The discharge print process, a critical aspect of screen printing, involves transferring ink from a screen onto a substrate to create vibrant, long-lasting prints. This process is widely used in various industries, including apparel, textiles, and graphics, due to its versatility and cost-effectiveness.
Understanding the discharge print process is crucial for achieving high-quality prints. It involves several steps, from screen preparation to printing and curing, each requiring precision and attention to detail.
Preparing for Discharge Printing
Before starting the discharge print process, several preparatory steps are essential to ensure a smooth and efficient workflow.
First, the artwork needs to be separated into different colors, and each color is then outputted onto a film positive. This film positive is then used to create a photo-sensitive emulsion on the screen, which is later exposed to ultraviolet light to harden the areas that will not print.
Screen Preparation
Screen preparation involves several steps. The first is coating the screen with a photo-sensitive emulsion. This emulsion hardens when exposed to UV light, creating the stencil through which the ink will be pushed onto the substrate.
After coating, the screen is exposed to UV light through the film positive. The areas of the screen not covered by the film harden, while the areas that will print remain unhardened. The screen is then washed to remove the unhardened emulsion, leaving behind the stencil.
Ink Preparation
Discharge ink is unique as it not only prints onto the substrate but also discharges the existing color, allowing for vibrant, full-color prints on dark garments. Preparing the discharge ink involves mixing the base ink with a reducer to achieve the correct viscosity for printing.
The ink is then poured into the screen printing machine's ink reservoir. The machine's squeegee pushes the ink through the screen's stencil onto the substrate, creating the print.
The Discharge Printing Process
Once the screens and ink are prepared, the discharge printing process can begin. This process involves several steps, each crucial for achieving high-quality prints.
The substrate, typically a garment or textile, is first placed on a platens, which holds it in place during printing. The screen is then registered over the substrate, ensuring that the print will be in the correct position.
Flooding and Scraping
The first step in the actual printing process is flooding the screen with ink. This involves using a floodbar to spread the ink evenly across the screen, ensuring that every part of the stencil is covered.
Excess ink is then scraped off the screen using a squeegee. This leaves a thin layer of ink on the screen, ready to be pushed through the stencil onto the substrate.
Printing
The squeegee is then used to push the ink through the stencil onto the substrate. The print head moves across the screen, applying even pressure to ensure that the ink is pushed through the stencil evenly.
The print head then lifts, and the substrate is moved to the next station for the next color, if applicable. This process is repeated until all colors have been printed.
Curing
After printing, the ink needs to be cured to ensure that it adheres to the substrate permanently. This is typically done using a conveyor dryer, which heats the print to a high temperature, curing the ink.
The cured print is then checked for quality and, if necessary, touched up. The final print is then ready for packaging and distribution.
Mastering the discharge print process requires practice and patience, but the results - vibrant, long-lasting prints on dark garments - make it a valuable skill in the screen printing industry. Whether you're printing t-shirts, tote bags, or posters, understanding and mastering the discharge print process will help you create high-quality prints that stand out.