Note: Descriptions are shown in the official language in which they were submitted.
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METAL PRETREATMENT COMPOSITION CONTAINING
ZIRCONIUM, COPPER, AND METAL CHELATING AGENTS
AND RELATED COATINGS ON METAL SUBSTRATES
RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional Patent
Application No.
61/420,509, filed December 7, 2010, which application is hereby incorporated
herein by
reference in its entirety.
TECHNICAL FIELD
[0002] This invention relates generally to coating compositions, in
particular, coating
compositions that can be applied to metal substrates to enhance paint adhesion
even after
extended coating times. The invention also relates to the coatings obtained
from the coating
composition, methods of applying these coatings and the coated substrate.
BACKGROUND OF THE INVENTION
[0003] A pretreatment coating is often applied to metal substrates,
especially metal
substrates that contain iron such as steel, prior to the application of a
protective or decorative
coating. The pretreatment coating minimizes the amount of corrosion to the
metal substrate.
In addition, the pretreatment coating can affect the adhesion of subsequently
applied
decorative coatings such as paints and clear coats. Many of the present
pretreatment coating
compositions are based on metal phosphates, and/or rely on a chrome-containing
rinse. The
metal phosphates and chrome rinse solutions produce waste streams that are
detrimental to
the environment. As a result, there is the ever-increasing cost associated
with their disposal.
There is an interest to develop pretreatment coating compositions and methods
of applying
such compositions without producing metal phosphate and chrome waste
solutions. It is also
preferred, that these pretreatment coating compositions be effective in
minimizing corrosion
and enhancing decorative coating adhesion on a variety of metal substrates
because many
objects of commercial interest contain more than one type of metal substrate.
For example,
the automobile industry often relies on metal components that contain more
than one type of
metal substrate. The use of a coating composition effective for more than one
metal substrate
would provide a more streamlined manufacturing process.
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[0004] The coating compositions of the present invention are called
pretreatment
coatings because they are typically applied after the substrate has been
cleaned and before the
various primer and decorative coatings have been applied. In the automotive
industry,
coatings often comprise the following layers in order from the substrate out:
a pretreatment
coating for corrosion resistance, an electrodeposited electrocoat, then a
primer layer, a base
coat paint, and then a top clear coat. In the present application, all
coatings after the
pretreatment coating are considered as paints unless otherwise noted. One
known
pretreatment coating is Bonderite 958 available from Henkel Adhesive
Technologies. The
Bonderite 958 provides a zinc-phosphate based conversion coating composition
that
includes zinc, nickel, manganese and phosphate. Currently, Bonderite 958 is a
standard
conversion coating used extensively in the automotive industry.
[0005] In attempts to move away from conversion coatings that include
heavy metals,
which as used herein will be understood by those in the conversion coating
arts to mean zinc,
nickel, cobalt, manganese, and chromium, or that produce phosphate waste
streams, a new
class of envirom-nentally friendly conversion coating compositions has been
created. The
new class of coatings generally comprises a zirconium-based conversion coating
deposited on
a metal substrate by contact with a working bath containing dissolved
zirconium in the
coating compositions. These conversion coating compositions , which are based
on a
zirconium coating technology, typically have no phosphates and no nickel or
manganese.
Zirconium-based coatings are finding increasing use in the automotive industry
as a
pretreatment coating.
[0006] Manufacturing plants' metal coating assembly lines are part of an
overall
process that is highly coordinated and carefully timed. Metal workpieces are
cut to size,
formed, cleaned, coated with a pretreatment coating, and then coated with
several over layers.
Several different types of metal may pass separately through parts of the
process to be joined
to each other in one step and then proceed through the remaining process steps
as an
assembly of dissimilar metals. These processes are carried out on hundreds of
pieces per
hour and the system requires precise movement of a metal workpiece through the
process.
From time to time, the processing line may be halted, sometimes unexpectedly
due to a
problem in one of the processes in the assembly line. When line stoppage
occurs, workpieces
are held in the various stages of the line for far longer than is desirable.
When a workpiece is
held in a pretreatment bath too long it is often found that the coated
workpiece does not
perform up to required standards. For example, the coated workpieces may not
exhibit the
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desired corrosion resistance or paint adhesion characteristics. This can lead
to increased
scrap rates and potential recalls, which can drive up costs of manufacturing.
Thus, it is
desirable to provide a pretreatment coating composition that has a longer pot
life, meaning
that a metal workpiece can be immersed in the bath for a longer period of time
without a
decrease in the performance of the coated metal workpiece in corrosion
resistance or paint
adhesion.
[0007] It is also desirable to provide increasing functionality in terms
of enhanced
corrosion protection and improved paint adhesion in pretreatment coatings to a
wide range of
metal substrates. At the same time, these improvements preferably do not
require changes to
existing industrial processes or the equipment used on these processing lines.
[0008] Many zirconium-based conversion coating baths contain copper,
either as an
additive to improve features of the pretreatment coating and/or process or as
a trace element
from water or metal workpieces being coated. Regardless of its source, the
present inventors
have discovered that copper from the zirconium-based coating bath that is
deposited in the
pretreatment coating at too high an amount relative to other coating
components can
negatively affect performance of the coated metal substrate. Accordingly, it
is desirable to
develop zirconium-based coating baths that overcome this deficiency.
SUMMARY OF THE INVENTION
[0009] In general terms, this invention provides a metal pretreatment
coating that is
zirconium-based and that provides a longer pot life and enhanced paint
adhesion without
decreasing the corrosion resistance. The invention also relates to the
coatings and coated
substrate obtained from the coating composition.
