JP2012056818A - Hexagonal boron nitride powder and high heat conductivity and high moisture resistance heat radiation sheet using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat radiation sheet excellent in heat conductivity and moisture resistance, and a hexagonal boron nitride powder used in the heat radiation sheet.SOLUTION: The hexagonal boron nitride powder has been subjected to a surface modification treatment with a silane coupling agent having an organic functional group containing a vinyl group, and has an aggregate shape formed by aggregating scale-like primary particles of hexagonal boron nitride having a methanol-soluble BOcontent of 0.01-0.10% without orientation. The high heat conductivity and high moisture resistance heat radiation sheet is prepared by formulating the hexagonal boron nitride powder into a resin and/or rubber.

Description

  The present invention relates to an aggregated hexagonal boron nitride powder in which primary particles of scaly boron nitride suitable for a high thermal conductive filler are aggregated without being oriented, and uses thereof.

  Hexagonal boron nitride powder is a white powder that has the same hexagonal layered structure as graphite and has excellent properties such as high thermal conductivity, lubricity, and electrical insulation. A resin / rubber composition containing a powder is used as an insulating heat dissipation sheet for efficiently releasing heat generated from an electronic component.

However, the insulating heat-radiating sheet using the conventional boron nitride powder has insufficient electrical insulation, and has a problem that moisture-conducting conduction occurs particularly when the humidity is high.
Therefore, in order to solve the above problem, it has been proposed that the boron nitride powder is “surface-modified with a silane coupling agent having an organic group containing a group selected from an amino group and a mercapto group” ( Patent Document 1).

In the invention described in Patent Document 1, the electrical insulation resistance after moisture absorption is improved by the surface modification treatment, but the thermal resistance is comparable to that without the surface modification treatment. In the case of using for the above, further improvement in thermal conductivity (heat dissipation) has been desired.
Patent Document 1 also shows, as a comparative example, boron nitride powder surface-modified with a silane coupling agent having an organic functional group containing a vinyl group, but the electrical insulation resistance after moisture absorption is improved. No results have been reported (paragraphs [0025] and [0026]).

  On the other hand, for the purpose of providing a boron nitride powder that can be highly filled into a resin or rubber, a boron nitride powder having a “boron oxide content of 2.0 wt% or less” is known (see Patent Document 2). Reference 2 specifically shows that the amount of boron oxide is 0.1% (paragraph [0037] Table 2). In order to obtain a heat dissipation sheet, this boron nitride powder was silane coupled. It is not shown that it is surface-modified with an agent and blended into resin or rubber.

  Further, “boron nitride powder having an average particle diameter of 5 to 25 μm and an ethanol-soluble boron oxide content of 1% by mass or less (including 0%)” is known (see Patent Document 3). Specifically, boron nitride powder having an ethanol-soluble boron oxide content of 0.04% is also shown (paragraph [0027] Table 1). This boron nitride powder is blended with resin or rubber. It is not shown to be a heat dissipation sheet.

Patent Document 4 discloses an aggregated hexagonal boron nitride powder in which flaky primary particles of hexagonal boron nitride do not contain a binder and are assembled without being oriented, and this boron nitride powder It is also shown that an insulating heat-dissipating sheet is blended with silicone rubber, but this boron nitride powder is surface-modified with a silane coupling agent, and the electrical insulation resistance after moisture absorption of the sheet is improved. Is not described, and the amount of B ₂ O ₃ of the hexagonal boron nitride powder after firing at 2000 ° C. is not described.

Japanese Patent No. 4070345 JP 2000-7310 A JP 2006-124203 A Japanese Patent No. 3461651

  In view of the prior art as described above, an object of the present invention is to provide a heat radiating sheet excellent in thermal conductivity and moisture resistance, and to provide a hexagonal boron nitride powder used for the heat radiating sheet.

