CA2237889A1 - Composition and process for zinc phosphate conversion coating - Google Patents
Composition and process for zinc phosphate conversion coating Download PDFInfo
- Publication number
- CA2237889A1 CA2237889A1 CA 2237889 CA2237889A CA2237889A1 CA 2237889 A1 CA2237889 A1 CA 2237889A1 CA 2237889 CA2237889 CA 2237889 CA 2237889 A CA2237889 A CA 2237889A CA 2237889 A1 CA2237889 A1 CA 2237889A1
- Authority
- CA
- Canada
- Prior art keywords
- conversion
- bath
- treatment
- ions
- zinc
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Abstract
A zinc phosphate-type conversion film having microfine-sized crystals is formed on metal surfaces using a conversion treatment bath that contains zinc ions and phosphate ions along with 50 to 1500 ppm of an organoperoxide conversion accelerator, and optionally surfactant. Surface-conditioning treatments can be omitted from this method. The presence of the surfactant makes possible simultaneous execution of surface cleaning and conversion treatment.
Description
-CA 02237889 l998-0~-l3 W O 97~20964 PCT~US96/19144 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 CA 02237889 l998-0~-l3 W O 97/20964 PCT/US96/lgl44 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 WO 97~0964 PCTAUS96/19144 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.
CA 02237889 1998-0~-13 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 WO 97nog64 PCT~US96/19144 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 CA 02237889 1998-0~-13 W O 97/20964 PCT~US96/19144 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 CA 02237889 l998-0~-l3 WO 97120964 PCT/US96~19144 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.
CA 02237889 1998-0~-13 W O 97/20964 PCT~US96/19144 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.
CA 02237889 1998-0~-13 W O 97/20964 PCTnUS96~19144 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-CA 02237889 1998-0~-13 W O 97/20964 PCT~US96/19144 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-CA 02237889 1998-0~-13 W O 97120964 PCT~US96/19144 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.
CA 02237889 1998-0~-13 W O 97/20964 PCT~US96/19144 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.
-CA 02237889 l998-0~-l3 W O 97/20964 PCT~US96/lgl44 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, _ CA 02237889 1998-0~-13 W O 97/20964 PCT~US96/19144 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 -CA 02237889 1998-0~-13 W O 97/20964 PCT~US96/19144 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 CA 02237889 1998-0~-13 W O 97/20964 PCT~US96/19144 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.
-CA 02237889 1998-0~-13 W O 97/20964 PCT~US96/19144 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 CA 02237889 1998-0~-13 W O 97/20964 PCT~S96/19144 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;
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 CA 02237889 l998-0~-l3 W O 97/20964 PCT/US96/lgl44 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 WO 97~0964 PCTAUS96/19144 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.
CA 02237889 1998-0~-13 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 WO 97nog64 PCT~US96/19144 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 CA 02237889 1998-0~-13 W O 97/20964 PCT~US96/19144 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 CA 02237889 l998-0~-l3 WO 97120964 PCT/US96~19144 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.
CA 02237889 1998-0~-13 W O 97/20964 PCT~US96/19144 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.
CA 02237889 1998-0~-13 W O 97/20964 PCTnUS96~19144 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-CA 02237889 1998-0~-13 W O 97/20964 PCT~US96/19144 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-CA 02237889 1998-0~-13 W O 97120964 PCT~US96/19144 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.
CA 02237889 1998-0~-13 W O 97/20964 PCT~US96/19144 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.
-CA 02237889 l998-0~-l3 W O 97/20964 PCT~US96/lgl44 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, _ CA 02237889 1998-0~-13 W O 97/20964 PCT~US96/19144 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 -CA 02237889 1998-0~-13 W O 97/20964 PCT~US96/19144 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 CA 02237889 1998-0~-13 W O 97/20964 PCT~US96/19144 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.
-CA 02237889 1998-0~-13 W O 97/20964 PCT~US96/19144 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 CA 02237889 1998-0~-13 W O 97/20964 PCT~S96/19144 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;
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 CA 02237889 1998-0~-13 WO 97/20964 PCT/US96~19I44 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 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.
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....
-WO 97/20964 ~ PC~/US96~19144 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.
