Polyolefin Composition Reduces Sink Marks in Injection Molding
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Solution Overview
Problem
Injection molded articles often exhibit sink marks, which are undesirable due to their aesthetic and hygiene implications, and existing solutions for improving scratch resistance do not address the formation of sink marks during the molding process.
Innovation Solution
A polymer composition comprising at least 50 wt% polypropylene and up to 40 wt% polyethylene, with specific melt flow rates and density ranges, is used to reduce or eliminate sink marks in injection molded articles, offering improved surface quality and replacing ABS in various applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If polypropylene is used for injection molding, then good strength-toughness combination and ease of fabrication are achieved, but sink marks are formed in thicker sections and regions above ribs or bosses
Solution Approach 1:
The patent uses a composite material system consisting of polypropylene homopolymer or copolymer combined with polyethylene homopolymer or copolymer. This composite approach allows the material to exhibit both the strength-toughness properties of polypropylene and the sink mark resistance provided by polyethylene, resolving the contradiction between structural performance and surface quality.
Solution Approach 2:
The patent modifies the material parameters by controlling the ratio of polypropylene to polyethylene components and adjusting their molecular weight distributions. By optimizing these parameters, the material achieves both good mechanical properties and reduced sink mark formation during injection molding.
2Manufacturing precision
If sink marks are present in injection molded articles, then aesthetic appearance and hygiene are compromised, but the material composition remains simple
Solution Approach 1:
The patent employs a two-component composite material system (polypropylene and polyethylene) that is relatively simple in structure but effective in function. This composite approach improves surface quality and eliminates sink marks without requiring complex multi-layer structures or intricate material formulations.
3Strength
If polyethylene is added to polypropylene to improve scratch resistance, then scratch resistance is improved, but this does not address sink mark formation during molding
Solution Approach 1:
The patent applies polyethylene to the polypropylene base material to achieve multiple functions simultaneously: it improves scratch resistance during service and prevents sink mark formation during molding. This multi-functional approach eliminates the need for separate solutions for different problems.
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 composition effectively minimizes sink marks in injection molded articles, enhancing their appearance and hygiene, while also providing advantages over ABS in terms of cost, energy consumption, and recyclability.
Implementation Method 1
During the cooling down, often sink marks are formed that can only be observed after that the article is released from the mould cavity
Implementation Method 2
During the cooling down, often sink marks are formed
Data Source
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AI summary
The invention relates to the use of a polymer composition to reduce sink marks in an injection moulded article, the polymer composition comprising: A1) at least one polypropylene polymer and A2) at least one polyethylene polymer.