Boron nitride powder, method for producing boron nitride powder, and resin molded body

Abstract

To provide a boron nitride powder that can impart heat dissipation properties to a resin sheet even at low filling levels. [Solution] One aspect of this disclosure is a material comprising a lump of hexagonal boron nitride primary particles aggregated together, having a crushing strength of 10.0 MPa or more, and a tap density of 0.50 to 0.66 g / cm³. 3 The present invention provides boron nitride powder.

Description

[Technical Field]

[0001] This disclosure relates to boron nitride powder, a method for producing boron nitride powder, and a resin molded article. [Background technology]

[0002] The primary particles of hexagonal boron nitride have a relatively thin, flaky shape. When filled into resin and molded, the primary particles tend to orient in a certain direction within the resin molded body due to molding pressure and other factors. For example, in a resin sheet formed by extrusion molding after filling with hexagonal boron nitride powder, the primary particles of boron nitride generally tend to orient parallel to the main surface of the resin sheet and the long axis of the primary particles. Furthermore, due to the anisotropy of the shape of the primary particles of hexagonal boron nitride, anisotropy can occur in various physical properties. While the thermal conductivity of the primary particles of hexagonal boron nitride is high in the in-plane direction (a-axis direction) at approximately 400 W / (m·K), the thermal conductivity in the thickness direction (c-axis direction) remains at approximately 2 W / (m·K), demonstrating significant anisotropy in physical properties depending on the direction.

[0003] For the reasons mentioned above, when preparing a heat dissipation sheet using hexagonal boron nitride powder as a filler in a resin, methods are being considered to take advantage of the high thermal conductivity of the primary particles in the a-axis direction by adjusting the orientation so that the a-axis direction of the primary particles is parallel to the thickness direction of the heat dissipation sheet. For example, a technique is known for orienting the primary particles of hexagonal boron nitride so that the a-axis direction of the primary particles is parallel to the thickness direction of the heat dissipation sheet (e.g., Patent Document 1).

[0004] Furthermore, from the viewpoint of reducing the anisotropy based on the shape described above, a method has been considered for forming aggregates by aggregating and fusing a large number of primary particles so that their c-axis directions are oriented in different directions from one another. Patent Document 2 discloses boron nitride aggregate particles formed by the aggregation of boron nitride primary particles, and describes how the collapse of the aggregate particles can be suppressed even when a predetermined molding pressure is applied, thereby suppressing the orientation of the boron nitride primary particles in the same direction.

[0005] Patent Document 3 describes a hexagonal boron nitride powder containing aggregates of primary particles of hexagonal boron nitride, wherein the primary particle diameter is less than 10 μm, the ratio of the average major axis (L1) of the primary particles to the average thickness (d1) [L1 / d1] is between 5.0 and 20, and the BET specific surface area is 10 m². 2 A hexagonal boron nitride powder is disclosed, wherein the particle size distribution curve of the hexagonal boron nitride powder, which is classified to a particle size of 45 μm to 106 μm, has one maximum peak in the range of 45 μm to 150 μm, and the peak reduction rate of the maximum peak when the dispersion of the hexagonal boron nitride powder in water is ultrasonically treated for 1 minute is 10% to less than 40%.

[0006] Patent Document 4 describes a hexagonal boron nitride aggregate with a maximum torque of 0.20-0.50 Nm, a DBP absorption of 50-100 ml / 100 g, and a tap bulk density of 0.66-0.95 g / cm³, as measured and calculated in accordance with JIS-K-6217-4. 3 A hexagonal boron nitride powder characterized by the following is disclosed.

[0007] Patent Document 5 describes aggregated particles composed of aggregated primary boron nitride particles, with a tap density of 0.9 g / cm³. 3 A powder is disclosed that has a high tap density and can improve the amount that can be filled into resin, such as boron nitride powder, which has an average particle diameter of 20 μm or less and a crushing strength of the aggregated particles of 10 MPa or more. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2000-154265 [Patent Document 2] Japanese Patent Publication No. 2016-135731 [Patent Document 3] International Publication No. 2017 / 038512 [Patent Document 4] International Publication No. 2018 / 123571

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0009] For example, a heat dissipation sheet used for a member such as a flexible semiconductor substrate that is expected to deform during use requires flexibility in the heat dissipation sheet itself from the perspective of following other members. On the other hand, in a heat dissipation sheet with a high filler content from the perspective of improving heat dissipation, the sheet itself is hard and tends to be inferior in flexibility, and a different approach from the conventional one is required in situations where flexibility is required. It would be useful to provide a heat dissipation filler that can impart heat dissipation even in a situation with a low filling amount (for example, 30% by volume or less).

[0010] An object of the present disclosure is to provide boron nitride powder that can impart heat dissipation to a resin sheet even when the filling amount is low. Another object of the present disclosure is to provide a method for producing boron nitride powder.

Means for Solving the Problems

[0011] The present disclosure provides the following [1] to [7].

