JP7152617B2 - Heat dissipation sheet - Google Patents

Description

The present disclosure relates to a heat dissipation sheet.

2. Description of the Related Art As electronic devices become more sophisticated, it is necessary to efficiently dissipate heat generated in various components that constitute the electronic devices. For example, some power devices, CPUs (Central Processing Units), or light emitting diode (LED) backlights generate heat of 150° C. or higher. If the heat generated from the above-described heat generating elements accumulates inside the electronic device, it may cause problems such as malfunction of the electronic device. Therefore, various techniques have been studied to radiate the heat generated from the heating element.

For example, Japanese Patent Application Laid-Open No. 2017-36190 describes a boron nitride aggregated particle composition having an average particle diameter (D ₅₀ ) of 1 μm to 200 μm, wherein the boron nitride aggregated particle composition is characterized by satisfying specific conditions. is disclosed.

For example, Japanese Unexamined Patent Application Publication No. 2016-98301 discloses a resin composition containing 30 to 60% by volume of hot-melt fluororesin and 40 to 70% by volume of boron nitride particles, wherein the boron nitride particles are Composed of particles (A) and particles (B), the particles (A) are spherical aggregate particles having an average particle diameter of 55 μm to 100 μm and an aspect ratio of 1 to 2, and the particles (B) are A resin composition is disclosed in which the particles have an average particle diameter of 8 to less than 55 μm, and the volume ratio of the particles (A) to the total amount of boron nitride is 80 to 99% by volume.

For example, Japanese Unexamined Patent Application Publication No. 2010-174173 describes a thermally conductive adhesive composition containing boron nitride particles and an acrylic polymer component, wherein boron nitride particles having a particle size of 3 μm or more and 300 μm or less are contained. In addition, the boron nitride particles include 5 to 45% by volume of boron nitride particles having a particle size of 3 μm or more and 20 μm or less, 30 to 70% by volume of boron nitride particles having a particle size of more than 20 μm to 60 μm or less, and more than 60 μm. A thermally conductive adhesive composition is disclosed which contains 10 to 40% by volume of boron nitride particles having a particle size of 300 μm or less.

For example, WO 2016/092951 discloses a resin composition containing 10 to 90% by volume of a specific hexagonal boron nitride powder.

The compositions described in JP-A-2017-36190, JP-A-2016-98301, JP-A-2010-174173, and WO 2016/092951 dissipate heat by being processed into a sheet, for example. Used as a sheet. However, even with the conventional heat dissipation sheets as described above, sufficient thermal conductivity and insulation cannot be obtained. Therefore, there is a demand for a heat-dissipating sheet having high thermal conductivity and high insulating properties.

The present disclosure has been made in view of the circumstances described above.
An object of one aspect of the present disclosure is to provide a heat dissipation sheet that is excellent in thermal conductivity and insulation.

The present disclosure includes the following aspects.
<1> Contains a resin binder and boron nitride particles, and in a particle size distribution based on the number of the boron nitride particles, the particle size D1 at which the frequency is maximized is in the range of 60 μm to 90 μm, and the boron nitride A value obtained by dividing the number of boron nitride particles A having a particle size of 2 μm to 60 μm among the particles by the number of boron nitride particles B having a particle size of 90 μm to 150 μm among the above boron nitride particles is 2. .5 to 5.0 of the heat radiation sheet.
<2> In the particle size distribution based on the number of the boron nitride particles, the particle size D1 and the particle size D2 when the frequency on the smaller diameter side than the particle size D1 is 50% of the maximum frequency are D2>(D1+2 μm )/2, the heat-dissipating sheet according to <1>.
<3> The heat dissipating sheet according to <2>, wherein the particle size D2 is in the range of 30 μm to 50 μm.
<4> In the particle size distribution based on the number of the boron nitride particles, the particle size D1 and the particle size D3 when the frequency on the larger diameter side than the particle size D1 is 50% of the maximum frequency is D3 < ( D1+150 μm)/2.2 The heat-dissipating sheet according to any one of <1> to <3>.
<5> The heat dissipating sheet according to <4>, wherein the particle size D3 is in the range of 80 μm to 130 μm.
<6> The heat dissipating sheet according to any one of <1> to <5>, wherein the number of peaks observed in the particle size distribution based on the number of boron nitride particles is one.
<7> The heat dissipating sheet according to any one of <1> to <6>, which has a porosity of 0% to 5%.
<8> The heat dissipating sheet according to any one of <1> to <7>, wherein the content of the boron nitride particles is 45% by mass to 80% by mass with respect to the total mass of the heat dissipating sheet.

According to one aspect of the present disclosure, it is possible to provide a heat dissipation sheet with excellent thermal conductivity and insulation.

FIG. 1 is a schematic diagram for explaining the particle size distribution.

Hereinafter, embodiments of the present disclosure will be described in detail. The present disclosure is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the purpose of the present disclosure.

In the present disclosure, a numerical range represented using "to" means a range including the numerical values described before and after "to" as lower and upper limits. In the numerical ranges described step by step in the present disclosure, upper or lower limits described in a certain numerical range may be replaced with upper or lower limits of other numerical ranges described step by step. In addition, in the numerical ranges described in the present disclosure, upper or lower limits described in a certain numerical range may be replaced with values shown in Examples.
In the present disclosure, the amount of each component in the composition means the total amount of the multiple substances present in the composition unless otherwise specified when there are multiple substances corresponding to each component in the composition. .
In the present disclosure, a combination of two or more preferred aspects is a more preferred aspect.
In the present disclosure, the term "step" includes not only independent steps, but also if the intended purpose of the step is achieved even if it cannot be clearly distinguished from other steps. .
In the present disclosure, "% by mass" and "% by weight" are synonymous, and "parts by mass" and "parts by weight" are synonymous.
In the present disclosure, "total solids weight" means the total weight of ingredients excluding solvent.
In the present disclosure, the symbols (e.g., A and B) after the terms representing the components are marks used to distinguish the components, and indicate the number of components and the superiority or inferiority of the components. It is not restrictive.

