Anilox roller cleaning principle and method

With the continuous development of our country's flexographic technology, the cleaning of the anilox roller, the key component of flexographic printing, becomes more and more important.
The amount of ink transferred by the anilox roller will directly affect the printing quality. Many printing companies do not know much about the ink transfer performance of the anilox roller, neglecting the cleaning work of the anilox roller and causing the printing quality to decline, but they cannot find it. The specific reason. In fact, many of the reasons for the decrease in printing quality are caused by the clogging of the anilox roller and the decrease in ink transfer performance. Therefore, this article focuses on the cleaning principles and cleaning methods of several anilox rollers.
The following are the four currently used cleaning methods.
First, the chemical cleaning method Chemical cleaning method is the key to the use of corrosive cleaning agents, the use of smearing, drip, or high-pressure spray, soaking, etc., so that the anilox roller on the dissolved material. The principle is to first soften the stockpiles, and then use high-pressure water to clean the anilox roll. The chemical liquids used in this method are generally strongly alkaline. PH values ​​above 12 and permeability are also strong. Anilox rolls above 1000 lines per inch can also penetrate into the bottom of the cell.
The most common use of Europe in the 1970s and 1980s was chemical cleaning. The washing machine is a closed container, the anilox roll is placed in a container, and a chemical cleaning agent is added to soak the 1/2 to 2/3 of the anilox roll, and then the cleaning agent is heated to 40-60. °C. The anilox roll rotates in a dense container for about 2 hours in a rotating manner to achieve the effect of softening the deposit and infiltrating the interior of the cell. Afterwards, the rotating anilox roll is sprayed with high-pressure water to remove the cleaning liquid and the dissolved residue. Finally, the entire cleaning process is completed by drying with high-pressure gas.
Although this method can achieve the purpose of cleaning the impurities in the anilox roller net, it will not damage the net hole. However, for some advanced deep hole type anilox rollers, the softened ink residue and debris are under the effect of washing. Can not be discharged in time, will result in repeated accumulation of the phenomenon.
The biggest drawback of the chemical cleaning method is that the discharge of the cleaning solution causes environmental pollution. Entering the 1990s, environmental regulations in Europe, the United States, Canada, and Australia have explicitly prohibited the discharge of highly alkaline liquids.
Daily cleaning with a small amount of cleaning solution is possible, but for deep cleaning of the anilox roller, chemical cleaning methods are not the best choice. Therefore, this article only describes the principles and methods of chemical cleaning, and does not recommend carton factory.
Second, the physical cleaning method The principle of physical cleaning method is to use the pressure of compressed air to promote the cleaning medium, and collide with the accumulations in the cell to achieve the purpose of cleaning the interior of the cell.
1. Physical cleaning method requirements (1) The cleaning medium must be softer than the roll body material so as not to damage the cells.
(2) Advancing the pressure of air must be sufficient to clear the stolen goods in the net without damaging the net.
(3) The nozzle must be positioned at an optimal distance from the roll body so that the medium it ejects forms a scattering surface and is evenly sprayed on the roll, rather than being concentrated on one point, because concentrating on one point will damage the mesh edge.
(4) The cleaning medium must be tiny particles so that it can directly impact the bottom of the cell.
(5) The correct choice of spray angle is an important condition for ensuring work efficiency and cleaning quality. The wrong choice of spray angle will not only result in lower work efficiency, unclean cleaning, and even damage the wall of the cell. The author recommends using an injection angle of 14° with the horizontal line of rotation, as shown in Figure 1.

(6) The nozzle movement speed should be about 100mm/min. Of course, the speed of the roller body, the scattering angle of the nozzle, and the ejection area should be taken into consideration when selecting this speed. The cleaning speed of 100mm/min is only recommended in this article and is for reference only.
(7) The sprayed cleaning medium must be evenly and evenly sprayed onto the roll body. This is very important. If the cleaning medium cannot be uniformly sprayed onto the roll, it will be ejected in a mass, which will not only cause a decrease in cleaning quality, but also Can cause damage to the wall of the cell.
