Co-injection Molded Plastic Articles with Interlocking Core Layers
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Solution Overview
Problem
In injection molding processes, achieving adhesion between the interior core layer and skin layers of plastic articles without using adhesives is challenging, as the barrier and skin materials often do not adhere to each other effectively, necessitating the addition of adhesives to improve bonding.
Innovation Solution
The method involves creating intentional pulsations in the thickness of the interior core stream during co-injection molding to form cohesion members that physically interlock with the skin layers, and adjusting the volumetric flow ratio of the inner and outer polymeric streams to ensure structural interlocking of the interior core layer with the skin layers, thereby enhancing adhesion without the need for adhesives.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If adhesive material is added to improve bonding between interior core layer and skin layers, then adhesion is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The interior core stream is configured to self-interlock with the skin layers through controlled thickness pulsations and flow adjustments, enabling the material to bond with itself and the skin layers without requiring external adhesive materials. The cohesion members form automatically during the molding process through the natural flow and cooling of the polymeric material.
Solution Approach 2:
The thickness of the interior core stream is dynamically adjusted during the molding process by changing flow parameters and volumetric flow ratios. These parameter changes create intentional pulsations that form cohesion members with interlocking geometries, transforming the bonding mechanism from adhesive-dependent to geometry-dependent.
2Strength
If adhesive material is added to bond layers together, then adhesion is improved, but manufacturing time and process steps increase
Solution Approach 1:
The bonding function and the molding function are merged into a single simultaneous process. The cohesion members form and bond the layers together during the same time the article is being molded, eliminating the need for separate adhesive application and curing steps that would extend manufacturing cycle time.
3Strength
If cohesive force between layers is increased through structural interlocking, then delamination is prevented, but manufacturing precision requirements increase
Solution Approach 1:
The interior core stream thickness is modulated with periodic pulsations at controlled intervals during injection. These periodic variations in thickness create a series of evenly spaced cohesion members throughout the article, distributing the interlocking force uniformly and reducing the precision required at any single location compared to a continuous thick barrier layer.
Data Source
AI summary
Disclosed herein are methods and systems for the preparation of a co-injection molded multilayer plastic article. Some methods include co-extruding a combined polymeric stream having an interior core stream encased by an inner stream and an outer stream. One or more pulses in a thickness of the interior core stream create portions of an edge of the outer flow stream flowing along different streamlines. A first portion of an outer edge of the interior core stream flows beyond a second portion of the outer edge thereby forming one or more cohesion members that physically interlock the interior layer with the inner layer, with the outer layer or with both. Some embodiments reduce or eliminate a need for addition of an adhesive in the composite stream to prevent delamination of layers of the resulting multilayer plastic article. In some embodiments, cohesion members may be employed to produce a desired cosmetic effect in a resulting article.