Urethane foam molded body

Abstract

To provide a urethane foam molded body which has softness and an excellent thermal conductivity.SOLUTION: A urethane foam molded body includes a base material made of polyurethane foam; composite particles oriented and contained in the base material; and insulating inorganic particles dispersed in the base material. The composite particles have thermally conductive particles, and magnetic particles bonded to surfaces of the thermally conductive particles with a binder. The circularity of the insulating inorganic particles is 0.8 or more and 1 or less. The content of the insulating inorganic particles is 20 vol.% or more and 40 vol.% or less when the volume of the urethane foam molded body is 100 vol.%.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to a urethane foam molded article that can be used as a thermally conductive material. [Background technology]

[0002] In battery packs and electronic devices mounted on electric vehicles, heat sinks, cooling plates, and other heat sinks are used to dissipate heat generated during use to the outside. A thermally conductive material called a thermal interface material (TIM) is placed between the heat generating body and the heat dissipating body to reduce the thermal resistance between the heat generating body and the heat dissipating body and improve the heat dissipation. As thermally conductive materials, various materials such as grease, gel, phase change material (PCM), and sheet-shaped molded bodies have been developed depending on the application. For example, Patent Document 1 describes a thermally conductive sheet comprising a binder component that is a mixture of a silicone matrix and a hydrocarbon-based compound, and a thermally conductive filler that is dispersed in the binder component and contains an anisotropic filler that is oriented in the thickness direction. However, a material in which a thermally conductive filler is mixed with a solid polymer matrix has poor flexibility and does not have sufficient followability to the heat generating body or heat dissipating body. For example, a battery cell housed in a battery pack repeatedly expands and contracts with charging and discharging. Electronic components in electronic devices may also be deformed, such as warping, by repeatedly heating and cooling. Therefore, thermally conductive materials used in contact with these are required to have flexibility so as to be able to follow the deformation of the heating element and the like.

[0003] As a molding having high flexibility, a foam such as polyurethane foam is known. However, the foam has a large number of bubbles inside and has a low thermal conductivity. In this regard, Patent Document 2 describes a polyurethane foam molding in which composite particles, which are a composite of thermally conductive particles and magnetic particles, are oriented and arranged in polyurethane foam, and a heat conduction path is formed in the orientation direction, thereby improving heat dissipation. The same document describes that by dispersing insulating inorganic particles in addition to the composite particles in polyurethane foam, electrical insulation is imparted, and heat dissipation and flame retardancy can be improved depending on the characteristics of the insulating inorganic particles. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2022-121447 A [Patent Document 2] International Publication No. 2013 / 042611 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the urethane foam molded body described in Patent Document 2 was developed as a sound absorbing material, and therefore the thermal conductivity is insufficient for a thermal conductive material whose main purpose is heat dissipation. For example, it is possible to increase the content of composite particles having thermally conductive particles to increase the thermal conductivity, but since the composite particles need to be oriented in the direction of thermal conduction, there is a limit to how much they can be increased. On the other hand, it is possible to use particles with high thermal conductivity as insulating inorganic particles dispersed in polyurethane foam and increase their content. However, when a large amount of insulating inorganic particles is mixed into the foamed urethane resin raw material when manufacturing a urethane foam molded body, the viscosity of the mixed raw material increases, making it difficult to mold. In addition, the orientation of the composite particles may be hindered during molding, or the dispersibility of the insulating inorganic particles may decrease, causing the particles to be unevenly distributed. As a result, even if the content of the insulating inorganic particles is increased, the thermal conductivity of the urethane foam molded body may decrease.

[0006] The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a urethane foam molded body that is flexible and has excellent thermal conductivity. [Means for solving the problem]

[0007] (1) In order to solve the above problems, the urethane foam molded body of the present disclosure comprises a base material made of polyurethane foam, composite particles contained in an oriented manner in the base material, and insulating inorganic particles dispersed in the base material, the composite particles comprising thermally conductive particles and magnetic particles bonded to the surfaces of the thermally conductive particles with a binder, the insulating inorganic particles having a circularity of 0.8 or more and 1 or less, and a content of the insulating inorganic particles of 20 volume % or more and 40 volume % or less when the volume of the urethane foam molded body is 100 volume %.

[0008] The urethane foam molded body of the present disclosure has composite particles oriented and arranged in a substrate, and insulating inorganic particles dispersed in the substrate. The composite particles having thermally conductive particles as cores are strung together in a rosary shape to form a heat transfer path in the substrate. The insulating inorganic particles are particles of an inorganic material having insulating properties. The presence of the insulating inorganic particles makes it difficult for the composite particles to be electrically connected to each other, improving the electrical insulation of the urethane foam molded body. In addition, heat transfer occurs not only through the composite particles but also through the insulating inorganic particles, improving the thermal conductivity of the urethane foam molded body.

