Polypropylene Preform Injection Temperature and Catalyst
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Solution Overview
Problem
Existing methods for preparing polypropylene preforms for injection-stretch-blow-moulding processes fail to achieve an ideal balance of optical, thickness distribution, stacking, and drop test properties, especially at low temperatures.
Innovation Solution
A two-stage injection-stretch-blow-moulding method using polypropylene resin prepared with a Ziegler-Natta catalyst system, with a melt flow index of 1 to 20 dg/min, injected at a temperature of at least 265 °C, and optionally containing up to 5000 ppm of nucleating agents, to produce preforms with optimized properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional polypropylene resins with narrow polydispersity (metallocene-produced) are used, then processing uniformity is improved, but optical properties and thickness distribution are insufficient
Solution Approach 1:
The invention changes the key parameter of polydispersity index from narrow (metallocene) to broad (Ziegler-Natta, 3.0-6.0), and combines it with specific injection temperature (265-300°C) and resin composition parameters (ethylene content 1-6%, melt index 1-20 dg/min) to achieve optimal optical properties and thickness distribution that cannot be obtained with narrow polydispersity resins alone
Solution Approach 2:
The invention uses a composite resin system comprising Ziegler-Natta polypropylene combined with specific copolymer components (ethylene-propylene copolymer with 1-6 wt% ethylene), creating a multi-component material system that achieves superior bi-orientation characteristics, optical clarity, and wall thickness uniformity compared to single-component metallocene resins
2Manufacturing precision
If high injection temperature (at least 265 °C) is used, then preform quality is improved, but energy consumption increases
Solution Approach 1:
The invention optimizes the injection temperature parameter to a specific range (265-300°C) that is higher than conventional processes but justified by the broad polydispersity resin characteristics, achieving superior preform quality and final article properties while managing energy consumption through efficient process design
3Manufacturing precision
If broad polydispersity index resin (ZN catalyst) is used, then bi-orientation properties are improved, but processing consistency becomes more difficult
Solution Approach 1:
The invention changes the polydispersity index parameter to broad (3.0-6.0) using Ziegler-Natta catalyst, which improves bi-orientation and optical properties, and compensates for processing variability through optimized injection temperature (265-300°C) and resin composition control
Solution Approach 2:
The broad polydispersity resin provides different molecular weight fractions that respond differently during processing: lower MW fractions provide flow and filling, while higher MW fractions provide strength and orientation, creating local functional differentiation within the material that improves overall article quality
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 results in polypropylene bottles with excellent optical properties, improved thickness distribution, and enhanced drop test and stacking performance, suitable for various applications including medical packaging and food storage.
Implementation Method 1
The polypropylene resin used in the present invention is prepared with a Ziegler-Natta (ZN) catalyst system
Implementation Method 2
wherein polypropylene is injected at a melt temperature of at least 265 °C
Implementation Method 3
The injection rate v inj is preferably lower than 20 g/s and most preferably of at most 15 g/s
Data Source
AI summary
This invention discloses a method for preparing a preform for two-stage injection- stretch-blow-moulding (ISBM) from polypropylene resin produced with a Ziegler- Natta catalyst system and having a melt flow index MI2 of from 1 to 20 dg/min, wherein polypropylene is injected at a melt temperature of at least 265 °C. Also disclosed are the preforms obtainable by the method, the use of the preforms for preparing bottles, and the bottles prepared from the preforms.