Note: Descriptions are shown in the official language in which they were submitted.
9~ A A ~ A ~ PCT/US95/11404
- WO96110461
TREATME?~T TO IM~ROVE CORROSION RESISTANOE OF AUTODEPOSITED
COATINGS ON METAL~C SURFAOES
BACKGROUND OF THE rNVENTION
s Field ofthe Inventinn
This invention rdates to the h~ of ~l~todeposited co~ r~ in order to retain
longer or to P 'r~Anre the collos;on rc~ e provided by the CO~ pc on metallic sur-
faces, particularly fc.,;f~,lous articles, inc~urlinP zinc coated (also called "galvanized")
steel.
o Sta~ c"L of Rela~ed Art
Autod~po.,;h~ is a generic term used to descri~e the deposition of a subs~;~mi~lly
uniforrn orgar~ic binder co~ lP film on a metal surface, ~enerally preferab~y pre-
c~n~A without the use of externally imposed electric current in the deposition process.
o~t,o~ .. involves the use of an aqueous coating co~ oS;I;on co..lh;..;.lP dispersed
ts organic resin, usually at relatively low solids conce..hallon such as ~ to 12 %, normally
less than 10 %, to for;m a coating of relatively high solids COI~C~ ahol~ usually greater
than 10 %, on a metallic surface i,..l~ ed therein, with the coating i~ Gsulg in thick-
ness and mass the longer the time that the met~tliC surface is ill~lllc.ae~ in the coating
~llll~oai~ion. Because the 3t~tode~Gs;lion ~lOCLSS iS driven ~ ;r~lly, rather than elec-
20 trically, it coats whw~ r the solution wets the surface ofthe aulJall~e, depositing a rda-
tively ~uru--u coating on even ~lh;C~lC or co.~ , shapes or designs of the substrate.
In generaL ~tudP~os;~;..D Cc,~ G, l;0~5 are ~ lc acid r~ol~l;nl~ ha~ g solid
I
W096110461 0 ~ ~ ~ F~S95lll4o4
resin particles dispersed therein in very finely di~ided forrn. The coating forrned while
the metal substrate used is in~,l.e~ed in the bath is generally wet and fairly weak,
~AIthollEh suffisiently strong to I~lAil~t5l;ll itself against gravity and moderate spraying
forces. In this state the coating is described as "uncured". To make an autodeposition
s coated object suitable for normal practical use, the uncured coating is dried, usually with
the aid of heat. The coating is then described as "curedN.
Basic co~ctihlents of an A~ltodepositing composition are water, resin solids dis-
persed in the ~u~ous medium of the comptjsilion, and activator, that is, an ingredient or
ingte~l;c.ll~ which convert the composition into one which will form on a metallic surface
10 a resinous coating which increases in thickness or areal density as long as the surface is
inl,lle,sed in the composition. Various types of activators or activating systems are
known. The activating system generally comprises an acidic oxidizing system, foreA&~le: hydrogen peroxide and HF; HNO3; a ferric ion contAinin~ compound and HF;and other ~l..~h~alions of (i) soluble metal cG..l~;n;ng compounds such as, for example,
15 silver fluoride, ferrous oxide, cupric sulfate, cobqltous nitrate, silver ac~t~te ferrous
phosphate, chromium fluoride, s~tlmil~m fluoride, stannous fluoride, lead dioxide, and
silver nitrate, in an amount between about 0.025 and about ~0 grams per liter (hereinafter
often abbreviated as "g/l,"), with (ii) one or more acids such as hydrofluoric, sulfuric,
hydrochloric, nitric, and phosphoric acids and organic acids such as, for example, acetic,
20 chloroacetic, and trichloroacetic acids.
Autodeposition composition can be used to form coatings which have good aes-
thetic prope~ lies and which protect the underlying metallic substrate from being degrad-
ed, e.g., corroded by water. Many applications however require the autodeposited coat-
ing have particularly good propel lies for use. Various means have been developed to irn-
25 prove the propel lies of autodeposited coatings including:(a) chemical prel-~al...enl ofthe met~llic surface prior to forming the coatings;
~b) selection of specific particular resins which form the coating and
(c) chemical post-l, e à~ of the freshly formed or uncured coating.
U.S. Patent 4,800,106, the entire disclosure of which, except to the extent that it
30 may be inconsistent with any explicit ~l~len~e~,t herein, is hereby incorporated herein by
reference, describes a number of references dealing with various treatments of uncured
~ulodeposited coal;n~,s inclu~ing the l~.,al ...~.~l of freshly formed autodeposited coatings
9 8 3
wo 96rl046l PCI/IJS95/11404
with acidic, ~qu~us solution of one or more chromium compounds to improve corrosion
resist~nce. While chemiç~l lt.~ e.~s such as "reaction rinses" (which are defined as
any rinses c~nl~in;l~g deliberately added ingredie.~ls other than water and air), following
- autodeposition coAtingc can provide for improved corrosion resict~rlce~ gloss or other
s prope.lies, o~entimes the ~leS~ creates problems such as waste disposal problems.
Thus the use of chromium cGn~ ;-,g compounds in post~ ,AI~lf l~t raises a disposal and
en~"ro-..~ .lAI proble.ll or disadvantage because the chromium must first be removed or
otherwise treated before disposal to waste.
