BRPI0905654B1 - method of producing an enameled steel substrate and use of a steel substrate - Google Patents

Abstract

Method of producing an enameled steel substrate and use of a steel substrate The present invention relates to a method of producing an enameled steel substrate comprising the steps of: - presenting a steel substrate; applying on the surface of said steel substrate a solution comprising a solvent, a polymer precursor and at least one metal or metal oxide, being metal or metal oxide suitable for promoting the adherence of an enamel layer to the surface of the substrate. steel; curing said steel sheet, thereby removing said solvent and forming an organic layer comprising at least one said metal or metal oxide; and applying to the aforementioned organic layer an enamel layer followed by a baking step to obtain the enameled steel substrate.

Description

“METHOD OF PRODUCTION OF AN ENAMELED STEEL SUBSTRATE AND USE OF A STEEL SUBSTRATE”

Field of the invention [0001] The present invention relates to a method of producing an enamel layer on a steel substrate, such as a steel sheet or molded product. The present invention also relates to the enamelled steel substrate itself, preferably obtained by the method of the invention. General background [0002] The protection of metal surfaces by applying a layer of glazed enamel is well known and widely used due to the resistance of the enamel to high temperatures and because it gives the surface a protection against chemical aggression. Glazed enamelled products are thus widely used in different applications such as washing machines, sanitary ware, kitchenware, appliances and construction materials.

[0003] exist several processes for the production in products in steel enamelled. The process conventional in production in an sheet of enamelled steel white wraps at

following steps:

- application of a first layer of enamel containing oxides that promote adhesion, such as oxides of cobalt, nickel, copper, antimony or molybdenum;

- a first cooking operation;

- application of a second coat of enamel covering; and

- a second cooking operation.

[0004] This approach is called “2 layers, 2 cooking

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2/15 (2-coat, 2 fire - 2C / 2F). The adhesion of a first layer of enamel to the steel is obtained by means of firing between 800 ° C and 850 ° C, through chemical reactions of oxi-reduction between the elements in the steel, such as carbon and iron, and the promoting oxides adherence to enamel. However, these oxides give the enamel a dark color. Consequently, it is necessary to apply a second layer of white enamel to obtain a white enameled steel sheet.

[0005] In order to avoid the use of a large amount of enamel and double firing, which are expensive, it is known to apply a direct white enamelling (DWE) process (“1 layer / 1 firing) that allows to obtain a foil of white enameled steel by applying a single layer of enamel on the steel sheet and then subjecting the steel sheet to a single cooking operation.

• process comprises the steps of:

- an extensive surface preparation procedure, consisting of • degreasing, stripping and rinsing a sheet of decarburized steel to remove a given amount of iron. Stripping is necessary to obtain the right roughness. A decolorized substrate is necessary to obtain the correct surface of the enamelled product.

• application in an layer of nickel by middle of treatment chemical, - application in an layer of enamel; and - cooking gives layer of enamel typically to a temperature between 750 and 900 ° C. [0006] In this case the enamel does not include oxides promoters

of the grip, so it doesn't change color. The adherence of this

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3/15 type of enamel is due to the previous operation of acid pickling and pretreatment with nickel. However, this type of pre-treatment is neither ecological nor cheap.

[0007] In order to avoid the pre-treatment steps associated with DWE, a method was developed in which a base enamel and a covering enamel are applied, which are then baked together (“2 layers, 1 cooking). The disadvantage of this method, however, lies in the need for large amounts of enamel (2 layers of enamel).

[0008] In addition, various chemicals and pre-coating techniques for depositing them are known in the art. Everyone seeks to present a pre-coated steel suitable for direct white enamelling without the nickel stripping and pretreatment operations, and requiring only a layer of enamel and a cooking treatment.

[0009] Document EPA0964078 focuses on pre-coatings of Zn and Zn alloys, applied by hot dip or electrolytic coating and includes all coatings of Zn or Zn alloy with a thickness of the Zn coating between 1 pm and 30 pm , in particular between 7 pm and 25 pm. Chemistry includes all Zn contents above 50%, with a content of other alloy components up to 15% (Al, Fe, Mg, Si, Cr, Ni, Co, Cu, Mn). The patent applies to decarburized steel surfaces (C <0.08%, particularly <0.004%) of IF steel surfaces (all carbon trapped in precipitates).

