U.S. patent application number 10/694597 was filed with the patent office on 2004-05-13 for method for supplying zinc ions to alkaline zinc plating solution.
Invention is credited to Sekiguchi, Osamu, Usui, Shigetaka.
Application Number | 20040089553 10/694597 |
Document ID | / |
Family ID | 32179147 |
Filed Date | 2004-05-13 |
United States Patent
Application |
20040089553 |
Kind Code |
A1 |
Sekiguchi, Osamu ; et
al. |
May 13, 2004 |
Method for supplying zinc ions to alkaline zinc plating
solution
Abstract
A method for supplying zinc ions to an alkaline zinc plating
bath, wherein a source of zinc ions and a zinc dissolution
accelerating metal are put in the same vessel and brought into
direct contact with each other or put in different vessels and
connected via an electric conductor, and the source of zinc ions
and the zinc dissolution accelerating metal are moved in the
vessel(s) in a plating solution by shaking, vibrating or rotating
the vessel(s) in order to accelerate zinc dissolution.
Inventors: |
Sekiguchi, Osamu;
(Chigasaki-shi, JP) ; Usui, Shigetaka;
(Chigasaki-shi, JP) |
Correspondence
Address: |
MARSHALL, GERSTEIN & BORUN LLP
6300 SEARS TOWER
233 S. WACKER DRIVE
CHICAGO
IL
60606
US
|
Family ID: |
32179147 |
Appl. No.: |
10/694597 |
Filed: |
October 27, 2003 |
Current U.S.
Class: |
205/101 ;
205/305 |
Current CPC
Class: |
C25D 21/14 20130101 |
Class at
Publication: |
205/101 ;
205/305 |
International
Class: |
C25D 003/22 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 8, 2002 |
JP |
2002-325097 |
Jun 26, 2003 |
JP |
2003-182916 |
Claims
What is claimed is:
1. A method for supplying zinc ions to an alkaline zinc plating
bath, wherein a source of zinc ions and a zinc dissolution
accelerating metal are brought into electrically direct or indirect
contact with each other, and the source of zinc ions and the zinc
dissolution accelerating metal are shaken, vibrated or rotated in a
plating solution in order to accelerate zinc dissolution from the
source of zinc ions.
2. The method according to claim 1, wherein the source of zinc ions
and the zinc dissolution accelerating metal are put in a same
vessel, brought into direct contact with each other and moved in
the vessel in the plating solution by shaking, vibrating or
rotating the vessel in order to accelerate zinc dissolution.
3. The method according to claim 1, wherein the source of zinc ions
and the zinc dissolution accelerating metal are put in different
vessels, connected via an electric conductor, and moved in the
vessels in the plating solution by shaking, vibrating or rotating
the vessels in order to accelerate zinc dissolution.
4. The method according to any of the claims 1 to 3, wherein the
source of zinc ions comprises one or more kinds selected from zinc,
zinc alloy, zinc or zinc alloy whose surface is plated or contacted
with metal that is more electropositive than zinc, and the zinc
dissolution accelerating metal comprises; 1) metal that is more
electropositive than zinc, 2) metal that is more electropositive
than zinc, with which one or more kinds selected from iron, cobalt,
nickel, carbon, silicon, manganese, chromium, molybdenum and
tungsten are contacted, 3) metal that is more electropositive than
zinc, in which one or more kinds selected from iron, cobalt,
nickel, carbon, silicon, manganese, chromium, molybdenum and
tungsten are dispersed, 4) alloy comprising metal that is more
electropositive than zinc and one or more kinds selected from iron,
cobalt, nickel, carbon, silicon, manganese, chromium, molybdenum
and tungsten, or 5) a composite or mixture of two or more kinds
selected from above 1) to 4).
5. The method according to any of the claims 1 to 3, wherein a
degree of contact both or either of the source of zinc ions and the
zinc dissolution accelerating metal have with a plating solution is
controlled in response to an analysis of a zinc ion concentration
in the plating solution to adjust the zinc ion concentration in the
plating solution.
6. The method according to claim 4, wherein the degree of contact
both or either of the source of zinc ions and the zinc dissolution
accelerating metal have with the plating solution is controlled in
response to the analysis of the zinc ion concentration in the
plating solution to adjust the zinc ion concentration in the
plating solution.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method for supplying zinc
ions to an alkaline zinc plating solution.
