JP7308650B2 - Large particle size alumina dispersion - Google Patents

Description

The present invention relates to a large particle size alumina dispersion.

As a technology related to an alumina-based dispersion containing a neutral region, the applicant of the present application disclosed an alumina colloid-containing aqueous solution having a pH of 5.5 to 9 in Patent Document 1. This alumina colloid-containing aqueous solution contains a colloid composed of alumina hydrate etc. and an ionic aluminum compound. indicates pseudo-boehmite. This alumina colloid-containing aqueous solution is excellent in binder power, which was disclosed in Patent Document 2.

Japanese Patent No. 5582999 Japanese Patent No. 5733758

The alumina colloid-containing aqueous solution described in Patent Document 1 is excellent in binder power as described above. They were extremely fine particles of about 30 nm. Taking advantage of the ultrafine particles, the particles can easily enter into the gaps between the granular substrates to be bound, and can exhibit a sufficient binder performance.

On the other hand, depending on the type and application of the granular base material to be bound, a larger particle size may be required. As mentioned above, in the technique of alumina colloid-containing aqueous solution described in Patent Document 1, only ultrafine particles of about 30 nm at maximum were obtained, so it exhibits excellent binder performance even though it has a larger particle size. It has been desired to develop a new technology related to an alumina-based dispersion that can be used.

The present invention is as follows.
[1] A large-diameter alumina dispersion having alumina particles as dispersed particles and satisfying all of the following properties (1) to (5).
(1) The average particle size of dispersed particles is in the range of 50 nm to 3000 nm.
(2) The crystal form of alumina when the large particle size alumina dispersion is dried at 100°C is boehmite or pseudo-boehmite.
(3) The pH of the large particle size alumina dispersion is in the range of 5.5-9.
(4) The large particle size alumina dispersion contains an organic acid and an alkali, the organic acid is lactic acid and/or malic acid, and the alkali is ammonia, alkali metals, or alkaline earth metals. is.
(5) The amount ratio of the organic acid and alumina (Al ₂ O ₃ ) contained in the large particle size alumina dispersion is Al ₂ where A is the product of the number of moles of organic acid and the number of carboxyl groups in the organic acid When the number of moles of O ₃ is B, A/B is in the range of 1.0 to 2.0.
[2] The large particle size alumina dispersion according to [1] above, which has a bending strength of 0.3 MPa or more in the following three-point bending test.
[Three-point bending test]
43 g of the large particle size alumina dispersion and 300 g of sintered alumina (a mixture of 135 g of "Aluminite AS-28 mesh" and 165 g of "Aluminite AS-325 mesh" manufactured by Itochu Ceratec) are mixed, and this is molded. (Length 8 cm, Width 2 cm, Height 2 cm) and dried at 100°C. After drying, it is removed from the mold and fired at 500°C for 12 hours.
Place the fired product on the support part of a three-point bending tester with a distance between fulcrums of 50 mm, and measure the entire part perpendicular to the long side of the upper surface of the fired product at the midpoint of the long side. The bending strength is defined as the force when the fired product cracks when pressure is applied from the direction.
[3] A powder obtained by drying the large particle size alumina dispersion described in [1] or [2] above.

It is the photograph which showed the mode of the three-point bending test in an Example.

The present invention will be described in detail below based on preferred embodiments, but the present invention is not limited to the following embodiments, and various modifications are possible within the scope of the claims.
In the present invention, the notation "numerical value 1 to numerical value 2" regarding the numerical range means a numerical range including numerical value 1 and numerical value 2 at both ends, with numerical value 1 as the lower limit and numerical value 2 as the upper limit. It is synonymous with "numerical value 1 or more and numerical value 2 or less".

The large particle size alumina dispersion of the present invention uses alumina particles as dispersed particles and satisfies all of the following properties (1) to (5).
(1) The average particle size of dispersed particles is in the range of 50 nm to 3000 nm.
(2) The crystal form of alumina when the large particle size alumina dispersion is dried at 100°C is boehmite or pseudo-boehmite.
(3) The pH of the large particle size alumina dispersion is in the range of 5.5-9.
(4) The large particle size alumina dispersion contains an organic acid and an alkali, the organic acid is lactic acid and/or malic acid, and the alkali is ammonia, alkali metals, or alkaline earth metals. is.
(5) The amount ratio of the organic acid and alumina (Al ₂ O ₃ ) contained in the large particle size alumina dispersion is Al ₂ When the number of moles of O ₃ is B, A/B is in the range of 1.0 to 2.0.

