Heat-storable heat-conductive material

Abstract

To provide a heat-storable heat-conductive material which has such followability as to be capable of being filled into a narrow part without a gap, and has less deterioration of a heat storage amount by a change with the elapse of time.SOLUTION: A heat-storable heat-conductive material contains a heat storage material, a heat-conductive filler, and an oil gelling agent.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a heat storage type heat conductive material.

Background Art

[0002] Heat conductive materials provided between a heating element and a heat radiating member for propagating heat are known in various forms, such as grease type, gap filler type, sheet type, etc. By using these heat conductive materials, for example, heat generated by a heating element can be efficiently radiated from a heat radiating member such as a metal housing or a heat sink. By installing such a heat conductive material between a heating element and a heat radiating member, the thermal resistance between the heating element and the heat radiating member can be reduced.

[0003] In the field of automotive parts and the like, in recent years, markets such as lithium-ion batteries (LIBs) as automotive power sources for electric vehicles (EVs) have been expanding. However, in the battery cases of secondary batteries such as these lithium-ion batteries (LIBs), due to miniaturization and high output, heat generated by the secondary battery during charging and discharging tends to stay inside the housing, and there is a problem that the use limit temperature of the secondary battery is reached in a short time. In particular, in automotive parts and the like, the interior temperature of the vehicle may be exposed to a thermally severe environment where it reaches 40°C or higher. Under such high temperature conditions, there is a problem that the secondary battery immediately reaches the use limit temperature and the continuous operation time of the battery becomes short.

[0004] For this reason, the development of heat dissipation design for such secondary batteries and the like is urgently required. In particular, in lithium-ion secondary batteries, if a high temperature state exceeding the use limit temperature continues for a long time, there is a risk of battery damage. Therefore, heat countermeasures to suppress and mitigate the temperature rise of the battery are an urgent task.

[0005] In order to be used even in such thermally severe ambient environmental conditions where it is difficult to obtain a temperature difference from the ambient environment, the use of a heat storage material is effective as a heat dissipation measure for components with which it is difficult to obtain a temperature difference. In Patent Document 1, by combining a thermoplastic base polymer, a thermally conductive filler, and a heat storage material, a molded body with a predetermined hardness is ensured to enhance the adhesion to the object to be cooled, and the temperature rise of the object to be cooled under conditions where it is difficult to obtain a temperature difference from the ambient environment due to the influence of a thermally severe ambient environmental temperature (atmospheric temperature) is suppressed and mitigated effectively.

[0006] In particular, in the case where a battery, for example, a lithium ion battery or the like, is the object to be cooled, by using a heat storage material that utilizes the latent heat having a phase change temperature within the operating temperature range of the battery, the temperature rise of the battery within the operating temperature region of the battery can be mitigated. At this time, if only the heat storage material is used, the heat dissipation effect is limited because the temperature rises again when the heat storage capacity limit is exceeded. However, since the thermally conductive filler is included, a heat conduction path is ensured, so that the heat dissipation property is enhanced and the operable time can be extended (for example, refer to Patent Document 1).

[0007] For such heat storage, a technique of using the latent heat of phase transition during solidification and melting of a substance is known. Among them, paraffin compounds in particular have excellent characteristics such as high heat storage density and no corrosiveness to metals. Further, when the heat generating portion is present inside the housing that houses it, a heat transfer material having a low viscosity and fluidity may be poured into the housing for use. In the heat transfer material used in such a case, as the integration of various electronic devices progresses, a material that can be injected and filled into a narrower space without entrapping bubbles or the like and without gaps is required.

[0008] For example, Patent Document 2 discloses a latent heat storage material that is excellent in durability and has no seepage or phase separation of the latent heat storage material from the carrier material even under a heat cycle in which phase transition due to solidification and melting is repeated.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0010] However, the latent heat storage material disclosed in Patent Document 2 has a structure in which a latent heat storage material composed of n-paraffin is supported on a hydrogenated styrene-ethylene / propylene block copolymer. For this reason, there has been a problem that it has almost no fluidity and cannot be injected into a narrow gap for use. Also, regarding durability, there has been a concern that the heat storage amount decreases due to changes over time.

