Phenomenon and Causes:

Ink stripping refers to the phenomenon where ink does not rotate with the ink fountain and separates from the fountain axis, resulting in the inability of the ink transfer rollers and metering rollers to pick up ink. This phenomenon affects the normal ink transfer on the rollers, causing the printing plates to receive insufficient ink and leading to inconsistencies in the ink color of the printed products.

Common causes of ink stripping include:

1．Insufficient oil content in the ink and low viscosity, causing the ink to fail to move with the rotation of the fountain axis, which leads to stripping.

2．Poor ink fluidity, making it difficult for the ink to flow between the ink knife shaft and the blade, affecting the ink transfer and causing stripping.

3．The ink being in a gelled or frozen state, which reduces its viscosity and fluidity, resulting in a loss of printing performance and subsequently causing stripping.

4．Too little oil content and excessive powder in the ink, preventing effective transfer of pigment particles and causing the ink to remain in the fountain, leading to stripping.

5．Rapid drying of the ink, which causes the fountain axis to solidify, losing its ink transfer capabilities and blocking the gap between the fountain roller and the blade, resulting in stripping.

6．Excessive impurities such as ink skin and residues in the ink, which clog the gap between the fountain and the blade, affecting ink transfer and causing stripping.

7．The acidity of the fountain solution being too high or excessive use of gum arabic.

Solutions:

1．If ink problems lead to roller stripping, this is more common with black inks. Inks made from soot have high oil content and are less likely to strip. In contrast, black inks made from carbon powder have poor oil content and may occasionally experience stripping. Thinning the ink with diluted ink oil can help; if the product image has strong contrast and cannot be diluted, adding a small amount of oleic acid to the ink may resolve the issue.

2．If the ink viscosity is too low, often seen in light inks mixed with thinning agents, these inks can easily emulsify. Acidic liquids from the fountain may penetrate the ink, corroding the surface of the ink rollers and causing the rollers to develop a hydrophilic layer, leading to ink stripping. Adding concentrated ink oil to the ink can help increase viscosity.

3．When ink roller stripping occurs, efforts should be made to reduce moisture on the plates and lower the acidity of the fountain solution, as well as removing the gum arabic solution.

4．If the ink is too thick or hard, adding ink oil No. 6 can help increase its fluidity.

5．Regularly stir the ink fountain and remove ink skins and impurities to prevent ink from drying or gelling, thereby avoiding stripping phenomena.