JP2007002049A - Method for producing polymer composite and polymer nanocomposite - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a molecular weight of an organic polymer from being lowered, when a polymer composite is produced from the organic polymer and alumina particles at a nano-order level having a major axis of 10-500 nm, and to prevent mechanical characteristics, such as impact resistance, of the polymer from being deteriorated, nor transparency thereof from being deteriorated by discoloration. <P>SOLUTION: A method for producing the polymer composite comprises drying absorbed water contained in the alumina particles having the major axis of 10-500 nm, so as to attain a loss on heating to 150°C from room temperature of not more than 2 wt%, and then mixing the dried alumina particles with the organic polymer, so as to form them into the composite. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a production method extremely excellent for producing a polymer composite having excellent mechanical properties and industrially advantageous, and a polymer composite obtained by the production method.

  As a technique to improve various physical properties of organic polymers, while maintaining the flexibility, low density and moldability that are the characteristics of organic polymers, the high strength, high elastic modulus, heat resistance, and electrical characteristics that are the characteristics of inorganic compounds As a method for improving these physical properties, composite materials using nano-order level inorganic fine particles instead of conventional glass fiber or talc-reinforced resin, so-called polymer nano-materials, have been developed. Composites are gaining attention. Examples of such composite materials include “composite materials and methods for producing the same (Patent No. 2519045 / Toyota Chuken)”, “polyamide composite materials and methods for producing the same (JP-B-7-47644 / Ube Industries, etc.)”, “ Polyolefin-based composite material and production method thereof (Japanese Patent Laid-Open No. 10-30039 / Showa Denko) ”and the like.

  Conventionally, inorganic fine particles such as silicon dioxide, titanium dioxide, and aluminum oxide have been widely used as organic polymer fillers. In applying the inorganic fine particles to this application, the particle diameter of the inorganic fine particles is preferably as small as possible. By increasing the surface area, the interaction is strengthened, and unprecedented characteristics are exhibited.

  Among inorganic fine particles, alumina particles are generally present as coarse micron-order particles, so that they have been used by pulverizing them. However, in recent years, nano-order levels can also be synthesized. An example is the ultrafine alumina “AEROXIDE® Alu C” manufactured by Degussa.

  However, when the alumina particles are mixed with the organic polymer, the molecular weight of the organic polymer decreases, and as a result, the impact resistance that should be maintained as a composite is lost or coloring occurs. There was a drawback that the physical properties of the film were greatly impaired. This problem is known to have a more serious effect on fine particles even with the same amount of filling, and the smaller the alumina particles, the larger the surface area and the more the interface with the matrix polymer. . In “Coated fibrous aluminum oxide filler and thermoplastic resin composition containing the same (Japanese Patent Application Laid-Open No. 2004-149687 / Teijin)”, there is a description of a technique for reducing moisture by azeotroping alumina particles and a solvent. The purpose of this is to improve the modification effect of the silane coupling agent, and the silane coupling agent loses its hydrolyzability when it becomes extremely low in moisture. It is judged that it is premised to remain, and as a result, it does not solve the disadvantage that the physical properties of the organic polymer are greatly impaired when the composition is formed.

Patent No. 2519045 JP 7-47644 Japanese Patent Laid-Open No. 10-30039 JP2004-149687

  In the polymer composite composed of an organic polymer and nano-order level alumina particles, the present invention suppresses a decrease in molecular weight of the organic polymer, and deteriorates mechanical properties such as impact resistance of the polymer and transparency due to coloring. The purpose is to suppress.

In order to achieve the above object, the present invention provides:
In a polymer composite composed of an organic polymer and alumina particles having a major axis of 10 to 500 nm,
A method for producing a polymer composite, wherein the adsorbed water contained in the alumina particles is dried to a weight loss of 2 wt% or less from room temperature to 150 ° C. and then mixed with the organic polymer to form a composite. About.

  In order to solve the above-mentioned problems, the present inventors have tried and errored that alumina particles have chemically active OH groups, and these active hydroxyl groups are mixed in the organic polymer when mixed with the organic polymer. It was found that the relatively weak part contained in the polymer attacked to cause hydrolysis and oxidative degradation, which caused the molecular weight reduction and coloring of the organic polymer. Such an active hydroxyl group is considered to be derived from adsorbed water.

  That is, in the past, when alumina particles were composited with an organic polymer, the alumina particles were simply dried by a general drying method such as spray drying or drying at room temperature or mild temperature. Insufficient removal of the hydroxyl group of the alumina particles causes hydrolysis and oxidative degradation due to the hydroxyl group as described above, causing deterioration of mechanical properties and transparency due to a decrease in molecular weight of the organic polymer. It was.

  On the other hand, in the present invention, the alumina particles are removed by a freeze-drying method, or by a method selected from a combination of high temperature over 100 ° C to 300 ° C under normal pressure or reduced pressure, and a combination thereof. Was found to be sufficiently dried, the alumina particle hydroxyl group could be reduced to a practically no problem level, and the above-mentioned problems caused by the hydroxyl group could be solved.

  According to the present invention, the organic polymer is hydrolyzed and oxidatively deteriorated, and the molecular weight of the organic polymer is reduced, and the alumina particle hydroxyl group, which is a cause of coloring, is reduced as much as possible. And deterioration of the mechanical properties and coloring of the polymer nanocomposite composed of the alumina particles can be suppressed. Therefore, in producing the polymer nanocomposite, the organic polymer and the alumina particles can be arbitrarily selected from commercially available ones without selecting a special combination of the organic polymer as a matrix and the alumina particles as a filler. It can be selected, and it can be said that it is an industrially very advantageous method for producing a polymer composite because a polymer composite can be produced simply by performing drying and removing water according to the present invention without requiring complicated steps.

  Hereinafter, other features and advantages of the present invention will be described in detail based on the best mode for carrying out the invention.

(Drying method)
In the present invention, alumina particles to be polymer composite are dried until the adsorbed water is reduced to 2 wt% or less as a heating loss from room temperature (25 ° C) to 150 ° C, and the adsorbed water is almost completely removed. Detach. Although it is not particularly limited as such a drying method, it can be performed by freeze drying method, ignition by applying a temperature of 100 ° C to 300 ° C under normal pressure or reduced pressure, and a combination of these methods. preferable. Thereby, the above-described drying can be efficiently performed in a relatively short time.

