Urethane foam molded body

Abstract

The urethane foam molded body has a base material made of polyurethane foam, composite particles oriented and contained in the base material, and first insulating inorganic particles dispersed in the base material. The composite particles have thermally conductive particles and magnetic particles bonded to the surface of the thermally conductive particles with a binder. The first insulating inorganic particles have large-diameter particles having a median diameter of 55-200 μm.

Description

Urethane foam molding

[0001] The present disclosure relates to a urethane foam molded article having high thermal conductivity.

[0002] In automobiles and other vehicles, measures are taken to reduce noise generated by engines, transmissions, and other components in order to reduce noise leaking outside the vehicle or into the passenger compartment. In electric vehicles (EVs) and hybrid electric vehicles (HEVs), the drive noise of the electric powertrain, which consists of an inverter, motor, gearbox, and other components, is also a target for reduction. Soundproofing materials made of foams such as polyurethane foam are used as noise countermeasures. Foams have a large number of internal cells (air bubbles) and therefore have low thermal conductivity. Therefore, if they are placed around a heat-generating noise source, heat may accumulate, causing problems.

[0003] From the viewpoint of improving the heat dissipation properties of soundproofing materials using foams, for example, Patent Document 1 describes a urethane foam molded product in which composite particles, which are a composite of thermally conductive particles, magnetic particles, and insulating inorganic particles, are oriented and arranged in polyurethane foam, thereby forming a heat transfer path in the direction of the orientation, thereby improving heat dissipation properties. The same document also describes that by dispersing insulating inorganic particles separately from the composite particles in the polyurethane foam, electrical insulation properties can be imparted, and heat dissipation properties and flame retardancy can be improved depending on the properties of the insulating inorganic particles.

[0004] International Publication No. 2013 / 042611

[0005] However, conventional urethane foam molded bodies have the problem of low heat resistance, specifically, that physical properties such as elongation decrease when exposed to high temperatures of around 150°C. Poor heat resistance makes it difficult to apply them to components that become exposed to high temperatures, such as various ECUs (Electronic Control Units) and junction boxes installed in vehicles. Patent Document 1 only evaluates the thermal conductivity and electrical insulation properties of urethane foam molded bodies, but does not consider heat resistance.

[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 article that has excellent thermal conductivity and heat resistance.

[0007] (1) In order to solve the above-mentioned problems, the urethane foam molded article of the present disclosure has a base material made of polyurethane foam, composite particles contained in the base material and oriented in the base material, and first insulating inorganic particles dispersed in the base material, the composite particles having thermally conductive particles and magnetic particles bonded to the surfaces of the thermally conductive particles with a binder, and the first insulating inorganic particles having large diameter particles with a median diameter of 55 μm or more and 200 μm or less.

[0008] The urethane foam molded article of the present disclosure has composite particles oriented and arranged in a substrate and first insulating inorganic particles dispersed in the substrate. The composite particles, each having a thermally conductive particle as a core, are strung together in a beaded pattern, forming a heat transfer path in the substrate. This allows for the desired thermal conductivity to be achieved. The first insulating inorganic particles are particles of an insulating inorganic material. The presence of the first insulating inorganic particles reduces electrical conductivity between the composite particles, improving the electrical insulation of the urethane foam molded article. Furthermore, when the thermal conductivity of the first insulating inorganic particles is relatively high, a heat transfer path is formed by the first insulating inorganic particles in addition to the heat transfer path by the composite particles. This further improves the thermal conductivity of the urethane foam molded article. Furthermore, when the first insulating inorganic particles are flame-retardant, the flame-retardant properties of the urethane foam molded article are improved.

[0009] Paragraph

[0047] of the above-mentioned Patent Document 1 states, "The insulating inorganic particles dispersed in the substrate preferably have a median diameter of 1 μm or more and 20 μm or less." As such, relatively small diameter particles are used as the insulating inorganic particles dispersed in the polyurethane foam, taking into consideration factors such as their influence on the foaming and curing reaction. Small particle diameters of insulating inorganic particles result in a large specific surface area, increasing the contact area with the polyurethane foam substrate. The present inventors conducted extensive research focusing on insulating inorganic particles and discovered that a large contact area between the insulating inorganic particles and the polyurethane foam increases the influence of the insulating inorganic particles, which is one factor contributing to the deterioration of the heat resistance of the urethane foam molded body. For example, if the insulating inorganic particles are alkaline upon reaction with water, an alkaline atmosphere is generated when the insulating inorganic particles react with the water contained in the polyurethane foam. It is believed that exposure to high temperatures in this state accelerates hydrolysis of the polyurethane, accelerating its degradation.

