Unlike typical four-color printing, where the colors are clearly divided, four-color printing involves wet-on-wet printing where the colors overlap so they mix and produce thousands of different shades.
Four-color screen printing requires some extra time, knowledge, and setup, but screen printers who offer four-color printing end up with beautiful prints that can wow their customers. As you select and color-separate your artwork, choose the correct substrate, set up your screen printer, and print your images, you need to take careful steps.
High-quality artwork is the key to success
While all good screen printing starts with good artwork, good artwork becomes even more important when printing four-color printing. You need high-resolution images for four-color processing jobs. In fact, many screen printers will use oversized images to achieve the level of detail required for these screen printing jobs.
When separating colors for the screen, you will need to change some settings in your separation program, since most programs default to settings suitable for printing on paper. First, you need to make sure your separations are set to CMYK. You'll also need to verify that your program uses the same cyan, magenta, yellow, and black recipes as your inks. Some ink companies provide plug-in files that can synchronize the colors in a graphics program with their ink colors.
You'll also want to adjust the screen angle for each color within the following ranges: 5 percent for yellow, 55 percent for cyan, 22 percent for magenta, and 80 percent for black. A common line count for screen printing is 26.6 lines per centimeter. The halftone dot density needs to be set between 15% and 85%. Finally, the shape of the dots needs to be adjusted; ovals are often used for screen printing because it works well within the squares created by the screen mesh.
Substrate really matters
In four-color screen printing, the substrate is very important. For light (usually white or beige) garments, a four-color process print is recommended, as the different color variations will not stand out on dark garments. However, good four-color printed images can be printed on dark substrates with white undertones, but this is not common. The substrate you choose should have a tight weave so that the individual dots have a surface to print on; although you do need to be wary of heavy materials that are woven from thick threads, as they will interfere with the detail of the halftone dots.
Pay attention to the details in the settings
The four-color process works in great detail. Because of this, you will be laying down the finest coats of each ink color, and your screen press settings will reflect this. Four-color process screen printing requires a densely woven screen, and most experienced screen printers recommend 305 mesh, or even slightly higher. The point weave or thickness of the mesh should also be fine - 34 microns is a good rule of thumb for a 305 count mesh.
Ensuring adequate screen tension is also important. Loose stencils move during printing rather than coming cleanly from the ink, causing blur and incorrect color blending. Screen tension should be around 25 N/cm²; screen tension should not be less than 22 or greater than 30.
Because you're laying down a layer of light halftones using four-color printing screen printing, you want to create as little non-contact distance as possible. A no-contact distance of 0.040 inches is recommended. A squeegee with a hardness of 70 to 75 should be used to create good ink shear, and the squeegee and overflow bar angle on the screen printing machine should be set at about 15 degrees.
When you need to print a four-color process job, you will print from the lightest color to the darkest, so your color order will be yellow, magenta, cyan, black. If you print with a white background, you will print first. Because the goal of four-color screen printing is to allow the ink colors to mix to create an infinite number of shades, you will be printing wet-on-wet. There is no flicker between colors unless you print a white base, in which case only the base is flash cured.
The biggest challenge with four-color screen printing is placing the same amount of ink on each substrate to create a consistent image. Therefore, automatic screen printing machines are suitable for four-color printing. However, it can also be successful on a manual screen printing press, but care needs to be taken, only one printing stroke can be used per color, and once printed, the ink needs to be lifted and retouching of the stencil is not allowed. To apply just a thin layer of ink, use a low-angled squeegee to print gently.
Your first four-color print job can present a major challenge for your shop, but with good artwork and the right apparel, and careful setup and execution of your screen printing process, you will achieve beautifully detailed screens printed matter.
