TWI492972B - Thermal conductive sheet - Google Patents

Description

Thermally conductive sheet

The present invention relates to a thermally conductive sheet, and more particularly to a thermally conductive sheet that can be used in power electronics.

In recent years, in a hybrid device, a high-brightness LED (light emitting diode) device, an electromagnetic induction heating device, and the like, a power electronic technology that converts and controls electric power by a semiconductor element is used. In power electronics technology, in order to convert a large current into heat or the like, a material disposed in the vicinity of a semiconductor element is required to have high heat dissipation (high thermal conductivity).

For example, a heat conductive sheet containing a plate-like boron nitride powder and an acrylate copolymer resin is proposed (for example, see JP-A-2008-280496).

In the heat conduction sheet of Japanese Laid-Open Patent Publication No. 2008-280496, the boron nitride powder is aligned in the longitudinal direction of the boron nitride powder (the direction perpendicular to the thickness of the boron nitride powder) along the thickness direction of the sheet. Thereby, the thermal conductivity of the thermally conductive sheet in the thickness direction is improved.

However, the thermally conductive sheet may have high thermal conductivity in the orthogonal direction (surface direction) orthogonal to the thickness direction depending on the application and purpose. In the heat conduction sheet of Japanese Laid-Open Patent Publication No. 2008-280496, the long axis direction of the boron nitride powder is orthogonal (intersected) with respect to the plane direction, and thus the thermal conductivity in the surface direction is insufficient.

Moreover, the heat conductive sheet also requires excellent flexibility from the viewpoint of workability.

An object of the present invention is to provide a thermally conductive sheet which is excellent in flexibility and surface thermal conductivity.

The thermally conductive sheet of the present invention is characterized in that it contains plate-like boron nitride particles, and the content ratio of the boron nitride particles is 35 vol% or more, and the thermal conductive sheet has an orthogonal direction with respect to the thickness direction. The thermal conductivity is above 4 W/m‧K.

Further, in the thermally conductive sheet of the present invention, it is preferred that the boron nitride particles have an average particle diameter of 20 μm or more as measured by a light scattering method.

Further, in the heat conductive sheet of the present invention, it is preferable that the bending resistance test according to the cylindrical mandrel method according to JIS K 5600-5-1 is evaluated by the following test conditions. A fracture was observed on the above thermally conductive sheet.

Test conditions

Test device: Model I

Mandrel: 10 mm in diameter

Bending angle: 90 degrees or more

Thickness of the above thermally conductive sheet: 0.3 mm

Moreover, it is preferable that the heat conductive sheet of the present invention further contains a resin component, and the dynamic viscosity test according to JIS K 7233 (bubble viscosity meter method) in the resin component (temperature: 25 ° C ± 0.5 ° C, solvent: butyl card) The dynamic viscosity measured by the concentration of the alcohol and the solid content: 40% by mass was 0.22 × 10 ^-4 to 2.00 × 10 ^-4 m ² /s.

In the heat conductive sheet of the present invention, the flexibility and the thermal conductivity in the plane direction orthogonal to the thickness direction are excellent.

Therefore, the thermally conductive sheet which is excellent in workability and excellent in thermal conductivity in the surface direction can be used for various heat dissipation applications.

The thermally conductive sheet of the present invention contains boron nitride particles.

Specifically, the thermally conductive sheet contains boron nitride (BN) particles as an essential component, and further contains, for example, a resin component.

The boron nitride particles are formed into a plate shape (or a scaly shape) and are dispersed in a direction in which a thermally conductive sheet is aligned in a specific direction (described later).

The average length of the boron nitride particles in the longitudinal direction (the maximum length in the direction orthogonal to the thickness direction of the sheet) is, for example, 1 to 100 μm, preferably 3 to 90 μm. Further, the average length of the boron nitride particles in the longitudinal direction is preferably 5 μm or more, preferably 10 μm or more, particularly preferably 20 μm or more, particularly preferably 30 μm or more, and most preferably 40 μm or more, and is usually, for example, 100 μm or less, preferably 90 μm or less.

Further, the average thickness of the boron nitride particles (the length in the thickness direction of the sheet, that is, the length in the short side direction of the particles) is, for example, 0.01 to 20 μm, preferably 0.1 to 15 μm.

Further, the aspect ratio (length in the longitudinal direction/thickness) of the boron nitride particles is, for example, 2 to 10,000, preferably 10 to 5,000.

Further, the average particle diameter of the boron nitride particles measured by a light scattering method is, for example, 5 μm or more, preferably 10 μm or more, particularly preferably 20 μm or more, particularly preferably 30 μm or more, and most preferably 40 μm or more. , usually less than 100 μm.

Further, the average particle diameter measured by the light scattering method is a volume average particle diameter measured by a dynamic light scattering type particle size distribution measuring apparatus.

When the average particle diameter of the boron nitride particles measured by the light scattering method does not satisfy the above range, the thermally conductive sheet becomes brittle and the workability is lowered.

Further, the bulk density (JIS K 5101, apparent density) of the boron nitride particles is, for example, 0.3 to 1.5 g/cm ³ , preferably 0.5 to 1.0 g/cm ³ .

Further, as the boron nitride particles, commercially available products or processed products obtained by processing them can be used. For example, "PT" series (for example, "PT-110") manufactured by Momentive Performance Materials Japan Co., Ltd., and "SHOBN UHP" manufactured by Showa Denko Co., Ltd., may be mentioned as a commercial product of the boron nitride particles. Series (for example, "SHOBN UHP-1", etc.).

The resin component is a dispersion medium (matrix) in which boron nitride particles are dispersed, that is, a dispersion of boron nitride particles, and examples thereof include a resin component such as a thermosetting resin component and a thermoplastic resin component.

Examples of the thermosetting resin component include an epoxy resin, a thermosetting polyimide, a phenol resin, a urea resin, a melamine resin, an unsaturated polyester resin, a diallyl phthalate resin, and a polyfluorene. Oxygen resin, thermosetting amine ester resin, and the like.

Examples of the thermoplastic resin component include polyolefin (for example, polyethylene, polypropylene, ethylene-propylene copolymer, etc.), acrylic resin (for example, polymethyl methacrylate), polyvinyl acetate, and ethylene-vinyl acetate. Ester copolymer, polyvinyl chloride, polystyrene, polyacrylonitrile, polyamidamine (nylon (registered trademark)), polycarbonate, polyacetal, polyethylene terephthalate, polyphenylene ether, polyphenylene Thioether, polyfluorene, polyether oxime, polyetheretherketone, polyallyl fluorene, thermoplastic polyimine, thermoplastic amine ester resin, polyamine-based bismaleimide, polyamidoximine, poly Ether quinone imine, bismaleimide Resin, polymethylpentene, fluororesin, liquid crystal polymer, olefin-vinyl alcohol copolymer, ionomer, polyarylate, acrylonitrile-ethylene-styrene copolymer, acrylonitrile-butadiene-styrene copolymer , acrylonitrile-styrene copolymer, and the like.

These resin components may be used alone or in combination of two or more.

Among the resin components, an epoxy resin is preferable as the thermosetting resin component, and a polyolefin is preferable as the thermoplastic resin component.

The epoxy resin is in any form of liquid, semi-solid and solid at normal temperature.

Specifically, examples of the epoxy resin include bisphenol type epoxy resins (for example, bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, and hydrogenated bisphenol A type). Epoxy resin, dimer acid modified bisphenol type epoxy resin, etc.), novolak type epoxy resin (for example, phenol novolak type epoxy resin, cresol novolak type epoxy resin, biphenyl type epoxy resin, etc.) ), naphthalene type epoxy resin, fluorene type epoxy resin (for example, bisaryl fluorene type epoxy resin), triphenylmethane type epoxy resin (for example, trishydroxyphenylmethane type epoxy resin, etc.) Epoxy resin, such as triepoxypropyl isocyanurate (triglycidyl isocyanurate), beta-ureganil epoxy resin and other nitrogen-containing epoxy resin, such as aliphatic epoxy resin An alicyclic epoxy resin (for example, a bicyclic ring type epoxy resin), a glycidyl ether type epoxy resin, a glycidylamine type epoxy resin, or the like.