[00010] In one embodiment, a zirconium-based metal pretreatment coating
composition comprising water and dissolved Zr, a source of fluoride, a copper
chelating
agent, optionally materials comprising one or more of silicon, boron and
yttrium and optional
added dissolved Cu is provided. Desirably, the zirconium-based metal
pretreatment coating
composition said copper chelating agent is capable of reducing amounts of
copper deposited
in a zirconium based coating on a metal substrate by contact with the
zirconium based metal
pretreatment coating composition, said copper chelating agent present in an
amount sufficient
to thereby produce an average total ratio of atomic % of Cu to atomic % of Zr
in said coating
deposited on the metal substrate that is equal to or less than 1.1.
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[00011] In one embodiment, a zirconium-based metal pretreatment coating
composition is provided, comprising:
A.) 50 to 300 ppm of said dissolved Zr,
B.) 0 to 50 ppm of said added dissolved Cu,
C.) 0 to 100 ppm of Si02,
D.) 150 to 2000 ppm of total Fluoride,
E.) 10 to 100 ppm of free Fluoride and
F.) at least 10 ppm of said copper chelating agent.
[00012] In one embodiment, the added dissolved Cu is present in the
coating
composition and the copper chelating agent is present in an amount of 25 to
1500 ppm.
[00013] In one embodiment, the copper chelating agent is selected from
molecules
having multiple carboxylic and/or phosphonic functional groups. Desirably the
copper
chelating agent is selected from the group consisting of aminosalicylic acid,
ascorbic acid,
aspartic acid, benzoic acid, citric acid, cyanuric acid, diethylenetriamine-
pentamethylene
phosphonic acid, dihydroxybenzoic acid, dimethylenetriaminepentaacetic acid,
ethylenediaminetetraacetic acid, gluconic acid, glutamic acid, hydroxyacetic
acid,
hydroxyethylidene diphosphonic acid, hydroxyglutamic acid, iminodisuccinic
acid, kojic
acid, lactic acid, malonic acid, nitrilotriacetic acid, nitrobenzenesulfonic
acid, nitrosalicylic
acid, oxalic acid, polyacrylic acid, polyaspartic acid, salicylic acid,
tartaric acid, and salts of
said acids.
[00014] In one embodiment, the zirconium-based metal pretreatment coating
composition described above has a copper chelating agent comprising tartaric
acid and/or
salts thereof.
[00015] Another aspect of the invention is a method for improving paint
adhesion to a
metal substrate comprising the steps of:
a) optionally cleaning a metal substrate;
b) applying to the metal substrate a zirconium-based metal pretreatment
coating
composition according to any one of the preceding claims, thereby forming a
pretreatment
coating on the metal substrate;
wherein the copper chelating agent is present in said zirconium-based metal
pretreatment
coating composition in an amount sufficient to result in an average total
ratio of atomic % of
Cu to atomic % of Zr in the pretreatment coating deposited on the metal
substrate is equal to
or less than 1.1; and
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c) applying a paint to the metal pretreatment coated metal substrate.
[00016] Another aspect of the invention is a method for improving paint
adhesion to a
metal substrate that is subjected to a pretreatment with a zirconium-based
pretreatment
coating composition comprising the steps of:
a) contacting a metal substrate with a pre-rinse comprising a copper
chelating agent, and
optionally copper, prior to application of a zirconium-based pretreatment
coating composition
to the metal substrate;
b) applying to the metal substrate a zirconium-based metal pretreatment
coating
composition comprising dissolved Zr, a source of fluoride, optionally
materials comprising
one or more of silicon, boron and yttrium and optional added dissolved Cu,
thereby forming a
pretreatment coating on the metal substrate;
wherein the copper chelating agent is present in the pre-rinse in an amount
sufficient to
control the amount of copper deposited onto the metal substrate by the
zirconium-based
pretreatment coating composition such that the average total ratio of atomic %
of Cu to
atomic % of Zr in the pretreatment coating deposited on the metal substrate is
equal to or less
than 1.1.
[00017] In one embodiment, the copper chelating agent is present in an
amount of at
least 10 ppm and at most 2000 ppm.
[00018] Another aspect of the invention is an article of manufacture
comprising a
coated metal substrate comprising: a metal substrate; and deposited on said
metal substrate, a
pretreatment coating comprising metal from said substrate, zirconium, oxygen,
copper, and
optional elements fluorine and carbon; wherein the pretreatment coating on the
metal
substrate has an average total ratio of atomic % of Cu to atomic % of Zr that
is equal to or
less than 1.1.
[00019] In one embodiment, the article of manufacture is provided wherein
average
total ratio of atomic % of Cu to atomic % of Zr in the pretreatment coating on
the metal
substrate is about 0.9 to 0.02.
[00020] In one embodiment, the article of manufacture is provided wherein
atomic %
of Cu in said pretreatment coating measured at a series of depths from an
outer surface of the
pretreatment coating to the metal substrate does not exceed 33 atomic % Cu at
any of said
depths.
[00021] In one embodiment, the article of manufacture is provided further
comprising
at least one paint applied to the pretreatment coating resulting in a painted
coated substrate
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that achieves at least 95% paint remaining when tested according to ASTM 3330M
(Revised
Oct. 1, 2004).
[00022] In one embodiment, the article of manufacture is provided further
comprising
at least one paint applied to the pretreatment coating resulting in a painted
coated substrate
that achieves 1.9 mm or less average corrosion creep when tested according to
ASTM B117
(Revised Dec. 15, 2007) for 500 hours.
[00023] In one embodiment, the invention is directed to an aqueous metal
pretreatment
coating composition comprising: 50 to 300 ppm of dissolved Zr, 0 to 50 ppm of
dissolved Cu,
0 to 100 ppm of Si02, 150 to 2000 ppm of total Fluoride, 10 to 100 ppm of free
Fluoride and
a chelating agent.
