At present, there are two main detection methods for color box printing quality: density mode and chroma mode. Among them, the density mode is a process control mode, according to the thickness of the ink layer to control the key links in the printing production process. Chromaticity mode is a high-precision system control mode. Color control is performed based on intuitive measurement of chromaticity or spectroscopic spectrum, but it needs comprehensive consideration of printing materials, application environment, and testing purposes. In terms of implementation, either manual sampling offline or automatic detection online can be used.
1. Inspection and control of printing quality of special materials
In color box packaging, the application and innovation of special materials and new materials is a trend. For example, cigarette packs have developed from paper soft packs and cardboard hard packs to aluminum foil gold and silver cardboard hard packs. These high-gloss surface composite or coating materials have metallic luster and refractive surfaces. After printing exquisite patterns of various colors, they give people the feeling of high-end elegance, which can greatly enhance the value-added space of the product and are widely used in high-end color boxes.
This kind of high-gloss surface material has a strong metallic luster due to the smooth surface coating. When the incident light is irradiated, a strong specular reflection will occur. Therefore, the color appearance of the surface of the object will change with the change of the observation angle, resulting in the color of the printing process is not easy to control, so that the printing factory faces the same batch of printed products, or even the ink color of different batches of printed products Quality control problems and special testing technical requirements.
In addition to the four-color printing of color boxes, the color boxes printed with special materials also have many spot colors and anti-counterfeiting processes. The detection content includes density, dot expansion, registration and gloss. Due to the limitation of the surface gloss of special materials, in the measurement of density and dots, a test instrument using d / 0 to measure the optical geometric conditions must be used. It is best to use the principle of spectrometry to divide the visible light 400-700nm band into 31 measurement intervals to measure objects. Spectral reflectance of color spectrum, and then the color CIELab value and color difference, such as SP series of X-Rite. Therefore, the accuracy and reliability of the measurement data of high-gloss surface materials are guaranteed. Measuring instruments applied to 0/45 geometric conditions of common materials, such as the X-Rite900 series, cannot achieve consistent and accurate results.
2. Detection 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 color is eye-catching, and the shelf display effect is good; the color difference caused by dot overprinting and dot deformation is reduced, the color is stable, and it is easy to identify. Color printing is its basic feature. At present, domestic color box printing companies are relatively backward in the measurement and control of spot colors. Most of them are still at the stage of relying on the experience of worker masters to prepare spot color inks. There are inaccurate ratios of spot color inks, long preparation time, and subjective factors. Disadvantages. Therefore, the use of color matching system is the best solution to the problem, and is also the mainstream technology and development direction of international color box quality control and inspection.
Spot color ink matching system is a system composed of computer, color matching software, spectrophotometer, analytical balance, ink leveling instrument, ink spreading instrument and printing suitability instrument. The spot color matching system can store the parameters of 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 spectrophotometry based on the spot color samples provided by the customer. Perform color matching analysis and color matching operations, control color matching conditions based on the CIELab value, density value, and △ E of customer samples and color matching samples, and provide printing control parameters, so that the data of spot color matching ink can be realized. Such as the Swiss GretagMacbeth ink formulation system including the hardware spectrophotometer SpectroEye and InkFormulation, its SpectroEye can not only measure the dots and density values ​​of the printed matter, but also measure the Hue, Saturation and Luminosity; InkFormulation only needs to be An accurate database can be established with a small concentration ladder. The color matching data can be used for Offset Printing, flexo printing, gravure printing, and screen printing. It can provide a variety of ink formulation sorting methods, such as similarity by hue, metamerism value, spot color ink unit price, ink usage, Ink layer thickness, etc. As a result, the application of numbers has fundamentally broken through the constraints of empirical color matching to meet the development requirements of the color box printing industry with higher quality, shorter cycle time and lower cost.
3. Online detection and control technology of color box printing quality
With the development of digital image acquisition technology and processing technology, the online detection and control technology of printing quality that uses closed-circuit control system to detect and adjust the entire image of printed products is being continuously popularized and optimized. International mainstream printer manufacturers have adopted online image detection systems as standard equipment, such as Manroland PECOM, Heidelberg CPC32, Swiss BOBST, American PROIMAGE, Japanese DAC and TOKIMEC.
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