Ink Spitting

/ɪŋk ˈspɪtɪŋ/

General Definition

Ink Spitting, also known as "misting" or "slinging," is a common defect in flexographic printing characterized by small, irregular droplets of ink appearing in non-image areas or across halftone dots. This phenomenon occurs when ink accumulates behind the doctor blade and is ejected due to hydrodynamic pressure or blade vibration, landing directly on the substrate or the anilox roller. This issue is particularly prevalent during high-speed production runs and when using inks with high viscosity, severely compromising the final print's cleanliness and sharpness.

Real-World Usage

In practical pressroom operations, Ink Spitting is usually caused by an imbalance between the press speed and the blade's ability to contain the ink. As the anilox roller speed increases, centrifugal force ejects ink from the Cell Volume with greater intensity against the blade edge. If the Doctor Blade lacks sufficient flexibility or is installed at an incorrect angle, it may momentarily lift off the roller surface—a phenomenon known as aquaplaning—allowing ink droplets to escape.

Operators often mistakenly increase blade pressure to stop the spitting, but this significantly shortens the roller's life by rapidly wearing down the Cell Depth. The scientific solution lies in using specialized blade tip geometries and precisely controlling ink viscosity. Additionally, using anilox rollers with 60-degree hexagonal or "open cell" geometries can reduce air entrapment under the blade, preventing the buildup of hydrodynamic pressure which is the primary driver of ink spitting. Proper maintenance of the blade chamber is also essential to ensure consistent results.

Consultant's Note

Technical consultants believe that Ink Spitting should not be viewed merely as a mechanical failure but as a challenge related to ink rheology. At high speeds, ink must be able to exit and re-enter the cells rapidly. Any mismatch between Anilox Volume and the ink's surface tension can trap air in the cells, increasing pressure behind the blade. Utilizing "anti-spitting" blades, which feature vibration-resistant edges, is a smart strategy for maintaining quality at speeds exceeding 400 meters per minute.

Remember that continuous monitoring of ink temperature is vital, as temperature changes directly affect viscosity and the ink's tendency to spit. For high-sensitivity projects, it is recommended to use anilox rollers with advanced laser engravings (such as GTT or similar elongated patterns) that promote laminar flow across the surface. This approach not only eliminates the spitting defect but also stabilizes the TVI, ensuring color consistency throughout the entire run and reinforcing the client's confidence in the facility's technical expertise. Mastering this dynamic is key to high-performance flexographic production.

Packdemy Council Insight

Help us refine this definition. The Packdemy Expert Council welcomes new Advisors from the industry to contribute their specialized knowledge. Learn more about becoming an Advisor.