  Freeze drying is performed using a commercial industrial freeze drying apparatus. Examples of the apparatus include freeze dryers RLEII series and RL-B series manufactured by Kyowa Vacuum Technology Co., Ltd. The process is performed as follows. (1) An aqueous dispersion suspension of alumina particles is set on a shelf of a freeze-drying apparatus and frozen for 2 to 5 hours. (2) During this time, the trap is also cooled in parallel. (3) Evacuate sufficiently within 10 to 20 minutes to a vacuum of about 0.02 to 0.5 Torr. (4) Freeze-dry for about 1 day to sublimate moisture. (5) Secondary drying is performed at 25 to + 50 ° C. for several hours to remove slightly remaining moisture. (6) Return to normal pressure with nitrogen or dry air. The obtained dry powder is hermetically stored until compositing.

  However, instead of the alumina suspension, the freeze-drying may be performed by setting powdery alumina particles in the freeze-drying apparatus.

  In the hot drying, a commercially available hot air drying oven is used in the case of normal pressure conditions. Examples of the apparatus include Espec Co., Ltd. hot air circulation type open LC224, 234, Kawata Co., Ltd. ACE dryer ADA series, Kuroda Industries Co., Ltd. conveyor type hot air dryer, and the like. As an operation, an aqueous dispersion suspension of alumina particles is set on an oven shelf, and depending on the temperature, the amount of suspension, and the volatilized area, it takes several hours to a day at 150 ° C and 200 ° C. For about 3 hours to half a day. Since the condensation of AlOH groups proceeds little by little at temperatures exceeding 250 ° C., drying is performed at 250 ° C. or less, preferably 200 ° C. or less.

  In the case of ignition under reduced pressure, a commercially available vacuum dryer is used. Examples of the apparatus include a vacuum heat transfer dryer DPTH-40 manufactured by Matsui Seisakusho Co., Ltd., and a DECO-DV series manufactured by Kawata Co., Ltd. As an operation, an aqueous dispersion of alumina particles is set in a dryer, and depending on the temperature, the amount of suspension, and the volatilized area, drying takes about 2 to 5 hours at 150 ° C and 2 Torr. Do.

  However, in the case of ignition drying, the freeze-drying is performed by setting powdery alumina particles in the freeze-drying apparatus instead of the alumina suspension in both the normal pressure condition and the reduced pressure condition. It can also be.

  The removal / desorption effect by drying the adsorbed water can be confirmed by thermogravimetric analysis (TG). The TG analysis is performed at a heating rate of 5 ° C./min in air or in a nitrogen gas atmosphere. The alumina particles are dried under the conditions that the weight loss from 25 ° C. to 150 ° C. is 2 wt% or less in this analysis. Most of the weight loss measured in this analysis is basically adsorbed moisture. The drying is performed until the adsorbed water is preferably 1 wt% or less, more preferably 0.5 wt% or less. As a result, even if the alumina particles are blended with the organic polymer, the polymer chain can be brought to a level where there is almost no damage due to oxidative degradation or hydrolysis of the polymer chain.

  The alumina particles used in the present invention are nano-order alumina particles having a major axis of 10 to 500 nm. The major axis here is the length of the longest axis in anisotropic particles, that is, the length of the major axis. For isotropic particles such as regular octahedrons and spherical particles, there is no distinction between major and minor axes. It corresponds to the diameter.

  When the major axis is larger than 500 nm, the surface area becomes small and the interaction becomes insufficient, and the effect of improving the physical properties with respect to the organic polymer cannot be obtained satisfactorily, or the product becomes brittle. If the thickness is less than 10 nm, the production process becomes complicated, aggregation tends to proceed, and this is industrially disadvantageous.

  The shape of the alumina fine particles in the present invention is not particularly limited, and not only a general polyhedron but also a rectangular parallelepiped, a plate shape, a needle shape, and the like can be used.

  Among the alumina particles, particularly remarkable effects of the present invention include boehmite crystalline alumina hydrate. “Essentially” as used herein means that it is difficult industrially to obtain 100% purity in the synthesis process of alumina, so that there are mixed crystal systems other than about 5% different boehmite. It is essentially boehmite, meaning that it can be regarded as boehmite as a whole.

  Among various hydrates of alumina, trihydrates such as gibbsite and vialite substantially correspond to aluminum hydroxide rather than alumina hydrate, and are retained as crystal water even after the drying treatment. Since there are many OH group equivalents, it is often impossible to suppress damage to organic polymers. In addition, α-alumina having no crystal water generally has a large particle size, and it is industrially difficult to make the major axis finer than 100 nm. Therefore, in order to expect the interaction with the polymer, it is somewhat disadvantageous compared to boehmite. Further, as alumina having a small amount of water of crystallization and a large surface area, there can be mentioned ultrafine particulate alumina “AEROXIDE (registered trademark) Alu C” manufactured by Degussa, which is δ-alumina, but this alumina has already undergone a combustion hydrolysis process, Since coarse particles are contained and the surface activity is reduced by shochu and interaction with the organic polymer cannot be obtained sufficiently, it is somewhat disadvantageous compared to boehmite.

  Among the boehmites that are crystalline alumina hydrates, those having particularly remarkable effects of the present invention include those having a rod-like or rectangular parallelepiped shape. In this case, it is desirable that the particles are essentially boehmite crystalline alumina hydrate particles having a minor axis length of 1 to 10 nm, a major axis length of 10 to 500 nm, and an aspect ratio of 5 to 100. The short axis length is the diameter of the rod or cuboid in the lateral direction, and the long axis length is the length in the direction giving the maximum length. The aspect ratio is a value given by the major axis length / minor axis length. The larger the aspect ratio value, the longer the particles. Such particles having a large aspect ratio are particularly effective in reducing the coefficient of linear expansion when a composite with an organic polymer is synthesized. In the case of a transparent polymer, it is often a useful particle because it can be converted into a composite without sacrificing its transparency.

  Here, the shape of the boehmite particles is set to a short axis length of 2 to 10 nm and a long axis length of 10 to 500 nm. The range of the long axis length is as described above. When the major axis is synthesized and crystallized so as to be 10 to 500 nm, the minor axis length of the primary particles is substantially 2 to 10 nm.

  The alumina particles may be suspension or powder, but when performing freeze-drying, a suspension type dispersed in water is desirable for handling. It is necessary to perform the operation. The concentration of the suspension is preferably 2 to 50 wt%. If it is less than 2%, a large amount of water is distilled off when it is volatilized, which is industrially disadvantageous. If it is more than 50%, it becomes substantially solid, so it is introduced into a freeze dryer. Sometimes the operation becomes complicated.

