Note: Descriptions are shown in the official language in which they were submitted.
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Desc, iplion
COMPOSITION AND PROCESS FOR ZINC PHOSPHATE CONVERSION COATING
FIELD OF T~E INVENTION
~ The present invention relates to zinc phos,cl,ate-based conversion
coating or treatment compositions for application to metals, for example, steelsand zinc-plated steels, and to methods for the zinc phosphate-based conversion
~ dl.l l ll31 ll or coating of metals. More particularly, this invention relates to a zinc
phospl ,ale-based conversion treatment composition, often hereinafter called a
"bath" for brevity, even when used by some method other than immersion, and
method that can uniformly coat metals with a fine, dense zinc phosphate-type
conversion coating that contains extremely small conversion crystals and that,
based on the presence of said microfine crystals, can improve the adherence of
the zinc phosphate-type conversion film to paint films.
DESCRIPTION OF RELATED ART
At present, a zinc p hosphale-based conversion treatment is executed as
a pretreatment on various metals when the metal is to be painted or subjected
to cold working. This pretreatment is carried out in the former case in order toimprove the post-painting co"osio" ~esisl~r,ce and the paint film adherence and
in the latter case in order to improve lubrication during cold working.
The conversion treatment baths used in zinc phosphate-based conver-
sion treal",enl:j are essentially acidic a~ueo~ Is solutions that contain zinc ions,
phosphate ions, and oxidizer. Nitrite salts, chlorate salts, hydrogen peroxide,
organic nitro compounds, hydroxylamine, and the like, are usually considered
for use as the oxidizer. These oxidizers function to accelerate the conversion
reactions and so are generally called conversion accelerators. While a nitrate
salt may be present in the conversion l,eal,nent bath, nitrate salts do not exhibit
an oxidizing function in zinc phosphate-based conversion treatment baths and
so are distinct from conversion accelerators.
In the case of the conversion treatment of ferriferous metals, one role of
the conversion accelerator in zinc phosphate-based conversion treatment is to
oxidize the divalent iron ions eluted into the bath to trivalent iron ions. The
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conversion reactions are inhibited, for example, by the accumulation of divalentiron ions during the continuous conversion treatment of rel, ir~r.,us metals, so the
role of the conversion accelerator in preventing accumulation of the divalent iron
ions is extremely important.
However, the known conversion accelerators are each ~ssociated with
problems that must be solved. For example, in the case of the nitrite salts,
which are at present the most widely used conversion accelerators, these are
unstable in the acidic region and are thus consumed by spontaneous decompo-
sition even when no conversion treatment is being run and the bath is merely
0 stored. This requires continual make up of the consumed amount in order to
maintain a constant concer,l, dlion.
Furthermore, as is known some of the nitrite salt is converted to NOx
during the spontaneous decomposition or the intended oxidation activity, and
this NOx diffuses into the atmosphere as a pollutant.
In the case of chlorate salt conversion acceler~lo, ~, chloride ions are pro-
duced during conversion treatment as a decor"~osition product and accumulate
in the conversion treatment bath. The corrosion resistance of the metal suffers
a drastic decline when even a trace amount of the chloride ions in the conver-
sion treatment bath (er"c.;ns present on the surface of the treated metal. More-over, although chlorate salts are generally used in combination with another
conversion accelerator, such as a nitrite salt, the use of a chlorate salt by itself
results in a sl ~hsPntial reduction in the conversion reaction rate.
The use of hydrogen peroxide as a conversion accelerator is associated
with ,.,ru~,!e. "s of stability in the conversion treatment bath, and hydrogen perox-
ide is readily deco",posed by dissolved oxygen in the conversion bath. In addi-
tion, hydrogen peroxide has a narrow optimal conce~ ILI alion range in conversion
treatment, which makes management of the conversion treatment bath quite dif-
ficult. When the dissolved hydlogen peroxide concent,dLioll is too high, a poorly
adherent powder-like conversion film is deposited on the metal surface.
Problems also occur with the use of nitrogenous orgal~ic compounds such
as organic nitro compounds (e.g., nitroguanine, sodium meta-nitrobenzene
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sulrondle, etc.) as a conversion accelerator. For example, in the case of nitro-guanine this co",pound has a low water solubility and thus cannot be
formulated as a concentrate for addilion to the conversion treatment bath.
Moreover it has a weak oxidizing activity for divalent iron ions and so providespoor control of the divalent iron ions conce"l,dlion in the conversion bath.
Sodium meta-nilrobel ,,ene sulfonate by itself has a poor conversion activity and
must generally be used in combination with another stronger conversion acceler-
ator. Its co"cer,l, ~lion management also requires large-scale measurement in-
strume~ iion such as an ion chromatograph. In addition, the accumulation of
~0 these orya,-ic nitro compounds and their decor"position products in the conver-
sion lr~alme"l bath causes an increase in the COD of the conversion treatment
effluent which has a negative effect on the enviroi)l"enl
With regard to the use of a hydroxylamine compound as a nitrogenous
organic conversion acceler~lor such a compound must for best results, be add-
ed to the conversion treatment bath in concentrations of at least 1 000 ppm
which c~l ~ses a large uneconon,ical consumption of the conversion acceierator.
The use of cl)rolll.~ acid and ~el"~anganale salts as a conversion acceler-
ator for zinc phospl ,ale-based conversion ll ~all "e, ll baths has been investigated
(Norio Sato et al. Boshoku Gijutsu ~English title: Corrosion Engineenngl, Vol-
ume 15 I~lo. 5 (1966))~ These authors reported that the formation of conversion
coatings was not observed at conce"lraLions of 5 or 10 millimoles per liter.
Many of the already known conversion accelerators as described above
are nitrogenous compounds. These nitrogenous co,n,~ounds are refractory to
removal by chemical wastewater treatment methods and must be removed by
microbiological treal"~e"ls. However microbiological treatments have trouble
removing high concenl, ~lions of nitrogenous compounds and cannot completely
remove even low concentrations. Nitrogenous compounds have recently been
one factor conl, iL,uting to the eutrophication of bodies of water and have there-
fore been larg~led for increasingly stringent d;sc;har~e regulations. These envir-
onmental considerations have created demand for the development of a nitrog-
enous compound-free zinc phosphate-based conversion treatment bath.
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At present, zinc phosphale-based conversion treatments and chromate
l(ealn ,ei lls are widely used to provide unc~e".ail ~I coatings for the purpose of im-
proving the post-painting corrosion resistance and paint film adherence of vari-ous metals. Metal sul~sl,ates of iron and composite materials comprising combi-
nations o~ diFferent materials are primarily subjected to zinc phosphate-based
conversion treatments due to the difficulties encountered in the chro"~ate treat-
ment of these types of sl~slrales.
The size of the crystals in the coatings afforded by zinc phosphate-based
conversion treatment generally undergo large variations as a function of the
0 treatment condiLiol-s. Thick co~lings of coarse crystals are satisfactory when the
goal is rust prevention or cold working. However, such coatings do not afford
a saLi~rac~ory paint film adherence when they are subsequently painted, and the
zinc pl ,ospl ,aLe-based conversion films employed as underpaint coatings must
in fact be thin films of uniform, fine, and dense film crystals.
Two methods are known for obLaining thin zinc phosphate-type conver-
sion films. One m eLl~od cons;~ls of ~r" ,;, lali"g the film deposition reactions dur-
ing the course of these reactions by interrupting contact with the conversion
bath. This method results in incomplete deposition of the conversion film and
thus in incomplete coverage of the substrate metal. As a result, not only can
rusting occur on the substrate metal during post-conversion steps such as the
water rinse and drying, but the post-painting corrosion resistance often will also
be unsatisfactory.
The other method cc r,~ of gel ,er~lir,g microfine sizes for the film crys-
tals. In this method, the film deposition reactions end with the coating in a thin
film form. As a result, the completed conversion film entirely covers the sub-
strate metal and this method is thus able to provide both a satisfactory paint film
adherence and post-painting corrosion resistance.
The above-described zinc phosphate-based conversion treatment tech-
nolcgies are mainly implemented by immersion and spraying. Immersion tech-
nologies not only do not provide ",.~orine film crystals, but usually re~uire leng-
thy conversion treatment times when the treatment temperature is not at least
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55 ~C. Spray treatment, on the other hand, does provide fiim crystals that are
somewhat finer sized than in i,)lll,el~ion treatment, but which are still not at a
level that provides a satisfactory painting pe, ronl,a"ce. And again, treatment
temperatures of at least 55 ~C are required in order to carry out treatment in arelatively short time.
A titanium coiloid surface-conditioning treatment must usualiy be applied
to the metal surface i"""edidLely prior to conversion treatment in order to obtain
(a) fine-crystal rO"~laliOl ~ in the coating and (b) a reduction in the treatment tem-
perature to 50 ~C and below. This surface-conditioning l~eal,ne,~t activates the~o surface of the metal work with the result that, regardless of the use of immersion
or spraying, the treatment temperature can be lowered, the treatment time can
be shortened, and a fine-sized crystalline film can be formed that provides an
entirelys~lisr~d~ /paintingpe,ru",~"ce. However, manage",enlofthesurface
con.JiLio,)er l, eal"~enl bath is complicated and this l~aal~ ~e~ ~l also requires addi-
tional racililies and an e~ansiol, of the treatment space. These considerations
have quite recently strengthened the demand for a conversion accelerator that
can provide a good-quality conversion fiim on metal surfaces even without the
.ec~ ~tion of a surface-conditioning step.
