COATING COMPOSITION WITH HIGH PIGMENT-VOLUME-CONCENTRATION

Abstract: A composition for use in coating ceilings, comprising a resin dispersion, a filler, a pigment, a thickener and water, has a Pigment Volume Concentration (PVC) of at least 70 %. Preferably, rust prevention agents, a biocide and a preservative are added to the formulation. Preferably, this composition is used to refurbish suspended ceiling systems.

Description: COATING COMPOSITION WITH HIGH PIGMENT-VOLUME-CONCENTRATION The present invention relates to a refurbishing coating for ceilings, and more preferably a coating for suspended ceiling systems. One typical suspended ceiling system comprises a multitude of tiles, usually manufactured from mineral fibre, plaster, metal or plastic faced plasterboard, held in position by a supporting exposed grid system. In this type of ceiling system it is essential to maintain continual access to the area above the tiles, which commonly accommodates water, power, communication and ventilation services. In order to reach the area above the tiles, to service and maintain these supplies, it is essential that the ceiling tiles are pushed above and away from the metal grid system. At present, suspended ceiling tiles are refurbished using traditional water-based emulsion paints, of which a standard formulation is 33.5% of vinyl acrylate VeoVa 10 copolymer 19.0% of Titanium dioxide 10.0% of China clay 6.0% of Calcium carbonate 0.6% of Cellulose thickener 0.8% of Biocide 30.1% of Water However, upon applying these paints, a film is formed between the tile and the grid, thus joining the tile to the metal grid system, known in the art as "bridging" . Accordingly, upon forcing the tiles upwards in order to access the ceiling void, the film between the tiles and metal grid system is broken, resulting in cracks in the decorative finish of the tiles and, often, tile breakages. In some circumstances, the formation of a film between the tile and the metal grid system completely prevents any movement of the tile. In addition, the mineral fibre tiles are highly absorbent, absorbing a great deal of paint and hence a number of coats of traditional emulsion paint have to be applied to the tiles to achieve the desired finish. This often causes the tiles to bow and warp under the weight of the wet paint. The absorbency of the tiles is also a problem when traditional emulsion paints are diluted with water, in an attempt to avoid a film forming between the tile and the metal grid system. The tiles absorb the water, resulting in bowing and warping. In all cases watering down the paint leads to insufficient coverage of stains on the old tiles and is, therefore, an unacceptable solution to the problem of bridging. Another type of suspended ceiling system is a concealed grid system. This comprises ceiling tiles fixed into the grid by the use of splines, with the result that the grid system is not visible from below. When this type of ceiling system is painted with a traditional water-based emulsion paint, a film of paint is formed between the tiles. This prevents the tiles from being removed, and often results in tile breakages and an aesthetically unsatisfactory finish. A further disadvantage of using traditional emulsion paints on suspended ceiling systems is that the acoustic properties of the ceiling are altered, since the film-forming nature of these paints causes the face texture, patterns, fissures and perforations of the tiles to be blocked. This also results in a change in the ceiling's appearance. A further disadvantage is that tiles refurbished with traditional emulsion paint cannot adapt to changes in temperature and humidity conditions since these emulsion paints are not so vapour permeable. The tiles become non- porous due to the formation of a film on the tiles and metal grid system, thus resulting in distortion of the tiles. In addition, the grid system cannot be cleaned after being coated with a traditional emulsion, as these paints do not provide suitable durability and adhesion, and accordingly such a decorative finish on a metal grid system can be rubbed off with detergent. This is a particular problem when the tiles are also metal. Suspended ceiling systems may also be refurbished by replacing only those tiles stained or damaged. However, this creates a patchwork effect on the ceiling, due to the differing appearance of new and old tiles. This results in a ceiling of low aesthetic quality. In addition, it is possible to replace a complete set of tiles into an old supporting grid system. However, this is a slow process and may cause an unacceptable level of contamination in sensitive environments such as computer installations. The supporting grid system remains discoloured and dirty. To refurbish the grid, the tiles must be first removed and the grids painted by hand using a solvent based paint, followed by the installation of new ceiling tiles. This is an expensive and inconvenient method. It is possible to refurbish a ceiling by complete replacement of tiles and the supporting grid system. This is time consuming, expensive and inconvenient. The present invention seeks to provide a method of renovating and decorating both suspended ceiling tiles and their respective supporting metal grid system, without bridging the interface between the tile and the supporting grid, thus