TECHNICAL FIELD

A method of coating a substrate with a cementitious formulation is disclosed. Also disclosed is the preparation of the formulation for coating the substrate, as well as the resultant substrate coated with that formulation. Such a method and formulation can provide the substrate with aesthetic appeal when employed e.g. as a decorative finish in various building and interior decoration applications, and the method and formulation will be described in this context. However, it should be appreciated that the method and formulation are not limited to such applications.

BACKGROUND ART

Cementitious compositions for coating substrates have been known for many years. For example, US 5,077,349 discloses a polyurethane coating formed from an isocyanate, a polyol, water and a cement such as a Portland or blast furnace cement. US 3,538,038 discloses a polyurethane composition formed from a polyisocyanate, a polyhydroxy compound, water and activated alumina. US 3,310,511 discloses a hydraulic cement and epoxy resin composition formed from Portland cement and an aqueous emulsion of epoxy resin. US 4,003,873 discloses a composition comprising Portland cement and a phenolic resin, and in which water is produced during curing of the phenolic resin.

In each of these documents water reacts with the cement material to induce the known cement-gel reaction, and so as to cure the cement together with the cured resin.

US 5,965,207 discloses a method in which layer of cement is coated on particle board, and then a protective coating of a polyurethane is applied over the top of the cement layer.

The above references to the background art do not constitute an admission that the art forms a part of the common general knowledge of a person of ordinary skill in the art. The above references are also not intended to limit the application of the cementitious composition as disclosed herein. SUMMARY OF THE DISCLOSURE

In a first aspect there is disclosed a method of coating a substrate. The substrate can, for example, take the form of a panel, tile, board, sheet, plate, pane, etc. The substrate can be planar, curved, be concave or convex, have compound curves, etc. The material for the substrate can, for example, be synthetic or natural including wood, stone, fibreboard, plasterboard, plastic, metal, glass, concrete, etc. The coated substrate can provide a decorative finish when employed in various building and interior decoration applications. The coating can also be applied to the substrate in an unadorned form, or applied in a patterned or varying manner.

The method of coating the substrate comprises the steps of:

- forming a dispersion of a cementitious material in a non-aqueous thermosetting polymer;

- applying the dispersion to the substrate;

- allowing the dispersion to cure on the substrate.

In the method of the first aspect the cementitious material can be evenly dispersed throughout the non-aqueous thermosetting polymer. Because the

thermosetting polymer is non-aqueous, the cementitious material does not set or gel, but rather retains much of its nascent qualities, so that at least some of these qualities are preserved/retained by the dispersed material in the coating once the thermosetting polymer has cured. This can give the substrate a "cement effect" (e.g. the look and feel of cement, cement render, polished cement, etc).

Also, because the cementitious material is dispersed throughout the coating, its qualities can be revealed, enhanced or augmented when the surface of the coated substrate is e.g. subjected to an additional finishing stage.

In one embodiment the cementitious material comprises a cement powder.

Because hydraulic cements are abundant and easily available, usually the cement powder comprises hydraulic cement. However, there is no reason why a non- hydraulic cement (such as a non-hydraulic lime plaster, a non-hydraulic gypsum plaster, an oxychloride cement, etc) could not be employed to achieve different aesthetic, textural, etc effects in the coated substrate. In one embodiment the hydraulic cement may comprise one or more of an alkaline earth metal hydroxide or oxide, a calcium aluminate, an optionally activated bauxite, a pozzolan, a slag-lime cement, gypsum, anhydrite, an alkaline earth metal sulfoaluminate, belite, an alkali metal silicate, an aluminosilicate, etc.

Because of their abundance and availability the hydraulic cement employed in the method typically comprises either or both of Portland cement and limestone. The Portland cement and limestone may be dispersed in the thermosetting polymer in a weight ratio ranging from 10:90 to 90: 10. These two cementitious materials have been found to be easy to work with and have also been observed to provide a range of interesting aesthetic effects.