[00024] In one embodiment, the zirconium-based pretreatment coating
composition of
the invention provides a pretreatment coating wherein the average total ratio
of atomic % of
Cu to atomic % of Zr in the pretreatment coating on the metal substrate is
less than 1.1. In a
further embodiment, this ratio ranges downward from, in order of increasing
preference 1.10,
1.05, 1.0, 0.95, 0.90, 0.85, 0.80, 0.75, 0.70, 0.65, 0.60, 0.55, 0.50 and is
not less than, in
increasing order of preference 0.0001, 0.0005, 0.0010, 0.0050, 0.010, 0.050.
In certain
embodiments, for example where no added Cu is present in the coating
composition, the ratio
of Cu to Zr in the deposited coating may be zero.
[00025] In another embodiment, the invention is directed to a method for
improving
paint adhesion to a metal substrate comprising the steps of: providing a metal
substrate;
applying to the metal substrate an aqueous, zirconium-based metal pretreatment
coating
composition comprising 50 to 300 ppm of dissolved Zr, 0 to 50 ppm of dissolved
Cu, 0 to
100 ppm of Si02, 150 to 2000 ppm of total Fluoride, 10 to 100 ppm of free
Fluoride and a
chelating agent thereby forming a pretreatment coating on the metal substrate
wherein a
chelating agent is present in an amount such that the average total ratio of
atomic % of Cu to
atomic % of Zr in the pretreatment coating on the metal substrate is equal to
or less than 1.1;
and applying a paint to the metal pretreatment coated metal substrate.
[00026] The pretreatment coating can be used on a variety of metal
substrates
including cold rolled steel (CRS), hot-rolled steel, stainless steel, steel
coated with zinc metal,
zinc alloys such as electrogalvanized steel (EG), 55% Aluminum-Zinc alloy
coated sheet
steel, such as Galvalume0, galvanneal (steel sheet with a fully alloyed iron-
zinc coating)
(HA), and hot-dipped galvanized steel (HDG), aluminum alloys such as AL6111
and
aluminum plated steel substrates. One advantage the invention offers is that
components
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containing more than one type of metal substrate can be passivated in a single
process
because of the broad range of metal substrates that can be passivated by the
pretreatment
coating compositions of the invention.
[00027] In another embodiment, the invention is directed to a coated
substrate
comprising a metal substrate having deposited on said metal a pretreatment
coating
comprising metal from the substrate, zirconium, oxygen, copper and optional
elements
fluorine and carbon; wherein average total ratio of atomic % of Cu to atomic %
of Zr in the
pretreatment coating on the metal substrate is equal to or less than 1.1. In
one embodiment,
the coated substrate further comprises at least one paint applied to the
pretreatment coating
wherein the painted coated substrate achieves at least 95% paint remaining
when tested
according to ASTM 3330M (Revised Oct. 1, 2004).
[00028] These and other features and advantages of this invention will
become more
apparent to those skilled in the art from the detailed description of a
preferred embodiment.
Except in the claims and the operating examples, or where otherwise expressly
indicated, all
numerical quantities in this description indicating amounts of material or
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
preferred. Also, throughout this description, unless expressly stated to the
contrary: percent,
"parts of', and ratio values are by weight; the description of a group or
class of materials as
suitable or preferred for a given purpose in connection with the invention
implies that
mixtures of any two or more of the members of the group or class are equally
suitable or
preferred; description of constituents in chemical terms refers to the
constituents at the time
of addition to any combination specified in the description or of generation
in situ by
chemical reactions specified in the description, and does not necessarily
preclude other
chemical interactions among the constituents of a mixture once mixed;
specification of
materials in ionic form additionally implies the presence of sufficient
counter ions to produce
electrical neutrality for the composition as a whole (any counter ions thus
implicitly specified
should preferably be selected from among other constituents explicitly
specified in ionic
form, to the extent possible; otherwise such counter ions may be freely
selected, except for
avoiding counter ions that act adversely to the objects of the invention); the
term "paint"
includes all like materials that may be designated by more specialized terms
such as primer,
lacquer, enamel, varnish, shellac, topcoat, and the like; and the term "mole"
and its variations
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may be applied to elemental, ionic, and any other chemical species defined by
number and
type of atoms present, as well as to compounds with well defined molecules.
BRIEF DESCRIPTION OF THE DRAWINGS
[00029] The drawings that accompany the detailed description are described
below.
Figures 1A, 1B, 1C, and 1D are scanning electron microscope (SEM) images of
pretreatment
coatings on cold rolled steel;
[00030] Figure 2A is an SEM image of the sample shown in Figure 1A with
several
circled areas of interest, Figure 2B is a graph of the chemical composition of
the areas circled
in Figure 2A;
[00031] Figure 3A is an SEM image of the sample shown in Figure 1B with
several
circled areas of interest, Figure 3B is a graph of the chemical composition of
the areas circled
in Figure 3A;
[00032] Figure 4 is a graph of an X-ray photoelectron spectroscopy
analysis of a
pretreatment coating composition of Figure lA according to the invention; and
[00033] Figure 5 is a graph of an X-ray photoelectron spectroscopy
analysis of the
pretreatment coating composition of Figure 1B.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[00034] The present invention is directed to a metal pretreatment coating
composition,
and a method for applying the same, as well as to articles of manufacture
comprising coatings
according to the invention. The invention provides surprising improvements in
performance
in zirconium-based conversion coating pretreatments such as, by way of non-
limiting
example, zirconium-based conversion coatings deposited on a metal substrate by
contact with
a working bath containing dissolved zirconium in the coating compositions.
These
conversion coating compositions are exemplified by aqueous coating baths
comprising
dissolved zirconium and free fluoride that form coatings comprising zirconium
and oxygen.
The baths are typically aqueous, neutral to acidic, and comprise dissolved
zirconium,
dissolved copper, either as an additive or as a trace element from water or
metal substrates,
and a source of fluoride. Optional components may be present including
materials
comprising one or more of silicon (e.g. silica, silicates, silanes), boron,
yttrium, particular
embodiments of which have no phosphates and no zinc, nickel, cobalt,
manganese, and
chromium.