<Heat release sheet>
The heat-dissipating sheet according to the present disclosure contains a resin binder and boron nitride particles, and in the particle size distribution based on the number of the boron nitride particles, the particle size D1 at the maximum frequency is in the range of 60 μm to 90 μm. Among the boron nitride particles, the number of boron nitride particles A having a particle size in the range of 2 μm to 60 μm is divided by the number of boron nitride particles B having a particle size in the range of 90 μm to 150 μm. The value is between 2.5 and 5.0.

The heat dissipation sheet according to the present disclosure is excellent in thermal conductivity and insulation by having the above configuration. Although the reason why the heat-dissipating sheet according to the present disclosure exhibits the above effects is not clear, it is speculated as follows. In JP-A-2017-36190, JP-A-2016-98301, JP-A-2010-174173, and International Publication No. 2016/092951, each boron nitride particle in the process of processing the composition into a sheet. It is presumed that voids are formed between them. On the other hand, the heat dissipation sheet according to the present disclosure contains a resin binder and boron nitride particles, and in the particle size distribution based on the number of the boron nitride particles, the particle size D1 at the maximum frequency is 60 μm to 90 μm. and the number of boron nitride particles A having a particle size in the range of 2 μm to 60 μm among the boron nitride particles, and the number of boron nitride particles B having a particle size in the range of 90 μm to 150 μm among the boron nitride particles Since the value obtained by dividing by the number is 2.5 to 5.0, it is presumed that the boron nitride particles are arranged so as to fill the voids. As a result, the ratio of the boron nitride particles in the heat dissipation sheet (that is, the filling rate) can be made larger than in the conventional heat dissipation sheet. Therefore, the heat dissipation sheet according to the present disclosure is presumed to be excellent in thermal conductivity and insulation.

<<Resin Binder>>
A heat dissipation sheet according to the present disclosure includes a resin binder.

The resin binder is not limited, and known resin binders can be used. Examples of resin binders include epoxy resins, phenol resins, polyimide resins, cresol resins, melamine resins, unsaturated polyester resins, isocyanate resins, polyurethane resins, polybutylene terephthalate resins, polyethylene terephthalate resins, polyphenylene sulfide resins, fluorine resins, and A polyphenylene oxide resin may be mentioned.

Among the above, the resin binder is preferably an epoxy resin from the viewpoint of having a small coefficient of thermal expansion and being excellent in heat resistance and adhesiveness.

The epoxy resin is not limited, and known epoxy resins can be used. Epoxy resins include, for example, bifunctional epoxy resins and novolak-type epoxy resins.

Bifunctional epoxy resins include, for example, bisphenol A type epoxy resins, bisphenol F type epoxy resins, and bisphenol S type epoxy resins.

Examples of novolak-type epoxy resins include phenol novolak-type epoxy resins and cresol novolak-type epoxy resins.

In addition, the resin binder is preferably a cured product of a polymerizable monomer from the viewpoint that it is easy to add functions such as heat resistance.

The polymerizable monomer is not limited as long as it is a polymerizable compound, and known polymerizable monomers can be used.

The polymerizable monomer preferably has a polymerizable group. As the polymerizable group in the polymerizable monomer, at least one polymerizable group selected from the group consisting of an acryloyl group, a methacryloyl group, an oxiranyl group and a vinyl group is preferred.

The polymerizable monomer may have a single polymerizable group, or may have two or more polymerizable groups. Also, the number of polymerizable groups in the polymerizable monomer may be one, or two or more. From the viewpoint of excellent heat resistance of the cured product, the number of polymerizable groups in the polymerizable monomer is preferably two or more, and more preferably three or more. There is no upper limit on the number of polymerizable groups in the polymerizable monomer. The number of polymerizable groups in the polymerizable monomer is often 8 or less, for example.

Specific polymerizable monomers include, for example, epoxy compounds, phenol compounds, imide compounds, melamine compounds, isocyanate compounds, urethane compounds, acrylate compounds, and methacrylate compounds.

Examples of polymerizable monomers include epoxy resin monomers and acrylic resin monomers described in paragraph 0028 of Japanese Patent No. 4118691, epoxy compounds described in paragraphs 0006 to 0011 of JP-A-2008-13759, and particularly Also included are epoxy resin monomers described in paragraphs 0032 to 0100 of JP-A-2013-227451.

The heat-dissipating sheet according to the present disclosure may contain a single resin binder, or may contain two or more resin binders.

The content of the resin binder is preferably 10% by mass to 50% by mass with respect to the total mass of the heat-dissipating sheet, from the viewpoint of the thermal conductivity of the heat-dissipating sheet, the dispersibility of the boron nitride particles, and the film quality of the heat-dissipating sheet. It is preferably 20% by mass to 50% by mass.

<<Boron nitride particles>>
A heat-dissipating sheet according to the present disclosure includes boron nitride particles. Since the heat dissipation sheet according to the present disclosure contains boron nitride particles, the heat conductivity of the heat dissipation sheet can be improved.

The boron nitride particles are not limited, and known boron nitride particles can be used. Boron nitride particles are available, for example, as “HP-40 MF100” manufactured by Mizushima Ferroalloy Co., Ltd.

The boron nitride particles may be primary particles or secondary particles (ie, aggregates of primary particles).

The shape of the boron nitride particles is not limited. Examples of cross-sectional shapes of boron nitride particles include perfect circles, ellipses, polygons, and irregular shapes.

