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, an oil gelling agent, and an antioxidant.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 to conduct 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 downsizing and higher 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, the secondary battery immediately reaches the use limit temperature, resulting in problems such as a short continuous operation time of the battery.

[0004] Therefore, 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 heat dissipation object, and for a heat dissipation object 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), the effect of suppressing and alleviating its temperature rise is enhanced.

[0006] In particular, for those using a battery, such as a lithium ion battery or the like, as a heat dissipation object, by using a heat storage material utilizing the latent heat having a phase change temperature within the operating temperature range of the battery, the temperature rise of the battery can be alleviated within the operating temperature region of the battery. At this time, if only the heat storage material is used, the heat dissipation effect is limited because the temperature rises again when the limit of the heat storage capacity 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, techniques using the latent heat of phase transition during the solidification and melting of substances are known. Among them, paraffin compounds in particular have excellent characteristics such as a high heat storage density and no corrosiveness to metals. Also, when the heat generating part is present inside the housing that houses it, a heat transfer material with 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 without gaps, without entraining bubbles, into a narrower space is required.

[0008] For example, Patent Document 2 discloses a latent heat storage material with excellent durability, without seepage or phase separation of the latent heat storage material from the carrier material even under a heat cycle repeating phase transition by solidification and melting.

Prior Art Documents

Patent Documents

[0009] Patent Document 1 Japanese Patent No. 6893741 Patent Document 2 Japanese Unexamined Patent Application Publication No. 2016-196578 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 that has fluidity that can be filled into a narrow part without gaps and has 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 characterized by including a heat storage material, a thermal conductive filler, an oil gelling agent or a two-component curable base resin, and an antioxidant.

[0013] (2) Aspect 2 of the present invention is the heat storage thermal conductive material according to Aspect 1, wherein the antioxidant is a hindered phenol-based or hindered amine-based radical scavenger.

[0014] (3) Aspect 3 of the present invention is the heat storage thermal conductive material according to Aspect 1 or 2, wherein the antioxidant is contained in an amount of 0.5 parts by mass or more with respect to 100 parts by mass of the heat storage material.

[0015] (4)Aspect 4 of the present invention is characterized in that, in any one of the heat storage thermal conductive materials of Aspects 1 to 3, the heat storage material contains a paraffin compound or a fatty acid.

[0016] (5)Aspect 5 of the present invention is characterized in that, in any one of the heat storage thermal conductive materials of Aspects 1 to 4, the heat storage material is microcrystalline wax. [Advantages of the Invention]

[0017] According to the present invention, it is possible to provide a heat storage thermal conductive material that has fluidity enabling it to be filled into narrow spaces 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 thermal conductive material according to an embodiment of the present invention will be described. Each of the embodiments shown below is specifically described for better understanding of 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, the main parts enlarged 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 thermal conductive material of the present embodiment includes a heat storage material, a thermal conductive filler, an oil gelling agent or a two-component curable base resin, and an antioxidant. 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 from the surrounding environment due to the influence of a harsh surrounding environmental temperature (ambient temperature).

[0020] Examples of such heat storage materials may be mixtures of alkanes having 16 or more carbon atoms, i.e., paraffins. As an example of paraffin, normal paraffin (especially a mixture of linear alkanes having 16 to 40 carbon atoms) can be mentioned. As an example of a heat storage material, normal paraffin having 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 in which heat is 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.

[0021] Also, microcrystalline wax can be used as a heat storage material. Microcrystalline wax is a wax that is solid at normal temperature, has more carbon atoms and a higher molecular weight than general paraffin wax, and also has a higher melting point. For example, the carbon number distribution of microcrystalline wax is generally about 30 to 60, the molecular weight is about 500 to 800, and the melting point is about 70 °C to 110 °C.

[0022] Such microcrystalline wax is defined in JIS as a wax that is solid at normal temperature separated and purified from the residue of vacuum distillation of crude oil or heavy distillate oil, and is classified into a plurality of categories depending on the melting point and the like. Microcrystalline wax has a composition mainly composed of hydrocarbons (isoparaffins) having side chains on the main chain, and contains a small amount of linear hydrocarbons (normal paraffins) and cyclic hydrocarbons (napthenes). Due to the large amount of isoparaffins and cycloparaffins with small crystal grain sizes in terms of composition, it becomes microcrystalline. Such microcrystalline wax has high viscosity, is rich in stretchability, and is excellent in brittleness resistance at low temperatures below room temperature.

