Continuous Thermoforming of Polymeric Foam Sheets
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Solution Overview
Problem
Current thermoforming processes for polymeric foam articles often require a curing period due to low pressure in foamed cells, leading to cell collapse and inefficiencies in extrusion and thermoforming stages, resulting in defects and uneven heating, which complicates the production of high-quality foam articles.
Innovation Solution
A continuous manufacturing method involving the extrusion and immediate thermoforming of a blowing agent containing thermoplastic sheet, where the sheet is heated to foam and then formed into a shape within a short time frame, typically less than one hour, to achieve a lower density thermoformed article with reduced cell size and improved mechanical and insulation properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a curing period is allowed for foamed sheet before thermoforming, then cell pressure equilibrates and prevents collapse, but production time increases and efficiency decreases
Solution Approach 1:
The patent changes the pressure parameter by foaming the sheet immediately before thermoforming while the cells are still under pressure, eliminating the need for a curing period. The blowing agent is introduced during extrusion, and the sheet is thermoformed immediately while cell pressure is maintained, thus resolving the contradiction between reliability and time loss.
Solution Approach 2:
The patent applies preliminary action by introducing the blowing agent during the extrusion process itself, so that foaming occurs immediately before thermoforming. This preliminary foaming action ensures cells are formed while under pressure, eliminating the need for subsequent curing time and maintaining cell structure stability throughout the process.
2Ease of manufacture
If extrusion and thermoforming are performed as separate processes, then each process can be optimized independently, but defects may not be detected until later and rework increases
Solution Approach 1:
The patent merges the extrusion and thermoforming processes into a single continuous operation. The blowing agent is introduced during extrusion, the sheet foams immediately, and thermoforming follows without interruption. This combination allows defects to be detected and corrected in real-time, improving manufacturing precision while maintaining ease of manufacture through process integration.
3Ease of operation
If foamed sheet is reheated for thermoforming, then the material becomes formable, but the insulating nature of foam causes uneven heating and may overheat the surface
Solution Approach 1:
The patent maintains continuity of useful action by keeping the sheet in a continuous state of heating and foaming without interruption. The blowing agent is introduced during extrusion, and the sheet is immediately thermoformed while still hot, eliminating the need for separate reheating cycles that cause uneven temperature distribution and surface overheating.
4Quantity of substance
If the sheet is foamed before thermoforming, then material content is reduced with cost benefits, but the low density makes the sheet difficult to heat uniformly
Solution Approach 1:
The patent applies preliminary action by introducing the blowing agent during extrusion, so that the sheet is foamed immediately before thermoforming. This timing allows the sheet to be heated while still dense enough for uniform heat penetration, and the foaming occurs during the heating process itself, combining material reduction with efficient energy use.
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 method allows for the production of thermoformed polymeric foam articles with lower density and improved properties, such as small cell sizes and enhanced mechanical and insulation qualities, while reducing material costs and cycle times, and enabling high-throughput production without the need for a curing period.
Implementation Method 1
a blowing agent containing thermoplastic sheet
Implementation Method 2
thermoforming is a well established method for forming three dimensional articles from flat polymeric sheets
Implementation Method 3
on cooling after foaming the gas in the newly created cells contracts and the pressure in the cells is reduced to below atmospheric pressure
Implementation Method 4
atmospheric gases diffuse into the cells and equilibrate the pressure prior to thermoforming
Data Source
AI summary
Thermoformed polymeric foam articles are described herein In some embodiments, the articles are made by a manufacturing method (e.g., a continuous process) which involves the extrusion and subsequent thermoforming of a blowing agent containing thermoplastic sheet. The thermoformed polymeric foam articles may have a lower density than the precursor sheet from which they are formed. In some but not all embodiments, the precursor sheet is a multi-layer sheet which includes at least one foam layer. In such embodiments, the thermoformed articles also include multiple layers and at least one foam layer.