ANTIFOULING PAINT

Abstract: Antifouling paint having no essential biocidal activity. It comprises a slightly soluble pigment having little or no biocidal activity, an essentially insoluble film-forming binder, the pigment volume concentration (PVC) being in the region of the critical pigment volume concentration (CPVC), and optionally an organic or aqueous solvent.

Description: ANTIFOULING PAINT The present invention relates to an antifouling paint for controlling and minimizing the attachment and growth of marine fouling organisms to those parts of various objects which are submerged in sea water, fresh water or brackish water. The attachment and growth of marine fouling organisms to ships, marine structures etc. cause considerable problems, and various antifouling paints are in use for controlling the attachment and growth of marine fouling organisms . A common type of antifouling paint is that which contains a biocidal agent dispersed in a suitable binder or a mixture of binders . A commonly used biocidal agent is cuprous oxide. During use the biocidal agent will dissolve and be released to the surrounding water and will thus provide an antifouling property. Another type of antifouling paint is the so-called self polishing type. In such a paint, the antifouling agent which is chemically bound to the binder, gradually dissolves or hydrolyzes in water to release the antifouling agent. Well-known paints of this type are those which are based on acrylic polymers in which carboxyl groups have been esterified with organotin groups. During use the polymers will be hydrolyzed in sea water to release free trialkyltin compounds while carboxyl groups are formed in the polymer. The released trialkyltin compound will act as an antifouling agent . During recent years certain restrictions have been made with respect to the use of biocidal agents in paints. Thus, it has been found that in certain cases biocidal agents such as cuprous oxide or tin compounds or groups as described above, may have an undesired detrimental effect on the envi- ronment . There is accordingly a need for antifouling paints which do not exhibit these undesired properties. We have now found a new principle which may be used in antifouling paints, and which is not uniquely dependant on any biocidal activity of components of the paint. According to the present invention we provide an anti¬ fouling paint having no essential biocidal activity, which comprises a slightly soluble pigment having little or no biocidal activity, an essentially insoluble film-forming binder, the pigment volume concentration (PVC) being in the region of or above the critical pigment volume concentration (CPVC) , and optionally an organic or aqueous solvent. The terms "PVC" and "CPVC" are well known in the paint art. See e.g. "Principles of Paint Formulation", edited by R. Woodbridge, Blackie, Glasgow and London, p. 69-70, and "Protective Coatings" by Clive H. Hare, Technology Publishing Company, Pittsburgh, Pennsylvania, SSPC 94-17. p. 6-13. During use the pigment will gradually dissolve and be removed from the surface of the paint together with any marine fouling organisms . Due to the rather high amount of pigment compared to the amount of binder, this effect may be considered as "chalking" which is not dependant on any biocidal effect. If the PVC/CPVC ratio is too low, the surface of the coating will form a continuous film with no pigment exposed on the surface, and no "chalking" effect will be obtained. Suitable binders are for instance selected from, but not limited to epoxy resin, alkyd resin, acrylic resin, vinyl resin, polyurethane, silicone, silicates and synthetic rubber. The binder may be formed from one or more components. With two or more components, these may react with each other when they are mixed. It is also possible to include a plasticizer and/or a co-binder to modify the properties of the essentially insoluble binder. When calculating the PVC/CPVC ratio, the optional extender and other possible additives in particle form should be included as a part of the pigment . These may be ordinary paint additives such as silica dust or minor amounts of other pigments and, if desired, biocides. Normally biocides are not required but may be used if an enhanced antifouling effect is desired, i.e. a "chalking" as well as a biocidal effect. Similarly, the optional plasticizer and co-binder should be included as a part of the binder when making said calculation. Since the PVC should be in the region of the CPVC, there will always be some pigment exposed to the surrounding water. If the PVC was lower, there might be formed a complete film without any pigment exposed to the water. Below the CPVC region film properties dominate the behaviour of the coating, and no "chalking" effect would be obtained, and marine fouling organisms may attach to the surface. The essential feature of the pigment is that it is slightly soluble so that some of it will continuously disappear from the surface of the coating. Some of the pig¬ ment will dissolve and pigment particles no longer bound into the coating will crumble away, or "chalk", by the movement of the water. This will ensure that no fouling organisms may attach to the surface. Any slightly soluble pigment may be used, such as, but not restricted to: metals, such as zinc, iron, aluminium; inorganic oxides and salts, such as calcium, magnesium and ammonium oxides and salts, in addition to zinc, iron and aluminium oxides and salts; organic salts; and glasses. The biocidal activity of the pigment should preferably not be greater than that of zinc oxide. The use of zinc compounds in combination with biologically highly active materials, such as organotin and cuprous oxide, is well known. In that case, the antifouling effects are due to biological activity of the organotin and cuprous oxide, and not to a "chalking" effect. Together with the slightly soluble pigment it is also possible to use an essentially insoluble pigment which will act as an extender. Such an extender is generally chosen to maintain the desired PVC, modify the solubility, and to control coating properties such as "chalking", film toughness, overcoatability, colour, costs, etc. "Chalking" properties are related to the rate of solubility of the soluble pigment, which in turn is influenced by its intrinsic solubility, particle size, shape and surface area. Thus, a porous particle may result in a much higher solubility rate than a compact bead. The higher the fouling severity, the higher the "chalking" should be. The "chalking" may be increased by increasing the PVC, by increasing the solubility of the pig¬ ment and by increasing the surface area of the pigment particles. The "chalking" may also be increased by using a co-binder which is slightly soluble, and possibly also one or more plasticizers, so that more pigment may be exposed to the surrounding water. It may be advantageous to use a pigment which has an anticorrosive effect, such as metallic zinc, since the substrate upon which the antifouling paint is applied, will then also be protected against corrosion and not only against fouling. In addition to the different components mentioned above, the paint of the invention may also contain conventional paint additives. Four different paints (Examples 1-4) containing varying amounts of acrylic resin as binder and zinc oxide as pigment were prepared and tested. Similarly, five paints (Examples 5-9) based on epoxy resin were prepared and tested. Panels coated with the paint were kept submerged in seawater for 3 months at a temperature of about 25°C. The composition of the paints as well as the test results will appear from the following table . The control sample was a panel with gel coat only, i.e. the same as those used as substrate for the other examples. Two paints (Examples 10 and 11) having the higher PVC/CPVC ratios of 1.3 and 1.5 respectively were also prepared and applied to the same type of substrate. These were not subjected to the same long time antifouling testing described above since it is obvious in view of the other tests that the antifouling effect will be satisfactory. However, the test panels were subjected to adhesion tests, and the durability of the films was found to be satisfactory. The PVC/CPVC ratio should not be higher than 1.5 and preferably not higher than 1.3, particularly less than 1.2. The PVC/CPVC ratio is in practice above 0.7, normally above 0.8, in particular above 0.9. Apparently the best balance between antifouling effect and durability is normally found when said ratio in the range 0.8-1.2. However, this will depend on several factors such as the type of polymer and pigment as well as the particle size of the latter. PANEL TEST AT MARINE FACILITY Series A Series B Series C FORMULATION COMPONENTS VOLUM% DRY FILM Example Control 1 2 3 4 5 6 7 8 9 10 11 Acffyl film forming resin 35.1 39.4 48.3 58.2 20.4 13.5 (Neocryl B-725) Plasticizer 9.5 10.7 13.1 15.7 12.0 8.0 (Chlorparaffin 42) 10 Epoxy Resin 1001-type 26.4 31.0 37.6 42.1 47.8 Amine Curing Agent 13.8 16.3 19.7 22.1 25.1 Adδosil 200 0.8 0.9 1.1 1.3 0.5 0.3 Zinc Oxide 54.6 49.0- 37.5 24.8 59.8 52.7 42.7 35.8 27.1 67.1 78.2 PVC/CPVC 1.1 1.0 0.8 0.6 1.1 1.0 0.8 0.7 0.5 1.3 1.5 RfiMults panel test Total fouling ) 42 0 0 5 78 3 6 11 26 42 3 months Barnacles ) exposure 3 0 0 0 7 1 1 1 1 2 25 (area%) Algae ) 15 0 0 3 70 2 5 10 25 40 It should be noted that the test with acrylic resin was not carried out at the same time as the test with the epoxy re

