How to expose a screen for screen printing.

1. Introduction: Hey, it's Chessie from Squeegee & Ink. And in this course I'm going to demonstrate how to expose screens with photosensitive emulsion and film positives. I'm also going to help you determine your own personal exposure times and walk you through any troubleshooting you might have when it comes to exposing screens. In this course, we'll cover preparing your artwork for exposure, coating and drying your screens. The method of exposing the screens with photosensitive emulsion, exposure unit types. How to find your exposure time, washing out your design, how to know if your exposure is perfect. And lastly, troubleshooting poorly exposed screens when taking this course, you have full access to our exposure calculator, which you can print at home and helps you determine your exposure times. By the end of this course, you'll have all the knowledge you need to get screen printing and have perfectly exposed screens. 2. Preparing your artwork for exposure: A good quality exposure starts with quality films. And they need to be a 100% black. And not only black, but they need to be opaque. They need to stop the light from reaching the photosensitive emulsion. So even though these two are black, there's only one of these that's actually going to work as a good exposure for screen printing. The first positive I have here is printed with black ink, but there's not enough deposit of the black ink to be able to block the light. And easy way for you to see whether your positives are strong enough is if you were to hold your hand behind them, you can see the profile of your hand and moving, buying them. So the light is still getting through and your hand is casting a shadow through that. So that's just an easy indication to see her. That's not very good. Whereas this one, I can move my hand behind it and I can't see it at all. This one is very likely to be strong enough to block the light from reaching the screen during the exposure. In order to obtain this nice rich film positive, I'm using an inkjet, Epson printer. I'm also using an old black ink system. So by that I mean, technically this has five different ink cartridges, and normally that would be used for CMYK, lots of different colors. However, I filled all my ink cartridges up with black ink that I'm just laying black over black. And it's really dense. I'm also using something called a RIP software. This is in-between the computer and the printer, and it just tells the printer how much ink to deposit onto the film. So there's very dense and I can manipulate half tones and how black and how much ink is being deposited on my film. So I can get the richest, most dense positive possible. Let's jump onto the computer to show you what I mean by that. Using Adobe Illustrator to output my films. On this, I have my blind market logo. The first thing I need to check for, I output my films is that the color mode of the document is CMYK. I can check that by pressing file, going down to Document Color Mode and making sure it's CMYK color is checked. That just means that it's going to output as CMYK printing and it's gonna be ideal for optimum posted. The next thing I need to check is that this is actually pure black and not just a very dark gray. I can do that by selecting a part of the image, going up and pressing select same fill, color and stroke. Hopefully it selects all of your image with the same black. Then I can double-check in the little swatch here, this little fellow swatch. Now I'll bring up my color picker. Now identify the color that's in the image at the moment, is all the zeros at the moment in this little hex box, which is perfect. Often you'll get it where it looks very dark and it looks it looks very black, but is in fact touchy, just a dark gray. And that would be a combination of letters and numbers in the hex box. We just want to drag that all the way down on the color picker, brought the way to all the zeros and press Okay, to make sure that it's gonna be a very opaque Blackburn printed. We can also check the size of the positive at this point, but it will look very good. I'm ready to output. I'm actually going to be using a RIP software in between the computer and the printer. That just makes just gives me the options to deposit more ink. It also allows me to apply halftones if needed. But in this occasion I just wanted to print a solid black color, like a press Command pay or print. You can just see here that the printer is running through the accurate. And then onto my EPS and inkjet, I'm ready to press, Print and output my film. 3. Coating and drying your screens: In order to get good exposure on your screens, it's important to decrease and have your screens a 100% drug for coating way using a jewel your emotion. And it happens to be the Asacol set one. This has a di acid mixture which we mix up with distilled water and we add to the emulsion to make it sensitized. We'd like to use this one because it's resistant against lots of different inks that you could choose some emotion that's right for your setup when asking your supplier which emotion to get for you. It's important for everyone to have a good scoop coater. And this is the best one we've tried is called the prior angle. The reason that's good is because it's got these extended lips here which pick up any of the extra beading along the edge of your codes. That just means your screens dry quicker. That the application of the motion on the mesh is very nice and smooth. We like to call it our screens once on each side and to drive them nice and flat. That just means that the emotion encapsulates the mesh. And it always gives us a really good clean level exposure if we can trust. Another important thing when it comes to drawing new screens off to them being connected is that the screen lies flat. And by that I mean with the print side down in Iraq and try and let it dry as long as possible when you're enjoying your screen