JP2006213577A - Inorganic particulate agglomerate and its producing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inorganic particulate agglomerate where inorganic particulates can be dispersed in a resin to a primary particle level. <P>SOLUTION: The inorganic particulate agglomerate is obtained by the steps of obtaining a solidified product by drying a mixed liquid of the inorganic particulates and an inorganic salt, removing the inorganic salt from the solidified product by using a solvent, and drying the resulted product. The inorganic particulate agglomerate is formed by coagulation force between the inorganic particulates where the coagulation force is generated by the drying performed at a temperature that surface fusion between the inorganic particulates is not caused. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an inorganic fine particle aggregate having a low strength, which is formed by an aggregation force between inorganic fine particles without substantially fusing the inorganic fine particles on the surface, and a method for producing the same. More specifically, the present invention relates to an inorganic fine particle aggregate capable of physically dispersing inorganic fine particles to the primary particle level when melt-mixed with a resin, wherein the inorganic fine particles are dispersed at the nano level. The present invention relates to an inorganic fine particle aggregate that can be provided and a method for producing the same.

Conventionally, a resin composition having higher performance is required in various fields, and physical properties and moldability are improved by dispersing a filler in the resin.
In particular, Japanese Patent Application Laid-Open No. 2001-152030 discloses a porous silica material having an average particle size of 100 nm to 1000 nm obtained by firing a porous aggregate composed of porous glass or silica fine particles having an average primary particle size of 12 nm at a temperature of 600 ° C. or higher. An additive selected from metals, metal salts, and inorganic compounds or a flame retardant is previously supported on the body, melted and mixed with the resin, the inorganic porous body is crushed, and the average particle size is 10 nm to 100 nm. A resin composite composition in which particles carrying an agent or a flame retardant are pulverized in a resin and a method for producing the same are described.

  However, since the structure of the porous glass described in the above publication is usually produced at a high temperature of 1200 ° C. or higher, it is a covalent bond between silicon and oxygen, and crushing the porous glass breaks the covalent bond. In particular, since large energy is required, it is extremely difficult to crush and disperse the porous glass by melt mixing with the resin.

  An inorganic porous body having an average particle size of 100 nm to 1000 nm obtained by firing an aggregate of inorganic fine particles composed of silica fine particles having an average primary particle size of 12 nm at 600 ° C. to 700 ° C. Since only the surface layer is slightly melted by the surface melting of the silica particle aggregate) and fused to each other and solidified into a skeleton having a strong bond, the strength of the porous body is high (resource and material, Vol 118). , P202, 2002), even if melt-mixed with a resin in a melt-mixing device, the average particle size of polystyrene (PS) and the inorganic porous material after melt-mixing is 290 nm, and the inorganic porous is 40 nm to 100,000 nm in polystyrene. It has a wide distribution of (100 μm) and has not been successfully crushed to the original primary particles (Proceedings of the 13th Symposium on Polymer Materials, P10, 2003) . For this reason, the mechanical properties remarkably deteriorate due to the presence of many inorganic fine particle aggregated sintered bodies having an average particle size of 10 μm or more in the polystyrene resin.

  On the other hand, when inorganic fine particles or inorganic nanoparticles (fine particles of nanometer level) are melt-mixed in a resin, the agglomeration force of fine particles per unit volume increases as the particle size decreases, so that the fine particles reaggregate. Therefore, even if the nanoparticles are directly melt-mixed with the resin, it is extremely difficult to nano-disperse the nanoparticles in the resin as they are.

  Furthermore, recently, in polymer nanocomposites in which nanofillers such as carbon nanotubes and carbon nanofibers are added to polymer materials and these nanofillers are dispersed in the resin during the melt mixing process, the nanofillers depend on the polarity of the resin used. The dispersion state of the polymer changes, and nano fillers can be uniformly dispersed to some extent in polar resins such as nitrile rubber (NBR), but carbon nanotubes can be uniformly dispersed in hydrophobic resins such as ethylene propylene rubber (EPDM). Is difficult (Polymer Preprints, Japan, Vol 52, P1785, 2003). Accordingly, the dispersion state of the inorganic fine particles or inorganic nanoparticles varies greatly depending not only on the kind and surface properties of the inorganic fine particles or inorganic nanoparticles but also on the kind of the resin to be dispersed and the hydrophobicity / hydrophilicity.

