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: The method for producing modified hexagonal boron nitride powder of the present invention 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 first surface treatment step of contacting the re-calcination hexagonal boron nitride powder after the heating step with a first surface treatment agent. From the heating step to the first surface treatment step is performed under an environment of re-calcination hexagonal boron nitride powder at an absolute humidity of 15 g / m3 or less.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] In recent years, with the miniaturization and high-powerization of electronic components, an increase in the heat generation of electronic components has become a problem. Therefore, in order to efficiently dissipate heat from electronic components, the development of materials with excellent thermal conductivity has been carried out.

[0003] Hexagonal boron nitride powder is blended with a resin used for electronic components to improve the thermal conductivity of the resin. The physical properties such as thermal conductivity and filling property into the resin of this hexagonal boron nitride powder may be improved by surface treatment with a surface treatment agent. For example, Patent Document 1 discloses a method of modifying the surface of hexagonal boron nitride powder by heating the powder at a specific temperature.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Hexagonal boron nitride powder lacks functional groups with which a surface treatment agent can react. It is conceivable that even if a surface treatment agent is applied to the powder after the surface modification treatment described in Patent Document 1, the desired surface treatment cannot be achieved. Therefore, for hexagonal boron nitride powder before surface treatment, further modification of the powder surface is required.

[0006] One aspect of the present invention aims to realize a method of effectively reacting a surface treatment agent with hexagonal boron nitride powder and the like.

Means for Solving the Problems

[0007] In order to solve the above problems, a method for producing modified hexagonal boron nitride powder according to one aspect of the present invention 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 first surface treatment step of bringing the re-fired hexagonal boron nitride powder after the heating step into contact with a first surface treatment agent, and from the heating step to the first surface treatment step, the re-fired hexagonal boron nitride powder has an absolute humidity of 15 g / m 3 It is carried out under the following environment.

[0008] In the method for producing modified hexagonal boron nitride powder according to one aspect of the present invention, in the first surface treatment step, the temperature of the re-fired hexagonal boron nitride powder may be adjusted to be 25°C or higher and lower than the decomposition temperature of the first surface treatment agent.

[0009] In the method for producing modified hexagonal boron nitride powder according to one aspect of the present invention, the first surface treatment agent may be a silane coupling agent.

[0010] In the method for producing modified hexagonal boron nitride powder according to one aspect of the present invention, in the heating step, the hexagonal boron nitride powder may be heated for 30 minutes or more and less than 10 hours.

[0011] In the method for producing modified hexagonal boron nitride powder according to one aspect of the present invention, in the first surface treatment step, after the temperature of the re-fired hexagonal boron nitride powder after the heating step has dropped, it may be brought into contact with the first surface treatment agent.

[0012] In order to solve the above problems, the modified hexagonal boron nitride powder according to one aspect of the present invention carries a first surface treatment agent on its surface, and the content of C (carbon) is 0.02% by mass or more.

[0013] In the modified hexagonal boron nitride powder according to one aspect of the present invention, the first surface treatment agent may be a silane coupling agent.

Advantages of the Invention

[0014] According to one aspect of the present invention, it is possible to realize a method for effectively reacting a surface treatment agent with hexagonal boron nitride powder, etc.

Brief Description of Drawings

[0015]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0016] 〔Embodiment 1〕 Hereinafter, one embodiment of the present invention will be described in detail.

[0017] (Method for Producing Modified Hexagonal Boron Nitride Powder) The method for producing 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 bringing the re-fired hexagonal boron nitride powder after the heating step into contact with a first surface treatment agent.

[0018] As a result of conducting detailed studies on the surface modification of hexagonal boron nitride powder, the present inventors have succeeded in obtaining new findings. That is, by heating hexagonal boron nitride powder under specific ranges of temperature and absolute humidity, the surface of the powder is activated and becomes easily reactive with a surface treatment agent, which has been uniquely discovered. Further, by performing surface treatment on hexagonal boron nitride powder that is easily reactive with a surface treatment agent under a specific range of absolute humidity, it has been uniquely discovered that the surface treatment agent can be effectively reacted with the hexagonal boron nitride powder.