In one embodiment the non-aqueous thermosetting polymer comprises polyurethane, an epoxy resin, or a polyester resin. Again, whilst other thermosetting polymers may be employed, the afore-mentioned resin types are easy to avail and work with.

The thermosetting polymer is formulated such that, prior and up to curing, it has sufficient viscosity to maintain the cementitious material evenly dispersed there- throughout. Polyurethane in particular can be readily formulated to facilitate and maintain excellent dispersion of the cementitious material during coating formulation and up until curing occurs.

The polyurethane employed in the method may comprise a "resin" component and a "hardener" component. The weight ratio of resin component to hardener component can be around 4:1, though may be varied depending on the adhesion achieved or required for a given substrate material. The resin component primarily comprises an acrylic polyol in a solvent of: mixed xylenes, a ketone and methoxy propyl acetate. The hardener component primarily comprises a polyisocyanate in a solvent of: xylene, a ketone and methoxy propyl acetate.

In one embodiment of the method a chemical initiator/catalyst is added to the non-aqueous synthetic polymer to initiate polymer curing when applied to the substrate. Usually the initiator/catalyst is added prior to or during dispersion of the cementitious material in the polymer (i.e. so as to maintain the cementitious material dispersed throughout the polymer up until curing). In this embodiment, the chemical initiator/catalyst may already be present in the resin component such that resin curing is initiated upon mixing of the resin and hardener components.

In one form of the method the dispersion can be applied to the substrate by spraying, pouring, screeding, or moulding. When the dispersion is applied to the substrate by spraying, the dispersion can be sprayed by a gravity-fed or pressurised spray gun (e.g. the dispersion is supplied to the gun from a pressure pot).

In one form the method can comprise a further step of surface finishing the cured dispersion on the substrate. For example, the further step of surface finishing may comprise either or both of finely abrading an exposed surface of the cured dispersion and polishing the finely abraded surface.

The step of finely abrading the exposed surface typically comprises sanding the surface (e.g. in a dry-sanding procedure). The step of polishing the finely abraded surface typically comprises polishing the surface with a rapidly moving natural or synthetic fibrous material. Each of sanding and polishing can be performed using a machine that is able to be fitted with a sanding or polishing head having the sanding or polishing material fastened thereto (e.g. specific sanding and polishing tools/appliances, or an interchangeable head of a tool or appliance, etc).

In a second aspect there is disclosed a method of formulating a coating for a substrate. The method of formulating can be tailored to the substrate (e.g. to be both suitable to its format [panel, tile, board, sheet, plate, pane, etc] and its shape [planar, curved, undulating, etc], and so that the coating is suitable to bind/adhere to the substrate material [synthetic or natural wood, stone, fibreboard, plasterboard, plastic, metal, glass, concrete, etc]). The method of formulating can produce a coating on the substrate for use in various building and interior decoration applications.

The method of formulating the coating comprises the steps of:

- formulating a non-aqueous thermosetting polymer to have a viscosity whereby a cementitious material is able to be evenly dispersed throughout the polymer;

- mixing the cementitious material with the polymer formulation in a manner that evenly disperses it throughout the polymer formulation. Thus, in the method of the second aspect, the coating is formulated so as to preserve and maintain the dispersion of the cementitious material in the coating once coated and cured on the substrate. This results in cementitious material being located (i.e. exposed) at a surface of the cured coating, thus providing both aesthetic and textural effects. It also allows the cementitious material to be subjected to various surface finishing steps, as outlined above.

The non-aqueous thermosetting polymer and the cementitious material employed in the formulating method are typically as defined in the first aspect.

In the formulating method of the second aspect a chemical initiator/catalyst can be added to the non-aqueous synthetic polymer during or immediately after formulating of the polymer or during or immediately after mixing of the cementitious material with the polymer formulation.

