Mechanical Strength Evaluation of Functional Film Used in Smartphones

Recently, a wide range of multi-functional films have been developed which possess a variety of special characteristics designed to provide such functionality as enhanced protection and visibility in display screens for smartphones and LCD televisions. These multi-functional plastic films can also be designed to provide enhanced security, insulation, and light shielding for automotive and architectural glass products. This page introduces an example of the strength evaluation of self-repair coating film used on the functional protective film that covers the LCD screens of such products as smartphones and tablets.

Table 1 Test Conditions

Table 2 Sample

Fig. 3 shows the time-course changes in the self-repair coating film at the sample surface that were extracted from the TRViewX tensile test video. Here, the characteristic changes that occurred in the sample at various states during tensile loading are displayed in photographs. The captured states include: (1) Initial appearance of cracks: the point at which localized minute cracks first appear in self-repair coating film, (2) Crack appearance point 1: the point at which the c racks become c lear l y ev ident , and (3) Crac k appearance point 2: the point at which the cracks become evident over the entire coating film, imparting a whitening effect.

Fig. 3 State of Self-Repair Coating on Sample

Next, using the TRViewX Point Pick feature, we quantified the test force loaded onto the sample and the amount of deformation that occurred at states (1), (2), and (3) of the self-repair coating film. Fig. 4 shows the Test Force -Stroke curve.

Table 3 Test Results

Fig. 4 Test Force - Stroke Curve

Fig. 4 reveals that the cracks occur in the self-repair coating film after the sample exhibits non-linear behavior - that is, when the plastic region has been reached. It is therefore presumed that the self-repair coating film possesses strength properties that prevent its damage in the elastic region. The cracks in the coating film appeared at about the 135 N load point, and after the cracks became clearly evident at a load point of about 137 N, the cracking suddenly became very pronounced over the range of 137 N-140 N.