  In the case of ripening, a suspension or a powder may be used, but a powder is desirable for handling and the drying time can be shortened. In the case of a suspension, it is necessary to perform the drying operation for a long time.

  The method for producing the alumina particles is not particularly limited, and can be obtained by an arbitrary method such as a gas phase method, a sol-gel method, a colloidal precipitation method, a molten metal spray oxidation method, or an arc discharge as long as the particle size can be controlled. Although it may be a thing, as a commercial item with comparatively high anisotropy, pseudoboehmite like "Cataloid-AS-3" by a catalyst chemical industry Co., Ltd. is mentioned, for example. For the synthesis of boehmite particles having a sufficiently large aspect ratio, the gel sol method (Japanese Patent Application No. 2004-239442) by hydrothermal synthesis invented by the inventors is most desirable.

(Composite)
The concentration of the alumina particles in the polymer composite in the present invention is preferably in the range of 1 to 70% by weight as the solid content. If it is less than 1% by weight, it is difficult to recognize improvement in various properties such as mechanical strength. If it exceeds 70% by weight, not only the increase in specific gravity can not be ignored, but also the decrease in impact strength cannot be ignored. Generally, when a large amount of inorganic fine particles are blended in a polymer, the impact strength is reduced. However, since the nanocomposite of the present invention has nano-order alumina fine particles uniformly dispersed, the decrease in impact strength is practically small, but 70% by weight. If it exceeds, this cannot be ignored. More preferably, the content is 3 to 30% by weight.

  The method for producing the composite of the present invention can be appropriately selected according to the type of organic polymer used. In the case of the simplest direct kneading method, a general resin kneader may be used. For example, a twin screw extruder is preferable, and manufacturing from small to large machines such as a vacuum microkneading extruder and a lab plast mill is possible. Select according to the scale. In this case, in order not to adsorb moisture, resin pellets and alumina particle powder can be quickly added to the hopper of the kneader, kneaded, extruded as it is, and molded into the desired shape, and once stored as composite pellets May be.

  One method for producing a composite is a solvent dispersion method. Specifically, the organic polymer and alumina particles are mixed in an organic solvent, and the solvent is distilled off to obtain a composition. According to this method, the organic polymer and the alumina particles can be mixed more uniformly.

  In this method, it is preferable to first prepare an alumina particle dispersion solution in which the alumina particles are dispersed in a predetermined organic solvent. Examples of the organic solvent used here include aliphatic hydrocarbon solvents such as pentane, hexane, heptane, and cyclohexane, aromatic hydrocarbon solvents such as benzene, toluene, xylene, and chlorobenzene, acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. Such as ketone solvents, ester solvents such as methyl acetate, ethyl acetate, butyl acetate, ether solvents such as diethyl ether, tetrahydrofuran, dioxolane, dioxane, alcohols such as methanol, ethanol, propanol, isopropanol, butanol, cyclohexanol Solvents, halogenated alkyl solvents such as chloroform, 1,2-dichloroethane, methylene chloride, carbon tetrachloride, fluorine organic solvents such as trifluoromethylbenzene, N, N-di Chill formamide, N, N- dimethylacetamide, dimethyl sulfoxide, and the like can be exemplified aprotic polar solvents such as N- methylpyrrolidone.

  Next, a polymer dispersion solution in which the organic polymer is dispersed in a predetermined organic solvent is prepared. In this case, the organic solvent is selected from solvents capable of dissolving the organic polymer, and preferably has a polarity close to that of the solvent used for suspending and dispersing the alumina particles. For example, in the case of polycarbonate, tetrahydrofuran, chloroform, methylene chloride, 1,3-dioxolane, 1,4-dioxane, cyclohexanone, 1,1,1-trichloroethane and the like can be mentioned.

  Next, the alumina polymer dispersion solution and the polymer dispersion solution are mixed, and then only the solvent is distilled off, whereby the intended polymer composite can be obtained.

  Further, when a vinyl polymer such as an acrylic resin is used as the matrix organic polymer, a solution polymerization method can be used. In the solution polymerization method, a monomer is dissolved in an alumina particle-dispersed organosol, polymerization is advanced by a radical initiator, and after completion of the reaction, a polymer composite is precipitated by pouring into a poor solvent. For example, in the case of methyl methacrylate, a composite can be deposited by radical polymerization in toluene and injection into hexane.

  Furthermore, a melt polymerization method may be mentioned as a method for producing a composite when a condensation polymerization polymer is used as a matrix organic polymer. In this method, a mixture containing a condensable monomer and an alumina particle-dispersed organosol is heated while stirring under reduced pressure, the condensation polymerization of the monomer proceeds by distilling off the solvent of the organosol, and the resulting condensation by-product is produced. The polymer composite is obtained by removing. For example, in the case of polyethylene terephthalate, a nanocomposite can be obtained by mixing terephthalic acid, ethylene glycol, and alumina particle sol and then distilling off the water generated by condensation with the solvent of the sol by stirring, heating, and vacuum distillation. .

  According to the method described above, the alumina particles can be uniformly dispersed with high efficiency in the target polymer composite. Therefore, the mechanical strength and dimensional stability of the resulting nanocomposite can be improved by various properties inherent to the organic polymer and the interaction of the alumina particles.

(Polymer nanocomposite: product)
The polymer nanocomposite of the present invention is obtained through the steps described above,
A) Alumina particles having a major axis of 10 to 500 nm with an adsorption moisture content of 2 wt% or less as heat loss from 25 ° C to 150 ° C
B) It is characterized by comprising an organic polymer.

  As the alumina particles, boehmite which is preferably crystalline alumina hydrate due to the above-described production method, and the shape thereof is a rod or a rectangular parallelepiped, the short axis length is 1 to 10 nm, The long axis length is 10 to 500 nm and the aspect ratio is 5 to 100. However, based on the manufacturing method described above, any other alumina particles can be used as long as the effects of the present invention are not lost.

  The alumina particles may be subjected to a surface modification treatment using an organometallic compound such as a silane coupling agent, a silylating agent, a titanium coupling agent, alkyl lithium, or alkyl aluminum. What is necessary is just to select the modification group suitably according to the kind of organic polymer to mix.

