Multilayer Film Skin Layer Reduces Xylene Solubility
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Solution Overview
Problem
Random propylene/ethylene copolymers exhibit high xylene solubility fractions, leading to operational difficulties and deterioration of optical and organoleptic properties, making them unsuitable for certain applications like food wrapping films without additional processing steps to remove the soluble fraction.
Innovation Solution
Multilayer films with a skin layer comprising propylene ethylene copolymers characterized by specific ethylene content and molecular weight distribution, processed using a catalyst system containing Ti, Mg, Cl, and an electron donor compound with Bi, which results in improved sealing initiation temperature and organoleptic properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If random propylene/ethylene copolymers are used to modify molecular structure and reduce crystallinity, then melting temperature and sealing temperature are lowered, but xylene solubility increases significantly
Solution Approach 1:
The patent applies local quality by creating a multilayer film structure where different layers have different compositions and properties. The skin layer contains the random copolymer with specific ethylene content (1-15 wt%) to provide desired sealing temperature, while the core layer uses different materials to control overall xylene solubility. This spatial differentiation allows simultaneous optimization of both temperature properties and solubility characteristics.
Solution Approach 2:
The invention uses composite materials by combining random propylene/ethylene copolymer with other polymers in a multilayer configuration. The core layer may contain polypropylene homopolymer or copolymers with different ethylene content, creating a composite structure where each material contributes specific properties. This composite approach enables the film to achieve low sealing temperature from the copolymer skin layer while maintaining low xylene solubility through the core layer composition.
2Temperature
If comonomer content is increased to modify polymer properties, then crystallinity and melting temperature decrease, but flowability deteriorates due to increased soluble fraction
Solution Approach 1:
The patent segments the polymer structure by controlling comonomer distribution within the copolymer chains. By using specific catalyst systems (metallocene or post-metallocene) that enable controlled random distribution of ethylene units, the polymer achieves modified crystallinity and melting temperature without excessive soluble fraction formation. This controlled segmentation at the molecular level maintains flowability while achieving the desired thermal properties.
Solution Approach 2:
The invention applies parameter changes by precisely controlling the ethylene content (1-15 wt%) and molecular weight distribution (Mw/Mn > 4.0) of the copolymer. These parameter optimizations ensure that the copolymer provides the necessary melting temperature reduction while maintaining adequate flowability. The specific relationship between ethylene content and xylene solubility is controlled through these parameter adjustments.
3Ease of manufacture
If soluble fraction is present in significant amounts, then processing becomes difficult, but optical properties deteriorate over time due to blooming
Solution Approach 1:
The patent extracts or removes the harmful soluble fraction effect by using a multilayer configuration where the core layer acts as a barrier. The core layer contains materials with low xylene solubility that prevent the migration of soluble fractions to the film surface. This extraction of the blooming problem through structural design protects optical properties while allowing the skin layer to provide easy processing characteristics.
Solution Approach 2:
The core layer serves as an intermediary between the skin layer and the external environment. It mediates by preventing direct contact between xylene and the copolymer in the skin layer, thereby stopping the dissolution and subsequent blooming process. This intermediary layer maintains both processing ease (by allowing soluble fraction in skin layer) and optical stability (by preventing its migration to surface).
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 solution provides multilayer films with improved sealing initiation temperature and dyne retention, maintaining printability even after long-term treatments, and extending shelf life by reducing xylene solubility and enhancing surface tension.
Implementation Method 1
processed using a catalyst system containing Ti, Mg, Cl, and an electron donor compound with Bi
Data Source
AI summary
A multilayer film is characterized by having at least a skin layer comprising a propylene -- ethylene copolymers characterized by the following features: ethylene derived units content of between 1.0 wt% and 15.0% wt%; molecular weight distribution (MWD), expressed in terms of Mw/Mn, greater than 4.0; - the content of xylene soluble fraction (XS) and the ethylene derived units content (C2) fulfill the following relation: XS< 1.0296⋅e0.435C2 where XS is the percentage by weight of the fraction soluble in xylene at 25°C and C2 is the percentage by weight of ethylene units in the said copolymers determined via NMR.