U.S. patent number 3,634,212 [Application Number 05/035,261] was granted by the patent office on 1972-01-11 for electrodeposition of bright acid tin and electrolytes therefor.
This patent grant is currently assigned to M & T Chemicals Inc.. Invention is credited to Frank Passal, Sylvester Paul Valayil.
United States Patent |
3,634,212 |
Valayil , et al. |
January 11, 1972 |
**Please see images for:
( Certificate of Correction ) ** |
ELECTRODEPOSITION OF BRIGHT ACID TIN AND ELECTROLYTES THEREFOR
Abstract
Improved baths or solutions are provided for the electroplating
of tin, and containing as the primary brightener therefor the
reaction product of furfural with crotonaldehyde in the presence of
a catalytic amount of an alkali. In addition, this invention is
concerned with brightening additive compositions for
tin-electroplating baths, and with methods for preparing such
additive compositions and for electroplating bright tin
deposits.
Inventors: |
Valayil; Sylvester Paul
(Detroit, MI), Passal; Frank (Detroit, MI) |
Assignee: |
M & T Chemicals Inc. (New
York, NY)
|
Family
ID: |
21881579 |
Appl.
No.: |
05/035,261 |
Filed: |
May 6, 1970 |
Current U.S.
Class: |
205/104; 205/304;
549/483; 549/498 |
Current CPC
Class: |
C07D
307/46 (20130101); C25D 3/32 (20130101) |
Current International
Class: |
C07D
307/00 (20060101); C07D 307/46 (20060101); C25D
3/30 (20060101); C25D 3/32 (20060101); C23b
005/14 (); C23b 005/46 () |
Field of
Search: |
;204/54R,54L,43,44,120
;106/1 ;117/13E ;260/347.8 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Kaplan; G. L.
Claims
While the methods and compositions herein disclosed form preferred
embodiments of this invention, this invention is not limited to the
specific methods and compositions, and changes can be made therein
without departing from the scope of this invention which is defined
in the appended claims.
1. An aqueous acid bright tin-electroplating solution including a
tin salt, free acid, and, as the primary brightener therefor, an
amount sufficient to produce a bright tin electrodeposit, of a
yellow brown liquid reaction product characterized as being
produced by the steps which comprise placing furfural and
crotonaldehyde as reactants in a reaction zone, said reactants
being placed in said reaction zone in the ratio in the range
between equimolar quantities and 15-percent mole excess of
furfural; maintaining the temperature of the said reaction zone
between about -5.degree. and 50.degree. C.; reacting the said
reactants in the presence of a catalytic amount of an alkali to
obtain a reaction product; adding an acid to said reaction product
for the acidification thereof; and separating the reaction product
from the acid reaction zone.
2. A solution as recited in claim 1 in which about 10-percent mole
excess of furfural to crotonaldehyde is added to said reaction
zone.
3. A solution as recited in claim 2 and including as the secondary
brightener formaldehyde.
4. A solution as recited in claim 3 and including a wetting
agent.
5. A solution as recited in claim 4 in which said wetting agent is
nonionic.
6. A solution as recited in claim 4 in which said wetting agent is
a polyethoxylated nonyl phenol having an average of 15 oxyethylene
groups.
7. A solution as recited in claim 1 which comprises the steps of
dissolving sodium hydroxide in water, carrying out the reaction
step by adding the aqueous solution of sodium hydroxide dropwise to
said reaction zone, and in which the contents of said reaction zone
are stirred during the reaction step.
8. A solution as recited in claim 7 and including as the secondary
brightener formaldehyde.
9. A solution as recited in claim 26 and including a wetting
agent.
10. A solution as recited in claim 8 in which said wetting agent is
nonionic.
11. A solution as recited in claim 8 in which said wetting agent is
a polyethoxylated nonyl phenol having an average of 15 oxyethylene
groups.
12. A solution as recited in claim 1 wherein the said separating
step is carried out by extracting the reaction product by the
addition of a plurality of separate portions of chloroform, and
withdrawing the chloroform from the product in said extracting step
to obtain the reaction product of the said reacting step.
13. A solution as recited in claim 12 and including as the
secondary brightener formaldehyde.
14. A solution as recited in claim 13 and including a wetting
agent.
15. A solution as recited in claim 14 in which said wetting agent
is nonionic.
