NO178631B - Anti-fouling paints containing particulate polytetrafluoroethylene - Google Patents

Description

The present invention relates to an anti-fouling paint, containing particulate polytetrafluoroethylene (PTFE) with a particle size below 20 pm.

The paint prevents or counteracts adhesion to

and fouling of organisms that live in water, for example bacterial or diatom slime, algae, snails, clams, tube

field, ship ground, moss, teredos, limnoria, martesia, sphaeroma, oysters, bryozoans, etc., and prevents or counteracts the attachment and fouling of these and other organisms in aqueous environments, such as lakes, waterways and seawater, as well as for example in pipelines and industrial plant, e.g. heat exchangers, cooling towers and the like.

The paint according to the invention is characterized by the fact that PTFE can either be present as an anti-fouling binder, together with an additional binder, in which case PTFE has a molecular weight of up to 6000, or as an anti-fouling additive, with the proportion of PTFE to be at least 25% by weight based on the total binder, and that the paint further contains at least 5% by weight, calculated on the finished product,

dry coatings, of Cu powder or a Cu compound, which in and of themselves are known anti-fouling additives, as well as dispersants and solvents and possibly further components such as fillers, pigments and other anti-fouling agents, as the dispersant and/or solvent must be selected from the group which has a swelling effect on PTFE, if PTFE is to serve as a binder.

For polytetrafluoroethylene, the density is suitably 2.14 - 2.20, especially approx. 2.16. The melting point (crystalline) is suitably 280 - 330°C, especially approx. 300°C. The average molecular weight can vary within wide limits, e.g. 1000 to<*>20,000, or 2000 to 5000, preferably approx. 3700.

The softening point (ASTM E-28-58-T) can vary, e.g. between 240 and 280°C, e.g. about. 265°C.

It is appropriate that the solvent or dispersant has a certain dissolving effect on the fluorohydrocarbon polymer, particularly when the molecular weight is up to 6000, e.g. dissolves up to 25% or 1-15%, preferably approx. 10%. Also lower degrees of resolution, e.g. 0.1-1%, can produce a certain effect. This dissolving effect can be partial so that the polymer only swells or forms a type of colloid.

The anti-fouling component in the paint can be chosen from a number of materials that have proven suitable for counteracting fouling of surface coatings in water. Such materials are described in several publications, and as an example reference can be made to US patent documents 3 787 217, 3 854 960 and 3 912 519. As examples, copper metal in powder form such as copper oxide, e.g. Cu20, as well as copper salts.

The quantity of anti-fouling agents can vary within wide limits. Calculated on the weight of the finished coating, the paint may contain anti-fouling agent,

up to 50%, and especially up to 25%. Also smaller content, e.g. up to 10%, is suitable for certain types. The lowest effective limit also varies, depending on the type of agent, and can e.g. be between 5 and 10%.

The paint can also contain e.g. additional binder and pigment as well as similar filler. Suitable binders are e.g. epoxy resins and other binders of the thermoplastic or hardenable type, which can be used together with PTFE. A number of such materials are described in the literature, e.g. in the Swedish patent document 219 806, and what is stated in this patent document is intended to form part of the present description.

As examples can be mentioned such curable and non-curable plastics as phenol resins, carbamide-formaldehyde resins, alkyd resins, epoxy resins, polyurethane resins and alkyl silicon resins, silicones.

It is also possible to apply the paint according to the invention to a surface that has first been equipped with some form of priming treatment or base coating of a well-known type in and of itself, e.g. surface conversion coatings of the phosphate coating type, chromate coating, oxalate coating and the like, as well as primer coatings of the paint type containing binder components. A number of such priming agents or primers are currently known.

The paint contains as dispersant and/or solvent halogen hydrocarbons, in particular fluorine

and/or chlorohydrocarbons with 1, 2, 3 or 4 carbon atoms in the chain, preferably with at least half or all hydrogen atoms substituted with fluorine and possibly chlorine, e.g. freon hydrocarbons, such as trifluorotrichloroethane, trichloroethane and trichloroethylene, aromatic hydrocarbons, e.g. toluene, alcohols, ketones with 2-8 carbon atoms or water, preferably in an amount of at least 10%, calculated on the total weight.

The thickness of the applied coating can be varied. Generally, a coating thickness of less than 50 µm, preferably less than 25 µm, is used, e.g. under 10 or under 5 jum. A common lower thickness limit is 1 - 5 jum, and a preferred thickness interval is 5 - 15 tonnes. The amount of anti-fouling agent, i.e. copper powder or copper oxide, can therefore vary, e.g. up to 50 g/m 2 , preferably up to 25 g/m 2 , e.g. up to 10 or 15 g/m 2. A suitable lower limit is often between 1 and 5 g/m 2 , but also o lower content, e.g. 0.1 g/m , are applicable. A content of 25 - 75%, preferably approx. 50% of the binder weight is often suitable, e.g. for copper powder and the like.

