Note: Descriptions are shown in the official language in which they were submitted.
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1CNIIANCING SIL'V'ER TAIINISII-RESIaTANCE
FIELV OF THE IhIVENTIQN
s The present invention relates to the use of organo-sulphur compounds in
the enhancement of the tarnish resistance of silver alloys, to silvez articles
of
enhanced tarnish resistarxce that have been surface-treated with the organo-
sulphar compounds and to methods of keeping and display of the treated
articles.
It also relates to a water-based composition that can be u$ed far the
treatment of a
to metal which may be a silver allay but which may also be another metal
requiring
surface treatment to impart tarnish resistance e. r. copper, brass or nickel.
BAt=.'K~ROUND TO THE INVENTIf)N
13 Silver alloys and their tarnish-resistance
Standaxd Sterling silver proviaea manufacturers and silversmiths with a
versatile and reliable material but it is inevitable fat finished articles
will require
further clemin'e, and polishing to temporarily remove undesired tarnish
products.
z0 It is yvell-known that yvith exposure to everyday atmospheric conditions,
silver
and silver alloys develop a lustre-destroying dark film known as tarnish.
Since znoient times it has been appreciated that unalloyed 'one' silver is
too soft to 'withstand normal usage, sad it has been the practice to add a
25 proporiivn of a. base metal to izicrease hardness rrnd strength. In the
U'K,
IegislatiQn that bas existed since the fourteenth century specifies a minimum
silver content of articles for sale at 92.5% {the Sterling standard), but does
not
specify the Ease metal GOFISLItlli:ntS, Experience 4onvinced early
silversn3iths That
copper was the most suitable of the rrtetals available to them. Ivlodern
silver sheet
3o manufacturers generally adhcr~; to this composition, although sc~metirnes
s,
proportion of copper is replaced by cadmium to attain even greater ductility.
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z .-
Sterling ,,vith a 2.5% cadrniurn content is a standard material for sp~ii~g
and
stamping. Lower grades of silv':r alloys are eorr~xnorz in many parts of
Europe for
the production of hollow-ware and cutlery. The 800-grade alloys (Ag parts per
thousand) arc predominantly used in southern and mid-Europe whereas .in
Scandinavia the 830 standard is predominant.
In all btrt the largest manufacturing companies, most of the annealing and
sbldering required to assemble finished or semi-finished articles is carried
out
with the flame of an air-gas blowtorch. The oxidising or reducizlg nature of
the
flame and the temperature of the articles are controlled only by the drill of
the
silversmith. Pure silver allows oxygen to pass easily through it, particularly
when
the silver is heated to above red heat, Silver does not oxidise in uir, but
the copper
in a silver/copper alloy is oxidised to cuprous or cupric oxide. Pickling of
the
oxidised surface of tl~e article in ltot dilute sulphuric acid removes the
superficial
but not the deeper-seated copper oxide so that the surface consists of fine or
unalloyed silver covering a layer of silverlcopper oxide mixture. The pure
silver
is easily permeated fluxing further heating, allowing copper located deeper
below
the surface to beco~.e oxidised, Successive annealing, cold working and
pickling
produces a surface thatwexhibits the pure lustre of silver when lightly
polished but
z0 . with heavier polishing reveals dark and disfiguring stains known as
'firestain' or
'fire'. Soldering operations are much more produc,~tive of deep firestain
because of
the higher tenrrperaturas involved. Wlaen the depth of the firestain exceeds
about
0.025mm (0.010 inches) the alloy is additionally prone to cracking Fmd
diflicuZt to
solder because an oxide surface is not wetted by solder so that a proper
ZS nlstallurgical'band is not formed.
Patent GB-B-2255348 (R,ateau; Albert and Johns; Metaleurop Recherche)
disclosed a novel silver allay that maizitaimed the properties of hardness and
lustre
inherent in Ag-Cu alloys while reducing problems resultW Q from the tendency
of
3~ the copper content to oxidise. The alloys were ternary Ag-Cu-Ge alloys
containing at least 92.5 w-t°l° Ag, O.S-3 wt% Go and the
bal<~nce, apart from
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inzpuritics, copper. The alloys were stated to be stainless in ambient air
riuri~~g
conventional production, transforzr,ation and f nishing operations, to be
easily
deformable when cold, to be easily brazed end not to give rise to significant
shrinkage on casting. They were also stated to extzibit superior ductility
acrd
S tensile strength and to be annealable to a required hardnLss. Germanium was
stated to exert a protective function that toes responsible for the
advantageous
combination of properties exhibited by the new alloys, and was in solid
solution
in both the silver and the Copper phases. The microstructure of the alloy was
said
to be constituted by two phases, a solid solution of germanium and copper in
to silver surrounded by a filamentous solid solution. of gennauium anal silver
and
coppex. 1~e germanium in the copper-rich phase was said to inhibit .surface
oxidation of that phase by forming a thin Ge0 or Ge4z protective coating which
prevented the appearance of fire5tain dtu trig brazing and flame annealing
wlzioh
results from the oxidation of copper at high temperatures. Furthermore the
15 development of tarnish was appreaiubly delayed by the addition of
germanium,
the surface turned sliglxtly yellow xather than black and tarnish products
wore
costly reazoved by ordinary tap water, The alloy was said to be useful inter
crlia in
ja~vellery. However, the alloy disclosed in the above patent Suffers
limitations
insofar as it cm exlubit large grain size, leading to poor deformatGOn
properties
20 and formation of large pools from low-melting eutectics resulting
in~localiscd
surface melting when the alloy is subject to the heat of an air torah,
Patents CTS-~-6168071 and ~P-B-0729398 (Johns) disclose a
silverlgennanium alloy which carnpxiscd a silver contEnt of at Isast 77 wt %
and a
25 germaniu;n content of between 0.4 and 7%, the remainder princfpally being
copper apart froze any impurities, which alloy contains elemental boron as a
Srain
refiner at a concentration of more than (?ppm and less than 20ppm. The boron
content of the alloy can be aehievzd by providing the boron in a master
eapperlboron alloy having 2 v4~t % elemental boron. Zt was roported that such
low
30 conGontrations of boron surprisingly provide excellent grain refining in a
silverlgerrrzaniunz alloy, impa~rking e~reater strength and ductility to the
alloy
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c~
compared with a silverlgermaniuxn. alloy without boron. The boron in the alloy
inhibits grain growth even at temperatures used in the jewellery trade for
soldering, and samples of the alloy were reported to have xesisted pitting
even
upon heating repeatedt~r to temperatures where in conventional alloys the
copperlgezmanium eutectic in the alloy would melt, Strong and aesthetically
pleasing joints between separate elements of the alloy oar be obtained without
using a filler material between the free surfaces of the two elements and a
butt or
lap joust can be formed by a diffusion process or resistance or laser welding
techniques. Compared to a weld in Sterling silver, a weld in the above-
described
to alloy has a much smaller average grain size that irzzproved the
formabiliL3~ and
ductility of the welds, and an S3q alloy has bccn wcldcd by plasma welding and
polished without the need for grinding.
Ternary and quaternary allays e.g. Ag-Cu-Ge alloys and A,g-Cu-Zn-Ge
alloys include two base metal. ahoying elements, Gu and Ge, in a noble parent
metal, Ag. Grx exposure to an oxidising at~.osplaere, two oxidation xeaatiorts
have
to be considered. Firstly, the oxidation of copper to cuprous oxide:
~l[Cu~anoy 'E- ~z (g) -; 2Cu20 (s) t1)
Secondly, the oxidation, of germznium tv gerrmxnium {di)oxide:
[~''le~~lloy ~ 02 (f) '~' ~~d2 (5)
The above equation shows formation of germanium {1V) oxide, Ge02, but there
may also be formed germanium (1l) o:dde, Ge0 or an intermediate material
Ge,;Oy where x is 1 and y is greatex tht~n 1 bttt less than Z. Under standard
conditions, i.e. for pure Cu and pure Ge each reacting with pure oxygen gas at
1
tttm pressure to forms the pure oxide phase, both reactions are feasible, with
the
chemical driving force for xeaction~ (2) being hi;her than that of reaction
(1) by a
factor of 1.65.