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[00035] Many zirconium-based coating baths contain copper, either as an
additive or
as a trace element from water or from metal workpieces being coated.
Regardless of its
source, the present inventors have discovered that copper from the zirconium-
based coating
bath that is deposited in the coating can negatively affect performance of the
coated metal
substrate, if present in amounts such that undesirable morphologies in the
coating arise and/or
in amounts above desirable levels.
[00036] Many zirconium-based pretreatment coating compositions may benefit
from
the invention. The coating baths typically are aqueous, neutral to acidic, and
comprise
dissolved zirconium, dissolved copper, a source of fluoride and counter ions
for the dissolved
metals, for example sulfates and/or nitrates. Optional components may be
present including
materials comprising one or more of silicon (e.g. silica, silicates, silanes),
boron, yttrium.
The zirconium-based pretreatment coating compositions may contain acid,
generally a
mineral acid, but optionally organic acids; and/or an alkaline source. The
acid and/or alkali
may be a source of other components in the composition, may be used to control
pH or both.
The zirconium-based pretreatment coating compositions according to the
invention may
likewise, consist essentially of or consist of the materials described herein.
[00037] The coating composition according to the invention provides
zirconium-based
coatings having improved paint adhesion and maintained corrosion resistance.
These and
other benefits are achieved by adding to a zirconium-based coating
composition, either a bath
or the concentrate, a chelating agent, preferably a copper metal chelating
agent, to control the
amount of copper deposited onto the metal substrate by the zirconium-based
pretreatment
coating composition. This chelating agent can be added to the zirconium-based
pretreatment
coating composition even where no copper is present in the unused zirconium-
based
pretreatment coating composition, as a protective agent to prevent later
copper deposition as
the bath ages and copper is incorporated into the bath as a trace element from
water, such as
from prior cleaning or rinse steps, and/or from metal workpieces being coated.
The inclusion
of the chelating agent also extends the pot life of the pretreatment coating
bath because is
allows for a wider range of immersion times without negative effects on paint
adhesion or
corrosion protection.
[00038] In one embodiment of the invention, a zirconium-based pretreatment
coating
composition is provided comprising 50 to 300 ppm of dissolved Zr, 0 to 50 ppm
of dissolved
Cu, 0 to 100 ppm of Si02, 150 to 2000 ppm of total Fluoride, 10 to 100 ppm of
free Fluoride
and a chelating agent. That is, the composition may comprise amounts within
the disclosed
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ranges, such as: 50, 60, 70, 80, 90, 100, 120, 130, 140 or 150 ppm to 160,
170, 180, 190, 200,
210, 220, 230, 240, 250, 260, 270, 280, 290 or 300 ppm of dissolved Zr; 0, 5,
10, 15, or 20
ppm to 25, 30, 35, 40, 45, or 50 ppm of dissolved Cu; 0, 5, 10, 15, 20, 25,
30, 35, 40, 45, or
50 ppm to 60, 65, 70, 75, 80, 85, 90, 95 or 100 ppm of Si02; 150, 170, 190,
200, 225, 250,
275, 300, 325, 350, 375, 400, 425, 450, 475, 500, 525, 550, 575, 600, 700,
800, 900, or 1000
ppm to 1150, 1170, 1190, 1200, 1225, 1250, 1275, 1300, 1325, 1350, 1375, 1400,
1425,
1450, 1475, 1500, 1525, 1550, 1575, 1600, 1700, 1800, 1900, or 2000 ppm of
total Fluoride;
10, 15, 20, 25, 30, 35, 40, 45, or 50 ppm to 60, 65, 70, 75, 80, 85, 90, 95 or
100 ppm of free
Fluoride and a chelating agent.
[00039] In another embodiment of the invention, a zirconium-based
pretreatment
coating composition is provided comprising 100 to 300 ppm of dissolved Zr, 0
to 50 ppm of
dissolved Cu, 0, 25, 50, 75, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000
or 2000 ppm to
2500, 3000, 4000, 4500 or 5000 ppm of SO4, 100 to 1600 ppm of total Fluoride,
10 to 200
ppm of free Fluoride and a chelating agent.
[00040] The chelating agent may be any chelating agent capable of reducing
the
amount of copper deposited in the zirconium based coating. The chelating agent
may be a
copper metal chelator. A partial list of exemplary chelating agents, many of
which are
molecules having multiple carboxylic and/or phosphonic functional groups, that
can be used
in the present invention includes the following: adenine, adenosine, alanine,
aminosalicylic
acid, ascorbate/ascrobic acid, aspartate/aspartic acid, benzoic acid,
citrate/citric acid, cyanuric
acid, cysteine, cuprizone, diethanolamine, diethylenetriamine,
diethylenetriamine-
pentamethylene phosphonic acid, dihydroxybenzoic acid, dimethylenediamine,
dimethylenetriamine, dimethylenetriaminepentaacetate (DTPA), dimethylglycine,
dimethylglyoxime, ethylenediaminetetraacetate (EDTA), ethyleneglycol,
gluconate/ gluconic
acid, glutamate/ glutamic acid, glycerol, glycine, guanine, guanosine,
histadine, histamine,
hydroxyacetic acid, hydroxyethylidene diphosphonic acid (HEDP),
hydroxyglutamic acid,
hydroxylamine, iminodisuccinate, kojic acid, lactate/lactic acid, leucine,
malonic acid,
mannitol, methylglycine, molybdate, nitrilotriacetate, nitrosalicylic acid,
omithine, oxalic
acid, polyacrylates, polyaspartates, phenylalanine, salicylic acid,
salicylaldoxime, sodium
nitrite, sodium nitrobenzenesulfonate, tartrate/ tartaric acid, triethanol
amine (TEA),
triethylenetriamine (TETA), tris (2-aminoethyl)amine (diethylenetriamine), or
thioacetamide.
