EA018759B1 - Method for producing an enamelled steel substrate - Google Patents

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.

Description

Field of Invention

The present invention relates to a method for manufacturing an enamel layer on a steel substrate, such as a steel sheet, or a molded product. The invention equally relates to the enamelled steel substrate itself, preferably obtained by the method of the invention.

State of the art

The protection of metal surfaces by applying a layer of glazed enamel is well known and widely used due to the enamel's resistance to high temperature and the protection of the surface from chemically aggressive substances. Therefore, glazed enameled products are widely used for various purposes, such as washing machines, plumbing products, stoves, household appliances, as well as building materials.

There are many ways to make enameled steel products. The usual method of manufacturing a white enameled steel sheet includes the following steps:

applying a first layer of enamel containing adhesion promoting oxides such as cobalt, nickel, copper, antimony or molybdenum oxides;

first firing;

applying a second layer of white cover enamel;

second firing.

This is the so-called approach of 2 applications, 2 firing (2C / 2E). The adhesion of the first enamel layer on steel is achieved by firing at approximately 800-850 ° C, by redox chemical interactions between elements in steel, such as carbon and iron, and oxides that promote adhesion in enamel. However, these oxides lead to dark enamel. Therefore, the application of a second layer of white enamel is required to obtain a white enamelled steel sheet.

In order to avoid the use of a large amount of enamel and double firing, which is quite expensive, it is known that you can apply the method of direct application of white enamel (ΠΨΕ) (1 application, 1 firing), which makes it possible to obtain a white enameled steel sheet by applying one layer enamel on a steel sheet, and then subject the steel sheet to a single firing. This method includes the steps of an enhanced surface preparation method consisting of degreasing, pickling and washing decarburized steel sheet to remove a predetermined amount of iron. Etching is necessary to obtain the necessary roughness. The decarburized substrate is necessary to obtain the desired surface of the enameled product, applying a layer of nickel by chemical treatment;

applying the enamel layer and firing the enamel layer is typically at a temperature in the range of 750 to 900 ° C.

In this case, the enamel does not contain oxides that promote adhesion, so it does not change color. Adhesion in this type of application of enamel occurs due to preliminary etching and nickel plating. However, this type of pretreatment is environmentally harmful and expensive.

In order to avoid the pretreatment stages associated with E \ UE. a method has been developed in which soil enamel and coating enamel are applied and then fired together (2 applications, 1 firing). However, the disadvantage of this method is the need for large quantities of enamel (2 enamel coatings).

In addition, several chemicals are known in the art that are used prior to coating and methods for their application. All of them serve to obtain pre-coated steel, suitable for direct coating with white enamel without etching and nickel plating, and require the application of only one layer of enamel and one firing.

EP-A-0964078 focuses on precoatings based on Ζη and Ζη alloy, applied by hot dip or by electrolytic coating, and includes all coatings based on Ζη or Ζη alloy, having a thickness of Ζη coating from 1 to 30 μm, in particular from 7 to 25 microns. The chemical composition has a total content Ζη of more than 50% with a content of other alloy components up to 15% (A1, Ee, Md, 8ί, Cr, N1, Co, Cu, Μη). This technical solution is used for decarburized steel surfaces (C <0.08%, in particular <0.004%) or 1E steel surfaces (all carbon is bound in precipitation).

Documents UO-A-0250326 and UO-A-0252055 describe a coating based on a nickel-molybdenum alloy, applied by electrolytic coating or by chemical reduction, which is then subjected to heat treatment in the temperature range from 500 to 900 ° C.

Documents 1P-A-04107752 and 1P-A-04107753 describe cold-rolled steel sheet coated with molybdenum iron for direct adhesion of enamel. An iron-molybdenum coating is obtained by electrolytic coating in a bath containing, for example, iron sulfates and ammonium salts of molybdenum. After coating, the steel sheet is heat treated while

- 1 018759 temperatures ranging from 500 to 900 ° C.

Documents 1Р-Л-04107754 and 1Р-Л-04107755 describe a steel sheet coated with iron-cobalt-molybdenum obtained by electrolytic coating and then heat treatment at temperatures from 500 to 900 ° C. The coating technology has some disadvantages related to environmental problems arising from the use of chemical compounds such as salts and sulfates in an electrolytic bath.

Document TV 2805277 relates to a direct enameling method for steel sheets that are coated with a polymer-based corrosion protection layer. The density of the surface of the layer is chosen sufficiently low, so that the stage of degreasing is not required before applying the enamel, although at the same time, the density is high enough to provide the required corrosion protection. However, this method does not provide the opportunity to obtain optimal characteristics in terms of adhesion. Strict requirements regarding surface density also complicate this method.

Document I8 1962617 relates to the manufacture of an enamelled product comprising bonding oxides promoting adhesion, 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 application to the surface, and then the surface is dried.

