Wood used in furniture and flooring applications must be able to withstand the rigors of everyday life while retaining its natural beauty and warmth.
Topcoats and primers help to protect tables, cabinets, desks and floors. They act as a line of defense against scratches, marring and water while still allowing the natural wood grain texture and color to show through.
Coating manufacturers are continually improving coating formulations to allow for longer-lasting, more durable and clearer coatings.
By using a waterborne acrylic-polyurethane dispersion (PUD) blend, formulators can create wood coatings with greater hardness and resistance as well as improved in-can and wet film clarity.
The case for coatings
While the requirements for a coating vary depending on the substrate and end application, virtually all coatings are designed to provide a layer of protection.
“Many of our customers are creating coatings for hardwood flooring and wood furniture, where protecting the surfaces is extremely important,” says Tradd Kirkland, Market Manager at BASF. “Chemical resistance, scratch and mar resistance, and stain resistance are all very important to end users.”
Most wood coatings are made up of a few key components, including resins or binders, solvents and diluents, pigments or nanopigments (in certain cases), and other additives.
Aside from protection, coatings can also bring some unique attributes to the feel or finish of a wood substrate through their own properties.
“In composite wood applications, for example, if you wanted to add certain properties, you would have to change the formulation of that composite board. That requires a lot of additive materials,” says Ziniu Yu, Technical Specialist at BASF. “But you can also add these properties by using coatings that are only between 25 or 50 microns thin instead of changing the formulation of the entire board.”
Why use a blend?
The dispersions or binders used in a coating can have a major impact on its performance and attributes when applied.
JONCRYL® 9530-A is a waterborne acrylic binder that offers superior clarity and chemical resistance in wood topcoats and primers. Its strong adhesion and ability to blend with other resins allows formulators the freedom to create specific coatings for a wide variety of end-use applications.
“JONCRYL 9530-A has a very fine particle size. That delivers wet-film clarity as well as in-can clarity, and it’s also self-crosslinking,” says Yu. “It offers fast drying time and strong block resistance.”
JONCRYL® U 4500 is an aliphatic polyurethane dispersion that delivers exceptional scratch and mar resistance as well as a low minimum film formation temperature, allowing formulators to create coatings with lower VOC emissions.
“JONCRYL U 4500 offers a good balance of hardness and flexibility, and the scratch and chemical resistance is really strong due to its self-crosslinking capabilities,” says Yu. “It's also aliphatic or non-aromatic and more resistant to yellowing.”
When combined, these additives build off each other’s unique properties to increase the effectiveness of a coating while also offering cost-savings.
“From a cost point of view, a PUD is a little bit more expensive than traditional acrylic resins, so by blending it with the acrylic resin you're adding some cost benefits,” says Yu. “More importantly, a PUD itself has some unique properties: it’s normally more stretchable and has a great balance of flexibility and hardness.”
By properly formulating the blend with the right chemistry, this enables enhanced adhesion, improved drying time, and the strong scratch, mar, abrasion and chemical resistance required by even strenuous flooring applications.
To evaluate its performance, the waterborne acrylic-polyurethane dispersion blend was pitted against a benchmark commercial waterborne acrylic topcoat in a variety of tests.
"Compared to the competition, the dry time for a WB-PUD blend was considerably better than commercially available sports flooring coatings," says Kirkland. "Along the same lines, scratch and water resistance was much better than competitors."
In the Cobb water resistance test under ASTM D5795 standards, the JONCRYL 9530-A/PUD blend achieved a Cobb number of 3, compared to 7 for a C2-PUD blend and 47 for a traditional sports floor coating.
In the block (heat) resistance test, the coatings are exposed to 55° C for 8 mins with a Carver press (ASTM D2793). The JONCRYL 9530-A/PUD blend could withstand over 650 PSI of pressure, in comparison to around 550 for the sports floor coating and less than 300 for the C2/PUD blend.
Another important characteristic is the high clarity of the blend, both in-can and after application, providing confidence in the coating’s ability to let the warmth of the wood substrate to show through.
“In North America especially, the clarity of the resin is extremely important,” says Kirkland. “If a customer gets something that's milky in the can, it can be a psychological hit on the product, and they might be less inclined to think that it's performing well.”
Cutting down on VOCs and NMP
NMP, or N-Methylpyrrolidone, is used as a solvent or surface deposition medium in a variety of industries and applications, such as paint and coating removal, petrochemical processing, engineering plastics coatings, agricultural chemicals, electronic cleaning and industrial/domestic cleaning.
It’s also a reproductive toxicant and can cause serious eye, skin and respiratory irritation, and has been restricted in the EU because of this.
“A big thing with this [wood coatings] blend is that it’s NMP-free,” says Kirkland. “This is pretty ubiquitous throughout Europe, but you can still find some PUD coatings within North America that utilize NMPs. It’s about preparing for that regulatory change to occur in North America and get people on board with not using an NMP in their formulations.”
As coating makers search for formulations that offer strong protective capabilities while simultaneously meeting increasingly stringent sustainability regulations, a blend of JONCRYL 9530-A and JONCRYL U 4500 offers easy blending and formulation latitude to meet the demands of consumers in the wood furniture and flooring industry.
Additional additives, such as HYDROPALAT® WE 3370 for improved chemical resistance or HYDROPALAT® SL 3682 for boosted abrasion resistance, can also be implemented in the blend, providing customizability and flexibility for formulators to create a coating suited to their exact requirements.
“We provide these resins to formulators who are very experienced and can add additives based on their needs,” says Yu. “With our starting point formulation based on our extensive experience, we provide a high-performance blend that’s already as good as commercial coatings, and then formulators can boost the look and the performance even more.”
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