The sharpness, pressure of the doctor blade, and the contact position with the cylinder all influence the quality of the finished print. Therefore, changing these influence factors according to requirements can solve many printing problems.
The sharpness of the doctor blade
The sharpness of the blade depends on the extent of wear of the blade, sandpaper type and the angle of the blade when sharpening it.
A doctor blade with reasonable sharpness can remove excess ink efficiently and reduce ink streaks. Besides, an overly sharp blade will increase cylinder wear and ink streaks.
The distance between blade and cylinder
Small distances between the blade and cylinder can help remove excess ink, but also will result in hazing. On the contrary, large distance can reduce the hazing and ink streaks, but will decrease the efficiency of removing ink.
The evenness of blade
The evenness of doctor blade depends on the installation method. The granules in the doctor blade holder or on the blade and top plate also will influence the evenness of the blade.
A doctor blade with low evenness will cause some dots and streaks in the edge of the print.
The pressure of between blade and cylinder
The pressure between the blade and cylinder depends on the cylinder pressure, hardness of the blade and the contact angle of the blade-cylinder. Besides, the larger contact angle, the higher pressure. Excessive pressure will decrease the efficiency of removing ink, increasing the wear of the blade and cylinder, and low pressure can cause hazing and ink streaks.
The shift of blade
The left and right shift of blade can reduce ink streaks and cylinder wear, increasing the efficiency of removing ink. If the shift is abnormal, adjustment is necessary. Ink streaks may result from cylinder wear and blunt blade. Foreign materials sticking to the blade also will cause the problem. You can move the blade back and forth, up and down in order to throw them away. If it is useless, you must stop the printing press to clean the doctor blade.