The large-particle-size alumina dispersion of the present invention uses alumina particles as dispersed particles, but allows the inclusion of an ionic aluminum compound as another form of existence of the aluminum component. The presence or absence of an ionic aluminum compound can be examined by filtering the large particle size alumina dispersion of the present invention through an ultrafiltration membrane with a cutoff molecular weight of 10,000 and measuring Al ₂ O ₃ in the filtrate. . In the large particle size alumina dispersion of the present invention, the Al ₂ O ₃ in the filtrate is preferably 40% by mass or less, more preferably 20% by mass or less, relative to the Al ₂ O ₃ in the aqueous solution before filtration. is. Although the lower limit is not particularly limited, it is, for example, 0% by mass.

Further, the Al ₂ O ₃ concentration in the large particle size alumina dispersion of the present invention is preferably 20% by mass or less. If it exceeds 20% by mass, the viscosity tends to increase and the handling property tends to deteriorate. Although there is no particular limitation on the lower limit of the Al ₂ O ₃ concentration, it is preferably 1% by mass from an economical point of view. Therefore, a suitable range of Al ₂ O ₃ concentration can be exemplified from 1 to 20% by mass. More preferably, the lower limit of the above range is 3% by mass. Further, the upper limit is more preferably 15% by mass.

The large particle size alumina dispersion liquid of the present invention preferably uses water as a dispersion medium, but may contain a hydrophilic organic solvent as long as the dispersion stability is not impaired. Examples of hydrophilic organic solvents include methanol, ethanol, and ethylene glycol.

Regarding the average particle size range of 50 nm to 3000 nm of the dispersed particles related to the characteristic (1), the lower limit of the range is preferably 70 nm, more preferably 100 nm, from the viewpoint of defining a larger particle size. Here, the average particle size of the dispersed particles is the median size measured with a dynamic light scattering particle size distribution analyzer "LB-500" manufactured by Horiba, Ltd.

The analysis of the crystal form of alumina relating to characteristic (2) may be carried out by a conventional method, a good example of which is analysis by powder X-ray diffraction.

With respect to the pH range of 5.5 to 9 related to the characteristic (3), gelation is less likely to occur within this range. The large-particle-size alumina dispersion of the present invention may precipitate during storage, but since it can be redispersed by stirring, it is considered that there is no problem in normal use.

Among the organic acids and alkalis related to the property (4), the content ratio of the organic acid is as specified in the property (5). The alkali content is not particularly limited as long as the pH of the large particle size alumina dispersion of the present invention falls within the range of 5.5 to 9 in the characteristic (3) according to the content of the organic acid. Preferred examples of alkali metals are sodium and potassium, and preferred examples of alkaline earth metals are magnesium and calcium.

With respect to the A/B range of 1.0 to 2.0 relating to the characteristic (5), gelation is unlikely to occur within this range.

In addition to the properties (1) to (5), the properties of the large particle size alumina dispersion of the present invention include, for example, light transmittance. The light transmittance (measurement conditions: wavelength 500 nm, optical path length 10 mm) of the large particle size alumina dispersion of the present invention when Al ₂ O ₃ is 7.2% by mass is, for example, 85% or less. Since the light transmittance decreases as the particle size increases, the light transmittance is, for example, 80% or less, and more preferably 75% or less. The lower limit is not particularly limited, but is, for example, 5%, and further 10%. Since this light transmittance is obtained when the Al ₂ O ₃ concentration of the large particle size alumina dispersion of the present invention is set to 7.2% by mass, the light transmittance of the Al ₂ O ₃ concentration of less than 7.2% by mass is When subjected to rate measurement, it is preferable to concentrate in advance to 7.2% by mass by a method such as ultrafiltration.

One feature of the large particle size alumina dispersion of the present invention is that it has excellent binder power. One suitable method for evaluating binder strength is the following three-point bend test. In this three-point bending test, if the bending strength is 0.3 MPa or more, it can be evaluated that the binder strength is excellent. The bending strength is preferably 0.4 MPa or more. Although the upper limit of bending strength is not particularly limited, it is, for example, 2 MPa.

