GB2120267A - Antifouling paint composition - Google Patents

Abstract

There is provided an antifouling point composition comprising a vehicle, an effective amount of a water- insoluble copper compound, and a water-insoluble reducing agent having an oxidation-reduction potential less than that of copper. The reducing agent is preferably selected from powdered metals such as Sn, Sb, Zn, Cr, Fe, Ni, Pb, Ti or alloys of these metals.

Description

SPECIFICATION Antifouling paint composition This invention relates to an antifouling paint composition for protecting ships or other marine constructions from fouling with marine organisms.

A variety of fouling organisms are living in the marine environment. They include animals classified in phyla from Protozoa to Prochordata and various marine plants such as seaweeds, diatoms and the like.

Antifouling agents to be incorporated in antifouling paint compositions require to have a long-term antifouling activity against all or as many fouling organisms as possible while exhibiting low toxicities to the human body and also to the natural environment. Recently, organotin compounds such as triaikyl- or triphenyl-tin compounds, organic chlorine compounds such as DDT or BHC, and organic sulfur compounds such as tetraalkylthiuram disulfide or zinc dialkithiocarbamate have been used for the antifouling purposes.

However, these antifouling agents are effective against only limited classes of fouling organisms but not effective against other organisms, particularly against various seaweeds. At a higher concentration effective against substantially all fouling organisms they are too toxic to the human body and the natural environment.

On the other hand, copper-containing antifouling agents typically represented by cuprous oxide exhibit a remarkable antifouling activity to substantially all fouling organisms while having relatively lowtoxicities to the human body and the natural environment. Therefore, these agents have long been used in practice.

However, experiments have shown that cuprous oxide is unstable and may be easily oxidized to a cupric compound in the seawater so that its dissolving rate falls below the minimum effective level of 10g/cm2/day as copper ions and eventually loses its effectiveness completely although the copper compound still remains in the coated film containing the same. Although the present invention should not be bound to a particular theory, it is postulated that this is because cuprous ions released from cuprous oxide are immediately oxidized to cupric ions and then react with existing hydroxide and carbonate ions to form more insoluble basic cupric carbonate.Cuprous oxide has a solubility of 3-5x 10-5 mole/liter of sea water at 20"C at pH8.2, whereas the corresponding vaiue of basic cupric carbonate is 2-4 x 1 o-6 mole/liter.

It has been known that cuprous ions or cupric ions are reduced to a lower ion or elementary copper by the action of various metallic and nonmetallic elements having an oxidation-reduction potential lower than that of copper.

It has now been discovered that the above-described disadvantages of conventional antifouling paint compositions containing water-insoluble, copper-containing antifouling agents may be overcome by incorporating therein a reducing agent having an oxidation-reduction potential lower than that of copper.

Obviously, not all of elements having an oxidation-reduction potential lower than that of copper are usable for this purpose. They should be nonharmful to the human body and the natural environment and also capable of reducing cupric ions to cuprous ions at a constant rate in the seawater for a long period of time.

Usable metals which meet these requirements include Sn, Sb, Zn, Cr, Fe, Ni, Pb and Ti. Hydrolyzable metals such as Na and Mg, metals which form an insoluble compound with copper ions such as Al and Co, ecologically unacceptable metals such as Cd and As, and elements which are rapidly consumed in the seawater such as P are not satisfactory for this purpose. The above-mentioned metals may assist the release of copper ions at a suitable rate not only from cuprous oxide but also from insoluble copper compounds having a solubility of less than 3x 10-6 mole/liter in the seawater such as cupric hydroxide or basic cupric carbonate.Although the invention is not bound to a particular theory, it is considered that, in addition to a series of reactions in which cuprous ions are oxidized to cupric ions and then excess cupric ions are converted to insoluble cupric hydroxide or basic cupric carbonate, a reverse reaction occurs in which insoluble cupric hydroxide or basic cupric carbonate is reduced back to cuprous ions by the added metal so that an equilibrium is reached between the oxidation and reduction reactions thereby maintaining a steady release of copper ions into the seawater for a long period of time.

Accordingly, there is provided by the present invention an antifouiing paint composition comprising an effective amount of water-insoluble copper compound and a water-insoluble reducing agent having an oxidation-reduction potential less than that of copper uniformly dispersed in a vehicle. The term "water-insoluble copper compound" used herein means those having a solubility less than 1 xlO-4mole/liter in the seawater at pH8.2 at 20"C. The same applies to the water-insoluble reducing agent.

