METHOD FOR PRODUCING AN ORGANOMETALLIC COATING AND APPLYING AN ORGANOMETALLIC COATING TO METAL PARTS AND ORGANOMETALLIC COATING

Abstract

A process for producing a metal-organic coating, characterized in that it comprises the following steps: a) Mixing parts A (zinc and aluminum paste), B (aqueous medium) and C (viscosity of active ingredient), whereby part B is gradually added to the previously homogenized part A and then part C is gradually added to the mixture of parts A and B and the mixture is then stirred for 24 hours in a mechanical stirrer with a centrifugal propeller at a stirring speed of not more than 3,000 rpm, whereby - Part A comprises 20% to 40% metallic zinc, 2 to 10% metallic aluminum, 20% to 30% dipropylene glycol, 2 to 5% non-ionic surfactant and 15% to 20% demineralized water; - Part B comprises 1% to 7% silane (A-187), 70 to 90% demineralized water, 0.1% to 0.2% boric acid, and 2% to 3% sodium silicate; and - Part C contains a thickener for water-based paints selected from the group consisting of hydroxyethylcellulose, guar gum, fumed silica, and polyvinyl alcohol, as well as thixotropic agents, wherein parts A, B, and C are mixed in a ratio of 42% by weight of A, 57% by weight of B, and between 0.3% and 0.7% by weight of C, based on the total weight of A+B+C, wherein part C is added in the specified range until the viscosity of the mixture is in the range of 60 to 80, according to Zahnbecher No. 2; and b) gradually adding 15% by weight of colloidal silica solution, based on the total weight of the coating composition, with moderate stirring and continuing to stir for at least 1 hour in a mechanical stirrer with a centrifugal propeller at a stirring speed of not more than 3,000 rpm, the colloidal silica solution containing 15% to 32% colloidal silica, 6% to 8% 2-butoxyethanol, 6% to 10% methanol and 50% to 63% water.

Description

FIELD OF INVENTION

[0001] The present invention relates to a process for producing a metal-organic coating based on lamellar zinc in aqueous solution. In particular, the present invention relates to the production of a zinc flake-type coating containing a low percentage of aluminum (containing 10% to 20% metallic zinc and 1% to 5% metallic aluminum). In particular, the present invention teaches a process for producing a coating for metal parts with improved surface hardness and high corrosion resistance.

[0002] The present invention also relates to organometallic coatings provided by this method and their application in metal parts. FUNDAMENTALS OF THE INVENTION

[0003] In the field of coatings for metal parts, organometallic coatings differ from electrolytic coatings in that they are not susceptible to hydrogen embrittlement. In the field of organometallic coatings, there are notable efforts to develop technologies that are free of heavy metals and environmentally friendly. In this context, the state of the art includes water-based organometallic coatings, such as Geomet® 321 / 720, which consists of an aqueous dispersion containing zinc and aluminum flakes and other specific chemical active ingredients and is specifically formulated to protect substrates made of iron, aluminum, zinc, and their alloys.

[0004] However, despite high corrosion resistance, conventional organometallic coatings exhibit low surface hardness and weathering resistance. When it comes to zinc flake coatings, zinc and aluminum flakes form a film that is not rigid enough to provide mechanical strength for certain applications. For example, the formation of pores due to the alignment between the zinc and aluminum particles favors the penetration of weathering agents. This technical problem becomes apparent even when applying multiple layers and even when using top coats (sealants).

[0005] In this context, the state of the art includes documents aimed at improving the mechanical properties of coatings. For example, the dissertation by LV Mora evaluates the incorporation of nanoparticles into coatings for metal structures. This document discloses the incorporation of functionalized and non-functionalized silica nanoparticles into a sol-gel-based coating and a polysiloxane matrix. It was shown that the incorporation of these nanofillers into the polymer matrix enables the provision of coatings with improved mechanical properties. Furthermore, this document mentions the relevance of the dispersion of nanoparticles within the matrix for providing improved mechanical properties. However, the document in question does not contain any information on organometallic zinc and aluminum coatings, and thus on such water-based organometallic coatings.

[0006] Document CN102344738A deals with a composite material for anti-corrosive coatings for steel structures, containing flaky zinc powder as a sacrificial electrode and an inorganic nanofiller. This inorganic nanofiller may consist of silicon oxide. However, in addition to a coating with high corrosion resistance, this document proposes a solution to the problem of adhesion to the substrate associated with conventional zinc-rich coatings. To this end, the document in question teaches the preparation of a coating based on epoxy resin and zinc flake powder in the presence of a mixed solvent of xylene and n-butanol.

