In the production of silicone protective film, bubble formation is a key factor affecting yield, stemming from multiple aspects including raw materials, process parameters, equipment status, and environmental control. Effectively reducing bubbles requires control at the source, through a systematic solution involving optimized material selection, adjusted process parameters, improved equipment design, and strengthened environmental management.
The purity and state of raw materials directly affect bubble formation. If silicone raw materials contain moisture or volatile components, gas evaporation during volatilization will cause gas retention, forming bubbles. Therefore, low-moisture silicone substrates should be selected, and plasticizers, reinforcing agents, and other compounding agents should be pretreated before mixing, such as by heating to evaporate moisture or vacuum drying, to reduce volatile content. Simultaneously, the wetting properties of the adhesive are crucial. Insufficient surface tension matching with the film will lead to uneven coating, localized cavities, and ultimately, bubbles. This can be addressed by adding wetting agents or adjusting the adhesive formulation to enhance its wetting ability on the film, ensuring a uniform and dense coating layer.
Precise control of process parameters is the core element in reducing bubbles. The vulcanization temperature and time need to be set appropriately based on the silicone formula and film thickness: too low a temperature will lead to incomplete vulcanization, preventing gas from escaping; too high a temperature may cause premature surface curing, trapping internal gas. Generally, the vulcanization temperature should be controlled within a reasonable range, and gas should be gradually released through staged heating. The vulcanization time must be matched with the temperature to ensure complete vulcanization. Furthermore, the balance between coating speed and pressure is equally crucial: too high a speed will result in insufficient adhesive wetting, while too low a pressure will fail to remove air bubbles. The optimal process window needs to be determined experimentally to ensure sufficient venting of the coating layer before mold closing.
Equipment condition has a decisive impact on bubble control. The precision and maintenance of the coating roller directly affect coating uniformity: roller wear or dirt can lead to insufficient localized adhesive application, forming cavities. The coating roller needs to be inspected regularly, and timely chrome plating or replacement should be performed, along with enhanced cleaning management during use. The temperature and pressure distribution of the laminating roller must be uniform to avoid residual air bubbles due to insufficient localized pressure. A high-precision temperature control system and pressure feedback device can be used to adjust process parameters in real time to ensure a stable lamination process. Furthermore, the application of vacuum vulcanizing machines can significantly reduce bubbles: under negative pressure, gases escape more easily, resulting in more thorough vulcanization. If conditions are limited, steel pipes can be used to assist in venting during the venting stage, mechanically removing bubbles.
Environmental control is an easily overlooked yet crucial aspect. Humidity and temperature in the production workshop must be strictly controlled: high humidity environments easily cause the film to absorb moisture, which reacts with NCO groups during vulcanization to generate CO₂, forming bubbles. The environment must be kept dry, and moisture-absorbing materials such as nylon must be pre-dried. Simultaneously, the sealed storage and filtration of chemicals such as curing agents can prevent the introduction of impurities, reducing the causes of bubbles. In addition, the application of electrostatic elimination devices can prevent the film from attracting dust due to static electricity, leading to surface defects in the coating layer, indirectly reducing the risk of bubbles.
The rationality of mold design directly affects the efficiency of bubble removal. The mold parting method, venting groove layout, and runner design need to be optimized according to the product structure: venting grooves that are too shallow or improperly positioned can cause gas stagnation, while an unreasonable runner design may result in uneven filling of the rubber compound. The vulcanization process needs to be simulated using mold flow analysis software to optimize the mold structure and ensure smooth gas expulsion. Simultaneously, the surface finish of the mold must meet requirements to prevent friction from causing the rubber compound to overheat and prematurely vulcanize, forming bubbles.
Operational details during production are equally crucial. Strict control of stirring speed and time is necessary during rubber compound mixing: excessive stirring introduces air, while insufficient stirring leads to uneven dispersion of additives. A combination of low-speed stirring and vacuum degassing is required to ensure a uniform, bubble-free rubber compound. Furthermore, operators must adhere to standardized operating procedures, such as minimizing time spent outside the mold and stabilizing mold temperature, to prevent bubble formation due to human error.
By systematically optimizing raw materials, process parameters, equipment status, environmental control, mold design, and operational details, bubble problems in silicone protective film production can be significantly reduced, improving yield. This process requires experimental verification and continuous improvement to develop a standardized process suitable for the company's production conditions, ultimately achieving efficient, stable, and high-quality production.