In order to solve the above problems, the following means are adopted in the present invention.
(1) A hexagonal boron nitride powder which has been surface-modified with a silane coupling agent having an organic functional group containing a vinyl group, and the amount of methanol-soluble B ₂ O ₃ is 0.01 to 0.10% This is an aggregated hexagonal boron nitride powder characterized in that the flaky primary particles of hexagonal boron nitride are aggregated without being oriented.
(2) A high heat conductivity and high moisture resistance heat radiation sheet, wherein the hexagonal boron nitride powder of (1) is blended with a resin and / or rubber.
(3) The high thermal conductivity and high moisture resistance heat radiation sheet according to (2), wherein the resin and / or rubber is silicone.

  The heat radiating sheet using the hexagonal boron nitride powder of the present invention has an effect of being excellent in thermal conductivity and moisture resistance.

  In the present invention, aggregated hexagonal boron nitride powder (hereinafter referred to as “hBN”) can be produced by the method disclosed in Patent Document 4.

First, as described in Patent Document 4, as a raw material, melamine borate (C ₃ N ₆ H ₆ .2H ₃ BO formed by holding a mixture of boric acid and melamine in an atmosphere containing appropriate water vapor is used. ₃ ) Use particles or a mixture containing them.

Next, melamine borate particles or a mixture containing the same is crystallized using a conventional crystallization catalyst. As the crystallization catalyst used in the present invention, a catalyst which is inexpensive and hardly changes its catalytic ability during the firing process is suitable. Examples thereof include boric acid, alkali metal or alkaline earth metal borates, and alkali metal or alkaline earth metal compounds that can react with boric acid to form alkali metal or alkaline earth metal borates. More specifically, alkali metal or alkaline earth metal borates include anhydrous borax (Na ₂ B ₄ O ₇ ), calcium borate (χCaO · B ₂ O _3, where χ = 0.5-3 ] Or the like, and alkali metal or alkaline earth metal compounds that can react with boric acid to form an alkali metal or alkaline earth metal borate include sodium carbonate (Na ₂ CO ₃ ) and calcium carbonate (CaCO ₃ ). Etc.

  The crystallization catalyst is added at the stage where melamine borate is formed at the time of raw material mixing, and further, after calcination, amorphous BN or low crystalline hBN exceeding GI value 2.5 is formed. Any of these stages may be used, but when calcination is performed, it may be added before or after calcination.

The amount of crystallization catalyst used is the molar ratio of melamine borate (C ₃ N ₆ H ₆ .2H ₃ BO ₃ ) to the B ₂ O ₃ equivalent of the crystallization catalyst (C ₃ N ₆ H ₆ .2H ₃ BO ₃ / B ₂ O ₃ ) is an amount that makes 5 to 100. In addition, when the raw material is calcined to form amorphous BN or low crystalline hBN exceeding the GI value of 2.5, the nitrogen (N) of hBN and the B ₂ O ₃ equivalent of the crystallization catalyst The molar ratio (N / B ₂ O ₃ ) is 10 to 300. When the molar ratio is larger than the above (the amount of catalyst is small), the generated hBN powder has low crystallinity, and when the molar ratio is small (the amount of catalyst is large), the generated hBN powder is aggregated in the form of scaly particles. No longer.

The calcination is performed by mixing the melamine borate particles or a mixture containing the crystallization catalyst with the crystallization catalyst in a non-oxidizing gas atmosphere at a temperature of 1800 to 2200 ° C. In an oxidizing gas atmosphere, calcination is performed at a temperature of 500 ° C. or more and less than 1700 ° C. to obtain amorphous BN or hBN having a GI value exceeding 2.5, and then a crystallization catalyst is added. Performed at ~ 2200 ° C. When the firing temperature is less than 1800 ° C., it is difficult to obtain a target hBN powder having an amount of B ₂ O _3, and when it exceeds 2200 ° C., the decomposition of the hBN powder becomes remarkable. Non-oxidizing gases include nitrogen gas, hydrogen gas, ammonia gas, hydrocarbon gases such as methane and propane, rare gases such as helium and argon, and carbon monoxide gas. Of these, nitrogen gas is most suitable because it is easily available, inexpensive, and has a large effect of suppressing the decomposition of hBN at high temperatures of 2000 to 2200 ° C. The firing time is preferably 1 to 24 hours, particularly 2 to 10 hours.

