Heat dissipation sheet and method for manufacturing heat dissipation sheet

Abstract

To provide a heat dissipation sheet having excellent thermal conductivity and insulation, and a manufacturing method of the heat dissipation sheet having excellent thermal conductivity and insulation.SOLUTION: In a heat dissipation sheet according to the present invention formed by molding a heat conductive resin composition containing a resin and boron nitride powder containing at least agglomerated boron nitride particles formed by aggregating hexagonal boron nitride primary particles, an oxygen permeability coefficient is 1×10-11 to 1×10-7 cm3 cm / (cm2 s cmHg). A manufacturing method of the heat dissipation sheet according to the present invention includes the steps of blending a resin with boron nitride powder containing at least agglomerated boron nitride particles formed by agglomerating hexagonal boron nitride primary particles to prepare a heat conductive resin composition, molding the heat conductive resin composition into a sheet state to produce a heat conductive resin composition sheet, and heating and pressurizing the heat conductive resin composition sheet under vacuum.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a heat dissipation sheet formed by molding a thermally conductive resin composition containing a boron nitride powder containing at least aggregated boron nitride particles formed by aggregation of hexagonal boron nitride primary particles and a resin, and a method for manufacturing the heat dissipation sheet.

Background Art

[0002] In heat-generating electronic components such as power devices, transistors, thyristors, and CPUs, how to efficiently dissipate the heat generated during use is an important issue. Conventionally, as such heat dissipation measures, (1) making the insulating layer of a printed wiring board on which a heat-generating electronic component is mounted have high thermal conductivity, and (2) attaching the heat-generating electronic component or the printed wiring board on which the heat-generating electronic component is mounted to a heat sink via an electrically insulating thermal interface material (Thermal Interface Materials) have generally been performed. As the insulating layer of the printed wiring board and the thermal interface material, those obtained by filling a silicone resin or an epoxy resin with ceramic powder are used.

[0003] As the ceramic powder, boron nitride powder having characteristics such as high thermal conductivity, high insulation, and low relative dielectric constant has attracted attention. For example, Patent Document 1 discloses a boron nitride powder formed by aggregation of primary particles of boron nitride, which has a peak A existing in a region of 5 μm or more and less than 30 μm and a peak B existing in a region of 50 μm or more and less than 100 μm in a volume-based particle size distribution.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Using the boron nitride powder described in Patent Document 1, a heat dissipation sheet excellent in thermal conductivity and insulation can be obtained. However, with the recent miniaturization of electronic devices and the increase in the amount of heat generated by heat-generating electronic components, a heat dissipation sheet with even better thermal conductivity and insulation is required. Therefore, an object of the present invention is to provide a heat dissipation sheet excellent in thermal conductivity and insulation and a method for manufacturing the heat dissipation sheet excellent in thermal conductivity and insulation.

Means for Solving the Problems

[0006] As a result of intensive research, the present inventors have found that a heat dissipation sheet having a specific oxygen permeability coefficient can solve the above problems. The present invention is based on the above findings and has the following gist. [1] A heat dissipation sheet formed by molding a thermally conductive resin composition containing a boron nitride powder containing at least aggregated boron nitride particles formed by aggregation of hexagonal boron nitride primary particles and a resin, wherein the oxygen permeability coefficient is 1×10 -11 ~1×10 -7 cm 3 ·cm / (cm 2 ·s·cmHg). [2] The particle size distribution of the boron nitride powder has at least a first maximum point, a second maximum point having a larger particle size than the first maximum point, and a third maximum point having a larger particle size than the second maximum point, and the particle size of the first maximum point is 0.4 μm or more and less than 10 μm, the particle size of the second maximum point is 10 μm or more and less than 40 μm, and the particle size of the third maximum point is 40 μm or more and 110 μm or less. The heat dissipation sheet according to [1] above. [3] The absolute value of the difference between the particle size at which the integrated amount of frequency in the particle size distribution of the boron nitride powder is 10% and the particle size of the minimum point between the minimum particle size maximum point and the second minimum particle size maximum point in the particle size distribution of the boron nitride powder is 3 to 30 μm. The heat dissipation sheet according to [2] above. [4] The maximum point adjacent to the first maximum point is the second maximum point, the maximum point adjacent to the second maximum point is the third maximum point, and the absolute value of the difference between the particle size of the first minimum point between the first maximum point and the second maximum point and the particle size of the second minimum point between the second maximum point and the third maximum point is 15 to 60 μm. The heat dissipation sheet according to [2] or [3] above. [5] The heat dissipation sheet according to any one of [2] to [4] above, wherein the half-value width of the peak having the third maximum point is 20 to 60 μm. [6] The heat dissipation sheet according to any one of [1] to [5] above, wherein the crushing strength of the aggregated boron nitride particles is 5 to 18 MPa. [7] A step of preparing a thermally conductive resin composition by blending a boron nitride powder containing at least aggregated boron nitride particles formed by aggregation of hexagonal boron nitride primary particles and a resin, a step of forming the thermally conductive resin composition into a sheet shape to produce a thermally conductive resin composition sheet, and a step of heating and pressurizing the thermally conductive resin composition sheet under vacuum. The method for manufacturing a heat dissipation sheet according to any one of [1] to [6] above. [Advantages of the Invention]

[0007] According to the present invention, it is possible to provide a heat dissipation sheet excellent in thermal conductivity and insulation, and a method for manufacturing a heat dissipation sheet excellent in thermal conductivity and insulation. [Brief Description of the Drawings]

[0008]

