April 27, 2016
In our second installment of “Ask the Expert”, Sean McDonald, our M.L. Campbell Product Manager, sheds some light on one of the questions he gets most often. Sean has been managing M.L. Campbell products since 1989 and has been with Atlantic for almost 11 years – 5 of those as our MLC manager.
What is the difference between nitrocellulose lacquer and catalyzed coatings ?
Basic Nitrocellulose Lacquer was developed in the 1920’s after World War I. There were large stockpiles of cotton used in the manufacturing of smokeless gun powder left over from the war. Chemists found that they could turn this cotton into a fast drying finish. By treating the cellulose fibers of cotton with nitric and sulfuric acid, they were able to develop Nitrocellulose. This helped to give lacquer its fast drying qualities. Resins were added to give the coating better building qualities, plasticizers were added to improve the flexibility of the coating, and finally, solvents were added so the coating could be atomized into small particles when sprayed through a spray gun. The drying process of Nitrocellulose Lacquer occurs through the evaporation of the solvents in the coating. This fast evaporation of solvents results in fast curing of the coating but makes it difficult to brush. The continued popularity of the basic nitrocellulose lacquer is mainly due to the ease of application, fast dry time, the variety of solvents that can be used allowing you to apply in all weather conditions, and the ease to repairing. Some of the cons to using a nitrocellulose lacquer are the lower durability characteristics of the coating including scratch resistance and water resistance, and the possibility of softening with heat as it is a thermoplastic coating. ML Campbell’s Design-R-Classic Lacquer was recently to their line to fill the increased need of a nitrocellulose lacquer due to furniture manufacturing returning to the United States from China.
Catalyzed coatings, also known as conversion finishes, were developed in the 1930’s. They were developed for the furniture industry where consumers often demanded a higher durability finish. There are many types of catalyzed coatings in the industry but the main types we use in the cabinet and furniture industry are pre-catalyzed and post-catalyzed coatings. Catalyzed coatings do not cure by solvent evaporation, but rather by the addition of a catalyst. The addition of the catalyst starts a reaction between the amino and alkyd resins and causes them to crosslink and form a very durable finish. Pre-catalyzed coating have the catalyst already added to the finish with enough solvent to keep the reaction from starting before the coating is applied. As the pre-catalyzed coating is applied, the solvents will start to evaporate and the curing process will begin. Pre-catalyzed lacquers have a limited shelf life, (120 days for ML Campbell’s MagnaMax, 1 year for ML Campbell’s Magnalac) that is catalyzed at the factory. Shelf lives should be indicated on the can or you can contact your ML Campbell Lacquer Specialist. Post catalyzed lacquers like ML Campbell’s Krystal or KlearVar use a stronger catalyst that must be added to the product by the end user just prior to spraying the product. The pot life of post catalyzed coatings can range from 12 hours to 24 hours, depending on the product. Refer to the product information sheet or contact your ML Campbell Lacquer Specialist for proper pot life. A catalyzed coating past it’s pot life will normally cure, but the durability will be greatly diminished. It is highly recommended to stay within the specs of the product. A catalyzed lacquer like ML Campbell DuraVar is basically the same as a conversion varnish with the exception of nitrocellulose being added to a catalyzed lacquer to speed up the curing process. The addition of the nitrocelluse will slightly lower the durability of the product and will cause the coating to amber over time. While all catalyzed coatings have excellent scratch, mar, and water durability, you will find a post-catalyzed coating to be more durable and typically out-perform a pre-catalyzed coating. I would recommend a post-catalyzed coating on tables and areas with high water contact such as bath vanities. Some of the disadvantages of using a catalyzed coating would be the shorter pot life of the coatings, and the difficulty to repair or strip the coating once cured.
In summary:
For additional technical assistance with M.L. Campbell products, contact Sean or your local Lacquer Specialist.
Sean can be reached at 781-424-4413 and smcdonald@atlanticplywood.com
