Definition
An offset ink spreader is a specialized laboratory testing instrument used to simulate the offset printing process and evaluate the color performance and color development characteristics of inks on specific substrates. It uses a standardized mechanical operation to evenly apply the ink to the test substrate, forming a color sample that can be used for color measurement and visual evaluation. This instrument provides key technical means for color quality control, formulation research and development, and printing suitability prediction of inks in printing, packaging, ink manufacturing, and material testing industries.
Principle
The core working principle of the instrument is to simulate the ink transfer and uniforming process of anilox roller printing on offset printing. It is mainly composed of a precisely controlled coating mechanism, ink uniforming system and substrate fixture. When working, the amount of ink to be measured is taken and placed on the ink homogenization system or specific coating components, and driven by a motor, so that the ink homogenizer roller is uniformized at the set pressure and speed to ensure uniform ink distribution. Subsequently, the coating mechanism transfers and lays the uniform ink on the surface of a fixed test substrate (such as paper, film, etc.), forming a controllable and uniform ink film. This process eliminates the interference of variable factors in actual printing, such as press status, environmental fluctuations, resulting in highly repeatable standard color spreads.
Measurement and evaluation methods
After the excellent sample is prepared using an offset ink color spreader, it is usually quantitatively evaluated in combination with subsequent instruments. Color measurement mainly uses spectrophotometer to measure CIELAB chromaticity value (L*, a*, b*), color aberration (ΔE), color intensity and density of color samples. When evaluating the color development characteristics of inks, the surface uniformity, gloss and coloring power of the ink film are often concerned. The determination of coloring power can be achieved by mixing the test ink with the standard white ink in proportion and spreading the color, comparing its color difference with the standard proof. The formula can be expressed as a correlation between the percentage of coloring force and the color aberration ΔE, ΔE = √((ΔL*)² + (Δa*)² + (Δb*)²). In addition, visual contrast is still a necessary aid in evaluating color performance and ink layer flatness.
Key factors that influence measurement results
The accuracy and repeatability of the measurement results are affected by multiple factors. Instrumental factors include coating pressure, coating speed, uniform ink time, and pressure, which need to be calibrated and harmonized according to standard methods such as ISO 2834, GB/T 13217. Ink factors involve ink viscosity, thixotropy, and pigment dispersion stability, which affect uniformity and transfer. Substrate factors such as the absorbency, smoothness, whiteness of the paper, and the surface tension of the film can significantly change the apparent color and gloss of the ink film. Environmental factors such as temperature and humidity in the laboratory should be controlled within the standard range to avoid changes in the rheological properties of inks and the physical state of the substrate. The operating factors include the amount of sampling, the degree of cleanliness and the consistency of the operation technique.
Applications
The application of offset ink color spreader runs through multiple industrial links. In the ink manufacturing industry, it is used for new formulation development, batch-to-batch color quality control, and standard determination of coloring power and hue. In printing and packaging companies, it is used to predict the final printing effect of ink on a specific material, assisting in color matching and signature before printing. In quality inspection institutions and R&D laboratories, it is used as a tool for ink performance compliance testing according to international standards (such as ISO) or national standards. It can also be used to evaluate the effect of different substrates on the color performance of inks at the relevant material suppliers.
Key points to consider in selection
Technical parameters and functional requirements should be comprehensively considered when selecting. The core parameters include coating width, coating speed range, control accuracy and adjustable range of coating thickness or pressure, which need to match the type of ink to be tested (e.g., sheetfed offset ink, UV ink) and the size of the commonly used substrate. In terms of function, it should be considered whether it has functions such as automatic ink uniforming, pressure digital display and memory, and multi-program storage to improve test efficiency and consistency. The instrument should be constructed from durable and easy to clean to avoid cross-contamination. In terms of compatibility, it is necessary to confirm that its operation complies with the prevailing standard methodology followed by the target market or industry. In addition, the supplier's technical support, calibration services and the sustainability of the spare parts supply are also factors that ensure long-term use.