JP6452873B2 - Boron nitride powder and method for producing the same - Google Patents

Description

  The present invention provides boron nitride powder obtained by a reduction nitriding method, a method for producing the same, and further uses as a filler for the boron nitride powder.

  Boron nitride powder is a white powder generally having a hexagonal layered structure similar to that of graphite. High thermal conductivity, high electrical insulation, high lubricity, corrosion resistance, mold release, high temperature stability, chemical It has many characteristics such as stability. Therefore, the resin composition filled with boron nitride powder is suitably used as a heat conductive insulating sheet by molding.

  In this case, as the resin of the resin composition, a silicone resin, an epoxy resin, an acrylic resin, or the like can be used, but a silicone resin is preferably used from the viewpoint of molding processability, thermal shock, flexibility, weather resistance, and heat resistance. (See Patent Document 1).

  When making a thermally conductive insulating sheet using boron nitride powder as a filler, the thermal conductivity improves as the filling amount of boron nitride powder increases. Therefore, boron nitride powder is generally a thermally conductive insulating sheet. 40 vol% (vol.%) Or more, preferably 60 vol. Highly filled to more than%.

  On the other hand, various methods for producing boron nitride powder have been proposed. Among them, oxygen-containing boron compounds are reduced and nitrided by using carbon as a reducing agent and reacting with nitrogen at a high temperature. A manufacturing method based on the “nitriding method” (see Patent Document 2) is industrially advantageous and widely implemented.

  However, when boron nitride powder obtained by the reduction nitriding method is used as a filler for silicone resin, when the boron nitride powder is highly filled, the curability of the resulting silicone resin composition is lowered, and in some cases it can be cured. It turns out that there is no problem.

JP 2012-56818 A JP-A-10-203806

  Accordingly, an object of the present invention is to provide a boron nitride powder obtained by a reductive nitriding method, which is preferably used for a silicone resin composition, and a filler for a silicone resin comprising the boron nitride powder.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive studies. As a result, the substance that inhibits the curing of the silicone resin is a phosphorus component contained as an impurity in the boron nitride powder, and the phosphorus component inactivates a platinum-based curing agent that is a silicone resin curing catalyst, The knowledge which can solve the said problem was obtained by controlling the quantity of this phosphorus component to specific quantity, and came to complete this invention.

  That is, according to the present invention, there is provided a boron nitride powder obtained by the reduction nitriding method, wherein the phosphorus component present on the particle surface is 3 to 4 ppmw in terms of phosphorus element.

  The present invention also provides a filler for a silicone resin comprising the boron nitride powder.

  Furthermore, the present invention proposes a method for producing boron nitride powder. That is, according to the present invention, the boron by-product obtained by reducing and nitriding the oxygen-containing boron compound by using carbon as a reducing agent and reacting with nitrogen is pulverized, and the remaining by-product is acid washed. A step of removing by the above-described acid cleaning, wherein the phosphorous component present on the particle surface of the obtained boron nitride powder is subjected to the acid cleaning so that the phosphorus content is 4 ppmw or less in terms of phosphorus element. A method is provided.

  Although the boron nitride powder of the present invention is obtained by a reductive nitriding method using carbon as a reducing agent, it has a feature that the surface phosphorus component has a very low concentration, and a silicone resin composition It is possible to produce a molded body such as a highly heat-conductive insulating sheet by using a silicone resin composition that is highly filled with boron nitride powder without inhibiting the curing of the silicone resin when highly filled.

  Further, the boron nitride powder of the present invention is not limited to the filler for the silicone resin composition, and can be used for known applications. Examples of applications that are preferably used include raw materials for processed products of boron nitride such as cubic boron nitride and boron nitride molded products, nucleating agents for engineering plastics, and the purpose of improving electrical insulation and imparting thermal conductivity. Additives to resin molded products, phase change materials, solid or liquid thermal interface materials, mold release materials for molten metals and molten glass molds, cosmetics, composite ceramic materials, and the like.

  In the present invention, the silicone resin composition contains a silicone resin, a platinum-based curing agent that is an addition reaction catalyst, and boron nitride powder obtained by a reductive nitriding method using carbon as a reducing agent.

