Ultra-low temperature curing for MDF applications

By Cal EzeAgu, TS&D Manager, Americas, PCR Technologies Division, allnex Resins, Alpharetta, Georgia

When powder coating technology was invented in the 1940s and 1950s, it was primarily used on metal substrates

As powder technology continues to mature, the need to further reduce curing temperatures becomes even more important

Why Use Ultra Low Bake Powder Coatings? 

The global wood coating resin market is estimated at USD 3.

The performance of coating heat-sensitive substrates is one of the reasons for the increased demand for ultra-low-curing and fast-curing powder coatings

Another reason for the need for ultra-low cure technology is the need for slow heat component cure

Ultra Low Bake Challenge 

Appearance, workability and cure cycle are the three main hurdles that must be overcome to balance the desired properties and coating properties of low temperature and fast curing powder coatings

Given these challenges, this paper presents an advanced chemical technique for indoor non-metallic applications

Advanced Chemical Technology for MDF Coating 

New innovative and performance-oriented technologies are designed to meet the delicate balance of low temperature bake conditions for MDF coatings

The technology is compatible with the production conditions of conventional powder coatings

Process and heat curing

The quality of coatings prepared by this new process is maximized when cured in a catalytic gas infrared oven

Figure 8 shows the minimum oven temperature and time required to achieve full cure

Table 4 shows the process steps for treating various MDFs cured at an average temperature of 125°C for 5 minutes (target temperature)
.

Coating Performance Characteristics

Table 5 summarizes industry requirements for basic coating properties for kitchen and bathroom cabinet applications
.
The MDF selected for this evaluation is available online or from stock
.
We evaluated parts of different shapes to verify their consistency in appearance and performance
.
Depending on the configuration of the IR oven and coated part hanger, achieving an even distribution of energy across the surface of the part can be a challenge
.
The use of MDF with different profiles in the tests not only ensures the consistency of component performance, but also validates the robustness of the new technology
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The purpose of high film formation is to avoid multicoating and sanding
.

The edge cracking test is a rigorous requirement established by IKEA to determine the likelihood of cracking in MDF powder coatings and wood panels
.
When conducting this test, the new technology showed excellent performance with no cracking after 48 hours of exposure, as shown in Figure 9
.

Since the coating is suitable for use on kitchen and bathroom vanity cabinets, the technology is designed to withstand certain substances and the harsh environments typically exposed to kitchens and bathrooms
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According to Tables 6 and 7, Stain Resistance and Destruction Physical Testing by an accredited independent testing laboratory in accordance with the ANSI/KC-MA A161.
1-2017 method showed no discoloration, stains, or damage to the coating after 24 hours whitened
.
The results also meet the requirements of destructive physical testing conducted by ANSI/KCMA and SEFA 8-5 edition standards
.

Storage Stability and Handling 

The glass transition temperature (Tg) of the powder coating formulation not used by the new technology was high enough to demonstrate that it did not age and cause premature cure, and to ensure good storage stability under standard use conditions (Figure 10)
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DSC thermal analysis of powder coatings exposed to 35°C for five days showed a 1°C change in onset temperature compared to unexposed samples (Figure 11)
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This small change indicated little or no chemical change or any handling issues after five days of exposure at 35°C
.
 

After 60 days, the technology was evaluated at room temperature (20-22°C) to observe any changes in properties such as appearance, gloss, chemical and mechanical resistance,
etc.
It was observed that none of the key properties were negatively affected after 60 days
.

technology expansion 

Most applications in MDF kitchen and bathroom cabinets specify a matte finish because it provides physical and aesthetic properties, a warm and soft appearance, is easy to clean, and makes the coated surface less susceptible to exposure to sunlight
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In addition to the one-shot matte technology capable of achieving 10-20 units of gloss over a 60° gloss range at 120°C, there are other gloss options available with this technology, which are available in toilet seat and cabinet applications.
High gloss (HG) and matte dry blend (MDB) low gloss finishes
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The MDB method uses a traditional two-component paint (Part A and Part B) mixed together in a 50:50 ratio to obtain a finished matte paint
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Tables 9 and 10 show reference formulations for high gloss and MDB technologies
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The two sister products also follow the same process parameters and offer similar performance and handling characteristics to the one-off matte (OSM) technology discussed earlier
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Typical coating performance characteristics of HG and MDB systems are shown in Table 11
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Summarize 

What is interesting about this technology is that it not only has excellent adhesion to metals, but also enables a matte finish at such low temperatures without compromising its excellent chemical resistance, smoothness and productivity
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This development furthers allnex's strategic position as the innovation leader in ultra-low bake powder coatings, expanding its product range and expanding the application of powder coatings on heat-sensitive substrates such as plastics, fiberglass and siding
.