Definition
Paper coating measuring rod usually refers to an instrument or tool component used in laboratories or production sites to quantitatively measure the coating layer on the surface of paper or cardboard. Its core function is to accurately determine the coating amount of coated materials (such as pigments, adhesives, etc.) on paper per unit area, which directly affects the paper's gloss, printability, barrier properties and other key quality indicators. In the paper manufacturing and processing industry, the control and measurement of coating volume is the basic link to ensure product quality stability and process economy.
Principle
The measurement principle of paper coating measuring rod is mainly based on the physical peel and weighing method. Typically, the instrument uses a precision cutting device to obtain a sample of a known area of the circular coating layer on the surface of the specimen. Subsequently, the coating layer is completely separated from the paper substrate using specific chemical solvents or physical methods. The separated coating layer is cleaned, dried, and weighed using a high-precision analytical balance. The amount of coating (usually measured in grams per square meter, g/m²) is calculated by dividing the measured layer mass by the sampling area. Its basic relationship can be expressed as:
Coating Amount = (Coating Layer Quality) / (Sampling Area)
Some advanced systems may integrate non-contact measurement principles such as optics or β-ray for in-line or rapid screening, but peel weighing is often considered a reference method due to its direct and reliable nature.
Measurement method
Standardized measurement methods usually follow relevant international or national standards, such as ISO standards or TAPPI methods. The operation process generally includes the following steps: First, a representative paper sample is collected according to the prescribed method and balanced under standard temperature and humidity conditions. Second, one or more circular specimens are cut on the sample using a sampler equipped with a standard-sized cutting ring. The specimen is then soaked in a specific solvent to separate the coating from the fiber substrate, a process that may require heat or ultrasound assistance. The coating particles are then collected using a filtration device and thoroughly washed and dried. Finally, the quality of the dried coating layer is weighed using a balance that meets the required accuracy, and the coating amount is calculated using the above formula. To ensure the accuracy of the results, experiments often require parallel testing.
Influencing factors
The accuracy and repeatability of measurement results are affected by a variety of factors. The uniformity of the sample itself is fundamental, and if the coating layer is unevenly distributed, single-point sampling may be unrepresentative. Ambient temperature and humidity affect the paper's balanced moisture as well as solvent volatility, so it needs to be tested under standard conditions. The choice of solvent is critical, as it needs to be effective in dissolving or stripping the coating layer without damaging or dissolving the paper substrate fibers. Details during operation, such as soaking time, peeling force, thoroughness of washing, and degree of drying, can introduce errors. In addition, analyzing the calibration status of the balance, the dimensional accuracy of the cutting ring, and the proficiency of the operator are also factors that cannot be ignored.
Application:
Paper coating measuring rods and related measurement technologies are widely used in the paper industry and its upstream and downstream industrial chains. In the production line of a paper mill, it is used to monitor the amount of coating on board and optimize the adjustment of process parameters to stabilize product quality and control raw material consumption. In the R&D and technical services departments of coating chemical suppliers, this technology is used to evaluate the coverage efficiency and suitability of different coating formulations. In paper processing and printing companies, the measurement of coating volume helps predict the printing performance, varnishing effect or composite adaptability of a material. In addition, in third-party testing institutions and scientific research institutes, this method is an important means for paper performance research, quality arbitration and standard formulation.
Selection
When choosing the right coating measurement solution, there are many aspects to consider. First, the main measurement object, i.e., the type of coating layer (e.g., water-based coating, solvent-based coating, etc.), determines the compatibility of the desired stripping solvent and method. Second, depending on the amount of inspection (R&D occasional or in-line frequent testing) and the required accuracy, it is decided whether to choose a manual peel weighing kit or a more automated integrated instrument. The measurement range needs to cover the expected coating range of the sample to be tested. The user-friendly design of the operation, such as the simplification of steps and the safe handling of hazardous solvents, is related to the efficiency and safety of long-term use. In addition, whether an instrument or method follows or is compatible with industry-common standard methods is directly related to ensuring data comparability and reliability. Finally, the supplier's technical support capabilities and after-sales service network are also considerations to ensure the continuous and stable operation of the equipment.