off to his being coated with emotion, It's important to leave it in a dark room. 4. The method of exposing with photosensitive emulsion: When the emotion is dry, and by dry, I just mean touch dry. But typically you could leave it overnight just to make sure now it's ready to expose. What happens to photosensitive emulsion is when it comes into contact with UV light, it undergoes a chemical reaction. It creates more bonds and it becomes hardened. Any of the photosensitive emulsion that doesn't come into contact with UV light is still water-soluble and you'd be able to rinse it away. The objective, exposing a screen with a film positive is to block light from reaching certain parts of the coated screen and then leave some areas so that light can reach them and they can pardon? So in this case, we want the light to be blocked away from the black of the image in this film positive so that we can rinse out that unsanitized motion. Then once it's all dry again, we'll be able to pass ink through the open mesh. The Inquiry be able to get through the blocks mesh where the motion has hardened. In our setup, we have a metal halide bulb and our exposure unit is very large fc you don't need one just like this. But the fundamentals of all exposure units are very similar. You're going to find is you've got a light source. Then you've got maybe a piece of gauze just to hold the film. And the screen on. The film is going to be blocking out the light. It goes light source glass. Though. Then you can do the flat side of your screen. In lots of cases, you're going to find some kind of exposure blanket or piece of foam holding all those things in close contact with each other. The reason for having something waited on top is to keep it nice and close so that the light doesn't get around and bend the round your lines and make your line work appear kind of like shady, old ghosted. We want a nice close contact. We're gonna put our exposure blanket down. We're actually going to go back home, which again helps the emulsion and really come close towards the film and the goals. 5. Exposure unit types: In this course we're using our exposure unit, which has a metal halide bulb. However, there's lots of different types of methods and exposure units that you can use to express your screens. Here with five of the top most frequently used methods of expression. The top one and the most effective in our opinion is the metal high bulk exposure unit. That's because the bulb moments and very rich source of UV. However, these units are often very large and not accessible to many people. The second method is LED bulbs in an expression unit. That's a great method because it's very easy to run, very energy-efficient. However, the light is coming from lots of different angles. You might experience some undercutting. But in most studios, That's not something that you're really going to notice on the screens. So you find any day exposure units and lots of professional studios. A cheaper, more accessible version of the LED experiencing it is number three, and that's the fluorescent tubes exposure unit. The good thing about these is they often come in quite a compact size to expose screens for T-Shirt Printing, especially. They often have in vacuum Blackett to hold your screen in place. There are issues with them because the light is being emitted from lots of different tubes and the tubes can degrade and you can have dark practicing your screens. However, it's still an effective way to expose your screens. In fourth place, we've got the overhanging lamp. So lots of people getting into screen printing. We use a lamp which are suspended over the screen. The problems meant that might be that you actually can't expose huge screens because the light can only go so far and actually make the chemical reaction on the screen. The benefits, those types of overhung lamps are very cheap and they do technically output some UV light, but it's not very rich. So you're gonna have to die it in your exposure times. Very, very fine amount of time. Lastly, we've got the sun, so we don't recommend using the sun as an explosion method. And that's just because it's so variable as to how much, how much time you're going to have to leave your screen out in the sun. So we probably don't advise that for professional setups or even really having any consistency in your exposure times. 6. How to find your exposure time: You're going to find that your exposure time is properly different to somebody else's. This because everyone's got different variables in there setup. These variables might be the strength of their job, the mesh on the screen, the emotion they using, and lots of other different things. So we will have to find out or an exposure times independently of each other. There's two main methods to funny out your exposure time. The first being trying to narrow, which might take quite a long time and lots of screens. And I'm going to show you the results of trial and error, the exposing later in the video. And the second one is more efficient and that's by using an exposure calculator. You can print your own file of this at home. And as long as you're using a 100% dense inkjet ink onto acetate film, you'll be able to produce your own exposure calculator. I'm going to run through how to use the exposure calculator. Now, when we're using the exposure calculator, we're basically doing, is doing ten mini exposures and then working back to see which one works the best. So the way we can use it as we can follow some of the maths at the bottom and it's explained on how to do that. Then we can attach the exposure calculator from the flat side of our screen with the ink facing down. I'm just going to tape it to the emulsion. This is because I don't want them to shift as I'm blocking the light from reaching that part of the emulsion. Now the exposure calculator is securely in place. I can flip it around. Then what I'm trying to do is block the light from