Waterborne Wood Furniture Coatings Time is NOW!

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1 I. Introduction Waterborne Wood Furniture Coatings Time is NOW! (Written by: Robert Duan) State-of-the-art waterborne coatings that deliver excellent aesthetic appearances on furniture and interior wood décor while reducing the impact on the user and the environment have now reached the levels of maturity that could be considered as the products of choice for many furniture manufactures seeking to convert their entire existing solvent coated systems or to expand their product portfolios to reach more customers. Waterborne Coatings use water (H 2 O) as the carrier to deliver the coating which results in a 100% green and environmentally friendly finish to the market. Water is an economical, vast, recyclable and non polluting resource of our planet. The principle virtues of waterborne furniture coatings lie in the fact that they are economical, have low toxicity, have excellent non-yellowing resistance, a good film build and are non flammable. Waterborne furniture coatings contain the minimum of noxious substances, thus guaranteeing that the people and our environment remain protected during the coating process and day-to-day use of the furniture by the end consumer. Valspar s complete range of waterborne sealer, lacquer, color, glaze have allowed furniture manufactures achieved the look, feel and performances of traditional finish while retains the ease of application of the traditional finish. In this article, we will present detailed case studies based on our experiences to convert existing customers running traditional NC/PU based finish to waterborne finish. While cost of the conversion is a concern, we have found with most of our customers that it varies from factory to factory depending on their current line/equipment set-up. In some factories, only minimum line modifications are necessary. Moreover, coating formulation and application know-how played key roles in the successful conversion from solventborne to waterborne. Our efficient and eco-friendly approach can help to facilitate the furniture manufacture in the greenest way possible by reducing unpleasant solvent emissions as far as possible and at the same time doing it economically. II. Key Differences between Solventborne and Waterborne Coatings Table1. Key Differences between Solventborne and Waterborne Coatings Solventborne Waterborne Solvent Main Resin Organic Solvents such as Toluene, Xylene, Mineral Spirits, BAC etc. Nitrocellulose, Alkyds, Polyol, Isocynates Water and a small amount of film forming solvents (<5%) Waterborne Acrylics, Waterborne Polyurethane Dispersions Plasticizers Phthalate Containing DOP, DNIP Typically no need to use any plasticizers

2 Application Environment Fire Protection Storage and Transportation Need to consider formulation changes to cater to winter and summer temperature changes Strict due to the flammable nature of the coating Shipping dangerous cargoes require D/G compliant transportation Need to provide consistent environment for drying, Dust Protection, Stainless Steel Pipe, and maintain line environmental temperature above 18 C. None-flammable Require heated storage and transportation to maintain temperature above freezing. The key differences of solventborne and waterborne coating are listed in the Table 1. Besides the common knowledge of the solvent differences of the two systems, the resin used is also vastly different. In the solventborne system, Nitrocellulose (NC) and Alkyds are commonly used. In a typical 2K PU system polyol and isocynates are used. These polymers are fully dissolved in the solvents such as Toluene, Xylene (Figure 1). In the waterborne system, emulsions of acrylics and polyurethane dispersion are used as the main resin. These resins exist as sub-micron particles in the coating (Figure 2) so maintaining the stability of the emulsion from production all the way to actual application becomes a significant challenge for both the coating formulators and for the furniture manufactures. Therefore the application environment, the storage and transportation conditions need to be specified. Failure to do so can resulted in a gelled coating which, unlike many of the solventborne systems, could not be used again. The resin differences between the solvent-based coating and waterborne coating have not been stressed in many of the articles discussing the two systems. The waterborne system uses high molecular weight synthetic resins such as PUD or Acrylics that are intrinsically more flexible and, unlike many of the solvent-born nitrocellulose coatings for example, do not require plasticizers. Waterbased coating system also improves the coating s antiyellowing performances and therefore it is excellent on white finishes. The PUD and Acrylic resins are typically softer and therefore getting high mar resistance, heat resistance for waterborne coating typically would require the addition of crosslinker in the system. Figure 1. Micrograph of a Typical Polymer Solution

3 Figure 2. Scanning Electron Micrograph of Typical Acrylic Emulsion Particles III. Performances and Appearances There is a general misconception in the industry that the appearance of products finished with waterborne coatings is inferior to the traditional solventborne finish. Some furniture manufactures described pieces finished with waterborne stains as being "muddy," or lacking the "depth" of a typical solvent-borne stain. Pieces that receive only a sealer and/or topcoat may appear to have a green tint in the wood, instead of the amber tint associated with solvent-borne coatings. This phenomenon is related to the film formation of waterborne coating. Figure 3 shows the three stages involved in the film formation process of the WB system. We know from Figure 2 that the waterborne coating is dominated by these sub-micron sized particles. The first stage of the drying is the evaporation of water. This brought the particles together. The particles in the second stage start to deform with the help of the remaining film formation solvent in the system which is slower to release than water. During the third stage, these particles further soften and start to dissolve into each other to form uniformed and transparent film. This third film formation stage is commonly called coalescence when referred to the WB film formation.

