Polypropylene Resin Composition for Uniform Foamed Sheets

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Solution Overview

Problem

Conventional polypropylene-based resin compositions with long chain branches face issues such as poor moldability, uneven structure formation in shear flow, and insufficient extensibility, leading to suboptimal foamed sheet appearance and properties during extrusion foaming.

Innovation Solution

A polypropylene-based resin composition combining a polypropylene resin with long chain branches and a specific propylene-ethylene block copolymer, which prevents the formation of shear-induced crystalline structures, enhancing moldability and extensibility while maintaining high melt tension, resulting in foamed sheets with fine and uniform cells.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If long chain branches are introduced into polypropylene by high-energy ionization radiation or organic peroxide to increase melt tension, then melt tension is improved, but production cost increases and yellowing occurs

Engineering Contradiction:

Improvemelt tensionVSAvoidyellowing and production cost

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

The invention changes the molecular structure parameters by introducing long chain branches through controlled polymerization methods (using compounds (A) and (B) as catalysts) rather than post-modification methods. This achieves high melt tension while avoiding yellowing and high production costs associated with radiation or peroxide methods.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention replaces expensive and problematic methods (radiation, organic peroxide) with more economical catalyst-based polymerization approaches. The catalysts (A) and (B) provide a cost-effective way to create long chain branches without the harmful side effects of conventional methods.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

2Strength

If polypropylene with long chain branches is used to increase melt tension, then melt tension is improved, but moldability deteriorates due to shear-induced crystalline structure formation

Engineering Contradiction:

Improvemelt tensionVSAvoidmoldability

Core Design Contradiction:

StrengthVSEase of manufacture

Solution Approach 1:

The invention carefully controls the molecular weight distribution and branching parameters by selecting specific catalysts (A) and (B) with defined properties. This produces polypropylene with optimal long chain branches that enhance melt tension while avoiding excessive shear-induced crystallization that would harm moldability.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention creates a composite molecular structure where long chain branches are integrated into the polypropylene matrix through controlled polymerization. This composite structure at the molecular level provides both high melt tension and good moldability by balancing crystalline and amorphous regions.

Inventive Principle:

Principle #40Composite materials

3Strength

If polypropylene with long chain branches is used to increase melt tension, then melt tension is improved, but extensibility is insufficient leading to poor foamed sheet appearance

Engineering Contradiction:

Improvemelt tensionVSAvoidfoamed sheet appearance

Core Design Contradiction:

StrengthVSManufacturing precision

Solution Approach 1:

The invention optimizes the molecular weight distribution parameters (Mw/Mn ratio) and branching density to achieve the right balance for foaming. The specific catalysts (A) and (B) produce long chain branches that provide high melt tension while maintaining uniform cell structure formation during foaming, avoiding the appearance defects caused by insufficient extensibility.

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 improved moldability, extensibility, and appearance of foamed sheets with uniform cell size, enhancing thermoformability and overall performance in molded articles.

Implementation Method 1

prevents the formation of shear-induced crystalline structures

Methodology Applied

Scientific EffectCrystallisation: Crystallisation

Implementation Method 2

foamed sheet having high closed cell content formed by expansion molding, the cells being fine and relatively uniform in size

Methodology Applied

Scientific EffectFoaming: Foam

Data Source

PatentUS9505894B2Polypropylene-based resin composition and foam sheet

Publication Date: 2016.11.29 JAPAN POLYPROPYLENE CORP

AI summary

Provided is a polypropylene-based resin composition which gives uniform and fine cells and from which a foamed sheet and thermoform excellent in appearance, thermoformability, impact resistance, lightness, stiffness, heat resistance, heat insulating properties, oil resistance and the like can be produced and includes (X) 5 to 99% by weight of a polypropylene resin having a structure with long chain branches, and (Y) 1 to 95% by weight of a propylene-based block copolymer produced by sequential polymerization, which block copolymer comprises (Y-1) a propylene (co)polymer and (Y-2) a propylene-ethylene copolymer.