The polymer can be supplied pre-formulated (i.e. already possessing a suitable viscosity) or it can be formulated at the coating site (the e.g. two component parts of the formulation can be mixed on site in the correct proportion to have a suitable viscosity and consistency).

The coating formulated according to the second aspect can be applied to the substrate in accordance with the method of the first aspect. In a third aspect there is disclosed a coating formulation for a substrate comprising a non-aqueous thermosetting polymer and a cementitious material. In the coating formulation the non-aqueous thermosetting polymer is provided with a viscosity whereby the cementitious material is able to be maintained evenly dispersed throughout the polymer until it cures.

The coating formulation of the third aspect can be formulated in accordance with the method of the second aspect.

Also disclosed is a substrate coated in accordance with the method of the first aspect, or formulated in accordance with the method of the second aspect, or coated with a formulation according to the third aspect. The substrate can, for example, take the form of a panel, tile, board, sheet, plate, pane, etc; it can be planar or non-planar in shape (e.g. curved, undulated, corrugated, compound curves, etc); and the material for the substrate can, for example, be synthetic or natural including wood, stone, fibreboard, plasterboard, plastic, metal, glass, concrete, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms which may fall within the scope of the method and formulation as defined in the Summary, specific embodiments will now be described, by way of example only, and with reference to the accompanying drawing in which Figure 1 shows a schematic exploded perspective view of a panel coated with a cementitious formulation.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Referring now to Figure 1 , a coated substrate is shown in an exploded (i.e. coating-separated) schematic depiction, with the form shown in Figure 1 comprising a coated panel 10. The coated panel 10 comprises a panel base 12 and a coating 14 that comprises a cementitious formulation.

Whilst a square panel base 12 is shown in Figure 1 it can, for example, instead take the form of tile, board, sheet, plate, pane, etc and have various shapes, thicknesses and dimensions. Instead of being planar, the base 12 can be, curved, be concave or convex, have compound curves, etc. The material of the panel base 12 may comprise engineered fibreboard although the material can, for example, be formed of a variety of synthetic or natural materials including wood, stone, plasterboard, plastic, hardboard, metal, glass, concrete, etc.

The formulation of coating 14 comprises a dispersion of a cementitious material in a non-aqueous thermosetting polymer. The coating 14 is formulated such that the cementitious material is able to be (and remain) evenly dispersed throughout the polymer. Thus, when the upper surface of the coating 14 (as shown in Figure 1) is subjected to surface finishing, the qualities (both nascent and actual) of the cementitious material can be revealed, enhanced or augmented. In addition, because the thermo setting polymer is non-aqueous, the cementitious material does not set or gel or expand and crack in the coating 14. In other words, the cured coating 14 is able to present a dispersed and captured form of the original cementitious material.

Because the qualities, properties and characteristics of the cementitious material are revealed in the finished product, enhanced aesthetic and textural effects are produced. In addition, the coating can provide "cement effect" to the base. In this regard, the look and feel of coating can be like cement, cement render, polished cement, etc.

In coating 14, the cementitious material typically comprises a cement powder. Because hydraulic cements are abundant and easily available, usually the cement powder comprises hydraulic cement, although there is no reason why a non- hydraulic cement could not be employed to achieve different aesthetic and textural effects in the coated substrate.

In any case, because of their abundance, availability and ease of use, and also because of the desirable aesthetic and textural effects they present in the coating, the hydraulic cement powder employed in coating 14 typically comprises either or both of Portland cement and limestone. The Portland cement and limestone can be added to the coating in approximately equal measures by volume throughout the thermosetting polymer, or the Portland cement can predominate over the limestone.

In coating 14, the polymer typically comprises polyurethane, again because it is easy to avail and work with. However, it can alternatively comprise an epoxy resin, a polyester resin, etc.