Object of the invention

The objective of the invention is to provide a method of manufacturing a steel substrate, in particular a steel sheet, which is directly subjected to the application of white or colored enamel in the form of a coating layer of enamel that does not have the disadvantages inherent in the methods of the prior art. In particular, the present invention is to provide a method of manufacturing a steel substrate in which there is strong adhesion between the steel sheet and the enamel, and which is carried out with any type of steel suitable for applying enamel, and which is an environmentally friendly and simple method.

SUMMARY OF THE INVENTION

The invention relates to a method and a product, such as those described in the claims. The invention primarily relates to a method for manufacturing an enameled steel substrate, wherein said method comprises the following steps:

take a steel substrate;

applying a solution containing a solvent, a polymer precursor and at least one metal or metal oxide to the surface of said steel substrate, wherein said metal or metal oxide is suitable for promoting adhesion of the enamel layer to the surface of the steel substrate;

drying said steel sheet, thereby removing said solvent and obtaining an organic layer containing said at least one metal or metal oxide;

an enameled layer is applied to said organic layer, followed by a calcination step to obtain an enameled steel substrate.

According to the invention, when the metal is not in the form of an oxide, the metal is present in an unbound form or in an alloy with one or more other metals suitable for promoting adhesion of enamel, for example, an alloy of one or more transition metals and / or 8b. The metal is not presented in the form of ceramics based on oxygen-free compounds, such as carbide or silicide, as well as in the form of any other organometallic compound.

Preferred embodiments are described in any combination of claim 1 with one or more of claims 2-11.

Preferably, said metal is selected from the group consisting of 8c, VI, V, Co, Cu, N1, Fe, Mn, Mo, and 8b, wherein said metal oxide is an oxide of a metal selected from the group consisting of V, Co, Cu , N1, Pe, Mn, Mo, and 8b.

Preferably, said metal is selected from the group consisting of N1, Cu, Co, Mo, wherein said metal oxide is a metal oxide selected from the group consisting of N1, Cu, Co, Mo.

Preferably, said at least one metal or metal oxide is added in powder form to said organic layer.

Preferably, said powder has an average particle size of less than 2 microns.

Advantageously, said organic layer has a thickness of from 100 nm to 10 μm, preferably from 100 nm to 6 μm.

Preferably, said solution is applied to the substrate by coilcoating, dipping or spraying. Preferably, said drying step is carried out at a temperature of from 80 to 250 ° C.

Preferably, said firing step is carried out at a temperature of from 700 to 900 ° C.

Preferably, the calcining step is preceded by a drying step of the enamel layer.

Preferably, said steel substrate is subjected to a forming and / or cutting step after the step of applying said organic layer and before the step of applying said enamel layer.

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The present invention also relates to a steel substrate having on its surface an organic coating consisting of a polymer layer containing at least one metal or metal oxide, wherein said metal or metal oxide is suitable to facilitate adhesion of the enamel layer to the surface of the steel substrate.

Advantageously, said organic coating is a thin organic coating having a thickness of 100 nm to 10 μm and preferably 100 nm to 6 μm.

Preferably, said substrate is a sheet of steel.

Finally, the present invention also relates to the use of the steel substrate defined above for producing an enamelled steel sheet or part thereof.

Detailed Description of Preferred Embodiments of the Present Invention

In accordance with the invention, a steel substrate (e.g., a sheet) is coated with an organic coating containing metal or metal oxides, suitable to promote adhesion of the enamel layer. The organic coating consists of a polymer layer containing in the specified layer one or more than one metal and / or metal oxide promoting adhesion, where these adhesion promoting substances are in the form of particles immersed in said matrix. Preferably, the coating is a so-called thin organic coating having a thickness of 100 nm to 10 μm. Then the enamel layer is applied to the substrate and subjected to firing. The organic coating is prepared from a solution containing a solvent, for example water, and polymers dispersed, dissolved or emulsified in this solvent. Polymers are organic coating precursors.

According to a preferred embodiment of the present invention, these precursors are applied, i.e. mixed with a filler, which is suitable in order to promote the adhesion of the enamel layer to the surface of the steel substrate.

In other words, the filler material is able to interact at high temperature with the steel surface and the elements in the enamel composition to form a boundary between them. The filler is preferably introduced into the solution in the form of a powder with an average particle size of less than 2 microns, more preferably from 1 to 1000 nm. The specified powder is added to the solution by dispersion. The solvent containing the polymer and the filler is applied to the steel sheet using a known method, for example, coilcoating, dipping or spraying.

