JP6994229B2 - Method for manufacturing surface-modified boron nitride - Google Patents

Description

The present invention relates to a method for producing surface-modified boron nitride.

Boron nitride (BN) has excellent insulating properties and high thermal conductivity, and is used as a filler for, for example, a heat radiating material by taking advantage of this property. In order to improve the thermal conductivity of the heat-dissipating material, it is necessary to increase the filling amount of the filler to be blended in the matrix. However, when a resin is used for the matrix, there is a problem that the filling amount of boron nitride cannot be sufficiently increased because boron nitride has a low affinity (familiarity) with the resin. Therefore, various attempts have been made to modify the surface of boron nitride to improve its affinity with the resin.

Patent Document 1 discloses a method of oxidizing the surface of a boron nitride powder using supercritical water or subcritical water having a temperature of 375 ° C. or higher and 450 ° C. or lower and a pressure of 25 MPa or higher and 40 MPa or lower. Further, in Patent Document 1, the surface of the oxidized boron nitride powder is organically prepared by treating the boron nitride powder and organic modifiers such as thiols, amines and carboxylic acids together in subcritical water or supercritical water. A method of modifying with a modifier is also disclosed.

Patent Document 2 discloses a method of modifying the surface of boron nitride by heating boron nitride under the conditions of 800 ° C. to 1300 ° C. for 1 to 8 hours in an oxygen atmosphere.

Japanese Unexamined Patent Publication No. 2012-121744 Japanese Patent Application Laid-Open No. 09-012771

By the way, it is preferable that the surface modification of boron nitride is carried out at a low temperature and a low pressure as much as possible from the viewpoint of manufacturing cost and the like.

In this respect, since the method of Patent Document 1 is carried out under high temperature and high pressure using subcritical water or supercritical water, the apparatus for carrying out the method is expensive and the amount of processing per batch is small. Manufacturing costs tend to be high. In addition, it is difficult to increase the size of a device for realizing subcritical or supercritical, and even if the device can be increased in size, there is a danger in manufacturing using the device. Further, it is presumed that reaction control is difficult under high temperature and high pressure, and it is difficult to obtain surface-modified boron nitride satisfying desired physical properties.

Since the method of Patent Document 2 is carried out at a high temperature of 800 ° C. to 1300 ° C., the manufacturing cost is high and there is a concern that the boron nitride particles are fused to each other.

An object of the present invention is to provide a production method capable of producing surface-modified boron nitride at low cost.

The present invention provides the inventions of the following aspects.
(Item 1)
Heat treatment of boron nitride under saturated steam,
A method for producing surface-modified boron nitride, which is characterized by the above.
(Item 2)
Heat treatment of substantially only boron nitride,
The method for producing surface-modified boron nitride according to item 1, wherein the surface-modified boron nitride is produced.
(Item 3)
The heat treatment is carried out in a dry manner.
The method for producing surface-modified boron nitride according to item 1 or 2.
(Item 4)
The heat treatment is carried out at 180 ° C. or higher and 205 ° C. or lower.
The method for producing surface-modified boron nitride according to any one of items 1 to 3.
(Item 5)
The liquid absorption amount of the liquid paraffin is 75% by mass to 97% by mass with respect to the liquid absorption amount of the liquid paraffin of boron nitride before treatment.
The method for producing surface-modified boron nitride according to any one of items 1 to 4.

In the production method of the present invention, surface modification of boron nitride is performed under a relatively low temperature and low pressure of saturated steam, so that surface-modified boron nitride can be produced at low cost.

The method for producing surface-modified boron nitride of the present invention is characterized by heat-treating (hydroheat-treating) a powder of boron nitride as a raw material under saturated steam. Specifically, the boron nitride powder and water are placed in a pressure vessel such as an autoclave and heated to a predetermined temperature to treat the boron nitride powder under saturated steam.

The heat treatment can be carried out dry or wet.

