Multilayer Polyester Shrink Film with Segmented Copolyester Layers
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Solution Overview
Problem
Multilayer polyester shrink films used in packaging and shrink labels often suffer from defects such as blocking, angular distortion, and inadequate adhesion, leading to high defect and reject rates, especially during processing and printing.
Innovation Solution
A film structure comprising three layers, each made of a copolyester with specific compositions and proportions, including diacid and diol moieties, where the first and second layers are neopentyl-glycol-modified and the third layer is 1,4-cyclohexanedimethanol-modified, with high weight percentages and optimized for crystallization half-life time and orientation, reducing shrinkage stress and twist angle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If shrink films are made from CHDM-glycol-modified polyesters to achieve shrink performance similar to PVC, then shrinkage performance is improved, but blocking defects and ghosting occur during unwinding after corona discharge
Solution Approach 1:
The film is divided into three layers with different copolyester compositions. The outer layers (first and second) use NPG-modified copolyester to provide low blocking properties, while the inner layer (third) uses CHDM-modified copolyester to provide the required shrinkage performance. This segmentation allows each layer to fulfill its specific function without the harmful effects appearing in the final product.
Solution Approach 2:
Different regions of the film have different material properties tailored to their specific functions. The outer layers have low blocking characteristics suitable for unwinding, while the inner layer has high shrinkage characteristics suitable for the shrinking function. This local differentiation of material properties resolves the contradiction between shrinkage performance and blocking defects.
2Reliability
If shrink films are made from CHDM-glycol-modified polyesters to achieve shrink performance similar to PVC, then shrinkage performance is improved, but angular distortion (twist or bowing) occurs during shrinkage
Solution Approach 1:
The film structure segments the shrinkage function from the structural stability function. The third layer provides the shrinkage drive, while the first and second layers provide structural stability and resistance to angular distortion during the shrinking process, resulting in minimal twist or bowing.
3Reliability
If shrink films are made from CHDM-glycol-modified polyesters to achieve shrink performance similar to PVC, then shrinkage performance is improved, but adhesion of the adhesive bond becomes inadequate
Solution Approach 1:
The film structure segregates the adhesive bonding function from the shrinkage function. The first and second layers provide excellent adhesion for solvent-based adhesives, while the third layer provides the shrinkage function, thereby resolving the contradiction between adhesion strength and shrinkage performance.
4Reliability
If multilayer film structure is implemented with different copolyester compositions, then processing properties and defect rate are improved, but device complexity increases
Solution Approach 1:
The invention uses composite materials with different copolyester compositions in a multilayer structure. Each layer is made of a specific copolyester blend tailored to provide particular properties (adhesion, low blocking, or shrinkage). This composite approach allows the film to achieve excellent processing properties and low defect rates despite the increased structural complexity.
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 achieves a defect rate and reject rate of less than 1%, with improved shrink performance similar to PVC, reduced blocking and angular distortion, and enhanced adhesive bonding, while maintaining low shrinkage stress and twist angle.
Implementation Method 1
where the first copolyester is a semicrystalline or amorphous copolyester and has a crystallization half-life time of at least 5 minutes in the molten state
Data Source
AI summary
A film is provided that has three layers. The inventive films are made of semicrystalline or amorphous copolyesters and further include two exterior layers and an interior layer. The exterior layers include neopentyl-glycol-modified polyethylene terephthalate, while the interior layer includes 1,4-cyclohexanedimethanol-modified polyethylene terephthalate. The inventive films advantageously provide a shrink film that has a shrink performance similar to that of shrink films made of PVC.