reaching certain parts of the calculator in steps. So I have this handy bit of black teflon. But you could use some black card or something that's very opaque and it's going to block the light from reaching certain parts of the screen. We're gonna do is we're gonna hold the screen and block the light from reaching most of the screen apart from the first section, that's labeled number one and it says homeroom, we're going to expose that to light according to what you worked out in a little bit of mass at the bottom of the expression calculator. Then when that exposure is done, we're gonna move the black a longer channel to reveal the second column. We're going to expose that to light and just keep doing that process all the way. Then we're going to expose it to number three, all the way down to number ten. Where the last you've got the whole screen exposed to light for a short period of time, then we're ready to wash it out and determine what is the best and most ideal amount of time to expose our screens for. When you're looking at the results, when your exposure calculator, when you're trying to look out for is the zone on the calculator that is the clearest and has the finest detail exposed onto the screen. In our case, we're actually looking at number eight in this channel typically lies around five or six. We now know that with this particular message type being a yellow 7070 mesh, that if we did it for a minute and a half, then we'd get a good clean exposure on this particular combination. So again, it's very important to do your own tests. And there are gonna be variations between lower meshes and high meshes and even between yellow and white meshes. Another thing to note is that we've got a metal halide bulb, and that is actually something that takes a little while to heat up and get going. So they will also change our results. Again, you can't take our results at face value. I'm just trying to illustrate the kind of results and techniques you can use to hone in your own exposure times. Now I have determined what my exposure time is. Ready to go ahead and expose my real screen. 7. Washing out your design: For best results when you're washing out your screen, It's good to use a PowerShell. What we do is we lightly missed this inside of the screen first, and then we do the same on the other side, just to wet them and let the loosened unexposed emulsion start falling away from the mesh. And then once it's had about 30 seconds to loosen up, then we go and spray it with the PowerShell to fully clear out all the unexposed motion. Another method of letting the screen SOC, which can be quite handy when you've got lots of screens to wash out, is to leave the screen in a dip tank but full of just water. That way the emotion can soak off and then you can very, very quickly spray or any excess that's still in the mesh. It's also important to wash your screen out properly from the flat side because this is the side where the emotion is mainly set once you've dried, it says Actually President on this side of the screen. So it's stronger and can take some of that pressure. I'm really happy with the results and it will stop really nicely. So I'm going to drive this screen off and get it into production. 8. How to know if your exposure is perfect: I have gone ahead and exposed to more screens. And that is to show you the difference between an underexposed screen and an overexposed screen. The first screen hit is an underexposed screen. So I'm going to wash it out and talk you through how you can determine if your screen is underexposed too. There are two quite subtle things about this screen that showed to me that this screen is underexposed. The first thing that I can see really quite plainly is the fact that I could see all the film outline around the image in like a rectangle where the film was printed. I can see that impression on the screen. That circuit really quick indicator that the screen is underexposed. And the second thing is if I turn the school ground, this a sliminess to it. If I touch this bit, it can almost see there's under cured motion. It kind of like a film and you can feel it on your hands as well. It's not just wet like certain areas. There's like a a film of underexposed motion which is going to leak into the open mesh areas when I'm drawing it. That will give partial blockages and we'll probably break down and press as well. So even though in first impressions it doesn't look too bad, and I got the whole outline of the image. Those two things are going to affect us when we're in production. This second screen is overexposed, so we cranked up the exposure time and it's also got a weak positive so that all the light is getting through prematurely. So at the moment I can see a faint impression, but I'll wash it out and show you what to look out for with an overexposed scrape. This is a really good example of an overexposed screen. As you can see, the emotion didn't just fall out like with a well exposed screen. And that means that the UV light has got through the film positives where we're trying to block the image out. It's got through that and then started exposing and hardening the emotional entity. Even though I can see the faintest impression, I actually have to use the force of the power for really quite close for awhile. Shade this and that open mesh there is the result of me putting a lot of force on that motion. You can see that the line edge has all from board off because I was putting so much pressure on the emotion as well. That would take me probably about three or four minutes, full pressure to get it out and the lines and never, never, never gonna be nice and slick how they are intended. So that's really good at example of an overexposed screen where the film positive especially wasn't strong enough to block the light from reaching their designs. 