At present, the detection technology of color box printing quality mainly includes density method and chromaticity method. Among them, the density method is a process control mode, which controls the key links of the printing production process according to the thickness of the ink layer. The chromaticity method is a high-precision system control mode, which controls the color according to the intuitive measurement of chromaticity or spectroscopy, but requires comprehensive consideration of printing materials, application environment and test purposes. In terms of implementation, either the offline method of manual sampling or the online method of automatic detection can be used.
1. Inspection and control of printing quality of special materials
In the color box packaging, the application and innovation of special materials and new materials is a trend, such as the development of cigarette packages from paper soft bags and cardboard hard bags to aluminum foil gold and silver cardboard hard bags. These high-gloss surface composite or coating materials have metallic luster and refractive surface. After being printed with exquisite patterns in various colors, they feel high-end and elegant, which can greatly increase the value-added space of products and are widely used in high-end color boxes.
This kind of high-gloss surface material has a strong metallic luster due to its smooth surface coating, and strong specular reflection occurs when incident light is irradiated. Therefore, the color appearance of the surface of the object will change with the change of the observation angle, which makes it difficult to control the color in the printing production process, so that the printing factory can ensure that the ink color of the same batch of printed products or even different batches of printed products is consistent. The quality control problem and its special testing technical requirements.
In addition to the four-color printing color image, the color box printed with special materials also has many spot colors and anti-counterfeiting processes. The detection content includes density, dot expansion, registration and gloss. Due to the restriction of the surface gloss of special materials, in density and dot measurement, a test instrument that uses d/0 to measure optical geometric conditions must be used. It is best to use the principle of spectroscopy to divide the visible light from 400 to 700 nm into 31 measurement intervals to measure the object. Color spectrum reflectance, and then obtain the color CIELab value and color difference spectrophotometer, such as X-Rite’s SP series. Thus, the accuracy and reliability of the measurement data of high-gloss surface materials are ensured. It is impossible to obtain consistent and accurate results for measuring instruments that are applied to the 0/45 geometric conditions of ordinary materials, such as the X-Rite900 series.
2. Inspection and control of spot color printing quality
In the printing of color box packaging products, because spot color printing has a large area of solid color blocks, the colors are eye-catching, and the shelf display effect is good; it reduces the color difference caused by dot overprinting and dot deformation, and the color is stable and easy to identify. Therefore, a large number of special colors are used. Color printing is its basic feature. At present, domestic color box printing companies have relatively backward measurement and control methods for spot colors, and most of them are still in the stage of relying on the experience of workers to mix spot color inks. The spot color ink ratio is not accurate enough, the adjustment time is long, and subjective factors have a large impact. shortcoming. Therefore, the use of color matching system is the best solution to the problem, and it is also the mainstream technology and development direction of international color box quality control and inspection.
The spot color ink matching system is a system composed of a computer, color matching software, spectrophotometer, analytical balance, ink distributing instrument, ink spreading instrument and printing suitability instrument. The spot color ink matching system can store the printing materials, inks and color matching data of the color box printing company in the system database through tests and experiments. The color matching software can perform spectrophotometric measurement according to the spot color sample provided by the customer, and use a computer to automatically Perform color matching analysis and color matching operations, control color matching conditions according to the CIELab value, density value, and △E of customer samples and color matching samples, and provide printing control parameters, so as to realize the digitization of spot color ink matching. For example, the Swiss GretagMacbeth ink formulation system including hardware spectrophotometer SpectroEye and InkFormulation, its SpectroEye can not only measure the dot and density value of printed products, but also measure hue, saturation and luminosity; InkFormulation only needs extreme An accurate database can be established with a few concentration scales. Color matching data can be used for offset printing, flexo printing, gravure printing and screen printing. It can provide a variety of ink formula sorting methods, such as similarity of hue, metamerism value, unit price of spot color ink, ink consumption, Ink layer thickness, etc. As a result, the application of numbers fundamentally breaks through the constraints of empirical color matching, and meets the development requirements of the color box printing industry for higher quality, shorter cycles, and lower costs.
3. On-line inspection and control technology for color box printing quality
With the development of digital image acquisition technology and processing technology, the use of a closed-circuit control system to detect the entire image of the printed product and make immediate adjustments to print quality online detection and control technology is being popularized and optimized. International mainstream printer manufacturers have adopted online image inspection systems as standard configurations, such as manroland PECOM, Heidelberg CPC32, Swiss BOBST, American PROIMAGE, Japanese DAC and TOKIMEC.
The online printing quality inspection and control system uses a high-definition, high-resolution high-speed camera lens to capture images, and uses the standard sample data as the standard. Marks, ink dots, chromatic aberration and other errors). Defects with a size of 0.10mm can be accurately found, even if this type of defect has only one gray level difference from the standard image. This system can completely eliminate human error, realize high-speed, high-precision, and 100% real-time detection of color box prints, and establish a unified and quantifiable inspection standard.
In short, the digitalization of color box printing quality detection and control is a new direction that represents the future of color box printing production, and is a technical guarantee for the integrated production of design, printing and post-press processing. At present, although there are still some deficiencies or technical bottlenecks in the digitalization of color box printing quality inspection and control in China, the main difficulties are being eliminated, and a bright future has been seen. Mastering the digital technology of quality control, establishing its own innovative technology, and realizing refined operations will become the key to the profit distribution of the huge color box printing market and the fundamental issue of the sustainable development of color box printing enterprises.