(Each raw material)
In the present invention, a known silicone resin is used without any particular limitation. Specifically, a composition comprising an alkenyl group-containing organopolysiloxane as a main agent and an organohydrogensiloxane as a cross-linking agent is common.

  The alkenyl group-containing organopolysiloxane is an organopolysiloxane having two or more alkenyl groups bonded to silicon atoms per molecule. The main chain of the alkenyl-containing organopolysiloxane generally repeats a diorganosiloxane unit, but may contain a partially branched structure or a cyclic structure.

  As the alkenyl group, a vinyl group, an allyl group, a propenyl group, an isopropenyl group, and the like are common. Among them, a vinyl group is preferable, and the alkenyl group is bonded to only a silicon atom at the end of the molecular chain. It is preferable.

  Other than the above alkenyl groups, the functional group bonded to the silicon atom includes alkyl groups such as methyl, ethyl and propyl groups, cycloalkyl groups such as cyclopentyl and cyclohexyl groups, and allyl groups such as phenyl, xylyl and biphenylyl groups. And monovalent hydrocarbon groups such as an aralkyl group such as a benzyl group, a phenylethyl group, and a phenylpropyl group. Further, a group in which part or all of the hydrogen atoms bonded to the carbon atom of the monovalent hydrocarbon group are substituted with a halogen atom such as fluorine, chlorine or bromine, a cyano group, or the like may be used. The functional groups other than the alkenyl group bonded to the silicon atom may not all be the same.

  In the present invention, the organohydrogenpolysiloxane acts as a crosslinking agent for the organopolysiloxane. As the organohydrogenpolysiloxane, those having 2 to 100 Si-H groups in one molecule are preferable.

  In the present invention, the platinum-based curing agent is known as a catalyst used in the addition reaction (hydrosilylation reaction) of the alkenyl group-containing organopolysiloxane and the Si-H group of the organohydrogensiloxane. For example, platinum metal alone such as platinum black, platinum chloride, chloroplatinic acid, chloroplatinate and the like can be used.

  In the present invention, the boron nitride powder used as a filler in the silicone resin composition is obtained by a reductive nitriding method as described later, and the concentration of the phosphorus component present on the surface with respect to the boron nitride powder is In order to adjust the ratio of the phosphorus component to the platinum catalyst in the silicone resin composition to be described later, it is preferable that it is 4 ppmw or less, preferably 3 ppmw or less in terms of phosphorus element. That is, when a boron nitride powder obtained by a conventional reductive nitriding method in which the concentration of the phosphorus component present on the surface is higher than the above range is used, the phosphorus component increases in the silicone resin composition, and the silicone based on the platinum catalyst is used. The problem of inhibiting the curing of the resin is likely to occur.

  Note that boron nitride powder obtained by the reductive nitriding method using carbon as a reducing agent has an unexpectedly large amount of phosphorus components derived from the carbon, which may affect the curing of the silicone resin. As confirmed by the inventors, at the same time, the removal of the phosphorus component is usually not sufficient in an industrial pickling step, and the surface of boron nitride powder obtained by the same reductive nitriding method is not sufficient. It was also confirmed that a phosphorus component exceeding 10 ppmw was present.

  Therefore, in the boron nitride powder obtained by the reductive nitriding method using the carbon as a reducing agent, the concentration of the phosphorus component existing on the surface with respect to the boron nitride powder is 4 ppmw or less in terms of phosphorus element. Moreover, it is useful as a filler for silicone resin compositions.

  In the present invention, the shape of the boron nitride powder is not particularly limited, and may be a general scale shape or a thick shape having a small major axis / thickness ratio. In addition, the agglomerated and non-agglomerated states of the boron nitride powder are not particularly limited, and may be agglomerated by granulation as necessary, or may be crushed and non-agglomerated.

  The average particle size of the boron nitride powder is not particularly limited, and the primary particle size is generally 0.01 to 50 μm, and the aggregated particles are generally 0.05 to 300 μm.

