Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Reexamination Certificate
2000-01-24
2002-01-29
Le, Hoa T. (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
C428S328000, C428S329000, C428S402000, C428S403000
Reexamination Certificate
active
06342293
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an alumina sol and an alumina hydrate powder, and processes for their production.
A recording medium has been known which has an ink-receiving layer containing pseudoboehmite formed on a substrate (JP-A-2-276670, JP-A-4-37576). Such an ink-receiving layer is a porous layer formed by coating an alumina sol on a substrate, followed by gelation. In order for such a recording medium to attain recording of high quality, it is required that the ink-receiving layer has high transparency, and the pore size and the pore volume of the ink-receiving layer, are large.
In order to increase the color density of ink after printing, the amount of the printing ink is increased. However, if the pore size and the pore volume in the ink-receiving layer are not sufficiently large, it takes time for ink absorption, and a problem of beading or running of ink is likely to result, and further, the circularity of printed dots tends to be poor, whereby it tends to be difficult to attain recording of high quality.
If the transparency of the ink-receiving layer is low, even if a transparent substrate is used, it will be impossible to obtain a recording medium having a good transparency, which is useful as a film for an overhead projector (hereinafter referred to simply as OHP). When an opaque substrate is employed, low transparency of the ink-receiving layer result in low reflective color density of the ink after printing, and it will be difficult to attain recording of high quality.
As a method for producing an alumina sol, a method is known wherein aluminum isopropoxide is hydrolyzed, and then, an acid is added for peptization (B. E. Yoldas, Amer. Ceram. Soc. Bull., 54, 289 (1975)). The alumina sol obtained by this method is a transparent sol and can be used for various applications.
Further, a method is known wherein an alkali metal hydroxide is added to an alkali metal aluminate, if necessary, and an acid or an acid salt such as aluminum chloride, sulfate or nitrate, is mixed, or an alkali metal aluminate or an acid salt of an aluminum is ion-exchanged by an ion exchange resin to obtain an alumina hydrate precipitation, which is aged and then peptized to obtain an alumina sol.
Further, a method is also known wherein an alumina precipitation obtained by hydrolysis of aluminum dodexide, is aged to form a sol (JP-A-7-232473).
However, the xerogels obtained by drying alumina sols obtained by the above three methods were inadequate in their ink absorptivity, as their average pore radii or pore volumes were small.
As a method for producing an alumina having a large pore volume, a method of calcining an alumina sol obtained by continuously adding an aluminum salt and a pH controlling agent to a slurry of aluminum hydroxide to maintain the pH at a level of from 6 to 11 (JP-A-58-190823), or a method of calcining an alumina gel obtained by repeating a plurality of times an operation of adding an aluminum-containing neutralizing agent to a slurry of aluminum hydroxide to adjust the pH at a level of from 6 to 11 (JP-A-58-213632), has been known. However, in either method, the product was anhydrous alumina particles calcined at 500° C., and an ink-receiving layer formed by such alumina particles, was poor in transparency.
A method is also known wherein an alumina precipitation obtained by neutralization or ion exchange of an aluminum salt or an alkali metal aluminate, is dried and pulverized to obtain a xerogel having a large pore volume, which is then mixed with a suitable binder to form an ink-receiving layer (JP-B-3-24906). However, with such a xerogel, the secondary particle size of the alumina hydrate was large, whereby there was a drawback that when formed into an ink-receiving layer, the transparency was poor.
Namely, no alumina hydrate powder has heretofore been obtained which has large pore size and pore volume and which has high transparency.
SUMMARY OF THE INVENTION
The present invention provides a process for producing an alumina sol, which comprises stirring a dispersion of an alumina hydrate having a solid content of from 1 to 40 wt % at a pH of from 7 to 12 with an effective consumptive power of at least 0.5 kW/m
3
for aggregation treatment, and then adding an acid thereto for peptization treatment.
Further, the present invention provides a process for producing an alumina hydrate powder, which comprises stirring a dispersion of an alumina hydrate having a solid content of from 1 to 40 wt % at a pH of from 7 to 12 with an effective consumptive power of at least 0.5 kW/m
3
for aggregation treatment, followed by drying.
The present invention also provides an alumina sol, which comprises an alumina hydrate as sol particles and an acid-containing water as a medium, and which is characterized in that an alumina hydrate powder obtainable by removing water from the alumina sol, has an average pore radius of at least 7 nm and a total volume of pores having pore radii of from 1 to 100 nm of from 0.80 to 2.00 cc/g, and the transmittance of a light having a wavelength of 530 nm through the alumina sol having a sol concentration of 0.5 wt %, is from 5 to 70%.
Still further, the present invention provides an alumina hydrate powder consisting essentially of an acid-containing alumina hydrate, which has an average pore radius of at least 7 nm and a total volume of pores having pore radii of from 1 to 100 nm of from 0.80to 2.00 cc/g, and which is characterized in that the transmittance of a light having a wavelength of 530 nm through a sol having a sol concentration of 0.5 wt % obtained by dispersing the alumina hydrate powder in water, is from 5 to 70%.
In the present invention, the alumina hydrate powder means a xerogel of an alumina hydrate. The average pore radius and the pore volume are values measured by means of a nitrogen absorption-desorption apparatus, for an alumina sol, with respect to a xerogel obtained by drying the alumina sol at 140° C. to a constant weight, and for an alumina hydrate powder, with respect to one vacuum-deaerated as it is under 1×10
−2
Torr at 120° C. for two hours.
Further, in the present invention, the light transmittance of an alumina sol is a numerical value obtained by measuring the transmittance of a light having a wavelength of 530 nm through an alumina sol in a thickness of 10 mm having the concentration adjusted so that the sol concentration becomes 0.5 wt % (hereinafter referred to as the light transmittance at 0.5 wt %) by a spectral photometer. Here, the sol concentration is a solid content obtained by calculation based on the weight of a xerogel obtained by drying an alumina sol at 140° C. to a constant weight.
DETAILED DESCRIPTION OF THE INVENTION
Now, the present invention will be described in detail with reference to the preferred embodiments.
In the present invention, it is important to carry out the aggregation treatment which consists of stirring a dispersion of an alumina hydrate having a solid content of from 1 to 40 wt % at a pH of from 7 to 12 intensively with an effective consumptive power of at least 0.5 kW/m
3
. It is heretofore known to carry out aging at a pH of from 7 to 12 in the production of an alumina hydrate. As a result of an extensive research, the present inventors have found that when intensive stirring is carried out during the aging, crystal growth and aggregation of alumina hydrate particles take place efficiently, whereby the pore size and the pore volume remarkably increase.
In the present invention, the effective consumptive power for stirring means a consumptive power obtained by subtracting the consumptive power during a no load running from the total consumptive power for stirring. In the present invention, as such an effective consumptive power, intensive stirring is carried out with a power of at least 0.5 kW/m
3
per unit volume of the dispersion of the alumina hydrate. If the power is less than 0.5 kW/m
3
, the crystal growth and aggregation of the alumina hydrate particles do not adequately proceed, and the pore size and pore volume do not become sufficient
Hirano Hachiro
Matsubara Toshiya
Nakahara Katsumasa
Yamada Kenji
Asahi Glass Company Ltd.
Le Hoa T.
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