Innovative water-based acrylic resins can be used in industrial wood coatings

Industrial wood coatings cover a wide range of market applications, including furniture, kitchen cabinets, building materials and decorative coatings. The requirements for these markets depend to a large extent on the application area. Outdoor coatings focus on high durability and moisture resistance, while indoor coatings emphasize chemical resistance and wear resistance.
largest indoor wood coatings market is the furniture industry. Several resin technologies used in this market include solvent-based (SB), water-based (WB), UV-cured polyurethane dispersions (UV PUDs) and self-linked acrylic resins. When deciding which technology to use, the following criteria should be considered: processing process, performance, appearance, VOC, and cost.
the North American wood coatings market with solvent-based technologies, including nitro paint (NC) and amino acid curing coatings. These coatings have many advantages, including fast drying times, high gloss, and enhanced wood appearance. They are also very economical and easy to spray, roll, spray and immerse. However, the use of these materials also has a major drawback, namely, high VOC and harmful air pollutants (HAP) and short mixing times. As regulations on low VOC content and formaldehyde emissions become more stringent, there is also a growing demand for environmentally friendly coatings1. This has facilitated the industry's shift to water-based technologies, including UV-cured polyurethane dispersions (UV PUDs) and self-linked acrylics.
UV PUDs are increasingly recognized as an alternative to solvent-based resins due to their extremely low emissions. They have high performance and minimize process problems. Because UV PUDs are polymers of high molecular weight, their curing network has a low crosslink density compared to 100% solid part system, limiting the contraction after curing, so the adhesion between most substrates is excellent. Excellent mechanical properties due to the hard-chain segments of polyurethanes and urea containing hydrogen bonds, combined with soft segments based on polyols. Some of the challenges associated with water-related UV curing (WB UV) applications are related to the process. Complete dehydration before curing is essential, and considerations such as humidity should also be taken into account in order to minimize secondary product due to incomplete drying. In addition, the cost of this technology is higher than solvent-based technology.
also includes self-interlinked acrylic dispersions in water-based resin technology. In general, they have good durability and can be used to make high-performance coatings with low film-forming additive content due to the phase separation form of polymer particles. Depending on the polymerization method applied, several types of patterns can be obtained, which can also affect film-forming properties, such as anti-adhesion (Figure 2). These materials can also be mixed with water-based UV resins for a more economical formulation while maintaining good performance. Areas of concern include the presence of surfactants required for polymer particle collage stabilization. These groups migrate to the membrane surface, making the membrane water sensitive and possibly causing foam problems in the formulation. In terms of appearance, there is no particular emphasis on acrylic to improve the appearance of wood substrates, often lacking transparency. Although the solid content of water-based acrylic is high compared to solvent-based nitro paint, it usually does not produce a smooth feel.
presents a new type of self-connected acrylic, Alberdingk
®
AC 3630, and examines its performance in KCMA and furniture coating applications, compared to traditional self-connected acrylic and solvent-based finishes, especially commercial varnishes. Features of the AC 3630 include excellent transparency, good wood texture, strong contamination resistance, short drying times, difficulty in burring, and excellent filming on porous substrates. In addition, compared with traditional emulsions, the surface active agent content of this product is low, so low foam and good water resistance.
test
table 1 summarizes the performance of acrylic emulsions included in the scope of this study. Single-phase and multi-phase products with an MFFT range of approximately 20-45 degrees C were evaluated. These resins are specially designed for industrial wood applications, based on the Kitchen Appliance Manufacturers Association (KCMA)2 and the VOC targets of less than 200 g/L from furniture manufacturers. All formulations are adjusted to the same level and include a variety of standard additives, defystants, waxes, leveling agents and fluid modifiers. The study also evaluated a commercially processed varnish. The total VOC content is 550 g/L, free of solvents.
the coated plank is prepared in four steps:
1. Spray a wet film with a thickness of about 4-5 mil on the cherry wood panel;
2. Air dry for 15 minutes;
3. Force dry for 15 minutes at 50 degrees C and then cool for 15 minutes;
4. Grind the panel with 320 stearic acid and ultra-fine matte sponge and repeat the process with a second coating.
KCMA and furniture testing methods
Chemical resistance/contamination resistance: a 0.25 to 0.5 inch diameter stain on the test panel with enough chemicals and stains to cover the surface dish. Wait 16 to 20 hours. Remove chemicals and stains and clean panel surfaces with water. Each chemical and stain test point is assessed, 0 represents the paint film surface completely damaged, 5 represents the paint film surface is not affected. The chemicals used include vinegar, lemon juice, orange juice, grape juice, tomato sauce, coffee, olive oil, 1% detergent solution, mustard and water.
