JP2012039063A - Heat-conductive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat conductive sheet that exhibits excellent thermoconductivity in the plane direction and also excels in heat resistance.SOLUTION: The heat-conductive sheet 1 comprising plate-like boron nitride particles 2 has a coefficient of thermoconductivity of ≥4 W/m K in the plane direction (orthogonal direction) SD orthogonal to the thickness direction TD of the heat-conductive sheet 1, and 5% weight loss temperature of ≥250°C. The heat-conductive sheet 1 exhibits excellent thermoconductivity in the plane direction orthogonal to the thickness direction and also excels in heat resistance. As a result, the heat-conductive sheet 1 can suppress decomposition when exposed to a high temperature and can be used in various heat radiation application as a heat-conductive sheet excellent both in handleability and in thermoconductivity in the plane direction.

Description

  The present invention relates to a heat conductive sheet, and more particularly to a heat conductive sheet used in power electronics technology.

  In recent years, power electronics technology that converts and controls electric power using a semiconductor element has been adopted in hybrid devices, high-brightness LED devices, electromagnetic induction heating devices, and the like. In the power electronics technology, in order to convert a large current into heat or the like, a material disposed in the vicinity of the 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 has been proposed (see, for example, Patent Document 1).

  In the heat conductive sheet of Patent Document 1, the boron nitride powder is oriented so that its long axis direction (direction orthogonal to the plate thickness of the boron nitride powder) is along the thickness direction of the sheet. The thermal conductivity in the thickness direction of the conductive sheet is improved.

JP 2008-280496 A

  However, the thermal conductive sheet may be required to have high thermal conductivity in the orthogonal direction (plane direction) orthogonal to the thickness direction depending on the application and purpose. In that case, in the heat conductive sheet of Patent Document 1, since the long axis direction of the boron nitride powder is orthogonal (crossed) to the surface direction, the heat conductivity in the surface direction is insufficient. There is a bug.

  Moreover, since such a heat conductive sheet is used, for example, to conduct (dissipate) heat generated from various devices, excellent heat resistance is required so as not to be decomposed by the heat. The

  An object of the present invention is to provide a thermally conductive sheet that is excellent in thermal conductivity in the plane direction and also excellent in heat resistance.

  In order to achieve the above object, the thermally conductive sheet of the present invention is a thermally conductive sheet containing plate-like boron nitride particles, and has a thermal conductivity in a direction perpendicular to the thickness direction of the thermally conductive sheet. 4 W / m · K or more, and 5% weight loss temperature is 250 ° C. or more.

  In the heat conductive sheet of this invention, it is excellent in the heat conductivity of the surface direction orthogonal to the thickness direction, and also excellent in heat resistance.

  Therefore, the thermal conductive sheet of the present invention can be used for various heat dissipation applications as a thermal conductive sheet that can suppress decomposition even when exposed to high temperatures and has excellent handling properties and excellent thermal conductivity in the surface direction. .

FIG. 1 shows a perspective view of one embodiment of the thermally conductive sheet of the present invention. 2A and 2B are process diagrams for explaining a method of manufacturing the heat conductive sheet shown in FIG. 1, wherein FIG. 2A is a process of hot pressing a mixture or a laminated sheet, and FIG. The process of dividing into pieces, (c) shows the process of laminating the divided sheets.

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

  Specifically, the heat 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 in a plate shape (or scale shape), and are dispersed in a form oriented in a predetermined direction (described later) in the heat conductive sheet.

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

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

  The aspect ratio (length / thickness in the longitudinal direction) of the boron nitride particles is, for example, 2 to 10000, preferably 10 to 5000.

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

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

  If the average particle diameter measured by the light scattering method of the boron nitride particles is less than the above range, the thermally conductive sheet may become brittle and the handleability may deteriorate.

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 .

  As the boron nitride particles, a commercially available product or a processed product obtained by processing it can be used. Examples of commercially available boron nitride particles include the “PT” series (for example, “PT-110”, etc.) manufactured by Momentive Performance Materials Japan, and the “Shobi N UHP” series (manufactured by Showa Denko) ( For example, “Shoubi N UHP-1” and the like are included.

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

  Examples of the thermosetting resin component include epoxy resins, thermosetting polyimides, phenol resins, urea resins, melamine resins, unsaturated polyester resins, diallyl phthalate resins, silicone resins, and thermosetting urethane resins.

