At present, the color box printing quality detection technology mainly includes two kinds of density and color. Among them, the density mode is a process control mode, which controls the key steps of the printing production process according to the ink layer thickness. The color mode is a high-precision system control mode, and the color control is performed according to the visual measurement of the colorimetric or spectroscopic spectrum, but it needs to comprehensively consider the printed material, the application environment, and the test purpose. In terms of implementation, both manual offline sampling and automatic online detection can be used.
1. Detection and control of printing quality of special materials
In the box packaging, the application and innovation of special materials and new materials is a trend, such as the development of cigarette packs from paper soft packs, cardboard hard packs, and aluminum foil gold and silver cardboard hard packs. These high-gloss surface composite or coating materials have metallic luster and refractive surface. After printing beautiful patterns of various colors, people feel high-grade and elegant, which can greatly increase product value-added space and are widely used in high-end color box.
Such high-gloss surface materials have a strong metallic luster due to the smooth surface coating, and when the incident light is irradiated, a strong specular reflection occurs. Therefore, the color appearance of the object surface will change with the change of the viewing angle, resulting in the color in the printing production process is not easy to control, so that the printing factory face the same ink color to ensure that the same batch of printing products, even different batches of printing products. The quality control problems and their special testing requirements.
In addition to the four-color printing color pictures, the color box printed with special materials has many spot colors and anti-counterfeiting technologies. The detection contents include density, dot gain, registration, and gloss. Due to the restriction of surface gloss of special materials, in the measurement of density and dot, it is necessary to use a test instrument that uses d/0 to measure optical geometric conditions. It is best to divide the visible light from 400 to 700 nm into 31 measurement intervals according to the principle of spectroscopy. Spectral reflectance of color, and then to obtain color CIELab value and color difference spectrophotometer, such as X-Rite's SP series. Thus, the accuracy and reliability of the measurement data of the high gloss surface material are guaranteed. Measurement instruments used in the geometric conditions of common materials 0/45, such as the X-Rite 900 series, cannot achieve consistent and accurate results.
2. Detection and control of spot color printing quality
In the printing of color box packaging products, due to the spot color printing with a large area of color blocks, the color is dazzling, and the shelf display effect is good; the color difference due to dot overprinting and dot distortion is reduced, the color is stable, and the identification is easy, so a large amount of special Color printing is its basic feature. At present, the domestic color box printing companies are lagging behind in the measurement and control of spot colors. Most of them are still in the stage of relying on the experience of the workers to allocate spot color inks. The proportion of spot color inks is not precise enough, and the deployment time is long. The subjective factors have a great influence. Disadvantages. 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 detection.
The spot color ink distribution system is a system composed of a computer, a color matching software, a spectrophotometer, an analytical balance, an evenness meter, an ink exhibition machine, and a printability meter. The spot color ink distribution system can store the parameters of the printing materials, inks and color matching data of color box printing companies in the system database through testing and experiments. The color matching software can perform spectrophotometric measurement according to the color swatches provided by the customer, and can be applied to the computer automatically. Color matching and color matching operations are performed, and color matching conditions are controlled according to CIELab values, density values, and ΔE of customer samples and color matching samples, and printing control parameters are provided, thereby realizing dataization of spot color ink distribution. For example, the SpectroEye Swiss ink formulation system including spectrophotometer SpectroEye and InkFormulation not only can measure the print dot, density value, but also can measure Hue, Saturation and Luminosity; InkFormulation only A small concentration scale creates an accurate database. Color matching data can be offset-oriented or flexo-, gravure- and screen-printable, providing a variety of ink formulation sorting methods, such as hue similarity, metamerism value, spot ink unit price, ink usage, Ink thickness and so on. Therefore, the application of numbers fundamentally breaks through the constraints of empirical color matching and satisfies the development requirements of the higher quality, shorter cycle, and lower cost of the color box printing industry.
3, online quality inspection and control technology of box printing
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 perform immediate adjustment of the print quality on-line detection and control technology is constantly popularizing and optimizing. International mainstream printer manufacturers have adopted online image inspection systems as standard configurations, such as Manroland PECOM, Heidelberg CPC32, Switzerland's BOBST, USA's PROIMAGE, Japan's DAC and TOKIMEC.
The online print quality inspection and control system uses high-definition, high-resolution, high-speed camera lenses to capture images. Standard sample data is used as the standard. Differences and differences between real-time contrast-detected images and standard samples (such as those generated during the printing process) Traces, dots, chromatic aberrations and other errors). The 0.10mm size defect can be accurately found even if the defect is only one gray level difference from the standard image. This system can completely eliminate human error, achieve high-speed, high-precision, 100% real-time detection of color box prints, and establish a unified, quantifiable inspection standard.
In a word, the digitalization of color box printing quality detection and control is a new direction representing the future of color box printing production, and it is the technical guarantee for integrated production of design, printing and post-press processing. At present, although there are still some deficiencies or technical bottlenecks in the detection and control of digital color box printing in China, the major difficulties are being eliminated and bright prospects have been seen. Grasping the digital technology of quality control, establishing its own innovative technology, and realizing refined operations will become the key to the distribution of profits in the huge color box printing market, and it is also the fundamental issue for the sustainable development of color box printing enterprises.