Accordiatg to Wn 01095082 (Johns) tarnish resista~zGe ofternary alloys of
silver, copper and gern~azZiunl or quaternary alloys of silver, copper, Zinc
and
getmatrium can ho increased by casting a molten mixture to form the alloy and
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annealiz~ the alloy to reduce its thielcnoss and rc-crystalline the trait's in
tlm
ahoy, the annealing being carried out under ~. selectively oxidizing
atmosphere
e.g HzIH20 or COICOz iv pxomote the formation of GeOz while preventing the
formation of Cu20.
~'raatnient coxxApasitions for removing br pre~Veutielb silver tarnisv
Various proposals have been made for cleaning or protecting Sterling
salver and other known grades of silver to rexnove tarnish t~ridlpr to inhibit
the
t o Poxmation of tarnish.
US-!~-2841501 discloses a silver polish based on z1n abrasive powder and
a C12-Czo n-atkane thiol which is said to be nonytoxic, to have a mild odor
and to
protect silver against tarnishing by fdr~ning a manomolecular layer R-S-Ag
1s wherein ft represents the alkane chain of the thiol, said Iayer forming a
physical
barrier between t1e silver and reactive ingredients of the atmosphere.
GI3-A,-1130540 is concerned with the prot~etion of a finished surface of
Slerlir~ or >3xitannia silver as a step in a production run, and discloses a
process
z0 that comprises the steps of
wetting cz clean silver surface of an article v~dth a solution comprising 99
parts by weight of a volatile organic solvent, for e~:ample trichloroethylene
or
1,1,1-trichloroethane and from O.I-1.8 parts by weight of an organic solute
containing a -SH group and capable of forming a transparent colourless
z5 pxotective layer on, the silver surface, for example stearyl and cetyl
~ercaptan or
thioglycollate;
allowing the solution to react with the surface to form such a layer .and
allowing the solvent to evaporate; and
vrashzng the surface with a deterge~~t solution, rinsing the suxface with hot
30 water and allowing it to dry. The above process is stated to provide a
"long-term
finish" intended to last the intended shelf life until the article reaches the
user.
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Halohydrocarbons 'were said to be the xzaost suitable solvents but theic~
suitability on environmental growtds is now open to ciuestion. Lthers ~Yere
said lU
be flanunablc and toxic, and lo~,ver alcohols were said to be poor solvents.
VTater
is not mentioned as a soIverrt. Applicants have seen a report on the Internet
fCOm
s ATQ'FINA Cherz~icals lnc that the solubility of mereaptans in water
decreases
progressively from 23.30 gllitre for maihyl mercaptan to 0.00115 gllitre for
nonyl
mercaptan, and data for for both hexadecyl and octadecyl mercaptan {CAS 2$85-
00-9) reports them as water- insoluble.
tU US-A-61S381S (Snick) also teacbes that treatments of the above kind are
xesult in the fuzxnation of a saltassernbled coating derived fzom the thiol
compow~ds in which tha sulphur atoms are bound onto the metal surface and the
allryl tails ore directed pwuy from the metal surface. In the examples of that
specification, iluoroaIkyl arnides e.g. CFa{CFz)sCONH(CH2)ZSH iri aqueous
is alcohols e.g_ aqueous isopropanol are sprayed auto the surface of silver,
after
which the surface is rinsed ttnd dried with a salt cloth. The fluoraaikyl
amides
lank detectable odour and can dissolve in lower alcohaIs or alcohoilwater
mixtures, although it is apparont from the description and examples that not
all
alcoholic solvents prod .t~ce good films.
2tI
Yousong lCim et a! repvrl that the adsorption of thiols onto silver proceeds
through an anodic oxidation reaction that produces a shift of the open circuit
potential of the substrate metal irt the negative diz~ction or if the
potential is f xed
an anodic ctu-rent peak:
25 RSH -t-1~(0) --> RS-1vI(I) + 1h' + a (M) {M = Au or Ag), sae
httwllt-vHVV.elecJrachem.or lm~ eetirt~sl,~ast1200/ab ~t~ raclsl_
SaYmpcsiylhlll026 pdf
KWEiIl K11T1, AC~SDY~7lTUi1 v?itc~ lteactioyi of Thlots aYecl S2rlfide5 ort
Noble
Nletals, Rarxzan SRS-2404, I4-I7 Au~ast 2000, ~.aimen, Fujian, China,
30 Itttx~;//I?coss.orgricoz~sxtnlpaper~7cut~t~cim.pdf , also iliscIuses the
formation of self-
assernblecl morsolayers and discloses that alkanetliols, diaLl;yl sulfides and
dialkyl
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disulfides self assemble on silver surfaces with aliphatic dithiols farming
dithoiolates by forming two Ag-S bonds.
In oontr~st, the literature an formation of alkylthiols of germanium is
relatively sparse, The dissaciztive adsorption of H~5 at a Ge I00 sttrfS.ce to
yield
adsorbed -SH groups and adsorbed hydrides has been raported by 3~lelen e~ al.,
.lpplred Surface Science. 1.~0, 65-72 (1999), see
htto~/lv~ww.chem.missauri.edu/Greenlief/aubslOD005797.gdf.~ see also a report
by
Professor Michael Cxreenlief of the University of Missouri-Coluarbia
t0 http:lhvww chetn rt~i~souri.edulGreenlieflReseareh.htm3 that room
te~nnperature
exposure of H2S to Ge(14D) results in dissociative adsorptiUn that can be
fol3owed
easily by ultraviolet photoelectron spectroscopy. The reaction of alkanethiols
with
Ge to farm a high quality monolayer has been reported in the context of
semiconductor and nanoteehnolo~y by Han et al, .l. .4m_ Chem. Soc., 123, 2422
(24Q7.), In the experiment described, a Ge(111) wafer is sonicated in acetone
to
dissolve organic contaminants and immersed in Concentrpted HF to remove
residual oxide and produce a hydrogen-terminated surface, after which the
wafer
is immersed in an alkanethiol solution in isopropanol, soz~icated in pzopanol
and
dried.
z0
S~)IvrMAI~Y OF THE INVENTION
Althou~li GB-A-1I30540 was alleged to provide a Long-tenor finish, the
experience of one of the inventors who is a silvexsniiih is this type of
treatment
z5 does not fully solve the difficulties Created ny tarnish in the period
between
manufacture and supply to the ultimate purchaser or user and suffers from a
number of shortcomings. A.Ithough a silver prtsduct might arnve at the
retailer in
an untarnished state, it was largely tho result of the wrapping applied by the
manufacturer, which protected the article from air. Once the wrapping was
3o removed and the article was displayed in a retail environment such as a
display
case in a hotel where it was subject to ambient air and the heat of artificial
CA 02520807 2005-09-28
lighting, an article of conventional Sterling silver would require rc-
polishing after
one week and after two weeks t~rou.ld normally be so tarnished as to be un-
saleable. At an e.Yhibition, the life of an article on display before
significant
tarnish sets in may be as sham as 3-4 days. Re-polishing produces wear and
fine
handling scratch~;s, so that unless the article can be sold quickly it looses
its
pristine appearance. The need to polish display silver at frequent intervals
adds to
the labour cost of a jeweller or other retail establishment, whose management
take
the view that its staff should be employed to sell producas and not to clean
stock.
Tamis'b at point of sale or display is therefoxe a serious problem that
reduces the
to willingness uF those in the distribution chain to stock and display silver
products,
and which has not yet been adequaiely solved.
V~hen the product reaches the ultimate putcl~aser, it is of course desirable
that the t<~sk of tarnish removal should be made as infrequent anti
undemanding ns
pnssible.
silver alloys according to the teaching of GB-E-22~53~8 and EP B-
0729398 are now commercially available in Europe and in the LTSA under the
trade mark Argeniium~and the word ".Argentium" as used herein refers to these
alloys. Although they e:rhibit improved tarnish resistance compared to e.g.
Sterling silver, and any tartzish that forms can be removed by simple washing,
there is still room far improvement in tarnish resistance. 'fizat rc.~nains
true even
when annealing is conducted in a selectively oxidising atmosphere as disclosed
in
WQ 02/0950$2.
