JPWO2020194867A1 - Heat dissipation sheet precursor and heat dissipation sheet manufacturing method - Google Patents

Abstract

It contains a resin binder and inorganic nitride particles, and the content of the inorganic nitride particles is 50% by mass to 80% by mass with respect to the total mass of the heat radiation sheet precursor, and the void ratio is 30. The ratio of the intensity of the diffraction peak on the (002) plane of the inorganic nitride particles to the intensity of the diffraction peak on the (100) plane of the inorganic nitride particles, which is% to 45% and is measured by the X-ray diffractometry. , 18 or less, and a method for manufacturing a heat radiating sheet, which comprises a step of pressurizing the heat radiating sheet precursor.

Description

The present disclosure relates to a heat radiating sheet precursor and a method for manufacturing the heat radiating sheet.

As the performance of electronic devices increases, it is necessary to efficiently dissipate the heat generated in various components that make up the electronic devices. For example, some power devices, CPUs (Central Processing Units), or light emitting diode (LED: Light Emitting Diode) backlights generate heat of 150 ° C. or higher. If the heat generated from the heating element as described above accumulates inside the electronic device, it may cause a malfunction such as malfunction of the electronic device. Therefore, various techniques have been studied in order to dissipate heat generated from a heating element.

In International Publication No. 2014/199650, a step of applying a specific thermosetting resin composition to a releasable substrate and drying it, and pressurizing the coated dried product with a press pressure of 0.5 MPa or more and 50 MPa or less. A method for producing a thermally conductive sheet, which comprises a step of curing is disclosed.

Japanese Unexamined Patent Publication No. 2015-35580 discloses a heat conductive sheet containing a curable resin composition, heat conductive fibers, and heat conductive particles and having a compression ratio of 40% or more.

Japanese Patent Application Laid-Open No. 2013-177563 describes a heat conductive sheet formed from a plate-shaped boron nitride particles and a heat conductive composition containing a rubber component, wherein the above heat conductive sheet contains the above boron nitride. Disclosed is a heat conductive sheet characterized in that the content ratio of particles is 35% by volume or more and the heat conductivity in the direction orthogonal to the thickness direction of the heat conductive sheet is 4 W / m · K or more. Has been done.

Japanese Unexamined Patent Publication No. 2016-127046 discloses a heat-dissipating resin composition containing a specific granulated powder and a thermosetting resin, and a heat-dissipating sheet made of the above-mentioned heat-dissipating resin composition.

In International Publication No. 2018/181606, between the first surface layer containing the insulating material A, the second surface layer containing the insulating material A, and the first surface layer and the second surface layer. The insulating material A includes a first boron nitride sintered body having an orientation degree of hexagonal boron nitride primary particles of 0.6 to 1.4. , The first thermosetting resin composition impregnated in the first boron nitride sintered body is contained, and the insulating material B has a degree of orientation of hexagonal boron nitride primary particles of 0.01 to 0. Disclosed is a heat transfer member comprising a second boron nitride sintered body of 0.05 and a second thermosetting resin composition impregnated in the second boron nitride sintered body. ing.

In the conventional heat dissipation sheet, voids having low thermal conductivity may be formed. Increasing the proportion of voids contained in the heat radiating sheet may lead to a decrease in the thermal conductivity of the heat radiating sheet. For example, in the method for producing a heat conductive sheet described in International Publication No. 2014/199650, the coated dried product is cured while being pressed with a specific press pressure. However, it is considered difficult to sufficiently reduce the voids even by the above method. Further, the rate at which voids are generated tends to be high in the heat radiating sheet containing inorganic nitride particles as the heat conductive material.

This disclosure has been made in view of the above circumstances.
One aspect of the present disclosure is to provide a heat dissipation sheet precursor capable of forming a heat dissipation sheet having few voids and excellent thermal conductivity.
Another aspect of the present disclosure is to provide a method for manufacturing a heat radiating sheet capable of forming a heat radiating sheet having few voids and excellent thermal conductivity.

The means for solving the above problems include the following aspects.
<1> A resin binder and inorganic nitride particles are contained, and the content of the inorganic nitride particles is 50% by mass to 80% by mass with respect to the total mass of the heat radiation sheet precursor, and the void ratio. Is 30% to 45%, and the intensity of the diffraction peak on the (002) plane of the inorganic nitride particles with respect to the intensity of the diffraction peak on the (100) plane of the inorganic nitride particles, which is measured by the X-ray diffraction method. Heat dissipation sheet precursor having a ratio of 18 or less.
<2> The heat dissipation sheet precursor according to <1>, wherein the inorganic nitride particles have an average aspect ratio of 5 or more.
<3> The heat dissipation sheet precursor according to <1> or <2>, wherein the average particle size of the inorganic nitride particles is 10 μm or more.
<4> The description in any one of <1> to <3>, wherein the thickness T1 before pressurization and the thickness T2 after pressurization satisfy the relationship of 0.55 ≦ T2 / T1 ≦ 0.70. Heat dissipation sheet precursor.
<5> The heat dissipation sheet according to any one of <1> to <4>, wherein the density D1 before pressurization and the density D2 after pressurization satisfy the relationship of 1.40 ≦ D2 / D1 ≦ 1.90. precursor.
<6> The heat dissipation sheet precursor according to any one of <1> to <5>, wherein the inorganic nitride particles are boron nitride particles.
<7> The heat-dissipating sheet precursor according to any one of <1> to <6>, wherein the resin binder is an epoxy resin.
<8> The heat-dissipating sheet precursor according to any one of <1> to <7>, wherein the content of the resin binder is 20% by mass to 50% by mass with respect to the total mass of the heat-dissipating sheet precursor. ..
<9> The method for manufacturing a heat radiating sheet, which comprises a step of pressurizing the heat radiating sheet precursor according to any one of <1> to <8>.