[0003] 2. Prior Art
[0004] In zinc electroplating of general materials, a non-cyanide
alkaline zincate bath (hereinafter called "zincate bath") has been
widely used since it has advantages in corrosion resistance,
throwing power, environmental effect and the like. However, in the
zincate bath, since metal zinc used for an anode is nonuniformly
passivated, fluctuation of cathode current density distribution
increases, and thickness of plated film, gloss, properties of film
and the like are adversely affected. Moreover, since insoluble
substances such as oxide (called "anode slime") formed by
passivation of zinc pollute a plating solution, passivation of zinc
anode is a cause of degradation of plating quality. Therefore,
there arises an extreme opinion that the quality of zinc plating
depends on the control of anode.
[0005] To avoid the adverse effect of zinc anode on the plating
solution, methods for supplying zinc ions from other than a plating
anode, in which an insoluble anode is used, are suggested. For
example, Japanese patent No. 58-6792B discloses a method in which
zinc dissolution is accelerated by forming a cell between zinc and
metal which generates higher hydrogen overvoltage than zinc in
another dissolution tank. However, this method was disadvantageous
in that a large dissolution bath was required since zinc
dissolution rate was low and that a quantitative control of zinc
dissolution was difficult since deactivation of zinc surface
proceeded and zinc dissolution rate became extremely low as time
elapsed. Additionally, Japanese patent No. 57-149498A discloses an
electrolytic method using zinc as an anode. However, this method
was disadvantageous in that enough zinc dissolution rate could not
be achieved and the same power as that for zinc plating was
additionally required since passivation of anode zinc occurred when
anode current was increased in order to accelerate the zinc
dissolution rate.
[0006] [Patent Literature 1]
[0007] Japanese Patent No. 58-6792B
[0008] [Patent Literature 2]
[0009] Japanese Patent No. 57-149498A
SUMMARY OF THE INVENTION
[0010] Accordingly, one object of the invention is to make the rate
of zinc ions supply faster than that of zinc ions consumption, and
to stabilize and control the zinc dissolution rate in order to
stably maintain and control zinc ion concentration in an alkaline
zinc plating solution.
[0011] After having extensively conducted researches to solve the
problems, the inventors have reached a method for supplying zinc
ions to an alkaline zinc plating bath, wherein a source of zinc
ions and a zinc dissolution accelerating metal are brought into
electrically direct or indirect contact with each other, and the
source of zinc ions and the zinc dissolution accelerating metal are
shaken, vibrated or rotated in a plating solution in order to
accelerate zinc dissolution from the source of zinc ions.
[0012] More specifically, the inventors have reached the method for
supplying zinc ions to the alkaline zinc plating bath, wherein the
source of zinc ions and the zinc dissolution accelerating metal are
put in the same vessel and brought into direct contact with each
other, or put in different vessels and connected via an electric
conductor, and the source of zinc ions and the zinc dissolution
accelerating metal are moved in the vessel or vessels in the
plating solution by shaking, vibrating or rotating the vessel or
vessels in order to accelerate zinc dissolution.
[0013] Furthermore, the inventors have found out that the zinc
dissolution rate could become several times higher than ever and
stabilize at a high level by carrying out the above-mentioned
method for supplying zinc ions to the alkaline zinc plating bath,
by using one or more kinds selected from zinc, zinc alloy, zinc or
zinc alloy whose surface is plated or contacted with metal that is
more electropositive than zinc as the source of zinc ions, and by
using; 1) metal that is more electropositive than zinc, 2) metal
that is more electropositive than zinc, with which one or more
kinds selected from iron, cobalt, nickel, carbon, silicon,
manganese, chromium, molybdenum and tungsten are contacted, 3)
metal that is more electropositive than zinc, in which one or more
kinds selected from iron, cobalt, nickel, carbon, silicon,
manganese, chromium, molybdenum and tungsten are dispersed, 4)
alloy comprising metal that is more electropositive than zinc and
one or more kinds selected from iron, cobalt, nickel, carbon,
silicon, manganese, chromium, molybdenum and tungsten, or 5)
composite or mixture of two or more kinds selected from above 1) to
4) as the zinc dissolution accelerating metal.
