The Kiwo Exposure Calculator helps screen printers determine the correct exposure time for screen printing emulsions. Accurate exposure is crucial for producing high-quality prints and ensuring the durability of the stencil. This tool considers various factors such as light source, emulsion type, and distance to calculate the optimal exposure time.
Inputs
- Light Source (LS): The type of light source used (e.g., UV lamp, halogen lamp).
- Emulsion Type (ET): The type of emulsion applied to the screen (e.g., diazo, photopolymer).
- Distance (D): The distance between the light source and the screen, usually measured in inches or centimeters.
- Coating Thickness (CT): The thickness of the emulsion coating on the screen, measured in microns or millimeters.
- Screen Mesh Count (MC): The number of threads per inch or centimeter on the screen.
Formulas and Calculations
1. Base Exposure Time (BET)
Each emulsion type has a recommended base exposure time provided by the manufacturer. This time is adjusted based on other factors.
2. Distance Adjustment Factor (DAF)
Exposure time changes with the distance between the light source and the screen. The adjustment factor for distance is calculated using the inverse square law:
[ \text{DAF} = \left(\frac{D_{\text{standard}}}{D}\right)^2 ]
where:
- ( D_{\text{standard}} ) = Standard distance (usually provided by the manufacturer, e.g., 1 meter)
- ( D ) = Actual distance
3. Coating Thickness Adjustment (CTA)
The thickness of the emulsion affects exposure time. Thicker coatings require longer exposure. This is usually provided as a percentage adjustment by the manufacturer.
4. Mesh Count Adjustment (MCA)
Higher mesh counts may require different exposure times. Manufacturers often provide guidelines for adjusting exposure based on mesh count.
Example Calculation
Inputs:
- Light Source (LS): UV lamp
- Emulsion Type (ET): Photopolymer
- Distance (D): 24 inches
- Coating Thickness (CT): 10 microns
- Screen Mesh Count (MC): 120 threads/inch
- Determine Base Exposure Time (BET):
Assume the manufacturer recommends 60 seconds as the base exposure time for photopolymer emulsion with a UV lamp at a standard distance of 1 meter.
- Calculate Distance Adjustment Factor (DAF):
[ DAF = \left(\frac{39.37}{24}\right)^2 ]
[ DAF = \left(1.6404\right)^2 ]
[ DAF = 2.69 ]
- Adjust for Distance:
[ \text{Adjusted Exposure Time} = \text{BET} \times \text{DAF} ]
[ \text{Adjusted Exposure Time} = 60 \times 2.69 ]
[ \text{Adjusted Exposure Time} = 161.4 \text{ seconds} ]
- Adjust for Coating Thickness:
Assume the manufacturer suggests adding 10% for each 5 microns above the standard thickness (standard thickness being 5 microns).
[ \text{Thickness Adjustment} = 161.4 \times 1.10 ]
[ \text{Thickness Adjustment} = 177.54 \text{ seconds} ]
- Adjust for Mesh Count:
Assume the manufacturer suggests reducing exposure time by 10% for mesh counts above 100.
[ \text{Mesh Adjustment} = 177.54 \times 0.90 ]
[ \text{Mesh Adjustment} = 159.79 \text{ seconds} ]
Summary
For a screen with a photopolymer emulsion, using a UV lamp at 24 inches distance, with 10 microns coating thickness and 120 mesh count, the optimal exposure time is approximately 160 seconds.
Conclusion
The Kiwo Exposure Calculator is an essential tool for screen printers to determine the correct exposure time for various emulsion types and printing setups. By inputting the light source, emulsion type, distance, coating thickness, and mesh count, users can achieve precise and consistent results, ensuring high-quality prints and durable stencils.