"Wet" is the most common hydrothermal heat treatment (hydrothermal synthesis) method. Boron nitride powder as a raw material and water are mixed in advance to prepare a mixture (slurry), and liquid water is prepared under saturated steam pressure. It means that boron nitride is heat-treated under pressure. The method of the "wet" treatment is not particularly limited as long as the boron nitride is pressure-heated in liquid water. For example, as a heating method, there are a method of introducing steam generated by a boiler into a pressure vessel and a method of heating the pressure vessel containing the above-mentioned slurry from the outside with an electric heater or heat medium oil. Further, the slurry may be pressurized and heated in a stationary state without stirring, or may be stirred.

On the other hand, the "dry type" means that the boron nitride powder is heat-treated under saturated steam without adding water to the raw material boron nitride powder. In the dry heat treatment, for example, a container containing boron nitride powder is placed in a pressure vessel, and the pressure vessel is filled with saturated steam to heat-treat the boron nitride powder. The method of generating water vapor is not particularly limited, but for example, a method of putting a sufficient amount of water in the pressure vessel to generate saturated water vapor and heating the pressure vessel to evaporate the water to generate water vapor. , A method of putting steam generated by a boiler or the like into a pressure vessel. The boron nitride powder in the pressure vessel is heat-treated while being pressurized by steam. In the dry heat treatment, the boron nitride powder and water (in a liquid state) do not come into direct contact with each other during the heat treatment.

Since the dry heat treatment does not add water to the boron nitride powder, it has the following advantages over the wet heat treatment. That is, the amount of boron nitride powder charged per batch can be increased, the energy cost and heat treatment time can be reduced because the water in the slurry does not need to be heated, and the dehydration step and drying after the heat treatment is completed. Since no process is required, the manufacturing cost can be reduced.

In the production method of the present invention, it is preferable to heat-treat substantially only boron nitride. "Practically heat-treating only boron nitride" means that a substance other than water is not intentionally added to the boron nitride powder during the heat treatment, and the boron nitride powder is heat-treated together with unavoidable impurities. Is acceptable.

The heating temperature in the heat treatment is 100 ° C. or higher and 300 ° C. or lower, preferably 130 ° C. or higher and 270 ° C. or lower, and more preferably 170 ° C. or higher and 250 ° C. or lower. The heating temperature is not particularly limited as long as the surface modification of boron nitride progresses, but at high temperatures, the temperature may be 250 ° C. or lower due to a decrease in yield due to accelerated decomposition of the boron nitride surface and an increase in manufacturing cost. Especially preferable. Since the heat treatment is carried out under saturated steam, the pressure during the heat treatment is the same as the saturated water vapor pressure.

The heating time is not particularly limited as long as the surface modification of boron nitride proceeds, but the heat treatment for 48 hours or more is uneconomical.

The boron nitride powder after the heat treatment may be washed and dried, if necessary. For example, cleaning of the boron nitride powder may be performed to remove a compound (for example, −B (OH) ₂ or the like) formed on the surface of the boron nitride powder by heat treatment for the purpose of increasing the purity of the boron nitride. can. The drying method after washing is not particularly limited as long as it is a method capable of evaporating water from the boron nitride powder.

The liquid absorption amount (mass) of the liquid paraffin of the boron nitride powder after the heat treatment is preferably 75% by mass to 97% by mass with respect to the liquid absorption amount of the liquid paraffin of the raw material boron nitride powder. The liquid absorption amount is a value obtained by multiplying the mass (g) of the liquid paraffin required for the boron nitride powder to become one mass when liquid paraffin is added to 1 g of the boron nitride powder (that is, nitrided). It is a value converted per 100 g of boron powder). The amount of liquid absorbed is an index showing the affinity between the boron nitride powder and the matrix (for example, resin). The smaller the amount of liquid absorbed, the smaller the amount of matrix required to knead the boron nitride powder, that is, the filling ratio of the boron nitride powder to the matrix when filling the matrix with the boron nitride powder. Means that can be enhanced.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples.

Table 1 shows the experimental conditions and experimental results of Examples 1 to 9 and Comparative Examples 1 to 4. In addition, Comparative Examples 1, 3 and 4 are measurement data of the raw material boron nitride powder.

