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Патент USA US2411674

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Patented Nov. 26, 1946
2,411,674‘ '
UNITED _' STATES PATENT ' OFFICE, .
ART OF ELEGTRQDEPOSITION OF COPPER
Ernest D. Wilson, Worcester, Mass., assignor to
Arthur D. Little, 1210., Cambridge, Mass., a cor
poration of Massachusetts
.
No Drawing. I Application March 4, 1943, .
'
'
Serial No. 478.009
32 Claims- (Cl. 204-52)
2
I This invention relates to the art of electro- '
deposition of copper.
-
_
.
,
Substantially all commercial copper plating
' processes involve the use of either copper cyanide
'
c
it suitable for subsequent plating directly with—
out any necessity for the mechanical polishing
operations, such as bu?ing, and consequent loss
of the plating metal.
type baths or acid copper baths. Both types or
,
of the electro-deposited plating so as to render
-
Other objects and advantages of the invention
will be apparent to those skilled in the art from
.the following description.
While acid copper baths have the advantage
In accordance with the present invention, I
of high cathode e?lciency and simplicity, they,
cannot be used- commercially for plating iron, in form a; copper plating bath by admixing ‘a suit
able copper salt, an alkylene amine and water.
steel and zinc articles because, with such a bath,
. Various copper salts may be used, for example,
copper is deposited on iron, steel or zinc by immer
copper sulphate, copper acetate or copper car
sion. As a result, it‘ is practically impossible to
bonate. I have found, however, that copper sul
obtain satisfactory electro-depositions on such
15 phate gives the best results. I have also found
metals.
.
that what [are now considered the best results
With copper cyanide plating baths, copper is
are obtained by using ethylene diamine as the I
not deposited by immersion. Consequently, more
bath, however. are subject to various disad- _
vantages.
‘
-
.
I
.l
alkylene amine constituent.
' Other alkylene
or less satisfactory, adherent electro-deposits can
be obtained. While such ‘baths are used exten
amines may, however, be used with reasonably
are objectionable for other reasons.
ample, they have low cathode efficiency and they
the polymers of ethylene diamine, such as di
ethylene triamine or triethylene tetramine, and
are highly poisonous.
propylene diamine.
sively for plating iron, steel and zinc articles, they 20 satisfactory results. These'include, for example,
For ex
They are relatively un
'
-
' '
In carrying out the invention to what is now
stable and their composition must be carefully
controlled and frequently re-adjusted. Also,
25
they tend to pick up carbon dioxide from‘ the
atmosphere, whereby they acquire too high a
considered the best advantage, I also'admix in
the bath'a hydroxy acid, such, for example, as
lacticlacid. Other hydroxy acids, such as citric
acid and tartaric acid, may be used with some
what diiierent results as to the color of copper
acid copper solutions are used, the plated articles’ 30 depositeda Alkali salts of hydroxy acids, such as
sodium lactate and Rochelle salts, may also be
must be buffed. One reason for this is that the
used with reasonably satisfactory results. I have
copper deposit is dull and buffing is necessary to
found, however, that the best results are obtained
obtain the necessary high polish or bright surface
with lactic acid.
'
before the article can be nickel plated or other
j In conjunction. with the presence of the alkyl-'
wise ?nished. Secondly, the copper deposits or
ene polyamine in the electrolytic bath, it is found
film almost invariably contains many “pinholes.”
that the addition of such hydroxy acid or one
Unless the plate is bulied to cause the copper
of its alkali metal salts, and more especially the _
to ?ow over or into these pinholes, the basis metal
carbonate content. >
_ ‘Moreover
'
whether copper cyanide baths or
addition of lactic acid, contributes greatly to the
_
'
The builing operation is commercially disad 40 adherence of the plating deposited to the surface
vantageous because a considerable amount of . of the base metal, to which it is applied in ac
cordance with the present invention. For ex,
hand labor is involved and the cost of buiiing
ample, in the electroplating of steel with copper,
usually greatly exceeds the cost of the plating
.it was found that while thin coatings could be
itself. Furthermore, the bumng operation re
applied satisfactorily without such addition, the
moves ‘some copper and the initial deposit must
. tendency of thick coatings of copper to peel from"
consequently, be thicker than is desired for the
is apt to corrode.