  As described above, the method for producing boron nitride powder with a remarkably small amount of phosphorus component on the particle surface of the present invention is not particularly limited, but oxygen-containing boron compound is used as a reducing agent, carbon is used, A step of removing the remaining by-product by acid washing after pulverizing the boron nitride mass obtained by reaction and reduction nitridation with a phosphorus component present on the particle surface of the resulting boron nitride powder However, it can obtain by performing the said acid washing so that it may become 4 ppmw or less in conversion of phosphorus element.

  In the method for producing boron nitride powder, as the oxygen-containing boron compound, any compound containing a boron atom can be used without limitation. For example, boric acid, anhydrous boric acid, metaboric acid, perboric acid, hypoboric acid, sodium tetraborate, sodium perborate and the like can be used, but generally available boric acid is preferably used.

  The average particle diameter of the oxygen-containing boron compound to be used is not particularly limited, but is preferably 1 to 1000 μm, more preferably 10 to 900 μm, and still more preferably 20 to 800 μm, from the viewpoints of operability and reduction reaction control. That is, when the average particle diameter of the oxygen-containing boron compound is larger than 1 μm, the handling becomes easy, and when it becomes smaller than 1000 μm, the reduction reaction of the oxygen-containing boron compound is easily controlled.

  In the method for producing boron nitride powder, known carbon is used as the reducing agent without any particular limitation. For example, highly reactive amorphous carbon such as carbon black and activated carbon is preferable, and carbon black is particularly preferably used in terms of industrial quality control. Moreover, as said carbon black, acetylene black, furnace black, thermal black, etc. can be used. The average particle diameter of the carbon is preferably 0.01 to 5 μm, more preferably 0.02 to 4 μm, and particularly preferably 0.05 to 3 μm. That is, when the average particle diameter of the carbon source is 5 μm or less, the reactivity of carbon is increased, and when it is 0.01 μm or more, handling becomes easy.

  The carbon used as the reducing agent preferably has a phosphorus content of 50 ppmw or less, preferably 20 ppmw or less, more preferably 10 ppmw or less in terms of phosphorus element. That is, in producing boron nitride powder by the reduction nitriding method, the phosphorus component contained in the boron nitride powder is mainly derived from the phosphorus component contained in the carbon, and the phosphorus content is more than 50 ppmw. When carbon is used, a large amount of phosphorus component adheres to the surface of the obtained boron nitride powder, and a heavy load is imposed on the carbon removal step in the subsequent acid cleaning step, making industrial implementation difficult.

  In the method for producing boron nitride powder, the ratio of oxygen-containing boron compound to carbon is 0.4 to 1.1, preferably 0.5 to 1.0, in terms of B / C (element ratio). Preferably it is 0.6-0.9. If the ratio of oxygen-containing boron compound to carbon exceeds 1.1, the ratio of oxygen-containing boron compound that volatilizes without being reduced increases, the yield decreases, and the volatilization component adversely affects the production line. May affect. On the other hand, if the ratio of oxygen-containing boron compound to carbon is less than 0.4, the proportion of unreacted carbon increases, and substances such as boron carbide are by-produced, and the yield is also lowered.

  Furthermore, in the method for producing the boron nitride powder, it is preferable to use a crystallizing agent, and it is generally mixed with the raw material in advance. As the crystallization agent, known ones can be used without particular limitation, including commonly used calcium compounds. For example, calcium compounds such as calcium carbonate, calcium hydrogen carbonate, calcium hydroxide, calcium oxide, calcium nitrate, calcium sulfate, and calcium oxalate, magnesium compounds such as magnesium carbonate, and sodium compounds such as sodium carbonate can be used. It is also possible to use a mixture of two or more of these. Among them, it is preferable to use calcium oxide and calcium carbonate because the crystallinity of the obtained boron nitride powder is high and the formation of a porous bulk body is easy, and calcium carbonate is particularly preferable because it has foamability. preferable. The average particle size of the crystallization agent is preferably 0.01 to 500 μm, more preferably 0.05 to 400 μm, and particularly preferably 0.1 to 300 μm. If it is 0.01 μm or more, it is easy to handle and if it is 300 μm or less, the reactivity is sufficiently high. The amount of the crystallization agent added is such that the element ratio of the metal element of the crystallization agent to the boron element of the boron compound is 0.01 to 0.3, more preferably 0.02 to 0.2, and still more preferably. Is 0.03-0.1. When the element ratio is less than 0.01, boron nitride powder with high crystallinity cannot be obtained, and when it exceeds 0.3, the impurity concentration of the obtained boron nitride powder becomes high, which is not preferable.

