Doctor blade hardness is lower than the chromium cladding of the cylinder hardness
High hardness of the blade will accelerate cylinder wear and cause ink streaks or lines. Low durability of blade also will cause the doctor blade to wear and fail to remove excess ink completely and result in ink streaks. If so, changing the doctor blade is inevitable.
Gap of doctor blade edge
The gap of the doctor blade will cause regular ink streaks in prints. The type of ink streak can be recognized easily and if the gap is small, you can grind the doctor blade using sandpaper or oilstone to make the edge smooth.
If the gap is large, changing the doctor blade is inevitable. Before changing, clean the ink in the groove and top plate to ensure the evenness of doctor blade and the length of the blade exposed to air should be 5mm.
During printing, some doctor blades need time before achieving the best removal effect. At that time, you can grind the doctor blade by using metallographic sandpaper in order to get better effect and improve efficiency.
The evenness of doctor blade
The low evenness will cause ink streaks. So the good evenness is necessary during installation in order to make blade have uniform pressure.
The pressure and angle also will influence the appearance of ink streaks. In printing, change the angle and pressure of blade according to ink removing extent and printing situation in order to get better effect and reduce ink streaks.
Doctor blade made of high density material and with suitable hardness is most appropriate. During operation, using doctor blade with suitable angle and pressure can get better effect and reduce the wear of blade and cylinder, improve the lifespan of doctor blade and cylinder, reduce ink streaks.
In printing, we usually use solvent to change the viscosity and humidity of the ink. And solvents which have high volatile velocity and can dissolve a wide range of compounds are suitable, such as isopropanol and acetic ether.
Different inks should be dissolved in different solvents. Wrong solvents which can’t dissolve ink completely may make ink stick to doctor blade and cause ink streaks. The type of ink streaks are lines without ink and appear sometimes.
This ink streaks usually appear when ink is made of metal granules. Bronze ink is made of bronze powder, oil and solvent. Because bronze power has high density and is easy to precipitate, if solvent can’t dissolve bronze ink completely and the stirring is not sufficient, the bronze granules will gather together because of the uneven distribution. Besides, when ink gathers in the edge of the blade, thick streaks without ink will appear. This streaks will disappear after appearing for a period of time, and then form again, which seriously effects the quality of prints and is difficult to remove. So we need dissolve the ink with a suitable solvent and stir it to dissolve it completely, in order to resolve the problem before printing. During printing, maintaining good circulation of the ink is also important.