[0012] [1] A boron nitride powder containing massive particles in which a plurality of primary particles of hexagonal boron nitride aggregate and the crushing strength is 10.0 MPa or more, and the tap density is 0.50 to 0.66 g / cm 3 3 [2] The boron nitride powder according to [1], having an orientation index of 10.0 or less. [3] The boron nitride powder according to [1] or [2], having an average particle diameter of 30.0 to 90.0 μm. [4] The boron nitride powder according to any one of [1] to [3], having a BET specific surface area of 10.0 m 2 2 / g or less. [5] A nitriding step to obtain boron carbonitride powder by calcining boron carbide powder at 1800-2200°C under a nitrogen pressure atmosphere of 0.60 MPa or higher, A firing step in which the boron carbonitride powder is fired in the atmosphere, The process includes a decarburization step, in which the boron carbonitride powder that has undergone a calcination process is mixed with a boron source and heated in a nitrogen-containing atmosphere to generate primary particles of hexagonal boron nitride, thereby obtaining a lump-like particle composed of multiple aggregated primary particles. The nitriding process is as follows: The first nitriding process involves holding the temperature at 1800-1900°C for more than 3 hours, The second nitriding process involves holding the temperature at a higher temperature than the first nitriding process, but below 2200°C, for more than 10 hours. A method for producing boron nitride powder, including [the specified substance]. A resin molded article comprising boron nitride powder as described in any of [6][1] to [4] and a resin. [7] The resin molded article according to [6], wherein the content of the boron nitride powder is 30% by volume or less. [Effects of the Invention]

[0013] According to this disclosure, it is possible to provide boron nitride powder that can impart heat dissipation properties to a resin sheet even when the filling amount is low. According to this disclosure, it is also possible to provide a method for producing the boron nitride powder described above. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a schematic cross-sectional view showing an example of a heat dissipation sheet. [Figure 2] Figure 2 is a scanning electron microscope image showing the boron nitride powder of Example 1. [Modes for carrying out the invention]

[0015] The embodiments of this disclosure are described below. However, the embodiments described below are illustrative examples for the purpose of illustrating this disclosure and are not intended to limit this disclosure to the following.

[0016] Unless otherwise specified, the materials exemplified herein may be used individually or in combination of two or more. The content of each component in a composition means the total amount of any multiple substances present in the composition, unless otherwise specified, if there are multiple substances corresponding to each component in the composition.

[0017] In this specification, a primary particle of hexagonal boron nitride means a single particle of hexagonal boron nitride. A clump of particles is a particle formed by the aggregation of multiple primary particles that constitute an aggregated particle, where the in-plane direction (a-axis direction) is not oriented in one direction but in multiple directions; it can also be called a secondary particle.

[0018] One embodiment of boron nitride powder includes agglomerate particles composed of multiple aggregates of hexagonal boron nitride primary particles, with a crushing strength of 10.0 MPa or more. The tap density of the boron nitride powder is 0.50 to 0.66 g / cm³. 3 That is the case.

[0019] The low tap density of the boron nitride powder mentioned above suggests that the interior of the clumps within the powder is sparse. Therefore, compared to powders with high tap density, there are more clumps per unit mass, and when the same mass is used to fill a resin molded body, a relatively large number of clumps will be present in the molded body. As a result, even with a relatively low filling amount, it is possible to fill resin molded bodies such as resin sheets with high uniformity, and excellent heat dissipation properties can be imparted to the resin molded body. In other words, the amount of boron nitride powder to be filled can be kept low, which is particularly beneficial when flexibility is required in the resulting resin molded body. Furthermore, although the clumps contained in the powder have a sparse structure, they exhibit relatively high crush strength, and since high pressure can be used when manufacturing resin molded bodies, the impregnation of resin into the interior of the clumps and the voids between the clumps can be made more sufficient, and insulation properties can be improved.

[0020] The lower limit of the crushing strength of the agglomerate particles contained in the boron nitride powder may be, for example, 10.5 MPa or higher, 11.0 MPa or higher, 11.5 MPa or higher, or 12.0 MPa or higher. By having the lower limit of the crushing strength of the agglomerate particles within the above range, when used as a filler for resin molded articles, the collapse of the agglomerate particles is further suppressed even when molded under relatively high pressure, and impregnation of resin components into the agglomerate particles is made possible. This reduces the anisotropy of the heat dissipation of the resulting resin molded article, reduces voids inside the aggregated particles, and improves the insulation properties of the resin molded article. The upper limit of the crushing strength of the agglomerate particles is not particularly limited, but may be, for example, 30.0 MPa or lower, 28.0 MPa or lower, 25.0 MPa or lower, 22.0 MPa or lower, 20.0 MPa or lower, 18.0 MPa or lower, or 15.0 MPa or lower. By keeping the upper limit of the crushing strength within the above range, it is possible to allow appropriate deformation of the lump particles during mixing or molding with the resin, thereby suppressing the generation of voids and further improving the insulation properties of the resulting resin molded article. The crushing strength of the lump particles contained in the boron nitride powder may be adjusted within the above range, for example, 10.0 to 30.0 MPa or 10.0 to 15.0 MPa.

[0021] In this specification, crushing strength refers to the value measured in accordance with JIS R 1639-5:2007 "Fine ceramics - Method for measuring granular properties - Part 5: Single granular crushing strength". The crushing strength σ (unit: MPa) of a single agglomerate particle is given by σ = α × P / (π × d), where α (α = 2.48), a dimensionless number that changes depending on the position within the agglomerate particle, P (unit: N), and particle diameter d (unit: μm). 2 The value is calculated using the following formula: ( ). The measurement is performed on 20 or more clumped particles, and the value at the point of cumulative fracture rate of 63.2% is calculated. A microcompression tester can be used for the measurement. For example, the "MCT-W500" (product name) manufactured by Shimadzu Corporation can be used as a microcompression tester.