[0009] Paragraph

[0047] of the above Patent Document 2 states that "the shape of the insulating inorganic particles dispersed in the base material is not particularly limited, and may be spherical or flaky." However, the degree of "spherical", such as whether it is better to be closer to a perfect sphere, is not considered. The present inventor has conducted repeated studies focusing on the shape of the insulating inorganic particles, and has found that if the insulating inorganic particles have a shape close to a perfect sphere, the viscosity increase when they are mixed with a foamed urethane resin raw material is small. The circularity of the insulating inorganic particles in the urethane foam molded body of the present disclosure, which is set based on this finding, is 0.8 or more and 1 or less. The circularity will be described later, but the closer the circularity is to 1, the closer the shape of the insulating inorganic particles is to a perfect sphere. When insulating inorganic particles with a shape close to a perfect sphere are used, the viscosity increase is suppressed even if a relatively large amount of the insulating inorganic particles are mixed with the foamed urethane resin raw material. Therefore, the content of the insulating inorganic particles can be increased compared to the conventional case. Specifically, the content of insulating inorganic particles in the urethane foam molded body can be 20% by volume or more and 40% by volume or less, assuming that the volume of the urethane foam molded body is 100% by volume. Even if the content of insulating inorganic particles is increased in this way, it is possible to obtain a urethane foam molded body in which the insulating inorganic particles are highly dispersed without interfering with the orientation and moldability of the composite particles. Since the insulating inorganic particles can be highly filled, the properties of the insulating inorganic particles, such as thermal conductivity and flame retardancy, can be more easily exhibited. For example, a urethane foam molded body highly filled with insulating inorganic particles having a relatively high thermal conductivity is suitable as a flexible thermal conductive material.

[0010] (2) In the above configuration, the total content of the composite particles and the insulating inorganic particles may be 40% by volume or more and 60% by volume or less, based on the volume of the urethane foam molded body being 100% by volume. This configuration can maximize the effects of the composite particles and the insulating inorganic particles, such as improved thermal conductivity, while minimizing the effect on the orientation of the composite particles.

[0011] (3) In any of the above configurations, the median diameter of the insulating inorganic particles may be 1 μm or more and 30 μm or less. With this configuration, the surface area of ​​the insulating inorganic particles in contact with the foamed urethane resin raw material is made relatively small, which makes it possible to suppress an increase in the viscosity of the mixed raw material and maintain the orientation and moldability of the composite particles. In addition, since the dispersibility of the insulating inorganic particles is unlikely to decrease, uneven distribution can be suppressed.

[0012] (4) In any of the above configurations, the insulating inorganic particles may be configured to have a thermal conductivity of 15 W / m K or more. With this configuration, the insulating inorganic particles have a large effect of improving thermal conductivity.

[0013] (5) In the above configuration (4), the particles having a thermal conductivity of 15 W / m K or more may be one or more selected from the group consisting of aluminum oxide particles, magnesium oxide particles, zinc oxide particles, boron nitride particles, and silicon nitride particles. With this configuration, it is relatively easy to obtain particles having a shape close to a perfect sphere.

[0014] (6) In any of the above configurations, the thermally conductive particles may include expanded graphite particles. The expanded graphite particles are formed by inserting a substance that generates gas when heated between layers of scaly graphite. When heat is applied to the expanded graphite particles, the generated gas expands the gap between the layers and forms a layer that is stable against heat and chemicals. The formed layer acts as a heat insulating layer and prevents the transfer of heat, thereby providing a flame retardant effect.

[0015] Usually, a urethane foam molded body that has been given flame retardancy has a dropping action that drops the fire and suppresses the spread of the fire even when exposed to a flame. However, if magnetic particles are blended, the dropping action is impaired, and the self-extinguishing property of the urethane foam molded body may be reduced. In the urethane foam molded body of the present disclosure, the composite particles are oriented. Therefore, the heat applied to the urethane foam molded body is easily transferred to the thermally conductive particles, and the expanded graphite particles quickly reach the expansion start temperature. This allows the flame retardant effect of the expanded graphite particles to be exerted quickly. Therefore, according to this configuration, the decrease in the self-extinguishing property of the urethane foam molded body can be suppressed, and the flame retardancy can be maintained. Effect of the Invention

[0016] In the base material of the urethane foam molded body of the present disclosure, composite particles having thermally conductive particles as cores are oriented, and insulating inorganic particles are dispersed. Since the shape of the insulating inorganic particles is close to a perfect sphere, it is possible to suppress an increase in the viscosity of the mixed raw material when producing the urethane foam molded body, and a relatively large amount of insulating inorganic particles can be contained without impairing the orientation of the composite particles. By highly filling the insulating inorganic particles in addition to the composite particles, it is possible to realize a urethane foam molded body that is flexible and has excellent thermal conductivity. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, embodiments of the urethane foam molded article of the present disclosure will be described. Note that the embodiments are not limited to the following embodiments, and various modifications and improvements that can be made by those skilled in the art can be made.

[0018] <Urethane foam molding> The urethane foam molded product of the present disclosure has a substrate made of polyurethane foam, composite particles contained and oriented in the substrate, and insulating inorganic particles dispersed in the substrate.

[0019] [Base material] The polyurethane foam of the base material is produced from urethane foam resin raw materials such as polyisocyanate components and polyol components. The urethane foam resin raw materials may be prepared from already known raw materials such as polyols and polyisocyanates. The polyol may be appropriately selected from polyhydric hydroxy compounds, polyether polyols, polyester polyols, polymer polyols, polyether polyamines, polyester polyamines, alkylene polyols, urea-dispersed polyols, melamine-modified polyols, polycarbonate polyols, acrylic polyols, polybutadiene polyols, phenol-modified polyols, and the like. The polyisocyanate may be appropriately selected from, for example, tolylene diisocyanate, phenylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, triphenylmethane triisocyanate, polymethylene polyphenyl isocyanate, naphthalene diisocyanate, and derivatives thereof (for example, prepolymers obtained by reaction with polyols, modified polyisocyanates), and the like.

