JPS5939516B2 - Electrolytic bath for gold alloy plating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a basic sulphite electrolytic bath for gold alloy plating, particularly for bright, uniform white-gray electrodeposition of gold-zinc alloys with relatively low gold content.

A number of processes based on alkaline or acidic baths and gold sulfite complexes are already known for gold and gold alloy deposition.

Such processes are currently gaining importance because they are cyanide-free and do not have the toxicity of conventional gold cyanide baths. For example, U.S. Patent No. 3,057;
No. 789 (Smith) discloses an alkaline sulfite gold bath consisting of polyamines, polyphosphates or EDTA (ethylene diamine tetraacetic acid) in addition to gold complexes and giving a semi-bright gold plating.

When the disclosed bath further includes copper in EDTA complexed form, the electrodeposit contains trace amounts of copper alloyed with gold. 19
U.S. Patents No. 3 and 6, registered in 1965 and 1966.
No. 66,640 (SEL-REX) and No. 3,475
, No. 292 (TECHNIC) discloses alkaline sulfite baths for alloy plating of gold and common metals, respectively.

Besides gold and the usual metal salts, these baths contain conductive salts such as free alkali sulfites, alkali salts of mineral and organic acids, and chelating or complexing agents such as ED.
Contains aminopolycarboxylic acids such as TA, NTA (nitrilotriacetic acid), HEDTA (hydroxyethyl-ethylenediaminetriacetic acid, lactic acid, etc.).To improve the gloss of the coating, small amounts of arsenic, antimony or selenium may be added to these baths. The coatings obtained by the bath procedures described in these patents are actually pure gold (24 karat) or very high karat gold (23 karat or more) having only a few alloying common metals. ).Such alloys are shiny and have a slightly different yellow color, which is close to that of pure gold.1
British Patent No. 1,325,352, registered in 1969
ζ West German Patent No. 2,039,159 (SE[REX) discloses a sulfite gold bath that can be operated in acidic conditions and is made from a new gold complex.

This complex is obtained by reacting an Au compound sequentially with an amine and an alkali or ammonium sulfite. This bath contains conductive salts, As, Sb or Se.
may include brighteners such as EDTA or DTPA, strong keylating agents such as EDTA or DTPA, hydroxycarboxylic acids and alloying metals, ie copper. This bath makes it possible to obtain both pick-coloured, low-carat (less than 16 carats) bright coatings of gold-copper alloys as well as pure gold deposits (24 carats) in acidic media. West German Patent No. 2,244,437 with 1971 priority. (0MFCa1if0rnia
) and West German Patent No. 2,222,310 (Konig), filed in 1972, disclose sulfite baths for plating gold-palladium and gold-platinum alloys.

Additionally, these baths containing conventional metals as the metallic component to form the third alloy consist of amines, strong aminocarboxylic acid chelators, and hydroxycarboxylic acids, and contain commercially undesirable precious metals (gold plus gold). We supply light-colored alloy plating containing a high proportion of palladium or platinum. West German patents 2 and 33 share a priority date of 1972
No. 4,813 (Degussa) and No. 2,340,
No. 462 (OxyMeta1Industr-Ies)
Low karat gold alloyed with a tertiary or quaternary alloying metal such as copper, nickel and cobalt can be prepared by adding an organophosphorus chelating agent to the sulfite gold alloy plating bath as described in A gold cadmium coating could be deposited.

Baths containing, in addition to the metals mentioned above and others still used as brighteners, also contain hydroxycarboxylic acids, chelating agents such as EDTA, and conductive salts, which are almost white in color and are generally commercially available as white gold (White Gold).
d) and provides an expensive light-colored alloy coating.
However, over time, these alloys develop a faint yellow color and their corrosion resistance is not very high. Also, the presence of the highly toxic component cadmium in the alloy makes it highly undesirable for coating objects that normally come into physical contact with living organisms. Because of the toxicity of the cadmium, it was planned to replace it with the actually harmless component zinc.