[0022] The upper limit of the tap density of the above boron nitride powder is, for example, 0.64 g / cm³. 3Hereinafter, 0.62 g / cm 3 Hereinafter, or 0.60 g / cm 3 Hereinafter, it may be. Since the boron nitride powder according to the present disclosure can impart heat dissipation properties to a resin molded body even at low filling, the upper limit value of the tap density of the boron nitride powder may be within the above range. In this case, a decrease in the flexibility of the obtained resin molded body (for example, a heat dissipation sheet) can be further suppressed. The lower limit value of the tap density of the boron nitride powder is, for example, 0.52 g / cm 3 or more, 0.54 g / cm 3 or more, or 0.56 g / cm 3 or more. By the lower limit value of the tap density being within the above range, it is possible to suppress an excessive increase in the viscosity when the boron nitride powder is blended and kneaded with a resin. The tap density of the boron nitride powder may be adjusted within the above-described range, for example, 0.52 to 0.66 g / cm 3 , 0.55 to 0.64 g / cm 3 .

[0023] The "tap density" in this specification means a value obtained in accordance with the method described in JIS R 1628:1997 "Method for Measuring Bulk Density of Fine Ceramic Powders". Specifically, the boron nitride powder is filled into a dedicated container of 100 cm 3 , and after tapping is performed under the conditions of a tapping time of 180 seconds, a tapping number of 180 times, and a tap lift of 18 mm, the bulk density is measured, and the obtained value is taken as the tap density. For the measurement, a commercially available device can be used, for example, "Powder Tester" (product name) manufactured by Hosokawa Micron can be used.

[0024] The boron nitride powder described above may consist mainly of clumpy particles, but may also contain primary particles (single particles) that do not constitute clumpy particles. The orientation index of the boron nitride powder may be, for example, 10.0 or less. In a powder, if there are clumpy particles that are substantially not oriented relative to the primary particles, and the proportion of these clumpy particles is large, the orientation index tends to approach a value of around 6 to 7. On the other hand, in powders composed of primary particles that do not contain clumpy particles, or in powders where the proportion of the above primary particles is large, the orientation index tends to be larger.

[0025] The upper limit of the orientation index of the boron nitride powder may be, for example, 10.0 or less, 9.5 or less, 9.0 or less, 8.5 or less, 8.0 or less, 7.5 or less, or 7.0 or less. Having the upper limit of the orientation index within the above range corresponds to a higher proportion of bulky particles in the boron nitride powder, and when the boron nitride powder is used as a filler in a resin molded article, it can further reduce the anisotropy related to the heat dissipation of the resin molded article. The lower limit of the orientation index of the boron nitride powder may be, for example, 6.0 or more, 6.2 or more, 6.4 or more, 6.6 or more, or 6.8 or more. The orientation index of the boron nitride powder can be adjusted within the above range, for example, 6.0 to 10.0, 6.0 to 8.0, or 6.0 to 7.5.

[0026] In this specification, the orientation index refers to a value measured according to the following method: An X-ray diffraction spectrum of boron nitride powder is obtained by performing an X-ray diffraction measurement on the boron nitride powder. Then, peak intensities I(002) and I(100) corresponding to the (002) plane and (100) plane are obtained from the said X-ray diffraction spectrum. The orientation index [I(002) / I(100)] of the boron nitride powder is calculated using the obtained peak intensities. As an X-ray diffractometer, for example, "ULTIMA-IV" (product name) manufactured by Rigaku Corporation can be used.

[0027] The lower limit of the average particle diameter of the boron nitride powder may be, for example, 30.0 μm or more, 35.0 μm or more, or 40.0 μm or more. By having the lower limit of the average particle diameter within the above range, sufficient thermal conductivity can be imparted to the resin composition even under conditions where the amount of boron nitride powder packed in is low. The upper limit of the average particle diameter of the boron nitride powder may be, for example, 90.0 μm or less, 85.0 μm or less, 80.0 μm or less, 70.0 μm or less, 60.0 μm or less, or 55.0 μm or less. By having the upper limit of the average particle diameter within the above range, it is possible to suppress an excessive increase in viscosity when the boron nitride powder is blended into the resin and melted. The average particle diameter of the boron nitride powder may be adjusted within the above range, for example, 30.0 to 90.0 μm.

[0028] In this specification, the average particle size of boron nitride powder refers to the 50% cumulative diameter (median diameter) in the volume-based cumulative particle size distribution. More specifically, it refers to the particle size (D50) when the cumulative value in the volume-based cumulative particle size distribution obtained by laser diffraction scattering for boron nitride powder reaches 50%. The laser diffraction scattering method is measured in accordance with the method described in JIS Z 8825:2013 "Particle size analysis - Laser diffraction and scattering method". A laser diffraction scattering particle size distribution analyzer can be used for measurement. For example, the "LS-13 320" (product name) from Beckman Coulter can be used as a laser diffraction scattering particle size distribution analyzer. When measuring, the measurement should be performed in the presence of clumpy particles without homogenizing.

[0029] The upper limit of the BET specific surface area of ​​the above boron nitride powder is, for example, 10.0 m². 2 / g or less, 8.0m 2 / g or less, 7.0m 2 / g or less, 6.5m 2 / g or less, 6.0m 2 / g or less, 5.5m 2 / g or less, 5.0m 2 / g or less, 4.5m 2 / g or less, or 4.0m 2It may be less than or equal to / g. If the upper limit of the BET specific surface area is within the above range, the primary particle size of boron nitride is sufficiently large, and when formed into a resin molded body, it can exhibit better heat dissipation. The lower limit of the specific surface area of ​​the boron nitride powder is, for example, 1.5m². 2 / g or more, 2.0m 2 / g or more, 2.5m 2 / g or more, or 3.0m 2 It may be greater than or equal to / g. When the lower limit of the BET specific surface area is within the above range, the contact between primary boron nitride particles is relatively large, and the crushing strength of the lump particles tends to be sufficiently high. This makes it possible to further suppress the collapse of lump particles when mixing or molding the boron nitride powder with resin. The specific surface area of ​​the boron nitride powder may be adjusted within the above range, for example, 1.5 to 10.0 m². 2 / g, 2.0~8.0m 2 / g, or 2.5~5.0m 2 / g is acceptable.

