Affecting The Printing From Doctor Blade on Flexographic Printing Machine

From the perspective of printing principle, the function of doctor blade is to remove excess ink on the surface of anilox roller and transfer the ink in the mesh of anilox roller to the printing plate. If the doctor blade does not remove the excess ink on the surface of anilox roller, the excess ink will be transferred to the printing plate along with the anilox roller, resulting in printing defects such as increased dots and excessive printing color density.

1. Doctor blade width

Poor doctor blade scraping quality will lead to increased printing defects, ink waste and reduced production efficiency. Therefore, in order to adjust the scraping quality to the best state, the selection of doctor blade width is particularly important.

If a doctor blade with non-compliant width is used, it may cause a change in the contact angle with the anilox roller. Practical experience shows that wider blades tend to produce flatter contact angles, and narrower blades tend to produce sharper angles. Both situations will cause a decrease in scraping quality. In addition, a blade that is too thin will easily cause doctor blade deflection due to factors such as excessive printing speed and excessive ink viscosity, thereby affecting the scraping quality.

2. Doctor blade edge shape

The doctor blade edge shape will also affect the scraping quality. At present, the common doctor blades have three edge shapes: round head, oblique head and square head. The edge shape of the round doctor blade is arc-shaped, which is generally suitable for printed products with low ink viscosity and low printing precision requirements. Square head and oblique head scrapers are widely used and are the best choice for printing high-definition products.

In addition, factors such as excessive pressure applied by the doctor blade, blade misalignment, damaged or dirty knife holders, and mismatch between blade length and equipment will also cause the scraping quality of flexographic printing machines to decline. Therefore, communicate with the doctor blade supplier in advance and comprehensively consider various data to select the doctor blade that best suits the existing equipment.

3. Doctor blade material

In the development of flexographic printing, carbon steel material is the most widely used material for doctor blades, and it is still the case today. Carbon steel doctor blades are the most economical and affordable choice for printing and processing of small batch orders and some non-abrasive product applications.

Ideally, label printing companies hope that the doctor blade can continuously complete the printing production of the entire order without any downtime maintenance or even suspension of production caused by the scraper. However, if the carbon steel doctor blade is used for long-run printing, it will inevitably stop and change the blade during printing. Therefore, considering the impact of the doctor blade material on the service life, the doctor blade made of plastic material can ensure its good service life. Since the metal doctor blade will rust after long-term use, adding a coating to the tip of the metal doctor blade can also extend the service life of the doctor blade, thereby improving the quality of doctor blade scraping.

4. Doctor blade performance

In the printing process, poor scraping quality is usually associated with "blade wear", and frequent blade replacement or reduced blade life is considered to be the main reason affecting production. However, when we carefully observe and analyze the used blades, we will find that the wear on the blades is actually very small, and sometimes no wear is found. So what is the problem?

There may be many reasons why the performance of the doctor blade is not as expected. In the final analysis, it is necessary to communicate and cooperate with the doctor blade supplier to determine the specific reasons. Sometimes, the doctor blade we choose is not suitable for existing equipment. In this case, the doctor blade supplier needs to provide a blade analysis report. Detailed data is an important judgment tool to determine the doctor blade settings and achieve its expected performance.

5. Ink Corrosivity

Some special inks are more abrasive than other inks, which will also have a certain impact on the doctor blade's scraping quality. It is well known that white, metallic and pearlescent inks are more wear-prone to doctor blades. If abrasive inks are used on one unit and ordinary inks are used on the remaining units, it is recommended to use doctor blades with longer service life on the unit using abrasive inks and lower-cost blades on other units. In this ideal situation, the service life of all doctor blades is balanced, so that the entire process of printing production can continue, the time for downtime to replace blades is reduced, and the doctor blade scraping quality is improved while maximizing production efficiency.