These epoxy resins may be used alone or in combination of two or more.

It is preferable to use a semi-solid epoxy resin alone, and it is more preferable to use a semi-solid aromatic epoxy resin alone. More specifically, such an epoxy resin is a semi-solid bismuth type epoxy resin.

Further, a combination of a liquid epoxy resin and a solid epoxy resin is preferable, and a combination of a liquid aromatic epoxy resin and an aromatic solid epoxy resin is more preferable. As such a combination, a combination of a liquid bisphenol type epoxy resin and a solid triphenylmethane type epoxy resin, a combination of a liquid bisphenol type epoxy resin and a solid bisphenol type epoxy resin can be cited.

In the case of a semi-solid epoxy resin or a combination of a liquid epoxy resin and a solid epoxy resin, the step followability (described later) of the thermally conductive sheet can be improved.

Further, the epoxy equivalent of the epoxy resin is, for example, 100 to 1000 g/eqiv., preferably 180 to 700 g/eqiv., and the softening temperature (ring and ball method) is, for example, 80 ° C or less (specifically 20 to 80 ° C), It is preferably 70 ° C or less (specifically, 35 to 70 ° C).

Further, the epoxy resin has a melt viscosity at 80 ° C of, for example, 10 to 20,000 mPa·s, preferably 50 to 10,000 mPa·s. When two or more types of epoxy resins are used in combination, the melt viscosity of the mixture is set to the above range.

Further, when two or more kinds of epoxy resins are used in combination, for example, an epoxy resin which is solid at normal temperature and an epoxy resin which is liquid at normal temperature can be used in combination. Further, when two or more kinds of epoxy resins are used in combination, the softening temperature may be, for example, a first epoxy resin of not more than 45 ° C, preferably 35 ° C or less, and a softening temperature of, for example, 45 ° C or higher, preferably 55 ° C. The second epoxy resin above. Thereby, the dynamic viscosity (according to JIS K 7233, later described) of the resin component (mixture) can be set to a desired range.

Further, the epoxy resin may contain, for example, a curing agent and a curing accelerator to prepare an epoxy resin composition.

The curing agent is a latent curing agent (epoxy resin curing agent) which can cure the epoxy resin by heating, and examples thereof include an imidazole compound, an amine compound, an acid anhydride compound, a guanamine compound, an anthraquinone compound, an imidazoline compound, and the like. . Further, in addition to the above, a phenol compound, a urea compound, a polysulfide compound, or the like may be mentioned.

Examples of the imidazole compound include 2-phenylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, and 2-phenyl-4-methyl-5-hydroxymethylimidazole.

The amine compound may, for example, be a polyamine such as ethylenediamine, propylenediamine, diethylenetriamine or triethylenetetramine, or an amine adduct or the like, such as m-phenylenediamine or diaminodiphenyl. Methane, diaminodiphenyl hydrazine, and the like.

Examples of the acid anhydride compound include phthalic anhydride, maleic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, 4-methyl-hexahydrophthalic anhydride, and methylation resistance. Anic anhydride, pyromellitic dianhydride, dodecenyl succinic anhydride, dichlorosuccinic anhydride, benzophenone tetracarboxylic dianhydride, chloric anhydride, and the like.

Examples of the guanamine compound include dicyanodiamine, polyamine, and the like.

Examples of the ruthenium compound include diammonium adipate and the like.

Examples of the imidazoline compound include methyl imidazoline, 2-ethyl-4-methylimidazoline, ethyl imidazoline, isopropyl imidazoline, 2,4-dimethylimidazoline, and phenylimidazole. Porphyrin, undecyl imidazoline, heptadecyl imidazoline, 2-phenyl-4-methylimidazoline and the like.

These hardeners may be used alone or in combination of two or more.

As the curing agent, an imidazole compound is preferred.

Examples of the curing accelerator include tertiary amine compounds such as triethylenediamine and tris-2,4,6-dimethylaminomethylphenol, such as triphenylphosphine and tetraphenylphosphonium tetraphenylborate. A phosphorus compound such as a salt or tetra-n-butylphosphonium-o,o-diethyldithiophosphate, such as a quaternary ammonium salt compound, for example, an organic metal salt compound, such as such a derivative. These hardening accelerators may be used alone or in combination of two or more.

The blending ratio of the curing agent in the epoxy resin composition is, for example, 0.5 to 50 parts by mass, preferably 1 to 10 parts by mass, based on 100 parts by mass of the epoxy resin, and the blending ratio of the hardening accelerator is, for example, 0.1 to 10 parts by mass. The portion is preferably 0.2 to 5 parts by mass.

The curing agent and/or the curing accelerator may be used as a solvent solution and/or a solvent dispersion which is dissolved and/or dispersed by a solvent, if necessary.

The solvent may, for example, be a ketone such as acetone or methyl ethyl ketone, or an ester such as ethyl acetate, or an organic solvent such as decylamine such as N,N-dimethylformamide or the like. Further, examples of the solvent include water, for example, an aqueous solvent such as an alcohol such as methanol, ethanol, propanol or isopropanol. The solvent is preferably an organic solvent, and more preferably a ketone.

The polyolefin is preferably a polyethylene or an ethylene-propylene copolymer.

Examples of the polyethylene include low density polyethylene and high density polyethylene.

Examples of the ethylene-propylene copolymer include a random copolymer of ethylene and propylene, a block copolymer, and a graft copolymer.

These polyolefins may be used alone or in combination of two or more.

Further, the weight average molecular weight and/or the number average molecular weight of the polyolefin is, for example, 1,000 to 10,000.

Further, the polyolefin may be used singly or in combination of plural kinds.

Among the resin components, a thermosetting resin component is preferable, and an epoxy resin is more preferable.

Further, the resin component was subjected to a dynamic viscosity test in accordance with JIS K 7233 (bubble viscosity meter method) (temperature: 25 ° C ± 0.5 ° C, solvent: butyl carbitol, resin component (solid content) concentration: 40% by mass) The measured dynamic viscosity is, for example, 0.22 × 10 ^-4 to 2.00 × 10 ^-4 m ² /s, preferably 0.3 × 10 ^-4 to 1.9 × 10 ^-4 m ² /s, more preferably 0.4 × 10 ^-4 ~ 1.8 × 10 ^-4 m ² / s. Further, the dynamic viscosity may be set to, for example, 0.22 × 10 ^-4 to 1.00 × 10 ^-4 m ² /s, preferably 0.3 × 10 ^-4 to 0.9 × 10 ^-4 m ² /s, more preferably 0.4. ×10 ^-4 ~ 0.8 × 10 ^-4 m ² /s.

When the dynamic viscosity of the resin component exceeds the above range, there is a case where excellent flexibility and step followability (described later) cannot be imparted to the thermally conductive sheet. On the other hand, when the dynamic viscosity of the resin component does not satisfy the above range, the boron nitride particles may not be aligned in a specific direction.

Furthermore, in the dynamic viscosity test according to JIS K 7233 (bubble viscosity meter method), the rising speed of the bubble in the resin component sample is compared with the rising speed of the bubble in the standard sample (the known dynamic viscosity is known). The dynamic viscosity of the standard sample in which the rising speed was determined was determined as the dynamic viscosity of the resin component, and the dynamic viscosity of the resin component was measured.

Further, in the heat conductive sheet, the volume ratio of the boron nitride particles is based on the solid content, that is, when the resin component contains the thermoplastic resin component, the total volume of the boron nitride particles relative to the thermoplastic resin component and the boron nitride particles The volume percentage) is 35% by volume or more, preferably 60% by volume or more, more preferably 75% by volume or more, and is usually, for example, 95% by volume or less, preferably 90% by volume or less.

When the content ratio of the volume basis of the boron nitride particles does not satisfy the above range, the boron nitride particles cannot be aligned in a specific direction in the thermally conductive sheet. On the other hand, when the content ratio of the volume of the boron nitride particles is more than the above range, the thermally conductive sheet becomes brittle, and the workability and the step followability (described later) are lowered.