2. The choice of injection form Currently, there are two types of injections in the world: positive pressure and negative pressure.
(1) The positive-pressure injection method is to install the cleaning medium in a sealed container and use the pressure of the compressed air (1 to 1.2 MPa) to spray the cleaning medium onto the roller body for cleaning. The advantage of this method is that the injection surface is large. The disadvantage is that the dispersion of the sprayed medium is uneven and intermittent phenomena occur. Moreover, the injection pressure is too large to control and it is easy to damage the wall of the cell wall. In addition, the gas volume is also relatively large. Need more than 1.2m3/min of air flow, the United States in the 1960s more than this method.
(2) Negative Pressure Propulsion The so-called negative pressure propulsion is to use the principle of shooting flow (Figure 2):

When the compressed air enters the ejector, a vacuum is generated in the chamber B, and the cleaning medium is sucked into the a tube under the action of the atmospheric pressure so as to be ejected from the ejector C under the urging of the compressed air. Most countries in Europe and America now use this type of cleaning.
The advantage of this method is that the pressure of the compressed air is relatively low (0.6-0.8 MPa), which basically does not cause damage to the anilox roll; the gas consumption is also economical, being only 0.8 m3/min.
The disadvantage is that since the cleaning medium in the B-cavity is layered, under the influence of a single atmospheric pressure, the dispersed medium is not evenly dispersed, and intermittent phenomena sometimes occur; in addition, the distance for advancing the medium is short. , It is generally valid in the range of 2 ~ 3m.
(3) Two-stage negative pressure and forced hybrid propulsion This method of propulsion is a patent of our country. The injection principle is shown in Figure 3:
When the compressed air H enters the primary jet element A, a vacuum is formed in the B cavity and the B1 tube, the cleaning medium in the hopper is sucked into the B cavity and the B1 tube, and then enters the B2 tube. At this time, the compressed air passes through the G port again into the secondary jet. In the element C, a higher negative pressure zone is formed in the B2 tube than in the primary jet element A, so that the mixture of the cleaning medium and the air flowing into the B2 tube is evenly sprayed through the nozzle P onto the anilox roller to be cleaned.
Since the first-stage jet element A causes the negative pressure generated in the B-cavity to form in the form of natural convection at atmospheric pressure, a phenomenon such as accumulation of the cleaning medium and insufficient gas pressure occurs. Therefore, the second-stage negative pressure, forced-mixing type cleaning apparatus increases. The inlet of the compressed air F is required to generate strong convection in the cavity B, so that the cleaning medium and the air in the cavity B form a mixture to increase the fluidity of the cleaning medium and achieve the best cleaning effect.
This cleaning method is currently the world's most advanced cleaning method. Its cleaning equipment is only produced in China. It is a patented product in China and is the first cleaning method in this article.
The advantages of this cleaning method are: evenness of scattering surface; uniform distribution of sprayed medium; low pressure (0.4~0.6 MPa), safe pressure, no damage to the anilox roller body; low gas consumption, 0.8m3 /min is sufficient; the amount of spray medium can be tuned by adjusting the air flow rate of the compressed air F; the conveying distance can reach 10-15m; the requirement for the cleaning medium is not high and can be used for any medium.
The disadvantage is that it requires a lot of experience in adjusting the air pressure and air flow in various parts.
The point of the secondary negative pressure, forced hybrid propulsion system is the ratio of the compressed air G to the compressed air H and the flow rate for producing the forced mixed gas compressed air F. The recommended air flow ratio in this paper is:
G:H = 4:1 to 7:1 (at the same pressure)
H:F = 5:1 to 8:1 (at the same pressure, tuned according to the needs of the medium to be advanced)
3. Selection of Cleaning Medium (1) Sodium Bicarbonate (Soda Powder)
Sodium bicarbonate is a kind of powdery cleaning medium with special formula. Its main features are:
1) The nature is very mild, and there are a variety of particles to choose from, suitable for cleaning a variety of tiny cell points.
