Insulating composition

Abstract

[Problem] To provide an insulating composition that contains hollow silica particles and can form a coating film with excellent mechanical characteristics, electrical characteristics (low relative permittivity, low dissipation factor, etc.), insulating properties, and the like, and to provide a base material comprising the coating film. [Solution] An insulating composition containing a resin and 5-70 vol% of hollow silica particles, wherein the hollow silica particles have a secondary particle median diameter (D50) of 0.2-10 μm and a specific gravity of at least 0.3 g / cm3 and less than 1.00 g / cm3, and the specific gravity of the hollow silica particles is less than the specific gravity of the resin.

Description

Insulating composition

[0001] The present invention relates to an insulating composition containing hollow silica particles.

[0002] In recent years, to cope with the miniaturization of electronic devices, the increasing speed of signals, and the increasing density of wiring, there has been a demand for high-performance insulating layers (low dielectric constant, low dielectric loss tangent, low thermal expansion, etc.) used as materials for insulating resin sheets such as adhesive films and prepregs, printed circuit boards for communication equipment, and wire coating layers. Various studies using hollow particles as fillers have been conducted. Patent Document 1 proposes a resin composition containing specific hollow silica particles with low true density as a material for multilayer printed circuit boards, wire coatings, semiconductor encapsulants, etc. Patent Document 2 proposes a resin composition for encapsulation containing epoxy resin, a curing agent, silica filler, and specific hollow silica particles. Patent Document 3 proposes a resin composition for wire coating containing multiple voids formed by hollow fillers dispersed in an insulating resin matrix. Patent Document 4 proposes a resin composition for wires in which a predetermined amount of specific hollow glass particles are dispersed in a polymer binder having a sea-island structure. Patent Document 5 proposes a filler containing mineral oil, a specific block copolymer, petroleum wax, hollow glass microspheres, and a thixotrope agent in specific proportions as a resin composition for communication cables such as electronic cables.

[0003] International Publication No. 2024 / 085219, Japanese Patent Publication No. 2023-127421, Japanese Patent Publication No. 2020-053302, Japanese Patent Publication No. 2010-129387, Japanese Patent Publication No. 2007-510034

[0004] However, when attempting to improve electrical properties (such as relative permittivity and low dielectric loss tangent) by increasing the content of hollow particles in a resin composition containing hollow particles, the dispersibility of the constituent components tends to decrease, and the effect is not fully obtained. The inventors have found that this tendency becomes more pronounced when increasing the void space of the hollow particles to lower the specific gravity and enhance the effect. In particular, when coating a resin composition containing such hollow particles onto a substrate with a curved surface to form a film, the hollow particles become easily damaged, and there is even a tendency for the desired article not to be obtained. In other words, in a resin composition containing hollow particles, it is necessary to consider the affinity and uniform dispersibility of the constituent components, and to ensure the uniformity of the resulting molded product such as a film, while imparting physical properties such as electrical properties (such as relative permittivity and low dielectric loss tangent) and insulating properties based on the hollow particles. The inventors have found that by balancing the specific gravity of the hollow particles and the resin in a predetermined relationship and setting the particle size of the hollow particles within a predetermined range, the dispersion state of the hollow particles in the composition can be improved, and the above-mentioned tendency can be eliminated. We discovered that such compositions can form an insulating layer (insulating film) with excellent mechanical properties, electrical properties (low dielectric constant, low dielectric loss tangent, etc.), and other characteristics, leading to the present invention. The object of the present invention is to provide an insulating composition containing hollow silica particles that can form a film with excellent mechanical properties, electrical properties (low dielectric constant, low dielectric loss tangent, etc.), and insulating properties, and a substrate equipped with said film.

[0005] The present invention has the following aspects: [1] It contains 5 to 70 volume percent of hollow silica particles and a resin, wherein the hollow silica particles have a median diameter (D50) of secondary particles of 0.2 to 10 μm and a specific gravity of 0.3 g / cm³. ３ 1.00g / cm or more ３ An insulating composition wherein the specific gravity of the hollow silica particles is less than the specific gravity of the resin. [2] The specific gravity of the hollow silica particles is 0.4 to 0.8 g / cm³. ３[1] The insulating composition. [3] The insulating composition of [1] or [2], wherein the median diameter (D50) of the secondary particles of the hollow silica particles is 0.5 to 5 μm. [4] The insulating composition of any one of [1] to [3], wherein the average primary particle diameter of the hollow silica particles is 50 nm to 10 μm. [5] The BET specific surface area of ​​the hollow silica particles is 1 to 100 m². ２ An insulating composition of any of [1] to [4], wherein the amount of SiO in the hollow silica particles. [6] ２ An insulating composition according to any of [1] to [5], having a content of 99% by mass or more and a Na content of less than 1000 ppm by mass. [7] The specific gravity of the resin is 1.0 g / cm³. ３ Super 2.4g / cm ３ An insulating composition according to any of [1] to [6] below. [8] An insulating composition according to any of [1] to [7] wherein the softening temperature of the resin is 120°C or more and 320°C or less. [9] An insulating composition according to any of [1] to [8] wherein the resin is at least one selected from the group consisting of polyimide, polyamideimide, polyolefin-based thermoplastic resin, olefin-based elastomer, styrene-based elastomer, fluororesin, epoxy resin, and silicone resin.

[10] An insulating composition according to any of [1] to [9] wherein the specific gravity of the hollow silica particles relative to the specific gravity of the resin is 0.25 to 0.75.

[11] An insulating composition according to any of [1] to

[10] containing 20 volume% or more of the hollow silica particles.

[12] An insulating composition according to any of [1] to

[11] wherein the ratio of the volume% of the resin to the volume% of the hollow silica particles is 1.0 or more and 1.5 or less.

[13] An insulating composition from any of [1] to

[12] , further containing a liquid dispersion medium.

[14] An insulating composition from any of [1] to

[13] , used to form a coating on the outer periphery of a substrate.

[15] A substrate having a coating formed on its outer periphery made of an insulating composition from any of [1] to

[14] .

[0006] According to the present invention, an insulating composition can be provided that contains hollow silica particles and can form a coating (film) with excellent mechanical properties, electrical properties (low dielectric constant, low dielectric loss tangent, etc.), and insulating properties.

[0007] The present invention contains 5 to 70% by volume of hollow silica particles and a resin. The median diameter (D50) of the secondary particles of the hollow silica particles is 0.2 to 10 μm, and the specific gravity is 0.3 g / cm ３ or more and less than 1.00 g / cm ３ and the specific gravity of the hollow silica particles is smaller than that of the resin. It is an insulating composition (hereinafter also referred to as "this composition").