[0010] In the urethane foam molded body of the present disclosure, the first insulating inorganic particles dispersed in the substrate are large-diameter particles with a median diameter of 55 μm or more and 200 μm or less. Therefore, compared to when small-diameter particles are used, the contact area between the first insulating inorganic particles and the polyurethane foam is smaller, thereby reducing the impact of the first insulating inorganic particles. This prevents deterioration of the polyurethane and reduces the decrease in physical properties such as elongation, even when the urethane foam molded body is placed under high temperatures. On the other hand, if the particles dispersed in the substrate are too large, this can lead to a decrease in moldability and physical properties. In this regard, by setting the upper limit of the median diameter of the large-diameter particles to 200 μm, the impact on moldability is reduced and the occurrence of cracks, etc. is suppressed. As a result, desired physical properties such as elongation can be maintained. As a result, the urethane foam molded body of the present disclosure has excellent thermal conductivity and heat resistance.

[0011] (2) In the above configuration, the content of the first insulating inorganic particles may be 5% by volume or more and 20% by volume or less, based on the volume of the urethane foam molded body taken as 100% by volume. This configuration can provide the effects of the first insulating inorganic particles, such as imparting electrical insulation and improving thermal conductivity, while minimizing the influence on the foaming and curing reaction and moldability.

[0012] (3) In any of the above configurations, the thermal conductivity of the first insulating inorganic particles may be 5 W / m·K or more. With this configuration, the first insulating inorganic particles can provide an effect of improving thermal conductivity.

[0013] (4) In any of the above configurations, the first insulating inorganic particles may comprise one or more selected from aluminum hydroxide, aluminum oxide, aluminum nitride, magnesium hydroxide, magnesium oxide, talc, calcium carbonate, clay, mica, and silica. The first insulating inorganic particles of this configuration are relatively inexpensive and easily available. Among these, aluminum hydroxide, aluminum oxide, aluminum nitride, magnesium hydroxide, magnesium oxide, and talc have relatively high thermal conductivities and are therefore suitable for increasing the thermal conductivity of the urethane foam molded body.

[0014] (5) In any of the above configurations, the large-diameter particles may be particles that exhibit alkalinity upon reaction with water. "Particles that exhibit alkalinity upon reaction with water" refer to particles that exhibit a pH greater than 7 when 2 g of the target particle powder is dispersed in 50 mL of ion-exchanged water at room temperature (20°C ± 5°C, hereinafter). Particles that exhibit alkalinity upon reaction with water (hereinafter sometimes referred to as "alkaline inorganic particles") may react with water contained in the polyurethane foam substrate to generate an alkaline atmosphere, potentially promoting hydrolysis of the polyurethane. Therefore, when alkaline inorganic particles are used as the first insulating inorganic particles, increasing the particle size of the particles—specifically, by setting the median diameter to 55 μm or more and 200 μm or less—reduces the contact area between the alkaline inorganic particles and the polyurethane foam, thereby suppressing polyurethane hydrolysis. This configuration is thus effective in improving the heat resistance of urethane foam molded bodies.

[0015] (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 flake 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, preventing the transfer of heat and thereby providing a flame-retardant effect.

[0016] Typically, flame-retardant urethane foam molded articles have a dropping effect that drops embers and prevents the spread of fire when exposed to flames. However, the incorporation of magnetic particles can impair this dropping effect, potentially reducing the self-extinguishing properties of the urethane foam molded article. In the urethane foam molded article of the present disclosure, the composite particles are oriented. This facilitates transfer of heat applied to the urethane foam molded article to the thermally conductive particles, allowing the expandable graphite particles to quickly reach their expansion initiation temperature. This allows the expandable graphite particles to rapidly exert their flame-retardant effect. Therefore, this configuration can prevent a decrease in the self-extinguishing properties of the urethane foam molded article and maintain its flame retardancy.

[0017] (7) In any of the above configurations, the composite particles may have second insulating inorganic particles bonded to the surfaces of the thermally conductive particles with a binder. In this configuration, the second insulating inorganic particles may be directly bonded to the surfaces of the core thermally conductive particles or indirectly bonded via magnetic particles. Ferromagnetic materials such as stainless steel and iron are used as the magnetic particles. Therefore, composite particles formed by combining thermally conductive particles and magnetic particles have high electrical conductivity. When second insulating inorganic particles are bonded to the composite particles in this state, even if the composite particles are oriented in a contacting state, the thermally conductive particles and magnetic particles (conductive particles) between adjacent composite particles are less likely to come into contact with each other. This increases the electrical resistance between the composite particles. Furthermore, contact between the composite particles via the second insulating inorganic particles can interrupt electrical continuity between the composite particles. As a result, the desired electrical insulation can be achieved in the urethane foam molded product of the present disclosure. Thus, this configuration can impart electrical insulation in addition to high thermal conductivity and heat resistance. Therefore, the urethane foam molded article of this configuration is also suitable for applications requiring both heat dissipation and electrical insulation, such as heat dissipation components in electronic devices.

