Clay-like thermally conductive composition

Abstract

The present invention relates to a liquid polyol composition characterized by comprising a liquid polyol and an inorganic filler, the amount of the inorganic filler being in the range of 1000-3300 parts by mass per 100 parts by mass of the liquid polyol, the viscosity index being 10 g.s or more, and the viscosity index being 10 g.s or more. Wherein the viscosity index is defined by an integrated value of a region in which the probe is loaded with a tensile load when the probe is pulled in a viscosity testing machine.

Description

Technical Field

[0001] The present invention relates to a clay-like heat conductive composition, which is disposed, for example, between a heating element and a heat dissipation member, and efficiently transfers heat generated from the heating element to the heat dissipation member.

[0002] This application claims priority based on Japanese Patent Application No. 2023-001565 filed on January 10, 2023 and Japanese Patent Application No. 2023-205643 filed on December 5, 2023, and incorporates their contents herein. Background Art

[0003] In recent years, with the development of high performance / integration of various electronic devices, a structure with improved heat dissipation performance is required so that heat generated during the operation of components (heating elements) can be efficiently dissipated to the outside using a heat dissipation member.

[0004] Therefore, in order to reduce the thermal resistance between the heating element and the heat dissipation member, a heat conductive sheet is sometimes disposed between the heating element and the heat dissipation member.

[0005] For example, Patent Document 1 proposes a polyurethane resin composition for improving heat dissipation by mixing inorganic substances such as ceramic powder, metal powder, and carbonaceous materials in polyurethane as a base material, and a heat conductive sheet composed of the polyurethane resin composition.

[0006] Also, Patent Document 2 proposes a fluorine-containing elastomer composition for a heat dissipation material for improving heat dissipation by adding an insulating heat conductive filler such as alumina to a fluorine-containing elastomer as a base material, and a heat conductive sheet composed of the fluorine-containing elastomer composition for a heat dissipation material.

[0007] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2010-248350 (A)

[0008] Patent Document 2: Japanese Patent No. 6493616 (B)

[0009] However, in the polyurethane resin composition and the heat conductive sheet described in Patent Document 1, polyurethane is synthesized by a urethane curing reaction in which polyol and isocyanate are crosslinked via a urethane bond. Here, the isocyanate used in the urethane curing reaction has a potential toxicity hazard and is difficult to handle. Also, the sheet produced by the curing reaction lacks shape followability and cannot ensure close contact with the heating element and the heat dissipation member. When either the heating element or the heat dissipation member has irregularities, etc., it may not be possible to sufficiently reduce the thermal resistance between the heating element and the heat dissipation member.

[0010] In addition, in the fluorine-containing elastomer composition for a heat dissipation material and the heat conductive sheet described in Patent Document 2, since no curing reaction occurs, it is soft and has excellent shape followability compared to the heat conductive sheet of Patent Document 1. However, fluorine-containing elastomers are relatively expensive, which may lead to an increase in production costs. Moreover, the wettability of fluorine-containing elastomers with inorganic substances is poor, and there is a possibility that pores may be generated inside the heat conductive sheet, resulting in a decrease in thermal conductivity. SUMMARY OF THE INVENTION

[0011] The present invention has been completed in view of the above circumstances, and an object thereof is to provide a clay-like heat conductive composition that is in a clay-like state, has particularly excellent shape followability, and has particularly excellent thermal conductivity due to sufficient inclusion of inorganic fillers.

[0012] As a result of intensive studies to solve the above problems, the present inventors have obtained the following insights: Since liquid polyols have hydrophilic hydroxyl groups, they have good wettability with inorganic fillers. Even when a large amount of inorganic fillers are contained, they become clay-like and can ensure shape followability. In addition, the following insight has been obtained: By evaluating the viscosity index using a viscosity tester, shape followability can be ensured.

[0013] The clay-like heat conductive composition according to Aspect 1 of the present invention is characterized by containing a liquid polyol and an inorganic filler, wherein the amount of the inorganic filler is in the range of 1000 parts by mass or more and 3300 parts by mass or less relative to 100 parts by mass of the liquid polyol, and the viscosity index of the clay-like heat conductive composition is 10 g·s or more, where the viscosity index is defined by the integral value of the region where the probe is loaded with a tensile load when the probe is pulled up in a viscosity tester.

[0014] In the clay-like heat conductive composition according to Aspect 1 of the present invention, since it contains a liquid polyol and an inorganic filler, and the amount of the inorganic filler is in the range of 1000 parts by mass or more and 3300 parts by mass or less relative to 100 parts by mass of the liquid polyol, the inorganic filler is highly filled, and the thermal conductivity is particularly excellent.

