Emulsions: The Do's, The Don'ts, and How To Use Them

Today we are going to take a look at emulsions and everything about them. From the different types, to applications, to picking out specific colors, you’ll get the whole shake down on an essential part of the screen printing process. What is an emulsion in screen printing? An emulsion is a light-sensitive coating that goes on the screen mesh, creating a stencil that allows ink to pass through in certain areas of the screen. The stencil acts as an ink barrier that allows ink to pass through only the desired areas.

I. Types of Emulsions

Explaining emulsions at a deeper level, it’s important to know the different types, their benefits and the most practical usage for each one. There are three main types of emulsions: Diazo, Dual-cure, and SBQ (Styryl Basolium Quaternary aka photopolymer).

Diazoemulsions are great for beginners and hobbyists. Diazo emulsions are typically inexpensive, forgiving on exposure time, and generally easier to work with. They need to be mixed with a diazo sensitizer (typically a powder) to be used. Once mixed, diazo emulsions are built to last one to two months on the shelf. As the least expensive kind of emulsion, diazo unfortunately does have a harder time with more intricate designs. Therefore, we recommend it for simpler jobs & smaller workloads.

Dual-Cureemulsions are the hybrid solution of SBQ and diazo emulsions. They require mixing like diazo emulsions, but the exposure time sits in between diazo and SBQ. Bringing quality in printing details such as halftones, compatibility with solvent inks, greater durability and an easier window to find your right exposure time, dual-cure emulsions have primarily been used in the graphic printing sector for decorating posters, labels, pens, glass, and other promotional printing.

Photopolymer (SBQ) based emulsions on the other hand, do not require any mixing. They cure much faster, with exposure time being only a few seconds with a high-powered exposure unit. Having a faster exposure time also runs the risk of overexposure, as they are much more sensitive to light; this makes handling coated screens in UV-filtered lighting essential. With a longer shelf life than diazo emulsions (more than one year), SBQ emulsions also tend to be the most expensive type of emulsion you can buy. It is worth noting that a majority of T-shirt printers today utilize SBQ emulsions.

Now that we have them explained, let's take a look at a chart that highlights their differences:

Now that we've covered the different types of emulsions, it is important to know there are multiple materials required for handling an emulsion at different stages of the process. Let's take a closer look:

II. How They Work

Now that we've gone over the materials needed at separate phases of the emulsion process, we can look further into the actual process. It can feel like quite a cumbersome or tedious process due to so many steps, but we can assure you they are all necessary. Without further ado, let's look into the emulsion workflow.

Preparation

Here is where all the setup happens for the rest of the process - you'll want to make sure clean and degrease your screens. you'll need to scrub with a brush to remove oils, fingerprints and dust, and rinse thoroughly. Afterwards, let the screen dry in a dust free environment before proceeding. Next you'll want to mix the emulsion powder (if you're using diazo or dual-cure) with luke-warm tap water (3/4 full), and shake! Once that mixture is combined, you can dump it into the emulsion and begin mixing. SPR Tip:We recommend writing the date mixed on the label, so you have an idea of where you stand on the 4-6 week pot life.

Coating

Now that we have our emulsion mixed and ready, we can coat our screen. Here is where you want a scoop coater to apply the emulsion to the screen. We recommend a dimly lit area, specifically a red/yellow safelight area. Murakami actually has a wonderfully written technical guide for achieving consistent screen coating results that would be a great tool for finding your perfect form.

Drying The Coat

Now, to dry the coat we applied, we want to place the screen in a dark and dust-free environment. During this process, you want ot print out or photocopy your design (printed in blacl) onto transparency. It's advised to place them on a drying rack or somewhere with clean supports, since these are sensitive to a lot of factors such as lighting and dirt/debris.

Exposure
Since the exposure component is a big part of the emulsion process, it's important to have a little prep here too. Whether you have an industrial exposure unit or a make-shift one, getting it right will without a doubt be a process. Due to varying conditions, we suggest that you work out a methodology to determine what is the correct exposure time for your screens (based on your emulsion, equipment, lighting, etc.). Use a piece of glass or acrylic to hold the transparency film tight against the screen.

Here is where you will use your light source and expose the screen for an appropriate time. What that time is, will have to be determined by trial and error based on guidelines from manufacturer recommendations. Ultimately, you will want to find your own sweet spot (it ranges from 1 to 15 minutes). Another great resource for you to utilize from an industry leader is this article onhow to calculate exposure from Dave Dennings at Kiwo.

Washout/Develop

Once finished with your design, it's time to wash out the screen. Find the nearest washout booth or sink, and rinse them out with water. You'll want to let it soak for a little bit before proceeding to rinse it completely. For this phase you'll want a pressurized water stream (you'll need gentle pressure and a lot of patience for this part) to fully flush out your design. Focus the water stream on the design and you will begin to see it wash out. Develop the image by doing most of the spraying onto the print side of the screen. It is important to note that you should not be using hot water, as it can ruin the emulsion.

Dry Screen

Now that all the leg work is done, we need to let the screen dry one more time. Here is where we want to make sure that there aren't any pinholes. Once the screen has been inspected, you are ready to print!

Post Printing - Quality Checks

After you've used your screen to achieve the print you're looking for, we move on to the final steps of clean up and quality control. Here is where we check for cracks, lifts, or peeling of the emulsion. If there are flakes or soft spots across your design, it is indicative of underexposure or incorrect drying. You can also verify this on your print - fuzziness in the design is a sign something went wrong along the way. It can stem from an emulsion breakdown, mesh that hasn't been cleaned & degreased properly, or incorrect exposure. As mentioned before, finding your ideal parameters will be unique to your equipment and situation, but a few test prints will help you reverse-engineer what you're looking for.

