Polypropylene Random Copolymer Catalyst for Low Odour Stiffness
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Solution Overview
Problem
Current polypropylene random copolymers used in injection molding for thin-walled packaging, especially for food applications, face challenges with high melt flow rates leading to brittleness, high odour and taste levels, and insufficient stiffness, which are not adequately addressed by existing catalyst systems and processing methods.
Innovation Solution
A polymerization process using a Ziegler-Natta procatalyst with a trans-esterification product of a lower alcohol and a phthalic ester as internal donor, combined with an organometallic cocatalyst and a specific external donor, to produce polypropylene random copolymers with high melt flow, low odour, and increased stiffness without additional processing steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If polypropylene is processed by controlled rheology techniques to improve flowability, then melt flow increases, but odour and taste levels increase due to peroxide residues
Solution Approach 1:
The invention extracts and eliminates the harmful peroxide residues and odour-causing byproducts from the polymerization process by using a Ziegler-Natta catalyst system that inherently produces low odour and taste levels, avoiding the need for secondary controlled rheology processing that introduces peroxides
Solution Approach 2:
The Ziegler-Natta catalyst system acts as an intermediary that enables direct production of high melt flow polypropylene without requiring peroxide-based controlled rheology processing, thereby preventing odour and taste contamination from the outset
2Ease of operation
If polypropylene is processed to achieve high melt flow for thin-walled applications, then processability improves, but stiffness becomes insufficient
Solution Approach 1:
The invention changes the molecular parameters of the polypropylene through catalyst system optimization, achieving a unique combination where high melt flow (≥25 g/10 min) coexists with high stiffness, producing articles with tensile modulus ≥1000 MPa - a parameter combination previously considered mutually exclusive
3Ease of manufacture
If conventional catalyst systems are used for polypropylene production, then manufacturing cost is reduced, but odour and taste levels increase
Solution Approach 1:
The invention changes the chemical parameters of the catalyst system by specifying particular components (magnesium compound with specific surface area 5-20 m²/g, titanium compound with TiCl3 or TiCl4, specific internal donors like esters or ethers, and external donors), achieving low odour and taste levels while maintaining manufacturing feasibility
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 results in polypropylene random copolymers with improved high melt flow, reduced odour and taste levels, and increased stiffness, making them suitable for injection molding applications, particularly for thin-walled packaging, while meeting regulatory requirements for food contact materials.
Implementation Method 1
a polymerization process using a Ziegler-Natta procatalyst with a trans-esterification product of a lower alcohol and a phthalic ester as internal donor, combined with an organometallic cocatalyst and a specific external donor
Data Source
AI summary
Process for the production of polypropylene random copolymers containing 2.5 to 5.0 wt % of ethylene as comonomer and having an MFR2 in accordance with ISO 1 133 (230° C., 2.16 kg load) of ≧25 g/10 min to 100 g/10 min and a hexane-solubles content, determined according to FDA CFR 21 §177.1520 below 5 wt %, said process comprising the step of polymerizing propylene and ethylene in the presence of a catalyst system comprising (i) a Ziegler-Natta procatalyst which contains a trans-esterification product of a lower alcohol and a phthalic ester as internal donor and (ii) an organometallic cocatalyst and (iii) an external donor represented by formula (I) or (II) Si(OCH2CH3)3(NR1R2) (I) or Si(OCH3)2(CH3(cyclohexyl) (II) wherein R1 and R2 can be the same or different and represent a hydrocarbon group having 1 to 12 carbon atoms, the polypropylene random copolymers with a low level of odor and taste themselves and their use for injection molding applications, preferably for thin-wall packaging for food packaging in non-cooking applications and for medical packaging.