Martin Medvetz, Domestic Sales Manager for Chromaline Screen Print Products, sat down with Cam Earven from The Print Life for a Master Class on Emulsion Screen Printing Tips and Tricks. They covered a wide range of topics including how emulsions work, what light source to use for exposing your screens, high density printing, storage conditions and much more.
Marty started his career utilizing his chemistry degree to create an emulsion line from scratch for a polymer manufacturing company. After coating thousands of screens and perfecting this product line, Marty then moved into technical support for his customers. In 2007, Chromaline purchased this line of emulsions and Marty became a Territory Sales Rep for Chromaline. Today, Marty pulls on his 20+ years of emulsion experience as the Domestic Sales Manager for Chromaline. Click below to watch the full video, or keep reading for a recap.
How Do Emulsions Work?
An emulsion is a suspension of particles within a solution. To make our emulsions we suspend polymers (the particles) in water (the solution). The polymers start out as water soluble. When UV light hits the emulsion, the diazo sensitizer causes cross-linking between the polymers. This reaction causes the polymers to become water insoluble. This means that any areas of your screen that were exposed to UV light will not wash out. The areas of your screen that were blocked from the UV light will remain water soluble and wash out.
The two base polymers in our simple Diazo emulsion are Polyvinyl Acetate (PVAc), which is water resistant, and Polyvinyl Alcohol (PVA), which is solvent resistant. The emulsion is mixed depending on how much water resistance vs. solvent resistance is needed. Because chemicals are limited, within a simple Diazo emulsion we are limited as to how much water resistance or solvent resistance we can have. Watch the YouTube video for an in-depth explanation on how these emulsions work.
The Four Types of Emulsions:
- Diazo: Made up of PVAc and PVA polymers. Need to add a diazo sensitizer to create the cross-links.
- Dual Cure Diazo Photopolymer: Made up of PVAc and PVA polymers with UV Photopolymer (UV curable, like a clear UV ink) added. The diazo sensitizer creates twice the number of cross-links, which makes Dual Cure emulsions more resistant to chemicals and more mechanically resistant to squeegee beatings.
- One-Part SBQ Pure Photopolymer: Made up of PVAc with a SBQ sensitizer added. These emulsions come ready-to-use and a diazo sensitizer does not need to be added. The SBQ sensitizer is stable and allows the emulsion to be premixed with a shelf life of two years. The chemical cross-linking structure is similar to the Diazo, and not as durable as the Dual Cure. The SBQ Photopolymer is fast to react, causing quicker exposure times.
- One-Part Hybrid Photopolymer: Made up of PVAc with SBQ sensitizer and UV Photopolymer added. The hybrid photopolymer emulsions are ready-to-use but have dual cure capabilities in it. This emulsion has better cross-linking, solvent resistance and water resistance. Once you add the optional diazo sensitizer, you are creating an extremely durable stencil.
Wave Lengths and Light Source for Emulsions
For screen printing, it is important to choose the correct light source and wavelength in order to trigger the cross-linking reactions within emulsions. We can hit an emulsion with as much light as we want, but if it's not the right light, we won't get the cure we are looking for.
Metal halide bulbs have traditionally worked the best for exposing emulsions. Today, LED lights with specific nanometer wavelengths are showing great results.
- SBQ: 310-380 nm, peak at 340
- Diazo: 340-420 nm, peak at 370
High Density Stencils for Screen Printing
When it comes to high density screen printing, you can either use a coated film like Super Phat, or you can build up an emulsion. When using an emulsion, always coat wet on wet. Don't let the layers of emulsion dry between coating. As you can see from the image below, the type of emulsion also makes a big difference. Our ChromaBlue or PC 701 emulsions are great options for building up high density stencils. Watch the video for additional tips on high density screen printing.
Stencil Profile vs. Print Quality
Click below to download a pdf of a detailed graph for Stencil Profile vs. Print Quality
The Print Life is a screen print channel on YouTube in which Cam Earven documents his life as a screen printing shop owner. Cam provides screen printing tutorials, screen print vlogs, and a live screen printing show every Wednesday at 6 pm MST. Follow along for the ride as Cam works through daily problems ranging from the mundane to the epic on his journey to grow from a small t-shirt screen printing business into a print shop regarded by the industry as one of the best.