  The organic polymer is selected from any thermosetting or thermoplastic polymer. As the effect of the present invention is particularly remarkable, an ester bond, an ether bond, an amide bond, an imide is added to the repeating unit of the chemical structure of the skeleton. Examples thereof include a polymer including a bond, a urethane bond, a sulfide bond, and a sulfone bond. It is considered that active hydroxyl groups on the surface of alumina particles attack the relatively weak parts such as ester bonds and ether bonds contained in these organic polymers in a high temperature environment during resin molding, causing hydrolysis and oxidative degradation.

  Examples of the organic polymer include polycarbonate resin (PC), acrylic resin such as PMMA and PMA, polyester resin such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), phenol resin, polyarylate (PAR), and polyphenylene ether (PPE). , Polysulfone (PSU), polyethersulfone (PES), polyetheretherketone (PEEK), epoxy resin-phenoxy resin, nylon resin, polyimide resin, urethane resin, phenol resin, polyacetal, polyvinyl acetal, and the like.

  The nanocomposite obtained by the present invention has the characteristics that it has improved rigidity, has a low coefficient of thermal expansion, and can suppress deformation, warpage, distortion, etc. at high temperatures, and therefore these functions are required. For example, it can be said to be a material suitable for electronic parts, optical parts, automobile interior / exterior materials, and transparent members / equipment / furniture used for home appliances and houses.

  Examples are given below, but the present invention is not limited thereto.

[Example]
Example 1. (Freeze-drying-solution mixing)
1-1: Moisture removal of alumina particles (freeze drying)
Kyowa Vacuum Technology is a pseudo-boehmite-type alumina particle dispersion "Cataloid-AS-3" (major axis length 100nm, minor axis length 10nm, solid content 7%, specific gravity 1.05) manufactured by Catalyst Kasei Kogyo Co., Ltd. Using a freeze dryer RLEII-52 manufactured by Co., Ltd., freeze-drying was performed as follows. (1) The alumina particle water solution was divided into 500 g portions, set on three shelves of a freeze-drying apparatus, and frozen at −40 ° C. for 3 hours. (2) During this time, the cold trap was also cooled to −50 ° C. in parallel. (3) The air was exhausted quickly within 10 minutes, and the vacuum was set to 0.2 Torr. (4) Freeze-drying was performed for 20 hours to sublimate the water. (5) Secondary drying was performed at + 30 ° C. for 4 hours to remove a slight residual moisture. (6) The pressure was returned to normal pressure with dry air. As a result of this series of operations, 103 g of dry pseudoboehmite type alumina powder was obtained. When this powder was subjected to TG analysis, the heat loss from 25 ° C. to 150 ° C. was 0.6 wt%, and it was confirmed that sufficient moisture removal and drying were performed.

1-2: Alumina particle redispersion / modification Under a nitrogen atmosphere, 15 g of the alumina powder obtained in 1-1 was added to 85 g of anhydrous tetrahydrofuran manufactured by Kanto Chemical Co., Ltd. with a stirring blade and a three-one motor (BL300R manufactured by HEIDON). Redispersed with stirring. Thereafter, 0.15 g of “KBM-403” (= γ-glycidoxypropyltrimethoxysilane) manufactured by Shin-Etsu Chemical Co., Ltd. was added as a modifier and mixed at room temperature for 10 minutes. Thereafter, 0.01 g of triethylamine was diluted 10-fold with isopropanol while stirring was continued, and then dropped, and mixing was continued at 60 ° C. for 10 hours to sufficiently react the modifier.

1-3: Composition (solution mixing)
To 100 g of the alumina particle dispersion (solid content 15%) prepared in 1-2, add 85 g of polycarbonate “Novalex 7025A” (weight average molecular weight 54000) manufactured by Mitsubishi Engineering Plastics Co., Ltd. in 400 g of methylene chloride. A uniform solution. The solvent is removed while gradually increasing the degree of vacuum, and finally, drying is performed at 100 ° C. under a reduced pressure of 1 Torr or less for 4 hours. Further, the mixture is used with “Vacuum microkneading extruder IMC-1170B type” manufactured by Imoto Seisakusho Co., Ltd. And kneaded at 260 ° C. for 15 minutes to obtain a polymer composite. The ash content of the product was 14.5 wt%, and it was confirmed that the added alumina particles were all composited. This product had a colorless and almost transparent appearance, was not yellowed, and retained toughness. The impact strength (Izod) was 203 J / m. When the matrix polymer content of the composite was extracted and analyzed by GPC, the weight average molecular weight was 48900, and the initial molecular weight was almost maintained.

Example 2 (Freeze drying-direct kneading)
2-1: Alumina particle water removal (freeze drying)
700 g of “Nanotech Alumina-Alcohol Dispersed Product” (particle size: 31 mm, solid content: 15%) manufactured by CI Kasei Co., Ltd. was used as the alumina particle dispersion, and the same dry drying operation as in Example 1-1 was performed for adsorption. Water was removed. As a result of the operation, 104 g of dry alumina powder was obtained. The result of TG analysis of this powder was 0.3 wt% as the heat loss from 25 ° C. to 150 ° C., and it was confirmed that sufficient water removal and drying were performed.

2-2: Alumina particle kneading dispersion / composition (direct kneading)
In a nitrogen atmosphere, 15 g of the alumina powder obtained in 2-1 and 85 g of polycarbonate “Novalex 7025A” (weight average molecular weight 54000) manufactured by Mitsubishi Engineering Plastics Co., Ltd. are kneaded by a Weisenberg kneading extruder. While dispersing. At this time, 0.15 g of “KBM-403” (= γ-glycidoxypropyltrimethoxysilane) manufactured by Shin-Etsu Chemical Co., Ltd. was added as a modifier. The kneading was performed for 30 minutes at 260 ° C. and 40 rpm while venting to obtain a polymer composite. The ash content of the product was 15.2 wt%, and it was confirmed that the added alumina particles were all composited. This product had a milky white appearance, was not yellowed, and retained toughness. The impact strength (Izod) was 123 J / m. When the matrix polymer content of the composite was extracted and analyzed by GPC, the weight average molecular weight was 52000, and the initial molecular weight was almost maintained.

