Propylene Copolymer Sealing Layer for Low Heat Initiation
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Solution Overview
Problem
Polypropylene films face challenges in achieving high hot tack strength, low heat sealing initiation temperature, broad processing window, low stickiness, and good optical properties, which are often conflicting requirements in polymer film applications, particularly in the food packing industry.
Innovation Solution
A multi-layer polymer film comprising a core layer and a sealing layer made from a propylene copolymer composition with high comonomer content, featuring two different fractions of polypropylene, one with low and one with high comonomer content, optimized for low heat sealing initiation temperature, high hot tack strength, and broad processing window, while maintaining good optical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polypropylene is used for sealing applications, then sealing properties are improved, but hot tack strength and heat sealing initiation temperature are difficult to optimize simultaneously
Solution Approach 1:
The patent changes the compositional parameters of the sealing layer by incorporating a propylene copolymer with high comonomer content (3.0-8.0 wt.-%, preferably 4.0-6.0 wt.-%) of C5-C12 α-olefins. This parameter change in copolymer composition directly lowers the heat sealing initiation temperature to 112°C or below while maintaining adequate hot tack strength, resolving the contradiction between sealing reliability and temperature control.
Solution Approach 2:
The patent creates a composite sealing layer by combining polypropylene (A) with polypropylene (B) in a specific weight ratio range of 20/80 to 80/20, preferably 30/70 to 70/30. This composite structure integrates the high melting temperature characteristics of polypropylene (A) with the low heat sealing initiation temperature properties of the high comonomer content polypropylene (B), achieving both low SIT and high hot tack strength simultaneously.
2Ease of manufacture
If polypropylene with high melting temperature is used, then stickiness and blocking during film manufacture are reduced, but heat sealing initiation temperature increases
Solution Approach 1:
The patent modifies the compositional parameters by incorporating C5-C12 α-olefin comonomers at 3.0-8.0 wt.-% content into the polypropylene structure. This parameter change introduces lower melting point components that reduce heat sealing initiation temperature and stickiness during film manufacture, while the overall composition maintains sufficient thermal stability for processing.
Solution Approach 2:
The patent applies local quality by creating a sealing layer with distinct compositional characteristics different from the core layer. The sealing layer specifically contains the propylene copolymer composition with high comonomer content, while the core layer can use different polymers. This localized compositional differentiation allows the sealing layer to have low stickiness and low SIT without compromising the overall film structural integrity.
3Reliability
If traditional sealing materials are used, then sealing function is achieved, but optical properties of the film are compromised
Solution Approach 1:
The patent changes the chemical composition parameters of the sealing layer by using a propylene copolymer with controlled comonomer content (3.0-8.0 wt.-%) and specific comonomer types (C5-C12 α-olefins). This compositional parameter optimization achieves the right balance between sealing functionality and optical clarity, allowing the sealing layer to perform its function while maintaining good light transmission and appearance.
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 film exhibits improved hot tack strength, low heat sealing initiation temperature, broad processing window, and reduced stickiness, making it suitable for various applications, including food packaging, with enhanced optical properties.
Implementation Method 1
all extrusion products have a window within which sealing may occur, i.e. in which the sealing layer becomes partly molten
Data Source
AI summary
A multi-layer polymer film comprising a core layer and a sealing layer,said sealing layer comprises a propylene copolymer composition, said propylene copolymer compositionhas a comonomer content in the range of 3.0 to 8.0 wt.-%, the comonomers are C5 to C12 α-olefins,comprises a polypropylene (A) and a polypropylene (B) in the weight ratio [(A)/(B)] of 20/80 to 80/20,whereinsaid polypropylene (A) has a comonomer content of equal or below 4.0 wt.-%, the comonomers are C5 to C12 α-olefins, andsaid propylene copolymer (B) has a comonomer content of 4.0 to 20.0 wt.-%, the comonomers are C5 to C12 α-olefins.