A specific polyurethane employed in the coating 14 comprises an acrylic polyol and a polyisocyanate. Other polyols can be employed including polyether polyols: glycerol, trimethylolpropane, pentaerythritol, bisphenol A, ethanolamine,

diethanolamine, propanolamine, triethanolamine, ethylene diamine, diethylenetriamine, triethylenetetramine, etc. Other isocyanates that can be employed include ethyl-based isocyanate or diisocyanate, etc.

A chemical initiator/catalyst is added to the polyurethane to initiate curing of the coating 14 on the panel base 12. The chemical initiator/catalyst employed is an organometallic compound (e.g. dibutyltin dilaurate and/or zinc-2-ethylhexanoate). Usually the chemical initiator/catalyst is present in the solvent of the acrylic polyol, such that initiation of resin curing occurs upon mixing of the acrylic polyol and polyisocyanate.

Other initiator/catalysts able to be employed include tertiary amines such as dimethylcyclohexylamine, or other organometallic compounds such as bismuth octanoate, or a urethane gel initiator such as l,4-diazabicyclo[2.2.2]octane, or an isocyanate trimerization catalyst such as potassium octoate.

Examples

Non-limiting examples will now be provided to illustrate embodiments of the method and formulation as disclosed herein.

Example 1 - Formulation of the Coating

In an industrial grade, lab-scale mixer a polyurethane was formulated from an acrylic polyol and a polyisocyanate, with the solvents comprising these two components being mixed in the weight ratio of around 4: 1. It was noted that this ratio was variable in accordance with the adhesion achieved and/or required for the given base material.

The acrylic polyol had hydroxy functionality and comprised 30 - 60%w/w of the solvent. The solvent in which the acrylic polyol was supplied comprised a mixture of ortho-, meta-and para-xylene (30 - 60%w/w); ethyl benzene (<10%w/w); methyl isobutyl ketone (10 - 30%w/w); and l-methoxy-2-propyl acetate (<10%w/w). The solvent was also supplied with the initiators/catalysts: dibutyl bis (lauroyloxy) stannane (di-butyl tin di-laurate 98%) (<0.1 %w/w) and zinc-2-ethylhexanoate (<0.1%w/w) already added thereto.

The polyisocyanate comprised an aliphatic polyisocyanate (30 - 60%w/w) and free monomeric hexamethylene-1, 6- diisocyanate (< 0.5%w/w). The solvent in which the polyisocyanate was supplied comprised a mixture of xylene (10 - 30%w/w); ethyl benzene (< 10%w/w), 1 -methoxy-2-propyl acetate (10 - 30%w/w) and methyl isobutyl ketone (10 - 30%w/w).

These proportions of components were observed to produce a coating with sufficient viscosity to suspend and maintain dispersed a powdered cementitious material throughout the mixture, but still allowed for ease of application (e.g. by spraying) of the resultant coating.

As soon as the polyol- and polyisocyanate-containing solvents were mixed, the already present catalysts started to initiate formation of the polyurethane. However, the amount of catalyst had been pre-regulated so as to ensure a controlled (timed) curing.

Immediately after mixing, finely powdered Portland cement and finely powdered limestone were added under mixing into the now-catalysed polyol and polyisocyanate mixture. For each litre of polyol/polyisocyanate, cement was added in the range of 500 - 2000 grams, and typically around 1500 grams. The added Portland cement and limestone mixture were pre-mixed in weight ratios ranging from 10:90 to 90:10. The mixing of powder and resin was continued until the powdered Portland cement and limestone were evenly dispersed throughout the catalysed

polyol/polyisocyanate mixture.

The proportions of polyol, polyisocyanate and catalyst were selected to provide the now fully mixed coating formulation with sufficient viscosity up to curing, to maintain an excellent level/degree of dispersion of the Portland cement and limestone powder there-throughout (i.e. so that the powder did not settle out in the viscous liquid before it cured, and so that powder was present at the cured coating surface).

