Single-Material Foamed Cup Injection Molding
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The recycling of disposable cups with mixed materials is challenging due to the difficulty in separating paper and plastic components, and they often leak when tilted, as the seam in paper cups allows liquids to escape.
Innovation Solution
A method for forming articles with both translucent expanded cellular foam regions and transparent unexpanded regions using controlled pressure during injection and packing phases in injection molding, ensuring the entire container is made of a single recyclable material and eliminating seams that can cause leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a thick wall is used in conventional injection moulding to create thermal insulation, then thermal insulation is improved, but the density and weight of the cup increase
Solution Approach 1:
The patent applies foamed plastic material with cellular structure to create thermal insulation. The foam structure provides air pockets that reduce heat transfer, achieving thermal insulation without requiring a thick solid wall, thereby reducing the cup's weight and density while maintaining insulation performance.
Solution Approach 2:
The patent uses composite foamed plastic material combining polymer matrix with blowing agent cells. This composite structure provides both mechanical strength and thermal insulation properties, allowing thin-walled cups to achieve the insulation performance of thick-walled cups without the added weight.
2Temperature
If a blowing agent is added to create a foamed structure to improve thermal insulation and reduce density, then thermal insulation and weight reduction are improved, but the manufacturing process complexity increases
Solution Approach 1:
The patent employs self-expanding foamed plastic material that automatically expands during or after injection molding without requiring additional expansion equipment or processes. The blowing agent is pre-mixed with the polymer, and the foam expansion occurs naturally during cooling, simplifying the manufacturing process while achieving thermal insulation and weight reduction.
Solution Approach 2:
The patent controls foam expansion by adjusting processing parameters such as injection temperature, pressure, and cooling rate. By optimizing these parameters, the patent achieves consistent foam structure and thermal insulation performance without complicating the manufacturing process, as the expansion is controlled through standard injection molding parameter adjustment rather than additional process steps.
3Reliability
If paper cups with plastic lining are used to provide barrier properties, then liquid barrier performance is improved, but recyclability deteriorates due to difficulty in separating materials
Solution Approach 1:
The patent uses a single-material foamed plastic construction throughout the cup, eliminating the need for paper-plastic composites. This homogeneous single-material structure maintains liquid barrier performance while significantly improving recyclability, as the entire cup can be processed through standard plastic recycling streams without requiring separation of different materials.
4Shape
If paper cups with seams are used to form the cup structure, then cup formation is achieved, but liquid leakage occurs when the cup is tilted due to seams at the rim
Solution Approach 1:
The patent eliminates seams by using injection molding to create an integrated, seamless cup structure. The foamed plastic material is molded as a single continuous piece without joins or seams at the rim, preventing liquid leakage when the cup is tilted, while still achieving the desired cup shape and structure.
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 method results in articles that are easily recyclable, have high stiffness and thermal insulation, and are leak-proof, with unfoamed regions appearing transparent and providing structural and aesthetic benefits.
Implementation Method 1
the plastic composition is exposed to a pressure lower than the minimum pressure threshold, for example atmospheric pressure, to form in the article at least one first portion comprising expanded cellular foam formed from the plastic composition
Implementation Method 2
the injected plastic composition in contact with the first and second cavity-forming surfaces is cooled to form first and second solid skins respectively adjacent to and in contact with the first and second cavity-forming surfaces
Implementation Method 3
as the cellular foamed plastic composition, typically a thermoplastic polymer such as a polyolefin, typically polypropylene, cools slowly, due to its thermal insulation qualities, the crystallinity of the plastic composition can increase
Data Source
Figure 1~3
AI summary
The present invention provides a method of forming an article (100) from a molten plastic composition comprising a polymer and a blowing agent. The method provides that during an injecting step (c) and a packing step (d), the injection pressure and the packing pressure, respectively, are maintained above a minimum pressure threshold in at least one second region (32) of the cavity (8) to maintain the physical blowing agent as a gas dissolved in the polymer so that substantially no gas bubbles are formed in the at least one second region, during a mould opening step (e), at least some of the molten plastic composition is exposed to an external pressure lower than a minimum pressure threshold to form in the article at least one first portion comprising expanded cellular foam formed from the plastic composition, and prior to the opening step (e), the plastic composition in the at least one second region of the cavity has been cooled so as to be fully solidified to form in the article at least one second portion comprising a substantially homogeneous, solid phase, unexpanded plastic composition