Screen Printing Technology (3)

(Screen Printing Techniques) Wire Mesh With the increase in the number of screen prints, the types of screen materials and screen plates have also increased. In general, wire mesh materials were originally borrowed from other industries, and later some other types of materials were developed with the need for screen printing. However, although a wide variety of non-metal wire mesh materials have been used in the screen printing industry such as silk, nylon, and polyester, they still cannot meet all screen printing needs. For example, wire mesh materials used for dye printing or porcelain ink printing must withstand long-term etching of inks and solvents, screen plates need to be recycled, and the like. In order to meet these screen printing needs, people urgently needed a screen with a long life and good stability. Thus, a screen called “wire mesh” was industrially born. Because the wire mesh has a very uniform diameter and can be very fine, it can print the finest patterns. Metal mesh mesh (mesh) is also very consistent, but also larger than other mesh material mesh, and metal mesh is not like easy to absorb ink non-metallic mesh, its wire does not absorb ink or solvent, Therefore, a relatively flat ink film layer can be obtained. Its advantages are many: the frequent replacement of the template will not cause damage to the metal mesh; the ink can also easily pass through the metal mesh; especially suitable for printing with porcelain ink, glass frit ink, flake copper ink and dye ink. Occasion; can be used for more delicate work; metal mesh can get a thick ink film layer; good rigidity, accurate printing overprint; can be used for mechanical automation, semi-automatic or manual printing. In the past, because wire meshes were not easily stretchable and expensive, they were generally used only for making small screens, but they are now increasingly used in medium and large screens. Although it is relatively expensive and elastic, it is not good, but its consistency and infinitely available features reduce the overall cost. And properly stretched and printed technology can compensate for the shortcomings of elasticity. There are two types of wire mesh for screen printing, namely plain weaving and weaving. Among them, plain weaving is more commonly used, and twisted weaving is used in very fine work. As shown in Figures 14 and 15, flat weave is a single line of latitude and longitude, while weaving is a double line of latitude and weft. The screen meshes woven by both weaving methods have a square shape. The weaving method results in a thicker screen. Like other screens, metal screens are classified by the number of meshes (the number of screen wires). Only square meshes are used in screen printing instead of rectangular meshes. Square meshes have the same number of meshes and the same large mesh size in the lengthwise and widthwise directions. The calculation of the number of meshes per inch or centimeter is the number of all meshes at a distance of 1 inch from any one of the mesh lines. For example, 80 mesh should have 8080 meshes per square inch, ie 6400 meshes; 300 meshes should have 300,300 meshes per square inch, ie 90,000 meshes. Wire mesh is generally marked with the words "Number 80" or "8080", "Number 165" or "165X165". The type of wire mesh usually has 80 lines/inch (31 lines/cm) to 635 lines/inch (250 lines/cm). However, more rough metal wire mesh is also available in the market. The lower the number of wire mesh, the larger the mesh; conversely, the higher the number of wires, the smaller the mesh. In wire mesh, the diameter of the wire is in inches or millimeters. The choice of screen depends on the condition of the reproduction, the type of ink, and the condition of the printing surface. You can purchase from the screen printer any screen cloth of any size above 1 square foot (0.09 square meters). Its width can range from 36 inches (91 centimeters) to approximately 79 inches (200.7 centimeters). Stretching a Wire Mesh Although a wire mesh is not easily stretched and fixed on a frame, it does not pose a problem to the printer. It can be nailed to the wooden frame, fixed to the floating net frame (Figure 17), welded and glued to the metal frame, and fixed on other special frames. Vendors and manufacturers recommend that metal mesh is best used for fine work on metal mesh frames because there will not be any deformation of the metal mesh frames. If you use a wooden frame, the strength must be better. In practice, the use of a wooden net frame can generally be performed first, that is, the net frame is first soaked in a solvent, and linseed oil is coated on the float rod. When fixing the wire mesh, the screen cloth must first be fixed to the longer side of the frame, and then fixed the shorter side, and then fix the opposite long side, and finally fix the remaining short side. When fixing the screen cloth, it is best to use a puller (Figure 18) to stretch it. The front of the screen is a wide splint that does not damage the screen. This netting tool is available from the supplier and is very useful if a large pull force is required on the screen. The fixing of the screen cloth is best done with two or three layers of paper (Fig. 19) to prevent breakage. The paper fibers used are approximately 1/64 inch (0.398 mm) thick. For the novice, the practical and reliable way to fix the screen and pull the net is to use a floating net frame. Three to four tie rods are used for the wire mesh. The dimensions of the tie rods are recommended to be the same as the inner frame of the frame. It is best to use a rigid net frame or a wooden net frame impregnated with linseed oil. Since metal mesh frames have to be used for a long time, they must be taken seriously during the final processing. Wire mesh can be nailed to the float rod. When pulling the screen, use enough tension on the screws to tighten the screen. Be careful not to leave anything on the screen when processing the screen plate, otherwise the screen will have knots, gaps, or sag. If you have a commercial pull tool like the one shown in Figure 12, you can use it to pull the wire mesh. In the actual operation, the metal wire mesh stretching method is manual, semi-automatic and fully automatic. They are easy to stretch the wire and quickly fasten it to the frame. After the wire mesh is properly prepared, it can be foiled. Photographic stencils such as polyvinyl alcohol, polyvinyl acetate, modified plastics, commercial screen printing stencils, gel stencils, pressure sensitive transfer sheets, direct-indirect screen printing sheets, knife cutting sheets and the like may be attached thereto. The most important step in the preparation before making the screen plate is to ensure that the metal screen is very clean, because the metal is not absorbent, must be clean and free of oil, grease, regenerant, fingerprints, in order to facilitate the template to better Adhere to the wire mesh. Most wire screen meshes are coated with protective oil protective coatings and treatments. These materials must be thoroughly removed prior to patterning. The following methods can be used to clean the wire mesh: (1) The wire mesh can be cleaned with a 5 to 10% glacial acetic acid solution for 5 minutes, and then rinsed off with hot water to remove any residual liquid; (2) The metal wire mesh is directly passed through the gas. Flame or Bunsen burner, then wipe with a cleaning brush to prepare for the film. However, be careful not to make it spend too much time on the flame; (3) Any diluted caustic can be used to clean the wire mesh and then wash away the corrosive agent with hot water; (4) An old method of cleaning the wire mesh is to put the metal Mesh is inserted into a shelf that is as thick as a mesh frame, polished with an emery cloth soaked in pumice, volatile oil or paint thinner, and then washed with hot water, after which the stencil can be attached to the wire mesh; ( 5) 10% lye or 20% ammonia solution can also be used to clean or degrease the wire mesh; (6) Special cleaning solvents can also be purchased from the supplier. The use of each of the above methods can achieve the purpose of cleaning, but it should be noted that after screen cleaning, avoid leaving fingerprints on the screen, that is to say, do not touch the screen with your hands. The wire mesh should also be stored with care not to leave anything on the wire mesh to maintain its cleanliness.