Compositions – Inorganic luminescent compositions – Compositions containing halogen; e.g. – halides and oxyhalides
Reexamination Certificate
1999-12-10
2001-07-24
Koslow, C. Melissa (Department: 1755)
Compositions
Inorganic luminescent compositions
Compositions containing halogen; e.g., halides and oxyhalides
C252S30140P, C252S30160R, C252S30160P, C427S215000, C428S403000, C428S404000
Reexamination Certificate
active
06264855
ABSTRACT:
TECHNICAL FIELD
The invention relates to a process for preparing a water resistant luminous pigment.
BACKGROUND ART
A luminous pigment means a pigment having the ability to keep luminescence in a high luminance for a given length of time even in case of keeping it in a dark place after irradiation with light, and is also called a light-storage pigment.
Conventionally, various kinds of pigments are known for such luminous pigments in which a metal sulfide such as calcium sulfide, zinc sulfide, cadmium sulfide or the like is doped with copper, bismuth or the like. However a duration time of luminescence in a dark place is short, and these pigments cannot help being used under an extremely restricted condition.
To improve this point attempts have been made in which various radioactive substances are added to the above compounds, but it was extremely restricted from the safety point of view, because the effect to a human body due to the use of the radioactive substances cannot be neglected.
Consequently, as those having no such defects, and having a long luminous time in a dark place and further no safety problem, luminous pigments consisting of compounds, which are made of some kind of metal oxides doped with rare-earth metal elements, were developed (JP, A, H9-143463, Japanese Patent No. 2543825, Japanese Patent No. 2697733, Japanese Patent No. 2697688).
However, it was found that such luminous pigments have a fatal disadvantage in that they are easily decomposed in the presence of water. This problem cannot be solved by merely changing the type of a vehicle component. These pigments lose a luminous effect by moisture adsorption, condensation or the like regardless of an outdoor or indoor use, and it was a fact that said pigments could not practically be used while retaining their properties.
Recently, water resistant pigments were thus developed (JP, A, H10-273654, Japanese Patent No. 2929162). Especially, the patented invention of the Japanese Patent No. 2929162 by the present inventors, relates to water resistant luminous pigments, in which a metal oxide is doped with a rare-earth metal element, and then treated by at least one compound of acids and acid generating substances.
However, it has been found that it lost water resistance when used at a high temperature for a long period of time, though there is no particular problem in its use under ordinary temperature, and thus, it became necessary to undertake the solution.
DISCLOSURE OF THE INVENTION
The invention has an object to provide a water resistant luminous pigment with durability.
The inventors have made intensive studies to solve the above problems, and found that a luminous pigment, consisting of a compound, made of metal oxide doped with a rare-earth metal element, when treated with acid (Japanese Patent No. 2929162), and then followed by a further alkaline treatment under certain conditions, results in an increase of the durability in the water resistance. As a result of further studies the inventors have accomplished the invention.
Namely, the present invention relates to the following:
(1) A process for preparing a water resistant luminous pigment, characterized in that a luminous pigment, in which an oxide matrix comprising at least one element selected from the group consisting of Mg, Ca, Sr, Ba and Zn and at least one element selected from the group consisting of B, Al, P and Ga is doped with at least one rare-earth metal element, is acid treated under the condition of a pH of not more than 3 using at least one acidic compound selected from the group consisting of acids and acid generating compounds, and is subsequently given an alkaline treatment under the condition of a pH of 4-9 using at least one alkaline compound selected from the group consisting of alkalis and alkali generating compounds.
(2) A process for preparing a water resistant luminous pigment according to (1) above, wherein the luminous pigment has the following formula:
MAl
2
O
4
:R or M
4
Al
14
O
25
:R
in which
M is at least one element selected from the group consisting of Ca, Sr and Ba;
R is at least one element selected from the group consisting of Tb, Dy, Nd, Eu and Tm.
(3) A process for preparing a water resistant luminous pigment according to (2) above, wherein R comprises at least one element selected from the group consisting of Tb, Dy, Nd and Tm, and Eu.
(4) A process for preparing a water resistant luminous pigment according to (1), (2) or (3) above, wherein the acidic compound is at least one compound selected from the group consisting of phosphoric acid, phosphorous acid, polyphosphoric acid, sodium dihydrogenphosphate or sulfuric acid.
(5) A process for preparing a water resistant luminous pigment according to (1), (2), (3) or (4) above, wherein the alkaline compound is at least one compound selected from the group consisting of sodium hydroxide, potassium hydroxide, calcium hydroxide, strontium hydroxide, lithium hydroxide, trisodium phosphate or strontium oxide.
The invention is based on a new finding that surprisingly, a durability of a water resistance increases and a heat resistance is also given when a pigment disclosed in Japanese Patent No. 2929162 made by the present inventors is further treated under a particular alkaline condition.
Although the water resistance of the pigment disclosed in Japanese Patent No. 2929162 is given by the acid treatment, it is presumed that, the water resistance is caused by a formation of a water resistant membrane on the surface of the luminous pigment by reacting an acidic compounds with a metal oxide of the pigment component.
Then, as to the increase of durability of the water resistance in the present invention, it is regarded that a water resistant membrane formed on the surface of a luminous pigment is all the more strengthened because of the alkaline treatment in the invention, and as a result, the durability of said membrane is increased and the heat resistance is also given.
In any event, the invention is aiming at the durability of the water resistance of luminous pigments by applying a particular alkaline treatment to those diclosed in Japanese Patent No. 2929162.
Therefore, the luminous pigment of the present invention has not only a durability for its water resistance, but is also endurable at high temperature for long periods of time, and can be used under any environment.
Consequently, a water resistant luminous pigment of the present invention can be used in any industrial and technical field and is very useful as described below.
EMBODIMENT FOR CARRYING OUT THE INVENTION
Embodiments for carrying out the invention are further described in detail in the following.
A water resistant luminous pigment with durability in the present invention can be prepared by an acid treatment of a luminous pigment, as a starting material, with at least one acidic compound selected from the group consisting of acids and acid generating compounds under the condition of pH of not more than 3, and subsequently by an alkaline treatment with at least one alkaline compound selected from the group consisting of alkalis and alkali generating compounds under the condition of pH 4-9.
1 Luminous Pigments
A luminous pigment as an object of an acid treatment can be any type if it is a luminous pigment in which an oxide matrix comprising at least one element selected from the group consisting of Mg, Ca, Sr, Ba and Zn, and at least one element selected from the group consisting of B, Al, P and Ga is doped with at least one rare-earth metal element.
As such a luminous pigment is illustrated as having a kind of ceramic structure in which an oxide matrix comprising at least one element selected from the group consisting of Mg, Ca, Sr, Ba and Zn, and at least one element selected from the group consisting of B, Al, P and Ga is mixed with at least one rare-earth metal element selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu and sintered.
An amount of the rare-earth element to be doped is not particularly restricted, but it is enough in 0.0001-30% by weight, pre
Hoshikawa Ryuichi
Kitagawa Yosuke
Dinnin & Dunn P.C.
Koslow C. Melissa
Matsui Shikiso Chemical Co. Ltd.
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