However, the electrodeposition of uniform low-karat gold-zinc alloys is
At first, it seemed extremely difficult in view of the vastly different electrochemical properties of the two metals. However, after long and patient exploration, it was found that gold was a bright, low-karat, uniform, gray to white color. Electrodeposition of Zinc Alloys We have successfully prepared a suitable cyanide-free alkaline sulfite bath containing gold in the form of gold sulfite complexes; zinc in the form of water-soluble salts or complexes or chelates; Alkali metal sulphites, complexing agents or chelating agents; at least one water-soluble salt as a homogenizer or internal stress reducer for gold-zinc alloys, as a third alloying metal in the form of a complex salt or chelate; It consists of indium or gallium,
This is the basic bath for the present invention. The bath of the present invention is characterized in that it additionally contains a fourth alloying metal in addition to the gold-zinc and the third alloying metal indium or gallium contained in the basic bath.

The metals forming this fourth alloy, which are added in water-soluble form and complexed by the bath complexing agent, include, for example, nickel,
Mention may be made of tin, cobalt or other common metals. The concentration of these metals is within a range of compatibility with other bath components and is approximately 0.1 to 10 9 /l. This fourth alloying metal is co-electrodeposited with the alloying metals of the coating in the base bath and provides improved properties to the coating.
Thus, the small amount of nickel added increases the hardness and heat resistance of the white gold-zinc coating. A feature of the bath of the present invention is that the chelating agent
at least one nitrogen- and/or phosphorus-containing organic acid () with K between 6 and 15 and at least two a′D′ alcoholic 0H number to acidic group number ratios equal to or greater than 1; at least one organic hydroxy acid selected from acyl hydroxy acids and ω-cycloaliphatic or aromatic hydroxy acids containing a hydroxyl group,
and that the metal forming the fourth alloy is selected from nickel, tin, or cobalt.

Those that can be used as the first component (1) of the chelating agent or complexing agent include, for example, phosphorescent compounds,
They are aminocarboxylic compounds or aminophosphonic compounds.

As such, N-(2-hydroxyethyl)
Ethylenediamine-triacetic acid (HEDTA), PKzn
l4.5; N,N'-di(2-hydroxyethyl)ethylenediamine-diacetic acid (HEDDA), PKznl2;
Ethylenediamine-N,N'-diacetic acid, PKznll;
Nitrilotriacetic acid (NTA), PKznlO. 5; Nitrilo-trimethanephosphonic acid (NTP), PKz
nl3; N-(2-hydroxyethyl)-iminodiacetic acid (HIDA), PKzn8-9; ethylene diamine-
N-diacetic acid, PKznl2; iminodiacetic acid (DA), P
Kzn7-7.3; 1-hydroxyethane 1,1-diphosonic acid and phosphonomethyliminodiacetic acid. EDTAL or DTP with PK greater than 15
It is noteworthy that strong caraminocarboxylic chelators such as A are unsuitable.

It should also be noted that the above list should not be considered exhaustive and that other compounds of PK within the above limits known to the skilled artisan are also suitable. (Reference example: L.G.Sllen & A.EMartell:S
tabiitycOns-TantsOfmetal
iOncOmplex,. theChemicalSO
ciety. LOndOnl964&Suppl
l97l) As 0-hydroxy acids (a), hydroxy acids containing at least 3 carbon atoms, at least 2 of which carry the alcoholic 0H function, can be used; such acids include glycerin, Examples include threonic acid, arabonic acid, glycolic acid, heptagluconic acid, chloric acid, mannolic acid, allonic acid and galactonic acid. As acid (a), polyhydroxydicarboxylic acids such as acetic acid, dihydroxy acetic acid, trihydroxy glutaric acid, saccharic acid, mucic acid, etc. can also be used.

Hydrosilic acids having bonds other than C--C bonds in the main chain of the molecule; for example ester or ether bonds can also be used. Thus, a compound obtained by combining the acid function of a mineral or organic acid with the alcohol function of a polyol can be used in a state in which this bond is stable in the operating bath. Thus, for example, glycerophosphate, which is stable in an aqueous medium,
Many of them can also be used as detergents or surfactants. Hydrogen sulfate salts of polyols (eg of decaglycerol) can be used as well. On the other hand, addition products which are unstable in aqueous media, such as glucocitric acid, are unsuitable.