DESCRIPTION OF THE SPECIAL EMBODIMENTS
[0014] The method of the present invention for supplying zinc ions
can be applied to alkaline zincate bath zinc plating, alkaline
cyanide bath zinc plating, alkaline zinc alloy plating such as
zinc-iron, zinc-cobalt, zinc-nickel and zinc-manganese, and
alkaline zinc composite plating such as zinc-silica and zinc-resin.
The zincate bath zinc plating is the most effective among them.
[0015] The invention provides a method for supplying zinc ions to
an alkaline zinc plating solution by means of zinc dissolution,
which utilizes a difference in hydrogen overvoltage between the
source of zinc ions and the zinc dissolution accelerating metal.
The inventors have found out zinc dissolution accelerating metals
that can much improve the zinc dissolution rate and that the zinc
dissolution rate is much increased by a method wherein the source
of zinc ions and the zinc dissolution accelerating metal are put in
a vessel or vessels and moved in a plating solution by shaking,
vibrating or rotating, etc., which causes agitation and mutual
friction, to activate their surfaces. Moreover, the invention has
achieved to provide a stably high dissolution rate and an easy
control of zinc ion concentration in the plating solution.
[0016] As the source of zinc ions in the invention, metal zinc can
be used. In order to make the dissolution rate faster, zinc alloy
comprising zinc and metal that is more electropositive than zinc
such as iron, nickel, cobalt, copper, silver, platinum and gold, or
zinc to whose surface metal that is more electropositive than zinc
such as iron, nickel, cobalt, copper, silver, platinum and gold is
deposited by plating, substituting or the like methods can be
used.
[0017] As the zinc dissolution accelerating metal in the invention,
1) metal that is more electropositive than zinc, 2) metal that is
more electropositive than zinc, with which one or more kinds
selected from iron, cobalt, nickel, carbon, silicon, manganese,
chromium, molybdenum and tungsten are contacted, 3) metal that is
more electropositive than zinc, in which one or more kinds selected
from iron, cobalt, nickel, carbon, silicon, manganese, chromium,
molybdenum and tungsten are dispersed, 4) alloy comprising metal
that is more electropositive than zinc and one or more kinds
selected from iron, cobalt, nickel, carbon, silicon, manganese,
chromium, molybdenum and tungsten, or 5) a composite or mixture of
two or more kinds selected from above 1) to 4) can be used. It is
noted that oxides of iron, chromium, molybdenum and tungsten can be
also used in case of above 3) or 4).
[0018] The followings are the concrete examples of the zinc
dissolution accelerating metal. Almost all kinds of metal that is
more electropositive than zinc can be used but iron, nickel, cobalt
and the like are advantageous from an economical point of view.
Carbon alloyed metal, carbon dispersed metal or metal contacted
with carbon, such as carbon impregnated metal (alloy), carburizing
steel to whose surface carbon is adhered after dissolving its
surface by an acid or the like (combination of alloy and contact),
iron casting such as gray iron casting and malleable iron casting
(combination of alloy and dispersion), carbon dispersed copper
plating, carbon dispersed nickel plating and carbon dispersed
cobalt plating onto metal that is more electropositive than zinc
(combination of dispersion and contact), iron plating, nickel
plating, cobalt plating, copper plating, silver plating, platinum
plating, gold plating and the like onto the surface of carbon
(contact), can be also used. And as metal that includes one or more
kinds among chromium, molybdenum and iron, metal that is more
electropositive than zinc to which chromium oxide, molybdenum oxide
or iron oxide is adhered (contact), dispersed iron plating,
dispersed copper plating, dispersed nickel plating and dispersed
cobalt plating on metal that is more electropositive than zinc
wherein chromium oxide, molybdenum oxide, iron oxide or the like is
dispersed in the plating (combination of dispersion and contact)
and chromium molybdenum steel (alloy), etc, can be mentioned.
[0019] The source of zinc ions and the zinc dissolution
accelerating metal are put in the same vessel and brought into
direct contact with each other or put in different vessels and
connected via an electric conductor, and the vessel or vessels are
shaken, vibrated or rotated, etc. in a plating solution to move the
source of zinc ions and the zinc dissolution accelerating metal,
which causes agitation of solution and mutual friction of metal
surfaces and accelerates the zinc dissolution. Moreover, the
friction maintains an activated state of the surface of the source
of zinc ions and the zinc dissolution accelerating metal and keeps
the dissolution rate high.