[0019] 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 heating in a 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.

[0020] <Hexagonal boron nitride powder> Hexagonal boron nitride powder can be produced by a known method. 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. In terms of 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") being significantly evident and cost reduction, it is preferable to produce hexagonal boron nitride powder by the reduction nitridation method. Hereinafter, the production of hexagonal boron nitride powder by the reduction nitridation method will be described.

[0021] <Production of hexagonal boron nitride powder by reduction nitridation method> In the reduction nitridation method, generally, an oxygen-containing boron compound and an auxiliary are mixed to obtain a raw material mixed powder. The raw material mixed powder is then heated under 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.

[0022] 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. It is preferable to use boric acid or boron oxide because of easy availability.

[0023] Examples of the above-mentioned auxiliary agents 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, and the like. In terms of cost reduction, etc., it is preferable to use carbon black. Examples of the oxygen-containing alkaline earth metal compound include magnesium oxide, calcium oxide, magnesium carbonate, calcium carbonate, magnesium hydrogen carbonate, calcium hydrogen carbonate, magnesium hydroxide, calcium hydroxide, magnesium nitrate, calcium nitrate, magnesium sulfate, calcium sulfate, magnesium phosphate, calcium phosphate, magnesium oxalate, calcium oxalate, and the like. The oxygen-containing alkaline earth metal compound may be one type or two or more types.

[0024] As an example of a mixing method of the oxygen-containing boron compound and the auxiliary agent (carbon source and oxygen-containing alkaline earth metal compound), general mixers such as a vibration mill, a bead mill, a ball mill, and a mixer may be used for mixing.

[0025] The heating temperature of the raw material mixed powder under a nitrogen atmosphere is preferably 1500 °C or higher, more preferably 1800 °C or higher, in terms of being able to easily obtain hexagonal boron nitride powder by reducing the formation of amorphous boron nitride powder. Also, the heating temperature is preferably 2000 °C or lower. The heating time is usually 0.5 hour or more and 12 hours or less, preferably 1 hour or more and 8 hours or less.

[0026] Impurities such as by-products and unreacted substances can be removed by washing the boron nitride powder obtained by heating the raw material mixed powder with, for example, an acid. Examples of the acid include hydrochloric acid, nitric acid, sulfuric acid, acetic acid, and the like. The washing method with an acid is not particularly limited as long as by-products and impurities can be removed. For example, the boron nitride powder can be washed by mixing 50 parts by mass or more and 200 parts by mass or less of concentrated hydrochloric acid (37% HCl aqueous solution) and 200 parts by mass or more and 500 parts by mass or less of pure water with respect to 100 parts by mass of the boron nitride powder and stirring for 6 hours or more.

[0027] After washing with an acid, the nitride powder may be washed with pure water to remove the acid remaining in the nitride powder, and the pure water may be removed by drying. The drying temperature may be 50°C or higher and 250°C or lower. Further, it may be dried in the air or under a reduced-pressure atmosphere.

[0028] Before performing the heating process described below, the hexagonal boron nitride powder obtained by the reduction nitridation method may be subjected to treatments such as pulverization, disintegration, and classification, if necessary.

[0029] [Heating Process] In the heating process, the hexagonal boron nitride powder is heated at a temperature of 1300°C or higher and 2200°C or lower in a nitrogen atmosphere. By this heating process, the water repellency and crystallinity of the hexagonal boron nitride powder (re-fired hexagonal boron nitride powder) after the heating process can be improved.

[0030] The above heating process can be performed, for example, by supplying the hexagonal boron nitride powder to a furnace such as a heating furnace and carrying out the process in a nitrogen atmosphere. As the heating furnace, a known heating furnace capable of controlling the reaction atmosphere and absolute humidity can be used. For example, an atmosphere-controlled high-temperature furnace for performing heat treatment by high-frequency induction heating or heater heating can be mentioned. Further, continuous furnaces such as batch furnaces, pusher-type tunnel furnaces, and vertical reaction furnaces can also be used as heating furnaces.

