Rotomoulded Polypropylene Composition Warpage Reduction

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Solution Overview

Problem

Rotomoulding of polypropylene is challenging due to its brittleness and slow crystallization, leading to warpage and reduced impact strength in rotomoulded articles, as existing polypropylene compositions fail to balance sintering properties, impact resistance, and dimensional stability effectively.

Innovation Solution

A polymer composition comprising at least two polypropylene components, a nucleating agent, and an impact modifier, with specific propylene polymer components having different crystallization temperatures and comonomer contents, and a polymeric nucleating agent, is used to enhance sintering and impact resistance while maintaining stiffness and dimensional stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If a nucleating agent is added to reduce spherulite size and improve microstructure, then the crystallinity increases, but warpage and impact strength decrease

Engineering Contradiction:

Improvemicrostructure uniformityVSAvoidimpact strength

Core Design Contradiction:

Manufacturing precisionVSStrength

Solution Approach 1:

The patent changes the chemical composition parameters of the polypropylene by incorporating specific comonomers (ethylene, 1-butene, 1-hexene) at controlled levels to modify crystallization behavior and reduce the negative effects of nucleating agents on impact strength

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent creates a composite polypropylene material system combining multiple polypropylene components with different properties (homopolymer, copolymers with different comonomer contents) to achieve a balance between crystallinity, impact strength, and warpage resistance

Inventive Principle:

Principle #40Composite materials

2Strength

If polypropylene is used to improve stiffness and heat resistance, then thermo-mechanical properties improve, but brittleness increases and impact strength decreases

Engineering Contradiction:

Improvestiffness and heat resistanceVSAvoidbrittleness

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

The patent employs a composite polypropylene composition consisting of multiple components including homopolymer and copolymers with different comonomer contents, creating a material system that balances stiffness, heat resistance, and impact strength

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent introduces local quality variations by incorporating copolymer components with specific comonomer contents (2-10 mol% ethylene, 2-8 mol% 1-butene, 2-6 mol% 1-hexene) to create regions with different properties that collectively improve overall toughness while maintaining stiffness

Inventive Principle:

Principle #3Local quality

3Temperature

If asymmetrical cooling occurs during rotomoulding, then the outer wall cools faster than the inner wall, but this creates asymmetrical residual stresses and warpage

Engineering Contradiction:

Improvecooling rateVSAvoiddimensional stability

Core Design Contradiction:

TemperatureVSShape

Solution Approach 1:

The patent modifies the thermal parameters of the polypropylene composition by controlling crystallization temperature and degree of crystallinity through comonomer selection and nucleating agent usage, reducing the thermal contraction differences that cause warpage during asymmetrical cooling

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 composition achieves high impact resistance, stiffness, and low warpage in rotomoulded articles, facilitating the production of products with improved thermal and mechanical properties.

Implementation Method 1

a nucleating agent... to reduce the spherullite size... The finer microstructure of nucleated propylene polymer is generally associated with a higher degree of crystallinity

Methodology Applied

Scientific EffectCrystallisation: Crystallisation

Implementation Method 2

an impact modifier... to improve the impact strength of polypropylene

Methodology Applied

Scientific EffectImpact absorption: Impact Force

Implementation Method 3

A key step in rotomoulding is therefore sintering of the moulding powder. This is characterised by the occurrence of coalescence of the moulding powder and the production of a porous three dimensional network

Methodology Applied

Scientific EffectSintering: Sintering

Implementation Method 4

the volume contraction due to crystallisation induces asymmetrical residual stresses and warpage in the final product

Methodology Applied

Scientific EffectThermal contraction: Thermal Contraction

Data Source

PatentEP2054471B1Use of polypropylene composition

Publication Date: 2011.04.20 BOREALIS TECH OY

AI summary

This invention relates to use of a polymer composition for rotomoulding, wherein said composition comprises: (i) at least two propylene polymer components, (ii) a nucleating agent; and (iii) an impact modifier.