In the present invention, as described above, for example, by changing the time for firing (purification treatment) at 2000 ° C., the desired hBN powder having the amount of B ₂ O ₃ can be obtained. For example, B ₂ O ₃ amount is 0.10% of the hBN powder obtained in 2 hours calcination, the longer the sintering time so that 0.02% of the hBN powder is obtained in 5 hours firing B ₂ O ₃ The amount is reduced.

  Examples of the firing furnace include batch furnaces such as muffle furnaces, tubular furnaces, and atmospheric furnaces, and continuous furnaces such as rotary kilns, screw conveyor furnaces, tunnel furnaces, belt furnaces, pusher furnaces, and vertical continuous furnaces. These are properly used according to the purpose. For example, a batch furnace is used when small quantities of many types of hBN powders are produced, and a continuous furnace is adopted when a certain quantity is produced in large quantities.

About the obtained hBN powder, the content of methanol-soluble B ₂ O ₃ remaining in the hBN powder was measured by the measurement method shown below.
The hBN powder was immersed in methanol, and B ₂ O ₃ remaining in the hBN powder was reacted with methanol to obtain metaboric acid. Metaboric acid was evaporated by heating the hBN powder after being immersed in methanol at 120 ° C., and the amount of methanol-soluble B ₂ O ₃ was determined from the amount of decrease in the mass of the hBN powder.
1. The washed and dried weighing bottle is taken out of the dryer and cooled with a desiccator. (Cooling for 1 to 1.5 hours)
2. About 5 g (A) of hBN powder is precisely weighed in a weighing bottle. (5.0-5.5g)
3. Dry for 2 hours or more in an electric constant temperature dryer.
4). After drying, the weighing bottle is taken out, cooled in a desiccator, and the mass (B) is measured with a balance.
5. The moisture is calculated by the following formula.
Moisture (%) = [hBN powder source mass (A)-mass after drying (B)] / hBN powder source mass (A)
6). 15 ml of methanol is added to the sample in the weighing bottle after the moisture is determined, and the methanol is volatilized in an explosion-proof dryer at 80 ° C. for 1.5 to 2.0 hours.
7). Next, the temperature of the dryer is raised to 120 ° C., and drying is performed at 120 ° C. for 1.5 hours. (Methanol is volatilized completely).
8). The weighing bottle is taken out, cooled in a desiccator, and weighed (C).
9. The amount of methanol-soluble B ₂ O ₃ is calculated by the following formula.
Methanol-soluble B ₂ O ₃ amount (%) = [mass after drying hBN powder (B) −mass after methanol volatilization (C)] / mass after drying hBN powder (B)

A silane coupling agent having an organic functional group containing a vinyl group from an aggregated hBN powder having a methanol-soluble B ₂ O ₃ content in the range of 0.01 to 0.10% measured as described above. When heat-treating the surface, the heat-dissipating sheet obtained by blending this hBN powder with resin and / or rubber has a low thermal resistance and high thermal conductivity, and the insulation resistance after moisture absorption is significantly improved, resulting in moisture absorption resistance. As a result, the present invention has been achieved.
When the amount of methanol-soluble B ₂ O _{3 in the} hBN powder is less than 0.01, the thermal resistance increases and the thermal conductivity decreases. On the other hand, when the amount of methanol-soluble B ₂ O ₃ exceeds 0.10%, the thermal conductivity is lowered and the moisture absorption resistance is also lowered. Therefore, in the present invention, the amount of methanol-soluble B ₂ O ₃ in the hBN powder is set to 0.01 to 0.10%. The amount of methanol-soluble B ₂ O ₃ is preferably 0.03 to 0.06%.
Moreover, even if the amount of methanol-soluble B ₂ O ₃ is within the scope of the present invention, the scale-like hBN powder that is not aggregated has a high thermal resistance and a low thermal conductivity.

