Squeegee may seem simple, but in fact squeegee is a very complex part of screen printing.In other forms of printing, to make inks
The transfer tools are squeegee, ink roller, pressure roller and glue, each of which has its own unique function.In screen printing, the functions of squeegee are mainly in the following four aspects:
1. Transfer the ink through the screen to the substrate.
2. Scrape the excess ink off the screen.
3. Keep the screen in contact with the substrate.
4. Able to print substrate of different shapes.
Only the above four functions of the squeegee get a good play, in order to print quality prints.And the physical properties of the scraper
It plays a decisive role in the above functions.(for example: a hard squeezer will do a good job of scraping off excess ink, but will not do a good job of satisfying the various substrate shapes required).Therefore, in the selection of squeegee, it is necessary to fully consider the performance of squeegee factors on the above functions, to avoid adverse effects on the printing effect.The following four factors should be taken into consideration when selecting the suitable performance of the squeegee: 1. Hardness: The squeegee is usually made of polyurethane, and the hardness of the squeegee can be measured with a hardness meter.The hardness, size and blade shape of the squeegee determine its bending, flexibility and pressure.Hardness ranges from 55 to 90 degrees (Shaw A).The hardness value was measured by the Shaw A hardness tester.55A-65A is low hard squeegee, 66A-75A is medium hard, and over 75A is high hard.
High hardness squeezer for the first three functions of the squeezer is very beneficial, the ink pressed into the screen and transferred from the fine screen to bear
Print, and maintain the screen and substrate line contact.The only defect of high hardness squeezer is that it cannot satisfy the printing of different substrate, and the quality requirement of squeezer is also very high when the printing surface is rough and uneven.
Effective width: refers to the width of the squeegee inserted into the aluminum scraper handle and extended from the aluminum scraper handle.This width is important in determining the bending of the squeegee under pressure.The curvature is the cubic value of the effective width.If you double the effective width you get a curvature greater than 23.The bending of the squeegee will cause two changes: the Angle between the squeegee and the screen;The printing pressure transferred 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 force transferred becomes smaller and smaller.The squeezer printing Angle decreases, 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, the ink layer is thickened.(In this case, the printing operator will increase the printing pressure, the squeegee bending will increase, the resulting ink layer is still not ideal.The solution is to increase the hardness of the squeegees, squeegees Angle.This is how the effective width of the squeegee affects the four functions of the squeegee.
The effective width of the squeegee is usually between 20MM and 30MM.The choice of the best effective width is based on the flatness of the substrate, the image resolution of the screen layout and other printing parameters such as: squeezer Angle, speed and type of ink.Small effective width (less than 20MM), high hardness and rapid printing with appropriate ink when printing high resolution images on flat/smooth substrate.In the uneven, rough substrate, effective width to increase (sometimes big 30MM), hardness, and low hardness of the squeegee adaptability is poor, can not be excessive bending, can also use the middle hard on both sides of the soft three layer or double layer scraping.In general, the effective width increases, the printing speed decreases and the printing Angle increases.
Scratch shape: Scratch shape refers to the cross section of the scratch.Most squeegees are simple square squeegees, other squeegees are used for specific printing conditions.For example, hard squeegee performance is better than soft squeegee, but the substrate adaptability is poor.There are three kinds of squeegees for printers to choose: square squeegees (or right Angle squeegees), all kinds of slanting squeegees and round squeegees (horn squeezes).Square scraping is applicable to a wide range, can provide the maximum printing pressure, printing Angle is determined according to the effective width.Diagonal scraping provides maximum flexibility, reduced printing pressure and a smaller printing Angle than the set Angle.Adaptability of round scraping
Worst, it provides the lowest printing pressure, and the printing Angle can be set freely (often the smallest Angle).The above reasons will affect the amount of ink.
Knife edge: The knife edge is an important part to complete the four functions of the squeezer.The sharpness of the squeegee is a factor that initially controls the amount of ink.The sharp spatula provides the smallest amount of ink and the finest image.Blunt and round edge, the amount of ink under the increase, at the same time will affect the color and line fineness.When large areas and simple patterns are printed with transparent oil, the change in color and line fineness is not obvious.While printing fine lines and four color dot, with translucent (UV) and transparent ink, you will soon find the deformation of the knife edge, the first and last one of the printing to determine when the squeezes should be polished.
Since the selection of squeegee is an important part of printing quality control, the maintenance of squeegee is also to ensure the normal use of squeegee
Important link.The best way to ensure the quality of the squeegees is to have a clear process for the maintenance of squeegees before and after printing and how to polish the squeegees.
1. Store the squeegees horizontally and do not roll them into loops, which may cause permanent bending.
2. The aluminum scraper handle should be placed downward, not downward.
3. Clean the squeegees immediately after printing. It is easy to wash off the ink at this time, otherwise the ink will be damaged if you wipe off thousands of knots.
4. Do not soak the squeegee in solvent.Although the squeegees are solvent resistant, they become brittle because of solvent absorption.
5. The squeegees that have just been cleaned are still soft and the solvent is completely volatized, so they cannot be polished immediately.After 12 to 24 hours of rest can be used again.This can not only improve the grinding effect but also improve the printing effect.
6. According to the specific printing quality requirements, the squeegees should be polished regularly. During cleaning and polishing, the loss of squeegees should be reduced as much as possible.