Cup-type container and method of forming the same
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Solution Overview
Problem
Cup-type containers formed by compression molding with a ratio of container height to mouth diameter greater than 1.0 face challenges in achieving uniform molecular orientation, leading to inadequate heat resistance and gas barrier properties, especially in the bottom portion, due to anisotropic molecular orientation and issues with the formation of β-crystals and intermediate gas-barrier layers.
Innovation Solution
A cup-type container with a multi-layer structure comprising polypropylene and a gas-barrier resin, where the intermediate layer is positioned on the outer side and extends from the bottom to the flange portion, and the compression forming process is optimized to ensure uniform molecular orientation by controlling the rate of compression and resin flow, preventing exposure of the intermediate layer to the surface and maintaining isotropic orientation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If compression forming is used to form cup-type containers with height-to-diameter ratio not less than 1.0, then the container can achieve uniform molecular orientation and improved heat resistance, but the resin flows poorly during forming and it becomes difficult to form thin-walled containers with uniform thickness
Solution Approach 1:
The patent applies parameter changes by controlling the compression rate during forming and adjusting the temperature distribution in the mold to optimize resin flow characteristics. By carefully managing these parameters, the process achieves uniform molecular orientation and wall thickness while maintaining formability for tall containers (L/D ≥ 1.0).
Solution Approach 2:
The patent employs preliminary action by pre-heating the resin or pre-positioning the resin in a specific configuration before compression begins. This preliminary preparation ensures that the resin maintains adequate fluidity during the compression process, enabling uniform flow and orientation even in tall container geometries where flow path is long.
2Ease of operation
If the body portion includes a portion thicker than 1.0 mm to form a stacking portion, then stacking is enabled, but no β-crystal is formed and mechanical strength is reduced
Solution Approach 1:
The patent applies local quality by creating different wall thicknesses in different regions of the container. The stacking portion has increased thickness for mechanical interlocking, while the main body maintains optimal thickness (≤1.0 mm) for β-crystal formation. This localized differentiation allows both stacking capability and high mechanical strength to coexist.
Solution Approach 2:
The patent segments the container wall into functional zones: a stacking portion with greater thickness for structural support and interlocking, and a body portion with controlled thickness for optimal crystal formation. This segmentation allows each region to fulfill its specific function without compromising the other.
3Productivity
If injection forming or pressure forming is used, then the container can be formed efficiently, but scrap resins are necessarily generated
Solution Approach 1:
The compression forming process is inherently more material-efficient than injection or pressure forming because it directly forms the container from a pre-measured resin mass without requiring sprues, gates, or runners that become scrap. The resin is placed in the mold and compressed into the final shape, eliminating the need for separate trimming and recycling operations.
4Reliability
If the intermediate gas-barrier layer is positioned closer to the inner surface, then gas barrier property is improved, but the layer becomes affected by water component and loses its property
Solution Approach 1:
The patent uses an intermediate adhesive layer as a mediator between the inner polypropylene layer and the outer gas-barrier layer. This adhesive layer provides a transition zone that protects the gas-barrier layer from direct contact with water and food contents, while still maintaining the gas barrier function. The adhesive layer acts as a buffer that prevents water penetration to the sensitive gas-barrier layer.
Solution Approach 2:
The patent employs a multi-layer composite structure consisting of polypropylene layers, adhesive layers, and gas-barrier layers in specific configurations. This composite construction allows each material to perform its optimal function: the polypropylene provides structural integrity and water resistance, the adhesive provides bonding and protection, and the gas-barrier layer provides gas barrier properties. The combination achieves both gas barrier reliability and protection from water damage.
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 solution results in a cup-type container with enhanced heat resistance, mechanical strength, and gas barrier properties, maintaining uniform molecular orientation and preventing degradation of the gas-barrier layer, even when exposed to water, while allowing for efficient stacking and mass production.
Implementation Method 1
a cup-type container obtained by compression-forming a thermoplastic resin
Implementation Method 2
feeding a molten resin mass into the lower metal mold, and compressing the molten resin mass
Implementation Method 3
attention has been given to the β-crystals in the crystal structure of the polypropylene. Namely, the β-crystals are made present in at least locally in the body portion making it possible to impart excellent heat resistance
Implementation Method 4
a thin cup-type container made from a polypropylene by injection forming or pressure forming has a high degree of anisotropy in the molecular orientation of the container
Implementation Method 5
the resin must flow through the limited space. Therefore, anisotropy occurs in the molecular orientation
Data Source
AI summary
A cup-type container obtained by compression-forming a thermoplastic resin and including at least a flange portion, a body portion and a bottom portion, wherein a ratio (L/D) of the height of the container to the diameter of the opening is not less than 1.0, and if the direction of height of a test piece cut out from the body portion of the container is denoted by x and the circumferential direction thereof by y, a half-value width P at a half peak of a Miller index at a diffraction angle 2θ=14.5° that represents the diffraction by the crystal plane (110), is in a range of 1.25 to 1.5 over the whole body portion in a peak intensity profile in the direction of height (x-direction) of a Debye's ring obtained by measuring the diffraction intensities by causing the X-rays to be incident on an x-y plane of the test piece at right angles thereto. The cup-type container is evenly oriented in the direction of height of the container and in the circumferential direction thereof, has an even strength in all directions and has excellent heat resistance. The invention, further, provides a method of forming the cup-type container.