4 Stage 1 Stage 2 Stage 3 Figure 3. The Waterborne Coating Film Formation Process The coalescence process of the stage 3 is critical as it directly affects the performance and appearance of the coating. At Valspar, we have worked closely with our customers to adjust the coating formulation and have solved appearance issues related to poor film formation. Figure 4 shows our waterborne coated color panels. Compared with products made with our traditional NC based paint, the two finishes looked identical. Figure 4. Waterborne Coated Color Panels One area of the performances those earlier generations of waterborne coating failed is in the hot water resistance area. In this test, 100 o C boiling water is purred into a stainless steel cup placed on top of the waterborne coated wood furniture. The coating has to maintain its integrity and appearances which are important especially for the dinning room table top applications. Earlier generations of the coating would often turn white under the heat. This is typically caused by the lower softening point of the coating which would partially melt under the stainless steel cup and recrystallize to cause the white appearance. The use of higher heat resistance resin or the addition of some crosslinking agent can usually improve this performance (as seen in Figure 5.)

5 Figure 5. Our Waterborne Coating Passes 100C Hot Water Test Another difficulty often associated with waterborne coatings is grain raise. The water in the coatings is absorbed by the wood, causing it to swell. Grain-raise results in a finish that has a rougher feel and appearance. However, we have found that, with the proper combination of coatings, equipment, and sanding, grain raise can be minimized to an acceptable level. Some of our customers chose to use only a waterborne sealer and topcoat instead of a full waterborne system as a transition step before going to full waterborne. IV. Converting to Waterborne Furniture Coating Converting to waterborne coatings generally is a much less costly method of reducing emissions than converting to for example UV-cured coatings. Capital investment ranges from nominal to several thousand dollars to purchase stainless steel lines and heating equipment. For some customers using PU based finish line, where the line is already equipped with oven, dust free spraying booths, etc. virtually no modifications are necessary to make the switch to waterborne. Other customers replaced several gun or pump components, added some heating unit along the production line. Waterborne coatings often require a longer drying time than typical solvent-borne coatings because the water in the coating does not evaporate as quickly as the solvent. Larger facilities often have already install ovens for use between coating steps to drying and the same facilities can be used for waterborne. Adjustments in terms of temperature and the length of drying need to be implemented for waterborne. Waterborne coatings generally are applied using spray guns, although dipping, roll coating, and wiping also are used. Workers typically do not need to wear masks during spray operation and the smell of the solvent is absent in the production. Application of waterborne coatings by spray gun requires a different operator technique than that used to

6 apply solvent-borne coatings. Some operator training is needed to achieve the consistent performance. V. Case Studies: 1) Usage/Consumption Comparison Table 2 lists a typical dining room table finishing system. We recorded the coating usage for the waterborne (WB) and nitrocellulose coating (NC) to achieve the similar aesthetic appearance, hand feel and coating performances. In all the steps involved, we have observed that lower WB usage can be used to achieve the requirements. This perhaps can be attributed to the high molecular weight nature of the waterborne resin which offers better film integrity and mechanical properties at lower thickness than the nitrocellulose based coating. We have also observed that in general, only one topcoat is necessary for our WB coating to achieve the look of the NC based coating, resulting an overall 28% of the saving on the coating usage. As we know, the WB coating is more expensive than NC coating. However, with this reduced coating usage and optimized coating finishing system, furniture manufactures could bring the cost of WB finish to be close to the traditional NC and PU finishes. We believe the remaining cost increase of WB finish furniture could be absorbed by the market as customers seek health and environmentally friendly furniture products to be placed in their homes. Table 2. Waterborne (WB) and Nitrocellulose Coating (NC) Usage Comparison Finishing Item: Dining Table Finishing Area WB ( ) System WB Usage (kg/ ) NC System NC Usage (kg/ ) 7.46 NGR Stain NGR Stain Wash Coat Wash Coat Glaze Glaze Sealer Sealer Sealer Sealer Topcoat Topcoat Topcoat Total Usage ) Switching Cost Most furniture manufactures do not understand the cost for switching from sloventborne system to waterborne system. Frequently, the total conversion cost has been exaggerated.