[Three-point bending test]
43 g of the large particle size alumina dispersion of the present invention and 300 g of sintered alumina (a mixture of 135 g of "Aluminite AS-28 mesh" and 165 g of "Aluminite AS-325 mesh" manufactured by Itochu Ceratec) were mixed. is poured into a mold (length 8 cm, width 2 cm, height 2 cm) and dried at 100°C. After drying, it is removed from the mold and fired at 500°C for 12 hours.
Place the fired product on the support of a three-point bending tester with a distance between fulcrums of 50 mm, and measure the entire part perpendicular to the long side of the upper surface of the fired product at the midpoint of the long side. The bending strength is defined as the force when the fired product cracks when pressure is applied from the direction.

A preferred embodiment of the present invention relates to a powder obtained by drying the large particle size alumina dispersion of the present invention. The powder is redispersible in water. Here, "redispersible" means that when the powder is suspended in water, it returns to the large particle size alumina dispersion of the present invention. The above powder can be used as it is or at a high concentration by dispersing it in a small amount of water. As a drying method, commonly used methods such as spray drying, stationary drying, and stream drying can be employed. As for the drying temperature, 150° C. or less is preferable.

(Production method)
In one embodiment of the preferred method for producing the large particle size alumina dispersion of the present invention, alumina having a boehmite or pseudoboehmite crystal (hereinafter referred to as "alumina A"), an organic acid and an alkali agent are mixed and heated. It is a way to

Types of organic acids are lactic acid and/or malic acid as described above. Examples of types of alkaline agents are ammonia, ammonium carbonate, ammonium hydrogen carbonate, alkali metal hydroxides, alkali metal carbonates, alkali metal hydrogen carbonates, alkaline earth metal hydroxides, alkaline earth metal carbonates, alkaline earth metal hydrogen carbonates, and the like. Here, as described above, preferred examples of alkali metals are sodium and potassium, and preferred examples of alkaline earth metals are magnesium and calcium.

The method of mixing and heating the alumina A, the organic acid and the alkaline agent is not particularly limited. For example, an aqueous dispersion of alumina A, an organic acid dissolved in water, and an alkali agent may be mixed and heated. Alternatively, after adding alumina A to an aqueous solution of an organic acid and heating, the alkaline agent may be added while maintaining the temperature of the heated state so as not to drop. The mode of addition may be continuous or intermittent, and the rate of addition is not particularly limited, but it is desirable to avoid adding a large amount at once. Moreover, the mixing mode may be a normal stirring method, and the mixing time may be appropriately set. The heating temperature is preferably 50-200°C, more preferably 70-160°C. The heating method is not particularly limited, and ordinary heating methods, autoclaves, and the like can be exemplified.

EXAMPLES The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to these.

[Example 1]
An aqueous ammonium bicarbonate solution was slowly added to an aqueous aluminum sulfate solution until the pH reached 7.5, followed by ultracleaning to obtain an alumina hydrate gel of 10% by mass as Al ₂ O ₃ . A slurry with pseudo-boehmite alumina crystalline form was prepared by heating the alumina hydrate gel at 55° C. for 1 hour. To 100 parts by mass of this slurry, 88% lactic acid was added so that A/B=1.6, and 25% ammonia water was added so that NH ₃ /Al ₂ O ₃ (molar ratio)=1.0. It was heated at 120° C. for 4 h.
The resulting dispersion had an Al ₂ O ₃ concentration of 7.3% by mass, an average particle size of 52.2 nm, a crystal form of pseudo-boehmite, a pH of 8.2, and an A/B value of 1.6. It corresponded to a dispersion liquid. The light transmittance at an Al ₂ O ₃ concentration of 7.2% by mass (measurement conditions: wavelength 500 nm, optical path length 10 mm) was 83.6%.
Further, the large particle size alumina dispersion obtained above was dried with a spray dryer ADL310 manufactured by Yamato Scientific Co., Ltd. (inlet temperature: 200°C, outlet temperature: 100°C) to obtain powder. Next, when this powder was suspended in water so as to have an Al ₂ O ₃ concentration of 7.2%, it was well dispersed to obtain a dispersion liquid. Therefore, this powder was found to be redispersible in water. Since this dispersion had a pH of 6.2 and an average particle size of 58 nm, it was confirmed that a large particle size alumina dispersion was obtained again.