  Examples of the thermoplastic resin component include polyolefin (for example, polyethylene, polypropylene, ethylene-propylene copolymer, etc.), acrylic resin (for example, polymethyl methacrylate, etc.), polyvinyl acetate, ethylene-vinyl acetate copolymer, Polyvinyl chloride, polystyrene, polyacrylonitrile, polyamide (nylon (registered trademark)), polycarbonate, polyacetal, polyethylene terephthalate, polyphenylene oxide, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polyallylsulfone, thermoplastic polyimide, Thermoplastic urethane resin, polyamino bismaleimide, polyamideimide, polyetherimide, bismaleimide triazine resin, polymethylpentene, fluorine Resin, liquid crystal polymer, an olefin - vinyl alcohol copolymer, ionomer, polyarylate, acrylonitrile - ethylene - styrene copolymers, acrylonitrile - butadiene - styrene copolymer, acrylonitrile - styrene copolymer.

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

  Of the thermosetting resin components, an epoxy resin is preferable.

  The epoxy resin is in a liquid, semi-solid, or solid form at normal temperature.

  Specifically, as the epoxy resin, for example, bisphenol type epoxy resin (for example, bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, water-added bisphenol A type epoxy resin, dimer acid modified bisphenol type) Epoxy resin), novolak epoxy resin (eg, phenol novolac epoxy resin, cresol novolac epoxy resin, biphenyl epoxy resin), naphthalene epoxy resin, fluorene epoxy resin (eg, bisarylfluorene epoxy resin, etc.) ), Aromatic epoxy resins such as triphenylmethane type epoxy resin (for example, trishydroxyphenylmethane type epoxy resin), for example, triepoxypropyl isocyanurate (Triglycidyl isocyanurate), nitrogen-containing ring epoxy resins such as hydantoin epoxy resins, for example, aliphatic type epoxy resins, for example, alicyclic epoxy resins (for example, dicyclocyclic type epoxy resins), for example, glycidyl ether type An epoxy resin, for example, a glycidylamine type epoxy resin can be used.

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

  The epoxy resin has an epoxy equivalent of, for example, 100 to 1000 g / eqiv. , Preferably 180 to 700 g / eqiv. The softening temperature (ring and ball method) is, for example, 80 ° C. or lower (specifically 20 to 80 ° C.), preferably 70 ° C. or lower (specifically 35 to 70 ° C.).

  Moreover, the melt viscosity at 80 ° C. of the epoxy resin is, for example, 10 to 20000 mPa · s, and preferably 50 to 10000 mPa · s. When using 2 or more types of epoxy resins together, the melt viscosity as a mixture thereof is set within the above-described range.

  When two or more epoxy resins are used in combination, for example, a combination of a liquid epoxy resin and a solid epoxy resin, more preferably a liquid aromatic epoxy resin and a solid aromatic epoxy resin. Examples include combinations. Specific examples of such a combination include a combination of a liquid bisphenol type epoxy resin and a solid triphenylmethane type epoxy resin, or a combination of a liquid bisphenol type epoxy resin and a solid bisphenol type epoxy resin. It is done.

  Moreover, as an epoxy resin, Preferably, the single use of a semi-solid epoxy resin is mentioned, More preferably, the single use of a semi-solid aromatic epoxy resin is mentioned. More specifically, such an epoxy resin includes a semi-solid fluorene type epoxy resin.

  If it is a combination of a liquid epoxy resin and a solid epoxy resin, or a semi-solid epoxy resin, the step followability (described later) of the heat conductive sheet can be improved.

  When two or more epoxy resins are used in combination, the softening temperature is, for example, less than 45 ° C, preferably 35 ° C or less, and the softening temperature is, for example, 45 ° C or more, preferably Combined with a second epoxy resin at 55 ° C. or higher. Thereby, the kinematic viscosity (conforming to JIS K 7233, which will be described later) of the resin component (mixture) can be set in a desired range, and the step followability of the thermally conductive sheet can be improved.

  Moreover, an epoxy resin can be prepared as an epoxy resin composition by containing a hardening | curing agent and a hardening accelerator, for example.

  The curing agent is a latent curing agent (epoxy resin curing agent) that can cure the epoxy resin by heating. For example, an imidazole compound, an amine compound, an acid anhydride compound, an amide compound, a hydrazide compound, an imidazoline compound, and the like. Is mentioned. In addition to the above, phenol compounds, urea compounds, polysulfide compounds and the like can also be mentioned.

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

  Examples of the amine compound include aliphatic polyamines such as ethylenediamine, propylenediamine, diethylenetriamine, and triethylenetetramine, and aromatic polyamines such as metaphenylenediamine, diaminodiphenylmethane, and diaminodiphenylsulfone.