[0030] In this specification, the BET specific surface area refers to the value measured using a specific surface area measuring device in accordance with the description in JIS Z 8830:2013 "Method for measuring the specific surface area of ​​powders (solids) by gas adsorption," and is calculated by applying the BET single-point method using nitrogen gas. As a specific surface area measuring device, for example, the "MONOSORB MS-22" (product name) manufactured by QUANTACHROME can be used.

[0031] One embodiment of a method for producing boron nitride powder includes a nitriding step of firing boron carbide powder at 1800 to 2200°C under a nitrogen pressurized atmosphere of 0.60 MPa or higher to obtain boron carbonitride powder; a firing step of firing the boron carbonitride powder in an atmosphere; and a decarburization step of mixing the boron carbonitride powder obtained through the firing step with a boron source and heating it in a nitrogen-containing atmosphere to generate primary particles of hexagonal boron nitride, thereby obtaining a lump-like particle composed of aggregates of multiple primary particles.

[0032] The above nitriding process includes a first nitriding step in which the material is held at a temperature of 1800-1900°C for 3 hours or more, and a second nitriding step in which the material is held at a temperature higher than that of the first nitriding step, but 2200°C or lower, for 10 hours or more.

[0033] The manufacturing method described above is an application of the so-called boron carbide (B4C) method. In the boron carbide method, in the nitriding step in which boron carbide particles are pressurized and nitrided, nitriding proceeds in a way that causes cracks to form in the boron carbide particles. Then, in the subsequent decarburization step, the carbon content is reduced from the boron carbonitride and crystallization proceeds to form primary boron nitride particles, resulting in the formation of agglomerate particles in which the primary particles have aggregated. Through the inventors' studies, it has been found that the change in shape of the boron carbide particles accompanying the progression of nitriding in the above-mentioned nitriding step affects the properties of the agglomerate particles of boron nitride obtained through the subsequent atmospheric heating step and decarburization step. Furthermore, while conventional methods for manufacturing boron nitride generally perform the nitriding step at high temperature and for a short time from the viewpoint of improving productivity, the manufacturing method according to this disclosure includes a first nitriding step in which the nitriding step is held at a relatively low temperature and for a relatively long time. By allowing nitriding to proceed slowly under relatively mild conditions, the way cracks form in the boron carbide raw material can be controlled, suppressing a reduction in the crushing strength of the resulting lumpy particles while adjusting the tap density to be low. According to the above manufacturing method, a boron nitride powder can be prepared that contains lumpy particles with relatively high crushing strength, yet has a relatively low tap density overall. Furthermore, this boron nitride powder can be filled with high uniformity into resin molded bodies such as resin sheets, even when the filling amount is relatively low, and can impart excellent heat dissipation properties to the resin molded bodies. In addition, because the lumpy particles constituting the boron nitride powder have high crushing strength, it is possible to use high pressure during the manufacturing of resin molded bodies, which allows for more sufficient resin impregnation into the inside of the lumpy particles and the voids between the lumpy particles, thereby improving insulation properties.

[0034] The above nitriding process includes at least a first nitriding process and a second nitriding process. The first nitriding process is preferably a process of holding the material at a specific temperature in the temperature range of 1800 to 1900°C for 3 hours or more. The second nitriding process is a process of holding the material at a temperature higher than that of the first nitriding process and 2200°C or lower for 10 hours or more, but it may consist of multiple processes, or it may be a process of raising the temperature in multiple stages and holding for a predetermined time.

[0035] The final temperature reached in the nitriding process is 2200°C or lower, but may be, for example, 2150°C or lower, 2100°C or lower, 2050°C or lower, or 2000°C or lower.

[0036] The nitrogen gas concentration in the nitrogen pressurized atmosphere during the nitriding process may be, for example, 95.0% by volume or more, 98.0% by volume or more, or 99.9% by volume or more.

[0037] The lower limit of the pressure (atmospheric pressure) in the nitriding process is 0.6 MPa or higher, but may be, for example, 0.7 MPa or higher, or 0.8 MPa or higher. By setting the lower limit of the pressure in the nitriding process within the above range, the nitriding of boron carbide can be carried out more sufficiently. The upper limit of the pressure (atmospheric pressure) in the nitriding process may be, for example, 1.0 MPa or lower, or 0.9 MPa or lower. By setting the upper limit of the pressure in the nitriding process within the above range, the increase in the manufacturing cost of boron nitride powder can be suppressed. The pressure may be adjusted within the above range, for example, 0.6 to 1.0 MPa, or 0.8 to 0.9 MPa.

[0038] The lower limit of the firing time in the nitriding process may be, for example, 6 hours or more, 8 hours or more, or 10 hours or more. The upper limit of the firing time in the nitriding process may be, for example, 30 hours or less, 25 hours or less, or 20 hours or less. The firing time in the nitriding process may be adjusted within the above ranges, for example, 6 to 30 hours, 8 to 25 hours, or 10 to 20 hours.

[0039] The upper limit of the temperature at which the material is held for three hours or more in the first nitriding step (holding temperature) may be, for example, 1850°C or less, or 1825°C or less. By keeping the upper limit of the holding temperature within the above range, the tap density of the resulting boron nitride powder can be further reduced. The lower limit of the holding temperature in the first nitriding step may be, for example, 1810°C or higher, or 1820°C or higher. By keeping the lower limit of the holding temperature within the above range, insufficient nitriding can be more effectively suppressed.