JP 2001-152030 A 13th Symposium on Polymer Materials, P10, 2003

Accordingly, the inventors of the present invention have arrived at the present invention as a result of earnestly researching the development of an inorganic fine particle aggregate capable of dispersing inorganic fine particles in a resin to the primary particle level of the inorganic fine particles.
The present invention provides an inorganic fine particle aggregate that can be dispersed in a resin up to the primary particle level of inorganic fine particles.
The present invention provides an inorganic fine particle aggregate with low strength formed by the cohesive force between inorganic fine particles without the inorganic fine particles being substantially fused on the surface.

  The present invention is an inorganic fine particle aggregate obtained by drying from a mixed solution of inorganic fine particles and an inorganic salt by drying, removing the inorganic salt from the solidified material using a solvent and drying, Provided is an inorganic fine particle aggregate formed by agglomeration force between inorganic fine particles obtained by drying at a temperature at which surface fusion between the inorganic fine particles does not substantially occur.

  The inorganic fine particles described above in which the crushing strength of the inorganic fine particle aggregate is 4.50 MPa or less is a preferred embodiment of the present invention.

  The above-mentioned inorganic fine particle aggregate in which the average primary particle size of the inorganic fine particles is 1 μm or less is a preferred embodiment of the present invention.

  Any of the inorganic fine particles described above in which the compressive load of the inorganic fine particle aggregate is 110 mN or less is a preferred embodiment of the present invention.

  The above-mentioned inorganic fine particle aggregate in which the inorganic fine particles are composed of silicon oxide, titanium oxide, aluminum oxide, or a composite oxide of zinc oxide and antimony pentoxide is a preferred embodiment of the present invention.

  The inorganic fine particle aggregate described above, wherein the inorganic salt is at least one selected from alkali metal salts, alkaline earth metal salts or ammonium salts of hydrohalic acid, phosphoric acid, sulfuric acid, nitric acid and molybdic acid. This is a preferred embodiment.

The inorganic fine particle aggregate described above is a preferred embodiment of the present invention, wherein the inorganic salt is at least one selected from potassium bromide, potassium chloride, ammonium molybdate, sodium dihydrogen phosphate, calcium chloride, and ammonium bromide. is there.

  The low-strength inorganic fine particle aggregate described above, which is dried at a temperature at which surface fusion between the inorganic fine particles does not occur, is a preferred embodiment of the present invention.

The above-mentioned inorganic fine particle aggregate is obtained by performing the drying at a ratio (T ₀ / T _m ) of the drying temperature (T ₀ ) indicated by the absolute temperature and the melting point (T _m ) of the inorganic fine particles to 0.23 or less. This is a preferred embodiment of the invention.

  The present invention further provides a method of obtaining a solidified product by drying from a mixed liquid of inorganic fine particles and an inorganic salt, and removing the inorganic salt from the solidified product using a solvent, followed by drying. There is provided a method for producing any one of the above-mentioned inorganic fine particle aggregates, which is carried out at a temperature at which surface fusion does not substantially occur.

According to the present invention, an inorganic fine particle aggregate formed by the cohesive force between inorganic fine particles is provided without the inorganic fine particles being substantially fused on the surface.
ADVANTAGE OF THE INVENTION According to this invention, the inorganic fine particle aggregate which can be crushed and disperse | distributed physically to a nano level when it melt-mixes using it as a filler of various resin is provided.
The inorganic fine particle aggregate provided by the present invention can be physically crushed and dispersed to the nano level when melt-mixed with various resins, so that the resin can be made into a so-called nanocomposite.
The present invention provides a method for producing the above-described characteristic inorganic fine particle aggregate.
The resin nanocomposite molded product that can be provided by the present invention is excellent in mechanical properties, dimensional stability, flame retardancy, melt moldability, friction resistance and wear characteristics, and can be applied to various molded products. Is.

  The present invention is an inorganic fine particle aggregate obtained by drying from a mixed solution of inorganic fine particles and an inorganic salt by drying, removing the inorganic salt from the solidified material using a solvent and drying, Provided is an inorganic fine particle aggregate formed by agglomeration force between inorganic fine particles obtained by drying at a temperature at which surface fusion between the inorganic fine particles does not substantially occur.

  The present invention is also a method for obtaining a solidified product by drying from a mixed solution of inorganic fine particles and an inorganic salt, and removing the inorganic salt from the solidified product using a solvent, followed by drying. The present invention provides a method for producing an inorganic fine particle agglomerate which is carried out at a temperature at which substantially no surface fusion occurs.

