Definition
A dyne pen, also known as a surface tension test pen, is a portable tool that quickly evaluates the surface wetting tension or surface energy of a solid material by forming continuous or discontinuous ink lines on the surface of a material. The measurement results are usually measured in millitons per meter, and this tool is widely used in industrial production and laboratories to qualitatively or semi-quantitatively judge the surface treatment effect of materials and their adaptability to adhesion to inks, coatings, adhesives, etc.
Principle
The working principle of the dyne pen is based on the spread and wetting of liquids on solid surfaces. The pen is filled with a test solution with a specific surface tension, and its formulation is usually a mixed solution of formamide and ethylene glycol monoether, with different proportions corresponding to different tension values. When the test solution is applied to the surface of the material, if the surface tension of the test solution is less than or equal to the critical wetting tension of the material surface, the liquid can be evenly spread to form a continuous ink film. On the contrary, if the surface tension of the test solution is higher than the surface energy of the material, the ink line will shrink and break into droplets. By trying test pens with different tension values, the critical wetting tension range of the material surface can be roughly determined.
The process can be described theoretically by Young's equation, and the relationship between the contact angle θ and the tension of each interface is as follows: γSV = γSL + γLV cosθ, in which γSVIt is the tension of the solid gas interface, γSLIt is the tension of the solid-liquid interface, γLVIt is used to test the surface tension of the liquid. When θ approaches 0°, full spreading occurs, at which point γSV ≥ γLV + γSL, simplified judgment often γLVComparison with the surface of the material as a practical basis.
Measurement method
Before measuring, ensure that the surface to be measured is clean, dry and free of contamination. A dyne pen with a nominal tension value close to the estimate was selected and an ink line of about 25 mm long was drawn on the surface of the sample at moderate speed and pressure. Observe the state change of the ink line in the next 2 to 3 seconds: if the ink line remains continuous and uniform, it indicates that the surface tension of the material is equal to or higher than the nominal value of the test pen; If the ink line shrinks rapidly and breaks into solitary droplets, it indicates that the surface tension of the material is lower than the nominal value of the test pen. By changing the test pen with different nominal values for multiple tests, it can be gradually approached to determine the maximum tension value that keeps the ink line continuous, which is the approximate value of the wetting tension on the surface of the material. The test should be repeated in multiple locations to improve the representativeness of the results.
Influencing factors
Measurement results are influenced by a variety of factors. The properties of the material itself, such as surface chemical composition, crystallinity, roughness, and porosity, directly affect its surface energy. Environmental conditions such as temperature and humidity may change the volatilization rate and surface tension of the test solution. Consistency in the technique, including stroke speed, angle, and pressure, can also introduce deviations. In addition, the storage time and conditions of the test solution may lead to solvent volatilization or composition changes, affecting the accuracy of its nominal tension value. Cleanliness of the sample surface is critical, and grease, dust, or release agent residue can significantly reduce the measured value.
Applications
Dyne pens are mainly used in processes that require control of surface adhesion properties. In the plastic film printing and lamination packaging industry, it is used to evaluate the effects of corona treatment or flame treatment to ensure the adhesion of inks and adhesives. In the field of electronics manufacturing, it is used to check the cleanliness, solderability, and coatingability of surfaces such as circuit boards and plastic parts in housings. In the automotive industry, it is used to inspect the surface treatment quality of plastic parts before spraying. In the coatings and adhesives industry, it is used for the evaluation of the surface energy of substrates as a reference for coating formulation and construction processes. Its fast and easy nature makes it suitable for on-site inspection and quality control on the production line.
Selection considerations
When choosing a dyne pen, determine the appropriate tension range based on the application requirements. Common test pen kits typically cover a range from 30 to 70 mN/m at intervals of 2 or 5 mN/m. The user should choose a pen set that covers this range based on the common surface energy level of the material to be tested. Consider the certification of the test fluid and give preference to products that meet relevant industry standards or provide reference material comparison reports. The design of the pen tip should ensure that the ink is uniform and wear-resistant. It is also necessary to pay attention to whether the supplier provides detailed operating guidelines and tension value calibration services. For long-term or frequent use, consider the stability of the test solution and the tightness of the pen, as well as whether it is easy to refill the test fluid to maintain the consistency and economy of the measurement.