KR101579890B1 - A method for synthesizing nano-sized highly disperse a-alumina and a method for synthesizing the insulated high thermal conductivity a-alumina sol - Google Patents

Abstract

The present invention provides a method for synthesizing a nano-sized highly-dispersible a-alumina and an insulating high thermal conductivity a-alumina sol synthesized by the method. The α-alumina synthesis method of the present invention is capable of synthesizing uniformly highly dispersed nanoparticles containing no coarse particles at a low temperature of about 300 ° C. for a comparatively short period of time, using a solvent heating method, and exhibiting excellent insulating properties and excellent thermal properties . Also, by controlling the type of boehmite and the particle size and number of the alumina seed, the particle size and distribution of the a-alumina particles can be easily controlled.

Description

METHOD FOR PREPARATION OF ALUMINUM WITH HIGH DISPERSIBLE NANOSIZE PARTICLES AND ELECTRICALLY INSULATED THERMAL CUNDUCTIVE ALUMINA SOL PREPARED THEREFORM The present invention relates to a method of synthesizing a high-

The present invention relates to a process for synthesizing nano-sized highly disperse a-alumina and to an insulating high thermal conductivity alumina sol synthesized by the method.

The α-alumina has excellent mechanical, electrical and optical properties and is used in various applications such as abrasives, plasma spray materials, fillers, raw materials for sintered products, raw materials for fluorescent materials, insulating materials, and optical materials. Especially recently, there is a demand for the use of a-alumina having a fine and homogeneous structure and a narrow particle size distribution as a precision abrasive.

The Bayer method, which is capable of mass-producing an a-alumina powder at low cost on an industrial scale, is a method for producing a-alumina by converting bauxite to aluminum hydroxide or transition alumina, followed by calcination in air. However, since the α-alumina having good properties in terms of crystallinity and purity can not be obtained by the above method, large aggregates appear in the intermediate aluminum hydroxide or transitional alumina state. Therefore, the α-alumina powder obtained by calcining the α- It has an irregular particle shape including coarse coarse particles. In addition, the degree of transition depends on the temperature and time of heat treatment, and a disadvantage is that a high temperature of about 1230 ° C is required for complete transition within a reasonable time.

As a method for synthesizing α-alumina to solve such problems, studies on solution synthesis methods such as sol-gel method, hydrothermal synthesis method and coprecipitation method have been actively studied. High-purity stoichiometric crystalline ceramic microparticles can be obtained by the liquid phase synthesis method. In particular, the hydrothermal synthesis method is capable of growing single crystal grains in a solution state at a much lower temperature than the solid phase reaction, and controlling the particle size and shape, and thus, many researches and commercial applications have been made. Also, synthesis of a-alumina by hydrothermal reaction is known, but since a high temperature and high pressure are required in a closed reactor, there is a problem that the synthesis speed of a single phase material is slow.

Thus, synthesis using an organic solvent rather than an aqueous solution has been studied, and Adair et al. Have synthesized a-alumina using a glycol solution of a dihydric alcohol to obtain a narrow particle size distribution, The speed was adjusted to obtain particle size and shape control results. However, when aluminum hydroxide produced by the precipitation method is used as a precursor, contamination of alkali metals such as Na, K and the like can not be avoided, and there is a problem that a high-purity a-alumina can not be produced. Also, coarse particles can be synthesized together by aggregation of primary particles.

Therefore, there is a further demand for a method for producing a-alumina having uniform particle shape and particle size distribution and free of coarse particles.

An object of the present invention is to provide a method of synthesizing a highly highly dispersible a-alumina free from coarse particles of 500 nm in a short time at a low temperature by the solvent heating method.

Another object of the present invention is to provide an insulating high thermal conductivity? -Alumina sol prepared by the above synthetic method.

In order to achieve the above object, one aspect of the present invention is to provide a process for producing a zeolite having a boehmite (AlO (OH)), an a-alumina seed as a precursor and a zeolite as a solvent, Treated at 300 DEG C for 12 to 48 hours, and a method of synthesizing highly dispersed a-alumina having an average particle diameter (D50) of 80 nm to 150 nm.

The synthesis method according to one specific example comprises the following steps.