Figure 1

[0009] [Heat Dissipation Sheet] The heat dissipation sheet of the present invention is formed by molding a thermally conductive resin composition containing a boron nitride powder containing at least aggregated boron nitride particles formed by aggregation of hexagonal boron nitride primary particles and a resin. And the oxygen permeability coefficient of the heat dissipation sheet of the present invention is 1×10 -11~1×10 -7 cm 3 ·cm / (cm 2 ·s·cmHg). The oxygen permeability coefficient of the heat dissipation sheet is 1×10 -7 cm 3 ·cm / (cm 2 ·s·cmHg). If it is greater than 1×10 -7 cm 3 ·cm / (cm 2 ·s·cmHg), the insulation property of the heat dissipation sheet deteriorates. This is considered to be because excessive voids exist in the heat dissipation sheet when the oxygen permeability coefficient of the heat dissipation sheet is greater than 1×10 -11 cm 3 ·cm / (cm 2 ·s·cmHg). If the oxygen permeability coefficient of the heat dissipation sheet is less than 1×10 -11 cm 3 ·cm / (cm 2 ·s·cmHg), the insulation property of the heat dissipation sheet improves, but the thermal conductivity of the heat dissipation sheet deteriorates. This is considered to be because although the voids existing in the heat dissipation sheet decrease when the oxygen permeability coefficient of the heat dissipation sheet is less than 1×10 -11 cm 3 ·cm / (cm 2 ·s·cmHg), the aggregation of the aggregated boron nitride particles in the heat dissipation sheet is broken. From such a viewpoint, the oxygen permeability coefficient of the heat dissipation sheet of the present invention is preferably 1×10 -10 ~5×10 -8 cm 3 ·cm / (cm 2 ·s·cmHg), and more preferably 1×10 -9 ~1×10 -8 cm 3 ·cm / (cm 2 ·s·cmHg). The oxygen permeability coefficient of the heat dissipation sheet can be measured by the method described in the examples below. Further, the oxygen permeability coefficient of the heat dissipation sheet can be controlled, for example, by adjusting the pressure when pressing the thermally conductive resin composition sheet according to the strength of the aggregated boron nitride particles and the like in the method for manufacturing the heat dissipation sheet described below.

[0010] (boron nitride powder) The particle size distribution of the boron nitride powder contained in the thermally conductive resin composition for the heat dissipation sheet of the present invention preferably has at least a first peak point, a second peak point having a particle size larger than that of the first peak point, and a third peak point having a particle size larger than that of the second peak point. The particle size of the first peak point is preferably 0.4 μm or more and less than 10 μm, the particle size of the second peak point is preferably 10 μm or more and less than 40 μm, and the particle size of the third peak point is preferably 40 μm or more and 110 μm or less. Thereby, it becomes easier to adjust the oxygen permeability coefficient of the heat dissipation sheet of the present invention within the range of 1×10 -11 ~1×10 -7 cm 3 ·cm / (cm 2 ·s·cmHg).

[0011] Referring to FIG. 1, the boron nitride powder contained in the thermally conductive resin composition for the heat dissipation sheet of the present invention will be described in detail. FIG. 1 is a conceptual diagram showing the particle size distribution of the boron nitride powder contained in the thermally conductive resin composition for the heat dissipation sheet of the present invention. The vertical axis of the particle size distribution shown in FIG. 1 is linear, and the horizontal axis is logarithmic. Note that the particle size distribution of the boron nitride powder shown in FIG. 1 is merely a conceptual diagram and does not limit the boron nitride powder contained in the thermally conductive resin composition for the heat dissipation sheet of the present invention.

[0012] The boron nitride powder contained in the thermally conductive resin composition for the heat dissipation sheet of the present invention is a boron nitride powder containing at least aggregated boron nitride particles formed by aggregation of hexagonal boron nitride primary particles. In the particle size distribution of the boron nitride powder shown in FIG. 1, reference sign MAX1 indicates the first maximum point, reference sign MAX2 indicates the second maximum point, and reference sign MAX3 indicates the third maximum point. And it is preferable that the particle size of the first maximum point (MAX1) is 0.4 μm or more and less than 10 μm, the particle size of the second maximum point (MAX2) is 10 μm or more and less than 40 μm, and the particle size of the third maximum point (MAX3) is 40 μm or more and 110 μm or less. Thereby, since the filling property of the boron nitride powder in the heat dissipation sheet is enhanced, it becomes easier to control the oxygen transmission coefficient of the heat dissipation sheet by adjusting the pressure when pressing the thermally conductive resin composition sheet in the manufacturing method of the heat dissipation sheet described later. Further, thereby, since the filling property of the boron nitride powder in the heat dissipation sheet is enhanced, the thermal conductivity of the heat dissipation sheet can be made further excellent. The particle size distribution of the boron nitride powder can be measured by the method of the examples described later.

[0013] The particle size of the first maximum point (MAX1) is preferably 0.4 μm or more and less than 10 μm. When the particle size of the first maximum point (MAX1) is 0.4 μm or more and less than 10 μm, the filling property of the boron nitride powder in the heat dissipation sheet is enhanced, and thereby, it becomes easier to control the oxygen transmission coefficient of the heat dissipation sheet and the thermal conductivity of the heat dissipation sheet is further improved. From such a viewpoint, the particle size of the first maximum point (MAX1) is more preferably 1.0 to 8.0 μm, and even more preferably 3.0 to 6.0 μm.

[0014] The particle size of the second maximum point (MAX2) is preferably 10 μm or more and less than 40 μm. When the particle size of the second maximum point (MAX2) is 10 μm or more and less than 40 μm, the filling property of the boron nitride powder in the heat dissipation sheet is enhanced, and thereby, it becomes easier to control the oxygen transmission coefficient of the heat dissipation sheet and the thermal conductivity of the heat dissipation sheet is further improved. From such a viewpoint, the particle size of the second maximum point (MAX2) is more preferably 15 to 35 μm, and even more preferably 18 to 30 μm.

[0015] The particle size of the third maximum point (MAX3) is preferably 40 to 110 μm. When the particle size of the third maximum point (MAX3) is 40 to 110 μm, the filling property of the boron nitride powder in the heat dissipation sheet is enhanced, whereby the control of the oxygen permeability coefficient of the heat dissipation sheet becomes easier and the thermal conductivity of the heat dissipation sheet is further improved. From such a viewpoint, the particle size of the third maximum point (MAX3) is more preferably 55 to 95 μm, and still more preferably 65 to 90 μm.

[0016] The maximum point adjacent to the first maximum point (MAX1) is the second maximum point (MAX2), the maximum point adjacent to the second maximum point (MAX2) is the third maximum point (MAX3), and the absolute value of the difference between the particle size of the first minimum point (MIN1) between the first maximum point (MAX1) and the second maximum point (MAX2) and the particle size of the second minimum point (MIN2) between the second maximum point (MAX2) and the third maximum point (MAX3) is preferably 15 to 60 μm. When the absolute value of the difference between the particle size of the first minimum point (MIN1) and the particle size of the second minimum point (MIN2) is 15 to 60 μm, the filling property of the boron nitride powder in the heat dissipation sheet is enhanced, whereby the control of the oxygen permeability coefficient of the heat dissipation sheet becomes easier and the thermal conductivity of the heat dissipation sheet is further improved. From such a viewpoint, the absolute value of the difference between the particle size of the first minimum point (MIN1) and the particle size of the second minimum point (MIN2) is more preferably 21 to 43 μm, and still more preferably 25 to 35 μm.

