With the rapid rise of flexographic printing, printing companies are constantly increasing, and the competition for printing quality and price is becoming increasingly fierce. This forces printing companies to find ways to control costs and pursue higher quality. As the “heart” of flexographic printing machines – the anilox roller, its healthy operation is crucial for printing enterprises. A set of correct and reasonable cleaning and maintenance methods for the anilox roller can maximize the lifespan of the anilox roller and accurately transfer ink, improve the repeatability and stability of printing, and greatly save printing costs..
There are various cleaning methods for the anilox roller, and the cleaning effect is also controversial. This article will first analyze the principles and advantages and disadvantages of several commonly used cleaning methods for anilox rolls, in order to help everyone find a suitable cleaning method for themselves.
At present, there are four main cleaning methods for anilox rolls: chemical cleaning, physical cleaning, a combination of chemical and physical cleaning, and laser cleaning.
1、 Chemical cleaning method
The common chemical cleaning methods currently include manual cleaning with chemical solution and automatic cleaning systems for the equipment itself. Main principles of manual cleaning with chemical solution
Yes, apply chemical solution to the surface of the anilox roller to soften the residue inside the mesh, and then use a steel (copper) wire brush to clean the residue. Ceramic anilox rollers are brushed with steel wire, while metal anilox rollers are brushed with copper wire, moving in circles on the roller surface for better results. Liquid medicine manual cleaning is suitable for users with smaller mesh rollers or without cleaning equipment. It has the advantages of low cost, convenience, and the disadvantages of incomplete and uneven cleaning, which may have an impact on the operator’s health. It is recommended to wear goggles, protective gloves, and safety clothing.
Some equipment that installs an automatic cleaning system on the machine is also cleaned through chemical principles. The automatic cleaning system on the machine uses chemical solution to clean the anilox roller, ink chamber, and ink pipeline. A normal and complete ink cleaning system should be: ink supply – fast ink return – water supply – water return – cleaning solution supply – waste cleaning solution recovery – water supply – water return – next ink supply.
2、 Physical cleaning method
The physical cleaning method mainly refers to the low-pressure spray cleaning method. The low-pressure spray cleaning method uses air flow to blow small particles of the cleaning medium towards the anilox roller to remove residual ink in the mesh, and generally adopts a two-stage negative pressure pushing type. The two-stage negative pressure propulsion type can enhance the fluidity and uniform distribution of the cleaning medium, and the required air pressure is also lower (usually 0.6~0.8 MPa), ensuring that the cleaning medium does not damage the mesh and is safer to use. The spray cleaning method is divided into the following types according to the cleaning medium.
1. Spray washing method with baking soda powder
Baking soda powder is a soluble, safe, non-toxic, and harmless substance that is beneficial for environmental protection. The texture of baking soda (sodium bicarbonate) is better than that of mesh
The surface coating of the roller is much softer, with smaller particles that can enter the mesh, resulting in higher cleaning efficiency and ensuring the safety of the surface of the anilox roller. Baking soda powder cleaning is not suitable for mesh rollers with medium to high wire numbers above 600 LPI, as the mesh opening is small, making it difficult for baking soda powder particles to enter.
2. Dry ice spray washing method
The dry ice spray cleaning method involves loading pre made dry ice particles or blocks into the cleaning equipment. Driven by compressed air, the dry ice particles (-78.5 ℃) impact the surface of the anilox roller, causing the dirt to freeze to embrittlement and burst, and the solid C O2 rapidly sublimates into gas. Within a few thousandths of a second, the volume expands hundreds of times, causing a micro explosion at the impact point, crushing the dirt layer, thereby playing a cleaning role. However, due to the large size of dry ice particles, it is difficult to enter the mesh, and the rapid cooling of the roller base and the different shrinkage rates of the ceramic layer can lead to the risk of ceramic layer cracking. This method is rarely used on anilox rolls.
3. Plastic bead spray washing method
Plastic beads are usually specially made of polyethylene material and use a polyethylene plastic medium. The particles are very soft, but not ground, and have sharp edges
Edge. When it comes into contact with the anilox roller, it can remove residual ink residue, resin, paint, etc. from the mesh, achieving the goal of thorough cleaning without any damage to the surface of the ceramic anilox roller mesh. It is also not suitable for mesh rollers with medium to high wire numbers above 600 LPI, as the mesh opening is small and particles are difficult to enter.