[0010] WO-A-0250326 and WO-A-0252055 describe a nickel-molybdenum alloy coating applied by electrolytic or chemical coating, which is then subjected to heat treatment at a temperature between 500 ° C and 900 ° C .

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4/15 [0011] JP-A-04107752 and JP-A-04107753 describe a cold-rolled steel sheet coated with ferro-molybdenum for direct adhesion to the enamel. The ferro molybdenum coating is obtained by electrolytic coating in a bath containing, for example, iron sulphates and ammonium molybdate salts. After coating, the coated steel sheet is subjected to heat treatment at temperatures between 500 ° C and 900 ° C.

[0012] Documents JP-A-04107754 and JP-A-04107755 describe a sheet of steel coated with iron-cobaltomolybdenum, obtained by electrolytic coating, followed by heat treatment at temperatures between 500 ° C and 900 ° C. The coating technology has some disadvantages related to environmental issues, resulting from chemical compounds such as salts and sulfates used in the coating bath.

[0013] The document - FR2805277 - refers to a method of direct enameling of steel sheets that are covered by a corrosion barrier based on a polymer. The surface density of the layer must be low enough so that a degreasing step is not necessary before applying the enamel, while at the same time the density is sufficiently high to guarantee adequate anti-corrosion protection. However, this technique does not allow for optimal adherence characteristics. Strict requirements for surface density also complicate the process.

[0014] The document - US1962617 - is related to the manufacture of enamel articles, involving the application of a layer of oxides that promote adhesion, such as oxides of

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5/15 cobalt, on a steel surface. The oxides are mixed with a solvent and suspending agent, such as ammonium linoleate, clay or bentonite, before being applied to the surface, subsequently drying the surface.

Objectives of the invention [0015] The invention seeks to provide a method of producing a steel substrate, in particular a steel sheet which is enamelled directly with white color, with a coating enamel layer.

Summary of the invention [0016] The invention relates to a method and a product as described in the appended claims.

[0017] The present invention relates primarily to a method of producing an enamelled steel substrate, this method comprising the steps of:

- presentation of a steel substrate,

- application on the surface of the mentioned steel substrate of a solution comprising a solvent, a polymer precursor and at least one metal or metal oxide, metal or metal oxide being suitable for promoting the adhesion of an enamel layer to the surface of the substrate of steel,

- curing the mentioned steel sheet, thereby removing the mentioned solvent and forming an organic layer comprising at least one metal or metal oxide mentioned.

- application of an enamel layer to the mentioned organic layer followed by a cooking step to obtain the enameled steel substrate.

[0018] According to the invention, when there is no

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6/15 in the form of oxide, the metal is in unbound form or in an alloy with one or more different 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, or any other organometallic compound.

[0019] Preferred embodiments are described in any combination of claim 1 with one or more of secondary claims 2 to 11.

[0020] Preferably, the mentioned metal is chosen from the group consisting of Sc, Ti, V, Co, Cu, Ni, Fe, Mn, Mo, W and Sb and in which the mentioned metal oxide is the oxide of a chosen metal of the group consisting of V, Co, Cu, Ni, Fe, Mn, Mo, W and Sb.

[0021] Preferably, the mentioned metal is chosen from the

constituted group per Ni, Cu, Co, Mo and in what O oxide metallic mentioned it's the oxide of a metal chosen of group consisting of Ni, Ass, How. [0022] Preferably, at least a metal or oxide

mentioned metal is / are added to the mentioned organic layer in the form of a powder.

[0023] Preferably, the mentioned powder has an average particle size of less than 2 microns.

[0024] Advantageously, the mentioned organic layer has a thickness between 100 nm and 10 microns, preferably between 100 nm and 6 microns.

[0025] Preferably, the mentioned solution is applied to the substrate by continuous coil treatment, tempering or spraying.

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7/15 [0026] Preferably, the mentioned curing step occurs at a temperature between 80 ° C and 250 ° C.

[0027] Preferably, the cooking step mentioned occurs at a temperature between 700 ° C and 900 ° C.