2) It is non-toxic and non-hazardous, and it can clean the net points quickly and effectively.
3) The air pressure used is only 0.4 MPA.
4) It is not easy to damage the roll body. Specially treated sodium bicarbonate cleaning medium is used by more than 80% of the world's manufacturers, and more than 65% of China's cleaning equipment uses sodium bicarbonate as a cleaning medium.
(2) Plastic beads This is a kind of plastic beads specially made of PCE material. When the soft and sharp protrusion of the beads impacts the anilox roller, it will deform and be bounced out. In this process, the accumulations in the cells are carried away by beads, thus cleaning.
The advantage of using plastic beads as a cleaning medium is that it can be reused (by separating the ink and other debris from the beads with a pressure cleaning method, and separating the iron scraps with a magnetic block so that they can be reused), which is safe and reliable. low cost.
The method of cleaning the anilox roller with plastic beads is rising in Europe and the United States. At present, China is also researching and producing such plastic beads.
(3) Dry ice medium Dry ice medium is a solid dry ice bead made of liquid carbon dioxide. When it is an anilox roller cleaning medium, an air pressure of 0.8 to 1.2 MPa is required to achieve the purpose of cleaning the net hole. However, the diameter of dry ice beads is generally around 1mm, and it is not possible to clean the bottom of the net properly. Therefore, in many European countries, a set of crushed dry ice is often added to make it smaller. Microparticle device.
The advantage of using dry ice pellets as a cleaning medium is that it will not pollute the environment; it will not produce any waste.
The disadvantage is that it cannot be used to clean anilox rollers with a high number of screens; the medium has a short shelf life.
Into the 1990s, the dry ice media used to clean the anilox roll has basically been eliminated.
Third, the ultra-field wave cleaning method Ultrasonic wave cleaning method is the use of ultrasonic vibration frequency cleaning, the principle is to be cleaned anilox roller completely immersed in the liquid, and then use the mechanical way to produce a large number of liquid particles in the bubble , Under the influence of ultrasonic vibration frequency, make the bubbles inside the liquid pressure, when these bubbles approach the surface of the anilox roller, the pressure inside the bubble, the frequency of the ultrasonic wave in the liquid and the frequency of the vibration of the roller body under the influence of the ultrasonic wave Under the influence of the difference, the air bubbles close to the surface of the anilox roller will burst by themselves, and the strong vibration and flushing force generated at this time can clean the foreign matter inside the cell cavity. Due to this vibration and the continuous rotation of the roller body, the microbubbles in the liquid continuously come close to the roller body, continuously generating bursts and vibrations, and continuously impacting the roller body and the ink hidden in the depth of the cell space under the action of the ultrasonic wave. Slag, so that the ink residue in the cell hole is constantly shaken off, so as to achieve the purpose of cleaning.
The ultrasonic cleaning of the anilox roller is an effective method, but its effect has a great relationship with the operation level of the operator, the ultrasonic equipment and the depth of the cell wall.
1. Operation Ultrasonic cleaning requires high operator requirements and requires extensive experience. At present, most of the anilox roller ultrasonic cleaning devices in the world require pre-softening of the anilox roller before cleaning, which can effectively protect the cell site from damage and shorten the ultrasonic emission time by 80% to 90%.
The so-called softening treatment is to apply a special formulation of cleaning agent, a highly alkaline chemical agent on the surface of the anilox roller, remove the accumulation of the surface material, and soften the accumulation of material within the cell, and then ultrasonic cleaning. When cleaning the anilox roller, the control of the ultrasonic frequency and the length of the cleaning time requires the operator to have rich experience. The ultrasonic frequency and cleaning time recommended by the equipment manufacturer are not enough.
2. When ultrasonic equipment is selected for ultrasonic cleaning equipment, it is necessary to consider first