Also, the titanium colloid dispersed in the surface-conditioning treatment
bath aggregates with elapsed time after bath preparation, leading to a timewise
decline in the surface cor,dilioning activity. Japanese Patent Publication [Koko-
ku] Number Sho 62-9190 [9,190/1987] teaci ,es management of the Mg/P2O7 ra-
tio in the surface-conditioning treatment bath in order to increase the stability of
the titanium colloid, while ~apanese Patent Application Laid Open lKokai or Un-
examined] Number Sho 63-18084 [18,084/1988] discloses addition to the sur-
face-conditioning l, adll "ent bath of an organic material as a stabilizer for the ti-
tanium colloid. Each of these methods, however, suffers from inadequate ef-
fects, with the result that in practice aged bath must be discharged and freshlypre~oar~d bath must be supplied on a continuous basis in order to cope with the
decline in activity. This preparation and management of the surface-condition-
ing ll ~dll "a, ll bath is com~lex and labor intensive and entails a major economic
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burden due to its heavy reagent consumption. And of course, since treatment
faciiities are required in order to implement the surface-conditionin~ treatment,
this raises such issues as maintenance of the facilities and an expansion of thetreatment space.
As a conse~.lence of the various issues ~iscussed above, there has re-
cently been a strengthening in demand for the development of a surface treat-
ment method that can omit the problematic titanium colloid surface-conditioning
treatment while still being able to equip the metal surface with the uniform, fine,
dense, and thin conversion films that are optimal as underpaint coatings.
A general example of the treatment method used to form a zinc phos-
phate-type conversion film on metals comprises the execution of the following
processes in the given sequence: t1 ) alkaline degreasing, (2) water rinse, (3)
conversion, (4) water rinse, and (5) drain and dry. When the film will be used
as an under~aint coali"g, the conversion process (3) is preceded by a surface-
conditioning step using a titanium colloid treatment bath for the purpose of gen-
erating uniform, fine, and dense conversion film crystals.
The first drawback to the prior-art surface treatment technologies de-
s~ i~ed above is that they use a large number of process steps, thus making the
overall process quite lengthy. As a result, the necessary treatment facilities are
large and take up s~,L):jla~ llial space. While the surface treatment methods de-
scribed above are structured from 5 or 6 step processes, the alkaline degreasingstep and water rinse step are themselves frequently implemented as multistage
treal",e,)Ls in order to improve the cleaning efficiency. This raises equipment
costs even more and in addiliol, causes lower productivity, because even longer
26 times are required to complete the overall treatment process.
A second drawback to the prior-art technologies as described above is
that they require the manage" ,e, ~1 of a large number of parameters. As examp-
les, in the alkaline degreasing step the alkalinity (total alkalinity, free alkalinity)
in the degreasing bath must be managed, while in the conversion step the acid
co,)cerll,dlion in the treatment bath (total acidity, free acidity) must be managed.
This a")pliri~lion of the pd~d" ,ale, ~ under management increases the operating
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overhead. At the same time, the cost burden is raised by reagent cons~ .Lion
in the separ~Le ,~"~cess steps. Finally, the storage stability of a titanium colloid
disper~ion is by no means guaranteed, and it requires appropriate management
and periodic disposal and repienishme~ IL.
One method that can be considered for solving these two drawbacks is
the exea Jtion of the steps from alkaline deyreasing to conversion in a single pro-
cess step through the use of a su, rd~,~"L-containing zinc phosphate-based con-
version bath that combines degreasing and conversion. However, when de-
greasing and conversion are run at the same time, the conversion reactions initi-
.O ate sequentially from those regions of the metal work that have been cleaned.
This creates a strong tendency for the quality and appearance of the resulting
conversion film to be nonuniform.
Another possi~iliL~/ would be to add the surFace conditioner to the conver-
sion treatment bath in expectation of producing a surface-conditioning effect onthe metal during treatment in the conversion bath. In this case, however, a sur-face~"diLioning effect must be completely ruled out, because the titanium col-
loid main iny, ediel IL is unstable in the acid region. Thus, not only will the com-
bined use of surface conditioner and conversion bath not yield microfine-sized
film crystals, through a retardation of the film deposition rate it will also lead to
an addiLi~)l lal e m ,cl ,asi~il ,g of inhomogeneities in the appearance of the conver-
sion film.
In sum, then, there is strong demand for a contraction of the treatment
pr~Jcess as currently pr~cticed, a re~ ction in equipment and reagent costs, anda simplification in treatment bath management. However, this demand has in
act~ ty remained unsali~ried to date due to the high technical barriers involved in meeting it.
OBJECTS OF THE INVENTION
The pr~senl invention provides a zinc phosphale-based conversion treat-
ment bath and method for application to metals that can deposit uniform, fine,
and dense zinc phosphate-type conversion films on the surface of metal sub-
strates and that can induce a microfine-sizing of the conversion film crystals.
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In ad-lil;on, the present invention provides a zinc phosphate-based con-
version lreaL",~n( bath and l,e~l",el~l rll~lhod that--even without the execution
on the metal surface of surface conditioning with a surface conditioner--can
deposit thereon a uniform, fine, and dense zinc phosphate-type conversion film
that contains microfine crystals that are highly adherent to paint films and that
is effective as an underpaint layer (undercoat) for paint films.
SUMMARY OF THE INVENTION
The aforesaid ob,ects are achieved by a zinc phosphate-based conver-
sion treatment bath and treatment method according to the present invention as
10 described below. A zinc pl)osphate-based conversion treatment bath accGrdi, lg
to the presenl invention for application to metals characteristically contains zinc
ions and phospl ~ale ions as its main components and also contains 50 to 1500
parts per million by weight (hereinafter usually abbreviated as "ppm"~ of conver-
sion accelerator consisting of at least one organoperuxi~le.
The total cc "le, ll of n it~ù~enous compounds in the zinc phosphate-based
conversion ll'~d~ n L bath ac~,~ g to the present invention is pr~rera~ly limit-ed to 0 to 200 ppm, measured as its stoichiometric equivalent as nitrogen. The
said organoperoxide is preferably water soluble and preferably has a peroxy
structure or percarboxyl structure. In addition, the subject organoperoxide is
prererdbly selected from ethyl h~/dluperù~ide, isopr~pyl hydroperoxide, tert-butyl
hydroperoxide, tert-hexyl hy~ll operoxide, diethyl peroxide, di-tert-butyl peroxide,
acetylacetone peroxide, cumene hydroperoxide, tert-butylperoxymaleic acid,
peracetic acid, monoper~hll ~alic acid, and persuccinic acid.
A zinc ,uhosl-hale-based conversion treatment bath according to the pres-
ent invention may also contain surfactant.
The zinc phosphaLe-based conversion treatment method accordil Ig to the
present invention for application to metals is characterized by the formation ofa zinc phosphate-type conversion film on the surface of a metal by bringing the
metal surface into conlacl with a conversion treatment bath that contains zinc
30 ions and phosphate ions as its main corl,po,1enls and that also contains 50 to
1500 ppm of conversion accelerator consisting of at least 1 organoperoxide.
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The total conlenl of nitrogenous compounds in the said treatment bath
used in the zinc p ho~,c31 ,ate-based conversion lre~l"~el ll method according to the
p,t:se"~ invention is preferably limited to 0 to 200 ppm as the nitrogen content.
The said conversion accelerator is prererably water soluble and prefqr~bly has
a peroxy structure or percarboxyl structure. In addition the subject conversion
bath preferably has a pH from 2.0 to 4.0 and prererably is kept at a temperatureof 25 ~C to 50 ~C. The surface of the metal may also be subjected to a cleaning
step i,n" ,ecliately before the subject conversion (. e~Ln ,enL
A conversion treatment bath used in the zinc phosphate-based conver-
sion lre~",enl method according to the present invention may also contain sur-
factant in order to simultaneously effect cleaning and conversion coating of themetal surface. When a surfactant is used its conce"lralion in the conversion
treatment bath is preferably from 0.5 to 5 g/L.
DETAILS OF THE INVENTION AND iTS PREFERRED EMBODIMENTS
It has been discovered that (1) an o,~anopero,tide conversion accelerator
did not require the co-use of another prior-art conversion accelerator or a nitric
acid compound which made possible the formulation of a nitrogenous com-
pound-free conversion bath; (2) even without the execution of a surface-condi-
tioning treatment a uniform fine and dense zinc phosphate-type conversion
film could be formed on metal surfaces when organoperoxide was used as the
conversion accelerator; and (3) a good pe, r.,r" lil ,g zinc phosphate-type conver-
sion film can be formed on metals without narrow restrictions originating with the
treatment ten ,peralure or zinc concenlr~lion of the treatment bath. The presentinvention was achieved based on these discoveries.
As stated above the total content of nitrogenous compounds in the con-
version bath accordi"g to the present invention is limited to 0 to 200 ppm, pref-
erably to 0 to 100 ppm more preferdbly to 0 to 50 ppm and even more prefer-
ably to 0 to 20 ppm in each case measured as its stoichiometric equivalent as
nitrogen.
The most preferred range for the zinc ions content in a conversion bath
accor~l;"s~ to the present invention will vary as a function of the particular appli-
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cation of the conversion film. The preferred zinc ions content in the conversionbath is from 0.5 to 15 grams per iiter, hereinafter usually abbreviated as "g/L".
For example, when the conversion bath according to the present inven-
tion is used to provide an underpaint coating on the metal~ the preferred conver-
sion film weight is from about 0.5 to 1~.0 grams per square meter of surface
treated with the bath, I ,erei. ,~ner usually abbreviated as "g/m2". Oue to this, the
prere" ~d concer,l, dLio n range for the zinc ions in the conversion bath for this ap-
plication will be from 0.5 to 5.0 g/L. When the zinc ions concentration is less
than 0.5 g/L, the resulting zinc phosphate-type conversion film will have a re-
0 duced coverage ratio and the post-painting paint film adherence and post-paint-
ing corrosion resistance usually will be unsatisfactory. At above 5.0 g/L, the
post-painting paint film adherence in particular is reduced due to a coarsening
of the film crystals.