Adding boehmite (AlO (OH)) as a precursor to a dispersion medium and stirring to form a dispersion;

Adding a-alumina seed to a boehmite dispersion to prepare a colloidal solution, and then adding 1,4-butanediol to obtain a mixed solution;

Treating the mixed solution at 60 ° C for 30 minutes to remove the solvent;

Alumina powder by heating the reaction vessel at a heating rate of 80 to 150 ° C / hr and holding the resultant at 250 to 300 ° C for 12 to 48 hours and then cooling it to room temperature; And

Centrifuging the obtained? -Alumina powder.

The boehmite used as the precursor preferably has a primary particle size of 5 nm to 40 nm, for example, but is not limited to, Catapal® 200, Dispal® 18N4, and Dispal® T25N4.

The α-alumina seed may be a powder obtained by milling α-alumina synthesized by pyrolysis using ammonium alum (Al (NH ₄ ) (SO ₄ ) ₂ ) as a starting material. More specifically, a nano-alumina dispersion sol having an average particle size (D50) of 50 nm to 100 nm obtained by milling an α-alumina crystal obtained by calcining ammonium alum at 1,200 ° C. for 1 to 3 hours and milling the mixture for 0.5 to 5 hours, can be used as an? -alumina seed. Here, centrifugation is preferably performed at 5,000 rpm for 5 minutes to 10 minutes. If necessary, nitric acid (HNO ₂ , HNO ₃ ) or aqueous ammonia (HN ₄ OH) may be added during the production of the alumina dispersed sol.

The number of the? -Alumina seeds is preferably in the range of 3 x 10 ¹² to 5 x 10 ¹² seeds, which makes it suitable for producing smaller-sized? -Alumina particles.

Another aspect of the present invention provides an insulating high thermal conductivity? -Alumina sol having an average particle diameter (D50) of 80 nm to 150 nm prepared by the above-described synthesis method.

The? -Alumina sol has a high dispersibility with a ratio of coarse particles having a particle diameter of 500 nm or more of 0.1% or less.

When the α-alumina sol of the present invention is dispersed in the PAI resin to form a composite, the thermal conductivity of the α-alumina sol is improved compared to the PAI resin.

The α-alumina synthesis method of the present invention is capable of synthesizing uniformly dispersed nanoparticles containing no coarse particles at a low temperature of about 300 ° C. using a solvent heating method, and exhibiting excellent insulation and excellent thermal conductivity . Also, by controlling the type of boehmite and the particle size and number of the alumina seed, the particle size and distribution of the a-alumina particles can be easily controlled. Therefore, the α-alumina of the present invention can be variously applied to the preparation of nano-alumina dispersed sol, surface modified alumina dispersion sol through surface modification, NMP solvent replacement, and silane modified alumina-PAI resin composite research.

Fig. 1 is a step diagram of a process of synthesizing highly-dispersible a-alumina according to an embodiment of the present invention.
Fig. 2 is a graph of the particle size distribution of three kinds of precursors, i.e., boehmite {a; Catapal® 200, b; Dispal® 18N4, c; Dispal® T25N4}
Fig. 3 shows the XRD pattern of the? -Alumina seed dispersed sol according to the calcination temperature. {(A) γ-alumina and (b) α-alumina}
4 is a graph of particle size of an a-alumina seed dispersed sol with respect to milling time.
5 is a graph of the particle size of an a-alumina seed dispersion sol according to the amount of nitric acid added.
6 is a graph of particle size of an a-alumina seed dispersion sol according to centrifugation before and after milling.
7 is an SEM image of synthesized? -Alumina according to the number of seeds.
Fig. 8 shows the average particle size distribution of? -Alumina obtained in Example 1. Fig.
9 is an SEM image of a-alumina synthesized by seed size.
10 is an XRD graph of a-alumina synthesized by seed size ((a) seed size: 100 nm, (b) seed size: 79 nm, (c) seed size: 70 nm}.

Hereinafter, the present invention will be described in detail.

The present invention relates to synthesis of nano-sized a-alumina. In the past, the solid phase method was used mainly at a temperature of 1100 to 1200 ° C. or higher, but the cost of the process was high and the synthesized alumina had a high content of coarse particles. In addition, when the α-alumina particles are synthesized by the pyrolysis method or the solid phase method, the size of the primary particles is small, but there is a drawback that the particles aggregate. Accordingly, the present inventors have succeeded in synthesizing a highly highly dispersible a-alumina having almost no coarse particles of 500 nm by using a solvothermal synthesis method which can be carried out at a low temperature, and a synthesized? -Alumina sol.