In addition, the blending ratio of the mass ratio of the boron nitride particles is, for example, 40 to 95 parts by mass based on 100 parts by mass of the total amount (the total amount of solid components) of each component (boron nitride particles and resin component) forming the thermally conductive sheet. It is preferably 65 to 90 parts by mass, and the blending ratio of the resin component is, for example, 5 to 60 parts by mass, preferably 10 to 35 parts by mass, based on 100 parts by mass of the total amount of each component forming the thermally conductive sheet. . In addition, the blending ratio of the boron nitride particles to the mass basis of 100 parts by mass of the resin component is, for example, 60 to 1900 parts by mass, preferably 185 to 900 parts by mass.

When the two types of epoxy resins (the first epoxy resin and the second epoxy resin) are used in combination, the mass ratio of the first epoxy resin to the second epoxy resin (the mass of the first epoxy resin / the second The mass of the epoxy resin can be appropriately set according to the softening temperature of each epoxy resin (the first epoxy resin and the second epoxy resin), and is, for example, 1/99 to 99/1, preferably 10/90~ 90/10.

Further, the resin component may contain, for example, a polymer precursor (for example, a low molecular weight polymer containing an oligomer) and/or a monomer in addition to the above respective components (polymer).

Fig. 1 is a perspective view showing an embodiment of a thermally conductive sheet of the present invention, and Fig. 2 is a view showing a step of explaining a method of manufacturing the thermally conductive sheet shown in Fig. 1.

Next, a method of manufacturing an embodiment of the thermally conductive sheet of the present invention will be described with reference to Figs. 1 and 2 .

In this method, the above components are first formulated by the above-mentioned blending ratio, and stirred and mixed, whereby a mixture is prepared.

In the stirring and mixing, in order to mix the components efficiently, for example, a solvent may be blended with each of the above components, or a resin component (preferably a thermoplastic resin component) may be melted, for example, by heating.

The solvent is the same as the above-mentioned organic solvent. Further, when the curing agent and/or the curing accelerator are prepared as a solvent solution and/or a solvent dispersion, the solvent of the solvent solution and/or the solvent dispersion may be directly supplied as a solvent for stirring without stirring. Mixed solvent mixture. Alternatively, a solvent may be further added as a mixed solvent when stirring and mixing.

When stirring and mixing using a solvent, the solvent was removed after stirring and mixing.

In order to remove the solvent, for example, it is allowed to stand at room temperature for 1 to 48 hours, or for example, at 40 to 100 ° C for 0.5 to 3 hours, or for example, under a reduced pressure of 0.001 to 50 kPa, at a temperature of 20 to 60 ° C. ~3 hours.

When the resin component (preferably a thermoplastic resin component) is melted by heating, the heating temperature is, for example, near or above the softening temperature of the resin component, specifically 40 to 150 ° C, preferably 70 to 140 ° C.

Then, in the method, the resulting mixture is subjected to hot pressing.

Specifically, as shown in FIG. 2(a), the mixture is hot-pressed via, for example, two release films 4 as needed, whereby the pressed sheet 1A is obtained. The temperature of the hot pressing is, for example, 50 to 150 ° C, preferably 60 to 140 ° C, and the pressure is, for example, 1 to 100 MPa, preferably 5 to 50 MPa, and the time is, for example, 0.1 to 100 minutes, preferably 1 to 1. 30 minutes.

More preferably, the mixture is subjected to vacuum hot pressing. The vacuum degree of the vacuum hot pressing is, for example, 1 to 100 Pa, preferably 5 to 50 Pa, and the temperature, pressure, and time are the same as the temperature, pressure, and time of the above hot pressing.

When the temperature, the pressure, and/or the time of the hot pressing are outside the above range, the void ratio P (described later) of the thermally conductive sheet 1 may not be adjusted to a desired value.

The pressed sheet 1A obtained by hot pressing has a thickness of, for example, 50 to 1000 μm, preferably 100 to 800 μm.

Then, in this method, as shown in FIG. 2(b), the pressed sheet 1A is divided into a plurality of (for example, four) sheets to obtain a divided sheet 1B (dividing step). In the division of the pressed sheet 1A, the pressed sheet 1A is cut along the thickness direction thereof by being divided into a plurality of pieces when projected in the thickness direction. In addition, the pressed sheet 1A is cut so that each divided sheet 1B has the same shape when projected in the thickness direction.

Then, in this method, as shown in FIG. 2(c), each of the divided sheets 1B is laminated in the thickness direction to obtain a laminated sheet 1C (layering step).

Then, in this method, as shown in Fig. 2 (a), the laminated sheet 1C is subjected to hot pressing (preferably vacuum hot pressing) (hot pressing step). The conditions of hot pressing are the same as those of the above mixture.

The thickness of the laminated sheet 1C after the hot pressing is, for example, 1 mm or less, preferably 0.8 mm or less, and is usually 0.05 mm or more, preferably 0.1 mm or more.

Then, in the thermally conductive sheet 1, in order to effectively align the boron nitride particles 2 in the resin component 3 in a specific direction, the above-described dividing step (Fig. 2(b)) and the laminating step (Fig. 2 (c) are repeatedly performed. )) and a series of steps in the hot pressing step (Fig. 2(a)). The number of repetitions is not particularly limited, and may be appropriately set depending on the filling state of the boron nitride particles, and is, for example, 1 to 10 times, preferably 2 to 7 times.

Thereby, the thermally conductive sheet 1 can be obtained.

The thickness of the obtained thermally conductive sheet 1 is, for example, 1 mm or less, preferably 0.8 mm or less, and is usually 0.05 mm or more, preferably 0.1 mm or more.

In addition, the volume ratio of the boron nitride particles in the thermally conductive sheet 1 (the solid content, that is, the volume percentage of the boron nitride particles to the total volume of the resin component and the boron nitride particles) is as described above. 35 vol% or more (preferably 60 vol% or more, more preferably 75 vol% or more) is usually 95% by volume or less (preferably 90% by volume or less).

When the content ratio of the boron nitride particles does not satisfy the above range, there is a method in which the boron nitride particles are blended in a specific direction in the thermally conductive sheet.

Further, when the resin component 3 is a thermosetting resin component, the uncured (or semi-cured (B-stage)) thermally conductive sheet 1 is subjected to the hot pressing step (Fig. 2 (a)). The heat-curable sheet 1 after hardening is produced by heat hardening.

When the thermally conductive sheet 1 is thermally cured, the above-described hot press or dryer can be used. It is preferred to use a dryer. The temperature hardening condition is, for example, 60 to 250 ° C, preferably 80 to 200 ° C. When a hot press is used, the pressure is, for example, 100 MPa or less, preferably 50 MPa or less.

Further, in the thermally conductive sheet 1 thus obtained, as shown in FIG. 1 and a partially enlarged schematic view, the longitudinal direction LD of the boron nitride particles 2 intersects with the thickness direction TD of the thermally conductive sheet 1 (positive The direction of the face is SD and is aligned.

Further, the arithmetic mean of the angle between the longitudinal direction LD of the boron nitride particles 2 and the surface direction SD of the thermally conductive sheet 1 (the alignment angle α of the boron nitride particles 2 with respect to the thermally conductive sheet 1) is, for example, 25 degrees. Hereinafter, it is preferably 20 degrees or less, and usually 0 degrees or more.

Further, the alignment angle α of the boron nitride particles 2 with respect to the thermally conductive sheet 1 is calculated as follows: the thermally conductive sheet 1 is cut in the thickness direction by a cross section polisher (CP, Cross Section Polisher) The cross section thus formed was photographed by a scanning electron microscope (SEM) at a magnification at which the field of view of 200 or more boron nitride particles 2 was observed, and the longitudinal direction LD of the boron nitride particles 2 was obtained from the obtained SEM photograph. The inclination angle α of the surface direction SD of the thermally conductive sheet 1 (the direction orthogonal to the thickness direction TD) is calculated as the average value.

