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25
2018
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08
Process Control in the Die-Cutting of Protective Films
As is well known, protective films are an indispensable component of electronic devices; whether it’s a smartphone, a camera, or a tablet, a protective film is applied before shipment to safeguard the device’s screen.
As is well known, protective films are an indispensable component of electronic devices; whether it’s a smartphone, a camera, or a tablet, a protective film is applied before shipment to safeguard the device’s screen.
The transparency, flatness, and cleanliness of protective films significantly influence consumers’ perception of electronic products. A high‑quality protective film can also enhance the product’s overall aesthetic appeal; accordingly, die‑cutting facilities implement stringent process controls throughout production.
Protective Film Material Selection
When producing protective films, several considerations should be taken into account during material selection. First, the chosen material should not only meet customer requirements but also be well-suited for printing and die-cutting—exhibiting excellent scratch resistance, strong ink adhesion, and minimal ink bleeding, for example.
Control of the Production Environment for Protective Films
Quality control for protective film products hinges on two critical factors: preventing scratches and avoiding contamination. To meet these requirements, a conducive production environment is essential; therefore, die-cutting facilities are equipped with dedicated cleanrooms for manufacturing protective films. A cleanroom—also referred to as a clean workshop or clean room—is a specially designed space that removes airborne particulates, harmful gases, bacteria, and other contaminants within a defined area, while precisely controlling indoor temperature, cleanliness, pressure, air velocity and distribution, noise and vibration levels, lighting, and electrostatic charge—all within specified limits. Regardless of external environmental conditions, the cleanroom must maintain its set parameters for cleanliness, temperature, humidity, and pressure. Depending on the specific product being manufactured, cleanrooms are classified into different cleanliness grades, including Class 100, Class 1,000, Class 10,000, Class 100,000, and Class 300,000.
In a cleanroom, under dynamic conditions, operators are the primary source of bacterial and particulate contamination. Therefore, before entering the cleanroom, personnel must don cleanroom garments and undergo a 15-second air shower to remove airborne particles adhering to their clothing.
Protective Film Printing Process Control
Most plastic films, such as polyolefin films, are nonpolar polymers with low surface tension, typically ranging from 29 to 30 mN/m. Theoretically, if a substrate’s surface tension falls below 33 mN/m, no currently available inks or adhesives can achieve strong adhesion; therefore, corona treatment is required to modify the surface. Protective films are predominantly made of polyolefins and must undergo corona treatment prior to printing, usually at a power level of 4.0 W and a speed of 30 m/min. After corona treatment, the film should be fed into the printing press within 5 minutes; if left for more than 10 minutes, it must be re‑coronated before processing.
During the printing process, the protective‑film material comes into contact with the impression rollers, and friction can cause surface scratches. Therefore, all impression rollers that touch the protective film must be wrapped in a soft, clean layer. As is well known, protective films are an indispensable component of electronic devices; whether it’s a smartphone, a camera, or a tablet, a protective film is applied before shipment to safeguard the device’s screen. The transparency, flatness, and cleanliness of the protective film significantly influence consumers’ perception of the product, and a high‑quality film can even enhance its overall aesthetic appeal. Consequently, die‑cutting facilities implement stringent process controls over the production of protective films.
Protective film die-cutting process
After the protective film is printed, it must be fed into a rotary die‑cutting machine for die‑cutting and shaping. During the die‑cutting process, care should be taken to prevent scratches and ink chipping; the latter typically manifests as localized areas along the product edges where the ink layer, which should be uniform and smooth, is instead missing.
The primary cause of ink chipping during die-cutting is insufficient adhesion between the ink and the protective film. When the die‑cutting process reaches the edges of the product, the ink layer can separate from the protective film, resulting in jagged or serrated edges. Therefore, after printing, the protective film should be inspected for ink adhesion; only when the ink adheres well should die‑cutting proceed. Additionally, excessively thick ink layers can also lead to ink chipping.
There are several reasons why scoring can occur during die-cutting, the most common being uneven rotation of the pressure roller, which causes relative slippage between the material and the roller and results in scratches. Therefore, before die-cutting, it is essential to inspect the pressure roller’s rotation to ensure that all rollers in contact with the material turn smoothly. Additionally, foreign particles on the pressure roller can scratch the protective film and leave indentations; thus, prior to die-cutting, the roller should be wiped with a clean cloth dampened with alcohol to ensure its surface is clean and free of contaminants.
The die-cut shape of a protective film is typically designed according to the customer’s specifications, primarily based on the external dimensions of the smartphone’s screen. It is usually a rectangular form with rounded corners, featuring a small tab at the lower‑right corner. The tab is printed on the back side and then covered with a PET film, which facilitates assembly for the manufacturer and makes it easier for consumers to peel the film off the screen. For die‑cutting protective films of various shapes, round knives are used; however, more complex designs require additional round knives. For instance, when a tab needs to be attached, two round knives are employed—one to cut the tab and the other to define the overall contour.
Protective Film Packaging Process Control
After die-cutting, protective films are typically wound into rolls. During packaging, they are first slit into individual sheets, with 500 sheets grouped together for packing. The process begins by wrapping each sheet in stretch film, followed by placement in a sealed plastic bag. Cleanliness is paramount during sealing, so operators wear finger cots and perform manual handling. For instance, one particular protective film requires hand‑applied handles after processing; operators must affix the handles to the adhesive side of the film—on the inner surface—at precisely designated locations, while ensuring the product remains free of contamination and foreign particles. All these operations must be carried out in a dust‑free cleanroom.
Although screen protectors may seem simple and their manufacturing process not particularly complex, each step demands strict adherence to quality standards. Overall, it’s essential to maintain impeccable cleanliness at all times and to avoid bending or scratching the film. It is precisely these meticulous details that determine the product’s level of quality.
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