  Examples of the acid anhydride compound include phthalic anhydride, maleic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, 4-methyl-hexahydrophthalic anhydride, methyl nadic acid anhydride, and pyromellitic acid. Anhydride, dodecenyl succinic anhydride, dichlorosuccinic anhydride, benzophenone tetracarboxylic acid anhydride, chlorendic acid anhydride and the like can be mentioned.

  Examples of the amide compound include dicyandiamide and polyamide.

  Examples of the hydrazide compound include adipic acid dihydrazide.

  Examples of the imidazoline compound include methyl imidazoline, 2-ethyl-4-methyl imidazoline, ethyl imidazoline, isopropyl imidazoline, 2,4-dimethyl imidazoline, phenyl imidazoline, undecyl imidazoline, heptadecyl imidazoline, 2-phenyl-4-methyl. Examples include imidazoline.

  These curing agents can be used alone or in combination of two or more.

  As the curing agent, an imidazole compound is preferable.

  Examples of the curing accelerator include tertiary amine compounds such as triethylenediamine and tri-2,4,6-dimethylaminomethylphenol, such as triphenylphosphine, tetraphenylphosphonium tetraphenylborate, tetra-n-butylphosphonium- Phosphorus compounds such as o, o-diethyl phosphorodithioate, for example, quaternary ammonium salt compounds, for example, organometallic salt compounds, for example, derivatives thereof and the like can be mentioned. These curing accelerators can be used alone or in combination of two or more.

  The compounding 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 with respect to 100 parts by mass of the epoxy resin. For example, 0.1 to 10 parts by mass, preferably 0.2 to 5 parts by mass.

  The above-mentioned curing agent and / or curing accelerator can be prepared and used as a solvent solution and / or a solvent dispersion dissolved and / or dispersed with a solvent, if necessary.

  Examples of the solvent include organic solvents such as ketones such as acetone and methyl ethyl ketone, esters such as ethyl acetate, amides such as N, N-dimethylformamide, and the like. Examples of the solvent also include aqueous solvents such as water, for example, alcohols such as methanol, ethanol, propanol, and isopropanol. The solvent is preferably an organic solvent, more preferably ketones and amides.

  Of the thermoplastic resin components, preferably, polyolefin is used.

  Preferred examples of the polyolefin include polyethylene and ethylene-propylene copolymer.

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

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

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

  Moreover, the weight average molecular weight and / or number average molecular weight of polyolefin are 1000-10000, for example.

  Polyolefins can be used alone or in combination.

In addition, according to a kinematic viscosity test (temperature: 25 ° C. ± 0.5 ° C., solvent: butyl carbitol, resin component (solid content) concentration: 40% by mass) based on JIS K 7233 (foam viscometer method) of the resin component The measured kinematic 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. s, more preferably 0.4 × 10 ^{−4 to} 1.8 × 10 ⁻⁴ m ² / s. Further, the kinematic viscosity of the, for ^{example, 0.22 × 10 -4 ~1.00 × 10} -4 m 2 / s, ^{preferably, 0.3 × 10 -4 ~0.9 × 10} -4 m 2 / S, more preferably 0.4 × 10 ^{−4 to} 0.8 × 10 ⁻⁴ m ² / s.

  When the kinematic viscosity of the resin component exceeds the above range, it may be impossible to impart excellent flexibility and step following ability (described later) to the heat conductive sheet. On the other hand, when the kinematic viscosity of the resin component is less than the above range, the boron nitride particles may not be oriented in a predetermined direction.

  In the kinematic viscosity test based on JIS K 7233 (foam viscometer method), the rising speed of the foam in the resin component sample is compared with the rising speed of the foam in the standard sample (kinematic viscosity is known). The kinematic viscosity of the resin component is measured by determining that the matching kinematic viscosity of the standard sample is the kinematic viscosity of the resin component.

  In the thermally conductive sheet, the volume-based content ratio of the boron nitride particles (solid content, that is, the volume percentage of the boron nitride particles with respect to the total volume of the resin component and the boron nitride particles) is, for example, 35% by volume or more, preferably Is 60% by volume or more, preferably 75% by volume or more, and usually 95% by volume or less, preferably 90% by volume or less.

  When the volume-based content ratio of the boron nitride particles is less than the above range, the boron nitride particles may not be oriented in a predetermined direction in the thermally conductive sheet. On the other hand, when the volume-based content ratio of the boron nitride particles exceeds the above-described range, the thermally conductive sheet becomes brittle, and the handleability and the step following ability may be deteriorated.

