How to effectively apply computer color matching in gravure printing
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Computer color matching has been widely adopted in today's lithographic ink dispensing process, and the industry is also very accepting and valued. However, recently, the author has been questioned by many peers in the gravure printing industry. Why do the colors of their gravure inks have problems every day? Regardless of whether the inks are dispensed by the ink supplier or by themselves, they are not able to accurately match the color of the ink. Even if the color can be successfully blended, it takes a lot of time and wastes a lot of ink. Although the industry will use a computer color matching system to assist in the deployment of gravure inks, although time can indeed save a lot, they still feel that the accuracy is not enough. In fact, compared with the color matching of lithographic inks, the color matching process of gravure inks is complicated and difficult, because the variables affecting the color of gravure inks are numerous. Here I try to share my past experience with you.
Referring to the variables that affect the color of the gravure ink, the industry will first point out that the mesh fineness on the mesh cylinder will affect the color, and the answer is basically correct but not complete. In principle, the fineness of the mesh does affect the color, but generally gravure printing technicians will consider this issue. In fact, in addition to the fineness of the net, another factor that has been forgotten is often overlooked. In gravure printing, the viscosity of the ink is often neglected by the printing technician, and the viscosity is seriously ignored when formulating the formulation. Even ink suppliers and printers can make ink color errors due to viscosity.
The high and low viscosity of the printing gravure ink is related to the printing speed. Generally, the faster the printing speed, the lower the viscosity of the ink will be required to match the high speed operation of the printing machine. I once visited a gravure printing factory, and their technicians told me something that surprised me. He said that before the press operator was near work, they would speed up the printing process in order to finish the work on their hands. Adding a large amount of solvent to the ink reduces the draft and works with the press. This does increase the printing efficiency, but the color of the printed matter is not guaranteed. Adding a large amount of solvent to reduce the viscosity will make the printed matter lighter, that is, its printing density or concentration will be lower than normal. Because when a large amount of solvent is added to the ink, the pigment concentration in the ink (the number of ink pigments per cubic meter) will decrease in real time, and the number of ink pigments per square centimeter of the print color will naturally decrease relative to the same mesh cylinder. Density or concentration drops sharply or the color fades. Basically, the formulation of the intaglio ink must be adjusted to suit different printing environmental conditions, including printing speed, ink viscosity, and mesh fineness.
Generally, after the gravure ink factory produces the gravure ink, the stability and transportation cost of the ink are taken into consideration when shipped. The ink is not added with a suitable solvent at the factory, that is, the ink is delivered to the customer in a high concentration and high viscosity state. When the printer receives the ink, because the ink concentration and viscosity are too high, the printer's technician will add the solvent by itself until the viscosity of the ink drops to a suitable printing environment. This process will lead to two problems. First, what criteria does the technician use to determine whether the viscosity of the ink meets the requirements? Most technicians do not use the viscosity flow cup to measure the viscosity. They will use an ink knife or a stick to stir the ink, and then the ink knife or the stick will be inked up. Pulling, and then feeling the viscosity of the ink, so that the viscosity of the ink is at least one to three seconds change is undetectable. If the viscosity of the gravure ink differs by two seconds, the entire printing color will also change. On the other hand, the quality and concentration of the solvent used in the printing plant may be different from that of the ink factory. Therefore, the color of the intaglio ink is also changed on the raw material. In the ink factory, only the solvent is generally considered. In fact, the printing plant can use the raw materials of the ink factory, and then use some standard viscosity testing equipment, such as viscosity flow cups. Moreover, it is necessary to inform the ink factory of the viscosity of the printing factory before the color matching of the ink factory, so that the ink factory can adjust the formula.
In addition to the viscosity of the gravure ink, the printer will ignore the problem of "whitening". Especially in plastic packaging printing, since the gravure ink is printed on the plastic film, its color is often transparent, so the color is more susceptible to the background. Therefore, in the printing process, a layer of white ink is often applied to the printed ink, that is, "whitening", the main reason is to increase the hiding power of the overall ink, making the color opaque and in the same state. Rendered to avoid color deviations caused by background colors. This layer of white ink has already affected the overall color. It is like the color of the paper affects the color of the printed matter and its ink formulation when lithographic printing is used. The white ink used for "whitening" is like white paper, so it must be clear before color matching. Understand the color of the white ink of "whitening" in order to adjust the formula.
Pay more attention to the printing machine speed, ink viscosity, mesh fineness and "whitening" and other environmental conditions, not only in the use of computer color matching, even artificial color matching should also be considered, so the artificial adjustment of the gravure ink color formula is very difficult. When manually blending, the color can often be adjusted, but the viscosity is not controlled to match the speed of the printing machine. Finally, the solvent is added to adjust the viscosity, which in turn makes the printing color lighter. Therefore, as long as the computer color matching system can input the relevant environmental conditions such as ink viscosity, mesh fineness and "whitening" into the computer, the computer can calculate the appropriate formula. This formula can not only prepare accurate colors according to different mesh fineness and printing machine speed, but also control ink viscosity.