[0031] Examples of the gas introduced into the heating furnace include nitrogen gas and ammonia gas. A gas in which a non-oxidizing gas such as hydrogen, argon, or helium is mixed with nitrogen gas or ammonia gas may be used. As the gas introduced into the heating furnace, nitrogen gas is preferable. Further, regarding the nitrogen gas, it is preferably nitrogen gas with the dew point temperature controlled, and the dew point temperature is preferably -85°C or lower.

[0032] The heating temperature in the above heating process is 1300°C or higher and 2200°C or lower. If the heating temperature is less 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. Further, if the heating temperature exceeds 2200°C, the recrystallized hexagonal boron nitride powder may decompose or turn yellow.

[0033] In terms of being able to more effectively react the surface treatment agent in the surface treatment process (the first surface treatment process or the second surface treatment process) described later, the lower limit of the heating temperature in the above heating process is preferably 1400°C or higher, and more preferably 1600°C or lower. Further, from the viewpoint of equipment cost etc., the upper limit of the heating temperature is preferably 2000°C or lower, and more preferably 1900°C or lower.

[0034] The heating time in the above heating process can be appropriately selected according to the conditions of the nitrogen atmosphere and the heating temperature. In terms of being able to more effectively react the surface treatment agent in the surface treatment process described later, the lower limit of the heating time is preferably 30 minutes or longer, more preferably 1 hour or longer, and even more preferably 2 hours or longer. Further, from the viewpoint of equipment cost 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.

[0035] A first surface treatment step of bringing the recrystallized hexagonal boron nitride powder obtained in the above heating process into contact with a first surface treatment agent and / or a second surface treatment step of bringing it into contact with a second surface treatment agent is performed. Hereinafter, the first surface treatment step will be described in the present embodiment, and the second surface treatment step will be described in the subsequent Embodiment 2.

[0036] [First Surface Treatment Step] In the first surface treatment step, the recrystallized hexagonal boron nitride powder obtained in the above heating process is brought into contact with a first surface treatment agent.

[0037] In the production method according to Embodiment 1, the absolute humidity is 15 g / m 3Under the following environment, the above heating process and the first surface treatment process are performed. Under an environment with an absolute humidity of 15 g / m 3 When the above heating process and the first surface treatment process are performed under an environment with an absolute humidity exceeding 3 , the heat-treated hexagonal boron nitride powder is likely to react with water and hydrolyze. Due to this hydrolysis, it becomes difficult for the first surface treatment agent to react with the heat-treated hexagonal boron nitride powder. Also, under an environment with an absolute humidity of 15 g / m 3 By performing the above heating process and the first surface treatment process under the following environment, it is possible to effectively react the heat-treated hexagonal boron nitride powder with an activated surface (especially the end face) and the first surface treatment agent. The absolute humidity can be measured using a known absolute humidity sensor or the like.

[0038] In terms of more effectively reacting the heat-treated hexagonal boron nitride powder and the first surface treatment agent, the above absolute humidity is preferably 12 g / m 3 or less, more preferably 10 g / m 3 or less, even more preferably 7 g / m 3 or less, still more preferably 5 g / m 3 or less, even still more preferably 2 g / m 3 and particularly preferably 0 g / m 3 and most preferably 0 g / m.

[0039] As the first surface treatment agent used in the above first surface treatment process, a known surface treatment agent used for surface treatment of hexagonal boron nitride powder can be used. In the manufacturing method according to Embodiment 1, since the absolute humidity is controlled and the heating process and the first surface treatment process are performed in a state where the water content is controlled, the first surface treatment agent is preferably a silane coupling agent, and more preferably a silane coupling agent having a reactive functional group or hexamethyldisilazane. 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, and the like.

[0040] 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 with respect to the total amount of the re-fired hexagonal boron nitride powder.