FIG. 1 shows a process of synthesizing highly dispersed .alpha.-alumina according to an embodiment of the present invention. Hereinafter, the present invention will be described in detail with reference to FIG.

The first step (S1) for the synthesis of a-alumina by the solvent thermo-synthetic method is a step of forming a dispersion by adding boehmite as a precursor to a dispersion medium and stirring the mixture.

The boehmite used as the precursor is produced as a by-product in the process of producing an alcohol having a composition formula of AlO (OH) and having a large number of carbon atoms. The boehmite preferably has a primary particle size of 5 nm to 40 nm. For example, Catapal® 200, Dispal® 18N4, Dispal® T25N4 and the like can be used. The Catapal® 200 is brick-shaped and has a primary particle size of about 40 nm x 40 nm x 20 nm and an average particle size of about 175 nm as shown in Fig. 2 (a). The Dispal (R) 18N4 is platelet-shaped and has a primary particle size of about 15 nm x 15 nm x 5 nm and an average particle size of about 112 nm as shown in Fig. 2 (b). The Dispal (R) T25N4 is a blade-shaped, with a primary particle size of about 15 nm x 8 nm x 5 nm and an average particle size of about 81 nm.

The present inventors have studied the particle size and crystallization time of a-alumina according to the type of boehmite precursor, and found that when a precursor having a small particle size is used as a starting material, the crystallization time of a-alumina is short and the crystal size is small Confirmed. Therefore, particles of alumina synthesized using a precursor of Dispal® T25N4 having a small particle size were the smallest.

The boehmite precursor is preferably dispersed in a dispersion medium such as, for example, methanol with a uniform sol. The dispersion can be performed by ultrasonication for about 5 minutes to form a uniform dispersion medium.

In the next step (S2), α-alumina seed is added to the boehmite dispersion to form a colloid, and then 1,4-butanediol is added to obtain a mixed solution.

The? -Alumina seed may be used in a form dispersed in a dispersion medium.

The α-alumina seed may be a powder obtained by milling α-alumina synthesized by pyrolysis using, as a starting material, ammonium alum (Al (NH ₄ ) (SO ₄ ) ₂ ) in a preferred example. In a specific example, the α-alumina seed is prepared by milling an α-alumina crystal obtained by calcining ammonium alum at 1,200 ° C. for 1 to 3 hours and then centrifuging for 0.5 to 5 hours to obtain an average particle size (D50) of 70 nm to 100 nm Lt; RTI ID = 0.0 > alumina < / RTI >

As the milling, a known milling mechanism such as a ball mill or a jet mill may be used, and the powder may be milled alone, or an additive such as a milling aid and deagglomerating agent may be added. Examples of the grinding aid include, but are not limited to, alcohols such as methanol, ethanol and propanol, glycols such as propylene glycol, polypropylene glycol and ethylene glycol, and the like. The milling time can preferably be carried out for 2-5 hours.

The centrifugation can be performed at 5,000 rpm for 5 minutes to 10 minutes.

The initial starting particle size of the a-alumina seed can be determined and the size of the a-alumina nanoparticles can be controlled through the seed concentration (number). That is, as the number of seeds increases, the particle size of synthesized alumina decreases. Thus, the number of 500nm exceeds desired α- alumina seed to minimize the formation of coarse particles and obtain a uniform particle size distribution which may be 3x10 ¹² to 5x10 ¹² seed.

The glycol solution is preferably a solution of 1,4-butanediol or a mixture of 1,4-butanediol and distilled water.

In some cases, nitric acid (HNO ₂ , HNO ₃ ) or aqueous ammonia (HN ₄ OH) may be added to the seed solution of the alumina dispersed sol for the purpose of preventing abrupt reaction with the precursor. For example, the nitric acid may be contained in an amount of 1.0-1.9 wt%.

The mass ratio of the boehmite precursor: a-alumina seed: 1,4-butanediol in the colloidal solution is preferably about 1: 10: 250.

In the next step (S3), the mixed solution is placed in a reaction vessel and heat-treated at 60 DEG C for 30 minutes to remove the solvent. In this process, the volatile alcohol solvent evaporates because the surface of the alumina powder may not be uniform and smooth when a large amount of alcohol solvent remains.