  The inorganic fine particle aggregate formed by the cohesive force between the inorganic fine particles in the present invention is an aggregate formed by the cohesive force between the inorganic fine particles without the inorganic fine particles being substantially fused on the surface.

  Since the inorganic fine particle aggregate of the present invention is formed by a relatively weak cohesive force between the inorganic fine particles, it is a low-strength inorganic fine particle aggregate and can be dispersed in the resin to the primary particle level of the inorganic fine particles. It has a feature that could not be achieved by the prior art.

  In the present invention, an inorganic fine particle aggregate having a low strength, in which a structure is formed in advance by the cohesive force between adjacent inorganic fine particles, the inorganic fine particles include silicon oxide, titanium oxide, zeolite, Zirconium oxide, alumina, antimony pentoxide, silicon carbide, aluminum nitride, silicon nitride, barium titanate, aluminum borate, boronite, lead oxide, zinc oxide, tin oxide, cerium oxide, magnesium oxide, cerium zirconate, calcium silicate And a dispersion of nano-inorganic fine particles such as zirconium silicate (hereinafter sometimes referred to as sol). These inorganic fine particles can be used alone or in combination of two or more.

  The aggregate of inorganic fine particles of the present invention is obtained by removing inorganic salt from a solidified product of inorganic fine particles and inorganic salt obtained from a mixture of inorganic fine particles and inorganic salt using a solvent that elutes the inorganic salt, followed by drying. Can be obtained.

  The inorganic fine particle aggregate of the present invention is capable of physically dispersing inorganic fine particles to the primary particle level when melt-mixed with a resin. When the inorganic fine particles are nano inorganic fine particles, the inorganic fine particle aggregate of the present invention can provide a resin nano composite in which the inorganic fine particles are dispersed at the nano level in the resin. Therefore, the nano inorganic fine particles are suitable as the inorganic fine particles of the present invention.

  The solidified product of inorganic fine particles and inorganic salt is preferably a solidified product of inorganic fine particles and inorganic salt obtained by mixing a sol of inorganic fine particles and an inorganic salt and drying the mixed solution. Drying for obtaining a solidified product is performed at a temperature at which surface fusion between the inorganic fine particles does not substantially occur, preferably at a temperature at which the formation of a neck described later does not occur.

Inorganic fine particles obtained by removing inorganic salt from a solidified product of nano-inorganic fine particles and inorganic salt and then drying at a temperature at which surface fusion between the inorganic fine particles does not occur substantially after removing the inorganic salt Aggregates are a preferred embodiment of the aggregates of the present invention.
It can be confirmed that surface fusion between the inorganic fine particles is not substantially caused by the fact that surface fusion is not observed at a substantial ratio in the observation of the obtained aggregate by electron micrograph.

  Since the inorganic fine particle aggregate of the present invention is an aggregate formed by the cohesive force between the inorganic fine particles, a mixture of the inorganic fine particles and the inorganic salt is fired at a high temperature to fuse the inorganic fine particles. The inorganic fine particle aggregate is lower in strength than the inorganic fine particle aggregate (Japanese Patent Laid-Open No. 2001-152030).

  In the present invention, the inorganic fine particle aggregate obtained by removing the inorganic salt with a solvent and drying at a temperature at which surface fusion between the inorganic fine particles does not substantially occur is usually coarse particles or massive aggregates having a large average particle size. Aggregates are obtained, but may be appropriately pulverized and classified as necessary. The average particle size of the aggregate of inorganic fine particles of the present invention is preferably in the range of 50 μm to 400 μm, preferably in the range of 70 μm to 300 μm, from the viewpoint of biting in the hopper of the extruder. When the aggregates are pulverized and classified, it is preferable that the average particle diameter be in the above range.

  The solvent for eluting the inorganic salt from the solidified product of the inorganic fine particles and the inorganic salt may be the same as or different from the solvent used for the mixed liquid of the inorganic fine particles and the inorganic salt, but is inert to the inorganic fine particles. It is preferable. As such a solvent, a polar solvent which is a poor solvent for inorganic fine particles and a good solvent for inorganic salts can be appropriately selected and used. Water is one suitable example of such a solvent. Since the inorganic salt is eluted and removed using a solvent that elutes the inorganic salt from the solidified product, it acts as a kind of pore-forming agent for the resulting aggregate.

