Compositions: coating or plastic – Coating or plastic compositions – Metal-depositing composition or substrate-sensitizing...
Reexamination Certificate
1999-06-28
2001-05-22
Klemanski, Helene (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Metal-depositing composition or substrate-sensitizing...
C106S001190, C106S001220, C106S001230, C106S001240, C106S001260, C106S001280
Reexamination Certificate
active
06235093
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a technique for obtaining metals by reductive deposition process, more particularly, to a process for obtaining noble metals by the chemical reduction by allowing an aqueous solution of a noble metal to contain a —SH or —S— containing compound as a reducing agent.
2. Description of the Prior Art
Chemical reduction and deposition of metals from their aqueous solutions with the aid of a reducing agent has been utilized in the method of obtaining metal coatings known as autocatalytic electroless plating and also in the process for producing (fine) metal particles for catalyst and other applications.
Reducing agents thus far reported for use in depositing metals from their solutions have included: e.g., for the deposition of gold, borohydride, dimethylamine borane, phosphinic acid, hydrazine, hydroxylamine, hydrazine boron, thiourea, ascorbic acid, titanium trichloride, formaldehyde, tartaric acid, glyoxylic acid, and formic acid; for platinum, hydrazine; for silver, glucose, formaldehyde, dextrin, glyoxal, ascorbic acid, sorbitol, hydroxylamine, hydrazine, borohydride, and dimethylamine borane; and for palladium, hydrazine, phosphinic acid, and trimethylamine borane (all inclusive of their salts).
Deposition can take place with reducing agents other than those mentioned above for the respective metals. However, gold, platinum, silver, palladium, etc. are noble metals, and the deposition potentials being noble, they are easily reduced and hence their deposition rates are rather difficult to control. There has generally been a contradictory fact that from the standpoint of productivity a high deposition rate is desirable but the conditions that permit fast deposition tend to make the solution and hence the complex unstable.
With these in view, the present invention is aimed at developing novel reducing agents f or the deposition of noble metals by chemical reduction and also developing aqueous solutions from which noble metals can be obtained by chemical reduction, the solutions remaining stable under the conditions that make high rates of deposition possible.
SUMMARY OF THE INVENTION
The present inventors took notice of the fact that compounds containing sulfur in the form of —SH or —S— have reducing action and exert complexing action on noble metals such as gold, platinum, silver, and palladium. They have studied intensively with the idea that, when such a compound was utilized as a reducing agent, increasing the concentration of the agent would raise the deposition rate, while at the same time increasing the complexing agent concentration and thereby achieving the stability of the solution. As a result it has now been found that the below-mentioned compounds can serve as novel reducing agents for the noble metals such as gold, platinum, silver, and palladium, and the industrial problems in the formation of noble metal coatings or in the production of fine particles of noble metals by chemical reduction method have just been settled.
Thus the invention provides an aqueous solution for obtaining a noble metal coating or fine particles by chemical reduction process characterized in that the solution contains one or two or more of water-soluble compounds or complexes of a metal selected from the group consisting of gold, platinum, silver, and palladium as a source or sources of the metal to be deposited and which solution also contains one or two or more of a mercapto compound or sulfide compound or their salts as a reducing agent or agents.
The aforementioned problems have now been solved by the discovery that the use of the compounds defined in (A) to (C) below as reducing agents permits the preparation of a solution which satisfies both of the contradictory conditions referred to above:
(a) a mercapto compound, a sulfide compound, and/or their salt or salts represented by the general formula (1)
in which p, m, and n each are integers of 1 or 0, not all being 0 at the same time, X
1
and X
2
are hydrogen, OH, NH
2
, or COOH independently of each other, X
3
is hydrogen, OH, NH
2
, SO
3
H, or COOH, X
1
, X
2
, or X
3
being not duplicated as COOH, COOH and SO
3
H being not overlapped, nor all being hydrogen concurrently, X
4
is hydrogen, methyl group, NHCOCH
3
, or a carboxyl group esterified by condensation with the hydroxyl group of glucose with the proviso that when X
4
is NHCOCH
3
, p, m and n are all 1, and R is hydrogen, a methyl or ethyl group;
(B) an aromatic mercapto compound represented by the general formula (2)
HS—&phgr;-(X)
n
(2)
in which n is an integer of 0-3, &phgr; is a benzene ring, and X is hydrogen, NH
2
, or COOH, which may be different when n is 2 or 3; and/or (C) a compound of imidazole, benzimidazole, thiazole, benzothiazole, imidazoline, thiazoline, triazole, benzotriazole, or thiadiazole in which the hydrogen on the carbon of the five-member ring is substituted by mercapto group.
Of these compounds, those which may be cited as examples particularly suited for industrial use are mercaptoacetic acid, 2-mercaptopropionic acid, 2-aminoethanethiol, 2-mercaptoethanol, glucose cysteine, 1-thioglycerol, sodium mercaptopropanesulfonate, N-acetylmethionine, thiosalicylic acid, 2-thiazoline-2-thiol, 2,5-dimercapto-1,3,4-thiadiazole, 2-benzothiazolethiol, and 2-benzimidazolethiol.
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Derwent absrtact of JP01/268876, 10/1989.*
Derwent abstract of jp04/032575, 2/1992.*
Derwent avstract of JP07/331452, 12/ 1995.*
Electroless Plating: Its Basic Applications, Edited by Society of Electroplating, Japan, pp. 2-6, (May 30, 1994), (translation of p. 3).
Tokuzo Kanbe,Electroless Plating, pp. 80-81, 84-85, 88-89, 166-167, (Jun. 5, 1986), (translation of pp. 80 & 84).
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Kohashi Yasuhito
Nawafune Hidemi
Obata Keigo
Okuhama Yoshiaki
Takeuchi Takao
Akin Gump Strauss Hauer & Feld L.L.P.
Daiwa Fine Chemicals Co., Ltd.
Klemanski Helene
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