[0020] The urethane foam resin raw material may further contain a catalyst, a blowing agent, a foam stabilizer, a plasticizer, a crosslinking agent, a chain extender, a flame retardant, an antistatic agent, a viscosity reducer, a stabilizer, a filler, a colorant, etc. Examples of the catalyst include amine catalysts such as tetraethylenediamine, triethylenediamine, and dimethylethanolamine, and organometallic catalysts such as tin laurate and tin octanoate. Water is a suitable blowing agent. Other than water, methylene chloride, fluorocarbons, CO 2 Gases, etc. From the viewpoint of reducing the amount of bubbles and increasing the thermal conductivity of the urethane foam molded body, the amount of foaming agent may be reduced, or no foaming agent may be used. In addition, silicone foam stabilizers are suitable as foam stabilizers, and triethanolamine, diethanolamine, etc. are suitable as crosslinking agents.

[0021] The shape, size, etc. of the substrate are not particularly limited and may be appropriately determined depending on the application. The composite particles contained in the substrate may be arranged in the direction of heat conduction. For example, they may be arranged in a straight line or a curved line between one end and the other end of the urethane foam molded body (not necessarily at an end 180° opposite to the one end). They may also be arranged radially from the center toward the periphery.

[0022] [Composite particles] The composite particles oriented in the substrate are particles in which magnetic particles or the like are bonded to the surface of the core thermally conductive particle by a binder. The thermally conductive particles may be non-magnetic and have a large thermal conductivity. In this specification, diamagnetic and paramagnetic materials other than ferromagnetic and antiferromagnetic materials are referred to as non-magnetic materials. For example, the thermal conductivity of the thermally conductive particles is preferably 200 W / m·K or more. Examples of the material of the thermally conductive particles include carbon materials such as graphite and carbon fiber. Aluminum, gold, silver, copper, and alloys using these as the base material may also be used. The thermally conductive particles may be single particles or aggregate particles in which multiple particles are integrated.

[0023] The shape of the thermally conductive particles is not particularly limited as long as they can be composited with other particles such as magnetic particles. For example, various shapes such as flakes, fibers, columns, spheres, ellipsoids, and oval spheres (a pair of opposing hemispheres connected by a cylinder) can be adopted. When the thermally conductive particles are in a shape other than a sphere, the contact area between the composite particles is large. This makes it easier to ensure a heat transfer path and increases the amount of heat transferred. For example, graphite particles can be obtained at a low cost compared to metal particles, even if they have a shape with a large aspect ratio. For this reason, graphite particles are suitable as the thermally conductive particles. Examples of graphite include natural graphite such as scaly graphite, scaly graphite, and earthy graphite, and artificial graphite. Artificial graphite is less likely to become scaly. For this reason, natural graphite is suitable because it is scaly and has a high effect of improving thermal conductivity. In addition, expanded graphite, in which a substance that generates gas when heated is inserted between the layers of scaly graphite, may be used as the graphite. When heat is applied to the expanded graphite, the gas generated causes the gap between the layers to expand and forms a layer that is stable against heat and chemicals. This stable layer acts as a heat insulating layer and prevents the transfer of heat, thereby providing a flame retardant effect. Therefore, in consideration of flame retardancy, expanded graphite particles are suitable as thermally conductive particles. The expanded graphite particles may be appropriately selected in consideration of the expansion start temperature, expansion coefficient, etc. The expansion start temperature must be higher than the heat generation temperature during molding of the urethane foam molded body, so expanded graphite particles with an expansion start temperature of 150°C or higher are suitable.

[0024] From the viewpoint of increasing the thermal conductivity, the median diameter of the thermally conductive particles is desirably 100 μm or more, and more preferably 700 μm or more. On the other hand, if the thermally conductive particles are too large, there is a risk that the molded body will become brittle due to cracks originating from the thermally conductive particles. Therefore, the median diameter of the thermally conductive particles is desirably 3000 μm or less, and more preferably 2000 μm or less. Unless otherwise specified, the median diameter in this specification refers to the value (D 50 When using commercially available products, the catalog value may be used.

[0025] The magnetic particles may be any particles capable of orienting the composite particles, and may be, for example, ferromagnetic materials such as iron, nickel, cobalt, gadolinium, stainless steel, magnetite, maghemite, manganese zinc ferrite, barium ferrite, and strontium ferrite, MnO, Cr 2 O 3 , FeCl 2 Particles of antiferromagnetic materials such as MnAs and alloys using these are preferred. Among these, iron, nickel, cobalt, and iron-based alloys (including stainless steel) are preferred from the viewpoints of being easily available as fine particles and having high saturation magnetization. Iron, in particular, is relatively inexpensive and easily available, so that it is possible to reduce manufacturing costs and is suitable for mass production.

[0026] The magnetic particles may be directly attached to the surface of the thermally conductive particles, or may be indirectly attached via insulating inorganic particles for composite particles, which will be described later. The magnetic particles may be attached only to a part of the surface of the thermally conductive particles, or may be attached so as to cover the entire surface. The size of the magnetic particles may be appropriately determined in consideration of the size of the thermally conductive particles, the orientation of the composite particles, and the thermal conductivity between the composite particles. For example, the particle diameter of the magnetic particles is preferably 1 / 10 or less of the particle diameter of the thermally conductive particles. In this case, the "particle diameter" is the equivalent diameter of a sphere of equal volume. When the size of the magnetic particles is smaller, the saturation magnetization of the magnetic particles tends to decrease. Therefore, in order to orient the composite particles with a smaller amount of magnetic particles, it is desirable to set the median diameter of the magnetic particles to 100 nm or more. It is more preferable to set it to 1 μm or more, and even more preferable to set it to 5 μm or more.