[0018] (8) In the configuration of (7) above, the particle diameter of the second insulating inorganic particles may be 1 / 10 or less of the particle diameter of the thermally conductive particles, and the median diameter may be 1 μm or more and 20 μm or less. If the second insulating inorganic particles are too large, their adhesion to the thermally conductive particles and the thermal conductivity between the composite particles may be reduced. Furthermore, since the second insulating inorganic particles are adhered to the thermally conductive particles and are only a part of the composite particles, their contact area with the polyurethane foam of the base material is small and their impact on the polyurethane foam is minimal. Therefore, this configuration makes it possible to realize composite particles with good adhesion of the second insulating inorganic particles and maintain good thermal conductivity between the composite particles.

[0019] (9) In the configuration of (7) or (8) above, the second insulating inorganic particles may comprise one or more selected from aluminum hydroxide, aluminum oxide, aluminum nitride, magnesium hydroxide, magnesium oxide, talc, calcium carbonate, clay, mica, and silica. As described in the configuration of (4) above, the second insulating inorganic particles of this configuration are relatively inexpensive and easily available. Among them, talc and mica are flaky and have excellent coating properties. Furthermore, aluminum hydroxide, aluminum oxide, aluminum nitride, magnesium hydroxide, magnesium oxide, and talc have relatively high thermal conductivities and therefore are unlikely to inhibit thermal conductivity between composite particles.

[0020] The urethane foam molded article of the present disclosure has a substrate in which composite particles with thermally conductive particles as cores are oriented and first insulating inorganic particles are dispersed. The first insulating inorganic particles have large diameter particles with a median diameter of 55 μm or more and 200 μm or less. The use of large diameter particles reduces the contact area between the first insulating inorganic particles and the substrate, thereby reducing the effect of the first insulating inorganic particles on the polyurethane. This prevents deterioration of the polyurethane and reduces declines in physical properties such as elongation, even when the urethane foam molded article is placed under high temperatures. Therefore, the urethane foam molded article of the present disclosure has excellent thermal conductivity and heat resistance.

[0021] The following describes embodiments of the urethane foam molded article of the present disclosure. 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 are possible.

[0022] <Urethane foam molded product> 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 first insulating inorganic particles dispersed in the substrate.

[0023] [Substrate] The polyurethane foam substrate is produced from urethane foam resin raw materials such as a polyisocyanate component and a polyol component. The urethane foam resin raw materials may be prepared from known raw materials such as polyol and polyisocyanate. 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, etc. 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.

[0024] The urethane foam resin raw material may further contain catalysts, blowing agents, foam stabilizers, plasticizers, crosslinking agents, chain extenders, flame retardants, antistatic agents, viscosity reducers, stabilizers, fillers, colorants, etc. Examples of catalysts include amine catalysts such as tetraethylenediamine, triethylenediamine, and dimethylethanolamine, and organometallic catalysts such as tin laurate and tin octoate. Water is also suitable as a blowing agent. Other than water, other suitable blowing agents include methylene chloride, chlorofluorocarbons, CO ２ As the foam stabilizer, a silicone-based foam stabilizer is suitable, and as the crosslinking agent, triethanolamine, diethanolamine, etc. are suitable.

[0025] The shape, size, etc. of the substrate are not particularly limited and may be determined appropriately depending on the application. The composite particles contained in the substrate may be arranged with a certain regularity. 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 (the ends do not have to be 180° opposite to the one end). Alternatively, they may be arranged radially from the center toward the periphery.

[0026] [Composite Particles] The composite particles oriented in the substrate are particles in which magnetic particles or the like are bonded to the surface of core thermally conductive particles with a binder. The thermally conductive particles may be non-magnetic and have high 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 higher. Examples of materials for the thermally conductive particles include carbon materials such as graphite and carbon fiber. Aluminum, gold, silver, copper, and alloys using these as a base material may also be used. The thermally conductive particles may be single particles or aggregate particles in which multiple particles are integrated.

[0027] 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. Various shapes can be employed, including, for example, flakes, fibers, columns, spheres, ellipsoids, and spheroids (a pair of opposing hemispheres connected by a cylinder). When the thermally conductive particles have a shape other than a sphere, the contact area between the composite particles increases. This facilitates the establishment of a heat transfer path and increases the amount of heat transferred. For example, graphite particles, even those with a high aspect ratio, are more inexpensively available than metal particles. For this reason, graphite particles are preferred as thermally conductive particles. Examples of graphite include natural graphite such as flake graphite, flaky graphite, and earthy graphite, as well as artificial graphite. Artificial graphite is less likely to become flaky. For this reason, natural graphite is preferred because of its flaky shape and its high thermal conductivity improvement effect. Expanded graphite, in which a substance that generates gas upon heating is inserted between the layers of flaky graphite, may also be used as the graphite. When heat is applied to expanded graphite, the gas generated causes the layers to expand and forms a layer that is stable against heat and chemicals. This stable layer acts as a heat insulating layer, preventing the transfer of heat and 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 selected appropriately taking into consideration 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 article, so expanded graphite particles with an expansion start temperature of 150°C or higher are suitable.

[0028] From the viewpoint of increasing the thermal conductivity, the median diameter of the thermally conductive particles is preferably 100 μm or more. 700 μm or more is more preferable. On the other hand, if the thermally conductive particles are too large, cracks may occur from the particles, making the molded body brittle. Therefore, the median diameter of the thermally conductive particles is preferably 3000 μm or less. 2000 μm or less is more preferable. Unless otherwise specified, the median diameter in this specification refers to the value (D ) calculated from the volume-based particle size distribution measured by laser diffraction / scattering method. ５０ ) For commercially available products, catalog values ​​may be used.

[0029] The magnetic particles may be any particles capable of orienting the composite particles, and examples thereof include 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 thereof (including stainless steel) are preferred from the viewpoints of easy availability as fine particles and high saturation magnetization. Iron, in particular, is relatively inexpensive and easily available, allowing for reduced manufacturing costs and making it suitable for mass production.

[0030] The magnetic particles may be directly adhered to the surface of the thermally conductive particles, or may be indirectly adhered via second insulating inorganic particles, as described below. The magnetic particles may be adhered to only a portion of the surface of the thermally conductive particles, or may be adhered so as to cover the entire surface. The size of the magnetic particles may be determined appropriately, taking into consideration 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" refers to the equivalent diameter of a sphere of equal volume. As the size of the magnetic particles decreases, 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 for the median diameter of the magnetic particles to be 100 nm or more. A diameter of 1 μm or more, or even 5 μm or more, is more preferable.

[0031] The shape of the magnetic particles is not particularly limited. For example, when the magnetic particles are 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 molded body is improved. Furthermore, when the magnetic particles are flat, the magnetic particles and the thermally conductive particles come into contact with each other through their surfaces. In other words, the contact area between the two is increased. This improves the adhesive strength 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.

[0032] From the viewpoint of enabling the composite particles to be oriented even in a relatively weak magnetic field, the content of the magnetic particles is desirably 20% by mass or more, where the mass of the thermally conductive particles in the substrate is taken as 100% by mass. Furthermore, from the viewpoint of achieving cost reduction and weight reduction, the content of the magnetic particles is desirably 130% by mass or less. 100% by mass or less, and even 80% by mass or less, is more preferable.

[0033] The binder that bonds the thermally conductive particles and the magnetic particles may be appropriately selected taking into consideration factors such as adhesiveness and its effect on the foaming and curing reaction. Water-soluble polymers are preferred because they have little effect on the foaming and curing reaction and are environmentally friendly. Examples include methyl cellulose, carboxymethyl cellulose, hydroxypropyl methyl cellulose, polyvinyl alcohol, and starch. Among these, starch is preferred because it is relatively inexpensive, has high adhesiveness, and has excellent granulation properties.

[0034] The thermally conductive particles and magnetic particles are electrically conductive. Therefore, when the composite particles are aligned, a conductive path is formed in the substrate. For example, composite particles can be formed by adhering second insulating inorganic particles to the surface of the thermally conductive particles with a binder in addition to the magnetic particles. By doing so, even if the composite particles are aligned, the electrical resistance between adjacent composite particles can be increased or electrical conduction can be blocked. As a result, electrical insulation can be imparted to the urethane foam molded article.

[0035] The second insulating inorganic particles may be particles of an inorganic material having insulating properties, similar to the first insulating inorganic particles dispersed in the base material. Examples of the second insulating inorganic material include aluminum hydroxide, aluminum oxide, 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 coating properties. Furthermore, from the viewpoint of not inhibiting thermal conductivity between composite particles, particles with relatively high thermal conductivity may be used.

[0036] The second insulating inorganic particles may be directly adhered to the surface of the thermally conductive particles, or may be indirectly adhered via magnetic particles or the like. The second insulating inorganic particles may be adhered to only a portion of the surface of the thermally conductive particles, or may be adhered 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 molded body, it is desirable that the second insulating inorganic particles be disposed in the outermost layer of the composite particles. The binder that adheres the magnetic particles to the thermally conductive particles and the binder that adheres the insulating inorganic particles may be the same or different.

[0037] The size of the second insulating inorganic particles may be determined appropriately, taking into consideration the adhesiveness to the thermally conductive particles and magnetic particles, and the electrical insulation and thermal conductivity between the composite particles. If the second insulating inorganic particles are too large, the adhesiveness and thermal conductivity between the composite particles will decrease. For example, the particle diameter of the second insulating inorganic particles is preferably 1 / 10 or less of the particle diameter of the thermally conductive particles. In this case, the "particle diameter" refers to the equivalent diameter of an equal-volume sphere. Furthermore, since the second insulating inorganic particles are adhered to the thermally conductive particles and are only a part of the composite particles, their contact area with the polyurethane foam substrate is small, and their impact on the polyurethane foam is minimal. Therefore, the median diameter of the second insulating inorganic particles may be 1 μm or more and 20 μm or less.

[0038] The shape of the second insulating inorganic particles is not particularly limited. For example, when the second insulating inorganic particles are flat, the distance between adjacent thermally conductive particles can be shortened compared to when the second insulating inorganic particles are spherical. Therefore, the thermal conductivity between adjacent composite particles is less likely to be impaired. Furthermore, the increased contact area with the thermally conductive particles makes the second insulating inorganic particles less likely to peel off.

[0039] The content of the composite particles may be determined taking into consideration 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 preferably 5% by volume or more, with the volume of the urethane foam molded product being 100% by volume. 10% by volume or more is more preferable. On the other hand, from the viewpoint of not inhibiting the foaming and curing reaction and improving moldability, the content of the composite particles is preferably 50% by volume or less, and more preferably 20% by volume or less.

[0040] [First Insulating Inorganic Particles] The type of first insulating inorganic particles dispersed in the base material may be the same as or different from the second insulating inorganic particles added as constituent particles of the composite particles. The shape of the first insulating inorganic particles is not particularly limited and may be spherical or flaky. The first insulating inorganic particles may be one type or two or more types. The aforementioned aluminum hydroxide, aluminum oxide, aluminum nitride, magnesium hydroxide, magnesium oxide, talc, calcium carbonate, clay, mica, silica, etc. are also suitable for the first insulating inorganic particles. Furthermore, from the viewpoint of increasing the thermal conductivity of the urethane foam molded body, particles with a relatively high thermal conductivity are desirable. For example, a thermal conductivity of 5 W / m·K or higher is preferred for the first insulating inorganic particles. Among these, aluminum hydroxide is preferred because it also has flame retardancy.

[0041] The first insulating inorganic particles have large diameter particles with a median diameter of 55 μm or more and 200 μm or less. When the median diameter is 55 μm or more, the contact area between the substrate and the polyurethane foam is reduced, thereby reducing the effect of the first insulating inorganic particles on the polyurethane foam. For example, when the large diameter particles are particles that react with water to exhibit alkalinity (alkaline inorganic particles), deterioration due to hydrolysis of polyurethane is suppressed, and physical properties such as elongation are less likely to decrease even when the urethane foam molded body is placed at high temperatures. On the other hand, when the median diameter is 200 μm or less, there is little effect on moldability, and the occurrence of cracks and the like is suppressed. From the perspective of further improving moldability and physical properties under normal conditions, it is preferable that the median diameter of the large diameter particles is 150 μm or less. The first insulating inorganic particles may be composed solely of large diameter particles, or may contain particles other than large diameter particles as long as the desired heat resistance and moldability can be achieved.

[0042] Considering the influence on the foaming and curing reaction of the polyurethane foam and moldability, the content of the first insulating inorganic particles is preferably 20% by volume or less, and more preferably 15% by volume or less, of the volume of the urethane foam molded product taken as 100% by volume. Furthermore, in order to achieve desired effects such as imparting electrical insulation and improving thermal conductivity, the content is preferably 5% by volume or more, and more preferably 8% by volume or more.

[0043] <Method for producing urethane foam molded article> 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, the method for producing the urethane foam molded article of the present disclosure includes a composite particle production step, a raw material mixture production step, and a foam molding step. Each step will be described below.

[0044] [Composite particle manufacturing process] This process is a process for manufacturing composite particles by stirring a granulation raw material containing a powder of thermally conductive particles, a powder of magnetic particles, a powder of second insulating inorganic particles (if blended as needed), a binder, and water. The blending amounts of the powders and binder used may be appropriately adjusted taking into consideration the magnetic field orientation of the composite particles, the electrical insulation and thermal conductivity of the urethane foam molded body, etc.

[0045] Considering the magnetic field orientation of the composite particles, the blending amount of magnetic particle powder is preferably 20 parts by mass or more per 100 parts by mass of thermally conductive particle powder. On the other hand, considering cost and weight reduction, it is preferable to set it to 130 parts by mass or less. 100 parts by mass or less, and even more preferable to set it to 80 parts by mass or less. The blending amount of binder is preferably 2% by mass or more, where the total mass of the powders to be bonded is 100% by mass, as a necessary and sufficient amount for particle adhesion. On the other hand, excessive binder may cause aggregation of the composite particles. Therefore, the blending amount of binder is preferably 10% by mass or less, and more preferably 5% by mass or less. The binder may be solid or liquid. When using a water-soluble powder 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] When the granulation raw material contains powder of second insulating inorganic particles and the second insulating inorganic particles are arranged in the outermost layer of the composite particles, this process may be configured to include a first stirring process in which a first raw material containing powder of thermally conductive particles, powder of magnetic particles, a binder, and water is stirred, and a second stirring process in which powder of second insulating inorganic particles is added to the stirred first raw material and further stirred.

[0047] [Mixed Raw Material Producing Step] 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 first insulating inorganic particles, and a urethane foam resin raw material.

[0048] As described above, the urethane foam 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 first insulating inorganic particles, and a urethane foam resin raw material using a stirring blade or the like. Alternatively, the composite particle powder and the first insulating inorganic particle powder may be added to at least one of the two components of the urethane foam 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 urethane foam resin.

[0049] [Foam Molding Step] In this step, the mixed raw material produced in the previous step 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 magnetic field may be formed in the direction in which the composite particles are oriented. For example, when aligning the composite particles linearly, 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. 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, sandwiching the foaming mold. The magnets may be permanent magnets or electromagnets. Using an electromagnet allows the magnetic field to be instantly switched on and off, making it easy to control the strength of the magnetic field. This makes it easy to control the foam molding. It is also desirable that the magnetic field lines that make up the magnetic field form a closed loop. This prevents leakage of the magnetic field lines and allows a stable magnetic field to be formed in the cavity.

[0051] In this process, the magnetic field is formed so that the magnetic flux density within the cavity is approximately uniform. For example, the difference in magnetic flux density within the cavity is preferably within ±10%, more preferably within ±5%, and even more preferably within ±3%. Forming a uniform magnetic field within the cavity of the foaming mold can suppress uneven distribution of the composite particles and achieve the desired orientation state. Furthermore, foam molding is preferably performed at a magnetic flux density of 150 mT or more and 350 mT or less. This ensures that the composite particles in the mixed raw material are aligned. It is desirable to apply the magnetic field while the viscosity of the urethane foam resin raw material is relatively low. If the magnetic field is applied after the urethane foam resin raw material has thickened and foam molding has been completed to a certain extent, the composite particles will not be aligned, making it difficult to achieve the desired thermal conductivity. It is not necessary to apply the magnetic field for the entire duration of foam molding.

[0052] After 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, depending on the foam molding method, a skin layer is formed on at least one end of the urethane foam molded article. This skin layer may be removed (or, of course, not removed) depending on the application.

[0053] Next, the present disclosure will be described more specifically with reference to examples. In these examples, urethane foam molded articles were produced using several first insulating inorganic particles having different median diameters, and the properties thereof were evaluated.

[0054] <Production of Composite Particles> Composite particles were produced by stirring a granulation raw material containing expanded graphite powder as thermally conductive particles, stainless steel powder as magnetic particles, starch powder as a binder, talc powder as second insulating inorganic particles, and water. First, 1,000 parts by mass of expanded graphite powder, 600 parts by mass of stainless steel powder, and 100 parts by mass of starch powder were placed in the container of a high-speed stirring mixer granulator and mixed using a blade stirrer. 400 parts by mass of water was then added and mixed for 1 minute. Next, 400 parts by mass of talc powder was added and mixed for an additional 4 minutes. The stirring speed was 400 rpm. The resulting powder was dried to produce composite particle powder. Details of the materials used are listed below (a) to (d). (a) Thermally conductive particles: Expanded graphite powder: "SYZR 502FP" manufactured by Shijiazhuang Aidite Trading Co., Ltd., particle size 300 μm or more: 80% or more. (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 Cornstarch Co., Ltd. (d) Second insulating inorganic particles: Talc powder: "Micro Ace (registered trademark) K-1" manufactured by Nippon Talc Co., Ltd., median diameter 8 μm.

[0055] <Production of urethane foam molded body> A urethane foam molded body was produced using the produced composite particle powder and the first insulating inorganic particle powder. 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 blowing agent, 1.5 parts by mass of a 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 Dow Corning Toray Co., Ltd., "SZ-1333") were mixed to prepare a polyol raw material. In addition, a diphenylmethane diisocyanate (MDI) modified product was prepared as a polyisocyanate raw material. The MDI-modified product was produced by mixing polyether polyol (same as above) and 4,4'-diphenylmethane diisocyanate ("Millionate MT" manufactured by Tosoh Corporation) so that the isocyanate (NCO) content was 70% by mass, and reacting the mixture at 100°C for 180 minutes under nitrogen purging. Next, 80 parts by mass of composite particle powder and 60 parts by mass of first insulating inorganic particle powder were added to 100 parts by mass of the polyol raw material and mixed to prepare a premix polyol. Subsequently, 100 parts by mass of the premix polyol and 10 parts by mass of the polyisocyanate raw material (MDI-modified product) were mixed to obtain a mixed raw material.

[0056] The powders of the first insulating inorganic particles used were the following six types (A) to (F). Of these, the thermal conductivity of aluminum hydroxide powders (A), (C), and (D) was 8 W / m K, the thermal conductivity of magnesium oxide powder (B) was 45 to 60 W / m K, and the thermal conductivity of aluminum oxide powders (E) and (F) was 20 to 35 W / m K. The median diameter of each powder was measured using a laser diffraction / scattering particle size distribution measuring device (Microtrac MT3000EX-II manufactured by Microtrac-Bell Co., Ltd.). Powders (C) to (E) are included in the concept of "large diameter particles" in the present disclosure. In addition, 2 g of each powder was dispersed in 50 mL of ion-exchanged water at room temperature, and the pH of the dispersion after 5 minutes was measured using a glass electrode pH meter. The pH of aluminum hydroxide powders (A), (C), and (D) was 8, the pH of magnesium oxide powder (B) was 10, and the pH of aluminum oxide powders (E) and (F) was 7. (A) Aluminum hydroxide powder: "B143" manufactured by Nippon Light Metal Co., Ltd., median diameter 2 μm. (B) Magnesium oxide powder: "Pyroxma (registered trademark) 3020" manufactured by Kyowa Chemical Industry Co., Ltd., median diameter 20 μm. (C) Aluminum hydroxide powder: "SB53" manufactured by Nippon Light Metal Co., Ltd., median diameter 55 μm. (D) Aluminum hydroxide powder: "SB93" manufactured by Nippon Light Metal Co., Ltd., median diameter 105 μm. (E) Aluminum oxide powder: ball milled product of "SakuLundum (registered trademark) 40SH" manufactured by Nippon Carlit Co., Ltd., median diameter 200 μm. (F) Aluminum oxide powder: "SakuLundum (registered trademark) 40SH" manufactured by Nippon Carlit Co., Ltd., median diameter 300 μm.

[0057] The mixed raw material was then poured into an aluminum foam mold (cavity: rectangular parallelepiped, 130 mm long x 130 mm wide x 5 mm thick), and the foam mold was sealed. The foam mold was then placed in a magnetic induction foam molding machine to perform foam molding. A uniform magnetic field was formed within the foam mold cavity by approximately parallel magnetic field lines running from top to bottom. The magnetic flux density within the cavity was 200 mT, and the difference in magnetic flux density within the cavity was within ±3%. Foam molding was performed with a magnetic field applied for the first two minutes and without for the following approximately five minutes. After foam molding was completed, the mold was removed to obtain a urethane foam molded body. The resulting urethane foam molded bodies are referred to as urethane foam molded bodies A to F, corresponding to the type of first insulating inorganic particles used. The composite particle content in urethane foam molded bodies A to F was 7.5 vol %, and the first insulating inorganic particle content was 12.5 vol % (in all cases, the volume of the urethane foam molded body is taken as 100 vol %). Urethane foam molded bodies C, D, and E are included in the concept of the urethane foam molded body of the present disclosure.

[0058] <Evaluation of Urethane Foam Molded Articles> The produced urethane foam molded articles were evaluated for thermal conductivity, elongation, heat resistance, and flame retardancy. The evaluation results are summarized in Table 1 below. The evaluation methods are as follows.

[0059] [Thermal Conductivity] The thermal conductivity of the urethane foam molded article was measured using an "HC-110" manufactured by Eiko Seiki Co., Ltd. in accordance with the heat flow meter method of JIS A1412-2:1999.

[0060] [Elongation] Five dumbbell-shaped No. 1 test pieces as specified in JIS K 6251:2017 were prepared from the urethane foam molded products, and a tensile test as specified in JIS was performed on each test piece at a tensile speed of 200 mm / min to calculate the elongation at break (Eb). If the elongation at break of all test pieces was 50% or more, the physical properties at normal state were evaluated as extremely good (indicated by a circle in Table 1 below); if at least one but not all test pieces had an elongation at break of 50% or more, the physical properties at normal state were evaluated as good (indicated by a triangle in the same table); and if the elongation at break of all test pieces was less than 50%, the physical properties at normal state were evaluated as poor (indicated by an x ​​in the same table).