  The mixing ratio of the boron nitride particles based on the total amount (solid content) of each component (boron nitride particles and resin component) forming the heat conductive sheet is, for example, 40 to 95 parts by mass, preferably The blending ratio of the resin component based on 100 parts by mass of the total amount of each component forming the heat conductive sheet is, for example, 5 to 60 parts by mass, preferably 10 to 35 parts by mass. is there. In addition, the mixture ratio of the mass reference | standard of boron nitride particle with respect to 100 mass parts of resin components is 60-1900 mass parts, for example, Preferably, it is also 185-900 mass parts.

  Further, when two types of epoxy resins (first epoxy resin and 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 mass of the second epoxy resin) ) Can be appropriately set according to the softening temperature of each epoxy resin (first epoxy resin and second epoxy resin), for example, 1/99 to 99/1, preferably 10/90 to 90 / 10.

  The resin component includes, for example, a polymer precursor (for example, a low molecular weight polymer including an oligomer) and / or a monomer in addition to the above-described components (polymerized products).

  FIG. 1 is a perspective view of one embodiment of the thermally conductive sheet of the present invention, and FIG. 2 is a process diagram for explaining a method for producing the thermally conductive sheet shown in FIG.

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

  In this method, first, the above-described components are blended at the blending ratio described above, and the mixture is prepared by stirring and mixing.

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

  Examples of the solvent include the same organic solvents as described above. In addition, when the above-described curing agent and / or curing accelerator is prepared as a solvent solution and / or a solvent dispersion, the solvent of the solvent solution and / or the solvent dispersion without adding a solvent in the stirring and mixing. Can be used as a mixed solvent for stirring and mixing as it is. Alternatively, a solvent can be further added as a mixed solvent in the stirring and mixing.

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

  To remove the solvent, for example, it is allowed to stand at room temperature for 1 to 48 hours, for example, heated at 40 to 100 ° C. for 0.5 to 3 hours, or reduced pressure of 0.001 to 50 kPa, for example. Heat at 20-60 ° C. for 0.5-3 hours under atmosphere.

  When the resin component (preferably the 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.

  In this method, the resulting mixture is then hot pressed.

  Specifically, as shown in FIG. 2A, the mixture is hot-pressed through, for example, two release films 4 as necessary to obtain a press sheet 1A. The conditions of the hot press are that the temperature is, for example, 50 to 150 ° C., preferably 60 to 140 ° C., 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 30 minutes.

  More preferably, the mixture is vacuum hot pressed. The degree of vacuum in the vacuum hot press is, for example, 1 to 100 Pa, preferably 5 to 50 Pa, and the temperature, pressure, and time are the same as those in the above-described hot press.

  When the temperature, pressure and / or time in the hot press are out of the above range, the porosity P (described later) of the heat conductive sheet 1 may not be adjusted to a desired value.

  The thickness of 1 A of press sheets obtained by hot press is 50-1000 micrometers, for example, Preferably, it is 100-800 micrometers.

  Next, in this method, as shown in FIG. 2B, the press sheet 1A is divided into a plurality (for example, four) to obtain a divided sheet 1B (a dividing step). In the division of the press sheet 1A, the press sheet 1A is cut along the thickness direction so as to be divided into a plurality when projected in the thickness direction. The press sheet 1A is cut so as to have the same shape when the divided sheets 1B are projected in the thickness direction.

  Next, in this method, as shown in FIG. 2C, the divided sheets 1B are laminated in the thickness direction to obtain a laminated sheet 1C (laminating step).

  Thereafter, in this method, as shown in FIG. 2A, the laminated sheet 1C is hot-pressed (preferably vacuum hot-pressed) (hot-pressing step). The conditions for the hot press are the same as the conditions for the hot press of the mixture described above.

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

  Thereafter, in order to efficiently orient boron nitride particles 2 in the resin component 3 in a predetermined direction in the heat conductive sheet 1, the above-described dividing step (FIG. 2B), laminating step (FIG. 2C), and A series of steps of the hot press step (FIG. 2A) is repeatedly performed. The number of repetitions is not particularly limited, and can be appropriately set according to the filling state of the boron nitride particles, and is, for example, 1 to 10 times, preferably 2 to 7 times.

  Thereby, the heat conductive sheet 1 can be obtained.

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

  Further, as described above, the volume-based content ratio of the boron nitride particles in the heat conductive sheet 1 (solid content, that is, the volume percentage of the boron nitride particles with respect to the total volume of the resin component and the boron nitride particles) is, for example, 35 Volume% or more (preferably 60 volume% or more, more preferably 75 volume% or more), usually 95 volume% or less (preferably 90 volume% or less).