16. A solution as recited in claim 14 in which said wetting agent
is a polyethoxylated nonyl phenol having an average of 15
oxyethylene groups.
17. A solution as recited in claim 1 and including as the secondary
brightener formaldehyde.
18. A solution as recited in claim 17 and including a wetting
agent.
19. A solution as recited in claim 18 in which said wetting agent
is nonionic.
20. A solution as recited in claim 18 in which said wetting agent
is a polyethoxylated nonyl phenol having an average of 15
oxyethylene groups.
21. In a method for electrodepositing bright tin on an article and
having tin as the anode, a source of plating current and means
providing current flow communication from said source to said
anode; the steps which comprise making said article the cathode in
an aqueous solution as recited in claim 19, directing a plating
current from said source to said anode through flow communication
means, and plating tin from said anode onto said article.
22. A method as recited in claim 21 which includes the additional
step of sequentially applying and interrupting plating current
through said flow communication means.
23. A method as recited in claim 23 in which said sequence provides
for the application of current for a period of time between about
10 and 20 seconds, and the interruption of current for a period of
time of between about 1 and 5 seconds.
24. A method as recited in claim 23 in which said current
application portion of the sequence is for 10 seconds and said
current interruption portion of the sequence is 2 seconds.
25. A method as recited in claim 21 in which said reacting step is
carried out in the presence of an aqueous solution of sodium
hydroxide.
26. A method as recited in claim 25 which includes the additional
step of dissolving sodium hydroxide in water, and in which said
reacting step is carried out by adding the aqueous solution of
sodium hydroxide dropwise to said reaction zone, and in which the
contents of said reaction zone are stirred during the said reacting
step.
27. A method as recited in claim 21 in which about 10-percent mole
excess of furfural to crotonaldehyde is added to said reaction
zone.
28. A method as recited in claim 21 in which the said separating
step is carried out by extracting the product by the addition of a
plurality of separate portions of chloroform, and withdrawing the
chloroform from the product in said extracting step to obtain the
reaction product of the said reacting step.
Description
Generally speaking, this invention relates to electrolytic tin
plating. More particularly, this invention relates to new and
improved baths and methods for electroplating of bright acid tin
deposits, to brightening additive compositions for
tin-electroplating baths and to methods for the preparation of such
additive compositions.
Bright acid tin deposits are being used increasingly for such
applications as printed circuits for the various components of
devices used in the electronics industry, parts used to establish
electrical contacts, and for such purposes as tools and implements
for handling packaging in the food products industry. In printed
circuit applications, for example, it is most important that the
deposits be bright because such bright deposits provide added
protection to the circuits for later handling in that they protect
the circuits much better from finger staining. In addition, the
bright deposits, for reasons which are not completely understood,
solder easier in later handling and/or connection of the circuits
when they are incorporated into various devices being used.
Further, as will be understood, bright tin deposits utilized in the
electronics industry for printed circuits, and in other
applications involve mass production techniques in which literally
thousands of the same object may be produced in a single production
run. Thus, it is most important that baths for such tin deposits
provide consistency and ease of operation because mass production
techniques require the processes providing the products therefor to
be economically feasible.
In plating bright tin, different well-known procedures may be
utilized including rack plating in which items to be plated are
suspended on insulated fixtures (or racks), and barrel plating. In
rack plating, a single item may be plated or a plurality of that
item, or there may be different parts to be plated of a variety of
sizes and configurations. Further, parts may be bulk plated, in
which generally smaller parts, usually all the same and which lend
themselves to a tumbling action, are disposed in a rotating
barrel.
In electroplating, because of the size, number, and shape
complexity of the parts being plated, it is important that the bath
be formulated in a manner to provide the widest possible bright
plate current density range. Furthermore, it is important that the
limiting current density (the current density at which the deposit
ceases to be sound in structure and appearance) be as high as
possible to allow for the wide variations in cathode current
density which may be encountered due to the size and shape
complexity of the parts being plated.
Commercially used bright acid tin-plating solutions in the past
generally have contained as brighteners such materials as tar and
tar fractions obtained in the destructive distillation of wood.