[0041] The method of bringing the re-fired hexagonal boron nitride powder into contact with the first surface treatment agent may be carried out using a known method. For example, by mixing the re-fired hexagonal boron nitride powder and the first surface treatment agent, the first surface treatment agent comes into contact with the surface of the re-fired hexagonal boron nitride powder.

[0042] In the above 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. Also, the upper limit of the temperature is preferably less than 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 re-fired hexagonal boron nitride powder to the above temperature range, the re-fired hexagonal boron nitride powder and the first surface treatment agent can react more effectively.

[0043] In the above first surface treatment step, it is preferable to bring the first surface treatment agent into contact with the re-fired hexagonal boron nitride powder whose temperature has been lowered after the heating step. 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 inside of the heating furnace. The temperature of the re-fired hexagonal boron nitride powder whose temperature has been lowered after the heating step is preferably 25°C or lower, and more preferably 20°C or lower. By lowering the temperature of the re-fired hexagonal boron nitride powder, it becomes difficult to react with moisture in the air when the furnace is opened to the atmosphere. Also, if a device for continuously performing the above heating step and the first surface treatment step is designed, the first surface treatment step can be performed without opening the heating furnace, so that the re-fired hexagonal boron nitride powder can be surface-treated without coming into contact with the moisture-containing atmosphere.

[0044] (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 content of C (carbon) of 0.02% or more and carrying (surface-treated with) a first surface treatment agent on the surface. Such a 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.

[0045] 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, it can be said that the modified BN powder having such a C content is one carrying (surface-treated with) the first surface treatment agent on the surface.

[0046] As described above, the surface of the modified BN powder according to Embodiment 1 reacts effectively with the first surface treatment agent. Therefore, according to such a modified hexagonal boron nitride powder, for example, the peel strength of the copper foil attached to the resin filled with the modified boron nitride powder can be easily improved. Also, the interaction with the resin to be filled is improved, enabling high fillability into the resin and imparting high thermal conductivity. Further, if the surface is coated with a hydrophobic first surface treatment agent, it is possible to impart water repellency to the modified hexagonal boron nitride powder, and the moisture resistance reliability as a resin composition can be improved.

[0047] 〔Embodiment 2〕 Other embodiments of the present invention will be described below. For convenience of explanation, the description of the configurations described in the above embodiments will not be repeated.

[0048] (Manufacturing method of modified hexagonal boron nitride powder) In the manufacturing method of the modified hexagonal boron nitride powder according to the present embodiment, a second surface treatment step is carried out in place of, or in addition to, the first surface treatment step, from the method according to Embodiment 1. Also, in the manufacturing method of the modified hexagonal boron nitride powder according to the present embodiment, the absolute humidity is 15 g / m 3It is not essential to perform the above heating process and surface treatment process (the second surface treatment process, or the first surface treatment process and the second surface treatment process) under the following environment.

[0049] [Second surface treatment process] The second surface treatment process is a process of bringing the recrystallized hexagonal boron nitride powder after the above heating process into contact with a second surface treatment agent having a conjugated double bond.

[0050] In the recrystallized hexagonal boron nitride powder after the heating process, the residual O (oxygen) in the particles has been replaced by N (nitrogen). Therefore, the recrystallized hexagonal boron nitride powder has a lower O content in the particles compared to the hexagonal boron nitride powder before the heating process. It can be said that the lower the O content in the hexagonal boron nitride powder, the closer the crystal structure is to the ideal state (higher crystallinity). The state of high crystallinity of the hexagonal boron nitride powder is a state in which B and N in the crystal structure are not replaced by other molecules such as vacancies or O, and the crystal structure of hexagonal boron nitride has no atomic defects. Also, it can be said that the lower the O content in the hexagonal boron nitride powder, the fewer the adsorbed molecules such as water molecules on the surface.