The effect of glucocitric acid disappears in solution after a few hours. Also, it should be noted that three COOH groups and one 0
Citric acid, which has H groups, is less suitable because the resulting plating becomes yellow on standing. Addition compounds between boric acid and polyalcohols, such as glyceroboric acid, for example, are also unsuitable; the reason for this defect is not known, but may be based on the presence of boron atoms. The upper limit for the number of carbons contained in such acids has not been determined, but is probably very high.

In fact, certain hydroxy-carboxylated polymers, such as hedenoid powder, or some oxidation products of cellulose (carboxymethyl cellulose), exhibit some positive effects as long as they are soluble in water. Cyclic hydroxy acid (
As a), for example, the following hydroxy cyclic fatty acids and hydroxy aromatic acids, kojic acid, quinic acid, shikimic acid,
Mention may be made of salicylic acid and dihydroxybenzoic acid.

The exact types of structural changes that somehow limit the use of other cyclic hydroxy acids in the baths of the present invention are not known. It should be noted, however, that in view of the complexing power of cyclic hydroxy acids with zinc and other metals, there should be little concern that co-electrodeposition of these metals will be stopped. Furthermore, it should be noted that the effect of gallic acid with 3vic-phenol groups is rather weak, since the coating obtained in its presence lacks gloss. The amounts of each of the various components in the baths of the present invention can vary considerably.

However, to some extent they are interdependent. Furthermore, due to lack of time, it was not possible to completely determine whether all possible changes belonging to each such parameter were self-related or not. However, for gold contents between 2 and 209/l, preferably between 4 and 129/l, this bath should contain between 0.5 and 159/l of zinc, between 0.1 and 159/l.
59/l indium or gallium, 0.1-109
/l nickel or tin or cobalt, 5-100
It may contain 9/l of chelating agent (1) and 1 to 1009/l of hydroxy acid (a) or (b). This bath also contains 5 to 509/l or more of free alkali sulfites and, in normal practice, in order to somehow improve the conductivity, sulfates, acetates, pyrophosphates, phthalates, etc. Other buffering agents such as salts or conductive salts may be included. The amount of such salts can vary extremely and will be determined in each case by skilled persons as necessary. The concentration values above are not absolute;
It can be lowered or exceeded in some cases if necessary.

It should also be remembered that, as mentioned above, these different ranges of concentrations are not independent of each other. In other words, when selecting the concentration of one or other ingredients, it is generally preferred to take into account the remaining ingredients already selected. Thus, for example, when it comes to chelating agents, when one or the other ingredient is in low concentration, the other ingredients, e.g. It is desirable to avoid using high concentrations. The optimal concentration is a function of the affinity of each mutual constituent,
It should also be remembered, for example, that it is a function of the complexation constant value of the chelating agent chosen for the bath metal. The form in which metals other than gold are added to the bath is not critical, and generally they may be added in mineral or organic water-soluble form (salts, complexes or chelates). When dissolved, these metals will be partially bound and partially dissociated as a function of the complexing strength of the bath formulation. In fact, these metals, with the exception of halides and nitrates,
Preferably it is added as sulfate or acetate or other similar derivatives. The bath of the present invention under basic conditions:
Preferably between PH9 and 11, and better still PH
Operate between 9.5 and 10.5.

Current density of about 0.1~3A/Dm'', preferably 0.3~
It is operated at between 40-70°C, preferably around 50-65°C, under 1.5 A/Dm2. Under these conditions, a glossy, homogeneous alloy with a carat weight of 17 to 19 is obtained which is particularly stable, stretchable and corrosion resistant. The baths of the invention may also optionally contain wetting agents or surfactants.

