AU2020478543A1

AU2020478543A1 - Anticorrosive coating composition

Info

Publication number: AU2020478543A1
Application number: AU2020478543A
Authority: AU
Inventors: Andrew Lim
Original assignee: PPG Industries Pty Ltd; PPG Industries Australia Pty Ltd
Current assignee: PPG Industries Pty Ltd
Priority date: 2020-11-30
Filing date: 2020-11-30
Publication date: 2023-06-29
Also published as: WO2022109651A3; WO2022109651A2

Abstract

There is provided an anticorrosive coating composition comprising an epoxy ester resin and a non-leafing grade aluminium pigment.

Description

Anticorrosive coating composition

Field of the invention

[01] The invention relates to an anticorrosive coating composition. In particular, the present invention provides improved corrosion protection for metal substrates.

Background of the invention

[02] In this specification, unless the contrary is expressly stated, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date, publicly available, known to the public, part of common general knowledge; or known to be relevant to an attempt to solve any problem with which this specification is concerned.

[03] Corrosion is caused by a chemical reaction between a metal and its environment (water or other fluids or prolonged exposure to UV radiation), typically producing an oxide or a salt of the original metal. Protection of a metal substrate from corrosion is often vitally important to increase its durability and lifespan, such as, for example, when such metals are used to construct components incorporated into automotive, aerospace, architectural, bridges, gas pipelines and other industrial structures and parts. Various methods have been employed to achieve varying levels of corrosion protection.

[04] Existing products of single pack epoxy metallic anticorrosive coating in the retail and trade markets currently do not offer an adequate level of corrosion protection, especially for applications in the coastal regions where there are soluble chlorides in the atmosphere. For example, steel panels coated with leading anticorrosive coating products in the market have shown heavy flash rusting after being exposed to salt fog in an enclosed chamber for only three days.

[05] There is thus a need for an anticorrosive coating composition which can be used in the retail and trade markets that provides improved rust protection. Summary of the invention

[06] According to the present invention, there is provide an anticorrosive coating composition comprising:

(a) an epoxy ester resin, and

(b) a non-leafing grade aluminium pigment.

Brief Description of Drawings

[07] Figure 1 shows the test specimens in Example 2 before salt spray testing.

[08] Figure 2 shows the test specimens in Example 2 after salt spray testing.

[09] Figure 3 shows the test specimens in Example 3 after 100% relative humidity testing.

[10] Figure 4 shows the test specimens in Example 4 after salt spray testing.

[11] Figure 5 shows selected test specimens in Example 4 after adhesion testing.

Detailed description

[12] For the purposes of the following detailed description, it is to be understood that the invention may assume various alternative variations and step sequences, except where expressly specified to the contrary. Moreover, other than in any operating examples, or where otherwise indicated, all numbers expressing, for example, quantities of ingredients used in the specification and claims are to be understood as being modified in all circumstances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[13] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard variation found in their respective testing measurements.

[14] Also it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of "1 to 10" is intended to include all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10.

[15] In this application, the use of the singular includes the plural and plural encompasses the singular, unless specifically stated otherwise. In addition, in this application, the use of "or" means "and/or" unless specifically stated otherwise, even though "and/or" may be explicitly used in certain instances.

[16] There are generally three protective mechanisms into which anticorrosive coatings are classified: barrier coatings, inhibitor coatings and sacrificial coatings. Sacrificial coatings are metal-rich coatings which provide a sacrificial layer containing a more easily corroded metal (such as zinc) to be the anode to the protected metal’s cathode so that this metal will corrode instead of the protected metal. Inhibitor coatings release a chemical which interferes with the electrolyte and stops the corrosion process, and include oil based coatings with corrosion inhibitor additives such as zinc, aluminium, zinc oxide. Barrier coatings are non-porous coatings designed to prevent aggressive/corrosive factors coming into contact with the substrate. Some anti-corrosive coatings may use a combination of these mechanisms. The most common combination coatings are barrier / sacrificial coatings.

[17] The main components in anticorrosive barrier coatings are the binder and pigment. The binder must ensure a number of properties, including adhesion to the metal substrate, cohesion within the coating, high mechanical strength and low permeability. The development of both aesthetic appearance and anticorrosive performance relies on the choice and curing of the binder. The most common types of binders used in prior art anticorrosive coatings include epoxy resins (polyepoxides), acrylic resins, polysiloxanes, alkyd resins, polyurethanes and polyesters.

