Emulsion Exposure Calculator

Your expert tool for dialing in the perfect screen printing exposure time.

Mesh Factor: —

Emulsion Factor: —

Color Factor: —

What is an Emulsion Exposure Calculator?

An emulsion exposure calculator is a tool used in screen printing to determine the ideal amount of time to expose a coated screen to a UV light source. Achieving the correct exposure is one of the most critical steps for creating a durable and detailed stencil. Underexposing can lead to a soft, slimy emulsion that breaks down during printing or washout, while overexposing can cause fine details to be lost. This calculator helps you adjust your exposure time when changing variables like screen mesh count or emulsion type, using a known, successful exposure as a baseline.

Emulsion Exposure Formula and Explanation

The calculation is based on applying adjustment factors to a known good exposure time. The formula used by this calculator is:

New Time = Baseline Time * (New Mesh / Baseline Mesh) * Emulsion Factor * Mesh Color Factor

This formula adjusts the time based on the principle that higher mesh counts have smaller openings, requiring more light and thus more time to properly cure the emulsion.

Variables Affecting Exposure Time

Variable	Meaning	Unit / Type	Typical Range
Baseline Time	A known correct exposure time from a previous test.	Seconds	60 – 900
Mesh Count	The number of threads per inch in the screen mesh.	Threads/Inch	86 – 355
Emulsion Type	The chemical composition of the emulsion (Diazo vs. Photopolymer).	Factor	0.7 – 1.0
Mesh Color	Color of the mesh fabric (white or yellow).	Factor	1.0 – 1.3

Practical Examples

Example 1: Switching to a Higher Mesh Count

• Inputs: You have a perfect exposure at 300 seconds on a 156 white mesh with Diazo emulsion. You want to find the time for a 230 yellow mesh.
• Calculation: The calculator applies the mesh count and color factors.
• Results: The new recommended time would be significantly longer, around 574 seconds, to ensure the light properly cures the emulsion through the finer, light-scattering mesh.

Example 2: Changing Emulsion Type

• Inputs: You have a perfect exposure at 480 seconds on a 110 white mesh with Diazo emulsion. You are switching to a faster-exposing Photopolymer emulsion on the same mesh.
• Calculation: The calculator applies the emulsion factor of 0.7.
• Results: The new recommended time would be shorter, around 336 seconds (480 * 0.7).

How to Use This Emulsion Exposure Calculator

1. Establish a Baseline: First, perform a step wedge test to find the perfect exposure time for one of your common setups (e.g., a 156 mesh with your standard emulsion). This is your most critical data point.
2. Enter Baseline Data: Input your known good time and the corresponding mesh count into the “Baseline” fields.
3. Enter New Variables: Input the mesh count for the new screen you are preparing. Select the correct emulsion type and mesh color.
4. Analyze the Result: The calculator will instantly provide a new estimated exposure time. It’s always a good practice to run a small test print to confirm, but this value will get you very close.

Key Factors That Affect Emulsion Exposure

• Emulsion Type: Pre-sensitized (Photopolymer/SBQ) emulsions expose much faster than dual-cure or diazo emulsions.
• Emulsion Thickness (EOM): A thicker coat of emulsion, known as Emulsion Over Mesh (EOM), requires a longer exposure time to fully cure. Consistent coating is key.
• Mesh Count: Higher mesh counts have less open area and require longer exposure times.
• Mesh Color: Yellow or orange mesh scatters UV light, preventing undercutting and improving detail, but requires about 30% more exposure time than white mesh.
• Light Source: The wattage, type (LED vs. Metal Halide), and distance of your light source dramatically affect exposure time. A stronger light source exposes faster.
• Humidity: High humidity (above 40-50%) in your drying area can prevent emulsion from drying properly, leading to exposure issues.

Frequently Asked Questions (FAQ)

1. What is a step wedge test?

A step wedge test is a method to find the optimal exposure time by exposing a single screen in sections for different amounts of time. A physical test film, often called an exposure calculator, is used to gauge the result.

2. Why is my emulsion slimy after washout?

A slimy or gooey feeling on the substrate side of the screen after washing out the image is a classic sign of underexposure. The emulsion hasn’t received enough UV light to fully harden.

3. Why am I losing fine detail in my stencil?

This is often a sign of overexposure. The UV light starts to “burn through” the edges of your film positive, hardening the emulsion in areas that should wash out.

4. Does Emulsion Over Mesh (EOM) really matter?

Yes, significantly. EOM refers to the thickness of the emulsion gasket on the print side of the screen. A proper EOM (often 10-20% of the mesh thickness) ensures a sharp-edged print by preventing ink from bleeding under the stencil.

5. How often should I test my exposure times?

You should run a new test whenever you change a major variable: a new batch or type of emulsion, a new light bulb in your exposure unit, or if you start using a different mesh count or color.

6. Can I use the sun to expose my screens?

While technically possible, it is highly discouraged. The sun’s UV output is incredibly variable depending on the time of day, season, and cloud cover, making it impossible to get consistent, repeatable results.

7. My exposure times seem very long, what could be wrong?

Long exposure times are often caused by a weak light source (low wattage or old bulb), a great distance between the light and the screen, or a very thick emulsion coating.

8. What is the difference between Diazo and Photopolymer emulsions?

Diazo emulsions require you to mix in a sensitizer and have a longer shelf life before mixing. They expose slower but are often more durable. Photopolymer (SBQ) emulsions are pre-sensitized, expose very quickly, and typically offer high detail resolution.