Example 3
3-1: Alumina particle water removal (normal pressure ignition)
The alumina particle dispersion was ignited with high heat using a hot air circulating oven LC224 manufactured by Espec Co., Ltd. as follows. 500 g of “Cataloid-AS-3” (major axis length 100 nm, minor axis length 10 nm, solid content 7%, specific gravity 1.05) manufactured by Catalyst Kasei Kogyo Co., Ltd., which is a pseudo boehmite type alumina particle dispersion liquid, is -IWAKI-120 mm 100 g each was put into five flat-bottomed evaporating dishes, set on an oven shelf, and dried at 200 ° C. for 12 hours. The obtained dried product was once pulverized in an agate mortar, and further dried at 200 ° C. for 6 hours. As a result, 35 g of dry pseudoboehmite type alumina powder was obtained. When this powder was subjected to TG analysis, the heat loss from 25 ° C. to 150 ° C. was 0.8 wt%, and it was confirmed that sufficient moisture removal and drying were performed.

3-2: Redispersion / Modification of Alumina Particles In a nitrogen atmosphere, 15 g of the alumina powder obtained in 3-1 was redispersed in 85 g of anhydrous tetrahydrofuran as in 1-2, and then γ-glycid as a modifier. Surface modification was performed by adding 0.15 g of xylpropyltrimethoxysilane.

3-3: Composition (solution mixing)
The same operation as in 1-3 was performed on the alumina particle dispersion prepared in 3-2. In other words, 100 g of alumina particle dispersion (solid content 15%) was added with 85 g of polycarbonate “NOVALEX 7025A” dissolved in 400 g of methylene chloride to obtain a uniform solution, the solvent was removed, and the mixture was further kneaded. As a result, a polymer composite was obtained. The ash content of the product was 15.0 wt%, and it was confirmed that the added alumina particles were all composited. This product had a white appearance, was not yellowed, and retained toughness. The impact strength (Izod) was 144 J / m. When the matrix polymer content of the composite was extracted and analyzed by GPC, the weight average molecular weight was 46300, and the initial molecular weight was almost maintained.

Example 4
4-1: Alumina particle water removal (low pressure ignition)
The alumina particle dispersion was dried under reduced pressure and ignition using a reduced pressure heat transfer type dryer DPTH-40 manufactured by Matsui Seisakusho Co., Ltd. as follows. As an operation, 1000 g of “Cataloid-AS-3” (major axis length 100 nm, minor axis length 10 nm, solid content 7%, specific gravity 1.05) manufactured by Catalyst Kasei Kogyo Co., Ltd., which is a pseudo boehmite type alumina particle dispersion. Then, it was set in a dryer, set at a temperature of 150 ° C., and dried at a reduced pressure of 2 Torr over 6 hours. The obtained dried product was once pulverized in an agate mortar, and further dried at 150 ° C./2 Torr for 2 hours. Finally, the pressure was returned to normal pressure with dry nitrogen gas. As a result, 68 g of dry pseudoboehmite type alumina powder was obtained. When this powder was subjected to TG analysis, the heat loss from 25 ° C. to 150 ° C. was 0.4 wt%, and it was confirmed that sufficient water removal and drying were performed.

4-2: Redispersion / Modification of Alumina Particles In a nitrogen atmosphere, 15 g of the alumina powder obtained in 4-1 was redispersed in 85 g of anhydrous tetrahydrofuran as in 1-2, and then γ-glycid as a modifier. Surface modification was performed by adding 0.15 g of xylpropyltrimethoxysilane.

4-3: Composition (solution mixing)
The same operation as in 1-3 was performed on the alumina particle dispersion prepared in 4-2. In other words, 100 g of alumina particle dispersion (solid content 15%) was added with 85 g of polycarbonate “NOVALEX 7025A” dissolved in 400 g of methylene chloride to obtain a uniform solution, the solvent was removed, and the mixture was further kneaded. As a result, a polymer composite was obtained. The ash content of the product was 15.3 wt%, and it was confirmed that the added alumina particles were all composited. This product had a milky white appearance, was not yellowed, and retained toughness. The impact strength (Izod) was 165 J / m. When the matrix polymer content of the composite was extracted and analyzed by GPC, the weight average molecular weight was 53,000, and the initial molecular weight was almost maintained.

Example 5
5-1: Alumina particle synthesis and moisture removal (high aspect product)
Place aluminum chloride hexahydrate (2.0M, 20ml, 25 ° C) in a Teflon beaker equipped with a mechanical stirrer and stir (700rpm) with sodium hydroxide (4.80M, 20ml, 25 ° C) Was dripped. Stirring was continued for another 10 minutes after the completion of dropping, and the pH of the solution was measured after the stirring was finished (pH = 4.54). Next, the solution was divided into 10 ml autoclaves each equipped with a Teflon (registered trademark) liner, and allowed to pass in an oven at 120 ° C. for 24 hours (first heat treatment). Next, the autoclave was transferred to an oil bath and heated at 180 ° C. for 20 minutes (second heat treatment). Then, it was put into cold water (about 10 ° C.) within 40 seconds and rapidly cooled (third heat treatment). This third heat treatment was continued for 1 hour. Subsequently, the previous autoclave was placed in the oven again, and heating was continued at 140 ° C. for one week (fourth heat treatment). Next, the autoclave is cooled with running water, and the supernatant in the autoclave is removed by centrifugation (18000 rpm, 30 min), followed by centrifugal washing with an aqueous solution of sodium nitrate (0.5M), centrifugal water washing once, water methanol mixed solution. (Volume ratio water: methanol, 0.5: 9.5) Centrifugal washing was performed once.

  When this boehmite was observed with a transmission electron microscope, it was a needle crystal having a major axis length of 350 nm, a minor axis diameter of 5.5 nm, and an aspect ratio of about 65.

  Thereafter, freeze-drying was performed by performing the same operation as 1-1 using a freeze dryer RLEII-52 manufactured by Kyowa Vacuum Technology Co., Ltd., thereby obtaining boehmite colorless crystal powder. When this powder was subjected to TG analysis, the heat loss from 25 ° C. to 150 ° C. was 0.2 wt%, and it was confirmed that sufficient water removal and drying were performed.

5-2: Redispersion / modification of alumina particles Under a nitrogen atmosphere, 15 g of the boehmite powder obtained in 5-1 was redispersed in 85 g of anhydrous tetrahydrofuran as in 1-2, and then γ-glycid as a modifier. Surface modification was performed by adding 0.15 g of xylpropyltrimethoxysilane.

