When it comes to Pet Preform molds, defects that are not easily observed usually lead to the biggest problem. 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 have not easily “seen” IV, but things are different now. Manufacturers should never find themselves inadvertently carrying unqualified preforms on top of the game. The location of the bottle.
The measured intrinsic viscosity of PET is related to the molecular weight. It is known that bottles having a high molecular weight or intrinsic viscosity have better physical properties and barrier properties than bottles having a low or intrinsic viscosity. This makes high IV resins ideal for packaging pressurized beverages such as carbonated soft drinks. The resins specified for these applications typically have an initial IV in the range of 0.83 – 0.86 dL / g. Some IV losses should be expected during melt processing, while for carbonated soft drinks, the minimum acceptable value for minimum 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. The obtained preform IV can also be reduced by simply receiving a defective raw material resin. Regardless of the source of the IV excess loss, it is easy to ignore it without the proper tools and training. However, this is not the case.
With the right 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 achieve this capability is usually one day of machine time, followed by analytical testing. After the data is compiled, it can be used to set limits to trigger an alarm on the molding machine or to provide meaningful limits for the statistical process control system. Alternatively, the predicted preform IV can be reported directly using the system upgrade machine. If you want to get products with few defects, it is a good choice to choose a China Pet Bottle manufacturer.