Solid material comminution or disintegration – Processes – With application of fluid or lubricant material
Reexamination Certificate
1999-12-21
2001-11-13
Rosenbaum, Mark (Department: 3725)
Solid material comminution or disintegration
Processes
With application of fluid or lubricant material
C241S030000, C241S184000
Reexamination Certificate
active
06315222
ABSTRACT:
TECHNICAL FIELD
This invention relates to a method of producing paste containing flaky aluminum powder.
BACKGROUND OF THE INVENTION
The topcoat paint for automobiles comprises aluminum paste, a hydrocarbon based solvent such as xylene, a hardener, etc. When the paint at a thickness of approximately 40 &mgr;m is applied to the surface of the body of an automobile, the aluminum flaky powder having a large water-covering area (approximately half of its specific surface area) becomes evenly distributed within the paint layer. As such, not only does it maintain appropriate luster, but it also serves to protect the coating layer on the surface of the body of an automobile by sealing off the outside air. At that time, however, if the average particle size of flaky aluminum powder is 40 &mgr;m or larger, the powder protrudes out of the painting layer, resulting in poor external appearance, and fails to serve as a protective layer. If the average particle size is 10 &mgr;m or less, the external appearance after painting appears dark, and thus it is not preferable. Consequently, the average particle size of flaky aluminum powder for automobiles should be 10 &mgr;m to 40 &mgr;m. At the same time, it should have a water-covering area of 5,000cm
2
/g or larger, and the aluminum flaky powder should be non-leafing in the solvent.
The conventional method of producing aluminum paste for topcoat of automobiles comprises as follows: placing the gas-atomized powders, balls, mineral spirits, etc. in a vessel; ball-milling the same to obtain an intermediate paste containing flaky aluminum powder; vacuum-drying or filtering the same, followed by adjusting the amount of solvent to obtain the final product of aluminum paste containing over 60 wt % of aluminum powder. The above conventional method of utilizing the gas-atomized powders, however, requires a melting furnace, a high-pressure gas system, a large chamber, and a sieving system. In addition, at the time of melting aluminum, a large supply of electricity is required, which in turn translates into high investment costs along with high production costs for the powder.
SUMMARY OF THE INVENTION
In line with solving the aforementioned problems, the objective of the present invention is to provide a method of producing paste containing flaky aluminum at a relatively low cost by means of cutting the thin and long scraps, obtained as by-products from the production process of aluminum foil, and using it as a starting raw material for ball-milling.
To achieve the aforementioned objectives, the invention provides a method of producing the final product of paste for automobiles. The method is performed with the use of a ball-milling vessel having a milling ball with a known diameter and comprises: (i) charging the vessel with scraps cut to a size smaller than the diameter of the ball in the milling vessel from long and thin aluminum foil of less than or equal to about 80 &mgr;m in thickness; balls to mill and induce the same into flaky particles; mineral spirits such as a hydrocarbon-based solvent to prevent oxidation during the milling process; and an unsaturated fatty acid, e.g., oleic acid, to facilitate milling of the scraps, to cause uniform dispersion of aluminum powder in a hydrocarbon-based solvent, and to enhance the efficiency of the milling process; (ii) ball-milling the same to obtain an intermediate paste containing aluminum flaky powder; (iii) vacuum-drying or filtering the same; and (iv) adjusting the amount of the solvent. Preferably, the ball-milling vessel is charged with the unsaturated fatty acid after it has been charged with the aluminum scrap, balls and mineral spirits.
If the thickness of the foil scrap is more than about 80 &mgr;m, it is impossible to mill the scrap into powders even after milling for 45 hours or more. In the case of less than or equal to about 80 &mgr;m in foil thickness, as the thickness of the foil decreases, it can be milled into powders in a shorter period of time. As such, it is possible to produce fine powder with a large water-covering area. Further, since the foil scrap can be generally made into about 4 &mgr;m or more in thickness, it is appropriate to use the foil with about 4-80 &mgr;m in thickness as raw material.
Meanwhile, depending on the thickness of the foil scrap, the milling time for producing flaky powder and paste can vary.
When the milling is carried out onto the foil of 4~15 &mgr;m in thickness for six hours or less, the average size of the powder so obtained is 40 &mgr;m or more, which is inadequate for use as aluminum paste for automobiles. If the milling is carried out for more than 45 hours, it is also inadequate since the particle size of the powder falls to 10 &mgr;m or less, which is too small, and consequently it appears dark in color after painting. Therefore, it is appropriate to carry out the milling for 6-45 hours.
If the ball-milling is carried out onto the foil of 16~80 &mgr;m in thickness for 40 hours or less, the average size of powder becomes 40 &mgr;m or more. If the ball-milling is carried out for 70 hours or more, the average particle size thereof becomes 10 &mgr;m or less. Therefore, it is appropriate to carry out the milling for 40~70 hours.
Further, if the charged amount of the balls falls below the level of 25 vol % of the volume of the vessel, it is not easy to mill the scraps into powders. At the level of 60 vol %, the charge amount is too small to be economical. Therefore, it is appropriate to charge the balls in the vessel at 25~60 vol %.
Further, if the charge amount of mineral spirits is 50 wt % or less of that of the scrap, the lubrication action by the added oleic acid is too high to cause a serious slippery phenomenon of the scraps between the balls. As such, it is impossible to mill the scraps into flaky powder of less than 40 &mgr;m in average particle size. If it is more than 600 wt %, it takes too long at the time of drying.
Hence, as for the hydrocarbon-based solvent, e.g., mineral spirits, it is appropriate to use 50~600 wt % of the weight of the charged scrap.
In addition, as for the unsaturated fatty acid such as oleic acid used as an additive at the time of ball-milling, it is appropriate to use 1.0~4.5 wt % of the powder obtained at the time of drying. If 1.0 wt % or less is added thereto, it is not easy to mill the scrap even with the extended milling time. Also, it is not easy to maintain the average size of the powder at 40 &mgr;m or less. If 4.5 wt % or more is added thereto, the scrap is milled into fine powder of 10 &mgr;m or less, and the degree of luster of the coating layer becomes deteriorated.
After the ball-milling process, the amount of solvent is reduced by vacuum-drying the paste or placing the same under pressure via filter-press. Then, when the solvent is added again, the weight of the aluminum powder in the paste is adjusted to 60 wt % or more in order to produce the aluminum paste for the topcoat of automobiles.
REFERENCES:
patent: 4292087 (1981-09-01), Bell
patent: 4436809 (1984-03-01), Akao et al.
patent: 5082744 (1992-01-01), Akao et al.
Hong Seong-Hyeon
Kim Byoung-Kee
Lee Dong-Won
Korea Institute of Machinery and Materials
Lowe Hauptman & Gilman & Berner LLP
Rosenbaum Mark
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