[0017] The full width at half maximum of the peak having the third maximum point (MAX3) is preferably 20 to 60 μm. When the full width at half maximum of the peak having the third maximum point (MAX3) is 20 to 60 μm, the filling property of the boron nitride powder in the heat dissipation sheet is enhanced, whereby the control of the oxygen permeability coefficient of the heat dissipation sheet becomes easier and the thermal conductivity of the heat dissipation sheet is further improved. From such a viewpoint, the full width at half maximum of the peak having the third maximum point (MAX3) is more preferably 28 to 53 μm, and still more preferably 40 to 50 μm. Note that the full width at half maximum of the peak having the third maximum point (MAX3) is the width of the peak at the frequency that is half of the frequency of the third maximum point (MAX3).

[0018] The absolute value of the difference between the particle size at which the integrated amount of frequency in the particle size distribution of the boron nitride powder becomes 10% and the particle size at the minimum point between the maximum point with the smallest particle size and the second maximum point with the smallest particle size in the particle size distribution of the boron nitride powder is preferably 3 to 30 μm. For example, in the case of the particle size distribution of the boron nitride powder shown in FIG. 1, the symbol D10 indicates the particle size at which the integrated amount of frequency becomes 10%. The maximum point with the smallest particle size in the particle size distribution of the boron nitride powder is the first maximum point (MAX1), and the second maximum point with the smallest particle size in the particle size distribution of the boron nitride powder is the second maximum point (MAX2). The minimum point between the maximum point with the smallest particle size and the second maximum point with the smallest particle size is the first minimum point (MIN1). When the absolute value of the difference in the above particle sizes is 3 to 30 μm, the filling property of the boron nitride powder in the heat dissipation sheet is enhanced. As a result, the control of the oxygen permeation coefficient of the heat dissipation sheet becomes easier, and the thermal conductivity of the heat dissipation sheet is further improved. From such a viewpoint, the absolute value of the difference in the above particle sizes is more preferably 4 to 17 μm, and even more preferably 6 to 15 μm.

[0019] The integrated amount of frequency (V1) between the peak start and the peak end at the peak having the first maximum point (MAX1) is preferably 2 to 25% by volume. When the integrated amount (V1) is 2 to 25% by volume, the filling property of the boron nitride powder in the heat dissipation sheet is enhanced, whereby the control of the oxygen permeability coefficient of the heat dissipation sheet becomes easier and the thermal conductivity of the heat dissipation sheet is further improved. From such a viewpoint, the integrated amount (V1) is more preferably 5 to 20% by volume. The peak start at the peak having the first maximum point (MAX1) is the minimum point on the side with a smaller particle size with respect to the first maximum point (MAX1). When there is no minimum point on the side with a smaller particle size with respect to the first maximum point (MAX1), the peak start is the end (DS) on the side with a smaller particle size of the particle size distribution. The peak end at the peak having the first maximum point (MAX1) is the minimum point (MIN1) on the side with a larger particle size with respect to the first maximum point (MAX1). The integrated amount of frequency (V1) is the integrated amount of frequency from the particle size of the minimum point on the side with a smaller particle size with respect to the first maximum point (MAX1) or the particle size of the end (DS) on the side with a smaller particle size of the particle size distribution to the particle size of the minimum point (MIN1) on the side with a larger particle size with respect to the first maximum point (MAX1), minus the frequency of the particle size of the minimum point (MIN1) on the side with a larger particle size with respect to the first maximum point (MAX1). Subtracting the frequency of the particle size of the minimum point (MIN1) on the side with a larger particle size with respect to the first maximum point (MAX1) is to prevent the frequency of the particle size of the minimum point (MIN1) on the side with a larger particle size with respect to the first maximum point (MAX1) from being added in both the integrated amount of frequency between the peak start and the peak end at the peak having the first maximum point (MAX1) and the integrated amount of frequency between the peak start and the peak end at the peak having the second maximum point (MAX2).

[0020] The integrated amount of frequency (V2) between the peak start and the peak end at the peak having the second maximum point (MAX2) is preferably 15 to 50% by volume. When the integrated amount (V2) is 15 to 50% by volume, the filling property of the boron nitride powder in the heat dissipation sheet is enhanced. As a result, the control of the oxygen permeability coefficient of the heat dissipation sheet becomes easier, and the thermal conductivity of the heat dissipation sheet is further improved. From such a viewpoint, the integrated amount (V2) is more preferably 20 to 45% by volume. The peak start at the peak having the second maximum point (MAX2) is the minimum point (MIN1) on the side with a smaller particle size with respect to the second maximum point (MAX2). Also, the peak end at the peak having the second maximum point (MAX2) is the minimum point (MIN2) on the side with a larger particle size with respect to the second maximum point (MAX2). And the integrated amount of frequency (V2) is the integrated amount of frequency from the particle size of the minimum point (MIN1) on the side with a smaller particle size with respect to the second maximum point (MAX2) to the particle size of the minimum point (MIN2) on the side with a larger particle size with respect to the second maximum point (MAX2), minus the frequency of the particle size of the minimum point (MIN2) on the side with a larger particle size with respect to the second maximum point (MAX2). Subtracting the frequency of the particle size of the minimum point (MIN2) on the side with a larger particle size with respect to the second maximum point (MAX2) is to prevent the frequency of the particle size of the minimum point (MIN2) on the side with a larger particle size with respect to the second maximum point (MAX2) from being added in both the integrated amount of frequency between the peak start and the peak end at the peak having the second maximum point (MAX2) and the integrated amount of frequency between the peak start and the peak end at the peak having the third maximum point (MAX3).

