Propylene Block Copolymer Flow Mark Reduction
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Solution Overview
Problem
Existing polypropylene-based resin compositions face challenges in reducing flow-mark molding defects, such as tiger stripes, which impair the appearance of molded articles, especially in automotive components, while maintaining desired properties and flowability.
Innovation Solution
A propylene-based block copolymer comprising 80-60% crystalline propylene polymer and 20-40% propylene/ethylene random copolymer, with specific intrinsic viscosity ratios and ethylene content, is incorporated in a small amount to improve moldability and appearance by enhancing the viscosity ratio and reducing shear stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a propylene/ethylene block copolymer with high-MFR propylene homopolymer portion and high-viscosity random copolymer portion is incorporated to improve flow marks, then appearance is improved, but the resin composition changes undesirably when incorporated in large amounts
Solution Approach 1:
The patent changes the molecular weight parameters of the block copolymer components. Specifically, it uses a propylene homopolymer portion with intrinsic viscosity of 0.70 dL/g or less (lower than conventional high-MFR materials) and a propylene/ethylene random copolymer portion with intrinsic viscosity of 3.0 dL/g or less. This parameter change allows the block copolymer to improve flow marks while maintaining resin composition flexibility at lower incorporation amounts.
Solution Approach 2:
The patent creates a composite block copolymer structure combining propylene homopolymer and propylene/ethylene random copolymer in specific proportions (60-90 wt% homopolymer, 10-40 wt% random copolymer). This composite structure provides both the low viscosity needed for flow improvement and the compatibility needed to maintain resin composition flexibility, resolving the contradiction between appearance improvement and composition adaptability.
2Manufacturing precision
If propylene/ethylene block copolymer is incorporated in large amount to improve flow mark appearance, then flow marks are reduced, but other desired properties of the resin composition are adversely affected
Solution Approach 1:
The patent changes the intrinsic viscosity parameters to lower values (homopolymer: 0.70 dL/g or less, random copolymer: 3.0 dL/g or less) compared to conventional block copolymers. This parameter change enables effective flow mark improvement at lower incorporation amounts (5-50 wt%), thereby maintaining resin property stability and avoiding adverse effects on other desired properties.
3Productivity
If molded articles with down gauging are produced in shorter molding time, then productivity is improved, but flow mark defects occur more frequently
Solution Approach 1:
The patent uses a block copolymer with reduced intrinsic viscosity parameters (homopolymer: 0.70 dL/g or less) that provides superior flow characteristics. This allows the resin to fill thin-walled molds effectively even at high injection speeds required for short molding cycles, thereby maintaining appearance quality while achieving improved productivity through faster cycling.
Data Source
AI summary
An object of the present invention is to prevent an occurrence of flow-mark molding defects to improve an appearance of molded articles, and as a means for achieving the object, a propylene-based block copolymer is used as an appearance improver, the copolymer comprising 80 to 60% by weight of crystalline propylene polymer portion which has an intrinsic viscosity [η]p of 0.90 dL/g or less and 20 to 40% by weight of propylene/ethylene random copolymer portion which has an ethylene content of 35 to 50% by weight and an intrinsic viscosity [η]c of 7.0 dL/g or higher ([η]c/[η]p being 7.5 to 30), in which the propylene-based block copolymer has a MFR of 10 to 50 g/10 min.