[0015] In addition, since the viscosity index defined by the integral value of the region where the probe is loaded with a tensile load when the probe is pulled up in a viscosity tester is 10 g·s or more, the shape followability is excellent, the close contact with the heating element and the heat dissipation component can be ensured, and the thermal resistance between the heating element and the heat dissipation component can be sufficiently reduced.

[0016] The clay-like heat conductive composition according to Aspect 2 of the present invention is characterized in that, in the clay-like heat conductive composition according to Aspect 1 of the present invention, the liquid polyol is one or more selected from polybutadiene polyol, polyester polyol, polyisoprene polyol, and polyolefin polyol.

[0017] The clay-like heat conductive composition according to aspect 2 of the present invention has excellent wettability with inorganic fillers because the liquid polyol is one or more selected from polybutadiene polyol, polyester polyol, polyisoprene polyol, and polyolefin polyol, and can reliably contain a large amount of inorganic fillers, and is particularly excellent in heat conductivity.

[0018] The clay-like heat conductive composition according to aspect 3 of the present invention is characterized in that, in the clay-like heat conductive composition according to aspect 1 or aspect 2 of the present invention, the inorganic filler is one or more selected from alumina, aluminum nitride, boron nitride, silicon nitride, silicon carbide, magnesium oxide, and zinc oxide.

[0019] According to the clay-like heat conductive composition of aspect 3 of the present invention, since the inorganic filler is one or more selected from alumina, aluminum nitride, boron nitride, silicon nitride, silicon carbide, magnesium oxide, and zinc oxide, the heat conductivity and insulation are excellent, and it is particularly suitable for applications requiring insulation.

[0020] The clay-like heat conductive composition according to aspect 4 of the present invention is characterized in that, in the clay-like heat conductive composition according to any one of aspects 1 to 3 of the present invention, the average particle diameter of the inorganic filler is in the range of 0.1 μm or more and 200 μm or less.

[0021] According to the clay-like heat conductive composition of aspect 4 of the present invention, since the average particle diameter of the inorganic filler is in the range of 0.1 μm or more and 200 μm or less, the inorganic filler can be dispersed relatively uniformly, and when highly filled, hardening of the composition can also be suppressed.

[0022] According to the present invention, it is possible to provide a clay-like heat conductive composition that is in a clay-like state, has particularly excellent shape followability, and is particularly excellent in heat conductivity due to sufficient inclusion of inorganic fillers. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic explanatory diagram showing an evaluation method of the viscosity index of the clay-like heat conductive composition as an embodiment of the present invention.

[0024] Figure 2A It is a schematic explanatory diagram showing an evaluation method of the adhesiveness of the clay-like heat conductive composition as an embodiment of the present invention.

[0025] Figure 2B It is a schematic explanatory diagram showing an evaluation method of the adhesiveness of the clay-like heat conductive composition as an embodiment of the present invention. Arrows in the vertical direction on the paper surface indicate the vertical stretching when the test piece is stretched up and down with a tensile testing machine to measure the adhesive strength and elongation. DETAILED DESCRIPTION OF THE INVENTION

[0026] Hereinafter, a clay-like thermal conductivity composition as an embodiment of the present invention will be described with reference to the accompanying drawings. In addition, each of the embodiments shown below is specifically described for better understanding the gist of the invention, and the present invention is not limited thereto unless otherwise specified.

[0027] The clay-like thermal conductivity composition as an embodiment of the present invention is, for example, a composition disposed between a heating element and a heat dissipation member and transferring heat generated from the heating element to the heat dissipation member.

[0028] The clay-like thermal conductivity composition of the present embodiment is a composition containing a liquid polyol and an inorganic filler, and the amount of the inorganic filler is in the range of 1000 parts by mass or more and 3300 parts by mass or less relative to 100 parts by mass of the liquid polyol.

[0029] Moreover, for the clay-like thermal conductivity composition of the present embodiment, the viscosity index defined by the integral value of the region where the probe is loaded with a tensile load when the probe is pulled up in a viscosity tester is 10 g·s or more.

[0030] Here, when the amount of the inorganic filler is less than 1000 parts by mass relative to 100 parts by mass of the liquid polyol, since the inorganic filler is not sufficiently contained, it may not be possible to ensure the thermal conductivity.

[0031] On the other hand, when the amount of the inorganic filler is more than 3300 parts by mass relative to 100 parts by mass of the liquid polyol, the clay-like thermal conductivity composition becomes hard, and the shape followability may be insufficient.

