Propylene-Hexene-1 Copolymer Tanks for Creep Resistance

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Solution Overview

Problem

Plastic tanks, particularly expansion tanks, face issues with cracking and leakage due to mid-long term temperature and pressure cycles, which existing propylene-hexene-1 copolymers fail to address effectively in terms of high temperature creep resistance and mechanical properties.

Innovation Solution

Propylene-hexene-1 copolymers with a specific Melt Flow Rate (MFR) to melting temperature (Tm) ratio (A·Tm/B) greater than 70, combined with a xylene soluble fraction lower than 5%, and optimized polymerization using Ziegler-Natta catalysts, provide enhanced mechanical properties and high temperature resistance suitable for injection molding.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If existing propylene-hexene-1 copolymers are used, then the tanks can be produced by injection moulding, but the tanks exhibit poor high temperature creep resistance and develop cracks under temperature and pressure cycles

Engineering Contradiction:

Improvehigh temperature creep resistanceVSAvoidresistance to cracking under stress

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The patent applies parameter changes by establishing a specific relationship between MFR, melting temperature, and hexene-1 content through the formula A·Tm/B > 70. This quantitative parameter optimization resolves the contradiction by selecting copolymers with precisely controlled molecular weight distribution and composition, achieving both processability and high temperature creep resistance without cracking under thermal cycling

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent uses composite material principles by creating a propylene-hexene-1 copolymer with a specific microstructure that combines the crystalline rigidity of propylene with the flexibility introduced by hexene-1 comonomer units. This composite molecular structure at the polymer level provides both injection moulding suitability and enhanced creep resistance at high temperatures

Inventive Principle:

Principle #40Composite materials

2Stability of the object's composition

If copolymers with higher hexene-1 content are used to improve elongation, then the mechanical properties at high temperature deteriorate

Engineering Contradiction:

Improveelongation at breakVSAvoidmechanical properties at high temperature

Core Design Contradiction:

Stability of the object's compositionVSTemperature

Solution Approach 1:

The patent resolves this contradiction through parameter optimization by constraining the hexene-1 content within a specific range (0.5-5 wt%) and establishing the quantitative relationship A·Tm/B > 70. This ensures the copolymer maintains sufficient elongation at break while preserving high temperature mechanical properties, as the controlled comonomer content prevents excessive disruption of the crystalline structure

Inventive Principle:

Principle #35Parameter changes

3Strength

If copolymers with lower MFR are used to improve rigidity, then the injection moulding processability worsens

Engineering Contradiction:

ImproverigidityVSAvoidinjection moulding processability

Core Design Contradiction:

StrengthVSEase of manufacture

Solution Approach 1:

The patent applies parameter changes by establishing the relationship A·Tm/B > 70, which couples MFR with melting temperature. This allows selection of copolymers with MFR in the range of 0.8-30 g/10min that provide adequate rigidity while maintaining sufficient melt flow for injection moulding. The relationship ensures that lower MFR (higher rigidity) is compensated by appropriate melting temperature to maintain processability

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 solution offers optimal balance between rigidity and high temperature creep resistance, ensuring the propylene-hexene-1 copolymers can be used for plastic tanks, specifically expansion tanks, with improved tensile modulus, Izod impact strength, and Flexural Modulus, preventing cracking and leakage under high stress conditions.

Implementation Method 1

optimal balance between mechanical properties such as rigidity and mid-long term high temperature creep resistance

Methodology Applied

Scientific EffectCreep resistance: Creep

Implementation Method 2

Tm is the melting temperature measured by DSC expressed in ° C.

Methodology Applied

Scientific EffectMelting: Melting

Data Source

PatentUS8252399B2Plastic tanks made from random copolymers of propylene and hexene-1

Publication Date: 2012.08.28 BASELL POLIOLEFINE ITALIA SRL

AI summary

Plastic tanks comprising a propylene-hexene-1 copolymer having a xylene soluble fraction lower than 5% wt with respect to the total weight of the copolymer and satisfying the following relation:A·TmB>70wherein A is the MFR measured according to the method ISO 1133 (230° C., 5 kg) expressed in g/10 min, Tm is the melting temperature measured by DSC expressed in ° C. and B is the hexene-1 content expressed in percentage by weight with respect to total weight of the copolymer.