5-3: Composition (solution mixing)
The boehmite dispersion prepared in 5-2 was subjected to the same operation as in 1-3. That is, 100g of boehmite particle dispersion (15%), 85% polycarbonate "NOVAREX 7025A" dissolved in 400g methylene chloride is added to make a uniform solution, the solvent is removed, and the mixture is kneaded. Thus, a polymer composite was obtained. The ash content of the product was 14.8 wt%, and it was confirmed that the added boehmite particles were all composited. This product had a colorless and transparent appearance, was not yellowed, and retained toughness. The impact strength (Izod) was as high as 277 J / m. When the matrix polymer content of the composite was extracted and analyzed by GPC, the weight average molecular weight was 50900, and the initial molecular weight was almost maintained.

Example 6
(Mold polymerization composite)
6-1: Moisture removal of alumina particles (freeze drying)
Using “Nanotech Alumina / Alcohol Dispersed Product” (particle size: 31 nm, solid content: 15%) manufactured by CI Kasei Co., Ltd. as the alumina particle dispersion, drying operation by freeze drying similar to Example 2-1 was performed.

6-2: Alumina particle redispersion / modification Under a nitrogen atmosphere, 60 g of the alumina powder obtained in 6-1 was redispersed in 140 g of anhydrous chloroform manufactured by Kanto Chemical Co., Ltd., and Shin-Etsu Chemical Co., Ltd. ) "KBE-903" (= γ-aminopropyltriethoxysilane) 0.6g was added and mixed for 10 minutes at room temperature, then heated to 50 ° C and mixed for 5 hours to react the modifier sufficiently. I let you.

6-3: Composition (melt polymerization)
Alumina prepared in 6-2 by adding 18 mg (0.1 mmol) of zinc acetate as a catalyst to 124.1 g (2 mol) of ethylene glycol manufactured by Kanto Chemical Co., Ltd. and 194.2 g (1 mol) of dimethyl terephthalic acid manufactured by Kanto Chemical Co., Ltd. Add 40g of particle dispersion (solid content 30%), gradually raise the degree of vacuum and raise the temperature to 195 ° C to sufficiently remove the solvent and water generated, and proceed with the transesterification, then 280 ° C Was polymerized for 3 hours under a reduced pressure of 3 mTorr or less, and this was further kneaded at 280 ° C. for 15 minutes to obtain a polymer composite. The ash content of the product was 4.9 wt%, and it was confirmed that almost all of the added alumina was composited. This composition was colorless and translucent, did not yellow, and had toughness. The impact strength (Izod) was 65 J / m. When the matrix polymer content of the composite was extracted and analyzed by GPC, the weight average molecular weight was 54,000, and a sufficient high molecular weight was maintained.

Example 7
(Solution polymerization composite)
7-1: Alumina particle water removal (freeze drying)
“Cataloid-AS-3” (major axis length 100 nm, minor axis length 10 nm, solid content 7%, specific gravity 1.05) manufactured by Catalyst Kasei Kogyo Co., Ltd., which is a pseudo boehmite type alumina particle dispersion, is a 1-1 method. And freeze-dried. When this powder was subjected to TG analysis, the heat loss from 25 ° C. to 150 ° C. was 0.6 wt%, and it was confirmed that sufficient moisture removal and drying were performed.

7-2: Redispersion / Modification of Alumina Particles 60 g of the alumina powder obtained in 7-1 was redispersed in 140 g of toluene manufactured by Kanto Chemical Co., Ltd. and mixed at room temperature for 20 minutes.

7-3: Composition (solution polymerization)
In 400 mL of toluene, 100.1 g (1 mol) of methyl methacrylate manufactured by Kanto Chemical Co., Ltd. and 12.2 g (0.05 mol) of V-40 manufactured by Wako Pure Chemical Industries, Ltd. as a radical initiator were added. 150 g of the prepared alumina particle dispersion (solid content 30%) was added, the temperature was raised to 90 ° C. to initiate radical reaction, and polymerization was continued for 3 hours while stirring. After the reaction, the reaction solution was poured into 2 L of hexane, dried at 80 ° C. under reduced pressure of 1 Torr or less for 4 hours, and then kneaded at 200 ° C. for 15 minutes to obtain a polymer composite. The ash content of the product was 30.9 wt%, and it was confirmed that almost all of the added alumina was composited. This composition was colorless and transparent, did not yellow, and had some toughness. The impact strength (Izod) was 28 J / m. When the matrix polymer content of the composite was extracted and analyzed by GPC, the weight average molecular weight was 62000, and a sufficient high molecular weight was maintained.

Examples 8-14
In place of the polycarbonate resin of Example 1, the following polymers were respectively subjected to the same drying / moisture removal operation and compositing operation as in Example 1.
8: Polyacetal <"Duracon HP-90X" manufactured by Polyplastics Co., Ltd.>
9: Polyphenylene ether (PPE) <“YPX-100F” manufactured by Mitsubishi Gas Chemical Company, Inc.>
10: Polyamide 6 <"Novamid ST145" manufactured by Mitsubishi Engineering Plastics Co., Ltd.>
11: Thermoplastic polyimide <“ARUUM” manufactured by Mitsui Chemicals, Inc.>
12: Polysulfone <Solvay Advanced Polymer "Udel">
13: Polyphenylene sulfide <Da Nippon Ink Chemical Co., Ltd. “DIC / PPSFZ-1140”>
14: Thermoplastic polyurethane <Kuraray Co., Ltd. “Kuramylon U2000”>

[Comparative example]
In the comparative example, a case where sufficient water removal operation was not performed in the drying of the alumina particles in the above example is described.

Comparative Example 1
1-1: Water removal of alumina particles (evaporator drying)
500 g of “Cataloid-AS-3” (major axis length 100 nm, minor axis length 10 nm, solid content 7%, specific gravity 1.05) manufactured by Catalyst Kasei Kogyo Co., Ltd., which is a pseudo boehmite type alumina particle dispersion, is used as an IWAKI rotary evaporator. Was used to evaporate water with a 60 ° C. pressurized water aspirator and dried for 1 hour. When this powder was subjected to TG analysis, the heat loss from 25 ° C. to 150 ° C. was 3.5 wt%, and moisture removal and drying were incomplete.

1-2: Alumina particle redispersion / modification In a nitrogen atmosphere, 15 g of the alumina powder obtained in Comparative Example 1-1 was redispersed in 85 g of anhydrous tetrahydrofuran in the same manner as in Example 1-2. While adding 0.15 g of γ-glycidoxypropyltrimethoxysilane and continuously stirring, 0.01 g of triethylamine was added dropwise, and mixing was continued at 60 ° C. for 10 hours to sufficiently react the modifier.

