U.S. patent application number 12/698197 was filed with the patent office on 2010-07-08 for method for coating a metal surface with an ultra-fine layer.
This patent application is currently assigned to CENTRE DE RECHERCHES METALLURGIQUES ASBL-CENTRUM VOOR RESEARCH IN DE METALLURGIE VAW. Invention is credited to Sebastien LE CRAZ.
Application Number | 20100173106 12/698197 |
Document ID | / |
Family ID | 34682722 |
Filed Date | 2010-07-08 |
United States Patent
Application |
20100173106 |
Kind Code |
A1 |
LE CRAZ; Sebastien |
July 8, 2010 |
METHOD FOR COATING A METAL SURFACE WITH AN ULTRA-FINE LAYER
Abstract
The present invention relates to a method for continuously
coating a substrate in motion such as a metal strip made of steel,
the coating formed being an ultra-fine film of a thickness between
10 and 100 nm, deposited on the substrate: from a solution
containing nanoparticles of oxides, in conditions of controlled pH,
said substrate being at a temperature higher than 120.degree. C.,
the total duration of the deposition being less than 5 seconds and
preferably less than 1 second, characterised in that at least one
chemical additive, called a "refiner", is incorporated into said
solution, said refiner having, mutatis mutandis, the effect of
restricting the formation of said coating.
Inventors: |
LE CRAZ; Sebastien; (Liege,
BE) |
Correspondence
Address: |
JACOBSON HOLMAN PLLC
400 SEVENTH STREET N.W., SUITE 600
WASHINGTON
DC
20004
US
|
Assignee: |
CENTRE DE RECHERCHES METALLURGIQUES
ASBL-CENTRUM VOOR RESEARCH IN DE METALLURGIE VAW
|
Family ID: |
34682722 |
Appl. No.: |
12/698197 |
Filed: |
February 2, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10580245 |
May 22, 2006 |
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PCT/BE04/00157 |
Nov 2, 2004 |
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12698197 |
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Current U.S.
Class: |
428/34.5 ;
428/215; 428/336; 428/337; 428/389; 428/450; 428/469; 428/472;
428/472.2; 977/773; 977/811 |
Current CPC
Class: |
C23C 26/00 20130101;
Y10T 428/2958 20150115; Y10T 428/265 20150115; C23C 24/00 20130101;
C09D 1/00 20130101; C23C 2/04 20130101; C23C 24/08 20130101; Y10T
428/1314 20150115; C23C 2/26 20130101; Y10T 428/24967 20150115;
C23C 2/02 20130101; Y10T 428/266 20150115 |
Class at
Publication: |
428/34.5 ;
428/469; 428/450; 428/472; 428/472.2; 428/336; 428/389; 428/337;
428/215; 977/773; 977/811 |
International
Class: |
B32B 15/04 20060101
B32B015/04; B32B 7/02 20060101 B32B007/02; B32B 5/16 20060101
B32B005/16; B32B 15/02 20060101 B32B015/02; B32B 18/00 20060101
B32B018/00; B32B 1/08 20060101 B32B001/08 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 17, 2003 |
BE |
BE 2003/0666 |
Claims
1-32. (canceled)
33. A flat or long metallurgical product coated with an ultra-fine
protective layer, said protective layer comprising nanoparticles of
oxides or a mixture of these oxides.
34. The product according to claim 33, wherein the oxides are
Al.sub.2O.sub.3, Y.sub.2O.sub.3, SiO.sub.2, SnO.sub.2, TiO.sub.2,
ZnO, S.sub.2O.sub.5, ZrO.sub.2 or CeO.sub.2.
35. The product according to claim 33, wherein the protective layer
has a thickness of less than 100 nm.
36. The product according to claim 33, wherein the product is a
strip, wire, profiled section or tube.
37. The product according to claim 33, wherein an initial thickness
of the product prior to being coated with the protective layer is
between 0.15 and 5 mm.
38. A flat or long metallurgical product coated with an ultra-fine
protective layer, said protective layer comprising nanoparticles of
oxides or a mixture of these oxides, wherein the oxides are
Al.sub.2O.sub.3, Y.sub.2O.sub.3, SiO.sub.2, SnO.sub.2, TiO.sub.2,
ZnO, S.sub.2O.sub.5, ZrO.sub.2 or CeO.sub.2; wherein the protective
layer has a thickness of less than 100 nm; wherein the product is a
strip, wire, profiled section or tube; and wherein an initial
thickness of the product prior to being coated with the protective
layer is between 0.15 and 5 mm.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the improvement of the
method described in international patent application WO-A-03/048403
by the use of chemical additives affecting the deposition reaction
of an ultra-fine layer of oxide nanoparticles. The addition of such
compounds allows to obtain layers of a thickness that is even less
than in the above-mentioned patent application, i.e. of a thickness
of typically less than 100 nm.