CA 02237889 1998-0~-13 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-CA 02237889 l998-0~-l3 WO 97120964 PCT/US9~i/19144 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-CA 02237889 1998-0~-13 W O 97/20964 PCT~US96/19144 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:
CA 02237889 1998-0~-13 W O 97/20964 PCTflUS96/~9144 (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 CA 02237889 1998-0~-13 W O 97/20964 PCT~US96/19144 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:
CA 02237889 l998-0~-l3 WO 97/20964 PC'rnJS96~1914 (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.
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".
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 CA 02237889 1998-0~-13 W O 97/20964 PCTAUS96~19144 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.
W O 97/20964 PCT~US96/19144 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.
(~) 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 CA 02237889 1998-0~-13 WO 97/20964 PCT/US96~19I44 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 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.
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....
-WO 97/20964 ~ PC~/US96~19144 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.
CA 02237889 1998-0~-13 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-CA 02237889 l998-0~-l3 WO 97120964 PCT/US9~i/19144 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-CA 02237889 1998-0~-13 W O 97/20964 PCT~US96/19144 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:
CA 02237889 1998-0~-13 W O 97/20964 PCTflUS96/~9144 (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 CA 02237889 1998-0~-13 W O 97/20964 PCT~US96/19144 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:
CA 02237889 l998-0~-l3 WO 97/20964 PC'rnJS96~1914 (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.
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".
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 CA 02237889 1998-0~-13 W O 97/20964 PCTAUS96~19144 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.
W O 97/20964 PCT~US96/19144 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 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 CA 02237889 1998-0~-13 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, CA 02237889 1998-0~-13 W O 97/20964 PCT~US96/19144 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 -CA 02237889 1998-0~-13 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 '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.
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.
W O 97/20964 PCTnUS96/19144 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) CA 02237889 1998-0~-13 W O 97/20964 PCTfUS96/19144 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) CA 02237889 1998-0~-13 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.
CA 02237889 1998-0~-13 W O 97/20964 PCT~US96/19144 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 CA 02237889 1998-0~-13 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.
d : ni~ite ions e : chlorate ions 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 CA 02237889 1998-0~-13 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, CA 02237889 1998-0~-13 W O 97/20964 PCT~US96/19144 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 -CA 02237889 1998-0~-13 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 '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.
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.
W O 97/20964 PCTnUS96/19144 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) CA 02237889 1998-0~-13 W O 97/20964 PCTfUS96/19144 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) CA 02237889 1998-0~-13 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.
CA 02237889 1998-0~-13 W O 97/20964 PCT~US96/19144 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 CA 02237889 1998-0~-13 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.
Claims (17)
1. A liquid zinc phosphate conversion coating bath composition comprising water, zinc ions, phosphate ions, and from 50 to 1500 ppm of conversion accelerator selected from the group consisting of organoperoxides.
2. A bath composition according to claim 1, wherein nitrogenous compounds are present, if at all, only in an amount having a stoichiometric equivalent as nitrogen of not more than 200 ppm.
3. A bath composition according to claim 2, comprising from 50 to 1500 ppm of organoperoxides that are water-soluble and have a peroxy structure or a percarboxyl structure.
4. A bath composition according to claim 1, comprising from 50 to 1500 ppm of organoperoxides that are water-soluble and have a peroxy structure or a percarboxyl structure.
5. A bath composition according to claim 4, wherein said organoperoxides are selected from ethyl hydroperoxide, isopropyl hydroperoxide, tert-butyl hydroperoxide, tert-hexyl hydroperoxide, diethyl peroxide, di-tert-butyl peroxide, acetylacetone peroxide, cumene hydroperoxide, tert-butylperoxymaleic acid, peracetic acid, monoperphthalic acid, and persuccinic acid.
6. A bath composition according to claim 3, wherein said organoperoxides are selected from ethyl hydroperoxide, isopropyl hydroperoxide, tert-butyl hydro-peroxide, tert-hexyl hydroperoxide, diethyl peroxide, di-tert-butyl peroxide, acetylacetone peroxide, cumene hydroperoxide, tert-butylperoxymaleic acid, peracetic acid, monoperphthalic acid, and persuccinic acid.