Among the boron nitride particles contained in the heat dissipation sheet according to the present disclosure, the number of boron nitride particles A having a particle size in the range of 2 μm to 60 μm (hereinafter sometimes referred to as “BN particles (A)”) is A value divided by the number of boron nitride particles B (hereinafter sometimes referred to as "BN particles (B)") having a particle size in the range of 90 μm to 150 μm among the boron nitride particles contained in the heat dissipation sheet according to (i.e. , [number of BN particles (A)]/[number of BN particles (B)]) is 2.5 to 5.0. When the value obtained by dividing the number of BN particles (A) by the number of BN particles (B) is within the above range, the ratio of voids contained in the heat dissipation sheet can be reduced, so the thermal conductivity of the heat dissipation sheet, And insulation can be improved. The value obtained by dividing the number of BN particles (A) by the number of BN particles (B) is preferably 3.0 to 5.0, more preferably 3.0 to 4.0.

In the present disclosure, the particle diameter of boron nitride particles is the major axis of the boron nitride particles measured by the following method.
(1) A heat dissipation sheet is cut by irradiation with a focused ion beam (FIB).
(2) A scanning electron microscope (SEM) is used to observe the cross section of the heat-dissipating sheet, and then an image of the boron nitride particles is obtained.
(3) Measure the length of the boron nitride particles. Here, the "major diameter of the boron nitride particle" refers to the length of the longest line segment among the line segments connecting any two points on the contour line of the boron nitride particle. For example, when the boron nitride particles observed in the above image are perfectly circular, the major axis of the boron nitride particles refers to the diameter of the boron nitride particles.

In the particle size distribution based on the number of boron nitride particles, the particle size D1 (also referred to as “mode diameter”, hereinafter sometimes simply referred to as “particle size D1”) when the frequency is maximized is 60 μm to 90 μm. is in the range of In the present disclosure, "particle size distribution based on the number of boron nitride particles" means a particle size distribution in which the ratio (that is, frequency) of boron nitride particles to the particle size of boron nitride particles is expressed on a number basis. When the particle diameter D1 is within the above range, the ratio of voids contained in the heat dissipation sheet can be reduced, so that the thermal conductivity and insulation properties of the heat dissipation sheet can be improved. The particle size D1 is preferably in the range of 60 μm to 90 μm, more preferably in the range of 65 μm to 85 μm.

Here, the particle size D1 will be described with reference to the drawings. FIG. 1 is a schematic diagram for explaining the particle size distribution. However, FIG. 1 does not accurately represent the particle size distribution of the boron nitride particles contained in the heat dissipation sheet according to the present disclosure.

In FIG. 1, the horizontal axis represents the particle size (unit: μm), and the vertical axis represents the number-based frequency (unit: %). The grain size increases from left to right on the horizontal axis. The frequency increases from bottom to top on the vertical axis. As shown in FIG. 1, the frequency is highest at point 10 on the curve of the particle size distribution. In FIG. 1, the particle size D1 at point 10 is the particle size at which the frequency is maximum.

Examples of a method for adjusting the particle size distribution (that is, the relationship between the particle size and the abundance ratio) of the boron nitride particles contained in the heat dissipation sheet according to the present disclosure include classification. For example, the particle size distribution of the boron nitride particles contained in the heat-dissipating sheet according to the present disclosure can be adjusted by manufacturing the heat-dissipating sheet using boron nitride particles whose particle size distribution has been adjusted by classification.

In the particle size distribution based on the number of boron nitride particles, the particle size D1 and the particle size D2 when the frequency on the smaller diameter side than the particle size D1 is 50% of the maximum frequency (hereinafter, sometimes simply referred to as "particle size D2" ) preferably satisfies the relationship D2>(D1+2 μm)/2. When the particle size D1 and the particle size D2 satisfy the above relationship, the ratio of voids included in the heat dissipation sheet can be reduced, so that the thermal conductivity and insulation properties of the heat dissipation sheet can be improved. In the relational expression D2>(D1+2 μm)/2, the units of D1 and D2 are micrometers (μm).

In the present disclosure, "particle diameter D2 when the frequency is 50% of the maximum frequency on the smaller diameter side than particle diameter D1" means that the frequency is the maximum on the curve of the particle size distribution located on the smaller diameter side than particle diameter D1. It means the particle size corresponding to the point located on the largest diameter side among the points at which the frequency is 50%. That is, the particle size D1 and the particle size D2 satisfy the relationship of D1>D2.

Here, the particle size D2 will be described with reference to the drawings. The frequency of point 20 shown in FIG. 1 is 50% of the maximum frequency. That is, the point 20 is the largest side of the points where the frequency is 50% of the maximum frequency on the curve of the particle size distribution located on the smaller diameter side than the particle size D1 (i.e., the place closest to the particle size D1). It is a point located in In FIG. 1, the particle diameter D2 at the point 20 is the particle diameter when the frequency is 50% of the maximum frequency on the smaller diameter side than the particle diameter D1.

The relational expression expressed by "D2>(D1+2 μm)/2" will be described in detail. “(D1+2 μm)/2” represents the particle size obtained by dividing the sum of particle size D1 and 2 μm by 2. The particle size represented by "(D1+2 μm)/2" lies in the particle size distribution between 2 μm and particle size D1 (see, for example, FIG. 1). A relational expression represented by "D2>(D1+2 μm)/2" means that the particle size D2 is larger than the particle size represented by "(D1+2 μm)/2". That is, D1 and D2 satisfying the relationship of D2>(D1+2 μm)/2 means that, in the particle size distribution, the spread of the peak with the highest frequency on the small diameter side is small.

The particle size D2 is preferably 25 μm or more, more preferably 30 μm or more. The upper limit of the particle diameter D2 is not limited as long as it is smaller than the particle diameter D1. The particle size D2 is preferably 55 μm or less, more preferably 50 μm or less.