In the past, cold rolled steel and galvanized steel often required dilrcrent autode-
10 posited co~ requiring di~re"t post-l~e.~nle..~ i.e. di~.enl reaction rinses for the
coatin~c. One object of the present invention is to provide a process which incl~ldes a
reaction rinse which will retain, or improve, the corrosion resistance properties of the
autodeposited coating while employing non-chromium cont~ining materials which are
en~iron...~ -~ally acceptable, raising no disposal problems.
s A further object of the present invention is to provide a single reaction rinse for
~1 ;n~ on a variety of metal substrates, paricularly on both cold rolled steel and galva-
nized steel. In this way a single reaction rinse may be used for composite objects that
contain two or more distinct types of metal surface areas and autodeposited coatings
. . thereon, so that cimlllt~neollc processing of such composite objects can be more efficient-
Iy carried out.
DESCRIPTION OF THE INVENTION
General Principles of Description
Except in the claims and the operating examples, or where otherwise expressly
indicated, all numerical quantities in this description indicating amounts of material or
2s conditions of reaction and/or use are to be understood as modified by the word "about"
in describing the broadest scope of the invention. Practice within the numerical limits
stated is generally p~t;rt"~d. Also, unless c~, cssly stated to the contrary: percent, "parts
of", and ratio values are by weight; the term "polymer" includes "oligomer", "copoly-
mer", "terpolymer", and the like; the description of a group or class of materials as suit-
30 able or p,~re-,ed for a given purpose in connection with the invention implies that mix-
tures of any two or more ofthe members ofthe group or class are equally suitable or pre-
ferred; desc i~,on of con~tinlçnt~ in chemical terms refers to the conctituents at the time
WO 96110461 ~ 3 PCT/US95/11404
of addition to any combination specified in the description, and does not necessarily
preclude chemical interactions among the constituents of a mixture once mixed; speci-
fication of materials in ionic form implies the presence of sufficient counterions to
produce electrical neutrality for the composition as a whole (any counterions thus impli-
s citly specified should preferably be selected from among other constit-lents explicitly
specified in ionic form, to the extent possible; otherwise such counterions may be freely
selected, except for avoiding counterions that act adversely to the objects of the inven-
tion); and the term "mole" and its variations may be applied to ele ..~ -t~l ionic, and any
other chemical species defined by number and type of atoms present, as well as to
10 compounds with well defined molecules.
Summary of the Invention
In accordance with this invention, the corrosion resict~nce of a metal substratecoated with a dried and optionally cured autodeposited coating is improved from the
level that would be achieved by rinsing the wet, uncured autodeposited coating with plain
15 water, by treating the uncured coating on the metallic substrate with an aqueous rinse so-
lution that comprises, preferably consisls essçnti~lly of, or still more prefe~ably consisls
of, water and anions that consist of (i) at least four fluorine atoms and (ii) at least one
atom of an element selected from the group cons;sling of tit~nillm~ zirconium, h~fnium~
siIicon, and boron and, optionally, ~iii) one or more oxygen atoms; the rinse solution may
20 also contain other ingredients, for such purposes as pH adjuctment or in general any
other inyedients that do not act adversely to the objects of the invention. The anions
may be introduced into the rinse solution by addition of the corresponding acids or of
salts in~llldinE the anions; in either case, the stoichiometric equivalent as the specified
anions is con~idered for the purposes of this description to be present when any such ma-
25 terial is dissolved in a ll r~ el~l rinse solution, irrespective of the actual degree of ioni-
zation in the solution.
Description of P, ere" ed Embodiments
Except for use of a specific type of reaction rinse as described herein, a process
accoldillg to this invention preferably is like those of prior art autodeposition processes.
30 Thus, in a co r'~e process, before autodeposition coating the metal substrate is prefer-
ably cleaned, generally using an ~lk~lin~., cornmercially available cleaner. The cleaning
is carried out by spraying, immersion or any other effective method or colnbinalion of
W0 96110461 ' ~ PCr/US95/11404
methods, afller which the coated workpiece preferably is rinsed with water to remove any
residual cl~ning solution, prior to deposition of the coating The autodeposited film is
preferably applied by i"~ ..sion of the substrate into a coating bath cont~ining the
desired polymer latex, emulsion or dispersion for a time sufficient to coat the substrate
s with a wet film thickness that preferably is, with increas;ng preference in the order given,
at least 2, 4, 5, 6.0, 6.5, 6.8, 7.1, 7.4, 8.0, 9.0, 10, 11, 12, 13, 14, or 15 micrometers (here-
ina~er often abbreviated "Il") and jnd~pc~d&~ y preferably is, with inereasing pref~rence
in the order given, not more than 50, 40, 30, 28, 27, 26, or 25 Il. The time and tem-
perature during autodeposition will vary dependil g on the nature of the particular resins
10 in the coating After the coating is deposited, a reaction rinse is applied in the present
invention to improve the cGll~sion re~;~t~nce ofthe lata fonned cured coating
The chemical composition of the a~todeposition bath may be selected without
limit from all the con,po~ilions that produce coalhlgs useful for any purpose, in particular
including those compositions taught in U. S. Patents 3,585,084, 3,709,743, 3,776,848,
4,180,603, 4,191,676, 4,313,861, 4,347,172, 4,366,195, 4,657,788, all of which, to the
extent that they desc.il~ c~ ;ons suitable for autodeposition baths and are not incon-
sistent with any explicit s~le .-e~l herein are hereby incorporated herein by reference.
~ l~r~ d cGd~ which are treated acco,~li ,g to the process of the present inven-
tion are formed from an autodepositing composition in which particles of resin are dis-
20 persed in an aqueous acidic solution which is plepared by combining hydrofluoric acidand a soluble ferric iron-cont~ining ingredient, most preferable ferric fluoride.
