Method for producing modified hexagonal boron nitride powder and modified hexagonal boron nitride powder

Abstract

To provide a method for producing hexagonal boron nitride powder in which a hexagonal boron nitride powder is effectively reacted with a surface treatment agent.SOLUTION: Provided is a method for producing modified hexagonal boron nitride powder, and includes a heating step of heating hexagonal boron nitride powder at a temperature of 1300°C or higher and 2200°C or lower in a nitrogen atmosphere, and a second surface treatment step of contacting the re-calcination hexagonal boron nitride powder after the heating step with a surface treatment agent having a conjugated double bond.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing modified hexagonal boron nitride powder and to modified hexagonal boron nitride powder. [Background technology]

[0002] In recent years, as electronic components have become smaller and more powerful, the amount of heat generated by them has become an issue. Therefore, materials with excellent thermal conductivity are being developed to efficiently dissipate heat from electronic components.

[0003] Hexagonal boron nitride powder can be blended with resins used in electronic components to improve the thermal conductivity of the resin. Surface treatment of this hexagonal boron nitride powder with a surface treatment agent can sometimes improve its physical properties, such as thermal conductivity and fillability into resin. For example, Patent Document 1 discloses a composition for forming a thermally conductive material that contains boron nitride, a resin binder or its precursor, and a compound that functions as a surface modifier. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-98800 Summary of the Invention [Problem to be solved by the invention]

[0005] However, hexagonal boron nitride powder has a poor functionality with which surface treatment agents can react, making it difficult to effectively treat the surface of the powder.

[0006] An object of one aspect of the present invention is to provide a method for effectively reacting a surface treatment agent with hexagonal boron nitride powder. [Means for solving the problem]

[0007] In order to solve the above problems, a method for producing a modified hexagonal boron nitride powder according to one embodiment of the present invention includes a heating step of heating hexagonal boron nitride powder at a temperature of 1300 to 2200°C in a nitrogen atmosphere, and a second surface treatment step of contacting the re-fired hexagonal boron nitride powder after the heating step with a second surface treatment agent having a conjugated double bond.

[0008] In the method for producing a modified hexagonal boron nitride powder according to one aspect of the present invention, the re-fired hexagonal boron nitride powder may have an O (oxygen) content of 0.3 mass % or less.

[0009] In the method for producing a modified hexagonal boron nitride powder according to one aspect of the present invention, the re-fired hexagonal boron nitride powder may have a graphitization index, which indicates crystallinity, of 1.0 to 2.5.

[0010] In the method for producing a modified hexagonal boron nitride powder according to one aspect of the present invention, the second surface treatment agent may be an aromatic compound.

[0011] In the method for producing a modified hexagonal boron nitride powder according to one aspect of the present invention, the second surface treatment agent may be a compound containing a six-membered ring structure.

[0012] In one embodiment of the present invention, a method for producing a modified hexagonal boron nitride powder is carried out at an absolute humidity of 15 g / m from the heating step to the second surface treatment step. 3 It may be executed under the following circumstances:

[0013] In the method for producing a modified hexagonal boron nitride powder according to one aspect of the present invention, the heating step may involve heating at the temperature for 30 minutes or more and less than 10 hours.

[0014] In order to solve the above problems, the modified hexagonal boron nitride powder according to one embodiment of the present invention has a graphitization index indicating crystallinity of 1.0 to 2.5, and carries a second surface treatment agent having conjugated double bonds on its surface.

[0015] The modified hexagonal boron nitride powder according to one aspect of the present invention may have an O (oxygen) content of 0.3 mass % or less.

[0016] The modified hexagonal boron nitride powder according to one aspect of the present invention may have a C (carbon) content of 0.02 mass % or more. [Effects of the Invention]

[0017] According to one aspect of the present invention, there is provided a method for effectively reacting a surface treatment agent with hexagonal boron nitride powder. It is possible to realize laws, etc. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 shows the results of UV-Vis absorption spectrum measurements of samples containing Unipac extract. [Figure 2] FIG. 1 shows the results of measuring the UV-Vis absorption spectrum of EtOH. DETAILED DESCRIPTION OF THE INVENTION

[0019] [Embodiment 1] Hereinafter, one embodiment of the present invention will be described in detail.

[0020] (Method for manufacturing modified hexagonal boron nitride powder) The method for producing a modified hexagonal boron nitride powder according to this embodiment includes a heating step of heating hexagonal boron nitride powder, and a first surface treatment step of contacting the re-fired hexagonal boron nitride powder obtained after the heating step with a first surface treatment agent.

[0021] The present inventors have conducted extensive research into the surface modification of hexagonal boron nitride powder, and as a result have succeeded in obtaining a new finding. Specifically, they independently discovered that by heating hexagonal boron nitride powder within a specific range of temperature and absolute humidity, the surface of the powder is activated and placed in a state that is prone to react with a surface treatment agent. They also independently discovered that by surface treating hexagonal boron nitride powder that is prone to react with a surface treatment agent within a specific range of absolute humidity, the surface treatment agent can be made to react effectively with the hexagonal boron nitride powder.

[0022] In this specification, the term "re-fired hexagonal boron nitride powder" is intended to mean hexagonal boron nitride powder obtained by heating (such as reduction nitridation) to obtain hexagonal boron nitride powder and by heating in the heating step described below (to improve the water repellency of the powder surface). Also, in this specification, the term "modified hexagonal boron nitride powder" is intended to mean re-fired hexagonal boron nitride powder whose surface has been modified.

[0023] <Hexagonal boron nitride powder> Hexagonal boron nitride powder can be produced by known methods. Examples of methods for producing hexagonal boron nitride powder include a reduction-nitridation method in which an oxygen-containing boron compound is reacted at high temperature, and a melamine method in which melamine borate is thermally decomposed. Production of hexagonal boron nitride powder by the reduction-nitridation method is preferred because it significantly exhibits the effects of the method for producing modified hexagonal boron nitride powder according to this embodiment (hereinafter referred to as the "production method according to embodiment 1") and because it reduces costs. The production of hexagonal boron nitride powder by the reduction-nitridation method is described below.

[0024] <Production of hexagonal boron nitride powder by reduction nitridation method> In the reduction nitridation method, a raw material powder mixture is generally obtained by mixing an oxygen-containing boron compound with an auxiliary agent. The raw material powder mixture is then heated in a nitrogen atmosphere to efficiently obtain nitrided powder. By-products and impurities are then removed from the nitrided powder to obtain hexagonal boron nitride powder.

[0025] Examples of oxygen-containing boron compounds used as boron sources include boric acid, boron trioxide, diboron dioxide, tetraboron trioxide, boric anhydride, metaboric acid, perboric acid, hypoboric acid, sodium tetraborate, sodium perborate, etc. Boric acid or boron oxide is preferably used because of its easy availability.

[0026] Examples of the auxiliary agent include a carbon source and an oxygen-containing alkaline earth metal compound. Examples of the carbon source include carbon black, activated carbon, nanocarbon, boron carbide, etc. Carbon black is preferably used in terms of cost reduction, etc. Examples of the oxygen-containing alkaline earth metal compound include magnesium oxide, calcium oxide, magnesium carbonate, calcium carbonate, magnesium bicarbonate, calcium bicarbonate, magnesium hydroxide, calcium hydroxide, magnesium nitrate, calcium nitrate, magnesium sulfate, calcium sulfate, magnesium phosphate, calcium phosphate, magnesium oxalate, calcium oxalate, etc. One type of oxygen-containing alkaline earth metal compound may be used, or two or more types may be used.

[0027] As an example of a method for mixing the oxygen-containing boron compound and the auxiliary (carbon source and oxygen-containing alkaline earth metal compound), they may be mixed using a general mixer such as a vibration mill, a bead mill, a ball mill, or a mixer.

[0028] The heating temperature of the raw material mixed powder in a nitrogen atmosphere is preferably 1500°C or higher, and more preferably 1800°C or higher, in order to reduce the generation of amorphous boron nitride powder and easily obtain hexagonal boron nitride powder. The heating temperature is also preferably 2000°C or lower. The heating time is usually 0.5 hours or longer and 12 hours or shorter, and preferably 1 hour or longer and 8 hours or shorter.

[0029] The nitride powder obtained by heating the raw material mixed powder can be washed with an acid to remove impurities such as by-products and unreacted materials. Examples of such acids include hydrochloric acid, nitric acid, sulfuric acid, and acetic acid. The method of washing with an acid is not particularly limited as long as it can remove by-products and impurities. For example, the nitride powder can be washed by mixing 50 to 200 parts by mass of concentrated hydrochloric acid (37% HCl aqueous solution) and 200 to 500 parts by mass of pure water per 100 parts by mass of nitride powder, and stirring the mixture for 6 hours or more.

[0030] After washing with acid, the nitride powder is washed with pure water to remove the acid remaining in the nitride powder, and then the pure water is removed by drying. The drying temperature may be 50° C. or higher and 250° C. or lower. The drying may be performed in the air or under reduced pressure.

[0031] The hexagonal boron nitride powder obtained by the reduction-nitridation method may be subjected to treatments such as pulverization, crushing, and classification, if necessary, before being subjected to the heating step described below.

[0032] [Heating process] In the heating step, the hexagonal boron nitride powder is heated in a nitrogen atmosphere at a temperature of 1300° C. to 2200° C. This heating step can improve the water repellency and crystallinity of the hexagonal boron nitride powder after the heating step (re-fired hexagonal boron nitride powder).

[0033] The heating step can be carried out, for example, by supplying hexagonal boron nitride powder to a furnace such as a heating furnace and carrying out the heating step under a nitrogen atmosphere. Known heating furnaces capable of controlling the reaction atmosphere and absolute humidity can be used as the heating furnace. For example, an atmosphere-controlled high-temperature furnace that performs heat treatment by high-frequency induction heating or heater heating can be used. Continuous furnaces such as batch furnaces, pusher-type tunnel furnaces, and vertical reactors can also be used as the heating furnace.

[0034] Examples of gases introduced into the heating furnace include nitrogen gas and ammonia gas. A mixture of nitrogen gas or ammonia gas with a non-oxidizing gas such as hydrogen, argon, or helium may also be used. Nitrogen gas is preferred as the gas introduced into the heating furnace. Furthermore, nitrogen gas with a controlled dew point is preferred, with the dew point being -85°C or lower.

[0035] The heating temperature in the heating step is 1300°C or higher and 2200°C or lower. If the heating temperature is lower than 1300°C, hydrophilic functional groups such as amino groups and hydroxy groups present on the surface of the hexagonal boron nitride powder may not be sufficiently removed. If the heating temperature is higher than 2200°C, the re-fired hexagonal boron nitride powder may decompose or turn yellow.

[0036] In order to more effectively react the surface treatment agent in the surface treatment step (first surface treatment step or second surface treatment step) described below, the lower limit of the heating temperature in the heating step is preferably 1400° C. or higher, and more preferably 1600° C. or lower. In terms of equipment costs, etc., the upper limit of the heating temperature is preferably 2000° C. or lower, and more preferably 1900° C. or lower.

[0037] The heating time in the heating step can be appropriately selected depending on the conditions of the nitrogen atmosphere and the heating temperature. In order to allow the surface treatment agent to react more effectively in the surface treatment step described below, the lower limit of the heating time is preferably 30 minutes or more, more preferably 1 hour or more, and even more preferably 2 hours or more. In terms of equipment costs, etc., the upper limit of the heating time is preferably less than 10 hours, more preferably 8 hours or less, and even more preferably 6 hours or less.

[0038] The re-fired hexagonal boron nitride powder obtained in the heating step is subjected to a first surface treatment step in which it is contacted with a first surface treatment agent and / or a second surface treatment step in which it is contacted with a second surface treatment agent. Hereinafter, the first surface treatment step will be described in this embodiment, and the second surface treatment step will be described in the following embodiment 2.

[0039] [First surface treatment process] In the first surface treatment step, the re-fired hexagonal boron nitride powder obtained in the heating step is brought into contact with a first surface treatment agent.

[0040] In the manufacturing method according to the first embodiment, the absolute humidity is 15 g / m 3 The heating step and the first surface treatment step are carried out under the following conditions: absolute humidity 15 g / m 3 When the heating step and the first surface treatment step are carried out in an environment of above absolute humidity 15 g / m, the re-fired hexagonal boron nitride powder reacts with water and is easily hydrolyzed. This hydrolysis makes it difficult for the first surface treatment agent to react with the re-fired hexagonal boron nitride powder. 3 By carrying out the heating step and the first surface treatment step under the following conditions, the re-fired hexagonal boron nitride powder with activated surfaces (particularly end faces) can be effectively reacted with the first surface treatment agent. The absolute humidity can be measured using a known absolute humidity sensor or the like.

[0041] In order to more effectively react the re-fired hexagonal boron nitride powder with the first surface treatment agent, the absolute humidity is set to 12 g / m 3 Preferably, it is 10 g / m or less. 3 More preferably, it is 7 g / m or less. 3 More preferably, it is 5 g / m or less. 3 Even more preferably, it is 2 g / m or less. 3 It is particularly preferable that 3 It is most preferable that:

[0042] The first surface treatment agent used in the first surface treatment step can be a known surface treatment agent used in the surface treatment of hexagonal boron nitride powder. In the manufacturing method according to the first embodiment, the heating step and the first surface treatment step are performed under controlled absolute humidity and moisture content. Therefore, the first surface treatment agent is preferably a silane coupling agent, more preferably a silane coupling agent having a reactive functional group or hexamethyldisilane. Examples of the reactive functional group include a phenyl group, a vinyl group, an epoxy group, a (meth)acrylic group, an amino group, a ureido group, a mercapto group, an isocyanate group, etc.

[0043] The amount of the first surface treatment agent brought into contact with the re-fired hexagonal boron nitride powder may be adjusted to be 0.01% by mass or more and 3% by mass or less relative to the total amount of the re-fired hexagonal boron nitride powder.

[0044] The re-fired hexagonal boron nitride powder and the first surface treatment agent can be brought into contact with each other by a known method. For example, the re-fired hexagonal boron nitride powder and the first surface treatment agent are mixed together, so that the first surface treatment agent comes into contact with the surface of the re-fired hexagonal boron nitride powder.

[0045] In the first surface treatment step, the lower limit of the temperature of the re-fired hexagonal boron nitride powder is preferably 25° C. or higher, more preferably 30° C. or higher, and even more preferably 50° C. or higher. The upper limit of the temperature is preferably below the decomposition temperature of the first surface treatment agent, more preferably 150° C. or lower, and even more preferably 100° C. or lower. By adjusting the temperature of the re-fired hexagonal boron nitride powder to within the above range, the re-fired hexagonal boron nitride powder and the first surface treatment agent can react more effectively.

[0046] In the first surface treatment step, it is preferable to contact the re-fired hexagonal boron nitride powder, the temperature of which has been lowered after the heating step, with the first surface treatment agent. For example, after the heating step, the temperature of the re-fired hexagonal boron nitride powder can be lowered by flowing nitrogen gas into the heating furnace to cool the furnace. The temperature of the re-fired hexagonal boron nitride powder lowered after the heating step is preferably 25°C or lower, more preferably 20°C or lower. Lowering the temperature of the re-fired hexagonal boron nitride powder makes it less likely to react with moisture in the air when the furnace is opened to the atmosphere. Furthermore, by designing an apparatus that can perform the heating step and the first surface treatment step consecutively, the first surface treatment step can be performed without opening the heating furnace, allowing the re-fired hexagonal boron nitride powder to be surface-treated without contacting the air containing moisture.

[0047] (Modified hexagonal boron nitride powder) The modified hexagonal boron nitride powder obtained by the manufacturing method according to embodiment 1 is a modified hexagonal boron nitride powder having a C (carbon) content of 0.02% or more and carrying a first surface treatment agent on its surface (surface-treated with the first surface treatment agent). This modified hexagonal boron nitride powder (hereinafter sometimes referred to as the modified BN powder according to embodiment 1) is also included in one aspect of the present invention.

[0048] The C contained in the modified BN powder according to embodiment 1 may be derived from the first surface treatment agent used in the first surface treatment step. Therefore, modified BN powder having such a C content can be said to have the first surface treatment agent carried on its surface (i.e., to have been surface-treated with the first surface treatment agent).

[0049] As described above, the surface of the modified BN powder according to embodiment 1 reacts effectively with the first surface treatment agent. Therefore, this modified hexagonal boron nitride powder can easily improve the peel strength of, for example, a copper foil attached to a resin filled with the modified boron nitride powder. Furthermore, the interaction with the filled resin is improved, enabling high resin loading and high thermal conductivity. Furthermore, coating the surface with a hydrophobic first surface treatment agent can impart water repellency to the modified hexagonal boron nitride powder, improving the moisture resistance reliability of the resin composition.

[0050] [Embodiment 2] Other embodiments of the present invention will be described below. For the sake of convenience, the configurations described in the above embodiments will not be described again.

[0051] (Method for manufacturing modified hexagonal boron nitride powder) In the method for producing a modified hexagonal boron nitride powder according to this embodiment, a second surface treatment step is carried out instead of or in addition to the first surface treatment step of the method according to embodiment 1. Also, in the method for producing a modified hexagonal boron nitride powder according to this embodiment, the powder is heated at an absolute humidity of 15 g / m 3 It is not essential to carry out the heating step and the surface treatment step (the second surface treatment step, or the first surface treatment step and the second surface treatment step) under the following environment.

[0052] [Second surface treatment process] The second surface treatment step is a step in which the re-fired hexagonal boron nitride powder obtained after the heating step is brought into contact with a second surface treatment agent having a conjugated double bond.

[0053] After the heating process, the remaining O (oxygen) in the particles of the re-fired hexagonal boron nitride powder is replaced with N (nitrogen). Therefore, the re-fired hexagonal boron nitride powder has a lower O content in the particles compared to the hexagonal boron nitride powder before the heating process. The lower the O content of the hexagonal boron nitride powder, the closer the crystal structure is to the ideal state (higher crystallinity). A highly crystalline hexagonal boron nitride powder is one in which the B and N in the crystal structure are not replaced by vacancies or other molecules such as O, and the hexagonal boron nitride crystal structure does not have atomic defects. Furthermore, the lower the O content of the hexagonal boron nitride powder, the fewer adsorbed molecules such as water molecules there are on the surface.

[0054] It is known that the more the crystal structure of a monolayer of hexagonal boron nitride deviates from the ideal state, the more easily it adsorbs carbon dioxide or water molecules (Beilstein J. Nanotechnol. 2019, 10, 540-548; Catalysis Today, 2011, 175, 271-275). The closer the crystal structure of hexagonal boron nitride powder is to the ideal state, the fewer structures there are that inhibit the bonding of the second surface treatment agent to the surface, making it easier for the second surface treatment agent to bond with it. The second surface treatment agent will be discussed later.

[0055] From the viewpoint of bonding with the second surface treatment agent, the re-fired hexagonal boron nitride powder preferably has an O content of 0.3 mass% or less, more preferably 0.25 mass% or less, more preferably 0.2 mass% or less, more preferably 0.15 mass% or less, and even more preferably 0.1 mass% or less.

[0056] The state of hexagonal boron nitride powder can be expressed by the graphite index (GI). The GI is calculated by dividing the sum of the peak areas originating from the (100) and (101) planes in the X-ray diffraction spectrum by the peak area originating from the (102) plane. The higher the crystallinity, the lower the GI. Fully crystallized (graphitized) hexagonal boron nitride powder has a GI of 1.6, but in the case of hexagonal boron nitride powder with high crystallinity and fully grown particles, the GI can be even lower depending on the orientation of the powder.

[0057] From the viewpoint of bonding strength with the second surface treatment agent, the re-fired hexagonal boron nitride powder preferably has a GI value of 1.0 to 2.5, more preferably 1.3 to 2.0, even more preferably 1.4 to 1.8, even more preferably 1.5 to 1.7, and most preferably 1.6.

[0058] It has been difficult to consistently obtain such highly crystalline hexagonal boron nitride powder in the past. The present inventors have uniquely and novelly discovered that a re-fired hexagonal boron nitride powder immediately after a heating step is performed on hexagonal boron nitride powder has the above-mentioned O content and GI value, and is in a highly crystalline state. The second surface treatment step in the method for producing a modified hexagonal boron nitride powder according to this embodiment is a step in which the re-fired hexagonal boron nitride powder after the heating step is brought into contact with a second surface treatment agent.

[0059] The second surface treatment agent is not particularly limited as long as it is a compound having a conjugated double bond, but is preferably, for example, an aromatic compound or a compound having a six-membered ring structure, such as benzene, biphenyl, triphenylene, anthracene, indole, purine, quinoline, isoquinoline, and chromene.

[0060] Although there are no particular limitations on such second surface treatment agents, it is believed that they bond well to the surface of the re-fired hexagonal boron nitride powder due to π-π interactions that occur between at least the conjugated double bond moieties and the surface of the re-fired hexagonal boron nitride powder. As mentioned above, it is believed that the higher the crystallinity of the re-fired hexagonal boron nitride powder, i.e., the closer the GI value is to 1.6, the more easily the second surface treatment agent will bond to the surface of the re-fired hexagonal boron nitride powder. Note that the term "bonding" does not refer to a specific bonding mode, but rather encompasses all bonding modes that can occur between the second surface treatment agent and the re-fired hexagonal boron nitride powder, including chemical adsorption via π-π interactions.

[0061] The modified hexagonal boron nitride powder obtained by the manufacturing method according to this embodiment is a hexagonal boron nitride powder whose surface has been modified with a second surface treatment agent. Such modified hexagonal boron nitride powder has excellent interaction with resins. Therefore, the modified hexagonal boron nitride powder easily interacts with resins. Therefore, the modified hexagonal boron nitride powder can easily improve the peel strength of, for example, a copper foil attached to a resin filled with the modified boron nitride powder. Furthermore, the interaction with the filled resin is improved, enabling high resin filling and high thermal conductivity. Furthermore, coating the surface with a hydrophobic second surface treatment agent can impart water repellency to the modified hexagonal boron nitride powder, improving the moisture resistance reliability of the resin composition.