Thereby, the thermal conductivity of the surface direction SD of the thermally conductive sheet 1 is 4 W/m‧K or more, preferably 5 W/m‧K or more, more preferably 10 W/m‧K or more, and particularly preferably 15 W/m‧K or more, especially preferably 25 W/m‧K or more, usually 200 W/m‧K or less.

In addition, the thermal conductivity of the surface direction SD of the thermally conductive sheet 1 is substantially the same before and after the thermosetting when the resin component 3 is a thermosetting resin component.

When the thermal conductivity of the surface direction SD of the thermally conductive sheet 1 does not satisfy the above range, the thermal conductivity in the surface direction SD may be insufficient, and it may not be used for the heat dissipation application in which the thermal conductivity of the surface direction SD is required.

Further, the thermal conductivity of the surface direction SD of the thermally conductive sheet 1 was measured by a pulse heating method. The pulse heating method was a "FLA-447 type" (manufactured by NETZSCH Co., Ltd.) using a xenon flash analyzer.

Further, the thermal conductivity of the thermally conductive sheet 1 in the thickness direction TD is, for example, 0.5 to 15 W/m‧K, preferably 1 to 10 W/m‧K.

Further, the thermal conductivity in the thickness direction TD of the thermally conductive sheet 1 is measured by a pulse heating method, a laser flash method, or a TWA (Temperature Wave Analysis) method. The same applies to the pulse heating method. The laser flash method uses "TC-9000" (manufactured by ULVAC-RIKO Co., Ltd.), and the TWA method uses "ai-Phase mobiIe" (manufactured by ai-Phase Co., Ltd.).

Thereby, the ratio of the thermal conductivity of the surface direction SD of the thermally conductive sheet 1 to the thermal conductivity of the thickness direction TD of the thermally conductive sheet 1 (thermal conductivity in the plane direction SD / thermal conductivity in the thickness direction TD) For example, it is 1.5 or more, preferably 3 or more, more preferably 4 or more, and usually 20 or less.

Moreover, although the heat conductive sheet 1 is not illustrated in FIG. 1, for example, a void (gap) can be formed.

The ratio of the voids in the thermally conductive sheet 1, that is, the void ratio P, can be obtained by the ratio of the content of the boron nitride particles 2 (volume basis), and further the hot pressing of the mixture of the boron nitride particles 2 and the resin component 3 (Fig. 2 (a The temperature, pressure, and/or time are adjusted, and specifically, the temperature, pressure, and/or time of the hot pressing (Fig. 2(a)) are set within the above range.

The porosity P in the thermally conductive sheet 1 is, for example, 30% by volume or less, preferably 10% by volume or less.

The void ratio P is measured by, for example, first cutting the thermally conductive sheet 1 in the thickness direction by a cross-section polisher (CP), and the resulting cross section is scanned by a scanning electron microscope (SEM). The image was observed at 200 times, and the void portion and the other portions were subjected to binarization treatment based on the obtained image, and then the area ratio of the void portion to the entire cross-sectional area of the thermally conductive sheet 1 was calculated.

In the thermally conductive sheet 1, the void ratio P2 after curing is, for example, 100% or less, preferably 50% or less, with respect to the void ratio P1 before curing.

In the measurement of the porosity P (P1), when the resin component 3 is a thermosetting resin component, the thermally conductive sheet 1 before thermal curing can be used.

When the porosity P of the thermally conductive sheet 1 is within the above range, the step followability (described later) of the thermally conductive sheet 1 can be improved.

In addition, in the bending resistance test of the cylindrical mandrel method according to JIS K 5600-5-1, the thermal conductive sheet 1 was evaluated by the following test conditions, for example, no fracture was observed.

Test conditions

Test device: Model I

Mandrel: 10 mm in diameter

Bending angle: 90 degrees or more

Thickness of the thermally conductive sheet 1 : 0.3 mm

Further, a perspective view of the test device of the model I is shown in Figs. 9 and 10, and a test device of the model I will be described below.

In the test apparatus 10 of the model I, the first flat plate 11 and the second flat plate 12 arranged in parallel with the first flat plate 11 are provided to relatively rotate the first flat plate 11 and the second flat plate 12 in FIGS. 9 and 10 . Mandrel (rotation axis) 13.

The first flat plate 11 is formed in a substantially rectangular flat plate shape. Further, a stopper portion 14 is provided at one end portion (free end portion) of the first flat plate 11. The stopper portion 14 is formed on the surface of the second flat plate 12 so as to extend along one end portion of the second flat plate 12.

The second flat plate 12 is formed in a substantially rectangular flat plate shape, and one side thereof is adjacent to one side of the first flat plate 11 (one side of the other end portion (base end portion) on the side opposite to the end portion on which the stopper portion 14 is provided). The way to configure.

The mandrel 13 is formed to extend along one side of the first flat plate 11 and the second flat plate 12 adjacent to each other.

As shown in Fig. 9, the test apparatus 10 of the model I had the same plane as the surface of the second flat plate 12 before the start of the bending resistance test.

Further, when the bending resistance test is performed, the thermally conductive sheet 1 is placed on the surface of the first flat plate 11 and the surface of the second flat plate 12. Further, the thermally conductive sheet 1 is placed such that one side thereof abuts against the stopper portion 14.

Then, as shown in FIG. 10, the first flat plate 11 and the second flat plate 12 are relatively rotated. Specifically, the free end portion of the first flat plate 11 and the free end portion of the second flat plate 12 are rotated only by a specific angle around the mandrel 13 . Specifically, the first flat plate 11 and the second flat plate 12 are rotated such that the surfaces of the free end portions thereof approach (opposite).

Thereby, the thermally conductive sheet 1 is bent around the mandrel 13 while following the rotation of the first flat plate 11 and the second flat plate 12.

Preferably, in the above-described test conditions, the thermally conductive sheet 1 is not observed to have a fracture even when the bending angle is set to 180 degrees.

When the fracture was observed on the thermally conductive sheet 1 in the bending resistance test by the above bending angle, the thermal conductive sheet 1 could not be provided with excellent flexibility.

In the bending resistance test, when the resin component 3 is a thermosetting resin component, the thermally conductive sheet 1 before thermosetting can be used.

Moreover, in the three-point bending test according to JIS K 7171 (2008), the thermal conductive sheet 1 was evaluated by the following test conditions, and for example, no fracture was observed.

Test conditions

Test piece: size 20 mm × 15 mm

Distance between fulcrums: 5 mm

Test speed: 20 mm/min (pressure speed under the head)

Bending angle: 120 degrees

Evaluation method: The presence or absence of cracks such as cracks in the center portion of the test piece when the test was carried out under the above test conditions was visually observed.

In the three-point bending test, when the resin component 3 is a thermosetting resin component, the thermally conductive sheet 1 before thermosetting can be used.

Therefore, since the thermally conductive sheet 1 was not observed to be broken in the above three-point bending test, the step followability was excellent. In addition, the step followability refers to a characteristic that follows when the thermally conductive sheet 1 is placed on a setting object having a step difference, and is closely adhered along the step.

Further, for example, a mark such as a character or a symbol may be attached to the thermally conductive sheet 1. That is, the thermally conductive sheet 1 is excellent in the adhesion of the mark. The term "marking adhesion" means a property in which the above-mentioned mark can be surely adhered to the thermally conductive sheet 1.

Specifically, the mark can be attached (coated, fixed or fixed) to the thermally conductive sheet 1 by printing, engraving or the like.

Examples of the printing include inkjet printing, letterpress printing, gravure printing, and laser printing.

Further, when the mark is printed by inkjet printing, letterpress printing or gravure printing, for example, an ink fixing layer for improving the fixing property of the marking can be provided on the surface (printing side) of the thermally conductive sheet 1.

Further, when the mark is printed by laser printing, for example, a toner fixing layer for improving the fixing property of the mark can be provided on the surface (printing side) of the heat conductive sheet 1.

As the engraving, for example, laser marking, engraving, and the like can be cited.

Further, the volume resistance R of the thermally conductive sheet 1 is, for example, 1 × 10 ¹⁰ Ω ‧ cm or more, preferably 1 × 10 ¹² Ω ‧ cm or more, and usually 1 × 10 ²⁰ Ω ‧ cm or less.