In the particle size distribution based on the number of boron nitride particles, the particle size D1 and the particle size D3 when the frequency on the larger diameter side than the particle size D1 is 50% of the maximum frequency (hereinafter simply referred to as "particle size D3" ) preferably satisfies the relationship D3<(D1+150 μm)/2.2. When the particle size D1 and the particle size D3 satisfy the above relationship, the proportion of voids in the heat dissipation sheet can be reduced, so that the thermal conductivity and insulation properties of the heat dissipation sheet can be improved. In the relational expression of D3<(D1+150 μm)/2.2, the units of D1 and D3 are micrometers (μm).

In the present disclosure, "particle diameter D3 when the frequency is 50% of the maximum frequency on the larger diameter side than particle diameter D1" means that the frequency on the curve of the particle size distribution located on the larger diameter side than particle diameter D1 means the particle size corresponding to the point located on the smallest diameter side among the points where is 50% of the maximum frequency. That is, the particle size D1 and the particle size D3 satisfy the relationship of D1<D3.

Here, the particle size D3 will be described with reference to the drawings. The frequency of point 30 shown in FIG. 1 is 50% of the maximum frequency. That is, the point 30 is the smallest diameter side (i.e., the place closest to the particle size D1) among the points where the frequency is 50% of the maximum frequency on the curve of the particle size distribution located on the larger diameter side than the particle size D1. It is a point located in In FIG. 1, the particle size D3 at the point 30 is the particle size when the frequency is 50% of the maximum frequency on the larger diameter side than the particle size D1.

The relational expression expressed by "D3<(D1+150 μm)/2.2" will be described in detail. “(D1+150 μm)/2.2” represents the particle size obtained by dividing the sum of particle size D1 and 150 μm by 2.2. The particle size represented by "(D1+150 μm)/2.2" lies in the particle size distribution between particle size D1 and 150 μm (see, for example, FIG. 1). The relational expression expressed by "D3<(D1+150 μm)/2.2" means that the particle diameter D3 is smaller than the particle diameter expressed by "(D1+150 μm)/2.2". That is, D1 and D3 satisfying the relationship of D3<(D1+150 μm)/2.2 means that the peak with the highest frequency has a small spread on the large diameter side in the particle size distribution.

The particle size D3 is preferably 130 μm or less, more preferably 115 μm or less. The lower limit of the particle size D3 is not limited as long as it is a value larger than the particle size D1. The particle size D3 is preferably 80 μm or more, more preferably 85 μm or more.

The number of peaks observed in the particle size distribution based on the number of boron nitride particles is not limited. For example, the number of peaks observed in the range of 2 μm to 60 μm may be 1 or 2 or more. The number of peaks observed in the particle size distribution based on the number of boron nitride particles is preferably one. In the present disclosure, "the number of peaks is one" means that there is one point showing the maximum frequency in the particle size distribution curve. Since the number of peaks is one, that is, the uniformity of the particle size distribution is high, it is possible to reduce the proportion of voids contained in the heat-dissipating sheet.

The average aspect ratio of the boron nitride particles is preferably 3 or more, more preferably 5 or more, and particularly preferably 8 or more. When the boron nitride particles have an average aspect ratio of 5 or more, the thermal conductivity of the heat dissipation sheet can be improved. The upper limit of the average aspect ratio of boron nitride particles is not limited. The average aspect ratio of the boron nitride particles is preferably 20 or less, more preferably 15 or less, from the viewpoint of particle dispersibility in the composition described later. The average aspect ratio of the boron nitride particles is determined by arithmetically averaging the aspect ratios of 100 arbitrarily selected boron nitride particles.

In the present disclosure, the aspect ratio of boron nitride particles is the ratio of the major axis to the minor axis (major axis/minor axis) of the boron nitride particles measured by the following method.
(1) A heat dissipation sheet is cut by irradiation with a focused ion beam (FIB).
(2) A scanning electron microscope (SEM) is used to observe the cross section of the heat-dissipating sheet, and then an image of the boron nitride particles is obtained.
(3) Measure the major and minor diameters of the boron nitride particles. Here, the “minor axis of the boron nitride particle” is the line segment that is perpendicular to the line segment that defines the major axis of the boron nitride particle and connects any two points on the contour line of the boron nitride particle. The length of a long line segment.
(4) Find the ratio of the major axis to the minor axis of the boron nitride particles (long axis/short axis).

The heat-dissipating sheet according to the present disclosure may contain a single type of boron nitride particles, or may contain two or more types of boron nitride particles.

The content of boron nitride particles is preferably 40% by mass to 80% by mass, more preferably 45% by mass to 80% by mass, and 50% by mass to 80% by mass with respect to the total mass of the heat dissipation sheet. % is particularly preferred. When the content of the boron nitride particles is 40% by mass or more, the thermal conductivity of the heat dissipation sheet can be improved. When the content of the boron nitride particles is 80% by mass or less, the film quality of the heat dissipation sheet can be improved.

The content of the boron nitride particles is preferably 90 parts by mass to 400 parts by mass, more preferably 100 parts by mass to 350 parts by mass, with respect to 100 parts by mass of the resin binder, from the viewpoint of thermal conductivity of the heat dissipating sheet. is more preferred.

<<Porosity>>
The porosity of the heat dissipation sheet according to the present disclosure is preferably 0% to 5%, more preferably 0% to 3%, even more preferably 0% to 2%, and 0% to 1%. % is particularly preferred. When the porosity of the heat dissipation sheet according to the present disclosure is within the above range, the heat conductivity of the heat dissipation sheet can be improved. In addition, as the porosity of the heat-dissipating sheet according to the present disclosure decreases, the insulating properties of the heat-dissipating sheet tend to improve.

The porosity of the heat dissipation sheet according to the present disclosure is measured by the following method.
(1) Using a three-dimensional X-ray microscope (for example, “nano3DX” manufactured by Rigaku Corporation), an observation image (field of view: 200 μm×200 μm) of the heat dissipation sheet is obtained.
(2) Any five observation images (visual field range: 200 μm×200 μm) are subjected to binarization processing, and the porosity ([area of void]/[area of visual field range]) is calculated from each observation image.
(3) Calculate the porosity (%) of the heat dissipation sheet by arithmetically averaging the five measured values.

