Note: Descriptions are shown in the official language in which they were submitted.
~ W092t08822 2 0 9 5 810 PCT/GB91/01958
....s
Coating composition and process
This invention concerns a composition for coating metal
surfaces and to a process for coating metal surfaces.
;In the manufacture of zinc-, zinc alloy-, aluminium- or
other metal-coated metal articles or sheetf or articles or
sheet of aluminium, aluminium alloys, copper, copp~r alloys~ '
steel or of other metals or alloys, it is desirable to apply
one or more protective coatings to the surface with a view
to alleviating the problems of'deterioration of the surface
in storage and/or of the provision of an effective base for
later painting, varnishing, priming, enamelling or like
operations. It is to these problems that the invention
particularly relates.
.
A zinc-coated steel surface, for example, has a ~endency/ if
untreated, to develop a white coloured powdery deposit in
storage, so-called "white rust', which detracts from the
appear~nce of the surface and possibly adversely affects the key
of paint and the like onto the surface.
European Patont Specification No. 356855 relates to the
problem outlined above. That specification refexs to the
established usage of chromium compounds to achieve the
inhibition of corrosion of aluminium and zinc, and cites the
considerable pxoblems of effluent monitoring and di~posal and the
need to take precautions to en~ure the
protection of plant operatives which arises from the
extremely toxic nature of the chromium compounds. The
specification teaches that certain aluminium-zirconium complexes
may be used in place of the chromium compounds.
The approach disclosed in European Patent Specification
No. 356855 derived from the earlier teachings in United States
Patent No. 4650526 which utilised similar aluminium-
zirconium complexes to treat metal surfaces which had
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W092/08822 ~ PCT/G~9~0~9S8
already been subjected to a phosphating treatment to improve
corrosion resistance, a purpose of the aluminium-zirconium
treatment being to improve the adhesion of later siccative
organic coatings to the phosphate-treated surface. ~he
United States patent teaches the use of aqueous solutions
containing 0.OOS to 5% by volume of the commercial
aluminium-zirconium complex product. In many instances the
performance of the phosphated, aluminium-zirconium complex~
treated metal surfaces were found to be inferior to that of
chromated metal surfaces in respect of corrosion prevention
and adhesion of alkyd paint films.
In order to improve the performance of aluminium-
zirconium complex-treated metal surfaces European Patent
Specification No. 356855 teaches the coating of the complex~
treated surface, after rinsing and drying, with an aqueous
solution, emulsion or dispersion of a film-forming agent, such as
polyacrylic acid. The aluminium-zirconium complex is used at
concentrations of 0.1% or 1.0~ by volume of the commercial fonmp
which contains 20-24% wt of the complex, and the organic ~ilm~
forming composition in 0.5 to 1 g/l. It has been found, however~
that the process described in the European patent specificati.on
may not provide adequate, long-term resistance to surface
deterioration since the zircoaluminate coating tends to shrink on
drying, before the film-forming agent is applied, leaving regions
of the metal surface effectively untreated with complex.
According to the present invention it has been found
that excellent corrosion prevention and adhesion properties
may be obtained on the aforesaid metals, for example on
phosphated or non-phosphated surfaces of zinc-, zinc alloy-
or aluminium-coated metals, using a one-coat non-rinse `
process, by the use of a treating composition characterised in
that the composition comprises an aqueous solution, emulsion or
dispersion of an organic film-forming polymer and one or more
aluminium-zirconium complexes. Galvanised steel panels coated
with the compositions of the present invention demonstrate a long
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~ W092/08822 2 0 9 ~ ~ I O PCT/GB91/01958
term resistance to surface deterioration c~mmensurate with known
chromium-based coatings. Further, the compositions of the present
invention tend not to suffer the 'shrinkage problems associated
with known aluminozirconate coatings.
Aluminium-zirconium complexes which may be utilised
according to the invèntion are, for example, the reaction product
of a chelated aluminium moiety, a zirconium oxyhalide and an
organofuctional ligand. The organofunctional ligand is complexed
with and chemically bound to the chelated aluminium moiety and
the zirconium moiety.
The chelate-stabilised aluminium moiety has the general formula- -
A12(O~lo)aAbBc (I)
wherein
A and B are halo-, preferably chloro-, or hydroxy-,
~a" is a numerical value of from 0.05 to 2, preferably from 0~1
to 1,
"b" is a numerical value of from 0.05 to 5.5, preferably from 1
to 5,
"c" is a numerical value of from 0.05 to 5.5, preferably from 1
to 5,
provided that 2a + b + c = 6, and
-OR10- is either an alpha-beta or alpha-gamma glycol group
in which Rl is an alkyl, alkenyl, or alkynyl group having
from 1 to 6 carbon atoms, preferably an alkyl group and
preferably having 2 or 3 carbon atoms; or an alpha-hydroxy
carboxylic acid residue of the formula -oCH(R3)-CooH, where R3 is
H- or an-alkyl- group ha~ing from 1 to 4 carbon atoms, preferably
from`2 to 3 carbon atoms.