[0032] In addition, the lower limit of the amount of the inorganic filler is preferably 1200 parts by mass or more, more preferably 1500 parts by mass or more relative to 100 parts by mass of the liquid polyol. On the other hand, the upper limit of the amount of the inorganic filler is preferably 3000 parts by mass or less, more preferably 2800 parts by mass or less relative to 100 parts by mass of the liquid polyol.

[0033] And, the mass ratio of the filler in the clay-like thermal conductivity composition is, for example, 90% by mass or more and 97% by mass or less. The thermal conductivity of the clay-like thermal conductivity composition can be about 3.5 to 10 W / (m·K).

[0034] Next, with reference to Figure 1 , a method for evaluating the viscosity index of the clay-like thermal conductivity composition of the present embodiment will be described.

[0035] The viscosity tester for evaluating the viscosity index includes: a stage on which the clay-like thermal conductivity composition (PASTE) is placed; a probe (PROBE) that moves up and down relative to the stage; and a load measuring mechanism that measures the load applied to the probe.

[0036] First, by lowering the probe, the probe is brought close to / into contact with the clay-like thermally conductive composition placed on the stage.

[0037] Further, the probe is continuously lowered and pressed into the clay-like thermally conductive composition to extrude it. It is maintained in this state for a certain period of time. At this time, as Figure 1 shown, the probe is loaded with a compressive load.

[0038] Next, the probe is raised and pulled up. Thus, as Figure 1 shown, the clay-like thermally conductive composition is pulled up while adhering to the probe. As a result, the probe is loaded with a tensile load.

[0039] Then, if the probe is further raised, the clay-like thermally conductive composition separates from the probe and the probe is no longer loaded with a load.

[0040] Here, as Figure 1 shown, the integral value of the region where the probe is loaded with a tensile load when pulling up the probe is defined as the "viscosity index". If this viscosity index is high, the clay-like thermally conductive composition easily adheres to the probe and has excellent shape followability.

[0041] In the clay-like thermally conductive composition of the present embodiment, since the above-mentioned viscosity index is 10 g·s or more, the shape followability is very excellent.

[0042] In addition, the viscosity index of the clay-like thermally conductive composition is preferably 30 g·s or more, more preferably 50 g·s or more. On the other hand, there is no particular limitation on the upper limit of the viscosity index of the clay-like thermally conductive composition, but in order to suppress the sense of stickiness and make the handling easy, it is preferably 1000 g·s or less, more preferably 500 g·s or less.

[0043] Liquid polyol is a polyol that is liquid at normal temperature (25 °C) and has hydrophilic hydroxyl groups (-OH). Therefore, it has excellent affinity with inorganic fillers and can highly fill inorganic fillers compared with other liquid polymers. Therefore, the thermal conductivity can be greatly improved. And it can suppress the generation of pores around the inorganic fillers.

[0044] Here, in the present embodiment, as the liquid polyol, it is preferable to use one or more selected from polybutadiene polyol, polyester polyol, polyisoprene polyol, and polyolefin polyol.

[0045] The inorganic filler is composed of inorganic substances such as ceramics and metals and is made of a material with better thermal conductivity than the liquid polyol.

[0046] In addition, when insulation is required for the clay-like thermally conductive composition of the present embodiment, as the inorganic filler, it is preferable to use one or more selected from alumina, aluminum nitride, boron nitride, silicon nitride, silicon carbide, magnesium oxide, and zinc oxide.

[0047] On the other hand, when insulation is not required for the clay-like thermal conductive composition of the present embodiment, metal powder with excellent thermal conductivity is preferably used.

[0048] Moreover, the average particle diameter of the inorganic filler is preferably in the range of 0.1 μm or more and 200 μm or less.

[0049] By setting the average particle diameter of the inorganic filler to 0.1 μm or more, even when a large amount of the inorganic filler is contained, hardening of the clay-like thermal conductive composition can be suppressed, and the inorganic filler can be reliably and highly filled, improving the thermal conductivity.

[0050] On the other hand, by setting the average particle diameter of the inorganic filler to 200 μm or less, the inorganic filler can be further uniformly dispersed.

[0051] In addition, the lower limit of the average particle diameter of the inorganic filler is more preferably 0.5 μm or more, and further preferably 1 μm or more. On the other hand, the upper limit of the average particle diameter of the inorganic filler is more preferably 150 μm or less, and further preferably 100 μm or less.

