What are the common quality problems of pvc calendering film?
pvc calendering film is made by calendering process. What are the common quality problems of pvc calendering film?
What are the common quality problems of pvc calendering film
(1) The film shrinks too much
after biaxial stretching, PVC calendering film not only widens the width, but also becomes smaller in thickness, thus solving the deficiencies in the production of calendering film. At the same time, due to the directional stretching arrangement of macromolecular chains along the stretching direction, some properties of PVC calendering film are greatly improved: tensile strength, elastic elongation and impact strength are greatly improved; The refractive index increases and the surface finish increases; Improved heat resistance and weather resistance, and prolonged service life; Improved wear resistance.
If the stretching of PVC calendering film is carried out under the condition of higher than Vicat softening temperature, and then cooling is carried out, then the orientation of molecular chain segments is frozen; When reheating, due to the movement of molecular segments, the film has a tendency to restore the size before stretching, which is called/elastic memory 0. Heat Shrinkable film is based on this principle.
The size of biaxially stretched PVC calendering film should be as stable as possible. For this reason, on the one hand, the stretching ratio in two directions should be controlled during stretching to make the film isotropic and shrink evenly; On the other hand, the temperature during biaxial stretching should be maintained for a period of time and then slowly cooled to room temperature. The specific method is: install heating device under the rear half of the expansion equipment; Give warm water to the slow cooling roller to slowly cool the film; Keep the factory temperature not lower than 20e; At the same time, factors such as air convection caused by ventilation should be considered.
(2) Uneven film thickness
There are two reasons for uneven PVC calendering film thickness: & sup1; The thickness of the film from the calender is uneven, °Stretching causes uneven film thickness. For the former, measures such as cross of middle roller, pre-bending of lower roller and adjustment of roller temperature can be adopted to solve the problem. For the latter, because the film has fast heat dissipation on both sides, low temperature and thick film, heat preservation measures can be taken on both sides of the expansion; In addition, the influence of air convection caused by ventilation on the film temperature should also be considered.
(3) The film coiling roller is not neat
This problem should be checked from four aspects:
1. Whether the speed of the film coiling roller is stable or not; 2. Whether the film sticks to the roller; 3. Whether the tension roller is properly adjusted; 4. Whether the film is flat and the thickness is uniform.