[0011] The present invention has been made in view of such a background, and an object thereof is to provide a heat storage thermal conductive material having fluidity that can be filled into a narrow part without gaps and having little deterioration in the heat storage amount due to changes over time.

Means for Solving the Problems

[0012] In order to solve the above problems, the heat storage thermal conductive material according to an embodiment of the present invention proposes the following means. (1) The heat storage thermal conductive material according to Aspect 1 of the present invention is a heat storage thermal conductive material characterized by including a heat storage material, a thermal conductive filler, and an oil gelling agent.

[0013] (2) Aspect 2 of the present invention is the heat storage thermal conductive material according to Aspect 1, wherein the oil gelling agent includes a fatty acid metal salt or a mixture of a fatty acid metal salt and a fatty acid.

[0014] (3) Aspect 3 of the present invention is the heat storage thermal conductive material according to Aspect 2, wherein the oil gelling agent is aluminum 2-ethylhexanoate.

[0015] (4)Aspect 4 of the present invention is characterized in that in the heat storage and heat conduction material according to any one of Aspects 1 to 3, the heat conductive filler contains ceramic particles.

[0016] (5)Aspect 5 of the present invention is characterized in that in the heat storage and heat conduction material according to any one of Aspects 1 to 4, the heat storage material contains a paraffin compound or a fatty acid.

Advantages of the Invention

[0017] According to the present invention, it is possible to provide a heat storage and heat conduction material that has fluidity enabling filling in a narrow space without gaps and has little deterioration in the heat storage amount due to changes over time.

Embodiments for Carrying Out the Invention

[0018] Hereinafter, with reference to the drawings, a heat storage and heat conduction material according to an embodiment of the present invention will be described. Note that each of the embodiments shown below is specifically described to better understand the gist of the invention, and does not limit the present invention unless otherwise specified. In addition, the drawings used in the following description may show, for the sake of convenience, an enlarged view of the main part in order to make the features of the present invention easier to understand, and the dimensional ratios of each component are not necessarily the same as the actual ones.

[0019] The heat storage and heat conduction material of the present embodiment contains a heat storage material, a heat conductive filler, and an oil gelling agent. The heat storage material is for enhancing the effect of suppressing and alleviating the temperature rise of a heat dissipation object even under conditions where it is difficult to obtain a temperature difference with the ambient environment due to the influence of a harsh ambient temperature (atmospheric temperature). As an example of such a heat storage material, a mixture of alkanes having 16 or more carbon atoms, that is, paraffin, may be used. As an example of paraffin, normal paraffin (especially a mixture of linear alkanes having about 16 to 40 carbon atoms) can be mentioned. As an example of the heat storage material, normal paraffin with a melting point of 48°C and a latent heat of fusion of 206 J / g can be mentioned. The number of carbon atoms of normal paraffin depends on the temperature range to be stored, but 16 to 40 is preferable. In this case, the melting point is about 18°C to 81°C, which is suitable for the use of the present invention.

[0020] Such paraffin is a latent heat storage material of the solid-liquid phase transition type. This solid-liquid phase transition type latent heat storage material is a phase change type heat storage material (phase change material) that, when absorbing heat from a heat dissipation object, undergoes a phase change from a solid phase to a liquid phase and stores heat by the latent heat of the phase change (melting).

[0021] Among the latent heat storage materials of the solid-liquid phase transition type, paraffin in particular has a relatively large latent heat, a large heat storage amount per unit volume, and can obtain stable heat dissipation and heat storage effects even when melting and solidification are repeated. In addition, it has favorable properties as a heat storage material in that it is less likely to corrode the heat dissipation object, is inexpensive, and can easily adjust the phase change temperature (melting point) according to the molecular weight, etc.

