Note: Descriptions are shown in the official language in which they were submitted.
1~S~75 S0526
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates generally to a bright
tin-nickel plating electrolyte, ancl moxe particularly to an aqueous
pyrophosphate electroplating bath for obtaining a bright tin-nickel
alloy plating.
Description of the Prior Art
An acid fluoride bath is generally used for achieving
a tin-nickel alloy plating, but an electroplated layer formed from
such bath is very brittle and is apt to crack when a stress is
exerted thereon, for example, due to flexing o~ the plating
substrate. Further, a tin-nickel alloy acid bath including a
fluoride is disadvantageous in that it requires difficult and
expensive treatment of exhaust fumes and of the aqueous bath prior
to discharge thereof into the atmosphere and adjacent sewer or
waterway~ respectively, for avoiding pollution oE the environment.
It is also known to provide a tin-nickel alloy plating
electrolyte which has, as its main component, an aqueous plating
liquid containing a stannous salt, a nickel salt and an alkali-metal
pyrophosphate, with the addition thereto, as a brightening agent,
of ammonium citrate and/or gelating, an a-amino acid such as
glycine, or an ~amino acld and a mercaptan derivative. However,
such aqueous pyrophosphate bath, even when containing one or more
of the mentioned brightening agents, is incapable o~ producing a
tin-nickel alloy plating of high brightness.
-2
lr~s~75
SUMMARY OF THE INVENTION
Accordingly, it is an object of this invention to
provide a bright tin-nickel alloy plating electrolyte which is
capable of producing a plating layex of improved toughness, 1exi-
bility and brightness.
Another object is to provide a bright tin-nickel
alloy plating electrolyte, as aforesaid, which is free of any
fluorides so as to minimize the ecological problems resulting from
its use.
A further object is to provide a bright tin-nickel
alloy plating electrolyte having, as its main component, an aqueous
plating liquid containing stannous a-~ liquid salts and an alkali-
metal pyrophosphate, with a ~rightener additive which results in
a plating layer of extremely high brightness.
The present invention is based on the discovery that
the brightness of the plating layer formed from a tin-nickel alloy
plating electrolyte having, as its main component, an aqueous
pLating liquid containing stannous and nickel salts and an alkali-
metal pyrophosphate, can be greatly enhanced by adding to such main
plating liquid, as a brightener additive, at least one compound
containing a plurality of amino groups as its only functional groups.
The bright tin-nickel alloy plating electrolyte
according to this invention, as aforesaid, may further have ammonia
or an ammonium salt advantageously added to its main plating liquid
in addition to the previously mentioned essential compound containing
a plurality of amino groups as i~s only functional groups. The
electrolyte according to this invention, wi~ or without the addition
.
~ 4 ~ 7 S
of ammonia or ammonium salts thereto, may further advantageou31y
contain a compound having an -SX group, in which X represents
hydrogen, sodium or potassium, peptone and/or a protein, or a neutral
amino acid without sulphur or a sal.t of such neutral amino acid.
In the bright tin-nickel alloy plating electrolyte
according to the inventi on, the stannous salt may be present in
the main plating liquid in an amount between 2 and 20 g/l., calcu-
lated as stannous ion; the nickel salt may be present in the main
plating liquid in an amount between 5 and 30 g/l., calculated as
nickel ion, and the alkali-metal pyrophosphate may be present in
the main plating liquid in an amount between 150 and 600 g/l. The
alkali-metal pyrophosphate o~ the main plating liquid may be, for
example, potassium pyrophosphate or sodium pyrophosphate, while the
stannous and nickel salts o such main plating liquid may be
respectively stannous pyrophosphake, stannous chloride, stannous
sulfate or the like, and nickel pyrophosphate, nickel chloride,
nickel sulfate or the like.
The brightener additive which is essentially added to
the main plating liquid and which, in accordance with this invention,
contains a plurality of ami-no groups as its only functional groups
may be advantageously selected from the group consisting of ethylene-
diamine, 1,2-propanediamine, 1,3-propanediamine, 194-butanediamine,
pentamethylenediamine, hexamethylenediamine, hydrazine, guanidine,
urea and thiourea. The amount of such brightener additive introduced
into the main plating liquid is preferably between 0.1 and 100 g/L.
of the main plating liquid.
-4-
.
.
: ' :
~ ~ 5~ 7 S
In the case where ammonia is added to the plating
electrolyte, it may be in the form of 28% aqueous ammonia in the
amount between 5 and lOO g/l. of the main plating liquid. When
ammonium salt is added, such addition may be ammonium chloride,
ammonium sulfate, ammonium nitrate, ammonium citra~e, a~monium
tartrate, ammonium acetate or the like, and is present in an amount
between 1.0 and 150 g/l. of the main plating liquid.
