screen emulsion

Screen-Printing Basics: Emulsion and Screen Coating

Mary Yaeger is a webmaster for Texsource Screen Printing Supply. Along with maintaining their website and social media pages, she writes for the Texsource blog. She can be reached at mary@texsourceonline.com

Texsource can be found on various social media platforms including Facebook, Twitter, Instagram, YouTube, and Pinterest.

Coating a screen is also referred to as making a stencil. The process is done with emulsion, which is a thick liquid that is sensitive to UV light. When you place artwork on the photo-sensitive emulsion and expose it, a negative stencil is created. This negative stencil is what allows the ink to be printed on a garment.

Before we get into coating a screen we need to discuss the different types of emulsions that are available. There are three types of emulsion and capillary film (used as an alternative to coating the screen). All emulsions work with plastisol inks. Water-based inks eat through most emulsions so an emulsion formulated for water-based printing is necessary.

Diazo Emulsion

Diazo emulsions have been used for many decades and are still preferred when low production cost is a major consideration. Diazo emulsions are either water resistant or resistant to UV and solvent-based inks. Plastisol inks may be used with either diazo emulsion type.

Dual-Cure Emulsion

Diazo-photopolymer emulsions, also known as dual-cure emulsions, offer the largest variety of features and applications. Dual-cure photo-stencil systems provide remarkable image quality and exceptionally durable stencils. These are premium emulsions for use with UV, plastisol, water-based, and solvent-based inks. Whether you need an emulsion with high chemical resistance or one specifically for ceramic inks, our selection provides the right emulsion for your requirements.

Pure Photopolymer Emulsion

Photopolymer emulsions are one-component emulsion systems that are pre-sensitized and ready for use. They offer very fast exposure speed and can be used universally, but often are developed for specific applications and exposure equipment such as direct projection, high emulsion over mesh ratio, or for coarse mesh counts. Photopolymer emulsions are typically resistant to UV, solvent-based and plastisol inks.

Capillary Film

Capillary film can replace liquid emulsion and has the technology necessary to meet a wide range of decorator demands, including textured garments, textured prints, and higher resolution images at a lower production cost. Capillary film is not messy like liquid emulsion, does not require mixing ingredients, does not require storage in the refrigerator, and has a longer shelf life. Because you only cut off the amount need, capillary film does not produce waste. 

Application

Emulsion scoop coaters are a must-have tool for coating screens with all direct liquid emulsions. Emulsion scoop coaters are the perfect way to get a smooth, even emulsion layer on your screen.  Simply pour an appropriate amount of emulsion into the coater reservoir then position the coater against the screen and move slowly and smoothly from the bottom to the top, adjusting the angle of the coater slightly as you go to ensure good coverage.  

It is usually best to get an emulsion scoop coater about 2" to 3" narrower than the inside screen frame width. You want the coater to be just wide enough to cover the entire emulsion width in one pass. For heavier ink deposits or to increase the durability of the screen for longer runs, additional coatings may be desired after the first application dries. This provides a thicker more durable stencil. 

Now, start with a degreased and dried screen (one that's not contaminated with dust, lint, or finger prints). Next, fill the scoop coater with emulsion. Place the screen frame in an upright position and secure it in place. Use two hands to hold the scoop coater.

When coating screens the emulsion needs to be even on the mesh. Thick and thin spots cause problems during drying and exposure. The thin spots expose faster and cause the image to not wash out due to over exposure. The thick spots expose slower and cause the image to break down and wash out.

Coating Methods

1-and-1 Coat: Apply one coat of emulsion on the print side, rotate the screen 180-degrees, and apply on the squeegee side. Dry in a horizontal position.

2-and-2 Coat: Coat twice on the print side, then twice on the squeegee side. After each coat, rotate the screen 180-degrees. Dry the screen print side down. This requires a longer dry time, longer exposure time, and yields a thicker stencil. This coating method works well with athletic printing.

3-and-3 Coat: Start by using the second method above. After complete drying of the emulsion, add an additional coat on the print side and dry again. This method produces the sharpest edges and thickest stencil and ink deposit.

After coating the screens, let them sit overnight to dry. Screens must be dry to the touch before exposing.