U.S. patent application number 13/568277 was filed with the patent office on 2014-02-13 for steel pre-paint treatment composition.
The applicant listed for this patent is Patrizia Angeli, Roberto Zoboli. Invention is credited to Patrizia Angeli, Roberto Zoboli.
Application Number | 20140041764 13/568277 |
Document ID | / |
Family ID | 50065279 |
Filed Date | 2014-02-13 |
United States Patent
Application |
20140041764 |
Kind Code |
A1 |
Zoboli; Roberto ; et
al. |
February 13, 2014 |
Steel Pre-Paint Treatment Composition
Abstract
An aqueous conversion coating composition for treating steel
substrates to provide a conversion coating thereon. The conversion
coating composition comprises a) a source of aluminum ions; b)
hexafluorozirconic acid or its salts; c) at least one pH adjuster;
and d) optionally, a surfactant. The conversion coating composition
provides a corrosion resistant coating on the metal surface and
improves the adhesion of subsequently applied layers.
Inventors: |
Zoboli; Roberto; (Novara
(NO), IT) ; Angeli; Patrizia; (Invorio (NO),
IT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Zoboli; Roberto
Angeli; Patrizia |
Novara (NO)
Invorio (NO) |
|
IT
IT |
|
|
Family ID: |
50065279 |
Appl. No.: |
13/568277 |
Filed: |
August 7, 2012 |
Current U.S.
Class: |
148/247 ;
148/22 |
Current CPC
Class: |
C23C 22/34 20130101 |
Class at
Publication: |
148/247 ;
148/22 |
International
Class: |
C23C 22/34 20060101
C23C022/34 |
Claims
1. An aqueous conversion coating composition comprising: a) from 0
g/l to 300 g/l of aluminum ions; b) hexafluorozirconic acid or
salts thereof; c) at least one pH adjuster; d) optionally, a
surfactant.
2. The aqueous conversion coating composition according to claim 1,
wherein the conversion coating composition does not contain
chromium or sequestering agents for zinc.
3. The aqueous conversion coating composition according to claim 1,
wherein the pH adjuster comprises ammonium hydroxide.
4. The aqueous conversion coating composition according to claim 1
wherein the aluminum ions are from a source comprising aluminum
hydroxide.
5. The aqueous conversion coating composition according to claim 1
wherein the concentration of aluminum ions is from 1 g/l to 50
g/l.
6. A method of treating a steel substrate to form a conversion
coating thereon, the method comprising the steps of a) contacting
the steel substrate with a composition comprising: i) from 0 g/l to
300 g/l of aluminum ions; ii) hexafluorozirconic acid or its salts;
iii) at least one pH adjuster; iv) optionally, a surfactant; and b)
thereafter drying the treated steel surface.
7. The method according to claim 6, wherein the conversion coating
composition does not contain chromium or sequestering agents for
zinc.
8. The method according to claim 6, wherein the pH adjuster
comprises aluminum hydroxide.
9. The method according to claim 6, wherein the aluminum ions are
from a source comprising aluminum hydroxide.
10. The method according to claim 6, wherein the concentration of
aluminum ions is from 1 g/l to 50 g/l.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to compositions and
methods for the formation of protective, corrosion-inhibiting
coatings on metals, or other materials coated with metals.
BACKGROUND OF THE INVENTION
[0002] Metals such as steel tend to corrode rapidly in the presence
of water due to their low oxidation-reduction (redox) potentials or
ease of oxide formation. In addition, steel can also have a
significant problem with paint adhesion, because the as-formed
metal surfaces are typically very smooth, and tend to form weakly
bound surface oxides, which do not normally provide a robust base
on which subsequent applied paints can anchor themselves.
[0003] One method of enhancing the corrosion resistance of steel is
through the use of a conversion coating, which is a self-healing,
corrosion-inhibiting layer formed during intentional exposure of
the metal to a chemically reactive solution. Conversion coatings
are particularly useful in surface treatment of metals such as
steel. The conversion coating process forms an adherent surface
containing an integral corrosion inhibitor that can provide
protection to coating breaches. The metal is exposed to a compound
that chemically alters the surface and forms a coating that
provides a high degree of corrosion resistance. Thus, a chemical
conversion coating applied to the surface of a less-noble alloy can
reduce the extent and severity of aqueous corrosion, provide
long-term property stability, and extend the useful life of the
object of manufacture.