1-3: Composition (solution mixing)
In the same manner as in Example 1-3, 100 g of the alumina particle dispersion (solid content: 15%) prepared in Comparative Example 1-2 was polymerized with 85 g of polycarbonate “Novalex 7025A” (weight average molecular weight 54000). The ash content of the product was 14.2 wt%. This product had a yellowish amber appearance and poor toughness, and even a 2 mm thick sample plate could be broken by hand. The impact strength (Izod) remained at 14 J / m. When the matrix polymer content of the composite was extracted and analyzed by GPC, the weight average molecular weight was 9600, which was greatly reduced from the initial molecular weight.

Comparative Example 2
2-1: Alumina particle water removal (spray drying)
Okawara Chemical Industry Co., Ltd. made of Catalytic Chemical Industry Co., Ltd. “Cataloid-AS-3” (major axis length 100 nm, minor axis length 10 nm, solid content 7%, specific gravity 1.05) is a pseudo-boehmite type alumina particle dispersion. Using a spray dryer L-8, the water was volatilized by spray drying under conditions of a hot air temperature of 250 ° C. and an exhaust air temperature of 100 ° C., and drying was performed for about 15 minutes. When this powder was subjected to TG analysis, the heat loss from 25 ° C. to 150 ° C. was 2.9 wt%, and moisture removal and drying were incomplete.

2-2: Alumina particle redispersion / cost change After redispersion in anhydrous tetrahydrofuran under the same conditions as in Comparative Example 1-2, the modifier was reacted.

2-3: Compositionization (solution mixing)
Similarly to Comparative Example 1-3, a polycarbonate “Novalex 7025A” (weight average molecular weight 54000) and a polymer composite were formed so as to have a solid content of 15 wt%. The ash content of the product was 13.9 wt%. The product had a yellowed brown appearance, poor toughness, and impact strength (Izod) remained at 34 J / m. When the matrix polymer content of the composite was extracted and analyzed by GPC, the weight average molecular weight was 16,200, which was significantly lower than the initial molecular weight.

Comparative Example 3
3-1: Alumina particle moisture removal (normal pressure low temperature drying)
A flat bottom evaporating dish of 500 g of “Cataloid-AS-3” (major axis length 100 nm, minor axis length 10 nm, solid content 7%, specific gravity 1.05) manufactured by Catalyst Kasei Kogyo Co., Ltd., which is a pseudo boehmite type alumina particle dispersion. Divided into 100 gram portions, placed on open shelves of the hot air circulation open LC224 manufactured by Espec Co., Ltd., and dried at 70 ° C. for 18 hours. When this powder was subjected to TG analysis, the heat loss from 25 ° C. to 150 ° C. was 5.8 wt%, and moisture removal / drying was incomplete.

3-2: Redispersion / Modification of Alumina Particles After redispersion in anhydrous tetrahydrofuran under the same conditions as in Comparative Example 1-2, the modifier was reacted.

3-3: Composition (solution mixing)
Similarly to Comparative Example 1-3, a polycarbonate “Novalex 7025A” (weight average molecular weight 54000) and a polymer composite were formed so as to have a solid content of 15 wt%. The ash content of the product was 13.9 wt%. This product had a yellowish pale brown appearance and poor toughness, and even a 2 mm thick sample plate could be broken by hand. The impact strength (Izod) remained at 11 J / m. When the matrix polymer content of the composite was extracted and analyzed by GPC, the weight average molecular weight was 6200, which was greatly reduced from the initial molecular weight.

Comparative Example 4
4-1: Alumina particle water removal (vacuum drying at reduced pressure)
500 g of “Cataloid-AS-3” (major axis length 100 nm, minor axis length 10 nm, solid content 7%, specific gravity 1.05) manufactured by Catalyst Kasei Kogyo Co., Ltd., which is a pseudo boehmite type alumina particle dispersion, It was set in a reduced pressure heat transfer dryer DPTH-40 manufactured by Matsui Seisakusho, set at a temperature of 70 ° C., dried at a reduced pressure of 2 Torr over 4 hours, and then returned to normal pressure with dry nitrogen gas. When this powder was subjected to TG analysis, the heat loss from 25 ° C. to 150 ° C. was 3.3 wt%, and moisture removal and drying were incomplete.

4-2: Redispersion / Modification of Alumina Particles After redispersion in anhydrous tetrahydrofuran under the same conditions as in Comparative Example 1-2, the modifier was reacted.

4-3: Composition (solution mixing)
Similarly to Comparative Example 1-3, a polycarbonate “Novalex 7025A” (weight average molecular weight 54000) and a polymer composite were formed so as to have a solid content of 15 wt%. The ash content of the product was 14.4 wt%. This product had a yellowish amber appearance and poor toughness, and even a 2 mm thick sample plate could be broken by hand. Impact strength (Izod) remained at 20 J / m. When the matrix polymer content of the composite was extracted and analyzed by GPC, the weight average molecular weight was 8700, which was greatly reduced from the initial molecular weight.

Comparative Example 5
5-1: Alumina particle water removal (micron size particles)
100 g of “alumina white H” (particle size 3 μm, solid content 80%, specific gravity 2.4) manufactured by Daimei Chemical Co., Ltd., which is a pseudo boehmite type alumina particle dispersion, is dried by the same freeze drying operation as in Example 1-1. I let you. When this powder was subjected to TG analysis, the heat loss from 25 ° C. to 150 ° C. was 0.3 wt%, and it was confirmed that sufficient moisture removal and drying were performed.

5-2: Redispersion / Modification of Alumina Particles After redispersion in anhydrous tetrahydrofuran under the same conditions as in Example 1-2, the modifier was reacted.

5-3: Composition (solution mixing)
In the same manner as in Example 1-3, a polycarbonate “Novalex 7025A” (weight average molecular weight 54000) and a polymer composite were formed so as to have a solid content of 15 wt%. The ash content of the product was 15.4 wt%. Although this product had a white appearance without yellowing, it had poor toughness, and even a 2 mm thick sample plate could be broken by hand. The impact strength (Izod) remained at 39 J / m.

