In recent years, the printing color number of gravure-printed flexible packaging products has shown a sharp increase trend, and the amount of gravure-colored printing plates and gravure-colored inks has been increasing year by year. The increase in the number of printing colors has made the printing of flexible packaging products more difficult, and the rate of defective products has increased, especially the number of defective products due to chromatic aberration has rapidly increased.
There are many reasons for the chromatic aberration, and gravure spot color ink is one of them. In the preparation of gravure spot color inks, most domestic ink manufacturers still rely on the experience of technicians to carry out color matching, and judge by the naked eye; foreign and joint venture ink manufacturers have long used computer color matching software, spectrodensitometer and Automatic proofing system to ensure color consistency of gravure spot color inks.
In the process of preparation of gravure spot color inks, the film substrate for printing, gravure plate roll and printing process setting are some key issues that ink manufacturers must understand and master, and the final production of gravure color inks The quality will have a big impact.
Relationship between film substrate and color reproduction of gravure spot color ink
In the actual production of flexible packaging enterprises, there are many types of film substrates for printing. Often, customers need to print the same graphics on different film substrates due to different product series and specifications (especially with spot inks). Graphic), such as QS logo, company LOGO, etc., and requires that the color of these graphics must be consistent, the color difference is as small as possible. Therefore, whether the same gravure spot color ink can meet this requirement needs to be judged by experiments.
Relationship between gravure roll and color reproduction of gravure spot color ink
At present, the gravure plate roller is usually electronically engraved. After the image file is finished, it is necessary to determine the specific electrosurgical process parameters for each color plate roller (including the spot color plate roller, for example, the number of engraving lines, the angle of the engraving needle, and the engraving). Cable angle, engraving curve, dark tone, highlight and channel. Since the selected electro-engraving process parameters will directly affect the depth of the printing grid, the amount of transfer of the gravure spot color ink is determined, thereby affecting the color effect on the final print. Therefore, it is necessary to experiment and confirm that the main electro-engraving process parameters of the spot color gravure roll are the two prerequisites for accurately preparing the gravure spot color ink.
Practice has proved that even if the same printing ink, the same printing speed, and the same film substrate are used, the color of the final printed matter will be greatly different due to the different engraving process parameters of the gravure plate roller, and the ΔE is more than 6. Therefore, in the design stage of gravure spot color ink, it is necessary to clarify the process parameters of the spot color plate engraving of the product to be printed, and consider the matching between the spot color ink and the gravure plate roller as an important reference. .
Relationship between printing process (ink viscosity, printing method, whether white ink is used) and color reproduction of gravure spot color ink
Gravure printing machines are usually designed to have the highest printing speed, and the actual printing speed in normal production is generally lower than the highest printing speed of the design, so as to ensure that the gravure printing machine is in a stable and stable working state, and the equipment loss is minimized. Gravure ink is a kind of liquid ink with good fluidity. The general rule between viscosity and printing speed is: the faster the printing speed, the lower the working viscosity of the ink is required, and vice versa, the higher the working viscosity of the ink is required; Within a certain range, the printing speed of the gravure press is inversely proportional to the working viscosity of the gravure ink. The gravure spot color ink is also suitable for this general rule. The working viscosity directly affects the color density of the gravure spot color ink, and the change of the color density of the gravure spot color ink will cause the color difference of the spot color on the printed matter.
The same printing ink, the same gravure plate roll, the same film substrate, when the ink viscosity is different, the final print color will also have a large difference, â–³ E up to more than 10. Therefore, it is necessary to clarify the printing speed of the customer gravure printing machine and the working viscosity of the gravure spot color ink required at this printing speed, which is the third requirement for preparing the gravure color ink.
The same printing ink, the same gravure plate roll, the same film substrate, using different printing methods, the final print color will have a certain difference, â–³ E up to 7 or more. Therefore, it is necessary to clarify the printing method of the products to be printed by the customer is the necessary condition for preparing the gravure color ink.
The film substrate, gravure roll, printing process, etc. described in this paper are the key factors affecting the formulation of gravure spot color inks. Generally, soft packaging companies regard this as a potential quality requirement. To this end, gravure ink manufacturers need to identify, quantify, and convert these implied quality requirements into gravure color inks at the beginning of gravure ink design to determine the appropriate ink production. Process, design the correct experimental ink formula, in order to continuously improve and improve, and ultimately close to or achieve the goal of customer satisfaction.
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