[00041] These chelating agents may be utilized according to the following
methods:
they may be incorporated into a pre-rinse applied prior to contacting the
metal substrate with
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a zirconium-based pretreatment coating composition; the chelating agents may
be
incorporated into a zirconium-based pretreatment coating composition as
discussed above;
the chelating agents may also be applied as a post-rinse applied after the
metal substrate has
been contacted with a zirconium-based pretreatment coating composition.
[00042] The chelating agents are used a level sufficient to ensure that in
the deposited
pretreatment coating the average total ratio of the atomic % of Cu to the
atomic % of Zr in
the pretreatment coating on the metal substrate is equal to or less than 1.1,
preferably from
0.9 to 0.02, and most preferably from 0.30 to 0.10.
[00043] The amount of chelating agent in the coating composition may range
from
lOppm to 2000ppm. The amount required is affected by, for example, the amount
of copper
present in the coating composition, the temperature of the coating bath, the
substrate being
coated, whether the composition is a concentrate or the working bath and the
particular
chelating agent being used. Chelating agents with multiple coordination sites
may be used at
lower levels. In one embodiment the chelating agent is present in an amount
ranging from
25-100 ppm in the coating bath. More chelating agent may be added provided the
concentration does not adversely affect bath performance. Desirably, the
amount of chelating
agent in the pretreatment coating composition is an amount sufficient to
achieve a desired
Cu:Zr ratio in the deposited coating and preferably the chelating agent amount
is at least, in
increasing order of preference 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65,
70 or 75 ppm and
is at most, in increasing order of preference, 2000, 1500, 1000, 900, 800,
700, 600, 500, 400,
300, 200, 100 ppm.
[00044] The average total ratio of atomic % of Cu to atomic % of Zr may
range
downward from, in order of increasing preference 1.10, 1.05, 1.0, 0.95, 0.90,
0.85, 0.80, 0.75,
0.70, 0.65, 0.60, 0.55, 0.50. For some zirconium-based pretreatment coating
compositions,
copper is a desirable part of the composition and the coating. For some such
coating
compositions, the ratio of copper to zirconium is desirably not less than, in
increasing order
of preference 0.0001, 0.0005, 0.0010, 0.0050, 0.010, 0.050.
[00045] Zirconium-based pretreatment coatings of the invention may have a
variety of
components in the coating provided that the amount of copper in the coating is
not such that
undesirable coating morphology and performance failures result.
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Examples
[00046] In a standard industrial coating process, the immersion bath time
for a
pretreatment coating step is about 120 seconds, but during an assembly line
stoppage this
time can be 10 minutes or longer. To simulate a line stoppage and to test
various parameters
an alternative protocol was developed by the present inventors. The process
used in the
experiments described in the present specification is as shown in TABLE 1
below.
[00047] The standard pretreatment process for all of the data, unless
otherwise noted,
is as described below in TABLE 1. The Parco Cleaner 1533R is an alkaline
cleaner
available from Henkel Adhesive Technologies. The Ridosol 1270 is a basic
nonionic
surfactant and is available from Henkel Adhesive Technologies. The weight
ratio of Parco to
Ridosol used was 8.33 to 1. Aging of the cleaner was simulated by adding the
oil Tirmil 906
available from Tirreno Industries, to age the cleaner at 4 grams/liter. The
base pretreatment
composition was a zirconium-based pretreatment. The electrodeposited paint
coating used in
all of the paint adhesion tests was BASF Cathoguard 310X available from BASF.
This is a
standard coating used in the automotive industry.
TABLE 1.
Stage Treatment Product Application Time, Temp
seconds C
1 Clean Parco Cleaner Spray 70 60
1533R/Ridosol 1270
fresh or aged
2 Clean Parco Cleaner Immersion 150 60
1533R/Ridosol 1270
fresh or aged
3 Rinse City water Spray 60 _ 28
4 Rinse Deionized water Spray 60 25
Pretreatment zirconium-based Immersion 600 25
pretreatment bath
6 Pretreatment zirconium-based Spray 30 25
pretreatment bath
7 Rinse Deionized water Spray 60 25
8 Electrodeposited BASF Cathoguard 310 immersion 120 32 (230V)
coating X
9 Rinse Deionized water Spray 30 25
Bake 1200 350 F or
electrodeposited 375 F
paint
Example 1
[00048] The zirconium-based pretreatment bath used for Example 1 included
180 parts
per million (ppm) of zirconium, 30 ppm of copper, 35 ppm of free and 400 ppm
of total
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fluoride, 42 ppm of Si02; the zirconium-based pretreatment bath pH was set at
4.2 Two
different batches of commercially available, cold rolled steel (CRS 1 and CRS
2), as is
typically used in automobile manufacture, were processed according to Table 1.
The
zirconium coating weight in milligrams Zr per square meter was determined for
each sample.
[00049] In addition for each sample, the paint adhesion of the BASF
Cathoguard 310
X was determined using the following protocol. A sample area was cross hatched
down to
the level of the substrate with a razor using a line spacing of 1 millimeter
and 6 lines for each
direction. Then a 75 millimeter long strip of adhesive tape 20 millimeters
wide was applied
to the cross hatched area. The tape adhesively bonds to steel according to
ASTM 3330M
(Revised Oct. 1, 2004) with a 180 degree peel strength value of 430 N/m. After
5 to 10
seconds of adhesion, the tail end of the tape was grasped and pulled upward
with a rapid
jerking motion perpendicular to the paint. The percent paint remaining
attached to the
substrate (indicative of paint adhesion) was determined as a percentage of the
area covered by
the tape. The results of Example 1 are reported below in TABLE 2.
