BACKGROUND OF THE INVENTION

[0001] The invention relates to improvements in construction panels and, in particular, to ceiling tiles made from a water slurry or a water based paste.

PRIOR ART

[0002] Construction panels, particularly, water pervious ceiling tiles have a tendency to become stained when exposed to water. One mechanism that occurs to bring water droplets in contact with a ceiling tile is

condensation on pipes and ductwork existing in the space above the ceiling. The condensate can drip onto the backside of the ceiling tile and migrate to the visible appearance side of a tile. Staining can occur because the water can carry off contaminants from surfaces it contacts and, often, because the water droplets migrate through a ceiling tile and leach tannin from recycled newsprint or other plant based cellulose materials and staining agents from other components used in the tile composition bringing such staining agents to the front surface of the tile.

[0003] As is typical of most products, cost is critical and there is a need for an economical solution to minimize water stains on the appearance sides of

construction panels, particularly, water pervious ceiling tiles .

SUMMARY OF THE INVENTION

[0004] The invention provides an economical solution to water staining at the visible face of

construction panels due to water migration through the panel. More specifically, the invention involves the realization that by creating a barrier to water droplets locally at the backside of a panel, the droplets can be caused to evaporate before their liquid content can migrate through a panel.

[0005] It has been discovered that commercially available material used to impart water repellency to fabric is an excellent medium for accomplishing the

objective of the invention. Such material is widely available, non-toxic, and relatively inexpensive in the limited coverage found to be effective in practicing the invention. The preferred waterproof material can be applied with a water carrier by a simple application of the same to the backside of a rigid mat from which the tile is fabricated. The very light coverage and consequent low cost of the waterproofing treatment and the simplicity of application makes it practical for use in even the less expensive product lines of a panel manufacturer.

[0006] The core mat or tile is preferably subjected to an elevated temperature to quickly force dry or cure the waterproofing material before the carrier water can be absorbed through the core mat. Preferably, this drying process can be done simultaneously with the conventional process step used to dry a finish coat or paint on the visible side of the tile or panel.

BRIEF DESCRIPTION OF THE DRAWING

[0007] FIG. 1 is a diagrammatic isometric view of a ceiling tile embodying the invention;

[0008] FIG. 2 is a schematic diagram of a process utilizing the invention. DESCRIPTION OF THE PREFERRED EMBODIMENT

[0009] The invention is applicable to various construction panels that can be used to cover walls or ceilings. One suitable form of a construction panel is a ceiling tile or panel used in suspended ceilings. Other forms of construction panels include gypsum based wall tiles and wallboard. Ceiling tiles made from a water slurry or paste and not backed with a water impervious film or sheet are especially benefited by the present invention. In describing the manufacture of a ceiling tile

incorporating the invention, reference is made to FIGS. 1 and 2 of the drawing. A rectangular ceiling tile 10 is adapted to be used as a lay-in panel in a rectangular grid in a suspended ceiling system of generally known

construction. The tile, typically, will have a thickness of between about 1/2" to about 7/8" and nominal planar dimensions of 2 ' x 2', 2 ' x 4', and 2-1/2' x 5' or metric equivalents of these panel sizes. Suspended ceiling panels or tiles are typically made from a water felting process or a paste like water based castable formulation. Where the panel 10 is derived from a water felting process, a typical approximate formulation, on a weight basis, can comprise:

65% perlite filler

18% paper fiber

7% unmodified starch binder, and

10% mineral wool fiber.

[0010] The mineral wool content can vary

considerably, say up to about 25% and in such a case, the perlite can be reduced accordingly. Besides paper fiber, other cellulose sources can be used such as wood or woody plant materials. When these constituents have been

properly mixed in a water slurry and spread on a screen, in the case of a water felted product, or similar constituents are spread on a pan in the case of a cast tile, they are dewatered and/or dried into a rigid board. Thereafter, the appearance or front side of the board or tile preform is coated with an appearance coating or paint usually a water based material having some latex or other binder component. In the case of a water felted mat or core, the finish side of the mat, if necessary, can be ground to create a flat surface prior to coating with a finish or top coating.

Additionally, prior to application of the finish coat, a primer coat, that may be clay based, for example, can be applied to the face side of the mat. The tile 10 of FIG. 1 is shown in its installed orientation and includes an appearance coating 11 on its lower, visible face, a primer coat 12, a water felted mat or core 13, and a waterproof coating 14, discussed below, on its back or upper face.

[0011] The appearance coat 11 on the finish side of the tile 10, as mentioned, is typically a water based coating with a white pigment color to provide high light reflectivity. It has been discovered that

commercially available fabric waterproofing material can be used to successfully waterproof the back of the tile 10 by coating the mat 13 with such material. Surprisingly, it has been found that only relatively small quantities of such material need be used to achieve satisfactory results. An example of a product suitable for practicing the

invention is a fluorocarbon polymer emulsion such as that marketed by Daikin Chemical Europe GmbH, Dusseldorf,

Germany, under the brand TG-5601. This product is a water based emulsion which can be greatly diluted with water while remaining effective even when the application rate is imprecise. The result of the dilution of the original emulsion is a very light coating of waterproofing solids of about 1/5 to 1/4 grams/sq. ft. Despite such a low

concentration of solids, it has been found that a

surprising degree of waterproofing and resistance is achieved. With the disclosed solids coverage rate, water droplets on the coating 14 simply bead-up and eventually evaporate .

[0012] FIG. 2 illustrates an example of a process for practicing the invention. A dried mat or board 13 made by a conventional water felting process with a solids content such as described above is carried on a conveyor 20 into a spray booth 21 where a water based top coat or paint 11 is applied. The top coat or appearance coat 11 faces up in this process but when the tile is installed in a

ceiling, the top coat faces down. The mat 13 is conveyed from the spray booth to a dryer 22 by a roller conveyor 23. A sprinkler 24 carrying a plurality of spray nozzles extends between a pair of rolls of the conveyor 23 across the width of the conveyor. The sprinkler 24 sprays the underside of the mat 13 with dilute waterproofing liquid 14 described above. The mat 13 coated with the top coat 11 and waterproof material 14 is conveyed by a conveyor 26 through the dryer 22 where these coatings are preferably simultaneously dried and/or cured for example, at a

temperature of about 220° C. for a duration of about 45 seconds. Other methods of applying the top coat and waterproofing material are contemplated. For example, roll coating or flooding can be employed.

[0013] Water condensate dripping from piping and ducts within the space or plenum above a suspended ceiling can fall onto the backside of a prior art ceiling tile eventually causing discoloration on the face or appearance side. This mechanism of discoloration or staining can be attributed to percolation of the condensate water through a tile. The condensate may be contaminated by surfaces it passes over before reaching the tile. Additionally, as the water percolates through the body of the tile, it can leach stain producing material such as tannins present in the paper or cellulose fibers. The contaminated water can leak through the appearance coating and thereby stain it. Water passage through a tile, where the invention is not

employed, is commonplace where there is a source of water, since it is desirable that the ceiling tile be porous to exhibit good sound absorbing characteristics. Adding to the desired porosity of a typical ceiling tile is its original water based character which inherently leaves it permeable to water.

[0014] It should be evident that this disclosure is by way of example and that various changes may be made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this disclosure. The invention is therefore not limited to particular details of this disclosure except to the extent that the following claims are necessarily so limited.