Print Overlap

The Screen Printing Process

Here is something I wrote for all of those that continue to ask me how to screen print. It's a bit of a long read, but it's informative enough to give you a good idea of exactly what takes place. It's not completely detailed out (there are many small steps missing) but it is the key elements in screen printing.

1. Artwork. The artwork you start art with is VERY important. If you have jagged or grainy artwork, you will reproduce this. There are many art services on the internet that will supply you will screen printing artwork. If you fax them a logo, they can redraw it for you and send you a file in which you can use for the making of screens.

You can also create (or recreate) artwork yourself.   It is imperative to use a vector art program like Adobe Illustrator, Corel Draw or Macromedia FreeHand. Using these programs will ensure that you will have high quality artwork in the end. Photoshop can be used as well, but this is more for full color printing, etc., which is not good to start out with since there are special techniques to master before moving into this realm.

2. Film Positives. When you have artwork that is ready to print, you can print your artwork out on a clear film instead of paper.  There are different types of paper for inkjet and laserjet printers, so be sure you select the right type. For every color you have, you will print it out as a black plate on a separate film. For example, if you have a logo that is Red & Black, you would separate the two colors from themselves and print each out, changing the red to black and printing and then printing the black. Each of these would be printed on their own film.

This is simply known as art separations, or “seps”. If the colors are touching in the final version of the logo, then you need to have what is called trap or choke. Basically, it's an overlapping of the artwork by a small margin. This small margin is just enough so you can register the colors so there is no space between them. On the films, you will also place registration marks. These marks usually are a circle with a verticle and horizontal line passing through it. These marks will be on the same spot on each film. This will help you line up the art later so the images match up perfectly.

3. Screen Making. When screen printing began it was called silk screening. The reason for this is, the screens used to be made from silk. Since this is no longer the case (now they are made from polyester), the name changed. A screen is simply a wooden or metal frame that has a fine mesh stretched over and attached to it. This mesh has different counts. Some examples would be 83, 110, 125, 140, 330 and on and various numbers in between. The lower the mesh count, the less detail you can print and the thicker the ink lays down. So it is an artform to say the least in dealing with correct mesh.

The actual process of screen making is quite simple, just time consuming. Capillary film is stilled used but the most common technique is using a light sensitive liquid emulsion. Emulsion can be used under a yellow light so that you still can see what you are doing, but the UV light is filtered out so as not to effect the emulsion. A scoop coater is needed. You pour emulsion into the scoop coater and place it on a vertical screen. Pressing up against the screen and pulling up, you will lay a thin layer of emulsion on the outside of the screen. Turn the screen around and do the same for the inside of the screen. Turn it back around and do it once more on the outside.

Once the emulsion dries, you can "expose" the screen. You need a good light source for this process. We have an exposure unit that can expose 20" x 24" screen. It has a halogen light along with 2 black lights to help diffuse (or even out) the light. The exposure unit is basically a box with a glass top and a lid that has a black matte and a vacuum frame. The light source would be contained in this box.  Some “do it yourself” printers that work from home actually use the sun for this process.  It’s very time consuming, but it works!

To expose a screen, taking the film positive you created and place it on the glass top with the right reading being up. Then take the dried screen and place it on the glass top with the film positive under it. The screen mesh will be touching the film positive. When you close the lid, there is a vacuum frame that will suck all of the extra air out of the frame. This vacuum frame will pull the matte close to the screen frame. This is essential for a crisp image to be burned into the screen mesh.

At this point, the length of time will be dependent on your emulsion and light source. This is something you can talk to your emulsion supplier about. It’s really a matter of testing. Most problems occur in this stage, so it is critical that you understand this process through testing, training and trial and error. The better you are in this area, the better your prints will be.

Once the image is exposed into your emulsion, you can take the screen to a washout booth. Lightly spray both sides of the screen with water. I garden hose with a sprayer on the end works well for this procedure. You do not want a lot of pressure but you do want some. After waiting for a couple of minutes, you can go back and begin spraying your screen with water. Spray on the outside of the frame, or the side that was touching the film. The inside will naturally be softer because the light had to shine through the emulsion to get to that side. As you spray down the screen, you will see the image on your screen. What happened is, wherever there was black on your film, the light did not shine through. Since the light could not expose the emulsion, it remained water solulable. Wherever the light shine through the emulsion, it hardened and will not wash away. Let the screen(s) dry.

4. Printing Press. Choosing a printing press isn’t nearly as critical, although you are looking for a quality press. To be honest, you may want to stay away from all-in-one units and similar machines. They are a waste of money. Even though you can print just as good of a print with these machines, they are costly and they slow your process down. When I started, I was told a 4 color 4 station press is just about all I needed. They were right. Very rarely did I ever need to print anything more than a 4 color design. Later, as I grew, I purchased more machines that allowed for more colors. But the first 5 years of my business, I believe I had 1 6 color job and 1 5 color job. So it wasn’t critical for me to spend more money on a 6 color machine. What you are looking for in a press is a solid frame, micro registration and rotating platens. Outside of this, you don’t need much more than that.  Obviously, a auto-press is what we use now (and is preferred), but these can run anywhere from $50,000 - $100,000 or even more.