U.S. Patent Nos. 4,347,172 and 4,411,937 which disclose the preferred activatingsystem disclose the optional use in the composition of an oxidizing agent in an amount
to provide from about 0.01 to about 0.2 oxidizing equivalent per liter of composition.
25 F.~ p~i of suitable o~udi~"~g agents are hydrogen peroxide, dicl,lo,nate, perm~ng~n~te,
nitrate, persulfate, perborate, p-benzoquinone and p-nitrophenol. Hydrogen peroxide is
most pr~f~ d.
With respect to particular resins that can be used in the coating composition ofthe present invention, one ~ler~lle;d class can be p.e~,a,ed by copolynle,~il-g (A) vinyli-
30 dene chloride monomer with (B) ,llonolne, ~ such as meth~crylic acid, methyl methacryl-
ate, acrylonitrile, and vinyl chloride and (C) a water soluble ionic material such as sodi-
um sulfoethyl methacrylate. .Alth-~ugh the constin~ ts CGllllJIiSil~g the above-desired res-
WO 96/10461 PCI/US95/11404
~ ~ ~t ~ 3
in can vary over a relatively wide range, in general the resin will comprise the polymer-
- ized constituents in the following amounts
I) between 45 and 99 %, based on the total weight of ."ono~ used, of vinylidene
chloride n~onG~
2) from about 0 5 to 30 weight percent based on the total weight of (1) and (2) of a
second relatively more hydrophilic ethylenically unsaturated monomeric material
wherein such ...- n~ ;c material has a solubility in both the water phase and the
oil phase of the polymer latex of at least I weight percent at the tc.,.~e. alllre of
poly",e~ ion; and
10 3) from about 0.1 to about ~ weight percent based on the total weight of other mono-
mers of an ionic, si~ificnntly water-soluble material which is copol~-"e.i~able
with (2) and is selected from the group of sulfonic acids and their salts having the
formula:
R-Z-Q-(SO3)M~,
wherein the moiety "R" is selected from the group cor~sistin~ of vinyl and substi-
tuted vinyl, for example, alkyl-substituted vinyl; the symbol "Z" represents a di-
functional linking group which will activate the double bond in the vinyl group;-Q- is a divalent hydrocarbon moiety having its valence bonds on dirrerent
carbon atoms; and the symbol "M~ ,plesellls a cation.
20 Examples of resins plepared from such monomers are disclosed in U S Patent No 3,617,368
The relatively hydrophilic monomers of (2) above include those materiaJs which
are readily copolymerizable with (1) in aqueous dispersion, that is, which copolymerize
within a period of about 40 hours at a temperature ranging from the freezing point of the
25 IllollGllRlic serum up to about 100 C, and which have a solubility in both the water and
the oil phase of the polymer latex of at least I weight percent at the temperature of po-
lymerization. Exemp1ary of prefell~id materials, particularly when used in conjunction
with ..~ono~e. ic vinylidene chloride, are methacrylic acid and methyl methacrylate Oth-
er monomers which may be advantageously employed include the hydroxyethyl and
30 propyl acrylates, hydroxyethylmeSh~crylate, ethyl hexylacrylate, acrylic acid, acryloni-
trile, meth~crylonitrile, acrylamide, and the lower alkyl and dialkylacrylamides, acrolein,
methyl vinyl ketone, and vinyl acetate.
WO 96110461 ~ PCI/US95/11404
-
These monomers, which can be employed in amounts of from 0.5 to 30 weight
percent, based on the total weight ofthe nonionic monomers used, provide for the neces-
- sary reactivity with the copolymerizable ionic material of (3) and also provide for the re-
quired water solubility of the interpolymer in water. Thus, such materials may be re-
ferred to as "go-between" ,-,ono,nc.~. It is to be understood that the optimum amount of
such relatively hydrophilic ,llonoll-e,~ may vary somewhat within the presc,ibed range
~e~ g upon the amount of h~dluphobic ",ono",el used in p~epalin~, the resin, as weD
as upon the amount and type ofthe copol~",cli~ble ionic monomer used.
The copol~",~.i~ble ionic monomers used in preparing the aforementioned type
resins are those monomeric materials which contain in their structure both an ionizable
group and a reactive double bond, are c~ c~tly soluble in water, are copolymerizable
with the hydlophilic Inor~om~r conctit~ent (2) and in which the substituent on the double
bond is chemically stable under the conditions normally encountered in emulsion polym-
enzation.
s Examples of the afore.,.e.,lioned divalent hydrocarbon moiety Q having its val-
ence bonds on di~l.,.lt carbon atoms include alkylene and arylene divalent hydrocarbon
moieties. ~hhou~h the alkylene group can contain up to about 20 carbon atoms, it pref-
erably has 1 to about 8 carbon atoms.
The solubility of the defined copol~l"e.i~able ionic material as described herein
iS strongly irlfllJenced by the cation M~. Exemplary cations are the hydrated protons
characterstic of aqueous free acids, alkali metal ions, ammonium, sulfonium and substi-
tuted ammonium and sulfonium ions, incl.~tling quaternary ammonium ions. Preferred
are the free acids, alkali metals, particularly sodium and pot~ssil~m, and ammonium.
It is further noted that, with one ofthe ions above, and the usual choices for R and
2s Z, the solubility of the monomer depçn~s on Q. As intlicate-l, this group can be either
aliphatic or aromatic and its size will determine the hydrophilic/ hydrophobic balance in
the molecule, that is, if Q is relatively small, the monomer is water soluble, but as Q be-
comes progressively larger, the surface activity of such monomer increases until it be-
comes a soap and l-him~tely a water insoluble wax. It is to be understood, however, that
the limiting size of Q depends on R, Z, and M~. As exemplary of the above, it has been
found that sodium sulfoethyl rneth~rrylate is a highly acceptable copolymerizable ionic
material for use in the present invention.