Claims: P a t e n t c l a i m s : 1. Antifouling paint having no essential biocidal activity, characterised in that it comprises a slightly soluble pigment having little or no biocidal activity, an essentially insoluble film-forming binder, the pigment volume concentration (PVC) being in the region of the critical pigment volume concentration (CPVC) , and optionally an organic or aqueous solvent. 2. The paint of claim 1, characterised in that the PVC/CPVC ratio is in the range 0.7-1.5, preferably 0.8- 1.3, in particular 0.9-1.2. 3. The paint of any of claims 1-2, characterised in that it also contains an essentially insoluble pigment as an extender. 4. The paint of any of claims 1-3, characterised in that the essentially insoluble binder is formed from two or more components which react with each other upon mixing. 5. The paint of any of claims 1-4, characterised in that it contains a plasticizer and/or a co-binder. 6. The paint of any of claims 1-5, characterised in that the binder is selected from epoxy resin, alkyd resin, acrylic resin, vinyl resin, polyurethane, silicone, silicates and synthetic rubber. 7. The paint of any of claims 1-6, characterised in that the pigment is selected from metallic zinc, iron and aluminium, and slightly soluble salts and oxides thereof and of calcium, magnesium and ammonium. 8. The paint of any of claims 1-7, characterised in that the pigment has an anticorrosive effect . 9. The paint of any of claims 1-8, characterised in that the slightly soluble pigment is zinc oxide. 10. The use of a paint according to any of claims 1-9 for coating objects which are submerged in water.

Inventors: ARNOLD DAVID E J, GULSETH STEIN, ARNOLD, DAVID, E., J., GULSETH, STEIN
Applicants: ARNOLD DAVID E J, GULSETH STEIN, JOTUN AS, ARNOLD, DAVID, E., J., GULSETH, STEIN, JOTUN A/S
Application year: 1996
Main classification: C09D5
IPC codes: C09D5