U.S. patent application number 12/812140 was filed with the patent office on 2011-01-13 for method for producing an enamelled steel substrate.
This patent application is currently assigned to Arcelormittal Investigacion Y Desarollo Sl. Invention is credited to Javier Gonzalez, Marc Leveaux.
Application Number | 20110008537 12/812140 |
Document ID | / |
Family ID | 39473874 |
Filed Date | 2011-01-13 |
United States Patent
Application |
20110008537 |
Kind Code |
A1 |
Leveaux; Marc ; et
al. |
January 13, 2011 |
Method for Producing an Enamelled Steel Substrate
Abstract
The present invention is related to a method for producing an
enamelled steel substrate, said method comprising the steps of:
providing a steel substrate, applying to a surface of said steel
substrate a solution comprising a solvent, a polymer precursor, and
at least one metal or metal oxide, said metal or metal oxide being
suitable for promoting the adhesion of an enamel layer to the
surface of the steel substrate, curing said steel sheet, thereby
removing said solvent, and forming an organic layer comprising said
at least one metal or metal oxide, applying to said organic layer,
an enamel layer, followed by a firing step, to obtain the enamelled
steel substrate.
Inventors: |
Leveaux; Marc; (Marcq En
Baroeul, FR) ; Gonzalez; Javier; (Gent, BE) |
Correspondence
Address: |
REINHART BOERNER VAN DEUREN P.C.
2215 PERRYGREEN WAY
ROCKFORD
IL
61107
US
|
Assignee: |
Arcelormittal Investigacion Y
Desarollo Sl
Sestao
ES
|
Family ID: |
39473874 |
Appl. No.: |
12/812140 |
Filed: |
January 9, 2009 |
PCT Filed: |
January 9, 2009 |
PCT NO: |
PCT/EP09/50214 |
371 Date: |
September 21, 2010 |
Current U.S.
Class: |
427/226 |
Current CPC
Class: |
C23D 3/00 20130101 |
Class at
Publication: |
427/226 |
International
Class: |
C23D 3/00 20060101
C23D003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 10, 2008 |
EP |
08150162.9 |
Claims
1-15. (canceled)
16. A method for producing an enamelled steel substrate, said
method comprising the steps of: providing a steel substrate,
applying to a surface of said steel substrate a solution comprising
a solvent, a polymer precursor, and at least one metal or metal
oxide, said metal or metal oxide being suitable for promoting the
adhesion of an enamel layer to the surface of the steel substrate,
curing said steel sheet, thereby removing said solvent, and forming
an organic layer comprising said at least one metal or metal oxide,
applying to said organic layer, an enamel layer, followed by a
firing step, to obtain the enamelled steel substrate.
17. The method according to claim 16, wherein said metal is chosen
from the group consisting of Sc, Ti, V, Co, Cu, Ni, Fe, Mn, Mo, W
and Sb and wherein said metal oxide is the oxide of a metal chosen
from the group consisting of V, Co, Cu, Ni, Fe, Mn, Mo, W and
Sb.
18. The method according to claim 17, wherein said metal is chosen
from the group consisting of Ni, Cu, Co, Mo and wherein said metal
oxide is the oxide of a metal chosen from the group consisting of
Ni, Cu, Co, Mo.
19. The method according to claim 16, wherein said at least one
metal or metal oxide is/are added to said organic layer in the form
of a powder.
20. The method according to claim 19, wherein said powder has a
mean particle size smaller than 2 microns.
21. The method according to claim 16, wherein said organic layer
has a thickness between 100 nm and 10 microns, preferably between
100 nm and 6 microns.
22. The method according to claim 16, wherein said solution is
applied to the substrate by coil coating, dipping or spraying.
23. The method according to claim 16, wherein said curing step
takes place at a temperature between 80<0>C and
250<0>C.
24. The method according to claim 16, wherein said firing step is
performed at a temperature between 700[deg.]C and
900<0>C.
