How to choose high-quality doctor blade to reduce printing failures?

How to choose high-quality doctor blade to reduce printing failures?

Doctor blade is an important factor in printing. Selecting a high-quality doctor blade can reduce or avoid many printing failures! The doctor blade can wipe the ink on the surface of the anilox roller more cleanly, keep the ink transfer volume of the anilox roller stable, and the printing accuracy will be improved.

The width of flexographic printing presses ranges from 200 mm to 4000 mm, and the printing speeds also range from 50 m / min to 600 m / min. The ink scraping pressure should be minimized during printing. The single-doctor blade system is generally used for printing machines with smaller door widths or slower machine speeds, and is generally a reverse single-doctor blade system. Wide format high speed printing presses generally use closed doctor blade systems. Generally, doctor blade blades with a thickness of 0.15 to 0.2 mm are used for flexo printing. Problems encountered during the use of flexo doctor blade blades, such as: dirty scraping, fast doctor blade wear, closed chamber leakage, ceramic layer scratches, etc.

These are all related to the selection, material, processing accuracy and installation method of the scraper.

Classification by doctor blade material:

Carbon steel doctor blade, high carbon steel material, hardness HV580, is the most common and common doctor blade.

Stainless steel doctor blade blade, stainless steel, hardness HV565, when it needs acid and alkali corrosion resistance, the cost is slightly higher.

Plastic doctor blade blade, polyester material, can reduce the problem of premature drying of ink caused by heat accumulation at the blade edge during high-speed operation.

Coated doctor blade blade, carbon steel doctor blade blade with special coating, high hardness, long life, suitable for large particle ink and long single printing, but of course the cost is relatively high.

Most of the doctor blades seen in the market are made of carbon steel, but the quality is different.

 

The steel on the left (the material of our doctor blade) is significantly better than the right (the material commonly used in the market) because its metallographic structure and carbide distribution are relatively uniform, the carbide particles are small, the chemical composition is relatively pure, and impurities less. In terms of scraping effect, the scraping blade of the steel on the left will wear slowly and evenly.

Therefore, the same are doctor blade blades, but the price can be quite different, mainly reflected in the material. Some products have low prices, but the ink scraping effect is uneven, unstable and prone to failure, which may not be the ideal choice.

According to the shape of the knife edge:

The doctor blade is not a steel strip directly, but a knife edge will be ground on the end surface of the doctor blade. With the evolution of technology, different knife edge shapes have also been developed. Different knife-edge shapes have different characteristics, which are also introduced by the way.

Round knife edge is to grind the knife edge into a circle. Its advantages are very durable, but its disadvantages are that the ink-scraping effect is normal, and it enters the working state slowly, and it can only be used for printing with normal quality and usually low line count.

 

Thin blade, the blade is ground thinner, but the thickness of the blade is uniform. The blade is thinner, and the adhesion with the anilox roller is better, so the ink scraping effect is better, and the printing quality is better. In addition, it is more elastic under pressure when scraping ink, so it is more durable than oblique blade.

According to the shape of the knife edge:

The doctor blade is not a steel strip directly, but a knife edge will be ground on the end surface of the doctor blade. With the evolution of technology, different knife edge shapes have also been developed. Different knife-edge shapes have different characteristics, which are also introduced by the way.

Round knife edge is to grind the knife edge into a circle. Its advantages are very durable, but its disadvantages are that the ink-scraping effect is normal, and it enters the working state slowly, and it can only be used for printing with normal quality and usually low line count.

Thin blade, the blade is ground thinner, but the thickness of the blade is uniform. The blade is thinner, and the adhesion with the anilox roller is better, so the ink scraping effect is better, and the printing quality is better. In addition, it is more elastic under pressure when scraping ink, so it is more durable than oblique blade.

doctor blade specifications:

Width: 20/25/30/35/40 mm is commonly used for flexo printing. (The width of the doctor blade needs to be matched with the knife holder, so it cannot be changed at will)

Thickness: Common thickness for flexo printing is 0.15 / 0.2 mm.

Knife edge selection: The thinner the knife edge, the better the scraping effect, but the shorter the life; the thicker the knife edge, the worse the scraping effect, but the longer the life. Inclined blades are most commonly used. Round anvils can be used for low-line anilox rollers, and thin blades and wing-shaped blades can be used for high-line numbers.

Tips: The width of a thin blade is generally 1.3 to 2.86 mm; the thickness of a thin blade is usually 50% of the thickness of the blade; the fillet radius of a round blade is generally 50% of the thickness of the blade.

Therefore, the correct selection of the scraper material and the loading method is beneficial to the stability of the scraping effect and the service life of the scraper.

It is recommended to use a thin blade or a plastic scraper, which is helpful to avoid or reduce the chance of scratching the anilox roller.

 

For more product information about the scraper, please click the picture below to get: