Antifouling paint composition

Abstract

The present invention relates to antifouling paint compositions comprising a combination of a binder or base elastomer, a solvent capable of dissolving the binder, and copper salt and / or copper particles. The binder or base elastomer is selected from PIB, BIMS, or PIB mixed with BIMS.

Description

[0001] Antifouling paint composition

[0002] Technical field of the invention

[0003] The present invention relates to antifouling paint compositions.

[0004] Background of the invention

[0005] Using copper in ship paint, particularly in the form of copper-based antifouling coatings, has been a common practice for several decades to mitigate biofouling on ship hulls. Biofouling refers to the accumulation of marine organisms, such as algae, barnacles, and mussels, on underwater surfaces. This can significantly reduce a ship’s efficiency by increasing drag and fuel consumption. The copper component in these paints acts as a biocide, preventing or inhibiting the growth of these organisms. However, its use comes with both benefits and environmental concerns.

[0006] Copper acts as a biocide, releasing ions that are toxic to marine organisms. When embedded in paint, it can slowly release these ions into the surrounding seawater, creating a zone around the hull that is hostile to fouling organisms. This reduces drag, improves fuel efficiency, and decreases the frequency of dry-docking for hull cleaning.

[0007] While copper ions are effective against biofouling organisms, they are also toxic to non-target marine species. Elevated levels of copper in marine environments can harm various marine organisms, including fish, invertebrates, and algae. Over time, copper can accumulate in marine sediments and enter food chains, potentially affecting the entire ecosystem. Due to environmental concerns, many countries have implemented regulations to limit the use of copper-based antifouling paints. For instance, the International Maritime Organization (IMO) has taken steps to regulate the use of certain harmful antifouling systems, leading to the development of alternative biocide-free coatings. Some regions, such as the European Union, have also tightened regulations on copper emissions in marine areas.

[0008] There are notable differences between using copper salts and copper particles in ship paints, especially in terms of their effectiveness as antifouling agents, release mechanisms, and environmental impacts. Copper salts are compounds where copper is chemically bonded with other elements (e.g., copper oxide, or copper sulphate). Copper salts are usually dissolved or suspended in the paint matrix. When exposed to seawater, they dissociate to release copper ions, which act as biocides to inhibit the growth of fouling organisms. Copper particles are metallic copper particles, which are typically embedded in the paint’s matrix. Unlike salts, copper particles are released more slowly into the surrounding environment, as they first undergo oxidation when in contact with seawater, gradually forming copper ions (Cu2+) that provide the antifouling effect. With a slower release of copper ions, copper particles pose a lower acute environmental risk compared to copper salts. The slower leaching means that the environmental impact is more spread out but potentially less concentrated than with copper salts.

[0009] Different types of paints are formulated to accommodate copper ions and copper particles, and the choice of paint type depends on factors like how the biocide is delivered, the intended duration of protection, and environmental considerations. Self-polishing copolymer (SPC) paints are widely used for both copper salts and copper particles because they offer controlled release of the antifouling agents. These paints are designed to gradually erode, releasing copper ions over time. Ablative paints work by gradually wearing away over time as the ship moves through water, thereby releasing the antifouling agent. These paints are suitable for both copper salts and copper particles, as they expose new layers of paint, ensuring that copper ions continue to be released over time. Hard antifouling paints do not wear away like ablative or self-polishing paints, but instead leach copper ions from the paint matrix. These paints are more durable and are often used on vessels that require a long-lasting, hard surface, such as racing boats or ships that are drydocked frequently.

[0010] Hybrid antifouling paints with copper are designed to combine the advantages of both hard and ablative paints, offering a balance between durability and controlled release of antifouling agents. These paints typically use modified acrylic, silicone- based, or fluoropolymer binders, which gradually erode or leach biocides like copper oxide to prevent biofouling. However, despite their efficacy, these paints come with several significant drawbacks, particularly concerning their environmental impact. As the paint wears away through gradual erosion, small fragments of the polymer matrix are released into the sea. The binders used in hybrid paints, such as acrylic or silicone-based polymers, are designed for their durability and controlled erosion, but this very property makes them resistant to natural biodegradation processes. In the marine environment, these polymers degrade very slowly due to the lack of microbial activity that can break down synthetic plastics, especially in deep or cold waters. This leads to the accumulation of polymer fragments over time, contributing to the persistence of microplastics in the ocean. Another drawback of hybrid paints is the difficulty in managing these materials at the end of their life cycle. Hybrid binders, which incorporate complex mixtures of acrylics, silicones, or fluoropolymers, are difficult to recycle. These materials cannot be reprocessed into new materials. When ships are scrapped, the hulls coated with hybrid paints pose a significant disposal problem.

[0011] Hard antifouling paints with copper are often based on epoxy or vinyl resin binders, which create durable and long-lasting surfaces.

[0012] When ships coated with these paints are scrapped, recycling becomes extremely difficult. Epoxy and vinyl resins are thermosetting plastics, meaning that once they cure, they cannot be melted down and reprocessed like thermoplastics. This characteristic makes it challenging to recycle the steel or other materials to which these paints are applied. Paint removal is an energy-intensive and costly process, and the copper dispersed within the paint matrix further complicates recycling. The contamination of scrap metal by these paints often results in additional processing requirements, raising both economic and environmental costs.

[0013] US6925952B1 discloses a thin laminate for application to a submerged object, such as a boat hull, to provide anti-fouling protection to the object. The laminate comprises a first layer of a transfer adhesive, a second strengthening layer of a plastic or synthetic rubber film, a third layer of a blended mixture of a synthetic rubber and cuprous oxide, and a removable fourth layer of a plastic film.

[0014] Summary of the invention

[0015] It is an object of the present invention to provide an alternative antifouling paint that solves, or at least alleviates, some of the above-mentioned problems. The inventor of the present invention has realized that the combination of a binder or base elastomer, selected from PIB, BIMS, or PIB mixed with BIMS, and copper salt and / or copper particles provides for an antifouling coating composition that is durable and long-lasting and at the same time possible to separate from the coated material, e.g., metal, during recycling of the coated object.

[0016] A first aspect relates to an antifouling paint composition comprising:

[0017] - a binder or base elastomer selected from PIB, BIMS, or PIB mixed with BIMS;

[0018] - an organic solvent capable of dissolving the binder; and

[0019] - a copper salt and / or copper particles.

[0020] A second aspect relates to an immersed marine structure, such as a ship hull or a buoy, being coated with an antifouling paint composition according to the first aspect.

[0021] A third aspect relates to the use of the antifouling paint composition according to the first aspect for coating an immersed marine structure, such as a ship hull or a buoy.

[0022] The present invention will now be described in more detail in the following.

[0023] Detailed description of the invention

[0024] In the present context, the term “in general” when used when mentioning a feature relating to the present invention, it must be understood that the feature may be used with all embodiments of the invention, even if the mentioning is made in the detailed part of the document.

[0025] In general, the antifouling composition comprises:

[0026] - a binder or base elastomer selected from PIB, BIMS, or PIB mixed with BIMS;

[0027] - an organic solvent capable of dissolving the binder; and

[0028] - a copper salt and / or copper particles. Polyisobutylene (PIB), butyl rubber (BIMS), and mixtures of PIB with BIMS have been found to be highly suitable binders for use in antifouling compositions according to the present invention, e.g., due to the requirement of balance between flexibility and hardness. PIB is a synthetic rubber known for its excellent flexibility, elastic recovery, and impermeability. These qualities make it a strong candidate for coatings that need to maintain flexibility, even under varying conditions. Additionally, PIB’s chemical inertness and resistance to oxygen, ozone, and chemicals further enhance its utility in protective coatings. PIB’s adhesive properties also contribute to its ability to bond effectively with other components in a coating system. PIB (polyisobutylene) is a synthetic polymer composed of isobutylene monomers. It has a highly saturated hydrocarbon backbone, which makes it chemically inert and resistant to degradation. It is of high molecular weight (in the present context, preferably within the range of 40,000-500,000,000 expressed in equivalents of PS) and lack of functional groups that can be easily broken down by microbes, which make it highly stable. In the antifouling coating compositions according to the present invention (either applied as a sheet material or a paint), PIB acts as a highly effective binder due to its adhesive properties, ensuring that the coating remains intact over time and adheres well to a variety of surfaces. Its hydrophobic nature also contributes to water resistance, making PIB ideal for coatings that require a strong barrier against moisture. Moreover, PIB exhibits a low glass transition temperature, which gives coatings elasticity and prevents cracking, particularly in environments subjected to fluctuating temperatures. BIMS (Brominated Isobutylene- co-paramethylstyrene) is a copolymer where brominated isobutylene units are incorporated into the polymer chain along with paramethylstyrene. Like PIB, BIMS is fully saturated, and is thus chemically resistant to e.g., oxygen, and ozone. BIMS can be vulcanised, but for the present application, it is preferred that BIMS remains unvulcanised.

[0029] The copper salt and / or copper particles, apart from their biocidal effect, also contribute to hardness, as the particles reinforce the polymer matrix, thereby balancing the flexibility of PIB with increased mechanical strength. The flexible nature of the binder would counterbalance the brittleness of the copper particles, creating a composite material that is both hard and flexible. A mixture of PIB and BIMS as binders may be advantageous. PIB’s flexibility and impermeability combined with BIMS’s adhesion and durability could result in a binder system that is versatile and adaptable for various coating applications. By adjusting the ratio of PIB to BIMS, the mechanical properties of the coating could be fine-tuned. For example, a higher PIB content would provide increased flexibility, while a greater proportion of BIMS would enhance thermal stability and durability.