?nished article.
*
It is an object 01' the present invention to pro
vide a ,copper plating solution vand method of
plating such that the objectionable features 01
' copper cyanide and acid copper baths are avoided.
More particularly, it is an object of the inven
tion to provide a plating solution and method of
plating such that copper is not deposited by
immersion‘on iron or zinc; and such that the
resulting electro-deposition is of a character that
does not require bu?ing.
\
,
the base metal was substantially overcome by
making such addition to the electrolyte. In con- _
sequence platings so provided will withstand
impact tests which actually puncture the base
metal, without peeling off.
I have also discovered that improved results
,are obtained if some boric acid is added to the
bath.
,
' The addition of boric acid to the electrolyte is
not essential to the obtainment of the improve
ment in the adherence of-the plating applied to
the base metal. But when added to the electrolyte
as prepared in accordance with this invention, it
metal, as well as a lustrous ?nish to the surface 60 does not interfere with such improvementvand,
Further objects of the invention are to provide
an improved adhesion of the plating to the base
2,411,674
3
4
supplemental thereto, has the very desirable and
advantageous e?ect of imparting a lustrous bril_
necessary in the proportion 01' the other starting
liancy and dense structure to the surface of the
electro-plating deposit so that it may serve di
If the hydroxy acid is not used, the amount
of alkylene amine may be reduced accordingly.
For example, if the lacticacid is omitted from
the formula above set forth, the amount of eth
ylene diamine may be reduced by about 3%
materials.
rectly for the application of subsequent electro
plating operations and deposits without further
preparation or treatment. It thus effects a great
»
saving in operations, equipment and material, as
pounds. Generally speaking, substantially the
well as time.
same ratio may be followed. _Also the pH of the
solution should be adjusted to 8.2 to 8.5 for the
best results. This adjustment may be attained
»
The proportions of the several starting mate
rials may vary within a considerable range.
The
invention may be satisfactorily carried out, how
ever, according to the following example:
I form a bath with the following starting ma
terials (commercial form) :
Copper sulphate (CuSO4.5HzO) ___pounds__
Ethylene diamine (70% ) _________.___do____
by means of sulphuric acid or amine.v While a
bright plate may be obtained without the use of
the hydroxy acid, its use is recommended because
15 it results in a copper deposit having better ad
herent qualities.
50
55
Lactic acid (85%) _______________ __do__.__
11
Boric acid ______________________ __do____ 16%
Water to make ________________ __gallons__ 100
According to the present example ‘I ?rst dis
'
As indicated from the example above given.
with reference to the copper salt present in the
electrolyte, the hydroxy acid, such as lactic acid,
is added in approximately the proportion 01' one
half 9. mol and the boric acid in equimolecular
' proportions. But these may be varied somewhat
solve the copper sulphate in a convenient amount
as indicated by the following‘ranges of propor
of hot water and add the other ingredients with
tions which are satisfactory, with reference to one
su?icient agitation to obtain a proper mix.
25 mol of C11S04.5H2O in solution for example:
The solution may, if desired, be diluted to about
,
.
Mole
twice the volume above set forth or made 24
Lactic acid ______ __‘ _____ _,_ _________ -_ .3to .9
times more concentrated, and still give a good
plate.
Citric acid _' _______________________ __ .3 to .4
_
The articles to be plated are then subjected to 30
the electrolytic action of the bath described, us-'
ing the type or anode ordinarily used in copper
Rochelle salt _______________________ __ .
.2
Boric acid _________________________ __ .7 to 1.75
In general, the alkylene polyamine may ad
vantageously be present in excess of equimolecu
vary, I have found that operation at room tem
lar proportions, with reference to the copper salt,
peratures, at a current density of about 10 am 35 but it may vary considerably (so long as it is not
peres per square foot, gives satisfactory results. . too greatly reduced) without appreciably affect
With the plating bath described, there is no, ing the results to be obtained with the electrolyte
plating.
