Waterborne lacquer and polyurethane

      What is the difference? March 23, 2002

Question
What is the difference between a waterborne lacquer and a waterborne polyurethane? I now spray Kem Aqua waterborne lacquer.

Forum Responses
From contributor P:
I have been hard pressed to ascertain if there is any difference. Waterbornes don't fit into any of the traditional finish categories, ie varnish, poly or lacquer, so to say that a waterbased lacquer is different than a waterbased poly is misleading. The folks in marketing are once again trying to pull a fast one on us.



From contributor D:
Basically, whether you're talking waterborne or solvent borne, it all comes down to the resin system. With solvent, you start with nitrocellulose, one step up is acrylic, two steps up is acrylic urethane and next is single component urethane, followed by 2 component urethane (isocyanate hardener + urethane resin). Waterborne or solvent borne, this hierarchy stays the same except that with waterborne there is no nitrocellulose equivalent. The price goes up as the resins get more expensive. Just that simple.


The above is correct. The terms used on some products can be very misleading. Also, many of these waterbornes have more co-solvents in them than water. I think somebody needs to draw the line and limit the amount of co-solvents to 10% of formula to be a true waterborne product.

Bob Niemeyer, forum technical advisor



From contributor P:
Contributor D, when you say a "step up", are you referring to the complexity of the formulation, or its characteristics as a finish (ie hardness)?


From contributor D:
Characteristics as a finish - primarily hardness, toughness and chemical resistance.


Where do the "alkyd" resins come in?


Alkyds are neither lacquer nor straight polyurethane, though you can buy oil modified polyurethane, which is a one-component poly that is easily purchased at a box store. It is a DIY poly. Alkyds are the standard workhorse for enamels used in the DIY market and many industrial uses. They are cooked and are a blend of phthalic anhydride (usually) and an oil, like soya or linseed. Sometimes other materials are used for increased hardness or flexibility. Alkyds will usually yellow on exposure, so do not use them over a white. They are not as durable as a two-component product, but have better exterior durability than a lacquer.

Waterbased technology has taken a quantum leap within the last few years. Some latexes that are called waterbased lacquers are being replaced with polyurethane dispersions that self cross link chemically on drying and give an almost solvent based quality finish.

The world of coatings is complex and there are exceptions to every rule. You have to talk to an expert if you have specific needs or requirements.



The difference between a waterborne lacquer and a waterborne polyurethane is based on the resin structure used to create the film forming agent, the final physical performance characteristics and the intended use of said film. When properly formulated, each WB system should emulate their solvent-based counterpart as closely as technology will allow.

A qualifying waterborne lacquer will exhibit good to excellent clarity, good to excellent chemical resistance and a high degree of burn-in, or remulsifying capabilities when layered upon itself, or upon a coating that will allow the solvent structure of this film to chemically attach itself to the wb lacquer, much like a solvent-based lacquer. Generally, an acrylic system is used to create this film-forming agent due to their ability to remulsify into themselves when the appropriate co-solvents are used to promote platicization and coalescing.

A waterborne polyurethane is either a composition of acrylic and urethane resins blended together to create a specific film-forming agent that is designed to meet a wide range of physical specifications, or depending on the overall requirements of the film properties and the intended use, can be a pure wb urethane based on polyester or polycarbonate resins. These systems are often used for wood floor applications or other architectural applications that demand extreme hardness. WB polyurethanes qualify in the marketing arena as "polyurethanes" due to their progressive film-forming nature and overall toughness. Due to the high costs of pure polyester/carbonate WB resins, acrylics are added to lower the cost so as to meet certain marketing requirements. First and second generation "polycylics" required an external cross-linker to toughen up the final film formation. Now, self cross-linking resins are being used that allow for the carboxyl ring to close on its own without the use of external agents.

I would like to ask each of you to set up a 1.5 million dollar manufacturing facility and begin to produce and market a complete line of coatings that are properly labeled as: Self Cross-Linking Copolymer Acrylic Remulsifying Hybrid Emulsion Film Forming Agents. See if any of your potential customers ask you "So what the hell is this stuff?" Your response will be "It's a waterborne lacquer, and it will blow the doors off of any nitrocellulose system that you have ever caught a buzz off of."

Pundits openly carp that "If it's not cellulose based, it's not a lacquer". From an extremely conservative point of view they might be right. But if you take into consideration the generational development and engineering aspects of any technology, the sophistication of a system will grow and develop, whereas the terminology will often lag behind.



The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor A:
Generally in the world of coatings, a polyurethane is specific to the type of resin. A lacquer is a marketing term for a clear varnish, coating, etc.



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