[0028] Preferably, the cooking step is preceded by a drying step of the enamel layer.

[0029] Preferably, the mentioned steel substrate is subjected to a molding and / or cutting step after the application stage of the mentioned organic layer and before the application stage of the mentioned enamel layer.

[0030] The present invention, as a second objective, also relates 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, the metal or mentioned metal oxide suitable for promoting the adhesion of an enamel layer to the surface of the steel substrate.

[0031] Advantageously, the mentioned organic layer is a Thin Organic Coat with a thickness between 100 nm and 10 microns, preferably between 100 nm and 6 microns.

[0032] Preferably, the substrate mentioned is a sheet of steel.

[0033] Finally, the present invention also relates to the use of a steel substrate as defined above for the production of an enamelled steel sheet or part.

Detailed description of the preferred embodiments of the present invention [0034] According to the invention, a steel substrate (for example a sheet) is coated with an organic coating

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8/15 comprising metal or metal oxides which are suitable for promoting the adhesion of the enamel layer. The organic coating consists of a polymer layer comprising in the mentioned layer one or more metals and / or metal oxides that promote adhesion, the materials that promote adhesion are found in the form of particles incorporated in the mentioned matrix. Preferably, the coating is a Thin Organic Coat, with a thickness between 100 nm and 10 microns. Then, a layer of enamel is applied to the substrate and subjected to the cooking step. The organic coating is prepared from a solution comprising a solvent, for example water and polymers dispersed, dissolved or emulsified in this solvent. Polymers are the precursors of the organic coating.

[0035] According to a preferred embodiment of the present invention, these precursors are charged, i.e. mixed with a filler that is suitable for promoting the adhesion of an enamel layer to the surface of the steel substrate.

[0036] In other words, the filler material is capable of reacting at high temperature with the steel surface and elements present in the enamel composition, in order to form a permeable contact surface. The filler is preferably administered to the solution in the form of a powder, the average particle size being less than 2 microns, more preferably between 1 and 1000 nm. The mentioned powder is added to the solution by means of dispersion. The solvent comprising polymer and filler is applied to the steel sheet by known technique, for example

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9/15 continuous coil treatment, tempering or spraying.

[0037] The material of the filler 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. 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 include particles which are themselves constituted by a mixture of metals and / or metal oxides, for example 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 surface chemistry of the filler particles to facilitate dispersion of these particles.

[0038] Metals / metal oxides that are suitable for promoting enamel adhesion are known in the art, for example cobalt or cobalt oxide. Any of these known adhesion promoters 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 the form of oxide, in the charge. All of these metal oxides are suitable adhesion promoters in that they can all be reduced at low temperatures and all are chemically and physically compatible with iron. For example, they can also form titanates by reacting with titanium dioxide from the glass composition.

[0039] A more preferred embodiment uses a

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10/15 or more of the metals Ni, Cu, Co, Mo and / or respective oxides in the filler.

[0040] 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 form the organic coating on the surface of the sheet. This curing step can be performed according to known techniques of TOC application, such as hot air (convection) curing at temperatures between 80 ° C and 250 ° C or infrared curing. The result is an organic coating, preferably a Thin Organic Coat, as previously defined, consisting of a layer of polymer and incorporated adhesion promoting materials. The final thickness of TOC is preferably between 100 nm and 10 microns, more preferably between 100 nm and 6 microns, more preferably between 1 and 3 microns.

[0041] According to a preferred embodiment, the following TOC compositions are obtained after curing by the method of the invention:

[0042] Polymer between 20% by weight and 95% by weight, more preferably between 33% by weight and 80% by weight.

[0043] Adhesion promoter (i.e., filler, for example, metal or metal oxide): between 5 and 80% by weight, more preferably between 20% by weight and 66% by weight. Expressed in surface density, the filler is preferably found in the TOC at a density between 100 and 6,000 mg / m ² .

[0044] The coating enamel layer is applied according to a known technique, such as dry or wet electrostatic spraying technologies, pneumatic spraying, immersion or spray enamelling. Possibly, the

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11/15 enamelling can be preceded by cutting or molding steps. The application of the enamel layer is not preceded by degreasing, pickling or pretreatment with nickel.

[0045] A covering enamel is defined as the enamel applied to the external surface, unlike the base enamel, used as a base layer for further treatment and additional coating. A coating enamel does not usually contain adhesion promoters.

[0046] The coating enamel layer is finished with a cooking step according to a known technique, preferably at a temperature between 700 ^S C and 900 ° C and possibly preceded by drying the enamel layer (for wet application technologies ). The cooking step causes the organic layer to burn. In other words, the polymer of the layer is burnt and removed in this way.

[0047] The steel sheet can be decarburized or not and can be any sheet suitable for enamelling, for example, calmed Al, with high oxygen content, with Ti, with Nb, with B.

[0048] In according to invention, the sheet pre-made steel coated is coated with a single layer enamel in roof without substantial metal oxides promoters gives grip at the enamel and it's subject to the stage of cooking. The

Adhesion-promoting metal oxides found in the preliminary coating provide good adhesion of the enamel layer, without the need for preliminary sheet treatments, such as nickel pretreatment. The enamel does not darken due to the absence of elements promoting the

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12/15 adhesion on the enamel layer itself.

[0049] Additional advantages of an organic coating according to the invention relate to specific capacities of this particular type of coating, that is, consisting of a polymeric matrix as previously described. It was found that these coatings have low friction characteristics, allowing the product on which the coating is to be deformed, that is, with deep stamping or another deformation process, without damaging the coating. This would be impossible in the case of an organic coating based on clay or bentonite, as described in the prior art.

[0050] Like the coatings of the prior art, the coatings of the invention provide anti-corrosion protection comparable to the anti-corrosion protection provided by the lubrication of cold-rolled steel sheets. This is important because pre-treated products can be subjected to longer transport or storage periods before the enamelling step is carried out.

[0051] Finally, the coatings according to the invention are water resistant, which cannot be claimed for clays or bentonite as documented by the prior art. This makes it easier for pre-treated products to be easily cleaned with water, for example after a period of storage, before the enamelling step is carried out.

[0052] These advantages open the possibility of performing cutting and shaping steps directly on the product prepared with an organic coating according to the invention, this shaping / cutting taking place before the enameling step. Thanks to the low friction characteristics it is not

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13/15 oil is needed during the molding process, so there is no need for a degreasing step before enameling. As indicated, there is also no need for pickling or pretreatment with nickel, leading to a simplified process for obtaining enamelled products.

Examples [0053] Formulations C1 to C8 listed in Table 1 below were prepared (all numerical data are in% by weight). After weighing the ingredients, the products were mixed using first a high speed centrifugal mixer, containing ceramic balls and then an ultrasonic cell in order to fragment the final aggregates.

Table 1

C1 C2 C3 C4 C5 C6 C7 C8 Beetafin LS9010 35 53 36 36.5 36 27.5 35 28 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

[0054] Products: Beetafin LS9010 is a current polyurethane dispersion, manufactured by BIP Limited, UK. NiO and Co3O4 powder are currently nanopowders manufactured by Inframat Advanced Materials LLC, USA.

[0055] All the dilutions obtained are applied by spraying on the previously defatted steel surface of suitable quality for enamelling (DC03ED, as defined in standard EN10209) and cured at 90 ° C for 1 minute after drying. The thickness of the thin organic coating was measured after curing (see tables 2 and 3).

[0056] Organic coated sheet steel as described above was covered directly after curing

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14/15 of the thin organic coating, without any additional surface treatment such as degreasing, with white coating enamel powder dispersed in water. The enamelled samples were first dried at about 80 ° C for 4 minutes and then subjected to cooking. After cooking at different temperatures and times, the thickness of the enamel layer was measured and the bonding of the enameled sheet steel was subsequently tested, according to the EN10209 standard (Tables 2 and 3). For all samples, it was found that the thickness of the enamel after cooking was greater than 100 pm. Good bonding was observed in all cases because the surface of the enamel layer is smooth and shiny, with no surface defects such as bites, craters or bubbles.

