Kevin Kauth, Chromaline's Technical Sales Representative for the Midwest/Western states region, was recently a guest on the Squeegee & Ink Podcast. Squeegee & Ink is a screen printing studio based in the UK ran by Chassie and Emily that provides templates and learning resources for other screen printing studios and new screen printers. They also expose screens, print film positives and host workshops and consultations. They started the Squeegee & Ink Podcast in January of 2022.

In this episode of the Squeegee & Ink Podcast Chessie asks Kevin some of her top listener questions about making screens for screen printing. Below is just a small sampling of some of the questions Kevin discussed with Chessie. For even more screen making tips listen to and/or watch the entire podcast linked below.

LISTEN TO/WATCH FULL PODCAST: S02 E27 | Emulsion & Screen Exposure with The Emulsion Guru

KEVIN: Hello, I'm Kevin Kauth with Chromaline. I've been with Chromaline since 2010. Prior to my gig at Chromaline I worked for Sefar, the mesh manufacturer, as their application specialist. All of my background and everything that I've done from the professional side of this industry has all been from the manufacturer side of things so I have learned good habits. Part of my job is breaking the bad habits that have been passed down from person to person in the screen room.

The screen room people are the heartbeat of the entire screen printing business. The people that make the screens have the most important job in the entire facility. If you don't have a good screen you're never going to be able to get a good print. I like to give my background so you know what I bring to this conversation. The screen making side of screen printing is my main focus. I don't worry about the ink, I don't worry about the garments. As a shop owner you have to worry about all of that, but I don't. I only have to worry about emulsion and making screens, so I can focus my energy and my thought process on one specific part of this industry versus having to deal with far more things.

Follow Kevin on Instagram: @emulsionguru

CHESSIE: Let's go straight into the questions that our followers have loaded us up with. This question is from Josh. After washing an exposed screen should the emulsion still be runny on the squeegee side?

KEVIN: No. That is a telltale sign of under exposure. A screen is exposed linearly and the reason why you need a given amount of time for the correct exposure time is to give the light enough time to make it all the way through to the back side of the screen. If the emulsion is still slimy on the back side of the screen or colors are running off on your hand when you rub it, it's telling me that light hasn't gotten all the way through that stencil to expose thoroughly all the way through.

CHESSIE: I watched one of your YouTube videos in your series, Quick Tips From The Screen Room, about your step test exposure calculator. Tou said that where the color of the emulsion changes for the first time is an indication that it's hardened enough. Is that consistent with all emulsions? Is overexposing always a bad thing or should we shoot to overexpose rather than underexpose?

KEVIN: That color shift is predominant in dual cure emulsions because of the diazo that's in there. It's more of a tanning process of the diazo, so each one of those underexposed steps you'll see a color change, color change, color change. Then it stops and you'll see all the rest of the steps from that point look to be about the same color. That's telling me that's the hardening point of that emulsion. Each emulsion has an exposure window so the hardening point is the very bottom side of that exposure window. I recommend where that color shift stops, to add about 10 percent to that. That puts you right in the middle of that exposure window. With pure photopolymers they don't have the diazo in so that color shift is still there but it's not actually the the color of the emulsion it's more of a visual because the reason for that color shift is emulsion washing away from the back side. So it really isn't actually a change in color of the emulsion like it is with the diazo based and dual cure emulsions. With pure photopolymers it does still have a color shift but it's because of the thickness of that stencil. If you hold it up to the light it still is going to look like a different color. You can't see it as easy as you can with dual cures and diazo based emulsions, but you can still go off of that.

This helps to account for fluctuation in seasons, fluctuation in humidity in your screen room, and fluctuation of temperature in your screen room. All of those environmental factors make an emulsions exposure fluctuate as well. So if you put the exposure in the middle of that exposure window when it fluctuates up or down it's still within that exposure latitude window. Whereas, if you just put it right at the very bottom it might dip below the exposure window to the point where it's underexposed at times.

CHESSIE: Is there a way to coat screens without a dark room?