[0062] The modified hexagonal boron nitride powder preferably has a C content of 0.02 mass% or more. The C contained in the modified hexagonal boron nitride powder may be derived from the second surface treatment agent. Therefore, modified hexagonal boron nitride powder having such a C content can be said to have been surface-treated with the second surface treatment agent.

[0063] In this embodiment, the heating step to the second surface treatment step are carried out at an absolute humidity of 15 g / m 3 It is preferable to carry out the process under the following conditions: The environment in which the heating process through the second surface treatment process are carried out is an absolute humidity of 12 g / m 3More preferably, it is 10 g / m or less. 3 More preferably, it is 7 g / m or less. 3 More preferably, it is 5 g / m or less. 3 More preferably, it is 2 g / m or less. 3 It is particularly preferable that 3 It is most preferable that:

[0064] As mentioned above, the re-fired hexagonal boron nitride powder after the heating step has a low O content, and therefore a GI value close to 1.6. However, when the re-fired hexagonal boron nitride powder comes into contact with HO, it reacts with the HO, increasing the O content and potentially reducing crystallinity. In an environment with the above-mentioned absolute humidity, the re-fired hexagonal boron nitride powder after the heating step comes into contact with and reacts with the second surface treatment agent before coming into contact with a large amount of HO, effectively preventing the risk of a reduction in crystallinity.

[0065] In addition, when both the first surface treatment step and the second surface treatment step are performed after the heating step, these steps are performed at an absolute humidity of 15 g / m 3 It is preferable to carry out the process under the following conditions: Either the first surface treatment process or the second surface treatment process may be carried out first.

[0066] (Modified hexagonal boron nitride powder) One aspect of the present invention may also include the following modified hexagonal boron nitride powder. That is, one aspect of the present invention is a modified hexagonal boron nitride powder having a graphitization index indicating crystallinity of 1.0 to 2.5, and having a second surface treatment agent having a conjugated double bond supported on its surface (surface-treated with a second surface treatment agent). Also, in one aspect of the present invention, the O content of the modified hexagonal boron nitride powder is preferably 0.3 mass% or less. Furthermore, in one aspect of the present invention, the C content of the modified hexagonal boron nitride powder is preferably 0.02 mass% or more.

[0067] The modified hexagonal boron nitride powders according to the first and second embodiments described above have improved physical properties, such as thermal conductivity and resin fillability. Using these powders as raw materials for electronic components can promote the miniaturization and high power of electronic components, contributing to energy conservation. This can increase the rate of improvement in energy efficiency and contribute to the achievement of the Sustainable Development Goals (SDGs).

[0068] [Additional Notes] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Example]

[0069] [Preparation Example 1] Preparation of hexagonal boron nitride powder Hexagonal boron nitride powder was prepared by a reduction-nitridation method. 700 g of boron oxide, 300 g of carbon black, 200 g of calcium carbonate, and 66 g of boron carbide were mixed in a mixer. The resulting mixture was heated to 1500°C in a graphite Tammann furnace under a nitrogen gas atmosphere and held at 1500°C for 6 hours. After holding at 1500°C, the temperature was raised to 1880°C and reduced and nitrided at 1880°C for 2 hours to obtain nitride powder. The resulting nitride powder was then crushed in a stone mill and placed in a polyethylene container. 500 g of nitride powder was mixed with 500 g of hydrochloric acid (37 wt% HCl) and 1500 g of pure water to prepare an acid slurry, which was then stirred for 8 hours for acid washing. After washing with acid, the acid slurry was filtered using a Buchner funnel, and then pure water was added in an amount 10 times (by weight) or more of the nitride powder to prepare a water slurry for washing.Then, the nitride powder was dehydrated by suction filtration until the moisture content was 40% by weight or less.

[0070] The nitride powder was then dried at atmospheric pressure at 200°C for 15 hours to reduce the moisture content to 0.1% by weight, and then classified using a 90 μm mesh sieve, and the undersieve was collected to obtain hexagonal boron nitride powder.

[0071] [Preparation Example 2] Preparation of unre-fired modified hexagonal boron nitride powder 10 g of the hexagonal boron nitride powder obtained in Preparation Example 1 was mixed with 0.05 g of hexamethyldisilazane for surface treatment to obtain a non-re-fired modified hexagonal boron nitride powder.