  In the boron nitride production method, the form of the mixture containing each of the above raw materials is not particularly limited during the reduction nitridation, and may remain in powder form, but a porous bulk body may be formed. In addition, this porous bulk body, for example, put the mixed powder containing the boron compound, carbon, and calcium carbonate in a container and heat it in the range of 100 to 300 ° C. for about 1 to 10 hours to produce metaboric acid from boric acid. Examples include a method in which a bulk body is formed by melting metaboric acid, and in the state where metaboric acid is melted, carbon dioxide gas is generated by decomposition of calcium carbonate and foamed.

  In addition, the shape of the porous bulk body may be appropriately determined according to the shape of the container or the like used for heating the mixed powder, and is not particularly limited, but for example, a quadrangular prism shape, a cylindrical shape, a spherical shape, Examples of the shape include a polygonal shape, an indefinite shape, a needle shape, and a plate shape. From the viewpoint of handling properties, a shape such as a quadrangular prism shape, a cylindrical shape, or a spherical shape is preferable. Further, the size is generally about 5 to 300 mm in diameter (equivalent diameter other than spherical).

  In the present invention, the mixing method of the oxygen-containing boron compound, carbon, and oxygen-containing calcium compound is not particularly limited, and general mixing such as a vibration mill, a bead mill, a ball mill, a Henschel mixer, a drum mixer, a vibration stirrer, a V-shaped mixer, etc. The machine is ready for use.

  In the method for producing boron nitride powder, the reduction nitriding can be performed by heating the raw material mixture in an atmosphere containing nitrogen gas. In this case, the nitriding temperature and the treatment time can generally be set as conditions under which boron nitride powder can be obtained. If the nitriding temperature is 1500 ° C. or higher, highly crystalline boron nitride powder can be obtained, and if it is 2000 ° C. or lower, the amount of heat can be used for the nitriding reaction with high efficiency.

  The gas used during nitriding may be any gas that can give nitrogen to boron under the above nitriding conditions, and ammonia gas may be used instead of nitrogen gas. A gas obtained by mixing ammonia gas with a non-oxidizing gas such as hydrogen, argon or helium can also be used.

  The above reaction can be performed using a known apparatus capable of controlling the reaction atmosphere. For example, an atmosphere-controlled high-temperature furnace that performs heat treatment by high-frequency induction heating or heater heating can be used. In addition to a batch furnace, a continuous furnace such as a pusher-type tunnel furnace or a vertical reaction furnace can also be used.

  In the method for producing boron nitride powder, the most important step is a step of pulverizing a boron nitride block obtained by reductive nitriding and then removing the remaining by-product by acid cleaning. That is, in this process, the phosphorus component present on the particle surface of the obtained boron nitride powder is adjusted to 4 ppmw or less in terms of phosphorus element. It is important to perform the acid cleaning. The substance obtained immediately after the above reduction nitriding (by-product containing boron nitride) is mainly composed of boron nitride, but also contains compounds such as calcium borate. Wash). Specifically, the acid cleaning is performed by immersing the above-mentioned by-product-containing boron nitride in an acid aqueous solution such as an aqueous hydrochloric acid solution, and then washing off the acid by further washing with water as necessary. However, in order to industrially implement the phosphorus component concentration, acid cleaning while irradiating ultrasonic waves, acid cleaning at high temperature and high pressure in an autoclave, or a combination of these means Is recommended.

  In the method using ultrasonic waves, byproduct-containing boron nitride is immersed in an acid aqueous solution, and, for example, 50 to 400 W is preferable, and treatment is preferably performed at 100 to 300 W for 1 hour or more, preferably 2 hours or more. preferable.

  The acid cleaning under the high temperature and high pressure involves immersing the by-product-containing boron nitride in an acid aqueous solution, for example, in an autoclave at a temperature of 100 to 180 ° C, preferably 110 to 150 ° C, and a pressure of 0.1. The condition of treatment at ˜0.8 MPa, preferably 0.2˜0.5 MPa for 10 minutes or longer, preferably 30 minutes or longer is preferably employed.