In the present invention, hBN powder having an amount of methanol-soluble B ₂ O _{3 in} the range of 0.01 to 0.10% is surface-modified with a silane coupling agent having an organic functional group containing a vinyl group. This is very important.
As the silane coupling agent having an organic functional group containing a vinyl group, vinyltris (methoxyethoxy) silane, vinylmethoxysilane, vinylmethyldimethoxysilane, vinyltrichlorosilane, and the like can be used.
It is preferable to add 0.03-10 mass% of silane coupling agents which have an organic functional group containing a vinyl group with respect to hBN.

Silane coupling containing dimethyl group instead of vinyl group even when hBN powder having a methanol-soluble B ₂ O ₃ content in the range of 0.01 to 0.10% is used, as shown in a comparative example described later. Hygroscopicity is reduced when surface modification is performed with an agent, and moisture absorption is improved when surface modification is performed with a silane coupling agent containing an epoxy group, methacryl group or amino group. However, it is not preferable because the thermal conductivity is lowered.

  As a method of surface-modifying the hBN powder with a silane coupling agent, as shown in the examples described later, when the hBN powder is blended with a resin and / or rubber, a silane coupling agent together with a solvent such as toluene. It is preferable to employ a method of mixing the two simultaneously. Alternatively, the hBN powder may be previously treated with a silane coupling agent by a conventional method, and this may be blended with the resin and / or rubber.

In the present invention, as the resin and / or rubber in which hBN powder subjected to surface modification treatment with a silane coupling agent having an organic functional group containing a vinyl group is blended, silicone resin, epoxy resin, polyamide resin, polycarbonate Resin, silicone rubber, polystyrene rubber and the like can be used, but silicone resin or silicone rubber is preferable.
The blending ratio of hBN with respect to the resin and / or rubber is preferably 138 to 163% by volume.

Example 1
1 kg of H ₃ BO ₃ and 0.87 kg of melamine were mixed with a ribbon blender, and this was kept in an atmosphere containing water vapor at a temperature of 80 ° C. and a relative humidity of 80% in the atmosphere for 24 hours using a thermo-hygrostat. The obtained mixture is aggregated to such an extent that it can be easily crushed when pressed lightly with a finger. According to SEM observation, it is confirmed that the mixture is a mixture containing particles in which primary particles of melamine borate crystals are aggregated. It was.

  This was calcined continuously using a screw conveyor furnace in an ammonia atmosphere so as to pass through a heating section at a temperature of 800 ° C. in 2 hours. When the obtained calcined product was subjected to powder X-ray diffraction analysis, it was confirmed to be amorphous BN.

Next, 9% by mass of calcium carbonate (CaCO ₃ ) was internally added as a crystallization catalyst to the calcined product, and calcined at 2000 ° C. for 8 hours in a nitrogen atmosphere using an atmosphere furnace. When the fired sample was pulverized to 150 μm or less and subjected to powder X-ray diffraction measurement, it was confirmed to be a mixture of hBN and calcium borate (3CaO · B ₂ O ₃ ). This was mixed with a dilute nitric acid solution, filtered, and dried to remove calcium borate and the SEM photograph was observed. confirmed.
With respect to the obtained hBN powder, the amount of methanol-soluble B ₂ O ₃ was measured as described above, and it was 0.010%.

  100 parts by mass of a dimethyl silicone polymer, 346 parts by mass of the above hBN powder, 3 parts by mass of vinyltris (methoxyethoxy) silane (Z-6172 manufactured by Toray Dow Corning Co., Ltd.) as a surface treatment agent for hBN powder, and water 0.4 1 part by weight of 2,5-dimethyl-2,5-di (t-butylperoxy) hexane as a crosslinking agent is dispersed in 502 parts by weight of toluene and mixed with a stirrer for 15 hours to obtain a silicone rubber composition. Adjusted. The surface modification treatment of the hBN powder is performed simultaneously with mixing with the silicone polymer and toluene.