~he zirconium oxyhalide, preferably an oxychloride, has the
general formula:
ZrAdBe (II)
wherein
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WO 92/08822 2 ~ 9 ~ 81 0 PCI`/GB91/07958
:~ --4 -
:: A and s are as defined for ( I ) above, preferably one of A and B
is chloro- and the other of A and B is hydroxy-, and
"d" and "e" independantly have numerical values of from OOOS to
~: 4,
provided that d + e = 4.
.
The organofunctional ligand (LIG) is derived from one'or more of
:~ the following:
-
1) an alkyl-, alkenyl-, alkynyl-, aryl- or aralkyl-carboxylic
acid having from 2 to 36 carbon atoms, preferably from 2 to 18
carbon atoms, more preferably from 4 to 18 carbon atoms and even
more preferably from 2 to 6 carbon atoms;
2) an aminofunctional carboxylic acid having from 2 to 36
carbon atoms, preferably from 2 to 18 carbon atoms, more
preferably from 4 to 18 carbon atoms and moxe preferably from 2
to 6 carbon atoms;
3) a,dibasic carboxylic acid having from 2 to 18 carbon
atoms, preferably from 2 to 6 carbon atoms, and wherein both
carboxy groups are preferably terminal;
- 4),,acid,anhydrides of,dibasic acids having from 2 to 18
carbon atoms, preferably from 2 to 6 carbon atoms;
5) a mercapto functional carboxylic acid having from 2 to
18 carbon atoms, preferably 2 to 6 carbon atoms; and
6) an epoxy functional carboxylic acid having from 2 to 18
carbon atoms, preferably from 2 to 6 caxbon atoms.
The aluminium~zirconium complex may be empirically
represented by the general formula:
[A12(0Rlo)aAbBc~x[LIG]y~2rAdBc]z
wherein A and B are as abo~e-defined, and a,b,c,d and e are
as defined abo~e, except that, in order to form the bonds
depicted, the substituents attached to the metal groups are
appropriately reduced, i.e. 2a + h + c = 4 (2a + b + c = 5
when the aluminium moiety is a terminal group), and d + e =
2~9.581~
WO 92/08822 PC~/GB91/019S8
'` ~ .
--5--
2 (d + e = 3 when the zirconium moiety is a terminal group).
When the aluminium moiety or the zirconium moiety terminates
the above formula, one of the A or B groups may be replaced
by a (Cl-C6)alkoxy- group. x, y and z are independantly at least
1 and may vary from 1 to 100 or more. The molar ratio of x to z
may vary from 1.5 to 10 with the preferred ratio being from 3 to
6 and the ratio of (y/(2x + z)) may vary from 0.05 to 3,
preferably from 0.05 to 2.0, and more preferably from 0.1 to 0.5O
Nethods for the preparation of the above described
complexes are described in United States Patent
Specifications No. 4539048 and 4539049, the disclosures of which
are incorporated herein by reference.
Very suitably the aluminium-zirconium complexes
utilised according to this invention may be those available
under the Trade Name Manchem as about ~0% to 25% vol
solutions in polar solvents such as the lower alcohols,
glycols, or glycol ethers of which suitable products are~
for example,those desiynated APG-X, in which the carboxylic
acid component is NH2-(CH2)2-COOH, or CPG or CPM, in which
the carboxylic acid components are HOOC-(CH2)4-COOH.
.
The organic film-forming polymer may be any polymer
which is available as and curable in an aqueous solution
dispexsion or emulsion. Preferably, however, the film-
forming polymer is selected from suitable vinyl polymers or
copolymers, for example vinyl-acrylic copolymers,
polyacrylic and polymethacrylic acids, and polyacrylates and
polymethacrylates. The most preferred film-forming pol~mers are
emulsions of acrylic coplymers such as those emulsions
available under the Trade Name Neocryl (from ICI). Suitably such
polymers may themselves contain corrosion inhibitors. A
suitable solids content for the organic film-forming polymer
is from about 30% to 50%, or even up to 75~, by weight.
The aluminium-zirconium complex may be present in the composition
of the present invention in an amount of from n . 2% to 20% by
, :
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W092/08822 . 2 0 9 ~ ~1 0 PCT/GB91/019S~
weight based on the weight of the total aqueous composition
although particularly successful results have been achieved us ng
at least 5% by weight, for example 5 to 20% by weight, on the
same basis. The film-forming polymer may be present in greater
than 2%, for example from 2% to 20%, by weight of polymer solids
on the same basis. A solution of the aluminium-zirconium
compound in an organic polar water-miscible solvent may be mixed
with the aqueous solution, dispersion, or emulsion of the film-
forming polymer, preferably to give the above stated solids
concentrations and the resulting product may therefore have a
substantial content of said organic polar solvent.