[Example 2]
A slurry having a pseudo-boehmite alumina crystal form was prepared by heating a 10% by weight alumina hydrate gel as Al ₂ O ₃ obtained in the same manner as in Example 1 at 57° C. for 1 hour. To 100 parts by mass of this slurry, 88% lactic acid was added so that A/B=1.3, and 25% ammonia water was added so that NH ₃ /Al ₂ O ₃ (molar ratio)=0.9. It was heated at 140° C. for 3 h.
The resulting dispersion had an Al ₂ O ₃ concentration of 7.0% by mass, an average particle size of 186.6 nm, a crystal form of pseudo-boehmite, a pH of 8.2, and an A/B value of 1.3. It corresponded to a dispersion liquid. The light transmittance at an Al ₂ O ₃ concentration of 7.2% by mass (measurement conditions: wavelength 500 nm, optical path length 10 mm) was 71.0%.

[Example 3]
A slurry having a pseudo-boehmite alumina crystal form was prepared by heating a 10% by weight alumina hydrate gel as Al ₂ O ₃ obtained in the same manner as in Example 1 at 61° C. for 1 hour. To 100 parts by mass of this slurry, 88% lactic acid was added so that A/B=1.7, and 25% ammonia water was added so that NH ₃ /Al ₂ O ₃ (molar ratio)=1.1. This was heated at 100°C for 8h.
The resulting dispersion had an Al ₂ O ₃ concentration of 7.2% by mass, an average particle size of 224.0 nm, a crystal form of pseudo-boehmite, a pH of 8.3, and an A/B value of 1.7. It corresponded to a dispersion liquid. The light transmittance at an Al ₂ O ₃ concentration of 7.2% by mass (measurement conditions: wavelength 500 nm, optical path length 10 mm) was 64.4%.

[Example 4]
A slurry having a pseudo-boehmite alumina crystal form was prepared by heating a 10% by weight alumina hydrate gel as Al ₂ O ₃ obtained in the same manner as in Example 1 at 63° C. for 1 hour. To 100 parts by mass of this slurry, 88% lactic acid was added so that A/B=1.6, and 25% ammonia water was added so that NH ₃ /Al ₂ O ₃ (molar ratio)=1.0. This was heated at 130°C for 5h.
The resulting dispersion had an Al ₂ O ₃ concentration of 7.1% by mass, an average particle size of 742.2 nm, a crystal form of pseudo-boehmite, a pH of 8.2, and an A/B value of 1.6. It corresponded to a dispersion liquid. The light transmittance at an Al ₂ O ₃ concentration of 7.2% by mass (measurement conditions: wavelength 500 nm, optical path length 10 mm) was 29.7%.

[Example 5]
A slurry having alumina crystalline form of boehmite was prepared by heating a 10% by weight alumina hydrate gel as Al ₂ O ₃ obtained in the same manner as in Example 1 at 70° C. for 1 hour. To 100 parts by mass of this slurry, 88% lactic acid was added so that A/B=1.5, and 25% ammonia water was added so that NH ₃ /Al ₂ O ₃ (molar ratio)=1.0. It was heated at 140° C. for 3 h.
The resulting dispersion had an Al ₂ O ₃ concentration of 7.3% by mass, an average particle size of 1957.0 nm, a crystal form of boehmite, a pH of 8.1, and an A/B value of 1.5. It corresponded to the liquid. The light transmittance at an Al ₂ O ₃ concentration of 7.2% by mass (measurement conditions: wavelength 500 nm, optical path length 10 mm) was 16.5%.

[Example 6]
A slurry having alumina crystalline form of boehmite was prepared by heating a 10 mass % alumina hydrate gel as Al ₂ O ₃ obtained in the same manner as in Example 1 at 80° C. for 1 hour. To 100 parts by mass of this slurry, 88% lactic acid was added so that A/B=1.7, and 25% ammonia water was added so that NH ₃ /Al ₂ O ₃ (molar ratio)=1.1. It was heated at 140° C. for 3 h.
The resulting dispersion had an Al ₂ O ₃ concentration of 7.2% by mass, an average particle size of 2315.0 nm, a crystal form of boehmite, a pH of 7.7, and an A/B value of 1.7. It corresponded to the liquid. The light transmittance at an Al ₂ O ₃ concentration of 7.2% by mass (measurement conditions: wavelength 500 nm, optical path length 10 mm) was 12.1%.