WO 96/10461 PCT/US95111404
~ ~ S ~ 3
Further, the selection of R and Z is governed by the reactivity needed, and the se-
- lection of Q is usually determined by the reaction used to attach the sulfonic acid to the
base monomer (or vice versa)
~locesses for ple~.aling latexes con~aining resins ofthe afore.,.e,llioned type are
s known, such latexes being commercially available and belng referred to herein as "self-
stabilizing latexes", that is, latexes, the polymeric particles of which contain in the poly-
mer molecule fi-nctio~ groups that are effective in ...~ a~ the polyrneric particles
L~.~ in the ~queous phase ofthe latex. As mentioned above, such latexes do not re-
quire the pres~nce of an external surfactant to m~int~in the particles in their dispersed
state. Latexes of this type generally have a surface tension very close to that of water
(about 72 dynes/cm). It has been observed that autodepositing compositions con~ining
such latexes forrn coatin~ which build up at a relatively fast rate.
An ~y~mpl~ry method for ple~alu~g such latexes involves plep~lion of an aque-
ous dispeKion by an essenti~lly continuous, carefully controlled addition of the requisite
pol~,l,e~i~lion cor-stituer-t~ (incluAing polyrnerization initiator systems, if desired) to the
aqueous me~ium having the desired pH value, followed by the subsequent addition of
the necessary pol~"l~,.;~lion initiator, to form a polymeric seed latex in order to aid in
the control of particle size. When forming such polyrneric seed latexes, very small
arnounts of conventional surf~ct~ntc, such as alkali soaps or the like, may be incorporated
in the aqueous medium to further aid in the attainrnent of particles of desired size. The
addition of such surf~ct~tltc however, is not critical for the production of the highly stab-
le, internally stabilized, aqueous colloidal dispersions of polymeric particles of the type
described above. In any event, additions of surfactants are lirnited so that the total
arnount present in the aqueous phase of the final coating solution is less than the critical
micelle co,-~enl~aliorl, as taught in U.S. Patent No. 4,191,676. Following the formation
of the polymeric seed latex, the rem~ining polymerization constituents are simultaneous-
ly and con~inuo-lcly added under carefully controlled conditions to the aqueous meAillm
Highly stable polymer latexes for use in the present invention are characterizedby the virtual absence of undesirable coa~lh-m which often results when polymeric la-
texes are stabilized by conventional water soluble surfact~nts. Thus, such latexes com-
bine the highly beneficial prope,lies of optimum colloidal stability, reduced viscosities
at relatively high polymer solids content, low foarning tendencies, and excellent product
WO96/10461 ~ 2 ~ PCI/US95/11404
wur~ y and reproducibility Such highly stable latexes which are internally stabilized
are disclosed, for eY~mrle~ in U S Patent No 3,617,368
One prefc..~,d embodiment of this invention co--lt,--ses the use of vinylidene
chJoride-cor~ g latexes in which a water soluble ionic material such as, for e~mrle,
s sodium sulfoethyl methqcrylate is copolymerized with the comono..,ers con.p.ising the
copolymer. Sodium sulfoethyl methacrylate is particularly effective for use with mono-
meric vinylidene chloride and the relatively hydrophilic ...ono.~.a methyl l~.ell.ae,ylate
or ...~ a~;-ylic acid when used in the amounts and in the manner called for by the present
invention
Particularly ~,refelled latexes for use in this invention are latexes with about 35
to about 60 weight % solids co-n~ , a polymeric composition pn,parc~ by em~-lQ;cn
polymerization of vinylidene chloride with one or more comonomers selected from the
group concisti~ of vinyl chloride, acrylic acid, a lower alkyl acrylate (such as methyl
acrylate, ethyl acrylate, butyl acrylate), meth~crylic acid, methyl meth~crylate, acryloni-
1S trile, ell~c-ylonitrile, acrylamide, and meth~rrylamide and stabilized with sulfonic acid
or sulfonic acid salt of the formula R-Z-(CH2)n-(S03) M+, wherein R rep. ~se.,ls vinyl or
lower alkyl-substituted vinyl; Z ~ epre3en~s one of the difunctional groups:
o o o o
-C- , -C-O- , -O-C- , or -C-N (T) -,
where T reples~.~ls hydrogen or an alkyl group; n is an integer from 1 to 20, preferably
I to 6, and M~ is hydrogen or an alkali metal cation, preferably sodium or potassium
One subgroup of prere.led polymers are those having at least 50 % by weight of
vinylidene chloride, but less than 70 %, 5 to 35 % vinyl chloride, and 5 to 20 % of a
2s vinyl compound sPle~e~ from the group consisting of acrylic acid, methyl acrylate, ethyl
acrylate, butyl acrylate, ...elh~t~ylic acid, methyl meth~srylate, acrylonitrile, meth~crylo-
nitrile, acrylamide and meth~crylamide, and co.,-b;"alions thereof, and 1 to 3 % by
weight of sulfoethyl rneth~crylate
One particularly plert;.led group of latexes, however, are latexes co..~ g about30 to about 70 % of solids forrned by emulsion polyll,e.i~alion of about 50 to about 99
%, more preferably at least 80 %, of vinylidene chloride, based on total weight of poly-
mer, and about 0 1 to about 5 % by weight of sulfoethyl meth~çrylate, with optionally
other comono"~ selected from the group cons;sling of vinyl chloride, acrylic and
WO96/10461 ~ ~ ~P !~ ~ Q ~ ~ PCT/US95111404
methacrylic monomers such as acrylonitriles, acrylamides, methacrylamides and
mixtures thereof in amounts between about 5 and about 50 % by weight~ and
s ~l,sliv~ ly free of unpolyrnerized surfactant or protective colloid. Most ~,ere.ably, the
vinylidene chloride copolyrner is crystalline in nature. Exemplary crysta!line resins are
describedinU.S.PatentNo 3,922,451 andaforementionedU.S.PatentNo. 3,617~368.