While the operating conditions may ‘
deposit of copper by immersion on iron or zinc so
that the di?iculty inherent in acid copper solu, tions is avoided.
in question.
'
.
I
‘
.
Accordingly the present invention, by the appli
The solution does not have the 40 cation of the hydroxy acids of the class indi
poisonous character of copper cyanide baths and
is relatively stable, requiring substantially no con
trol or readjustment. With‘ the bath described
the cathode ei?ciency is 100%. There is no evo
lution of hydrogen or gassing in the solution dur '
ing operation.
One of the most important advantages of the
present invention is that articles copper plated‘
in accordance therewith do not require bu?ing.
The bath described givesv a bright plate that re
quires no bu?lng- as a precedent to nickel plating
or other ?nishing. Moreover, the deposit ob
cated or their soluble salts, especially to electro
lytes containing an alkylene polyamine, makes
possible the ready and assured formation of dense,
?rmly adherent electroplatings of copper and also
the provision of a highly lustrous. brilliant, elec
troplated surface when boric acid is also added,
which requires no subsequent treatment such as
buf?ng in order to make the surface satisfactory
as a ?nished product and hence without the mi
nute marks or she'en which is likely to accom
pany the most expert mechanical workmanship
It appears generally to be most favorable, under
tained is extremely ?ne grained with no-“pin
actual operating conditions and for best results,
holes” so that bu?ing is not necessary to protect
to employ the member of the hydroxy acid group,
the basis metal. As a result, there is a marked
such as lactic acid in particular, in a molecular
saving in cost and inconvenience and the serious
proportion relative to one mol of the copper salt
objections to both copper cyanide and acid copper
in solution in'the electrolyte, of from about one
baths are avoided.
'
quarter to about one mol, either when used alone
- A further advantage of the bath described is
or when used in conjunction with the boric acid.
that it has an extremely ‘high throwingv power, 60 With regard to the boric acid a wider range of
even greater than. that or a copper cyanide bath.
proportions of from about one-half mol to about
While the chemical reactions involved are not
two mols, relative to one mol of the copper salt,
entirely understood and need not be understood
such as copper sulphate in solution may be most
to carry out the invention, it is believed that the
effectively employed for the purposes indicated
amine forms with the sulphate a copper complex
of securing both an improved adherent plate and
having a ratio of 2 molecules of amine to one of
at the same time providing a highly polished sur
copper sulphate. This complex is so stable that
face suitable for subsequent direct plating there
I ‘the pH of the solution may be lowered to 2 with
on of other metals such as silver.
out decomposing it. It is believed, also, that the
This is a continuation-in-part of my copend
hydroxy acid forms a copper complex of unknown
ing application Serial No. 185,809, filed January
formula-
20, 1938.
.
The function of the. boric acid is not known.
A good deposit may be obtained without it but
when it is present it appears to result in a brighter
deposit. If the boric acid is omitted, no change is
i
I claim:
1. A. process of electroplating that comprises
.electro-depositing copper as a bright, smooth,
firmly adherent deposit from an undivided cell
‘2,411,674
6
5
electro-depositing copper as a bright, smooth,
containing an aqueous electrolyte consisting es
?rmly adherent deposit-‘from an undivided cell
sentially of-a solublercopper salt and a sufilcient
containing an aqueouselectrolyte consisting es
quantity of an alkylene polyamine to form a com
sentially of a soluble copper salt and a su?icient
plex with said salt, and a compound selected from
the group consisting of lactic, citric and tartaric: Ch quantity of an alkylene polyamine to form a com
' plex with said salt and a'compound selected from
acids and the alkali metal salts of such acids.
the group consisting of. lactic, citric and tartaric
2. A process of electroplating that comprises
acids and the alkali metal salts of such acids, in
electro-depositing copper as a bright, smooth,'
approximately one-half molecular ratio and boric
?rmly adherent deposit from an undivided cell
acid in approximately equal molecular propor
containing an aqueous electrolyte consisting es
sentially of a soluble copper salt and a. su?icient
quantity oi’ an alkylene polyamine to form a com
‘ tion, with reference to the copper salt.