<Experimental methods of Examples 1 to 6>
In Examples 1 to 6, boron nitride was heat-treated by a dry method.
(1) A stainless steel vat containing 60 g of boron nitride powder (manufactured by Denka Co., Ltd., HGP: 5 μm product) was placed in an autoclave. A sufficient amount of water was placed in the autoclave to generate saturated steam at the target heating temperature. Since the boron nitride powder is contained in the stainless steel vat, the boron nitride powder and the water in the autoclave do not come into direct contact with each other during heating.
(2) The temperature was raised from room temperature to the target heating temperature at a predetermined rate of temperature rise (87.5 ° C./h when the target heating temperature was 205 ° C., 75 ° C./h when the target heating temperature was 180 ° C.).
(3) After reaching the target heating temperature, the temperature was maintained at that heating temperature for a predetermined time. The heating holding time of 0 hours in Example 1 means that the heating was stopped immediately after reaching the target heating temperature of 205 ° C.
(4) After the heating holding time had elapsed, the heating was stopped and the mixture was naturally cooled.
(5) The boron nitride powder after the heat treatment was washed with ion-exchanged water until the filtrate had a pH of 7.5 or less and an electric conductivity of 0.4 mS / m or less, and then dried at 120 ° C. for 24 hours to prepare a sample. Was produced.

<Experimental method of Example 7>
In Example 7, the boron nitride was heat-treated by a wet method.
(1) 60 g of the same boron nitride powder as above and 300 g of ion-exchanged water were placed in a stainless steel vat and mixed to prepare a slurry. A stainless steel vat containing the slurry was placed in an autoclave. A sufficient amount of water was placed in the autoclave to generate saturated steam at the target heating temperature. Since the slurry is contained in a stainless steel vat, the slurry does not come into direct contact with the water in the autoclave during heating.
(2) The steps after (1) above are the same as the steps (2) to (5) in the dry heat treatment of Examples 1 to 6.

<Experimental method of Example 8>
The test was carried out by the same method as in Example 3 except that the raw material boron nitride powder of Example 3 was replaced with boron nitride powder (manufactured by Denka Corporation, MGP: 10 μm product).

<Experimental method of Example 9>
The test was carried out by the same method as in Example 3 except that the raw material boron nitride powder of Example 3 was replaced with boron nitride powder (MBN-010T: 0.8 μm product manufactured by Mitsui Chemicals, Inc.).

<Experimental method of Comparative Example 2>
(1) An alumina crucible containing 120 g of the same boron nitride powder as above was placed in an electric furnace.
(2) The temperature was raised from room temperature to 900 ° C. at a heating rate of 200 ° C./h, and the temperature was maintained at 900 ° C. for 10 hours.
(3) After that, natural cooling was performed, and the same washing step and drying step as in the steps (5) in Examples 1 to 6 were performed to prepare a sample.

<Measurement of liquid absorption>
The liquid absorption measurement carried out in Examples 1 to 9 and Comparative Examples 1 to 4 was carried out using liquid paraffin with reference to the oil method for boiled flax of JIS5101-13-2. The measurement procedure is as follows.
(1) 1 g of boron nitride powder was placed on a glass petri dish.
(2) Liquid paraffin was added from the dropper in two drops at a time. Each time liquid paraffin was added, the liquid paraffin was kneaded into the boron nitride powder with a palette knife.
(3) The liquid absorption amount is the value obtained by multiplying the mass (g) of the liquid paraffin required up to that point by 100 times the mass (g) of the liquid paraffin required up to that point, with the end point being the place where the lumps of the liquid paraffin and the boron nitride powder are formed by repeating the operation of the above (2). And said.
(4) The liquid absorption amount measured in Examples 1 to 9 and Comparative Example 2 is the liquid absorption amount of the comparative example of the same raw material grade (that is, the liquid absorption of Comparative Example 1 in Examples 1 to 7 and Comparative Example 2). Amount, in Example 8, the amount of liquid absorbed in Comparative Example 3, and in Example 9, the amount of liquid absorbed in Comparative Example 4) divided by the value converted into a percentage and the amount of change in liquid absorption (the amount of liquid absorbed by the raw material boron nitride powder). Rate of change).