The filler substance is a metal or metal oxide, or a mixture of one or more than one metal, or a mixture of one or more than one metal oxide, or a mixture of metals and metal oxides. Thus, the filler may be a mixture of particles of various metals or various metal oxides or various metals and metal oxides and / or the filler may contain particles which themselves are composed of a mixture of metals and / or metal oxides, for example, an alloy of two or more than two metals, promoting adhesion. The filler particles can be pre-coated with a polymer or other organic coating to modify the chemical composition of the surface of the filler particles, to facilitate dispersion of these particles.

Metals / metal oxides that are suitable for promoting enamel adhesion are known in the art, for example cobalt or cobalt oxide. Any of such known adhesion promoters may be used in the present invention. According to a preferred embodiment, one or more of one of the metals selected from the group consisting of V, Co, Cu, N1, Pe, Mn, Mo, and Bb is used in pure form or in the form of oxide in the filler. All of these metal oxides are suitable adhesion promoters since all can be reduced at low temperatures and are all chemically and physically compatible with iron. For example, they can form titanates reacting with titanium dioxide from a glass composition.

In a more preferred embodiment, one or more of the metals N1, Cu, Co, Mo and / or their oxides in the filler are used.

After applying the solution to the steel surface, the steel sheet is subjected to a drying step to remove the solvent and form an organic coating on the steel surface. This drying step can be carried out in accordance with known methods of applying TOP (thin organic coating), such as drying with hot air (convection) at temperatures from 80 to 250 ° C or infrared drying. The result is an organic coating, preferably a thin organic coating as defined above, consisting of a polymer layer and adhesion promoters immersed in it. The final thickness of the TOP is preferably from 100 nm to 10 μm, more preferably from 100 nm to 6 μm, more preferably from 1 to 3 μm.

In accordance with a preferred embodiment, the following TOP compositions after drying are obtained using the method of the invention:

a polymer from 20 to 95 wt.%, more preferably from 33 to 80 wt.%;

adhesion promoter (i.e. filler, for example metal or metal oxide): from 5 to 80 wt.%, more preferably from 20 to 66 wt.%. Being expressed as surface density, the filler is preferably presented in TOP with a density of from 100 to 6000 mg / m ² .

- 3 018759

The coating enamel is then applied using a known method, such as wet or dry electrostatic spraying, pneumatic spraying, dipping, or jet coating methods. Perhaps the application of enamel may be preceded by a cutting or molding step. The application of the enamel layer is not preceded by degreasing, etching or nickel plating.

Coating enamel is defined as enamel applied in the form of an external surface that is opposite to the ground enamel used as the base layer for subsequent processing and coating. Coating enamel, as a rule, does not contain substances that promote adhesion.

The enamel coating layer is fixed using a firing step in accordance with a known method, preferably at a temperature of from 700 to 900 ° C., and possibly this is preceded by drying of the enamel layer (for wet application technologies). The calcination step causes the organic layer to burn out. In other words, the polymer layer burns out and is thus removed.

The steel sheet may or may not be decarburized and may be any sheet suitable for enamel application, for example, steel deoxidized with aluminum (A1), high oxygen steel, with the addition of Τι, with the addition of N6, with the addition of Τί-Νό. with the addition of B.

In accordance with the invention, the pre-coated steel sheet is coated with one coating layer of enamel without any significant amount of adhesion promoting metal oxides in the enamel and subjected to a calcination step. The adhesion promoting metal oxides present in the precoat provide good adhesion to the enamel layer without the need for sheet pretreatments such as nickel plating. Enamel does not tarnish due to the lack of adhesion promoting elements in the enamel layer itself.

Further advantages of the organic coating of the invention relate to the specific features of this particular type of coating, i.e. consisting of a polymer matrix as described above. It was found that such coatings have low friction characteristics, making it possible to deform the coated product, for example, in a deep drawing method or other deformation method, without breaking the coating. The latter is not possible when the organic coating is based on clay or bentonite, as described in the prior art.

In addition, unlike the later coatings of the prior art, the coatings of the invention provide corrosion protection comparable to the corrosion protection provided by oiling cold rolled steel sheets. The latter is important because pre-processed products can be subjected to longer periods of transportation or storage before the enamel application step.

Finally, the coatings of the invention are water resistant, which cannot be said for clays or bentonite, such as those documented in the prior art. This makes it possible for easy cleaning of pre-treated products with water, for example, after a period of storage, before the implementation of the enamel coating step.

These advantages make it possible to carry out the cutting and molding steps directly with the organic coated product in accordance with the invention, wherein said molding / cutting is carried out before the enamel coating step. Due to the low friction characteristics, there is no need for oil during the molding process, therefore, a degreasing step is not required before applying the enamel. As indicated, etching or nickel plating is also not required, which simplifies the process for producing enameled products.

Examples

Prepared preparations C1-C8, listed in table. 1 (all numerical data are given in wt.%). After weighing the ingredients, they were mixed together using first a high-speed disintegrator containing ceramic balls, and then an ultrasonic cell was used to destroy the resulting final aggregates.