When, on the other hand, the conversion bath will be used for cold work-
ing of the metal treated with it, a thick film with a film weight of about 5.0 to 15.0
g/m2 is pr~r~rably laid down in order to provide a conversion film capable of fol-
lowing the plastic derom~dLion of the workpiece. In this case, the prerer,ed zinc
ions conce"l(~lio" range for the conversion bath will be from 5.0 to 15.0 g/L. At
zinc ions conce~ lions below 5.0 g/L, it can be difficult to obtain film weightsas specified above for this application. The coating weight no longer increases
at above 15.0 g/L, which makes such concentrations uneconomical.
The zinc ions needed in a composition according to the invention can be
provided by dissolving zinc oxide or zinc hydroxide in the acid component in theconversion bath, or by dissolving a water-soluble salt, for example, zinc phos-
26 phate or sulfate in the conversion bath.
The phosphate ions CGnCel ,lralion in the conversion bath according to the
presenl invention is prereraL ly from 5.0 to 30.0 g/L. The formation of a normalconversion film becomes problematic at values below 5.0 g/L. The effects of the
phosphate ions no longer increase at above 30.0 g/L, which makes such con-
cer~L~dLicJ~ Is uneconomical. The phosphate ions can be generated by the addi-
tion of phosphoric acid or its aqueous solution to the conversion bath or by dis-
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solution in the conversion bath of a salt of phosphoric acid, such as the sodium,
potassium, magnesium, or zinc salt.
A zinc phosphate-based conversion treatment bath according to the pres-
ent invention pr~rerably is an acidic aqueous solution with a pH value from 2.0
5 to 4.0 and more prere,ably about 2.5 to 3.~. In this pH region, orthophosphoric
~ acid (~13P04) has an equilibrium relationship with dihydrogen phosphate ions
(H2POi), hydrogen phosphate ions (HPOi2), and phosphate ions (Po43-), and
the stoichiometric equivalent as phosphate ions of all of these species, along
with any of the condensed pllospl ,oric acids and their salts in which phosphorus
0 has its +5 valence state, are considered to be part of the "phosphate ions" con-
tent as used herein, irrespective of whatever degree of ionization may actually
exist in the composition.
A conversion bath according to the present invention contains conversion
accelerator cc, IsisLing of at least one selection from the organoperoxides. This
organoperuxide is pr~re~ably water soluble and is preferably selected from com-
pounds having a peroxy structure or pe, c~, IJOXYI structure. The organoperoxideused by the pr~senl invention enM~"passes arc",~a~ic peroxides, cyclic aliphatic,c eroxides, and ali~ lic peroxides, and aliphatic peroxides having 1 to 7 carbon
atoms are preferred. Orga"Gperoxides bearing long-chain alkyl and aromatic
peroxides can be inadequately soluble in water and thus can have an unsatis-
factory conversion accelerating activity.
O, gano~eroxides effective as a conversion accelerator are preferably se-
lected from those with a simple peroxy structure, such as ethyl hydroperoxide,
;SG~rOPYI hydroperoxide, tert-butyl hydroperoxide, tert-hexyl h~dlùperoxide, di-
ethyl peroxide, di-tert-butyl peroxide, acetylacetone peroxide, cumene hydroper-oxide, and tert-butylperoxymaleic acid, and those with a percarboxyl structure,
such as peracetic acid, monoperphthalic acid, and persuccinic acid.
When the organoperoxide has a low solubility in the conversion bath, the
poorly soluble compound can be solubilized by the additiGi, to the treatment bath
30 of a small amount o~ water-soluble organic solvent, for example, tert-butyl alco-
hol or isopropyl alcohol.
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A working conversion treatment bath according to the present invention
as desc, ibed above pl ererably contains the conversion accelerator at a concen-tration of 50 to 1,500 ppm and pre~era~ly 80 to 1,200 ppm. The conversion ac-
celerating activity will usually be u"sali:,ra.,~ry when the conversion accelerator
conc~ r~lionis less than 50 ppm. The conversion accelerating activity no long-
er increases at conversion accelerator concentrations above 1,500 ppm, which
makes such concentrations uneconomical.
Since the conversion treatment bath accordi,1g to the present invention
also has the ability to microfine-size the deposiled zinc phosphate-type crystals,
~0 it can produce a uniform, fine, and dense zinc phosphate-type conversion film
even in the absence of any preceding surface-conditioning treatment for the pur-pose of microfine-sizing the film crystals. Moreover, since the conversion treat-
ment bath according to the present invention need not co"Lain nitric acid, nitrous
acid, an ~rg~"ic nitro compound, etc., it can be formulated completely free of ni-
trogenous co",pounds. In this case, effluent tr~dl"1ent will not require a process
for treating nil, uge"ous compounds. Although the addition of nitrogenous com-
pounds to the conversion bath according to the present invention is not preclud-ed, the nitrogen concenlralion is prererably limited as discussed above to 0 to
200 ppm.
In ~d~ition to zinc ions, a zinc phosphate-based conversion bath accord-
ing to the present invention may also conlain supple, nental y metal ions. Thesesupplementary metal ions can function as an etchant in order to induce a uni-
form etch of the surface of the metal substrate, or, in the case of application as
an underpaint coating, they can function to improve the painting performance.
Such non-zinc surJp'Ementaly metal ions can be nickel ions, manganese
ions, cobalt ions, iron ions, magnesium ions, calcium ions, and so forth. These
su~plerr,er,lary metal ions can be provided in a composition according to the in-
vention by dissolving their oxides, hydroxides, carbonates, sulfates, phosphates,
etc., in the treatment bath.
Suppler"entaly metal ions can be added to the conversion bath according
to the present invention at 100 to 3,000 ppm and prererably at 200 to 2,000 ppm.
-
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When renife,uus material is lre~le.l with a conversion bath accordin53 to
the present invention, trivalent iron ions will dissolve from the metal into thel,t:al",e"l bath and will accumulate at levels of 10 to 50 ppm. The accumulationof this amount of trivalent iron ions does not have a negative influence on the
effects of the treatment bath and m ~lhod according to the present invention. Ac-
cordingly, trivalent iron ions may be added to or may be present in the treatment
bath within this range prior to conversion treatment.
Depending on the particular requirements, a conversion bath according
to the present invention may conlain fluoride ions or fluorine-containing anions,
0 for example, complex fluoride ions such as fluosilicate ions or fluo,i~col ,ale ions.
Fluorine-containing anions can be provided in a composition according to this
invention by dissolving a fluorine-containing compound in the conversion bath,
for example, hydrofluoric acid, fluosilicic acid, fluo~i~conic acid, fluotitanic acid,
and their metal salts (sodium salts, potassium salts, magnesium salts).
6 A method according to the present invention includes a process in which
the surface of the metal is brought into conlacL with the zinc phosphate-based
conversion treatment bath. When the metal already has a clean sur~ace, the
zinc phosphate-based conversion treatment can be directly executed on the
clean metal by the method according to the present invention. However, when
the surface of the metal work is cont~ll,inated with microscopic metal particles,
dust, or grease, the co, ILdl ni, Idl llS should preferal~ly be removed from the metal
surface prior to the conversion treatment, by executing a cleaning treatment on
the metal surface, ~referably a cleaning treatment using a waterborne alkaline
degreasin~ bath, waterborne cleaning emulsion, or cleaning solvent. When a
2~ walerl~o, r,e cleaning bath is used, any of it remaining on the surface is prerer~b-
ly removed by rinsing the metal surFace with water.
In general, prior to conversion treatment the surface of the metal is de-
greased with an alkaline degreaser and then rinsed with water. In addition, after
the conversion l, ealn ,enl the conversion film is rinsed with water and then dried.
Both the degreasing and rinse processes may be implemented as multistage
processes. When the conversion film is to be used as an underpaint coating,
_
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the final rinse preferably uses deionized water.
In addition, when the conversion film is placed on the metal surface to
function as an under-;oaling for paint films, a surface-conditioning treatment us-
ing a titanium co""~ound colloid-containing surface conditioner is preferably exe-
cuted on the metal surface immediately prior to the conversion treatment. How-
ever, this surface-condilio,1ing treatment can be omitted in the method accol-ling
to the present invention.
The conversion treated surface of the metal is rinsed with water, dried as
necessary, and then painted.
0 When the conversion treatment bath according to the present inventionwill be used to lay down a conversion film in order to support cold working of the
metal, the degreasing and water rinse steps are preferably followed by an acid
rinse of the metal in order to remove scale from the metal surface.
When the conversion film is to be used to support cold working, the film
surface is prefer~bly lubl icaled with a lubricant, for example, a soap, in order to
improve the lubricating properties of the conversion film.
Contact between the metal being treated and the conversion treatment
composition in a method according to the present invention is generally effectedby, for exd" "~le, immersion, spraying, or a combination thereof. When the con-
21) version treatment is being run in order to provide an undercoat for paint films,
the treatment is preferably run for 0.5 to 5 minutes at a temperature from ambi-ent temperature to 60 ~(~. When the conversion treatment is being run on metal
that will be cold worked, the treatment temperature is prererably from S0 ~C to
90 ~C and the lredll~enl time is ,crerera~ly from 1 to 15 minutes. The above-de-scribed tredl~l,enl conditions will yield the desired conversion films.
Rer,~l ~se the organoperoxide (conversion accelerator) in the conversion
bath according to the present invention f~,l ,.:tions as an oxidizer, its reaction and/
or decc " "~osition products will accumulate in the treatment bath. For example,alcohol is produced by the reaction and/or decomposition of hydroperoxidel
while alcohol and carboxylic acid are produced by the reaction andJor decompo-
sition of peroxyester. Carboxylic acid is also produced by the reaction and/or
-
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decomposilio" of percarboxylic acid. The awumulation of these reaction and/or
decomposition products does not exercise a negative influence on the Ll edll 1 lel 1~
bath and method according to the presenl invention. As a consequence, prior
to conversion ll~2dLIllelll the reaction and/or decomposition products of the or-
ganope, oxide may be present in the treatment bath according to the present in-
~ vention, or may even be added to the bath, in either case without normally caus-
ing any problems.