According to one aspect of the present disclosure, there is provided a heat dissipation sheet precursor capable of forming a heat dissipation sheet having few voids and excellent thermal conductivity.
According to another aspect of the present disclosure, there is provided a method for manufacturing a heat radiating sheet capable of forming a heat radiating sheet having few voids and excellent thermal conductivity.

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

In the present disclosure, the numerical range represented by using "~" means a range including the numerical values before and after "~" as the lower limit value and the upper limit value. In the numerical range described stepwise in the present disclosure, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in another stepwise description. Further, in the numerical range described in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the value shown in the examples.
In the present disclosure, the amount of each component in the composition means the total amount of the plurality of substances present in the composition when a plurality of substances corresponding to each component are present in the composition, unless otherwise specified. ..
In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment.
In the present disclosure, the term "process" is included in this term not only as an independent process but also as long as the intended purpose of the process is achieved even if it cannot be clearly distinguished from other processes. ..
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, the "total solid content mass" means the total mass of the components excluding the solvent.

<Heat dissipation sheet precursor>
The heat radiating sheet precursor according to the present disclosure contains a resin binder and inorganic nitride particles, and the content of the inorganic nitride particles is 50% by mass to 80% by mass with respect to the total mass of the heat radiating sheet precursor. (002) of the inorganic nitride particles with respect to the intensity of the diffraction peak of the (100) plane of the inorganic nitride particles, which is mass%, has a void ratio of 30% to 45%, and is measured by the X-ray diffraction method. ) The ratio of the intensity of the diffraction peaks on the surface is 18 or less.

In the present disclosure, the "heat dissipation sheet precursor" means a material that forms a heat dissipation sheet by pressure processing. In other words, the heat-dissipating sheet precursor refers to a product at a stage before the heat-dissipating sheet is formed by pressure processing.

According to the heat dissipation sheet precursor according to the present disclosure, a heat dissipation sheet having few voids and excellent thermal conductivity is formed. The reason why the heat dissipation sheet precursor according to the present disclosure exerts the above effect is not clear, but it is presumed as follows.
The heat radiating sheet precursor according to the present disclosure contains a resin binder and inorganic nitride particles, and the content of the inorganic nitride particles is 50% by mass to 80% by mass with respect to the total mass of the heat radiating sheet precursor. (002) of the inorganic nitride particles with respect to the intensity of the diffraction peak of the (100) plane of the inorganic nitride particles, which is mass%, has a void ratio of 30% to 45%, and is measured by the X-ray diffraction method. ) When the ratio of the intensity of the diffraction peak of the surface is 18 or less, the effect of reducing the voids that are likely to be formed when the inorganic nitride particles having a low affinity with the resin binder is used by the pressure processing becomes large. Therefore, a heat radiating sheet having few voids and excellent thermal conductivity is formed.

As described above, the heat-dissipating sheet precursor according to the present disclosure can be used as a pre-stage material for forming the heat-dissipating sheet. Therefore, the thermal conductivity of the heat-dissipating sheet precursor tends to be lower than that of a normal heat-dissipating sheet. An example of the thermal conductivity of the heat dissipation sheet precursor according to the present disclosure is less than ^{6 Wm -1} K ^-1. The thermal conductivity of the heat-dissipating sheet precursor according to the present disclosure is measured by the same method as the method for measuring the thermal conductivity described later.

Hereinafter, each component of the heat dissipation sheet precursor according to the present disclosure will be described.

[Resin binder]
The heat dissipation sheet precursor according to the present disclosure contains a resin binder.

As the resin binder, a known resin binder can be used without limitation. Examples of the resin binder include epoxy resin, phenol resin, polyimide resin, cresol resin, melamine resin, unsaturated polyester resin, isocyanate resin, polyurethane resin, polybutylene terephthalate resin, polyethylene terephthalate resin, polyphenylene sulfide resin, fluororesin, and Examples include polyphenylene oxide resin.

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.

As the epoxy resin, a known epoxy resin can be used without limitation. Examples of the epoxy resin include a bifunctional epoxy resin and a novolak type epoxy resin.

Examples of the bifunctional epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, and bisphenol S type epoxy resin.

Examples of the novolak type epoxy resin include phenol novolac type epoxy resin and cresol novolak type epoxy resin.

Further, the resin binder is preferably a cured product of the polymerizable monomer from the viewpoint that it is easy to add functions such as heat resistance. Here, the polymerizable monomer is a compound that is cured by heat or light.

As the polymerizable monomer, a known polymerizable monomer can be used. Examples of the polymerizable monomer include the epoxy resin monomer and the acrylic resin monomer described in paragraph 0028 of Patent No. 4118691, the epoxy compound described in paragraphs 0006 to 0011 of JP-A-2008-13759, and the Japanese Patent Laid-Open No. Examples thereof include the epoxy resin monomers described in paragraphs 0032 to 0100 of Japanese Patent Application Laid-Open No. 2013-227451.

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 oxylanyl group, and a vinyl group is preferable.

The polymerizable monomer may have one type of polymerizable group alone, or may have two or more types of polymerizable groups. Further, the number of polymerizable groups in the polymerizable monomer may be one or two or more. The number of polymerizable groups in the polymerizable monomer is preferably two or more, and more preferably three or more, from the viewpoint of excellent heat resistance of the cured product. The upper limit of the number of polymerizable groups in the polymerizable monomer is not limited. The number of polymerizable groups in the polymerizable monomer is often 8 or less.

The heat-dissipating sheet precursor according to the present disclosure may contain one type of resin binder alone, or may contain two or more types of resin binders.

The content of the resin binder is preferably 10% by mass to 50% by mass, preferably 20% by mass, based on the total mass of the heat dissipation sheet precursor, from the viewpoints of thermal conductivity, dispersibility of the inorganic nitride particles, and film quality. It is more preferably from mass% to 50% by mass, and particularly preferably from 20% by mass to 40% by mass.

[Inorganic nitride particles]
The heat dissipation sheet precursor according to the present disclosure contains inorganic nitride particles. The heat dissipation sheet precursor contains inorganic nitride particles, which improves thermal conductivity. Therefore, the heat dissipation of the obtained heat dissipation sheet is improved.

Examples of the inorganic nitride constituting the inorganic nitride particles, for example, boron nitride (BN), carbon nitride _{(C 3 N} 4), silicon nitride _{(Si 3 N} 4), gallium nitride (GaN), indium nitride (InN) , Aluminum Nitride (AlN), Chromium Nitride (Cr ₂ N), Copper Nitride (Cu ₃ N), Iron Nitride (Fe ₄ N or Fe ₃ N), Lantern Nitride (La N), _{Lithium Nitride (Li 3 N),} Magnesium Nitride (Mg ₃ N ₂ ), Molybdenum Nitride (Mo ₂ N), Niobium Nitride (NbN), Tantal Nitride (TaN), Titanium Nitride (TiN), Tungsten Nitride (W ₂ N, WN ₂ , or WN), Nitride Yttrium (YN) and zirconium nitride (ZrN) can be mentioned.

The inorganic nitride particles are preferably inorganic nitride particles containing at least one atom selected from the group consisting of a boron atom, an aluminum atom, and a silicon atom from the viewpoint of thermal conductivity of the heat dissipation sheet. It is more preferably an inorganic nitride particle containing at least one atom selected from the group consisting of an atom and an aluminum atom, and particularly preferably an inorganic nitride particle containing a boron atom.

The inorganic nitride particles are preferably at least one kind of inorganic nitride particles selected from the group consisting of boron nitride particles, aluminum nitride particles, and silicon nitride particles from the viewpoint of thermal conductivity of the heat dissipation sheet. It is more preferably at least one kind of inorganic nitride particles selected from the group consisting of boron nitride particles and aluminum nitride particles, and particularly preferably boron nitride particles.

Commercially available products may be used as the inorganic nitride particles. The inorganic nitride particles are available, for example, as "HP-40 MF100" (boron nitride particles) manufactured by Mizushima Ferroalloy Co., Ltd.

(Degree of orientation)
The ratio of the intensity of the diffraction peak on the (002) plane of the inorganic nitride particles to the intensity of the diffraction peak on the (100) plane of the inorganic nitride particles as measured by the X-ray diffraction method ([(002) of the inorganic nitride particles). [Intensity of diffraction peak on surface] / [Intensity of diffraction peak on (100) surface of inorganic nitride particles]) is 18 or less. Hereinafter, the ratio of the intensity of the diffraction peak on the (002) plane of the inorganic nitride particles to the intensity of the diffraction peak on the (100) plane of the inorganic nitride particles may be referred to as “degree of orientation of the inorganic nitride particles”. When the degree of orientation of the inorganic nitride particles is 18 or less, the thermal conductivity of the heat radiating sheet is improved.

The smaller the degree of orientation of the inorganic nitride particles, the more preferable it is from the viewpoint of the thermal conductivity of the heat radiating sheet. The degree of orientation of the inorganic nitride particles is preferably 17 or less, more preferably 15 or less, and particularly preferably 14 or less.

The lower limit of the degree of orientation of the inorganic nitride particles is not limited. The degree of orientation of the inorganic nitride particles can be appropriately set in the range of, for example, 0.1 or more.

The degree of orientation of the inorganic nitride particles is measured by an X-ray diffraction method. Specifically, based on the X-ray diffraction pattern obtained by irradiating the heat radiation sheet precursor with CuKα rays (characteristic X-rays), the inorganic nitride particles are inorganic with respect to the intensity of the diffraction peak on the (100) plane. The ratio of the intensity of the diffraction peak of the (002) plane of the nitride particles is obtained. As an apparatus used for the X-ray diffraction method, a known X-ray diffractometer (for example, XRD-6100, manufactured by Shimadzu Corporation) can be used. Further, in the X-ray diffraction method, the tube voltage is 30 kV and the tube current is 15 mA.

As a method for adjusting the degree of orientation of the inorganic nitride particles, a known method can be used without limitation. For example, by using the inorganic nitride particles having a large aspect ratio, the degree of orientation of the inorganic nitride particles can be reduced. Further, a method of appropriately adjusting the average particle size of the inorganic nitride particles and a method of appropriately selecting the type of solvent that can be contained in the resin composition described later can also be mentioned.