The next step (S4) is a Glucoderm reaction which is a solvent thermal reaction. The reaction is carried out by heating the reaction vessel at a heating rate of 80 to 150 占 폚 / hr, maintaining the reaction vessel at 250 to 300 占 폚 for 12 to 48 hours, to be. In one specific example, it is preferred that the reaction vessel is heated at a rate of elevated temperature of 100 占 폚 / hr and maintained at about 300 占 폚 for about 12 hours.

The final step (S5) is a step of centrifuging the obtained a-alumina powder. By the centrifugation, the fine particles are not sedimented but still suspended in the supernatant liquid. On the other hand, since the coarse particles having a relatively large particle size are precipitated, the supernatant liquid is separated from the precipitate by solid / liquid separation, Can be obtained. The powder obtained by centrifugal separation may be used in a state of being dispersed in a solvent, and may be subjected to washing and drying steps if necessary.

The α-alumina synthesized by the solvent thermal reaction according to the present invention is an insulating high thermal conductivity α-alumina sol having an average particle diameter (D50) of 80 nm to 150 nm. The ratio of coarse particles having a particle size exceeding 500 nm to the total number of particles is 0.1% or less.

The? -Alumina of the present invention exhibits an insulating property and a high thermal conductivity, and thus can be used in the form of a composite dispersed in a PAI resin.

In addition, the a-alumina of the present invention is useful as a starting material for producing an a-alumina sintered body. The a-alumina sintered body is used as a material for cutting tools, bioceramics and bulletproof plates which require high strength. But also to electronic parts such as equipment parts for manufacturing semiconductor devices such as wafer handlers and enzyme sensors. It can also be applied to light-permeable tubes such as sodium lamps and metal halide lamps. Furthermore, the present invention can be applied to a ceramic filter used for removal of solids contained in a gas such as exhaust gas, filtration of aluminum melt, and filtration of foods such as beer. Ceramic filters include selective permeate filters for selective permeation of hydrogen in the fuel cell and selective permeation of vapor phase components such as carbon monoxide, carbon dioxide, nitrogen and oxygen which are produced during refining of petroleum, And may be used as a catalyst carrier for supporting the catalyst component.

The produced fine? -Alumina particles are used as a cosmetic additive, an additive for brake lining and a catalyst carrier, or a material such as an electrically conductive sintered body and a thermally conductive sintered body.

When the sintered body is produced by sintering the ceramic powder which is hardly sintered, fine a-alumina particles produced as sintering aids to be added to the ceramic powder for promoting sintering can also be used.

The fine? -Alumina particles can be used as a starting material from which fine aluminum nitride powder, yttrium-aluminum-garnet (YAG) powder, powdered phosphor, etc. can be prepared.

In addition, the produced fine? -Alumina particles can be used as an additive added to the coating layer of the coating magnetic medium to improve the head cleaning property and the frictional resistance in the form of a powder similar to a general? -Alumina powder. The fine? -Alumina particles can also be used as a toner. The fine? -Alumina particles can also be used as a filler added to the resin. The fine? -Alumina particles can also be used as abrasives and can be formed into slurries of particles dispersed in a medium such as, for example, water, used for polishing semiconductor CMPs and hard disk substrates, And can be used for precision polishing of components such as a hard disk and a magnetic head.

Hereinafter, the present invention will be described in detail with reference to Examples and Experimental Examples. However, the present invention is not limited thereto.

[ Manufacturing example  One] Ammonium alum Pyrolysis method  Preparation of α-alumina seeds

Ammonium alum _{(Al (NH 4) (SO} 4) 2) was prepared in the α- alumina seed powder to the thermal decomposition method using. The pyrolysis temperature was 900 ~ 1200 ℃ and the holding time was 1 ~ 3 hours. The prepared alumina powders were calcined at a calcination temperature of 1000 캜 and at a temperature of 1200 캜 by using a sand mill.

[ Experimental Example  1] of [alpha] -alumina seed At calcination temperature  Characterization

The crystal structure and grain size of the? -Alumina seed obtained in Preparation Example 1 were X-ray diffraction (XRD), particle shape was FE-SEM (Field Emission-Scanning Electron Microscope), particle size and cohesion were TEM (Transmission Electron Microscope) , The specific surface area is BET (Brunauer-Emmett-Teller), the agglomerated phase of particles is PSA (Particle Size Analysis), the true density of powder is gas-pycnometer, the heat loss and moisture content are TGA (Thermogravimetric Analysis) (Inductively coupled plasma).