The compound having an -SX group which may be optionally
added to the bright tin-nickel alloy plating electrolyte according
to this inventlon may be advantageously selected from among
dithioammelide, 4-amino-3,5-dimercapto-4,1,2-~riazol, ethylene
thiuram monosul~ide, 2,5-dimercapto-1,3,4-thiazol, thiocarbohydrazide,
hydrazoldithiodicarvoneamide, ethylene-bis-dithiocarbomic acid soda
and the like, and is added in an amount between 0.01 and 5 g/l. of
the main plating liquid.
When peptone and/or protein is added to the electrolyte,
the amount thereof is between 0.1 and 10 gll. of the main plating
liquid. The protein thus added may be, for example, glue, gelatine
or gluten. The peptone and/or protein is preferably dissolved in
water, in an aqueous solution of potassium pyrophosphate or in an
alcohol, such as, methanol or ethanol, before being added to the
main plating liquid of the electrolyte.
When a neutral amino acid without sulphur is added
to the electrolyte according to this invention, such additive may
be advantageously selected from glycine, alanine, serine,Q~in~b~Tyri~
acid, leucine, isoleucine, proline, hydroxyproline, phenyl-alinine,
thyroxine, triptophan and the like, and is added in an amount
-5-
~5~7S
greater than a. Ql mol~l. of the main plating li~Uid. -i
T~e pH of the plat~ng electrolyte i~ adjusted to
within t~e range of 8 to 12 with aqueous ammon~a solution, ^-
caustic potash, pyrophosphoric acid and the like.
In its broadest aspect, the invention provides a
bright tin-nickel alloy plating electrolyte having a pH in the
range from 8 to 12 and consisting essentially of an aqueous
main plating liquid containing:
a. a stannous salt selected from the group
consisting of stannous pyrophosphate, stannous chloride and
stannous sulfate, and which is present in said main plating
liquid in an amount between 2 and 20 g/l. calcula~ed as
stannous ion;
b. a nickel salt selected from the group consisting
of nickel pyrophosphate, nickel chloride and nickel suIfate, -
and which lS present in said maln plating liquid in an amount
b~tween 5 and 30 g/l. calculated as nickel ion;
c. an alkali-metal pyrophosphate selected from the
group consisting of potassium pyrophosphate and sodium
pyrophosphate, and which is present in said main plating
liquid in an amount between 150 and 600 g/l;
d. at least one brightener additive in said plating
liquid in an amount between 0.1 and 100 g/l of said main
plating liquid and being selected from the group consisting
of ethylenediamine, 1,2-propanediamine, 1,3-propanediamine,
1,4-butanediamine, pentamethylenediamine, hexamethylenediamine,
hydrazine, guanidine, urea and,thiourea; and ;
., ,. , :..... ~.
e. at least one further additive selected from the
group consisting o~ a compound hav~ng at least one-SX group -`~
(where X represents hydrogen, sod~um or potassium~, peptone, -
derived protein, neutral amino acid free of sulfur and
neutral amino acid salt free of sulfur; the said compound
-6-
. ' ;
.. , .; , .. .. ,,, , , . . .. ~, ., ... , . , ., ., , : .
slr375
having at least one -SX group is present in said main plating
liquid in an amount between 0.01 and g 5/1, the said peptone
and derived protein is present in an amount between 0.1 and
10 g/l, and the said neutral amino acid and salt of
thereof is present in an amount greater than 0.01 mol/1.
The invention is further described with reference to
the following specific examples thereof:
Example 1
An aqueous main plating liquid is provided contain-
ing 200 g/l. of potassium pyrophosphate, 30 g/1. o~ stannous
pyrophosphate and 50 g/1. of nickel pyrophosphate. Such main
plating liquld has added thereto 15 g/l. of ethylenediamine,
which is added as an 85% aqueous solution of the latter, and the
pH of the resulting plating electrolyte is adjusted to a value
of 9.5. The plating electrolyte is then subjected to mechani-
cal agitation at 30C with a carbon anode and a brass plate
plated with a bright nickel layer as a cathode. A current with
an average cathode current density of 0.5 A/dm2 is made to flow
for three minutes to carry out electrolytic plating. As a
result, a bright tin-nickel alloy (containing 67.2% tin) with
a bright stainless color is obtained.
Examples 2, 3 and 4
The procedures described above in Example 1 are
repeated but with the further addition to the main plating
liquid of ammonium chloride (Examples 2 and 4) or aqueous am-
monia (Example 3) and with the substitution of nickel chloride
for the nickel pyrophosphate (Examples 3 and 4), and the
results thereof are as shown on Table 1 below. ,
'i; '~
lj,;
-6a -
5~7~
TABLE l
Examples
:L 2 3 4
. . .