Such electrolytes are difficult to control, and it is not readily
possible to produce bright tin plates of consistent quality from
them over extended periods of time. Furthermore, tin deposits
obtained by many of the prior art baths suffered from the fact that
the resultant tin deposits did not have the required brightness to
be esthetically acceptable for certain purposes and/or to provide
such protection as a nonfinger-staining deposit for electronic
circuitry. In addition, many of the prior art baths may suffer from
certain operational problems such as extreme sensitivity to
agitation and the degree of agitation leading to striated
deposits.
By contrast, and quite unexpectedly, it has now been found, in
accordance with this invention, that by incorporating in otherwise
conventional acid tin baths, as one of the cooperating additives
therefor, the product obtained from the reaction of furfural and
crotonaldehyde, hereinafter referred to as primary brightener, that
tin deposits are obtained of enhanced brightness and in a fully
reproducible manner. Furthermore, cooperating brightening additives
and baths incorporating them, in accordance herewith, provide
enhanced bright deposits simultaneously with less cost, ease of
operation and consistency of results. In addition, the primary
brightener of this invention cooperates with known materials of the
prior art, such as secondary brighteners, and wetting agents, as
well known, which improve brightness and/or widen the effective
operating bright plate cathode current density range in which the
desired brightness for the deposits is obtained. With such an
arrangement, therefore, much less control is necessary over
extended periods of time thus making the arrangements and baths in
accordance herewith especially appropriate for mass production
techniques.
A further feature of this invention provides a method for bright
tin electroplating in which an otherwise conventional acid
tin-electroplating bath is utilized incorporating the primary
brightener in accordance herewith simultaneously with application
of a current interruption procedure in which current is applied
with the periodic momentary interruption thereof. This is carried
out in a specific predetermined cycle to provide deposits of even
greater continuity and luster than is achieved with the new primary
brightener here utilizing the usual steady current application
procedures.
The cooperating additives which may be employed in cooperation with
the primary brightener, in accordance herewith, may include
nonionic-alkoxylated wetting agents, and formaldehyde as the
secondary brightener, as well known. The wetting agent serves to
transform the loosely adherent, spotty, sometimes dendritically
crystalline tin deposit from an additive-free bath into a dense,
continuous, adherent, microcrystalline deposit. Formaldehyde acts
as a cathode depolarizer when used in cooperation with the wetting
agent and other additives in the bath to help increase cathode
current efficiency. When the formaldehyde is used only with the
wetting agent, and in the absence of the primary brightener in
accordance with this invention, an unsatisfactory deposit is
obtained.
Accordingly, it is one object of this invention to provide improved
baths or solutions for obtaining tin deposits having enhanced
brightness characteristics. In addition, it is another object of
this invention to provide a primary brightener for otherwise
conventional bright acid tin-plating baths.
It is a further object of this invention to provide methods for
preparing such additive compositions and methods for electroplating
bright tin deposits in which the primary brightener additive, in
accordance herewith, is utilized in combination with already known
secondary brighteners to provide enhanced brightness
characteristics over a much wider cathode current density range and
in a manner whereby the baths require relatively little control and
improved ease of operation. Additionally, methods are provided for
bright tin electroplating utilizing the improved baths, in
accordance herewith, simultaneously with an improved application of
current in a specific cycle of periodic current interruption.
With the foregoing and additional objects in view, this invention
will be described in more detail and other objects and advantages
will be apparent from the following description and the appended
claims.
Before describing this invention in more detail, it may be well to
note that this invention has been found applicable to a wide
variety of conventional acid tin baths such as, for example, baths
containing a bivalent tin salt, such as tin sulfate or tin
fluoroborate and an acid, such as sulfuric acid or fluoboric acid.
Furthermore, the compositions and methods herein are applicable to
other barrel-and-rack electroplating processes. The concentrations
of tin and free acid may be varied generally within the limits
conventional in this art. For example, a tin content of 10 to 100
g./1. and a free acid concentration of 20 to 200 g./1. are typical
of the sulfate, fluoborate, and aromatic sulfonate solutions known
in themselves, which may be utilized with the brightener of the
invention herein. Sulfuric, fluoboric and aromatic sulfonic acids
may be present simultaneously in the electrolytes in a manner not
novel in itself.
Such process variables as the configuration of the object which is
made the cathode during the plating process, the desired rate of
depositions, etc., will determine, in many cases the exact
composition of the plating bath, as well known. Furthermore, known
antioxidants used in acid tin-plating solutions may be utilized
when employed in the tin-plating solutions of the invention in
small amounts. The temperature of the plating solution is generally
ambient, and preferably held below 35.degree. C. and within the
range of between about 15.degree. - 20.degree. C. for optimum
plating performance.
