In the production process of pet non-silicone release film, reducing haze to improve transparency is the key link to improve product quality, which requires refined control from raw material selection, formula design to each link of the production process. First of all, the purity and quality of raw materials are the basis. The transparency of the PET substrate directly affects the haze of the final product, so high-purity, low-impurity PET raw materials must be selected to avoid light scattering due to residual catalysts, additives or uneven distribution of polymer molecular weight in the raw materials. At the same time, the coating materials of the non-silicone release layer, such as silicone-modified resins, fluorides, etc., also need to be strictly screened to ensure that they have good light transmittance and excellent compatibility with the PET substrate, so as to avoid phase separation or tiny particles during the coating process, thereby reducing the refraction and diffuse reflection of light.
The rationality of formula design is crucial to haze control. In the formulation of the non-silicone release layer, the selection and dosage of additives need to be carefully considered. For example, the addition of leveling agent can improve the fluidity of coating liquid and reduce defects such as orange peel and shrinkage cavities generated during coating, but excessive use may cause the additive molecules to aggregate on the film surface, forming tiny optically uneven areas. The role of dispersant is to ensure that the functional particles in the release layer material are evenly dispersed. If the dispersion is insufficient, the particle agglomerates are easy to become light scattering centers. Therefore, it is necessary to adjust the dispersant type and dispersion process to control the particle size below the visible light wavelength to avoid obvious haze. In addition, the type and degree of crosslinking agent will also affect the optical properties of the release layer. Excessive crosslinking may cause stress inside the material, causing microcracks or changes in the crystal structure, thereby affecting transparency.
Precise control of the extrusion casting process is a key step in reducing haze. In the production of PET substrates, extrusion temperature, melt viscosity and cooling rate are important factors affecting the transparency of the substrate. Excessive extrusion temperature will cause thermal degradation of PET raw materials, produce small molecular volatiles and color changes, and increase haze; too low temperature will cause poor melt plasticization, and there will be unmelted particles or crystal nuclei inside, affecting light transmission. The speed of cooling will affect the crystallinity of PET substrate. Rapid cooling can inhibit the orderly arrangement of macromolecular chains and form an amorphous structure, thereby improving transparency. If the cooling rate is too slow, larger crystalline particles are easily formed, resulting in enhanced light scattering. Therefore, it is necessary to optimize the temperature of each zone of the extruder, adjust the die gap and the temperature of the cooling roller, so that the PET substrate can form a uniform amorphous structure during the molding process and reduce crystallization defects.
The stability of the coating process is directly related to the uniformity and optical properties of the release layer. During the coating process, the accuracy of the coating head, the coating speed and the tension control are the key. The slit width and coating pressure of the coating head need to be precisely adjusted to ensure that the coating amount of the release layer is uniform and consistent to avoid thickness fluctuations or local accumulation. Too fast a coating speed may cause the coating liquid to not have time to level, forming stripes or spots; too slow a speed may cause the coating liquid to spread excessively on the surface of the substrate, or even penetrate into the interior of the substrate, changing the optical properties of the substrate. At the same time, the tension control of the substrate needs to be stable. Excessive tension may cause the PET substrate to stretch and deform, generate internal stress, and induce birefringence; too little tension may cause the substrate to wrinkle or relax during the coating process, affecting the coating uniformity. By adopting high-precision coating equipment and closed-loop tension control systems, the uniformity of the coating layer can be effectively improved and the increase in haze caused by coating defects can be reduced.
The parameter settings of the drying and curing processes have a significant impact on the optical properties of the release layer. After the release layer is coated, the evaporation rate of the solvent and the degree of curing reaction during the drying process need to be reasonably controlled. Insufficient solvent evaporation will cause small solvent molecules to remain inside the release layer. These small molecules may form tiny bubbles in the film layer or swell with the substrate, increasing the haze; if the drying temperature is too high or the time is too long, the release layer material may be over-crosslinked or oxidized, resulting in yellowing or structural degradation, affecting transparency. In the curing process, the intensity, irradiation time and irradiation angle of the ultraviolet light need to be optimized to ensure that the release layer material is fully crosslinked while avoiding shrinkage of the film layer or internal stress due to over-curing, thereby maintaining good optical uniformity.
The cleanliness management of the production environment is an important link that cannot be ignored. In the production process of pet non-silicone release film, if dust, microorganisms or other impurity particles in the air adhere to the surface of the substrate or release layer, they will become the center of light scattering, significantly increasing the haze. Therefore, it is necessary to establish a high-cleanliness production workshop, adopt an air filtration system, regularly clean equipment and floors, and strictly regulate the operator's dress and operating procedures to reduce pollutants brought in by humans. At the same time, the surface cleaning of the production equipment is also very important to avoid metal debris, lubricant volatiles and other contamination of the film material during the operation of the equipment, and ensure that the cleanliness of the entire production environment meets the production requirements of high-transparency release film.
Quality inspection and feedback mechanism is an important means to continuously optimize transparency. In the production process, professional equipment such as haze meters and transmittance testers are required to conduct real-time detection of the haze and transmittance of pet non-silicone release film. By establishing strict quality standards and setting control thresholds for haze and transmittance, timely trace the production links of products that do not meet the requirements, analyze the reasons and adjust the process parameters. For example, if the test finds that the haze exceeds the standard, the purity of the raw materials, the amount of formulation additives, the extrusion temperature, the coating uniformity and other aspects can be checked one by one, and the influencing factors can be determined through experimental comparison, and then the process can be optimized to form a closed-loop quality control system, thereby continuously improving the transparency and optical properties of the product.
