Problems with printing plates in the printing process

During the printing process, the user is most concerned about two aspects of the printing plate: The first is the ease of installation, adjustment and disassembly; the second is whether the graphic and non-graphical parts of the printing process can be clearly and carefully identified. Separated to form a high-definition, detail-rich image, the latter point in lithographic offset printing is more important than other printing processes, it is achieved by the chemical properties of the imaging part and the non-imaging part. (In gravure printing, the graphic part is lower than the plane of the metal plate cylinder; in relief printing, the graphic is higher than the plane of the plate.) In the printing process, the non-imaged part of the high-quality printing plate can be water. The roller is fully wetted and does not stick to the ink, while the ink roller transfers the ink to the unwet text part. It is not necessary for the printer to know all the knowledge of plate making, but knowing the nature of the plate and its ink transfer principle will help them produce high quality prints. Types of plates At present, there are several types of imaging plates, all of which have a common feature: that is, during the production process, photochemical means are used to divide the plate into two parts having different chemical properties. The imaged portion has the property of ink-repellent hydrophobicity, and the non-imaged portion has the property of being hydrophilic and ink-repellent. Thus, when the plate comes in contact with the dampening roller, only the non-imaged portion is wetted by the aqueous fountain solution, and when the wetted plate comes into contact with the ink roller, only the unwetted image portion is inked. The plate manufacturers are trying their best to make the graphic part more intimacy and hydrophobic rather than the graphic part more hydrophilic and ink-free. Operation workers should also pay attention to and strive to maintain this feature. Offset printing plates are made of different materials, but most of them are made of anodized silicon aluminum substrates, which can form a long-lasting hydrophilic surface. The printing plate is mostly coated with a photosensitive layer. After developing by rinsing, the coating layer having an affinity for the ink will remain on the plate to form a graphic portion, while the photosensitive coating layer in the non-graphic portion is removed. Offset printing plates are usually photoengraved (some of them are also laser-direct plate-making). Most of the traditional plate-making methods are made by close exposure to the film and then developed and fixed. Since the film used is a negative image, this type of printing plate is also called a negative or plate. Laser imaging plates should also belong to this category of printing plates. When the light is exposed on the plate through the film, the photosensitive layer of the graphic portion becomes hard and becomes insoluble. After development, only the unexposed non-textured portion of the coating layer can be dissolved by the solution, exposing the hydrophilic aluminum matrix, and the exposed ink-receptive coating layer remains during the development process to form an image, which is printed The process was very solid. Although the non-image part is already hydrophilic, it needs to be further improved in its hydrophilicity. This process is called gluing, that is, applying a thin layer of uniform Arabic gum or other similar solution. Decreases the oxidation of the surface of the plate to make it more hydrophilic. One type of plate, which is also known as an additive plate, is a plate that is made by the use of a film and is used to enhance the imaging effect of the plate with other materials during the development process. Although most additive plates are coated with a layer of additive by the plate manufacturer and belong to the instant printing plate, some pre-photosensitive additive plates are also commercially available. For the printer, in addition to knowing the above-mentioned commonly used plates, it is more beneficial to know about some other types of plates. Plates processed through positive negatives are called positive plates. This process is similar to a negative plate, except that the graphic portion is not exposed and the coating is insoluble; the non-image portion is exposed and becomes soluble after exposure is removed. Positive printing plates also belong to the reduced version category. Many positive-working plates can be repaired at high temperatures to increase their durability. The life of positive or negative plates can reach more than 1,000,000 times. There are also plates made of a variety of metals that have a longer life and are generally made of two or three layers of metal. Usually a metal is electroplated copper, because it is easy to absorb ink, used to make graphic parts; another metal is aluminum, stainless steel or chromium, they are easily wetted by water, used to make non-graphical parts. If there is a third metal, it usually refers to the base metal under the first two metals. This type of printing plate can use a negative or positive pattern process, and the uppermost metal surface is often coated with a