25. The method according to claim 16, wherein the firing step is
preceded by a step of drying the enamel layer.
26. The method according to claim 25, wherein said steel substrate
is subjected to a step of forming and/or cutting, after the step of
applying said organic layer and before the step of applying said
enamel layer.
27. A steel substrate, comprising on the surface of the steel
substrate an organic coating, consisting of a polymer layer
comprising at least one metal or metal oxide, said metal or metal
oxide being suitable for promoting the adhesion of an enamel layer
to the surface of the steel substrate.
28. The steel substrate according to claim 27, wherein said organic
coating is a Thin Organic Coating, having a thickness between 100
nm and 10 microns, preferably between 100 nm and 6 microns.
29. The substrate according to claim 27, wherein said substrate is
a steel sheet.
30. Use of a steel substrate according to claim 27, for producing
an enameled steel sheet or part.
Description
FIELD OF THE INVENTION
[0001] The present invention is related to a method for producing
an enamel layer on a steel substrate, such as a steel sheet or
formed product. The invention is equally related to the enamelled
steel substrate as such, preferably obtained by the method of the
invention.
GENERAL BACKGROUND
[0002] The protection of metallic surfaces by application of a
layer of vitrified enamel is well-known, and is widely used due to
the enamel's resistance to high temperature and because it gives
the surface a protection against chemical aggression. Vitrified
enamelled products are thus widely used in different applications
such as in washing machines, sanitary ware, cooking range, domestic
appliances, as well as construction materials.
[0003] A number of processes exist for producing enamelled steel
products. The conventional process for producing a white enamelled
steel sheet, involves the following steps: [0004] applying a first
layer of enamel, containing adhesion promoting oxides, such as
cobalt, nickel, copper, antimony or molybdenum oxides, [0005] a
first firing operation, [0006] applying a second layer of white
cover enamel, and [0007] a second firing operation.
[0008] This is the so-called `2-coat, 2 fire` approach (2C/2F). The
adhesion of the first enamel layer on the steel is obtained by
firing around 800.degree. C.-850.degree. C., via oxido-reduction
chemical reactions between the elements in the steel, such as
carbon and iron, and the adhesion promoting oxides in the enamel.
These oxides however give the enamel a dark colour. Consequently,
the application of a second layer of white enamel is required to
obtain a white enamel steel sheet.
[0009] In order to avoid the use of a large quantity of enamel and
double firing which are expensive, it is known to apply a direct
white enamelling (DWE) process (`1 coat/1 fire`), that allows to
obtain a white enamelled steel sheet by applying a single layer of
enamel on the steel sheet, and then subjecting the steel sheet to a
single firing operation.
That process comprises the steps of: [0010] an extended surface
preparation procedure, consisting of [0011] degreasing, pickling
and rinsing of a decarburized steel sheet to remove a given
quantity of iron. The pickling is necessary to obtain the correct
roughness. A decarburised substrate is necessary to obtain the
correct surface of the enamelled product. [0012] applying a layer
of nickel by a chemical treatment, [0013] applying a layer of
enamel, and [0014] firing the layer of enamel typically at a
temperature range of 750 to 900.degree. C.
[0015] In this case, the enamel does not comprise adhesion
promoting oxides, so that it does not change colour. The adhesion
in this type of enamelling is due to the prior pickling and
nickling operation. However, this type of pre-treatment operation
is environment-unfriendly and costly.
[0016] To avoid the pre-treatment steps associated with DWE, a
method was developed wherein a ground enamel and cover enamel are
applied, and subsequently fired together (`2 coat, 1 fire`). A
disadvantage of this method however, is that it needs large
quantities of enamel (2 enamel coats).