  The preferred form for obtaining the aggregate of the present invention is selected from silica sol, titanium oxide sol, alumina sol, antimony pentoxide sol, zinc oxide sol, composite oxide sol of zinc oxide and antimony pentoxide and zeolite sol as the inorganic fine particles. The form which uses water-soluble inorganic salt as an inorganic salt using at least 1 sort (s), water as a solvent can be mentioned. Examples of the water-soluble inorganic salt include at least one selected from alkali metal salts, alkaline earth metal salts, or ammonium salts of hydrohalic acid, phosphoric acid, sulfuric acid, nitric acid, and molybdic acid. Preferably, potassium nitrate, potassium iodide, ammonium molybdate, sodium dihydrogen phosphate, potassium bromide, ammonium bromide, potassium chloride, calcium chloride, calcium nitrate and the like can be mentioned. These inorganic salts can be used alone or in combination of two or more. Among the above forms, a form using silica sol as the inorganic fine particles is more preferable.

  Moreover, a high-purity inorganic fine particle aggregate can be obtained as an inorganic fine particle aggregate obtained when a high-purity solvent is used as the solvent. For example, when the residual inorganic salt is eluted repeatedly using pure water, an inorganic fine particle aggregate with extremely high purity can be obtained. When this method is applied to obtain an aggregate composed of silica particles using silica sol as a raw material, a high-purity aggregate composed of silica particles can be obtained. The high-purity agglomerates thus obtained are suitably used for parts that require purity, such as those used in semiconductor manufacturing equipment.

  When the aggregate of the present invention is melt-mixed with the resin, it can be physically dispersed to the level of primary particles by the shear stress generated in the melt-mixing device. Therefore, when nano-inorganic particles are used as the inorganic particles, It becomes possible to disperse the inorganic fine particles to the nano level.

  The strength of the inorganic fine particle aggregate having a low strength formed by the cohesive force between adjacent inorganic fine particles obtained by the present invention is low. Since it changes depending on the kind and content of the inorganic salt, the drying temperature, etc., the strength of the inorganic fine particle aggregate can be controlled by selecting these conditions.

  In addition, when the inorganic fine particle aggregate of the present invention is melt-mixed with the resin to disperse the inorganic fine particles in the resin, the type of resin to be melt-mixed, the structure of the melt-mixing device to be used (screw structure and combination), melting The average particle size and dispersion state of the inorganic fine particle aggregates dispersed in the resin vary depending on the mixing conditions (temperature and screw rotation speed). Therefore, in order to uniformly crush and disperse the resin and the inorganic fine particle aggregate in the heat-meltable fat uniformly to the original primary particle level, depending on the type of the inorganic fine particle aggregate and the resin used, It is necessary to select the conditions for melt mixing.

  In the case of a porous silica material, the strength is the sum of the interparticle adhesion forces acting at the contact points between a large number of primary silica particles forming the porous material. Depending on the diameter (Chemie Ingenieur Technik, vol 42, p538, 1970), in order to produce a porous silica as an inorganic fine particle aggregate having low strength, increase the porosity by increasing the content of inorganic salt, It is preferable to use a silica having a large average primary particle size. Therefore, the average primary particle size is preferably 50 nm or more, preferably 90 nm or more, and more preferably 110 nm or more. When the porosity is the same, the strength of the aggregate is inversely proportional to the primary particle size. When the average primary particle size is small, the strength of the aggregate is increased and it is difficult to be crushed in the melt mixing process. Further, in the case of using an aggregate of inorganic fine particles having the same strength, the nano-inorganic fine particles are uniformly crushed and dispersed in the resin when the fine particles are melt-mixed with a stronger shear stress.

  Since the inorganic salt used in the present invention serves as a kind of pore-forming agent for the aggregate of inorganic fine particles, the strength of the inorganic fine particle aggregate varies depending on the content of the inorganic salt. As the content of the inorganic salt relative to the inorganic fine particles increases, the strength of the nano inorganic fine particle aggregate decreases. However, if the content of the inorganic salt is too large, the inorganic fine particle aggregates are easily crushed in a measuring step or the like and returned to primary particles. Therefore, the content of the inorganic salt is 1 to 90% by volume, preferably 50 to 85% by volume, more preferably 60 to 80% by volume.