<Measurement of thermal conductivity>
(1) 5 g of boron nitride powder and 40 g of epoxy resin (Epomic (registered trademark) R140P manufactured by Mitsui Chemicals, Inc.) are placed in a rotating revolution mixer (ARE-310 manufactured by Shinky) and mixed at a revolution of 2000 rpm and a rotation of 1200 rpm for 2 minutes. did.
(2) To the mixture prepared in (1) above, 5 g of boron nitride powder was further added, and further mixing was carried out at the same rotation speed and mixing time as in (1) above.
(3) To the mixture prepared in (2) above, 5 g of boron nitride powder was further added, and further mixing was carried out at the same rotation speed and mixing time as in (1) above.
(4) To the mixture prepared in (3) above, 5 g of boron nitride powder and 0.8 g of 2-ethyl4-methylimidazole (manufactured by Wako Pure Chemical Industries, Ltd.) as an initiator are further added, and the above ( Further mixing was performed at the same rotation speed and mixing time as in 1), and after the mixing was completed, the defoaming treatment operation was performed for 2 minutes.
(5) The mixture prepared in (4) above was heat-cured at 120 ° C. for 2 hours to prepare a sample for measuring thermal conductivity.
(6) The sample prepared in (5) above was cut into a size of 40 mm × 40 mm × 20 mm and held in a constant temperature bath at 25 ° C. for 2 hours or more.
(7) The thermal conductivity of the sample obtained in (6) above was measured using a rapid thermal conductivity meter (QTM-500, manufactured by Kyoto Electronics Manufacturing Co., Ltd.).
(8) The thermal conductivity measured in Examples 1 to 9 and Comparative Example 2 is the thermal conductivity of the comparative example of the same raw material grade (that is, the thermal conductivity of Comparative Example 1 in Examples 1 to 7 and Comparative Example 2). The rate, the value converted into a percentage by dividing by the thermal conductivity of Comparative Example 3 in Example 8 and the thermal conductivity of Comparative Example 4 in Example 9) is the thermal conductivity change rate (when the raw material boron nitride powder is used). Rate of change with respect to thermal conductivity).

<Yield>
The value obtained by dividing the mass of the boron nitride powder recovered after the treatment by the mass of the boron nitride powder before the treatment and converting it into a percentage was defined as the yield.

<Particle observation>
The particle state of the boron nitride powder was observed with a scanning electron microscope (SEM).

When compared with the same raw material grade, the amount of liquid absorbed by the surface-modified boron nitride in each example was smaller than that in the comparative example. Therefore, if the surface-modified boron nitride of the example is used, the filling amount to the matrix can be increased.

When compared with the same raw material grade, the thermal conductivity of the resin composition kneaded with the surface-modified boron nitride powder of the example was higher than that of the comparative example. It is considered that this is because the surface modification of the surface-modified boron nitride powder increases the affinity between the surface-modified boron nitride powder and the resin, and as a result, the adhesion between the surface-modified boron nitride powder and the resin is improved. .. When the dry heat treatment (Example 3) and the wet heat treatment (Example 7) were compared, the dry heat treatment had a higher thermal conductivity.

In Examples 1 to 7, the yield was more than 90%. On the other hand, in Comparative Example 2, the yield was as low as 82.3%. When the dry heat treatment (Example 3) and the wet heat treatment (Example 7) were compared, the yield of the dry heat treatment was higher.

As a result of SEM observation, no fusion of particles was observed in the surface-modified boron nitride powder of the example. On the other hand, in the surface-modified boron nitride powder of Comparative Example 2, fusion of particles was observed.

Claims (3)

Boron nitride is not brought into contact with liquid water, and is subjected to dry heat treatment at a temperature of 180 ° C. or higher and 205 ° C. or lower under saturated steam pressure by steam generated from water.
A method for producing surface-modified boron nitride, which is characterized by the above. Heat treatment of substantially only boron nitride,
The method for producing surface-modified boron nitride according to claim 1. The amount of liquid paraffin absorbed is 75 relative to the amount of liquid paraffin of untreated boron nitride.
Mass% to 97% by mass,
The method for producing surface-modified boron nitride according to claim 1 or 2 .