Screen Printing Emulsion & Exposure Guide | Coat, Expose, Print
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Rob Krause
Owner, Battle Born Clothing & Print - Yerington, NV - Published March 11, 2026
TL;DR - Perfect Screens Make Perfect Prints
The screen room determines print quality before ink ever touches fabric. A poorly coated, under-exposed, or incorrectly washed screen will produce bad prints no matter how good your press, ink, or technique. Battle Born uses CCI LED photopolymer emulsion on EcoClick aluminum frames with Italian Saati Hi-TEX mesh, exposed on a custom-built vacuum LED exposure unit. This combination lets us hold halftone dots down to 5% on production screens - the foundation for every halftone and underbase print we produce.
Everyone talks about the press. The M&R GT-8. The 8-color automatic. The print-flash-print cycles. The squeegee angles. But the truth that experienced printers know is that 80% of print quality is determined in the screen room before the shirt ever hits the platen.
The screen room is where artwork becomes a physical stencil on a mesh screen. If the emulsion coating is uneven, the stencil will be uneven. If the exposure is too short, fine dots wash away and you lose detail. If the exposure is too long, small openings fill in and shadows go muddy. If the film is not in perfect contact with the emulsion during exposure, light undercuts the edges and you lose resolution.
This is the step nobody talks about because it is not glamorous. But it is the foundation that every print in this entire blog series depends on. Every halftone dot, every underbase layer, every specialty ink effect starts right here.
The Three Emulsion Types
Diazo (Single-Cure)
Requires mixing a diazo sensitizer before use. Cheapest option, most forgiving exposure latitude, but slowest exposure times and shortest shelf life (30-45 days after mixing). The yellow diazo bleaches during exposure, giving a visual indicator of cure. Being phased out in favor of dual-cure and photopolymer.
Best for: Beginners, budget operations, non-critical spot color work
Dual-Cure
Combines diazo and photopolymer chemistry. More forgiving than pure photopolymer but faster than straight diazo. Good chemical resistance for water-based and discharge inks. Wider exposure latitude means small timing errors are less destructive. Shelf life: 4-6 weeks after mixing.
Best for: Intermediate printers, varied ink types, environments with humidity fluctuation
Pure Photopolymer (SBQ) - Our Choice
Ready to use out of the container, no mixing. Fastest exposure times (as low as 10-30 seconds on LED). Highest resolution and finest dot holding. Longest shelf life (up to 1 year). Optimized for LED exposure at 405nm. This is what we run at Battle Born: CCI LED emulsion, a pure photopolymer engineered specifically for LED exposure units.
Best for: Production shops, LED exposure, halftones, fine detail, high volume
"Using 405nm LED gains printers the benefit of wider exposure latitude. During exposure, all sides of the emulsion layer are cured simultaneously. LED bulbs last way longer than halogen bulbs, which saves printers money."
Our Screen Room Workflow: Step by Step
Degrease and Prep the Screen
Clean screens are non-negotiable. Any residual ink, ghost haze, or grease prevents emulsion from bonding evenly to the mesh. We degrease every screen before coating, then dry completely. Screen tension is verified at 25+ Newtons on our EcoClick aluminum frames with Italian Saati Hi-TEX mesh. Loose screens cause registration drift, dot gain, and inconsistent off-contact.
Coat the Emulsion
Under yellow-safe lighting, we apply CCI LED emulsion using the sharp edge of a scoop coater. One coat on the print side (outside), one coat on the squeegee side (inside). For screens that will hold halftone dots or serve as underbases, we add a second coat on the print side after the first dries. The sharp edge gives a thin, even coat. Thin emulsion = finer resolution = better dot holding. The entire process happens in our climate-controlled screen room to prevent humidity from affecting the coating.
Dry the Screen Completely
The coated screen must be completely dry before exposure. Not "dry to the touch" - dry all the way through. Think of a tomato: it can be dry on the outside and wet inside. A partially wet screen will not expose properly because moisture interferes with the photochemical reaction. We dry screens print-side down in a dark, warm, low-humidity environment with air circulation.
Expose on the Vacuum LED Unit
This is where our setup makes the difference. The film positive is placed on the coated screen, and the vacuum draws the film flat against the emulsion for perfect contact. Even tiny air gaps between film and emulsion cause light undercut that destroys fine halftone dots. The LED array fires at 405nm, penetrating deeply into the emulsion for even crosslinking from surface to mesh. Exposure times on our CCI LED emulsion are measured in seconds, not minutes. We calibrate with a 21-step wedge for each mesh count and emulsion batch.
Washout and Inspect
After exposure, the screen is washed with water. The unexposed emulsion (where the design image blocked the light) dissolves and rinses away, leaving the stencil. We inspect every screen against the original artwork, checking that fine dots have held, edges are clean, and no pinholes are present. Pinholes are blocked out with emulsion and re-exposed. The screen is then dried completely before going to the press.
Why LED Exposure Beats Traditional UV
405nm wavelength: The sweet spot for emulsion crosslinking. This wavelength penetrates deeply into the emulsion layer, curing all the way through to the mesh threads. Traditional UV bulbs emit a broad spectrum that can overcure the surface while undercuring the bottom, creating a fragile stencil that breaks down during printing.
