In today's industrial production and daily life, PET protective film has become a powerful assistant for protecting the surfaces of various items due to its good transparency, high strength, and flexibility. From the screens of electronic devices such as smartphones and tablets, to the lenses of optical instruments such as camera lenses and microscope lenses, to the instrument panels and seat armrests in car interiors, PET protective film is ubiquitous. It can effectively prevent scratches and wear on the surface of the protected object, resist the invasion of dust, moisture, ultraviolet rays, etc., and significantly extend the service life of the item.

However, a troubling problem often arises - residual glue. When we want to replace or remove the PET protective film, we sometimes find that after the protective film is torn off, a sticky adhesive mark is left on the surface of the protected object. This not only seriously affects the appearance of the item, making it look dirty and sticky, reducing its aesthetic appeal, but may also damage the surface quality of the item. Improper operation during the removal of residual glue can easily scratch the surface, which can be fatal for some high-end furniture, precision instruments, etc. So, what exactly causes PET protective film to leave residual adhesive? Let's delve deeper into it.

1、 Why does PET protective film leave residue?

1. Adhesive quality

Adhesive, as the core material for PET protective film to achieve adhesive function, has a critical impact on the problem of residual adhesive due to its quality. High quality adhesive has strong temperature and weather resistance, with stable adhesion in common environments ranging from -10 ℃ to 60 ℃. It can firmly adhere to the protected surface and completely peel off without residue when removed. Poor quality glue is prone to failure due to temperature fluctuations or long-term use: it softens and becomes sticky at high temperatures, resulting in adhesive residue; at low temperatures, it becomes brittle and breaks, leaving behind adhesive blocks; and it has poor weather resistance. After exposure to light and moisture, it is prone to chemical changes and residue. Low priced mobile phone film and furniture film on the market are high-risk categories for residual glue problems due to poor quality glue.

2. Soft and hard segments of membrane material

The softness and hardness of the film material are also important factors affecting whether residual adhesive remains in PET protective film. If the material is too soft, the molecular activity is high. After long-term use or high temperature environment, pressure-sensitive adhesive is prone to penetrate into the surface pores of the adhered object, and the adhesive force continues to increase, making it difficult to peel off and leaving residual adhesive; On the contrary, if the material is too hard, its flexibility will be insufficient, and it will not be able to tightly adhere to curved or rough surfaces, which is prone to local delamination residue.

3. Temperature influence

Temperature is the "catalyst" for the performance of glue: high temperatures above 35 ℃ soften the glue and increase its viscosity, such as the protective film on car interiors that tends to stick tightly to the surface after exposure to sunlight; -If the temperature is below 10 ℃, the adhesive will become brittle and lose its stickiness, and it will easily break and leave adhesive when removed. In areas with large temperature differences between day and night, repeated thermal expansion and contraction of film materials are more likely to cause adhesive layer detachment and residue.

2、 Limitations of PET protective film performance evaluation methods

For a long time, the performance evaluation of PET protective films has relied on traditional methods such as mechanical property testing, rheological property analysis, and accelerated aging testing. However, these methods are no longer suitable for the current industry's high requirements for efficiency and accuracy, and their limitations are becoming increasingly prominent.

Mechanical performance testing (such as tensile testing) can only reflect the macroscopic mechanical behavior of membrane materials and cannot relate to the microstructure and adhesion mechanism. Even materials with similar parameters may have significant differences in actual adhesion performance.

Although rheological analysis can simulate the flow properties of materials under temperature changes, testing takes several hours, with low efficiency, and insufficient analysis of microstructural changes, making it difficult to guide the solution of residual adhesive problems.

The accelerated aging test predicts performance by simulating the extreme environment, but it takes several days to weeks and cannot meet the requirements of rapid iteration. Moreover, there are differences between the simulated environment and the actual situation, which limits the reliability of the results.

3、 The advantages of low field nuclear magnetic resonance method in the performance evaluation of PET protective film

Low field nuclear magnetic resonance technology is a detection technique based on the principle of nuclear magnetic resonance, which analyzes the microstructure and physical properties of a sample by measuring the relaxation time (T1, T2) of hydrogen protons in the sample.

Compared with traditional evaluation methods, low field nuclear magnetic resonance technology has many significant advantages. It belongs to non-destructive testing, and the samples do not require complex pre-treatment. After testing, they can be reused, which not only reduces sample loss, but also enables multiple tests on samples from the same batch, improving the reliability of test results. The testing speed of this technology is extremely fast, taking only a few minutes to complete a test. It can achieve efficient testing at the minute level, greatly shortening the R&D and production cycles and improving work efficiency. The low field nuclear magnetic resonance technology has high testing accuracy and can accurately capture subtle changes in the microstructure of materials, providing accurate data support for the evaluation of protective film performance. In addition, it can also be combined with a temperature control module to achieve dynamic temperature simulation, accurately capturing the adhesive behavior changes of materials in real application environments (such as high and low temperature cycles), providing more comprehensive and in-depth information for solving the problem of residual glue.