Screen printing with transparency film is a fundamental process used to create the stencil on your screen, which dictates where the ink will pass through onto your substrate. The transparency film serves as a "positive", a dark image that blocks UV light during the exposure process, preserving the emulsion beneath it.
The process involves preparing the transparency, using it to expose a photosensitive screen, and then washing out the unexposed areas to form the stencil.
Preparing Your Transparency Film Positive
The first step is creating the design positive on the transparency film. This film must be opaque enough to block UV light effectively.
Here are the key steps based on common practice and the provided reference:
- Load transparency film into your inkjet printer. Ensure the film is specifically designed for inkjet printers and is loaded correctly according to the film and printer instructions.
- Adjust printer settings to the highest quality print mode. Use the darkest black ink setting. Sometimes selecting a media type like "glossy photo paper" or "transparency" in the printer driver yields the best ink density.
- Print your design on the transparency. Print the design in solid black. The darker and more opaque the printed areas are, the better the film positive will block UV light, resulting in sharper stencil edges. For best results, some printers allow printing a design multiple times over the same area on the film to increase opacity.
Using the Film Positive to Create the Stencil
Once you have your printed transparency film positive, you use it to expose a screen coated with a photosensitive emulsion.
- Coat your screen with photo emulsion. Apply a thin, even layer of photosensitive emulsion to both sides of the screen using a scoop coater.
- Dry the emulsified screen. Allow the screen to dry completely and evenly in a dark or low-light environment. A dark drying cabinet is ideal.
- Position the transparency film on the screen. Place your dried film positive onto the screen. Ensure the ink side of the transparency is pressed firmly against the emulsion side of the screen. This minimizes light bleed and results in sharper stencils. Secure it in place with tape if necessary.
- Expose the screen to UV light. Place the screen and film positive in an exposure unit. The duration of exposure depends on the type of emulsion, the strength of the UV light source, and the distance from the light. Proper exposure is crucial – too little leaves the stencil soft; too much hardens the unexposed emulsion.
- Wash out the unexposed emulsion. After exposure, remove the film positive. Gently spray water (often lukewarm) onto the screen. The emulsion areas blocked by the black design on the film will wash away, creating the open areas of your stencil. The areas exposed to UV light will remain hardened.
- Dry the screen. Allow the washed-out screen to dry completely before printing. You may also need to block out any pinholes (small unwanted openings) using emulsion or block-out fluid.
The Screen Printing Process (Briefly)
With your screen stencil ready, you can proceed with the actual printing:
- Set up your screen on a press. Mount the screen securely onto your screen printing press.
- Align your substrate. Place the item you are printing on (t-shirt, paper, etc.) beneath the screen and align it correctly with your design.
- Apply ink. Pour a bead of screen printing ink across the top of your design on the screen.
- Pull the squeegee. Using a squeegee, pull the ink across the design with firm, even pressure and at the correct angle. This action pushes the ink through the open areas of the stencil and onto the substrate.
- Cure the ink. Depending on the ink type (plastisol, water-based), you will need to heat the printed item to cure the ink properly, making it durable and washable.
Tips for Success
- Density is Key: Always aim for the most opaque black print possible on your transparency film. This is the single most important factor for a sharp stencil.
- Quality Film: Use transparency film specifically designed for your printer type (inkjet or laser) and intended for screen printing positives.
- Proper Exposure: Calibrating your exposure time is essential for durable stencils and clean washouts.
- Darkroom Conditions: Handle photo emulsion and exposed screens in low light or a darkroom until after the washout process.
By following these steps, utilizing transparency film allows you to transfer your digital designs onto a screen, preparing it for the screen printing process.
