Letterpress printing is one of the oldest printing methods. It is printed using a letterpress plate with a raised surface. During printing, ink is applied to the surface of the typeface and then imprinted onto the paper. The ink on the surface of the typeface is transferred to the surface of the paper to form an imprint. Hand typesetting, Lino line typesetting, typography, electrotype printing and photorelief printing are all types of letterpress printing.
Gravure printing is a printing method that uses manual or mechanical engraving to score lines to form a concave character or image on the printing plate. When printing, first fill the lines or grooves with ink, and then press the prepared paper on them. The paper will stick the ink away to form an imprint. Etching, needle engraving and gravure are all examples of gravure printing.
Lithography is sometimes called chemical printing, which means that the printed image is on the same plane as the printing plate. It realizes printing based on the principle of "oil and water do not mix". This type of printing involves placing an image on a stone or metal surface mechanically or manually, and then chemically treating the surface to make parts of the image receptive to ink, while other blank parts are not receptive to ink. When printing, only the ink-friendly part of the image is transferred to the paper, forming an imprint. Phototype printing, photolithography and offset printing are all lithographic printing.
Modern screen printing is not only technically different from the other three printing types, but also the most widely applicable of the four printing types. Its printing objects can be paper, cardboard, wood products, plastics, textiles, ceramics, metals, furs and synthetic materials of the latter materials. It can be used not only to print flat objects, but also to print round, convex, concave and irregular shaped objects. Because of this, screen printing was an inevitable outcome. But because its technical details are a trade secret, its development proceeds only quietly. But no matter what, it is constantly progressing and developing, and has broad prospects.
In the development process of image transmission, although there are no particularly obvious different stages of development, screen printing is a creative process that occupies an important position in the international industry. Its principle is derived from simple mimeograph wax paper. copy. Wax paper copying is an ancient civilization and one of the oldest methods of image reproduction. But it is different from the ancient stencil copying, just as modern letterpress printing is different from the letterpress printing in Gutenberg's day.
Although the Japanese first printed using tension-free stencils woven from hair or silk with some slack in the middle, the development of modern screen printing originated in the United States. Counting from the pioneers of screen printing, Harry Leroy Hiett (Harry Leroy Hiett) and Edward A. Owens (Edward A. Owens), screen printing has already begun as early as the early 20th century (1901~1906) . The first attempt at screen printing was made by Francis Willette of Detroit, Michigan, USA, who screen printed felt pennants.
Silk screen printing involves attaching a template with an image or pattern to a silk screen for printing. Usually wire mesh is made of nylon, polyester, silk or metal mesh. When the substrate is placed directly under the screen with the template, the screen printing ink or paint passes through the mesh in the middle of the screen under the squeeze of the squeegee and is printed on the substrate (the squeegee has manual and Automatic two). The template on the screen seals part of the screen holes so that the paint cannot pass through the screen, but only the image part can pass through, so only the image part is imprinted on the substrate. In other words, screen printing actually uses ink to penetrate through the printing plate for printing. This is why it is called screen printing and not silk screen printing or silk screen printing, because not only silk is used as screen material, nylon, Polyester, cotton, cotton, stainless steel, copper, brass and bronze are all available as screen materials.
In the field of screen printing, equipment, materials, processes and technology are all prerequisites for being a worker. This article will start with the most basic screen knowledge to give readers a comprehensive understanding of screen printing.
Screen frame
The screen frame is an integral part of the screen plate, often made of wood, and plays a role in supporting the screen. As a component of screen printing, the screen frame includes wooden screen frames and iron screen frames, as well as a combination of the two materials. Although many screen printing plates are already made by screen printing factories, screen printing operators should know how to make their own screen frames and what type of screen frames are best for their job needs. The type and shape of the screen frame is determined by the job to be printed. When making the screen frame, the single best material should be used as much as possible, which will help ensure and improve the quality of printing.
The most common screen frame is the flat screen frame, which is mainly used for printing flat substrates. Most screen printers use kiln-dried white pine or basswood for their frames, and these materials are free of knots and other unevenness. When purchasing wooden strips, it is best to choose materials that can meet the requirements of the four sides of the screen frame. When making a screen frame with a size of 36inch x 36inch (81cm x 81cm), the frame border wood strips should be 2 inches thick and 2 inches wide (5cm x 5cm). For larger screen versions, the size of the screen frame wooden strips should be proportionally thicker and wider. If the screen frame is too thin, the screen will bend and deform after use, storage and stencil stretching. White pine is the most commonly used frame material, but sometimes printers also use materials such as mahogany, spruce, Gelsemium and boxwood for frames.
There are many ways to combine frames. As long as it is carefully produced, each method can meet the requirements of screen printing. The four corners of the screen frame should be fastened together with nails and glue or screws and glue. After bonding, excess glue should be wiped off immediately with a damp cloth. Nails must be used, and the nail position should be lower to prevent the nails from scratching the stencil fabric. No matter which combination method is used for the screen frame, the four corners of the screen frame should be reinforced with angle plates or angle irons to ensure its durability. All screen frame corners must be sanded into a slightly rounded shape, and all screen frame edges must be sanded to ensure there are no rough spots that could cause damage to the screen. If necessary, you can apply shellac or linseed oil on the screen frame before stretching the screen to increase the smoothness of the screen frame. There are four common methods of stretching the net. They use pin nails, grooves, automatic stretching machines and commercial patented stretching technology.
