Extrusion Blow Molding Apparatus for Polyester Articles
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Solution Overview
Problem
Polyester resins with high molecular weight, necessary for extrusion blow molding to achieve suitable melt strength, are prone to thermal degradation and increased processing costs, while branched PET copolymers, which enhance melt strength, hinder recyclability due to slow crystallization rates, causing issues in PET recycling streams.
Innovation Solution
An extrusion blow molding apparatus with a specific extrusion screw geometry and a closed-loop drying system is used to process thermoplastic polyester materials, combining virgin copolyester with regrind and optimizing crystallization to enhance melt strength and recyclability, incorporating chain extenders and branching agents to improve molecular weight and crystallinity, and using a desiccant bed for efficient drying.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high molecular weight PET is used to achieve suitable melt strength for EBM, then melt strength is improved, but thermal degradation increases and processing temperature must be increased
Solution Approach 1:
The patent changes the molecular structure parameters of PET by introducing branching agents and chain extenders to create branched copolymers with optimized molecular weight distribution. This allows achieving sufficient melt strength without requiring excessively high processing temperatures that cause thermal degradation.
Solution Approach 2:
The patent creates composite polyester materials by combining virgin PET with branched copolymers and adding chain extenders. This composite approach enhances melt strength while maintaining processability and reducing thermal degradation through synergistic effects of the different polymer components.
2Strength
If branched PET copolymers are used to enhance melt strength, then melt strength is improved, but crystallization rate decreases causing sticking and agglomeration during recycling
Solution Approach 1:
The patent carefully controls the branching degree and molecular weight distribution of the copolymer to optimize the balance between melt strength and crystallization rate. By adjusting these parameters, the material achieves sufficient melt strength while maintaining adequate crystallization speed to prevent sticking during recycling.
Solution Approach 2:
The patent creates local heterogeneity in the polymer structure through controlled branching, where the branched regions provide melt strength while the linear segments maintain crystallization capability. This local structural differentiation allows simultaneous optimization of both properties.
3Strength
If higher processing temperatures are used for high I.V. PET, then melt strength is improved, but resin thermal degradation increases resulting in more yellowness
Solution Approach 1:
The patent modifies the polymer structure by introducing branching agents that enhance melt strength at lower temperatures. This parameter change in molecular architecture allows achieving the required melt strength without the need for high processing temperatures that cause thermal degradation and yellowness.
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
The process achieves stable extrusion blow molding with improved melt strength and clarity, reducing thermal degradation and processing costs, while ensuring compatibility with PET recycling streams by enhancing crystallinity and preventing sticking and agglomeration during recycling.
Implementation Method 1
an extrusion screw disposed within the barrel, wherein the extrusion screw comprises a shaft and a spiral flight extending radially from the screw shaft along at least a portion of the length of the shaft. The flight has an outer edge in sliding contact with an inner surface of the barrel.
Implementation Method 2
extruding a polymer resin in a softened state through an annular die to form a molten hollow tube or parison
Implementation Method 3
using a desiccant bed for efficient drying
Implementation Method 4
enhancing crystallinity and preventing sticking and agglomeration during recycling
Data Source
AI summary
An extrusion blowmolding apparatus has an extrusion die having an upstream portion for receiving the thermoplastic polyester material and a downstream portion having a die head through which molten thermoplastic polyester material is flowed to form a parison suitable for extrusion blowmolding. The extrusion die has extending therethrough a generally cylindrical barrel and an extrusion screw disposed within the barrel having spiral flights along its length. In some aspects, the flight depths are lengthened so to provide a good melt at a suitable throughput. By also selecting an appropriate extrusion temperature profile, it is possible to eliminate or minimize unmelts, which can contribute to processing difficulties as well as defects in the resulting article. In other aspects, a closed-loop drying system is provided for achieving very low moisture levels in the polyester material to improve processing.