In the raw materials used for flexible packaging, various films account for a large proportion. The temperature difference caused by climate change can have different effects on the various properties of the films, resulting in quality problems of flexible packaging finished products. This article focuses on analyzing the impact of weather temperature changes on product quality and the corresponding control points.
1. Film Blowing
The principle of film production is to heat and melt plastic particles into a fluid, which is then extruded by a screw and cooled and shaped. Therefore, whether it is upward blowing, downward blowing, casting, water - cooling, or air - cooling, these are just different processing and forming methods, while the forming mechanism of the materials is the same.
2. Printing
The production process of printing: original manuscript → color separation → plate making → plate mounting → ink application and color adjustment → starting printing → ink drying → winding into finished products.
The production process of lamination: base film → gluing → drying (dry lamination) → bottom film → laminating → cooling and shaping → winding into finished products.
After the base film is coated with glue, it is dried through a drying tunnel. After the solvent of the glue volatilizes and dries, it is bonded to the bottom film. The lamination process is completed by heating and cooling rollers for shaping.
After the base film is coated with glue, it can be directly bonded to the bottom film. During the process, the entire glue supply system (glue tank, glue pump, glue mixing pipeline), gluing system (glue trough, transfer roller), lamination roller, etc. need to be heated.
Similar to the film - making process, the granular material is melted into a film and then directly coated on the substrate, which involves a heating and extrusion process as well as a cooling process.
Heat is maintained at a fixed temperature to allow the glue to cross - link and cure, so that different materials are bonded into one.
The sealing bar is heated, and through temperature and pressure, the film materials are melted and bonded together to form a seal.
From the description of the above production processes, it can be seen that temperature is a hard indicator. Once there is a deviation, there may be problems leading to quality accidents. Therefore, when setting process standards, we should develop SOP documents according to actual production conditions and require strict implementation of production in accordance with the standard documents.
For example, in summer, a series of problems often occur, such as reduced material transparency, increased film friction coefficient, even non - opening, ink drying on the plate, reverse sticking, increased solvent residue, bag adhesion, shallow screen drying on the plate, precipitation of film additives, poor heat - sealing, false sealing, increased foreign matter on the film surface, adhesion of bags after being packed in boxes, poor ink - jet coding due to astringent finished products, and hardening of made bags.
On the surface, these problems seem to occur inexplicably, which is very annoying and headache - causing. Carelessness may even lead to batch quality accidents with serious losses. These problems are very energy - consuming to deal with. Clearly, the production has been strictly controlled in accordance with the standard documents. Why do the problems still occur repeatedly? Where is the root cause of the problems?!
From the production perspective, it seems that there are no changes in people, machines, materials, methods, and the environment. However, the occurrence of any event always has a certain pattern.
In fact, both temperature and humidity have changed！
Temperature is closely related to our flexible packaging processing. From the equipment perspective, the component that feels the most obvious change in various processes such as film blowing (casting), printing, lamination, and bag - making is the rubber roller. In summer, the rubber roller is relatively soft, while in winter, it is extremely hard. When the rubber roller is soft, its elasticity is better, and we can slightly reduce the pressure during production. At the same time, the transfer rate of glue and ink will increase to some extent. When the rubber roller is extremely hard in winter, we need to appropriately increase the pressure. In severe cases, we need to consider whether the rubber roller will slip due to excessive pressure. At the same time, the transfer rate of glue and ink will decrease. These micro - changes need to be anticipated and solved in process design and actual production.
The change in weather temperature will also cause the temperature of glue and ink themselves to change. That is, the characteristics of the same glue and ink will change due to the change in temperature.
A viscosity change test of a certain resin at different temperatures was once carried out:
Of course, in actual production, because the viscosity - temperature curves designed for each resin or glue are different, and after being diluted with solvents, the difference in viscosity change may not be so large. However, it is an actual fact that the viscosity will change due to different room temperatures. This is also the reason why, even though a viscosity controller has been used in production and the viscosity is strictly controlled in accordance with the SOP, there is still a large deviation in the final quality.
At the same time, with the change in temperature, the temperature of the glue and ink themselves will also change. The glue and ink at a low temperature require more heat to volatilize the solvent, while at a high temperature, the solvent is extremely volatile.
Post time: Mar-03-2025