[0022] Note that the latent heat storage material may contain alkanes having 16 or more carbon atoms or any fatty acid. Examples of fatty acids include dodecanoic acid with a melting point of 44°C, tetradecanoic acid with a melting point of 54°C, hexadecanoic acid with a melting point of 63°C, docosanoic acid with a melting point of 82°C, and the like.

[0023] Thus, when using a phase change material such as a solid-liquid phase transition type as the heat storage material, a material corresponding to the required phase change temperature (in the case of a solid-liquid phase transition type phase change material, corresponding to the melting point), that is, a material having a phase change temperature (melting point) within the target temperature range may be selected.

[0024] Specifically, from the viewpoints of performance, durability, etc., those having a latent heat temperature range within the range of 18°C or higher and 81°C or lower are preferable. If the latent heat temperature range is less than 18°C, there is a concern that the heat storage capacity will immediately exceed the limit at high temperatures, making it difficult to effectively suppress the temperature rise of the battery. If the latent heat temperature range is greater than 81°C, the battery may become hot even at temperatures below the melting point of the heat storage material, and there is a possibility of characteristic degradation.

[0025] The heat conductive filler is for propagating the heat of the object to be cooled or the heat stored in the heat storage material toward the low temperature side. The heat conductive filler may be in the form of powder or particles that can be uniformly kneaded with the base resin. Further, when applying the heat storage and heat conductive material of the present embodiment to a heat dissipation medium such as an electrical component or a semiconductor element, it is preferable to use a material having insulating properties as the heat conductive filler. By using an insulating heat conductive filler, the heat storage and heat conductive material can also be made insulating.

[0026] The heat conductive filler may be, for example, ceramic particles having insulating properties. Specifically, metal oxides such as aluminum oxide, magnesium oxide, titanium oxide, zinc oxide, silicon oxide, beryllium oxide, copper oxide, zirconium oxide, calcium oxide, and metal nitrides such as boron nitride, aluminum nitride, and silicon nitride can be mentioned. Among these, aluminum oxide and boron nitride are preferable as the heat conductive filler. In particular, aluminum oxide is particularly preferable as a constituent component of the heat conductive filler in terms of being inexpensive and easily available. In the present embodiment, aluminum oxide (alumina) is used as the heat conductive filler. Note that the heat conductive filler in the present embodiment refers to a filler having a higher thermal conductivity than the base resin.

[0027] In addition, as the heat conductive filler, it is preferable to use particulate ones having a specific surface area of 0.5 m 2 / g or more and an average particle diameter (d50) of 40 μm or less. When the specific surface area of the heat conductive filler is less than 0.5 m 2 / g, there is a concern that the heat storage heat conductive material may fluidize and flow out from the placement location in the temperature range where the heat storage material is at or above the melting point. In addition, there is a concern that the heat conductive filler may precipitate and the heat storage heat conductive material may become non-uniform. Although there is no particular limitation on the upper limit of the specific surface area of the heat conductive filler, the specific surface area of the heat conductive filler is preferably 400 m 2 / g or less.

[0028] On the other hand, when the average particle diameter (d50) of the heat conductive filler measured by a laser diffraction / scattering type particle size distribution measuring device (MT3300EXII: manufactured by Microtrac Bell Co., Ltd.) exceeds 40 μm, there is a concern that the heat storage material may separate from the heat storage heat conductive material in the temperature range where the heat storage material is at or above the melting point. In addition, there is a concern that the heat conductive filler may precipitate and the heat storage heat conductive material may become non-uniform. Although there is no particular limitation on the lower limit of the average particle diameter of the heat conductive filler, the average particle diameter of the heat conductive filler is preferably 0.005 μm or more.