[0007] Document CN1563229A, in turn, deals with a zinc flake coating containing nanofiller powder, which may consist of nano-silica. This document proposes zinc flake as an alternative to conventional zinc powder-based paints, highlighting several advantages. In this context, it is mentioned that the lamellar structure of zinc flake alloys is satisfactory in terms of penetration by atmospheric agents and corrosive media. Therefore, this document does not contain explicit instructions for the incorporation of nanofillers to fill pores and reduce penetration by atmospheric agents. Furthermore, as described in this document, the coating is not water-soluble, and according to its production process, the coating is produced using organic solvents and epoxy resin.It is worth noting that the coating in question is applied to concrete and not to metal parts.

[0008] Further generic methods are known from US 2002 / 0119337 A1 and WO 2007 / 067203 A1.

[0009] As mentioned above, the prior art does not provide any teachings on improving the mechanical properties, such as increased surface hardness and abrasion resistance, of organometallic zinc and aluminum coatings. Furthermore, there is no information in the prior art on incorporating nanometric colloidal silica filler into a water-based organometallic compound matrix. In this scenario, the present invention provides a process that makes it possible to achieve an organometallic coating with high surface hardness and excellent corrosion resistance, in addition to being environmentally friendly, as it does not require the use of epoxy resins and organic solvents.

[0010] Thus, there are no reports in the prior art that provide a process for producing a metal-organic coating based on lamellar zinc in aqueous solution with mechanical and corrosion-resistant properties that are superior to those of previously known coatings. SUMMARY OF THE INVENTION

[0011] The present invention relates to a process for providing a metal-organic coating based on lamellar zinc in aqueous solution. More specifically, the present invention relates to a process for producing an aqueous zinc flake matrix coating, comprising the incorporation of nanometric colloidal silica filler in aqueous and / or alcoholic solution. The process object of this invention may additionally comprise the incorporation of nano- and / or microparticles of stainless steel powder 316-L or 304, glass fiber powder, micronized glass powder, or mixtures thereof.

[0012] The present invention aims to provide a processing route for producing a metal-organic coating having surface hardness and corrosion resistance superior to currently used metal-organic coatings.

[0013] Furthermore, the present invention aims to provide a metal-organic coating that is free of organic solvents and epoxy resins, thereby configuring an environmentally friendly proposal.

[0014] To achieve the above-described objectives, the present invention provides a process for producing a high-quality water-based organometallic coating. This process comprises: a) Mixing of parts A (zinc and aluminum paste), B (aqueous medium) and C (viscosity active ingredient); and b) gradually add the colloidal silica solution with moderate stirring and continue stirring for at least 1 hour.

[0015] Furthermore, the present invention proposes a method for applying the provided organometallic coating to metal parts. Preferably, the invention relates to the application of the coating by conventional methods of immersion and centrifugation, spraying, or immersion and dripping. The method for applying the coating according to the present invention comprises a curing step at a temperature in the range of 320°C to 335°C for a period of between 15 and 30 minutes.

[0016] Optionally, the present invention proposes the application of a sealant based on colloidal silicon dioxide nanoparticles to further increase corrosion and weather resistance.

[0017] These objects and other advantages of the present invention will become more apparent from the following description. BRIEF DESCRIPTION OF THE ILLUSTRATIONS Fig. Figure 1 shows an image obtained by scanning electron microscopy (SEM) of a conventional metal-organic coating film. Fig. Figure 2 shows an image obtained by scanning electron microscopy (SEM) of a metal-organic coating film with colloidal nanometric silica filler according to the present invention (at 2,500x magnification). Fig. Figure 3 shows an image obtained by scanning electron microscopy (SEM) of a metal-organic coating film with colloidal nanometric silica filler according to the present invention (at 10,000x magnification). Fig. Figure 4 illustrates images of metallic surfaces with and without the application of the sealing layer based on colloidal silica nanoparticles after 3,000 h of the salt spray test. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention relates to the preparation of a water-based organometallic coating including the incorporation of a nanometric colloidal silica filler.