<<Size of void>>
The size of the voids is preferably 10 μm or less, more preferably 5 μm or less, and particularly preferably 1 μm or less. When the size of the void is 10 μm or less, the thermal conductivity of the heat dissipation sheet can be greatly improved. The lower limit of the void size is not limited, and the closer to 0 μm, the better. The void size may be greater than or equal to 0 μm. The size of the voids is the average circle equivalent diameter obtained from the area of the voids. The area of voids is measured by a method according to the method for measuring void ratio.

<<Thickness>>
The thickness of the heat dissipation sheet according to the present disclosure is not limited. The thickness of the heat dissipation sheet according to the present disclosure is preferably in the range of 50 μm to 200 μm from the viewpoint of thermal conductivity.

<<other members>>
A substrate may be arranged on at least one surface of the heat dissipation sheet according to the present disclosure. Examples of the base material include the base materials described in the section "Manufacturing method" below. When using a thermally conductive sheet according to the present disclosure, the substrate may be removed prior to using the thermally conductive sheet, or may be used with the thermally conductive sheet. For example, if a copper substrate is disposed on one side of a heat-dissipating sheet according to the present disclosure, the heat-dissipating sheet may be used with the copper substrate without removing the copper substrate. However, the base material is not included in the constituent elements of the heat-dissipating sheet according to the present disclosure described in each of the above sections. For example, the thickness of the heat-dissipating sheet according to the present disclosure does not include the thickness of the substrate.

<<Manufacturing method>>
Examples of the method for producing the heat-dissipating sheet according to the present disclosure include a method using a composition containing a resin binder or a polymerizable monomer and boron nitride particles. For example, a heat-dissipating sheet can be produced by coating the above composition on a substrate and then drying or curing it as necessary. A method for producing a heat-dissipating sheet according to the present disclosure includes the steps of applying a composition containing a polymerizable monomer and boron nitride particles onto a substrate, and curing the composition applied onto the substrate. and preferably comprising the steps of: A preferred method for manufacturing the heat-dissipating sheet according to the present disclosure will be described below.

[Composition]
A method for preparing a composition containing a polymerizable monomer and boron nitride particles includes, for example, a method of mixing the polymerizable monomer and boron nitride particles. The mixing method is not limited, and known methods can be used.

Examples of the polymerizable monomers include the polymerizable monomers described in the section "Resin Binder" above. For example, by using an epoxy compound and a phenol compound as polymerizable monomers, an epoxy resin, which is a type of resin binder, can be produced.

The composition may contain a single polymerizable monomer, or may contain two or more polymerizable monomers.

The content of the polymerizable monomer in the composition is preferably 10% by mass to 50% by mass, more preferably 20% by mass to 50% by mass, relative to the total solid content in the composition. .

It is preferable to adjust the particle size distribution of the boron nitride particles so as to fall within the range described in the section "Boron Nitride Particles" above. Examples of methods for adjusting the particle size distribution of boron nitride particles include classification. The classification method is not limited, and known methods can be used. Classification methods include, for example, sieving. In the preparation of the composition, for example, by adjusting the amount of addition of one or more boron nitride particles having a predetermined particle size distribution, the particle size distribution of the boron nitride particles contained in the composition can be adjusted. can. By adjusting the particle size distribution of the boron nitride particles contained in the composition, the particle size distribution of the boron nitride particles contained in the heat-dissipating sheet according to the present disclosure can be adjusted.

The content of boron nitride particles in the composition is preferably 40% by mass to 80% by mass, more preferably 45% by mass to 80% by mass, relative to the total solid mass in the composition. , 50% by weight to 80% by weight.

The composition may contain other ingredients in addition to the resin binder and boron nitride particles. Other components include, for example, curing agents, curing accelerators, polymerization initiators, and solvents.

The curing agent is not limited, and known curing agents can be used. The curing agent is a compound having at least one functional group selected from the group consisting of a hydroxy group, an amino group, a thiol group, an isocyanate group, a carboxy group, an acryloyl group, a methacryloyl group, and a carboxylic anhydride group. More preferably, it is a compound having at least one functional group selected from the group consisting of a hydroxy group, an acryloyl group, a methacryloyl group, an amino group, and a thiol group.

The curing agent is preferably a compound having two or more of the above functional groups, more preferably a compound having two or three of the above functional groups.

Specific curing agents include, for example, amine-based curing agents, phenol-based curing agents, guanidine-based curing agents, imidazole-based curing agents, naphthol-based curing agents, acrylic-based curing agents, acid anhydride-based curing agents, and active ester-based curing agents. Curing agents, benzoxazine-based curing agents, and cyanate ester-based curing agents are included. Among these, the curing agent is preferably an imidazole curing agent, an acrylic curing agent, a phenolic curing agent, or an amine curing agent.

The composition may contain a single curing agent, or may contain two or more curing agents.

When the composition contains a curing agent, the content of the curing agent is preferably 1 to 50% by mass, preferably 1 to 30% by mass, based on the total solid content in the composition. more preferred.

The curing accelerator is not limited, and known curing accelerators can be used. Curing accelerators include, for example, triphenylphosphine, 2-ethyl-4-methylimidazole, boron trifluoride amine complex, and 1-benzyl-2-methylimidazole.

The composition may contain a single curing accelerator, or may contain two or more curing accelerators.

When the composition contains a curing accelerator, the content of the curing accelerator is preferably 0.1% by mass to 20% by mass with respect to the total solid mass in the composition.

The polymerization initiator is not limited, and known polymerization initiators can be used. For example, when the polymerizable monomer has an acryloyl group or a methacryloyl group, the polymerization initiator is the polymerization initiator described in paragraph 0062 of JP-A-2010-125782, or JP-A-2015-052710. A polymerization initiator described in paragraph 0054 is preferred.