Examples of water-insoluble copper compounds include oxides, sulfides, hydroxides, thiocyanates, ferrocyanates, basic carbonates, silicates and phosphates of copper, and organic copper compounds capable of gradually releasing copper ions in the seawater. Cuprous oxide is most preferable.

Examples of water-insoluble reducing agents include Sn, Sb, Zn, Cr, Fe, Ni, Pb and Ti. Alloys of these metals may also be used. The average particle size of these metals is a function of their reaction velocity and long-term activity, and is preferably less than 250 mesh particle size.

The combinations of particular copper compounds and particular reducing agents and their proportions used for formulating the antifouling paint composition of this invention may vary depending upon its intended use and purpose. For example, 20 to 35% by weight of cuprous oxide based on the entire composition and 0.1 to 30% by weight of a relatively strong reducing metal such as Sb, Fe or Ti relative to the amount of cuprous oxide may be formulated where the composition does not require a very long-term antifouling activity. Where a long-term antifouling activity for more than two years is to be expected, the composition may contain 40 to 50% by weight of cuprous oxide and 5 to 60% by weight relative to the amount of cuprous oxide of a metal having a moderate but long-lasting reducing power such as Ni, Zn, Pb and the like may be incorporated.A stable, long-lasting release rate may be obtained from cupric thiocyanate, cupric hydroxide, basic cupric carbonate and other copper compounds having solubilities less than that of cuprous oxide by combining therewith a relatively strong reducing metal for increasing the initial releasing rate and a moderate-reducing metal for obtaining a moderate releasing rate for a long period of time. In any event the copper ion-releasing rate should not be in large excess of the minimum releasing rate of 10,ag/cm2/day as copper ions.

The antifouling paint composition of this invention may contain pigments and other conventional additives and also other known antifouling agents such as organotin compounds, organic sulfur compounds and the like.

The vehicle composition may be conventional and is well-known in the art. However, rosin may be omitted from the vehicle composition although its presence has been considered essential for antifouling paints containing a water-insoluble copper compound, by improving the mechanical strength of the resulting film to a great extent.

The present invention is further illustrated by the following experiments and examples in which all parts and percentages are by weight unless otherwise indicated.

Experiment 1 59 of cuprous oxide and 2g of antimony powder were placed in a 500ml Erlenmeyer's flask and 300ml of seawater was-added thereto. The mixture was stored with stirring for a predetermined period and samples were taken at predetermined intervals for determining the solubility of copper ions at pH.2, at 20 C. During this storage, the seawater was exchanged every one week.

The results obtained are shown in Table 1.

Experiments 2-4 Experiment 1 was repeated except that antimony was replaced by tin, zinc and lead, respectively.

Experiment 5 Experiment 1 was repeated except that cuprous oxide was replaced by cupric hydroxide.

Experiment 6 Experiment 5 was repeated except that antimony was replaced by 8-chromium stainless steel powder.

Reference Example 1 Experiment 5 was repeated except that antimony was replaced by red phosphorus.

TABLE 1 Solubilities of Cu (molelliter in seawater at pH8.2, at 20 C) Sample 1st day 1 month 3 months 6 months 12 months Experiment 1 Cu2O/Sb 1.7x10-5 9.7x10-5 1.6x10-4 1.6x10-4 8.0x10-5 Experiment2 Cu2O/Sn 2.3x10-5 5.5x10-5 5.9x10-5 6.6x10-5 4.8x10-5 Experiment3 Cu2O/Zn 1.4x10-4 1.0x10-4 9.3x10-5 7.5x10-5 4.3x10-5 Experiment4 Cu2O/Pb 3.6x10-5 3.8x10-5 4.7x10-5 4.3x10-5 4.1x10-5 Experiment5 Cu(OH)2/Sb 2.6x10-5 1.0x10-4 5.2x10-5 6.5x10-5 5.4x10-5 Experiment 6 Cu(OH)2/8-Cr 7.1x10-5 1.2x10-4 8.2x10-5 3.2x10-5 1.3x10-5 stainless steel Ref.Example 1 Cu(OH)2/P 1.1x10-4 5.9x10-5 4.3x10-5 3.1x10-5 1.2x10-5 Control 1 Cu2O 4.5x 10-5 1.8x10-5 2.2X10-5 2.2x10-5 2.1x10-5 Control2 Cu(OH)2 3.1x10-6 3.9x10-6 3.4x10-6 3.2x10-6 3.8x10-s As shown in Table 1, the solubilities of insoluble copper compounds may be maintained at higher levels for a long period of time by incorporating a reducing agent thereto in accordance with the present invention.