[0008] From this composition, a film containing hollow silica particles and excellent in mechanical properties, electrical properties (low relative permittivity, low dielectric loss tangent, etc.), insulation properties, etc. can be formed. A substrate provided with such a film can be effectively used for various applications taking advantage of such properties. In particular, a linear substrate provided with such a film on its outer periphery can be effectively used as an electric wire coated with an insulating coating material. The reason why a film excellent in mechanical properties, electrical properties (low relative permittivity, low dielectric loss tangent, etc.), insulation properties, etc. can be formed from this composition is not necessarily clear, but it is considered as follows.

[0009] The homogeneity of a resin composition containing hollow silica particles, particularly a resin composition containing a predetermined amount of hollow silica particles, tends to depend on the physical properties and shape of the hollow silica particles in addition to the chemical interaction between silica and the resin. The inventors focused on the relationship between the specific gravity of the hollow silica particles and the median diameter (D50) of their secondary particles, and found that the effect of suppressing aggregation accompanying particle sedimentation obtained by making the former smaller than the specific gravity of the resin and the effect of improving the interaction with the resin obtained by setting the latter within a predetermined range are balanced. At the same time, by setting both within a predetermined range, the strength of the hollow silica particles themselves is also ensured, and when the composition is applied to a substrate layer to form a film, it is found that the effect of suppressing the breakage of the hollow silica particles is obtained. Therefore, it is considered that a dense film highly equipped with properties based on hollow silica particles is obtained from this composition.

[0010] The hollow silica particles in this composition have a shell layer (solid film) containing silica, and have a space inside the shell layer. The presence of a space inside the shell layer of a hollow silica particle can be confirmed by transmission electron microscopy (TEM) or scanning electron microscopy (SEM) observation. In the case of SEM observation, the hollowness can be confirmed by observing a broken particle with a partial opening. Spherical particles with a space inside, which can be confirmed by TEM or SEM observation, are defined as "primary particles." Note that, due to the firing and drying processes during manufacturing, the primary particles are partially bonded together, so hollow silica particles are often aggregates of secondary particles formed by the aggregation of primary particles. Furthermore, "having a space inside the shell layer" means that when observing the cross-section of a single primary particle, the shell layer surrounds a single space, resulting in a hollow state. In other words, one hollow particle has one large space and a shell layer surrounding it. When hollow silica particles have a structure in which there is space within the shell, more space can be secured in the composition containing the particles, and the dielectric constant can be lowered, making them suitable for use as insulating layers in electronic devices and as coatings for electric wires.

[0011] The specific gravity of hollow silica particles is 0.3 g / cm³. ３ 1.00g / cm or more ３ Less than 0.4-0.8 g / cm³ ３ It is more preferable that this is the case. In this specification, the "specific gravity" of hollow silica particles refers to the density of the particles determined by density measurement using a dry pycnometer with argon gas (hereinafter also referred to as "Ar density"). When the Ar density is within the above range, not only is the above-described mechanism of action more likely to occur, but the dielectric constant of the film formed from this composition is also easier to reduce.

[0012] Furthermore, the density of hollow silica particles, as determined by density measurement using a dry pycnometer with helium gas (hereinafter also referred to as He density), is 2.00 to 2.35 g / cm³. ３This is preferable. Since helium gas permeates through fine voids, the He density can also be positioned as the density corresponding to the true density of the silica portion of silica particles that have internal space. When the He density is within the above range, the amount of silanol remaining in the hollow silica particles decreases, making it easier to reduce the dielectric loss tangent.

[0013] The specific gravity (Ar density) of hollow silica particles can be adjusted by adjusting the primary particle size and shell thickness. When this composition contains a liquid dispersion medium described later, it is more preferable that the specific gravity (Ar density) of the hollow silica particles be close to that of the liquid dispersion medium, from the viewpoint of improving dispersibility. In a sample of hollow silica particles, the proportion of completely hollow particles in which the shell layer is not damaged and which have an internal space (hollow particle ratio) is such that the apparent density of the hollow silica sample decreases as the hollow particle ratio increases, and increases as the hollow particle ratio decreases. Using this, assuming a yield of 100%, the hollow particle ratio can be determined from the theoretical density obtained from the amount of raw material charged and the apparent density measured with a dry pycnometer. In this case, the hollow particle ratio is preferably 90% or more, and more preferably 95% or more. In this case, the hollow particle ratio is preferably 100% or less.

[0014] Furthermore, the hollow particle ratio can also be determined from the weight change during heat treatment using the filtration cake before the oil core is removed when manufacturing hollow silica particles. When the filtration cake is loosened and dried overnight, the oil components in the broken particles volatilize, while the oil components in the complete hollow particles are retained. The weight change during heat treatment can be calculated from the amount of raw material used for cases where all the added oil components volatilize (0% hollow particle ratio) and cases where all of them are retained (100% hollow particle ratio). Therefore, the hollow particle ratio can be determined from the weight change when the sample, dried overnight after filtration, is heat-treated to 800°C. In this case, a hollow particle ratio of 90% or more is preferable, and 95% or more is more preferable. In this case, a hollow particle ratio of 100% or less is preferable.

[0015] The BET specific surface area of ​​hollow silica particles is 1 to 100 m². ２ It is preferable that the amount is / g, and 1 to 50m ２ / g is more preferable. When the BET specific surface area is within the above range, not only is the above-described mechanism of action more easily expressed, but the dispersibility of hollow silica particles in the composition is particularly easily improved, and the viscosity increase of the composition is easily suppressed. The BET specific surface area can be measured using a specific surface area measuring device (such as Shimadzu Corporation's "Tristar II 3020"), after drying the hollow silica particles at 230°C until they reach 50 mTorr, and then measuring them using a multi-point method with nitrogen gas.

[0016] Furthermore, the specific gravity (Ar density) of hollow silica particles is A (g / cm³). ３ Let BET be the specific surface area (m²). ２ If we assume ( / g), the product of the two (A × B) is between 1 and 120 m ２ / cm ３ It is preferable that A x B is 80 m ２ / cm ３ The following is more preferable: 40m ２ / cm ３ The following is even more preferable: A x B is 2m ２ / cm ３ The above is more preferable, 2.5m ２ / cm ３ The above is even more preferable. A × B can also be considered as the specific surface area per unit volume when hollow silica particles are dispersed in a solvent. For example, when hollow silica particles are added to a resin, it represents the specific surface area of ​​the portion of a predetermined volume in the resin occupied by the hollow silica particles. When A × B is within the above range, not only is the above-described mechanism of action more easily manifested, but because the specific surface area of ​​the hollow silica particles in the composition is small, it is also easier to suppress the increase in viscosity of the composition when the composition contains a solvent described later. Furthermore, when A × B is within the above range, when the composition is used as an insulating layer, it is easier to lower the relative permittivity and dielectric loss tangent of the insulating layer and improve its electrical properties.

[0017] The sphericity of hollow silica particles is preferably between 0.75 and 1.0. When the sphericity is within this range, the hollow silica particles are less likely to break, it is easier to maintain the Ar density and specific surface area, and it is easier to lower the dielectric loss tangent. Sphericity is expressed as the average value obtained by measuring the maximum diameter (DL) and the minimum diameter (DS) perpendicular to it for any 100 particles in an image obtained by a scanning electron microscope (SEM), and calculating the ratio of the minimum diameter (DS) to the maximum diameter (DL) (DS / DL).

[0018] The average size of the primary particles of hollow silica particles (average primary particle diameter) is preferably in the range of 50 nm to 10 μm. More preferably, the average primary particle diameter is 70 nm or more, and even more preferably 100 nm or more. More preferably, the average primary particle diameter is 5 μm or less, and even more preferably 3 μm or less. When the average primary particle diameter of hollow silica particles is within the above range, they are easy to handle and it is easy to control the specific surface area, oil absorption, pore volume, and amount of SiOH on the particle surface. The average primary particle diameter of hollow silica particles is determined by measuring the size of any 100 primary particles from SEM observation images and taking the average of these values. The average primary particle diameter can also be considered to reflect the surface state of the secondary particles (aggregated particles) of the hollow silica particles and is a parameter that determines the specific surface area and oil absorption.

[0019] The hollow silica particles have the average primary particle diameter described above, preferably 35% or more of the total primary particles have a particle diameter within ±40% of the average primary particle diameter, more preferably 50% or more of the total primary particles have a particle diameter within ±40% of the average primary particle diameter, and even more preferably 70% or more of the total primary particles have a particle diameter within ±40% of the average primary particle diameter. In this case, the size of the hollow silica particles becomes more uniform, and shell defects of the hollow silica particles are less likely to occur.

[0020] The median diameter (D50) of the secondary particles (aggregated particles) of the hollow silica particles is 0.2 to 10 μm, preferably 0.5 to 5 μm. Such D50 is more preferably 0.6 μm or more, and even more preferably 0.7 μm or more. Such D50 is more preferably 4 μm or less, and even more preferably 3 μm or less. When such D50 is within the above range, not only is the above-described mechanism of action more likely to be expressed, but when the composition contains the solvent described below, its dispersion stability is likely to be improved, and the increase in the viscosity of the composition is also likely to be suppressed. Also, it is easy to reduce the graininess in the film formed from the composition.

[0021] Also, the coarse particle diameter (D90) of the secondary particles of the hollow silica particles is preferably 1 to 30 μm. Such D90 is more preferably 3 μm or more, and even more preferably 5 μm or more. Such D90 is more preferably 25 μm or less, and even more preferably 20 μm or less. When such D90 is within the above range, it is easy to enhance the productivity of the hollow silica particles, and it is also easy to reduce the graininess in the film formed from the composition. The particle diameter of the secondary particles of the hollow silica particles (the aggregation diameter at the time of aggregation of the primary particles) is determined by the laser diffraction / scattering method. That is, the particle size distribution is measured by the laser diffraction / scattering method, the cumulative curve is obtained with the total volume of the particle population as 100%, and the particle diameter at the point where the cumulative volume is 50% on the cumulative curve is D50, and the particle diameter at the point where the cumulative volume is 90% is D90.

[0022] The shell thickness of the hollow silica particles is preferably 0.01 to 0.3 when the diameter of the primary particle is 1, more preferably 0.02 or more, and even more preferably 0.03 or more. Also, the shell thickness of the hollow silica particles is more preferably 0.2 or less, and even more preferably 0.1 or less when the diameter of the primary particle is 1. When the shell thickness with respect to the diameter of the primary particle is within the above range, it is easy to maintain the strength of the hollow silica particles and easy to exhibit the characteristics based on the hollow shape. The shell thickness is determined by measuring the shell thickness of each particle by a transmission electron microscope (TEM).

[0023] In the hollow silica particles, SiO ２The content is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 99% by mass or more. SiO in hollow silica particles ２ The content may be 100% by mass, and is preferably 99.99% by mass or less. Here, SiO in hollow silica particles ２ The content refers to the amount of silica (SiO₂) contained in the shell layer that makes up the hollow silica particles. ２ This is the content of SiO in hollow silica particles, for example, "SiO in hollow silica particles" ２ "Having a content of 99% by mass or more" means that 99% by mass or more of the shell layer constituting the hollow silica particles is silica (SiO₂ ２ This means that it contains ). Residues in hollow silica particles include alkali metal oxides and silicates, alkaline earth metal oxides and silicates, carbon, etc. In other words, hollow silica particles may contain one or more metals M selected from the group consisting of Li, Na, K, Rb, Cs, Mg, Ca, Sr, and Ba. When metal M is included in hollow silica particles, it acts as a flux during firing, which reduces the specific surface area and tends to lower the dielectric loss tangent.

[0024] Metal M is incorporated into the hollow silica particles between the reaction step and the washing step during the manufacturing process. For example, metal M can be incorporated into the hollow silica particles by adding a metal salt of metal M to the reaction solution used to form the silica shell during the reaction step, or by washing the hollow silica precursor with a solution containing metal ions of metal M before firing. In the hollow silica particles of this composition, the concentration of metal M is preferably 50 ppm by mass or more and 1% by mass or less, more preferably 100 ppm by mass or more, even more preferably 150 ppm or more, and also preferably 1% by mass or less, more preferably 5000 ppm by mass or less, and even more preferably 1000 ppm by mass or less. When the total concentration of metal M is within the above range, the flux effect during firing promotes the condensation of bonded silanol groups, reducing the number of remaining silanol groups and thus lowering the dielectric loss tangent.

[0025] In the hollow silica particles in the present composition, the metal M is at least Na, and the Na content is preferably less than 1000 mass ppm. In other words, in the present composition, the SiO ２ content in the hollow silica particles is 99 mass% or more, and the Na content is particularly preferably less than 1000 mass ppm. In this case, not only is the above-described mechanism of action more likely to be exhibited, but the hollow silica particles are excellently balanced in their electrical properties and strength, and even when the present composition is applied to a substrate having a curved surface, cracking of the hollow silica particles is easily suppressed. The composition of the shell layer of the hollow silica particles can be measured by ICP emission spectrometry, flame atomic absorption spectrometry, or the like.

[0026] The hollow silica particles are preferably obtained by a production method including, for example, preparing an oil-in-water emulsion in which an oil phase is dispersed in water, which contains an aqueous phase, an oil phase, and a surfactant, and obtaining a hollow silica precursor in which a shell layer containing silica is formed on the outer periphery of the core in this oil-in-water emulsion, removing the core from this precursor, and performing heat treatment. Specifically, it is preferably produced by the method described in International Publication No. 2023 / 100676. When an alkali metal silicate is used as the silica raw material for forming the shell layer, the carbon (C) component derived from the raw material in the shell layer of the obtained hollow silica particles is less than when a silicon alkoxide is used as the silica raw material.

[0027] From the viewpoint of suppressing the adsorption of moisture and not deteriorating the dielectric loss of the film formed from the present composition, the pore volume of the hollow silica particles is preferably 0.2 cm ３ / g or less. The pore volume is determined by the BJH method based on the nitrogen adsorption method using a specific surface area and pore size distribution measuring device (for example, "BELSORP-miniIII" manufactured by Microtrac BEL Corporation, "TriStar II" manufactured by Micromeritics, etc.).

[0028] The surface of the hollow silica particles may be treated with a silane coupling agent. In this case, the amount of silane coupling agent attached is preferably in the range of 1 to 10 parts by mass per 100 parts by mass of hollow silica particles. When the surface of the hollow silica particles is treated with a silane coupling agent, the amount of remaining surface silanol groups is reduced, the surface becomes hydrophobic, moisture adsorption is suppressed and dielectric loss can be improved, and the affinity with the resin in this composition is increased, making it easier to disperse and improving the strength of the film formed from this composition. Examples of silane coupling agents include aminosilane coupling agents, epoxysilane coupling agents, mercaptosilane coupling agents, silane coupling agents, organosilazane compounds, etc. These may be used individually or in combination of two or more. The treatment of the surface of the hollow silica particles with a silane coupling agent can be confirmed by detecting peaks due to substituents of the silane coupling agent using IR. The amount of silane coupling agent attached can be measured by the amount of carbon.

[0029] The relative permittivity of hollow silica particles at 1 GHz is preferably 1.0 to 5.0, and more preferably 1.3 to 3.5. Furthermore, the dielectric loss tangent of hollow silica particles at 1 GHz is preferably 0.0001 to 0.05. The relative permittivity and dielectric loss tangent can be measured, for example, using a Keycom "Vector Network Analyzer E5063A" by the perturbation resonator method.

[0030] In this composition, the resin is selected such that the specific gravity of the hollow silica particles in the composition is less than the specific gravity of the resin in the composition. More specifically, the specific gravity of the hollow silica particles relative to the specific gravity of the resin is less than 1, and it is more preferable that the specific gravity of the hollow silica particles relative to the specific gravity of the resin is 0.25 to 0.75. The specific gravity of the resin in this composition is 1.0 g / cm³. ３ Super 2.4g / cm ３ Preferably, the specific gravity of the resin is 1.1 g / cm³. ３ Preferably, the amount is 1.2 g / cm³. ３ It is more preferable that the above conditions are met. Furthermore, the specific gravity of the resin should be 2.0 g / cm³. ３Preferably, it is 1.7 g / cm³. ３ It is more preferable that the following conditions are met: If the specific gravity of the hollow silica particles relative to the specific gravity of the resin, or the specific gravity of the resin itself, is within the aforementioned range, not only is the above-described mechanism of action more easily manifested, but the dispersibility of the hollow silica particles in the resin in the composition is improved, and the properties based on the hollow silica particles are more easily exhibited in the coating obtained from the composition.

[0031] The softening temperature of the resin is preferably between 120°C and 320°C, and more preferably between 125°C and 300°C. In this case, not only is the above-described mechanism of action more easily expressed, but the peeling of hollow silica particles when forming a film from this composition is also more easily suppressed. The softening temperature of fluororesin is the temperature corresponding to the maximum value of the melting peak of the resin measured by differential scanning calorimetry, the softening temperature of polyimide is the temperature measured in accordance with JIS C32166-6, the softening temperature of silicone resin is the temperature measured by the penetration method in thermomechanical analysis, and the softening temperature of epoxy resin is the temperature measured by the ring-sphere method of JIS-K-7234.

[0032] Examples of resins used in this composition include polyamides; polyamide-imides; polyimides; thermoplastic engineering plastics such as polyetherimides, polyetheretherketones, and polyethersulfones; polyolefin-based thermoplastic resins such as random copolymers or block copolymers of ethylene / propylene; olefin-based rubbers such as diene rubbers and ethylene-α-olefin-diene copolymers; olefin-based elastomers such as ethylene-octene copolymers; styrene-based elastomers such as styrene-ethylene / butylene (SEB), styrene-ethylene / propylene (SEP), styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS), styrene-ethylene / butylene-styrene (SEBS), and styrene-ethylene / propylene-styrene (SEPS); fluororesins such as tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymers (PFA), tetrafluoroethylene-hexafluoropropylene copolymers (FEP), and tetrafluoroethylene-ethylene copolymers (ETFE); epoxy resins; and silicone resins. These may be used individually or in combination of two or more types.

[0033] In particular, from the viewpoint of enhancing the effects of this composition, the resin itself is preferably at least one selected from the group consisting of polyimide, polyamide-imide, polyolefin-based thermoplastic resin, olefin-based elastomer, styrene-based elastomer, fluororesin, epoxy resin, and silicone resin, and more preferably at least one selected from the group consisting of polyimide, fluororesin, epoxy resin, and silicone resin.

[0034] The content of hollow silica particles in this composition is preferably 20% by volume or more, and more preferably 25% by volume or more. The content of hollow silica particles is preferably 60% by volume or less, and more preferably 50% by volume or less. Furthermore, in this composition, the ratio of the volume percentage of resin to the volume percentage of hollow silica particles is preferably 1.0 or more and 1.5 or less. When this ratio is within the above range, not only is the above-mentioned mechanism of action more easily expressed, but the hollow silica particles and resin in this composition are more easily dispersed, and the properties based on the hollow silica particles are more easily exhibited in the resulting molded product such as a coating (film).

[0035] This composition may further contain a liquid dispersion medium. The liquid dispersion medium that this composition may contain is a compound that is liquid at 25°C under atmospheric pressure, and is preferably a compound with a boiling point of 50 to 240°C. One type of liquid dispersion medium may be used, or two or more types may be used. When two or more liquid dispersion media are used, it is preferable that the two or more liquid dispersion media are mutually compatible. Examples of liquid dispersion media include non-polar solvents such as aliphatic hydrocarbons such as cyclohexane and aromatic hydrocarbons such as toluene; and polar solvents such as water, alcohols, ethers, amides, ketones, and esters.