After mixing the water-dispersed inorganic fine particle sol and the inorganic salt, the mixed solution is dried to produce a solidified product of the inorganic fine particles and the inorganic salt, and the inorganic salt from the solidified solid of the inorganic fine particles and the inorganic salt. As described above, the drying temperature at which drying is performed after removing the inorganic salt using a solvent that elutes the solvent is such that the surface fusion between the inorganic fine particles does not substantially occur, preferably the temperature at which neck formation does not occur. desirable. Since the melting point on the surface of the inorganic fine particles is lower than the melting point in the interior (bulk state), when the drying temperature is increased, a part of the surface of the inorganic fine particles melts, and the strength of the aggregates of the inorganic fine particles due to fusion between adjacent inorganic fine particles Becomes stronger. In addition, inorganic fine particles generally have defects in the crystal structure on the particle surface when they are generated, and since these defects are all thermally unstable, they can be rapidly recovered or moved when heated, A connecting portion (neck) is formed at a contact portion between adjacent inorganic fine particles. The formation of this neck also increases the strength of the aggregate of inorganic fine particles. The main cause of the formation of the neck is considered to be surface fusion between adjacent inorganic fine particles. The formation of the neck is indicated by the absolute temperature because the ratio (T ₀ / T _m ) of the drying temperature (T ₀ ) indicated by the absolute temperature and the melting point (T _m ) of the inorganic fine particles starts from 0.23. The ratio between the drying temperature and the melting point of the inorganic fine particles is 0.23 or less, preferably 0.21 or less. Therefore, for example, when the inorganic fine particles are silica, drying is desirably performed at a temperature of 150 ° C. or lower, preferably 120 ° C. or lower.

  As for the strength of the inorganic fine particle aggregate of the present invention, the compressive load is 110 mN or less, preferably 40 mN or less.

The inorganic particulate aggregate of the present invention, crush strength _{S t} is 4.50MPa or less, preferably at most 1.50MPa. Crush strength S _t is a measure of the effect was corrected intensity difference in particle size as described below.

  The present invention removes an inorganic salt from a solidified product obtained by drying a mixed liquid of inorganic fine particles and an inorganic salt using a solvent that elutes the inorganic salt, followed by drying. The present invention provides a method for producing a low-strength inorganic fine particle aggregate formed by the agglomeration force between the inorganic fine particles described above by carrying out at a temperature at which surface fusion does not substantially occur.

  When the low-strength inorganic fine particle aggregates of the present invention are melt-mixed using fillers of various resins, the aggregates of inorganic fine particles having low strength that are mixed together by the shear stress generated by the melt-mixing device are physically nanoscale. The resin can be made into a so-called nanocomposite by crushing and dispersing to the maximum. There is no particular limitation on the method of melt mixing, and the apparatus and conditions usually used for melt mixing of the resin can be applied.

  Molded products made from resin nanocomposites obtained in this way are excellent in mechanical properties, dimensional stability, flame retardancy, melt moldability, friction resistance, and wear characteristics, so they can be applied to various molded products. it can. Examples of the molded products that can be applied include tubes, sheets, rods, fibers, packings, linings, and wire coating.

  The present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples.

In the present invention, each physical property was measured by the following method.
(1) Compressive load and crushing strength of inorganic fine particle aggregates Using a micro compression tester (MCT-W500, manufactured by Shimadzu Corporation), about 100 mg of a sample is sprayed on a high-rigidity stage, and the particle size D of each sample is measured. Was measured, experimental force P (Compressive Load) and compressive displacement were measured, and the crushing strength S _t (or breaking strength) of the sample was obtained by the following formula (Japan Mining Association, vol. 81, p24, 1965). The experimental force P was a compression load.
The crushing strength was measured five times for each sample, and the average value was made the crushing strength (MPa). The inorganic fine particle aggregate of the present invention was selected to have an average particle size of about 150 μm and the crushing strength was measured. However, the average particle size of commercially available silica used as a comparative example is smaller than that of the sample of the present invention, although smaller values of the experimental force P, crushing strength S _t to the particle size effect of differences in is corrected becomes larger .
S _t = 2.8P / (πD ² )
S _t (MPa): Crushing strength (or breaking strength) of the sample
P (N): Experimental force measured with a micro compression tester (Compressive Load)
D (mm): Sample particle size