[0029] The blending ratio of the heat conductive filler is adjusted so that when the heat storage material is 90 parts by mass, the heat conductive filler accounts for 20 parts by mass or more. When the heat storage material is 90 parts by mass and the heat conductive filler is less than 20 parts by mass, there is a concern that the heat storage material may separate from the heat storage heat conductive material in the temperature range where the heat storage material is at or above the melting point. Although there is no particular limitation, it is desirable that the heat conductive filler is 3000 parts by mass or less when the heat storage material is 90 parts by mass.

[0030] The oil gelling agent is a shape-retaining component for preventing the heat storage material from melting and flowing when the heat storage heat conductive material reaches or exceeds the melting point and for retaining the shape. Specific examples of the oil gelling agent include fatty acid metal salts or a mixture of a fatty acid metal salt and a fatty acid. Examples of the fatty acid metal salt include 2-ethylhexanoate. Examples of 2-ethylhexanoate include aluminum 2-ethylhexanoate, zinc 2-ethylhexanoate, iron 2-ethylhexanoate, cobalt 2-ethylhexanoate, and manganese 2-ethylhexanoate. Among these, in the present embodiment, aluminum 2-ethylhexanoate (Al(-OH)[-OCOCH(C2H5)C4H9]2) having excellent shape retention properties was used. In addition, the fatty acid to be mixed with the fatty acid metal salt may be any monocarboxylic acid having a carboxy group in the hydrocarbon chain, and examples thereof include 2-ethylhexanoic acid.

[0031] In the present embodiment, the oil gelling agent may be added, for example, in the range of 1% by mass or more and 20% by mass or less when the heat storage material is 100 parts by mass. By adding such an oil gelling agent, when the temperature becomes equal to or higher than the melting point, the heat storage material is prevented from melting and flowing, deterioration of the heat storage and heat conductive material is suppressed, and for example, a decrease in the heat storage amount due to changes over time can be suppressed.

[0032] It is also preferable that the heat storage and heat conductive material of the present embodiment further includes a dispersant. The dispersant prevents aggregation of heat conductive fillers constituting the heat storage and heat conductive material, for example, ceramic particles, and appropriately disperses the ceramic particles in the heat storage and heat conductive material. Such a dispersant stabilizes the ceramic particles in the heat storage and heat conductive material by actions such as repulsion between particles due to charge and physical separation between particles caused by the attachment of the dispersant component to the outer peripheral surface of the ceramic particles so that the dispersed ceramic particles do not re-aggregate.

[0033] Examples of such a dispersant include sodium polycarboxylate, ammonium polycarboxylate, alkylamine salt of polycarboxylic acid, amino alcohol polyphosphate, and nonionic surfactants. In the present embodiment, a nonionic surfactant was used as the dispersant.

[0034] Nonionic surfactants are surfactants having hydrophilic groups that do not ionize when dispersed in water. Examples of nonionic surfactants include, as ester types, glycerin fatty acid esters, sorbitan fatty acid esters, sucrose fatty acid esters, etc., in which polyhydric alcohols such as glycerin, sorbitol, and sucrose (saccharose) are ester-bonded to fatty acids. Also, as ether types, polyoxyethylene alkyl phenyl ethers of the alkyl phenol type can be mentioned. Further, as ester-ether types, polyoxyethylene sorbitan fatty acid esters of the fatty acid type can be mentioned.

[0035] It is also preferable that the heat storage type heat conductive material of the present embodiment further contains an anti-settling agent. The anti-settling agent prevents the settlement of the heat conductive filler constituting the heat storage type heat conductive material and disperses it uniformly. As the anti-settling agent, for example, fumed silica can be used.

[0036] The heat storage type heat conductive material having the above configuration preferably has a viscosity before curing of 500 Pa·s or less. If the viscosity before curing exceeds 500 Pa·s, there is a concern that the fluidity of the heat storage type heat conductive material becomes too low and the heat storage type heat conductive material cannot be filled in fine gaps.