As an example of a suitable pigment with special properties, pigment with a layer lattice structure can also be mentioned, e.g. molybdenum disulphide, MoS2 or graphite. A suitable content of this material is from 0.1% up to 5 or 10%. With polyfluoro-hydrocarbon, M°S2 gives a special effect and also contributes to reduced friction and increased speed. Graphite can also be used as a substitute or together with M0S2.

The paints can be distributed in different ways, as single-component paints, but also as multi-component paints. A suitable type of two-component paint which includes a liquid component containing PTFE dispersed in a solvent and possibly a binder, as well as a pigment component containing an anti-fouling agent as well as any further additives and any dispersant. Preferably, the pigment part is solid and powdery, and is mixed with the liquid-containing component before use. Appropriate, e.g. a liquid component containing as main constituents one of PTFE, e.g. with a fluorocarbon polymer content of 20-80%, and the remainder liquid dispersant, e.g. of the "FREON" type, as well as approx. 80% additional solvent, e.g. trichloroethene or similar (e.g. "CHLOROTHENE NU", marketed by Dow Chemical Co.). The liquid component may also contain a binder of another type, e.g. those mentioned above. The pigment part can be e.g. of copper powder in an amount of 50-90% and molybdenum disulphide in an amount of 10-50%, e.g. about. 70% copper powder and 25% molybdenum disulfide. The weight ratio between liquid component and pigment component can be 25-200 g of pigment per 800-975 g of the liquid component, making the total weight 1000 g.

The suitable amount is approx. 875 g liquid component and approx. 125 g of pigment with the aforementioned composition of liquid, PTFE-containing component and pigment component.

A common size of copper<p>wool is 300 to 30 mesh, e.g. 50% "fine" and 50% 11 superfine". Preferably, chip-shaped particles are used with a thickness/diameter ratio of 1/10 to 1/100, preferably 1/20 to 1/50, whereby preferably at least 50%, and in particular at least 80% of the particles have such a size that the diameter is below 10 / mm.

The coatings can be applied in different ways, e.g. with brush, rollers, spraying, dipping, casting.

The coatings can also be melted onto the substrate by heating polytetrafluoroethylene, e.g. above 280°C,. such as 3.00 - 315°C, during 1 - 20, e.g. 5-10 minutes, or flame-sprayed, e.g. plasmas<p>are shed.

The paint can be applied to different substrates, e.g. steel, zinc, aluminium, stainless steel, plastic, concrete, stone (silicate) glass, porcelain, artificial stone, brick, wood, with or without undercoating of paints, varnish, varnish, phosphate layer, chromate layer, etc.

The paint may also contain corrosive ingredients, such as phosphoric acid and other acidic ingredients that attack a substrate and improve adhesion. These components can be of the Wash-primer type and also include e.g. zinc chromate or other chromates and polyvinyl butyral and similar known ingredients from Wash-primer. Other applicable ingredients, e.g. in compositions containing water as a dispersing or emulsifying agent are thermoplastic components, polyacrylates including copolymers of acrylic monomers with other unsaturated monomers, polyvinyl acetate, polystyrene, vinyl chloride-vinylidene chloride copolymer, other vinyl polymers, styrene-butadiene copolymer, chlorinated rubber, rosin resin, linear polyesters , such as polyethylene terephthalate, polybutylene terephthalate and the like.

As further examples of pigment and filler, rust-protective additives such as lead, zinc chromate, zinc metal powder, aluminum metal powder, aluminum bronze powder and the like can be mentioned.

As further examples of anti-fouling agents, particularly effective against balanids, e.g. sea urchins (anemones), clams, tubeworms and the like, mixtures of Cu^O and HgO can be mentioned.

The applicable silicones (organosilicon compounds)

can be of the oil or resin type as well as curable or non-curable, linear or cross-linked. Silicones are described in detail, e.g. in the book W. Noll: "Chemie und Technologi der Silicone", 2nd edition, Verlag Chemie, Weinheim, BRP, 1968, as well as

in "Chemie und Technologie der Kunststoffe", Volume II,

Akademische Verlagsgesellschaft Geest & Portig K-G, Leizig, 1963, pages 789 - 858. Also suitable silanes, preferably those which can form silicone polymers or siloxanes (polysiloxanes), can be included in compositions according to the invention.

The molecular weight of the organosilicon compounds used can vary within wide limits, e.g. between 20 and 100,000, e.g. 100 - 10,000.

The amount of organosilicon compound (including polymers) can vary based on the solids weight from zero up to 5%, preferably from 0.01%, in particular 0.1% and in particular 0.3% up to 3%, in particular up to 1%.

As examples of "antifouling" materials, mention can be made of organic and inorganic copper compounds, such as Cu-naphthenate, cuprooxyd, copper powder and cuprooxyd-mercurioxyd, (eg 3:1).