(Silicone resin composition)
In the silicone resin composition of the present invention, the mixing ratio of the alkenyl group-containing organopolysiloxane, organohydrogensiloxane and platinum-based curing agent constituting the silicone resin is not particularly limited, and is the same as that of a general silicone resin composition. be able to. The mixing ratio varies depending on the molecular weight and density of the main agent and the crosslinking agent, and the type of the platinum-based curing agent. Generally, the alkenyl group-containing organopolysiloxane has an alkenyl group content of 100 parts by mass of the alkenyl group-containing organopolysiloxane. The amount of the organohydrogensiloxane in which the Si—H group of the organohydrogensiloxane is 0.5 to 5 times the number of moles of the group, the amount of 0.0001 to 0.01 parts by mass in terms of platinum element It mixes in the ratio used as platinum hardening agent. Further, the mixing ratio of the boron nitride powder is not particularly limited, but in order to fully exhibit the effect of filling, the mixing ratio is 50 to 2000 parts by mass with respect to 100 parts by mass of the alkenyl group-containing organopolysiloxane. It is preferable to do.

  In the present invention, an important requirement is that, in the silicone resin composition, the phosphorus element equivalent amount of the phosphorus component present on the surface of the boron nitride powder is 5. 5 by mass ratio with respect to the platinum element equivalent amount of the platinum-based curing agent. The adjustment is made to be 0 or less, preferably 4.0 or less. That is, when the (P / Pt) mass ratio exceeds 5.0, the activity of the platinum-based curing agent is lowered due to the presence of the phosphorus component, and the silicone resin composition is not cured.

  The method for adjusting the (P / Pt) mass ratio to the above range is preferably performed in consideration of the phosphorus content and the filling amount of the boron nitride powder to be used. That is, as the amount of boron nitride powder used increases, it is necessary to use a lower phosphorus component as the boron nitride powder to be used. In particular, in the silicone resin composition, 40 vol. % Or more, and further, 60 vol. When boron nitride powder is used at a ratio of at least%, it is preferable to use boron nitride powder in which the concentration of the phosphorus component of such boron nitride powder is reduced to 3 to 4 ppmw in terms of phosphorus element. The upper limit for the ratio of the boron nitride powder may be within a range in which the silicone resin composition can be constituted, and practically 90 vol. %.

(Method for producing silicone resin composition)
The production method of the silicone resin composition of the present invention is similar to the production method of the known silicone resin composition as long as the concentration of the phosphorus component of the boron nitride powder is adjusted to a specific range. This can be done by mixing the raw materials.

  Specifically, it can be produced by mixing the above-mentioned alkenyl group-containing organopolysiloxane, organohydrogensiloxane, platinum-based curing agent, and boron nitride powder in the above mixing ratio. As a mixing method, mixing may be performed using a mortar or the like, or mixing may be performed using a general apparatus such as a gate mixer, a Banbury mixer, or a planetary mixer. In addition, the order of addition to the system at the time of mixing may be a known addition order without particular limitation.

  In the silicone resin composition of the present invention, the boron nitride powder may be used alone, but other fillers such as aluminum nitride, aluminum oxide, silicon oxide, etc. are generally used as fillers for the silicone resin composition. Can be used in combination.

  The silicone resin composition of the present invention may contain a dispersant, a flame retardant aid, a heat-resistant aid, etc., in addition to the silicone resin composed of a main agent and a crosslinking agent, an addition reaction catalyst, and a filler. Glass fiber cloth may be included as a skeleton.

(Method for curing silicone resin composition)
In the present invention, the method for curing the silicone resin composition can employ the same conditions as those for known curing methods for silicone resin compositions. For example, the silicone resin composition may be cured at room temperature, or may be accelerated by heating.

  EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples at all.

  In the examples, the concentration of the phosphorus component present on the particle surface of the boron nitride powder was determined by the following method.