(aspect ratio)
The average aspect ratio of the inorganic nitride particles is preferably 3 or more, more preferably 5 or more, and particularly preferably 8 or more. When the average aspect ratio of the inorganic nitride particles is 5 or more, the thermal conductivity of the heat radiating sheet can be improved.

The upper limit of the average aspect ratio of the inorganic nitride particles is not limited. The average aspect ratio of the inorganic nitride particles is preferably 20 or less, and more preferably 15 or less, from the viewpoint of particle dispersibility in the resin composition described later.

The average aspect ratio of the inorganic nitride particles is measured by the following method.
(1) The heat radiation sheet precursor is cut by irradiating with a focused ion beam (FIB).
(2) Using a scanning electron microscope (SEM), the cross section of the heat dissipation sheet precursor is observed, and then images of 100 randomly selected inorganic nitride particles are obtained.
(3) The major axis and the minor axis of each of the above-mentioned inorganic nitride particles are measured. In the present disclosure, the "major axis of the inorganic nitride particles" means the length of the longest line segment among the line segments connecting any two points on the contour line of the inorganic nitride particles. For example, when the inorganic nitride particles are a perfect circle in the above image, the major axis of the inorganic nitride particles means the diameter of the inorganic nitride particles. Further, in the present disclosure, the "minor diameter of the inorganic nitride particles" is a line segment orthogonal to a line segment defining a major axis and connecting any two points on the contour line of the inorganic nitride particles. The length of the longest line segment.
(4) Obtain the ratio of the major axis (major axis / minor axis) to the minor axis of each of the above-mentioned inorganic nitride particles.
(5) The arithmetic mean value of the obtained value is taken as the average aspect ratio of the inorganic nitride particles.

(Average particle size)
The average particle size of the inorganic nitride particles is preferably 10 μm or more, more preferably 20 μm or more, and particularly preferably 30 μm or more. When the average particle size of the inorganic nitride particles is 10 μm or more, the thermal conductivity of the heat radiating sheet can be further improved.

The average particle size of the inorganic nitride particles is preferably 200 μm or less, more preferably 150 μm or less. When the average particle size of the inorganic nitride particles is 100 μm or less, the surface irregularities can be reduced, and as a result, the heat dissipation is increased.

The average particle size of the inorganic nitride particles is measured by the following method.
(1) The heat radiation sheet precursor is cut by irradiating with a focused ion beam (FIB).
(2) Using a scanning electron microscope (SEM), the cross section of the heat dissipation sheet precursor is observed, and then images of 100 randomly selected inorganic nitride particles are obtained.
(3) The major axis of each of the above-mentioned inorganic nitride particles is measured.
(4) In the number-based particle size distribution based on the major axis of each inorganic nitride particle, the particle size (D50) when the number-based accumulation is 50% is defined as the average particle size of the inorganic nitride particles.

The heat-dissipating sheet precursor according to the present disclosure may contain one type of inorganic nitride particles alone, or may contain two or more types of inorganic nitride particles.

The content of the inorganic nitride particles is 50% by mass to 80% by mass with respect to the total mass of the heat radiation sheet precursor. When the content of the inorganic nitride particles is 50% by mass to 80% by mass, a heat radiating sheet having few voids and excellent thermal conductivity is formed. Further, when the content of the inorganic nitride particles is 80% by mass or less, the film quality of the heat radiating sheet can be improved. The content of the inorganic nitride particles is preferably 60% by mass to 80% by mass with respect to the total mass of the heat dissipation sheet precursor from the viewpoint of thermal conductivity of the heat dissipation sheet.

The content of the inorganic nitride particles is preferably 200 parts by mass to 400 parts by mass, and 250 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 dissipation sheet. Is more preferable.

[Porosity]
The porosity of the heat dissipation sheet precursor according to the present disclosure is 30% to 45%. Since the porosity of the heat radiating sheet precursor is 30% to 45%, the porosity contained in the heat radiating sheet can be reduced by the pressure processing. The porosity of the heat dissipation sheet precursor according to the present disclosure is preferably 35% to 45%, more preferably 40% to 45%. When the porosity of the heat radiating sheet precursor is within the above range, the porosity contained in the heat radiating sheet can be further reduced. As a result, the thermal conductivity of the heat dissipation sheet can also be improved.

The porosity of the heat dissipation sheet precursor is measured by the following method.
(1) The heat radiation sheet precursor is cut by irradiating with a focused ion beam (FIB).
(2) Using a scanning electron microscope (SEM), an image of a cross section of the heat dissipation sheet precursor is obtained. Specifically, an image of 5 fields of view arbitrarily selected from the cross sections of the heat radiation sheet precursor is obtained. The visual field range of each image is adjusted so that the area of the cross section and the area of the void can be appropriately calculated without intentionally excluding the void. Specifically, the viewing range of each image, it is preferable to set within the range of 20,000μm ² ~200,000μm ^2.
(3) From each of the above images, the ratio of the area of the void to the area of the cross section (area of the void / area of the cross section) is obtained.
(4) The arithmetic mean value (percentage) of the obtained value is used as the porosity of the heat radiation sheet precursor.

Examples of the method for adjusting the porosity of the heat-dissipating sheet precursor include a method of appropriately adjusting the content of inorganic nitride particles and a method of appropriately selecting the type of solvent that can be contained in the resin composition described later. ..