[0021] The integrated frequency amount (V3) between the peak start and the peak end at the peak having the third maximum point (MAX3) is preferably 30 to 80% by volume. When the integrated amount (V3) is 30 to 80% by volume, the filling property of the boron nitride powder in the heat dissipation sheet is enhanced, whereby the control of the oxygen permeability coefficient of the heat dissipation sheet becomes easier and the thermal conductivity of the heat dissipation sheet is further improved. From such a viewpoint, the integrated amount (V3) is more preferably 45 to 75% by volume. The peak start at the peak having the third maximum point (MAX3) is the minimum point (MIN2) on the side with a smaller particle size with respect to the third maximum point (MAX3). Also, the peak end at the peak having the third maximum point (MAX3) is the minimum point on the side with a larger particle size with respect to the third maximum point (MAX3). When there is no minimum point on the side with a larger particle size with respect to the third maximum point (MAX3), the peak end is the end (DE) on the side with a larger particle size of the particle size distribution. And the integrated frequency amount (V3) is the value obtained by subtracting the frequency of the particle size of the minimum point on the side with a larger particle size with respect to the third maximum point (MAX3) from the integrated frequency amount of the frequency from the particle size of the minimum point (MIN2) on the side with a smaller particle size with respect to the third maximum point (MAX3) to the particle size of the minimum point on the side with a larger particle size with respect to the third maximum point (MAX3), or the integrated frequency amount of the frequency from the particle size of the minimum point (MIN2) on the side with a smaller particle size with respect to the third maximum point (MAX3) to the particle size of the end (PE) on the side with a larger particle size of the particle size distribution. Note that subtracting the frequency of the particle size of the minimum point on the side with a larger particle size with respect to the third maximum point (MAX3) is to prevent the frequency of the particle size of the minimum point on the side with a larger particle size with respect to the third maximum point (MAX3) from being added in both the integrated frequency amount between the peak start and the peak end at the peak having the third maximum point (MAX3) and the integrated frequency amount between the peak start and the peak end at the peak having a maximum point on the side with a larger particle size with respect to the third maximum point and adjacent to the third maximum point (MAX3).

[0022] The crushing strength of the aggregated boron nitride particles in the boron nitride powder contained in the thermally conductive resin composition for the heat dissipation sheet of the present invention is preferably 5 to 18 MPa. When the crushing strength of the aggregated boron nitride particles is 5 MPa or more, it is possible to suppress the destruction of the aggregated boron nitride particles during the production of the heat dissipation sheet. When the crushing strength of the aggregated boron nitride particles is 18 MPa or less, the resin can sufficiently penetrate into the aggregated boron nitride particles in the heat dissipation sheet, and it is possible to suppress the remaining of air in the aggregated boron nitride particles in the heat dissipation sheet. From such a viewpoint, the crushing strength of the aggregated boron nitride particles in the boron nitride powder of the present invention is more preferably 6 to 15 MPa, and even more preferably 7 to 13 MPa. The crushing strength of the aggregated boron nitride particles can be measured by the method described in the examples below.

[0023] As long as the filling property of the boron nitride powder in the heat dissipation sheet is increased, whereby the control of the oxygen permeability coefficient of the heat dissipation sheet becomes easier and the thermal conductivity of the heat dissipation sheet is improved, the particle size distribution of the boron nitride powder of the present invention may have other maximum points in addition to the above-described first to third maximum points.

[0024] (Manufacturing method of boron nitride powder) An example of the manufacturing method of the boron nitride powder contained in the thermally conductive resin composition for the heat dissipation sheet of the present invention will be described below. The boron nitride powder contained in the thermally conductive resin composition for the heat dissipation sheet of the present invention can be produced, for example, by producing a first boron nitride powder having a particle size distribution with the above-described first maximum point, a second boron nitride powder having a particle size distribution with the above-described second maximum point, and a third boron nitride powder having a particle size distribution with the above-described third maximum point, respectively, and mixing the produced first to third boron nitride powders.

[0025] Among the first to third boron nitride powders, the second and third boron nitride powders are preferably boron nitride powders each containing at least aggregated boron nitride particles formed by aggregation of hexagonal boron nitride primary particles. Further, the first boron nitride powder may be aggregated boron nitride particles, but is preferably hexagonal boron nitride primary particles. The maximum points of the first to third boron nitride powders respectively mean the peaks in the particle size distributions of the first to third boron nitride powders. The particle size distributions of the first to third boron nitride powders are measured in the same manner as the particle size distributions of the boron nitride powders described above.

[0026] In the mixing step, the first to third boron nitride powders may be mixed so that the volume ratio of the third boron nitride powder is greater than the volume ratio of the second boron nitride powder, and the volume ratio of the second boron nitride powder is greater than the volume ratio of the first boron nitride powder. Thereby, the filling property of the boron nitride powder in the heat dissipation sheet is enhanced, the control of the oxygen permeability coefficient of the heat dissipation sheet becomes easier, and the thermal conductivity of the heat dissipation sheet is improved. From the viewpoints of controlling the oxygen permeability coefficient of the heat dissipation sheet and the thermal conductivity of the heat dissipation sheet, the volume ratio of the third boron nitride powder is preferably 30 to 80 parts by volume, more preferably 45 to 75 parts by volume, and still more preferably 50 to 70 parts by volume with respect to a total of 100 parts by volume of the first to third boron nitride powders. From the viewpoints of controlling the oxygen permeability coefficient of the heat dissipation sheet and the thermal conductivity of the heat dissipation sheet, the volume ratio of the second boron nitride powder is preferably 15 to 50 parts by volume, more preferably 20 to 4 5 parts by volume, and still more preferably 25 to 35 parts by volume. From the viewpoints of controlling the oxygen permeability coefficient of the heat dissipation sheet and the thermal conductivity of the heat dissipation sheet, the volume ratio of the first boron nitride powder is preferably 2 to 25 parts by volume, more preferably 5 to 20 parts by volume, and still more preferably 8 to 15 parts by volume with respect to a total of 100 parts by volume of the first to third boron nitride powders.

[0027] Each of the first to third boron nitride powders can be produced by a production method including, for example, a pulverization step of pulverizing massive boron carbide, a nitridation step of nitriding the pulverized boron carbide to obtain boron carbonitride, and a decarburization step of decarburizing the boron carbonitride.

[0028] In the pulverization step, massive boron carbide (boron carbide mass) is pulverized using a general pulverizer or crusher. At this time, for example, by adjusting the pulverization time and the charged amount of the boron carbide mass, a boron carbide powder having a desired maximum point can be obtained. The maximum point of the boron carbide powder can be measured in the same manner as the maximum point of the boron nitride powder described above. Thus, by adjusting the maximum point of the boron carbide powder to approach the maximum point of the desired boron nitride powder, the first to third boron nitride powders having the above-described maximum points can be obtained.

