PAINTING: Latex Spraying Revisited

Q. I read the letter from G.S. in the August issue concerning the spraying of a latex. f II remember correctly, a latex is an emulsion and retains its characteristics in another liquid. They are difficult to spray since they do not break down in the other liquid. It is not like a solution where one disperses into the other liquid to form a homogeneous liquid.

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I wonder what product he is spraying and why he is using a latex. He can get a reasonably fast air-dry material or use a two-part system to cure quickly, or he can probably get a water-borne material that will dry reasonably fast. If he were willing to use a solvent-reduced material, he would have even more options. I get the feeling that his volume is very small, and he is using an off-the-shelf material. S.B.

A. For the most part, your comments are true. According to the Coatings Encyclopedic Dictionary (CED), an emulsion is a “two-phase liquid system in which small droplets of one liquid (the internal phase) are immiscible in, and are dispersed uniformly throughout, a second continuous liquid phase (the external phase).” The CED also defines a latex as a “stable dispersion of a polymeric substance in an essentially aqueous medium.” The CED goes on to say, “Strictly speaking, after polymerization, a latex is a solid dispersed in water and, therefore is not an emulsion.” Latex and emulsions are often used synonymously in the paint industry.

Furthermore, G.S. is not developing a coating but a new type of high-volume, low-pressure (HVLP) spray gun. His problem is atomizing a typical latex paint using his experimental HVLP spray gun.
 

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