Stretching
When using pins to stretch the mesh, use 0.5-inch (1.2 cm) flat-headed carpet pins. The warp direction of the screen cloth should be consistent with the long side of the screen frame, because most screen cloths have better pulling force in this direction and can withstand the back and forth dragging of the squeegee. In addition, the cloth pattern must be consistent with the direction in which the squeegee is dragged to reduce image deformation during the printing process. When nailing the screen cloth to the screen frame, first start nailing in the center of one side of the screen frame, about 0.75 to 1 inch between each nail, and 3/8 inch (0.95 cm) away from the edge of the screen frame. Pull the wire mesh fabric tightly and nail a row of nails on one side of the mesh frame. The first row of nails is on the outside, and it must be tightened so that the tack nails are in close contact with the wooden frame. After nailing one side, nail the opposite side. Be sure to tighten it with your hands when nailing. Likewise, nail the other two sides of the screen frame. Finally, nail a circle of nails on the inside and outside of the screen frame at the staggered position to ensure that the screen cloth is tightly stretched on the screen frame.
After the screen cloth is nailed to the screen frame, it should be carefully cleaned with cold warm water or cold water or soapy water. It can not only remove any possible glue, but also help Tension the wire mesh. When the screen cloth is dry, check whether the taut screen cloth is smooth. If a spot is not tight enough, use a screwdriver to carefully remove the nail there, retighten the mesh there, and re-tack it. The screen cloth must be stretched very tightly, otherwise it will be difficult to adhere to the screen printing film or coating emulsion. Some screen printers gently roughen the fibers of nylon, polyester and other silk fabrics with fine pumice or clay balls before coating the screen cloth to facilitate firm bonding. But be careful not to weaken the elasticity of the mesh. In addition, there are many other methods of screen cleaning and degreasing in actual production.
Some screen printers paint shellac on the bottom of the screen frame, where the nails are driven, to prevent ink from leaking between the screen and the screen frame.
The grooved screen frame has a groove on the bottom edge of the screen frame. The groove can be dug with a circular saw, a special special trenching tool or a wood chisel. The depth of the groove should be slightly deeper than the thickness of the plywood. If the plywood is made from a harder wood such as maple or birch, it will last longer and can be reused. For plywood, about 3/8 inch (0.93 cm) is a good size. Its shape can be a square wooden bar or a round tip rod, suitable for being pressed into the groove.
When stretching the mesh, the wire mesh is forced into the groove by the splint. The edges of the grooves and plywood should be smoothed with emery cloth to avoid scratching the screen during extrusion. Secure with No. 4 or No. 5 flat-head wood wire nails approximately 3/4 in. (1.9 cm) long. The screw holes in the plywood should be countersunk holes to ensure that the screw heads can be tightly combined with the plywood when driving nails. Hole clearance is approximately two to four inches.
When stretching the mesh, first press one side of the mesh into the groove and add screws, but do not need to tighten it too tightly. Fix the plywood on the opposite frame to the same extent. Tighten the mesh as much as possible when fixing, but it doesn't matter if it is a little loose at one end of the plywood. You can adjust it later. In the same way, fix the other two sides. When all the cleats are secured, tighten the screws sequentially, a little at a time, to achieve consistent tension at all points of the mesh.
Using automatic machinery to stretch the net is a very fast and simple method. The stapler should be used in the same way as the stapler and should be in approximately the same position. If the stapler is pulled in a direction parallel to the screen cloth, it will tear the screen cloth. In actual operations, you can use a piece of cardboard to pad the screen cloth, and the stapler clamps the screen cloth and the paper together and pulls it together without directly pulling the screen cloth. Not only will this avoid tearing the screen, but it will also allow you to easily remove the stapler by pulling out the jammed paper.
The following provides a simple commercial stretch screen method that both beginners and advanced screen printers can get started quickly. This method is suitable for screens of various sizes, but the screen frame must have the same grooves as the grooved stretch screen frame. When stretching the net, place the wire mesh cloth on the groove, and use a tool to press a rope with a diameter of about 1/8 to 3/16 inches (0.31 to 0.47 cm) into the groove together with the wire mesh. The rope can be reused for multiple tightenings. At any time, when the mesh must be tightened again, the grooves can be dug deeper and the same rope is used to press the mesh back into the grooves.
In the actual screen production process, a screen stretching system is included. The system features an independent aluminum frame that automatically tightens on all four sides. The screen frame tightens the screen to the desired tension level. And after printing, the screen can be removed, rolled up and reinstalled for use.
No matter which method of stretching the net is used, there are a variety of ready-made net frames for use. However, for special product printing such as circuit printing or chemical machinery or special screen printing machines, it is best to use patented screen stretching equipment, which is beneficial to ensuring the quality of printed products.