[0052] In addition, the liquid polyol used in the present embodiment synthesizes polyurethane by crosslinking with isocyanate through a urethane bond (urethane curing reaction). When a large amount of polyurethane is synthesized, the viscosity index is significantly reduced to less than 10 g·s. Therefore, when isocyanate is included, its amount needs to be limited to an amount that can only cause a small amount of urethane curing reaction with the liquid polyol. That is, the clay-like thermal conductive composition of the present embodiment preferably does not contain substances that cause crosslinking reactions with the liquid polyol, and when substances that cause crosslinking reactions with the liquid polyol are included, the viscosity index of the clay-like thermal conductive composition is preferably 10 g·s or more.

[0053] The clay-like thermal conductive composition of the present embodiment is manufactured by separately weighing the above liquid polyol and inorganic filler to be in a specified ratio, and mixing and kneading them. In addition, the kneading method is not particularly limited, and existing methods such as a planetary mixer, two-roll mill, and kneader can be appropriately selected and applied.

[0054] Here, in order to efficiently and highly fill the inorganic filler, the viscosity of the liquid polyol before kneading is preferably 10 Pa·s or less, and more preferably 6 Pa·s or less. In addition, the lower limit of the viscosity of the liquid polyol before kneading is not particularly limited and is substantially 0.1 Pa·s or more.

[0055] Moreover, the viscosity of the clay-like thermal conductive composition after mixing and kneading the above liquid polyol and inorganic filler is preferably 500 Pa·s or more and 100000 Pa·s or less, and more preferably 1500 Pa·s or more and 50000 Pa·s or less.

[0056] The clay-like thermal conductivity composition of the present embodiment configured as described above contains a liquid polyol having a hydroxyl group and an inorganic filler, and since the amount of the inorganic filler is 1000 parts by mass or more with respect to 100 parts by mass of the liquid polyol, the inorganic filler can be highly filled, and the thermal conductivity is particularly excellent. Further, since the amount of the inorganic filler is 3300 parts by mass or less with respect to 100 parts by mass of the liquid polyol, it does not harden and has sufficient shape followability.

[0057] Moreover, for the clay-like thermal conductivity composition of the present embodiment, since the viscosity index defined by the integral value of the region where the probe is loaded with a tensile load when the probe is pulled up in a viscosity tester is 10 g·s or more, the shape followability is extremely excellent, the close contact with the heating element and the heat dissipation member can be ensured, and the thermal resistance between the heating element and the heat dissipation member can be sufficiently reduced.

[0058] Here, in the clay-like thermal conductivity composition of the present embodiment, when the liquid polyol is one or more selected from polybutadiene polyol, polyester polyol, polyisoprene polyol, and polyolefin polyol, the wettability with the inorganic filler is extremely excellent, a large amount of the inorganic filler can be reliably contained, and the thermal conductivity is particularly excellent. Further, the generation of pores around the inorganic filler can be suppressed.

[0059] Further, in the clay-like thermal conductivity composition of the present embodiment, when the inorganic filler is one or more selected from alumina, aluminum nitride, boron nitride, silicon nitride, silicon carbide, magnesium oxide, and zinc oxide, the thermal conductivity and insulation properties are excellent, and it is particularly suitable for applications requiring insulation properties.

[0060] Furthermore, in the clay-like thermal conductivity composition of the present embodiment, when the average particle diameter of the inorganic filler is in the range of 0.1 μm or more and 200 μm or less, the inorganic filler can be dispersed relatively uniformly, and even when highly filled, the hardening of the composition can be suppressed.

[0061] The above describes an embodiment of the present invention, but the present invention is not limited thereto, and can be appropriately changed without departing from the technical idea of the present invention.

[0062] In the present embodiment, the clay-like thermal conductivity composition disposed between the heating element and the heat dissipation member has been described, but it is not limited thereto, and it can also be used in other applications.

[0063] Examples

[0064] A confirmation experiment conducted to confirm the effectiveness of the present invention will be described.

[0065] As shown in Table 1, liquid polyols and inorganic fillers were weighed separately and mixed. After kneading the mixture, it was formed into a sheet with a thickness of 2 mm and used as a test sample for evaluation.

[0066] First, a sample with a size of 20 mm square × 2 mm thickness was collected from the test sample for evaluation. Using a texture analyzer (manufactured by IMADACO., LTD.), the thickness recovery rate was measured after compressing 50% in the thickness direction and releasing the compression after 100 minutes. When the thickness recovery rate was less than 50%, it was judged as "clay-like". The thickness recovery rate was (recovered thickness - thickness during compression) / (thickness before compression - thickness during compression). For example, when a sample with a thickness of 2 mm was compressed by 50% until it reached 1 mm and then released and recovered to 1.1 mm, the thickness recovery rate was (1.1 - 1) / (2 - 1) = 10%. The evaluation results are shown in Table 1.