The raw materials used in Examples, Comparative Examples and Reference Examples of the present invention are as follows.
(1) Silica sol Snowtex MP2040 (silica average primary particle size: 190 nm) manufactured by Nissan Chemical Industries,
Snowtex MP1040 (silica average primary particle size: 110 nm),
Snowtex ST-YL (silica average primary particle size: 57 nm),
Snowtex 30 (silica average primary particle size: 12 nm)
(2) Porous silica manufactured by Fuji Silysia Chemical, C-1504 (average particle size: 4 μm)
(3) Fused silica, FB-74 (average particle size: 32 μm), manufactured by Denki Kagaku Kogyo
(4) Polystyrene (PS)
Asahi Kasei, Stylon 685

Example 1
In a beaker, 1 L of water, 245.7 g of silica sol in which silica fine particles having the average particle size (primary particle size) shown in Table 1 were dispersed in water (silica particles 40 wt%), and 292.3 g of potassium bromide (KBr). In order, it stirred until all the KBr melt | dissolved, and in order to accelerate | stimulate aggregation of a silica particle, nitric acid was added so that it might become pH 4.0. Next, the stirred mixed solution was transferred to a fluororesin container and dried with a dryer at 80 ° C. until there was no change in weight. The dried sample was pulverized and classified with a sieve having openings of 300 μm and 75 μm to produce a solidified product having an average particle size of 75 μm to 300 μm. Then, 100 g of the sample after classification and 2.5 L of pure water are placed in a beaker, stirred at 200 rpm for 30 minutes while heating at 80 ° C., and then allowed to stand to precipitate a solidified product, which contains the eluted KBr. Removed. After removing the supernatant, the sample is dried for about 10 hours with a dryer at 120 ° C., and further vacuum-dried at 120 ° C. for 3 hours to remove KBr and leave only the SiO ₂ skeleton. S1 was obtained. The crushing strength of the obtained sample is shown in Table 1.

(Example 2)
Sample S2 was obtained in the same manner as in Example 1, except that silica sol (40% by weight) in which silica particles having an average primary particle size of 0.110 μm were dispersed in an aqueous solution was used. The crushing strength of the obtained sample is shown in Table 1.

(Example 3)
Sample S3 was obtained in the same manner as in Example 1, except that silica sol (40% by weight) in which silica particles having an average primary particle size of 0.057 μm were dispersed in an aqueous solution was used. The crushing strength of the obtained sample is shown in Table 1.

Example 4
Sample aggregate S4 was obtained in the same manner as in Example 1, except that 327.6 g of silica sol (silica particles 30 wt%) in which silica particles having an average primary particle size of 0.012 μm were dispersed in an aqueous solution was used. The crushing strength of the obtained sample is shown in Table 1. Moreover, the electron micrograph of sample S4 is shown in FIG.

(Comparative Example 1)
Into a beaker, add 1 L of water, 327.6 g of silica sol (silica fine particles 30 wt%) in which silica fine particles having an average particle size (0.012 μm) shown in Table 1 are dispersed in water, and 292.3 g of KBr in this order, and stir the fine particles. In order to promote the aggregation of the nitric acid, nitric acid was added so as to have a pH of about 4.0. Next, the stirred mixed solution was transferred to a fluororesin container and dried with a dryer at 80 ° C. until there was no change in weight. After drying, the mixture was pulverized and classified with a sieve having openings of 300 μm and 75 μm to obtain a solidified product having an average particle diameter of 75 μm to 300 μm. The obtained solidified product was placed on a baking dish and baked at a temperature of 600 ° C. shown in Table 1 for 2 hours in a fully automatic open / close tubular furnace (manufactured by ISUZU, EKRO-23). 100 g of the fired solidified product and 2.5 L of pure water were placed in a beaker and stirred while heating at 80 ° C., and then allowed to stand to precipitate the solidified product, and the supernatant liquid containing the eluted KBr was removed. After removing the supernatant, it is dried for about 10 hours with a dryer at 120 ° C., and further vacuum-dried at 120 ° C. for 3 hours to remove a silica fine particle aggregate sample S5 from which KBr is removed and only the skeleton of SiO ₂ remains. Obtained. The crushing strength of the obtained sample is shown in Table 1. An electron micrograph is shown in FIG.

(Reference Example 1)
Table 1 shows the crushing strength of a commercially available porous silica sample R1 (average particle diameter: 4 μm).

(Reference Example 2)
Table 1 shows the crushing strength of a commercially available fused silica sample R2 (average particle size: 32 μm).