[0029] Subsequently, in the nitridation step, boron carbonitride is obtained by firing the boron carbide powder under a pressure condition in an atmosphere in which the nitridation reaction proceeds.

[0030] The atmosphere in the nitridation step is an atmosphere in which the nitridation reaction proceeds, and may be, for example, nitrogen gas, ammonia gas, etc., and may be a single kind thereof or a combination of two or more kinds thereof. From the viewpoints of ease of nitridation and cost, the atmosphere is preferably nitrogen gas. The content of nitrogen gas in the atmosphere is preferably 95% by volume or more, more preferably 99.9% by volume or more.

[0031] The pressure in the nitriding process is preferably 0.6 MPa or more, more preferably 0.7 MPa or more, preferably 1.0 MPa or less, and more preferably 0.9 MPa or less. The pressure is more preferably 0.7 to 1.0 MPa. The firing temperature in the nitriding process is preferably 1800 °C or more, more preferably 1900 °C or more, preferably 2400 °C or less, and more preferably 2200 °C or less. The firing temperature is more preferably 1800 to 2200 °C. Since the pressure conditions and the firing temperature allow the nitridation of boron carbide to proceed more suitably and are also industrially appropriate conditions, they are preferably 1800 °C or more and 0.7 to 1.0 MPa.

[0032] The firing time in the nitriding process is appropriately selected within the range where nitridation proceeds sufficiently, and is preferably 6 hours or more, more preferably 8 hours or more, and may be preferably 30 hours or less, more preferably 20 hours or less.

[0033] In the decarburization process, the boron carbonitride obtained in the nitriding process is heat-treated by holding it at a predetermined holding temperature for a certain period of time in an atmosphere of normal pressure or higher. Thereby, aggregated boron nitride particles formed by aggregation of hexagonal boron nitride primary particles that have been decarburized and crystallized can be obtained.

[0034] The atmosphere in the decarburization process is an atmosphere of normal pressure (atmospheric pressure) or a pressurized atmosphere. In the case of a pressurized atmosphere, the pressure may be, for example, 0.5 MPa or less, preferably 0.3 MPa or less.

[0035] In the decarburization process, for example, first, after heating to a predetermined temperature (a temperature at which decarburization can start), the temperature is further increased to the holding temperature at a predetermined heating rate. The predetermined temperature (a temperature at which decarburization can start) can be set according to the system, and may be, for example, 1000 °C or more, may be 1500 °C or less, and is preferably 1200 °C or less. The rate of temperature increase from the predetermined temperature (a temperature at which decarburization can start) to the holding temperature may be, for example, 5 °C / min or less, and may preferably be 4 °C / min or less, 3 °C / min or less, or 2 °C / min or less.

[0036] The holding temperature is preferably 1800 °C or higher, more preferably 2000 °C or higher, from the viewpoint that grain growth can easily occur favorably and the thermal conductivity of the obtained boron nitride powder can be further improved. The holding temperature may preferably be 2200 °C or lower, more preferably 2100 °C or lower.

[0037] The holding time at the holding temperature is appropriately selected within a range where crystallization proceeds sufficiently. For example, it may exceed 0.5 hours, and from the viewpoint that grain growth can easily occur favorably, it is preferably 1 hour or longer, more preferably 3 hours or longer, still more preferably 5 hours or longer, and particularly preferably 10 hours or longer. The holding time at the holding temperature may be, for example, less than 40 hours, and it is possible to reduce excessive grain growth and a decrease in particle strength. Also, from the viewpoint of cost reduction, it is preferably 30 hours or shorter, more preferably 20 hours or shorter.

[0038] In the decarburization step, in addition to the boron carbonitride obtained in the nitridation step, a boron source may be mixed as a raw material to perform decarburization and crystallization. Examples of the boron source include boric acid, boron oxide, or a mixture thereof. In this case, other additives used in the technical field may be further used as necessary.

[0039] The mixing ratio of the boron carbonitride and the boron source is appropriately selected. When boric acid or boron oxide is used as the boron source, the ratio of boric acid or boron oxide may be, for example, 100 parts by mass or more, preferably 150 parts by mass or more, and may be, for example, 300 parts by mass or less, preferably 250 parts by mass or less, based on 100 parts by mass of the boron carbonitride.

[0040] A classification step (classification step) may be performed on the boron nitride powder obtained as described above so that a boron nitride powder having a desired particle size distribution is obtained by sieving. Thereby, the first to third boron nitride powders having desired maximum points can be more suitably obtained.

[0041] The obtained first to third boron nitride powders can be mixed to obtain the boron nitride powder contained in the thermally conductive resin composition for the heat dissipation sheet of the present invention. The mixing method is not particularly limited as long as the first to third boron nitride powders can be uniformly mixed. For example, the first to third boron nitride powders may be mixed using a container rotation type mixing device, or the first to third boron nitride powders may be mixed using a container fixed type mixing device, or the first to third boron nitride powders may be mixed using a fluid motion type mixing device.

[0042] (Resin) Examples of the resin contained in the thermally conductive resin composition for the heat dissipation sheet of the present invention include epoxy resin, silicone resin (including silicone rubber), acrylic resin, phenolic resin, melamine resin, urea resin, unsaturated polyester, fluororesin, polyamide (for example, polyimide, polyamideimide, polyetherimide, etc.), polyester (for example, polybutylene terephthalate, polyethylene terephthalate, etc.), polyphenylene ether, polyphenylene sulfide, wholly aromatic polyester, polysulfone, liquid crystal polymer, polyethersulfone, polycarbonate, maleimide-modified resin, ABS resin, AAS (acrylonitrile-acrylic rubber-styrene) resin, AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resin, and the like. Among these, from the viewpoints of heat resistance, flexibility, and adhesion to heat sinks, etc., silicone resin is preferable. The silicone resin is preferably one that is cured by vulcanization with an organic peroxide. Further, the viscosity of the thermally conductive resin composition at 25°C is, for example, 100,000 cp or less from the viewpoint of improving the flexibility of the sheet-like molded body.