An important thing to note, removing the emulsion and resetting the screen is a process known as reclaiming, where you use specific removal agent to clean up the screen. It has its own process, and for the sake of length (we've gone through a lot) we feel it would be better with its own post.

III. Emulsion Colors: What Are They & Are They Different?

You'll see them around often, emulsions that come specifically labeled in unique colors. Whether they are purple, green, blue, pink, or clear, the function of the emulsion remains unchanged. Certain colors, however, help you see imperfections more easily ebcause of the contrast they ahve with your screen. Is it one of the most critical factors in your emulsion process? Most likely not, but it can be used advantageously if you need it.

The color variance in emulsion is mainly designed to create a strong visual contrast for:

Your emulsion
Film positive
Light used for exposure

As we've said throughout the article, it is all about finding what works well for your setup. There are a few popular emulsions that we see our clients pickup regularly: Ulano Orange & Chromaline Blue.

Ulano Orange

Ulano's orange emulsion is without a doubt one of our most popular emlsions. It is an SBQ emulsion that is known for consistently delivering high quality results. Its strength relies on its ability to capture fine detail, even on the high mesh counts (200+). One of the identifying chracteristics that cause screen printers to choose Ulano Orange is the higher concentration of solids within the emulsion. As with SBQ emulsions, the exposure time is very fast, and does not require any mixing.

Chromaline Blue (ChromaBlue)

Another great emulsion that is widely regarded by screen printers for being highly effective is the ChromaBlue emulsion. This is also an SBQ emulsion like Ulano Orange, and similarly it has a high solid count in the emulsion. Therefore, the quality of stencils using ChromaBlue are some of the best that the industry has to offer. Not only that, but this also brings down the cost per screen, as users of CHromaBlue only need to coat 1+1 to get an ideal stencil thickness. In addition, ChromaBlue is also extremely easy to remove from the screen. Competing emulsions tend to be difficult to strip off the mesh - they either need to use even more emulsion remover or rigorous pressure washing.

These are considered some of the best emulsions in the industry, perfect for professionals that are really looking for high end detail from their stencils. For small text, half tones, or really fine detail, both ChromaBlue and Ulano Orange are really great choices. If you're at more of a hobbyist level or just getting started and want a diazo recommendation, try the Ulano 925. The 925 has been quite a popular emulsion and a local favorite dating back to the 80s, simply for its effectiveness and reliability for the cost.

IV. Emulsions: The Don'ts

With such a thorough and detailed process, you can assume that there is a lot of tweaking and fine tuning that comes with getting your screen correct for print. Emulsions are no different, as there are plenty of habits you want to stay away from or be wary of. Simple things handled early prevent a lot of headaches down the line, so let's take a look at some of them:

Don't apply emulsion on a dirty screen -If there is any residue such as oils, dust, debris, or leftover ink, the adhesion of the emulsion will drop. It is imperative that the screen is degreased and thoroughly dried before using.
Don't store your emulsions improperly or use expired ones -It is very important to store your emulsions in a cool and dark place. Poor light exposure can keep the emulsion from hardening properly. Similarly, expired emulsions also have difficulties hardening.
Don't use white light - ever! -You want to handle your emulsion in a yellow safelight area. White light leads to premature curing in emulsions. Due to chemical interactions between emulsions and white light, the end result becomes a fuzzy or blurred outline.
Don't guess your exposure time -We hate sounding redundant, but you must figure out your own exposure process. Not having this mapped out will lead to a lot of bad stencils and wasted supplies. If there is overexposure, your image will have a hard time rinsing out. If there is underexposure, your stencil will delaminate during the washout process.
Don't try to rush the drying process of your emulsion -The stencil can break down if the emulsion is still damp. Don't try to cheat the process, either with warmer room temps or certain light exposure. Make sure that it is drying in a cool and dark place, and give it ample time.
Don't use the incorrect emulsion for your ink type -This goes without saying (or so we hope), but please make sure to match the correct type of emulsion for your ink. Particularly if you are using water based inks, you will want to make sure to use the appropriate emulsion. Water based inks will break down SBQ emulsions

We've finally made it to the end (hooray!), and we thank you for sticking with us through this onslaught of information. After this breakdown of emulsions and the emulsion process, we hope that you have a greater understanding of the inner workings and can apply them to your shop or projects. Now you are equipped to pick out what emulsion works best for what you are doing, and which product uniquely fits your situation. Understanding the differences in emulsion type, color, and composition is knowledge that will help you in deciding what prints are in the realm of possibility and which aren't.

Whether you are looking to scale your shop to the next level, or you're just getting started in this bottomless pit of information and knowledge, having experts around is always a big advantage. Not every screen printer has the capacity or resources to go out and learn all the nuances of their craft, as there can be just as many things learned through experience as there is from technical guides. Don't get us wrong, there is a process and documentation for almost everything, but as life often shows us, the recipe should be unique to you and your goals. With the amount of moving parts or small things that can go wrong, it is important to understand these concepts at their core or root functionality. At Screen Printer's Resource, we emphasize on using our experiences to help build a workflow and system every client knows and understands for the future of their business. Got more questions about product, process, or future? Reach out to our deeply knowledgeable sales team and get the answers you're looking for! We're only a call away.