JP-2026075773-A - Thermal conductive sheet

Abstract

[Problem] To provide a thermal conductive sheet with high thermal conductivity. [Solution] The heat-conducting sheet of the present invention is made up of a plurality of flaky graphite particles oriented in an orientation. Furthermore, since the flake-shaped graphite particles are a laminate of graphene, and fibrous material is included between the flake-shaped graphite particles, with an average fiber length of 0.3 to 40 μm, and the weight ratio of the flake-shaped graphite particles to the fibrous material (flake-shaped graphite particles: fibrous material) is 100:1 to 100:10, the inter-particle distance in the in-plane direction of the flake-shaped graphite particles is reduced, making it possible to provide a thermal conductive sheet with high thermal conductivity. [Selection Diagram] Figure 2

Inventors

• 斎木 琢夫
• 白鳥 一幸

Assignees

• 日産自動車株式会社

Dates

Publication Date

20260511

Application Date

20241023

Claims (5)

1. A thermal conductive sheet comprising multiple flaky graphite particles oriented in a particular manner, The above-mentioned flake-like graphite particles are a layer of graphene, The above-mentioned flake-like graphite particles contain fibrous material between them, The average fiber length of the above fibrous material is 0.3 to 40 μm. A thermal conductive sheet characterized in that the weight ratio of the above-mentioned flake-like graphite particles to the above-mentioned fibrous material (flak-like graphite particles:fiber material) is 100:1 to 100:10.
2. The thermal conductive sheet according to claim 1, characterized in that the above-mentioned fibrous material is hydrophilic.
3. The average fiber length of the above-mentioned fibrous material is 20 to 30 μm. The thermal conductive sheet according to claim 1, characterized in that the weight ratio of the above-mentioned flake-like graphite particles to the above-mentioned fibrous material (flak-like graphite particles: fibrous material) is 100:2 to 100:5.
4. The thermal conductive sheet according to claim 1, characterized in that the above-mentioned fibrous material is cellulose and/or a cellulose derivative insoluble in water.
5. The graphite sheet according to claim 1, characterized in that its thermal conductivity at 25°C is 315 to 370 (W/mk).

Description

This invention relates to a thermal conductive sheet, and more particularly to thermal conductivity using graphite. Graphite sheets formed by stacking multiple layers of graphene have high thermal conductivity in the in-plane direction and are used as heat dissipation materials for automotive control electronic components and general-purpose electronic devices. Patent Document 1 discloses that a heat dissipation sheet, manufactured by adding fibers to a heat-conducting powder using a wet papermaking process, exhibits improved bending strength. Japanese Patent Publication No. 2010-34422 This figure shows the state after pressing a cake layer formed by depositing flake-shaped graphite particles.This is a schematic diagram showing the structure of the heat conductive sheet of the present invention.This diagram illustrates how fibrous material attracts flake-like graphite particles in the in-plane direction.This image shows the shrinkage state of the cake layer after it has been formed.This is a cross-sectional view of a thermal conductive sheet. The heat-conducting sheet of the present invention will be described in detail. The thermal conductive sheet of the present invention is composed of a plurality of oriented flake-shaped graphite particles, the flake-shaped graphite particles being a laminate of graphene, and having high thermal conductivity in the in-plane direction. Generally, thermal conductive sheets, in which multiple flaky graphite particles are oriented and deposited, are manufactured by filtering a slurry containing flaky graphite particles to orient them, forming a film, drying and firing it, and then pressing it. With this manufacturing method, as shown in Figure 1, while the flake-shaped graphite particles can be tightly packed together in the out-of-plane direction of the sheet by pressing, it is difficult to tightly pack the flake-shaped graphite particles together in the in-plane direction. This makes it easy for gaps to form between adjacent flake-shaped graphite particles in the in-plane direction, leading to a decrease in thermal conductivity. As shown in Figure 2, the thermal conductive sheet of the present invention contains fibrous material with an average fiber length of 0.3 to 40 μm between the flaky graphite particles. Therefore, the inter-particle distance in the in-plane direction of the flaky graphite particles is small, resulting in high thermal conductivity. In other words, the thermal conductive sheet of the present invention is formed by vacuum filtration of a slurry of flake-shaped graphite particles containing hydrophilic fibrous material. At this time, as shown in Figure 3, the flake-shaped graphite particles have OH groups or COOH groups in the defects on their end faces. Hydrophilic fibrous material is attracted to or bonded to these OH groups or COOH groups, causing the hydrophilic fibrous material to penetrate between the end faces of the flake-shaped graphite particles. As a result, the flake-shaped graphite particles in the slurry are connected by the hydrophilic fibrous material, forming clumps that spread in the in-plane direction. When this slurry is filtered and a film is formed, the amount of solvent decreases, causing the distance between fibers to shorten due to surface tension, and the flake-shaped graphite particles become closer together and oriented. Furthermore, when the oriented film of flake-shaped graphite particles dries, the hydrophilic fiber material, which was swollen by the solvent, shrinks, bringing the flake-shaped graphite particles even closer together. As a result, the flake-shaped graphite particles are closer together in the in-plane direction, improving thermal conductivity. When the average fiber length of the above-mentioned fibrous material exceeds 40 μm, the distance between flake-like graphite particles increases due to the increased length. Furthermore, the cohesive force weakens, making it difficult for the flake-like graphite particles to come close together. Additionally, particles can become trapped between the out-of-plane flake-like graphite particles, disrupting their orientation and reducing thermal conductivity. Furthermore, if the average fiber length of the above-mentioned fibrous material is less than 0.3 μm, when filtering the slurry and orienting the flake-like graphite particles to form a film, the solvent becomes difficult to remove, resulting in decreased productivity. The average fiber length of the above-mentioned fibrous material can be measured by image analysis using a scanning probe microscope. The above-mentioned flake-like graphite particles preferably have an ID/IG ratio of 0.15 or less obtained from the Raman spectrum, and more preferably 0.1 or less. The ID/IG ratio obtained from Raman spectroscopy is an indicator for evaluating the crystallinity of graphite. ID represents the intensity of the D-band originating from defects, while IG represents the intensity of the G-band inherent to graphite. A smaller