TECHNICAL FIELD

This invention provides a mechanical process by which a substrate formed of aromatic polyurethane, for example, can be coated in such a way that it becomes an abrasive-resistant, weatherable, and wood-like substrate, particularly for the use in exterior applications.

BACKGROUND OF THE INVENTION

Numerous man-made composites and natural materials are known for myriad uses, including exterior applications. For example, aromatic polyurethane is used in applications ranging from foam for car seats and bedding to rigid applications; the range of products made with this type of technology is vast. Exterior use of aromatic polyurethane, as well as other materials, has been limited due to degradation and discoloration upon exposure to ultra-violet light. Over time, ultra-violet light causes a radical reaction in aromatic polyurethane that breaks down the aromatic portions of the polymer, causing a severe yellowing of the substrate. In order to make an exterior product comprised mainly of aromatic polyurethane, or other materials susceptible to exterior conditions, it must be coated in such a way as to prevent ultra-violet light from reaching the substrate.

Coating composite materials for exterior use to look like wood has been carried out by various processes. Some composite materials are encapsulated in a cap-stock; this cap-stock is generally a thermoplastic type material that can be extruded. The look of wood is generally achieved by some type of embossing, in which the wood grain is three-dimensionally represented. The color variation is generally achieved by the incorporation of various colors during extrusion or pultrusion.

Coating of plastics has been achieved with a wide variety of techniques, some of which are used during the process described herein. A few techniques include, but are not limited to, general spray techniques such as high-pressure and low-pressure systems, roll-coating methods, powder coatings, hydrographics, and UV-curable coatings. Some manufacturers rely on the three dimensional wood-grain and a solid color, while others will work to add a variety of colors to the substrate using methods such as printing to achieve a wood-like appearance.

Described herein is a process by which aromatic polyurethane, for example, can be coated with a fully hiding coating which has been proven to protect the substrate while creating the appearance of wood by combining general techniques in a unique process to promote adhesion, while creating the desired wood-like appearance.

SUMMARY OF THE INVENTION

In accordance with the invention presented herein, a method is provided for coating a substrate made of, for example, aromatic polyurethane for exterior applications. The multi-step method begins with the mechanical sanding of the substrate that, in a preferred embodiment, is mostly aromatic polyurethane; this process creates a porous surface which enhances mechanical adhesion. The substrate is then coated with a plural-component coating via air assisted airless spray. The substrate can be embossed prior to or after this coating process to create the wood grain appearance. The embossed pattern is then filled with a contrasting agent that is under-indexed to prevent adhesion to all surfaces of the substrate. The excess contrasting agent is then removed using a reverse roll-coater, which is self-cleaning and provides for the reuse of the excess contrasting agent. The substrate is then coated with a clear, plural-component coating which is over-indexed and thereby upon curing allows for the contrasting agent and clear coating to adhere to the substrate. This final coat adds sheen to the substrate as well as abrasion resistance to allow for high traffic on the substrate with minimal wear and tear.

In accordance with one aspect, the present invention relates to a method for coating a substrate, comprised of the steps of pressure embossing a pattern into the substrate; base-coating the substrate with a base coating; applying an under-indexed contrasting agent to the embossed pattern of the substrate coated with the base coating; and coating the substrate applied with the under-indexed contrasting agent with an over-indexed coating.

In accordance with another aspect, the present invention relates to a method for coating an aromatic polyurethane substrate, comprising the steps of sanding the aromatic polyurethane substrate to create porosity via the opening of closed cells of the polyurethane; pressure embossing a pattern into the substrate; base-coating the substrate with a plural-component coating; applying an under-indexed contrasting agent to the substrate and subsequently removing excess contrasting agent, thereby leaving contrasting agent in the embossed pattern; and final-coating with an over-indexed clear coating.

In accordance with still another aspect, the present invention relates to a method for coating a substrate, comprising the steps of pressure embossing a pattern into the substrate; base-coating the substrate with a plural-component coating; applying a contrasting agent to the embossed pattern of the substrate, the contrasting agent comprising a plural component coating that does not have any catalyst, cross-linker, or hardening agent incorporated therein; and final-coating with a clear coating, the clear coating comprising a plural component coating that has an excess of catalyst, cross-linker, or hardening agent incorporated therein.

These and other features of the invention will become more apparent through the following summary, drawings, and description of the preferred embodiments.

