![]() ![]() Of course, no manufacturer is going to tout “low solids,” which I would consider to be less than 30%.Marty Medvetz However, with current photoemulsion technology, it would be acceptable to label a photoemulsion with 35% solids as “high solids ” however, this could better be described as “average.” A few manufacturers raise the bar by providing emulsions with 45% solids or more. Medium solids content to one manufacturer may be considered high for another manufacturer. Keep in mind that these terms do not reflect any industry standard–they are subjective descriptions given by the manufacturers. Some manufacturers use general references to solids content, such as “medium” and “high,” in describing the emulsions. If a photoemulsion contains 40% solids, the remaining 60% is composed of water, and possibly a small amount of volatile solvents. We refer to these residual chemicals as “solids,” and these are what remain on the screen after drying. Given that photoemulsions are water-based, a coating will eventually dry, leaving behind any non-volatile (non-evaporative) compounds. To understand why this is, we must first understand basic photoemulsion chemistry. While it is possible for a high-viscosity photoemulsion to also have high solids, the viscosity level is not necessarily a result of solids content. The truth is, there is no direct correlation between viscosity and solids content. The negative-forming emulsions used in screen printing contain light-sensitive molecules that are suspended in a carrier medium, hence the name photoemulsion.Įver hear the following statement on your production floor? “This emulsion is thick, so it must have high solids.” As a photoemulsion chemist, I cringe when I hear customers and salespeople equate high viscosity with high solids. In the screen-printing industry, we often say “emulsion” when referring to photoemulsions. Some common household examples of emulsions include mayonnaise, skin moisturizer, sun lotion, school glue, and paint. The scientific term “emulsion” refers to a suspension of particles in a liquid. We’ll review what they are, where they come from, and how they influence the buildup of the stencil during the coating process.įirst, let’s review what a photoemulsion is. In this discussion, we’ll focus on the last category–photoemulsion variables–and look closely at solids content, viscosity, and rheology. mesh variables, such as thread count, thread diameter, size of mesh openings, screen tension, etc. coating variables, including type of coating trough, coating speed, pressure, etc.Ģ. ![]() Creating a stencil to achieve specific printing characteristics requires the correct combination of many factors, which can be divided into three broad categories:ġ. Of course, stencil thickness isn’t just a result of emulsion properties. ![]() Solids, viscosity, and rheology are the three physical properties of a photoemulsion that affect the final stencil thickness we can achieve. But ask even an experienced printer to define another key emulsion variable– rheology–and their facial expression quickly turns to one of confusion. Most printers seem to have a grasp on the terms solids and viscosity, or at least they understand that these are important characteristics of liquid photoemulsions. But do you know the chemistry and physics behind the resulting stencil thickness? Did you know that some emulsions are more readily adaptable to different mesh counts? And, did you know that solids content and viscosity aren’t the only factors that influence the stencil thickness you can achieve? Sure, you know how to coat mesh with a liquid photoemulsion. Join the Screen Printing Brain Squad - and Make Your Voice Heard!.Get Your Free Subscription to Screen Printing magazine. ![]()
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