TECHNOLOGICAL BACKGROUND AND THE STATE OF THE ART
[0002] The method described in application WO-A-03/048403 A1 is
part of a global project intended to reduce the production costs of
pre-painted metal strips. In this context, the metallurgists hope
to incorporate the lacquering process at the end of the galvanising
line.
[0003] The main difficulty to obtain this result has been to find a
conversion treatment for the strip that is fast enough to be put
between the galvanising and the painting treatment. The
above-mentioned method has also been considered as an alternative
to treatments based on chromates.
[0004] Being based on the use of the strip's residual heat after
galvanising and spinning, this method does not require any external
energy input in order to work.
[0005] On the installation side, it is preferably carried out in
the descending section that follows the zinc bath. From a practical
point of view, it can be installed in place of the tank of
demineralised water that completes the cooling with jets of water
steam. The compact deposition system considered here may be a bath
or a spray system (wave of water, spraying with jets, etc.). Thus,
with the help of some modifications, the investment in the new
equipment is limited.
First Approach: Ultra-Fine Layer
[0006] Ultra-fine layers, typically less than 100 nm, produced by
the proposed method can only be considered for solutions with a low
concentration of particles, low strip temperatures or even both.
The possibility of also being able to produce deposits of this type
for solutions with high concentrations of nanoparticles and/or at
high temperature would be very usefully for a simple in-line
adaptation of the method.
[0007] Moreover, this objective is crucial for obtaining a deposit
that perfectly adheres to the metal and for good internal cohesion
of the oxide layer. Indeed, for a solution with a low
concentration, the nanoparticles in suspension are some distance
from each other and thus have little tendency to correctly
agglomerate when the solvent evaporates.
[0008] However, one problem caused by the use of solutions with
medium and high concentration is the formation of localised
excessive thicknesses that form a network of very friable "ribs" on
the surface of the oxide deposit, as shown in FIG. 1. These result
from the preferential precipitation at the interface between the
solution and the vapour phase caused during immersion, as
diagrammatically described in FIG. 2. This can be seen both on the
samples produced in a bath (FIG. 2.a) or by spraying (FIG. 2.b) and
it is detrimental to the subsequent adhesion of paint.
[0009] Document JP-A-63 072887 teaches a method for producing a
steel strip by hot dipping showing excellent resistance to
corrosion and good mechanical resistance so that, before the drying
of the first layer made of zinc or aluminium, an aqueous solution
containing dissolved silica and/or aluminium, lithium silicate,
etc. is pulverised on the surface of the strip so as to form an
oxide layer comprising SiO.sub.2, Al.sub.2O.sub.3 or Li.sub.2SiO,
separately or in a mixture. However, a film of chromate is also
formed on the oxide layer so as to increase the resistance to
corrosion and the adhesion of the oxide layer, in contrast to the
method of the previous application WO-A-03/048403, which was free
of hexavalent chrome. This shows that good adhesion of the
nanoparticles is far from certain.
[0010] Document JP-A-62 166667 discloses a method for forming an
oxide layer on the surface of a steel strip coated by hot dipping
with a layer of Zn or of a Zn--Al alloy with the aim of preventing
deep grey discoloration of the strip. A solution containing one or
several of the oxides ZrO.sub.2, Cr.sub.2O.sub.3, Al.sub.2O.sub.3,
Y.sub.2O.sub.3, CeO.sub.2, ZrBiO.sub.4 and Sb.sub.2O.sub.3 is
pulverised on the strip after immersion and thus its temperature is
.gtoreq.100.degree. C. at a concentration in the range of 1-100
mg/m.sup.2. The water is evaporated by the intense heat of the
steel strip, with the formation of the oxide film. A film of
chromate is then formed on the above-mentioned oxide layer. It
should be noted that a check of the thickness of the layer is
neither considered nor described although this is crucial for good
adhesion of the deposit. It seems that the layer of chromate is
there to compensate for this omission.
