Burning a Great Screen Part 1
How do you get from “Why doesn’t my screen image come out right?” to “My screens are great every time”? Figuring out how long to burn your screens can feel like calculating the vector force needed to achieve critical orbit around the moon, instead of the routine process it should be. In order to get to that point, you have to know the factors involved in the process. The main factors that go into a burn time are artwork, the light table, and screens and emulsions.
Within these factors, there are many variables that can affect exposure times, but ultimately, they come back to these factors. Over the next blog posts, we’re going to talk about all that relates to creating a great screen image. These posts will be extremely helpful if you’re just starting out in screen printing. And if you’re a seasoned pro, they will be a good refresher for you, and you might even pick up a couple of tips along the way. Look for a series of posts that will cover:
-The Light Table
-Emulsions and Screens
-Determining Optimum Burn Time
-Underexposed, Overexposed, or Just Right?
Artwork is by far the most important piece in the equation. Good artwork forgives a multitude of problems. While the complexity of the artwork is a factor, more important factors are the quality of the film, the ink, and the computer software.
Screen printers just starting out may tend towards the vellums because they are inexpensive and work decently for large block artwork. However, for most screen printers, printable transparencies are the medium of choice. Transparencies are printer dependent so you want to be sure to get a laser printer transparency for a laser printer and an inkjet transparency for an inkjet printer.
These transparencies are interchangeable. If you use a laser jet transparency in an inkjet printer, the ink will not bind to the transparency so it will rub off on anything it touches. If you use an inkjet transparency in a laser jet printer, the transparency could actually melt inside the printer because it is not designed to take the heat from the printer. Something else you will want is a transparency with a matte finish. The matte finish reduces the amount of reflection, which lessens the effectiveness of the light source.
Laser printers are able to make transparencies, but they are not always the best option. A laser printer uses static electricity to attract the toner to the drum, which then gets transferred to the paper. You can lighten the image on a laser printer by putting it into economy mode, but it is hard to make the image darker. There are toner sprays that can darken the toner, which do work, but they can also cause streaking and can smear the edges of the artwork.
Ink Jet printers are the printer of choice for most screen printers. Inkjet printers work by placing tiny dots of ink in a grid pattern to fill in the image area. You can adjust the settings in the printer to darken images for better light blocking ability. Something else you can use in an inkjet printer is a special ink that is designed to block UV light, which is the light that cures the emulsion. The more the artwork is able to block the UV light, the better the artwork will be on the screen.
Your software can also make a difference in the quality of the artwork. For larger block graphics, the software will not make much of a difference, but you’ll really notice the difference when you work with halftones. Traditional printer drivers are generic and generally geared towards document printing. Although photo printers are capable of doing much better detail, they don’t reach their full potential until used with a rip software. RIP software, or raster image processor software, gives you greater control over the printer in order to reproduce finer details in an image. The software allows the printer to adjust the size and spacing of the ink droplets as the image fades between colors. Traditional drivers use a consistent droplet size and spacing, which can make finer details look chunky and not as even.
Even though the artwork is the most important part of the equation, it is still just one part. Stay tuned for our next screenprinting blog post as we cover The Light Table.