Definition
Flexographic Printing Spreader Wheel is a laboratory inspection tool used in flexographic printing processes, whose primary function is to simulate the printing process to form a uniform layer of ink or varnish film on a specific substrate material. It is not a printing equipment directly used in production, but a key laboratory instrument for ink development, printability testing, color management, and process parameter optimization. Through its work, standardized prints can be obtained for subsequent performance measurements such as density, chromaticity, adhesion, abrasion resistance, etc.
Principle
The core working principle of flexographic printing color roller is to simulate the ink transfer process of anilox roller-plate-substrate in flexographic printing. The instrument typically consists of a precisely engraved metal anilox roller and a color spreader wheel with a flat rubber or photosensitive resin pad. During the test, the quantitative ink is applied to the anilox roller, and the excess ink is scraped off by the ink scraper, so that the anilox roller mesh cavity is filled with quantitative ink. The anilox roller then makes contact with the analog plate on the spreader wheel and transfers the ink to it, which then imprints the ink onto the surface of the substrate at a set pressure and speed, forming a uniform field color block or specific test pattern.
The amount of ink transfer is theoretically closely related to the mesh volume of the anilox roller, which can be expressed by the following equation:
V = K × A × D
Where V represents the theoretical ink transfer volume, A is the number of holes per unit area of the anilox roller, D is the depth of the hole, and K is the coefficient related to the geometry of the hole. The actual transfer amount is also affected by factors such as ink rheological characteristics, pressure, and speed.
Measurement and evaluation methods
Prints prepared using flexographic printing spreaders are the basis for a series of subsequent physical and chemical property measurements. Key measurement methods include: First, the lab value, chromatic aberration ΔE, and density values of the print are measured using a colorimeter or spectrophotometer to evaluate color performance and ink thickness uniformity. Secondly, an adhesion tester (such as the grid method) is used to evaluate the binding fastness of ink to the substrate. Furthermore, the anti-friction performance of the printed sample is tested by using a friction resistance tester. In addition, the reproducibility of the print dots or the flatness of the field part can be observed through a microscope, and the original performance of the ink and the printing effect can be correlated with the original performance of the ink using instruments such as a viscometer. All measurements are usually performed with reference to relevant industry standards (e.g., ISO, ASTM, GB/T series of standards on print testing) to ensure comparability and accuracy of results.
Influencing factors
The test results of flexographic color spreaders are influenced by multiple factors that interact to determine the quality of the final print. In terms of instrument parameters, the number of lines of the anilox roller, the shape and volume of the mesh cavity, and the pressure and speed setting of the color spreader are the basic variables. Material factors include ink viscosity, thixotropy, drying speed, and substrate's surface energy, roughness, and absorbency. Environmental conditions such as temperature and relative humidity in the laboratory can also affect the leveling and drying process of inks. Operational consistency, such as ink addition, squeegee angle and pressure, and cleanliness, are also important for ensuring test repeatability and reproducibility.
Applications
The application of flexographic printing color wheel runs through multiple links of the printing industry chain. In the field of ink manufacturing, it is a key tool for new product formulation research and development, batch quality stability control. In printing enterprises, it is used for pre-testing printing suitability, optimizing the process parameters of different substrate materials and ink combinations, and reducing debugging losses during formal printing. At packaging material suppliers, it can be used to evaluate the printing performance of substrates such as film, paper, corrugated cardboard, etc. In addition, in scientific research institutions and standard-setting units, the color roller is the basic equipment for studying printing mechanisms and formulating industry test method standards. Its application scope covers many major markets for flexographic printing such as food packaging, label printing, flexible packaging, and carton printing.
Selection considerations
Choosing a suitable flexographic printing color spreader wheel requires comprehensive consideration of actual needs and technical parameters. The primary consideration is the purpose of testing, for example, whether to focus on basic color proofing or to simulate fine dot printing, which will determine the requirements for anilox roller accuracy and color wheel control. The key parameters of the instrument include the range of lines of the anilox roller, the speed and pressure control accuracy and range of the color spreader. Instrument compatibility also requires consideration, such as the ability to replace different widths of color rollers to accommodate multiple widths of substrate, and whether it is easy to integrate into existing color management systems or laboratory workflows. The user-friendly design of operation, ease of maintenance, and the technical support provided by the manufacturer and the declaration of compliance with standards are also important selection reference factors. The final selection should be based on a system analysis of its own test needs and, where possible, real-world prototype testing and validation.