[0036] Examples of amides include N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-dimethylpropanamide, 3-methoxy-N,N-dimethylpropanamide, 3-butoxy-N,N-dimethylpropanamide, N,N-diethylformamide, hexamethylphosphoric triamide, and 1,3-dimethyl-2-imidazolidinone. Examples of ketones include acetone, methyl ethyl ketone, methyl isopropyl ketone, methyl isobutyl ketone, methyl n-pentyl ketone, methyl isopentyl ketone, 2-heptanone, cyclopentanone, cyclohexanone, and cycloheptanone. Examples of esters include methyl acetate, ethyl acetate, butyl acetate, methyl lactate, ethyl lactate, methyl pyruvate, ethyl pyruvate, methyl methoxypropionate, ethyl ethoxypropionate, ethyl 3-ethoxypropionate, γ-butyrolactone, and γ-valerolactone.

[0037] If the composition further contains a liquid dispersion medium, its content is preferably 5% by mass or more, and more preferably 10% by mass or more. The content of the liquid dispersion medium is preferably less than 40% by mass, and more preferably 30% by mass or less. Furthermore, the content of the liquid dispersion medium in the composition is preferably 10 to 100% by mass relative to the content of hollow silica particles.

[0038] This composition may further contain additives such as inorganic fillers, surfactants, thixotropic agents, viscosity modifiers, defoamers, dehydrators, plasticizers, weathering agents, antioxidants, heat stabilizers, lubricants, antistatic agents, whitening agents, colorants, conductive agents, mold release agents, and flame retardants, to the extent that they do not impair the effects of the present invention.

[0039] This composition is obtained by mixing hollow silica particles, a resin, and, if necessary, a liquid dispersion medium and additives. This composition may be obtained by mixing the hollow silica particles and the resin all at once, or by mixing them in multiple stages. When mixing, it is preferable to mix in such a way that the total mass of the hollow silica particles, the resin, and the liquid dispersion medium added as needed does not change substantially, and mixing in a closed system is preferable. As a result, each component is uniformly mixed, and a highly degassed composition is obtained.

[0040] Examples of mixing apparatus for obtaining this composition include stirring devices equipped with blades such as Henschel mixers, pressure kneaders, Banbury mixers, and planetary mixers; grinding devices equipped with media such as ball mills, attritors, basket mills, sand mills, sand grinders, Dino mills, disper mats, SC mills, spike mills, and agitator mills; and dispersion devices equipped with other mechanisms such as microfluidizers, nanomizers, ultimateizers, ultrasonic homogenizers, desolvers, dispersers, high-speed impellers, thin-film swirling high-speed mixers, rotational and revolving agitators, and V-type mixers. The mixing method may be either batch or continuous.

[0041] The viscosity of this composition is preferably 10 mPa·s or higher, and more preferably 100 mPa·s or higher. In this case, the viscosity of the composition is preferably 10,000 mPa·s or lower, and more preferably 5,000 mPa·s or lower. In this case, not only is the above-described mechanism of action more easily expressed, but the composition has less foaming, excellent coating properties, and easily forms a dense film. Furthermore, in the film formed from such a composition, the physical properties based on hollow silica particles are more easily expressed.

[0042] The thixotropy of this composition is preferably 1.0 to 5.0. In this case, the composition exhibits excellent coating properties and homogeneity, and easily forms a dense film. The viscosity or thixotropy of this composition may be adjusted by further adding a liquid dispersion medium. The viscosity of this composition is determined by measuring the composition using a B-type viscometer under conditions of 25°C and a rotation speed of 30 rpm. The thixotropy of this composition is the viscosity η of the composition measured under conditions of a rotation speed of 30 rpm.１ The viscosity η measured under the condition of a rotational speed of 60 rpm ２ It can be calculated by dividing by .

[0043] This composition can be suitably used to form a coating on the surface of a substrate. More preferably, this composition can be used to form a coating on the outer periphery of a substrate. In other words, a coating with excellent mechanical properties, electrical properties, and insulating properties can be formed on the outer periphery of a substrate based on the effects of this composition, thereby imparting these properties to the substrate. Furthermore, the coating of this composition, when used as a coating for motor coils, can not only lower the dielectric constant and improve voltage durability, but also improve the durability and lifespan of the motor coil against voltage because its dielectric constant does not change during buckling.

[0044] The base material is preferably a wire base material. Examples of wire base materials include linear metal base materials such as copper, nickel, aluminum, titanium, and their alloys. The shape of the base material can also be planar, curved, or uneven. This composition can form a coating on the surface of a curved base material that is highly uniform and does not damage the hollow silica particles. Among these, linear base materials are preferred, and linear metal base materials, in other words, the aforementioned wire base materials, are more preferred. When the base material is a metal wire such as a copper wire, the linear metal base material with a coating of this composition formed on its outer circumference can be manufactured as a wound product, which is also preferable from the viewpoint of improving productivity. The ten-point average roughness of the surface of the base material is preferably 0.01 to 0.05 μm.

[0045] This composition can form a coating on the surface or outer periphery of a substrate by applying known methods. For example, by coating the surface or outer periphery of a substrate with this composition to form a coating layer made of this composition on the surface or outer periphery of the substrate, and then heating the substrate having the coating layer, a coating can be formed on the surface or outer periphery of the substrate.

[0046] Methods for applying the composition to the surface or outer periphery of a substrate include coating, droplet dispensing, and immersion. Heating the substrate having the coating layer can be done, for example, by heating it to a temperature above the resin's softening temperature to form a film. Depending on the type of resin in the composition, the film may be further heated as needed to strengthen the resin structure within the film.

[0047] The heating methods described above include using an oven, using a forced-air drying oven, and irradiating with heat rays such as infrared rays. The heat source in the apparatus may be a contact type heat source (hot air, hot plate, etc.) or a non-contact type heat source (infrared rays, etc.). Heating may be carried out under normal pressure (atmospheric pressure) or under reduced pressure. The atmosphere during heating may be an air atmosphere or an inert gas atmosphere (helium gas, neon gas, argon gas, nitrogen gas, etc.).