[18] Preferred pigments in barrier coatings impede the transport of aggressive species to the substrate. Typically, the pigments are lamellar pigments which orient themselves parallel to the substrate surface and create a difficult path of diffusion to the substrate, and may assist with the mechanical properties of the coating. Common lamellar pigments used in prior art anticorrosive coatings include micaceous iron oxide, lamellar aluminium and glass flake pigments. Leafing grade aluminium is commonly used in prior art aluminium containing barrier coatings. For a combination barrier/sacrificial coating, sacrificial pigments may also be used, with metallic zinc particles being the most widely used sacrificial pigment.

[19] The present innovation relates to an anticorrosive coating composition that provides improved corrosion protection for metal substrates, in particular those containing iron or steel. More specifically, the present invention pertains to an anticorrosive composition comprising an epoxy ester resin and a non-leafing aluminium pigment which can be used as a direct-to-metal topcoat (ie single coat) having improved corrosion and barrier protection of metal substrates.

[20] According to the present invention, there is provide an anticorrosive coating composition comprising:

(a) an epoxy ester resin, and

(b) a non-leafing grade aluminium pigment.

[21] It has surprisingly been found that an anticorrosive coating composition comprising an epoxy ester resin provides improved anticorrosion properties when compared with prior art compositions comprising the commonly used alkyd or acrylic resins.

[22] The skilled person will know that any suitable film forming epoxy ester resin may be used in an anticorrosive coating composition according to the invention. The skilled person will know that choice of epoxy ester resin will impact properties such as drying time and brushing application. Examples of suitable epoxy ester resins are SETAL 212 and SETAL 0405. In one embodiment, the epoxy ester resin comprises more than 25% w/w of the total composition.

[23] It has surprisingly been further found that an anticorrosive coating composition comprising a non-leafing aluminium pigment provides improved anticorrosion properties when compared with prior art compositions comprising the commonly used leafing aluminium.

[24] The skilled person will know that any suitable non-leafing aluminium pigment may be used in an anticorrosive coating composition according to the invention. The term "non-leafing aluminium" is used to refer to aluminium pigments which become wetted and distribute themselves throughout the film (in contrast to leafing aluminium which floats to the surface of the film). One of the key factors to consider is the particle size of the pigment which will affect the final metallic appearance of the dry coating. The larger the particle size (ie the reflecting surface), the greater the metallic effect (ie brilliance, sparkle effect). The smaller the particle size, the greater the light scattering leading to a duller look (eg weathered galvanised steel appearance). The skilled person will also know that another key factor to consider is the shape of the particle.

[25] In one embodiment, the non-leafing aluminium pigment comprises 3 to 6% w/w of the total composition.

[26] The skilled person will know that the ratio of active pigments to epoxy ester resin is relevant to several properties of the anticorrosive coating composition. In one embodiment, the ratio of total active pigments, including the non-leafing aluminium pigment and any optional zinc pigment, to epoxy ester resin is in the range of from 30:70 to 40:60.

[27] The combination of an epoxy ester resin and a non-leafing aluminium pigment in the anticorrosive coating composition according to the invention provides an acceptable appearance and an improved adhesion and corrosion resistance when compared with prior commercial products.

[28] The anticorrosive coating composition according to the invention is suitable for use on metal substrates include steel, structural steel, wrought iron, galvanized iron and aluminium. These substances are very strong and used to make many structural products which need to be protected from corrosion.

[29] The skilled person will understand that the anticorrosive coating composition according to the invention comprises the epoxy ester resin as a binder, namely a film-forming binder. As used herein, the term "binder" refers to a material in which the metal particles are distributed and which serves to bond the coating composition to either a bare or previously coated substrate, such as a metal substrate. As used herein, the term "film-forming binder" refers to a binder that forms a self-supporting, substantially continuous film on at least a horizontal surface of the substrate upon removal of diluents and/or carriers that may be present in the anticorrosive coating composition. In addition to the epoxy ester resin, the anticorrosive coating composition according to the invention may further comprise one or more other binders. For example in one embodiment, an anticorrosive coating composition according to the invention may further comprise a thermoplastic acrylic resin to result in a hybrid binder with improved ultraviolet and yellowing resistance. [30] In one embodiment, the anticorrosive coating composition further comprises a zinc pigment. The zinc can be in the form of a zinc dust or zinc flakes. For example, a zinc dust containing greater than 98% metallic zinc. In some embodiments, the zinc pigment can improve the corrosion performance of the composition. In one embodiment, the zinc pigment comprises 2 to 12% w/w of the total composition.

[31] In one embodiment, the anticorrosive coating composition further comprises a wax.

