The original plate (or the original printing plate) made by color separation, screening, and imposition is copied to a metal plate through a printing machine to make a printing plate for printing (or proofing). This is called printing. .
Shaiban is carried out on the stencil. The original printing plate (glass plate or polyester film) is coated on the metal plate coated with a photosensitive liquid, and the vacuum plate is evacuated so that the original plate and the metal plate are closely adhered to each other, and the light source undergoes exposure, development, corrosion, and the like. Processed into a printing plate, which is an integral part of photolithography, and is also the main process between plate making and printing. It has a specific role in the quality of printing (including photography and retouching).
As far as the process of the printing process is concerned, it can be divided into several major processes such as the surface treatment of the plate, the application of the photosensitive liquid, the exposure and drying, the chemical treatment of the layout, and the quality inspection. After years of improvement, this process has also been evolving in the use of raw materials and process technology. It has transitioned from the negative plate protein version to the resin gravure plate, polyvinyl alcohol (PVA) gravure plate, multilayer metal plate, PS version and so on. The relevant process conditions are briefly described as follows:
1, plate preparation
Lithographic printing can print the same printed sheet repeatedly from the plate because it has stable wettability on the plate surface, that is, the blank part of the platen can absorb water and store water; and the graphic part of the plate can absorb and transfer the ink. . To make a plate with stable water absorption, it is necessary to perform surface treatment on the used plate material (the most commonly used before is zinc skin and aluminum skin, its thickness is generally 0.5-0.6 mm). The method of processing should be based on different conditions such as the nature of the plate, the plate making method, and the copying process. There are usually many methods such as mechanical and chemical methods.
a. Mechanical gravure method
Grinding with a plate-type plate grinder, commonly known as "grinding." Its purpose is to grind the plate into a trachoma with a subtle peak-to-valley shape, to enlarge the surface area of ​​the printing plate, to use the pores, to increase the adsorption center, to form the graphic part and blank part of the layout, and to balance the water and oil in the printing process. Create powerful conditions. Before the plate is grinded, the plate is finished, and the plate is inspected for serious damage. The oil and ink on the surface of the plate are then washed with gasoline, followed by degreasing. Degreasing, zinc plate using sodium hydroxide (NaOH) or potassium hydroxide (KOH), aluminum plate with nitric acid (HNO3) or sulfuric acid (H2SO4), can also use sodium hydroxide (NaOH) or sodium chloride (NaCl) solution. The purpose of the degreasing treatment is to prevent the oil or ink from contaminating the layout during the grinding process, thereby causing the printing plate to be dirty, and the other effect can also shorten the time for grinding. After degreasing, rinse with water.
Then, the plate was fixed in a grinding plate of a Tangban machine. Two layers of grinding marbles were placed on the plate material, followed by moistening with water, adding frosted sand, and driving a plate-grinding machine to grind. Due to impact and rolling of the marble, the sand is pressed against the surface of the plate material to generate friction, so that the surface of the plate material is formed with fine trachoma.
The ground plate is washed and then treated with a cleaning solution to prevent oxidation. After drying, it can be stored for use. When it is stored, it should be placed in a dry place. The base surface of the plate should be matched, and the two surfaces must not rub against each other.
There are many kinds of scrubs and their specifications are different. Commonly used are glass sand and corundum. Grinding marbles generally use glass marbles, steel marbles, and ceramic marbles. Matte particles, hardness, shape, marble texture, size, weight, quantity, and the plate speed, grinding time and other factors, determine the quality of the trachoma.
b. Wet sandblasting
The plate to be surface-treated is placed in a cylinder and the sand and water mixture is sucked into the top-blade vane disc by a sand pump, and the water and sand mixture is sprayed onto the surface of the metal plate with a rapidly rotating centrifugal force. On, so as to achieve the effect of grazing.