Examples 1-3 Antifouling paint compositions were prepared in accordance with the formulations as shown in Table 2 and applied on a test plate to a film thickness of 80 to 100 microns. Each plate was then immersed in the sea near Tamano-shi, Okayama, Japan and withdrawn at predetermined intervals for determining the dissolving rate of cupric ions from the paint film.

The results are shown in Table 3.

TABLE 2 Formulations (parts) Example Ref. Ref.

Material Ex, 1 Ex. 2 Ex. 3 Ex. 2 Ex. 3 Sb powder 5 Sn powder 5 Zn powder 5 red P 5 Cu2O 40 40 40 45 40 iron red 4 4 4 4 4 zing white 10 10 10 10 10 rosin 8.5 8.5 8.5 8.5 8.5 LAROFLEX MP-45 *1 6.5 6.5 6.5 6.5 6.5 TCP*2 2 2 2 2 2 xylene 24 24 24 24 24 Total 100.0 100.0 100.0 100.0 100.0 *1: Vinyl chloride/vinyl butyl ether copolymer, Sold by Hoechst AG.

*2: Tricresyl phosphate plasticizer TABLE 3 Dissolving rate of Cu++ ( g/cm2/day at 20 C, at pH8. 1) Immersed period Example 1 month 2 months 4 months 6 months 12 months Ex.1 22 36 18 14 12 Ex.2 33 38 20 15 13 Ex.3 32 15 14 12 10.5 Ref. Ex.2 20 27 12 10 8.5 Ref. Ex.3 52 29 9 6 6 As shown in Table 3, each antifouling paint composition of the present invention may release cupric ions at a rate greater than the required minimum rate of 10 X9 of Cu++/cm2/day for at least 12 months.

Various compositions were prepared and tested on their antifouling activities as shown in the following examples.

Example 4 Titanium powder 2.0 parts Cu2O 20.0 parts Triphenyltin hydroxide 10.0 parts Iron red 13.0 parts Talc 10.0 parts Rosin 10.0 parts Chlorinated rubber 10.0 parts TCP 5.0 parts Xylene 20.0 parts Total 100.0 parts Example 5 Antimony powder 5.0 parts Cu2O 20.0 parts Iron red 15.0 parts Talc 15.0 parts Rosin 10.0 parts Chlorinated rubber 10.0 parts TCP 5.0 parts Xylene 20.0 parts Total 100.0 parts Example 6 Nickel powder 10.0 parts Cu20 50.0 parts Rosin 8.0 parts Polyvinyl chloride (VYHH, sold by UCC) 6.0 parts TCP 2.0 parts Methyl isobutyl ketone 12.0 parts Toluene 12.0 parts Total 100.0 parts Example 7 Zinc powder 10.0 parts Cu2O 50.0 parts Polyvinyl chloride (VYHH, sold by UCC) 10.0 parts TCP 2.0 parts Methyl isobutyl ketone 14.0 parts Toluene 14.0 parts Total 100.0 parts Example 8 8-Chromium stainless steel powder 20.0 parts Cupric hydroxide 40.0 parts Rosin 8.0 parts Polyvinyl chloride (VYHH, sold by UCC) 6.0 parts TCP 2.0 parts Methyl isobutyl ketone 12.0 parts Toluene 12.0 parts Total 100.0 parts Example 9 Lead powder 15.0 parts Cu20 40.0 parts Rosin 15.0 parts Boiled linseed oil 10.0 parts Naphtha 20.0 parts Total 100.0 parts Reference Example 4 Cu2O 20.0 parts Triphenyltin hydroxide 10.0 parts Zinc white 10.0 parts Iron red 10.0 parts Talc 5.0 parts Rosin 10.0 parts Chlorinated rubber 10.0 parts TCP 5.0 parts Xylene 20.0 parts Total 100.0 parts Reference Example 5 Cu2O 50.0 parts Zine white 5.0 parts Iron red 5.0 parts Rosin 8.0 parts Polyvinyl chloride (VYHH, sold by UCC) 6.0 parts TCP 2.0 parts Methyl isobutyl ketone 12.0 parts Toluene 12.0 parts Total 100.0 parts Reference Example 6 Cu2O 40.0 parts Iron red 10.0 parts Talc 5.0 parts Rosin 15.0 parts Boiled linseed oil 10.0 parts Naphtha 20.0 parts Total 100.0 parts Reference Example 7 Iron red 25.0 parts Zinc white 20.0 parts Talc 5.0 parts Rosin 20.0 parts Chlorinated rubber 7.0 parts TCP 3.0 parts Xylene 20.0 parts Total 100.0 parts Examples 10-13 Example Ref.