[shape]
The shape of the heat dissipation sheet precursor according to the present disclosure is not limited. The shape of the heat radiating sheet precursor according to the present disclosure is preferably sheet-like from the viewpoint of processability.

[thickness]
The thickness of the heat dissipation sheet precursor according to the present disclosure is not limited, and may be appropriately set, for example, according to the intended use. The thickness of the heat dissipation sheet precursor according to the present disclosure is preferably 50 μm to 400 μm, more preferably 100 μm to 250 μm, from the viewpoint of heat dissipation and insulation. The thickness of the heat dissipation sheet precursor according to the present disclosure is measured by the same method as the method for measuring the thickness T1 before pressurization, which will be described later.

[Rate of change in thickness]
In the heat dissipation sheet precursor according to the present disclosure, it is preferable that the thickness T1 before pressurization and the thickness T2 after pressurization satisfy the relationship of 0.50 ≦ T2 / T1 ≦ 0.70, and 0.55. It is more preferable to satisfy the relationship of ≦ T2 / T1 ≦ 0.70, and it is particularly preferable to satisfy the relationship of 0.58 ≦ T2 / T1 ≦ 0.68. In the heat radiating sheet precursor according to the present disclosure, the voids contained in the obtained heat radiating sheet can be further reduced by satisfying the above relationship between the thickness T1 before pressurization and the thickness T2 after pressurization. As a result, the thermal conductivity of the heat dissipation sheet can also be improved.

The thickness T1 before pressurization is measured by the following method.
(1) The heat radiation sheet precursor is cut by irradiating with a focused ion beam (FIB).
(2) Using a scanning electron microscope (SEM), an image of a cross section of the heat dissipation sheet precursor is obtained.
(3) From the above image, the thickness of the heat dissipation sheet precursor is measured at three points.
(4) The arithmetic mean value of the obtained values is defined as the thickness T1 before pressurization.

The thickness T2 after pressurization is measured by the following method.
(1) The heat dissipation sheet precursor is calendar-processed under the conditions of temperature: 25 ° C., linear pressure: 100 kN / m, and transfer speed: 5 m / min. As the roll used in the calendar processing, a pair of rolls having a metal roll and a resin roll is used.
(2) According to the method for measuring the thickness T1 before pressurization, the thickness of the pressurized heat dissipation sheet precursor is measured at three points.
(3) The arithmetic mean value of the obtained values is defined as the thickness T2 after pressurization.

[Density change rate]
In the heat dissipation sheet precursor according to the present disclosure, the density D1 before pressurization and the density D2 after pressurization preferably satisfy the relationship of 1.40 ≦ D2 / D1 ≦ 1.90, and 1.45 ≦ D2 /. It is more preferable to satisfy the relationship of D1 ≦ 1.85, and it is particularly preferable to satisfy the relationship of 1.45 ≦ D2 / D1 ≦ 1.80. In the heat dissipation sheet precursor according to the present disclosure, since the density D1 before pressurization and the density D2 after pressurization satisfy the above relationship, the voids can be reduced by the pressurization process, so that the voids contained in the obtained heat dissipation sheet can be eliminated. It can be further reduced. As a result, the thermal conductivity of the heat dissipation sheet can also be improved.

The density D1 before pressurization is measured by the Archimedes method.

The density D2 after pressurization is measured by the following method.
The heat dissipation sheet precursor is calendar-processed under the conditions of temperature: 25 ° C., linear pressure: 100 kN / m, and transfer speed: 5 m / min. The density of the heat dissipation sheet precursor after calendar processing is measured by the Archimedes method. The obtained value is defined as the density D2 after pressurization.

[Manufacturing method of heat dissipation sheet precursor]
Examples of the method for producing the heat-dissipating sheet precursor according to the present disclosure include a method using a resin composition containing the above-mentioned resin binder and the above-mentioned inorganic nitride particles. The method for producing a heat radiation sheet precursor according to the present disclosure includes a step of applying a resin composition containing the above resin binder and the above inorganic nitride particles on the base material, and a step of applying the resin composition onto the base material. It is preferable to include a step of curing the resin composition.

(Resin composition)
The resin composition contains the above-mentioned resin binder and the above-mentioned inorganic nitride particles.

The content of the resin binder in the resin composition is preferably 10% by mass to 50% by mass, more preferably 20% by mass to 50% by mass, based on the total solid content mass in the resin composition. It is preferably 20% by mass to 40% by mass, and particularly preferably 20% by mass.

The content of the inorganic nitride particles in the resin composition is preferably 50% by mass to 80% by mass, preferably 60% by mass to 80% by mass, based on the total solid content mass in the resin composition. Is more preferable.

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

-Hardener-
As the curing agent, a known curing agent can be used without limitation. The curing agent may be 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 an anhydrous carboxylic acid group. It is more preferable that the compound has 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, and more preferably a compound having two or three of the above functional groups.

Specific examples of the curing agent include 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. Examples thereof include a curing agent, a benzoxazine-based curing agent, and a cyanate ester-based curing agent. Among the above, the curing agent is preferably an imidazole-based curing agent, an acrylic-based curing agent, a phenol-based curing agent, or an amine-based curing agent.

The resin composition may contain one kind of curing agent alone, or may contain two or more kinds of curing agents.