TABLE 2
Sample CRS sample Cleaner Zr coating Bake % paint
No. weight mg/m2 temperature F remaining
1 CRS 1 1533/1270 fresh 143 350 100
2 CRS 1 1533/1270 aged 203 350 100
3 CRS 1 1533/1270 fresh 143 375 99-100
4 CRS 1 1533/1270 aged 203 375 100
CRS 2 1533/1270 fresh 165 350 95-98
6 CRS 2 1533/1270 aged 182 350 99-100
7 CRS 2 1533/1270 fresh 165 375 60-70
8 CRS 2 1533/1270 aged 182 375 80
[00050] The results demonstrated a bake temperature effect on the
electrodeposited
coating adhesion. When the bake temperature of the electrodeposited paint was
raised from
350 F to 375 F, there was a reduction in paint adhesion, especially on the CRS
2 substrate.
The results for CRS 2 were also quite different than for CRS 1. Further
examination of
samples from each CRS revealed striking differences in the deposited
pretreatment coating
composition.
[00051] Figures 1 A and 1C are scanning electron microscope (SEM)
photographs of
CRS 1 coated with a pretreatment coating composition according to Example 1,
using fresh
1533/1270, a Zr coating weight of 143 mg/m2 and a bake temperature of 375 F
as described
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above (Sample 3). Figure lA and 1B are at a magnification of 10,000x and 1C
and 1D are a
magnification of 30,000x.
[00052] Figures 1B and 1D are SEM photographs of CRS 2 coated with a
pretreatment
coating according to Example 1, using fresh 1533/1270, a Zr coating weight of
165 mg/m2
and a bake temperature of 375 F as described above (Sample 7). Sample 7, the
CRS 2
sample exhibited poor paint adhesion. The photographs show that the deposited
pretreatment
coating of Sample 3 in Figures lA and 1C was composed of much smaller
substructures than
that found in the pretreatment coating surface of Sample 7 in Figures 1B and
1D. The surface
in Figures 1B and 1D had larger and more clumped looking substructures.
[00053] Figures 2A and 2B are a further analysis of the Sample 3 surface
shown in
Figures lA and 1C. Figure 2A shows an SEM photograph of the pretreatment
coating at a
magnification of 15,000x and also shows three circles labeled 1, 2, and 3.
Each of these areas
was subjected to Auger Emission Spectroscopy (AES) to identify the elements
and their
levels found in each area of analysis. The results were evaluated by looking
at the deviation
from the baseline for each area, to make comparison possible the baselines
were offset as can
be seen. The units on the y-axis in Figure 2B are (counts/second) X 105, that
is, the y-axis
amounts were increased by a factor of 100,000. The results show differences in
the levels of
copper between the three areas. The iron, zirconium and carbon levels were all
very similar in
the three areas. The largest substructure, area 1, had the highest level of
copper. By way of
contrast area 2, a very small substructure, had very little copper in it.
Finally, area 3, which
was taken between two larger substructures, showed a copper level that was
between areas 1
and 2. The actual levels of copper were as follows: area 1 had a copper level
of 27 atomic
percent; area 2 had a copper level of 5 atomic percent; and area 3 had a
copper level of 6
atomic percent. This represents a pretreatment coating (Sample 3) that led to
good paint
adhesion as shown in TABLE 2.
[00054] Figures 3A and 3B show a further analysis of the surface shown in
Figures 1B
and 1D (Sample 7). Figure 3A shows an SEM photograph of the pretreatment
coating at a
magnification of 15,000x and also shows two circles labeled 4 and 5. Each of
these areas
was subjected to AES to identify the elements and their levels found in each
spot of analysis.
The results were evaluated by looking at the deviation from the baseline for
each area, to
make comparison possible the baselines were offset as can be seen. The units
on the y-axis
of Figure 3B are (counts/second) X 104, that is, the y-axis amounts were
increased by a factor
of 10,000, therefore 1 unit in Figure 3B is equal to 10 units in Figure 2B.
Area 4 is of a large
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substructure and the AES analysis showed that it had a very high level of
copper, much
higher than that found in the large substructure shown in Figures 2A and 2B,
area 1. In
addition, area 5, a small substructure showed lower levels of copper than area
4, but much
higher than even area 1 of Figures 2A and 2B considering the differences in
the units. The
actual values for Sample 7, Figure 3B, were as follows: area 4 had a copper
level of 31
atomic percent and area 5 had a copper level of 25 atomic percent, much higher
on average
than those of Sample 3, which had good paint adhesion. These results show that
excess
copper in the deposited pretreatment coating caused poor paint adhesion and
led to formation
of larger substructures which was also not beneficial for paint adhesion.
Pretreatment
coatings with good paint adhesion tended to have smaller and fewer
substructures and less
deposited copper.
[00055] Figures 4 and 5 are graphical representations of the results from
X-ray
photoelectron spectroscopy (XPS) depth analysis of the two sample pretreatment
coatings
described in Figures 2 and 3, respectively. In this analysis an argon beam was
used to
penetrate the coating and as it moved through the coating the atomic
percentages of the
coating components were determined at a series of depths from the outer
surface of the
coating. The spot size for analysis was approximately 2 X 2 millimeters. Once
the atomic
percentage of iron (Fe) exceeded 50% the beam had reached the underlying CRS
substrate.
Turning to Figure 4, the box outline represents the pretreatment coating, it
can be seen that
the coating was approximately 145 nanometers thick while the coating of Figure
5 was
approximately 220 nanometers thick. The Figures further confirmed that higher
copper
levels in the coating correlated to poor paint adhesion: Figure 5, showing a
graph of Sample
7, the sample exhibiting poor paint adhesion, showed that the copper levels in
the deposited
pretreatment coating were much higher than in Sample 3, the pretreatment
coating exhibiting
good paint adhesion, whose graph is shown in Figure 4. Both the atomic
percentage and the
area under the curve for the copper were much greater in Figure 5 (Sample 7)
compared to
Figure 4 (Sample 3). The peak atomic % Cu in Figure 4 was 33 atomic %. The
peak atomic
% Cu in Figure 5 at any depth was 42.73 atomic %.
