Butene-1 Copolymer Tie Layer for Low Seal Temperature BOPP Film
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Solution Overview
Problem
Current heat-sealable films, particularly in multilayer structures, face challenges in achieving a balance between low seal initiation temperature and high hot tack and seal strength, which is crucial for demanding applications like form and fill packaging.
Innovation Solution
Bioriented polypropylene (BOPP) multilayer structures are developed, comprising a skin layer with a crystalline propylene copolymer and a tie layer with a high content of butene-1 copolymer, optimized for low crystallinity and high molecular weight, to enhance heat-sealability and hot tack properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If copolymers of propylene with other olefins are used to achieve low seal initiation temperature, then seal initiation temperature is reduced, but hot tack strength is insufficient
Solution Approach 1:
The patent employs composite materials by combining propylene copolymer seal layer with a tie layer comprising a blend of polyethylene and polypropylene. This multilayer composite structure allows the seal layer to provide low seal initiation temperature while the tie layer enhances hot tack strength, resolving the contradiction between low sealing temperature and adequate bonding strength during filling operations.
2Strength
If high content of comonomers is used in terpolymer to improve hot tack, then hot tack strength increases, but seal initiation temperature control becomes difficult
Solution Approach 1:
The patent segments the film structure into distinct functional layers: a seal layer made of propylene copolymer with controlled comonomer content (1-10 mol%) for low seal initiation temperature, and a separate tie layer for hot tack enhancement. This segmentation allows independent optimization of each layer's properties, enabling low sealing temperature without compromising hot tack strength.
Solution Approach 2:
The patent applies local quality by assigning different compositional characteristics to different layers. The seal layer has controlled comonomer content (1-10 mol%) optimized for low sealing temperature, while the tie layer contains the polyethylene-polypropylene blend optimized for hot tack. Each layer's composition is locally optimized for its specific function, resolving the trade-off between seal temperature and hot tack strength.
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 BOPP multilayer structures achieve a balance of low seal initiation temperature and high hot tack and seal strength, ensuring the film's ability to withstand product weight and pressure during the packaging process.
Implementation Method 1
hot tack is the bonding strength measurable while the polymer in the heat sealed portion of a film is still in the semi-molten/solidifying state
Implementation Method 2
seal initiation temperature - the minimum temperature needed to form a seal of one polypropylene film layer to one film layer
Data Source
AI summary
Multilayer film (BOPP) structure containing at least: A) a skin (outer) layer substantially consisting of a crystalline low seal Initiation temperature propylene copolymer; B) a tie layer substantially consisting of a butene-1 copolymer having flexural modulus (MEF) of 75 MPa or less; C) a core layer substantially consisting of one or more polypropylene homopolymers designed for BOPP.