In screen printing, an exposure calculator is a tool used to determine the proper exposure time for burning (exposing) the emulsion onto the screen mesh. The exposure time is crucial as it affects the quality and durability of the stencil on the screen.
How Does an Exposure Calculator Work?
An exposure calculator takes into account several factors that influence the exposure time, such as:
- Light Source: The type of light source used for exposure, such as a UV light box, affects the intensity and wavelength of the light, which impacts the exposure time.
- Emulsion Type: Different emulsion types (diazo, dual-cure, photopolymer, etc.) have varying sensitivity to light, requiring different exposure times.
- Mesh Count: The mesh count (threads per inch) of the screen affects the amount of emulsion that needs to be exposed. Finer meshes generally require longer exposure times.
- Stencil Thickness: Thicker stencils (created by coating more emulsion on the screen) require longer exposure times to ensure proper curing throughout the emulsion layer.
- Distance from Light Source: The distance between the screen and the light source can affect the intensity of the light hitting the emulsion, thus affecting the exposure time.
Using the Exposure Calculator
An exposure calculator typically consists of a series of filters or films with varying densities, each representing a different exposure factor or multiplier (e.g., x1, x0.7, x0.5, etc.). These factors are printed or marked under each filter section.
The process of using an exposure calculator involves the following steps:
- Start with an initial exposure time that you typically use, for example, 2 minutes (120 seconds).
- Choose a longer exposure time for testing purposes, let’s say 180 seconds.
- Note down the mesh count and coating technique you’re using.
- Expose a screen for 180 seconds using the exposure calculator.
- Wash out the screen and examine which filter section (with its corresponding exposure factor) shows the best detail and washout quality.
- If a particular filter section (e.g., the one marked x0.5) shows the best results, you need to adjust your exposure time accordingly. In this case, you would multiply your initial exposure time (180 seconds) by the exposure factor (0.5), giving you a new exposure time of 90 seconds (180 x 0.5 = 90).
- Expose another screen using the new calculated exposure time (90 seconds) and the same mesh count and coating technique.
- Evaluate the washout quality of this new screen. If the first filter section (x1) shows the perfect washout of lines and dots, you have found the optimal exposure time for that specific setup.
- If the washout is still not perfect, make slight adjustments to the exposure time in seconds, either increasing or decreasing it until you find the “sweet spot” for optimal exposure.
- Repeat this process for each combination of mesh count and coating technique, as the optimal exposure time may vary depending on these factors.
The exposure calculator helps you fine-tune the exposure time by providing a visual reference and exposure factors, allowing you to achieve consistent and high-quality stencils in screen printing. It’s a process that requires some trial and error, but it ultimately leads to improved consistency and better print quality on the screen printing press.
KIWO is well known for Exposure Calculators
