The flow speed of EVA (ethylene-vinyl acetate) film during the lamination process is influenced by several factors including temperature and the specific characteristics of the EVA material.
EVA is a thermoplastic material with a distinct melting point. When this point is crossed, the polymer is in a completely molten state. The melt flow index (MFI) of EVA is also significantly higher than other polymers like PVB (polyvinyl butyral). This means that when the EVA polymer is molten, it is also very “liquid”, which allows it to fill large voids efficiently during the lamination process. A typical vacuum oven process for EVA starts with a cold vacuum at room temperature (20°C), where usually the vacuum is kept for 30 minutes per square meter laminate surface. Then the vacuum bag can be heated up to 85°C in 30 minutes. In a second step, the oven is heated up further to 130°C –150°C, depending on the specific case. When a lot of flow is needed, like in case of glasses with a deep surface structure, a higher temperature is preferred. The high temperature needs to be maintained for 1 to 3 hours, depending on the thickness of the glass and the curing degree of the EVA. It’s also worth noting that EVA is ideally suited for autoclave-free vacuum oven manufacturing due to its good flow properties. It is often the method of choice when complex laminates with structured and/or curved glass and/or inserts need to be processed.
In summary, the flow speed of EVA film during lamination is influenced by the specific properties of the EVA material and the conditions under which the lamination process is conducted. The high melt flow index of EVA allows it to flow and fill voids efficiently during the lamination process, particularly when the process temperature is maintained at a high level.