Potassium pyrophosphate g/l. 200 200 200 200
Stannous pyrophosphate g/l. 30 30 30 30
Nickel pvrophosphate g/l. 50 50
- . .. ... ... ... . -
Nickel chloride _ g/l. 40 40 ~;
Ethylenediamine of æ5% g/l. 15 15 25 25
Ammonium chloride /l. 20 50
- -
A ueous ammonia of 28% cc/l 20
q ... _ ._ .
~H 9.5 9.5 9.5 9 5
, .
Temperature C 30 30 30 30
._ . .. . _ _ . ' '.' :.
A~itation Yes Yes No No -
_._ ~ ., .
Current denslty _ _ A/dm20.5 0.5 0.5 0.5
Anode __ _ Carbon Carbon Carbo_ Carbon ~`
Amount of tin contained
in deposited alloy __ _ % 67.2 62.1 66.3 67.1
. ,;.
Appearance Bright Bright Bright Bright
stain- stain- stain- stain- ;
less less less less :
color colox color color
tOmilar
__ _ white _ ;
The procedure of Examples l, 2, 3 and 4 are repeated,
but using, in turn,hydrazine, 1,2-propanediamine, 1,3-propane- -
diamine, 1,4-butanediamine, guanidine, urea, thiourea, pen-
tamethylenediamine and hexamethylenediame, in place of the
ethylene diamine, and, in each case, a bright tin-nickel alloy
plating similar in appearance to the platings obtained in
Examples 1, 2, 3 and 4 on Table 1 is obtained.
- 7 -
-
5~75
Examples 5, 6, 7,8 and 9
The procedures described ln Example 1 are repeated,
but with nickel chloride replacing the nickel pyr~phosphate
(Examples 7, 8 and 9), and with the further addition of a com-
pound having an -SX group, to wit, 2,5-dimercapto-1,3,4-
thiazol (Examples 5, 6 and 9), dithioammelide (Examples 7 and 9)
and hydrazodithiodicarvoneamide (Example 8), and the propor-
tions and results of such additives are as shown on Table 2
below.
TABLE 2
Examples
~_5 6 7 8 9
Potassium ;'
pyrophosphate g/l. 20C 200 200 200 200
Stannous
pyrophosphate g/l. 3C 30 30 30 30
Nickel
pyrophosphate g/l. 5C 50
Nickel ;
chloride g/l. ___ 40 40 40 '
Ethylenediamine .
of 85% g/l. 0.8 0.8 0.8 0.8 1 '
2,5-dimercapto-
1,3,4-thiazol g/l. 0.5 0.5 0.5
Dithioammelide
g/l. 1 0.5 _
Hydrazodithiodi-
carvoneamide g/l. 1 -'
_ _ ,
pH 9.5 9.5 9.5 9.5 9.5 ~-;
Temperature C 35 35 35 35 35
Agitation Yes Yes Yes Yes Yes
Current density 2 ~,~
A/dm 0.5 0.2 0.5 0.5 0.5 :~
Amount of tin contained
ir. deposited alloy % 72.1 71.5 73.1 70.1 70.3
~ppearance Bright' Bri~ht Bri~ht Bri~ht Bri~ht
stain- staln- staln- staln- staln-
less less less less less ~'
cQlor color color color color
wl-th wlth wlth wlth wlth
_ _____ _ black black black black black
- 8 -
.": '
~ 507S
: Examples 10,11~12,13 and 14 ~ :
The procedures of Examp~e 1 are repeated, but with j
the further addition of a compound having an -SX group, to wit,
2,5-dimercapto-1,3,4-thiazol (Examples 10,12,13 and 14) and/or ,~ -
- dithioammelide (Examples 11,13 and 14) and of either ammonium
chloride ~Examples 10,11 and 14) or aqueous ammonia (Examples 12
and 13), and the proportions and results of such further additives '~ ,
, !~ ~-
are as shown on Table 3 below.
TABLE 3
Examples
~1 1 1 2 1 3 14
Potassium Pyrophosphate
Vtl 200 200 7 200 200 200
r ~ ~ _
Stannous pyrophosphate ~Jl. 30 30 30 30 _ 30 .~
ickel PYrophosphate _ ~/l. 50 50 50 ¦ :
; Nickel chloride~/1. 40 40
__
Ethylenediamine of . ~:
85% . ~/1. 0.8 0.8 0.8 _ 0.8 0.8 ,
------ 2,5-dimercapto- .
