Graphite Sheet Thermal Diffusivity Ratio via Polymer Graphitization
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Solution Overview
Problem
Conventional graphite sheets exhibit high thermal diffusivity in the horizontal direction but low thermal diffusivity in the vertical direction, and are expensive, while also lacking flexibility and being prone to manufacturing limitations in producing thick films.
Innovation Solution
A graphite sheet is manufactured by coating a base of natural or synthetic fibers with a polymer, carbonized polymer, or graphite and thermally treating it, achieving a high ratio of thermal diffusivities in both horizontal and vertical directions, along with improved flexibility, using a relatively inexpensive fiber base instead of expensive polyimide films.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the graphite expansion method is used to prepare film-shaped graphite, then the thermal conductivity is improved, but the mechanical strength deteriorates and residual acids cause adverse impacts
Solution Approach 1:
The patent changes the processing parameters by using polymer graphitization instead of graphite expansion, treating polymer films at high temperatures (2000-3000°C) to convert them directly into graphite. This parameter change eliminates the need for acid treatment while achieving high thermal conductivity and good mechanical strength simultaneously.
Solution Approach 2:
The patent uses inexpensive polymer films (such as polyimide, polyacrylonitrile, or cellulose-based films) as starting materials that are temporarily present during processing and then completely transformed into graphite. These polymer substrates are disposable in the sense that they are consumed during the graphitization process to form the final graphite product, eliminating the need for expensive equipment and acid handling infrastructure.
2Temperature
If conventional graphite sheets are used, then high thermal diffusivity in horizontal direction is achieved, but thermal diffusivity in vertical direction remains low and cost increases
Solution Approach 1:
The patent changes the manufacturing approach from graphite expansion to polymer graphitization, which fundamentally alters the thermal properties of the resulting graphite. The polymer graphitization process produces graphite with isotropic or enhanced anisotropic thermal diffusivity depending on the polymer orientation, achieving high thermal diffusivity in both horizontal and vertical directions while using cheaper polymer substrates instead of expensive conventional graphite processing.
Solution Approach 2:
The patent creates composite structures by incorporating additives such as carbon nanotubes, graphite flakes, or metal particles into the polymer film before graphitization. This composite approach enhances the thermal conductivity in both horizontal and vertical directions, and the resulting composite graphite sheet maintains cost-effectiveness by using affordable polymer matrices combined with high-performance additives.
3Ease of manufacture
If polymer graphitization method is used, then simplicity and absence of impurities are improved, but production of thick film graphite becomes difficult
Solution Approach 1:
The patent divides the thick film production into multiple thin layers. Instead of attempting to graphitize a single thick polymer film, the method applies multiple thin polymer coatings (each easily graphitizable) onto a substrate or stack, then performs graphitization on the layered structure. This segmentation allows each layer to be processed independently while achieving overall thick film graphite production.
Solution Approach 2:
The patent transitions from producing thick films in the vertical dimension to building thickness through multiple horizontal layers. By stacking multiple thin polymer films and graphitizing them together, the method achieves thick graphite products by extending in the horizontal dimension (number of layers) rather than attempting to process a single thick vertical film, thereby maintaining process simplicity while increasing overall thickness.
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 resulting graphite sheet demonstrates high thermal diffusivity in the horizontal direction, low thermal diffusivity in the vertical direction, and excellent flexibility, while being cost-effective due to the use of inexpensive fiber bases, effectively addressing the limitations of existing methods.
Implementation Method 1
first coating one side or both sides of the base with a coating solution comprising at least one selected from the group consisting of a polymer, a carbonized polymer, and graphite
Implementation Method 2
graphitizing the coated base by thermally treating it
Implementation Method 3
graphitization by directly thermally treating a specific polymer film
Data Source
AI summary
A graphite sheet having a ratio of thermal diffusivity in horizontal and vertical directions of 300 or more is disclosed. Also, a graphite sheet having a ratio of thermal diffusivity in a vertical direction of 2.0 mm2/s or less is disclosed. The graphite sheet has excellent thermal conductivity in horizontal and vertical directions and excellent flexibility at the same time and can be produced at low manufacturing cost, thereby holding an economic advantage.