[0004] A critical feature of effective conversion coatings is their
ability to provide corrosion protection to the base metal in the
presence of a coating breach. Conversion coatings grow on the metal
without an externally applied electrical potential. The protective
film is produced by a chemical reaction between the metal surface
and the conversion coating solution. The film is composed both of
an oxide and integral corrosion inhibitor species formed during
exposure to the conversion coating solution.
[0005] It has previously been common to apply these conversion or
pretreatment coatings using hexavalent chromium-containing
solutions. While these coatings provide good corrosion resistance,
attempts have been made to provide more acceptable non-chromate
derived coatings or coatings derived from trivalent chromium
because of concern regarding the occupational, safety, health and
environmental effects of hexavalent chromium, which is highly toxic
and is a known carcinogen. Various efforts have been made to
develop such coating and examples of these coatings can be found
for example in U.S. Pat. No. 7,294,362 to Tanaka et al. in U.S.
Pat. Nos. 6,375,726, 6,521,029 and 6,669,764 to Matzdorf et al.,
and in U.S. Pat. No. 7,294,211 to Sturgill et al., the subject
matter of each of which is herein incorporated by reference in its
entirety.
[0006] The conversion-coated surface may be left bare or afforded
further protection by the application of additional films or
coatings. Conversion coatings need to adhere to the substrate and
should also result in a surface that will promote the formation of
a strong bond with subsequently applied coatings. Bonding with
subsequently applied coatings is a function of the morphology and
chemical composition of the conversion coating. Adhesion promoting
surface treatments may exhibit corrosion inhibiting
characteristics. Depending on the intended application, a
conversion coating, as described herein, may also be considered to
be an "adhesion promoter" and vice versa.
[0007] Conversion coatings are usually formed by the application of
a conversion coating solution to the metal surface. The solution
can be applied by immersion, spray, fogging, wiping, or other
similar means depending on the complexity of the surface of the
substrate being treated.
[0008] While various conversion coating chemistries have been
proposed, the inventors of the present invention have determined
that additional further improvement are still needed.
SUMMARY OF THE INVENTION
[0009] It is an object of the present invention to provide an
improved conversion coating composition that does not contain toxic
hexavalent chromium but affords improved corrosion protection of
the metal surface.
[0010] It is another object of the present invention to provide an
improved conversion coating composition that provides improved
corrosion protection for steel and increases the adhesion of
subsequently applied paint to the so treated steel.
[0011] It is still another object of the present invention to
provide a conversion coating composition that contains a stable
solution for the treatment of metal substrates.
[0012] To that end, the present invention relates generally to an
aqueous conversion coating composition comprising:
[0013] a) from 0 g/l to 300 g/l of aluminum ions;
[0014] b) hexafluorozirconic acid or its salts;
[0015] c) at least one pH adjuster;
[0016] d) optionally, a surfactant.
[0017] The present invention also relates to a method of using the
aqueous conversion coating composition of the invention to treat
metal substrates such as steel substrates to provide an improved
conversion coating thereon. In one embodiment, the aqueous
conversion coating composition of the invention is preferably
substantially free of phosphorous and/or chromium. As used
throughout this patent specification and claims, the word "steel"
means both raw steel and steel coated with zinc or zinc alloys.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] In one embodiment, the present invention relates generally
to acidic aqueous conversion coatings for the pretreatment of
metals, such as steel, and to a process for improving the corrosion
resistant properties of such metal substrates and the adhesion of
subsequently applied paint.
[0019] In one embodiment, the present invention relates generally
to compositions for pretreating steel substrates and to a process
of pretreating steel substrates at temperatures ranging from
ambient temperatures up to about 200.degree. F. These pretreatment
compositions typically comprise an acidic aqueous solution having a
pH in the range of about 0.5 to about 6 and preferably from about 4
to 5.
[0020] The pretreatment composition of the invention is an aqueous
solution that typically comprises:
[0021] a) from 0 g/l to 300 g/l of aluminum ions;
[0022] b) hexafluorozirconic acid or its salts;
[0023] c) at least one pH adjuster;
[0024] d) optionally, a surfactant.
[0025] The composition is preferably essentially free of hexavalent
chromium and sequestering agents for zinc. The composition is also
preferably free of all chromium compounds.