23
It has now been found that an alkanethiol, alkyl thioglycollale, dialkyl
sulphide or diall:yl disulphide Gan be used for the surface treatment o~ an
allay of
silver containhtg an amount of germanium that is effective to reduce frestain
andlur tartushing so as to reduce or further reduce tarnishing of the alloy
such tlaat
a sample can be subjected to hydrogen sulphide gas above a 20% solution of
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ammonium polysulplude for at least 30 minutes and typically ~5-60 minutes al
room temperature while retaining a generally untarnished appearance.
The invention therefore r4lates to ~r method for treating a finished or semi-
s finished shaped flatware, hollowware or jewellery article of a
silverlgermanium
alloy that has a silver content~of at Ieast 77 wt % and a germanitun content
of
bctrveen 0.4 and 7°~° the remainder principally being copper so
as to reduce or
further reduce tarnishing of the article such that a sample or the alley of
which the
article is made can be suppaz~ted close above a 20% solution of ammonium
1b polysulphide for at least 3~ minutes while retaining a generally
untarnished
appearance, said method comprising
surFac:e treating said article with an alkanethiol, alkyl thioglycollate,
daalkyi sulfide or dialkyl disulfide
15 The above method may include tire further step of introducing the article
into packaging.
The invention further provides a finished or semi-finished shaped
flatware, hollowware ~r jewellery ariiGle of an alloy of silver containing au
zo amount of germanium that is effective to reduce firestain andlor tarnishing
and
that ha,~ been treated with a C,2-C~4 allcanethiol, alkyl thioglycollate,
dialkyl
sulphide or dialkyl disulplude and that exhibits a tarnish resistance such
that a
sample of the alloy of which the article is made can be supported close above
a
20°/a solution of ammonium polysulphide for at least 30 minutes while
retaining a
25 generally untarnished appearance.
The above accelerated tarnish test in which the article is subject to
hydrogen sulphide gas front the amrnonim polysulphide solution above which it
is suspended at a height of e.g. 30mm correspozrds to a period of a year or
more in
3o a retail environment where an article is on display and e;~posed to ambient
atinosphes~e and may be subject to elevated temperatures. It is the
combination of
CA 02520807 2005-09-28
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the protective Function of the germanium content of the alloy with the further
protection from the argatto-sulphur compound that is believed to be
responsible
for the observed increase in tarnish resistance. 'The period during which the
article
zetains its untarnished Appearance under these severe conditions may be three
or
s more tithes the corresponding period for an article that has not been
treated with
an organo~sulpnur compound, ivhieh is unexpected because the same accelerated
tarnish test carried out under the same conditions vn a. conventiozu~I
Sterling silver
article not containing protective gcrnxanium does not reveal a siSnif Cant
increase
in untarnished lifetirxte between its untreated and angora-sulfur treated
states.
t0 Accelerated tarnishing trials carried out using Argentium and standard
Sterling
silver samples immersed in solutions of octadecyl merc3ptan and hexadecyl
mercapte~n Imve shown that the protective thiol is removed from the standard
Starling sample but not from the Argentium silver samples on rubbing with a
tissue soaked in a solvent (EnSolv 765, an n-propyl bromide based solvent
~3 cleaner discussed below), 1n accelerated testing the solvent-rubbed regions
of
standard Sterling silver discolour more rapidly than the un-rubbed regions
whereas in Argentium silver no noticeable difference in. appearence develops
between the rubbed trnd un-rubbed regions, suggesting that thiol bonding is
stronger or more effectjwe.
AcceIer-ated tatztishing tests with Argentium Stezling using amrctonium
polysulphide have been reported by the Society of American Silversmiths, see
htfi~/lwww ~ilversmithit~,~ comll or entium4 httn
and in a comparative test the Argentium Sterling remained untarnished after
one
hour whereas conventional Sterling became tarnished alter less than 1S
minutes.
However, in this test 0, 5mI of 20°lo atnmanium polysuifide solution is
mixed with
2UUml of distilled water, so that the test is ;neatly less severe than when
samples
are exposed to the 20% solution itself. In WO 0~1Q95082, samples ware '
suspended above 20% amnronium polysulphide, but the exposure times were
3o relatively short, and onset of yellowing was reported for Ag-Cu-Ge allays
after 3-
5 minutes exposure. Other tests reported it7 that specification involve
placing
CA 02520807 2005-09-28
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samples irz a clesiccator containing flowers of sulphur ~.id calcium uitxate
and are
less severe than the ammonium polysulphide test.
As part of their program for developing improved fbrn~ulatjoz~s for tl3e
s treatment agents described above, the applicants have unexpectedly
discovered
that the treatment agents cari be dissolved ar dispersed directly in aqueous
surfactant without the need far preliminary dissaiving of the treatment agent
in an
organic solvent and sui~sequent mixing of tlae zesulting solution with aqueous
liquid. >rmbodiments of the above compositions sue optically clear and storage-
stable at ambient temperatures for a period of weeks or months. The treatment
composition uiay therefore be water-based and comprise an alkanethiol, alkyl
thioglycollate, dialkyl sulfide oz dialhyl disuit'ide and a mixture of an
anionic
surfactant with a. neutrat or arrxphoteric surfactant and water.
i$
CA 02520807 2005-09-28
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D)~TATh.)CD AESCIt~TION OIf T~ I1~IVENT1G~1
Silver-copper-germanium alloys
s The allays that may be treated according to the invention include an alloy
of silver conta,inin,~ an amount of germanium that is effective to reduce
Brestain
and/or tarnishing. US-A-6406664 (l7iamond~ discloses that amounts of
germanium as low as O.lwt% can be effective provided that substantial amounts
of tin are present but although formulation examples are given, no test data
for
corrosion or firestuin is given either for articles made by coating or fox
articles
fabricated from sheet. The inventor considers that 0,5. wt% Ge provides a
preferred and more realistic lowex Iitnit pod that in practicE use of less
than lwt°/'o
is undesirable. A two-component coppex-free alloy could comprise 99°l0
.:1g and t
Ge, and a #arttish-free casting alloy for jewellery kas been reported that
comprises 2.5°.'°Pt, 1% Ge, balance Ag and optionally containing
Zr, Si or Sn.
The ternary Ag-Cu-Ge alloys and quaternary Ag-Cu-Zn Ge alloys that can
suitably be treated by. the method of the present invention arc those having a
silver content of at least 30%, prererably at least 60%, mare pxcfcrably at
least
80%, and roost preferably at least 9?.5%, by weight of the alloy, up to a
maxitniun of no more than 98%, preferably no more than 9?%. The gennaniurn
content of the Ag-Cu-(Zn)-Ge alIpys should be at least 0.1%, preferably at
least
0.5%, more preferably at least 1.1 %, and most preferably at least
1.5°/, by weight
of the t~lloy, up to a maxirnum of preferably rio more than 6.5%, morn
preferably
2s no more than 4%.
if desired, the germanium content may be substituted, in pact, by one or
more elements which have an oxidation potential selected from At, Ba, Be, Cd,
Co, Cr, Er, Ga, h~, Mg, Mn, Ni, Pb, )?d, Pt, 5i, Sn, Ti, V, 'Y, Yb and Zr,
provided
the effect of germanium in terms of providing f res#ain and tarnish resistance
is
not unduly adversely a~ff~cted. Tlxe weight ratio of gennpniwo to
substitutable
CA 02520807 2005-09-28
elements may range frort~, x00: 0 to 40; 40, preferably from 100: Q to $0_ 20.
Preferably, the gercnarzium content consist entirely of germanium, l. e. the
weight
ratio is 100; 0.