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

-Hardening accelerator-
As the curing accelerator, a known curing accelerator can be used without limitation. Examples of the curing accelerator include triphenylphosphine, 2-ethyl-4-methylimidazole, boron trifluoride amine complex, and 1-benzyl-2-methylimidazole.

The resin composition may contain one kind of curing accelerator alone or may contain two or more kinds of curing accelerators.

When the resin 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 content mass of the resin composition.

-Polymerization initiator-
When the resin composition contains a polymerizable monomer, the resin composition preferably contains a polymerization initiator. When the resin composition contains the polymerizable monomer and the polymerization initiator, the curing reaction of the polymerizable monomer can be efficiently promoted.

The polymerization initiator is not limited, and a known polymerization initiator can be used. When the polymerizable monomer has an acryloyl group or a methacryloyl group, the polymerization initiator is the polymerization initiator described in paragraph 0062 of JP2010-125782A or paragraph 0054 of JP2015-052710. It is preferable that it is the polymerization initiator described in 1.

The resin composition may contain one kind of polymerization initiator alone or may contain two or more kinds of polymerization initiators.

When the resin 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 content mass in the resin composition.

-Solvent-
The solvent is not limited, and a known solvent can be used. The solvent is preferably an organic solvent. Examples of the organic solvent include ethyl acetate, methyl ethyl ketone, dichloromethane, and tetrahydrofuran.

The resin composition may contain one kind of solvent alone or may contain two or more kinds of solvents.

The content of the solvent is not limited and may be appropriately set according to, for example, the composition of each component contained in the resin composition and the coating method. The content of the solvent is preferably 30% by mass to 80% by mass, more preferably 50% by mass to 70% by mass, based on the total mass of the resin composition.

-Manufacturing method of resin composition-
Examples of the method for producing the resin composition include a method of mixing the above components. For example, a resin composition can be obtained by mixing a solvent, a resin binder, and inorganic nitride particles. As the mixing method, a known method can be used without limitation.

(Base material)
Examples of the base material include a metal substrate and a release liner.

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

Examples of the release liner include paper (for example, kraft paper, glassin paper, and high-quality paper), resin film (for example, polyolefin and polyester), and laminated paper in which paper and a resin film are laminated. Examples of the polyolefin include polyethylene and polypropylene. Examples of the polyester include polyethylene terephthalate (PET).

The paper used as the release liner may be paper that has been subjected to a release treatment. The peeling-treated paper can be formed, for example, by further performing a peeling treatment on one side or both sides of the sealing-treated paper. The sealing 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 base material is not limited and may be appropriately set in the range of, for example, 10 μm to 300 μm.

(Applying method)
The coating method is not limited, and a known method can be used. Examples of the coating method include roll coating method, gravure printing method, spin coating method, wire bar coating method, extrusion coating method, direct gravure coating method, reverse gravure coating method, die coating method, spray method, comma coating method, and blade. The method and the inkjet method can be mentioned.

The resin composition applied on the substrate may be dried if necessary. Examples of the drying method include a method of applying warm air at 40 ° C. to 140 ° C. for 1 minute to 30 minutes to the resin composition applied on the substrate.

(Curing method)
The curing method is not limited, and a known method can be used. For example, the curing method may be appropriately selected depending on the composition of the resin composition.

As a curing method, a thermosetting reaction or a photocuring reaction is preferable, and a thermosetting reaction is preferable.

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

The heating time in the thermosetting reaction is not limited, and may be appropriately set according to, for example, the heating temperature.

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

In the method for producing a heat-dissipating sheet precursor according to the present disclosure, the curing reaction may be carried out a plurality of times, if necessary. When the curing reaction is carried out multiple times, the conditions of each curing reaction may be the same or different from each other.

<Manufacturing method of heat dissipation sheet>
The method for manufacturing a heat radiating sheet according to the present disclosure is not limited as long as it is a method using the heat radiating sheet precursor, but includes a step of pressurizing the heat radiating sheet precursor (hereinafter, referred to as "pressurizing step"). Is preferable.

When the above-mentioned base material is arranged on the surface of the heat radiating sheet precursor, the base material may be pressurized after peeling the base material from the heat radiating sheet precursor, or the base material may be pressed from the heat radiating sheet precursor. The heat dissipation sheet precursor may be pressurized together with the substrate without peeling. In the pressurizing step, from the viewpoint of ease of processing, it is preferable to pressurize the heat radiating sheet precursor after peeling the base material from the heat radiating sheet precursor.

The pressurizing method is not limited as long as it can pressurize the heat radiating sheet precursor (that is, a method that can reduce the proportion of voids contained in the heat radiating sheet precursor), and a known method can be used. Examples of the pressurizing method include press working and calendering. Among the above, the pressurizing method is preferably calendar processing from the viewpoint of productivity and porosity reduction.

The pressure in the pressurizing step is not limited, and may be appropriately set according to, for example, the pressurizing method, the composition of the heat radiating sheet precursor, and the porosity of the heat radiating sheet precursor. For example, when the pressurizing method is calendar processing, the pressure (linear pressure) is preferably 50 N / m to 200 N / m, and more preferably 100 N / m to 150 N / m.

The temperature in the pressurizing step is not limited, and may be appropriately set according to, for example, the pressurizing method, the composition of the heat radiating sheet precursor, and the porosity of the heat radiating sheet precursor. The temperature is preferably 20 ° C to 150 ° C, more preferably 25 ° C to 120 ° C.

