TAGS: Wood Coatings Architectural Coatings Environmentally Friendly Coatings
Wood coatings encompass a wide range of end-use markets and formulation technologies. Even narrowing the focus to interior applications includes applications such as:
- Furniture
- Pre-finished flooring and joinery, and
- Floor and woodwork refinishing
These coatings might be applied in a factory by robots or inside a building by contractors or DIY’er’s. As expected, this wide range of application conditions and customer expectations requires an extensive variation in formulas to accomplish diverse market goals.
Historically wood coatings were simple mixtures made from natural products like vegetable oils, shellac resin and beeswax. Over the years, factors, such as increased performance expectations, consumer tastes, advances in polymer chemistry or material science, and regulations conceded with pollution prevention or worker and consumer safety have changed the way wood coatings are formulated.
Let’s explore the five changing trends in detail...
Evolution in Consumer Tastes
Changing consumer tastes in furniture, flooring and interior decoration are changing the way wood coatings are formulated.
High gloss, transparent finishes are giving way to a different aesthetic. Since consumer trends cross markets and industries they affect wood coatings formulations from factory applied flat-pack furniture finishes to DIY coatings to refresh kitchen cabinets.
Home fashion is trending towards
lower gloss wood coatings in all markets. With a nostalgic longing for the
rustic “cottage core” look gaining momentum through social media influencers. The high gloss, “Plastic” looking wood finishes of the past are no longer in demand.
Rustic Furniture Finish
Possible Approaches to Formulate Low Gloss, Clear Wood Coatings
The formulation challenge for
low gloss, clear wood coatings lie in achieving the desired sheen without creating a
hazy appearance. This problem can be approached from several directions.
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One approach utilizes specialized flattening additives designed to lower gloss without affecting the clarity.
- Silicas and waxes flatten coatings but often impart a hazy look that obscures the character of the wood. A secondary effect of wax and silica flatteners is an increase in properties such as hardness, mar resistance and print resistance.
- Several suppliers offer matting agents specifically for clear wood finishes which do not cause haze in the cured film.
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Another way to formulate a low gloss, clear wood coating centers on polymers which form inherently low gloss films. Since flatteners are not used, imparting haze to the finish is not a concern. Many chemistries are incorporated into these matte binders, including:
Resin suppliers such as DSM, Covestro and allnex have recently introduced new inherently low gloss polymers for waterborne and UV-cured wood coatings and they are a development target for other material suppliers.
VOC Reduction – Alternative Technologies Come in Handy
Regulation of Volatile Organic Compounds (VOCs) in coatings began in the 1960s in California. These measures were enacted to help reduce the photochemical haze or “smog” plaguing the Los Angeles area. The idea of controlling the VOC content of paints caught on as a means of mitigating air pollution.
As environmental concern grew, VOC content regulations for paints and coatings became a global phenomenon. VOC reductions started by increasing the non-volatile content of paints and using solvents exempt from regulation because they did not form “smog”. With the coming of tougher restrictions, these methods were no longer effective and other solutions were needed.
Waterborne Technologies for Wood Coatings
Waterborne technologies began to gain popularity with the introduction of latex house paints, which now have the largest share of any global coatings market segment. Water reducible alkyd wood coatings were the earliest waterborne systems with the gloss and clarity required for clear applications. These coatings were not ideal since they cure slowly and possess poor mar resistance.
The best waterborne wood coatings today are formulated from advanced polymers including self-crosslinking or 2K PUDs,
acrylic dispersions and
polyester resins. Of the many waterborne coatings resins available two stand out.
- The first, particularly well-suited for flooring use, is Decovery® SP-2022 XP from Covestro. This low VOC capable polymer is 35% bio-based and forms inherently flat films without using matting agents.
- A crosslinker from Covestro, Bayhydur-eco® 701-90 is an innovative bio-based polyisocyanate developed to crosslink waterborne dispersions for use in furniture finishes.
Benefits of UV-cured Wood Coatings
UV-cured coatings are one of the fastest-growing wood coatings technologies. Among their many advantages are:
- Short curing cycles
- Very low volatile emissions, and
- Tough, durable films
Curing coatings on three-dimensional objects is a challenge for UV-cured coatings, but they
excel on flat surfaces like flooring and flat-pack home furnishings. The growing market share of UV-cured coatings means that material suppliers are increasing their allocation of resources geared to developing improved polymers for the formulator.
allnex has introduced UCECOAT® 7999 into one of the fastest-growing wood coatings markets, waterborne UV-cured coatings for industrial applications. In addition to clear and white wood finishes this zero-VOC, bio-based polymer can be used for
non-yellowing coatings on PVC flooring. Formulations utilizing UCECOAT® 7999 can be tailored to application methods ranging from spray to vacuum coaters.
Sustainability – Reducing Energy Usage from the Beginning
During the manufacturing of a product, coating processes consume a significant portion of the total energy required while generating a large fraction of the environmental pollution and waste.
Reducing energy consumption while reducing pollution and waste by improving the coating segments of manufacturing enhances sustainability.