Speed: LED exposure with photopolymer emulsion can be 10-30 seconds. Traditional metal halide might take 2-5 minutes for the same screen. Over a production day of 20-50 screens, that time difference compounds significantly.
Consistency: LED bulbs do not degrade the way halogen or metal halide bulbs do. Their output stays consistent for years, which means your exposure time stays calibrated. With traditional bulbs, you have to increase exposure time as the bulb ages - and if you forget to adjust, every screen is under-exposed.
Edge quality: The collimated nature of LED light produces sharper stencil edges than diffuse UV sources. This translates directly to crisper print edges on the garment.
Energy and bulb life: LED uses a fraction of the energy and the bulbs last 3-5+ years versus months for halogen. The ROI pays for the unit quickly.
Why Vacuum Contact Is Non-Negotiable for Halftones
Our exposure unit uses vacuum suction to pull the film positive flat against the coated screen during exposure. This seems like a small detail. It is not. Any air gap between the film and the emulsion allows light to scatter under the edges of the halftone dots, a phenomenon called light undercut. On a spot-color screen with solid shapes, a small amount of undercut is invisible. On a halftone screen where dots are 5-10% of the total area, undercut either destroys the dots entirely or makes them smaller than intended, shifting the tonal balance of the entire print.
Our custom-built vacuum LED exposure unit eliminates this variable. The vacuum draws the film into direct contact with the emulsion across the entire screen surface. Combined with the collimated LED light source, we get stencils that hold dots down to 5% on production screens. That 5% target is the difference between a halftone print with smooth highlight transitions and one that looks flat and muddy in the light areas.
Common Screen Room Problems and Fixes
Halftone dots washing away
Causes: Under-exposure, poor film density, wrong emulsion type, or no vacuum contact. Fix: Reduce exposure time (counter-intuitive but under-exposure is the usual culprit), use a RIP for denser film output, switch to photopolymer emulsion, and ensure vacuum contact.
Stencil breaking down during print run
Causes: Under-exposure (emulsion not fully crosslinked), wrong emulsion for ink type (standard emulsion with water-based ink), or excessive squeegee pressure. Fix: Increase exposure, use water-resistant emulsion for WB/discharge, and check screen tension and squeegee technique.
Pinholes in stencil
Causes: Dust or debris on screen during coating, uneven coating, or contaminated emulsion. Fix: Keep screen room clean, degrease screens thoroughly, stir emulsion before use, and inspect coated screens before exposure. Block out pinholes with spot emulsion and re-expose.
Emulsion hard to reclaim after printing
Causes: Over-exposure, post-exposure from ambient light during storage, or ink ghosting. Fix: Do not over-expose (use exposure calculator), store unexposed screens away from all light sources, and use proper haze remover for ghost images after reclamation.
Mesh Count Affects Exposure Time
Different mesh counts hold different amounts of emulsion. A 110 mesh screen with its larger openings holds more emulsion and needs slightly more exposure time. A 305 mesh holds less emulsion and exposes faster. The difference is typically 5-10%, but on photopolymer emulsion where exposure is measured in seconds, even a few seconds matter. We test and record optimal exposure times for every mesh count in our inventory.
Screens Made Right. Prints That Prove It.
Battle Born's screen room runs CCI LED emulsion on EcoClick frames with a custom vacuum LED exposure unit. Every screen is tested, every exposure calibrated, every dot verified. The result: production screens that hold 5% halftone dots and deliver the quality our customers expect.
Frequently Asked Questions
What type of emulsion is best for screen printing?
Depends on your setup. Pure photopolymer (SBQ) is fastest and holds finest detail - ideal for LED exposure and halftones. Dual-cure is more forgiving for beginners. Diazo is cheapest but slowest. For LED exposure with halftone work, Battle Born uses CCI LED photopolymer emulsion.
How do I coat a screen for screen printing?
Sharp edge of the scoop coater, one coat print side, one coat squeegee side. Add a second print-side coat for underbase/halftone screens after the first dries. Thin, even coats under yellow-safe light. Let dry completely before exposure.
How long should I expose my screen printing emulsion?
Varies by emulsion type, mesh count, and light source. Photopolymer on LED: as fast as 10-30 seconds. Always use a 21-step wedge or exposure calculator to find optimal time. Under-exposed = lost detail. Over-exposed = hard washout, filled-in dots.
What is the difference between LED and UV exposure?
LED emits a narrow peak at 395-405nm that penetrates emulsion deeply and evenly. Traditional UV uses broad-spectrum bulbs that degrade over time. LED is faster, more consistent, uses less energy, produces sharper edges, and bulbs last years instead of months.
Why do my halftone dots wash away during development?
Most common causes: under-exposure, poor film density (use a RIP for denser output), wrong emulsion type, or no vacuum contact between film and screen. Fix by dialing in exposure with a calculator, upgrading to photopolymer emulsion, and ensuring vacuum contact.
Do different mesh counts need different exposure times?
Yes. Lower mesh (110) holds more emulsion and needs slightly longer exposure. Higher mesh (305) holds less and exposes faster. The difference is typically 5-10%. Test each mesh count with an exposure calculator for your specific emulsion and light source.
The Complete Screen Printing Technical Series
This post is part of Battle Born's 8-post screen printing technical authority series. Read them all: