WO2021065248A1 - Thermally-conductive filler, thermally-conductive composite material, wire harness, and production method for thermally-conductive filler - Google Patents

Abstract

Provided are: a thermally-conductive filler that has reduced specific gravity and can exhibit high thermal conductivity; a thermally-conductive composite material and a wire harness that contain such a thermally-conductive filler; and a thermally-conductive filler production method capable of producing such a thermally-conductive filler.　This thermally-conductive filler has an organic part containing an organic polymer, and an inorganic layer that contains an inorganic material and that covers the surface of the organic part, and is in the form of particles. In addition, this thermally-conductive composite material contains the thermally-conductive filler and a matrix material, wherein the thermally-conductive filler is dispersed in the matrix material. In addition, this wire harness contains the thermally-conductive composite material.

Description

How to make thermally conductive fillers, thermally conductive composites, wire harnesses, and thermally conductive fillers

The present disclosure relates to thermally conductive fillers, thermally conductive composite materials, wire harnesses, and methods for producing thermally conductive fillers.
Regarding.

Thermally conductive fillers may be added to organic polymer materials for the purpose of improving heat dissipation and minimizing the effects of heat generation due to energization, etc., in the insulating members that make up electrical and electronic components. The thermally conductive filler is often composed of an inorganic compound having high thermal conductivity such as alumina, aluminum nitride, and boron nitride.

In recent years, various electric and electronic parts such as automobile electronics have been increasing in current and integrated, and the amount of heat generated when energized tends to increase. As a means for suppressing the influence of the heat generation, for example, in the case of a wire harness for an automobile, a member such as flattening the electric wire to increase the surface area of the electric wire and efficiently contacting the electric wire with an exterior material having high thermal conductivity. The heat dissipation is being improved by improving the shape and structure of the wire. On the other hand, it is also important to improve the heat dissipation of the material itself that constitutes the insulating member of the electric / electronic component, such as the electric wire coating and the electric wire exterior material.

If a large amount of filler is mixed with an organic polymer material or the like, the thermal conductivity of the material can be improved, but if a large amount of a filler made of an inorganic compound is mixed with the organic polymer material, the specific gravity of the material increases. It becomes difficult to reduce the weight of electrical and electronic components. From the viewpoint of weight reduction of the entire automobile, weight reduction is important for electric and electronic parts for automobiles. Therefore, weight reduction is desired in the material containing the heat conductive filler. As a method for that, attempts have been made to reduce the amount of filler added.

The shape and particle arrangement of the filler have been devised for the purpose of maintaining high thermal conductivity while keeping the amount of filler added small. For example, Patent Document 1 discloses a filler having a void portion inside and having a porosity within a predetermined range. In Patent Document 2, boron nitride particles are dispersed in a resin as a matrix in the state of exfoliated flat particles generated by undergoing an exfoliation step of delaminating secondary particles which are a laminate of primary particles. Organic composite compositions are disclosed. Patent Document 3 discloses a highly thermally conductive composite in which highly thermally conductive fillers having anisotropy in shape are in direct contact with each other to form a network structure in a matrix resin.

JP-A-2019-1849 Japanese Unexamined Patent Publication No. 2012-255055 Japanese Unexamined Patent Publication No. 2010-13580 Japanese Unexamined Patent Publication No. 2012-12257 Japanese Unexamined Patent Publication No. 2015-178543 Japanese Unexamined Patent Publication No. 2015-108058 Japanese Unexamined Patent Publication No. 2003-221453

Inorganic compounds such as alumina, aluminum nitride, and boron nitride exhibit high thermal conductivity, but have a large specific gravity, and when added as a filler to an organic polymer material or the like to form a composite material, the specific gravity of the composite material as a whole. It is difficult to achieve high thermal conductivity while keeping the size small. In particular, a filler made of an oxide such as alumina tends to have a large specific gravity. As described in Patent Documents 1 to 3, the amount of the inorganic compound added can be suppressed to some extent by devising the shape of the filler and the arrangement of the particles, but there is a limit to that. If the specific gravity of the filler itself can be reduced by examining the constituent materials of the filler, it is possible that the composite material to which the filler is added can achieve both weight reduction and high thermal conductivity at a higher level.

Therefore, a thermally conductive filler capable of exhibiting high thermal conductivity while keeping the specific gravity small, a thermally conductive composite material and a wire harness containing such a thermally conductive filler, and such a thermally conductive filler. An object of the present invention is to provide a method for producing a thermally conductive filler capable of producing a filler.

The thermally conductive filler of the present disclosure has an organic portion containing an organic polymer and an inorganic layer containing an inorganic substance that covers the surface of the organic portion, and is in the form of particles.

The thermally conductive composite material of the present disclosure includes the thermally conductive filler and the matrix material, and the thermally conductive filler is dispersed in the matrix material.

The wire harness of the present disclosure includes the heat conductive composite material.

The method for producing a thermally conductive filler of the present disclosure uses a raw material constituting the inorganic layer as it is or through a chemical reaction on the surface of polymer particles containing an organic polymer having an acidic group. The thermally conductive filler is produced by comprising a step of binding the raw material to the acidic group.

The thermally conductive filler according to the present disclosure is a thermally conductive filler capable of exhibiting high thermal conductivity while keeping the specific gravity small. Further, the heat conductive composite material and the wire harness according to the present disclosure include such a heat conductive filler. The method for producing a thermally conductive filler according to the present disclosure can produce such a thermally conductive filler.

FIG. 1 is a schematic view illustrating the structure of the heat conductive filler and the heat conductive composite material according to the embodiment of the present disclosure. FIG. 2 is a side view showing a wire harness according to an embodiment of the present disclosure. FIG. 3A is an SEM image of the cross section of the filler F1 observed. 3B to 3D are EDX element distribution images corresponding to the SEM image of FIG. 3A, where C is shown in FIG. 3B, Al is shown in FIG. 3C, and O is shown in FIG. 3D.

[Explanation of Embodiments of the present disclosure]
First, embodiments of the present disclosure will be listed and described.

The thermally conductive filler according to the present disclosure has an organic portion containing an organic polymer and an inorganic layer containing an inorganic substance that covers the surface of the organic portion, and is in the form of particles.

The above-mentioned heat conductive filler includes not only an inorganic substance but also an organic part containing an organic polymer as a constituent material. In many cases, the organic polymer has a lower specific gravity than the inorganic substance, so that the heat conductive filler contains the organic polymer, so that the specific gravity of the heat conductive filler as a whole is higher than that when the heat conductive filler consists of only the inorganic substance. Becomes smaller. On the other hand, in the particles of the thermally conductive filler, the inorganic layer containing the inorganic substance covers the surface of the organic portion containing the organic polymer, so that the filler particles are the other filler particles or other surrounding filler particles. It can come into contact with the material in the inorganic layer and exhibit high thermal conductivity. As described above, in the heat conductive filler, it is possible to secure high heat conductivity while keeping the specific gravity small.

Here, the organic polymer may have an acidic group. Then, due to the interaction with the acidic group on the surface of the organic part and the chemical reaction, the inorganic substance constituting the inorganic layer or the raw material which becomes the inorganic substance can be easily bonded to the surface of the organic part. As a result, a thermally conductive filler in which the surface of the organic portion is coated with an inorganic layer can be stably and easily formed.

The organic polymer may contain at least one of polyacrylic acid, an acrylic acid copolymer, and a maleic anhydride-modified polymer. These organic polymers have a small specific gravity, and by using them as an organic part, it is easy to keep the specific gravity of the heat conductive filler as a whole small, and in order to stably expose acidic groups on the particle surface, they are combined with the acidic groups on the surface. It is easy to form an inorganic layer on the surface by utilizing the bond by interaction or chemical reaction.

The inorganic substance may contain a metal oxide. Among various inorganic substances, metal oxides exhibit relatively high thermal conductivity and are easily formed in layers on the surface of an organic portion containing an organic polymer. Therefore, it is easy to form a thermally conductive filler having a low specific gravity and excellent thermal conductivity.

The inorganic substance may contain a compound containing at least one of Al and Mg. As for Al and Mg, compounds such as oxides exhibit high thermal conductivity. Further, Al and Mg, such as alkoxide and carbonate, are easily available as raw material compounds that can be bonded to the surface of organic polymer particles to form a stable compound film. Therefore, by forming the inorganic layer as a compound containing Al or Mg, a thermally conductive filler having both low specific gravity and high thermal conductivity can be easily produced.

The specific gravity of only the organic part is R1, the specific gravity of the heat conductive filler as a whole is R2, the specific gravity R of the inorganic layer is R = (R2-R1) / R1, and the specific gravity R of the inorganic layer is 5% or more. It is good to be. Then, the inorganic layer is formed by occupying a sufficient amount with respect to the organic portion, and it becomes easy to secure high thermal conductivity as the whole thermally conductive filler particles.

The specific gravity of only the organic part is R1, the specific gravity of the heat conductive filler as a whole is R2, the specific gravity R of the inorganic layer is R = (R2-R1) / R1, and the specific gravity R of the inorganic layer is 40% or less. It is good to be. Then, it is possible to prevent the effect of improving the thermal conductivity by the inorganic layer from being saturated, and to suppress an increase in the specific gravity of the thermal conductive filler due to the formation of an excessively thick inorganic layer.

The specific gravity R2 of the heat conductive filler as a whole is preferably 1.5 or less. In this case, the low specific gravity of the heat conductive filler can be sufficiently ensured.

The thermally conductive composite material according to the present disclosure includes the thermally conductive filler and the matrix material, and the thermally conductive filler is dispersed in the matrix material.

The heat conductive composite material contains the heat conductive filler having an organic part containing an organic polymer and an inorganic layer containing an inorganic substance covering the surface of the organic part described above. Therefore, it is possible to improve the heat dissipation by utilizing the high thermal conductivity of the thermally conductive filler while keeping the specific gravity of the thermally conductive composite material as a whole small.

Here, the matrix material may be an organic polymer. Most organic polymers have low thermal conductivity, but by mixing the above-mentioned thermally conductive filler having an inorganic layer on the surface, high heat dissipation can be ensured as a whole thermally conductive composite material. On the other hand, many organic polymers have a relatively small specific gravity, but the heat conductive filler to be mixed contains an organic part and the specific gravity is suppressed to be small, so that even when the heat conductive filler is added. , The specific gravity can be kept small.

The heat conductive composite material preferably has a specific gravity of 1.5 or less. In this case, the specific gravity of the thermally conductive composite material as a whole can be suppressed sufficiently small.

The thermally conductive composite material preferably has a thermal conductivity of 1.0 W / (m · K) or more at room temperature. In this case, a sufficiently high thermal conductivity is ensured for the entire thermally conductive composite material.

The wire harness according to the present disclosure includes the heat conductive composite material.

Since the wire harness contains the thermally conductive composite material described above, it is possible to utilize high thermal conductivity while keeping the specific gravity of the constituent members small. Therefore, high heat dissipation can be obtained while keeping the mass of the wire harness as a whole small. Therefore, even if heat is generated by energizing the electric wires constituting the wire harness while maintaining the light weight of the wire harness, the influence of the heat generation can be suppressed to a small value.

The method for producing a thermally conductive filler according to the present disclosure is to use a raw material constituting the inorganic layer as it is or through a chemical reaction on the surface of polymer particles containing an organic polymer having an acidic group. The thermally conductive filler is produced by comprising a step of binding the raw material to the acidic group of the above.

According to the above production method, an inorganic layer containing an inorganic substance is formed on the surface of an organic part containing an organic polymer, and a thermally conductive filler having a small specific gravity and high thermal conductivity can be easily produced. Can be done.

Here, the raw material may be at least one of a metal alkoxide and a metal carbonate. Then, an inorganic layer containing a metal oxide can be formed on the surface of the polymer particles by a simple chemical reaction step, and a thermally conductive filler can be obtained.

[Details of Embodiments of the present disclosure]
Hereinafter, a method for producing a thermally conductive filler, a thermally conductive composite material, a wire harness, and a thermally conductive filler according to the embodiment of the present disclosure will be described in detail with reference to the drawings. The thermally conductive composite material according to the embodiment of the present disclosure is configured by comprising the thermally conductive filler according to the embodiment of the present disclosure. Further, the wire harness according to the embodiment of the present disclosure is configured by including the thermally conductive composite material according to the embodiment of the present disclosure. Further, the production method according to the embodiment of the present disclosure can be used to produce the thermally conductive filler according to the embodiment of the present disclosure.

In this specification, various physical property values shall be measured at room temperature and in the air unless otherwise specified. Further, in the present specification, a certain component is a main component of a certain material means a state in which the component occupies 50% by mass or more with respect to the mass of all the components constituting the material.

<Thermal conductive filler>
First, a thermally conductive filler (hereinafter, may be simply referred to as “filler”) according to an embodiment of the present disclosure will be described. As shown in FIG. 1, the thermally conductive filler 10 according to the embodiment of the present disclosure has an organic portion 11 and an inorganic layer 12, and is in the form of particles. The inorganic layer 12 covers the surface of the organic portion 11.

The specific materials of the organic part 11 and the inorganic layer 12 will be described later, but the organic part 11 contains an organic polymer. On the other hand, the inorganic layer 12 contains an inorganic substance. Many organic polymers have a lower specific gravity than inorganic substances. On the other hand, many inorganic substances have higher thermal conductivity than organic polymers.

Since the thermally conductive filler 10 according to the present embodiment has an organic portion 11 containing an organic polymer having a small specific gravity, the specific gravity as a whole can be reduced as compared with the case where the whole is made of an inorganic substance. On the other hand, the heat conductive filler 10 according to the present embodiment covers the surface of the organic portion 11 and has an inorganic layer 12. The inorganic layer 12 has high thermal conductivity, and the thermal conductivity of the filler 10 as a whole can be enhanced. As shown in FIG. 1, the inorganic layer 12 on the surface of the filler particles 10 comes into contact with the matrix material 2 surrounding the filler particles 10 and the inorganic layer 12 on the surface of the other filler particles 10 to contact the filler particles 10. It contributes to heat conduction between the matrix material 2 and between the filler particles 10. Since the inorganic layer 12 is provided only on the surface of the organic portion 11, the volume of the filler particles 10 as a whole can be secured by the organic portion 11, and the small volume of the inorganic layer 12 can exhibit thermal conductivity. it can. Adjacent filler particles 10 can form a heat conduction path by contacting each other via the surface inorganic layer 12.

From the viewpoint of avoiding an increase in the mass of the filler 10, the specific gravity of the filler 10 as a whole is preferably 1.5 or less, more preferably 1.4 or less, 1.2 or less. On the other hand, from the viewpoint of avoiding that the inorganic layer 12 cannot be formed with a sufficient thickness by suppressing the specific gravity too small, the specific gravity of the filler 10 as a whole is 0.3 or more, preferably 0.6 or more, more preferably 0.6 or more. It should be 0.9 or more. The specific gravity of the filler 10 can be measured as the true density of the powdered filler 10 using, for example, a hydrometer. The specific gravity of the filler 10 as a whole is used as the specific gravity R2 in the formula (1) which will explain the ratio of the inorganic layer 12 later.

Here, the materials and the like constituting the organic part 11 and the inorganic layer 12 will be described. As described above, the organic part 11 contains an organic polymer. Preferably, the organic part 11 contains an organic polymer as a main component. The organic polymer constituting the organic part 11 may be any organic polymer such as various resins, elastomers and rubbers. However, the organic polymer constituting the organic part 11 preferably has an acidic group. Since the organic polymer has an acidic group, as will be described later, when the raw material inorganic compound to be the inorganic layer 12 is bonded to the surface of the polymer particles to be the organic part 11 to form the inorganic layer 12, the organic polymer is formed. This is because it is easy to form a stable inorganic layer 12 by forming a bond between the acidic group of the above and the raw material inorganic compound.

Examples of the acidic group contained in the organic polymer include a carboxylic acid group, a carboxylic acid anhydride group, a sulfonic acid group, and a phosphoric acid group. Of these acidic groups, an organic polymer having a carboxylic acid group is particularly preferable in terms of low specific gravity and availability. As a specific example of the organic polymer having a carboxylic acid group, the organic part 11 preferably contains at least one of polyacrylic acid, an acrylic acid copolymer, and a maleic anhydride-modified polymer. These polymers have a small specific gravity, and when they are made into polymer particles, it is easy to stably expose acidic groups on the surface.

The organic polymer constituting the organic part 11 may be only one kind or a mixture of two or more kinds. As long as the specific gravity of the organic part 11 can be kept smaller than the specific gravity of the inorganic layer 12, that is, as long as the specific gravity of the organic part 11 alone can be kept smaller than the specific gravity of the filler 10 as a whole, the organic part 11 is an organic polymer. In addition, various additives made of organic or inorganic substances such as flame retardant, stabilizer, and antioxidant may be appropriately contained. Further, the organic part 11 may have a layer of a surface treatment agent such as a surfactant as appropriate between the organic part 11 and the inorganic layer 12.

From the viewpoint of suppressing the specific gravity of the filler 10 as a whole, the specific gravity of the organic portion 11 is preferably small, for example, 1.2 or less, preferably 1.0 or less. Although no lower limit is set for the specific gravity of the organic portion 11, the specific gravity of the organic polymer particles is approximately 0.8 or more. The organic portion 11 is in the form of particles, and its particle size (average particle size D50; the same applies hereinafter) is not particularly limited, but is not excessively small with respect to the thickness of the inorganic layer 12. By doing so, the specific gravity of the filler 10 as a whole can be suppressed to a small value, and the thickness is preferably 1 μm or more, more preferably 5 μm or more. On the other hand, the particle size of the organic portion 11 is preferably 100 μm or less, more preferably 50 μm or less, from the viewpoint of suppressing the influence on the characteristics of the matrix material 2 to which the filler 10 is added to be small and increasing the specific surface area. ..

As described above, the inorganic layer 12 contains an inorganic substance. Preferably, the inorganic layer 12 contains an inorganic substance as a main component. The type of the inorganic substance is not particularly limited, and may be either a metal or a non-metal such as an inorganic compound. From the viewpoint of easily forming a stable inorganic layer 12 on the surface of the particles of the organic portion 11, the inorganic layer 12 preferably contains an inorganic compound, particularly a metal compound, as an inorganic substance. Here, it is assumed that the metal elements constituting the metal compound also include metalloids such as B and Si (the same applies hereinafter).

Examples of the metal compound constituting the inorganic layer 12 include oxides containing metal elements, nitrides, carbides, oxynitrides, carbonitrides, carbon oxides, hydroxides, borides, etc., and metal silicates and aluminates. , Titanate and the like can be exemplified. From the viewpoints of excellent thermal conductivity and easy formation of a film-like inorganic layer 12 on the surface of the organic portion 11, the inorganic layer 12 preferably contains a metal oxide among various metal compounds. It is particularly preferable that the inorganic layer 12 contains a metal oxide as a main component. Since the metal oxide tends to have a higher specific gravity than the metal nitride or the metal carbide, the filler 10 is formed as an inorganic layer 12 coexisting with the organic portion 11, so that the effect of reducing the specific gravity by the organic portion 11 can be obtained. You can enjoy it greatly.

The inorganic substance constituting the inorganic layer 12 preferably contains a compound containing at least one of Al and Mg among various metal compounds. In particular, it preferably contains Al. Further, Al and Mg preferably form an oxide. Al and Mg compounds such as oxides exhibit high thermal conductivity, and are in the form of a film that is stably and firmly adhered to the surface of the particulate organic portion 11 by using a commercially available raw material compound. This is because it is easy to form as the inorganic layer 12.

The inorganic substance constituting the inorganic layer 12 may be one kind or a plurality of kinds. Further, when a plurality of inorganic substances are used, the inorganic substances may be mixed, may form a complex, or may be laminated in layers. Further, the inorganic layer 12 may contain not only an inorganic substance but also an organic substance such as various additives and reaction residues. Further, when the matrix material 2 contains an organic polymer, an organic film may be provided on the surface of the inorganic layer 12 from the viewpoint of enhancing the affinity with the matrix material 2. However, from the viewpoint of enhancing the thermal conductivity by direct contact between the inorganic layers 12 between the adjacent filler particles 10, it is preferable not to provide such an organic film. The inorganic layer 12 may cover at least a part of the surface of the organic portion 11, but the contact between the filler particles 10 and the matrix material 2 and between the adjacent filler particles 10 via the inorganic layer 12 From the viewpoint of sufficiently securing the above, it is preferable that the inorganic layer 12 covers at least half of the surface area of the organic portion 11 and the entire surface of the organic portion 11 except for unavoidable defects and the like. ..

The proportion of the inorganic layer 12 in the filler 10 is not particularly limited, but the inorganic layer specific weight ratio R defined by the following formula (1) is preferably 5% or more.
R = (R2-R1) / R1 (1)
Here, R1 refers to the specific gravity of only the organic portion 11, and R2 refers to the specific gravity of the filler 10 as a whole. The larger the specific gravity ratio R of the inorganic layer, the larger the proportion of the region occupied by the inorganic layer 12 in the filler 10. Since the state of the organic part 11 does not substantially change due to the formation of the inorganic layer 12, the specific gravity R1 of the organic part 11 can be replaced by the specific gravity of the polymer particles used in producing the filler 10.

When the specific gravity ratio R of the inorganic layer is 5% or more, the filler 10 has a sufficient volume of the inorganic layer 12, so that the thermal conductivity of the filler 10 as a whole can be sufficiently enhanced. The inorganic layer specific weight ratio R is more preferably 10% or more, more preferably 20% or more. Further, the inorganic layer 12 preferably occupies 9% by mass or more in terms of mass ratio and 3% by volume or more in volume ratio with respect to the entire filler particles 10. The thickness of the inorganic layer 12 preferably occupies 1% or more of the particle size of the filler particles 10 on average.

On the other hand, even if the proportion of the inorganic layer 12 in the filler particles 10 is made too large, the effect of improving the thermal conductivity of the filler 10 is saturated, and the inclusion of the organic portion 11 has the effect of suppressing the specific gravity of the filler particles 10 to a small value. , Become smaller. From the viewpoint of avoiding these phenomena, it is preferable that the specific weight ratio R of the inorganic layer is 50% or less, more preferably 40% or less. Since the region occupied by the inorganic layer 12 in the filler particles 10 is thinner than the particle size of the organic portion 11, the particle size of the filler particles 10 as a whole is not significantly different from the particle size of the organic portion 11 and is 1 μm. Above, more preferably 5 μm or more, 100 μm or less, and further preferably 50 μm or less.

As described above, the thermally conductive filler 10 according to the present embodiment has a double structure in which the inorganic layer 12 is formed on the surface of the organic portion 11, so that the filler is an inorganic substance while maintaining high thermal conductivity. The specific gravity is reduced as compared with the case where only the material is used. Therefore, as in the case of the thermally conductive composite material described later, by combining the composite material with other substances to form the composite material, the thermal conductivity of the composite material is enhanced without significantly increasing the specific gravity of the composite material as a whole. Become.

<Manufacturing method of thermally conductive filler>
Next, a method for producing the thermally conductive filler according to the embodiment of the present disclosure, which can produce the above-mentioned thermally conductive filler 10, will be described. The thermally conductive filler 10 can be produced by carrying out the organic part preparation step and the inorganic layer forming step.

In the organic part preparation step, polymer particles containing an organic polymer, which will be the organic part 11 in the manufactured filler 10, are prepared. As the polymer particles, an organic polymer material having a desired chemical composition may be made into granules having a desired particle size by a chemical method such as liquid phase synthesis or a physical method such as pulverization. Preferably, if an organic polymer having an acidic group is used, the inorganic layer 12 containing the inorganic compound can be easily formed in the next inorganic layer forming step.

Next, in the inorganic layer forming step, the inorganic layer 12 is formed on the surface of the polymer particles. At this time, the inorganic layer 12 is formed by a direct forming method in which the inorganic substance itself constituting the inorganic layer 12 in the produced filler 10 is arranged on the surface of the polymer particles as a raw material, or by appropriately undergoing a chemical reaction. An indirect forming method may be adopted in which the raw material to be the inorganic substance to be used is placed on the surface of the polymer particles. When the direct forming method is adopted, the raw material material arranged on the surface of the polymer particles becomes the inorganic layer 12 as it is. Examples of the direct forming method include thin film deposition and precipitation. On the other hand, when the indirect forming method is adopted, the inorganic layer 12 is formed by arranging the raw material on the surface of the polymer particles and then causing a chemical reaction. As an indirect forming method, a raw material is bonded to the surface of polymer particles by an interaction such as electrostatic interaction (ionic bonding) or through a chemical reaction, and then the raw material is bonded to the bonded raw material. A method of forming the inorganic layer 12 having a desired composition by carrying out a chemical reaction can be mentioned. In particular, when the polymer particles contain an organic polymer having an acidic group and the acidic group is exposed on the surface, it is easy to easily and firmly achieve the binding of the raw material compound through an interaction or a chemical reaction. ..

When the step of forming an inorganic layer is carried out on a polymer particle having an acidic group on its surface through bonding of a raw material compound, first, a constituent material of the polymer particle and an inorganic layer 12 are formed in a dispersion medium (solvent). A raw material solution containing both of the raw material compounds as the inorganic substances to be used may be prepared. In the raw material liquid, the polymer particles may be dispersed or dissolved in the state of solid particles. Further, in the raw material liquid, the raw material compound which is an inorganic substance constituting the inorganic layer needs to be present in a liquid state, and may be in a molten state as well as in a state of being dissolved in a dispersion medium (solvent). Alternatively, it may be in a finely dispersed state. Hereinafter, a form in which the polymer particles are dispersed in the raw material liquid in the state of solid particles and the raw material compound constituting the inorganic layer is dissolved will be described. In this case, the dispersion medium (solvent) constituting the raw material solution is particularly limited as long as it can disperse the polymer particles without dissolving them and dissolve the raw material compound for forming the inorganic layer 12. However, organic solvents such as toluene and tetrahydrofuran (THF), and alcohols such as isobutyl alcohol can be exemplified.

When preparing the raw material liquid, for example, the polymer particles may be first added to the dispersion medium and sufficiently stirred to disperse the polymer particles. Next, the raw material compound to be the inorganic layer 12 may be added to the dispersion liquid of the polymer particles and dissolved by stirring or the like. In this operation, the raw material compound is bonded to the acidic group on the surface of the polymer particles by an interaction such as an electrostatic interaction (ionic bond) or through a chemical reaction. When it is necessary to decompose the raw material compound in order to make the raw material compound bondable to the acidic group of the polymer particles, or to form a bond between the raw material compound and the acidic group of the polymer particles through a chemical reaction. In some cases, if heating or addition of a reactant is required for the decomposition or chemical reaction, these operations may be carried out in combination with stirring as appropriate.

When the raw material compound is bonded to the surface of the polymer particles, the raw material compound may then undergo a chemical reaction to be converted into a desired inorganic substance constituting the inorganic layer 12. At this time, an operation may be performed according to the type of required chemical reaction. For example, in addition to stirring, heating, addition of a reactant, contact with gas molecules such as oxygen, and the like may be performed. It is preferable that the inorganic layer 12 can be easily formed if the conversion from the raw material compound can be completed only by heating, contact with the atmosphere, or both, in addition to stirring.

In the inorganic layer forming step, after forming the inorganic layer 12 on the surface of the organic part 11, the product may be appropriately isolated by filtration or the like. Further, the thermally conductive filler 10 can be obtained by removing the volatile components by performing heat drying or vacuum drying.

As the raw material compound used in the inorganic layer forming step, it is preferable to use a compound capable of forming metal-containing ions in the dispersion liquid of the polymer particles or on the surface of the polymer particles. The specific type of the compound is not particularly limited, and suitable examples of such a raw material compound include metal alkoxides and metal carbonates. When a metal alkoxide is used as the raw material compound, the metal alkoxide may be added to the dispersion liquid of the polymer particles, and the mixture may be stirred while heating. The metal alkoxide hydrolyzes to form a metal hydrate with the generation of alcohol. In particular, the presence of a trace amount of acidic groups on the surface of the polymer particles or in the dispersion medium increases the rate of formation of metal hydrates around them. The resulting metal hydrate forms an ionic bond with the acidic group on the surface of the polymer particles, and in the state of a film, firmly bonds to the surface of the polymer. Then, the reaction solution is appropriately heated and the dispersion medium is dried, so that the heat conductive filler has an inorganic layer 12 containing at least one of a metal hydroxide and a metal oxide after being oxidized by oxygen in the atmosphere. 10 is obtained. In many cases, oxidation in the inorganic layer 12 proceeds to the state of metal oxides. The type of metal alkoxide is not particularly limited, and methoxide, ethoxide, isopropoxide and the like can be exemplified, but aluminum isopropoxide and magnesium ethoxide are used in terms of safety and availability. Cheap.

When a metal carbonate is used as the raw material compound, when the basic carbonate is added to the dispersion liquid of the polymer particles, the metal hydroxide is formed on the surface of the polymer particles and is firmly bonded to the surface of the polymer particles. , Consists of the membrane. Then, as in the case of the above alkoxide, the reaction solution is appropriately heated and the dispersion medium is dried, so that the inorganic layer containing at least one of the metal hydroxide and the metal oxide is oxidized by oxygen in the atmosphere. A thermally conductive filler 10 having 12 is obtained. In many cases, oxidation in the inorganic layer 12 proceeds to the state of metal oxides.

<Thermal conductive composite material>
Next, a thermally conductive composite material (hereinafter, may be simply referred to as a composite material) according to an embodiment of the present disclosure will be described. As shown in FIG. 1, the heat conductive composite material 1 according to the present embodiment includes the heat conductive filler 10 according to the embodiment of the present disclosure described above and the matrix material 2. The filler 10 is dispersed in the matrix material 2.

Since the composite material 1 according to the present embodiment contains the thermally conductive filler 10 having the inorganic layer 12 on the surface of the organic portion 11 described above, the composite material is provided by the high thermal conductivity imparted by the inorganic layer 12. 1 As a whole, it exhibits high thermal conductivity and excellent heat dissipation. At the same time, due to the effect of lowering the specific gravity of the heat conductive filler 10 by the organic portion 11, the specific gravity of the composite material 1 as a whole becomes small.

The type of the matrix material 2 is not particularly limited, but the matrix material 2 preferably contains an organic polymer, and more preferably contains an organic polymer as a main component. The specific organic polymer constituting the matrix material 2 is not particularly limited, and may be the same as or different from the organic polymer constituting the organic portion 11 of the filler 10, but is organic. The part 11 has a limited degree of freedom in selecting a constituent material due to the availability of polymer particles and the possibility of forming the inorganic layer 12, whereas the matrix material 2 is not subject to such restrictions. It is preferable to select a material having desired properties from materials different from the above.

Specific examples of the organic polymer constituting the matrix material 2 include various resins, thermoplastic elastomers, rubber and the like. When a resin material is used as the organic polymer, it may be a curable resin, a thermoplastic resin, or a solvent-soluble plastic, depending on the desired application. Examples of the types of resins constituting the matrix material 2 include polyolefin resins such as polyethylene and polypropylene, polyvinyl chloride, polylactic acid, polystyrene-based resins, polyvinyl acetate, ABS resin, AS resin, acrylic resin, methacrylic resin, and polyamide. Resins, urethane resins, silicone resins, fluororesins, polyvinyl alcohols, polyimides, polyacetals, polycarbonates, modified polyphenylene ethers (PPE), polyethylene terephthalates, polybutylene terephthalates, polyphenylene sulfides, and epoxy resins, or copolymers of these resins. And polymer alloys. The matrix material 2 may contain only one type of organic polymer or may contain a plurality of organic polymers. Further, the matrix material 2 may appropriately contain additives such as a flame retardant, a filler, and a colorant in addition to the organic polymer.

The specific gravity of the matrix material 2 itself is not particularly limited, but it is preferably suppressed to 1.5 or less from the viewpoint of suppressing the specific gravity of the composite material 1 to which the filler 10 is added as a whole. The specific gravity of the matrix material 2 is not particularly limited, but when an organic polymer is used as the matrix material 2, the specific gravity is about 0.8 or more. Further, the thermal conductivity of the matrix material 2 itself is not particularly limited, but 0.1 W / (m · K) from the viewpoint of ensuring high thermal conductivity of the composite material 1 to which the filler 10 is added as a whole. It is preferable to keep the above. The thermal conductivity of the matrix material 2 is not particularly limited, but when an organic polymer is used as the matrix material 2, the thermal conductivity is approximately 0.6 W / (m · K) or less. The specific gravity of the matrix material 2 and the composite material 1 can be measured by a water substitution method or the like. Further, the thermal conductivity of these materials can be measured by a laser flash method, a hot wire method, or the like.

In the composite material 1 according to the present embodiment, the content of the filler 10 may be appropriately determined so that the desired specific gravity and thermal conductivity can be obtained for the composite material 1 as a whole. As the content of the filler 10 increases, the thermal conductivity of the composite material 1 increases. Therefore, the content of the filler 10 may be determined with the content at which the desired thermal conductivity can be obtained as the lower limit. For example, the content of the filler 10 may be determined so that the thermal conductivity of the composite material 1 is 5 times or more, more 6 times or more, the thermal conductivity of the matrix material 2 to which the filler 10 is not added. Alternatively, the content of the filler 10 may be determined so that the thermal conductivity of the composite material 1 is 1.0 W / (m · K) or more, further 1.2 W / (m · K) or more. The higher the thermal conductivity of the composite material 1, the more preferable it is. However, from the viewpoint of avoiding an increase in specific gravity due to excessive addition of the filler 10, the thermal conductivity of the matrix material 2 is 50 times or less, further 30 times or less. In addition, it is preferable to keep it at 8.0 W / (m · K) or less, and further at 5.0 W / (m · K) or less.

On the other hand, in the composite material 1, when the specific gravity of the composite material 1 as a whole increases as the content of the filler 10 increases, the upper limit of the content of the filler 10 is suppressed to a desired range. It may be determined as the content to be obtained. For example, the content of the filler 10 may be determined so that the specific gravity of the composite material 1 can be suppressed to 1.3 times or less, further 1.2 times or less, the specific gravity of the matrix material 2 to which the filler 10 is not added. Alternatively, the content of the filler 10 may be determined so that the specific gravity value of the composite material 1 can be suppressed to 1.5 or less, further 1.4 or less. The smaller the specific gravity of the composite material 1, the more preferable it is, and the lower limit is not particularly set.

When the content of the filler 10 is defined by the ratio of the filler 10 to the entire composite material 1, the content of the filler 10 is generally 40 from the viewpoint of sufficiently improving the thermal conductivity of the composite material 1. The volume may be% or more. On the other hand, from the viewpoint of suppressing an increase in the specific gravity of the composite material 1, it may be 60% by volume or less. Further, as shown in FIG. 1, the content of the filler 10 is preferably selected so that the inorganic layers 12 of the adjacent filler particles 10 come into contact with each other to form a heat conduction path.

As described above, the composite material 1 according to the present embodiment has both high thermal conductivity and low specific gravity. Therefore, the composite material 1 can be suitably used as a material for constituting a member that is required to have both light weight and heat dissipation, such as a wire harness described below. The composite material 1 according to the present embodiment can be produced by mixing the powdery filler 10 produced by the production method described above with the matrix material 2 at a predetermined blending ratio.

<Wire harness>
Finally, the wire harness according to the embodiment of the present disclosure will be described. The wire harness according to the present embodiment includes the heat conductive composite material 1 according to the embodiment of the present disclosure described above. As shown in FIG. 2, the wire harness 5 is provided with a connector 52 including a connection terminal (not shown) at the terminal portion of the insulated wire 51 having an insulating coating on the outer periphery of the wire conductor. In the wire harness 5, a plurality of insulated wires 51 may be bundled, and in this case, the tape 53 is used as an exterior material for bundling the insulated wires 51.

In the wire harness 5 according to the present embodiment, the composite material 1 according to the embodiment of the present disclosure described above can constitute various members that are required to have heat dissipation. Mainly, it is preferable to use the composite material 1 in which the filler 10 is added to the organic polymer as the matrix material 2 as the insulating member. As such an insulating member, an insulating coating constituting the insulated wire 51, an exterior material such as a tape 53 or a protective tube arranged outside the insulated wire 51, and an adhesive used for fixing or stopping water between the constituent members. , The connector housing and the like constituting the connector 52 can be exemplified.

In recent years, in the automobile field, especially in electric vehicles and hybrid vehicles, the current flowing through the electric wire tends to increase, and the amount of heat generated from the electric wire tends to increase accordingly. In addition, a large number of electric wires and electrical connection members are being arranged in close proximity to each other. In these cases, it is important that the various members constituting the wire harness 5 have high heat dissipation from the viewpoint of minimizing the influence of heat dissipation from the electric wires and the electrical connection members. In the wire harness 5, by forming such a member that may be affected by heat dissipation by using the composite material 1 having high thermal conductivity, it is possible to efficiently dissipate heat. Further, in the field of automobiles, weight reduction of constituent members is an important issue, and by using the composite material 1 having a small specific gravity, it is possible to contribute to weight reduction of the wire harness 5.

Examples are shown below. The present invention is not limited to these examples. Hereinafter, unless otherwise specified, samples are prepared and evaluated in the air at room temperature.

[1] Structure and characteristics of filler First, the structure of the filler according to the embodiment of the present disclosure was confirmed, and what kind of specific gravity and thermal conductivity could be obtained in the composite material to which the filler was added was confirmed.

[Test method]
(1) Preparation of filler First, three types of fillers, F1 to F3, were synthesized by changing the type of resin constituting the organic part. Hereinafter, a method for synthesizing each filler will be described.

・ Filler F1
5 g of polyacrylic acid particles (average molecular weight 1,000,000; manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were suspended in 100 mL of toluene. While stirring the suspension, 10 g of aluminum isopropoxide (manufactured by Tokyo Chemical Industry Co., Ltd.) was added, and the suspension was heated to 110 ° C. and stirred under reflux. Further, while continuing the heating / reflux stirring, 10 mL of pure water was added, and the heating / reflux stirring was continued for 40 hours. Then, the reaction solution was returned to room temperature and filtered, and the obtained solid component was dried at 100 ° C. for 48 hours to obtain filler F1. The average particle size of the polyacrylic acid particles used was 40 μm.

・ Filler F2
5 g of a freeze-milled product of carboxylic acid-modified polypropylene (PP) (“Polybond 1001” manufactured by Adivant Co., Ltd.) was suspended in 100 mL of isobutyl alcohol. While stirring the suspension, 10 g of aluminum isopropoxide (manufactured by Tokyo Chemical Industry Co., Ltd.) was added, and the suspension was heated to 110 ° C. and stirred under reflux. Further, while continuing the heating / reflux stirring, 10 mL of pure water was added, and the heating / reflux stirring was continued for 40 hours. Then, the reaction solution was returned to room temperature and filtered, and the obtained solid component was dried at 100 ° C. for 48 hours to obtain filler F2. The average particle size of the carboxylic acid-modified PP pulverized product used was 35 μm.

・ Filler F3
5 g of maleic anhydride-modified SEBS (MAH-SEBS; "Tuftec M1911" manufactured by Asahi Kasei Corporation) was dissolved in 200 mL of THF, and 10 g of aluminum isopropoxide (manufactured by Tokyo Kasei Kogyo Co., Ltd.) was added with stirring. The solution was heated to 80 ° C. and refluxed and stirred for 2 hours. Further, 20 mL of pure water was added to the reaction solution to make it emulsion, and then the mixture was heated to 100 ° C. while continuing stirring to distill off THF. After that, heating under reflux stirring at 110 ° C. was continued for 40 hours. The obtained reaction solution was returned to room temperature and filtered, and the solid component was dried at 100 ° C. for 48 hours to obtain filler F3. After undergoing a series of reactions, MAH-SEBS was in the form of particles having an average particle size of 40 μm.

In addition to the fillers F1 to F3, the following three types of fillers were prepared for reference.
-PAA: Polyacrylic acid particles (average molecular weight 1,000,000; manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)-Same as used for the synthesis of filler F1-CA-PP: Carboxylic acid-modified PP (manufactured by Adivant Co., Ltd.) Polybond 1001 ”) freeze-crushed product-the same as used for the synthesis of filler F2 ・ Alumina: Showa Denko Co., Ltd. Rounded alumina for filling (1-80 μm diameter; average particle size 40 μm)

(2) Preparation of Composite Material Each filler prepared above was dispersed in a matrix material to prepare a composite material for Samples A1 to A3 and Samples B1 to B5. Here, the matrix material constituting the composite material was a cured product of the following two-component epoxy resin.
-Epoxy main agent: glycidyl ether of bisphenol A ("jER828" manufactured by Mitsubishi Chemical Corporation; epoxy equivalent: 190 g / eq.)
-Epoxy curing agent: amine type (Mitsubishi Chemical Corporation "ST12"; amine value: 345 to 385 KOHmg / g)

Various fillers, epoxy main agent, and epoxy curing agent were mixed in an agate mortar at room temperature at the mass ratio shown in Table 2 below, and defoamed for 1 minute under normal temperature vacuum. Then, the mixture was heated by a hot press molding machine at 100 ° C. for 10 minutes to be cured. A resin cured product test piece (10 mm × 10 mm × 1 mm) was prepared by cutting out a portion of the cured product in which no bubbles were visually confirmed. The amount of the filler added shown in Table 2 was set so that the blending amount per volume was 50% by volume (31% by volume only for sample B5) based on the specific gravity measured as shown below. Is. For sample B1, a cured resin test piece was prepared from only the epoxy resin without adding a filler.

(3) Evaluation of filler structure The structures of fillers F1 to F3 were evaluated by observing them with a scanning electron microscope (SEM). Specifically, the filler particles were embedded in a resin and cut, and the cross section was observed by SEM. In addition to SEM observation, measurement by energy dispersive X-ray analysis (EDX) was also performed to evaluate the distribution of C and Al in the cross section.

Furthermore, the specific gravity (true density) of each filler was measured using an electronic hydrometer (manufactured by Alpha Mirage). The specific gravities of the polymer particles and alumina fillers constituting each filler were measured in the same manner.

(4) Evaluation of characteristics of composite material The density and thermal conductivity of each of the cured resin test pieces prepared above were measured. Density was measured by the underwater substitution method. The thermal conductivity was measured by a laser flash method using a heat conductive device (“LFA447” manufactured by NETZSCH).

[Test results]
(Filler structure)
FIG. 3A shows an SEM observation image (secondary electron image) of the cross section of the filler F1. The brighter the part, the larger the amount of secondary electrons detected, indicating that the charge is large. Further, FIGS. 3B to 3D show distribution images of C, Al, and O obtained by EDX measurement corresponding to the SEM observation of FIG. 3A, respectively. The brighter the area, the higher the concentration of each element. The filler on which the image is posted has a diameter of about 40 μm.

According to the SEM image of FIG. 3A, a layered region observed relatively dark is observed on the surface of the granular portion observed brightly. The thickness of the layer is about 2 μm, which corresponds to about 5% of the particle size of the resin particles. The brightly observed granular portion has a large charge and can be associated with a portion derived from the polymer particles which are organic substances. On the other hand, the layered portion has a small charge and is considered to be composed of an inorganic substance.

Furthermore, looking at the distribution image of C (carbon) in FIG. 3B, the density is high in the granular portion observed by SEM, and the density is considerably low in the layered portion on the surface. On the other hand, looking at the distribution image of Al (aluminum) in FIG. 3C, high-density Al is observed in the layered portion on the surface, whereas Al is hardly detected in the granular portion inside. Further, looking at the distribution image of O (oxygen) in FIG. 3D, in general, a large amount of O is distributed in the place where a large amount of Al is distributed in FIG. 3C.

From these observation results, the granular part inside can be associated with the organic part derived from the polymer particles. On the other hand, the layered portion of the surface can be associated with an inorganic layer composed of Al oxide (or hydroxide) formed from aluminum propoxide as a raw material. Further, it can be seen that the organic portion is substantially not affected by the formation of the inorganic layer such as the invasion of the Al compound. From the above, it was confirmed that the filler was formed as a granular material having a double structure in which the surface of the organic portion was coated with an inorganic layer. Although the results are omitted, the same double structure was observed for the fillers F2 and F3.

Next, for each filler, Table 1 shows the measurement results of the specific gravity of the entire filler and the polymer particles constituting the filler. The inorganic layer specific gravity ratio R calculated by the formula (1) based on those specific gravities is also shown in the table.

According to Table 1, in each of the fillers F1 to F3, the specific gravity is increased as compared with the case where only the polymer particles are used, because the inorganic layer is formed on the surface of the organic portion composed of the polymer particles. However, the specific gravity of each of these fillers is 1.5 or less, which is considerably smaller than the specific gravity of the alumina filler of 4.0. As described above, the specific gravity of the filler as a whole can be significantly reduced by forming the filler into a double structure in which the inorganic substances are layered on the surface of the organic portion instead of being composed of only the inorganic substances.

(Characteristics of composite material)
Table 2 shows the specific gravity and thermal conductivity of the composite materials for Samples A1 to A3 and Samples B1 to B5, along with the blending ratio (unit: mass%) of the filler and matrix material and the blending amount (unit: volume%) of the filler. Summarize the measurement results of the rate.

According to Table 2, in sample B4 to which 50% by volume of alumina filler, which is generally used as a thermally conductive filler, is added, the thermal conductivity is significantly improved as compared with sample B1 to which no filler is added. However, the specific gravity is more than doubled. In sample B5, even if the amount of filler added is reduced to 31% by volume, which is less than 1.0 W / (m · K) in thermal conductivity, the specific gravity is still about 1.7 times that of sample B1. .. As described above, if only an inorganic substance is used as the filler, the specific gravity of the composite material becomes large.

On the other hand, in the samples B2 and B3, the polymer particles themselves are added to the matrix material, and no increase in specific gravity is observed as compared with the sample B1. However, unlike the aluminum compound, it does not contain an inorganic substance exhibiting high thermal conductivity, so that the thermal conductivity shows a low value that is almost the same as that of sample B1. As described above, the polymer particles themselves cannot be used as a thermally conductive filler.

Unlike the samples B2 to B5, in the samples A1 to A3 in which the fillers F1 to F3 having a double structure of an organic part and an inorganic layer were added to the matrix material, even though the filler was added in an amount of 50% by volume. However, the specific gravity of the composite material to which the filler is added is suppressed to 1.5 or less. The rate of increase from the specific gravity of sample B1 to which no filler is added is 25% or less. In particular, in the samples A2 and A3, the specific gravity is rather lowered by adding the filler in response to the fact that the filler has a smaller specific gravity than the matrix material.

And, in each of the samples A1 to A3, the thermal conductivity is 1.0 W / (m · K) or more. These values correspond to 5 times or more the thermal conductivity of the sample B1 to which the filler is not added. From this result, in the samples A1 to A3 using the fillers F1 to F3 having the inorganic layer formed on the surface of the organic part, the filler contains the organic part having a low specific gravity, so that the entire composite material to which the filler is added is added. As a result, it can be seen that high thermal conductivity can be obtained while keeping the specific gravity small.

[2] Relationship between Amount and Characteristics of Inorganic Layer Next, in the filler according to the embodiment of the present disclosure, when the ratio occupied by the inorganic layer is changed, what are the characteristics of the filler itself and the composite material to which the filler is added? I investigated how it would change.

[Test method]
(1) Preparation of sample Fillers F1-1 to F1-7 were synthesized in the same manner as in which the filler F1 was synthesized in the above test [1]. However, in the synthesis of each filler, the amount of aluminum isopropoxide added to 5 g of polyacrylic acid as a raw material was changed as shown in Table 3. The filler F1-3 is the same as the filler F1 synthesized in the test [1].

Each of the obtained fillers was added to the epoxy resin to prepare a composite material for Samples C1 to C7. The preparation of the composite material and the preparation of the cured resin test piece were carried out in the same manner as in the test [1]. The amount of the filler added was such that the blending amount per volume was 50% by volume.

(2) Characteristic evaluation The specific gravity of each filler was measured in the same manner as in the test [1]. In addition, the specific gravity and thermal conductivity of each cured resin test piece were measured.

[Test results]
Table 3 shows the measurement results of the specific gravity and thermal conductivity of the samples C1 to C7 to which each filler was added, along with the compounding ratio (unit: mass%) of each component and the compounding amount (unit: volume%) of the filler. The left column shows the specific gravity and the specific gravity ratio R of the inorganic layer, as well as the amount of aluminum isopropoxide used in the synthesis for each filler. The specific gravity ratio R of the inorganic layer is calculated by setting the specific gravity of the organic part to 1.20, which is the value of PAA.

First, according to the left column of Table 3, in the fillers F1-1 to F1 to 7, the larger the amount of aluminum isopropoxide used at the time of synthesis, the higher the specific gravity of the filler, and accordingly, the higher the specific gravity of the inorganic layer. It has become. From this, the thickness of the inorganic layer formed on the surface of the polymer particles can be controlled by the concentration of the raw material compound of the inorganic layer used at the time of filler synthesis, and the higher the concentration of the raw material compound, the thicker the inorganic layer is formed. You can see that. Assuming that all the aluminum propoxides used in the filler F1-1 are alumina (Al ₂ O ₃ ) to form an inorganic layer, the ratio of the inorganic layer to the filler is 9% by mass in terms of mass ratio and volume ratio. Is estimated to be 3% by mass. The thickness of the inorganic layer with respect to the particle size of the polymer particles is estimated to be about 1%.

According to Table 3, in the samples C1 to C7 to which the fillers F1-1 to F1-7 were added, the greater the specific gravity of the inorganic layer of the added filler, the greater the specific gravity of the composite material as a whole. Regarding the thermal conductivity, in the region where the specific weight of the inorganic layer of the filler is relatively small, the higher the specific weight of the inorganic layer of the added filler, the higher the thermal conductivity tends to be. In sample C1 using the filler having the smallest inorganic layer specific gravity, the thermal conductivity was 0.18 W / (m · K), which is the value when no filler was added (see sample B1 in Table 2). However, when the inorganic layer specific gravity ratio of the filler is 5% or more in the samples C2 to C7, the thermal conductivity is greatly improved and exceeds 1.0 W / (m · K). ..

However, when the specific gravity of the inorganic layer of the filler is increased to more than 40% as in the samples C5 to C7, the improvement in thermal conductivity is saturated. That is, even if the specific gravity of the inorganic layer of the filler is increased and the proportion of the inorganic layer in the filler is increased too much, the thermal conductivity cannot be improved efficiently, but the specific gravity of the filler and the composite material is large. Become.

From the above results, it can be said that the inorganic layer specific gravity of the filler is preferably in the range of 5% or more and 40% or less from the viewpoint of achieving both improvement of thermal conductivity and reduction of specific gravity. As shown in Table 1, the inorganic layer specific weight ratio R of the fillers F2 and F3 is also within the range of 5% or more and 40% or less.

[3] Relationship between the amount of filler added and its properties Finally, the relationship between the amount of filler added in the composite material and its properties was investigated.

[Test method]
(1) Preparation of sample The filler F1 prepared in the above test [1] was added to the epoxy resin to prepare a composite material for samples D1 to D7. The preparation of the composite material and the preparation of the cured resin test piece were carried out in the same manner as in the test [1]. However, in each sample, the amount of filler added was changed as shown in Table 4. The sample D6 in which the blending amount of the filler is 50% by volume is the same as that of the sample A1 in Table 2.

(2) Characteristic evaluation In the same manner as in the test [1], the specific gravity and thermal conductivity of each cured resin test piece were measured.

[Test results]
Table 4 shows the measurement results of specific gravity and thermal conductivity together with the compounding ratio (unit: mass%) of each component and the compounding amount (unit: volume%) of the filler for each sample.

According to Table 4, the larger the amount of filler blended, the higher the thermal conductivity. Moreover, the larger the filler compounding amount, the larger the increase in thermal conductivity with respect to the increase in the filler compounding amount. This behavior is similar to the behavior of the thermal conductivity when the blending amount is increased for a filler made of a conventional general inorganic compound. From this result, even in the filler according to the embodiment of the present disclosure in which an inorganic layer is formed on the surface of the organic portion, the adjacent fillers come into contact with each other in the matrix material as in the case of the filler made of a conventional general inorganic compound. It can be seen that the improvement of the thermal conductivity is achieved by the mechanism that the heat conduction path is formed in.

According to the results in Table 4, from the viewpoint of improving the thermal conductivity of the composite material to 1.0 W / (m · K) or more, it can be said that the blending amount of the filler is preferably 40% by volume or more. On the other hand, the specific gravity of the composite material is suppressed to 1.5 or less even if the compounding amount of the filler is 70% by volume, but if it is desired to further suppress the specific gravity to 1.3 or less, the compounding amount of the filler is 60. The volume may be% or less.

Although the embodiments of the present disclosure have been described in detail above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention.

1 (heat conductivity) Composite material 10 (heat conductivity) Filler 11 Organic part 12 Inorganic layer 2 Matrix material 5 Wire harness 51 Insulated wire 52 Connector 53 Tape

Claims (15)

1. The organic part containing the organic polymer and
   It has an inorganic layer containing an inorganic substance that covers the surface of the organic portion, and has.
   A thermally conductive filler in the form of particles.
2. The heat conductive filler according to claim 1, wherein the organic polymer has an acidic group.
3. The thermally conductive filler according to claim 1 or 2, wherein the organic polymer contains at least one of polyacrylic acid, an acrylic acid copolymer, and a maleic anhydride-modified polymer.
4. The thermally conductive filler according to any one of claims 1 to 3, wherein the inorganic substance contains a metal oxide.
5. The thermally conductive filler according to any one of claims 1 to 4, wherein the inorganic substance contains a compound containing at least one of Al and Mg.
6. The specific gravity of only the organic part is R1, the specific gravity of the heat conductive filler as a whole is R2, and the specific gravity of the inorganic layer R is R = (R2-R1) / R1.
   The heat conductive filler according to any one of claims 1 to 5, wherein the inorganic layer specific weight R is 5% or more.
7. The specific gravity of only the organic part is R1, the specific gravity of the heat conductive filler as a whole is R2, and the specific gravity of the inorganic layer R is R = (R2-R1) / R1.
   The heat conductive filler according to any one of claims 1 to 6, wherein the inorganic layer specific weight R is 40% or less.
8. The heat conductive filler according to any one of claims 1 to 7, wherein the specific gravity R2 of the heat conductive filler as a whole is 1.5 or less.
9. The thermally conductive filler according to any one of claims 1 to 8 and a matrix material are included.
   A thermally conductive composite material in which the thermally conductive filler is dispersed in the matrix material.
10. The heat conductive composite material according to claim 9, wherein the matrix material is an organic polymer.
11. The thermally conductive composite material according to claim 9 or 10, wherein the specific gravity is 1.5 or less.
12. The heat conductive composite material according to any one of claims 9 to 11, wherein the heat conductivity at room temperature is 1.0 W / (m · K) or more.
13. A wire harness comprising the thermally conductive composite material according to any one of claims 9 to 12.
14. Using the raw material that constitutes the inorganic layer as it is or through a chemical reaction,
    A step of binding the raw material to the acidic group on the surface of the polymer particles containing the organic polymer having an acidic group is included.
    A method for producing a thermally conductive filler according to any one of claims 1 to 8.
15. The method for producing a thermally conductive filler according to claim 14, wherein the raw material is at least one of a metal alkoxide and a metal carbonate.
    
    

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