In one embodiment, the wax is a micronized wax having a particle size in the range of 3.5 to 5.5 microns. In one embodiment, the micronized wax is a micronized polyethylene wax. Without wishing to be bound by theory, the wax is typically thought to rise to the surface of the resultant film to provide an additional protection barrier against oxygen and water, and may also improve its surface mar resistance. In one embodiment, the wax comprises 0.1 to 2% w/w of the total composition.

[32] The anticorrosive coating composition according to the invention may further comprise other components such as additives and solvents. Additives are auxiliary products that are added in small amounts to improve certain coating properties of the coating composition. Suitable additives include extenders, anti-skinning agents, thickeners, rheology control agents, defoamers, anti-settling agents, drying agents, anti-caking agents, free-flowing agents, gelling agents, hydrophobizing agents, suspending agents, wetting agents, dispersing agents, moisture scavengers, plasticisers, evaporable oils, adhesion promoting agents, stabilisers to absorb ultraviolet radiation, curing additives and coupling agents. The skilled person will be experienced in the use of these components in the preparation of anti-corrosive compositions.

[33] Typically, an anticorrosive coating has multiple layers with different properties and purposes. The anticorrosive coating composition according to the invention may be used as a primer, intermediate or topcoat. The anticorrosive coating composition according to the invention is particularly suited for use as a direct-to-metal topcoat.

Examples

[34] The following examples are given to illustrate the present invention. It should be understood, however, that the invention is not to be limited to the specific conditions or details described in these examples, some of which are preferred embodiments of the invention. Example 1

[35] In this example, compositions were prepared as set out in the below table. Formulations 1 and 2 are anticorrosive coating compositions in accordance with the invention. Formulation 3 is a comparative formulation used in Examples 2 and 3.

Example 2

[36] In this example, an anticorrosive coating composition according to the invention was tested and compared with current commercial products and a comparative example.

[37] Four mild steel panels (95 mm x 300 mm) were sanded (180 grit sandpaper) and wiped cleaned with technical grade isopropanol. One half of each of the panels was covered with masking paper. A Leneta Form M12 spray monitor was attached to the masking paper next to the uncovered part on each panel for paint coverage check. Each of the paint samples was spray-applied to the uncovered part of a test panel and to fully cover the spray monitor. The coated panels were allowed to dry at room temperature for seven days.

[38] The paint samples tested were Leading Brand A fast drying epoxy based metallic zinc coating which contains some aluminium (Dy-Mark Silver Zinc), Leading Brand B zinc-rich anti-corrosive aerosol paint (Dulux Metalshield Bright Zinc), Formulation 1 from Example 1 and Comparative Formulation 3 from Example 1. [39] The test panels were then tested in a 72-hour salt spray test according to ASTM B 117. The results are set out in Table 1 below. Figure 1 shows the test specimens before Salt Spray Testing and Figure 2 shows the test specimens after Salt Spray Testing.

Table 1. Salt Spray Corrosion Resistance Results of Four Metallic Coatings after 72 Hours of Exposure

[40] The results demonstrate that under accelerated weathering conditions, the anticorrosive coating composition according to the invention, Formulation 1 from Example 1, provided greater corrosion protection of mild steel than the Leading Brands A and B and Comparative Formulation 3 from Example 1.

Example 3

In this example, the paint samples used in Example 2 were tested in 100% relative humidity.

Mild steel panels were prepared and coated as set out in Example 2 above. The coated panels were then tested according to ASTM D 2247.

Test specimens after the 2350 hour water resistance test according to ASTM D 2247 are shown in Figure 3. The test results are listed in Table 2. Table 2. Water Resistance Test Results after 2350 Hours of Exposure

[41] The results demonstrate that under the accelerated weathering conditions as per ASTM D2247, the anticorrosive coating composition according to the invention, Formulation 1 from Example 1, provided the greatest water resistance of mild steel than the Leading Brands A and B and Comparative Formulation 3 from Example 1.

Example 4

[42] In this example, an anticorrosive coating composition according to the invention was compared with comparative compositions.