[0051] It is known that a single layer of hexagonal boron nitride is more likely to adsorb carbon dioxide or water molecules as the crystal structure deviates from the ideal state (Beilstein J. Nanotechnol. 2019, 10, 540 - 548, Catalysis Today, 2011, 175, 271 - 275). The closer the crystal structure of the hexagonal boron nitride powder is to the ideal state, the fewer the structures that inhibit the binding of the second surface treatment agent to the surface, and it is considered to be in a state where it is easier to bind to the second surface treatment agent. The second surface treatment agent will be described later.

[0052] From the perspective of the binding property with the second surface treatment agent, the recrystallized 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.

[0053] The state of the hexagonal boron nitride powder can be represented by the graphitization index (GI value; Graphite Index score). The GI value is obtained by dividing the sum of the peak areas derived from the (100) plane and the (101) plane of the X-ray diffraction spectrum by the peak area derived from the (102) plane. The GI value becomes lower as the crystallinity is higher. In the case of completely crystallized (graphitized) hexagonal boron nitride powder, the GI value is 1.6. However, in the case of hexagonal boron nitride powder with high crystallinity and sufficient particle growth, the GI value can be even lower depending on the powder orientation.

[0054] From the viewpoint of the binding property with the second surface treatment agent, the GI value of the annealed hexagonal boron nitride powder is preferably 1.0 to 2.5, more preferably 1.3 to 2.0, still more preferably 1.4 to 1.8, even more preferably 1.5 to 1.7, and most preferably 1.6.

[0055] Conventionally, it has been difficult to stably obtain hexagonal boron nitride powder with high crystallinity as described above. The inventors of the present invention have found as a unique and novel finding that the annealed hexagonal boron nitride powder immediately after performing a heating step on the hexagonal boron nitride powder has the above-mentioned O content and GI value and is in a state of high crystallinity. The second surface treatment step in the method for producing the modified hexagonal boron nitride powder according to the present embodiment is a step of bringing the annealed hexagonal boron nitride powder after such a heating step into contact with the second surface treatment agent.

[0056] The second surface treatment agent is not particularly limited as long as it is a compound having a conjugated double bond. For example, it is preferably an aromatic compound and preferably a compound containing a six-membered ring structure. Examples of such compounds include benzene, biphenyl, triphenylene, anthracene, indole, purine, quinoline, isoquinoline, and chromene.

[0057] Such a second surface treatment agent is not particularly limited, but it is considered that it can be well bonded to the surface of the recrystallized hexagonal boron nitride powder due to the π-π interaction occurring between at least the conjugated double bond portion and the surface of the recrystallized hexagonal boron nitride powder. As described above, the higher the crystallinity of the recrystallized hexagonal boron nitride powder, that is, the closer the GI value is to 1.6, the easier it is for the second surface treatment agent to bond to the surface of the recrystallized hexagonal boron nitride powder. Here, the "bonding" does not refer to a specific bonding mode, but is a concept including all possible bonding modes that can occur between the second surface treatment agent and the recrystallized hexagonal boron nitride powder, including chemical adsorption due to π-π interaction.

[0058] The modified hexagonal boron nitride powder obtained by the manufacturing method according to this embodiment is a hexagonal boron nitride powder whose surface is modified by a second surface treatment agent. Such a modified hexagonal boron nitride powder has excellent interaction with resins. Therefore, the modified hexagonal boron nitride powder easily interacts with resins. Therefore, according to the modified hexagonal boron nitride powder, for example, the peel strength of a copper foil attached to a resin filled with the modified boron nitride powder can be easily improved. In addition, the interaction with the resin to be filled is improved, enabling high filling property into the resin and imparting high thermal conductivity. Also, if the surface is coated with a hydrophobic second surface treatment agent, it is possible to impart water repellency to the modified hexagonal boron nitride powder, and the moisture resistance reliability as a resin composition can be improved.

[0059] It is preferable that the modified hexagonal boron nitride powder has a C content of 0.02% by mass or more. The C contained in the modified hexagonal boron nitride powder may be derived from the second surface treatment agent. Therefore, it can be said that such a modified hexagonal boron nitride powder having a C content is surface-treated with a second surface treatment agent.