[0020] Shapes and materials of the vessels used in the invention
are not particularly restricted, provided that the vessels can
receive the source of zinc ions and the zinc dissolution
accelerating metal. Iron or iron castings which are the zinc
dissolution accelerating metal of the invention can be also used as
materials for the vessels such as baskets or barrels, for
instance.
[0021] Sizes and shapes of the source of zinc ions and the zinc
dissolution accelerating metal are not particularly restricted. But
it is preferred to make their-surface areas larger in order to
increase the amount of zinc dissolution and make operations such as
shaking, vibrating and rotating easier.
[0022] The ratio of the surface area of the source of zinc ions to
that of the zinc dissolution accelerating metal can not strictly be
specified since the surface area of the source of zinc ions
constantly varies due to zinc dissolution and cannot be
determined.
[0023] Thus, zinc dissolution to the plating solution is
accelerated and the rate of zinc dissolution becomes faster than
that of zinc ions consumption by the plating operation. And then,
controlling the degree of contact both or either of the source of
zinc ions and the zinc dissolution accelerating metal have with the
plating solution in response to the analysis of zinc ion
concentration in the plating solution enables automatic control of
zinc ion concentration in the alkaline zinc plating bath, which
contributes to quality stabilization of zinc plating products.
EXAMPLES
[0024] The followings describe examples of supplying zinc ions to
the alkaline zinc plating solution by means of zinc dissolution,
wherein vessels are rotated, which is a representative method of
the invention, and comparative examples, wherein vessels are not
rotated.
[0025] The dissolution test was implemented according to the
following procedure. The test system was prepared in such a manner
that the plating solution was overflowed from a plating bath (3
Litter) to a dissolution bath (2 Litter) and recycled to the
plating bath through a filter. In the plating bath, a temperature
adjusting apparatus and a barrel plating apparatus were provided.
In the dissolution bath, a plastic rotatable mini-barrel apparatus
(5 rpm) was provided (examples 1 to 10 and comparative examples 1
to 12), and a plastic plating mini-barrel containing the source of
zinc and a plastic plating mini-barrel containing the zinc
dissolution accelerating metal were provided and the contents in
the both barrels were connected via the electric conductor
(examples 11 to 14 and comparative examples 13 to 16). As the
plating solution, the following zinc plating zincate bath, zinc
plating cyanide bath, alkaline zinc-iron alloy plating bath and
alkaline zinc-nickel alloy plating bath were used. The following
source of zinc ions and the following zinc dissolution accelerating
metal were put into the rotatable mini-barrels in the dissolution
bath in such ratio that the total surface area of the source of
zinc ions is almost equal to that of the zinc dissolution
accelerating metal and zinc dissolution was implemented. The barrel
or barrels were pulled out of the plating solution in the
dissolution bath to stop zinc dissolution temporarily when zinc ion
concentration in the plating solution increased by 2 g/L.
Subsequently, zinc ion concentration in the plating solution was
decreased by 2 g/L by means of electrodeposition of zinc before the
barrels were again immersed in the plating solution and zinc ion
concentration was increased by 2 g/L. This procedure was repeated 5
times. Time required to increase zinc ion concentration by 2 g/L at
the first time and the fifth time were respectively compared with
the comparative examples.
[0026] Zinc ion concentration was measured every 30 minutes. In
case where zinc ion concentration did not increase by 2 g/L after
480 min of operation, the test was stopped and regarded as "no
increase".
[0027] The followings are the sources of zinc ions, the zinc
dissolution accelerating metals and the plating solutions used in
the example.
