Copolyester Composition for Extrusion Blow Molding

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Solution Overview

Problem

Polyethylene terephthalate (PET) compositions used in injection stretch blow molding cannot be easily processed via extrusion blow molding due to high crystalline melting points and rapid crystallization rates, leading to issues in the PET recycle stream, such as stickiness and hazy film or bottles when mixed with other PET flake.

Innovation Solution

Development of a copolyester composition comprising 90-100 mole % terephthalic acid, 42-60 mole % 1,4-cyclohexanedimethanol, 40-58 mole % ethylene glycol, and 2 mole % or less diethylene glycol, with a branching agent, which has improved recyclability, low haze values, and short crystallization half-times, allowing for extrusion blow molding without significant stickiness to manufacturing equipment.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If PET compositions with high crystalline melting points and rapid crystallization rates are used for injection stretch blow molding, then the containers have good structural integrity and clarity, but they cannot be easily processed using extrusion blow molding and cause problems in the PET recycle stream

Engineering Contradiction:

Improveprocessability via extrusion blow moldingVSAvoidstability in PET recycle stream

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent modifies the crystallization kinetics of PET by adding nucleating agents and adjusting compositional parameters (polycondensation temperature, catalysts) to achieve a crystallization half-time of 5-500 minutes at 160°C, transforming the material from too-rapid crystallization to optimal slow crystallization for extrusion blow molding while maintaining recycle stream compatibility

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent creates a composite polyester composition by incorporating specific additives (nucleating agents like sorbitol, citric acid, or tartaric acid at 0.01-5 wt%, and chain extenders) into the PET matrix, combining the structural integrity of PET with modified crystallization properties that enable both extrusion blow molding and recycle stream stability

Inventive Principle:

Principle #40Composite materials

2Ease of manufacture

If copolyester compositions with 25-75 mole% 1,4-cyclohexanedimethanol are used for extrusion blow molding, then the containers have clarity and toughness, but they cause stickiness in dryers and hazy film when mixed with ISBM PET flake

Engineering Contradiction:

Improveextrusion blow molding capabilityVSAvoidstickiness and hazy film in recycle stream

Core Design Contradiction:

Ease of manufactureVSObject-generated harmful factors

Solution Approach 1:

The patent precisely controls the 1,4-cyclohexanedimethanol content within 25-75 mole% range and adjusts processing parameters (polycondensation temperature, catalyst selection) to achieve optimal balance between extrusion blow molding processability and recycle stream compatibility, preventing both stickiness and hazy film formation

Inventive Principle:

Principle #35Parameter changes

3Strength

If PET is rapidly crystallized to maintain structural integrity, then the material has good mechanical properties, but it cannot be processed via extrusion blow molding due to low melt strength

Engineering Contradiction:

Improvemelt strength for extrusion blow moldingVSAvoidcrystallization control

Core Design Contradiction:

StrengthVSManufacturing precision

Solution Approach 1:

The patent introduces nucleating agents during polycondensation to pre-establish nucleation sites, which control subsequent crystallization kinetics during extrusion blow molding, ensuring adequate melt strength during processing while achieving desired crystalline structure in the final product

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent optimizes processing parameters including polycondensation temperature (200-280°C), catalyst concentration, and moisture content to control molecular weight and crystallization rate, achieving the delicate balance between melt strength and crystallization control

Inventive Principle:

Principle #35Parameter changes

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 new copolyester composition enables the production of transparent, non-crystalline articles with good impact strength, can be blended with ISBM PET without affecting properties, and is non-problematic in the PET recycle stream, allowing for the creation of large, rigid containers with handles.

Implementation Method 1

crystallization half-times

Methodology Applied

Scientific EffectCrystallization: Crystallisation

Data Source

PatentEP2240532B1Copolyesters and blends with improved recyclability, processes for their manufacture, and articles prepared therefrom

Publication Date: 2017.09.06 EASTMAN CHEM CO

AI summary

Described as one aspect of the invention are extrusion blow molded articles comprising at least one polyester which comprises: (a) a dicarboxylic acid component comprising: (i) about 90 to about 100 mole % of terephthalic acid residues; (ii) about 0 to about 10 mole % of aromatic and/or aliphatic dicarboxylic acid residues having up to 20 carbon atoms; and (b) a glycol component comprising: (i) about 42 to about 60 mole % ethylene glycol residues; and (ii) about 40 to about 58 mole % residues of 1,4- cyclohexanedimethanol; wherein the total mole % of the dicarboxylic acid component is 100 mole %, and wherein the total mole % of the glycol component is 100 mole %; and wherein the inherent viscosity of the polyester is from 0.50 to 1.0 dL/g as determined in 60/40 (wt/wt) phenol/ tetrachloroethane at a concentration of 0.25 g/50 ml at 250C.