The remainder of the ternary Ag-Cu.Ge alloys, apaxC from impurities and
any grain refiner, will be constituted by copper, which should be present in
an
amount t~f at least 0.5%, preferably at least 1°fo, wore preferably at
Ieast Z°lo, and
most preferably at least 4%, by weight of the alloy. For m '$Q0 grade' ternary
alloy, for example, a coppex content of 18.5% is suitable. 'I~e remaindex of
floe
to quaternary A,~-Cu-Zn-Ge ahoys, apart from impurities and any grain
retainer, will
be constituted by copper which should be present in an. amount of at least
Q.5°/v,
preferably at Icast 1%, more preferably at least 2%, and most preferably at
Ieast
~%, by weight of the allay, and zhtc which should be present in a ratio, by
weight,
to the copper of no more than 1: 1. Therefore, -zinc is optionally present in
the
silver-copper alloys in an amount of from 0 to 100 % by weight of the Copper
content. For an '$00 grade' ttuaternary alloy, for cxarnple, a vopper content
of
I0.5% and zinc content of 8°f° is suitable.
In addition to ,silver, popper and germanium, and optionally zinc, the
alloys preferably contain a grain refuxer to inhibit grain growth during
processing
of the alloy. Suitable graitz refiners include boron, fridittm, iron and
nickel, with
boron being particularly preferred, The grain refSner, prefCrably boron, rnay
be
present in the Ag-Cu (Zn)-Ge alloys in the range from I ppm to 1~ ppm,
preferably from 2 ppm to 50 ppzn, txioxe preferably from 4 pprn to ZO pprn, by
weight of the alloy.
In a przferred eznbodinzent, tha allay is a ternary alloy consisting, apart
from impurities and any grain refiner, of 80°/a to 96% silver, 0, 3
°ta to >%
germazuum and 1 % to 19.9% copper, by waight of the alloy. In a more preferred
3o embodiment, the alloy is a ternary alloy consisting, apart from impuriiies
and
grin rcfiuer, of 92.5°,~o to 98%v silver, 0.3°~o to 3% germanium
and 1% (v 7.2%
CA 02520807 2005-09-28
s
- 14 -
copper, Gy weight of the alloy, together with 1 ppm to 4U ppm haxon as grain
z~~n er. Zxz a further pret~rred embodiment, the alloy is a ternary alloy
consisting,
apart fnon~ impurities nnnd gain refizmr, of 92.5% to 96ro silver, 0. 5% to 2%
germanium, and 1 %u to 7% copper, by weight of zl~e alloy, togethex with 1 ppm
t~
40 ppm boxon as grain refiner.
ProteeEive itgents
As protective agent there may be used a compound cotztainit2g s long
io ahairz alkyl gxoup and a -SIB ox-S-S- group, e.g. an alkancthiol, dialkyl
sulfide or
dialkyl disulfides in which the chain is preferably at Least It) carbon atoms
long
and may tae Cz2-C24. The -STI or -S-S- compounds that many ba n,secl znclt~de
straight chain satuxt~ted aliphatic corupouuds containing 16-24 oarbon atoms
in
the chain, for example cetyl znercaptan (hexadccyl. mcreaptan) and stearyl
morcaptan (ocGadeeyt mercaptan) and cetyl aztd steary~ thioglyeoliates whose
forrnuiae appear blow.
HS
HS
4ctadecyl mercaptan is a white.to pale yellow waxy solid that is insoluble
in water and that melts at 15-16°C. Hexadecyl mercaptan is also a
tvhitc or pale
?5 yellow waxy solid that melts at 30°C,
CA 02520807 2005-09-28
- 15
formulations based au organic solvents
The prvteetivc agent may be used in solution in a solvent e.g. a non-polar
orgaziic solvent such as an alcohol e.g. methyl or etlryl alcohol, a ketone
e.g.
3 acetone or methyl ethyl ketane, nn ether e.g. diethyl ether, an ester e.g. n-
butyl
acetate, a hydrocarbon, a ' haiocarbon e.g. methylene chloride, l,l,l-
triehloroetlYane, trichloroethylene, perchlorosthylene or HCFC 14I b. The
protective agent may comprise 0.1-1 wt°/n of tt~e soivent. Sfllvents
based on alkyl
or aryl halides may be used e.g. n-propyl bromide which is pxesently preferred
on
z0 the ground of the short atmospheric life of that compound, its relatively
low
~toxieity corrzpared to other haloosrbons, its favourable chemical and
physical
propazBes and its boiling point, specific heat and Latent heat of
vaporisation_
US-A-56t6549 discloses a solvent mixture comprising: 90 percent to
15 about 96.5 percent n-propyl bromide; 0 percent to abocit 6.5 percent of a
mixture
of tcrPcnes, the terpene mixture comprising 35 percent to about 50 percent cis-
pinane and 35 percent to about SU percent trans-pinane; and 3.5 percent to
about 5
percent of a mixture of low boiling solvents, the low boiling solvent mixture
comprising 0.5 percent to 1 percent nitromethane, 0,5 percent to 1 pexccnt 1,~-
20 butylene oxide and 2.5 percent to.3 prscent 1,3-dioxolane. The solvent
mixture
has the following attvantages;
(l) it is properly stabilized against any free acid thQt might re;;~ult from
oxidation of the mixture in the presence of air, from hydzolysis of the
mixture in
the presence of water, and from pyrolysis of the mi.Yture under thi influence
of
25 high tempezatures;
(ix) it is non-flammable and non-corrosive;
(iii) the various components of the solvent mixture are nvt regulated by
the CJ.S. Clean Air Act; and
(ivy none of tlxe various components of the solvent mixture are known
3o cancer causing a4ents (i,a., the various components are not listLd by
N.T.I.,
LA.R.C. and California Proposition 65, nor are they reguated by ~SHA).
CA 02520807 2005-09-28
~j
1~'Ivrev~er, the salveiit mixture has a high solven~Gy with a kauri-butanol
value
above 12d and, more preferably, above 125. In addition, the solvent mixture
has
an evaporation rate of at least ~,9fi where 1,1,1-Trichloroethane=1, Upon
evaporation, the solvent 171LYt111P~ leaves a non-volatile residue (NVR) o1'
less than
2.5 mg and, more preferably, no residue, Solvents made in accordance with the
above patent are available from Enviro~Tech International, Inc of Melrose
Park,
IlliIlOAS, lJSA under the trade naare EnSolv.
Farraulatior~s based on organic solvent and W~tGx
IQ
For many purposes, e.g. light industrial applic~.tions, it may be preferred
to carry out the anti-tarnish treatment using a predominantly aqueous solvent
system, For this purpose, the protective agent may be dissolved in a water-
immiscible organic solvent, for example a solvent based an n-pzopyl bromide,
the
resulting solution may be mixed with a relatively concentrated water-based
soap
or detergent composition which acts as a "carrier", after which water is added
to
the resulting mixture to provide an aqueous treatment dip or combined
degreasing
and treatment solution. Thus an aqueous dip has the advantages that a solvent
degreasing system is npt necessary, the dip is easily made and may ba used
cold,
2o alt areas of immersed articles Can come into contact with the stearyl
rtrercaptan or
other treatment aSent, Argentium Silver only requires 2 minutes - 1 hour in
the
dip, rinsing and drying of articles are made easy as water droplets are
repelled
tiom the surface of the polished silver, and the clip cart be easily used in a
manufacturing environment before articles axe sent to retailers.
Preferred water-based detergents may be based on anionic, alkaxylated
non-ionic or water-soluble cationic surface active agents or mixW res of them
and
preferably have a pH at or close to 7. Anionic surfactants may be based on
alkyl
sulphates and alkyl benzene sulphonates, whose harshness on prolonged skin
exposure may be reduced by the ca-presence or use of alkyl ethox.y sulfshates
(US-A-3793233, Rose et u1.; 404075 Gilbert; 431 S82a Pancherni). Other kno~,vn
CA 02520807 2005-09-28
- 17 --
s«rfactants e.g. betaines may also be present, see e.g. US-A-4555360
(Bissett). A
suitable i~oulation cc>z~taiz~,zo.g S-15 wt% non-ionic surfactants and 15-3d
wt°/a
anionic surfactants is available cornnaercially in the UK under the trade name
Fairy Liquid (Praetor & Gamble).