The XRD diffraction pattern of alumina according to the calcination temperature is shown in Fig. 3 (a)). When calcined at 1000 ° C., gamma alumina (JCPDS 29-0063) having a standard peak of Cubic structure was obtained. In the case of calcination at 900 ° C., the ammonium alum was found to have an amorphous structure Was observed. Referring to FIG. 3 (b), when the calcination was performed at 1200 ° C., it was confirmed that the remaining amorphous structure was changed to a crystalline phase, which was consistent with the α-alumina (JCPDS 10-0173) diffraction pattern of hexagonal structure.

Table 1 shows the hkl =? (440) and? (113) half widths having the greatest diffraction intensities in the XRD peaks of? -Alumina and? -Alumina prepared at 1000 ° C and 1200 ° C, respectively, as calculated by Scherrer's equation Primary grain size, specific surface area, gas-type density, and water content by TGA measurement.

[Table 1]

According to Table 1, the size of α-alumina having a relatively high calcination temperature was increased to 34 nm, compared to 10 nm of γ-alumina. That is, it was confirmed that as the calcination temperature increases, the grain size increases and the specific surface area decreases. In addition, the gas density is measured to show a density difference of 92.60% (γ-alumina) and 99.49% (α-alumina) based on theoretical density. The relative thermal conductivity value can be indirectly estimated through the density difference.

[ Experimental Example  2] of [alpha] -alumina seed Milling time and  Analysis of physical properties according to amount of nitric acid

The dispersion sol was prepared by varying the milling time and the amount of nitric acid added in the preparation of the a-alumina seed. The results are shown in Figs. 4 to 5. First, to examine the effect of milling time on the grain size, the beads were added with 0.3φ and 2wt% nitric acid. As a result, as shown in FIG. 4, the sol was easily precipitated when it was milled for 30 minutes and 1 hour, but it took a stable sol form from 3 hours.

In order to investigate the effect of nitric acid concentration, beads 0.1 and 0.3 were mixed at a ratio of 1: 1, 1 to 2 wt% of nitric acid was added, and the particle size was analyzed after milling for 4 hours. When 2 wt% of nitric acid was added, the Dmax showed a particle size of 172 nm, but stabilized with an average particle size of 150 nm when 1.2 wt% of nitric acid was added. At this time, the average particle size of the? -Alumina dispersion sol was observed to be 80 nm.

[ Experimental Example  3] Following centrifugation of α-alumina seeds Particle size analysis

The results of particle size analysis are shown in the figure below before, after and after centrifugation of α-alumina sol. The milling conditions were optimized in the above milling experiments. The size of D _MAX before the sol-milling was 45 μm, but it was 172 nm after milling. It was 131.2 nm when centrifuged at 5,000 rpm and 100 nm when it was 10 minutes. D ₅₀ was also controlled to 83.8 nm after milling, 76.8 nm after 5 minutes of centrifugation, and 68.8 nm after 10 minutes of operation.

[ Example  1] Production of? -Alumina powder

First, 40 ml of methanol was added to 2 g of boehmite (AlO (OH)) and stirred, followed by ultrasonic treatment for 5 minutes to prepare a boehmite dispersion. The? -Alumina seed solution obtained in Preparation Example 1 is added to the boehmite dispersion and stirred to obtain a colloidal solution. At this time, the a-alumina seed was 3.96 x 10 ¹² , and the size was 70 nm. After 1,4-butanediol was added thereto, the mixture was stirred, and the mixture was kept at a temperature of 60 ° C for 30 minutes or more to evaporate the solvent. Next, a glycothermal reaction was carried out by heating to 300 ° C at a heating rate of 100 ° C / hr, holding the mixture for 12 hours, and cooling to room temperature. The resulting colloidal solution was centrifuged and washed with a methanol solution. The resulting powder was then dried at 120 占 폚. The average particle size distribution of the obtained powder is shown in Fig. As a result, it was confirmed that the distribution area was narrow and highly-dispersible, and α-alumina particles having an average particle size of about 113 nm were prepared.