When the pressurizing method is calendar processing, the transport speed of the heat dissipation sheet precursor is not limited, and may be appropriately set in the range of, for example, 1 m / min to 100 m / min.

The heat radiating sheet obtained by using the heat radiating sheet precursor according to the present disclosure has few voids, and therefore has excellent thermal conductivity. Therefore, the heat radiating sheet obtained by using the heat radiating sheet precursor according to the present disclosure can efficiently dissipate the heat generated in the heating element by contacting it with various heating elements. For example, by bringing the heat dissipation sheet into contact with various parts constituting an electronic device, the heat generated in the parts can be efficiently dissipated. Examples of the component include a power device and a CPU. Further, the heat radiating sheet obtained by using the heat radiating sheet precursor according to the present disclosure may be used by arranging it between a heating element such as a power device and a heat radiating body such as a heat sink.

Hereinafter, the present disclosure will be described in detail by way of examples, but the present disclosure is not limited thereto. Unless otherwise specified, "part" and "%" are based on mass.

<Example 1>
[Preparation of resin composition A]
The resin composition A was prepared by kneading the following components.

(component)
Monomer A1 (compound having the following structure: raw material of epoxy resin, QE-2405, manufactured by Combiblocks): 17 parts by mass

Monomer B (compound having the following structure: raw material of 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 (inorganic nitride particles, HP-40 MF100, manufactured by Mizushima Ferroalloy Co., Ltd.): 51 parts by mass

[Preparation of heat dissipation sheet precursor]
Using an applicator, the resin composition A is applied onto a mold release surface of a polyester film (NP-100A, thickness 100 μm, manufactured by Panac Co., Ltd.) so that the dried thickness becomes 250 μm, and then the resin composition A is applied to a thickness of 250 μm. A coating film was formed by drying with warm air at 130 ° C. for 5 minutes. A heat-dissipating sheet precursor with a polyester film was prepared by curing the coating film at 180 ° C. for 1 hour.

[Making a heat dissipation sheet]
The polyester film was peeled off from the precursor of the heat dissipation sheet with the polyester film. Next, the heat-dissipating sheet precursor was subjected to calendar processing under the following conditions to prepare a heat-dissipating sheet. In the calendar processing, a pair of rolls having a rubber roll and a SUS (stainless steel) roll was used.

(Calendar processing conditions)
・ Linear pressure: 100N / m
-Temperature: 80 ° C
・ Transport speed: 5m / min

<Example 2>
In Example 1, a heat dissipation sheet was produced by the same method as in Example 1 except that the content of the boron nitride particles with respect to the solid content in the resin composition A was changed to 65% by mass.

<Example 3>
In Example 1, a heat dissipation sheet was produced by the same method as in Example 1 except that the content of the boron nitride particles with respect to the solid content in the resin composition A was changed to 80% by mass.

<Example 4>
A heat dissipation sheet was prepared by the same method as in Example 1 except that the solvent (methyl ethyl ketone) used in Example 2 was changed to cyclohexanone.

<Example 5>
In Example 2, a heat dissipation sheet was produced by the same method as in Example 1 except that the average particle size (D50) of the boron nitride particles used was changed to the value shown in Table 1 by the classification operation.

<Example 6>
In Example 2, a heat dissipation sheet was produced by the same method as in Example 1 except that the average particle size (D50) of the boron nitride particles used was changed to the value shown in Table 1 by the classification operation.

<Example 7>
In Example 1, a heat dissipation sheet was produced by the same method as in Example 1 except that the monomer A1 used was changed to the following monomer A2.

The structure of the monomer A2 is shown below.

<Example 8>
A heat dissipation sheet was produced by the same method as in Example 1 except that the boron nitride particles used in Example 1 were changed to boron nitride particles (SGPS, manufactured by Denka Co., Ltd.).

<Comparative Example 1>
In Example 1, a heat dissipation sheet was produced by the same method as in Example 1 except that the content of the boron nitride particles with respect to the solid content in the resin composition A was changed to 47% by mass.

<Comparative Example 2>
In Example 1, a heat dissipation sheet was produced by the same method as in Example 1 except that the content of the boron nitride particles with respect to the solid content in the resin composition A was changed to 82% by mass.

<Comparative Example 3>
In Example 1, the same as in Example 1 except that the content of the boron nitride particles with respect to the solid content in the resin composition A was changed to 65% by mass and the mass part of the methyl ethyl ketone was changed to 130 parts by mass. A heat dissipation sheet was produced by the above method.

<Evaluation>
The porosity, film quality, and thermal conductivity of each of the heat dissipation sheets were evaluated by the following methods.

[Porosity (after processing)]
The porosity of each heat dissipation sheet was measured according to the procedure described in (1) to (4) below. The evaluation results are shown in Table 1 below.
(1) The heat dissipation sheet was cut by irradiating with a focused ion beam (FIB).
(2) An image of a cross section of the heat dissipation sheet was obtained using a scanning electron microscope (SEM). Specifically, images of 5 fields of view randomly selected from the cross sections of the heat dissipation sheet were obtained. 20,000μm was adjusted to the area of the cross section area and the gap can be properly calculated in the ^second range of ～200,000Myuemu ^2.
(3) From each of the above images, the ratio of the area of the void to the area of the cross section (area of the void / area of the cross section) was obtained.
(4) The obtained values were arithmetically averaged and then converted into percentages to determine the porosity of the heat dissipation sheet.