The volume resistance R of the thermally conductive sheet 1 is measured in accordance with JIS K 6911 (General Test Method for Thermosetting Plastics, 2006 Edition).

When the volume resistance R of the thermally conductive sheet 1 does not satisfy the above range, there is a case where it is impossible to prevent a short circuit between electronic components to be described later.

In the thermally conductive sheet 1, when the resin component 3 is a thermosetting resin component, the volume resistive R is a value of the thermally conductive sheet 1 after curing.

Further, the dielectric breakdown voltage of the thermally conductive sheet 1 measured in accordance with JIS C 2110 (2010 edition) is, for example, 10 kV/mm or more. When the dielectric breakdown voltage of the thermally conductive sheet 1 does not satisfy 10 kV/mm, there is a case where excellent insulation breakdown resistance (tracking resistance) cannot be ensured.

In addition, the above-mentioned dielectric breakdown voltage is measured in accordance with JIS C 2110-2 (2010 edition), "Test Method for Strength of Insulating Destruction - Part 2: Test for Applying DC Voltage". Specifically, a voltage at which insulation breakdown occurs in the thermally conductive sheet 1 is measured as a dielectric breakdown voltage by a short-time (rapid boost) test with a step-up speed of 1000 V/s.

Further, the dielectric breakdown voltage of the thermally conductive sheet 1 is preferably 15 kV/mm or more, and is usually 100 kV/mm or less.

When the resin component 3 is a thermosetting resin component, the dielectric breakdown voltage of the thermally conductive sheet 1 is substantially the same before and after thermal curing of the thermally conductive sheet 1.

Further, the glass transition point of the thermally conductive sheet 1 is, for example, 125 ° C or higher, preferably 130 ° C or higher, more preferably 140 ° C or higher, still more preferably 150 ° C or higher, further preferably 170 ° C or higher, and even more preferably It is 190 ° C or higher, more preferably 210 ° C or higher, and usually 300 ° C or lower.

When the glass transition point is at least the above lower limit, excellent heat resistance of the thermally conductive sheet can be ensured, so that deformation at a high temperature can be reduced and peeling can be suppressed.

In other words, when the heat conductive sheet 1 is bonded to various devices, the temperature of the device rises, and when the temperature exceeds the glass transition point of the thermally conductive sheet 1, the thermal conductive sheet 1 changes from the coefficient of linear expansion. The situation in which various devices are stripped. However, in the thermally conductive sheet 1, since the glass transition point is equal to or higher than the above upper limit, even if the temperature of the apparatus rises, the glass transition point exceeding the thermally conductive sheet 1 can be suppressed, and as a result, the thermally conductive sheet 1 can be lowered. Deformation inhibits peeling.

Further, the glass transition point was obtained in the form of a peak of tan δ (loss tangent) obtained by dynamic viscoelasticity measurement at a frequency of 10 Hz.

Further, the 5% mass reduction temperature of the thermally conductive sheet 1 is, for example, 250 ° C or higher, preferably 300 ° C or higher, and usually 450 ° C or lower.

When the 5% mass reduction temperature is at least the above lower limit, decomposition can be suppressed even when exposed to a high temperature, and heat generated by various devices can be efficiently conducted.

Further, the 5% mass reduction temperature can be measured by thermal mass analysis (temperature up rate 10 ° C / min, nitrogen atmosphere) in accordance with JIS K 7120.

Further, in the following initial adhesion test (1), the thermally conductive sheet 1 does not fall off from the adherend, for example. That is, the temporarily conductive state of the thermally conductive sheet 1 and the adherend is maintained.

Initial adhesion test (1): The thermally conductive sheet 1 was heat-compressed and bonded to the bonded body in the horizontal direction to be temporarily fixed, and after being left for 10 minutes, the adherend was inverted upside down.

Examples of the adherend include a substrate including stainless steel (for example, SUS304), or a package substrate for a notebook computer in which a plurality of IC (integrated circuit) chips, capacitors, coils, resistors, and the like are packaged. . Further, in the package substrate for a notebook computer, the electronic components are usually arranged at intervals in the surface direction (the surface direction of the package substrate for the notebook computer) on the upper surface (one surface).

In the pressure bonding, for example, the surface of the thermally conductive sheet 1 is rotated while pressing the thermal conductive sheet 1 with a sponge roll containing a resin such as a polyoxyn resin.

Moreover, when the resin component 3 is a thermosetting resin component (for example, an epoxy resin), the temperature of the heat-compression bonding is 80 degreeC, for example.

On the other hand, when the resin component 3 is a thermoplastic resin component (for example, polyethylene), for example, a temperature of 10 to 30 ° C is applied to the softening point or melting point of the thermoplastic resin component, preferably a thermoplastic resin. Adding a temperature of 15 to 25 ° C to the softening point or melting point of the component, more preferably adding a temperature of 20 ° C to the softening point or melting point of the thermoplastic resin component, specifically 120 ° C (ie, the softening point or melting point of the thermoplastic resin component is 100 °C, at a temperature of 20 ° C at 20 ° C).

When the thermally conductive sheet 1 is detached from the adherend in the initial adhesion test (1), that is, when the thermally conductive sheet 1 and the adherend are temporarily held, the thermally conductive sheet 1 cannot be reliably provided. The material 1 is temporarily fixed to the bonded body.

In the case where the resin component 3 is a thermosetting resin component, the thermally conductive sheet 1 to be subjected to the initial adhesion test (1) and the initial adhesion test (2) (described later) is an uncured heat conductive sheet 1 The thermally conductive sheet 1 is brought into the B-stage state by the thermal bonding in the initial adhesion test (1) and the initial adhesion test (2).

Further, when the resin component 3 is a thermoplastic resin component, the thermally conductive sheet 1 to be subjected to the initial adhesion test (1) and the initial adhesion test (2) (described later) is a solid heat conductive sheet 1 by initial In the adhesion test (1) and the initial adhesion test (2), the heat conductive sheet 1 was softened.

Preferably, the thermally conductive sheet 1 does not fall off from the adherend in the two tests of the initial adhesion test (1) and the initial adhesion test (2). That is, the temporarily conductive state of the thermally conductive sheet 1 and the adherend is maintained.

Initial adhesion test (2): The heat conductive sheet 1 is temporarily fixed by heat-compression bonding on the bonded body in the horizontal direction, and after being left for 10 minutes, the bonded body is placed in the vertical direction (up and down) Directional mode configuration.

The temperature at the time of the heat bonding of the initial adhesion test (2) was the same as the temperature at the time of the heat bonding of the initial adhesion test (1).

Further, in the thermally conductive sheet 1, the flexibility and the thermal conductivity in the plane direction SD are excellent.

Therefore, the thermally conductive sheet which is excellent in workability and excellent in thermal conductivity in the surface direction SD can be used for various heat dissipation applications, and specifically, can be used as a heat conductive sheet used in power electronics technology, and more specifically, For example, it can be used as a heat conductive sheet applied to an LED heat sink substrate or a battery heat sink.

Moreover, the thermal conductive sheet 1 is excellent in thermal conductivity in the plane direction SD, and the volume resistance R is in a specific range, and therefore is excellent in electrical insulating properties.

Therefore, if the electronic component is covered by the thermally conductive sheet 1, the electronic component can be protected, and the heat of the electronic component can be thermally efficiently conducted, and the short circuit between the electronic components can be prevented.

In addition, the electronic component to be coated on the thermally conductive sheet 1 is not particularly limited, and examples thereof include an IC (integrated circuit) wafer, a capacitor, a coil, a resistor, and a light-emitting diode. These electronic components are usually disposed on the substrate and are arranged at intervals in the plane direction (the direction of the surface of the substrate).

Further, the thermal conductive sheet 1 is excellent in thermal conductivity in the surface direction SD and has an insulation breakdown voltage within a specific range, and therefore is excellent in insulation breakdown resistance (striking resistance).

