Controlled Moisture Drying for PET Injection Molding
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Solution Overview
Problem
The high hygroscopic nature of PET chips leads to moisture absorption, causing hydrolytic degradation and a drop in intrinsic viscosity during processing, resulting in defects and the generation of harmful compounds like acetaldehyde, which complicates the molding process and increases energy consumption.
Innovation Solution
A method involving controlled drying of PET to a target moisture level between 60 ppm and 250 ppm to intentionally generate a controlled drop in intrinsic viscosity, allowing for easier injection molding and reduced energy consumption, while maintaining acceptable physical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PET chips are dried to very low moisture content (maximum 0.005% by weight) before molding, then hydrolytic degradation is prevented and polymer chain integrity is maintained, but drying time and energy consumption increase significantly
Solution Approach 1:
The invention changes the moisture content parameter from the conventional maximum 0.005% (50 ppm) to a higher range of 0.01-0.05% (100-500 ppm). This parameter change allows sufficient drying to prevent severe hydrolytic degradation while reducing the energy and time required for the drying process, as the desiccant bed does not need to achieve extremely low moisture levels
Solution Approach 2:
The invention converts the previously harmful moisture (which causes hydrolysis) into a beneficial factor by allowing controlled moisture levels that facilitate easier chain entanglement and improve melt elasticity. The moisture that was considered detrimental is now utilized to achieve desired rheological properties in the molded product
2Manufacturing precision
If PET chips are dried to very low moisture content (maximum 0.005% by weight) before molding, then defects such as bubbles and streaks are prevented, but the molding process becomes more complex and requires stricter control
Solution Approach 1:
The invention applies partial drying action by stopping the drying process at a moderate moisture level (0.01-0.05%) rather than continuing to extreme dryness. This partial action is sufficient to prevent the majority of hydrolysis-related defects while simplifying the drying system requirements and control mechanisms
Solution Approach 2:
By changing the target moisture content parameter to a higher range, the invention reduces the complexity of the drying system. The desiccant bed and associated controls do not need to achieve and maintain extremely low moisture levels, simplifying the overall drying process design and operation
3Reliability
If high intrinsic viscosity PET is used to maintain polymer chain integrity, then material quality is improved, but injection molding becomes more difficult and requires higher energy input
Solution Approach 1:
The invention performs preliminary chain entanglement during the drying and storage phase by allowing controlled moisture levels (0.01-0.05%). This preliminary action of partial hydrolysis creates initial chain entanglement that facilitates subsequent injection molding, reducing the energy and pressure required during the molding process while maintaining sufficient intrinsic viscosity
Solution Approach 2:
The invention changes the moisture content parameter to enable controlled partial hydrolysis that optimizes the balance between intrinsic viscosity and melt flow characteristics. This parameter change makes the material easier to process while maintaining adequate quality
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables the production of PET with a lower intrinsic viscosity, facilitating thinner wall thicknesses and more homogeneous molding, compatible with older equipment, and reducing energy and material costs while maintaining product quality.
Implementation Method 1
De-humidifying is carried out using a desiccant bed (generally in a desiccation tower) that must be periodically regenerated
Implementation Method 2
PET chips absorb moisture from the atmosphere until equilibrium is achieved
Implementation Method 3
Any water present at this stage rapidly hydrolyses the polymer, thereby reducing its molecular weight and damaging its physical properties
Data Source
AI summary
The inventions relates to a method for processing polyethylene terephthalate (PET) comprising supplying PET raw material (S1), drying the PET raw material (S4) to a target moisture level, plasticizing the PET (S5), and injecting the plasticized PET (S6) into a mold. In this method, the target moisture level is between 60 ppm and 250 ppm to generate hydrolysis of PET during plasticization (S5) resulting in a controlled drop of intrinsic viscosity of the PET. According to other aspects of the invention, there is provided a method for forming a bottle and a method for packaging still beverage in this bottle.