Factory-Applied UV- Curable Coatings
April 1, 2009
Most architectural coatings are applied on the job site, but that may change when it comes to building components produced from composites, vinyl and cement fiber. During the next few years, many manufacturers that produce decking, fencing, trim and siding from these materials are expected to introduce products with enhanced field performance achieved by factory-coating their products with new UV-curable coatings.
These patent-applied-for coatings, available in a wide range of colors, offer superior resistance to sun, moisture, heat build up and use damage. They can be applied using vacuum, spray roll or other common application techniques. The coating is then subjected to intense UV light and cured almost immediately. The coating can be applied as part of an in-line or off-line process and can be formulated to be soft and flexible or hard and scratch resistant. It can be a clear coat or pigmented in virtually any color or gloss level. From the manufacturer’s perspective, this system has the advantage of utilizing a coating that is 100% solids, so it contains no VOCs or HAPs and is not flammable.
CompositesOnce virtually every deck in the country was constructed of wood. Currently there are an estimated 30 million installed wood decks. But after a few years of exposure to the sun, rain and humidity, along with being spilled on and scratched during use, wood decks become a bit of an eyesore and need to be refinished – an oft-dreaded task whether deck owners do this themselves or pay to have it done. Fences, rails, door and window trim also require eventual maintenance.
First introduced in the 1990s, composites were promoted as eliminating or vastly reducing the need for maintenance. Sales of composite fence, decking and railing products are expected to reach $11.8 billion by 2012. Composite window and door components are also available, but it was learned that over time, composites also tend to exhibit poor fade, scratch, stain, abrasion and mold/mildew resistance. They may also retain heat during hot weather, an unappealing feature for a deck. As a result, regular maintenance is also required.
Composites are produced by blending a variety of raw materials. The mixture is then extruded into profiles with many shapes, sizes and lengths including dimension lumber type boards. Composites can generally be sawed, nailed, screwed and otherwise worked like lumber. Their inherent strength makes them ideal for decking and fencing applications. In order to give composites a wood-like appearance, pigments have been added during the mixing stage and wood patterns are embossed on the surface.
Wood plastic composites, which currently dominate this category, are produced by creating a blend of thermoplastic, wood flour and other chemicals. As time passes, manufacturers are using additional raw materials to replace wood such as fly ash, carpet fibers and agricultural fibers such as hemp and rice hulls as they strive to reduce their reliance on wood and create a “greener” product.
The application of UV-curable coatings appears to be the solution to the field performance problems exhibited by all of these composite substrates. Tests show that they provide long-term resistance to fading. UV-coated composite decks also resist scratching from pets walking or children playing on them as well as stains when food or beverages are spilled. The moisture-fighting feature of the coating prevents mold and mildew growth.
From a sustainability perspective, this process uses very little energy and has virtually zero waste. Within a manufacturing facility, it requires a very small footprint relative to other coating operations and can be easily adapted to any process making linear substrates.
Also significant is the fact that the broad color options for these coatings gives architects and designers the ability to utilize color as a primary decorative feature for a deck, a fence or house trim. In future years the composite can be repainted a new color if the home or building owner desires.
These UV-curable products are a coatings industry breakthrough. Historically, composites have resisted coatings because the surface of the substrate prevented adequate adhesion. The formulation of the patent-pending UV coatings allows them to bond tightly to the surface.
With composite manufacturers constantly experimenting with new raw materials, there may be differences in the ability of these products to accept coatings. In these instances, there are a variety of processes to treat the surface so it will accept the UV-curable coatings such as fluoro-oxidation, plasma, corona or flame.
Fiber Cement SidingThe demand for siding products may increase as homeowners opt to remodel their homes prior to trying to sell them during a soft housing market. Of all remodeling options, new siding is reported to generate the greatest return on a remodeling investment when those homes sell.
Fiber cement siding has been a construction industry staple since the early 1900s and can benefit from an increase in siding industry sales due to its long life span and reasonable installation costs, which are much less than natural stone, cedar or wood. And, manufacturers are on the verge of introducing new products to better meet the performance and creative demands of the construction business.
This siding is produced from a blend of cement, sand and cellulose fibers that are extruded into siding boards that achieve their strength and stability by being cured with pressurized steam. The cellulose fibers prevent cracking. The boards can be embossed with wood patterns or other designs. The result is a very long-lasting, durable product that resists moisture, termites and fire. Unlike composites, fiber cement siding can be painted without any type of pre-treatment. Normally a primer is applied first followed by another coating to achieve the desired color.
In most cases, the primer is applied in the factory. The color coat application can vary. Often, the primed board is shipped to the construction site where it is painted by the builder to match the color scheme of the building being completed. Builders often prefer pre-primed siding because it will not absorb moisture when stored at the construction site before it is installed. On occasion builders may order un-coated siding and will perform the priming and painting themselves. Any coating at the building site first requires that all dirt and debris from shipping or storage be washed away. Then the siding must be allowed to dry. Job site painting can sometimes be eliminated if the builder or building owner is purchasing from a manufacturer that offers a range of “stock colors” with which they are satisfied.
The coating dynamics in the fiber cement siding business will change with the pending arrival of one-step, single-application UV-curable coatings formulated for these products. UV coatings can be formulated in any color, shade or hue a builder requests and applied at the factory without the need for a primer coat. This means the products can be extruded, coated and cured in a single process with no “drying time” required between coating and shipping. As with composites, a manufacturer can extrude and inventory un-coated boards and then coat them to a builder’s color specifications. If the UV system is replacing a spray system using solvent or waterborne coatings, VOC emissions are eliminated and indoor air quality is improved. For those manufacturers serving builders who still want primed-only boards, a single application UV-curable primer is also available.
This new coating is highly durable and weather resistant. In future years, it can be repainted with a different color if the home or building owner chooses, an important advantage for a siding that lasts decades.
VinylVinyl building components such as siding, fencing, decking and trim are extremely popular among developers, builders and homeowners. Vinyl siding is used on a large number of new homes and is the most popular option in the replacement market. It is a material that is highly resistant to weather and abrasion while having a long life span.
Vinyl for construction materials is a blend of poly(vinyl chloride) resins, stabilizers, coloring, processing aids, UV inhibitors and plasticizers. The blend is extruded under heat and pressure to become pliable vinyl and sent through a die to create the desired building material. It is made rigid by cooling it with water.
Construction profiles may be created using a single or a co-extrusion process. As the name implies, using single extrusion, the profile is extruded once and all of the raw materials are spread throughout the product. Co-extrusion creates a two-layer vinyl product. The outside layer has a denser concentration of the elements, such as the UV inhibitors. The inner layer is essentially the same as the cap stock layer, but with a lowered concentration of UV inhibitors and color pigment.
If there is an opportunity to further enhance vinyl building components it lies in making more colors available. In a manner similar to WPCs, colors and hues have historically been created in the vinyl industry by adding pigments during the extrusion process. As a result, vinyl is primarily available in a limited number of colors.
A UV-curable coating system has been developed for vinyl producers, which allows them to offer their products in any color. The extruded profile is fed into a coating chamber where any color UV coating can be applied. Then it is fed immediately into a UV curing cabinet. For those producers who still prefer to use pigment to gain color, a clear UV coating can be applied to provide the necessary protection.
Making a decision on the use of wood, WPC, fiber cement or vinyl is of course the decision of architects, contractors and building owners. As a broader array of product options featuring the advantages of UV curable coatings come to market these decision makers will have an opportunity to weigh appearance, life span, maintenance and cost when making these selections.
For more information, see www.finishesunlimited.com.