Why does washi tape creep?

Washi tape adhesives can generally be tested for creep through tensile, elongation, shear, and cut tests, but what factors affect creep performance?

The creep of the washi tape is generally the relative deformation of the sample that changes over time when the external force (tensile force, shear force, and compression force) is fixed. Unlike stress relaxation, creep is a generalization of relaxation and vicious activity phenomena. The main influencing factors are polymer structure, temperature, stress, filler, and plasticizer.

1. The structure of the local polymer

Any elements that can increase the joint force between the large parts or the length of the segment (moving unit), such as the increase in the weight, the increase in side chains or groups, the increase in the polarity, and the degree of cross-linking. Addition, crystallization, etc., can reduce creep and stress relaxation.

2. External causes

The creep properties of washi tape strongly depend on temperature, especially in the glass transition region. Many polymers are near the glass transition point (Tg), and the creep rate presents a maximum value. In a very long time, only a minimal creep occurs. At a temperature higher than Tg, it will show a considerable medium length, but the creep rate is generally reduced.

The behavior of crystalline polymers is more complex. Not only is the temperature dependence of their creep properties strong, but crystalline polymers can sometimes creep more aggressively over time than amorphous complex and cross-linked polymers at a given temperature.

In a word, the temperature increase not only increases the creep rate of the washi tape but also increases the creep amount and may also change the creeping type from a resting type to a steady-state type or even an additive type.

For amorphous polymers, whose creep obeys the time-temperature equivalence (superposition) principle, WLF (displacement factor) can be used to process stress/time data over a wide temperature range, making the regularity of the results more transparent.

The stress effect of the washi tape is similar to the temperature effect. Adding the stress and adding the filler can reduce the creep value of the washi tape. A high or low-grade plasticizer will weaken the force of polymer separation, so it is conducive to creep because the dispersion of creep test results is significant, as long as there is a sufficient amount of Experiment with samples in order to get correct results.