An aqueous liquid may~also be made by dissolving the treatmvent agent il~
a non-organic solvent and adding a relatively concentrated aqueous detergent
liquid, fox example undiluted Fairy Liquid, This provides a detergent liquid
that
has a number of advantages: the soapy liquid is easily made, the liquid is
easily
to applied to the Argentium Silver articles with a damp sponge/cotton
wool/cloth
rte, the liquid and lather enables the stearyl tnercaptau or other treatment
agent to
get into those awkward areas on are article where a cloth may not be able to
xeach,
riming and drying of articles are mach easy as water droplets are repellod
from
the surface of the polished silver, the process can be easily used in a.
t 5 manufaoturing environnxent before articles are sent to retailers and cQn
also be
easily used in a retail or domestic environment. Furthermore, the hydrophobic
properties imparted to silverlsilver alloy on treatment with the present thiol-
based
treatment agents may alleviate ox overcome the problems of water-marks or
water-stainuag from , rinsing processes in a manufacturing or domestic
20 environment.
~ornaalations bused on aqucoets liquids
it has surprisingly bean found that formulations containing effective
zs amounts of the treatment agents Gan be made by dissolving the~u directly in
aqueous liquids containing an anionic and s. nexttral or araphoteric
surfactant and
free from water-immiscible organic solvents and preferably free from alt other
solvents. 'fhe treatment agents may be dissolved in xalatively concentrated -
swfactaz~t-co~ntainxng adueous liquids, which may be used as such or a#ler
3o subsequent dilution with -water, see in particular the instructions given
in the
preceding section.
CA 02520807 2005-09-28
t
'fhe treatment agent may be present in said composition, prior to
dilutiuan thereof, in an amount of at (east 0.1 wt % and preferably at least 1
wt %,
the solids content of the composition being at least S wt %, typically 3 0-4Q
wt
and possibly 50 w(% or mole. The ability of aqueous sui~faetant liquids to
dissolve
or disperse such relatively hig"ci concentrations of higher alkyl thiols and
other
treatment agents which are repoxted to be highly water-insoluble has not been
described. The resulting concentrates may be diluted with water to provide an
aqueous treatment dip ar combined degreasing solution and dip for use as
explained above, and it has been found that the treatment agent may remain in
l0 solutivrc yr suspension following such dilution and may remain effective
for the
surface 2reatnxexit of silver-copper or silver-copper-germanium alloys and
possibly
o~tler metals such as copper, brass and nickel where surface protection films
may
retard corrosion. Particularly good results from the stability and
effectiveness
standpoint may be obtained by mixing hcxadccyl mcrcaptan (in the liquid state)
straight into a surfactant "carrier" and using the solution as such or on
subseqtreztt
dilution with watex.
In particular, the present treatment agents can be successfully dispersed in
aqueous liquids contairfmg mixtures of neutral and anionic suxfact~zr~ts with
the
2o neutral surfactants providing e.g. about 33 w(% of the totfd surfactant
present.
Treatzt~ent agents that cans be dispersed in such agents include n-hexadecyl
thiol
and n-octudecyl thiol. They crzn also be successfully dispersed in aqueous
liquids
containing mixtures of arnphoteric or zwiterionic surfactants and anionic
si,u~'actants and such mixtures can provide relatively storage stable
optically clear
solutions witlx little or no tendency to re-precipitate the treatment agent.
In that
case the weight ratio of the arnplrateric or zwitterionic surfactant to the
anionic
surfactant may be from I :I O to 10: l, typicsliy close to 1:3.
Anlphvteric or zwitterionic surfactants that may be used alone or in
3o admixture with one another arrdlor with nonionic surfactants and,~or with
anionic
surfactants rnay ba derivatives of secondary or tertiary amines, derivatives
of
CA 02520807 2005-09-28
heterocyclic secondary and tertiary mnines, ar derivatives of quaternary
ammanimn, quaternary phasphoniunn or tertiazy sulfonium compounds. The
cationic atom in the duaterrtary compound can be part of a heteroeyelic ring,
In alI
of these compounds there is at least one aliphatic group, stralglxt chain or
branched, containing from about 3 to 18 carbon atoms and .pt least one
aliphatic
substitucnt containing an axiionie water-solubilixing group, e.g., carboxy,
sulfonate, sulfate, phosplzate, or phosphonate.
Examples of zwitterionic surfactants that may be employed include
betaine surfactants, which are preferred, imidazoline-based surfactants,
axnirioatkdnoate surfactants and in ~inodiallkaaoate surFactattts. S~zitable
such
surfactants include amidocarboxybetaines, such as
cocoamidodiznethylcaxboxymethylbetaine, Iaurylamidodimelhylcarboxymethyl-
betaina, celylam3dadimathylearbo:cy-methyibctainc, and coc4arnidd-bis-(2-
hydroxyethyl)carboxymethyl-betaine. Particularly preferred are
arnidocarboxybetaines betaines of flee formula below wherein R xopresents Ca-
Cps
alkyl e.g. cocanudopropyl betaine. That compound is generally regarded as
safe:
in axz Aznes test conducted by BASF it did zzot prove mutagenic to Salmonella
indicator organisms and in a human repeated patch insult Lost (APT) it did not
indicate either contact hypersensitivity or phatoallergy (see the IvIAFC? CAB
cocaeaidopropyl amino betaine data sheet published by BASF):
N~'' o
o
~N Q-
/R
Also useful are sulphobetaine stlzfactants, e.g amide sulfabetaines such as
?5 iauramido-sulfoprapylbetaine of formula indicdfcd below,
CA 02520807 2005-09-28
cacamido-2-hydroxypropylsulfobetaine, coeoaznidodimethylsulfopropyl-betaine,
stearylamido-dimethylsulfopropytbetainc, and laurylamido-bis-(2-liydroxyethyl)-
snlfopropylbetaine. Ellso useful may be imidazoline-based surfactants
including .
s gylcinate and arnphoacetate compounds e.g. cvcoamphocarboxypropivnate,
cvcoarrtphocarboxyprapionic acid, cocaamphocarbaxyglycinate, and
cacaamphoacetate, aminoalkanoRte surfactants e.g. n-alkylamino-propionates and
n-alkyliminodipropionates such as N-lauryl-(~-amino propionic acid and salts
thereof, and N-Iauryl~~3-izzxino-dipropionic acid and salts thereof:
ton-ionic surface-active agents that may be used alone ar in admixture
include compounds produced by the condensation of an alkyleim oxide with an
w
organic hydrophobic compound that may be aliphatic or alkyl aromatic. The
length of the hydrophilic or polyoxyalkylene moiety that is condensed with any
i5 particular hydrophobic compound can be adjusted to yield a water-soluble
compound having the desired balance bctwoezr hydrophilic and hydrophobic
moieties. Seuii-polar nozzianic surface active 'agents may also be used,
including
a~zZine oxides, phosphine prides, and sulfoxides. Suitable classes of compound
include;
z0 ~ Polyethylene oxide condensates of alkyl phenols. These compounds include
the condensation products of alkyl phenols having an alkyl group containinø
from about 6 to 1 ~ carbon atoms in either a straight or branched chain, with
ethylene oxide, the said ethylene oxide; being present in amounts equal to 5
to
~5 tz~ales of ethylene. oxide per mole of alkyl phenol. The alkyl substituent
in
CA 02520807 2005-09-28
- 2I -
such COmpDUndS may be derived, for example, From polymerized propylene,
diis4butylene, octene, or nonerae.
~ Condensation products oY aliphatic alcohols with ethylene oxide. The alkyl
chain of the aliphatic alcohol may either be straight oz' brtuzcf~ed and
generally
contaitta from about $ tv about 22 carbon atoms
Coudelisatian products of ethylene oxide vyith the product resulting from the
reaction of propylene oxide and ethylene diatiiine.
~ Atnine Oxide surfaat<~ts, for example dimcthyldodecylamum oxide,
dimefihyltetradecylatnine oxide, ethyhncthyltetradecylamine oxide,
cetyLdimethylamine oxide, dimethylstearyl~mine oxide,
cetylethylpropylamine oxide, diethyldadeGylamine oxide,
diethyltetradecylamine o:cide, dipropyldodecylamine oxide, bis-(2-
hydroxyethyl)dodecyiamine oxide, his-(2-hydroxyethyl)-3-dodecoxy-2-
hydroxyprapylamirie oxide, (Z-hydroxypropyl)methyltetradecylamine oxide,
ditnethyloleylamina oxide, dimethyl-(2-I~yd~oxydodecyl)a~ine ~xido, and thw
corresponding dec:yI, hexadecyl and octadecyl homologs of the above
compounds.