[0072] [Preparation Example 3] Preparation of re-fired hexagonal boron nitride powder 100 g of the hexagonal boron nitride powder obtained in Preparation Example 1 was loaded onto a carbon baking shelf coated with boron nitride and placed in a graphite Tammann furnace. After the furnace was depressurized, the mixture was heat-treated at 1890°C for 2 hours in a nitrogen atmosphere with a dew point of -85°C or lower to obtain re-fired hexagonal boron nitride powder.

[0073] [Preparation Example 4] Preparation of modified hexagonal boron nitride powder After the heat treatment of Preparation Example 3, the re-fired hexagonal boron nitride powder in the furnace was cooled to approximately 20°C by flowing nitrogen gas through the furnace. 10 g of the cooled re-fired hexagonal boron nitride powder was mixed with 0.05 g of hexamethyldisilazane to obtain a modified hexagonal boron nitride powder. The surface treatment was carried out at an absolute humidity of 12%.

[0074] [Evaluation Example 1] Measurement of C content and evaluation of water repellency The C content of the powders obtained in Preparation Examples 1 to 4 was measured using an EMIA-110 manufactured by Horiba Ltd.

[0075] Next, the water repellency of the powders was evaluated by a hydrophobicity test. Water (HO = 100), 10% by mass ethanol aqueous solution (HO / EtOH = 90 / 10), or 20% by mass ethanol aqueous solution (HO / EtOH = 80 / 20) was used as the solvent. 25 mL of the solvent was placed in a 50 mL vial, and 5 mg of each powder obtained in Preparation Examples 1 to 4 was added to evaluate whether the powder sank into the solvent.

[0076] Table 1 shows the measurement results of the C content and the evaluation results of water repellency for each powder.

[0077] [Table 1]

[0078] In Table 1, "○ Floats" indicates that the added powder floats near the surface of the solvent, resulting in high water repellency. "△ Slightly sinks" indicates that some of the added powder sinks to the bottom of the vial, resulting in slightly poor water repellency. "× Sinks" indicates that the added powder sinks to the bottom of the vial, resulting in poor water repellency.

[0079] As shown in Table 1, the C contents of the powders of Preparation Examples 2 and 4 were found to be increased by 0.017% and 0.015%, respectively, compared to the C contents of the powders of Preparation Examples 1 and 3. This confirmed the presence of a surface treatment agent on the surface of the powders of Preparation Examples 2 and 4. Furthermore, as shown in Table 1, it was found that the powder of Preparation Example 4 had the highest water repellency.

[0080] [Preparation Example 5] Preparation of unre-fired modified hexagonal boron nitride powder 10 g of the hexagonal boron nitride powder obtained in Preparation Example 1 was stored for 5 days in a polyethylene storage bag, Unipack (registered trademark) K8 (Sansan Nippon Sha). This storage resulted in unre-fired modified hexagonal boron nitride powder with the compound originating from the inner surface of Unipack (registered trademark) bonded to the surface.

[0081] [Preparation Example 6] Preparation of modified hexagonal boron nitride powder After the heat treatment of Preparation Example 3, the furnace was opened and the re-fired hexagonal boron nitride powder was removed. After cooling to room temperature, 10 g of the re-fired hexagonal boron nitride powder was stored in Unipack® K8 (Sansan Nippon Sha). This storage resulted in a modified hexagonal boron nitride powder in which the compound originating from the inner surface of Unipack® was bonded to the surface.

[0082] [Evaluation Example 2] Evaluation of physical properties by bonding a second surface treatment agent to re-fired hexagonal boron nitride powder First, we checked whether the physical properties (water repellency) of the re-fired hexagonal boron nitride powder changed when it was stored in a polyethylene storage bag, Unipack (registered trademark) K8 (Sansan Nippon Sha). This water repellency test confirmed whether the water repellency changed when a compound originating from the inner surface of Unipack bonded to the hexagonal boron nitride powder or re-fired hexagonal boron nitride powder that came into contact with the inner surface of Unipack.

[0083] The powders obtained in Preparation Examples 1, 3, 5 and 6 were evaluated for water repellency by carrying out the hydrophobization test carried out in Evaluation Example 1. The evaluation results are shown in Table 2.

