The stretched film shrinks too much during the stretched film process and cannot meet the width requirements of the product. In the secondary composite process, the thermal shrinkage is too large, exceeding the standard requirements, and cannot meet the width requirements of the product.

 

The raw material of the stretched film is an amorphous polymer. In a certain temperature range, when the stretched film force is greater than the yield strength, plastic stretch deformation occurs. During the deformation process, the polymer structural unit starts due to stretching. Directional. As the degree of orientation increases, the force between the macromolecules increases, leading to an increase in the viscosity of the polymer and a tendency to harden. The deformation becomes stable and no longer develops. This phenomenon is called stress hardening.

 

As the temperature increases, the elongation rate of the bundling stretched film is further increased, the stretch ratio increases, and even some polymers with poor stretch properties can be stretched. Deformation near very low working temperature at room temperature is usually called cold stretching. After the polymer undergoes stress hardening during the stretching process, the flow of polymer molecules will be restricted, thereby preventing the stretching ratio from further increasing. The stretched film returns to its original state after the tensile force is increased, resulting in greater shrinkage.

 

In fact, in the design process, we should consider the heat preservation and air convection in the workshop, because the heat loss of the electrical stretched film during the stretching process is very fast, and the thinner the stretch, the faster the heat dissipation. The surface temperature between the drawing port and the drawing port is reduced from 175 degrees Celsius to 135 degrees Celsius, so the temperature in the production workshop should not be lower than 20 degrees Celsius.

The purpose of the workshop design is to leave exhaust windows at the top and no windows at the bottom. In addition, in order to avoid cold dialing, a greenhouse can be made in the transverse stretch part to ensure the ambient temperature. By appropriately reducing the temperature of each machine The speed ratio can also reduce the tension of the stretched film.

 

Reasons for poor shrinkage of stretch film:

1. The temperature is not enough

Each kind of stretched film has its suitable temperature, especially the stretched film with larger shrinkage machine, which has higher temperature requirements, so the appropriate temperature is the main reason for the shrinkage effect.

 

2. Fast

After reaching the temperature, the speed is adjusted. If the speed is adjusted too fast, the stretched film will not shrink well. If the speed is too slow, the film will be burned. Therefore, the matching speed is also one of the factors affecting the shrinkage effect of the PE stretched film. Key factor.

 

3. Wind direction

The wind direction determines the heated parts of the product surface, especially the key parts of the cuff-type shrinking machine. The temperature of the cuff-type shrinking machine is higher, so the wind direction adjustment of the shrinking machine is very important.