Application of squeegee

Only when the following four functions of the squeegee are played well, can high-quality prints be printed. The physical properties of the scraper play a decisive role in the above functions. (For example: a squeegee with high hardness can scrape off excess ink well, but it cannot well meet the requirements of various substrate shapes). Therefore, when choosing a squeegee, the influence of the performance factors of the squeegee should be fully considered to avoid adverse effects on the printing effect. There are four factors to consider when choosing a squeegee with the right performance:

1. Hardness: The squeegee is usually made of polyurethane, and the hardness of the squeegee is measured with a durometer. The hardness, size and blade shape of the squeegee determine the squeegee's bendability, flexibility and pressure. Hardness ranges from 55 to 90 degrees (Shore A). Hardness values are measured with a Shore A durometer. 55A-65A is a low hardness squeegee, 66A-75A is a medium hardness, and more than 75A is a high hardness.

The high hardness squeegee is very beneficial to the first three functions of the squeegee, pressing the ink into the screen and transferring the ink from the fine screen to the substrate, and maintaining the line contact between the screen and the substrate. The only defect of high hardness squeegee is that it cannot meet the printing of different shapes of substrates, and the quality requirements of the squeegee are also very high when printing rough and uneven surfaces.

2. Effective width: It refers to the width of the squeegee extending from the aluminum squeegee handle when the squeegee is loaded into the aluminum squeegee handle. This width is important and determines how much the squeegee will bend under pressure. The curvature is the cubic value of the effective width. A curvature greater than 23 is obtained as twice the effective width.

The bending of the squeegee will cause two changes: the angle between the squeegee and the screen changes; the printing pressure transmitted to the substrate decreases. For example, the squeegee is compared to a set of springs. When the spring is stressed at a certain angle, the spring begins to bend, and the transmitted force becomes smaller and smaller. The squeegee printing angle is reduced, the printing pressure is insufficient, and the printing effect is not ideal. The printing angle is small, the printing pressure is reduced, the ink volume is large, and the ink layer is thickened. (In this case, the printing operator will increase the printing pressure, the curvature of the squeegee will increase, and the resulting ink layer is still not ideal. The solution is to increase the hardness of the squeegee and the angle of the squeegee.) This is the effectiveness of the squeegee The influence of width on the four functions of the squeegee.

Usually the effective width of the squeegee is between 20MM and 30MM. The selection of the optimum effective width is based on the flatness of the substrate, screen image resolution and other printing parameters such as squeegee angle, speed and ink type. When printing high-resolution images on flat/smooth substrates, the effective width is small (less than 20MM), high hardness, and fast printing with suitable inks. On uneven and rough substrates, the effective width should be increased (sometimes the size is 30MM), and the hardness should be reduced, while the low-hardness squeegee has poor adaptability and cannot be bent excessively. You can also use a three-layer squeegee or double-layer squeegee with a hard middle and a soft edge on both sides. layer scraping. Typically, as the effective width increases, the print speed decreases and the print angle increases.

3. Squeegee shape:

Squeegee shape refers to the cross section of the squeegee. Most squeegee shapes are simply square squeegees, other squeegee shapes are used for specific printing conditions. For example, a hard squeegee performs better than a soft squeegee, but is less adaptable to the substrate. Using an oblique squeegee, the printed edge is easily deformed (similar to a soft squeegee).

There are three shapes of squeegee for printers to choose from: square squeegee (or right-angle edge squeegee), various oblique squeegees and round squeegees (horn shaving). The square scraper has a wide range of applications and can provide the maximum printing pressure. The printing angle depends on the effective width. The diagonal squeegee provides maximum adaptability, the printing pressure is reduced, and the printing angle is smaller than the set angle. The circular squeegee is the least adaptable, provides the smallest printing pressure, and the printing angle can be freely set (often the smallest angle). The above reasons will affect the amount of ink.

4. Knife edge:

The knife edge is an important part to complete the four functions of the squeegee. The sharpness of the squeegee is a factor that initially controls the amount of ink being dropped. The sharp squeegee provides the smallest ink drop and the finest image. The blunt and rounded edge increases the amount of ink and affects the color and line fineness.

When printing large areas and simple patterns with transparent oil, the changes in color and line fineness are not obvious. And when printing fine lines and four-color dots, with semi-transparent (UV) and transparent inks, you will quickly notice the deformation of the knife edge. Compare the first and last printed sheets to determine when the squeegee should be applied. sanded.