ANTIFOULING COATING

Abstract

The present invention concerns a composition for a surface coating (10), in particular for aquatic applications, characterized in that the composition (12) has a polymer structure which is composed of at least three units, a first unit comprising a dendrimer structure based on a polyamidoamine, a second unit (14) comprising an epoxy resin, and a third unit (16) comprising an amine-reactive polysiloxane, the polymer structure being arranged such that the first unit is formed as a central unit to which the second unit (14) and the third unit (16) are each covalently bonded

Claims

1. A composition for a surface coating (10), in particular for aquatic applications, characterized in that the composition (12) has a polymer structure which is composed of at least three units, a first unit comprising a dendrimer structure based on a polyamidoamine, a second unit (14) comprising an epoxy resin, and a third unit (16) comprising an amine-reactive polysiloxane, the polymer structure being arranged such that the first unit is formed as a central unit to which the second unit (14) and the third unit (16) are each covalently bonded.

2. The composition according to claim 1, characterized in that the polyamidoamine comprises a zero- or first-generation polyamidoamine.

3. The composition according to claim 1, characterised in that the polysiloxane comprises a di-epoxy functionalised polydimethylsiloxane.

4. The composition according to claim 1, characterised in that the polysiloxane comprises a mono-epoxy functionalised polydimethylsiloxane.

5. The composition according to claim 1, characterized in that the epoxy resin is cured by a hardener.

6. The composition according to claim 1, characterised in that the dendrimer structure is present in the composition (12) in an amount of ≥0.3 wt.-% to ≤0.8 wt.-%.

7. The surface coating for a substrate, wherein the surface coating (10) is applied to the substrate, characterized in that the surface coating (10) comprises a composition according to claim 1.

8. The surface coating according to claim 7, characterised in that the units (16) comprising polysiloxane form domains (20) which at least in part have a size in a range from ≥0.05 μm to ≤1 μm, preferably from ≥0.9 μm to ≤0.4 μm.

9. The surface coating according to claim 7, characterised in that the units (16) comprising polysiloxane form domains (20) which at least partially have a distance from one another in a range from ≥0.7 μm to ≤4 μm, preferably from ≥1 μm to ≤3 μm.

10. The surface coating according to claim 7, characterised in that the units (16) comprising polysiloxane form domains (20) which, relative to a total surface area of the surface coating (10), have an amount of ≥10% to ≤80%.

11. The surface coating according to claim 7, characterised in that the substrate is a substrate for aquatic applications, in particular wherein the substrate is a hull for a watercraft or is a static element or a water-carrying volume.

12. The surface coating according to claim 7, characterised in that the surface coating (10) has a Martens hardness in a range of ≥150 N/mm2.

13. A method for producing a composition (12) for a surface coating (10), in particular for producing a composition (12) according to claim 1, comprising the method steps: a) Dissolving a dendrimer structure comprising a polyamidoamine in a solvent; b) Reacting the dendrimer structure with an amine-reactive polysiloxane; c) Reacting the dendrimer structure with an epoxy resin.

14. The method according to claim 13, characterized in that in method step b) the ratio of the functional groups of the polysiloxane to the functional groups of the dendrimer structure is in a range from ≥1:2 to ≤1:6.

15. A method for coating a substrate, comprising the process steps of: i) Providing a substrate; ii) Providing a composition for a surface coating (10); and iii) Applying the composition to the substrate, characterised in that the composition is arranged according to claim 1.

16. A method for producing a composition (12) for a surface coating (10), in particular for producing a surface coating (10) according to claim 7, comprising the method steps: a) Dissolving a dendrimer structure comprising a polyamidoamine in a solvent; b) Reacting the dendrimer structure with an amine-reactive polysiloxane; c) Reacting the dendrimer structure with an epoxy resin.

17. The method according to claim 16, characterized in that in method step b) the ratio of the functional groups of the polysiloxane to the functional groups of the dendrimer structure is in a range from ≥1:2 to ≤1:6.