The type, form, and dir"e"sions of metal subsl,~les that may be subjected
to the method according to the present invention are entirely unrestricted.
0 In specific terms, the method accor~li"g to the present invention can be
ar-pliQcl to various rel, irar~us m~lerials, for example, steel sheet and steel sheet
plated with ~i- .ci~(ous metal, and to various aluminiferous metals, for example,
aluminum and aluminum alloys such as aluminum-magnesium alloys and alumi-
num-silicon alloys.
J~ zinc phosphate-based conversion treatment bath accordi, ~g to the pres-
ent invention may as necess~ry also contain s~ ra.;lanl for cleaning the surfaceof the metal.
The metal surface can be cleaned when suRactant is present in the con-
version bath and, concurrently with this, can be covered with a zinc phosphate
conversion film. The surface of the metal may be soiled in this case, and there
are ~hsslntely no restrictions on these contaminants as long as they can be re-
moved by the surfactant-containing conversion bath. These co,-laminants in-
clude oils and greases, for example, grease, antirust oils, and press oils (these
may be conlaminated with dust); microfine metal particles; and other material.
The amount of col,la",inant is also not narrowly restricted.
Su, ra~lanl usable in the present invention comprises at least one selec-
tion from the nonionic, cationic, anionic, and amphoteric surfactants. However,
cationic su~ rdcldnUanionic su~ racla~ mbil IdLions should be avoided due to thecorresponding problems with treatment bath stability.
Nonionic su, ra.;Lanl~ usable in the method according to the present inven-
tion are exemplified by polyethylene glycol-type nonionic surfactants such as
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polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl ethers, polyoxyethyl-
ene fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethyl-ene-polyoxypropylene block polymers, and so forth; polyvalent alcohol-type non-
ionic su, ra~la"l~; such as sc, ~ l, fatty acid esters and so forth; and amide-type
nonionic surfactants such as fatty acid alkylolamides and so forth.
Cationic su, ractar,ts usable in the method accor~ling to the present inven-
tion are exemplified by amine salt-type cationic su, r~cla, lls such as the salts of
higher alkylamines, polyoxyethylene higher alkylamine salts, and so forth and
by quale" ,t,ry am")on Im salt-type cationic sul racidnls such as alk~ll, i" ,el~ "~lam-
0 monium salts and so forth.
~"~oho~eric SIJ~ racidl ll~; usable in the method according to the present in-
vention are exemplified by amino acid-type amphoteric surfactants such as
methyl alkylaminopropionate and so forth and by betaine-type amphoteric sur-
factants such as alkyldimethylbetaines and so forth.
Anionic surfactants, however, generally have low solubilities in the acid
region and for this reason their use in the present invention is frequently proble-
matic. However, types in which ethylene oxide has been added, as in the higher
alkyl ether sulfate ester salts, can be used since they retain good solubilitieseven in the acid region.
Col ,cer,l,alions of about 0.5 to 5 g/L are suitable for these surfactants in
a zinc phosphate-based conversion treatment bath in the method according to
the present invention. The type and concer,lralion of the surfactant should be
selet;te~l as ap~.r~".ridle as a function of the type and concenl, alion (add-on) of
the oil, grease, or other soil to be cleaned off.
The surface is cleaned at the same time as its conversion l, eal" len~ when
surfactant is present in the bath. When this method is run continuously, the
cleaned off soil will usually therefore accumulate in the treatment bath. Since
this accumulated soil is not inevitably benign or nondetrimental for the conver-sion treatment, its total accumulation is preferably limited to no more than 10
g/L. This restriction on the total accumulation will, however, vary as a function
of the type of soil and the type and content of the SLJ~ raclanl.
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After a conversion treatment with the surfactant-containing conversion
bath, the resulting conversion film is rinsed with water and the residual water is
eli~ aled from the surface of the conversion film. The water rinse may be im-
plemented as a single-step or multistep process, but the final water rinse prefer-
ably uses deionized water.
The aforesaid water elilll;natiGn process (drying process) is not an abso-
lute req~il el I ,enl when the conversion film-carrying surface of the metal is to be
coated with paint, for example, by electrodeposition. There are absolutely no
e:,ll ic~ions on the drying temperature or time, e.g., drying can be carried out at
0 room tel,~,ueral-lre or with heating.
This treatment of the metal surface with surfactant-containing conversion
bath according to the present invention provides a thorough elimination of the
oil, grease, dustt and/or metal particles and, at the same time as this cleaning,
accelerates the conversion film-forming reactions through the presence of the
conversion accelerator (organoperoxide~.
Thus, the surface of the metal will be cleaned and, concurrently with this
cleaning, a uniform, fine, and dense zinc phosphate-type conversion ~llm having
microfine film crystals will be formed on the cleaned metal surface.
The invention will be explained in greater detail below using working ex-
amples, which, however, are provided simply for purposes of explanation and
should not be construed as limiting the scope of the invention.
Exam~les 1 to 8 and Com~arative ExamPles 1 to 4
The following metals were used in these working and comparative examp-
les.
2~ (1) Cold-rolled steel sheet (SPCC-SD, abbreviated below as SPC) with a
sheet thickness of 0.8 mm.
(2) Galvanized steel sheet (abbreviated in the table as "plated") afforded by
electrogalvanizing, to an add-on mass of 20 g/m2, the type of cold-rolled steel
sheet described in (1).
- 30 These metals were each cut into 70 x 150 mm coupons.
In these examples and comparative exa",plcs, conversion films were
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formed on the above-described metals using the following process sequence,
unless otherwise stated. These films were intended for application as under-
paint coatings (ùndercoats):
(1) Degreasing (FINECLEANER~ L4460 alkaline degreaser, from Nihon
Péil keri~ing Cor"pany, Limited, 20 g/L of agent A, 12 g/L of agent B) at 43
~C for 120 seconds by immersion;
(2) Water rinse with tap water at ambient temperature for 30 seconds, spray;
(3) Surface conditioning (colloidal titanium surface conditioner, trademark:
PREPALENEt~) ZN from Nihon Parkerizing Company, Limited, 1 g/L aque-
.0 ous solution), at ambient temperature for 30 seconds, spray;
(4) Zinc ,uhospl ,ale-based conversion treatment, with compositions described
in the individual working and co",parali~/e ex~"~ s, at 43 ~C for 120 sec-
onds immersion;
(~) water rinse, with tap water at ambient temperature for 30 seconds, spray;
(6) deionized water rinse (deionized water, conductivity = 0.2 microSiem-
ens/cm) at ambient temperature for 2û seconds, spray;
(7~ drain and dry in a hot air current at 1 10 ~C for 180 seconds.
However, in Examples 5 and 7 and Comparative Example 3, the surface-condi-
tioning treatment in (3) was not run and the degreased and water rinsed metal
surface was submitted to the zinc phosphate-based conversion treatment as in
step (4) directly affer degreasing (1 ) and the water rinse in step (2).
The free acidity in the zinc pl)ospl ,aLe-based conversion baths in Examp-
les 1 to 8 and Con,parali~/e Examples 1 to 4 was adiusted to the specified val-
ues, vide in~ra, using sodium hydroxide. The free acidity was measured by titrat-
ing 10 milliliters, hereinafter usually abbreviated as "mL", of the particular treat-
ment bath to neutrality using 0.1 N aqueous sodium hydroxide and bromophenol
blue as the indicator. The number of milliliters (mL) of the aqueous sodium hy-
droxide solution required for the color change from yellow to blue was deter-
mined and is reported as ''poi"l~" of free acidity. The fluoride ions concenl, dlion
in the conversion baths was measured using a fluorine ion sensitive electrode.
The coating weight was measured as follows. The weight ("W1"~ in
18
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grams of the treated coupon after conversion treatment was first measured, snd
the treated coupon was then s~ cted to a film stripping treatment using the
stripping solution and stripping conditions reported below. The weight of the
stripped coupon was measured to give "W2" In grams, and the coating mass in
g/m2 was calculated from the formula (W1-W2)/(0.021).
Treatment for cold-rolled steel cou~ons
stripping solution: 5 % by weight of aqueous chromic acid soiution
stripping conditions: 75 ~C, 15 minutes, immersion.
Treatment for ~alvanized steel cou~ons
stripping solution: 2 % by weight of ammonium dich(c",ale + 49 % by
weight of 28 % ~queous a,lllllollia + 49 % by weight
of pure water
stripping conditions: ambient temperature, 15 minutes, immersion.
The app~di~t,ce of the cG~ings was inspected visually, and the morphol-
15 ogy and size of the grains in the conversion coating were evaluated by inspec-
tion with a scanning electron microscope (''SEMU).
Conversion treatment bath (1 ) with the following composition was pre-
pared in Example 1.
ComPosition of conversion treatment bath (1 )
phosphate ions : 15 g/L (from addition of 75 % phosphoric acid)
zinc ions : 1.3 g/L (from addition of zinc oxide)
nickel ions : 1.0 g/L (from addition of nickel carbonate)
manganese ions : 0.5 glL (from addition of manganese carbonate)
fluoride ions : 100 ppm (from addition of 55 % hydrofluoric acid)
2~ 450 ppm of tert-butyl hydroperoxide was added as the organoperoxide to the
conversion bath with the above composition, and the free acidity of the conver-
sion bath was then adjusted to 0.9 point. A cold-rolled steel test coupon was
subjected first to the colloidal titanium surface-conditioning treatment (3) andthen to conversion treatment at a temperature of 43 ~C for 120 seconds, using
30 the above-described conversion bath (1). The resulting conversion coating
weight was 1.2 g/m2. The coating crystals were plates with an average grain
19
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size of 6 I nic~ ~" ,~ s. The conversion coating was grayish black and was uni-
form, fine, and dense. Other test results are repo, led in Table 1.