[0023] Such normal paraffin and microcrystalline wax are solid-liquid phase transition type latent heat storage materials. This solid-liquid phase transition type latent heat storage material is a phase change type heat storage material (phase change material) that undergoes a phase change from a solid phase to a liquid phase when absorbing heat from a heat dissipation object, and stores heat by the latent heat of the phase change (melting).

[0024] Among the solid-liquid phase change type latent heat storage materials, normal paraffin and microcrystalline wax, in particular, have a relatively large latent heat, a large heat storage amount per unit volume, and can obtain stable heat release and heat storage effects even when melting and solidification are repeated. In addition, they are less likely to corrode the heat dissipation object, are inexpensive, and have favorable properties as a heat storage material in that the phase change temperature (melting point) can be easily adjusted according to the molecular weight and the like.

[0025] Thus, when using a phase change material such as a solid-liquid phase change type as a heat storage material, a material corresponding to the required phase change temperature (in the case of a solid-liquid phase change type phase change material, corresponding to the melting point), that is, a material having a phase change temperature (melting point) in the target temperature range may be selected.

[0026] Specifically, from the viewpoints of performance, durability, etc., those with a latent heat temperature range within 18°C or more and 81°C or less 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. From these points as well, normal paraffin and microcrystalline wax are suitable as latent heat storage materials.

[0027] These latent heat storage materials may contain alkanes having 16 or more carbon atoms or any fatty acids. 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.

[0028] 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 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 insulation properties as the heat-conductive filler. By using an insulating heat-conductive filler, the heat storage heat-conductive material can also be made insulating.

[0029] The heat-conductive filler may be, for example, ceramic particles having insulation properties. Specifically, metal oxides such as aluminum oxide, magnesium oxide, titanium oxide, zinc oxide, silicon oxide, beryllium oxide, copper oxide, zirconium oxide, calcium oxide, etc., and metal nitrides such as boron nitride, aluminum nitride, silicon nitride, etc. are mentioned. Among these, boron nitride and aluminum oxide are preferable as the heat-conductive filler. In particular, boron nitride is particularly preferable as a constituent component of the heat-conductive filler in that it has a high thermal conductivity (theoretical thermal conductivity in the a and b axis directions: 410 W / mK) as an insulating material. In the present embodiment, boron nitride 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.

[0030] Further, 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 region where the heat storage material becomes equal to or higher than the melting point. Also, 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, it is desirable that the specific surface area of the heat-conductive filler is 400 m 2 / g or less.

[0031] On the one hand, when the average particle diameter (d50) of the thermally conductive filler measured by a laser diffraction scattering type particle size distribution measuring device (MT3300EXII: manufactured by Microtrac Bell Corporation) exceeds 40 μm, there is a concern that the heat storage material may separate from the heat storage thermally conductive material in the temperature range where the heat storage material is above its melting point. In addition, there is a concern that the thermally conductive filler may precipitate and the heat storage thermally conductive material may become non-uniform. Although there is no particular limitation on the lower limit of the average particle diameter of the thermally conductive filler, it is preferably 0.005 μm or more.

[0032] When the heat storage material is 100 parts by mass, the blending ratio of the thermally conductive filler is preferably such that the thermally conductive filler accounts for 20 parts by mass or more. When the thermally conductive filler is less than 20 parts by mass when the heat storage material is 100 parts by mass, there is a concern that the heat storage material may fluidize and separate from the heat storage thermally conductive material in the temperature range where the heat storage material is above its melting point. In addition, when the heat storage material is 100 parts by mass, the thermally conductive filler is desirably 3000 parts by mass or less.

