WO2024122435A1 - Resin composition, prepreg, resin-coated metal substrate, and wiring board - Google Patents

Abstract

The present disclosure provides a resin composition containing a resin and hollow silica particles, wherein: the ratio of the median diameter (d50) of the hollow silica particles to d10 thereof is 6.0 or less, or the content of particles having an average particle diameter of 10 μm or more with respect to the total mass of the resin composition, as measured by the Coulter counter method, is 500 mass ppm or less; and d90 of the hollow silica particles is 15.0 μm or less.

Description

Resin composition, prepreg, resin-coated metal substrate, and wiring board

This disclosure relates to a resin composition, a prepreg, a resin-coated metal substrate, and a wiring board.

The electrical insulation layer of a printed wiring board is required to have properties such as a low dielectric constant, a low dielectric loss tangent, and a low linear expansion coefficient. In recent years, a resin composition containing a thermosetting resin and silica particles has been used to manufacture an electrical insulation layer of a metal clad laminate that can be processed into a printed wiring board (see Patent Documents 1 and 2). Specifically, a metal clad laminate is used in which a semi-cured product of the above resin composition is laminated on the surface of a metal substrate layer as an electrical insulation layer. As another example, a metal clad laminate is used in which a glass cloth impregnated with a resin composition is laminated on the surface of a metal substrate layer as an electrical insulation layer. Here, a filler is used as a material for a prepreg using a thermosetting resin, and the filler itself usually tends to increase the relative dielectric constant of the resulting prepreg. Among them, a metal clad laminate using a hollow filler can reduce the relative dielectric constant compared to when a solid filler is used, and therefore, as described in Patent Documents 3 to 5, it has been considered.

JP 2013-212956 A JP 2015-36357 A JP 2008-31409 A JP 2017-522580 A International Publication No. 2019/230661

The inventors have found that when a prepreg, cured product, etc. is produced using a conventionally known resin composition containing hollow particles and a resin, the hollow particles will settle or float excessively in the resin composition, forming aggregates. This phenomenon results in hollow particles being present non-uniformly in the prepreg and cured product produced using the conventionally known resin composition, and they have found that this may result in variations in the dielectric constant depending on the measurement location.

The problem that the first embodiment of the present disclosure aims to solve is to provide a resin composition capable of producing a prepreg and a cured product with small variation in relative dielectric constant, as well as a prepreg, a resin-coated metal substrate, and a wiring board using the resin composition.

Furthermore, when the resin composition is used to produce a molded product such as a prepreg or a cured product that requires insulating properties, the molded product is required to have excellent smoothness in order to reduce transmission loss.
If the smoothness of a molded product of a resin composition containing hollow fillers is low, this means that a large amount of hollow fillers are present on the surface of the molded product, and there is a risk that the hollow fillers will crack due to compression when producing a metal clad laminate, etc., and the dielectric constant will not be sufficiently reduced.

The problem that the second embodiment of the present disclosure aims to solve is to provide a resin composition that can be used to produce a prepreg and a cured product with excellent smoothness, as well as a prepreg, a resin-coated metal substrate, and a wiring board that use the resin composition.

The present disclosure includes the following aspects.
<1> A resin composition comprising a resin and hollow silica particles,
The resin composition, wherein the ratio of the median diameter (d50) to the d10 of the hollow silica particles is 6.0 or less.
<2> A resin composition comprising a resin and hollow silica particles,
The content of particles having an average particle diameter of 10 μm or more relative to the total mass of the resin composition, as measured by a Coulter counter method, is 500 ppm by mass or less;
The resin composition, wherein the hollow silica particles have a d90 of 15.0 μm or less.
<3> The resin composition according to <1> or <2> above, wherein the hollow silica particles have a density of 0.35 to 2.00 g/ ^cm3 .
<4> The resin composition according to any one of the above <1> to <3>, wherein the hollow silica particles have a BET specific surface area of 1.0 to 100.0 m ² /g.
<5> The resin composition according to any one of <1> to <4> above, wherein the hollow silica particles have a d50 of 0.1 to 10.0 μm.
<6> The resin composition according to any one of <1> to <5> above, wherein the hollow silica particles have a d10 of 0.1 to 2.0 μm.
<7> The resin composition according to any one of <1> to <6> above, wherein the resin comprises at least one selected from the group consisting of an epoxy resin, a polyimide resin, a polyphenylene ether resin, a resin containing a divinylbenzene skeleton, and a resin containing a pyrimidine skeleton.
<8> The resin composition according to any one of <1> to <7> above, wherein the content of the hollow silica particles is 10 to 70 volume% relative to the total volume of the resin composition.
<9> A prepreg comprising the resin composition or a semi-cured product thereof according to any one of <1> to <8> above, and a fibrous base material.
<10> The prepreg according to <9> above, wherein the fibrous base material contains a glass component.
<11> A resin-coated metal substrate comprising the resin composition or a semi-cured product thereof according to any one of <1> to <10> above, or the prepreg according to <9> or <10> above, and a metal substrate layer.
<12> The resin-coated metal substrate according to <11>, wherein the metal substrate layer is a copper foil.
<13> A wiring board comprising a cured product of the resin composition according to any one of <1> to <8> above and a metal wiring.

According to the first embodiment of the present disclosure, it is possible to provide a resin composition capable of producing a prepreg having a small variation in relative dielectric constant, as well as a prepreg, a resin-coated metal substrate, and a wiring board using the resin composition.
Furthermore, according to the second embodiment of the present disclosure, it is possible to provide a resin composition capable of producing a prepreg and a cured product having excellent smoothness, as well as a prepreg, a metal substrate with a resin, and a wiring board using the resin composition.

FIG. 1 is a top view showing a pressed prepreg produced in the examples.

Below, the form for carrying out the embodiment of the present disclosure will be described in detail. However, the embodiment of the present disclosure is not limited to the following embodiment. In the following embodiment, the components (including element steps, etc.) are not essential unless specifically stated. The same applies to the numerical values and their ranges, and they do not limit the embodiment of the present disclosure.

In the present disclosure, the numerical ranges indicated using "to" include the numerical values before and after "to" as the minimum and maximum values, respectively. In the numerical ranges indicated in stages in the present disclosure, the upper limit or lower limit indicated in one numerical range may be replaced with the upper limit or lower limit of another numerical range indicated in stages.
In the present disclosure, each component may contain multiple types of the corresponding substance. When multiple substances corresponding to each component are present in the composition, the content or amount of each component means the total content or amount of the multiple substances present in the composition, unless otherwise specified.
In the present disclosure, multiple types of particles corresponding to each component may be included. When multiple types of particles corresponding to each component are present in the composition, the particle size of each component means the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified.
In this disclosure, the term "lamination" refers to stacking layers, where two or more layers may be bonded together or two or more layers may be removable.
In this disclosure, the term "hollow silica particles" refers to a group of multiple hollow silica particles, unless otherwise specified.
In the present disclosure, the "BET specific surface area" is determined by the BET method based on the nitrogen adsorption method using a specific surface area/pore distribution measuring device (for example, "Tristar II" manufactured by Micromeritics, etc.).
In the present disclosure, the "sphericity" is determined by measuring the maximum diameter (DL) and the minor diameter (DS) perpendicular to the maximum diameter (DL) of 100 random particles in a photographic projection obtained by photographing with a scanning electron microscope (SEM), and calculating the ratio of the minimum diameter (DS) to the maximum diameter (DL) (
The average value of the calculated DS/DL is expressed.
In the present disclosure, the "dielectric tangent" and the "relative dielectric constant" are measured by a perturbation resonator method using a dedicated device (for example, "Vector Network Analyzer E5063A" manufactured by Keycom Corporation).
In the present disclosure, the term "semi-cured product" refers to a cured product in a state where an exothermic peak associated with the curing of a thermosetting resin appears when the cured product of a resin composition is measured by differential scanning calorimetry. In other words, the term "semi-cured product" refers to a cured product in a state where uncured thermosetting resin remains.
In the present disclosure, the term "cured product" refers to a cured product in a state where no exothermic peak associated with the curing of the thermosetting resin appears when the cured product of the resin composition is measured by differential scanning calorimetry. In other words, the term "cured product" refers to a cured product in a state where no uncured thermosetting resin remains.
In this disclosure, the "maximum height roughness Rz" is measured in accordance with JIS B 0601 (2013) (corresponding ISO: ISO 4287 1997).
In the present disclosure, the "weight average molecular weight" is determined using gel permeation chromatography (GPC) in terms of polystyrene.