In considering generally the conditions for achieving the most
enhanced results in connection herewith, which conditions are more
specifically set forth below, one may note that satisfactory tin
deposits are realized by introducing into an otherwise conventional
acid tin plating bath an amount of the primary brightener, in
accordance herewith, in substantially the same amount as the amount
of an already known primary brightener formulation which would be
introduced for the same purpose. In formulating the baths in
accordance herewith, the amounts and/or concentrations of the
secondary brightener and wetting agent will vary considerably
depending on the results desired.
As purely illustrative of acid tin-plating baths which may be used,
in accordance herewith, one may note the following bath
formulation:
Stannous sulfate (SnSO.sub.4) 30 g./l. Concentrated sulfuric acid
(S.G. 1.84) 105 ml./l. Primary brightener 0.25 g./l. Carrier 4
g./l. Secondary brightener 10 ml./l.
The secondary brightener is preferably formaldehyde in a 37 percent
solution. The carrier may be any well-known nonionic-alkoxylated
wetting agent, such as, for example, Tergitol NonIonic NP-35, a
product of Union Carbide and being a polyethoxylated nonyl phenol
having an average of 15 oxyethylene groups. The wetting agent is
generally added as an aqueous stock solution in the amount of 400
g./l., and added to the bath at a concentration of 40 ml./l., or 4
percent by volume. The primary brightener generally is added in the
form of a stock solution in an organic solvent such as, for
example, Cellosolve, ethylene glycol monoethyl ether, in the amount
of preferably 25 g./l. The stock solution is added to the bath at a
concentration of 10 ml./l., or 1 percent by volume.
As a further feature of this invention, it has been found that by
using a periodic current interruption cycle during plating, that
further enhanced results are achieved, in accordance herewith, of
deposits of brightness improved even over those deposits obtained
by utilizing the primary brightener in accordance herewith in
otherwise conventional acid tin-plating baths and procedures
without the periodic current interruption cycle taught herein. For
example, in utilizing the representative bath noted above, with an
ambient operating temperature, anodes of pure tin and a cathode
current density of between about 10-30 a.s.f., and cathode rod
agitation, that if periodic current interruption is applied in a
cycle of 10-seconds plating current followed by 2-seconds current
interruption, deposits of surprisingly increased brightness are
achieved. Whereas the sequence of periodic current interruption
noted above is preferred, it has been found, in accordance herewith
that a sequence within the range of between about 10-20 seconds
plating time followed by between about 1-5 seconds of current
interruption may be utilized in accordance herewith.
Although the periodic current interruption cycle may be used both
for rack-and-barrel plating, it is of particular advantage for rack
plating because in rack plating generally only moving cathode
rod-type agitation can be used, which does not always provide
sufficient agitation to maintain proper concentration of
brightening additives, especially adjacent the cathode surface.
With utilization of the periodic current interruption cycle, in
accordance with this invention however, these difficulties are
overcome because it has been found, in accordance herewith, that
during the current interruption period, fresh brightener diffuses
into the cathode film, thereby replenishing the brightener, and
providing enhanced luster which advantage has not been found before
in bright acid tin plating.
In considering generally the conditions for preparing the primary
brightener, in accordance herewith, it may be well to note that
satisfactory results have been achieved and under satisfactorily
and economically attractive conditions on commercial scale
operations by reacting furfural and crotonaldehyde in the range of
between about equimolar quantities and 15-percent mole excess of
furfural, and preferably about 10-percent mole excess of furfural
in the presence of a catalytic amount of an alkali, preferably
sodium hydroxide and preferably in an aqueous solution, although an
organic solvent may be employed, if desired, such as, for example,
Cellosolve, ethylene glycol monoethyl ether produced by Union
Carbide, or dioxane.
For example, 1.1 mole of furfural and 1 mole of crotonaldehyde may
be reacted. An excess of crotonaldehyde should be avoided because
it has been found that excessive concentrations of crotonaldehyde
may result in a self-polymerization product which is to be avoided
as it has been found to produce striations in the final deposits.
