Polypropylene Separator Resin with Bimodal Molecular Weight Control
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Solution Overview
Problem
Existing methods for preparing polypropylene for secondary battery dry separators fail to achieve satisfactory mechanical and thermal properties while maintaining resin flowability.
Innovation Solution
A bimodal process is applied to polymerize propylene monomers in the presence of a Ziegler-Natta catalyst, producing high and low molecular weight polypropylene with a specific co-catalyst and electron donor ratio, optimizing molecular weight distribution and crystallinity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If typical polypropylene preparation methods are used, then production cost is reduced and manufacturing is simplified, but mechanical and thermal properties are insufficient
Solution Approach 1:
The patent divides the polymerization process into two separate reactors: a first reactor for producing high molecular weight polypropylene (weight average molecular weight 450,000 to 650,000 g/mol) and a second reactor for producing low molecular weight polypropylene (weight average molecular weight 150,000 to 300,000 g/mol). This segmentation allows each reactor to be optimized for specific molecular weight ranges, thereby achieving superior mechanical and thermal properties while maintaining controllable process complexity through systematic division of the manufacturing process.
2Strength
If high molecular weight polypropylene is produced to improve mechanical strength, then tensile strength increases, but resin flowability deteriorates
Solution Approach 1:
The patent merges the outputs of two separate polymerization processes by mixing high molecular weight polypropylene from the first reactor with low molecular weight polypropylene from the second reactor. The high molecular weight component provides excellent tensile strength and mechanical properties, while the low molecular weight component ensures good resin flowability and processability. This combination creates a synergistic effect where the final polypropylene product achieves both high strength and good flowability simultaneously.
3Temperature
If co-catalyst and electron donor ratio is optimized to improve crystallinity, then thermal properties are enhanced, but catalyst system complexity increases
Solution Approach 1:
The patent optimizes the molar ratio of co-catalyst to electron donor within the range of 2 to 25 in the first reactor. This parameter optimization promotes the formation of highly crystalline polypropylene with weight average molecular weight of 450,000 to 650,000 g/mol and achieves a meltdown temperature of 166°C or higher. By systematically controlling this chemical parameter ratio, the patent enhances thermal properties while maintaining reasonable catalyst system complexity through defined compositional parameters.
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 method enhances mechanical and thermal properties of polypropylene, such as tensile strength, puncture strength, and meltdown temperature, while improving flowability during separator processing.
Implementation Method 1
polymerization reaction in the presence of a Ziegler-Natta catalyst
Implementation Method 2
the molar ratio of a co-catalyst and an electron donor added in step a) is adjusted to 2 to 25, thereby preparing the polypropylene
Data Source
AI summary
In the preparation of polypropylene for a dry separator of a secondary battery, disclosed is a method for preparing polypropylene for a separator of a secondary battery, having improved flowability of a resin while maximizing mechanical and thermal properties, compared to typical materials. The present invention provides a method for preparing polypropylene for a separator of a secondary battery by subjecting, in the presence of a Ziegler-Natta catalyst, propylene monomers to a polymerization reaction, wherein the propylene monomer polymerization reaction includes a) obtaining a high molecular weight polypropylene having a weight average molecular weight of 450,000 to 650,000 g/mol in a first reactor, and b) obtaining a low molecular weight polypropylene having a weight average molecular weight of 150,000 to 300,000 g/mol in a second reactor, and the molar ratio of a co-catalyst and an electron donor added in step a) is adjusted to 2 to 25, thereby preparing the polypropylene for a separator of a secondary battery.