In general, crystalline vinylidene chloride-co.~ resins have a relatively high pro-
portion of vinylidene chloride, for example, at least about 80 % thereof.
~ntemaUy ~ 7ed polymers or resins include as part of their chemical structure
a surfactant group which functions to mi~int~in polymer particles or resin solids in a dis-
10 pased state in an aqueous m~ m this being the function also p~;-Ço,.ed by an "extern-
al surfactant", that is, by a material which has surface-active prope, lies and which is ab-
sorbed on the surface of resin solids, such as those in colloidal dispersion. As is known,
the l)resence of an external surfactant tends to increase the water sensitivity of co~tin~c
formed from aqueous resin dispersions cont~inin~ the same and to adversely affect de-
si~red properties ofthe coa~ gc As described in U.S. Patent No. 4,191,676, the ~,resence
of an undue arnount of surfactant in autodepositing compositions can deter the build-up
of resin particles on the metallic surface being coated. In addition, the p. esence of undue
amounts of surfactant can also adversely affect desired coating properties, for example,
corrosion resistant properties. An advantage of internally stabilized vinylidene chloride-
cont~ininE polymers is that stable aqueous dispersions, jnclu-ling acidic aqueous disper-
sions of the type needed for autodepositing compositions, can be prepared without utiliz-
ing external s~-Ç~ nc (It is noted that there is a tendency in the literature to use inter-
changeably the following tenns in connection with describing surface active materials
which are used in polymerization processes for preparing polymers of the type to which
the present invention relates: surfactant, wetting agent, emulsifier or emulsifying agent,
and dis~ g agent. As used herein, the term "surfactant" is inten~ed to be synonymous
w.ith the afore~lcnlioned.)
Various types of internally stabilized vinylidene chloride-cont~ining polymers are
known and species thereof are available commercially. E~a nples of such latexes are the
SARANTM latexes such as, for exarnple, SARANTM 143 and SARANrM 112 available
from ~T~.nl.cl.;re Chemical Corp., T.çxin~on, M~cc~chllsettcJ USA and the SERFENElM
latexes available from Morton Chemic~l In accordance with the present invention, these
WO96/10461 ~ 2` ~ PCT/US9S/11404
commercial latexes can be used to excellent advantage. and internally stabilized latexes
in general are preferred.
Various surf~ct~nts which function to m~intain polyrneric particles in dispersed-state in aqueous medium include organic compounds which contain ionizabie groups in
5 which the anionic group is bound to the pl inc;pal organic moiety of the compound, with
the cationic group being a conctitl~ent such as, for eAar,.ple, hydrogen, an alkali metal,
and arn,lloni.lm. Speaking generally, e ~e~..pl -~ y anionic groups of widely used surfact-
ants contain sulfilr or phosyhorous~ for eA~-nple, in the form of sulf~tes, thiosulfate~, sul-
fonates, s~lfin~tes, sulr;~ ec~ phosph~tes~ pyrophosphates and phosphon~tes. Such
10surf~ct~ntc cGIllplis~ inorganic ionizable groups linked to an organic moiety.~ltho~ h various ways may be used to introduce into the molecular structure of
the vinylidene chloride resin such ionizable groups, it is believed that the most widely
used method for prepa~ g such resins will involve reacting vinylidene chloride with a
onolllt;lic surfactant and optionally one or more other monomers. In such reaction, the
5monomeric surfactant cGIll~Jlises a material which is polyllle-i~ble with mQnomçric vi-
nylidene chloride or with a mono~llc.ic material which is polymerizable with monomeric
vinylidene chloride and which is ionizable in the reaction mixture and in the acidic aque-
ous me~ m comprising an autodepositing composition.
Among other p.e~-.ed subclasses of resin for use in this invention are: disper-
20sions of copolymers of 50 to 90 % of butyl acrylate and I to 2 % by weight of sulfoethyl
methacrylate based on the total weight of polymer; latexes of vinylidene chloride-con-
taining polymers internally stabilized with sulfoethyl methacrylate and free of other
s~.racla..l, and including optionally vinyl chloride and one or more acrylic comonomers;
vinylidene chloride-co..l~it,i.~g copolymer havingl5 to 20 % of vinyl chloride, 2 to 5 %
2s butyl acrylate, 3 to 10 weight % acrylonitrile, and 1 to 2 % of sulfoethyl methacrylate.
~his particular copolymer will have less than 70 % by weight of vinylidene chloride
copolymer based upon total weight of comonolllers (including the sulfoethyl methacryl-
ate) used in the emulsion poly~.leli,alion.
The conc~ la~ion ofthe resin in the coating composition can vary over a wide
30 range. The lower concel~llalion limit of the resin particles in the composition is dictated
by the amount of resin needed to provide sufficient material to form a resinous coating.
