Anti-corrosive paints and coatings containing nanoparticles

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ANTI-CORROSIVE PAINTS AND COATINGS CONTAINING NANO PARTICLES

The present invention refers to nanoplatelet containing 5 anticorrosion paints and coatings.

Particularly the present invention refers to anticorrosion paints and coatings containing nano particles consisting of inorganic aluminium-silicate having a platelet shape, in the following defined as nanoclays.

It is known that coating, painting and primer formulations are 10 based on polymers containing solid particulates, pigments, plasticizing agents and others technological aids dissolved in organic solvents (organic based coatings) or water (water based coatings).

It is also known that, among currently commercially available anticorrosion paints and coatings, epoxy, polyurethane or acrylic paints 15 and coatings display excellent adhesion and durability properties and, particularly, are extensively used to coat steel structures in order to retard the corrosion effects resulting from oxygen and humidity combination activity.

However, as a result of inherent composition thereof, these 20 paints and coatings absorb humidity and do not represent an oxygen optimal barrier. The humidity absorption and oxygen passage are the reason for the corrosion process of coated metals, resulting in oxide formation at metal-coat interface. Such phenomenon is then followed by coating separation (debonding) and increasing degradation of metallic 25 substrate. in order to overcome these limitations of previously known paints and coatings, according to US No. 6,878,767 a reduced permeability paint formulation has been disclosed, comprising a filmogen agent, a pigment and a multitude of chemically treated nano-particles 30 having a platelet shape, that Is mostly bi-dimensionally developed, with a few hundred and about one nanometer as to lateral dimensions and thickness, respectively. According to said patent, the percentage of platelets (preferably aluminium-silicate, in any case consisting of water-impermeable material) dispersed within the formulation is 1 to 10% by 35 volume and the platelets are chemically treated with organic (IBce for example amino- or epoxy-terminated silane) or inorganic (Fike for example 2 an aliphatic acid) compounds in order to facilitate their orientation according to parallel direction of substrate, the paint is applied on, thus increasing the platelets intermolecular forces. By arranging according to substrate surface parallel direction, the platelets reduce available passage 5 spaces to corrosive liquid or gas molecules and increase the distance to be travelled in order to reach the coating layer and substrate interface, thus reducing the possibility of oxide formation on the interface and successive coat debonding.

On the other hand has been demonstrated that the formulations 10 according to US 6,878,767 do not allow an optimal platelet orientation, thus reducing the waterproofing effect the platelets are added for. By microscopic analysis, particularly Transmission Electron Microscopy (TEM), and permeation measurements it has been possible to verify that the order and the alignment at nanometer level of the nanoclays are 15 disturbed due to the excessive formulation viscosity, resulting in a lower barrier effect to the humidity and oxygen and consequently an increased corrosion. This results from the feet that, because of their shape with a particularly extended surface in respect to thickness (high aspect ratio), the platelets added to paint polymeric resins are easily Immobilized by 20 polymer molecules.

In the light of above, it is apparent the need to provide a formulation for anticorrosion paints and coatings containing nanometric sized platelets overcoming the limitations of the formulations according to US 6,878,767. 25 In this context it is offered the problem solution according to the present invention, aiming to provide a formulation for anticorrosion paints and coatings containing nanoclays, therein said nanoclays are chemically treated and the viscosity is controlled in such way to favour the alignment of nanoclays parallel to the substrate the formulation is applied on. 30 The object of the present invention is therefore to provide a formulation for anticorrosion paints and coatings containing nanoclays and a process for the production thereof allowing the limitations of the solutions according to known technology to be eliminated and previously described, technical results to be obtained A further object of the invention is that said formulation and process can be carried out at substantially reduced, both production and operating, costs.

Not last object of the invention is to propose a formulation and a 5 process substantially simple, safe and reliable.