It was noted that the polyurethane was able to be supplied to the cement powder mixing stage in a pre-formulated format (i.e. the two-part formulation of components mixed and un-catalysed and already possessing a suitable viscosity, with catalyst then added just before or at the powder mixing stage). Usually, however, the two-parts (polyol and polyisocyanate) were formulated (mixed) at the coating stage, so as to be in the correct proportion and of a suitable viscosity and adherence for the particular substrate to be coated.

Example 2 - Application of the Coating

Before it started to cure to any appreciable extent, the formulation prepared according to Example 1 was applied to a substrate by spraying. It was noted that the formulation could alternatively be applied to the substrate by pouring, screeding, or moulding The formulation was transferred from the mixing vessel into a holding pot of a sprayer. The sprayer comprised a spray gun which was either gravity-fed from the holding pot, or the holding pot was pressurised to force the formulation to and out of the spray gun.

The formulation was then sprayed onto individual panel bases 12, each comprising a cut square of engineered fibreboard. The coating was applied evenly from a nozzle of the sprayer by using a sweeping back-and-forth motion across each panel base. A coating of approximately 0.5mm resulted, although it was noted that thicker coatings could be applied (e.g. up to 5mm thick by pouring with a resin such as an epoxy resin, and/or by varying the coating viscosity, composition and size of the spray nozzle outlet aperture, etc).

Before coating, pattern templates were able to be positioned over the base so that, when the coating was applied, a range of patterns and other aesthetic effects were provided to the coating surface. It was also noted that more than one layer of coating could be applied to the base (e.g. a first layer applied in one manner, and a second layer applied in a different manner), to again produce different surface effects. These different layers might also comprise different resins and different cementitious materials.

As mentioned above, when the bases were other than planar, the orientation of the spray nozzle was adjusted accordingly by the user to promote an even coating to the base.

Example 3 - Optional Finishing of the Coating

Although for some applications, the spray coating as outlined in Example 2 might provide an acceptable level of surface finish, usually a surface finishing procedure was performed on the cured coated substrate. The surface finishing comprised at least the abrading of the upper surface of the coating 14, and this finely abraded surface was then usually finished off by a polishing of the abraded upper surface. To finely abrade the upper surface, the surface was sanded in a dry-sanding procedure starting with a sandpaper of 120 grit and "polishing" through to a sandpaper of 400 grit. The sandpapers were affixed to a hand-held orbital sander.

To polish the abraded upper surface, a rapidly moving natural or synthetic fibrous wool material was forced against the surface. The wool was affixed to a head in turn mounted to a hand-held rotary drill-type tool.

Alternatively, the sanding and polishing were able to be performed using an interchangeable head of the same hand-held tool.

It was noted that the surface finishing procedure was suitable for automation (i.e. to be performed by machine as part of a production line for producing coated product).

The sanding and polishing were observed to reveal and highlight the

cementitious material, both at the surface and throughout the coating. This was observed to provide unique aesthetic and textural effects.

Whilst a number of specific method and formulation embodiments have been described, it should be appreciated that the method and formulation may be embodied in many other forms.

For example, whilst a hydraulic cement is typically employed due its wide availability, a non-hydraulic cement such as a non-hydraulic lime plaster, a non- hydraulic gypsum plaster, an oxychloride cement, etc were able to be employed to achieve different aesthetic, textural, etc effects.

Also, instead of a common hydraulic cement being employed as the

cementitious material (i.e. such as Portland cement and/or limestone), the hydraulic cement was able to comprise other alkaline earth metal hydroxides or oxides, or a calcium aluminate cement, bauxite (e.g. that optionally is activated), a pozzolan, a slag- lime cement, gypsum, anhydrite, an alkaline earth metal sulfoaluminate, belite, an alkali metal silicate, an aluminosilicate, etc.

Usually the initiator/catalyst was added to one of the polymer components prior to the dispersion of the cementitious material in the polymer. However, the initiator/catalyst was able to be added during or after mixing of the cementitious material through the polymer.

In the following claims, and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the words "comprise", "comprises", "comprising" are used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in the various embodiments as disclosed herein.