The upper limit is dictated by the amount of resin particles which can be dispersed in the
WO 96/10461 PCT/US95111404
Q ~ ~
acidic aqueous composition. In general, the higher the amount of resin particles in the
composition, the heavier the coating forrned, other factors being the same. Although
coating compositions can be form~ ted with a range of about 5 to about 550 grams per
liter (he. ~inaller often abbreviated "g/L") of resin solids, the amount of the resin solids
s will tend to vary dcp~A;.~g on the other ingredients comprising the composition and also
on the specific latex or resin used. For most uses, the concenl~ dlion of binder resin solids
in an autodeposition co..,pos;lion or bath used as part of a process accGrding to this in-
vention pler~.~bly is, with inc,~asi,.g prerel ence in the order given, at lease 0.5, 1.0, 2.0,
3.0, 3.5, 4.0, 4.5, 4.7, or 4.9 % and indenpendently ~,ere~ably is, with increasing prefer-
ence in the order given, not more than 40, 30, 20, 17, 14, 12, 11, 10.5, or 10.0 %.
Optional ingredients can be added to the composition as desired. For ~--~. Ie,
it is believed that the present invention will be used most widely in applications where
it is desired to apply p.~ d coatin~ to the metallic substrate. For this purpose, suit-
able pigments can be included in the composition. Exalnples of pi~mçnts that can. be
15 used are carbon black phth~locyanine blue, phthalocyanine green, quinacridone red, ben-
zidene yellow, and tit~nillm dioxide. The pi,~ment should be added to the compositionin an amount which imparts to the coating the desired color and/or the desired depth or
degree of hue. It should be understood that the specific amount used will be governed
. . by the specific pigment used and the color of coating desired. Excellent results have
20 been achieved by using the aqueous dispersion in an amount such that the composition
contains about 0.2 to about 3 g of furnace black/100 g of resin solids.
Many pi~m~nts are available in aqueous dispersions which may include surfact-
ants or dispersing agents for ."~ the pigment particles in dispersed state. When
utilizing such pi~nent dispersions, they should be selected so that the surfactant concen-
2s tration in the aqueous phase ofthe composition is below the critical micelle concentration("CMC"), preferably below the surfactant concentration which corresponds to the inflec-
tion point on a graph of surface tension versus the logarithm of surfactant concentration
in the composition. A suitable pigmented composition is illustrated in examples herein.
Colored c~al;~ ~,c can be produced also by the use of dyes, examples of which in-
30 clude rhodamine derived dyes, methyl violet, safranine, anthraquinone derived dyes, nig-
rosine, and alizarin cyanine green. These are but a few exarnples of dyes that can be
used.
12
WO96/10461 ~ s~ ~ ~ PCT/US95/11404
Examples of other additives that may be used in the autodepositing composition
are those generally known to be used in formul~ting paint compositions, for example, W
stabilizers, viscosity modifiers, etc.
If a surfactant is added to the composition, either as a colnl,ol1enl ofthe latex, or
5 with a pi~ nt dispersion, or with other ingredients or additives, the total amount of sur-
factant in the aqueous phase of the composition should be .nAil~A;l~ed below the CMC.
Fl~f~lably~ the ~queol-~ phase of the composition c~nlains little or no surfactant.
If an external surfactant is utili7etl the pre~.led surf~ct~nts are anionic.
Examples of suitable anionic surf~ct~nts are the alkyl, alkyVaryl or naphth~lene sul-
10 fonates, for example, sodium dioctylsulfosucçin~te and sodium dodecylben2elle sulfon-
ate.
In prep~ing the autodepositing composition, the con~tituçnts thereof can be ad-
rnixed in any suitable way, for example, as des.,li~ed in U. S. Patent No. 4,191,676. In
prep~.ng a bath of pi~mented coating composition for use on an industrial scale, it is
pl~f~lled that the bath be prepa,ed by admixing:
A) an aqueous conce,ltlale comprising about 350 to ab~ut 550 g/l of resin
particles, preferable the aforementioned vinylidene chloride-co..~ l;n~
resin particles, and about 10 to about 550 g/l of pigment; and
. . B) an aqueous concell~rate p~pared from about 0.4 to about 210 g/l of HF
and a water soluble ferric-cont~ining compound in an amount equivalent
to about i to about 100 gA of ferric iron.
The bath can be pl e~,al ed by stirring water into concen~l a~e (A) and thereafter admL~cing
therewith the required arnount of concentrate (B) ~,vith stirring to provide a homogenous
composltion.
2s The complex fluoride anions required in a reaction rinse accordu1g to the inven-
tion are preferably added to the ~r~...enl solution in the forrn of nickel, ferric, or cobalt
salts, more preferably cobalt salts, and the anions themselves are preferably fluoborate
(i.e., BF;), fluosil;~te (i.e., SiF62), fluotitanate (i.e., TiF6-2), or fluozirconate (i.e., ZrF6~2)
with the latter most prerelled.
The conce,l~.~ion of the total of the complex fluoride anions present in the aque-
ous liquid rinse composition used according to the invention preferably is, with increas-
ing ~"t;re,el1ce in the order given, at least 0.002, 0.004, 0.008, 0.016, 0.023, 0.033, 0.040,
WO96/10461 ~'2 ~ Pcr/uS95/11404
0.047, 0.054, 0.061, or 0 068 moles per liter ("M") and independently preferably is, with
inc,~sing plerere~lcc in the order given, not more than 1.0, 0.7, 0.4, 0.20, 0.15, 0.100,
0.090, 0.080, 0.075, or 0.072 M. The pH of the rinse soluition used according to this in-
vention p,~.~ly is, with ;n~;,~si.~g p,eferellce in the order given, not less than 1.0, 1.5,
! 8 2.0, 2.5, 3.0, 3.1, 3.2, 3.3, 3.4, or 3.5 and independently preferably is, with increasing
p,~f~rellce in the order given, not more than 9, 8, 7.0, 6.5, 6.0, 5.8, 5.6, 5.4, 5.2, 5.0, 4.9,
4.8, 4.7, 4.6, or 4.5.