[0067] Next, the tackiness index was evaluated using a tackiness tester (TAC1000 manufactured by RHESCACO., LTD.). First, the sample was formed into a size of 20 mm square × 2 mm thickness. The sample was set in the tester, and a SUS probe with a diameter of 5 mm was pressed against the test sample for evaluation at a pressing speed of 2 mm / s until the load reached -3000 gf and held for 5 seconds. Then, the probe was lifted at a lifting speed of 1 mm / s to a height of 5 mm from the holding point.

[0068] At this time, the change in the load borne by the probe was graphed with the vertical axis as the load and the horizontal axis as the time, and the integral value of the region where the tensile load was applied (i.e., the region where the load was positive) was obtained as the tackiness index. The evaluation results are shown in Table 1.

[0069] As shown in Figure 2, regarding the adhesion, two aluminum bars were prepared, and after pressing each sample by sandwiching it between the two aluminum bars, the overflowing sample was removed. Thus, a test piece was made in which the sample formed (25 mm in length × 19 mm in width × 1 mm in thickness) was sandwiched by the two aluminum bars. Next, using a tensile testing machine (AGS-X: manufactured by Shimadzu Corporation), the aluminum bars of the test piece were stretched at a tensile speed of 50 mm / min, and thus the adhesive strength and elongation were measured, and based on this, the maximum stress of each test sample was calculated as the adhesion.

[0070] The sample was formed into a size of 10 mm square × 2 mm thickness, and the thermal conductivity was measured using a resin material thermal resistance measuring device (PCM series: manufactured by HITACHI TECHNOLOGIES AND SERVICES, LTD.). The measurement was carried out under the condition that the measurement load was in the range of 0.1 to 1 N in the thickness fixed mode.

[0071]

[0072] In Comparative Example 1, the amount of the inorganic filler was 900 parts by mass relative to 100 parts by mass of the liquid polyol, and the thermal conductivity was low, being 3.0 W / (m·K).

[0073] In Comparative Example 2, the amount of the inorganic filler was 3400 parts by mass relative to 100 parts by mass of the liquid polyol, the viscosity index was 4.5 g·s, the shape followability was poor, the adhesiveness was poor, being 0.01 MPa. Further, it is generally assumed that if the content of the inorganic filler increases, the thermal conductivity becomes higher. However, in Comparative Example 2, although the mass fraction of the inorganic filler is more than that in Example 5 of the present invention, the thermal conductivity becomes lower because both the shape followability and the adhesiveness are poor.

[0074] In contrast, in Examples 1 to 5 of the present invention, the amount of the inorganic filler is in the range of 1000 parts by mass or more and 3300 parts by mass or less relative to 100 parts by mass of the liquid polyol, the viscosity index is 10 g·s or more, the shape followability is excellent, the adhesiveness is excellent, being 0.03 MPa or more. Further, the thermal conductivity is 3.5 W / (m·K) or more, and the thermal conductivity is excellent.

[0075] As described above, according to the present invention, it was confirmed that a clay-like thermal conductive composition having a clay-like shape, particularly excellent shape followability, and particularly excellent thermal conductivity due to sufficient inclusion of an inorganic filler can be provided.

[0076] Industrial Applicability

[0077] A clay-like thermal conductive composition having a clay-like shape, particularly excellent shape followability, and particularly excellent thermal conductivity due to sufficient inclusion of an inorganic filler can be provided.

[0078] Symbol Explanation

[0079] 1 - Aluminum rod; 2 - Sample (25×19×1 mmt).

Claims

1. A clay-like thermally conductive composition, characterized in that: A liquid polyol and an inorganic filler, wherein the amount of the inorganic filler is within a range of 1000 parts by mass or more and 3300 parts by mass or less relative to 100 parts by mass of the liquid polyol. The clay-like thermally conductive composition has a viscosity index of 10 g·s or more, wherein the viscosity index is defined by an integral value of an area where a tensile load is applied to a probe when the probe is pulled up in a viscosity tester.

2. The clay-like thermally conductive composition according to claim 1, characterized in that The liquid polyol is one or more selected from polybutadiene polyol, polyester polyol, polyisoprene polyol and polyolefin polyol.

3. The clay-like thermally conductive composition according to claim 1 or 2, characterized in that: The inorganic filler is one or more selected from the group consisting of aluminum oxide, aluminum nitride, boron nitride, silicon nitride, silicon carbide, magnesium oxide and zinc oxide.

4. The clay-like thermally conductive composition according to claim 1 or 2, characterized in that: The average particle size of the inorganic filler is in the range of 0.1 μm or more and 200 μm or less.

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