TABLE 1
Identi~l- SubstrateConc. in Tre~ ; t Comp. of: Surface Acceler-
cation Condi- ator Used
Po4-3, ~ zn+2 ~ N?PPm tioner?
Ex 1 SPC 15 1.3 0 yes a
Ex 2 plated 15 1.3 0 yes a
Ex 3 SPC 15 1.3 0 yes a
Ex 4 SPC 15 1.3 500 yes a
Ex 5 SPC 15 1.3 0 no b
Ex 6 SPC 15 1.3 0 yes c
Ex 7 SPC 1~ 1.3 0 no a
Ex 8 SPC 1~ 1.3 1400 yes a
CE 1 SPC 15 1.3 0 yes a
CE 2 plated 15 1.3 0 yes a
CE 3 SPC 15 1.3 1400 no d
CE 4 SPC 15 1.3 0 yes e
~bbreviations in. and Other Notes for~ Table 1
"Ex" means"Fx~mple"; "CE' means "Co~ ive Example"; "Conc." means "Concentration";
"Comp." means "Composition"; "Acc." means "Accelerator"; ",um" means "micrometres".
In the column headed "Accelerator Used":
"a" means tert-butyl hydroperoxide;
"b" means tert-he~yl Lydrop~lo~ide;
"c" means peracetic acid;
"d" means nitrite ions;
"e" means chlorate ions.
... Table I is continued on the next p~ge....
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Identi-Conc. Points Coating Coating Appearance Coating Coating
fica- of of Mass, Clystal Grain
tion Acc., Free g/1112 Shape Size, ~m
ppm Acid
~ Ex 1 450 0.9 1.2Grayish black plates 6
Ex 2 450 0.9 2.8grayish white plates 4
Ex 3 80 0.6 0.9grayish black plates 8
Ex 4 1200 0.9 1.1grayish black plates 7
Ex 5 400 0.9 1.0grayish bla~k plates 6
Ex 6 100 0.6 1.3grayish black plates 10
Ex 7 500 0.6 1.1grayish black plates 10
Ex 8 450 0.9 1.1grayish black plates
CE 1 5 0.9 0.5yellow rust appeared columnar 13
CE 2 5 0.9 0.9sparse coating columnar 15
CE 3 150 0.9 0.1yellow rust appeared granular 80
Cl~i 4 1500 0.9 0.9sparse coating c~ mn~r 15
In Example 2, a galvanized steel test coupon was subjected first to the
same degreasing (1), water rinse (2), and surface-conditioning treatment (3) as
in Example 1 and then to conversion treatment as in Example 1 using conver-
sion treatment bath (1). The resulting conversion coating weight was 2.8 g/m2.
The crystals were plates with an avera~e grain size of 4 micrometers. The con-
version coating was grayish white and was uniform, fine, and dense.
In Example 3, a cold-rolled steel test coupon was subjected first to the
same surface-conditioning treatment as in Example 1 and then to conversion
treatment using the same conversion treatment bath as in Example 1, except
~o that the organoperoxide consisted of 80 ppm tert-butyl hydroperoxide and the
free acidity was adjusted to 0.6 point. The resulting conversion coating weight
was 0.9 g/m2. The crystals were plates with an average grain size of 8 micro-
metres. The conversion coating was grayish black and was uniform, fine, and
dense.
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In Example 4, a cold-rolled steel test coupon was subjected first to the
same surface-conditioning treatment as in Example 1 and then to conversion
treal",enl using the same conversion treatment bath as in Example 1, except
that 1200 ppm of tert-butyl hydl uperu,tide was the organoperoxide and sufficient
6 65.5 % nitric acid was added to give a nitrogen component conlent of 500 ppm.
The free acidity of the conversion bath was adiusted to 0.9 point. The resultingconversion coating weight was 1.1 g/m2. The coating crystals were plates with
an average grain size of 7 micrometers. The conversion coating was grayish
black and was uniform, fine, and dense.
,0 In Example 5, a cold-rolled steel test coupon, without any surface-condi-
tioning treatment, was subjected to conversion treatment as in Example 1, ex-
cept that 400 ppm of tert-hexyl hydroperoxide was the orgal ,operoxide. The freeacidity was adjusted to 0.9 point. The resulting conversion coating weight was
1.0 g/m2. The coating crystals were plates with an average grain size of 6 mi-
crometres. The conversion coaliny was grayish black and was uniform, fine,
and dense.
In Example 6, a cold-rolled steel test coupon was subjected first to the
same surface-conditioning treatment as in Example 1 and then to conversion
treatment using the same conversion treatment bath as in Example 1, except
that 100 ppm of peracelic acid was the organoperoxide, and the free acidity was
adjusted to 0.6 point. The resulting conversion coating weight was 1.3 glm2.
The coating crystals were plates with an average grain size of 10 micrometres.
The conversion coating was grayish black and was uniform, fine, and dense.
In Example 7, a cold-rolled steel test coupon, without any surface-condi-
tioning treatment, was subjected to conversion treatment using the same conver-
sion bath as in Exdll,ple 1, except that ~00 ppm of tert-butyl hydroperoxide wasadded as the organoperoxide, and the free acidity was adjusted to 0.6 point.
The resulting conversion coating weight was 1.1 g/m2. The coating crystals
were plates with an average grain size of 10 micrometers. The conversion coat-
3D ing was grayish black and was uniform, fine, and dense.
Conversion treatment bath ~2) with the following composition was pre-
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pared for Example 8:
ComPosition of conversion l,edl",enl bath (2)
phosphate ions : 15 g/L (from addition of 75 ~/O phosphoric acid)
zinc ions : 1.3 g/L (from addition of zinc oxide)
nickel ions : 1.0 g/L (from addition of nickel nitrate)
manganese ions : 0.5 g/L (from addition of manganese carbonate)
fluoride ions : 100 ppm (from addition of 55 % hydrofluoric acid)
nitrate ions : 7.2 g/L (from addition of sodium nitrate and nickel
nitrate)
0 (nitrogen concer,lr~lion = 1.4 g/L)
450 ppm of tert-butyl hydroperoxide was added as the organoperoxide to the
conversion bath with the above composition, and the free acidity of the con-
version bath was then adjusted to 0.9 point. A cold-rolled steel test coupon was.s~ ~je ~d first to the colloidal titanium surface-con-lilioning treatment and then
to conversion treatment (conversion temperature = 43 ~C treatment time = 120
seconds) using the above-described conversion bath. The resulting conversion
coating weight was 1.1 g/m2. The coating crystals were plates with an average
grain size of 5 mi~ ~,, ne~e, ~. The conversion coating was grayish black and was
uniform fine and dense.
In Co"lpa,alive Example 1 a cold-rolled steel test coupon was subjected
to the same surface-conditioning treatment as in Example 1 and was then sub-
mitted to the same conversion treatment as in Example 1 except that the
organoperoxide consisted of 5 ppm of tert-butyl hydroperoxide. The conversion
coali"g weight was 0.5 g/m2 and the development of yellow rust was observed.
In Comparative Example 2 a galvanized steel test coupon was subjected
to conversion treatment as in Example 1 except that the organoperoxide con-
sisted of 5 ppm of tert-butyl hydroperoxide. The conversion coating weight was
0.9 g/m2 the average grain size was 15 micrometers and the coating was
sparse.
In ~omparative Example 3 a cold-rolled steel test coupon without any
surface-conditioning l,eal" ,enl was s~ Ihiected to conversion treatment as in Ex-
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ample 8, except that 15~ ppm of nitrite ions were added to the conversion bath
in place of the orgar-operoxide. The conversion coating weight was 0.1 g/m2,
which indi~ ed that almost no conversion coating deposilion had occurred. Yel-
iow rust had developed over the entire surface.
In Compa(c~ e Exdlll,~Jlc 4, a cold-rolled steel test coupon was subjected
to conversion l, e~lrnenl as in Example 1. In this case, however, sodium chlorate
was added to the conversion bath in place of the o, ganoperc,xide to give a chlor-
ate ions concenl~dliGI ~ of 1.5 g/L. The conversion coating weight was 0.9 glm2.The coating crystals were columnar and the average grain size was 15 micro-
0 metres. The conversion coating was sparsely deposited, and yellow rust was observed.
The test results are reported in Table 1. The organoperoxide concentra-
tions used in Examples 1 to 8 were within the range from 50 to 1,500 ppm. It
was thereby cor ril,~,ed that this concentration range produced a good-quality
~5 conversion coating on cold-rolled steel sheet as well as galvanized steel sheet.
A uniform, dense, and fine coating was obtained even when the surface-condi-
tioning treatment was not used.
In contrast, Corl ,,c,a, al,ve Examples 1 and 2 used organoper~xide concen-
llialiG"s below 50 ppm, and it was confirmed that in these cases the oxidation ac-
tivity by the conversion accelerator was inadequate, resulting in the depositionof only s~llered coating crystals. The uniror",;'y of the coating on the substrate
metal was therefore diminished.
Co"~par~ /e Examples 3 and 4 used non-organoperoxide conversion ac-
celelalor~. In Comparative Example 3, nitrite ions were used as the conversion
2s accelerator and no surface-conditioning treatment was carried out. It was con-
firmed that in this case conversion coating deposition was entirely absent.
Chlorate ions were used by themselves as the conversion accelerator in Com-
parative Example 4. It was confirmed that in this case the conversion reaction
rate was substantially slowed.
Examples 9 to 15
The following metals were used in these examples:
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(1 ) Cold-rolled steel sheet (SPCC-SD, sheet thickness: 0.8 mm, abbreviated
below as "SPC")
(2) Zinc-ele~;t,opldLed steel sheet (sheet thickness: 0.8 mm, plating weight:
. both surfaces 30 g/m2, abbreviated below as "EG")
(3) Galvannealed hot-dip zinc-plated steel sheet (sheet thickness: 0.8 mm,
plating weight: both surfaces 45 g/m2, abbreviated below as "G~')
(4) Aluminum-~ I lay, ~esium alloy sheet (Japanese Industrial Standard-A5052,
sheet thickness: 1.0 mm, abbreviated below as "AL").