[0030] In one or more embodiments, the binder or base elastomer has an average molecular weight expressed in equivalents of PS, preferably according to ISO 16014:2019, of within the range of 40,000-5,000,000.

[0031] The high-molecular weight polyisobutylene has a viscosity average molecular weight of 400,000 to 5,000,000, and may have a viscosity average molecular weight of, for example, 800,000 to 2,500,000, 800,000 to 2,200,000, 800,000 to 2,000,000, 900,000 to 1 ,800,000, 900,000 to 1 ,500,000, 900,000 to 1 ,300,000, and 1 ,000,000 to 1 ,300,000. Commercially available high-molecular weight polyisobutylene, for example, Oppanol™ N 50, Oppanol™ N 80, Oppanol™ N100, Oppanol™ N 150 (BASF, Germany) and the like may also be used, if necessary. The low-molecular weight polyisobutylene has a viscosity average molecular weight of 40,000 to 100,000, and may have a viscosity average molecular weight of, for example, 40,000 to 90,000, 45,000 to 85,000, 45,000 to 75,000, 45,000 to 70,000, 45,000 to 65,000, 47,000 to 65,000, and 50,000 to 60,000. Commercially available low- molecular weight polyisobutylene, for example, Oppanol™B 10, Oppanol™B 11 , Oppanol™B 12, Oppanol™B 13, Oppanol™B 14, Oppanol™B 15 (BASF, Germany) and the like may also be used, if necessary.

[0032] In paint compositions according to the present invention, a moderate chain length is often preferred, balancing processability with film strength and flexibility. Lower molecular weight PIB or BIMS can be used in situations where ease of application and fast drying are prioritized, while higher molecular weight variants are better suited for applications that demand higher mechanical performance and flexibility. In one or more embodiments, the binder has an average molecular weight expressed in equivalents of PS, preferably according to ISO 16014:2019, of within the range of 40,000-500,000. The binder is present in 1-5% w / w of the total composition, provided that the composition comprises an organic solvent capable of dissolving the binder. The solvent is generally present in 10-90% w / w of the total composition. The solvent is present in 50-90% w / w of the total composition.

[0033] In general, the solvent may e.g., be hydrocarbons like C7-C10 alkanes, C7-C10 isoalkanes, or C7-C10 cyclic hydrocarbons, such as n-heptane, n-decane, n- isoheptane, cycloheptane, and isoheptane, to control the viscosity and drying time of the coating.

[0034] For the paint compositions, the copper salt and / or copper particles is present in 5- 40% w / w of the total composition, such as 10-20% w / w of the total composition.

[0035] Specifically, the paint composition comprises:

[0036] - 1-5% w / w of the total composition of the binder;

[0037] - 5-40% w / w of the total composition of the copper salt and / or copper particles;

[0038] - 40-90% w / w of the total composition of the solvent.

[0039] Apart from binder and copper particles, the composition may further comprise pigments to provide colour and opacity. The copper particles also act as filler to improve the mechanical properties of the final coating.

[0040] It should be noted that embodiments and features described in the context of one of the aspects of the present invention also apply to the other aspects of the invention.

Claims

Claims1. An antifouling composition comprising:- a binder or base elastomer selected from PIB, BIMS, or PIB mixed with BIMS; and- a copper salt and / or copper particles; characterized in that the antifouling composition is a paint composition that further comprises an organic solvent capable of dissolving the binder; and wherein the composition comprises:- 1-5% w / w of the total composition of the binder or base elastomer;- 5-40% w / w of the total composition of the copper salt and / or copper particles;- 50-90% w / w of the total composition of the solvent.

2. The antifouling paint composition according to claim 1 , wherein the binder or base elastomer has an average molecular weight expressed in equivalents of PS of within the range of 40,000-5,000,000.

3. The antifouling paint composition according to any one of the claims 1-2, wherein the binder or base elastomer is PIB.

4. The antifouling paint composition according to any one of the claims 1-2, wherein the binder or base elastomer is BIMS.

5. The antifouling paint composition according to any one of the claims 1-2, wherein the binder or base elastomer is PIB mixed with BIMS.

6. The antifouling paint composition according to any one of the claims 1-5, wherein the solvent is selected from one or more hydrocarbons to control the viscosity and drying time of the coating.

7. The antifouling paint composition according to claim 6, wherein the solvent is selected from n-heptane, n-decane, n- isoheptane, cycloheptane, and isoheptane.

8. The antifouling composition according to claim 6, wherein the solvent is selected from C7-C10 alkanes, C7-C10 isoalkanes, and C7-C10 cyclic hydrocarbons.

9. An immersed marine structure, such as a ship hull or a buoy, being coated with an antifouling paint composition according to any one of the claims 1-8.

10. Use of the antifouling paint composition according to any one of the claims 1-8 for coating an immersed marine structure, such as a ship hull or a buoy.