detergent and water resistance (water impregnation): Prepare 0.5% detergent solution and immerse it in a piece of s8 cellulose sponge. Place a coated panel on the sponge for 24 hours to observe changes in the surface of the paint film. Unblistered, whitened, or significantly colored to qualify.
scratch adhesion: cut a small 4x7-inch sample from each test panel. The Adhesion Tester with Bick Gardner Scratch Adhesion Tester weighs 5000 grams and uses a circular needle. Rated from 0 to 5, 0 represents that the surface of the lacquer film is completely damaged, and 5 represents that the surface of the lacquer film is not affected.
ball indentation experiment: cut a small 4x7-inch sample from each test panel. The Paint Film Ball Indentation Experiment was conducted using the Bik Gardner Scratch Adhesion Tester, weighing 300 grams and using a small pen of 5785.
to be evaluated after waiting 1 hour. Rating standards are classified as qualified and unqualified. A 24-inch indentation that is visible to the naked eye is unqualified.
water resistance: test the panel with 10 ml of boiling water. Place a ceramic coffee cup full of boiling water on it. Wait 1 hour. Remove the cup and wipe the panel with a paper towel. Wait 24 hours. Evaluate its whitening.
-Brite ™ scratch resistance: sampling from Form 3B-H Leneta paper jam (3 mil). Dry for 10 minutes, then force dry for 10 minutes at 50C. Wait 14 days for the test. Record coating gloss (60o). Remove a small 2-inch square piece from the green Sigao Baijie cloth. Place 200 grams of weight on top. Slide the cloth back and forth 10 times on the coating surface. Remove the cloth and record the gloss. Record the damage to gloss (%).
the Koënig: sampled from the glass panel (150 microns). Air dry for 10 minutes, then force dry for 10 minutes at 50C. Koenig's hardness was assessed after 7 days.
test results
As mentioned earlier, one of the main options for solvent-based coatings in industrial wood applications is varnish. The varnish is a mixture of oily alicyl resin, urea formaldehyde and melamine. Because they use strong acid catalysts such as toluene sulfonate, the mixing time is only 24 to 48 hours. Varnishes perform well in industrial wood applications, however, they have high VOC content and formaldehyde is classified as a carcinogen. The traditional varnish was compared with the water-based self-intersecting acrylic emulsion. Panels coated with traditional varnishes are transparent, dry for short periods of time, and have a good woody feel and wet surface. In acrylic resins, only the AC 630 has similar transparency, a good woody feel, and a good firmness and look on the substrate. In fact, the AC 3630 is much more transparent in the tank than other acrylics, as evidenced by the low turbidity of pure emulsions (Figure 3).
also observed that there were the fewest burrs on the wood surface compared to other acrylics. All coatings show good nail scratch resistance. In addition, the surface hardness after seven days was measured using the Koenig tester. All acrylics are much softer than varnishes (<100s), and AC 3630 is the hardest of them (Figure 4). Despite this difference, acrylic-coated components meet the anti-adhesion requirements in industrial environments.
chemical resistance tests were conducted in accordance with KCMA standards (Figure 5). All coatings except AC-03 have good performance and AC-03 has poor resistance to grape juice, coffee and ethanol (50%). Edge immersion tests were also carried out, and all coatings except AC-01 passed the test with good results. This test simulates spreading a detergent-soaked dishwashing cloth on a vertical cabinet door. When selecting acrylic, it should be taken into account that surfactants can make the surface of the paint film water-sensitive. Therefore, the use of low surfactant content of materials is extremely beneficial.
addition, several tests were conducted to assess performance in furniture coating. Various requirements are put forward for this market and are segmented according to commercial and residential applications. Figure 6 shows the scratch resistance data of the coating, records the gloss before and after friction, and calculates the percentage of gloss loss. The lower the value, the higher the performance. The loss rate of varnish gloss was 25%, and the performance of the lower acrylic of MFFT was similar. Mixing polyurethane dispersions with acrylic can further improve wear resistance. Scratch adhesion was also tested, and all acrylics were tested better than varnishes, which were layered and whitened. The test results for boiling water resistance are shown in Figure 7. Varnishes perform well, while other acrylic coatings show much superior performance.
summary
in industrial wood coating applications, water-based self-linked acrylic emulsions are suitable alternatives to solvent-based products. They have low VOC content, are not limited by mixing time, and have a variety of good properties for the preparation of high-performance coatings. At the same time, a new type of acrylic with low surfactant content has been introduced. This new development is better coated due to its superior atomization and wood wetting than solvent-based systems, good optical transparency, and wood warmth and less burrs. Further research and development is under way to explore pigment formulations and mixtures with polyurethane dispersions.
reference:
Howard, C. et al, From Evolution to Innovation. PCI Magazine, May 2014.
ANS/KCMA A161.1-2012, Performance and Construction Standard for Kitchen and Vanity Cabinets, 2012.
。