Therefore, when the electronic component used in the power electronic device and/or the package substrate packaged therewith is covered by the thermally conductive sheet 1, the insulation breakdown of the thermally conductive sheet 1 can be prevented, and the thermally conductive sheet 1 can be prevented by the thermal conductive sheet 1 The heat of the electronic component and/or the package substrate can be dissipated along the surface direction SD.

Examples of the electronic component used in the power electronics include an IC (integrated circuit) wafer (particularly, an electrode terminal portion having a narrow width in an IC chip), a thyristor (rectifier), a motor component, a transformer, and a power transmission component. Capacitors, coils, resistors, light-emitting diodes, etc.

Further, the electronic component is packaged on the surface (one surface) of the package substrate, and the electronic component is placed at a distance from each other in the plane direction (the direction of the surface of the package substrate).

Further, the thermally conductive sheet 1 covering the electronic component and/or the package substrate can be prevented from being deteriorated by high frequency noise or the like generated by the electronic component and/or the package substrate.

Further, in the above-described thermally conductive sheet 1, since the thermal conductivity in the surface direction SD is excellent and the glass transition point is within a specific range, heat resistance is also excellent.

Therefore, the thermally conductive sheet which is excellent in handleability and excellent in thermal conductivity in the surface direction can be used for various heat dissipation applications, and can be used as a power electronic technology. More specifically, the heat conductive sheet can be used, for example, as a heat conductive sheet applied to an LED heat sink substrate or a battery heat sink.

Further, in the above-described thermally conductive sheet 1, since the flexibility and the surface direction SD are excellent in thermal conductivity, and the 5% mass reduction temperature is within a specific range, heat resistance is also excellent.

In other words, the thermally conductive sheet 1 can be prevented from being decomposed even when exposed to a high temperature of 200 ° C or higher, and is used as a heat conductive sheet having excellent handleability and excellent thermal conductivity in the surface direction SD. Specifically, it can be used as a heat conductive sheet used in a power electronic technology that generates a high temperature of 200 to 250 ° C, and more specifically, for example, can be used for application of a SiC wafer, an LED heat sink substrate, and a battery for heat dissipation. Thermal conductive sheet of material.

Further, the thermal conductive sheet 1 is excellent in thermal conductivity in the plane direction SD, and in the initial adhesion test (1), for example, does not fall off from the adherend, and therefore the heating pressure is applied to the specific temperature of the adherend. The adhesion (initial adhesion) is also excellent.

Therefore, when the thermally conductive sheet 1 is heated and pressure-bonded to the adherend, the thermally conductive sheet 1 can be surely fixed (temporarily fixed) to the adherend.

Therefore, the thermally conductive sheet 1 is temporarily fixed to the adherend in the B-stage state, and then the thermally conductive sheet 1 is thermally cured by heating, whereby the thermally conductive sheet 1 can be surely bonded to the thermally conductive sheet 1 The heat of the adherend can be efficiently thermally conducted along the surface direction SD of the thermally conductive sheet 1 by the thermally conductive sheet 1 on the adhesive body.

In addition, the bonded body is not particularly limited, and examples thereof include a light-emitting diode and the like in addition to the above-described electronic component (IC chip, capacitor, coil, resistor, etc.).

On the other hand, after the heat conductive sheet 1 is temporarily fixed to the adherend, if necessary, it is temporarily peeled off for positional adjustment, and it is intended to be re-bonded (secondary processing), and the thermally conductive sheet 1 is B. The state of the order is good in secondary workability. Therefore, the thermally conductive sheet 1 can be prevented from remaining on the surface of the adherend at the time of peeling, and secondary processing can be easily performed.

Further, even if the thermally conductive sheet 1 remains on the surface of the adherend, if the thermally conductive sheet 1 is not cured (before curing), the residue can be easily wiped (removed).

Further, in the hot pressing (Fig. 2 (a)) step, for example, the mixture and the laminated sheet 1C may be rolled by a plurality of calender rolls or the like.

In addition, when the resin component 3 is a thermosetting resin component, the heat conductive sheet may be obtained as the uncured heat conductive sheet 1 as described above without performing thermal curing.

In other words, when the resin component is a thermosetting resin component, the heat conductive sheet of the present invention is not particularly limited in terms of the presence or absence of heat curing, and may be, for example, a laminate step (Fig. 2(c)) as described above. Or after the specific time from the above-mentioned hot pressing step (Fig. 2(a), hot pressing of the mixture, and hot pressing without thermal hardening), specifically, when applied to power electronics technology, or from the application After a certain period of time, heat hardening is performed.

Example

The present invention will be more specifically described by the following examples and comparative examples, but the present invention is not limited to the examples and comparative examples.

Example 1

According to the formulation of Table 1, the ingredients (boron nitride particles and epoxy resin composition) were blended and stirred, and left at room temperature (23 ° C) for 1 night to make methyl ethyl ketone (solvent/hardener of hardener) The dispersion medium is volatilized to prepare a semi-solid mixture.

Then, the obtained mixture was sandwiched by two release films treated with polyoxyxylene, and the load was 5 tons at 80 ° C in a 10 Pa environment (vacuum environment) by a vacuum heating press. (20 MPa) hot pressing for 2 minutes, whereby a pressed sheet having a thickness of 0.3 mm was obtained (refer to Fig. 2 (a)).

Then, the obtained pressed sheet is cut into a plurality of pieces when projected in the thickness direction of the pressed sheet, thereby obtaining a divided sheet (refer to FIG. 2(b)), and then the divided sheet is subjected to thickness direction. A laminated sheet is obtained by laminating (see Fig. 2(c)).

Then, the obtained laminated sheet was hot-pressed by the same conditions as above by the same vacuum heating press as described above (refer to Fig. 2 (a)).

Then, one of the above-described cutting, laminating, and hot pressing series operations (refer to FIG. 2) was repeated four times to obtain a thermally conductive sheet having a thickness of 0.3 mm.

Then, the obtained thermally conductive sheet was placed in a dryer and heated at 150 ° C for 120 minutes to be thermally cured.

Examples 2-8, 10-16, and Comparative Examples 1, 2

According to the formulation and manufacturing conditions of Tables 1 to 3, the treatment was carried out in the same manner as in Example 1 to obtain thermal conductivity of 0.3 mm in thickness of Examples 2 to 8, 10 to 16, and Comparative Examples 1 and 2, respectively. Sheet.

Example 9

According to the formulation of Table 2, each component (boron nitride particles and polyethylene) was blended and stirred to prepare a mixture. That is, when the components were stirred, the mixture was heated to 130 ° C to melt the polyethylene.

Then, the obtained mixture was sandwiched by two release films treated with polyfluorene, for a load of 1 ton in a 10 Pa environment (vacuum environment) by a vacuum heating press at 120 ° C. (4 MPa) was hot pressed for 2 minutes, whereby a pressed sheet having a thickness of 0.3 mm was obtained (refer to Fig. 2 (a)).

Then, the obtained pressed sheet is cut into a plurality of pieces when projected in the thickness direction of the pressed sheet, thereby obtaining a divided sheet (refer to FIG. 2(b)), and then the divided sheet is in the thickness direction. The laminate is laminated to obtain a laminated sheet (see Fig. 2(c)).

Then, the obtained laminated sheet was hot-pressed by the same conditions as above by the same vacuum heating press as described above (refer to Fig. 2 (a)).

Then, one of the above-described series of cutting, laminating, and pressurizing (refer to FIG. 2) was repeated four times, whereby a thermally conductive sheet having a thickness of 0.3 mm was obtained.

(Evaluation)

(1) Thermal conductivity

The thermal conductivity of the thermally conductive sheet obtained from each of the examples and the comparative examples was measured.

Namely, the thermal conductivity in the plane direction (SD) was measured by a pulse heating method using a 氙flash analyzer "LFA-447 type" (manufactured by NETZSCH Co., Ltd.). Moreover, the thermal conductivity in the thickness direction (TD) was measured by the TWA method using "ai-Phase mobile" (manufactured by ai-Phase Co., Ltd.).