5. Conveyer dryer and flash unit. To actually cure the ink, you need a heat source to reach 320 degrees for your ink. If you can reach 320 degrees in 1 second, it’s cured. If it’s 10 seconds, it’s cured. As long as it reaches 320 degrees, you are good. A flash unit is a unit that you place over your platen (arm that you place the shirt on). This flash unit is meant to flash the ink just long enough where it is not cured and it is not wet. This will allow you to print colors on top of colors if needed, and you will need it! Many people use these units to cure their shirts. This is not wise. If you have a flash unit over a platen, it has to reach 320 degrees to cure the ink. This heat will eventually warp your platens, causing printing problems in the long run. It will also heat your platen up enough that when you put another shirt on it and print, it will semi cure the ink in your screens, causing a clogging and poor printing. So buy the flash unit and use it for it’s intended purpose, to flash the ink, if you have to. If I print a single color on a shirt, I will not use a flash unit at all. If it is white printing, then I will. The reason for this is, you would print white on a shirt, flash it, then when the shirt comes back around to you, it needs a second print. This gives you a good vibrant white. If you are printing a color on a dark shirt, you would also print a white underbase, flash it, then print an exact image with a different screen over top of it with the color you need.

The conveyer dryer is needed to increase your production. When you finish printing a shirt, you pull it off of your platen and place it on the conveyer dryer. Basically, it’s a dryer that has a belt on it that goes through a tunnel of heat. When it comes out the other side, it is cured. There are temperature strips that you can place on the shirt to run through the dryer and make sure the heat and speed setting are correct. Raytek also makes a heat gun that when the shirt comes out, you point the laser beam at the ink and it will give you a temperature reading. Remember, 320 is the magic number!

6. Inks and miscellaneous. The ink you will use is a Plastisol ink. There are so many manufacturers and types of inks, it’s good to find one and stick with them. I can give you suggestions of what I feel are good, but it’s all up to you in the end. You will also need squeegees. A squeegee is basically a handle with a rubber blade on the end. This blade is what you use to push or pull the ink through the screen and onto the shirt. There are so many miscellaneous items that it would be good to talk to a supplier about what you need to get started.

7. Screen prep and registration. Your scoop coater cannot reach all areas of the screen, so you want to tape out the areas that did not have emulsion. There are special tapes made to do this, but packing tape works well if you remove it right away when you are finished. Simply tape the inside and outside of the screens wherever the emulsion did not cover. If you have a one color design, placing the screen on your press is quite simple. If you have more than one color, this is where the registration marks are needed. After placing your first screen on the press, you would do a test print. Place some ink on the screen and rest a squeegee on the frame close to the head. Pull the ink across the screen and onto the shirt. Next, take your second screen and place them on the next head. Align the registration marks on the screen to the marks on the print you made. Once in place, you can lock them in and adjust the micro registrations if necessary. Once locked in, do a test print. If everything is registered, you can tape up the registration marks on your screen and you are ready to print.

8. Your first print. You will be working upside down when you print t-shirts. The collar will be closest to you. After placing the shirt on the platen, pull your screen down. One thing I did not mention was off-contact. If you look between the shirt and the platen, you should have a gap. This is called your off-contact. You need about 1/8” between the screen and the platen. This will give you just enough room to make a print and allow for the screen to snap away from the shirt. This gives you a clean print. Some people will push their squeegee and others will pull. Whatever is comfortable to you is best for you. Personally, I’ve always pulled my squeegee. This means that when I pull down my screen, I grab my squeegee and pull the ink towards me. You want to have the sqeegee at an angle, but not too much. A 70 - 80 degree angle is good. If you go too much of an angle, you will get a heavy print and it won’t look very good. If the angle is a 90 degree, then you won’t get the proper pressure, giving you a light print. The good thing is, if the first print does not work out for you, you can print it again, right over top of it. The registration of the machine will be the same so even if you rotated the press and came back to it, it would still print good.

As with anything, practice is what is needed. Make sure that whatever you do that works, keep it consistent. A firm grip on the squeegee, a consistent angle and a quick stroke will give you a good print. When you find that print, keep it consistent. Good luck!

I know that throughout this article I left out smaller details of the process, but I figured this was long enough.  If you have any questions, feel free to contact me at 480.678.4488 during business hours.

-Michael D’Elena

Owner/President

Reckless T-shirts

Need screen printing? Check us out at: http://www.recklesstshirts.com or http://www.recklessts.com

About the Author

 

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