Second Approach: Better Stability of the Solution Depending on the
Temperature
[0011] When the strip is plunged into the bath, it transfers its
heat to the colloidal solution. So as to avoid overheating the
latter and thus adversely affecting the bath, it is clearly the
intention to remove the excess energy by means of external
circulation and a heat exchanger. In fact, despite the presence of
this equipment, it has been noted that the bath is adversely
affected. It seems that the excess heat retained at the
metal-solution interface is responsible for this and causes the
precipitation of the solution.
[0012] So as to be able to guarantee a satisfactory useful life of
the bath, it is absolutely necessary to find a method that allows
to use the solution right up until the solvent boils.
Third Approach: a Wider Margin for Manoeuvre
[0013] It is possible to adapt the cooling equipment preceding the
tank containing the colloidal solution or the banks of spray's so
as to be able to guarantee a constant entry temperature over time.
It is necessary to control this parameter so as to guarantee
constant thickness of the deposit of nanoparticles on the
substrate.
[0014] However, in order to be competitive relative to a cold strip
treatment placed on the same location, apart from the control of
the bath, which is common, it would be preferable to be able to
dispose of the need for precision in the temperature or to reduce
it. Thus, so that it is less of a restriction to the user, this
method should be able to function with a relatively high level of
uncertainty regarding the temperature level.
[0015] Another disadvantage of an "immersion deposit" treatment
such as this in comparison with a cold method is that it is, in
addition to being affected by a change in the temperature of the
substrate, sensitive to a variation in the thickness of the strip.
In fact, at a given temperature, for a given material, the quantity
of thermal energy stored is a function of the volume of the body,
hence of the thickness in the case of a flat product. In fact, on a
galvanising line, steel strips of different thicknesses can be
processed.
AIMS OF THE INVENTION
[0016] The present invention aims to provide a method for coating a
metal with an ultra-fine protective film of oxide, preferably of
silicon, titanium, zirconium, cerium, yttrium or antimony.
[0017] An additional aim of the invention is to allow maximum
flexibility of the method relative to the entry temperature of the
strip into the bath.
[0018] Another aim of the invention is to guarantee reproducibility
of the deposit in terms of thickness with a light or heavy weight
of the layer.
[0019] Another aim of the invention is to guarantee a useful life
of the solution that meets the metallurgist's requirements.
MAIN CHARACTERISTIC ELEMENTS OF THE INVENTION
[0020] A first aspect of the present invention relates to a method
for continuously coating a substrate in motion such as a metal
strip made of steel, the coating formed being an ultra-fine film of
a thickness of between 10 and 100 nm, deposited on the substrate:
[0021] from a solution containing nanoparticles of oxides, [0022]
in conditions of controlled pH, [0023] said substrate being at a
temperature higher than 120.degree. C., [0024] the total duration
of the deposition being less than 5 seconds, preferably less than 1
second, characterised in that at least one chemical additive,
called a "refiner", is incorporated into said solution, said
refiner having, mutatis mutandis, the effect of restricting the
formation of said coating.
[0025] In the context of the invention, the substrate to be coated
is either a bare metal, preferably steel, stainless steel (or
"inox"), aluminium, zinc or copper; or a first metal coated with a
second metal, preferably a steel strip coated with a layer of zinc,
aluminium, tin, or of an alloy of at least two of these metals.
[0026] The nanoparticles comprise oxides, preferably SiO.sub.2,
TiO.sub.2, ZrO.sub.2, Al.sub.2O.sub.3, CeO.sub.2, Sb.sub.2O.sub.5,
Y.sub.2O.sub.3, ZnO, SnO.sub.2 or mixtures of these oxides, are
hydrophilic and/or hydrophobic, have a size of between 1 and 100 nm
and are in the solution with a content of between 0.1 and 10%, and
preferably between 0.1 and 1%.
[0027] The concentration of refiner is between 1 and 20 g per litre
(g/L) of solution, preferably between 5 and 10 g/L.
[0028] More particularly, the refiner used for the deposit of
silica nanoparticles is selected from the group of compounds
comprising catechin and its derivatives, hydrofluoric and boric
acids, borates, sodium and potassium carbonates and hydrogen
carbonates, ammonium hydroxide and amines that are soluble in
water. The refiner used for a deposit of nanoparticles of stannous
or stannic oxide is selected from the group of compounds comprising
borates, potassium carbonates and hydrogen carbonates, ammonium
hydroxide and amines that are soluble in water. The refiner used
for the deposit of nanoparticles of cerium and zirconium oxide is
selected from the group of compounds comprising hydrofluoric, boric
and carboxylic acids, and preferably formic, acetic, ascorbic and
citric acids.