[0019] Colloidal silicon dioxide blends much more easily with the organometallic matrix than powdered silicon dioxide. In a preferred embodiment of the present invention, fillers made of nano- and / or microparticles of 316L or 304 stainless steel powder, glass fiber powder, micronized glass powder, or mixtures thereof are also incorporated. The nano- and microparticles of these materials are inert and do not alter the organometallic matrix, contributing positively to increasing surface hardness and resistance to corrosion, abrasion, and weathering. This results in a rigid coating structure with a "structural support" for the zinc and aluminum particles in the organometallic matrix. Fig. 2 and Fig. 3 show the reduced porosity of the zinc flake coating when incorporated into the colloidal silica filler, compared to a conventional metal-organic coating as in Fig. 1. According to the present invention, the colloidal silicon dioxide contains particles of 10 to 50 nm and consists of a solution comprising 15 to 32% colloidal silicon dioxide, 6 to 8% 2-butoxyethanol, 6 to 10% methanol, and 50 to 63% water.

[0020] The manufacturing process of the metal-organic coating, consisting of an aqueous zinc flake matrix containing nanometer-sized colloidal silica fillers, comprises the following steps: a) Mixing parts A (zinc and aluminum paste), B (aqueous medium) and C (viscosity of active ingredient), whereby part B is gradually added to the previously homogenized part A and then part C is gradually added to the mixture of parts A and B and the mixture is then stirred for 24 hours in a mechanical stirrer with a centrifugal propeller at a stirring speed of not more than 3,000 rpm, whereby - Part A comprises 20 to 40% metallic zinc, 2 to 10% metallic aluminium, 20 to 30% dipropylene glycol, 2 to 5% non-ionic surfactant and 15 to 20% demineralised water; - Part B comprises 1 to 7% silane (A-187), 70 to 90% demineralized water, 0.1 to 0.2% boric acid and 2 to 3% sodium silicate; and - Part C contains a thickener for water-based paints from the group consisting of hydroxyethylcellulose, guar gum, fumed silicon dioxide and polyvinyl alcohol, as well as thixotropic agents such as modified bentonites (organophilic clays); wherein parts A, B and C are mixed in a ratio of about 42 wt% A, about 57 wt% B and about 0.3 to about 0.7 wt% C, based on the total weight of the zinc flake matrix, with part C being added in the specified range until the viscosity of the mixture is in the range of 60 and 80, according to Zahnbecher No. 2; and b) gradually add, with moderate stirring, about 15 to about 20% by weight of the colloidal silica solution, based on the total weight of the coating composition, and continue stirring for at least 1 hour in a mechanical stirrer with a centrifugal propeller at a stirring speed of not more than 3,000 rpm.

[0021] Fillers consisting of nano- and / or microparticles of 316-L or 304 stainless steel powder, fiberglass powder, micronized glass powder, or mixtures thereof, if incorporated, are added in the following proportions: 1 to 5% nano- and / or microparticles of 316-L or 304 stainless steel, 1 to 5% fiberglass powder, and 1 to 5% micronized glass powder. All proportions are by weight, based on 100% of the colloidal silica weight. These additional fillers are incorporated into the silicon, and the mixture is vigorously stirred for 30 minutes in a mechanical stirrer with a centrifugal propeller, then allowed to stand for 8 to 12 minutes. After the standby / decanting period, only the suspended particles are used.

[0022] Furthermore, the present invention relates to a method for applying the provided organometallic coating to metal parts. This application process includes a preliminary alkaline degreasing of the parts to remove oils and other types of contaminants. The parts are then washed with hot water to remove the degreasing residues. Subsequently, the parts are abrasive-blasted with stainless steel microspheres to remove unwanted contaminants from the substrate surface and improve the metallurgical surface qualities. Finally, the application of the organometallic coating is carried out using conventional methods such as dipping and centrifuging, spraying, or dipping and dropping, and comprises the following steps: - Immerse yourself in the bath for 15 to 30 seconds; - Centrifuge between 250 rpm and 450 rpm for 15 to 30 seconds in each direction, clockwise and counterclockwise - Cure at a temperature of 320°C to 335°C for 15 to 30 minutes.

[0023] According to the present invention, the coating can be applied to the parts in up to three layers, so that the final coating layer ("total layer") has a thickness between 5 and 12 micrometers. In this context, the present invention offers corrosion resistance of up to 3,000 hours without the application of a colloidal silica nanoparticle-based sealant and corrosion resistance of up to 8,000 hours with the application of a sealant layer, according to the salt spray test ("salt spray") according to ASTM B-117 and ISO 9227. Fig.Figure 4 shows the results obtained in terms of the visual aspect that can be observed for a set of metal parts coated with the "full layer" metal-organic coating of the present invention and for a set of metal parts having an additional sealing layer, both subjected to a salt spray test for 3,000 hours.