The low-pressure spray cleaning equipment adopts a closed cleaning head and dust recovery device, and the entire cleaning process has no dust overflow, which can achieve large mesh patterns
The online cleaning of rollers on the machine brings great convenience to the cleaning of anilox rollers in corrugated printing or wide flexographic printing, while other cleaning methods are difficult to achieve direct cleaning of anilox rollers without dismantling them on the machine. The cleaning medium used for low-pressure spray cleaning, whether it is baking soda powder or plastic beads, is non-toxic and harmless, and will not pollute the surrounding environment. The safety of cleaning is very high.
3、 Combination of chemical and physical cleaning
The combination of chemical and physical cleaning methods mainly refers to high-pressure water flushing and ultrasonic cleaning.
1. High pressure water flushing method
The high-pressure water flushing method is currently widely recognized as a cleaning method for anilox rolls. The high-pressure water flushing method is not a simple physical concept
Cleaning often requires the use of alkaline chemical solutions together. For fresh ink on the roller surface and mesh, high-pressure water can be used to directly spray wash. But if the ink has dried up in the roller surface and mesh holes, directly spraying with high-pressure water does not have a significant effect. For anilox rolls with severe surface and mesh clogging, it is generally necessary to use specialized high-pressure water and be cleaned by a cleaning machine.
The high-pressure water mesh roller cleaning machine generally consists of two steps: medicine spray and high-pressure water spray. The previous step is to spray the surface of the anilox roller
Learning medicine to soften mesh residue belongs to the principle of chemistry. The time for spraying the medicine can be set based on the blockage of the mesh roller. After spraying the medicine for a period of time, high-pressure water is used to wash the softened mesh residue, which belongs to the physical principle. Due to the chemical solution being able to soften the dried residue of each mesh, high-pressure water can also spray and wash small mesh holes, which can clean high wire mesh rollers. This is not possible with low-pressure spray cleaning such as baking soda powder and dry ice. High pressure water spraying has high requirements for chemical solution. If non professional ordinary solution is used to spray and soften the mesh residue, its softening effect will be greatly reduced, which will affect the later stage__ The high-pressure water spraying effect is also the key to high-pressure water spraying.
2. Ultrasonic cleaning
Ultrasonic cleaning mainly uses chemical solution to soften the residual material in the mesh in advance, and then uses ultrasound to generate micro gas bubbles with pressure
The explosion generates strong shaking or scouring force, causing the residue at the bottom of the mesh to fall. Ultrasonic cleaning method not only has high requirements for chemical solution, but also
The power and frequency requirements of ultrasound are also very high. The effectiveness of ultrasonic cleaning is affected by the following factors and requires special attention.
(1) Ultrasonic intensity: It is best to refer to the ultrasonic intensity standard recommended by the cleaning equipment manufacturer.
(2) Ultrasonic frequency: The ultrasonic frequency is inversely proportional to the intensity of cavitation phenomenon. As the frequency increases, the bubbles become smaller and the cavitation intensity also decreases. In general, selecting bubbles generated with a minimum frequency of 40000 Hz is sufficient.
(3)Soaking temperature: It is generally better to maintain the temperature of the soaking solution at 60-70 ℃.
(4) Soaking time: Generally, it is advisable to soak the anilox roller in solution for 30-60 minutes.
(5) Chemical solution: The effect of chemical solution on softening the dried residue of the mesh roller and mesh directly determines the ultrasonic opening time and cleaning effect. The quality of chemical solutions varies, and choosing those that are cheap and of poor quality will directly reduce the cleaning effect. It is generally recommended to choose high-quality professional cleaning agents.
(6) Ultrasonic opening time: By understanding the principle of ultrasonic cleaning, one can understand the need to strictly control the opening time of the ultrasonic. If the opening time is too long, it may be
Directly leading to the fracture of the mesh wall and even the detachment of the ceramic layer and the bottom layer of the mesh roller. It is generally recommended to turn on the ultrasound for a duration of about 5 minutes. If the time is too short or too long, it may affect the cleaning effect and the service life of the anilox roller.