[0040] The heating temperature in the second nitriding step can be higher than the heating temperature in the first nitriding step and 2200°C or lower. For example, if the heating temperature in the first nitriding step is 1800°C, the heating temperature in the second nitriding step may be 1850°C. In this case, each temperature (for example, 1800°C and 1850°C in the above example) will be the final temperature reached.

[0041] In the firing process, the carbon content in the boron carbonitride powder can be reduced by firing the boron carbonitride powder under atmospheric pressure.

[0042] The lower limit of the firing temperature in the firing process may be, for example, 600°C or higher, 650°C or higher, or 700°C or higher. By keeping the lower limit of the firing temperature within the above range, the carbon content in the boron carbonitride can be further reduced. The upper limit of the firing temperature in the firing process may be, for example, 1000°C or lower, or 950°C or lower. By keeping the upper limit of the firing temperature within the above range, oxidation of the boron carbonitride after firing can be suppressed.

[0043] The lower limit of the firing time in the firing process may be, for example, 6 hours or more, or 7 hours or more. By keeping the lower limit of the firing time within the above range, it is possible to sufficiently reduce the carbon content in the boron carbonitride. Furthermore, by making the firing time relatively long, some of the boron atoms constituting the boron carbonitride are oxidized, generating boric acid, which further reduces the tap density of the boron nitride powder. The upper limit of the firing time in the firing process is not particularly limited, but may be, for example, 20 hours or less, or 15 hours or less. If the upper limit of the firing time is within the above range, the decrease in processing efficiency of the process can be more sufficiently suppressed. If the firing time is too short, the reduction in carbon content will be insufficient.

[0044] In the decarburization process, the boron carbonitride powder that has undergone the calcination process is mixed with a boron source and heated in a nitrogen-containing atmosphere to generate primary hexagonal boron nitride particles, thereby obtaining agglomerate particles composed of multiple aggregated primary particles.

[0045] The boron source described above may include at least one selected from the group consisting of boric acid and boron oxide.

[0046] In the decarburization process, it is preferable to keep the boron source content low. The upper limit of the boron source content may be, for example, less than 40% by mass, 35% by mass or less, 33% by mass or less, 30% by mass or less, 28% by mass or less, or 25% by mass or less, based on the total amount of the boron carbonitride powder and the boron source. By setting the upper limit of the boron source content within the above range, the amount of liquid phase, which is the growth field for the primary particles of boron nitride, can be reduced. As a result, excessive growth of the primary particles can be suppressed, and boron nitride containing bulk particles with superior crushing strength can be produced. The lower limit of the boron source content may be, for example, 15% by mass or more, 18% by mass or more, or 20% by mass or more, based on the total amount of the boron carbonitride powder and the boron source. By setting the lower limit of the boron source content within the above range, the crystallinity of boron nitride can be further improved, and primary particles of hexagonal boron nitride with superior purity can be obtained. The content of the boron source may be adjusted within the range described above, and may be, for example, 15-40% by mass, 15-28% by mass, or 18-25% by mass, based on the total amount of the boron carbonitride powder and the boron source.

[0047] The lower limit of the firing temperature in the decarburization process may be, for example, 1900°C or higher, or 2000°C or higher. By setting the lower limit of the firing temperature within the above range, the crystallinity of the primary particles of hexagonal boron nitride can be more sufficiently improved. The upper limit of the firing temperature in the decarburization process may be, for example, 2200°C or lower, or 2150°C or lower. By setting the upper limit of the firing temperature within the above range, the yellowing of the resulting boron nitride powder can be suppressed. The firing temperature in the decarburization process may be adjusted within the above range, for example, 1900 to 2200°C, or 2000 to 2150°C. It is preferable that the firing temperature in the decarburization process is lower than the firing temperature of the boron carbide powder in the nitriding process.

[0048] The pressure (ambient pressure) in the decarburization process may be normal pressure or pressure above atmospheric pressure. The pressure in the decarburization process may be, for example, 0.1 to 0.5 MPa, 0.1 to 0.3 MPa, or 0.1 to 0.2 MPa, or atmospheric pressure (0.1 MPa).

[0049] The lower limit of the firing time in the decarburization process may be, for example, 1 hour or more, 2 hours or more, or 3 hours or more. By setting the lower limit of the firing time within the above range, particle growth can be sufficiently advanced. The upper limit of the firing time in the crystallization process may be, for example, 40 hours or less, 30 hours or less, 20 hours or less, or 10 hours or less. By setting the upper limit of the firing time within the above range, an increase in manufacturing costs can be suppressed. The firing time may be adjusted within the above range, for example, 1 to 40 hours, or 2 to 30 hours.

[0050] The method for producing boron nitride powder may include other steps. These other steps may include, for example, a grinding step and a classification step. For example, in the method for producing boron nitride powder, a grinding step may be performed after the crystallization step. In the grinding step, a general-purpose grinder or crusher can be used. For example, a ball mill, vibration mill, jet mill, etc., can be used. In this specification, "grinding" also includes "crushing."

[0051] The boron nitride powder according to this disclosure has a relatively low tap density and high crushing strength of the clumpy particles contained in the powder. Therefore, it exhibits excellent thermal conductivity improvement when kneaded and used in resins and the like in regions with low filler content, and can be suitably used as a heat dissipation filler. Furthermore, resin molded articles (e.g., heat dissipation sheets, etc.) formed using a resin composition containing the above boron nitride powder can be expected to have excellent heat dissipation properties.

[0052] One embodiment of the resin composition contains a resin and the boron nitride powder described above.

[0053] Examples of resins include liquid crystal polymers, fluororesins, silicone resins, silicone rubber, acrylic resins, polyolefins (such as polyethylene), epoxy resins, phenolic resins, melamine resins, urea resins, unsaturated polyesters, polyimides, polyamideimides, polyetherimides, polybutylene terephthalate, polyethylene terephthalate, polyphenylene ether, polyphenylene sulfide, fully aromatic polyesters, polysulfones, polyethersulfones, polycarbonates, maleimide-modified resins, ABS (acrylonitrile-butadiene-styrene) resins, AAS (acrylonitrile-acrylic rubber-styrene) resins, and AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resins.

[0054] The lower limit of the resin content may be, for example, 70% by volume or more, 75% by volume or more, or 80% by volume or more, based on the total volume of the resin composition. Having the lower limit of the resin content within this range can more effectively suppress a decrease in the moldability of the resin composition. The upper limit of the resin content may be, for example, 90% by volume or less, 85% by volume or less, or 82% by volume or less, based on the total volume of the resin composition. Having the upper limit of the resin content within this range can further improve the thermal conductivity of the resin composition.

[0055] The resin composition of this disclosure uses the above-mentioned boron nitride powder, and therefore has an excellent effect in improving the thermal conductivity of heat dissipation sheets when heat dissipation sheets are prepared with a small amount of addition. The upper limit of the boron nitride powder content may be, for example, 30% by volume or less, 25% by volume or less, or 20% by volume or less, based on the total volume of the resin composition. By keeping the upper limit of the boron nitride powder content within the above range, a decrease in the moldability of the resin composition can be suppressed. The lower limit of the boron nitride powder content may be, for example, 10% by volume or more, 15% by volume or more, or 18% by volume or more, based on the total volume of the resin composition. By keeping the lower limit of the boron nitride powder content within the above range, the thermal conductivity of the resin composition can be improved, and a resin molded article with excellent heat dissipation properties can be obtained. The boron nitride powder content may be adjusted within the above range, and may be, for example, 10 to 30% by volume or 15 to 30% by volume, based on the total volume of the resin composition.

[0056] The resin composition may further contain a curing agent for curing the resin, in addition to the resin and boron nitride powder. The curing agent can be appropriately selected depending on the type of resin. When the resin is an epoxy resin, examples of curing agents include phenol novolac compounds, acid anhydrides, amino compounds, and imidazole compounds. The lower limit of the curing agent content may be, for example, 0.5 parts by mass or more, or 1 part by mass or more, per 100 parts by mass of resin. The upper limit of the curing agent content may be, for example, 15 parts by mass or less, or 10 parts by mass or less, per 100 parts by mass of resin.

[0057] The above resin composition can be used after molding, curing, etc. One embodiment of the resin molded article contains a resin and the above-mentioned boron nitride powder. The resin molded article may be a cured product of the resin composition. The shape of the resin molded article is not particularly limited and may be in the form of a block, a sheet, or a film. In the case of a sheet-shaped cured product (sheet), the thickness of the sheet may be, for example, 0.5 mm or less, 0.2 mm or less, or 0.1 mm or less. Since the above-mentioned resin molded article contains the above-mentioned boron nitride, it is useful for, for example, a heat dissipation member. The sheet-shaped resin molded article may be, for example, a heat dissipation sheet.

[0058] Figure 1 is a schematic cross-sectional view showing an example of a heat dissipation sheet. Figure 1(a) shows a heat dissipation sheet (an example of a sheet-like cured product) 100 according to the present disclosure, which consists of a heat dissipation filler 20 and a cured resin 30 (resin). When the boron nitride powder according to the present disclosure is used, the heat dissipation filler 20 (lump particles) has a low density, so compared to when it is filled to have the same mass as conventional high-density lump particles, the primary particles of hexagonal boron nitride can be arranged relatively uniformly throughout the heat dissipation sheet. For example, Figure 1(b) shows an image of a heat dissipation sheet 500 when a sheet is constructed using a high-density aggregate of hexagonal boron nitride primary particles known as a heat dissipation filler (conventional heat dissipation filler 50), and the proportion of boron nitride in the entire sheet is the same as that of the heat dissipation sheet 100. As shown in Figures 1(a) and (b), by using dense, lumpy particles of hexagonal boron nitride primary particles as the heat dissipation filler, it is possible to further suppress the uneven distribution of the heat dissipation filler across the entire sheet. This allows for the expected improvement in the thermal conductivity of the heat dissipation sheet, even with relatively small amounts of heat dissipation filler. Furthermore, since the amount of filler itself can be kept low, it is possible to prevent the heat dissipation sheet from becoming rigid, making it useful, for example, as a heat dissipation sheet used in the manufacture of flexible substrates.

[0059] Although several embodiments have been described above, this disclosure is not limited in any way to the embodiments described above. Furthermore, the descriptions of the embodiments described above are applicable to each other. [Examples]

[0060] The contents of this disclosure will be described in more detail below with reference to examples and comparative examples. However, this disclosure is not limited to the following examples.

[0061] (Example 1) [Preparation of boron carbide powder] 100 parts by mass of orthoboric acid (manufactured by Nippon Denko Co., Ltd., hereinafter simply referred to as "boric acid") and 35 parts by mass of acetylene black (HS100, manufactured by Denka Co., Ltd.) were mixed using a Henschel mixer and then packed into a graphite crucible. This graphite crucible was placed in an arc furnace and heated at 2200°C for 5 hours in an argon atmosphere to synthesize a lump of boron carbide (B4C) powder. The synthesized lump of boron carbide powder was pulverized in a ball mill for 1 hour and classified using a sieve with a mesh size of 63 μm. The boron carbide powder obtained below the sieve was further washed with an aqueous nitric acid solution to remove impurities such as iron, and then filtered and dried to produce boron carbide powder (B4C powder) with an average particle size of 15 μm.

