Common Drying Problems Of Water-Based Screen Printing Inks

Water-based screen printing inks use deionized water as the primary dispersion medium, with acrylic resin or polyurethane resin as the film-forming component, and matching colorants, defoamers, pH adjusters, and co-solvents. The drying system operates on a dual mechanism: volatile drying as the main process and reactive coagulation drying as the auxiliary process.

Volatile drying transfers water and low-boiling co-solvents from the inner ink layer to the surface via molecular diffusion, then removes them through air convection. Reactive coagulation drying triggers cross-linking of resin molecules after water volatilization, forming a continuous and dense ink film.

This mechanism differs fundamentally from solvent-based inks. Solvent-based inks rely on rapid volatilization of organic solvents, while water-based inks require controlled air flow and moderate temperature to complete water removal. Non-absorbent substrates such as PE, PP, aluminum foil, and PET lack capillary water absorption, so all moisture must be removed through surface air convection.

This failure occurs when the residual water content in the ink film exceeds 3%, resulting in surface tack and layer separation after rewinding.Typical on-site performance includes surface tack after printing, ink transfer during overprinting, pattern peeling after rewinding, and failure to pass the 3M tape adhesion test.

Root causes are quantifiable and observable:
1. Ink film thickness exceeds 12μm, caused by low line count anilox rollers, deep engraving depth, or high coating weight.
2. Drying air velocity is lower than 2.5m/s, leading to slow moisture removal.
3. Substrate surface tension is below 38mN/m, reducing ink wetting and spreading speed.
4. Ambient relative humidity exceeds 65%, increasing water vapor partial pressure and slowing diffusion.
5. pH value drops below 8.0, increasing ink viscosity to above 25s , reducing flow and diffusion rate.

This failure forms a dense resin film on the surface within 3–5 seconds, sealing residual water inside the ink layer.Typical performance includes dry surface touch, foaming and wrinkling during overprinting, and reduced adhesion after full curing.

Root causes focus on parameter mismatch:
1. Drying temperature exceeds 60°C, forming surface film before inner water diffusion.
2. Air flow is concentrated on the surface without penetration, failing to take away inner moisture.
3. Single-stage high-temperature drying replaces segmented drying, lacking pre-drying buffer.

Root causes are related to equipment layout and process parameters:
1. Drying air flow directly blows the screen plate, reducing ink residence time to below 2 seconds.
2. Printing speed is lower than 15m/min, extending ink exposure on the screen.
3. pH value exceeds 9.5, reducing color concentration and accelerating water volatilization.
4. High-shear stirring or rapid ink return impacts the liquid level, generating bubbles that accelerate drying.

This failure affects appearance and consistency, mostly occurring in high-humidity environments.Typical performance includes local color difference, white fog on the surface, dense pinholes, and reduced gloss.

Root causes are linked to environment, substrate and ink system:
1. Ambient humidity exceeds 70%, water vapor condenses into the ink film during solvent volatilization heat absorption.
2. Substrate surface contains grease or release agent, contact angle exceeds 50°, leading to wetting defects.
3. Excessive stirring speed produces air bubbles, leaving pinholes after rupture.

Root causes focus on substrate treatment and curing completeness:
1. Substrate lacks corona or flame treatment, surface tension below 38mN/m.
2. Resin cross-linking is incomplete, with curing time less than 24h at 25°C.
3. Mixing with alcohol-based or solvent-based inks destroys the emulsion system and film-forming structure.

Reduce drying load from the source by controlling ink film thickness:
1. Select anilox rollers with line count above 120LPI, engraving depth controlled at 18–22μm for shallow plate configuration.
2. Adopt multi-layer thin printing, single ink film thickness controlled below 10μm.
3. Match screen mesh count: fine patterns use 300–420 mesh screens to reduce single ink loading.

Replace single-stage high-temperature drying with two-stage segmented drying:
1. First stage: temperature 40–45°C, air velocity 1.0–1.5m/s, pre-dry surface to avoid rapid film formation.
2. Second stage: temperature 50–60°C, air velocity 3.0–4.0m/s, high convection to remove residual moisture.
3. Keep drying air away from the screen plate, only blow on the printed substrate to prevent premature drying.

Maintain stable ink performance with real-time monitoring:
1. Control pH value stably between 8.5–9.5, use special water-based pH adjusters for correction.
2. Control viscosity at 15–22s, avoid excessive water addition to maintain emulsion stability.
3. Detect every 30 minutes during continuous production, record and adjust parameters to prevent fluctuation.

Failure Phenomenon	Priority Check Item	On-Site Rapid Treatment
Insufficient drying and adhesion	Ink film thickness, humidity, air volume	Reduce coating weight, increase air velocity, start dehumidifier
False drying and re-adhesion	Excess temperature, insufficient air flow	Lower temperature, strengthen convection, extend second-stage drying
Screen blocking and stringing	Air blowing to screen, low printing speed	Adjust air duct, increase speed to above 15m/min, add slow-release agent
Blushing and fogging	Ambient humidity, water in diluent	Dehumidify, use water-based special diluent, adjust drying rate
Pinholes and bubbles	Substrate cleaning, defoaming, stirring	Degrease substrate, add defoamer, reduce stirring speed
Poor adhesion	Substrate treatment, drying degree	Enhance corona treatment, extend curing time to 24h

Drying problems of water-based screen printing inks are system engineering related to plate making, ink parameters, drying equipment, environment and substrate. Stable mass production requires standardized control system:

1. Adopt two-stage drying with moderate temperature and high air volume, avoid single-stage high-temperature baking.
2. Maintain pH at 8.5–9.5 and viscosity at 15–22s, correct with special additives.
3. Control ambient humidity at 40–60%, optimize air duct to avoid direct blowing on screen plate.
4. Use high-line-count shallow anilox rollers, treat non-absorbent substrates to improve wetting and drying efficiency.
5. Keep ink system independent, prohibit mixing with other ink types, store at above 5°C.

Implementing the above measures can reduce drying failure rate to below 1%, stabilize printing quality, and support the application of water-based inks in food packaging, daily chemical products, industrial labels and other fields.

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