[0027] The shape of the magnetic particles is not particularly limited. For example, when the shape of the magnetic particles is flat, the distance between adjacent thermally conductive particles is shorter than when the magnetic particles are spherical. This improves the thermal conductivity between adjacent composite particles. As a result, the thermal conductivity of the urethane foam molding is improved. In addition, when the shape of the magnetic particles is flat, the magnetic particles and the thermally conductive particles are in contact with each other on the surface. In other words, the contact area between the two particles is large. This improves the adhesive force between the magnetic particles and the thermally conductive particles. Therefore, the magnetic particles are less likely to peel off. In addition, the thermal conductivity between the magnetic particles and the thermally conductive particles is also improved. For these reasons, it is desirable to use flaky particles as the magnetic particles.

[0028] From the viewpoint of being able to orient the composite particles even in a relatively weak magnetic field, the content of the magnetic particles is desirably 20 parts by mass or more when the mass of the thermally conductive particles in the substrate is 100 parts by mass. From the viewpoint of improving the orientation of the composite particles and increasing the thermal conductivity, it is preferable that the content of the magnetic particles is 40 parts by mass or more, and even more preferable that the content of the magnetic particles is 60 parts by mass or more. On the other hand, from the viewpoint of reducing costs and reducing weight, it is desirably 150 parts by mass or less. It is more preferable that the content of the magnetic particles is 130 parts by mass or less, and even more preferable that the content of the magnetic particles is 80 parts by mass or less.

[0029] The binder that bonds the thermally conductive particles and the magnetic particles may be appropriately selected in consideration of the adhesiveness and the effect on the foaming and curing reaction. A water-soluble polymer is preferable because it has little effect on the foaming and curing reaction and is environmentally friendly. Examples include methyl cellulose, carboxymethyl cellulose, hydroxypropyl methyl cellulose, polyvinyl alcohol, and starch. Among them, starch is preferable because it is relatively inexpensive, has high adhesion, and has excellent granulation properties.

[0030] The thermally conductive particles and the magnetic particles are conductive. Therefore, the composite particles are aligned and oriented to form a conductive path in the base material. For example, the composite particles can be formed by adhering insulating inorganic particles to the surface of the thermally conductive particles in addition to the magnetic particles with a binder. By doing so, even if the composite particles are oriented, the electrical resistance between adjacent composite particles can be increased or the electrical connection can be blocked. As a result, electrical insulation can be imparted to the urethane foam molded body. In order to improve the orientation of the composite particles and increase the thermal conductivity, the content of the magnetic particles to be composited can be increased and a form in which the insulating inorganic particles are not adhered can be adopted.

[0031] The insulating inorganic particles added as constituent particles of the composite particles (hereinafter referred to as "insulating inorganic particles for composite particles") may be particles of an inorganic material having insulating properties, similar to the insulating inorganic particles dispersed in the base material. Examples of insulating inorganic materials include aluminum oxide, aluminum hydroxide, aluminum nitride, magnesium hydroxide, magnesium oxide, talc, calcium carbonate, clay, mica, and silica. One of these may be used alone, or two or more may be used in combination. Among these, talc and mica are preferred because they are flaky and have excellent covering properties. In addition, from the viewpoint of not inhibiting the thermal conductivity between the composite particles, those with a relatively high thermal conductivity may be used.

[0032] The insulating inorganic particles for composite particles may be directly attached to the surface of the thermally conductive particles, or may be indirectly attached via magnetic particles or the like. The insulating inorganic particles for composite particles may be attached only to a part of the surface of the thermally conductive particles, or may be attached so as to cover the entire surface. From the viewpoint of increasing the electrical resistance between the composite particles and improving the electrical insulation of the urethane foam molding, it is desirable that the insulating inorganic particles for composite particles are disposed in the outermost layer of the composite particles. The binder that bonds the magnetic particles to the thermally conductive particles and the binder that bonds the insulating inorganic particles for composite particles may be the same or different.

[0033] The size of the insulating inorganic particles for composite particles may be appropriately determined in consideration of the adhesiveness to the thermally conductive particles and the magnetic particles, the electrical insulating property between the composite particles, and the thermal conductivity. If the insulating inorganic particles for composite particles are too large, the adhesiveness and the thermal conductivity between the composite particles will decrease. For example, the particle diameter of the insulating inorganic particles for composite particles is desirably 1 / 10 or less of the particle diameter of the thermally conductive particles. In this case, the "particle diameter" is the equivalent volume sphere equivalent diameter. For example, the median diameter of the insulating inorganic particles for composite particles may be 1 μm or more and 20 μm or less. The shape of the insulating inorganic particles for composite particles is not particularly limited. For example, when the insulating inorganic particles for composite particles are flat, the distance between adjacent thermally conductive particles can be shortened compared to when they are spherical. Therefore, the thermal conductivity between adjacent composite particles is less likely to be hindered. In addition, the contact area with the thermally conductive particles is increased, so that the insulating inorganic particles for composite particles are less likely to peel off.

[0034] The content of the composite particles may be determined in consideration of thermal conductivity, the effect on the foaming and curing reaction of the polyurethane foam, moldability, etc. In order to achieve the desired thermal conductivity, the content of the composite particles is desirably 5% by volume or more when the volume of the urethane foam molded body is taken as 100% by volume. It is more preferable to set it to 10% by volume or more, and furthermore 20% by volume or more. On the other hand, from the viewpoint of not inhibiting the foaming and curing reaction and improving moldability, it is desirably the content of the composite particles is 40% by volume or less, and more preferable to set it to 30% by volume or less.