  When the content ratio of the boron nitride particles is less than the above range, the boron nitride particles may not be oriented in a predetermined direction in the thermally conductive sheet.

  Further, when the resin component 3 is a thermosetting resin component, for example, the above-described dividing step (FIG. 2B), laminating step (FIG. 2C), and hot pressing step (FIG. 2A). ) Is repeatedly performed in an uncured state (or semi-cured state (B stage state)), and after the hot pressing step (FIG. 2 (a)) in the final step, uncured (or semi-cured (B The thermally conductive sheet 1 in the stage state)) is thermally cured to produce the thermally conductive sheet 1 after curing.

  In order to thermally cure the heat conductive sheet 1, the above-described hot press or dryer is used. Preferably, a dryer is used. The thermosetting conditions are such that the temperature is, for example, 60 to 250 ° C., preferably 80 to 200 ° C., and the pressure is, for example, 100 MPa or less, preferably 50 MPa or less.

  In the heat conductive sheet 1 thus obtained, the longitudinal direction LD of the boron nitride particles 2 intersects the thickness direction TD of the heat conductive sheet 1 as shown in FIG. 1 and a partially enlarged schematic view thereof. They are oriented along the (orthogonal) plane direction SD.

  Further, the arithmetic average of the angles formed by the longitudinal direction LD of the boron nitride particles 2 in the surface direction SD of the thermal conductive sheet 1 (orientation angle α of the boron nitride particles 2 with respect to the thermal conductive sheet 1) is, for example, 25 degrees or less, Preferably, it is 20 degrees or less, and is usually 0 degrees or more.

  The orientation angle α of the boron nitride particles 2 with respect to the heat conductive sheet 1 is determined by cutting the heat conductive sheet 1 along the thickness direction with a cross-section polisher (CP), and the resulting cross section is scanned with an electron microscope. With (SEM), a photograph was taken at a magnification of the field of view where 200 or more boron nitride particles 2 can be observed. From the obtained SEM photograph, the surface direction SD of the thermal conductive sheet 1 in the longitudinal direction LD of the boron nitride particles 2 The inclination angle α with respect to (the direction orthogonal to the thickness direction TD) is acquired and calculated as an average value thereof.

  Thereby, the thermal conductivity in the surface direction SD of the heat 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 still more preferably, It is 15 W / m · K or more, particularly preferably 25 W / m · K or more, and usually 200 W / m · K or less.

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

  If the thermal conductivity in the surface direction SD of the thermal conductive sheet 1 is less than the above range, the thermal conductivity in the surface direction SD is not sufficient, and therefore for heat dissipation applications that require such thermal conductivity in the surface direction SD. It may not be used.

  In addition, the heat conductivity of the surface direction SD of the heat conductive sheet 1 is measured by the pulse heating method. In the pulse heating method, a xenon flash analyzer “LFA-447 type” (manufactured by NETZSCH) is used.

  Moreover, the heat conductivity of the thickness direction TD of the heat conductive sheet 1 is 0.5-15 W / m * K, for example, Preferably, it is 1-10 W / m * K.

  The thermal conductivity in the thickness direction TD of the thermal conductive sheet 1 is measured by a pulse heating method, a laser flash method, or a TWA method. In the pulse heating method, the same one as described above is used, in the laser flash method, “TC-9000” (manufactured by ULVAC-RIKO) is used, and in the TWA method, “ai-Phase mobile” (manufactured by Eye Phase). Is used.

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

  Further, although not shown in FIG. 1, for example, a gap (gap) is formed in the heat conductive sheet 1.

  The void ratio in the thermal conductive sheet 1, that is, the void ratio P is the content ratio (volume basis) of the boron nitride particles 2, and further, hot pressing of a mixture of the boron nitride particles 2 and the resin component 3 (FIG. )) Can be adjusted by the temperature, pressure and / or time. Specifically, the temperature, pressure and / or time of the above-described hot press (FIG. 2 (a)) is set within the above range. Can be adjusted.

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

  For example, the porosity P described above is obtained by first cutting the thermally conductive sheet 1 with a cross section polisher (CP) along the thickness direction, and using a scanning electron microscope (SEM) to show the cross section that appears. The image is obtained by observing at a magnification, and from the obtained image, the void portion and the other portion are binarized, and then the area ratio of the void portion to the cross-sectional area of the entire thermal conductive sheet 1 is determined. It is measured by calculating.

  In addition, in the heat conductive sheet 1, the porosity P2 after hardening is 100% or less with respect to the porosity P1 before hardening, for example, Preferably, it is 50% or less.

