Polypropylene thin-film paper cup packaging machine are not tightly sealed and may lead to leakage, contamination or product failure. Possible causes and solutions require systematic analysis in four areas: equipment parameters, material quality, mechanical structure and operating specifications. Details are as follows:
I. Equipment Parameter Issues
1.Insufficient or excessive sealing temperature
Reason:
The melting point of polypropylene films is 160-170°C. If the sealing temperature is less than 180 degrees Celsius, the film layer will not completely melt, resulting in poor adhesion.
Too high a temperature (over 200°C) can carbonize the film, making it less adherent.
Solutions:
The actual temperature of the sealed area is monitored using an infrared thermometer and the temperature controller settings is set to 180-190°C (depending on the thickness of the film).
Temperatures can rise to 185C in winter or low temperatures, and fall as low as 180C in summer.
2.Inadequate or uneven sealing pressure
Reason:
Pressure devices (e.g. cylinders or springs) have a low or uneven pressure setting (e.g. pressure difference of more than 5% at both ends of the sealing drum).
paper cup edges have burrs or deformation, resulting in local forces uneven.
Solutions:
Adjust the sealing pressure of the pressure regulator valve to 0.3-0.5 MPa (refer to the Equipment Manual for specific parameters).
Use pressure tester to check pressure at both ends of sealing roller. If the error exceeds 5%, calibrate or replace the pressure device.
Cut burrs from the edges of the paper cup to ensure smooth rims.
II. Material quality issues
1. Uneven thickness of PP films or Material Defects
Reason:
Thickness deviation of the film roll (e.g. greater than ±3μm) results in poor sealing.
Impurities attracted by oil, dust or static electricity may affect the adhesion of the film surface.
Solutions:
Use the film thickness tester to check the uniformity of the film roll. Replace with a roll with thickness deviation greater than ± 2 microns. Clean the surface of the film roll and add electricity removal (such as an ionizer) if necessary.
Case study bubble rate Bubbles in sealing decreased from 8% to 1% after a packaging plant switched to polypropylene films with thickness uniformity ± 1.5μm.
2. The compatibility between paper cups and PP film is poor.
Reason:
paper cup surface coating (such as PE) is not compatible with PP film, resulting in weak hot melt adhesive.
paper cup has too much water (>12%), which causes water to evaporate and bubbles when sealed at high temperature.
Solutions:
Use paper cups compatible with PP film (e.g. double-sided PE coated cups).
Keep the moisture content of the paper cups to 8-10%, and add drying step if necessary.