KEVIN: I wouldn't. Emulsion is light sensitive. I've heard people say it's not light sensitive until it's dried, well that's a myth. It's not true. Emulsion is affected by light even when you're coating screens and while it is still wet. Certain emulsions will be far more forgiving, so somebody that doesn't have a perfect dark room then I might lean towards something like a dual cure emulsion. A dual cure is slower exposing but far more forgiving, so it's not going to pre-expose as fast as a pure photopolymer emulsion. Pure photopolymer exposes so fast so you're going to have issues much faster. I always recommend working under UV blocking sleeves and the yellow amber colored sleeves, not the clear sleeves. The clear ones don't block the same UV to the same point. They're blocking it to a lower level so some light is still getting through and affecting those screens. You can get the sleeves that go over the fluorescent tubes or you can get rolls of the filter films that you can actually cut and lay into your light fixtures. It can take a little bit of time getting used to working in yellow lights but that's going to be your best case scenario and and you're going to have the best results.

CHESSIE: I notice that when you talk about exposure time you measure in units instead of minutes. Is that just mainly to do with metal halide bulbs diminishing over time and they're not putting out as much UV?

KEVIN: Correct. The UV light in metal halide and fluorescent tubes degrades over time, so with a brand new bulb one second might equal one light unit, but one year from now one light unit might actually equal three seconds. Most metal halides have a light integrator to help keep everything consistent. For example, if you find your exposure time is 50 light units, one year from now it will still be 50 light units but the time might actually be longer because it's compensating for that degradation. If you don't have a light integrator on your system I recommend doing an exposure test once a month to find out where you're at for exposure.

CHESSIE: Can you post-expose and do you believe that post-exposure is just compensating for poor exposure in the first place?

KEVIN: Great question. Post-exposure for pure photopolymers and hybrid photopolymers will continue to harden that stencil. Like you mentioned, it's more of a band-aid. It's not going to fix that initial exposure and the initial exposure is far more important than post-exposing. For people that are using pure photopolymers or hybrid photopolymers for water-based and discharge inks I do recommend doing post-exposure. If you're doing a long run with water-based inks or discharge inks or even solvent-based things post exposure will help. However, for dual cures and diazo based emulsions post-exposure isn't really doing anything for you because the diazo has been washed away during that developing process, so there isn't anything more for that diazo to keep cross-linking, so post-exposure is not necessary for those types of emulsions.

CHESSIE: I love that you said that. I'm just going to clip this little bit and I'll use that when people say, "You're a bad screen printer if you don't post expose." Here is another common question we get asked. What are the optimum coats per side for good opaque white on black garments for textile printing?

KEVIN: Everybody is after that one hit white, that one hit white that does everything right out of the gate. Well most of the time it's not so much about the ink but about the stencil. If you don't have the proper EOM you're never gonna get that one hit white. Both things work hand-in-hand with each other, obviously the ink plays a role, but before you get to that point the stencil does too. You can't really say one-over-one or two-over-two or three-over-one is the perfect coating for every single emulsion. There's a lot of variables involved like the viscosity of the emulsion and the solid content of that emulsion that really plays into how thick your screen is going to coat. For example, ChromaBlue is high in solids so just one coat on one side and one coat on the other side is perfect. That puts you right in that 10 to 20 percent EOM range. However, mesh tension, humidity, temperature, and everything else in the screen room plays into that so this is a generalized answer but again it's not going to be the same for absolutely everybody.

CHESSIE: Can you explain what EOM is?

KEVIN: EOM stands for Emulsion Over Mesh, which is the thickness of your stencil. You determine that by measuring the thickness of the mesh by itself and then measuring the thickness of the mesh plus the emulsion that's coated on that screen, then you subtract the two. That is where I shoot for that target of that that 10 to 20 percent which is an industry standard.

CHESSIE: And say we don't have an EOM measuring devices. Is there a cheapy version that anyone can get or should we rely on putting our fingers over the emulsion and being able to feel the details? Is that sufficient?

KEVIN: If you don't have the tool to measure EOM you can touch the screen and if you can feel the artwork edge it's telling me that there's emulsion over mesh. There's so many times that I'll walk into a shop and I'll feel a screen and it doesn't feel like there's anything coated on there because you can't feel the edge where the emulsion is, where the artwork is. If you can't feel that it's not giving you a good gasket. When the screen comes down, the stencil wall of that artwork is preventing the ink from seeping out, which is what gives you nice sharp clean images. If you can't feel it chances are the ink is going to seep out the edges of that stencil and it's not going to create a good gasket on the shirt, or or whatever you're printing on.