Phosphine oxide surfactants, e.g. din retlryldodecylphosphineoxide,
dimethyltetradecylphosphine oxide, ethylmethyltctradecylphosphineoxide,
2o cetyldin~ethylphosphine oxide, dimethylstearyIphosphineoxide,
cetylethylpropylphosphine oxide, diethyldodecylphosphineoxide,
diethyltetradecyLphospbinc: oxide, dipropyldodecylphosphineoxide,
diprvpyldodecylphosplzlne oxide, . bis-(hydroxymethyl)dodeeylphosphine
oxide, bis-(Z-hydraxyethyl)dodecylphosphine oxide, (2-
z5 hydroxypropyl)methyltetradecylphosphine Oxide,
dimethyloleylphosphine
oxide, and dimethyl-(2-hydroxydodecyl)phosphine the
oxide and
corresponding decyI, hexadecyl, and oct0.decyl hnmoiogsabove
of the
compounds.
Sulfoxide surfactants, for example oc;tadecyl methyl
sulfoxide, dodecyl
30 methyl sulfoxide, tetradecyl methyl sulfoxide, 3-hydroxytridecyl methyl
sulfoxide, 3-n~ethox5~tridecyl methyl sulfoxide, 3-laydroxy-~t-dodecoxybutyl
CA 02520807 2005-09-28
- 22 -
methyl salfoxide, octadecyl 2-hydraxyethyl sulfoxide, and dodecylathyl
sulfoxide.
~ Ethanolamide-based surfactants e.g. coconut fatty acid monoethanolamide or
diethanolamide.
wherein R represents C~o-G.ao, ~p Gtz-Gis allLyl e.g. ulsyl- or coco-, rurther
surfactants tray be based on diethylene triatnine (DETA)-based quaternaries,
such
as diamidoamine ethoxylates and irnidazolines, and esterquats. As a class,
asterquats can be based an compotmds incltuiing methyl diethanolaniine
lo (tvIDEA), triethanolamine ~TIiA?, and N,N-dirnethyl-3arninopropane-1.,2-
diol
(DMAI'D).
A wide variety of alkyl sulfates may be used as anionic surface-active
agents including fatty alcohol sulphates, fatty alcohol ether sulphates, alkyl
IS phenol ether sulphates, alkyl aryl sulphoniG acids and salts (hereof ,
cusnene,
toluene and xyle~ne sulphonates and salts thereof and alkyl sulphosuccinates
e.g.
soditun or ammonium lauryl sulfate, However, a preferred elttss o~ anionic
s~~rface active agents is polyol monpalkylether sulfates of the formula RQ-
(GHZCHz~S03M whez~in~~ represents Cao-C:1& alkyl, n is 2-6 (preferably about 2-
2Q 3) and M represents a rnanovalent ration. Such compounds ure sulfonated
ethoxylated C,o-Crs alkahols which may be derived from coconut oil or tallow
of
may be synEhetia. Sodium lauretk sui.fate which has beer! used succcssferlly
herein
is a sodium lauryl ether sulphate ethoxylated to an average of two moles of
ethylene oxide per mole of lauric . acid and sulfated, and is of fortvula
zs cH,(cz~z3~~cHztoc~z~G~rzhoso3Na.
In addition to sirrtple treatment agents, the above compositions may be
formulated into mefal polishes e.~. for silver or brass. Suc$ products may be
formulated as llLlufd prOdllCt5 lllt0 w171Ch objects such as jewellery ox
cutlery are
30 to be dipped. After dipping, the objects are exsuahy rinsed under water and
dried
CA 02520807 2005-09-28
_ '1~ _
with a soft cloth. Alternative formulations take the form of creams or pagtes
which are applied with a soft cloth and then z~er~.ioved.
Tor formulation into dipping composition, the active ingredients axe
s normally an acid having a pKa of not more than ~, c.g, phosphoric, citric,
oxalic,
or tartaric acid together with thiourea or a derivative thereat e.g. an alkyl
derivative such as methyl or ethyl thiourea. For formulation into creams or
pastes
there znay be e.g. about 25 wt°/a of a mild abrasive such as
precipitated chalk,
infusorial earth, silica or ~-aluinina (e.g. 0.05 tun grade). These
ingredients are
i4 believed compatible with the surfactants and treatment agents and can be
incorporated when convenient by simple mixing.
Treatment procedures
i s The surface treatment nzay be carried out after the manufacturing stages
for a shaped article made of the alloy have been completed. The article may be
of
flatvsrare, hollowware ar jewellery, Fabrication steps xn.ay include spinning,
pressing, forging, ousting, chasing, hammering from sheet, planishing, joining
by
soldering braying or ~yelding, annealing cad polishing using bmffslmops and
2o aluminium oxids or rouge.
An article to be lrea.ted may be de-greased by various methods:
~ Vapour degreasing with or without ulirasonics
~ Aqueous degreasing wish or without ultrasonies
25 ~ Organic Solvent C18~'8lslllg with or without ultrasunics (e.g. degreasing
with
ethanol or acetone poor to thiol trcatancnt which may provide very goad
accelerated tarnish test results)_
~ Simultaneous degreasing and thiol treatment, the thiol being present in an
organic or adueous degreasing medium.
CA 02520807 2005-09-28
por example, the artxcIc may be degreased ultrasonically in ~. treatment
bath, dipped into a bath containing the treatment agent e.g. 1 wt% steaxyl
mexcaptan in solvent e.g. IanSolv, rinsed in one or more baths of the solvent
and
allowed to dry by cvapotation. Rinsing excess thiol away with the sane solvent
s that is used for thiol treutiiicnt is preferred, so that tlliols that have
not reacted
with the metallic surface are removed and are unavailable to react with
anything
else. The solvent should leave no or substantially no residue, so that
subsequent
washing with water or aqueous solvents should be unnecessary and the article
cari
be allowed to dry. The article xuay then he packed for delivery into the
i0 distribution chair. This may include u~apping the article in one or more
protective sheets, placing it in a presentation box, and wrapping the
presantaticn
box in a protective wrapping e,b, or heat-shrunk plastics film, Articles which
have
been treated with au organic compound 4ontaining -SH or -S-S- groups as
aforesaid and packaged should not only reach their point of sale in goad
Condition
t5 but should if displayed e.g, on a shelf or in a cabinet for a~~ exter:ded
period,
expected to be at least 6 months and possibly 12 months or more, remain
without
development of significant tarnish.
The articles may~.lternatively simply be polished with a polish containing
z0 1-5wt% of the organo-sulphur compound e.g. stearyl mercaptan together
surfactants and a cleaning agent e.g. diatomaceous earth in a solvent. As a
further
R.Iternative; they may be simply polished with a cloth impregnated with the
sogano-sulphur compound e.g. cetyl or stearyl ruercaptan e.g by impregnation
with a treatulent agent in an organic solvent e.g. n-propyl bromide followed
by
2s drying, The advantages of a Cleaning cloth are that it is easily
manufactured, eau
he aasil~~ used in. a xetail or domestic environment and is good for general
upkeep
ofArgentium Silver (if required).
Tl~e treatment mothort of the invention would fmd paz-titular benefit in the
30 tarnish protection of blanks for stamping coins immediately before the
st<~mping
operation because it has beers found that embodiments of the present films can
CA 02520807 2005-09-28
- 25 --
largely or wholly survive the stamping operation and can provide pritection
against tarnishing for the newly rr~inted coins. It will be appreciated that
coins in
mini cvnditian are packaged far collectors with minitnsl handling, and that
every
ocasion of handling e.g. polishing with a saft cloth involves risk of damage
to the
coin, The rislt of such damage is reduced by the present treatlzienf which can
impart prolonged tarnish resistance.