[43] The paint samples tested were as follows: a) Control 1 is Formulation 1 from Example 1 according to the invention (comprising epoxy resin, zinc dust and non-leafing aluminium pigment) b) Sample 1 - similar to Formulation 1 from Example 1 but replacing the leafing aluminium pigment with non- leafing aluminium pigment c) Sample 2 - similar to Formulation 1 from Example 1 but without zinc dust d) Sample 3 - similar to Sample 1 but without zinc dust e) Sample 4 - similar to Formulation 1 from Example 1 but replacing the epoxy resin with a thermoplastic acrylic resin f) Sample 5 - similar to Sample 4 but with leafing aluminium pigments replacing the non-leafing aluminium pigments g) Sample 6 - similar to Sample 4 but without zinc dust h) Control 2 - similar to Sample 5 but without zinc dust

[44] Eight mild steel panels were sanded and wiped cleaned with technical grade isopropanol. Each paint sample was pre-thinned with an appropriate solvent to a viscosity of 22+1 seconds via a B4 viscosity cup prior to being applied. Each paint sample was spray- applied to fully cover the panel in three coats. Coated panels were allowed to dry at room temperature for seven days. Coated panels were submitted for 192-hour salt spray testing according to ASTM B 117. The results are set out in Table 3 below and illustrated in Figure 4.

Table 3. Salt Spray Corrosion Resistance Results after 192 Hours of Exposure [45] In addition to corrosion resistance, coating compositions also need to demonstrate appropriate adhesion to the substrate. This was assessed using a cross-hatch adhesion test (ASTM D3359) and a tape-pull test on the samples. The results for each sample are listed in Table 4. The test results for selected samples are shown in Figure 5.

Table 4. Cross-hatch Adhesion and Tape-Pull Tests’ Results using ASTM 3359 Method B Classification

Conclusion

[46] After being subjected to 192 hours of continuous salt spray as per ASTM B 117-03, Control 1, which is Formulation 1 from Example 1, was found to provide the best corrosion protection of mild steel.

[47] Taking into consideration the combined performance of each sample based on salt spray corrosion resistance and direct-to-metal adhesion, it was found that all the formulations with the epoxy ester resin as the binder outperformed those with the acrylic resin binder in corrosion protection (Sample 6, despite being blister-free, was excluded from the ranking due to its total lack of adhesion to the metal substrate). Further, all the samples formulated with the non-leafing aluminium pigment were superior in anti-corrosive performance than the ones formulated with the leafing aluminium pigment. [48] These results demonstrate that it is the combination of an epoxy ester resin with a non-leafing aluminium pigment in the anticorrosive coating composition according to the invention which provides the improved corrosion resistance while maintaining suitable adhesion to the substrate.

[49] The word ‘comprising’ and forms of the word ‘comprising’ as used in this description and in the claims does not limit the invention claimed to exclude any variants or additions.

[50] Modifications and improvements to the invention will be readily apparent to those skilled in the art. Such modifications and improvements are intended to be within the scope of this invention.

Claims

The claims defining the invention are as follows:

1 An anticorrosive coating composition comprising:

(a) an epoxy ester resin, and

(b) a non-leafing grade aluminium pigment.

2 The anticorrosive coating composition according to claim 1 wherein the epoxy ester resin comprises more than 25% w/w of the total composition.

3 The anticorrosive coating composition according to either of claims 1 or 2 wherein the non-leafing aluminium pigment comprises 3 to 6% w/w of the total composition.

4 The anticorrosive coating composition according to any one of claims 1 to 3 further comprising a zinc pigment.

5 The anticorrosive coating composition according to claim 4 wherein the zinc pigment comprises 2 to 12% w/w of the total composition

6 The anticorrosive coating composition according to any one of claims 1 to 5 wherein the ratio of non-leafing aluminium pigment, and any optional zinc pigment, to epoxy ester resin is in the range of from 30:70 to 40:60.

7 The anticorrosive coating composition according to any one of claims 1 to 6 further comprising a wax.

8 The anticorrosive coating composition according to claim 7 wherein the wax comprises 0.1 to 2% w/w of the total composition.

9 The anticorrosive coating composition according to any one of claims 1 to 8 further comprising one or more other components selected from the group consisting of additives and solvents.

10 The anticorrosive coating composition according to claim 9 wherein the additives are selected from the group consisting of extenders, anti-skinning agents, thickeners, rheology control agents, defoamers, anti-settling agents, drying agents, anti-caking agents, free-flowing agents, gelling agents, hydrophobizing agents, suspending agents, wetting agents, dispersing agents, moisture scavengers, plasticisers, evaporable oils, adhesion promoting agents, stabilisers to absorb ultraviolet radiation, curing additives and coupling agents. The anticorrosive coating composition according to any one of claims 1 to 10 further comprising one or more other binders. The anticorrosive coating composition according to claim 11 wherein the one or more other binders comprises a thermoplastic acrylic resin. A direct-to-metal topcoat comprising the anticorrosive coating composition according to any one of claims 1 to 12.