[0037] According to the heat storage type heat conductive material having the above configuration, by adding an oil gelling agent, a heat storage type heat conductive material can be obtained that has a viscosity that can be filled in narrow gaps without generating cavities and can suppress a decrease in the heat storage amount due to changes over time.

[0038] Although one embodiment of the present invention has been described above, this embodiment is presented as an example and is not intended to limit the scope of the invention. This embodiment can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. This embodiment and its modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as defined in the claims. [Example]

[0039] The effect of the heat storage thermal conductive material of the present invention was verified. The components are as follows: (Example 1 of the present invention) Heat storage material: Paraffin (Wax 145: manufactured by Nippon Seiro Co., Ltd.) melting point 63°C Thermally conductive filler: Alumina (AL43A: manufactured by Sumitomo Chemical Co., Ltd.) Shape-retaining ingredient: Aluminum 2-ethylhexanoate (Octope Aluminum T: manufactured by Hope Pharmaceutical Co., Ltd.) Anti-settling agent: fumed silica (Aerosil R972: manufactured by Nippon Aerosil Co., Ltd.) Dispersant: Nonionic surfactant (SN Dispersant 9228: manufactured by San Nopco Ltd.)

[0040] (Comparative Example 1) Heat storage material: Wax 145 (n-paraffin: manufactured by Nippon Seiro Co., Ltd.) melting point 63°C Thermally conductive filler: Alumina (AL43A: manufactured by Sumitomo Chemical Co., Ltd.) Shape retention component: Two-component curing urethane resin (R15HT: manufactured by Idemitsu Kosan Co., Ltd., MR200: manufactured by Tosoh Corporation) Anti-settling agent: fumed silica (Aerosil R972: manufactured by Nippon Aerosil Co., Ltd.) Dispersant: Nonionic surfactant (SN Dispersant 9228: manufactured by San Nopco Co., Ltd.)

[0041] The above-described constituent components were blended at the ratios (parts by mass) shown in Table 1 below to prepare the heat storage thermal conductive materials (samples) of the present invention examples and comparative examples. Then, for each of the heat storage thermal conductive materials, the initial thermal conductivity, the initial heat storage amount, the thermal conductivity after maintaining at 120°C for 24 hours, the thermal conductivity after maintaining at 120°C for 240 hours, and the presence or absence of yellowing at this time were confirmed. Further, based on these results, the remaining ratio of the initial heat storage amount at 120°C for 24 hours and the remaining ratio of the initial heat storage amount at 120°C for 240 hours were calculated, respectively. These results are shown in Table 1.

[0042]

Table 1

[0043] According to the results shown in Table 1, in the present invention example using an oil gelling agent (aluminum 2-ethylhexanoate) as the shape-retaining component, the thermal conductivity slightly increased after 240 hours at 120°C, and the decrease in the heat storage amount also remained at 70%. On the other hand, in the comparative example using a urethane resin as the shape-retaining component, the thermal conductivity decreased to about 60% after 240 hours at 120°C, and the decrease in the heat storage amount also reached 57%. Thus, the deterioration due to the change over time in a high-temperature environment was large. Also, the appearance showed progress of yellowing. Therefore, the deterioration resistance characteristics of the present invention example using an oil gelling agent as the shape-retaining component were confirmed.

Claims

**Claim 1** A heat storage thermal conductive material comprising a heat storage material, a thermal conductive filler, and an oil gelling agent. **Claim 2** The heat storage thermal conductive material according to claim 1, wherein the oil gelling agent comprises a fatty acid metal salt or a mixture of a fatty acid metal salt and a fatty acid. **Claim 3** The heat storage thermal conductive material according to claim 2, wherein the oil gelling agent is aluminum 2-ethylhexanoate. **Claim 4** The heat storage thermal conductive material according to any one of claims 1 to 3, wherein the thermal conductive filler comprises ceramic particles. **Claim 5** The heat storage thermal conductive material according to any one of claims 1 to 3, wherein the heat storage material comprises a paraffin compound or a fatty acid.

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