The rinse solution may be co~taGted, accoldil~g to the invention, with a wet un-cured ~utodçposiled coating by any convenient method or combination of methods, such
as spraying, cu~ain co~tin~, or ilnl,lel~;ol~, with the latter normally pref~"~. ~efc.ably
the time of contact between the rinse s~,lt~tion and the wet uncured autodepositied coating
is, with increasing p,eferènce in the order given, not less than 5, 10, 20, 30, 40, 45, 50,
55, or 60 seconds (hereinafter often abbreviated "secN) and independently preferably is,
with increasing prëfel ence in the order given, not more than 600, 400, 200, 120, 1 10,
100, 95, or 90 sec. The tell.pelalule ofthe rinse solution during contact with a wet un-
cured autodepo~iled coating may be any te~"?c~al~lre at which the rinse solution is liquid
but normally preferably is, with increasing plef.,rence in the order given, not less than
10, 15, 18, or 20 C and indepen-lently preferably is, with increasing preference in the
order given, not more than 60, 45, 35, 30, 27, 25, or 23 C.
A~er the reaction rinse ~ l"e,lt, the wet autodeposited coating as modified by
contact with the reaction rinse is so~.~el;~es rinsed again with water, preferably deionized
water if any, before being dried and, if desired as is usually pl efel ~ ed, cured by he~ting~t
an elevated te.l")elal~lre so selected that the protective p, Opel lies of the coating are fully
dcv~loped but not adversely affected. The tel~,pe.al~re and time of tre~tme~t will depend
on the nature ofthe particular resin in the autodeposited coating and the thickness of the
coating. With autodeposition baths con~ ;ng most types of organic binder resins, in-
cluding the most ~>leÇ~ d poly{vinylidene chloride} resins, during or a~er drying, the
autodeposited coatings preferably are heated to a temperature that is, ~ith increasing
plêfelellce in the order given, at least 22, 30, 40, S0, 60, 70, 80, 90, 100, 110, or 120
C and independently preferably is, with increasing preferellce in the order given, not
morethan200, 180, 160, 150, 140, 135, 130, 128, or 126 C. Times of heating for cur-
ing plefel~ly range from S seconds up to 30 mirnltec, dependent on the macs of the coat-
WO 96/10461 ~ PCT/US9S/11404
ed article. Preferably, the coating is heated for a period of time until the metallic sub-
strate has reached the temperature of the heated environl.lent, typically in a forced air
baking oven.
- The dried, cured coated articles are found to have excellent corrosion reCist~nce
s when tested in soak tests or the neutral salt spray ("NSS") test, such as ASTM B-l 17 and
scab corrosion cycles. Autodeposited ~ g~ treated according to the present invention
are particularly effective on both cold rolled steel and galvanized steel, thereby allowing
the two types to be processed together.
To further illustrate the various objects and advantages of the present invention,
the following examples, in which all parts and percentaEes are by weight unless other-
wise indicated, are provided. It is understood that their purpose is entirely illustrative
and in no way intended to limit the scope of the invention.
Example 1
This example illustrates the preparation of a metallic surface having an autode-posited resinous coating. The met~llic surface comprised steel panels, both cold rolled
steel (CRS) and zinc galvanized steel (GS) panels, which were cleaned with a conven-
tional alkaline cleaner composition and nnsed with water prior to being coated by irnrner-
sion in the autodepositing composition at arnbient temperature (about 21 C) for about
90 seconds. The autodepositing i"-n~e.~ion bath had the following composition: 60
grams per liter (he,e;llaner abbreviated as "g/L") of internally stabilized copolyrner of
vinylidene chloride, 2.5 g/L of carbon black, 0.4 g/L of HF, 1.5 gtL of ferric iron, and the
balance water.
Example 2
In this exarnple, the uncured coated panels from example I are treated with a re-
2s action rinse inunersion bath after first being rinsed with water. The reaction rinse with-
out cobalt cations contained 0.5 % by weight of H2ZrF6 and was adjusted to the pH
shown in the following tables with ammonia if needed. In the exarnples employing the
cobalt salt of hydrofluorozirconic acid, the concentration is shown in the tables below;
the pH was 3.5 for all the concenllalions shown.
After hnlne,~;on in the reaction rinse bath for one rninute, the panels were then
rinsed with water (deionized) and the panels were then cured for 20 minutes in an oven
at a telllpelal~lre of 105 C.
- -
WO 96/10461 ~ PCT/US95/11404
Example 3
This e,~ . ~!e illustrates the results of corrosion resistance testing of various pan-
els. Table 1 below illustrates salt spray performance and cyclic scab pe.ru~ ance on
galvanized steel, and Tables 2 - 7 i~dic~te pe.fo-~l,ance on other tests as noted.