[00056] In further testing it has been determined that enhanced paint
adhesion is seen
when the pretreatment coating composition has sufficient chelating agent to
ensure that the
deposited pretreatment coating on the metal substrate has a average total
ratio of the atomic
% of copper to the atomic % of zirconium equal to or less than 1.1, more
preferably the ratio
is from 0.9 to 0.02, and most preferably from 0.3 to 0.1. This ratio is
determined from the
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average overall atomic percentages of the Zr and Cu in the coating not from
the ratio at a
single depth. As can be seen in the data from Figures 4 and 5, as one moved
through the
coating composition down to the metal substrate the atomic percentage of the
coating
components varied by depth until one reached the metal substrate, so it is the
total overall
average atomic % ratio that must be determined. By way of contrast, the
overall average total
ratio of atomic % of Cu to atomic % of Zr seen in the deposited pretreatment
coating
composition shown in Figures 1B, 1D, 3, and 5 was 2.73. The results led the
inventors to
develop the hypothesis that controlling the amount of deposited copper in the
pretreatment
coating, in the presence of copper in the pretreatment bath, could improve
paint adhesion and
also extend the pot life of zirconium-based pretreatment coatings baths, which
was tested in
Example 2 below.
Example 2
[00057] In Example 2, the control pretreatment coating composition was a
zirconium-
based coating bath, wherein the Zr level was 180 ppm, Cu was 30 ppm, total
Fluoride was
400 ppm and free Fluoride was 35 ppm, the level of Si02 was 42 ppm. The test
pretreatment
coating composition was the same as the control and further comprising a
chelating agent,
tartrate introduced as tartaric acid at 50 ppm. The pH of the pretreatment
coating
compositions was adjusted to 4Ø The substrate was CRS that had been pre-
cleaned with
fresh Parco 1533 and rinsed as described in TABLE 1 above. The immersion time
in the
control and the test zirconium-based coating baths was either 4 minutes or 10
minutes,
simulating a shorter and a longer line stoppage. A portion of each set of
samples were then
further coated with BASF Cathoguard 310X as described above and baked at 375
F. The
baked samples were then tested for paint adhesion as described above. In
addition, the
coating weights of Zr in mg/m2 were determined for the samples. Finally the
average atomic
percentage of Zr and Cu in the pretreatment coatings was determined for each
sample. The
results are present below in TABLE 3.
TABLE 3
Example Zr Paint
Immersion coating Average Average Ratio adhesion
Pretreatment time wt. atomic atomic of
coating bath minutes mg/m2 % Cu % Zr Cu/Zr remaining
Comp. zirconium-
Ex. 2-1 based coating
bath 4 166 3.8 3.3 1.15 90
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Comp. zirconium-
Ex. 2-2 based coating
bath 10 340 9.1 7.6 1.20 50
Ex. 2-3 zirconium-
based coating
bath, plus 50
ppm tartrate 4 115 2.5 2.6 0.96 100
Ex. 2-4 zirconium-
based coating
bath, plus 50
ppm tartrate 10 182 4.0 5.2 0.77 100
[00058] The
results of Table 3 showed that an increased immersion time led to an
increase in Zr coating weight, amount of Zr deposited, and the amount of Cu
deposited.
Inclusion of the tartrate at 50 ppm reduced the Zr coating weight, the amount
of Zr deposited,
and the amount of copper deposited in the pretreatment coating. More
significantly, the
presence of tartrate enhanced the pot life of the zirconium-based coating
bath. This is seen
by the fact that with tartrate present in the coating bath, the paint adhesion
remains at 100%
even after a 10 minute immersion, whereas in the absence of tartrate, the
paint adhesion was
significantly reduced to 90% or 50% of the applied paint coating. This tends
to show that too
much copper, relative to zirconium, deposited during the zirconium-based
pretreatment
coating bath can reduce paint adhesion and shorten pot life of the coating
bath and that
chelating agents, particularly copper metal chelators can improve paint
adhesion and pot life.
Example 3
[00059] In a next series of experiments, the effect of inclusion of the
metal chelator
tartrate on corrosion performance was tested. Again the substrate was CRS. The
CRS was
treated as described below in TABLE 4. The 2 minute treatment in the zirconium-
based
coating immersion bath is a standard time used in the industry.
[00060] As a separate control samples of the CRS were also treated with
the
pretreatment coating Bonderite 958 and sealer Parcolene 91, both available
from Henkel
Adhesive Technologies per the manufacturer's directions. As a final control
CRS samples
were simply cleaned with Parco Cleaner 1533R/Ridosol 1270 fresh and rinsed
with no
pretreatment coating. Then all the samples were coated with the BASF
Cathoguard 310X,
rinsed and baked.
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TABLE 4
Stage Treatment Product Application Time, Temperature
seconds
1 Clean Parco Cleaner Spray 70 60
1533R/Ridosol 1270
fresh
2 Clean Parco Cleaner Immersion 150 60
1533R/Ridosol 1270
fresh
3 Rinse City water Spray 60 28
4 Rinse Deionized water Spray 60 25
Pretreatment zirconium-based Immersion 120 or 600 25
coating bath with or
without 50 ppm tartrate
6 Pretreatment zirconium-based Spray 30 25
coating bath with or
without 50 ppm tartrate
7 Rinse Deionized water Spray 60 25
8 Electrodeposited BASF Cathoguard 310 immersion 120 32
(230V)
coating X
9 Rinse Deionized water Spray 30 25
Bake 1200 375 F
electrodeposited
[00061] Samples were then scribed to the CRS substrate and subjected to
one of two
corrosion performance tests. The first test was according to ASTM B117
(Revised Dec. 15,
2007) for 500 hours. In a second test, a 31 cycle test, the sample panels were
subjected to 31
cycles of a 24 hour testing protocol using a salt misting spray. The salt
misting spray
comprised 0.9% by weight sodium chloride, 0.1% by weight calcium chloride, and
0.075%
by weight sodium bicarbonate at pH 6 to 9. The first 8 hours the panels were
kept at 25 C
and 45% Relative Humidity (RH) and misted 4 times during the 8 hours at time
0, 1.5 hours,
3 hours and 4.5 hours. The panels were then put at 49 C and 100% RH for the
next 8 hours
with a ramp up from 25 C to 49 C and 100% RH over the first hour. The final
8 hours were
at 60 C and less than 30% RH with a ramp to the new conditions of 3 hours.
