Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
  • B05D7/14—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials to metal, e.g. car bodies
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
  • B05D3/10—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by other chemical means
  • B05D3/102—Pretreatment of metallic substrates
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
  • B05D7/50—Multilayers
  • B05D7/51—One specific pretreatment, e.g. phosphatation, chromatation, in combination with one specific coating
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
  • B05D7/50—Multilayers
  • B05D7/52—Two layers
  • B05D7/54—No clear coat specified
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D2202/00—Metallic substrate
  • B05D2202/10—Metallic substrate based on Fe
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D2350/00—Pretreatment of the substrate
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D2350/00—Pretreatment of the substrate
  • B05D2350/60—Adding a layer before coating
  • B05D2350/65—Adding a layer before coating metal layer

Definitions

• the invention refers to the steel industry, particularly to the continuous process of steel strip production, and can be used by steel companies for producing pre-painted steel strips with polymer coatings that have longer durability and better corrosion resistance.
• Steel strips with multi-layer anti-corrosion coating is utilized in various areas, such as construction, automotive industry, manufacturing of equipment hulls, buildings' interior and exterior panels, etc.
• Zinc coatings or multi-layer coatings, where zinc, primer and top coat are applied consecutively, are traditionally used to protect steel against corrosion.
• the main reasons for using zinc as a base of a protective metallic coating is high technological effectiveness of zinc application process together with low zinc electrolytic potential with respect to iron, which provides for anti-corrosion protection of a steel sheet even in cases when the coating integrity gets damaged.
• the corrosion resistance of the coating itself can be improved by alloying zinc with other metals such as magnesium, aluminium, nickel, etc. Decreasing of zinc content in a coating may negatively affect the steel cathode protection on uncoated areas (e.g. edges, welds). On the other hand, the addition of magnesium and aluminium to the zinc coating improves its corrosion resistance by formation of a strong oxide layer during the interaction of magnesium and aluminium with the environment.
• the metal coating comprises zinc, aluminium and magnesium alloy in the following ratio: 0.1-20 wt % of aluminium, 0.1-10 wt % of magnesium, with the balance being zinc.
• the method comprises of the following steps:
• the main disadvantage of the proposed method is its low flexibility, not allowing use of the production lines intended for implementation of the known method of making a steel strip with various metallic and colour coatings that differ from the one disclosed in the patent application.
• magnesium hydroxide which is inevitably formed on the surface of a steel strip during implementation of the method, is to be necessarily removed.
• Another disadvantage of the known method is low quality of the coating. Oxidation of aluminium and magnesium on a steel strip during its transportation from the place of treatment with alkali and acid solutions to the painting line can cause formation of local areas with loose oxide films, and thus appearance of unprotected areas and cause delamination of top coat and primer at those areas due to poor adhesion between Zn-based metallic coating and polymer layers.
• the objective and technical result achieved by the claimed technical solution is production of a steel strip with enhanced anti-corrosion properties and higher strength.
• the improved anti-corrosion effect achieved by combining methods of corrosion protection on the steel surface in such a way that the successively located anti-corrosion layers have as high adhesion to each other as possible, and wherein the process parameters at all stages of the method cause forming the anti-corrosion layers all having as high quality as possible with no negative influence on the initial mechanical properties of the steel strip.
• the method for producing a steel strip with colour coating is proposed to address the issues mentioned above and to achieve the technical effect.
• the method comprises of:
• the strip to be treated using the proposed method is a strip of cold-rolled annealed steel, cold-rolled full-hard steel or hot-rolled structural steel.
• the steel strip temperature is preferably brought to 20-25 °C before applying the thermoset primer layer on the conversion layer.
