Teach you how to prevent UV ink splashes

Sonia Arcos, head of sales at Cheshire Anilox Technology, believes that good management and the right choice of anilox rolls are key to preventing ink splashes.

UV inks have many advantages, such as clearer printing and richer colors, making UV inks the ink of choice for most narrow-format printers. However, a condition commonly referred to as "splashing" occurs only when UV inks are used, which has become a major problem that plagues many printing operators.

"Splashing" means that the ink is randomly spilled on the substrate. This may be caused by the excessive squeegee pressure causing the squeegee to lift, causing the UV ink to be scraped off and spilled onto the substrate.

Splashing ink is a peculiar phenomenon of UV inks, while aqueous inks and solvent-based inks have never encountered such problems. But what is the cause of UV ink splashing? Although scientists have conducted a lot of research in recent years, there is still no unified conclusion. One of the reasons may be due to the higher viscosity of the UV ink, which is typically 5-7 times more viscous than the aqueous and solvent based inks. A higher viscosity exerts more pressure on the doctor blade, causing the doctor blade to lift.

Another reason is the thixotropy of UV inks. The viscosity of the UV ink drops when subjected to external force agitation, and when the ink comes into contact with the doctor blade, this external force is applied to the ink. The sudden decrease in viscosity of the ink when it comes into contact with the doctor blade causes it to pass directly under the blade, eventually causing problems with the ink splash. Understanding the various possible causes of splashing will help us find an effective way to solve this huge waste problem.

The main reasons for UV ink splashing are:
Higher ink viscosity (1000-1900 cp);
Printing speed is greater than 100 m / min;
Scraper material, blade shape and thickness;
The solvent of the anilox roll and the shape of the engraved cells.

Changing the viscosity of the ink and reducing the printing speed may not be a very appropriate commercial choice, but changing the doctor blade and anilox roller is a relatively effective method for controlling the problem of splashing.

Squeegee

Main considerations: angle and pressure

The range of the squeegee recommended for flexographic printing is generally 25 degrees - 40 degrees, and the optimum angle is about 30 degrees. A contact angle of less than 30 degrees will result in a poor film-hanging effect, which will leave ink on the surface of the anilox roll, causing problems with splashing. For UV inks, to minimize the problem of splashing, the contact angle should be at least 30 degrees or higher because the larger contact angle has a higher bending resistance.

If too much pressure is applied to the blade, the contact angle will be flat, causing the blade to leave the surface of the anilox roll. This causes the ink in the corresponding part to be unsuccessfully scraped off, and the ink is transferred from the anilox roll to the printing plate, which is transferred to the printing material, resulting in a problem of ink splashing.

thickness

The default principle in flexographic printing is to use the thinnest squeegee as possible while ensuring a uniform and stable squeegee effect. If the viscosity of the ink is high, it is usually necessary to choose a thicker blade because the thicker blade has a stronger bending resistance and can reduce the problem of splashing. However, the use of thick blades in printing can degrade the print quality, and thick blades can cause thicker ink layers, which will affect the accuracy and clarity of the printed image.

A new type of doctor blade solves this problem. The thick base of the blade reduces the degree of bending of the blade and ensures high-quality squeegee. The blade base has a higher hardness, which ensures a more stable blade, which not only ensures the effect of squeegee, but also withstands the pressure of a larger UV ink. The blade has better resistance to bending, which can reduce the occurrence of splashing.

material

The newly developed resin blade can solve the problem of ink splashing of UV ink from another aspect - the surface energy of the material. This new resin blade has a lower surface energy than a metal blade, helping to reduce the attractive force between the blade and the ink, thereby reducing the build-up of ink behind the blade. Because the accumulated ink will lift the blade, causing the ink to be incomplete and splashing.