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

  If the porosity P of the heat conductive sheet 1 is in the above-described range, the step following property (described later) of the heat conductive sheet 1 can be improved.

  The 5% weight loss temperature of the heat conductive sheet 1 is 250 ° C. or higher, preferably 300 ° C. or higher, and usually 450 ° C. or lower.

  If the 5% weight loss temperature is equal to or higher than the above lower limit, decomposition can be suppressed even when exposed to a high temperature, and heat generated from various devices can be efficiently conducted.

  The 5% weight loss temperature can be measured according to JIS K 7120 by thermogravimetric analysis (temperature increase rate: 10 ° C./min, under nitrogen atmosphere).

  Moreover, when the heat conductive sheet 1 is evaluated under the following test conditions in a bending resistance test based on the cylindrical mandrel method of JIS K 5600-5-1, preferably no breakage is observed.

Test conditions Test equipment: Type I
Mandrel: 10mm in diameter
Bending angle: 90 degrees or more Thickness of the thermal conductive sheet 1: 0.3 mm
More preferably, the thermal conductive sheet 1 is not observed to break even when the bending angle is set to 180 degrees under the test conditions described above.

  When the resin component 3 is a thermosetting resin component, the heat conductive sheet 1 subjected to the flexibility test is a semi-cured (B stage state) heat conductive sheet 1 (that is, before thermosetting). The heat conductive sheet 1).

  When breakage is observed in the heat conductive sheet 1 in the above-described bending resistance test at the bending angle, it may not be possible to impart excellent flexibility to the heat conductive sheet 1.

  Moreover, when this heat conductive sheet 1 is evaluated on the following test conditions in the 3 point | piece bending test based on JISK7171 (2008), a fracture | rupture is not observed, for example.

Test conditions Test piece: Size 20mm x 15mm
Distance between fulcrums: 5mm
Test speed: 20 mm / min (pressing speed of indenter)
Bending angle: 120 degrees Evaluation method: When tested under the above test conditions, the presence or absence of breakage such as cracks at the center of the test piece is 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 is used.

  Therefore, since this heat conductive sheet 1 is not observed in the above-described three-point bending test, the step followability is excellent. In addition, level | step difference followability is a characteristic which tracks so that it may closely_contact | adhere along the level | step difference, when providing the heat conductive sheet 1 in the installation object with a level | step difference.

  Moreover, marks, such as a character and a symbol, can be made to adhere to the heat conductive sheet 1, for example. That is, the heat conductive sheet 1 is excellent in mark adhesion. The mark adhesion is a characteristic that allows the above-described marks to be reliably adhered to the heat conductive sheet 1.

  Specifically, the mark is attached (applied, fixed, or fixed) to the heat conductive sheet 1 by printing or engraving.

  Examples of printing include ink jet printing, letterpress printing, intaglio printing, and laser printing.

  In addition, when a mark is printed by inkjet printing, letterpress printing, or intaglio printing, for example, an ink fixing layer for improving the fixability of the mark is provided on the surface (printing side surface) of the heat conductive sheet 1. be able to.

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

  Examples of the marking include laser marking and stamping.

  And in this heat conductive sheet 1, it is excellent in a softness | flexibility and the heat conductivity of the surface direction SD, and also excellent in heat resistance.

  That is, according to this heat conductive sheet 1, for example, various heat-conducting sheets that can suppress decomposition even when exposed to a high temperature of 200 ° C. or more and have excellent handling properties while being excellent in heat conductivity in the plane direction SD are various. More specifically, for example, as a heat conductive sheet employed in power electronics technology that generates a high temperature of 200 to 250 ° C., it is applied to, for example, SiC chips, LED heat dissipation substrates, and heat dissipation materials for batteries. It can be used as a heat conductive sheet.

  In the above-described hot pressing step (FIG. 2A), for example, the mixture and the laminated sheet 1C can be rolled with a plurality of calendar rolls.

  Moreover, when the resin component 3 is a thermosetting resin component, the heat conductive sheet of this invention can also be obtained as the uncured heat conductive sheet 1 without thermosetting as mentioned above.

  That is, in the heat conductive sheet of the present invention, when the resin component is a thermosetting resin component, the presence / absence and timing of thermosetting are not particularly limited. For example, as described above, the lamination step (FIG. 2C) ) Or after a predetermined period of time from the above-described hot pressing step (FIG. 2 (a), hot pressing of the mixture and not thermosetting), specifically, when applied to power electronics technology Alternatively, thermosetting can be performed after a predetermined period has elapsed since the application.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the examples.