1,3,4-thiazol gL~ 0.5 . _0.5 0.5
Dithioammelide~/1. 0.5 0.5 0,5
Ammonium chloride ~L~ 50 5 Q
Aqueous ammonia of 28% cc/l. 30 30 - ~ :
.9.5 9.5 9.5 9.5 9.5
Temperature C 35 35 35 35 35
A~itation Yes . Yes Yes Yes Yes ~'
- - , . . _._ . _ ~ '"
Current density A/dm2 0.5 0.. 5 _ 0.5 0 5 0.5 ~ -
Amount of tin contained .
in deposited alloy % 1 67.8 64 264.8 63.5 65 4
Bright Bright Bright Bright Bright ~:
Appearance stainless stain- ~stain- stain- stain- ~,
color less less less less
color color color color t
- ~ _ _ . ''` ~ '~
_9 ~ :
~',' .
,~
1.
l~S~75
Examples 15, 16 and 17
The procedures of Example 1 are repeated, but with
the further addition of peptone (Examples 15 and 17) or pro-
tein in the form of glue (Example 16) and also of ammonium
chloride (Example 17) and the proportions and results of such
additives are as shown on Table 4 below.
TABLE 4
. . . _
Examples
. . .
15 16 17
.. :~
Potassium pyrophosphate g/l. 200 200 200
_._ , _ .
Stannous pyrophosphate g/l. 30 30 30
._ _ __ _
Nickel pyrophosphate g/l. 50 50
._ . ~ .. . :,,
Nickel chloride g/l. 40 ~-
~ . . . .
Ethylenediamine of 85%g/l. 0.5 0.5 15
- ;:.
Peptone g/l. 1 1 `
Glue g/l. 1
Ammonium chloride g/l. 20
__ ..................................................... :~'~
pH 9.5 9.5 9.5
_ -- ---- _ .",
Temperature C 35 35 35 '
. ._ .__ . _ . _ __~
Agitation Yes Yes _ _ Yes _ __
Current density A/dm 0.3 0.3 0.3 `
.. _ . _ . .. __ :~.~,;, .
Amount of tin contained
in deposited alloy % 68.2 67.3 65.4
,
Appearance Bright Bright Bright
stainless stainless stainless '
color color color `
with with
black black
..... _ _~
-- 10 --
~4S~5 ``
Examples 18 and 19
-
The procedures of Example 1 are repeated, but with
the further addition of a neutral amino acid free of sulphur
or a salt thereof, to wit, sodium glycine (Example 18) or ~
alanine (Example 19), and also of aqueous ammonia (Example 19), ;
and the proportions and results of such further additions are
as shown on Table 5 below.
TABLE 5
Examples Reference
18 19
Potassiumpyrophosphate g/l. 200 200 200
Stannous pyrophosphate g/l. 30 30 30
Nickel pyrophosphate g/l.50 50 50
Ethylenediamine of 85% g/l. 0.8 _ 0.8
Sodium glycine g/l. 7 7
Alanine g/l. ~ 8
;.
Aqueous ammonia of 2~% cc/l.; 30
pH 9.5 9.5 9.5
Temperature C _35 ~ 35 35
Agitation Yes Yes Yes
2 _
Current density A/dm0.5 0.5 0.5
.
Anode carbon carbon carbon
Amount of tin contained
in deposited alloy % 67.4 ~68.2 84.2
Appearance Briyht Bright Grey
stainless stainless with ;
color color bright
_ ness
... . . . .
7~
Reference 1
In ord~r to demonstrate the essential character of the
additive compound having a plurality of amino groups as its only
func~ional groups, the procedure of Example 18 was repeated, but
with the ethylenediamine being omitted from the plating electrolyte
and, as shown on Table 5 above, the resulting pla~ing layer was grey
in color and devoid of brightness.
Thus, it will be apparent that, by the addition to the
main plating liquid, containing stannous salt, nickel salt and an
alkali-metal pyrophosphate~ of a compound having a plurality ~
amino groups as i~s only ~unctional groups, the present invention
produces a bright tin-nickel alloy plating layer with a brightness
that cannot be obtained with prior plating electrolytes
Further, it will be apparent that the brightness of
the tin-nickel alloy plating layer is urther enhanced by also
adding to the electrolyte a compound having an -SX group (in which
X represents hydrogen, sodium or potassium), peptone and/or protein,
or a neutral amino acid free of sulphur.
Finally, the further addition of ammonia or ammonium
salt to the plating electrolyte according to this invention is shown
to provide the bright plating layer with white color.
Al~hough specific examples of the invention have been
described in detail herein, it is to be understood that the invention
is not limited to those precise examples which are intended to be
illustrative, and that a person skilled in the art may effect
various changes and variations or modifications in the given examples
without departing frnm the scope or spirit of the inven~on as
defined in the appended claims.
~12-