[0033] The oil gelling agent and the two-component curable base resin are shape-retaining components for preventing the heat storage material from melting and flowing and maintaining the shape when the heat storage thermally conductive material reaches a temperature above its melting point. Specific examples of the oil gelling agent include fatty acid metal salts or mixtures of fatty acid metal salts and fatty acids. 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 this embodiment, aluminum 2-ethylhexanoate (Al(-OH)[-OCOCH(C2H5)C4H9]2) with excellent shape-retaining properties was used. In addition, the fatty acid mixed with the fatty acid metal salt may be any monovalent carboxylic acid having a carboxy group in the hydrocarbon chain, and examples include 2-ethylhexanoic acid.

[0034] In this embodiment, the oil gelling agent may be added in the range of, for example, 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, the deterioration of the heat storage thermal conductive material is suppressed, and for example, a decrease in the heat storage amount due to changes over time can be suppressed.

[0035] The two-component curable base resin is a resin that solidifies by mixing two liquid resin components, and mainly solidifies by polymerization. Examples of one of the materials of the two-component curable base resin include hydroxyl group-containing compounds such as polybutadiene polyol compositions and polyester polyol compositions. Examples of the other material of the two-component curable base resin include isocyanate compounds. By mixing these two components of resin, a resin that is a shape-retaining component is produced by a polymerization reaction.

[0036] The antioxidant is a deterioration prevention component for suppressing the quality deterioration due to the oxidation of the heat storage thermal conductive material. As the antioxidant, for example, a hindered phenol-based or hindered amine-based radical scavenger can be used. A radical scavenger is a chemical substance added for the purpose of stopping a chain reaction or decomposition, and by capturing peroxy radicals, alkyl radicals, etc. that cause the deterioration of the heat storage thermal conductive material, deterioration such as the oxidation of the resin component by these radicals is prevented.

[0037] Specific examples of the hindered phenol-based or hindered amine-based radical scavengers include 2,2-methylenebis(4-methyl-6-t-butylphenol): (KEMINOX 9425, manufactured by Chemipro Kasei Co., Ltd.), a mixture of bis(1,2,2,6,6-pentamethyl-4-piperidyl) decanedioate and methyl (1,2,2,6,6-pentamethyl-4-piperidyl) sebacate: (KEMISTAB 29, manufactured by Chemipro Kasei Co., Ltd.), hexadecyl 3,5-di-tert-butyl-4-hydroxybenzoate: (KEMISORB 114, manufactured by Chemipro Kasei Co., Ltd.), and the like.

[0038] The heat storage type heat conductive material of the present embodiment preferably further contains a dispersant. The dispersant prevents aggregation of the heat conductive filler constituting the heat storage type heat conductive material, for example, ceramic particles, and appropriately disperses the ceramic particles in the heat storage type heat conductive material. Such a dispersant can stably disperse the ceramic particles in the heat storage type heat conductive material by actions such as repulsion between particles due to charges 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.

[0039] Examples of such dispersants include sodium polycarboxylate, ammonium polycarboxylate, alkylamine salts of polycarboxylic acids, amino alcohol polyphosphates, nonionic surfactants, and the like. In the present embodiment, a nonionic surfactant was used as the dispersant.

[0040] Nonionic surfactants are surfactants with 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 (cane sugar) are ester-bonded to fatty acids. Also, as ether types, polyoxyethylene alkyl phenyl ethers of the alkyl phenol type, etc., can be mentioned. Further, as ester-ether types, polyoxyethylene sorbitan fatty acid esters of the fatty acid type, etc., can be mentioned.

[0041] It is also preferable that the heat storage thermal 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 thermal conductive material and disperses it uniformly. As the anti-settling agent, for example, fumed silica can be used.

[0042] The heat storage thermal conductive material having the above configuration preferably has a viscosity of 500 Pa·s or less before curing. If the viscosity before curing exceeds 500 Pa·s, there is a concern that the fluidity of the heat storage thermal conductive material becomes too low and the heat storage thermal conductive material cannot be filled in fine gaps.

[0043] According to the heat storage thermal conductive material having the above configuration, by combining a heat storage material having a melting point of 48°C or higher and a large molecular weight, such as microcrystalline wax, with an oil gelling agent or a two-component curable base resin, a heat storage thermal conductive material can be obtained that has a fillable viscosity without generating voids and can suppress a decrease in the heat storage amount due to changes over time.