It is therefore a First specific object of the present invention a formulation for anticorrosion paints and coatings, based on epoxy, polyurethane, acrylic, alkydic, polyester and mixtures thereof, dissolved in organic or inorganic solvents, and comprising a multitude of nanoparticles 10 mostly bi-dimensionally developed, with a few hundred and about one nanometer as to lateral dimensions and thickness, respectively, wherein the rotational viscosity of the formulation at Wrpm, measured according to ASTM D4212 is lower than 55000 mPa^s and preferably Is lower than 40000 mPa-s. 15 In particular, according to the invention, the amount of said nanoparticles is lower than 2% by weight, based on total weight of the formulation, preferably is lower than 1% by weight, based on total weight of the formulation and most preferably is equal to 0,5% by weight, based on total weight of the formulation. 20 Particularly, according to the invention, said nanoparticies consist of materials containing ions .‘available for ion exchange reactions, previously treated by ion exchange reaction with ions of long chain molecules, preferably of at least 16 carbon in order to achieve both: good intercalation of the Na+ nanoparticies and physical compatibility with di- 25 glycidic ether of bis-phenol A matrix.

Always according to the invention, preferably said nanoparticies consist of silico-aluminata based materials, still more preferably montmorillonite.

Moreover, again according to the present invention, said ions of 30 long chain molecules are obtained by protonising amines or other compounds compatible with other formulation components.

Further it is another specific object of the present invention a concentrated formulation for anticorrosion paints and coatings, based on epoxy, polyurethane, acrylic, alkydic, polyester resins and mixtures 35 thereof, comprising a multitude of nanoparticies mostly bi-dimensionally developed, with a few hundred and about one nanometer, respectively, as

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to lateral dimensions and thickness, wherein said nanoparticles consist of materials containing ions available for ion exchange reactions, previously treated by ion exchange reaction with ions of long chain molecules having at least 16 carbon atoms. 5 5

The invention now will b© described by an illustrative, but not limitative way, particularly with reference to preferred embodiments and 5 some illustrative examples.

According to the present invention, the platelets the formulation is made of are chemically treated in order to facilitate their orientation according to parallel direction of substrate the paint is applied on, thus increasing the platelets intermolecular forces. Moreover, the viscosity is 10 controlled in order not to reach values preventing the platelets to move easily within the matrix consisting of polymeric paint, that is to align parallel to the metallic substrate (anc! therefore to offer as high as possible corrosion protection) as a result of the mechanical action carried out by devices used to spread the paint layer on the substrate. Further, in order 15 to obtain low enough viscosities it is possible to add solvents to the paint (that are evaporated during drying) or reduce the solid content of the epoxy (like: calcium carbonate, metal oxides and other solids that are used in conventional paints).

Example 1, Nanoclav preliminary treatment 20 50g of Cloisite Na nanoclays (NC-Na), CAS N. 1315-93-0; 95Meq/100g, from Southern Clay Products, have been dispersed in 1500ml of water at room temp, for 30 minutes and the resuming dispersion then has been heated at 85“C and hold standing for 2 hours.

Apart a second solution, obtained by dissolving in 1300ml of 25 water, at temperature of bS’C, 19g of octadecylamine (ODA), C|BH30N, CAS N. 124-30-1, FW=269,51, from Fluka, cat N. 74752, has been prepared. Then hydrochloric acid (HCI) at 37% has been added up to pH 4,5, FW=36,5, and the solution stirred for 0,3 hours.

Then this solution has been added to the water nanoclay 30 dispersion by mixing at 85° C for 1 hour, subsequently allowing to cool.

In these conditions, a whit© colour precipitate has been formed, then separated from clarified liquid and successively washed, firstly with ethanol and then, for three times, with waier.

Solid precipitate then has been collected and dried by heating 35 at 80*C for 15 hours and successively at 110“C for 2 hours. s

Dried precipitate consisting of platelet shaped Cloisite Na functionalised nanoclays is ready to be added to paints.

The principle of nanoclays treatment is to allow Na+ ion exchange (or other ion occurring within the nanoclays to be treated) with a 5 long chain containing ion to be carried out. In this way the distance among the platelets forming the structure of ceramic nanoclays is increased, thus facilitating the de-lamination of the na noclays resulting in single nanoclays (1 nm thick).

As a long chain containing ion can be used an amine, 10 protonised with a such acid amount to allow the protonization to be carried out, that is, an ammonium ion which is exchanged with Na+ Ion (specifically for example 1 octadecyl amine is protonised with hydrochloric acid).