The antifouling agents are preferably insoluble in water.

Fillers can be included in the paint or coating, e.g. particles that improve the coating's wear resistance or holding strength. Organic or inorganic material can be used, e.g. fused or sintered water-resistant materials such as glass, ceramic materials, metals, etc. The particles may have a regular shape, e.g. spherical shape, such as glass balls, or irregular shape, e.g. chip form, fiber form, form obtained by crushing etc. The filler may also contain the antifouling agent and/or the fluorocarbon polymer incorporated into or bound to the surface of the filler particles. The filler can also have a pigment effect or consist of pigment.

When using balls made of glass or synthetic resin, e.g. of vinyl type, acrylic type or elastomer type, such as rubber, a diameter of 1-100 µm, preferably 5-50 µm or 5-30 µm is suitable. The balls can be incorporated to improve the coating's frictional properties in water.

Example 1

A paint with the following composition was produced: 100 g polytetrafluoroethylene, average molecular weight approx. 5000 100 g copper powder 30 - 300 mesh

30 g of molybdenum disulphide

whereby polytetrafluoroethylene was dispersed in 770 g of a mixture of 200 g of trifluorotrichloroethene and 570 g of trichloroethane, after which other components were dispersed in this dispersion.

This paint was applied to a film thickness of 5 - 10 um on ship bottoms made of plastic, aluminum and steel with and without an underlying paint layer, and gave good long-term effect against fouling in seawater.

The binding of this coating to the substrate can also be improved in a manner well known per se, e.g. with a primer coating, e.g. of the epoxy type, whereby the antifouling coating is applied at a time when the primer coating still gives a binding effect to the antifouling coating. In tests, the above-mentioned antifouling coating was applied to a primer coating of amide-cured epoxy resin obtained by mixing "Epon 1001" (Shell) and "Versamid" (General Mills), which was applied to substrates of iron, aluminum, zinc and plastic ( polyester) with good effect. Furthermore, the adhesion can be improved by incorporating a binder, as stated above. In the above mentioned paint

30 and 60 parts of the mixture of "Epon 1001" and "Versamid" were incorporated, calculated on the stated quantity parts. This composition was also tested on substrates of iron, aluminium, zinc and plastic (polyester) with good effect.

In further tests, the coating was heated for sintering to substrates of iron, aluminum and zinc.

The experiments according to the above were repeated using an addition of 10% glass beads with mean diameters of 5 µm and 30 µm respectively, calculated on the solids in the paint, nen.

Tests according to the example were repeated, whereby half or the entire amount of copper metal was replaced with Cu^O, whereby satisfactory results were obtained.

Example 2-4

A number of coating materials of the same type as in the previous example were produced with the poisons indicated in the examples. The material was also tested without the addition of poison. The investigated materials were coated on sheets of glass fiber reinforced polyester resin and were tested by immersion in seawater in Florida, USA.

The plate with material without poison addition showed overfouling of 100% of the plate's surface after 1 month. The materials with poison addition showed fouling of 20% of the plate's surface after the number of months indicated in the following table.

Claims (4)

1. Anti-fouling paint, containing particulate polytetrafluoroethylene (PTFE) with a particle size below 20 pm, characterized in that PTFE can either be present as an anti-fouling binder, together with an additional binder, in which case PTFE has a molecular weight of up to 6,000, or as an anti-fouling additive, the proportion of PTFE must be at least 25% by weight based on the total binder, and that the paint further contains at least 5% by weight, calculated on the finished, dry coating, of Cu powder or a Cu compound, which in and of themselves are known anti-fouling additives, as well as dispersants and solvents and possibly further components such as fillers, t pigments and other anti-fouling agents, as the dispersant and/or solvent must be selected from the group which has a swelling effect on PTFE, if PTFE is to serve as a binder. 2. Paint according to claim 1, characterized in that the coating as an antifouling agent contains copper metal powder, preferably in chip form, or copper oxide, preferably Cu20. 3. Paint according to any of the preceding claims, characterized in that the coating material as dispersant and/or solvent contains halogen hydrocarbons, in particular fluorine and/or chlorine hydrocarbons with 1, 2, 3 or 4 carbon atoms in the chain, preferably with at least half or all hydrogen atoms substituted with fluorine and optionally chlorine, e.g. freon hydrocarbons, such as trifluorotrichloroethane, trichloroethane and trichloroethylene, aromatic hydrocarbons, e.g. toluene, alcohols, ketones with 2-8 carbon atoms or water, preferably in an amount of at least 10%, calculated on the total weight. 4. Paint according to any of the preceding claims, characterized in that the coating material per 1000 g of total weight includes 800-975 g of a liquid component containing a polytetrafluoroethylene suspension in a solvent, as well as 25-200 g of anti-fouling agent, preferably copper powder.