattern may be better visible through said layer of paint, especially in the case of light or white paint. Dark spots may form better contrast through a light or white coat of paint than would for instance small perforations in the case that it would even be possible to cover such perforations with a layer of paint equal to that covering the material between the perforations, that is, in the case that the perforations would not clog up.

In a further embodiment of the invention the lasting changes which is forming the pattern in the fleece layer, is a changed texture, or, it is material removed from the fleece layer. This embodiment may result in a different visual effect than that obtained by a changed colour or tint. Often the two effects will be combined, i.e. the heating effect of the laser will result in a changed texture as well as a changed colour or tint.

In a further embodiment of the invention the mineral fibre board is being open to air diffusion and said fleece layer is being open to air diffusion. This will give the best sound absorbing properties for the sound absorbing panel. Preferably, also the paint layer should be open to air diffusion.

In a further embodiment of the invention the acoustical absorbing panel is prepared for being a ceiling panel to be arranged in a grid as part of a sus- pended ceiling. Such suspended ceilings are widespread, and often there is

a wish for providing such suspended ceilings with a decorative design pattern.

The invention is also related to a method of providing a decorative design pattern to the surface of an acoustic absorbing panel, said acoustic absorbing panel comprises a board comprising mineral fibres. This method is comprising a step of: applying a laser heat treatment, by use of a laser beam, to the fleece layer, said laser heat treatment is performed by scanning the laser beam over the fleece layer in a pre-selected pattern resulting in lasting changes in the fleece layer forming the decorative design pattern. The method also comprise a step of securing a fleece layer to at least one surface of the mineral fibre board, either before, during or after said laser heat treatment. The method also comprises a step of applying a layer of paint to said fleece layer after said laser heat treatment of the fleece layer. Finally, the method comprises the step of drying said applied paint, thereby forming a painted surface with the visible decorative design pattern.

In a preferred embodiment the laser heat treatment is performed after the fleece layer has been attached to the mineral fibre board.

In a further embodiment of the method according to the invention the applied paint layer is applied by moving the panel with the attached fleece layer through a curtain coat section, in which the flow of the falling paint in the curtain coat together with the speed of the passing panel defines the thickness of the applied paint layer.

In a further embodiment of the method according to the invention the applied paint layer is applied as two separate layers.

The invention is also related to an apparatus for manufacturing an acoustical absorbing panel, said acoustic absorbing panel comprising a board compris-

ing mineral fibres and a fleece layer, said apparatus comprising: a production line for transporting a mineral fibre board; and the apparatus comprises fleece attachment means for attaching a fleece layer to at least one surface of said mineral fibre board; and the apparatus comprises a laser prepared for scanning a laser beam over the fleece layer in a pre-selected pattern, said laser beam performing a heat treatment in the fleece layer resulting in lasting changes in the fleece layer, thereby forming a pattern of a decorative design pattern; and the apparatus comprises painting means for applying a layer of paint to the fleece layer.

Embodiments of the invention will now be described with reference to the figures, where

Figure 1 illustrates a cross-sectional view of a panel with a painted fleece layer.

Figure 2 illustrates a cross-sectional view of a panel where lasting changes in the fleece layer have been indicated.

Figure 3 illustrates a schematic process line for manufacturing a panel according to an embodiment of the invention.

Figure 1 shows a typical panel for acoustic absorption of noise. The panel 1 comprises a porous material such as board 2 of mineral fibres with a binder added. On at least one of the major surfaces of this board 2 a fleece layer 3 is secured by some adhesive. The fleece layer 3 is painted, thus forming a paint layer 4. This type of panel will often have the form of ceiling panels or ceiling tiles, which when installed are arranged in a grid as a suspended ceiling. For this purpose the side surfaces i.e. edges of the panels may also be provided with shapes or profiles making them fit with different types of grid

profiles. Such acoustic absorption panels are also known from panels to be arranged on a wall in a room where improved sound absorption is needed.

Figure 2 shows an acoustic absorbing panel 1 according to an embodiment of the invention. It is illustrated that the fleece layer 3 has been provided with lasting changes 10 by a laser. These lasting changes 10 can be in the form of changed colour or tint of the fleece material due to the heating effect by the laser. The change in colour or tint will occur due to partly burn of the glass fibres or of the binder.

The lasting change may also be a change in the texture, e.g. due to removal of material of the fleece layer by evaporation of glass fibre and/or binder material from the fleece layer. In some cases material may be removed to an extent such that the fleece layer 3 is perforated. In figure 2 a layer of paint 4 is illustrated on the fleece layer 3.

These lasting changes in the fleece layer may be arranged in any possible pattern.

The laser used for the purpose is any commercially available laser having sufficient power to burn material in the fleece such that its colour or tint is changed. The laser is arranged to cooperate with an optical system guiding the laser beam to the right spot on the fleece layer. The laser may be a pulsed laser, with a well-defined amount of energy in each pulse. The laser is arranged to cooperate with optical components, such as lenses and mirrors, guiding and forming the laser beam for optimal performance in the scanning and heat treatment.

The fleece layer is preferably a standard glass fibre fleece, comprising glass fibres and a binder. The amount of binder will often be 10 - 30 %. The fleece will preferably not comprise any oil, which is typically added to the mineral

fibre material. The surface weight of the fleece will be in the range 60 - 200 g/m ² . Example of an applicable fleece materials of glass fibres is the product A75 from Owens Corning in US having a binder content of 25 %, and a calorie value of 5,3 MJ/kg.

An example of a useful paint is a water based paint with approximately 50 % dry material and approximately 10 % binder, e.g. known under the trade name Rofa 8 which is manufactured by Soframap in France. The amount of wet paint applied will preferably be in the range 50 - 150 g/m ² , even more preferably in the range 80 - 120 g/m ² .

In order to be sufficiently sound absorbing the sound absorbing panel should be open to air diffusion. This means that the applied paint layer also must be open to air diffusion. This will be the case if e.g. small holes are formed in the paint during application or drying up.

Figure 3 schematically illustrates a production line 20 for manufacturing a panel 1 according to an embodiment of the invention. The boards 2 of mineral fibres are moved from left to right. In one step the fleece layer 3 is at- tached to a major surface of the board 2. The fleece layer is supplied from a roll of fleece 23 and is attached by use of an adhesive. In a following step a laser unit 21 is used for performing a heat treatment of the fleece layer 3. This heat treatment will induce lasting changes 10 forming a predetermined pattern in the fleece layer 3. These lasting changes 10 may be in the form of a changed colour or changed tint. The changes may also be in the form of a changed texture of the fleece layer 3, where part of the fleece is burnt away or evaporated.

In a following step a layer of paint 4 is applied. This layer must have a com- position and/or a thickness such that the changes of the fleece layer are visi-

ble through the layer of paint. Often the paint layer is applied in two separate steps, with the second layer being applied before the first layer has dried.

For the application of the one or two paint layers, a curtain coat has been found to give a good result with a smooth paint layer. A curtain coat is a well established method of painting an acoustical absorbing panel, where paint is flowing from a container 22 with a constant flow over an edge, arranged such that the flow on every part of this edge will be the same. The edge over which paint is flowing must have a width equivalent to the width of the panels to be painted. The flow of the falling paint in the curtain coat together with the speed of the passing panel defines the thickness of the applied paint layer. Furthermore, the process of the curtain coat is stable and easy to control.

When the paint is applied in two steps, i.e. two layers of paint, the panel will typically pass through two curtain coat sections.