[0017] Besides this, several pre-coat chemistries and techniques to
deposit them are known in the art. All aim to deliver a precoated
steel suitable for direct white enamelling without pickling and
nickeling operations and requiring only one enamel coating and one
firing treatment. [0018] The document EP-A-0964078 focuses on Zn
and Zn-alloy precoatings, applied by hot dipping or by electrolytic
plating, and includes all Zn or Zn-alloy coatings with a thickness
of the Zn-coating between 1 .mu.m and 30 .mu.m, in particular 7
.mu.m to 25 .mu.m. The chemistry includes all Zn-contents above 50%
with a content of the other alloy components of up to 15% (Al, Fe,
Mg, Si, Cr, Ni, Co, Cu, Mn). The patent applies for decarburised
steel surfaces (C<0.08%, in particular <0.004%) or IF steel
surfaces (all carbon tied in precipitates). [0019] The documents
WO-A-0250326 and WO-A-0252055 describe a nickel-molybdenum alloy
coating applied by electrolytic or electroless plating, which is
then subjected to a heat treatment in a temperature range between
500.degree. C. and 900.degree. C. [0020] The documents
JP-A-04107752 and JP-A-04107753 describe an iron-molybdenum coated
cold rolled steel sheet for direct adhesion of the enamel. The
iron-molybdenum coating is obtained by electrolytic plating in a
bath containing e.g. iron sulfates and molybdenum ammonium salts.
After plating, the plated steel sheet is heat treated at
temperatures between 500.degree. C. and 900.degree. C. [0021] The
documents JP-A-04107754 and JP-A-04107755 describe an
iron-cobalt-molybdenum coated steel sheet obtained by electrolytic
plating, followed by a heat treatment at temperatures between
500.degree. C. and 900.degree. C. The plating technology has some
disadvantages related to environmental issues, resulting from the
chemical compounds like salts and sulfates used in the plating
bath.
[0022] Document--FR2805277--is related to a method for direct
enamelling of steel sheets, which are covered by a polymer based
corrosion protection layer. The surface density of the layer is
chosen sufficiently low such that a degreasing step is not required
prior to the application of the enamel, while at the same time, the
density is high enough to ensure adequate corrosion protection.
This technique does however not allow to obtain optimum
characteristics in terms of adhesion. The strict requirements in
terms of surface density also complicate the process.
[0023] Document--US1962617--is related to the manufacture of enamel
ware, involving the application of a coating of adhesion promoting
oxides such as Cobalt oxides to a steel surface. The oxides are
mixed with a solvent and a suspending agent such as ammonium
linoleate, clay or bentonite, before being applied to the surface
and subsequently drying the surface.
AIMS OF THE INVENTION
[0024] The invention aims to provide a method for producing a steel
substrate, in particular a steel sheet which is directly enamelled
in white or colour by a cover coat enamel layer, which does not
have the drawbacks of the state of the art. In particular, the
present invention aims to provide a method for producing a steel
substrate wherein a strong adhesion between steel sheet and enamel
is observed, and which is produced with any kind of steels suited
for enamelling, and in an environment-friendly and simple
process.
SUMMARY OF THE INVENTION
[0025] The invention is related to a method and a product such as
described in the appended claims.
[0026] The invention is firstly related to a method for producing
an enamelled steel substrate, said method comprising the steps of:
[0027] providing a steel substrate, [0028] applying to a surface of
said steel substrate a solution comprising a solvent, a polymer
precursor, and at least one metal or metal oxide, said metal or
metal oxide being suitable for promoting the adhesion of an enamel
layer to the surface of the steel substrate, [0029] curing said
steel sheet, thereby removing said solvent, and forming an organic
layer comprising said at least one metal or metal oxide, [0030]
applying to said organic layer, an enamel layer, followed by a
firing step, to obtain the enamelled steel substrate.
[0031] According to the invention, when not in oxide form, the
metal is either present in unbound form or in an alloy with one or
more other metals suitable for promoting enamel adhesion, for
example an alloy of one or more transition metals and/or Sb. The
metal is not present in the form of a non-oxide ceramic, such as a
carbide or silicide, nor as any other organometallic compound.