CHESSIE: Something I've been thinking about recently is humidity. What humidity percentages should we be trying to hit before we expose the screens and how long does it have to be at that percentage?

KEVIN: Humidity is one of the biggest killers of stencil making. Emulsion is hydroscopic, which means it will suck up moisture. You can have a screen that's 100% dry in one area are your screen room and then bring it into a humid area and it's going to suck up moisture and re-wet. When there's moisture present the screen is going to act underexposed and break down on press. I typically look for above 30 to 40 percent relative humidity, targeting 30 percent. If you can be at 30% all day long every day great, but so many people are washing out screens right next to where they're drying screens, so 30% isn't always possible. Best practice is to coat the screen today and use the screen tomorrow.

Dehumidifiers are an excellent tool to have in a screen room but many of them have a waste water basket that collects the water and so many people forget to to dump that out. All the water that's sitting in there is just going to evaporate back into the screen room. If you have the ability to hook a hose up to that and run that line outside of that screen room you'll have a better chance of fighting that humidity.

CHESSIE: Brilliant. I know you supply complementary chemicals for the screen room. I have a product that says it strips the emulsion and degreases at the same time, but I don't trust it. Is using a separate degreaser overkill?

KEVIN: I like to use one product per process. I feel that when you're using one product that does multiple processes you're giving up something. Keep in mind a screen can't be too clean. okay can't be too clean. Many products in the screen printing process are oil based and emulsion is water-based. Oil and water don't mix so if there's anything left on that mesh then that's going to repel the emulsion when you go to coat your screen, leaving you with pinholes and thin spots. So using a separate degreaser is not overkill because a screen can't be too clean.

CHESSIE: This is jumping into a different topic again. How does capillary film encapsulate the mesh and can it do it as well as manually applied emulsion? Why doesn't it peel off?

KEVIN: It doesn't. It takes the capillary action and sucks into the mesh. For example, if you have a 30 micron cap film you're going to lose about 60% of that when the film sucks into the mesh, which will end up being maybe an EOM of 10 to 15 microns on that 30 micron film. It doesn't completely encapsulate the mesh. It's only applied to one side. Capillary film is really good at holding really high resolution, but it's not going to be as durable as direct emulsion because it's only applied to the one side of the screen. The coating is extremely consistent and flat like glass without any pinholes or imperfections, which is why it is perfect for high resolution. The electronics industry uses a lot of cap film but what they use the direct/indirect method, which is when you put cap film on the bottom side to get the consistency and sharp clean edges, then they back coat with direct emulsion to marry the two products together. The best of both worlds.

Something worth noting as well is you can't put cap film on on both sides of the mesh. The first piece of cap film absorbs so far into the mesh that the backside wouldn't be able to absorb down. You wouldn't get as good of a bite. You can't laminate a piece of cap film on on each side and expect good results.

CHESSIE: One more question. I know you probably have lots of unpopular opinions, but have you got one standout one that you want to get off your chest above all others?

KEVIN: I've got lots of unpopular opinions. I'm a very opinionated person. I think one of the things that's kind of an unpopular thing coming from a salesperson is what I tell printers and shop owners - trust those sales people! There's so many people who think they're getting duped into buying the next thing and that we're only out here trying to sell our products and then move on to the next thing. But that is not the case for all of us. We have a lot of knowledge that we can support you with and help with questions. I truly want all of my customers to be successful and the only way you can be successful is if you do things the proper way. There's a reason why we're in the screen printing business. If all of our products were junk we'd be out of business. I can tell you this, work with the people that support you and work with you and will give you the information you need. When our customers are successful, we are successful. Trust us. We're not all shady people, I'll tell you that.

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That was just the tip of the iceberg. Kevin and Chessie also delved into topics like if the Laser-To-Screen auto coater is worth it, printing quality positives, screen printing high builds, and if adding diazo to an emulsion that doesn't call for it is a thing. You can watch and listen to the full podcast episode on the Squeegee & Ink Podcast channel. If you have any further questions about any of our Chromaline screen printing products, please contact us today.