  Sample 10 g of boron nitride powder was collected in a 100 cc container made of polytetrafluoroethylene, and 50 cc of a mixed acid aqueous solution of nitric acid and sulfuric acid (nitric acid 35% by mass, sulfuric acid 45% by mass) was put in the pressure decomposition vessel. After treatment at a pressure of 0.2 MPa and a temperature of 120 ° C. for 30 minutes, the mixed acid aqueous solution is separated, washed with water, the separated mixed acid solution and the water used for washing are mixed, and this is applied to an ICP analyzer to determine the amount of phosphorus component The phosphorus component concentration was determined from the measured value obtained and the weight of the boron nitride powder.

  It was confirmed by laser ablation ICP mass spectrometry that no phosphorus component was present on the surface of the boron nitride particles after the above treatment.

Example 1
After mixing in a ball mill 100 g of boric acid having an average particle diameter of 600 μm, 24 g of carbon black having an average particle diameter of 0.1 μm, phosphorus content (phosphorus element equivalent) of 8 ppmw, and 16 g of calcium carbonate having an average particle diameter of 5 μm as a crystallization agent. Then, it was put into a stainless steel container having a bottom surface of 90 mm × 40 mm and a height of 40 mm and heated at 300 ° C. for 8 hours in an air atmosphere to obtain a bulk material for boron nitride production.

  The bulk material was nitrided at 1850 ° C. for 2 hours in a nitrogen gas atmosphere using a graphite Tamman furnace to obtain byproduct-containing boron nitride.

  The by-product-containing boron nitride is crushed and put into a glass container, and 5 times the amount of hydrochloric acid (7 wt% HCl) of the by-product-containing boron nitride is added, and 2 by an ultrasonic cleaner with an output of 200 W. Time processed. Subsequently, water washing was performed by washing and filtering five times with an equal amount of water of the byproduct-containing boron nitride. Boron nitride powder was obtained by drying after filtration.

  The concentration of the phosphorus component present on the surface of the boron nitride powder was 3.4 ppmw in terms of phosphorus element.

Example 2
The same procedure as in Example 1 was performed except that carbon black having a phosphorus content (in terms of phosphorus element) of 18 ppmw was used and the treatment time with an ultrasonic washer was 3 hours.

  The concentration of phosphorus component present on the surface of the obtained boron nitride powder was 3.7 ppmw in terms of phosphorus element.

Example 3
The same procedure as in Example 1 was performed except that carbon black having a phosphorus content (in terms of phosphorus element) of 40 ppmw was used and the treatment time with an ultrasonic washer was 6 hours.

  The concentration of the phosphorus component present on the surface of the obtained boron nitride powder was 3.8 ppmw in terms of phosphorus element.

Example 4
By-product-containing boron nitride is crushed and placed in a polytetrafluoroethylene container, and 5 times the amount of hydrochloric acid (7 wt% HCl) of the by-product-containing boron nitride is added to the lid, and set in an autoclave. And it carried out similarly to Example 1 except having performed acid washing by processing at 120 degreeC and 0.2 Mpa for 1 hour.

  The concentration of phosphorus component present on the surface of the obtained boron nitride powder was 3.0 ppmw in terms of phosphorus element.

Comparative Example 1
Using carbon black having a phosphorus content (in terms of phosphorus element) of 60 ppmw, the byproduct-containing boron nitride obtained after nitriding was crushed and put into a glass container. Double the amount of hydrochloric acid (7% by weight HCl) was added, and the same procedure as in Example 1 was performed, except that acid washing was performed by stirring at 800 rpm for 24 hours.

  The concentration of phosphorus component present on the surface of the obtained boron nitride powder was 7.1 ppmw in terms of phosphorus element.

Comparative Example 2
Using carbon black having a phosphorus content (in terms of phosphorus element) of 60 ppmw, the byproduct-containing boron nitride obtained after the nitriding treatment is crushed and charged into a glass container. Double the amount of hydrochloric acid (7% by weight HCl) was added, and the same procedure as in Example 1 was performed, except that acid cleaning was performed by stirring at 400 rpm for 10 hours.

  The concentration of phosphorus component present on the surface of the obtained boron nitride powder was 25 ppmw in terms of phosphorus element.

