Low Melt Flow Polypropylene Resins for Medical Vials
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Solution Overview
Problem
Existing methods for two-stage injection-stretch-blow-moulding processes do not produce medical vials with an ideal balance of properties, including optical, thickness distribution, stacking, and drop test performance, especially at low temperatures.
Innovation Solution
The use of low melt flow polypropylene resins with a Ziegler-Natta catalyst system, specifically random copolymers of propylene and ethylene with a melt flow index of 1 to 3 dg/min, and an injection temperature of at least 280°C, along with optimized injection-stretch-blow-moulding conditions, to produce preforms for medical vials with improved properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional polypropylene resins with higher melt flow index are used in two-stage injection-stretch-blow-moulding, then the processing is easier and injection temperature can be lower, but the resulting medical vials do not achieve ideal balance of optical properties, thickness distribution, stacking properties, and drop test performance
Solution Approach 1:
The patent changes the melt flow index parameter from conventional values (typically 5-50 dg/min) to a specific low range (1-3 dg/min), which fundamentally alters the processing requirements and enables achievement of ideal thickness distribution and optical properties through precise control at elevated temperatures
Solution Approach 2:
The patent utilizes the phase transition behavior of the low melt flow polypropylene resin at elevated temperatures (≥280°C) to achieve optimal melting and filling characteristics during injection moulding, enabling precise control of the melting phase for uniform thickness distribution
2Illumination intensity
If conventional polypropylene resins are used, then processing conditions can be maintained at standard temperatures, but the medical vials exhibit poor optical properties and insufficient stacking performance
Solution Approach 1:
The patent changes the melt flow index parameter from conventional values (typically 5-50 dg/min) to a specific low range (1-3 dg/min), which fundamentally alters the processing requirements and enables achievement of ideal thickness distribution and optical properties through precise control at elevated temperatures
3Strength
If standard injection moulding is used with conventional resins, then production efficiency is maintained, but the medical vials fail to achieve superior impact strength and drop test performance
Solution Approach 1:
The patent changes the melt flow index parameter from conventional values (typically 5-50 dg/min) to a specific low range (1-3 dg/min), which fundamentally alters the processing requirements and enables achievement of ideal thickness distribution and optical properties through precise control at elevated temperatures
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 resulting medical vials exhibit excellent optical properties, uniform wall thickness distribution, superior impact strength, and enhanced stacking and drop test performance, making them suitable for medical applications and potentially replacing glass bottles.
Implementation Method 1
the polypropylene resin used in the present invention is prepared with a Ziegler-Natta (ZN) catalyst system
Implementation Method 2
The injection temperatures cited in the examples are of 230 and 240° C. Preferably, the polypropylene resin used in the present invention is prepared with a Ziegler-Natta (ZN) catalyst system. The injection temperature for preparing the preform is of at least 280° C.
Implementation Method 3
the use of low melt flow polypropylene resins for preparing preforms for injection-stretch-blow-moulding in order to prepare medical vials having excellent optical properties after bi-orientation
Data Source
AI summary
The present invention discloses a method for preparing vials, preferably medical vials by two-stage injection-stretch-blow-molding with a random copolymer of propylene having a melt index MI2 of from 1 to 3 dg/min and an ethylene content of from 2 to 3.5 wt % based on the weight of the resin, and wherein the preform injection temperature is of at least 280° C.