[0028] The source of zinc ions;
[0029] A. Zinc grains (diameter 3 to 8 mm)
[0030] B. Iron-substituted zinc grains (diameter 3 to 8 mm)
[0031] C. Nickel-substituted zinc grains (diameter 3 to 8 mm)
[0032] The zinc dissolution accelerating metal;
[0033] (1) Iron grains (diameter about 8 mm)
[0034] (2) Cobalt plating iron grains (diameter about 8 mm)
[0035] (3) Carbon dispersed cobalt plating iron grains (diameter
about 8 mm)
[0036] (4) Iron casting grains (diameter 15 to 30 mm, gray cast
iron)
[0037] (5) Chromium molybdenum steel chips (about 5 mm square)
[0038] (6) None
[0039] The plating solution;
[0040] 1. Zinc plating zincate bath
[0041] zinc ions 10 g/L
[0042] sodium hydroxide 120 g/L
[0043] 2. Zinc plating cyanide bath
[0044] zinc ions 20 g/L
[0045] sodium hydroxide 60 g/L
[0046] sodium cyanide 45 g/L
[0047] 3. Zinc-iron alloy plating bath
[0048] zinc ions 18 g/L
[0049] iron ions 0.3 g/L
[0050] sodium hydroxide 120 g/L
[0051] BASE-R 100 g/L (a complexing agent available from Nippon
Hyoumenn Kagaku Corp.)
[0052] 4. Zinc-nickel alloy plating bath
[0053] zinc ions 10 g/L
[0054] nickel ions 1.8 g/L
[0055] sodium hydroxide 120 g/L
[0056] NI-T 100 g/L (a complexing agent available from Nippon
Hyoumenn Kagaku Corp.)
[0057] The results of examples 1 to 10 and comparative examples 1
to 12 are shown in Table 1, wherein the source of zinc ions and the
zinc dissolution accelerating metal were brought into direct
contact.
[0058] <Table 1>
[0059] The results of examples 11 to 14 and comparative examples 13
to 16 are shown in Table 2, wherein the source of zinc ions and the
zinc dissolution accelerating metal were put in different baths and
connected via the electric conductor.
[0060] <Table 2>
EFFECT OF THE INVENTION
[0061] The above examples showed that contacting the source of zinc
ions with the zinc dissolution accelerating metal and moving them
by rotating, shaking, etc. enables zinc dissolution to accelerate
considerably and zinc to dissolve stably, which allows the size of
the zinc dissolution bath to decrease and contributes to space
saving. Moreover, controlling the degree of contact both or either
of the source of zinc ions and the zinc dissolution accelerating
metal have with the plating solution in the dissolution baths
according to the analysis of zinc ion concentration in the plating
solution enables a stable control of zinc ion concentration and
quality zinc plating products to be provided.
1 TABLE 1 the source of zinc ions-the zinc dissolution accelerating
metal Barrel Dissolution rate (direct contact) rotation 1st time
5th time 1. Zinc plating zincate bath example1 A-(1) Yes 360 min
360 min comparative example1 A-(1) No (*) example2 A-(2) Yes 300
min 300 min comparative example2 A-(2) No (*) example3 A-(3) Yes
120 min 120 min comparative example3 A-(3) No 180 min 240 min
example4 A-(4) Yes 180 min 180 min comparative example4 A-(4) No
240 min 360 min example5 B-(1) Yes 120 min 120 min comparative
example5 B-(1) No 180 min 270 min example6 C-(1) Yes 120 min 120
min comparative example6 C-(1) No 150 min 210 min comparative
example7 A-(6) Yes (*) comparative example8 A-(6) No (*) 2. Zinc
plating cyanide bath example7 A-(2) Yes 300 min 300 min comparative
example 9 A-(2) No 420 min 450 min 3. Zinc-iron alloy plating bath
example8 B-(1) Yes 90 min 90 min comparative example 10 B-(1) No
120 min 180 min 4. Zinc-nickel alloy plating bath example9 A-(5)
Yes 60 min 60 min comparative example11 A-(5) No 120 min 150 min
example10 C-(5) Yes 60 min 60 min comparative example12 C-(5) No 90
min 120 min (*) = The test was stopped after 480 min of operation
because designated increase in zinc ion concentration was not
obtained.
[0062]
2 TABLE 2 the source of zinc ions-the zinc dissolution accelerating
metal (connected via an electric Barrel Dissolution rate conductor)
rotation 1st time 5th time 1. Zinc plating zincate bath example11
A-(1) Yes 450 min 450 min comparative example13 A-(1) No (*)
example12 A-(2) Yes 360 min 360 min comparative example14 A-(2) No
(*) example13 A-(3) Yes 180 min 180 min comparative example15 A-(3)
No 300 min 480 min example14 A-(4) Yes 210 min 210 min comparative
example16 A-(4) No 330 min 450 min (*) = The test was stopped after
480 min of operation because designated increase in zinc ion
concentration was not obtained.
* * * * *