The basic principle of offset printing with top up card was named after the development of early lithography. The plate of early lithography used stones to grind and then improved to metal zinc plate or aluminum plate, but the principle is unchanged.
There is no difference between the printing part and the non printing part, that is to say, it is flat. By using the principle of water oil non mixing, the printing image part can keep a layer of oil film rich in grease, while the page on the non printing part can absorb appropriate moisture. The lithographic printing machine is designed to make the printing ink repellent and absorb the ink after printing ink on the plate The grain part absorbs water and forms the anti ink effect. This method of printing is called "lithography".
After the development of lithography from early lithography, because of its unique characteristics of plate making and printing, and its simple work and low cost, lithography has been continuously studied and improved by experts in modern times, and has become the most commonly used method in today's printing.
Printing method
Lithography was developed from the early lithography transfer printing, and it was described on the transfer paper and then fell on the plate to become a reverse, and then printed on the paper as a normal grain. Due to the pressure of this method in printing, the original flat plate (i.e. the printing image part and the non printing image part are both flat), after the pressure, the ink occupied in the plate will expand and expand, resulting in poor line drawing. Therefore, it was later improved to be called offset (offset) The printing method is to make the page into normal pattern, which is transferred to the rubber cylinder as the reverse pattern, and then printed from the reverse pattern to the paper as the normal pattern, so as to improve the elasticity of the printing pressure.
In the early stage of lithography, lithography was developed into two types: lithography and circular press. Most of the lithography machines were used in special printing, such as proofing proofing and proofing. As for printing paper machines, they were all improved. Lithography round pressing is that the printing plate is placed horizontally, and the pressure part is a roller type cylinder. This printing method is similar to the lithography circular pressing machine in relief printing. The circular plate and round pressing type is to wrap the printing plate on the drum, which is called the plate cylinder. The other drum on the machine is covered with rubber, which is called the rubber cylinder. The pressure part is the roller type pressure cylinder. This kind of machine with three basic roller structures is called "offset press".
Advantages and disadvantages
① Advantages: plate making is simple and cheap. The printing plate is easy to copy. The print is soft and soft. It can print large quantities.
② Disadvantages: due to the influence of water glue in printing, the color reproduction is reduced and the brightness is lack. The printing ink is thin (it can only show 70% capacity, so the lampbox poster of offset printing must be printed on both sides to enhance its color). Special printing applications are limited.
Scope of application
① (8) the price of the newspaper and other materials, such as the price of the newspaper, the price of the newspaper and other materials.