In each case the metals were cut to 70 x 150 mm to prepare the specimens that
were then subjected to the treatments in the working and comparative examples.
Each test material was coated with 2 g/m2 of a commercial cleaning/rust-pre-
venting oil.
The same l, eal"~enls as in Example 1 were executed on the metal speci-
mens in each of Examples 9 to 15 with the following modifications: the surface-
conditioning treatment was omitted and conversion baths (3), (4), and (5) withthe compositions given below were used in place of conversion bath (1).
comPosition of conversion treatment bath (3)
phosphate ions : 15 g/L (from addition of 75% phosphoric acid)
zinc ions : 1.3 g/L (from addition of zinc oxide)
nickel ions : 0.5 g/L (from addition of nickel carbonate)
fluorine component : 1.0 g/L (from addition of sodium fluosilicate)
2-butanol : 30 glL
conversion accelerator : see below
free acidity : 0.6 point
Composition of conversion treatment bath (4)
phosphate ions : 13 g/L (from addition of 75 % phosphoric acid)
zinc ions : 1.1 g/L (from addition of zinc oxide)
cobalt ions : 0.4 g/L (from addition of basic cobalt carbonate)
fluorine component : 0.4 g/L (from addition of sodium fluoride)
30 conversion accelerator : see below
freeacidity : 0.4 point
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GomPosition of conversion treatment bath ~5)
phosphate ions : 17 g/L (from addition of 75 % phosphoric acid)
zinc ions : 1.5 g/L (from addition of zinc oxide)
conversion accelerator : see below
free acidity : 0.7 point
Each of the conversion baths (3) to (5) was adjusted to the specified free acidity
using sodium hydroxide. Otherwise, the free acidity (points), conversion coatingweight, and status and size of the coating crystals were measured as described
above.
~o Standards for rePortin~ the evaluation of the qrain size of the coatin~ crystals
(1 ) for cold-rolled steel sheet:
+ less than 3~ micrometers
x greater than or equal to 35 micrometers
(2) for zinc-electroplated steel sheet:
+ less than 25 mic;ror"eter~
x yl ea~er than or equal to 25 micrometers
(3) for galvannealed hot-dip zinc-plated steel sheet:
+ less than 30 I"i~;rlJrneters
x greater than or equal to 30 micrometers
(4) for aluminum-magnesium alloy sheet:
+ less than 30 micrometers
x greater than or equal to 30 micrometers
Sta"dard for rePortin~ evaluation of substrate metal coveraqe
Considered over the entire material:
+ absolutely no exposllre of substrate metal
x exposure of substrate metal was observed
Conversion-treated test panels were electrodeposition painted using a
cationic electrodeposition paint ~EIecronTM 2000 from Kansai Paint Kabushiki
Kaisha) to give a paint film with a film thickness of 20 micrometres. These
30 painted specimens were then subjected to the following painting performance
tests in order to evaluate the painting perforrnance:
26
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(1 ) Test of the Post-Paintinq corrosion resislance
A cut was introd~lced into the paint film on the painted sample. The
painted sample was thereafter i" " "e, aed for 240 hours in 5 % aqueous sodium
chloride solution heated to 50 ~C and then removed, rinsed with water, and
5 dried. The nei~l1boltlood of the cut was peeled using cellophane tape, and the",axil,~um width of paint film peeling on one side was measured after the tape
peel and reported on the following scale:
+ : maximum one-side width of peel is less than 7 mm
# : maximum one-side width of peel is at least 7 mm but less than 10
mm
x : maximum one-side width of peel is at least 10 mm
(2) Test of the water-resistant secondar~ adherence
The painted sample was i" Il l lersed for 240 hours in pure water heated to
40 ~C and then removed and dried. A cross was therea~ter scribed in the paint
15 film; the center of the cut was extruded 3 mm using an E~ sen tester; and, after
a cellopl ,ane tape peel, the paint film peel ratio (peeled area/extruded area) was
measured. The following scale was used for reporting:
+ : paint film peel ratio is less than 10 %
# : paint film peel ratio is at least 10 % but less than 20 %
20 X : paint film peel ratio is at least 20 %
In Example 9, 200 ppm of tert-butyl hydroperoxide was added as conver-
sion accelerator to conversion treatment bath ~3), which was then used to con-
version treat the cold-rolled steel sheet by immersion at a treatment temperature
of 45 ~C. The treatment condiliGns and test results are reported in Tables 2 and25 3, respectively.
In Example 10, 80 ppm of di-tert-butyl peroxide was added as conversion
accelerator to conversion treatment bath (3), which was then used to conversion
treat the zinc-eleuil opldled steel sheet by immersion at a treatment temperature
of 45 ~C. The treatment conditions and test results are reported in Ta~les 2 and30 3, respectively.
CA 02237889 1998-05-13
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TABLE 2
E~ # Sub. PO4~, z~+2 Other Pero~F, glL Free Treat- Con-
glL g/L Metal ide, glL Acid ment tact
Ion, g/L PointsTemp.,Method
~C
9 SPC15 1.3 Ni: 0.5 a: 200 1.0 0.6 45 imm.
EG 15 1.3 Ni: 0.5 f: 80 1.0 0.6 45 imm.
11 SPC13 1.1 Co: 0.4 a: 500 0.4 0.4 40 spray
12 EG 13 1.1 Co: 0.4 g 1100 0.4 0.4 40 imm.
13 SPC15 1.3 Ni: 0.5 f: 500 1.0 0.6 43 in~m.
14 GA 17 1.5 - a: 500 - 0.7 33 spray
AL 15 1.3 Ni: 0.5 f: 150 1.0 0.6 43 spray
Additional Abbreviations in and Other Notes for Table 2
"~" means "Number"; "Temp." means "Ti ~ "; "imm." means "illJlllCI~
In ~e column headed "Perox~de, ~/L":
"a" means "tert-bu~yl lly~llu~ d~";
"f" means "di-tert-butyl peroxide";
~g" means "ace~ylacetone peroxide".
TA8LE 3
F. ~ Coahng Coating Coverage Post-Painting Water
NumberMa~,glmZGrainSize Rating C~r.. ~ ~e~ A~
Rating Rating Rating
9 0.9 + + + +
3.5 + + + +
11 1.2 + + + +
12 3.2 + + + +
13 1.3 + + + +
14 4.3 + + # +
2.5 + + + +
In Example 11, 500 ppm of tert-butyl hydroperoxide was added as conver-
sion accelerator to conversion treatment bath (4~, which was then used to con-
version treat the cold-rolled steel sheet by spraying at a treatment temperatureof 40 ~C. The treatment conditions and test results are reported in Tables 2 and
28
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3, respectively.
In Example 12, 1100 ppm of acetylacetone peroxide was added as con-
version accelerator to conversion treatment bath (4), which was then used to
conversion treat the zinc-electroplated steel sheet by immersion at a treatment
t~r",~er~ re of 40 ~C. The treatment conditions and test results are reported in~ Tables 2 and 3, respectively.
In Example 13, 500 ppm of di-tert-butyl peroxide was added as conver-
sion acceierdlor to conversion treatment bath (3), which was then used to con-
version treat the cold-rolled steel sheet by immersion at a treatment temperature
~o of 43 ~C. The treatment conditions and test results are reported in Tables 2 and
3, respectively.
In Example 14, 500 ppm of tert-butyl hydroperoxide was added as conver-
sion accelerator to conversion treatment bath (5), which was then used to con-
version treat the galvannealed hot-dip zinc-plated steel sheet by spraying at a
treatment temperature of 33 ~C. The treatment conditions and test results are
reported in Tables 2 and 3, respectively.
In Example 15, 150 ppm of di-tert-butyl peroxide was added as conver-
sion ~ccelerator to conversion treatment bath (3), which was then used to con-
version treat the aluminum-magnesium alloy sheet by spraying at a treatment
~ 20 lem,OeldlUre of 43 ~C. The treatment conditions and test results are reported in
Tables 2 and 3, respectively.
ComParative ExamPles 5 to 9
In each of Comparative Examples 5 to 9, the same treatments and tests
were run as in Example 9, with the exception of the modifications given below.
In Comparative Example 5, 200 ppm nitrite ions was added as conversion
accelerator to conversion treatment bath (3), which was then used to conversion
treat the cold-rolled steel sheet by immersion in the treatment bath at a treat-ment temperature of 43 ~C. The treatment conditions and test results are report-ed in Tables 4 and 5, respectively.
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TABLE 4
CE # Sub. PO4~, z~l+2 Other Accel-F, g/L Fm Treat- Con-
g/L g/L Metal ~rAtor, Acid ment tact
Ions, glL Point~Temp.,Method
g/L ~C
SPC 15 1.3 Ni: 0.5d: 200 1.0 0.6 43 inlln.
6 SPC 15 1.3 Ni: 0.5 - 1.0 0.6 43 imm.
7 EG 13 1. I Co: 0.4e: 2000 0.4 0.4 40 imm.
8 GA 17 1.5 - - - 0.7 33 sp}ay
9 AL 15 1.3 Ni: 0.5 - 1.0 0.6 43 sp~ay
1iti- n~l Notes for Table 4
In ~e column headed "Ac~l~,l , g/L":
d : ni~ite ions
e : chlorate ions
TABLE 5
Comparative Coating CoatingCoveragePo~t-Painting Water ~ ~
F . ~ Ma~s,g/m2Gr~nSize Rating Ccr.. ' Ser _'-~ A "
Number Rating Rating Rating
4.0 x x ~ x
6 0.5 x x x #
7 5.2 x + # x
8 7.3 x + x x
9 1.3 x x x #
In Comparative Example 6, conversion treatment bath (3~--without the
addition of conversion accelerator--was heated to 43 ~C, and the cold-rolled
steel sheet was conversion treated by immersion in this treatment bath. The
treatment conditions and test results are reported in Tables 4 and 5, respective-
5 Iy.
In Com~a~dli~/e Example 7, 2000 ppm of chlorate ions was added as con-
version accelerator to conversion treatment bath (4), which was then used to
conversion treat the zinGelectroplated steel sheet by immersion at a treatment
temperature of 40 ~C. The treatment conditions and test results are reported in
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Tables 4 and 5, respectively.