11. A process of electroplating that comprises
*electro-‘depdsiting copper as a bright, smooth,
plex with said salt, boric acid, and a compound
?rmly adherent deposit from an undivided cell
selected from the group consisting of lactic, citric
and tartaric acids and the.» alkali metal salts of 15 containing an aqueous electrolyte consisting es
such acids.
.
sentially of a soluble copper salt and a suf?cient
.
quantity of an alkylene polyamine to form a com
plex with said salt, and a compound selected from
‘the ‘group consisting of lactic, citric and tartaric '
~ 3. A process of electroplating that comprises
electro-depositing. ‘copper as a bright, smooth,
?rmly adherent deposit from an undivided cell
containin'gan aqueous electrolyte consisting es 20 acids and the alkali metal salts 01' such acids in v
the molecular proportion of from about one
fourth mol to about one mol, relative to said cop
sentially of copper sulphate and ‘a su?icient quan- ,
tity of ethylene diamine to form a complex‘ with
said salt and a compound selected from the group
consisting of lactic, citric and tartaric acids and
per- salt.
'
12. A process of electroplating that comprises
the alkali metal salts-of such acids.
I .
~ 25 electro-depositing copper as a bright, smooth,
?rmly adherent, deposit from an undivided cell
4. A\- process of electroplating that comprises
containing an aqueous electrolyte consisting. es
electro-depositing copper as a bright, smooth,
sentially of a, soluble ‘copper salt and a su?lcient
?rmly adherent deposit from an undivided cell
quantity of an alkylene polyamine to form a com
containing an aqueous electrolyte consisting es
sentially of copper sulphate and a su?icient quan 30 plex with said salt, about one-half mol to about
two mols of boric acid, and a compoundv selected
tity of ethylene diamine to form a complex with
from the group consisting of lactic, citric and tar
said salt, boric acid, and a compound selected
taric acids and the alkali metal salts of such acids
from the group consisting of lactic,,citric and
in the molecular proportion of from about one
tartaric acids and the alkali metal salts of. such
acids.
,
35 i'ourth mol to about one mol, relative to said cop,-v
per salt.,
~, l
‘
5. A process of electroplating that comprises
13. A process of electroplating that comprises
electro-depositing copper as a bright, smooth,
?rmly adherent deposit from an undivided cell ‘.electrodepositing copper as a bright, smooth, ?rm
ly adherent deposit from an undivided cell'icon
containing an aqueous. electrolyte consisting es
sentially of a soluble copper salt and a su?lcient 40 taining an aqueous electrolyte consisting essen
tially of a soluble copper salt and a su?lcient, quantity of an alkylene polyamine to form a com
quantity of an alkylene polyamine to form a com
plex with said salt, and lactic acid.
,
plex with said salt, and lactic acid in the molec
_ 6. A process of electroplating that comprises
.electro-depositing copper as .a bright, ‘smooth, , ular- proportion of from about one-fourth mol ~
to about one mol, relative to said copper salt.
?rmly adherent deposit from an undivided cell
14; A process of ‘electroplating that comprises
containing an aqueous electrolyte consisting es
electro-depositing copper as a bright, smooth.
sentially of a soluble copper salt and a sui?cient
?rmly adherentdeposit from an undivided cell
quantity of an alkylene polyamine to form a com
containing an aqueous electrolyte consisting es- _ '
plex with said salt, and boric and lactic acids.
sentially of a'soluble copper salt and a su?icient' ‘
7. A process of electroplating that comprises
quantity of an alkylene polyamine to form a com
electro-depositing copper as a bright,-smooth,
plex'with said salt, aboutbne-hali ‘mol to about
?rmly adherent deposit from an undivided‘ cell
containing an aqueous electrolyte consisting es
' molecularproportion
two molsof boric acid,
of 'and'lactic
from ‘about acid
one-fourth
in‘the'
sentially 01’ copper sulphate and a su?lcient quan- _
mol to‘ about one mol, relative to said copper
tity of ethylene diamine to form, acomplex with
1 said salt, and lactic acid.