Table 1

C1 C2 sz C4 C5 C6 C7 C8 Vee1ayp 1.89010 35 53 36 36.5 36 27.5 35 28 No. O fifteen eleven eleven 14.5 8 Co304 18 fifteen 18 Water fifty 36 53 49 56 54.5 fifty 54 Total 100 100 100 100 100 100 100 100

Products: Ве1аПп Л89010 is the currently used polyurethane dispersion, manufactured by В1Р Уййт Great Britain. N10 and Co304 powders are currently available nanopowders manufactured by 1nGgasha1 Abuieeb Ma1epa15 Lc, USA.

- 4 018759

All dilutions obtained were applied by spraying onto a previously degreased surface of steel suitable for applying enamel (ES03EE. As defined in ΕΝ10209) and dried at 90 ° C for 1 min after spraying. The thickness of the thin organic coating was measured after drying (see tables. 2 and 3).

The previously described organic coated steel sheet was coated immediately after drying with a thin organic coating without any additional surface treatment, such as degreasing, using ordinary white powder enamel dispersed in water. Enamelled samples were first dried at approximately 80 ° C for 4 minutes and then calcined. After firing at various temperatures for different periods of time, the thickness of the enamel layer was measured, and the bond of the enameled steel sheet was then tested in accordance with ΕΝ10209 (Tables 2 and 3). For all samples, the enamel thickness after firing was approximately 100 μm. Good bonding was found in all cases because the surface of the enamel layer is smooth and glossy without any surface defects such as needle holes, craters or indentations.

A relationship of 1 in accordance with the ΕΝ10209 guidelines represents the best result obtained. The interface as a result of the interaction between steel, enamel and TOP completely covers the surface of the steel. In accordance with the standards and general practice in this technical field, communications equal to 1 and 2 are of very high quality, 3 is acceptable quality, 4 is critical and 5 is completely out of range.

Table 2 The bond in accordance with ΕΝ10209 obtained for various TOP containing N10 and calcined at various temperatures and for various periods of time

Communication in accordance with ΕΝ10209 obtained for various TOP,

Claims (15)

1. A method of manufacturing an enameled steel substrate, where the specified method includes the following stages: take a steel substrate; applying a solution containing a solvent, a polymer and at least one metal or metal oxide to the surface of said steel substrate, wherein said metal or metal oxide is suitable for promoting adhesion of the enamel layer to the surface of the steel substrate; drying said steel sheet, thereby removing said solvent and obtaining an organic layer consisting of a polymer matrix containing said at least one metal or metal oxide in the form of particles immersed in said matrix; an enameled layer is applied to said organic layer, followed by a calcination step to obtain an enameled steel substrate. 2. The method according to claim 1, where the specified metal is selected from the group consisting of 8c, VI, V, Co, Cu, N1, Be, Mn, Mo, and 8b, and where the specified metal oxide is a metal oxide selected from a group consisting of V, Co, Cu, N1, Be, Mn, Mo, and 8b. 3. The method according to claim 2, where the specified metal is selected from the group consisting of N1, Cu, Co, Mo, and where the specified metal oxide is a metal oxide selected from the group consisting of N1, Cu, Co, Mo. 4. The method according to any one of claims 1 to 3, where the specified at least one metal or metal oxide is added to the specified organic layer in powder form. 5. The method according to claim 4, where the specified powder has an average particle size of less than 2 microns. 6. The method according to any one of claims 1 to 5, wherein said organic layer has a thickness of from 100 nm to 10 μm, preferably from 100 nm to 6 μm. 7. The method according to any one of claims 1 to 6, where the specified solution is applied to the substrate by coilcoating, immersion or spraying. 8. The method according to any one of claims 1 to 7, where the specified stage of drying is carried out at a temperature of from 80 to 250 ° C. 9. The method according to any one of claims 1 to 8, where the specified stage of firing is carried out at a temperature of from 700 to 900 ° C. 10. The method according to any one of claims 1 to 9, where the stage of firing is preceded by a stage of drying the enamel layer. 11. The method according to claim 10, where the specified steel substrate is subjected to the stage of molding and / or cutting after the stage of applying the specified organic layer and before the stage of applying the specified enamel layer. 12. Steel substrate containing on its surface an organic coating consisting of a polymer matrix containing at least one metal or metal oxide in the form of particles immersed in the matrix, where the specified metal or metal oxide is suitable for promoting adhesion of the enamel layer to the steel surface the substrate. 13. The steel substrate according to item 12, where the specified organic coating is a thin organic coating having a thickness of from 100 nm to 10 μm, preferably from 100 nm to 6 μm. 14. The substrate according to p. 12 or 13, where the specified substrate is a sheet of steel. 15. The use of a steel substrate according to any one of paragraphs.12-14 for the manufacture of an enameled steel sheet or part thereof.