Propylene Polymer Composition for Biaxially Oriented Film Stiffness
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Solution Overview
Problem
Existing methods for producing biaxially oriented polypropylene (BOPP) films struggle to balance high-temperature stretching properties with mechanical properties, often requiring additional components that increase production costs and do not achieve satisfactory results in terms of stiffness and transparency.
Innovation Solution
A propylene polymer composition comprising a propylene random copolymer and homopolymer with an overall isotacticity index greater than 96.5%, achieved through two-step polymerization reactions using a Ziegler-Natta catalyst, which maintains a higher ethylene content and controlled molecular weight distribution to enhance film stiffness and transparency without the need for stiffening agents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the isotacticity index and melting temperature of polypropylene are reduced to improve processing and forming of BOPP film, then the film can be easier to process, but the mechanical properties such as tensile strength and stiffness of the film are reduced
Solution Approach 1:
The patent applies parameter changes by precisely controlling the isotacticity index (95-98%) and melting temperature (155-165°C) of the propylene polymer. This optimization allows the film to maintain both good processability during biaxial stretching and high mechanical strength in the final product, resolving the contradiction between ease of manufacture and strength.
2Strength
If C5-C9 petroleum resin is added to isotactic polypropylene material to increase modulus and improve stiffness, then the stiffness of the polypropylene film is improved, but the production cost increases and the steam barrier property and transparency are affected
Solution Approach 1:
The patent extracts and eliminates the need for C5-C9 petroleum resin additives by achieving the desired stiffness and mechanical properties through optimized polymer composition and structure. The propylene polymer with controlled isotacticity (95-98%) and specific melting temperature range (155-165°C) inherently provides the required modulus without external stiffening agents, thereby reducing production cost and maintaining transparency and steam barrier properties.
3Ease of manufacture
If ethylene content in propylene copolymer is increased to improve processability, then the film can be easier to process, but the transparency and stiffness of the film are reduced
Solution Approach 1:
The patent applies parameter changes by precisely controlling the ethylene content (0.8-1.5 wt%) in the propylene copolymer. This optimized composition allows the material to achieve good processability during extrusion and biaxial stretching while maintaining adequate transparency and stiffness in the final film, balancing the contradictory requirements.
4Temperature
If the MFR value difference between first polypropylene and second propylene random copolymer is increased to improve high-temperature stretching property, then the film can be stretched at higher temperature, but the molecular weight control becomes more difficult and mechanical properties are compromised
Solution Approach 1:
The patent applies parameter changes by optimizing the MFR values of the two polypropylene components (first polypropylene with MFR 0.5-2.0 g/10min and second propylene random copolymer with MFR 2.0-5.0 g/10min). This controlled difference in MFR values enables the film to exhibit good high-temperature stretching properties while maintaining proper molecular weight distribution and mechanical properties, resolving the contradiction between temperature resistance and manufacturing precision.
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 BOPP film exhibits improved stiffness, transparency, and mechanical properties, with higher Young's modulus and processability, enabling high-speed film production while maintaining excellent comprehensive properties.
Implementation Method 1
achieved through two-step polymerization reactions using a Ziegler-Natta catalyst
Data Source
AI summary
The present invention provides a propylene polymer composition for producing a biaxially oriented film, comprising propylene random copolymer and propylene homopolymer; wherein the propylene random copolymer is a copolymer of propylene and ethylene, optionally comprising one or more alpha-olefins of C4-C10; the propylene polymer composition has an overall isotacticity index, as determined by nuclear magnetic resonance method, of greater than or equal to 96.5%, and an ethylene content of greater than 0.3 wt %; and wherein, the melt flow rate of the propylene random copolymer is lower than that of the propylene homopolymer. The biaxially oriented polypropylene film produced by the propylene polymer composition of the present invention exhibits excellent physical properties, and has, in the absence of any stiffening agent, relatively higher modulus and stiffness. Moreover, the process for producing the biaxially oriented polypropylene film is featured with a good film-forming stability and a high film-forming stretching speed.