The above silicone rubber composition was coated on both surfaces of a 0.03 mm thick glass fiber cloth (H-12 manufactured by Unitika Co., Ltd.) with a doctor blade to a thickness of 0.6 mm, and then dried at 75 ° C. for 5 minutes. Then, press heating and pressing were performed for 25 minutes under conditions of a temperature of 150 ° C. and a pressure of 160 kg / cm ² to form a 0.3 mm sheet. Next, it was subjected to secondary heating for 4 hours at a normal pressure of 150 ° C. to obtain a heat radiating sheet.

(Example 2)
An hBN powder was obtained in the same manner as in Example 1 except that the firing time at 2000 ° C. was changed to 4.5 hours.
With respect to the obtained hBN powder, the amount of methanol-soluble B ₂ O ₃ was measured as described above, and it was 0.030%. Using this hBN powder, a heat radiating sheet was prototyped in the same manner as in Example 1.

Example 3
An hBN powder was obtained in the same manner as in Example 1 except that the firing time at 2000 ° C. was changed to 4 hours.
With respect to the obtained hBN powder, the amount of methanol-soluble B ₂ O ₃ was measured as described above, and it was 0.040%. Using this hBN powder, a heat radiating sheet was prototyped in the same manner as in Example 1.

Example 4
An hBN powder was obtained in the same manner as in Example 1 except that the firing time at 2000 ° C. was changed to 3 hours.
With respect to the obtained hBN powder, the amount of methanol-soluble B ₂ O ₃ was measured as described above, and it was 0.060%. Using this hBN powder, a heat radiating sheet was prototyped in the same manner as in Example 1.

(Example 5)
An hBN powder was obtained in the same manner as in Example 1 except that the firing time at 2000 ° C. was changed to 2 hours.
With respect to the obtained hBN powder, the amount of methanol-soluble B ₂ O ₃ was measured as described above, and it was 0.100%. Using this hBN powder, a heat radiating sheet was prototyped in the same manner as in Example 1.

(Comparative Example 1)
A heat radiating sheet was produced in the same manner as in Example 1 except that the hBN powder was in the form of scales (SGP grade, manufactured by Denki Kagaku Kogyo Co., Ltd.).

(Comparative Example 2)
A heat radiating sheet was prototyped in the same manner as in Example 1 except that the surface treatment agent for hBN powder was not added.

(Comparative Example 3)
An hBN powder was obtained in the same manner as in Example 1 except that the firing time at 2000 ° C. was changed to 22 hours.
With respect to the obtained hBN powder, the amount of methanol-soluble B ₂ O ₃ was measured as described above, and it was 0.005%. Using this hBN powder, a heat radiating sheet was prototyped in the same manner as in Example 1.

(Comparative Example 4)
An hBN powder was obtained in the same manner as in Example 1 except that the firing time at 2000 ° C. was changed to 1 hour.
With respect to the obtained hBN powder, the amount of methanol-soluble B ₂ O ₃ was measured as described above, and it was 0.130%. Using this hBN powder, a heat radiating sheet was prototyped in the same manner as in Example 1.

(Comparative Example 5)
A heat radiating sheet was produced in the same manner as in Example 1 except that dimethyldimethoxysilane (AY manufactured by Toray Dow Corning Co., Ltd.) was used as the surface treatment agent for the hBN powder.

(Comparative Example 6)
A heat radiating sheet was produced in the same manner as in Example 1 except that 3-glycidoxypropyltrimexisilane (A187 manufactured by MOMENTIVE Co., Ltd.) was used as the surface treatment agent for hBN powder.

(Comparative Example 7)
A heat radiating sheet was produced in the same manner as in Example 1 except that 3-methacryloxypropyltrimethoxysilane (A174 manufactured by MOMENTIVE Co., Ltd.) was used as the surface treatment agent for the hBN powder.

(Comparative Example 8)
A heat radiating sheet was produced in the same manner as in Example 1 except that γ-aminopropyltriethoxysilane (TSL8331 manufactured by MOMENTIVE Co., Ltd.) was used as the surface treatment agent for hBN powder.