The cycle was
carried out for a total of 31 times. The panels were then evaluated for
average creep and
maximum creep in millimeters from the scribe line. The results for the ASTM
B117 test are
presented in TABLE 5. The results for the 31 cycle corrosion test are
presented in TABLE 6.
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TABLE 5: ASTM B117
Pretreatment Maximum Corrosion Average Corrosion
creep, millimeters creep, millimeters
zirconium-based coating bath, 9 3.9
2 minutes
zirconium-based coating bath, 3.5 2.5
minutes
zirconium-based coating bath, 6 3
2 minutes, 50 ppm tartrate
zirconium-based coating bath, 3 1.9
10 minutes, 50 ppm tartrate
Bonderite 958/ Parcolene 91 2 1.3
TABLE 6: 31 Cycle Corrosion Test
Pretreatment coating Maximum Corrosion Average Corrosion
creep, millimeters creep, millimeters
Clean only 11 10.4
zirconium-based coating bath, 3.8 3.1
2 minutes
zirconium-based coating bath, 5.3 4.3
10 minutes
zirconium-based coating bath, 4.2 3.6
2 minutes, 50 ppm tartrate
zirconium-based coating bath, 4.5 3.8
10 minutes, 50 ppm tartrate
Bonderite 958/ Parcolene 91 2.2 2.2
[00062] The results indicate that inclusion of the tartrate did not have a
negative effect
on the ability of the zirconium-based pretreatment coating to provide
corrosion resistance to
the CRS. Under the ASTM B117 500 hour test the results of using the tartrate
were at least
as good as the standard zirconium-based coating bath and were slightly better
for extended
dwell time of the CRS in the bath evidencing the improved pot life from the
chelator. The
longer immersion times did not reduce the corrosion protection and may even
increase it. In
the 31 cycle test the benefit of using a pretreatment coating was shown, in
the clean only
sample there was much more corrosion than in any of the pretreatment coating
examples.
The presence or absence of the tartrate did not seem to affect the corrosion
protection ability
of the pretreatment coating. These results are important because if the
presence of a chelating
agent, such as the tartrate, was detrimental to the corrosion protection then
one would have to
balance that negative effect against the beneficial effect on paint adhesion.
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Example 4
[00063] In a next series of experiments the effects of another chelating
agent,
triethanolamine (TEA), were tested. The substrate was CRS and the pretreatment
coating and
BASF Cathoguard were applied as described below in TABLE 7. Again the
zirconium-based
coating bath included 180 ppm of Zr, 30 ppm of Cu, 35 ppm of free and 400 ppm
total
Fluoride and 42 ppm of Si02. Samples were then tested for Zr coating weight in
mg/m2,
paint adhesion, and corrosion protection under ASTM B117 for 500 hours. As a
control
samples were also prepared with a pretreatment coating of Bonderite 958 and
Parcolene 91
as described in Example 3. The results are presented below in TABLE 8. Only a
single
concentration of TEA was tested, the same level as used for tartrate of 50
ppm.
TABLE 7
Stage Treatment Product Application Time, seconds
Temperature
C
1 Clean Parco Cleaner Spray 70 60
1533R/Ridosol
1270 fresh
2 Clean Parco Cleaner Immersion 150 60
1533R/Ridosol
1270 fresh
3 Rinse City water Spray 60 28
4 Rinse Deionized water Spray 60 25
Pretreatment zirconium-based Immersion 240 or 600 25
coatings bath with
or without 50 ppm
TEA
6 Pretreatment zirconium-based Spray 30 25
coating bath with
or without 50 ppm
TEA
7 Rinse Deionized water Spray 60 25
8 Electrodeposited BASF Cathoguard immersion 120 32
(230V)
coating 310X
9 Rinse Deionized water Spray 30 25
Bake 1200 375 F
electrodeposited
paint
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TABLE 8
Pretreatment Zr coating Paint Maximum Average
weight adhesion % creep creep
mg/m2 remaining millimeters millimeters
zirconium-based coating bath, 4 122 60 9 3.9
minute immersion
zirconium-based coating bath, 10 202 50 3.5 2.5
minute immersion
zirconium-based coating bath, plus 115 98 11.8 8.8
50 ppm TEA, 4 minute immersion
zirconium-based coating bath, plus 231 90 4.8 3.3
50 ppm TEA, 10 minute immersion
Bonderite 958/ Parcolene 91 0 ND 2.0 1.3
ND¨not determined
[00064] The results again demonstrate the benefit of including a chelating
agent, in
particular a copper metal chelator, in the pretreatment coating on the paint
adhesion. In the
presence of 50 ppm of TEA the paint adhesion was significantly enhanced, even
with a long
immersion of 10 minutes. The results show that at this level of TEA there was
a negative
effect on corrosion protection. Clearly, the optimum level of copper metal
chelator is
dependent on the identity of the chelator. There was also no reduction of Zr
coating weight
with TEA at 50 ppm.
[00065] The foregoing invention has been described in accordance with the
relevant
legal standards, thus the description is exemplary rather than limiting in
nature. Variations
and modifications to the disclosed embodiment may become apparent to those
skilled in the
art and do come within the scope of the invention. Accordingly, the scope of
legal protection
afforded this invention can only be determined by studying the following
claims.
21