[0043] In the thermally conductive resin composition for the heat dissipation sheet of the present invention, the content of boron nitride powder is preferably 30 to 85% by volume, more preferably 40 to 80% by volume, based on a total of 100% by volume of the boron nitride powder and the resin. When the content of the boron nitride powder is 30% by volume or more, the thermal conductivity is improved, and sufficient heat dissipation performance is easily obtained. Also, when the content of the boron nitride powder is 85% by volume or less, it is possible to reduce the tendency of voids to occur during molding, and it is possible to suppress a decrease in insulation and mechanical strength. Further, the content of the resin component is preferably 15 to 70% by volume, more preferably 20 to 60% by volume, based on a total of 100% by volume of the boron nitride powder and the resin.

[0044] (Solvent) In order to adjust the viscosity of the thermally conductive resin composition, the thermally conductive resin composition may further contain a solvent. The solvent is not particularly limited as long as it can dissolve the resin and can be easily removed from the applied thermally conductive resin composition after application. When the resin is a silicone resin, examples of the solvent include toluene, xylene, and chlorinated hydrocarbons. From the viewpoint of easy removal, toluene is preferred among these solvents. The content of the solvent can be appropriately selected according to the target viscosity of the thermally conductive resin composition. The content of the solvent is, for example, 40 to 200 parts by mass with respect to 100 parts by mass of the components other than the solvent in the thermally conductive resin composition.

[0045] Note that the thermally conductive resin composition may contain components other than the boron nitride powder, the resin component, and the solvent. The other components are inorganic fillers other than the boron nitride powder, additives, impurities, etc. The content of the other components is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and still more preferably 1 part by mass or less, based on 100 parts by mass in total of the boron nitride powder and the resin.

[0046] (Thickness of the heat dissipation sheet) The thickness of the heat dissipation sheet of the present invention is preferably 100 to 1200 μm. When the thickness of the heat dissipation sheet is 100 μm or more, the heat dissipation sheet can be surely adhered to the heat-generating electronic component. When the thickness of the heat dissipation sheet is 1200 μm or less, the heat dissipation property of the heat dissipation sheet can be further improved. From such a viewpoint, the thickness of the heat dissipation sheet of the present invention is more preferably 150 to 800 μm, and still more preferably 200 to 600 μm.

[0047] [Method for manufacturing heat dissipation sheet] The method for manufacturing the heat dissipation sheet of the present invention includes a step (A) of preparing a thermally conductive resin composition by blending a boron nitride powder containing at least aggregated boron nitride particles formed by aggregation of hexagonal boron nitride primary particles and a resin, a step (B) of forming the thermally conductive resin composition into a sheet shape to prepare a thermally conductive resin composition sheet, and a step (C) of heating and pressurizing the thermally conductive resin composition sheet under vacuum.

[0048] (Step (A)) In step (A), a thermally conductive resin composition is prepared by blending a boron nitride powder containing at least aggregated boron nitride particles formed by aggregation of hexagonal boron nitride primary particles and a resin. The boron nitride powder used in step (A) is preferably the boron nitride powder contained in the thermally conductive resin composition for the heat dissipation sheet of the present invention. Since the boron nitride powder and the resin used in step (A) have already been described, the description is omitted.

[0049] (Step (B)) In step (B), the thermally conductive resin composition is formed into a sheet shape to prepare a thermally conductive resin composition sheet. For example, the thermally conductive resin composition can be formed into a sheet shape by the doctor blade method or calendering. However, when the thermally conductive resin composition passes through the calender roll, the aggregated boron nitride particles in the thermally conductive resin composition may be broken. Therefore, it is preferable to form the thermally conductive resin composition into a sheet shape by the doctor blade method.

[0050] (Step (C)) In step (C), the heat-conductive resin composition sheet is heated and pressed under vacuum. By adjusting the pressure when pressing the heat-conductive resin composition sheet, the oxygen transmission coefficient of the heat dissipation sheet can be controlled. For example, when the pressure at this time of pressing the heat-conductive resin composition sheet is increased, the oxygen transmission coefficient of the heat dissipation sheet becomes smaller. On the other hand, when the pressure at this time of pressing the heat-conductive resin composition sheet is decreased, the oxygen transmission coefficient of the heat dissipation sheet becomes larger. Further, by heating and pressing the heat-conductive resin composition sheet under vacuum, microvoids in the heat dissipation sheet can be further reduced, so that the thermal conductivity of the heat dissipation sheet can be improved, and the insulation of the heat dissipation sheet can also be improved. Furthermore, by heating and pressing the heat-conductive resin composition sheet under vacuum, the heat-conductive resin composition sheet is pressed. Even when the pressure at this time is small, microvoids in the heat dissipation sheet can be reduced, so that aggregation of aggregated boron nitride particles in the heat-conductive resin composition sheet can be suppressed from being broken. From such a viewpoint, the pressure of the vacuum environment when heating and pressing the heat-conductive resin composition sheet is preferably 0.1 to 5 kPa, more preferably 0.1 to 3 kPa. Also, the heating temperature of the heat-conductive resin composition sheet is preferably 120 to 200 °C, more preferably 130 to 180 °C. Furthermore, the pressure when pressing the heat-conductive resin composition sheet is preferably 80 to 250 kg / cm 2 and more preferably 100 to 200 kg / cm 2 is.

Examples

[0051] Hereinafter, the present invention will be described in detail with reference to examples and comparative examples. Note that the present invention is not limited to the following examples.

[0052] (Oxygen transmission coefficient) In accordance with JIS K7126-2:2006 (Plastics - Films and Sheets - Gas Permeability Test Methods - Part 2: Isobaric Method), the oxygen transmission coefficient of the heat dissipation sheet was measured under the following conditions. Test apparatus: Oxygen permeation tester (manufactured by MOCON, trade name "OX-TRN ML2 / 21") Temperature and humidity conditions: Temperature 23°C, humidity 60%RH Laboratory environment: Temperature 22 ± 1°C, humidity 55 ± 5%RH Test gas: Oxygen 100% Permeation area: 5 cm 2 (Aluminum mask treatment carried out)

[0053] (Particle size distribution) The particle size distribution of boron nitride powder was measured using a laser diffraction scattering method particle size distribution measuring device (LS-13 320) manufactured by Beckman Coulter, Inc. Then, from the obtained particle size distribution, the particle diameters (the 1st to 3rd maximum values) of the 1st to 3rd maximum points, the integrated amount of frequency from the peak start to the peak end in the peaks having the 1st to 3rd maximum points (the integrated amount of frequency of the 1st to 3rd), the particle diameter at which the integrated amount of frequency becomes 10%, and the absolute value of the difference between the particle diameter of the minimum point between the minimum point having the smallest particle diameter and the second smallest particle diameter (the distance between D10 and the first minimum point), the absolute value of the difference between the particle diameter of the 1st minimum point and the particle diameter of the 2nd minimum point (the distance between minimum points), and the half-width at half maximum of the peak having the 3rd maximum point (the half-width at half maximum of the 3rd maximum value) were determined.