Tl~e invention will now he further described, by way of illustration only,
with reference to tlae following exannples. Throughout the examples, the term
"~;.nhanced tarnzsh resistance" of samples treated with stearyl mercaptan
refers to
the eomparisan with samples of A,rgentium 5ih~er which have not had any
ireatmer~t except fcr polishing and degreasing.
CA 02520807 2005-09-28
Example 1
Soivenf dip application (solvcnf degreased samples}
s Solutions were made up containing stearyl mercaptan {0.I, 0.~ and l.0
gram) in EnSolv 765 (100 ml). Samples of Argentium Sterling Which had been
polished and ultrasonically degreased in EnSolv 765 for 2 minutes were each.
immersed in one of the stearyl mercaptan solutions for periods of 2 minutes, 5
minutes and 15 minutes. The samgles were then buffed with clean cotton wool.
In order to evaluate tarnish resistance, dZe alloy samples were supported
on a glass slide in a fume cupboard about 25mm above the surface of
20°/
annnnoniurrz polysulphids solution so as to be exposed to the hydrogen
sulphide
that arises from that solution. All of the samples demonstrated good tarnish
resistance during a one-hour test; with vary slight yellowing after 4S minutes
exposuxe to the hydrogen sulphide. The light film on the satzrples was easily
removed with a cleaning cloth impregnated with stearyi mercaptatz.
By ~teay of caparison, a standard Sterling silver sample started to
zo discolour as soon as it was subjected to the above test and alter one hover
had
formed a heavy black taztush which could not be removed with a Cleaning cloth
ii~iprognated with steary! rnerc:aptdn. The xesults obtained with x second
Starling
silver sample that had been wiped with the cleaning cloth were similar dad
discoloration started as soon as the sample had been placed into the test. An
Argentium StErling alloy produced in accordance with EP-B-0729398 showed
onset of tarnishing aftar 3 minutes. Another sample of the Argentium Sterluy
alloy that had been annealed in a selectively oxidising atmosphere as
disclosed in
'W0 02/09502 showed onset of tarnishing after 6 minutes. The markedly
increased delay in Qnset of tarnishing was unexpected in the absence of an
3o increased delay in the case of the standard Sterling Silver article.
CA 02520807 2005-09-28
- 2'7 -
Example 2
Effect o.k post-treataneut saivent cles~~uin~g
Example I was xepeated for the Argcntiut~n samples except that instead of
buffing witlz cotton wool afCer the mercaptan treatment, the samples were
ultrasonically dEgreased in L.nSoIv 765 for 2 minutes. Tl~e samples were then
tarnish tested as described ill Example 1 and all fotuid to shnw enhanced
tarnish
resistance. The ability of the protective effect of the 5teazyl mercaptau
treatment
tp to survive ultrasonic cleanity in EnSolv suggests that the tarnish
resistance is
being achieved by a surface reaction involving the stearyl mereaptan and
possibly
the gcrm~uxium in the Argentium Silver, and not by formation of a grease ox
oil
layer on the surface of the Ar~entium,
l s EaampIe 3
Aqueous dip appiieatian (salvent degreased samples)
An anti-tarnish treatment solution was prepared using the followinb
20 ingredients:
Stearyl m~ercaptan 1g
EnSuIv 765 5 ml
Detergent (Fairy Liquid) 40 ml
25 De-ionised water 100 nil
The Stearyl Mezcaptan was dissolved into the )JnSolv 765 after which the
resulting solution was mixed with detezgent (Fairy Liquid) and diluted with,
eater
to provide an aqueous dip. ~ampIes of Argentium silver were polished and
~o ultrasosucally degreased in EnSolv 7bS foz 2 minutes, immersed into the
abpve
aqueous dip for 2 min~~tes st ambient temperatures and then rinsed under
running
CA 02520807 2005-09-28
28 --
tap water It was noted the water was irruncdiately xepeiled from the polished
surface, which left the samples dty. St~mplcs were tarnish tested as described
izi
Exarnptc 1 and all showed enhanced tarnish resistance.
s lJxunxplc 4
Aqueous dip application 2 {detergent degreased samples)
Samples of Argentium Sterling were degreased in a 2% aqueous salutian
IO of a detergent (Fairy Liquid] and were then immersed in the treatu~ent
solution of
Example 3, Zt was noted that the treated samples had become wt~tez-repellent
as
descrihed in >rxample 3, Sauzples were tarnish tested as described in ExarnplC
1
and. all showed enhanced tarnish resistance. The above test was repeated
except
that the Fairy liquid in the treatment solution was replaced by a liquid hand
soap
1s (~0 r<xl). When exposed to ammouum polysulphide solution, the sarxtples did
not
show enhanced tarnish. resistance, It is passiblc that this nmy have bs;en
because
the hand soap was snore dilute,
zo
Example S
Simultaneous degreasing and anti-tarnish t~reatznent
The fpllowing solutions were prepared:-
25 - 1 gr-arn stearyl mereaptan
~ znl EnSolv 765
20ru1 detezgent (Faizy Liquid)
- 100mi de-ionised water
~o ' 1 gram 5tearyl mercaptan
- 5 zrzl EnSolv 765
CA 02520807 2005-09-28
- 29 -
- 30n z1 detergent (Fairy Liquid)
- 104m1 de-iaoised water
- 1 grant stearyl znercaptan (freferxed quantities)
' S mI Exz$oiv 765
- 40n~3 detergent (Fairy Liduid)
- I t)Oml de-ionised water
- 1 cram stearyl mercaptan
to - 5 m1 hnSolv 765
- 40m1 detergent (p'aixy Liquid)
- 500m1 de-ionised water
- 1 grain stearyl mercaptar~
is - 5 ml EnSolv 76S
- 40rn1 detergent (Fairy Lirluid)
I OOOmI de-ionised water.
The solutions were heated to 50°C in an ultrasonic cleaning tank.
zo Samples zzf polished Argezxtiuzn Silver were ultrasonically degreased in
the
solutions for Z minutes and were rinsed under rmuzing tap water. For the frst
three of the above treatrnent solutions, it was observed ittat water was
repelled off
of the surface leaving the samples dry. Samples treated with the first three
solutions above were tarnish tested as described in Example 1 and all showed
25 enhanced tarnish resistance. Hc~waver, in the case of the samples treated
with the
last two solutions, water 4vas not repelled off of the surface dttriz~g the
rinsing
siege. When the samples dried they Showed. streaks on the surface which
discoloured dozing the tarnish test. 'fhe sample treated with the SOOml
solution
showed less di5colouratiozz than the sample treated with the 104Qm1 solution.
The
3o above experiments show that Argentiuzn silver ca~a be simultaneously
degreased
azzd p:at~;ctcd against tarnish using a thiol treatment ag;.nt applied in an
aqueous
CA 02520807 2005-09-28
3a
system, and that the zn,ore concentrated the stcaryl
ntercaptanll;nSolv/detergentlWater solution, the better the taznish resistance
produced.
s Example G
nirect Appiicatiou - Neat Detergent Solutions (solvent degreased! xcitteatts
degreased samples)
t o Tlte following solutions were prepared:
- 1 gram stearyl rnercaptali
S nil EnSoIv '765
- 40m1 detergent (Fairy Liquid) {Preferred quantities)
1 gram stearyl xnercaptan
- 5 ml ErlSolv 7b5
- 40m,1 soap (liquid hand soap)
za The stearyl mercaptan was initially dissolved ixito tTie EnSolv, The
detergent was then u~ixed into the solutions. Samples of Argetuum Silver were
polished and ultrasonically degreased in EnSolv 765 for 2 minutes. Tlie
steaiyl
ar<ercaptaz~lEnSolv/detergeizt solutior~ were then directly applied to the
surface of
the Argentitun sammples using damp cotton wool and massaged into lather. T&e
samples were then rinsed under running tt~p canter. In each case, it was noted
that
watex was repelled off of the polished scufsce, leaving the s~nples dry.
