As we know, anilox plays a critical role in flexo printing process, especially the printing effect it results in.
This article will illustrate the most common solutions for anilox cleaning and maintenance. Currently, there are four types of cleaning: chemical cleaning, physical cleaning, chemical & physical combined cleaning, and laser cleaning.
1. Chemical cleaning
In most cases, anilox is cleaned by the ink washing system of the flexo printing machine. After clearing up the ink from the system, then add the cleaning agent and circulate the agent in the ink supplying system. In this way, the dry foreign substance in the anilox cells will be dissolved and cleaned thoroughly by circulating water.
The other way is to apply the anilox surface with acid and alkaline chemical solution. Usually it will take about 5 minutes to hours (subject to the corrosion degree of the chemical solution) to soften the foreign substance in the anilox cells. Then use the metal brush to clean it and wash it with water. The final step is to dry the anilox surface with compressed air.
Chemical cleaning is applicable to small size anilox or printing factories without anilox cleaner. The advantage of the chemical cleaning is the easy operation and low cost, but it cannot achieve an even and thorough cleaning effect.
2. Physical cleaning
Physical cleaning is achieved by low pressure spraying. The cleaning agent particles can be sprayed onto anilox by air flow to clear the remaining ink in the anilox cells. By using second level negative pressure, the cleaning agent can be evenly sprayed with due fluidity. The required air pressure is 0.6 to 0.8Mpa, which is low enough for preventing anilox from damage.
Thanks to the closed cleaning head and dust recovery device, the cleaning by low pressure spraying can be done inline, especially applicable to the field of preprinting, coating, milk package. There are three types of physical cleaning based on different types of cleaning agent.
a. Saleratus powder (Sodium bicarbonate) spraying
Saleratus powder is a harmless particle, which is very easy to dissolve. As its hardness is lower than the anilox coating surface, the saleratus power is able to achieve very efficient cleaning without cause any damage to the anilox. Generally, 5kg saleratus powder is enough to clean an average width anilox. However, saleratus powder is not applicable to cleaning anilox which exceeds 600 LPI because the saleratus powder is bigger than the cells of anilox.
b. Carbon ice spraying
After the carbon ice particle or tube is put into the cleaning unit, the carbon ice particles (-78.5℃) will be sprayed onto the anilox surface by compressed air. The carbon ice will turn into air and expand hundreds times of its original size. The sudden expansion or explosion will flush the residuals and wash the anilox. However, carbon ice particles sometimes too big to enter the anilox cells. The sudden temperature rise may cause anilox ceramic layer crack. Therefore, the carbon ice spraying is not widely used.
c. Micro plastic particle spraying
Micro plastic particle is very soft and sprayed onto the anilox surface to clear remaining ink, pigment, without cause any damage to the anilox cells. Similar to saleratus power, it is not applicable to cleaning anilox which exceeds 600 LPI because the micro plastic particle is bigger than the cells of anilox.
3. Chemical & physical combined cleaning
The chemical & physical combined cleaning includes the high pressure water wash and ultrasonic wash.
a. High pressure water wash
The high pressure water wash is widely used by printing factory. In most cases, fresh ink remaining in the anilox surface or cells can be washed by water. For cleaning drying ink, it is recommended to use chemicals with water. The high pressure water wash requires 100 to 160Kg pressure and keeps washing for 25 minutes.
By using chemicals, the dry residuals can be softened and washed by high pressure water. Therefore, even small anilox cells can be washed thoroughly.
b. Ultrasonic wash
The principle of ultrasonic wash: residuals in anilox cells are softened by using chemical liquid. When ultrasonic starts working, it will produce micro bubbles. The explosion of each bubble accumulates force, which flush the residuals from anilox cells. It is with high requirements on chemicals for ultrasonic wash. Moreover, it requires certain range of power and frequency of ultrasonic.
When using ultrasonic washing, attention must be paid to the following:
Ultrasonic frequency: 40,000 Hz
Soaking temperature: 60℃ to 70℃chemical liquid
Soaking time: 30 to 60 minutes
Ultrasonic running time: 5 minutes
4. Laser cleaning
Laser cleaning is a drying wash free from chemical liquid. It requires correct setting on the laser focus, power, ink type, and rotation speed. Laser cleaning can achieve very good cleaning effect and apply to both inline and offline cleaning. Another advantage is that laser cleaning is able to clean anilox which exceed 1000 LPI. Despite of these advantages, laser cleaning is not widely used because of its high investment and high requirements on operation.
Hope this article is useful for our client and the people who are involved in flexo printing.