The letters "GM" and the numbers and letters immediately following these lettersin the h6~riin~c of Tables 2 - 7 refer res~e~ rely to the General Motors Corporation and
to various specific corrosion tests that are part of pe~rGI"~ance specific~tions at that
company. Test details are readily available from General Motors. Briefly, the tests
reported here are described as follows:
10 1. Cyclic CorroSiQn - GM 9511P
Af'~er prepa.alion (1) the s&"lples are heated in an oven at 60C. for 1 hour fol-
lowed by (2) 30 minutes at -25 C. The samples are then (3) immersed in a 5 % NaCI
solution at room te"lpe~ re for 15 minutes, followed by (4) ambient drying for 75
minuteS The samples are then (5) held for 22.5 hours in a humidity challlber at 85 %
relative humidity ("RH") and 60 C. The fo,egoing is generally conducted over a 5-day
period after which the 5 steps may be repeated for any desired number of cycles.2. Cyclic Corrosion - GM 9540P. Cycle B
A~er p,e~)a,aLion~ the samples are treated at 25C. and 50 % RH environment for
8 hours, including 4 sprays at 90 minutes intervals with a solution cont~ining 0.9 %
NaCI, 0.1 % CaCI2, and 0.25 % NaHCO3 in deionized water. The samples are then sub-
jected to an 8 hour fog, 100 % RH at 40 C, followed by 8 hours at 60 C and less than
20 % RH. The entire treatment is repeated for the desired number of cycles, usually 40
cycles.
16
WO96/10461 ~ ~ fi ~ PCT/US9~/11404
Table 1
Reaction Rinse Concentration pH Corrosion Tes~ l~atings
(Paint Del~l;nalion from
Scribe, mm)
NSS (336 hr) 20 Cycles
Scâb
H~ZrF~ 0.5 % 3 0 - 2
H2ZrF~s 0 5 % 4 0 - 2
H2ZrF6 0.5 % 5 0 - 2 1.5
CoZrF6 4.5 g/L 3.5 0 - 2 1.5
CoZrF6 9.0 ,~/L 3.5 0 - 2 0.8
CoZrF6 18 g/L 3.5 0 - I 0.6
~able 2
(20 Cycles GM 9511 P on Cold Rolled Steel)
Reaction Coat- TotalWidth Creepback Gravel Rating
Rinse ing (mm)
Thick-
ness"u Aver- Ma~imum Minimum Impact After
age Dam- 20
a~e~Cycles
0 5%H2ZrF6 23 2.8 5.9 1 5 9 10 %
pH 5 20 3.3 6.0 1.0 9 rusted
CoZrF6 23 3.7 5.9 1.5 9 10 %
4.5 g/L 23 2.8 8.2 1.0 9 rusted
*Impact damage was measured as specified in GM 9508 P.
-
0 2 ~ 9 ~ pCr~US95/11404
wo 96110461
Table 3
(20 Cycles GM 951 1 P on Galvanized Steel) -`
Reaction Coating TotalWidth Creepback(mm) Gravel Rating
Rinse Thick-
ness,ll Average Ma~imum Minimum Before After
0.5% H2ZrF6 13 1.5 3.1 0.2 8 8
pH 5 17 0.6 1.9 0.2 8 8
CoZrF6 15 0.7 2.6 0.2 8 8
4.5 g/L 13 0.4 3.1 0.2 8 8
Table 4
(40 Cycles GM 9540 P, Cycle B, on Cold Rolled Steel)
Reaction Coating Total Width Creepback (mm) Field
RinseThickness, ~1
Average Ma~imum Minimum
0.5% 20 6.6 9.8 4.2 10 % n~sted
H~rF6
pH 5 20 6.5 9.5 3.8
CoZrF6 20 12.1 22.6 4.5 20 % rusted
4.5 glL 23 9.6 14.8 3.9
W096/10461 ~ ~` q ~ ~ ~ 8 3 PCI~/US9!i111404
Table 5
(40 Cycles Gm 9540 P, Cycle B, on Galvanized Steel)
Reaction Coating Total Width Creepback (mm) Field
RinseThickness, 11 Avera~e Masimum Minimum
0.5% 10 0.7 4.2 0.2 60 % rusted
H2ZrF6
pH S 11 1.0 2.7 0.2
CoZrF6 16 0.7 2.2 0.2 10 % rusted
4.5 g/L 15 0.8 2.6 0.2
Table 6
(5 cycles GM 9505 P, Cycle J, on Cold Rolled Steel)
ReactionCoatingMasimum Creepback from Scribe
RinseThickness,~ (mm)
Right Left Total
0.5% H2ZrF6 23 2.6 2.9 5.5
P 20 2.7 2.8 5.5
CoZrF6 20 3.4 3.0 6.4
4.5 g/L 20 2.4 2.9 5.3
19
- -
WO96/10461 tl 2~ PCT/US95/11404
Table 7 --
(5 Cycles GM 9505 P, Cycle J, on Galvani~ed Steel)
Reaction CoatingMa~imum Creepbllck from Scribe
Rinse Thickness, ~ (mm)
Ri~ht Left Total
0.5% H2ZrF6 13 2.8 3.1 5.9
P 15 3.0 2.7 5.7
CoZrF6 14 0.2 0.2 0.4
4.S g/L 12 0.2 0.2 0.4
3. Cyclic Corrosion - GM 9505P. Cycle J
A~er plCp~a~iOn, the samples are (I) held in a freezer at -30 C for 2 hours, fol-
lowed by ambient conditions for 2 hours and subsequently (2) in an oven at 70 C for 2
hours. The samples are then (3) subjected to a 5 % NaCI solution salt spray for 2 hours
s and then (4) held in a humidity cl.~llber at 38 C and 95 % RH for 64 hours. The sam-
ples are then (S) held in an oven at 60 C for I hour followed by (6) a freezer at -30 C
for 30 mi~ teS The samples are then subjected to (7) im nersion in a 5 % NaCI solution
at room temperature for 15 minutes and then (8) held at ambient conditions for 1.25
hours, followed by (9) a humidity chamber at 60C and 85 % RH for 6.5 hours, followed
~o (10) by 38 C for 64 hours. Steps (1) - (4) above are then repeated to complete the cycle
which is generally concluded in a 2-week period.