[0054] (Crushing strength) The crushing strength of agglomerated boron nitride particles was measured in accordance with JIS R 1639-5:2007. Specifically, after spraying agglomerated boron nitride particles on the sample stage of a micro compression tester (manufactured by Shimadzu Corporation, "MCT-W500"), 5 agglomerated boron nitride particles were selected and compression tests were performed one by one. Then, the crushing strength (σ: MPa) was calculated from the dimensionless number (α = 2.48) that varies depending on the position within the particle, the crushing test force (P: N), and the particle diameter (d: μm) using the formula σ = α × P / (π × d 2 ). The crushing strengths of 5 inorganic filler components were Weibull plotted in accordance with JIS R 1625:2010, and the crushing strength at which the cumulative fracture rate becomes 63.2% was taken as the crushing strength of the agglomerated boron nitride particles.

[0055] The following evaluations were performed on the heat dissipation sheets of the examples and comparative examples. (Insulation) The dielectric breakdown voltage of the heat dissipation sheet was evaluated based on the value measured by a short-time breakdown test (at room temperature of 23°C) in accordance with the method described in JIS C2110-1:2016. The results are shown in Table 1. The evaluation criteria for insulation are as follows. ◎: Dielectric breakdown voltage is 10 kV or more ○: Dielectric breakdown voltage is 5 kV or more and less than 10 kV ×: Dielectric breakdown voltage is less than 5 kV

[0056] (Thermal conductivity) The thermal resistance of the heat dissipation sheet was evaluated based on the value measured in accordance with the method described in ASTM D5470:2017. The results are shown in Table 1. The evaluation criteria for thermal conductivity are as follows. ◎: Thermal conductivity is 5 W / (m·K) or more ○: Thermal conductivity is 3 W / (m·K) or more and less than 5 W / (m·K) ×: Thermal conductivity is less than 3 W / (m·K)

[0057] Boron nitride powders A to I having one maximum point, which are raw materials for boron nitride powder having a plurality of maximum points, were prepared as follows.

[0058] (Boron nitride powder A) Boron nitride powder A was prepared through boron carbide synthesis, pressure nitridation process, and decarbon crystallization process as follows.

[0059] (Boron carbide synthesis) 100 parts by mass of orthoboric acid (hereinafter referred to as boric acid) manufactured by Shin Nippon Chemical Co., Ltd. and 35 parts by mass of acetylene black (HS100) manufactured by Denka Co., Ltd. were mixed using a Henschel mixer, filled into a graphite crucible, and heated in an argon atmosphere at 2200°C for 5 hours in an arc furnace to synthesize boron carbide (B 4 C). The synthesized boron carbide mass was pulverized with a ball mill for 1 hour, sieved to a particle size of 75 μm or less using a sieve, further washed with an aqueous nitric acid solution to remove impurities such as iron content, and then filtered and dried to produce boron carbide powder with an average particle size of 4 μm.

[0060] (Pressure nitriding process) The synthesized boron carbide was filled into a boron nitride crucible, and then heated in a resistance heating furnace at 2000°C and 9 atm (0.8 MPa) for 10 hours in a nitrogen gas atmosphere to produce boron carbonitride (B 4 CN 4 ) was obtained.

[0061] (Decarburization crystallization process) 100 parts by mass of the synthesized boron carbonitride and 90 parts by mass of boric acid were mixed using a Henschel mixer, then filled into a boron nitride crucible, and heated in a nitrogen gas atmosphere at a pressure of 0.2 MPa using a resistance heating furnace at a heating rate of 10 ° C / min from room temperature to 1000 ° C, and a heating rate of 2 ° C / min from 1000 ° C, and heated at a firing temperature of 2020 ° C, and held for 10 hours to synthesize aggregated boron nitride particles in which primary particles were aggregated into lumps. The synthesized aggregated boron nitride particles were decomposed and crushed in a Henschel mixer, and then classified using a nylon sieve with a mesh size of 150 μm. Boron nitride powder A was obtained by crushing and classifying the fired product.

[0062] The average particle size (D50) of the obtained boron nitride powder A measured by a laser scattering method was 4.5 μm. As a result of SEM observation, the obtained boron nitride powder A was found to be scaly particles.

[0063] (Boron nitride powder B) Boron nitride powder B was produced in the same manner as boron nitride powder A, except that boron carbide powder with an average particle size of 6 μm was used. The average particle size (D50) of the obtained boron nitride powder B measured by a laser scattering method was 8.0 μm. SEM observation revealed that the obtained boron nitride powder B was a scaly particle.

[0064] (Boron nitride powder C) Except for using boron carbide powder with an average particle size of 1 μm, boron nitride powder C was produced in the same manner as boron nitride powder A. The average particle size (D50) of the obtained boron nitride powder C measured by the laser scattering method was 1.0 μm. As a result of SEM observation, the obtained boron nitride powder C was flaky particles.

[0065] (Boron nitride powder D) Except for using boron carbide powder with an average particle size of 15 μm, boron nitride powder D was produced in the same manner as boron nitride powder A. The average particle size (D50) of the obtained boron nitride powder D measured by the laser scattering method was 23 μm. As a result of SEM observation, the obtained boron nitride powder D was agglomerated particles formed by aggregation of primary particles.

[0066] (Boron nitride powder E) Except for using boron carbide powder with an average particle size of 25 μm, boron nitride powder E was produced in the same manner as boron nitride powder A. The average particle size (D50) of the obtained boron nitride powder E measured by the laser scattering method was 35 μm. As a result of SEM observation, the obtained boron nitride powder E was agglomerated particles formed by aggregation of primary particles.

[0067] (Boron nitride powder F) Except for using boron carbide powder with an average particle size of 10 μm, boron nitride powder F was produced in the same manner as boron nitride powder A. The average particle size (D50) of the obtained boron nitride powder F measured by the laser scattering method was 15 μm. As a result of SEM observation, the obtained boron nitride powder F was agglomerated particles formed by aggregation of primary particles.

