Squeegee system for flexographic printing: double rubber roller system? Squeegee chamber system?
Like other printing methods, the process of flexographic printing is the process of transferring ink to the printed material. The development of flexographic printing can be said to challenge the ability to stably transfer thin layers of ink.
In the early stage of development, limited by the thicker printing ink layer, this printing method can only be used on thicker screens. Larger area and high quality printing can only be achieved by lithographic or gravure printing.
As the corrugated box industry and flexographic printing and packaging industry have increasing printing quality requirements, flexographic printing machinery manufacturers strive to find improved methods to control ink thickness, so scrapers are developed to scrape off excess ink on anilox rollers, which makes printing The anilox roller on the machine can control and transfer the set amount of ink according to the design requirements.
Through the continuous evolution of the doctor ink system and the drawdown blade chamber system, today's flexographic printing technology has developed to a high level, competing with other printing methods in terms of printing quality.
There are two types of doctoring systems currently used in the corrugated box industry: double rubber roller system and drawdown blade chamber system, both of which rely on the anilox roller as the basic component to transfer the accurate amount of ink to the printing plate, but The difference lies in how the ink is transferred to the anilox roll.
Double rubber roller system
The original double rubber roller system is still used today, it consists of four basic components: a rubber ink tank Fountain Roll, an anilox roll Anilox Roll, a printing plate cylinder Plate Cylinder, and an impression cylinder Impression Cylinder.
The rubber ink cartridge is partially submerged in the open ink fountain pan. When rotating, the ink is absorbed and transferred to the anilox roller, which then transfers the ink to the printing plate roller, and finally transfers the ink to the cardboard. The other end of the cardboard has Imprint cylinder.
Due to the lack of control over the amount of stored ink during the transfer process, the rubber ink cartridge cannot precisely scrape off the excess ink on the anilox roller, leaving an extra layer of ink on the anilox roller, which affects the anilox roller The accuracy of the originally designed ink transfer, the instability of the amount of ink transfer will produce unpredictable printed images and poor printing results.
As the speed of the printing machine increases, the generated hydraulic pressure will push the rubber ink cylinder and the anilox roller apart, causing the anilox roller to deviate from the rubber ink cylinder and skew, thereby affecting the color intensity on the cardboard. At this time, the operator needs to adjust the printing machine The speed is used to adjust the color intensity, and this adjustment process has caused a lot of waste of cardboard.
The transfer performance of the double rubber roller system will be affected by the hardness of the rubber ink cartridge. Soft rubber can hold more ink than harder rubber cartridges, and the hardness of each rubber ink cartridge can vary. The hardness also increases as the rubber ages, which also means that the printing press needs to be constantly adjusted.
In the production process of the double rubber roller system, there are many sensitive factors that need to be adjusted, such as the adjustment of the contact pressure between the rollers, the chemical composition of the open ink bucket, Amine is easy to volatilize, which affects the viscosity of the ink and the sliding force of the liquid surface, And factors such as factory dust falling into the ink bucket tray.
Contra-angle single scraper system
With the evolution of the flexographic printing system, a drawdown blade is added to the contra-angle single drawdown blade system, bringing important reforms to the traditional double rubber roller system.
In this single-squeegee system, a steel, plastic, or composite scraper is mounted on a fixture to remove excess ink from the anilox roll, resulting in better control of ink thickness on the press , making the ink carried on the anilox roller more accurate. Even at high speeds, the color intensity on the board remains stable and ink consumption is reduced.
The semi-closed single scraper system design also protects the amine components in the ink from volatilization, and it is more difficult for dust to mix into the ink fountain.
Closed scraper chamber system
The closed drawdown blade chamber system is a new flexo printing system, which uses an anilox roll, a plate cylinder plate cylinder, and an impression cylinder impression cylinder, and uses two drawdown blades to separate the drawdown blade chamber The ink on the screen is distributed to the anilox roller. Usually the two scrapers are separated by about two inches, a contra-angle scraper is used to scrape off excess ink on the anilox roller, and the other sealing knife is used to block the ink from remaining in the scraper cavity.
The two ends of the closed scraper chamber are sealed with foam, rubber or wool felt to seal the ink in the scraper chamber to prevent leakage. The ink in the closed drawdown blade chamber system is conveyed by the ink pump to the drawdown blade chamber through a closed circuit, and then back to the ink pump.
A tray needs to be placed under the anilox roll to collect ink spills and to collect liquid for cleaning the press at the end of the job.
Advantages of the scraper chamber system
print quality
The significant advantage of the scraper chamber system is that the printing machine can more stably control the amount of ink delivered to the printing plate during the ink delivery process.
Compared with the double rubber roller system, it is easy to leave excess ink layer on the anilox roller, the scraper chamber system can scrape off the ink on the anilox roller more cleanly, so that the printing machine can obtain a consistent ink thickness before and after, and present a better printing effect.
The closed scraper chamber system can reduce the volatilization of amine in ink and maintain the stability of ink viscosity.
job cost
A good ink control system can reduce ink consumption by about 15% a year. A closed doctor chamber system requires less ink than an open two-roller ink pan, and after each press stop, residual ink can be collected for reuse.
The cleaning process of the closed scraper chamber is extremely effective, less cleaning agent reduces unnecessary cleaning costs, faster and easier cleaning process, faster color change time of the printing press means more printing press running time. If an automatic cleaning system can be installed, the efficiency can be further improved and the operating cost can be reduced.
Basically, the annual maintenance cost of the scraper chamber system is lower than that of a double rubber roller system. The wear and replacement of rubber rollers, the repair of rubber rollers and the replacement of bearings are all a considerable expense. If you add the idle time and transportation costs when changing the rubber rollers, as well as the high consumption cost of the ink, these costs will make the cost of the double rubber roller system significantly higher than that of the doctor chamber system.
environmental factors
In the reduction of ink consumption and the treatment of waste ink, the drawdown blade chamber system is obviously more environmentally friendly than the double rubber roller system. In addition, less cleaning solvent and water are required when changing colors.
in conclusion
The long-term operating cost of a printing machine equipped with a scraper chamber system is much lower than that of a double rubber roller system. Whether it is a single scraper system or a closed scraper chamber system, the printing quality, operating efficiency, As well as environmental considerations, it has more advantages and productivity than the conditions of the double rubber roller system.