The resin composition according to the first embodiment of the present disclosure (hereinafter also referred to as "composition 1") contains a resin and hollow silica particles, and the ratio of the median diameter (d50) to the d10 of the hollow silica particles (hereinafter also referred to as "d50/d10") is 6.0 or less.

A prepreg and a cured product having a small variation in the relative dielectric constant can be produced by using Composition 1. The reason for this is not entirely clear, but is presumed to be as follows.
The d50/d10 of the hollow silica particles contained in the present composition 1 is 6.0 or less. This reduces the amount of fine hollow silica particles contained in the resin composition, suppresses the formation of aggregates of the hollow silica particles, and is presumably the reason for the above-mentioned effects.

The resin composition according to the second embodiment of the present disclosure (hereinafter also referred to as "composition 2") contains a resin and hollow silica particles, and the content of particles having an average particle diameter of 10 μm or more relative to the total mass of the resin composition, as measured by the Coulter counter method, is 500 mass ppm or less, and the d90 of the hollow silica particles is 9.0 μm or less.

A prepreg and a cured product having excellent smoothness can be produced by using Composition 2. The reason for this is not entirely clear, but is presumed to be as follows.
In composition 2, the content of particles having an average particle size of 10 μm or more relative to the total mass of the resin composition is 500 ppm by mass or less, as measured by a Coulter counter method, and the hollow silica particles contained in composition 2 have a d90 of 15.0 μm or less. It is presumed that the above-mentioned effects are achieved due to the low proportion of coarse particles contained in composition 2.

Hereinafter, Composition 1 and Composition 2 may be collectively referred to as "Composition."

The viscosity of the composition is preferably from 100 to 10,000 mPa·s, more preferably from 130 to 5,000 mPa·s, even more preferably from 150 to 3,000 mPa·s, particularly preferably from 180 to 1,500 mPa·s, and most preferably from 200 to 1,000 mPa·s.
In the present disclosure, the "viscosity" is measured at 25°C using a rotational rheometer (e.g., Modular Rheometer Physica MCR-301, manufactured by Anton Paar) at a shear rate of 1 rpm for 30 seconds, and the viscosity obtained at the 30 second point is measured.

The composition may contain one type of resin or two or more types. The resin contained in the composition is preferably a thermosetting resin. The composition may contain two or more types of thermosetting resin, but preferably contains one type.
In the present composition, the thermosetting resin may be partially cured. For example, the thermosetting resin may be partially polymerized with itself by reacting with the curable functional group of the thermosetting resin. In addition, when a polymerization initiator, a polymerization accelerator, a plasticizer, or other components have a functional group that reacts with the curable functional group of the thermosetting resin, a part of the thermosetting resin may be polymerized with these components.

Examples of the thermosetting resin include epoxy resin, polyphenylene ether resin, polyester resin, polyimide resin, phenol resin, resin containing a divinylbenzene skeleton, resin containing a pyrimidine skeleton, etc. From the viewpoint of adhesion, heat resistance, etc., the thermosetting resin is preferably one or more selected from the group consisting of epoxy resin, polyimide resin, polyphenylene ether resin, resin containing a divinylbenzene skeleton, and resin containing a pyrimidine skeleton.
The present composition is preferably in a liquid state at 25°C.

Examples of the epoxy resin include bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol S type epoxy resins, alicyclic epoxy resins, phenol novolac type epoxy resins, cresol novolac type epoxy resins, bisphenol A novolac type epoxy resins, diglycidyl ethers of polyfunctional phenols, and diglycidyl ethers of polyfunctional alcohols.
Examples of the polyimide resin include aromatic polyimide and aromatic polyamic acid.
The polyphenylene ether resin may be modified polyphenylene ether or unmodified polyphenylene ether, but from the viewpoint of adhesion, modified polyphenylene ether is preferred. The modified polyphenylene ether has a polyphenylene ether chain and a substituent bonded to the end of the polyphenylene ether chain. The substituent preferably has a carbon-carbon double bond. The substituent is preferably represented by the following formula (1) or (2), more preferably represented by the following formula (2).

In formula (1), n is an integer of 0 to 10, Z is an arylene group, and R ¹ to R ³ are each independently hydrogen or an alkyl group. When n in formula (1) is 0, Z is directly bonded to the end of the polyphenylene ether chain in the modified polyphenylene ether. In formula (2), R ⁴ is hydrogen or an alkyl group. In formulas (1) and (2), the alkyl group preferably has 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms.

The polyphenylene ether chain is preferably represented by the following formula (3):

In formula (3), m is a number within the range of 1 to 50, and R ⁵ to R ⁸ are each independently a hydrogen atom, an alkyl group, an alkenyl group, an alkynyl group, a formyl group, an alkylcarbonyl group, an alkenylcarbonyl group, or an alkynylcarbonyl group, with a hydrogen atom or an alkyl group being preferred. In formula (3), the alkyl group preferably has 1 to 10 carbon atoms, and more preferably 1 to 6 carbon atoms.

An example of a resin containing a divinylbenzene skeleton is ODV-XET manufactured by Nippon Steel Chemical & Material Co., Ltd.

Examples of resins containing a pyrimidine skeleton include the ELPAC HC-F series manufactured by JSR Corporation.

From the viewpoint of improving the adhesion and dielectric properties of the semi-cured product and the cured product, the weight average molecular weight (Mw) of the thermosetting resin is preferably 1,000 to 7,000, more preferably 1,000 to 5,000, and even more preferably 1,000 to 3,000. In this disclosure, improving the dielectric properties of the semi-cured product and the cured product means reducing their relative dielectric constant and dielectric tangent.

From the viewpoint of improving the adhesion and dielectric properties of the semi-cured product and the cured product, and further from the viewpoint of improving the smoothness of prepregs and the like in the second embodiment, the content of the curable resin relative to the total mass of the composition is preferably 10 to 40 mass%, more preferably 15 to 35 mass%, and even more preferably 20 to 30 mass%.

The composition may contain resins other than thermosetting resins (hereinafter, also referred to as "other resins"). Examples of other resins include polytetrafluoroethylene, polyethylene terephthalate, polyolefins, silicones, etc.

The content of other resins relative to the total mass of the composition is not particularly limited, and is, for example, 1 to 50 mass%.

From the viewpoint of producing a prepreg and a cured product with small variation in the relative dielectric constant, the density of the resin determined by a constant volume expansion method using argon gas and a dry pycnometer is preferably 0.5 to 3.0 g/ ^cm3 , and more preferably 0.8 to 2.3 g/ ^cm3 .
The density of the resin is measured at 25° C. after drying. In the case of a thermosetting resin, the density is measured after curing. The density can be measured by measuring the density of the cured resin with a dry pycnometer as described above.
When the composition contains two or more resins, the density of the resin is determined by measuring the density of the composition after drying or, in the case of a thermosetting resin, after heat curing, using an Ar pycnometer.
In addition, when a polymerization initiator, a polymerization accelerator, a plasticizer, other components, etc. can be incorporated by reacting with the resin, all of the components that can be incorporated into the resin are considered to be the "resin" in calculating the density of the resin.

