Block Copolymer Segmentation for Heat Shrinkable Film Fisheye Reduction
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Solution Overview
Problem
Block copolymers used in heat-shrinkable films and sheets often face challenges in achieving a balance between high tensile elongation and low gel formation (fisheye generation), which affects their impact resistance and appearance.
Innovation Solution
A block copolymer composition is developed, comprising a first vinyl aromatic block, a second vinyl aromatic block, and a copolymerization block with specific molecular weight ratios and monomer content, optimized to achieve high tensile elongation and minimal gel formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the block copolymer has high tensile elongation to improve impact resistance, then gel formation (fisheye generation) increases
Solution Approach 1:
The invention segments the vinyl aromatic blocks into two distinct blocks (S1 and S2) with different weight average molecular weights. The first vinyl aromatic block (S1) has a higher weight average molecular weight than the second vinyl aromatic block (S2). This segmentation allows the higher molecular weight block to provide impact resistance while the lower molecular weight block suppresses gel formation, thereby resolving the contradiction between improving strength and reducing harmful gel formation.
2Manufacturing precision
If the weight average molecular weight of the block copolymer is increased to improve tensile elongation, then gel formation increases
Solution Approach 1:
The invention applies local quality by creating non-uniform molecular weight distribution within the block copolymer structure. Specifically, the first vinyl aromatic block (S1) has a higher weight average molecular weight to provide tensile elongation, while the second vinyl aromatic block (S2) has a lower weight average molecular weight to suppress gel formation. This local differentiation of molecular weight properties allows simultaneous achievement of high tensile elongation and low gel formation.
3Strength
If the content ratio of the copolymerization block is increased to improve impact resistance, then the appearance quality deteriorates due to fisheye generation
Solution Approach 1:
The invention segments the vinyl aromatic components into two blocks with different molecular weights to decouple the functions of impact resistance and appearance quality. The first vinyl aromatic block (S1) with higher molecular weight contributes to impact resistance, while the second vinyl aromatic block (S2) with lower molecular weight suppresses fisheye generation. This segmentation allows the copolymerization block content to be optimized for impact resistance without compromising appearance quality.
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 proposed block copolymer composition exhibits improved impact resistance, tensile elongation, and reduced fisheye formation, resulting in enhanced mechanical properties and appearance for heat-shrinkable films and sheets.
Implementation Method 1
the block copolymer has at least one peak of a loss tangent value (tan δ) in a range of −70 to −35° C. when a dynamic viscoelasticity measurement is performed under conditions of a temperature increase rate of 4° C./min, a frequency of 1 Hz, and a strain of 0.02% in accordance with ISO6721-1
Data Source
AI summary
A block copolymer having a first vinyl aromatic block, a second vinyl aromatic block, and a copolymerization block, wherein an average molecular weight of the second vinyl aromatic block is equal to or less than an average molecular weight of the first vinyl aromatic block; the copolymerization block is substantially composed exclusively of the vinyl aromatic monomer unit and a conjugated diene monomer unit; a content ratio of which is 55 mass % or more and 82 mass % or less; a ratio of the first vinyl aromatic block is 50 mass % or more and 85 mass % or less; a content ratio of the copolymerization block is 38 mass % or more and 60 mass % or less; and the block copolymer has at least one peak of a loss tangent value in a range of −70 to −35° C. when a dynamic viscoelasticity measurement is performed.