When it comes to Pet Preform Mould, defects that are not easily observed usually lead to the biggest problems. For example, excessive loss of intrinsic viscosity (IV) is known to complicate the reheat stretch blow molding process, reduce stress crack resistance and cause other bottle quality problems. Historically, molders could not easily “see” IV, but now the situation is different. A manufacturer should never find themselves inadvertently carrying unqualified preforms at the top of their games. The location of the bottle.
The measured intrinsic viscosity of PET is related to the molecular weight. Bottles with high molecular weight or intrinsic viscosity are known to have better physical properties and barrier properties than bottles with low or intrinsic viscosity. This makes the high IV resin very suitable for packaging pressurized beverages, such as carbonated soft drinks. The resins designated for these applications typically have a starting IV in the range of 0.83-0.86 dL/g. Some IV losses should be expected during melt processing, whereas for carbonated soft drinks, the smallest accepted value for the smallest bottle IV is 0.80 dL / g.
Excessive IV loss during injection molding is often attributed to improper drying or melt processing conditions. However, it may also come from low molecular weight materials such as recycled materials, recycled PET, colorants and other additives. Simply receiving off-spec raw resins may also reduce the resulting preform IV. Regardless of the source of the IV excess loss, without the right tools and training, it can easily be ignored on the production line. However, this is not the case.
With proper training and equipment, your injection molding technician and quality team can predict preform IV in real-time in each machine cycle. The minimum requirement to obtain this capability is usually one day of machine time, followed by analytical testing. After the data is compiled, it can be used to set limit values to trigger alarms on the molding machine or to provide meaningful limits for the statistical process control system. Or a system upgrade machine can be used to report the predicted preform IV directly.