[Membrane quality]
The film quality (brittleness) of each heat dissipation sheet was evaluated according to the following criteria. The evaluation results are shown in Table 1 below.

(standard)
A: The heat dissipation sheet does not crack even if it is bent at 90 degrees with a bending radius of 5 cm or less.
B: When the heat dissipation sheet is bent at a bending radius of 5 cm or less and bent at 90 degrees, it breaks.
C: Even if the heat dissipation sheet is slightly bent, it will crack.

[Thermal conductivity]
The thermal conductivity of each heat dissipation sheet was measured by the following method, and the thermal conductivity of each heat dissipation sheet was evaluated according to the following criteria. The evaluation results are shown in Table 1 below.

(Measurement method of thermal conductivity)
(1) Using "LFA467" manufactured by NETZSCH, the thermal diffusivity in the thickness direction of the heat conductive sheet was measured by a laser flash method.
(2) The specific gravity of each heat dissipation sheet was measured using the balance "XS204" (using the "solid specific gravity measurement kit") manufactured by METTLER TOLEDO Co., Ltd.
(3) Using "DSC320 / 6200" manufactured by Seiko Instruments Inc., the specific heat of each heat dissipation sheet at 25 ° C. was determined using the software of DSC7 under the heating condition of 10 ° C./min.
(4) The thermal conductivity of each heat dissipation sheet was calculated by multiplying the obtained thermal diffusivity by the specific gravity and the specific heat.

(standard)
^{A: 14Wm -1 K} -1 or higher ^{B: 8Wm -1 K} -1 or ^more, less than ^{14Wm -1 K} -1 ^{C: 8Wm} less than -1 ^{K -1} D: unmeasurable

In Table 1, the "degree of orientation" is the ratio of the intensity of the diffraction peak on the (002) plane of the inorganic nitride particles to the intensity of the diffraction peak on the (100) plane of the inorganic nitride particles ([002 of the inorganic nitride particles. ) Surface diffraction peak intensity] / [Intensity of (100) surface diffraction peak of inorganic nitride particles]). The degree of orientation was measured by the method described above.

In Table 1, "T2 / T1" represents the ratio (T2 / T1) of the thickness T2 of the heat-dissipating sheet precursor after pressurization to the thickness T1 of the heat-dissipating sheet precursor before pressurization. T2 / T1 was measured by the method described above.

In Table 1, "D2 / D1" represents the ratio (D2 / D1) of the density D2 of the heat-dissipating sheet precursor after pressurization to the density D1 of the heat-dissipating sheet precursor before pressurization. D2 / D1 was measured by the method described above.

In Table 1, "porosity (before processing)" represents the porosity of the heat dissipation sheet precursor before pressurizing the calendar. The porosity (before processing) was measured by the method described above.

From Table 1, each heat dissipation sheet obtained by using each heat dissipation sheet precursor of Examples 1 to 8 is each heat dissipation sheet obtained by using each heat dissipation sheet precursor of Comparative Examples 1 to 3. It was found that there were few voids and the thermal conductivity was excellent. Further, each heat dissipation sheet obtained by using each heat dissipation sheet precursor of Examples 1 to 8 is superior to each heat dissipation sheet obtained by using each heat dissipation sheet precursor of Comparative Example 1. It was found to have a film quality.

The disclosure of Japanese Patent Application No. 2019-061229, filed March 27, 2019, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are to the same extent as specifically and individually stated that the individual documents, patent applications, and technical standards are incorporated by reference. Incorporated herein by reference.

Claims (9)

Containing a resin binder and inorganic nitride particles,
The content of the inorganic nitride particles is 50% by mass to 80% by mass with respect to the total mass of the heat dissipation sheet precursor.
The porosity is 30% to 45%,
The ratio of the intensity of the diffraction peak on the (002) plane of the inorganic nitride particles to the intensity of the diffraction peak on the (100) plane of the inorganic nitride particles measured by the X-ray diffraction method is 18 or less. precursor. The heat-dissipating sheet precursor according to claim 1, wherein the inorganic nitride particles have an average aspect ratio of 5 or more. The heat-dissipating sheet precursor according to claim 1 or 2, wherein the average particle size of the inorganic nitride particles is 10 μm or more. The heat radiation sheet precursor according to any one of claims 1 to 3, wherein the thickness T1 before pressurization and the thickness T2 after pressurization satisfy the relationship of 0.55 ≦ T2 / T1 ≦ 0.70. body. The heat dissipation sheet precursor according to any one of claims 1 to 4, wherein the density D1 before pressurization and the density D2 after pressurization satisfy the relationship of 1.40 ≦ D2 / D1 ≦ 1.90. The heat-dissipating sheet precursor according to any one of claims 1 to 5, wherein the inorganic nitride particles are boron nitride particles. The heat-dissipating sheet precursor according to any one of claims 1 to 6, wherein the resin binder is an epoxy resin. The heat-dissipating sheet precursor according to any one of claims 1 to 7, wherein the content of the resin binder is 20% by mass to 50% by mass with respect to the total mass of the heat-dissipating sheet precursor. The method for manufacturing a heat radiating sheet, which comprises a step of pressurizing the heat radiating sheet precursor according to any one of claims 1 to 8.