The composition may contain a single polymerization initiator, or may contain two or more polymerization initiators.

When the composition contains a polymerization initiator, the content of the polymerization initiator is preferably 0.1% by mass to 50% by mass with respect to the total solid mass in the composition.

The solvent is not limited, and known solvents can be used. The solvent is preferably an organic solvent. Organic solvents include, for example, ethyl acetate, methyl ethyl ketone, dichloromethane, and tetrahydrofuran.

The composition may contain a single solvent, or may contain two or more solvents.

The content of the solvent is not limited, and may be determined, for example, according to the composition of the composition and the coating method. The solvent content is preferably 30% by mass to 80% by mass, more preferably 30% by mass to 70% by mass, relative to the total mass of the composition.

[Base material]
Substrates include, for example, metal substrates and release liners.

Examples of metal substrates include iron substrates, copper substrates, stainless steel substrates, aluminum substrates, magnesium-containing alloy substrates, and aluminum-containing alloy substrates. Among the above, the metal substrate is preferably a copper substrate.

Examples of the release liner include paper (eg, kraft paper, glassine paper, and fine paper), resin film (eg, polyolefin and polyester), and laminated paper obtained by laminating paper and resin film.

Polyolefins include, for example, polyethylene and polypropylene.

Examples of polyester include polyethylene terephthalate (PET).

The paper used as the release liner may be release-treated paper. The release-treated paper can be formed, for example, by further performing a release treatment on one or both sides of the filler-treated paper. The filling treatment can be performed using, for example, clay or polyvinyl alcohol. The peeling treatment can be performed using, for example, a silicone-based resin.

The thickness of the substrate is not limited, and may be determined, for example, within the range of 10 μm to 300 μm.

[Application method]
The coating method is not limited, and a known method can be used. Examples of coating methods include roll coating, gravure printing, spin coating, wire bar coating, extrusion coating, direct gravure coating, reverse gravure coating, die coating, spraying, comma coating, and blade. method, and inkjet method.

The composition applied onto the substrate may optionally be dried. The drying method includes, for example, a method of applying hot air of 40° C. to 140° C. for 1 minute to 30 minutes to the composition applied on the substrate.

[Curing method]
The curing method is not limited, and known methods can be used. The curing method is preferably a thermosetting reaction or a photo-curing reaction, preferably a thermosetting reaction.

The heating temperature in the thermosetting reaction is not limited, and may be determined, for example, within the range of 50°C to 200°C.

The heating time in the thermosetting reaction is not limited, and may be determined according to the heating temperature. The heating time in the thermosetting reaction may be determined, for example, within the range of 1 minute to 60 minutes.

The curing reaction may be a semi-curing reaction. That is, the cured product to be obtained may be in a so-called B-stage state (semi-cured state).

In the method for manufacturing a heat-dissipating sheet according to the present disclosure, the curing reaction may be performed multiple times, if necessary. When the curing reaction is performed multiple times, the conditions for each curing reaction may be the same or different.

[Other processes]
The method for manufacturing a heat-dissipating sheet according to the present disclosure may include steps other than the steps described above (hereinafter, may be referred to as “other steps”). Other steps include, for example, a step of pressurizing a cured composition (hereinafter referred to as “cured product”).

When the substrate is arranged on the surface of the cured product, the cured product may be pressurized after the substrate is separated from the cured product. Alternatively, the cured product may be pressed together with the base material without separating the base material from the cured product. From the viewpoint of ease of processing, it is preferable to press the cured product after peeling the substrate from the cured product.

The pressurization method is not limited, and a known method can be used. Pressing methods include, for example, pressing and calendering. Among the above, the pressurization method is preferably calendering from the viewpoint of productivity and porosity reduction.

The pressure when applying pressure is not limited, and may be determined, for example, according to the method of applying pressure and the composition of the cured product. For example, when the pressurizing method is calendering, the pressure (linear pressure) is preferably 50 N/m to 200 N/m, more preferably 100 N/m to 150 N/m.

The temperature at which the pressure is applied is not limited, and may be determined, for example, according to the method of pressure application and the composition of the cured product. The temperature is preferably 20°C to 150°C, more preferably 25°C to 120°C.

When the pressing method is calendering, the conveying speed of the cured product is not limited. The conveying speed of the cured product may be determined, for example, within the range of 1 m/min to 100 m/min.

<<Usage>>
Since the heat dissipating sheet according to the present disclosure has excellent thermal conductivity and insulating properties, the heat generated in the heat generating elements can be efficiently dissipated by bringing the heat dissipating sheet according to the present disclosure into contact with various heat generating elements. For example, by bringing the heat dissipation sheet according to the present disclosure into contact with various parts that constitute an electronic device, heat generated in the parts can be efficiently dissipated. Examples of the components include power devices and CPUs. Also, the heat dissipation sheet according to the present disclosure may be used by being arranged between a heat generating body such as a power device and a heat dissipating body such as a heat sink.

EXAMPLES The present disclosure will be described in detail below with reference to Examples, but the present disclosure is not limited to these. "Parts" and "%" are based on mass unless otherwise specified.

<Example 1>
[Classification of boron nitride particles]
Boron nitride particles (HP-40 MF100, manufactured by Mizushima Ferroalloy Co., Ltd.) (1) and boron nitride particles (HP-40 MF100, manufactured by Mizushima Ferroalloy Co., Ltd.) are classified (classifier: manufactured by Nisshin Engineering Co., Ltd. Boron nitride particles (A1) were obtained by kneading with boron nitride particles (2) obtained by classifying with an Aerofine classifier, classification conditions: D50 = 62 μm) at a ratio of 5:5 (mass ratio).