_
8. A process of electroplating ‘that comprises
electro-depositing copper as a bright, smooth,
salt.
‘
-
15. A process of electroplating that comprises
electro-depositing copper as'a bright, smooth,
?rmly adherent depositlfrom an undivided cell
containing, an aqueous electrolyte consisting es 60 contalning an aqueous electrolyte consisting es
fsentially of copper sulphate and a su?lcient
sentially 01' copper sulphate and a su?lcient quan
quantity of ethylene diamine to form a complex
tity of ethylene diamine to form a complex with
with~said salt, and a compound selected from the
said salt, and boric and lactic acids.
, ?rmly adherent deposit from an undivided cell
group consisting of lactic, citric and tartaric
9. ‘A process of electroplating that comprises
electro-depositing copper as a bright, smooth, 65 acids and the alkali metal salts of such acids in
?rmly adherent, deposit, from an undivided vcell
"containing an aqueous electrolyte consisting-es
' sentially of a soluble copper salt and a su?icient
quantity of an alkylene polyamine to form a com
the molecular proportion of from about one
fourth mol to about one mol, relative to said
copper sulphate.
16. A process of electroplating that comprises
plex with said salt and a compound selected from 70 electro-depositin'g copper as'a bright, smooth,
?rmly adherent ‘deposit from an undivided cell
the group consisting of lactic, citric and tartaric
' acids and the alkali metal salts of such acids in
containing an aqueous electrolyte consisting es
approximately one-half molecular ratio with ref
sentially of copper sulphate and a suillcientv
erence to the copper salt.
quantity of ethylene diamine to form a complex
'
10. A process of electroplating that comprises 75 with said salt, about one-half mol to about two
, I
'
assume
8
mole of boric acid, and a compound selected from
the group consisting of lactic, citric and tartaric
26. An aqueous electrolyte for use in the elec
trodeposition of copper as a bright, smooth, ?rm
acids and the alkali metal salts of such acids in
ly adherent deposit that consists essentially of a
soluble copper salt, a su?icient quantity of an
the molecular‘ proportion of from about one
alkylene polyamine to form a complex with said
fourth mol to about one mol, relative to said
copper sulphate.
salt and a compound, selected from the group
17. An aqueous electrolyte for use in the electro
consisting of lactic, citric and tartaric acids and
deposition of copper as a bright, smooth, ?rmly
the alkali metal salts of such acids, in approxi_
adherent deposit that consists essentially of a
mately one-half molecular proportion and boric
soluble copper salt and a sufficient quantity of 10 acid in approximately equal molecular propor
an alkylene polyamine to form a complex with
tion, with reference to the copper salt.
said salt, and a compound selected from the
27. An aqueous electrolyte for use in the elec
group consisting‘ of lactic, citric and tartaric acids
trodepositlcn of copper as a bright, smooth, ?rm- _
and the alkali metal salts of such acids.
18. An aqueous electrolyte for use in the elec
tro-deposition of copper as a bright, smooth, ?rm
ly adherent deposit that consists essentially of a‘
ly adherent deposit that consists essentially of
salt, and a compound selected from the group
soluble copper salt and a su?lcient quantity of an
alkylene polyamine to form a complex with said
a soluble copper salt and a sufficient quantity of
consisting of lactic, citric and tartaric acids and
an alkylene polyamine to form a complex with
the alkali metal salts of such acids in the molec
said salt, borlc acid, and a compound selected 20 ular proportion of from about one-fourth mol to
from the group consisting of lactic, citric and
about one mol, relative to said copper salt.
tartaric acids and the alkali metal salts of such
28. An aqueous electrolyte for use in the elec
trodeposition of copper as a bright, smooth, ?rm
acids.
19. An aqueous electrolyte for use in the elec
ly adherent deposit that consists essentially of a
tro-deposition of copper as a bright, smooth, ?rm 26 soluble copper salt and a sufficient quantity of an
ly adherent deposit that consists essentially of
copper sulphate and a su?lcient quantity of
ethylene diaminc to form a complex with said salt,
and a compound selected from the group con
sisting of lactic, citric and tartaric acids and the
alkali metal salts of such acids.