[0035] [Insulating inorganic particles] The type of insulating inorganic particles dispersed in the base material may be the same as or different from the insulating inorganic particles for composite particles that constitute the composite particles. Examples of the insulating inorganic particles include the above-mentioned aluminum oxide, aluminum hydroxide, aluminum nitride, magnesium hydroxide, magnesium oxide, talc, calcium carbonate, clay, mica, and silica. One of these can be used alone or in combination of two or more. In order to increase the thermal conductivity of the urethane foam molded body, it is desirable to have a relatively high thermal conductivity. For example, it is desirable for the insulating inorganic particles to have particles with a thermal conductivity of 15 W / m·K or more. Examples of such particles include aluminum oxide particles, magnesium oxide particles, zinc oxide particles, boron nitride particles, and silicon nitride particles. In addition, when the insulating inorganic particles have flame retardancy, the flame retardancy of the urethane foam molded body is improved. Examples of particles having flame retardancy include aluminum hydroxide particles and magnesium hydroxide particles.

[0036] The circularity, which is an index showing the shape of the insulating inorganic particles, is 0.8 or more and 1 or less. The circularity is a value calculated by observing the insulating inorganic particles contained in the base material with a scanning electron microscope (SEM) at a magnification of 1000 times, measuring the area S and perimeter L of the particles from the obtained SEM image, and calculating it according to the following formula (I). In this specification, the arithmetic average value of the circularity of any 10 insulating inorganic particles dispersed in the base material is adopted as the "circularity". It is presumed that the closer the circularity is to 1, the closer the particle shape is to a true sphere. By using insulating inorganic particles with a circularity of 0.8 or more and 1 or less, the surface area of ​​the insulating inorganic particles in contact with the foamed urethane resin raw material can be reduced when producing a urethane foam molded body, and the increase in the viscosity of the mixed raw material can be suppressed. Circularity = S / A = 4πS / L 2 (I) [S: area of ​​the measured particle, A: area of ​​a sphere with the measured perimeter L {=π(L / 2π) 2}]

[0037] The area S and perimeter L of the insulating inorganic particles may be measured by manual calculation or by image processing using Python's "OpenCV" (Open Source Computer Vision Library). The circularity may be measured using the powder of insulating inorganic particles used in the manufacture of the urethane foam molded body, or using the powder extracted from the urethane foam molded body in the following steps (a) to (c). (a) The urethane foam molded body is immersed in a potassium hydroxide solution to hydrolyze. (b) Pure water is added to the hydrolysis liquid, and the liquid is shaken lightly, then the liquid is left to stand for 30 minutes and the supernatant liquid is discarded. This process is repeated four times. (c) The remaining portion is air-dried to remove moisture, and a powder is obtained.

[0038] The size of the insulating inorganic particles is not particularly limited, but for example, it is desirable that the median diameter is 1 μm or more and 30 μm or less. When the median diameter is 1 μm or more, the surface area of ​​the insulating inorganic particles in contact with the foamed urethane resin raw material can be reduced, which is effective in suppressing the increase in viscosity of the mixed raw material. On the other hand, when the median diameter is 30 μm or less, the dispersibility of the insulating inorganic particles is unlikely to decrease, which is effective in suppressing uneven distribution of the insulating inorganic particles.

[0039] The content of the insulating inorganic particles is set to 20% by volume or more when the volume of the urethane foam is taken as 100% by volume. If it is set to 25% by volume or more, the effect of the insulating inorganic particles in improving thermal conductivity and the like is increased, which is preferable. On the other hand, the content of the insulating inorganic particles is set to 40% by volume or less, taking into consideration the increase in viscosity of the mixed raw material and the orientation of the composite particles. In addition, it is desirable that the total content of the composite particles and the insulating inorganic particles is 40% by volume or more and 60% by volume or less when the volume of the urethane foam is taken as 100% by volume. This makes it possible to maximize the effect of the composite particles and the insulating inorganic particles in improving thermal conductivity and the like while minimizing the influence on the orientation of the composite particles.

[0040] [Volume of bubbles] From the viewpoint of flexibility, the amount of bubbles in the urethane foam molded product of the present disclosure is desirably 4% by volume or more, assuming the volume of the urethane foam molded product to be 100% by volume. On the other hand, from the viewpoint of improving thermal conductivity by increasing the content of composite particles and insulating inorganic particles per unit volume, the amount of bubbles is desirably 6% by volume or less. As will be described later, the amount of bubbles can be adjusted by the amount of mixed raw material placed in the foaming mold used to produce the urethane foam molded product. The amount of bubbles is also determined based on the unit volume of the urethane foam molded product (e.g., 1 cm). 3 The volume of the filler and polyurethane foam per unit volume, such as composite particles and insulating inorganic particles, can be calculated according to the following formula (II): In formula (II), the volume of the filler and polyurethane foam per unit volume can be calculated, for example, by adding up the filler volume calculated from the mass and specific gravity of the filler contained in the unit volume and the polyurethane foam volume calculated from the mass and specific gravity of the polyurethane foam. Air bubble volume (volume %) = (unit volume - volume of filler and polyurethane foam per unit volume) / unit volume × 100 (II)

[0041] [Thermal Conductivity] When the urethane foam molded article of the present disclosure is used as a thermally conductive material, the thermal conductivity is desirably 1.8 W / m·K or more, and more desirably 2.0 W / m·K or more, and even more desirably 3.0 W / m·K or more.