The reaction temperature is generally maintained within the range
of between about -5.degree. and 50.degree. C., and preferably
between about 0.degree. and 25.degree. C. Although effective
results have been achieved in the higher operating ranges, and even
up to the maximum of 50.degree. C., it appears from subsequent use
that the brightening constituents of the primary brightener herein
are obtained in higher concentrations when the lower operating
temperatures are utilized.
As purely illustrative of a procedure for obtaining the primary
brightener in accordance herewith, one may note example 1 below, in
which equimolar quantities of furfural and crotonaldehyde were
reacted.
EXAMPLE 1
41.4 ml. of furfural (0.5 mole) and 45 ml. of 90 percent
crotonaldehyde (0.5 mole) were added to 200 ml. of water. The
suspension obtained was cooled with an ice-salt bath to a
temperature within the range of between about -1.degree. and
+4.degree. C. 4 grams of sodium hydroxide (0.1 mole) were dissolved
in 50 ml. of water. The sodium hydroxide solution was thereafter
added to the aldehyde suspension drop by drop with cooling and
stirring. After the addition of the sodium hydroxide solution
during which a maximum temperature of 15.degree. C. was reached,
the stirring was continued for another 2 hours. Thereafter, the
solution was acidified to litmus with glacial acetic acid. The
bottom layer of product was extracted with three 150 ml. portions
of chloroform. The chloroform extract was then dried over anhydrous
magnesium sulfate and filtered. Thereafter, the low-boiling
components were removed under aspirator vacuum, keeping the bath at
a temperature of between about 70.degree. -80.degree. C. 83 grams
of reaction product were obtained. The product was a yellow brown
liquid, appearing slightly viscous.
The reactants for carrying out the procedure noted in example 1 are
readily available as commercial products. For example,
crotonaldehyde is available from Union Carbide as crotonaldehyde 89
percent in drum quantity, and furfural is available in almost 100
percent purity from Quaker Oats Company.
As further illustrative of methods, in accordance herewith for
obtaining the primary brightener of this invention, one may note
examples 2 and 3 below.
EXAMPLE 2
205 ml. of furfural (2.5 moles), 225 ml. of 90 percent
crotonaldehyde (2.5 moles) and 500 ml. of water were mixed and
cooled in an ice-salt bath. When the temperature went down below
0.degree. C., a solution of 20 grams of sodium hydroxide (0.5 mole)
dissolved in 150 ml. of water was added drop by drop with stirring
and cooling. A maximum reaction temperature below 20.degree. C. was
maintained.
After the addition of the sodium hydroxide solution, the resulting
solution was stirred for another 3 hours. 35 ml. of glacial acetic
acid (a slight excess of 0.5 mole) was added with stirring. The
reaction mixture was transferred to a 2-liter separatory funnel.
200 ml. of saturated sodium chloride solution were added to
facilitate the separation of the two layers. The bottom layer
containing the active component was separated (394 grams).
The aqueous layer was extracted with chloroform and 28 grams more
of a thick yellow brown liquid were obtained, to give a total
combined yield of 422 grams of primary brightener.
EXAMPLE 3
Reaction vessel:
25-gallon stainless steel container immersed in 100-gallon plastic
tank filled with crushed ice.
Materials:
Furfural (Quaker Oats) 6 gallons Crotonaldehyde (Union Carbide
anhydrous) 5 gallons Water 10 gallons Sodium Hydroxide 840 g. C.P.
pellets in 1 gal. water Glacial Acetic Acid 1,700 ml.
Procedure:
The furfural, crotonaldehyde and water were stirred together and
cooled to 1.degree. C. The NaOH solution was added slowly to the
mixture and when a total of 800 ml. had been added the temperature
began to rise. At about 45.degree. C. an internal tantalum coil
with 4.degree. C. water running through it was installed and the
maximum temperature rise was to 50.degree. C. within a time of
about 1 hour. When the temperature had been reduced to about
15.degree. C. after about 1 hour, the remainder of the NaOH
solution was added and no further rise in temperature occurred.
The mixture was then stirred for 4 hours and 1,700 ml. of glacial
acetic acid were added in small increments to pH of about 6.0. The
reaction mixture was allowed to stand overnight and the aqueous top
layer was siphoned off. The thick remaining material was
transferred into 13 polyethylene 1-gallon containers. These were
allowed to stand to effect further separation of water which was
then decanted off. Total weight of product was about 120
pounds.