When the protonised amine solution is added to the water 15 dispersion of ceramic nanoclays the ion exchange occurs, Resulting precipitate consist of ODA (which is hydrophobic) treated nanoclays.

Example 2, Preparation of a priming formulation (primer) containing functionalised nanoclays

Nanoclays obtained according to example 1 have been added 20 to an epoxy priming formulation (primer), depending on various compositions as reported in table 1 and mixed until an uniform dispersion has been obtained.

Various primer obtained compositions have been individually applied to identical metallic substrates, then analysed, with the results 25 reported in table 1.

Table 1 % NC Viscosity mPaS Thickness pm No. cf bubbles Resistance Ω cm2 0 27000 150 4 9x107 0,5 32000 140 0 8x109 1F0 37100 140 2 5x109 2,0 52400 142 2 1x109

Particularly,·in table 1, %NC shows the nanociay percentage on the total of the formulation, viscosity is rotational viscosity at 10 rpm, measured according to ASTM D4212, bubble number has been measured 30 after 700 hours of exposure to saline sprays (salt spray test: ASTM B117) 10 15 20 and resistance has been measured after 700 hours of exposure and thickness of 80 pm according to Electrochemical impedance Sprectoscopy: ISO 16773-3:2009.

Example 3. Preparation of a painting formulation containing functionalised nanociavs

Nanoclays obtained according to example 1 have been added to an epoxy painting formulation, depending on the various compositions as reported in table 2, and mixed until an uniform dispersion has been obtained.

Various paint obtained compositions have been individually applied to identical metallic substrates, then analysed, with the results reported in table 1..

Table 2 % NC Viscosity mPaS Thickness pm No. cf bubbles Resistance Ω cm2 0 26600 160 20 2x101° 0,5 39000 130 0 1x1012 1,0 51400 135 3 8x1011 2,0 85700 130 5 1x1011

Particularly, in table 2, %NC shows the nanoclay percentage on the total of the formulation, the viscosity is rotational viscosity at 10 rpm, measured according to ASTM D4212, the bubble number has been measured after 700 hours of exposure to saline sprays (salt spray test : ASTM B117) and resistance has been measured after 700 hours of exposure and thickness of 150 pm according to Electrochemical Impedence Sprectoscopy: ISO 16773-3:2009,

Example 4, Comparative evaluation of detachment strength..of painting formulation containing functionalised nanociavs

Nanoclays obtained according to example 1, and other closite nanoclays (30 B closite) not subjected to the same treatment, have been added to an epoxy painting formulation, according to various compositions as reported in table 3 (the first line of the table referring to a not nanoclay added formulation): individually applied to identical metallic substrates (to form a low thickness coating), and successively subjected to adhesion tests, by means of pull-off analysis, with results as reported in table 3. 25 212947/2 δ

Pull-Off test is a direct method, according to EN ISO 4624, aiming to check the quality of a coating and it is carried out by a destructive test allowing the detachment strength of the paint coating layer to be evaluated. For each formulation two adhesion tests in dry and one in 5 wet conditions have been carried out.

Table 3

Dry adhesion (MPa) Wet adhesion (MPa) Value 1 Value 2 Avera ge Without nanoclays 17,0 17,0 17,0 12,0 1% Example 1 13,4 15,0 14,2 16,4 1 % Closrte 30 B 5,2 6,0 5,6 3.6 2% Example 1 15,0 17,0 16,0 19,0 2% Closite 30 B 5,0 5,0 5,0 4,6

The examples allow to verify that the new formulation as described in the present invention inhibits the humidity and oxygen 10 permeation through the protective coatings on the metallic surface, so as to minimize the corrosion effects. Such inhibition occurs as a result from the ordered and paraDei orientation of surface extended inorganic nanoclays obtained by means of the treatment according to example 1.

Moreover, the examples show higher effectiveness of 15 functionalised nanoclays added anticorrosion formulations according to the present invention than not functionalised nanoclays added formulations.

With reference to the amount of nanociays added to the formulation for anticorrosion paints and coatings according to the present 20 invention, the amount of nanoclays to be used must be such not to result in an undesired viscosity increase. In order the viscosity objectives to be reached, the paint formulation can conveniently be diluted with not reacting reagents (organic or water based) reducing the viscosity level and evaporating after the coating curing. 25