[0068] (Boron nitride powder G) Except for using boron carbide powder with an average particle size of 55 μm, boron nitride powder G was produced in the same manner as boron nitride powder A. The average particle size (D50) of the obtained boron nitride powder G measured by the laser scattering method was 78 μm. Also, the half-value width of the peak of the particle size distribution of boron nitride powder G was 46 μm. As a result of SEM observation, the obtained boron nitride powder G was agglomerated particles formed by aggregation of primary particles.

[0069] (Boron nitride powder H) Except for using boron carbide powder with an average particle size of 70 μm, boron nitride powder H was produced in the same manner as boron nitride powder A. The average particle size (D50) of the obtained boron nitride powder H measured by the laser scattering method was 95 μm. As a result of SEM observation, the obtained boron nitride powder H was agglomerated particles formed by aggregation of primary particles. Also, the half-value width of the peak of the particle size distribution of boron nitride powder H was 53 μm.

[0070] (Boron nitride powder I) Except for using boron carbide powder with an average particle size of 40 μm, boron nitride powder I was produced in the same manner as boron nitride powder A. The average particle size (D50) of the obtained boron nitride powder I measured by the laser scattering method was 55 μm. Also, the half-value width of the peak of the particle size distribution of boron nitride powder I was 28 μm. As a result of SEM observation, the obtained boron nitride powder I was agglomerated particles formed by aggregation of primary particles.

[0071] Boron nitride powders A to I were mixed at the blending ratios shown in Table 1 to produce boron nitride powders 1 to 3.

[0072]

Table 1

[0073] (Production of heat dissipation sheet) For a total of 100% by volume of the obtained boron nitride powder and liquid silicone resin (methyl vinyl polysiloxane, manufactured by Dow Corning Toray Co., Ltd., trade name "CF-3110"), 60% by volume of boron nitride powder and 40% by volume of silicone resin, 1 part by mass of a curing agent (2,5-dimethyl-2,5-bis(t-butylperoxy)hexane, manufactured by Kayaku Nouryon Co., Ltd., trade name "Trigonox 101") per 100 parts by mass of the silicone resin, 0.5 part by mass of a silane coupling agent (dimethyl dimethoxysilane, manufactured by Dow Corning Toray Co., Ltd., trade name "DOWSIL Z-6329 Silane", viscosity at 25°C: 1 cp) per 100 parts by mass of the boron nitride powder, 15 parts by mass of water per 100 parts by mass of the silane coupling agent, and 110 parts by mass of toluene per 100 parts by mass of the above raw materials were charged into a stirrer (manufactured by HEIDON, trade name "Three One Motor") and mixed for 15 hours using a turbine-type stirring blade to prepare a slurry of the thermally conductive resin composition. Then, by the doctor blade method, the above slurry was coated on a PET film (carrier film) with a thickness of 0.05 mm to a thickness of 1.0 mm and dried at 75°C for 5 minutes to prepare a sheet-shaped molded body with a PET film. A PET film with a thickness of 0.05 mm was laminated on the thermally conductive resin composition surface of the obtained sheet-shaped molded body to prepare a laminate. The layer structure of this laminate was PET film / thermally conductive resin composition / PET film. Next, the obtained laminate was subjected to a heat press at a pressure shown in Table 2 for 30 minutes under vacuum (pressure 3.5 KPa) at a temperature of 150°C, and the PET films on both sides were peeled off to obtain a sheet. Then, it was subjected to secondary heating at normal pressure and 150°C for 4 hours to obtain a heat dissipation sheet.

[0074] Table 2 shows the evaluation results of the obtained boron nitride powder and heat dissipation sheet.

Table 2

[0075] From the evaluation results of the heat dissipation sheet of the example, the oxygen transmission coefficient of the heat dissipation sheet is 1×10 -11 ~1×10 -7 cm3 ·cm / (cm 2 It was found that when it is ·cm / (cm·s·cmHg), the thermal conductivity and insulation of the heat dissipation sheet are improved.

Claims

1. A heat dissipation sheet formed by molding a thermally conductive resin composition containing a boron nitride powder containing at least aggregated boron nitride particles formed by aggregation of hexagonal boron nitride primary particles and a resin, The oxygen transmission coefficient is 1.3×10 －９ ~9.5×10 -8 cm ３ ·cm / (cm ２ ·s·cmHg), and it is a heat dissipation sheet.

2. The particle size distribution of the boron nitride powder has at least a first maximum point, a second maximum point having a larger particle size than the first maximum point, and a third maximum point having a larger particle size than the second maximum point, The particle size of the first maximum point is 0.4 μm or more and less than 10 μm, The particle size of the second maximum point is 10 μm or more and less than 40 μm, The heat dissipation sheet according to claim 1, wherein the particle size of the third maximum point is 40 μm or more and 110 μm or less.

3. The absolute value of the difference between the particle size at which the integrated amount of frequency in the particle size distribution of the boron nitride powder becomes 10% and the particle size of the minimum point between the minimum point having the smallest particle size and the second smallest particle size in the particle size distribution of the boron nitride powder is 3 to 30 μm. The heat dissipation sheet according to claim 2.

4. The maximum point adjacent to the first maximum point is the second maximum point, The maximum point adjacent to the second maximum point is the third maximum point, The heat dissipation sheet according to claim 2 or 3, wherein the absolute value of the difference between the particle size of the first minimum point between the first maximum point and the second maximum point and the particle size of the second minimum point between the second maximum point and the third maximum point is 15 to 60 μm.

5. The heat dissipation sheet according to any one of claims 2 to 4, wherein the half-value width of the peak having the third maximum point is 20 to 60 μm.

6. The heat dissipation sheet according to any one of claims 1 to 5, wherein the crushing strength of the aggregated boron nitride particles is 5 to 18 MPa.

7. A step of preparing a thermally conductive resin composition by blending a boron nitride powder containing at least aggregated boron nitride particles formed by aggregation of hexagonal boron nitride primary particles and a resin, A step of forming the thermally conductive resin composition into a sheet shape to produce a thermally conductive resin composition sheet, and A method for manufacturing the heat dissipation sheet according to any one of claims 1 to 6, including a step of heating and pressurizing the thermally conductive resin composition sheet under vacuum.

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