(Reference Example 3)
59.51 g of polystyrene and 3.13 g (5% by weight) of silica fine particle aggregate (S1) were melt-mixed by a KF-70V small segment mixer manufactured by Toyo Seiki Seisakusho Co., Ltd. The phases of five Kneading discs were shifted by 0.5 pitch. Using a combination of high shear, melt mixing was performed at 180 ° C. and 200 rpm for 1 minute and 20 seconds to obtain a composite composition in which silica fine particles were dispersed in polystyrene. An electron microscope observation result of the obtained composite composition fracture surface is shown in FIG.

  From Table 1, it can be seen that the silica fine particle aggregates (Examples 1 to 4) which were only dried without firing were lower in crushing strength than the fired silica fine particle aggregated fired bodies (Comparative Example 1). This is because in the silica fine particle aggregates of the present invention (Examples 1 to 4), the skeleton was formed only by the cohesive force of the silica fine particles, and thus the inorganic fine particle aggregates having low crushing strength. However, the fired silica fine particle agglomerated fired body (Comparative Example 1) forms a skeleton having a strong bond by melting the surface layers of the silica fine particles by the surface melting of the fine particles during the firing process and fusing them together. This is because the resulting inorganic fine particle aggregate has high strength.

  It can be seen that in the silica fine particle aggregates (Examples 1 to 4) which were only dried without firing, the crushing strength was weaker as the silica average primary particle size was larger. This is because as the average particle size of the silica primary particles becomes larger, the cohesive force with the adjacent particles becomes weaker, and the crushing strength of the silica fine particle aggregates also becomes lower.

  In addition, the commercially available porous silica R1 (Reference Example 1) and the commercially available fused silica R2 (Reference Example 2) are not only the silica fine particle aggregates of the present invention (Examples 1 to 4) but also baked silica fine particles. The crushing strength is higher than that of the aggregate (Comparative Example 1). In particular, commercially available fused silica R2 (Reference Example 2) produced at a temperature of at least 1200 ° C. has a skeleton having a covalent bond between silicon (Si) and oxygen (O) because the silica is completely melted at a high temperature. The crushing of this structure corresponds to breaking a covalent bond and requires a large amount of energy, so that the crushing strength was 1800 times larger than that of the silica fine particle aggregate having the lowest crushing strength in Example 1.

Therefore, from FIG. 3, the silica fine particle aggregate obtained in Example 1 of the present invention has a crushing strength 1800 times lower than that of commercially available fused silica. As a result, it was found that even the primary silica particles (silica nanoparticles) were easily crushed and dispersed, and so-called polymer nanocomposites could be made.
FIG. 4 shows the concept for explaining the difference between the preparation procedure of the silica aggregate used in the present invention and the skeleton structure composed of silica fine particles depending on the drying / calcination temperature.

  FIG. 4 is a conceptual diagram showing a preferred embodiment of the method for producing an inorganic fine particle aggregate in the present invention. In FIG. 4 (1), the silica sol contained in the container is stirred by the stirring bar 4, and the silica fine particles 1 are in a dispersed state. (2) is an aqueous solution of potassium bromide (KBr). When silica gel and an aqueous KBr solution are mixed and stirred, a mixed liquid in which silica is forcibly dispersed is obtained as shown in (3). As shown in (4), when the stirring is stopped, the mixture seems to aggregate silica gel on KBr, but the aggregate is precipitated. Water is evaporated from the mixture of (4) and dried to obtain a solidified product (5) composed of silica gel fine particles and crystallized KBr. When KBr is eluted from the solidified product (5), a silica fine particle aggregate (6) having pore spaces 3 is obtained. By drying the fine particle aggregate (6) at a temperature at which surface fusion between the silica fine particles does not occur, the inorganic fine particle aggregate (7) formed by the cohesive force between the silica fine particles can be obtained.

  When the fine particle aggregate (6) of FIG. 4 is baked, the surface layers of the silica fine particles are melted and fused to each other, so that the high-strength silica fine particle aggregate (8) having a skeleton having a strong bond is formed. Become.

  In the present invention, the shear stress generated in the melt mixing device by melting and mixing the aggregate of the inorganic fine particles having low strength and the thermoplastic resin previously formed by the cohesion force between the nano inorganic fine particles and the relatively weak adjacent particles. It was shown that the aggregates of inorganic fine particles with low strength mixed together can be physically crushed and dispersed to the original nano inorganic fine particles.