• the following components can be added to the bath with the melt while the melt is consumed for forming the coating: 1.2-3.0 wt% of Mg, 1.2-2.0 wt% of Al, up to 0.5 wt % of impurities and the balance being Zn.
• the alkaline salt aqueous suspension used in the method can comprise 1.0-7.0 g/l of an anionic surfactant.
• 3-12 mg/m 2 of Ti can deposit into the conversion layer.
• a decorative enamel based on polyester, melamine-cross-linking polyester, polyurethane, PVDF, including polyurethane and polyesters with a wrinkled or textured structure as well as comprising acrylate and/or epoxy resins, can be used as a top coat polymer paint composition.
• the Ti-based conversion layer can comprise 2-10 mg/m 2 of dihydrogen hexafluortitanate and 2-10 mg/m 2 of hexafluorozirconic acid.
• a ZnAlMg coating is applied on the steel strip which is preliminarily degreased and cleaned off oxide films.
• the coating is applied in the bath of molten Zn (97.2-98.0 wt%) + Al (1-1.4 wt%) + Mg (1-1.4 wt%) at a temperature of 420-460 °C and at a speed of the strip through the bath of 40-165 m/min.
• the initial temperature of the steel strip before dipping in the bath and the residence time of the strip in the bath is defined by a required thickness of the protective coating.
• a layer of crystallized melt is preferably formed on the surface due to removal of excessive melt by air knives (air or nitrogen) and cooling the melt on the strip surface with the use of air or water cooling systems.
• Concentration of Zn, Al and Mg in the melt bath is monitored every 1.0-3.0 hours by an atomic-absorption spectroscopy method or by inductively coupled plasma mass spectrometer.
• the melt composition is maintained in a stable condition by adding ingots of Zn with 1.2-3.0 wt% of Mg and 1.2-2.0 wt% of Al.
• air knives air or nitrogen remove excessive liquid metal away from the strip surface, which allows forming a metallic coating with a thickness of 4-15 ⁇ m.
• the coating thickness can be controlled via both the speed of the strip passing the bath and via changing intensity of blowing off the strip with gas after the strip leaves the bath.
• the strip with the applied coating is cooled down at a speed of 1-20 °C/second, and a final crystalline structure of the coating is formed.
• the coating formed represents a Al/Zn/MgZn 2 matrix (up to 10 wt%) with a Zn phase (over 90 wt%) distributed therein in the form of separate grains or continuously associated grains.
• the high zinc content in the coating provides steel sheet cathode protection even in the areas where integrity can be damaged or where the coating would be perforated during operation activity.
• Corrosion products of Al and Mg formed during operation of the steel strips form layered double hydroxides, which function as an additional barrier protection between corrosive medium and the ZnAlMg coated steel strip.
• Corrosion resistance of the steel strip with such coating is 3-10 times higher than that of a steel sheet with standard zinc coating of the same thickness.
• a coating with the content of Al and Mg below the specified ranges is not remediious as compared to the traditional pure zinc coating, while an excess content of Mg and Al above the specified ranges significantly increases the costs and can lead to formation of loose oxide films on the surface that promotes peeling of the polymer coating.
• the coated steel surface is cleaned of possible organic contaminations with removal of oxides from the subsurface layer.
• a composition of a 15-40 g/l alkaline salts aqueous suspension and 1.0-7.0 g/l anionic surfactant is used for performing this cleaning operation 50-70°C.
• Application of said composition with alkaline pH ⁇ 10-12 allows to ensure an efficient surface cleaning and avoid noticeable metal dissolving and dragging-out from the ZnAlMg coating.
• the cleaned steel strip surface does not require any additional surface cleaning prior to the deposition of the conversion layer.
• the ZnAlMg coated steel strip is treated with the conversion chemical compositions based on dihydrogen hexafluortitanate or a combination of dihydrogen hexafluortitanate and hexafluorzirconic acid.
• a layer of insoluble titanium-based and zirconium-based compounds is formed on the surface of the ZnAlMg coating.
• This layer comprises a metal-oxide hydrated film containing TiO 2 ⁇ 2H 2 O or TiO 2 ⁇ 2H 2 O+ZrO 2 ⁇ 2H 2 O.
• This film provides an additional barrier protection against corrosion as well as improvement of the strip wettability resulting in better adhesion to the organic coating layers that are going to be deposited on the next step.
• concentration of the active components and the strip treatment time in the conversion solution is selected in such a way that the amount of Ti distributed in the conversion layer to be at the level of 3-12 mg/m 2 .