Although aqueous solutions were used in the three examples noted
above, it is within the purview of this invention that syntheses
may be carried out in which the reactants are dissolved in organic
solvents such as, for example, Cellosolve and dioxane, as separate
solvents. With such an arrangement, only a trace of sodium
hydroxide is sufficient to initiate the reaction and the products
obtained are essentially the same as those utilizing the aqueous
medium. The products obtained either in the aqueous or solvent
media have been found useful as the novel primary brightener, in
accordance herewith.
Although the exact identity and/or content of the reaction product
obtained for use as the primary brightener, in accordance herewith,
is not known it can be theorized that the product is comprised of a
plurality of components each of which may cooperate with the other
components in order to provide the enhanced results achieved in
accordance herewith. Although the exact identity and concentration
of each component is not known, it can be theorized further that
perhaps some of the components may be inert, or at least
brightener-inactive and that some interact in a manner not known in
order to provide the enhanced results obtained.
Although these components are not known, it can be theorized that
they may be comprised of such possible components as
2-furylacrolein; 2-furylpentadienal; 2-(1-hydroxy ethyl)
3-(2-furyl)-acrolein and acetaldehyde, and perhaps even some
unreacted starting materials. However, in certain tests carried
out, it was found that the proposed possible individual components
such as, for example, 2-furylacrolein, furfural and crotonaldehyde
do not provide any brightening action at all in the conventional
acid tin baths noted above. These proposed individual components
have not proved effective in combination in any known testing
procedures of the various individual combinations which can be made
from these proposed components. Thus, it can be theorized that the
entire reaction product obtained from syntheses such as those noted
above in examples 1-3, are necessary to achieve the results noted
in accordance herewith and that there is some cooperation, not
understood, which is necessary between some or possibly all the
components, to achieve the results, in accordance herewith.
As noted above, enhanced results are achieved in utilizing the
reaction products substantially the same as those obtained in the
three examples noted above as the primary brightener in otherwise
conventional bright acid tin-plating baths. This primary brightener
and/or additive cooperates with other additives to give a lustrous
deposit throughout a very wide current density range. The degree of
luster will depend on the degree of agitation, concentration of
brightener and how the current is manipulated. The periodic current
interruption noted above will markedly increase the rate of
brightening. The deposits obtained are very lustrous, and may have
a very slight haze providing an esthetically pleasing sheen to the
deposit. In addition, good low current density luster is obtained
in addition to good adhesion of the deposits on the metallic
substrate being coated. A large plurality of metallic substrates
may be plated in accordance herewith including iron, copper,
nickel, cobalt, and a variety of alloys containing these metals,
etc.
The range of concentration of the primary brightener, in accordance
herewith, contained in the bath will vary widely depending upon the
results attempting to be achieved, and the various other additives
and components of the bath. However, too low a content will result
in a grey to dull, nonuniform, somewhat grainy deposit. On the
other hand, too high a concentration level does not seem to do any
particular harm although the rate of consumption of the additive
may be increased, thus increasing the cost of the operation.
Generally, it can be said that the range of primary brightener in
the bath will be between about 0.1 g./l. and 1 g./l., with a
preferred range being between about 0.2 g./l. and 0.4 g./l.
As further illustrative of the results achieved in accordance
herewith, one may note the following examples in which a plurality
of Hull Cell tests were carried out utilizing the reaction products
of the examples 1-3, inclusive noted above.
EXAMPLE 4
Into a standard Hull Cell equipped with a magnetic stirrer to
provide mild agitation there were introduced 250 ml. of an acid tin
stock solution containing 30 g./l. SnSO.sub.4 and 105 ml./l. of
C.P. concentrated sulfuric acid (Sp. Gr. 1.84). To the solution
there were added 4 g./l. Tergitol NonIonic NP-35. A polished brass
panel was cleaned, given a 1-minute cyanide copper strike and after
water rinsing, dilute acid dipping and water rinsing was immersed
in the Hull Cell at a cell current of 1 ampere for 5 minutes at
room temperature.
The deposit obtained was dull white, uniform and smooth and gave
good low current density coverage.
EXAMPLE 5
Example 4 was repeated after adding as an additional bath component
10 ml./l. of 37 percent formaldehyde solution.
The high current density one-third of the panel area had a
nonuniform, dark, smutty deposit while the remainder of the plated
area was dull white as in example 4.