7 It is true that per Kg cost of the waterborne coating is typically a lot higher than the solventborne system; however, our experiences show that to achieve the same look of our traditional NC based coating finish, the overall waterborne applied cost is very similar to our solventborne. There are primarily three reasons: 1. In general the transfer efficiency of the waterborne coat from the spray gun to the wood substrate is 10% higher than the solventborne coating. This is because of the high surface tension of the water increases the average particle size of the spray. This would thereby minimize the lost of coating during the spray applications. 2. Waterborne coating uses water as the thinner solvent. The cost is almost negligible compared to the solvent thinners. 3. The resin used in the waterborne coating has much higher molecular weight; therefore it can achieve good film build and coverage. This can help to reduce the application steps and total coating applied weight. From equipment modification standpoint, it is true that all equipment must be stainless steel to prevent from rusting. On the other hand, we found the line modifications and capital investments were well tolerated by furniture manufactures. Table 3. list one typical case of the line modification cost to covert a previous NC line to waterborne. The majority of the cost is from the construction of a dust free room to allow the drying of the furniture. In many other cases, especially for customers who operate manual PU lines already equipped with the dust free room, the cost of switch is almost negligible. Table 3. Line Modification Cost from NC to WB Item Description Cost (RMB/per unit) Number Total Cost (RMB) 1 New W-71 spray gun for WB New pipe New pump 2, , New mixer 2, , Dehumidifier 10, , Dust free room , Grand Total 93, There are several positive financial savings where conversion to waterborne could bring about. For example, many furniture manufactures need to invest in infrastructures and safety equipment to ensure the safe handling and storage of solventborne coating. The storage facility needs to be certified for fire safety. They need to comply with the government regulations and being inspected by the government throughout the year to ensure their compliances. Waterborne coatings, on the other hand, are none flammable

8 materials and therefore require only routine investments in fire safety which can save costs. In all, the cost of switching to WB is typically not a road block of the conversion. 3) Comparison of WB performance with NC Table 4 comparisons are based on finish systems applied onto the same base wood panels and have achieve similar appearances using both Valspar WB and NC based coatings. For both natural and glazed systems, our WB coatings have matched and exceeded the performances of our NC based finish. The abrasion resistance and MEK double run (which correspond to chemical resistance) have shown dramatic improvements over their NC counter parts. Table 4, Physical testing Test Item DFT Adhesion Cycle Pencil hardness Print test Abrasion test MEK double rub MEK WB Natural Color!" mil 4~5B Passed 10 cycles #$ 10 % &' HB-F 3 PSI 24 () No marks *+, cycles 20 rubs no mark./ 2001,- NC Natural Color 23!" mil 4-5B Passed 10 cycles #$ 10 % &' 3B 3 PSI 24 () No marks *+,- 600 cycles 1 rub film destroyed./ WB Glaze Color 89" mil 4-5B Passed 10 cycles #$ 10 % &' B-HB 3 PSI 24 () No marks *+, cycles 20 rubs no mark./ 2001,- NC Glaze Color 2389" mil 4-5B Passed 10 cycles #$ 10 % &' B-HB 3 PSI 24 () No marks *+,- 600 cycles 1 rub film destroyed./ Besides physical testing on coating, house chemical resistant testing were also conducted. Eighteen common type of household chemicals (cold water; hot water; 50% ethyl alcohol; 10% ammonia solution; 10% lemon acid; soap; detergent; naphtha; lemon juice; olive oil, yellow mustard; Ketchup; Coffee, Tea; Coca cola; Lubricating oil; Orange Juice) were tested on the coated panel. The waterborne coating showed similar performance compared to the NC based coating and passed these tests. VI. Conclusions After many years of development and trials, our experiences have shown that waterborne coatings have now reached the levels of maturity that could be considered as the products of choice for many furniture manufactures seeking to convert their entire existing solvent

9 coated systems or to expand their product portfolios to reach more customers. At Valspar, we have coating systems that can deliver the traditional high end furniture finish appearances and performances while at the same time achieve cost competitiveness of a typical solventborne system. In addition, waterborne coating helps to protect our environment by reducing the solvent emission and increase the reputation and social responsibilities of our industry. Service, formulation know-how and application experiences are critical in determining the success of converting from solventborne to waterborne coating; therefore it is important for furniture manufacture to select the right coating supplier for the transition. In addition to VOC and HAP reductions, the main advantages cited by our customers that have switched to waterborne coatings include: elimination of the odor associated with solvent-borne coatings (protecting the factory workers); reduction of fire risks and associated ease of storage (an explosion-proof storage room is not required); reasonable capital investment to convert from solventborne coatings; a more durable finish; and reductions in permit paperwork and/or fees. After achieving the identical appearances, the finishing cost between the solventborne coating and waterborne coating is very similar. Overall, there is never been a good time like today to consider switch to waterborne coating. Waterborne wood coating time is now. Author Biography Robert G. Duan is a Technical Director for Asia Wood Coating at Valspar. He received his Ph.D. in Polymer Chemistry from the University of Minnesota and MBA in Marketing Management from the Rutgers University, USA. Robert has won many awards and honors including the Gold Award for Outstanding Research by the United States Materials Research Society and Scholarship Award from The United States Federation Society of Coatings Technology. He has appeared as a guest speaker at many technical and R&D innovation management conferences. He is an author of 15 scientific publications and a holder of 3 patents.