Many people are not familiar with the process of offset printing in color printing. So today we will introduce this printing process in detail.
In color printing, the adhesion of the ink of the latter color to the film layer of the ink of the previous color is called the overprinting of the ink, also called the transfer of the ink. Colors on color prints are generally displayed by overlapping or juxtaposing dots of yellow, magenta, cyan, and black with different area sizes. Therefore, the color reproduction effect of the printed matter is not only related to the optical properties of the ink, but also related to the sequence of ink overprinting and the amount of ink overprinting.
1. Overprint rate and its determination
Overprint rate, also known as the ink's strength, is a physical quantity that measures the degree of ink overprint. The higher the value of the overprint rate, the better the overprint effect. The overprint rate can be calculated by measuring the density of each color ink and the density value of the ink overprint. When studying the phenomenon of ink overprinting, the overprinting of the second color ink on the first color ink film layer is often the focus of discussion.
The color of the color printed matter is generally made of two or three colors of three colors of yellow (Y), magenta (M), and cyan (C). When measuring the density of a single-color ink, a color filter is installed in the density meter using the principle of subtractive color method. The color of the color filter is usually complementary to the color of the measured ink. For example, the blue filter is used to measure the density of yellow ink, the green filter is used to measure the density of magenta ink, and the red filter is used to measure the density of cyan ink.
2. Ink Overprinting of Monochrome Offset Press
When the first printed ink is fixed on the substrate and is nearly dry, the latter color ink is printed and attached to it, which is called dry printing. The ink overprinting of the monochrome offset press is carried out by wet pressing and drying, which belongs to dry printing.
After the ink is attached to the substrate, the original properties of the surface are changed by being covered by the ink. Therefore, the surface properties of the ink film become the main factors affecting the ink overprinting. For ink overprinting of a monochrome offset press, if the viscosity of the first color ink is greater than the viscosity of the second color ink, the second color ink can adhere well to the first color ink film, and the overprinting effect is good. On the contrary, if the viscosity of the second color ink is greater than that of the first color ink, the second color ink not only does not adhere well to the first color ink film, but also takes away the first color ink, making overprinting impossible achieve. It can be seen that the viscosity of the ink is very important for the overprinting of the ink.
In dry printing, if the printing interval of the two-color ink is not properly controlled, and the first ink is printed after the first ink has been dried, then the dried ink film has lost its viscosity and it is difficult for the post-printed ink to adhere to it. This causes the so-called "crystallization" of ink. In order to prevent the occurrence of ink crystallization, it is not advisable to add dry oil to the first color ink. Sometimes to delay the drying of the ink, it is also necessary to add an auxiliary agent to the ink to inhibit the drying of the ink.
In summary, in the actual production, in order to make the ink printing of the monochrome offset press smoothly, the ink layer printed first must have two characteristics:
â‘ To maintain a certain viscosity, the adhesion with the post-printing ink is greater than the cohesion of the post-printing ink.
â‘¡ Maintain a certain degree of wettability, which can be wetted by the post-printing ink and adhere to each other.
3. Ink Overprinting of Multicolor Offset Press
When printing with a multi-color offset press, the printing interval between each color is extremely short. The ink printed in the front needs to be overprinted with new ink within a fraction of a second. The ink printed first is too late to dry, and the ink of the next color will go up. Overprinting, ink films adhere to each other in a wet state, so it is called wet printing. Overprinting of ink is carried out in a wet press wet manner.
In dry printing, the post-printed ink is transferred to the pre-printed ink that has been fixed and gradually dried. The post-printed ink is separated in the middle of the ink film, that is, half is transferred to the previous color ink film, and the other half remains On the blanket roller surface. Wet printing is not the case, the latter color ink is generally split in the middle of the ink film of the two-color ink superimposed, a small part is transferred to the wet ink film of the previous color, and most of it remains on the surface of the blanket cylinder. Obviously, the ink overprint rate of wet printing is lower than that of dry printing. The ink transfer situation is far better than that of dry printing. The phenomenon that occurs during the overprinting process is more complicated, and there are many factors that affect the ink overprinting rate. Specifically, the most important factors affecting the multi-color offset printing ink overprinting are the viscosity, density and brightness of the ink. The following uses the ink used in the four-color offset press as an example to discuss in detail.
The viscosity of the ink has a great influence on the overprint effect of wet printing. The greater the viscosity of the ink, the greater the viscosity, and the ink layer shows greater cohesion. If the viscosity of the ink printed first is lower than the viscosity of the ink printed afterwards, the ink printed afterwards will rely on its own cohesive force to peel off the ink printed first, resulting in reverse overprinting, making wet printing impossible. Therefore, the ink used by the four-color offset printing machine should gradually reduce the viscosity of the ink in the order of the rollers of each unit. For yellow, magenta, cyan and black inks, the viscosity relationship is: black, cyan, magenta, yellow .
The density of the ink has a certain relationship with the thickness of the ink film. In a certain range, the thickness of the ink film gradually increases with the increase of the density value. For wet printing, the ink with a larger ink film thickness is printed in the subsequent color sequence, and the overprint effect is good.
Electric Stew Pot,Camping Cooking Set,Stainless Steel Soup Pot,Stainless Steel Stock Pot
SUZHOU JIAYI KITCHENWARE TECHNOLOGY CO.,LTD , https://www.jiayi-kitchenwares.com