Bio-based raw materials are gaining popularity as a means to create a greener, sustainable wood coatings. This is appropriate since wood itself is a sustainable material when properly sourced. For example,
Southern Yellow Pine grown in forests managed by sustainable principles provides a renewable raw material for furniture, joinery, and flooring. While not actually wood, bamboo is a renewable material utilized in applications such as flooring where wood is traditionally used.
Sustainable Forestry
Bio-based raw materials include vegetable oil-based waterborne and solvent-based alkyd resins, tall oil-based epoxies and acrylic polymers made from
bio-based monomers. The preferred sources for bio-based materials are non-food plants or waste products from other industries like paper mills.
A variety of curing mechanisms can be used to form tough, durable films from bio-based materials. These materials can be cured oxidatively, formulated as 2K systems or baking enamels, UV-cured through photoinitiation and self-crosslinking coatings.
Reducing energy usage in the application and curing of coatings contributes to sustainability. Reducing energy use during manufacturing contributes to a
product’s sustainability and
lowers its carbon footprint. Formulating coatings which require less energy input for the application and curing processes make for a more sustainable system. Increased durability and longer service life contribute to sustainability. The longer something lasts, the fewer times it needs to be replaced.
Consideration of how a coating affects the product life cycle is the first step toward using wood coatings to enable the circular economy. When a product reaches the end of its useful life a properly formulated finish can enable recycling.
IKEA has announced plans to become “climate positive” by 2030. In short, this means that they will remove more Greenhouse Gas (GHG) than operations produce.
Product durability, bio-based raw materials, reducing energy usage during manufacturing and product recycling/repurposing and wood coatings which enable these processes will play an important part in reaching that goal.
Indoor Air Quality Concerns
The
Green Building movement has influenced wood coatings formulation in many ways. Indoor air quality is an important metric for these initiatives. While coatings are not the only component releasing volatile organic compounds into occupied buildings, they can be formulated to reduce or eliminate their contribution to total emissions.
Volatile compounds such as
formaldehyde can cause “sick building syndrome” due to chemical exposure. Specific concerns over formaldehyde release have guided factory-applied wood coatings formulation away from the once-ubiquitous urea-formaldehyde or melamine crosslinked finishes.
Wood coatings formulation has pivoted to self-crosslinking and structured latex polymers,
avoiding any potential to generate or release formaldehyde into the built environment. Moving away from components in a formulation that is retained in the film and slowly released exposing building occupants is a critical step in producing wood coatings that address indoor air quality issues.
EHS/Worker Safety On Priority
Concerns over chemical exposures from coatings materials extend to the manufacturing workplace and the contractor’s worksite. The
reduction of volatile chemical emissions during the handling, application and curing of coatings is paramount to protecting workers. New formulation tools enabling the development of inherently safer wood coatings are the most effective control method. There are many programs to limit worker chemical exposure around the world.
One of the most comprehensive is the EU Registration, Evaluation, Authorization and Restriction of Chemicals (REACH) legislation and its Substances of Very High Concern (SVHC) program.
EU REACH SVHC lists 69 specific chemical compounds which are restricted for use within the EU member states. Additionally, new candidate substances are added to the list periodically.
When formulating wood coatings for use in or importation into the EU, the formulator must validate that the formula does not contain REACH restricted SVHC components. It would be advisable to also avoid any substances which are candidates for inclusion on the SVHC listing. Your due diligence should extend to breaking down all your formulas ingredients as far down as possible to make sure the final product is REACH compliant.
Make Sure that the Chemicals Used in the Final Product are REACH Compliant
One component of many
PUDs used in waterborne wood coatings is the
solvent 1-methyl-2-pyrrolidone (NMP) which is a candidate for restrictions on use under REACH. Raw Material suppliers now offer PUDs made without NMP to help the formulator comply with the EU regulations.
Isocyanate-free formulations are another example of the ways wood coatings are changing. Traditional 2K urethane coatings rely on
isocyanates to cure polyols into high molecular weight polymer films. Isocyanates are respiratory sensitizers which can cause allergic reactions as severe as fatal anaphylactic shock. Alternatives to 2K polyurethane coatings include wood finishes based on PUDs, self-crosslinking acrylics (low-temperature cure and baking systems) and UV-curing polymers.
With proper engineering controls coatings containing substances of concern can still be used in formulations.
- Methods which reduce worker exposure during application and curing or those that reduce overall coating usage are effective to control measures.
- Reformulating a coating to a higher volume solids content requires the application of less coating to achieve the same dry film thickness (DFT).
- Changing a formula’s rheological profile to enable using an application method with higher transfer efficiency, thereby reducing overspray also lowers worker exposure to hazardous volatile chemicals.
An example of this philosophy of reducing exposure is replacing a spray-applied 2K urethane coating for window profiles with a vacuum coater applied UV-cured coating.
In Closing
Many trends influence wood coatings formulations. It would be impossible to explore even the top five exhaustively in a short article. The author hopes this serves as a helpful introduction to the topic and provides insight into formulation solutions to the challenges posed.
Wood coatings have advanced greatly from the days of hand-rubbed, boiled Linseed Oil, who can predict what coming trends will influence their formulation in the future?
Commercially Available Ingredients for Wood Coatings
View all the commercially available
additives & resins suitable for wood & furniture coatings, analyze technical data of each product, get technical assistance or request samples.