ADVANTAGE OF THE INVENTION According to this invention, the inorganic fine particle aggregate which can be physically crushed and disperse | distributed to nanoscale by the shear stress which generate | occur | produces with a melt mixing apparatus when it melt-mixes with various resin is provided.
The inorganic fine particle aggregate provided by the present invention physically crushes and disperses to the nanoscale when melt-mixed with various resins, so that the resin can be made into a so-called nanocomposite and used as a filler for the resin. Is preferred.
The resin nanocomposite molded product that can be provided by the present invention is excellent in mechanical properties, dimensional stability, flame retardancy, etc., and can be expected in all fields where particles can be uniformly dispersed at the nano level. It can be applied to.
Examples of molded articles to which the low-strength inorganic fine particle aggregates provided by the present invention can be applied include tubes, sheets, rods, fibers, packings, linings, and wire coatings.

The electron micrograph of the silica fine particle aggregate (no baking) used for Example 4. FIG. 4 is an electron micrograph of the silica fine particle aggregated fired body fired at 600 ° C. used in Comparative Example 1. FIG. The electron micrograph of the reference example 3 sample by which the silica fine particle aggregate is crushed and disperse | distributed to the silica primary particle in polystyrene. The conceptual diagram explaining the difference in the preparation structure of the silica fine particle aggregate used for this invention, and the skeleton structure which consists of silica fine particle by drying and baking temperature.

Explanation of symbols

(1): Silica sol (2): Aqueous solution of potassium bromide (KBr) (3): Silica sol and KBr mixed solution in which silica is forcibly dispersed with stirring (4): Silica sol and KBr mixed solution Then, after the stirring is stopped, the silica and KBr aggregate and precipitate (5): the solidified product obtained from the mixed solution (6): the silica fine particle aggregate removed by eluting KBr (7): the silica fine particle The inorganic fine particle aggregate of the present invention in which a skeleton is formed only by a cohesive force.
(8): A high-strength inorganic fine particle aggregate in which the surface layer is melted by the surface melting of the silica fine particles in the firing process and fused together to form a skeleton having a strong bond.
1: Silica primary particles 2: KBr
3: Space from which KBr is removed (hole)
4: Stir bar

Claims (9)

  An inorganic fine particle aggregate obtained by obtaining a solidified product by drying from a mixed liquid of inorganic fine particles and an inorganic salt, removing the inorganic salt from the solidified product using a solvent and drying, wherein the drying is performed between the inorganic fine particles. An inorganic fine particle aggregate formed by the cohesive force of inorganic fine particles, obtained by performing at a temperature at which no surface fusion occurs.   The inorganic fine particle aggregate according to claim 1, wherein the inorganic fine particle aggregate has a crushing strength of 4.5 MPa or less.   The inorganic fine particle aggregate according to claim 1 or 2, wherein the average primary particle size of the inorganic fine particles is 1 µm or less.   The inorganic fine particle aggregate according to claim 1, wherein a crushing load of the inorganic fine particle aggregate is 110 mN or less.   The inorganic fine particle aggregate according to any one of claims 1 to 4, wherein the inorganic fine particles comprise silicon oxide, titanium oxide, aluminum oxide, or a composite oxide of zinc oxide and antimony pentoxide.   The inorganic salt is at least one selected from alkali metal salts, alkaline earth metal salts or ammonium salts of hydrohalic acid, phosphoric acid, sulfuric acid, nitric acid and molybdic acid. The inorganic fine particle aggregate according to any one of the above.   The inorganic fine particle aggregate according to claim 6, wherein the inorganic salt is at least one selected from potassium bromide, potassium chloride, ammonium molybdate, sodium dihydrogen phosphate, calcium chloride, and ammonium bromide. Aggregation. 2. The drying is performed at a ratio (T ₀ / T _m ) of a drying temperature (T ₀ ) expressed as an absolute temperature to a melting point (T _m ) of the inorganic fine particles of 0.23 or less. The inorganic fine particle aggregate in any one of -7.   A solidified product is obtained by drying from a mixed liquid of inorganic fine particles and an inorganic salt, and the inorganic salt is removed from the solid using a solvent, followed by drying. The method for producing an inorganic fine particle aggregate according to any one of claims 1 to 8, which is carried out at a temperature that does not substantially occur.

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