In Comp~l dli~e Example 8, conversion treatment bath (5)--without the
addilion of conversion accelerator--was heated to 33 ~C, and the galvannealed
hot-dip zinc-plated steel sheet was conversion treated by spraying with this bath.
The treatment conditions and test results are reported in Tables 4 and 5, re-
~ spectively.
In Comparative Exa~lpl~ 9, conversion treatment bath (3)--without theaddition of conversion accelerator--was heated to 43 ~C, and the aluminum-
magnesium alloy sheet was conversion treated by spraying with this bath. The
10 ll e~lmel ~t conditions and test results are reported in Tables 4 and 5, respective-
ly.
Examples 9 to 15, which employed a surface llt:dll,lenl method according
to the present invention, consisted of treatment using a conversion treatment
bath that contained organoperoxide as the conversion accelerator. As Tables
2 to 5 clearly show, in each case this resulted in the deposition of a thin, uni-
form, fine, and dense zinc phosphate-type conversion coating on the surface of
the metal work and in an excellent painting pel rOI, l lal ~ce (post-painting corrosion
re~isLance and water-resistant secondary adherence). In Comparative Examp-
les 6, 8, and 9, LreaL" ,enL was carried out using a conversion treatment bath that
was entirely free of conversion accelerator. In co"L, d~L to the examples, the oxi-
di~ing activity in these com~araLi~e examples was inadequate, and only sparse
coaLi"g crystals were deposited and the substrate metal was not uniformly cov-
ered. Comparative Examples ~ and 7 employed, respectively, nitrite ions, which
are the conversion accelerator most typically used in the prior art, and chlorate
26 ions. Fine, dense films were not deposited in these comparative examples and
a satisfactory painting performance was therefore not obtained.
ExamPles 16 to 22 and ComParative ExamPles 10 to 14
Examples 16 to 22 and Comparative Examples 1~ to 14 employed the
same cold-rolled steel sheet (SPC sheet) as in Example 9, the same zinc-elec-
troplated steel sheet and galvannealed hot-dip zinc-plated steel sheet (sheet
thickness: 2.8 mm, plating weight: both surfaces 4~ g/m2~ as in Example 10,
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and the same aluminum-magnesium alloy sheet as in ~xample 15. The metal
sheets were coated with 2 g/m2 of a commercial cleaning/rust-preventing oil
(NOX-RUSTTM 550 from Parker Kosan Kabushiki Kaisha).
The lrt:dllllenl processes cGr"",on to Examples 16 to 22 and ComparaLi~/e
Examples 10 to 14 are given below.
(1) cleaninq/conversion treatment
The specific conditions are given below in the respective working and
comparative examples.
(2) taP-water rinse
ambient temperature, 30 seconds, spray
(3) deionized water rinse
deionized water with a conductivity of 0.2 microSiemens/cm
ambient temperature, 20 seconds, spray
~4) drain/dry
hot air current at 1 10 ~C for 180 seconds
Each of the cleaning/conversion treatment baths used in the working and
comparative examples was adjusted to the specified free acidity, vide infra, using
sodium hydroxide unless specified otherwise. The free acidity (in points) of thetreatment baths was measured as in Example 1.
The conversion coalir,g weight was measured as in Example 1. The coating
was stripped in these measurements using the following procedures.
StriPPin~ conditions
(1 ) For the cold-rolled steel sheet
stripping solution: 5 % aqueous chromic acid
stripping conditions: 75 ~C, 15 minutes, immersion stripping
(2) For the zinc-plated sheet
stripping solution: 2 % by weight ammonium dichromate + 49 % by
weight of 28 % aqueous ammonia ~ 49 % by weight pure water
~ll ippil 19 conditions: room temperature, 15 minutes, immersion stripping
30 (3) For the aluminum-magnesium alloy sheet
stripping solution: 5 % aqueous chromic acid
32
-
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stripping conditions: room temperature, ~ minutes, immersion stripping
The deposiLed coating crystals were inspected with a scanning eiectron mi-
cn,scope ("SEM") at 1,000X. This magnified image was used to evaluate sub-
strate metal coverage (presence or absence of exposed substrate) and to mea-
5 sure the par~icle size of the conversion coating crystals for evaluation of finelysized crystal formation.
The following standards were used for reporting the substrate metal cover-
age and for evaluation of coating grain size.
~ Standard for evaluation of coatin~ ~rain size
10 + + less than 30 micrometres (good)
+ at least 30 micrometres but less than 50 micrometers (moderately poor)
x at least 50 ",icro,lletres (poor)
(2) Standard for evaluation of substrate metal covera~e
+ + absolutely no exposure of substrate metal (good)
5 + moderate exposure of substrate metal (moderately poor)
x substrate metal completely exposed (poor)
In Example 16, the cleaning/conversion treatment bath (6) specified be-
low was heated to 45 ~C and used to conversion treat the cold-rolled steel sheetby immersion for 180 seconds. The resulting coating weight was 1.2 glm2, and
2D the coating grain size and substrate metal coverage were both evaluated as
good.
ComPosition of conversion treatment bath (6)
phosphate ions : 15 g/L (from addition of 75 % phosphoric acid)
zinc ions : 1.3 g/L (from addition of zinc oxide)
nickel ions : 0.5 g/L (from addition of nickel carbonate)
fluorine component : 1.0 g/L (from addition of sodium fluosilicate)
orga"operoxide : 500 ppm (of tert-butyl hydroperoxide)
tert-butanol : 4.0 g/L
surfactant : 1.0 g/L
(addition of polyoxyethylene-polyoxypropylene block
polymer with an average molecular weight of
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'10,000 and an ethylene oxide addition proportion
of 80%)
oil component : 2.0 g/L (addition of NOX-RUSTTM 550)
free acidity : 0.6 point
rt The test results are reported in Table 6.
TABLE 6
Ident- Sub-Acc~l~. t~ (s) Sur" ' $~) Coating Cover-
ifica-strate Grain Size age
tion Rating Rating
Ex 16 SPC a: 500 A: 1.0 ++ ++
Ex 17 EG a: 500 A: 1.0 ++ +~
Ex 18 SPC f: 1000 B: I.O+C:0.5 ++ ++
Ex 19 EG f: 1000 B: 1.0 + C: 0.5 + + ~ +
Ex 20 SPC g: 100 D: 1.5 + E: 0.5 + + + +
Ex21 EG g: 100 D: I.5+E: 0.5 ++ ++
Ex22 AL g: 100 D:1.5 +E: 0.5 ++
CEI0 SPCd:lOO+h:7000 None None x
CE 11 EGd:lOO+h: 7000 A: 1.0 x ++
CE 12 SPC None B: 1.0 + C: 0.5 x x
CE 13 EG e: 1500 B: 1.0 + C: 0.5 x +
CE 14 AL e: 1500 B: 1.0 + C: 0.5 None x
ljtjctn~l Abbreviations in. and Notes for. Table 6
"a" means tert-butyl lly~llu~t~il t~c (an t~ u~tt;lv~iie); ~r~ means di-tert-butyl perûxide (an ~~ u~G~ idc);
"g" means acetylacetone peroxide (an ~ u~ u,~idc); "h" means nitrate ions; "d" means nitrite ions; "e" means
sodiurn chlorate.
"A" means poly~,.ytialylene-polyu~y~ e block pûlymer; "B" means polyu~yc~ l~le sorbitan m tnf~l ,
"C" means lauryl ether sulfate ester salt; "D" means polyuA~ lene oleyl ether; "E" means lauryldirne~ylbetaine.
In the column headed "Coating Grain Size Rating", the entry "None" means that no coating formed.
in Example 17, the cleaning/conversion treatment bath (6) described
in Example 16 was used to conversion treat the zinc-plated sheet by immersion
for 180 seconds. The resulting coating weight was 3.5 g/m2, and the coating
grain size and substrate metal coverage were both evaluated as good. The test
10 results are reported in Table 6.
34
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In Example 18 the clea"i"g/conversion treatment bath (7) specified be-
low was heated to 40 ~C and used to conversion treat the cold-rolled steel sheetby spraying for 120 seconds. The resuiting coating weight was 1.2 g/m2, and
the coating grain size and substrate metal coverage were both evaluated as
good.
ComPOSitiOn of conversion treatment bath (7)
phosphate ions : 14 g/L (from addition of 7~ % phosphoric acid)
zinc ions : 1.3 g/L (from addition of zinc oxide)
cobalt ions : 0.5 g/L (from addition of basic cobalt carbonate)
0 oryanoperoxide : 1000 ppm (from addition of di-tert-butyl peroxide)
tert-butanol : 2.0 g/L
surfactant : 1.0 g/L (from addition of polyoxyethylene sorbitan
monolaurate with moles of EO addition = 20)
0.5 g/L (from addition of lauryl ether sulfate ester
salt with moles of EO addition = 3)
oil component : 3.0 g/L (from addition of NOX-RUSTTM 550)
free acidity : 0.5 point
The test results are reported in Table 6.
In Example 19 the cleaning/conversion treatment bath (7) described in
20 Example 18 was used to conversion treat the zinc-plated sheet by spraying for120 seco, IdS. The resulting coating weight was 3.3 g/m2 and the coating grain
size and substrate metal coverage were both evaluated as good. The test re-
sults are reported in Table 6.