[0024] The foregoing description of the subject matter of the present invention should be considered only as one possible embodiment or embodiments, and any specific features introduced therein should be understood only as something written for convenience. As such, they are not to be considered as a limitation of the invention, which is limited to the scope of the claims.

[0025] The following examples illustrate the scope of the invention proposed herein. EXAMPLE 1: SALT SPRAY TEST

[0026] A salt spray test was conducted according to ASTM B-117 and ISO 9227 for 3,000 hours on two groups of metal sub-specimens: the first group coated with the "full layer" of the coating according to the present invention, and the second group with an additional sealing layer based on colloidal silica nanoparticles.

Claims

[1] Process for producing a metal-organic coating, characterized by that it includes the following steps: a) Mixing parts A (zinc and aluminum paste), B (aqueous medium) and C (viscosity of active ingredient), whereby part B is gradually added to the previously homogenized part A and then part C is gradually added to the mixture of parts A and B and the mixture is then stirred for 24 hours in a mechanical stirrer with a centrifugal propeller at a stirring speed of not more than 3,000 rpm, whereby - Part A comprises 20% to 40% metallic zinc, 2 to 10% metallic aluminum, 20% to 30% dipropylene glycol, 2 to 5% non-ionic surfactant and 15% to 20% demineralized water; - Part B comprises 1% to 7% silane (A-187), 70 to 90% demineralized water, 0.1% to 0.2% boric acid, and 2% to 3% sodium silicate; and - Part C contains a thickener for water-based paints selected from the group consisting of hydroxyethylcellulose, guar gum, fumed silica, and polyvinyl alcohol, as well as thixotropic agents, wherein parts A, B, and C are mixed in a ratio of 42% by weight of A, 57% by weight of B, and between 0.3% and 0.7% by weight of C, based on the total weight of A+B+C, wherein part C is added in the specified range until the viscosity of the mixture is in the range of 60 to 80, according to Zahnbecher No. 2; and b) gradually adding, with moderate stirring, 15% by weight of colloidal silica solution, based on the total weight of the coating composition, and continuing to stir for at least 1 hour in a mechanical stirrer with a centrifugal propeller at a stirring speed of not more than 3,000 rpm, the colloidal silica solution containing 15% to 32% colloidal silica, 6% to 8% 2-butoxyethanol, 6% to 10% methanol and 50% to 63% water. [2] A process for producing a metal-organic coating according to claim 1, characterized by that the colloidal silicon dioxide contains particles from 10 nm to 50 nm. [3] A process for producing a metal-organic coating according to claim 1, characterized bythat an additional step of incorporating additional loads of nano- and / or microparticles of stainless steel powder 316-L or 304, glass fiber powder, micronized glass powder or mixtures thereof is included, said additional step being carried out before step b). [4] A process for producing a metal-organic coating according to claim 3, characterized by that these additional charges are incorporated into the colloidal silica solution in the following proportions: 1% to 5% nano- and / or microparticles of 316L or 304 stainless steel powder, 1% to 5% glass fiber powder, and 1% to 5% micronized glass powder, all weight proportions being 100% based on the weight of the colloidal silica. [5] A process for producing a metal-organic coating according to claim 4, characterized bythat the mixture of additional charges and silica is shaken vigorously for 30 minutes in a mechanical stirrer with a centrifugal propeller and then allowed to stand for 8 to 12 minutes. [6] A method for applying a metal-organic coating according to claim 1 to metal parts, characterized by that includes: - alkaline degreasing of metal parts; - Washing metal parts with hot water; - blasting of metal parts with stainless steel microspheres; - Immersing the metal parts in the metal-organic coating bath for 15 to 30 seconds; - Centrifugation between 250 rpm and 450 rpm for 15 to 30 seconds in each direction, clockwise and counterclockwise; and - Cure at a temperature of 320°C to 335°C for 15 to 30 minutes. [7] A method for applying a metal-organic coating to metal parts according to claim 6, characterized bythat the coating can be applied to the parts in up to 3 layers. [8] A method for applying a metal-organic coating to metal parts according to claim 6, characterized by that additionally the application of a seal based on colloidal silicon dioxide nanoparticles is included. [9] Metal-organic coating, characterized by that it is obtainable by the process defined in claim 1, wherein the final layer of the coating is between 5 and 12 micrometers.

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