• the Ti content below 3 mg/m 2 results in a deterioration of the coating corrosion properties, while the Ti content of over 12 mg/m 2 causes reducing mechanical properties of the coating, e.g. decreasing of the bending strength.
• the steel strip is successively coated with the thermoset polymer primer and the thermoset polymer top coat that are applied by roll coaters.
• the polymer primer is applied followed by the finishing top coat.
• the finishing coating can be applied as a single layer (monolayer). Depending on the product type and order requirements, it is possible that either one side or both sides of the steel strip are covered with the primer and a finishing enamel or with the monolayer coating.
• Compounds with similar curing time at the selected curing temperatures should be selected as the primer or the finishing enamel.
• the difference in the curing temperatures should be no more than 0-5 °C, while the difference in the curing time should be no more than 0-10 sec.
• Selection of such parameters is based on the fact that when the polymer coatings with bases having different thermophysical properties are successively applied, there is an increased risk that such defects as blisters and pits are formed during the application of the organic layers. These defects have a negative impact on the corrosion resistance and mechanical properties of the finished pre-painted steel strip.
• the primers and finishing enamels are selected from the paints and varnishes based on polyesters, melamine-cross-linking polyesters, polyurethanes, PVDF, including wrinkled or textured polyurethanes and polyesters, as well as hot-curing epoxy resins with the curing temperature of 320-385 °C, peak metal temperature of 200-250 °C and curing dwell time in a pre-painting line of 21-34 seconds.
• primer and the finishing enamel composition may include particles of fillers and pigments based on such minerals as TiO 2 , BaSO 4 , SiO 2 , CaCO 3 , talc, kaolinite, wollastonite, ferromanganese spinel and others.
• a steel strip with the ZnAlMg coating was produced in the bath of Hot Dip Galvanizing Line (HDGL) according to the following process.
• a melt containing 97.6 ⁇ 0.4 wt % of Zn, 1.2 ⁇ 0.2 wt% of Al and 1.2 ⁇ 0.2 wt % of Mg was prepared.
• Al and Mg concentrations were monitored hourly via atomic-absorption spectroscopy and were maintained within the range 1.1-1.3 wt% of Al and 1.1-1.3 wt% of Mg by adding ingots of Zn with 1.2-3.0 wt% of Mg and 1.2-2.0 wt % of Al as far as the metal in the bath is being consumed.
• Melt temperature was maintained at 430 ⁇ 5 °C.
• the DC04 grade steel strip was degreased and cleaned of oxide films, annealed in preheated continuous furnace up to the temperature at the furnace exit of 435 °C, and then was dipped in the bath of molten metal at the running speed of 165 m/min in the HDGL, where the ZnAlMg coating was deposited on strip surface. Coating thickness at the output of the bath was maintained within the range of 8-10 ⁇ m by blowing the melt excess away by air knives. Then the steel strip was cooled down at the speed of 15 ⁇ 2 °C/s in a continuous cooling chamber. Further oiling in an oiling machine is possible to protect coils from white rust during their storage.
• Preparation of the strip surface to painting comprises the following steps:
• the polyester-based primer (P1) in accordance with GOST R 52146-2003 or EN 10169-2010 and the polyester-based topcoat (trade mark Beckrupol 3000) were used as the topcoat.
• the topcoat had an assumed viscosity 50 sec according to GOST 8420-74, nonvolatile-matter content 55 % and peak metal temperature of 240 °C.
• the primer and the finish enamel were deposited one after another by a roll coater of a painting line.
• Top side primer application, then primer drying in a continuous furnace at 340 °C within 25 seconds, then cooling, then top coat application, then paint drying in the continuous furnace at 340 °C during 25 seconds, and cooling.
• Back side one-layer coating application, then drying in the continuous furnace at 340 °C within 25 seconds, and cooling.
• Painted steel strip manufactured according to the above method was coiled and shipped to stock.

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• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Coating With Molten Metal (AREA)
• Laminated Bodies (AREA)

Applications Claiming Priority (2)

Publications (1)

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Cited By (1)

Citations (6)

• 2021
  • 2021-02-03 EP EP21155025.6A patent/EP3858495A1/de not_active Withdrawn

Patent Citations (6)

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