[0032] Preferred embodiments are described in any combination of
claim 1 with one or more of the subclaims 2 to 11.
[0033] Preferably, said metal is chosen from the group consisting
of Sc, Ti, V, Co, Cu, Ni, Fe, Mn, Mo, W and Sb and wherein said
metal oxide is the oxide of a metal chosen from the group
consisting of V, Co, Cu, Ni, Fe, Mn, Mo, W and Sb.
[0034] Preferably, said metal is chosen from the group consisting
of Ni, Cu, Co, Mo and wherein said metal oxide is the oxide of a
metal chosen from the group consisting of Ni, Cu, Co, Mo.
[0035] Preferably, said at least one metal or metal oxide is/are
added to said organic layer in the form of a powder.
[0036] Preferably, said powder has a mean particle size smaller
than 2 microns.
[0037] Advantageously, said organic layer has a thickness between
100 nm and 10 microns, preferably between 100 nm and 6 microns.
[0038] Preferably, said solution is applied to the substrate by
coil coating, dipping or spraying.
[0039] Preferably, said curing step takes place at a temperature
between 80.degree. C. and 250.degree. C.
[0040] Preferably, said firing step is performed at a temperature
between 700.degree. C. and 900.degree. C.
[0041] Preferably, the firing step is preceded by a step of drying
the enamel layer.
[0042] Preferably, said steel substrate is subjected to a step of
forming and/or cutting, after the step of applying said organic
layer and before the step of applying said enamel layer.
[0043] The present invention as a second object is equally related
to a steel substrate, comprising on the surface of the steel
substrate an organic coating, consisting of a polymer layer
comprising at least one metal or metal oxide, said metal or metal
oxide being suitable for promoting the adhesion of an enamel layer
to the surface of the steel substrate.
[0044] Advantageously, said organic coating is a Thin Organic
Coating, having a thickness between 100 nm and 10 microns and
preferably between 100 nm and 6 microns.
[0045] Preferably, said substrate is a steel sheet.
[0046] Finally, the present invention is also related to the use of
a steel substrate as defined here above for producing an enamelled
steel sheet or part.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE PRESENT
INVENTION
[0047] According to the invention, a steel substrate (e.g. a sheet)
is coated with an organic coating, comprising metal or metal oxides
that are suitable for promoting adhesion of an enamel layer. The
organic coating consists of a polymer layer comprising in said
layer one or more adhesion promoting metals and/or metal oxides,
said adhesion promoting materials being present in the form of
particles embedded in said matrix. Preferably, the coating is a
so-called Thin Organic Coating, having a thickness between 100 nm
and 10 microns. Subsequently, an enamel layer is applied to the
substrate and subjected to a firing step. The organic coating is
prepared from a solution comprising a solvent, e.g. water, and
polymers dispersed, dissolved or emulsified into this solvent. The
polymers are the precursors of the organic coating.
[0048] According to a preferred embodiment of the present
invention, these precursors are loaded, i.e. mixed with a filler
which is suitable for promoting the adhesion of an enamel layer to
the surface of the steel substrate. In other words, the filler
material is able to react at high temperature with the steel
surface and elements present in the enamel composition, in order to
form an interface in between. The filler is preferably administered
to the solution in the form of a powder, the mean particle size
being lower than 2 microns, more preferably between 1 and 1000 nm.
Said powder is added to the solution by dispersion. The solvent
comprising polymer and filler is applied to the steel sheet by a
known technique, e.g. coil coating, dipping or spraying.
[0049] The filler material is metal or metal oxide, or a mixture of
one or more metals, or a mixture of one or more metal oxides, or a
mixture of metals and metal oxides.
[0050] The filler can thus be a mixture of particles of different
metals or of different metal oxides or of different metals and
metal oxides, and/or the filler can comprise particles which are
themselves consisting of a mixture of metals and/or metal oxides,
e.g. an alloy of two or more adhesion promoting metals. The filler
particles can be pre-coated with a polymer or other organic
coating, to modify the chemistry of the surface of the filler
particles, in order to facilitate dispersion of these
particles.