The hollow silica particles have a shell layer containing silica and have a space inside the shell layer. The space can be confirmed by observation with a transmission electron microscope (TEM), a scanning electron microscope (SEM), or the like.
In the present disclosure, "having a space inside the shell layer" means that when a cross-section of a single hollow silica particle is observed, a hollow state exists in which a single space is surrounded by a shell layer.
The shell layer may have a single-layer structure or a multi-layer structure having two or more layers.

The content of silica in the shell layer is preferably 50% by mass or more, more preferably 80% by mass or more, and even more preferably 95% by mass or more, with the upper limit of the content being 100% by mass, and preferably 99.99% by mass.
From the viewpoint of improving the durability of the hollow silica particles and the adhesion and dielectric properties of the semi-cured product and the cured product, it is preferable that the shell layer contains at least one selected from the group consisting of alkali metals belonging to Group 1 or 2 of the periodic table and their silicates.
The content of alkali metals belonging to Group 1 or 2 of the periodic table relative to the total mass of the shell layer is preferably 30 ppm by mass or more, more preferably 100 ppm by mass or more, even more preferably 150 ppm by mass or more, and particularly preferably 300 ppm by mass or more. The content is preferably 1% by mass or less, more preferably 5000 ppm by mass or less, and most preferably 1000 ppm by mass or less.
That is, the content of alkali metals belonging to Group 1 or 2 of the periodic table relative to the total mass of the shell layer is preferably 30 ppm by mass to 1 mass%, more preferably 100 ppm by mass to 5000 ppm by mass, and even more preferably 150 ppm by mass to 1000 ppm by mass.
The composition of the shell layer is measured by ICP emission spectrometry, flame atomic absorption spectrometry, or the like.
From the viewpoint of ease of availability, among the alkali metal components (alkali metals and alkaline earth metals) belonging to Group 1 or 2 of the periodic table, the shell layer preferably contains one or more selected from sodium, potassium, magnesium, calcium, and strontium, and more preferably contains one or more selected from sodium, magnesium, and calcium.

From the viewpoint of improving the durability of the hollow silica particles and improving the adhesion and dielectric properties of the semi-cured product and the cured product, the average thickness of the shell layer is preferably 0.01 to 0.3, more preferably 0.02 to 0.2, and even more preferably 0.03 to 0.1, relative to the diameter of the primary particle of the hollow silica particles being 1.
The average thickness of the shell layer is an average value of the thicknesses of the shell layers of 20 hollow silica particles measured by TEM observation.

From the viewpoint of producing a prepreg and a cured product having small variation in the dielectric constant, and from the viewpoint of improving the dielectric properties of a semi-cured product and a cured product, the average primary particle diameter of the hollow silica particles is preferably 10 nm to 10 μm, more preferably 20 nm to 7 μm, even more preferably 50 nm to 5 μm, particularly preferably 70 nm to 3 μm, and most preferably 100 nm to 1 μm.
The average primary particle size of hollow silica particles is determined by directly observing the particle diameter (diameter, the average value of the long and short sides if the particle is not spherical) by SEM observation. Specifically, the primary particle sizes of 100 hollow silica particles are measured from an SEM image, and the value at which the cumulative distribution of the primary particle sizes obtained by averaging them is 50% is estimated to be the average primary particle size of all primary particles.

From the viewpoint of producing a prepreg and a cured product having a small variation in the relative dielectric constant, from the viewpoint of improving the dielectric properties of the semi-cured product and the cured product, and further from the viewpoint of improving the smoothness of the prepreg in the second embodiment, the median diameter of the hollow silica particles (hereinafter, also simply referred to as "d50") is preferably 0.1 to 10.0 μm, more preferably 0.2 to 10.0 μm, further preferably 0.25 to 8.0 μm, particularly preferably 0.3 to 7.0 μm, most preferably 0.3 to 5.0 μm, and may be 0.3 to 3.0 μm. Furthermore, by setting the d50 of the hollow silica particles to the above numerical range, the smoothness of the prepreg and the cured product can be improved, and the transmission loss in the circuit when the insulating layer is formed can be reduced.
In the present disclosure, "d50" refers to the volume-based cumulative 50% diameter of hollow silica particles determined by a laser diffraction particle size distribution measuring device (e.g., "MT3300EXII" manufactured by Microtrack Bell Co., Ltd.). That is, d50 refers to the particle diameter at the point on the cumulative curve where the cumulative volume is 50% when the particle size distribution is measured by a laser diffraction/scattering method and a cumulative curve is calculated with the total volume of the hollow silica particles set to 100%.
In the present disclosure, the d50 of the hollow silica particles is measured in a state including primary particles and secondary particles.

From the viewpoint of producing a prepreg and a cured product having a small variation in the relative dielectric constant, from the viewpoint of improving the dielectric properties of the semi-cured product and the cured product, and further from the viewpoint of improving the smoothness of the prepreg in the second embodiment, the d10 of the hollow silica particles is preferably 0.1 to 2.0 μm, more preferably 0.2 to 2.0 μm, further preferably 0.3 to 1.8 μm, and particularly preferably 0.3 to 1.5 μm. Moreover, in the first embodiment, by setting the d10 of the hollow silica particles to the above-mentioned numerical range, the smoothness of the prepreg and the cured product can be improved, and the transmission loss in the circuit when the insulating layer is formed can be reduced.
In the present disclosure, "d10" is the volume-based cumulative 10% diameter of hollow silica particles obtained by a laser diffraction particle size distribution measuring device (e.g., "MT3300EXII" manufactured by Microtrack-Bell Co., Ltd.). That is, d10 is the particle diameter at the point on the cumulative curve where the cumulative volume is 10% when the particle size distribution is measured by a laser diffraction/scattering method and a cumulative curve is obtained with the total volume of the hollow silica particles being 100%.
In the present disclosure, the d10 of the hollow silica particles is measured in a state including primary particles and secondary particles.

From the viewpoint of producing a prepreg and a cured product having a small variation in the relative dielectric constant, and from the viewpoint of improving the dielectric properties of a semi-cured product and a cured product, the d90 of the hollow silica particles is preferably 0.7 or more, more preferably 0.7 to 15.0 μm, even more preferably 0.8 to 12.0 μm, particularly preferably 0.9 to 10.0 μm, most preferably 0.9 to 8.0 μm, may be 0.9 to 6.0 μm, or may be 0.9 to 5.0 μm. Furthermore, by setting the d90 of the hollow silica particles to the above numerical range, the smoothness of the prepreg and the cured product can be improved, and the transmission loss in the circuit when an insulating layer is formed can be reduced.
In the present disclosure, "d90" refers to the volume-based cumulative 90% diameter of hollow silica particles determined by a laser diffraction particle size distribution measuring device (e.g., "MT3300EXII" manufactured by Microtrack Bell Co., Ltd.). That is, d90 refers to the particle diameter at the point on the cumulative curve where the cumulative volume is 90% when the particle size distribution is measured by a laser diffraction/scattering method and a cumulative curve is calculated with the total volume of the hollow silica particles being 100%.
In the present disclosure, the d90 of the hollow silica particles is measured in a state including primary particles and secondary particles.

In the present composition 1, from the viewpoint of producing a prepreg and a cured product with a small variation in the relative dielectric constant, d50/d10 is preferably 5.0 or less, more preferably 3.0 or less, and even more preferably 2.5 or less. The lower limit of d50/d10 in the present composition 1 is not particularly limited, and can be 1.3.

In the present composition 2, from the viewpoint of producing a prepreg and a cured product with a small variation in the relative dielectric constant, and from the viewpoint of improving the dielectric properties of the semi-cured product and the cured product, d50/d10 is preferably 6.0 or less, more preferably 5.0 or less, even more preferably 3.0 or less, and particularly preferably 2.5 or less. The lower limit of d50/d10 in the present composition 2 is not particularly limited, and can be 1.3.

In the present composition 1, from the viewpoint of improving the smoothness of the semi-cured product and the cured product, the content of hollow silica particles having an average particle size of 10 μm or more relative to the total mass of the present composition 1 measured by the Coulter counter method is preferably 500 ppm by mass or less, more preferably 200 ppm by mass or less, even more preferably 100 ppm by mass or less, and may be 0 ppm by mass.

In the present composition 2, from the viewpoint of improving the smoothness of the semi-cured product and the cured product, the content of hollow silica particles having an average particle size of 10 μm or more relative to the total mass of the present composition 2 measured by the Coulter Counter method is preferably 400 ppm by mass or less, more preferably 200 ppm by mass or less, even more preferably 100 ppm by mass or less, and may be 0 ppm by mass.

The content of particles with an average particle size of 10 μm or more can be adjusted by using a sieve, changing the firing temperature, changing the alkali metal content, etc.

From the viewpoint of producing a prepreg and a cured product having a small variation in the relative dielectric constant, and from the viewpoint of improving the dielectric properties of a semi-cured product and a cured product, the density of the hollow silica particles determined by a constant volume expansion method using argon gas and a dry pycnometer is preferably 0.35 to 2.00 g/ ^cm3 , more preferably 0.35 to 1.50 g/ ^cm3 , and even more preferably 0.40 to 1.00 g/ ^cm3 .
When the composition contains two or more types of hollow silica particles, the density of the hollow silica particles is determined by taking a weighted average of the densities of the individual hollow silica particles.
As the dry pycnometer, an AccuPycII 1340 manufactured by Micromeritics or an equivalent device can be used.

From the viewpoint of reducing the variation in the dielectric constant of prepregs, cured products, and the like, the composition contains a resin and hollow silica particles, and when the densities of the hollow silica particles and the resin determined by a constant volume expansion method using argon gas and a dry pycnometer are A (g/cm ³ ) and B (g/cm ³ ), respectively, A/B is preferably 0.3 to 1.5, and more preferably 0.4 to 1.0.

From the viewpoint of improving the dielectric properties of the semi-cured product and the cured product, and further from the viewpoint of improving the smoothness of the prepreg in the second embodiment, the BET specific surface area of the hollow silica particles is preferably 1.0 to 100.0 m ² /g, more preferably 1.0 to 50.0 m ² /g, and even more preferably 1.0 to 30.0 m ² /g.

From the viewpoint of improving the adhesion strength of the semi-cured product and the cured product, and from the viewpoint of reducing the relative dielectric constant, the product of the density of the hollow silica particles determined by a constant volume expansion method using argon gas and a dry pycnometer and the BET specific surface area of the hollow silica particles is preferably 1.0 to 120.0 m ² /cm ³ , more preferably 2.0 to 80.0 m ² /cm ³ , even more preferably 2.5 to 40.0 m ² /cm ³ , and particularly preferably 3.0 to 20.0 m ² /cm ³ .

From the viewpoint of producing a prepreg and a cured product having small variation in the dielectric constant, and from the viewpoint of improving the dielectric properties of a semi-cured product and a cured product, the porosity of the hollow silica particles is preferably 30 to 90%, more preferably 40 to 90%, and even more preferably 50 to 85%.
In the present disclosure, the porosity of hollow silica particles is calculated by dividing the density of hollow silica particles by the true density of hollow silica particles and multiplying the result by 100. The true density of hollow silica particles is measured using He gas with an AccuPycII 1340 manufactured by Micromeritics or an equivalent device.

The shape of each hollow silica particle contained in the hollow silica particles is not particularly limited and may be spherical or non-spherical, but from the viewpoint of a low dielectric tangent, a spherical shape is preferred. From the viewpoint of a low dielectric tangent, the sphericity of the spherical hollow silica particles is preferably 0.75 or more, more preferably 0.90 or more, even more preferably 0.93 or more, and particularly preferably 1.00. From the viewpoint of a low dielectric tangent, the hollow silica particles are preferably non-porous particles.

From the viewpoint of reducing transmission loss in the circuit when an insulating layer is formed, the dielectric tangent of the hollow silica particles is preferably 0.0020 or less at a frequency of 1 GHz, more preferably 0.0015 or less, and even more preferably 0.0012 or less.

From the viewpoint of producing a prepreg and a cured product having small variation in the relative dielectric constant, and from the viewpoint of improving the dielectric properties of a semi-cured product and a cured product, the oil absorption of the hollow silica particles is preferably from 20 to 500 mL/100 g, more preferably from 25 to 200 mL/100 g, even more preferably from 30 to 150 mL/100 g, particularly preferably from 30 to 100 mL/100 g, and most preferably from 30 to 80 mL/100 g.
In the present disclosure, "oil absorption" is measured in accordance with JIS K 5101-13-1 (2004) (corresponding ISO: ISO 787-5 1980). Note that the oil absorption in the present disclosure is a value obtained by multiplying the value measured in accordance with JIS K 5101-13-1 (2004) by the value of density/true density (oil absorption measured in accordance with JIS K 5101-13-1 (2004) × (density/true density)).

From the viewpoint of improving the dielectric properties of the semi-cured product and the cured product, the 20% burst pressure of the hollow silica particles as measured by mercury porosimetry is preferably 120 MPa or more, more preferably 150 MPa or more, even more preferably 200 MPa or more, and particularly preferably 250 MPa or more. The upper limit of the 20% burst pressure is not particularly limited, and can be, for example, 600 MPa or less.
In this disclosure, the "20% burst pressure" refers to the burst pressure measured by mercury porosimetry, and is the minimum pressure that indicates a 20% decrease in capacity from the maximum integrated capacity when pressure is applied from 0 to 400 MPa by mercury porosimetry.
The 20% collapse pressure of the hollow silica particles as determined by mercury intrusion porosimeter is measured in accordance with ASTM D 3102-78 using a mercury intrusion porosimeter (for example, AutoPore IV 9500 manufactured by MICROMERITICS INSTRUMENT).

From the viewpoint of improving the bending strength of the semi-cured product and the cured product, the charge amount of the hollow silica particles is preferably 0.005 μC/g or more, more preferably 0.010 μC/g or more, even more preferably 0.015 μC/g or more, and particularly preferably 0.020 μC/g or more. The upper limit of the charge amount is not particularly limited, and can be 0.080 μC/g or less.
In the present disclosure, the charge amount is measured by the following method. As a measuring device, for example, a powder triboelectric charge measuring device NS-K100 type (manufactured by Nano Seeds Corporation) can be used.
10 g of hollow silica particles are placed in an aluminum container (inner dimensions Φ42 mm, depth 70 mm) and fixed to a sample rotation arm. The left and right swing angles are 150 degrees left and 210 degrees right (swing speed is 540 deg/s), and 12 round trips are counted as one cycle (2 rotations of powder brushing off rotation are added at the end of the intermediate 6 round trips). After 3 cycles of friction stirring, the charged hollow silica particles are placed in a Faraday cage, the charge amount of the hollow silica particles is measured, and converted to the charge amount per mass (charge amount of hollow silica particles/10 g of hollow silica particles).

Each hollow silica particle may be treated with a silane coupling agent. By treating the surface of the hollow silica particle with a silane coupling agent, the amount of remaining silanol groups on the surface is reduced, the surface is hydrophobicized, moisture adsorption is suppressed, and the dielectric loss is improved. In addition, the affinity with the resin in the composition is improved, and the dispersibility and strength after the resin film are improved.
Examples of the silane coupling agent include aminosilane coupling agents, methacrylsilane coupling agents, epoxysilane coupling agents, mercaptosilane coupling agents, silane coupling agents, organosilazane compounds, etc. The silane coupling agents may be used alone or in combination of two or more.
The amount of the silane coupling agent attached is preferably 0.01 to 5 parts by mass, more preferably 0.02 to 5 parts by mass, and even more preferably 0.10 to 2 parts by mass, based on 100 parts by mass of the hollow silica particles.
The fact that the surface of the hollow silica particles has been treated with a silane coupling agent can be confirmed by detecting a peak due to a substituent of the silane coupling agent by IR. The amount of the silane coupling agent attached can be measured by the carbon amount.

The hollow silica particles may contain impurity elements as long as the effects of the first and second embodiments are not hindered. Examples of impurity elements include Al, Fe, Ti, etc.

From the viewpoint of producing prepregs and cured products with small variations in the dielectric constant, from the viewpoint of improving the dielectric properties and adhesion of semi-cured products and cured products, and from the viewpoint of reducing the water absorption of the composition, the content of hollow silica particles relative to the total volume of the composition is preferably 10 to 70 volume %, more preferably 15 to 65 volume %, and even more preferably 18 to 60 volume %.

The hollow silica particles may be commercially available or may be prepared by a conventional method. For example, hollow silica particles prepared by the methods described in WO 2019/131658, WO 2021/006697, WO 2021/172294, etc. may be used.

The composition may contain one or more solvents. Examples of the solvent include acetone, methanol, ethanol, butanol, 2-propanol, 2-methoxyethanol, 2-ethoxyethanol, toluene, xylene, methyl ethyl ketone, N,N-dimethylformamide, methyl isobutyl ketone, N-methyl-2-pyrrolidone, n-hexane, and cyclohexane. From the viewpoint of adhesion, it is preferable that the solvent contains at least one selected from the group consisting of toluene, cyclohexanone, methyl ethyl ketone, and N-methyl-2-pyrrolidone. The content of the solvent relative to the total mass of the composition is not particularly limited, and may be, for example, 10 to 60% by mass.

From the viewpoint of suppressing aggregation of the hollow silica particles, the surface tension of the solvent is preferably 40 mN/m or less, more preferably 35 mN/m or less, and even more preferably 30 mN/m or less. The lower limit of the surface tension is not particularly limited and may be, for example, 5 mN/m.
In this disclosure, "surface tension" is measured by the Wilhelmy method using a surface tensiometer for a solvent at 25°C.

The viscosity of the solvent is preferably 10 mPa·s or less at 25°C, and more preferably 5 mPa·s or less. The lower limit of the viscosity of the solvent is not particularly limited, and can be 2 mPa·s or more.

The content of the solvent relative to the total mass of the composition is not particularly limited, and can be, for example, 10% by mass to 90% by mass.

The composition may contain one or more polymerization initiators. Examples of polymerization initiators include α,α'-bis(t-butylperoxy-m-isopropyl)benzene, 2,5-dimethyl-2,5-di(t-butylperoxy)-3-hexyne, benzoyl peroxide, 3,3',5,5'-tetramethyl-1,4-diphenoquinone, chloranil, 2,4,6-tri-t-butylphenoxyl, t-butylperoxyisopropyl monocarbonate, and azobisisobutyronitrile. The content of the polymerization initiator per 100 parts by mass of resin is preferably 0.1 to 5 parts by mass.

The composition may contain one or more polymerization accelerators. Examples of polymerization accelerators include trialkenyl isocyanurate compounds such as triallyl isocyanurate, polyfunctional acrylic compounds having two or more acryloyl or methacryloyl groups in the molecule, polyfunctional vinyl compounds having two or more vinyl groups in the molecule, and vinylbenzyl compounds such as styrene having a vinylbenzyl group in the molecule. The content of the polymerization accelerator per 100 parts by mass of the resin is preferably 10 to 100 parts by mass.

The composition may contain one or more plasticizers. Examples of plasticizers include butadiene-styrene copolymers. The content of the plasticizer per 100 parts by mass of resin is preferably 10 to 50 parts by mass, and more preferably 20 to 40 parts by mass.

In addition to the above components, the composition may further contain other components such as surfactants, thixotropy imparting agents, pH adjusters, pH buffers, viscosity regulators, defoamers, silane coupling agents, dehydrating agents, plasticizers, weather resistance agents, antioxidants, heat stabilizers, lubricants, antistatic agents, brightening agents, colorants, conductive materials, release agents, surface treatment agents, flame retardants, and various organic or inorganic fillers, to the extent that the effects of the composition are not impaired.

This composition can be suitably used as a resin composition for producing electronic substrates for use in electronic devices such as personal computers, notebook computers, and digital cameras, and communication devices such as smartphones and game consoles. The resin composition of the present invention is also expected to be applied to prepregs, metal foil-clad laminates, printed wiring boards, resin sheets, adhesive layers, adhesive films, solder resists, resin compositions for bump reflow, rewiring insulating layers, die bond materials, encapsulants, underfills, mold underfills, and laminated inductors, etc., in order to reduce dielectric constant, transmission loss, moisture absorption, and improve peel strength.

The prepreg of the present disclosure includes the present composition or a semi-cured product thereof, and a fibrous substrate. Examples of the fibrous substrate include glass cloth, aramid cloth, polyester cloth, glass nonwoven fabric, aramid nonwoven fabric, polyester nonwoven fabric, and pulp paper. The fibrous substrate preferably contains a glass component. The thickness of the fibrous substrate is not particularly limited, and can be 12 to 1000 μm. Note that the present composition has been described above, so a description thereof will be omitted here.

The prepreg of the present disclosure can be produced by applying or impregnating the present composition to a fibrous substrate. After applying or impregnating the present composition, the resin composition may be heated and semi-cured.

The resin-coated metal substrate of the present disclosure includes the present composition or a semi-cured product thereof, or the prepreg, and a metal substrate layer. The metal substrate layer may be provided on one surface or both surfaces of the present composition or a semi-cured product thereof, or the prepreg.
The type of the metal substrate layer is not particularly limited, and examples of metals constituting the metal substrate layer include copper, copper alloys, stainless steel, nickel, nickel alloys (including alloy 42), aluminum, aluminum alloys, titanium, and titanium alloys. The metal substrate layer is preferably a metal foil, and more preferably a copper foil such as rolled copper foil or electrolytic copper foil. The surface of the metal foil may be rust-proofed (oxide film such as chromate) or may be roughened. As the metal foil, a carrier-attached metal foil consisting of a carrier copper foil (thickness: 10 to 35 μm) and an ultra-thin copper foil (thickness: 2 to 5 μm) laminated on the carrier copper foil surface via a peeling layer may be used. The surface of the metal substrate layer may be treated with a silane coupling agent. In this case, the entire surface of the metal substrate layer may be treated with a silane coupling agent, or a part of the surface of the metal substrate layer may be treated with a silane coupling agent. As the silane coupling agent, the above-mentioned ones can be used.

The thickness of the metal substrate layer is preferably 1 to 40 μm, more preferably 2 to 20 μm. From the viewpoint of reducing transmission loss when the resin-coated metal substrate is used as a printed wiring board, the maximum height roughness (Rz) of the metal substrate layer is preferably 6 μm or less, more preferably 4 μm or less.

In one embodiment, the resin-attached metal substrate of the present disclosure can be produced by applying the present composition to the surface of a metal substrate layer. After applying the present composition, the resin composition may be heated to be semi-cured.
In another embodiment, the resin-coated metal substrate of the present disclosure can be produced by laminating a metal substrate layer and a prepreg. Examples of a method for laminating the metal substrate layer and the prepreg include a method of thermocompression bonding them.

The wiring board of the present disclosure includes a cured product of the present composition and metal wiring. The metal wiring can be produced by etching the above-mentioned metal substrate layer, etc.

The wiring board of the present disclosure can be manufactured by a method of etching the metal substrate layer of the resin-coated metal substrate, or by a method of forming a pattern circuit on the cured surface of the composition by electrolytic plating (semi-additive method (SAP method), modified semi-additive method (MSAP method), etc.).

Next, embodiments of the present disclosure will be specifically explained using examples, but the embodiments of the present disclosure are not limited to these examples.

(Method for measuring d90, d50 and d10 of hollow silica particles and hollow particles)
The d90, d50 and d10 of the hollow silica particles and hollow particles used in each example were measured by a particle size distribution measuring device (Microtrack Bell, MT3300EXII) by a laser diffraction/scattering method. Specifically, the secondary particles of the hollow silica particles were dispersed by irradiating with ultrasonic waves for 120 seconds, and then the measurements were performed. The values at which the cumulative distribution of the particle sizes obtained was 90%, 10% and 50% were defined as d90, d10 and d50, respectively. In addition, the ratio of d50 to d10 (d50/d10) was calculated.

(Method of measuring average primary particle size of hollow silica particles and hollow particles)
The average primary particle size of the hollow silica particles and hollow particles used in each example was obtained by directly observing the particle size (diameter, the average value of the long side and short side if not spherical) by SEM observation. Specifically, the primary particle sizes of 100 hollow silica particles and hollow particles were measured from SEM images, and the value at which the cumulative distribution of the primary particle sizes obtained by averaging them was 50% was estimated as the average primary particle size of the entire primary particles.

(Content of particles of 10 μm or more)
The content of particles having a size of 10 μm or more relative to the total mass of the resin composition was measured by a Coulter counter method.

(Method of measuring the BET specific surface area of hollow silica particles and hollow particles)
The hollow silica particles and hollow particles used in each example were dried under reduced pressure at 230° C. to completely remove moisture, and used as samples. The specific surface area of each sample was measured by a multipoint BET method using nitrogen gas with an automatic specific surface area/pore distribution measuring device "Tristar II" manufactured by Micromeritics.

(Method of measuring density of hollow silica particles and hollow particles)
The hollow silica particles and hollow particles used in each example were dried under reduced pressure at 230° C. to completely remove moisture, and used as samples. The density of the samples was measured using a dry pycnometer (AccuPycII 1340 manufactured by Micromeritics). The measurement conditions were as follows.
(Measurement condition)
Sample cell: 10 ^cm3 cell Sample weight: 1.0 g
Measurement gas: Argon gas Purge times: 10 times Purge processing filling pressure: 135 kPag
Number of cycles: 10 Cycle filling pressure: 135 kPag
Rate to end pressure equilibration: 0.05 kPag/min

(Method of measuring the sphericity of hollow silica particles and hollow particles)
The sphericity of the hollow silica particles and hollow particles was determined by measuring the maximum diameter (DL) and the minor diameter (DS) perpendicular to the maximum diameter (DL) of any 100 particles in a photographic projection obtained by photographing with a scanning electron microscope (SEM), calculating the ratio (DS/DL) of the minimum diameter (DS) to the maximum diameter (DL), and calculating the average.

(Method of measuring dielectric tangent of hollow silica particles and hollow particles)
The dielectric loss tangent of the hollow silica particles and the hollow particles at a frequency of 1 GHz was measured by a perturbation resonator method using a vector network analyzer E5063A manufactured by Keycom Corporation.

(Method of measuring hollow silica particles and porosity of hollow particles)
The porosity of the hollow silica particles was calculated by dividing the density of the hollow silica particles by the true density of the hollow silica particles and multiplying the result by 100. The true density of the hollow silica particles was measured using an AccuPycII 1340 manufactured by Micromeritics. The porosity of the hollow particles was calculated in the same manner.

(Method of measuring oil absorption of hollow silica particles and hollow particles)
The oil absorption of the hollow silica particles and hollow particles was measured in accordance with JIS K 5101-13-1 (2004).

(Method of measuring resin density)
The density of the resin used in each example was measured as follows.
59 parts by mass of polyphenylene ether, 16 parts by mass of butadiene-styrene random copolymer, 25 parts by mass of triallyl isocyanurate, 1 part by mass of α,α'-di(t-butylperoxy)diisopropylbenzene, and 60 parts by mass of toluene were placed in a polyvinyl bottle and kneaded with a planetary disperser to obtain a resin. The resin obtained was vacuum dried at 120°C to remove the solvent, and then cured in a nitrogen oven at 200°C. It was then pulverized using a cutter mill, and the density was measured with an Ar pycnometer, which gave a density of 1.1 g/ ^cm3 .

<Examples 1A to 5A>
Among the following Examples 1A to 5A, Examples 1A to 4A are working examples of the first embodiment, and Example 5A is a comparative example of the first embodiment.

1. Preparation of each component for producing a resin composition <Thermosetting resin>
Polyphenylene ether: Modified polyphenylene ether in which the terminal hydroxyl groups of polyphenylene ether are modified with methacrylic groups, manufactured by SABIC, Noryl SA9000, Mw 1700, two functional groups per molecule

<Hollow Silica Particles A1>
The hollow silica particles A1 were prepared as follows.

(Preparation of emulsion)
4 g of EO-PO-EO block copolymer (Pluronic (registered trademark) F68, manufactured by ADEKA Corporation) was added to 1250 g of pure water and stirred until dissolved to obtain an aqueous solution. 42 g of n-decane in which 4 g of sorbitan acid monooleate (IONET (registered trademark) S-80, manufactured by Sanyo Chemical Industries, Ltd.) was dissolved was added to this aqueous solution, and the whole solution was stirred using an IKA homogenizer until it became uniform to prepare a crude emulsion.
This crude emulsion was emulsified at a pressure of 50 bar using a high-pressure emulsifier (LAB1000, manufactured by SMT Corporation) to produce an emulsion with an emulsion diameter of 1 μm.

(aging)
The resulting emulsion was allowed to stand at 40° C. for 12 hours.

(First shell layer formation)
After standing, 23 g of a diluted sodium silicate aqueous solution ( _SiO2 concentration 10.4 mass%, _Na2O concentration 3.6 mass%) and 2 M hydrochloric acid were added to 1,300 g of the emulsion so that the pH was 2, and the mixture was stirred while maintaining the temperature at 30° C. to obtain a mixed liquid.
Next, while stirring the mixture, a 1M aqueous solution of sodium hydroxide was slowly added dropwise so that the pH of the mixture became 6, thereby obtaining an oil core-silica shell particle dispersion. The obtained oil core-silica shell particle dispersion was retained and aged.

(Second shell layer formation)
The oil core-silica shell particle dispersion was heated to 70° C., and a 1M aqueous solution of sodium hydroxide was slowly added thereto with stirring to adjust the pH to 9.
Next, 330 g of a diluted aqueous sodium silicate solution ( _SiO2 concentration 10.4% by mass, _Na2O concentration 3.6% by mass) was gradually added together with 0.5 M hydrochloric acid to adjust the pH to 9.
This suspension was kept at 80° C. for 1 day and then cooled to room temperature (25° C.) to obtain a hollow silica precursor dispersion.

(Filtering, washing, drying, firing)
The entire amount of the hollow silica precursor dispersion was neutralized with 2M hydrochloric acid to pH 2, and then filtered using quantitative filter paper 5C. Then, 350 ml of 80° C. ion-exchanged water was added and pressure filtered again to wash the hollow silica cake.
The cake after filtration was dried in a nitrogen atmosphere at 100° C. for 1 hour and then at 400° C. for 2 hours (heating rate: 10° C./min) to remove the organic matter, thereby obtaining a hollow silica precursor.
The obtained hollow silica precursor was baked at 1000° C. for 1 hour (heating rate: 10° C./min) to bake and tighten the shell, thereby obtaining baked hollow silica particles.