[0042] <Method of manufacturing urethane foam molded body> The method for producing the urethane foam molded article of the present disclosure is not particularly limited. As a preferred embodiment of the production method, there can be mentioned a production method having a composite particle production step, a mixed raw material production step, and a foam molding step. Each step will be described below.

[0043] [Composite particle manufacturing process] This process is a process for producing composite particles by stirring a granulation raw material containing a powder of thermally conductive particles, a powder of magnetic particles, a powder of insulating inorganic particles for composite particles that is mixed as necessary, a binder, and water. The amounts of the powder and binder used may be appropriately adjusted in consideration of the magnetic field orientation of the composite particles, the electrical insulation and thermal conductivity of the urethane foam molding, etc.

[0044] The amount of magnetic particle powder is preferably 20 parts by mass or more per 100 parts by mass of thermally conductive particle powder, from the viewpoint of being able to orient the composite particles even in a relatively weak magnetic field. From the viewpoint of improving the orientation of the composite particles and increasing the thermal conductivity, it is preferable to make it 40 parts by mass or more, and even more preferable to make it 60 parts by mass or more. On the other hand, from the viewpoint of reducing costs and weight, it is preferable to make the amount of magnetic particle powder 150 parts by mass or less. It is more preferable to make it 130 parts by mass or less, and even more preferable to make it 80 parts by mass or less.

[0045] The amount of binder is preferably 2 parts by mass or more when the total mass of the powders to be bonded is 100 parts by mass, as a necessary and sufficient amount for particle adhesion. On the other hand, if the binder is excessive, the composite particles may aggregate. For this reason, the amount of binder is preferably 10 parts by mass or less. It is more preferable to use 5 parts by mass or less. The binder may be solid or liquid. When a water-soluble powder is used as the binder, it is recommended to add water after stirring the binder and other powder raw materials in advance. This can suppress particle aggregation.

[0046] In the case where the granulation raw material contains a powder of insulating inorganic particles for composite particles and the insulating inorganic particles for composite particles are disposed in the outermost layer of the composite particles, this process may include a first stirring process in which a first raw material having a powder of thermally conductive particles, a powder of magnetic particles, a binder, and water is stirred, and a second stirring process in which the powder of insulating inorganic particles for composite particles is added to the stirred first raw material and further stirred.

[0047] [Mixed raw material manufacturing process] This step is a step of producing a mixed raw material by mixing the powder of the composite particles produced in the previous step, the powder of the insulating inorganic particles to be dispersed in the base material, and a urethane foam resin raw material.

[0048] As described above, the foamed urethane resin raw material may be prepared from raw materials such as polyol, polyisocyanate, catalyst, blowing agent, and foam stabilizer. The mixed raw material can be produced, for example, by mechanically stirring a powder of composite particles, a powder of insulating inorganic particles, and a foamed urethane resin raw material using a stirring blade or the like. In addition, the powder of composite particles and the powder of insulating inorganic particles may be added to at least one of the two components of the foamed urethane resin raw material (polyol raw material, polyisocyanate raw material) to prepare two types of raw materials, and then the two raw materials may be mixed to produce the foamed urethane resin.

[0049] [Foam molding process] In this process, the mixed raw material produced in the previous process is injected into the cavity of a foaming mold, and foam-molded while applying a magnetic field so that the magnetic flux density in the cavity becomes approximately uniform.

[0050] The degree of foaming, in other words, the amount of bubbles in the resulting urethane foam molding, can be adjusted by the amount of the mixed raw material injected into the foaming mold. From the viewpoint of increasing the content of the composite particles and insulating inorganic particles per unit volume and improving thermal conductivity, it is desirable to increase the amount of the mixed raw material injected into the foaming mold and increase the pressure during foaming to reduce the amount of bubbles. Assuming that the foaming reaction proceeds sufficiently due to the foaming agent, the amount of bubbles is calculated by the following formula (III). Air volume (volume %) = (volume of foam mold - volume of mixed material to be poured) / volume of foam mold × 100 (III)

[0051] The magnetic field may be formed in the direction in which the composite particles are oriented. For example, when the composite particles are oriented in a linear manner, it is desirable to form the magnetic field lines in the cavity of the foaming mold so that they are approximately parallel from one end to the other end of the cavity. In order to form such a magnetic field, for example, magnets may be placed near both sides of one end and the other end of the foaming mold so as to sandwich the foaming mold. The magnets may be permanent magnets or electromagnets. When an electromagnet is used, the magnetic field formation can be instantly switched on and off, and the strength of the magnetic field can be easily controlled. Therefore, it is easy to control the foaming molding. In addition, it is desirable that the magnetic field lines that constitute the magnetic field form a closed loop. In this way, leakage of the magnetic field lines is suppressed, and a stable magnetic field can be formed in the cavity.

[0052] In this process, the magnetic field is formed so that the magnetic flux density in the cavity is approximately uniform. For example, the difference in magnetic flux density in the cavity is preferably within ±10%. It is more preferable that it is within ±5%, and furthermore within ±3%. By forming a uniform magnetic field in the cavity of the foaming mold, uneven distribution of the composite particles can be suppressed, and a desired orientation state can be obtained. In addition, the foaming molding is preferably performed at a magnetic flux density of 150 mT or more and 350 mT or less. In this way, the composite particles in the mixed raw material can be reliably oriented. It is desirable to apply the magnetic field while the viscosity of the foamed urethane resin raw material is relatively low. If a magnetic field is applied when the foamed urethane resin raw material thickens and the foaming molding is completed to a certain extent, the composite particles are difficult to orient, and it is difficult to obtain the desired thermal conductivity. It is not necessary to apply the magnetic field for the entire time of foaming molding.

