Preform Design for Hermetic Plastic Food Containers
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Solution Overview
Problem
Existing methods for forming thin-walled plastic containers with a flange for hermetic closure are inefficient due to high scrap production, uncertainty in closure reliability, and insufficient flange strength, particularly when trying to achieve a flange thickness below 0.3 mm and a smooth, thickened rim for reliable seaming with a metal lid.
Innovation Solution
A conical preform with a convex hemispherical bottom, where the body flares into a cylindrical neck with a radially extended flange and thickened rim, optimizing material flow and orientation for a thinner flange, allowing for precise seaming and improved strength, with a flange-to-neck thickness ratio of approximately 0.8 and an angle between the flange and neck within 60° to 90°, ensuring a secure metal lid connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the flange thickness is reduced below 0.3 mm to achieve thin-walled container design, then the container wall thickness can be minimized, but the flange strength becomes insufficient for reliable metal lid seaming
Solution Approach 1:
The preform incorporates a localized thickened rim at the flange periphery while maintaining thin walls elsewhere. This local quality variation allows the flange to have sufficient thickness (at least 0.3 mm) for reliable seaming while the container body remains thin-walled, resolving the contradiction between overall thinness and local strength requirements
Solution Approach 2:
The preform is injection molded with a pre-configured thickened rim structure before the blow molding process. This preliminary formation of the reinforced flange region ensures that when the container is subsequently blow molded, the flange already has the necessary thickness and material orientation for strong metal lid connection, eliminating the need for post-processing thickening
2Ease of manufacture
If conventional blow molding is used to form the flange as part of the side wall, then the manufacturing process is simple, but the flange thickness varies along the circumference and edges may become nicked
Solution Approach 1:
The thickened rim is pre-formed during injection molding of the preform with precise dimensional control. This preliminary action ensures uniform flange thickness and smooth edges before the blow molding process, preventing the variability and nicking that occur when the flange is formed as part of the side wall in conventional processes
Solution Approach 2:
The preform design separates the flange formation into a distinct, pre-configured component with a thickened rim, rather than forming it integrally with the variable-thickness side wall. This segmentation allows the flange to be optimized independently for uniform thickness and seaming quality while maintaining simple manufacturing
3Strength
If the material flow velocity is increased to reduce temperature decline during forming, then the flange strength improves, but the injection molding process becomes more difficult to control
Solution Approach 1:
The preform incorporates a localized thickened rim at the flange periphery while maintaining thin walls elsewhere. This local quality variation allows the flange to have sufficient thickness (at least 0.3 mm) for reliable seaming while the container body remains thin-walled, resolving the contradiction between overall thinness and local strength requirements
Solution Approach 2:
The preform is injection molded with a pre-configured thickened rim structure before the blow molding process. This preliminary formation of the reinforced flange region ensures that when the container is subsequently blow molded, the flange already has the necessary thickness and material orientation for strong metal lid connection, eliminating the need for post-processing thickening
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
This design enables efficient blow molding with reduced scrap, enhanced flange strength, and precise metal lid sealing, achieving reliable closure under pressure by ensuring a gradual thickness transition and strong material orientation, facilitating better seaming quality and reduced temperature decline during the forming process.
Implementation Method 1
The inflow of the material to the neck space and then to the flange is easy. This is due to the fact that the bottom at the injection point is relatively thick, the walls are appropriately inclined and their thickness tapers in a favourable manner. The material flow velocity in the mould is relatively high during the forming process
Implementation Method 2
The material flow velocity in the mould is relatively high during the forming process with the result that the time taken by the material to reach the preform peripheries, including the flange, is short and a decline in temperature of the flowing material is much lower
Data Source
AI summary
This invention relates to the preform to produce a plastic container for packaging foodstuffs, and especially to blow mould thin-walled containers which can be hermetically closed with a metal lid by double seaming. The preform (1) includes a body (4) and a convex hemispherical bottom (6). The body (4) has a conical shape that flares towards a cylindrical neck (2) surrounded by a flange (3) that terminates in a thickened rim (5). Preferably, the angle (α) at which the internal body surface (4) flares towards the cylindrical neck is greater than the angle (β) at which the external body surface (4) opens upwards, and the thickness (g2) of the cylindrical neck (2) is less than the thickness (g3) of the bottom (6).