[Preparation of composition (A)]
Composition (A) was prepared by kneading the following ingredients.
Monomer (A) (Raw material for epoxy resin, QE-2405, manufactured by Combiblocks): 17 parts by mass Monomer (B) (Raw material for epoxy resin, YX4000, manufactured by Mitsubishi Chemical Corporation): 34 parts by mass Methyl ethyl ketone: 65 parts by mass TPP (triphenylphosphine, curing accelerator): 0.5 parts by mass Boron nitride particles (A1): 51 parts by mass

The above monomer (A) is a compound having the following structure.

The above monomer (B) is a compound having the following structure.

[Production of heat dissipation sheet]
Using an applicator, the composition (A) is applied onto the release surface of a polyester film (NP-100A, thickness: 100 μm, manufactured by Panac Co., Ltd.) so that the thickness after drying is 250 μm, Then, it was dried with hot air at 130°C for 5 minutes to form a coating film. By curing the coating film at 180° C. for 1 hour, a heat-dissipating sheet precursor with a polyester film was produced. The polyester film was peeled off from the heat-dissipating sheet precursor with the polyester film. Next, a heat-dissipating sheet (thickness: 200 μm) was produced by calendering the heat-dissipating sheet precursor under the following conditions. In calendering, a pair of rolls having a rubber roll and a SUS (stainless steel) roll was used. The content of boron nitride particles in the heat dissipation sheet is 50% by mass.

(Conditions for calendering)
・Linear pressure: 100N/m
・Temperature: 25℃
・Conveyance speed: 5m/min

<Example 2>
[Classification of boron nitride particles]
The boron nitride particles (1) used in Example 1 and the boron nitride particles (HP-40 MF100, manufactured by Mizushima Ferroalloy Co., Ltd.) are classified (classifier: Aerofine Classifier manufactured by Nisshin Engineering Co., Ltd., classification conditions: Boron nitride particles (A2) were obtained by kneading with the boron nitride particles (3) obtained by making D50 = 74 µm at a ratio of 5:5 (mass ratio).

[Production of heat dissipation sheet]
A heat-dissipating sheet was produced in the same manner as in Example 1, except that the boron nitride particles (A1) in the composition (A) were changed to boron nitride particles (A2).

<Example 3>
[Classification of boron nitride particles]
The boron nitride particles (1) used in Example 1 and the boron nitride particles (HP-40 MF100, manufactured by Mizushima Ferroalloy Co., Ltd.) are classified (classifier: Aerofine Classifier manufactured by Nisshin Engineering Co., Ltd., classification conditions: D50=88 μm) and the boron nitride particles (4) were kneaded at a ratio of 5:5 (mass ratio) to obtain boron nitride particles (A3).

[Production of heat dissipation sheet]
A heat-dissipating sheet was produced in the same manner as in Example 1, except that the boron nitride particles (A1) in the composition (A) were changed to boron nitride particles (A3).

<Example 4>
[Classification of boron nitride particles]
Boron nitride particles ( A4) was obtained.

[Production of heat dissipation sheet]
A heat-dissipating sheet was produced in the same manner as in Example 1, except that the boron nitride particles (A1) in the composition (A) were changed to boron nitride particles (A4).

<Example 5>
[Classification of boron nitride particles]
Boron nitride particles ( A5) was obtained.

[Production of heat dissipation sheet]
A heat-dissipating sheet was produced in the same manner as in Example 1, except that the boron nitride particles (A1) in the composition (A) were changed to boron nitride particles (A5).

<Example 6>
[Classification of boron nitride particles]
The same as in Example 3 except that the mixing ratio (mass ratio) of the boron nitride particles (1) used in Example 1 and the boron nitride particles (4) used in Example 3 was changed to 6:4. Boron nitride particles (A6) were obtained by the method.

[Production of heat dissipation sheet]
A heat-dissipating sheet was produced in the same manner as in Example 1, except that the boron nitride particles (A1) in the composition (A) were changed to boron nitride particles (A6).

<Example 7>
[Classification of boron nitride particles]
The same as in Example 3 except that the mixing ratio (mass ratio) of the boron nitride particles (1) used in Example 1 and the boron nitride particles (4) used in Example 3 was changed to 4:6. Boron nitride particles (A7) were obtained by the method.

[Production of heat dissipation sheet]
A heat-dissipating sheet was produced in the same manner as in Example 1, except that the boron nitride particles (A1) in the composition (A) were changed to boron nitride particles (A7).

<Example 8>
[Classification of boron nitride particles]
By the same method as in Example 1, except that the mixing ratio (mass ratio) of the boron nitride particles (1) and the boron nitride particles (2) used in Example 1 was changed to 4.5:5.5. Boron nitride particles (A8) were obtained.

[Production of heat dissipation sheet]
A heat-dissipating sheet was produced in the same manner as in Example 1, except that the boron nitride particles (A1) in the composition (A) were changed to boron nitride particles (A8).

<Example 9>
[Classification of boron nitride particles]
Boron nitride particles ( A9) was obtained.

[Production of heat dissipation sheet]
A heat-dissipating sheet was produced in the same manner as in Example 1, except that the boron nitride particles (A1) in the composition (A) were changed to boron nitride particles (A9).

<Example 10>
[Classification of boron nitride particles]
Boron nitride particles ( A10) was obtained.

[Production of heat dissipation sheet]
A heat-dissipating sheet was produced in the same manner as in Example 1, except that the boron nitride particles (A1) in the composition (A) were changed to boron nitride particles (A10).

<Comparative Example 1>
[Classification of boron nitride particles]
The boron nitride particles (1) used in Example 1 and the boron nitride particles (HP-40 MF100, manufactured by Mizushima Ferroalloy Co., Ltd.) are classified (classifier: Aerofine Classifier manufactured by Nisshin Engineering Co., Ltd., classification conditions: Boron nitride particles (B1) were obtained by kneading them with boron nitride particles (5) obtained by sizing (D50=57 μm) at a ratio of 5:5 (mass ratio).