[0029] Still according to the invention, the pH of the solution is
adjusted so as to allow the pickling of surface oxides from the
metal substrate when it is in contact with the solution, so as to
give the particles a maximum electrical charge in order to avoid
any agglomeration in the solution and so as to make the particles
as reactive as possible without destabilising the solution.
[0030] In particular, the pH of the solutions based on
nanoparticles of SiO.sub.2, SnO.sub.2, TiO.sub.2, ZnO or
Sb.sub.2O.sub.5 is alkaline and is preferably between 9 and 13. The
pH of the solutions based on nanoparticles of ZrO.sub.2, CeO.sub.2,
SiO.sub.2 or Sb.sub.2O.sub.5 is acidic and is preferably between 1
and 5.
[0031] As an advantage, the pH of the solutions based on a mixture
of nanoparticles is adjusted so that the solution is stable over
time. Preferably, in the case of a surface layer of the substrate
comprising a component of zinc, aluminium, iron, tin, chrome,
nickel or copper, the pH is chosen to be either alkaline or
acidic.
[0032] According to a first preferred embodiment of the invention,
the deposit is achieved by immersing the substrate for a controlled
period of time in an immersion tank containing the solution.
[0033] According to a second preferred embodiment of the invention,
the deposit is achieved by spraying the solution onto the substrate
by means of a nozzle, i.e. a device, assisted or not, with gas
under pressure, that sprays droplets of the solution.
[0034] According to a third preferred embodiment of the invention,
the deposit is created by depositing the solution on the substrate
by means of a roller.
[0035] As an advantage, the solution that comes into contact with
the strip is kept at a temperature of less than 100.degree. C., and
preferably less than 80.degree. C.
[0036] As a further advantage, the temperature of the substrate at
the start of the deposition is higher than 125.degree. C. and lower
than 250.degree. C.
[0037] If the substrate already has a metallic coating before
treatment, the temperature of the substrate at the start of the
deposition is advantageously higher than 125.degree. C. and lower
by 30 to 100.degree. C. than the melting point of the coating
metal.
[0038] If the substrate has a metallic coating produced by
immersion, as in galvanisation by immersion, the deposition is
preferably achieved just after the deposition of the metallic
coating, before the substrate cools down.
[0039] Preferably, in the case of a substrate liable to a too-high
level of oxidation for this to be eliminated during the deposition,
the substrate is protected from excessive contact with air by means
of a neutral gas such as nitrogen (N.sub.2) or argon.
[0040] Preferably again, the deposition is limited in time by
varying the depth of immersion in the case of deposition in a
solution or the length sprayed in the case of spraying the solution
with nozzles.
[0041] Still according to the invention, the solution is an aqueous
solution or comprises any other solvent capable of effectively
dispersing said nanoparticles.
[0042] As an advantage, agents for the improvement of resistance to
corrosion and/or adhesion to the substrate or the paint and/or to
improve the glide during formation are added to the solution.
[0043] Provision can be made in the method of the invention for the
coated substrate to be rinsed after post-treatment with water or
with a solution based on organic silanes or carboxylic acid with an
ability to form a strong link with the organic.
[0044] Preferably, the method of the invention comprises the means
for: [0045] continuously measuring and regulating the pH, [0046]
ensuring the replenishment of the solution and the elimination of
surplus products of the reaction, [0047] ensuring the homogeneous
mixture of the bath so as to avoid turbulence on its surface.
[0048] According to an advantageous embodiment, the temperatures of
the strip and of the bath, the time the strip remains in the bath,
the concentration of nanoparticles in the bath and the pH of the
bath are controlled. If necessary, the temperature of the strip,
the length of spraying time, the concentration of nanoparticles in
the solution sprayed, the spraying flow and the pH are equally
controlled.
[0049] A second aspect of the present invention relates to an
installation for coating a steel strip, comprising a device for
obtaining a second coating layer on a first coating layer obtained
by hot dipping or by jet spraying, by implementing the
above-described method, characterised in that said installation is
located after elements ensuring the spinning and solidification
operations of the first coating layer, said second coating layer
being achieved in this installation at a temperature lower by at
least 100.degree. C. than the temperature at which the first
coating layer solidifies.