[0044] As described above, one embodiment of the present invention has been explained. However, this embodiment is presented as an example and is not intended to limit the scope of the invention. This embodiment can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. This embodiment and its modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and its equivalent scope.

Example

[0045] The effect of the heat storage thermal conductive material of the present invention was verified. The constituent components are as follows. (Example 1 of the present invention) · Heat storage substance: Microcrystalline wax (Hi-mic-2045: manufactured by Nippon Seiro Co., Ltd.), molecular weight 500 - 800, melting point 70°C · Thermal conductive filler: Hexagonal boron nitride (HFL: manufactured by Air Brown Co., Ltd.) · Shape-retaining component: Aluminum 2-ethylhexanoate (Octop Al T: manufactured by Hope Pharmaceutical Co., Ltd.) · Antioxidant: Hindered phenol-based radical scavenger (KEMINOX 9425: manufactured by Chempro Kasei Co., Ltd.) · Anti-settling agent: Fumed silica (Aerosil R972: manufactured by Nippon Aerosil Co., Ltd.) · Dispersant: Non-ionic surfactant (SN Dispersant 9228: manufactured by San Nopco Ltd.)

[0046] (Example 2 of the present invention) It is the same as Example 1 of the present invention except that the antioxidant is changed to a hindered amine-based radical scavenger (KEMISTAB 29: manufactured by Chempro Kasei Co., Ltd.).

[0047] (Examples 3, 4, 5 of the present invention) It is the same as Example 1 of the present invention except that the antioxidant is changed to a hindered phenol-based radical scavenger (KEMISORB 114: manufactured by Chempro Kasei Co., Ltd.).

[0048] (Comparative Example 1) It is the same as Example 1 of the present invention except that it does not contain an antioxidant as a component.

[0049] Each of the above-described constituent components was blended at the ratios (parts by mass) shown in Table 1 below to prepare the heat storage type thermal conductive materials (samples) of Examples 1 to 5 and Comparative Example 1 of the present invention. Then, for each of the heat storage type thermal conductive materials, the initial heat storage amount immediately after production, the heat storage amount after maintaining at 120°C for 24 hours, and the heat storage amount after maintaining at 120°C for 240 hours were confirmed. Further, based on these results, the residual rate of the initial heat storage amount at 120°C for 24 hours and the residual rate of the initial heat storage amount at 120°C for 240 hours were calculated, respectively. These results are shown in Table 1.

[0050]

Table 1

[0051] According to the results shown in Table 1, in Examples 1, 3 to 5 of the present invention to which an antioxidant was added, there was no decrease in the heat storage amount after 24 hours at 120°C, and even in Example 2 of the present invention, the decrease rate remained at 5%. Further, in Examples 1, 4, and 5 of the present invention, there was no decrease in the heat storage amount even after 240 hours at 120°C, and in Example 2 of the present invention, the decrease rate remained at 7%, and in Example 3 of the present invention, the decrease rate remained at 2%. On the other hand, in Comparative Example 1 to which no antioxidant was added, the decrease rate of the heat storage amount after 24 hours at 120°C reached 10%, and the decrease rate of the heat storage amount after 240 hours at 120°C reached 30%. Therefore, the deterioration resistance characteristics of the heat storage type thermal conductive materials of Examples 1 to 5 of the present invention to which an antioxidant was added were confirmed.

Claims

**Claim 1** A heat storage thermal conductive material comprising a heat storage material, a thermal conductive filler, an oil gelling agent or a two-component curable base resin, and an antioxidant. **Claim 2** The heat storage thermal conductive material according to claim 1, wherein the antioxidant is a hindered phenol-based or hindered amine-based radical scavenger. **Claim 3** The heat storage thermal conductive material according to claim 1 or 2, wherein the antioxidant is contained in an amount of 0.5 parts by mass or more based on 100 parts by mass of the heat storage material. **Claim 4** The heat storage thermal conductive material according to claim 1 or 2, wherein the heat storage material contains a paraffin compound or a fatty acid. **Claim 5** The heat storage thermal conductive material according to claim 1 or 2, wherein the heat storage material is microcrystalline wax.

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