Samples
were tarnish tested as in >rxample 1 by being exposed to neat ammonium
polysnlphide solution over a period of 1 hour. 'They a1I showed enhanced
tarnish
resistance. The above direct method for applying die Stearyl ~ercaptan was
3o tested on samples degreased in a 2°ro Faity Liquid aqueous solution,
Enhanced
t<~zush resistance was again achieved.
CA 02520807 2005-09-28
Example 7
CtQth Application (solvcn# degreased samples}
s
Cloths were hrepued by soaking clean cotton cloth in the following
solutions:and allowing the cloths to dry
D.1 grazxi Stearyl Mereaptarx dissolved in IOOmI ;E;nSolv
- 0.~ gram Stearyl Mercaptann dissolved in 100m1 l:nSolv
- 1.0 gram Stearyl Mercaptan dissolved in 100m1 EnSolv (Preferred)
Samples of Argentiu,m Silver twhich had been polished and ultrasonically
degreased in EnSolv 7bS ~ox 2 minutes) were wiped with the cloths then buffed
with clean cotton wool. Samples were tarnish tested as described in Example 1
by being exposed to itrnmoniutn polysulphida solution over a period of 1 hour.
All of the samples showed enhan.ecd tarnish resistance.
Example S
~exad~e~yl and aetudecyl morcaptan in ~stiry liguid
Hexadecyi rzzexcaptan (ig) in the liquid state was mixed with Fairy liquid
tsurfactant containing anionic anal nonionic surface active agents) ~zd with
water
z~ in the quantities indicated below:
Reforence Fairy liduid (m~} L7~ionised water (mI)
8.1 40 ' Nil
8.2 100 Nil
8.3 200 hril
s.-~ ~a loo
CA 02520807 2005-09-28
_ 32
8.5 ~0 244
The ingredients of silulion 8:? appeared to mix well without needing the
hekadecyl rn.ercaptart to be dissolved in art organic solvent bcfarehand, A
sample
of Argentium silver was immersed in the resulting solution for 10 minutes and
rinsed, The swface of the Argentiutn sample had became hydrophobic,
suggesting the formation of a layer of hexadecyl mercaptan attaohed to tho
surface of the Argentium silver. It rinsed well in water 'vithaue arxy
noticeable
deposit being lef~C on the surface after rinsing. A region of ih.e sample was
rubbed
1 o with cotton wool soaked in EnSolv 765 and then subjected to t~zxtish
testing with
neat amtnaniurn polysulplSide ovc;r a period of ~5 -minutes. Excellent tarnish
resistance was noted, without significant difference between the region that
had
'been treated with EnSolv ?6S and the region that had not been so treated.
Similar
solutions were prepared from octadecyl mercapf~n and fiairy liquid. Thep were
t 5 transparent at first, bztt of lesser stability with separation of a
surface layer of
octadecyl mercaptan after some months.
example 9
2o Hexadecyl mercaptan in Simply shower gel
Hexadecyl mercaptan in the liquid state was mixed with Siwple shower
gel (a clear shower gel frartt Aceentia Health and $eauty Ltd, Birminghttrn,
UTG,
and believed to contain sodium Iaureth sulfate and aoca.midopropyl betaine as
25 principal surfact~rtts, together with cocamide 17EA arid incidental
ingredieuts~ arid
with water in the quantities indicated below:
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- 33 -
Reference HDA~I (g) Simple (ml) Dcionised water
(rnl)
9.1 1 100 Nil
9.2 1 100 100
9.3 S 100 100
s 9_4 t X00 100
Shortly after mixing, solutions 9.1 and 9,4 weIe completely transp3ret11
viscous gels free from noticeable separation of the hexadecyl znercaptan.
Sample
9.2 was also Gamgletely transparent but had a water-like consistency and again
14 dad not exhibit sepfuation of hexadecyl ruexGaptan. Sample 9.3 which also
had a
water-like coz~slsteney appeared as a milky emulsion when shaken but exhibited
separation pf hexndecyl mexeaptan at the stud'aee ozz standing.
In a preliminary experiment, a sample of Argentitun silver was immersed
n in soiutiou 9.I for 10 minutes and rinsed. The surface of the Argentium
sample
bad become hydrophobic, suggesCinb the fornxatian of a layer of hexadecyl
mcrcaptan attached to the surfaee or the Argentium silver. Xt rinsed web in
water
without any noticeable deposit being left on the surface after rinsing. lVhen
tested with neat amrnoni~um polysulfide, excellent tarnish resistance was
noted.
Samples of Argentium silver and conventional Slerlinb silver were
prepared-as-follaws. Each scruple was polished with Steelbright polish,
followed
by raugc, and then ulfrasanically degreased for twa minutes in a 2 vvt% Fairy
Liquid solution in water at 54°C. 1t was then further degreased fox 5
minutes in
ethanol and immersed at ambient temperatures in the test solulxon. After
removal,
part of each sample was rubbed ~,vith tissue soaked in BnSolv ?65 and then
subjected to tarnish testing with neat ammonium polysulphide aver a period of
45
minutes. Argentium samples showed exeeIlent tarnish resistance and thial
bonding, especially good results being obtained with solutions 9.1 and 9.~
~0 compared to the higher water content solutions 9.2 and 9.3, Solutions 9.1
and 9.4
appeared to provide soma tarnish protcctior~ for standard Sterling silver
also, but
CA 02520807 2005-09-28
- 34 -
the tluol layer could be removed easily as was apparent from the differences
between the entreated and the IJnSolv 7t;5 treated ze~ions.
E~eampla IU
Mixtures df cocamidopropyl betaine (CPR) and sodium l:tureth sulfate (~ST.S)
The above tuaterials were supplied as a thick pourable aqueous liquid and
as a highly concentrated somewhat gelatinous liquid {7U°lo active) by
Surfachern
Ltd of T.,~ods, United Kindgom. Hexadeoyl mercaptarc (1 rnl) in the liquid
state
was mixed with these materials in the quantities indicated below;
Reference SLS {ml) CPB {ml} Water (onl}
10.1 40 40 100
I0.2 40 ?0 100
10.3 30 10 100
10.4 i0 3U 50
10.5 30 10 150
For solution 10. i, Itexadecyl mercaptan was added to a thick mixture of
sodium laureth sulphate and cocamidopropyl betaine aver which water was adt~ed
and the solution was mixed cold.. 'The resulting mixture initially had a thick
foamy-white texture which on settling ttur:.ed into a transparent gel.
Solution I0.2
was somewhat similar. Solution 10.3 was watery and was ioitiaily slightly
transparent with lots of bubbles on top ofthe solution., and on sett;ing
overnight it
became transparent. Solution I0.4 was mixed with gentle heating to about
35°C
Heat appeared to slightly help with the mixing procedure. Atter a few minutes
of
mixing the mixture foarncd severaly. ~'he mix.-tu.re was allowed to stand
overnighf
and fUrmed a viscous solution. Solution 10.5 vas heated to appi~oxirnately
35°C
v~hiIst mixing. Water was last in~retiient to be Rdded. Using heat fQr mixing
CA 02520807 2005-09-28
- 35 -
proved beneficial. The solution appeared very foamy but this settled over a
few
hours (within 12 houzs) to form a transpare»t solution slightly thinker than
water.
Argentium silver samples were prepared by polishing iri Steelbright and
then rouge, ultrasonically degreasing in a 2°/n aqueous Fairy Liquid.
solution
further degxeusing in acetone, immersion in the test solution at ambient
tempezatures for i0 mirmtes, and washing under cold rutviing tap water. A
lower
rebion of each sample was rubbed with tissue soaked in EnSolv in an attempt to
attempt to .remove any thiols, after which the sample was left to stead foz 45
to minutes and wezn then e,cposed to a neat ammonium polysuphide accelerated
t~unishing test far 45 tninnutes,
Ail the samples showed extremely good hydrophobic properties during the
rinsing process which indicates presence of thiols. Water drops were repelled
is and throe was no need to dry each sample. The samples performed well in the
tarnishing test with resistance to tarnishing and little difference between
the
rubbed and un-rubbed regions. It was concluded that the hexadanyl meoaptc~n.
in
each sample tested had created a tarnish-protective thioi-bonded layer on the
since of the Argentium silver.
zo