[0053] After the foam molding is completed in this step, the mold is removed to obtain the urethane foam molded article of the present disclosure. At this time, a skin layer is formed on at least one of one end and the other end of the urethane foam molded article depending on the foam molding method. The skin layer may be cut off depending on the application (or may not be cut off). EXAMPLES

[0054] Next, the present disclosure will be described in more detail with reference to examples. In the examples, urethane foam molded articles were produced using powders of multiple types of insulating inorganic particles that differ in material, particle shape, etc., and the moldability and thermal conductivity were evaluated.

[0055] <Production of composite particles> The composite particles were produced by stirring the granulation raw materials including expanded graphite powder as thermally conductive particles, stainless steel powder as magnetic particles, starch powder as binder, talc powder as insulating inorganic particles for composite particles, and water. First, 1000 parts by mass of expanded graphite powder, 600 parts by mass of stainless steel powder, and 100 parts by mass of starch powder were put into a container of a high-speed stirring type mixer granulator and mixed by blade stirring, and 400 parts by mass of water were added and mixed for 1 minute. Next, 400 parts by mass of talc powder were put in and mixed for another 4 minutes. The stirring speed was 400 rpm. The obtained powder was dried to obtain the powder of the composite particles. Details of the materials used are shown in the following (a) to (d). The median diameter of each powder is a catalog value. (a) Thermally conductive particles Expanded graphite powder: "EXA-50" manufactured by Fuji Graphite Industries Co., Ltd., median diameter 300 μm. (b) Magnetic particles Stainless steel powder: "AKT" manufactured by Mitsubishi Steel Corporation, median diameter 8.5 to 13.0 μm. (c) Binder Starch powder: "Instant Tender Gel C" manufactured by Nippon Corn Starch Co., Ltd. (d) Insulating inorganic particles for composite particles Talc powder: "Microace (registered trademark) K-1" manufactured by Nippon Talc Co., Ltd., median diameter 8 μm.

[0056] <Production of urethane foam molded body> A urethane foam molded body was manufactured using the powder of the manufactured composite particles and the powder of the insulating inorganic particles dispersed in the base material. First, 100 parts by mass of polyether polyol (manufactured by Sumika Covestro Urethane Co., Ltd., "SBU (registered trademark) Polyol 0248"), 2 parts by mass of diethylene glycol (manufactured by Mitsubishi Chemical Corporation) as a chain extender, 2 parts by mass of water as a foaming agent, 1 part by mass of tetraethylenediamine catalyst (manufactured by Kao Corporation, "Kao Raiser (registered trademark) No. 31"), and 0.5 parts by mass of a silicone foam stabilizer (manufactured by Toray Dow Corning Co., Ltd., "SZ-1333") were mixed to prepare a polyol raw material. Next, diphenylmethane diisocyanate (MDI) (manufactured by BASF INOAC Polyurethanes Co., Ltd., "NE1320B", NCO = 44.8 wt%) as a polyisocyanate component was added to the prepared polyol raw material and mixed to prepare a urethane foam resin raw material. Here, the compounding ratio of the polyol component and the polyisocyanate component (PO:ISO) was PO:ISO=78.5:21.5, with the total mass of both being 100%. Next, the manufactured composite particle powder and insulating inorganic particle powder were added to the prepared urethane foam resin raw material and mixed to prepare a mixed raw material.

[0057] The insulating inorganic particles used were five types (A) to (E). Of these, the thermal conductivity of the aluminum oxide powder (A) was 30 W / m·K, the thermal conductivity of the aluminum hydroxide powders (B) and (C) was 8 W / m·K, and the thermal conductivity of the aluminum oxide powders (D) and (E) was 30 W / m·K. The median diameter of each powder was a catalog value, and the circularity was measured as follows. First, each powder was observed with an SEM at a magnification of 1000 times, and the obtained SEM image was loaded into Python's "OpenCV". Next, 10 particles were selected from the loaded image, and the contours of the selected particles were detected to measure their area S and perimeter L. Then, the circularity of each particle was calculated using the above formula (I), and the arithmetic average value of the circularities of the 10 particles was taken as the circularity of the insulating inorganic particles. (A) Aluminum oxide powder: "Spherical Alumina DAW-20" manufactured by Denka Co., Ltd., median diameter 24 μm, circularity 0.88. (B) Aluminum hydroxide powder: "SB93" manufactured by Nippon Light Metal Co., Ltd., median diameter 105 μm, circularity 0.67. (C) Aluminum hydroxide powder: "B53" manufactured by Nippon Light Metal Co., Ltd., median diameter 55 μm, circularity 0.39. (D) Aluminum oxide powder: "A11" manufactured by Nippon Light Metal Co., Ltd., median diameter 55 μm, circularity 0.29. (E) Aluminum oxide powder: "SA31" manufactured by Nippon Light Metal Co., Ltd., median diameter 5 μm, circularity 0.51.