[0051] Metals/metal oxides which are suitable for adhesion
promotion of enamel are known in the art, e.g. Cobalt or Cobalt
oxide. Any of such known adhesion promotors can be used in the
present invention. According to the preferred embodiment, one or
more of the metals chosen from the group consisting of V, Co, Cu,
Ni, Fe, Mn, Mo, W and Sb are used--pure or in oxide form--in the
filler. All these metallic oxides of metals are suitable adhesion
promotors as all can be reduced at low temperatures, and all are
chemically and physically compatible with iron. For example, they
can form as well titanates reacting with titanium dioxide from the
glass composition.
[0052] A more preferred embodiment uses one or more of the metals
Ni, Cu, Co, Mo and/or their oxides in the filler.
[0053] After the solution has been applied to the steel surface,
the steel sheet is subjected to a curing step in order to remove
the solvent and to form the organic coating onto the steel surface.
This curing step may be performed according to known techniques for
applying TOC, such as hot air (convection) curing at temperatures
between 80.degree. and 250.degree. C. or Infra Red curing. The
result is an organic coating, preferably a Thin Organic Coating as
defined above, consisting of a polymer layer and adhesion promoting
materials embedded therein. The final thickness of the TOC is
preferably between 100 nm and 10 microns, more preferably between
100 nm and 6 microns, more preferably between 1 and 3 microns.
[0054] According to a preferred embodiment, the following
compositions of the TOC after curing are obtained by the method of
the invention:
Polymer between 20 wt % and 95 wt %, more preferably between 33 wt
% and 80 wt %. Adherence promotor (i.e. the filler, e.g. metal or
metal oxide): between 5 and 80 wt %, more preferably between 20 wt
% and 66 wt %. Expressed in surface density, the filler is
preferably present in the TOC in a density of between 100 and 6000
mg/m2.
[0055] Then the cover coat enamel layer is applied by a known
technique, such as wet or dry electrostatic spraying, pneumatic
spraying, dipping, or flow coating technologies. Possibly, the
enamelling can be preceded by cutting or forming steps. The
application of the enamel layer is not preceded by degreasing,
pickling or nickling. A cover coat enamel is defined as an enamel
applied as an outside surface, which is contrary to a ground coat
enamel, used as a base layer for subsequent further treatment and
coating. A cover coat enamel generally does not contain adherence
promotors.
[0056] The cover coat enamel layer is finalized by a firing step,
according to a known technique, preferably at a temperature between
700.degree. C. and 900.degree. C., and possibly preceded by drying
the enamel layer (for wet applicative technologies). The firing
step causes the burning out of the organic layer. In other words,
the polymer of the layer is burned and thereby removed.
[0057] The steel sheet can be decarburized or not, and can be any
sheet suitable for enamelling, e.g. Al-killed, high-oxygen,
Ti-added, Nb-added, Ti--Nb added, B-added steel.
[0058] According to the invention, the pre-coated steel sheet is
coated with a single cover coat enamel layer, without any
substantial adherence promoting metal oxides in the enamel, and
subjected to a firing step. The adhesion-promoting metal oxides
present in the pre-coat provide for a good adhesion of the enamel
layer, without necessitating pre-treatments of the sheet, such as
nickling. The enamel doesn't darken, due to the absence of adhesion
promoting elements in the enamel layer itself.
[0059] Additional advantages of an organic coating according to the
invention are related to specific capabilities of this particular
type of coating, i.e. consisting of a polymer matrix as described
above. It has been found that such coatings have low
friction-characteristics, allowing the product on which the coating
is present to be deformed, e.g. in a deep-drawing or other
deformation process, without damaging the coating. This would not
be possible when an organic coating based on clay or bentonite as
described in the prior art.