Description

[0130] The figures show the following:

[0131] FIG. 1 a schematic representation of a surface coating according to the invention;

[0132] FIG. 2 a diagram showing an exemplary size distribution of polysiloxane domains;

[0133] FIG. 3 a polymer structure as the main component of the composition; and

[0134] FIG. 4 a cross-linking reaction reacting an epoxy resin as component A and a hardener as component B.

[0135] FIG. 1 shows a top view of surface coating 10. The surface coating 10 is used especially for components for aquatic applications, for example as an antifouling coating.

[0136] It can be seen that the surface coating 10 has a composition 12, which is formed or has a polymer structure, respectively. The polymer structure is made up of three, i.e. at least three, units, wherein a first, not shown, unit comprises a dendrimer structure based on a polyamidoamine, wherein a second unit 14 comprises an epoxy resin, and wherein a third unit 16 comprises an amine-reactive polysiloxane, the polymer structure being constructed in such a way that the first unit is formed as a central unit to which the second unit 14 and the third unit 16 are each covalently bonded.

[0137] In this respect, FIG. 1 shows a matrix 18 of epoxy resin of the second unit 16, in which there are present domains 20 of polysiloxane of the third unit, for example polydimethylsiloxane, which are immiscible with the epoxy resin.

[0138] A surface coating 10 of this type allows effective antifouling properties due to the domains 20 and high mechanical stability due to the matrix 18. In aquatic applications, the occurrence of fouling can thus be prevented. Even if fouling does occur, effective cleaning processes can be carried out, such as using a high-pressure jet or ultrasound, without damaging the surface coating 10.

[0139] For example, it may be provided that the third units 16 comprising a polysiloxane form domains 20, at least some of which have a size in a range from ≥0.05 μm to ≤1 μm, preferably from ≥0.09 μm to ≤0.4 μm. This size is indicated by the diameter and as such by the arrow 22.

[0140] This is shown in FIG. 2, which shows an exemplary size distribution of domains 20. Here the x-axis shows the diameter of the domains 20 in μm and the y-axis shows a dimensionless number. It has been shown that a particularly effective antifouling effect can be achieved with such domain sizes.

[0141] Alternatively or additionally it may be provided that the third units 16 comprising a polysiloxane form domains 20 which at least partially have a distance from each other in a range from ≥0.7 μm to ≤4 μm, preferably from ≥1 μm to ≤3 μm. The distance is marked by the arrow 24.

[0142] It has been shown that the size and distribution of the approximately spherically shaped domains 20, i.e. in particular their spacing, and the smallest possible number of defects can be important for the antifouling effect. This can be adjusted or made possible in particular by setting suitable conditions when preparing the composition as described above.

[0143] The composition described here has a low surface energy due to its binding of polysiloxane, for example PDMS molecules, which is advantageous for preventing the attachment of microorganisms and thus counteracting fouling. The water contact angle can be close to that of silicone coatings. The optimum low adhesion is between 22-24 mN/m. The composition described above is in this range, in particular, independent of the specific design.

[0144] The surface also has a high degree of hardness and is therefore not only better able than other biofouling coatings to withstand everyday mechanical stresses, such as when painting a boat hull, for example, when dropping off or docking, stone chipping or impact from objects in the sea. Tests have also proven the resistance of the surface structure, which is important for the antifouling effect, to high-pressure cleaning and ultrasonic cleaning.

Example

[0145] The following is an example of the production of a composition according to the invention.

[0146] The composition is basically produced using dendrimers reacted with polydimethylsiloxane (PDMS), which are dispersed in a system of epoxy resin and corresponding hardener (room temperature curing). The dendrimers used are “PAMAM” type dendrimers of the 0th generation. They are reacted in ethanol with poly(dimethylsiloxane), diglycidyl ether terminated or biepoxy-functionalised, and in the ethanolic solution are added to the epoxy system consisting of epoxy resin and amine hardener.