Example 1
PT-110 (trade name, plate-like boron nitride particles, average particle diameter (light scattering method) 45 μm, manufactured by Momentive Performance Materials Japan) 13.42 g and JER828 (trade name, bisphenol A type epoxy resin) , Liquid, epoxy equivalent 184 to 194 g / eqiv, softening temperature (ring and ball method) less than 25 ° C., melt viscosity (80 ° C.) 70 mPa · s, manufactured by Japan Epoxy Resin Co., Ltd. 1 g, and EPPN-501HY (trade name, Tri Phenylmethane type epoxy resin, solid, epoxy equivalent 163 to 175 g / eqiv, softening temperature (ring and ball method) 57 to 63 ° C., manufactured by Nippon Kayaku Co., Ltd., and curing agent (Curesol 2PZ (trade name, Shikoku Kasei Co., Ltd.) 5% by weight methyl ethyl ketone solution) 3 g (0.15 g solid content) (JER828 which is an epoxy resin) And 5% by mass with respect to the total amount of EPPN-501HY), and stirred and allowed to stand overnight at room temperature (23 ° C.) to volatilize methyl ethyl ketone (dispersion medium for the curing agent). A mixture was prepared.

  In the above formulation, the volume percentage (volume%) of the boron nitride particles with respect to the total volume of the solid content excluding the curing agent (that is, the solid content of the boron nitride particles and the epoxy resin) was 70% by volume. .

  Next, the obtained mixture was sandwiched between two release films treated with silicone, and they were placed in a vacuum heating press machine at 80 ° C. in an atmosphere of 10 Pa (vacuum atmosphere) under a load of 5 tons (20 MPa) for 2 minutes. A press sheet having a thickness of 0.3 mm was obtained by hot pressing (see FIG. 2A).

  After that, when the obtained press sheet is projected in the thickness direction of the press sheet, a divided sheet is obtained by cutting so as to be divided into a plurality of pieces (see FIG. 2B), and then the divided sheet. Were laminated in the thickness direction to obtain a laminated sheet (see FIG. 2C).

  Subsequently, the obtained laminated sheet was hot-pressed under the same conditions as described above using a vacuum heating press similar to the above (see FIG. 2A).

  Subsequently, a series of operations of cutting, laminating and hot pressing (see FIG. 2) was repeated four times to obtain a thermally conductive sheet (B stage) having a thickness of 0.3 mm.

  Thereafter, the obtained heat conductive sheet was put into a drier and heated at 150 ° C. for 120 minutes for thermosetting.

Examples 2-9 and 11-16
Based on the formulation and production conditions in Tables 1 to 3, the same treatment as in Example 1 was performed to obtain a heat conductive sheet.

Example 10
In accordance with the formulation of Table 2, each component (boron nitride particles and polyethylene) was blended and stirred to prepare a mixture. That is, in stirring each component, the polyethylene was melted by heating to 130 ° C.

  Subsequently, the obtained mixture was sandwiched between two release films treated with silicone, and they were placed in a vacuum heating press machine at 120 ° C. in an atmosphere of 10 Pa (vacuum atmosphere) at a load of 1 ton (4 MPa) for 2 minutes. A press sheet having a thickness of 0.3 mm was obtained by hot pressing (see FIG. 2A).

  After that, when the obtained press sheet is projected in the thickness direction of the press sheet, a divided sheet is obtained by cutting so as to be divided into a plurality of pieces (see FIG. 2B), and then the divided sheet. Were laminated in the thickness direction to obtain a laminated sheet (see FIG. 2C).

  Subsequently, the obtained laminated sheet was hot-pressed under the same conditions as described above using a vacuum heating press similar to the above (see FIG. 2A).

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

(Evaluation)
1. Thermal conductivity The thermal conductivity was measured about the heat conductive sheet obtained by Examples 1-16.

  That is, the thermal conductivity in the plane direction (SD) was measured by a pulse heating method using a xenon flash analyzer “LFA-447 type” (manufactured by NETZSCH).

The results are shown in Tables 1 to 3.
2. Weight reduction measurement The 5% weight reduction temperature of the thermally conductive sheets obtained in Examples 1 to 16 was determined by JIS by thermogravimetric analysis (temperature increase rate 10 ° C / min, under nitrogen atmosphere) using a thermogravimetric analyzer. Measured according to K 7120 (2010).

The results are shown in Tables 1 to 3.
3. Porosity (P)
The porosity (P1) of the heat conductive sheet before thermosetting of Examples 1 to 16 was measured by the following measurement method.