[0061] [Heat Resistance] Dumbbell-shaped No. 1 test pieces were prepared in the same manner as in the previous evaluation of elongation, and were placed in an oven controlled at 150°C for 400 hours. After the test pieces were returned to room temperature, a tensile test was performed under the same conditions as in the previous evaluation of elongation, and the elongation at break (Eb) was calculated. If all test pieces had an elongation at break of 30% or more, the heat resistance was evaluated as very good (indicated by a circle in Table 1 below). If at least one test piece had an elongation at break of 30% or more, the heat resistance was evaluated as good (indicated by a triangle in the same table). If all test pieces had an elongation at break of less than 30%, the heat resistance was evaluated as poor (indicated by an x ​​in the same table).

[0062] [Flame Retardancy] A vertical flame test according to UL94 standards was conducted. In the vertical flame test, a gas burner flame is applied to the bottom of a vertically held sample for 10 seconds. If the burning stops within 30 seconds, the flame is applied for an additional 10 seconds. A sample is rated as V-0 if it meets all of the following five criteria: (1) The sample does not burn for more than 10 seconds in either of the two flame applications. (2) The total burning time for each of the five samples, after two flame applications, does not exceed 50 seconds. (3) None of the samples burn up to the position of the fixing clamp. (4) None of the samples drip burning particles, which ignites the cotton placed below the sample. (5) After the second flame application, the sample does not remain red-hot for more than 30 seconds.

[0063]

[0064] As shown in Table 1, urethane foam moldings C to E contain large-diameter first insulating inorganic particles. Therefore, their physical properties and heat resistance in the normal state were good. The median diameter of the first insulating inorganic particles in urethane foam molding E was larger than in urethane foam moldings C and D. As a result, some cracking occurred, resulting in a slight decrease in their physical properties and heat resistance in the normal state. Furthermore, urethane foam moldings C to E had a high thermal conductivity of 0.7 W / m·K or higher, and their flame retardancy was rated V-0. From the above, it was confirmed that urethane foam moldings C to E satisfied the thermal conductivity, heat resistance, and flame retardancy requirements.

[0065] In contrast, urethane foam molded bodies A and B, which did not contain large-diameter particles as the first insulating inorganic particles and had a median diameter of 20 μm or less, were satisfactory in thermal conductivity, normal state physical properties, and flame retardancy, but were inferior in heat resistance. Also, urethane foam molded body F, which did not contain large-diameter particles as the first insulating inorganic particles and had a median diameter of 300 μm as the first insulating inorganic particles, was satisfactory in thermal conductivity and flame retardancy, but exhibited poor moldability due to the occurrence of cracks, resulting in poor normal state physical properties and heat resistance.

[0066] The urethane foam molded article of the present disclosure is suitable as a soundproofing material used in vehicle parts such as battery covers, electric powertrain (eAxel) covers, seat motor covers, undercovers, floor mats, dash silencers, hood silencers, various ECUs, and junction boxes, as well as in electronic devices such as personal computers.

Claims

1. A urethane foam molded article comprising a base material made of polyurethane foam, composite particles contained in an oriented manner in the base material, and first insulating inorganic particles dispersed in the base material, wherein the composite particles comprise thermally conductive particles and magnetic particles bonded to the surfaces of the thermally conductive particles with a binder, and the first insulating inorganic particles are large-sized particles having a median diameter of 55 μm or more and 200 μm or less.

2. The urethane foam molded product according to claim 1, wherein the content of the first insulating inorganic particles is from 5 volume % to 20 volume % when the volume of the urethane foam molded product is 100 volume %.

3. The urethane foam molded article according to claim 1 or 2, wherein the thermal conductivity of the first insulating inorganic particles is 5 W / m·K or more.

4. A urethane foam molded article according to any one of claims 1 to 3, wherein the first insulating inorganic particles comprise one or more selected from the group consisting of aluminum hydroxide, aluminum oxide, aluminum nitride, magnesium hydroxide, magnesium oxide, talc, calcium carbonate, clay, mica, and silica.

5. The urethane foam molded article according to any one of claims 1 to 4, wherein the large-diameter particles are particles that react with water to become alkaline.

6. A urethane foam molded article according to any one of claims 1 to 5, wherein the thermally conductive particles comprise expanded graphite particles.

7. A urethane foam molded article according to any one of claims 1 to 6, wherein the composite particles have second insulating inorganic particles bonded to the surfaces of the thermally conductive particles with a binder.

8. The urethane foam molded body according to claim 7, wherein the particle diameter of the second insulating inorganic particles is 1 / 10 or less of the particle diameter of the thermally conductive particles, and the median diameter is 1 μm or more and 20 μm or less.

9. The urethane foam molded article according to claim 7 or 8, wherein the second insulating inorganic particles comprise one or more selected from the group consisting of aluminum hydroxide, aluminum oxide, aluminum nitride, magnesium hydroxide, magnesium oxide, talc, calcium carbonate, clay, mica, and silica.

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