Material (parts) Ex. 10 Ex. 11 Ex. 12 Ex. 13 Ex. 8 40% solution of polymeric organotin compound *3 55 55 55 55 55 Cu2O 30 30 30 30 30 Ti powder 2 Sb powder 5 Ni powder 5 Stainless steel powder 5 TiO2 8 5 5 5 10 Bentonite 1 1 1 1 1 Hydroquinone 0.1 0.1 0.1 0.1 0.1 Xylene 4 4 4 4 4 Total 100.1 100.1 100.1 100.1 100.1 *3: To a solution of 26 parts of tributyltin methacrylate and 14 parts of methyl methacrylate in 60 parts of xylene was added 0.4 parts of benzoyl peroxide. The temperature was gradually raised to the final temperature of 110 C over 8 hours with occasional cooling, if necessary. A 40% solution of the polymeric organotin compound was obtained.

Each antifouling paint composition of Examples 4-13 and Reference Examples 4-8 was applied onto a steel plate having a conventional anticorrosion coating. The treated steel plates were immersed in seawater at Uno port, Tamanoshi, Okayama, Japan for one year and compared the antifouling effects thereof. The results obtained are shown in Table 4. The results were classified into the following ranks depending upon percent fouled with a particular organism.

Ranking Percent fouled 5 > 80 4 40-80 3 20-40 2 10-20 1 < 10 0 none TABLE 4 Immersion test in seawater Period 6 months 12 months Organism Acorn Moss Acorn Moss paint barnacle organisms Slime seaweeds barnacle organisms Slime Seaweeds Ex. 4 0 0 0 0 1 0 2 0 Ex. 5 0 0 0 0 1 0 1 0 Ex. 6 0 0 0 0 0 0 0 0 Ex. 7 0 0 0 0 0 0 0 0 Ex. 8 0 0 0 0 0 0 0 0 Ex. 9 0 0 0 0 0 0 0 0 Ex. 10 0 0 1 0 0 0 1 0 Ex. 11 0 0 1 0 0 0 1 0 Ex. 12 0 0 1 0 0 0 1 0 Ex. 13 0 0 1 0 0 0 1 0 Ref. Ex.4 1 1 2 1 2 1 3 3 Ref. Ex.4 0 0 1 0 0 0 2 1 Ref. Ex.6 0 0 2 1 1 0 2 2 Ref. Ex.7 5 5 5 5 5 5 5 5 Ref. Ex.8 1 0 3 1 3 1 5 5 As shown in Table 4, each antifouling paint composition of this invention showed a remarkable antifouling effect against fouling organisms including seaweeds.

The above has been offered for illustrative purposes only, and it is not for the purpose of limiting the scope of this invention which is defined in the claims below.

Claims (8)

1. An antifouling paint composition comprising an effective amount of a water-insoluble copper compound and a water-insoluble reducing agent having an oxidation-reduction potential less than that of copper uniformly dispersed in a vehicle.

2. An antifouling paint composition as claimed in claim 1, wherein said reducing agent is a powdered metallic form of Sn, Sb, Zn, Cr, Fe, Ni, Pb, Ti or of an alloy of these metals.

3. An antifouling paint composition as claimed in claim 1 or claim 2, wherein the water-insoluble copper compound is an oxide, sulfide, hydroxide, thiocyanate, basic carbonate, silicate, or phosphate, of copper, or an organic copper compound capable of gradually releasing copper ions into the seawater.

4. An antifouling paint composition as claimed in any of the preceding claims wherein the water-insoluble copper compound is cuprous oxide.

5. An antifouling paint composition as claimed in claim 4 comprising 20 to 50% by weight of cuprous oxide based on the entire composition and 0.1 to 60% by weight of said powdered metal based on the amount of cuprous oxide present in the composition.

6. An antifouling paint composition as claimed in any one of the preceding claims substantially as herein described with reference to any one of the Examples.

7. A method of protecting ships, vessels and marine structures from fouling which comprises treating with a paint composition as claimed in any one of the preceding claims.

8. A ship, vessel or marine structure when treated with an antifouling paint composition as claimed in any one of claims 1 to 6.