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Functions and usage of glue scraping in silk printing

glue scraping seems simple, but in fact, glue scraping is a quite complex part of silk printing. In other forms of printing, the tools for ink transfer include scraper, ink roller, pressure roller and glue head, and each tool has its own unique functions. In silk printing, the function of glue scraping mainly includes the following four aspects:

1 Transfer the ink to the substrate through silk

2. Scrape off the excess ink on the silk

3. Keep the wire in contact with the substrate line

4. It can print substrates of different shapes

only when the above four functions of the squeegee are brought into full play can high-quality prints be printed. The physical properties of the scraper play a decisive role in the above functions. (for example, the rubber scraper with high hardness can scrape off the excess ink well, but it can not meet the requirements of different substrate shapes). Therefore, when selecting the squeegee, the influence of squeegee performance factors on the above functions should be fully considered to avoid adverse effects on the printing effect. When selecting a rubber scraper with appropriate performance, the following four factors need to be considered:

1 Hardness: the rubber scraper is usually made of polyurethane. Use a durometer to measure the soft hardness of the rubber scraper. The hardness, size and shape of the squeegee determine the bending, flexibility and pressure of the squeegee. Hardness ranges from 55 degrees to 90 degrees (Shore A). The hardness value is measured by shore a hardness tester. 55a-65a is low hard rubber scraper, 66a-75a is medium hard, and more than 75A is high hard

high hardness squeegee is very beneficial to the first three functions of squeegee. Press the ink into the wire, transfer the ink from the fine plate to the substrate, and keep the wire in contact with the substrate. The only defect of high hardness squeegee is that it can not meet the printing of substrates with different shapes, and the quality requirements of squeegee are also very high when printing rough and uneven surfaces

2. Effective width: refers to the width of the rubber scraper inserted into the aluminum scraper handle and extended from the aluminum scraper handle. This width is very important, which determines the curvature of the rubber scraper under pressure. Curvature is the cubic value of the effective width. For example, the curvature greater than 23 is obtained by doubling the effective width

the bending of the squeegee will cause two changes: the angle change between the squeegee and the wire; The printing pressure transmitted to the substrate decreases. For example, the rubber scraper is compared to a group of springs. When the springs are stressed at a certain angle, the springs begin to bend and the transmitted force becomes smaller and smaller. The printing angle of the squeegee 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 amount of ink is large, and the ink layer is thickened. (in this case, the printing operator will increase the printing pressure, the bending degree of the squeegee increases, and the obtained ink layer is still not ideal. The solution is to increase the hardness and angle of the squeegee.) This is the effect of the effective width of the squeegee on the four functions of the squeegee

generally, the effective width of the squeegee is between 20mm and 30mm. The selection of the best effective width is based on the flatness of the substrate, the resolution of the plate image and the correct connection solution of the aluminum alloy connector, which ultimately reflects the fundamental value of the aluminum alloy cable. Other printing parameters such as the angle, speed and ink type of the rubber scraper. When printing high-resolution images on flat/smooth substrates, the effective width is small (less than 20mm), high hardness, and suitable ink is used for rapid printing. On the uneven and rough substrate, the effective width should be increased (sometimes the size is 30mm), and the hardness should be reduced. However, the adaptability of the low hardness rubber scraper is poor, and it is not allowed to bend excessively. You can also use the three-layer scraper or double-layer scraper with hard middle and soft sides. Generally, the effective width increases, the printing speed decreases, and the printing angle increases

squeegee shape:

squeegee shape refers to the cross-section of the squeegee. Most of the squeegees are simple square squeegees. Other squeegees are used for specific printing conditions. For example, the hard squeegee performance is better than the soft squeegee, but the adaptability to the substrate is poor. Using oblique scraping, the printing edge is easy to deform (similar to soft rubber scraping)

there are three kinds of rubber scrapers for printers to choose: square scrapers (or right angle scrapers), various oblique scrapers and round scrapers (horn scrapers). The square scraper has a wide range of applications and can provide the maximum printing pressure. The printing angle depends on the effective width. Oblique scraping provides the greatest adaptability. Therefore, the energy consumption cost in the plastic granulation industry has become the second largest cost in the plastic granulation cost after raw materials. The printing pressure is reduced, and the printing angle is smaller than the set angle. The adaptability of the round scraper is the worst, the printing pressure provided is the smallest, and the printing angle can be set freely (often the smallest angle). The above reasons will affect the ink amount

knife edge:

knife edge is an important part of completing the four functions of rubber scraping. The sharpness of the squeegee is a factor that initially controls the amount of ink. The sharp blade provides the smallest amount of ink and the most delicate image. The blunt and round blade will increase the amount of ink, which will affect the color and line fineness at the same time

when printing large-area and simple patterns with transparent oil, the change of color and line fineness is not obvious. When printing fine lines and four-color dots, with translucent (UV) and transparent ink, you will soon find the deformation of the knife edge. Compare the first and last printed ones to determine when the rubber scraper should be polished

since the selection of type of squeegee is an important part of printing quality control, the maintenance of squeegee is also an important link to ensure the normal use of squeegee. The best way to ensure the quality of the squeegee is to clarify the maintenance of the squeegee before and after printing and how to polish the squeegee through a clear process

1. Store the rubber scraper flat and do not roll it into a circle, which may cause permanent bending

2. The aluminum scraper handle should be placed downward, and the knife edge should not be placed downward

3. Just after printing, clean the glue scraper immediately. At this time, it is easy to wash off the ink, otherwise the ink that needs to be wiped off will damage the knife edge

4. Do not regularly clean the mechanical and electrical parts with glue and immerse it in solvent. Although the squeegee is solvent resistant, the squeegee will become brittle due to solvent absorption

5. The newly cleaned rubber scraper is still soft, and the solvent is not finished. For example, leakage and total volatilization have occurred in the National Stadium and the National Grand Theater, so it cannot be polished immediately. It can only be used again after 12 to 24 hours of "rest". This can not only improve the grinding effect, but also improve the printing effect

6. According to the specific printing quality requirements, the rubber scraper should be polished frequently. When cleaning and polishing, the loss of rubber scraper should be reduced as much as possible

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