[0048] The thickness of the film formed from this composition is preferably in the range of 10 μm to 1000 μm. When the film thickness is within this range, the effects of the electrical properties, insulation, etc., based on this composition are more easily achieved. The relative permittivity of the film formed from this composition is preferably 3.8 or less, more preferably 3.4 or less, and even more preferably less than 3 at a frequency of 10 GHz. The relative permittivity is preferably 1.5 or more. Furthermore, the dielectric loss tangent of the film formed from this composition is preferably 0.01 or less, and more preferably 0.008 or less at a frequency of 10 GHz. When the relative permittivity and dielectric loss tangent of the film at a frequency of 10 GHz are within the above range, the electrical properties are excellent, and transmission loss in the circuit is easily suppressed. The relative permittivity and dielectric loss tangent can be measured using a split-post dielectric resonator (SPDR, for example, manufactured by Agilent Technologies).

[0049] The average linear expansion coefficient of the coating formed from this composition is preferably 10 to 80 ppm / °C. When the average linear expansion coefficient is within this range, it is close to the thermal expansion coefficient of copper wire, a typical linear substrate, and tends to have excellent electrical properties. The average linear expansion coefficient can be determined by using a thermomechanical analyzer (for example, Shimadzu Corporation's "TMA-60") to heat the coating with a load of 5 N and a heating rate of 2 °C / min, and measuring the dimensional change from 30 °C to 150 °C. The thermal conductivity of the coating formed from this composition is preferably 1 W / m·K or higher, and more preferably 3 W / m·K or higher. Note that the thermal conductivity of the coating refers to the thermal conductivity in the in-plane direction of the coating.

[0050] The partial discharge initiation voltage of the coating formed from this composition is preferably 30 kV / mm or higher, more preferably 35 kV / mm or higher, and even more preferably 40 kV / mm or higher. The partial discharge initiation voltage is preferably 100 kV / mm or lower. When the partial discharge initiation voltage is within the above range, the coating formed from this composition exhibits excellent insulation properties and can be suitably used as a wire coating material. The partial discharge initiation voltage can be measured by the method described in the examples later. The tensile breaking strength of the coating formed from this composition is preferably 30 to 100 N / mm or higher. When the tensile breaking strength is within the above range, the coating formed from this composition can be suitably used, particularly as a wire coating material. The tensile breaking strength can be measured in accordance with ASTM D638.

[0051] Suitable examples of this substrate include a linear metal substrate (wire substrate) and a wire having a coating (insulating layer) made of this composition on the outer circumference of the metal substrate.

[0052] The present invention also relates to a substrate (hereinafter also referred to as "the substrate") having a coating made of the present composition formed on its outer circumference. In the substrate, a linear metal substrate (wire substrate) is more preferable. Details of the metal substrate and the shape of the substrate are the same as described above. The preferred ranges for the thickness of the coating, relative permittivity, dielectric loss tangent, thermal conductivity, coefficient of linear expansion, partial discharge initiation voltage, and tensile breaking strength of the coating on the substrate are the same as the preferred ranges for the thickness of the coating, relative permittivity, dielectric loss tangent, thermal conductivity, coefficient of linear expansion, partial discharge initiation voltage, and tensile breaking strength of the coating formed from the present composition as described above.

[0053] This composition and substrate are useful as wire coatings (for antennas, aircraft wires, flat wires, FFC (Flexible Flat Cable), etc.), enamel wire coatings used in motors for electric vehicles, etc., and coatings for power generation.

[0054] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. 1. Preparation of each component [Hollow silica particles] Production example 1 (1) 4 g of ethylene oxide (hereinafter also referred to as "EO")-propylene oxide (hereinafter also referred to as "PO")-EO block copolymer (ADEKA Corporation's "Pluronic F68") was dissolved in 1250 g of pure water to make an aqueous solution. 42 g of n-decane in which 4 g of sorbitanic acid monooleate (Sanyo Chemical Industries' "Ionet S-80") was dissolved was added and the mixture was stirred with a homogenizer until the entire liquid was homogenized. Then, it was emulsified at a pressure of 50 bar using a high-pressure emulsifier (SMT Corporation's "LAB1000"), and left to stand at 40°C for 12 hours to obtain an emulsion with an emulsion diameter of 1 μm.

[0055] (2) Add 23 g of sodium silicate aqueous solution 1 (SiO₂) to 1300 g of the emulsion obtained in (1) above. ２ Concentration 10.4% by mass, Na ２ 3.6% by mass of oxygen and 2M hydrochloric acid were added to the reaction mixture so that the pH became 2, and the mixture was stirred while maintaining the internal temperature at 30°C. A 1M aqueous sodium hydroxide solution was gradually added dropwise to this mixture so that the pH became 6, and after the dropwise addition was complete, the mixture was held in place to obtain an oil core-silica shell particle dispersion.

[0056] (3) The entire amount of the oil core-silica shell particle dispersion obtained in (2) above was heated to 70°C, and a 1 M sodium hydroxide aqueous solution was gradually added while stirring to adjust the pH to 9. Next, 330 g of sodium silicate aqueous solution 1 and 0.5 M hydrochloric acid were gradually added to maintain the pH of the mixture at 9, and the suspension after the addition was held at 80°C for 24 hours and then cooled to 25°C. 2 M hydrochloric acid was added to the entire obtained suspension to adjust the pH to 2, and then the solid was recovered by filtration with quantitative filter paper 5C. After washing this solid with 350 ml of ion-exchanged water at 80°C, it was dried at 100°C for 1 hour under a nitrogen atmosphere, then the temperature was raised to 400°C at a rate of 10°C / min and it was dried at 400°C for 2 hours, and then the temperature was raised to 1000°C at a rate of 10°C / min and it was calcined at 1000°C for 1 hour to obtain hollow silica calcined particles 1.

[0057] (4) 0.1 g of N-phenyl-3-aminopropyltrimethoxysilane and 50 mL of N-methylpyrrolidone (NMP) were mixed with 10 g of the obtained hollow silica calcined particles 1 (corresponding to 7 vol% hollow silica calcined particles 1 and 93 vol% NMP). The mixture was stirred at 30 rpm for 2 hours using a mix rotor, and then stirred for another 10 minutes using an ultrasonic homogenizer. The obtained slurry was filtered, and the recovered material was dried under reduced pressure at 200°C for 3 hours to obtain hollow silica particles 1.

[0058] Production Example 2 In Production Example 1 (1), the amount of EO-PO-EO block copolymer used was changed from 4 g to 2 g, and the amount of sorbitanic acid monooleate used was changed from 4 g to 2 g. In Production Example 1 (3), the amount of sodium silicate aqueous solution 1 added was changed from 330 g to 220 g. The same procedure as in Production Example 1 was performed to obtain hollow silica particles 2.