7. A bath composition according to claim 6, which also contains from 0.5 to 5.0 g/L of surfactant.
8. A bath composition according to claim 5, which also contains from 0.5 to 5.0 g/L of surfactant.
9. A bath composition according to claim 4, which also contains from 0.5 to 5.0 g/L of surfactant.
10. A bath composition according to claim 3, which also contains from 0.5 to 5.0 g/L of surfactant.
11. A bath composition according to claim 2, which also contains surfactant.
12. A bath composition according to claim 1, which also contains surfactant.
13. A bath composition according to any one of claims 1 through 12, having a pH value from 2 to 4.
14. A process of forming a zinc phosphate conversion coating on a metal substrate, said process comprising a step of contacting the metal substrate witha composition according to claims 13.
15. A process according to claim 14 wherein contracting is performed at a temperature of 25 °C to 50 °C.
16. A process of forming a zinc phosphate conversion coating on a metal substrate, said process comprising a step of contacting the metal substrate witha composition according to any one of claims 1 through 12.
17. A process according to claim 16 wherein contracting is performed at a temperature of 25 °C to 50 °C.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP7/318311 | 1995-12-06 | ||
| JP31831195A JPH08302477A (en) | 1994-12-06 | 1995-12-06 | Zinc phosphate-base chemical conversion solution for metallic material and treatment |
| PCT/US1996/019144 WO1997020964A1 (en) | 1995-12-06 | 1996-12-06 | Composition and process for zinc phosphate conversion coating |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2237889A1 true CA2237889A1 (en) | 1997-06-12 |
Family
ID=29404606
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2237889 Abandoned CA2237889A1 (en) | 1995-12-06 | 1996-12-06 | Composition and process for zinc phosphate conversion coating |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2237889A1 (en) |
-
1996
- 1996-12-06 CA CA 2237889 patent/CA2237889A1/en not_active Abandoned
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| EP1404894B1 (en) | Corrosion resistant coatings for aluminum and aluminum alloys | |
| CN107345297B (en) | Alkaline cleaning solution, phosphating solution and metal surface treatment method | |
| CA2206805C (en) | Zinc phosphate coating compositions containing oxime accelerators | |
| US20040065389A1 (en) | Method for applying a phosphate coating and use of metal parts coated in this manner | |
| MXPA97003675A (en) | Compositions of zinc phosphate pararecubriment containing ox accelerators | |
| US10378110B2 (en) | Painting pre-treatment processes with low environments impact, as an alternative to conventional phosphating treatments | |
| US8663443B2 (en) | Zirconium phosphating of metal components, in particular iron | |
| US6231688B1 (en) | Composition and process for zinc phosphate conversion coating | |
| US4220486A (en) | Conversion coating solution for treating metallic surfaces | |
| Ogle et al. | Phosphate conversion coatings | |
| JPH06228766A (en) | Method of forming phosphate film | |
| US5888315A (en) | Composition and process for forming an underpaint coating on metals | |
| JP2001342575A (en) | Aqueous metal surface treatment agent | |
| JPH08302477A (en) | Zinc phosphate-base chemical conversion solution for metallic material and treatment | |
| EP1668170B1 (en) | Composition and process for improving the adhesion of a siccative organic coating compositions to metal substrates | |
| JP2000144445A (en) | Alkali degreasing treating solution for metallic material and its use | |
| AU699822B2 (en) | Composition and process for forming an underpaint coating on metals | |
| CA2237889A1 (en) | Composition and process for zinc phosphate conversion coating | |
| US5932292A (en) | Zinc phosphate conversion coating composition and process | |
| EP0793737B1 (en) | Zinc phosphate conversion coating composition and process | |
| WO1996027693A1 (en) | Composition and process for simultaneously cleaning and conversion coating metal surfaces | |
| WO1997020964A1 (en) | Composition and process for zinc phosphate conversion coating | |
| WO2000014301A1 (en) | Alkaline liquid composition and method for degreasing metals | |
| WO2000004207A1 (en) | Degreasing and zinc phosphate conversion treatment of oily metal substrates in a single process operation | |
| KR102403600B1 (en) | simultaneously treating agent of remove oxide layer and coating film formation, and continuous painting method using thereof |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Dead |