EXAMPLE 6
Example 5 was repeated after adding as an additional bath component
0.25 g./l. of the primary brightener of example 1 as a 25 g./l.
stock solution in Cellosolve.
The deposit obtained was uniformly lustrous throughout the entire
current density range of 0 to about 6 amperes per square decimeter
(ASD) and had a pronounced gloss.
EXAMPLE 7
In this example, example 6 was repeated but as the primary
brightener the product obtained from example 2 above was used as a
25 g./l. stock solution in Cellosolve. Again, the deposit obtained
was uniformly lustrous throughout the entire current density range,
and had a pronounced glossy appearance.
EXAMPLE 8
In this example, example 6 was repeated but using as the primary
brightener the product obtained from example 3 noted above as a 25
g./l. stock solution in Cellosolve with essentially the same
results obtained.
EXAMPLE 9
A 4-liter volume of acid tin stock solution having a concentration
of 30 g./l. SnSO.sub.4 and 105 ml./l. of C.P. concentrated sulfuric
acid (SP. Gr. 1.84) was set for electrolysis at ambient temperature
(about 20.degree. C.) in a rectangular glass battery jar. In the
solution there was immersed, by suspending from a titanium wire, a
slab of 99.99 percent pure tin as anode. The cathode was a polished
brass strip having dimensions of 20.3.times. 2.54.times. 0.1 cm.
After cleaning, it was immersed in the plating bath to a depth of
18 cm. at a distance of 10 cm. from the anode with the front of the
cathode parallel to the anode. The cathode was moved in a plane
parallel to the anode using a 5 cm. reciprocating stroke with a
total distance travel of about 160 cm. per minute.
To the 4-liter bath there were added 0.25 gram of the primary
brightener of example 2, 4 g./l. of Tergitol NonIonic NP-35 and 10
ml./l. of 37 percent formaldehyde solution. A current of 2.5
amperes was applied for 10 minutes. The deposit was uniformly
glossy but had a definite milky appearance.
EXAMPLE 10
Example 9 was repeated using a periodic current interruption cycle
of 10 seconds plate--2-seconds no-plate and using a current of 2.5
amperes for a total time of 12 minutes to give the same total
plating time as for example 9. The resulting deposit was remarkably
brighter than the one of example 9, with only a very slight milky
haze.
EXAMPLE 11
Using the 4-liter solution of example 9, additives included, a
barrel-plating test was run using a small laboratory Lucite barrel
of the horizontally rotating type having the following
description:
Cross section hexagonal Length 25 cm. Diameter (ave.) 10 cm. Speed
of rotation 5 r.p.m. Anodes External, slab 99.99% pure tin
A load of steel nails weighing 310 grams, length of each 3.8 cm.,
total area 930 sq. cm., was suitable cleaned and transferred into
the plating barrel. The load was plated for 1 hour using a cell
current of 5 amperes (to give an average cathode current density of
0.5 ASD). After plating the load was thoroughly rinsed and dried.
The deposit on the nails had a uniform, brilliant appearance and
the deposit thickness obtained was an average of 0.00064 cm.
EXAMPLE 12
Example 11 was repeated using a current of 10 amperes for 30
minutes. The resulting deposit was uniform and brilliant and also
had an average thickness of 0.00064 cm.
As further illustrative of the results achieved in accordance
herewith, a life test was run with the bath of example 9 for a
period of 3 weeks, with 8 hours of daily electrolysis, and with
periodic additive replenishment. At the end of the 3-week period,
the bath was still in excellent operating condition. Furthermore,
no accumulation of harmful decomposition products of additives were
evidenced in this life test.
Accordingly, and as will be apparent from the foregoing, there are
provided in accordance herewith, methods and compositions for
imparting bright lustrous tin deposits on a variety of metallic
substrates with baths containing the primary brightener in
accordance herewith of the reaction product obtained from reacting
furfural and crotonaldehyde, and in a manner in which the baths are
easily maintained and controlled. Furthermore, baths incorporating
the primary brightener in accordance herewith may be maintained
over extended periods of time with only replenishment of the bath
components and the primary brightener in accordance herewith in the
absence of the problem of the baths becoming inoperable, thus
making the methods and compositions in accordance herewith highly
advantageous commercially. In addition, methods are provided here
for a program of current manipulation in which even further
enhanced results are achieved, as desired.
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