[0059] Production Example 3 Hollow silica particles 3 were obtained by performing the same procedure as in Production Example 1, except that the amount of sodium silicate aqueous solution 1 added was changed from 330 g to 480 g in Production Example 1 (3). Production Example 4 Hollow silica particles 4 were obtained by performing the same procedure as in Production Example 1, except that the amount of sodium silicate aqueous solution 1 added was changed from 330 g to 540 g in Production Example 1 (3). Production Example 5 Hollow silica particles 5 were obtained by performing the same procedure as in Production Example 1, except that step (4) in Production Example 1 was omitted and 1 g of the obtained hollow silica calcined particles was pulverized for 2 seconds on setting 2 using a Wonder Blender (Osaka Chemical Co., Ltd. "WB-1"), except that the procedure was performed as in Production Example 1.

[0060] Manufacturing Example 6: In Manufacturing Example 1, step (4) was omitted, and 1 g of the resulting hollow silica calcined particles was used as hollow silica particles 6.

[0061] [Particles other than hollow silica particles] Particle C1: Solid silica particles, "SC4050" manufactured by Admatex Corporation Particle C2: Hollow aluminosilicate particles obtained in accordance with the method of Example 1 of Japanese Patent Application Publication No. 2021-143089

[0062] The median diameter (D50), specific gravity, BET specific surface area, and Na content of each particle were determined as follows. The results are shown in Table 1. <Median Diameter (D50)> The obtained hollow silica particles (secondary particles) were measured using a diffraction scattering particle distribution analyzer (MT3300) manufactured by Microtrac-Bell, and the median value (median diameter, D50) of the particle distribution (diameter) was measured. The measurement was performed twice, and the average value was calculated.

[0063] <Specific Gravity> The Ar density of the particles was measured using a dry pycnometer (AccuPycII 1340, Micromeritics) under the following measurement conditions: • Sample cell: 10 cm ３Cell / sample mass: 1.0 g Measurement gas: Argon Number of purges: 10 Purge filling pressure: 135 kPag Number of cycles: 10 Cycle filling pressure: 135 kPag Rate to complete pressure equilibrium: 0.05 kPag / min <Specific surface area> The obtained particles were dried under reduced pressure at 230°C to completely remove moisture and were used as a sample. The specific surface area of ​​this sample was measured using the multi-point BET method with nitrogen gas using the Micromeritic "Tristar II" automatic specific surface area and pore distribution analyzer. <Na content> Perchloric acid and hydrofluoric acid were added to the obtained particles and strongly heated to remove the main component silicon. Then, the Na content was measured using ICP-AES (Inductively Coupled Plasma Emission Spectroscopy) with an ICPE-9000 (Shimadzu Corporation).

[0064]

[0065] [Resin] The resins shown in Table 2 below were used.

[0066] 2. Examples of Composition and Film Production [Example 1] In a pot, 50 parts by mass of resin 1 as the resin solid content and parts by mass of hollow silica particles 1 in an amount equal to 30 volume percent of the resin solid content were added, and alumina balls with a diameter of 20 mm were added and mixed at 30 rpm for 12 hours to obtain insulating composition 1. The obtained insulating composition 1 was applied to the release-treated surface of a release-treated polyethylene terephthalate (PET) film (Lintec Corporation's "PET5011 550", thickness 50 μm) using an applicator, dried in a gear oven at 100°C for 10 minutes, the release PET film was removed to obtain a self-supporting film, and then heated at 150°C for 1 hour to cure it to obtain a film 1 with a thickness of 100 μm.

[0067] [Examples 2 to 6] The same procedure as in Example 1 was performed except that the type and volume percentage of hollow silica particles were changed as shown in Table 2, to obtain insulating compositions 2 to 6 and films 2 to 6 with a thickness of 100 μm.

[0068] [Example 7] In a pot, 50 parts by mass of resin 2 and 30% by mass of hollow silica particles 1 were placed, and alumina balls with a diameter of 20 mm were added and mixed at 30 rpm for 12 hours. After removing the alumina balls, an insulating composition 7 was obtained as a mixed powder. The obtained insulating composition 7 was placed in a 100 μm spacer, heated and pressed at 250°C for 5 minutes, and then cooled and pressed for 5 minutes to obtain a film 7 with a thickness of 120 μm.

[0069] [Example 8] An insulating composition 8 was obtained as a mixed powder by the same procedure as in Example 7, except that resin 3 was used instead of resin 2. The obtained insulating composition 8 was placed in a 100 μm spacer, heated and pressed at 350°C for 5 minutes, and then cooled and pressed for 5 minutes to obtain a film 8 with a thickness of 120 μm.

[0070] [Example 9] 33 parts by mass of resin 4, 16 parts by mass of curing agent (Showa Denko Materials "MHAC-P"), 30% by mass of hollow silica particles 1, and 20 parts by mass of methyl ethyl ketone were mixed and mixed at 2000 rpm for 5 minutes in a rotation-orbiting agitator (Thinky Co., Ltd. "Awatori Rentaro (registered trademark) ARE310") to obtain insulating composition 9. The obtained insulating composition 9 was coated onto a release PET film with an applicator and dried in a gear oven at 100°C for 10 minutes. The release PET film was then removed to obtain a self-supporting film, which was then heated at 150°C for 1 hour to cure, obtaining a film 9 with a thickness of 100 μm.

[0071] [Example 10] In Example 9, instead of mixing resin 4, curing agent, hollow silica particles 1 and methyl ethyl ketone, 50 parts by mass of resin 5, parts by mass of hollow silica particles 1 in an amount of 30% by volume of the total, and 20 parts by mass of toluene were mixed. The same procedure as in Example 9 was followed to obtain an insulating composition 10 and a film 10 with a thickness of 100 μm. [Examples 11-12] In Example 1, the same procedure as in Example 1 was followed, except that the type of hollow silica particles was changed as shown in Table 2. Insulating compositions 11-12 and films 11-12 were obtained.

[0072] [Example 13] An insulating composition 13 and a film 13 were obtained by performing the same procedure as in Example 9, except that hollow silica particles 3 were used instead of hollow silica particles 1. [Example 14] An insulating composition 14 and a film 14 were obtained by performing the same procedure as in Example 10, except that hollow silica particles 3 were used instead of hollow silica particles 1. [Example 15] An insulating composition 15 and a film 15 were obtained by performing the same procedure as in Example 8, except that hollow silica particles 2 were used instead of hollow silica particles 1.

[0073] [Example 16] Resin 1 was coated onto a release PET film with an applicator and dried in a gear oven at 100°C for 10 minutes. The release PET film was then removed to obtain a self-supporting film, which was then heated at 400°C for 10 hours to obtain a film 16 with a thickness of 100 μm.