[0060] Also contrary to the latter prior art coatings, the coatings
of the invention provide corrosion protection comparable to the
corrosion protection offered by oiling of cold rolled steel sheets.
This is important because pre-treated products may be subject to
longer periods of transport or storage before the enamelling step
is performed.
[0061] Finally, the coatings according to the invention are
resistant to water, which cannot be said of clays or bentonite such
as documented in the prior art. This allows the pre-treated
products to be easily cleaned with water, e.g. after a period of
storage, before performing the enamelling step.
[0062] These advantages provide the possibility to perform cutting
and forming steps directly on the product provided with an organic
coating according to the invention, said forming/cutting taking
place before the enamelling step. Because of the low friction
characteristics, no oil is needed during the forming process, so no
degreasing step is required before enamelling. As stated, no
pickling or nickling is required either, leading to a simplified
process for obtaining enamelled products.
Examples
[0063] The formulations C1 to C8 listed in table 1 below were
prepared (all numerical data provided in weight %). After weighting
the ingredients, the products were mixed together using first a
high speed centrifugal mixer containing ceramic balls and then an
ultrasonic cell in order to break the final aggregates.
TABLE-US-00001 TABLE 1 C1 C2 C3 C4 C5 C6 C7 C8 Beetafin 35 53 36
36.5 36 27.5 35 28 LS9010 NiO 15 11 11 14.5 8 Co3O4 18 15 18 Water
50 36 53 49 56 54.5 50 54 total 100 100 100 100 100 100 100 100
[0064] Products: Beetafin LS9010 is a current polyurethane
dispersion manufactured by the company BIP Limited, UK. Ni0 and
Co304 powders are current nano powders manufactured by Inframat
Advanced Materials LLC, USA.
[0065] All the dilutions obtained were applied by spraying onto the
previously degreased surface of steel grade suitable for enamelling
(DCO3ED, as defined in the norm EN10209) and cured at 90.degree. C.
during 1 minute after spraying. The thickness of the thin organic
coating was measured after curing (see tables 2 and 3).
[0066] Organic coated sheet steel as described before was covered
directly after curing the thin organic coating without any
additional surface treatment such as degreasing, with a
conventional white cover coat enamel powder dispersed in water.
Enamelled samples were first dried at about 80.degree. C. during 4
minutes and then fired. After firing at different temperature and
time, the thickness of the enamel layer was measured and the bond
of enamelled sheet steel was tested afterwards according to the
norm EN10209 (tables 2 and 3). For all samples, the thickness of
the enamel after firing was found over 100 .mu.m. Good bond was
observed in all cases because the surface of the enamel layer is
smooth and glossy, without any surface defect such as pin holes,
craters or blisters.
[0067] A bond quoted 1 according to the norm EN10209 is the best
result to obtain. A dense interface issued from the reaction
between steel, enamel and TOC is fully covering the steel surface.
According to the norm and general practice in this technical
domain, bonds quoted 1 & 2 are very high quality, 3 is
acceptable, 4 critical and 5 fully out of range.
TABLE-US-00002 TABLE 2 bond according to EN10209 obtained for
different TOC containing NiO and fired at different temperatures
and times Thickness 830.degree. C.- 830.degree. C.- 840.degree. C.-
840.degree. C.- 860.degree. C.- composition TOC .mu.m 3' 30'' 4' 3'
30'' 4' 4' C2 2 1 C2 1.5 1 C3 1.6 1 C1 3.9 1 C4 2.4 3 C5 2.2 2
TABLE-US-00003 TABLE 3 bond according to EN10209 obtained for
different TOC containing Co304 and fired at different temperatures
and times. Thickness 820.degree. C.- 840.degree. C.- 860.degree.
C.- 840.degree. C.- composition TOC .mu.m 4' 4' 4' 7' C6 2.1 2 1 C6
2.8 2 1 C7 1.5 1
* * * * *