Definition
Surface Dyne Pen is a handheld inspection tool used to quickly assess the surface wettability of solid materials. It is widely used to judge the adhesion compatibility of material surfaces to liquids (especially inks, coatings, and adhesives) by measuring the critical value of material surface tension and indirectly reflecting the surface energy level of materials. This tool is not a precision quantitative instrument, but it is often used as a rapid screening method on the production site or in the laboratory due to its ease of operation and intuitive results.
Principle
The working principle of the Surface Nendine Pen is based on the phenomenon of the spread of liquids on solid surfaces. The pen contains a test solution with a specific surface tension, usually a mixture of formamide and glycol ether, and its surface tension values are precisely calibrated and calibrated in millinewtons per meter (mN/m). When the test solution is applied to the surface of the material, if the liquid maintains a continuous liquid film for 2 to 3 seconds, it indicates that the surface of the material can be higher than the surface tension of the test solution. If the liquid shrinks into droplets or breaks, the surface of the material can be lower than the surface tension of the test fluid. By using dyne pen series with different nominal values, the approximate range of surface energy of the material can be gradually approached.
The theoretical basis of this method can be simplified to the wetting equilibrium relationship described by Young's equation:
γSV = γSL + γLV cosθ
Among them, γSVIt is the solid-gas interface tension (i.e., surface energy), γSLIt is the tension of the solid-liquid interface, γLVis the surface tension of the test liquid, and θ is the contact angle. When θ approaches 0°, the test fluid is fully spread, at which point it γSV ≥ γLV。
Measurement method
Before measuring, ensure that the surface to be measured is clean, dry and free of contamination. A dyne pen with a nominal value estimated to be higher than the surface energy of the material is selected to draw a liquid line about 25 mm long on the surface at moderate speed and pressure. Observe the liquid line status: If the liquid film remains intact for more than 2 seconds, replace the dyne pen with a higher nominal value and repeat the test; If the liquid film shrinks rapidly, replace the dyne pen with a lower nominal value. When a nominal value is found that keeps the liquid film intact for about 2 seconds, this value can be approximately regarded as the lower limit reference value of the material's surface energy. Each set of tests is recommended to be repeated three times in different positions to improve result consistency.
Influencing factors
The properties of the material itself are the basic factors that determine the surface energy, including chemical composition, crystal morphology, polar group distribution, etc. Surface treatment processes such as corona treatment, flame treatment, and plasma treatment can significantly alter the surface energy. Ambient temperature and humidity may affect the volatilization rate of the test solution and the surface condition of the material. Surface contamination, including grease, dust, and release agent residues, can significantly reduce the measured value. The consistency of the test operation, including stroke speed, angle, and pressure, can also have an impact on the observations.
Application:
In the printing and packaging industry, it is used to evaluate the surface treatment effect of plastic films and metal foils to ensure the adhesion of inks or coatings. In automobile manufacturing, it is used to check the surface cleanliness and activation of plastic parts (e.g., bumpers, interior parts) before painting. It is commonly used in the electronics industry to test the surface adhesion of solder masks and shell materials of circuit boards. The composites field is used to verify the surface treatment quality of substrates before lamination. In addition, in the quality control process, it can be used to quickly screen batches of material for surface state consistency.
Selection
The selection of the type is primarily based on the approximate range of surface energy of the material to be measured. Common polymers (e.g., polyethylene, polypropylene) have low surface energy and usually require a dyne pen with a nominal value of 30 to 40 mN/m; Treated surfaces or polar materials (e.g., polyester, nylon) may require 40 to 50 mN/m or more. It is recommended to purchase a set that covers a wide range (e.g. from 30 to 60 mN/m) to accommodate different material tests. Attention should be paid to whether the test solution formulation complies with relevant industry standards (e.g., ASTM D2578). For volatile or sensitive materials, choose a model with a slower evaporation rate of the test solution solvent to reduce the potential impact on the sample. Regular calibration and verification of dyne pens using standard reference photos is a necessary step to ensure the reliability of measurement results.