The color management in the printing process is a very important position in the whole color management system, because the quality of this stage is directly related to the quality of the batch products, especially in the field of cigarette printing with stability as the first requirement. Poor control, light batch scrapping, customer complaints return, and directly affect their reputation.
First, the importance of data standards
The so-called standardization is the maximum standardization. The same process conditions, in different locations, different time, different operations staff to print, the effect should be exactly the same. This requires measurement and control of process parameters and stability of process conditions. This requires us to determine the key processes in the printing process, according to the characteristics of the company, all processes in the printing process are controlled, in order to achieve the purpose of specialized production.
In the traditional printing production, the employees' thinking is emotional, empirical, and disorderly. The skill is often taught by the master with the apprentice. In the thinking habits of some masters, it is always believed that printing production relies on the experience passed down from generation to generation. It is unclear and unclear. It is natural to know more about it. In fact, this is an unscientific and imprecise approach. Modern printing requires many steps to accomplish together, maximizing cost savings, increasing production efficiency, and ensuring stable print quality. A scientific, rigorous system and process flow is required.
Standardization and standardization of enterprises can form strong productivity. Research institutions in London have done a lot of long-term statistics. It is concluded that 13 of Europe's economic growth is due to standardization, which is much higher than the driving of patent technology. We must be keenly aware that the rational age of the printing industry has arrived. In recent years, the Business Strategy Alliance, a consortium of suppliers from a number of printing industries and academic groups, has implemented a unified “job identification format†that is controlled by establishing standard “output†and “input†information formats. The effective operation of the production process has become the consensus of “standardization, digitization and standardization†in the industry, and is called the milestone of printing industry standardization.
Standardization does help print quality control, reduce costs and improve service levels. The printing production process is long and complicated. The control of printing quality lies in the whole process. Any process link is not handled properly. The skill level of operators in each link is uneven and the operation is not standardized. It is impossible to produce printing products. For the production process, the control points and control elements are set to meet the standard requirements, and the process control is performed as the basis for the flow into the next process.
Second, the color data of cigarette packages
For printing companies, while developing the color quality standards for printed products, it is necessary to simultaneously develop quality standards for printing materials (inks and papers) and to effectively control them to achieve the required quality of printed products. The tolerance of the color of the printed product and the tolerance of the paper can be the same as the control standard of the printing user (cigarette enterprise); or, according to the production conditions of the printing enterprise, relatively strict control standards are established.
The standard chromaticity coordinate value of the ink can be determined by using the same standard chromaticity coordinate value as the specified target color of the printed product; or the data obtained by measuring the ink color swatch obtained by the specified ink smear using an automatic ink scraping machine as the The standard chromaticity coordinate value of the ink. In this way, it is a comprehensive performance of all the influencing factors to facilitate the detection and control of the color difference of the printed matter without the need for printing on the factory. Therefore, the quality control of the incoming ink must be relatively strict. Scope, so that the printed product obtained after the printing combined with the chromatic aberration caused by other influencing factors can reach the final quality requirement.
1. Formulation of target color standard chromaticity values
The color quality management of cigarette trademarks can use a spectrophotometer and a color data processing system. The minimum measuring aperture is 3mm; therefore, the actual measured area of ​​the measured color on the cigarette trademark must be greater than 3mm; it must be greater than 5mm to facilitate the worker to detect and obtain good repeatability.
After the cigarette label is wrapped, the detection color block of 5 to 8 mm diameter is printed on all the colors to be controlled without affecting the application of the glue.
Samples of 20 to 100 or more proofing marks are sampled, and the proofing marks that meet the design color requirements and the differences between the proofs are within the wide capacity of the human eye are used as standard color samples after being visually observed by the human eye-setting department.
Perform colorimetric measurement on each color of the above standard color sample and perform statistical calculation, calculate the average value of L, a, b as the standard chromaticity value of the color in the trademark; or use the target color in the color quality control software Set the average value measurement in the function to set the standard chromaticity value.
Repeat the above operation to formulate the relevant L, a, b standard chromaticity value target color tolerance range for different trademarks and different colors.
2. Use the ΔECMC eligibility determination method to establish the tolerance range
According to the product quality requirements, a reasonable business index difference value (different colors with the same color quality requirements only need to set the same value) as the final color quality qualification judgment tolerance range.
3. Production process control means
In general, process technicians always want to maintain constant process parameters and technical methods for production. However, in the actual production process, it is often difficult to achieve such ideal production conditions due to changes in one or the other factors. In particular, inks, because manufacturers are constrained by the chemical and pigment industries, inks produced in different batches are unlikely to maintain the same level of quality, especially between batches with longer production dates. Therefore, before printing, it is necessary to adjust the specific process parameters on the basis of the original process standards for the actual production conditions such as material changes, in order to ensure satisfactory and stable color quality of different batches of printed products.
Example 1: When the ink color saturation is slightly higher than the standard and a new printing plate with a relatively deep nick is used, the viscosity of the ink should be lowered or the printing speed should be adjusted to reduce the thickness of the ink layer to reduce the printing. Color saturation.
Example 2: When the ink color is the same as the standard, the paper is slightly yellowish. Then, the printed ink color obtained by large-area solid printing must be slightly yellowish. Therefore, it is necessary to replace the paper having a relatively high whiteness or to appropriately adjust the yellow component of the ink color. In this way, the final quality requirements for the color of the print can be achieved.
4, quality control
In the printing process, due to the random error of the printing equipment, the technical ability of the operator, the evaporation and viscosity changes of the ink composition, the blocking of the printing plate, the fluctuation of the printing speed, the change of the drying temperature, and the change of the temperature and humidity of the environment, etc., Both will cause fluctuations in the color quality of the same batch of prints. Therefore, it is necessary to use a color difference meter to carry out timely sampling inspection of the semi-finished products in the printing process, to understand the deviation of the color difference of the printing products and to adjust the process parameters in time, and to control the color quality of the printing products to fluctuate within the minimum variation range. Thereby reducing the scrap rate of printed products and improving economic efficiency. According to whether the printing equipment has a slitting mechanism, the corresponding random sampling time is set, and the printed semi-finished products are sampled in time.
5. Using color difference measurement to detect random sample products for color difference analysis
Note: The color difference analysis in the quality control process is not a print qualification test. If the sampling test results exceed the tolerance range, adjusting the process parameters for control will result in many unnecessary scraps. Therefore, it is necessary to adjust the process parameters in time according to the actual degree of deviation of the color difference. Combining the relevant content of the CIELAB system in the basic theory of color, the color difference deviation analysis is performed on the above sampling data.
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