[0058] The prepared mixed raw material was poured into an aluminum foaming mold (cavity was a rectangular parallelepiped with length 130 mm × width 130 mm × thickness 2 mm), and the foaming mold was sealed. The amount of the mixed raw material poured was adjusted so that the amount of bubbles was 3 to 7% by volume, assuming that the foaming reaction would proceed sufficiently with water. Then, the foaming mold was placed in a magnetic induction foaming molding device to perform foaming molding. In the cavity of the foaming mold, a uniform magnetic field was formed by magnetic field lines that were approximately parallel from above to below. The magnetic flux density in the cavity was 200 mT, and the difference in magnetic flux density in the cavity was within ±3%. The foaming molding was performed while applying a magnetic field for the first 2 minutes, and then without applying a magnetic field for the following 5 minutes. After the foaming molding was completed, the mold was removed to obtain a urethane foam molded body in which the composite particles were oriented in the thickness direction. The obtained urethane foam molded body is called urethane foam molded body sample A1, B1, etc., depending on the type of insulating inorganic particle powder used. The content and circularity of the insulating inorganic particles in each sample are shown in Table 1. Samples A1 to A4, which used aluminum oxide powder (A) as the insulating inorganic particles, are included in the concept of the urethane foam molded article of the present disclosure.

[0059] [Table 1]

[0060] <Evaluation of urethane foam molded products> The moldability and thermal conductivity of the produced urethane foam molded articles were evaluated.

[0061] [Evaluation method] (1) Formability When preparing a mixed raw material by mixing a powder of composite particles and a powder of insulating inorganic particles with a urethane foam resin raw material, if the viscosity of the mixed raw material becomes too high, uniform mixing becomes difficult. As a result, during foam molding, partial curing failure occurs, the composite particles cannot be oriented in the desired state, or the insulating inorganic particles are unevenly distributed. Therefore, in this embodiment, the urethane foam molded body at the time of demolding after foam molding was visually observed, and when demolding was smooth and no defects due to poor mixing were observed, it was evaluated as good moldability (shown by a circle in Table 1 above), when demolding was possible but some defects due to poor mixing were observed, it was evaluated as slightly poor moldability (shown by a triangle in the same table), and when demolding was not possible, it was evaluated as poor moldability (shown by a cross in the same table).

[0062] (2) Thermal conductivity The thermal conductivity of the urethane foam molded body was measured using "HC-110" manufactured by Eiko Seiki Co., Ltd., which complies with the heat flow meter method of JIS A1412-2:1999.

[0063] [Evaluation Results] The evaluation results of moldability and thermal conductivity are summarized in Table 1 above. As shown in Table 1, the circularity of the insulating inorganic particles contained in samples A1 to A4 is 0.88. Therefore, even if the insulating inorganic particles are blended in a larger amount than in the past, specifically, even if the insulating inorganic particles are blended in a volume ratio of 20% or more, the viscosity increase of the mixed raw material is small, and a good foamed molded body in which the composite particles are magnetically oriented and the insulating inorganic particles are dispersed can be produced. Thus, in samples A1 to A4, the insulating inorganic particles are contained in a relatively large amount and the amount of bubbles is small at 6% or less, so the thermal conductivity is high. In particular, in samples A2 to A4, in which the insulating inorganic particles are 25% or more by volume, the thermal conductivity is 2.0 W / m·K or more. From the above, it was confirmed that the urethane foamed molded body of the present disclosure can be used as a thermal conductive material, as shown in samples A1 to A4 as an example. Note that even if the same insulating inorganic particles are used, when the content is small as in sample A5, the thermal conductivity cannot be increased. On the other hand, when the content was too high, as in sample A6, the viscosity of the mixed raw material increased, and it was not possible to produce a foamed molded article under the same production conditions.

[0064] In contrast, in each sample containing insulating inorganic particles (B) to (E) with a circularity of less than 0.8, when the content of insulating inorganic particles is as low as 10 volume %, the increase in viscosity of the mixed raw material is small and moldability is good, but the thermal conductivity is low and it is found that it is unsuitable as a thermal conductive material. When the content of insulating inorganic particles (B) or (C) is increased to 20 volume % as in samples B2 and C2, the thermal conductivity increases slightly, but the viscosity of the mixed raw material increases and moldability decreases. In samples D2 and E2, when the content of insulating inorganic particles (D) or (E) is 20 volume %, it is not possible to produce a foamed molded product.

Claims

1. The present invention has a substrate made of polyurethane foam, composite particles contained in the substrate in an oriented state, and insulating inorganic particles dispersed in the substrate, The composite particle has a thermally conductive particle and a magnetic particle bonded to a surface of the thermally conductive particle by a binder, The circularity of the insulating inorganic particles is 0.8 or more and 1 or less, The content of the insulating inorganic particles is 20% by volume or more and 40% by volume or less, based on 100% by volume of the urethane foam.

2. 2. The urethane foam according to claim 1, wherein a total content of the composite particles and the insulating inorganic particles is 40 volume % or more and 60 volume % or less, where the volume of the urethane foam is 100 volume %.

3. The urethane foam molded article according to claim 1 , wherein the insulating inorganic particles have a median diameter of 1 μm or more and 30 μm or less.

4. The urethane foam molded article according to claim 1 , wherein the insulating inorganic particles have a thermal conductivity of 15 W / m·K or more.

5. 5. The urethane foam molded article according to claim 4, wherein the particles having a thermal conductivity of 15 W / m·K or more are at least one selected from the group consisting of aluminum oxide particles, magnesium oxide particles, zinc oxide particles, boron nitride particles, and silicon nitride particles.

6. The urethane foam molded article according to claim 1 , wherein the thermally conductive particles comprise expanded graphite particles.

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