A new characterization approach for heat sealing of polymer packaging films identifying optimum sealing parameters using Pareto‐based trade‐off analysis

Abstract

This paper presents a new approach for characterizing heat sealing processes in packaging machines, which identifies all appropriate and optimum sealing parameters subject to given quality criteria. The presented approach is distinct from established methods, such as heat seal curves or response surface plots, in three aspects: It provides an easy-to-read chart indicating optimum and appropriate settings of sealing temperature and dwell time, as well as process robustness for each parameter set. The data points of the charts are generated directly from experiments without using any regression model. The design of experiments features a determinate sequence of tests and no iterative loops are necessary. The approach stems from a 'trade-off' model of heat sealing and a specific multi-objective optimization method. This trade-off model states that improving seam quality, reducing sealing temperature, reducing dwell time, and increasing process robustness are conflicting objectives. This hypothesis is deduced from a literature review and verified by experiments. The optimization method claims that all optimum sealing parameters are part of the solution of a multi-objective optimization problem, the Pareto-frontier. This hypothesis is elaborated into a design of experiments using the normal-boundary-intersection method, and is verified using a peelable seam and tear seam scenario.

A design of experiments based on the Normal‐boundary‐intersection method to identify optimum machine settings in manufacturing processes

“…The most critical influencing factor is the overall thickness d of the packaging film layers to seal, which determines robustness of the heat sealing process by $$\mathcal {U}_\mathrm{s}=\lbrace d \vert d^{\rm low} \le d \le d^{\rm upp} \rbrace$$, compare ref. [7]. Thus, the sealing function $$$$\begin{equation} \sigma _\mathrm{s}=f_\mathrm{s}(t_\mathrm{d},T_\mathrm{s},d) \end{equation}$$$$formally describes the heat sealing process, compare ref.…”

“…[8]. Although, there is no comprehensive model of the underlying mechanisms of heat conduction [6] and molecular diffusion [8], it is generally accepted that increasing sealing temperature and dwell time increases seal strength, and that thicker films require higher sealing temperatures and longer dwell times [7]. Formally, this means that the sealing function is continuous and monotonic.…”

“…Definitions 2.3 to 2.5 apply for the heat sealing process by the following, compare ref. [7]: the technical restrictions of the packaging machine and the material properties of the packaging film define the set of the feasible settings with $$\mathcal {F}_\mathrm{s}=\lbrace \mathbf {p}_\mathrm{s} \vert t_\mathrm{d}^{\rm min}\le t_\mathrm{d} \le t_\mathrm{d}^{\rm max},T_\mathrm{s}^{\rm min}\le T_\mathrm{s} \le T_\mathrm{s}^{\rm max} \rbrace$$. The set of the appropriate settings is given by $$\mathcal {A}_\mathrm{s}=\lbrace \sigma _\mathrm{s} \vert \sigma _\mathrm{s}=f_\mathrm{s}(t_\mathrm{d},T_\mathrm{s},d),\sigma _\mathrm{s}\in \mathcal {Q}_\mathrm{s},d\in \mathcal {U}_\mathrm{s} \rbrace$$ in respect of the quality and robustness criteria.…”

“…The most critical influencing factor is the overall thickness 𝑑 of the packaging film layers to seal, which determines robustness of the heat sealing process by  s = {𝑑|𝑑 low ≤ 𝑑 ≤ 𝑑 upp }, compare ref. [7]. Thus, the sealing function…”