Deformable Membrane Bottom for Hot-Fill Container Stability
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Solution Overview
Problem
Conventional stretch-blow molding of thermoplastic containers induces residual stresses that cause deformation during hot-filling, leading to unsuitable containers due to bi-orientation and subsequent retraction effects, which existing solutions fail to adequately address, especially under demanding visual quality criteria.
Innovation Solution
A plastic container design featuring a rigidified body with a deformable annular membrane in the shape of a spherical cap at the bottom, incorporating ribs and a recess structure that allows for controlled deformation during hot-filling and cooling, combined with heat-setting to enhance mechanical and aesthetic properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If stretch-blow molding is used to produce containers, then structural rigidity is improved through bi-orientation of material, but residual stresses are induced that cause deformation during hot-filling
Solution Approach 1:
The bottom of the container is segmented into distinct functional zones: a deformable membrane area that can accommodate stress-induced deformations, a flat region for structural stability, and a reinforced zone with ribs. This segmentation allows different parts of the bottom to respond differently to residual stresses, with the membrane absorbing deformations while other areas maintain shape stability.
Solution Approach 2:
Different regions of the container bottom are given different mechanical properties. The membrane region is designed to be more compliant and deformable, while the flat region and rib-reinforced areas provide rigidity and shape stability. This local differentiation of material properties allows the container to simultaneously achieve overall structural rigidity while accommodating localized stress relief through controlled deformations in specific areas.
2Manufacturing precision
If heat set treatment is applied to decrease deformation during hot-filling, then residual stresses are partially relieved, but the container still undergoes retraction during cooling that affects visual quality
Solution Approach 1:
The container bottom is pre-formed with a specific geometry including a deformable membrane with predetermined curvature radius (50-150 mm) and a flat region. This preliminary shaping creates built-in compliance that anticipates and accommodates the retraction that occurs during cooling, allowing the container to maintain visual quality despite the volume decrease of the liquid and air during cooling.
Solution Approach 2:
The membrane's curvature radius is specifically controlled within the range of 50-150 mm to optimize its deformability. This parameter control allows the membrane to sufficiently deform during cooling to accommodate retraction while maintaining adequate structural support. The geometric parameters of the bottom structure (membrane curvature, flat region extent, rib positioning) are optimized to balance deformation capacity with visual appearance requirements.
3Shape
If the body of the container is equipped with deformable panels to absorb retraction, then visual quality is improved, but structural complexity increases
Solution Approach 1:
The deformability function is extracted from the main container body and concentrated specifically in the bottom membrane region. This allows the body to remain simple and rigid while the bottom provides the necessary compliance for absorbing retraction. The complexity is localized to the bottom structure rather than being distributed throughout the entire container, simplifying manufacturing and design.
4Strength
If ribs are added to the bottom structure to enhance deformation control, then mechanical strength is improved, but manufacturing complexity increases
Solution Approach 1:
The membrane is given a spherical cap geometry with a controlled curvature radius (50-150 mm). This curved geometry inherently provides structural strength while allowing uniform deformation distribution during hot-filling and cooling. The curvature naturally reinforces the membrane without requiring additional complex rib structures, simplifying manufacturing while maintaining mechanical strength.
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 container design localizes deformations on the bottom, preserving the body's shape during hot-filling and cooling, while heat-setting increases material crystallinity, resulting in improved mechanical strength and visual appeal by minimizing uncontrolled deformations and retraction effects.
Implementation Method 1
a deformable annular membrane in the shape of a spherical cap extending substantially perpendicular to the body between the step and the recess
Implementation Method 2
it is known to complete the stretch-blow molding through a thermal treatment called heat set, by which the just-formed container is held in contact with the wall of the heated mold at a temperature between 120° C. and 250° C. for a predetermined time
Implementation Method 3
through a thermal treatment called heat set, by which the just-formed container is held in contact with the wall of the heated mold
Implementation Method 4
while cooling, the liquid and the air above the liquid in the capped container undergo a decrease in volume that tends to make the container retract
Data Source
AI summary
Plastic container (1), characterized in that it comprises:a rigidified body (5),a bottom (8) extending to a lower end of the container (1) and comprising:an annular base (9) extending substantially perpendicular to the body (5) in the prolongation thereof;an annular step (10) extending from the base (9) towards the interior of the container (1),a recess (12) at the center of the bottom (8) projecting towards the interior of the container (1),a deformable annular membrane (11) in the shape of a spherical cap extending substantially perpendicular to the body (5) between the step (10) and the recess (12).