[0062] [Preparation of boron carbonitride powder] The prepared boron carbide powder was packed into a boron nitride crucible. Using a resistance heating furnace, under a nitrogen gas atmosphere of 0.85 MPa, the temperature was first raised to 1850°C and held at this temperature for 6 hours (first nitriding step). Next, the temperature was raised to 2000°C and held at this temperature for 12 hours to obtain boron carbonitride (B4CN4) powder (second nitriding step).

[0063] The obtained boron carbonitride powder was placed in a muffle furnace and heated at 700°C for 5 hours in an atmospheric environment (calcination process) to obtain a heat-treated product.

[0064] [Preparation of boron nitride powder] To 100 parts by mass of the above heat-treated material, boric acid was added so that the content of boron source boric acid was 30 parts by mass, and the mixture was mixed using a Henschel mixer to obtain a mixture. The mixture was packed into a boron nitride crucible and decarburized by heating in a resistance heating furnace to synthesize boron nitride powder containing aggregated particles formed by the aggregation of primary particles (decarburization process). The conditions for the decarburization process were a nitrogen gas atmosphere at a pressure of 13 kPa, heating from room temperature to 2000°C, and holding at that temperature for 5 hours. The synthesized boron nitride powder was crushed in a mortar for 10 minutes, and then classified using a nylon sieve with a mesh size of 75 μm. For reference, a scanning electron microscope image showing the appearance of the obtained boron nitride powder is shown in Figure 2.

[0065] (Example 2) Boron nitride powder was prepared in the same manner as in Example 1, except that the holding time in the first nitriding step was changed to 3 hours.

[0066] (Example 3) Boron nitride powder was prepared in the same manner as in Example 1, except that the holding temperature in the first nitriding step was changed to 1800°C.

[0067] (Example 4) Boron nitride powder was prepared in the same manner as in Example 1, except that the holding temperature in the first nitriding step was changed to 1900°C.

[0068] (Comparative Example 1) Boron nitride powder was prepared in the same manner as in Example 1, except that the second nitriding step was omitted and the holding temperature in the first nitriding step was changed to 2000°C and the holding time to 18 hours.

[0069] (Comparative Example 2) Boron nitride powder was prepared in the same manner as in Example 1, except that the second nitriding step was omitted and the holding temperature in the first nitriding step was changed to 2100°C and the holding time to 15 hours.

[0070] (Comparative Example 3) Boron nitride powder was prepared in the same manner as in Example 1, except that the holding temperature in the first nitriding step was changed to 1600°C and the holding time to 20 hours, and the holding temperature in the second nitriding step was changed to 2000°C and the holding time to 20 hours.

[0071] (Comparative Example 4) Boron nitride powder was prepared in the same manner as in Example 1, except that a second nitriding step was omitted and the holding temperature in the first nitriding step was changed to 1850°C and the holding time to 60 hours.

[0072] <Evaluation of the properties of boron nitride powder> For the boron nitride powders prepared in Examples 1-4 and Comparative Examples 1-4, the crushing strength of the aggregate particles, the tap density of the powder, the orientation index, the average particle size, and the BET specific surface area were measured using the following methods. The results are shown in Tables 1 and 2.

[0073] [Crushing strength of agglomerate particles] Crushing strength was measured in accordance with JIS R 1639-5:2007 "Fine ceramics - Method for measuring granular properties - Part 5: Single granular crushing strength". Measurements were performed on 20 or more lumpy particles, and the value was calculated at a cumulative fracture rate of 63.2%. A microcompression tester ("MCT-W500" (product name) manufactured by Shimadzu Corporation) was used for the measurements.

[0074] [Powder tap density] The tap density was determined in accordance with the method described in JIS R 1628:1997 "Method for Measuring the Bulk Density of Fine Ceramic Powders". Specifically, boron nitride powder was subjected to a 100 cm³ test. 3 The material was filled into a dedicated container, and after tapping under the conditions of a tapping time of 180 seconds, 180 taps, and a tap lift of 18 mm, the bulk density was measured, and the obtained value was defined as the tap density. A "powder tester" (product name) manufactured by Hosokawa Micron was used for the measurement.

[0075] [Powder orientation index] First, the X-ray diffraction spectrum of the boron nitride powder was obtained by performing X-ray diffraction measurements on the powder. Then, the peak intensities I(002) and I(100) corresponding to the (002) and (100) planes were obtained from the X-ray diffraction spectrum. Using the obtained peak intensities, the orientation index [I(002) / I(100)] of the boron nitride powder was calculated. The X-ray diffractometer used was "ULTIMA-IV" (product name) manufactured by Rigaku Corporation.

[0076] [Average particle size of powder] The average particle size was defined as the particle size (D50) at which the cumulative value of the volume-based cumulative particle size distribution obtained by laser diffraction scattering for boron nitride powder reached 50%. The laser diffraction scattering method was performed in accordance with the method described in JIS Z 8825:2013 "Particle size analysis - Laser diffraction and scattering method". A laser diffraction scattering particle size distribution analyzer (Beckman Coulter "LS-13 320" (product name)) was used for the measurement. The measurement was performed without homogenizing, in the presence of clumpy particles.

[0077] [BET specific surface area] The BET specific surface area was calculated using the BET single-point method with nitrogen gas, in accordance with the description in JIS Z 8830:2013 "Method for measuring the specific surface area of ​​powders (solids) by gas adsorption," using a specific surface area measuring device. The specific surface area measuring device used was the "MONOSORB MS-22" (product name) manufactured by QUANTACHROME.