[Production of heat dissipation sheet]
A heat-dissipating sheet was produced in the same manner as in Example 1, except that the boron nitride particles (A1) in the composition (A) were changed to boron nitride particles (B1).

<Comparative Example 2>
[Classification of boron nitride particles]
The boron nitride particles (1) used in Example 1 and the boron nitride particles (HP-40 MF100, manufactured by Mizushima Ferroalloy Co., Ltd.) are classified (classifier: Aerofine Classifier manufactured by Nisshin Engineering Co., Ltd., classification conditions: Boron nitride particles (B2) were obtained by kneading them with boron nitride particles (6) obtained by sizing (D50=96 μm) at a ratio of 5:5 (mass ratio).

[Production of heat dissipation sheet]
A heat-dissipating sheet was produced in the same manner as in Example 1, except that the boron nitride particles (A1) in the composition (A) were changed to boron nitride particles (B2).

<Comparative Example 3>
[Classification of boron nitride particles]
By the same method as in Example 1, except that the mixing ratio (mass ratio) of the boron nitride particles (1) and the boron nitride particles (2) used in Example 1 was changed to 3.3:6.7. Boron nitride particles (B3) were obtained.

[Production of heat dissipation sheet]
A heat-dissipating sheet was produced in the same manner as in Example 1, except that the boron nitride particles (A1) in the composition (A) were changed to boron nitride particles (B3).

<Comparative Example 4>
[Classification of boron nitride particles]
By the same method as in Example 1, except that the mixing ratio (mass ratio) of the boron nitride particles (1) and the boron nitride particles (2) used in Example 1 was changed to 6.6:3.4. Boron nitride particles (B4) were obtained.

[Production of heat dissipation sheet]
A heat-dissipating sheet was produced in the same manner as in Example 1, except that the boron nitride particles (A1) in the composition (A) were changed to boron nitride particles (B4).

<Porosity>
The porosity of the heat-dissipating sheets produced in Examples and Comparative Examples was measured by the following method. Table 1 shows the measurement results.
(1) A three-dimensional X-ray microscope (“nano3DX” manufactured by Rigaku Corporation) was used to obtain an observation image (field of view: 200 μm×200 μm) of the heat-dissipating sheet.
(2) Any five observation images (visual field range: 200 μm×200 μm) were binarized, and the porosity ([area of void]/[area of visual field]) was calculated from each observation image.
(3) The porosity (%) of the heat dissipation sheet was calculated by arithmetically averaging the five measured values.

<Withstand voltage>
The withstand voltage of the heat-dissipating sheets (single sheet) produced in Examples and Comparative Examples was measured by the following method. In the dielectric breakdown test conducted by the method according to "JIS C 2110-1:2016", the highest voltage at which the test piece does not cause dielectric breakdown was taken as the withstand voltage. Table 1 shows the measurement results. It means that the higher the value of the withstand voltage, the higher the insulation.

<Thermal conductivity>
The thermal conductivity of the heat-dissipating sheets (single sheet) produced in Examples and Comparative Examples was measured by the following method. Table 1 shows the measurement results. A higher thermal conductivity means a higher thermal conductivity.
(1) Using "LFA467" manufactured by NETZSCH, the thermal diffusivity in the thickness direction of the heat dissipation sheet was measured by the laser flash method.
(2) The specific gravity of the heat-dissipating sheet was measured using a balance “XS204” manufactured by Mettler-Toledo Corporation (using a “solid specific gravity measurement kit”).
(3) Using "DSC320/6200" manufactured by Seiko Instruments Inc., the specific heat of each heat-dissipating sheet at 25°C was determined using DSC7 software under a temperature increase condition of 10°C/min.
(4) The obtained thermal diffusivity was multiplied by the specific gravity and the specific heat to calculate the thermal conductivity of the heat dissipation sheet.

From Table 1, it was found that Examples 1 to 10 are superior to Comparative Examples 1 to 4 in thermal conductivity and insulation.

The disclosure of Japanese Patent Application No. 2019-173834 filed on September 25, 2019 is incorporated herein by reference in its entirety. All publications, patent applications and technical standards mentioned herein are to the same extent as if each individual publication, patent application and technical standard were specifically and individually indicated to be incorporated by reference. incorporated herein by reference.

Claims (8)

including a resin binder and boron nitride particles,
In the particle size distribution based on the number of boron nitride particles, the particle size D1 at which the frequency is maximized is in the range of 60 μm to 90 μm,
A value obtained by dividing the number of boron nitride particles A having a particle size of 2 μm to 60 μm among the boron nitride particles by the number of boron nitride particles B having a particle size of 90 μm to 150 μm among the boron nitride particles. is 2.5 to 5.0. In the particle size distribution based on the number of the boron nitride particles, the particle size D1 and the particle size D2 when the frequency on the smaller diameter side than the particle size D1 is 50% of the maximum frequency are D2>(D1+2 μm)/2 The heat dissipation sheet according to claim 1, which satisfies the relationship of 3. The heat dissipating sheet according to claim 2, wherein the particle size D2 is in the range of 30 μm to 50 μm. In the particle size distribution based on the number of the boron nitride particles, the particle size D1 and the particle size D3 when the frequency on the larger diameter side than the particle size D1 is 50% of the maximum frequency are D3 < (D1 + 150 μm) / 4. The heat dissipating sheet according to any one of claims 1 to 3, which satisfies the relationship of 2.2. 5. The heat dissipating sheet according to claim 4, wherein the particle size D3 is in the range of 80 μm to 130 μm. 6. The heat dissipating sheet according to any one of claims 1 to 5, wherein the number of peaks observed in the particle size distribution based on the number of boron nitride particles is one. 7. The heat dissipating sheet according to any one of claims 1 to 6, which has a porosity of 0% to 5%. The heat dissipation sheet according to any one of claims 1 to 7, wherein the content of the boron nitride particles is 45% by mass to 80% by weight with respect to the total weight of the heat dissipation sheet.

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