[0074] [Example 17] In a pot, 50 parts by mass of resin 6 as the resin solid content, parts by mass of particles C1 in an amount of 30% by volume of the total, and 20 parts by mass of NMP were added, and alumina balls with a diameter of 20 mm were added. The mixture was mixed at 30 rpm for 12 hours to obtain composition 17. The obtained composition 17 was coated onto a release PET film with an applicator and dried in a gear oven at 100°C for 10 minutes. The release PET film was then removed to obtain a self-supporting film, which was then heated at 400°C for 10 hours to obtain a film 17 with a thickness of 100 μm.

[0075] [Example 18] The same procedure as in Example 17 was performed except that particle C2 was used instead of particle C1 to obtain composition 18 and a film 18 with a thickness of 100 μm.

[0076] [Example 19] In a pot, 50 parts by mass of resin 6 as the resin solid content, parts by mass of polyethylene particles with an average particle size of 3 μm in an amount equivalent to 20 volume percent of the total, and 20 parts by mass of NMP were added, and alumina balls with a diameter of 20 mm were added. The mixture was then mixed at 30 rpm for 12 hours to obtain composition 19. The obtained composition 19 was coated onto a release PET film with an applicator and dried in a gear oven at 100°C for 10 minutes. The release PET film was then removed to obtain a self-supporting film, which was then heated at 400°C for 10 hours to obtain a film 19 with a thickness of 100 μm having voids with an average pore size of 3 μm.

[0077] 3. Film Evaluation <Relative Permittivity> For each example, the relative permittivity (measurement frequency: 10 GHz) was measured for the film obtained using a split-post dielectric resonator (manufactured by Agilent Technologies).

[0078] <Partial Discharge Initiation Voltage> Under conditions of 25±2℃ and 50±5%RH, a 20mm diameter spherical electrode was used as the upper electrode and a 25mm diameter flat plate electrode as the lower electrode of probe 1. The voltage was increased from 0V to the partial discharge initiation criterion at a frequency of 1kHz and a boosting rate of 17Vrms / s, and a charge of 500pC was maintained continuously for 5 seconds. The voltage at which the partial discharge initiation criterion was reached was measured at a point 10mm or more inside from both ends of each film. The obtained value was divided by the thickness of the measurement area (measured with a high-precision digital length measuring instrument "Lightmatic" manufactured by Mitutoyo Corporation) to calculate the partial discharge initiation voltage 1. Measurements were taken at three different locations on the same film, and the average value was adopted. In Examples 1, 16, and 19, the partial discharge voltage 2 was calculated in the same manner as above, except that a 20 mm diameter spherical electrode was used as the upper electrode and a 20 mm diameter spherical electrode was used as the lower electrode of the probe 2. In Examples 1 and 16, no difference was observed between the partial discharge voltage 1 and the partial discharge voltage 2, but in Example 19, the partial discharge initiation voltage 2 decreased by 3 kV / mm.

[0079] <Tensile Strength> The tensile breaking strength of each film was measured in accordance with ASTM D638.

[0080] The results are shown in Table 3.

[0081] Compositions in which the specific gravity of hollow silica particles is low relative to the specific gravity of the resin, particularly films (coatings) formed from the compositions of Examples 1, 4, and 15, exhibit a good balance of relative permittivity, partial discharge initiation voltage, and tensile strength.

[0082] Next, the films of Example 1, Example 3, Example 4, and Example 6 were subjected to a flexibility test in accordance with JIS C 6471 (temperature: 25°C, stroke length: 20 mm, bending radius: 2 mm, number of bends: 500), and the relative permittivity and partial discharge initiation voltage at 10 GHz were measured after the test. The results are shown in Table 4.

[0083]

[0084] It was found that when the specific gravity of the particles is around 0.5 relative to the specific gravity of the resin, the dielectric constant and partial discharge initiation voltage after the bending test tend to be superior.

[0085] The insulating composition of the present invention can form a coating (film) with excellent mechanical properties, electrical properties (low dielectric constant, low dielectric loss tangent, etc.), and insulating properties. A substrate equipped with this coating can be effectively used in various applications that take advantage of these properties, and in particular, a linear substrate equipped with this coating on its outer circumference can be effectively used, for example, as an electric wire covered with an insulating coating material.

Claims

1. The material contains 5 to 70 volume percent of hollow silica particles and resin, wherein the hollow silica particles have a median diameter (D50) of secondary particles of 0.2 to 10 μm and a specific gravity of 0.3 g / cm³. ３ 1.00g / cm or more ３ An insulating composition wherein the specific gravity of the hollow silica particles is less than the specific gravity of the resin.

2. The specific gravity of the hollow silica particles is 0.4 to 0.8 g / cm³. ３ The insulating composition according to claim 1.

3. The insulating composition according to claim 1, wherein the median diameter (D50) of the secondary particles of the hollow silica particles is 0.5 to 5 μm.

4. The insulating composition according to claim 1, wherein the average primary particle diameter of the hollow silica particles is 50 nm to 10 μm.

5. The BET specific surface area of ​​the hollow silica particles is 1 to 100 m². ２ The insulating composition according to claim 1, wherein the amount is / g.

6. SiO in the hollow silica particles ２ The insulating composition according to claim 1, wherein the content is 99% by mass or more, and the Na content is less than 1000 ppm by mass.

7. The specific gravity of the resin is 1.0 g / cm³. ３ Super 2.4g / cm ３ The insulating composition according to claim 1, which is as follows:

8. The insulating composition according to claim 1, wherein the softening temperature of the resin is 120°C or higher and 320°C or lower.

9. The insulating composition according to claim 1, wherein the resin is at least one selected from the group consisting of polyimide, polyamideimide, polyolefin-based thermoplastic resin, olefin-based elastomer, styrene-based elastomer, fluororesin, epoxy resin, and silicone resin.

10. The insulating composition according to claim 1, wherein the specific gravity of the hollow silica particles relative to the specific gravity of the resin is 0.25 to 0.

75.

11. The insulating composition according to claim 1, comprising 20% ​​by volume or more of the hollow silica particles.

12. The insulating composition according to claim 1, wherein the ratio of the volume percentage of the resin to the volume percentage of the hollow silica particles is 1.0 or more and 1.5 or less.

13. The insulating composition according to claim 1, further comprising a liquid dispersion medium.

14. An insulating composition according to any one of claims 1 to 13, used for forming a coating on the outer periphery of a substrate.

15. A substrate having a coating formed on its outer circumference, made of the insulating composition described in any one of claims 1 to 13.

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