For sleeve type anilox rolls or aluminum based anilox rolls, ultrasonic cleaning is not recommended. The sleeve type anilox roller is made of various materials such as fiberglass, compressed foam layer, and aluminum base. Prolonged immersion in liquid medicine can damage the structure of the anilox roller. Aluminum based anilox rollers can also be affected by prolonged immersion and vibration in the solution, which can affect the bonding between the ceramic layer and the roller base, resulting in ceramic detachment and shortening the service life of the anilox roller.
4、 Laser cleaning method
In addition to the above mentioned methods, there is also one cleaning method for the anilox roller, which is laser cleaning. Laser cleaning using excitation with special optical devices
Clean the anilox roller with a light device. In the cleaning system, the laser is placed in the optical device to protect the surface of the ceramic anilox roller, but it can evaporate impurities such as residual ink on the anilox roller. It is a dry cleaning method that does not use any chemicals. If set correctly (laser focus, power, ink type, speed), the effect is good and suitable for offline and online cleaning. It is generally believed that laser cleaning can clean ceramic anilox rolls with a capacity of over 1000 liters per liter. However, due to the high cost of laser cleaning equipment and the high requirements for management and usage experience (poor settings can cause permanent damage such as ceramic surface cracks), coupled with the current low-priced high-pressure water spray cleaning, which can meet the requirements of high line number anilox roll cleaning, there are few users and laser cleaning is currently rarely used in China.
Cleaning Summary
Under normal circumstances, not only do we need to clean the anilox roller after stopping work every day, but we also need to perform periodic deep cleaning. Because daily manual and automatic cleaning on the machine cannot completely clean the mesh, the accumulation of residue at the bottom of the mesh is becoming increasingly serious, which will affect the efficiency and function of the mesh’s storage and ink transfer, and reduce the effective ink transfer amount of the mesh. Therefore, it is very important for each printing enterprise to develop a reasonable cleaning process based on the actual situation. Daily manual or on machine automatic cleaning system+daily cleaning solution; Use highly corrosive liquid medicine in emergency situations (wear protective equipment when using); Periodic deep cleaning can be done manually using deep cleaning solution, and if possible, cleaning equipment can be used to assist for better results.
Before we use chemical solution to clean the anilox roller, it is important to understand its composition. Usually there are alkaline sodium hydroxide and potassium hydroxide, acidic sulfuric acid and phosphoric acid. Sodium hydroxide cleaning solution reacts with aluminum to release hydrogen gas, which dissolves the aluminum base. Therefore, aluminum based anilox rollers are prohibited. Potassium hydroxide cleaning solution mainly utilizes its corrosiveness and reactivity to acids. Acidic cleaning solution is generally highly corrosive. When used in emergency response, it quickly corrodes and reduces the volume of the mesh. The fewer times it is used, the better. Cleaning personnel must wear complete equipment. The acceptable pH range for cleaning solution is 6.5-11.8.
When cleaning the sleeve anilox roller, protective end caps must be added at both ends to prevent cleaning solution from entering and corroding the internal composite materials, resulting in layered damage to the sleeve.
Precautions after cleaning the anilox roller:
1. Use clean and lint free fabric to absorb water stains on the roller surface, or use clean and dry compressed air to blow dry the roller surface. Due to long-term retention of water on the surface of the anilox roller, it is easy to corrode the anilox roller.
2. Reasonable storage:
a. A dry and ventilated indoor storage area that avoids direct sunlight makes the anilox roller less susceptible to damage from moisture and exposure to sunlight.
b. The sturdy and reasonable bracket and wooden box make access more secure, convenient, and fast.
c. The breathable and soft protective cover blocks dust and accidental scratches.
With the continuous expansion of the application range of anilox rolls, more users of anilox rolls will encounter problems in cleaning and maintenance of anilox rolls. Due to the special importance of anilox rollers in the printing and coating process, as well as the continuous improvement of industry requirements for printing and coating accuracy, the correct cleaning and maintenance of anilox rollers are becoming increasingly important.