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Scratch Resistance of Cellphone Screen Protectors

Scratch Resistance of Cellphone Screen Protectors

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Importance of Testing Screen Protectors

Although phone screens are designed to resist shattering and scratching, they are still susceptible to damage. Daily phone usage causes them to wear and tear, e.g. accumulate scratches and cracks. Since repairing these screens can be expensive, screen protectors are an affordable damage prevention item commonly purchased and used to increase a screen’s durability.


Using the Nanovea PB1000 Mechanical Tester’s Macro Module in conjunction with the acoustic emissions (AE) sensor, we can clearly identify critical loads at which screen protectors show failure due to scratch1 testing to create a comparative study between two types of screen protectors.


Two common types of screen protector materials are TPU (thermoplastic polyurethane) and tempered glass. Of the two, tempered glass is considered the best as it provides better impact and scratch protection. However, it is also the most expensive. TPU screen protectors on the other hand, are less expensive and a popular choice for consumers who prefer plastic screen protectors. Since screen protectors are designed to absorb scratches and impacts and are usually made of materials with brittle properties, controlled scratch testing paired with in-situ AE detection is an optimal test setup for determining the loads at which cohesive failures (e.g. cracking, chipping and fracture) and/or adhesive failures (e.g. delamination and spallation) occur.



Measurement Objective

In this study, three scratch tests were performed on two different commercial screen protectors using Nanovea’s PB1000 Mechanical Tester’s Macro Module. By using an acoustic emissions sensor and optical microscope, the critical loads at which each screen protector showed failure(s) were identified.




Test Procedure and Procedures

The Nanovea PB1000 Mechanical Tester was used to test two screen protectors applied onto a phone screen and clamped down to a friction sensor table. The test parameters for all scratches are tabulated in Table 1 below.




Results and Discussion

Because the screen protectors were made of a different material, they each exhibited varying types of failures. Only one critical failure was observed for the TPU screen protector whereas the tempered glass screen protector exhibited two. The results for each sample are shown in Table 2 below. Critical load #1 is defined as the load at which the screen protectors started to show signs of cohesive failure under the microscope. Critical load #2 is defined by the first peak change seen in the acoustic emissions graph data.


For the TPU screen protector, Critical load #2 correlates to the location along with the scratch where the protector began to visibly peel off the phone screen. A scratch appeared on the surface of the phone screen once Critical load #2 was surpassed for the remainder of the scratch tests. For the Tempered Glass screen protector, Critical load #1 correlates to the location where radial fractures began to appear. Critical load #2 happens towards the end of the scratch at higher loads. The acoustic emission is a larger magnitude than the TPU screen protector, however, no damage was done to the phone screen. In both cases, Critical load #2 corresponded to a large change in depth, indicating the indenter had pierced through the screen protector.













Conclusion




In this study we showcase the Nanovea PB1000 Mechanical Tester’s ability to perform controlled and repeat-able scratch tests and simultaneously use acoustic emission detection to accurately identify the loads at which adhesive and cohesive failure occur in screen protectors made of TPU and tempered glass. The experimental data presented in this document supports the initial assumption that Tempered Glass performs the best for scratch prevention on phone screens.


The Nanovea Mechanical Tester offers accurate and repeatable indentation, scratch, and wear measurement capabilities using ISO and ASTM compliant Nano and Micro modules. The Mechanical Tester is a complete system, making it the ideal solution for determining the full range of mechanical properties of thin or thick, soft or hard coatings, films, and substrates.

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