Polyolefin Composition Transparency Impact Resistance
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Solution Overview
Problem
Existing polypropylene copolymers used in extrusion processes for extrusion blow molded articles face challenges in maintaining transparency while achieving improved impact resistance, particularly at low temperatures, due to the loss of transparency after molding and/or re-heating/annealing when heterophasic compositions are used.
Innovation Solution
A polyolefin composition comprising 75-85% of a propylene copolymer with up to 15% ethylene or C4-C10 α-olefins and 15-25% of a copolymer of ethylene with C4-C10 α-olefins, processed through sequential polymerization in the presence of a stereospecific Ziegler-Natta catalyst, achieving specific ratios and solubility fractions to maintain transparency and impact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If propylene-ethylene elastomeric copolymer is added to improve impact resistance, then impact resistance is improved, but transparency is lost
Solution Approach 1:
The patent applies parameter changes by precisely controlling the comonomer content (ethylene and C4-C10 α-olefins) within specific ranges (10-25% for component 2, with C4-C10 α-olefin content of 12-20%), and controlling the xylene-soluble fraction (40-60% for component 2). These parameter optimizations allow the elastomeric copolymer to provide impact resistance while maintaining transparency by preventing excessive crystallization that would cause haze.
Solution Approach 2:
The patent uses a composite material approach by creating a heterophasic composition with two distinct polyolefin components: component 1 (propylene copolymer with specific properties) and component 2 (elastomeric copolymer with 15-25% C4-C10 α-olefins). This composite structure allows the different phases to provide complementary functions - the crystalline phase maintains transparency while the rubbery phase provides impact resistance.
2Strength
If heterophasic compositions are used to balance properties, then impact properties at low temperatures are improved, but transparency is lost after molding and/or re-heating/annealing
Solution Approach 1:
The patent controls the xylene-soluble fraction of component 2 within 40-60%, and sets the ratio of component 2 to C4-C10 α-olefins in component 2 at 0.80 or higher. These parameter changes ensure that the elastomeric phase remains compatible and uniformly distributed, preventing phase separation and crystallization-induced haze during molding and annealing processes, thus maintaining transparency while providing low-temperature impact resistance.
Solution Approach 2:
The patent creates local quality differences by having component 2 (elastomeric copolymer) specifically distributed to provide low-temperature impact resistance in critical areas, while component 1 (propylene copolymer with lower comonomer content) maintains the overall transparency and structural integrity. The specific composition ratios ensure that the rubbery phase provides localized impact protection without compromising overall optical properties.
3Strength
If comonomer content is increased to improve impact resistance, then impact resistance is improved, but manufacturing precision and property balance become difficult to maintain
Solution Approach 1:
The patent establishes precise parameter ranges to balance impact resistance and manufacturing precision: component 2 contains 10-25% C4-C10 α-olefins (preferably 12-20%), with the ratio of component 2 to C4-C10 α-olefins being 0.80 or higher. The xylene-soluble fraction of component 2 is controlled at 40-60%. These optimized parameters ensure consistent phase distribution and crystallization behavior, making the composition easy to manufacture with reproducible properties.
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 a balanced set of properties including high flexural modulus, improved impact resistance, and retention of transparency across various temperature conditions, suitable for applications like sheet extrusion/thermoforming and blow molding.
Implementation Method 1
processed through sequential polymerization in the presence of a stereospecific Ziegler-Natta catalyst
Data Source
AI summary
Polyolefin composition, comprising in percent by weight:1) 75-85% of a copolymer of propylene, said copolymer containing up to 15% by weight, of ethylene and/or C4-C10 α-olefin(s) and having a fraction soluble in Xilene at room temperature lower than 6% by weight, and2) 15-25% of a copolymer of ethylene with one or more C4-C10 α-olefin(s) containing from 10 to 25% by weight of said C4-C10 α-olefin(s);said composition having the value of MFR, measured at 230° C., 2.16 kg, of less than 2.5 g/10 min, the total content of ethylene of from 14 to 22% by weight, the total content of C4-C10 α-olefin(s) of less than 4.5% by weight, the ratio of the total content of ethylene to the total content of C4-C10 α-olefin(s) equal to or higher than 4, the value of the intrinsic viscosity of the total fraction soluble in xylene at room temperature equal to or less than 1.5 dl/g, and the ratio of the amount of component 2) and the amount of C4-C10 α-olefin(s) in component 2) equal to or higher than 0.80.