[0084] [Table 2]

[0085] As shown in Table 2, the hexagonal boron nitride powder before the processing step (Preparation Examples 1 and 5) sank in all solvents, regardless of whether it was stored in Unipack. On the other hand, the re-fired hexagonal boron nitride powder after the processing step (Preparation Examples 3 and 6) was less likely to sink in the solvent compared to before the processing step. In particular, only the powder stored in Unipack did not sink in the 20% by mass ethanol aqueous solution, indicating that it had the highest water repellency. This result suggests that only the re-fired hexagonal boron nitride powder after the processing step (Preparation Example 6) was bonded with compounds derived from the inner surface of Unipack, thereby improving its water repellency.

[0086] [Evaluation Example 3] Examination of the types of compounds originating from the inner surface of Unipack Next, we investigated the types of compounds originating from the Unipack inner surface. Regarding the compounds present on the Unipack inner surface, 10 mL of ethanol was poured into the Unipack, and the Unipack inner surface was allowed to come into contact with the ethanol for 3 minutes. The ultraviolet-visible (UV-Vis) absorption spectrum of the components extracted into the ethanol after contact (Unipack extract) was measured. As a solvent control, the UV-Vis spectrum of a 30% by mass aqueous ethanol solution was also measured. The measurement was performed using a UV-1800 (Shimadzu Corporation) with a cell volume of 1 mL and a cell length of 10 mm.

[0087] The UV-Vis absorption spectra of the sample containing Unipac extract and the solvent control (EtOH) are shown in Figures 1 and 2, respectively. As shown in Figures 1 and 2, the sample containing Unipac extract exhibited absorption around 200 nm and 280 nm. Absorption below 200 nm may be due to ethanol or air, and not Unipac extract. On the other hand, absorption around 280 nm suggests that the Unipac extract may be a compound with conjugated double bonds.

[0088] These results indicate that the compound derived from Unipac is a compound with a covalent double bond, and that it bonds to the re-fired hexagonal boron nitride powder as a second surface treatment agent. Furthermore, it was shown that the re-fired hexagonal boron nitride powder containing the second surface treatment agent has improved water repellency. Improved water repellency leads to improved fillability into resin. [Industrial Applicability]

[0089] The modified hexagonal boron nitride powder of the present invention has improved physical properties such as thermal conductivity and fillability into resin, and can be used as a raw material for materials used in electronic parts.

Claims

1. a heating step of heating the hexagonal boron nitride powder at a temperature of 1300 to 2200°C in a nitrogen atmosphere; a first surface treatment step of contacting the re-fired hexagonal boron nitride powder after the heating step with a first surface treatment agent comprising a silane coupling agent or a second surface treatment step of contacting the re-fired hexagonal boron nitride powder after the heating step with a second surface treatment agent having a conjugated double bond, The heating step through the first surface treatment step or the second surface treatment step are carried out at an absolute humidity of 15 g / m ３ Run it under the following environment: The re-fired hexagonal boron nitride powder has a graphitization index, which indicates crystallinity, of 1.0 to 2.

5.

2. A method for producing a hexagonal boron nitride powder, comprising: a heating step of heating the hexagonal boron nitride powder at a temperature of 1300 to 2200°C in a nitrogen atmosphere; a first surface treatment step of contacting the re-fired hexagonal boron nitride powder after the heating step with a first surface treatment agent comprising a silane coupling agent or a second surface treatment step of contacting the re-fired hexagonal boron nitride powder after the heating step with a second surface treatment agent having a conjugated double bond, The steps from the heating step to the first surface treatment step or the second surface treatment step are carried out in an environment with an absolute humidity of 15 g / m 3 or less, A method for producing a modified hexagonal boron nitride powder, wherein the re-fired hexagonal boron nitride powder has an O (oxygen) content of 0.3 mass % or less.

3. 3. The method for producing a modified hexagonal boron nitride powder according to claim 1, wherein the second surface treatment agent is an aromatic compound.

4. 4. The method for producing a modified hexagonal boron nitride powder according to claim 1, wherein the second surface treatment agent is a compound containing a six-membered ring structure.

5. 5. The method for producing a modified hexagonal boron nitride powder according to claim 1, wherein in the heating step, heating is performed at the temperature for 30 minutes or more and less than 10 hours.

6. A modified hexagonal boron nitride powder having a graphitization index indicating crystallinity of 1.0 to 1.7, and carrying on its surface a first surface treatment agent consisting of a silane coupling agent or a second surface treatment agent having a conjugated double bond.

7. 7. The modified hexagonal boron nitride powder according to claim 6, wherein the O (oxygen) content is 0.3 mass % or less.

8. 8. The modified hexagonal boron nitride powder according to claim 6 or 7, wherein the C (carbon) content is 0.02 mass % or more.

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