[0057] A connection designated 1, according to standard EN10209 is the best result to obtain. A contact surface resulting from the reaction between steel, enamel and TOC completely covers the surface of the steel. In accordance with the standard and general practice in this technical field, the designated connections 1 and 2 are of very high quality, 2 is acceptable, 4 is critical and 5 totally outside the limit.

Table 2: connection according to standard EN10209 obtained for different TOCs containing NiO and cooked at different temperatures and times

Composition Thickness TOC pm 830 ° C 3'30 830 ° C 4 ' 20.0 g / kg 3'30 840 ° C 4 ' 860 ° C 4 ' C2 2 1 C2 1.5 1 C3 1 . 6 1 CI 3.9 1 C4 2.4 3 C5 2.2 2

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15/15

Table 3: connection according to standard EN10209 obtained for

Different TOCs containing Co ₃ O4 and cooked at different temperatures and times.

Composition Thickness 820 ° C 4 ' 840 ° C 4 ' 860 ° C 4 ' 840 ° C 7 ' TOC pm C6 2 . 1 2 1 C6 2 . 8 2 1 C7 1 . 5 1

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Claims (14)

1. Method for producing an enamelled steel substrate, characterized by the fact that it comprises the steps of: - present a steel substrate; - applying to a surface of the mentioned steel substrate a solution comprising a solvent, a polymer and at least one metal or metal oxide, metal or metal oxide being suitable for promoting the adhesion of an enamel layer to the surface of the steel substrate; - curing the mentioned steel sheet, thereby removing the mentioned solvent and forming an organic layer comprising a polymeric matrix, comprising at least one metal or metal oxide mentioned, in the form of particles incorporated in said matrix; and - apply a layer of enamel to the aforementioned organic layer followed by a cooking step to obtain the enameled steel substrate. 2. Method, according to claim 1, characterized by the fact that the mentioned metal is chosen from the group consisting of Sc, Ti, V, Co, Cu, Ni, Fe, Mn, Mo, W and Sb and in which the oxide mentioned metal is the oxide of a metal chosen from the group consisting of V, Co, Cu, Ni, Fe, Mn, Mo, W and Sb. 3. Method, according to claim 2, characterized in that the mentioned metal is chosen from the group consisting of Ni, Cu, Co, Mo and in which the mentioned metal oxide is the oxide of a metal chosen from the group consisting of Ni , Cu, Co, Mo. Method according to any one of claims 1 to 3, characterized in that at least one metal or oxide Petition 870180138592, of 10/08/2018, p. 22/25 2/3 metal mentioned to be added to the mentioned organic layer in the form of a powder. 5. Method according to claim 4, characterized in that the mentioned powder has an average particle size of less than 2 microns. Method according to any one of claims 1 to 5, characterized in that the mentioned organic layer has a thickness between 100 nm and 10 microns, preferably between 100 nm and 6 microns. Method according to any one of claims 1 to 6, characterized in that the mentioned solution is applied to the substrate by continuous coil treatment, tempering or spraying. Method according to any one of claims 1 to 7, characterized in that the curing step takes place at a temperature between 80 ° C and 250 ° C. Method according to any one of claims 1 to 8, characterized in that the cooking step takes place at a temperature between 700 ° C and 900 ° C. Method according to any one of claims 1 to 9, characterized in that the cooking step is preceded by a drying step of the enamel layer. 11. Method according to claim 10, characterized in that the aforementioned steel substrate is subjected to a molding and / or cutting step after the mentioned organic layer application step and before the enamel layer application step. mentioned. 12. Use of a steel substrate, characterized by the fact that it comprises on the surface of the steel substrate an organic coating consisting of a polymeric matrix, comprising Petition 870180138592, of 10/08/2018, p. 23/25 3/3 at least one metal or metal oxide, in the form of particles incorporated in the said matrix, the metal or metal oxide mentioned being suitable for promoting the adhesion of an enamel layer to the surface of the steel substrate, for the production of a sheet or part of an enamelled steel sheet. 13. Use according to claim 12, characterized in that the mentioned organic coating is a thin organic coating with a thickness between 100 nm and 10 microns, preferably between 100 nm and 6 microns. 14. Use according to claim 12 or 13, characterized in that the substrate mentioned is a sheet of steel.