light-sensitive material. Negative-tone printing plates are usually composed of two kinds of metals, and generally copper plating is applied to the other metal. During exposure, light passes through the transparent image area to stiffen this portion of the ink-receptive coating. During the development process, the unexposed non-graphic coating dissolves to reveal the metallic copper. After that, the exposed metallic copper is removed by an etchant, exposing aluminum or stainless steel that forms a non-graphical portion. Photolithography is similar to negative platemaking, except that the coating layer becomes soluble after exposure. During the printing process of the printing plate, the exposed coating is dissolved to expose copper, and then the non-image portion of copper is removed by the etchant to expose aluminum or stainless steel that forms a non-graphical portion. Regardless of the type of plate, and how they are made, their printing capabilities are not much different. For better printing results, it is best to follow the plate manual and use the relevant products and printing materials recommended by the manufacturer. The type of plate will only be mentioned if there is a problem in the printing process that needs to be resolved. Waterless printing plate: The waterless printing plate is composed of an aluminum substrate, a primer layer, a photopolymer layer, an ink repellent silicone layer, and an uppermost transparent protective layer. This printing plate can be washed manually or by using a machine on a dedicated device. Use with care, any scratches left on the ink repellent silicone layer may leave an image, affecting the print quality. When the waterless printing plate is prepared by the positive drawing method, it is first exposed to ultraviolet light under vacuum, so that the photosensitive layer of the non-graphic part is bonded to the silicone rubber layer. Remove the top protective layer, rinse and develop, remove the silicone layer on the photosensitive layer of the graphic part, and the printing plate is considered to have been successfully produced. The Yin picture plate process is basically the same as this. The difference is that the exposure to UV light will weaken the light-sensitive layer's photosensitive layer and the silica gel layer. After exposure, the protective layer is uncovered and a pre-treated solution is used which will allow the photosensitive layer of the non-exposed, non-textured portion to bond more tightly with the silicone layer. In this way, remove the silicone layer on the photo-sensitive layer part of the line on the line. Waterless printing plates can be used for sheet-fed or web commercial printing. Its printing quality is very high, with the characteristics of high reproduction accuracy. In general, waterless prints are very clear and can print 200 to 600 lines per inch. Direct Digital Plates: With the development of imaging technology, many plates can be directly digitally imaged by an imaging or platemaking machine under a low-energy laser beam. This type of plate is called a direct-digital plate. Because it does not rely on film media, it directly relies on digital file exposure imaging, so this technology is also known as "direct platemaking" or "computer-to-plate" (CTP). ("Direct platemaking" also refers to the process by which a plate is exposed to light on a camera-like plate-making machine through reflection of light from a replica, but it should be called "Photo-direct Plate".) When using a laser beam for plate exposure, the plate rotates slowly and the laser beam scans quickly. In this case, exposure time of several microseconds can be obtained for each tiny printed dot. At present, there are several types of plates for computer-to-plate making in the world, including silver-based, electrophotographic, and photosensitive resin coating methods, which are applicable to the current three major laser beams (including laser diode infrared light, argon ion blue-green Light and red light). They use a photosensitive coating layer, greatly speeding up the imaging speed. Plates can also be made directly on the press. The original Presstek technology used on the GTO-DI machine at Heidelberg employs a special spark-discharge plate imaging technology. Its plate consists of three layers of material: the silicone layer, the aluminum surface, and a 7 mm thick polyester base layer. Its imaging head is a set of 16-needle tungsten electrodes. It uses an electric spark to remove the silica gel layer and aluminum layer on the image part, exposing the polyester ink-receptive layer to form an ink-receptive structure, and its silicone layer. It is ink-repellent, which forms a waterless printing system. The plate imaging resolution is 1016 dots per inch (pdi). In 1993, Presstek adopted a new PEARL platemaking system that replaced the original spark discharge imaging technology. PEARL uses a set of sixteen infrared laser tubes instead of electric sparks to remove the silicone layer. Its plate consists of three parts: the bottom layer of 6 mm thick polyester or metal body, the middle is no longer aluminum but an infrared absorption material, the top layer is still silicone. The life and strength of this type of printing plate has been improved a lot compared to the past.