P&P editor Melanie Attlesey was invited to Screen Print World’s HQ in Kidderminster to get hands on and learn how to screen print. As a complete novice a lesson was definitely learnt!
Having only held a squeegee once before in my life, I don’t think Dave Roper, managing director, quite knew what he was letting himself in for by trying to teach me to screen print.
Screen Print World regularly holds workshops and one-to-one training courses to enable experienced screen printers to perfect their trade and for novices like myself to learn the basics. Dave and his team have even produced a manual for attendees to take away so they can brush up on their newly learnt skills.
Below is a brief overview of what I was taught during my workshop experience.
Screen and mesh
Firstly, I was told that to make a good screen print, you must firstly have a good screen. This means using a new or reclaimed screen that has good tension. The best ‘stretch and glue’ screens to use are aluminum screens because they hold a higher tension, last longer and don’t warp. Dave said to make sure the screen is degreased before use to prevent poor emulsion adhesion, screen breakdown on a print run as well as produce a higher quality exposure.
Dave informed: “Different mesh counts are used for different applications in the screen printing process. The higher the mesh count, the finer the mesh, and the higher the detail you are able to expose and print with a screen.
“Having tension on your mesh is important during the printing process for registration, ink transfer, ink deposit, speed and consistency. Most stretch and glue screens have a tension somewhere between 15–25 Newtons. This tension in the mesh allows for a ‘snap back’ motion when you press down pushing the ink through the screen. The off-contact distance also plays a part here. The off-contact is the distance between the screen and the substrate you’re printing on. The distance should be around a pound’s thickness. Good tension and the correct off-contact allows for the mesh to ‘snap back’ when you push the squeegee over the print. It prevents smudging and allows for a higher quality print.”
The next step in the process was exposing the screen. As with so many other aspects of textile screen printing, Dave explained that there are no rules or standards that spell out the right way to coat and process a screen. Many textile printers use the 2:1 coating method. This means that they coat the print side of the screen with emulsion twice and then finish with a third coat on the squeegee side of the screen.
I was told that a screen printing scoop coater will help here. What’s that I asked? Well, it is an aluminum tool used to coat the screen. It holds the emulsion and has a sharp edge to apply the emulsion evenly.
Once my screen was coated, we let it dry. Once dried, Dave was then ready to show me how to expose my design.
During the screen exposure, Dave explained: “Firstly, it’s important that the design is printed onto the film as opaque as possible. Exposing involves placing your film positive directly on the screen and allowing light to hit the emulsion surrounding the dark black design. Where the light hasn’t been able to get to your emulsion, because it’s blocked by the design on the film, the emulsion will be soft and wash out. Leaving behind your design exposed onto the screen.”
Positive pressure between the screen and film is extremely important in creating a crisp image. If the film positive is not pressed extremely tight against the screen, light will work its way around the edge of the image and expose a soft line instead of a sharp line.
Once exposed, I rinsed both sides of the screen to wash out the soft emulsion. Dave watched carefully and advised that I made my final wash from the shirt side, as this was the side that received the most light and was slightly stronger.
After getting slightly wet while rinsing my screen, Dave then showed me how to take my screen and tape it around the inside of the frame where the emulsion has not covered the mesh.
He showed me how to ensure that all of my adjustments on the press were in the middle position and to place the screen in the screen clamps. Dave informed: “At this point you will need to register the job if it requires more than one colour.”
I was shown how to check that my off contact was correct, which is approximately a pound’s thickness between the bottom of the screen and the garment.
Adhesive on the pallets
When printing you don’t want the T shirt to move, especially when printing more than one colour as this will create some dodgy-looking prints, which is what I was trying avoid on my first attempt.
I was advised to use adhesive (water-based or aerosol spray tack) to temporarily adhere the fabric to the platen. Dave suggested the tip of using pallet masking tape to avoid wasted time cleaning the pallets.
Before attempting to print for real, Dave suggested that I do a test print first – hopefully to avoid costly mistakes.
“When printing, your squeegee should be at approximately a 45° angle when pulling or pushing the ink over the design. You will need to apply some pressure when printing the design, after the print stroke, the mesh should be open and free of ink,” Dave said. Maintaining an even pressure is something I struggled with, but I guess this is something that gets easier over time.
Once finished, I reviewed the test print and made adjustments as needed. “I suggest reprinting until the image is correctly lined up. Once the design is in register continue to print the job,” said Dave.
After several attempts at printing, the final step in the process was to cure the ink. While the T shirt was going through the tunnel dryer, Dave provided the following information: “In order for plastisol or water-based ink to cure it has to reach 160°C throughout the ink. If the ink does not reach that temperature, it will not cure and is likely to wash out of the shirt prematurely. However, different inks will have different guidelines on curing, it is advisable to wash test production regularly.
“The best way to ensure your curing temperature is correct, is to use a laser temperature gun and scan the shirt under the flash or when it is inside the conveyor, if the ink temperature is reaching 160°C it is most likely cured. If the ink is thicker, it may need to stay at that temperature for a longer time in order to cure throughout the ink deposit. You can test your cure by pulling on the garment (gently); if the ink stretches with the garment, it is cured.
“Wash testing should be a standard operating procedure because it is the only reliable way to ensure that prints are properly cured.”
And with that, my time in the workshop was complete and I had printed my first batch of T shirts.
I certainly had fun during my workshop session with Dave and his team, and I feel like I learnt a lot about what it takes to screen print. I even received a certificate for my efforts!
My advice for anyone struggling with any aspect of garment decoration is to get in touch with your suppliers for advice, no matter how small you think the issue is. They are the experts and will only be too glad to help you to improve your skills and level of production.