There are other methods for forcing the ink through the screen plate in addition to the squeegee, such as the vacuum pressure method or the roller method, but the squeegee blade is the most commonly used tool. The squeegee consists of several parts: a wooden board with a groove as a handle; a rubber blade inserted in the groove of the board, projecting the groove; and a fixing device. The most common squeegee is made of two wooden boards. The method of connecting the squeegee blade and the blade is also different.
Most of the squeegee blades are wooden and aluminum. Groove handles can be made from either hardwood or softwood but must be dry and free from nicks. Cork (such as white pine) is used because it not only has sufficient strength, but also is lighter and can make large-sized handles. This is because the length of the squeegee can reach about 72 inches (183 cm), so its weight is very important. The lighter squeegee is easier to use.
The handle of the squeegee should be in contact with the operator's hand, so the edges of the handle should be rounded to prevent rubbing hands. The rubber blade must be in good agreement with the groove of the handle. If it cannot be well matched, the ink of different colors will dry in the gap between the blade and the handle groove, affecting the color of the printing ink. Some operators apply shellac where the blades come into contact with the handle grooves to prevent the ink from drying and make it easy to clean. In large screen printing shops that use three and four colors for printing, different squeegees are used for each color, and are washed after use to leave the same color printed. The wooden part of the squeegee should be sanded to ensure that there are no rough spots.
Rubber can also be used to make blades, which can be polyurethane or other types, but must have good moisture resistance, corrosion resistance, and heat resistance. It must be resistant to animals, minerals, vegetable oils, and oils. It must also be able to withstand the oxidation effects of the metal components contained in the ink. The eraser is not affected by benzene, alcohol, paint, enamel, screen cleaning solution, and film solution. Man-made rubber has better fire resistance and better printability than natural rubber. The natural rubber life is short, easy to deform, and easy to be dissolved by the solution. The source of the rubber material is the same as all pigments and compounds. The rubber blade has a variety of different hardnesses, generally 45 to 80 hardness blades for screen printing. In general, suppliers have three types of blades: soft, medium, and hard. 45~50 hardness is a very soft blade, 75~80 is a very hard blade.
The edge of the blade determines the uniformity and thickness of the ink, and the edge of the blade must be parallel to the printed surface. The blade should be well fitted in the middle of the groove or between the two planks and fixed with a wooden screw. Fix the wooden wire nails four inches away. Cross the nails and pass through one side of the board first and then the other. The blade thickness is approximately 1/4 to 1/2 inch (0.63 to 1.27 cm); the height is approximately 1.5 to 3 inches (3.8 to 7.6 cm). The thickness, height and length of the blade depend on the size of the squeegee blade and the length of the squeegee. Although some printers can use hand tools to make the squeegee, it is not practical after all. The best squeegee for a variety of purposes is available from screen printing suppliers and is inexpensive, and its price varies with the length of the squeegee. A good squeegee can be purchased in various lengths, and the blades and handles can be purchased separately.
The length of the squeegee is determined by the job to be completed and the size of the frame used. It is recommended that the squeegee used is 2 to 3 inches (5 to 7.6 cm) smaller than the screen size, but it must cover the entire printed pattern in one stroke.
In order to maintain the two printing gaps so that the squeegee and the ink are not in contact with each other and give the staff a time of breathing, it is necessary to insert a support rod in the middle of the squeegee. There is also a method of inserting a support rod in the vertical direction of the squeegee blade. The squeegee is usually controlled with two hands. When the squeegee is controlled by only one hand, the other hand can be left free to rest.
The squeegee knife, like all tools, has some areas that need attention. This is mainly to maintain the sharpness and straightness of the blade. Its sharpness and straightness can be tested using a ruler or a ruler. When the blades become blunt, damaged, and uneven, the squeegee needs to be handled by a worker or a screen supplier to restore sharpness and straightness. If the squeegee is not sharp or straight, the ink layer of the printed product is not even, and poorly-technical workers may sometimes think of the cause of the ink or screen cloth. When using a screen printer for printing, the straightness of the squeegee blade must be checked regularly to ensure the uniformity of the print ink layer.
Using a sharpener or a special machine, the sharp edges can be sharpened. The fixture is very simple to make and it can be made of wood. The length is 1 to 3 feet (0.305 to 0.914 meters). Grinding media for grinding tool holders can use No. 0 sandpaper, or emery cloth with 80 to 120 grit, or new (and also old) sandpaper. Sharpening method is to hang the squeegee in a vertical position, pull the friction material back and forth until the blade becomes smooth. If you have a belt sander or disk sander, you will save a lot of work for workers. The speed of the sander is between 1000 and 1300 rpm. If the speed exceeds 1300 rpm, the eraser may melt, because most synthetic rubbers are thermoplastic and soften when exposed to heat. If this is the case, add a small amount of water to cool it and prevent decomposition and softening. In addition, lightly press the rubber so that it can be rubbed without melting.
Another method of sharpening the blade is to cut a portion of the blunt blade with a knife that is sharper than the blade, a manual knife or a mechanical knife. If the blade or paper knife is rubbed with a damp cloth, it will cut off the rubber blade more easily. If the blade is so badly damaged that it cannot be polished, then you have to replace it with a new one.
The squeegee must be kept clean. It should be cleaned with a cleaning agent for cleaning the screen. Unclean squeegee is more difficult to clean after sticking ink. Also, the dry ink may react with various colors of ink printed later. After the squeegee is cleaned, it should be stored for two hours before use to completely evaporate the solution. In addition, if the storage time is long, it is recommended to use French lime powder sprayed on the blade to protect the cutting edge. Normally, it should be hung or placed on the knife holder during storage.
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