[0060] In this embodiment, it is preferable to perform the steps from the heating step to the second surface treatment step in an environment with an absolute humidity of 15 g / m 3 or less. Also, the environment for performing the steps from the heating step to the second surface treatment step has an absolute humidity of 12 g / m 3It is more preferably as follows, 10 g / m 3 It is more preferably as follows, 7 g / m 3 It is more preferably as follows, 5 g / m 3 It is more preferably as follows, 2 g / m 3 It is particularly preferably 0 g / m 3 It is most preferably so.

[0061] The recrystallized hexagonal boron nitride powder after the heating step has a low O content as described above, and thus the GI value also approaches 1.6. However, when the recrystallized hexagonal boron nitride powder comes into contact with H 2 O, it may react with H 2 O to increase the O content and reduce the crystallinity. In an environment with the absolute humidity as described above, before the recrystallized hexagonal boron nitride powder after the heating step comes into contact with a large amount of H 2 O, by contacting and reacting with the second surface treatment agent, the possibility of a decrease in crystallinity can be effectively prevented.

[0062] In addition, when both the first surface treatment step and the second surface treatment step are carried out after the heating step, it is preferable to carry out this series of steps in an environment with an absolute humidity of 15 g / m 3 or less. Note that either the first surface treatment step or the second surface treatment step may be carried out first.

[0063] (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 the surface (surface-treated with the second surface treatment agent). Further, in one aspect of the present invention, it is preferable that the O content of the modified hexagonal boron nitride powder is 0.3 mass% or less. Furthermore, in one aspect of the present invention, it is preferable that the C content of the modified hexagonal boron nitride powder is 0.02 mass% or more.

[0064] The modified hexagonal boron nitride powder according to the above-mentioned Embodiments 1 and 2 has improved physical properties such as thermal conductivity and filling property into resins. By using the powder as a raw material of a material used in electronic components, miniaturization and high-powerization of electronic components can be promoted, and energy conservation can be contributed. As a result, the improvement rate of energy efficiency can be increased, and it can contribute to the achievement of sustainable development goals (SDGs).

[0065] 〔Supplementary Matters〕 The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope indicated in the claims. Embodiments obtained by appropriately combining the technical means respectively disclosed in different embodiments are also included in the technical scope of the present invention.

Examples

[0066] 〔Preparation Example 1〕Preparation of hexagonal boron nitride powder The 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 and stirred in a mixing stirrer. The obtained mixture was heated to 1500° C. in a nitrogen gas atmosphere using a graphite-made Tamman furnace and held at 1500° C. for 6 hours. After holding at 1500° C., the temperature was raised to 1880° C., and a reduction nitridation treatment was performed at 1880° C. for 2 hours to obtain a nitrided powder. Next, the obtained nitrided powder was crushed with a mortar grinder, then put into a polyethylene container, 500 g of hydrochloric acid (37 wt% HCl) and 1500 g of pure water were added to 500 g of the nitrided powder to prepare an acid slurry, and washing with acid was performed by stirring for 8 hours. After washing with acid, the acid slurry was filtered using a Buchner funnel, then added to pure water in an amount 10 times or more (weight ratio) of the nitrided powder to prepare a water slurry for washing, and dehydration was performed by suction filtration until the moisture content of the nitrided powder became 40 wt% or less.

[0067] Thereafter, the nitrided powder was dried at 200° C. for 15 hours under atmospheric pressure to a moisture content of 0.1 wt%, then classified with a sieve having an aperture of 90 μm, and the undersize was collected to obtain hexagonal boron nitride powder.

[0068] 〔Preparation Example 2〕Preparation of unannealed modified hexagonal boron nitride powder Surface treatment was carried out by mixing 10 g of the hexagonal boron nitride powder obtained in Preparation Example 1 and 0.05 g of hexamethyldisilazane to obtain unannealed modified hexagonal boron nitride powder.