Preferably, a substantial proportion of a silane, ~or example
from 2 to 15% by weiyht of a commercial silane composition which
may for example contain from 50% to 95~ active material, ba~ed on
the weight of the total aqueous composition, is included in the
composition of this invention to increase the adhesion of
subsequent organic surface coatings to the treated metal surEaceO
Preferably the silane has alkoxy groups, pre~erably 2 or 3 such
groups, hydrolysis of which will permit reaction with acti~e
sites on the metal substrate, and 1 or more organic groups
capable of giving compatability with the film-forming polymer
and/or polymers present in subsequent surface coatings. Ex~mples
of suitable silanes are 3-aminopropyl-triethoxysilane, N-
aminoethyl-3-aminopropyl trimethoxysilane and vinyl
triethoxysilane which may suitably be in the form of 50% to 95%
concentration products.
A small ~uantity of a defoamer and/or surfactant is also
preferably included. A suitable quantity of each is about 0 5 01~
to 0.5% by weight of the total composition may be used. Suitable
materials may be that available under the trade name Bevaloid
6575M, polyoxyethylene-polyoxypropylene block copolymers,
fluorosurfactants or non-ionic hydrocarbon surfactants.
When prepared for use in a dip tank, each litre of a
preferred composition of the present invention will typically
comprise from 20 to 200g, preferably 30 to 150g, of aluminium-
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W092/08822 2 0 9 5 ~1 U pcr/cBs1/ol~5g
zirconium complex and from 1 to lOOg (polymer solids), preferably
from 30 to 95g, of film-forming polymer.
.
The composition according to the present invention may
be applied to the metal surfaces to be treated for example
to a metal coil after hot dip or electrogalvanising or
aluminium coating and after the temperature of the metal has
~allen to below about 85C preferably to below 80C. The
method of application may be by spray or by immersion wi~h
surplus liquid being removed, suitably by passing the metal
between rollers or by the use of an air-knife. The metal
may then be air or oven dried, for example at from 65C to
85C.The thickness of the coating is preferably up to about
50 microns, for example l to 10 microns which may be
controlled by adjusting the solids concentration of the
treating composition appropriately.
The coatings attained by the use of the prese~t
invention adhere strongly to the metal surface to which they
are applied, help to retain the metal surface in bright,
uncorroded form, and give a good key to subsequent surface
coatings. Accordingly, the compositions of the present invention
may suitably be used in or as coatings, such as prLmers or
finishes.
These properties may be tested by the following tests.
a) Salt spray corrosion test (ASTM B.117)
b) Humidity test (1) BS.3900:Part F2:1~73~1983).
-resistance to humidity-cyclic conden~ation.
(2) BS.3900:Part F9:1982(1985)
-resiskance to humidity-continuous condensation.
c) Stack test ( Butler Building Test).
Stacking under artificially humid conditions provided
by interleaved wetted filter paper for a number of days
followed by a determination of the proportion of the area
covered by white rust.
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WO 92/(181iZ2 ~ ? 5 819 PCI/GB91/(~)958
d) Adhesion test. BS.3900:Part E6:1974.
Cross cut test.
The invention will now be illustrated by refer~nce to
the following Examples and the drawings in which:
FIG 1 is a photograph of a galvanised steel panel treated in
accordance with ~he process of EP-A-0356855 and illustrates the
problems of l~shrinkage" where the metal surface has dark and
light regions indicating where the metal surface is coated with
zircoaluminate composition or uncoated respectively.
Example I
Galvanised steel panels were treated with a composition according
to the invention comprising water, 15~ by weight of Haloflex
vinylidene chloride copolymer (ICI), 10% by weight of a
commercial ~inyl triethoxysilane product, 5~ by weight of Nanchem
APG-X zircoaluminate product and 0.5% by weight of Synperonic
PE/L61 polyoxyethylene block copolymer (ICI). The composition was
applied at 5%v/v concentxation at 20 C by roller application to
give an even film with a thickness of 5+/-2 microns (10-Çm) after
drying. The panels were (a) left unpainted or were coated with
~b) a polyester or (c) ~n alkyd paint.
The panels were tested with the following resulks:
Test Unpainted Painted
Polyester Alkyd
a)Salt 48 Hours 250 Hours 120 Hours
spray >10%white pass pass
rust
b)(l) 162 Hours - -
Humidity <10~ White
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~ WO 92/08822 2 o 9 s 8 1 ~ Pcr/~Bgl/olg58
--q-- f
St
b)Sta~k 30 Days-pass b - -
test ~10% White
` rust (galvanised `
tube.
I
c)Cross
cut test - Class O Class 1
Acce~kable
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