providing continual access to the ceiling void, and maintaining a ceiling of high aesthetic quality. In one embodiment of the present invention, there is provided a composition, for use in coating ceilings, comprising a resin dispersion, a filler, a pigment, a thickener and water, wherein the Pigment Volume Concentration (PVC) of the composition is at least 75%, and preferably wherein the PVC is 80%. The PVC value is calculated as the percentage of pigment and filler in the dry applied coating, calculated on a volume basis. To calculate the PVC, the components of the formulation should be given in percentage weights. The volume is then calculated from the specific gravity, or density, of each component. The volume of the resin in the resin dispersion must be calculated separately, as it is only the density of the solid resin, and not that of water, that is relevant to this calculation. The PVC is then expressed as the volume of the pigment and extender as a percentage of the sum of the volume of pigment, extender, solid resin and any other solids present, such as cellulose thickener and biocide solids. One feature of this invention is the realisation that paints which do not bridge the interface between the tiles and the metal supporting grid system have a higher PVC than those paints that are film forming and bridge the tile to the grid. Accordingly, this invention is directed to the production of paints with high PVC, thus resulting in a paint with non bridging properties. Traditional emulsion paints, which are known to bridge the tile to the grid upon application to suspended ceiling systems, have now been calculated to have a PVC of between 40% and 65%. Formulations according to the present invention contain higher amounts of pigment and lower amounts of filler or extender than traditional paints with a lower PVC. This new formulation comprises a mixture of organic and inorganic fillers and pigments, together with certain beneficial additives, which when the coating is dry, are bonded with a water based organic resin dispersion. A typical formulation for a non bridging coating is :- 8 to 20%, preferably 10 to 20% of 50% solids vinyl acetate/VeoVa 10 copolymer dispersion. 3 to 15%, preferably 10 to 25% of Titanium dioxide (pigment) 10 -to 40%, preferably 8 to 15% of China clay (filler) 10 to 25% of Calcium carbonate (filler) 1 to 10% of Silica (filler) 0.1 to 5% of Sodium nitrite 1 to 7% of Sodium benzoate 0.1 to 5% of Alkyl aryl trimethyl ammonium chloride 0.05 to 0.25%, preferably 0.2% of Cellulose ether 25 to 45%, preferably 25 to 35% of Water All values are percentage by weight. The high pigment/filler volume of such a formulation provides the non-bridging element between the tile and the supporting grid, and also provides the essential feature of water vapour permeability to the coating. Calculation of PVC The PVC of a typical formulation as described above is calculated as follows:- Component % by weiαht Density % Volume Vinyl acetate/ 7.5 1.04 7.21 VeoVa dry resin Water 7.5 - - Titanium dioxide 21.0 4.20 5.00 China Clay 12.0 2.60 4.60 Calcium Carbonate 21.0 2.70 7.80 Silica 3.0 2.30 1.30 Cellulose Thickener 0.2 1.33 0.15 Biocide 0.2 1.15 0.17 Water 27.6 _ _ Total volume of pigment and extender = 18.85 Total volume of Pigment/Extender/resin + solids = 26.23 PVC = 71.9% The use of a formulation as described, in order to refurbish suspended ceiling systems, does not create a bridging film between the tiles and the supporting metal grid system. This maintains continual access to the ceiling void. The coating provides a decorative finish to the tile surface, yielding a non-reflective sheen at a low of the ceiling are maintained, as a formulation of this kind does not fill in the fissures, face textures, patterns or perforations of the ceiling tiles. The coating described is vapour permeable, and is applied as a single coat, thus preventing warping, or bowing, as it allows the tiles to expand or contract to changing temperature and humidity conditions within the building. The coating is also odourless, allowing almost immediate re-occupation of the restored areas. Since the formulation is water based, it is non hazardous and non-toxic. Use of this formulation allows complete renovation of ceilings damaged by smoke, water stains, soot and nicotine and also provides a long lasting, maintenance free coating protection to the metal supporting grid system, which allows the supporting grid system to be easily and efficiently cleaned and maintained after application. A formulation as described also maintains fire ratings at class '0' and class '1 » as defined by British Standard 476: part 6 and 7. Any resin dispersion typically used in the art may be used in the formulation of the present invention. It would be immediately apparent to a person of skill in the art as to which resin dispersions are suitable. Preferably, the resin dispersion is a copolymer of vinyl acetate and the vinyl ester of Versatic 10 (also known as VeoVa 10) , the structure of Versatic 10 being \ rt I wherein R 1# R 2 and R 3 are alkyl groups, at least one of which is always methyl. Alternative resin dispersions that may also be used include a copolymer of Butyl Acrylate with the vinyl ester of Versatic 10, a vinyl acetate/ethylene/vinyl chloride terpolymer dispersion, a styrene/acrylic ester dispersion or