[0069] 〔Preparation Example 3〕Preparation of annealed hexagonal boron nitride powder 100 g of the hexagonal boron nitride powder obtained in Preparation Example 1 was filled into a carbon firing shelf surface-coated with boron nitride and placed in a graphite Tanaka furnace. After reducing the pressure in the furnace, heat treatment was carried out at 1890 °C for 2 hours in a nitrogen atmosphere with a dew point temperature of -85 °C or lower to obtain annealed hexagonal boron nitride powder.

[0070] 〔Preparation Example 4〕Preparation of modified hexagonal boron nitride powder After the heat treatment in Preparation Example 3, the inside of the furnace was cooled by flowing nitrogen gas, and the annealed hexagonal boron nitride powder in the furnace was cooled to about 20 °C. Surface treatment was carried out by mixing 10 g of the cooled annealed hexagonal boron nitride powder and 0.05 g of hexamethyldisilazane to obtain modified hexagonal boron nitride powder. The surface treatment was carried out under a condition of an absolute humidity of 12%.

[0071] 〔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 EMIA-110 manufactured by Horiba, Ltd.

[0072] Next, the water repellency of the powders was evaluated by a hydrophobization test. As solvents, water (H 2 O = 100), 10 mass% ethanol aqueous solution (H 2 O / EtOH = 90 / 10) or 20 mass% ethanol aqueous solution (H 2 O / EtOH = 80 / 20) was used. After charging 25 mL of the solvent into a 50 mL vial, 5 mg of each powder obtained in Preparation Examples 1 to 4 was added, and it was evaluated whether the powder sank in the solvent.

[0073] The measurement results of the C content and the water repellency evaluation results of each powder are shown in Table 1.

[0074]

Table 1

[0075] In Table 1, "〇 floats" indicates that the added powder floats near the surface of the solvent, showing high water repellency. "△ slightly sinks" indicates that some of the added powder sinks to the bottom of the vial, showing slightly inferior water repellency. "× sinks" indicates that the added powder sinks to the bottom of the vial, showing inferior water repellency.

[0076] As shown in Table 1, it was found that the C content of the powders in Preparation Examples 2 and 4 increased by 0.017% and 0.015% respectively compared to the C content of the powders in Preparation Examples 1 and 3. From this, it was confirmed that the surface treatment agent was present on the surfaces of the powders in Preparation Examples 2 and 4. Also, as shown in Table 1, it was found that the powder in Preparation Example 4 had the highest water repellency.

[0077] 〔Preparation Example 5〕Preparation of unrefired modified hexagonal boron nitride powder 10 g of the hexagonal boron nitride powder obtained in Preparation Example 1 was stored in a Unipack (registered trademark) K8 (manufactured by Seijo Co., Ltd.), a polyethylene storage bag, for 5 days. By this storage, an unrefired modified hexagonal boron nitride powder in which a compound derived from the inner surface of the Unipack (registered trademark) was bonded to the surface was obtained.

[0078] 〔Preparation Example 6〕Preparation of modified hexagonal boron nitride powder After the heat treatment in Preparation Example 3, the furnace was opened and the recrystallized hexagonal boron nitride powder was taken out. Then, after cooling to room temperature, 10 g of the recrystallized hexagonal boron nitride powder was stored in a Unipack (registered trademark) K8 (manufactured by Seijo Co., Ltd.) for 5 days. By this storage, a modified hexagonal boron nitride powder in which a compound derived from the inner surface of the Unipack (registered trademark) was bonded to the surface was obtained.

[0079] 〔Evaluation Example 2〕Evaluation of physical properties by binding of the second surface treatment agent to the recrystallized hexagonal boron nitride powder First, it was confirmed whether the physical properties (water repellency) of the recrystallized hexagonal boron nitride powder changed during storage in a polyethylene storage bag, Unipak (registered trademark) K8 (manufactured by Seisan Nippon Co., Ltd.). This water repellency test confirmed the presence or absence of a change in water repellency by the binding of a compound derived from the inner surface of the Unipak to the hexagonal boron nitride powder or the recrystallized hexagonal boron nitride powder that had come into contact with the inner surface of the Unipak.