The results are shown in Tables 1 to 3 (Examples 1 to 16 and Comparative Examples 1 and 2) and Fig. 8 (Examples 1 to 4 and Comparative Examples 1 and 2).

(2) Observing the section by electron microscope

The thermally conductive sheets of Examples 1, 3, and 5 and Comparative Examples 1 and 2 were cut in the thickness direction by a cross-section polisher, and the cut surface thereof was observed by an electron microscope (SEM).

The image processing maps are shown in Figures 3 to 7 respectively.

(3) Bending resistance (softness)

The heat conductive sheet of each of the examples and the comparative examples was subjected to a bending resistance test in accordance with JIS K 5600-5-1 bending resistance (cylindrical mandrel method).

Specifically, first, for the thermally conductive sheets of Examples 1 to 8, 10 to 16, and Comparative Examples 1 and 2, a laminated sheet having a thickness of 0.3 mm before curing was prepared as a sample, and this was subjected to a bending resistance test.

Further, with respect to the thermally conductive sheet of Example 9, the obtained thermally conductive sheet having a thickness of 0.3 mm was directly subjected to a bending resistance test.

Then, the bending resistance (softness) of each of the heat conductive sheets was evaluated by the following test conditions.

Test conditions

Test device: Model I

Mandrel: 10 mm in diameter

Further, each of the uncured heat conductive sheets was bent at a bending angle of more than 0 degrees and not more than 180 degrees, and evaluated according to the angle at which the thermally conductive sheet was broken (damaged).

The results are shown in Tables 1 to 3.

◎: 180 degrees, and no breakage occurred even when bent.

○: 90 degrees or more is less than 180 degrees, and if it is bent, cracking occurs.

△: 10 degrees or more is less than 90 degrees, and if it is bent, cracking occurs.

×: Less than 0 degrees is less than 10 degrees, and if it is bent, cracking occurs.

(4) Void ratio (P)

The porosity (P1) of the thermally conductive sheet before thermal curing of each of the examples and the comparative examples was measured by the following measurement method.

Method for measuring void ratio: First, the thermally conductive sheet was cut in the thickness direction by a cross-section polisher (CP), and the cross-section thus obtained was observed by scanning electron microscopy (SEM) at 200 times. image. Then, the void portion and the other portions are subjected to binarization processing based on the obtained image, and then the area ratio of the void portion to the entire cross-sectional area of the thermally conductive sheet is calculated.

The results are shown in Tables 1 to 3.

(5) Step followability (three-point bending test)

The three-point bending test under the following test conditions was carried out in accordance with JIS K 7171 (2010) in accordance with JIS K 7171 (2010) for the thermally conductive sheets before thermal curing of the respective examples and the comparative examples, thereby evaluating the step following in accordance with the following evaluation criteria. Sex. The results are shown in Tables 1 to 3.

Test conditions

Test piece: size 20 mm × 15 mm

Distance between fulcrums: 5 mm

Test speed: 20 mm/min (pressure speed under the head)

Bending angle: 120 degrees

(evaluation benchmark)

◎: No break was observed at all.

○: Little break was observed.

×: A fracture was clearly observed.

(6) Print mark visual recognition (print mark adhesion: mark adhesion by inkjet printing or laser printing)

The thermally conductive sheets of Examples 1 to 16 were printed with marks by inkjet printing and laser printing, and the marks were observed.

As a result, any of the thermally conductive sheets of Examples 1 to 16 was able to visually recognize the marks obtained by both inkjet printing and laser printing, and confirmed that the printed mark adhesion was good.

(7) Volume resistance

The volume resistance (R) of the thermally conductive sheet of each of the examples and the comparative examples was measured.

That is, the volume resistance (R) of the thermally conductive sheet was measured in accordance with JIS K 6911 (General Test Method for Thermosetting Plastics, 2006 Edition).

The results are shown in Tables 1 to 3.

(8) Insulation failure test (JIS C 2110 (2010 edition))

The dielectric breakdown voltage was measured in accordance with JIS C 2110 (2010 edition) for the thermally conductive sheets obtained in the respective examples and comparative examples.

That is, the dielectric breakdown voltage is based on JIS C 2110-2 (2010 edition), "Test method for strength of dielectric electrical insulation - Insulation damage - Part 2: Test for applying DC voltage", A short time (rapid boost) test of 1000 V/s was performed.

The results are shown in Tables 1 to 3.

(9) Glass transfer point

The glass transition point was measured about the heat conductive sheet obtained from each Example and each comparative example.

In other words, the thermal conductive sheet was analyzed by a dynamic viscoelasticity measuring apparatus (model: DMS6100, manufactured by SEICO Electronics Industrial Co., Ltd.) at a temperature increase rate of 1 ° C/min and a frequency of 10 Hz.

Based on the obtained data, the glass transition point was obtained in the form of the peak of tan δ.

The results are shown in Tables 1 to 3.

(10) Quality reduction measurement

The 5% mass reduction temperature of the thermally conductive sheet obtained from each of the examples and the comparative examples was measured in accordance with JIS K 7120 by thermal mass analysis using a thermal mass spectrometer (temperature rising rate: 10 ° C/min, nitrogen atmosphere).

The results are shown in Tables 1 to 3.

(11) Initial adhesion test A. Initial adhesion test for package substrates for notebook computers

For the uncured heat conductive sheets of the respective examples and the comparative examples, initial adhesion test (1) and (2) for a package substrate for a notebook computer in which a plurality of electronic components were packaged were carried out.

That is, using a sponge roll containing a polyoxyxylene resin, the thermally conductive sheet was placed on the surface of the package substrate for notebook computers (the side on which the electronic components were packaged) at 80 ° C (Examples 1 to 8 and implemented). In Example 10 to 16) or 120 ° C (Example 9), the film was fixed by heat and pressure bonding, and after being left for 10 minutes, the notebook substrate for the notebook computer was placed in the vertical direction (initial adhesion test (2) )).

Then, the package substrate for the notebook computer is placed such that the thermally conductive sheet is directed to the lower side (that is, the upper and lower sides are reversed from the state immediately after being temporarily fixed) (initial adhesion test (1)).

Further, in the initial adhesion test (1) and the initial adhesion test (2), the thermally conductive sheet was evaluated in accordance with the following criteria. The results are shown in Tables 1 to 3.

<benchmark>

○: It was confirmed that the thermally conductive sheet did not fall off from the package substrate for the notebook computer.

x: It was confirmed that the thermally conductive sheet was peeled off from the package substrate for the notebook computer.

B. Initial adhesion test for stainless steel substrates

The initial adhesion test (1) and (2) for a stainless steel substrate (manufactured by SUS304) were carried out in the same manner as above for the uncured heat conductive sheets of the respective examples and the comparative examples.

Further, in the initial adhesion test (1) and the initial adhesion test (2), the thermally conductive sheet was evaluated in accordance with the following criteria. The results are shown in Tables 1 to 3.

<benchmark>

○: It was confirmed that the thermally conductive sheet did not fall off from the stainless steel substrate.

×: It was confirmed that the thermally conductive sheet fell off from the stainless steel substrate.

(12) Orientation angle of boron nitride particles (α)

The heat conductive sheet is cut along the thickness direction by a profile polishing machine (CP), and the resulting cross section is photographed by a scanning electron microscope (SEM) at 100 to 2000 times, according to the obtained SEM photograph (refer to 3 to 7), the inclination angle (α) of the longitudinal direction (LD) of the boron nitride particles with respect to the plane direction (SD) of the thermally conductive sheet is obtained, and the boron nitride particles are calculated as the average value thereof. Orientation angle (α).

The results are shown in Tables 1 to 3.

(13) Dynamic viscosity of resin component

The dynamic viscosity of the resin component used in each of the examples and the comparative examples was measured by a dynamic viscosity test in accordance with JIS K 7233 (bubble viscosity meter method).

Specifically, the resin component and the standard product were first dissolved in a solvent (butyl carbitol) at a temperature of 25 ± 0.5 ° C at a solid concentration of 40% by mass to prepare a resin component sample and a standard sample. Furthermore, the standard samples are classified into A5~A1, A~Z, and Z1~Z10 according to their dynamic viscosity, and the corresponding dynamic viscosity is 0.005×10 ^-4 m ² /s~1066×10 ^-4 m. Within the range of ² / s.