9. Troubleshooting | Weak Transparencies: There are lots of reasons why your screen may not be exposing very well. We see lots of common issues happen in the industry. So I'm just going to run through a couple of the most common problems and issues. The most common problem with exposures is weak transparencies. So the effects on the screen can look like even sliminess at the emotion. It can look like you've got an impression of the image. But then when you go to wash it out, it's very difficult to wash out. It doesn't just fall off after 30 seconds. You might find that the line edge is Jacket. There's lots and lots of different horrible effects that, that can have on your screen. That the only way around that is to maintain a nice thick deposit of ink on your film positives. And it might even be the case that in the initial stages of getting up and running that you get your film posteriors printed by a professional. 10. Troubleshooting | Image ghosting: The next most common problem is imaged ghosting. That might mean that your image looks like it's all there, but actually there's a faint haziness around it or a doubling up of your image. This can happen because some people put two of the week transparencies stuck together to try and make the effect of a very strong transparency. And it might be the case that the light isn't quite like, they're not lined up perfectly, so then it causes the impression of ghosting. There's other reasons as well. So even if you have a nice dense film positive, you don't have really close contact between the glass, the film and the screen, then the light can actually undercut the film positive and kind of like make a blurry edge to design. The way to fix that particular issue is to have dense film positives and have very close contact between the film screen and the glass. Some people wait it down. And in my case, I use a vacuum blanket to keep the contact nice and close. 11. Troubleshooting | Un even exposure: You might also have a problem where you're fine details like half-tones, very fine lines aren't coming out. This may just be that your mesh count isn't high enough to achieve that type of detail. You just need to up your mesh count. Because the find that the mesh, the more detail that screen can hold. 12. Troubleshooting | Fine lines not coming out: Another common problem is uneven exposures. So you might even find that half your screen is exposing well and the other half has issues. Troubleshooting for that would involve making sure that the coat of emulsion is nice. And even. So by that I mean having an even pressure when you're cutting and maybe coating just one time on each side of the screen. You might also need to make sure you have a high attention mesh on your screen. So to avoid like handmade screens and stapled screens so the fascism or wobbly. And there's also some other things that you can look out for on your exposure unit. You might have an exposure unit with lots of different lights. And one of those lights might be broken or it might be doubling and you've got dead patches in your exposure. Check your light sources. Have your COVID Martian nice and even, and tap your mesh tight on your screen. And that should mean that you're getting even consistent exposures. 13. Troubleshooting | Emulsion breaking down on press: Emulsion breaking down on the press is one of the most annoying consequences of a poorly exposed screen. This can happen because your emotion isn't suited to the ink that you're using. So some are designed specifically for water-based ink, some are designed for plastic. So that's the first thing to check. Second thing is it's very likely that your screen is underexposed and any moisture getting into the screen at this point is then having the consequences of breaking it down further and moving around any young kid emotion. Another reason why your screen might break down on press is because the emulsion wasn't dry enough when you expose that. There's a really easy solution for that. Just let your screens drive, maybe overnight in a nice, warm, not humid environment. And that will allow your emotion to really try out, get a really good clean exposure. 14. Troubleshooting | Pinholes in exposure: Finally, a very common thing is pinholes, these little dots in the finished exposure. You can really easily rectified by having a decrease of your screen before you come to coat it. So use a degreaser, rinse off, dry it, and then you can coat your screen. That's, that will get rid of most of your greenhouse. And then one other thing to look out for is little dots of dust and on your actual glass on your exposure unit every day or just before you're about to expose them screens, clean your glasses and glass cleaner and Iraq. And that will eliminate that issue for you when it comes to printing, one more way to avoid pinholes is to dry them in a dust free environment. We do that in orange studio by hoovering the exposure room, often, frequently. And also, if you're aiming a fan directly at your screens, you might be blowing up dust that you see as they're into the wet emulsion and just leaving it in the wetter motion. You can dry your dry your screens, but just try and put the fan heater pointing away from the screen so that it's not blowing that dusk directly into the screens. 15. Outro: Thank you so much for watching this course. I really hope you found it useful and I really wanted to see how your exposures came out as a result of watching it. So things to think about with your project. How long you express your screen for, what kind of emotions did you end up using? And what kind of setup do you have to express your screens? Screen exposures can be tricky, but once you've mastered this, you're going to be a much better printer and more consistent. And you're probably going to have a better time. There's lots of variables with IQ screen exposure. So please ask in the comments any queries that you have along this process and I'm sure we'll be able to help you and point you in the right direction to get your exposure is looking perfect every single time.