The insulation evaluation of the heat-radiation sheets of Examples 1 to 5 and Comparative Examples 1 to 8 manufactured as prototypes was performed as follows. The thermal resistance was measured using a sheet sandwiched between a TO-3 type transistor and a copper plate and attached at 5 kgf · cm. Furthermore, the sheet is sandwiched between an aluminum plate and a copper nickel plated plate 55 × 70 mm plate, and torque 7 using M5 screws.
The one attached with kgf · cm was absorbed for 5 hours under the conditions of a temperature of 85 ° C. and a relative humidity of 85%, and the electrical resistance after moisture absorption was measured in that atmosphere. The measurement results are shown in Table 1.

From Table 1, an aggregated hBN powder formed by aggregation of hBN scaly primary particles having an amount of methanol-soluble B ₂ O ₃ of 0.01 to 0.10% without orientation is used. In Examples 1 to 5 in which the surface modification treatment was performed with a silane coupling agent having an organic functional group containing N, the thermal resistance was as low as 0.12 to 0.16 ° C./W, and the thermal conductivity was low. It can be seen that the electrical resistance after moisture absorption is as high as 3.0 × 10 ^{9 to} 4.7 × 10 ¹⁰ Ω, and the moisture resistance is excellent.
In particular, when an aggregated hBN powder having an amount of methanol-soluble B ₂ O ₃ of 0.03 to 0.06% is used, the thermal resistance is remarkably reduced to 0.12 to 0.13 ° C./W, The electrical resistance after moisture absorption is remarkably high at 2.4 × 10 ^{10 to} 4.7 × 10 ¹⁰ Ω, and a heat dissipation sheet having excellent heat conductivity and moisture resistance can be obtained.

On the other hand, in Comparative Example 3 using the hBN powder having an amount of methanol-soluble B ₂ O ₃ of less than 0.01, the thermal resistance is increased to 0.17 ° C./W and the thermal conductivity is lowered. In Comparative Example 4 using hBN powder having an amount of methanol-soluble B ₂ O ₃ exceeding 0.10%, the thermal resistance is increased to 0.17 ° C./W, the thermal conductivity is lowered, and the electric power after moisture absorption is reduced. The resistance is lowered to 2.4 × 10 ⁷ Ω, and the moisture absorption resistance is also lowered.
Further, even when the amount of methanol-soluble B ₂ O ₃ is 0.02%, in Comparative Example 1 using scale-like hBN powder that is not aggregated, the thermal resistance is as high as 0.23 ° C./W, and heat conduction is increased. Sex is reduced.

Even when the same hBN powder as in Example 1 having a methanol-soluble B ₂ O ₃ content of 0.01% was used, when the surface modification treatment was performed with a silane coupling agent containing a dimethyl group, the electrical resistance after moisture absorption Is reduced to 2.4 × 10 ⁷ Ω, resulting in a decrease in moisture absorption resistance. Also, when surface modification is performed with a silane coupling agent containing an epoxy group, a methacryl group or an amino group, the moisture absorption resistance is improved. However, the thermal resistance is increased to 0.22 to 0.27 ° C./W, and the thermal conductivity is lowered.

  By using the hexagonal boron nitride powder of the present invention, the heat radiating sheet becomes highly heat-conductive and highly moisture-resistant, so it can be used as an insulating heat-radiating sheet for efficiently releasing heat generated from electronic components. it can.

Claims (3)

A hexagonal boron nitride powder which has been surface-modified with a silane coupling agent having an organic functional group containing a vinyl group, wherein the amount of methanol-soluble B ₂ O ₃ is 0.01 to 0.10%. Aggregated hexagonal boron nitride powder, characterized by aggregation of crystalline boron nitride scaly primary particles without orientation.   A high thermal conductivity, high moisture resistance heat-radiating sheet comprising the hexagonal boron nitride powder according to claim 1 in a resin and / or rubber.   The heat- and heat-resistant heat-dissipating sheet according to claim 2, wherein the resin and / or rubber is silicone.