Then, the rising speed of the bubble in the resin component sample is compared with the rising speed of the bubble in the standard sample (the known dynamic viscosity is known), and the dynamic viscosity of the standard sample having the same rising speed is determined as the dynamic viscosity of the resin component. Thus, the dynamic viscosity of each resin component was measured.

The results are shown in Tables 1 to 3.

Table 1

Table 2

table 3

The numerical values in the respective components in Tables 1 to 3 indicate the number of g unless otherwise specified.

Furthermore, in the column of boron nitride particles in Tables 1 to 3, the value of the upper stage is the blending mass (g) of the boron nitride particles, and the value of the middle stage is the boron nitride particle in the thermally conductive sheet relative to the hardening. The volume fraction (% by volume) of the total volume of the solid component outside the agent (ie, the solid content of the boron nitride particles and the epoxy resin or polyethylene), and the value of the lower segment is the solid content of the boron nitride particles relative to the thermally conductive sheet. (volume percentage (% by volume) of the total volume of the boron nitride particles and the solid content of the epoxy resin and the hardener).

In addition, among the components of Tables 1 to 3, the details of the components with the symbols of ※ are described below.

PT-110 ^*1 : Trade name, plate-shaped boron nitride particles, average particle size (light scattering method) 45 μm, manufactured by Japan Momentive Advanced Materials Co., Ltd.

UHP-1 ^*2 : Product name: SHOBN UHP-1, plate-shaped boron nitride particles, average particle size (light scattering method) 9 μm, manufactured by Showa Denko

Epoxy Resin A ^*3 : OGSOL EG (trade name), bisaryl fluorene epoxy resin, semi-solid, epoxy equivalent 294 g/eqiv., softening temperature (ring and ball method) 47 ° C, melt viscosity (80 ° C) 1360 mPa‧s, manufactured by Osaka Gas Chemicals

Epoxy resin B ^※4 : JER828 (trade name), bisphenol A epoxy resin, liquid, epoxy equivalent 184~194 g/eqiv., softening temperature (ring and ball method) less than 25 ° C, melt viscosity (80 ° C ) 70 mPa‧s, made by Japan Epoxy Resins

Epoxy resin C ^※5 : JER1002 (trade name), bisphenol A epoxy resin, solid, epoxy equivalent 600~700 g/eqiv., softening temperature (ring and ball method) 78°C, melt viscosity (80°C) 10000 mPa‧s or more (above the measurement limit), manufactured by Japan Epoxy Resin Co., Ltd.

Epoxy resin D ^※6 : EPPN-501HY (trade name), triphenylmethane epoxy resin, solid state, epoxy equivalent 163~175 g/eqiv., softening temperature (ring and ball method) 57~63°C, Nipponization Manufactured by a pharmaceutical company

Hardener ^*7 : 5 mass% methyl ethyl ketone solution of Curezol 2PZ (trade name, manufactured by Shikoku Chemicals Co., Ltd.)

Hardener ^*8 : 5 mass% methyl ethyl ketone dispersion of Curezol 2P4MHZ-PW (trade name, manufactured by Shikoku Chemicals Co., Ltd.)

Polyethylene ^※9 : Low density polyethylene, mass average molecular weight (Mw) 4000, number average molecular weight (Mn) 1700, manufactured by Aldrich

In addition, the above description is provided as an exemplified embodiment of the present invention, which is merely illustrative and not limiting. It should be understood by those skilled in the art that modifications of the present invention are also included in the scope of the claims described below.

1. . . Thermally conductive sheet

1A. . . Pressed sheet

1B. . . Split sheet

1C. . . Laminated sheet

2. . . Boron nitride particles

3. . . Resin composition

4. . . Release film

10. . . Model I test device

11. . . First tablet

12. . . 2nd tablet

13. . . Mandrel

14. . . Stop

LD. . . Long side direction

SD. . . Face direction

TD. . . Thickness direction

α. . . Orientation angle

Fig. 1 is a perspective view showing an embodiment of a thermally conductive sheet of the present invention.

2 is a step diagram for explaining a method of manufacturing the thermally conductive sheet shown in FIG. 1, and

(a) indicates the step of hot pressing the mixture or laminated sheet,

(b) shows the step of dividing the pressed sheet into a plurality of pieces,

(c) is a step of displaying a laminated sheet.

3 is an image processing diagram showing an SEM photograph of a cross section along the thickness direction of the thermally conductive sheet after curing in Example 1. FIG.

4 is an image processing diagram showing an SEM photograph of a cross section along the thickness direction of the thermally conductive sheet after curing in Example 3. FIG.

Fig. 5 is an image processing diagram showing an SEM photograph of a cross section along the thickness direction of the thermally conductive sheet after curing in Example 5.

Fig. 6 is an image processing diagram showing an SEM photograph of a cross section along the thickness direction of the thermally conductive sheet after curing of Comparative Example 1.

Fig. 7 is an image processing diagram showing an SEM photograph of a cross section along the thickness direction of the thermally conductive sheet after curing of Comparative Example 2.

Fig. 8 is a graph showing the relationship between the content ratio of boron nitride particles in Examples 1 to 4 and Comparative Examples 1 and 2 and the thermal conductivity of the thermally conductive sheet.

Fig. 9 is a perspective view showing a test device (before the bending resistance test) of the model I of the bending resistance test.

Fig. 10 is a perspective view showing a test device (in the middle of the bending resistance test) of the model I of the bending resistance test.

1. . . Thermally conductive sheet

2. . . Boron nitride particles

3. . . Resin composition

LD. . . Long side direction

SD. . . Face direction

TD. . . Thickness direction

α. . . Orientation angle

Claims (7)

A thermally conductive sheet containing plate-like boron nitride particles and a resin component, and a boron nitride particle content ratio of 35% by volume or more, and the boron nitride particles described above with respect to the heat conductive sheet The alignment angle is 25 degrees or less, and is calculated as an arithmetic mean of the angle between the longitudinal direction of the boron nitride particles and the direction perpendicular to the thickness direction of the thermally conductive sheet, and the thermally conductive sheet is used. The thermal conductivity in the orthogonal direction with respect to the thickness direction is 4 W/m ‧ K or more. The thermally conductive sheet according to claim 1, wherein the boron nitride particles have an average particle diameter of 20 μm or more as measured by a light scattering method. The heat conductive sheet according to claim 1, wherein in the bending resistance test according to the cylindrical mandrel method according to JIS K 5600-5-1, when the heat conductive sheet is evaluated by the following test conditions, A fracture was observed on the above thermally conductive sheet: Test condition test apparatus: Model I mandrel: diameter 10 mm Bending angle: 90 degrees or more The thickness of the above thermally conductive sheet: 0.3 mm. The thermally conductive sheet of claim 1, wherein the resin component is subjected to a dynamic viscosity test according to JIS K 7233 (bubble viscosity meter method) (temperature: 25 ° C ± 0.5 ° C, solvent: butyl carbitol, solid The component concentration: 40% by mass) and the measured dynamic viscosity was 0.22 × 10 ^-4 to 2.00 × 10 ^-4 m ² /s. The thermally conductive sheet according to any one of claims 1 to 4, which is prepared by the steps of: hot pressing a mixture prepared by mixing the above boron nitride particles and the above resin component to prepare a pressed sheet, The step of dividing the pressed sheet into a plurality of divided sheets, the step of laminating the plurality of divided sheets to form a laminated sheet, and the step of hot pressing the laminated sheet. The thermally conductive sheet according to claim 5, which is prepared by repeatedly performing the above-described dividing step, the laminating step and the hot pressing step, and the number of repetitions of the steps is 2 to 7 times. The thermally conductive sheet according to claim 1, wherein a ratio of a thermal conductivity in the orthogonal direction of the thermally conductive sheet to a thermal conductivity in the thickness direction of the thermally conductive sheet is 4 or more and 20 or less.