[0080] For the powders obtained in Preparation Examples 1, 3, 5, and 6, the water repellency was evaluated by conducting the hydrophobization test performed in Evaluation Example 1. The evaluation results are shown in Table 2.

[0081] [Table 2]

[0082] As shown in Table 2, the hexagonal boron nitride powders before the processing step (Preparation Examples 1 and 5) sank in any solvent regardless of storage in the Unipak. On the other hand, the recrystallized hexagonal boron nitride powders after the processing step (Preparation Examples 3 and 6) were less likely to sink in the solvent compared to before the processing step. In particular, for a 20 mass% ethanol aqueous solution, it was shown that they did not sink only under the condition of storage in the Unipak and had the highest water repellency. This result suggests that a compound derived from the inner surface of the Unipak bound only to the recrystallized hexagonal boron nitride powder after the processing step (Preparation Example 6), thereby improving the water repellency.

[0083] [Evaluation Example 3] Examination of the types of compounds derived from the inner surface of the Unipak Next, an examination was conducted on the types of compounds derived from the inner surface of the Unipak. For the compounds present on the inner surface of the Unipak, 10 mL of ethanol was poured into the Unipak, and the inner surface of the Unipak was brought into contact with the ethanol for 3 minutes. The ultraviolet-visible (UV-Vis) absorption spectrum of the components extracted into the ethanol after contact (Unipak extract) was measured. As a solvent control, the UV-Vis spectrum was also measured for a 30 mass% ethanol aqueous solution. The measurement was carried out using a UV-1800 (manufactured by Shimadzu Corporation) under the conditions of a cell volume of 1 mL and a cell length of 10 mm.

[0084] The UV-Vis absorption spectra measurement results of the sample containing the Unipac extract and the solvent control (EtOH) are shown in Figures 1 and 2, respectively. As shown in Figures 1 and 2, absorption was observed near 200 nm and near 280 nm in the sample containing the Unipac extract. The absorption below 200 nm may be derived from ethanol or the atmosphere and may not be derived from the Unipac extract. On the other hand, since absorption was observed near 280 nm, it was suggested that the Unipac extract might be a compound having conjugated double bonds.

[0085] From the above results, it was shown that the compound derived from Unipac is a compound having a covalent double bond and binds to the re-fired hexagonal boron nitride powder as the second surface treatment agent. In addition, it was shown that the re-fired hexagonal boron nitride powder containing the second surface treatment agent has improved water repellency. The improvement in water repellency leads to an improvement in the fillability into the resin.

Industrial Applicability

[0086] The modified hexagonal boron nitride powder of the present invention has improved physical properties such as thermal conductivity and fillability into a resin, and can be used as a raw material for a material used in electronic components.

Claims

1. 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 first surface treatment step of bringing the calcined hexagonal boron nitride powder after the heating step into contact with a first surface treatment agent. A method for producing modified hexagonal boron nitride powder, wherein the process from the heating step to the first surface treatment step is carried out in an environment where the recrystallized hexagonal boron nitride powder has an absolute humidity of 15 g / m ３ or less.

2. The method for producing a modified hexagonal boron nitride powder according to claim 1, wherein in the first surface treatment step, the temperature of the calcined hexagonal boron nitride powder is adjusted to be 25°C or higher and lower than the decomposition temperature of the first surface treatment agent.

3. The method for producing a modified hexagonal boron nitride powder according to claim 1 or 2, wherein the first surface treatment agent is a silane coupling agent.

4. The method for producing a modified hexagonal boron nitride powder according to any one of claims 1 to 3, wherein in the heating step, the hexagonal boron nitride powder is heated for 30 minutes or more and less than 10 hours.

5. The method for producing a modified hexagonal boron nitride powder according to any one of claims 1 to 4, wherein in the first surface treatment step, after the temperature of the calcined hexagonal boron nitride powder after the heating step has dropped, it is brought into contact with the first surface treatment agent.

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