[Example 7]
A slurry having alumina crystalline form of boehmite was prepared by heating an alumina hydrate gel containing 10 mass % as Al ₂ O ₃ obtained in the same manner as in Example 1 at 100° C. for 1 hour. To 100 parts by mass of this slurry, 88% lactic acid was added so that A/B=1.6, and 25% ammonia water was added so that NH ₃ /Al ₂ O ₃ (molar ratio)=1.0. It was heated at 150° C. for 3 h.
The resulting dispersion had an Al ₂ O ₃ concentration of 7.3% by mass, an average particle size of 2970.0 nm, a crystal form of boehmite, a pH of 5.9, and an A/B value of 1.6. It corresponded to the liquid. The light transmittance at an Al ₂ O ₃ concentration of 7.2% by mass (measurement conditions: wavelength 500 nm, optical path length 10 mm) was 12.1%.
Further, the large particle size alumina dispersion obtained above was dried at 100° C. for 12 hours in a ventilation dryer to obtain a powder. Next, when this powder was suspended in water so as to have an Al ₂ O ₃ concentration of 7.2%, it was well dispersed to obtain a dispersion liquid. Therefore, this powder was found to be redispersible in water. Since this dispersion had a pH of 5.8 and an average particle size of 2910 nm, it was confirmed that a large particle size alumina dispersion was obtained again.

The methods for analyzing the dispersions obtained in the above Examples are as follows.
-Crystal form: The obtained dispersion was dried at 100°C, and the dried product was measured and analyzed with an X-ray diffractometer "XRD-7000" manufactured by Shimadzu Corporation.
• Average particle size: The obtained dispersion was measured using a dynamic light scattering type particle size distribution analyzer "LB-500" manufactured by Horiba, Ltd.
・Light transmittance: The obtained dispersion was adjusted to 7.2% by mass as Al ₂ O ₃ using a UV-visible near-infrared spectrophotometer “V-670” manufactured by JASCO Corporation, at a wavelength of 500 nm, Measured under the condition of an optical path length of 10 mm.

[Three-point bending test]
As the sintered alumina, one prepared by mixing 135 g of "Aluminite AS-28 mesh" manufactured by Itochu Ceratec and 165 g of "Aluminite AS-325 mesh" manufactured by Itochu Ceratec was used.
43 g of each dispersion obtained in Examples and 300 g of sintered alumina were mixed, poured into a mold (length 8 cm, width 2 cm, height 2 cm) and dried at 100°C. After drying, it was removed from the mold and fired at 500°C for 12 hours.
As a three-point bending tester, a universal strength tester manufactured by Marubishi Kagaku Kikai Seisakusho was used. The distance between the fulcrums was set to 50 mm, and the fired product was placed on the support. The entire portion of the upper surface of the fired product that is perpendicular to the long side at the midpoint of the long side was pressurized from the vertical direction by the suspension part, and the force when the fired product cracked was defined as the bending strength. A photograph during the test is shown in FIG.

Table 1 shows the results of the three-point bending test. From Table 1, it was found that all of the dispersions in the examples had a bending strength of 0.3 MPa or more, indicating excellent binder power.

Claims (3)

A large-diameter alumina dispersion liquid that uses alumina particles as dispersed particles and satisfies all of the following properties (1) to (5).
(1) The average particle size of dispersed particles is in the range of 50 nm to 3000 nm.
(2) The crystal form of alumina when the large particle size alumina dispersion is dried at 100°C is boehmite or pseudo-boehmite.
(3) The pH of the large particle size alumina dispersion is in the range of 5.5-9.
(4) The large particle size alumina dispersion contains an organic acid and an alkali, the organic acid being lactic acid and/or malic acid, and the alkali being at least one of ammonia and an alkali metal .
(5) The amount ratio of the organic acid and alumina (Al ₂ O ₃ ) contained in the large particle size alumina dispersion is Al ₂ where A is the product of the number of moles of organic acid and the number of carboxyl groups in the organic acid When the number of moles of O ₃ is B, A/B is in the range of 1.0 to 2.0. 2. The large particle size alumina dispersion according to claim 1, which has a bending strength of 0.3 MPa or more in the following three-point bending test.
[Three-point bending test]
43 g of the large particle size alumina dispersion and 300 g of sintered alumina (a mixture of 135 g of "Aluminite AS-28 mesh" and 165 g of "Aluminite AS-325 mesh" manufactured by Itochu Ceratec) are mixed, and this is molded. (Length 8 cm, Width 2 cm, Height 2 cm) and dried at 100°C. After drying, it is removed from the mold and fired at 500°C for 12 hours.
Place the fired product on the support of a three-point bending tester with a distance between fulcrums of 50 mm, and measure the entire part perpendicular to the long side of the upper surface of the fired product at the midpoint of the long side. The bending strength is defined as the force when the fired product cracks when pressure is applied from the direction. A powder obtained by drying the large particle size alumina dispersion according to claim 1 or 2.

Images