(surface treatment)
10 g of hollow calcined silica particles, 150 ml of isopropanol, and 0.1 g of vinyltrimethoxysilane were added to a 200 ml glass beaker and refluxed for 1 hour at 100° C. Thereafter, the mixture was filtered under reduced pressure using a hydrophobic PTFE membrane filter, washed with 20 ml of isopropanol, and then vacuum-dried for 2 hours in a vacuum dryer adjusted to a temperature of 150° C. to obtain surface-treated hollow silica particles A1.
The sodium content relative to the total mass of the first shell layer and the second shell layer was 500 ppm by mass.

<Hollow Silica Particles A2>
Hollow silica particles A2 were obtained in the same manner as hollow silica particles A1, except that the amount of EO-PO-EO block copolymer used was changed to 2 g and the amount of sorbitan acid monooleate used was changed to 2 g.

<Hollow Silica Particles A3>
Hollow silica particles A3 were obtained in the same manner as hollow silica particles A1, except that the amount of EO-PO-EO block copolymer ("Pluronic (registered trademark) F68" manufactured by ADEKA Corporation) was changed to 20 g, sorbitan acid monooleate (IONET (registered trademark) S-80 manufactured by Sanyo Chemical Industries, Ltd.) was not used, and the pressure in emulsification was changed to 100 bar.

<Hollow Silica Particles A4>
Hollow silica particles A4 were obtained in the same manner as hollow silica particles A1, except that the amount of EO-PO-EO block copolymer ("Pluronic (registered trademark) F68" manufactured by ADEKA Corporation) was changed to 40 g, sorbitan acid monooleate (IONET (registered trademark) S-80 manufactured by Sanyo Chemical Industries, Ltd.) was not used, and the pressure in emulsification was changed to 100 bar.

<Hollow Particles B1>
Aluminosilicate hollow particles were obtained in accordance with the method of Example 1 of JP 2021-143089 A.

[Example 1A]
59 parts by mass of polyphenylene ether resin, 16 parts by mass of butadiene-styrene random copolymer, 25 parts by mass of triallyl isocyanurate, 1 part by mass of α,α'-di(t-butylperoxy)diisopropylbenzene, parts by mass of hollow silica particles A1 accounting for 20% by volume of the total, and 80 parts by mass of toluene were placed in a polyvinyl chloride bottle and kneaded using a planetary dispenser to obtain a resin composition.
The resin composition was applied to a glass cloth of IPC spec 2116 by impregnation, and then heated and dried at 160° C. for 4 minutes to obtain a prepreg.
Three sheets of prepreg were stacked, low-profile copper foil (thickness: 18 μm, Rz: 3.5 μm, Mitsui Kinzoku Co., Ltd., 3EC-M3-V-18) was laminated on the top and bottom, and the resulting mixture was heated and molded at 230° C. and a pressure of 30 kg/cm ² for 120 minutes to obtain a metal substrate with resin.

[Examples 2A to 5A]
Except for changing the hollow silica particles A1 to the hollow silica particles or hollow particles shown in Table 1, a resin composition, a prepreg, and a resin-coated metal substrate were produced in the same manner as in Example 1A.

<Measurement of standard deviation of dielectric constant>
The copper foil was etched from the resin-coated metal substrates of Examples 1A to 5A, thoroughly washed with distilled water, and then dried for 10 minutes in an oven at 100° C. to obtain pressed prepregs. The relative dielectric constant of the pressed prepregs obtained was measured by a perturbation resonator method using a "Vector Network Analyzer E5063A" manufactured by Keycom Corporation.
Specifically, the dielectric constant was measured at three points, 1/4L, 2/4L, and 3/4L, at the center X in the short side direction of the pressed prepreg shown in Figure 1, where L is the total length in the long side direction, and the standard deviation of the dielectric constant was calculated. The measurement results are summarized in Table 1. In Figure 1, the prepreg is indicated by the reference symbol 10.

<Dispersibility evaluation>
The entire prepreg was observed at a magnification of 100 times using an optical microscope (VHX-8000 manufactured by Keyence Corporation), and the dispersibility of the hollow silica particles or hollow particles in the prepreg was evaluated according to the following evaluation criteria.
(evaluation)
A: Hollow silica particles or hollow particle aggregates having a diameter of 0.5 mm or more were not observed.
B: Hollow silica particles or hollow particle aggregates having a diameter of 0.5 mm or more were observed.

<Measurement of relative dielectric constant and dielectric loss tangent>
The resin-coated metal substrates produced in Examples 1A to 5A were immersed in an etching solution (H-1000A, ferric chloride aqueous solution, manufactured by Sanhayato Corporation) to completely remove the copper foil on one side, and then dried in an oven at 100°C for 10 minutes. The obtained pressed prepregs were used to measure the relative dielectric constant and dielectric loss tangent (measurement frequency: 10 GHz) using a vertical split post dielectric resonator (manufactured by Agilent Technologies). The results are shown in Table 1.

As shown in Table 1, the prepreg obtained using composition 1 has a low standard deviation of the dielectric constant.

<Examples 1B to 7B>
Among the following Examples 1B to 7B, Examples 1B to 3B are working examples of the second embodiment, and Examples 4B to 7B are comparative examples of the second embodiment.

1. Preparation of each component for producing a resin composition [thermosetting resin]
Polyphenylene ether: Modified polyphenylene ether in which the terminal hydroxyl groups of polyphenylene ether are modified with methacrylic groups, manufactured by SABIC, Noryl SA9000, Mw 1700, two functional groups per molecule

<Hollow Silica Particles A1>
The hollow silica particles A1 were prepared as follows.

(Preparation of emulsion)
4 g of EO-PO-EO block copolymer (Pluronic (registered trademark) F68, manufactured by ADEKA Corporation) was added to 1250 g of pure water and stirred until dissolved to obtain an aqueous solution. 42 g of n-decane in which 4 g of sorbitan acid monooleate (IONET (registered trademark) S-80, manufactured by Sanyo Chemical Industries, Ltd.) was dissolved was added to this aqueous solution, and the whole solution was stirred using an IKA homogenizer until it became uniform to prepare a crude emulsion.
This crude emulsion was emulsified at a pressure of 50 bar using a high-pressure emulsifier (LAB1000, manufactured by SMT Corporation) to produce an emulsion with an emulsion diameter of 1 μm.

(aging)
The resulting emulsion was allowed to stand at 40° C. for 12 hours.

(First shell layer formation)
After standing, 23 g of a diluted sodium silicate aqueous solution ( _SiO2 concentration 10.4 mass%, _Na2O concentration 3.6 mass%) and 2 M hydrochloric acid were added to 1,300 g of the emulsion so that the pH was 2, and the mixture was stirred while maintaining the temperature at 30° C. to obtain a mixed liquid.
Next, while stirring the mixture, a 1M aqueous solution of sodium hydroxide was slowly added dropwise so that the pH of the mixture became 6, thereby obtaining an oil core-silica shell particle dispersion. The obtained oil core-silica shell particle dispersion was retained and aged.

(Second shell layer formation)
The oil core-silica shell particle dispersion was heated to 70° C., and a 1M aqueous solution of sodium hydroxide was slowly added thereto with stirring to adjust the pH to 9.
Next, 330 g of a diluted aqueous sodium silicate solution ( _SiO2 concentration 10.4% by mass, _Na2O concentration 3.6% by mass) was gradually added together with 0.5 M hydrochloric acid to adjust the pH to 9.
This suspension was kept at 80° C. for 1 day and then cooled to room temperature (25° C.) to obtain a hollow silica precursor dispersion.