[0026] The composition preferably comprises aluminum ions. In one
preferred embodiment, the source of aluminum ions is aluminum
hydroxide. Although aluminum hydroxide is typically preferred,
alkali hexafluoride aluminates such as sodium hexafluoride
aluminate may also be used in the practice of the present
invention. In another preferred embodiment, the source of aluminum
ions is pure aluminum powder which is used in combination with
hexafluorozirconic acid, whereby the aluminum powder is thus
dissolved in the solution by the acidity of the hexafluorozirconic
acid. The concentration of aluminum ions in the composition can be
from 0 g/l to 300 g/l, but is preferably from 1 g/l to 50 g/l.
[0027] The composition also comprises hexafluorozirconic acid or
salts thereof. Water-soluble potassium, sodium, lithium, or
ammonium salts of these anions are typical, with ammonium salts of
these anions being preferred.
[0028] The pH adjuster, which may include one or more alkali metal
hydroxide, ammonium hydroxide, ammonium bicarbonate, ammonium
carbonate, sodium carbonate, and sodium bicarbonate and
combinations of one or more of the foregoing. Other compounds would
also be known to those skilled in the art. Preferably the pH of the
composition is maintained from 0.5 to 6, most preferably from 4 to
5.
[0029] The composition may also comprise a surfactant. The
inventors have found the following surfactants to be useful:
TRITON.RTM. DF12, ethylene oxide-propylene oxide copolymers,
DOWFAX.RTM. 63N10, polypropylene glycol, polyethylene glycol, and
ethoxylated alcohols such as the LUTENSOL.RTM. series of
surfactants.
[0030] Another optional ingredient that may beneficially be
included in some formulations prepared in accordance with the
present invention is a preservative. One preferred preservative is
hexahydro-1,3,5-tris(2-hydroxyethyl)-s-triazine, sold under the
tradename Surcide P (available from Surety Laboratories, Cranford,
N.J.). Other similar preservatives would also be known to those
skilled in the art.
[0031] Table 1 sets forth one preferred composition for Formula A
prepared in accordance with the present invention.
TABLE-US-00001 TABLE 1 Composition of Formula A Component
Grams/liter hexafluorozirconic acid 2.2 g/l aluminum hydroxide 0.1
g/l Triton .RTM. DF-16 0.4 g/l Water To 1 liter Ammonium hydroxide
(37%) to pH 4.5
[0032] The metal substrate for use in the process of the present
invention may be any substrate having a metal surface. Examples of
usable substrates include those having a surface made of steel or
steel coated with zinc or zinc alloys. Particularly preferred are
steel sheet substrates.
[0033] Examples of steel sheet substrates include hot-dip
galvanized steel sheets, electrogalvanized steel sheets, iron-zinc
alloy plated steel sheets, nickel-zinc alloy plated steel sheets,
aluminum-zinc alloy plated steel sheets and the like. Also usable
as steel sheet substrates are zinc-based metal plated steel sheets
that have been subjected to chemical conversion treatment such as
chromate treatment, zinc phosphate treatment or composite oxide
film treatment. Further, a steel sheet assembly can be employed as
a steel sheet substrate.
[0034] The coating composition of the present invention can be
applied to a metal substrate by any known process, such as dip
coating, shower coating, spray coating, roll coating and
electrocoating. The duration of contact ranges from about 30
seconds to about 5 minutes, but longer contact may be required if
the solution is weak or if the temperature of the solution is
relatively low. The aqueous solution temperature is normally below
100.degree. C., for example in the range of 15.degree. to
75.degree. C., and more preferably at about 50.degree. C.
[0035] It is generally preferable that the composition be dried for
about 2 seconds to about 30 minutes by heating under such
conditions that the substrate reaches a maximum temperature of
about 60 to 250.degree. C.
[0036] Prior to performing the pretreatment, the substrates may be
treated by cleaning and/or activating as is generally well known in
the art. The substrates may then be contacted with the composition
of the invention for a sufficient period of time to form a
conversion coating layer on the surface of the substrate and then
allowed to dry.
[0037] The treatment composition provided for herein, generally
produces a blue conversion coating on steel with very good
resistance to corrosion and adhesion to paint subsequently
applied.
[0038] While the invention has been described above with reference
to specific embodiments thereof, it is apparent that many changes,
modifications, and variations can be made without departing from
the inventive concept disclosed here. Accordingly, it is intended
to embrace all such changes, modifications, and variations that
fall within the spirit and broad scope of the appended claims. All
patent applications, patents, and other publications cited herein
are incorporated by reference in their entirety.
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