Abstract:

Objective In the thermal transfer printing process, the thermal transfer film ribbon causes drive tension changes in the the film ribbon when winding through various structures of the drive system, which often results in the phenomena of ribbon relaxation, unclear transfer quality and even ribbon breakage. In order to ensure the stability of the film ribbon drive during the thermal transfer printing process and to achieve high quality transfer printing, this paper analyzes and establishes a tension model of the thermal transfer printing ribbon drive system.

Method Based on studying the composition of the thermal transfer printing ribbon drive system and the transfer printing principle, the drive path of the ribbon was divided. Combined with the viscoelasticity of the thermal transfer printing ribbon web, a film ribbon tension model was established for the inter-roll section. The intluence of friction on the tension of the film ribbon drive was analyzed, a tension drop coefficient was proposed to evaluate the tension loss in the unwinding area, and a stepper motor load model was constructed to solve the ribbon tension in the winding area.

Results The composition and transfer printing principle of the thermal transfer printing ribbon drive system were studied, and the drive path of the ribbon was delineated. The Voigt model was adopted to describe the viscoelasticity of film ribbons under small deformation, and combined with Hooke's law and Amontons-Coulomb's law, the tension formation mechanism of the inter-roll section was analyzed, and the classical tension equation of the winding system was improved to establish an equivalent tension model of film ribbons in the complex domain. By studying the composition of the drive system and drive principle, it was found that the ribbon tension in the unwinding section was mainly affected by three types of friction, i.e., rolling friction of the traction roller, relative sliding friction of the ribbon and the traction roller, and contact friction of the print head downward pressure and movement. However, in the actual operation of the system, the weakening effect of the tension was only considered by the rolling friction of the traction roller, and therefore, a tension drop coefficient was put forward to evaluate the loss of tension and to solve for the unwinding. Therefore, a tension drop coefficient was proposed to evaluate the tension loss and solved the unwinding section tension. Through the kinetic analysis of the winding section, it was found that the ribbon tension was nonlinear time-varying and was affected by the change in speed and the diameter of the ribbon roll. A stepper motor load model was constructed, and the transfer printing function of the tension in the winding section was deduced from the relevant parameters of the stepper motor. Taking the thermal transfer printing mixed-base ribbon as an example, the experimental platform of the ribbon drive system was built for tension test, and the simulation and experimental data are compared, it was found that the simulation was the same as the experimental data in intermittent mode, and the rebound phenomenon occurred in continuous mode, which was about 4 s periodicity.

Conclusion The thickness and width of thermal transfer printing ribbons affect their tension properties, and the classical tension model is improved by combining their viscoelasticity. Friction and changes in the stepper motor input pulse cause fluctuations in the ribbon drive tension. The simulation results in the intermittent mode are basically consistent with the experimental results, and the ribbon tension model is accurate, which can be used as a reference for the subsequent research on the design of the tension control scheme.

Key words: thermal transfer printing, film ribbon, tension modeling, viscoelasticity, tension reduction coefficient, nonlinear time-varying