Daetwyler’s Sarkar demystifies doctor blade for narrow-web flexo

Sarkar initiated the presentation by citing the challenges faced by doctor blade manufacturers.

Sarkar said, “We as a manufacturer come across various bottlenecks due to the wide range of varying parameters in use in the industry. Today, there are variety of ink systems available, ranging from low and high viscosity inks and varnishes, abrasive inks, acidic or alkaline inks etc. Also, the different cell geometries on anilox rollers, roller surface finishes etc have been posing challenges for us.”

According to Sarkar, when a doctor blade comes in contact with the anilox roller it is acted upon by several physical forces and undergoes chemical reactions. “The physical forces include hydraulic force, transverse force, the frictional force and the normal force and this generates pressure on the blade. Also, the nature of inks, whether acidic or alkaline, leads to rusting and etching of steel thereby damaging the coating and finish of the doctor blade.

In his presentation, Sarkar stressed upon the doctor blade setting and importance of blade alignment with the roller. At high pressure the doctor blade  traps the contaminants of inks. “These ink contaminants may cause score lines on the anilox roller leading to wear and tear of anilox cell walls,” added Sarkar.

The excessive pressure on doctor blade may cause deformation. “This leads to accumulation of burr between the doctor blade and the roller causing scoring lines to appear on the roller and thereby causing ink spitting on the image,” informed Sarkar.

According to Sarkar, selecting a right doctor blade angle can eliminate all these issues. Sarkar said, “The doctor blade should make an angle of 30degrees with the roller surface for smooth performance.”

Sarkar summarised the functions of doctor blade for label production. He said, “It constantly doctors the anilox roller along the width and circumference with minimum pressure during the entire run and efficient doctoring of cell walls of anilox roller. The doctor blades ensures accurate filling of the cells without squeezing out ink from the cells. It increases the life of anilox roller and reduces all kinds of printing problems during production run and wastage.”

In his concluding comments, Sarkar said, “The new generation doctor blades are highly engineered products. In future, the doctor blade will help to adapt the changes in printing value chain.”