20. An aqueous electrolyte for use in the electro
deposition of copper as a bright, smooth, ?rmly
adherent deposit that consists essentially of cop
alkylene pclyamine to form a complex with said
salt, about one-half mol to about two mols oi’
borlc acid, and a compound selected from the
group consisting of lactic, citric and tartaric acids
and the alkali metal salts vof such acids in the
molecular proportion of from about one-fourth
mol to about one mol, relative,to said copper salt.
29. An aqueous electrolyte for use in the elec
trodeposition of copper as a bright, smooth, ?rm
per sulphate and a suihcient quantity of ethylene 35 ly adherent deposit ‘that consists essentially of
diamine to form a complex with said salt, boric
a soluble copper salt and a su?lcient quantity of
acid, and a. compound selected from the group
an alkylene polyamine to form a complex with
consisting of lactic, citric and tartaric acids and
said salt, and lactic acid in the molecular pro
the alkali metal salts of such acids.
portion of from about one-fourth mol to about
21. An aqueous electrolyte for use in the electro 40 one mol, relative to said copper salt.
1
deposition of copper as a bright, smooth, ?rmly
30. An aqueous electrolyte for use in the elec»
adherent deposit that consists essentially of a
trodeposition of copper as a bright, smooth, ?rm
- ‘soluble copper salt and a suf?cient quantity of
ly adherentdeposit that consists essentially of a
an alkylene polyamlne to form a complex with
soluble copper salt and a su?icient quantity of
said salt, and lactic acid.
an alkylene polyamine to form a complex with
22. An aqueous electrolyte for use in the e1ec
said salt,yabout one-half mol to about two mols of
trodeposition of copper as a bright, smooth, ‘?rm
boric acid and lactic acid in the molecular pro~
ly adherent deposit that consists essentially of a
portion of from about one-fourth mol to about
soluble copper salt and a su?icient quantity of an
one mol, relative to said copper salt.
alkylene polyamine to form a complex with said
31. An aqueous electrolyte for use in the elec
salt, and boric and lactic acids.
trodeposition of copper as a bright, smooth, ?rm
23. An aqueous electrolyte for use in the elec
ly adherent deposit that consists essentially of
trodeposition of copper‘as a bright, smooth, ?rm
copper sulphate and a su?lcient quantity of eth
ly adherent deposit that consists essentially of
ylene diamine to form a complex with said salt,
copper sulphate and a suiiicient quantity of eth
and a compound selected from the group con
ylene diamine to form a complex with said salt,
sisting of lactic, citric and tartaric acids and the
and lactic acid.
I
‘
alkali metal salts of such acids in the molecular
24. An aqueous electrolyte for use in the elec
proportion of from about one-fourth mol to about
trodeposition of copper as a bright, smooth, ?rm
one mol. relative to said copper sulphate.
1y adherent deposit that consists essentially of 60
32. An aqueous electrolyte for use in the elec
copper sulphate and a sumcient quantity oieth
trodeposition of copper as a bright, smooth, ?rm_
ylene diamlne to form a complex with said salt,
ly adherent deposit that consists essentially of
and toxic and lactic acids.
1
-
copper sulphate and a su?lcient quantity of eth~
ylene diamine to form a complex with said salt,
65 about one-half mol -to about two mols of boric
1y adherent deposit that consists essentially of a
acid, and a compound selected from the group
soluble copper salt, a su?icient quantity of an
consisting of lactic. citric and tartaric acids and
alltylene polyamine to form a complex with said
the alkali metal salts of such acids in the molec
salt, and a compound. selected from the group
ular proportion of from about one-fourth mol to
consisting of lactic, citric and tartaric acids and 70 about one mol, relative to said copper sulphate.
the alkali metal salts of such acids, in approxi
mately one-half molecular proportion, with reti
ERNEST D. WILSON.
erence to the copper salt.
25. An aqueous electrolyte for use in the elec
trcdeposition of copper as a bright, smooth, firm
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