[0050] A third aspect of the present invention relates to a flat or
long metallurgical product, preferably a strip, wire, profiled
section or tube, coated with an ultra-fine protective layer by
means of the above-described method, characterised in that said
protective layer comprises nanoparticles of oxide or of a mixture
of these oxides, preferably Al.sub.2O.sub.3, Y.sub.2O.sub.3,
SiO.sub.2, SnO.sub.2, TiO.sub.2, ZnO, Sb.sub.2O.sub.5, ZrO.sub.2 or
CeO.sub.2, and has a thickness of less than 100 nm.
[0051] As an advantage, the invention relates to a metallurgical
product of the strip coated type as described, the thickness of
which, possibly the initial thickness before the profiled section
or tube is produced, is between 0.15 and 5 mm.
BRIEF DESCRIPTION OF THE FIGURES
[0052] FIG. 1, already mentioned, shows a scanning electron
microscope image of a surface treated according to the invention, a
layer of SiO.sub.2 being deposited at a concentration of 2% by
weight.
[0053] FIGS. 2.a and 2.b already mentioned diagrammatically show
the potential precipitation zones when the method of the invention
is implemented, in a bath (a) or with a spray (b) respectively.
[0054] FIG. 3 diagrammatically shows the development, measured with
XPS, of the thickness of the silica coating on galvanised steel,
implemented according to the present invention, depending on the
temperature. The coating is achieved by immersion in a solution of
2% of SiO.sub.2, with and without the effect of a refiner, in this
case sodium borate (5 g/L).
DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
[0055] The innovation introduced in the context of the present
invention is based on the principle of obtaining ultra-fine layers
of nanoparticles of oxides, where the thickness of said layers is
limited by the incorporation in the bath of chemical additives that
restrict the deposition reaction, which for this reason are called
"refiners" by the Applicant.
[0056] The phenomenon of precipitation during the deposition and
the stability of the bath are based on the same chemical
principles. In fact, the precipitation by immersion is a
competition between two opposing mechanisms. There is on the one
hand the force that provides the stability of the solution and thus
allows the links between the nanoparticles to be broken and on the
other hand, the force that allows precipitation.
[0057] To control these phenomena as well as possible, compounds
comprising some highly specific chemical elements are introduced
into the solution.
[0058] The role of these compounds is to catalyse the dissolution
of the ultra-fine layer and thus to combat massive and chaotic
precipitation, i.e. to eliminate the network of ribs on the surface
of the oxide, for example. These compounds are called "refiners" by
the Applicant because they allow to reduce the weight of the
deposit layer. From the chemical point of view, they are to some
extent "poisonous" to the deposition reaction.
[0059] The discovery of these compounds that restrict the reaction
allows to envisage qualities of deposit equivalent to or better
than those obtained by conventional cold treatments.
[0060] They may allow, in a very wide range of temperature of the
strip, to obtain a homogeneous thickness of deposit of
nanoparticles (see FIG. 3) and thus an effective control of the
weight of the layer of the deposit. It is therefore of interest to
note that the addition of these types of chemical allows a
deposition at lower temperatures, possibly down to as low as
120.degree. C.
[0061] Depending on their concentration, they can also allow to
obtain in the bath layers of ultra-fine thickness for any
concentration of nanoparticles.
[0062] This type of compound must be soluble in the solvent in the
ranges of pH of the colloidal solutions envisaged and not cause
destabilisation of the suspension. In addition, thanks to their
ability to break the inter-nanoparticle links, they may enhance the
stability areas of colloidal solutions, either in terms of
temperature or of pH or both.
[0063] In order to be of value, the effectiveness of these
compounds must increase with temperature.
[0064] According to the present invention, types of mineral or
organic chemicals are associated with one or several types of
nanoparticles. Thus, a refiner for silica is not necessarily suited
for zirconium oxide.
[0065] For the deposition of silica nanoparticles, the most
effective types are principally catechin, hydrofluoric and boric
acids or borates, sodium and potassium carbonates and hydrogen
carbonates, ammonium hydroxide and amines that are soluble in
water.
[0066] For stannous and stannic oxides borates, potassium
carbonates and hydrogen carbonates, ammonium hydroxide and amines
that are soluble in water will be advantageously used.
[0067] Lastly, for cerium and zirconium oxides, hydrofluoric, boric
or carboxylic acid or formic, acetic, ascorbic and citric acid will
be used to advantage.
[0068] Once the deposit is formed, the surplus of the nanoparticles
that have not agglomerated under the effect of the refiner and the
residual refiners themselves can be rapidly eliminated by a
rinse.
[0069] It is also of interest to emphasise that in order to conform
to the logic of respecting the environment, the compounds used are
not carcinogenic.
* * * * *