In Example 20 the cleaning/conversion treatment bath (8) specified
25 below was heated to 43 ~C and used to conversion treat the cold-rolled steel
sheet by spraying for 30 seconds and then immersion for 90 seconds. The
resulting coating weight was 1.3 g/m2 and the coating grain size and substrate
metal coverage were both evaluated as good.
ComPosition of conversion treatment bath (8)
30 phosphate ions : 17 g/L (from addition of 75 % phosphoric acid)
zinc ions : 1.5 g/L (from addition of zinc oxide)
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fluorine component : 0.4 g/L (from addition of sodium fluoride)
organoperoxide : 100 ppm (from addition of acetylacetone peroxide)
oil col"po,lent : 2.0 g/L (from addition of NOX-RUSTrM 550)
sul rdclal ll 1.5 g/L (from addition of polyoxyethylene oleyl ether
s with moles of EO addition = 7)
0.5 g/L (from addition of lauryldimethylbetaine)
freeacidity : 0.7 point
The test results are reported in Table 6.
In Example 21, the conversion treatment bath (8) described for Example
0 20 was used to conversion treat the zinc-plated sheet by spraying for 30 sec-
onds and then imnler~ion for 90 seconds. The resulting coating weight was 3.6
g/m2, and the coating grain size and substrate metal coverage were both evalu-
ated as good.
The test results are reported in Table 6.
In Example 22, the conversion treatment bath (8) described for Example
20 was used to conversion treat the aluminum alloy sheet by spraying for 30
seco,1ds and then il l Imer:,ion for 90 seconds. The resulting coating weight was
2.5 g/m2, and the coating grain size and substrate metal coverage were both
evaluated as good.
The test results are reported in Table 6.
In Comparali~e Example 10, the conversion treatment bath (9) specified
below was heated to 45 ~C and used to conversion treat the cold-rolled steel
sheet by immersion for 180 second~. Because neither organoperoxide nor sur-
factant was added to this treatment bath, the oil component was not removed
even upon completion of the treatment and coating deposition was completely
absent.
~omposition of conversion treatment bath (9)
phosphate ions : 15 g/L (from addition of 75 % phosphoric acid)
zinc ions : 1.3 glL (from dissolution of zinc oxide)
nickel ions : 0.5 glL (from addition of nickel nitrate)
fluorine component : 1.0 g/L (from addition of sodium fluosilicate)
36
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W O 97/20964 PC~rnUS96~19144
nitrate ions : 7.0 g/L (from addition of nickel and sodium nitrates)
nitrite ions : 100 ppm (from addition of sodium nitrite)
oil component : 2.0 g/L (from addition of NOX-RUSTTM 550)
free acidity : 0.6 point
5 The test results are reported in Table 6.
In Co",~ardli~/e Example 11, the conversion treatment bath (10) specified
below was heated to 45 ~C and used to conversion treat the zinc-plated sheet
by i"""er~io" for 18~ seconds. The resulting coating weight was 5.3 g/m2, and
the sul.~ le metal coverage was evaluated as good. However, because no or-
~O ganoperoxide was present, the crystal particles were coarse and coating grainsize was evaluated as poor.
ComRosition of conversion treatment bath (10)
phospha~e ions : 15 g/L (from addition of 75 % phosphoric acid)
zinc ions : 1.3 g/L (from addition of zinc oxide)
~s nickel ions : 0.5 g/L (from addition of nickel nitrate)
fluorine component : 1.0 g/L (from addition of sodium fluosilicate)
nitrate ions : 7.0 glL (from addition of nickel and sodium nitrates)
nitrite ions : 100 ppm (from addition of sodium nitrite)
surfactant : 1.0 g/L
(from addilio,) of polyoxyethylene-polyoxypropylene
block polymer with an average molecular weight of
10,000 and an ethylene oxide addition proportion
of 80%)
oil co",ponel~l : 2.0 g/L (from addition of NOX-RUSTTM 550)
freeacidity : 0.6point
The test results are reported in Table 6.
In Compd, aLi~re Example 12, the conversion treatment bath (1 1 ) specified
below was heated to 40 ~C and used to conversion treat the cold-rolled steel
sheet by spraying for 120 seconds. The resulting coating weight was 0.3 g/m2.
30 However, there was an absence of organoperoxide, and the coating grain size
and substrate metal coverage were both evaluated as poor.
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ComPosition of conversion treatment bath (11~
phosphate ions : 14 g/L (from addition of 75 % phosphoric acid)
zinc ions : 1.3 g/L (from addition of zinc oxide)
cobalt ions : 0.5 g/L (from addition of basic cobalt carbonate)
surfactant : 1.0 g/L (from addition of polyoxyethylene sorbitan
monolaurate with moles of EO ~ddition = 20)
0.5 g/L (from addition of lauryl ether sulfate ester
salt with moles of EO addition = 3)
oil component : 3.0 g/L (from addition of NOX-RUSTTM 550)
0 free acidity : 0.5 point
The test results are reported in Table 6.
In Compar~live Example 13, the conversion treatment bath (12) specified
below was heated to 40 ~C and used to conversion treat the zinc-plated steel
sheet by spraying for 120 seconds. The resulting coating weight was 2.1 g/m2.
However, there was an absence of organoperoxide, and the coating grain size
was evalu~terl as poor and the substrate metal coverage was evaluated as mod-
erately poor.
ComPosition of conversion treatment bath (12)
phosphate ions : 14 g/L (from addition of 75 % phosphoric acid)
zinc ions : 1.3 g/L (from addition of zinc oxide)
cobalt ions : 0.5 glL (from addition of basic cobalt carbonate)
chlorate ions : 1.5 g/L (from addition of sodium chlorate)
surfactant : 1.0 g/L (from addition of polyoxyethylene sorbitan
monolaurate with moles of EO addition = 20)
0.5 glL (from addition of iauryl ether sulfate ester
salt with moles of EO addition = 3)
oil component : 3.0 g/L (addition of NOX-RUSTTM 550)
free acidity : 0.5 point
The test results are reported in Table 6.
In Compa(dli~/e Exdm,cl~ 14, the conversion treatment bath described for
Comparative Example 13 was used to conversion treat the aluminum sheet by
CA 02237889 1998-0~-13
W O 97120964 PCT~US96/19~44
spraying for 120 seconds. However, film deposition was entirely absent due to
the absence of the organoperoxide.
Table 6 reports the substrates, the conversion accelerators and surfact-
ants in the conversion treatment baths, and the results of the post-treatment
evaluation of the coating crystals for Examples 16 to 22 and Colo,uarali~e Ex-
amples 10 to 14. These results confirm that E~-d~ les 16 to 22, which employed
a surface treatment method according to the present invention, were able to
clean even the surface of oil-coated metal while simultaneously depositing
thereon a uniform, fine, and dense zinc phosphate-type conversion coating.
Comparative Example 10 involved treatment with a su~ ra~;ldl ~l-free con-
version treatment bath, and in contrast to the above results was unable to de-
posit a conversion film due to an inadequate removal of the oil/grease compon-
ent. Co,npa, ~ /e Example 12 involved treatment with a conversion accelerator-
free treatment bath, and in this case the microfine-sizing of the crystals in the
coating and codLil ,9 coverage were inadequate. Comparative Examples 11 and
13 concerned treatment with oryanoperoxide-free baths that contained inorganic
conversion accelerators. In these cases, the film crystals were coarse, so that
a uniform, fine, and dense conversion film was not obtained. Co""~ardlive ~x-
ample 14 used an i"oryanic conversion acceleraLor, but a conversion film was
not formed.
Benefits of the Invention
Because a zinc phosphate-based conversion treatment bath according
to the prese"L invention--and hence a bath used in a Ll t :~L, I ~e, IL method accord-
ing to the present invention--is substantially free of nitrogenous compounds,
effluent from the " ,ell ,od accol dins~ to the present invention is also environment-
ally rlo~ olluting as a practical matter, and the bath and method accordil,g to the
present invention are therefore able to meet environmental regulations and re-
strictions. The general limitation of the total nitrogenous compound content in
the bath to 0 to 200 ppm as nitrogen poses very little risk of environmental pollu-
tion.
A conversion treatment bath and surface treatment method according to
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W O 97/20964 PCT~US96/19144
the present invention cause the deposition of uniform, fine, and dense zinc
phosphate-type conversion films on metals. These films also support an excel-
lent painting pe5 ro""ance~ for e~dr~ lE~ in terms of post-painting corrosion resist-
ance and water-resistant secondary adherence. Moreover, the invention uses
5 a very simple process sequence, i.e., cleaning (degreasing) - conversion treat-
ment - water rinse. As a result, the surface treatment m elhod using a conversion
bath according to the present invention does not require the suRace-condition-
ing treatment required in the prior art for the deposition of uniform, fine, anddense conversion films. As this provides a number of advantages, such as a
10 simpliric~lio~ I of the ll t:dt"~enl facilities, release from complicated bath manage-
ment, and savings because surface conditioner is no longer required, the bath
and method accor~ g to the present invention clearly represent a major techno-
logical advance.
Moreover, through the introduction of a surfactant for surface cleaning
15 into the conversion bath according to the present invention, degreasing and zinc
,c hos,vl ,dle-based conversion 11 ~dll "enl can be simultaneously effected in a sing-
le step on the surfaces of metals that bear, for example, oil and/or grease. This
also yields a uniform, fine, and dense conversion coating. The merits accruing
to the use of the cleaning/conversion 11 ealme, 1l method according to the present
20 invention extend over a broad range, including, for example, a substantial short-
ening of the l, ~dl" ,enl sequence, simplification of the treatment facilities, space
savings, increased productivity, a reduction in reage~l costs, simplification of re-
agent management, and so forth.