[0078] <Evaluation of boron nitride powder as a heat dissipation filler> The heat dissipation and insulation properties of resin sheets prepared using the boron nitride powder prepared in Examples 1-4 and Comparative Examples 1-4 as heat dissipation fillers were evaluated as follows. The results are shown in Tables 1 and 2.

[0079] [Preparation of evaluation sheet] A resin composition was obtained by mixing 100 parts by mass of naphthalene-type epoxy resin (DIC Corporation, HP4032) with 10 parts by mass of an imidazole compound (Shikoku Chemicals Co., Ltd., 2E4MZ-CN) as a curing agent, and then adding boron nitride powder to a mixture that amounted to 20% by volume. A mixing machine manufactured by Shinki Co., Ltd. was used for kneading the resin. The kneading conditions were 1600 rpm for 3 minutes. The obtained resin composition was applied to a PET film to a thickness of 0.3 mm. Afterward, it was subjected to curing at a temperature of 150°C and a load of 50 kgf / cm². 2 A 0.3 mm thick resin sheet (evaluation sheet) was prepared by heating and pressurizing under relatively mild conditions for 60 minutes.

[0080] [Measurement of thermal conductivity and evaluation of heat dissipation] The thermal conductivity was measured using the evaluation sheet described above. Thermal conductivity H (unit: W / (m·K)) is defined as thermal diffusivity A (unit: m 2 ( / second), density B (unit: kg / m³) 3 The thermal diffusivity A was calculated from the values ​​of the thermal density B and specific heat capacity C (unit: J / (kg·K)) based on the formula H = A × B × C. The thermal diffusivity A was determined by processing an evaluation sheet to a length: 10 mm, width: 10 mm, and thickness: 0.3 mm and using the laser flash method. The measurement device used was a xenon flash analyzer (NETZSCH, product name: LFA447NanoFlash). The density B was determined using the Archimedes method. The specific heat capacity C was determined using a DSC (Rigaku Corporation, product name: ThermoPlusEvoDSC8230). From the results, the heat dissipation performance was evaluated according to the following criteria. A: The thermal conductivity is 7.0 W / mK or higher. B: The thermal conductivity is 6.5 W / mK or higher and less than 7.0 W / mK. C: The thermal conductivity is 6.0 W / mK or higher and less than 6.5 W / mK. D: The thermal conductivity is 5.5 W / mK or higher and less than 6.0 W / mK. E: The thermal conductivity is 5.0 W / mK or higher and less than 5.5 W / mK. F: Thermal conductivity is less than 5.0 W / mK.

[0081] [Measurement of dielectric breakdown voltage and evaluation of insulation properties] The dielectric breakdown voltage was measured for the evaluation sheets described above. The dielectric breakdown voltage of the obtained evaluation sheets was measured using a withstand voltage tester (manufactured by Kikusui Electronics Co., Ltd., device name: TOS-8650) in accordance with the description in JIS C 6481-1996 "Test Method for Copper-Clad Laminates for Printed Wiring Boards". The insulation properties were evaluated based on the following criteria from the measurement results. A: The dielectric breakdown voltage is 40kV / mm or higher. B: The dielectric breakdown voltage is 35kV / mm or more and less than 40kV / mm. C: The dielectric breakdown voltage is 30kV / mm or more and less than 35kV / mm. D: The dielectric breakdown voltage is 25kV / mm or more and less than 30kV / mm. E: The dielectric breakdown voltage is less than 25kV / mm.

[0082] [Table 1]

[0083] [Table 2] [Industrial applicability]

[0084] According to this disclosure, it is possible to provide boron nitride powder that can impart heat dissipation properties to a resin sheet even when the filling amount is low. According to this disclosure, it is also possible to provide a method for producing the boron nitride powder described above. [Explanation of Symbols]

[0085] 20... Heat dissipation filler, 30... Curing resin, 50... Conventional heat dissipation filler, 100, 500... Heat dissipation sheet.

Claims

1. It contains agglomerate particles composed of multiple aggregates of hexagonal boron nitride primary particles, with a crushing strength of 10.0 MPa or more. Tap density is 0.50–0.66 g / cm³ ３ This is boron nitride powder.

2. The boron nitride powder according to claim 1, wherein the orientation index is 10.0 or less.

3. The boron nitride powder according to claim 1 or 2, wherein the average particle size is 30.0 to 90.0 μm.

4. BET specific surface area is 10.0 m² ２ Boron nitride powder according to claim 1 or 2, wherein the amount is less than or equal to / g.

5. A nitriding step to obtain boron carbonitride powder by calcining boron carbide powder at 1800 to 2200°C under a nitrogen pressurized atmosphere of 0.60 MPa or higher, A firing step in which the boron carbonitride powder is fired in the atmosphere, The process includes a decarburization step, in which the boron carbonitride powder that has undergone a calcination process is mixed with a boron source and heated in a nitrogen-containing atmosphere to generate primary particles of hexagonal boron nitride, thereby obtaining a lump-like particle composed of multiple aggregated primary particles. The nitriding process is as follows: The first nitriding process involves holding the temperature at 1800-1900°C for more than 3 hours, A second nitriding step involves holding the temperature at a temperature higher than the first nitriding step, but below 2200°C, for more than 10 hours. A method for producing boron nitride powder, including [the specified substance].

6. A resin molded article comprising the boron nitride powder according to claim 1 or 2 and a resin.

7. The resin molded article according to claim 6, wherein the content of the boron nitride powder is 30% by volume or less.

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