[0147] For example, a defined stock solution can be produced first. For this purpose, one mole of dendrimers is dissolved in ethanol in a flask while stirring. The mixture is heated to 100° C. under reflux and a catalytic quantity of N-benzyldimethylamine and 2 moles of diepoxy-PDMS are added. This solution is stirred for 1 h at 100° C. The PAMAM G0 has 4 —NH.sub.2 groups and is reacted in the ratio of 1 mol dendrimer to 2 mol PDMS in such a way that, in the calculated ideal case, 25% of the NH.sub.2 groups have reacted. After the reaction there is a distribution of dendrimers, at least some of which have functional groups on the PDMS substituents. This is possible, for example, by adjusting the corresponding concentrations, when the dendrimer has a comparatively low concentration. A reaction of 25% of the NH.sub.2 groups can for example be realised by reacting a difunctional polysiloxane with only one NH.sub.2 group of a dendrimer. The reaction can be stopped or inhibited by stopping the heating and stirring to such an extent that the molecules are prevented from further reacting. Since the dendrimers do not cross-link when there is enough solvent, but they do when the solvent is removed, at least some free epoxy groups may remain.

[0148] This reaction is an addition reaction between the amine and epoxy groups. The resulting product is reduced to a 5% solution. (1 g dendrimer to 20 g ethanol).

[0149] The stock solution thus comprises a dendrimer structure reacted with polysiloxane.

[0150] The dendrimer solution is then added to a solution of epoxy resin EP 140 (ISO 3219 11000-15500 mPa.Math.s) and hardener (EH 637), with epoxy resin and hardener being present in a ratio of 2:1, and stirred with a dissolver at 1000 rpm for 10 minutes. The stock solution is added so that a mass fraction of 0.5% of the PDMS dendrimer is present in the formulation.

[0151] For test purposes, this formulation is squeezed onto a substrate at 300 μm and dried at room temperature. For application on e.g. a ship's hull, the formulation can also be brushed or sprayed. The proportions of the individual units in the applied coating are then as follows: Epoxy resin content: 58.82% by weight, hardener content: 29.41% by weight, PDMS content: 1.76% by weight and dendrimer structure content: 0.59% by weight, wherein the rest missing to 100% may be formed by solvents and additives such as pigments or similar.

[0152] Table 1 shows the molar masses and manufacturers or sources of supply of the chemicals used in the example:

TABLE-US-00001 TABLE 1 Chemicals used in the example Molar mass Manufacturer/ Name [g/mol] Supplier Beckopox EP 140 (epoxy resin) 180-190 Allnex Poly(dimethylsiloxane), diglycidyl 800 Aldrich ether terminated (Polysiloxan) N-Benzyldimethylamine (catalyst) 135 Alfa Aesar PAMAM Dendrimer, 518 CYD Ethylenediamine core, Generation 0, CYD-N1 Dendrimer Beckopox EH 637 (hardener) 100 Allnex

[0153] Regarding the hardener, it may be an advantage that it is an aliphatic hardener, such as a cycloaliphatic amine, as this can give better results than an aromatic hardener.

[0154] The hardness of the coatings produced in this way was also tested. A FISCHERSCOPE HM2000 S was used for the test. The test was carried out according to DIN EN ISO 14577 to determine the Martens hardness. The results were as follows, whereby the reaction described above was repeated with a monosubstituted PDMS under identical conditions:

TABLE-US-00002 Polysiloxane used Martens hardness (HM) / N/mm.sup.2 Mono-PDMS 177 Bifunctional PDMS 237

[0155] As indicated above, the hardness of the surface coating is very high, which indicates a high mechanical stability. Furthermore, a particularly high hardness could be achieved by using a bifunctional polysiloxane, which is due to a particularly firm anchorage in the matrix.

[0156] In test, the coating was rinsed with a high-pressure cleaner and the changes were examined microscopically. No damage to the coating was found.

REFERENCE SIGN

[0157] 10 Surface coating [0158] 12 Composition [0159] 14 Unit [0160] 16 Unit [0161] 18 Matrix [0162] 20 Domain [0163] 22 Arrow [0164] 24 Arrow