[ Experimental Example  4] Bohemite  Study of crystallization time according to kinds and additives

The boehmite particles of different particle sizes were used to determine the alumina phase change over time. In this study, three types of boehmite precursors were used: Catapal® C200, Dispal® 18N4, and Dispal® T25N4, and α-alumina crystal grains were obtained by solvent thermo-synthesis without adding α-alumina seeds. The average particle sizes of Catapal® 200, Dispal® 18N4, and Dispal® T25N4 are 175 nm, 112 nm and 81 nm, respectively (see FIG. 2) in the particle size distributions of the three boehmite precursors.

As a result, it can be confirmed that the crystallization time of alumina varies depending on the size and crystallinity of the precursor. Capatal® C200 with high particle size and high crystallinity is synthesized as α-alumina at a reaction time of 36 hours using a precursor, 18 hours at Dispal® 18N4 and 9 hours at Dispal® T25N4.

In addition, when nitric acid was added as the starting material of Catapal® C200, which had the slowest crystallization time among the three raw materials, the crystallization time was slowed down and the raw material Boehmite remained because the crystallization was not completed in 36 hours. In addition, even when Dispal® 18N4 and T25N4 are used as raw materials, the BET of alumina prepared under acid addition conditions is small, and the crystallization time is relatively slow, and the crystal grain size is estimated to be relatively larger. Therefore, it was confirmed that the crystallization time was influenced by the additive.

 [ Experimental Example  5] Particle size of α-alumina according to the number of seeds

To 2 g of precursor boehmite, 50 ml of 1,4-butanediol was added and the number of seeds was increased. The size of the seed used herein is 100 nm in average particle size. FIG. 7 shows synthesized alumina XRD images according to the number of seeds, and analysis of alumina synthesized through SEM revealed that homogeneous and dispersed a-alumina was synthesized. As a result of comparing average particle size of PSA particles, it was observed that the particle size of synthesized alumina decreased with increasing seed number at 310 nm and 280 nm when the number of seeds was 1.32 * 10 ¹² and 3.52 * 10 ¹² , respectively.

[ Experimental Example  6] Particle size of a-alumina with seed size

9 to 10 are SEM, XRD and PSA data of alumina synthesized by seed size. 2 g of precursor boehmite and 25 ml of 1,4-butanediol solvent were added and the number of seeds was made equal to 3.96 * 10 seeds. Alumina was synthesized using seeds having average particle diameters of 100 nm, 79 nm and 70 nm, respectively.

XRD and SEM showed that uniform α-alumina particles were synthesized. Also, it can be seen that as the seed size becomes smaller, the larger particles of synthesized alumina sharply decrease.

[ Experimental Example  7] Thermal conductivity analysis

The thermal conductivity of α-alumina synthesized by the solvent thermo-synthetic method in Example 1 was measured by the content of PAI resin. After the α-alumina filler was dispersed in ultra sonication in PAI resin, PAI was cured at 160 ° C to prepare a composite. The thermal conductivity is measured by the laser flash method. After the sample is stabilized at the desired temperature (T ₀ ), an almost instantaneous energy pulse is irradiated on the front surface of the sample, and the temperature change (DTt) The results are shown in Table 2 below.

[Table 2]

It was confirmed that the thermal conductivity increased when the content of alumina filler was increased than that of PAI alone resin.

[ Experimental Example  8] Breakdown voltage analysis

The dielectric breakdown voltage was measured using the composite prepared in Experimental Example 7. Table 3 shows average values measured five times per sample.

[Table 3]

It can be seen that the insulation breakdown voltage is similar when the PAI single resin is used and when the filler content is 20 wt%. However, when the content is increased to 50 wt%, it is confirmed that the breakdown voltage is lowered. The breakdown voltage divided by the composite thickness shows that the 20wt% / PAI sample is the highest.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention as defined by the appended claims. It is therefore intended that such variations and modifications fall within the scope of the appended claims.

Claims (11)

delete delete delete delete delete delete delete delete Is prepared by heat treatment at 250 to 300 DEG C for 12 to 48 hours by a solvothermal method using boehmite (AlO (OH)), alpha-alumina seed and glycol as precursors, (D50) of 80 nm to 150 nm is dispersed in the PAI resin in an amount of 20 wt% relative to the PAI resin. 10. The method of claim 9,
Wherein the? -Alumina sol has a ratio of coarse particles having a particle diameter of 500 nm or more of 0.1% or less. 10. The method of claim 9,
Wherein the thermal conductivity of the insulating high thermal conductive composite is higher than that of the PAI resin.

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