Surfactant Migration Impact on Dynamic Surface Tension in Hardwood Stock
Residual surfactant migration in hardwood stock depresses dynamic surface tension below forty millinewtons per meter, triggering jetting print defects.
TAPPI T 458
Testing Procedure
Standardized testing procedures developed by the Technical Association of the Pulp and Paper Industry provide a method for measuring the water resistance of paper surfaces. Performing TAPPI T 458 involves measuring the initial contact angle of a water droplet and the rate of change of that angle over time. This metric provides a reliable way to evaluate the effectiveness of surface sizing on various paper and board grades.
Measurement Protocol
Technicians use a goniometer or an automated image analysis system to capture the profile of a liquid droplet as it sits on the paper surface. The test requires recording the contact angle at a specific start time, usually five seconds, and again after sixty seconds of exposure. When a paper grade has high water resistance, the angle remains high over this duration, indicating a slow wetting rate.
This change in contact angle reflects the rate of liquid absorption into the fibrous structure of the sheet.
Industrial Utility
Paper manufacturers use this standardized method to control the dosage of sizing agents during the papermaking process. If the water resistance is too low, printing inks may feather or bleed, which ruins the sharp lines of the design. Conversely, excessive sizing can prevent water-based glues from adhering properly during carton converting.
By maintaining the values within the specified range of this standard, mills deliver a consistent product that runs smoothly through printing and converting lines, reducing waste and downtime.