Comparative Example 3
Using carbon black having a phosphorus content (in terms of phosphorus element) of 60 ppmw, the byproduct-containing boron nitride obtained after the nitriding treatment is crushed and charged into a glass container. Double the amount of hydrochloric acid (7% by weight HCl) was added, and the same procedure as in Example 1 was performed, except that acid cleaning was performed by stirring at a rotation speed of 800 rpm for 48 hours.

  The concentration of phosphorus component present on the surface of the obtained boron nitride powder was 6.2 ppmw in terms of phosphorus element.

Examples 5 and 6
A silicone resin composition was prepared using the boron nitride powder prepared in Example 1. As the alkenyl group-containing organopolysiloxane, a vinyl-terminated polydimethylsiloxane (component A) having a general formula of (1), an average molecular weight of 24,000 g / mol, and a kinematic viscosity of 800 cSt measured with an Ostwald viscometer was used. As the organohydrogensiloxane, hydrogen-terminated polydimethylsiloxane (component B) having a general formula of (2), an average molecular weight of 1200 g / mol, and a kinematic viscosity measured by an Ostwald viscometer of 10 cSt was used. As a platinum type hardening | curing agent, what dissolved the chloroplatinic acid in xylene so that platinum concentration might be set to 200 ppmw in conversion of a platinum element (C component) was used. After mixing the above A to C components in a quartz mortar, the boron nitride powder produced in Example 1 was added to the mixture of the A to C components and further mixed to obtain a silicone resin composition. Table 2 shows the respective AC components, the weight of boron nitride powder, the volume ratio occupied by boron nitride powder, the amount of phosphorus component, and the amount of platinum component. The silicone resin composition is transferred to a disk-shaped mold having a diameter of 30 mm and a thickness of 8 mm, and molded using a heatable press machine at 150 ° C. for 30 minutes to cure the silicone resin composition. A cured product was obtained. The hardness of the cured silicone resin composition was measured (based on JIS K 6253) using a durometer GS-719N manufactured by Teclock Corporation. The hardness of the cured silicone resin composition is as shown in Table 2.

Example 7
Example 5 was repeated except that the boron nitride powder produced in Example 4 was used. Table 2 shows the volume ratio of the boron nitride powder in the silicone resin composition, the amount of phosphorus component, the amount of platinum component, and the hardness of the cured silicone resin composition.

Example 8
Example 5 was repeated except that the boron nitride powder prepared in Example 3 was used. Table 2 shows the volume ratio of the boron nitride powder in the silicone resin composition, the amount of phosphorus component, the amount of platinum component, and the hardness of the cured silicone resin composition.

Comparative Example 4
Example 5 was repeated except that the boron nitride powder produced in Comparative Example 1 was used. Table 2 shows the volume ratio of the boron nitride powder, the amount of phosphorus component, and the amount of platinum component in the silicone resin composition. The silicone resin composition did not cure even after thermoforming, and the hardness could not be measured.

Comparative Example 5
Example 5 was repeated except that the boron nitride powder produced in Comparative Example 3 was used. Table 2 shows the volume ratio of the boron nitride powder, the amount of phosphorus component, and the amount of platinum component in the silicone resin composition. The silicone resin composition did not cure even after thermoforming, and the hardness could not be measured.

  As described above, according to the present invention, a boron nitride powder that does not inhibit the curing of the silicone resin composition can be produced, and a silicone resin composition that is highly filled with boron nitride powder by using the boron nitride powder. It can be provided.

Claims (4)

  A boron nitride powder obtained by a reduction nitriding method, wherein a phosphorus component present on the particle surface of the boron nitride powder is 3 to 4 ppmw in terms of phosphorus element.   A step of removing the remaining by-product by acid washing after pulverizing a boron nitride block obtained by reducing and nitriding the oxygen-containing boron compound by using carbon as a reducing agent and reacting with nitrogen; At this time, the above-mentioned acid cleaning is performed so that the phosphorus component present on the particle surface of the obtained boron nitride powder is 4 ppmw or less in terms of phosphorus element.   The method for producing boron nitride powder according to claim 2, wherein carbon having a phosphorus content of 50 ppmw or less in terms of phosphorus element is used.   The filler for silicone resins containing the boron nitride powder of Claim 1.