(Filtering, washing, drying, firing)
The entire amount of the hollow silica precursor dispersion was neutralized with 2M hydrochloric acid to pH 2, and then filtered using quantitative filter paper 5C. Then, 350 ml of 80° C. ion-exchanged water was added and pressure filtered again to wash the hollow silica cake.
The cake after filtration was dried in a nitrogen atmosphere at 100° C. for 1 hour and then at 400° C. for 2 hours (heating rate: 10° C./min) to remove the organic matter, thereby obtaining a hollow silica precursor.
The obtained hollow silica precursor was baked at 1000° C. for 1 hour (heating rate: 10° C./min) to bake and tighten the shell, thereby obtaining baked hollow silica particles.

(surface treatment)
10 g of hollow calcined silica particles, 150 ml of isopropanol, and 0.1 g of vinyltrimethoxysilane were added to a 200 ml glass beaker and refluxed for 1 hour at 100° C. Thereafter, the mixture was filtered under reduced pressure using a hydrophobic PTFE membrane filter, washed with 20 ml of isopropanol, and then vacuum-dried for 2 hours in a vacuum dryer adjusted to a temperature of 150° C. to obtain surface-treated hollow silica particles A1.
The sodium content relative to the total mass of the first shell layer and the second shell layer was 500 ppm by mass.

<Hollow Silica Particles A2>
Hollow silica particles A2 were obtained in the same manner as hollow silica particles A1, except that the amount of EO-PO-EO block copolymer used was changed to 2 g and the amount of sorbitan acid monooleate used was changed to 2 g.

<Hollow Silica Particles A5>
Hollow silica particles A5 were obtained in the same manner as in the preparation of hollow silica particles A1, except that the hollow silica cake was washed with 350 ml of tap water instead of ion-exchanged water.

<Hollow Silica Particles A6>
Hollow silica particles A6 were obtained in the same manner as in the preparation of hollow silica particles A1, except that the hollow silica cake was washed with 700 ml of tap water instead of ion-exchanged water.

<Hollow Silica Particles A7>
Hollow silica particles A7 were obtained in the same manner as in the preparation of hollow silica particles A1, except that the hollow silica cake was washed with 1,050 ml of tap water instead of ion-exchanged water.

<Hollow Particles B1>
Aluminosilicate hollow particles were obtained in accordance with the method of Example 1 of JP 2021-143089 A.
The content of the alkali metal (Na) contained in the shell layer of the hollow particles B1 relative to the total mass of the shell layer was 1 mass % or more.

<Hollow Particles B2>
Glass Bubbles iM16K (glass balloons with a median diameter of 17 μm, 3M Company) were used as is.
The content of alkali metal (Na) contained in the shell layer of hollow particle B2 relative to the total mass of the shell layer was 1 mass % or more.

[Example 1B]
59 parts by mass of polyphenylene ether resin, 16 parts by mass of butadiene-styrene random copolymer, 25 parts by mass of triallyl isocyanurate, 1 part by mass of α,α'-di(t-butylperoxy)diisopropylbenzene, parts by mass of hollow silica particles A1 accounting for 20% by volume of the total, and 80 parts by mass of toluene were placed in a polyvinyl chloride bottle and kneaded using a planetary dispenser to obtain a resin composition.
The resin composition was allowed to stand in an environment of 25° C. and a relative humidity of 50% for 12 hours.
After standing, the resin composition was applied to impregnate a glass cloth of IPC spec 2116, and then heated and dried at 160° C. for 4 minutes to obtain a prepreg.
Three sheets of prepreg were stacked, low-profile copper foil (thickness: 18 μm, Rz: 3.5 μm, Mitsui Kinzoku Co., Ltd., 3EC-M3-V-18) was laminated on the top and bottom, and the resulting mixture was heated and molded at 230° C. and a pressure of 30 kg/cm ² for 120 minutes to obtain a metal substrate with resin.

[Examples 2B to 7B]
Except for changing the hollow silica particles A1 to the hollow silica particles or hollow particles shown in Table 2, a resin composition, a prepreg, and a resin-coated metal substrate were produced in the same manner as in Example 1B.

<Measurement of Rz of resin-coated metal substrate>
The Rz of the copper foil surface opposite to the prepreg surface of the resin-coated metal substrates produced in Examples 1B to 7B was measured using a contact surface roughness meter (Tokyo Seimitsu Co., Ltd., "SURFCOM NEX001"). The results are shown in Table 2.
In the above measurements, a conical measuring probe with a tip radius of 2 μm (taper angle: 60°) was used, the cutoff values were λc of 0.8 mm and λs of 2.5 μm, the reference length of the roughness curve was 0.8 mm, and the evaluation length of the roughness curve was 4.0 mm.

<Measurement of relative dielectric constant and dielectric loss tangent>
The resin-coated metal substrates produced in Examples 1B to 7B were immersed in an etching solution (H-1000A, ferric chloride aqueous solution, manufactured by Sanhayato Corporation) to completely remove the copper foil on one side, and then dried in an oven at 100°C for 10 minutes. The obtained pressed prepregs were used to measure the relative dielectric constant and dielectric loss tangent (measurement frequency: 10 GHz) using a vertical split post dielectric resonator (manufactured by Agilent Technologies). The results are shown in Table 2.

As shown in Table 2, the molded product of Composition 2 has a high smoothness and few cracks in the hollow silica particles, resulting in a low relative dielectric constant.

10: Pressed prepreg, X: Center of the pressed prepreg in the short side direction, L: Total length of the pressed prepreg in the long side direction

Claims (16)

A resin composition comprising a resin and hollow silica particles,
The resin composition, wherein the ratio of the median diameter (d50) to the d10 of the hollow silica particles is 6.0 or less. A resin composition comprising a resin and hollow silica particles,
The content of particles having an average particle diameter of 10 μm or more relative to the total mass of the resin composition, as measured by a Coulter counter method, is 500 ppm by mass or less;
The resin composition, wherein the hollow silica particles have a d90 of 15.0 μm or less. The resin composition according to claim 1 or 2, wherein the hollow silica particles have a density of 0.35 to 2.00 g/ ^cm3 . 3. The resin composition according to claim 1, wherein the hollow silica particles have a BET specific surface area of 1.0 to 100.0 m ² /g. The resin composition according to claim 1 or 2, wherein the hollow silica particles have a d50 of 0.1 to 10.0 μm. The resin composition according to claim 1 or 2, wherein the d10 of the hollow silica particles is 0.1 to 2.0 μm. The resin composition according to claim 1 or 2, wherein the hollow silica particles have a d90 of 0.7 μm or more. The resin composition according to claim 1 or 2, wherein the resin comprises at least one selected from the group consisting of epoxy resins, polyimide resins, polyphenylene ether resins, resins containing a divinylbenzene skeleton, and resins containing a pyrimidine skeleton. The resin composition according to claim 1 or 2, wherein the content of the hollow silica particles relative to the total volume of the resin composition is 10 to 70 volume %. A prepreg comprising the resin composition or a semi-cured product thereof according to claim 1 or 2, and a fibrous base material. The prepreg according to claim 10, wherein the fibrous base material contains a glass component. A resin-coated metal substrate comprising the resin composition or semi-cured product thereof according to claim 1 or 2, and a metal substrate layer. A resin-coated metal substrate comprising the prepreg according to claim 10 and a metal substrate layer. The resin-coated metal substrate according to claim 12, wherein the metal substrate layer is copper foil. The resin-coated metal substrate according to claim 13, wherein the metal substrate layer is copper foil. A wiring board comprising a cured product of the resin composition according to claim 1 or 2 and metal wiring.