Mechanical properties of the Lexan films
Chart 8: Tensile behaviour at room temperature
These properties are important for the usage of adhesive tapes as well as at processing of films on rolls.
Tension and elongation
Diagram 2: Typical tension-/elongation curve
Tensions can be calculated with the help of fundamental technical equations for mechanical properties. They are based on Hooke’s law of elasticity, therefore the tension acts directly proportional to the elongation in the linear region. Above the proportional limit the material behaviour differs from this constant.
According to Hooke, it applies:
E= σ / ε
Whereat: σ = Tensile strength (N/mm2)
E = elasticity modulus (N/mm2)
ε = Elongation (mm/mm)
Like most thermoplasts, Lexan®, Valox® and Ultem® also show a resilient behaviour at tensile strength in the area up to the proportional limit. That means that the films elongate and when the tensile is relieved, they return in their original status. The conjoined measurement differences should be considered during printing and/or die-cutting tense films.
This behaviour can be calculated relative precise or compensate with the help of this formula:
ε = F / A x E
Whereat: ε = Elongation (mm/mm)
F = Draw (N)
A = Cross-section area of the film (mm², width x thickness)
E = Tensile modulus (N/mm²), depends on the temperature
The value “E” changes with temperature.
Under tension a corresponding change of width can be quantified with the help of the Poisson ratio. This number is 0.38 for Lexan® and Valox® films (Ultem® films 0.42). When multiplied by the elongation from the above mentioned formula, it can be calculated how much the width minimizes.
Chart 9: tear resistance and –propagation strength