Multilayer Heat Shrinkable Films with PVDC Barrier
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Solution Overview
Problem
Conventional methods for manufacturing multilayer heat-shrinkable films with PVDC barrier layers face challenges such as thermal incompatibility, degradation of PVDC layers, and curling issues due to the use of high-melting-point polymers like aromatic polyesters, leading to suboptimal optical properties, sealability, and processability.
Innovation Solution
Incorporating a specifically formulated adhesive (tie) layer and optimizing the relative amounts and positions of stiff resins like polyamides and polyesters, along with a new extrusion-coating process that separates the PVDC layer from high-melting aromatic polyesters using insulating layers to prevent thermal degradation, resulting in a polymer blend comprising modified ethylene-alpha-olefin and ethylene-vinyl acetate copolymers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high-melting-point polymers like aromatic polyesters are used to increase film stiffness and abuse resistance, then film rigidity and machine direction strength are improved, but PVDC barrier layer degradation occurs due to thermal incompatibility
Solution Approach 1:
An adhesive tie layer comprising a blend of modified ethylene-alpha-olefin copolymer and ethylene-vinyl acetate copolymer is introduced as an intermediary between the PVDC barrier layer and the aromatic polyester layer. This tie layer acts as a thermal buffer and bonding interface, allowing the high-melting-point polyester to provide stiffness and abuse resistance while preventing direct thermal degradation of the PVDC layer during processing.
2Reliability
If PVDC barrier layer is used to provide excellent barrier properties, then gas and moisture barrier performance are improved, but optical properties deteriorate due to wrinkling when combined with high-shrink films
Solution Approach 1:
The shrinkage parameters of the film are optimized by controlling the orientation ratios and heat treatment conditions to achieve a balance between barrier performance and optical properties. The film maintains sufficient shrinkage for tight packaging while limiting excessive wrinkling that would degrade the optical appearance of the PVDC barrier layer.
3Strength
If film thickness is increased to improve stiffness and abuse resistance, then mechanical strength is improved, but process efficiency and packaging speed decrease
Solution Approach 1:
A multilayer composite structure is employed combining PVDC barrier layer, adhesive tie layer, and stiffening layer of aromatic polyester or polyamide. This composite architecture provides high stiffness and abuse resistance at reduced thickness compared to single-layer films, enabling faster packaging speeds while maintaining mechanical strength and barrier properties.
4Reliability
If adhesive tie layer is introduced to improve interlayer adhesion, then layer bonding is improved, but device complexity and manufacturing steps increase
Solution Approach 1:
The adhesive tie layer is formulated with a specific blend of modified ethylene-alpha-olefin copolymer and ethylene-vinyl acetate copolymer that provides multiple functions simultaneously: adhesion to both PVDC and aromatic polyester layers, thermal buffering during processing, and contribution to overall film flexibility and processability. This multi-functionality reduces the need for additional specialized layers.
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 achieves excellent optical properties, reduced curling, and improved adhesion between layers, enabling the production of films with enhanced shrinkage, abuse resistance, and processability while maintaining the integrity of the PVDC layer, resulting in robust and aesthetically pleasing packaging solutions.
Implementation Method 1
a polymer blend comprising: from 50% to 85% by weight of at least a modified ethylene- alpha -olefin copolymer; from 50% to 15% by weight of at least a modified ethylene and vinyl acetate copolymer
Implementation Method 2
a new extrusion-coating process that separates the PVDC layer from high-melting aromatic polyesters using insulating layers to prevent thermal degradation
Implementation Method 3
Upon evacuating the atmosphere from the package followed by heat-sealing of the film, the resulting closed package should tightly shrink around the meat product
Data Source
Figure 1
AI summary
The present invention relates to a polymer blend and to multilayer heat shrinkable films containing at least a layer made of said polymer blend, to flexible containers made of said film, such as bags, pouches and the like, useful for packaging articles, in particular food items. The invention also relates to a process for the manufacturing of such multilayer heat shrinkable films.