Plastic Closure Membrane Tear Line via Post-Molding Cut
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Solution Overview
Problem
The production of plastic closure parts with a membrane that can be easily opened and closed is hindered by the need for high injection pressures and limited material flow due to the requirement of a tear line, which also makes it difficult to tear open the membrane without excessive force, and the existing injection molding process struggles to achieve precise dimensional accuracy and sufficient wall thickness for the tear line.
Innovation Solution
Introducing a cut or punch in the membrane after the injection molding process to create a tear line with a precise and thin remaining wall thickness, allowing for easier material flow during molding and reducing the force required to open the membrane, while also simplifying the mold structure and allowing for a wider choice of plastic materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a tear line is integrated into the membrane during injection molding, then the membrane can be opened, but high injection pressures are required and material flow is limited
Solution Approach 1:
The tear line is pre-formed as a cut or punch mark in the membrane before the product reaches the customer. This preliminary action creates a stress concentration point that guides the tearing process, allowing the membrane to be opened with minimal force during use while avoiding the need for high injection pressures during manufacturing.
Solution Approach 2:
The membrane is segmented by introducing a cut or punch mark that creates a discontinuity in the material structure. This segmentation allows the membrane to be divided into separate portions during opening, reducing the force required compared to tearing a continuous membrane.
2Ease of operation
If the tear line is formed during injection molding, then the membrane can be opened, but dimensional accuracy and wall thickness precision are difficult to achieve
Solution Approach 1:
The tear line is pre-formed as a cut or punch mark with precise dimensions controlled during manufacturing. This preliminary action establishes exact starting points and geometries for the tear line, ensuring consistent dimensional accuracy and wall thickness precision that would be difficult to achieve through molding constraints alone.
Solution Approach 2:
The mechanical constraint of forming a tear line through injection molding geometry is replaced by a post-molding cut or punch operation. This substitution allows for more precise control of the tear line dimensions and wall thickness using dedicated cutting tools rather than relying on molding cavity design.
3Force
If the membrane wall thickness is reduced for easier tearing, then opening force is reduced, but the membrane strength and sealing capability are compromised
Solution Approach 1:
The membrane exhibits different wall thicknesses at different locations: a reduced wall thickness at the tear line location to facilitate easy opening, and a sufficient wall thickness in the sealing and structural regions to maintain strength and sealing capability. This local variation in quality allows the membrane to satisfy both contradictory requirements.
Solution Approach 2:
The cut or punch mark is pre-formed to create a specific geometry with reduced wall thickness only where needed for tearing. This preliminary action locally reduces the material cross-section at the tear line while preserving the full wall thickness elsewhere in the membrane, enabling easy opening without compromising overall membrane strength.
4Ease of operation
If a complex mold structure is used to form the tear line during molding, then the membrane can be opened, but manufacturing complexity and cost increase
Solution Approach 1:
The complex mechanical system of a specialized injection molding die with precise flow channels and constriction features is replaced by a simple cut or punch operation. This substitution uses a straightforward cutting tool or punching die instead of a complex molding cavity design, significantly reducing mold structure complexity and manufacturing cost.
Solution Approach 2:
The tear line is created as a separate preliminary operation (cutting or punching) after the basic membrane is formed, rather than attempting to form it during injection molding. This separates the simple membrane formation process from the tear line creation process, allowing each to be optimized independently and avoiding the need for a complex integrated mold system.
Data Source
AI summary
The invention concerns a plastic closure part (10) which can be fixed to a container or a further closure part to be fixed to the container, comprising a tubular discharge portion (3) whose cross-section is closed by a membrane (7) which has a tear line (8) extending peripherally over more than 180° along its outer edge and a corresponding method for the production of such a closure. In order to develop a closure part having the features set forth in the opening part of this specification and a method for the production thereof to the effect that the problems occurring upon injection moulding due to narrow flow passages are eliminated it is provided according to the invention that the tear line (8) is formed by a cut introduced into the material of the membrane (7) with a cutting or punching tool.