an acrylic dispersion. Titanium dioxide is a white pigment essential for the production of a white paint. A combination of titanium dioxide and Ropaque OP-62LO, an opaque white organic polymer dispersion, may also be used in the formulation. The inclusion of Ropaque OP-62LO gives better washability. The inclusion of titanium dioxide, at 10-25%, provides the sufficient opacity to the resultant coating. Traditional emulsion paints, with less true pigment, lack sufficient opacity for use as ceiling coatings. China clay, calcium carbonate and silica are fillers, or extenders, which provide the necessary high pigment/filler volume to result in the non bridging element of this formulation. The use of silica in the formulation produces minimal light reflection at a low angle of incidence. Cellulose ether is a thickener which helps to stabilise the pigment/extender dispersion in the resin dispersion and also provides the necessary rheology to the formulation, in order that it may be applied to the ceiling by either brush, roller or spray. Other thickeners, such as starch-like products may also be used, as will be well understood by the skilled practitioner. Further water is added to the formulation to aid its application to the ceiling. Rust prevention agents, such as sodium nitrite and sodium benzoate may be added to the formulation, to prevent "flash rusting" when the coating is added to any ferrous metal surface. A biocide may also be added to the formulation to prevent mould and bacterial growth on the surface of the dry coating. Alkyl aryl trimethyl ammonium chloride is commonly used as such a biocide. An in-can preservative may also be added to the formulation to prevent biochemical breakdown of the components in the wet paint. A typical preservative of this kind is Acticide BX. Such a formulation as described may be manufactured by wetting the pigment and extenders with the cellulose ether solution in water, followed by dispersion using a Greaves, Silverson or Cowles mixer. The resin dispersion and the additional components such as rust-prevention agents and biocides, are then slowly added to complete the formulation. An alternative formulation, which is of particular use on metal surfaces is: INGREDIENT % by weight Water 25.4 Dispersant 0.25 Defoamer 0.1 Coalescent 0.78 Bactericide (In-can preservative) 0.2 China Clay 6.31 Calcium Carbonate 34.6 Titanium Dioxide 18.93 Vinyl acetate/VeoVa 10 Copolymer dispersion 11.4 Humectant (Mono propylene glycol) 1.9 Cellulose Ether 0.13 This formulation has a P.V.C. of 80% and a specific gravity of 1.58. The W/W solids is 65.8% and the V/V solids is 39.7%. This has a particularly matt finish and a longer drying time than the first formulation. A third alternative formulation, also of use on metal surfaces, is: INGREDIENT % by weight Water 33.2 Dispersant 0.23 Defoamer 0.11 Coalescent 0.77 Bactericide (In-can preservative) 0.19 China Clay 5.63 Calcium Carbonate 30.7 Titanium Dioxide 16.6 Vinyl acetate/VeoVa 10 Copolymer dispersion 10.69 Humectant (Mono propylene glycol) 1.75 Cellulose Ether (Thickener) 0.13 This formulation has a P.V.C. of 80% and a specific gravity of 1.5 ± 0.1. The V/V solids is 35%. This also has a good matt finish and a longer drying time than the first formulation.

Claims: CLAIMS 1. A composition, for use in coatingcomprising a resin dispersion, a filler, a pigment, a thickener and water, wherein the Pigment Volume Concentration (PVC) of the composition is at least 70%. 2. A composition according to Claim 1, wherein the PVC is at least 80%. 3. A composition according to Claim 1 or 2, wherein the resin dispersion is a copolymer of vinyl acetate or butyl acrylate with VeoVa 10, a styrene acrylic ester, a vinyl acetate/ethylene/vinyl chloride terpolymer or an acrylic dispersion. 4. A composition according to Claim 1, 2 or 3, wherein the filler is china clay, calcium carbonate or silica. 5. A composition according to any one of the preceding claims, wherein the thickener is a cellulose ether. 6. A composition according to any one of the preceding claims, further comprising a rust prevention agent. 7. A composition according to Claim 6, wherein the rust prevention agent is sodium nitrite or sodium benzoate. 8. A composition according to any of the preceding claims, further comprising a biocide. 9. A composition according to Claim 8, wherein the biocide is alkyl aryl trimethyl ammonium chloride. 10. A composition according to any one of the preceding claims, further comprising a preservative. 11. A composition according to Claim 10, wherein the preservative is Acticide BX. 12. Use of a composition according to any one of the preceding claims in coating suspended ceiling systems. 13. Use according to Claim 12 wherein application is effected by brush, roller or spray.. 14. A method of coating ceilings comprising applying to a ceiling a composition according to any one of Claims 1 to 11. 15. A composition for use in coating ceilings substantially as hereinbefore described.

Inventors: HARRISON SHANE RICHMOND, HILL DEREK ALFRED WHEELER, HARRISON, SHANE, RICHMOND, HILL, DEREK, ALFRED, WHEELER
Applicants: HARRISON SHANE RICHMOND, HILL DEREK ALFRED WHEELER, SURFACE COATINGS INTERNATIONAL, HARRISON, SHANE, RICHMOND, HILL, DEREK, ALFRED, WHEELER
Application year: 1996
Main classification: C09D5
IPC codes: C04B26, C09D5, C09D131