Comparative Example 6
(Normal pressure heating and internal polymerization)
“Nanotech alumina alcohol dispersion product” manufactured by C-I Kasei Co., Ltd. used in Example 6 was dried at 70 ° C. for 18 hours in the same manner as in Comparative Example 3-1, instead of freeze-drying. After that, it was mixed with a monomer of PET resin and made into a composition by internal addition polymerization. This product had a yellowish pale brown appearance and poor toughness, and even a 2 mm thick sample plate could be broken by hand. The impact strength (Izod) remained at 10 J / m. When the matrix polymer content of the composite was extracted and analyzed by GPC, the weight average molecular weight was 10400, which was significantly lower than the molecular weight of Example 6.

Comparative Example 7
(Normal pressure heating / solution polymerization)
“Cataloid-AS-3” (major axis length 100 nm, minor axis length 10 nm, solid content 7%, specific gravity 1.05) manufactured by Catalyst Kasei Kogyo Co., Ltd., prepared in Comparative Example 3-1, In the same manner as in Examples 7-2 and 7-3, the mixture was mixed into the acrylic resin monomer solution to form a composition by solution polymerization. This product had a yellowish reddish brown appearance and extremely poor toughness, and even a sample plate having a thickness of 3 mm could be easily broken by hand. The impact strength (Izod) remained at 3 J / m. When the matrix polymer content of the composite was extracted and analyzed by GPC, the weight average molecular weight was 20900, which was significantly lower than the molecular weight of Example 6.

Comparative Examples 8-14
Similarly, a polymer composite was obtained by performing the same operation except that the alumina particle sol in Examples 8 to 14 was used in the next step with the adsorbed water remaining. These composites were yellowed and inferior in toughness, and most 2 mm sample plates were easily broken by hand.

  The data of the above Examples and Comparative Examples are summarized in Tables 1 to 4.

  The present invention has been described in detail above with reference to specific examples. However, the present invention is not limited to the above contents, and various modifications and changes can be made without departing from the scope of the present invention.

  For example, the resin composition of the present invention contains an antioxidant and a heat stabilizer (including hindered phenols, hydroquinones, thioethers, phosphites, and their substitution products and combinations thereof), ultraviolet absorption, if necessary. Agents (for example, resorcinol, salicylate, benzotriazole, benzophenone, etc.), lubricants, mold release agents (for example, silicon resin, montanic acid and salts thereof, stearic acid and salts thereof, stearyl alcohol, stearylamide, etc.), dyes (for example, nitrocin) , Coloring agents containing facials (for example, cadmium sulfide, phthalocyanine, etc.), additive additives (for example, silicon oil), crystal nucleating agents (for example, talc, kaolin, etc.), etc. can be added alone or in appropriate combination. .

  Specifically, in order to improve thermal stability, partially acrylated polyphenols represented by hindered phenols such as Irganox 1010 and 1076 (manufactured by Ciba-Geigy), Sumilizer GS, and GM (manufactured by Sumitomo Chemical Co., Ltd.) An appropriate amount of a heat stabilizer such as a phosphorus compound typified by phosphites such as Irgafos 168 (manufactured by Ciba Geigy) may be added.

Claims (17)

In a polymer composite composed of an organic polymer and alumina particles having a major axis of 10 to 500 nm,
A method for producing a polymer composite, wherein the adsorbed water contained in the alumina particles is dried to a weight loss of 2 wt% or less from room temperature to 150 ° C. and then mixed with the organic polymer to form a composite. .   The adsorbed water contained in the alumina particles is removed by a freeze-drying method, or a high temperature applied at a temperature of 100 ° C. to 300 ° C. under normal pressure or reduced pressure, and a means selected from a combination thereof, The method for producing a polymer composite according to claim 1, wherein the polymer composite is formed into a composite with an organic polymer.   The adsorbed water contained in the alumina particles is removed by preparing the suspension of the alumina particles and then performing the freeze drying on the suspension. Method for producing polymer nanocomposite.   The method for producing a polymer nanocomposite according to claim 3, wherein the concentration of the alumina particles in the suspension is 2-50 wt%.   The polymer nano particles according to claim 2, wherein the adsorbed water contained in the alumina particles is removed by producing the powder of the alumina particles and then subjecting the powder to the strong heat. Composite manufacturing method.   The method for producing a polymer composite according to any one of claims 1 to 5, wherein the alumina particles are essentially crystalline alumina hydrate in the form of boehmite.   The polymer nanocomposite according to claim 6, wherein the alumina particles exhibit anisotropy having a minor axis length of 2 to 10 nm, a major axis length of 10 to 500 nm, and an aspect ratio of 5 to 100. Method.   The method for producing a polymer nanocomposite according to any one of claims 1 to 7, wherein the concentration of the alumina particles in the polymer nanocomposite is 1 to 70 wt% as a solid content.   The repeating unit of the chemical structure of the organic polymer includes an ester bond, an ether bond, an amide bond, an imide bond, a urethane bond, a sulfide bond, and a sulfone bond, according to any one of claims 1 to 8. A method for producing the polymer composite described.   The method of producing a polymer nanocomposite according to any one of claims 1 to 9, wherein the compositing is performed by melt-kneading the organic polymer and the alumina particles.   10. The polymer nano according to claim 1, wherein the composite is performed by dispersing the organic polymer and the alumina particles in an organic solvent and then distilling the solvent. Composite manufacturing method.   The polymer according to any one of claims 1 to 9, wherein the compositing is performed by mixing a dispersion solution of the alumina particles and a monomer of the organic polymer and then proceeding with polymerization. A method for producing a nanocomposite. Polymer composite A containing at least the following components as essential components and obtained as a mixed product A) Alumina particles B having a major axis of 10 to 500 nm with an adsorption moisture content of 2 wt% or less as a heating loss from 25 ° C. to 150 ° C. Organic polymer.   The polymer composite according to claim 13, wherein the repeating unit of the chemical structure of the organic polymer includes an ester bond, an ether bond, an amide bond, an imide bond, a urethane bond, a sulfide bond, and a sulfone bond.   15. A polymer composite according to claim 13 or 14, characterized in that the alumina particles are crystalline alumina hydrate in the form of boehmite.   The polymer nanocomposite according to claim 15, wherein the alumina particles exhibit anisotropy having a minor axis length of 2 to 10 nm, a major axis length of 10 to 500 nm, and an aspect ratio of 5 to 100.   The polymer nanocomposite according to any one of claims 13 to 16, wherein the concentration of the alumina particles in the polymer nanocomposite is 1 to 70 wt% as a solid content.