  Method for measuring porosity: First, a thermally conductive sheet is cut along a thickness direction by a cross section polisher (CP), and a cross section that appears is observed at 200 times with a scanning electron microscope (SEM). And got a statue. Thereafter, the void portion and other portions were binarized from the obtained image, and then the area ratio of the void portion to the cross-sectional area of the entire heat conductive sheet was calculated.

The results are shown in Tables 1 to 3.
4). Step following ability (3-point bending test)
About the heat conductive sheet before thermosetting of Examples 1-16, by carrying out the 3 point | piece bending test in the following test conditions based on JISK7171 (2008), level | step difference followability is evaluated with the following evaluation criteria. Evaluated according to. The results are shown in Tables 1 to 3.

Test conditions Test piece: Size 20mm x 15mm
Distance between fulcrums: 5mm
Test speed: 20 mm / min (pressing speed of indenter)
Bending angle: 120 degrees (evaluation criteria)
A: No fracture was observed at all.

  ○: Fracture was hardly observed.

X: Breakage was clearly observed.
5. Print mark visibility (print mark adhesion: mark adhesion by inkjet printing or laser printing)
A mark was printed on the heat conductive sheets of Examples 1 to 16 by inkjet printing and laser printing, and the mark was observed.

  As a result, for any of the thermally conductive sheets of Examples 1 to 16, it was confirmed that marks by both ink jet printing and laser printing could be seen well, and the print mark adhesion was good.

  The numerical value in each component in Tables 1 to 3 indicates the number of grams unless otherwise specified.

  In the column of boron nitride particles in Tables 1 to 3, the upper numerical value is the compounding mass (g) of boron nitride particles, and the intermediate numerical value is the solid content excluding the curing agent in the thermally conductive sheet (that is, , The volume percentage (volume%) of the boron nitride particles to the total volume of the boron nitride particles and the solid content of the epoxy resin or polyethylene), and the lower number is the solid content of the thermally conductive sheet (that is, boron nitride particles) And the volume percentage (volume%) of the boron nitride particles with respect to the total volume of the solid content of the epoxy resin and the curing agent.

Details of the components marked with * among the components in Tables 1 to 3 are described below.
PT-110 ^{* 1} : Product name, plate-like boron nitride particles, average particle size (light scattering method) 45 μm, UHP-1 manufactured by Momentive Performance Materials Japan Ltd. ^{* 2} : Product name: Shovie N UHP- 1, plate-like boron nitride particles, average particle diameter (light scattering method) 9 μm, Showa Denko Epoxy Resin A ^{* 3} : Ogsol EG (trade name), bisarylfluorene type epoxy resin, semi-solid, epoxy equivalent 294 g / Eqiv. , Softening temperature (ring and ball method) 47 ° C., melt viscosity (80 ° C.) 1360 mPa · s, epoxy resin B manufactured by Osaka Gas Chemical Co., Ltd. ^{* 4} : JER828 (trade name), bisphenol A type epoxy resin, liquid, epoxy equivalent 184 to 194 g / Eqiv. , Softening temperature (ring ball method) less than 25 ° C., melt viscosity (80 ° C.) 70 mPa · s, epoxy resin C ^{* 5} manufactured by Japan Epoxy Resin Co., Ltd .: JER1002 (trade name), bisphenol A type 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 (measurement limit or more), epoxy resin D ^{* 6} manufactured by Japan Epoxy Resin Co., Ltd .: EPPN-501HY (trade name), triphenylmethane type epoxy Resin, solid, epoxy equivalent 163-175 g / eqiv. , Softening temperature (ring and ball method) 57-63 ° C., Nippon Kayaku Co., Ltd. curing agent ^{* 7} : Curazole 2PZ (trade name, manufactured by Shikoku Kasei Co., Ltd.) 5 mass% methyl ethyl ketone solution curing agent ^{* 8} : Cureazole 2P4MHZ-PW (Product) Name, manufactured by Shikoku Kasei Co., Ltd.) 5% by weight methyl ethyl ketone dispersion polyethylene ^{* 9} : low density polyethylene, weight average molecular weight (Mw) 4000, number average molecular weight (Mn) 1700, manufactured by Aldrich

DESCRIPTION OF SYMBOLS 1 Thermal conductive sheet 2 Boron nitride particle 3 Resin component TD Thickness direction SD Plane direction (orthogonal direction)

Claims (1)

A thermally conductive sheet containing plate-like boron nitride particles,
The thermal conductivity in the direction orthogonal to the thickness direction of the thermal conductive sheet is 4 W / m · K or more,
A thermally conductive sheet having a 5% weight loss temperature of 250 ° C or higher.

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