Such compounds, currently commonly used in plating baths, often have a favorable effect on the appearance and other properties of the plating (surface condition, internal stresses, etc.). As surfactants, very economical products can be used for the purpose of improving the surface tension of water-soluble materials. For example, fatty acids, hydrogen sulfates, naphthalene mono- and polysulfonic acids, polyglycols, hydrogen phosphates, their alkali salts and other comparable compounds (see examples: Swiss Patent No. 556,916 column 586; also Mc. CutcheOnO）ゞDet
ergcnts &Emulsifiers;MCPub
llshingCO. , RidgewOOd, . N.J.O.
745l. USA). The amount of surfactant that must be added to the bath to produce a visible effect is variable and depends on the nature of the surfactant and the effect sought. Thus, 0.019/j or 0.01 m1/l
Even small amounts can be effective. Although interference generally does not occur even at high concentrations that are not really needed, 0.1
~5 g/l (0.1-5TL1/l) is preferably used. Next, basic baths for constructing the bath of the present invention are shown as comparative examples, and Examples 1 to 3 include nickel, which is a metal forming the fourth alloy of the property improver for gold-zinc alloy coating,
A bath to which cobalt and tin were added is shown.

In these comparative examples and examples, parts are given by weight and temperatures are given in °C, unless otherwise indicated. Comparative Example 1 A gold alloy plating bath was prepared by dissolving the following ingredients in water: The bath was operated at 55° C. under 1 A/D ml and was coated with approximately 19 karat bright white gold (WhitegOld).
) electrolytic plating was applied.

Comparative Example 2 The following baths were prepared as in the example with the following formulations.

The bath was operated at 60 DEG C. and 0.8 A/Dm and gave about 18 carats of white and gray plating.

When dihydroxychlorite was removed, a plating with a high density but with low uniformity and poor elongation was obtained. Comparative Example 3 This was operated as in Example 1 with the following bath; 1A
An operating bath at 60°C under /Dm2 gave a white-gray plating.

Replacing the acid in this bath with citric acid gives the plating an undesirable yellow sheen and poor storage stability. Comparative example
4 The following bath was prepared and used: At 60° C. and 1 A/d, this bath gave a bright 18 carat plating.

Comparative example 5 The following baths were used in preparation: At 70°C under 1A/DTI, Gave Tsuto's white-gray metsuki.

EXAMPLE 1 The following baths were prepared and used: This bath was prepared using a white-gray alloy containing about 18 carats of nickel (approx.
The corrosion resistance, hardness and resistance were improved.

Example 2 Example 1 was repeated, except that 2.0 g/l (as sulphate) of cobalt was used instead of nickel.

Under the same plating conditions as in Example 1, approximately 18 carats of a white and gray alloy (approximately 76% Au, approximately 20% Zn, the remainder being n plus 60 ppm (7) CO) was produced, and this alloy had a hardness and Abrasion resistance was improved. Example 3 Example 2 was repeated, except that 2.0 f1/l (as sulfate) of tin was used instead of cobalt.

Claims (1)

[Scope of Claims] 1 Gold as sulfite complex 2-20 g/l free alkali metal sulfite 5-50 g/l; zinc as water-soluble salt, complex or chelate 0.5-15 g/l: complex a chelating agent or a chelating agent; and 0.1 to 5 g/l of a third alloying metal as a water-soluble salt, complex or chelate which acts as an internal stress reducer for the gold-zinc alloy; The agent has a PK of 6 for zinc under working conditions.
5 to 100 g/l of at least one nitrogen- and/or phosphorous-containing acid (I) between ~15 and 1 to 100 g/l of at least one hydroxy acid (II), said hydroxy acid ( II) is a) at least 2 OH
acylhydroxy acids containing groups and having a ratio of the number of alcoholic OH groups to the number of acid groups equal or greater than 1; and b)
aliphatic or aromatic cyclic hydroxy acids, and the third alloying metal is selected from indium or gallium. A fourth alloying metal in a water-soluble form of at least one selected from nickel, cobalt and tin which can be co-electrodeposited with the zinc alloy to improve its properties.
A cyanide-free basic sulfite electrolytic bath for bright, uniform, white-gray, low carat gold-zinc alloy electrodeposition comprising adding 1 to 10 g/l. 2. The electrolytic bath according to claim 1, further comprising a surfactant or a wetting agent.